Approaches to crystallization from ionic liquids: complex solvents-complex results, or, a strategy for controlled formation of new supramolecular architectures?

There are now more than 1200 papers a year describing research results using the 'neoteric' solvents, known as ionic liquids (ILs). If ILs are such highly studied solvents, why has there been so comparatively little research in their use in crystallization? Here we explore this question and discuss possible strategies for utilization of the mundane and the unique aspects of ILs for novel crystallization strategies including crystallization of high and low melting solids using thermal shifts; "solvothermal" techniques; slow diffusion; electrocrystallization; and use of a co-solvent. The results presented here and those appearing in the literature indicate both the complex nature of these solvents and their promise in delivering unique solvation, metal ion coordination numbers, coordination polymer motifs, and metal-anion interactions, to name but a few. These complex, but fascinating, results and the promise of much more intimate control over crystallization processes will drive a growing interest in using ILs as crystallization solvents.