REDUCTION OF CADMIUM(II) IN PRESENCE OF MIXED LIGANDS AT D.M.E.

Abstract

Polarographic analysis of the electrode behaviour of cadmium(Memalonate-thiocyanate and cadmium(II)  succinate,thiocyanate systems have been made in aqueous medium at 25 ± 0 . 1°C. Two  mixed complexes [Cd (MAL) (SCN)1 - and [Cd (MAL): (SCN)13- and [Cd (SUCC) (Sat  and [Cd (SUCC) (SCN)] 3- were observed in both the systems, where MAL = malonatc,  SCH = thiocyanate and SUCC = svccinate ions. Their log stability constants came out  to be 3. 08, 3.57 and 2- 91, 2.50 respectively. These complexes were found to undergo reversible  reduction at d.m.e. in the presence of 3 - 0 M ionic strength and 6. 6 pH. The negative values of the  stability constants for [Cd (MAL) (SCN) 21 2- and [Cd (SUCC) (SCN:12- indicate the absence of these  species. It is observed that the mixed ligind complexes have higher stabilities than would be predicted  on statistical considerations. The observed enhancements of the complexation constant of the mixed  complex species were attributed to the possibilities of (i) some weak bonding between unlike bound  ligands and (ii) the gross statistical effects .