Cocrystal formation between chiral compounds: How cocrystals differ from salts

A cocrystal screening of a series of chiral target compounds was performed in order to investigate the propensity for two optically active compounds to cocrystallize in an enantiospecific manner. Thirteen novel cocrystal systems were identified, out of which 11 are enantiospecific and two present a diastereomeric cocrystal pair, yielding a total of 15 novel cocrystals. Six of these are structurally characterized in this study. A meticulous search in the Cambridge Structural Database (CSD) has allowed expanding this study. The results led us to the conclusion that enantiospecific cocrystallization seems to be the common rule of thumb, as over 85% of cocrystal systems behave enantiospecifically. Directionality of the hydrogen bonding motifs is likely responsible for the cocrystals' predilection toward enantiospecificity, while salts are mainly stabilized by less directional electrostatic interactions, leading to the formation of diastereomeric pairs.