studies on the synthesis, … on the synthesis, characterisation and antimicrobial applications of...

STUDIES ON THE SYNTHESIS, CHARACTERISATION AND ANTIMICROBIAL

APPLICATIONS OF RARE EARTH METAL SCHIFF BASE COMPLEXES

A THESIS

Submitted by

LEKHA L.

Under the guidance of

Dr. D. EASWARAMOORTHY

in partial fulfillment for the award of the degree of

DOCTOR OF PHILOSOPHY

in CHEMISTRY

B.S.ABDUR RAHMAN UNIVERSITY (B.S. ABDUR RAHMAN INSTITUTE OF SCIENCE & TECHNOLOGY)

(Estd. u/s 3 of the UGC Act. 1956)

www.bsauniv.ac.in

JUNE 2014

ii


(Estd. u/s 3 of the UGC Act. 1956) www.bsauniv.ac.in

BONAFIDE CERTIFICATE

Certified that this thesis report STUDIES ON THE SYNTHESIS,

CHARACTERISATION AND ANTIMICROBIAL APPLICATIONS OF RARE

EARTH METAL SCHIFF BASE COMPLEXES is the bonafide work of

LEKHA L. (RRN: 1091212) who carried out the thesis work under my

supervision. Certified further, that to the best of my knowledge the work

reported herein does not form part of any other thesis report or dissertation

on the basis of which a degree or award was conferred on an earlier

occasion on this or any other candidate.


RESEARCH SUPERVISOR

Professor & Head

Department of Chemistry

B.S. Abdur Rahman University

Vandalur, Chennai – 600 048.

iii


(Estd. u/s 3 of the UGC Act. 1956) www.bsauniv.ac.in

CERTIFICATE

This is to certify that my Ph.D student Ms. L.Lekha

(RRN: 1091212), has incorporated all the corrections suggested by the

examiners in her thesis report entitled STUDIES ON THE SYNTHESIS,

CHARACTERISATION AND ANTIMICROBIAL APPLICATIONS OF RARE

EARTH METAL SCHIFF BASE COMPLEXES.


RESEARCH SUPERVISOR

Professor & Head

Department of Chemistry

B.S. Abdur Rahman University

Vandalur, Chennai – 600 048.

v

ABSTRACT

Condensation of carbonyl compounds with primary amines is one

of the traditional reactions in chemistry, leading to the formation of Schiff

base compounds. Rare earth metal complexes having N, O donor Schiff

bases play a vital role in pharmaceutical, biological and industrial chemistry,

due to their diverse applications as contrast enhancing agents in NMR

imaging, luminescent probes in medicine and biology, radiometal-labeled

agents for diagnostic imaging, catalyst, supramolecular assemblies with

enhanced physiochemical properties and even for rare earth separation.

With these objectives in mind, Schiff base rare earth metal

complexes are synthesised and characterised. In addition, the Schiff base

ligands and their rare earth metal complexes are screened for their invitro

antimicrobial activities against Escherichia coli, Pseudomonas aeruginosa,

Staphylococcus aureus, Streptococcus agalactiae, Candida and Aspergillus

species and also for catalytic activities.

The experimental part of this thesis includes, the synthesis of

Schiff base ligands like, Sodium 2-(5-bromo-2-hydroxybenzylideneamino)-3-

hydroxypropanoate (SeBrS denoted as L1), Sodium 2-(5-bromo-2-

hydroxybenzylideneamino)-3-hydroxybutanoate (ThBrS as denoted L2) and

Sodium 2-(5-bromo-2-hydroxybenzylidene amino)-4-methylpentanoate (LBrS

denoted as L3 and their corresponding rare earth metal complexes like

Gd (III), Pr (III), Er (III), Sm (III), Tb (III) and Yb(III) Schiff base complexes.

The typical procedure and experimental setup for anti-bacterial, antifungal

studies and aniline oxidation has been incorporated in chapter 3. The results

and discussion part of the thesis describe the characterisation and

application of these newly synthesised complexes. The following

observations have been made based on the spectral and analytical data:

vi

Spectral study and thermal data of the rare earth metal Schiff base

complexes derived from serine showed that two nitrate groups are bound in

a bidentate manner to the central Ln (III) ions in the coordination sphere

while another nitrate is in the outer coordination sphere in complexes. The

fluorescence data reveals that the Sm (III), Tb (III) and Er (III) Schiff base

complexes exhibit characteristic luminescence of corresponding +3 ions,

which indicates that the ligand (L1) is a good organic chelator to absorb and

transfer energy to Sm (III), Tb (III) and Er (III) ions. The synthesised rare

earth Schiff base complexes derived from leucine exhibits the coordination of

the ligand with the central Ln (III) ion through phenolic oxygen, azomethine

nitrogen and the carboxylic oxygen with 1:1 stoichiometry. The samarium

and terbium Schiff base complexes show interesting fluorescence properties.

The in vitro antibacterial activity results showed that most of the

synthesised complexes using serine, threonine and leucine based Schiff

bases, possess good antibacterial activity against bacteria like Escherichia

coli, Proteus, Staphylococcus aureus and Pseudomonas aeruginosa. The

rare earth Schiff base complexes were found to possess enhanced

antimicrobial activity than the corresponding free Schiff base ligands. In

addition, antifungal activity of the complexes is higher than that of the

antibacterial activity of the complexes.

The above complexes possess good catalytic ability for the

oxidation of aniline under mild conditions and Gd (III) Schiff base complex

derived from leucine was utilised to check the generality and efficiency of

oxidation of various substituted anilines. The result herein reveals that the

leucine based rare earth Schiff base complexes are good catalysts for

reactions of commercial importance and suitable to catalyse aniline oxidation

reaction under mild experimental conditions. The catalytic study could be

further extended for other newly synthesised complexes. Further, research

and developments in the application of this Schiff base rare earth metal

complexes would be highly useful to industries and academic world.

vii

ACKNOWLEDGEMENT

At this moment of accomplishment, first of all I pay respect to my guide, Dr. D. Easwaramoorthy, Head & Professor of chemistry department,

B.S.Abdhur Rhaman University, Vandalur. This work would not have been possible without his guidance, support and encouragement.

I am also extremely indebted to Dr. I.Mohammed Bilal, COE,

B.S.Abdhur Rhaman University, for his valuable suggestions and corrections during the review of my thesis progress. I warmly thank Dr. S.Kutti Rani, for her valuable advice, constructive criticism and her extensive discussion around my work.

I gratefully acknowledge Dr. G. Rajagopal and Dr. K.K. Balasubramaniam for their encouragement and personal attention

during my Ph.D. tenure. I also thank my Doctoral committee members, Dr. Riyazuddin and Dr. J. Herbert Mabel for their helpful suggestions and comments.

I am indebted to my student colleagues Mr. R. Mohanraj, Mr. K. Devaraj, Mr. M. Saminathan, Mr. S.Dhivakar, Mr. M. Saravanan, Mr. V. Thiruvengadam and Ms. M. Sasikala for their constant support.

It’s my fortune to gratefully acknowledge the support of some special individuals. Words may fail me to express my gratitude to Dr. K. Kanmani Raja for his support, generous care towards my research

programme. He uses to motivate me during my hard moments and gave a good shape in formatting my thesis. Thanks doesn’t seem sufficient to Dr. K. Shivasankari, Dr. R. Hariharan and Dr. M. Sathish for their support,

care, understanding and precious friendship.

Last but not least, I would like to pay high regards to my lovable husband Mr. V.S. Babu and my ward L. Kaushick Babu who has been a moral support and all of my family members for their continuous

encouragement and inspiration. I thank them all whole heartedly.

L. LEKHA

viii

TABLE OF CONTENTS

CHAPTER NO. TITLE PAGE NO.

ABSTRACT v

ACKNOWLEDGEMENT vii

LIST OF TABLES xiii

LIST OF FIGURES xv

LIST OF SCHEMES xxvi

LIST OF ABBREVIATIONS xxvii

LIST OF SYMBOLS xxviii

1. INTRODUCTION 1

1.1 SCHIFF BASE 3

1.1.1 Amino Acid Schiff Base 5

1.2 RARE EARTH METAL CHEMISTRY 6

1.2.1 General Characteristics 6

1.2.2 Magnetic Properties 7

1.2.3 Coordination Chemistry 7

1.2.4 Photophysical Properties 8

1.3 DONORS 9

1.4 SCHIFF BASE – RARE EARTH METAL

COMPLEXES

10

1.5 BIOLOGICAL IMPORTANCE 11

1.5.1 Antimicrobial Activities 11

1.6 CATALYTIC ACTIVITIES 12

1.7 METALLO – ELEMENTS UNDER

INVESTIGATION

13

1.7.1 Praseodymium 13

1.7.2 Gadolinium 14

ix


1.7.3 Samarium 14

1.7.4 Terbium 15

1.7.5 Erbium 16

1.7.6 Ytterbium 16

2. LITERATURE OVERVIEW 21

2.1 INTRODUCTION 21

2.2 ANTIMICROBIAL PROPERTIES 21

2.3 LUMINESCENT PROPERTIES 25

2.4 CATALYTIC PROPERTIES 28

2.5 AIM AND OBJECTIVE 28

2.6 OUTLINE OF THE THESIS 28

3. EXPERIMENTAL METHODS AND TECHNIQUES

31

3.1 MATERIALS EMPLOYED 31

3.2 SOLVENTS 31

3.3 EXPERIMENTAL METHODS 32

3.3.1 Synthesis of Schiff Base Ligand [l1] 32

3.3.2 Synthesis of [Ln(L1)(NO3)2(H2O)]NO3

Complexes

32

3.3.3 Synthesis of Schiff Base Ligand [l2] 34


Complex

35

3.3.5 Synthesis of Schiff Base Ligand 36


Complex

37

3.3.7 In vitro Antibacterial Study 38

3.3.8 In vitro Antifungal Study 39

3.3.9 Catalytic Oxidation of Aniline 40

x


3.4 ANALYTICAL METHODS 40

3.4.1 Microanalysis 40

3.4.2 Molecular Weight Determination 40

3.5 INSTRUMENTAL METHODS 41

3.5.1 Infrared Spectra 41

3.5.2 Electronic Spectra 41

3.5.3 NMR Spectra 42

4. SCHIFF BASE DERIVED FROM SERINE AND ITS LANTHANIDE (III) COMPLEXES

43

4.1 INTRODUCTION 43

4.2 RESULTS AND DISCUSSION 44

4.2.1 Elemental Analysis 45

4.2.2 Mass Spectra 46

4.2.3 Molar Conductance 55

4.2.4 Thermo Gravimetric Analysis 55

4.2.5 1H NMR Spectra 64

4.2.6 IR Spectra 66

4.2.7 Electronic Spectroscopy 75

4.2.8 Fluorescence Studies 81

4.2.9 Antibacterial Studies 83

4.2.10 Antifungal Studies 89

4.3 CONCLUSION 93

5. SCHIFF BASE DERIVED FROM THREONINE AND ITS LANTHANIDE (III) COMPLEXES

94

5.1 INTRODUCTION 94



xi






5.2.6 IR Spectra 118


5.2.8 Fluorescence Study 134



5.3 CONCLUSION 145

6. SCHIFF BASE DERIVED FROM LEUCINE AND ITS LANTHANIDE (III) COMPLEXES

146

6.1 INTRODUCTION 146







6.2.6 IR Spectra 170


6.2.8 Fluorescence Studies 186



6.3 CONCLUSION 198

7. CATALYTIC ACTIVITY OF LANTHANIDE (III) SCHIFF BASE COMPLEXES DERIVED

199

xii


FROM LEUCINE

7.1 INTRODUCTION 199

7.2 CATALYTIC OXIDATION OF ANILINE AND

SUBSTITUTED ANILINES

200

7.3 CONCLUSION 217

8. SUMMARY AND CONCLUSION 218

8.1 Ln (III) SCHIFF BASE (L1) COMPLEXES 218



8.4 CATALYTIC ACTIVITY OF Ln (III) SCHIFF

BASE (L3) COMPLEXES

220

9. SCOPE FOR FUTURE WORK 221

10. REFERENCES 222

LIST OF PUBLICATIONS 250

TECHNICAL BIOGRAPHY

252

xiii

LIST OF TABLES

TABLE NO. TITLE PAGE NO.

3.1 Physical properties and the percentage yield of

the Schiff base ligand [L1] and its Ln (III)

complexes 34



complexes 36



complexes 38

4.1 Elemental Analysis of the ligand [L1] and Ln (III)

Schiff base complexes in DMF 46

4.2 Molar conductance of the ligand [L1] and Ln (III)

Schiff base complexes 55

4.3 Infrared spectral data for the ligand [L1] and the

Ln (III) complexes 67

4.4 UV-visible Spectral Data max. (nm) for the ligand

[L1] and the Ln (III) complexes 81

4.5 Antibacterial results of the Schiff base ligand [L1]

and their Ln (III) complexes for maximum

concentration 85

4.6 Antifungal results of the Schiff base ligand [L1]


concentration 90





xiv

TABLE NO. TITLE PAGE NO.







concentration 137



concentration 142











concentration 190



concentration 195

7.1 Oxidation of aniline catalysed by various Ln (III)

complexes in CH2Cl2 at RT 202

7.2 Oxidation of aniline and substituted anilines

catalysed by Gd (III) complex in CH2Cl2 at RT

203

xv

LIST OF FIGURES

FIGURE NO. TITLE PAGE NO.

2.1 Emission spectrum of the complex

[TbL(NO3)2(H2O)2](NO3) 26

2.2 The Fluorescence spectra of (a) Tb (III) and (b)

Sm (III) complexes 27

4.1 Sodium salt of the Schiff base ligand [L1] 44

4.2 Mass Spectrum of the Schiff base ligand [L1] 47

4.3 Mass Spectrum of the [Pr(L1)(NO3)2(H2O)]NO3

complex 48

4.4 Mass Spectrum of the

[Sm(L1)(NO3)2(H2O)]NO3 complex 49

4.5 Mass Spectrum of the [Gd(L1)(NO3)2(H2O)]NO3

complex 50

4.6 Mass Spectrum of the [Tb(L1)(NO3)2(H2O)]NO3

complex 51

4.7 Mass Spectrum of the [Er(L1)(NO3)2(H2O)]NO3

complex 52

4.8 Mass Spectrum of the [Yb(L1)(NO3)2(H2O)]NO3

complex 53

4.9 HR-MS of the [Pr(L1)(NO3)2(H2O)]NO3 complex 54

4.10 TG / DTA curves of Schiff base ligand [L1] 57

4.11 TG/DTA curves of the [Pr(L1)(NO3)2H2O].NO3

complex 58

4.12 TG/DTA curves of the [Sm(L1)(NO3)2H2O].NO3

complex 59

4.13 TG/DTA curves of the [Gd(L1)(NO3)2H2O].NO3

complex 60

xvi


4.14 TG/DTA curves of the [Tb(L1)(NO3)2H2O].NO3

complex 61

4.15 TG/DTA curves of the [Er(L1)(NO3)2H2O].NO3

complex 62

4.16 TG/DTA curves of the [Yb(L1)(NO3)2H2O].NO3

complex 63

4.17 1H NMR spectrum of the Schiff base ligand [L1] 65

4.18 IR spectrum of the Schiff base ligand [L1] 68

4.19 IR spectrum of the

[Pr(L1)(NO3)2H2O].NO3complex 69


[Sm(L1)(NO3)2H2O].NO3complex 70


[Gd(L1)(NO3)2H2O].NO3complex 71


[Tb(L1)(NO3)2H2O].NO3complex 72


[Er(L1)(NO3)2H2O].NO3complex 73


[Yb(L1)(NO3)2H2O].NO3complex 74

4.25 UV-visible spectrum of the Schiff base ligand

[L1] in DMF solution (1.0 10-6 M) at room

temperature. 76

4.26 UV-visible spectrum of the

[Pr(L1)(NO3)2H2O].NO3complex in DMF

solution (1.0 10-6 M) at room temperature. 77


[Sm(L1)(NO3)2H2O].NO3complex in DMF


xvii



[Gd(L1)(NO3)2H2O].NO3complex in DMF



[Tb(L1)(NO3)2H2O].NO3complex in DMF



[Er(L1)(NO3)2H2O].NO3complex in DMF



[Yb(L1)(NO3)2H2O].NO3complex in DMF


4.32 Comparative UV-visible spectra of the Schiff

base ligand [L1] and Ln (III) Schiff base

complexes in DMF solution (1.0 10-6 M) at

room temperature. 80

4.33 Emission spectra of Sm (III) and Tb (III) Schiff

base complexes in DMF solution (1.0 10-6 M)

at room temperature. Emission spectrum is

obtained with exc. = 360 nm. 83

4.34 Zone of inhibition of a. Sm (III) b.Sm (III) c. Er

(III) complexes of L1 Ligand for bacterial

species 86

4.35 Percentage Inhibition of Schiff base ligand [L1]

and their Ln (III) Schiff base complexes against

Escherichia coli 87



Proteus 87

xviii




Pseudomonas aeruginosa

88



Staphylococcus aureus 88

4.39 Zone of inhibition of Tb (III) complex of L1

Ligand for fungal species 91



Candida 92



Aspergillus 92




complex 100




complex 102


complex 103


complex 104


complex 105



xix


5.11 TG/DTA curves of the [Pr(L2)(NO3)2H2O]NO3

complex 110

5.12 TG/DTA curves of the [Sm(L2)(NO3)2H2O]NO3

complex 111

5.13 TG/DTA curves of the [Gd(L2)(NO3)2H2O]NO3

complex 112

5.14 TG/DTA curves of the [Tb(L2)(NO3)2H2O]NO3

complex 113

5.15 TG/DTA curves of the [Er(L2)(NO3)2H2O]NO3

complex 114

5.16 TG/DTA curves of the [Yb(L2)(NO3)2H2O]NO3

complex 115



5.19 IR spectrum of the [Pr(L2)(NO3)2H2O]NO3

complex 122

5.20 IR spectrum of the [Sm(L2)(NO3)2H2O]NO3

complex 123

5.21 IR spectrum of the [Gd(L2)(NO3)2H2O]NO3

complex 124

5.22 IR spectrum of the [Tb(L2)(NO3)2H2O]NO3

complex 125

5.23 IR spectrum of the [Er(L2)(NO3)2H2O]NO3

complex 126

5.24 IR spectrum of the [Yb(L2)(NO3)2H2O] NO3

complex 127



temperature. 129

xx



[Pr(L2)(NO3)2H2O].NO3 complex in DMF

solution (1.0 10-6 M) at room temperature

129

5.27 UV-visible spectrum of the [Sm(L2)(NO3)2H2O]

NO3complex in DMF solution (1.0 10-6 M) at


5.28 UV-visible spectrum of the [Gd(L2)(NO3)2H2O]



5.29 UV-visible spectrum of the [Tb(L2)(NO3)2H2O]



5.30 UV-visible spectrum of the [Er(L2)(NO3)2H2O]



5.31 UV-visible spectrum of the [Yb(L2)(NO3)2H2O]



5.32 Comparative UV-visible spectra of the Schiff

base ligand [L2] and Ln (III) Schiff base





at room temperature. Emission spectrum is

obtained with exc. = 360 nm. 135

5.34 Zone of inhibition of a. Gd (III) b.Gd (III)

c. Yb (III) d. Er (III) complex of L2 Ligand for

bacterial species 138

xxi




Escherichia coli

139



Streptococcus agalactiae 139



Pseudomonas aeruginosa 140




5.39 Zone of inhibition of a. Gd (III) b. Sm

(III) complex of L2 Ligand for fungal species 143



Candida 144



Aspergillus 144




complex 152




complex 154


complex 155

xxii



complex 156


complex 157



6.11 TG/DTA curves of the [Pr(L3)(NO3)2H2O]NO3

complex 162

6.12 TG/DTA curves of the [Sm(L3)(NO3)2H2O]NO3

complex 163

6.13 TG/DTA curves of the [Gd(L3)(NO3)2H2O]NO3

complex 164

6.14 TG/DTA curves of the [Tb(L3)(NO3)2H2O]NO3

complex 165

6.15 TG/DTA curves of the [Er(L3)(NO3)2H2O]NO3

complex 166

6.16 TG/DTA curves of the [Yb(L3)(NO3)2H2O]NO3

complex 167



6.19 IR spectrum of the [Pr(L3)(NO3)2H2O]NO3

complex 174

6.20 IR spectrum of the [Sm(L3)(NO3)2H2O]NO3

complex 175

6.21 IR spectrum of the [Gd(L3)(NO3)2H2O]NO3

complex 176

6.22 IR spectrum of the [Tb(L3)(NO3)2H2O]NO3

complex 177

6.23 IR spectrum of the [Er(L3)(NO3)2H2O]NO3

complex 178

xxiii


6.24 IR spectrum of the [Yb(L3)(NO3)2H2O]NO3

complex 179



temperature

182

6.26 UV-visible spectrum of the [Pr(L3)(NO3)2H2O]NO3 complex in DMF

solution (1.0 10-6 M) at room temperature 182


[Sm(L3)(NO3)2H2O]NO3 complex in DMF


6.28 UV-visible spectrum of the [Gd(L3)(NO3)2H2O]NO3 complex in DMF


6.29 UV-visible spectrum of the [Tb(L3)(NO3)2H2O]NO3 complex in DMF


6.30 UV-visible spectrum of the [Er(L3)(NO3)2H2O]NO3 complex in DMF solution

(1.0 10-6 M) at room temperature. 184

6.31 UV-visible spectrum of the [Yb(L3)(NO3)2H2O].NO3complex in DMF


6.32 Comparative UV-visible spectra of the Schiff base ligand [L3] and Ln (III) Schiff base





at room temperature. Emission spectrum is obtained with exc. = 395 nm. 188

xxiv


6.34 Zone of inhibition of a. Tb (III) b. Tb (III) c. Gd

(III) d. Tb (III) complexes of L3 Ligand for

bacterial species 191



Escherichia coli 192



Streptococcus agalactiae 192


and their Ln(III) Schiff base complexes against

Pseudomonas aeruginosa 193




6.39 Zone of inhibition of Tb (III) complex of L3

Ligand for fungal species 196



Candida 197



Aspergillus 197

7.1 1H NMR spectrum of Diphenyl-diazene 205

7.2 1H NMR spectrum of Di-p-tolyl-diazene 206

7.3 1H NMR spectrum of Bis-(4-chloro-phenyl)-

diazene 207

7.4 1H NMR spectrum of Bis-(4-nitro-phenyl)-

diazene 208

xxv


7.5 1H NMR spectrum of Bis-(4-methoxy-phenyl)-

diazene

209

7.6 1H NMR spectrum of Bis-(3-nitro-phenyl)-

diazene 210


diazene

211


diazene 212

7.9 1H NMR spectrum of Di-m-tolyl-diazene 213


diazene 214


diazene 215

7.12 1H NMR spectrum of Azodibenzoicacid 216

xxvi

LIST OF SCHEMES

SCHEME NO. TITLE PAGE NO.

1.1 Process of condensation of aldehyde and

primary amine 3

1.2 Process of formation of Schiff base with

carbinolamine intermediate 4

2.1 Catalytic oxidation of aniline using hydrogen

peroxide 26

2.2 Catalytic oxidation of 4-methoxyaniline 26

2.3 Oxidation of anilines with hydrogen peroxide

over Si-Co 27

3.1 Synthesis of Schiff base ligand [L1] 32

3.2 Synthesis of rare earth metal Schiff base [L1]

complexes. 33



complexes. 36



complexes. 38

3.7 Catalytic oxidation of aniline 40

4.1 Synthesis of Schiff base ligand [L1] and Ln (III)

Schiff base complex 45




Schiff base Complexes 148

xxvii

LIST OF ABBREVIATIONS

CDCl3 - Deuterated Chloroform

cm-1 - Per centimeter oC - Degree Celsius

DCM - Dichloromethane

DMF - Dimethyl Formamide

DMSO - Dimethyl Sulfoxide

DPPH - 2,2-diphenyl-1-picrylhydrazyl.

EtOH - Ethanol

FTIR - Fourier Transform Infrared Spectroscopy

h - Hour

HPLC - High Performance Liquid Chromatography

HRMS - High Resolution Mass Spectroscopy

M - Molar

MeOH - Methanol mg - Milligram

MHz - Mega Hertz

mL - Millilitre

mol - Mole

µgmL-1 - Microgram per millilitre

nm - Nanometer

NMR - Nuclear Magnetic Resonance Spectroscopy

pH - potence Hydrogen

ppm - Parts Per Million

RT - Room Temperature

SCm2mol-1 - Siemens Square Centimeter per mole

TG/DTA - Thermogravimetric / Differential Thermogravimetric

Analysis

TLC - Thin Layer Chromatography

TMS - Tetramethylsilane

xxviii

LIST OF SYMBOLS

* - Anti-bonding pi orbital

- Chemical shift

- Epsilon

- Equivalent conductance

µ - micro

% - Percentage

- Pi orbital

E2 - Second order elimination

- Wavelength

- Wavenumber

1

1. INTRODUCTION

The accomplishment of antimicrobial agents, ranging from direct

killing of invading pathogens to immune response modulation and other

complex biological responses, has stimulated research and clinical interest

for more than two decades. However the area is still flourishing due to

emerging discoveries in the functions, roles and regulation of antimicrobial

agents. An antimicrobial agent kills microorganisms or inhibit their growth

and they can be grouped according to the microorganisms against which

they act on; antibacterial are used against bacteria and antifungal are used

against fungi.

There are several indications that new approaches are required to

combat emerging infections and the global spread of drug-resistant

pathogens. There is no doubting the need for new strategies and new

molecules to treat pathogens that are resistant to nearly the full array of

contemporary antibiotics [1]. We are at a critical point, not seen since the

pre-antibiotic era, at which infections caused by some bacterial pathogens

are untreatable. Treatment of bacterial, fungal, and viral infections selects for

the emergence of resistant organisms that may be rare in the initial

population but become increasingly prevalent under selective drug pressure.

In fact, the presence of an antibiotic can accelerate mutation and

recombination in bacterial populations and contribute directly to its own

obsolescence.

Design of strategies for novel antimicrobial calls for the exploration

of antimicrobials which fight against the infectious microbes that exploits the

beneficial and commensal microbes in sites where normal microbiota reside.

Recently, the lanthanide Schiff base complexes have acquired special

2

attention in medicinal and pharmaceutical field since they show excellent

biological activities.

Some of the lanthanide complexes are used in biomedical analysis

as MRI contrast agents [2]. Because of special, photophysical and biological

properties, lanthanide complexes can be used as biological probes in the

areas of clinical chemistry and molecular biology [3]. Due to their special

electronic configuration, lanthanide complexes have inspired many efforts on

the design and synthesis as potential anticancer and antibacterial agents [4-

7]. Polydentate ligands such as Schiff bases, assisted by metal ions, provide

highly organised supramolecular metal complexes. Such complexes possess

binding sites and cavities for various cations, anions and organic molecules

[8].

The versatile nature of the lanthanide Schiff base complexes,

make them an important candidate in catalysis of numerous organic

transformations like oxidation of amines to their corresponding oxygen

containing derivatives. . Some of the Schiff base complexes containing N

and O donor atoms are effective stereospecific catalysts for oxidation [9],

reduction [10], hydrolysis [11], biological activities [12,13], and other organic

and inorganic transformations. These organic transformations are

environmentally friendly and hence they are highly desirable for the

treatment of waste water which contains toxic organic pollutants. Aniline one

such pollutant, is used in the manufacturing of dyes, polymers, which

includes rubber, herbicides, pesticides, fungicides, and pharmaceuticals, is

released into environment from these industries. Aniline is also found in the

effluents of petroleum refinery plants. Aniline containing chemicals find wider

applications in various arenas. Because of its toxic and unmanageable

nature it is considered to be an increasing threat to both the environment

and human health. Therefore, aniline has aroused great attention and is

classified as a persistent organic pollutant. So there is an urgent need to

develop efficient and economical methods to remove this pollutant from

wastewater.

3

Several solutions have been proposed in this regard, including

adsorption, chemical oxidation, biological and catalytic oxidation. During the

past decade, great interest has been focused on a promising technology

based on the oxidation of the hazardous and refractory organic compounds,

by the use of advanced oxidation processes. Various combinations of

hydrogen peroxide, ozone and ultraviolet light are used to generate hydroxyl

radicals.

Focus of the current research is to synthesis the lanthanide

complexes of Schiff base ligands and to study their applications as

antimicrobial agents and in catalysis.

1.1 SCHIFF BASE

Schiff bases are condensation products of primary amines with

carbonyl compounds and they were first reported by Hugo Schiff in 1864.

The common structural feature of these compounds is the azomethine group

with a general formula RN=CH-R1, where R and R1 are alkyl, aryl, cyclo alkyl

or heterocyclic groups which may be variously substituted. These

compounds are also known as anils, imines or azomethines [14 -17].

R NH2 + R' C

O

H R N CH R' + H2O

Primary amine Aldehyde Schiff base By product

Scheme 1.1 Process of condensation of aldehyde and primary amine

Schiff bases that contain aryl substituents are substantially more

stable than alkyl substituents. Schiff bases of aliphatic aldehydes are

relatively unstable and readily polymerizable, while those of aromatic

aldehydes have effective conjugation and stability.

4

The formation of a Schiff base from an aldehydes or ketones is a

reversible reaction and generally takes place under acid or base catalysis, or

upon heating [18].

C

O

H R'+ NH2R CH R'

OH

NHR

CH R'

NR

+ H2O

Aldehyde Primary amine Carbinolamine Imine By product

Scheme 1.2 Process of formation of Schiff base with carbinolamine intermediate

The formation is generally driven to the completion by separation

of the product or removal of water or both. Many Schiff bases can be

hydrolysed back to their aldehydes or ketones and amines by aqueous acid

or base [19].

The mechanism of Schiff base formation is another variation on

the theme of neucleophilic addition to the carbonyl group. In this case, the

neucleophile is the amine. In the first part of the mechanism, the amine

reacts with the aldehyde or ketone to give an unstable addition compound

called carbinolamine. The carbinolamine loses water by either acid or base

catalysed pathways. Since the carbinolamine is an alcohol, it undergoes acid

catalysed dehydration.

Typically the dehydration of the carbinolamine is the rate-

determining step of Schiff base formation and that is why the reaction is

catalysed by acids. Yet the acid concentration cannot be too high because

amines are basic compounds. If the amine is protonated and becomes non-

neucleophilic, equilibrium is pulled to the left and carbinolamine formation

cannot occur. Therefore, many Schiff bases synthesis are best carried out at

mildly acidic pH [20].

5

The dehydration of carbinolamines is also catalysed by base. This

reaction is somewhat analogous to the E2 elimination of alkyl halides except

that it is not a concerted reaction. It proceeds in two steps through an anionic

intermediate. The Schiff base formation is really a sequence of two types of

reactions, i.e. addition followed by elimination.

Because of the relative easiness of preparation, synthetic flexibility

and the special property of C=N group, Schiff bases are generally excellent

chelating agents, especially when a functional group like –OH or –SH is

present close to the azomethine group so as to form a five or six membered

ring with the metal ion. Several studies showed that the presence of a lone

pair of electrons in a sp2 hybridised orbital of nitrogen atom of the

azomethine group is of considerable chemical and biological importance

[21].

The electron-donating groups, such as azomethines can trap

metal ions with large radii and high coordination numbers. In such a case,

the two or more metal atoms are located in one cavity in close proximity to

each other and which in turn can be characterised by unusual magnetic

properties and catalytic activity [22]. Versatility of Schiff base ligands,

biological, analytical and industrial applications of their complexes make

further investigations in this area highly desirable.

1.1.1 Amino Acid Schiff Base

Schiff base complexes of amino acids have gained importance

because of their physiological and pharmacological activities. The

complexes of amino acid Schiff bases are considered to constitute new kinds

of potential antimicrobial and anticancer reagents due to the presence of

azomethine functional group [23].

Several structural studies have been carried out on Schiff base

complexes of transition and rare earth metals derived from salicylaldehyde

6

and amino acids, in view of the fact that, these complexes can be used as

non-enzymatic model analogous to the key intermediates in many metabolic

reactions of amino acids such as transamination, decarboxylation, and -

elimination and racemisation [24]. Further, the reactive functional group

associated with the amino acid side chain enhances the bridging nature of

the ligand with the central metal ion playing a vital role in metabolic activities.

The Schiff base derived amino acid have been considered to be

suitable candidate, which allow easy artificial linkage of various functional

groups with N-terminal to generate a variety of multidentate metal

complexes. The coordination behaviour of aminoacid – salicylaldehyde

derived ligands with diverse metal ions has been well explored [25].

Synthetic metallo nucleases, showing photo-induced nuclease

activity are of importance in photodynamic therapy of cancer. Hence, protein

binding and photo induced protein cleavage activity of metal complexes of

Schiff base ligands derived from amino acids have been well documented.

These are used as new generation metal based anticancer drugs to control

tumor metastases [26].

1.2 RARE EARTH METAL CHEMISTRY

1.2.1 General Characteristics

The lanthanides exhibit a number of features in their chemistry

that differentiate them from the d-block metals. The reactivity of the elements

is greater than that of the transition metals, because they exhibit a very wide

range of coordination numbers, generally 6–12 [27]. Their coordination

geometries are determined by ligand steric factors rather than crystal field

effects.

The lanthanides form labile ‘ionic’ complexes that undergo facile

exchange of ligand. The 4f orbitals in the Ln3+ ion do not participate directly

in bonding, being well shielded by the 5s2 and 5p6 orbitas. Their

7

spectroscopic and magnetic properties are thus largely uninfluenced by the

ligand [28]. Lanthanides have small crystal-field splitting and very sharp

electronic spectra in comparison with the d-block metals. They prefer anionic

ligands with donor atoms of rather high electronegativity (e.g. O, F).

They readily form hydrated complexes, on account of the high

hydration energy of the small Ln3+ ion and this can cause uncertainty in

assigning coordination numbers. Insoluble hydroxides precipitate at neutral

pH unless complexing agents are present. The chemistry is largely that of

one (3+) oxidation state, certainly in aqueous solution. They do not form

Ln=O or Ln N multiple bonds of the type known for many transition metals

and certain actinides [29]. Unlike the transition metals, they do not form

stable carbonyls and have virtually no chemistry in the zero oxidation state.

1.2.2 Magnetic Properties

With the exception of La3+ and Lu3+, the Ln3+ ions all contain

unpaired electrons and are paramagnetic. Their magnetic properties are

determined entirely by the ground state, as the excited states are so well

separated from the ground state, owing to spin–orbit coupling and are thus

thermally inaccessible [30]. The ground state for a given lanthanide ion is

unaffected by the ligands bound to it and thus crystal field splittings are weak

because of the shielding of the 4f electrons by the filled 5s and 5p orbitals.

Since the magnetic moment of the Ln3+ ions is essentially independent of

environment, one cannot distinguish between coordination geometries as is

sometimes possible for transition metals, in the case of octahedral and

tetrahedral Co2+ complexes.

1.2.3 Coordination Chemistry

Compared with transition metals, lanthanide elements have two

distinct characteristics in terms of their coordination number [31]:

8

i) Large coordination numbers. For example, the

coordination number of 3d transition metals is generally four

or six. However, the most common coordination number of

lanthanide complexes is eight or nine. This number is close

to the sum of the 6s, 6p, and 5d orbitals. Another fact

responsible for the large coordination number of lanthanide

complexes is the large ionic radius of the lanthanide

elements. The ionic radius of Fe3+ and Co3+ are 55 and 54

pm, respectively for the coordination number six. However,

the ionic radius of La3+, Gd3+, and Lu3+ are 103.2, 93.8, and

86.1 pm, respectively for the same coordination number.

ii) Variable coordination numbers. The coordinating

stabilisation energy (about 4.18 kJ·mol 1) of lanthanide ions

is much smaller than the crystal field stabilisation energy of

transition metals (typically 418 kJ·mol 1). Therefore, the

coordinating bonds of lanthanide complexes are not

directional and the coordination number varies from 3 to 12.

1.2.4 Photophysical Properties

The ground state spectral terms of lanthanide elements in the

periodic table can be sorted into two categories and these are divided by

gadolinium: the first category consists of elements before gadolinium, which

includes lanthanum, cerium, praseodymium, neodymium, promethium,

samarium, europium, and gadolinium, while the second category contains

the elements after gadolinium, which includes gadolinium, terbium,

dysprosium, holmium, erbium, thulium, ytterbium, and lutetium [32].

Because the 4f shells of lanthanide elements are unfilled, different

arrangements of 4f electrons generate different energy levels. The 4f

electron transitions, between the various energy levels, could generate

numerous absorption and emission spectra.

9

1.3 DONORS

Binding of metallo elements with polydentate ligands to form ring

structure, where the metal atom is part of the ring, is called chelation. In

chelates, metal is firmly held by a number of ligand atoms usually nitrogen,

oxygen or sulphur through coordinate covalent bonds.

Ligands that contain significantly different chemical functions such

as hard and soft donors find increasing use in chemistry because of their

selectivity introduced in the metal-ligand interactions and their possible

dynamic behavior [33].

Schiff bases are generally bi, tri or tetra dentate ligands capable of

forming very stable complexes with rare earth metals. Monodentate Schiff

bases are not known to form stable complexes, probably due to the

insufficient basic strength of the imino nitrogen of the C=N group. Bi or

tridentate Schiff base ligands are able to coordinate with many different

metal ions through both azomethine group and OH/SH group [34], and to

stabilize them in various oxidation states, enabling the use of Schiff base

metal complexes for a large variety of useful organic transformations.

The presence of hard N- and soft S-donor atoms in the backbone

of Schiff base ligands, enable them to react readily with both transition and

main group metal ions yielding stable metal complexes, some of which have

been shown to exhibit interesting physico-chemical properties and significant

biological activities [35]. There has been much interest in hard / soft mixed

donor ligands for use in catalysis [36].

The rare earth metal complexes having N and O donor Schiff

bases possess unusual configuration, structural liability and are sensitive to

molecular environment because of the versatility of their steric and electronic

properties, which can be modified by choosing the appropriate amine

10

precursors and ring substituents. They have shown an exponential increase

in their activity as inorganic catalyst for various organic transformations.

1.4 SCHIFF BASE – RARE EARTH METAL COMPLEXES

The luminescent properties of lanthanides have attracted much

attention for their wide applications in light emitting diodes, liquid crystal,

fluoro immune assays, biophysics, Laser technology and optical

telecommunication systems [37]. The luminescent intensities of the

lanthanide metal complexes are strongly dependent on (i) the efficiency of

the organic ligand to absorb UV light, (ii) the efficiency of energy transfer

from the ligand to metal, and (iii) the efficiency of lanthanide metal

luminescence.

Recently, the design and construction of lanthanide-based

complexes have sparked increasing interest not only on account of the

intriguing variety of architectures and topologies in supramolecular chemistry

and crystal engineering, but also the special photo/electroluminescence,

photocatalytic, and magnetic characteristics [38].

Schiff-base ligands with N, O donor sets have often been used

since the Schiff-base ligands may assemble coordination architectures

directed by the lanthanide (III) ions, while the lanthanide ions can promote

Schiff-base condensation and can give access to complexes. Owing to the

stabilisation of Schiff bases by coordination with lanthanide ions, it is

possible to study applications of the complexes. Complexes of Schiff base

and lanthanide are extensively used as catalysts for RNA hydrolysis, agents

in cancer radiotherapy, contrast agents for NMR imaging and luminescent

probes in visible and near IR domain [39].

11

1.5 BIOLOGICAL IMPORTANCE

Schiff bases were reported to possess antibacterial, antifungal and

antitumor activities. Several researchers have studied the synthesis,

characterisation and structure-activity relationship of Schiff bases.

The rare earth complexes of hydroxycoumarin derivatives are also

subjects of increasing interest in bioinorganic and coordination chemistry.

Lanthanides (III) complexes show antitumor activity and some interesting

lanthanide (III) complexes of coumarin derivatives have been reported [40].

Lanthanides and lanthanide compounds have attracted a great

deal of interest in recent years because they have applications in medicinal

inorganic chemistry and in materials science. In medicine, lanthanide

complexes are exploited as contrast agents for magnetic resonance imaging

(MRI) and are gaining importance in other diagnostic procedures and also as

radio therapeutic drugs [41].

1.5.1 Antimicrobial Activities

The presence of both hard nitrogen or oxygen and soft sulphur

donor atoms in the backbones, makes the ligands readily coordinate with a

wide range of transition metal ions yielding stable and intensely coloured

metal complexes, some of which have been shown to exhibit interesting

physical and chemical properties and potentially useful biological activities

[42].

In recent years, there have been several reports about the studies

on the preparation, characterisation, and antimicrobial properties of rare

earths combine with antibacterial materials. These studies all indicate that

rare earths can increase antibacterial properties. It has been established that

the antibacterial materials containing rare earths can release many free

hydroxylic radicals, which can kill bacteria efficiently [43].

12

Cleiton da Silva et al [44] have reported the synthesis and

antimicrobial activity of a series of Schiff bases derived from the

condensation of 5-chloro-salicylaldehyde and primary amines and found that

they were most active against the standard bacterial species. They have

also reported the efficiency of the Schiff bases to inhibit the growth of fungi

of clinical interest, such as Aspergillus fumigatus, Aspergillus flavus,

Trichophyton mentagrophytes and Penicillium marneffei.

Halli et al have reported a series of Co(II), Ni(II), Cu(II), Cd(II),

Zn(II) and Hg(II) complexes of neutral bidentate Schiff base with azomethine

nitrogen and carbonyl oxygen donor atoms. All compounds showed varying

antioxidant activities while Ni(II), Zn(II), and Hg(II) complexes have shown

good antioxidant activity compared to the Schiff base ligand. Further, the

DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging capacity of the

synthesised compounds dependents on the concentration [45].

1.6 CATALYTIC ACTIVITIES

Oxidation reaction is so important that it continues to be an area

attracting intense interest among academic and industrial chemists. An ideal

oxidation system would employ inexpensive, readily abundant, terminal and

environment friendly oxidants like H2O2, molecular oxygen and so on,

instead of the noxious traditional oxidants such KMnO4, K2Cr2O7, OsO4 etc.,

[46, 47].

The utilisation of peroxides as surrogates of dioxygen has been

extensively investigated for the oxidation of various organic substrates,

including amines, sulfides, alkanes, alkenes or alcohols [48]. The alkali metal

added to the supported Lanthanum catalysts caused selective promotion of

the catalytic activity for the partial oxidation of benzyl alcohol [49].

Oxidation of amines to their corresponding oxygen containing

derivatives has attracted much attention during the past few decades.

13

Azobenzene, azoxybenzene, nitrobenzene and nitrosobenzene have been

formed in the oxidation of aniline by organic and inorganic oxidants. The

product composition in the oxygenation of amines depends on the oxidant,

catalyst, quaternary ammonium salts and reaction conditions employed [50].

C. F. Chang et al (2009) have reported their results on the

oxidation of amines by aqueous hydrogen peroxide under the influence of

Si-Co as catalyst, in which quantised amount of catalyst, oxidant and

reaction time was observed for carrying out the catalytic reaction [51]. Hence

the rare earth metal complexes have received attention as promising

oxidation catalysts in the selective oxygenation of aromatic and aliphatic

amines, in term of lesser quantum of catalyst and load time.

1.7 METALLO – ELEMENTS UNDER INVESTIGATION

1.7.1 Praseodymium

Praseodymium is a chemical element that has the symbol Pr and

atomic number 59. Praseodymium is a soft, silvery, malleable and ductile

metal in the lanthanide group. It is too reactive to be found in native form,

and when artificially prepared, it slowly develops a green oxide coating.

Compounds of praseodymium occur in oxidation states +2, +3

and/or +4. Praseodymium (IV) is a strong oxidant, instantly oxidizing water to

elemental oxygen (O2), or hydrochloric acid to elemental chlorine. Thus, in

aqueous solution, only the +3 oxidation state is encountered. Praseodymium

(III) salts are yellow-green and, in solution, present a fairly simple absorption

spectrum in the visible region, with a band in the yellow-orange at 589–

590 nm (which coincides with the sodium emission doublet), and three

bands in the blue/violet region, at 444, 468 and 482 nm approximately.

Praseodymium is paramagnetic at any temperature above 1K [52].

These positions vary slightly with the counter-ion. Praseodymium oxide, as

obtained by the ignition of salts such as the oxalate or carbonate in air, is

14

essentially black in colour with a tint of brown or green and contains +3 and

+4 praseodymium in a somewhat variable ratio, depending upon the

conditions of formation. Its formula is conventionally rendered as Pr6O11.

Praseodymium oxide in solid solution with ceria, or with ceria-zirconia, have

been used as oxidation catalysts [53].

1.7.2 Gadolinium

Gadolinium is a chemical element with symbol Gd and atomic

number 64. It is a silvery-white, malleable and ductile rare-earth metal. It is

found in nature only in combined (salt) form. Gadolinium is paramagnetic at

room temperature, with a ferromagnetic curie point of 20 °C [54].

Gadolinium combines with most elements to form Gd (III)

derivatives. Nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon

and arsenic at elevated temperatures, forming binary compound [55].

Unlike other rare earth elements, metallic gadolinium is relatively

stable in dry air. However, it tarnishes quickly in moist air, forming a loosely

adhering gadolinium (III) oxide (Gd2O3), which spalls off, exposing more

surfaces to oxidation

Gadolinium has no known native biological role, but its compounds

are used as research tools in biomedicine. Gd3+ compounds are components

of MRI contrast agents. It is used in various ion channel electrophysiology

experiments to block sodium leak channels and stretch activated ion

channels.

1.7.3 Samarium

Samarium is a chemical element with symbol Sm and atomic

number 62. It is a moderately hard silvery metal that readily oxidizes in air.

Being a typical member of the lanthanide series, samarium usually assumes

the oxidation state +3. Compounds of samarium (II) are also known, most

15

notably the monoxide SmO, mono chalcogenides SmS, SmSe and SmTe, as

well as samarium (II) iodide. The last compound is a common reducing

agent in chemical synthesis. Samarium has no significant biological role and

is only slightly toxic.

Important application of samarium and its compounds is as

catalyst and chemical reagent. Samarium catalysts assist decomposition of

plastics, dechlorination of pollutants such as polychlorinated biphenyls

(PCBs), as well as the dehydration and dehydrogenation of ethanol [56].

Samarium metal has no biological role in human body. Its salts

stimulate metabolism, but it is unclear whether this is the effect of samarium

or other lanthanides present with it. The total amount of samarium in adults

is about 50 micrograms, mostly in liver and kidneys and with about 8

micrograms per liter being dissolved in the blood. Samarium is not absorbed

by plants to a measurable concentration and therefore is normally not a part

of human diet. However, a few plants and vegetables may contain up to 1

part per million of samarium. Insoluble salts of samarium are non-toxic and

the soluble ones are only slightly toxic [57].

1.7.4 Terbium

Terbium is a chemical element with the symbol Tb and atomic

number 65. It is a silvery-white rare earth metal that is malleable, ductile and

soft enough to be cut with a knife. Terbium is never found in nature as a free

element, but it is contained in many minerals, including cerite, gadolinite,

monazite, xenotime and euxenite. The most common valence state of

terbium is +3, as in Tb2O3. The +4 state is known in TbO2 and TbF4 [58].

Terbium burns readily to form a mixed terbium (III, IV) oxide.

Terbium oxide is used in green phosphors in fluorescent lamps

and colour TV tubes. Sodium terbium borate is used in solid state devices.

The brilliant fluorescence allows terbium to be used as a probe in

16

biochemistry, where it somewhat resembles calcium in its behavior. Terbium

"green" phosphors (which fluorescence a brilliant lemon-yellow) are

combined with divalent europium blue phosphors and trivalent europium red

phosphors to provide the "trichromatic" lighting technology which is by far the

largest consumer of the world's terbium supply. Trichromatic lighting

provides much higher light output for a given amount of electrical energy

than the incandescent lighting [59].

1.7.5 Erbium

Erbium is a chemical element in the lanthanide series, with the

symbol Er and atomic number 68. A silvery-white solid metal when artificially

isolated, natural erbium is always found in chemical combination with other

elements on Earth [60].

Erbium's everyday uses are varied. It is commonly used as a

photographic filter and because of its resilience it is useful as a metallurgical

additive. A large variety of medical applications (i.e. dermatology, dentistry)

utilize erbium ion's 2940 nm emission, which is highly absorbed in water

(absorption coefficient about 12000/cm). Such shallow tissue deposition of

laser energy is necessary for laser surgery, and the efficient production of

steam for laser enamel ablation in dentistry.

Erbium does not have a biological role, but erbium salts can

stimulate metabolism. Human consume 1 milligram of erbium a year on

average [61]. The highest concentration of erbium in human is in the bones,

but there is also erbium in the human kidneys and liver.

1.7.6 Ytterbium

Ytterbium is a chemical element with symbol Yb and atomic

number 70. It is the fourteenth and penultimate element in the lanthanide

series, or last element in the f-block, which is the basis of the relative stability

of the +2 oxidation state. However, like the other lanthanides, the most

17

common oxidation state is +3, seen in its oxide, halides and other

compounds. In aqueous solution, like compounds of other late lanthanides,

soluble ytterbium compounds form complexes with nine water molecules.

Because of its closed-shell electron configuration, its density and melting

and boiling points differ from those of the other lanthanides.

The ytterbium +3 ion is used as a doping material in active laser

media, specifically in solid state lasers and double clad fiber lasers.

Ytterbium lasers are highly efficient, have long lifetimes and can generate

short pulses; ytterbium can also easily be incorporated into the material used

to make the laser [62]. Ytterbium lasers commonly radiate in the 1.06–

1.12 µm band being optically pumped at wavelength 900 nm–1 µm,

dependently on the host and application. The small quantum defect makes

ytterbium a prospective dopant for efficient lasers and power scaling [63].

Ytterbium can also be used as a dopant to help improve the grain

refinement, strength and other mechanical properties of stainless steel.

Some ytterbium alloys have rarely been used in dentistry [64].

18

2. LITERATURE OVERVIEW

2.1 INTRODUCTION

Nowadays, the research field dealing with Schiff base coordination

chemistry has expanded enormously. The importance of Schiff base

complexes for bioinorganic chemistry, biomedical applications,

supramolecular chemistry, catalysis and material science, separation and

encapsulation processes, and formation of compounds with unusual

properties and structures has been well recognised and reviewed. In this

chapter the various fields where the Schiff base complexes finds applications

and several aspects explored by the researchers has been reviewed in

detail.

2.2 ANTIMICROBIAL PROPERTIES

Schiff bases have been reported to show a variety of biological

actions by virtue of the azomethine linkage, which is responsible for various

antibacterial, antifungal, herbicidal and clinical activities. They form an

interesting class of ligands that has enjoyed popular use in the coordination

chemistry of transition, inner transition and main group elements.

Biological and pharmaceutical activities of Schiff base derived

from 2-thiophene carboxaldehyde and aminobenzoic acid have been studied

in comparison to Cu, Fe, Zn, Ni and Co complexes by Safaa et al (2011)

[65]. These compounds were screened for the antimicrobial activity against

bacterial species and fungal species. E. coli was inhibited by Fe, Cu and Zn

complexes and Candida species was inhibited with low inhibition zone.

19

Taha et al (2011) [66] reported the synthesis of Ln (III) complexes

of the Schiff base ligand bis-(salicyladehyde)-1,3-propylenediimine and

screened them for the antibacterial activity. The results obtained reflected

that the ligand exhibited a good activity against Pseudomonas aeruginosa

and Shigella dysenteriae and do not show any activity against Proteus

vulgaris. Most of the tested Ln (III) complexes possessed a high

antibacterial activity against the Gram-negative bacteria tested.

Jadhav et al (2011) [67] explored the antimicrobial activity of the

Schiff base ligands synthesised from dehydroacetic acid, o-phenylene

diamine and fluoro benzaldehyde and its metal complexes of Cu(II), Ni(II),

Co(II), Fe(III) and Mn(II). The results of investigation indicated that all the

ligands and their metal complexes arrested the growth of Aspergillus niger

and Trichoderma. Metal complexes showed considerable increase in fungi

toxicity compared to their ligands. The in vitro antibacterial activity against

bacteria such as Staphylococcus aureus and Escherichia coli, by paper disc

plate method, show that the inhibition by metal complexes was higher than

that of the free ligands and corresponding metal salts against the same

organism under identical experimental conditions.

A series of La(III), Th(IV) and VO(IV) complexes with Schiff bases

derived from 8-formyl-7-hydroxy-4-methylcoumarin and o-phenylenediamine

/ ethylenediamine have been synthesised and screened for their in vitro

antimicrobial activity by Kulkarni et al (2009) [40]. Antibacterial study

revealed that, Schiff bases and some metal complexes were found to be

highly active against Escherichia coli, Pseudomonas aeruginosa and

Salmonella typhi. In case of antifungal studies, both Schiff bases and some

of their complexes were found to be highly active against Aspergillus niger,

Aspergillus flavus and Cladosporium fungi.

The antimicrobial activity of nine Ln (III) complexes of the Schiff

base ligand derived by the condensation of 2-hydroxy-1 naphthaldehyde

with 1,6-hexanediamine, was explored by Ajlouni et al (2012) [22]. All the

20

nine Ln (III) complexes and the Schiff base ligand was studied against

Pseudomonas aeruginosa, Klebsiella and Escherichia coli bacteria. It was

observed from the result that most of the synthesised complexes of the

tested series possessed good antibacterial activity against bacteria and the

microbial activity of the complexes in most cases is higher than that of the

corresponding ligand.

The anti-oxidant potential of Schiff base ligand and its lanthanide

complexes, [Ln(H2L)(NO3)2 . 2H2O]NO3, ((Ln = La, Pr, Nd, Sm, Eu, Gd, Tb,

Dy and Er) (H2L = Schiff base ligand)) was determined by its scavenging

ability on the stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical by

Ajlouni et al (2012) [68]. Ln (III) complexes are significantly more efficient in

quenching DPPH radical than the free ligand. Ligand interacts with the

positively charged Ln (III). The electron density is drawn from the oxygen

that makes the O–H bond more polarised; as a result, the H atom has a

greater tendency to ionize than those in the free ligand. Due to the above

reasons the lanthanide complexes show stronger antioxidant activities than

the ligand alone.

Teng-Jin et al (2014) [69] synthesised two multidentate Schiff

bases by reacting S-4 picolyldithiocarbazate with 4-carboxybenzaldehyde

(Cb4PDTC) and pyridine-2-carboxaldehyde (Pc4PDTC) and their transition

metal Ni(II), Cu(II), Zn(II) and Cd(II)) complexes. Moreover, their anti-

microbial, cytotoxic and antioxidant activities were evaluated. The result

which showed that only copper (II) and cadmium (II) complexes are active

against four types of fungi and bacteria

The antioxidant activities of four Ag(I), Cd(II) and Cu(II) complexes

[Ag2L2](ClO4)2, [CdL(NO3)2], [Cd2L2Cl4] and [Cu2L2 (ClO4)3](ClO4) with the

Schiff base ligand derived from 1-(pyrazin-2-yl) ethanone and 1,2-

ethanediamine were described by Omer et al (2014) [70]. The metal

complexes showed better antioxidant activities than the ligand. Among these

complexes, [Cu2L2 (ClO4)3] (ClO4) complex showed a higher activity than the

21

other complexes. This was attributed to the chelation of the organic

molecules with the metal ions to generate a strong effect on scavenging

radicals in the biological system. The antioxidant activity of the ligand and its

complexes showed a guiding role for the design and synthesis of potential

antioxidants and therapeutic agents for some diseases.

Wider investigations were carried out by Ceyhan et al (2011) [71]

on biological activities of the Schiff base ligands (HL1 and HL2 obtained from

2,6-di-tert-butyl-4-hydroxy aniline, and two carbonyl compounds 2,6-di-

formyl-4-isopropyl phenol and 2,6-di-formyl-4-tert-butyl phenol) and their

metal complexes against the bacteria and yeast. The organisms used were

C. xerosis, B. brevis, B.megaterium, B. cereus, M. smegmatis, S. aureus, M.

luteus and E. faecal (as Gram-positive bacteria) and P. aeruginosa, K.

pneumoniae, E. coli, Y. enterocolitica, K. fragilis, S. cerevisiae, and C.

albicans (as Gram-negative bacteria). The diffusion agar technique has been

used to evaluate the antibacterial activity of the synthesised complexes. The

results of the bactericidal screening showed that the Schiff base ligand HL1

has no activity on B. megaterium, M. luteus, S. cerevisiae, and K. fragilis, it

shows activity against the other microorganisms. The ligand HL2 does not

show any activity against M. smegmatis, M. luteus, E. faecalis, E. coli,

S. cerevisiae, and C. albicans, but, it has moderate activity against the other

microorganisms.

The antimicrobial properties of the novel transition metal Schiff

base complexes derived from 5-bromosalicylaldehyde and 1,2-bis(4-chloro-

2-aminophenoxy)ethane has been well explored by Salih et al (2014) [72].

The Schiff and its all metal complexes showed weak antibacterial activities

against E. coli, while Ligand (L), Cu(II), Ni(II), Co(II), Zn(II), Ti(III), V(III) and

Fe(III) complexes showed weak antibacterial activities against B. subtilis

except Mn(II). On the other hand, Ni(II) complex exhibited strong

antibacterial activity against M. luteus, Zn(II) and Mn(II) showed weak

antibacterial activities against M. luteus. The ligand and it’s all metal

complexes did not exhibit antibacterial activities against P. aeruginosa.

22

Kavitha et al [73] reported the antimicrobial properties for a series

of Co(II) complexes of 3-formyl chromone Schiff bases the ligands either

exhibited no activity or having low to moderate activity against bacteria and

fungi strains. But their Co (II) complexes showed moderate to good activity

compared to the standard antibiotics. Among all the Co(II)complexes,

[Co(L2)2].3H2O (L2=2-((4-oxo-4H-chromen-3 yl)methylneamino) benzoicacid)

complex showed effective activity against all bacteria and fungi strains.

However [Co(L4)2].3H2O (L4=3-((2-mercaptophenylimino)methyl)-4H-

chromen-4-one)does not show activity against P.vulgaris and C.albicans. In

comparison, the activity of all the strains was increased by ligands when

coordinated with Co (II) ion.

2.3 LUMINESCENT PROPERTIES

Organo lanthanide complexes attract considerable interest, not

only because of their structures, but also potential applications of their

luminescent properties. The luminescence of a complex depends not only on

the metal ion but also on the coordination environment, e.g., a metal-

centered, ligand sensitised luminescence may occur when a suitable ligand

efficiently absorbs the excitation energy followed by energy transfer to the

metal center.

Taha et al (2011) [66] synthesised and characterised the

tetradentate Schiff base ligand L (L = bis-(salicyladehyde)-1,3-

propylenediimine) and its Ln (III) complexes. The Tb and Dy complexes

exhibited characteristic luminescence of Tb and Dy ions whereas the Nd, La,

Gd, Er, Sm and Pr complexes showed only the fluorescence characteristic of

the ligand. This indicated that the ligand L was a good organic chelator to

absorb and transfer energy to Tb and Dy ions. They explained that the

energy gap between the lowest triplet state energy level of the ligand and

the lowest excited state level of Tb (III) favour to the energy transfer process

for Tb.

23

Figure 2.1 Emission spectrum of the complex [TbL(NO3)2(H2O)2](NO3)

Pengfei Yan et al (2007) [74] synthesised six new 1D lanthanide

Schiff base coordination polymers and characterised them by elemental

analysis and spectroscopic analysis. Fluorescent spectroscopic analysis

indicated that ligand tunes the luminescent properties of the lanthanide ions.

The triplet state energy level of the Schiff base ligand matched well with the

lowest excited state (4G5/2) level of Sm3+ ion. Hence they observed that the

lanthanide schiff-base complexes are promising luminescent materials. The

studied the design of analogous polymers using various Schiff bases and

explored the accessibility of the Lewis acid lanthanide metal sites in the

complexes.

Pawan et al (2011) [75] has reported the mesogenic Schiff-base,

N,N-di-(4-decyloxysalicylidene)- l,6-diaminohexane, coordinates to Ln (III)

as a neutral bi-dentate species to yield seven-coordinate complexes with La,

Pr, Nd, Sm, Eu, Gd, Tb, Dy and Ho, the polyhedron being possibly distorted

mono-capped octahedron. The zwitterion-species of the neutral bi-dentate

ligand, coordinated to the Ln (III) metal ion through two phenolate oxygens.

The fluorescence studies indicate that the ligand appeared to be a suitable

organic chelator for energy transfer to Tb (III) ion.

24

Figure 2.2 The fluorescence spectra of (a) Tb (III) and (b) Sm (III) complexes

Tian-Lin et al (2007) [76] reported the synthesis of a new Schiff

base ligand with tripodal structure, N,N,N-tri-(3-indolemethanal)

triaminotriethylamine and its complex with terbium. The author revealed that

the Schiff base ligand could form stable complex with terbium ion and was

coordinated to Schiff base nitrogen atoms and the bridgehead nitrogen atom

of the ligand. The terbium complex with ligand can emit intrinsic spectrum of

the ion under excitation of ultraviolet light. The results indicated that H+ could

strongly enhance the luminescence of terbium complex with ligand in

aqueous solutions. The results demonstrate that the nitrogen atom of indole

is important for the fluorescence enhancement of the switch. The

mechanism of the fluorescence enhancement by protonation of the indole

nitrogen atom is due to the suppressed photoinduced electron transfer

(PIET) fluorescence quenching when adding acid.

Jean-Claude et al (2007) [77] has explored the wide choice of

luminescence properties displayed by lanthanide ions, as well as the well-

mastered introduction of these ions into a wealth of different molecular and

extended structures such as coordination polymers and microporous

materials, which is a fantastic playground for scientists and engineers. This

also revealed that the lanthanides will be the key elements in helping

scientists to meet all the future technological challenges, including solving

25

the energy problem. This will also boost the capability to monitor biological

processes essential to life and help physicians curing major diseases such

as cancer.

2.4 CATALYTIC PROPERTIES

Organic pollutants in industrial wastes predominantly contain

amines. Research has been widely carried out to oxidise these amines into

nontoxic products. Schiff base ligands and its transition and rare earth metal

complexes are used as catalyst for this oxidation studies. Researchers have

been aiming to oxidise the amines to the desired products and also enhance

the life cycle of the catalyst under optimum conditions.

A new approach for polymerisation of aniline has been reported by Nabid et al (2007) [78] by using transition-metal tetrasulfonated phthalocyanine as catalysts. This approach provided a distinct advantage over similar reactions employing native enzymes due to higher stability and lower price of the catalysts. The polymerisation was accomplished in an aqueous buffer at pH 2. The results indicate that application of Fe complexes in polymerisation of aniline is better than Mn and Co as catalysts. Also they have shown that the metallophthalocyanines are better catalysts than metalloporphyrin.

Alizadeh et al (2005) [50] showed that the oxidation of aniline by 35% hydrogen peroxide, catalysed by H3PW12O40 family (under two-phase conditions at room temperature or under reflux) provided a simple and general procedure for the preparation of nitrosoaniline, which was difficult to prepare selectively by conventional methods. The results clearly demonstrated that this oxidation system was more efficient in the selective oxidation of aniline with hydrogen peroxide.

The oxidations of primary aromatic amines were investigated by Wenchao Lu et al (2008) [79]. Cuprous chloride-air system can catalyze the oxidation of primary aromatic amines to azo derivatives, anils and quinone

26

anils. They have reported that the experimental procedure is simple and the products could be easily isolated in high yields.

Scheme 2.1 Catalytic Oxidation of aniline using hydrogen peroxide

Scheme 2.2 Catalytic Oxidation of 4-methoxyaniline

The catalytic activities of the lanthanum (La) catalysts supported

on the zeolite and SiO2 and the alkali metal-added counterparts (alkali

metal/La/support) were studied by Masaya et al (2004) [49] using the gas-

phase catalytic oxidation of benzyl alcohol. The addition of alkali metal to the

La/NaZSM-5 and La/SiO2 catalysts caused an increase in the oxidation

activity, particularly the partial oxidation activity of benzyl alcohol. The added

alkali metal was indicated to play an important role in activating the reactant

through the adsorption of benzyl alcohol, in addition to inhibiting the

deposition of carbonaceous materials on the catalyst.

Chang et al (2009) [51] have given the procedure in their work

which offers several advantages for the preparation of azoxybenzenes from

the corresponding aniline such as low loading of catalyst, mild conditions,

high yields and clean reactions, which make it a useful and attractive

27

methodology for organic synthesis. The simple workup procedure is also

beneficial to this method. Although the preparation of the catalyst was

nontrivial, it offers information for the future design of new catalysts.

Scheme 2.3 Oxidation of anilines with hydrogen peroxide over Si-Co

Through the literature review it has been observed that the Schiff

bases show a variety of biological actions by virtue of the azomethine

linkage, which is responsible for various antibacterial, antifungal and

antioxidant properties. Upon complexation, these properties found to

enhance due to the coordination with the central metal ions. In addition, it

has been reported that the Schiff base complexes of transition, rare earth

metal ions have played a significant role in various reactions to enhance

their yield and product selectivity. The convenient route of synthesis and

thermal stability of Schiff base ligands have contributed significantly for their

possible applications in catalysis as metal complexes. Catalytic activity of

Schiff base complexes show significant variations with structure and type of

Schiff base ligands used. These studies have clearly demonstrated that the

Schiff base complexes of rare earth metals are versatile and efficient

catalysts for reaction of commercial importance and suitable to catalyze

various reactions under mild conditions.

Keeping all these facts in mind and the efficacy of the Schiff base

metal complexes, new type of Schiff base ligands using aminoacid

derivatives and rare earth Schiff base complexes are synthesized and they

are screened for various applications like antibacterial, antifungal,

luminescent and catalytic properties.

28

2.5 AIMS AND OBJECTIVES

The major objectives of the current study are:

i) to prepare new Schiff bases having N, O donor ligands using

the derivatives of aminoacids viz., serine, threonine and

leucine respectively with 5-bromo salicylaldehyde.

ii) to synthesise complexes with the above ligands using rare

earth metals like Pr, Sm, Gd, Tb, Er and Yb.

iii) to characterise the various Schiff base ligands and rare earth

metal complexes using spectral / analytical techniques like

FTIR, NMR, UV, mass and TGA/DTA.

iv) to study the fluorescence effect of Ln (III) Schiff base

complexes derived from serine, threonine and leucine.

v) to study the applicability towards the antimicrobial activity of

the rare earth metal Schiff base complexes derived from

serine, threonine and leucine.

vi) to study the catalytic effect of rare earth metal Schiff base

complexes derived from leucine, in the oxidation of aniline

and substituted anilines.

2.6 OUTLINE OF THE THESIS

The content of the current thesis has been divided into ten

chapters.

Chapter one: This chapter throws light on the fundamental

concepts and brief introduction of the present work.

Chapter two: This chapter reviews the literature concerning

various Schiff bases derived from amino acid, importance of Schiff bases,

29

their characterisation and rare earth metal Schiff base and their applications

in various fields.

Chapter three: A detailed description of all the reagents and

materials used, procedures for physical measurements has been discussed

in this chapter. Also, the procedures for the preparation of Schiff bases in

addition to the synthesis of their corresponding rare earth metal complexes,

procedures for antimicrobial, antioxidant and the catalytic activities of the

synthesised compounds has been discussed.

Chapter four: This chapter illustrates the preparation and

characterisation of the rare earth metal Schiff base complexes of type

[Ln(L1)(NO3)2(H2O)].NO3.Where, Ln = Pr (III), Sm (III), Gd (III), Tb (III), Er

(III) and Yb (III) and L1 = Sodium 2-(5-bromo-2-hydroxybenzylideneamino)-

3-hydroxypropanoate, derived from L-serine and 5-bromosalicylaldehyde.

Fluorescence characteristics of the above said complexes have been

studied and the complexes are screened for their antimicrobial activities.

Chapter five: The synthesis of various rare earth metal

complexes of the Schiff base ligand L2 derived from threonine and 5-

bromosalicylaldehyde, L2 = Sodium 2-(5-bromo-2-hydroxybenzylidene

amino)-3-hydroxybutanoate and the spectral characterisation of the newly

synthesised complexes have been expressed in this chapter, along with their

fluorescence, antimicrobial activities.

Chapter six: This chapter describes the synthesis of new

lanthanide complexes of Pr (III), Sm (III), Gd (III), Tb (III), Er (III) and Yb

(III) with the Schiff base, Sodium 2-(5-bromo-2-hydroxybenzylideneamino)-

4-methylpentanoate, derived from leucine and 5-bromosalicylaldehyde.

Their fluorescence and antimicrobial nature have also been studied.

Chapter Seven: This chapter describes the catalytic nature of the

synthesised lanthanide complexes, Pr (III), Sm (III), Gd (III), Tb (III), Er (III)

30

and Yb (III) with the Schiff base, derived from leucine towards the oxidation

of anilines and substituted anilines with H2O2 as oxidant.

Chapter Eight: This is a concluding chapter which focuses on the

summary of the present work. Various tridentate Schiff base ligands L1, L2,

L3 and their Ln (III) complexes were synthesised and characterised by

elemental analysis, TGA/DTA, spectral analysis like 1H NMR, UV, FT-IR and

Mass Spectrometry. The fluorescence studies of the synthesised complexes

indicate that the ligand L is a good organic chelator to absorb energy and

transfer it to Ln (III) ions. The biological studies of the complexes show that

most of the synthesised complexes possess a good biological activity

against pathogens tested than the corresponding free Schiff base ligand.

The Ln (III) complexes of the Schiff base ligand L3 possess good catalytic

ability for oxidation of aniline under mild conditions and [Gd(L3)(NO3)2

(H2O)]NO3 complex was chosen as standard to check the generality and

efficiency of oxidation of various substituted anilines.

Chapter Nine: The future prospect of the current investigation has

been presented in this chapter.

Chapter Ten: The list of references used throughout the thesis

has been given in this chapter.

31

3. EXPERIMENTAL METHODS AND TECHNIQUES

The details of the general experimental techniques adopted,

analytical procedures and materials employed along with details like

preparation of ligands, preparation of metal complexes, solvent purification

are described in this chapter.

3.1 MATERIALS EMPLOYED

The following chemicals were used at various stages of this work:

The sources of the chemicals are given within parenthesis. 5-bromo

salicylaldehyde, L-Leucine (Sigma-Aldrich), L-Serine (Sigma-Aldrich),

L-Threonine (Sigma-Aldrich), Praseodymium (III) nitrate hexahydrate (Rare

Earths), Samarium (III) nitrate hexahydrate (Rare Earths), Gadolinium

(III) nitrate hexahydrate (Rare Earths), Erbium (III) nitrate hexahydrate

(Rare Earths), Terbium (III) nitrate hexahydrate (Rare Earths), Ytterbium

(III) nitrate hexahydrate (Rare Earths), Sodiumhydroxide pellets (SRL),

Phenylamine (Sigma-Aldrich), p-Tolylamine (Sigma-Aldrich), 4-Chloro-

phenylamine (Sigma-Aldrich), 4-Nitro-phenylamine (Sigma-Aldrich),

4-Methoxy-phenylamine (Sigma-Aldrich), m-phenylenediamine (Sigma-

Aldrich), 3-Methoxy-phenylamine (Sigma-Aldrich), 3-Chloro-phenylamine

(Sigma-Aldrich), m-Tolylamine (Sigma-Aldrich), 2-Chloro-phenylamine

(Sigma-Aldrich), 2-Methoxy-phenylamine (Sigma-Aldrich), Amino-benzoic

acid (Sigma-Aldrich), 30 % H2O2 (SRL).

3.2 SOLVENTS

Common solvents like ethanol, methanol, acetone, acetonitrile,

chloroform, dichloromethane, hexane, petroleum ether, DMSO, DMF(HPLC

Grade), and CDCl3 used at various stages of this work were purified

32

according to the standard procedures described either in Weissberger series

(Weissberger et al 1970) or in qualitative analysis by Vogel (Vogel 1978).

3.3 EXPERIMENTAL METHODS

3.3.1 Synthesis of Schiff Base Ligand [L1]

The sodium salt of the Schiff base ligand L1 was synthesised as

per the following literature procedure [80]. To an aqueous solution of

L-Serine (0.002 mol) in 10 mL water containing NaOH (0.002 mol),

5-bromosalicyaldehyde (0.002 mol) in 10 mL ethanol was added drop wise

with constant stirring and heated under reflux for 3-5 h on a mantle at 50oC.

Then, the reaction mixture was cooled to room temperature. Fine shining

yellow precipitate of the sodium salt of the Schiff base ligand L1 (sodium 2-

(5-bromo-2-hydroxybenzylideneamino)-3-hydroxypropanoate) formed was

filtered off, washed with ethanol-water mixture and stored in a vacuum

desiccator over anhydrous calcium chloride.

H2NOH

OOH

serine

+HO

OBr

5-bromosalicylaldehyde

OHN

Br

OOH

ONaEtOH/NaOH

Reflux - 3h

L1sodium 2-(5-bromo-2-hydroxybenzylideneamino)-3-

hydroxypropanoate

Scheme 3.1 Synthesis of Schiff base ligand [L1]

3.3.2 Synthesis of [Ln(L1)(NO3)2(H2O)].NO3 Complexes

The rare earth Schiff base complexes were synthesised as per the

following general literature procedure [80]. A 0.002 mol of a Schiff base

ligand L1 was dissolved in 10 mL of ethanol. To this solution, a solution of

0.002 mol Ln(NO3)3.xH2O in 10 mL water, was added drop wise with

33

constant stirring and finally heated under reflux for 3 – 5 h on a hot plate at

50oC. The reaction mixture was cooled to room temperature. A fine yellow

precipitate of the solid complexes formed was filtered off, washed with

ethanol-water mixture and stored in a vacuum desiccator over anhydrous

calcium chloride.

The following Ln (III) complexes were prepared using the similar

procedure and its physical properties are tabulated in Table 3.1.

[Pr(L1)(NO3)2(H2O)] NO3,

[Sm(L1)(NO3)2(H2O)] NO3,

[Gd(L1)(NO3)2(H2O)] NO3,

[Tb(L1)(NO3)2(H2O)] NO3,

[Er(L1)(NO3)2(H2O)] NO3,

[Yb(L1)(NO3)2(H2O)] NO3.

CH

O

N CO

LnO

NO3

NO3

H2O NO3

OH

OHN

Br

OOH

ONa

L1

BrLn(NO3)3.xH2OReflux3-5 h

+EtOH / H2O mixture

Scheme 3.2 Synthesis of rare earth metal Schiff base [L1] complexes.

34

Table 3.1 Physical properties and the percentage yield of the Schiff base ligand [L1] and its Ln (III) complexes

Compound Molecular Formula Colour Yield (%)

L1 C10H9O4NBrNa Bright Yellow 79

[Pr(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrPr Yellow 86

[Sm(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrSm Yellow 84

[Gd(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrGd Pale Yellow 96

[Tb(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrTb Yellow 92

[Er(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrEr Yellow 74

[Yb(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrYb Yellow 81


The sodium salt of the Schiff base ligand L2 was synthesised as

per the following literature procedure [81]. To an aqueous solution of

threonine (0.002 mol) in 10 mL water containing NaOH (0.002 mol),

5-bromosalicyaldehyde (0.002 mol) in 10 mL ethanol was added drop wise

with constant stirring and heated under reflux for 3-5 h. on a mantle at 50oC.


yellow precipitate of the sodium salt of the Schiff base ligand (sodium 2-(5-

bromo-2-hydroxybenzylideneamino)-3-hydroxybutanoate) formed was

filtered, washed with ethanol-water mixture and stored in a vacuum

desiccator over anhydrous calciumchloride.

35

NH2

OH

OHO

Threonine

+HO

OBr


OHN

Br

OOH

ONaEtOH/NaOH

Reflux - 3h


hydroxybutanoate


3.3.4 Synthesis of [Ln(L2)(NO3)2(H2O)].NO3 Complex

The rare earth Schiff base complexes were synthesised as per the



0.002 mol Pr(NO3)3.xH2O in 10 mL water, was added drop wise with

constant stirring and finally heated under reflux for 3 – 5 h. on a hot plate at


precipitate of the solid complex formed was filtered, washed with ethanol-

water mixture and stored in a vacuum desiccator over anhydrous calcium

chloride.



[Pr(L2)(NO3)2(H2O)] NO3,

[Sm(L2)(NO3)2(H2O)] NO3,

[Gd(L2)(NO3)2(H2O)] NO3,

[Tb(L2)(NO3)2(H2O)] NO3,

[Er(L2)(NO3)2(H2O)] NO3,

[Yb(L2)(NO3)2(H2O)] NO3.

36

OHN

Br

OOH

ONa

L2

Ln(NO3)3.xH2OReflux3-5 h

NO3

+EtOH / H2O mixture

CH

O

N CO

LnO

NO3

NO3

H2O

OH

Br

Scheme 3.4 Synthesis of rare earth metal Schiff base [L2] complexes.




[Pr( L2)(NO3)2(H2O)]NO3 C11H12O11N3BrPr Yellow 93


[Gd(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrGd Yellow 86

[Tb(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrTb Pale Yellow 94


[Yb(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrYb Pale Yellow 79


The sodium salt of the Schiff base ligand was synthesised as per

the following literature procedure [82]. To an aqueous solution of Leucine

(0.002 mol) in 10 mL water containing NaOH (0.002 mol), 5-

bromosalicyaldehyde (0.002 mol) in 10 mL ethanol was added drop wise

with constant stirring and heated under reflux for 3-5 h. on a mantle at 50oC.


yellow precipitate of the sodium salt of the Schiff base ligand (sodium 2-(5-

bromo-2-hydroxybenzylideneamino)-4-methylpentanoate) formed was

37

filtered off, washed with ethanol-water mixture and stored in a vacuum

desiccator over anhydrous calcium chloride.

NH2

O

HO

Leucine

+HO

OBr


OHN

Br

O

ONaEtOH/NaOH

Reflux - 3h

L3

sodium 2-(5-bromo-2-hydroxybenzylideneamino)-4-methylpentanoate


3.3.6 Synthesis of [Ln(L3)(NO3)2(H2O)] NO3 Complex

The rare earth Schiff base complex was synthesised as per the



0.002 mol Ln(NO3)3.xH2O in 10 mL water, was added drop wise with

constant stirring and finally heated under reflux for 3 – 5 h. on a hot plate at


precipitate of the solid complex formed was filtered off, washed with ethanol-

water mixture and stored in a vacuum desiccator over anhydrous calcium

chloride.



[Pr(L3)(NO3)2(H2O)] NO3,

[Sm(L3)(NO3)2(H2O)] NO3,

[Gd(L3)(NO3)2(H2O)] NO3,

[Tb(L3)(NO3)2(H2O)] NO3,

[Er(L3)(NO3)2(H2O)] NO3,

[Yb(L3)(NO3)2(H2O)] NO3.

38

NO3OHN

Br

O

ONa

L3

Ln(NO3)3.xH2O

Reflux3-5 h

+EtOH / H2O mixture

CH

O

N C

O

Ln

O

NO3

NO3

H2OBr

Scheme 3.6 Synthesis of rare earth metal Schiff base [L3] complexes




[Pr( L3)(NO3)2(H2O)]NO3 C13H16O10N3BrPr Yellow 96


[Gd(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrGd Yellow 96

[Tb(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrTb Yellow 95


[Yb(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrYb Yellow 89

3.3.7 In vitro Antibacterial Study

The synthesised Schiff base ligand L1 and their corresponding

Ln (III) complexes were screened for antibacterial activity against the gram

negative and gram positive pathogens namely, Escherichia coli, Proteus,

Pseudomonas aeruginosa, Staphylococcus aureus, L2, L3 and their

corresponding Ln (III) complexes against the pathogens namely Escherichia

coli, Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus

agalactiae by the reported method [83]. The stock solution (1 mg mL-1) of

the test chemical was prepared in DMF solution. The stock solution was

39

further diluted with sterilised distilled water to different dilutions in µg mL-1.

The test chemicals of different dilutions were added to sterile blank

antimicrobial susceptibility discs. The bacteria were subcultured in agar

medium and the discs were kept onto the same. The petridishes were

incubated for 24 h at 37oC. The Standard antibacterial drug (ciprofloxacin/

Amikacin) was also screened under similar conditions for comparison.

Activity was determined by measuring the zones of growth inhibition

surrounding the discs. Growth inhibition was compared with the standard

drug. In order to clarify the effect of solvent (DMF) on the biological

screening, DMF alone was added to separate discs and used as control, and

it showed no activity against bacterial strains.

3.3.8 In vitro Antifungal Study

The synthesised Schiff base ligand L1, L2, L3 and their

corresponding Ln (III) complexes were screened for in vitro antifungal

activity according to the disc diffusion method. The assay was determined

against the fungal species Candida and Aspergillus by the reported method

[84, 85]. The stock solution (1 mg mL-1) of the test chemical was prepared in

DMF solution. The stock solution was further diluted with sterilised distilled

water to different dilutions in µg mL-1. The test chemicals of different dilutions

were added to sterile blank antimicrobial susceptibility discs. The fungi were

sub cultured in potato dextrose agar (PDA) and the discs were kept onto the

same. The petridishes were incubated for 72 h at 28°C. The standard

antimicrobial drug Ketoconazole was also screened under similar conditions

for comparison. The results were recorded by measuring the zones of

growth inhibition surrounding the discs. The mean value obtained from three

independent replicates was used to calculate the zone of growth inhibition of

each sample. In order to clarify the effect of solvent (DMF) on the

antimicrobial screening, DMF alone was added to separate discs and used

as control, and it show no activity against the fungal strains.

40

3.3.9 Catalytic Oxidation of Aniline

To a stirred solution of the catalyst (0.015 mmol) and 30 % of

H2O2 (10 mmol) in CH2Cl2 (7 mL), aniline (8 mmol) was added and the

reaction mixture was stirred at room temperature for the required time.

Progress of the reaction was monitored by TLC at regular intervals and

continued for mentioned reaction time. After removal of the solvent, the

residue was purified by Silica gel flash chromatography to afford

azobenzene. All the azobenzene thus obtained were identified by

comparing 1H NMR data with values reported in the literature and those of

the authentic samples. The desired 3,3’-azotoluene was obtained (Yield:

66 %), for which, 1H NMR (CDCl3, 200 MHz): (ppm) = 2.44 (s, 6H), 7.27–

7.73 (m, 14H). 13C NMR (CDCl3, 100 MHz): (ppm) = 20.9, 119.7, 123.4,

128.7, 131.4, 138.0, 152.4.

Scheme 3.7 Catalytic oxidation of aniline

3.4 ANALYTICAL METHODS

3.4.1 Microanalysis

Carbon, hydrogen and nitrogen contents of the newly prepared

ligands and complexes were analysed at CDRI, Lucknow and IIT, Madras.

3.4.2 Molecular Weight Determination

Molecular weight determination was done by Rast micro method

by determining the freezing point depression of a solvent. Diphenyl (71oC)

CH2Cl2(2 ml), r.t.

NH2

Phenylamine

GdL1(NO3)2H2O].NO3/H2O2 N N

Diphenyl-diazene

[GdL1 (NO3) 2H2O]NO3/H2O2

CH2Cl2 (2mL), 30oC

41

was used as the solvent which was calibrated using naphthalene. About 10

mg of the complex was introduced to 100 mg of diphenyl to determine its

melting point depression. The molecular weight was determined by

employing the equation,

3f

f

K wM 10T W

(3.1)

Where Kf = cryoscopic constant of the solvent employed, w = weight of

the solute, Tf = freezing point depression and W = weight of the

solvent taken.

3.5 INSTRUMENTAL METHODS

3.5.1 Infrared Spectra

The infrared spectra of all the complexes and the ligands were

recorded on a Perkin-Elmer 577 (4000-400 cm-1) double beam infrared

spectrophotometer or Perkin-Elmer 783 spectrophotometer or on a JASCO

FT / IR 5300 model spectrophotometer.

KBr pellet method was used here, which involves the mixing of

powdered KBr with the solid sample and pressing the mixture under high

pressure. The KBr pellet thus obtained was inserted into the holder in the

spectrometer and the spectrum was obtained.

3.5.2 Electronic Spectra

Electronic spectra were recorded in DMF (HPLC Grade) solution

on a Shimadzu UV-Vis. 160 spectrophotometer in the range 200-800 nm.

The concentration of the samples prepared was (1.0 10-6 M) and the

spectrum was recorded at room temperature.

42

3.5.3 NMR Spectra

Proton magnetic resonance spectral measurements were made on

a Brucker 300 MHz (or) Perkin-Elmer R32, 90 MHz (or) Joel, GSX 400, 400

MHz spectrometer in deuterated organic solvent DMSO with

tetramethylsilane (TMS) as the internal standard. Frequencies were

measured by the side band technique and area was determined

planimetrically.

43

4. SCHIFF BASE DERIVED FROM SERINE AND ITS LANTHANIDE (III) COMPLEXES

4.1 INTRODUCTION

An enhanced global change has given a pressing need to develop

an alternate synthetic approach for biologically and synthetically important

compounds. Schiff base ligands and their metal complexes have been

shown to exhibit a variety of application including biological, clinical,

analytical and industrial in addition to their important roles in catalysis and

organic synthesis [86-90] and hence continue to occupy as a vital ligands in

metal coordination chemistry [91-93], even almost a century since their

discovery. Since, chemistry of lanthanides is a promising research area

stimulated by a wide variety of applications, coordination chemistry of

lanthanides and its complexes have aroused much interest [94]. Schiff

bases can coordinate to many lanthanide systems, because of their

excellent coordination nature to the rare earth ions and the ability of

sensitizing the properties of lanthanide ions [95, 96]. An interesting

coordination chemistry of lanthanide Schiff base complexes and their role in

chemical, medical and industrial processes are enough to recognize them as

worthwhile for the synthesis of new complexes. Therefore, an attempt has

been made to describe synthesis, characterisation and biological evaluation

of some lanthanide (III) Schiff base complexes containing N, O donor atoms.

A novel tridentate Schiff base ligand [L1] (Figure 4.1) and its six

lanthanide (III) complexes were synthesised (Chapter 3). The coordination

behaviour of lanthanide(III) ions with Schiff base ligand [L1] have been

studied using 1HNMR , elemental analysis, Thermal studies, Mass, FT-IR

and UV-Vis., data. Moreover, Fluorescence behaviour and antimicrobial

44

efficiency of these complexes against different microorganisms have also

been studied.

OHN

Br

OOH

ONa

L1

sodium 2-(5-bromo-2-hydroxybenzylideneamino)-3-hydroxypropanoate

Figure 4.1 Sodium salt of the Schiff base ligand [L1]

4.2 RESULTS AND DISCUSSION

In the present investigation, the Schiff base ligand [L1] and its six

new lanthanide metal complexes were synthesised and characterised by

different analytical techniques. The ligand [L1] was synthesised by the one

step condensation of L-serine with 5-bromosalicyaldehyde and characterised

by UV-Vis, FT-IR, 1H NMR, Mass and TG Analysis. All the Ln (III)

complexes (Ln= Pr, Sm, Gd, Tb, Er and Yb) were synthesised as per the

scheme given in Scheme 4.1, in which Ln(NO3)3.xH2O was used as the

source of metal and they correspond to the formula [LnL1(NO3)2(H2O)] NO3.

All the complexes were non-hygroscopic powders and stable in air, soluble

in DMSO and DMF, sparingly soluble in methanol, ethanol, acetonitrile and

ethylacetate.

45

H2NOH

OOH

serine

+ HO

OBr


OHN

Br

OOH

ONaEtOH/NaOH

Reflux - 3h

L1

sodium 2-(5-bromo-2-hydroxybenzylideneamino)-3-hydroxypropanoate

Reflux 3-5h

Ln(NO3)3.xH2O

CH

O

N CO

LnO

NO3

NO3

H2O NO3

OH

Br

Ln(III) complexes

Scheme 4.1 Synthesis of Schiff base ligand [L1] and Ln (III) Schiff

base complex [Ln = Pr (III), Sm (III), Gd (III), Tb (III), Er (III) and Yb (III)]

4.2.1 Elemental Analysis

Table 4.1 shows the list of the elemental analysis of the Schiff

base ligand [L1] and synthesised Ln (III) Schiff base complexes which are in

good agreement with the calculated values.

46

Table 4.1 Elemental Analysis of the ligand [L1] and Ln (III) Schiff base complexes

Compound Molecular Formula

Molecular weight

Cal.(Exp.)%

C H N

L1 C10H9O4NBrNa 310 38.73(38.67) 2.93(3.23) 4.52(4.73)

[Pr(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrPr 569.01 21.11(21.45) 1.77(1.56) 7.38(7.53)

[Sm(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrSm 578.46 20.76(21.06) 1.74(1.92) 7.26(7.59)

[Gd(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrGd 585.35 20.52(20.76) 1.72(1.53) 7.18(7.42)

[Tb(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrTb 587.03 20.46(20.22) 1.72(1.31) 7.16(7.32)

[Er(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrEr 595.36 20.17(20.45) 1.96(1.38) 7.06(7.23)

[Yb(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrYb 601.14 19.98(19.57) 1.68(1.36) 6.99(6.55)

4.2.2 Mass Spectra

A mass spectrum of the newly synthesised Schiff base ligand

confirms the proposed formula by detecting the molecular fragments. Mass

spectrometry chemical ionisation of the ligand and the lanthanide complexes

(Figures 4.1 and 4.9) show abundant molecular ions at various m/z values.

The mass spectrum of the ligand shows molecular ions [C10H9O4BrNNa]+. at

m/z = 310 and important fragments at m/z = 256 [C9H6O3BrN]+, 185

[C7H5BrO]+ , 125 [C3H4O3NNa]+ and 79 [Br]+. Some isotopic peaks of the

compounds are also found around these peaks [97].

The mass spectrum of the Pr (III) complex shows molecular ions

[C10H10O11N3BrPr]+. at m/z = 569 and important fragments at m/z = 425

[C10H8O4NBrPr]+, 184 [C7H4BrO]+ , 102 [C3H4O3N]+ and 79 [Br]+.

The mass spectrum of the Sm (III) complex shows molecular ions

[C10H10O11N3BrSm]+. at m/z = 578 and important fragments at m/z = 459

[C10H8O4NBrSm]+, 184 [C7H4BrO]+ , 102 [C3H4O3N]+ and 79 [Br]+.

47

The mass spectrum of the Gd (III) complex shows molecular ions

[C10H10O11N3BrGd]+. at m/z = 585 and important fragments at m/z = 442

[C10H8O4NBrGd]+, 184 [C7H4BrO]+ , 102 [C3H4O3N]+ and 79 [Br]+.

The mass spectrum of the Tb (III) complex shows molecular ions

[C10H10O11N3BrTb]+. at m/z = 587 and important fragments at m/z = 445

[C10H8O4NBrTb]+, 184 [C7H4BrO]+ , 102 [C3H4O3N]+ and 79 [Br]+.

The mass spectrum of the Er (III) complex shows molecular ions

[C10H10O11N3BrEr]+. at m/z = 595 and important fragments at m/z = 453

[C10H8O4NBrEr]+, 184 [C7H4BrO]+ , 102 [C3H4O3N]+ and 79 [Br]+.

The mass spectrum of the Yb (III) complex shows molecular ions

[C10H10O11N3BrYb]+. at m/z = 601 and important fragments at m/z = 459

[C10H8O4NBrYb]+, 184 [C7H4BrO]+ , 102 [C3H4O3N]+ and 79 [Br]+.

Figure 4.2 Mass Spectrum of the Schiff base ligand [L1]

m/z

%

48

Figure 4.3 Mass Spectrum of the [Pr(L1)(NO3)2(H2O)]NO3 complex

m/z

%

49

Figure 4.4 Mass Spectrum of the [Sm(L1)(NO3)2(H2O)]NO3 complex

m/z

%

50

Figure 4.5 Mass Spectrum of the [Gd(L1)(NO3)2(H2O)]NO3 complex

m/z

%

51

Figure 4.6 Mass Spectrum of the [Tb(L1)(NO3)2(H2O)]NO3 complex

m/z

%

52

Figure 4.7 Mass Spectrum of the [Er(L1)(NO3)2(H2O)]NO3 complex

m/z

%

53

Figure 4.8 Mass Spectrum of the [Yb(L1)(NO3)2(H2O)]NO3 complex

m/z

%

54

Figure 4.9 HR-MS of the [Pr(L1)(NO3)2(H2O)]NO3 complex

55

4.2.3 Molar Conductance

Molar conductivity data for all the Ln (III) Schiff base complexes in

DMF solution at room temperature are observed to be in the range of

110-121 Scm2mol-1 and are given in Table 4.2. This suggests 1:1

electrolytes and the two nitrate are coordinated to the Ln (III) ion [98].

Table 4.2 Molar conductance of the ligand [L1] and Ln (III) Schiff base complexes in DMF

Compound

Molecular Formula m

(S cm2 mol 1)

L1 C10H9O4NBrNa -

[Pr(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrPr 121.02

[Sm(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrSm 119.52

[Gd(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrGd 117.82

[Tb(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrTb 116.24

[Er(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrEr 112.63

[Yb(L1)(NO3)2(H2O)]NO3 C10H10O11N3BrYb 110.02

4.2.4 Thermo Gravimetric Analysis

Thermogravimetric and differential thermogravimetic analysis were

carried out for the Schiff base ligand [L1] and its corresponding Ln (III)

complexes within the temperature range from ambient temperature to 900oC

under N2 flow. The correlation between the different decomposition steps of

Ln (III) complexes with corresponding weight losses are discussed in terms

of proposed formula of the Ln (III) complexes. The water content was

determined by the thermogravimetric analysis (TGA). The TGA results

showed that the ligand [L1] (Figure 4.10) is thermally stable in the

temperature range 25 – 223oC. The decomposition starts at 223oC and gets

completed at 3000C with one decomposition step.

56

The thermal behaviour studies of all the complexes are almost

same. The thermogram of Ln (III) Schiff base complexes are depicted in

Figure 4.11 – 4.16. In the thermogram of all Ln (III) complexes, the

coordinated water molecules decomposes around 103 - 106oC with a weight

loss about 3%, lattice nitrate and coordinated nitrate molecules decomposed

in the region 140 - 145oC and 340 - 342oC with a weight loss about 10.4%

and 20.6% respectively.

The Gd (III) complex decomposed significantly around 415oC due

to loss of organic moiety with the weight loss about 34.2%. Finally, these

processes were followed by the last step, in which, oxidation Gd (III) occurs

to give corresponding oxide as residue [99].

The Pr (III) Schiff base complex was stable up to 342°C and its

decomposition started at this temperature. The complexes underwent

decomposition in the range 342–520°C with DTG peak at 415°C

corresponds to loss of organic moiety.

The Sm (III) Schiff base complex was stable up to 343°C and its




The Yb (III) Schiff base complex was stable up to 340°C and its




The Tb (III) Schiff base complex was stable up to 346°C and its




57

Figure 4.10 (a) TG and (b) DTA curves of Schiff base ligand [L1]

a

b

58

Figure 4.11 TG/DTA curves of the [Pr(L1)(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

59

Figure 4.12 TG/DTA curves of the [Sm(L1)(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

60

Figure 4.13 TG/DTA curves of the [Gd(L1)(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

61

Figure 4.14 TG/DTA curves of the [Tb(L1)(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

62

Figure 4.15 TG/DTA curves of the [Er(L1)(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

63

Figure 4.16 TG/DTA curves of the [Yb(L1)(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

64

The Er (III) Schiff base complex was stable up to 342°C and its




4.2.5 1H NMR SPECTRA

The 1H NMR Spectra of Schiff base ligand [L1] (Figure 4.17) in

DMSO-d6 shows signal of triplets at 4.09 ppm and doublet at 4.12 are

due to , methine and methylene hydrogen atom respectively [100]. The

multiplets in 6.65-7.62 ppm region are assigned to the protons of

benzylidene ring groups. The broad singlet at 3.32 ppm and 2.0 ppm is

due to the aromatic hydroxyl and allylic hydroxyl group respectively [101].

The strong singlet at 8.11 ppm is assigned for the azomethine roton [102].

This is in accordance with what the following IR data have revealed.

65

Figure 4.17 1H NMR spectrum of the Schiff base ligand [L1]

66

4.2.6 IR Spectra

The IR band assignments are given in Table 4.3 and spectra in

Figure 4.18 – 4.24. The IR spectra of Ln (III) complexes displays the ligand

characteristic bands with the appropriate shifts due to complex formation and

the IR spectra of all the complexes displays similarity. The IR band at 1678

cm-1 of the free Schiff base ligand is due to the presence of azomethine

group. Upon complexation, these bands are shifted to lower wave number by

20 cm-1 indicating [95] a stronger double bond character of the imine band

and a coordination of the azomethine nitrogen atom to the Ln (III) ion

[103,104]. This coordination is further supported by the appearance of

medium intensity band around 474 cm-1 assigned to Ln-N vibration.

IR spectrum of the free Schiff base ligand exhibits a broad band at

3100 and 3400cm-1, which is attributed to the stretching frequencies of

aromatic hydroxyl substituent and allylic hydroxyl substituent. The

disappearance of aromatic hydroxyl group after complexation denotes the

coordination through phenolic –OH with the central metal ion [105]. The

characteristic band around 3365cm-1 remains in the spectra of the

complexes shows the non-coordination of allylic –OH to the central metal

ion.

The coordination of Ln (III) ion with the phenolic -OH is further

supported by the appearance of a medium intensity band around 536 cm-1

assigned to Ln-O vibration [95]. The absorption bands of coordinated nitrates

were observed at about 1465( 1), 1159( 2), 829( 3), 1323( 4). In addition,

the separation of two highest frequency band ( 1- 4) is approximately 140

cm-1 and accordingly the coordinated NO3- ion in the complexes is a

bidentate ligand [106-108]. The band at 1383 cm-1 in the spectrum of the

complexes indicates that the existence of free nitrate group in the

coordination sphere [109].

67

Table 4.3 Infrared spectral data for the ligand [L1] and the Ln (III) complexes

Compounds R-OH C=N

NO3-

asym (COO

-) sym (COO

-) Ln-O Ln-N

1 2 3 4 0

L 3323 1678 - - - - - - - - -

[PrL(NO3)2(H2O)]NO3 3392 1631 1454 1158 829 1323 1383 1525 1381 540 474

[SmL(NO3)2(H2O)]NO3 3385 1648 1466 1159 827 1323 1383 1525 1390 534 473

[GdL(NO3)2(H2O)]NO3 3395 1652 1466 1159 829 1325 1383 1515 1390 540 474

[ErL(NO3)2(H2O)]NO3 3392 1658 1465 1158 826 1323 1383 1510 1390 540 474

[TbL(NO3)2(H2O)]NO3 3380 1649 1466 1157 825 1325 1383 1520 1384 536 473

[YbL(NO3)2(H2O)]NO3 3365 1654 1465 1159 829 1323 1383 1525 1384 536 474

68

Figure 4.18 IR spectrum of the Schiff base ligand [L1]

69

Figure 4.19 IR spectrum of the [Pr(L1)(NO3)2H2O]NO3 complex

70

Figure 4.20 IR spectrum of the [Sm(L1)(NO3)2H2O]NO3 complex

71

Figure 4.21 IR spectrum of the [Gd(L1)(NO3)2H2O]NO3 complex

72

Figure 4.22 IR spectrum of the [Tb(L1)(NO3)2H2O]NO3 complex

73

Figure 4.23 IR spectrum of the [Er(L1)(NO3)2H2O]NO3 complex

74

Figure 4.24 IR spectrum of the [Yb(L1)(NO3)2H2O]NO3 complex

75

The complexes show strong band in the region 1510 -1525 cm-1

and a weaker band in the region 1381 - 1390 cm-1 assigned to asymmetric

and symmetric stretching frequencies of COO- group respectively. The

frequency difference between the asymmetric and symmetric stretching

frequencies comes around 215 cm-1, which suggests the monodentate

coordination of the carboxyl group of amino acid with the Ln (III) ion [110].

The existence of medium intensity band around 1625 cm-1 is due to the

symmetric and the asymmetric O–H stretching vibrations of inner-sphere

water molecule [111].

4.2.7 Electronic Spectroscopy

The UV-visible absorption spectra of the Schiff base ligand [L1]

and its Ln (III) complexes (Figures 4.25 – 4.31) were carried out in DMF at

room temperature. The values of the absorption wavelength and its band

assignments are listed in Table 4.4 and comparative spectrum is shown in

Figure 4.32. The absorption of the ligand [L1] is characterised by three main

absorption bands at 232, 261 and 385 nm. The band appearing at lower

energy is attributed to n * transition of conjugation between the lone pair

of electrons of p orbital of N atom in azomethine group and conjugated

bond of the benzene ring [112]. The bands appearing at higher energy are

attributed to * of the benzene ring and * transition of the

azomethine group [113,114].

The UV-visible absorption spectra of all the Ln (III) Schiff base

complexes show similarities, which indicates similarity in their structures and

generally show the characteristic bands of the free ligands with some

changes both in frequencies and intensities. Upon complexation, the

absorption bands of the complexes are slightly shifted to shorter wavelength

(Blue shift) compared to those of the free ligand. These modifications of the

shifts and intensity of the absorption bands indicates the coordination of the

ligand to the metal ion. In general, the lanthanide ions do not appreciably

76

contribute to the spectra of their complexes, since f-f transitions are Laporte-

forbidden and very weak in nature [115].

The Sm (III) and Gd (III) complexes have high absorbance when

compared to other complexes. This is due to the difference in their molar

absorptivity of the complexes that cause the spectrum to become more

intense which is referred to as hyperchromic shift and the decrease in

absorbance is referred to as a hypochromic shift. There is a variety of factors

that can cause these changes. One of the factors is found in a process

known as solvatochromism. It can also be due to the solvent polarizability

as well. Basically it is the change in the colour of a material, as a function of

the dielectric properties of the solvent.

Figure 4.25 UV spectra of the Schiff base ligand [L1] in DMF solution

(1.0 10-6 M) at room temperature

Wavelength (nm)

Abs

orba

nce

77

Figure 4.26 UV-visible spectrum of the[Pr(L1)(NO3)2H2O]NO3complex

in DMF solution (1.0 10-6 M) at room temperature

Figure 4.27 UV-visible spectrum of the [Sm(L1)(NO3)2H2O]NO3

complex in DMF solution (1.0 10-6 M) at room

temperature

Wavelength (nm)

Abs

orba

nce

Wavelength (nm)

Abs

orba

nce

78

Figure 4.28 UV-visible spectrum of the [GdL1)(NO3)2H2O]NO3


temperature

Figure 4.29 UV-visible spectrum of the [Tb(L1)(NO3)2H2O]NO3


temperature

Wavelength (nm)

Abs

orba

nce

Wavelength (nm)

Abs

orba

nce

79

Figure 4.30 UV-visible spectrum of the [Er(L1)(NO3)2H2O]NO3


temperature

Figure 4.31 UV-visible spectrum of the [Yb(L1)(NO3)2H2O]NO3


temperature

Wavelength (nm)

Abs

orba

nce

Wavelength (nm)

Abs

orba

nce

80

Figure 4.32 Comparative UV spectra of the Schiff base ligand [L1] and Ln (III) Schiff base complexes in DMF solution

(1.0 10-6 M) at room temperature

81

Table 4.4 UV-Vis Spectral Data max. (nm) for the ligand [L1] and the complexes

Compound max (nm) Band assignment

L1 232,261 385

* *

[Pr(L1)(NO3)2(H2O)]NO3 221,248 323

* *

[Sm(L1)(NO3)2(H2O)]NO3 226,244 346

* *

[Gd(L1)(NO3)2(H2O)]NO3 214,243 376

* *

[Tb(L1)(NO3)2(H2O)]NO3 224,244 343

* *

[Er(L1)(NO3)2(H2O)]NO3 226,246 352

* *

[Yb(L1)(NO3)2(H2O)]NO3 222,243 352

* *

4.2.8 Fluorescence Studies

The rare earth elements still have a unique and important impact

on our lives. The unfilled 4f electronic structure of the rare earth elements

makes them have special properties in luminescence, magnetism and

electronics, which could be used to develop many new materials for various

applications such as phosphors, magnetic materials, hydrogen storage

materials and catalysts.

The emission spectra of the Schiff base ligand and its Ln (III)

complexes are shown in Figure 4.8. The emission spectrum were recorded

upon excitation at 360 nm and the free ligand [L1] exhibits broad

fluorescence band around 425 nm attributed to * transition [116,117].

82

The emission spectrum of Sm (III) displays five luminescence bands

corresponding to the * transition at 440 nm, 4G5/2 6H3/2 at 485 nm, 4G5/2 6H5/2 at 565 nm,4G5/2 6H7/2 at 598 nm, 4G5/2

6H9/2 at 644 nm

respectively. The intensity sequence of the peaks is I4G5/2 6H9/2 I4G5/2 6H7/2

I4G5/2 6H5/2 I4G5/2 6H3/2 [118].

For Er (III) complex, the emission spectrum excited at 300 nm

shows four luminescence bands corresponding to * at 440 nm, 4S3/2 4I15/2 at 486 nm , 4S3/2 4I13/2 at 613 nm, 4S3/2 4I11/2 at 647 nm

transitions, respectively.

For Tb (III) complex, the emission spectrum excited at 300 nm

shows five luminescence bands. * broad band at 433nm. Further,

sharp luminescence bands corresponding to 5D4 7F6 at 480 nm, 5D4 7F6 at 545 nm, 5D4 7F6 at 586 nm,

5D4 7F6 at 625 nm transition

respectively. The appearance of small band at 840 nm denotes the

secondary derivatives of the rare earth Schiff base complexes. These

results indicate that the ligand L1 is a good chelating organic chromophore

and can be used to absorb and transfer energy to the Ln (III) ions.

The Gd (III), Pr (III) and Yb (III) complexes, shows a broad

emission band around 438-456 nm, which is assigned to * transition.

The fluorescence intensity of these complexes are less while compare with

other complexes, this may be attributed to the complexation occurs with

ligands evident from lesser binding constant values.

83

Figure 4.33 Emission spectra of Sm (III) Er (III) and Tb (III) Schiff

base complexes in DMF solution (1.0 10-6 M) at room

temperature. Emission spectrum is obtained with

exc. = 360 nm

4.2.9 Antibacterial Studies

The Schiff-base ligand [L1] and its Ln (III) complexes reported

here were evaluated for antibacterial activity against Escherichia coli,

Proteus, Staphylococcus aureus and Pseudomonas aeruginosa and the

percentage inhibition detail of the same for maximum concentration

(100 µg mL-1) are tabulated in Table 4.5. The Schiff base ligand [L1] is

biologically active and its activity arise from the presence of imine group

which imports in elucidating the mechanism of transformation reaction in

biological systems. However, its Ln (III) complexes showed remarkable

antibacterial activity as a result of chelation of metal with organic ligand

synergistically increasing its effect [119].

From the results obtained, the antibacterial activity of Ln (III) Schiff

base complexes is found to be higher than that of a free Schiff base ligand,

84

against the same microorganism under identical experimental conditions.

This is similar to earlier observations [120].

Remarkable enhancement in activity was found for Sm (III) Schiff

base complex against the species Escherichia coli. For the species Proteus

Sm (III) Schiff base complex showed higher activity than the other Ln (III)

complexes. In a similar manner the percentage inhibition was higher for

Er (III) complex against both Staphylococcus aureus and Pseudomonas

aeruginosa pathogens. The percentage inhibition for the Schiff base ligand

and all the Ln (III) complexes have been depicted in Figure 4.35 - 4.38.

This increased activity of the Ln (III) complexes upon chelation is

attributed to Tweedy’s chelation theory, according to which, the chelation

reduces the polarity of the metal atom mainly because of the positive charge

of the metal partially shared with donor atoms present on the ligand and

there is electron delocalisation over the whole chelate ring [121]. This, in

turn, increases the lipophilic character of the metal chelate and favors its

permeation through the lipid layers of the bacterial membranes [109].

Generally, it is suggested that the chelated complexes deactivate

various cellular enzymes, which play a vital role in various metabolic

pathways of these microorganisms. Other factors such as solubility,

conductivity and dipole moment, affected by the presence of metal ions, may

also increase the biological activity of the metal complexes compared to the

ligand.

85

Table 4.5 Antibacterial results of the Schiff base ligand [L1] and their Ln (III) complexes for maximum concentration (100 µg mL-1)

Compound % inhibition against bacteria

E. coli Proteus P. aeruginosa S. aureus

L1 70.43 50.61 44.93 55.32

[Pr(L1)(NO3)2(H2O)]NO3 85.46 60.23 46.42 72.45

[Sm(L1)(NO3)2(H2O)]NO3 85.92 70.16 56.43 82.53

[Gd(L1)(NO3)2(H2O)]NO3 84.57 75.73 60.82 72.82

[Tb(L1)(NO3)2(H2O)]NO3 82.92 53.72 47.24 75.69

[Er(L1)(NO3)2(H2O)]NO3 71.95 44.32 74.21 68.32

[Yb(L1)(NO3)2(H2O)]NO3 70.94 58.41 49.34 65.46

DMF - - - -

Ciproflaxacin 100 100 100 100

86

(a) Escherichia coli (b) Staphylococcus aureus

(c) Pseudomonas aeruginosa

C – Control; 1 – 25 µg mL-1 ; 2 – 50 µg mL-1 ;

3 - 75 µg mL-1 ; 4 – 100 µg mL-1

Figure 4.34 Zone of inhibition of (a) Sm(III) (b) Sm(III) (c) Er(III) complexes of Schiff base Ligand [L1] for bacterial species

87

Figure 4.35 Percentage Inhibition of Schiff base ligand [L1] and their Ln (III) Schiff base complexes against Escherichia coli

Figure 4.36 Percentage Inhibition of Schiff base ligand [L1] and their Ln (III) Schiff base complexes against Proteus

0102030405060708090

100

L Pr(III) Sm(III) Gd(III) Tb(III) Er(III) Yb(III)

Escherichia coli

0102030405060708090

100


Proteus

% in

hibi

tion

% in

hibi

tion

88

Figure 4.37 Percentage Inhibition of Schiff base ligand [L1] and their Ln (III) Schiff base complexes against Pseudomonas aeruginosa

Figure 4.38 Percentage Inhibition of Schiff base ligand [L1] and their Ln (III) Schiff base complexes against Staphylococcus aureus

0102030405060708090

100



0102030405060708090

100


Staphylococcus aureus

% in

hibi

tion

% in

hibi

tion

89

4.2.10 Antifungal Studies

The antifungal activity of the Schiff-base ligand [L1] and its Ln (III)

complexes reported here were evaluated for Candida and Aspergillus

species and the percentage inhibition detail of the same for maximum

concentration (100 µg mL-1) are tabulated in Table 4.6. The comparative

antifungal activity have been depicted in Figure 4.40 and 4.41. The Schiff

base ligand [L1] and all the Ln (III) complexes show high antifungal activity

against the reported species. However the Ln (III) complexes showed

remarkable antibacterial activity than the Schiff base ligand. This is probably

due to the greater lipophilic nature of the complexes [119].

It was observed that the antifungal activity of few complexes were

very near to the standard antifungal agent Ketokonazole. Compared to all

other Ln (III) complexes the Yb (III) complex shows very high activity

against the species Candida. In the case of Aspergillus species, the Sm (III)

complex has higher activity among other Ln (III) complexes.

It was evident from the data that this activity significantly increased

on coordination. This enhancement in the activity may be rationalised on the

basis that their structures mainly possess an additional C=N bond. It has

been suggested that the Schiff base with nitrogen and oxygen donor

systems inhibit enzyme activity, since the enzymes which require these

groups of their activity appear to be especially more susceptible to

deactivation by metal ions on coordination.

Moreover, coordination reduces the polarity of the metal ion mainly

because of the partial sharing of its positive charge with the donor groups

[120] within the chelate ring system formed during coordination. The activity

of the complexes can be related to the strength of the metal–ligand bond,

besides other factors such as size of the cation, receptor sites, diffusion and

a combined effect of the metal and the ligands for inactivation of the

biomolecules.

90

Table 4.6 Antifungal results of the Schiff base ligand [L1] and their Ln (III) complexes for maximum concentration (100 µg mL-1)

Compound % inhibition against fungi

Candida Aspergillus

L1 65.45 60.29

[Pr(L1)(NO3)2(H2O)]NO3 67.87 75.25

[Sm(L1)(NO3)2(H2O)]NO3 89.35 90.47

[Gd(L1)(NO3)2(H2O)]NO3 95.25 72.49

[Tb(L1)(NO3)2(H2O)]NO3 94.76 89.91

[Er(L1)(NO3)2(H2O)]NO3 93.86 95.12

[Yb(L1)(NO3)2(H2O)]NO3 97.83 89.75

DMF - -

Ketokonazole 100 100

91

(a) Candida (b) Aspergillus

C – Control; 1 – 25 µg mL-1 ; 2 – 50 µg mL-1

3 - 75 µg mL-1 ; 4 – 100 µg mL-1

Figure 4.39 Zone of inhibition of Tb (III) complex of Schiff base Ligand [L1] for fungal species

92

Figure 4.40 Percentage Inhibition of Schiff base ligand [L1] and their Ln (III) Schiff base complexes against Candida

Figure 4.41 Percentage Inhibition of Schiff base ligand [L1] and their Ln (III) Schiff base complexes against Aspergillus

0102030405060708090

100


Candida

0102030405060708090

100


Aspergillus

% in

hibi

tion

% in

hibi

tion

93

4.3 CONCLUSION

The results of the spectral studies of the synthesised tridentate

Schiff base ligand L1 and its Ln (III) complexes under investigation

supported the suggested structures. Thermal study reveals that these

complexes are stable up to 340°C. The fluorescence data reveals that the

Sm (III), Tb (III) and Er (III) complexes exhibit characteristic luminescence

of Sm (III), Tb (III) and Er (III) ions, which indicates that the ligand L1 is a

good organic chelator to absorb and transfer energy to Sm (III), Tb (III) and

Er (III) ions. The antibacterial activity results show that most of the

synthesised complexes possess a good antimicrobial activity against the

pathogens tested than the corresponding free Schiff base ligand.

94

5. SCHIFF BASE DERIVED FROM THREONINE AND ITS LANTHANIDE (III) COMPLEXES

5.1 INTRODUCTION

Lanthanide complexes attract considerable interest in bioinorganic

and coordination chemistry Schiff base complexes derived from amino acids

are important due to their ability to possess unusual configurations and

biological importance [122,123]. Lanthanide Schiff base complexes have

some advantages for luminescence research because of their special

structures [124]. Exhibiting outstanding optical properties and a broad

spectrum of biological activities, rare-earth metal complexes of Schiff-base

type ligands derived from amino acids attract great interest of researchers in

recent years [125,126]. In general, lanthanide complexes display varying

cytotoxic effects [127,128].

Such properties of this type of complexes encouraged us [129]

further to synthesize, characterize and study the fluorescence and biological

activity of the Pr (III), Sm (III), Gd (III), Er (III), Tb (III) and Yb (III)

complexes of the Schiff base ligand [L2] (Figure 5.1). All the synthesised

compounds are screened in vitro for their antibacterial and antifungal

activities using disc diffusion assay. Human pathogenic bacteria Escherichia

coli, Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus

agalactiae and fungi Candida, Aspergillus are evaluated based on their

toxicity to different concentrations of Ln (III) Schiff base complexes.

95

OHN

Br

OOH

ONa


hydroxybutanoate

Figure 5.1 Sodium salt of the Schiff base ligand L2




different analytical techniques. The ligand [L2] was synthesised by one step

condensation of L-threonine with 5-bromosalicyaldehyde and characterised

by UV-Vis, FT-IR, 1H NMR, Mass and TG analysis. All the Ln (III)

complexes were synthesised as per the scheme given in Scheme 5.1, in

which Ln(NO3)3.xH2O was used as the source of metal and they correspond

to the formula [Ln(L2)(NO3)2(H2O)].NO3. All the complexes were stable in air

and non-hygroscopic powders, soluble in DMSO and DMF, sparingly soluble

in methanol, ethanol, acetonitrile and ethylacetate.

L2

96

NH2

OH

OHO

Threonine

+ HO

OBr


OHN

Br

OOH

ONaEtOH/NaOH

Reflux - 3h


hydroxybutanoate

Ln(NO3)3.xH2OReflux3-5 h

NO3CH

O

N CO

LnO

NO3

NO3

H2O

OH

Br

Ln (III) Complexes

Scheme 5.1 Synthesis of Schiff base ligand [L2] and Ln (III) Schiff base complexes [Ln = Pr (III), Sm (III), Gd (III), Tb (III), Er (III) and Yb (III)]



base ligand [L2] and synthesised Ln (III) Schiff base complexes which are in

good agreement with the calculated values based on the proposed

molecular formula.

97


Compound Molecular Formula Molecular weight Cal.(Exp.)%

C H N

L2 C11H11O4NBrNa 324.1 40.72(40.76) 3.39(3.42) 4.31(4.32)

[Pr(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrPr 583.04 24.03(24.06) 2.67(2.69) 7.01(7.01)

[Sm(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrSm 592.49 22.27(22.30) 2.02(2.04) 7.08(7.09)

[Gd(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrGd 599.38 22.02(22.04) 2.00(2.02) 7.00(7.01)

[Tb(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrTb 601.06 21.96(21.98) 1.99(2.01) 6.98(6.99)

[Er(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrEr 609.39 21.66(21.68) 1.96(1.98) 6.89(6.90)

[Yb(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrYb 615.17 21.45(21.48) 1.95(1.97) 6.82(6.83)

98

5.2.2 Mass Spectra

A mass spectrum of the newly synthesised Schiff base ligand

confirms the proposed formula by detecting the molecular fragments. Mass

spectrometry chemical ionisation of the ligand and the lanthanide complexes

as shown in Figures 5.2 – 5.9, show abundant molecular ions at various m/z

values. The mass spectrum of the ligand shows molecular ions

[C11H11O4BrNNa]+. at m/z = 323 and important fragments at m/z = 245

[C11H11O3NNa]+, 185 [C7H5BrO]+, 141 [C4H6O3NNa]+ and 79 [Br]+. Some

isotopic peaks of the compounds are also found around these peaks [97].



[C11H10O4NBrPr]+, 184 [C7H4BrO]+ , 116 [C4H6O3N]+ and 79 [Br]+.



[C11H10O4NBrSm]+, 184 [C7H4BrO]+ , 116 [C4H6O3N]+ and 79 [Br]+.



[C11H10O4NBrGd]+, 184 [C7H4BrO]+ , 116 [C4H6O3N]+ and 79 [Br]+.



[C11H10O4NBrEr]+, 184 [C7H4BrO]+ , 116 [C4H6O3N]+ and 79 [Br]+.



[C11H10O4NBrTb]+, 184 [C7H4BrO]+ , 116 [C4H6O3N]+ and 79 [Br]+.



[C11H10O4NBrYb]+, 184 [C7H4BrO]+ , 116 [C4H6O3N]+ and 79 [Br]+.

99


%

m/z

100


%

m/z

101


%

m/z

102


%

m/z

103


%

m/z

104


%

m/z

105


%

m/z

106


107



DMF solution at room temperature are observed to be in the range of 112-

123 Scm2mol-1 are tabulated in Table 5.2. This suggests 1:1 electrolytes and

the two nitrate are coordinated to the Ln (III) ion [98].

Table 5.2 Molar conductance of the ligand [L1] and Ln (III) Schiff base complexes

Compound Molecular Formula m

(S cm2 mol 1)

L2 C11H11O4NBrNa -

[Pr(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrPr 123.03

[Sm(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrSm 121.32

[Gd(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrGd 119.62

[Tb(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrTb 115.42

[Er(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrEr 113.35

[Yb(L2)(NO3)2(H2O)]NO3 C11H12O11N3BrYb 112.12


Thermogravimetric and differential thermogravimetic analysis were

carried out for the Schiff base ligand [L2] and its corresponding Ln (III)

complexes within the temperature range from ambient temperature to 800°C

under N2 flow. The correlation between the different decomposition steps of

Ln (III) complexes with corresponding weight losses are discussed in terms

of proposed formula of Ln (III) complexes. The TGA results show that the

ligand [L2] (Figure 5.10 - 5.16) is thermally stable in the temperature range

25 – 275°C. The decomposition starts at 275°C and gets completed at 330°C

with one decomposition step.

The thermal behavior studies of all the complexes are almost

same. Hence, the Ln (III) complex has been discussed. In the thermogram

108

of all Ln (III) complex, the coordinated water molecules decomposes around

104oC with a weight loss of about 2.7%, lattice nitrate and coordinated

nitrate molecules decomposed in the region 154°C and 373°C with a weight

loss of about 9.4% and 18.5% respectively.

The Gd (III) complex decomposes significantly around 445°C due

to the loss of organic moiety with the weight loss of about 45.8%. Finally,

these processes are followed by the last step, in which, oxidation Gd (III)

occurs to give the corresponding oxide as residue [99]. The Pr (III) Schiff

base complex was stable up to 378°C and its decomposition started at this

temperature. The complexes underwent decomposition in the range 378–

570 °C with DTG peak at 450°C corresponds to loss of organic moiety.

















109

Figure 5.10 TG/DTA curves of the Schiff base ligand [L2] (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

110

Figure. 5.11 TG/DTA curves of the [PrL2(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

111

Figure. 5.12 TG/DTA curves of the [SmL2(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

112

Figure. 5.13 TG/DTA curves of the [GdL2(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

113

Figure 5.14 TG/DTA curves of the [TbL2(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

114

Figure 5.15 TG/DTA curves of the [ErL2(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

115

Figure 5.16 TG/DTA curves of the [YbL2(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

116

5.2.5 1H NMR Spectra

The 1H NMR Spectra of Schiff base ligand in DMSO-d6 has been

depicted in Figure 5.17. It shows that the signal of doublets at 4.04 ppm

and 4.0 ppm are due to methine and methylene hydrogen atom respectively

[100]. The multiplets in 6.93-7.34 ppm region are assigned to the protons

of aromatic benzylidene ring groups. The broad singlet at 5.0 ppm and

2.0 ppm is due to the aromatic hydroxyl and allylic hydroxyl group

respectively [101]. The strong singlet at 8.13 ppm is assigned for the

azomethine proton [102]. This is in accordance with what the following IR

data has revealed.

117

Figure 5.17 1H NMR spectra of the Schiff base ligand [L2]

118

5.2.6 IR Spectra

The IR band assignments are given in Table 5.3 and spectra in

Figures 5.18 – 5.24. The IR spectra of Ln (III) complexes displays the ligand

characteristic bands with appropriate shifts due to the complex formation,

and the IR spectra of all the complexes display similarity. The IR band at

1694 cm-1 of the free Schiff base ligand is due to the presence of

azomethine group. Upon complexation, these bands are shifted to lower

wave number by 20-40 cm-1 indicating [95] a stronger double bond character

of the imine band and a coordination of the azomethine nitrogen atom to the

Ln (III) ion [103,104]. This coordination is further supported by the

appearance of medium intensity band around 470 cm-1 assigned to Ln-N

vibration.

IR spectrum of the free Schiff base ligand exhibits a broad band at

3050 and 3250 cm-1, which is attributed to the stretching frequencies of

aromatic hydroxyl substituent and allylic hydroxyl substituent. The

disappearance of aromatic hydroxyl group after complexation denotes the

coordination through phenolic –OH with the central metal ion [105]. The

characteristic band around 3239 cm-1 remains in the spectra of the

complexes and shows the non-coordination of allylic –OH to the central

metal ion.

The coordination of Ln (III) ion with the phenolic -OH is further

supported by the appearance of a medium intensity band around 535 cm-1

assigned to Ln-O vibration [95]. The absorption bands of coordinated nitrates

were observed at about 1466( 1), 1163( 2), 828( 3), 1375( 4). In addition,

the separation of two highest frequency bands ( 1- 4) is approximately 90

cm-1 and accordingly the coordinated NO3- ion in the complexes is a

bidentate ligand [106-108]. The band at 1395 cm-1 in the spectrum of the

complexes indicates that the existence of free nitrate group in the

coordination sphere [109]. The complexes show strong band in the region

1540-1565 cm-1 and a weak band in the region 1275 - 1370 cm-1 assigned to

119

asymmetric and symmetric stretching frequencies of COO- group

respectively. The frequency difference between the asymmetric and

symmetric stretching frequencies comes around 170 cm-1, which suggests

the monodentate coordination of the carboxyl group of amino acid with the

Ln (III) ion [110]. The existence of medium intensity band around 1610 cm-1

is due to the symmetric and the asymmetric O–H stretching vibrations of

inner-sphere water molecule [111].

120

Table 5.3 Infrared spectral data for the ligand [L2] and the Ln (III) complexes

Compounds R-OH C=N NO3

- asym(COO

-) sym(COO

-) Ln-O Ln-N

1 2 3 4 0

L 3250 1694 - - - - - - - - -

[PrL(NO3)2(H2O)]NO3 3242 1651 1458 1160 829 1373 1388 1555 1281 540 474

[SmL(NO3)2(H2O)]NO3 3228 1668 1466 1159 827 1363 1385 1549 1280 534 473

[GdL(NO3)2(H2O)]NO3 3225 1652 1466 1159 829 1365 1383 1515 1390 540 474

[ErL(NO3)2(H2O)]NO3 3235 1658 1467 1160 829 1355 1383 1510 1390 540 472

[TbL(NO3)2(H2O)]NO3 3240 1659 1466 1157 825 1360 1383 1520 1382 536 471

[YbL(NO3)2(H2O)]NO3 3239 1675 1466 1163 828 1375 1395 1564 1275 535 470

121


122


123


124


125


126


127


128


The UV-Vis. absorption spectra for the freshly prepared solutions

of the Schiff base ligand [L2] and its Ln (III) complexes (Figures 5.25 – 5.31)

in DMF are recorded at room temperature. The values of the absorption

wavelength and its band assignments are listed in Table 5.4 and

comparative spectrum is shown in Figures 5.32. The absorption of the

ligand [L2] is characterised by three main absorption bands at 237, 271 and

376 nm. The band appearing at lower energy is attributed to n *

transition of conjugation between the lone pair of electrons of p orbital of N

atom in azomethine group and conjugated bond of the benzene ring [112].

The bands appearing at higher energy are attributed to * of the

benzene ring and * transition of the azomethine group [113,114].

The UV-visible absorption spectra of all the Ln (III) Schiff base

complexes show similarities, which indicate similarity in their structures and

generally show the characteristic bands of the free ligands with some

changes both in frequencies and intensities. Upon complexation, the

absorption bands of the complexes are slightly shifted to shorter wavelength

(Blue shift) compared to those of the free ligand. These modifications of the

shifts and intensity of the absorption bands indicate the coordination of the

ligand to the metal ion. In general, the lanthanide ions do not appreciably

contribute to the spectra of their complexes, since f-f transitions are Laporte-

forbidden and very weak in nature [115].

The difference in absorbance among the lanthanide (III) metal

complexes is attributed to their difference in molar absorptivity. The increase

in absorption is referred to as hyperchromic shift and the decrease in

absorption is referred to as hypochromic shift. These shifts are caused due

to the factor known as solvatochromism. This leads to the change in colour

of the complexes as a function of the dielectric properties of the solvent. It

was observed that the Sm (III) and Gd (III) complexes have high

129

absorbance when compared to other complexes. The reasons of which may

also be due to the solvent polarizability factor.

Figure 5.25 UV-visible spectrum of the Schiff base ligand [L2] in DMF

solution (1.0 10-6 M) at room temperature.

Figure 5.26 UV-visible spectrum of the [Pr(L2)(NO3)2H2O]NO3


temperature

Abs

orba

nce

Wavelength (nm)

Abs

orba

nce

Wavelength (nm)

130



temperature

Figure 5.28 UV-visible spectrum of the [Gd(L2)(NO3)2H2O]NO3


temperature

Abs

orba

nce

Wavelength (nm)

Abs

orba

nce

Wavelength (nm)

131



temperature


complex in DMF solution (1.0 10-6 M) at room temperature

Abs

orba

nce

Wavelength (nm)

Abs

orba

nce

Wavelength (nm)

132



temperature

Figure 5.32 Comparative UV-visible spectra of the Schiff base ligand

L2 and its Ln (III) complexes in DMF solution (1.0 10-6

M) at room temperature

Abs

orba

nce

Wavelength (nm)

Abs

orba

nce

Wavelength (nm)

133

Table 5.4 UV-visible Spectral Data max. (nm) for the ligand [L2] and the complexes

Compound max (nm) Band assignment

L2 237,271 376

* *

[Pr(L2)(NO3)2(H2O)]NO3 219,246

353 * *

[Sm(L2)(NO3)2(H2O)]NO3 226,241

367 * *

[Gd(L2)(NO3)2(H2O)]NO3 219,243

358 * *

[Tb(L2)(NO3)2(H2O)]NO3 226,253

339 * *

[Er(L2)(NO3)2(H2O)]NO3 228,252

362 * *

[Yb(L2)(NO3)2(H2O)]NO3 221,249

335 * *

134


The emission spectra of the ligand [L2] and its Ln (III) complexes

(1.0 10 5M in DMF solution) are recorded at the room temperature.

The emission spectrum of the free ligand exhibits broad

fluorescence band centered at 430 nm attributed to * transitions

[116,117]. Inspection of emission spectra ( exc.= 360 nm) shown in

Figure 5.33. indicate that [Sm(L2)(NO3)2(H2O)].NO3, [Er(L2)(NO3)2(H2O)]NO3

and [Tb(L2)(NO3)2(H2O)].NO3 complexes exhibit the characteristic emission

spectra of the Sm (III), Er (III) and Tb (III) ions, respectively. This indicates

that the Schiff base ligand is a good chelating organic chromophore and can

be used to absorb and transfer energy to the Ln (III)ions.

The sensitised emission spectrum of the [Sm(L2)(NO3)2

(H2O)].NO3complex displays three luminescence bands at 560, 610and 640

nm corresponding to the 4G5/26H5/2,4G5/2

6H7/2 and 4G5/26H9/2 transitions

respectively.

For the Tb (III) complex, the emission spectrum excited at 300 nm

shows three luminescence bands at 501, 535, and 599 nm corresponding to

the 5D47F6, 5D4

7F5 and 5D47F4 transitions respectively.

For Er (III) complex, the emission spectrum shows three

luminescence bands at 490, 520 and 650 nm corresponding to the blue

emission 4F9/26H15/2, 4F9/2

6H13/2 and 4F9/26H11/2 transitions respectively.

The above three Schiff base complexes was sensitised by its

chelating organic ligand, which was acting as photosensitiser. The emission

of Ln (III) ions can be mainly observed by sensitisation process upon the

excitation of the chelating Schiff base organic moiety, since the organic

chromophores have large molar absorption coefficients of several orders as

compared with those of Ln (III) ions.

135

Figure 5.33 Emission spectra of Sm (III), Er (III) and Tb (III) Schiff

base complexes in DMF solution (1.0 10-6 M) at room

temperature. Emission spectrum is obtained with

exc. = 360 nm.

136


The Schiff-base ligand [L2] and its Ln (III) complexes reported

here were evaluated for antibacterial activity against Escherichia coli,

Streptococcus agalactiae, Staphylococcus aureus, and Pseudomonas

aeruginosa and the percentage inhibition detail of the same for different

concentrations (60,40 and 20µg mL-1) are tabulated in Table 5.5. The Schiff

base ligand [L2] is biologically active and its activity arise from the presence

of imine group which imports in elucidating the mechanism of transformation

reaction in biological systems. However its Ln (III) complexes showed

remarkable antibacterial activity as a result of chelation of metal with organic

ligand synergistically increasing its effect [119].

From the results obtained, the antibacterial activity of Ln (III) Schiff

base complexes is found to be higher than that of a free Schiff base ligand,

against the same microorganism under identical experimental conditions.

This is similar to earlier observations [120].

Remarkable enhancement in activity was found for Gd (III) Schiff

base complex against the species Escherichia coli. For the species

Streptococcus agalactiae Sm (III) and Pr (III) Schiff base complex showed

higher activity than the other Ln (III) complexes. In a similar manner the

percentage inhibition was higher for Er (III) complex against both

Staphylococcus aureus, and Pseudomonas aeruginosa pathogens. The

percentage inhibition for the Schiff base ligand and all the Ln (III) complexes

have been depicted in Figure 5.35 - 5.38.

This increased activity of the Ln (III) complxes upon chelation is

attributed to Tweedy’s chelation theory, according to which, the chelation

reduces the polarity of the metal atom mainly because of the positive charge

of the metal partially shared with donor atoms present on the ligand and

there is electron delocalisation over the whole chelate ring [121]. This, in

137

turn, increases the lipophilic character of the metal chelate and favors its

permeation through the lipid layers of the bacterial membranes [109].

Generally, it is suggested that the chelated complexes deactivate

various cellular enzymes, which play a vital role in various metabolic

pathways of these microorganisms. Other factors such as solubility,

conductivity and dipole moment, affected by the presence of metal ions, may

also increase the biological activity of the metal complexes compared to the

ligand.



E. coli S.agalactiae P. aeruginosa S. aureus

L2 51.15 64.70 73.48 76.47

[Pr(L2)(NO3)2(H2O)]NO3 56.43 70.58 58.42 76.47

[Sm(L2)(NO3)2(H2O)]NO3 64.70 70.58 72.58 82.35

[Gd(L2)(NO3)2(H2O)]NO3 70.58 64.70 94.11 82.35

[Tb(L2)(NO3)2(H2O)]NO3 59.28 62.83 81.73 80.25

[Er(L2)(NO3)2(H2O)]NO3 59.46 72.85 60.12 85.56

[Yb(L2)(NO3)2(H2O)]NO3 65.06 72.87 74.46 82.45

DMF - - - -

Amikacin 100 100 100 100

138

(a) Escherichia coli (b) Pseudomonas aeruginosa

(c) Streptococcus agalactiae (d) Staphylococcus aureus

C – Control; 1 - 20 µg mL-1 ; 2 – 40 µg mL-1 ; 3 – 60 µg mL-1

Figure 5.34 Zone of inhibition of (a) Gd (III) (b) Gd (III) (c) Yb (III)

(d) Er (III) complex of Schiff base Ligand [L2] for bacterial species

139


Figure 5.36 Percentage Inhibition of Schiff base ligand [L2] and their Ln (III) Schiff base complexes against Streptococcus agalactiae

0102030405060708090

100


Escherichia coli

0102030405060708090

100


Streptococcus agalactiae

% in

hibi

tion

% in

hibi

tion

140



0102030405060708090

100



0102030405060708090

100



% in

hibi

tion

% in

hibi

tion

141


The antifungal activity of the schiff-base ligand [L2] and its Ln (III)

complexes reported here were evaluated for Candida and Aspergillus

species and the percentage inhibition detail of the same for different

concentrations (60,40 and 20 µg mL-1) are tabulated in Table 5.6. The

comparative antifungal activity have been depicted in Figure 5.40 and 5.41.

The Schiff base ligand [L2] and all the Ln (III) complexes show high

antifungal activity against the reported species. However the Ln (III)

complexes showed remarkable antibacterial activity than the Schiff base

ligand. This is probably due to the greater lipophilic nature of the complexes

[119].

It was observed that the antifungal activity of few complexes were

very near to the standard antifungal agent Ketokonazole. Compared to all

other Ln (III) complexes the Sm (III) complex shows very high activity

against the Candida species. In the case of Aspergillus species also the

Sm (III) complex has high activity of all the Ln (III) complexes.

It was evident from the data that this activity significantly increased

on coordination. This enhancement in the activity may be rationalised on the

basis that their structures mainly possess an additional C=N bond. It has

been suggested that the Schiff base with nitrogen and oxygen donor

systems inhibit enzyme activity, since the enzymes which require these

groups for their activity appear to be especially more susceptible to

deactivation by metal ions on coordination.

Moreover, coordination reduces the polarity of the metal ion mainly

because of the partial sharing of its positive charge with the donor groups

[120] within the chelate ring system formed during coordination. The activity

of these complexes can be related to the strength of the metal–ligand bond,

besides other factors such as size of the cation, receptor sites, diffusion and

142

a combined effect of the metal and the ligands for inactivation of the

biomolecules.



Candida Aspergillus

L2 62.14 52.18

[Pr(L2)(NO3)2(H2O)]NO3 64.70 65.49

[Sm(L2)(NO3)2(H2O)]NO3 98.92 94.11

[Gd(L2)(NO3)2(H2O)]NO3 100 70.58

[Tb(L2)(NO3)2(H2O)]NO3 96.42 85.24

[Er(L2)(NO3)2(H2O)]NO3 97.54 93.74

[Yb(L2)(NO3)2(H2O)]NO3 98.45 92.62

DMF - -


143


C – Control; 1- 20 µg mL-1 ; 2 – 30 µg mL-1 ; 3 – 60 µg mL-1

Figure 5.39 Zone of inhibition of (a) Gd(III) (b) Sm(III) complex of Schiff base Ligand [L2] for fungal species

144



0

10

20

30

40

50

60

70

80

90

100


Candida

0102030405060708090

100


Aspergillus

% in

hibi

tion

% in

hibi

tion

145

5.3 CONCLUSION

The chapter presented includes the synthesis of the Ln (III)

complexes of the tridentate Schiff base ligand L2 formed by the

condensation of L-Threonine and 5-bromosalicyaldehyde. The structures

of the Schiff base ligand L2 and the lanthanide metal complexes have been

confirmed by various spectral studies like 1H NMR, UV, FT-IR and Mass

Spectrometry. The results of investigation support the suggested structures.

The coordination number eight is suggested for the metal ion in these

lanthanide(III) complexes. The fluorescence data reveals that the Sm (III),

Tb (III) and Er (III) complexes exhibit characteristic luminescence of

Sm (III), Tb (III) and Er (III) ions. The synthesised complexes exhibit

enhanced antimicrobial activity than the corresponding free Schiff base

ligand. All the newly synthesised compounds possess higher antifungal

properties than the antibacterial property.

146

6. SCHIFF BASE DERIVED FROM LEUCINE AND ITS LANTHANIDE (III) COMPLEXES

6.1 INTRODUCTION

Schiff base ligands have gained paramount importance due to

their versatility like straight forward synthesis, electron donor property and

multidentate nature, which results in very high binding constants for d- and

f-block metals [130, 131]. The condensation between –NH2 group of the

amino acids and carbonyl group of the aldehydes or ketones needs a

special condition due to Zwitter ionic effect of aminoacids. It has been

observed that pH plays a vital role in the process of condensation [132, 133].

The trivalent lanthanide ion, complexes with strongly chelating species

containing highly electronegative donor atoms, forms stable complexes

[134]. Lanthanide and lanthanide complexes have attracted a great deal of

interest in recent years because they have applications as antioxidants

[135], in medicinal inorganic chemistry [136, 137], catalysis [138],

luminescence chemical probes and sensors [139] and pharmacological

activities [140, 141]. Further the lanthanide complexes were found to exhibit

extremely sharp emission [142].

As a result of the above facts, and in view of the diversified

roles of lanthanide Schiff base metal complexes, in continuation of our work

[129, 143], we have synthesised and studied the physicochemical properties

of lanthanide(III) complexes derived from Schiff base ligand [L3] (Figure

6.1) with N, O donor atoms. The structures of the isolated complexes have

been established using spectral techniques like UV-visible, FT-IR, 1H NMR

and Mass Spectrometry. The fluorescence study and investigation of

antimicrobial activity of rare earth metal Schiff base complexes were made.

147

OHN

Br

O

ONa

L3


Figure 6.1 Sodium salt of the Schiff base ligand L3




different analytical techniques. Scheme 6.1 summarizes the multi-step

procedure leading to the target complexes. The ligand was synthesised by

the one step condensation of leucine and 5 bromosalicylaldehyde

and characterised by UV-Vis, FT-IR, 1H NMR, Mass and TG Analysis.

All the Ln (III) complexes were synthesised by the multistep

procedure in which Ln(NO3)3.xH2O was used as the source of metal and

they correspond to the formula [Ln(L3)(NO3)2(H2O)].NO3. All the complexes

were stable in air and non-hygroscopic powders, soluble in DMSO, DCM

and DMF, sparingly soluble in methanol, ethanol, acetonitrile and

ethylacetate.

148

NH2

O

HO

Leucine

+ HO

OBr


OHN

Br

O

ONaEtOH/NaOH

Reflux - 3h

L3


Reflux 3-5h

Ln(NO3)3.xH2O

NO3CH

O

N C

O

Ln

O

NO3

NO3

H2OBr

Ln(III) complexes

Scheme 6.1 Synthesis of Schiff base ligand [L3] and Ln (III) Schiff

base Complexes [Ln = Pr (III), Sm (III), Gd (III), Tb (III), Er (III) and Yb (III)]



base ligand and synthesised Ln (III) Schiff base complexes which are in

good agreement with the calculated values.

149


Compound Molecular Formula Molecular weight Cal.(Exp.)%

C H N

L3 C13H16O3NBrNa 336 46.45(46.65) 4.50(4.49) 4.17(4.15)

[Pr( L3)(NO3)2(H2O)]NO3 C13H16O10N3BrPr 596 26.16(26.18) 2.85(2.85) 7.03(7.04)

[Sm(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrSm 605 25.75(25.76) 2.78(2.80) 6.93(6.93)

[Gd(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrGd 612 25.48(25.47) 2.76(2.77) 6.84(6.85)

[Tb(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrTb 613 25.40(25.40) 2.74(2.76) 6.85(6.84)

[Er(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrEr 621 25.05(25.06) 2.74(2.73) 6.73(6.74)

[Yb(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrYb 628 24.81(24.83) 2.69(2.70) 6.65(6.68)

150

6.2.2 Mass Spectra

A mass spectrum of the newly synthesised Schiff base ligand [L3] confirms the proposed formula by detecting the molecular fragments. Mass spectrometry chemical ionisation of the ligand [L3] (Figure 6.2- 6.9) shows m/z at 336. The HRMS of the complexes (Figure 6.2) show the molecular ions [M]+. at various m/z values. Some isotopic peaks are also found around the fragment peaks [144].



[C13H14O3NBrPr]+, 184 [C7H4BrO]+ , 128[C6H10O2N]+ and 79 [Br]+.



[C13H14O3NBrSm]+, 184 [C7H4BrO]+ , 128[C6H10O2N]+ and 79 [Br]+.



[C13H14O3NBrGd]+, 184 [C7H4BrO]+ , 128[C6H10O2N]+ and 79 [Br]+.



[C13H14O3NBrTb]+, 184 [C7H4BrO]+ , 128[C6H10O2N]+ and 79 [Br]+.



[C13H14O3NBrEr]+, 184 [C7H4BrO]+ , 128[C6H10O2N]+ and 79 [Br]+.



[C13H14O3NBrYb]+, 184 [C7H4BrO]+ , 128[C6H10O2N]+ and 79 [Br]+.

151


%

m/z

152


%

m/z

153


%

m/z

154


%

m/z

155


%

m/z

156


%

m/z

157


%

m/z

158


159



DMF solution at room temperature are observed to be in the range of

110-125 Scm2mol-1 are tabulated in Table 6.2. This suggests 1:1 electrolytes

and the two nitrate are coordinated to the Ln (III) ion [98].

Table 6.2 Molar conductance of the ligand [L3] and Ln (III) Schiff base complexes

Compound Molecular Formula m

(S cm2 mol 1)

L3 C13H16O3NBrNa -

[Pr( L3)(NO3)2(H2O)]NO3 C13H16O10N3BrPr 112

[Sm(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrSm 116

[Gd(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrGd 110

[Tb(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrTb 125

[Er(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrEr 122

[Yb(L3)(NO3)2(H2O)]NO3 C13H16O10N3BrYb 119


The presence of water molecules and the thermal behaviour of the

Schiff base ligand and the complexes were investigated by thermal analysis.

Thermogravimetric curves, TGA and DTA for the ligand Figure 6.10 and

[Ln(L3)(NO3)2(H2O)]NO3complexes have been obtained in nitrogen

atmosphere between 0-800°C. Figures 6.11-6.16 represents the TGA and

DTA curves for Ln (III) Schiff base complexes.

160

The thermogram of all the Ln (III) Schiff base complexes shows

that the appearance of small endothermic peak on DTA curve around 100°C

corresponds to the loss of the water molecule [145]. The corresponding

weight loss on TGA curve is 2.7% due to the release of water molecule. A

further increase of temperature up to 200°C, leads to the elimination of

HNO3 molecule, 28.31%.

The enhancement of temperature up to 400°C in Pr (III) complex,

leads to the decomposition of organic moiety with the weight loss of 40.23 %

[146]. The final residue of 28.76 %corresponds to the Pr2O3 [163]. The

thermal behaviour of the other lanthanide complexes is similar to

[Pr(L3)(NO3)2(H2O)]NO3which indicates that the complexes undergo two

major steep degradation steps. In the first stage, the coordinated water

molecules are eliminated followed by the elimination of nitric acid, the

second stage decomposition corresponding to the elimination of the Schiff

base ligand and beyond 640oC the TGA curve show no change, possibly

due to the complexes being decomposed to its corresponding Ln2O3 [147].

The Gd (III) Schiff base complex was stable up to 196°C and its


decomposition in the range 196 - 530°C with DTG peak at 426°C










161

Figure 6.10 TG/DTA curves of the Schiff base ligand [L3] (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

162

Figure. 6.11 TG/DTA curves of the [PrL3(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

163

Figure. 6.12 TG/DTA curves of the [SmL3(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

164

Figure. 6.13 TG/DTA curves of the [GdL3(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

165

Figure. 6.14 TG/DTA curves of the [TbL3(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

166

Figure. 6.15 TG/DTA curves of the [ErL3(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

167

Figure. 6.16 TG/DTA curves of the [YbL3(NO3)2H2O]NO3 complex; (a) TG – thermogravimetric analysis curve; (b) DTA – differential thermal analysis curve

a

b

168









6.2.5 1H NMR Spectra

The 1H NMR Spectra of Schiff base ligand in DMSO-d6 is shown

in Figure 6.17, which shows signal of multiplets at 0.84-0.88 ppm

equivalent to the 6H of two methyl groups. Singlet at 1.69 ppm

corresponds to the methine protons associated with two methyl groups.

Multiplets at 2.43-2.56 ppm are due to , methylene hydrogen atom

associated with a azomethine group [148]. The multiplets in 6.59-7.49

ppm region are assigned to the protons of the benzylidene ring groups

[149]. The singlet at 3.32 ppm is due to the water impurity of the

deuterated DMSO, and the strong singlet at 8.34 ppm is assigned to

the azomethine proton [150]. This is in accordance with the IR data.

169

Figure 6.17 1H NMR spectra of the Schiff base ligand [L3]

170

6.2.6 IR Spectra

The IR spectral data for the Schiff base ligand and Ln (III)

complexes, are listed in Table 6.3 and the comparative spectrum of the

Schiff base ligand and the complex is shown in Figures 6.18 – 6.24. In order

to study the binding mode of the Schiff base ligand to the metal ion in the

complexes, the IR Spectrum of the free Schiff base ligand was compared

with the spectra of the complexes. The change in profile of stretching

frequencies in the complexes, while compared with those observed for the

isolated ligand confirms the coordination of the ligand with the central metal

ion. The IR spectral shifts of different complexes are similar, indicating

similar structures of the Ln (III) complexes.

The IR spectrum of the ligand shows a strong absorption band

around 1665 cm-1, which may be attributed to the azomethine group and it

was found that this absorption frequency shifted to 1640 cm-1 in the spectra

of the complex indicates a stronger double bond character of the imine bond

and a coordination of the azomethine nitrogen atom to the Ln (III) ion

[151,152]. This coordination is further confirmed through the appearance of

a medium intensity band around 420 cm-1 assigned to an Ln-N vibration.

The IR spectrum of the free Schiff base ligand exhibits a broad band around

3400 cm-1, which is attributed to the stretching frequency of the aromatic

hydroxyl substituent group, perturbed by intramolecular hydrogen bonding

[O-H…N] between phenolic hydrogen and azomethine nitrogen atoms

[153,154]. Further, the appearance of the –OH band around 3490 cm-1 in

the spectra of the complexes with an increase in intensity indicates that the

hydroxyl oxygen is coordinated to the Ln (III) ion without proton

displacement [94].

The appearance of band near 1260 cm-1 in the free Schiff base

ligand is associated with the Ar-O band of the phenolic hydroxyl substituent

[155]. The shift in the stretching frequency of Ar-O band around 1270 cm-1

in the spectra of the Ln (III) complexes suggest the coordination of Ln (III)

171

ion occurs through the oxygen atom of the hydroxyl benzene of the Schiff

base ligand [156]. The complexes show a strong band in the region 1500 -

1525 cm-1 and a weaker band in the region 1380 - 1400 cm-1 assigned to

asymmetric and symmetric stretching frequencies of COO- group

respectively. The frequency difference between the asymmetric and

symmetric stretching frequencies comes around 215 cm-1, which

suggests the monodentate coordination of the carboxyl group of amino

acid with the Ln (III) ion [157]. This is further confirmed through the

appearance of a medium intensity band around 540 cm-1, which may be

assigned to Ln-O vibration [158]. The infrared spectra of the Ln (III)

complexes displays several intense band at 1470 cm-1 ( 1), 1028 cm-1

( 2), 825 cm-1 ( 3) and 1290 cm-1 ( 4), which represents the

coordinated nitrate ions with the central metal ion. The difference in

frequency separation is approximately 180 cm-1, which suggests that the

mode of coordination of NO3- ion with the central metal ion is bidentate in

nature [159,160]. The IR band at 1383 cm-1 in the spectrum of the complex

indicates the existence of the free nitrate group in the coordination

sphere. The existence of medium intensity band around 1615 cm-1 is

due to the symmetric and the asymmetric O–H stretching vibrations of

inner-sphere water molecule [161]. The presence of coordinated water is

also established and supported by TG/DTA analysis of these complexes.

172

Table 6.3 Infrared spectral data for the Schiff base ligand [L3] and the Ln (III) complexes

Compounds OH C=N Ar-O NO3

- asym(COO

-) sym(COO

-) Ln-O Ln-N

1 2 3 4 0

L3 3400 1665 1260 - - - - - - - - -

[Pr( L3)(NO3)2(H2O)]NO3 3490 1640 1268 1470 1028 825 1290 1383 1505 1380 540 420

[Sm(L3)(NO3)2(H2O)]NO3 3485 1642 1270 1471 1029 827 1292 1383 1515 1390 548 421

[Gd(L3)(NO3)2(H2O)]NO3 3495 1640 1270 1470 1029 825 1290 1383 1505 1380 545 420

[Tb(L3)(NO3)2(H2O)]NO3 3492 1638 1268 1471 1028 826 1292 1383 1500 1380 540 422

[Er(L3)(NO3)2(H2O)]NO3 3480 1641 1270 1470 1028 825 1292 1383 1510 1390 546 420

[Yb(L3)(NO3)2(H2O)]NO3 3498 1640 1270 1470 1029 826 1292 1383 1525 1400 545 418

173


Wavenumber (1/cm)

% T

174


Wavenumber (1/cm)

% T

175


Wavenumber (1/cm)

% T

176


Wavenumber (1/cm)

% T

177


Wavenumber (1/cm)

% T

178


Wavenumber (1/cm)

% T

179


Wavenumber (1/cm)

% T

180


The UV-visible absorption spectra for the Schiff base ligand

and the Ln (III) complexes were carried out in DMF at room temperature.

The numerical values of the maximum absorption wavelength ( max) are

listed in Table 6.4 and shown in Figures 6.25 – 6.32. The absorption of the

ligand is characterised by four main absorption bands in the regions 200-500

nm. The band at the max = 203 nm and at 241 nm is attributed to *

transition state [162, 163]. The band at the max = 334 nm corresponds to the

* transition state of the azomethine group and the max = 424 nm is

attributed to the n * transition state associated with the azomethine

group with an intra - molecular charge transfer [164].

The high extinction coefficient for absorption in the near UV-visible

range of Schiff base rare earth metal complexes, leads to the more effective

energy transfer from the ligand to the coordinated rare earth metal center.

This leads to the difference in spectral intensity of the Ln (III) complexes.

The UV-visible spectra of the complexes generally show the

characteristic bands of the free ligands with some changes both in

frequencies and intensities. These modifications of the shifts and the

intensity of the absorption bands confirmed the coordination of the ligand

to the metal ion. The UV-visible absorption spectra of all the Ln (III) Schiff

base complexes show a similarity, which indicates similarity in their

structures. In general, the lanthanide ions do not appreciably contribute to

the spectra of their complexes, since f-f transitions are Laporte-forbidden

and very weak in nature [165]. The absorption bands around 200, 330, 420

nm are slightly shifted to lower frequencies upon complexation. The

appearance of a new band around 270 nm, being absent in the ligand

gives further evidence for the complexation. The band at 273 nm is

attributed to the ligand metal charge transfer [166] and the one around 360

nm may assigned to the * transition state of the azomethine group

coupled with charge transfer from ligand to central metal ion [167].

181

Table 6.4 UV-Visible Spectral Data max. (nm) for the ligand [L3] and the complexes

Compound max (nm) 104(cm2 mol-1) Band assignment

L3 203,241,334, 424

5.05,4.52,3.28, 1.61

* *

[Pr( L3)(NO3)2(H2O)]NO3 200,229,364, 273 429

3.58,2.41,0.31, 0.47 0.05

* LMCT

*

[Sm(L3)(NO3)2(H2O)]NO3 202,242,359 280 442

3.17,0.79,0.15, 0.20 0.07

* LMCT

*

[Gd(L3)(NO3)2(H2O)]NO3 200,230,369, 276 428

3.40,1.36,0.0, 0.34 0.094

* LMCT

*

[Tb(L3)(NO3)2(H2O)]NO3 201,229,361, 273 433

4.09,3.30,0.52, 0.7 0.085

* LMCT

*

[Er(L3)(NO3)2(H2O)]NO3 203,229,364, 273 429

3.58,1.59,0.21, 0.34 0.05

* LMCT

*

[Yb(L3)(NO3)2(H2O)]NO3 200,222,339, 252 407

3.49,1.77,0.21, 0.83 0.071

* LMCT

*

182

Figure 6.25 UV-visible spectrum of the Schiff base ligand [L3] in DMF

solution (1.0 10-6 M) at room temperature

Figure 6.26 UV-visible spectrum of the [Pr(L3)(NO3)2H2O]NO3

complex in DMF solution (1.0 10-6 M) at room temperature.

Abs

orba

nce

Wavelength (nm)

Abs

orba

nce

Wavelength (nm)

183



temperature

Figure 6.28 UV-visible spectrum of the [Gd(L3)(NO3)2H2O]NO3


temperature

Abs

orba

nce

Wavelength (nm)

Abs

orba

nce

Wavelength (nm)

184



temperature



temperature.

Abs

orba

nce

Wavelength (nm)

Abs

orba

nce

Wavelength (nm)

185



temperature

Figure 6.32 Comparative UV-visible spectra of the Ln (III) complexes

in DMF solution (1.0 10-6 M) at room temperature

Abs

orba

nce

Wavelength (nm)

Abs

orba

nce

Wavelength (nm)

186


Photophysical studies of the ligand and its rare earth metal

complexes have been explored in this article. Figure 6.33 gives the

emission spectrum of the Samarium and Terbium Schiff base complexes in

DMF solution at room temperature. Fluorescence properties refer to any

process, which increases, decreases the fluorescence intensity or a shift of

the maximum absorption of a sample. These include excited state reaction,

molecular rearrangement, energy transfer, ground state complex formation

and quenching due to collision [146].

The emission spectra of the complexes were recorded upon the

excitation at 395 nm. The ligand present fluorescence band at 485 nm. The

fluorescence spectra of the complexes present bands that indicate the

formation of complexes and fluorescence property of the metallic ions. The

strongest emission was located around 485 nm for the free ligand, may be

attributed to * transition state, which shifts upon the complexation.

Due to the shielding of 4f orbitals from the environment by an outer shell of

5s and 5p orbitals, the f–f absorption bands are very narrow, which causes

the minimally perturbed spectral properties of the lanthanide ions by the

external field generated by the ligands [168]. An organic ligand is necessary

to improve the quantum yield of luminescent emission for the lanthanide

ions, since the absorption coefficients of the ligand are many orders of

magnitude larger than the intrinsically low molar absorption coefficients of

the trivalent lanthanide ions [169]. Besides, the direct coordination of an

organic ligand to a lanthanide ion can further improve the energy-transfer

rates by reducing the distance between the ligand and the lanthanide ion

[170, 171]. This energy excites the ligand to the excited singlet (S1) state,

followed by an energy migration via intersystem crossing from the S1 state to

a ligand triplet (T) state. The energy is then transferred from the triplet state

of the ligand to a resonance state of the coordinated lanthanide ion without

187

radiation, which in turn undergoes subsequent emission in the visible region

[172-175].

Inspection of emission spectra at exc. 395 nm exhibits the

characteristic emission spectra of Sm (III) and Tb (III) complexes. This

indicates the coordination nature of the ligand with rare earth metal (III) ions

for absorption and transfer of energy.

The sensitised emission spectra of Sm (III) Schiff base complexes

display two luminescence bands at 565 nm and 600 nm corresponding to

the 4G5/2 6H5/2 and 4G5/2 6H7/2 respectively and a shoulder at 642 nm

is due to 4G5/2 6H9/2.

The Tb (III) Schiff base complexes also display two fluorescence

bands around 556 nm and 590 nm, this may attributed to 5D4 7F5 and 5D4

7F4 respectively and a shoulder at 624 nm due to 5D4 7F3. This

indicates that the energy-transfer chain is successfully completed from the

excitation of the ligand to the emission of the coordinated Sm (III) and

Tb (III) central metal ions [162]. The appearance of small band at 840 nm

denotes the secondary derivatives of the rare earth Schiff base complexes.

188

Figure 6.33 Emission spectra of Sm (III) and Tb (III) Schiff base

complexes in DMF solution (1.0 10-6 M) at room

temperature. Emission spectra is obtained with

exc. = 395 nm

189


All the synthesised Ln (III) metal complexes and their parent Schiff

base ligand L3 were screened for their in vitro antibacterial activity against

Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus,

Streptococcus agalactiae. The percentage inhibition details of the same for

maximum concentration (100 µg mL-1) are tabulated in Table 6.5.

The antibacterial suggested that, the Schiff base L3 and its Ln (III)

metal complexes were found to be biologically active and some of the

Ln (III) metal complexes showed significantly enhanced antibacterial

activities. It is, however, known that, chelation tends to make the Schiff

bases to act as more powerful and potent bactereostatic agents [176,177],

thus inhibiting the growth of bacteria more than the parent Schiff bases.

Tb (III) Schiff base complex showed remarkable enhancement in

activity against the pathogens Escherichia coli, Streptococcus agalactiae,

and Pseudomonas aeruginosa. For the species Staphylococcus aureus

Gd (III) Schiff base complex showed higher activity than the other Ln (III)

complexes. The percentage inhibition for the Schiff base ligand L3 and all its

Ln (III) complexes have been depicted in Figure 6.35 - 6.38. From the result

obtained it is clear that the Tb (III) Schiff base complex acts as a better

antibacterial agent than the other Ln (III) complexes, which is evident from

the fact that, it shows greater activity against all the species under

investigation.

190



E. coli S. agalactiae P. aeruginosa S. aureus

L3 53.76 63.24 75.79 75.46

[Pr(L3)(NO3)2(H2O)]NO3 58.35 69.45 59.54 73.76

[Sm(L3)(NO3)2(H2O)]NO3 59.79 71.73 70.61 81.94

[Gd(L3)(NO3)2(H2O)]NO3 64.26 63.61 88.64 83.18

[Tb(L3)(NO3)2(H2O)]NO3 65.92 72.49 94.79 79.76

[Er(L3)(NO3)2(H2O)]NO3 53.45 70.54 64.91 80.54

[Yb(L3)(NO3)2(H2O)]NO3 61.76 71.34 76.38 81.23

DMF - - - -

Amikacin 100 100 100 100

191

(a) Escherichia coli (b) Streptococcus agalactiae

(c) Staphylococcus aureus (d) Pseudomonas aeruginosa

C – Control ; 1 - 20 µg mL-1 ; 2 – 40 µg mL-1 ; 3 – 60 µg mL-1 ;

4 – 80 µg mL-1 ; 5 - 100 µg mL-1

Figure 6.34 Zone of inhibition of (a) Tb(III) (b) Tb(III) (c) Gd(III) (d) Tb(III) complexes of Schiff base Ligand [L3] for bacterial species

192


Figure 6.36 Percentage Inhibition of Schiff base ligand [L3] and their Ln (III) Schiff base complexes against Streptococcus agalactiae

0102030405060708090

100


Escherichia coli

0102030405060708090

100


Streptococcus agalactiae

% in

hibi

tion

% in

hibi

tion

193



0102030405060708090

100



0102030405060708090

100



% in

hibi

tion

% in

hibi

tion

194


Synthesised Ln (III) metal complexes and their Schiff base ligand

L3 were screened for their in vitro antifungal activity against Candida and

Aspergillus. The percentage inhibition detail of the same (Figure 6.40 - 6.41)

for maximum concentration (100 µg mL-1) are tabulated in Table 6.6.

Antifungal activity of synthesised Schiff base ligand L3 and some

of their complexes are almost nearer to the standard drug Ketokonazole. It

was evident from the data that this activity significantly increased on

coordination. This enhancement in the activity of the Schiff base may be

rationalised on the basis that the structure mainly possess C=N bond. It has

been suggested that the ligands with nitrogen and oxygen donor systems

inhibit enzyme activity, since the enzymes which require these groups for

their activity appear to be more susceptible for the deactivation by metal ions

on coordination [178,179].

From the observed data it was concluded that, the Schiff base

ligand L3 and its Ln (III) metal complexes are found to possess higher

antifungal activity than the antibacterial activity.

It was also observed that the antifungal activity of few complexes

were very near to the standard antifungal agent Ketokonazole. Compared to

all other Ln (III) complexes, Tb (III) complex shows greater activity against

the fungal species Candida and Aspergillus. Hence, the Tb (III) Schiff base

complex acts as the better antifungal agent.

195



Candida Aspergillus

L3 63.42 54.37

[Pr(L3)(NO3)2(H2O)]NO3 62.49 63.81

[Sm(L3)(NO3)2(H2O)]NO3 89.07 87.25

[Gd(L3)(NO3)2(H2O)]NO3 97.18 73.15

[Tb(L3)(NO3)2(H2O)]NO3 99.04 95.23

[Er(L3)(NO3)2(H2O)]NO3 96.18 90.18

[Yb(L3)(NO3)2(H2O)]NO3 96.91 89.49

DMF - -


196


C – Control ; 1- 20 µg mL-1 ; 2 – 40 µg mL-1 ; 3 – 60 µg mL-1 ;

4 – 80 µg mL-1 ; 5 - 100 µg mL-1

Figure 6.39 Zone of inhibition of Tb(III) complex of Schiff base Ligand [L3] for fungal species

197



0102030405060708090

100


Candida

0102030405060708090

100


Aspergillus

% in

hibi

tion

% in

hibi

tion

198

6.3 CONCLUSION

This chapter reports the synthesis and characterisation of the

tridentate Schiff base ligand L3, obtained by the condensation of L-

Leucine and 5-bromosalicyaldehyde and its Ln (III) complexes. The

analytical and spectral data reveal that the ligand coordinate to the central

Ln (III) ion by its phenolic oxygen, azomethine nitrogen and the carboxylic

oxygen with 1:1 stoichiometry and their coordination number is eight. The

samarium and terbium complexes exhibit interesting fluorescence properties.

The synthesised complexes show enhanced antimicrobial activity than the

corresponding free Schiff base ligand L3. All the synthesised Ln (III)Schiff

base complexes possess higher antifungal properties than the antibacterial

property. All the above facts reveal that these complexes can be

recommended for establishing a new line of search for antimicrobial agents.

199

7. CATALYTIC ACTIVITY OF LANTHANIDE (III) SCHIFF BASE COMPLEXES DERIVED FROM LEUCINE

7.1 INTRODUCTION

Catalytic oxidation has gained much interest among the academic

and industrial chemists [180]. Especially, oxidation of organic substrates by

inexpensive, readily abundant, terminal and environmental friendly oxidants

like aqueous H2O2, molecular oxygen are very attractive from the view point

of industrial technology and synthetic purposes [181]. Concerning the

green oxidant, hydrogen peroxide is one of the most powerful candidates

besides oxygen, because of its high atom efficiency, and water is expected

as the only by-product to be generated from the reaction [182,183].

Catalytic oxidation of amines to their corresponding oxygen

containing derivative has attracted much attention during the past few

decades [184]. Only few examples have been reported [185,186], among

which, it was found that transition-metal-catalysed oxidative reaction of

anilines to corresponding azobenzene is highly desirable under atmospheric

conditions [187].

Anilines are most widespread and principal contaminants of

industrial waste waters. These comprise an important class of environmental

contaminants and they are the building blocks for many textile dyes,

agrochemicals and other class of synthetic chemicals. The reaction

pathways of aromatic amines in natural systems are dominated by redox

reactions with soil and sediment constituents. Oxidation of such compounds

to harmless products is the important goal for basic research and industrial

applications [188]. Oxidation of anilines leads to the formation of

200

azobenzene [189], azoxybenzene [190,191], nitrobenzene [192] and

nitrosobenzene [193] by organic [194] and inorganic oxidants [189]. The

product composition in the oxygenation of amines depends on the oxidant,

catalyst and reaction condition employed. The oxidation of aniline leading to

the azo compound as a single product becomes a research interest for

chemists.

As a result of the above facts, and in view of the diversified roles

of lanthanide Schiff base metal complexes, in continuation of our work [129,

195], we have investigated the oxidation of aniline into their corresponding

azobenzene, using H2O2 as an oxygen source in the presence of rare earth

metal Schiff base complexes derived from leucine.

7.2 CATALYTIC OXIDATION OF ANILINE AND SUBSTITUTED ANILINES

The oxidation of aniline and its derivatives to the corresponding

azo compound have been carried out smoothly in an almost quantitative

yield using H2O2 as an oxidant and rare earth metal Schiff base complexes

as catalyst.

Table 7.1 gives the results of aniline oxidation into their

corresponding azobenzene as the product. All the reactions were carried

out at room temperature, by using 30 % H2O2 as an oxidant combined with

the catalytic amount of rare earth metal Schiff base complexes. The

azobenzene was produced in good yield at room temperature in CH2Cl2 with

the reaction time less than an hour.

Initially, the reaction was carried out without catalyst (Table 7.1,

entry 1) and enhanced amount of oxidant, it proceeds with the formation of

product with poor yield and greater reaction time. Then six types of catalyst

were tested (Table 7.1, entries 2-7), 70 – 90 % yields of azo benzene with

excellent conversions were obtained. To our surprise, among the various

201

catalyst used, the conversion of aniline to corresponding azobenzene in the

presence of [Gd(L3)(NO3)2(H2O)]NO3 with 10 mmol of H2O2, results 85 % of

yield within 15 minutes of reaction time at reflux (Table 7.1, entry 3).

Elevation of reaction temperature has no effect on the aniline oxidation with

the above Gd (III) Schiff base complex as a catalyst. The other tested

catalyst also gave moderate to good yield of oxidation product

(Table 6.5, entries 4-6). Although, the [Sm(L3)(NO3)2(H2O)]NO3 and

[Yb(L3)(NO3)2(H2O)]NO3 complexes gave the good yield of the product

(90 %), the reaction time (30 min. and 60 min. respectively) was the fact that

carries less importance in the purview of industrial and academics. The

effect of catalyst without oxidant (Table 7.1, entry 8) was also tested. No

starting material was converted into the product in the absence of H2O2.

After these testing, [Gd(L3)(NO3)2(H2O)]NO3 was chosen as the catalyst and

10 mL of H2O2 as an oxidant as the best reaction conditions.

To our delight 85 % of azobenzene was produced in CH2Cl2 with

total conversion of staring material and only 2 mol % of catalyst were utilised

for the oxidation purpose. With the best reaction condition (Table 7.1, entry

3) the experiment was carried out to check the generality and efficiency of

this methodology with the various kinds of substituted anilines are shown in

Table 7.2 Under the optimised conditions, aniline (entry 1) and various

substituted anilines were oxidised to its corresponding products in good to

excellent yields. The oxidative reaction of aromatic aniline with an electron

withdrawing substituted group such as nitro, acid and chloro group on the

phenyl ring proceeds with the yield of trace amount (entries 3, 4, 8 ,10 and

12) under the reaction conditions. This was suspected due to the low

electron density of phenyl ring. Further, among the various ortho, meta and

para substituted anilines, para substituted anilines results excellent yield of

the oxidative products (entries 2 and 5) while compared with meta

substituted aniline, which results good yield of the desired product (entries

6, 7 and 9) and ortho substituted aniline, which results a moderate yield of

202

the desired product (entry 11). The desired products were characterised by 1H NMR as shown in Figures 7.1 – 7.12.

In summary, a general rare earth metal Schiff base catalysed

oxidation of aniline and substituted aniline to the corresponding azo

compounds have been developed. The reaction proceeds at room

temperature and use H2O2 as the green oxidant, provides a simple and

general procedure for the preparation of azo derivatives that is difficult to

prepare by conventional methods. The result clearly demonstrates that this

oxidation system is more efficient in the oxidation of aniline to azobenzene

with H2O2 as an oxidant and [Gd(L3)(NO3)2(H2O)]NO3 complex as a catalyst.

Table 7.1 Oxidation of aniline catalysed by various Ln (III) complexes in CH2Cl2 at RT

Entry Catalyst Oxidant Yield (%)

Reaction Time (min.)

1 - Enhanced conc. H2O2

30 180

2 [Sm (L3) (NO3)2(H2O)]NO3 H2O2 90 30

3 [Gd (L3)(NO3)2(H2O)]NO3 H2O2 85 15

4 [Pr (L3)(NO3)2(H2O)]NO3 H2O2 70 25

5 [Eu (L3)(NO3)2(H2O)]NO3 H2O2 80 30

6 [Tb (L3) (NO3)2(H2O)]NO3 H2O2 75 25

7 [Yb (L3) (NO3)2(H2O)]NO3 H2O2 90 60

8 [Gd (L3) (NO3)2(H2O)]NO3 - - 240

203

Table 7.2 Oxidation of aniline and substituted anilines catalysed by Gd (III) complex in CH2Cl2 at RT

Entry Anilines Product Yield (%)

1

NH2

Phenylamine

N N

Diphenyl-diazene

85

2

NH2

CH3

p-Tolylamine

N N

H3C CH3

Di-p-tolyl-diazene

88

3

NH2

Cl4-Chloro-phenylamine

N N

Cl Cl

Bis-(4-chloro-phenyl)-diazene

30

4 NH2

O2N

4-Nitro-phenylamine

N N

O2N NO2

Bis-(4-nitro-phenyl)-diazene

12

5

OCH3

NH2

4-Methoxy-phenylamine

OCH3NNH3CO

Bis-(4-methoxy-phenyl)-diazene

88

6

m-phenylenediamine

NH2H2N

N NO2N NO2

Bis-(3-nitro-phenyl)-diazene

60

204

Table 7.2 (Continued)

Entry Anilines Product Yield (%)

7 OCH3

NH2


N

OCH3


H3CO

N

62

8 Cl

NH2

3-Chloro-phenylamine

NN

ClCl


20

9 CH3

NH2

m-Tolylamine

N N

H3C CH3

Di-m-tolyl-diazene

66

10

NH2

Cl2-Chloro-phenylamine

N N

Cl Cl


12

11

NH2

OCH3


N N

OMe MeO


25

12

NH2

Amino-benzoic acid

COOH

azodibenzoicacid

NN

OHO

OHO

12

205

Figure 7.1 1H NMR spectra of Diphenyl-diazene

ppm

206

Figure 7.2 1H NMR spectra of Di-p-tolyl-diazene

ppm

207

Figure 7.3 1H NMR spectra of Bis-(4-chloro-phenyl)-diazene

ppm

208

Figure 7.4 1H NMR spectra of Bis-(4-nitro-phenyl)-diazene

ppm

209

Figure 7.5 1H NMR spectra of Bis-(4-methoxy-phenyl)-diazene

ppm

210

Figure 7.6 1H NMR spectra of Bis-(3-nitro-phenyl)-diazene

ppm

211


ppm

212


ppm

213

Figure 7.9 1H NMR spectra of Di-m-tolyl-diazene

ppm

214


ppm

215


ppm

216

Figure 7.12 1H NMR spectra of Azodibenzoic acid

ppm

217

7.3 CONCLUSION

The Ln(III) Schiff base complexes have been applied as catalyst

for the oxidation of aniline and substituted aniline to the corresponding azo

compounds. Among them, the [Gd(L3)(NO3)2(H2O)]NO3 complex found to

possess good catalytic ability for oxidation of aniline under mild conditions

using the green oxidant H2O2 . It gave results 85 % of yield within 15 minutes

of reaction time.

218

8. SUMMARY AND CONCLUSION

8.1 Ln (III) SCHIFF BASE (L1) COMPLEXES

The tridentate Schiff base ligand L1 and its Ln (III) complexes of

the type [Ln(L1)(NO3)2(H2O)] NO3 were synthesised and characterised by

elemental analysis, TGA/DTA, spectral analysis like 1H NMR, UV, FT-IR and

Mass Spectrometry. The results of investigation support the suggested

structures of the lanthanide metal complexes. Thermal study reveals

thermal stability of complexes. Spectral study and thermal data showed that

two nitrate groups are bound in a bidentate manner to the central Ln (III)

ions in the coordination sphere while another nitrate is in the outer

coordination sphere in complexes. Hence, coordination number eight is

suggested for the metal ion in these lanthanide(III) nitrate complexes. The

fluorescence data reveals that the Sm (III), Tb (III) and Er (III) complexes

exhibit characteristic luminescence of Sm (III), Tb (III) and Er (III) ions,

which indicates that the ligand L1 is a good organic chelator to absorb and

transfer energy to Sm (III), Tb (III) and Er (III) ions. The antibacterial

activity results show that most of the synthesised complexes possess a good

antimicrobial activity against the pathogens tested than the corresponding

free Schiff base ligand.


Ln (III) complexes of the general formula [LnL(NO3)2(H2O)] NO3

has been synthesised from the tridentate Schiff base ligand L2 formed by the

condensation of L-Threonine and 5-bromosalicyaldehyde. The bonding of

ligand to the metal ions has been confirmed by elemental analysis,

TGA/DTA, spectral analyses like 1H NMR, UV, FT-IR and Mass

219

Spectrometry. The results of investigation support the suggested structures

of the lanthanide metal complexes. Thermal study reveals the presence of

water molecules and thermal stability of the complexes. Spectral study and

thermal data show that two nitrate groups are bound in a bidentate manner

to the central Ln (III) ions in the coordination sphere, while another nitrate is

in the outer coordination sphere in complexes. Hence, coordination number

eight is suggested for the metal ion in these lanthanide(III) complexes. The

fluorescence data reveals that the Sm (III), Tb (III) and Er (III) complexes

exhibit characteristic luminescence of Sm (III), Tb (III) and Er (III) ions,

which indicate that the Schiff base ligand is a good organic chelator to

absorb and transfer energy to Ln (III) ions. The synthesised complexes

exhibited enhanced antimicrobial activity than the corresponding free Schiff

base ligand. All the newly synthesised compounds possess higher

antifungal properties than the antibacterial property.


The rare earth metal complexes of the tridentate Schiff base

ligand L3, obtained by the condensation of L-Leucine and

5-bromosalicyaldehyde were characterised by elemental analysis,

TGA/DTA, spectral analysis like 1H NMR, UV, FT-IR, and Mass

Spectrometry. These analytical and spectral data reveal that the ligand

coordinate to the central Ln (III) ion by its phenolic oxygen, azomethine

nitrogen and the carboxylic oxygen with 1:1 stoichiometry and their

coordination number is eight. The samarium and terbium complexes present

interesting fluorescence properties. The synthesised complexes exhibited

enhanced antimicrobial activity than the corresponding free Schiff base

ligand L3. All the synthesised Ln (III) Schiff base complexes possess higher

antifungal properties than the antibacterial property.

220

8.4 CATALYTIC ACTIVITY OF Ln (III) SCHIFF BASE (L3) COMPLEXES

The Ln (III) Schiff base complexes of the ligand L3 have been

applied as catalyst for the oxidation of aniline and substituted aniline to the

corresponding azo compounds. The Ln (III) complexes possesses good

catalytic ability for oxidation of aniline under mild conditions using the green

oxidant H2O2 . The result clearly demonstrates that this oxidation system is

more efficient with [Gd(L3)(NO3)2(H2O)]NO3 complex as a catalyst. Hence,

this [Gd(L3)(NO3)2(H2O)]NO3 complex was utilised to check the generality

and efficiency of oxidation of various substituted anilines. This system

provides a simple and general procedure for the preparation of azo

derivatives, which are difficult to prepare by conventional methods.

221

9. SCOPE FOR FUTURE WORK

The following objectives are planned for future studies:

To obtain single crystal for all the Schiff base ligands and its

Ln (III) complexes and to explore the crystal structures.

To study the selective oxidation of aniline and substituted

anilines using the Ln (III) complexes derived from L1 and L2.

To investigate the reaction mechanism of oxidation of aniline.

To investigate methods for the recovery and reuse of catalyst

used for organic transformations.

To impregnate the synthesised Schiff base ligands and its

complexes into the ZnO nano particles and investigate further

their nature.

To explore the biological activities including antimicrobial,

antioxidant and anticancer efficiency of the above said nano

particles.

To investigate the luminescence property of the Ln (III) Schiff

base complexes embedded in the ZnO nano particle.

222

10. REFERENCES

1. Wilson M. “Microbial Inhabitants of Humans: Their Ecology and Role

in Health and Disease”, Cambridge, UK: Cambridge University

Press; 2005.

2. Aime S., Crich S.G., Gianolio E., Giovenzana G.B., Tei L. and

Terreno E., “High sensitivity lanthanide(III) based probes for MR-

medical imaging”, Coord. Chem. Rev., Vol.250, pp. 1562-1579,

2006.

3. Gassner A.L., Duhot C., Bunzli J.C.G. and Chauvin A.S.,

“Remarkable Tuning of the Photophysical Properties of Bifunctional

Lanthanide tris(Dipicolinates) and its Consequence on the Design of

Bioprobes”, Inorg. Chem., Vol.47, pp. 7802-7812, 2008.

4. Eliseeva S.V. and Bunzli J.C.G., “Lanthanide luminescence for

functional materials and bio-sciences”, Chem. Soc. Rev., Vol.39,

pp.189-227, 2010.

5. Hermann P., Kotek J., Kubicek V. and Lukes I., “Gadolinium(III)

complexes as MRI contrast agents: ligand design and properties of

the complexes”, Dalton Trans., Vol. 23, pp. 3027-3047, 2008.

6. Supkowski R.M., Bolender J.P., Smith W.D., Reynolds L.E.L. and

Horrocks W.D., “Lanthanide ions as redox probes of long-range

electron transfer in proteins”, Coord. Chem. Rev., Vol.186,

pp.307-319, 1999.

223

7. Martens S. and Mithofer A., “Flavones and Flavone synthases”,

Phytochemistry, Vol.66, pp.2399-2407, 2005.

8. Dixit N., Mishra L., Mustafi S.M., Chary K.V.R. and Houjou H.,

“Synthesis of a ruthenium(II) bipyridyl complex coordinated by a

functionalised Schiff base ligand: Characterisation, spectroscopic

and isothermal titration calorimetry measurements of M2+ binding and

sensing (M2+ = Ca2+, Mg2+)”, Spectrochim. Acta, Part A, Vol.73,

pp. 29-34, 2009.

9. Kureshy R.I., Khan N.H., Abdi S.H.R., Patel S.T. and Iyer P.J.,

“Chiral Ru(II) Schiff base complex-catalysed enantio selective

epoxidation of styrene derivatives using iodosyl benzene as oxidant.

II”, J. Mol. Catal. A: Chem., Vol.150, pp. 175-183, 1999.

10. Aoyama Y., Kujisawa J.T., Walanawe T., Toi A. and Ogashi H.,

“Catalytic reactions of metalloporphyrins. 1. Catalytic modification of

borane reduction of ketone with rhodium(III) porphyrin as catalyst”, J.

Am. Chem. Soc., Vol.108, pp. 943-947, 1986.

11. Kelly T.R., Whiting A. and Chandrakumar N.S., “A rationally

designed, chiral Lewis acid for the asymmetric induction of some

Diels-Alder reactions” J. Am. Chem. Soc., Vol.108, pp. 3510-3512,

1986.

12. Sengupta P., Ghosh S. and Mak T.C.W., “A new route for the

synthesis of bis(pyridine dicarboxylato)bis(triphenylphosphine)

complexes of ruthenium(II) and X-ray structural characterisation of

the biologically active trans-[Ru(PPh3)2(L1H)2] (L1H2=pyridine 2,3-

dicarboxylic acid)”, Polyhedron, Vol.20, pp. 975-980, 2001.

224

13. Ramasubramanian A.S., Ramachandra B.B. and Dileep R.,

“Thermal and Antibacterial Studies of Novel Lanthanide–Schiff Base

Complexes”, Synth. React. Inorg.Met.-Org., Nano-Met.Chem.,

Vol.42, pp. 548-553, 2012.

14. Cimerman Z., Miljanic S. andGalic N., “Schiff bases derived from

aminopyridines as spectrofluorimetric analytical reagents,”

CroaticaChemicaActa, Vol. 73, No.1, pp. 81-95, 2000.

15. Spichiger-Keller U., “Chemical Sesors and Biosensors for Medical

and Biological Applications”, Wiley-VCH, Weinheim, 1998.

16. Patel P. R., Thaker B. T. and Zele S., “Synthesis, Spectroscopic

Characterisation and Antimicrobial Activities of Some Rare Earth

Metal Complexes of Biologically Active Asymmetrical Tetradentate

Ligand” Indian J. Chem., Vol. 38 A, pp. 563-569, 1999.

17. Layer R.W., “The Chemistry of imines”, Chem. Rev., Washington,

DC, U.K., Vol. 63, pp. 489-510, 1963.

18. Cozzi P. G. “Metal–Salen Schiff base complexes in catalysis:

practical aspects”, Chem. Soc. Rev., Vol. 33, pp. 410-421, 2004.

19. Fessenden R. J. and Fessenden, J. S., “Organic Chemistry”, Sixth

Edition, Brooks/Cole Publishing Company, USA, pp. 563-564, 1998.

20. Streitwieser A., Heathcock C. H. and Kosower E. M., “Introduction to

Organic Chemistry”, Fourth Edition, Prentice Hall, New Jersey USA,

1998.

21. Kabak M., Elmali A. and Elerman Y., “Keto–enoltautomerism,

conformations and structure of N-(2-hydroxy-5-methylphenyl), 2-

hydroxybenzaldehydeimine” J. Mol. Struct., Vol. 477, pp.151-153,

1999.

225

22. Ajlouni A.M., Taha Z. A, Al Momani W., Hijazi A. K, Mohammad

Ebqa’ai, “Synthesis, characterisation, biological activities, and

luminescent properties of lanthanide complexes with N,N0-bis(2-

hydroxy-1-naphthylidene)-1,6-hexadiimine”, Inorg. Chim. Acta, Vol.

388, pp. 120–126, 2012.

23. Sattari D., Alipour E., Shriani S., Amighian J., “Metal complexes of N-

salicylideneamino acids” J. Inorg. Biochem., Vol. 45, pp. 115-122,

1992.

24. Sreenivasulu B., Vittal J. J., “Hydrogen-bonded copper(II)

and nickel(II) complexes and coordination polymeric structures

containing reduced Schiff base ligands”, Inorg. Chim. Acta, Vol. 362,

pp. 2735–2743, 2009.

25. Yun-Zhu Cao, Hai-Yan Zhao, Feng-Ying Bai, Yong-Heng Xing,

Dong-Ming Wei, Shu-Yun Niu, Zhan Shi, “Aminoacid-derivatised

oxidovanadium complexes: Synthesis, structure and bromination

reaction activity”, Inorg. Chim. Acta, Vol. 368, pp. 223–230, 2011.

26. Ameerunisha M.S., Saha S., Nethaji M. and Chakravarthy A.R.,

“Synthesis, crystal structures and protease activity of amino acid

Schiff base iron(III) complexes”, Ind. J. Chem., Vol. 48A,

pp. 473-479, 2009.

27. Ketelle B.H. and Boyd G.E., “The Exchange Adsorption of Ions from

Aqueous Solutions by Organic Zeolites. IV. The Separation of the

Yttrium Group Rare Earths” J. Am. Chem. Soc., Vol. 69,

pp. 2800-2812, 1947.

226

28. Spedding F.H., Fulmer E.I., Powell J.E. and Butler J.A., “The Separation of Rare Earths by Ion Exchange.1 IV. Further

Investigations Concerning Variables Involved in the Separation of Samarium, Neodymium and Praseodymium”, J. Am. Chem. Soc., Vol. 72, pp. 2349-2354, 1950.

29. Jensen W.B., “Positions of La and Lu in the Periodic Table”, J. Chem. Educ., Vol.59, pp. 634-636, 1982.

30. Karraker D.G., “Hypersensitive transitions of hydrated neodymium-(III)holmium-(III) and erbium-(III) ions”, Inorg. Chem., Vol. 7,

pp. 473-479, 1968.

31. Buono-core G.E., Li H., and Marciniak B., “Quenching of excited states by lanthanide ions and chelates in solution”, Coord. Chem.

Rev., Vol. 99, pp. 55–87, 1990.

32. Jingqing R. and Guangxian X., “INDO studies on the electronic structure and chemical bonding of a rare earth cluster compound, Gd10C4Cl18”, Lant. Act. Res., Vol. 2, pp. 67–78, 1987

33. Braunstein P., “Functional ligands and complexes for new structures,

homogeneous catalysts and nanomaterials”, J. Organomet. Chem., Vol. 689, pp. 3953-3967, 2004.

34. Maheswaran S. and Ramesh R., “Synthesis, Spectra, Dioxygen affinity and antifungal activity of Ru(III) Schiff base complexes”, J.

Inorg. BioChem., Vol. 96, pp. 457-462, 2003.

35. Akbar Ali M., Abu Bakar H. J. H., Mirza A. H., Smith S. J., Gahan L.

R. and Bernhardt P. V., “Preparation, spectroscopic characterisation and X-ray crystal and molecular structures of nickel(II), copper(II) and zinc(II) complexes of the Schiff base formed from isatin and S-

methyldithiocarbazate (Hisa-sme)”, Polyhedron, Vol. 27, pp. 71-79, 2008.

227

36. McGuinness D. D., Wasserscheid P., Morgan D. H. and Dixon J. T.,

“Ethylene Trimerisation with Mixed-Donor Ligand (N, P,S) Chromium

Complexes: Effect of Ligand Structure on Activity and Selectivity”,

Organometallics, Vol. 24, pp. 552-556, 2005.

37. Tahaa Z.A., Ajlounia A.M., Al-Hassanb K. A., Ahmed K. Hijazi, Ari B.

Faiqa, “Syntheses, characterisation, biological activity and

fluorescence properties of bis-(salicylaldehyde)-1,3-propylenediimine

Schiff base ligand and its lanthanide”, Spect. Chim. Acta Part A,

Vol. 81, pp. 317– 323, 2011.

38. Li Zhang, YufeiJi, XuebinXu ,ZhiliangLiuan, Jinkui Tang, “Synthesis,

structure and luminescence properties of a series of dinuclearLnIII

complexes (Ln=Gd, Tb,Dy,Ho,Er)”, J. Lumi., Vol. 132, pp. 1906–1909,

2012.

39. Lijuan Zhang, Fei Jiang, Yunshan Zhou, “Structures and

fluorescence of two new hetero-dinuclearlanthanide(III) complexes

derived from a Schiff-base ligand”, J. Coord. Chem., Vol. 62,

pp. 1476–1483, 2009.

40. Kulkarni A., Patil S.A., Badami P.S., “Synthesis, characterisation,

DNA cleavage and in vitro antimicrobial studies of La(III), Th(IV) and

VO(IV) complexes with Schiff bases of coumarin derivatives”, Europ.

J. Med. Chem., Vol. 44, pp. 2904–2912, 2009.

41. Salehzadeh S., Nouri S.M., Keypour H., Bagherzadeh M., “Synthesis

of gadolinium(III) and samarium(III) complexes of new potentially

heptadentate (N4O3) tripodal Schiff base ligands, and a theoretical

study”, Polyhedron, Vol. 24, pp. 1478–1486, 2005.

228

42. Omar M.M., Mohamed G.G., Ibrahim A.A., “Spectroscopic

characterisation of metal complexes of novel Schiff base. Synthesis,

thermal and biological activity studies”, Spect. Chimi. Acta Part A,

Vol. 73, pp. 358–369, 2009.

43. Zhang Bin, Lin Yan, Tang Xiaoning, XuYinhua and Xie Gang,

“Mechanism of antibacterial activity of silver and praseodymium-

loaded white carbon black”, J. Rare earths, Vol. 28, pp. 442-448,

2010.

44. Cleiton M. da Silva, Daniel L. da Silva, Luzia V. Modolo, Rosemeire

B. Alves, Maria A. de Resende, Cleide V.B. Martins and Angelo de

Fa´ tima, “Schiff bases: A short review of their antimicrobial

activities”, J. Adv. Res., Vol. 2, pp. 1–8, 2011.

45. Halli M.B. and Sumathi R.B., “Synthesis, physico-chemical

investigations and biological screening of metal (II) complexes with

Schiff base derived from naphthofuran-2-carbohydrazide and citral”,

Arab. J. Chem., Article in press, 2013.

46. Casuscelli S., Herrero E., Crivello M. and Perez C., “Application of

complex heteropolytungstates in limonene epoxidation by H2O2 in

biphasic medium”, Catal. Today, Vol. 107, pp. 230-234, 2005.

47. Mao J., Li N., Li H. and Hu X., “Novel Schiff base complexes as

catalysts in aerobic selective oxidation of -isophorone”, J.Mol.

Catal.A: Chem., Vol. 258, pp. 178-184, 2006.

48. Hosseini-Monfared H., Nather C., Winkler H. and Janiak C., “Highly

selective and ‘‘green’’ alcohol oxidations in water using aqueous 10%

H2O2 and iron-benzenetricarboxylate metal–organic gel”, Inorg.

Chim. Acta, Vol. 391 pp. 75–82, 2012.

229

49. Furukawa M., Nishikawa Y., Nishiyama S. and Tsuruya S., “Effect of

alkali metal added to supported La catalysts on the catalytic activity

in the gas-phase catalytic oxidation of benzyl alcohol”, J. Mol. Cat.

A: Chemical, Vol. 211 pp. 219–226, 2004.

50. Alizadeha M.H. andTayebee R., “Catalytic Oxidation of Aniline by

Aqueous Hydrogen Peroxide in the Presence of Some

Heteropolyoxometalates”, J. Braz. Chem. Soc., Vol. 16(1), pp.108-111,

2005.

51. Ching-Fu Chang and Shiuh-Tzung Liu, “Catalytic oxidation of anilines

into azoxybenzenes on mesoporoussilicas containing cobalt oxide”,

J. Mol. Cat. A: Chem., Vol. 299, pp. 121–126, 2009.

52. Jackson M., “Magnetism of Rare Earth”, The IRM quarterly Vol. 10,

No. 3, pp. 1-8, 2000.

53. Borchert Y., Sonstrom P., Wilhelm M., Borchert H. and Baumer M.,

"Nanostructured Praseodymium Oxide: Preparation, Structure, and

Catalytic Properties". J. Phy. Chem. C, Vol. 112, No. 8, pp. 3054-3063,

2008.

54. Lide D. R., “CRC Handbook of Chemistry and Physics”, Eighty sixth

Edition, Boca Raton (FL): CRC Press, ISBN 0-8493-0486-5,

pp. 4.122, 2005.

55. Cotton, “Advanced inorganic chemistry”, Sixth Edition, Wiley-India,

ISBN 81-265-1338-1, pp. 1128-1166, 2007.

56. Okazaki T., Suenaga K., Hirahara K., Bandow S., Iijima S. and

Shinohara H., "Electronic and geometric structures of

metallofullerene peapods", Physica B, 323, pp. 97-99, 2002,

230

57. Emsley, John, “Nature's Building Blocks: An A–Z Guide to the

Elements”, Oxford, England, UK: Oxford University Press,

ISBN 0-19-850340-7, pp. 371–374, 2001.

58. Gruen D.M., Koehler W.C., and Katz J.J., “Higher Oxides of the

Lanthanide Elements: Terbium Dioxide”, J. Ameri. Chem.

Soc.,Vol.73, No.4, pp. 1475–1479, 1951.

59. Patnaik, Pradyot, “Handbook of Inorganic Chemical Compounds”,

McGraw-Hill, pp. 920–992, 2003.

60. Georges A., Bersillon O., Blachot J. and Wapstra A.H., "The

NUBASE Evaluation of Nuclear and Decay Properties”, Nuc. Phy. A

(Atomic Mass Data Center), Vol. 729, pp. 3–128, 2003.

61. Sato V., Suenaga V., Okubo V., Okazaki T. and Iijima S., “Structures

of D5d-C80 and Ih-Er3NC80Fullerenes and Their Rotation Inside

Carbon Nanotubes Demonstrated by Aberration-Corrected Electron

Microscopy”, Nano Letters, Vol. 7, No.12, pp. 3704,2007.

62. Girard P., Namy J.L. and Kagan H. B., “Divalent lanthanide

derivatives in organic synthesis. 1. Mild preparation of samarium

iodide and ytterbium iodide and their use as reducing or coupling

agents”, J. Ameri. Chem. Soc., Vol. 102, No.8, pp. 2693-2724, 1980.

63. Grukh Dmitrii A., Bogatyrev V. A., Sysolyatin A.A., Paramonov

Vladimir M., Kurkov Andrei S. and Dianov Evgenii M., “Broadband

radiation source based on an ytterbium-doped fibre with fibre-length-

distributed pumping”, Quant. Electron., Vol. 34, No.3 pp. 247-248,

2004.

64. Emsley John, “Nature's building blocks: An A-Z guide to the

elements”, Oxford University Press, pp. 492–494, 2003.

231

65. Safaa Eldin H. Etaiwa, Dina M. Abd El-Aziza, Eman H. Abd El-Zaherb and Elham A. Ali, “Synthesis, spectral, antimicrobial and

antitumor assessment of Schiff base derived from 2-aminobenzothiazole and its transition metal complexes”, Spectrochim. Acta A., Vol.79, pp. 1331-1337, 2011.

66. Tahaa Z. A., AjlouniA. M., Al Momanib W. and Al-Ghzawia A. A., “Syntheses, characterisation, biological activities and photophysical properties of lanthanides complexes with a tetradentate Schiff base

ligand”, Spectrochim. Acta A., Vol.81, pp.570-577, 2011.

67. Jadhav S. M., Shelke V. A., Shankarwar S.G., MundeA. S. and ChondhekarT. K., “Synthesis, spectral, thermal, potentiometric and antimicrobial studies of transition metal complexes of tridentate

ligand”, J. Saudi. Chem. Soc., Vol.18, pp.27–34, 2011.

68. Ajlouni A. M., Tahaa Z. A., Al-HassanK. A. and AbuAnzeh A. M., “Synthesis, characterisation, luminescence properties and antioxidant activity of Ln (III) complexes with a new aryl amide

bridging ligand”, J. Lumines., Vol.132, pp. 1357-1363, 2012.

69. Khoo T.-J., Khaled M., Break B., Crouse K.A., Ibrahim M., Tahir

A.M., Ali A.R., Cowley D.J., Watkin M.T.H. and Tarafder, “Synthesis, characterisation and biological activity of two Schiff base ligands and their nickel(II), copper(II), zinc(II) and cadmium(II) complexes derived

from S-4-picolyldithiocarbazate and X-ray crystal structure of cadmium(II) complex derived from pyridine-2-carboxaldehyde”, Inorg. Chim. Acta, Vol.413, pp. 68–76, 2014.

70. Mohammed A.S., Omer, Jia-Cheng Liu, Wen-Ting Deng A, and

Neng-Zhi Jin, “Syntheses, crystal structures and antioxidant properties of four complexes derived from a new Schiff base ligand (N1E,N2E)-N1,N2-bis(1-(pyrazin-2-yl)ethylidene)ethane-1,2diamine”,

Polyhedron Vol.69, pp. 10–14, 2014.

232

71. Ceyhana G., Cumali C., ElikbUrus S., Demirtas I., Mahfuz Elmastas

and Tümer M., “Antioxidant, electrochemical, thermal, antimicrobial

and alkane oxidation properties of tridentate Schiff base ligands and

their metal complexes”, Spectrochim. Acta A, Vol.81, pp. 184-198,

2011.

72. Salih I., Baykara H., Oztomsuk A., Okumus V., Levent A., Seyitoglu

S.M. and Ozdemir S., Synthesis and characterisation of 1,2-bis(2-(5-

bromo-2 hydroxybenziliden amino)-4-chlorophenoxy)ethane and its

metal complexes: An experimental, theoretical, electrochemical,

antioxidant and antibacterial study”, Spectrochimica Acta Part A:

Molecular and Biomol. Spect., Vol.118, pp.632-642, 2014.

73. Kavitha P., Ramachary M., Singavarapu B.V.V.A. and Laxma Reddy

K., “Synthesis, characterisation, biological activity and DNA cleavage

study of tridentate Schiff bases and their Co(II)complexes”, J. Saudi

Chem. Soc., (Article in press) (DOI: 10.1016/j.jscs.2013.03.005),

2013.

74. Yan P., Sun W., Li G., Nie C., Gao T. and Yue Z., Synthesis,

characterisation and fluorescence of lanthanide Schiff-base

complexes, Journal of Coordination Chemistry, Vol. 60, No. 18, pp.

1973–1982, 2007.

75. Shakya P.R., Singh A.K. and Rao T.R., “Homo dinuclearlanthanide

(III) complexes of a mesogenic Schiff-base, N,N-di-(4-

decyloxysalicylidene)-1,6-diaminohexane: Synthesis and

Characterisation”, Spectrochim. Acta A, Vol.79, pp.1654-1659, 2011.

76. Yang T.-L. and Qin W.-W., “Synthesis and novel fluorescence

phenomenon of terbium complex with a new Schiff base ligand

derived from condensation of triaminotriethylamine and 3-

indolemethanal”, Spectrochim. Acta A, Vol.67, pp. 568–571, 2007.

233

77. Bunzli J.-C. G., Comby S., Chauvin A.-S. and Vandevyver C. D. B.,

“New Opportunities for Lanthanide Luminescence”, J. Rare Earths,

Vol.25, pp. 257-274, 2007.

78. Nabid M.R., Sedghi R., Jamaat P.R., Safari N. and Entezami A.A.,

“Catalytic oxidative polymerisation of aniline by using transition-metal

tetrasulfonatedphthalocyanine”, Appl. Catal. A: Gen., Vol.328,

pp.52–57, 2007.

79. Lu W. and Xi C., “CuCl-catalysed aerobic oxidative reaction of

primary aromatic amines”, Tetrahedron Letters, Vol.49, pp.4011–

4015, 2008.

80. Gawryszewska P. and Lisowski J., “Lanthanide(III) complexes of

N4O4 Schiff base macrocycle: luminescence and formation of

heterodinuclear d-f complexes”, Inorg. Chim. Acta, Vol.383,

pp. 220-229, 2012.

81. Friscic T., Kaitner B. and Mestrovic E., “Meštrovi , Synthesis and

structure of N,N'-butylene- and N,N'-hexylenebis(2-oxy-1-

naphthaldimine)”,Croat. Chem. Acta, Vol.71, pp. 87-98, 1998.

82. Mohanan K., Subhadrambika N., Selwin Joseyphus R., Swathy S.S.

and Nisha V.P. “Synthesis, spectroscopic characterisation, solid

state D.C. electrical conductivity and biological studies of some

lanthanide(III) chloride complexes with a heterocyclic Schiff base

ligand”, http://dx.doi.org/10.1016/j.jscs.2012.07.007

83. Sadana A.K., Miraza Y., Aneja K.R. and Prakash O., “Hypervalent

iodine mediated synthesis of 1-aryl/hetryl-1,2,4-triazolo[4,3-a]

pyridines and 1-aryl/hetryl 5-methyl-1,2,4-triazolo[4,3-a]quinolines as

antibacterial agents”, Eur. J. Med. Chem., Vol.38, pp. 533-536, 2003.

234

84. Greenwood D., Snack R. and Peurtherer J. “Medical microbiology, A

guide to microbial infections, Pathogensis, immunity, laboratory

diagnosis and control”, 15th ed., 1997.

85. Bilgari F., Alkarkhi A.F.M. and Easa A.M., “Antioxidant activity and

phenolic content of various date palm (phoenix dactylifera) fruits from

Iran”, Food Chem., Vol.107, pp. 1636-1641, 2008.

86. Abd El-halim H.F., Omar M.M. and Mohamed G.G., “Synthesis,

structural, thermal studies and biological activity of a tridentate Schiff

base ligand and their transition metal complexes”, Spectrochim.

Acta: A., Vol.78, pp. 36-44, 2011.

87. Ouyang X.M., Fei B.L., Okamuro T.A., Sun W.Y., Tang W.X. and

Ueyama N., “Synthesis, Crystal Structure and Superoxide Dismutase

(SOD) Activity of Novel Seven-Coordinated Manganese(II) Complex

with Multidentate Di-Schiff Base Ligands”, Chem. Lett., Vol.3, pp.

362-363, 2002.

88. Datta N.K., Karan S. Mitra G. and Rosair, Z. Naturforsch “Synthesis

and Structural Characterisation of [Cu(NH2CH2C6H4N = CHC5H5N)

Cl2]”, Vol.576, pp. 999-1005, 2002.

89. Jayabalakrishnan K. Natarajan, “Ruthenium(II) carbonyl complexes

with tridentate Schiff bases and their antibacterial activity“ Trans.

Met. Chem., Vol.27, pp. 75-79, 2002.

90. Sharghi H. and Nasseri M.A., “Schiff base metal (II) complexes as

new catalyst in efficient, mild and region selective conversion of

1,2epoxyethanes to 2 hydroxyethylthiocyanates with

ammoniymthiocyanate”, Bull. Chem. Soc. (Jpn.), Vol.76, pp. 137-142,

2003.

235

91. Przybylski P., Huczynski A., Pyta K., Brzezinski B. and Bartl F.,

“Biological properties of Schiff bases and azo derivatives of phenols”

Curr. Org. Chem., Vol.13, pp. 124-148, 2009.

92. Da Silva C.M., Da Silva D.L., Modolo L.V., Alves R.B., De Resende

M.A., Martins C.V.B. and de Fatima A., “Schiff bases: a short review

of their antimicrobial activities”, J. Adv. Res., Vol.2, pp. 1-8, 2011.

93. Maurya R.C. and Patel P., “Synthesis, magnetic and special studies

of some novel metal complexes of Cu(II), Ni(II), Co(II), Zn[II), Nd(III),

Th(IV), and UO2(VI) with Schiff bases derived from sulfa drugs, viz.,

Sulfanilamide/Sulfamerazine and o-vanillin”, Spectrosc. Lett., Vol.32,

pp. 213-236, 1999.

94. Ajlouni A.M., Taha Z.A., Al Momani W., Hijazi A.K. and Ebqa’ai M.,

“Synthesis, characterisation, biological activities, and luminescent

properties of lanthanide complexes with NN -bis (2-hydroxy-1-

naphthylidene)-1, 6-hexadiimine”, Inorg. Chim. Acta., Vol.388,

pp.120-126, 2012.

95. Ajlouni A.M., Taha Z.A., Al-Hassan K.A. and AbuAnzeh A.M.,

“Synthesis, characterisation, luminescence properties and

antioxidant activity of Ln (III) complexes with a new aryl amide

bridging ligand”, J. Lumin., Vol.132, pp. 1357-1360, 2012.

96. Singh G., Singh R., Girdhar N.K. and Ishar M., “A versatile route to 2-

alkyl-/aryl-amino-3-formyl- and hetero-annelated-chromones, through

a facile nucleophilic substitution at C2 in 2-(N-methylanilino)-3-

formylchromones”, Tetrahedron, Vol.58, pp. 2471-2480, 2002.

97. Schildcrout S.M., SriHari S. and Masnovi J., “Comparative Chemical-

Ionisation and Electron-Ionisation Mass-Spectra of SALEN

Complexes with Metals of the First Transition Series”, Inorg. Chem.

Vol.34, pp. 4117-4122, 1995.

236

98. Geary W., “The use of conductivity measurements in organic

solvents for the characterisation of coordination compounds”, Coord.

Chem. Rev., Vol.7, pp.81-122, 1971.

99. Cardoso M.C.C., Arau´ joMelo D.M., Schpector J. Z., Zinnera L.B.

and Vicentini G., “Spectroscopic, TG and DSC studies of lanthanide

picrate complexes with 1,4-pyrazine-dioxide (pyzDO): crystal

structure of the terbium complex”, J. Alloys Compd., Vol.344, pp. 83-

87, 2002.

100. Raman N., Pothiraj K. and Baskaran T., “DNA interaction,

antimicrobial, electrochemical and spectroscopic studies of metal(II)

complexes with tridentate heterocyclic Schiff base derived from 2 -

methylacetoacetanilide”, J. Mol. Struct., Vol.1000, pp. 135-144, 2011.

101. Bhattacharieea C.R., Goswami P., Pramanika H.A.R., Paula P.C.

and Mondal P., “Reactivity of tris(acetylacetonato) iron(III) with

tridentate [ONO] donor Schiff base as an access to newer mixed-

ligand iron(III) complexes”, Spectrochim. Acta A., Vol.78, pp.1408-

1413, 2011.

102. Shakya P.R., Singh A.K. and Rao T.R., “Homo

dinuclearlanthanide(III) complexes of a mesogenic Schiff-base, N,N -

di-(4-decyloxysalicylidene)-1 ,6 -diaminohexane: Synthesis and

characterisation”, Spectrochim. Acta A., Vol.79, pp.1654-1659, 2011.

103. Leniec G., Kaczmarek S.M., Typek J., Ko odziej B., Grech E. and

Schilf W., “Spectroscopic and magnetic properties of gadolinium

macrobicycliccryptate complex”, J. Phys. Condens. Matter, Vol.18,

pp. 9871-9880, 2006.

104. Kaczmarek S.M. and Leniec G., “EPR and IR investigations of some

chromium (III) phosphate (V) compounds”, J. Non-Cryst. Solids,

Vol.355, pp.1289-1438, 2009.

237

105. Shahawi M.S. El, Jahdali M.S. Al, Bashammakh A.S. Sibaai A.A. Al

and Nassef H.M., “Spectroscopic and electrochemical

characterization of some Schiff base metal complexes containing

benzoin moiety”, Spectrochim. Acta A, Vol.113, pp.459-465, 2013.

106. Paryzek W., Zankowska E. and Luks E., “Coordination compounds of

2,6-diacetylpyridinedihydrazone-II. Preparation and characterisation

of the complexes with heavier lanthanide chlorides, perchlorates and

nitrates”, Polyhedron, Vol.7, pp. 439-442, 1988.

107. Yan P., Sun W., Li G., Nei C., Gao T. and Yue Z., “Synthesis,

characterisation and fluorescence of lanthanide Schiff-base

complexes”, J. Coord. Chem., Vol.60, pp.1973-1979, 2007.

108. Wang W., Huang Y. and Tang N., “Synthesis and infrared and

fluorescence spectra of rare earth complexes with a novel amide-

based ligand”, Spectrochim. Acta, Vol.66, pp. 1058-1062, 2007.

109. Jadhav S.M., Shelke V.A., Shankarwar S.G., Munde A.S. and

Chandrashekar T.K., “Synthesis, spectral, thermal, potentiometric

and antimicrobial studies of transition metal complexes of tridentate

ligand’, J. Saudi Chem. Soc., Vol.18, pp. 27-34, 2014.

110. Shakir M., Shahid N., Sami N., Azam M. and Khan A.U., “Synthesis,

spectroscopic characterisation and comparative DNA binding studies

of Schiff base complexes derived from L-leucine and glyoxal”,

Spectrochim. Acta A: Biomol. Spectrosc, Vol.82, pp. 31-36, 2011.

111. Costes J. P., Laussac J.P. and Nicodeme F., “Complexation of

a Schiff base ligand having two coordination sites (N2O2and O2O2)

with lanthanide ions (Ln = La, Pr): an NMR study”, J. Chem. Soc.

Dalton. Trans, pp. 2731-2736, 2002.

238

112. Youssef T.A., “Reactions of chromium and molybdenum carbonyls

with bis-(salicylaldehyde)-1,3-propylenediimine Schiff base”, J.

Coord. Chem., Vol.61, pp. 816-819, 2008.

113. Guo L., Wu S., Zeng F. and Zhao J., “In situ synthesis of copper

nanoparticles and poly(o-toluidine): A metal–polymer composite

material“, Eur. Polym. J., Vol.42, pp. 670-675, 2006.

114. Felico R.C., Canalheiro E.T.G. and Dockal E.R., “Preparation,

characterisation and thermogravimetric studies of [N,N -cis-1,2-

cyclohexylene bis(salicylideneaminato)]cobalt(II) and [N,N -(±)-trans-

1,2-cyclo-hexylene bis(salicylideneaminato)]cobalt(II)”, Polyhedron.

Vol.20, pp.261-268, 2001.

115. Görller-Walrand C. and Binnemans K., Handbook on the Physics

Chemistry of Rare Earths, North-Holland Publishers, Amsterdam,

Vol. 25, pp. 101-110, 1998.

116. Ho Y., Yu W.Y., Cheung K.K. and Che C.M., “Blue luminescent

zinc(II) complexes with polypyridylamine ligands: crystal structures

and luminescence properties”, J. Chem. Soc. Dalton Trans., Vol.10,

pp.1581-1586, 1999.

117. Li J.X., Du Z.X., Zhou J., An H.Q., Wang S.R., Zhu B.L., Zhang S.M.,

Wu S.H. and Huang W.P., “Syntheses, crystal structures and

properties of Cd(II) and Co(II) complexes with 4,4 -dipyridylsulfide

ligand”, Inorg. Chim. Acta, Vol.362, pp. 4884-4890, 2009.

118. Zheng Y.X., Fu L.S., Zhou Y.H., Yu J.B., Yu Y.N., Wang S.B. and

Zhang H.J., “Electroluminescence based on a beta-diketonate

ternary samarium complex “, J. Mater. Chem., Vol.12, pp. 919-923,

2002.

239

119. Chohan Z.H. and Shad H.A., “Structural elucidation and biological

significance of 2-hydroxy-1-naphthaldehyde derived sulfonamides

and their first row d-transition metal chelates”, J. Enz. Inhib. Med.

Chem., Vol.23, pp.369-379, 2008.

120. Badwaik V.B. and Aswar A.S., “Synthesis, characterisation, and

biological studies of some Schiff base complexes”, Russ. J. Coord.

Chem., Vol.33, pp. 755-760, 2007.

121. Thangadurai D.T. and Natarajan K., “Synthesis and characterisation

of new ruthenium(III) complexes containing tetradentate Schiff

bases”, Synth. React. Inorg.Met. Org. Chem., Vol. 31, pp. 549-555,

2001.

122. Dhankar R.P., Rahatgaonkar A.M. and Chorghade M.S., “Spectral

and in vitro antimicrobial properties of 2-oxo-4-phenyl-6-styryl-

1,2,3,4-tetrahydro-pyrimidine-5-carboxylic acid transition metal

complexes”, Spectrochim. Acta, A, Vol.93, pp. 348-353, 2012.

123. Arish D. and Nair M.S., “Synthesis, characterisation, antimicrobial,

and nuclease activity studies of some metal Schiff-base complexes”,

J. Coord.Chem., Vol.63, pp.1619-1628, 2010.

124. Archer R.D. and Chen H., “Synthesis, Characterisation, and

Luminescence of Europium(III) Schiff Base Complexes”, Inorg.

Chem., Vol.37, pp. 2089-2095, 1998.

125. Danghui W., Yixin Y., Yiqin Y., Tiancheng Z., Xing W., Shaokang W.,

Yao H. and Weizong C., “Synthesis and properties of a Pr (III)

complex with 2-acetylbenzimidazoledehyde-glycine Schiff-base

ligand”, China. Sci. Bull., Vol.51, pp. 785-790, 2006.

240

126. Samir M.S. Zoromb and Hanan F.A.E., “Lanthanide amino acid Schiff

base complexes: synthesis, spectroscopic characterisation, physical

properties and in vitro antimicrobial studies”, J. Rare Earths, Vol.31,

pp. 715-721, 2013.

127. Kostova I., Petar G., Stefan B. and Tsvetanka S., “Synthesis,

characterisation and cytotoxicity of new Ho(III) and Er (III)

complexes”, Ind. J. Biotech., Vol.10, pp. 387-394, 2011.

128. Kostova I. and Georgi M., “Synthesis, spectral and pharmacological

studies on lanthanide(III) complexes of 3,5-pyrazoledicarboxylic

acid”, J. Coord. Chem., Vol.61, pp. 3776-3792, 2008.

129. Lekha L., Raja K.K., Rajagopal G. and Easwaramoorthy D.,

“Synthesis, spectroscopic characterisation and antibacterial studies

of lanthanide(III) Schiff base complexes containing N, O donor

atoms”, J. Mol. Struc., Vol.1056–1057, pp. 307–313, 2014.

130. Salehzadeh S., Nouri S.M., Keypour H. and Bagherzadeh M.,

“Synthesis of gadolinium(III) and samarium(III) complexes of new

potentially heptadentate (N4O3) tripodal Schiff base ligands, and a

theoretical study”, Polyhedron, Vol.24, pp. 1478-1486, 2005.

131. Andruh M., Tuna., In; M.A. Cato (Eds.), Focus on Organometallic

Chemistry Research, Nova Publishers, Hauppauge,2005.

132. Nawar N.A., Shallaby A.M., Hosny N.M. and Mostafa M., “Mono- and

binuclear Schiff base complexes derived from glycine, 3-

acetylpyridine and transition metal ions”, Trans. Met. Chem., Vol.26,

pp. 180-185, 2001.

133. Hosny N.M., “Synthesis, characterisation, theoretical calculations and

catalase-like activity of mixed ligand complexes derived from alanine

and 2-acetylpyridine”, Trans. Met.Chem., Vol.32, pp.117-124, 2007.

241

134. Tamboura F.B., Haba P.M., Gaye M., Sall A. S., Barry A.H. and

Jouini T., “Structural studies of bis-(2,6-diacetylpyridine-bis-(phenyl

hydrazone)) and X-ray structure of its Y(III), Pr (III), Sm (III) and Er

(III) complex”, Polyhedron., Vol.23, pp. 1191-1197, 2004.

135. Wang M.-F., Yang Z.-Y., Liu Z.-C., Li Y., Li T.-R., Yan M.-H. and

Cheng X.-Y., “Synthesis and crystal structure of a Schiff base

derived from two similar pyrazolone rings and its rare earth

complexes: DNA-binding and antioxidant activity”, J. Coord. Chem.,

Vol.65, pp.3805-3820, 2012.

136. Thunus L. and Lejeune R., “Overview of transition metal and

lanthanide complexes as diagnostic tools”, Coord.Chem. Rev.,

Vol.184, pp.125-155, 1999.

137. Cutler C.S., Smith C.J., Ehrhardt G.J., Tyler T.T., Jurisson S.S. and

Deutsch E., “ Current and Potential Therapeutic Uses of Lanthanide

Radioisotopes” , Cancer Biother. Radiopharm., Vol.15, pp. 531-545,

2000.

138. Li Z., Xue M., Yao H., Sun H., Zhang Y. and Shen Q., “Enol-

functionalised N-heterocyclic carbene lanthanide amide complexes:

Synthesis, molecular structures and catalytic activity for addition of

amines to carbodiimides”, J. Organomet. Chem., Vol.713, pp.27-34,

2012.

139. Yang T.-L. and Wu Qin W.-, “Synthesis and novel fluorescence

phenomenon of terbium complex with a new Schiff base ligand

derived from condensation of triaminotriethylamine and

3-indolemethanal”, Spectrochim. ActaA., Vol.67, pp. 568-571, 2007.

242

140. Wang M., Yang Z., Li Y. and Li H., “Lanthanide complex of 1-phenyl-

3-methyl-5-hydroxypyrazole-4-carbaldehyde-(isonicotinoyl) hydrazone:

crystal structure and DNA-binding properties”, J. Coord. Chem.,

Vol.64, pp. 2974-2983, 2011.

141. Reddy P.R., Shilpa A., Raju N. and Raghavaiah P., “Synthesis,

structure, DNA binding and cleavage properties of ternary amino acid

Schiff base-phen/bipy Cu(II) complexes”, J.Inorg. Biochem., Vol.

105, pp. 1603-1612, 2011.

142. Robinson M.R., O’Regan M.B. and Bazan G.C., “Synthesis,

morphology and optoelectronic properties of tris[(N-ethylcarbazolyl)

(3 ,5 -hexyloxybenzoyl)methane](phenanthroline)europium”,

Chem. Comm., Vol.17, pp. 1645-1646 , 2000.

143. Kanmani Raja K., Indira Gandhi N, Lekha L, Easwaramoorthy D and

Rajagopal G., “Synthesis, spectral, electrochemical and catalytic

properties of Ru(III) Schiff base complexes containing N, O donors”,

J. Mole. Struc., Vol.1060, pp. 49-57, 2014.

144. Leniec G., Kaczmarek S.M., Typek J., Ko odziej B., Przybylski P.,

Brzezi ski B. and Grech E., “FT-IR, ESI and EPR studies of a Dy(III)

Schiff base pod and complex”, J. Non-Cryst. Solids, Vol.355, pp.

1355-1359, 2009.

145. GuoL. and Yan B., “Photoluminescent rare earth inorganic–organic

hybrid systems with different metallic alkoxide components through

2-pyrazinecarboxylate linkage”, J. Photochem.Photobio. A:Chem.,

Vol.224, pp. 141-146, 2011.

146. Pui A., Malutan T., Tataru L., Mualtuan C., Humelnicu D. and Carja

G., “New complexes of lanthanide Ln (III), (Ln = La, Sm, Gd, Er) with

Schiff bases derived from 2-furaldehyde and phenylenediamines”,

Polyhedron., Vol.30, pp. 2127-2131, 2011.

243

147. Li X., Wang C.Y. and Hu H.-M., “The first example of tetranuclear

lanthanide complexes with 2-sulfobenzoate and 1,10-

phenanthroline”, Inorg. Chem. Commun., Vol.11, pp. 345-348, 2008.

148. Gansow O.A., Loeffler E., Davis R., Lenkinski M. and Wilcott R.,

“Contact vs. pseudocontact contributions to lanthanide-induced shifts

in the nuclear magnetic resonance spectra of isoquinoline and of

endo-norbornenol”, J. Am. Chem. Soc., Vol.98, pp. 4250-4258,

1976.

149. Carnall W., Siegel S., Ferrano J., Tani B. and Gebert E., “New series

of anhydrous double nitrate salts of the lanthanides. Structural and

spectral characterisation”, Inorg. Chem., Vol.12, pp. 560-564, 1973.

150. Shelke V.A., Jadhav S.M., Patharkar V.R., Shankarwar S.G.,

Munde A.S. and Chondhekar T.K., “Synthesis, spectroscopic

characterisation and thermal studies of some rare earth metal

complexes of unsymmetrical tetradentate Schiff base ligand”,

Arabian J. Chem., Vol. 5, pp.501-507, 2012.

151. Mohanan K. and Devi, S.N. “Synthesis, characterisation, thermal

stability, reactivity and antimicrobial properties of some novel

lanthanide(III) complexes of 2-(N-salicylideneamino)-3-carboxyethyl-

4,5,6,7-tetrahydrobenzo[b]thiophene”, Russ. J. Coord. Chem.,

Vol.32, pp. 600-610, 2006.

152. Shebl M., Seleem H.S. and El-Shetary B.A., 2010. “Ligational

behavior of thiosemicarbazone, semicarbazone and

thiocarbohydrazone ligands towards VO(IV), Ce(III), Th(IV) and

UO2(VI) ions: synthesis, structural characterisation and biological

studies”, Spectrochim. Acta A, Vol.75, pp. 428-433.

244

153. Salavati-Niasari M., SalimiZ., Bazarganipour M. and DavarF.,

“Synthesis, characterisation and catalytic oxidation of cyclohexane

using a novel host (zeolite-Y)/guest (binuclear transition metal

complexes) nanocomposite materials”, Inorg. Chim. Acta., Vol.362,

pp.3715-3716, 2009.

154. Kumar D.N. andGarg B.S., “Synthesis and spectroscopic studies of

complexes of zinc(II) with N2O2 donor groups”, Spectrochim. Acta

Part A., Vol.64, pp. 141-147, 2006.

155. Mohanan K., Athira C.J., Sindhu Y. and Sujamol, M.S., “Synthesis,

spectroscopic characterisation and thermal studies of some

lanthanide(III) nitrate complexes with a hydrazoderivative of 4-

aminoantipyrine”. J. Rare Earths, Vol.27, No.5, pp. 705-708, 2009.

156. E.S. Aazam, A.F. EL Husseiny and H.M. Al-Amri., “Synthesis and

photoluminescent properties of a Schiff-base ligand and its

mononuclear Zn(II), Cd(II), Cu(II), Ni(II) and Pd(II) metal complexes”,

Arab. J. Chem., Vol.5, pp. 45-53, 2012.

157. Deacon G. B. and Phillips R. J., “Relationships between the carbon-

oxygen stretching frequencies of carboxylato complexes and the type

of carboxylate coordination”, Coord.Chem. Rev., Vol.33, pp. 227-

250, 1980.

158. Bellamy L. J., “The infrared Spectra of complex Molecules”, J. Wiley,

NewYork, 1971.

159. Sun W.B., Yan P.F., Li G.M., Xu H. and Zhang J.W., “N,N -

bis(salicylidene) propane-1,2-diamine lanthanide(III) coordination

polymers: Synthesis, crystal structure and luminescence properties”,

J. Solid State Chem., Vol.182, pp. 381-388, 2009.

245

160. Wang W., Huang Y. and Tang N., “Synthesis and infrared and

fluorescence spectra of rare earth complexes with a novel amide-

based ligand”, Spectrochim. Acta., Vol.66, pp. 1058-1062, 2007.

161. TahaZ. A., AjlouniA. M., Al-Hassan K. A., HijaziA. K. andFaiqA. B.,

“Synthesis, characterisation, biological activity and fluorescence

properties of bis-(salicylaldehyde)-1,3-propylenediimine Schiff base

ligand and its lanthanide complexes”, Spectrochimica Acta A, Vol.81,

pp. 317-323, 2011.

162. Zolezzi S., Decinti A. and Spodine E., “Syntheses and

characterisation of copper(II) complexes with Schiff-base ligands

derived from ethylenediamine, diphenylethylenediamine and nitro,

bromo and methoxysalicylaldehyde”, Polyhedronl, Vol.18, pp.897-904,

1999.

163. Karaoglu K., Baran T., Serbest K. and De girmencio glu M. Er, I.,

“Two novel macroacyclic Schiff bases containing bis-N2O2 donor set

and their binuclear complexes: synthesis, spectroscopic and

magnetic properties”, J. Mol. Struct., Vol.922, pp.39–45, 2009.

164. Gorller-Walrand C. and Binnemans K., “Spectral intensities of f–f

transitions”, in: K.A. Gschneidner Jr., L. Eyring (Eds.), Handbook on

the Physics Chemistry of Rare Earths, vol. 25, North-Holland

Publishers, Amsterdam, pp. 101-264, Chapter 167, 1998.

165. Walrand C.G. and Binnemans K., Handbook on the Physics

Chemistry of Rare Earths, North-Holland Publishers, Amsterdam,

Vol. 25, pp. 101-2641998.

166. Xie W., Heeg M.J. and Wang P.G., “Formation and Crystal Structure

of a Polymeric La(H2salen) Complex”, Inorg. Chem., Vol.38, pp.

2541-2543, 1999.

246

167. Moawad M.M. and Hanna W.G., “Structural and Antimicrobial

Studies of Some Divalent Transition Metal Complexes with Some

New Symmetrical Bis (7-Formylanil Substituted-Sulfoxine) Schiff

Base Ligands”, J. Coord. Chem., Vol.55, pp. 439-457, 2002.

168. Sabbatini N., Guardigli M. andLehn J.M., “Luminescent lanthanide

complexes as photochemical supramolecular devices”, Coordi.

Chem. Rev., Vol.123, pp. 201-228, 1993.

169. Wu S., Zeng F., Wu S., Yao S., She W. and Luo D., “All-optical

switching properties of poly(methyl methyacrylate) azobenzene

composites”, J. Mat. Sci., Vol.38, pp. 401-405, 2003.

170. Dexter D.L., “A Theory of Sensitised Luminescence in Solids”, J.

Chem. Phys., Vol.21, pp. 836-837, 1953.

171. Kolchinski A.G., “Anhydrooligomers of o-aminobenzaldehydes—the

rich chemistry of the Busch macrocycles”, Coord.Chem. Rev.,

Vol.174, pp. 207-239, 1998.

172. Haynes A. V. and Drickamer H.G., “High pressure luminescence

studies of energy transfer in rare earth chelates “, J. Chem. Phys.,

Vol.76, pp. 114-118, 1982.

173. Inoue K., Sasaki Y. and ItayaT., “Polymerisation of styrenes with

pendant aminophosphazenes and fluorescence behaviors of their

Eu3+ complexes”, Eur. Polym. J., Vol. 33, pp. 841-847, 1997.

174. Du C.X., Ma L. and Xu Y., “Synthesis and photophysical

characterisation of terbium-polymer complexes containing salicylate

ligand”, Eur. Polym. J., Vol.34, pp. 23-29, 1998.

247

175. Kim D.H., Cho HI. And ZyungT., “New tetradentate Schiff-base

polymers: preparation of poly[2,5-(didodecyloxy)phenylene-1,

4-diyl-alt-N,N -(o-phenylene)-bis(salicylideneiminato-4,4 -diyl)] and

poly [2,5-(didodecyloxy)phenylene-1,4-diyl-alt-N,N -(alkylidene)-bis

(salicylideneiminato-4,4 -diyl)]s”, Eur. Polym. J., Vol.38, pp. 133-137,

2002.

176. Chohan Z.H., Supuran C.T. and Scozzafava A., “Metalloantibiotics:

Synthesis and Antibacterial Activity of Cobalt(II), Copper(II), Nickel(II)

and Zinc(II) Complexes of Kefzol”, J. Enzym. Inhib. Med. Chem.,

Vol.19, No.1, pp.79–84, 2004.

177. Chohan Z.H. and Praveen M., “Synthesis, characterisation,

coordination and antibacterial properties of novel asymmetric 1,1 -

disubstituted ferrocene-derived Schiff-base ligands and their Co(II),

Cu(II) Ni(II) and Zn(II) complexes”, Appl. Organomet. Chem., Vol.15,

pp. 617-625, 2001.

178. Chohan Z.H., Scozzafava A. and Supuran C.T., “Unsymmetrical 1,1 -

disubstituted Ferrocenes: Synthesis of Co(ii), Cu(ii), Ni(ii) and Zn(ii)

Chelates of Ferrocenyl -1-thiadiazolo-1 -tetrazole, -1-thiadiazolo-1 -

triazole and -1-tetrazolo-1 -triazole with Antimicrobial Properties”, J.

Enzym. Inhib. Med. Chem., Vol.17, pp. 261-266, 2002.

179. Hassan M.U., Chohan Z.H. and Supuran C.T., “Antibacterial Zn(II)

Compounds of Schiff Bases Derived from Some Benzothiazoles”,

Main Group Met Chem., Vol.25, pp. 291-297, 2002.

180. Shilov A.E. and Shul’pin G.B., “Activation of C H Bonds by Metal

Complexes”, Chem.Rev., Vol.97, pp. 2879-2932, 1997.

181. Hains A.H., Methods for the Oxidation of Organic Compounds,

Academic: London, 1985.

248

182. Mizuno N., Yamaguchi K. and Kamata K., “Epoxidation of olefins with

hydrogen peroxide catalysed by polyoxometalates”, Coord.Chem.

Rev., Vol.249, pp. 1944-1956, 2005.

183. Ramnauth R., Al-JuaidS.,Parkin B.C. and Sullivan A.C., “Synthesis,

Structure, and Catalytic Oxidation Chemistry from the First

Oxo Imido Schiff Base Metal Complexes”, Inorg. Chem., Vol.43, pp.

4072-4079, 2004.

184. AhluwaliaV.K., “ Organic Reaction Mechanisms”, Parashar Publisher

CRC Press: New Delhi, 2002.

185. Samec J. S.M., E´ ll A.H. and Ba¨ckvall J.-E., “Efficient Ruthenium-

Catalysed Aerobic Oxidation of Amines by Using a Biomimetic

Coupled Catalytic System”, Chem. Eur. J., Vol.11, pp. 2327-2334,

2005.

186. Satoru S., Miura M. and Nomura M., “Oxidation of 3- or 4-substituted

N,N-dimethylanilines with molecular oxygen in the presence of either

ferric chloride or [Fe(salen)]OAc”, J. Org. Chem., Vol.54, pp. 4700-

4702, 1989.

187. Wenchao Lu and Chanjuan Xi, “CuCl-catalysed aerobic oxidative

reaction of primary aromatic amines”, Tetrahedron Lett., Vol.49,

pp. 4011-4015, 2008.

188. Mansoor S. S. and Shafi S. S., , “Oxidation of aniline and some para-

substituted anilines by benzimidazolium fluorochromate in aqueous

acetic acid medium – A kinetic and mechanistic study”, Arabian J.

Chem., Vol. 7, pp. 171-176, 2014.

189. Wheeler O. H. and Gonzales D., “Oxidation of primary aromatic

amines with manganese dioxide”, Tetrahedron, Vol.20, pp. 189-193,

1964.

249

190. Nezhadali, M. Akbarpour, “Selective oxidation of primary substituted

aromatic amines to azoxy products using lacunary catalyses”, Chin.

Chem.Lett., Vol.21, pp. 43-46, 2010.

191. Zhao R., Tan C.,Xie Y.,Gao C., Liu H. andJiang Y., “One step

synthesis of azo compounds from nitroaromatics and anilines”,

TetrahedronLett., Vol.52, pp. 3805-3809, 2011.

192. White R.W. and Emmons W. D., “The chemistry of permaleic acid”,

Tetrahedron, Vol.17, pp. 31-34, 1962.

193. Baumgarten H. E., Staklis A. and Miller E. M., “Reactions of Amines.

XIII. The Oxidation of N-Acyl-N-arylhydroxylamines with Lead

Tetraacetate”, J. Org. Chem., Vol.30, pp. 1203-1206, 1965.

194. Emmons W.D., “The Oxidation of Amines with Peracetic Acid”, J. Am.

Chem. Soc., Vol.79, pp. 5528-5530, 1957.

195. Raja K.K., Easwaramoorthy D., Rani S.K., Rajesh J., Jorapur Y.,

Thambidurai S., Athappan P.R. and Rajagopal G., “Synthesis,

spectral, electrochemical and catalytic properties of Cu(II), Ni(II) and

Co(II) complexes containing N, O donors”, J. Mol. Catal. A: Chem.,

303, pp. 52-59, 2009.

250

LIST OF PUBLICATIONS

1. Lekha L, Kanmani Raja K, Rajagopal G. and Easwaramoorthy D,

“Synthesis, Spectroscopic characterisation and Antibacterial Studies

of Lanthanide(III) Schiff base complexes containing N, O donor

atoms”, J. Mol. Struct., Vol. 1056–1057, pp. 307–313, 2014.

2. Lekha L, Kanmani Raja K, Rajagopal G. and Easwaramoorthy D,

“Schiff Base Complexes of Rare Earth Metal ions: Synthesis,

Characterisation and Catalytic Activity for the Oxidation of Aniline and

substituted Anilines”, J. Organomet. Chem. Vol. 753, pp. 72-80,

2014.

3. Lekha L, Kanmani Raja K, Rajagopal G, Sivakumar D. and

Easwaramoorthy D, “Synthesis, spectral characterisation and

antimicrobial assessment of Schiff Base ligand derived from amino

acid and its transition metal complexes” – Int. J. chem. pharm. Sci.,

Vol. 4 (2), pp. 48-54, 2013.

4. Kanmani Raja K, Lekha L, Easwaramoorthi D. and Rajagopal G,

“Synthesis, Spectral, Electrochemical and Catalytic properties of

Ru(III) Schiff base complexes containing N, O donors”, Journal of

Molecular Structure, Vol. 1060, pp. 49-57, 2014.

5. Kanmaniraja K, Lekha L, Easwaramoorthi D. and Rajagopal G,

“Synthesis, Spectral, Electrochemical and Catalytic properties of

VO(IV) Schiff base complexes containing N, O donors”, Journal of

Molecular Structure, Vol. 1075, pp. 227-233, 2014.

251

PAPERS COMMUNICATED

1. Lekha L, Kanmani Raja K, Hariharan R, Sathish M, Rajagopal G.

and Easwaramoorthy D, “Synthesis, spectral characterisation,

antimicrobial and antioxidant assessment of Schiff Base ligand

derived from threonine and its rare earth metal complexes”,

J. Appl. Organomet. Chem.

252

TECHNICAL BIOGRAPHY

Mrs. L. Lekha was born on May 31st, 1981 in Chennai,

Tamilnadu, India. She did her schooling in St. Thereasa’s Girls Higher

Secondary School, Pallavaram, Chennai. She was graduated with distinction

in chemistry from Meenakshi College for Women (Affiliated to University of

Madras), Kodambakkam, Chennai and got her Master degree in Chemistry

from Queen Mary’s College (Affiliated to University of Madras), Mylapore,

Chennai. She obtained her Master of Philosophy in Chemistry from

Bharathidasan University, Thiruchirappalli.

She joined, Ph.D Programme in the Department of Chemistry,

B. S. Abdur Rahman University, Chennai, in January 2010. She carried out

her research in the thrust area of “Studies on the Synthesis, Characterisation

and Antimicrobial Applications of Rare Earth Metal Schiff Base Complexes”.

She has published four papers and communicated two papers in

international peer-reviewed journals. Also, she has presented a paper in

National Conference at Gurunanak College, Chennai.

She has about nine years of teaching experience at various levels

and presently she is working as Assistant Professor in the Department of

Chemistry, Saveetha School of Engineering, Chennai. Her e-mail ID is:

[email protected] and the contact number is: 9940611001.

studies on the synthesis, … on the synthesis, characterisation and antimicrobial applications of...

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