Solution cocrystallization, an effective tool to explore the variety of cocrystal systems: caffeine/dicarboxylic acid cocrystals

Abstract

Although cocrystals have undergone a recent boost in popularity, limited time is spent on exploring the variety of possible cocrystal phases, which is likely due to the popularity and success of grinding methods. The number of studies where cocrystallization is systematically applied in solution remains limited. In this contribution, we present a rapid method for cocrystal synthesis in solution, which not only provides single crystals suitable for X-ray diffraction structural analysis but also allows one to explore the variety of cocrystal systems (polymorphs and solvates). Applying this approach to caffeine/dicarboxylic acid systems, we discovered 7 cocrystals and solved the structures for 6 of them. Astonishingly, the caffeine/mesaconic acid cocrystal system not only seems to be stoichiometrically diverse but furthermore also shows no less than 4 polymorphs of the 2 : 1 cocrystal.