Conformational Polymorphism of Elsulfavirine Sodium Salt

The X-ray diffraction analysis of two polymorphs of sodium ( cis )-N-((4-(2-(4-bromo-3-(3-chloro-5-cyanophenoxy)-2-fluorophenyl)acetamido)-3-chlorophenyl)sulfonyl)propioimide shows that the organic anion in them is in elongated and globular conformations. Both conformations are characterized by the absence of strong intramolecular interactions. According to the quantum chemical study, both the isolated anion in the globular conformation and the polymorph containing it are more thermodynamically stable, and the difference in free energies of the polymorphs increases with temperature, which is explained by the role of the entropy factor. The elongated conformation is stabilized in the crystal by interanionic Hal…π interactions and stacking interactions involving the phenyl groups.