Structural and dynamic studies of substrate binding in porous metal-organic frameworks

Variation in Catalytic Efficacies of a 2D pH-Stable MOF by Altering Activation Methods

Although it is well-known that the Lewis acidity of Metal-Organic Frameworks (MOFs) can effectively enhance their catalytic activity in organic transformations, access to these Lewis-acidic sites remains a key hurdle to widespread applications of Lewis-acidic catalysis by MOFs. Easy accessibility of strong Lewis acidic sites onto 2D MOFs by using proper activation methods can be a cornerstone in attaining desired catalytic performance. Herein, we report a new 2D chemically stable MOF, IITKGP-60, which displayed excellent framework robustness over a wide pH range (2-12). Benefiting from the abundant open metal sites (OMSs) and framework robustness, the catalytic activity of the developed material was explored in one-pot three-component Strecker reaction and Knoevenagel condensation reaction. Moreover, the developed catalyst is superior in catalyzing the reactions involving sterically hindered substrate (1-naphthaldehyde) with high turnover number. A comparative catalytic study was conducted using different activation methods (chloroform and methanol exchanged activated samples), highlighting the significant effect of activation methods on its catalytic performances. The sustainable synthetic pathway under solvent-free conditions for a broad scope of substrates using low catalyst loading and excellent recyclability made the developed pH-stable framework a promising heterogeneous catalyst.

Toward Developing Superior Cu-Based Metal-Organic Framework-Derived Materials for Electrocatalytic Oxidation of Ethanol

This project addresses the urgent need for efficient and cost-effective development of electrocatalysts for the ethanol oxidation reaction (EOR). This reaction offers promising renewable energy solutions but faces challenges due to the slow EOR kinetics, typically requiring costly noble metal catalysts. To overcome these limitations, this study focuses on developing CuZn-based EOR catalysts derived from metal-organic frameworks (MOFs), focusing on understanding the structure-performance relationship between pristine MOF-based electrocatalysts and their pyrolyzed counterparts. Herein, bimetallic MOF materials with varying Cu/Zn ratios were synthesized, followed by pyrolysis to produce carbonized counterparts while preserving the fundamental structure but with altered physicochemical properties. Comparative EOR studies revealed the superior performance of pyrolyzed MOFs, demonstrating that optimized Zn-loading is crucial over Cu-based framework for catalyst performance and durability. Overall, this work highlights the potential of MOF-derived Cu-based catalysts for renewable energy applications and provides insights into optimizing their performance through controlled synthesis and post-treatment strategies.

Structural Design and Energy and Environmental Applications of Hydrogen-Bonded Organic Frameworks: A Systematic Review

Hydrogen-bonded organic frameworks (HOFs) are emerging porous materials that show high structural flexibility, mild synthetic conditions, good solution processability, easy healing and regeneration, and good recyclability. Although these properties give them many potential multifunctional applications, their frameworks are unstable due to the presence of only weak and reversible hydrogen bonds. In this work, the development history and synthesis methods of HOFs are reviewed, and categorize their structural design concepts and strategies to improve their stability. More importantly, due to the significant potential of the latest HOF-related research for addressing energy and environmental issues, this work discusses the latest advances in the methods of energy storage and conversion, energy substance generation and isolation, environmental detection and isolation, degradation and transformation, and biological applications. Furthermore, a discussion of the coupling orientation of HOF in the cross-cutting fields of energy and environment is presented for the first time. Finally, current challenges, opportunities, and strategies for the development of HOFs to advance their energy and environmental applications are discussed.

Direct Observation of Enhanced Iodine Binding within a Series of Functionalized Metal-Organic Frameworks with Exceptional Irradiation Stability

Optimization of active sites and stability under irradiation are important targets for sorbent materials that might be used for iodine (I2) storage. Herein, we report the direct observation of I2 binding in a series of Cu(II)-based isostructural metal-organic frameworks, MFM-170, MFM-172, MFM-174, NJU-Bai20, and NJU-Bai21, incorporating various functional groups (-H, -CH3, - NH2, -C≡C-, and -CONH-, respectively). MFM-170 shows a reversible uptake of 3.37 g g-1 and a high packing density of 4.41 g cm-3 for physiosorbed I2. The incorporation of -NH2 and -C≡C- moieties in MFM-174 and NJU-Bai20, respectively, enhances the binding of I2, affording uptakes of up to 3.91 g g-1. In addition, an exceptional I2 packing density of 4.83 g cm-3 is achieved in MFM-174, comparable to that of solid iodine (4.93 g cm-3). In situ crystallographic studies show the formation of a range of supramolecular and chemical interactions [I···N, I···H2N] and [I···C≡C, I-C═C-I] between -NH2, -C≡C- sites, respectively, and adsorbed I2 molecules. These observations have been confirmed via a combination of solid-state nuclear magnetic resonance, X-ray photoelectron, and Raman spectroscopies. Importantly, γ-irradiation confirmed the ultraresistance of MFM-170, MFM-174, and NJU-Bai20 suggesting their potential as efficient sorbents for cleanup of radioactive waste.

Metal-organic framework-based adsorbents for blood purification: progress, challenges, and prospects

Blood purification, such as hemodialysis (HD), plasma exchange (PE), and hemoperfusion (HP), is widely applied in patients with organ failure (such as kidney and liver failure). Among them, HP mainly relies on porous adsorbents to efficiently adsorb accumulated metabolic wastes and toxins, thus improving purification efficiency. Metal-organic frameworks (MOFs), with a high porosity, large surface area, high loading capacity, and tailorable topology, are emerging as some of the most promising materials for HP. Compared with non-metal framework counterparts, the self-built metal centers of MOFs feature the intrinsic advantages of coordination with toxin molecules. However, research on MOFs in blood purification is insufficient, particularly in contrast to materials applied in other biomedical applications. Thus, to broaden this area, this review first discusses the essential characteristics, potential mechanisms, and structure-function relationship between MOFs and toxin adsorption based on porosity, topology, ligand functionalization, metal centers, and toxin types. Moreover, the stability, utilization safety, and hemocompatibility of MOFs are illustrated for adsorbent selection. The current development and progress in MOF composites for HD, HP, and extracorporeal membrane oxygenation (ECMO) are also summarized to highlight their practicability. Finally, we propose future opportunities and challenges from materials design and manufacture to the computational prediction of MOFs in blood purification. It is anticipated that our review will expand the interest of researchers for more impact in this area.

Phase behavior of patchy colloids confined in patchy porous media

A simple model for functionalized disordered porous media is proposed and the effects of confinement on self-association, percolation and phase behavior of a fluid of patchy particles are studied. The media are formed by randomly distributed hard-sphere obstacles fixed in space and decorated by a certain number of off-center square-well sites. The properties of the fluid of patchy particles, represented by the fluid of hard spheres each bearing a set of the off-center square-well sites, are studied using an appropriate combination of the scaled particle theory for the porous media, Wertheim's thermodynamic perturbation theory, and Flory-Stockmayer theory. To assess the accuracy of the theory a set of computer simulations have been performed. In general, predictions of the theory appeared to be in good agreement with the computer simulation results. Confinement and competition between the formation of bonds connecting the fluid particles, and connecting fluid particles and obstacles of the matrix, gave rise to a re-entrant phase behavior with three critical points and two separate regions of the liquid-gas phase coexistence.

Water-stable metal-organic frameworks (MOFs): rational construction and carbon dioxide capture

Metal-organic frameworks (MOFs) are considered to be a promising porous material due to their excellent porosity and chemical tailorability. However, due to the relatively weak strength of coordination bonds, the stability (e.g., water stability) of MOFs is usually poor, which severely inhibits their practical applications. To prepare water-stable MOFs, several important strategies such as increasing the bonding strength of building units and introducing hydrophobic units have been proposed, and many MOFs with excellent water stability have been prepared. Carbon dioxide not only causes a range of climate and health problems but also is a by-product of some important chemicals (e.g., natural gas). Due to their excellent adsorption performances, MOFs are considered as a promising adsorbent that can capture carbon dioxide efficiently and energetically, and many water-stable MOFs have been used to capture carbon dioxide in various scenarios, including flue gas decarbonization, direct air capture, and purified crude natural gas. In this review, we first introduce the design and synthesis of water-stable MOFs and then describe their applications in carbon dioxide capture, and finally provide some personal comments on the challenges facing these areas.

The {Cu2I2} cluster bearing metal organic frameworks: crystal structures and fluorescence detecting performances towards cysteine and explosive molecules

Two {Cu2I2} cluster-bearing metal organic frameworks (MOFs) of {[Eu(CuI)2(INA)3DMF]·0.95DMF}n (Eu-CuI-INA) and {K[(CH3)2NH2]Sr4(INA)2(DMF)2{(Cu2I2)2(INA)8}·2H2O}n (Sr-K-CuI-INA, HINA = isonicotinic acid, DMF = N,N-dimethyl formamide) were prepared and characterized in this work. Both materials feature a three-dimensional (3-D) structure, in which the {Cu2I2} clusters and Eu3+ (or Sr2+) metal ions are coordinated by INA- ligands with pyridine and carboxylic groups, respectively. Impressively, Sr-K-CuI-INA exhibits sensitive fluorescence sensing behaviors towards cysteine and nitro-bearing molecules, demonstrating potential FL sensing applications for bio and explosive molecules. This work would provide a good reference for designing fluorescent MOF probes containing CuI molecules.

Unlocking Diabetic Acetone Vapor Detection by A Portable Metal-Organic Framework-Based Turn-On Optical Sensor Device

Despite exhaled human breath having enabled noninvasive diabetes diagnosis, selective acetone vapor detection by fluorescence approach in the diabetic range (1.8-3.5 ppm) remains a long-standing challenge. A set of water-resistant luminescent metal-organic framework (MOF)-based composites have been reported for detecting acetone vapor in the diabetic range with a limit of detection of 200 ppb. The luminescent materials possess the ability to selectively detect acetone vapor from a mixture comprising nitrogen, oxygen, carbon dioxide, water vapor, and alcohol vapor, which are prevalent in exhaled breath. It is noteworthy that this is the first luminescent MOF material capable of selectively detecting acetone vapor in the diabetic range via a turn-on mechanism. The material can be reused within a matter of minutes under ambient conditions. Industrially pertinent electrospun luminescent fibers are likewise fabricated alongside various luminescent films for selective detection of ultratrace quantities of acetone vapor present in the air. Ab initio theoretical calculations combined with in situ synchrotron-based dosing studies uncovered the material's remarkable hypersensitivity toward acetone vapor. Finally, a freshly designed prototype fluorescence-based portable optical sensor is utilized as a proof-of-concept for the rapid detection of acetone vapor within the diabetic range.

Analysis and Refinement of Host-Guest Interactions in Metal-Organic Frameworks

ConspectusMetal-organic frameworks (MOFs) are a class of hybrid porous materials characterized by their periodic assembly using metal ions and organic ligands through coordination bonds. Their high crystallinity, extensive surface area, and adjustable pore sizes make them promising candidates for a wide array of applications. These include gas adsorption and separation, substrate binding, and catalysis, of relevance to tackling pressing global issues such as climate change, energy challenges, and pollution. In comparison to traditional porous materials such as zeolites and activated carbons, the design flexibility of organic ligands in MOFs, coupled with their orderly arrangement with associated metal centers, allows for the precise engineering of uniform pore environments. This unique feature enables a rich variety of interactions between the MOF host and adsorbed gas molecules, which are fundamental to understanding the observed uptake capacity and selectivity for target gas molecules and thus the overall performance of the material.In this Account, a data set for three-dimensional MOFs has been constructed based upon the structural analysis of host-guest interactions using the largest experimental database, the Cambridge Structural Database (CSD). A full screening was performed on structures with guest molecules of H2, C2H2, CO2, and SO2, and the relationship between the primary binding site, the isosteric heats of adsorption (Qst), and the adsorption uptake was extracted and established. We review the methodologies to refine host-guest interactions based primarily on our studies on the host-guest chemistry of MOFs. The methods include ligand functionalization, variation of metal centers, formation of defects, addition of single atom sites, and control of pore size and structure. In situ structural and dynamic investigations using diffraction and spectroscopic techniques are powerful tools to visualize the details of host-guest interactions upon the above modifications, affording key insights into functional performance at a molecular level. Finally, we give an outlook of future research priorities in the study of host-guest chemistry in MOF materials. We hope this Account will encourage the rational development and improvement of future MOF-based sorbents for applications in challenging gas adsorption, separations, and catalysis.

Direct Conversion of Methane to Ethylene and Acetylene over an Iron-Based Metal-Organic Framework

Conversion of methane (CH4) to ethylene (C2H4) and/or acetylene (C2H2) enables routes to a wide range of products directly from natural gas. However, high reaction temperatures and pressures are often required to activate and convert CH4 controllably, and separating C2+ products from unreacted CH4 can be challenging. Here, we report the direct conversion of CH4 to C2H4 and C2H2 driven by non-thermal plasma under ambient (25 °C and 1 atm) and flow conditions over a metal-organic framework material, MFM-300(Fe). The selectivity for the formation of C2H4 and C2H2 reaches 96% with a high time yield of 334 μmol gcat-1 h-1. At a conversion of 10%, the selectivity to C2+ hydrocarbons and time yield exceed 98% and 2056 μmol gcat-1 h-1, respectively, representing a new benchmark for conversion of CH4. In situ neutron powder diffraction, inelastic neutron scattering and solid-state nuclear magnetic resonance, electron paramagnetic resonance (EPR), and diffuse reflectance infrared Fourier transform spectroscopies, coupled with modeling studies, reveal the crucial role of Fe-O(H)-Fe sites in activating CH4 and stabilizing reaction intermediates via the formation of an Fe-O(CH3)-Fe adduct. In addition, a cascade fixed-bed system has been developed to achieve online separation of C2H4 and C2H2 from unreacted CH4 for direct use. Integrating the processes of CH4 activation, conversion, and product separation within one system opens a new avenue for natural gas utility, bridging the gap between fundamental studies and practical applications in this area.

Mixed-ligand metal-organic frameworks as an effective photocatalyst for selective oxidation reaction

By incorporating tetrakis(4-carboxyphenyl)porphyrin and bis(3,5-dicarboxyphenyl)pyridine into one single metal-organic framework (MOF), a multifunctional mixed-ligand Zn-MIX with large pores was obtained. Under visible-light irradiation, Zn-MIX exhibits high photocatalytic activity for the oxidation of amines and sulfides.

Supramolecular Assembly of One-Dimensional Coordination Polymers for Efficient Separation of Xenon and Krypton

Efficient separation and purification of xenon (Xe) from krypton (Kr) represent an industrially crucial but challenging process. While the adsorption-based separation of these atomic gases represents an energy-efficient process, achieving highly selective adsorbents remains a difficult task. Here, we demonstrate a supramolecular assembly of coordination polymers, termed as M(II)-dhbq (M = Mg, Mn, Co, and Zn; dhbq = 2,5-dihydroxy-1,4-benzoquinone), with high-density open metal sites (5.3 nm-3) and optimal pore size (5.5 Å), which are able to selectively capture Xe among other chemically inert gases including Kr, Ar, N2, and O2. Among M(II)-dhbq materials, Mn-dhbq exhibits the highest Xe uptake capacity of 3.1 mmol/g and a Xe/Kr selectivity of 11.2 at 298 K and 1.0 bar, outperforming many state-of-the-art adsorbents reported so far. Remarkably, the adsorption selectivity of Mn-dhbq for Xe/O2, Xe/N2, and Xe/Ar at ambient conditions reaches as high as 70.0, 139.3, and 64.0, respectively. Direct breakthrough experiments further confirm that all M(II)-dhbq materials can efficiently discriminate Xe atoms from other inert gases. It is revealed from the density functional theory calculations that the strong affinity between Xe and the coordination polymer is mainly attributed to the polarization by open metal sites.

Molecular docking with SARS-CoV-2 and potential drug property of a bioactive novel Zn(II) polymer: A combined experimental and theoretical study

A new Zn(II) coordination polymer based on o-phthalato (Phth) and 2-aminopyridine (2-Ampy) viz. {[Zn(2-Ampy)₂(Phth)]∙(H₂O)]}_n (1) has been synthesized at room temperature and characterized by elemental analyses, electronic spectroscopy, FT-IR spectroscopy, thermal analysis (TGA/DSC), powder X-ray diffraction (PXRD) and single crystal X-ray diffraction. The basic trimeric units of 1 form a polymeric chain by N-H⋯O and π⋯π interactions. These polymeric chains interconnect through various non-covalent interactions in two perpendicular directions to ultimately give rise to a 3D architecture of 1. The interesting non-covalent interactions in 1, contributing to its stability in the solid state are studied by Hirshfeld surface analysis and other different theoretical tools. Molecular docking study of 1 is performed against six different proteins of SARS-CoV-2. The drug potential of the synthesized compound is evaluated by ADMET calculations.

Optimizing Acetylene Sorption through Induced-fit Transformations in a Chemically Stable Microporous Framework

Developing practical storage technologies for acetylene (C₂ H₂ ) is important but challenging because C₂ H₂ is useful but explosive. Here, a novel metal-organic framework (MOF) (FJI-H36) with adaptive channels was prepared. It can effectively capture C₂ H₂ (159.9 cm³  cm^-3 ) at 1 atm and 298 K, possessing a record-high storage density (561 g L^-1 ) but a very low adsorption enthalpy (28 kJ mol^-1 ) among all the reported MOFs. Structural analyses show that such excellent adsorption performance comes from the synergism of active sites, flexible framework, and matched pores; where the adsorbed-C₂ H₂ can drive FJI-H36 to undergo induced-fit transformations step by step, including deformation/reconstruction of channels, contraction of pores, and transformation of active sites, finally leading to dense packing of C₂ H₂ . Moreover, FJI-H36 has excellent chemical stability and recyclability, and can be prepared on a large scale, enabling it as a practical adsorbent for C₂ H₂ . This will provide a useful strategy for developing practical and efficient adsorbents for C₂ H₂ storage.

Plasma Meets MOFs: Synthesis, Modifications, and Functionalities

As a porous and network materials consisting of metals and organic ligands, metal-organic frameworks (MOFs) have become one of excellent crystalline porous materials and play an important role in the era about materials science. Plasma, as a useful tool for stimulating efficient reactions under many conditions, and the plasma-assisted technology gets more attractions and endows MOFs more properties. Based on its feature, the research about the modifications and functionalities of MOFs have been developing a certain extent. This review contains a description of the methods for plasma-assisted modification and synthesis of MOFs, with specifically focusing on the plasma-assisted potential for modifications and functionalities of MOFs. The different applications of plasma-assisted MOFs were also presented.

Real-Space Imaging of the Node-Linker Coordination on the Interfaces between Self-Assembled Metal-Organic Frameworks

Surface and interface, with unique local characteristics different from bulk structure, are of great significance in various applications of metal-organic frameworks (MOFs), which should be studied by real-space imaging methods, such as electron microscopy. However, it is still challenging to atomically resolve these local structures in MOFs, because they are even more sensitive to electron irradiation. Here, we use integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM) to achieve the atomic imaging of both the metal nodes and organic linkers in UiO-66 (Zr) nanocrystals and their assembly. After adding acetic acid, we modulate the whole process of MOF assembly and observe the organic linkers at both the surfaces and twin interfaces in the chemically assembled UiO-66 (Zr) crystals by the iDPC-STEM. These results bring us a deeper understanding on the role of acid modulators that promote the MOF assembly by generating the missing-linker defects on the crystal surface.

Bimetal NiCo-MOF-74 for highly selective NO capture from flue gas under ambient conditions

The mixed bimetal metal-organic framework Ni_0.37Co_0.63-MOF-74 has been constructed by the solvothermal method for NO adsorption. The results showed that bimetal Ni_0.37Co_0.63-MOF-74 takes up NO with a capacity of up to 174.3 cc g^-1 under ambient conditions, which is 16.3% higher than that of the best single metal Co-MOF-74. The IAST adsorption selectivity for a NO/CO₂ binary mixture can reach a maximum of 710 at low adsorption partial pressure, while the regeneration performance can be retained even after five cyclic adsorption-desorption experiments. Its separation performance was further confirmed by breakthrough experiments, indicating this new bimetal Ni_0.37Co_0.63-MOF-74 as one of the best materials for NO adsorption and separation in flue gas.

Photo-induced reversible nitric oxide capture by Fe-M(CO2H)4 (M = Co, Ni, Cu) as a building block of mixed-metal BTC-based MOFs

Metal-organic frameworks incorporating mixed-metal sites (MM-MOFs) have emerged as promising candidates in the development of sensing platforms for the detection of paramagnetic species. In this context, the present study explores the photo-induced switching behavior of mixed-metal Fe-M (M = Co, Ni, Cu) formate (Fe-M(CO₂H)₄), as an experimentally feasible strategy for the reversible capture of nitric oxide (NO). Using Fe-M(CO₂H)₄ as a building block of synthesized MOFs based on BTC (benzene-1,3,5-tricarboxylic acid), molecular simulations of NO adsorption on Fe-M(CO₂H)₄ were conducted to provide a template for evaluating the behavior of BTC-based MOFs towards NO. Accordingly, the relationship between the magnetic properties and adsorption behaviors of Fe-M(CO₂H)₄ towards NO gas molecules was evaluated before and after photoexcitation. We show that the photo-induced effect on the magnetic properties of Fe-M(CO₂H)₄ changes the interaction strength between NO and the Fe-M(CO₂H)₄ systems. NO chemisorption over Fe-Ni(CO₂H)₄ indicates that nickel-doped Fe-BTC MOFs can be efficiently applied for capturing purposes. Moreover, our calculations show a switching behavior between physisorption and chemisorption of the NO molecules over Fe-Co(CO₂H)₄, occurring through magnetic modulation under UV-Vis irradiation. As far as we know, this is the first study that proposes light-controlled reversible NO capture using MOFs. The present study provides a promising platform for reversible NO capture using MM-MOF-incorporated BTC building blocks.

Metal-organic frameworks for pharmaceutical and biomedical applications

Metal-organic framework (MOF) materials provide unprecedented opportunities for evaluating valuable compounds for various medical applications. MOFs merged with biomolecules, used as novel biomaterials, have become particularly useful in biological environments. Bio-MOFs can be promising materials in the global to avoid utilization above toxicological substances. Bio-MOFs with crystallin and porosity nature offer flexible structure via bio-linker and metal node variation, which improves their wide applicability in medical science.

Slow CO2 Diffusion Governed by Steric Hindrance of Rotatory Ligands in Small Pores of a Metal-Organic Framework

Understanding the adsorption and diffusional dynamics of CO₂ in metal-organic frameworks (MOFs) is essential in the application of these materials to CO₂ capture and separation. We show that the dynamics of adsorbed CO₂ is related to the rotational motion of ligands located in the narrow pore windows of a MOF using solid-state nuclear magnetic resonance (NMR) spectroscopy. NMR analyses of local dynamics reveal that CO₂ adsorbed in the pore hinders the rotation of the ligands. The rate of diffusion of adsorbed CO₂ monitored by ¹³C NMR is much less than that in the larger pores of MOFs and decreases cooperatively with ligand mobility, which indicates that the rate of diffusion is influenced by the steric hindrance of the rotatory ligands. Adsorbed CH₄ also showed slow diffusion in the MOF, suggesting molecular size-selective effect of the mobile steric hindrance on the rate of adsorbate diffusion.

Effects of Recycled Sponge Iron on Phosphorus Recovery from Polluted Water

Phosphorus in water not only degrades water quality but also leads to a waste of resources. In this study, adsorption thermodynamics and kinetics were used to study the effect of sponge iron on phosphorus removal, and a filtration bed was used to simulate the phosphorus removal in polluted water. The results showed that the maximum theoretical adsorption capacity of the modified sponge iron was increased from 4.17 mg/g to 18.18 mg/g. After desorption with 18.18 mol/L of sodium hydroxide and reactivation with 6% (w%) sulfuric acid, the activation rate of modified sponge iron can reach 98%. In a continuous operation experiment run for approximately 200 days, the sponge iron phosphorus removal percolation bed showed a good phosphorus removal ability. Under the condition of TP = 10 mg/L, HRT = 1 H, the comprehensive phosphorus removal rate was 30–89%, and the accumulated phosphorus adsorption per unit volume was 6.95 kg/m3. Wastewater from the regeneration of the sponge iron base can be used to recover guano stone. The optimum conditions were pH = 10, n (Mg2+):n (PO43−):n (NH4+) = 1.3:1:1.1. Under the optimum conditions, the phosphorus recovery rate could reach 97.8%. The method provided in this study has theoretical and practical significance for the removal and recycling of phosphorus in polluted water.

Direct Observation of Ammonia Storage in UiO-66 Incorporating Cu(II) Binding Sites

The presence of active sites in metal-organic framework (MOF) materials can control and affect their performance significantly in adsorption and catalysis. However, revealing the interactions between the substrate and active sites in MOFs at atomic precision remains a challenging task. Here, we report the direct observation of binding of NH3 in a series of UiO-66 materials containing atomically dispersed defects and open Cu(I) and Cu(II) sites. While all MOFs in this series exhibit similar surface areas (1111-1135 m2 g-1), decoration of the -OH site in UiO-66-defect with Cu(II) results in a 43% enhancement of the isothermal uptake of NH3 at 273 K and 1.0 bar from 11.8 in UiO-66-defect to 16.9 mmol g-1 in UiO-66-CuII. A 100% enhancement of dynamic adsorption of NH3 at a concentration level of 630 ppm from 2.07 mmol g-1 in UiO-66-defect to 4.15 mmol g-1 in UiO-66-CuII at 298 K is observed. In situ neutron powder diffraction, inelastic neutron scattering, and electron paramagnetic resonance, solid-state nuclear magnetic resonance, and infrared spectroscopies, coupled with modeling reveal that the enhanced NH3 uptake in UiO-66-CuII originates from a {Cu(II)···NH3} interaction, with a reversible change in geometry at Cu(II) from near-linear to trigonal coordination. This work represents the first example of structural elucidation of NH3 binding in MOFs containing open metal sites and will inform the design of new efficient MOF sorbents by targeted control of active sites for NH3 capture and storage.

Eosin Y-Containing Metal-Organic Framework as a Heterogeneous Catalyst for Direct Photoactivation of Inert C-H Bonds

Xanthene dyes as a class of ideal organic homogeneous photocatalyst have received significant attention in C-H bond activation; however, the inherent nature of fast carrier recombination/deactivation and low stability limits their practical applications. Herein, by the ingenious decoration of eosin Y into a porous metal-organic framework (MOF), a high-performance heterogeneous MOF-based photocatalyst was prepared to efficiently activate inert C-H bonds on the reactants via the hydrogen atom transfer pathway for the functionalization of the C-H bonds. Taking advantage of the fixation effect of a rigid framework, the incorporation of eosin Y into MOF leads to great enhancement of their chemical durability. More importantly, by the introduction of the second auxiliary ligand, the carbonyl groups of xanthene on the eosin Y dyes were perfectly retained and periodically aligned within the confined channels of this rigid framework, which could effectively form excited state radicals to prompt inert C-H bond activation, promoting reaction efficiency by the host-guest supramolecular interaction. New eosin Y-based MOFs were recyclable for six times without reducing photocatalytic activity. This eosin Y functionalized MOF-based heterogeneous photocatalytic system provides an availably catalytic avenue to develop a scalable and sustainable synthetic strategy for the practical application of organic dyes.

The benefits of Cu Kβ radiation for the single-crystal X-ray structure determination of crystalline sponges

The crystalline sponge method facilitates the X-ray structure determination of samples that do not crystallize or are too sparsely available to afford viable crystallization. By including these materials in a metal-organic framework, the structure of the guest molecules can be determined. Some of the inherent difficulties of this method are discussed and the use of Cu Kβ radiation is presented as a simple and effective means to improve the quality of the diffraction data that can be obtained from a sponge crystal.

Confinement of Luminescent Guests in Metal–Organic Frameworks: Understanding Pathways from Synthesis and Multimodal Characterization to Potential Applications of LG@MOF Systems

This review gives an authoritative, critical, and accessible overview of an emergent class of fluorescent materials termed “LG@MOF”, engineered from the nanoscale confinement of luminescent guests (LG) in a metal–organic framework (MOF) host, realizing a myriad of unconventional materials with fascinating photophysical and photochemical properties. We begin by summarizing the synthetic methodologies and design guidelines for representative LG@MOF systems, where the major types of fluorescent guest encompass organic dyes, metal ions, metal complexes, metal nanoclusters, quantum dots, and hybrid perovskites. Subsequently, we discuss the methods for characterizing the resultant guest–host structures, guest loading, photophysical properties, and review local-scale techniques recently employed to elucidate guest positions. A special emphasis is paid to the pros and cons of the various methods in the context of LG@MOF. In the following section, we provide a brief tutorial on the basic guest–host phenomena, focusing on the excited state events and nanoscale confinement effects underpinning the exceptional behavior of LG@MOF systems. The review finally culminates in the most striking applications of LG@MOF materials, particularly the “turn-on” type fluorochromic chemo- and mechano-sensors, noninvasive thermometry and optical pH sensors, electroluminescence, and innovative security devices. This review offers a comprehensive coverage of general interest to the multidisciplinary materials community to stimulate frontier research in the vibrant sector of light-emitting MOF composite systems.

Design of a MOF based on octa-nuclear zinc clusters realizing both thermal stability and structural flexibility

An octa-nuclear zinc (Zn₈) cluster-based two-fold interpenetrated metal-organic framework (MOF) of [(CH₃)₂NH₂]₂[Zn₈O₃(FDC)₆]·7DMF (denoted as Zn8-as; H₂FDC = 9H-fluorene-2,7-dicarboxylic acid; DMF = N,N-dimethylformamide) was synthesized by the reaction of a hard base of a curved dicarboxylate ligand (H₂FDC) with the borderline acid of Zn(II) under solvothermal conditions. Zn8-as shows significant crystal volume shrinkage upon heating, yielding a solvate-free framework of [(CH₃)₂NH₂]₂[Zn₈O₃(FDC)₆] (Zn8-de). Zn8-de displays gated adsorption for C₂H₂ and type-I adsorption for CO₂, attributed to the framework flexibility and the different interactions between the gas molecules and the host framework.

Fabrication of zirconium-based metal-organic frameworks@tungsten trioxide (UiO-66-NH2@WO3) heterostructure on carbon cloth for efficient photocatalytic removal of tetracycline antibiotic under visible light

Designing recyclable photocatalysts with high activity and stability has drawn considerable attention in the fields of sewage treatment. Herein, a series of heterojunctions constructed by zirconium-based metal-organic frameworks (UiO-66-NH₂) and tungsten trioxide (WO₃) is immobilized on carbon cloth via a facile solvothermal method, resulting in highly recyclable photocatalysts. Multiple characterization techniques, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy, verify the successful synthesis of UiO-66-NH₂ nanospheres on the surface of needlelike WO₃ modified carbon cloth. Results show that the optimal heterojunction photocatalyst exhibits excellent photocatalytic degradation efficiency for the removal of tetracycline (TC) from water, for which nearly 100% of TC is degraded within 60 min under visible light. Trapping experiments and electron spin resonance (ESR) spectra analyses demonstrate that the superoxide radicals O₂^- and photogenerated hole h⁺ play a dominant role in the degradation process. Excellent photocatalytic activity is dominantly attributed to the effective separation of photoinduced carriers in this type-Ⅱ heterostructure system. Moreover, the possible photocatalytic oxidation degradation pathway is confirmed by analyzing intermediates using liquid chromatography mass spectrometry (LC-MS). This study offers a highly efficient strategy to design recyclable heterojunction photocatalysts for the degradation of refractory antibiotics in sewage.

Recent advances in metal-organic framework-based materials for anti-staphylococcus aureus infection

The rapid spread of staphylococcus aureus (S. aureus) causes an increased morbidity and mortality, as well as great economic losses in the world. Anti-S. aureus infection becomes a major challenge for clinicians and nursing professionals to address drug resistance. Hence, it is urgent to explore high efficiency, low toxicity, and environmental-friendly methods against S. aureus. Metal-organic frameworks (MOFs) represent great potential in treating S. aureus infection due to the unique features of MOFs including tunable chemical constitute, open crystalline structure, and high specific surface area. Especially, these properties endow MOF-based materials outstanding antibacterial effect, which can be mainly attributed to the continuously released active components and the exerted catalytic activity to fight bacterial infection. Herein, the structural characteristics of MOFs and evaluation method of antimicrobial activity are briefly summarized. Then we systematically give an overview on their recent progress on antibacterial mechanisms, metal ion sustained-release system, controlled delivery system, catalytic system, and energy conversion system based on MOF materials. Finally, suggestions and direction for future research to develop and mechanism understand MOF-based materials are discussed in antibacterial application.

Templated synthesis of zirconium(IV)-based metal-organic layers (MOLs) with accessible chelating sites

Metal-organic layers (MOLs) are of great interest in heterogeneous catalysis, particularly materials that can accommodate extraneous metal centres. Here, we demonstrate a two-step preorganisation/delamination synthetic strategy using CuI as a template to prepare Zr-based MOLs with accessible 'syn' bis-pyrazolyl chelating sites (named UAM-2·ns) that are poised for quantitative post-synthetic metalation with late transition metals.

MOFs in the time domain

Many of the proposed applications of metal-organic framework (MOF) materials may fail to materialize if the community does not fully address the difficult fundamental work needed to map out the 'time gap' in the literature - that is, the lack of investigation into the time-dependent behaviours of MOFs as opposed to equilibrium or steady-state properties. Although there are a range of excellent investigations into MOF dynamics and time-dependent phenomena, these works represent only a tiny fraction of the vast number of MOF studies. This Review provides an overview of current research into the temporal evolution of MOF structures and properties by analysing the time-resolved experimental techniques that can be used to monitor such behaviours. We focus on innovative techniques, while also discussing older methods often used in other chemical systems. Four areas are examined: MOF formation, guest motion, electron motion and framework motion. In each area, we highlight the disparity between the relatively small amount of (published) research on key time-dependent phenomena and the enormous scope for acquiring the wider and deeper understanding that is essential for the future of the field.

Competitive tetrel bond and hydrogen bond in benzaldehyde-CO2: characterization via rotational spectroscopy

The rotational spectrum of the 1 : 1 benzaldehyde-CO₂ complex has been investigated using pulsed-jet Fourier transform microwave spectroscopy complemented with quantum chemical calculations. Two isomers, both characterized by one C⋯O tetrel bond (n → π* interaction) and one C-H⋯O hydrogen bond (n → σ* interaction), have been observed in the pulsed jet. Competition between the tetrel bond and the hydrogen bond has been disclosed by natural bond orbital analysis: isomer I is characterized by one dominating OC_CO2⋯O tetrel bond (12.6 kJ mol^-1) and a secondary (C-H)_formyl⋯O hydrogen bond (2.2 kJ mol^-1); by contrast, in isomer II the (C-H)_phenyl⋯O hydrogen bond (7.6 kJ mol^-1) becomes the dominant bond, while the OC_CO2⋯O tetrel bond (5.8 kJ mol^-1) becomes much weaker with respect to that of isomer I. Using intensity measurements the relative population ratio of the two isomers was estimated to be N_I/N_II ≈ 2/1.

Electrospun rhodamine@MOF/polymer luminescent fibers with a quantum yield of over 90

Tailored luminescent guest@metal-organic framework (Guest@MOF) materials with outstanding photophysical properties are enabling materials for emergent technologies in smart sensors and optoelectronics. However, the practical utility of Guest@MOF currently is impaired by its poor stability and difficult-to-handle powder form. Here, we combine a luminescent-sensing Guest@MOF system with a non-luminescent polymer matrix and, for the first time, demonstrated the easy-to-apply electrospinning of luminescent fibers comprising nanocrystals of RhB@ZIF-71 (rhodamine B@zeolitic imidazolate framework-71) homogeneously dispersed in a polyvinylidene difluoride (PVDF) matrix. The luminescence of RhB@ZIF-71/PVDF fiber is tunable and exhibits a quantum yield exceeding 90%. Compared with RhB fluorophore in PVDF fiber, the ZIF-71 (host) protects the nanoconfined RhB guest molecules (especially the J-aggregates of RhB), giving the composite fiber its unique thermofluorochromic response and enhanced thermal stability to 200°C. Our results reveal the exciting opportunities for implementing electrospun luminescent fibers functionalized with bespoke Guest@MOF nanocrystals for multifunctional device applications.

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Thermofluorochromic fibers incorporating Guest@MOF engineered by electrospinning

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J-aggregates of rhodamine B (RhB) interact through adjacent ZIF-71 nanocrystals

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RhB@ZIF-71/PVDF fiber has a quantum yield exceeding 90%

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ZIF-71 host enhances the thermal stability of nanoconfined RhB guest

Single-Crystal-to-Single-Crystal Transformations of Metal-Organic-Framework-Supported, Site-Isolated Trigonal-Planar Cu(I) Complexes with Labile Ligands

Transition-metal complexes bearing labile ligands can be difficult to isolate and study in solution because of unwanted dinucleation or ligand substitution reactions. Metal-organic frameworks (MOFs) provide a unique matrix that allows site isolation and stabilization of well-defined transition-metal complexes that may be of importance as moieties for gas adsorption or catalysis. Herein we report the development of an in situ anion metathesis strategy that facilitates the postsynthetic modification of Cu(I) complexes appended to a porous, crystalline MOF. By exchange of coordinated chloride for weakly coordinating anions in the presence of carbon monoxide (CO) or ethylene, a series of labile MOF-appended Cu(I) complexes featuring CO or ethylene ligands are prepared and structurally characterized using X-ray crystallography. These complexes have an uncommon trigonal planar geometry because of the absence of coordinating solvents. The porous host framework allows small and moderately sized molecules to access the isolated Cu(I) sites and displace the "place-holder" CO ligand, mirroring the ligand-exchange processes involved in Cu-centered catalysis.

MOF matrix isolation: cooperative conformational mobility enables reliable single crystal transformations

Obtaining structural information for highly reactive metal-based species can provide valuable insight into important chemical transformations or catalytic processes. Trapping these metal-based species within the cavities of porous crystalline hosts, such as metal-organic frameworks (MOFs), can stabilise them, allowing detailed structural elucidation by single crystal X-ray diffraction. Previously, we have used a bespoke flexible MOF, [Mn3L2L'] (MnMOF-1, where L = bis-(4-carboxyphenyl-3,5-dimethylpyrazolyl)methane and L = L', but L' has a vacant N,N'-chelation site), which has a chelating site capable of post-synthetically binding metal ions, to study organometallic transformations and fundamental isomerisation processes. This manuscript will report the underlying conformational flexibility of the framework, demonstrate the solvent dependency of post-synthetic metalation, and show that the structural flexibility of the linker site and framework are critical to controlling and achieving high levels of metal loading (and therefore site occupancy) during chemical transformations. From these results, a set of design principles for linker-based "matrix isolation" and structure determination in MOFs are derived.

Deep Desulfurization with Record SO2 Adsorption on the Metal-Organic Frameworks

Selective elimination of sulfur dioxide is significant in flue gas desulfurization and natural gas purification, yet developing adsorbents with high capture capacity especially at low partial pressure as well as excellent cycling stability remains a challenge. Herein, a family of isostructural gallate-based MOFs with abundant hydrogen bond donors decorating the pore channel was reported for selective recognition and dense packing of sulfur dioxide via multiple hydrogen bonding interactions. Multiple O···H-O hydrogen bonds and O···H-C hydrogen bonds guarantee SO₂ molecules are firmly grasped within the framework, and appropriate pore apertures afford dense packing of SO₂ with high uptake and density up to 1.86 g cm^-3, which is evidenced by dispersion-corrected density functional theory calculations and X-ray diffraction resolution of a SO₂-loaded single crystal. Ultrahigh adsorption uptake of SO₂ at extremely low pressure (0.002 bar) was achieved on Co-gallate (6.13 mmol cm^-3), outperforming all reported state-of-the-art MOFs. Record-high IAST selectivity of SO₂/CO₂ (325 for Mg-gallate) and ultrahigh selectivity of SO₂/N₂ (>1.0 × 10⁴) and SO₂/CH₄ (>1.0 × 10⁴) were also realized. Breakthrough experiments further demonstrate the excellent removal performance of trace amounts of SO₂ in a deep desulfurization process. More importantly, M-gallate shows almost unchanged breakthrough performance after five cycles, indicating the robust cycling stability of these MOFs.

Intermediate snapshots of a 116-nuclear metallosupramolecular cage-of-cage in a homogeneous single-crystal-to-single-crystal transformation

Soaking crystals of an AuI72CdII40NaI4 cage-of-cage in aqueous Co(NO3)2 afforded an analogous AuI72CoII44 cage-of-cage, accompanied by the exchange of NaI and CdII by CoII with retention of the single crystallinity. The homogeneous progress of the transformation led to the direct observation of intermediate species by single-crystal X-ray crystallography.