In-situ monitoring of the formation of crystalline solids

The processes occurring during the early stages of the formation of crystalline solids are not well understood thus preventing the rational synthesis of new solids. The investigation of the structure-forming processes is an enormous challenge for both analytical and theoretical methods because very small particles or aggregates with different chemical composition and different sizes must be probed, both before and during nucleation. Furthermore, these precursors are present in a complex and dynamic equilibrium. This Review gives a survey of the in-situ methods available for the study of the early stages of crystallization of solids and how they can help in the synthesis of metastable polymorphs, of transient intermediates, and/or precursors displaying new or improved properties. Examples of actual research demonstrate the necessity and potentials but also the limitations of in-situ monitoring of the formation of crystalline solids.