Two stacking types of three-dimensional cocrystal structures based on multiple hydrogen bonds†

Abstract

Two new three-dimensional (3D) cocrystals of trithiocyanuric acid (TTCA) with hexamethylenetetramine (HMTA) have been synthesized and characterized. In the cocrystal, the monolayer structure forms through N–H⋯N hydrogen bonds due to the establishment of recognition between the thioamide moiety and the N-hetero atom and is further enhanced by the in-plane C–H⋯S hydrogen bonds. Simultaneously, the lamellas consist of two layers, which are recognized by lone-pair⋯π interactions between TTCA molecules, and assembled by the out-of-plane C–H⋯S hydrogen bonds in combination with the spatial van der Waals repulsion between HMTA. Then, the π–hole-based recognizing interaction between the HMTA and TTCA in the neighbouring lamellas, which was assisted by multiple adaptive C–H⋯S hydrogen bonds, contributed to the enhancement of 3D directionality, leading to the construction of 3D structures. And the study found that the stacking types between the lamellas could change due to the competing intermolecular interactions and adaptive C–H⋯S hydrogen bonds, yielding the unit cell structures of two different molecular packing parameters. Thus, two 3D structures of cocrystals, the octahedral (Phpm-o) and polyhedral (Phpm-p), are generated. The growth of these cocrystals was systematically evaluated by predicting the BFDH morphology. Moreover, the importance of each type of intermolecular interaction was quantified by Hirshfeld surface analysis, especially the N–H⋯N, C–H⋯S, etc. Combined with Hirshfeld analysis, the important role of non-covalent forces in the construction of 3D structures was confirmed.