The symmetry breaking phenomenon in heteronine analogues due to the pseudo Jahn-Teller effect.

The pseudo Jahn-Teller effect (PJTE) is employed in CAH (A = O, S, Se, Te), and CEH (E = N, P, As, Sb) with planar configurations to show symmetry breaking phenomena (SBP) in heteronine analogues, and to explain why molecules with (C) high-symmetry configurations cannot maintain planarity and pucker to their (C) and (C) lower-symmetry structures, respectively. To investigate this phenomenon, geometry optimization and frequency calculations through the density functional B3LYP method using the cc-pVTZ basis set (for Te, and Sb cc-pVTZ-PP) were carried out for all compounds in the series. The state average-complete active space self-consistent field wave-function method was employed to calculate the electronic ground and several low-lying excited states to specify the adiabatic potential energy surface along the a and b puckering nuclear displacements. The PJTE (A + A + A') a2 and (A + B + A') b problems were formulated as the effects originating via the PJTE theorem. Moreover, replacing hydrogen atoms in CNH, a stable planar structure, with fluorine ligands demonstrated that SBP occur from C to C symmetry. Furthermore, thermochemical calculations via B3LY/cc-pVTZ illustrated that the planarity of the CE ring is restored in CEH (E = P, As, Sb) anions ,with the change in free energy corresponding to spontaneous deprotonation reactions as 23.67 kJ mol, 21.88 kJ mol, and 16.57 kJ mol, respectively. In fact, despite CEH having a donor electron-pair and potentially being Lewis base compounds, it acts as a Bronsted-Lowry acid releasing a H proton instead in this case.