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

Summary 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. H for the conversions were determined. NiL₂(HCCl₂CO₂)₂] (5) undergoes an irreversible phase transition (178–188°C; H=4.4kJ mol^–1]. NiL(HCCl₂CO₂)₂·H₂O shows an exothermic irreversible phase transition (104–128°C; H=–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.