Hydrogen bonding vs stacking interaction in the crystals of the simplest coumarin derivatives: study from the energetic viewpoint
The crystal structures of the carboxamide and thiocarboxamide derivatives of coumarin and 2-iminocoumarin have been studied thoroughly using the comparison of pairwise interaction energies calculated by quantum chemistry methods. The crystals of coumarin-3-carboxamide and 2-iminocoumarin-3-carboxamide proved to be isostructural despite the predictable different properties of the carbonyl and imino groups in formation of intermolecular interactions. The strongest interaction in these crystals is the N–H•••O hydrogen bonds which form the centrosymmetric dimer. Stacked column of such dimers have been recognized as the main structural motif of columnar crystals of carboxamide derivatives. The weakening of thiocarboxamide group acceptor properties as compared to carboxamide group results in the close interaction energies of the hydrogen bonded and stacked dimers in coumarin-3-thiocarboxamide crystal. Both these interactions form corrugated chain as the primary structural motif. The stacking interactions proved to be the strongest in the 2-iminocoumarin-3-thiocarboxamide crystal where it forms the stacked column as the primary basic structural motif. The neighbouring chains interact stronger in two opposite directions forming the layer as the secondary structural motif in both crystals of thiocarboxamide derivatives. These crystals have a columnar-layered structure.