Abstract
Postsynthetic reactions of metal-organic frameworks (MOFs) are versatile tools for producing functional materials, but the methods of evaluating these reactions are cumbersome and destructive. Here we demonstrate and validate the use of in situ NMR spectroscopy of species in the liquid state to examine solvent-assisted ligand exchange (SALE) and postsynthetic modification (PSM) reactions of metal-organic frameworks. This technique allows functionalization to be monitored over time without decomposing the product for analysis, which simplifies reaction screening. In the case of SALE, both the added ligand and the ligand leaving the framework can be observed. We demonstrate this in situ method by examining SALE and PSM reactions of the robust zirconium MOF UiO-67 as well as SALE with the aluminum MOF DUT-5. In situ NMR spectroscopy provided insights into the reactions studied, and we expect that future studies using this method will permit the examination of a variety of MOF–solute reactions.
Highlights
We investigated the use of in situ 1H nuclear magnetic resonance (NMR) to monitor reactions of metal-organic frameworks (MOFs) with dissolved species, and to derive time-resolved information about the functionalization of MOF
In order to minimize the effect of mass transfer on reactions in the NMR tube, the MOF was ground before use
The multiphase solvent-assisted ligand exchange (SALE) reaction can only be followed by in situ 1H NMR if the exchanging linker is present in the liquid state, rather than adsorbed on or in the MOF
Summary
We investigated the use of in situ 1H NMR to monitor reactions of MOFs with dissolved species, and to derive time-resolved information about the functionalization of MOF. The multiphase SALE reaction can only be followed by in situ 1H NMR if the exchanging linker is present in the liquid state, rather than adsorbed on or in the MOF. Ground UiO-67-bpdc was combined with a solution of bpydc(sol) in an NMR tube to give a mixture with linker(frame):linker(sol) in the range 0.5–1.5.
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