Model compounds of the Mn cluster in oxygen-evolving complex of PSII

Six model compounds have been synthesized and used for probing the structural features of the Mn cluster in oxygen-evolving complex (OEC) of photosystem II (PS II). The model compounds contain Mn-2(mu -O)(2) and mu -O-mu -carboxylato di-manganese structural units, which offer Mn-Mn, Mn......Mn, and Mn-O (N) structural parameters consistent with the corresponding data of the OEC in PS II, implying that the Mn cluster in OEC may possess similar structural features. Two model compounds containing halide anion have been used for discussing the binding of Cl- to Mn in PS II. It is suggested that in the five S states, ligand exchange would lead to the ligation of chloride to Mn in the S states with Mn of higher valence.