Synthesis, structure and redox properties of mixed ligand complexes of trivalent ruthenium with deprotonated 2-carbamoylpyridine derivatives and 2,2 '-bipyridine

Five mixed ligand complexes of trivalent ruthenium with general formula [Ru (L)(bpy)Cl-2], where L = p-substituted N-phenyl derivatives of 2-carbamoylp yridine and bpy = 2,2'-bipyridine, have been synthesised and characterised. X-ray crystal structural characterisation of a representative complex, i.e . where L = 2-(N-(4-nitrophenyl)carbamoyl)pyridine, shows that the amide-co ntaining ligand coordinates to the ruthenium(III) centre via the pyridyl ni trogen and the amidato nitrogen, forming a five-membered chelate ring. The complexes are paramagnetic (low spin d(5), S = 1/2) and show a single signa l in their EPR spectra in 1:1 dichloromethane-toluene solution at 77 K. In dichloromethane solution, these complexes show intense ligand to metal char ge transfer transitions in the visible region. All the complexes display tw o cyclic voltammetric responses, a ruthenium(III)-ruthenium(IV) oxidation i n the range from +0.63 to +0.93 V and a ruthenium(III)-ruthenium(II) reduct ion in the range from -0.63 to -0.73 V(vs ferrocene-ferrocenium couple). Th e potentials of both couples for all the complexes are found to be sensitiv e to the nature of the substituents present on the amide ligands, L. (C) 20 01 Elsevier Science Ltd. All rights reserved.