Abstract
Metal-organic frameworks (MOFs) are a new category of advanced porous materials undergoing study by many researchers for their vast variety of both novel structures and potentially useful properties arising from them. Their high porosities, tunable structures, and convenient process of introducing both customizable functional groups and unsaturated metal centers have afforded excellent gas sorption and separation ability, catalytic activity, luminescent properties, and more. However, the robustness and reactivity of a given framework are largely dependent on its metal-ligand interactions, where the metal-containing clusters are often vulnerable to ligand substitution by water or other nucleophiles, meaning that the frameworks may collapse upon exposure even to moist air. Other frameworks may collapse upon thermal or vacuum treatment or simply over time. This instability limits the practical uses of many MOFs. In order to further enhance the stability of the framework, many different approaches, such as the utilization of high-valence metal ions or nitrogen-donor ligands, were recently investigated. This review details the efforts of both our research group and others to synthesize MOFs possessing drastically increased chemical and thermal stability, in addition to exemplary performance for catalysis, gas sorption, and separation.
Highlights
Metal-organic frameworks are composed of metal-containing secondary building units (SBUs) connected by rigid or semirigid polytopic organic linkers
This study mainly covered how the functional groups changed the flexibility and swelling of the framework, but it showed that most functional groups did not cause a large change in the thermal stability of the framework. Another example of superhydrophobic N-based Metal-organic frameworks (MOFs) stable to moisture was the Ni- bis-pyrazolate MOFs developed by Padial et al [50]
MOF research, though based on decades of research on coordination polymers and traditional porous materials, blossomed after the discovery of porous, functionalizable Zn2+ and Cu2+ frameworks that could be grown as single crystals and characterized [2, 5]
Summary
Metal-organic frameworks are composed of metal-containing secondary building units (SBUs) connected by rigid or semirigid polytopic organic linkers. In PCN-222, our group synthesized single crystals of an extremely stable Zr-based MOF with porphyrin-containing ligands that can themselves bind different metal ions, enabling a variety of catalytic activities, which was enabled both by the actual catalytic sites and by the high pore size and water and temperature stability of this MOF [32]. By using similar Zr SBUs along with tetrahedral ligands, stability was maintained alongside a higher surface area (BET 3411 m2 g−1) in PCN-521 (Figure 5), which mimicked the topology of fluorite by exploiting the cubic nature of the 8-connected Zr6O8 clusters in combination with the 4-connected tetrahedral linkers [24] All of these Zr-MOFs exhibited high chemical stability due to the strong Zr–O bonds, and all were synthesized as single crystals by carefully varying the type and amount of modulating reagent. Other examples of waterstable Zr4+-based MOFs after the use of modulating reagents have been published [38]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
