Synthesis and properties of heterometallic cluster models of biological and heterogeneous water oxidation catalysts

Heterometallic clusters are found in biol. and heterogeneous water oxidn. catalysts, but the roles of different metal sites are currently not well understood. Targeting rational syntheses of models for these catalysts, triphenylbenzene moieties appended with pyridine and alkoxide donors were employed as multinucleating ligands for first- row transition metals. Trinuclear complexes were utilized as precursors to more elaborate metal oxide clusters. Tetranuclear complexes displaying Mn_3M and Fe_3M motifs (M = Na^+, Ca^(2+), Sr^(2+), Zn^(2+), Sc, Y^(3+)) with varied no. of bridging oxo ligands were synthesized and studied. The redn. potentials of these clusters span a window of over 1 V. With the pK of metal (M) aqua complex as a measure of Lewis acidity, structurally analogous series of clusters display linear dependence between redn. potential and acidity. Implications for the function of oxygen evolving catalysts will be discussed