Thermal studies of N¹-isopropyl-2-methyl-1,2-propanediamine complexes of zinc (II) and cadmium (II) in the solid phase

Abstract

CdL₃(ClO₄)₂, ZnL₂X₂, CdL₂X′₂• nH₂O (where L is N¹-isopropyl-2-methyl-l,2-propane-diamine, X is Cl, Br, I, ClO₄, SCN, 0.5SO₄ and 0.5SeO₂; n = 0 when X′ is Cl, Br, I, SCN and 0.5SO₄; n = 3 when X′ is ClO₄; n = 4 when X′ is 0.5SeO₄) and MLX₂ (M is Zn(II) or Cd(II) and X is Cl, Br and I) were synthesized from solution. The species CdL₂(ClO₄)₂ and MLX₂,(M is Zn(II) or Cd(II) and X is Cl, Br and I) were synthesized from the corresponding parent complexes by the temperature-arrest technique. CdL₂(SCN) ₂ exists in two isomeric forms and both have been synthesized. One of the isomers undergoes an irreversible phase transition (102–120°C, ΔH = 12.8 kJ mol⁻¹) and transforms to the other form in the solid phase. ZnL₂(ClO₄)₂ shows a reversible phase transition (178–208°C, ΔH = 9.2 kJ mol⁻¹) upon heating in the solid phase. CdL₂(ClO₂)₂ undergoes a reversible phase transition (73–98°C, ΔH = 4.4 kJ mol⁻¹) and then on further heating shows time-dependent reversible phase transitions (136–190°C, ΔH = 15.3 kJ mol⁻¹) in the solid phase. The phase transition in CdL₂(SCN) ₂ is due to the change in coordination mode of the thiocyanate ion, whereas in CdL₂(ClO₄)₂, the time-dependent reversible phase transition is due to conformational changes in the diamine chelate rings.