THERMAL INVESTIGATION AND STEREOCHEMICAL STUDIES OF SOME CYCLIC LIGAND COMPLEXES OF NICKEL(II), COPPER(II), ZINC(II) AND CADMIUM(II) IN THESOLID-STATE .2.

N-methylmorpholine (Mmorph) and N,N'-dimethylpiperazine (DMP) complexe s of nickel(II), copper(II), zinc(II) and cadmium(II) were synthesized . Thermal investigations were carried out and the stereochemical chang es that occur during the thermal decomposition reactions were studied. The complexes were found to have the following compositions [Ni(Mmorp h)Br2] . H2O, [Cu(Mmorph)Br2] . H2O, [Zn(Mmorph)2Br2], [Ni(DMP)2(H2O)2 Br2], [Cu(DMP)Br2],[2ZnBr2 . 3DMP], and [Cd(DMP)Br2]. Attempts to prep are a methylmorpholine complex of CdBr2 failed. Some intermediate comp lexes were isolated using a temperature-arrest technique (pyrolysis). The characterization and study of the conformational and configuration al changes were carried out using elemental and thermal analyses, IR s pectral data and magnetic moment measurements. Most of the complexes o f methylmorpholine and dimethylpiperazine appeared to be tetrahedral; however, [Zn(MmorPh)2Br2], [Ni(DMP)2(H2O)2Br2] and [2ZnBr2 . 3DMP] are octahedral. The thermodynamic parameters such as activation energy E( a), enthalpy change DELTAH, and entropy change DELTAS were evaluated for the dehydration steps and decomposition reactions of the complexes using some standard methods and their values compared. The stability trend of the complexes with respect to activation energy is compared. A linear correlation obtained by plotting E(a) against DELTAS values showed that a system with a higher entropy change DELTAS will require less energy E(a) for its thermal decomposition.