Stabilization of the DMSO Solvate of 2-Chloro-5-nitrobenzoic acid (Mesalazine Impurity M) by Bifurcated Hydrogen Bonds: Crystallographic, Spectroscopic, Thermal and Computational Studies

The strategy for choosing the optimal solvent DMSO to produce the solvate of Mesalazine impurity M is demonstrated and the possibility of selective crystallization as a means to remove the impurity from the drug substance is proposed. The single crystal XRD was undertaken to identify molecular interactions that take place to compensate for the unsatisfied arrangement of hydrogen bonds in the supramolecular architecture. Interestingly, formation of O–H⋯S, O–H⋯O, and C–H⋯O connections leads to loop/ring motifs stabilizing the crystal entity. In the present study, purification of the drug molecule remains a chief objective for future investigations, since crystallization of Mesalazine impurity M alone cannot conclusively guarantee separation of impurity. Graphical Abstract: The present work emphasized hydrogen bonding interactions that play an important role in the supramolecular assembly of DMSO solvate of the Mesalazine impurity M.[Figure not available: see fulltext.]