Crystalline forms of 1,3,5-benzene-tri(pyridinyl)carboxamides: Isolated site hydrates as polymorphs and solvates

The crystallization of 3-pyridyl (1) and 4-pyridyl (2) analogues of the title compound results in different crystalline hydrates and polymorphs and their crystal structures reveal that 1 and 2 exhibit conformational isomerism. The molecule 1 forms three crystalline forms from MeOH solution depending on concentration of the solution. Among these three forms, two are polymorphic monohydrates. However, the crystallization of 2 was found to be dependent on the solvent of crystallization and resulted in new crystalline form from DMF as a dihydrate. The hydrates of both 1 and 2 can be classified as isolated site hydrates. In these crystal structures, water molecules found to exhibit three types of coordination environments with regard to hydrogen bonds.