Mapping the Crystallographic Landscape of Antivitamin Ionic Liquids: Structural Blueprints for Novel Architectures

This work presents the first in-depth crystallographic study of antivitamin-derived ionic liquids. Seven new amprolium salts incorporating hallmark ionic-liquid anions such as bis-(trifluoromethanesulfonyl)-imide (NTf₂ ^-), bis-(pentafluoroethanesulfonyl)-imide (BETI^-), tetrafluoroborate (BF₄ ^-), and hexafluorophosphate (PF₆ ^-) were synthesized and crystallized, and their structures and interactions were elucidated through crystallographic and computational analyses. The well-documented biological functions of amprolium can help simplify future applications of these compounds as well as open the pathway for the development of novel cations for ionic liquid development. Despite their dicationic nature and bearing multiple H-bonding donors and acceptors, these compounds exhibited unexpectedly low melting points and displayed challenging crystallization conditions. The analysis identified key structural features explaining this behavior: (i) two points of conformational disorder in the pyrimidine ring and propyl moiety; (ii) three distinct cation conformations affecting aromatic components; and (iii) novel high-energy conformations of anions, reported here for the first time. Hydrogen interactions dominated intermolecular forces (85% of total interactions), with H-bonding to oxygen and fluorine being most prevalent. These insights advance our understanding of how to engineer functional materials from natural sources for potential applications in sustainability and medicine. The combined experimental-computational approach validates these design principles, providing a foundation for more targeted development of similar compounds with tailored properties.