Halogen bonding:: the σ-hole
Halogen bonding:: the σ-hole
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DOI：
10.1007/s00894-006-0130-2
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发表时间：
2007-02-01
影响因子：
2.2
通讯作者：
Politzer, Peter
中科院分区：
文献类型：
--
作者：
Clark, Timothy;Hennemann, Matthias;Politzer, Peter
卤素键是指某些分子RX中的卤素原子X与其他分子上的负位点的非共价相互作用。这可以解释为在卤素表面的最外部分上存在正静电势区域，即以R-X轴为中心的σ孔。我们对CF_3X（X = F，Cl，Br，I）分子进行了自然键级B_3LYP分析。结果表明，分子中Cl、Br和I原子近似于s（2）p（x）（2）p（y）（2）p（z）（1）构型，其中z轴沿着R-X键。这三对未共享的电子在X的中心部分周围产生一个负静电势带，留下最外面的区域为正，即σ空穴。这在氟的情况下没有发现，对于氟，其高电负性加上显著的sp-杂化的组合引起中和σ-空穴的电子电荷的流入。在生成Cl、Br和I的过程中，这些因素逐渐变得不那么重要，它们的影响也被分子其余部分中吸电子取代基的存在所抵消。因此，在CF 3Cl中观察到Cl的σ空穴，但在CH 3Cl中没有。
Halogen bonding refers to the non-covalent interactions of halogen atoms X in some molecules, RX, with negative sites on others. It can be explained by the presence of a region of positive electrostatic potential, the sigma-hole, on the outermost portion of the halogen's surface, centered on the R-X axis. We have carried out a natural bond order B3LYP analysis of the molecules CF3X, with X = F, Cl, Br and I. It shows that the Cl, Br and I atoms in these molecules closely approximate the s(2)p(x)(2)p(y)(2)p(z)(1) configuration, where the z-axis is along the R-X bond. The three unshared pairs of electrons produce a belt of negative electrostatic potential around the central part of X, leaving the outermost region positive, the sigma-hole. This is not found in the case of fluorine, for which the combination of its high electronegativity plus significant sp-hybridization causes an influx of electronic charge that neutralizes the sigma-hole. These factors become progressively less important in proceeding to Cl, Br and I, and their effects are also counteracted by the presence of electron-withdrawing substituents in the remainder of the molecule. Thus a sigma-hole is observed for the Cl in CF3Cl, but not in CH3Cl.