Phenyl-Perfluorophenyl Synthon Mediated Cocrystallization of Carboxylic Acids and Amides

The significance of face-to-face π−π stacking of phenyl and perfluorophenyl rings (Ph-Ph F ), a robust supramolecular synthon in aromatic and perfluoroaromatic crystal structures, is studied in the cocrystallization of simple aromatic carboxylic acids and amides. X-ray crystal structures of C 6 H 5 COOH·C 6 F 5 COOH 1, C 6 H 5 CONH 2 ·C 6 F 5 CONH 2 2, and C 6 H 5 CONH 2 ·C 6 F 5 COOH 3 are analyzed to understand the role of Ph-Ph F synthon in directing self-assembly and hydrogen bonding in these cocrystals. The strong hydrogen bond donor acidity of C 6 F 5 COOH and C 6 F 5 CONH 2 together with mixed stacks of phenyl and perfluorophenyl rings steer acid···acid and amide···amide hydrogen bonding in cocrystals 1 and 2 . Acid···amide hydrogen bonding is sufficiently strengthened by donor acidity and acceptor basicity in 3 that the role of the Ph-Ph F synthon is weaker because the aromatic rings stack with lateral offset. The complex C 6 H 5 COOH·C 6 F 5 CONH 2 4 could not be obtained under similar crystallization conditions. The crystal structure of C 6 F 5 CONH 2 is determined to compare molecular conformation and hydrogen bonding with motifs in the cocrystals. This study shows the viability of the Ph-Ph F synthon in the presence of strong hydrogen bonding COOH and CONH 2 groups for crystal engineering.