Biomimetic approach to the oxygen evolving center: resonance Raman investigation of a manganese mu-oxo dimer in three oxidation states

A biologically relevant dinuclear manganese mono-mu -oxo complex with a bou nd phenolate ligand in three oxidation states, (III,III), (III,TV) and (IV, IV), was studied using resonance Raman spectroscopy. Depending upon the exc itation frequency, phenolate vibrations or mu -oxo vibrations were enhanced , which allowed us to assign the UV-visible absorption spectra. In the case of the mixed valence species (III,IV), the mu -oxo vibration at 854 cm(-1) has been assigned by isotopic substitution ((H2O)-O-18) to v(as)(Mn-O-Mn). This preferential enhancement of the asymmetric vibration stresses the asy mmetric character of the bridge.