Three-dimensional Metal-organic Framework Research Articles

Temperature and frequency dependence of dielectric relaxation in a metal–organic perovskite-like framework

This study dielectrically analyzed the three-dimensional metal–organic framework complex of imidazolium magnesium formate [(C3N2H5)(Mg(HCOO)3)] (HImMg) to investigate the temperature–frequency dependence of the perovskite-like structure’s dielectric relaxation processes. HImMg was synthesized via solution diffusion at room temperature. The high-temperature phase transition of the HImMg was confirmed at around 178 °C by differential scanning calorimetry and temperature-dependent X-ray powder diffraction. Single-crystal X-ray diffraction revealed a monoclinic structure in the space group P21/n, indicating a centrosymmetric system, with the HIm+ dipole in the cages of the Mg(HCOO)3. The dielectric values were recorded between −50 °C and 200 °C and at radio and microwave frequency ranges between 1 kHz and 1 GHz. Dielectric relaxation was calculated using the Arrhenius and Cole–Cole relationships. Low-temperature activation energies of 0.14, 0.35, and 0.25 eV were connected to the gradual freezing of the imidazolium cations’ reorientation movements. This behavior may demonstrate that the dielectric relaxations of HImMg are caused by the orientational motion of dipolar guest molecules.

Synthesis, crystal structure and characterization of two new metal-organic frameworks with 1,3,5-tris[(1H-imidazol-1-yl)methyl]benzene and cyclohexane-1,3,5-tricarboxylate ligands

Two new metal-organic frameworks (MOFs) {[Cu3(timb)2(chtc)2]·14H2O}n, (I) and {[Co3(timb)2(chtc)2]·6H2O}n, (II) were hydrothermally synthesized by corresponding metal salt with mixed organic ligands of 1,3,5-tris[(1H-imidazol-1-yl)methyl]benzene (timb) and cyclohexane-1,3,5-tricarboxylic acid (H3chtc). Crystal structural analysis reveals that they exhibit varied structures. In the MOFs (I), CuII adopts an four coordination geometry, timb and cyclohexane-1,3,5-tricarboxylate ligands bridge neighboring CuII centers to result in two different one-dimensional knotted chains along the [0 − 1 2] and [1 0 − 1] directions, respectively. The two kinds of chains intersect each other vis CuII centers, resulting in a two-dimensional layered structure running parallel to the (1 2 1) plane. Adjacent layers are further linked by water moleculars via classical O–H…O hydrogen-bonding interactions, giving rise to a three-dimensional supramolecular network structure in the solid state. While in MOFs (II), the cyclohexane-1,3,5-tricarboxylate anions link the CoII cations to generate a two-dimensional sheeted metal-organic structure running parallel to the bc plane. Adjacent sheets are further bridged by timb ligands, forming a porous three-dimensional metal-organic framework with a rare (3, 4)-connected (6.82)2(62.84)3(62.8)2 topology. The solvent water molecules guest in the micropores of porous framework via water-carboxylate O–H…O hydrogen bonds. In addition, their thermal stabilities have also been investigated.

Template-directed synthesis of three-dimensional metal organic framework 199-derived highly porous copper nano-foam fiber for solid-phase microextraction of some antibiotics prior to their quantification by High performance liquid chromatography

The in-situ preparation of three-dimensional MOF-199 (3D MOF-199) derived from the electrochemically prepared highly porous nano Cu foam on the surface of a flexible copper wire is reported. The 3D-Cu foam coating was used as a precursor and template for fabrication of MOF-199. The microextraction ability of the in-situ prepared 3D-MOF-199 fiber was evaluated using the prepared fiber for solid phase microextraction (SPME) of selected antibiotics including amoxicillin, azithromycin, ciprofloxacin, cefixime and gentamicin coupled to high-performance liquid chromatography with UV detection. Under the optimized condition, the calibration curves were linear in the range of 1–100 µg L − 1 (r2 above 0.9921) for both water and urine matrices. Limits of detection and limits of quantification were 0.14–0.62 µg L − 1 and 0.53–2.17 µg L − 1 in the selected matrices, respectively. In addition, the repeatability of the method was evaluated by considering the relative standard deviation (RSD%). The intra-day and inter-day RSDs of the method with the single fiber was in the range of 2.8% to 4.9% and from 3.1% to 4.9%, respectively. Furthermore, the fiber-to-fiber reproducibility ranged from 2.9% to 5.5%. The enrichment factors were also in the range of 32 to 55. Finally, the method was successfully used for analysis of amoxicillin, azithromycin, ciprofloxacin, cefixime and gentamicin in urine samples. Relative recoveries for spiked urine samples were in the range of 90–105%.

Dual-Functional Metal-Organic Framework for Luminescent Detection of Carcinoid Biomarkers and High Proton Conduction.

It remains a challenge to exploit dual-functional metal-organic frameworks (MOFs) for applications, including luminescence detection and proton conduction. With the deliberate selection of the bifunctional organic ligand 5-sulfoisophthalic acid monosodium salt (NaH2bts), and the phosphonic acid ligand N,N'-piperazine (bismethylenephosphonic acid; H4L), a robust three-dimensional (3D) noninterpenetrating dual-functional MOF, [Tb(H2L)(H2bts)(H2O)]·H2O (1), has been synthesized hydrothermally. On the basis of the excellent thermal and chemical as well as superior luminescence stabilities in water and solutions with different pHs, 1 can serve as the simple, rapid, and highly selective and sensitive luminescence detection of the carcinoid biomarkers 5-hydroxytryptamine (HT) and its metabolite 5-hydroxyindole-3-acetic acid (HIAA) with detection limits of nanomolar magnitude in water and in simulated blood plasma and urine systems. Due to the change in the signals that could be readily differentiated by the naked eye under a UV lamp, a portable test paper has been developed. The probable quenching mechanisms are discussed in detail. In addition, a great number of hydrogen-bonding networks are formed among the uncoordinated carboxylic oxygen atoms, sulfonate oxygen atoms, protonated nitrogen atoms, and water molecules, which provide potential proton-hopping sites for proton conduction, leading to a maximum proton conductivity of 2.3 × 10-4 S cm-1 at 368 K and 95% relative humidity. The above results suggest that rationally designed dual-functional MOFs can open an avenue for the development of occupational diagnostic tools and alternative energy technology.

One-Step Electrochemical Growth of 2D/3D Zn(II)-MOF Hybrid Nanocomposites on an Electrode and Utilization of a PtNPs@2D MOF Nanocatalyst for Electrochemical Immunoassay.

To date, two-dimensional (2D) and three-dimensional (3D) metal organic frameworks (MOFs) have been promising materials for applications in electrocatalysis, separation, and sensing. However, the exploration of a simple method for simultaneous fabrication of 2D/3D MOFs on a surface remains challenging. Herein, a one-step and in situ electrosynthesis strategy for fabrication of 2D Hemin-bridged MOF sheets (Hemin-MOFs) or 2D/3D Zn(II)-MOF hybrid nanocomposites on an electrode is reported. It exhibits varied morphologies at different electrodeposition times and attains a 2D/3D complex morphology by adding 1,3,5-benzenetricarboxylic acid (H3BTC) as an organic ligand. The morphology and size of 2D Hemin-MOFs are important factors that influence their performance. Since Pt nanoparticles (PtNPs) are grown on 2D Hemin-MOF sheets, this composite can serve as the peroxidase mimics and PtNPs can act as an anchor to capture the antibody. Therefore, this hybrid nanosheet-modified electrode is used as an electrochemical sensing platform for ultrasensitive pig immunoglobulin G (IgG) and the surface-protective antigen (Spa) protein of Erysipelothrix rhusiopathiae immunodetection. Moreover, this work provides a new avenue for the electrochemical synthesis of 2D/3D MOF hybrid nanocomposites with a high surface area and biomimetic catalysts.

Two-dimensional coordination polymers containing permethylated motifs - promising candidates for 2D emerging materials. Structural, behavioral and functional particularities

Although three-dimensional metal-organic frameworks (3D MOFs) currently enjoy great attention in the scientific world due to their utility to address challenges concerning energy, environment cleaning and not only, very recently two-dimensional version of these, rather considered two-dimensional coordination polymers (2D CPs), have become of interest from the perspective of their approach as ultra-thin layered 2D materials. Different from the emerging 2D materials that are generally inorganic in nature (graphene or 2D allotropes of various elements, MXenes, etc.), 2D CPs contain both inorganic and organic blocks, offering wider possibilities for structural diversification and area of applicability. However, in the crystallization process, 2D CP layers often stack on the basis of intermolecular interactions, leading to higher dimensional materials, which limit the manifestation of the size-effect properties. Their isolation individually or in multilayers with thickness/surface aspect ratio as small as possible is a challenge that seeks solutions through top-down or bottom-up approaches, each of them having certain limits. An original pathway consists in the use of a permethylated ligand with lower surface energy which, through its orientation in the coordination process to the metal ion, favors the anisotropic growth of the polymer and ensures the shielding of the formed nanosheet structure preventing the establishment of noticeable interlayer interactions. Such unique two-dimensional coordination polymers recently reported by the authors and some new data about them are reviewed here from the perspective of their structural particularities, properties, reactivity, functionality, and reusability/recyclability potential.

Quinone-Based Conducting Three-Dimensional Metal–Organic Framework as a Cathode Material for Lithium-Ion Batteries

The low electronic conductivity of organic electrode materials leads to sluggish reaction kinetics and inferior electrochemical performance of lithium-ion batteries. Herein, the conducting three-dimensional metal–organic framework (3D-MOF) (NBu4)2Fe2(DHBQ)3 was synthesized through a facile aqueous addition reaction. The intramolecular charge delocalization through the robust π–d conjugation between DHBQ ligands and Fe3+ centers is favorable for long-range electron migration, resulting in high electronic conductivity of the 3D hollow (NBu4)2Fe2(DHBQ)3. When applied as the cathode material, (NBu4)2Fe2(DHBQ)3 delivers a reversible capacity of 137.2 mA h g–1 at 10 mA g–1 and 95.2 mA h g–1 at 1000 mA g–1. The capacity retention reached up to 91.4% after 350 cycles at 500 mA g–1 with about 100% Coulombic efficiency. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy tests reveal that the conjugated carbonyls of DHBQ organic linkers contribute the redox centers and undergo a 5e– reaction mechanism during charge and discharge processes. These excellent electrochemical performances could be attributed to the fast electron/ion migration kinetics because of high electronic conductivity and the hollow structure of (NBu4)2Fe2(DHBQ)3. All the positive results could facilitate the implementation of conductive MOFs for energy conversion and storage acceleration.

Graphene quantum dot incorporation in the zeolitic imidazolate framework with sodalite (SOD) topology: Synthesis and improving the adsorption ability in liquid phase

An amazing combination of zero-dimensional graphene quantum dots (GQDs) with three-dimensional metal-organic frameworks (MOFs) improves the resulting nanocomposite properties. Herein, The GQD was incorporated in the ZIF-8 surface, to emphasize another application of GQD that has been less considered before. The characteristics of synthesized nanomaterials were confirmed by FTIR, XRD, TGA, BET, Raman, SEM, and HRTEM. The removal of malachite green (MG) was investigated to compare the adsorption properties of nanocomposite with pristine GQD and ZIF-8. The effects of GQD loading dose in composite (2–20%), adsorbents dosage (0.7–2.5 mg), initial dye concentration (20–50 mg/L), and the pH of MG solution (4−7) as the influential parameters on pollutant removal were investigated. The dye adsorption capacity of hybrid nanocomposite (2500 mg/g) was reasonably better than pure GQD (294 mg/g) and MOF (1111 mg/g). Besides, this process was in good agreement with the pseudo-second-order kinetics and the Langmuir isotherm model

In(III) Metal–Organic Framework Incorporated with Enzyme-Mimicking Nickel Bis(dithiolene) Ligand for Highly Selective CO2 Electroreduction

Inspired by the exciting physical/chemical properties in metal-organic frameworks (MOFs) of the redox-active tetrathiafulvalene (TTF) ligands, nickel bis(dithiolene-dibenzoic acid), [Ni(C2S2(C6H4COOH)2)2], has been designed and developed as an inorganic analogue of the corresponding TTF-type donors (such as tetrathiafulvalene-tetrabenzoate, TTFTB), where a metal site (Ni) replaces the central C═C bond. In this work, [Ni(C2S2(C6H4COOH)2)2] and In3+ have been successfully assembled into a three-dimensional MOF, (Me2NH2+){InIII-[Ni(C2S2(C6H4COO)2)2]}·3DMF·1.5H2O (1, DMF = N,N-dimethylformamide), with satisfying chemical and thermal stabilities. With the combination of reversible redox activity and unsaturated metal sites originated from [Ni(C2S2(C6H4COOH)2)2], 1 showed a significantly enhanced performance in electrocatalytic CO2 reduction compared with the isomorphic MOF, (Me2NH2+)[InIII-(TTFTB)]·0.7C2H5OH·DMF (2, with TTFTB ligand). More importantly, by mimicking the active [NiS4] sites of formate dehydrogenase and CO-dehydrogenase, a prominently higher conversion rate and Faradaic efficiency (FE), with FEHCOO- increasing from 54.7% to 89.6% (at -1.3 V vs RHE, jHCOO- = 36.0 mA cm-2), were achieved in 1. Mechanistic investigations further confirm that [NiS4] can serve as a CO2 binding site and efficient catalytic center. This unprecedented effect of redox-active nickel dithiolene-based MOF catalysts on the performance of electroreduction of CO2 provides an important strategy for designing stable and efficient crystalline enzyme-mimicking catalysts for the conversion of CO2 into high-value chemical stocks.

Polydopamine-based multilevel molecularly imprinted nanocomposite membranes comprising metal organic frameworks for selective recognition and separation

Molecularly imprinted nanocomposite membranes with three-dimensional metal–organic frameworks (MOFs)-based structure (MINMs-TM) were successfully prepared by using propranolol as template molecule. Importantly, for the first time, polycarbonate track etch membranes had been used as the supporting surfaces to construct the polydopamine (PDA)-induced MOFs composite structure, in which the as-prepared PDA-modified surface would promote the crystallization and nucleation of ZIF-8-based composite layer. Based on the entire preparation processes of our design, the as-prepared PDA-induced ZIF-8-modified surfaces could be regarded as the imprinted-initiated units of sol–gel imprinting polymerization. Abundant recognition sits of propranolol were achieved in MINMs-TM, which showed characteristic properties of permeability and selectivity. Therefore, high adsorption capacity (41.31 mg/g) and fast adsorption equilibrium rate (within 30 min) had been successfully achieved. Meanwhile, excellent permselectivity rates (β) of MINMs-TM toward propranolol were also obtained as 5.04, 4.79 and 5.14, which MINMs-TM the successful synthesis of high-affinity and high-density propranolol-imprinted sites. Overall, for the practical selective separation and scalability, we had successfully MINMs-TM the preparation of MINMs-TM-based to selective rebinding and separation of propranolol from complex solution system and mimetic water sample, which had further confirmed the desired and potential applications of many environmental pollutants.

Magnetism and Luminescence of a MOF with Linear Mn3 Nodes Derived from an Emissive Terthiophene-Based Imidazole Linker.

A new terthiophene-based imidazole luminophore 5,5’-(1H-thieno[3,4-d]imidazole-4,6-diyl)bis(thiophene-2-carboxylic acid) (TIBTCH2, 5) was synthesized in one step from previously reported 4,6-di(thiophen-2-yl)-1H-thieno[3,4-d]imidazole (DTTI, 4), and their photophysical properties were studied and compared accordingly. Under solvothermal conditions, reacting 5 with Mn(OAc)2 yielded a new three-dimensional metal-organic framework (MOF, 6) which was structurally defined by single-crystal X-ray diffraction. In 6, all Mn(II) ions octahedrally bind to carboxylate-O atoms to form a linear Mn3 secondary building unit (SBU) that contains three distinct coordination modes. Importantly, 6 exhibits dual functional properties of ligand-based emission and metal-based magnetic behaviors.

Fabricating polyoxometalates-stabilized single-atom site catalysts in confined space with enhanced activity for alkynes diboration

Effecting the synergistic function of single metal atom sites and their supports is of great importance to achieve high-performance catalysts. Herein, we successfully fabricate polyoxometalates (POMs)-stabilized atomically dispersed platinum sites by employing three-dimensional metal-organic frameworks (MOFs) as the finite spatial skeleton to govern the accessible quantity, spatial dispersion, and mobility of metal precursors around each POM unit. The isolated single platinum atoms (Pt1) are steadily anchored in the square-planar sites on the surface of monodispersed Keggin-type phosphomolybdic acid (PMo) in the cavities of various MOFs, including MIL-101, HKUST-1, and ZIF-67. In contrast, either the absence of POMs or MOFs yielded only platinum nanoparticles. Pt1-PMo@MIL-101 are seven times more active than the corresponding nanoparticles in the diboration of phenylacetylene, which can be attributed to the synergistic effect of the preconcentration of organic reaction substrates by porous MOFs skeleton and the decreased desorption energy of products on isolated Pt atom sites.

Molybdenum Disulfide Supported on Metal-Organic Frameworks as an Ultrasensitive Layer for the Electrochemical Detection of the Ovarian Cancer Biomarker CA125.

Metal-organic frameworks (MOFs) are composed of metal ions/clusters and organic ligands, showing accessible functional sites, ultra-high porosity, and large specific surface area. Tricopper benzene-1,3,5-tricarboxylate (CuBTC), as a three-dimensional MOF architecture with an open and robust micro-/nanoconfiguration, possesses excellent catalytic performance and superior electric conductivity as compared to bulk MOF. In this study, CuBTC was used as a substrate on which molybdenum disulfide (MoS2) was in situ constructed by a hydrothermal reaction to enhance the electron- and ion-transfer capability. Then, gold nanoparticles (AuNPs) were electroreduced on a CuBTC@MoS2-modified electrode by linear sweep voltammetry for strengthening the connection between CA125 antibodies (CA125 Ab) and the substrate material. Due to the synergistic effect of CuBTC@MoS2 and AuNPs, our biosensor showed excellent electrochemical performance. Subsequently, CuBTC@MoS2-AuNPs/CA125 Ab-functionalized electrodes were used for the detection of the ovarian cancer biomarker CA125 from 0.5 mU/mL to 500 U/mL by differential pulse voltammetry. The results showed that the peak current decreased with the increase of concentration, and there was a logistic regression relationship between peak current variation and concentration. As interfering substances, carcinoembryonic antigen, human epididymis protein 4, and bovine serum albumin were applied for specific analysis. Our biosensor showed an obviously large response signal for CA125 detection than those observed for other interfering substances. Finally, serum samples collected from five patients were tested on our sensors with good consistency toward clinical standards, showing high practicability. This work demonstrated a tactic for simultaneously integrating the nanostructure, electroconductivity, and biocompatibility to construct advanced biosensors for cancer biomarkers.

Dimensional Reduction of Lewis Acidic Metal-Organic Frameworks for Multicomponent Reactions.

Owing to hindered diffusions, the application of porous catalytic materials has been limited to relatively simple organic transformations with small substrates. Herein we report a dimensional reduction strategy to construct a two-dimensional metal-organic framework (MOF), Zr6OTf-BTB, with 96% accessible Lewis acidic sites as probed by the bulky Lewis base pivalonitrile. With nearly free substrate accessibility, Zr6OTf-BTB outperformed two three-dimensional MOF counterparts of similar Lewis acidity (Zr6OTf-BPDC and Zr6OTf-BTC) in catalyzing sterically hindered multicomponent reactions (MCRs) for the construction of tetrahydroquinoline and aziridine carboxylate derivatives with high turnover numbers (TONs). Zr6OTf-BTB was also superior to the homogeneous benchmark Sc(OTf)3 with nearly 14 times higher TON and 9 times longer catalyst lifetime. Furthermore, the topology-activity relationships in these Zr-based Lewis acidic MOFs were rationalized by comparing their Lewis acidity, numbers of Lewis acidic sites, and sterically accessible Lewis acidic sites. Zr6OTf-BTB was successfully used to construct several bioactive molecules via MCRs with excellent efficiency. This dimensional reduction strategy should allow the development of other MOF catalysts for synthetically useful and complicated organic transformations.

Construction of 2D Interdigitated Polyrotaxane Layers and their Transformation to a 3D Polyrotaxane by a Photocycloaddition Reaction between Wheels.

Following the pioneering work of Sauvage and Stoddart on rotaxanes, construction of higher dimensional polyrotaxanes in metal-organic frameworks (MOFs) via a modified protocol is challenging. We present the formation of a two-dimensional (2D) polyrotaxane and its conversion to a three-dimensional (3D) polyrotaxane MOF via a photoreaction between interdigitated "olefin wheels". For this purpose, a 2-fold entangled 2D MOF [Pb2(bpp)(sdc)2] (1), showing a 2D + 2D → 2D polyrotaxane motif, has been synthesized from the solvothermal reaction of lead(II) nitrate, 3,3'-stilbenedicarboxylic acid (H2sdc) containing an olefin group, and 1,4-bis(4-pyridyl)piperazine (bpp). The single-crystal X-ray diffraction analysis of 1 revealed that the adjacent entangled 2D layers are interdigitated, with the separation of 3.72 Å between C═C bond pairs in adjacent layers satisfying Schmidt's criteria for the occurrence of a [2 + 2] photocycloaddition reaction. Irradiation of the single crystals of 1 under UV light resulted in formation of a 3D polyrotaxane, [Pb2(bpp)(rctt-tccb)]n (2), due to a [2 + 2] photocycloaddition reaction between two wheels via a single-crystal to single-crystal transformation. The photocycloaddition and partial thermal cleavage reaction between 1 and 2 were confirmed by 1H NMR and powder X-ray diffraction (PXRD) in solution and the solid state, respectively. The present approach could contribute to the understanding of the construction of higher dimensional polyrotaxanes which are not accessible by the traditional routes.

Highly stable terbium(III)-based metal-organic framework for the detection of m-dinitroaromatics and Fe3+ in water

A highly luminescent three-dimensional terbium-based metal organic framework [Tb(cpia)(H2O)2]n·nH2O (1) has been employed for the selective detection of m-dinitroaromatics and Fe3+. Stability tests suggest that compound 1 exhibits good stability in hot water and acidic and basic conditionswithin the pH range of 4–13. The strong green emission of 1 could be efficiently quenched by 1,3-dinitrobenzene, 2,4-dinitrotoluene, 2,6-dinitrotoluene in ethanol. Significantly, compound 1 can also be used to detect 1,3-dinitrobenzene in aqueous phase with high sensitivity and low detection limit (1.89 μM), indicating the detection of m-dinitroaromatics in aqueous medium can be realized. Furthermore, compound 1 also exhibits superior luminescence quenching behavior towards Fe3+ with high sensitivity and selectivity among various metal cations. In addition, the luminescence quenching mechanisms towards different analytes are also discussed in detail. These results demonstrate that compound 1 is a promising luminescent sensor for the simultaneous selective detection of m-dinitroaromatics and Fe3+ in water.

Synthesis, structural characterization, and carbon dioxide and hydrogen adsorption of a new three-dimensional metal organic framework Zn(BTC)4

A novel three-dimensional porous metal organic framework Zn(BTC)4 (BTC = benzene-1,3,5-tricarboxylic acid) is synthesized by the solvothermal method. This structure is characterized by single-crystal X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. This metal organic framework crystallizes in a monoclinic (P2(1)/n, V = 1795.7(2) Å3, Z = 4, Dc = 1.449 mg/cm3, α = 90.00°, β = 97.2200(10)°, γ = 90.00°, a = 9.5077(5) Å, b = 16.3950(16) Å, c = 11.6119(9) Å). The thermogravimetric analysis shows the material can be stabilized up to 350 °C, then the skeleton collapses between 350~510 °C. A luminescence test shows that the material gives out strong emission at 384 and 462 nm. The hydrogen storage capacity of this metal organic framework is 2.01 wt% at 77 K and a pressure of 10 bar. The carbon dioxide storage capacity of this metal organic framework is 4.17 mmol/g at 298 K and a pressure of 10 bar.

A new metal-organic framework of 3,9-diazatetraasterane-1,5,7,11-tetracarboxylic acid-3,6,9,12-tetraphenyl with sodium ion: Synthesis, characterization and DFT calculations

A new three-dimensional metal-organic framework with regular 1D channel, [Na2(DATA)1/2(H2O)2·H2O]n, NaTADA, was synthesized by solvothermal reaction of 3,9-diazatetraasterane-1,5,7,11-tetracarboxylic acid-3,6,9,12-tetraphenyl (DATAH4) with sodium hydroxide, and characterized by X-Ray single-crystal diffraction, thermogravimetric analysis (TGA) and FT-IR spectroscopy. Besides, electronic structures analysis, including molecular frontier orbitals, molecular electrostatic potential surface distribution, were also performed basing on electronic wavefunction obtained at the same calculated level for revealing intrinsic molecular structural characteristics.

Single-Crystalline Ultrathin 2D Porous Nanosheets of Chiral Metal-Organic Frameworks.

Two-dimensional (2D) materials with highly ordered in-plane nanopores are crucial for numerous applications, but their rational synthesis and local structural characterization remain two grand challenges. We illustrate here that single-crystalline ultrathin 2D MOF nanosheets (MONs) with intrinsic porosity can be prepared by exfoliating layered metal-organic frameworks (MOFs), whose layers are stabilized by sterically bulky groups. As a result, three three-dimensional (3D) isostructural lanthanide MOFs possessing porous layer structures are constructed by coordinating metal ions with an angular dicarboxylate linker derived from chiral 1,1'-biphenyl phosphoric acid with pendant mesityl groups. The Eu-MOF is readily ultrasonic exfoliated into single-crystalline nanosheets with a thickness of ca. 6.0 nm (2 layers) and a lateral size of 1.5 × 3.0 μm2. The detailed structural information, i.e., the pore channels and individual organic and inorganic building units in the framework, is clearly visualized by a low-dose high-resolution transmission electron microscopy (HRTEM) technique. Benefiting from their ultrathin feature, the nanosheets are well embedded into the polymer matrix to form free-standing mixed-matrix membranes. In both the solution and membrane phase, the fluorescence of the MONs can be effectively quenched by a total of 17 chiral terpenes and terpenoids through supramolecular interactions with uncoordinated chiral phosphoric acids, leading to a chiral optical sensor for detecting vapor enantiomers, which is among the most challenging molecular recognition tasks.

A Cu4 cluster-based MOF as a supercapacitor electrode material with ultrahigh capacitance

Developing new pristine metal-organic framework (MOF)-based electrode material for high-performance supercapacitors is a considerable attractive task. Herein, a Cu4 cluster-based three-dimensional (3D) MOF ([Cu4(μ3-OH)2(atrz)2(1,3-BDC)3]·2H2O, Cu-atrz-BDC; atrz, 4-amino-1,2,4-triazole; 1,3-H2BDC, 1,3-benzenedicarboxylic acid) was synthesized and characterized by infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis, nitrogen adsorption-desorption, scanning electron microscopy, and X-ray photoelectron spectroscopy. The Cu-atrz-BDC firstly was used as an electrode material for supercapacitor. In a three-electrode system, the Cu-atrz-BDC electrode exhibited ultrahigh specific capacitance of 5525 F g−1 at 1 A g−1 and its specific capacitance can also keep about 886 F g−1 after 1000 cycles at 3 A g−1. Importantly, the Cu-atrz-BDC as the positive electrode and the rGO as the negative electrode were assembled into an asymmetric supercapacitor with excellent cycling stability, displaying the maximum energy density of 9.96 Wh kg−1 at a power density of 0.81 kW kg−1. The high supercapacitive performance might be ascribed to its porous three-dimensional structure, the nanosized particles, and better conductivity.