PKU-3: An HCl-Inclusive Aluminoborate for Strecker Reaction Solved by Combining RED and PXRD

BO3 Triangle and B@Zn2O3 Cationic Layer in the Structure of the Hybrid Zinc Acetate Borate [ZnAc]·[ZnBO3]

A zinc acetate borate, [ZnAc]·[ZnBO₃] (1), was synthesized under mild conditions; the B@Zn₂O₃ layer of 1 contains a 6-membered ring embedded with a rare BO₃ unit. The layers are pillared by acetate ions to form a 3D framework. The pillared structure of 1 supplies enough space as a nanoreactor, and the related application of CO₂-to-CO reduction has been confirmed.

Identification of key oxidative intermediates and the function of chromium dopants in PKU-8: catalytic dehydrogenation of sec-alcohols with tert-butylhydroperoxide

t-BuOO* activated by Cr-PKU-8 from TBHP is the key intermediate to the highly selective dehydrogenation of sec-alcohols.

Two new Cu-based borate catalysts with cubic supramolecular cages for efficient catalytic hydrogen evolution

Focusing on renewable energy, we are devoted to developping efficient, robust and low cost water reduction catalysts (WRCs). Two new Cu-based borate catalysts, namely H₂Na₂K₂[(μ₄-O)Cu₄@B₂₀O₃₂(OH)₈]·21H₂O (1) and H₂Rb_1.6K_2.4[(μ₄-O)Cu₄@B₂₀O₃₂ (OH)₈]·15H₂O (2), with cubic supramolecular cages were synthesized under a hydrothermal condition. Moreover, new copper complexes were applied as water reduction catalysts (WRCs) in the presence of [Ir(ppy)₂(dtbbpy)][PF₆] as photosensitizer and triethanolamine (TEOA) as the sacrificial electron donor. Nevertheless, the main active place is attributed to the centre of Borates [(μ₄-O)Cu₄@B₂₀O₃₂(OH)₈], and the atomic radius of the counter cation would be the critical factor of the photocatalytic activity. Increasing the atomic radius from the Na atom to the Rb atom, causes the photocatalytic activity to decrease efficiently. The experimental results match well with the density functional theory (DFT) conclusion. It is noteworthy to mention that our research not only enriches the Cu-based borate chemistry, but also investigates the photocatalytic activity of Cu-based borates. This would guide us through the borate synthesis and to develop their applications toward energy and the environment.

Pressure-induced semiconductor-to-metal phase transition of a charge-ordered indium halide perovskite

Phase transitions in halide perovskites triggered by external stimuli generate significantly different material properties, providing a great opportunity for broad applications. Here, we demonstrate an In-based, charge-ordered (In⁺/In³⁺) inorganic halide perovskite with the composition of Cs₂In(I)In(III)Cl₆ in which a pressure-driven semiconductor-to-metal phase transition exists. The single crystals, synthesized via a solid-state reaction method, crystallize in a distorted perovskite structure with space group I4/m with a = 17.2604(12) Å, c = 11.0113(16) Å if both the strong reflections and superstructures are considered. The supercell was further confirmed by rotation electron diffraction measurement. The pressure-induced semiconductor-to-metal phase transition was demonstrated by high-pressure Raman and absorbance spectroscopies and was consistent with theoretical modeling. This type of charge-ordered inorganic halide perovskite with a pressure-induced semiconductor-to-metal phase transition may inspire a range of potential applications.

Isostructural Three-Dimensional Covalent Organic Frameworks

Herein, we reported the designed synthesis of three isostructural three-dimensional covalent organic frameworks (3D COFs) with -H, -Me, or -F substituents, which have similar crystallinity and topology. Their crystal structures were determined by continuous rotation electron diffraction (cRED), and all three 3D COFs were found to adopt a fivefold interpenetrated pts topology. More importantly, the resolution of these cRED datasets reached up to 0.9-1.0 Å, enabling the localization of all non-hydrogen atomic positions in a COF framework directly by 3D ED techniques for the first time. In addition, the precise control of the pore environments through the use of different functional groups led to different selectivities for CO₂ over N₂ . We have thus confirmed that polycrystalline COFs can be definitely studied to the atomic level as other materials, and this study should also inspire the design and synthesis of 3D COFs with tailored pore environments for interesting applications.

Continuous solid solutions constructed from two isostructural octahedron-based molecular sieves: preparation, acidity regulation and catalytic application in Strecker reactions

Al_xGa_1−x-PKU-1 solid solutions were used as acidity-tunable solid acids to catalyze the nucleophilic addition of the cyanide anion to imines.

K2[B4O5(OH)4]·H2O and K2[B4O5(OH)4]: two new hydrated potassium borates with isolated [B4O5(OH)4]2− units and different structural frameworks

Two new hydrated potassium tetraborates with isolated [B₄O₅(OH)₄]²⁻ units were obtained via a mild hydrothermal method.

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).

Propylsulfonic acid-anchored isocyanurate-based periodic mesoporous organosilica (PMO-ICS-Pr-SO3H): A new and highly efficient recoverable nanoporous catalyst for the one-pot synthesis of bis(indolyl)methane derivatives

A new propylsulfonic acid-anchored isocyanurate bridging periodic mesoporous organosilica (PMO-ICS-Pr-SO₃H) was prepared and shown to be a highly efficient recyclable nanoporous catalyst for the one-pot synthesis of bis(indolyl)methane derivatives in good to excellent yields from indole and different aldehydes in EtOH under mild reaction conditions in short reaction times. Moreover, the nanoporous catalyst was recovered and reused at least four times without significant decrease in its catalytic activity. The PMO-ICS-Pr-SO₃H catalyst was characterizred by Fourier transform infrared (FTIR) spectroscopy, thermogravimetry analysis (TGA) and N₂ adsorption-desorption isotherms techniques as well as field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray (EDX) spectroscopy. Compared to the classical methodologies, this method illustrated significant advantages including low loading of the catalyst, high to excellent yields, short reaction times, avoiding the use of toxic transition metals or reactive reagents for modification of the catalytic activity, easy separation and purification of the products, and reusability of the catalyst.

A novel supramolecular magnesoborate framework with snowflake-like channels built by unprecedented huge B69 cluster cages

A novel magnesoborate with a 3D supramolecular framework has been made under solvothermal conditions, showing wonderful snowflake-like motif channels assembled from unprecedented B₆₉ cluster cage units.

B-site ordered double perovskite LaBa1-xSrxZnSbO6 (0 ≤ x ≤ 1): Sr(2+)-doping-induced symmetry evolution and structure-luminescence correlations

The study of perovskites has been active for a long time. Here, we rationally designed and prepared a double perovskite, LaBaZnSbO6, by selecting Zn(2+) and Sb(5+) with large size and charge differences, and, indeed, complete B-site ordering can be achieved. Careful study using powder X-ray diffraction data pinpointed its space group to be I2/m, which has rarely been seen in double perovskites. Thereafter, an interesting observation of Sr(2+)-doping-induced symmetry evolution from I2/m to P21/n was confirmed in the complete solid solutions LaBa1-xSrxZnSbO6, where the tilting system also transferred from a(-)a(-)c(0) to a(-)a(-)c(+). The transition boundary is around x = 0.4. It can also be visualized by the variation of θ (defined as c/[(a + b)/2]), which is associated with the anisotropic shrinkage of the unit cell lattice and indeed shows a minimum at x = 0.4. Such a successive modulation of both the structural symmetry and the average La/Ba/Sr-O bond distances (revealed by Rietveld refinements) motivated us to study the Eu(3+) luminescence in La0.95Eu0.05Ba1-xSrxZnSbO6. Interestingly, the maximum of charge transfer absorption of Eu(3+) shows a precise changing tendency with the A-O bond distances along with the Sr(2+) doping, clearly revealing the structure-luminescence correlations.

Structure determination of modulated structures by powder X-ray diffraction and electron diffraction

The combination of PXRD and ED is applied to determine modulated structures which resist solution by more conventional methods.

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.

Octahedron-based gallium borates (Ga-PKU-1) with an open framework: acidity, catalytic dehydration and structure–activity relationship

The octahedron-based Ga-PKU-1 catalyst with an open framework acted as an efficient solid acid catalyst for isopropanol decomposition.