Stacking Interactions of Resonance-Assisted Hydrogen-Bridged Rings and C6-Aromatic Rings

Abstract

Stacking interactions between six-membered resonance-assisted hydrogen-bridged rings (RAHB) and C6-aromatic rings are systematically studied by analyzing crystal structures in Cambridge Structural Database (CSD). The interaction energies were calculated by quantum-chemical methods. Although the interactions are stronger than benzene/benzene stacking interactions (-2.7 kcal/mol) the strongest calculated RAHB/benzene stacking interaction (-3.7 kcal/mol) is significantly weaker than the strongest calculated RAHB/RAHB stacking interaction (-4.7 kcal/mol), but for particular composition of RAHB rings RAHB/benzene stacking interactions can be weaker or stronger than the corresponding RAHB/RAHB stacking interactions. They are also weaker than the strongest calculated stacking interaction between five-membered saturated hydrogen-bridged rings and benzene (-4.4 kcal/mol) and between two five-membered saturated hydrogen-bridged rings (-4.9 kcal/mol). SAPT energy decomposition analyses show that the strongest attractive term in RAHB/benzene stacking interactions is dispersion, however, it is mostly canceled by repulsive exchange term, hence the geometries of the most stable structures are determined by electrostatic term.