Crystallographic and quantum-chemical study of stacking interactions of resonance-assisted hydrogen-bridged rings

Abstract

Mutual contacts between resonance-assisted hydrogen-bridged (RAHB) rings,1 as well as contacts between RAHB rings and C6 -aromatic rings2 are systematically analyzed by searching Cambridge Structural Database (CSD) (Fig. 1) It is observed that the tendency of forming stacking interactions is very high in RAHB/RAHB contacts, since 91% of them corresponds to stacked arrangement. At the other side, the tendency of forming stacked contacts is not so pronounced in RAHB/C6 - aromatic contacts, although the majority of them (59%) corresponds also to stacking. The high level quantum-chemical calculations (CCSD(T)/CBS) are performed on model systems that are based on abundance in CSD. The energies of the strongest calculated RAHB/RAHB stacking interactions can reach -4.7 kcal/mol. The strongest calculated RAHB/benzene stacking interactions are weaker (-3.7 kcal/mol), but they can be also stronger than the corresponding RAHB/RAHB stacking interactions, depending on the RAHB system considered.