The solution behaviour of nickel(II) halide complexes of 1,2-bis(diphenylphosphino)ethane (dpe): The existence of five-co-ordinate [Ni(dpe) 2X] + species

Abstract

Nickel(II) halide complexes with the bidentate ligand 1,2-bis(diphenylphosphino)ethane (dpe) have been reinvestigated, with particular regard to their behaviour in solution. Conclusive evidence of the existence of low-spin five co-ordinate [Ni(dpe) 2X] + species (X = Cl, Br, I), in equilibrium with cis-planar [Ni(dpe)X 2] species, is given on the basis of spectrophotometric and conductometric data. Calorimetric measurements suggest that the stability of five-co-ordinate [Ni(dpe) 2−Br] + is comparable to that of the previously reported [Co(dpe) 2Br] + complex.