二元和三元复合物中阳离子硫键与磷键的理论研究

采用MP2/cc-pVDZ和cc-pVTZ基组分别对复合物XH₂S⁺…NCH₂P和NCH₂P…PyX(X=NH₂, CH₃, H, CN, F, Cl, Br)中的硫键和磷键进行了研究, 讨论了键长、 键临界点的电荷密度(ρ)、 拉普拉斯密度(▽²ρ)、 范德华表面穿透距离、 二阶稳定化能和电荷转移量对硫键和磷键相互作用能的影响. 结果表明, 当取代基X为吸电子基团时, 形成的硫键较强. 当X为给电子基团时, 形成的磷键较强. 利用能量分解方法分析了取代基—CN导致硫键稳定性反常的可能原因. 还进一步讨论了三元复合物H₃S⁺…NCH₂P…PyX(X=NH₂, CH₃, H, CN, F, Cl, Br)中硫键和磷键的协同相互作用以及取代基对复合物稳定性的影响. 并通过对比相同的2种单体在三元复合物和二元复合物中的二阶稳定化能和相互作用能的差值, 说明了硫键与磷键起到相互促进的正协同作用, 增强了三元复合物的稳定性.

Theoretical Studies on Cationic Chalcogen and Pnicogen Bonds in Binary and Ternary Complexes†

The cationic chalcogen bonds and pnicogen bonds in binary complexes XH₂S⁺…NCH₂P and ternary complexes NCH₂P…PyX(X=NH₂, CH₃, H, CN, F, Cl, Br) with MP2/cc-pVDZ and cc-pVTZ were investigated theoretically. The effects of cationic chalcogen and pnicogen bond length, charge density ρ and ▽²ρ at bond critical points, van der Waals’s surface penetrating distance, the second order stabilization energy and charge transfer on the complex interaction energy were discussed. The results show that cationic chalcogen bond becomes stronger when the substituting group X is an electron-withdrawing group and that pnicogen bond becomes stronger when X is electron-donating group. The possible reason of the abnormal effect of the substituting group —CN on the stability of XH₂S⁺…NCH₂P complex was investigated with the energy-decomposition method. Further, we investigated the synergistic effects of cationic chalcogen and pnicogen bonds in the H₃S⁺…NCH₂P…PyX(X=NH₂, CH₃, H, CN, F, Cl, Br) complexes, and the influences of substituting group on the stability of these ternary complexes. By comparing the second-order stabilization energy and interaction energy of the monomers in these ternary and binary complexes, it is found that cationic chalcogen bond and pnicogen bond have positive synergistic effects on enhancing the stability of these ternary complexes.