Family Of Metal-organic Frameworks Research Articles

Design and Application of a Non‐enzymatic Sensor Based on Metal‐organic Frameworks for the Simultaneous Determination of Carbofuran and Carbaryl in Fruits and Vegetables

AbstractA novel, stable and sensitive non‐enzymatic sensor was developed with metal‐organic frameworks (MOFs) that have attracted great attention in electrochemical sensors applications in recent years. The pore structures of MIL (Fe)‐101 and MIL (Fe)‐53 are the families of MOFs that were constructed via a simple solvothermal procedure. The 35MIL‐101(Fe)‐reduced graphene oxide nanocomposite has been used for modification of glassy carbon electrode for the determination of carbofuran (CBF) and carbaryl (CBR). The porosity of the composites increased the voltammetric responses significantly for CBF and CBR in a mixed solution that makes the simultaneous determination of both carbamate pesticides possible. Characterization of MIL (Fe)‐101 and MIL (Fe)‐53 were performed with FT‐IR, XRD, BET and SEM. Finally, the introduced sensor under the optimal conditions showed low detection limits of 1.2 and 0.5 nM within the linear ranges of 5.0–200.0 nM and 1.0–300.0 nM for CBF and CBR, respectively. The non‐enzymatic sensor was successfully used to monitoring of carbamates residue in vegetable and fruit samples.

High-Pressure in Situ 129Xe NMR Spectroscopy: Insights into Switching Mechanisms of Flexible Metal-Organic Frameworks Isoreticular to DUT-49.

Flexible metal–organic frameworks (MOFs) are capable of changing their crystal structure as a function of external stimuli such as pressure, temperature, and type of adsorbed guest species. DUT-49 is the first MOF exhibiting structural transitions accompanied by the counterintuitive phenomenon of negative gas adsorption. Here, we present high-pressure in situ 129Xe NMR spectroscopic studies of a novel isoreticular MOF family based on DUT-49. These porous materials differ only in the length of their organic linkers causing changes in pore size and elasticity. The series encompasses both, purely microporous materials as well as materials with both micropores and small mesopores. The chemical shift of the adsorbed xenon depends on xenon–wall interactions and thus on the pore size of the material. The xenon adsorption behavior of different MOFs can be observed over the whole range of relative pressure. Chemical shift adsorption/desorption isotherms closely resembling the conventional, uptake-measurement-based isotherms were obtained at 237 K where all materials are rigid. The comparable chemical environment of the adsorbed xenon in these isoreticular MOFs allows to establish a correlation between the chemical shift at a relative pressure of p/p0 = 1.0 and the mean pore diameter. Furthermore, the xenon adsorption behavior of MOFs is studied also at 200 K. Here, structural flexibility is found for DUT-50, a material with an even longer linker than that of the previously known DUT-49. Its structural transitions are monitored by 129Xe NMR spectroscopy. This compound is the second known MOF showing the phenomenon of negative gas adsorption. Further increase in the linker length results in DUT-151, a material with an interpenetrated network topology. In situ 129Xe NMR spectroscopy proves that this material exhibits another type of flexibility compared to DUT-49 and DUT-50. Further surprising observations are made for DUT-46. Volumetric xenon adsorption measurements show that this nonflexible microporous material does not exhibit any hysteresis. In contrast, the in situ 129Xe NMR spectroscopically detected xenon chemical shift isotherms exhibit a hysteresis even after longer equilibration times than in the volumetric experiments. This indicates kinetically hindered redistribution processes and long-lived metastable states of adsorbed xenon within the MOF persisting at the time scale of hours or longer.

Design, Synthesis, and Characterization of Metal–Organic Frameworks for Enhanced Sorption of Chemical Warfare Agent Simulants

Metal–organic frameworks (MOFs) and specifically the UiO family of MOFs have been extensively studied for the adsorption and degradation of chemical warfare agents (CWAs) and their simulants. We present a combined experimental and computational study of the adsorption of dimethyl methylphosphonate (DMMP), a CWA adsorption simulant, in functionalized UiO-67. We have used density functional theory (DFT) to design functionalized MOFs having a range of binding energies for DMMP. We have selected three different functionalized MOFs for experimental synthesis and characterization from a total of eight studied with DFT. These three MOFs were identified as having the weakest, intermediate, and strongest binding energies for DMMP of the set, as predicted by our DFT calculations. We find that the order of predicted binding energies agrees with data from temperature-programmed desorption experiments. Moreover, the values of the binding energies are also in good agreement. This serves as a proof of concept that ab in...

Cover Feature: Alkali Phosphonate Metal–Organic Frameworks (Chem. Eur. J. 48/2019)

A new family of metal organic frameworks, namely Alkali-Phosphonate-MOFs, has been reported. The new alkali-phosphonate-MOF shows exceptional thermal stability and has a high surface area due to rectangular void channels. More information can be found in the Communication by Y. Zorlu, G. Yücesan, et al. on page 11214.

Pressure promoted low-temperature melting of metal-organic frameworks.

Metal-organic frameworks (MOFs) are microporous materials with huge potential for chemical processes. Structural collapse at high pressure, and transitions to liquid states at high temperature, have recently been observed in the zeolitic imidazolate framework (ZIF) family of MOFs. Here, we show that simultaneous high-pressure and high-temperature conditions result in complex behaviour in ZIF-62 and ZIF-4, with distinct high- and low-density amorphous phases occurring over different regions of the pressure-temperature phase diagram. In situ powder X-ray diffraction, Raman spectroscopy and optical microscopy reveal that the stability of the liquid MOF state expands substantially towards lower temperatures at intermediate, industrially achievable pressures and first-principles molecular dynamics show that softening of the framework coordination with pressure makes melting thermodynamically easier. Furthermore, the MOF glass formed by melt quenching the high-temperature liquid possesses permanent, accessible porosity. Our results thus imply a route to the synthesis of functional MOF glasses at low temperatures, avoiding decomposition on heating at ambient pressure.

Theoretical realization of two-dimensional M3(C6X6)2 (M = Co, Cr, Cu, Fe, Mn, Ni, Pd, Rh and X = O, S, Se) metal–organic frameworks

Two-dimensional (2D) conductive metal–organic framework (MOF) lattices have recently gained remarkable attentions because of their outstanding application prospects. Most recently, Cu-hexahydroxybenzene MOF was for the time experimentally realized, through a kinetically controlled approach. Cu-HHB belongs to the family of conductive MOFs with a chemical formula of M3(C6X6)2 (X=NH, O, S). Motivated by the recent experimental advance in the fabrication of Cu-HHB, we conducted extensive first-principles simulations to explore the thermal stability, mechanical properties and electronic characteristics of M3(C6X6)2 (M=Co, Cr, Cu, Fe, Mn, Ni, Pd, Rh and X=O, S, Se) monolayers. First-principles results confirm that all considered 2D porous lattices are thermally stable at high temperatures over 1500K. It was moreover found that these novel 2D structures can exhibit linear elasticity with considerable tensile strengths, revealing their suitability for practical applications in nanodevices. Depending on the metal and chalcogen atoms in M3(C6X6)2 monolayers, they can yield various electronic and magnetic properties, such as; magnetic semiconducting, perfect half metallic, magnetic and nonmagnetic metallic behaviors. This work highlights the outstanding physics of M3(C6X6)2 2D porous lattices and will hopefully help to expand this conductive MOF family, as promising candidates to design advanced energy storage/conversion, electronics and spintronics systems.

Heat capacities and thermodynamic functions of the ZIF organic linkers imidazole, 2-methylimidazole, and 2-ethylimidazole

Metal organic frameworks (MOFs) are a novel class of materials that consist of a lattice of metal centers linked by organic molecules. Previously, heat capacities and thermodynamic functions have been reported for a series of crystalline polymorphs of Zn(EtIm)2, a zeolitic imidazolate framework family of MOFs that have potential applications in CO2 sequestration. In those studies, an anomalous trend in the heat capacity and thermodynamic functions was observed that was not predicted. To further investigate these materials and their thermodynamic data, the low-temperature heat capacities of imidazole, 2-methylimidazole, and 2-ethylimidazole, organic linkers that are present in Zn(EtIm)2 and similar materials, were measured by a Quantum Design Physical Property Measurement System (PPMS) from 1.8–300 K. The data collected was fit to theoretical functions below 10 K, orthogonal polynomials from 5–60 K, and a sum of Debye and Einstein functions above 50 K. These functions were used to generate Cp,m°, Δ0TSm°, Δ0THm°, and Φm° values at smoothed temperatures from 0–300 K. This investigation revealed the presence of a second-order phase transition in 2-ethylimidazole that may yield insight into the anomalous heat capacity behavior present in Zn(EtIm)2.

Comparing Geometry and Chemistry When Confined Molecules Diffuse in Monodisperse Metal-Organic Framework Pores.

The monodisperse pore structure of MOFs (metal-organic frameworks) is advantageous for investigating how porosity influences diffusion. Here we report translational and rotational diffusion using fluorescence correlation spectroscopy and time-correlated single-photon counting, using the three-dimensional pores of the zeolitic-like metal-organic framework family. We compare the influence of size and electric charge as well as dependence on pore size that we controlled through postsynthetic cation-exchange modifications. Charge-charge interactions with the MOF appeared to produce transient adsorption, manifested as a relatively fast and a slower diffusion process, but diffusants without net electric charge displayed a single diffusion process. Obtained from this family of guest molecules selected to be fluorescent, these findings suggest potentially useful general design rules to predict how pore size, guest size, and host-guest interaction control guest mobility within nanopores. With striking fidelity, diffusion coefficient scales with the ratio of cross-sectional areas of diffusant and host pores when charge is taken into account.

Facile Mechanosynthesis of the Archetypal Zn-Based Metal–Organic Frameworks

Mechanochemical methods have been successful in providing rapid access to a number of inorganic-organic functional materials under mild conditions. Recently, we demonstrated a novel mechanochemical strategy for metal-organic framework (MOF) preparation based on predesigned oxo-centered secondary building units. Herein, we develop this method for the facile preparation of the isoreticular MOF (IRMOF) family members based on a combination of an oxozinc amidate cluster, [Zn4(μ4-O)(NHOCPh)6], and selected ditopic aminoterephthalate and 4,4'-biphenyldicarboxylate as well as tritopic 1,3,5-benzenetribenzoate ligands. The resulting IRMOF-3, IRMOF-10, and MOF-177 crystalline materials were characterized using powder X-ray diffraction, IR spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis. We found that the character of the organic linker strongly affects the nature of the resulting MOF crystallites after activation processes. The SEM images demonstrate that IRMOF-3 formed microcrystallites in the range of 400-500 nm, while the two other materials exhibited microstructures of amorphous phases. The porosity of each sample was estimated by N2 sorption measurements at 77 K. These results provide an efficient and general method for the mechanosynthesis of Zn-based MOF materials using a predesigned oxozinc cluster.

Electrosynthesis of Well-Defined Metal-Organic Framework Films and the Carbon Nanotube Network Derived from Them toward Electrocatalytic Applications.

An efficient and controllable method to synthesize continuous metal-organic framework (MOF) films is highly desired. Herein, we demonstrate a facile and universal electrochemical method to synthesize homogeneous and uniform zeolitic imidazolate framework (ZIF, a typical class of MOF family) films on various macroconductive substrates (e.g., conductiveglass, Ni foam and carbon cloth) as well as nanostructured substrates (one-dimensional nanorod array, two-dimensional nanowall array, and three-dimensional nanoframework). Particularly, the MOF film can be easily transformed into hierarchical ordered carbon nanotube networks, which display multifunctional electrocatalytic performances, such as excellent activity and good long-term stability in overall water splitting and oxygen reduction. It is worth mentioning that this is the first reported work for electrosynthesis of ZIF films on various conductive substrates, illustrating the great potential of the fast and economical method for constructing functional and integrated films or electrodes toward energy-related applications.

Dielectric Properties of Zeolitic Imidazolate Frameworks in the Broad-Band Infrared Regime.

The field of metal-organic framework (MOF) materials is rapidly advancing toward practical applications; consequently, it is urgent to achieve a better understanding and precise control of their physical properties. Yet, research on the dielectric properties of MOFs is at its infancy, where studies are confined to the static dielectric behavior or lower-frequency response (kHz-MHz) only. Herein, we present the pioneering use of synchrotron-based infrared reflectivity experiments combined with density functional theory (DFT) calculations to accurately determine the dynamic dielectric properties of zeolitic imidazolate frameworks (ZIFs, a topical family of MOFs). We show, for the first time, the frequency-dependent dielectric response of representative ZIF compounds, bridging the near-, mid-, and far-infrared (terahertz, THz) broad-band frequencies. We establish the structure-property relations as a function of framework porosity and structural change. Our comprehensive results will pave the way for novel ZIF-based terahertz applications, such as infrared optical sensors and high-speed wireless communications.

New Metal-Organic Frameworks for Chemical Fixation of CO2.

A novel series of two zirconium- and one indium-based metal-organic frameworks (MOFs), namely, MOF-892, MOF-893, and MOF-894, constructed from the hexatopic linker, 1',2',3',4',5',6'-hexakis(4-carboxyphenyl)benzene, were synthesized and fully characterized. MOF-892 and MOF-893 are two new exemplars of materials with topologies previously unseen in the important family of zirconium MOFs. MOF-892, MOF-893, and MOF-894 exhibit efficient heterogeneous catalytic activity for the cycloaddition of CO2, resulting in a cyclic organic carbonate formation with high conversion, selectivity, and yield under mild conditions (1 atm CO2, 80 °C, and solvent-free). Because of the structural features provided by their building units, MOF-892 and MOF-893 are replete with accessible Lewis and Brønsted acid sites located at the metal clusters and the non-coordinating carboxylic groups of the linkers, respectively, which is found to promote the catalytic CO2 cycloaddition reaction. As a proof-of-concept, MOF-892 exhibits high catalytic activity in the one-pot synthesis of styrene carbonate from styrene and CO2 without preliminary synthesis and isolation of styrene oxide.

Carbon dioxide measurements using long period grating optical fibre sensor coated with metal organic framework HKUST-1

An optical fibre long period grating (LPG) based carbon dioxide (CO2) sensor coated with HKUST-1, a material from the metal organic framework family, functional coating is presented. In-situ crystallization and layer by layer (LbL) techniques of HKUST-1 thin film synthesis are compared in terms of the feasibility of the deposition procedure (time and cost efficiency) and the sensitivity of the film to carbon dioxide. The sensing mechanism is based on the measurement of the change of the refractive index (RI) of the coating that is induced by the penetration of CO2 molecules into the HKUST-1 pores. The HKUST-1 film was characterized by scanning electron microscopy (SEM). The thickness and refractive index (RI) of the 10, 20 and 40 layers thick films were determined using ellipsoetry. The crystallinity of the films was examined by X-ray diffraction pattern (XRD). While no response to CO2 was observed for the sensor coated using the in-situ crystallization technique, an LPG modified with 10, 20 and 40 layers of HKUST-1 films using LbL method upon exposure to CO2 in the range of 500 ppm to 40,000 ppm showed good sensitivity. The film containing 40 layers exhibited the highest sensitivity to CO2 with an obtained detection limit of 401 ppm.

First-principles study of elastic mechanical responses to applied deformation of metal-organic frameworks

We use density functional theory to compute the elastic constant tensors of two families of metal-organic frameworks (MOFs) to establish relationships between their structures and mechanical properties. The Zn family consist of Zn4O centers each coordinated by six organic linkers along the ⟨100⟩ directions; we studied three linkers of increasing lengths: 1,4-benzenedicarboxylate (BDC), 4,4’-biphenyl-dicarboxylate (BPDC), and 4,4’’-terphenyl-dicarboxylate. This relatively weak connectivity leads to high anisotropy; in fact, Zn-MOFs exhibit extremely low shear modulus and are near a mechanical instability. In contrast, Zr family studied consists of Zr6O4(OH)4 centers each linked by fumarate, BDC, and BPDC ligands along the twelve ⟨110⟩ directions. The higher structural connectivity results in stiffer frameworks with lower anisotropy. The smallest Zr-MOF exhibits nearly isotropic elasticity with a Zener ratio of 1.06. The stiffest and most compliant directions of both families are directly related to the orientation of the organic linkers. Temperature has a significant effect on elastic moduli; for example, we observed reduction of average Young’s modulus and shear modulus by about 30% from 0 K to 300 K in Zn-BPDC even when it exhibits large negative thermal expansion. We find the effect of temperature to be directionally dependent, leading to an increase in anisotropy upon increasing temperature. The predicted effects of temperature and anisotropy help reconcile a longstanding discrepancy between experiments and first principles calculations.

Continuous One-Step Synthesis of Porous M-XF6 -Based Metal-Organic and Hydrogen-Bonded Frameworks.

Metal-organic frameworks (MOFs) built up from connecting M-XF6 pillars through N-donor ligands are among the most attractive adsorbents and separating agents for CO2 and hydrocarbons today. The continuous, one-step spray-drying synthesis of several members of this isoreticular MOF family varying the anionic pillar (XF6 =[SiF6 ]2- and [TiF6 ]2- ), the N-donor organic ligand (pyrazine and 4,4'-bipyridine) and the metal ion (M=Co, Cu and Zn) is demonstrated here. This synthetic method allows them to be obtained in the form of spherical superstructures assembled from nanosized crystals. As confirmed by CO2 and N2 sorption studies, most of the M-XF6 -based MOFs synthesised through spray-drying can be considered "ready-to-use" sorbents as they do not need additional purification and time consuming solvent exchange steps to show comparable porosity and sorption properties with the bulk/single-crystal analogues. Stability tests of nanosized M-SiF6 -based MOFs confirm their low stability in most solvents, including water and DMF, highlighting the importance of protecting them once synthesised. Finally, for the first time it was shown that the spray-drying method can also be used to assemble hydrogen-bonded open networks, as evidenced by the synthesis of MPM-1-TIFSIX.

Robust Multifunctional Yttrium-Based Metal-Organic Frameworks with Breathing Effect.

Phosphonate- and yttrium-based metal-organic frameworks (MOFs), formulated as [Y(H5btp)]·5.5H2O (1), [Y(H5btp)]·2.5H2O (2), (H3O)[Y2(H5btp)(H4btp)]·H2O (3), and [Y(H5btp)]·H2O·0.5(MeOH) (4), were prepared using a "green" microwave-assisted synthesis methodology which promoted the self-assembly of the tetraphosphonic organic linker [1,1'-biphenyl]-3,3',5,5'-tetrayltetrakis(phosphonic acid) (H8btp) with Y3+ cations. This new family of functional materials, isolated in bulk quantities, exhibits a remarkable breathing effect. Structural flexibility was thoroughly studied by means of X-ray crystallography, thermogravimetry, variable-temperature X-ray diffraction, and dehydration and rehydration processes, ultimately evidencing a remarkable reversible single-crystal to single-crystal (SC-SC) transformation solely through the loss and gain of crystallization solvent molecules. Topologically, frameworks remained unaltered throughout this interconversion mechanism, with all compounds being binodal 6,6-connected network with a Schäfli symbol of {413.62}{48.66.8}. Results show that this is one of the most stable and thermally robust families of tetraphosphonate-based MOFs synthesized reported to date. Porous materials 2 and 3 were further studied to ascertain their performance as heterogeneous catalysts and proton conductors, respectively, with outstanding results being registered for both materials. Compound 2 showed a 94% conversion of benzaldehyde into (dimethoxymethyl)benzene after just 1 h of reaction, among the best results registered to date for MOF materials. On the other hand, the protonic conductivity of compound 3 at 98% of relative humidity (2.58 × 10-2 S cm-1) was among the highest registered among MOFs, with the great advantage of the material to be prepared using a simpler and sustainable synthesis methodology, as well as exhibiting a good stability at ambient conditions (temperature and humidity) over time when compared to others.

CFA-4 - a fluorinated metal-organic framework with exchangeable interchannel cations.

The syntheses and crystal structures of the fluorinated linker 1,4-bis(3,5-bis(trifluoromethyl)-1H-pyrazole-4-yl)benzene (H2-tfpb; 1) and the novel metal-organic framework family M[CFA-4] (Coordination Framework Augsburg University-4), M[Cu5(tfpb)3] (M = Cu(i), K, Cs, Ca(0.5)), are described. The ligand 1 is fully characterized by single crystal X-ray diffraction, photoluminescence-, NMR-, IR spectroscopy, and mass spectrometry. The copper(i)-containing MOF crystallizes in the hexagonal crystal system within the chiral space group P6322 (no. 182) and the unit cell parameters are as follows: a = 23.630(5) Å, c = 41.390(5) Å, V = 20 015(6) Å3. M[CFA-4] features a porous 3-D structure constructed from pentanuclear copper(i) secondary building units {Cu(pz)6}- (pz = pyrazolate). Cu(I)[CFA-4] is fully characterized by synchrotron single crystal X-ray diffraction, thermogravimetric analysis, variable temperature powder X-ray diffraction, IR spectroscopy, photoluminescence and gas sorption measurements. Moreover, thermal stability and gas sorption properties of K[CFA-4] and Cu(I)[CFA-4] are compared.

Fine tuning of catalytic and sorption properties of metal-organic frameworks via in situ ligand exchange.

Metal-organic frameworks (MOFs) are gaining considerable attention not only because of their diverse structures but also due to their interesting properties and potential applications. However, fabrication of MOFs with desired structures and properties remains a great challenge. In this study, a strategy based on ligand exchange via single-crystal-to-single-crystal (SCSC) transformation has been undertaken, which can be used to achieve MOFs not available by direct synthesis and also to enrich the family of isoreticular MOFs. Direct X-ray crystallographic observation provides undoubted evidence that the pyrazine (pyz) ligand in [Cu3(L)2(pyz)(H2O)] (L3- = [1,1':3',1''-terphenyl]-4,4'',5'-tricarboxylate) was replaced by its derivatives without damaging the framework. Furthermore, the catalytic and sorption properties of the MOFs are able to be fine-tuned by introducing definite substituent group decorated on the pore surface. Thus, it is expected that the ligand exchange will be powerful for replacing linker molecules with others having desirable substituents, and as a result to afford desired MOFs.

A Polymetallic Metal‐Organic Framework‐Derived Strategy toward Synergistically Multidoped Metal Oxide Electrodes with Ultralong Cycle Life and High Volumetric Capacity

Metal‐organic frameworks (MOFs) are very convenient self‐templated precursors toward functional materials with tunable functionalities. Although a huge family of MOFs has been discovered, conventional MOF‐derived strategies are largely limited to the sole MOF source based on a handful of the metal elements. The limitation in structure and functionalities greatly restrains the maximum performance of MOF‐based materials for fulfilling the practical potential. This study reports a polymetallic MOF‐derived strategy for easy synthesis of metal‐oxide‐based nanohybrids with precisely tailored multicomponent active dopants. A variety of MoO2‐based nanohybrids with synergistical co‐doping of W, Cu, and P are yielded by controlled pyrolysis of tailor‐made polymetallic MOFs. The W doping induces the formation of MoxW1−xO2 solid solution with better activity. The homogeneous dispersion of Cu nanocrystallites in robust P‐doped carbon skeleton creates a conductive network for fast charge transfer. Boosting by synergistically multidoping effect, the Mo0.8W0.2O2‐Cu@P‐doped carbon nanohybrids with optimized composition exhibit exceptionally long cycle life of 2000 cycles with high capacities but very slow capacity loss (0.043% per cycle), as well as high power output for lithium storage. Remarkably, the co‐doping of heavy W and Cu elements in MoO2 with high density makes them particularly suitable for high volumetric lithium storage.

Furnishing Amine-Functionalized Metal-Organic Frameworks with the β-Amidoketone Group by Postsynthetic Modification.

Postsynthetic modification (PSM) of amino-functionalized metal-organic frameworks (MOFs) to those bearing pendant β-amidoketone arms using diketene is herein reported. Three unique MOF families demonstrate the scope of this transformation, which both is atom-economical and yields high conversions. In each case, the crystallinity was retained, and instances of exceptional solid-state ordering were observed in the PSM products, which has allowed detailed crystallographic characterization in multiple instances.