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

Abstract

Abstract Nickel(II), zinc(II) and cadmium(II) complexes of piperazine (pipz), and 1,4-diazacycloheptane (dach) with the composition [Ni(pipz)(TCA) 2(H 2O 2) 2], [M(dach) 2(TCA) 2] (M = Ni or Cd), [Zn(pipz) 2(TCA) 2]·H 2O, [Z(dach) 2(TCA) 2]·H 2O and [Cd(pipz) 2(TCA) 2]·2H 2O (where TCA represents trichloroacetate ion) have been synthesised. Attempts to prepare N-methylpiperazine and N, N'-dimethylpiperazine complexes of all the metal ions failed. Some intermediate complexes were isolated by pyrolysis. Configurational and conformational changes have been studied by elemental analyses, IR spectra, magnetic moment measurements and thermal analyses. All the complexes and the intermediates appear to be octahedral. Activation energies ( E a *), enthalpy (Δ H) and entropy changes (Δ S) for the dehydration and decomposition reactions of the complexes have been evaluated. The order of stability of the complexes (with respect to E a *) follows the trend pipz > dach. A linear correlation has been found between E a * and Δ S for the decomposition of the complexes.