Dinuclear complexes contributing to softness of metal acceptors

Since emf measurements with amalgam electrodes have been used, in most studies of the stabilities of complexes between soft metal acceptors and halide ions a series of investigations of the kinetics of electrode reactions were accomplished with halide systems of metal ions in the Groups 11 and 12 in aqueous and/or DMSO solutions. The aim was to establish which complexes contribute to the exchange current density, i(o). Such measurements are found to be a very sensitive method for identifying dinuclear complexes that can display much higher charge transfer rate constants than mononuclear complexes can. From these results it can be stated that hard acceptors do not show any tendency to form dinuclear halide complexes, whereas soft acceptors are apt to do so. This fact leads to the conclusion that dinuclear complexes have a strong internuclear bond. In determinations of the overall stability constant beta(j) of a complex MLj there is an influence from a complex M2Lj with a constant beta(j)', resulting in the substitution of beta(j) for (beta(j) + 2a(j) beta(j)'), where a(j) = [M] when the ligand number n = (C-L - [L])/C-M has the value j. An approximate value of the association constant, K-ass, of the internuclear bond can be calculated from beta(j)' if beta(j) is known. On the basis of these measurements the most probable types of the internuclear bonds are discussed