Thermal studies of N¹-isopropyl-2-methyl-1,2-propanediamine complexes of nickel (II)X₂ [X = I⁻, CF₃CO⁻₂, 0.5SO²⁻₄ and 0.5SeO²⁻₄] in the solid state

Abstract

The complexes NiL₂X₂•nH₂O (L = N¹-isopropyl-2-methyl-1,2-propanediamine; X = 0.5SO²⁻₄ when n = 0; X = I⁻ when n = 2; X = CF₃CO⁻² when n = 0 or 2 and X = 0.5SeO²⁻₄ when n = 0 or 3) have been synthesized and their thermal behaviour has been studied. All the hydrated complexes are yellow in colour and on heating lose water of hydration accompained by a yellow → light blue thermochromic transition, except in the case of the iodide complex, which retains the original yellow colour on dehydration. However, NiL₂I₂ undergoes an irreversible exothermic phase transition (166–193°C; ΔH = −7.5 kJ mol⁻¹) with change in colour from yellow to reddish yellow. NiL₂(CF₃CO₂)₂ shows a reversible phase transition (heating cycle, 144–170°C; ΔH = 3.1 kJ mol⁻¹; cooling cycle, 158–135°C; ΔH = −3.1 kJ mol⁻¹) with no visual change in colour. All the yellow complexes possess square-planar geometry and the light blue complexes NiL₂X₂(X = CF₃CO⁻², 0.5SO²⁻₄ and 0.5SeO²⁻₄) are expected to be pentacoordinated. The phase transition occurring in NiL₂X₂ (X = I⁻ and CF₃CO⁻²) is due to conformational changes of the diamine chelate rings.