Automated Diffraction Tomography for the Structure Elucidation of Twinned, Sub-micrometer Crystals of a Highly Porous, Catalytically Active Bismuth Metal-Organic Framework

Synthesis and Structure Evolution in Metal Carbazole Diphosphonates Followed by Electron Diffraction

To access porous metal phosphonates, a new V-shaped, rigid, and sterically demanding diphosphonic acid, namely 3,6-diphosphono-9H-carbazole (H₄L), was designed and employed in a high-throughput investigation. Screening of different metal salts and subsequent optimization studies resulted in the isolation of two porous metal phosphonates [Cu₂(H₂O)₂(L)]·2H₂O (CAU-37) and [Zn_6.75(H₂O)_1.5(HL)_2.5(L)_1.5]·8H₂O (CAU-57). Structure determination was accomplished by electron diffraction and the dehydration behavior of CAU-37 was followed in situ. A rare case of intralayer water de-/adsorption in CAU-37 was found which leads to a cell volume change of 11.9%. Rod-shaped inorganic building units (IBUs) are connected to layers and structural flexibility is due to "accordion-like" structural changes within the layers. In contrast, in CAU-57 a layered IBU is found, which usually results in the formation of dense structures. Due to the shape and rigidity of the linker, the interconnection of the IBUs results in the formation of pores. Water sorption measurements in combination with powder X-ray diffraction data confirmed the reversibility under structural retention.

Framework Adaptability and Concerted Structural Response in a Bismuth Metal-Organic Framework Catalyst

Bismuth metal-organic frameworks (MOFs) as heterogeneous catalysts are scarce, and there is little knowledge on the influence of the MOF features on their resulting activity and behavior. Here, we present the synthesis, characterization, and catalytic activity in the one-pot multicomponent Strecker reaction with ketones of three new MOFs prepared with the combination of indium or bismuth and 4,4',4'',4'''-methanetetrayltetrabenzoic acid. One of them, denoted BiPF-7, is very robust and chemically stable, and demonstrates a high activity in the formation of the desired α-aminonitriles. The interaction of the catalytic substrates with the metal centers in this MOF has been crystallographically characterized, showcasing a concerted framework adaptability process that involves structural changes in framework components that are not directly involved in the binding of the guests.

Synthesis, crystal structure, and topology of a polycatenated bismuth coordination polymer

Solvothermal reaction of Bi(NO3)3·5H2O with the flexible ligand 1,3,5-tris[4-(carboxyphenyl)oxamethyl]-2,4,6-trimethylbenzene (H3TBTC) in methanol at 120 °C for 1 h led to the formation of a novel coordination polymer (CP) with the composition of Bi(TBTC). The structure of the microcrystalline material was determined through three-dimensional electron diffraction (3DED) measurements and phase purity was confirmed by a Pawley refinement, elemental analysis, and thermal analysis. The compound crystallizes in the triclinic space group P 1 ‾ $P\overline{1}$ with one Bi3+ cation and one TBTC3− trianion in the asymmetric unit. Edge-sharing of BiO7 polyhedra leads to the formation of dinuclear Bi2O12 units, which through coordination to six TBTC3− ions form a layered two-periodic structure. Upon heating the material in air, the unit cell volume contracts by 9%, which is attributed to a shift in the inter-layer arrangement and to the flexibility of the building units of the structure. The compound starts to decompose at ∼300 °C. Topological analysis revealed layers consisting of 3-c and 6-c nodes, consistent with the two-periodic kgd net – the dual of the Kagome net (kgm). However, due to the non-planar nature of the Bi(TBTC) layers, adjacent layers are interlaced by polycatenation.

Direct-Space Structure Determination of Covalent Organic Frameworks from 3D Electron Diffraction Data

Structure determination of covalent organic frameworks (COFs) with atomic precision is a bottleneck that hinders the development of COF chemistry. Although three-dimensional electron diffraction (3D-ED) data has been used to solve structures of sub-micrometer-sized COFs, successful structure solution is not guaranteed as the data resolution is usually low. We demonstrate that the direct-space strategy for structure solution, implemented using a genetic algorithm (GA), is a successful approach for structure determination of COF-300 from 3D-ED data. Structural models with different geometric constraints were considered in the GA calculations, with successful structure solution achieved from room-temperature 3D-ED data with a resolution as low as ca. 3.78 Å. The generality of this strategy was further verified for different phases of COF-300. This study demonstrates a viable strategy for structure solution of COF materials from 3D-ED data of limited resolution, which may facilitate the discovery of new COF materials in the future.

Automated electron diffraction tomography - development and applications

Electron diffraction tomography (EDT) has gained increasing interest, starting with the development of automated electron diffraction tomography (ADT) which enables the collection of three-dimensional electron diffraction data from nano-sized crystals suitable for ab initio structure analysis. A basic description of the ADT method, nowadays recognized as a reliable and established method, as well as its special features and general applicability to different transmission electron microscopes is provided. In addition, the usability of ADT for crystal structure analysis of single nano-sized crystals with and without special crystallographic features, such as twinning, modulations and disorder is demonstrated.

Phosphinic Acid Based Linkers: Building Blocks in Metal-Organic Framework Chemistry

Metal-organic frameworks (MOFs) are a chemically and topologically diverse family of materials composed of inorganic nodes and organic linkers bound together by coordination bonds. Presented here are two significant innovations in this field. The first is the use of a new coordination group, phenylene-1,4-bis(methylphosphinic acid) (PBPA), a phosphinic acid analogue of the commonly used terephtalic acid. Use of this new linker group leads to the formation of a hydrothermally stable and permanently porous MOF structure. The second innovation is the application of electron-diffraction tomography, coupled with dynamic refinement of the EDT data, to the elucidation of the structure of the new material, including the localization of hydrogen atoms.

Exploring physical and chemical properties in new multifunctional indium-, bismuth-, and zinc-based 1D and 2D coordination polymers

Main group element coordination polymers (MGE-CPs) are important compounds for the development of multifunctional materials. However, there has been a shortage of studies regarding their structural, optical, catalytic, mechanical, and antibacterial properties. This work presents an exhaustive study of a set of crystalline MGE-CPs obtained from bismuth and indium metals and iminodiacetate, 1,2,4,5-benzenetetracarboxylate, and 2,2'-bipyridine as building blocks. An in-depth topological analysis of the networks was carried out. Additionally, nanoindentation studies were performed on two representative low-dimensional compounds in order to find the relationships between their structural features and their intrinsic mechanical properties (hardness and elasticity). The solid-state photoluminescence (SSPL) properties were also studied in terms of excitation, emission, lifetimes values, and CIE chromaticites. Moreover, the heterogeneous catalytic activities of the compounds were evaluated with the cyanosilylation reaction using a set of carbonylic substrates under solvent-free conditions. Finally, the inhibitory effect of the Bi-CPs on the growth of microorganisms such as Escherichia coli, Salmonella enterica serovar Typhimurium, and Pseudomonas aeruginosa, which are associated with relevant infectious diseases, is reported.

Synthesis and crystal structure of three new bismuth(III) arylsulfonatocarboxylates

Three new bismuth arylsulfonatocarboxylates [Bi(OH)(SB)] (1), [Bi4(ST)2(HST)O2(H2O)2]·H2O (2) and [Bi4(ST)2O3(H2O)2] (3) were synthesized under solvothermal reaction conditions at 180°C using the potassium or sodium salt of 4-sulfobenzoic acid (H2SB) and 2-sulfoterephthalic acid (H3ST), respectively. The compounds were characterized in detail and the crystal structures were determined from single crystal X-ray diffraction data. Phase purity was confirmed by powder X-ray diffraction and elemental analysis. Structural comparisons to the only three other known bismuth sulfonatocarboxylates are presented. Due to the higher reaction temperatures employed for the synthesis of the title compounds a higher degree of condensation of the BiOx polyhedra (X=7 or 8) to tetrameric units, 1D chains or a 2D layer is observed. Connection through the organic linker molecules leads to the formation of 3D coordination polymers in all three title compounds.

Synthesis, functionalisation and post-synthetic modification of bismuth metal–organic frameworks

Two new Bi-MOFs were discovered, synthesised and characterised, and the amino-functionalised Bi-MOF was post-synthetically modified using anhydrides and 1,3-propane sultone.

Defect-Engineered Metal-Organic Frameworks

Defect engineering in metal-organic frameworks (MOFs) is an exciting concept for tailoring material properties, which opens up novel opportunities not only in sorption and catalysis, but also in controlling more challenging physical characteristics such as band gap as well as magnetic and electrical/conductive properties. It is challenging to structurally characterize the inherent or intentionally created defects of various types, and there have so far been few efforts to comprehensively discuss these issues. Based on selected reports spanning the last decades, this Review closes that gap by providing both a concise overview of defects in MOFs, or more broadly coordination network compounds (CNCs), including their classification and characterization, together with the (potential) applications of defective CNCs/MOFs. Moreover, we will highlight important aspects of "defect-engineering" concepts applied for CNCs, also in comparison with relevant solid materials such as zeolites or COFs. Finally, we discuss the future potential of defect-engineered CNCs.

Evidence of noncentrosymmetry of human tooth hydroxyapatite crystals

Herein, we investigate human single hydroxyapatite crystals (enamel and dentine) by convergent-beam electron diffraction (CBED) and automated electron-diffraction tomography (ADT). The CBED pattern shows the absence of the mirror plane perpendicular to the c axis leading to the P63 space group instead of the P63 /m space group considered for larger-scale crystals, this is confirmed by ADT. This experimental evidence is of prime importance for understanding the morphogenesis and the architectural organization of calcified tissues.

Polymorph identification and crystal structure determination by a combined crystal structure prediction and transmission electron microscopy approach

Electron diffraction offers advantages over X-ray based methods for crystal structure determination because it can be applied to sub-micron sized crystallites, and picogram quantities of material. For molecular organic species, however, crystal structure determination with electron diffraction is hindered by rapid crystal deterioration in the electron beam, limiting the amount of diffraction data that can be collected, and by the effect of dynamical scattering on reflection intensities. Automated electron diffraction tomography provides one possible solution. We demonstrate here, however, an alternative approach in which a set of putative crystal structures of the compound of interest is generated by crystal structure prediction methods and electron diffraction is used to determine which of these putative structures is experimentally observed. This approach enables the advantages of electron diffraction to be exploited, while avoiding the need to obtain large amounts of diffraction data or accurate reflection intensities. We demonstrate the application of the methodology to the pharmaceutical compounds paracetamol, scyllo-inositol and theophylline.