Synthesis and Characterization of a Series of Sulfamethazine Multicomponent Crystals with Various Benzoic Acids

Nine multicomponent crystals consisting of sulfamethazine (sz) with benzoic acid and its derivatives were synthesized and characterized. Eight of the nine multicomponent crystals are cocrystals, while one is a molecular salt. The coformers used to form multicomponent crystals with sz include 2-chloro-4-nitrobenzoic acid (2c4n), 2-chloro-5-nitrobenzoic acid (2c5n), salicylic acid (2hba), 3-hydroxybenzoic acid (3hba), 4-hydroxybenzoic acid (4hba), 4-bromobenzoic acid (4Brba), benzoic acid (ba), cinnamic acid (ca), and toluic acid (ta). These multicomponent crystals were characterized by single-crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD), and differential scanning calorimetry (DSC). SC-XRD showed that eight of the coformers that interacted with sz formed the amidine-carboxyl synthon; the only exception to this was sz + 4hba, which formed the imidine-carboxyl synthon formed instead. PXRD confirmed that the single crystals were representative of the bulk material. DSC showed most of the multicomponent crystals to have only a melting phase transition, which differed from the melting points of the coformers. The only exceptions were sz + 4brba and sz + ca, where an additional endothermic peak was observed, which corresponds to an amorphous phase transition before melting.