Framework Cationization by Preemptive Coordination of Open Metal Sites for Anion‐Exchange Encapsulation of Nucleotides and Coenzymes

Cationic frameworks can selectively trap anions through ion exchange, and have applications in ion chromatography and drug delivery. However, cationic frameworks are much rarer than anionic or neutral ones. Herein, we propose a concept, preemptive coordination (PC), for targeting positively charged metal–organic frameworks (P‐MOFs). PC refers to proactive blocking of metal coordination sites to preclude their occupation by neutralizing ligands such as OH^?. We use 20 MOFs to show that this PC concept is an effective approach for developing P‐MOFs whose high stability, porosity, and anion‐exchange capability allow immobilization of anionic nucleotides and coenzymes, in addition to charge‐ and size‐selective capture or separation of organic dyes. The CO₂ and C₂H₂ uptake capacity of 117.9 cm³ g^?1 and 148.5 cm³ g^?1, respectively, at 273 K and 1 atm, is exceptionally high among cationic framework materials.     

Fluorescent “Turn‐on” Sensing Based on Metal–Organic Frameworks (MOFs)

Metal–organic frameworks (MOFs) have evolved as an exciting class of materials in the domain of porous materials. The unique features of these materials arise from the combined properties of metal ions/clusters and organic struts which form the building blocks of these fascinating architectures. Among other multifarious applications, MOFs have shown tremendous applications as sensory materials for a wide variety of species. The signal transduction induced mechanism in these confined nanospaces generate optical output in response to a particular analyte which can be detected by wide variety of detection techniques. Fluorometric methods of sensing is one of widely studied method over past few decades. MOF‐based fluorometric detection is a key research theme developed over the past few years. In this review, we give a brief overview of the recent developments of MOFs as “turn‐on” sensors for a wide range of analytes (viz. cations, anions, volatile organic compounds (VOCs), etc.).     

Ordered Large‐Pore MesoMOFs Based on Synergistic Effects of TriBlock Polymer and Hofmeister Ion

Ordered mesoporous metal–organic frameworks (mesoMOFs) were constructed with a uniform pore size up to about 10 nm and thick microporous walls, opening up the possibility for the mass diffusion of large‐size molecules through crystalline MOFs. The synergistic effects based on triblock copolymer templates and the Hofmeister salting‐in anions promote the nucleation of stable MOFs in aqueous phase and the in situ crystallization of MOFs around templates, rendering the generation of a microcrystal with periodically arranged large mesopores. The improved mass transfer benefiting from large‐pore channels, together with robust microporous crystalline structure, endows them as an ideal nanoreactor for the highly efficient digestion of various biogenic proteins. This strategy could set a guideline for the rational design of new ordered large‐pore mesoMOFs with a variety of compositions and functionalities and pave a way for their potential applications with biomacromolecules.     

金属有机框架材料在分离分析领域的研究进展

金属有机框架材料是由金属离子节点和有机配体通过配位键连接形成的具有序多孔骨架的材料, 因其具有比表面积大、 孔隙可调及表面性质可控等优点而备受关注. 通过对有机配体和金属离子进行选择及对金属有机框架材料进行后修饰处理, 可实现对金属有机框架材料表面性质的调控, 以提升其选择性吸附及特异性识别等性能, 进而拓展其在分离分析等领域的应用. 本文从金属有机框架材料的表面性质调控出发, 介绍了其表面性质与分离分析性能的关系, 总结了近年来该领域的代表性工作, 并展望了金属有机框架材料在分离分析领域的应用前景.     

A Highly Sensitive and Recyclable Ln‐MOF Luminescent Sensor for the Efficient Detection of Fe3+ and CrVI Anions

Two new three‐dimensional (3D) Ln^III metal‐organic frameworks (MOFs) were designed and successfully obtained via a solvothermal reaction between lanthanide(III) nitrates and a semi‐flexible carbazole tetracarboxylate acid linker as a high‐performance chromophore. 1 and 2 possess porous 3D networks with channels along the a axis, and more importantly, they show a highly sensitive and selective fluorescence quenching response to Fe³⁺ and Cr^VI anions. The sensing mechanism investigation revealed that the weak interactions of Fe³⁺ with nitrogen atoms of carbazole and deprotonated carboxylic acids protruding into the pores of MOFs quenched the luminescence of 1 and 2 effectively. In addition, the competition absorption also played an important role in the luminescence quenching detection of Fe³⁺ based on 1 , and Cr^VI anions based on 1 and 2 . Therefore, 1 and 2 represent an alternative example of regenerable luminescence based sensors for the quantitative detection of Fe³⁺ and Cr^VI anions.     

Synthetic strategies for chiral metal-organic frameworks

By direct synthesis route, chiral metal-organic frameworks are synthetized with enantiopure ligands or spontaneous resolution; by indirect method, post-synthetic method and chiral inductionare introduced to construct chiral metal-organic frameworks.     

手性金属有机骨架材料的合成及其在对映异构体选择性分离中的应用

手性现象在自然界中广泛存在,手性分离在药物研发、农用化学、药理学、环境科学和生物学等诸多领域具有重要意义。手性金属有机骨架化合物材料(MOFs)是一类具有特殊拓扑结构和可设计的孔道结构的新型多孔材料,加之其比表面积高、孔隙率大、热稳定性良好和溶剂耐受性好等特性,使得MOFs在分析化学领域的应用与研究日益深入。本文简要综述了手性MOFs的合成方法,着重讨论了手性MOFs在对映异构体选择性分离方面的应用及相关机理,最后对该类材料的发展前景做了展望。     

Construction of Flexible‐on‐Rigid Hybrid‐Phase Metal–Organic Frameworks for Controllable Multi‐Drug Delivery

Multi‐component MOFs contain multiple sets of unique and hierarchical pores, with different functions for different applications, distributed in their inter‐linked domains. Herein, we report the construction of a class of precisely aligned flexible‐on‐rigid hybrid‐phase MOFs with a unique rods‐on‐octahedron morphology. We demonstrated that hybrid‐phase MOFs can be constructed based on two prerequisites: the partially matched topology at the interface of the two frameworks, and the structural flexibility of MOFs with acs topology, which can compensate for the differences in lattice parameters. Furthermore, we achieved domain selective loading of multiple guest molecules into the hybrid‐phase MOF, as observed by scanning transmission electron microscopy–energy‐dispersive X‐ray spectrometry elemental mapping. Most importantly, we successfully applied the constructed hybrid‐phase MOF to develop a dual‐drug delivery system with controllable loading ratio and release kinetics.     

Biomimetic Ion Nanochannels as a Highly Selective Sequential Sensor for Zinc Ions Followed by Phosphate Anions

A novel biomimetic ion‐responsive multi‐nanochannel system is constructed by covalently immobilizing a metal‐chelating ligand, 2,2′‐dipicolylamine (DPA), in polyporous nanochannels prepared in a polymeric membrane. The DPA‐modified multi‐nanochannels show specific recognition of zinc ions over other common metal ions, and the zinc‐ion‐chelated nanochannels can be used as secondary sensors for HPO₄^2? anions. The immobilized DPA molecules act as specific‐receptor binding sites for zinc ions, which leads to the highly selective zinc‐ion response through monitoring of ionic current signatures. The chelated zinc ions can be used as secondary recognition elements for the capture of HPO₄^2? anions, thereby fabricating a sensing nanodevice for HPO₄^2? anions. The success of the DPA immobilization and ion‐responsive events is confirmed by measurement of the X‐ray photoelectron spectroscopy (XPS), contact angle (CA), and current–voltage (I–V) characteristics of the systems. The proposed nanochannel sensing devices display remarkable specificity, high sensitivity, and wide dynamic range. In addition, control experiments performed in complex matrices suggest that this sensing system has great potential applications in chemical sensing, biotechnology, and many other fields.     

功能化金属有机骨架材料去除饮用水污染物的研究进展

金属有机骨架(MOFs)材料是一类以过渡金属为中心、含杂原子的有机物为配体、通过配位作用形成的周期性网络多孔晶体材料。与其他的多孔材料相比,MOFs配体种类繁多,比表面积极大,孔径大小可调控且具有特殊(饱和或不饱和)的金属位点,在气体存储、催化、吸附与分离等领域有广阔的应用前景。近年来,功能化MOFs对污染物的富集和去除成为学者关注的热点。这是由于通过对MOFs进行功能化修饰,能够改变MOFs的孔径大小、表面带电性质等物化性质,从而实现对目标物更高效的吸附。该文综述了近年来功能化MOFs对饮用水污染物吸附的研究进展,包括饮用水污染物的类型及危害、功能化MOFs的制备方法以及去除饮用水污染物的应用,并对今后的发展前景进行了展望。     

Ordered Large-Pore MesoMOFs Based on Synergistic Effects of TriBlock Polymer and Hofmeister Ion

Ordered mesoporous metal–organic frameworks (mesoMOFs) were constructed with a uniform pore size up to about 10 nm and thick microporous walls, opening up the possibility for the mass diffusion of large-size molecules through crystalline MOFs. The synergistic effects based on triblock copolymer templates and the Hofmeister salting-in anions promote the nucleation of stable MOFs in aqueous phase and the in situ crystallization of MOFs around templates, rendering the generation of a microcrystal with periodically arranged large mesopores. The improved mass transfer benefiting from large-pore channels, together with robust microporous crystalline structure, endows them as an ideal nanoreactor for the highly efficient digestion of various biogenic proteins. This strategy could set a guideline for the rational design of new ordered large-pore mesoMOFs with a variety of compositions and functionalities and pave a way for their potential applications with biomacromolecules.     

An In Situ One‐Pot Synthetic Approach towards Multivariate Zirconium MOFs

Chemically highly stable MOFs incorporating multiple functionalities are of great interest for applications under harsh environments. Herein, we presented a facile one‐pot synthetic strategy to incorporate multiple functionalities into stable Zr‐MOFs from mixed ligands of different geometry and connectivity. Via our strategy, tetratopic tetrakis(4‐carboxyphenyl)porphyrin (TCPP) ligands were successfully integrated into UiO‐66 while maintaining the crystal structure, morphology, and ultrahigh chemical stability of UiO‐66. The amount of incorporated TCPP is controllable. Through various combinations of BDC derivatives and TCPP, 49 MOFs with multiple functionalities were obtained. Among them, MOFs modified with FeTCPPCl were demonstrated to be catalytically active for the oxidation of ABTS. We anticipate our strategy to provide a facile route to introduce multiple functionalities into stable Zr‐MOFs for a wide variety of potential applications.     

Single Crystal‐to‐Single Crystal Site‐Selective Postsynthetic Metal Exchange in a Zn–MOF Based on Semi‐Rigid Tricarboxylic Acid and Access to Bimetallic MOFs

The metal ions in a neutral Zn–MOF constructed from tritopic triacid H₃L with inherent concave features, rigid core, and peripheral flexibility are found to exist in two distinct SBUs, that is, 0D and 1D. This has allowed site‐selective postsynthetic metal exchange (PSME) to be investigated and reactivities of the metal ions in two different environments in coordination polymers to be contrasted for the first time. Site‐selective transmetalation of Zn ions in the discrete environment is shown to occur in a single crystal‐to‐single crystal (SCSC) fashion, with metal ions such as Fe³⁺, Ru³⁺, Cu²⁺, Co²⁺, etc., whereas those that are part of 1D SBU sustain structural integrity, leading to novel bimetallic MOFs, which are inaccessible by conventional approaches. To the best of our knowledge, site‐selective postsynthetic exchange of an intraframework metal ion in a MOF that contains metal ions in discrete as well as polymeric SBUs is heretofore unprecedented.     

Anion separation by selective crystallization of metal-organic frameworks

A novel approach for the separation of anions from aqueous mixtures was demonstrated, which involves their selective crystallization with metal-organic frameworks (MOFs) containing urea functional groups. Self-assembly of Zn2+ with the N,N'-bis(m-pyridyl)urea (BPU) linker results in the formation of one-dimensional MOFs including various anions for charge balance, which interact to different extents with the zinc nodes and the urea hydrogen-bonding groups, depending on their coordinating abilities. Thus, Cl-, Br-, I-, and SO4(2-), in the presence of BPU and Zn2+, form MOFs from water, in which the anions coordinate the zinc and are hydrogen-bonded to the urea groups, whereas NO3- and ClO4- anions either do not form MOFs or form water-soluble discrete coordination complexes under the same conditions. X-ray diffraction, FTIR, and elemental analysis of the coordination polymers precipitated from aqueous mixtures containing equivalent amounts of these anions indicated total exclusion of the oxoanions and selective crystallization of the halides in the form of solid solutions with the general composition ZnCl(x)Br(y)I(z).BPU (x + y + z = 2), with an anti-Hofmeister selectivity. The concomitant inclusion of the halides in the same structural frameworks facilitates the rationalization of the observed selectivity on the basis of the diminishing interactions with the zinc and urea acidic centers in the MOFs when going from Cl- to I-, which correlates with decreasing anionic charge density in the same order. The overall crystal packing efficiency of the coordination frameworks, which ultimately determines their solubility, also plays an important role in the anion crystallization selectivity under thermodynamic equilibration.     

Phosphate‐Binding Characteristics and Selectivity Studies of Bifunctional Organotin Carriers

The selective recognition of the orthophosphate anion by a series of bifunctional Lewis acidic organotin compounds is investigated. The binding affinity of these carriers to anions, as measured by NMR titrations in CH₂Cl₂ obeyed the potentiometric selectivity order phosphate > sulfate > perchlorate, and provided the corresponding complex‐formation constants. More accurate calculations of these values were obtained by the segmented‐sandwich‐membrane method performed directly inside the liquid polymeric membrane. These carriers were also studied potentiometrically in polymeric liquid membranes. The results indicate that (PhBr₂Sn)₂CH₂ is 2 to 5 orders of magnitude more selective towards phosphate over other oxoanions. These results set the ground for the development of a new series of highly selective anions carriers with a wide range of possible applications.     

Crystal Dynamics in Multi‐stimuli‐Responsive Entangled Metal–Organic Frameworks

An understanding of solid‐state crystal dynamics or flexibility in metal–organic frameworks (MOFs) showing multiple structural changes is highly demanding for the design of materials with potential applications in sensing and recognition. However, entangled MOFs showing such flexible behavior pose a great challenge in terms of extracting information on their dynamics because of their poor single‐crystallinity. In this article, detailed experimental studies on a twofold entangled MOF ( f‐MOF‐1) are reported, which unveil its structural response toward external stimuli such as temperature, pressure, and guest molecules. The crystallographic study shows multiple structural changes in f‐MOF‐1 , by which the 3 D net deforms and slides upon guest removal. Two distinct desolvated phases, that is, f‐MOF‐1 a and f‐MOF‐1 b , could be isolated; the former is a metastable one and transformable to the latter phase upon heating. The two phases show different gated CO₂ adsorption profiles. DFT‐based calculations provide an insight into the selective and gated adsorption behavior with CO₂ of f‐MOF‐1 b . The gate‐opening threshold pressure of CO₂ adsorption can be tuned strategically by changing the chemical functionality of the linker from ethanylene (?CH₂?CH₂?) in f‐MOF‐1 to an azo (?N=N?) functionality in an analogous MOF, f‐MOF‐2 . The modulation of functionality has an indirect influence on the gate‐opening pressure owing to the difference in inter‐net interaction. The framework of f‐MOF‐1 is highly responsive toward CO₂ gas molecules, and these results are supported by DFT calculations.     

Chiral Isocamphoric Acid: Founding a Large Family of Homochiral Porous Materials

Homochiral metal–organic frameworks (MOFs) are an important class of chiral solids with potential applications in chiral recognition; however, relatively few are available. Of great importance is the availability of low‐cost, racemization‐resistant, and versatile enantiopure building blocks. Among chiral building blocks, d ‐camphoric acid is highly prolific, yet, its trans‐isomer, l ‐isocamphoric acid, has remained unknown in the entire field of solid‐state materials. Its rich yet totally untapped synthetic and structural chemistry has now been investigated through the synthesis of a large family of homochiral metal isocamphorates. The first observation of diastereoisomerism in isostructural MOFs is presented. Isocamphorate has a powerful ability to create framework topologies unexpected from common inorganic building blocks, and isocamphoric acid should allow access to hundreds of new homochiral materials.     

Pore‐Surface Engineering by Decorating Metal‐Oxo Nodes with Phenylsilane to Give Versatile Super‐Hydrophobic Metal–Organic Frameworks (MOFs)

Hydrophobization of metal‐organic frameworks (MOFs) is important to push forward their practical use and thus has attracted increasing interest. In contrast to the previous reports, which mainly focused on the modification of organic ligands in MOFs, herein, we reported a novel strategy to decorate the metal‐oxo nodes of MOFs with phenylsilane to afford super‐hydrophobic NH₂‐UiO‐66(Zr), which shows highly improved base resistance and holds great promise in versatile applications, such as organic/water separation, self‐cleaning, and liquid‐marble fabrication. This work demonstrates the first attempt at metal‐oxo node modification for super‐hydrophobic MOFs, advancing a new concept in the design of MOFs with controlled wettability for practical applications.     

MOFs光催化材料的设计和调控

环境污染和能源短缺是制约当今社会发展的重大问题。光催化技术可直接利用太阳能驱动一系列重要的化学反应,具有能耗低、反应条件温和、无二次污染等优点,是解决这一问题的有效途径。实现这个过程的关键在于寻找设计高效的光催化剂。目前,光催化材料主要由无机半导体组成,其结构的改造和修饰难度很大,难以根据实际需要来控制其大小、形状以及物理化学特性。而有机化合物具有优良的分子剪裁与修饰的功能,但它们却在坚固性与稳定性等方面具有明显的缺点。因此如果能发展既具有无机化合物的稳定性又具有有机化合物的可剪裁与修饰性的新型光催化材料,无疑将促进光催化的发展和应用。金属-有机骨架材料(Metal-Organic Frameworks, MOFs)正是这样一类结合了无机物的稳定性和有机物的可修饰性的杂化材料。 MOFs是一类以金属阳离子为节点、有机配体为连接体的多孔配位聚合物的总称。这类材料不仅拥有超高的比表面积、丰富的拓扑结构,而且其结构兼具可剪裁性、可设计性、易调变等特点,在气体吸附储存、分离、传感等领域都有广泛的应用。在催化领域MOFs也显示出巨大的应用前景：(1)比表面积大,有利于对反应底物的吸附,促进催化反应的进行;(2)组成多样,结构具可剪裁性、可设计性、易调变等特点,通过对其金属单元或者配体进行改变修饰,可以实现对MOFs结构和性能的调变;(3)MOFs中金属-氧单元之间由有机配体隔开,相当于分立的半导体量子点,在反应中不易发生团聚。并且各个分立的金属-氧单元之间可能存在协同效应,有利于保持催化剂的稳定性和产生高的催化活性。因此, MOFs材料是一类非常有潜力的异相催化剂。光催化是一类典型的多相催化技术,与传统半导体光催化材料相比, MOFs由于具有可在分子水平进行灵活调控的优点,在光催化领域的应用更有优势。此外, MOFs结构上的确定性为研究催化剂的界面电荷迁移和光催化机理提供了便利条件,通过对其构-效关系的研究和光催化反应机理的探索反过来有助于我们从微观尺度上进一步认识光催化的本质。 MOFs材料在光催化领域已经有了初步的研究。越来越多的MOFs材料被成功应用于光催化降解染料、选择性转化有机物、光解水制氢和CO2还原等反应。典型的有MOF-5、UiO-66和MIL-125系列等。近年来,已有少量的文献综述了MOFs这类材料在光催化领域的研究。这些文献主要围绕MOFs在光催化过程中所起到的作用,比如作为催化剂、助催化剂或载体来展开;或者是从MOFs的光催化应用领域,比如污染物降解、产氢、二氧化碳还原、有机物转化来分类展开。本文围绕如何设计合成高效的MOFs光催化剂,综述了近年来国内外关于提高MOFs的光催化性能而开展的相关研究工作,包括理论研究MOFs的能级结构及化学性质、在MOFs配体上修饰官能团调变其能带结构、染料或者金属化合物光敏化MOFs提高其光吸收性能、负载金属/碳材料及半导体复合提高光生载流子的分离效率等。最后,本文对MOFs光催化剂的未来发展趋势进行了展望,强调开发新型的MOFs光催化剂,并加强对MOFs光催化机制的研究,有助于指导现有MOFs催化剂的改良和设计新型光催化剂。     

Electrochemical Characterisation of Polypyrrole Doped with p‐Sulfonatocalix[4]arene

Polypyrrole (PPy) films doped with macrocyclic calixarene anions are attractive materials for the development of selective sensor materials and membrane systems as the incorporation of the macrocycles can confer specific recognition sites within the polymer matrix. However, unlike many other PPy films a calixarene‐doped system is more complicated as calixarenes are themselves electroactive. Here we present results on the electroactivity, impedance properties and morphology of polypyrrole doped with p‐sulfonatocalix[4]arene. The calixarene in the polymer was found to be irreversibly oxidised at potentials greater than 0.500 V vs. SCE and reacted to form a new redox active species that was trapped within the polymer matrix. The results from the impedance and EQCM studies indicated that the calixarene was permanently trapped within the polymer matrix and the polymer acted as a cation exchange material. In addition, the data acquired from the EQCM experiments showed that while the material displayed simple cation exchange properties at high scan rates, at lower scan rates the transport of neutral species was also observed. Overall, our findings indicate that the PPy‐C4S system is suitable for use as a stable conducting polymer doped with an immobile anion within the potential window of ?0.800 V to 0.500 V vs. SCE.