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.

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“The medieval theory of levels of meaning in the biblical text, with all its undoubted defects, flourished because it is true, while the modern theory of a single meaning, with all its demonstrable virtues, is false. Until the historical-critical method becomes critical of its own theoretical foundations and develops a hermeneutical theory adequate to the nature of the text which it is interpreting, it will remain restricted—as it deserves to be—to the guild and the academy, where the question of truth can endlessly be deferred.”

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