Chapter 3

Materials, Experimental Techniques and

Characterisation of the Complexes

3.1 Introduction

This chapter deals with the details regarding the reagents employed in the

preparation of the complexes, the analytical and physical measurements

used for the characterisation of the complexes. A detailed description of

the instruments used for the physicochemical studies and some of the

procedural details are also given.

3.2 Metal Salts

All the metal salts employed for the synthesis were analar grade supplied

by Rankem. Wherever the AR grade metal salts were not available, the

salts were synthesised using AR grade metal carbonates and

corresponding acid.

3.3 Ligands

Ammonia (specific gravity 0.89) and Ethylenediamine (specific gravity

0.895) supplied by Rankem were used as such.

3.4 Other Reagents

The solvents used in the preparation of the complexes were ethanol,

acetone and diethyl ether of AR grade. Ethanol was purified using a

standard procedure.1 The purified product was distilled over calcium

oxide.

102 Chapter 3

3.5 Analyses of the Complexes

3.5.1 Estimation of nickel

Nickel content in the complex was determined by gravimetry.2 The

weighed amount of complex was dissolved in water and added 5 ml 1:1

HCl and diluted to 200 ml. Heated to 70-80°C, added excess of dimethyl

glyoxime reagent followed by dilute ammonia solution drop wise directly

to the solution with constant stirring till complete precipitation took place.

Heated on a steam water bath for 20-30 minutes. Allowed the precipitate

to settle for 1 hr with cooling at the same time. Filtered the cold solution

through a sintered crucible, which was previously heated to 110-120°C

and weighed after cooling in a desiccator. Washed the precipitate with

water until free from chloride and dried it at 110-120°C for 45-50

minutes. Allowed to cool in a desiccator and weighed.

3.5.2 Estimation of halides

The halides were estimated using Volhard’s method.2 An accurate

quantity of complex (about 100 mg) was dissolved in 50 ml AR methanol.

Added 15 ml of 6N HNO3 and 10 ml of standard AgNO3 solution. Then 3

ml of Nitrobenzene was added and heated to about one and a half hours.

Cooled and added 1 ml of ferric alum indicator and titrated against

standard NH4CNS in the burette. The end point is the appearance of the

faint reddish brown colour.

Materials, Experimental Techniques and Characterisation of the Complexes 103

3.6 Physical Measurements

3.6.1 Infrared and electronic spectral measurements

Infrared spectra were recorded on a Shimadzu 1600 spectrophotometer

using KBr pellet technique (400-4000 cm-1

). Electronic spectra in the

solid state were recorded using Shimadzu UV probe.

3.6.2 CHNS analysis

CHNS analyses were carried out in a Vario El III analyser. The results are

given in Table 3.1.

Table 3.1

Elemental analysis data

Complexes

Nickel

(%)

Carbon

(%)

Hydrogen

(%)

Nitrogen

(%)

Sulphur

(%)

Chlorine

(%)

Bromine

(%)

Obsd.

(calcd.)

Obsd.

(calcd.)

Obsd.

(calcd.)

Obsd.

(calcd.)

Obsd.

(calcd.)

Obsd.

(calcd.)

Obsd.

(calcd.)

[Ni(NH3)6]SO4 22.5

(22.9)

6.9

(7)

32.5

(32.7)

12.1

(12.5)

[Ni(en)3]SO4 17.2

(17.5)

21.5

(21.5)

7.2

(7.2)

24.9

(25.1) 9.5 (9.6)

[Ni(NH3)6](NO3)2 21.2

(20.6)

6.1

(6.3)

39

(39.3)

[Ni(en)3](NO3)2 16

(16.2)

19.5

(19.8)

6

(6.6)

29.2

(30.9)

[Ni(NH3)6]Cl2 24.9

(25.3)

8.1

(7.8)

36.1

(36.3)

31.1

(30.6)

[Ni(NH3)6]Br2 17.7

(18.3)

6

(5.6)

26.7

(26.2)

50.1

(49.9)

[Ni(en)3]C2O4.2H2O 15.9

(16.2)

26.5

(26.4)

7.2

(7.7)

23.7

(23.1)

104 Chapter 3

3.6.3 Temperature resolved X-ray diffraction studies

Temperature resolved X-ray diffraction (TR-XRD) can be used as a

powerful technique in thermal analyses. TR-XRD is often the most

appropriate tool to study a solid state reaction when crystalline materials

are involved either as reactants or products. This method enables the

recording of series of diffraction patterns, while the samples are heated

continuously, step wise or isothermally during the reaction. These series

contain the information on the lattice of the solids and on the structural

changes as a function of temperature. Besides, since peak intensities of a

phase correlate with its concentration, by insitu measurement it is possible

to probe the kinetics of solid state reaction.

X-ray powder patterns were recorded on a Bruker D8 Advance

diffractometer attached with a programmable temperature device (TTK

450) from Anton Paar using Cu Kα radiation (λ = 1.542 Å). The

measurements were performed by placing the sample on a flat sample

holder, while the samples were heated by a programmable temperature

controller. Crystallite size was calculated using Scherrer equation,

t = 0.9 λ / β cos θ,

where t is the thickness of the particle, λ is the wave length, β is the line

broadening (FWHM) and cos θ is the corresponding angle.

3.6.4 SEM analysis

The morphology of the complexes, intermediates separated at different

temperatures and the residues were analysed by JEOL JSM 6390

Scanning Electron Microscope. For this the samples were spread on a

carbon tape and made uniform by blowing air and coated with platinum.

Materials, Experimental Techniques and Characterisation of the Complexes 105

The intermediates and residues were separated by heating the complexes

in a muffle furnace simulating the conditions in a TG instrument.

3.7 Thermal Studies

3.7.1 TG/DTA measurements

The TG and DTA were recorded using a Shimadzu DTG 60 instrument. It

is a simultaneous TG and DTA recording instrument and is connected to

TA 60 online analyzer. The measurements were recorded in air at a

purging rate of 50 ml min-1

. Platinum pans were used as the sample

container. The temperature limit of Shimadzu DTG 60 is up to 1000°C.

3.7.2 DSC measurements

The DSC profiles were recorded using a Shimadzu DSC 60 connected

with TA60 thermal analyser. The experiments were done in nitrogen

atmosphere at a flow rate of 50 ml min-1

. Aluminum sample pans were

used for the experiment. The temperature limit of Shimadzu DSC 60 is up

to 400°C. DSC measurements were carried out only for the nitrate

complexes viz., hexaamminenickel(II) nitrate and tris(ethylenediamine)

nickel(II) nitrate, since the decomposition of these complexes complete

before 400°C.

3.7.3 TG/DTA-MS measurements

TG/DTA-MS studies were carried out in a thermogravimetric apparatus

(TG; Rigaku, TG-8120) combined with mass spectroscopy (Anelva, M-

QA200TS) with a heating rate of 5, 10, 15,25oC min

-1 under high-purity

He gas (99.9999%) at a flow rate of 200 ml min-1

. The TG/DTA-MS

experiments were done up to 1000°C.

106 Chapter 3

3.8 Calibration of the Instruments

All the instruments were calibrated as per the procedure given by the

manufacturers.The temperature reproducibility is 0.1K and the

temperature accuracy is 0.1K.

3.9 Entropy Measurements

The entropy of activation was calculated by the following equation

#

expskT SA

h R

where k is the Boltzmann constant, h is the Planck’s constant and #S is

the entropy of activation.

3.10 Particle Size Determination

The particles were sieved through a Fisher sub-sieve sizer to make the

particle size uniform so that the effect of particle size can be avoided. The

average particle size was 50 µm.

3.11 Characterisation of the Complexes

3.11.1 IR spectra

The main absorption peaks for the complexes are given in Table 3.2. The

tentative assignments are based on the spectral data available for the

amine complexes. The intense bands at 3370-3330 cm-1

are assigned to

the N – H stretching vibrations of the amino group. Similar bands

observed in the hydrated complex can be attributed to the combination of

both N – H and O – H stretching. The bands in the range 410-380 cm-1

are

due to the metal – nitrogen stretch.3

Materials, Experimental Techniques and Characterisation of the Complexes 107

Sulphate complexes

The free sulphate ion belongs to the high symmetry point group Td. Of the

four fundamental modes only ν3 and ν4 are IR active. If the ion is

coordinated to a metal, the symmetry is lowered and the splitting of the

degenerate mode occurs, together with the appearance of new bands in the

IR spectrum. When it functions as a unidentate ligand, the coordinated

oxygen is no longer equivalent to the other three and the effective

symmetry is lowered to C3v. Since the M-O-S chain is normally bent, the

actual symmetry is even lower, but this perturbation of C3v symmetry

does not measurably affect the IR spectra. When two oxygen atoms

become coordinated, the symmetry is lowered still further to C2v.4

In the non coordinated sulphate ion, ν3 and ν4 do not split and ν2 does not

appear, although ν1 is observed, it is very weak. The bands observed are

in good agreement with the stoichiometric composition of the sulphate

complexes as [Ni(NH3)6]SO4 and [Ni(en)3]SO4.

Nitrate complexes

In the nitrate complexes, the nitrate ion can acts as counter anion. The

nitrate ion is planar and belongs to the D3h point group.5 It possesses four

fundamental modes of vibrations viz., ν1 (symmetric stretch), ν2 (out of

plane deformation, 830 cm-1

), ν3 (asymmetric stretch, 1390 cm-1

) and ν4

(doubly degenerate in plane bend, 720 cm-1

). Among these ν1 is IR

inactive, but sometimes becomes weakly active through crystal

interaction.4 Therefore, effectively IR spectra of ionic nitrate shows three

bands. The nitrate group can acts as a monodentate, bidentate or bridging

ligand. The symmetry will be lowered from D3h to C2v in all the three

108 Chapter 3

cases. Then ν3 frequency undergoes splitting into ν4 (asymmetric stretch,

1460 cm-1

) and ν1 (symmetric stretch, 1280 cm-1

) and the corresponding

(ν2) N–O stretch is observed around 1000 cm-1

. The non planar rocking

vibration (ν6) is observed at 800 cm-1

.6

In the IR spectra of [Ni(NH3)6](NO3)2 and [Ni(en)3](NO3)2, the strong

bands observed at 1380 and 1382 cm-1

respectively can be attributed ν3 of

ionic nitrate (asymmetric stretch). The strong bands at 825 and 820 cm-1

for these complexes are due to out of plane deformation (ν2) while the

bands at 656 and 660 for these complexes are due to ν4. The assigned

bands in the present amine complexes are in agreement with the

stoichiometric composition of the nitrate complexes as [Ni(NH3)6](NO3)2

and [Ni(en)3](NO3)2.

Oxalate complex

For ionic carboxalate, the characteristic carbonyl absorption vanishes and

is replaced by two bands between 1612–1543 cm-1

and 1454–1307 cm-1

,

which correspond to the antisymmetrical and symmetrical vibrations of

the COO-

structure. Among these bands the former is much more

characteristic as it has generally more constant in frequency while many

other skeletal vibrations occur in the wide range 1400-1300 cm-1

.7

The broad band at 1595 cm-1

may be due to the combination of the

antisymmetric –C=O stretch and NH deformation. The elemental analysis

is in agreement with the formula [Ni(en)3]C2O4.2H2O.

The analytical results for the halide complexes are also in agreement with

the formula [Ni(NH3)6]X2 where X = Cl, Br.

Materials, Experimental Techniques and Characterisation of the Complexes 109

Table 3.2

IR Spectral bands (in cm-1

) for the nickel amine complexes

[Ni(NH3)6]SO4 [Ni(en)3]SO4 [Ni(NH3)6](NO3)2 [Ni(en)3](NO3)2 [Ni(NH3)6]Cl2 [Ni(NH3)6]Br2 [Ni(en)3]C2O4.

2H2O

Tentative

assignments

3359

3201

3479

3294

3167

2923

2881

3479

3294

3167

3500

2955

2885

3344.3

3244.1

3190

3352.1

3251.8

3483.2

3290.3

3251

3163

ν a, ν NH

or

ν NH +

νOH

2923 2954 2931 ν a, C-H

1627

1593

1600 1608.5 1604.7 1595

NH def or

NH def +

C-N str

ν aC=O +

C-N str

1380 1382 ν 3NO3

1257 1277 1184.2 1188.1 δs NH

1103 1112 ν 3SO4

1034 1030 1026 ν C-N str

980 978 980 ν C-C str

976 978 ν 1SO4

825 820 ν 2NO3

656 660 ν 4NO3

617 613 ν 4SO4

532

447

505

408 521 530 520 523

528

497 ν M-N

110 Chapter 3

3.11.2 Electronic spectra

The electronic spectral properties of Nickel(II) complexes have been

extensively studied.8-10

For Ni2+

with a d8 configuration, three d – d transitions

are possible. The expected d – d transitions for octahedral nickel(II) complexes

have transitions as 3A2g(F)→

3T1g(P),

3A2g(F) →

3T1g (F) and

3A2g(F)→

3T2g(F). According to quantum mechanical selection rules a transition between

levels of different spin multiplicity is forbidden. Thus in Ni(II) complexes all

the three transitions are allowed. The electronic spectral bands of the amine

complexes and their magnitudes are given in Table 3.3.

Table 3.3

Electronic spectral bands of Nickel(II) amine complexes (solid state)

Complexes Spectral bands (nm) Assignments

[Ni(NH3)6]SO4

886 ( 11,287 cm-1

)

587 (17,036 cm-1

)

341 (29,326 cm-1

)

d – d transition

d – d transition

d – d transition

[Ni(en)3]SO4

882 (11,338 cm-1

)

542 (18,450 cm-1

)

341 (29,326 cm-1

)

d – d transition

d – d transition

d – d transition

[Ni(NH3)6](NO3)2

881 (11,350 cm-1

)

559 (17,889 cm-1

)

353 (28,328 cm-1

)

d – d transition

d – d transition

d – d transition

[Ni(en)3](NO3)2

880 (11, 363 cm-1

)

565 (17,699 cm-1

)

347 (28,818 cm-1

)

d – d transition

d – d transition

d – d transition

[Ni(NH3)6]Cl2

908 (11,013 cm-1

)

600 (16,667 cm-1

)

373 (26,809 cm-1

)

d – d transition

d – d transition

d – d transition

[Ni(NH3)6]Br2

886 (11,287 cm-1

)

569 (17,575 cm-1

)

361 (27,701 cm-1

)

d – d transition

d – d transition

d – d transition

[Ni(en)3]C2O4. 2H2O

875 (11,429 cm-1

)

538 (18,587 cm-1

)

337 (29,674 cm-1

)

d – d transition

d – d transition

d – d transition

Materials, Experimental Techniques and Characterisation of the Complexes 111

Owing to spin orbital interactions, forbidden transition between levels of

different multiplicity may appear with a very low intensity in the spectrum.

However, the intensity of these bands is smaller by several orders of

magnitude than those of the allowed transitions and hence these are not

observed.11-12

3.12 Treatment of Data

From the recorded TG curves, the fractional decomposition α was

calculated and was employed for the calculation of kinetic parameters.

The values of the procedural decomposition temperature (Ti), the final

temperature (Tf) and the temperature of the summit (Ts) were noted from

the respective curves. Similar values were recorded from DTA and DSC.

3.13 Computational Work

The kinetic parameters by the non-mechanism based equations and

mechanism based equations (model fitting) were done using C

programme. The linear curves were drawn by the method of least squares

and the corresponding correlation coefficients were calculated, as it is an

index of the linearity of the curves. The reliabilities of the non linear

curve fits were established by the F-test.13-14

For the isoconversional

methods the calculations were done using excel work sheet.

112 Chapter 3

References

1. A. Weissberger, P. S. Proskauer, J.A. Riddick, E. Troops, Organic

Solvents, Vol. 2, Interscience Publishers, New York, 1956.

2. A. I. Vogel, A Text Book of Quantitative Inorganic Analysis, 4th edn.,

Longmann, New York, 1978.

3. K. Nakamoto, P. J. McCarthy, Spectroscopy and Structure of

Metal Chelate Complexes, John Wiley, New York, 1968.

4. K. Nakamoto, Infrared and Raman Spectra of Inorganic and

Coordination Compounds; Theory and Applications in Inorganic

Chemistry, John Wiley & Sons, 6th edn., New York, 2009.

5. R. S. Drago, Physical Methods in Chemistry, W.B. Saunders

Company, London, 1977.

6. J. R. Ferraro, J. Inorg. Nucl. Chem., 10, 1959, 319.

7. L. J. Bellamy, The Infrared Spectra of Complex Molecules, Vol. 1,

3rd edn., Chapman & Hall, London, 1978.

8. E. Uhling, Coord. Chem. Rev., 10, 1973, 227.

9. P. L. Orioli, Coord. Chem. Rev., 6, 1971, 285.

10. M. Campiolini, Struct. Bonding (Berlin), 6, 1969, 52.

11. K. Burger, Coordination Chemistry: Experimental Methods,

Butterworth & Co. Ltd., London, 1973.

12. D. N. Sathyanarayana, Electronic Absorption Spectroscopy &

Related Techniques, University Press (India) Ltd., 2001.

13. M. R. Spiegel, Theory and Problems of Statistics in SI Units, 1st

edn., McGraw - Hill, 1972.

14. J. E. Freud, Mathematical Statistics, 5th edn., Prentice Hall Inc.,

New Jersey, 1992.