Postsynthetic Modification of Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are porous crystalline materials that are built from metal ions or metal ion clusters and organic ligands. There has been much interest in designing functionalized MOFs with enhanced host-guest interactions for potential applications in gas storage, catalysis, and separation. However, it has remained a challenge to synthesize functionalized MOFs directly through traditional MOF synthesis. This dissertation focuses on the development of postsynthetic modification (PSM) as a method for functionalizing MOFs. A systematic overview of PSM will be presented to highlight PSM as a general, versatile approach for enhancing the physical and chemical properties of MOFs. In the first half of this dissertation, IRMOF-3, an amino-containing MOF, is modified with a series of alkyl anhydrides, and the effects of reagent size on modification extent are explored. In the next chapter, other amino-containing MOFs systems (DMOF-1-NH₂ and UMCM-1-NH₂) are synthesized and modified using PSM. Through this study, PSM is shown to be a practical approach for functionalizing MOFs, and also indicates MOF topology can influence the modification outcome. The second half of this dissertation focuses on using PSM to develop MOFs for gas storage and catalysis applications. IRMOF-3, DMOF-1-NH₂, and UMCM-1-NH₂ are modified and tested for H₂ storage. The MOFs are modified with certain functionalities (e.g., alkyl vs. aromatic) to determine if H₂ uptake and heat of adsorption is improved. In a separate study, UMCM-1-NH₂ is modified with metal binding substituents, and is metallated with different metal ions to generate a series of potential Lewis acid MOF catalysts. The metallated UMCM MOFs are tested for the Mukaiyama aldol reaction and for epoxide ring opening catalysis, and the catalytic results are presented. Lastly, a new functionalization technique, named postsynthetic deprotection (PSD), is introduced. Two new BDC ligands are synthesized with photolabile protecting groups and are incorporated into MOFs. The MOFs are then exposed to UV light, which results in the removal of the photolabile groups to produce MOFs with free, uncoordinated hydroxyl groups. This is the first example of using light to unmask functionalities in a MOF, and presents a novel route for obtaining MOFs with more complex functionalities