1,1,1,3,3-pentaiododiphosphanium cations, P2I5+EI4- (E = Al, Ga or In):: synthesis and characterisation by 31P MAS NMR, IR and Raman spectroscopy

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 I-2/EI3 (E = Al, Ga or In). The products have been characterised by solid-state P-31 MAS NMR, Raman and IR spectroscopy. The solid-state P-31 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).