Solvation Effect of Li+ on the Voltammetric Properties of [PMo12O40]3−. Part 2: Comparative Studies on the Preferential Solvation in Acetonitrile+S and Acetone+S Mixtures

For [PMo12O40]3−, the presence of Li+ produced a two-electron wave at nearly the same potential as the first one-electron wave in acetonitrile or acetone. The voltammetric behavior of [PMo12O40]3− in a binary mixture of acetonitrile and solvent S was compared with those in a mixture of acetone and S. When the donor number (DN) of S>20, the first two-electron wave was converted into one-electron waves in such binary mixtures. The conversion occurred at lower mole fractions of S in an acetonitrile+S mixture than in an acetone+S mixture. The 7Li NMR results showed that the preferential solvating ability of Li+ with S was greater in the former mixture. A linear relationship was found between the iso-solvation point xiso(S) and the reciprocal of the difference between the DNs of S and acetonitrile, which gave the basis to explain the anomalies observed for a mixture of acetonitrile and H2O.