Raman spectra and isomerism of some bromophenylphosphoranes PhnPBr5–n(1 ⩽n⩽ 3) and their salts

Abstract

A synthetic and Raman investigation of isomerism in the bromophenylphosphoranes has shown no evidence for ionic–covalent isomerism analogous to that in the chlorophenylphosphoranes. Two ionic modifications of PhPBr₄ have been identified by Raman spectroscopy, whereas Ph₂PBr₃ was found to exist in only one ionic form, Ph₂PBr₂⁺Br^–. A recent proposal that Ph₃PBr₂ is a molecular four-co-ordinate species is disputed and evidence supporting an ionic formulation Ph₃PBr⁺Br^– is presented. Vibrational Raman assignments for the bromophenylphosphoranes and some of their tetrabromoborate and tetrabromoaluminate salts are given.