Wang Changwei, Danovich David, Shaik Sason, Mo Yirong
College of Science, China University of Petroleum (East China), Changjiangxi Road 66, 266580, Tsingtao, P. R. China.
Institute of Chemistry and Lise Meitner Minerva Center for Computational Quantum Chemistry, The Hebrew University, Jerusalem, 91904, Israel.
Chemistry. 2017 Jun 27;23(36):8719-8728. doi: 10.1002/chem.201701116. Epub 2017 Jun 5.
Polyhalogen monoanions [X ] (X=Cl and Br; n=1, 2, 3, 4, and 5) have been systematically studied using the block-localized wave function (BLW) method, which offers a valence bond (VB) analysis. For each species, the most stable isomer can be described as a central halide anion X non-classically bonded to a number of dihalogen molecules X via "halogen bonds". VB analyses confirm the dominant role of the charge-transfer interaction between the lone pair on X and the σ-anti-bonding orbital of X molecule (n→σ*) in X and higher analogues. Thus, our study demonstrates that these halogen bonds are essentially dative covalent interactions. Importantly, the charge-transfer interaction between [X ] and X decreases with the increasing n, in accord with the weakening of the Lewis basicity as characterized by the corresponding HOMO energy. The reduction of the charge transfer interaction underscores the reduction of covalence in halogen bonds in [X ] . This tendency highlights the anti-cooperative effect in polyhalogen monoanions. All in all, the halogen bond between X and nX molecules exhibits the same trends as in X with a single X molecule. In other words, halogen bonding in the larger clusters derives from the same bonding mechanism as the [X ] anion. As such, the X ⋅⋅⋅X halogen bond at different bond lengths forms a gauge of covalence for the entire [X ] family.
使用提供价键（VB）分析的块定域波函数（BLW）方法，对多卤单阴离子[X]（X = Cl和Br；n = 1、2、3、4和5）进行了系统研究。对于每个物种，最稳定的异构体可描述为中心卤化物阴离子X通过“卤键”与多个二卤分子X进行非经典键合。VB分析证实了X上孤对电子与X分子的σ反键轨道（n→σ*）之间的电荷转移相互作用在X及其更高类似物中的主导作用。因此，我们的研究表明这些卤键本质上是配位共价相互作用。重要的是，[X]与X之间的电荷转移相互作用随着n的增加而降低，这与以相应的最高占据分子轨道（HOMO）能量表征的路易斯碱性减弱相一致。电荷转移相互作用的降低突出了[X]中卤键中共价性的降低。这种趋势突出了多卤单阴离子中的反协同效应。总而言之，X与n个X分子之间的卤键与单个X分子的X表现出相同的趋势。换句话说，较大簇中的卤键源于与[X]阴离子相同的键合机制。因此，不同键长的X⋅⋅⋅X卤键形成了整个[X]家族共价性的量度。
