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Two mononuclear ruthenium(II) complexes of the types [Ru(trpy)(HL 1 )-(OH 2 )] 2+ (1 Aq ) and [Ru(trpy)(L 2 -κ-N 2 O)] (2) [where trpy = 2,2′:6′,2″-terpyridine, HL 1have been synthesized and thoroughly characterized by analytical and spectroscopic [UV−vis, NMR, high-resolution mass spectrometry, and IR] techniques. Complex 1 Aq has been further characterized by X-ray crystallography. In an acidic aqueous medium (pH 1), complex 2 undergoes carboxylate/water exchange readily to form an aqua-ligated complex, [Ru(trpy)(H 2 L 2 -κ-N 2 )(OH 2 )] 2+ (2 Aq ), having a dangling carboxylic group. This exchange phenomenon has been followed by IR, 1 H NMR, and UV−vis spectroscopic techniques. Electrochemical analyses of 1 Aq and 2 Aq (Pourbaix diagram) suggest the generation of a formal Ru V O species that can potentially promote the oxidation of water. A comparative study of the water oxidation activity catalyzed by 1 Aq and 2 Aq is reported here to see the effect of a dangling carboxylic group in the catalytic performance. Complex 2 Aq shows an enormously higher rate of reaction than 1 Aq . The pendant carboxylic group in 2 Aq participates in an intramolecular O−O bond formation reaction with the reactive formal Ru V O unit to form a percarboxylate intermediate and provides an electron-deficient carbon center where water nucleophilic attack takes place. The isotope labeling experiment using 18 O-labeled water verifies the attack of water at the carbon center of the carboxylic group rather than a direct attack at the oxo of the formal Ru V O unit. The present work provides experimental evidence of the uncommon functionality of the carboxylic group, the oxide relay, in molecular water oxidation chemistry.

Bulk CuAlO 2 with the delafossite structure was processed using two different methods. In one case, stoichiometric CuAlO 2 powder was processed using the solution technique, and consolidation was carried out by pressureless sintering in air. In the second case, high purity starting powders of alumina and copper (I) oxide were consolidated by spark plasma sintering. The sintered body was then subjected to a high temperature anneal in air. Reduction of the bulk CuAlO 2 samples resulted in a novel composite microstructure with copper forming a continuous intergranular phase. The prior CuAlO 2 grains decomposed into an intimate two-phase mixture of metallic copper and h-alumina. The scale of the composite structures ranged from nanometers to microns. Previous work on the delafossite family has focused primarily on the electronic properties of thin films. The present study suggests that the reduction of this class of mixed oxides gives rise to metal-ceramic structures with unique interfacial and morphological properties.

Cerium(IV)-driven water oxidation catalysis mediated by a mononuclear ruthenium(III) complex, [Ru(L)(pic) 3 ] (H 3 L = 2,2′-iminodibenzoic acid, pic = 4-methylpyridine), has been demonstrated in this work. The mechanistic details of water oxidation have been investigated by the combined use of spectroscopy, electrochemistry, kinetic analysis, and computational studies. It was found that water oxidation proceeds via formal high-valent Ru VII species. The capability of accessing such a high-valent state is derived from the non-innocent behavior of the anionic tridentate ligand frame which helps in accumulation of oxidative equivalents in cooperation with metal center. This metal−ligand cooperation facilitates the multi-electron-transfer reaction such as water oxidation. Kinetic analysis suggests water oxidation at a single site of Ru where O−O bond formation occurs via radical−radical coupling pathway between the oxygen atom of ruthenium-oxo species and the oxygen atom of the hydroxocerium(IV) ion.