Polymorphism in molecular crystals and cocrystals

Abstract

Polymorphism refers to a compound's ability to exist in more than one crystalline modification through variations in the solid-state structures. Over the years, polymorphism has received extensive academic and industrial attention because of its impact on physical and chemical properties of active pharmaceutical ingredients and materials. It is preferable to develop the most stable polymorph to avoid unwanted phase transformation during processing and manufacturing. Therefore, a thorough polymorph screening and complete characterization of all the polymorphs are vital for understanding stability and phase transformations among different polymorphs. Recent advances in screening methodologies and analytical techniques paved ways for successful identification of potential polymorphs.While polymorphism in active pharmaceutical ingredients and single-component crystals is widely studied, such studies in multicomponent crystals such as cocrystals have received significant attention only in recent years. This chapter highlights some recent polymorphic systems of molecular crystals and cocrystals and emphasizes the potential implications of polymorphism in pharmaceutical and materials science. A brief history of polymorphism, factors that control the crystallization of polymorphs, thermodynamic aspects, and recent advances in screening methodologies and analytical techniques are also covered.