Five-co-ordinate copper(II) complexes of the quadridentate Schiff-base ligand NN′-bis-(2-pyridylmethylene)ethane-1,2-diamine, and some related ligands

Abstract

Three classes of complexes of copper(II) with the quadridentate Schiff-base ligand (bpe) derived from pyridine-2-carbaldehyde and ethane-1,2-diamine are described: (a) Cu₂ bpe X₄(where X = Cl, Br, and NCS); (b) Cu bpe X′X″(where X′= X″= ClO₄ and Br, and X′= l, X″= ClO₄); and (c)[Cu₂ bpe₃](ClO₄)₄. Complexes of the first type appear to be polymeric, possibly based on a five-co-ordinate copper(II) stereochemistry. Evidence is given for the existence of the five-co-ordinate cations [Cu bpe X]⁺(where X = Br, I) in the solid compounds of type (b), and in solution in nitromethane (X = Cl, Br, l). Details are given of a reaction in which the compound Cu bpe (ClO₄)₂ reacts with alcohol solutions of a tetra-alkylammonium halide or thiocyanate to form five-co-ordinate compounds of the type [Cu(bpe,ROH)X]ClO₄(where R = Me, Et; and X = Cl, Br, l, NCS). One molecule of alcohol adds across only one of the Schiff-base CN groups. The rationalisation of this reaction by consideration of the steric requirements of the ligand is supported by a recent X-ray structural determination of one of the crystalline compounds. Compounds of the homologous Schiff-base ligand (bpt) derived from pyridine-2-carbaldehyde and propane-1,3-diamine, Cu bpt (ClO₄)₂ and [Cu bpt I] ClO₄ are also described.