Synthesis and electrochemical characterisation of [Ru(bpy)3]3[P2W18O62]

Addition of [Ru(bpy)(3)][Cl(2)] to K(6)P(2)W(18)O(62).15H(2)O in aqueous solution resulted in the formation of the ionic complex [Ru(bpY)(3)](3)[P(2)W(18)O(62)]. The complex was characterised by elemental analysis, spectroscopic (UV-Vis, (31)P-NMR, IR spectroscopy) techniques and cyclic voltammetry. Solution phase studies gave a range of redox couples associated with the Ru(3+/2+) and bipyridine ligands of the cationic [Ru(bpy)(3)](2+) moiety and the tungsten-oxo framework of the associated Dawson parent heteropolyanion (HPA), [P(2)W(18)O(62)](6-). With 0.5 mM [Ru(bpy)(3)](3)[P(2)W(18)O(62)] in dimethylsulphoxide (DMSO) (0.1 M Bu(4)NPF(6)), precipitation onto the electrode surface occurs upon oxidation through the Ru(3+/2+) system. This results in the formation of the mixed anion salt, [Ru(bpy)(3)](3)[P(2)W(18)O(62)][PF(6)]. Enhanced levels of surface based processes are also observed in the voltammetry of [Ru(bpy)(3)](3)[P(2)W(18)O(62)] in DMSO (0.01 M Bu(4)NPF(6)) with the [P(2)W(18)O(62)](7-/8-) and RU(3+/2+) redox systems both exhibiting surface behaviour. Voltammetric studies of adsorbed films of [Ru(bpy)(3)](3)[P(2)W(18)O(62)] were performed in pHs of 2.0, 4.5 and 7.0. The film was found to exhibit the same solution pH dependence for the tungsten-oxo framework of the HPA with better stability towards redox cycling in pH 2.00 as compared to pH 7.00. Mechanically attached solid state films of [Ru(bpy)(3)](3)[P(2)W(18)O(62)] were formed on carbon macroelectrodes and the electrochemical behaviour of the microparticles was investigated in a variety of electrolytes. Upon redox switching between the Ru(2+/3+) redox states the solid-state charge-transfer processes are coupled to insertion/expulsion of anions from/to the aqueous solution phase. Scanning electron microscopy of the mechanically attached deposit, reveals that voltammetric cycling in 1.0 M HClO(4) through the redox processes associated with the tungsten-oxo framework converts the amorphous array of microscopically small particles into a plate-like semi-crystalline form. (C) 2003 Elsevier B.V. All rights reserved.