Synthesis, characterization and anion selectivity of copper (II) complexes with a tetradentate Schiff base ligand

Abstract

A new mononuclear Cu(II) complex, [CuL(ClO₄)₂] (1) has been derived from symmetrical tetradentate di-Schiff base, N,N′-bis-(1-pyridin-2-yl-ethylidene)-propane-1,3-diamine (L) and characterized by X-ray crystallography.The copper atom assumes a tetragonally distorted octahedral geometry with two perchlorate oxygens coordinated very weakly in the axial positions.Reactions of 1 with sodium azide, ammonium thiocyanate or sodium nitrite solution yielded compounds [CuL(N₃)]ClO₄ (2), [CuL(SCN)]ClO₄ (3) or [CuL(NO₂)]ClO₄ (4), respectively, all of which have been characterized by X-ray analysis.The geometries of the penta-coordinated copper (II) in complexes 2–4 are intermediate between square pyramid and trigonal bipyramid (tbp) having the Addition parameters (τ) 0.47, 0.45 and 0.58, respectively.In complex 4, the nitrite ion is coordinated as a chelating ligand and essentially both the O atoms of the nitrite occupy one axial site.Complex 1 shows distinct preference for the anion in the order SCN^- > N₃^- > NO₂^- in forming the complexes 2–4 when treated with a SCN^-/ N₃^-/ NO₂^- mixture. Electrochemical electron transfer study reveals Cu^IICu^I reduction in acetonitrile solution.