[L2Mn2(.mu.-O)2(.mu.-O2)](ClO4)2. The first binuclear (.mu.-peroxo)dimanganese(IV) complex (L = 1,4,7-trimethyl-1,4,7-triazacyclononane). A model for the S4 .fwdarw. S0 transformation in the oxygen-evolving complex in photosynthesis

Light-driven oxidation of water to molecular oxygen in photosystem II (PS II) has been shown to occur at an active site comprising four manganese ions. There are five kinetically resolved intermediates in the catalytic cycle which have been designated S{sub 0} to S{sub 4}. S{sub 0} represents the most reduced and S{sub 4} the most oxidized level. Here the authors report the synthesis and x-ray structure of the first ({mu}-peroxo)dimanganese(IV) complex, (L{sub 2}Mn{sub 2}({mu}-O){sub 2}({mu}-O{sub 2}))(ClO{sub 4}){sub 2} (1) (L = 1,4,7-trimethyl-1,4,7-triazacyclononane), as a model for part of the S{sub 4} {yields} S{sub 0} transformation in PS II.