Generic Postfunctionalization Route from Amino-Derived Metal−Organic Frameworks

Structure-Assisted Boronic Acid Implanted Mesoporous Metal-Organic Frameworks for Specific Extraction of cis-Diol Molecules

cis-Diol-containing molecules, an essential type of compounds in living organisms, have attracted intensive research interest from various fields. The analysis of cis-diol-containing molecules is still suffering from some drawbacks, including low abundance and abundant interference. Metal-organic frameworks (MOFs) have proven to be an ideal sorbent for sample preparation. However, most of the reported MOFs are mainly restricted to a microporous regime (pore size <2 nm), which greatly limits the application. Herein, a facile strategy is established to construction of boronate affinity MOFs via the postsynthetic ligand-exchange process. Owing to the fact that the ligand-exchange process was assisted by the structural integrity of the primitive metal-organic framework and the great compatibility of click chemistry, the obtained EPBA-PCN-333(Fe) is able to realize the maximum maintaining the porosity and crystallinity of the parent material. Several intriguing features of EPBA-PCN-333(Fe) (e.g., excellent selectivity, efficient diffusion, good accessibility, and size exclusion effect) are experimentally demonstrated via a series of cis-diol-containing molecules with different molecular sizes (small molecules, glycopeptides, and glycoproteins). The binding performance of EPBA-PCN-333(Fe) is evaluated by employing catechol as the test molecule (binding capacity: 0.25 mmol/g, LOD: 200 ng/mL). Finally, the real-world applications of EPBA-PCN-333(Fe) were demonstrated by the detection of nucleosides of human urine samples.

Enhanced adsorption and removal of Cd(II) from aqueous solution by amino-functionalized ZIF-8

Zeolite imidazolate framework-8 (ZIF-8), which is a special subgroup of metal-organic frameworks (MOFs), was synthesized and modified by ethylenediamine (ZIF-8-EDA) to prepare an efficient adsorbent for the high sorption of Cd2+ ions from solution. The synthesized and modified ZIF-8 (ZIF-8-EDA) were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FE-SEM) with energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM) analysis. The optimum conditions for dosage of adsorbent, initial ion concentration, pH, and contact time were 0.05 g/l, 50 mg/l, 6, and 60 min, respectively, for cadmium ion sorption from aqueous solutions with a removal efficiency of 89.7% for ZIF-8 and 93.5% for ZIF-8-EDA. Adsorption kinetics and equilibrium data were analyzed using the Langmuir and Freundlich equations. The Langmuir model fitted the equilibrium data better than the Freundlich model. According to the Langmuir equation, the maximum uptake for the cadmium ions was 294.11(mg/g). The calculated thermodynamic parameters (ΔG°, ΔH°, and ΔS°) indicated that the adsorption process was feasible, spontaneous, and endothermic at 20-50 °C. Based on the results, the amino functionalized ZIF-8 had improved adsorption performance due to the replacing of the starting linker with organic ligands that had effective functional groups, leading to chemical coordination due to the interaction of metal ions with the non-bonding pair of electrons on the N atoms of the amino functional group. The selectivity toward metal ion adsorption by ZIF-8-EDA was Cd2+ > Pb2+ > Ni2+‏.

Synthesis and Application of Task-Specific Bimetal-Organic Frameworks in the Synthesis of Biological Active Spiro-Oxindoles

The use of click chemistry as a smart and suitable method for the development of new heterogeneous catalysts is based on metal-organic frameworks as well as the production of organic compounds. The development of the click chemistry method can provide a new strategy to achieve superior properties of MOFs. Here, the two metals Co and Fe are used to create a bimetallic-organic framework. In the following, the click chemistry and postmodification method are well organized and an acidic heterogeneous porous catalyst is developed. This prepared catalyst was used as a highly efficient catalyst for the preparation of new spiro-oxindoles obtained through click chemistry with good to excellent yields (80-94%). This presented catalytic system can compete with the best reported catalytic systems. The findings showed that the presence of Co and Fe metals in the MOF, and the presence of the triazole ring on the catalyst, can increase the catalytic efficiencies. This study offers novel insights into the architecture of Metal-Organic Frameworks (MOFs), click chemistry, and biologically active compounds. Additionally, the research explores the antibacterial properties of the synthesized spiro-oxindoles and catalysts. The findings reveal significant antibacterial activities of the synthesized compounds against S. aureus, MRSA, and E. coli bacteria.

Synthesis and analytical characterization of Ca-BTC metal organic framework

Metal Organic framework (MOF) has been a class of great interest during the past few years owing to its decidedly applicative, easily synthesized and improved characteristics. Ca-BTC MOF is synthesized by Hydrothermal technique and reported for the first time. Its structural morphology was analyzed using XRD, SEM, and EDS, showing the tetragonal crystal structure having grain size of 24.92 nm and purity of sample respectively. FTIR, Raman Spectroscopy ensures the metal organic framework between Calcium and the tri-carboxylic group. Photoluminescence measures the energy gap of 3.792 eV, showing approximately the semiconducting behavior of synthesized material. Zeta potential having value of -13.5 mV confirms the instability having good microbial activity and conductivity i.e 0.290 mS/cm which reveals important insights into its electrical properties.

Covalent connections between metal-organic frameworks and polymers including covalent organic frameworks

Hybrid composite materials combining metal-organic frameworks (MOFs) and polymers have emerged as a versatile platform for a broad range of applications. The crystalline, porous nature of MOFs and the flexibility and processability of polymers are synergistically integrated in MOF-polymer composite materials. Covalent bonds, which form between two distinct materials, have been extensively studied as a means of creating strong molecular connections to facilitate the dispersion of "hard" MOF particles in "soft" polymers. Numerous organic transformations have been applied to post-synthetically connect MOFs with polymeric species, resulting in a variety of covalently connected MOF-polymer systems with unique properties that are dependent on the characteristics of the MOFs, polymers, and connection modes. In this review, we provide a comprehensive overview of the development and strategies involved in preparing covalently connected MOFs and polymers, including recently developed MOF-covalent organic framework composites. The covalent bonds, grafting strategies, types of MOFs, and polymer backbones are summarized and categorized, along with their respective applications. We highlight how this knowledge can serve as a basis for preparing macromolecular composites with advanced functionality.

A DNA-engineered metal-organic-framework nanocarrier as a general platform for activatable photodynamic cancer cell ablation

Activatable photodynamic cancer cell ablation constitutes a promising approach to performing highly effective photodynamic therapy (PDT) with mitigated phototoxicity. Regretfully, so far strategies to fabricate activatable PDT agents are only applicable to a limited number of photosensitizers (PSs). Herein, an activatable photodynamic cancer cell ablation platform that can be adopted for versatile PSs is presented. Thereinto, by engineering an iron(iii) carboxylate-based metal-organic framework (MOF), MIL-101(Fe), with DNA grafted after PS loading, both hydrophilic and hydrophobic PSs can undergo negligible unspecific leakage and significant suppression of photosensitization during delivery. Following the reaction between MIL-101 and H₂O₂ whose level is greatly increased inside the tumor, MIL-101 is selectively degraded to release the loaded PDT agents and recover their photosensitization, controllably killing cancer cells upon H₂O₂ activation. Such a strategy assisted by a DNA-functionalized MOF significantly expands the varieties of PSs applicable for activatable PDT.

Tetrazine Linkers as Plug-and-Play Tags for General Metal-Organic Framework Functionalization and C60 Conjugation

The value of covalent post-synthetic modification in expanding the chemistry and pore versatility of reticular solids is well documented. Here we use mesoporous crystals of the metal-organic framework (MOF) UiO-68-TZDC to demonstrate the value of tetrazine connectors for all-purpose inverse electron-demand Diels-Alder ligation chemistry. Our results suggest a positive effect of tetrazine reticulation over its reactivity for quantitative one-step functionalization with a broad scope of alkene or alkyne dienophiles into pyridazine and dihydropyridazine frameworks. This permits generating multiple pore environments with diverse chemical functionalities and the expected accessible porosities, that is also extended to the synthesis of crystalline fulleretic materials by covalent conjugation of fullerene molecules.

Nanoengineered metal-organic framework for adsorptive and photocatalytic mitigation of pharmaceuticals and pesticide from wastewater

Rapidly expanding water pollution has transformed into significant dangers around the world. In recent years, the pharmaceutical and agriculture field attained enormous progress to meet the necessities of health and life; however, discharge of trace amounts of pharmaceuticals and pesticides into water significantly have a negative influence on human health and the environment. Contamination with these pollutants also constitutes a great threat to the aquatic ecosystem. To deal with the harmful impacts of such pollutants, their expulsion has attracted researchers' interest a lot, and it became essential to figure out techniques suitable for the removal of these pollutants. Thus, many researchers have devoted their efforts to improving the existing technology or providing an alternative strategy to solve this environmental problem. One of the attractive materials for this purpose is metal-organic frameworks (MOFs) due to their superior high surface area, high porosity, and the tunable features of their structures and function. Among various techniques of wastewater treatment, such as biological treatment, advanced oxidation process and membrane technologies, etc., metal-organic frameworks (MOFs) materials are tailorable porous architectures and are viably used as adsorbents or photocatalysts for wastewater treatment due to their porosity, tunable internal structure, and large surface area. MOFs are synthesized by various methods such as solvo/hydrothermal, sonochemical, microwave and mechanochemical methods. Most common method used for the synthesis of MOFs is solvothermal/hydrothermal methods. Herein, this review aims at providing a comprehensive overview of the latest advances in MOFs and their derivatives, focusing on the following aspects: synthesis and applications. This review comprehensively highlights the application of MOFs and nano-MOFs to remove pharmaceuticals and pesticides from wastewater. For the past years, transition metal-based MOFs have been concentrated as photocatalyst/adsorbents in treating contaminated water. However, work on main group metal-based MOFs is not so abundant. Hence, the foremost objective of this review is to present the latest material and references concerning main group element-based MOFs and nanoscale materials derived from them towards wastewater treatment. It summarizes the possible research challenges and directions for MOFs and their derivatives as catalysts applied to wastewater treatment in the future. With the context of recent pioneering studies on main group elements-based MOFs and their derivatives; we hope to stimulate some possibilities for further development, challenges and future perspectives in this field have been highlighted.

Maltose-functional metal-organic framework assisted laser desorption/ionization mass spectrometry for small biomolecule determination

A series of functional metal-organic frameworks (MOFs) were facilely prepared through an one-pot procedure or post-synthetic modification strategy and used as matrices in laser desorption ionization mass spectrometry (LDI-MS). Compared with traditional organic matrices and other MOFs, maltose-functional MOF MIL-101-maltose demonstrated ultrahigh ionization efficiency, free matrix background, uniform crystallization, and good dispersibility. A simple, general, and efficient LDI-MS platform was developed for rapid detection of various small biomolecules using MIL-101-maltose as matrix, providing several advantages including low sample consumption of 500 nL, short analysis time of few seconds, strong salt tolerance (500 mM NaCl), and satisfactory reproducibility. The MIL-101-maltose matrix was used for serum glucose determination and successfully distinguished the diabetic patients from the healthy controls. This work provides a generic LDI-MS platform for fast determination of small biomolecules with high potential in clinical diagnosis and disease monitoring.

Combined Deep Learning and Classical Potential Approach for Modeling Diffusion in UiO-66

Modeling of diffusion of adsorbates through porous materials with atomistic molecular dynamics (MD) can be a challenging task if the flexibility of the adsorbent needs to be included. This is because potentials need to be developed that accurately account for the motion of the adsorbent in response to the presence of adsorbate molecules. In this work, we show that it is possible to use accurate machine learning atomistic potentials for metal-organic frameworks in concert with classical potentials for adsorbates to accurately compute diffusivities though a hybrid potential approach. As a proof-of-concept, we have developed an accurate deep learning potential (DP) for UiO-66, a metal-organic framework, and used this DP to perform hybrid potential simulations, modeling diffusion of neon and xenon through the crystal. The adsorbate-adsorbate interactions were modeled with Lennard-Jones (LJ) potentials, the adsorbent-adsorbent interactions were described by the DP, and the adsorbent-adsorbate interactions used LJ cross-interactions. Thus, our hybrid potential allows for adsorbent-adsorbate interactions with classical potentials but models the response of the adsorbent to the presence of the adsorbate through near-DFT accuracy DPs. This hybrid approach does not require refitting the DP for new adsorbates. We calculated self-diffusion coefficients for Ne in UiO-66 from DFT-MD, our hybrid DP/LJ approach, and from two different classical potentials for UiO-66. Our DP/LJ results are in excellent agreement with DFT-MD. We modeled diffusion of Xe in UiO-66 with DP/LJ and a classical potential. Diffusion of Xe in UiO-66 is about a factor of 30 slower than that of Ne, so it is not computationally feasible to compute Xe diffusion with DFT-MD. Our hybrid DP-classical potential approach can be applied to other MOFs and other adsorbates, making it possible to use an accurate DP generated from DFT simulations of an empty adsorbent in concert with existing classical potentials for adsorbates to model adsorption and diffusion within the porous material, including adsorbate-induced changes to the framework.

Post-exfoliation functionalisation of metal-organic framework nanosheets via click chemistry

The liquid exfoliation of layered metal-organic frameworks (MOFs) to form nanosheets (MONs) exposes buried functional groups making them useful in a range of sensing and catalytic applications. Here we show how high yielding click reactions can be used post-exfoliation to systematically modify the surface chemistry of MONs allowing for tuning of their surface properties and their use in new applications. A layered amino-functionalised framework is converted through conventional post-synthetic functionalisation of the bulk MOF to form azide functionalised frameworks of up to >99% yield. Ultrasonic liquid exfoliation is then used to form few-layer nanosheets, which are further functionalised through post exfoliation functionalisation using Cu(I)-catalysed azide-alkyne cycloaddition reactions. Here we demonstrate the advantages of post-exfoliation functionalisation in enabling: (1) a range of functional groups to be incorporated in high yields; (2) tuning of nanosheet surface properties without the need for extensive recharacterisation; (3) the addition of fluorescent functional groups to enable their use in the sensing of hazardous nitrobenzene. We anticipate that the versatility of different functional groups that can be introduced through high yielding click reactions will lead to advances in the use of MONs and other 2D materials for a variety of applications.

Generation of Strong Basicity in Metal-Organic Frameworks: How Do Coordination Solvents Matter?

Solid strong bases with an ordered pore structure (OPS-SSBs) have attracted much attention because of their high catalytic activity and shape selectivity as heterogeneous catalysts in various reactions. Nevertheless, high temperatures are required to fabricate OPS-SSBs by using traditional methods. Herein, we report for the first time that the coordination solvents affect basicity generation in metal-organic frameworks (MOFs) greatly and that strong basicity can be formed at comparatively low temperatures. A typical MOF, MIL-53, was employed, and three different solvents, namely, water, methanol, and N,N-dimethylformamide (DMF), were coordinated, respectively, by means of solvent exchange. Thermogravimetry-mass spectrometer analysis shows that the conversion temperature of base precursor KNO₃ is quite different on MIL-53 coordinated with different solvents. The conversion of KNO₃ to basic sites takes place at 350, 300, and 250 °C on MIL-53 coordinated with water, methanol, and DMF, respectively. It is fascinating to observe the generation temperature of strongly basic sites at 250 °C, which is noticeably lower than that on various supports, such as mesoporous silica SBA-15 (600 °C), zeolite Y (700 °C), and metal oxide ZrO₂ (730 °C). This is due to the redox interaction between coordination solvents and KNO₃, leading to a significant decrease in the temperature for KNO₃ conversion. Consequently, OPS-SSBs were prepared successfully with an ordered pore structure and strong basicity. The obtained OPS-SSBs show good shape selectivity in Knoevenagel condensation of aromatic aldehydes with different active methylene compounds. Moreover, these solid bases are highly active in the synthesis of dimethyl carbonate through transesterification reaction. This work might open up a new avenue for the fabrication of various functional materials at low temperatures through redox interactions.

Reversible Diels-Alder and Michael Addition Reactions Enable the Facile Postsynthetic Modification of Metal-Organic Frameworks

Functionalization of metal-organic frameworks (MOFs) is critical in exploring their structural and chemical diversity for numerous potential applications. Herein, we report multiple approaches for the tandem postsynthetic modification (PSM) of various MOFs derived from Zr(IV), Al(III), and Zn(II). Our current work is based on our efforts to develop a wide range of MOF platforms with a dynamic functional nature that can be chemically switched via thermally triggered reversible Diels-Alder (DA) and hetero-Diels-Alder (HDA) ligations. Furan-tagged MOFs (furan-UiO-66-Zr) were conjugated with maleimide groups bearing dienophiles to prepare MOFs with a chemically switchable nature. As HDA pairs, phosphoryl dithioester-based moieties and cyclopentadiene (Cp)-grafted MOF (Cp-MIL-53-Al) were utilized to demonstrate the cleavage and rebonding of the linkages as a function of temperature. In addition to these strategies, the Michael addition reaction was also applied for the tandem PSM of IRMOF-3-Zn. Maleimide groups were postsynthetically introduced in the MOF lattice, which were further ligated with cysteine-based biomolecules via the thiol-maleimide Michael addition reaction. On the basis of the versatility of the herein presented chemistry, we expect that these approaches will help in designing a variety of sophisticated functional MOF materials addressing diverse applications.

A post-synthetically modified metal–organic framework for copper catalyzed denitrative C–N coupling of nitroarenes under heterogeneous conditions

Post-synthesis modification of DMOF, afforded a desired material for strategic infusion of catalytically active centers in a porous matrix. The catalyst is capable for denitrative C–N coupling reactions of nitroarenes under heterogeneous conditions.

Microscopic and Mesoscopic Dual Postsynthetic Modifications of Metal-Organic Frameworks

We report the dual postsynthetic modification (PSM) of a metal-organic framework (MOF) involving the microscopic conversion of C-H bonds into C-C bonds and the mesoscopic introduction of hierarchical porosity. MOF crystals underwent single-crystal-to-single-crystal transformations during the electrophilic aromatic substitution of Co₂ (m-DOBDC) (m-DOBDC^4- =4,6-dioxo-1,3-benzenedicarboxylate) with alkyl halides and formaldehyde. The steric hindrance caused by the proximity of the introduced functional groups to the coordination bonds reduced bond stability and facilitated the transformation into hierarchically porous mesostructures by etching with in situ generated protons (hydroniums) and halides. The numerous defect sites in the mesostructural MOFs are potential water-sorption sites. However, since the introduced functional groups are close to the main adsorption sites, even methyl groups are able to considerably decrease water adsorption, whereas hydroxy groups increase adsorption at low vapor pressures.

Atmospheric low-temperature plasma for direct post-synthetic modification of UiO-66

A low-temperature plasma-based post-synthetic modification method was developed to directly introduce the hydroxy group into UiO-66 metal-organic frameworks (MOFs). UiO-66 can be endowed with greatly enhanced fluorescence properties after plasma treatment, with which a reliable sensing platform for arsenic has been established.

Significant Decrease in Activation Temperature for the Generation of Strong Basicity: A Strategy of Endowing Supports with Reducibility

Mesoporous solid strong bases are quite attractive due to their good catalytic performance for applications as environmentally friendly catalysts in various reactions. However, pretty harsh conditions are usually compulsory for the fabrication of strong basicity by using traditional thermal activation (e.g., 700 °C for the activation of base precursor KNO₃ supported on mesoporous Al₂O₃). This is energy intensive and harmful to the mesoporous structure. In this study, we report a strategy of endowing supports with reducibility (ESWR) by doping low-valence Cr³⁺ into mesoporous Al₂O₃, so that the activation temperature for basicity generation is decreased significantly. Fascinatingly, KNO₃ on mesoporous Al₂O₃ can be motivated to basic sites completely at the temperature of 400 °C via the ESWR strategy, which is much lower than the conventional thermal activation (700 °C). We have demonstrated that the redox reciprocity between KNO₃ and Cr³⁺ is responsible for the low-temperature conversion, and Cr⁶⁺ is formed quantitatively as the oxidation product. The obtained solid bases possessing ordered mesostructure and strong basicity provide promising candidates for base-catalyzed synthesis of dimethyl carbonate via transesterification. The catalytic activity is obviously higher than a typical solid base like MgO as well as a series of reported basic catalysts containing alkali metal and alkaline-earth metal oxides.

Novel Synthesis of Cu-Schiff Base Complex@Metal-Organic Framework MIL-101 via a Mild Method: A Comparative Study for Rapid Catalytic Effects

The use of metal complex immobilized/decorated porous materials as catalysts has found various applications. As such, finding a new and mild method for synthesis of metal complex immobilized over porous material is of great interest. Immobilized porous materials for styrene oxidation were reported in this work. Immobilized porous material of Cu-Schiff base complex @MIL-101 were described, in which immobilized Cu-Schiff base complex within super cage of a metal-organic framework (MOF)-based porous material, chromium (III) terephthalate MIL-101. They were systematically characterized by using elemental analysis, powder X-ray diffraction, fourier transform infrared spectroscopy, N2 absorption-desorption, and so on, also used as catalyst for the selective oxidation of styrene to benzaldehyde. Comparatively, the immobilized heterogeneous catalyst of Cu-Schiff base complex@MIL-101 acted as an efficient heterostructure catalyst in the oxidation of styrene to benzaldehyde up to six cycles, and showed superior activity for styrene oxidation over MIL-101.

Amino modified metal-organic frameworks as pH-responsive nanoplatforms for safe delivery of camptothecin

MIL-100(Fe) and MIL-101(Fe) metal-organic frameworks (MOFs) are excellent vehicles for drug delivery systems (DDSs) due to their high biocompatibility and stability in physiological fluids, as well as their pore diameter in the mesoporous range. Although they are appropriate for the internal diffusion of 20-(S)-camptothecin (CPT), a strongly cytotoxic molecule with excellent antitumor activity, no stable delivery system has been proposed so far for this drug based in MOFs. We here present novel DDSs based in amine functionalized MIL-100(Fe) and MIL-101(Fe) nanoMOFs with covalently bonded CPT. These CPT nanoplatforms are able to incorporate almost 20% of this molecule and show high stability at physiological pH, with no non-specific release. Based on their surface charge, some of these CPT loaded nanoMOFs present improved cell internalization in in vitro experiments. Moreover, a strong response to acid pH is observed, with up to four fold drug discharge at pH 5, which boost intracellular release by endosomolytic activity. These novel DDSs will help to achieve safe delivery of the very cytotoxic CPT, allowing to reduce the therapeutic dose and minimizing drug secondary effects.

Recyclable and Reusable Heteroleptic Nickel Catalyst Immobilized on Metal-Organic Framework for Suzuki-Miyaura Coupling

Metal-organic frameworks (MOFs) provide highly versatile platforms to stabilize molecular catalysts that are not readily accessible under homogeneous conditions, thus enabling access to a new set of catalytic materials. Herein, we describe a recyclable and highly active nickel catalyst immobilized on MOF for Suzuki-Miyaura coupling reaction, which operates under mild conditions. This mixed ligand catalyst forms from the combination of 1 equiv of MOF-immobilized ligand, 1 equiv of nickel source, and 1 equiv of PPh₃. The nature of the catalyst was verified through a series of analytical tests and catalysis experiments. The immobilized catalyst was reusable for at least up to 7 cycles without decrease in the yield of the coupled product. We also verified that this reaction does not work under homogeneous conditions and that the reaction is truly heterogeneous through "hot filtration" experiments. We identified that the reaction is first order in arylborane concentration and negative order in arylbromide concentration through the effect of substrate concentrations on the initial rate. This informed us to conduct the catalysis under slow addition of the arylbromide and reduce the catalyst loading to 1% from 3%, without detriment to the yield or rate of the reaction. The catalyst gave good to excellent isolated yields with a range of functionalities, including heterocycles on aryl bromide with widely varying electronic properties.

Post-Synthetic Modification of Nonporous Adaptive Crystals of Pillar[4]arene[1]quinone by Capturing Vaporized Amines

Postsynthetic modification in crystalline solids without disruption of crystallinity is very important for exerting control that is unattainable over chemical transformation in solution. This has been achieved in porous crystalline frameworks via solid-solution reactions to endow them with multiple functions. However, this is rather rare in nonporous molecular crystals, especially via solid-vapor reactions. Herein, we report unique solid-vapor postsynthetic modification of nonporous adaptive crystals (NACs) of a pillar[4]arene[1]quinone (EtP4Q1) containing four inert 1,4-diethoxybenzene units and one active benzoquinone unit. Amine vapors that can be physically adsorbed by EtP4Q1 NACs react with the EtP4Q1 backbone via Michael addition with in situ formation of new crystal structures. First, amines are physically adsorbed into cavities of EtP4Q1 molecules and slowly react due to their juxtapsition with the benzoquinone units. Amines that are too bulky to enter EtP4Q1 NACs do not react. Moreover, the process displays both reactant-size and -shape selectivities because of the rigid cavity of EtP4Q1 and the different binding strengths of various amines with EtP4Q1.

SuFEx in Metal-Organic Frameworks: Versatile Postsynthetic Modification Tool

A new type of click reaction, sulfur(VI) fluoride exchange (SuFEx), has been utilized to prepare five postsynthetically modified UiO-67 series metal-organic frameworks (MOFs). The postsynthetic modification (PSM) via SuFEx can be achieved selectively for the sulfonyl fluoride (R-SO₂F) without degrading the MOF structure as confirmed by X-ray crystallographic analysis. The present SuFEx method provides a straightforward tool for introducing new functionality inside MOFs. Introduction of an imidazolium group into the MOF afforded a heterogeneous catalyst for the benzoin condensation reaction.

New Azo-DMOF-1 MOF as a Photoresponsive Low-Energy CO2 Adsorbent and Its Exceptional CO2/N2 Separation Performance in Mixed Matrix Membranes

A new generation-2 light-responsive metal-organic framework (MOF) has been successfully synthesized using Zn as the metal source and both 2-phenyldiazenyl terephthalic acid and 1,4-diazabicyclo[2.2.2]octane (DABCO) as the ligands. It was found that Zn-azo-dabco MOF (Azo-DMOF-1) exhibited a photoresponsive CO₂ adsorption both in static and dynamic condition because of the presence of azobenzene functionalities from the ligand. Further application of this MOF was evaluated by incorporating it as a filler in a mixed matrix membrane for CO₂/N₂ gas separation. Matrimid and polymer of intrinsic microporosity-1 (PIM-1) were used as the polymer matrix. It was found that Azo-DMOF-1 could enhance both the CO₂ permeability and selectivity of the pristine polymer. In particular, the Azo-DMOF-1-PIM-1 composite membranes have shown a promising performance that surpassed the 2008 Robeson Upper Bound.

From fundamentals to applications: a toolbox for robust and multifunctional MOF materials

In recent years, metal-organic frameworks (MOFs) have been regarded as one of the most important classes of materials. The combination of various metal clusters and ligands, arranged in a vast array of geometries has led to an ever-expanding MOF family. Each year, new and novel MOF structures are discovered. The structural diversity present in MOFs has significantly expanded the application of these new materials. MOFs show great potential for a variety of applications, including but not limited to: gas storage and separation, catalysis, biomedicine delivery, and chemical sensing. This review intends to offer a short summary of some of the most important topics and recent development in MOFs. The scope of this review shall cover the fundamental aspects concerning the design and synthesis of MOFs and range to the practical applications regarding their stability and derivative structures. Emerging trends of MOF development will also be discussed. These trends shall include multicomponent MOFs, defect development in MOFs, and MOF composites. The ever important structure-property-application relationship for MOFs will also be investigated. Overall, this review provides insight into both existing structures and emerging aspects of MOFs.

Post-Synthetic Mannich Chemistry on Metal-Organic Frameworks: System-Specific Reactivity and Functionality-Triggered Dissolution

The Mannich reaction of the zirconium MOF [Zr6 O4 (OH)4 (bdc-NH2 )6 ] (UiO-66-NH2 , bdc-NH2 =2-amino-1,4-benzenedicarboxylate) with paraformaldehyde and pyrazole, imidazole or 2-mercaptoimidazole led to post-synthetic modification (PSM) through C-N bond formation. The reaction with imidazole (Him) goes to completion whereas those with pyrazole (Hpyz) and 2-mercaptoimidazole (HimSH) give up to 41 and 36 % conversion, respectively. The BET surface areas for the Mannich products are reduced from that of UiO-66-NH2 , but the compounds show enhanced selectivity for adsorption of CO2 over N2 at 273 K. The thiol-containing MOFs adsorb mercury(II) ions from aqueous solution, removing up to 99 %. The Mannich reaction with pyrazole succeeds on [Zn4 O(bdc-NH2 )3 ] (IRMOF-3), but a similar reaction on [Zn2 (bdc-NH2 )2 (dabco)] (dabco=1,4-diazabicyclo[2.2.2]octane) gave [Zn3 (bdc-NH2 )1.32 (bdc-NHCH2 pyz)1.68 (dabco)]⋅2 C7 H8 5, whereas the reaction with imidazole gave the expected PSM product. Compound 5 forms via a dissolution-recrystallisation process that is triggered by the "free" pyrazolate nitrogen atom competing with dabco for coordination to the zinc(II) centre. In contrast, the "free" nitrogen atom on the imidazolate is too far away to compete in this way. Mannich reactions on [In(OH)(bdc-NH2 )] (MIL-68(In)-NH2 ) stop after the first step, and the product was identified as [In(OH)(bdc-NH2 )0.41 (bdc-NHCH2 OCH3 )0.30 (bdc-N=CH2 )0.29 ], with addition of the heterocycle prevented by steric interactions.

A high-valent di-μ-oxo dimanganese complex covalently anchored in a metal–organic framework as a highly efficient and recoverable water oxidation catalyst

A biomimetic homogeneous catalyst is successfully anchored inside MOFs, exhibiting high activity and reliable durability in the water oxidation reaction.

Investigating the crystal engineering of the pillared paddlewheel metal–organic framework Zn2(NH2BDC)2DABCO

We examined the characterization data for Zn₂(NH₂BDC)₂DABCO to gain mechanistic insight into the crystal engineering of pillared paddlewheel MOFs.

Post-synthetic modification of zirconium metal–organic frameworks by catalyst-free aza-Michael additions

UiO-66-NH₂ reacts with acrylonitrile, acrylic acid, methyl acrylate and methyl vinyl ketone leading to post-synthetic modification of the MOF through C–N bond formation. The acrylonitrile-modified MOF undergoes further reaction to form a tetrazolate-modified MOF.

Highly conductive and robust composite anion exchange membranes by incorporating quaternized MIL-101(Cr)

With well-defined channels and tunable functionality, metal-organic frameworks (MOFs) have inspired the design of a new class of ion-conductive compounds. In contrast to the extensive studies on proton-conductive MOFs and related membranes attractive for fuel cells, rare reports focus on MOFs in preparation of anion exchange membranes. In this study, chloromethylated MIL-101(Cr) was prepared and incorporated into chloromethylated poly (ether ether ketone) (PEEK) as a multifunctional filler to prepare imidazolium PEEK/imidazolium MIL-101(Cr) (ImPEEK/ImMIL-101(Cr)) anion exchange membrane after synchronous quaternization. The successful synthesis and chloromethylation of MIL-101(Cr) were verified by transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy while the enhanced performance of composite membranes in hydroxide conductivity, mechanical strength and dimensional stability were evaluated by alternating-current impedance, electronic stretching machine and measurement of swelling ratio. Specifically, incorporating 5.0wt% ImMIL-101(Cr) afforded a 71.4% increase in hydroxide conductivity at 20°C, 100% RH. Besides, the composite membranes exhibited enhanced dimensional stability and mechanical strength due to the rigid framework of ImMIL-101(Cr). At room temperature and the ImMIL-101(Cr) content of 10wt%, the swelling ratio of the ImPEEK/ImMIL-101(Cr) was 70.04% lower while the tensile strength was 47.5% higher than that of the pure membrane.

Chemically reprogrammable metal organic frameworks (MOFs) based on Diels–Alder chemistry

We pioneer a new class of reprogrammable MOFs able to switch their interlattice chemistry via a facile Diels–Alder based cycloreversion process.

A Combined Experimental and Theoretical Study on the Extraction of Uranium by Amino-Derived Metal-Organic Frameworks through Post-Synthetic Strategy

A novel carboxyl-functionalized metal-organic framework for highly efficient uranium sorption was prepared through a generic postsynthetic strategy, and this MOF's saturation sorption capacity is found to be as high as 314 mg·g^-1. The preliminary application illustrated that the grafted free-standing carboxyl groups have notably enhanced the sorption of uranyl ions on MIL-101. In addition, we have performed molecular dynamics simulation combined with density functional theory calculations to investigate the molecular insights of uranyl ions binding on MOFs. The high selectivity and easy separation of the as-prepared material have shown tremendous potential for practical applications in the nuclear industry or radioactive water treatment, and the functionalized MOF can be extended readily upon the versatility of click chemistry. This work provides a facile and purposeful approach for developing MOFs toward a highly efficient and selective extraction of uranium(VI) in aqueous solution, and it further facilitates the structure-based design of nanomaterials for radionuclide-containing-medium pretreatment.