A new solvate of clonixin and a comparison of the two clonixin solvates

A new solvate of clonixin (CLX), a dimethylacetamide (DMA) solvate, has been obtained by crystal growth in DMA. The new form was characterized by NMR, single-crystal X-ray diffraction, and PXRD. The crystal structure is stabilized by a strong hydrogen bond between the carboxylic acid OH ofCLXand the DMA carbonyl, the strength of which is on par with those of the four solvent-free forms ofCLXand the DMF solvate. These previously known forms are based on either the acid-acid homosynthon or the acid-pyridine heterosynthon, depending on the dihedral angle between the two aromatic rings ofCLX, or the heterodimer betweenCLXand DMF. The new solvate loses DMA to convert into formIofCLX, as confirmed by differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD), similar to how the DMF solvate does. A comparison of the two solvates was carried out and theoretical studies were performed to shed light on the conformational difference between the twoCLXmolecules in the two solvates and the packing differences between them. The insight gained on this solvatomorphic system could aid the design of new solvates and cocrystals ofCLX.