Postsynthetic Modification of Metal-Organic Frameworks

The current interest in MOFs is largely a consequence of their porosity. Many MOFs, especially those based on polycarboxylate and imidazolate linkers, show permanent porosity on removal of the solvent molecules from the pores and channels of the as-synthesized materials. This property has been utilized for a wide range of potential applications including hydrogen storage/ separations, and heterogeneous catalysis.  

The properties of a MOF are related to the nature of the pores, and by introducing specific functional groups onto the pore surface, these properties can be tuned. Simple functional groups such as amines or halides can often be incorporated into a MOF through using the functionalized linker in the synthesis. This approach is, however, limited as many functional groups are not tolerant of the conditions used for MOF synthesis or lead to changes in the nature 

The idea of modifying the pores of a preformed extended network to tailor its properties was first suggested by Hoskins and Robson in 1990, and the first reports of this being carried out in practice were published independently by the groups of Lee, Kim, and Williams in 1999 and 2000. After this initial activity, the field lay largely dormant for several years before being revived by Wang and Cohen in 2007.  

Covalent PSM this involves eovalent modification of a linker ligand and is the most well-developed type of PSM in MOF chemistry. 

Dative PSM this involves coordination of a metal center to a linker. 

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Wang ZQ, Cohen SM. Postsynthetic modification of metal-organic frameworks. Chem Soc Rev 2009 38 1315-29. 

Mechanochemical Approaches to Metal-Organic Frameworks Porphyrinic Metal-Organic Frameworks Postsynthetic Modification of Metal-Organic Frameworks Recent Solid-State NMR Studies of Quadrupolar Nuclei in Metal-Organic Frameworks Patterning Techniques for Metal-Organic Frameworks. 

Edible Metal-Organic Frameworks Metal-Organic Frameworks for Removal of Harmful Gases Postsynthetic Modification of Metal-Organic Frameworks Open Metal Sites in Metal-Organic-Frameworks Adsorption of Hydrocarbons and Alcohols in Metal-Organic Framework Materials. 

Photoreactive Metal-Organic Frameworks Porphyrinic Metal-Organic Frameworks Postsynthetic Modification of Metal-Organic Frameworks. 

Wang Z, Tanabe KK, Cohen SM (2010) Tuning hydrogen sorption properties of metal-organic frameworks by postsynthetic covalent modification. Chem Eur J 16 212-217... 

Tanabe KK, Wang Z, Cohen SM (2008) Systematic functionalization of a metal-organic framework via a postsynthetic modification approach. J Am Chem Soc 130 8508-8517... 

Wang Z, Cohen SM (2007) Postsynthetic covalent modification of a neutral metal-organic framework. J Am Chem Soc 129 12368-12369... 

Taylor-Pashow KML, Rocca JD, Xie Z et al (2009) Postsynthetic modifications of iron-carboxylate nanoscale metal-organic frameworks for imaging and drug delivery. J Am Chem Soc 131 14261-14263... 

AAS = atomic absorption spectroscopy ATOF-MS = aerosol time-of-flight mass spectrometry 2,6-ndc = 2,6-naphthalenedicarboxylate bdc = 1,4-benzenedicar-boxylate bpdc = 1,3,5-benzenetricarboxylate bpydc = 2,2 -bipyridine-5,5 -dicarboxylate btb = 4,4, 4"-benzene-1,3,5-triylbenzoate btc = 1,3,5-benzenetricarboxylate 3D = three-dimensional dabco = l,4-diaza[2.2.2]bicyclo-octane EDX = energy-dispersive X-ray spectroscopy EXAFS = extended X-ray fine structure Fc = ferrocenyl ICP-AES = inductively coupled plasma atomic emission spectroscopy MOF = metal-organic framework PSD = postsynthetic deprotection PSM = Postsynthetic modification PXRD = Powder X-ray diffraction 1,4-ndc = 1,4-naphthalenedicarboxylate SALE = solvent-assisted linker exchange SBU = secondary building unit ... 

There are several basic approaches to the design of heterogeneous catalysts based on MOFs the use of MOFs as classical supports for an active metal, the immobilization of a catalytically active site in the framework per se (in the inorganic node or in the organic linker), host-guest interaction, postsynthetic modification of the framework, and so forth. These approaches will be discussed later in more detail. 

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