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Polymorphism in molecular crystals is a prevalent phenomenon and is of great interest to the pharmaceutical community. The solid-state form is a key quality attribute of a crystalline product. Inconsistencies in the solid phase produced during the manufacturing and storage of drug substances and drug products may have severe consequences. It is essential to understand the solid-state behavior of the drug and to judiciously select the optimal solid form for development. This review highlights the pervasiveness and relevance of polymorphism and describes solid form screening and selection processes. Moreover, case studies on controlling polymorphs from a chemical development perspective are provided.

Single‐crystal X‐ray diffraction (SCXRD) is the preferred and most accurate technique for determining molecular structures. However, it can present challenges when dealing with specific small molecules and active pharmaceutical ingredients (APIs), as many do not form quality crystals without coformers or can be unstable. In this study, we introduce tetrakis(guanidinium) pyrenetetrasulfonate (G4PYR), a robust guanidinium‐organosulfonate (GS) framework that efficiently encapsulates small molecules and APIs rich in functional groups. The hydrogen bonding frameworks formed by G4PYR display well‐ordered structures with predictable pyrene‐pyrene distances, making them ideally suited for targeting arene‐based APIs with pendant groups. Successful encapsulation of various guests, including benzaldehyde, benzamide, and arenes containing multiple hydrogen bond donors and acceptors like uracil and thymine, was achieved. Furthermore, we successfully encapsulated important pharmaceutical and biologically relevant compounds, such as lidocaine, ropinirole, adenosine, thymidine, and others. Notably, we present a workflow for investigating host‐guest complex formation using powder X‐ray diffraction and high throughput experimentation. [ABSTRACT FROM AUTHOR]