Weak interactions in barbituric acid derivatives. Unusually steady intermolecular organic “sandwich” complexes. π–π Stacking versus hydrogen bonding interactions

The 4-methoxy-6,6-dimethyl-5,6,7,8-tetrahydro[1,3]dioxolo[4,5-g]isoquinolin-6-ium (1) and 2-(1H-indol-3-yl)-1-ethanaminium (tryptaminium) (2) salts of 1,3-dimethyl-2,4,6-trioxoperhydro-pyrimidine-5-spiro-6′-{4′-methoxy-7′-(1,3-dimethyl-2,4,6-trioxoper-hydropyrimidin-5-yl)-5′,6′,7′,8′-tetrahydro[1,3]dioxolo[4,5-g]naphthalene} (3) have been prepared and their structures have been investigated by single-crystal X-ray diffraction analysis. It has been found on the basis of the crystal packing arrangement as well as physical and chemical properties that derivatives 1 and 2 form unusually steady intermolecular sandwich-like complexes both in the crystal and in solution, which are stabilized by weak CH…n(OC) hydrogen bonds and π–π stacking. The interplay between the intermolecular π–π stacking and strong NH…O hydrogen bond interactions and its influence on the “sandwich” structures of 1 and 2 are discussed.