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This study of 3‐(5‐phenyl‐1,3,4‐oxadiazol‐2‐yl)‐2H‐chromen‐2‐one, C17H10N2O3, 1, and 3‐[5‐(pyridin‐4‐yl)‐1,3,4‐oxadiazol‐2‐yl]‐2H‐chromen‐2‐one, C16H9N3O3, 2, was performed on the assumption of the potential anticancer activity of the compounds. Three polymorphic structures for 1 and two polymorphic structures for 2 have been studied thoroughly. The strongest intermolecular interaction is stacking of the 'head‐to‐head' type in all the studied crystals. The polymorphic structures of 1 differ with respect to the intermolecular interactions between stacked columns. Two of the polymorphs have a columnar or double columnar type of crystal organization, while the third polymorphic structure can be classified as columnar‐layered. The difference between the two structures of 2 is less pronounced. Both crystals can be considered as having very similar arrangements of neighbouring columns. The formation of polymorphic modifications is caused by a subtle balance of very weak intermolecular interactions and packing differences can be identified only using an analysis based on a study of the pairwise interaction energies. [ABSTRACT FROM AUTHOR]

During a comprehensive study of a series of 2‐(N‐arylimino)coumarin‐3‐carboxamides with the aryl group substituted in the ortho‐position by either a halogen atom, a methyl group or a methoxy group, the existence of three groups of isotypic crystal structures has been revealed. The similarity of crystal structures belonging to the same groups was confirmed by the analysis based on the comparison of pairwise interactions energies obtained from quantum chemical calculations. Group I includes unsubstituted, methyl‐substituted and polymorphic modification 1 of fluoro‐substituted 2‐(N‐arylimino)coumarin‐3‐carboxamide. Structures of polymorphic modification 2 of fluoro‐substituted derivative, chloro‐substituted and polymorphic modification 1 of bromo‐substituted 2‐(N‐arylimino)coumarin‐3‐carboxamide may represent group II. Group III contains structures of polymorphic modification 2 of bromo‐substituted derivative, iodine‐ and methoxy‐substituted 2‐(N‐arylimino)coumarin‐3‐carboxamides. Structures of the same type group have extremely close parameters of the unit cell as well as those of molecular and crystal structures. But they are not identical. Polymorphic modifications of fluoro‐ and bromo‐substituted 2‐(N‐arylimino)coumarin‐3‐carboxamides belong to different crystal types mainly due to different arrangement of basic structural motifs separated out using quantum chemical calculations. [ABSTRACT FROM AUTHOR]