Electrochemical characterization of Langmuir–Blodgett films from the ruthenium complex mer-[RuCl 3(dppb)(4-Mepy)

Abstract

Ruthenium complexes containing diphenylphosphine ligands serve as good catalysts in hydrogenation reactions, and may be used as precursors for other Ru complexes. Their properties may also be exploited in Langmuir–Blodgett (LB) films, which is the focus of the present paper. We report on electrochemical properties of LB films from the pure ruthenium (III) complex, mer-[RuCl 3(dppb)(4-Mepy)] (dppb=PPh 2(CH 2) 4PPh 2; 4-Mepy=4-methylpyridine) (Ru–Pic), and from mixtures of stearic acid (SA) and Ru–Pic. Y-type LB films from these materials were deposited on indium tin oxide (ITO) substrates and analyzed using cyclic voltammetry. The overall shape of the voltammogram was the same for LB films of pure Ru–Pic and mixed with SA, with the redox peaks being ascribed to the Ru III/II conversion. However, in the mixed film, the potentials for the cathodic and anodic peaks were shifted toward more anodic and cathodic potentials, respectively, and this is attributed to the presence of SA within the coordination sphere of Ru, consistent with Fourier-transform infrared spectroscopy (FTIR) measurements. Even though Ru–Pic films at the air/water interface are not true monolayers, LB films from pure Ru–Pic display higher electroactivity than the mixed films, owing to the absence of the insulating stearic acid matrix and to the greater roughness of the pure films.