Structural Landscape of an Antimicrobial Sulfa Drug Sulfachloropyridazine: Polymorphs, Solvates, and Cocrystals

Experimentally identified unique crystal forms (polymorphs, solvates, and molecular complexes) of a particular compound logically reside in a certain low-energy point in the crystal landscape. The observed crystal forms offer an effective route to access different landmarks in the crystal landscape of a compound, which in turn is a profile of the structural and energetic changes occurring at the late stage of crystallization. We experimentally determined nine novel crystal forms-a polymorph, two solvates, and six cocrystals-of the sulfa drug sulfachloropyridazine. The spectral, thermal, and diffraction studies unequivocally establish the structural characteristics and the stability relationship of the polymorphs. The added coformers, with no specific chemical similarity but related by geometric and interaction types, lead to the convergence of torsional preferences and supramolecular synthons and hence a modular design of crystal structures.