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

Abstract

Reaction of N-(aryl)picolinamide (HL–R; R = OCH₃, CH₃, H, Cl and NO₂) with ruthenium trichloride or [Ru(DMSO)₄Cl₂] 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.