The electrochemical behaviour of dithiocarbamato complexes of palladium(II) in DMSO at the mercury electrode

Abstract

The reduction of palladium(II) dithiocarbamates at the mercury electrode in DMSO has been investigated using a number of electrochemical techniques. All the palladium dithiocarbamates gave similar polarograms with only one main reduction wave. Limiting currents varied linearly with ν h in the concentration range 0.20–1.0 m M and the electrode reaction was first order with respect to the depolarizer. Half-wave potentials were independent of ligand concentration over the range 2.0 m M to 0.128 M. Log-plot analyses gave linear plots with slopes indicative of a one-electron, quasi-reversible reduction. On examination by cyclic voltammetry, most of the complexes exhibited voltammograms consisting of seven peaks, four cathodic reduction peaks and three anodic oxidation peaks. In agreement with the results of polarography, cyclic voltammetry and chronoamperometry showed that, for the main reduction wave, electron transfer is essentially quasi-reversible: however, there was evidence for increasing departure from diffusion control and for the presence of an ECE-type reaction. The chemical reaction involves a dissociation to produce a palladium species more easily reduced than the palladium dithiocarbamate. For the five complexes investigated, rate constants for the chemical step showed a time dependence at electrolysis time above 3 s, consistent with an ECE mechanism. Exhaustive reduction of palladium dithiocarbamate at the mercury pool electrode gave non-integral n values (2> n>1), also in agreement with an ECE mechanism.