Remarkable solvent effect on the structure and electrochemical properties of [M(bipyridyl)3](ClO4)3 (M = Co, Fe and Ru) films

In low dielectric constant media the electrooxidation of bipyridyl complexes of transition divalent metal cations, such us Fe(II), Co(II), and Ru(II) results in the precipitation of microcrystalline film on the electrode surface. In most solvents, the film is reversibly reduced. However, films formed in the presence of acetonitrile are electrochemically inactive over a large potential range. The morphology and crystallographic structure of solid phase formed on the electrode surface during the electrochemical oxidation of bipyridyl complexes of Co(II), Fe(II), and Ru(II) have been investigated by the scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier transformation-IR/horizontal attenuated total reflectance (FT-IR/HATR) spectroscopy and elemental analysis. A correlation between the electrochemical properties and the structure of the film has been found. The electrochemically inactive films of Co(II) and Fe(II) complexes formed in the presence of acetonitrile in solution consist of densely packed column-like crystallites. They exhibit monoclinic symmetry P/2m (no. 10). The other films formed in acetonitrile free solutions, form flower-like aggregates of orthorhombic symmetry Pmmm crystals (no. 47). These films are very porous.