Ligand-Directed Conformational Control over Porphyrinic Zirconium Metal-Organic Frameworks for Size-Selective Catalysis

Single-Crystal Structural Analysis of 2D Metal-Organic Frameworks and Covalent Organic Frameworks by Three-Dimensional Electron Diffraction

ConspectusIn the development of 2D metal-organic frameworks (MOFs) and 2D covalent organic frameworks (COFs), obtaining structural details at the atomic level is crucial to understanding their properties and related mechanisms in potential applications. However, since 2D-MOFs and COFs are composed of layered structures and often exhibit sheet-like morphologies, it is challenging to grow large crystals suitable for single-crystal X-ray diffraction (SCXRD). Therefore, ab initio structure determination, which refers to solving the structure directly from experimental data without using any prior knowledge or computational input, is extremely rare for 2D-MOFs and COFs. In contrast to SCXRD, three-dimensional electron diffraction (3DED) only requires crystals sized in tens or hundreds of nanometers, making it an ideal method for single-crystal analysis of 2D-MOFs and COFs and obtaining their fine structural details.In this Account, we describe our recent development of the 3DED method and its application in structure determination and property studies of 2D-MOFs and COFs. A key development is the establishment of a continuous 3DED data collection protocol. By collecting electron diffraction (ED) patterns continuously while performing crystal tilting, the electron dose applied to the target nanocrystal is greatly reduced. This allows the acquisition of high-resolution 3DED data from 2D-MOFs and COFs by minimizing their damage under the electron beam. We have also developed an approach to couple 3DED with real-space structure solution methods, i.e., simulated annealing (SA), for single-crystal structural analysis of materials that do not have high crystallinity. We successfully determined two 2D-COF structures by combining 3DED with SA.We provide several examples demonstrating the application of 3DED for the ab initio structure determination of 2D-MOFs and COFs, revealing not only their in-plane structures but also their stacking modes at the atomic level. Notably, the obtained structural details serve as the foundation for further understanding the properties of 2D-MOFs and COFs, such as their electronic band structures, charge mobilities, etc. Beyond structure determination, we describe our work on using 3DED as a high-throughput method for the discovery of new materials. Using this approach, we discovered a novel MOF that was present only in trace amounts within a multiphasic mixture. Through this discovery, we were able to tune the synthesis conditions to obtain its pure phase.We detail how 3DED can be used to probe different levels of molecular motions in MOFs through the analysis of anisotropic displacement parameters (ADPs). Additionally, we show that 3DED can provide accurate information about intermolecular weak interactions such as hydrogen bonding and van der Waals (vdW) interactions. Our studies demonstrate that 3DED is a valuable method for the structural analysis of 2D-MOFs and COFs. We envision that 3DED can accelerate research in these fields by providing unambiguous structural models at the atomic level.

Superhydrophobic MOF/polymer composite with hierarchical porosity for boosting catalytic performance in an humid environment

The poor hydrostability of most reported metal-organic frameworks (MOFs) has become a daunting challenge in their practical applications. Recently, MOFs combined with multifunctional polymers can act as a functional platform and exhibit unique catalytic performance; they can not only inherit the outstanding properties of the two components but also offer unique synergistic effects. Herein, an original porous polymer-confined strategy has been developed to prepare a superhydrophobic MOF composite to significantly enhance its moisture or water resistance. The selective nucleation and growth of MOF nanocrystals confined in the pore of PDVB-vim are closely related to the structure-directing and coordination-modulating properties of PDVB-vim. The resultant MOF/PDVB-vim composite not only produces superior superhydrophobicity without significantly disturbing the original features but also exhibits a novel catalytic activity in the Friedel-Crafts alkylation reaction of indoles with trans-β-nitrostyrene because of the accessible sites and synergistic effects.

Positron emission tomography guided synergistic treatment of melanoma using multifunctional zirconium-hematoporphyrin nanosonosensitizers

Sonodynamic therapy (SDT) has emerged as a useful approach for tumor treatment. However, its widespread application is impeded by poor pharmacokinetics of existing sonosensitizers. Here we developed a metal-organic nanoplatform, wherein a small-molecule sonosensitizer (hematoporphyrin monomethyl ether, HMME) was ingeniously coordinated with zirconium, resulting in a multifunctional nanosonosensitizer termed Zr-HMME. Through post-synthetic modifications involving PEGylation and tumor-targeting peptide (F3) linkage, a nanoplatform capable of homing on melanoma was produced, which could elicit robust immune responses to suppress tumor lung metastasis in the host organism. Importantly, after seamless incorporation of positron-emitting 89Zr into this nanosonosensitizer, positron emission tomography (PET) could be used to monitor its in vivo pharmacokinetics. PET imaging studies revealed that this nanoplatform exhibited potent tumor accumulation and strong in vivo stability. Using intrinsic fluorescence from HMME, a dual-modal diagnostic capability (fluorescence and PET) was confirmed for this nanosonosensitizer. In addition, the mechanisms of how this nanoplatform interacted with immune system were also investigated. The collective data proved that the coordination structure between small-molecule drug cargos and metals may enhance the functions of each other while mitigating their weaknesses. This straightforward approach can expand the potential applications of suitable drug molecules.

Design and Advanced Manufacturing of NU-1000 Metal-Organic Frameworks with Future Perspectives for Environmental and Renewable Energy Applications

Metal-organic frameworks (MOFs) represent a relatively new family of materials that attract lots of attention thanks to their unique features such as hierarchical porosity, active metal centers, versatility of linkers/metal nodes, and large surface area. Among the extended list of MOFs, Zr-based-MOFs demonstrate comparably superior chemical and thermal stabilities, making them ideal candidates for energy and environmental applications. As a Zr-MOF, NU-1000 is first synthesized at Northwestern University. A comprehensive review of various approaches to the synthesis of NU-1000 MOFs for obtaining unique surface properties (e.g., diverse surface morphologies, large surface area, and particular pore size distribution) and their applications in the catalysis (electro-, and photo-catalysis), CO2 reduction, batteries, hydrogen storage, gas storage/separation, and other environmental fields are presented. The review further outlines the current challenges in the development of NU-1000 MOFs and their derivatives in practical applications, revealing areas for future investigation.

Accelerated Diffusion of a Copper(I)-Functionalized COF Packed Bed Reactor for Efficient Continuous Flow Catalysis

Flow chemistry provides a neo-orientation for the research and development of chemical technology, in which heterogeneous continuous catalysis based on packed beds can realize rapid separation and recycling. However, options for heterogeneous catalysts are still limited. In this work, we gradually grow covalent organic frameworks (COFs, TpBpy) on the surface of a silica gel (SiO2)-supported substrate to obtain a stable copper(I)-chelated high-loading heterogeneous catalyst (SiO2@CuI-TpBpy). SiO2@CuI-TpBpy shows high catalytic activity in three-component Huisgen 1,3-dipolar cycloaddition, giving the corresponding triazoles with excellent yields and reposeful recyclability under batch conditions. The structures of the catalysts remain steady, and the copper contents are basically unchanged after five cycles. Then, the catalysts are successfully applied for three-component heterogeneous catalysis in a one-pot continuous flow to prepare rufinamide in 89% yield for 24 h stably and efficiently with mere traces of copper ions remaining. More importantly, the catalytic system reveals a minuscule effect of catalyst particle size on internal diffusion. This COF encapsulation strategy presents a new possibility for the design of industrial heterogeneous catalysts with high metal loading and low internal diffusion resistance.

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.

A General Synthesis of Nanostructured Conductive Metal-Organic Frameworks from Insulating MOF Precursors for Supercapacitors and Chemiresistive Sensors

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) are emerging as a unique subclass of layer-stacked crystalline coordination polymers that simultaneously possess porous and conductive properties, and have broad application potential in energy and electronic devices. However, to make the best use of the intrinsic electronic properties and structural features of 2D c-MOFs, the controlled synthesis of hierarchically nanostructured 2D c-MOFs with high crystallinity and customized morphologies is essential, which remains a great challenge. Herein, we present a template strategy to synthesize a library of 2D c-MOFs with controlled morphologies and dimensions via insulating MOFs-to-c-MOFs transformations. The resultant hierarchically nanostructured 2D c-MOFs feature intrinsic electrical conductivity and higher surface areas than the reported bulk-type 2D c-MOFs, which are beneficial for improved access to active sites and enhanced mass transport. As proof-of-concept applications, the hierarchically nanostructured 2D c-MOFs exhibit a superior performance for electrical properties related applications (hollow Cu-BHT nanocubes-based supercapacitor and Cu-HHB nanoflowers-based chemiresistive gas sensor), achieving over 225 % and 250 % improvement in specific capacity and response intensity over the corresponding bulk type c-MOFs, respectively.

Isoreticular Metal-Organic Frameworks Confined Mononuclear Ru-Hydrides Enable Highly Efficient Shape-Selective Hydrogenolysis of Polyolefins

Upcycling nonbiodegradable plastics such as polyolefins is paramount due to their ever-increasing demand and landfills after usage. Catalytic hydrogenolysis is highly appealing to convert polyolefins into targeted value-added products under mild reaction conditions compared with other methods, such as high-temperature incineration and pyrolysis. We have developed three isoreticular zirconium UiO-metal-organic frameworks (UiO-MOFs) node-supported ruthenium dihydrides (UiO-RuH2), which are efficient heterogeneous catalysts for hydrogenolysis of polyethylene at 200 °C, affording liquid hydrocarbons with a narrow distribution and excellent selectivity via shape-selective catalysis. UiO-66-RuH2 catalyzed hydrogenolysis of single-use low-density polyethylene (LDPE) produced a C12 centered narrow bell-shaped distribution of C8-C16 alkanes in >80% yield and 90% selectivity in the liquid phase. By tuning the pore sizes of the isoreticular UiO-RuH2 MOF catalysts, the distribution of the products could be systematically altered, affording different fuel-grade liquid hydrocarbons from LDPE in high yields. Our spectroscopic and theoretical studies and control experiments reveal that UiO-RuH2 catalysts enable highly efficient upcycling of plastic wastes under mild conditions owing to their unique combination of coordinatively unsaturated single-site Ru-active sites, uniform and tunable pores, well-defined porous structure, and superior stability. The kinetics and theoretical calculations also identify the C-C bond scission involving β-alkyl transfer as the turnover-limiting step.

Coordination-Driven Heterochiral Self-Assembly: Construction of Cd(II) Coordination Polymers with Sorption Behaviors for Iodine and Dyes

A racemic bispyridyl ligand (L) was synthesized via a Schiff base condensation reaction. Four Cd(II) complexes, {[CdL2Cl2]·2DMF}n (1), [CdLI2]n (2), {[CdL2Br2]·4H2O}n (3), and {[CdL2(H2O)2](NO3)2·2CH3OH·8H2O}n (4), were synthesized and further characterized based on this ligand. Single-crystal structures show that the coordination-driven assembly of the bispyridyl ligand with Cd(II) salts bearing different counteranions can lead to multidimensional coordination polymers via a heterochiral self-discrimination process. Complex 1 exists as a one-dimensional (1D) looped chain polymer, and complex 2 exists as a 1D zigzag chain polymer. Complex 3 is a 2D grid coordination polymer, and complex 4 exists as a 3D framework polymer. Furthermore, the iodine sorption capacities of the four complexes were investigated in the solution of n-hexane and water as well as in the iodine steam. The dye sorption behaviors were investigated in water, which showed that complex 2 exhibited good adsorption for crystal violet (CV), while complex 4 had good adsorption capability toward direct yellow 4 (DY).

Catalysis of a Diels-Alder Reaction between Azachalcones and Cyclopentadiene by a Recyclable Copper(II)-PEIP Metal-Organic Framework

Metal-organic frameworks (MOFs) have attracted considerable interest as emerging heterogeneous catalysts for organic transformations of synthetic utility. Herein, a Lewis-acidic MOF, {[Cu3(PEIP)2(5-NH2-mBDC)(DMF)]·7DMF}∞, denoted as Cu(ΙΙ)-PEIP, has been synthesized via a one-pot process and deployed as an efficient heterogeneous catalyst for a Diels-Alder cycloaddition. Specifically, the [4 + 2] cycloaddition of 13 substituted azachalcone dienophiles with cyclopentadiene has been investigated. MOF-catalyzed reaction conditions were optimized, leading to the selection of water as the solvent, in the presence of 10% mol sodium dodecyl sulfate (SDS) to address substrate solubility. The Cu(II)-PEIP catalyst showed excellent activity under these green and mild conditions, exhibiting comparable or, in some cases, superior efficiency to a homogeneous catalyst often employed in Diels-Alder reactions, namely, Cu(OTf)2. The nature of the azachalcone substituent played a significant role in the reactivity of the dienophiles, with electron-withdrawing (EW) substituents enhancing conversion and electron-donating (ED) ones exhibiting the opposite effect. Coordinating substituents appeared to enhance the endo selectivity. Importantly, the Cu(II)-PEIP catalyst can be readily isolated from the reaction mixture and recycled up to four times without any significant reduction in conversion or selectivity.

Quantitative Time-Resolved Visualization of Catalytic Degradation Reactions of Environmental Pollutants by Integrating Single-Drop Microextraction and Fluorescence Sensing

Current methods for evaluating catalytic degradation reactions of environmental pollutants primarily rely on chromatography that often suffers from intermittent analysis, a long turnaround period, and complex sample pretreatment. Herein, we propose a quantitative time-resolved visualization method to evaluate the progress of catalytic degradation reactions by integrating sample pretreatment [single-drop microextraction, (SDME)], fluorescence sensing, and a smartphone detection platform. The dechlorination reaction of chlorobenzene derivatives was first investigated to validate the feasibility of this approach, in which SDME plays a critical role in direct sample pretreatment, and inorganic CsPbBr₃ perovskite encapsulated in a metal-organic framework (MOF-5) was utilized as the fluorescent chromogenic agent (FLCA) in SDME to realize fast in situ colorimetric detection via the color switching from green (CsPbBr₃) to blue (chlorine lead bromide, inorganic CsPbCl₃ perovskite). The smartphone, which can calculate the B/G value of FLCA, serves as a data output window for quantitative time-resolved visualization. Further, a [Eu(PMA)]_n (PMA= pyromellitic acid) fluorescent probe was constructed to use as an FLCA for the in situ evaluation of cinnamaldehyde and p-nitrophenol catalytic reduction. This approach not only minimizes the utilization of organic solvents and achieves quantitively efficient time-resolved visualization but also provides a feasible method for in situ monitoring of the progress of catalytic degradation reactions.

Hierarchical conductive metal-organic framework films enabling efficient interfacial mass transfer

Heterogeneous reactions associated with porous solid films are ubiquitous and play an important role in both nature and industrial processes. However, due to the no-slip boundary condition in pressure-driven flows, the interfacial mass transfer between the porous solid surface and the environment is largely limited to slow molecular diffusion, which severely hinders the enhancement of heterogeneous reaction kinetics. Herein, we report a hierarchical-structure-accelerated interfacial dynamic strategy to improve interfacial gas transfer on hierarchical conductive metal-organic framework (c-MOF) films. Hierarchical c-MOF films are synthesized via the in-situ transformation of insulating MOF film precursors using π-conjugated ligands and comprise both a nanoporous shell and hollow inner voids. The introduction of hollow structures in the c-MOF films enables an increase of gas permeability, thus enhancing the motion velocity of gas molecules toward the c-MOF film surface, which is more than 8.0-fold higher than that of bulk-type film. The c-MOF film-based chemiresistive sensor exhibits a faster response towards ammonia than other reported chemiresistive ammonia sensors at room temperature and a response speed 10 times faster than that of the bulk-type film.

Peptide-derived coordination frameworks for biomimetic and selective separation

Peptide-derived metal-organic frameworks (PMOFs) have emerged as a class of biomimetic materials with attractive performances in analytical and bioanalytical chemistry. The incorporation of biomolecule peptides gives the frameworks conformational flexibility, guest adaptability, built-in chirality, and molecular recognition ability, which greatly accelerate the applications of PMOFs in enantiomeric separation, affinity separation, and the enrichment of bioactive species from complicated samples. This review focuses on the recent advances in the engineering and applications of PMOFs in selective separation. The unique biomimetic size-, enantio-, and affinity-selective performances for separation are discussed along with the chemical structures and functions of MOFs and peptides. Updates of the applications of PMOFs in adaptive separation of small molecules, chiral separation of drug molecules, and affinity isolation of bioactive species are summarized. Finally, the promising future and remaining challenges of PMOFs for selective separation of complex biosamples are discussed.

Endowing Porphyrinic Metal-Organic Frameworks with High Stability by a Linker Desymmetrization Strategy

The fabricating of metal-organic frameworks (MOFs) that integrate high stability and functionality remains a long-term pursuit yet a great challenge. Herein, we develop a linker desymmetrization strategy to construct highly stable porphyrinic MOFs, namely, USTC-9 (USTC represents the University of Science and Technology of China), presenting the same topological structure as the well-known PCN-600 that readily loses crystallinity in air or upon conventional activation. For USTC-9, the involved porphyrinic linker (TmCPP-M) with carboxylate groups located in the meta-position presents a chair-shaped conformation with lower C_2h symmetry than that (D_4h) of the common porphyrinic carboxylate (TCPP) linker in PCN-600. As a result, the wrinkled and interlocked linker arrangements collectively contribute to the remarkable stability of USTC-9. Given the high stability and porosity as well as Lewis acidity, USTC-9(Fe) demonstrates its excellent performance toward catalytic CO₂ cycloaddition with diverse epoxides at moderate temperature and atmospheric pressure.

Covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) as electrochemical sensors for the efficient detection of pharmaceutical residues

Pharmaceutical residues are the undecomposed remains from drugs used in the medical and food industries. Due to their potential adverse effects on human health and natural ecosystems, they are of increasing worldwide concern. The acute detection of pharmaceutical residues can give a rapid examination of their quantity and then prevent them from further contamination. Herein, this study summarizes and discusses the most recent porous covalent-organic frameworks (COFs) and metal-organic frameworks (MOFs) for the electrochemical detection of various pharmaceutical residues. The review first introduces a brief overview of drug toxicity and its effects on living organisms. Subsequently, different porous materials and drug detection techniques are discussed with materials' properties and applications. Then the development of COFs and MOFs has been addressed with their structural properties and sensing applications. Further, the stability, reusability, and sustainability of MOFs/COFs are reviewed and discussed. Besides, COFs and MOFs' detection limits, linear ranges, the role of functionalities, and immobilized nanoparticles are analyzed and discussed. Lastly, this review summarized and discussed the MOF@COF composite as sensors, the fabrication strategies to enhance detection potential, and the current challenges in this area.

A robust and porous titanium metal-organic framework for gas adsorption, CO2 capture and conversion

A robust and porous titanium metal-organic framework (Ti-MOF; LCU-402) has been hydrothermally synthesized through combining a tetranuclear Ti2Ca2(μ3-O)2(μ2-H2O)1.3(H2O)4(O2C-)8 cluster and a tritopic 1,3,5-benzene(tris)benzoic (BTB) ligand. LCU-402 shows remarkable stability and permanent porosity for CO2, CH4, C2H2, C2H4, and C2H6 gas adsorption. Moreover, LCU-402 as a heterogeneous catalyst can smoothly convert CO2 under a simulated flue atmosphere into organic carbonate molecules by cycloaddition reactions of CO2 and epoxides, indicating that LCU-402 might be a promising catalyst candidate in practical applications. We are confident that the identification of a persistent titanium-oxo building unit would accelerate the development of new porous Ti-MOF materials.

Sequential Assembly and Stabilization of Cu6S6 Octahedral Clusters in NaCl-, NiAs-, and CdI2-Related Structures and Their Utility toward Thermochromism and Multicomponent Hantzsch Reaction

Seven new inorganic-organic coordination polymer compounds have been synthesized and their structures are determined by single-crystal structure determination. The compounds were prepared by the sequential assembly of a [Cu₆(mna)₆]^6- moiety in the presence of a Mn salt and a secondary amine ligand. Of the seven compounds, [{Cu₆(mna)₆}Mn₃(H₂O)(H₂O)_1.5]·5.5H₂O (I), [{Cu₆(mna)₆}Mn₃(H₂O)(Im)_1.5]·3.5H₂O (Ia), [{Cu₆(mna)₆}{Mn(BPY)(H₂O)}₂{Mn(H₂O)₄}]·2H₂O (III), and [{Cu₆(mna)₆}{Mn(BPE)_0.5(H₂O)₂}₂{Mn(BPE)(H₂O)₂}] (IV) have a three-dimensional structure, whereas [{Cu₆(mna)_4.5(Hmna)_1.5}{Mn(BPA)(H₂O)₂}{Mn(H₂O)}]{Mn_0.25(H₂O)₃}·7H₂O (II), [{Cu₆(mna)₆}{Mn(4-BPDB)_0.5H₂O}{Mn(H₂O)₂}].{Mn(H₂O)₆}·6H₂O (V), and [{Cu₆(mna)₄(Hmna)₂}·{Mn(H₂O)₃}₂]·(4-APY)₂·6H₂O (VI) have a two-dimensional structure. Some of the prepared compounds exhibit structures that closely resemble the classical inorganic structures, such as NaCl (Ia, III), NiAs (I), and CdI₂ (IV and VI). The stabilization of such simple structures from the assembly of octahedral Cu₆S₆ clusters and different Mn species and aromatic nitrogen-containing ligands suggests the subtle interplay between the constituent reactants. The compounds were examined for the multicomponent Hantzsch reaction, which gave the product in good yields. The compounds, II and VI, on heating to 70 °C change color reversibly from pale yellow to deep red, which suggests the possible use of these compounds as thermochromic materials. The present study suggests that the Cu₆S₆ octahedral clusters can be assembled into structures that resemble classical inorganic structures.

Zr- and Ti-based metal-organic frameworks: synthesis, structures and catalytic applications

Recently, Zr- and Ti-based metal-organic frameworks (MOFs) have gathered increasing interest in the field of chemistry and materials science, not only for their ordered porous structure, large surface area, and high thermal and chemical stability, but also for their various potential applications. Particularly, the unique features of Zr- and Ti-based MOFs enable them to be a highly versatile platform for catalysis. Although much effort has been devoted to developing Zr- and Ti-based MOF materials, they still suffer from difficulties in targeted synthesis, especially for Ti-based MOFs. In this Feature Article, we discuss the evolution of Zr- and Ti-based MOFs, giving a brief overview of their synthesis and structures. Furthermore, the catalytic uses of Zr- and Ti-based MOF materials in the previous 3-5 years have been highlighted. Finally, perspectives on the Zr- and Ti-based MOF materials are also proposed. This work provides in-depth insight into the advances in Zr- and Ti-based MOFs and boosts their catalytic applications.

A novel flower-shaped Ag@ZIF-67 chemiluminescence sensor for sensitive detection of CEA

In this work, a chemiluminescence (CL) aptasensor for sensitive carcinoembryonic antigen (CEA) detection was constructed based on the CL system of luminol-H₂O₂-NaOH. Magnetic carbon nanotubes (MCNTs), as the base material, was modified with CEA-aptamer and DNA1, and was combined with the novel flower-shaped Ag@ZIF-67 of modified with DNA2 through the principle of base complementary pairing. CEA combined with aptamer when it existed in the solution. At the same time, MCNTs was adsorbed at the bottom of the container under the influence of external magnetic field, and Ag@ZIF-67 enhanced the CL signal. The CL aptasensor demonstrated high selectivity and sensitivity for CEA in human serum sample with (1-4): a detection limit of 4.53 × 10^-3 ng/mL in case the detection range was 0.05-500 ng/mL. Furthermore, the proposed method had been shown great potential in cancer diagnosis.

Expanding the Structural Topologies of Rare-Earth Porphyrinic Metal-Organic Frameworks through Ligand Modulation

Expanding the structural diversity of porphyrinic metal-organic frameworks (PMOFs) is essential to develop functional materials with novel properties or enhanced performance in different applications. Herein, we establish a strategy to construct rare-earth (RE) PMOFs with unprecedented topology via rational functionalization of porphyrinic ligands. By introducing phenyl/pyridyl groups to the meso-positions of the porphyrin core, the symmetries and connectivities of the ligands are tuned, and three RE-PMOFs (BUT-224/-225/-226) with new topologies are successfully obtained. In addition, BUT-225(Co), with both the Lewis basic and acidic sites, exhibits enhanced CO₂ uptake and higher catalytic activity for the cycloaddition of CO₂ and epoxides under mild conditions. This work reveals that the RE-PMOFs with novel topologies can be rationally designed and constructed through ligand functionalization, which provides insights into the construction of tailored PMOFs for various applications.

Fine Pore-Structure Engineering by Ligand Conformational Control of Naphthalene Diimide-Based Semiconducting Porous Coordination Polymers for Efficient Chemiresistive Gas Sensing

Exploring new porous coordination polymers (PCPs) that have tunable structure and conductivity is attractive but remains challenging. Herein, fine pore structure engineering by ligand conformation control of naphthalene diimide (NDI)-based semiconducting PCPs with π stacking-dependent conductivity tunability is achieved. The π stacking distances and ligand conformation in these isoreticular PCPs were modulated by employing metal centers with different coordination geometries. As a result, three conjugated PCPs (Co-pyNDI, Ni-pyNDI, and Zn-pyNDI) with varying pore structure and conductivity were obtained. Their crystal structures were determined by three-dimensional electron diffraction. The through-space charge transfer and tunable pore structure in these PCPs result in modulated selectivity and sensitivity in gas sensing. Zn-pyNDI can serve as a room-temperature operable chemiresistive sensor selective to acetone.

Triazine-Porphyrin-Based Hyperconjugated Covalent Organic Framework for High-Performance Photocatalysis

Covalent organic frameworks (COFs) with porphyrins as structural units are a new kind of porous organic polymers, which have a regular and ordered structure, abundant porosity, and good stability. In the past, the construction of porphyrin COFs was generally synthesized by routes such as a Schiff base reaction. Here, we report a new COF structure by linking the porphyrin with the triazine ring. Using a cyano group-terminated porphyrin as a structural unit precursor, a new triazine-porphyrin hyperconjugated COF (TA-Por-sp²-COF) was constructed through the cyano group's self-polymerization. The extension of porphyrin units in two directions that stemmed from the cyano group at para-positions accounts for the establishment of a highly ordered two-dimensional topological structure. Attributing to the collaboration of electron-donating and withdrawing blocks for photo-induced carrier separation and adequate porosity for mass diffusion, this hyperconjugated system showed high photocatalytic performance in organic reactions such as the aerobic coupling reaction of benzylamine and thioanisole selective oxidation.

Bifunctional Fe@PCN-222 nanozyme-based cascade reaction system: Application in ratiometric fluorescence and colorimetric dual-mode sensing of glucose

This work innovatively integrated the peroxidase-mimicking activity and red emission property of Fe@PCN-222 framework, designed a cascade reaction system for dual-mode glucose sensing. The Fe³⁺ doping significantly improved the catalytic activity of Fe@PCN-222 that can oxidize the substrate o-phenylenediamine (OPD) to generate diminophenazine (DAP) with emission at 566 nm in the presence of H₂O₂. Similarly, the Fe@PCN-222 was used to catalyze the colorless TMB to produce blue oxidized TMB (oxTMB) showed absorption at 652 nm. When coupled with glucose oxidase (GOx), the linear ranges of ratiometric fluorescence mode and colorimetric mode for glucose sensing were 1-100 and 10-300 μM, respectively. And the limits of detection (LOD) of 0.78 and 2.41 μM for two modes were obtained, respectively. In addition, the practicability of Fe@PCN-222 nanozyme-based cascade reaction system for detection of glucose in human serum and saliva samples was successfully investigated. It is of great importance to integrate more functions into one skeleton to achieve dual-mode and optimal-performance sensing for expanding potential applications.

RhB-Embedded Zirconium-Biquinoline-Based MOF Composite for Highly Sensitive Probing Cr(VI) and Photochemical Removal of CrO42-, Cr2O72-, and MO

How to accurately detect and efficiently sweep Cr(VI) from contaminated water has come into focus. Zirconium-based metal-organic frameworks (MOFs) play vital roles in water environmental chemistry due to excellent hydrolysis-resistant stability. However, as photochemical probes and photocatalysts, poor performances in detection sensitivity, selectivity, and photosensitiveness limit sole Zr-MOFs' applications. So, it is urgent to quest valid strategies to break through the dilemmas. Embedding luminous dyes into MOFs has been considered one of the most feasible avenues. Herein, a dual-emissive RhB@Zr-MOF with orange-yellow fluorescence has been assembled by in situ-encapsulating rhodamine B (RhB) into a zirconium-biquinoline-based MOF. Actually, within RhB@Zr-MOF, the aggregation fluorescence quenching (ACQ) effect of RhB molecules was effectively avoided. Notably, RhB@Zr-MOF exhibits a rapid fluorescence quenching response toward Cr(VI) ions with high selectivity, sensitivity, and anti-interference abilities. More interestingly, unlike the most widely reported fluorescence resonance energy transfer (FRET) between MOFs and encapsulated guest modules, photoinduced electron transfer from RhB to Zr-MOF has been confirmed by modeling the ground state and excited states of RhB@Zr-MOF using density functional theory (DFT) and time-dependent DFT (TD-DFT). The effective electron transfer makes RhB@Zr-MOF more sensitive in probing Cr₂O₇^2- and CrO₄^2- ions with ultralow detection limit (DL) values of 6.27 and 5.26 ppb, respectively. Prominently, the detection sensitivity based on DL values has been increased about 6 and 9 times, respectively, compared with pristine Zr-MOF. Moreover, rather negative CB and positive VB potentials make RhB@Zr-MOF have excellent photochemical scavenging ability toward Cr(VI) and MO.

Metal-Organic Framework Accelerated One-Step Capture and Reduction of Palladium to Catalytically Active Nanoparticles

Recovery of noble metals and in situ transforming to functional materials hold great promise in the sustainability of natural resources but remain as a challenge. Herein, the variable chemical microenvironments created by the inorganic-organic hybrid composition of metal-organic frameworks (MOFs) were exploited to tune the metal-support interactions, thus establishing an integrated strategy for recovering and reducing palladium (Pd). Assisted by sonic waves and alcoholic solvent, selective capture of Pd(II) from a complicated matrix to directly afford Pd nanoparticles (NPs) in MOFs can be achieved in one step within several minutes. Mechanism investigation reveals that the Pd binding site and the energy barriers between ionic and metallic status are sensitive to chemical environments in different frameworks. Thanks to the clean, dispersive, and uniform nature of Pd NPs, Pd@MOFs synthesized from a complicated environment exhibited high catalytic activity toward 4-nitrophenol reduction and Suzuki coupling reactions.

Construction of Cu(I)-Organic Frameworks with Effective Sorption Behavior for Iodine and Congo Red

The assembly of a tetradentate pyridine-derived ligand with CuX has afforded two isostructural Cu(I)-organic frameworks [Cu₂X₂(TBD)·DMF]_n (X = Cl for 1 and Br for 2) in this work. Structural analysis indicates that the compounds feature hybrid layered architectures, and the three-dimensional supramolecular frameworks are finally fabricated through the alternative stacking of adjacent layers wherein large open channels are simultaneously constructed. The chemical stability has been studied showing the excellent skeleton maintenance of the prepared solids in various solvents and even in water. Moreover, the iodine and dye sorption performance for compound 1 has been further tested. The Cu(I)-based metal-organic framework exhibits outstanding sorption and separation abilities on the targeted species, which could be considered as a promising adsorbent with high efficiency and selectivity.

Ferric iron loaded porphyrinic zirconium MOFs on corncob for the enhancement of diuretics extraction

Herein, corncob waste was used as a scaffold for the fabrication of effective adsorbents. Porphyrinic zirconium metal-organic frameworks (MOFs) PCN-223 and PCN-224 constructed by different numbers of Zr6 cluster nodes were grown on the surface of the corncob. Fe (Ш) ions were implanted in the porphyrin ring by post-synthesis modification. The results showed that the extraction capacity of diuretics on PCN-224@corncob containing suitable pore size was larger than that of PCN-223@corncob. The adsorption of diuretics was further enhanced because of the electrostatic effect caused by implantation of Fe (Ш) ions. PCN-224-Fe@corncob was recyclable and selective for the extraction of furosemide (Fur) and bumetanide (Bum). Coupled in-syringe solid phase extraction (IS-SPE) with ultra-performance liquid chromatography (UPLC), an efficient, sensitive, and stable method was established. With a sensitivity between 0.6 and 1.0 μg/L and a recovery between 83.2% and 119.2%, it is used for the analysis of trace amounts of Fur and Bum in weight loss products and environmental water. The functionalized corncob has potential application for the adsorption of diuretics, and the metal ions implantation in MOFs provides a promising strategy for enhancing extraction capacity.

Single-crystal structure determination of nanosized metal-organic frameworks by three-dimensional electron diffraction

Metal-organic frameworks (MOFs) have attracted considerable interest due to their well-defined pore architecture and structural tunability on molecular dimensions. While single-crystal X-ray diffraction (SCXRD) has been widely used to elucidate the structures of MOFs at the atomic scale, the formation of large and well-ordered crystals is still a crucial bottleneck for structure determination. To alleviate this challenge, three-dimensional electron diffraction (3D ED) has been developed for structure determination of nano- (submicron-)sized crystals. Such 3D ED data are collected from each single crystal using transmission electron microscopy. In this protocol, we introduce the entire workflow for structural analysis of MOFs by 3D ED, from sample preparation, data acquisition and data processing to structure determination. We describe methods for crystal screening and handling of crystal agglomerates, which are crucial steps in sample preparation for single-crystal 3D ED data collection. We further present how to set up a transmission electron microscope for 3D ED data acquisition and, more importantly, offer suggestions for the optimization of data acquisition conditions. For data processing, including unit cell and space group determination, and intensity integration, we provide guidelines on how to use electron and X-ray crystallography software to process 3D ED data. Finally, we present structure determination from 3D ED data and discuss the important features associated with 3D ED data that need to be considered. We believe that this protocol provides critical details for implementing and utilizing 3D ED as a structure determination platform for nano- (submicron-)sized MOFs as well as other crystalline materials.

Two Solvent-Induced In(III)-Based Metal-Organic Frameworks with Controllable Topology Performing High-Efficiency Separation of C2H2/CH4 and CO2/CH4

For pure acetylene manufacturing and natural gas purification, the development of porous materials displaying highly selective C₂H₂/CH₄ and CO₂/CH₄ separation is greatly important but remains a major challenge. In this work, a plausible strategy involving solvent-induced effects and using the flexibility of the ligand conformation to make two In(III) metal-organic frameworks (MOFs) is developed, showing topological diversity and different stability. The X-shaped tetracarboxylic ligand H₄TPTA ([1,1':3',1″-terphenyl]-4,4',4″,6'-tetracarboxylic acid) was selected to construct two new heteroid In MOFs, namely, {[CH₃NH₃][In(TPTA)]·2(NMF)} (MOF 1) and {[In₂(TPTA)(OH)₂]·2(H₂O)·(DMF)} (MOF 2). MOF 1 is a (4, 4)-connected net showing a pts topology with a large channel that is not conducive to fine gas separation. By contrast, with the reduction of SBU from uninucleated In to an {In-OH-In}_n chain, MOF 2 has a (4, 6)-connected net with the fsc topology with an ∼5 Å suitable micropore to confine matching small gas. The permanent porosity of MOF 2 leads to the preferential adsorption of C₂H₂ over CO₂ with superior C₂H₂/CH₄ (332.3) and CO₂/CH₄ (31.2) separation selectivities. Meanwhile, the cycling dynamic breakthrough experiments showed that the high-purity C₂H₂ (>99.8%) capture capacities of MOF 2 were >1.92 mmol g^-1 from a binary C₂H₂/CH₄ mixture, and its separation factor reached 10.

Organoamine Templated Multifunctional Hybrid Metal Phosphonate Frameworks: Promising Candidates for Tailoring Electrochemical Behaviors and Size-Selective Efficient Heterogeneous Lewis Acid Catalysis

The successful discovery of novel multifunctional metal phosphonate framework materials that incorporate newer organoamines and their utilization as a potential electroactive material for energy storage applications (supercapacitors) and as efficient heterogeneous catalysts are the most enduring challenges at present. From this perspective, herein, four new inorganic-organic hybrid zinc organodiphosphonate materials, namely, [C₅H₁₄N₂]₂[Zn₆(hedp)₄] (I), [C₅H₁₄N₂]_0.5[Zn₃(Hhedp) (hedp)]·2H₂O (II), [C₆H₁₆N₂][Zn₃(hedp)₂] (III), and [C₁₀H₂₄N₄][Zn₆(Hhedp)₂(hedp)₂] (IV) (H₄hedp = 1-hydroxyethane 1,1-diphosphonic acid), have been synthesized through the introduction of different organoamines and then structurally analyzed using various techniques. The compounds (I-IV) possess a three-dimensional network through alternate connectivity of zinc ions and diphosphonate ligands, as confirmed using single-crystal X-ray diffraction. The investigations of electrochemical charge storage behaviors of the present compounds indicate that compound III exhibits a high specific capacitance of 190 F g^-1 (76 C g^-1) at 1 A g^-1, while compound II shows an excellent cycling stability of 90.11% even after 5000 cycles at 5 A g^-1 in the 6 M KOH solution. Further, the present materials have also been utilized as active heterogeneous Lewis acid catalysts in the ketalization reaction. The screening of various substrate scopes during the catalytic process confirms the size-selective heterogeneous catalytic nature of the framework compounds. To our utmost knowledge, such a size-selective heterogeneous Lewis acid catalytic behavior has been observed for the first time in the amine templated inorganic-organic hybrid framework family. Moreover, the excellent size-selective catalytic efficiencies with the d¹⁰ metal system and recyclability performances make the compounds (I-IV) more efficient and promising Lewis acid heterogeneous catalysts.

Improved performance of the pyrimidine-modified porous In-MOF and an in situ prepared composite Ag@In-MOF material

A stable porous In-MOF 1 was prepared for the first time via an asymmetric N,O-containing (2-pyrimidin-5-yl)terephthalic acid (H₂L). It was found that the 1,4-benzenedicarboxylate anions (bdc^2-) were formed in the synthesis process of 1. Thus, another new isomorphic In-MOF 2 was formed by employing the H₂bdc ligand in the synthesis process of 1. More importantly, when adding AgNO₃ in the synthesis process of 1 and 2, only composite Ag@1 was obtained via the in situ reduction of Ag(I) to Ag NPs without additional reducing agent. MOF 1 and Ag@1 had great sorption capacity; in particular, 1 had remarkable dynamic selectivity for C₂H₂/CH₄ and CO₂/CH₄, and they were also efficient catalysts for fixing CO₂ and epoxides. It is hoped that this work may supply an effective strategy to build stable MOFs and composite Ag@MOF materials with excellent multifunctional applications.

Fluorescence Biosensor for One-Step Simultaneous Detection of Mycobacterium tuberculosis Multidrug-Resistant Genes Using nanoCoTPyP and Double Quantum Dots

The diagnosis of multidrug-resistant tuberculosis (MDR-TB) is crucial for the subsequent drug guidance to improve therapy and control the spread of this infectious disease. Herein, we developed a novel florescence biosensor for simultaneous detection of Mycobacterium tuberculosis (Mtb) multidrug-resistant genes (rpoB531 for rifampicin and katG315 for isoniazid) by using our synthesized nanocobalt 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (nanoCoTPyP) and double quantum dots (QDs). Several nanoCoTPyPs with different charges and morphology were successfully prepared via the surfactant-assisted method and their quenching ability and restoring efficiency for DNA detection were systematically analyzed. It was found that spherical nanoCoTPyP with positive charge exhibited excellent quenching effect and sensing performance for the two DNAs' detection due to its affinity differences towards single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). ssDNA attached on QDs (QDs-ssDNA) was specifically hybridized with targets to form QDs-dsDNA, resulting in fluorescence recovery due to the disruption of the interactions between nanoCoTPyP and ssDNA. Two drug-resistant genes could be simultaneously quantified in a single run and relatively low limits of detection (LODs) were obtained (24 pM for T1 and 20 pM for T2). Furthermore, the accuracy and reliability of our method were verified by testing clinical samples. This simple and low-cost approach had great potential to be applied in clinical diagnosis of MDR-TB.

A high-efficient electrochemical synthesis of a low-nuclearity copper-cluster-based metal–organic framework for the size-selective oxidation of alcohols

A copper-cluster-based micropore MOF, namely H-1e, possessing excellent oxidation activity for alcohols (mini-size) to aldehydes with over 99% selectivity and 99% yield, has been obtained by a highly efficient electrochemical synthesis.

Ligand regulated metal–organic frameworks for synergistic photoredox and nickel catalysis

Synergistic photoredox and nickel catalytic cross-coupling systems have created a great attraction as a promising methodology to produce the aryl C−N bonds under mild conditions as well as extreme challenge,...

Switchable Ionic Transportation in the Nanochannels of the MOFs Triggered by Light and pH

The construction of a biomimetic ionic channel is of great significance for the fabrication of smart biodevices or logic circuit. Inspired by the selective permeability of the cell membrane toward bioions, a light-induced and pH-modulated artificial nanochannel is herein prepared by integrating the multistimuli-response molecule of carboxylated spiropyran (SP-COOH) into the frameworks of NU-1000 (Zr-based MOFs defined by Northwestern University). The loading density of the SP-COOH could reach as high as 7 wt % while keeping unchanged crystallinity and high porosity. Thanks to the precise matching of pore size of NU-1000 and molecular dimensions of SP-COOH, the loaded molecules could proceed free and reversible for isomerization between the hydrophilic and hydrophobic states. The ion-switchable characteristics of the channel are implemented by the amphiphilic change of the light-controlled gate molecule. Additionally, in the hydrophilic state, the channel presents reversible affinity toward cations or anions due to the reverse charge state induced by pH, thus constructing a pH-controlled subgate. Taking [Ru(NH₃)₆]³⁺ and [Fe(NH₃)]^3- as the model cation and anion, their redox peak currents occur as reversible change under different signal combinations of light and pH. Moreover, in accordance with the ionic selective permeability, several logic circuits/devices are designed to display the relationships between exogenous stimuli and ionic transportations in a computer language, prefiguring their wide application prospects in electronic devices and life sciences.