Enhancement effect of lithium bonding on the strength of π-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 'pi-hole' bonding. In this study, ab initio calculations are performed to study the cooperativity effects between the pi-hole bond and lithium bond interactions in O2S center dot center dot center dot NCLi center dot center dot center dot NCX and O2S center dot center dot center dot CNLi center dot center dot center dot 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 center dot center dot center dot N(C) and Li center dot center dot center dot N(C) bonds coexist in the same complex. The results indicate that the interaction energies of lithium and pi-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 pi-hole interaction by 18%-28%. The electrostatic interaction is found to be a dominant factor in enhancing both types of interactions.