Bifunctional Gyroidal MOFs: Highly Efficient Lewis Base and Lewis Acid Catalysts

Improving Ethane/Ethylene Separation Performance under Humid Conditions by Spatially Modified Zeolitic Imidazolate Frameworks

Gas separation performances are usually degraded under humid conditions for many crystalline porous materials because of the lack of water stability and/or the competition of water vapor toward the interaction sites (e.g., open metal sites). Zeolitic imidazolate frameworks (ZIFs) are suitable candidates for practical applications in gas separation because of their excellent physical/chemical stabilities. However, the limitation of substituent positions in common ZIFs has prevented extensive pore engineering to improve their separation performance. In a type of gyroidal ZIFs with gie topology, the Schiff base moiety provides additional substituent positions, making it possible to modify the spatial arrangement of hydrophobic methyl groups. Herein, a new gyroidal ZIF, ZnBAIm (H₂BAIm = 1,2-bis(1-(1H-imidazol-4-yl)ethylidene)hydrazine), is designed, synthesized, and characterized. The spatially modified ZnBAIm exhibits improved thermal/chemical/mechanical stabilities compared to ZnBIm (H₂BIm = 1,2-bis((5H-imidazol-4-yl)methylene)hydrazine). ZnBAIm can remain intact up to about 480 °C in a N₂ atmosphere and tolerate harsh treatments (e.g., 5 M NaOH aqueous solution at room temperature for 24 h and 190 MPa high pressure in the presence of water). Moreover, the modified pore and window sizes have improved significantly the ethane/ethylene selectivity and separation performance under humid conditions for ZnBAIm. Breakthrough experiments demonstrate efficient separation of a C₂H₆/C₂H₄ (50/50, v/v) binary gas mixture under ambient conditions; more importantly, the C₂H₆/C₂H₄ separation performance is unaffected under highly humid conditions (up to 80% RH). The separation performance is attributed to combined thermodynamic (stronger dispersion interaction with C₂H₆ than with C₂H₄) and kinetic factors (diffusion), determined by density functional theory calculations and kinetic adsorption study, respectively.

A Stable Y(III)-Based Amide-Functionalized Metal-Organic Framework for Propane/Methane Separation and Knoevenagel Condensation

Here, a Y(III)-based metal-organic framework, JLU-MOF112 {[Y₃(μ₃-O)₂(μ₃-OH)(H₂O)₂(BTCTBA)₂]·2[(CH₃)₂NH₂]·5DMF·C₆H₅Cl·4H₂O}, has been successfully synthesized under solvothermal conditions. JLU-MOF112 was constructed with amide-functionalized tricarboxylate ligands and Y(III)-based infinite chains, where the Y₃ repeating units are arranged in a trans order. The overall framework could be viewed as a novel (3,5)-connected net with two types of channels along the [100] and [010] directions. JLU-MOF112 possesses a large BET surface area (1553 m² g^-1), a permanent pore volume (0.67 cm³ g^-1), and outstanding thermal and chemical stability, which give JLU-MOF112 potential for the purification of natural gas, especially the equimolar separation of C₃H₈/CH₄ with a high selectivity of 176. In addition, benefiting from the amide functional groups as Brønsted basic sites and the exposure of open metal sites as Lewis acid sites after activation, JLU-MOF112 can serve as a high-efficiency heterogeneous catalyst for Knoevenagel condensation by the reactions of malononitrile with benzaldehyde (yield of 98%, turnover number of 392, and turnover frequency of 3.27 min^-1) and diverse aldehyde compounds. A rational mechanism was put forward that the Knoevenagel condensation was catalyzed by the synergistic effect of the Lewis acid sites and Brønsted basic sites, engendering the polarization of the carbonyl groups and the deprotonation of the methylene groups for nucleophilic attack.

Bimetallic Metal-Organic Frameworks MIL-53(xAl-yFe) as Efficient Catalysts for H2S Selective Oxidation

Catalytic oxidation of H₂S is a crucial green pathway that can fully convert H₂S into value-added elemental S for commercial use. However, achieving high catalytic stability and S selectivity by traditional-metal-based catalysts still remain a major challenge. Herein, a facile one-step solvothermal strategy is designed for the fabrication of bimetallic MIL-53(xAl-yFe) catalysts. The as-synthesized MIL-53(1Al-5Fe) possesses ample coordinatively unsaturated metal sites, which served as efficient catalytic sites for the selective oxidation of H₂S. As a result, the representative MIL-53(1Al-5Fe) achieves a S yield of nearly 100% at 100-160 °C with almost no obvious decrease of catalytic stability in the run of 30 h. Under the defined reaction conditions, the bimetallic metal-organic frameworks are obviously superior to MIL-53(Al) (49.3%) and MIL-53(Fe) (70.5%) in S yield. This study suggests that the introduction of elemental Al into MIL-53(xAl-yFe) could effectively modulate the electronic properties and spatial configuration of the catalysts, further conducing the adsorption and activation of H₂S and thus accelerating the dissociation of H₂S into a key intermediate S* and improving their catalytic performance.

An Overview of Metal-free Sustainable Nitrogen-based Catalytic Knoevenagel Condensation Reaction ‎

Knoevenagel condensation reaction counts as a vital condensation in organic chemistry due to the synthesis of valuable intermediates, ‎heterocycles, and fine chemicals from commercially available reactants through forming new C=C...

Metal-organic frameworks with the gyroid surface: structures and applications

Gyroid materials have received considerable attention from scientists due to their beautiful structures and advanced functions. On the other side, metal-organic frameworks are inorganic-organic hybrid crystalline porous materials with atomic precision, and can provide good structural models and rich topologies for gyroid materials. In this review, we will briefly introduce the structures of gyroid metal-organic frameworks and their topologies. In addition, their applications in gas adsorption, catalysis, sensors, and luminescent materials are also discussed in detail.

Self-assembly of mixed-valence and heterometallic metallocycles: efficient catalysts for the oxidation of alcohols to aldehydes in ambient air

Two mixed-valence Cu^II/Cu^I and two heterometallic Cu^II/Ag^I metallocycles have been synthesized by the assembly of designed metalloligands and Cu^I/Ag^I ions, respectively.