Structural and Resonance Raman Studies of an Oxygen-Evolving Catalyst. Crystal Structure of [(bpy)2(H2O)RuIIIORuIV(OH)(bpy) 2](ClO4)4

The oxidized form of the blue dimer water oxidation catalyst [(bpy){sub 2}(H{sub 2}O)Ru{sup III}ORu{sup IV}(OH)(bpy){sub 2}](ClO{sub 4}){sub 4} (bpy is 2,2{prime}-bipyridine) has been characterized structurally by X-ray crystallography. Comparisons with [(bpy){sub 2}(H{sub 2}O)Ru{sup III}-ORu{sup III}(OH{sub 2})(bpy){sub 2}](ClO{sub 4}){sub 4}{center_dot}2H{sub 2}O, [(bpy){sub 2}ClRu{sup III}ORu{sup IV}Cl(bpy){sub 2}](ClO{sub 4}){sub 3}{center_dot}H{sub 2}O, and [(tpy)(bpy)Os{sup III}OOs{sup IV}(bpy)-(tpy)]Na(ClO{sub 4}){sub 6}{center_dot}3H{sub 2}O (tpy is 2,2{prime}:6{prime},2{double_prime}-terpyridine) reveal that oxidation of Ru{sup III}-O-Ru{sup III} to Ru{sup III}-O-Ru{sup IV} results in significant structural changes at the {mu}-oxo bridge. There is an increase toward linearity along M-O-M, a decrease in the M-O bond distances at the bridge, and an increase in the H{sub 2}O-Ru-O bridge angle. These changes are discussed in the context of the structural requirements for O...O coupling and O{sub 2} evolution in higher oxidation states. Resonance Raman spectra of these and related complexes reveal that internal ligand vibrations as well as overtone and combination bands of an intense, symmetrical M-O-M stretch at 360-400 cm{sup {minus}1} contribute significantly to the Raman spectra. Additional M-O-M bands are identified near 800 cm{sup {minus}1} and, tentatively, near 130 cm{sup {minus}1}. It is not possible to assign bands to Ru-OH{sub 2} or Ru-OH stretches; bands at low energy appear to originate from modesmore » that are highly mixed.« less