Pseudo Jahn–Teller origin tracking for symmetry breaking in halogenabenzene: How can a bird fly?

Abstract

The cyclic iodabenzene molecule (CH) 5 I was first introduced and characterized as planar configuration and zwitterionic valence structure by Glukhovtsev in 1991. Recently, it caused researchers' great interest due to the theoretical discovery of a stable bird-like structure by Hoffmann et al. in 2017 which has similar electronic structure and charge distribution as wellknown Meisenheimer complex C 6 H − 7 . Inspired by this, we continue to tell the halogenabenzene story by revealing the origin of the bird-like structure and understanding how the electronic behavior affects the geometrical symmetry for a molecule. By combining the Pseudo Jahn-Teller effect (PJTE) theory with the ab initio calculations for halogenabenzenes (CH) 5 X (X = F, Cl, Br, I) and C 6 H − 7 , it is illustrated that the vibronic coupling of 1 A 1 ground state and 1 B 1 excited states with C 2v planar structure along the out-of-plane b 1 distortion triggers the symmetry breaking of planar configuration to form a preferred bird-like structure. This interpretation can be also applied to explain their different stabilization energies by analyzing numerically the energy gaps of coupled electronic states and PJTE vibronic coupling parameters. Taking use of the PJTE formulation above, we also tracked the origin of restoring to be planar for (CH) 5 X 2+ cation, as well as their isoelectronic species (CH) 5 O + and (CH) 5 N, and suggests an effective strategy to stabilize the planar configuration for halogenabenzenes. K E Y W O R D S excited state, halogenabenzene, pseudo Jahn-Teller effect, symmetry breaking, vibronic coupling 1 | INTRODUCTIONWhen referring to halogen-substituted benzene compounds, most of attention has been paid to the cases that hydrogen atoms in different positions of benzene are substituted for halogen atoms, such as C 6 H 5 X [1][2][3][4] and C 6 H 4 X 2 or C 6 X 6 [2-7] (X = F, Cl, Br, I). In contrast, the systems in which the carbon atom is replaced by halogen atom have been rarely reported. The cyclic (CH) 5 I molecule, called iodabenzene, was firstly introduced by Glukhovtsev in 1991 and found to show a planar configuration with 8π electron system based on the semiempirical AM1 and MNDO calculations. [8] More recently, Hoffmann and his coworkers performed more accurate DFT and MP2 calculations on iodabenzene and obtained a stable bird-like minimum structure, which is expected optimistically to be detected and isolated in experiment. [9] It was also described that iodabenzene and its analogues (CH) 5 X (X = F, Cl, Br) have the similar geometric configuration and zwitterionic valence electronic structure to the famous Meisenheimer complexes. [10,11] Besides the neutral halogenabenzene molecules, the cation (CH) 5 X 2+ (X = F, Cl, Br, I), as well as their iso-valence electronic pyrylium cation (CH) 5 O + and pyridine (CH) 5 N, also attracted great interest in literatures. [12][13][14][15] As very common chemical reagents, (CH) 5 O + and (CH) 5 N are applied extensively in the field of organic chemistry. The (CH) 5 O + is used ...

Sub-lattice of Jahn-Teller centers in hexaferrite crystal

“…The primary force constant K E (defined without taking into account of the JTE) that enters Eqs. (12)(13)(14)(15) and (18) determines the elastic energy of the JT complex related to www.nature.com/scientificreports www.nature.com/scientificreports/ symmetrized (in our case of tetragonal type) deformations. In the cluster model used for molecules, it is defined as .…”

“…Although the JTE results from electron-phonon coupling and is not a spin-dependent phenomenon, it can indirectly affect the spin-dependent parameters via spin-orbit interaction. The systems, where it can be observed, include single crystals [4][5][6][7] , thin films 8 , non-organic and organic molecules [9][10][11] , and even biomolecules [12][13][14][15] . The JTE approach is used for description of properties of functional materials, such as semiconductors [16][17][18] , magnetic materials 5,6,[19][20][21] , superconductors 22 , optical materials 10,18 , and multiferroics 4,17,23,24 .…”

Pseudo Jahn–Teller Origin of Buckling Deformation of Two-dimensional Group-IV-Based Triphosphides as an Anode of Sodium-Ion Batteries

“…Moreover, the origin of buckling structures still remains unknown, which is a symmetry-breaking configuration from a high-symmetry planar one. Based on the vibronic coupling theory, it is well known that the pseudo Jahn–Teller effect (PJTE) is the only reason for any spontaneous symmetry breaking of the high-symmetry configuration in the nondegenerate electronic state. , The PJTE has been proved to be crucial to rationalize the origin of specific molecular configuration − and sudden polarization property, as well as ferroelectric instability in perovskites. − In recent years, Datta et al performed time-dependent density functional theory (DFT) calculations for the P 6 H 6 molecule to reveal the PJTE origin of different geometrical structures of blue and black P n . Similar approaches were successfully used in explaining the origin of structural distortions for other 2D materials, such as stanene, germanene, silicene, graphitic carbon nitride, and so on.…”