Recent research progress on crystallization strategies for difficult-to-crystallize organic molecules

Both natural organic products and complex compounds synthesized by organic chemists often contain many stereochemical configurations, so the identification of their structures and their absolute configurations are very important. Single-crystal X-ray crystallography is considered to be the most reliable method to determine their structures and their absolute configurations. With this method, it is important to obtain their single crystals before they are studied by X-ray crystallography. However, some organic molecules with flexible structures, especially oily organic molecules, are not easy to crystallize, such as vaseline and decane. To solve this problem, various approaches have been developed. This review focuses on a variety of crystallization strategies for organic molecules, especially for the difficult-to-crystallize organic molecules. In this review, the basic principles, characteristics, applicability, and application examples of these crystallization methods are summarized to broaden the research and their applications, providing a reference for difficult-to-crystallize organic molecules.