In the spirit of the mounting interest in noncovalent interactions, the present study was conducted to scrutinize a special type that simultaneously involved both σ-hole and lone pair (lp) interactions with aromatic π-systems. Square-pyramidal pentavalent halogen-containing molecules, including X-Cl-F₄, F-Y-F₄, and F-I-X₄ compounds (where X = F, Cl, Br, and I and Y = Cl, Br, and I) were employed as σ-hole/lp donors. On the other hand, benzene (BZN) and hexafluorobenzene (HFB) were chosen as electron-rich and electron-deficient aromatic π-systems, respectively. The investigation relied upon a variety of quantum chemical calculations that complement each other. The results showed that (i) the binding energy of the X-Y-F₄···BZN complexes increased (i.e., more negative) as the Y atom had a larger magnitude of σ-hole, contrary to the pattern of X-Y-F₄···HFB complexes; (ii) the interaction energies of X-Y-F₄···BZN complexes were dominated by both dispersion and electrostatic contributions, while dispersive interactions dominated X-Y-F4···HFB complexes; and (iii) the X₄ atoms in F-I-X₄···π-system complexes governed the interaction energy pattern: the larger the X₄ atoms were, the greater the interaction energies were, for the same π-system. The results had illuminating facets in regard to the rarely addressed cases of the σ-hole/lp contradictory scene.

中文翻译：

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方形金字塔形五价卤素化合物与π系统的共空间σ孔和孤对相互作用：量子力学研究

本着对非共价相互作用越来越感兴趣的精神，进行了本研究以研究一种特殊类型，该类型同时涉及与芳香族π系统的σ孔和孤对（lp）相互作用。使用包括X-Cl-F ₄，FYF ₄和FIX ₄化合物（其中X = F，Cl，Br和I且Y = Cl，Br和I）的正方形金字塔形五价含卤素分子作为σ -孔/ lp供体。另一方面，分别选择苯（BZN）和六氟苯（HFB）作为富电子和缺电子的芳族π系统。研究依赖于相互补充的各种量子化学计算。结果表明：（i）XYF ₄的结合能当Y原子具有更大的σ孔大小时，BZN络合物增加（即，更负），这与XYF _4· HFB络合物的模式相反；（ii）XYF ₄ ···BZN配合物的相互作用能主要由色散和静电作用决定，而色散相互作用则主要由XY-F4···HFB配合物决定；和（iii）在X _4个中FIX原子₄ ···π系统络合物管辖的相互作用能量图案：越大X _4个原子是，相互作用能是较大的，对于相同的π体系。关于σ-hole/ lp矛盾场景很少解决的情况，结果具有启发性的方面。