Theoretical study of electronic structures of [(H2O)3(O-)Mn(mu-oxo)2Mn(OH2)4]q+ (q = 2 or 3) with Mn-O bond.

Molecular geometries and electronic structures of manganese binuclear complexes, [(H(2)O)(3)(O-)Mn(bis-mu-oxo-O(2))Mn(OH(2))(4)](q+) (q = 2 or 3), which are model complexes of the S(3) state in the Kok cycle of OEC, were examined using hybrid density functional theory and broken symmetry method. The complexes of q = 2 and 3, which have a Mn-O bond, correspond to those derived from Mn(2)(II,III) and Mn(2)(III,III) at the S(0) state of the Kok cycle. The conformers with the Mn-O bond axial to the Mn(2)O(2) core are lower in energy than those with the equatorial Mn-O bond.