Crystalline molecular flasks
TL;DR: The principles, development and applications of crystalline molecular flasks, solid-state crystalline networks with pores within which pseudo-solution-state reactions can take place, are described.
Abstract: Crystalline networks containing empty cavities can host a variety of molecules but also promote reactions between guests. Through robust crystallinity and a pseudo-solution state (dynamic movements) within their pores, these crystalline molecular flasks enable the direct observation of species — including unstable intermediates — during a reaction by in situ X-ray diffraction.
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TL;DR: The work enriches the cluster-based metal-organic framework portfolio, bridges the gap between silver chalcogenide/chalcogenolate clusters and metal- organic frameworks, and provides a foundation for further development of functional silver-cluster-based materials.
Abstract: Silver(i) chalcogenide/chalcogenolate clusters are promising photofunctional materials for sensing, optoelectronics and solar energy harvesting applications. However, their instability and poor room-temperature luminescent quantum yields have hampered more extensive study. Here, we graft such clusters to adaptable bridging ligands, enabling their interconnection and the formation of rigid metal–organic frameworks. By controlling the spatial separation and orientation of the clusters, they then exhibit enhanced stability (over one year) and quantum yield (12.1%). Ultrafast dual-function fluorescence switching (<1 s) is also achieved, with turn-off triggered by O2 and multicoloured turn-on by volatile organic compounds. Single-crystal X-ray diffraction of the inclusion materials, obtained by single-crystal-to-single-crystal transformation, enables precise determination of the position of the small molecules within the framework, elucidating the switching mechanism. The work enriches the cluster-based metal–organic framework portfolio, bridges the gap between silver chalcogenide/chalcogenolate clusters and metal–organic frameworks, and provides a foundation for further development of functional silver-cluster-based materials. The properties of discrete species can sometimes be improved by fixing them into extended materials. This strategy has now been applied to silver(I) chalcogenide/chalcogenolate clusters, resulting in a metal–organic framework with enhanced stability and fluorescent sensing capabilities. Crystallographic analysis allows precise structural determination of guest binding, which is responsible for both emission turn-off and multicoloured turn-on.
692 citations
TL;DR: Artificial catalysts and biomacromolecule hybrid catalysts which constitute good models towards the development of truly competitive artificial enzymes are presented.
Abstract: The design of artificial catalysts able to compete with the catalytic proficiency of enzymes is an intense subject of research. Non-covalent interactions are thought to be involved in several properties of enzymatic catalysis, notably (i) the confinement of the substrates and the active site within a catalytic pocket, (ii) the creation of a hydrophobic pocket in water, (iii) self-replication properties and (iv) allosteric properties. The origins of the enhanced rates and high catalytic selectivities associated with these properties are still a matter of debate. Stabilisation of the transition state and favourable conformations of the active site and the product(s) are probably part of the answer. We present here artificial catalysts and biomacromolecule hybrid catalysts which constitute good models towards the development of truly competitive artificial enzymes.
663 citations
TL;DR: The influence of building block replacement on the stability and properties of MOFs will be discussed, and some insights into their mechanistic aspects are provided.
Abstract: Metal–organic frameworks (MOFs) are hybrid porous materials with many potential applications, which intimately depend on the presence of chemical functionality either at the organic linkers and/or at the metal nodes. Functionality that cannot be introduced into MOFs directly via de novo syntheses can be accessed through post-synthesis modification (PSM) on the reactive moieties of the linkers and/or nodes without disrupting the metal–linker bonds. Even more intriguing methods that go beyond PSM are herein termed building block replacement (BBR) which encompasses (i) solvent-assisted linker exchange (SALE), (ii) non-bridging ligand replacement, and (iii) transmetalation. These one-step or tandem BBR processes involve exchanging key structural components of the MOF, which in turn should allow for the evolution of protoMOF structures (i.e., the utilization of a parent MOF as a template) to design MOFs composed of completely new components, presumably via single crystal to single crystal transformations. The influence of building block replacement on the stability and properties of MOFs will be discussed, and some insights into their mechanistic aspects are provided. Future perspectives providing a glimpse into how these techniques can lead to various unexplored areas of MOF chemistry are also presented.
661 citations
TL;DR: A protocol for SCD analysis that does not require the crystallization of the sample is reported, which allows the direct characterization of multiple fractions and unambiguously determined the structure of a scarce marine natural product using only 5 micrograms of the compound.
Abstract: X-ray single-crystal diffraction (SCD) analysis has the intrinsic limitation that the target molecules must be obtained as single crystals. Here we report a protocol for SCD analysis that does not require the crystallization of the sample. In our method, tiny crystals of porous complexes are soaked in a solution of the target, such that the complexes can absorb the target molecules. Crystallographic analysis clearly determines the absorbed guest structures along with the host frameworks. Because the SCD analysis is carried out on only one tiny crystal of the complex, the required sample mass is of the nanogram–microgram order. We demonstrate that as little as about 80 nanograms of a sample is enough for the SCD analysis. In combination with high-performance liquid chromatography, our protocol allows the direct characterization of multiple fractions, establishing a prototypical means of liquid chromatography SCD analysis. Furthermore, we unambiguously determined the structure of a scarce marine natural product using only 5 micrograms of the compound. Chemists need reliable methods to analyse and determine molecular structures. Nuclear magnetic resonance (NMR) and mass spectrometry are indispensable tools in daily chemical research for rapidly analysing molecular structures, but, strictly speaking, they provide only speculative molecular structures that are sometimes assigned incorrectly. However, X-ray SCD provides direct structural information at the atomic level and is recognized as the most reliable structure determination method 1–3 . Unfortunately, X-ray SCD has some critical limitations. First, the crystallization of samples before measurement can not be automated and usually requires a time-consuming trial-and-error procedure. Second, the method is in principle not applicable to non-crystalline molecules. In this Article, we describe an advance in crystallographic analysis based on a new X-ray analysis protocol that does not require the crystallization of the sample molecules themselves. Our idea is to use networked porous metal complexes 4–7 as ‘crystalline sponges’ 8 . Owing to the high molecular-recognition ability of the pores, the crystalline sponges can absorb target sample molecules from their solution into the pores, rendering the incoming molecules regularly ordered in the crystal. Accordingly, the molecular structure of the absorbed guest will be displayed, along with the host framework, by the crystallographic analysis of the networked porous complexes. We emphasize that even trace amounts of samples (,0.1mg) can be analysed by this method because the experiment can be performed with only one tiny crystal (,0.1 mm to a side). In the following discussion, we thus describe the crystallographic analysis of non-crystalline compounds and nanogram–microgram-scale X-ray crystallography based on our method. The great advantage of trace-amount X-ray analysis is particularly emphasized by its application to liquid chromatography SCD analysis (see below), where high-performance liquid chromatography (HPLC) fractions are directly collected by the crystalline sponge and analysed by X-ray crystallography. Furthermore, we successfully determine the structure of a scarce marine natural product, miyakosyne A, including the absolute configuration of its chiral centre, which could not be determined by conventional chemical and spectroscopic methods. X-ray crystallography of liquid samples
641 citations
TL;DR: This review overviews the recent developments of catalysis at single metal sites in MOF-based materials with emphasis on their structures and applications for thermocatalysis, electrocatalysis, and photocatalysis.
Abstract: Metal-organic frameworks (MOFs) are a class of distinctive porous crystalline materials constructed by metal ions/clusters and organic linkers. Owing to their structural diversity, functional adjustability, and high surface area, different types of MOF-based single metal sites are well exploited, including coordinately unsaturated metal sites from metal nodes and metallolinkers, as well as active metal species immobilized to MOFs. Furthermore, controllable thermal transformation of MOFs can upgrade them to nanomaterials functionalized with active single-atom catalysts (SACs). These unique features of MOFs and their derivatives enable them to serve as a highly versatile platform for catalysis, which has actually been becoming a rapidly developing interdisciplinary research area. In this review, we overview the recent developments of catalysis at single metal sites in MOF-based materials with emphasis on their structures and applications for thermocatalysis, electrocatalysis, and photocatalysis. We also compare the results and summarize the major insights gained from the works in this review, providing the challenges and prospects in this emerging field.
571 citations
References
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TL;DR: The aim is to present the state of the art chemistry and physics of and in the micropores of porous coordination polymers, and the next generation of porous functions based on dynamic crystal transformations caused by guest molecules or physical stimuli.
Abstract: The chemistry of the coordination polymers has in recent years advanced extensively, affording various architectures, which are constructed from a variety of molecular building blocks with different interactions between them. The next challenge is the chemical and physical functionalization of these architectures, through the porous properties of the frameworks. This review concentrates on three aspects of coordination polymers: 1). the use of crystal engineering to construct porous frameworks from connectors and linkers ("nanospace engineering"), 2). characterizing and cataloging the porous properties by functions for storage, exchange, separation, etc., and 3). the next generation of porous functions based on dynamic crystal transformations caused by guest molecules or physical stimuli. Our aim is to present the state of the art chemistry and physics of and in the micropores of porous coordination polymers.
9,661 citations
TL;DR: This work has shown that highly porous frameworks held together by strong metal–oxygen–carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.
Abstract: The long-standing challenge of designing and constructing new crystalline solid-state materials from molecular building blocks is just beginning to be addressed with success. A conceptual approach that requires the use of secondary building units to direct the assembly of ordered frameworks epitomizes this process: we call this approach reticular synthesis. This chemistry has yielded materials designed to have predetermined structures, compositions and properties. In particular, highly porous frameworks held together by strong metal-oxygen-carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.
8,013 citations
TL;DR: A critical review of the emerging field of MOF-based catalysis is presented and examples of catalysis by homogeneous catalysts incorporated as framework struts or cavity modifiers are presented.
Abstract: A critical review of the emerging field of MOF-based catalysis is presented. Discussed are examples of: (a) opportunistic catalysis with metal nodes, (b) designed catalysis with framework nodes, (c) catalysis by homogeneous catalysts incorporated as framework struts, (d) catalysis by MOF-encapsulated molecular species, (e) catalysis by metal-free organic struts or cavity modifiers, and (f) catalysis by MOF-encapsulated clusters (66 references).
7,010 citations
6,030 citations
TL;DR: The state-of-the-art on hybrid porous solids, their advantages, their new routes of synthesis, the structural concepts useful for their 'design', aiming at reaching very large pores are presented.
Abstract: This critical review will be of interest to the experts in porous solids (including catalysis), but also solid state chemists and physicists. It presents the state-of-the-art on hybrid porous solids, their advantages, their new routes of synthesis, the structural concepts useful for their ‘design’, aiming at reaching very large pores. Their dynamic properties and the possibility of predicting their structure are described. The large tunability of the pore size leads to unprecedented properties and applications. They concern adsorption of species, storage and delivery and the physical properties of the dense phases. (323 references)
5,187 citations