Counterintuitive Substituent Effect of the Ethynyl Group in Ion-π Interactions

In this article, we report a high-level theoretical study (SCS-RI-MP2(full)/aug-cc-pVTZ) that deals with the substituent effect of the ethynyl group on ion-pi interactions in 1,3,5-triethynylbenzene systems. The ethynyl group is able to act as an electron-withdrawing group, thus favoring the anion-pi interaction. Unexpectedly, it has little influence on the cation-pi interaction. This behavior has been studied by examining the geometrical and energetic features of the complexes, AIM, and charge analyses and partitioning the interaction energy. The simultaneous interaction of 1,3,5-triethynylbenzene with cations and anions by opposite sides of the ring has also been studied.