Isomeric ruthenium(III) complexes of N-phenyl-2-pyridine carboxaldimine. Synthesis, characterization and electron-transfer properties

Abstract

Three geometric isomers of [RuCl₂L₂](ClO₄) (L=N-phenyl-2-pyridine carboxaldimine) have been isolated by stereoretentive oxidation of the corresponding isomeric ruthenium(II) complexes using Cl₂(g) as an oxidant, followed by the addition of aqueous sodium perchlorate. These complexes are paramagnetic (low-spin d⁵, S= ½) and display rhombic EPR spectra at 77 K. The electronic transition energies have been computed, using the observed g values, which agree well with the experimentally observed transitions in the IR region of the optical spectra. In addition to the ligand field transitions, all the complexes also show multiple charge-transfer transitions in the visible region. Each of the complexes display a reversible reductive response due to an Ru^III/Ru^II couple in the range 0.3-0.5 V versus SCE at a platinum electrode. Chemical reductions of these trivalent complexes by hydrazine revert almost quantitatively to the parent bivalent ruthenium complexes. In acetonitrile, RuCl₂L₂⁺ complexes act as mild oxidants.