ESTIMATION OF THE OUTER-SPHERE CONTRIBUTION TO THE ACTIVATION VOLUME FOR ELECTRON-EXCHANGE REACTIONS USING THE MEAN SPHERICAL APPROXIMATION

The outer-sphere contribution to the volume of activation of homogeneo us electron exchange reactions is estimated for selected solvents on t he basis of the mean spherical approximation (MSA), and the calculated values are compared with those estimated by the Stranks-Hush-Marcus ( SHM) theory and with activation volumes obtained experimentally for th e electron exchange reaction between tris(hexafluoroacetylacetonato)ru thenium(III) and -(II) in acetone, acetonitrile, methanol and chlorofo rm. The MSA treatment, which recognizes the molecular nature of the so lvent, does not improve significantly upon the continuous-dielectric S HM theory, which represents the experimental data adequately for the m ore polar solvents.