SCHEDULED MAINTENANCE
Theoretical study of the electronic structure of XCCP molecules (X =
H, F, Cl, Br, I): carbene![[italic v (to differentiate from Times ital nu)]](https://www.rsc.org/images/entities/i_char_e0f5.gif)
s. phosphinidene
Abstract
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 ![[triple bond, length half m-dash]](https://www.rsc.org/images/entities/char_e007.gif)
C–P)
framework, both triplet and open-shell singlet states feature a linear
geometry (3Σ−); 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–CP) 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.
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![[italic v (to differentiate from Times ital nu)]](https://www.rsc.org/images/entities/h2_char_e0f5.gif)
s. phosphinidene
