Research paper of the month
July 2014 - Amorphous Metal−Organic Frameworks
In this Account, we describe the preparation of amorphous metal-organic frameworks (αMOFs) by introduction of disorder into their parent crystalline frameworks. αMOFs may find applications in multiple areas, especially those that might involve the collapse of porous MOF structures around guest species. Reversible gas storage using pressure-induced amorphization and irreversible long-term harmful substance storage have already been suggested, while release times of drug-loaded MOFs might also be tailored using partial amorphization. In addition, zeolite collapse has been shown to produce inorganic glasses, and similar processes might be used as routes to functional hybrid glasses. A third route of exploration involves understanding the process of amorphization itself (thermal or pressure-induced), in order to provide greater insight into the processing of MOF powders (sintering and densification).
Figure: Powder X-ray diffraction pattern and atomic configurations for a crystalline (bottom) and amorphous (top) metal-organic framework. Application of stress (temperature, ball-milling or hydrostatic pressure) is used to convert between the two. Guests (e.g. drug molecules, lanthanide ions or toxic gases) can be irreversibly trapped in these collapsed structures.
Thomas D. Bennett and Anthony K. Cheetham, "Amorphous Metal−Organic Frameworks", Acc. Chem. Res., Article ASAP (2014)