Co-crystals of 9,9′-bianthracene-10,10′-dicarboxylic acid with linear bidentate basic ligand molecules: synthesis, crystal structure, and properties based on the layer structure exfoliated by water†
Co-crystals of 9,9′-dianthracene-10,10′-dicarboxylic acid (1) with the linear bidentate bases 9,9′-biacridine (bac), phenazine (phez), 4,4′-dipyridine (dpy), and DABCO (dabco) were synthesized. In the crystal structures of the co-crystals of 1 and bac, phez, and dpy, one-dimensional (1D) structures were formed through the hydrogen bonding between the acid and the base. For each combination of the acid and the bases, several kinds of polymorphic co-crystals with a similar structure were obtained. Among them, a combination of 1 and dabco gave three kinds of co-crystals which had a layered structure. In one of the co-crystals, a phenomenon where layers of the crystals could be exfoliated by dropping water was observed. The two-dimensional (2D) fingerprinting plot of the co-crystals showed that the major interaction to form the 1D structure was O–H⋯N hydrogen bonding and that to form the layered structure was the CH–π interaction, and the influence of the latter interaction on the robustness of the crystal was stronger than the former in the co-crystals.