Hydrothermal and solid-state transformation of ruthenium-supported Keggin-type heteropolytungstates [XW11O39{Ru(ii)(benzene)(H2O)}]n− (X = P (n = 5), Si (n = 6), Ge (n = 6)) to ruthenium-substituted Keggin-type heteropolytungstates

A new pathway for the preparation of mono-ruthenium (Ru)(III)-substituted Keggin-type heteropolytungstates with an aqua ligand, [PW11O39Ru(III)(H2O)]4− (1a), [SiW11O39Ru(III)(H2O)]5− (1b) and [GeW11O39Ru(III)(H2O)]5− (1c), using [Ru(II)(benzene)Cl2]2 as a Ru source was described. Compounds 1a–1c were prepared by reacting [XW11O39]n− (X = P, Si and Ge) with [Ru(II)(benzene)Cl2]2 under hydrothermal condition and were isolated as caesium salts. Ru(benzene)-supported heteropolytungstates, [PW11O39{Ru(II)(benzene)(H2O)}]5− (2a), [SiW11O39{Ru(II)(benzene)(H2O)}]6− (2b) and [GeW11O39{Ru(II)(benzene)(H2O)}]6− (2c), were first produced in the reaction media, and then transformed to 1a, 1b and 1c, respectively, under hydrothermal conditions. Calcination of Ru(benzene)-supported heteropolytungstates, 2a, 2b and 2c, in the solid state produced mixtures of 1a, 1b and 1c with CO (carbon monoxide)-coordinated complexes, [PW11O39Ru(II)(CO)]5− (4a), [SiW11O39Ru(II)(CO)]6− (4b) and [GeW11O39Ru(II)(CO)]6− (4c), respectively. From comparison of their catalytic activities in water oxidation reaction, it was indicated that ruthenium should be incorporated in the heteropolytungstate in order to promote catalytic activity.