Photoredox Reactions of Mixed-Valence Compounds Induced by Intervalence Excitation

A variety of mixed-valence systems were shown to be photoactive in aqueous solution upon light absorption by the intervalence (IT) band. IT excitation leads to an electron transfer from a reducing to an oxidizing metal center. Co(III), Ru(III), Cr(III), and Os(III) complexes were used as electron acceptors while [Fe(CN) 6 ] 4- , [Ru(CN) 6 ] 4- , and [Os(CN) 6 ] 4- servede as electron donors. Inner- as well as outer-sphere systems were studied. The inner-sphere IT interaction was mediated by bridging cyanide ligands in binuclear complexes. Outer-sphere IT systems were formed by ion pairs of the oxidizing complexes as cations and the reducing hexacyanide anions. Light-induced metal to metal electron transfer was followed by secondary processes which yields stable photoproducts.