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

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, [Ru-3(mu(3)-O)(mu- CH3CO2)(6)(L)(2)(C2PY)]ClO4, where C2PY = {NC5H4CH2NHC(O)(CH2)(2)S-}(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)(4)NPF6/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 3a and 4b on Au(111) electrodes (4a/Au and 4b/Au) exhibit a single reversible redox wave, ascribed to the Ru,(III,III,III/II,III,III) redox process for the surface-attached clusters. The redox potential and the shape of the cyclic voltammograms of Ru, cluster modified SAMs were affected by the kind of terminal ligands and supporting electrolytes. (C) 1999 Elsevier Science S.A. All rights reserved.