Synthetic cluster models of biological and heterogeneous oxygen evolving catalysts

Redox-inactive metals are found in biol. and heterogeneous water oxidn. catalysts, but their roles are currently not well understood. Targeting synthetic model clusters of these catalysts, triphenylbenzene moieties appended with pyridine and alkoxide donors were utilized as multinucleating ligands for first-row transition metals. Complexes of Mn^2+, Fe^2+, Co^2+, Ni^2+, Cu^2+, Zn^2+ were synthesized and found to display trinuclear cores supported by bridging alkoxides. Trimanganese complexes were used as precursors for more elaborate metal oxide clusters. Tetranuclear complexes displaying Mn_4, Mn_3Ca and other Mn3M and M'3M motifs (M=Na^+, Sr^2+, Zn^2+, Sc^3+, Y^3+; M'=Fe, Co) with varied no. of bridging oxo ligands were prepd. and studied. A significant variation of redn. potentials on the nature of the redox inactive metal was obsd. Implications to the function of the oxygen evolving complex of photosystem II and synthetic oxygen prodn. catalysts will be discussed.