For the most part, the many practical applications of metal–organic frameworks (MOFs) are a result of the properties of these structures in the crystalline state. Where other materials (such as metals) may be easily melt-cast or reshaped — retaining their chemical composition and functional properties — the instability of crystalline MOFs has prevented similar processing into other forms. Now, Thomas Bennett and colleagues report a new phase transition behaviour observed on heating zeolitic imidazole frameworks (ZIFs). By carefully increasing temperature over time they were able to prevent ZIF degradation, and instead observed framework melting into an amorphous liquid. On further heating a dense crystalline phase was observed, which can also be remelted. Subsequent quenching yields a hybrid glass. Apart from the potential new practical applications for MOFs that this behaviour may allow, this process may also offer a route for the synthesis of glasses with controllable chemical functionality.
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Hennessy, J. Melting frameworks. Nature Mater 14, 962 (2015). https://doi.org/10.1038/nmat4438