Synthesis and characterization of copper(II) complexes with unsymmetrical quadridentate Schiff bases derived from β-diketone, diamine, and o-hydroxybenzaldehyde ligands

Abstract

Several copper(II) complexes with unsymmetrical quadridentate Schiff bases derived from β-diketone (acetylacetone, benzoylacetone), diamine (ethylenediamine, trimethylenediamine), and o-hydroxybenzaldehyde (salicylaldehyde, o-hydroxyacetophenone, 2-hydroxy-1-naphthalenecarbaldehyde) have been prepared and characterized. The physical properties (melting points, absorption maxima, absorption coefficients) of the unsymmetrical copper(II) complexes are intermediate between the corresponding symmetrical copper(II) complexes. One of the unsymmetrical complexes, trimethylene-N-(acetylacetoneiminato)-N′-salicylideneiminatocopper(II), has been subjected to a single-crystal X-ray analysis; the result verified the detailed structure in which the copper(II) atom assumes a distorted-tetrahedral co-ordination geometry, with a dihedral angle of 19.1 ° between two OCuN planes. The unsymmetrical copper(II) complexes react with ethyl isocyanate and with phenyl isocyanate to produce compounds substituted at the methine position of the β-diketonate moiety. The ligands were prepared by the reaction of the copper(II) complexes with gaseous hydrogen sulphide. The copper(II) complexes and the ligands have been characterized by elemental analyses, i.r., ¹H n.m.r., e.s.r., and electronic spectra.