Classical Electrostatic Interaction Is the Origin for Blue-Shifting Halogen Bonds
Classical Electrostatic Interaction Is the Origin for Blue-Shifting Halogen Bonds
复制标题
经典静电相互作用是蓝移卤素键的起源
DOI：
10.1021/acs.inorgchem.9b00875
复制
发表时间：
2019
影响因子：
4.6
通讯作者：
Mo Yirong
中科院分区：
文献类型：
--
作者：
Wang Changwei;Mo Yirong
研究表明，一方面，电荷转移（CT）在卤素键（D···X - a） （D =给体；X =卤素原子；a =受体）中起着关键作用，表明卤素键具有相当的共价特性。但另一方面，也有人提出卤素原子X上带正电的σ-空穴与带负电的给体D之间的静电吸引是卤素成键的主要原因。同时，从给体D到反键的σ*(X - a)的CT会使X - a键变弱并变长。然而，有趣的是，在卤素键中存在蓝移现象，其中X-A键以增强的拉伸振动频率收缩。本文以典型的H3N··ClNO2和H3N··XNY2（X = Cl, Br， I; Y = O， S）为例，探讨了蓝移卤素键的性质。H3N···ClNO2表现出蓝移现象，并伴有强CT相互作用。通过将结合能分解为若干能量分量，并利用块定域波函数（BLW）方法探索它们的能量分布与卤素键距离的关系，我们发现经典静电相互作用是X-N键蓝移的控制因素。当配合物中的nh3被原子点电荷取代时，得到了类似程度的蓝移，这进一步支持了这一点。或者，通过沿X-N键方向施加外电场（e场），可以识别蓝到红的移位跃迁。这是因为极化和CT相互作用都倾向于拉伸X-N键，并且在外加电场下两者同时增强。最后，利用基于BLW能量分解方法的力分析，重新确定了各个能量分量的作用。
Studies have shown that, on the one hand, charge transfer (CT) plays a key role in halogen bonds (D···X–A) (D = donor; X = halogen atom; A = acceptor), suggesting considerable covalent character of halogen bonding. But, on the other hand, it has been proposed that halogen bonding is dominated by the electrostatic attraction between the electropositive σ-hole at the halogen atom X and the electronegative donor D. It has also been well-recognized that the CT from the donor D to the antibonding σ*(X–A) would weaken and lengthen the X–A bond. Yet, intriguingly, there is a blue-shifting phenomenon in halogen bonding, where the X–A bond contracts with an enhanced stretching vibrational frequency. Here we explored the nature of blue-shifting halogen bonds with the iconic case of H3N···ClNO2, which exhibits the blue-shifting phenomenon along with a strong CT interaction and its analogous H3N···XNY2(X = Cl, Br, and I; Y = O, S). By decomposing the binding energy to a number of energy components and exploring their energy profiles along with the halogen-bonding distances with the block-localized wave function (BLW) method, we showed that the classical electrostatic interaction is the governing factor for the blue-shifting of the X–N bonds. This is further supported by the similar magnitudes of blue-shifting obtained when NH3is replaced with atomic point charges in the complexes. Alternatively, by applying external electric field (E-field) along the X–N bond direction, the blue-to-red shifting transition can be identified. This is because both polarization and CT interactions tend to stretch the X–N bond, and both are enhanced simultaneously under the external E-field. Finally, roles of individual energy components are reconfirmed using the force analysis based on the BLW energy decomposition approach.