Role of Face-to-Face and Edge-to-Face Aromatic Interactions in the Inclusion Complexation of Cyclobis(paraquat-p-phenylene): A Theoretical Study

A B3LYP/6-31G(d,p) and MP2/6-31G(d,p)//B3LYP/6-31G(d,p) computational study of the gas-phase complexation of cyclobis(paraquat-p-phenylene) (14+) with four typical arom. guests, namely, 1,4-dimethoxybenzene (2), 1,5-dimethoxynaphthalene (3), benzidine (4), and tetrathiafulvalene (5), was carried out. The structure of the host was successively split into two responsible substructures, respectively, for the face-to-face and edge-to-face interactions with the guests. The sum of the two interactions calculated at the B3LYP/6-31G(d,p) and MP2/6-31G(d,p)//B3LYP/6-31G(d,p) levels for each guest proved to be in good agreement with the overall binding energy of the host calculated at the corresponding level of theory. The binding of the complexes is primarily due to London dispersion interactions which require wave function-based correlation methods for an adequate description. Face-to-face interactions are about 1 order of magnitude more important than edge-to-face interactions in determinating the overall binding energy. While edge-to-face interactions essentially depend on London dispersion forces, face-to-face interactions depend about one-half on electrostatic and frontier orbital contributions (the latter being more important) and the other half on London dispersion forces.