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(CF₃ CO₂)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.