Resonance Raman (RR) and optical spectroelectrochemical titrations of the cis,cis-[(bpy)2Ru(OH2)]2O4+ ion (denoted [3,3] to indicate the formal oxidation state of the Ru−O−Ru unit) were made over the range 0.8−2.0 V vs Ag/AgCl in 0.5 M trifluoromethanesulfonic acid; the results revealed sequential accumulation of three higher oxidation states. Two of these states were identified by redox titration with Os(bpy)3 2+ as one-electron ([3,4]) and four-electron oxidized species ([5,5]); spectroscopic analysis of reaction products formed upon mixing the [3,3] and [5,5] ions indicated that the third oxidation state is a two-electron oxidized species ([4,4]). The [5,5] ion underwent first-order decay to the [4,4] ion with a rate constant, k ≃ 9.5 × 10-3 s-1, that was nearly identical with the catalytic turnover rate for O2 evolution, k cat ≃ 1.3 × 10-2 s-1 measured under comparable conditions. The [4,4] ion underwent degradation more slowly to the [3,4] ion, which was stable on these time scales. An analogue bearing 4,4‘-dimethyl-2,2‘-bipyridine ligands exhibited very similar behavior, except that the oxidation steps were shifted by ∼50 mV to lower potentials. 18O isotope labeling experiments on the underivatized complex established that there was no oxygen exchange at the bridging μ-oxo position during catalytic turnover. Frozen solutions of the [5,5] ion displayed unusual low-temperature spectroscopic features, including the following:  (i) a narrow g = 2.02 axial EPR signal exhibiting an apparent six-line hyperfine interaction from a minor component; (ii) a concentration-dependent broad rhombic EPR signal in mixtures also containing the [4,4] ion; and (iii) a concentration-dependent replacement of its characteristic ruthenyl RuO stretching mode at 818 cm-1 in the RR spectrum when chemically oxidized with Ce4+ by an 18O isotope sensitive set of three bands in the 650 cm-1 region. The RR spectrum of this new species is consistent with further coordination of the terminal oxo ligands by Ce4+ to form additional ligand bridges.

The cis,cis-[(bpy)(2)Ru(III)(OH(2))](2)O(4+) micro-oxo dimeric coordination complex is an efficient catalyst for water oxidation by strong oxidants that proceeds via intermediary formation of cis,cis-[(bpy)(2)Ru(V)(O)](2)O(4+) (hereafter, [5,5]). Repetitive mass spectrometric measurement of the isotopic distribution of O(2) formed in reactions catalyzed by (18)O-labeled catalyst established the existence of two reaction pathways characterized by products containing either one atom each from a ruthenyl O and solvent H(2)O or both O atoms from solvent molecules. The apparent activation parameters for micro-oxo ion-catalyzed water oxidation by Ce(4+) and for [5,5] decay were nearly identical, with DeltaH(++) = 7.6 (+/-1.2) kcal/mol, DeltaS() = -43 (+/-4) cal/deg mol (23 degrees C) and DeltaH(++) = 7.9 (+/-1.1) kcal/mol, DeltaS(++) = -44 (+/-4) cal/deg mol, respectively, in 0.5 M CF(3)SO(3)H. An apparent solvent deuterium kinetic isotope effect (KIE) of 1.7 was measured for O(2) evolution at 23 degrees C; the corresponding KIE for [5,5] decay was 1.6. The (32)O(2)/(34)O(2) isotope distribution was also insensitive to solvent deuteration. On the basis of these results and previously established chemical properties of this class of compounds, mechanisms are proposed that feature as critical reaction steps H(2)O addition to the complex to form covalent hydrates. For the first pathway, the elements of H(2)O are added as OH and H to the adjacent terminal ruthenyl O atoms, and for the second pathway, OH is added to a bipyridine ring and H is added to one of the ruthenyl O atoms.

Scanning electrochemical microscopy (SECM) was used to microfabricate and quantify diaphorase-pattemed glass surfaces. Deactivated circular and linear micropattems were produced at diaphorase-immobilized substrates by a localized surface reaction. The oxidation of Br~and Clã t a microelectrode generated a reactive species which deactivated the localized enzyme molecules at the substrate. The diaphorase-pattemed surfaces were characterized by SECM on the basis of detection of catalytic current of ferrocenylmethanol coupled with oxidation of NADH. The concentration of the immobilized diaphorase