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

Multitopic Phosphine Linker에서 Low-Valent MOF의 합성

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.

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

Multitopic Phosphine Linkers로부터 저가 금속-유기 프레임워크의 합성을 위한 실험적 접근법

Our research aims to explore the synthesis and properties of metal organic frameworks constructed from low-valent metal ions. How to prepare these materials and their characteristics are not widely understood, but they likely hold tremendous opportunities for solid-state catalysis and other applications. Beyond our own work, there have been only a handful of reports on MOFs prepared from low-valent metal ions.Perhaps the most notable are those by Professor Joshua Figueroa here at UC San Diego who has described MOFs prepared from bulky isocyanate ligands and zero or monovalent metals. Because there are so few descriptions of low-valent MOFs, our protocol is providing a first baseline protocol that works for making these materials. That stated, our protocol is specifically designed for phosphine ligands and may not be readily translatable to different ligand systems such as isocyanates.Our findings open up opportunities to explore MOF materials with distinct characteristics from most MOFs described to date. For example, we have a new paper in press reporting a solid-state analog of Vaska's complex, which binds oxygen reversibly in a unique manner compared to the few other MOFs that do this. We are interested in opening up new opportunities to make low-valent MOFs, particularly as new solid-state catalysts.We want to answer questions such as:What other low-valent metal ions can be used to make LV MOFs, and can we mimic the reactivity of low-valent compounds using these solid-state materials?

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)  

분말 X선 회절(PXRD)에 의한 MOF 제품의 특성화

약 20-30mg의 결정성 고체 MOF 생성물을 실리콘 PXRD 샘플 홀더로 옮기고 회절계에 넣습니다. 악기의 문을 닫고 4에서 40까지 2-theta에서 PXRD 패턴을 수집합니다. 데이터를 실리콘 팔라듐 저가 MOF의 시뮬레이션된 분말 패턴과 비교합니다.이 그림에는 깨끗한 주석-팔라듐 저가 MOF의 PXRD 패턴이 나와 있습니다. 여기서, 청색은 실험적인 PXRD 패턴이고, 검정색은 결정화된 구조로부터 얻어진 실리콘 팔라듐 저가 MOF의 시뮬레이션된 PXRD 패턴이다. 주석-팔라듐 저가 MOF의 비정질 샘플에 대해 얻은 PXRD 패턴이 여기에 나와 있습니다.샘플은 트리페닐포스핀 조절제 없이 제조되었고, 그 결과 비정질 또는 불량한 결정질 물질이 생성되었습니다.

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

610 조회수.  University of California, San Diego. 약 20-30mg의 결정성 고체 MOF 생성물을 실리콘 PXRD 샘플 홀더로 옮기고 회절계에 넣습니다. 악기의 문을 닫고 4에서 40까지 2-theta에서 PXRD 패턴을 수집합니다. 데이터를 실리콘 팔라듐 저가 MOF의 시뮬레이션된 분말 패턴과 비교합니다.이 그림에는 깨끗한 주석-팔라듐 저가 MOF의 PXRD 패턴이 나와 있습니다. 여기서, 청색은 실험적인 PXRD 패턴이고, 검정색은 결정화된 구조로부?...