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Tolerance of Metal-Organic Frameworks to Functionalization

  • Author(s): Allen, Corinne An-Li
  • et al.
Abstract

Metal-Organic Frameworks (MOFs) are porous coordination polymers with the potential to excel in catalysis and gas storage/separation. This dissertation will first discuss relevant types of MOFs, their characteristics, and previous functionalization methods. To fully gauge the utility of MOFs, novel materials with tunable properties are required as are appropriate design strategies to create these materials. Of specific interest is MOFs embedded with secondary metal binding groups. Chapter 2 will discuss a mild method to incorporate these functional groups into MOFs. The utilization of photocleavable protecting groups, a nitrobenzyl ether masking an aryl hydroxyl group, allows for the liberation of secondary metal binding sites upon photoirradiation. By combining mixed MOF systems with photochemical and chemical modification methods, multifunctional materials can be accessed from a single starting MOF. Exploration of new postsynthetic modification reactions is explored in Chapter 3. Initial studies focused on a radical initiated photochemical-click reaction to modify a terminal alkene with a free thiol to create a thioether. Depending on the chemical stability and pore size of the MOF material, this reaction was moderately successful at best. Additionally, optimization proved to be difficult due to the number of chemical species present during the course of the reaction. A simpler click Diels-Alder cycloaddition was studied as an alternative route to modify a terminal alkene embedded inside the MOF. The cycloaddition was found to proceed only if there was sufficient space available within the MOF pores and around the alkene moiety. Finally, in Chapter 4, chemically crosslinked organic ligands are studied to probe the tolerance of certain MOFs for geometrically restricted components. Extended oligomeric ligands based on these criteria are also discussed. Even using ligands with up to four organic struts tethered together, the canonical IRMOF structure can still be formed. This indicates that the limitations of coordination polymers are much less stringent than originally thought

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