Characterisation of the tetrahalophosphonium cations PBrnI4 − n+ (0 ≤ n ≤ 4) by 31P MAS NMR, IR and Raman spectroscopy and the crystal structures of PI4+AlCl4−, PI4+AlBr4− and PI4+GaI4−

Abstract

The novel tetrahalophosphonium salts PBr4+AsF6−, PI4+AlCl4− and PI4+EBr4− (E = Al, Ga) have been synthesised. A variety of solid complexes containing PBr4+ (e.g. PBr4+AsF6−, PBr4+AlBr4− PBr4+GaBr4−), PI4+ (e.g. PI4+AlCl4−, PI4+AlBr4−, PI4+GaBr4−) or the mixed species PBrnI4 − n+ (0 ≤ n ≤ 4, containing AlBr4−, GaBr4−, AsF6− or SbF6−) have been studied by solid-state 31P MAS NMR and vibrational spectroscopy. The influence of the counter-ion on the chemical shift and the vibrational frequencies are discussed. The crystal structures of PI4+AlCl4−, PI4+AlBr4− and PI4+GaI4− are reported. Evidence for the existence of the hitherto unknown mixed bromoiodophosphonium cations PBr3I+, PBr2I2+ and PBrI3+ has been confirmed by spin–orbit corrected density functional calculations of isotropic 31P chemical shifts for PBrnI4 − n+.