Effect of the Functional Group Position in Coformers on Ternary Cocrystals: A Case of Sulfamoylbenzoic Acids

Ternary cocrystals are an interesting and important topic of multicomponent crystals in crystal engineering. Although some cases of ternary cocrystals and strategies have been reported, the number remains limited, and the related principles are not yet well developed. Herein, 4-chloro-3-sulfamoylbenzoic acid and 2,4-dichloro-5-sulfamolybenzoic acid were selected as model materials, and pyridine carboxamides (picolinamide, nicotinamide, and isonicotinamide) and lactams (2-hydroxy-3-methylpyridine, 2-pyridone, and 2-hydroxy-6-methylpyridine) were used as coformers for synthesizing ternary cocrystals. With the help of powder X-ray diffraction, thermal analysis, and nuclear magnetic resonance spectra, four new ternary cocrystals were found, and the single crystal structures of three of them were successfully analyzed. The functional group position in coformers is found to have two effects on ternary cocrystals. On the one hand, it affects the tendency to generate binary products. On the other hand, there is a certain match between the two types of coformers. Further theoretical calculations show that geometrical recognition among the three components is more important for the formation of ternary cocrystals than the lattice energy.