The pseudo Jahn–Teller effect of puckering in pentatomic unsaturated rings C4AE5, A = N, P, As, E = H, F, Cl

Abstract

Pyrrole, phosphole, arsole, and six of their pentafluoro and pentachloro derivatives (C4AE5) were investigated in order to understand the origin of puckering instability of their planar configurations based on the pseudo Jahn–Teller effect (PJTE) theorem. Optimization and following frequency calculations in the C4AE5 series illuminated that seven compounds in the series such as phosphole derivatives (C4PE5), arsole derivatives (C4AsE5), and pentafluoropyrrole (C4NF5) compound, are unstable in their high-symmetry planar (with C2v symmetry) configuration and all of these seven compounds were puckered to lower Cs symmetry stable geometry. Moreover, due to the vibronic coupling interaction between the 1A1 ground state, 1A1′ and 1B1 excited states, the (1A1+1A1′+1B1)⊗b1 PJTE problem was found to be the reason of the breaking symmetry phenomena and non-planarity of the C4A pentatomic unsaturated ring in those compounds. Finally, the numerical fitting of adiabatic potential energy surface (APES) cross-sections along the b1 puckering coordination was employed to estimate the vibronic coupling constants of the PJTE problems for seven folded derivatives in the C4AE5 series.