Parra Rubén D
Department of Chemistry and Biochemistry, DePaul University, Chicago, IL, 60614, USA.
J Mol Model. 2024 Oct 3;30(11):363. doi: 10.1007/s00894-024-06160-3.
The strength and nature of the two halogen bonds in the NCI···CHI···CN halogen-bonded ternary complex are studied in the gas phase via ab initio calculations. Different indicators of halogen bond strength were employed to examine the interactions including geometries, complexation energies, Natural Bond Order (NBO) Wiberg bond indices, and Atoms in Molecules (AIM)-based charge density topological properties. The results show that the halogen bond is strong and partly covalent in nature when CHI donates the halogen bond, but weak and noncovalent in nature when CHI accepts the halogen bond. Significant halogen bond cooperativity emerges in the ternary complex relative to the corresponding heterodimer complexes, NCI···CHI and CHI···CN, respectively. For example, the CCSD(T) complexation energy of the ternary complex (-18.27 kcal/mol) is about twice the sum of the complexation energies of the component dimers (-9.54 kcal/mol). The halonium transfer reaction that converts the ternary complex into an equivalent one was also investigated. The electronic barrier for the halonium transfer was calculated to be 6.70 kcal/mol at the CCSD(T) level. Although the MP2 level underestimates and the MP3 overestimates the barrier, their calculated MP2.5 average barrier (6.44 kcal/mol) is close to that of the more robust CCSD(T) level. Insights on the halonium ion transfer reaction was obtained by examining the reaction energy and force profiles along the intrinsic reaction coordinate, IRC. The corresponding evolution of other properties such as bond lengths, Wiberg bond indices, and Mulliken charges provides specific insight on the extent of structural rearrangements and electronic redistribution throughout the entire IRC space.
The MP2 method was used for geometry optimizations. Energy calculations were performed using the CCSD(T) method. The aug-cc-pVTZ basis set was employed for all atoms other than iodine for which the aug-cc-pVTZ-PP basis set was used instead.
通过从头算计算在气相中研究了NCI···CHI···CN卤键三元络合物中两个卤键的强度和性质。采用不同的卤键强度指标来研究相互作用，包括几何结构、络合能、自然键序（NBO）维伯格键指数以及基于分子中的原子（AIM）的电荷密度拓扑性质。结果表明，当CHI提供卤键时，卤键很强且部分具有共价性质；而当CHI接受卤键时，卤键较弱且为非共价性质。相对于相应的异二聚体络合物NCI···CHI和CHI···CN，三元络合物中出现了显著的卤键协同作用。例如，三元络合物的CCSD(T)络合能（-18.27 kcal/mol）约为组分二聚体络合能之和（-9.54 kcal/mol）的两倍。还研究了将三元络合物转化为等效络合物的卤鎓转移反应。在CCSD(T)水平下，卤鎓转移的电子势垒计算为6.70 kcal/mol。尽管MP2水平低估了势垒，MP3水平高估了势垒，但它们计算的MP2.5平均势垒（6.44 kcal/mol）与更可靠的CCSD(T)水平接近。通过沿着内禀反应坐标（IRC）研究反应能量和力曲线，获得了关于卤鎓离子转移反应的见解。键长、维伯格键指数和穆利肯电荷等其他性质的相应演变，为整个IRC空间中结构重排和电子重新分布的程度提供了具体的见解。
使用MP2方法进行几何结构优化。使用CCSD(T)方法进行能量计算。除碘原子外，所有原子均采用aug-cc-pVTZ基组，碘原子采用aug-cc-pVTZ-PP基组代替。
