1,1,1,2,2-Pentaiododiphosphanium cations, P2I5+EI4– (E = Al, Ga or In): synthesis and characterisation by 31P MAS NMR, IR and Raman spectroscopy

Abstract

The compound P₂I₅⁺AlI₄^– and the novel compounds P₂I₅⁺GaI₄^– and P₂I₅⁺InI₄^– have been prepared in two different ways either from PI₃ and EI₃ or from P₂I₄ and I₂/EI₃ (E = Al, Ga or In). The products have been characterised by solid-state ³¹P MAS NMR, Raman and IR spectroscopy. The solid-state ³¹P MAS NMR spectra are compared with NMR studies of related PI₄⁺ salts and alkylphosphorus tetraiodides. Vibrational assignments for the normal modes for the solid-state species P₂I₅⁺EI₄^– (E = Al, Ga or In) have been made on the basis of their Raman and IR spectra. These results are in excellent agreement with density functional calculations for the P₂I₅⁺ cation and are consistent with the ionic formulation P₂I₅⁺EI₄^– (E = Al, Ga or In).