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

Addition of [Ru(bpy)3][Cl2] to K6P2W18O62·15H2O in aqueous solution resulted in the formation of the ionic complex [Ru(bpy)3]3[P2W18O62]. The complex was characterised by elemental analysis, spectroscopic (UV–Vis, 31P-NMR, IR spectroscopy) techniques and cyclic voltammetry. Solution phase studies gave a range of redox couples associated with the Ru3+/2+ and bipyridine ligands of the cationic [Ru(bpy)3]2+ moiety and the tungsten-oxo framework of the associated Dawson parent heteropolyanion (HPA), [P2W18O62]6−. With 0.5 mM [Ru(bpy)3]3[P2W18O62] in dimethylsulphoxide (DMSO) (0.1 M Bu4NPF6), precipitation onto the electrode surface occurs upon oxidation through the Ru3+/2+ system. This results in the formation of the mixed anion salt, [Ru(bpy)3]3[P2W18O62][PF6]. Enhanced levels of surface based processes are also observed in the voltammetry of [Ru(bpy)3]3[P2W18O62] in DMSO (0.01 M Bu4NPF6) with the [P2W18O62]7−/8− and Ru3+/2+ redox systems both exhibiting surface behaviour. Voltammetric studies of adsorbed films of [Ru(bpy)3]3[P2W18O62] 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[P2W18O62] were formed on carbon macroelectrodes and the electrochemical behaviour of the microparticles was investigated in a variety of electrolytes. Upon redox switching between the Ru2+/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 HClO4 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.