Effects of redox-inactive metals on heterometallic manganese-oxido complexes

Abstract

Lewis acidic redox-inactive metal ions affect many chem. transformations of metal oxo compds., including electron transfer, hydrogen atom transfer, and oxygen atom transfer processes. Redox-inactive metals also play essential roles in both heterogeneous and biol. metal oxide catalysts such as the oxygen-evolving complex (OEC) of photosystem II, which contains a CaMn_4O_x cluster. A series of structurally related high oxidn. state heterometallic trimanganese dioxido clusters and a related series of trimanganese tetraoxido cubane clusters contg. redox-inactive metals of various charge were prepd. and structurally characterized. Electrochem. studies demonstrated that the redn. potentials of the clusters are linearly correlated to the Lewis acidity of the incorporated redox-inactive metal. Reactivity studies show that varying the redox-inactive metals in isostructural compds. also affects the rates of oxygen atom transfer from the clusters as well as hydrogen atom transfer to the clusters. These studies suggest that the Ca^2+ ion plays a role in modulating the redn. potential and oxygen atom transfer activity of the OEC during catalysis.

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