Blue copper models. Spectroscopic and electrochemical studies of copper(II) complexes with new ligand systems containing sulphur and nitrogen donor atoms

Abstract

A Series of new polyfunctional ligands derived from the condensation of 1-isopropyl- or 1-phenyl-3-formyl-2(1H)-pyridinethione with aminoalkylthioalkylbenzimidazoles having alkyl chains of various lengths between the donor atoms and the corresponding copper(II) complexes have been synthesized and spectroscopically characterized. The complexes show marked structural variations according to the length of the alkyl chains of the ligans, square plannar, square pyramidal, trigonal bipyramidal, and distorted five-co-ordinate, and for one complex a wider range of distorted structures, including four- and five-co-ordinate, is accessible depending on the solvent and physical state. Electrochemistry in non-aqueous solvents indicates that the copper(II) complexes undergo a quasi-reversible one-electron reduction at markedly positive potentials, in the range from +0.23 to 0.35 V vs. saturated calomel electrode. The complete chemical reversibility of the Cu^II–Cu^I redox change has been tested by controlled-potential electrolysis. The five-co-ordinate complexes exhibit reduction potentials ≈ 0.1 V higher than the square-planer complexes, independently of their actual geometry, square pyramidal, trigonal bipyramidal, or intermediate between these.