Comparison of σ-Hole and π-Hole Tetrel Bonds Formed by Pyrazine and 1,4-Dicyanobenzene: The Interplay between Anion-π and Tetrel Bonds

Abstract

The σ-hole tetrel bond in pyrazine/1,4-dicyanobenzene⋅⋅⋅TH₃ F (T=C and Si) and the π-hole tetrel bond in pyrazine/1,4-dicyanobenzene⋅⋅⋅F₂ TO have been compared. The π-hole tetrel bond is stronger than the corresponding σ-hole tetrel bond, with a larger interaction energy, shorter binding contact, greater electron density, and bigger charge transfer. Pyrazine forms a more stable tetrel-bonded complex than 1,4-dicyanobenzene even though the nitrogen atom in the former has a smaller negative electrostatic potential than the latter. An interesting cooperative effect was found when anion-π and tetrel-bond interactions coexisted in the same multicomponent complex of X^- ⋅⋅⋅pyrazine/1,4-dicyanobenzene⋅⋅⋅TH₃ F/F₂ TO (X=F, Cl, and Br). Both interactions displayed a positive cooperative effect, as shown by the larger interaction energies, shorter binding separations, and greater electron densities. The enhancement in the tetrel bond is dependent on the strength of the anion-π interaction and it becomes larger in the order Br^- <Cl^- <F^- . The enhancement in the tetrel bond changes its nature from a purely closed-shell interaction to a partially covalent interaction. Conversely, the anion-π interaction shows a prominent strengthening of up to -38 kcal mol^-1 . This effect has been analyzed in terms of electrostatic potentials and charge transfer.

Keywords: cooperative effects; density functional calculations; noncovalent interactions; pi interactions; tetrel bonds.