A Crystalline Mesoporous Germanate with 48-Ring Channels for CO2Separation

About the Dominance of Mesopores in Physisorption in Amorphous Materials

Amorphous, porous materials represent by far the largest proportion of natural and men-made materials. Their pore networks consists of a wide range of pore sizes, including meso- and macropores. Within such a pore network, material moisture plays a crucial role in almost all transport processes. In the hygroscopic range, the pores are partially saturated and liquid water is only located at the pore fringe due to physisorption. Therefore, material parameters such as porosity or median pore diameter are inadequate to predict material moisture and moisture transport. To quantify the spatial distribution of material moisture, Hillerborg’s adsorption theory is used to predict the water layer thickness for different pore geometries. This is done for all pore sizes, including those in the lower nanometre range. Based on this approach, it is shown that the material moisture is almost completely located in mesopores, although the pore network is highly dominated by macropores. Thus, mesopores are mainly responsible for the moisture storage capacity, while macropores determine the moisture transport capacity, of an amorphous material. Finally, an electrical analogical circuit is used as a model to predict the diffusion coefficient based on the pore-size distribution, including physisorption.

Pillared-layered indium phosphites templated by amino acids: isoreticular structures, water stability, and fluorescence

Two crystalline open-framework indium phosphites (denoted SCU-31 and SCU-32) were prepared using amino acids as structure-directing agents. They have isoreticular pillared-layered structures built up from 6 × 1 and 4 = 1 clusters. Notably, the two compounds show excellent water stability and exhibit blue fluorescence under UV light irradiation at room temperature. The proton-conducting behaviour of SCU-31 was also investigated.

Versatile Platform of Ion Conducting 2D Anionic Germanate Covalent Organic Frameworks with Potential for Capturing Toxic Acidic Gases

Anionic covalent organic framework is an emerging class of functional materials in which included ionic species of the opposite charges play an important role in the ion conduction and selective gas adsorption. Herein, we reported a facile method to construct a series of germanate-based anionic COFs (Ge-COFs) by reticulating dianionic hexa-coordinated GeO₆ nodes with anthracene building blocks adopting a hcb topology in an extended 2D framework. A systematic change of pore properties in Ge-COFs was observed through the incorporation of three different alkali metal cations: Li⁺, Na⁺, and K⁺. The intrinsically negatively charged backbone provides a host matrix with a homogeneous distribution of counter cations and poses variable and exciting features for gas adsorption and ionic conduction. Among the series, K⁺-based Ge-COF-K with a surface area of 1252 m²/g and pore volume of 0.84 cm³/g shows a maximum CO₂ uptake of 126 cm³/g (247.4 mg/g) at 273 K and 1 bar, an IAST selectivity of 140 over N₂. Ge-COF-K also exhibits a high SO₂ kinetic breakthrough capacity of 154 mg/g at low ppm of SO₂ concentration under ambient conditions among recently reported porous materials. Moreover, reasonably high lithium, sodium, and potassium ionic conductivities were observed with the values of 1.2 × 10^-4, 3.4 × 10^-5, and 2.2 × 10^-5 S/cm for propylene carbonate infiltrated Ge-COF-Li, Ge-COF-Na, and Ge-COF-K at 100 °C, respectively.

Crystalline Anionic Germanate Covalent Organic Framework for High CO2 Selectivity and Fast Li Ion Conduction

The metalloid-centered covalent organic framework has attracted great interest from both its structure and application. Heavier elements have seldomly been incorporated in the covalent organic frameworks, even if they exhibit special structural features and properties. Herein, we reported the first crystalline germanate covalent organic framework with hexacoordinated germanate linked by an anthracene linker. The existence of counterion lithium ions in the framework provides a high CO₂ uptake of 88.5 cm³  g^-1 at 273 K and a high CO₂ /N₂ selectivity of 101. A significantly improved lithium ion conductivity of 0.25 mS cm^-1 at room temperature was observed due to the soft germanium center.

Synthesis of Organosilyl-Functionalized Cage-Type Germanoxanes Containing Fluoride Ions

Eight corners of a double-four ring cage-type germanoxane, containing a fluoride ion, were successfully silylated by the combination of chlorosilanes and silazanes. Three different silyl groups, trimethylsilyl, dimethylsilyl, and dimethylvinylsilyl, were attached on the corners of germanoxane cage. The solubility and reactivity of the cage modified with dimethylvinylsilyl groups were significantly increased, allowing for further reaction. Hydrosilylation reaction between dimethylvinylsilylated cage geramanoxanes and dimethylsilylated cage siloxanes afforded porous solids. Functionalization of the corners of germanoxanes with silyl groups should provide valuable building blocks in various functional materials.

Cluster–oxalate frameworks with extra-large channels: solvent-free synthesis, chemical stability, and proton conduction

Two cluster–oxalate frameworks (denoted as SCU-62 and SCU-65) were prepared under solvent-free conditions.

PKU-21: A Novel Layered Germanate Built from Ge7 and Ge10 Clusters for CO2 Separation

The attractive properties of layered inorganic materials, which make them suitable for numerous applications in chemical industries and life sciences, originated from their crystalline framework structures. Here, we report a new layered germanate PKU-21, which was prepared by the hydrothermal synthesis method using 2-propanolamine (MIPA) as the structure-directing agent. The structure of PKU-21 was determined from synchrotron single-crystal X-ray diffraction and synchrotron powder X-ray diffraction data. It reveals a complicated framework structure containing 18 unique Ge atoms in the asymmetric unit. PKU-21 is the first layered germanate built from both Ge₇ and Ge₁₀ clusters, following the 3-dimensional germanate PKU-17. The preparation and structure of PKU-21 are discussed in comparison with PKU-17, which provides new insight into the formation mechanism of germanates. Gas sorption experiments indicate that the layered PKU-21 sample exhibits a better CO₂ sorption selectivity over N₂ and CH₄ at 298 K than at 273 K, making it a promising candidate for CO₂ separation.

Application of X-ray Diffraction and Electron Crystallography for Solving Complex Structure Problems

All crystalline materials in nature, whether inorganic, organic, or biological, macroscopic or microscopic, have their own chemical and physical properties, which strongly depend on their atomic structures. Therefore, structure determination is extremely important in chemistry, physics, materials science, etc. In the past centuries, many techniques have been developed for structure determination. The most widely used one is X-ray crystallography (single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD)), and it remains the most important technique for structure determination of crystalline materials. Although SCXRD and PXRD are successful in many cases, a number of reasons limit their applications, such as SCXRD for nanosized crystals, intergrowth, and defects and PXRD for complex structures, multiphasic samples, impurities, peak overlaps, etc. Another most valuable technique for structure determination is electron crystallography (EC). With the electron as a probe, EC alone can also be used for structure determination, especially for crystals that are too small to be studied by SCXRD or too complex for PXRD. As electrons interact much more strongly with matter than X-rays do, both electron diffraction (ED) patterns and high-resolution transmission electron microscopy (HRTEM) images can be obtained from nanosized crystals. However, collecting a complete set of ED patterns or recording a good HRTEM image requires considerable expertise on the operation of electron microscopes and crystallography. The strong interactions between electrons and materials can also lead to dynamical effects and beam damage. These difficulties make structure determination from ED patterns and HRTEM images not straightforward. Recently, two three-dimensional (3D) electron diffraction techniques, automated electron diffraction tomography (ADT) and rotation electron diffraction (RED), have been developed, which perform the data collection in an automated manner. Although the dynamical effects in the newly developed 3D electron diffraction techniques (ADT, RED) are reduced significantly, for some structures there are still problems with obtaining an initial model because of beam damage. The X-ray diffraction and EC methods discussed above are both powerful techniques but have their own limitations. In many complicated cases, one technique alone is not enough to solve the crystal structure, and different techniques that supply complementary structural information have to support each other for the complete structure determination. In this Account, we provide a summary of the advantages and disadvantages of X-ray diffraction (PXRD and SCXRD) and EC (HRTEM and ED) for structure determination and include a review of applications of X-ray diffraction and EC for solving complex structure problems such as peak overlap, impurities, pseudosymmetry and twinning, disordered frameworks, locating guests, aperiodic structures, etc. Some of the latest advances in structure determination are also presented briefly, namely, revealing hydrogen positions by ED, protein crystal structure solution by 3D electron diffraction, and structure determination using an X-ray free electron laser (XFEL).

Two New Copper Borates with Mesoscale Cubic Supramolecular Cages Assembled from {Cu4 @B20 } Clusters

Two new copper borates, namely H₆ [(μ₄ -O)Cu₄ @B₂₀ O₃₂ (OH)₈ ]⋅25 H₂ O (1) and H₆ [(μ₄ -O)Cu₄ @B₂₀ O₃₂ (OH)₈ ]⋅34 H₂ O⋅8 H₃ BO₃ (2), with 3D supramolecular framework have been made under solvothermal conditions, which built by novel cubic supramolecular cages with mesoscale cavities via the H-bondings. Interestingly, the cage is assembled by [(μ₄ -O)Cu₄ @B₂₀ O₃₂ (OH)₈ ] ({Cu₄ @B₂₀ }) cluster units with different point-group symmetry. Owing to extra H₃ BO₃ molecules participated in building the supramolecular framework, 2 has a larger cubic cage size and higher non-framework volume, leading to the cage size extended to mesoporous size set as a version of ''1 plus".

A series of color-tunable light-emitting open-framework lanthanide sulfates containing extra-large 36-membered ring channels

A series of lanthanide sulfates contain 36-ring channels with the pore size (22.0 × 16.8 Å) based on Eu₁₀clusters.

Interrupted silicogermanate with 10-ring channels: synthesis and structure determination by combining rotation electron diffraction and powder X-ray diffraction

Structure determination of silicogermanate with sti layers pillared by D4R/Ge₇ units by rotation electron diffraction and powder X-ray diffraction.

A multi-dimensional quasi-zeolite with 12 × 10 × 7-ring channels demonstrates high thermal stability and good gas adsorption selectivity

A novel quasi-zeolite PKU-15, with a rare 3-dimensional structure containing interconnected large (12-ring), medium (10-ring) and small (7-ring) multi-pore channels, was hydrothermally synthesised and characterised. A unique tri-bridging O2- anion is found to be encapsulated in the cage-like (Ge,Si)12O31 building unit and energetically stabilises the PKU-15 framework. The removal of this oxygen atom would convert PKU-15 into a hypothetical zeolite PKU-15H. Thus, PKU-15 can be considered as a unique 'quasi-zeolite', which bridges porous germanates and zeolites. Owing to the absence of terminal Ge-OH groups in its structure, PKU-15 shows a remarkably high thermal stability of up to 600 °C. PKU-15 is also the first microporous germanate that exhibits permanent porosity, with a BET area of 428 m2 g-1 and a good adsorption affinity toward CO2.

A zeolite CAN-type aluminoborate with gigantic 24-ring channels

A well crystalline chiral aluminoborate with extra-large 24-ring channels was solvothermally made by using amines as templates. It exhibits a rare zeolite CAN-type net with very low framework density and high nonframework volume by incorporating B₅O₁₀ clusters and AlO₄ tetrahedra.