Intervalence Charge Transfer and Electron Exchange Studies of Dinuclear Ruthenium Complexes

Abstract

This chapter discusses the theory of mixed-valence systems and theory of electron exchange. In the case of strong coupling, for which it is no longer appropriate to use perturbation theory, the interaction of states is so great that bonding and antibonding potential energy curves result. Because the ground state is delocalized between metal ions, it is not strictly appropriate to describe the intervalence transition band of a class III complex as a metal-to-metal charge transfer transition. The metal-to-metal charge transfer (MMCT) designation is used for the sake of simplicity. The dependence of intervalence transition energy on the activation barrier to thermal electron transfer allows the solvent dependence of intervalence transitions to be understood in terms of relationships developed for the Marcus Theory of electron transfer. The Hush model is the preferred method of analysis of mixed valence complexes for the experimentalist because of its readily understandable derivation, its overlap with the Marcus theory of electron transfer, and the facility of its application. However, it is applicable only to weakly coupled class II complexes. A quantitative theory that is applicable to all mixed valence complexes is desirable.