The bonding picture in hypervalent XF₃ (X = Cl, Br, I, At) fluorides revisited with quantum chemical topology

Abstract

Hypervalent XF (X = Cl, Br, I, At) fluorides exhibit T-shaped C equilibrium structures with the heavier of them, AtF , also revealing an almost isoenergetic planar D structure. Factors explaining this behavior based on simple "chemical intuition" are currently missing. In this work, we combine non-relativistic (ClF ), scalar-relativistic and two-component (X = Br - At) density functional theory calculations, and bonding analyses based on the electron localization function and the quantum theory of atoms in molecules. Typical signatures of charge-shift bonding have been identified at the bent T-shaped structures of ClF and BrF , while the bonds of the other structures exhibit a dominant ionic character. With the aim of explaining the D structure of AtF , we extend the multipole expansion analysis to the framework of two-component single-reference calculations. This methodological advance enables us to rationalize the relative stability of the T-shaped C and the planar D structures: the Coulomb repulsions between the two lone-pairs of the central atom and between each lone-pair and each fluorine ligand are found significantly larger at the D structures than at the C ones for X = Cl - I, but not with X = At. This comes with the increasing stabilization, along the XF series, of the planar D structure with respect to the global T-shaped C minima. Hence, we show that the careful use of principles that are at the heart of the valence shell electron pair repulsion model provides reasonable justifications for stable planar D structures in AX E systems. © 2017 Wiley Periodicals, Inc.

Quantum chemical topology at the spin–orbit configuration interaction level: Application to astatine compounds

“…[8,9,[11][12][13][14][15]) or (b) determine the electron density in the real space, its topology (QTAIM), [16] as well as that of the electron localization function (ELF) [17,18] at relativistic DFT levels with or without the SOC (see refs. [7,[19][20][21][22][23][24][25][26][27][28] for case studies).…”

Astatine Facing Janus: Halogen Bonding vs. Charge-Shift Bonding

“…We will focus more specifically on the influence of the spin–orbit interaction, at the origin of the significant effect shown by Alvarez-Thon and co-workers (i.e., perastatobenzene becoming more aromatic than benzene) [ 26 ]. The tools of QCT, and especially the QTAIM and ELF topological analyses, have previously demonstrated their benefits for such studies [ 55 , 56 , 57 , 58 , 59 ].…”

Quantum chemical topology from tight augmented core densities

“…We review here typical examples where the applicability of the methodology is illustrated for a panel of molecular systems selected through the periodic table. The implementation was tested for CuCO (C s ), [ 55 ] Ferrocene FeCp 2 (D 5d ), [ 56 ] IF 3 (C 2v ), [ 57 ] AuKrBr (C ∞v ) [ 58 ] and for the uranyl cation UO 2 2+ (D ∞h ) [ 59 ] compound. The robustness of the approach for various small‐core as well as large‐core ECPs was investigated.…”