Chemistry of [Ru(tpy)(pap)(L′)n+ (tpy = 2,2′,6′,2"-terpyridine; pap = 2-(phenylazo)pyridine; L′ = Cl-, H2O, CH3CN, 4-picoline, N3-; n = 1,2.: X-ray crystal structure of [Ru(tpy)(pap)(CH3CN)](ClO4)2 and catalytic oxidation of water to dioxygen by [Ru(tpy)(pap)(H2O)]2+

The reaction of [Ru(tpy)Cl-3] with pap has afforded [Ru(tpy)(pap)Cl](+) which has been isolated and characterized as the perchlorate salt. Treatment of [Ru(tpy)(pap)Cl](+) with Ag+ in aqueous solution gives [Ru(tpy) (pap) (H2O)](2+). This aquo-complex has been reacted with three monodentate ligands (L' = CH3CN, 4-picoline and N-3(-)) to afford complexes of type [Ru(tpy)(pap)(L')](n+). Structure determination of [Ru(tpy)(pap) (CH3CN)](ClO4)(2) by X-ray crystallography shows that tpy is coordinated to ruthenium in the usual meridional fashion and the pap ligand is bound to ruthenium with the ate-nitrogen trans to CH,CN. All these complexes except [Ru(tpy)(pap)(H2O)](2+) show a Ru(II)-Ru(III) oxidation in the range 1.11-1.50 V vs SCE and three ligand(pap/tpy)-based reductions on the negative side of SCE. The aquo-complex Shows a Ru-II-OH2/Ru-IV=0 couple in aqueous solution (pH = 1-4), the E degrees of this oxidation is estimated to be 0.82 V vs SCE. Attempt to chemically oxidize the aquo-complex by Ce4+ in aqueous solution (1 M HClO4) results in the catalytic oxidation of water to dioxygen. (C) 1998 Elsevier Science Ltd. All rights reserved.