Influence of oxygen and sulphur donor atoms on the electrochemistry of bis-chelates of nickel(II)

The comparative effects of oxygen and sulphur donor atoms upon the electrochemical behaviour of isostructural bis-chelates of nickel(II) has been investigated by d.c. and a.c. polarography in acetone. Substitution of oxygen by sulphur as a donor atom has been found to affect the redox processes both thermodynamically and kinetically. Thus, reductions of the oxygen based compounds occur at more negative potentials than do those of their sulphur analogues and are characterised by slower rates of heterogeneous charge transfer (k_s). Uncertainties in the relative magnitudes of k_s values due to double layer effects are minimised in this system as a result of the small potential range within which the E_1/2-values fall. Brief comments on a related NiS₂N₂ complex and on Ni(mnt)₂]^2? are also included for comparison purposes.