The synthesis and! atomic structure of [Mn4O4L6](+)(CF3SO3-). 1(+)OTf(-) (L = diphenylphosphinate), is reported. This new model for the photosynthetic water oxidizing complex extends the known [Mn4O4](n+) cubane core type to the Mn-4(III,3IV) oxidation state. Synthesis of this cluster is achieved by one-electron oxidation of Mn4O4L6 (1) by molecular oxygen in a series of steps initiated by the protonation or silylation of one oxide bridge in 1.