characterization of the mof product by powder x-ray diffraction (pxrd)

Síntesis de MOF de baja valencia a partir de enlazadores de fosfina multitópicos

Metal-organic frameworks, or MOFs, are a class of crystalline, porous materials1. MOFs are constructed from metal ions or metal ion cluster nodes, often referred to as secondary building units (SBUs), and multitopic organic linkers to give two- and three-dimensional network structures2. Over the past three decades, MOFs have been studied extensively due to their potential use in gas storage3 and separation4, biomedicine5, and catalysis6. The overwhelming majority of MOFs reported are composed of high-oxidation state metal nodes and hard, anionic donor linkers, such as carboxylates2. However, many homogeneous catalysts utilize soft, low-valent metals in combination with soft donor ligands, such as phosphines7. Therefore, expanding the scope of MOFs that contain low-valent metals can increase the range of catalytic transformations to which MOFs can be applied.
The established strategies for the incorporation of low-valent metals into MOFs using embedded soft donor sites are limited in scope and reduce the free pore volume of the parent MOF structure6,8,9,10. An alternative approach is to use low-valent metals directly as nodes or SBUs in combination with multitopic soft donor ligands as linkers to construct the MOF. This strategy not only provides a high loading of low-valent metal sites in the MOF but may also reduce or prevent metal leaching into the solution as a result of the stability of the framework structure11. For example, Figueroa and co-workers used multitopic isocyanide ligands as soft donor linkers and Cu(I)12 or Ni(0)13 as low-valent metal nodes to produce two- and three-dimensional MOFs. Similarly, Pederson and co-workers synthesized MOFs containing zero-valent group 6 metal nodes using pyrazine as a linker14. More recently, our laboratory reported tetratopic phosphine ligands as linkers for the construction of MOFs containing Pd(0) or Pt(0) nodes (Figure 1)15. These MOFs are particularly interesting due to the prevalence of phosphine-ligated low-valent metal complexes in homogeneous catalysis7. Nevertheless, low-valent MOFs (LVMOFs) as a general class of materials are relatively underexplored in the MOF literature but have great promise for applications in heterogeneous catalysis for reactions such as azide-alkyne coupling16, Suzuki-Miyaura coupling17,18, hydrogenation17, and others11.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/65317/65317fig01v2.jpg" /> 
Figure 1: Synthesis of LVMOFs using phosphine linkers. Sikma and Cohen15 reported the synthesis of three-dimensional LVMOFs, E1-M, using tetratopic phosphine ligands, E1, as linkers, Pd(0) and Pt(0) as nodes, and triphenylphosphine as a modulator. The central atom, E, can be Si or Sn. <a href="https://www.jove.com/files/ftp_upload/65317/65317fig01largev2.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
While the differences in the nature of the linkers and nodes of LVMOFs may give them unique properties compared to conventional MOF materials, these differences also introduce synthetic challenges. For example, many of the metal precursors and linkers that are commonly used in the MOF literature can be used in air2. In contrast, the successful synthesis of phosphine-based LVMOFs requires the exclusion of both air and water15. Similarly, the types of modulators used to promote crystallinity and the solvents used in the synthesis of phosphine-based LVMOFs are unusual compared to those used in most of the MOF literature15. As a result, the synthesis of these materials requires equipment and experimental techniques that even experienced MOF chemists may be less familiar with. Therefore, in an effort to minimize the impact of these obstacles, a step-by-step method for the synthesis of this new class of materials is provided here. The protocol outlined here covers all aspects of the synthesis of phosphine-based LVMOFs, including the overall experimental procedure, air-free techniques, the required equipment, the proper storage and handling of LVMOFs, and characterization methods. The choice of the metal precursor, modulator, and solvent are also discussed. Enabling the entry of new researchers into this field will help accelerate the discovery of novel LVMOFs and related materials for applications in catalysis.

Autor destacado: Enfoques experimentales para la síntesis de marcos metal-orgánicos de baja valente a partir de enlazadores de fosfina multitópicos  

Enfoques experimentales para la síntesis de estructuras metal-orgánicas de baja valencia a partir de enlaces de fosfina multitópicos

Watch this Scientific Journal Video about Characterization of the MOF Product by Powder X-Ray Diffraction PXRD at JoVE.com

Characterization of the MOF Product by Powder X-Ray Diffraction (PXRD)  

Caracterización del producto MOF por difracción de rayos X en polvo (PXRD)

Transfiera aproximadamente de 20 a 30 miligramos del producto MOF sólido cristalino a un soporte de muestra PXRD de silicio y colóquelo en el difractómetro. Cierre la puerta del instrumento y recoja el patrón PXRD de 4 a 40 2-theta. Compare los datos con el patrón de polvo simulado de silicio paladio MOF de baja valencia.El patrón PXRD del prístino MOF de estaño-paladio de baja valencia se muestra en esta figura. Aquí, el azul es el patrón experimental PXRD, y el negro es el patrón PXRD simulado del silicio paladio de baja valencia MOF obtenido de su estructura cristalizada. Aquí se muestra el patrón PXRD obtenido para una muestra amorfa del MOF de estaño-paladio de baja valencia.La muestra se preparó sin ningún modulador de trifenilfosfina, lo que resultó en un material amorfo o poco cristalino.

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JoVE Journal

Chemistry

Characterization of the MOF Product by Powder X-Ray Diffraction (PXRD)

617 vistas. Transfiera aproximadamente de 20 a 30 miligramos del producto MOF sólido cristalino a un soporte de muestra PXRD de silicio y colóquelo en el difractómetro. Cierre la puerta del instrumento y recoja el patrón PXRD de 4 a 40 2-theta. Compare los datos con el patrón de polvo simulado de silicio paladio MOF de baja valencia.El patrón PXRD del prístino MOF de estaño-paladio de baja valencia se muestra en esta figura. Aquí, el azul es el patrón experimental PXRD, y el negro es el ...

Video: Characterization of the MOF Product by Powder X-Ray Diffraction (PXRD)  

Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, energy, and catalysis. Recently, low-valent MOFs (LVMOFs) have been explored for their potential use as heterogeneous catalysts, and multitopic phosphine linkers have been shown to be a useful building block for the formation of LVMOFs. However, the synthesis of LVMOFs using phosphine linkers requires conditions that are distinct from those in the majority of the MOF synthetic literature, including the exclusion of air and water and the use of unconventional modulators and solvents, making it somewhat more challenging to access these materials. This work serves as a general tutorial for the synthesis of LVMOFs with phosphine linkers, including information on the following: 1) the judicious choice of the metal precursor, modulator, and solvent; 2) the experimental procedures, air-free techniques, and required equipment; 3) the proper storage and handling of the resultant LVMOFs; and 4) useful characterization methods for these materials. The intention of this report is to lower the barrier to this new subfield of MOF research and facilitate advancements toward novel catalytic materials.

Here, we describe a protocol for the synthesis of low-valent metal-organic frameworks (LVMOFs) from low-valent metals and multitopic phosphine linkers under air-free conditions. The resulting materials have potential applications as heterogeneous catalyst mimics of low-valent metal-based homogeneous catalysts.

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, ...