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Mononuclear ruthenium complexes catalyse water oxidation with evolution of oxygen under homogeneous as well as heterogeneous conditions.

Glasses of sec-butyl chloride containing both naphthalene and pyrene were ..gamma.. irradiated to a dose of 2 x 10/sup 22/ eV/kg at 77/sup 0/K. The pyrene-cation yield is dependent on pyrene concentration but independent of naphthalene concentration. A simple model for capture of migrating holes is presented. Excited states of either solvent cations or solvent aggregate cations hop in a glass, losing the excitation energy. These are migrating holes. The resonant charge transfer occurs when the energy of the migrating excited state becomes as high as the energy levels of the highest occupied orbitals of the solute molecules. This model indicates that pyrene whose ionization potential is lower than that of naphthalene captures the hole before naphthalene does. (LK)

In quenching of the pyrene fluorescence by copper(II) ions in dodecyl sulfate micelles whose surface is covered by sodium and copper(II) ions, the pyrene-cation quantum yield decreases, after reaching a certain maximum yield, with increasing copper(II)-ion fraction. The decrease suggests that the micellar structure becomes unfavorable for electron transfer quenching as copper(II) ions displace sodium ions on the micellar surface.

An amide-bridged dinuclear ruthenium complex adsorbed on ion-exchange resins has been prepared and used as a solid phase catalyst in water oxidation to evolve oxygen.

Efficient visible light cleavage of water with simultaneous evolution of hydrogen and oxygen has been achieved by a system mimicking photosystem II, composed of CdS photoanode modified with a polymer membrane incorporating a highly active water oxidation catalyst.

Oxygen evolution by electrochemical water oxidation has been studied. The reaction was carried out through electrochemical water oxidation mediated by polynuclear complexes embedded in a Nafion film. The polynuclear complexes used were the µ-oxo-trinuclear ruthenium complex, [(NH3)5 RuORu(NH3)4ORu(NH3)5]Cl6 and [graphic omitted]. These complexes are effective as mediators for enhanced oxygen evolution. The mediated water oxidation has been demonstrated by potential vs. current characteristics and by oxygen analysis by gas chromatography.

Electrochemical and water oxidation studies have been carried out for the bridged complexes (1) and (2). [graphic omitted] Three consecutive reversible two-electron processes were shown to occur. Repeated continuous cyclic scans of the redox processes, however, led to the decomposition of the dimers to the monomeric complex. Visible spectra showed that the decomposition leads to the formation of cis-[Ru(bpy)–2(H2O)2]2+. The dimer complexes are stable at a Nifion-coated graphite electrode in their adsorbed state even on repeated cyclic scans of the redox processes. It was shown by gas chromatography as well as by mass spectroscopy that oxygen was evolved by water oxidation on adding CeIV ion to an aqueous solution of the dinuclear complex. The turnover number showed that the complexes worked as catalysts for water oxidation, although they suffer partial decomposition during the catalysis. The nitrite complex was more stable than the water complex against decomposition.

The electrochemical studies of a trinuclear ruthenium complex (Ruthenium red) have been carried out. Di- and tri-nuclear ruthenium complexes were adsorbed onto clay and ion-exchange resin and were then used as homogeneous and heterogeneous (clay-and resin-adsorbed) catalysts for water oxidation to evolve oxygen. The gas-chromatographic and mass-spectral data clearly show that oxygen evolved by water oxidation is catalysed by the polynuclear ruthenium complexes in the presence of CeIV oxidant. The turnover numbers and stabilities of the catalysts were evaluated under various conditions. The observed data show that the trinuclear ruthenium complexes are more efficient towards water oxidation than the dinuclear ruthenium complexes. Based on these results, the four-electron water oxidation process is discussed.