Proton-coupled redox properties and water oxidation catalysis of an aqua-coordinated (μ-oxo)diruthenium(III) complex

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(mu-O,OH2)-[Ru-2(mu-O)(mu-CH3COO)(2)(bpy)(2)(H2O)(2)] (PF6)(2)center dot 3H(2)O ([1](PF6)(2)center dot 3H(2)O; 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 (RuRuII)-Ru-III in [1](2+) has successfully reached the higher oxidation states including (RuRuIV)-Ru-IV and (RuRuV)-Ru-V 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 similar to 0.38 V. A turnover number of 23 was obtained by using (NH4)(2)Ce(NO3)(6 )as the oxidant. A nucleophilic-attack catalytic mechanism was proposed.

Automated summary

The aqua-coordinated oxo-bridged diruthenium(III) complex demonstrates electronic absorption properties, redox behavior, and catalytic capabilities for water oxidation reaction. The complex displays different visible absorption bands under different pH conditions and exhibits proton-coupled electron transfer behaviors at different pH values.