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-Polarographic half-wave potentials for the reduction of

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Half-wave potentials of the alkali metal cations and of Tl+, Cu+, Ag+, Zn2+, Cd2+, Cu2+, and Pb2+ as well as the potentials of Ag/0.01 mol dm™3 Ag+ electrodes in 22 nonaqueous solvents were used as a basis for investigating solvent effects on electrode potentials. The variations of half-wave potentials were found to be a function of Lewis-type donor-acceptor interactions including the concept of hard and soft acids and bases. Linear regression analysis of the data for the cations vs. the half-wave potentials of K+ and vs. the potentials of the Ag/0.01 mol dm™3 Ag+ ion electrodes made it possible to assign the change in half-wave potentials to either hard or soft interactions of the solvent molecules with the cations. Predictions of the change of electrode potentials of any of the cations studied are possible from the changes of the half-wave potentials of K+ or the changes of the electrode potential for the Ag/0.01 mol dm™3 silver ion electrode. On the basis of the observed correlations between half-wave potentials and the potentials of the Ag/0.01 mol dm™3 Ag+ ion electrodes it becomes possible to assign the nature of interactions for ambidentate solvents. Changes of half-wave potentials of soft cations in soft solvents can be employed to express the degree of softness of such solvents quantitatively. Solvent parameters that reflect changes of hard-hard interactions with cations and their ability to predict changes in half-wave potentials are also discussed.

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