Symmetry-Guided Synthesis of Highly Porous Metal-Organic Frameworks with Fluorite Topology

Interpenetrated Metal-Organic Frameworks with Topology and Versatile Functions

Through an "isoreticular expansion" strategy, a large number of highly porous zirconium-based metal-organic frameworks (Zr-MOFs) have been achieved using extended organic linkers in the past few years. However, interpenetrated Zr-MOFs with ftw topology have scarcely been reported, mainly owing to the used bulky tetratopic linkers that effectively prevent the network interpenetration. Here, we report a new family of zirconium and lanthanide (Ln) MOFs with ftw topology, constructed by hexanuclear Zr or Ln (Ln = Eu, Tb, Gd, Dy, Tm, Yb, Nd, and Er) clusters and a spirobifluorene-center tetracarboxylate linker. Our studies reveal that the isostructural Zr and Ln MOFs are all doubly interpenetrated with ultrahigh thermal and chemical stability. The observed unusual interpenetration can be attributed to the specific geometry of the spirobifluorene-center tetratopic linker. Gas adsorption studies show that the interpenetrated Zr-MOF is still highly porous and exhibits high performance for CO₂ storage, which can be attributed to the strong CO₂ binding environment contributed by the reduced pore size. In addition, the presented MOFs display strong characteristic luminescence in the UV-vis-NIR region. Moreover, the incorporation of the spiro-center linker into the framework can efficiently produce two-photon-excited photoluminescence with a large action cross-section value, which also benefited from the high packing density of the nonlinear optical chromophore linker in the interpenetrated structure.

Application of Various Metal-Organic Frameworks (MOFs) as Catalysts for Air and Water Pollution Environmental Remediation

The use of metal-organic frameworks (MOFs) to solve problems, like environmental pollution, disease, and toxicity, has received more attention and led to the rapid development of nanotechnology. In this review, we discuss the basis of the metal-organic framework as well as its application by suggesting an alternative of the present problem as catalysts. In the case of filtration, we have developed a method for preparing the membrane by electrospinning while using an eco-friendly polymer. The MOFs were usable in the environmental part of catalytic activity and may provide a great material as a catalyst to other areas in the near future.

Fabrication of (4, 10) and (4, 12)-Connected Multifunctional Zirconium Metal-Organic Frameworks for the Targeted Adsorption of a Guest Molecule

Following the principle of a topology guide, a zirconium MOF (PCN-207) based on the H₄TPTA ligand (tetramethyl(4,4',4″,4‴-(pyrazine-2,3,5,6-tetrayl))tetrabenzoic acid) with C₂ symmetry and an 8-connected Zr₆(μ_3-OH)₈(OH)₈]⁸⁺ cluster with D_4h symmetry has been synthesized. PCN-206 can also be obtained by modulating the benzoic acid usage to change the flexibility of the H₄TPTA ligand. The unique positions of 8-connected Zr₆ clusters in the flu and scu networks and the flexibility of the tetratopic primary linker enable the precise insertion of fumarate (FA), 1,4-benzenedicarboxylic acid (H₂BDC), and even 2,6-naphthalenedicarboxylic acid (H₂NDC) in a one-pot reaction. Auxiliary linkers are used to generate new MOF structures or topologies or to split the pore spaces, which may significantly change the porosity and chemical and physical properties of scaffold MOFs. The results provide a successful strategy for the rational design of multicomponent Zr-MOFs. Because of differences in composition and configuration between structures, PCN-207 shows the highest separation capability of light hydrocarbons; moreover, PCN-206 exhibits the highest adsorption capacity of 2,4-D and DCF among MOFs at present.

A multifunctional Cd(ii)-based metal–organic framework with amide groups exhibiting luminescence sensing towards multiple substances

By incorporating flexible amide group onto skeleton of a tetracarboxylate linker endows it with potential to serve as tetrahedral node and facilitate the construction of a flu net, which significantly demonstrates multi-responsive behavior.

Self-assembly of zirconocene-based metal–organic capsules: the structure, luminescence sensing of Fe3+ and iodine capture

Three new nanosized Zr-based MCs were synthesized under solvothermal conditions with excellent selectivity for luminescence sensing of Fe³⁺ and high performance for I₂ sorption and release.

Optimizing zirconium metal–organic frameworks through steric tuning for efficient removal of Cr2O72−

Three Zr-based MOFs are obtained through steric tuning. The synergistic effect between porous structures and functional groups enhanced the adsorption capacity and adsorption rate for Cr₂O₇²⁻.

Topology and porosity control of metal-organic frameworks through linker functionalization

Tetratopic organic linkers have been extensively used in Zr-based metal-organic frameworks (MOFs) where diverse topologies have been observed. Achieving meticulous control over the topologies to tune the pore sizes and shapes of the resulting materials, however, remains a great challenge. Herein, by introducing substituents to the backbone of tetratopic linkers to affect the linker conformation, phase-pure Zr-MOFs with different topologies and porosity were successfully obtained under the same synthetic conditions. The conversion of CO2 to valuable cyclic carbonates is a promising route for the mitigation of the greenhouse gas. Owing to the presence of substrate accessible Lewis acidic Zr(iv) sites in the 8-connected Zr6 nodes, the Zr-MOFs in this study have been investigated as heterogenous acid catalysts for CO2 cycloaddition to styrene oxide. The MOFs exhibited drastically different catalytic activities depending on their distinct pore structures. Compared to previously reported MOF materials, a superior catalytic activity was observed with the mesoporous NU-1008, giving an almost 100% conversion under mild conditions.

Synthesis, characterization, and post-synthetic modification of a micro/mesoporous zirconium–tricarboxylate metal–organic framework: towards the addition of acid active sites

Synthesis of defective microporous/mesoporous MOF-808.

A robust cage-based framework for the highly selective purification of natural gas

A robust cage-base framework exhibits highly selective purification of natural gas.

A robust and water-stable two-fold interpenetrated metal–organic framework containing both rigid tetrapodal carboxylate and rigid bifunctional nitrogen linkers exhibiting selective CO2 capture

A robust and water-stable two-fold interpenetrated metal–organic framework containing both rigid tetrapodal carboxylate and rigid bifunctional nitrogen linkers exhibiting selective CO₂ capture is reported.

Metal-Organic Frameworks Encapsulating Active Nanoparticles as Emerging Composites for Catalysis: Recent Progress and Perspectives

Beyond conventional porous materials, metal-organic frameworks (MOFs) have aroused great interest in the construction of nanocatalysts with the characteristics of catalytically active nanoparticles (NPs) confined into the cavities/channels of MOFs or surrounded by MOFs. The advantages of adopting MOFs as the encapsulating matrix are multifold: uniform and long-range ordered cavities can effectively promote the mass transfer and diffusion of substrates and products, while the diverse metal nodes and tunable organic linkers may enable outstanding synergy functions with the encapsulated active NPs. Herein, some key issues related to MOFs for catalysis are discussed. Then, state-of-the art progress in the encapsulation of catalytically active NPs by MOFs as well as their synergy functions for enhanced catalytic performance in the fields of thermo-, photo-, and electrocatalysis are summarized. Notably, encapsulation-structured nanocatalysts exhibit distinct advantages over conventional supported catalysts, especially in terms of the catalytic selectivity and stability. Finally, challenges and future developments in MOF-based encapsulation-structured nanocatalysts are proposed. The aim is to deliver better insight into the design of well-defined nanocatalysts with atomically accurate structures and high performance in challenging reactions.

From fundamentals to applications: a toolbox for robust and multifunctional MOF materials

In recent years, metal-organic frameworks (MOFs) have been regarded as one of the most important classes of materials. The combination of various metal clusters and ligands, arranged in a vast array of geometries has led to an ever-expanding MOF family. Each year, new and novel MOF structures are discovered. The structural diversity present in MOFs has significantly expanded the application of these new materials. MOFs show great potential for a variety of applications, including but not limited to: gas storage and separation, catalysis, biomedicine delivery, and chemical sensing. This review intends to offer a short summary of some of the most important topics and recent development in MOFs. The scope of this review shall cover the fundamental aspects concerning the design and synthesis of MOFs and range to the practical applications regarding their stability and derivative structures. Emerging trends of MOF development will also be discussed. These trends shall include multicomponent MOFs, defect development in MOFs, and MOF composites. The ever important structure-property-application relationship for MOFs will also be investigated. Overall, this review provides insight into both existing structures and emerging aspects of MOFs.

Stable Metal-Organic Frameworks: Design, Synthesis, and Applications

Metal-organic frameworks (MOFs) are an emerging class of porous materials with potential applications in gas storage, separations, catalysis, and chemical sensing. Despite numerous advantages, applications of many MOFs are ultimately limited by their stability under harsh conditions. Herein, the recent advances in the field of stable MOFs, covering the fundamental mechanisms of MOF stability, design, and synthesis of stable MOF architectures, and their latest applications are reviewed. First, key factors that affect MOF stability under certain chemical environments are introduced to guide the design of robust structures. This is followed by a short review of synthetic strategies of stable MOFs including modulated synthesis and postsynthetic modifications. Based on the fundamentals of MOF stability, stable MOFs are classified into two categories: high-valency metal-carboxylate frameworks and low-valency metal-azolate frameworks. Along this line, some representative stable MOFs are introduced, their structures are described, and their properties are briefly discussed. The expanded applications of stable MOFs in Lewis/Brønsted acid catalysis, redox catalysis, photocatalysis, electrocatalysis, gas storage, and sensing are highlighted. Overall, this review is expected to guide the design of stable MOFs by providing insights into existing structures, which could lead to the discovery and development of more advanced functional materials.

Unusual and Tunable Negative Linear Compressibility in the Metal-Organic Framework MFM-133(M) (M = Zr, Hf)

High-pressure single-crystal X-ray structural analyses of isostructural MFM-133(M) (M = Zr, Hf) of flu topology and incorporating the tetracarboxylate ligand TCHB^4- [H₄TCHB = 3,3',5,5'-tetrakis(4-carboxyphenyl)-2,2',4,4',6,6'-hexamethyl-1,1'-biphenyl] and {M₆(μ₃-OH)₈(OH)₈(COO)₈} clusters confirm negative linear compressibility (NLC) behavior along the c axis. This occurs via a three-dimensional wine-rack NLC mechanism leading to distortion of the octahedral cage toward a more elongated polyhedron under static compression. Despite the isomorphous nature of these two structures, MFM-133(Hf) shows a higher degree of NLC than the Zr(IV) analogue. Thus, for the first time, we demonstrate here that the NLC property can be effectively tuned in a framework material by simply varying the inorganic component of the frameworks without changing the network topology and structure.

Rational design of a flu-type heterometallic cluster-based Zr-MOF

Following the HSAB principle, the cooperative assembly of tetrahedral [Cu₄I₄(Ina)₄]^4- metalloligands and 8-connecting [Zr₆(μ₃-OH)₈(OH)₈]⁸⁺ building units leads to the first heterometallic cluster-based Zr-MOF (1). The results provide a successful strategy for rational design of heterometallic cluster-based Zr-MOFs.

A pyrene-involved luminescent MOF for monitoring 1-hydroxypyrene, a biomarker for human intoxication of PAH carcinogens

A robust pyrene-involved MOF is developed as a luminescent platform for sensitive detection of 1-hydroxypyrene, a human intoxication biomarker of PAH carcinogens, by utilizing the efficient host–guest π–π charge transfer interactions.

Heterogeneous Catalysis in Zeolites, Mesoporous Silica, and Metal-Organic Frameworks

Crystalline porous materials are important in the development of catalytic systems with high scientific and industrial impact. Zeolites, ordered mesoporous silica, and metal-organic frameworks (MOFs) are three types of porous materials that can be used as heterogeneous catalysts. This review focuses on a comparison of the catalytic activities of zeolites, mesoporous silica, and MOFs. In the first part of the review, the distinctive properties of these porous materials relevant to catalysis are discussed, and the corresponding catalytic reactions are highlighted. In the second part, the catalytic behaviors of zeolites, mesoporous silica, and MOFs in four types of general organic reactions (acid, base, oxidation, and hydrogenation) are compared. The advantages and disadvantages of each porous material for catalytic reactions are summarized. Conclusions and prospects for future development of these porous materials in this field are provided in the last section. This review aims to highlight recent research advancements in zeolites, ordered mesoporous silica, and MOFs for heterogeneous catalysis, and inspire further studies in this rapidly developing field.

The modulator driven polymorphism of Zr(IV) based metal-organic frameworks

The reaction of ZrCl₄ and 2,5-thiophenedicarboxylic acid (H₂tdc) in the presence of trifluoroacetic acid (Htfa) as modulator results in the formation of the new metal-organic framework (MOF) named DUT-126 (DUT = Dresden University of Technology). The nature and concentration of modulators are found to be decisive synthetic parameters affecting the topology of the formed product. DUT-126 ( HBR: ) extends the series of polymorphs differing in topology, namely DUT-67 ( REO: ), DUT-68 ( BON: ) and DUT-69 ( BCT: ) to four, where DUT-67 and DUT-68 show the same eight-connected secondary building units as in DUT-126. In DUT-126, linker molecules have a peculiar orientation, resulting in HBR: topology, which is described for the first time in this work for MOFs. DUT-126 contains three pore types, including two micropores surrounding mesoporous channels. DUT-126 is stable against hydrolysis and features permanent porosity with a specific surface area of 1297 m² g^-1 and a total pore volume of 0.48 cm³ g^-1, calculated from the nitrogen physisorption isotherm measured at 77 K.This article is part of the themed issue 'Coordination polymers and metal-organic frameworks: materials by design'.