A novel ruthenium surfactant: electronic spectra, ZINDO analysis and Langmuir–Blodgett studies of trans-dichloro(6,6′-bis(N-dodecylbenzimidazol-2-yl)-2,2′-bipyridine)ruthenium(II)

Abstract

The complex, dichloro(6,6′-bis(N-dodecylbenzimidazol-2-yl)-2,2′-bipyridine)ruthenium(II), Ru(ddbbbpy)Cl₂ was prepared from the reaction of the free ligand and RuCl₂(Me₂SO)₄. Structural characterization of the compound by ¹H NMR revealed that 6,6′-bis(N-dodecylbenzimidazol-2-yl)-2,2′-bipyridine ligand lies symmetrically about the equatorial plane with the chlorides axial to each other. The electronic structure of the compound shows several ligand π–π* transitions in the ultraviolet and a broad d_π–p_π* MLCT manifold in the visible region of the spectrum. A ZINDO/S calculation reproduces, in some detail, the general features of the electronic spectrum of the title species. The electronic characteristics of the frontier orbitals are analysed. The parent neutral compound shows a fully reversible oxidation wave at −0.04 V vs. the Cp₂Fe⁺/Cp₂Fe couple in 0.1 M (C₄H₉)₄NPF₆/CH₂Cl₂. The low temperature (77 K) EPR spectrum of the one-electron oxidized product is typical for a rhombohedrally distorted Ru(III) complex with g values of 2.73, 2.20 and 1.82. Surface analysis of the parent complex as studied using Langmuir–Blodgett methods show a typical isotherm from which an area per molecule of 126 Ų can be derived. Thin films of the complex were readily transferred to quartz and indium doped tin oxide (ITO) plates. Thin films are conductive as indicated by the cyclic voltammetry of the complexes on ITO slides.