Xiaodong Zou is a full professor and chair of the Inorganic and Structural Chemistry Unit and deputy head of the Department of Materials and Environmental Chemistry, Stockholm University.
She received her Bachelor of Science in Physics 1984 at Peking University and Master of Science in Metal Physics 1986 at Beijing University of Technology, under the supervision of Prof. K.H. Kuo. In 1987 she moved to Sweden to pursue her Ph.D. studies and received her PhD in structural chemistry at Stockholm University in 1995. She carried out her postdoctoral research at Lund University, working with the Tage Erlander Professor David R. Veblen from John Hopkins University, USA. She joined the faculty at Stockholm University in 1996 and became professor 2005.
One of her main research interests is method development for accurate atomic structure determination of nano-sized crystals by electron crystallography. Her group has solved a number of complex structures of zeolites and mesoporous crystals by transmission electron microscopy. She is also working on synthesis, structure determination, topology analysis and applications of inorganic open-framework materials and metal-organic frameworks.
Xiaodong Zou’s research projects cover several research topics, including Electron crystallography and advanced TEM, X-ray and neutron crystallography, Materials for energy, Materials for health. They are summarized below.
For full information about our research projects, please refer to our group page and project pages, link in the column on the right.
Electron crystallography and analytical TEM
Revealing atomic structures, charge states and molecular interactions in macromolecules by microcrystal electron diffraction. Swedish Research Council (VR), 2020-2030.
Electron crystallographic methods to probe 3D atomic structures and charge states in macromolecules.
Knut and Alice Wallenberg Foundation (Wallenberg Scholars), 2020-2024.
Knowing the 3D atomic structures is crucial for understanding the functions of biological macromolecules. Many proteins are involved in redox processes and charge-transfer reactions, which are performed by accommodating different electronic and charged states. Obtaining both the geometric structure and charge states is thus central to understanding the chemical processes and mechanisms in.
Nanoporous materials: from synthesis and structure to catalysis;
Subproject: Accurate atomic structures from nano- and micrometer-sized crystals by electron crystallography
Swedish Research Council (VR), 2017-2022.
This is part of my VR project that aims at developing new strategies and methods for data collection using continuous rotation electron diffraction (cRED), and makeing the structure determination as fast, feasible and accurate as by X-ray crystallography. The new methods will be applied on various zeolites and metal-organic frameworks. We aim to locate hydrogen atoms and determine the oxidation states of atoms, which are not achievable by X-ray diffraction.
Structure characterization of nanoporous materials
ExxonMobil Research & Engineering Co. 2017-2021.
X-ray and neutron crystallography
Nanoporous materials: from synthesis and structure to catalysis; Subproject: Fundamental understanding of reaction mechanisms in organic transformations using porous materials as catalyst supports.
Swedish Research Council (VR), 2017-2022.
This is part of my VR project that aims at developing synchrotron-based in-situ/operando powder X-ray diffraction and X-ray absorption spectroscopy to identify active catalytic species during organic synthesis using a custom-built in-situ reactor. We will gain new insights on the reaction mechanisms and use them to improve the catalysts and optimize the catalytic reactions. We will introduce synchrotron-based in-situ/operando techniques to the organic chemistry community for developing new catalysts for organic synthesis.
Materials for energy
Nanoporous materials: from synthesis and structure to catalysis;
Subproject: Rational design and synthesis of novel zeolites
The Swedish Research Council (Vetenskapsrådet, VR), 2017-2022.
This is part of my VR project that aims at developing new approaches for rational design and synthesis of novel zeolites based on common structural features. This will revolutionize the zeolite synthesis from current trial-and-error to targeted synthesis.
Catalytic Composites for Sustainable Synthesis (CATSS);
Subproject: Characterization, modeling and understanding of the catalytic materials
Knut and Alice Wallenberg Foundation (KAW), 2017-2022.
The aim of this project is to develop novel multifunctional catalytic composites that use two of the most abundant and sustainable feedstocks, carbon dioxide and water, for organic synthesis.
Materials for health
Access to potent medical drugs (APIs) through crystallization enabled by ionic liquids (ILs);
Subproject: Crystallization from ILs – Techniques and Process Monitoring Tools.
Knut and Alice Wallenberg Foundation (KAW) 2020-2024. About the project in Swedish
Full list of publications is available from Diva
A selection from Stockholm University publication database
3D reconstruction of atomic structures from high angle annular dark field (HAADF) STEM images
Tom Willhammar, Alvaro Mayoral, Xiaodong Zou.
A Stacking Faults-containing Silicogermanate with 24-ring Channels and Unbranched Zweier Silica Double Chains
Liqiu Tang (et al.). Crystal Growth & DesignArticle
A method for accurate orientation determination for rotation electron diffraction patterns
Bin Wang (et al.).
A numerical method for calculating the frame orientation of a crystal from indexed electron diffraction patterns is developed. The algorithm uses the observed reflection indices and unit cell parameters of the crystal, and operates by minimizing the summed distances in reciprocal space between the observed reflections and the Ewald sphere. Partiality correction is proposed by making use of the information about the rotation axis. The accuracy of the orientations is found to be around 0.01° for each of the frames in a rotation dataset.
A method for determination of angular accuracy of the goniometer on a transmission electron microscope
Bin Wang, Sven Hovmöller, Xiaodong Zou.
For collection and reconstruction of 3D electron diffraction or electron tomography data, it is essential to have reliable goniometer tilt angles. Thus, it is important to know the accuracy of tilt angles a goniometer can provide on a transmission electron microscope (TEM). In this paper, a method to determine the angular accuracy of a goniometer is presented, which is based on the orientation determination of rotation electron diffraction (RED) data from a crystal with known unit cell. The method was demonstrated on a JEOL JEM 2100 LaB6 TEM. The result showed that the uncertainty for the goniometer was 1.75% from the expected rotation angle. Meanwhile, the readout error from the TEM hardware followed a combination of sinusoidal and linear components, indicating a more complicated readout error source than only linear errors. A quality assessment method for general TEM goniometers is proposed.
A simple pressure-assisted method for MicroED specimen preparation
Jingjing Zhao (et al.).
Micro-crystal electron diffraction (MicroED) has shown great potential for structure determination of macromolecular crystals too small for X-ray diffraction. However, specimen preparation remains a major bottleneck. Here, we report a simple method for preparing MicroED specimens, named Preassis, in which excess liquid is removed through an EM grid with the assistance of pressure. We show the ice thicknesses can be controlled by tuning the pressure in combination with EM grids with appropriate hole sizes. Importantly, Preassis can handle a wide range of protein crystals grown in various buffer conditions including those with high viscosity, as well as samples with low crystal contents. Preassis is a simple and universal method for MicroED specimen preparation, and will significantly broaden the applications of MicroED.
A simple pressure-assisted method for cryo-EM specimen preparation
Jingjing Zhao (et al.).
A two-dimensional aluminosilicate PST-9 and its structure evolution to a 3D zeolite EU-12
Juna Bae (et al.).
An aluminosilicate zeolite EMM-28 containing extra-large cavities
Magdalena O. Cichocka (et al.).
Atomic Structure of Amyloid Crystals
C. Bortolini (et al.).
A deep understanding of the self-assembly and crystallization of biomolecules as highly ordered biomaterials is crucial to enable the design and the generation of complex functional systems for cutting-edge applications in nanotechnology and biomedicine. In this work, we determined the atomic structure of Aβ16-20 crystals, a fragment of amyloid-β which aberrant folding is linked to the etiology of Alzheimer’s disease, the most common cause of dementia. We detailed the hierarchical aggregation mechanism of Aβ16-20 into highly ordered crystals and revealed that the self-assembly is reversible, leading to the formation of oligomers as an intermediate. Our structural investigation combined with molecular dynamics simulations highlights how a combination of favorable non-covalent interactions drives the efficient fast self-assembly and enhanced stability. We studied the chemical and surface properties of amyloid crystals, including their mechanical properties and their capability to transmit light; the long-rang order of Aβ16-20 crystals enables them to be used as optical waveguide materials for biologically based modulation and sensing. Our results shed new light on pathogenic amyloid assembly at the atomic level and reveal the potential of amyloid crystals for applications in nanotechnology.
Automated serial rotation electron diffraction combined with cluster analysis
Bin Wang, Xiaodong Zou, Stef Smeets. IUCrJArticle
Dynamical structure refinement of Ni3Si2 against rotation electron diffraction data
Yunchen Wang (et al.).
EMM-26: a two-dimensional medium pore borosilicate zeolitewith 10x10 ring channels solved by rotation electron diffraction
Peng Guo (et al.).
Electron Crystallography Method for Rapid and Accurate Structure Determination of Small Organic Molecules
Hongyi Xu (et al.).
Highly porous isoreticular lanthanide metal-organic frameworks
Qingxia Yao (et al.).
As an emerging type of porous materials, metal–organic frameworks (MOFs) have the advantages over conventional inorganic porous materials in that their structures and functions are systematically and predictably designable. Isoreticular expansion is an efficient way for systematic design and control of pore size and shape for MOFs. By using our proposed strategy, a series of highly porous isoreticular lanthanide-based metal-organic frameworks with systematic pore apertures has been obtained, which afford an isoreticular series of MIL-103 structures (termed SUMOF-7I to IV) with pore apertures ranging from 7.2 Å to 23 Å. These materials demonstrated exhibit robust architectures with permanent porosity, and exceptional thermal stability and chemical stability in various solvents. The combination of luminescence property and significant porosity of these MOFs enable them as a potential platform for multifunctional purpose.
Introduction of an N-heterocyclic Carbene Iridium Complex into a Zirconium Metal–Organic Framework for Catalysis
Fabian Carson (et al.).
Luminescence Properties for a Family of Highly Stable Lanthanide Metal-Organic Frameworks
Hani Abdelhamid (et al.).
Nanocrystalline TON-type zeolites synthesized under static conditions
Yunxiang Li (et al.).
On the quality of the continuous rotation electron diffraction data for accurate atomic structure determination of inorganic compounds
Yunchen Wang (et al.).
Probing the active catalytic species generated from Pd(II)@MIL-101-NH2 in Heck coupling reactions: An operando X-ray absorption spectroscopy study
Ning Yuan (et al.).Article
Rational synthesis and structure of a borosilicate zeolite with intersecting 10- and 11-ring channels
Yifeng Yun (et al.).
A. Ken Inge (et al.).
A. Ken Inge (et al.).
Synthesis and Structure Determination of a Layered Zeolitic Fluoroaluminophosphate and its Transformation to a Three-dimensional Zeolite Framework
Peng Guo (et al.).
Synthesis and characterization of two new nickel germanates
Shiliang Huang (et al.).
Synthesis and electron transfer processes in a new family of coupled Mn2–Ru complexes
Erik A. Karlsson (et al.).
Synthesis and structure of a 22×12×12 extra-large pore zeolite ITQ-56 determined from continuous rotation electron diffraction data
Elina Kapaca (et al.).
Template-Free Synthesis of Hierarchical Porous Zeolitic Imidazole Frameworks Nanoparticles and their CO2 Sorption
Hani Abdelhamid, Xiaodong Zou.
The first stable high silica zeolite with extra-large 24-ring channels
Tom Willhammar (et al.).
The first zeolite with a tri-directional extra-large 14-ring pore system derived using a phosphonium-based organic molecule
Yifeng Yun (et al.).
A new germanosilicate zeolite (denoted as ITQ-53) with extra-large 14-ring pores has been synthesized using tri-tertbutylmethylphosphonium cation as the organic structure directing agent (OSDA). The new rotation electron diffraction (RED) method was used to both identify and solve the structure of ITQ-53 from an initially synthesized sample containing impurities, which facilitated the synthesis optimization that led to pure ITQ-53. The structure was refined against PXRD data. ITQ-53 is the first example of extra-large pore zeolites with tri-directional interconnected 14 × 14 × 14-ring channels. It is built from double 3-rings (D3Rs), double 4-rings (D4Rs), and a new composite building unit [42.54.63]. D3Rs are very rare, previously only found in two zeolitic silicogermanates. ITQ-53 is stable up to at least 450 °C. The structure of ITQ-53 was changed from monoclinic to orthorhombic up on calcination.
Three Low-Dimensional Open-Germanates Derived from the 4^4 Net
A. Ken Inge (et al.). CrystEngCommArticle
Enhanced Selectivity and Stability of Finned Ferrierite Catalysts in Butene Isomerization
2022. Heng Dai (et al.). Angewandte Chemie International Edition 61 (8)Article
Designing zeolite catalysts with improved mass transport properties is crucial for restrictive networks of either one- or two-dimensional pore topologies. Here, we demonstrate the synthesis of finned ferrierite (FER), a commercial zeolite with two-dimensional pores, where protrusions on crystal surfaces behave as pseudo nanoparticles. Catalytic tests of 1-butene isomerization reveal a 3-fold enhancement of catalyst lifetime and an increase of 12 % selectivity to isobutene for finned samples compared to corresponding seeds. Electron tomography was used to confirm the identical crystallographic registry of fins and seeds. Time-resolved titration of Bronsted acid sites confirmed the improved mass transport properties of finned ferrierite compared to conventional analogues. These findings highlight the advantages of introducing fins through facile and tunable post-synthesis modification to impart material properties that are otherwise unattainable by conventional synthesis methods.
Growing single crystals of two-dimensional covalent organic frameworks enabled by intermediate tracing study
2022. Chengjun Kang (et al.). Nature Communications 13Article
Resolving single-crystal structures of two-dimensional covalent organic frameworks (2D COFs) is a great challenge, hindered in part by limited strategies for growing high-quality crystals. A better understanding of the growth mechanism facilitates development of methods to grow high-quality 2D COF single crystals. Here, we take a different perspective to explore the 2D COF growth process by tracing growth intermediates. We discover two different growth mechanisms, nucleation and self-healing, in which self-assembly and pre-arrangement of monomers and oligomers are important factors for obtaining highly crystalline 2D COFs. These findings enable us to grow micron-sized 2D single crystalline COF Py-1P. The crystal structure of Py-1P is successfully characterized by three-dimensional electron diffraction (3DED), which confirms that Py-1P does, in part, adopt the widely predicted AA stacking structure. In addition, we find the majority of Py-1P crystals (>90%) have a previously unknown structure, containing 6 stacking layers within one unit cell.
Indomethacin Polymorph δ Revealed To Be Two Plastically Bendable Crystal Forms by 3D Electron Diffraction
2022. Molly Lightowler (et al.). Angewandte Chemie International Edition 61 (7)Article
Indomethacin is a clinically classical non-steroidal anti-inflammatory drug that has been marketed since 1965. The third polymorph, Form δ, was discovered by both melt and solution crystallization in 1974. δ-indomethacin cannot be cultivated as large single crystals suitable for X-ray crystallography and, therefore, its crystal structure has not yet been determined. Here, we report the structure elucidation of δ-indomethacin by 3D electron diffraction and reveal the truth that melt-crystallized and solution-crystallized δ-indomethacin are in fact two polymorphs with different crystal structures. We propose to keep the solution-crystallized polymorph as Form δ and name the melt-crystallized polymorph as Form θ. Intriguingly, both structures display plastic flexibility based on a slippage mechanism, making indomethacin the first drug to have two plastic polymorphs. This discovery and correction of a 47-year-old misunderstanding signify that 3D electron diffraction has become a powerful tool for polymorphic structural studies.
Metal-hydrogen-pi-bonded organic frameworks
2022. Jie Zhu (et al.). Dalton Transactions 51 (5), 1927-1935Article
We report the synthesis and characterization of a new series of permanently porous, three-dimensional metal–organic frameworks (MOFs), M-HAF-2 (M = Fe, Ga, or In), constructed from tetratopic, hydroxamate-based, chelating linkers. The structure of M-HAF-2 was determined by three-dimensional electron diffraction (3D ED), revealing a unique interpenetrated hcb-a net topology. This unusual topology is enabled by the presence of free hydroxamic acid groups, which lead to the formation of a diverse network of cooperative interactions comprising metal–hydroxamate coordination interactions at single metal nodes, staggered π–π interactions between linkers, and H-bonding interactions between metal-coordinated and free hydroxamate groups. Such extensive, multimodal interconnectivity is reminiscent of the complex, noncovalent interaction networks of proteins and endows M-HAF-2 frameworks with high thermal and chemical stability and allows them to readily undergo postsynthetic metal ion exchange (PSE) between trivalent metal ions. We demonstrate that M-HAF-2 can serve as versatile porous materials for ionic separations, aided by one-dimensional channels lined by continuously π-stacked aromatic groups and H-bonding hydroxamate functionalities. As an addition to the small group of hydroxamic acid-based MOFs, M-HAF-2 represents a structural merger between MOFs and hydrogen-bonded organic frameworks (HOFs) and illustrates the utility of non-canonical metal-coordinating functionalities in the discovery of new bonding and topological patterns in reticular materials.
2022. Yi Luo (et al.). Inorganic Chemistry 61 (10), 4371-4377Article
Zeolites with large cavities that are accessible via wide pore windows are desirable but very rare. They have been dominantly used as catalysts in industry. Here we report a novel porous germanosilicate SCM-25, the zeolite structure containing ordered meso-cavities (29.9 × 7.6 × 6.0 Å3) interconnected by 10- and 12-ring channels. SCM-25 was synthesized as nanosized crystals by using a simple organic structure-directing agent (OSDA). Three-dimensional (3D) electron diffraction shows that SCM-25 crystallizes in the orthorhombic space group Cmmm with a = 14.62 Å, b = 51.82 Å, c = 13.11 Å, which is one of the zeolites with the largest unit cell dimensions. We demonstrate that 3D electron diffraction is a powerful technique for determining the complex structure of SCM-25, including the disorders and distributions of framework atoms silicon and germanium. SCM-25 has a high surface area (510 m2/g) and high thermal stability (700 °C). Furthermore, we propose a potential postsynthetic strategy for the preparation of zeolites with ordered meso-cavities by applying the ADOR (assembly–disassembly–organization–reassembly) approach.
Single-walled zeolitic nanotubes
2022. Akshay Korde (et al.). Science 375 (6576), 62-66Article
We report the synthesis and structure of single-walled aluminosilicate nanotubes with microporous zeolitic walls. This quasi-one-dimensional zeolite is assembled by a bolaform structure-directing agent (SDA) containing a central biphenyl group connected by C10 alkyl chains to quinuclidinium end groups. High-resolution electron microscopy and diffraction, along with other supporting methods, revealed a unique wall structure that is a hybrid of characteristic building layers from two zeolite structure types, beta and MFI. This hybrid structure arises from minimization of strain energy during the formation of a curved nanotube wall. Nanotube formation involves the early appearance of a mesostructure due to self-assembly of the SDA molecules. The biphenyl core groups of the SDA molecules show evidence of π stacking, whereas the peripheral quinuclidinium groups direct the microporous wall structure.
Three-dimensional electron diffraction
2022. Laura Samperisi, Xiaodong Zou, Zhehao Huang. CrystEngCommArticle
Understanding crystal structures and behaviors is crucial for constructing and engineering crystalline materials with various properties and functions. Recent advancement in three-dimensional electron diffraction (3D ED) and its application on structural characterizations have expanded single-crystal analysis into nano-sized materials. Herein, we provide an overview on 3D ED, including its development, data collection protocols, and their applications for investigating crystal structures. We focus on metal-organic frameworks (MOFs) and small-molecule-based organic crystals, and highlight the insights provided by 3D ED such as structure-property relationships, polymorphism, hydrogen bonding, and crystal chirality, which are crucial subjects in crystal engineering. With more and more laboratories setting up 3D ED techniques, we envision that it will not only continue providing critical structural information, but also establish a wide impact on chemistry, materials science and life science.
3D electron diffraction as an important technique for structure elucidation of metal-organic frameworks and covalent organic frameworks
2021. Zhehao Huang (et al.). Coordination chemistry reviews 427Article
Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have emerged as the most widely investigated classes of porous materials during the past two decades. The almost unlimited combination of building units (metal clusters and organic molecules) endows highly tuneable porosities and functionalities that are appealing for a wide scope of applications. The applications of MOFs and COFs depend on their physical and chemical properties, which in turn are determined by the arrangement of atoms - the crystal structures. Therefore, structure determination is arguably the most important characterization step for MOFs and COFs. While single crystal X-ray diffraction (SCXRD) is the most widely used method for structure determination, many MOFs and COFs are synthesized in too small sizes or their crystal qualities are too low for SCXRD. During recent years, three-dimensional electron diffraction (3DED) methods has undergone rapid developments and can be used for structure determination of nano- and submicro-sized crystals to overcome this fundamental drawback. In this review, we summarize the development of 3DED methods and their applications for structure elucidation of MOFs and COFs. Advances of 3DED data collection techniques are described, from step-wise rotation to continuous rotation of the crystal. The latter allows fast data collection which is crucial for beam sensitive materials including MOFs and COFs. Examples of ab initio structure determination of various MOFs and COFs by using 3DED are presented, with highlighted examples for solving the structures of mesoporous MOFs, mixed-metal MOFs, flexible MOFs, and for studying host-guest interactions. Finally, the accuracy and reproducibility of structure determination by 3DED are presented. We show the structure information obtained from 3DED provides crucial insights into structure-property relationships, which could further accelerate the development of new functional materials.
A Comparison of Structure Determination of Small Organic Molecules by 3D Electron Diffraction at Cryogenic and Room Temperature
2021. Taimin Yang (et al.). Symmetry 13 (11)Article
3D electron diffraction (3D ED), also known as micro-crystal electron diffraction (MicroED), is a rapid, accurate, and robust method for structure determination of submicron-sized crystals. 3D ED has mainly been applied in material science until 2013, when MicroED was developed for studying macromolecular crystals. MicroED was considered as a cryo-electron microscopy method, as MicroED data collection is usually carried out in cryogenic conditions. As a result, some researchers may consider that 3D ED/MicroED data collection on crystals of small organic molecules can only be performed in cryogenic conditions. In this work, we determined the structure for sucrose and azobenzene tetracarboxylic acid (H4ABTC). The structure of H4ABTC is the first crystal structure ever reported for this molecule. We compared data quality and structure accuracy among datasets collected under cryogenic conditions and room temperature. With the improvement in data quality by data merging, it is possible to reveal hydrogen atom positions in small organic molecule structures under both temperature conditions. The experimental results showed that, if the sample is stable in the vacuum environment of a transmission electron microscope (TEM), the data quality of datasets collected under room temperature is at least as good as data collected under cryogenic conditions according to various indicators (resolution, I/σ(I), CC1/2 (%), R1, Rint, ADRA).
A Tunable Multivariate Metal-Organic Framework as a Platform for Designing Photocatalysts
2021. Yang Wang (et al.). Journal of the American Chemical Society 143 (17), 6333-6338Article
Catalysts for photochemical reactions underlie many foundations in our lives, from natural light harvesting to modern energy storage and conversion, including processes such as water photolysis by TiO2. Recently, metal–organic frameworks (MOFs) have attracted large interest within the chemical research community, as their structural variety and tunability yield advantages in designing photocatalysts to address energy and environmental challenges. Here, we report a series of novel multivariate metal–organic frameworks (MTV-MOFs), denoted as MTV-MIL-100. They are constructed by linking aromatic carboxylates and AB2OX3 bimetallic clusters, which have ordered atomic arrangements. Synthesized through a solvent-assisted approach, these ordered and multivariate metal clusters offer an opportunity to enhance and fine-tune the electronic structures of the crystalline materials. Moreover, mass transport is improved by taking advantage of the high porosity of the MOF structure. Combining these key advantages, MTV-MIL-100(Ti,Co) exhibits a high photoactivity with a turnover frequency of 113.7 molH2 gcat.–1 min–1, a quantum efficiency of 4.25%, and a space time yield of 4.96 × 10–5 in the photocatalytic hydrolysis of ammonia borane. Bridging the fields of perovskites and MOFs, this work provides a novel platform for the design of highly active photocatalysts.
A simple pressure-assisted method for MicroED specimen preparation
2021. Jingjing Zhao (et al.). Nature Communications 12 (1)Article
Micro-crystal electron diffraction (MicroED) has shown great potential for structure determination of macromolecular crystals too small for X-ray diffraction. However, specimen preparation remains a major bottleneck. Here, we report a simple method for preparing MicroED specimens, named Preassis, in which excess liquid is removed through an EM grid with the assistance of pressure. We show the ice thicknesses can be controlled by tuning the pressure in combination with EM grids with appropriate carbon hole sizes. Importantly, Preassis can handle a wide range of protein crystals grown in various buffer conditions including those with high viscosity, as well as samples with low crystal concentrations. Preassis is a simple and universal method for MicroED specimen preparation, and will significantly broaden the applications of MicroED.
Can 3D electron diffraction provide accurate atomic structures of metal-organic frameworks?
2021. Zhehao Huang (et al.). Faraday discussions (Online) 225 (0), 118-132Article
Many framework materials such as metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) are synthesized as polycrystalline powders, which are too small for structure determination by single crystal X-ray diffraction (SCXRD). Here, we show that a three-dimensional (3D) electron diffraction method, namely continuous rotation electron diffraction (cRED), can be used for ab initio structure determination of such materials. As an example, we present the complete structural analysis of a biocomposite, denoted BSA@ZIF-CO3-1, in which Bovine Serum Albumin (BSA) was encapsulated in a zeolitic imidazolate framework (ZIF). Low electron dose was combined with ultrafast cRED data collection to minimize electron beam damage to the sample. We demonstrate that the atomic structure obtained by cRED is as reliable and accurate as that obtained by single crystal X-ray diffraction. The high accuracy and fast data collection open new opportunities for investigation of cooperative phenomena in framework structures at the atomic level.
2021. Jung Cho (et al.). Chemistry of Materials 33 (11), 4146-4153Article
The structure of the novel medium-pore borosilicate zeolite EMM-25 has been determined by continuous rotation electron diffraction (cRED). EMM-25 crystallizes in the space group Cmcm with unit cell parameters a = 11.055, b = 22.912, and c = 24.914 angstrom and a composition of IC4H8(C11H25N)(2)I (2)[Si112.5B3.5O232]. The EMM-25 framework possesses a two-dimensional channel system composed of 10-ring channels connected via 11-ring windows. Its channel system is analogous to that of the medium-pore zeolite NU-87 framework but with 11- rather than 12-ring windows, suggesting a different shape selectivity. EMM-25 was first obtained using 1,4-bis(N-methyl-N,N-dihexylammonium)butane as an organic structure directing agent (OSDA). Based on a molecular docking study of the OSDA within the pores of the determined framework structure, a new ammonium dication OSDA with an improved fit was devised. By using this new OSDA, the synthesis time was reduced 80%, from 52 to just 10 days. Furthermore, cRED data revealed a structural disorder of the EMM-25 framework present as swinging zigzag chains. The introduction of the disorder, which is a consequence of geometry relaxation, was crucial for an accurate structure refinement. Lastly, the cRED data from as-made EMM-25 showed residual potential consistent with the location of the OSDA position determined from the Rietveld refinement, concluding a complete refinement of the as-made structure based on the cRED data.
High-Throughput Electron Diffraction Reveals a Hidden Novel Metal-Organic Framework for Electrocatalysis
2021. Meng Ge (et al.). Angewandte Chemie International Edition 60 (20), 11391-11397Article
Metal-organic frameworks (MOFs) are known for their versatile combination of inorganic building units and organic linkers, which offers immense opportunities in a wide range of applications. However, many MOFs are typically synthesized as multiphasic polycrystalline powders, which are challenging for studies by X-ray diffraction. Therefore, developing new structural characterization techniques is highly desired in order to accelerate discoveries of new materials. Here, we report a high-throughput approach for structural analysis of MOF nano- and sub-microcrystals by three-dimensional electron diffraction (3DED). A new zeolitic-imidazolate framework (ZIF), denoted ZIF-EC1, was first discovered in a trace amount during the study of a known ZIF-CO3-1 material by 3DED. The structures of both ZIFs were solved and refined using 3DED data. ZIF-EC1 has a dense 3D framework structure, which is built by linking mono- and bi-nuclear Zn clusters and 2-methylimidazolates (mIm(-)). With a composition of Zn-3(mIm)(5)(OH), ZIF-EC1 exhibits high N and Zn densities. We show that the N-doped carbon material derived from ZIF-EC1 is a promising electrocatalyst for oxygen reduction reaction (ORR). The discovery of this new MOF and its conversion to an efficient electrocatalyst highlights the power of 3DED in developing new materials and their applications.
Investigation of the Deactivation and Reactivation Mechanism of a Heterogeneous Palladium(II) Catalyst in the Cycloisomerization of Acetylenic Acids by In Situ XAS
2021. Ning Yuan (et al.). ACS Catalysis 11 (5), 2999-3008Article
A well-studied heterogeneous palladium(II) catalyst used for the cycloisomerization of acetylenic acids is known to be susceptible to deactivation through reduction. To gain a deeper understanding of this deactivation process and to enable the design of a reactivation strategy, in situ X-ray absorption spectroscopy (XAS) was used. With this technique, changes in the palladium oxidation state and coordination environment could be studied in close detail, which provided experimental evidence that the deactivation was primarily caused by triethylamine-promoted reduction of palladium(II) to metallic palladium nanoparticles. Furthermore, it was observed that the choice of the acetylenic acid substrate influenced the distribution between palladium(II) and palladium(0) species in the heterogeneous catalyst after the reaction. From the mechanistic insight gained through XAS, an improved catalytic protocol was developed that did not suffer from deactivation and allowed for more efficient recycling of the catalyst.
Ligand-Directed Conformational Control over Porphyrinic Zirconium Metal-Organic Frameworks for Size-Selective Catalysis
2021. Liting Yang (et al.). Journal of the American Chemical Society 143 (31), 12129-12137Article
Zirconium-based metal-organic frameworks (Zr-MOFs) have aroused enormous interest owing to their superior stability, flexible structures, and intriguing functions. Precise control over their crystalline structures, including topological structures, porosity, composition, and conformation, constitutes an important challenge to realize the tailor-made functionalization. In this work, we developed a new Zr-MOF (PCN-625) with a csq topological net, which is similar to that of the well-known PCN-222 and NU-1000. However, the significant difference lies in the conformation of porphyrin rings, which are vertical to the pore surfaces rather than in parallel. The resulting PCN-625 exhibits two types of one-dimensional channels with concrete diameters of 2.03 and 0.43 nm. Furthermore, the vertical porphyrins together with shrunken pore sizes could limit the accessibility of substrates to active centers in the framework. On the basis of the structural characteristics, PCN-625(Fe) can be utilized as an efficient heterogeneous catalyst for the size-selective [4 + 2] hetero-Diels-Alder cycloaddition reaction. Due to its high chemical stability, this catalyst can be repeatedly used over six times. This work demonstrates that Zr-MOFs can serve as tailor-made scaffolds with enhanced flexibility for target-oriented functions.
On the completeness of three-dimensional electron diffraction data for structural analysis of metal-organic frameworks
2021. Meng Ge (et al.). Faraday discussions (Online) 231Article
Three-dimensional electron diffraction (3DED) has been proven as an effective and accurate method for structure determination of nano-sized crystals. In the past decade, the crystal structures of various new complex metal-organic frameworks (MOFs) have been revealed by 3DED, which has been the key to understand their properties. However, due to the design of transmission electron microscopes (TEMs), one drawback of 3DED experiments is the limited tilt range of goniometers, which often leads to incomplete 3DED data, particularly when the crystal symmetry is low. This drawback can be overcome by high throughput data collection using continuous rotation electron diffraction (cRED), where data from a large number of crystals can be collected and merged. Here, we investigate the effects of improving completeness on structural analysis of MOFs. We use ZIF-EC1, a zeolitic imidazolate framework (ZIF), as an example. ZIF-EC1 crystallizes in a monoclinic system with a plate-like morphology. cRED data of ZIF-EC1 with different completeness and resolution were analyzed. The data completeness increased to 92.0% by merging ten datasets. Although the structures could be solved from individual datasets with a completeness as low as 44.5% and refined to a high precision (better than 0.04 angstrom), we demonstrate that a high data completeness could improve the structural model, especially on the electrostatic potential map. We further discuss the strategy adopted during data merging. We also show that ZIF-EC1 doped with cobalt can act as an efficient electrocatalyst for oxygen reduction reactions.
Probing Molecular Motions in Metal-Organic Frameworks by Three-Dimensional Electron Diffraction
2021. Laura Samperisi (et al.). Journal of the American Chemical Society 143 (43), 17947-17952Article
Flexible metal-organic frameworks (MOFs) are known for their vast functional diversities and variable pore architectures. Dynamic motions or perturbations are among the highly desired flexibilities, which are key to guest diffusion processes. Therefore, probing such motions, especially at an atomic level, is crucial for revealing the unique properties and identifying the applications of MOFs. Nuclear magnetic resonance (NMR) and single-crystal X-ray diffraction (SCXRD) are the most important techniques to characterize molecular motions but require pure samples or large single crystals (>5 x 5 x 5 mu m(3)), which are often inaccessible for MOF synthesis. Recent developments of three-dimensional electron diffraction (3D ED) have pushed the limits of single-crystal structural analysis. Accurate atomic information can be obtained by 3D ED from nanometer- and submicrometer-sized crystals and samples containing multiple phases. Here, we report the study of molecular motions by using the 3D ED method in MIL-140C and UiO-67, which are obtained as nanosized crystals coexisting in a mixture. In addition to an ab initio determination of their framework structures, we discovered that motions of the linker molecules could be revealed by observing the thermal ellipsoid models and analyzing the atomic anisotropic displacement parameters (ADPs) at room temperature (298 K) and cryogenic temperature (98 K). Interestingly, despite the same type of linker molecule occupying two symmetry-independent positions in MIL140C, we observed significantly larger motions for the isolated linkers in comparison to those reinforced by p-p stacking. With an accuracy comparable to that of SCXRD, we show for the first time that 3D ED can be a powerful tool to investigate dynamics at an atomic level, which is particularly beneficial for nanocrystalline materials and/or phase mixtures.
Synthesis and Structure of a 22 x 12 x 12 Extra-Large Pore Zeolite ITQ-56 Determined by 3D Electron Diffraction
2021. Elina Kapaca (et al.). Journal of the American Chemical Society 143 (23), 8713-8719Article
A multidimensional extra-large pore germanosilicate, denoted ITQ-56, has been synthesized by using modified memantine as an organic structure-directing agent. ITQ-56 crystallizes as plate-like nanocrystals. Its structure was determined by 3D electron diffraction/MicroED. The structure of ITQ-56 contains extra-large 22-ring channels intersecting with straight 12-ring channels. ITQ-56 is the first zeolite with 22-ring pores, which is a result of ordered vacancies of double 4-ring (d4r) units in a fully connected zeolite framework. The framework density is as low as 12.4 T atoms/1000 angstrom(3). The discovery of the ITQ-56 structure not only fills the missing member of extra-large pore zeolite with 22-ring channels but also creates a new approach of making extra-large pore zeolites by introducing ordered vacancies in zeolite frameworks.
Three-Dimensional Electron Diffraction for Structural Analysis of Beam-Sensitive Metal-Organic Frameworks
2021. Meng Ge, Xiaodong Zou, Zhehao Huang. Crystals 11 (3)Article
Electrons interact strongly with matter, which makes it possible to obtain high-resolution electron diffraction data from nano- and submicron-sized crystals. Using electron beam as a radiation source in a transmission electron microscope (TEM), ab initio structure determination can be conducted from crystals that are 6-7 orders of magnitude smaller than using X-rays. The rapid development of three-dimensional electron diffraction (3DED) techniques has attracted increasing interests in the field of metal-organic frameworks (MOFs), where it is often difficult to obtain large and high-quality crystals for single-crystal X-ray diffraction. Nowadays, a 3DED dataset can be acquired in 15-250 s by applying continuous crystal rotation, and the required electron dose rate can be very low (<0.1 e s(-1) angstrom(-2)). In this review, we describe the evolution of 3DED data collection techniques and how the recent development of continuous rotation electron diffraction techniques improves data quality. We further describe the structure elucidation of MOFs using 3DED techniques, showing examples of using both low- and high-resolution 3DED data. With an improved data quality, 3DED can achieve a high accuracy, and reveal more structural details of MOFs. Because the physical and chemical properties of MOFs are closely associated with their crystal structures, we believe 3DED will only increase its importance in developing MOF materials.
Three-dimensional electron diffraction for porous crystalline materials
2021. Zhehao Huang, Tom Willhammar, Xiaodong Zou. Chemical Science 12 (4), 1206-1219Article
Porous crystalline materials such as zeolites, metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have attracted great interest due to their well-defined pore structures in molecular dimensions. Knowing the atomic structures of porous materials is crucial for understanding their properties and exploring their applications. Many porous materials are synthesized as polycrystalline powders, which are too small for structure determination by X-ray diffraction. Three-dimensional electron diffraction (3DED) has been developed for studying such materials. In this Minireview, we summarize the recent developments of 3DED methods and demonstrate how 3DED revolutionized structural analysis of zeolites, MOFs, and COFs. Zeolites and MOFs whose structures remained unknown for decades could be solved. New approaches for design and targeted synthesis of novel zeolites could be developed. Moreover, we discuss the advances of structural analysis by 3DED in revealing the unique structural features and properties, such as heteroatom distributions, mixed-metal frameworks, structural flexibility, guest-host interactions, and structure transformation.
3D-3D topotactic transformation in aluminophosphate molecular sieves and its implication in new zeolite structure generation
2020. Zhehao Huang (et al.). Nature Communications 11 (1)Article
Zeolites have unique pore structures of molecular dimensions and tunable compositions, making them ideal for shape selective catalysis and separation. However, targeted synthesis of zeolites with new pore structures and compositions remains a key challenge. Here, we propose an approach based on a unique 3D-3D topotactic transformation, which takes advantage of weak bonding in zeolites. This is inspired by the structure transformation of PST-5, a new aluminophosphate molecular sieve, to PST-6 by calcination. The structure of nano-sized PST-5 crystals is determined by 3D electron diffraction. We find that the 3D-3D topotactic transformation involves two types of building units where penta- or hexa-coordinated Al is present. We apply this approach to several other zeolite systems and predict a series of new zeolite structures that would be synthetically feasible. This method provides a concept for the synthesis of targeted zeolites, especially those which may not be feasible by conventional methods.
A Layered Cationic Aluminum Oxyhydroxide as a Highly Efficient and Selective Trap for Heavy Metal Oxyanions
2020. Pu Bai (et al.). Angewandte Chemie International Edition 59 (44), 19539-19544Article
Cationic framework materials, especially pure inorganic cationic frameworks that can efficiently and selectively capture harmful heavy metal oxyanions from aqueous solution are highly desired yet scarcely reported. Herein, we report the discovery of a 2D cationic aluminum oxyhydroxide, JU-111, which sets a new benchmark for heavy metal oxyanion sorbents, especially for Cr-VI. Its structure was solved based on 3D electron diffraction tomography data. JU-111 shows fast sorption kinetics (ca. 20 min), high capture capacity (105.4 mg g(-1)), and broad working pH range (3-10) toward Cr(VI)oxyanions. Unlike layered double hydroxides (LDHs), which are poorly selective in the presence of CO32-, JU-111 retains excellent selectivity for Cr(VI)even under a large excess of CO32-. These superior features coupled with the ultra-low cost and environmentally benign nature make JU-111 a promising candidate for toxic metal oxyanion remediation as well as other potential applications.
A Porphyrinic Zirconium Metal-Organic Framework for Oxygen Reduction Reaction
2020. Magdalena Ola Cichocka (et al.). Journal of the American Chemical Society 142 (36), 15386-15395Article
The oxygen reduction reaction (ORR) is central in carbon-neutral energy devices. While platinum group materials have shown high activities for ORR, their practical uses are hampered by concerns over deactivation, slow kinetics, exorbitant cost, and scarce nature reserve. The low cost yet high tunability of metal-organic frameworks (MOFs) provide a unique platform for tailoring their characteristic properties as new electrocatalysts. Herein, we report a new concept of design and present stable Zr-chain-based MOFs as efficient electrocatalysts for ORR. The strategy is based on using Zr-chains to promote high chemical and redox stability and, more importantly, tailor the immobilization and packing of redox active-sites at a density that is ideal to improve the reaction kinetics. The obtained new electrocatalyst, PCN-226, thereby shows high ORR activity. We further demonstrate PCN-226 as a promising electrode material for practical applications in rechargeable Zn-air batteries, with a high peak power density of 133 mW cm(-2). Being one of the very few electrocatalytic MOFs for ORR, this work provides a new concept by designing chain-based structures to enrich the diversity of efficient electrocatalysts and MOFs.
Breathing Metal-Organic Framework Based on Flexible Inorganic Building Units
2020. Erik Svensson Grape (et al.). Crystal Growth & Design 20 (1), 320-329Article
Five novel bismuth carboxylate coordination polymers were synthesized from biphenyl-3,4',5-tricarboxylic acid (H3BPT) and [1,1':4',1 '']terphenyl-3,3 '',5,5 ''-tetracarboxylic acid (H4TPTC). One of the phases, [Bi(BPT)]center dot 2MeOH (denoted SU-100, as synthesized), is the first example, to the best of our knowledge, of a reversibly flexible bismuth-based metal-organic framework. The material exhibits continuous changes to its unit cell parameters and pore shape depending on the solvent it is immersed in and the dryness of the sample. Typically, in breathing carboxylate-based MOFs, flexibility occurs through tilting of the organic linkers without significantly altering the coordination environment around the cation. In contrast to this, the continuous breathing mechanism in SU-100 involves significant changes to bond angles within the Bi2O12 inorganic building unit (IBU). The flexibility of the IBU of SU-100 reflects the nondiscrete coordination geometry of the bismuth cation. A disproportionate increase in the solvent accessible void volume was observed when compared to the expansion of the unit cell volume of SU-100. Additionally, activated SU-100 (SU-100-HT) exhibits a large increase in unit cell volume, yet has the smallest void volume of all the studied samples.
Continuous Variation of Lattice Dimensions and Pore Sizes in Metal-Organic Frameworks
2020. Shuai Yuan (et al.). Journal of the American Chemical Society 142 (10), 4732-4738Article
The continuous variation of the lattice metric in metal-organic frameworks (MOFs) allows precise control over their chemical and physical properties. This has been realized herein by a series of mixed-linker and Zr-6-cluster-based MOFs, namely, continuously variable MOFs (CVMOFs). Similar to the substitutional solid solutions, organic linkers with different lengths and various ratios were homogeneously incorporated into a framework rather than being allowed to form separate phases or domains, which was manifested by single-crystal X-ray diffraction, powder X-ray diffraction, fluorescence quenching experiments, and molecular simulations. The unit cell dimension, surface area, and pore size of CVMOFs were precisely controlled by adopting different linker sets and linker ratios. We demonstrate that CVMOFs allow the continuous and fine tailoring of cell-edge lengths from 17.83 to 32.63 angstrom, Brunauer-Emmett-Teller (BET) surface areas from 585 to 3791 m(2)g(-1), and pore sizes up to 15.9 angstrom. Furthermore, this synthetic strategy can be applied to other MOF systems with various metal nodes thus allowing for a variety of CVMOFs with unprecedented tunability.
Finned zeolite catalysts
2020. Heng Dai (et al.). Nature Materials 19 (10), 1074-1080Article
Nanosized zeolites enable better catalytic performance; however, their synthesis is non-trivial. Here, a simple treatment is presented that enables the growth of nanosized fins on zeolites that act as pseudo-nanoparticles, reducing deactivation rates for methanol-to-hydrocarbon catalysis. There is growing evidence for the advantages of synthesizing nanosized zeolites with markedly reduced internal diffusion limitations for enhanced performances in catalysis and adsorption. Producing zeolite crystals with sizes less than 100 nm, however, is non-trivial, often requires the use of complex organics and typically results in a small product yield. Here we present an alternative, facile approach to enhance the mass-transport properties of zeolites by the epitaxial growth of fin-like protrusions on seed crystals. We validate this generalizable methodology on two common zeolites and confirm that fins are in crystallographic registry with the underlying seeds, and that secondary growth does not impede access to the micropores. Molecular modelling and time-resolved titration experiments of finned zeolites probe internal diffusion and reveal substantial improvements in mass transport, consistent with catalytic tests of a model reaction, which show that these structures behave as pseudo-nanocrystals with sizes commensurate to that of the fin. This approach could be extended to the rational synthesis of other zeolite and aluminosilicate materials.
Hexahydroxytriphenylene for the synthesis of group 13 MOFs - a new inorganic building unit in a beta-cristobalite type structure
2020. S. Leubner (et al.). Dalton Transactions 49 (10), 3088-3092Article
Two new, microporous MOFs of framework composition ((CH3)(2)NH2)(2)[M3O(HHTP)(HHTP center dot)], M = Al3+, Ga3+, H6HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene, are described. Electron diffraction combined with molecular simulations show that these compounds crystallize in the beta-cristobalite structure, containing a new type of trinuclear inorganic building unit for MOFs and radical anions.
Hierarchical micro-reactor as electrodes for water splitting by metal rod tipped carbon nanocapsule self-assembly in carbonized wood
2020. Xia Sheng (et al.). Applied Catalysis B 264Article
Materials design of efficient electrochemical micro-reactors is challenging, although hierarchically structured, self-standing electrodes with catalyst arrays offer promise. Herein, catalyst function in compact micro-reactor electrodes is designed by nanostructural tailoring of carbonized wood for efficient water splitting. Specifically, NiFe rod tipped, N-doped graphitic carbon nanocapsule arrays are self-assembled in hierarchical wood, and the benefit of this unique presentation and its promotive effect on accessibility of the catalyst surfaces is apparent. This report also comprises the first wood based micro-reactor electrodes for electrocatalytic water oxidation demonstrating excellent performance. The overpotential for oxygen evolution reaction was as low as 180 mV for 10 mA cm(-2) current density and TOFredox was high at a level of 5.8 s(-1) (at 370 mV overpotential). This hierarchical electrode can also work as bifunctional catalyst (both as anodic and as cathodic electrode) for total water splitting with a cell potential of 1.49 V for 10 mA cm(-2) in alkaline solution, suggestive of their potential also in other electrochemical applications.
High Thermopower in a Zn-Based 3D Semiconductive Metal-Organic Framework
2020. Jihye Park (et al.). Journal of the American Chemical Society 142 (49), 20531-20535Article
Conductive metal-organic frameworks (c-MOFs) have drawn increasing attention for their outstanding performance in energy-related applications. However, the majority of reported c-MOFs are based on 2D structures. Synthetic strategies for 3D c-MOFs are under-explored, leaving unrealized functionality in both their structures and properties. Herein we report Zn-HAB, a 3D c-MOF comprised of hexaaminobenzene and Zn(II). Zn-HAB is shown to have microporosity with a band gap of approximately 1.68 eV, resulting in a moderate conductivity of 0.86 mS cm(-1) and a high Seebeck coefficient of 200 mu V K-1 at 300 K. The power factor of 3.44 nW m(-1) K-2 constitutes the first report of the thermoelectric properties of an intrinsically conductive 3D MOF.
In Situ Structural Determination of a Homogeneous Ruthenium Racemization Catalyst and Its Activated Intermediates Using X-Ray Absorption Spectroscopy
2020. Karl P. J. Gustafson (et al.). Chemistry - A European Journal 26 (15), 3411-3419Article
The activation process of a known Ru-catalyst, dicarbonyl(pentaphenylcyclopentadienyl)ruthenium chloride, has been studied in detail using time resolved in situ X-ray absorption spectroscopy. The data provide bond lengths of the species involved in the process as well as information about bond formation and bond breaking. On addition of potassium tert-butoxide, the catalyst is activated and an alkoxide complex is formed. The catalyst activation proceeds via a key acyl intermediate, which gives rise to a complete structural change in the coordination environment around the Ru atom. The rate of activation for the different catalysts was found to be highly dependent on the electronic properties of the cyclopentadienyl ligand. During catalytic racemization of 1-phenylethanol a fast-dynamic equilibrium was observed.
2020. Maria Roslova (et al.). Journal of applied crystallography 53, 1217-1224Article
A DigitalMicrograph script, InsteaDMatic, has been developed to facilitate rapid automated 3D electron diffraction/microcrystal electron diffraction data acquisition by continuous rotation of a crystal with a constant speed, denoted as continuous rotation electron diffraction. The script coordinates microscope functions, such as stage rotation, and camera functions relevant for data collection, and stores the experiment metadata. The script is compatible with any microscope that can be controlled by DigitalMicrograph and has been tested on both JEOL and Thermo Fisher Scientific microscopes. A proof of concept has been performed through employing InsteaDMatic for data collection and structure determination of a ZSM-5 zeolite. The influence of illumination settings and electron dose rate on the quality of diffraction data, unit-cell determination and structure solution has been investigated in order to optimize the data acquisition procedure.
Kinetically Controlled Reticular Assembly of a Chemically Stable Mesoporous Ni(II)-Pyrazolate Metal-Organic Framework
2020. Tao He (et al.). Journal of the American Chemical Society 142 (31), 13491-13499Article
The application scope of metal-organic frameworks (MOFs) is severely restricted by their weak chemical stability and limited pore size. A robust MOF with large mesopores is highly desired, yet poses a great synthetic challenge. Herein, two chemically stable Ni(II)-pyrazolate MOFs, BUT-32 and -33, were constructed from a conformation-matched elongated pyrazolate ligand through the isoreticular expansion. The two MOFs share the same sodalite-type net, but have different pore sizes due to the network interpenetration in BUT-32. Controlled syntheses of the two MOFs have been achieved through precisely tuning reaction conditions, where the microporous BUT-32 was demonstrated to be a thermodynamically stable product while the mesoporous BUT-33 is kinetically favored. To date, BUT-32 represents the first example of Ni-4-pyrazolate MOF whose structure was unambiguously determined by single-crystal X-ray diffraction. Interestingly, the kinetic product BUT-33 integrates 2.6 nm large mesopores with accessible Ni(II) active sites and remarkable chemical stability even in 4 M NaOH aqueous solution and 1 M Grignard reagent. This MOF thus demonstrated an excellent catalytic performance in carbon-carbon coupling reactions, superior to other Ni(II)-MOFs including BUT-32. These findings highlight the importance of kinetic control in the reticular synthesis of mesoporous MOFs, as well as their superiority in heterogeneous catalysis.
2020. Donghui Jo (et al.). Angewandte Chemie International Edition 59 (40), 17691-17696Article
Herein we report the synthesis, structure solution, and catalytic properties of PST-24, a novel channel-based medium-pore zeolite. This zeolite was synthesized via the excess fluoride approach. Electron diffraction shows that its structure is built by composite cas-zigzag (cas-zz) building chains, which are connected by double 5-ring (d5r) columns. While the cas-zz building chains are ordered in the PST-24 framework, the d5r columns adopt one of two possible arrangements; the two adjacent d5r columns are either at the same height or at different heights, denoted arrangements S and D, which can be regarded as open and closed valves that connect the channels, respectively. A framework with arrangement D only has a 2D 10-ring channel system, whereas that with arrangement S only contains 3D channels. In actual PST-24 crystals, the open and closed valves are almost randomly dispersed to yield a zeolite framework where the channel dimensionality varies locally from 2D to 3D.
Phase dependent encapsulation and release profile of ZIF-based biocomposites
2020. F. Carraro (et al.). Chemical Science 11 (13), 3397-3404Article
Biocomposites composed of Zeolitic Imidazolate Frameworks (ZIFs) are generating significant interest due to their facile synthesis, and capacity to protect proteins from harsh environments. Here we systematically varied the composition (i.e. relative amounts of ligand (2-methylimidazole), metal precursor (Zn(OAc)(2)center dot 2H(2)O), and protein) and post synthetic treatments (i.e. washes with water or water/ethanol) to prepare a series of protein@ZIF biocomposites. These data were used to construct two ternary phase diagrams that showed the synthesis conditions employed gave rise to five different phases including, for the first time, biocomposites based on ZIF-CO3-1. We examined the influence of the different phases on two properties relevant to drug delivery applications: encapsulation efficiency and release profile. The encapsulation efficiencies of bovine serum albumin and insulin were phase dependent and ranged from 75% to 100%. In addition, release profiles showed that 100% protein release varied between 40 and 300 minutes depending on the phase. This study provides a detailed compositional map for the targeted preparation of ZIF-based biocomposites of specific phases and a tool for the straightforward analysis of the crystalline phases of ZIF based materials (web application named ZIF phase analysis). These data will facilitate the progress of ZIF bio-composites in the fields of biomedicine and biotechnology.
Polymorph evolution during crystal growth studied by 3D electron diffraction
2020. Edward T. Broadhurst (et al.). IUCrJ 7, 5-9Article
3D electron diffraction (3DED) has been used to follow polymorph evolution in the crystallization of glycine from aqueous solution. The three polymorphs of glycine which exist under ambient conditions follow the stability order beta < alpha < gamma. The least stable beta polymorph forms within the first 3 min, but this begins to yield the alpha-form after only 1 min more. Both structures could be determined from continuous rotation electron diffraction data collected in less than 20 s on crystals of thickness similar to 100 nm. Even though the gamma-form is thermodynamically the most stable polymorph, kinetics favour the alpha-form, which dominates after prolonged standing. In the same sample, some beta and one crystallite of the gamma polymorph were also observed.
Rapid desolvation-triggered domino lattice rearrangement in a metal-organic framework
2020. Sheng-Han Lo (et al.). Nature Chemistry 12 (1), 90-97Article
Topological transitions between considerably different phases typically require harsh conditions to collectively break chemical bonds and overcome the stress caused to the original structure by altering its correlated bond environment. In this work we present a case system that can achieve rapid rearrangement of the whole lattice of a metal-organic framework through a domino alteration of the bond connectivity under mild conditions. The system transforms from a disordered metal-organic framework with low porosity to a highly porous and crystalline isomer within 40s following activation (solvent exchange and desolvation), resulting in a substantial increase in surface area from 725 to 2,749m(2)g(-1). Spectroscopic measurements show that this counter-intuitive lattice rearrangement involves a metastable intermediate that results from solvent removal on coordinatively unsaturated metal sites. This disordered-crystalline switch between two topological distinct metal-organic frameworks is shown to be reversible over four cycles through activation and reimmersion in polar solvents. A disordered metal-organic framework converts into a more porous, crystalline phase within 40s following solvent exchange and desolvation. The rapid domino rearrangement of the whole lattice, which involves carboxylate migration on coordinatively unsaturated metal sites, is accompanied by a substantial increase in surface area.
Synthesis and Exfoliation of a New Layered Mesoporous Zr-MOF Comprising Hexa- and Dodecanuclear Clusters as Well as a Small Organic Linker Molecule
2020. Sebastian Leubner (et al.). Journal of the American Chemical Society 142 (37), 15995-16000Article
A new layered mesoporous Zr-MOF of composition [Zr30O20(OH)26(OAc)18L18] was synthesized by employing 5-acetamidoisophthalic acid (H2L) using acetic acid as the solvent. The new MOF, denoted as CAU-45, exhibits a honeycomb structure of stacked layers which comprise both hexa- and dodecanucelar zirconium clusters. Its structure was solved from submicrometer-sized crystals by continuous rotation electron diffraction (cRED). Liquid phase exfoliation and size selection were successfully performed on the material.
Visualizing drug binding interactions using microcrystal electron diffraction
2020. Max T. B. Clabbers (et al.). Communications biology 3 (1)Article
Visualizing ligand binding interactions is important for structure-based drug design and fragment-based screening methods. Rapid and uniform soaking with potentially reduced lattice defects make small macromolecular crystals attractive targets for studying drug binding using microcrystal electron diffraction (MicroED). However, so far no drug binding interactions could unambiguously be resolved by electron diffraction alone. Here, we use MicroED to study the binding of a sulfonamide inhibitor to human carbonic anhydrase isoform II (HCA II). We show that MicroED data can efficiently be collected on a conventional transmission electron microscope from thin hydrated microcrystals soaked with the clinical drug acetazolamide (AZM). The data are of high enough quality to unequivocally fit and resolve the bound inhibitor. We anticipate MicroED can play an important role in facilitating in-house fragment screening for drug discovery, complementing existing methods in structural biology such as X-ray and neutron diffraction. Clabbers et al. utilize MicroED to present the structure of both apo and inhibitor-bound human carbonic anhydrase II at a high resolution to clearly identify the interaction of the inhibitor, acetazolamide. This method eases the difficulty of both crystallizing the protein and soaking the inhibitor in a smaller protein crystal.
In Situ XAS Investigation of the Deactivation and Reactivation Mechanisms of a Heterogeneous Palladium(II) catalyst during the Cycloisomerization of Acetylenic Acids
2019. Ning Yuan (et al.).
The cause and mechanism of deactivation of a well-studied heterogeneous palladium(II) catalyst in the intramolecular lactonization of acetylenic acids to γ-alkylidene lactones have been investigated. It was shown that the deactivation was driven by the formation of reduced palladium species following the addition of the base triethylamine. In this work, X-ray absorption spectroscopy (XAS) was used to identify the palladium species and follow their evolution over the course of the reaction. It was also found that the choice of substrates has significant influences on the Pd species under the same reaction conditions. With these insights into the deactivation mechanism derived from XAS, different strategies were tested and illustrated to regain or maintain the active state of the catalyst. This information was further used to develop a new protocol, which can effectively prevent the deactivation of the catalyst and prolong its usage.
A metal-organic framework for efficient water-based ultra-low-temperature-driven cooling
2019. Dirk Lenzen (et al.). Nature Communications 10Article
Efficient use of energy for cooling applications is a very important and challenging field in science. Ultra-low temperature actuated (T-driving< 80 degrees C) adsorption-driven chillers (ADCs) with water as the cooling agent are one environmentally benign option. The nanoscale metal-organic framework [Al(OH)(C6H2O4S)] denoted CAU-23 was discovered that possess favorable properties, including water adsorption capacity of 0.37 g(H2O)/g(sorbent) around p/p(0 )= 0.3 and cycling stability of at least 5000 cycles. Most importantly the material has a driving temperature down to 60 degrees C, which allows for the exploitation of yet mostly unused temperature sources and a more efficient use of energy. These exceptional properties are due to its unique crystal structure, which was unequivocally elucidated by single crystal electron diffraction. Monte Carlo simulations were performed to reveal the water adsorption mechanism at the atomic level. With its green synthesis, CAU-23 is an ideal material to realize ultra-low temperature driven ADC devices.
Automated serial rotation electron diffraction combined with cluster analysis
2019. Bin Wang, Xiaodong Zou, Stef Smeets. IUCrJ 6, 854-867Article
Serial rotation electron diffraction (SerialRED) has been developed as a fully automated technique for three-dimensional electron diffraction data collection that can run autonomously without human intervention. It builds on the previously established serial electron diffraction technique, in which submicrometre-sized crystals are detected using image processing algorithms. Continuous rotation electron diffraction (cRED) data are collected on each crystal while dynamically tracking the movement of the crystal during rotation using defocused diffraction patterns and applying a set of deflector changes. A typical data collection screens up to 500 crystals per hour, and cRED data are collected from suitable crystals. A data processing pipeline is developed to process the SerialRED data sets. Hierarchical cluster analysis is implemented to group and identify the different phases present in the sample and to find the best matching data sets to be merged for subsequent structure analysis. This method has been successfully applied to a series of zeolites and a beam-sensitive metal-organic framework sample to study its capability for structure determination and refinement. Two multi-phase samples were tested to show that the individual crystal phases can be identified and their structures determined. The results show that refined structures obtained using automatically collected SerialRED data are indistinguishable from those collected manually using the cRED technique. At the same time, SerialRED has lower requirements of expertise in transmission electron microscopy and is less labor intensive, making it a promising high-throughput crystal screening and structure analysis tool.
2019. Sahar Sultan (et al.). Advanced Functional Materials 29 (2)Article
3D printing is recognized as a powerful tool to develop complex geometries for a variety of materials including nanocellulose. Herein, a one-pot synthesis of 3D printable hydrogel ink containing zeolitic imidazolate frameworks (ZIF-8) anchored on anionic 2,2,6,6-tetramethylpiperidine-1-oxylradical-mediated oxidized cellulose nanofibers (TOCNF) is presented. The synthesis approach of ZIF-8@TOCNF (CelloZIF8) hybrid inks is simple, fast (approximate to 30 min), environmentally friendly, takes place at room temperature, and allows easy encapsulation of guest molecules such as curcumin. Shear thinning properties of the hybrid hydrogel inks facilitate the 3D printing of porous scaffolds with excellent shape fidelity. The scaffolds show pH controlled curcumin release. The synthesis route offers a general approach for metal-organic frameworks (MOF) processing and is successfully applied to other types of MOFs such as MIL-100 (Fe) and other guest molecules as methylene blue. This study may open new venues for MOFs processing and its large-scale applications.
Chemoenzymatic Dynamic Kinetic Resolution of Primary Benzylic Amines using Pd-0-CalB CLEA as a Biohybrid Catalyst
2019. Karl P. J. Gustafson (et al.). Chemistry - A European Journal 25 (39), 9174-9179Article
Herein, we report on the use a biohybrid catalyst consisting of palladium nanoparticles immobilized on cross-linked enzyme aggregates of lipase B of Candida antarctica (CalB CLEA) for the dynamic kinetic resolution (DKR) of benzylic amines. A set of amines were demonstrated to undergo an efficient DKR and the recyclability of the catalysts was studied. Extensive efforts to further elucidate the structure of the catalyst are presented.
Electrocatalytic Hydrogen Evolution from a Cobaloxime-Based Metal-Organic Framework Thin Film
2019. Souvik Roy (et al.). Journal of the American Chemical Society 141 (40), 15942-15950Article
Molecular hydrogen evolution catalysts (HECs) are synthetically tunable and often exhibit high activity, but they are also hampered by stability concerns and practical limitations associated with their use in the homogeneous phase. Their incorporation as integral linker units in metal-organic frameworks (MOFs) can remedy these shortcomings. Moreover, the extended three-dimensional structure of MOFs gives rise to high catalyst loadings per geometric surface area. Herein, we report a new MOF that exclusively consists of cobaloximes, a widely studied HEC, that act as metallo-linkers between hexanuclear zirconium clusters. When grown on conducting substrates and under applied reductive potential, the cobaloxime linkers promote electron transport through the film as well as function as molecular HECs. The obtained turnover numbers are orders of magnitude higher than those of any other comparable cobaloxime system, and the molecular integrity of the cobaloxime catalysts is maintained for at least 18 h of electrocatalysis. Being one of the very few hydrogen evolving electrocatalytic MOFs based on a redox-active metallo-linker, this work explores uncharted terrain for greater catalyst pathways.
Hierarchical porous zeolitic imidazolate frameworks nanoparticles for efficient adsorption of rare-earth elements
2019. Ahmed F. Abdel-Magied (et al.). Microporous and Mesoporous Materials 278, 175-184Article
Hierarchical porous zeolitic imidazolate frameworks nanoparticles (ZIF-8 NPs) were synthesized at room temperature via a template-free approach under dynamic conditions (stirring) using water as a solvent. The ZIF-8 NPs were evaluated as adsorbents for rare earth elements (La3+, Sm3+ and Dy3+). Adsorption equilibrium was reached after 7h and high adsorption capacities were obtained for dysprosium and samarium (430.4 and 281.1 mg g(-1), respectively) and moderate adsorption capacity for lanthanum (28.8 mg g(-1)) at a pH of 7.0. The high adsorption capacitiese, as well as the high stability of ZIF-8 NPs, make the hierarchical ZIF-8 materials as an efficient adsorbent for the recovery of La3+, Sm3+ and Dy3+ from aqueous solution.
In Situ XAS Study of the Local Structure and Oxidation State Evolutions of Palladium in a Reduced Graphene Oxide Supported Pd(II) Carbene Complex during an Undirected C−H Acetoxylation Reaction
2019. Ning Yuan (et al.). Catalysis Science & Technology 9 (8), 2025-2031Article
In situ X-ray absorption spectroscopy (XAS) investigations have been performed to provide insights into the reaction mechanism of a palladium(II) catalyzed undirected C–H acetoxylation reaction in the presence of an oxidant. A Pd(II) N-heterocyclic carbene complex p-stacked onto reduced graphene oxide (rGO) was used as catalyst. The Pd speciation during the catalytic process was examined by XAS, which revealed a possible mechanism over the course of the reaction. Pd(II) complexes in the as-synthesized catalyst first go through a gradual ligand substitution where chloride ions bound to Pd(II) are replaced by other ligands with a bond distance to Pd corresponding to carbon, nitrogen and/or oxygen (L). Parallel to this the mean oxidation state of Pd increases indicating the formation of Pd(IV) species. At a later stage, a fraction of the Pd complexes start to slowly transform into Pd nanoclusters. The mean average oxidation state of Pd decreases to the initial state at the end of the experiment which means that comparable amounts of Pd(0) and Pd(IV) are present. These observations from heterogeneous catalysis are in good agreement with its homogeneous analog and they support a Pd(II)-Pd(IV)-Pd(II) reaction mechanism.
Insights into the Exfoliation Process of V2O5 center dot nH(2)O Nanosheet Formation Using Real-Time V-51 NMR
2019. Ahmed S. Etman (et al.). ACS Omega 4 (6), 10899-10905Article
Nanostructured hydrated vanadium oxides (V2O5 center dot nH(2)O) are actively being researched for applications in energy storage, catalysis, and gas sensors. Recently, a one-step exfoliation technique for fabricating V2O5 center dot nH(2)O nano-sheets in aqueous media was reported; however, the underlying mechanism of exfoliation has been challenging to study. Herein, we followed the synthesis of V2O5 center dot nH(2)O nanosheets from the V2O5 and VO2 precursors in real using solution- and solid-state V-51 NMR. Solution-state V-51 NMR showed that the aqueous solution contained mostly the decavanadate anion [H2V10O28](4-) and the hydrated dioxova-nadate cation [VO2 center dot 4H(2)O](+), and during the exfoliation process, decavanadate was formed, while the amount of [VO2 center dot 4H(2)O](+) remained constant. The conversion of the solid precursor V2O5, which was monitored with solid-state V-51 NMR, was initiated when VO2 was in its monoclinic forms. The dried V2O5 center dot nH(2)O nanosheets were weakly paramagnetic because of a minor content of isolated V4+. Its solid-state V-51 signal was less than 20% of V2O5 and arose from diamagnetic V4+ or V5+.This study demonstrates the use of real-time NMR techniques as a powerful analysis tool for the exfoliation of bulk materials into nanosheets. A deeper understanding of this process will pave the way to tailor these important materials.
Luminescence properties of a family of lanthanide metal-organic frameworks
2019. Hani Nasser Abdelhamid (et al.). Microporous and Mesoporous Materials 279, 400-406Article
Two isostructural series of lanthanide metal-organic frameworks denoted as SUMOF-7II (Ln) and SUMOF-7IIB (Ln) (Ln = La, Ce, Pr, Nd, Sm, Eu, and Gd) were synthesized using4,4',4 ''-(pyridine-2,4,6-triyl)tris(benzoic acid) (H(3)L2) and a mixture of H(3)L2 and 4,4',4 ''-(benzene-1,3,5-triyl)tris(benzoic acid) (H3BTB) as linkers, respectively. Both series were characterized using powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermal analysis (TGA), and photoluminescence spectroscopy. Photoluminescence measurements show that Eu-MOFs demonstrate a red emission while Pr- and Nd-MOFs display an emission in the near-infrared (NIR) range. On the other hand, La-, Ce-, Sm- and Gd-MOFs exhibit only a ligand-centered emission. The average luminescence lifetimes in the SUMOF-7IIB series are 1.3-1.4-fold longer than the corresponding ones in the SUMOF-7II series. SUMOF-7IIs show a good photo- and thermal stability. Altogether, the properties of SUMOF-7II and SUMOF-7IIB render them promising materials for applications including sensing, biosensing, and telecommunications.
Magneto-structural correlations of novel kagome-type metal organic frameworks
2019. M. Infas H. Mohideen (et al.). Journal of Materials Chemistry C 7 (22), 6692-6697Article
Here, we report the in situ formation of two novel metal organic frameworks based on copper and cobalt using tetrazole-5-carboxylate ethyl ester as the ligand synthesized by a hydrothermal route. Both MOFs show isostructural three-dimensional networks with kagome ' tilling topology and show high chemical stability. Despite the iso-structural nature, both systems show distinct magnetic features. For the Cu-based kag-MOF system, the co-existence of energetically competing ferromagnetic and antiferromagnetic interactions resulted in the establishment of a long-range ferromagnetic order sustainable up to 52 K. On the contrary, dominant antiferromagnetic interactions identified in the Co-based MOF material were responsible for an antiferromagnetic order evolving below 7 K. Importantly, chemically different metallic ions gave rise to distinct magnetic ordering with different strength and temperature-sustainability. No dynamic magnetic phenomena were observed, implying that the concentration of the metal ions within the structure exceeded the percolation limit favoring the formation of the long-range magnetic order in the studied systems. Both designed kagome ' -type MOFs were thus found to show a coexistence of high frustration and long range magnetic ordering with limited orbital quenching, resulting from the choice of the ligands and crystal arrangement. Thus, the results demonstrated the potentiality to effectively control and alter the magnetic features within the particular kagome ' -type MOF lattice due to the chemical nature and structural incorporation of individual metal ions. The presented approach offers a promising strategy to further fine tune the physical characteristics of the MOF-based systems equipping them with more competitive potential and extending their application portfolio to other fields.