Ultra‐Tuning of the Rare‐Earth fcu‐MOF Aperture Size for Selective Molecular Exclusion of Branched Paraffins

Using isoreticular chemistry allows the design and construction of a new rare‐earth metal (RE) fcu ‐MOF with a suitable aperture size for practical steric adsorptive separations. The judicious choice of a relatively short organic building block, namely fumarate, to bridge the 12‐connected RE hexanuclear clusters has afforded the contraction of the well‐defined RE‐ fcu ‐MOF triangular window aperture, the sole access to the two interconnected octahedral and tetrahedral cages. The newly constructed RE (Y³⁺ and Tb³⁺) fcu ‐MOF analogues display unprecedented total exclusion of branched paraffins from normal paraffins. The resultant window aperture size of about 4.7 Å, regarded as a sorbate‐size cut‐off, enabled a complete sieving of branched paraffins from normal paraffins. The results are supported by collective single gas and mixed gas/vapor adsorption and calorimetric studies.     

A Metal–Organic Framework Containing Unusual Eight‐Connected Zr–Oxo Secondary Building Units and Orthogonal Carboxylic Acids for Ultra‐sensitive Metal Detection

Two metal–organic frameworks (MOFs) with Zr–oxo secondary building units (SBUs) were prepared by using p,p′‐terphenyldicarboxylate (TPDC) bridging ligands pre‐functionalized with orthogonal succinic acid (MOF‐ 1 ) and maleic acid groups (MOF‐ 2 ). Single‐crystal X‐ray structure analysis of MOF‐ 1 provides the first direct evidence for eight‐connected SBUs in UiO‐type MOFs. In contrast, MOF‐ 2 contains twelve‐connected SBUs as seen in the traditional UiO MOF topology. These structural assignments were confirmed by extended X‐ray absorption fine structure (EXAFS) analysis. The highly porous MOF‐ 1 is an excellent fluorescence sensor for metal ions with the detection limit of <0.5 ppb for Mn²⁺and three to four orders of magnitude greater sensitivity for metal ions than previously reported luminescent MOFs.     

A Water‐Stable Terbium(III)–Organic Framework as a Chemosensor for Inorganic Ions,Nitro‐Containing Compounds and Antibiotics in Aqueous Solutions

Effective detection of organic/inorganic pollutants, such as antibiotics, nitro‐compounds, excessive Fe³⁺ and MnO₄^?, is crucial for human health and environmental protection. Here, a new terbium(III)–organic framework, namely [Tb(TATAB)(H₂O)]?2H₂O ( Tb‐MOF , H₃TATAB=4,4′,4′′‐s‐triazine‐1,3,5‐triyltri‐m‐aminobenzoic acid), was assembled and characterized. The Tb‐MOF exhibits a water‐stable 3D bnn framework. Due to the existence of competitive absorption, Tb‐MOF has a high selectivity for detecting Fe³⁺, MnO₄^?, 4‐nirophenol and nitroimidazole (ronidazole, metronidazole, dimetridazole, ornidazole) in aqueous through luminescent quenching. The results suggest that Tb‐MOF is a simple and reliable reagent with multiple sensor responses in practical applications. To the best of our knowledge, this work represents the first Tb^III‐based MOF as an efficient fluorescent sensor for detecting metal ions, inorganic anions, nitro‐compounds, and antibiotics simultaneously.     

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.     

Polyisobutylene‐based polyurethanes. VIII. Polyurethanes with ‐O‐S‐PIB‐S‐O‐ soft segments

We describe the synthesis, characterization, and select properties of a novel polyurethane (PU) prepared using a new polyisobutylene diol, HO‐CH₂CH₂‐S‐PIB‐S‐CH₂CH₂‐OH, soft segment and conventional hard segments. The diol is synthesized by terminal functionalization of ally‐telechelic PIB followed by low‐cost thiol‐ene click chemistry. Properties of ‐S‐ containing PU (PIB_S‐PU) containing 72.5% PIB were investigated and compared to similar PUs made with HO‐PIB‐OH (PIB_O‐PU). Hydrolytic resistance was studied by contact with phosphate‐buffered saline, oxidative resistance by immersing in concentrated HNO₃, and metal ion oxidation resistance by exposure to CoCl₂/H₂O₂. Hydrolytic and oxidative resistances of PIB_S‐PU and PIB_O‐PU are similar and superior to a commercial PDMS‐based PU, Elast‐Eon? E2A. According to ¹H NMR spectroscopy the ‐S‐ in PIB_S‐PUs remained unchanged upon treatment with HNO₃, however, oxidized mainly to ‐SO₂‐ by CoCl₂/H₂O_2. Static mechanical properties of PIB_S‐PU and PIB_O‐PU are similar, except creep resistance of PIB_S‐PU is surprisingly superior. The thermal stability of PIB_S‐PUs is ～15 °C higher than that of PIB_O‐PU. FTIR spectroscopy indicates H bonded S atoms (N‐H…S) between soft and hard segments, which noticeably affect properties. DSC and XRD studies suggest random low‐periodicity crystals dispersed within a soft matrix. Energy dispersive X‐ray spectroscopy–scanning electron microscopy indicates homogeneous distribution of S atoms on PIB_S‐PU surfaces. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1119–1131     

Layer‐by‐Layer Assembled Conductive Metal–Organic Framework Nanofilms for Room‐Temperature Chemiresistive Sensing

The utility of electronically conductive metal–organic frameworks (EC‐MOFs) in high‐performance devices has been limited to date by a lack of high‐quality thin film. The controllable thin‐film fabrication of an EC‐MOF, Cu₃(HHTP)₂, (HHTP=2,3,6,7,10,11‐hexahydroxytriphenylene), by a spray layer‐by‐layer liquid‐phase epitaxial method is reported. The Cu₃(HHTP)₂ thin film can not only be precisely prepared with thickness increment of about 2 nm per growing cycle, but also shows a smooth surface, good crystallinity, and high orientation. The chemiresistor gas sensor based on this high‐quality thin film is one of the best room‐temperature sensors for NH₃ among all reported sensors based on various materials.     

A Nitro‐Functionalized Metal–Organic Framework as a Reaction‐Based Fluorescence Turn‐On Probe for Rapid and Selective H2S Detection

The toxic gas H₂S has recently emerged as one of the important signaling molecules in biological systems. Thus understanding the production, distribution, and mode of action of H₂S in biological system is important, but the fleeting and reactive nature of H₂S makes it a daunting task. Herein we report a biocompatible, nitro‐functionalized metal–organic framework as reaction‐based fluorescence turn‐on probe for fast and selective H₂S detection. The selective turn‐on performance of MOF remains unaffected even in presence of competing biomolecules.     

A Versatile AlIII‐Based Metal–Organic Framework with High Physicochemical Stability

A unique Al^III‐based metal–organic framework (467‐MOF) with two types of square channels has been designed and synthesized by using a flexible tricarboxylate ligand under solvothermal conditions. 467‐MOF exhibits superior thermal and chemical stability and, moreover, shows high CO₂ sorption selectivity over H₂, with a selectivity, based on the ideal adsorbed solution theory (IAST) of approximately 45 at 273 or 293 K. Furthermore, its solvent‐dependent photoluminescence makes it an applicable sensor in the detection of nitrobenzene explosives through fluorescence quenching.     

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.     

A Recyclable bi‐functional Luminescent Zinc (II) metal–organic framework as highly selective and sensitive sensing probe for nitroaromatic explosives and Fe3+ ions

By introducing carboxyl tag to the aromatic ligands system and borrowing the organic template open framework idea, a stable fluorescent Zn metal–organic framework was successfully prepared through a rigid ligand H₆L (3,5‐bis‐(3‐carboxyphenoxy)benzoic acid) under hydrothermal conditions. The selectivity and sensitivity of the Zn‐MOF to metal ions and nitro‐aromatic compounds (NACs) were investigated by fluorescence quenching. And the Zn‐MOF showed a high sensibility of nitro‐aromatic compounds (NACs) and Fe³⁺ ions, especially for 4‐(4‐nitropheny lazo) resorcinol (NPLR). More importantly, the detection limit of the Zn‐MOF for detecting NPLR solution was found to be 1.71 ppb. Moreover, this sensor is remarkable recyclable and is promisingly applied for rapid, on‐site and sensing of explosive residuals.     

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.     

Template‐Directed Self‐Recognition of Alkyl‐Bridged Bis(catechol) Ligands in the Formation of Helicate‐Type Complexes

A controlling influence on the self‐assembly in the complexation reaction of a mixture of methylene‐ and ethylene‐bridged bis(catechol) ligands ( 1 ‐H₄ and 2 ‐H₄, respectively) with titanium(IV ) ions is exerted by alkali metal cations (see scheme). Thus, not a complicated mixture of complexes, but as a result of a self‐recognition of the ligands only well‐defined products are formed.     

Nano‐ and Microstructure Fabrication by Using a Three‐Component System

Two‐component amphiphiles based on hydrogen‐bonded complexes between terephthaloylbisalanine (H₂TBA) and dodecylamine (DA) are able to self‐assemble into nano‐ and microsized superstructures in an aqueous solvent. It is possible to modulate the morphology of these self‐assembled superstructures by modifying the composition of the complexes, which can be achieved by changing the molar ratio of the two components or by changing the chirality of H₂TBA. For example, right‐handed microhelical ribbon structures were formed with L ‐TBA_1.0DA_2.0, whereas in the case of rac‐TBA_1.0DA_2.0, flat ribbonlike structures were observed. Although L ‐TBA_1.0DA_1.0 exhibited entangled fibrous structures, rac‐TBA_1.0DA_1.0 exhibited wire structures. Different ratios of H₂TBA and DA were self‐assembled into fiber‐, wire‐, and tubulelike superstructures, as well as monoclinic, columnar, and lamellar aggregation patterns. The self‐assembled superstructures of TBA_xDA_y were significantly changed by adding metal ions. Transition metal (Cd^II, Co^II, and Zn^II) complexes with L ‐TBA_xDA_y self‐assembled into rod‐, tubule‐, wire‐, and platelike superstructures. Metal‐ion complexes with rac‐TBA_xDA_y exhibited different superstructures. Our work suggests that it is possible to fabricate a wide variety of nano‐ and microsized superstructures by using two‐ and three‐component amphiphiles.     

Hybridized Polyoxometalate‐Based Metal–Organic Framework with Ketjenblack for the Nonenzymatic Detection of H2O2

The rational design and development of efficient and affordable enzyme‐free electrocatalysts for electrochemical detection are of great significance for the large‐scale applications of sensor materials, and have aroused increasing research interest. Herein, we report that a typical polyoxometalate (POM)‐based metal–organic framework (NENU5) that was hybridized with ketjenblack (KB) was a highly efficient electrochemical catalyst that could be used for the highly sensitive nonenzymatic detection of H₂O₂. The composite catalyst exhibited superb electrochemical detection performance towards H₂O₂, including a broad linear range from 10–50 mm , a low detection limit of 1.03 μm , and a high sensitivity of 33.77 μA mm ⁻¹, as well as excellent selectivity and stability. These excellent electrocatalytic properties should be attributed to the unique redox activity of the POM, the high specific surface area of the metal–organic framework (MOF), the strong conductivity of KB, and the synergistic effects of the multiple components in the composites during the electrolysis of H₂O₂. This work provides a new pathway for the exploration of nonenzymatic electrochemical sensors.     

Highly sensitive and selective detect of p‐arsanilic acid with a new water‐stable europium metal–organic framework

The p‐arsanilic acid (p‐ASA), as an aromatic organoarsenic compounds, had received considerable concerns for their potential toxicity and carcinogenic properties. It was essential to detect p‐ASA with a facile method. In this paper, an europium based fluorescent metal–organic framework (MOF) [Eu₂(clhex)·2H₂O)]·H₂O ( BUC‐69 ) was successfully prepared under hydrothermal conditions with 1,2,3,4,5,6‐cyclohexanehexacarboxylic acid (H₆clhex) as organic linker. BUC‐69 displayed superior fluorescence capability to achieve selective and sensitive detection toward p‐ASA in water, which presented the first example of a MOF‐based sensor to detect p‐ASA. BUC‐69 showed excellent chemical stability in solutions under pH ranging from 4 to 12, which makes it be a potential sensor both in acidity and alkalinity condition. Significantly, BUC‐69 performed well in fluorescent sensing of p‐ASA at a low concentration (10^?6 M) in the simulated wastewater prepared with real lake water, and the results were comparable to the values detected by Inductively Coupled Plasma Optical Emission Spectrometer (ICP‐OES). The corresponding mechanism of fluorescent sensing toward p‐ASA with BUC‐69 was proposed and affirmed.     

Assembling Quasi‐enantiomeric Octahedral Complexes of Different Metals via Quasi‐racemate Crystallization

Aiming at a general methodology for binary co‐assembly of complexes of different metals through quasiracemate crystallization, the hexadentate ligand 1 comprised of the chiral bipyrrolidine core and two bipyridine peripheral arms is introduced. Ligand 1 was found to bind in a fully diastereoselective and uniform mode around Zn^II, Fe^II and Cd^II giving coordinatively inert octahedral “chiral‐at‐metal” complexes with the Δ₄Λ₂/Λ₄Δ₂ wrapping mode. Equimolar mixtures of quasienantiomeric pairs of these complexes exhibited a clear tendency to pack as quasiracemates as was revealed from the crystallographic structures of [(R,R)‐ 1 ‐Zn](PF₆)₂/[(S,S)‐ 1 ‐Fe](PF₆)₂ and [(R,R)‐ 1 ‐Zn](PF₆)₂/[(S,S)‐ 1 ‐Cd](PF₆)₂, in an isomorphous fashion to that of the racemic compound [rac‐ 1 ‐Zn](PF₆)₂ in space group C2/c.     

Ultrathin Metal–Organic Framework Nanosheets with Ultrahigh Loading of Single Pt Atoms for Efficient Visible‐Light‐Driven Photocatalytic H2 Evolution

A surfactant‐stabilized coordination strategy is used to make two‐dimensional (2D) single‐atom catalysts (SACs) with an ultrahigh Pt loading of 12.0 wt %, by assembly of pre‐formed single Pt atom coordinated porphyrin precursors into free‐standing metal–organic framework (MOF) nanosheets with an ultrathin thickness of 2.4±0.9 nm. This is the first example of 2D MOF‐based SACs. Remarkably, the 2D SACs exhibit a record‐high photocatalytic H₂ evolution rate of 11 320 μmol g^?1 h^?1 via water splitting under visible light irradiation (λ>420 nm) compared with those of reported MOF‐based photocatalysts. Moreover, the MOF nanosheets can be readily drop‐casted onto solid substrates, forming thin films while still retaining their photocatalytic activity, which is highly desirable for practical solar H₂ production.     

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 2D Metal‐Organic Framework Based on 9‐(Pyridin‐4‐yl)‐9H‐carbazole‐3,6‐dicarboxylic Acid: Synthesis,Structure and Properties

A metal‐organic framework (MOF ) formulated as [Cd₂(μ₃‐L)₂(DMF )₄]•H₂O ( CdL ) [H₂L =9‐(pyridin‐4‐yl)‐ 9H ‐carbazole‐3,6‐dicarboxylic acid, DMF =N ,N ‐dimethylformamide] was synthesized under solvothermal condition. Crystal structural analysis reveals that CdL features the layered 2D framework with L^{2 −} ligands as 3‐connected nodes. The compound CdL emits blue‐violet light with the narrow emission peak and the emission maximum at 414 nm upon excitation at the maximum excitation wavelength of 340 nm. The compound CdL has a similar emission spectrum curve to the free H₂L ligand that indicates the emission of compound CdL should be originated from the coordinated L^{2 −} ligands.     

A Tale of Two Trimers from Two Different Worlds: A COF‐Inspired Synthetic Strategy for Pore‐Space Partitioning of MOFs

The introduction of a symmetry‐ and size‐matching pore‐partitioning agent in the form of either a molecular ligand, such as 2,4,6‐tri(4‐pyridinyl)‐1,3,5‐triazine ( tpt ), or a metal‐complex cluster, into the hexagonal channels of MIL‐88/MOF‐235‐type (the acs net) to create pacs ‐type (partitioned acs ) crystalline porous materials is an effective strategy to develop high‐performance gas adsorbents. We have developed an integrated COF–MOF coassembly strategy as a new method for pore‐space partitioning through the coassembly of [(M₃(OH)_1?x(O)_x(COO)₆] MOF‐type and [B₃O₃(py)₃] COF‐type trimers. With this strategy, the coordination‐driven assembly of the acs framework occurred concurrently and synergistically with the COF‐1‐type condensation of pyridine‐4‐boronic acid into a C₃‐symmetric trimeric boroxine molecule. The resulting boroxine‐based pacs materials exhibited dramatically enhanced gas‐sorption properties as compared to nonpartitioned acs ‐type materials and are among the most efficient NH₃‐sorption materials.