Carbon Phosphide Anions

Abstract

Stable carbon phosphide anions have been prepared by the reaction of small carbon anions (C _n ⁻ n = 3–9) with gaseous P₄. The C _n ⁻ anions, produced by laser ablation, were trapped and reacted in a Fourier transform ion cyclotron resonance mass spectrometer. The compositions of the anions formed were C _n P, C _n P₂, C₄P₄, C _n P₅. All the anions for n = 3–9 are covered in this paper and have been investigated theoretically using density functional calculations, incorporating gradient corrections and numerical basis sets. The [C _n P]⁻ and [C _n P₂]⁻ anions are calculated to be linear, with the P atoms at one and both ends of the C _n chain, respectively. The [C₄P₄]⁻ anion is the only ion containing four P atoms, and never has more than minor intensity; three structures close in energy are calculated for [C₄P₄]⁻, with the most stable possessing a CP₄ mononocycle at the end of the C₄ chain. The [C _n P₅]⁻ anions observed when n = 4, 6 or 8 have a lowest energy structure with one phosphorus atom at one end of the chain and a P₄ ring at the other end.