Hydrothermal and solid-state transformation of ruthenium-supported Keggin-type heteropolytungstates [XW ₁₁O ₃₉{Ru(II)(benzene) (H ₂O)}] ^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, [PW ₁₁O ₃₉Ru(iii)(H ₂O)] ^4- (1a), [SiW ₁₁O ₃₉Ru(iii)(H ₂O)] ^5- (1b) and [GeW ₁₁O ₃₉Ru(iii)(H ₂O)] ^5- (1c), using [Ru(ii)(benzene)Cl ₂] ₂ as a Ru source was described. Compounds 1a-1c were prepared by reacting [XW ₁₁O ₃₉] ^n- (X = P, Si and Ge) with [Ru(ii)(benzene)Cl ₂] ₂ under hydrothermal condition and were isolated as caesium salts. Ru(benzene)-supported heteropolytungstates, [PW ₁₁O ₃₉{Ru(ii)(benzene)(H ₂O)}] ^5- (2a), [SiW ₁₁O ₃₉{Ru(ii)(benzene)(H ₂O)}] ^6- (2b) and [GeW ₁₁O ₃₉{Ru(ii)(benzene)(H ₂O)}] ^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, [PW ₁₁O ₃₉Ru(ii)(CO)] ^5- (4a), [SiW ₁₁O ₃₉Ru(ii)(CO)] ^6- (4b) and [GeW ₁₁O ₃₉Ru(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.