Thermal investigation and stereochemical studies of some cyclic ligand complexes of nickel(II), copper(II), zinc(II) and cadmium(II) in the solid state. Part 1

Abstract

Nickel(II), copper(II), zinc(II), and cadmium(II) complexes of N-methylmorpholine (Mmorph) and N,N′-dimethylpiperazine (DMP), with the compositions [Ni(Mmorph)Cl2], [2CuCl2 · 3Morph], [Zn(Mmorph)Cl2], [Ni(DMP)Cl2], [Cu(DMP)Cl2] · H2O, [Zn(DMP)-Cl2] and [Cd(DMP)Cl2], have been synthesized in order to carry out thermal investigations (TGA and DTA) and to study stereochemical changes during their thermal decomposition. Attempts to prepare a methylmorpholine complex of CdCl2 failed. Some intermediate complexes were isolated by the temperature arrest technique. Configurational and conformational changes were studied from elemental and thermal analyses, IR spectral data, and magnetic moment measurements. All the complexes of methylmorpholine and dimethylpiperazine appeared to be tetrahedral, except [2CuCl2 · 3Morph] which is octahedral and dimeric. The activation energy E*a, and the enthalpy ΔH and entropy ΔS changes for the dehydration and decomposition reactions were evaluated with some standard equations and are compared. The order of stability of the complexes with respect to the activation energy is also discussed. A linear correlation is found between E*a and ΔS for the dehydration and decomposition reactions of the complexes.