Synthetic and electrochemical studies of heterometallic manganese oxido complexes

Abstract

Redox-inactive metals are important in both biol. electron transfer reactions and in heterogeneous catalysis. A series of high oxidn. state mixed-metal trimanganese dioxido and tetraoxido clusters with incorporated redox-inactive metals of various charge (M = Na^+, Ca^(2+), Sr^(2+), Zn^(2+), Y^(3+), Sc^(3+)) were synthesized. Structural characterization of these clusters using single crystal X-ray diffraction demonstrated that the dioxido clusters contain a conserved [Mn_3M(m_4-O)(m_2-O)] core, while the tetraoxido clusters are contain [MMn_3O_4] cubane clusters of relevance to the cuboidal subsite of the oxygen-evolving complex (OEC) in photosystem II. Electrochem. studies of these cluster show that the redox potentials are linearly correlated to the Lewis acidity of the redox-inactive metal, spanning a window of ca. These results suggest that the Ca^(2+) ion modulates the potential of the OEC, and that other redox-inactive ions may be used to tune the redox potentials of heterogeneous electrocatalysts.