Chapter 7: Electron Transfer Reactions of Metal Complexes

Reactions in which a metal complex donates or receives electrons to or from another compound or an electrode are called oxidation and reduction reactions, respectively, or redox reactions together. In terms of electrons, oxidation and reduction reactions are electron transfer reactions between a metal complex and another compound or an electrode. In this chapter, the basics of electrochemistry are briefly introduced before the electron transfer reactions of metal complexes are described. Metal elements, especially transition metal elements, have multiple oxidation states, and therefore, metal complexes exhibit a variety of redox and electron transfer reactions. As for electron transfer reactions between metal complexes, a reaction in which electrons are transferred from one complex to another without any changes in the coordination sphere of the metal complexes is called an outer-sphere electron transfer mechanism. On the other hand, an inner-sphere electron transfer mechanism is one in which electrons are transferred with substitution of ligands in the coordination sphere, usually through a bridging ligand. This chapter discusses the mechanisms of the outer- and inner-sphere electron transfer mechanisms, Marcus theory, and mixed-valence complexes, which are closely related to electron transfer reactions.