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

Abstract

Nickel(II) complexes of piperazine (pipz) and N- methylpiperazine (N-Mepipz) have been prepared. These complexes having the composition [NiL 2- (NCSe) 2]·2H 2O (L=pipz and N-Mepipz) appear to possess O h symmetry and have been characterized by elemental analyses, IR spectral and magnetic moment data, conductivity measurement and thermal analyses in the solid state. An attempt to prepare the N,N′- dimethylpiperazine complex of nickel(II) failed. Stereochemical studies have been made with the help of IR spectral and magnetic moment data. Thermo- dynamic parameters like activation energy (E a *), enthalpy change (▵ H) and entropy change (▵ S) for each step of the dehydration and decomposition reactions of the complexes are evaluated by using some standard methods. Probable mechanistic paths of decomposition reactions have been proposed. The order of stability of the complexes (with respect to DTA peak temperatures) follows the trend pipz > N- Mepipz. A linear correlation between E a * and ▵ S for the decomposition reactions of the complexes has been found.