Phosphine π-acceptor properties in dihalogenobis(triphenylphosphine)-nickel(II) and -cobalt(II)

Abstract

Principal paramagnetic susceptibilities of single crystals of [ML₂X₂](M = Ni or Co; L = triphenylphosphine; X = Cl or Br) have been measured by the Faraday method throughout the temperature range 20–300 K. The magnetic properties, together with literature spectral data from single crystals and powders, have been interpreted within the angular overlap model (a.o.m.). No symmetry idealizations have been made. Fitting regions within the parametric models are broad but there emerges an unambiguous conclusion that large, negative, a.o.m. parameters are to be associated with the phosphine ligands in all cases. This evidence for π-acid behaviour for these ligands is associated with the observation of large nephelauxetic effects in these systems.