PCCP does exist

Abstract

Neutral and cationic [C₂,P₂] were investigated by a combination of mass spectrometry and electronic structure calculations. The cationic [C₂ ,P₂]^•+ potential energy surface including all relevant minima, transition states and fragmentation products was calculated at the B3LYP/6-311G(3df) level of theory. The most stable structures are linear PCCP^•+1^•+ (E_rel=0 kcal mol⁻¹), a three-membered ring with exocyclic phosphorus c-(PCC)-P 2^•+ (E_rel=40.8 kcal mol⁻¹), and the rhombic isomer 3^•+ (E_rel=24.9 kcal mol⁻¹). All fragmentation channels are significantly higher in energy than any of the [C₂,P₂]^•+ isomers. Experimentally, [C₂,P₂]^•+ ions are generated under high vacuum conditions by electron ionization of two different precursors. The fragmentation of [C₂ ,P₂]^•+ on collisional activation is preceded by rearrangement reactions which obscure the structural connectivity of the ions. The existence and the high stability of neutral [C₂,P₂] were proved by a neutralization–reionization (NR) experiment. Although an unambiguous structural assignment of the neutral species cannot be drawn, both theory and experiment suggest that the long-sought neutral, linear PCCP 1 is generated using the NR technique.