chapter 4 synthesis and spectral characterisation...

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CHAPTER 4

SYNTHESIS AND SPECTRAL CHARACTERISATION OF

Ni (II) COMPLEXES DERIVED FROM PARENT AND N(4)

SUBSTITUTED 5–CHLORO-2–HYDROXYACETOPHENONE

METHYL THIOSEMICARBAZONES

4.1 INTRODUCTION

Nickel is divalent and exists as Ni (II) in most complexes.

Ni (II) complexes exhibit usually four coordinate square planer or

tetrahedral geometries. Six coordinate octahedral complexes of Ni (II) are

also reported [141, 142]. Ni (II) complexes are generally diamagnetic and

some paramagnetic complexes have also been reported [143], square

pyramidal complexes of Ni (II) are rather unusual and when encountered

exists as a result of particular circumstances in the complex rather than any

intrinsic tendency on the part of Ni (II) ion to attain the structure. It has

been shown that many metal complexes with sulphur containing schiff

bases exhibit anticancer activity [90]. Ni (II) complexes of

thiosemicarbazones of aromatic ortho–hydroxy aldehydes, in particular

salicylaldehyde are used as homogeneous catalysts. [144, 145]. In most of

the thiosemicarbazones NNS tridentate system is present with carcinostatic

potency [146]. This chapter describes the synthesis, spectral

characterization of four and five coordinate Ni (II) complexes derived from

parent and N(4) substituted 5–chloro-2–hydroxy acetophenone methyl

thiosemicarbazone.

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4.2 EXPERIMENTAL:

4.2.1 Chemicals and Methods:

5–Chloro-2–hydroxy acetopohenone thiosemicarbazone and

N(4) substituted methyl thiosemicarbazone, NiCl2.6H2O (Aldrich), ethanol

(A.R. Grade).

4.2.2 Synthesis of complexes and adducts:

Procedure for the synthesis of Ni (II) complexes of L :

The nickel chloride (NiCl2.6H2O 0.001 M) dissolved in

minimum quantity of ethanol was added to hot ethanoic solution of L

(0.001 M). The reaction mixture was heated on hot plate at 80–90 °C for 7–8

hours with constant stirring. The complex which separated overnight as

microcrystalline powder was thoroughly washed with hot water, cold

ethanol and finally with diethyl ether and dried in vacuum.

Reflux

OH

ClN

NH

NH2 Cl

O

NN NH2

SNi

OH2

NiCl2.6H2O

CH3CH3

S

Procedure for the synthesis of adducts :

Adducts of the type NiLB (B = pyridine, 2,2' bipyridine, 1,10

phenanthroline, a–picoline, b–picoline) were prepared by mixing 0.001

mole of heterocyclic base in ethanol with a hot solution of L (0.001 M) in

ethanol (20 ml) and adding a hot and filtered solution of NiCl2.6H2O (0.001

M) in ethanol with constant stirring. The mixture was heated under reflux

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for 7–8 hours. The adducts which separated overnight as microcrystalline

powders were thoroughly washed with hot water, cold ethanol and then

finally with diethyl ether and dried over P4O10 in vacuum.

Reflux

OH

Cl

CH3

N

NH

NH2

S

O

Cl

CH3

N

N NH2

SNi

B

O

Cl

CH3

N

N NH2

SNi

NN

B + NiCl2.6H2O

(Where B = pyridine,α/β-picoline, = bipyridine, 1,10 phenanthroline )

Procedure for the synthesis of Ni (II) complex of L’:

The nickel chloride (NiCl2.6H2O, 0.001 M) dissolved in

minimum quantity of ethanol was added to hot ethanolic solution of L’

(0.001 M). The reaction mixture was heated on hot plate at 80–90 °C for 7–8

hours with constant stirring. The complex which separated overnight as

microcrystalline powder was thoroughly washed with hot water, cold

ethanol and finally with diethyl ether and dried in vacuum.

Reflux

OH

ClN

NH

NH

CH3

Cl

O

NN NH

SNi

OH2

NiCl2.6H2O

CH3CH3

CH3

S

90

Procedure for the Synthesis of Adducts –

Adducts of the type NiL’B (B = pyridine, 2–2 bipyridine, 1,10

phenanthroline, a–picoline, b–picoline) were prepared by mixing 0.001

mole of heterocyclic base in ethanol with a hot solution of L’ (0.001 M) in

ethanol (20 ml). To this was added hot and filtered solution of NiCl2.6H2O

(0.001 M) in ethanol with constant stirring. The mixture was heated under

reflux for 5–8 hours. The adducts which separated overnight as

microcrystalline powders were thoroughly washed with hot water, cold

ethanol and then finally with diethyl ether and dried over P4O10 in vacuum.

Reflux

OH

Cl

CH3

N

NH

NH

S

O

Cl

CH3

N

N NH

SNi

B

O

Cl

CH3

N

N NH

SNi

NN

CH3

CH3

CH3

B + NiCl2.6H2O

(Where B = pyridine,α/β-picoline, = bipyridine, 1,10 phenanthroline )

4.2.3 Physical Measurements :

Colour yield, molar conductivity and magnetic behaviour of

metal complexes is presented in Table No.4.2.3.

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Table No. 4.2.3 : Colour yield, molar conductance and magnetic moments

of nickel complexes

Sr.

No.

Complex Colour Yield

%

Molar

conductance

Ώ-1cm2mole-1

Magnetic

moment in B.M.

1. [NiLH2O] Brown 50.63 41.6 Diamagnetic

2. [NiLpy] Reddish

Brown

56.04 83.6 Diamagnetic

3. [NiLbipy] Brown 71.98 52.6 3.08

4. [NiLphen] Brown 71.94 41.6 3.09

5. [NiLa–pico] Brown 67.02 93.6 Diamagnetic

6. [NiLb–pico] Brown 69.15 83.6 Diamagnetic

7. [NiL’H2O] Brown 52.08 31.2 Diamagnetic

8. [NiL’py] Brown 67.42 93.6 Diamagnetic

9. [NiL’bipy] Brown 69.31 62.4 3.08

10. [NiL’phen] Brown 83.80 72.8 3.06

11. [NiL’a–pico] Brown 65.79 52.0 Diamagnetic

12. [NiL’b–pico] Brown 67.98 62.4 Diamagnetic

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4.3 SPECTRAL DATA OF SYNTHESIZED COMPLEXES AND

ADDUCTS :

4.3.1 Analytical Data (Fig.No.4.3.1 A→L) :

1. Ni (II) Complex of L :

Anal. calcd. for C9H10N3O2SClNi . ESI–MS m/z, ion 319.01

M+, Ni, 18.43 %; C, 33.95 %; H, 3.17 %; N, 13.20 %; S, 10.07 %. Found: ESI–

MS, m/z, ion 319.79; Ni, 18.01 %; C, 34.02 %; H, 3.44 %; N, 13.25 %; S,

10.33 %.

2. Ni (II) Lpy adduct:

Anal. calcd. for C14H13N4OSClNi. ESI–MS m/z, ion 366.33,


MS, m/z, ion 366.96, M+, Ni, 15.69 %; C, 46.76 %; H, 3.31 %; N, 11.02 %; S,

8.33 %.

3. Ni (II) Lbipy adduct:



MS, m/z, ion 457.00, M+, Ni, 12.78 %; C, 49.08 %; H, 3.10 %; N, 15.05 %; S,

8.33 %.

4. Ni (II) Lphen adduct:



MS, m/z, ion 481.80, Ni, 12.20 %; C, 52.11 %; H, 3.12 %; N, 14.74 %; S,

6.34 %.

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5. Ni (II) La–pico adduct:


M+, Ni, 14.91; C, 45.78 %; H, 3.84 %; N, 14.24 %; S, 8.15 %. Found: ESI–MS,

m/z, ion 395.00, M+, Ni, 15.10 %; C, 45.52 %; H, 3.37 %; N, 14.54 %; S,

8.71 %.

6. Ni (II) Lb–pico adduct :



MS, m/z, ion 394.64, M+, Ni, 15.11 %; C, 45.52 %; H, 3.62 %; N, 14.54 %; S,

8.37 %.

7. Ni (II) Complex of L’ :

Anal. calcd. for C10H12N3O2SClNi. ESI–MS m/z, ion 333.09,


MS, m/z, ion 333.54, M+, Ni, 17.43 %; C, 36.40 %; H, 3.87 %; N, 12.85 %; S,

9.98 %.

8. Ni (II)L’py adduct :



MS, m/z, ion 395.00, M+, Ni, 14.53 %; C, 45.13 %; H, 3.41 %; N, 14.77 %; S,

8.47 %.

9. Ni (II) L’bipy adduct:



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MS, m/z, ion 471.65, M+, Ni, 12.78 %; C, 51.32 %; H, 3.52 %; N, 14.64 %; S,

7.12 %.

10. Ni (II) L’phen adduct :



MS, m/z, ion 495.00, M+, Ni, 11.62 %; C, 53.64 %; H, 3.97 %; N, 14.47 %; S,

6.05 %.

11. Ni (II) L’a–pico adduct :

Anal. calcd. for C16H17N4O4SClNi. ESI–MS m/z, ion 406.54,

M+, Ni, 14.47 %; C, 47.39 %; H, 3.73 %; N, 13.82 %; S, 7.91 %. Found : ESI–

MS, m/z, ion 406.05, M+, Ni, 14.11 %; C, 47.12 %; H, 3.32 %; N, 13.51 %; S,

7.32 %.

12. Ni (II) L’b–pico adduct:

Anal. calcd. for C16H17N4O4SCl Ni . ESI–MS m/z, ion 406.54,


Ms, M/z, ion 406.05, M+, Ni, 14.53 %; C, 46.99 %; H, 3.32 %; N, 13.67 %; S,

8.05 %.

4.3.2 Infrared Spectra :

The significant IR bands of Ni (II) complexes are :

1. NiLH2O : n (C = N) 1603; n (C = N – N = C) 1555, n (C–S) 750, 1304;

n (N–N) 1136; n (M–N) 423; n (M–O) 518; n (M–S) 312; n (C–O) 1226.

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2. NiLpy : n (C = N) 1598; n (C = N – N = C) 1555, n (C–S) 687, 1297;

n (N–N) 1072; n (M–N) Base 282; n (M–N) 425; n (M–O) 516; n (M–S)

311; n (C–O) 1229; Bands due to HB 619.

3. NiLbipy : n (C = N) 1597; n (C = N – N = C) 1545, n (C–S) 682, 1301;


324; n (C–O) 1226; Bands due to HB 1404 , 1013.

4. NiLphen : n (C = N) 1618; n (C = N – N = C) 1545, n (C–S) 685, 1301;


316; n (C–O) 1227; Bands due to HB 1466, 470, 613.

5. NiLa–pico : n (C = N) 1609; n (C = N – N = C) 1528, n (C–S) 686,

1311; n (N–N) 1103; n (M–N) Base 278; n (M–N) 419; n (M–O) 500;

n (M–S) 300; n (C–O) 1238; Bands due to HB 1405, 762, 469.

6. NiLb–pico : n (C = N) 1589; n (C = N – N = C) 1545, n (C–S) 674,


n (M–S) 309; n (C–O) 1228; Bands due to HB, 674, 420.

7. NiL’H2O : n (C = N) 1696; n (C = N – N = C) 1577, n (C–S) 671, 1276;

n (N–N) 1113; n (M–N) 423; n (M–O) 509; n (M–S) 309; n (C–O) 1235.

8. NiL’py : n (C = N) 1577; n (C = N – N = C) 1555, n (C–S) 665, 1296;


301; n (C–O) 1250; Bands due to HB 1296.

9. NiL’bipy : n (C = N) 1685; n (C = N – N = C) 1560, n (C–S) 665, 1309;

n (N–N) 1111; n (M–N) 269; n (M–N) 425; n (M–O) 514; n (M–S) 313;

n (C–O) 1219; Bands due to HB 1404, 763, 665.

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10. NiL’phen : n (C = N) 1590; n (C = N – N = C) 1579, n (C–S) 728, 1297;


309; n (C–O) 1227; Bands due to HB 1460, 665.

11. NiL’a–pico : n (C = N) 1590; n (C = N – N = C) 1530, n (C–S) 687,


n (M–S) 311; n (C–O) 1234; Bands due to HB 618, 468.

12. NiL’b–pico : n (C = N) 1590; n (C = N – N = C) 1545, n (C–S) 688,


n (M–S) 314; n (C–O) 1238.

4.3.3 Electronic Spectra (Fig.No.4.3.3 A→F)

The electronic spectral data in cm-1 of complexes in solution

are listed in Table No.4.3.3

Table No.4.3.3

Complex State d–d L → M n → p* p → p*

NiLH2O DMF 17,367 23,810 32,051 36,232

NiLpy DMF 17,094 26,247 27,548 38,023

NiLbipy DMF 17,543 23,810

27,778

30,030 34,014

NiLphen DMF 16,502 23,641

25,840

32,052 36,232

NiLa–pico DMF 16,502 23,364 30,960 38,911

NiLb–pico DMF 17,094 23,474

25,042

31,746 36,765

NiL’H2O DMF 16,807 23,697,

26,667

30,769 40,000

NiL’py DMF 16,807 24,691 32,787 40,161

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NiL’bipy DMF 17,007 24,096,

27,933

28,986,

32,788

39,682

NiL’phen DMF 17,123 23,529 30769 40,323

NiL’a–pico DMF 16,807 23,810 32,787 40,160

NiL’b–pico DMF 16,863 23,697 32,258 39,841

4.3.4 Differential Scanning Calorimetry (Fig.No.4.3.4 A,B)

The thermal stability, melting, crystallisation, decomposition,

desolvation, sublimation and glass transition temperature of complexes can

be studied by carrying out differential scanning calorimetry (DSC). This

technique also detects any reaction or transformation involving absorption

or release of heat. DSC thermograms gave thermal characteristic data,

melting point corresponding to endothermic peak and decomposition

temperature (exothermic peak). The results are summarised as –

NiLH2O : Endothermic; onset temperature 170.51 °C; peak, 171.81 °C,; End

set temperature, 175.75 °C, DH, – 71.57 J g–1; Tg, 248.75 °C, Exothermic;

onset temperature, 292.5 °C; Peak, 295.0 °C; End set temperature; 310 °C.

NiL’H2O : Endothermic; onset temperature 166.25 °C, peak, 175.0 °C; End

set temperature, 187.5 °C, Tg, 275 °C, Exothermic; onset temperature,

323.87 °C; Peak, 326.46 °C; End set temperature; 310 °C, DH, – 130.84 Jg–1.

4.3.5 Thermogravimetric Analysis (TGA) (Fig.No.4.3.4 A, B)

The TGA curves of NiLH2O and NiL’H2O complexes were

carried out within a temperature range 38 °C to 800 °C.

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NiLH2O : First step, 117.86 °C, mass loss %, 5.51; Second step, 225 °C; mass

loss %, 17.52.; Third step, 357.14 °C; mass loss %, 54.00; Residue, 732.14 °C;

% of NiO, 24.01 (calc. NiO % = 23.46).

NiL’H2O : First step, 125.0 °C, mass loss %, 5.02; Second step, 200 °C; mass

loss %, 7.52.; Third step, 378.0 °C; mass loss %, 56.5, Residue, 800.0 °C; % of

NiO, 23.02 (calc. NiO % = 22.47).

4.4 RESULTS AND DISCUSSION:

Elemental analyses for M:L, 1:1 complexes matched with

[NiLH2O] formula for both L and L’ ligands. Elemental analysis data are

consistent with 1:1:1 ratio of metal ion; thiosemicarbazone; heterocyclic

base for all complexes prepared. The complexes are insoluble in most of

common polar and non–polar solvents. They are soluble in DMF and

therefore conductivity measurements were made in DMF. All the

complexes showed non–electrolyte nature [119]. The most important

bands in the infrared spectra of the synthesized Ni (II) complexes of

thiosemicarbazones are well in agreement with their tentative assignments.

The position of these bands are helpful to detect the bonding sites of all

ligand molecules interacted with metal. The coordination of azomethine

nitrogen shifts n(7C = 1N) to lower wavenumbers by 15 to 25 cm–1. The

band in spectra of uncomplxed thiosemicarbazones at 1624 and 1638 cm–1

are found to shift to lower wavenumbers in spectra of complex. The n(NN)

shifting to higher wavenumber in spectra of complexes than that of

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thiosemicarbazones confirm the coordination of azomethine nitrogen [147].

The presence of new band at 400 – 470 cm–1 assignable to n(Ni – N) in the

complexes, confirms the coordination of azomethine nitrogen. There is a

loss of – 2NH proton on coordination via thiolate sulphur [148]. Decrease

in frequency (10–90 cm–1) of the n(C = S) bands found at 758, 1374 in L and

795, 1358 cm–1 in L’ and the presence of new band in the 300–325 cm–1

range assignable to n(NiS), confirm the coordination through sulphur. The

phenolic oxygen occupies the third coordination on the loss of OH proton.

This causes shifting of n(CO) to lower wavenumbers by 50–60 cm–1 from

1281 and 1288 cm–1 in the spectra of L and L’ respectively. The band at

500–521 cm–1 is assignable to nNiO. The coordination of heterocyclic

nitrogen atom (s) is confirmed by the presence of n NiN band in the range

260–285 cm–1. The characteristic bands of coordinated heterocyclic bases

are also observed in IR spectra of all the adducts.

The room temperature magnetic susceptibility of the

complexes showed that complexes No. 1, 2, 5, 6, 7, 8, 11, and 12 are

diamagnetic. Five coordinate high spin complexes have magnetic

moments in the range 3.20 – 3.40 B.M. [149]. The observed values of µeff

for complexes 3, 4, 9, 10 are slightly lower than those calculated for five

coordinate trigonal bipyramidal configuration [150]. Lower µeff values for

Ni (II) complexes [151] arise from quenching of the orbital contribution to

the magnetic moment due to distortion of D3h symmetry or due to strong

in plane p–bonding [152, 153].

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Typical planer Ni (II) spectra show a strong visible band in

the 15,000 – 25,000 cm–1 range and in many cases a second strong band

between 23,000 and 30,000 cm–1. These are referred to as n2 and n3 bands.

Lower energy n1 band has been observed in planer complexes containing

S–ligands [154]. The planer complexes can be readily distinguished from

octahedral and tetrahedral complexes by absence of transitions below

10,000 cm–1. The electronic spectra show band in 36,000-41,000 cm-1 range

and 27,000 – 33,000 cm-1 range, these can be assigned to p – p* (aromatic

ring) and n – p* (thiosemicarbazone moiety) transitions respectively. The

broad bands in 27548 – 32788 range are assigned for n – p* transitions [155].

The shift of p – p* bands to the longer wavelength region is the result of the

C = S bond being weakened and conjugation system being enhanced after

the formation of the complex [156]. NiLpy, NiLH2O, NiLa–pico, NiLb–pico

(L = L or L’) show shoulder bands at 16000 – 17094 cm–1 range. These d–d

spectral transitions are assigned to 'A1g → 'Eg and 'A1g → 'A2g [157]. The

d–d bands appearing as weak shoulders centred around 17000 cm–1 region

are typically of square planer Ni (II) complexes [158]. The presence of

intense p – p* and n – p* transitions cause the lower energy d–d bands and

LMCT bands to appear as weak shoulders. The bands at 23000 – 27933

cm–1 range correspond to L → M. It is associated with 'A1g → 'Eg

transition. No band below 10000 cm–1 confirms the planer structure of

these complexes. This is because of large crystal field splitting in square

planer complex the energy separation between dx²–y² and lower orbital is

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greater than 10000 cm–1 [53]. NiLa–pico and NiLb–pico (L = L or L’) show

broad band at 23000 – 26050 cm–1 range. This band may be due to

tetrahedral complex in addition to square planer complexes. This indicates

the probability of tetrahedral º square planer equilibrium in the

complexes. The electronic spectra of NiLbipy and NiLphen do not

resemble the spectra of five coordinate [153, 159] but resemble to pseudo –

octahedral Ni (II) complexes [53, 160].

In DSC thermograms of the complexes, a sharp endothermic

process corresponds to melting points and exothermic corresponds to

decomposition of the complex.

Two sharp peaks were observed in DSC thermogram of

NiLH2O. One peak corresponds to endothermic and another for

exothermic (Fig. 4.3.4.1, 4.3.4.2). The sharp endothermic peak at 171.81 °C

corresponds to the melting point of the complex. The exothermic peak at

295.0 °C corresponds to the decomposition of the complex.

In case of NiL’H2O also two sharp peaks were observed in

DSC thermogram, one peak corresponds to endothermic and another for

exothermic (Fig. 4.3.4.3, 4.3.4.4). The sharp endothermic peak at 175.0 °C

corresponds to melting point of the complex. The exothermic peak at

326.46 °C corresponds to the decomposition of the complex.

The TGA data of NiLH2O complex indicated that the

decomposition of the complex proceed in several steps. In between the

temperature 30 °C – 100 °C molecules of water of hydration were lost. One

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coordinated water molecule was lost between the temperature 100 °C and

117.86 °C. There are two breaks in curves due to decomposition of organic

ligand at 225 °C and 357.14 °C. The decomposition was complete and NiO

was formed at 732.14 °C.

The TGA data of NiL’H2O complex indicated that the

hydration of water molecules was lost in between temperature 30 °C –

100 °C. One coordinated water molecule was lost between the temperature

100 °C – 125 °C. There are two breaks in curves at 200 °C and 378.57 °C

due to evaporation of organic ligand. NiO was formed and decomposition

completed at 800 °C.

All spectral characterisations confirm the NiLH2O, NiLpy, Ni

L a/b pico (L = L or L’) complexes have square planer and for NiL bipy,

NiL phen complexes five coordinate pseudo–octahedral geometry with

thiosemicarbazones acting as ONS tridentate ligand and N–atom (s) of

heterocyclic base occupying the fourth (and fifth) coordination site about

the Ni (II) atom. The TGA curves indicated coordinated water molecule in

NiLH2O and NiL’H2O.

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Expected structures :

(Where B=H2O, pyridine, α/β-picoline)

N

N

Cl

O

NN NH2

SNi

CH3

N

N

Cl

O

NN NH

SNi

CH3CH3

Cl

O

NN NH2

SNi

N

N

CH3

Cl

O

NN NH

SNi

N

N

CH3CH3

112

Fig. 4.3.3.A : UV-visible spectrum of NiLH2O in DMF

Fig. 4.3.3.B : UV-visible spectrum of NiLPy in DMF

Fig. 4.3.3.C : UV-visible spectrum of NiLbipy in DMF

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Fig. 4.3.3.D : UV-visible spectrum of NiLphen in DMF

Fig. 4.3.3.E : UV-visible spectrum of NiLa-pico in DMF

Fig. 4.3.3.F : UV-visible spectrum of NiLb-pico in DMF

chapter 4 synthesis and spectral characterisation...

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