Thermally induced solid-state isomerisation and decomposition of 2,2-dimethyl-1,3-propanediamine nikel(II) complexes

Abstract

Complexes [NiL3]Br2·H2O (L=2,2-dimethyl-1,3-propanediamine), [NiL2X2] (X=Cl, Br, NCS, CF3CO2, HCCl2CO2 or CCl3CO2 and X2=SO4 or SeO4) and [NiL(HCCl2CO2)2]·H2O have been synthesised and their thermal studies have been investigated in the solid state. The complexes, [NiL2X2] (X=Cl or Br) and NiLX2 (X=Cl or HCCl2CO2) have been isolated thermally in the solid state. All the complexes possess octahedral geometry. [NiL2Br2] and [NiL2(CF3CO2)2] exist in two interconvertible isomeric forms. ΔH for the conversions were determined. [NiL2(HCCl2CO2)2] (5) undergoes an irreversible phase transition (178–188°C; ΔH=4.4kJ mol−1]. NiL(HCCl2CO2)2·H2O shows an exothermic irreversible phase transition (104–128°C; ΔH=−5.8 kJ mol−1) after losing water. The phase transitions are assumed to be due to the conformational changes in the chelate ring of diamine.