Deepa P, Pandiyan B Vijaya, Kolandaivel P, Hobza Pavel
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6, Czech Republic.
Phys Chem Chem Phys. 2014 Feb 7;16(5):2038-47. doi: 10.1039/c3cp53976h.
The stabilisation energies of five ionic and neutral organic crystal structures containing various halogen bonds (I···I, Br···Br, I···Br, I···S and Br···S) were calculated using the DFT-D3 method (B97D/def2-QZVP). Besides them, the ionic I3(-)···I2 and neutral I2···I2, complexes (in the crystal geometries) were also studied. The nature of the bonds was deduced from the electrostatic potential evaluated for all subsystems. In almost all the cases, the σ-hole was positive; it was negative only for the ionic I3(-) system (although more positive than the respective belt value). The strongest halogen bonds were those that involved iodine as a halogen-bond donor and acceptor. Among ionic X···I3(-) and neutral X···I2 and X···Y dimers, the neutral X···I2 complexes were, surprisingly enough, the most stable; the highest stabilisation energy of 13.8 kcal mol(-1) was found for the I2···1,3-dithiole-2-thione-4-carboxylic acid complex. The stabilisation energies of the ionic I3(-)···I2 and neutral I2···1,3-dithiole-2-thione-4-carboxylic acid (20.2 and 20.42 kcal mol(-1), respectively) complexes are very high, which is explained by the favourable geometrical arrangement, allowing the formation of a strong halogen bond. An I···I halogen bond also exists in the neutral I2···I2 complex, having only moderate stabilisation energy (3.9 kcal mol(-1)). This stabilisation energy was, however, shown to be close to that in the optimal gas-phase L-shaped I2···I2 complex. In all the cases, the dispersion energy is important and comparable to electrostatic energy. Only in strong halogen bonds (e.g. I3(-)···I2), the electrostatic energy becomes dominant.
使用DFT-D3方法（B97D/def2-QZVP）计算了包含各种卤键（I···I、Br···Br、I···Br、I···S和Br···S）的五个离子型和中性有机晶体结构的稳定化能。除此之外，还研究了离子型I3(-)···I2和中性I2···I2配合物（处于晶体几何结构中）。键的性质是根据对所有子系统评估的静电势推导出来的。在几乎所有情况下，σ-空穴都是正的；仅离子型I3(-)系统的σ-空穴为负（尽管比相应的带状值更正）。最强的卤键是那些涉及碘作为卤键供体和受体的键。在离子型X···I3(-)和中性X···I2以及X···Y二聚体中，令人惊讶的是，中性X···I2配合物最稳定；对于I2···1,3-二硫杂环戊烯-2-硫酮-4-羧酸配合物，发现其最高稳定化能为13.8 kcal mol(-1)。离子型I3(-)···I2和中性I2···1,3-二硫杂环戊烯-2-硫酮-4-羧酸配合物（分别为20.2和20.42 kcal mol(-1)）的稳定化能非常高，这是由有利的几何排列所解释的，这种排列允许形成强卤键。中性I2···I2配合物中也存在I···I卤键，其稳定化能仅为中等（3.9 kcal mol(-1)）。然而，该稳定化能被证明与最佳气相L形I2···I2配合物中的稳定化能相近。在所有情况下，色散能都很重要，且与静电能相当。仅在强卤键（例如I3(-)···I2）中，静电能占主导地位。
