Metal@MOF

Fig. 4. a) Primary and secondary budding units in the aluminosilicate zeolite system, b) Primary and secondary building units as found in transition-metal MOFs. c) Primary and secondary building units present in uranyl containing CPs and MOFs. These polyhedral representations of uranyl square-, pentagonal-, and hexagonal bipyramids will be used throughout this review. 

A brief review of Ln coordination chemistry is warranted as a precursor to appreciating the structural systematics of extended solids comprised thereof. In addition, this section aims to exemplify a number of Ln-specific properties and coordination preferences with the goal of distinguishing these materials from transition metal MOFs and CPs. It is felt that there are a number of attractive features of the/-elements (specifically their luminescent behavior) that make Ln-MOFs potentially more appropriate for certain applications (e.g., sensing). 

Most of the examples of metal MOFs and metaloxides MOFs discussed up to now have been synthesized in order to obtain novel kinds of supported nanoparticles with potentially advantageous properties for applications in catalysis. The catalytic properties of the composite materials Pd MOF-5 and Cu MOF-5 were among the first to be tested. The Pd MOF-5 composite that was obtained by the gas phase loading/photolysis synthetic protocol (35.6 wt% Pd) showed moderate activity in catalysis of hydrogenation of cyclooctene [59], The Pd MOF-5 (1 wt%) synthesized by the incipient wemess technique from [PdCacac) ] was tested as catalyst in hydrogenation of styrene, 1-octene and c/x-cyclooctene, and exhibited a shghtly higher catalytic activity than Pd supported on activated carbon (Pd/Norit A Fig. 23) [51]. 

Finally, in an approach analogous to that used for porous carbons and zeolites, highly robust MOFs have been used as surface supports for metal atoms and clusters. An example here is the chemical vapour deposition of various metals into MOF-5, yielding materials classified as metal MOF-5 for which the nature of metal inclusion and the extent of exogenous loading is currently unknown. Of these, Cu MOF-5 is active in the synthesis of methanol from syngas and Pd MOF-5 catalyses the reduction of cyclooctene by hydrogen. ... 

While in situ assembly strategies described in the previous section are generally preferred for preparing Metal MOF and Polymer MOF composites, template synthesis is the most extensively used strategy for the preparation of MOFs having discrete molecular species encapsulated. The following are two selected examples that serve to illustrate the use of these preparation procedures and their potential. 

Nevertheless, a clear limitation of this method for preparing Metal MOFs is that the substances used for stabilizing the NPs suspension (MUA or PVP in the previous examples) also remain entrapped inside the pore system of the MOF and may obstruct the interaction of the metal sites with adsorbed molecules, which can be a drawback for the potential of these materials in catalytic applications. 

Meilikhov M, Yusenko K, Esken D, Turner S, Van Tendeloo G, Fischer RA. Metals MOFs—loading MOFs with metal nanoparticles for hybrid functions. Eur J Inorg Chem 2010 2010 3701-14. 

Hermes S, Fischer RA, Khodeir L, Schroeder F, Schmid R, Schroeter MK, et al. Metal MOF perspectives of metal organic open frameworks as novel host matrices for imbedding functional nanoparticles. Abstracts of Papers of the American Chemical Society 2006 231 83-lNOR. 

Hermes S, Schroter MK, Schmid R, Khodeir L, Muhler M, Tissler A, et al. Metal MOF loading of highly porous coordination polymers host lattices by metal organic chemical vapor deposition. Angew Chem, Int Ed 2005 44 6237-41. 

A very new reaction route for the synthesis of MOFs is the so-called postsynthetic ligand and metal ion exchange (PSE) processes. A1-MIL-53-NH2 and Al-MIL-53-Br were used in this study and ligand exchange reactions were demonstrated to take place under mild reaction conditions. In another experiment the incubation of AI-MIL-53-Br led to a mixed metal MOF Al/Fe-MIL-53-Br. 

MOF metal MOF linker (MOF acronym) Polymers Gas or gas mixture References... 

Hermes S, Schroder F, Amirjalayer S, Schmid R, Fischer RA. Direct imaging of loaded metal-organic framework materials (Metal MOF-5). J Mater Chem 2006 16 2464-72. 

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