Interaction between anions and substituted molecular bowls

Complexes formed by anions and substituted molecular bowls were studied by means of computational calculations with density functional theory methods. An empirical dispersion term was included to correct the well known flaws of common functionals to describe dispersion interactions. The modified bowls consisted of corannulene molecules substituted with five or ten F, Cl, or CN units, whereas Cl-, Br- and BF4 - where the anions considered. Substitution with F, Cl and CN produces an inversion of the molecular electrostatic potential of the bowls, which become positive over the two faces of the bowl, therefore interacting favorably with anions. Three different structures were found for each of the complexes, corresponding to one arrangement with the anion interacting with the concave side of the bowl and two different arrangements with the anions interacting with the convex side of the bowl. The strength of the interaction roughly follows the values of molecular electrostatic potential, being more stable as more positive is the potential. However, the role of dispersion arises as essential for having a correct order of stabilities. In fact, when dispersion is included, most complexes are more stable by the concave face, where the closer proximity of the atoms allows for a larger dispersion effect. Also, it is dispersion which makes the complexes formed with a larger anion as BF4 - as stable as those formed with Cl- or Br-. The results suggest the possibility of employing these substituted molecular bowls as receptors for anions with a preferential concave complexation, specially for structured anions where dispersion effects will be larger.