Spectroscopic and electrochemical study of dinuclear and mononuclear copper complexes with the bidentate ligand of the 2,2′-diquinoline series

Abstract

The newly synthesized complex (2) of copper(I) chloride with di-n-hexyl 2,2′-biquinoline-4,4′-dicarboxylate (L) was spectroscopically and electrochemically characterized. The X-ray diffraction study showed that the crystals of complex 2 consist of the dinuclear moieties [L2Cu1 2(μ-Cl)2] containing Cu2(μ-Cl)2 clusters. Spectrophotometric studies and ESI-mass spec-trometric measurements showed that after the dissolution of complex 2 in acetonitrile (AN) and N-methyl-2-pyrrolidone (NMP), the solution contained not only the dinuclear complexes [L2Cu1 2(μ-Cl)2] but also [L2Cu1]Cl, [LCu1Cl(Sol)], and [Cu1Cl(Sol)] (Sol is the solvent). The electrochemical data also confirm the conclusion that bridged dinuclear chloride complex 2 dissociates both in NMP and AN to form the tetrahedral bis-biquinoline complex [L2Cu1]Cl. In solutions of complex 2 in alcohols and N,N-dimethylformamide (DMF), only [L2Cu1]Cl and [Cu1Cl(Sol)] are present. In EtOH, AN, and DMF, [Cu1Cl(Sol)] undergoes disproportionation to [Cu11Cl(Sol)] and Cu0.