Spectral Studies on Cobalt (II) and Nickel (II) Complexes of Bis(1-Phenyl Tetrazoline)-5,5’-Disulphide

R. N. Pandey*,  A. K. Nag, Prasashti Pande and Sanjay K. Singh

P.G. Center of Chemistry (MU), College of Commerce, Patna - 800 020 (India).

Bis(1-phenyl tetrazoline)-5,5’-disulphide forms stable complexes having general formula [CoA2 (ligand) 2] X and [Ni(H2O) 4 (ligand) 2] X (A = CH3COO – and H2O, X = ClO4 -, NO3 -, SO4 - -) at pH = 6. Cobalt (II) complexes are square planar having magnetic Bis (1-phenyl tetrazoline) –5,5’-disulphide forms stable complexes having general moment 2.74 – 2.76 BM. Sub-normal magnetic moment of octahedral Ni (II) complexes observed between 1.47 – 1.66 BM indicates square planar and octahedral equilibrium. The ligand field parameters n2 /n1 = 1.61, B’ = 764.9 cm-1, 10 Dq = 9943.7 cm-1 and B = 0.96 cm-1 also supports octahedral structure. IR spectra suggest bonding through one of the disulphide sulphur of ligand.

Heterocyclic organic disulphide; spectral properties Ni(II) and Co(II) complexes

Introduction

Organic disulphides are very important class of organic compounds of great biological significance¹. They have unique and interesting insights into structure and bonding and used as ligands by several workers^2-6. The present study describes the complexes of Co(II) and Ni(II) with heterocyclic organic disulphide, bis(1-phenyl-tetrazoline)-5,5’-disulphide (Fig I)

Figure 1: DST Click here to View figure

Experimental

All chemicals were chemically pure grade. The ligand was prepared by the method described earlier⁷. Complexes were prepared using a general method. Alcoholic solution of metal salt was mixed ligand solution in benzene using appropriate molar ratios. The reaction mixture was then refluxed on water-bath and the volume of solution mixture reduced to ca.40 mL by evaporation. The complexes formed were digested on water bath for half an hour, centrifuged, washed with ice-cold ethanol and dried at 110^oC in an electric oven.

Electronic absorption spectra of the complexes were recorded with the help of Cary, Model 17D Spectrophotometer n nujol mull. The magnetic measurements on all solid complexes were made at room temperature (300K) on the gouy balance. Calibration was done using Hg[Co(NCS)₄] as standard. The conductivity of complexes were measured in DMF(10^-3M) solution with the help of a systronic conductometer. Carbon, hydrogen and nitrogen analysis and IR spectra were recorded at CDRI, Lucknow. Analytical and physical data of complexes are given in TABLE 1.

Results and Discussion

Bis(1-phenyl tetrazoline)-5,5’-disulphide forms stable coloured solid having general formula [CoA₂(DST)₂]X and [Ni(H₂O) ₄ (DST) ₂] X (A=CH3COO^–&H₂O, X=ClO₄ ^–,NO₃ ^–,SO₄^–) at PH=6. All complexes are insoluble in common organic solvents but fair solubility was attributed in DMF and solution of complexes in DMF (10^-3M) supports their formulation⁸ (Table 1) . The magnetic moment of Co(II) complexes were found to be 2.74- 2.76 BM which corresponds square planar in structure⁹. A very intense absorption band at 27027 cm^-1 in Co(II) complexes is assigned to charge transfer band either due to M→L or L→M. However, strong absorption bands at 16666 cm^-1 and at 14285 – 14766 cm^-1 indicate that these Co(II) complexes are square planar ¹⁰ and the bands are assigned due to 2A₁g→ B₁g and 2A₁g→2B₁g translations respectively.

The magnetic moment of Ni (II) complexes observed between 1.47-1.66 BM is intermediate between zero (square planar) and 2.83 BM (octahedral) probably due to square planar and octahedral equilibrium ¹¹. Similar observations have been reported by Saha etal ¹² and Benzer and Co-workers ¹³. If two water molecules associated with each Ni(II) ion revert to uncoordinated form to coordinated form and vice-versa then square planar and octahedral equilibrium is probable.

Electronic spectral bands and their assignment of Ni(II) complexes has been given in TABLE 2. All complexes display three major bands ¹⁴of weak intensity. This is the characteristic of octahedral Ni(II) complexes. The ν₁/ν₂ value lies between 1.61-1.64 supports the octahedral geometry to complexes and suggest a strong configuration interaction between the high spin T₁g (P) and T₂g(F) excited state. The value of â in the range 0.84-.96 puts the ligand (DST) towards the strong end of the nephelauxetic series. Schaffer et al ¹⁵ and Jorgensen¹⁶ have pointed out that ligands which coordinate through sulphur cause very pronounced nephelauxetic effects. Thus, coordination through sulphur may be suggested. It may be further noted that the v₂ band is calculated to be equal to 12 D_q + 15 B’, which is equal to 23405 cm^-1 in the case of [Ni(H₂O)₄(DST) ₂]SO₄. This is in good agreement with the observed band at 23239 cm^-1. The other ligand field parameters ν₂/ν₁=1.61, B’=764.9 cm^-1, 10 Dq = 9943.7 cm^-1 and β = 0.96 of the complex also supports the octahedral structure ¹⁸.

Table 1: Analytical and physical data of complexes