Nanoporous {Y2}-Organic Frameworks for Excellent Catalytic Performance on the Cycloaddition Reaction of Epoxides with CO2 and Deacetalization-Knoevenagel Condensation

Copper-Based Bio-MOF/GO with Lewis Basic Sites for CO2 Fixation into Cyclic Carbonates and C-C Bond-Forming Reactions

Several measures, including crude oil recovery improvement and carbon dioxide (CO2) conversion into valuable chemicals, have been considered to decrease the greenhouse effect and ensure a sustainable low-carbon future. The Knoevenagel condensation and CO2 fixation have been introduced as two principal solutions to these challenges. In the present study for the first time, bio-metal-organic frameworks (MOF)(Cu)/graphene oxide (GO) nanocomposites have been used as catalytic agents for these two reactions. In view of the attendance of amine groups, biological MOFs with NH2 functional groups as Lewis base sites protruding on the channels' internal surface were used. The bio-MOF(Cu)/20%GO performs efficaciously in CO2 fixation, leading to more than 99.9% conversion with TON = 525 via a solvent-free reaction under a 1 bar CO2 atmosphere. It has been shown that these frameworks are highly catalytic due to the Lewis basic sites, i.e., NH2, pyrimidine, and C═O groups. Besides, the Lewis base active sites exert synergistic effects and render bio-MOF(Cu)/10%GO nanostructures as highly efficient catalysts, significantly accelerating Knoevenagel condensation reactions of aldehydes and malononitrile as substrates, thanks to the high TOF (1327 h-1) and acceptable reusability. Bio-MOFs can be stabilized in reactions using GO with oxygen-containing functional groups that contribute as efficient substitutes, leading to an expeditious reaction speed and facilitating substrate absorption.

Synthesis, Characterization, and Catalytic Performance of a New Heterobimetallic Y/Tb Metal-Organic Framework with High Catalytic Activity

A three-dimensional heterobimetallic porous structure with the formula {[Y3.5Tb1.5L6(OH)3(H2O)1.5 (DMF)1.5] n ·1.5H2O·DMF} n (L = 3-amino-4-hydroxybenzoate) (Y/Tb-MOF) has been synthesized and characterized by single crystal and powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), inductively coupled plasma mass spectrometry (ICP-MS), electrophoretic mobility, and Fourier transform infrared (FTIR) spectroscopy. The structure presents two metal environments: a bioaugmented isosceles wedge (mm2) MO8 and a tricapped trigonal prism (-6m2) MN3O6. These configurations facilitate the creation of channels with a diameter of 10.7 Å, enabling its utilization as an active catalyst where the heterobimetallic nature of the assembly will be explored. This mixed-metal metal-organic framework has been tested in the cycloaddition of epoxides with carbon dioxide as well as in the cyanosilylation and hydroboration reactions of carbonylic substrates. Additionally, a monometallic Tb-MOF analogue has been synthesized for comparative evaluation of their catalytic performances. Both the mixed metal and monometallic variants exhibit outstanding activity in the cyanosilylation and hydroboration of carbonyls and in the synthesis of carbonates under CO2 pressure. However, only the latter exhibits high recyclability.

Enhanced cycloaddition between CO2 and epoxide over a bismuth-based metal organic framework due to a synergistic photocatalytic and photothermal effect

The cycloaddition reaction between CO2 and epoxide is an efficient way to convert CO2 into high value-added chemicals. Therefore, it is particularly important to develop efficient catalysts that can catalyze the reaction under mild conditions. In this work, a metal-organic framework (Bi-HHTP, consisting of bismuth (Bi) as metal dots and 2,3,6,7,10,11-hexahydroxy-triphenylene (HHTP) as organic linkers) with zigzagging corrugated topology was successfully synthesized, which shows excellent catalytic activity under visible light irradiation. Various characterizations suggest that the excellent activity is derived from the following reasons: (1) the abundant exposed Bi sites provide Lewis sites for adsorption of epoxides and CO2; (2) the free holes produced over Bi-HHTP under light irradiation which could oxidize epoxide, which consequently facilitateing the subsequent ring-opening reaction; and (3) the existence of synergistic photocatalytic and photothermal effect in Bi-HHTP. This study provides a new avenue of developing bismuth-based metal organic frameworks to promote the efficiency of cycloaddition of CO2 under mild conditions.

Isomorphous Substitution of Organic Cage Crystal by Pd Nanoclusters for Selective Hydrogenation

For supporting active metal, the cavity confinement and mass transfer facilitation lie not in one sack, a trade-off between high activity and good stability of the catalyst is present. Porous organic cages (POCs) are expected to break the trade-off when metal particles are properly loaded. Herein, three organic cages (CC3, RCC3, and FT-RCC3) are employed to support Pd nanoclusters for catalytic hydrogenation. Subnanometer Pd clusters locate differently in different cage frameworks by using the same reverse double-solvents approach. Compared with those encapsulated in the intrinsic cavity of RCC3 and anchored on the outer surface of CC3, the Pd nanoclusters orderly assembled in FT-RCC3 crystal via isomorphous substitution exhibit superior activity, high selectivity, and good stability for semi-hydrogenation of phenylacetylene. Isomorphous substitution of FT-RCC3 crystal by Pd nanoclusters is originated from high crystallization capacity of FT-RCC3 and specific interaction of each Pd nanocluster with four cage windows. Both confinement function and H2 accumulation capacity of FT-RCC3 are fully utilized to support active Pd nanoclusters for efficient selective hydrogenation. The present results provide a new perspective to the heterogeneous catalysis field in terms of crystalizing metal nanoclusters in POC framework and outside the cage for making the best use of both parts.

Zn-MOF as a Single Catalyst with Dual Lewis Acidic and Basic Reaction Sites for CO2 Fixation

Continuous increase in carbon dioxide (CO2) emissions are causing imbalances in the environment, which impact biodiversity and human health. The conversion of CO2 to cyclic carbonates by means of metal-organic frameworks (MOFs) as a heterogeneous catalyst is a prominent strategy for rectifying this imbalance. Herein, we have developed nitrogen-rich Zn (II) based metal-organic framework, [Zn(CPMT)(bipy)]n (CPMT = 1-(4-carboxyphenyl)-5-mercapto-1H-tetrazole; bipy = 4,4'-bipyridine), synthesized via a mixed ligand strategy. This Zn-MOF showed high chemical stability in both acidic and basic conditions, and in organic solvents for a long time. On account of the concurrent presence of acid-base active sites and strong chemical stability under abrasive conditions, this Zn-MOF was employed as an effective catalyst for the coupling of CO2 and epoxides, under atmospheric pressure, mild temperature, and neat conditions. This Zn-MOF shows remarkable activity by producing high yields of epichlorohydrin carbonate (98%) and styrene carbonate (82%) at atmospheric CO2 pressure, 70 °C temperature, and 24 h reaction time, with turnover numbers (TON) of 217 and 181, respectively. The Zn-MOF could be reused for up to seven cycles with structural and framework integrity. Overall, this work demonstrates the synthesis of a novel and highly efficient MOF for CO2 conversion.

Two isostructural Zn/Co-MOFs with penetrating structures: multifunctional properties of both luminescence sensing and conversion of CO2 into cyclic carbonates

Two new metal-organic frameworks (MOFs), namely, {[Zn(HL)(bpea)]·DMF}n (Zn-MOF-1) and {[Co(HL)(bpea)]·DMF}n (Co-MOF-2) (H3L = 3-(3,5-dicarboxybenzyloxy)benzoic acid, bpea = 1,2-di(pyridyl)ethane), were obtained by the reaction of H3L and N-containing ligand bpea with Zn(NO3)2·6H2O and Co(NO3)2·6H2O, respectively. The isomorphic Zn-MOF-1 and Co-MOF-2 featured a 3D penetrating framework with different stabilities, luminescence, and catalytic properties. Luminescence measurement indicated that Zn-MOF-1 could be used to detect Al3+ through a turn-on effect with a detection limit of 0.42 μM. The sensing mechanism experiments showed that the enhanced luminescence of Zn-MOF-1 toward Al3+ may be due to the weak interaction between Al3+ and Zn-MOF-1 and the absorbance-caused enhancement (ACE) mechanism. Meanwhile, both Zn-MOF-1 and Co-MOF-2 showed interesting CO2 adsorption properties and could catalyze the cycloaddition of CO2 to epoxides resulting in 96 and 92% ideal products within 12 hours, respectively. They can be cycled up to 5 times without significant loss of catalytic efficiency.

Site-Memory-Triggered Reversible Acronym Encryption in a Nitrogen-Rich Pore-Partitioned MOF for Ultrasensitive Monitoring of Roxarsone and Dichloran over Multiple Platform

Stimuli-responsive emission color modulation in fluorescent metal-organic frameworks (MOFs) promises luminescence-ink-based security application, while task-specific functionality-engineered pores can aid fast-responsive, discriminative, and ultralow detection of harmful organo-aromatics in the aqueous phase. Considering practical applicability, a self-calibrated fluoro-switch between encrypted and decrypted states is best suited for antiforgery measures, whereas image-based monitoring of organo-toxins by repetitive and handy methods over multiple platforms endorses in-field sensory potential. Herein, we constructed a mixed-ligand based chemically stable and bilayered-pillar MOF from -NH2-hooked pyridyl linker and tricarboxylate ligand that embraces negatively charged [Cd3(μ2-OH)(COO)6] node and shows pore-space-partitioning by nitrogen-rich flanked organic struts. Owing to the presence of a self-calibrating triazolylamine moiety-grafted auxiliary linker, this anionic MOF delineates reversible and multicyclic fluoro-swapping between protonated-encrypted and deprotonated-decrypted domains in the alternative presence of acid and base. Such pH-triggered, site-specific luminescence variation is utilized to construct highly regenerative anticounterfeiting labels for vivid acronym encryption. The intense fluorescence signature of the material is further harnessed in extremely selective and quick responsive sensing of harmful feed additive roxarsone (ROX) and dichloran (DCNA) pesticide in highly recyclable fashion with significant quenching and nanomolar limits of detection (ROX: 52 ppb; DCNA: 26.8 ppb). Notably, the ultrasensitive fluoro-detection of both these organo-toxins is successfully demonstrated via a handy paper-strip method as well as on the vegetable surface for real-time monitoring. Comprehensive density functional theory studies validate the electron transfer mechanism through redistribution of molecular orbital energy levels by each of the targeted analytes in this electron-rich framework besides evidencing MOF-analyte supramolecular interactions.

Nanoporous {Co3}-Organic framework for efficiently seperating gases and catalyzing cycloaddition of epoxides with CO2 and Knoevenagel condensation

Enhancing the catalysis of metal-organic frameworks (MOFs) by regulating inherent Lewis acid-base sites to realize the efficient seperation and chemical fixation of inert carbon dioxide (CO2) is crucial but challenging. Herein, the solvothermal self-assembly of Co2+, 5'-(4-carboxy-2-nitrophenyl)-2,2',2'',4',6'-pentanitro-[1,1':3',1''-terphenyl]-4,4''-dicarboxylic acid (H3TNBTB) and 4'-phenyl-4,2':6',4''-terpyridine (PTP) generated a highly robust cobalt-organic framework of {[Co3(TNBTB)2(PTP)]·7DMF·6H2O}n (NUC-82). In NUC-82, the tri-core clusters of {Co3} with linear shape are bridged by TNBTB3- to form two-dimensional structure in ac plane, which is further linked by PTP to generate a three-dimensional framework with two kinds of solvent-accessible channels: rhombic-like (ca. 11.57 × 10.76 Å) along a axis and rectangular-like (ca. 7.32 × 11.56 Å) along b axis. Furthermore, it is worth emphasizing that the confined pore environments are characterized by plentiful Lewis acid-base sites of tricobalt clusters, grafted nitro groups and free pyridinyl, high specific surface area and solvent-free nano-caged windows. Activated NUC-82a owns the ultra-high ethylene (C2H2) separation performance over the mixture of C2H2/CH4 and CO2/CH4 with the selectivity of 223.1 and 44.7. Thanks to the great Lewis-acid sites as well as the large pore volume, activated NUC-82a displays the high catalytic performace on the cycloaddition of CO2 with epoxides under wield condtions such as amibient pressure. Furthermore, because of the rich Lewis base sites, NUC-82a can efficiently catalyze Knoevenagel condensation of aldehydes and malononitrile. In the above organic reactions, NUC-82a not only shows the high catalytic activity, but also exhibits the high selectivity, satifactory recyclability and easy-to-separate heterogeneity, confirming that NUC-82a is a promising catalyst. Hence, this work provides in-depth insight into the construction of multifunctional MOFs by modifying the traditional ligands with as many Lewis acid-base active sites as possible.

Holmium-Containing Metal-Organic Frameworks as Modifiers for PEBA-Based Membranes

Recently, there has been an active search for new modifiers to create hybrid polymeric materials for various applications, in particular, membrane technology. One of the topical modifiers is metal-organic frameworks (MOFs), which can significantly alter the characteristics of obtained mixed matrix membranes (MMMs). In this work, new holmium-based MOFs (Ho-MOFs) were synthesized for polyether block amide (PEBA) modification to develop novel MMMs with improved properties. The study of Ho-MOFs, polymers and membranes was carried out by methods of X-ray phase analysis, scanning electron and atomic force microscopies, Fourier transform infrared spectroscopy, low-temperature nitrogen adsorption, dynamic and kinematic viscosity, static and dynamic light scattering, gel permeation chromatography, thermogravimetric analysis and contact angle measurements. Synthesized Ho-MOFs had different X-ray structures, particle forms and sizes depending on the ligand used. To study the effect of Ho-MOF modifier on membrane transport properties, PEBA/Ho-MOFs membrane retention capacity was evaluated in vacuum fourth-stage filtration for dye removal (Congo Red, Fuchsin, Glycine thymol blue, Methylene blue, Eriochrome Black T). Modified membranes demonstrated improved flux and rejection coefficients for dyes containing amino groups: Congo Red, Fuchsin (PEBA/Ho-1,3,5-H3btc membrane possessed optimal properties: 81% and 68% rejection coefficients for Congo Red and Fuchsin filtration, respectively, and 0.7 L/(m2s) flux).

Ratiometric Fluorescence Thermometry, Quantitative Gossypol Detection, and CO2 Chemical Fixation by a Multipurpose Europium (III) Metal-Organic Framework

A lanthanide-based molecular crystalline material endows metal-organic frameworks (MOFs) with many fascinating applications such as fluorescence detection and CO2 chemical fixation. Herein, we describe and study a multipurpose europium(III) MOF with the formula of {[Eu2(TATAB)2]·2.5H2O·2DMF}n (Eu-MOF) (where H3TATAB is 4,4',4″-((1,3,5-triazine-2,4,6-triyl)tris(azanediyl))tribenzoic acid ligand) for photoluminescence sensor matrix and CO2 chemical fixation. This Eu-MOF features 1D square channels along the c direction with a pore size of ca.14.07 Å × 14.07 Å, occupied by lattice water and DMF molecules. The obtained Eu-MOF can achieve simultaneous luminescence of the H3TATAB ligand and Eu3+ ions, which can be developed as the sensor matrix for ratiometric fluorescence thermometry. The luminescence of the Eu-MOF demonstrates an obvious color change from red to yellow as temperature rises from 303 to 373 K and the Eu-MOF has a satisfying relative sensitivity of 3.21% K-1 and a small temperature uncertainty of 0.0093 K at 333 K. Moreover, sensitive detection of gossypol was achieved with a quenching constant Ksv of 1.18 × 105 M-1 and a detection limit of 4.61 μM. A combination of the competitive absorption and photoinduced electron transfer caused by host-guest interactions and strengthened π-π packing effect synergistically between gossypol molecules and the Eu-MOF skeleton realizes the "turn-off" sensing of gossypol. Importantly, the nature of the Eu-MOF allows showing CO2 chemical fixation under mild conditions. Thus, the Eu-MOF can be utilized as a multipurpose material for ratiometric fluorescence thermometry, quantitative gossypol detection, and CO2 chemical fixation.

Thermocatalytic Conversion of CO2 to Valuable Products Activated by Noble-Metal-Free Metal-Organic Frameworks

Thermocatalysis of CO2 into high valuable products is an efficient and green method for mitigating global warming and other environmental problems, of which Noble-metal-free metal-organic frameworks (MOFs) are one of the most promising heterogeneous catalysts for CO2 thermocatalysis, and many excellent researches have been published. Hence, this review focuses on the valuable products obtained from various CO2 conversion reactions catalyzed by noble-metal-free MOFs, such as cyclic carbonates, oxazolidinones, carboxylic acids, N-phenylformamide, methanol, ethanol, and methane. We classified these published references according to the types of products, and analyzed the methods for improving the catalytic efficiency of MOFs in CO2 reaction. The advantages of using noble-metal-free MOF catalysts for CO2 conversion were also discussed along the text. This review concludes with future perspectives on the challenges to be addressed and potential research directions. We believe that this review will be helpful to readers and attract more scientists to join the topic of CO2 conversion.

Coordination-directed self-assembly of nano-cages: metal ion-change, ligand-extending, shape-control and transdermal drug delivery

The combination of different pyridyl ligands and metal ions has proven to be a very reliable strategy for controlling the coordination mode of the heterometallic coordination nano-cages. Adjusting the length of the ligands could result in the selective synthesis of several heterometallic coordination nano-cages, either [8Rh + 2M]-4L, [8Rh + 2M]-5L or [8Rh + 4M]-6L cages, derived from the very same precursors (LH3tzdc) through half-sandwich rhodium self-assembly. Moreover, a series of [8Rh + 4M]-6L cages was chosen to exemplify the preparation. The rigidity of various pyridyl donor ligands caused the vertical nano-cage to be energetically preferred and was able to change the self-assembly process through ligand flexibility to selectively give the inclined nano-cage and cross nano-cage.

Coordination Unsaturation and Basic Site-Immobilized Nanochannel in a Chemorobust MOF for 3-Fold-Increased High-Temperature Selectivity and Fixation of CO2 under Mild Conditions with Nanomolar Recognition of Roxarsone

A multifaceted metal-organic framework (MOF) with task-specific site-engineered pores can promise high-temperature and moisture-tolerant capture and non-redox fixation of CO2 under mild conditions as well as ultrasensitive detection of carcinogenic contaminants in water. Herein, we report a pillar-bilayered MOF that holds a nanochannel with contrasting functionalities for both these sustainable applications with improved performance characteristics. The twofold entangled robust framework exhibits CO2 adsorption at elevated temperatures with considerable MOF-gas interaction. Interestingly, CO2 selectivity unveils nearly a 3-fold improvement upon the rise of temperature, affording a CO2/N2 value of 820 at 313 K, which outperforms many porous adsorbents. Additionally, breakthrough simulation establishes complete separation and attests the potential of this MOF in the separation of flue gas mixture. Importantly, minor CO2 loss during multiple capture-release cycles and under a relative humidity of 75% promise practical usability of the material. Density functional theory (DFT) not only portrays the atomistic level snapshots of temperature-triggered CO2 inclusion inside this microporous vessel alongside the role of diverse CO2-philic sites but also validates the basis of N2-phobicity of an azo-functionalized linker on such increased selectivity. The guest-free MOF further demonstrates non-redox and recyclable CO2 fixation with wide epoxide tolerance under solvent-free mild conditions and even works at atmospheric pressure and room temperature. The crucial roles of high-density acid-base sites in both adsorption and catalysis are supported by control experiments and by comparing the activity of an unfunctionalized MOF. The hydrolytic stability and strong luminescence signature benefit the framework in aqueous-phase selective and fast responsive detection of detrimental roxarsone (ROX) with high quenching (7.56 × 104 M-1) and very low sensitivity (68 nM). Apart from varying degrees of an energy-transfer mechanism, the fluorosensing of ROX is comprehensively supported by in-depth DFT studies that manifest alteration of MOF energy levels in the presence of organoarsenic compounds and depict MOF-analyte supramolecular interactions.

Study on Gas Sorption and Iodine Uptake of a Metal-Organic Framework Based on Curcumin

Medi-MOF-1 is a highly porous Metal-Organic framework (MOF) constructed from Zn(II) and curcumin. The obtained crystal was characterized using powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). A micrometer-sized crystal with similar morphology was successfully obtained using the solvothermal method. Thanks to its high surface area, good stability, and abound pores, the as-synthesized medi-MOF-1 could be used as a functional porous material to adsorb different gases (H₂, CO₂, CH₄, and N₂) and iodine (I₂). The activated sample exhibited a high I₂ adsorption ability of 1.936 g g^-1 at room temperature via vapor diffusion. Meanwhile, the adsorbed I₂ could be released slowly in ethanol, confirming the potential application for I₂ adsorption.

Insight into the In-Situ Encapsulation-Reassembly Strategy To Fabricate PW12@NiCo-LDH Acid-Base Bifunctional Catalysts

Acid-base bifunctional catalysts have attracted increasing attention due to the improved overall efficiency of synthetic reactions. Herein, we reported the successful fabrication of a PW₁₂@NiCo-LDH acid-base bifunctional catalyst by using the in-situ encapsulation-reassembly strategy. The evolution process of morphology and structure was monitored carefully by various time-dependent characterizations. X-ray absorption fine structure (XAFS) and density functional theory (DFT) calculations demonstrated that the terminal oxygen of PW₁₂ in PW₁₂@NiCo-LDH preferred to assemble with the oxygen vacancies on NiCo-LDH. When applied for deacetalization-Knoevenagel condensation, the PW₁₂@NiCo-LDH displayed >99% conversion of benzaldehyde dimethyl acetal (BDMA) and >99% yield of ethyl α-cyanocinnamate (ECC). Moreover, PW₁₂@NiCo-LDH can be recycled at least 10 cycles without obvious structural change, which can be attributed to the confinement of PW₁₂ into the NiCo-LDH nanocage. Such excellent catalytic activity of PW₁₂@NiCo-LDH was benefited from the short mass transfer pathway between acid sites and base sites, which was caused by the stable assembly between PW₁₂ and NiCo-LDH.

Redox-Active and Urea-Engineered-Entangled MOFs for High-Efficiency Water Oxidation and Elevated Temperature Advanced CO2 Separation Cum Organic-Site-Driven Mild-Condition Cycloaddition

Development of the multifaceted metal-organic framework (MOF) with in situ engineered task-specific sites can promise proficient oxygen evolution reaction (OER) and high-temperature adsorption cum mild-condition fixation of CO₂. In fact, effective assimilation of these attributes onto a single material with advance performance characteristics is practically imperative in view of renewable energy application and carbon-footprint reduction. Herein, we developed a three-fold interpenetrated robust Co(II) framework that embraces both redox-active and hydrogen-bond donor moieties inside the microporous channel. The activated MOF demonstrates notable OER catalysis in alkaline medium via quasi-reversible Co²⁺/Co³⁺ couple and unveils low overpotential with impressive 53.5 mV/dec Tafel slope that overpowers some benchmark, commercial, as well as contemporary materials. In particular, significantly increased turnover frequency (3.313 s^-1 at 400 mV) and fairly low charge-transfer resistance (3.02 Ω) compared to Co₃O₄, NiO, and majority of redox-active MOFs together with 91% Faradaic efficiency and notable framework durability after multiple OER cycles endorse high-performance water oxidation. Pore-wall decked urea groups benefit appreciable CO₂ adsorption even at elevated temperatures with considerable MOF-CO₂ interactions and exhibit recurrent capture-release cycles at diverse temperatures. Interestingly, CO₂ selectivity displays radical upsurge with temperature rise, affording 40% improved CO₂/N₂ value of 200 at 313 K, which outperforms many porous adsorbents and delineates real-time CO₂ scavenging potential. The guest-free MOF effectively catalyzes solvent-free CO₂ cycloaddition with broad substrate tolerance and satisfactory reusability under relatively mild condition. Opposed to the common Lewis acid-mediated reaction, two-point hydrogen-bonding activates the substrate, as supported from controlled experiments, juxtaposing the performance of an un-functionalized MOF and fluorescence modification-derived framework-epoxide interaction, providing valuable insights on unconventional cycloaddition route in the MOF.

Thermally activated bipyridyl-based Mn-MOFs with Lewis acid-base bifunctional sites for highly efficient catalytic cycloaddition of CO2 with epoxides and Knoevenagel condensation reactions

Metal-organic frameworks (MOFs) have become preferred heterogeneous catalytic materials for many reactions due to their advantages such as porosity and abundant active sites. Here, a 3D Mn-MOF-1 [Mn₂(DPP)(H₂O)₃]·6H₂O (DPP = 2,6-di(2,4-dicarboxyphenyl)-4-(pyridine-4-yl)pyridine) was successfully synthesized under solvothermal conditions. This Mn-MOF-1 possesses a 3D structure constructed by the combination of a 1D chain and the DPP^4- ligand and features a micropore with a 1D drum-like shaped channel. Interestingly, Mn-MOF-1 can maintain the structure unchanged by the removal of coordinated and lattice water molecules, whose activated state (denoted as Mn-MOF-1a) contains rich Lewis acid sites (tetra- and pentacoordinated Mn²⁺ ions) and Lewis base sites (N_pyridine atoms). Furthermore, Mn-MOF-1a shows excellent stability, which can be used to catalyze CO₂ cycloaddition reactions efficiently under eco-friendly, solvent-free conditions. In addition, the synergistic effect of Mn-MOF-1a resulted in its promising potential in Knoevenagel condensation under ambient conditions. More importantly, the heterogeneous catalyst Mn-MOF-1a can be recycled and reused without an obvious decrease of activity for at least 5 reaction cycles. This work not only paves the way for the construction of Lewis acid-base bifunctional MOFs based on pyridyl-based polycarboxylate ligands but also demonstrates that Mn-based MOFs hold great promise as a heterogeneous catalyst toward both CO₂ epoxidation and Knoevenagel condensation reactions.

Highly Robust {In2}-Organic Framework for Efficiently Catalyzing CO2 Cycloaddition and Knoevenagel Condensation

To improve the catalytic performance of metal-organic frameworks (MOFs), creating higher defects is now considered as the most effective strategy, which can not only optimize the Lewis acidity of metal ions but also create more pore space to enhance diffusion and mass transfer in the channels. Herein, the exquisite combination of scarcely reported [In₂(CO₂)₅(H₂O)₂(DMF)₂] clusters and 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (H₅BDCP) under solvothermal conditions generated a highly robust nanoporous framework of {[In₂(BDCP)(DMF)₂(H₂O)₂](NO₃)}_n (NUC-65) with nanocaged voids (14.1 Å) and rectangular nanochannels (15.94 Å × 11.77 Å) along the a axis. It is worth mentioning that an In(1) ion displays extremely low tetra-coordination modes after the thermal removal of its associated four solvent molecules of H₂O and DMF. Activated {[In₂(BDCP)](Br)}_n (NUC-65Br), as a defective material because of its extremely unsaturated metal centers, could be generated by bromine ion exchange, solvent exchange, and vacuum drying. Catalytic experiments proved that the conversion of epichlorohydrin with 1 atm CO₂ into 4-(chloromethyl)-1,3-dioxolan-2-one catalyzed by 0.11 mol % NUC-65Br could reach 99% at 65 °C within 24 h. Moreover, with the aid of 5 mol % cocatalyst n-Bu₄NBr, heterogeneous NUC-65Br owns excellent universal catalytic performance in most epoxides under mild conditions. In addition, NUC-65Br, as a heterogeneous catalyst, exhibits higher activity and better selectivity for Knoevenagel condensation of aldehydes and malononitrile. Hence, this work offers a fresh insight into the design of structure defect cationic metal-organic frameworks, which can be better applied to various fields because of their promoted performance.

Functionalized β-Cyclodextrins Catalyzed Environment-Friendly Cycloaddition of Carbon Dioxide and Epoxides

Ammonium, imidazole, or pyridinium functionalized β-cyclodextrins (β-CDs) were used as efficient one-component bifunctional catalysts for the coupling reaction of carbon dioxide (CO₂) and epoxide without the addition of solvent and metal. The influence of different catalysts and reaction parameters on the catalytic performance were examined in detail. Under optimal conditions, Im-CD1-I catalysts functionalized with imidazole groups were able to convert various epoxides into target products with high selectivity and good conversion rates. The one-component bifunctional catalysts can also be recovered easily by filtration and reused at least for five times with only slight decrease in catalytic performance. Finally, a possible process for hydroxyl group-assisted ring-opening of epoxide and functionalized group- induced activation of CO₂ was presented.

Robust acid-base Ln-MOFs: searching for efficient catalysts in cycloaddition of CO2 with epoxides and cascade deacetalization-Knoevenagel reactions

A family of microporous and robust Ln(iii)-based metal-organic frameworks (1-Ln, Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) have been obtained using 4,4',4''-nitrilotribenzoic acid (H₃NTB) in NMP-HCl solvent. Both single-crystal and powder X-ray diffraction analyses demonstrate that 1-Ln are isostructural and possess 3D frameworks with permanent porosity for Ar and CO₂ adsorption. Strikingly, the incorporation of both Lewis acidic lanthanide ions and the basic triphenylamine group into 1-Ln makes them efficient acid-base catalysts for both cycloaddition of epoxides with CO₂ and one-pot cascade deacetalization-Knoevenagel reactions. The systematic catalytic studies show that 1-Tb and 1-Yb possess the best catalytic activities for both reactions, indicating the catalytic activities of these Ln-MOFs are strongly dependent on metal Lewis acid sites embedded in the frameworks.

Fluorine-Functionalized NbO-Type {Cu2}-Organic Framework: Enhanced Catalytic Performance on the Cycloaddition Reaction of CO2 with Epoxides and Deacetalization-Knoevenagel Condensation

The high catalytic activity of metal-organic frameworks (MOFs) can be realized by increasing their effective active sites, which prompts us to perform the functionalization on selected linkers by introducing a strong Lewis basic group of fluorine. Herein, the exquisite combination of paddle-wheel [Cu₂(CO₂)₄(H₂O)] clusters and meticulously designed fluorine-funtionalized tetratopic 2',3'-difluoro-[p-terphenyl]-3,3″,5,5″-tetracarboxylic acid (F-H₄ptta) engenders one peculiar nanocaged {Cu₂}-organic framework of {[Cu₂(F-ptta)(H₂O)₂]·5DMF·2H₂O}_n (NUC-54), which features two types of nanocaged voids (9.8 Å × 17.2 Å and 10.1 Å × 12.4 Å) shaped by 12 paddle-wheel [Cu₂(COO)₄H₂O)₂] secondary building units, leaving a calculated solvent-accessible void volume of 60.6%. Because of the introduction of plentifully Lewis base sites of fluorine groups, activated NUC-54a exhibits excellent catalytic performance on the cycloaddition reaction of CO₂ with various epoxides under mild conditions. Moreover, to expand the catalytic scope, the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile were performed using the heterogenous catalyst of NUC-54a. Also, NUC-54a features high recyclability and catalytic stability with excellent catalytic performance in subsequent catalytic tests. Therefore, this work not only puts forward a new solution for developing high-efficiency heterogeneous catalysts, but also enriches the functionalization strategies for nanoporous MOFs.

Three novel Co(II)-based MOFs: Syntheses, structural diversity, and adsorption properties

In this paper, three new cobalt-based metal organic frameworks (MOFs) with different topologies, namely {[Co(HL)(tib)(H2O)]·2H2O}n (1), [Co3(L)2(bibp)4(H2O)2]n (2) and [Co2(L)(bip)(μ3-OH)]n (3) (H3L = 3-(3,5-dicarboxylphenoxy)-6-carboxylpyridine, tib = 1,3,5-tirs(1-imidazolyl)benzene, bibp = 4,4'-bis(imidazolyl)biphenyl,...