Weak interactions in 1,3-dimethyl-5-arylmethyl-5-cytisylmethylbarbituric acids. Unusually steady intramolecular organic “sandwich” complexes

The structure of 1,3-dimethyl-2-thio-5-(9-anthrylmethyl)-5-cytisylmethylbarbituric acid (1m) has been investigated by the combination of single-crystal X-ray diffraction analysis and 1H NMR spectroscopy. It has been revealed that 1m adopts unusually steady intramolecular sandwich-like conformation both in the solid state and in solution, which is stabilized by weak attractive interactions, such as π–π stacking and CH⋯π and CH⋯n (lone pair) hydrogen bonds. The “sandwich” conformation observed indicates that the π–π stacking interactions between planar π-systems act even at significant deviations from the strictly parallel arrangement. The nature of the attractive interactions in 5-arylmethyl-5-cytisylmethylbarbituric acids (1) is discussed.