Preparation of tetrabutylammonium salt of a mono-Ru(III)-substituted α-Keggin-type silicotungstate with a 4,4'-bipyridine ligand and its electrochemical behaviour in organic solvents.

The tetrabutylammonium (TBA) salt of a mono-ruthenium(III)-substituted α-Keggin-type silicotungstate with a 4,4'-bipyridine (bipy) ligand, TBA5[α-SiW11O39Ru(III)(bipy)] (1), which is soluble in various organic solvents, was prepared by a cation exchange reaction of Cs5[α-SiW11O39Ru(III)(bipy)] with tetrabutylammonium bromide. Compound 1 was characterised using IR, (1)H-NMR, elemental analysis, single crystal X-ray analysis, X-ray absorption near-edge structure (XANES) analysis (Ru L3-edge), electron spin resonance (ESR), cyclic voltammetry (CV) and UV-Vis. Single crystal X-ray analysis of 1 revealed that the Ru(III) unit was incorporated into the α-Keggin-type silicotungstate framework and coordinated by a bipy molecule through a Ru-N bond. CV indicated that the incorporated Ru(III)-bipy was reversibly oxidised to the Ru(IV)-bipy derivative and reduced to the Ru(II)-bipy derivative in organic solvents. The redox potential of Ru(IV/III)-bipy was found to be affected by organic solvents. Moreover, the Ru(V)-bipy derivative was observed in acetonitrile.