Department of Chemistry, Youngstown State University, Youngstown, OH 44555, USA.
Instituto de Química Médica (IQM-CSIC), Juan de la Cierva, 3, E-28006 Madrid, Spain.
Molecules. 2017 Nov 12;22(11):1955. doi: 10.3390/molecules22111955.
MP2/aug'-cc-pVTZ calculations have been carried out to investigate the halogen-bonded complexes formed when CO and CS act as electron-pair donors through C to ClF, ClNC, ClCl, ClOH, ClCN, ClCCH, and ClNH₂. CO forms only complexes stabilized by traditional halogen bonds, and all ClY molecules form traditional halogen-bonded complexes with SC, except ClF which forms only an ion-pair complex. Ion-pair complexes are also found on the SC:ClNC and SC:ClCl surfaces. SC:ClY complexes stabilized by traditional halogen bonds have greater binding energies than the corresponding OC:ClY complexes. The largest binding energies are found for the ion-pair SC-Cl⁺:Y complexes. The transition structures which connect the complex and the ion pair on SC:ClNC and SC:ClCl potential surfaces provide the barriers for inter-converting these structures. Charge-transfer from the lone pair on C to the σ-hole on Cl is the primary charge-transfer interaction stabilizing OC:ClY and SC:ClY complexes with traditional halogen bonds. A secondary charge-transfer occurs from the lone pairs on Cl to the in-plane and out-of-plane π antibonding orbitals of ClY. This secondary interaction assumes increased importance in the SC:ClNH₂ complex, and is a factor leading to its unusual structure. C-O and C-S stretching frequencies and C chemical shieldings increase upon complex formation with ClY molecules. These two spectroscopic properties clearly differentiate between SC:ClY complexes and SC-Cl⁺:Y ion pairs. Spin-spin coupling constants J(C-Cl) for OC:ClY complexes increase with decreasing distance. As a function of the C-Cl distance, J(C-Cl) and ¹J(C-Cl) provide a fingerprint of the evolution of the halogen bond from a traditional halogen bond in the complexes, to a chlorine-shared halogen bond in the transition structures, to a covalent bond in the ion pairs.
已进行 MP2/aug'-cc-pVTZ 计算，以研究 CO 和 CS 通过 C 向 ClF、ClNC、ClCl、ClOH、ClCN、ClCCH 和 ClNH₂ 充当电子对供体时形成的卤素键合配合物。CO 仅形成通过传统卤素键稳定的配合物，所有 ClY 分子均与 SC 形成传统的卤素键合配合物，除了仅形成离子对配合物的 ClF。离子对配合物也存在于 SC:ClNC 和 SC:ClCl 表面上。通过传统卤素键稳定的 SC:ClY 配合物具有比相应的 OC:ClY 配合物更大的结合能。最大的结合能出现在离子对 SC-Cl⁺:Y 配合物中。连接 SC:ClNC 和 SC:ClCl 势能表面上的配合物和离子对的过渡态提供了这些结构相互转化的障碍。C 上的孤对电子向 Cl 上的 σ-hole 的电荷转移是稳定 OC:ClY 和 SC:ClY 配合物的主要电荷转移相互作用通过传统卤素键。从 Cl 上的孤对电子到 ClY 的面内和面外 π反键轨道发生二次电荷转移。这种二次相互作用在 SC:ClNH₂ 配合物中变得更为重要，并且是导致其异常结构的一个因素。与 ClY 分子形成配合物后，C-O 和 C-S 伸缩振动频率以及 C 化学屏蔽增加。这两个光谱性质清楚地区分了 SC:ClY 配合物和 SC-Cl⁺:Y 离子对。OC:ClY 配合物的自旋-自旋耦合常数 J(C-Cl)随距离的减小而增加。作为 C-Cl 距离的函数，J(C-Cl)和 ¹J(C-Cl)提供了从配合物中的传统卤素键到过渡态中的氯共享卤素键，再到离子对中的共价键的卤素键演化的指纹。
