Synthesis and electrochemical characterization of self-assembled monolayers of redox-active oxide-bridged triruthenium(III) clusters on Au(111)

Abstract

Novel self-assembled monolayers of oxide and acetate-bridged triruthenium(III) complexes have been prepared on Au(111) electrode surface. Parent discrete triruthenium(III) complexes with a terminal disulfide ligand, [Ru3(μ3-O)(μ-CH3CO2)6(L)2(C2PY)]ClO4, where C2PY={NC5H4CH2NHC(O)(CH2)2S–}2, L=4-methylpyridine (mpy, 4a) and 1-methylimidazole (MeIm, 4b), were isolated through multistep synthesis. Complex 4a exhibits three reversible redox waves, while complex 4b exhibits two reversible and one irreversible redox waves in (n-C4H9)4NPF6/CH3CN, all ascribed to one-electron redox of the triruthenium cluster core. In aqueous solution containing a 0.1 M supporting electrolyte (NaClO4 or Na2SO4), self-assembled monolayers of 4a and 4b on Au(111) electrodes (4a/Au and 4b/Au) exhibit a single reversible redox wave, ascribed to the Ru3(III,III,III/II,III,III) redox process for the surface-attached clusters. The redox potential and the shape of the cyclic voltammograms of Ru3 cluster modified SAMs were affected by the kind of terminal ligands and supporting electrolytes.