Raman spectra and isomerism of some bromophenylphosphoranes Ph_nPBr_5–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 PhPBr, have been identified by Raman spectroscopy, whereas Ph,PBr, was found to exist in only one ionic form, Ph,PBr,+Br-. A recent proposal that Ph,PBr, is a molecular fourco-ordinate species is disputed and evidence supporting an ionic formulation Ph,PBr+Br--is presented. Vibrational Raman assignments for the bromophenylphosphoranes and some of their tetrabromoborate Receitred 18th January 1994; Paper 4/003 16K

The structure of R3PBr2 compounds in the solid state and in solution; geometrical dependence on R, the crystal structures of tetrahedral ionic Et3PBr2 and molecular trigonal bipyramidal (C6F5)3PBr2

“…The geometrical dependence of R 3 PBr 2 compounds on R is therefore clearly illustrated. This phenomenon has previously been observed for R 3 AsBr 2 15 and R 3 PCl…”

Structural isomerism in tris-tolyl halo-phosphonium and halo-arsonium tri-halides, [(CH3C6H4)3EX][X3], (E = P, As; X = Br, I)

“…The frequencies of the ν(P-Br) symmetric stretches for [R 3 PBr] + cations have been shown to be dependent on the nature of R, the band being observed around 239-251 cm −1 when R = Ph, 34 and 413-429 cm −1 when R = Me. 35 Peaks are observed in the spectra of the R 3 PBr 4 compounds 7 to 9 between 237 and 256 cm −1 , and these are assigned as ν(P-Br) stretches.…”