Binuclear Copper(II), Nickel(II) and Cobalt(II) Complexes with N₂O₂ Chromophores of Glycylglycine Schiff-Bases of Acetylacetone, Benzoylacetone and Thenoyltrifluoroacetone

Abstract

Binuclear copper, nickel and cobalt complexes of the Schiff-bases obtained by condensation of glycylglycine with acetylacetone, benzoylacetone, dibenzoylmethane and thenoyltrifluoroacetone were prepared by template synthesis. The complexes were characterized by elemental analysis, conductivity measurements, magnetic moments, i.r., u.v.–vis. spectra, e.s.r., X-ray diffraction, t.g.a., d.t.a. and d.s.c. thermal analysis. All the complexes are non-electrolytes with low magnetic moments that indicate spin–spin or antiferromagnetic exchange interactions. Spectral properties support square planar and square pyramidal or trigonal bipyramidal structure provided by the N₂O₂ chromophores. E.s.r. spectra of the copper complex confirm the binuclear structure and the presence of magnetic interaction. Thermal studies supported the chemical formulation of these complexes and showed that they decompose in three to four steps depending on the type of ligand. Activation energies E_a and enthalpies ΔH, associated with the thermal decomposition of the complexes were calculated and correlated with the type of complexed metal. A mechanism for thermal decomposition is proposed for the complexes.