This renewal award is made in the Inorganic, Bioinorganic and Organometallic Chemistry Program in support of the research of Dr. Daniel Nocera. The thrust of the research is the photo-driven, two-electron oxidation-reduction reaction between metal centers in binuclear transition metal complexes. The research will include the synthesis of quadruply-bonded tungsten and molybdenum complexes, mixed-valence binuclear rhodium complexes, and layered vanadium and niobium phosphates intercalated with dimolybdenum and dirhodium cores. Photoexcited intermediates will be characterized by picosecond and nanosecond time-resolved excited-state spectroscopy with the ultimate objective of understanding the mechanisms of multi-electron processes. %%% Some of the chemical systems to be studied in this project are appropriate to energy-converting multi-electron transformations such as splitting hydrogen chloride into hydrogen and chlorine, while other systems will be used to prepare novel photoactive layered solids possessing multi-electron reactivity.