Enhancement effect of lithium bonding on the strength of <i>π</i>-hole interactions in O₂S···NCLi···NCX and O₂S···CNLi···CNX complexes (X = H, F, CN, OH and CH₃)

As with Groups IV and V, some Group VI atoms may exhibit regions of low electronic density that are perpendicular to portions of a molecular framework. These positive regions can interact in a highly directional manner with any negative site, thereby giving rise to a directional interaction. This type of interaction is labelled as ‘π-hole’ bonding. In this study, <i>ab initio</i> calculations are performed to study the cooperativity effects between the π-hole bond and lithium bond interactions in O₂S···NCLi···NCX and O₂S···CNLi···CNX complexes, where X = H, F, CN, OH and CH₃. These effects are investigated in terms of geometric and energetic features of the complexes, which are computed by the MP2/aug-cc-pVTZ method. Cooperative effects are found when S···N(C) and Li···N(C) bonds coexist in the same complex. The results indicate that the interaction energies of lithium and π-hole bonds in the triads are more negative relative to the respective dyads. The interaction energy of the lithium bond is increased by 9%–14%, whereas that of the π-hole interaction by 18%–28%. The electrostatic interaction is found to be a dominant factor in enhancing both types of interactions.

与第四族（Group IV）和第五族（Group V）元素类似，部分第六族（Group VI）原子可呈现出与分子骨架部分区域垂直的低电子密度区域。此类正电性区域可与任意负电位位点以高度定向的方式发生相互作用，进而形成定向相互作用，该类相互作用被定义为π空穴键（π-hole）。
本研究采用从头算（ab initio）方法，针对O₂S···NCLi···NCX与O₂S···CNLi···CNX复合物中π空穴键与锂键（lithium bond）之间的协同效应展开研究，其中取代基X的取值为H、F、CN、OH及CH₃。
本研究通过MP2/aug-cc-pVTZ方法计算复合物的几何结构与能量特征，以此分析上述协同效应。当S···N(C)与Li···N(C)键共存于同一复合物时，即可观测到协同效应。
结果表明，相较于对应的二元复合物（dyads），三元复合物（triads）内锂键与π空穴键的相互作用能更负（即相互作用强度更高）。其中锂键的相互作用能提升了9%~14%，而π空穴相互作用的相互作用能提升了18%~28%。进一步分析显示，静电相互作用是增强这两类相互作用的主导因素。