Complex Formation of Co(II) with N-Benzenesulphonyl- L-Cysteine

Department of Pure Chemistry, Inorganic Chemistry Laboratory, University College of Science, 92, Acharya Prafulla Chandra Road, Calcutta-700 009, India

Manuscript received 8 November 1979, accepted 30 December 1979

pH-metric study of the reaction between Co(II) and N-benzene-sulphonyl-L­cysteine C₆H₅SO₂NHCH(COOH)CH₂SH indicated the formation of 1 : 1 and 1 : 2 metal : ligand complexes having the co-ordination patterns [CoNS] and [CoN₂S₂] respectively. Complete deprotonation of the -COOH group before the start of complex formation suggested non-involvement of this group in co-ordination. Stepwise formation constants (K₁ and K₂) and the successive acid dissociation constants (k_2NH, k_1NH) of the 1 : 2 complex have been evaluated by following the procedure of Irving and Rossotti. Values of logK₁, logK₂, pk_2NH and Pk_1NH are 6.03±0.03, 5.60±0.03, 11.55±0.04 and 13.30±0.04 respectively at 30±0.5°, in 50% (v/v) water-dioxan medium having ionic strength 0.50M (NaClO₄). The pk_COOH, pk_SH and pk_NH values of the ligand have been found to be 4.43±0.02, 11.05±0.02 and 13.44±0.04 respectively under identical condition.

Enhancement of acidity the imido (-NH-) group in the 1 : 2 complex indicated the formation of Co-N bonds. The extent of enhancement was, however, small compared to the corresponding Zn(II) compound (found pk_2NH, 8.20 and Pk_1NH 10.30), as probably Co(II) formed its best bonds with (Thiol) sulphur.