title: On the directionality of anion-π interactions.
abstract: The directionality of two important noncovalent interactions involving aromatic rings (namely anion-π and cation-π) is investigated. It has been recently published that the anion-π interactions observed in X-ray structures where the anion is located exactly over the center of the ring are scarce compared to cation-π interactions. To explain this behavior, we have analyzed how the interaction energy (RI-MP2/aug-cc-pVDZ level of theory) is affected by moving the anion from the center of the ring to several directions in anion-π complexes of chloride with either hexafluorobenzene or trifluoro-s-triazine. We have compared the results with the directionality of the cation-π interaction in the sodium-benzene complex. The results are useful to explain the experimental differences between both ion-π interactions. We have also computed the van der Waals radii of several halide anions and we have compared them to the neutral halogen atoms.
authors.affiliation: Departament de Química, Universitat de les Illes Balears, Palma de Mallorca, Spain.
authors.forename: Carolina
authors.initials: C
authors.lastname: Estarellas
authors.forename: Antonio
authors.initials: A
authors.lastname: Bauzá
authors.forename: Antonio
authors.initials: A
authors.lastname: Frontera
authors.forename: David
authors.initials: D
authors.lastname: Quiñonero
authors.forename: Pere M
authors.initials: PM
authors.lastname: Deyà