Thermal investigation and stereochemical studies of some cyclic ligand complexes of nickel(II) and zinc(II) in the solid state

Abstract

1,4-Morpholine (morph) and 1,4-thioxane (thiox) complexes of nickel(II) and zinc(II) were synthesized. A thermal investigation was carried out and the stereochemical changes which occured during thermal decomposition were studied. The complexes were found to have the compositions [NiCl 2(morph)(H 2O) 2], [NiBr 2(morph)(H 2O) 2], [Ni(SCN) 2(morph) 2], [ZnCl 2-(morph)], [ZnBr 2(morp) 2], [Zn(SCN) 2(morph) 2]· 2H 2O, [ZnCl 2(thiox)], [ZnBr 2(thiox)] · 2H 2O and (Zn(SCN) 2(thiox)]. Attempts to prepare thioxane complexes of Ni II and dithiane complexes of Ni II and Zn II failed. The characterization and study of configurational and conformational changes were studied with the help of elemental and thermal analyses, IR, far-IR, magnetic moment and conductivity measurements. The morpholine complexes of nickel(II) and zinc(II) appeared to be octahedral except [ZnCl 2(morph)], which is tetrahedral, and thioxane complexes of zinc(II) appeared to be tetrahedral. Thermodynamic parameters, such as activation energy E a ★, enthalpy change Δ H and entropy change Δ S, were evaluated for the dehydration steps and decomposition reactions of the complexes using some standard methods. A linear correlation was found between E a ★ and Δ S for the decomposition reactions of the complexes.