Thermally induced phase transition and X-ray crystal structure of bis(N,N′-dimethyl-1,2-ethanediamine)di-isothiocyanatonickel(II)

Abstract

The complex [Ni(MeNHCH₂CH₂NHMe)₂(NCS)₂](1) has been synthesised and characterised by X-ray crystallography. It undergoes an irreversible endothermic phase transition (452.5–468.5 K, ΔH= 13.4 kJ mol^–1) to species (2) which reverts to (1) in a humid atmosphere. Complex (1) crystallises in the monoclinic space group C2/c with a= 13.069(2), b= 9.783(3), c= 15.074(4)Å, β= 111.40(2)°, and Z= 4. The structure has been solved by Patterson and successive Fourier methods and refined to R= 0.032 for 1 240 independent observed reflections. The co-ordination around the nickel atom, lying on a crystallographic inversion centre, is close to octahedral with the two thiocyanate N atoms in trans position. The chelate rings exist in the δλ conformation. For complex (2), a=b= 8.16(3), c= 7.53(2)Å, α=β= 107.0(2), γ= 73.6(3)°, and Z= 1. Crystallographic and i.r. spectroscopic data suggest a non-centrosymmetric structure for (2) with a qualitative change in the conformation of the complex to δδ or λλ.