Multifunctional Dysprosium(III)–Organic Framework for Efficiently Catalyzing the Cycloaddition of CO₂ and Knoevenagel Condensation under Mild Conditions

Two-dimensional (2D) materials with higher order in-plane nanoscale pores play a crucial role in innumerable applications, but their precise and reasonable preparation remains a huge challenge. Herein, we report the highly robust 2D dysprosium(III)–organic framework {[Dy(H2BDTP)(DMF)2]·2DMF·3H2O}n (NUC-101) with higher order in-plane nanoscale pores (15.2 × 6.4 Å2) (H5BDTP = 2,6-bis(2,4-dicarboxyphenyl)-4-(2H-tetrazol-5-yl)pyridine). After activation, the scarcely reported 2D host framework [Dy2(H2BDTP)2]n is of great interest due to that it not only contains voids of 15.2 × 11.7 × 6.4 Å3 but also is functionalized by free carboxyl, pyridinyl, and tetrazolyl groups in the upper and lower parts. Thanks to the excellent physicochemical properties including omnidirectional opening pores, ultrahigh porosity, larger specific surface area, and plentiful coexisting Lewis acid–base sites of open dinuclear Dy3+ ions, carboxyl, pyridinyl, and tetrazolyl groups, the cycloaddition of CO2 with epoxides and Knoevenagel condensation of malonitrile and aldehydes can be efficiently catalyzed by NUC-101a under comparatively mild conditions with high selectivity and turnover frequency. This work provides a valuable insight that the development of 2D functionalized nanoporous materials is more feasible for achieving the goal of catalytic applications

Robust {Cd₄}‑Organic Framework for Efficiently Catalyzing CO₂ Cycloaddition and Knoevenagel Condensation

The high-value-added carbonates generated from CO2 have attracted the attention of more and more researchers because of which the optimization of metal–organic framework (MOF)-based catalysts has seen a considerable upsurge at present. The scarcely reported cadmium(II)-based MOFs inspire us to explore CdOFs with excellent catalytic activity and high reusability. Herein, the unification of the unreported {Cd4(μ3-OH)2(CH3CO2–)} cluster and 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (H5BDCP) led to a highly robust nanoporous crystalline material of {(Me2NH2)5[Cd4(BDCP)2(μ3-OH)2(CH3CO2)(H2O)2]·3DMF·2H2O}n (NUC-67) with 57.4% void volume. Structural analysis displays that the inner surface of channels in activated NUC-67a is functionalized by Lewis acid sites of unsaturated Cd2+ ions and Lewis base sites of μ3-OH– groups, CH3CO2– anions, free pyridine, and CO groups. Under solvent-free conditions, NUC-67a exhibits high catalytic performance on the cycloaddition of CO2 with epoxides; for instance, the conversion rate of propylene oxide (PO) into propylene carbonate (PC) with 1 atm CO2 can reach 99% within 6 h at 55 °C, resulting in a 660 turnover number and 110 h–1 turnover frequency. Moreover, Knoevenagel condensation reactions of aldehydes and malononitrile can be efficiently catalyzed by activated NUC-67a. Encouragingly, NUC-67a shows strong structural stability and good reversible cyclicity in the above two organic reactions with metal leaching below 8 ppb. Hence, this work proves that the optimization of MOF-based catalysts should focus on the design and selection of organic ligands, which plays a decisive role in structural regulation, such as cluster-based nodes, high defect of metal sites, unexpected insertion of Lewis base sites, and high-porosity channels

Porous MB@Cd-MOF Obtained by Post-Modification: Self-Calibrated Fluorescent Turn-on Sensor for Highly Sensitive Detection of Carbaryl

Abuse of pesticides has caused great threat to the environment, so it is urgent to find a fast and sensitive method to detect pesticide residues in agricultural products and water. Herein, a 3D Cd-MOF was designed and synthesized by the reaction of 3,5-di­(2′,5′-dicarboxylphenyl)­pyridine (H4DDPP) and Cd­(NO3)2 under solvothermal conditions. Meanwhile, a stable MB@Cd-MOF composite with dual-emitting characteristic was constructed by the in situ encapsulation of methylene blue (MB) into the channel of Cd-MOF. Compared with Cd-MOF, MB@Cd-MOF exhibits sensitive sensing for carbaryl with the detection limit of 6.7 ng·mL–1 and high accuracy, which are attributed to the fluorescence enhancement effect and dual-emitting characteristics of MB@Cd-MOF. Finally, the fluorescence enhancement mechanisms indicate that the excellent fluorescence properties of MB@Cd-MOF as a self-calibrated sensor are mainly ascribed to energy transfer from carbaryl to MB@Cd-MOF and the photoinduced electron transfer from carbaryl to H4DDPP. At the same time, the relative standard deviation of MB@Cd-MOF for carbaryl in real samples is less than 4.44%, indicating that MB@Cd-MOF has excellent sensing accuracy for carbaryl. Therefore, the rapid fluorescence response and good stability of MB@Cd-MOF endow it with the capacity to sense carbaryl in practical application

Nanochannel {InZn}–Organic Framework with a High Catalytic Performance on CO₂ Chemical Fixation and Deacetalization–Knoevenagel Condensation

The rare combination of InIII 5p and ZnII 3d in the presence of a structure-oriented TDP6– ligand led to a robust hybrid material of {(Me2NH2)­[InZn­(TDP)­(OH2)]·4DMF·4H2O}n (NUC-42) with the interlaced hierarchical nanochannels (hexagonal and cylindrical) shaped by six rows of undocumented [InZn­(CO2)6(OH2)] clusters, which represented the first 5p–3d nanochannel-based heterometallic metal–organic framework. With respect to the multifarious symbiotic Lewis acid–base and Brønsted acid sites in the high porous framework, the catalytic performance of activated NUC-42a upon CO2 cycloaddition with styrene oxide was evaluated under solvent-free conditions with 1 atm of CO2 pressure, which exhibited that the reaction could be well completed at ambient temperature within 48 h or at 60 °C within 4 h with high yield and selectivity. Moreover, because of the acidic function of metal sites and a central free pyridine in the TDP6– ligand, deacetalization–Knoevenagel condensation of acetals and malononitrile could be efficiently facilitated by an activated sample of NUC-42a under lukewarm conditions

Construction of Metal−Organic Frameworks with Novel {Zn₈O₁₃} SBU or Chiral Channels through <i>in Situ</i> Ligand Reaction

By control of in situ ligand reaction, two zinc metal−organic frameworks (1, 2) have been isolated hydrothermally. Both complexes are 3D open frameworks. Complex 1, which is based on an unprecedented {Zn8O13} SBU constructed of 2H-imidazole-4,5-dicarboxylic acid (H3IMDC), has the same topology as that of MOF-5. Complex 2 contains large homochiral channels based on the in situ generated 4,5-di(1H-tetrazol-5-yl)-2H-imidazole (H3DTIM). Both H3IMDC and H3DTIM ligands are in situ generated from the same precursor, 2H-imidazole-4,5-dicarbonitrile

Bifunctional Zn Coordination Polymers for High-Performance Fluorescence Turn-On Detection of l‑Glutamate and Adsorption of Malachite Green in Aqueous Medium

Two time-induced Zn(II) coordination polymers (CPs), namely {[Zn(BIPA-TC)0.5(1,3-bimb)]·0.75DMF}n (1) and {[Zn(BIPA-TC)0.5(1,3-bimb)]·0.5EtOH·DMF·H2O}n (2) were constructed based on 5,5′-(1,3,6,8-tetraoxybenzo[3,8]phenanthroline 2–7-substituent) bis-1,3-benzoic acid (H4BIPA-TC) and zinc salts. The structure analysis showed that 1 is 3D networks with the point symbol {62, 84} {64, 82}2 and 2 is 2D layered structures with the point symbol of {4, 64, 8}2 {42, 64}. Interestingly, the transformation from single crystal 1 to 2 is only due to the prolongation of reaction time, which can be confirmed by structural analysis and powder X-ray diffraction patterns. Meanwhile, the fluorescence sensing properties of 1 and 2 showed that both 1 and 2 had high sensitivity for l-glutamate with limits of detection of 0.10 (1) and 0.13 μM (2). The fluorescence mechanism analysis showed that the fluorescence enhancement of 1 and 2 is attributed to absorbance caused enhancement and photoinduced electron transfer. In addition, 1 and 2 can also be used as recyclable adsorbents to remove malachite green (MG) in aqueous medium. The adsorption isotherms and kinetics of both 1 and 2 follow the Freundlich model and the quasi-second-order kinetic model, respectively. The maximum equilibrium adsorption capacities of 1 and 2 for MG can reach 351.06 and 250.45 mg/g, respectively. The excellent adsorption properties of 1/2 for MG can be attributed to π–π interaction, hydrogen bonding, and electrostatic interaction between 1/2 and the MG molecule. Therefore, 1 and 2 have potential application prospects in fluorescence recognition and adsorption

Nanoporous {Pb₃}‑Organic Framework for Catalytic Cycloaddition of CO₂ with Epoxides and Knoevenagel Condensation

Because of increasingly serious environmental problems and resource shortages, chemically fixing surplus CO2 into value-added products has gradually become a challenging and hot research topic, in which the preparation of zeolite-like metal–organic frameworks (MOFs) with rich Lewis acid–base sites and nanopores is the cornerstone. Herein, the butterfly-shaped [Pb3(COO)6(H2O)2(Npyridine)2] cluster, polynitro tritopic carboxylic acid of 2,4,6-tri­(4-carboxy-2-nitrophenyl)-1,3,5-trinitrobenzene (H3TCNT), and 2,4,6-tri­(pyridin-4-yl)-1,3,5-triazine (TPT) engender a highly robust microporous framework of [Pb3(TCNT)2(TPT)­(H2O)2]n (NUC-91) with rectangular nanochannels (15.28 × 12.16 Å2) along the b axis. Because of extremely rich functional sites such as Lewis acidic sites of Pb2+ ions and Lewis basic sites of free nitrogen atoms on the inner surface of void volumes, activated NUC-91a as a heterogeneous catalyst can effectively catalyze the cycloaddition of CO2 with various epoxides under mild conditions. For substrates 2-methyloxirane, 2-fluorooxirane, 2-ethyloxirane, 2-(trifluoromethyl)­oxirane, oxiran-2-ylmethanol, 2-vinyloxirane, and 2-phenyloxirane, the transformation to related cyclic carbonates could reach 99% with turnover number (TON) and turnover frequency (TOF) of 825 and 206 h–1, respectively. Moreover, Knoevenagel condensation reactions of aldehydes and malononitrile could be efficiently effected by NUC-91a. Therefore, this work provided a simple strategy for effectively prefunctionalizing widely used ligands, which can be employed to design highly catalytic metal–organic frameworks to facilitate the capture and conversion of CO2

Nanoporous {Pb₃}‑Organic Framework for Catalytic Cycloaddition of CO₂ with Epoxides and Knoevenagel Condensation

Because of increasingly serious environmental problems and resource shortages, chemically fixing surplus CO2 into value-added products has gradually become a challenging and hot research topic, in which the preparation of zeolite-like metal–organic frameworks (MOFs) with rich Lewis acid–base sites and nanopores is the cornerstone. Herein, the butterfly-shaped [Pb3(COO)6(H2O)2(Npyridine)2] cluster, polynitro tritopic carboxylic acid of 2,4,6-tri­(4-carboxy-2-nitrophenyl)-1,3,5-trinitrobenzene (H3TCNT), and 2,4,6-tri­(pyridin-4-yl)-1,3,5-triazine (TPT) engender a highly robust microporous framework of [Pb3(TCNT)2(TPT)­(H2O)2]n (NUC-91) with rectangular nanochannels (15.28 × 12.16 Å2) along the b axis. Because of extremely rich functional sites such as Lewis acidic sites of Pb2+ ions and Lewis basic sites of free nitrogen atoms on the inner surface of void volumes, activated NUC-91a as a heterogeneous catalyst can effectively catalyze the cycloaddition of CO2 with various epoxides under mild conditions. For substrates 2-methyloxirane, 2-fluorooxirane, 2-ethyloxirane, 2-(trifluoromethyl)­oxirane, oxiran-2-ylmethanol, 2-vinyloxirane, and 2-phenyloxirane, the transformation to related cyclic carbonates could reach 99% with turnover number (TON) and turnover frequency (TOF) of 825 and 206 h–1, respectively. Moreover, Knoevenagel condensation reactions of aldehydes and malononitrile could be efficiently effected by NUC-91a. Therefore, this work provided a simple strategy for effectively prefunctionalizing widely used ligands, which can be employed to design highly catalytic metal–organic frameworks to facilitate the capture and conversion of CO2

Construction of Metal−Organic Frameworks with Novel {Zn₈O₁₃} SBU or Chiral Channels through <i>in Situ</i> Ligand Reaction

By control of in situ ligand reaction, two zinc metal−organic frameworks (1, 2) have been isolated hydrothermally. Both complexes are 3D open frameworks. Complex 1, which is based on an unprecedented {Zn8O13} SBU constructed of 2H-imidazole-4,5-dicarboxylic acid (H3IMDC), has the same topology as that of MOF-5. Complex 2 contains large homochiral channels based on the in situ generated 4,5-di(1H-tetrazol-5-yl)-2H-imidazole (H3DTIM). Both H3IMDC and H3DTIM ligands are in situ generated from the same precursor, 2H-imidazole-4,5-dicarbonitrile

Construction of Metal−Organic Frameworks with Novel {Zn₈O₁₃} SBU or Chiral Channels through <i>in Situ</i> Ligand Reaction

By control of in situ ligand reaction, two zinc metal−organic frameworks (1, 2) have been isolated hydrothermally. Both complexes are 3D open frameworks. Complex 1, which is based on an unprecedented {Zn8O13} SBU constructed of 2H-imidazole-4,5-dicarboxylic acid (H3IMDC), has the same topology as that of MOF-5. Complex 2 contains large homochiral channels based on the in situ generated 4,5-di(1H-tetrazol-5-yl)-2H-imidazole (H3DTIM). Both H3IMDC and H3DTIM ligands are in situ generated from the same precursor, 2H-imidazole-4,5-dicarbonitrile