Synthesis, structure and electrochemical properties of a group of ruthenium(III) complexes of N-(aryl)picolinamide

Reaction of N-(aryl) picolinamide (HL-R; R = OCH3, CH3, H, Cl and NO2) with ruthenium trichloride or [Ru(DMSO)(4)Cl-2] in refluxing 2-methoxyethanol in the presence of a base (NEt3) affords tris complexes of the type [Ru(L-R)(3)]. The structure of the [Ru(L-OCH3)(3)] complex has been determined by X-ray crystallography. In these complexes the amide ligands are coordinated to the metal center as monoanionic bidentate N, N-donors. All the [Ru(L-R)(3)] complexes are one-electron paramagnetic and show rhombic ESR spectra at 77 K. They also show intense LMCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a ruthenium(III)/ruthenium(IV) oxidation within the range of 0.89 to 1.21 V vs. SCE and a ruthenium(III)/ruthenium(II) reduction within the range of -0.22 to -0.41 V vs. SCE. Representative one-electron oxidized and reduced complexes, viz. [Ru-IV(L-H)(3)](+) and [Ru-II(L-H)(3)](-), respectively, have also been generated in solution and characterized spectroscopically as well as electrochemically.