Electron-transfer properties of a series of bimetallic rhodium(I) and iridium(I) complexes

Abstract

The electron-transfer properties of [NBu₄][M₂(dcbmi)(CO)₄], [NBu₄][M₂(dcbmi)(cod)₂], (M = Rh or Ir) and [NBu₄][Rh₂(dcbmi)(CO)₂(PPh₃)₂](H₃dcbmi = 2-methylimidazole-4,5-dicarboxylic acid, cod = cycloocta-1,5-diene) were determined by electrochemical UV/VIS and infrared spectroelectrochemical, and synthetic investigations. Relatively easy oxidations, but no reduction processes, were observed in acetonitrile, methylene chloride or tetrahydrofuran. The effect of the solvent on the electron-transfer properties of these complexes is discussed and the spectroelectrochemical results establish the site of electron transfer. Surface effects are observed and for [NBu₄][Ir₂(dcbmi)(CO)₄] the growth of a conducting film has been monitored by cyclic voltammetry. Partial oxidation of [Ir₂(dcmbi)(CO)₄]^– results in formation of [NR₄]_0.5[Ir₂(dcbmi)(CO)₄](R = Bu or Pr). Isotropic conductivities, measured on pressed pellets at room temperature, were 8 × 10^–5 ohm^–1 cm^–1 for R = Pr and 2 × 10^–5 ohm^–1 cm^–1 for R = Bu. The synthesis of [ttf][Rh₂(dcbmi)(CO)₄](ttf = tetrathiofulvalene) and the mixed-valence species [Rh₂(dcbmi)(CO)₄] is also reported; the former exhibits solid-state conductive properties, presumably due to the ttf cation.