The solvates of sulfamerazine: structural, thermochemical, and desolvation studies

The ability of an antibacterial agent, sulfamerazine (SMZ), to form solvates is investigated. Six solvates, with the solvents 1,4-dioxane (1 : 1 and 1 : 0.5), dimethylacetamide, dimethylformamide, cyclopentanone and 3-picoline, were identified and characterized by various analytical techniques, namely, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction. Crystal structure analysis revealed a dimer via a pair of intermolecular N-H center dot center dot center dot N hydrogen bonds between two molecules of SMZ and extended hydrogen bonded networks mediated by the solvent molecules. The conformationally flexible SMZ molecule adopts different conformations in the crystal structures. Thermal analysis established the stability and confirmed molar ratios of the reported solvates. Crystal structures of the sulfonamide drugs were retrieved from the Cambridge Structural Database (CSD) and analyzed to rationalize the factors that favour the solvate formation in sulfonamide drugs. It was found that the CSD statistics under-represent the true prevalence of solvates and polymorphs of sulfonamide drugs, and solvents that contain hydrogen bond acceptor groups have higher likelihood of forming solvates with sulfonamide drugs. Furthermore, a one-dimensional hydrogen bond chain motif was predominantly observed in the crystal structures of solvates/hydrates.