Structure and properties of copper-(II) and -(I) complexes with 2,6-bis[2-(thiophen-2-ylmethylimino)ethyl]pyridine

Abstract

Positive-ion FAB mass spectroscopy, elemental analysis, EPR spectroscopy and X-ray diffraction analysis have revealed the structure of the copper(II) complex of 1 : 2 (Cu : L) stoichiometry obtained by mixing in methanol 1 equivalent of Cu(ClO₄)₂·6H₂O and 1 equivalent of 2,6-bis[2-(thiophen-2-ylmethylimino)ethyl]pyridine (L). The copper(II) ion is co-ordinated to six nitrogen atoms in an octahedral arrangement not involving the thiophene S atoms. The planes of the two trans pyridine subunits are perpendicular (94°); the Cu–N bond distances are 1.924 and 1.983 Å for the pyridine, 2.098, 2.118 and 2.284, 2.330 Å for the imine indicating slight distortion in the structure. Cyclic voltammetry in acetonitrile showed reversible behaviour for the [Cu^IIL₂]²⁺-[Cu^IL₂]⁺ couple, and the redox potential E was –0.61 V vs. 10 mmol dm^–3 Ag–Ag⁺ in MeCN. Spectroscopic investigation of acetonitrile solutions having a 1 : 1 Cu : L molar ratio indicated the formation of species with 1 : 1 overall stoichiometry. The electrochemical measurements revealed that these complexes decompose during the electron transfer leading to the [Cu^IIL₂]²⁺–[Cu^IL₂]⁺ redox process.