Synthesis and characterisation of novel ruthenium multi-substituted polyoxometalates: α,β-[SiW 9O 37Ru 4(H 2O) 3Cl 3] 7−

Abstract

Novel ruthenium multi-substituted polyoxometalate compounds of general formulae K 6Na[SiW 9O 37Ru III 4(H 2O) 3Cl 3]· nH 2O (α- and β-SiW 9O 34 isomers) were synthesised via the reactions of the trilacunary Keggin α- and β-[SiW 9O 34] 10 − anions with RuCl 3 in aqueous solution. Characterisation was performed by analytical, spectroscopic, magnetic, and electrochemical techniques. The results are in accordance with the new polyoxometalates having the trivacant Keggin anion (α or β isomer) linked to a cubane-type Ru 4O 4 cluster. The co-ordination sphere of ruthenium is completed with water molecules and chloride anions. Magnetic measurements showed that the majority of the molecules have the Ru ions cluster in a compensated configuration constrained to an antiferromagnetic alignment at very low temperature and following a Curie-Weiss like behaviour. For both isomers, cyclic voltammetry revealed quasi-reversible redox processes at the ruthenium centres, namely Ru IV/III and Ru III/II, which were found to be pH dependent. The novel polyoxotungstates incorporate the highest content of ruthenium (W:Ru = 2.25:1) ever reported for Keggin-, Dawson or sandwich-type transition metal-substituted polyoxometalates and may find promising applications as oxidative catalysts.