Stacking Interactions of Resonance-Assisted Hydrogen-Bridged Rings. A Systematic Study of Crystal Structures and Quantum-Chemical Calculations

Stacking interactions of resonance-assisted hydrogen-bridged rings are quite common, as 44% of their crystal structures show mutually parallel contacts. High-level quantum-chemical calculations by the CCSD(T)/CBS method indicate that these interactions are quite strong, up to -4.7 kcal/mol. This strength is comparable to the stacking interactions of saturated hydrogen-bridged rings (-4.9 kcal/mol), while it is substantially stronger than stacking interaction between two benzene molecules (-2.7 kcal/mol). Symmetry-adapted perturbation theory energy decomposition analysis shows that the dispersion component makes the major contribution in total interaction energy, but it is mostly canceled by the exchange-repulsion term in some systems, while electrostatic attraction terms are very significant in all systems. The electrostatic terms can be dominant or similar to the net dispersion term.