A new member of the Mn-oxo cubane core complex family [(Mn4O4L6)-O-2III,2IV] (1), where L = (p-MeOPh)(2)PO2-, has been synthesized and characterized. Compound 1 possesses structurally inequivalent Mn-III and Mn-IV with clear valence electron localization in the crystal phase, quite unlike the structurally equivalent sites, tetrahedral core symmetry, and delocalized valence of its analogue where L = Ph2PO2-. Compound 1 exhibits appreciable positive shifts (0.1-0.3 V) of both the oxidation and reduction electrochemical potentials, attributable to the remote electron donating p-MeO groups. Reduction of 1 by methanol yields a novel core complex [Mn-III O-4(2)(OMe)(2)(MeOH){(p-MeOph)(2)PO2}(6)] (2). Each Will of 2 is tetragonally distorted due to the Jahn-Teller effect with elongated Mn-O bonds that are directed at the two mu(3)-MeO bridges and neither of the two mu(3)-oxos. These electronically driven distortions provide a structural rationale for the greater basicity of the former sites and explain why 2 of the 4 corner oxos are preferentially reduced to water molecules.