Spectroscopic and redox studies of some copper(II) complexes with biomimetic donor atoms: implications for protein copper centres

Abstract

The redox chemistry and e.s.r. spectra of a number of copper(II) complexes with nitrogen- and sulphur-donor ligands have been examined, including complexes with 2,2′-bi-imidazole, histamine, and cyclic and acyclic saturated amine and thioether ligands. The tetrahedral Cu^IIS₄ centre generated by γ-irradiation of single crystals of a thioacetamide complex of Cu^I has a low value of |A_∥|. Tetrahedral distortion of otherwise tetragonal copper(II) centres increases g_∥ and decreases |A_∥| for N-, S-, and O-donor ligands, and is a more effective source of reduction of |A_∥| than charge effects. The quotient g_∥/|A_∥| appears to be a convenient empirical index of distortion of the donor set from planar toward tetrahedral, indicating that most type I copper in proteins is tetrahedrally, rather than tetragonally, co-ordinated.