A Unified Theory for the Blue- and Red-Shifting Phenomena in Hydrogen and Halogen Bonds
A Unified Theory for the Blue- and Red-Shifting Phenomena in Hydrogen and Halogen Bonds
复制标题
氢键和卤素键蓝移和红移现象的统一理论
DOI：
10.1021/acs.jctc.6b01133
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发表时间：
2017
影响因子：
5.5
通讯作者：
王长崴
中科院分区：
文献类型：
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作者：
王长崴
典型的氢键和卤素键在形成氢键和卤素键合络合物（表示为D···Y-A，Y = H和X）时显示出其振动频率的红移。在某些配合物中发现蓝移是非常有趣的，这导致了对该现象起源的许多研究。因为电荷转移混合（即，超共轭）被认为是键合系统中的关键力之一，比较电荷转移效应“打开”和“关闭”的键合复合物的结构和振动频率将是有启发性的。关闭电荷转移混合可以通过采用块局域波函数（BLW）方法来实现，该方法是从头算价键（VB）方法。此外，使用BLW方法，在复合物形成中获得的整体稳定性可以根据一些物理上有意义的术语进行分析。因此，BLW方法提供了一个统一的和物理上清晰的方式来探索氢键和卤素键合复合物中的红移和蓝移现象的本质。在这项研究中，建立了一个直接的关系，总的稳定性和Y-A键长的变化之间的基础上，我们的BLW计算，并阐明了一致的作用，所有的能量成分。然后（D）→ σ*（Y-A）电子转移拉伸了Y-A键，而由于相互作用部分的接近而导致的极化减小了HOMO-LUMO能隙，并导致YA单体内更强的轨道混合。因此，电荷转移和极化都稳定了键合系统，其中Y-A键被拉伸并使Y-A键的振动频率红移。值得注意的是，冻结波函数的能量是唯一倾向于Y-A键收缩的能量成分，因此是导致相关蓝移的原因。Y-A键长和相应的伸缩振动频率的总变化是由冻结能项与极化能项和电荷转移能项之和之间的竞争决定的。由于冻结能量是由静电和泡利交换相互作用和频率移动是一个长期的现象，我们得出结论，长程静电相互作用是背后的冻结能量项的驱动力。
Typical hydrogen and halogen bonds exhibit red-shifts of their vibrational frequencies upon the formation of hydrogen and halogen bonding complexes (denoted as D···Y–A, Y = H and X). The finding of blue-shifts in certain complexes is of significant interest, which has led to numerous studies of the origins of the phenomenon. Because charge transfer mixing (i.e., hyperconjugation in bonding systems) has been regarded as one of the key forces, it would be illuminating to compare the structures and vibrational frequencies in bonding complexes with the charge transfer effect “turned on” and “turned off”. Turning off the charge transfer mixing can be achieved by employing the block-localized wave function (BLW) method, which is an ab initio valence bond (VB) method. Further, with the BLW method, the overall stability gained in the formation of a complex can be analyzed in terms of a few physically meaningful terms. Thus, the BLW method provides a unified and physically lucid way to explore the nature of red- and blue-shifting phenomena in both hydrogen and halogen bonding complexes. In this study, a direct correlation between the total stability and the variation of the Y–A bond length is established based on our BLW computations, and the consistent roles of all energy components are clarified. Then(D) → σ*(Y–A) electron transfer stretches the Y–A bond, while the polarization due to the approach of interacting moieties reduces the HOMO–LUMO gap and results in a stronger orbital mixing within the YA monomer. As a consequence, both the charge transfer and polarization stabilize bonding systems with the Y–A bond stretched and red-shift the vibrational frequency of the Y–A bond. Notably, the energy of the frozen wave function is the only energy component which prefers the shrinking of the Y–A bond and thus is responsible for the associated blue-shifting. The total variations of the Y–A bond length and the corresponding stretching vibrational frequency are thus determined by the competition between the frozen-energy term and the sum of polarization and charge transfer energy terms. Because the frozen energy is composed of electrostatic and Pauli exchange interactions and frequency shifting is a long-range phenomenon, we conclude that long-range electrostatic interaction is the driving force behind the frozen energy term.