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 PBr_nI_4 − 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 PBr_nI_4 − n⁺.