original research article doi: 10.26479/2019.0503.01 rare ...schiff base ligand is present due to...

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Original Research Article DOI: 10.26479/2019.0503.01

RARE EARTH METAL COMPLEXES WITH SCHIFF BASE LIGAND:

SYNTHESIS, CHARACTERIZATION AND BIOCHEMICAL EVALUATION

Hitesh Patel1*, L. S. Bhutadiya1, Jabali J.Vora2, Toral H. Yadav1

1. Chemistry Department Sheth M. N. Science College, Patan, Gujarat, India.

2. Department of Chemistry, Hem. North Gujarat University, Patan, Gujarat, India.

ABSTRACT: The lanthanide ions are having the distinctive qualities like lanthanide contraction,

magnetic properties, etc. The product of lanthanide ions with N-salicylaldehyde-anthranilic acid

(NSAA) ligand to form coordination compounds is an important area of current research. N-

salicylaldehyde-anthranilic acid (NSAA) has massive biological importance like anti-Alzheimer

and antiulcer activity[1-3]. Synthesized complexes were characterized by IR spectroscopy,

elemental analysis, TGA, mass spectrometry, electronic spectra, magnetic susceptibility, and molar

conductance. On the basis of analytical data, the stoichiometry of metal to ligand in complexes is

found as 1:2 combination of metal and Schiff base ligand. The bioactivity of the prepared complexes

has been examined with antibacterial activity.

KEYWORDS: complexes of lanthanide ions, Schiff base, antibacterial activity, catalysis.

Corresponding Author: Hitesh Patel*

Chemistry Department Sheth M. N. Science College, Patan, Gujarat, India.

1.INTRODUCTION

The chemistry of Schiff base is in an important zone of research with increasing interest due to their

simple formation, versatility, the diverse range of medicinal application of their metal complexes

e.g. anticancer, as anti-bactericidal agents, antiviral agent and other biological properties. Also, they

find uses in polymers and dyes, agriculture [4-6]. A Schiff base is a nitrogen analogue of an aldehyde

or ketone in which the C=O group is replaced by C=N-R group. It is normally formation by

condensation of an aldehyde or ketone with primary amine [7-8]. The inner transition metals and

transition metals are known to form Schiff base complexes [9]. The lanthanide elements recently

found to possess a wide range of coordination numbers and geometries [10]. Rare earth’s

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coordination compounds are most crucial in cancer diagnosis and cure. It may be due to the

paramagnetic properties of lanthanides and their complexes. These compounds are generally used

in medicine as a difference media for MRI [11-12].

2. MATERIALS AND METHODS

All the chemicals used for whole work were of analyticalgrade. Salicylaldehyde, anthranilic

acid, ethanol were used for preparation of Schiff base. 0.3M perchloric acid, 0.1M perchlorate

were prepared from 70% perchloric acid and M(III) ions in aqueous solution.

Synthesis of Schiff base ligand

N-salicylaldehydeanthranilic acid was synthesized by adding equal volumes of 0.04 mol ethanolic

solution of salicylaldehyde to a solution of 0.04 mol ethanolic solution of anthranilic acid and the

mixture was stirred for 3hrs. The solution was concentered and orange coloured Schiff base of N-

salicylaldehyde-anthranilic acid was generated. The precipitated Schiff base was filtered and

recrystallized twice from alcohol, M.P 205 0C.

Table 01: physical data of ligand

Figure 01: Ligand structure(NSAA)

Preparation of Complexes

The formation of complexes was carried out by the mixing of 60 ml of 0.1M metal perchlorate

solution and 60 ml 0.1M ligand solution in 50% ethanol-water. The mole ratio of ligand and metal

was (1:1). The reaction mixture was refluxed for 2 to 3 hrs at 90-100 0C. Then after some time the

mixture was cooled and complex slowly precipitated. The pH of the above solution was raised up

to 5.5 using 0.1M NaOH solution and the precipitated complex was filtered and washed with hot

alcohol and dried at room temperature.

3. RESULTS AND DISCUSSION

Analysis and Physical Measurement

M.P. and TLC (Solvent toluene: methanol 7:3) were taken in usual method. TLC indicated single

spot so confirming the complex formation. The UV visible spectrum measured by Shimadzu UV-

1800 UV-VIS spectrophotometer (double beam) in the range of 200 nm to 800 nm using DMF

solvent. Elemental analysis was performed with a ThermoFinnigan FLASH EA 1112 Series CHN

analyzer. The metal percentage was determined with EDTA back titration method. Magnetic

susceptibility was determined by Gouy’s method with utilizing Hg[Co(NCS)4] as a calibrant on

About NSAA ligand

Mol. Formula: C14H11NO3

Formula Wt.: 241.242 g/mol

Color: Orange






Polytronic electromagnet HEM-100. The FTIR of all compounds were obtained in the range of

4000-400 cm-1using KBr pellets on a Shimadzu IR Affinity 1 S spectrophotometer. T.G.A/D.S.C

measured by Perkin-Elmer Diamond Thermogravimetric/Differential Thermal Analyzer.

The molar conductance value suggested non-electrolytic nature. Although, a high degree of

dissociation of complexes was inferred from molar conductance values.

Results of Physical Measurements

Table02: Analytical Data and Some Physical Properties of the Ligand and Metal Complexes

Complex Colour

Formul

a weight

Gm/mol

M.P.

(C)

Magn

Sus.

(BM)

R.F

value

Molar

Conductance

S cm2 mol-1

Elemental Analysis

Found

(calc) %

C H N M

Ligand

NSAA

Orange 241.24 205 - 0.61 -

68.07

(69.70)

4.765

(4.59)

5.79

(5.80)

-

La-

NSAA

Light

orange

691 >300

Dia

Magn

etic

0.57 23.67

49.30

(48.71)

3.98

(3.94)

4.09

(4.06)

19.44

(20.12)

Ce-

NSAA

Red

Orange

709

>300 2.39 0.53 27.45

50.94

(47.39)

4.06

(4.12)

4.39

(3.95)

18.21

(19.74)

Pr- NSAA

Yellow

Orange

729 >300 3.46 0.50 37.61

47.33

(46.17)

3.78

(4.29)

3.84

(3.85)

18.31

(19.34)

Infrared Spectroscopy

The IR spectra of the Schiff base and Ln(III) complexes are given in table 03. The IR spectra of

Ln(III) complexes show the ligand characteristic bands with the proper shifts due to complex

formation and spectra of all complexes are discussed as below. The IR band at 1618 cm-1 of the free

Schiff base ligand is present due to the azomethine group in complexation This band is shifted to

lower wave number in complexes. In NSAA the signal at 3470 cm-1 was from the stretching

vibration of phenolic –OH [13]group but in metal complexes the phenolic –OH frequency vanishes,

it confirmed that the oxygen atom of phenolic group is making complexes with metals. In NSAA

carboxylic group showed 2954 cm-1,1686 cm-1,1292 cm-1bands for respectively –OH group, C=O

group and C-O group [14-15]. In complexation, all of these signals are shifted to lower wave number.

The stretching vibration bands of 3475 to 3579 cm-1 assigned for coordinated H2O in La-NSAA to

Pr-NSAA respectively. Some new frequencies emerge in metal complexes in the favour of M-N and






M-O, for La-NSAA it shows at 622.90, 577.55 cm-1, for Ce-NSAA 623.01, 575, 553.57 cm-1, for

Pr-NSAA 626.87, 559.36 cm-1 [16-17].

Table 03: IR spectra of ligand and complexes

Compound

ν(̶ C=N)

Str.

(cm-1)

Phenolic

vH2O

(cm-1)

COOH

ν(M ̶ O)

(cm-1)

ν(M ̶ N)

(cm-1)

ν(O ̶ H)

Str.

(cm-1)

ν(C ̶ O)

Str.

(cm-1)

ν(O ̶ H)

Str.

(cm-1)

ν(C=O)

Str.

(cm-1)

ν(C ̶ O)

Str.

(cm-1)

Ligand 1618

3470

1246 - 2954

1686

1292 - -

La-NSAA 1613.8 -

1228

3475 2947 1633 1277.70 577.55 622.90

Ce- NSAA 1614.42 - 1232.51 3500 2837

1660

1276 575,

553.57 623.01

Pr-NSAA 1597 - 1232 3579 2951 1608 1276 559.36 626.87

Mass Spectra

Table 04: Mass spectra of ligand and complexes

Compound Possible Fragments m/z value

Calculated Found

NSAA

C14H11NO3

C13H10NO

C7H5NO2

241.24

196.22

135.12

241.8

195.9

136.8

La-NSAA

C28H21N2O7La

C14H13NO5La

C7H5NO2

636.38

414.16

135.12

637.3

412.1

136.26

Ce-NSAA C7H7NO2Ce

C7H5NO2

277.25

135.12

282.1

136.06

Pr-NSAA C14H19NO8Pr

C7H5NO2

470.21

135.12

468.2

137.10






Figure 02: ligand mass spectra






Figure 03: La-NSAA Mass spectrum

Figure 04: Ce-NSAA Mass spectrum

Figure 05: Pr-NSAA Mass spectrum






Magnetic Moments

Gouy’s method used for measurement of the magnetic moments. At room temperature magnetic

moment for solid complexes of La3+, Ce3+, Pr3+, respectively 0 BM, 2.39 BM, 3.46 BM. This

suggests that 0,1 and 2 unpair electron for La(III), Ce(III) and Pr(III) ions respectively, considering

spin-orbit coupling [18-20].

Electronic Spectral Study

Lanthanum (III) hаѕnо significant absorption in thе visible region, duеtоthе absence оf 4f orbital

electrons. The absorption spectra of lanthanide complexes show presence due to laporte forbidden

f-f transitions. 4f orbitals of lanthanide metals are deep-seated therefore not exposed to surrounding

ligands. Ce(III) exhibits broad bands due to L→Mcharge transfer transitions [21-22].

Table 05: Electronic spectra of ligand and complexes

Compounds Λmax Cm-1 Band assignments

NSAA

332.5

263

204

30075.18

38022.81

49019.60

n→π*

π→π*

π→π*

La-NSAA

333

281.5

258

230

211

30030.03

35523.97

38759.68

43478.26

47281.32

Ligand and C.T.

transitions

Ce-NSAA 330

245

30303.03

40816.32

2F5/2→2D3/2

2F5/2 →5D5/2

Pr-NSAA 327.5

219.5

30534.35

45558.08

3H4→3P2

3H4→1S0

Figure 06: Electronic spectra of ligand and complexes






Thermal analysis

It is observed that at 150 0Ctemperature in La-NSAA complex 50.23 gm weight loss per mole

occurred, which implies that two H2O molecules of crystallization with La-NSAA is present and at

250 0C temperature 35.56 gm weight loss per mole occurred which implies that two H2O molecules

coordinate with La-NSAA. Thermogravimetric analysis for 1 mole of Ce-NSAA at 150 0C

temperature 20.35 gm weight loss per mole occurred which implies there is one water molecule of

crystallization and at 250 0C temperature 79.40 gm weight loss per mole occurred which implies

that four H2O molecules coordinate with Ce-NSAA. For Pr-NSAA at 150 0C 41.9 gm weight loss

per mole occurred which implies that two H2O molecules of crystallization and at 250 0C

temperature 63.42 gm weight loss per mole occurred which implies that three H2O molecules

coordinate with Pr-NSAA. Nikolaev et al thought-about water eliminated below 150°C as lattice

water and higher than 150°C as coordinated water to the metal ions [23-24].

Table 06: Thermogravimetric Analysis

Complexes RT-150 0C

Water of crystallization

150 0C-250 0C

Water of coordination

% Loss Loss of

Weight

Water

molecules % Loss

Loss of

Weight

Water

molecules

La-NSAA 7.27 50.23 2 5.02 35.56 2

Ce-NSAA 2.80 20.35 1 11.2 79.40 4

Pr-NSAA 5.9 41.9 2 8.92 63.42 3

RT= Room Temperature

Figure 07: TGA of complexes






Based upon TGA the results complexes coordination number

Table 07: Complexes and Coordination Numbers*

Complexes

Coordination number

of metal in the suggested

structures

Usual coordination number *

of metal ion

La-NSAA 08 4,8-11

Ce-NSAA 10 9,10,12

Pr-NSAA 09 6,9,12

*See reference no [25-26]

As the above results of physicochemical analyses, their probable structures are shown in figures

below.

OH2OH2

O OH

N

O-

O O-

N

O-

La3+

OH2 2

Figure 08: Possible STRUCTURE of La-NSAA complex

Figure 09: Possible STRUCTURE of Ce-NSAA complex

OH2

OH2

OH2

OH2

O OH

N

O-

O O-

N

O-

Ce3+

OH2






Figure 10: Possible STRUCTURE of Pr-NSAA complex

Catalysis of an organic reaction

A mixture of furan (1.5 ml) and maleic acid (2.32 gm) in water (15 ml) was stirred for 3 hours at

room temperature the solid colorless compound synthesized, was filtered and washed with water,

dried and recrystallized with MeOH. M.P 138-140oC. yield 2.67 gm (72.7 %). This is a standard

organic reaction [27-28] which on carrying out for 3hrs and results in in72.7 % yield. The same

reaction was carried out for 2 hrs. The 2.07 gm (56.49 %) yield found.the same reaction was carried

out using 1mol % catalytic amount of complexes, % yield and % increases in yield of the reaction

are indicated in table no.08.

Figure 11: Dies-Alder reaction

Table 08:% Yield of Organic reaction

Temperature

Time

% yield

Standard

reaction

% yield

with

ligand

La-NSAA

% yield

with

ligand

Ce-NSAA

% yield

with

ligand

Pr-NSAA

% yield

increase

with La-

NSAA

% yield

increase

with Ce-

NSAA

% yield

increase

with Pr-

NSAA

Room temp.

(25 0C)

2 hrs.

56.25% 58.42% 61.68% 62.77% 3.86% 9.66% 11.59%






Kinetics study

Table 09:Reaction rate with Ln-NSAA and without Ln-NSAA

Reaction KBrO3 + KI + HCl K2S2O8 + KI H2O2 + KI+H2SO4

k without metal

complex 2.28 x 10-4 3.00 x 10-5 3.91 x 10-4

k with La-NSAA 4.99 x 10-4 3.56 x 10-5 3.84 x 10-4

k with Ce-NSAA 3.05 x 10-4 3.15 x 10-5 5.75 x 10-4

k with Pr-NSAA 4.18 x 10-4 3.05 x 10-5 3.00 x 10-4

% Increase in

reaction rate at 305 k

temp. La-NSAA

119.0 % 18.7 % -1.9 %

% Increase in


temp. Ce-NSAA

33.8 % 5.0 % 47.0 %

% Increase in


temp. Pr-NSAA

83.3 % 1.7 % -23.4 %

Where, k indicates the rate of reaction, Negative sign indicates decrease in reaction rate

The catalytic study shows that metal complexes of La, Ce and Pr were found to increase the rate of

reaction between potassium bromate and potassium iodide while the complex of La exhibited the

good enhancement in the reaction rate between the reaction of potassium persulphate and potassium

iodide. In the reaction between hydrogen peroxide and potassium iodide, Ce-complex was found to

increase the reaction rate while other two complexes were found to reduce the rate of reaction.

Overall the La-complex was able to act as a good catalyst and impressively catalyzed the redox

reaction of potassium bromate and potassium persulphate with potassium iodide respectively and

between the reaction of hydrogen peroxide and potassium iodide, Ce-complex was found as a good

catalyst compared with Pr and La complexes.

Activation energy determination by Broido method

Broido method can be applied to TGA data to estimate activation energy as well as other kinetic

parameters [29-30]. The equation of Broido method is as follows:

𝑙𝑛𝑙𝑛 (1

𝑦) = − (

𝐸𝑎

𝑅) (

1

𝑇) + 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡

Where, y denotes the fraction of number of initial molecules not yet decomposed. Slope of plot

lnln(1/y) vs. 1000/K related with activation energy as follow:






Activation energy (Ea) = -2.303 x R x slope

Where, R = gas constant

Activation energy evaluated for thermal decomposition of complexes are shown in table :10

Table 10: Activation energy of complexes

Complexes Temp. range Activation energy

La-NSAA 43°C to 128°C 74.05 kJ·mol-1

Ce-NSAA 57°C to 127°C 28.50kJ·mol-1

Pr-NSAA 36°C to 96°C 93.61kJ·mol-1

Figure 12: Graph of ln[ln(1/y)] vs 1000/T for complexes

The activation energy of thermal degradation of La-NSAA, Ce-NSAA, and Pr-NSAA were found

to be 74.05 kJ mol-1, 28.50 kJ mol-1, and 93.61 kJ mol-1respectively.






Antibacterial activity

Table 11:Results of antibacterial activity of ligand and its metal complexes

Sr.

no

Bacterial species μg/ml NSAA La-

NSAA

Ce-

NSAA

Pr-

NSAA

Ciprofloxacin

1 B. subtilis

(G+)

100 μg/ml + + + + ++++

200 μg/ml + +++ ++ ++ ++++

300 μg/ml + +++ +++ +++ ++++

400 μg/ml ++ ++++ ++++ +++ ++++

2 Staphylococcus

Aureus

(G+)

100 μg/ml + ++ + + ++++

200 μg/ml + +++ + ++ ++++

300 μg/ml + ++++ ++ +++ ++++

400 μg/ml ++ ++++ ++ ++++ ++++

3 E. coli

(G-)

100 μg/ml - + - + ++++

200 μg/ml - ++ - ++ ++++

300 μg/ml + ++ + ++ ++++

400 μg/ml + +++ + +++ ++++

4 P. aeruginosa

(G-)

100 μg/ml - + - - ++++

200 μg/ml - ++ + + ++++

300 μg/ml + +++ + + ++++

400 μg/ml + ++++ ++ ++ ++++

++++ indicates 26 to 30 mm, +++ indicates 21 to 25 mm, ++ indicates 16 to 20 mm, + indicates 11

to 15 mm, – indicates no zone

The ligand is moderately active and the complexes are more active as antibacterial[31]. Ligand-

NSAA is more active against Gram’s positive bacteria as compared to Gram’s negative bacteria.

Mostly all the lanthanide complexes were found to exhibit antibacterial activities against four

bacterial species (two Gram’s positive and two Gram’s negative) with concentration ranging from

100 to 400 µg/mL as shown in the table 07. Gram’s positive Bacillus subtilis was the most affected

bacterial species followed by Staphylococcus aureus. The activity increases with increase in

concentration of complexes. The complex La- NSAA was the most effective inhibitor against all

the four bacteria followed by Ce-NSAA, Pr-NSAA.Ligand–NSAA at all its concentrations shows

inhibitory effect on Gram’s positive bacteria: Bacillus Subtilis and Staphylococcus Aureus, but at

100 and 200 µg/mL concentrations, it could not exhibit any inhibitory effect onGram’s negative

bacteria: Escherichia Coli and Pseudomonas Aeruginosa. At 400 µg/mL concentration, all the

complexes were less active compared to Ciprofloxacin. Ce- NSAA is the only one complex which

did not demonstrate any inhibitory effect againstEscherichia Coli at 100 and 200 µg/mL






concentrations. Whereas at 100 µg/ml concentration, Ce- NSAA and Pr- NSAA both did not show

any inhibitory activity against Pseudomonas aeruginosa.In general, all the complexes were able

to inhibit Gram’s positive bacteria and not Gram’s negative one.

4. CONCLUSION

Inner Transition metal complexes of La(III), Ce(III) and Pr(III) with Schiff base derived from

anthranilic acid and salicylaldehyde have been synthesized from their corresponding

metal perchlorate and characterized. The structure of the Schiff base and metal

complexes are determined with the assistance of elemental analysis, IR, Uv-visible spectra,

mass spectrometry, molar conductance, magnetic moment and thermal analysis. The catalytic

effect of complexes on Dies-Alder reaction has been also studied. Kinetic study on three well-

known redox reactions, La-NSAA was found to increase the rate of reaction of potassium

bromate and potassium iodide. The activation energy for thermal decomposition was calculated

from TGA data by Broido method. The higher activation energy indicating complexes have

good thermal stability and ability to pass on energy consequently good catalysis ability. Schiff

base and every complex were screened for antibacterial activity against Bacillus subtilis,

Staphylococcus Aureus, Escherichia coli, Pseudomonas aeruginosa Victimization

ciprofloxacin antibiotic drug as standards. It had been shown that La, Ce and Pr complexes

show increased antimicrobial activity than Schiff base.

CONFLICT OF INTEREST

The authors have declared that they have no conflict of interest.

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