A New Strategy for Storage and Transportation of Sensitive High‐Energy Materials: Guest‐Dependent Energy and Sensitivity of 3D Metal–Organic‐Framework‐Based Energetic Compounds

Reaction of Co(II) with the nitrogen‐rich ligand N,N‐bis(1H‐tetrazole‐5‐yl)‐amine (H₂bta) leads to a mixed‐valence, 3D, porous, metal–organic framework (MOF)‐based, energetic material with the nitrogen content of 51.78%, [Co₉(bta)₁₀(Hbta)₂(H₂O)₁₀]_n?(22 H₂O)_n ( 1 ). Compound 1 was thermohydrated to produce a new, stable, energetic material with the nitrogen content of 59.85% and heat of denotation of 4.537 kcal cm^?3, [Co₉(bta)₁₀(Hbta)₂(H₂O)₁₀]_n ( 2 ). Sensitivity tests show that 2 is more sensitivity to external stimuli than 1 , reflecting guest‐dependent energy and sensitivity of 3D, MOF‐based, energetic materials. Less‐sensitive 1 can be regarded as a more safe form for storage and transformation to sensitive 2 .     

Two‐dimensional π‐conjugated metal‐organic framework with high electrical conductivity for electrochemical sensing

A two‐dimensional π‐conjugated metal‐organic framework (MOF) with long‐range delocalized electrons has been prepared and applied as modified electrode material without further post‐modification. The MOF (Cu₃(HHTP)₂) is composed of Cu(II) centers and a redox‐active linker (2,3,6,7,10,11‐hexahydroxytriphenylene, HHTP). Compared to most MOFs, Cu₃(HHTP)₂ displays higher electrical conductivity and charge storage capacity owing to the collective effect of metal ions and aromatic ligands with π–π conjugation. In order to confirm the superior properties of this material, the electrochemical detection of dopamine (DA) was conducted and the satisfactory results were obtained. The currents increase linearly with the concentration of DA in the range 5.0 × 10^?8 to 2.0 × 10^?4 M with a detection limit of 5.1 nM. Furthermore, Cu₃(HHTP)₂ presents high selectivity and applicability in serum samples for electrochemical DA sensing. Overall, this material has excellent potential as a promising platform for establishing an MOF‐based electrochemical sensor.     

A CdII‐Based Metal‐Organic Framework with pcu Topology as Turn‐On Fluorescent Sensor for Al3+

A new metal‐organic framework (MOF) {[Cd₂(bbib)₂(ndc)₂]?2DMF}_n ( JXUST‐1 ) (bbib=1,3‐bis(benzimidazolyl)benzene, H₂ndc=1,4‐naphthalenedicarboxylic acid, DMF=N,N‐dimethylformamide) has been solvothermally synthesized and characterized by single‐crystal X‐ray diffraction, PXRD, TGA, IR and elemental analysis. JXUST‐1 exhibits a three‐dimensional 6‐connected pcu topology with a Schläfli symbol {4¹².6³} constructed by [Cd₂(CO₂)₃] secondary building units. Fluorescence studies show that this MOF can sensitively and selectively recognize Al³⁺ via a fluorescence enhancement effect, and the detection limit is 0.048 ppm. Furthermore, JXUST‐1 displays relatively good thermal and chemical stabilities as well as reusability. All these results suggest JXUST‐1 to be a highly selective and recyclable luminescent sensing material for the detection of Al³⁺.     

Air‐Free Synthesis of a Ferrous Metal‐Organic Framework Featuring HKUST‐1 Structure and its Mössbauer Spectrum

Single crystals of the Fe^II metal‐organic framework (MOF) with 1,3,5‐benzenetricarboxylate (BTC) as a linker were solvothermally obtained under air‐free conditions. X‐ray diffraction analysis of the crystals demonstrated a structure for Fe^II‐MOF analogous to that of [Cu₃(BTC)₂] (HKUST‐1). Unlike HKUST‐1, however, the Fe^II‐MOF did not retain permanent porosity after exchange of guest molecules. The Mössbauer spectrum of the Fe^II‐MOF was recorded at 80 K in zero field yielding an apparent quadrupole splitting of ΔE_Q = 2.43 mm · s^–1, and an isomer shift of δ = 1.20 mm · s^–1, consistent with high‐spin central iron(II) atoms. Air exposure of the Fe^II‐MOF was found to result in oxidation of the metal atoms to afford Fe^III. These results demonstrate that Fe^II‐based MOFs can be prepared in similar fashion to the [Cu₃(BTC)₂], but that they lack permanent porosity when degassed.     

Selective Sensing of Fe3+ and Al3+ Ions and Detection of 2,4,6‐Trinitrophenol by a Water‐Stable Terbium‐Based Metal–Organic Framework

A water‐stable luminescent terbium‐based metal–organic framework (MOF), {[Tb(L₁)_1.5(H₂O)] ? 3 H₂O}_n (Tb‐MOF), with rod‐shaped secondary building units (SBUs) and honeycomb‐type tubular channels has been synthesized and structurally characterized by single‐crystal X‐ray diffraction. The high green emission intensity and the microporous nature of the Tb‐MOF indicate that it can potentially be used as a luminescent sensor. In this work, we show that Tb‐MOF can selectively sense Fe³⁺ and Al³⁺ ions from mixed metal ions in water through different detection mechanisms. In addition, it also exhibits high sensitivity for 2,4,6‐trinitrophenol (TNP) in the presence of other nitro aromatic compounds in aqueous solution by luminescence quenching experiments.     

A Calixarene‐Based Metal–Organic Framework for Highly Selective NO2 Detection

A calixarene‐based metal–organic framework (Zr‐cal, [Zr₆O₄(OH)₄(FA)₆]₂(cal)₃], FA=formate, cal=1,3‐alt‐25,26,27,28‐tetrakis[(carboxy)methoxy]calixarene) was synthesized and characterized by single‐crystal X‐ray diffraction. The three‐dimensional framework is a 4,6‐connected network of gar topology and exhibits two equal but nonintersecting three‐dimensional pore systems. It has a specific BET surface area of 670 m² g^?1, and the calixarene cavities are accessible through the pore systems. The exposed calixarenes can be used for the visual detection and encapsulation of NO₂ through the formation of deeply colored charge–transfer complexes inside the MOF. The highly selective complexation was analyzed by UV/Vis and IR spectroscopy, and the stability of the material was confirmed by powder X‐ray diffraction and ¹H NMR spectroscopy. Finally, the MOF was used as a sensor material in a home‐made sensor cell and showed high sensitivity for NO₂.     

Unprecedented Second‐Timescale Blue/Green Emissions and Iodine‐Uptake‐Induced Single‐Crystal‐to‐Single‐Crystal Transformation in ZnII/CdII Metal–Organic Frameworks

The long‐persistent phosphorescent metal–organic framework (MOF) is a kind of highly desirable but rare material. Here, two new molecular MOF materials, {[Zn(tipa)Cl] ? NO₃ ? 2 DMF}_n ( 1 ) and {[Cd₂(tipa)₂Cl₄] ? 6 DMF}_n ( 2 ) (tipa=tri(4‐imidazolylphenyl)amine), which have 3D twofold interpenetrated ( utp ) and 2D noninterpenetrated ( kgd ) topologies, respectively, are reported. They exhibit unexpected long‐persistent emissions yet reported: At 77 K, they persist in glowing after stopping the UV irradiation on a timescale up to seconds at 77 K, which can be detected by the naked eye (ca. 2 s). Compounds 1 and 2 also undergo single‐crystal‐to‐single‐crystal (SC‐SC) transformations through different routes; a simple anion‐exchange route for 1 and a complicated replacement of μ₁‐Cl^? ions by DMF molecules accompanying I₃^? captured in the void for 2 .     

Structural analysis of interpenetrated methyl‐modified MOF‐5 and its gas‐adsorption properties

The first example of an interpenetrated methyl‐modified MOF‐5 with the formula Zn₄O(DMBDC)₃(DMF)₂, where DMBDC^2? is 2,5‐dimethylbenzene‐1,4‐dicarboxylate and DMF is N,N‐dimethylformamide (henceforth denoted as Me₂MOF‐5‐int ), namely, poly[tris(μ₄‐2,5‐dimethylbenzene‐1,4‐dicarboxylato)bis(N,N‐dimethylformamide)‐μ₄‐oxido‐tetrazinc(II)], [Zn₄(C₁₀H₈O₄)₃O(C₃H₇NO)₂]_n, has been obtained from a solvothermal synthesis of 2,5‐dimethylbenzene‐1,4‐dicarboxylic acid and Zn(NO₃)₂·6H₂O in DMF. A systematic study revealed that the choice of solvent is of critical importance for the synthesis of phase‐pure Me₂MOF‐5‐int , which was thoroughly characterized by single‐crystal and powder X‐ray diffraction (PXRD), as well as by gas‐adsorption analyses. The Brunauer–Emmett–Teller surface area of Me₂MOF‐5‐int (660 m² g^?1), determined by N₂ adsorption, is much lower than that of nonpenetrated Me₂MOF‐5 (2420 m² g^?1). However, Me₂MOF‐5‐int displays an H₂ uptake capacity of 1.26 wt% at 77 K and 1.0 bar, which is comparable to that of non‐interpenetrated Me₂MOF‐5 (1.51 wt%).     

Copper‐based Metal‐organic Framework Applied in the Development of an Electrochemical Biomimetic Sensor for Catechol Determination

In this study, the synthesis and characterization of a Cu‐based metal‐organic framework (MOF) [Cu₃(BTC)₂(H₂O)₃]_n (where BTC=benzene‐1,3,5‐tricarboxylate), known as HKUST‐1, were performed. The Cu‐MOF was applied in the modification of a carbon paste to obtain a biomimetic sensor for the electrochemical determination of catechol. Kinetic assays confirmed that the Cu‐MOF acts as a catalyst for the oxidation of catechol and it can be considered as a catechol oxidase mimetic. Under optimized conditions, the calibration curve for catechol presented a linear range of 8.0×10⁻⁷ to 3.2×10⁻⁵ mol L⁻¹, with detection limit of=1.0×10⁻⁷ mol L⁻¹. The sensor demonstrated good intra‐day repeatability and inter‐electrode reproducibility (relative standard deviations of 3.8 % (n=10) and 4.3 % (n=6), respectively). In the selectivity study, an adequate peak‐to‐peak separation was observed for hydroquinone and uric acid in relation to catechol, demonstrating that this sensor has the potential for use in the simultaneous determination of these compounds. This sensor was successfully applied in the determination of catechol in water samples.     

Surface‐Anchored MOF‐Based Photonic Antennae

The loading of a metal‐organic framework (MOF), [Cu₃(btc)₂xH₂O] HKUST‐1, with europium β‐diketonate complexes is studied with the goal to using the porous molecular framework as a photonic antenna. Whereas loading of HKUST‐1 powder particles produced via the conventional solvothermal synthesis method was strongly hindered, for HKUST‐1 SURMOFs, thin MOF films fabricated using the liquid phase epitaxy method, a high filling factor can be achieved. The optical properties of the HKUST‐1‐MOFs before and after loading were analysed with the aid of luminescence spectroscopy. Careful analysis of the absorption spectra reveals the presence of an effective energy transfer between the HKUST‐1 framework and the Eu³⁺ centers.     

A Multi‐responsive Regenerable Europium–Organic Framework Luminescent Sensor for Fe3+, CrVI Anions,and Picric Acid

A novel luminescent microporous lanthanide metal–organic framework (Ln‐MOF) based on a urea‐containing ligand has been successfully assembled. Structural analysis revealed that the framework features two types of 1D channels, with urea N?H bonds projecting into the pores. Luminescence studies have revealed that the Ln‐MOF exhibits high sensitivity, good selectivity, and a fast luminescence quenching response towards Fe³⁺, Cr^VI anions, and picric acid. In particular, in the detection of Cr₂O₇^2? and picric acid, the Ln‐MOF can be simply and quickly regenerated, thus exhibiting excellent recyclability. To the best of our knowledge, this is the first example of a multi‐responsive luminescent Ln‐MOF sensor for Fe³⁺, Cr^VI anions, and picric acid based on a urea derivative. This Ln‐MOF may potentially be used as a multi‐responsive regenerable luminescent sensor for the quantitative detection of toxic and harmful substances.     

A Layered Hybrid Perovskite Solar‐Cell Absorber with Enhanced Moisture Stability

Two‐dimensional hybrid perovskites are used as absorbers in solar cells. Our first‐generation devices containing (PEA)₂(MA)₂[Pb₃I₁₀] ( 1 ; PEA=C₆H₅(CH₂)₂NH₃⁺, MA=CH₃NH₃⁺) show an open‐circuit voltage of 1.18 V and a power conversion efficiency of 4.73 %. The layered structure allows for high‐quality films to be deposited through spin coating and high‐temperature annealing is not required for device fabrication. The 3D perovskite (MA)[PbI₃] ( 2 ) has recently been identified as a promising absorber for solar cells. However, its instability to moisture requires anhydrous processing and operating conditions. Films of 1 are more moisture resistant than films of 2 and devices containing 1 can be fabricated under ambient humidity levels. The larger bandgap of the 2D structure is also suitable as the higher bandgap absorber in a dual‐absorber tandem device. Compared to 2 , the layered perovskite structure may offer greater tunability at the molecular level for material optimization.     

Tetrazine Chromophore‐Based Metal–Organic Frameworks with Unusual Configurations: Synthetic,Structural, Theoretical,Fluorescent, and Nonlinear Optical Studies

Three unusual three‐dimensional (3D) tetrazine chromophore‐based metal–organic frameworks (MOFs) {(Et₄N)[WS₄Cu₃(CN)₂(4,4′‐pytz)_0.5]}_n ( 1 ), {[MoS₄Cu₄(CN)₂(4,4′‐pytz)₂] ? CH₂Cl₂}_n ( 2 ), and {[WS₄Cu₃(4,4′‐pytz)₃] ? [N(CN)₂]}_n ( 3 ; 4,4′‐pytz=3,6‐bis(4‐pyridyl)tetrazine) have been synthesized and characterized by using FTIR and UV/Vis spectroscopy, elemental analysis, powder X‐ray diffraction, gel permeation chromatography, steady‐state fluorescence, and thermogravimetric analysis; their identities were confirmed by single‐crystal X‐ray diffraction studies. MOF 1 possesses the first five‐connected M/S/Cu (M=Mo, W) framework with an unusual 3D (4⁴?6⁶) topology constructed from T‐shaped [WS₄Cu₃]⁺ clusters as nodes and single CN^?/4,4′‐pytz bridges as linkers. MOF 2 features a novel 3D MOF structure with (4²⁰?6⁸) topology, in which the bridging 4,4′‐pytz ligands exhibit unique distorted arch structures. MOF 3 displays the first 3D MOF structure based on flywheel‐shaped [WS₄Cu₃]⁺ clusters with a non‐interpenetrating honeycomb‐like framework and a heavily distorted “ACS” topology. Steady‐state fluorescence studies of 1 – 3 reveal significant fluorescence emissions. The nonlinear optical (NLO) properties of 1 – 3 were investigated by using a Z‐scan technique with 5 ns pulses at λ=532 nm. The Z‐scan experimental results show that the π‐delocalizable tetrazine‐based 4,4′‐pytz ligands contribute to the strong third‐order NLO properties exhibited by 1 – 3 . Time‐dependent density functional theory studies afforded insight into the electronic transitions and spectral characterization of these functionalized NLO molecular materials.     

A Novel Electrochemical Sensor Based on Copper‐based Metal‐Organic Framework for the Determination of Dopamine

A glassy carbon electrode (GCE) modified with a copper‐based metal‐organic framework (MOF) [HKUST‐1, HKUST‐1 = Cu₃(BTC)₂ (BTC = 1,3,5‐benzenetricarboxylicacid)] was developed as a highly sensitive and simple electrochemical sensor for the determination of dopamine (DA). The MOF was prepared by a hydrothermal process, and the morphology and crystal phase of the MOF were characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD), respectively. Meanwhile, the electrochemical performance was investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Under optimized conditions, the modified electrode showed excellent electrocatalytic activity and high selectivity toward DA. The linear response range was from 5.0 × 10⁻⁷ to 1.0 × 10⁻⁴ M and the detection limit was as low as 1.5 × 10⁻⁷ M. Moreover, the electrochemical sensor was used to detect DA in real samples with excellent results. MOF‐based sensors hold great promise for routine sensing applications in the field of electrochemical sensing.     

Direct Observation of Molecular‐Level Template Action Leading to Self‐Assembly of a Porous Framework

The molecular steps involved in the self‐assembly of Cu₃(BTC)₂ (BTC=1,3,5‐benzenetricarboxylic acid) metal–organic frameworks that enclose Keggin‐type H₃PW₁₂O₄₀ heteropolyacid molecules were unraveled by using solution ¹⁷O, ³¹P, and ¹⁸³W NMR spectroscopy, small‐angle X‐ray scattering, near‐IR spectroscopy, and dynamic light scattering. In aqueous solution, complexation of Cu²⁺ ions with Keggin‐type heteropolyacids was observed. Cu²⁺ ions are arranged around the Keggin structure so that linking through benzenetricarboxylate groups results in the formation of the Cu₃(BTC)₂ MOF structure HKUST‐1. This is a unique instance in which a templating mechanism that relies on specific molecular‐level matching and leads to explicit nanoscale building units can be observed in situ during formation of the synthetic nanoporous material.     

Influence of the Base on Pd@MIL‐101‐NH2(Cr) as Catalyst for the Suzuki–Miyaura Cross‐Coupling Reaction

The chemical stability of metal–organic frameworks (MOFs) is a major factor preventing their use in industrial processes. Herein, it is shown that judicious choice of the base for the Suzuki–Miyaura cross‐coupling reaction can avoid decomposition of the MOF catalyst Pd@MIL‐101‐NH₂(Cr). Four bases were compared for the reaction: K₂CO₃, KF, Cs₂CO₃ and CsF. The carbonates were the most active and achieved excellent yields in shorter reaction times than the fluorides. However, powder XRD and N₂ sorption measurements showed that the MOF catalyst was degraded when carbonates were used but remained crystalline and porous with the fluorides. XANES measurements revealed that the trimeric chromium cluster of Pd@MIL‐101‐NH₂(Cr) is still present in the degraded MOF. In addition, the different countercations of the base significantly affected the catalytic activity of the material. TEM revealed that after several catalytic runs many of the Pd nanoparticles (NPs) had migrated to the external surface of the MOF particles and formed larger aggregates. The Pd NPs were larger after catalysis with caesium bases compared to potassium bases.     

MOF‐on‐MOF: Oriented Growth of Multiple Layered Thin Films of Metal–Organic Frameworks

The precise alignment of multiple layers of metal–organic framework (MOF) thin films, or MOF‐on‐MOF films, over macroscopic length scales is presented. The MOF‐on‐MOF films are fabricated by epitaxially matching the interface. The first MOF layer (Cu₂(BPDC)₂, BPDC=biphenyl‐4,4′‐dicarboxylate) is grown on an oriented Cu(OH)₂ film by a “one‐pot” approach. Aligned second (Cu₂(BDC)₂, BDC=benzene 1,4‐dicarboxylate, or Cu₂(BPYDC)₂, BPYDC=2,2′‐bipyridine‐5,5′‐dicarboxylate) MOF layers can be deposited using liquid‐phase epitaxy. The co‐orientation of the MOF films is confirmed by X‐ray diffraction. Importantly, our strategy allows for the synthesis of aligned MOF films, for example, Cu₂(BPYDC)₂, that cannot be grown on a Cu(OH)₂ surface. We show that aligned MOF films furnished with Ag nanoparticles show a unique anisotropic plasmon resonance. Our MOF‐on‐MOF approach expands the chemistry of heteroepitaxially oriented MOF films and provides a new toolbox for multifunctional porous coatings.     

A Three‐dimensional DyIII‐based Metal‐organic Framework: Smart Drug Carrier and Anti‐lung Cancer Activity

A 3D lanthanide metal‐organic framework (MOF) with the formula [Dy₂(L)₂(H₂O)₂]_n ( 1 ) (H₃L = biphenyl‐3,4′,5‐tricarboxylic acid) was synthesized under solvothermal conditions and structurally characterized by elemental analysis, powder X‐ray diffraction analysis, infrared spectroscopy, and single‐crystal X‐ray diffraction analysis. Compound 1 features a 3D porous framework based on 1D rod‐shaped Dy^III‐carboxylate chains. The efficient encapsulation and controllable release of an anticancer drug (5‐Fu) make it a promising drug delivery host. Furthermore, the GCMC simulation was used to probe the drug‐framework interaction at the atomic lever. The in vitro anti‐lung cancer activity of 1 and 5‐Fu loaded 1a were also evaluated using MTT assay.     

A Methylthio‐Functionalized‐MOF Photocatalyst with High Performance for Visible‐Light‐Driven H2 Evolution

Recently, the emergence of photoactive metal–organic frameworks (MOFs) has given great prospects for their applications as photocatalytic materials in visible‐light‐driven hydrogen evolution. Herein, a highly photoactive visible‐light‐driven material for H₂ evolution was prepared by introducing methylthio terephthalate into a MOF lattice via solvent‐assisted ligand‐exchange method. Accordingly, a first methylthio‐functionalized porous MOF decorated with Pt co‐catalyst for efficient photocatalytic H₂ evolution was achieved, which exhibited a high quantum yield (8.90 %) at 420 nm by use sacrificial triethanolamine. This hybrid material exhibited perfect H₂ production rate as high as 3814.0 μmol g^?1 h^?1, which even is one order of magnitude higher than that of the state‐of‐the‐art Pt/MOF photocatalyst derived from aminoterephthalate.     

Microwave‐Assisted Synthesis of HKUST‐1 and Functionalized HKUST‐1‐@H3PW12O40: Selective Adsorption of Heavy Metal Ions in Water Analyzed with Synchrotron Radiation

A simple, rapid and efficient synthesis of the metal‐organic framework (MOF) HKUST‐1 [Cu₃(1,3,5‐benzene‐tri‐carboxilic‐acid)₂] by microwave irradiation is described, which afforded a homogeneous and highly selective material. The unusually short time to complete the synthesis by microwave irradiation is mainly attributable to rapid nucleation rather than to crystal growth rate. Using this method, HKUST‐1‐MW (MW=microwave) could be prepared within 20 min, whereas by hydrothermal synthesis, involving conventional heating, the preparation time is 8 h. Work efficiency was improved by the good performance of the obtained HKUST‐1‐MW which exhibited good selective adsorption of heavy metal ions, as well as a remarkably high adsorption affinity and adsorption capacity, but no adsorption of Hg²⁺ under the same experimental conditions. Of particular importance is the preservation of the structure after metal‐ion adsorption, which remained virtually intact, with only a few changes in X‐ray diffraction intensity and a moderate decline in surface area. Synthesis of the polyoxometalate‐containing HKUST‐1‐MW@H₃PW₁₂O₄₀ afforded a MOF with enhanced stability in water, due to the introduced Keggin‐type phosphotungstate, which systematically occluded in the cavities constituting the walls between the mesopores. Different Cu/W ratios were investigated according to the extrusion rate of cooper ions concentration, without significant structural changes after adsorption. The MOFs obtained feature particle sizes between 10–20 μm and their structures were determined using synchrotron‐based X‐ray diffraction. The results of this study can be considered important for potentially wider future applications of MOFs, especially to attend environmental issues.