Thermally induced isomerization and decomposition of N-methyl-1,3-propanediamine complexes of nickel (II) in the solid state

Abstract

[NiL₂(H₂O)Cl]Cl•nH₂O (L = N-methyl-1,3-propanediamine: n = 0 and 1). [NiL₂X₂] [X = Br, CF₃CO₂ and CCl₃CO₂] and [NiL₂,(H₂O)Y]•H₂O (Y = SO₂ and SeO₄) have been synthesized and their thermal investigations have been carried out in the solid state. [NiL₂(H₂O)Cl]Cl•nH₂O and [NiL₂(H₂O)Y]•H₂O exist in the trans form. On deaquation they transform to cis-[NiL₂Cl₂] and cis-[NiL₂Y]. [NiL₂(SO₂)] undergoes a reversible endothermic phase transition (117–169 °C ΔH = 6.5 kJ mol⁻¹). The complex trans-[NiL₂(CF₃ CO₂)₂] has been found to transform into its isomer upon heating, showing an endotherm (135–150 °C, ΔH = 18.9 kJ mol⁻¹); on keeping the product in a humid atmosphere (relative humidity 60–70 %), it reverts to its original form. [NiL₂Cl₂], [NiLCl₂] and [NiL(SO₄)] have been synthesized pyrolytically in the solid state from their parent diamine complexes. All the complexes possess octahedral geometry and diamine is chelated in all of them except in [NiL(SO₄)] where it is bridged. The occurrence of phase transition phenomena is supposed to be due to conformational changes in the six-membered chelate rings.