Metal Hydrogen-Bonded Organic Frameworks as Open Lewis Acid Catalysts for Two Types of CO2 Transformations

Efficient and multiple CO2 utilization into high-value-added chemicals holds significant importance in carbon neutrality and industry production. However, most catalysis systems generally exhibit only one type of CO2 transformation with the efficiency to be improved. The restricted abundance of active catalytic sites or an inefficient utilization rate of these sites results in the constraint. Consequently, we designed and constructed two metal hydrogen-bonded organic frameworks (M-HOFs) {[M3(L3-)2(H2O)10]·2H2O}n (M = Co (1), Ni (2); L = 1-(4-carboxyphenyl)-1H-pyrazole-3,5-dicarboxylic acid) in this research. 1 and 2 are well-characterized, and both show excellent stability. The networks connected by multiple hydrogen bonds enhance the structural flexibility and create accessible Lewis acidic sites, promoting interactions between the substrates and catalytic centers. This enhancement facilitates efficient catalysis for two types of CO2 transformations, encompassing both cycloaddition reactions with epoxides and aziridines to afford cyclic carbonates and oxazolidinones. The catalytic activities (TON/TOF) are superior compared with those of most other catalysts. These heterogeneous catalysts still exhibited high performance after being reused several times. Mechanistic studies indicated intense interactions between the metal sites and substrates, demonstrating the reason for efficient catalysis. This marks the first instance on M-HOFs efficiently catalyzing two types of CO2 conversions, finding important significance for catalyst design and CO2 utilization.

Cholinium Pyridinolate Ionic Pair-Catalyzed Fixation of CO2 into Cyclic Carbonates

A halide-free ionic pair organocatalyst was proposed for the cycloaddition of CO2 into epoxide reactions. Cholinium pyridinolate ionic pairs with three different substitution positions were designed. Under conditions of temperature of 120 °C, pressure of 1 MPa CO2, and catalyst loading of 5 mol %, the optimal catalyst cholinium 4-pyridinolate ([Ch]+[4-OP]-) was employed. After a reaction time of 12 h, styrene oxide was successfully converted into the corresponding cyclic carbonate, and its selectivity was improved to 90%. A series of terminal epoxides were converted into cyclic carbonates within 12 h, with yields ranging from 80 to 99%. The proposed mechanism was verified by 1H NMR and 13C NMR titrations. Cholinium cations act as a hydrogen bond donor to activate epoxides, and pyridinolate anions combine with carbon dioxide to form intermediate carbonate anions that attack epoxides as nucleophiles and lead to ring opening. In summary, a halide-free ionic pair organocatalyst was designed and the catalytic mechanism in the cycloaddition of CO2 into epoxides reactions was proposed.

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.

Two novel Ln8 clusters bridged by CO32- effectively convert CO2 into oxazolidinones and cyclic carbonates

It is difficult and challenging to design and construct high-nuclearity Ln(III)-based clusters due to the high coordination numbers and versatile coordination geometries of Ln(III) ions. Herein, two novel octanuclear Ln(III)-based clusters [Ln₈(H₂L^-)₄(HL^2-)₄(NO₃)₆ (CO₃)₂](NO₃)₂·2CH₃CN (Ln = Nd (1) and Sm (2)) have been synthesized under solvothermal conditions. The X-ray single analysis reveals that both 1 and 2 are octanuclear structures and the eight central Ln(III) ions are bridged by two CO₃^2- anions. Catalytic study revealed that 1 and 2 can effectively catalyze the cycloaddition reaction of CO₂ and aziridines or epoxides simultaneously under mild conditions. What is more, cluster 1, as a heterogeneous catalyst, can be reused at least three times without obvious loss in catalytic activity for coupling of CO₂ and epoxides. To our knowledge, cluster 1 is the first Ln(III)-based cluster catalyst used for the conversion of CO₂ with aziridines or epoxides simultaneously. This work provides a successful strategy to integrate high-nuclear Ln(III)-based clusters for CO₂ conversion, which may open a new space for the construction of multifunctional high-nuclear Ln(III)-based clusters as efficient catalysts for CO₂ conversion.

Novel MCM-41 Supported Dicationic Imidazolium Ionic Liquids Catalyzed Greener and Efficient Regioselective Synthesis of 2-Oxazolidinones from Aziridines and Carbon Dioxide

A type of MCM-41 supported dicationic imidazolium ionic liquid nanocatalyst has been synthesized and found to be competent for the synthesis of 2-oxazolidinones through the sustainable chemical conversion of CO₂ with aziridines. It was shown that the highest efficiency was achieved in the cycloaddition of a series of aziridines and CO₂ in the presence of a catalytic amount of the solid catalyst MCM-41@ILLaCl₄ under mild conditions. Merits of this meticulously designed protocol are the use of a novel supported ionic liquid catalyst, the easy work-up process, good to excellent yields, a short reaction time, and purification without column chromatography. Overall, the present protocol of synthesizing 2-oxazolidinones under cocatalyst- and solvent-free conditions using MCM-41@ILLaCl₄ is promising for industrial applications.

Self-Assembly Bifunctional Tetranuclear Ln2Ni2 Clusters: Magnetic Behaviors and Highly Efficient Conversion of CO2 under Mild Conditions

A series of heterometallic tetranuclear clusters, Ln₂Ni₂(NO₃)₄L₄(μ₃-OCH₃)₂·2(CH₃CN) (Ln = Gd(1), Tb(2), Dy(3), Ho(4), Er(5); HL = methyl 3-methoxysalicylate), were synthesized solvothermally. The intramolecular synergistic effect of two metal centers of Ln(III) and Ni(II) and the exposed multimetallic sites serving as Lewis acid activators greatly increase the efficiency of the CO₂ conversion, and the yield for cluster 3 can be achieved at 96% at atmospheric pressure and low temperature. In particular, the self-assembly multimetal center with polydentate ligand shows good generality and enhanced recyclability. The design of such 3d-4f heterometallic clusters provides an effective strategy for the conversion of CO₂ under greener conditions. Meanwhile, magnetic investigations indicate that cluster 1 is a good candidate for magnetic refrigerant materials with a relatively large magnetocaloric effect (MCE) (-ΔS_m = 28.5 J kg^-1 K^-1 at 3.0 K and 7.0 T), and cluster 3 shows single-molecular magnet behavior under zero dc field. Heterometallic clusters with special magnetic properties and good catalytic behavior for the conversion of CO₂ are rare. Thus, they are potential bifunctional materials applied in practice.

Selectively Regulating Lewis Acid-Base Sites in Metal-Organic Frameworks for Achieving Turn-On/Off of the Catalytic Activity in Different CO2 Reactions

Regulating Lewis acid-base sites in catalysts to investigate their influence in the chemical fixation of CO₂ is significant but challenging. A metal-organic framework (MOF) with open metal Co sites, {(NH₂ Me₂ )[Co₃ (μ₃ -OH)(BTB)₂ (H₂ O)]⋅9 H₂ O⋅5 DMF}_n (1), was obtained and the results of the catalytic investigation show that 1 can catalyze cycloaddition of CO₂ and aziridines to give 99 % yield. The efficiency of the cyclization of CO₂ with propargyl amines is only 32 %. To improve the catalytic ability of 1, ligand XN with Lewis base sites was introduced into 1 and coordinated with the open Co sites, resulting in a decrease of the Lewis acid sites and an increase in the Lewis base sites in a related MOF 2 ({(NH₂ Me₂ )[Co₃ (μ₃ -OH)(NHMe₂ )(BTB)₂ (XN)]⋅8 H₂ O⋅4 DMF}_n ). Selective regulation of the type of active centers causes the yield of oxazolidinones to be enhanced by about 2.4 times, suggesting that this strategy can turn on/off the catalytic activity for different reactions. The catalytic results from 2 treated with acid solution support this conclusion. This work illuminates a MOF-construction strategy that produces efficient catalysts for CO₂ conversion.

Study on Selected Metal-Organic Framework-Based Catalysts for Cycloaddition Reaction of CO2 with Epoxides: A Highly Economic Solution for Carbon Capture and Utilization

The level of carbon dioxide in the atmosphere is growing rapidly due to fossil fuel combustion processes, heavy oil, coal, oil shelter, and exhausts from automobiles for energy generation, which lead to depletion of the ozone layer and consequently result in global warming. The realization of a carbon-neutral environment is the main focus of science and academic researchers of today. Several processes were employed to minimize carbon dioxide in the air, some of which include the utilization of non-fossil sources of energy like solar, nuclear, and biomass-based fuels. Consequently, these sources were reported to have a relatively high cost of production and maintenance. The applications of both homogeneous and heterogeneous processes in carbon capture and storage were investigated in recent years and the focus now is on the conversion of CO2 into useful chemicals and compounds. It was established that CO2 can undergo cycloaddition reaction with epoxides under the influence of special catalysts to give cyclic carbonates, which can be used as value-added chemicals at a different level of pharmaceutical and industrial applications. Among the various catalysts studied for this reaction, metal-organic frameworks are now on the frontline as a potential catalyst due to their special features and easy synthesis. Several metal-organic framework (MOF)-based catalysts were studied for their application in transforming CO2 to organic carbonates using epoxides. Here, we report some recent studies of porous MOF materials and an in-depth discussion of two repeatedly used metal-organic frameworks as a catalyst in the conversion of CO2 to organic carbonates.

Efficient Cycloaddition of CO2 and Aziridines Activated by a Quadruple-Interpenetrated Indium-Organic Framework as a Recyclable Catalyst

On the basis of the global warming effect, it is of great significance to convert CO₂ into the high value-added products oxazolidinones, but investigations on main-group-based metal-organic frameworks (MOFs) as heterogeneous catalysts still have not been reported so far. In this work, a quadruple-interpenetrated porous indium-based MOF, {[NH₂(CH₃)₂][In(CPT)₂]·3CH₃CN·3DMA}_n (1), is constructed from the organic ligand 3,5-bis(4'-carboxyphenyl)-1,2,4-triazole through solvothermal reactions, and N₂ adsorption proves that the framework has a high Brunauer-Emmett-Teller surface areas with 2024 m²/g. The catalytic research on CO₂ conversion reveals that compound 1 has high reactivity for the cycloaddition of CO₂ with aziridines, and the product 3-ethyl-5-phenyloxazolidin-2-one can be obtained with a yield of 99% under mild conditions. In addition, 1 exhibits excellent activity for different kinds of substrates and can be reused at least five cycles without any significant deactivation, suggesting that 1 is a potential candidate for the chemical conversion of CO₂ and aziridines. Mechanistic explorations indicate that the high efficiency of 1 is attributed to the indium center in the framework as a Lewis acid site, and the large porosity can enrich substrates. Importantly, 1 behaved as the first main-group MOF-based catalyst in the reported coupling reaction of CO₂ with aziridines.

An uncommon multicentered ZnI-ZnI bond-based MOF for CO2 fixation with aziridines/epoxides

A novel cluster-based MOF with uncommon multicentered Zn^I-Zn^I bonds {[K_1.2Na_2.8Zn^I₈(HL)₁₂]·4H₂O}_n (HL = tetrazole monoanion) (1) was synthesized, which showed higher stability than the reported Zn^I-Zn^I bonded compounds. Moreover, 1 can effectively and circularly catalyze the cyclization of CO₂ and aziridines or epoxides with five substituent groups. Importantly, this is the first time that the catalytic properties of MOFs with multicentered metal-metal bonded clusters as the catalyst have been studied.

A more effective catalysis of the CO2 fixation with aziridines: computational screening of metal-substituted HKUST-1

A vital issue for the fixation and conversion of CO₂ into useful chemical products is to find effective catalysts. In this work, in order to develop more effective and diverse catalysts, we implemented the first computational screening study (at M06-2X//B3LYP level) on the cycloaddition of CO₂ with aziridines under eighteen metal-substituted HKUST-1 MOFs and tetrabutylammonium bromide (TBAB) as a co-catalyst. For all considered catalytic systems, the ring-opening of aziridine is calculated to be the rate-determining step. Up to 11 M-HKUST-1 systems, i.e., Rh (31.87 kcal mol^-1), Y (31.02), Sc (30.50), V (30.02), Tc (29.90), Cd (29.80), Ti (29.32), Mn (29.05), Zn (28.29), Fe (27.85) and Zr (25.09), possess lower ring-opening barrier heights than the original Cu-HKUST-1 (32.90), indicative of their superior catalytic ability to the original Cu-HKUST-1 in theory. With the lowest ring-opening barrier, Zr-HKUST-1 is strongly advocated for future synthetic and catalytic studies.

Synthesis of Porphyrin Zr-MOFs for the Adsorption and Photodegradation of Antibiotics under Visible Light

The release of antibiotics into the water environment can pose a serious threat to human and ecological health, so it is of great significance to effectively remove antibiotics from wastewater. In this work, porphyrinic zirconium metal-organic framework material, PCN-224, was first explored for the adsorption removal of antibiotics from water using tetracycline (TC) and ciprofloxacin (CIP) as examples. We prepared a series of PCN-224 with different particle sizes (150 nm, 300 nm, 500 nm, and 6 μm). Benefiting from the huge surface area (1616 m² g^-1), the 300 nm-PCN-224 sample had the best adsorption properties for TC and CIP. Remarkably, it exhibits fast removal rates and high adsorption capacities of 354.81 and 207.16 mg g^-1 for TC and CIP, respectively. The adsorption of TC and CIP in 300 nm-PCN-224 is consistent with the pseudo-second-order kinetic model and Langmuir isotherm model, which indicates that the adsorption can be regarded as homogeneous monolayer chemisorption, and the adsorption is exothermic, which has been confirmed by thermodynamic studies. Under visible-light irradiation, 300 nm-PCN-224 exhibited high photocatalytic activity for TC and CIP. The adsorption studies confirmed that the adsorption of adsorbates takes place via the formation of hydrogen bonding, π-π interactions, and electrostatic attraction. In addition, the adsorbent can be simply regenerated by photocatalysis under visible light, and the adsorption-desorption efficiency is still above 85% after repeated use five times. The work of MOFs to remove antibiotics from water shows that MOFs have great potential in this field and are worthy of further study.

Non-precious metal carbamates as catalysts for the aziridine/CO2 coupling reaction under mild conditions

The catalytic potential of a large series of easily available metal carbamates (based on thirteen different non-precious metal elements) was explored for the first time in the coupling reaction between 2-aryl-aziridines and carbon dioxide, working under solventless and ambient conditions and using tetraalkylammonium halides as co-catalysts. The straightforward synthesis of novel [NbCl3(O2CNEt2)2], NbCl, and [NbBr3(O2CNEt2)2], NbBr, is reported. The niobium complex NbCl, in combination with NBu4I, emerged as the best catalyst of the overall series to convert aziridines with small N-alkyl substituents into the corresponding 5-aryl-oxazolidin-2-ones.

Quest for an Efficient 2-in-1 MOF-Based Catalytic System for Cycloaddition of CO2 to Epoxides under Mild Conditions

We have devised a straightforward tandem postsynthetic modification strategy for Zr-based metal-organic framework (MOF) materials, which resulted in a series of well-defined 2-in-1 heterogeneous catalysts, cat1-cat8, exhibiting high catalytic activity in the synthesis of cyclic carbonates under solvent-free and co-catalyst-free conditions. The materials feature precisely located co-catalyst moieties decorating the metal nodes throughout the bulk of the MOF and yield cyclic carbonates with up to 99% efficiency at room temperature. We use diffuse reflectance infrared Fourier transform (DRIFT) and solid-state nuclear magnetic resonance (NMR) measurements to elucidate the role of each component in this model catalytic reaction. Establishing a method to precisely control the co-catalyst loading allowed us to observe the cooperativity between Lewis acid sites and the co-catalyst in the 2-in-1 heterogeneous system.

Exploring Reversible Thermochromic Behavior in a Rare Ni(II)-MOF System

Thermochromic metal-organic frameworks (MOFs) are promising functional materials for a wide range of applications due to their ability to exhibit color variation under external temperature stimuli, yet the development of them with high cyclability and efficient regeneration processes remains challenging. Here, presented is a rare example of an ultrastable Ni(II)-MOF exhibiting an unprecedented reversible four-step color change between two complementary colors in a wide temperature range, which could be repeated for at least 500 cycles without losing crystallinity and thermochromic performance. Notably, the regeneration can be achieved within 1 min by simply letting the crystals cool naturally in the air, facilitated by the unique nature of the channels' inner surface. The reversible thermochromic behavior is owing to a series of reversible crystal structure changes with temperature, including the stepwise dehydration/rehydration process, and structural changes. This work facilitates the future development of more MOF-based reversible thermochromic materials with excellent performance and improved practical applicability.

Imidazolium-based ionic liquid immobilized on functionalized magnetic hydrotalcite (Fe3O4/HT-IM): as an efficient heterogeneous magnetic nanocatalyst for chemical fixation of carbon dioxide under green conditions

Fe₃O₄/HT-IM with plate-like morphology was synthesized as a novel and highly effective magnetic nanocatalyst and applied in chemical fixation.

Magnetically controlled colorimetric aptasensor for chlorpyrifos based on copper-based metal-organic framework nanoparticles with peroxidase mimetic property

The fabrication of a magnetically controlled colorimetric aptasensor for chlorpyrifos is reported. The aptasensor was fabricated by the attachment of the colorimetric labels onto the magnetic carrier due to the hybridization reaction between the complementary DNA and aptamer. Chlorpyrifos detection was realized by monitoring the color changes of the TMB/H₂O₂ solution before and after incubation of the aptasensor with chlorpyrifos via exposure to external magnetic force. The color change was monitored at 650 nm by UV-Vis spectrophotometer. Under the optimal conditions, this magnetically controlled Cu-MOF-based aptasensor showed a detection limit of 4.4 ng/mL with a linear range of 0-1250 ng/mL. The colorimetric aptasensor displayed high selectivity for chlorpyrifos toward other interfering pesticides. The aptasensor was successfully applied for the spiked test of chlorpyrifos in fruits and vegetable samples with good recovery, which were in agreement with data obtained by GC-MS analysis. This magnetically controlled Cu-MOF-based sensing strategy not only leads to development of efficient and facile phase separation, but also expands the MOF's target scope from H₂O₂ or glucose to pesticides. Graphical abstract.

Ultrasensitive detection of Cr(VI) (Cr2O72-/CrO42-) ions in water environment with a fluorescent sensor based on metal-organic frameworks combined with sulfur quantum dots

Accurate, simple and quick detection methods for Cr(VI) detection are urgently needed for water quality monitoring. Herein, a novel and facile method of detecting Cr(VI) (Cr₂O₇^2-/CrO₄^2-) ions is developed via the fluorescent detection technology based on metal-organic frameworks (MOFs) doped with sulfur quantum dots (SQDs) (SQDs@UiO-66-NH₂). The blue-light-emitting SQDs@UiO-66-NH₂ composites exhibit excellent fluorescent properties in water environment with high quantum yield (68%) and ideal fluorescent stability, thus demonstrating excellent potential for serving as a chemical sensor. After characterizing the performance and stability of SQDs@UiO-66-NH₂, qualitative and quantitative detection of Cr₂O₇^2- and CrO₄^2- ions was successfully conducted. The fluorescence of SQDs@UiO-66-NH₂ composites in aqueous solution was quenched effectively with more than 90% quenching efficiency by Cr(VI) via the inner filter effect. The detection system provides considerable advantages such as rapid response (10 s), high sensitivity with a low detection limit of 0.16 μM in a broad linear range of 0-200 μM (R² = 0.99) for Cr₂O₇^2- and 0.17 μM for CrO₄^2- in a broad linear range of 0-220 μM (R² = 0.99), high selectivity and reproducibility for at least five cycles with simple washing with alcohol. In practical applications, the sensor showed rapid response, high sensitivity and excellent recoveries (96.7%-105.4%) for detecting Cr₂O₇^2- in real water samples. Furthermore, a SQDs@UiO-66-NH₂-based fluorescent test paper was successfully developed, providing a simple, reliable and portable method for Cr(VI) (Cr₂O₇^2-/CrO₄^2-) detection in water environment.

Ln-CPs constructed from unsymmetrical tetracarboxylic acid ligand: Tunable white-light emission and highly sensitive detection of CrO42-, Cr2O72-, MnO4- in water

A series of isostructural lanthanide coordination polymers (Ln-CPs), [Ln(Hbptc)(H₂O)₄]·H₂O [Ln = Er (1), Pr (2), Dy (3), Sm (4), Gd (5), Nd (6) and Tb(7); H₄bptc = 2,3,3',4'-biphenyl tetracarboxylic acid] have been isolated based on an unsymmetrical tetracarboxylic acid. Single-crystal X-ray diffraction analysis reveals that all CPs featured a two dimensional (2D) layer with (6, 6, 6)-connected 6³ topology. Luminescent spectra demonstrate that CPs 1-7 exhibit impressive UV-visible luminescence in the solid state at room temperature. More significantly, a single-component white-light material with International Commission on Illumination (CIE) coordinates of (0.335, 0.334) for 4 (Sm-CP), very closing to the pure white-light of (0.333, 0.333) was obtained by finely tuning of the excitation wavelength. In addition, the luminescent detection for anions of 7 is investigated. Fluorescence measurements show that 7 can detect oxoanion pollutants Cr₂O₇^2-, CrO₄^2-, and MnO₄^- anions in aqueous solutions with high selectivity and sensitivity, which suggests that the Tb-CP is a promising functional luminescence probe for toxic oxoanions. The possible mechanisms of the quenching effect were also discussed in detail.

A comparative study between Cu(INA)2-MOF and [Cu(INA)2(H2O)4] complex for a click reaction and the Biginelli reaction under solvent-free conditions

The catalytic activity of metal–organic framework Cu(INA)₂ (INA = isonicotinate ion) and the complex [Cu(INA)₂(H₂O)₄] were studied in the Copper-catalyzed Azide–Alkyne Cycloaddition (CuAAC) and Biginelli reaction under solvent-free reaction conditions. The robust, efficient and eco-friendly new method allowed the preparation of a variety of 1,2,3-triazole compounds in good to excellent yields and high selectivity for the 1,4-disubstituted triazole. Moreover, for the Biginelli reaction between aldehydes, ethyl acetoacetate and urea, the corresponding dihydropyrimidinones (DHPMs) were also obtained in satisfactory yields under mild reaction conditions for both catalysts. The comparative study between Cu(INA)₂-MOF and [Cu(INA)₂(H₂O)₄] complex demonstrated better results for the Cu-MOF, for both the yields and the regioselectivity of the products. Furthermore, no change in the heterogeneous catalyst structure was observed after the reaction, allowing them to be recovered and reused without any loss of activity.

The catalytic application of Cu(INA)₂-MOF in click and Biginelli reactions was investigated and a comparative study with the [Cu(INA)₂(H₂O)₄] complex was performed.

Formation of CX Bonds in CO2 Chemical Fixation Catalyzed by Metal-Organic Frameworks

Transformation of CO₂ based on metal-organic framework (MOF) catalysts is becoming a hot research topic, not only because it will help to reduce greenhouse gas emission, but also because it will allow for the production of valuable chemicals. In addition, a large number of impressive products have been synthesized by utilizing CO₂ . In fact, it is the formation of new covalent bonds between CO₂ and substrate molecules that successfully result in CO₂ solidly inserting into the products, and only four types of new CX bonds, including CH, CC, CN, and CO bonds, are observed in this exploration. An overview of recent progress in constructing CX bonds for CO₂ conversion catalyzed by various MOF catalysts is provided. The catalytic mechanism of generating different CX bonds is further discussed according to both structural features of MOFs and the interactions among CO₂ , substrates, as well as MOFs. The future opportunities and challenges in this field are also tentatively covered.

Defect-engineering a metal–organic framework for CO2 fixation in the synthesis of bioactive oxazolidinones

Three-component, solvent-free cycloaddition of epoxides with aromatic amines and CO₂.

Highly Selective and Sensitive Detection of PO4 3- Ions in Aqueous Solution by a Luminescent Terbium Metal-Organic Framework

A luminescent terbium metal-organic framework [Tb(HPIA-)(PIA2-)(H2O)2] (Tb-MOF), synthesized by a lanthanide metal ion (Tb3+) and nitric heterocyclic carboxylic acid ligands H2PIA (H2PIA = 5-(1H-pyrazol-3-yl)isophthalic-acid), was structurally characterized as a three-dimensional skeleton structure in which layered coordination frameworks are connected by hydrogen bonds. Based on the antenna effect, Tb-MOF can emit bright green fluorescence under 254 nm excitation, and the fluorescence emission presents excellent durability in aqueous solutions among a wide pH range. Moreover, the structure of Tb-MOF also possesses outstanding thermal stabilities. In some ways, PO4 3- and its derivatives are thought to be a kind of pollutant ion causing series environmental and health problems. The as-synthesized Tb-MOF exhibits prominent selectivity and remarkable sensitivity for detecting PO4 3- as an easy-to-use fluorescent probe with low detection limit, fast response, and wide detection range. Therefore, Tb-MOF has significant applications in the fields of human health and environmental monitoring.

Synthesis of Oxazolidinones by using Carbon Dioxide as a C1 Building Block and an Aluminium-Based Catalyst

Oxazolidinone synthesis through the coupling of carbon dioxide and aziridines was catalysed by an aluminium(salphen) complex at 50-100 °C and 1-10 bar pressure under solvent-free conditions. The process was applicable to a variety of substituted aziridines, giving products with high regioselectivity. It involved the use of a sustainable and reusable aluminium-based catalyst, used carbon dioxide as a C₁ source and provided access to pharmaceutically important oxazolidinones as illustrated by a total synthesis of toloxatone. This protocol was scalable, and the catalyst could be recovered and reused. A catalytic cycle was proposed based on stereochemical, kinetic and Hammett studies.

Cycloaddition of atmospheric CO2 to epoxides under solvent-free conditions: a straightforward route to carbonates by green chemistry metrics

The conversion of carbon dioxide (CO2) into value-added organic compounds has received more and more attention over recent years, not only because this gas is one of the major anthropogenic greenhouse gases, but also because it has been regarded as an abundant, inexpensive, nontoxic, nonflammable, and renewable one-carbon (C1) resource. Along these lines, the synthesis of five-membered cyclic carbonates employing CO2 as a safe alternative to toxic reagents such as phosgene or its derivatives is of great interest because of their wide range of applications in organic synthesis. However, most of CO2 incorporation reactions into carbonates are carried out in toxic and non-recyclable organic solvents. Furthermore, these transformations usually proceed at elevated pressures or supercritical CO2 conditions. Recently, several catalytic systems have been developed that allow the synthesis of functionalized carbonates from the reaction of atmospheric CO2 with corresponding epoxides under solvent-free conditions. This review is an attempt to summarize the most important advances and discoveries in this interesting research arena. The review is divided into three major sections. The first section will discuss ionic liquid catalyzed coupling reactions. The second will cover organocatalyzed reactions. The third focuses exclusively on metal-catalyzed fixations. Notably, the third section has been classified based on the metal element that carries out the catalysis (i.e. copper, palladium, zinc).

Direct Catalytic Conversion of CO2 to Cyclic Organic Carbonates under Mild Reaction Conditions by Metal—Organic Frameworks

The reduction of the representative greenhouse gas, carbon dioxide (CO2), is significantly an important theme for the current research in the modern chemical world. For the last two decades, the development of new metal-organic framework (MOF) systems with highly selective capture of CO2, in the presence of other competing gaseous molecules, has flourished to capture or separate CO2 for environmental protection. Nonetheless, the ultimate resolution to lessen the atmospheric CO2 concentration may be in the chemical or electrochemical conversion of CO2 to other compounds. In this context, the catalytic cycloaddition reaction of CO2 into organic epoxides to produce cyclic carbonates is a more attractive method. MOFs are being proven as efficient heterogeneous catalytic systems for this important reaction. In this review, we collected very recent progress in MOF-based catalytic systems, fully operable under very mild reaction conditions (room temperature and 1 atm CO2).

Two luminescent coordination polymers as highly selective and sensitive chemosensors for CrVI-anions in aqueous medium

Two luminescent coordination polymers with considerable stability in aqueous media were synthesized. Sensing experiments indicate that they can serve as highly selective and sensitive fluorescent probes toward Cr^VI-anions.