framework-structured solids
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This study made use of a recently developed combination of advanced methods to reveal the atomic structure of a disordered nanocrystalline zeolite using exit wave reconstruction, automated diffraction tomography, disorder modelling and diffraction pattern simulation. By applying these methods, it was possible to determine the so far unknown structures of the hydrous layer silicate RUB-6 and the related zeolite-like material RUB-5. The structures of RUB-5 and RUB-6 contain the same dense layer-like building units (LLBUs). In the case of RUB-5, these building units are interconnected via additional SiO4/2 tetrahedra, giving rise to a framework structure with a 2D pore system consisting of intersecting 8-ring channels. In contrast, RUB-6 contains these LLBUs as separate silicate layers terminated by silanol/sil-oxy groups. Both RUB-6 and RUB-5 show stacking disorder with intergrowths of different polymorphs. The unique structure of RUB-6, together with the possibility for an interlayer expansion reaction to form RUB-5, make it a promising candidate for interlayer expansion with various metal sources to include catalytically active reaction centres.
Weakness in a material, especially when challenged by chemical, mechanical or physical stimuli, is often viewed as something extremely negative. There are countless examples in which interesting-looking materials have been dismissed as being too unstable for an application. But instability with respect to a stimulus is not always a negative point. In this Perspective we highlight situations where weakness in a material can be used as a synthetic tool to prepare materials that, at present, are difficult or even impossible to prepare using traditional synthetic approaches. To emphasize the concept, we will draw upon examples in the field of nanoporous materials, concentrating on metal-organic frameworks and zeolites, but the general concepts are likely to be applicable across a wide range of materials chemistry. In zeolite chemistry, there is a particular problem with accessing hypothetical structures that this approach may solve.
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
In this paper, we review and illustrate applications, reported in the literature or used in our group, of 27Al-27Al double-quantum single-quantum (DQ-SQ) MAS NMR experiments for the structural characterization of Al-containing microporous solids, namely zeolites, aluminophosphates and metal-organic frameworks. Information regarding the periodic frameworks or the localization of the various aluminum species in the materials are obtained from the analysis of the two-dimensional NMR spectra, which allows getting local structural details sometimes inaccessible from other characterization technique. An application of 27Al-27Al of the DQ-SQ experiment for the detection of aluminum pairing in zeolite is shown.
- Klíčová slova
- DQ-SQ, Porous solids, Al-27, Quadrupolar nuclei,
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
Drug discovery efforts largely depend on access to structural diversity. Multicomponent reactions allow for time-efficient chemical transformations and provide advanced intermediates with three or four points of diversification for further expansion to a structural variety of organic molecules. This review is aimed at solid-phase syntheses of small molecules involving isocyanide-based multicomponent reactions. The majority of all reported syntheses employ the Ugi four-component reaction. The review also covers the Passerini and Groebke-Blackburn-Bienaymé reactions. To date, the main advantages of the solid-phase approach are the ability to prepare chemical libraries intended for biological screening and elimination of the isocyanide odor. However, the potential of multicomponent reactions has not been fully exploited. The unexplored avenues of these reactions, including chiral frameworks, DNA-encoded libraries, eco-friendly synthesis, and chiral auxiliary reactions, are briefly outlined.
- Klíčová slova
- Ugi four-component reaction, convertible isocyanides, drug discovery, multicomponent reactions, post-Ugi transformations, solid-phase synthesis,
- MeSH
- kyanidy chemická syntéza chemie MeSH
- objevování léků * metody MeSH
- syntetické pryskyřice chemie MeSH
- techniky syntetické chemie * MeSH
- techniky syntézy na pevné fázi * metody MeSH
- vztahy mezi strukturou a aktivitou MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
- Názvy látek
- kyanidy MeSH
- syntetické pryskyřice MeSH
We present a toolbox for the rapid characterisation of powdered samples of paramagnetic metal-organic frameworks at natural abundance by 1 H-detected solid-state NMR. Very fast MAS rates at room and cryogenic temperatures and a set of tailored radiofrequency irradiation schemes help overcome the sensitivity and resolution limits often associated with the characterisation of MOF materials. We demonstrate the approach on DUT-8(Ni), a framework containing Ni2+ paddle-wheel units which can exist in two markedly different architectures. Resolved 1 H and 13 C resonances of organic linkers are detected and assigned in few hours with only 1-2 mg of sample at natural isotopic abundance, and used to rapidly extract information on structure and local internal dynamics of the assemblies, as well as to elucidate the metal electronic properties over an extended temperature range. The experiments disclose new possibilities for describing local and global structural changes and correlating them to electronic and magnetic properties of the assemblies.
- Klíčová slova
- DUT-8(Ni), fast magic-angle spinning, metal-organic framework, paramagnetic NMR, proton detection,
- Publikační typ
- časopisecké články MeSH
Rare-earth layered hydroxides with intercalated tetrasulfonated porphyrins and corresponding to the chemical formula Ln2(OH)4.7(Por)0.33·2H2O (Ln = Eu(3+), Tb(3+); Por = 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and PdTPPS) have been prepared to investigate their photophysical properties. A slight variation of the synthetic procedure led to the metal-organic framework (MOF) assembled from a distorted octahedral oxometalate clusters [Eu6(μ6-O)(μ3-OH)8(H2O)14](8+). These secondary building units (SBUs) are linked together by six distorted porphyrin units. During activation, the original SBU loses not only water molecules from the coordination sphere but also the central μ6-O atom. The loss of the central atom results in the distortion of the octahedral [Eu6(μ6-O)(μ3-OH)8(H2O)14](8+) SBU into a trigonal antiprismatic [Eu6(μ3-OH)8(H2O)2](10+) SBU with two μ3-OH groups nearly in plane with the europium atoms and the reduction of pores to approximately 2 × 3 Å. As a result, the MOF has no accessible porosity. This transformation was thoroughly characterized by means of single-crystal X-ray crystallographic analysis of both phases. Solid-state photophysical investigations suggest that the MOF material is fluorescent; however, in contrast to the prepared layered hydroxides, the as-prepared MOF is an effective sensitizer of singlet oxygen, O2((1)Δg), with a relatively long lifetime of 23 ± 1 μs. The transition is also accompanied by variation in photophysical properties of the coordinated TPPS. The alteration of the fluorescence properties and of the O2((1)Δg) lifetime presents an opportunity for preparation of MOFs with oxygen-sensing ability or with oxidation potential toward organic molecules by O2((1)Δg).
The difficulty in the prediction of the complicated solid-state structure of boronic acid derivatives, resulting from the complex pathway of reversible covalent interactions, represents a significant obstacle to the development of a new generation of advanced supramolecular systems such as covalent organic frameworks of efficient anticancer drugs. In this contribution, various 2D 11B-11B solid-state NMR correlation techniques supported by DFT calculations were explored to formulate a reliable tool for monitoring the covalent assembly of boronic acid residues in the solid state. This way, the self-condensation of bortezomib molecules was investigated, different local constitutions of boroxine motifs were unveiled, and the previously unreported boroxine structures of bortezomib polymorphs exhibiting secondary coordination were discovered and described in detail. The recorded 11B NMR parameters responded sensitively to subtle changes in the local geometries, which were reliably interpreted and directly visualized by the DFT calculations. A uniform 2.6 Å distance in bortezomib 11B-11B spin pairs was conclusively identified by the through-space 11B-11B double-quantum (DQ) coherence build-up curves, whereas distinct 2D 11B-11B DQ correlation patterns revealed unique boroxine structures existing in the crystalline as well as amorphous state. The boroxine rings were found to be internally stabilized through the transformation of the trigonal boron sites toward tetrahedral geometry, as the secondary five-membered rings were formed. This way, the nature of bortezomib polymorphism is disclosed, and an efficient strategy for exploring the assembly of boronic acid derivatives in the solid state, for which no crystallographic data are available, is thus demonstrated.
- Publikační typ
- časopisecké články MeSH
The assembly-disassembly-organization-reassembly (ADOR) mechanism is a recent method for preparing inorganic framework materials and, in particular, zeolites. This flexible approach has enabled the synthesis of isoreticular families of zeolites with unprecedented continuous control over porosity, and the design and preparation of materials that would have been difficult-or even impossible-to obtain using traditional hydrothermal techniques. Applying the ADOR process to a parent zeolite with the UTL framework topology, for example, has led to six previously unknown zeolites (named IPC-n, where n = 2, 4, 6, 7, 9 and 10). To realize the full potential of the ADOR method, however, a further understanding of the complex mechanism at play is needed. Here, we probe the disassembly, organization and reassembly steps of the ADOR process through a combination of in situ solid-state NMR spectroscopy and powder X-ray diffraction experiments. We further use the insight gained to explain the formation of the unusual structure of zeolite IPC-6.
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Municipal solid waste (MSW) is one of the issues associated with the growth of economic and urban population. The aim of this study is to develop an integrated design of waste management systems in support of a Circular Economy by P-graph (a bipartite graphical optimisation tool) as an effective decision support tool. The case study considers four MSW compositions based on different country income levels. Solving the P-graph model identifies the most suitable treatment approaches, considering the economic balance between the main operating cost, type, yield, quality of products, as well as the GHG emission (externality cost). The identification of near-optimal solutions by P-graph is useful in dealing with the trade-offs between conflicting objectives, e.g. local policy and practical implementation, that are difficult to monetise. For a lower-income country, the optimal solution includes a combination of at source separation, recycling, incineration (heat, electricity), anaerobic digestion (biofuel, digestate) and the landfill. It avoids an estimated 411 kg CO2eq/t of processed MSW and achieves a potential profit of 42 €/t of processed MSW. The optimisation generally favours mechanical biological treatment as the country income level rises, which affects the composition of the MSW. The relative prices of biofuel, electricity and heat (>20%) cause a significant impact on the highest-ranking treatment structure and overall profit. This study shows that the developed framework by P-graph is an effective tool for MSW systems planning. For future study, localised data inputs can be fed into the proposed framework for a customised solution and economic feasibility assessment.
- Klíčová slova
- Circular Economy, GHG emission, P-graph, Waste to resources,
- Publikační typ
- časopisecké články MeSH
Covalent organic frameworks (COFs), materials constructed from organic building blocks joined by robust covalent bonds, have emerged as attractive materials in the context of electrochemical applications because of their high, intrinsic porosities and crystalline frameworks, as well as their ability to be tuned across two- and three-dimensions by the judicious selection of building blocks. Because of the recent and rapid development of this field, we have summarized COFs employed for electrochemical applications, such as batteries and capacitors, water splitting, solar cells, and sensors, with an emphasis on the structural design and resulting performance of the targeted electrochemical system. Overall, we anticipate this review will stimulate the design and synthesis of the next generation of COFs for use in electrochemical applications and beyond.
