Name: Characterization of the MOF by Powder X-Ray Diffraction (PXRD) and Nuclear Magnetic Resonance (NMR) After Digestion
Uploaded: 2023-06-23T14:05:00
Description: Watch this Scientific Journal Video about Characterization of the MOF by Powder X-Ray Diffraction PXRD and Nuclear Magnetic Resonance NMR After Digestion at JoVE.com

characterization of the mof by powder x-ray diffraction (pxrd) and nuclear magnetic resonance (nmr) after digestion

Sintesi e caratterizzazione di Zr-MOF funzionalizzati con triazolo e tetrazolo

Metal-organic frameworks (MOFs) are three-dimensional porous materials that are formed through coordination bonds between metal clusters and multi-topic organic ligands. MOFs have garnered significant attention due to their permanent porosity, low density, and ability to associate organic and inorganic components, which enables diverse applications1,2. Moreover, the vast range of metal nodes and strut organic linkers offer MOFs theoretically unlimited structural combinations. Even with identical framework structures, MOFs&#39; physical and chemical properties can be modified through ligand functionalization with chemical tags. This modification process offers a promising route to tailor the properties of MOFs for specific applications3,4,5,6,7,8,9.
Both the pre-functionalization of ligands prior to MOF synthesis and post-synthetic modification (PSM) of MOFs have been employed to introduce and/or modify functional groups in MOF ligands10,11. In particular, covalent PSMs have been extensively studied to introduce new functional groups and generate a range of MOFs with diverse functionalities12,13,14. For instance, UiO-66-NH2 can be converted to amide-functionalized UiO-66-AMs with different chain lengths (ranging from the shortest acetamide to the longest n-hexyl amide) through acylation reactions with appropriate acyl halides (such as acetyl chloride or n-hexanoyl chloride)15,16. This approach demonstrates the versatility of covalent PSMs to introduce specific functional groups onto MOF ligands, paving the way for a broad range of applications.
In addition to covalent PSMs, post-synthetic ligand exchange (PSE) is a promising strategy for modifying MOFs (Figure 1). Since MOFs are composed of coordination bonds between metals and ligands (such as carboxylates), these coordination bonds can be replaced with external ligands from a solution. Exposing MOFs to a solution containing the desired ligand with chemical tags can be incorporated into the MOFs via PSE17,18,19,20,21,22. Since the PSE process is accelerated by the existence of coordinative solvents, the phenomenon is also called solvent-assisted ligand exchange (SALE)23,24. This approach offers a flexible and facile method for functionalizing MOFs with a wide range of external ligands, enabling a broad spectrum of applications25,26,27,28,29.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/65619/65619fig01.jpg" /> 
Figure 1: Synthesis of triazole and tetrazole-functionalized H2BDC ligands and preparation of triazole- and tetrazole-functionalized UiO-66 MOF through PSE. <a href="https://www.jove.com/files/ftp_upload/65619/65619fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The progress of the PSE process can be controlled by adjusting the ligand ratio, exchange temperature, and time. Notably, room temperature PSE can be employed to obtain functionalized MOFs by exchanging ligands from a solution into MOF solids20. The PSE strategy is particularly useful for introducing both thermally unstable functional groups (such as azido groups) and coordinative functional groups (such as phenol groups) into MOF structures18. In addition, the PSE strategy has been applied to various MOFs with metal and coordination bond variations. This exchange is a universal process in the chemistry of MOFs30,31,32. In this study, we present a detailed protocol for PSE to obtain functionalized MOFs from pristine, non-functionalized MOFs, and we provide a characterization strategy to confirm successful functionalization of the MOFs. This method demonstrates the versatility and convenience of PSE for modifying MOFs with diverse functional groups.
Tetrazole-containing benzene-1,4-dicarboxylic acid (H2BDC-Tetrazole)33, and triazole-containing benzene-1,4-dicarboxylic acid (H2BDC-Triazole) are synthesized as target ligands and utilized in the PSE of UiO-66 MOFs to obtain novel, coordination-free, triazole-containing MOFs. Both triazoles and tetrazoles possess acidic N-H protons on their heterocyclic rings and can coordinate with metal cations, thus enabling their use in constructing MOFs34,35. However, there are limited studies on incorporating coordination-free tetrazoles and triazoles into MOFs and related structures. In case of triazole-functionalized Zr-MOFs, UiO-68 type MOFs were investigated to photophysical properties through direct solvothermal synthesis with benzotriazole functionalities36. For tetrazole-functionalized Zr-MOFs, the mixed direct synthesis was employed33. These heterocycle-functionalized MOFs could provide potential coordinating sites in MOF pores for catalysis, selective molecular uptake by binding affinity, and energy-related applications, such as proton conduction in fuel cells.

Autore in primo piano: Funzionalizzazione delle strutture metallo-organiche: progressi, sfide e il potere dello scambio di ligandi post-sintetici 

Sintesi di strutture metallo-organiche a base di triazolo e tetrazolo funzionalizzate a Zr attraverso lo scambio di leganti post-sintetici

Our main research topic is functionalizing the porous metal-organic frameworks, MOFs, with interesting functional groups through various techniques. This study is focused on heterocycle installation in MOFs. PSE, post-synthetic ligand exchange is the main technique in this work.The ligand with target functional group could be installed in presynthesized MOFS throughout the solid-solution exchange process. Especially, some of the unstable ligands and ligands with coordinating groups could be efficiently incorporated into MOFs through the PSE techniques. Both triazole and tetrazole functional groups have multiple coordinating nitrogen grooves.Therefore, there is competition for coordination between metal carboxylate and metal triazolate or tetrazolate. The incorporation ratio of target ligands is easily controlled in the PSE process and multiple targets could be installed in a single MOF through this approach.

Watch this Scientific Journal Video about Characterization of the MOF by Powder X-Ray Diffraction PXRD and Nuclear Magnetic Resonance NMR After Digestion at JoVE.com

Characterization of the MOF by Powder X-Ray Diffraction (PXRD) and Nuclear Magnetic Resonance (NMR) After Digestion  

Caratterizzazione del MOF mediante diffrazione di raggi X in polvere (PXRD) e risonanza magnetica nucleare (NMR) dopo digestione

Trasferire circa 10 milligrammi del solido MOF scambiato con UiO-66-triazolo in un portacampioni di diffrazione a raggi X in polvere. Posizionare il supporto del campione nel diffrattometro e raccogliere il modello di diffrazione dei raggi X della polvere. Per iniziare la caratterizzazione NMR, trasferire circa 30 milligrammi del solido MOF scambiato in una fiala fresca da quattro millilitri.Quindi spostare 400 microlitri di DMSO-d6 sul campione MOF utilizzando una micro pipetta. Trasferire 200 microlitri di soluzione di ossido di deuterio al fluoruro di ammonio 4,14 molari in una sospensione DMSO-d6 di polvere MOF utilizzando una micro pipetta. Sonicare la miscela eterogenea per 30 minuti fino a quando il MOF non viene sciolto nel solvente misto di ossido di deuterio dimetilsolfossido dopo la digestione.Una volta fatto, rimuovere eventuali solidi insolubili rimanenti filtrando la soluzione attraverso un filtro a siringa in difluoruro di polivinilidene mentre lo si trasferisce dalla fiala da quattro millilitri a un tubo di risonanza magnetica nucleare. Per determinare il successo dello scambio, sono stati misurati i modelli di diffrazione dei raggi X della polvere e confrontati con UiO-66 MOF incontaminato per la cristallinità. La posizione dei picchi di riflessione, l'intensità relativa e l'ampiezza nei modelli di diffrazione dei raggi X in polvere di UiO-66-triazolo e UiO-66-tetrazolo scambiati corrispondono a MOF UiO-66 incontaminati, indicando che lo scambio di ligando non ha avuto alcun impatto sulla struttura del framework.I rapporti di scambio sono stati determinati confrontando l'integrazione di BDC non funzionalizzato e BDC-triazolo o BDC-tetrazolo. I rapporti di scambio per Triazolo e Tetrazolo sono risultati essere rispettivamente del 33% e del 30% dall'analisi post-scambio di liganti sintetici.

Research

JoVE Journal

Chemistry

Characterization of the MOF by Powder X-Ray Diffraction (PXRD) and Nuclear Magnetic Resonance (NMR) After Digestion

Synthesis of Triazole and Tetrazole-Functionalized Zr-Based Metal-Organic Frameworks Through Post-Synthetic Ligand Exchange

Metal-organic frameworks (MOFs) are a class of porous materials that are formed through coordination bonds between metal clusters and organic ligands. ...