SOLVENT INFLUENCES ON ELECTRON-TRANSFER REACTIONS

The term (1/n(2) - 1/epsilon(s)) for the solvent dependence of electron-transfer rates in transition-state theory is replaced by S', of the united solvation model (USM) to estimate the influence of nonspecific solvation on the rates. The equation Delta G(double dagger) = PS' + W is derived. Specific interactions with the solvent are accommodated by adding appropriate terms for the donor-acceptor interaction to this equation. In this manner, electron-transfer rates of several metallocene systems are correlated without the need of any solvent friction correction. In addition to fitting the data, the USM analysis results in a detailed model for the influence of solvent on a reaction coordinate with effects from coordination, solvent polarity, and coupled anion migration contributing to the electron-transfer reactions.