Polymorphism in cocrystals: a review and assessment of its significance

Cocrystals have gained much interest in recent years owing to their potential to improve the physicochemical properties of the parent compounds. It was once thought that cocrystals could be a means to prevent polymorphism but many recent examples of cocrystal polymorphism have been discovered and reported. Similar to single component crystals, polymorphs of cocrystals can display significantly different properties. In this contribution, we present a survey of polymorphic cocrystals. The different types of polymorphs, namely synthon, conformational, packing, and tautomeric, are identified and discussed with representative examples. In addition, polymorphs of cocrystals that showed distinct physicochemical properties are highlighted.