Benznidazole, the primary drug used in Chagas’ disease treatment, has known side effects, which may limit its widespread use. Its low solubility could negatively interfere in the bioavailability, even accentuating the toxic effects. Cocrystals have been extensively used to modify and optimize physicochemical properties, but, as single-component raw materials, they are susceptible to the phenomenon of polymorphism. In this work, we report a trimorphic cocrystal containing a 1:1 ratio of benznidazole and salicylic acid. The crystalline structures of three polymorphs were elucidated by single-crystal X-ray diffraction. Moreover, several isostructural solvates were also synthesized and analyzed. The same carboxylic acid-imidazole supramolecular heterosynthon is present in the four forms, but the main structural feature is an extended column based on amide–amide hydrogen bonds. On the basis of the crystalline structures, the trimorphic system was classified as conformational and packing polymorphism. Furthermore, the dissolution profiles of the stable forms were determined and showed a significant solubility improvement over the raw material.

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The hormone estradiol 17β valerate (E2V), used in hormone replacement therapy, undergoes a structural phase transition at 251.1 K on cooling. The crystalline structures of the low and room temperature phases were determined showing that neither the space group nor the site symmetry and number of atoms are altered. These phases are related by a large conformational reorientation of the valerate chain. In addition, thermal analysis, solid state nuclear magnetic resonance, and infrared spectroscopy show that the transformation is reversible, discontinuous, and first order, evidencing the occurrence of an isosymmetric phase transition, rare for organic compounds.

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