Homo- or heterosynthon? A crystallographic study on a series of new cocrystals derived from pyrazinecarboxamide and various carboxylic acids equipped with additional hydrogen bonding sites

Article abstract of DOI:10.1021/cg300140w

Four new cocrystals of a well studied active pharmaceutical ingredient (API), namely, pyrazinecarboxamide (PZA), with various monocarboxylic acids equipped with additional hydrogen bonding sites such as vanillic acid (VA), gallic acid (GA), 1-hydroxy-2-naphthoic acid (1HNA), and indole-2-carboxylic acid (I2CA) have been successfully prepared and characterized by FT-IR, ¹H NMR, differential scanning calorimetry (DSC), and single crystal and powder X-ray diffraction (SXRD and PXRD, respectively) techniques. In the majority of the cases, preferential occurrence amide-amide and acid-acid homosynthons has been observed. Since the heterosynthon is energetically preferred to homosynthon, such unusual occurrence of homosynthon in these cocrystals is intriguing.