LAUSR

Abstract The electronic absorption and redox properties as well as the catalysis for water oxidation reaction (WOR) of an aqua-coordinated oxo-bridged diruthenium(III) complex trans(µ-O,OH2)-[Ru2(µ-O)(µ-CH3COO)2(bpy)2(H2O)2](PF6)2·3H2O ([1](PF6)2·3H2O; bpy = 2,2′-bipyridine) in aqueous media are reported. [1]2+ displays a visible absorption band at 566 nm ascribed to metal-to-metal charge transition (MMCT) within the Ru2O core. This visible band redshifts due to the deprotonation of the terminal aqua ligands of [1]2+ in alkaline solutions. [1]2+ shows proton-coupled electron transfer behaviors in aqueous solutions at pH 0–14. The oxidation of RuIIIRuIII in [1]2+ has successfully reached the higher oxidation states including RuIVRuIV and RuVRuV which are stabilized by the deprotonation of the terminal aqua ligands and are important for catalytic water oxidation. WOR catalyzed by [1]2+ in acidic solutions was studied using electrochemical and chemical oxidation. In the solution of [1]2+ at pH 1.0, the overpotential for WOR was ~0.38 V. A turnover number of 23 was obtained by using (NH4)2Ce(NO3)6 as the oxidant. A nucleophilic-attack catalytic mechanism was proposed.