Interaction of anions with substituted buckybowls. The anion's nature and solvent effects

Complexes formed by CN-substituted corannulene and sumanene with monovalent anions have been computationally studied to evaluate the effect of anion's nature and solvent upon the interaction. The results indicate that the most stable complex arrangement corresponds in all cases to the anion located by the center of the concave face of the bowl. All complexes are remarkably stable in the gas phase, with interaction energies ranging from -47 to -24 kcal/mol depending on the anion and the bowl considered. The order of stability for the different anion complexes in the gas phase is CO2H(-) > Cl(-) > Br(-) > NO3(-) ≫ ClO4(-) > BF4(-). Regarding the bowl employed, the intensity of the interaction is largest with the sumanene derivative substituted in the C-H aromatic groups. The weakest interactions are obtained with the sumanene derivative substituted in the CH2 groups, whereas complexes with the corannulene derivative give intermediate values. NO3(-) is oriented parallel to the bowl in the most stable complexes, whereas CO2H(-) prefers being oriented perpendicular to the bowl; ClO4(-) and BF4(-) arrange themselves with three bonds pointing to the bowl. These orientations are preferred on the basis of larger electrostatic and dispersion interactions. The preference of anions for the concave face of the bowl not only is mainly related to larger electrostatic interactions but also is because dispersion and induction are larger than in other arrangements considered. The presence of solvent modeled with a continuum model has a deep impact on the interaction energies already in solvents with low dielectric constant. All complexes remain stable, though energies in water hardly reach -7 kcal/mol. Br(-) complexes are the most stable in solvent, whereas CO2H(-) ones suffer a large penalty in solvent, becoming among the least stable complexes despite being the most stable in the gas phase.