The molecular and electronic structures of XCCP molecules, with X = H, F, Cl, Br and I, were investigated using both unrestricted and restricted CCSD(T), CASSCF/CASPT2 and B3LYP methods, with basis sets up to 6-311++G(3df,2p) and cc-pVTZ. Our results indicate that these molecules possess two distinct types of electronic structure, namely phosphinidene and carbene. The triplet phosphinidene is clearly favoured over the singlet carbene. In the ethynyl-phosphinidene (X-C≡C-P) framework, both triplet and open-shell singlet states feature a linear geometry (3∑-); the corresponding singlet-triplet energy gaps vary from 70 to 80 kJ mol-1. Except for the closed-shell singlet of HCCP which is also linear, the phosphaethynyl-halocarbenes (X-C-C≡P) are characterized by a bent form (1A′) with rather small barriers to linearity. The standard heats of formation (ΔfH° at 298.15 K) of the triplet phosphinidenes have been evaluated as follows (values in kJ mol-1): HCC-P, 421; FCC-P, 292; ClCC-P, 420; BrCC-P, 465; and ICC-P, 569.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry