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)(2)( H2O)(RuORuIV)-O-III(OH)(bpy)(2)](ClO4)(4) (bpy is 2,2'-bipyridine) has been characterized structurally by X-ray crystallography. Comparisons with [(bpy)(2)(H2O)Ru-III- ORuIII(OH2)(bpy)(2)](ClO4)(4) . 2H(2)O, [( bpy)(2)(ClRuORuCl)-O-III-Cl-IV(bpy)(2)](ClO4)(3) . H2O, and [(tpy)(bpy )(OsOOsIV)-O-III(bpy)(tpy)]Na(ClO4)(6) . 3H(2)O (tpy is 2,2':6',2 ''-t erpyridine) reveal that oxidation of Ru-III-O-Ru-III to Ru-III-O-Ru-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 bo nd distances at the bridge, and an increase in the H2O-Ru-O bridge-ang le. These changes are discussed in the context of the structural requi rements for O ... O coupling and Oz evolution in higher oxidation stat es. 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(-1) contribute significantly to the Raman spectra. Additional M-O-M bands are identif ied near 800 cm(-1) and, tentatively, near 130 cm(-1). It is not possi ble to assign bands to Ru-OH2 or Ru-OH stretches; bands at low energy appear to originate from modes that are highly mixed.