Systematic study of pi center dot center dot center dot pi interactions of structurally characterized compounds containing parallel benzene and/or pyridine rings was carried out. The gathered geometrical parameters were analyzed in statistical terms. The quantum mechanical calculations were made for the above-mentioned ring systems in different arrangements and the calculated interaction energy values were referred to the statistical data. The maximum bonding energy of the studied systems is about 3 kcal/mol. The ring rotation about the vertical axis has almost no influence on the system binding energy. In the specific ring arrangements, the stacking interactions can be bonding even for ring centroid distances larger than 6 angstrom. The results prove that the application of the generally accepted geometrical criteria of stacking interactions leads to the omission of the multiple bonding intermolecular interactions during the interpretation of the reactivity, self-assembly, as well as the properties of the supramolecular compounds.
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