Planarity takes over in the CxHxP6−x (x = 0–6) series at x = 4

Abstract

In this work we examine a structural transition from non-planar three-dimensional structures to planar benzene-like structures in the C_xH_xP_6−x (x = 0–6) series. The global minima of P₆, CHP₅, and C₂H₂P₄ species are benzvalene-like structures. The benzvalene and benzene-like structures of C₃H₃P₃ are close in energy with the former being slightly more stable at our best level of theory. The transition occurs at x = 4 (C₄H₄P₂), where the benzene-like structures become significantly more stable than the benzvalene-like structures. We show that the pseudo Jahn–Teller effect, which is responsible for the deformation of planar P₆, CHP₅, and C₂H₂P₄ structures, is completely suppressed at x = 3 (benzene-like structures of C₃H₃P₃). We present NICS_zz values of all the benzene-like isomers in the series.