The Face-to-Face σ-Hole...σ-Hole Stacking Interactions: Structures, Energies, and Nature

The existence of the pi...pi stacking interaction is well-known. Similarly, it is reasonable to assume the existence of the sigma-hole...sigma-hole stacking interaction. In this work, the structures, energies, and nature of the face-to-face sigma-hole...sigma-hole stacking interactions in the crystal structures have been investigated in detail by the quantum chemical calculations. The calculated results clearly show that the face-to-face sigma-hole...sigma-hole stacking interactions exist and have unique properties, although their strengths are not very significant. The energy component analysis reveals that, unlike many other dispersion-dominated noncovalent interactions in which the induction energies always play minor roles for their stabilities, for the face-to-face sigma-hole...sigma-hole stacking interaction the contribution of the induction energy to the total attractive energy is close to or even larger than that of the electrostatic energy. The structures, energies, and nature of the face-to-face sigma-hole...sigma-hole stacking interactions confined in small spaces have also been theoretically simulated. One of the important findings is that encapsulation of the complex bound by the face-to-face sigma-hole...sigma-hole stacking interaction can tune the electronic properties of the container.

Automated summary

This study investigates the face-to-face sigma-hole...sigma-hole stacking interactions in crystal structures using quantum chemical calculations, showing that they exist with unique properties despite their weak strength. Unlike other dispersion-dominated interactions, the contribution of the induction energy to the attraction energy of this interaction is significant. The study also suggests that the encapsulation of complexes bound by these interactions can tune the electronic properties of the container.