Kinetically Controlled Reticular Assembly of a Chemically Stable Mesoporous Ni(II)-Pyrazolate Metal–Organic Framework

Controlling the Degree of Interpenetration in Chiral Three-Dimensional Covalent Organic Frameworks via Steric Tuning

Network interpenetration plays a crucial role in functionalizing porous framework materials. However, controlling the degree of interpenetration in covalent organic frameworks (COFs) to influence their pore sizes, shapes, and functionalities still remains a significant challenge. Here, we demonstrate a steric tuning strategy to control the degree of COF interpenetration and modulate their physicochemical properties. By imine condensations of 1,1'-bi-2-naphthol-derived tetraaldehydes bearing different alkyl substituents with the monomer tetra(p-aminophenyl)-methane, we synthesized and characterized a family of two-component and three-component chiral COFs with different interpenetrated dia networks. The alkyl groups are periodically appended on the pore walls, and their types/contents that can be synthetically tuned control the interpenetration degree of COFs by minimizing repulsive interactions between the alkyl groups. Specifically, the COF with -OH groups adopts an interpenetrated dia-c5 topology, those with -OMe/-OEt groups take an interpenetrated dia-c4 topology, whereas those with the bulky -OnPr/-OnBu groups exhibit a noninterpenetrated dia-c1 topology. The multivariate COFs with both -OH and -OnBu groups display either a noninterpenetrated or dia-c5 topology, depending on the proportion of -OnBu groups. The extent of interpenetration in COFs significantly affects their porosity, thermal stability, and chemical stability, resulting in varying selective performances in the adsorption and separation of dyes and asymmetric catalysis. This work highlights the potential of using steric hindrance to tune and control interpenetration, porosity, stability, and functionalities of COFs materials, broadening the range of their applications.

Elucidating the transport of water and ions in the nanochannel of covalent organic frameworks by molecular dynamics

Inspired by biological channels, achieving precise separation of ion/water and ion/ion requires finely tuned pore sizes at molecular dimensions and deliberate exposure of charged groups. Covalent organic frameworks (COFs), a class of porous crystalline materials, offer well-defined nanoscale pores and diverse structures, making them excellent candidates for nanofluidic channels that facilitate ion and water transport. In this study, we perform molecular simulations to investigate the structure and kinetics of water and ions confined within the typical COFs with varied exposure of charged groups. The COFs exhibit vertically arrayed nanochannels, enabling diffusion coefficients of water molecules within COFs to remain within the same order of magnitude as in the bulk. The motion of water molecules manifests in two distinct modes, creating a mobile hydration layer around acid groups. The ion diffusion within COFs displays a notable disparity between monovalent (M+) and divalent (M2+) cations. As a result, the selectivity of M+/M2+ can exceed 100, while differentiation among M+ is less pronounced. In addition, our simulations indicate a high rejection (R > 98%) in COFs, indicating their potential as ideal materials for desalination. The chemical flexibility of COFs indicates that would hold significant promise as candidates for advanced artificial ion channels and separation membranes.

Metalation of metal-organic frameworks: fundamentals and applications

Metalation of metal-organic frameworks (MOFs) has been developed as a prominent strategy for materials functionalization for pore chemistry modulation and property optimization. By introducing exotic metal ions/complexes/nanoparticles onto/into the parent framework, many metallized MOFs have exhibited significantly improved performance in a wide range of applications. In this review, we focus on the research progress in the metalation of metal-organic frameworks during the last five years, spanning the design principles, synthetic strategies, and potential applications. Based on the crystal engineering principles, a minor change in the MOF composition through metalation would lead to leveraged variation of properties. This review starts from the general strategies established for the incorporation of metal species within MOFs, followed by the design principles to graft the desired functionality while maintaining the porosity of frameworks. Facile metalation has contributed a great number of bespoke materials with excellent performance, and we summarize their applications in gas adsorption and separation, heterogeneous catalysis, detection and sensing, and energy storage and conversion. The underlying mechanisms are also investigated by state-of-the-art techniques and analyzed for gaining insight into the structure-property relationships, which would in turn facilitate the further development of design principles. Finally, the current challenges and opportunities in MOF metalation have been discussed, and the promising future directions for customizing the next-generation advanced materials have been outlined as well.

A Robust Pyrazolate Metal-Organic Framework for Efficient Catalysis of Dehydrogenative C-O Cross Coupling Reaction

Construction of robust heterogeneous catalysts with atomic precision is a long-sought pursuit in the catalysis field due to its fundamental significance in taming chemical transformations. Herein, we present the synthesis of a single-crystalline pyrazolate metal-organic framework (MOF) named PCN-300, bearing a lamellar structure with two distinct Cu centers and one-dimensional (1D) open channels when stacked. PCN-300 exhibits exceptional stability in aqueous solutions across a broad pH range from 1 to 14. In contrast, its monomeric counterpart assembled through hydrogen bonding displays limited stability, emphasizing the role of Cu-pyrazolate coordination bonds in framework robustness. Remarkably, the synergy of the 1D open channels, excellent stability, and the active Cu-porphyrin sites endows PCN-300 with outstanding catalytic activity in the cross dehydrogenative coupling reaction to form the C-O bond without the "compulsory" ortho-position directing groups (yields up to 96%), outperforming homogeneous Cu-porphyrin catalysts. Moreover, PCN-300 exhibits superior recyclability and compatibility with various phenol substrates. Control experiments reveal the synergy between the Cu-porphyrin center and framework in PCN-300 and computations unveil the free radical pathway of the reaction. This study highlights the power of robust pyrazolate MOFs in directly activating C-H bonds and catalyzing challenging chemical transformations in an environmentally friendly manner.

Advanced Functionalized Nanoclusters (Cu, Ag, and Au) as Effective Catalyst for Organic Transformation Reactions

A considerable amount of research has been carried out in recent years on synthesizing metal nanoclusters (NCs), which have wide applications in the field of optical materials with non-linear properties, bio-sensing, and catalysis. Aside from being structurally accurate, the atomically precise NCs possess well-defined compositions due to significant tailoring, both at the surface and the core, for certain functionalities. To illustrate the importance of atomically precise metal NCs for catalytic processes, this review emphasizes 1) the recent work on Cu, Ag, and Au NCs with their synthesis, 2) the parameters affecting the activity and selectivity of NCs catalysis, and 3) the discussion on the catalytic potential of these metal NCs. Additionally, metal NCs will facilitate the design of extremely active and selective catalysts for significant reactions by elucidating catalytic mechanisms at the atomic and molecular levels. Future advancements in the science of catalysis are expected to come from the potential to design NCs catalysts at the atomic level.

Continuously Tunable MOFs Enable Precise Mass Transfer for High-Performance Isomer Separation

Modulating mass transfer is crucial for optimizing the catalytic and separation performances of porous materials. Here, we systematically developed a series of continuously tunable MOFs (CTMOFs) that exhibit incessantly increased mass transfer. This was achieved through the strategic blending of ligands with different lengths and ratios in MOFs featuring the fcu topology. By employing a proportional mixture of two ligands in the synthesis of UiO-66, the micropores expanded, facilitating faster mass transfer. The mass transfer rate was evaluated by dye adsorption, dark-field microscopy, and gas chromatography (GC). The GC performance proved that both too-fast and too-slow mass transfer led to low separation performance. The optimized mass transfer in CTMOFs resulted in an exceptionally high separation resolution (5.96) in separating p-xylene and o-xylene. Moreover, this study represents the first successful use of MOFs for high-performance separation of propylene and propane by GC. This strategy provides new inspiration in regulating mass transfer in porous materials.

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.

Isoreticular Expansion and Linker-Enabled Control of Interpenetration in Titanium-Organic Frameworks

Titanium-organic frameworks offer distinctive opportunities in the realm of metal-organic frameworks (MOFs) due to the integration of intrinsic photoactivity or redox versatility in porous architectures with ultrahigh stability. Unfortunately, the high polarizing power of Ti4+ cations makes them prone to hydrolysis, thus preventing the systematic design of these types of frameworks. We illustrate the use of heterobimetallic cluster Ti2Ca2 as a persistent building unit compatible with the isoreticular design of titanium frameworks. The MUV-12(X) and MUV-12(Y) series can be all synthesized as single crystals by using linkers of varying functionalization and size for the formation of the nets with tailorable porosity and degree of interpenetration. Following the generalization of this approach, we also gain rational control over interpenetration in these nets by designing linkers with varying degrees of steric hindrance to eliminate stacking interactions and access the highest gravimetric surface area reported for titanium(IV) MOFs (3000 m2 g-1).

Thiacalix[4]arene-protected alkynyl Agn (n = 9, 18) nanoclusters: syntheses, structural characterizations, photocurrent responses and fluorescence properties

Two thiacalix[4]arene-protected silver(I) alkynyl nanoclusters, [Na2(H2O)2][Ag9(TC4A)(tBuCC)4(CH3OH)2(SbF6)0.5(OH)2.5]·3.5H2O·CH3OH (1, abbreviated as Ag9) and [Ag9(TC4A)(tBuCC)4(CF3COO)]2·4CH3OH (2, abbreviated as Ag18), were synthesized by the reaction of [tBuCCAg]n, p-tert-butylthiacalix[4]arene (H4TC4A), NaBH4, and AgSbF6 or CF3COOAg in the mixed solvent of methanol-trichloromethane-toluene under solvothermal conditions, respectively. Driven by SbF6- and CF3COO- with different coordination properties, the structural unit [Ag9(TC4A)(tBuCC)4]+ in both the compounds migrated in different modes, accompanied by distinct Ag⋯Ag distances. Ag9 and Ag18 exhibit similar UV-Vis absorption and diffuse reflection spectra along with contrary tendency between photocurrent responses and solid-state fluorescence. The solution stability of Ag9 and Ag18 was demonstrated by 1H NMR and MALDI-TOF mass spectrometry. The fluorescence responses of Ag9 and Ag18 towards different organic molecules were also investigated, which indicated that the polarity of solvent has a certain effect on the emission intensities of Ag9 and Ag18. This study provides a positive guide for the controlled synthesis and further study of the structure-activity relationship of thiacalix[4]arene-protected silver alkynyl nanoclusters.

Self-Catalysis Transformation of Metal-Organic Coordination Polymers

Designing a multidimensional transformation of metal-organic coordination polymers (MOPs) is highly attractive yet very challenging. Herein, by combining the dynamicity of the coordination bond with the controllability of the chemical reaction, the concept of self-catalysis transformation of MOPs is first proposed. It uses the metal in MOPs as the catalyst to catalyze the chemical reaction of the ligand in the frameworks, simultaneously changing the coordination environment of the metal and the structure of the ligand, resulting in the controllable multidimensional transformation in the morphology and structure of MOPs. The self-catalysis transformation of MOPs can be triggered by heat or light, and crystals with various morphologies and structures can be obtained. Significantly, because the self-catalysis reaction is constraint in the framework, the products at different transformation processes are relatively stable. Monitoring and characterizing the transformation of MOPs give evidences for the exploration of the self-catalysis reaction, and a plausible transformation mechanism is proposed and proved. It can be foreseen that this novel self-catalysis transformation strategy might open up a new direction for the diverse development of MOPs and provide a powerful tool for the study of organic reaction mechanism.

A customized MOF-polymer composite for rapid gold extraction from water matrices

With the fast-growing accumulation of electronic waste and rising demand for rare metals, it is compelling to develop technologies that can promotionally recover targeted metals, like gold, from waste, a process referred to as urban mining. Thus, there is increasing interest in the design of materials to achieve rapid, selective gold capture while maintaining high adsorption capacity, especially in complex aqueous-based matrices. Here, a highly porous metal-organic framework (MOF)-polymer composite, BUT-33-poly(para-phenylenediamine) (PpPD), is assessed for gold extraction from several matrices including river water, seawater, and leaching solutions from CPUs. BUT-33-PpPD exhibits a record-breaking extraction rate, with high Au³⁺ removal efficiency (>99%) within seconds (less than 45 s), a competitive capacity (1600 mg/g), high selectivity, long-term stability, and recycling ability. Furthermore, the high porosity and redox adsorption mechanism were shown to be underlying reasons for the material's excellent performance. Given the accumulation of recovered metallic gold nanoparticles inside, the material was also efficiently applied as a catalyst.

Hollow Carbon Nanopillar Arrays Encapsulated with Pd-Cu Alloy Nanoparticles for the Oxygen Evolution Reaction

Delicate design and bottom-up synthesis of hollow nanostructures for oxygen evolution electrocatalysts is a promising way to accelerate the reaction kinetics of overall water splitting. Herein, an efficient and versatile strategy for the controllable preparation of Pd-Cu alloy nanoparticles encapsulated in carbon nanopillar arrays (PD-Cu@HPCN) is developed. Core-shell structured MOF@imidazolium-based ionic polymers (ImIPs) have been prepared and adopted as a template, along with the decomposition of the inner Cu-MOFs when an anion exchange occurs between sodium tetrachloropalladate in solution and bromides in the external ImIP shell. Pd nanoparticles will be highly dispersed in the resulting Pd-Cu@HO-ImIP array, and subsequent topotactic transformation generates Pd-Cu@HNPC. No hazardous reagents or tedious steps are used to remove the inner Cu-MOF templates in contrast to the traditional top-down methods. Remarkably, the Pd-Cu@HPCN catalyst possesses outstanding oxygen evolution reaction (OER) activity, including small overpotential with 10 mA cm^-2 at an overpotential of 188 mV, a large double layer capacitance (73.8 mF cm^-2), and high stability (20 h). This simple, green, and efficient synthesis methodology represents a new way to design metal alloys for OER electrocatalysts or other electrocatalytic devices.

An Atomically Precise Pyrazolate-Protected Copper Nanocluster Exhibiting Exceptional Stability and Catalytic Activity

The synthesis of atomically precise copper nanoclusters (Cu-NCs) with high chemical stability is a prerequisite for practical applications, yet still remains a long-standing challenge. Herein, we have prepared a pyrazolate-protected Cu-NC (Cu8), which exhibited exceptional chemical stability either in solid-state or in solution. The crystals of Cu8 are still suitable for single crystal X-ray diffraction analysis even after being treated with boiling water, 8 wt % H₂ O₂ , high concentrated acid (1 M HCl) or saturated base (≈20 M KOH), respectively. More importantly, the structure of Cu8 in solution also remained intact toward oxygen, organic acid (100 eq. HOAc) or base (400 eq. dibutylamine) confirmed by ¹ H NMR and UV/Vis analysis. Taking advantage of high alkali-resistant, Cu8 illustrates excellent catalytic activity for the synthesis of indolizines, and it can be reused for at least 10 cycles without losing catalytic performance.

Construction of a MOF-Supported Palladium Catalyst via Metal Metathesis

A new MOF-supported heterogeneous palladium catalyst Pd/NBB-1 has been synthesized successfully through the effective metal metathesis between Pd(CF₃ COO)₂ and NBB-1. NBB-1 is a two-dimensional zinc metal-organic framework constructed from 2-aminoterephthalate (NH₂ -H₂ BDC) and 2,2'-bipyridine-5-carboxylate (HBPC) by solvothermal method. The replacement efficiency of Pd(II) to Zn(II) is up to 72% after only 24 hours, which is beneficial to the catalytic application. Pd/NBB-1 with a low loading of 2 mol% works efficiently in the 1,4-addition reaction of arylboronic acids with α,β-unsaturated ketones in air, and its catalytic activity keeps unchanged after 3 reaction cycles. This work provides a new strategy to effectively prepare supported noble metal/MOF catalysts, which would further increase the practical applications of metal-organic frameworks.

Remarkable proton conducting behavior driven by synergistic effects in acid-base conjugated MOFs impregnated with sulphuric acid molecules

The Coulomb force between protons and negative charges usually leads to low proton diffusion and poor proton conductivity. Herein, acid-base conjugated MOFs of UiO-66-SO₃^--NH₃⁺ were constructed by linking sulfonic acid and amine groups to an organic skeleton. According to the XPS and elemental analysis, the ratio of 2-aminoterephthalic acid/2-sulfoterephthalic acid was ∼1.9 in UiO-66-SO₃^--NH₃⁺. After introducing sulphuric acid molecules, the MOF-based electrolyte exhibited a remarkable proton conductivity of 5.40 × 10^-1 S cm^-1 and low activation energy of 0.15 eV at 100% RH and 90 °C. This remarkable proton conducting behavior was generated by the synergistic system in the MOF, which contained certain synergistic effects such as between -SO₃^-⋯H⁺⋯SO₄^2- and NH₃⁺⋯SO₄^2-, therefore possessing a Grotthuss mechanism, which facilitates facile proton transport.

Catalytic ozone decomposition and adsorptive VOCs removal in bimetallic metal-organic frameworks

Atmospheric ozone has long been a threat to human health, however, rational design of high-performance O₃-decomposition catalysts remains challenging. Herein, we demonstrate the great potential of a series of isomorphous bimetallic MOFs denoted as PCN-250(Fe₂M) (M = Co²⁺, Ni²⁺, Mn²⁺) in catalytic O₃ decomposition. Particularly, PCN-250(Fe₂Co) showed 100% O₃ removal efficiency for a continuous air flow containing 1 ppm O₃ over a wide humidity range (0 ‒ 80% RH) at room temperature. Mechanism studies suggested that the high catalytic performance originated from the introduction of open Co(II) sites as well as its porous structure. Additionally, at low pressures around 10 Pa, PCN-250(Fe₂Co) exhibited high adsorption capacities (89 ‒ 241 mg g^-1) for most VOCs, which are not only a class of hazardous air pollutants but also the precursor of O₃. This work opens up a new avenue to develop advanced air purification materials for O₃ and VOCs removal in one.

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.

Biomimetic material degradation for synergistic enhanced therapy by regulating endogenous energy metabolism imaging under hypothermia

Inefficient tumour treatment approaches often cause fatal tumour metastases. Here, we report a biomimetic multifunctional nanoplatform explicitly engineered with a Co-based metal organic framework polydopamine heterostructure (MOF-PDA), anethole trithione (ADT), and a macrophage membrane. Co-MOF degradation in the tumour microenvironment releases Co²⁺, which results in the downregulation of HSP90 expression and the inhibition of cellular heat resistance, thereby improving the photothermal therapy effect of PDA. H₂S secretion after the enzymatic hydrolysis of ADT leads to high-concentration gas therapy. Moreover, ADT changes the balance between nicotinamide adenine dinucleotide/flavin adenine dinucleotide (NADH/FAD) during tumour glycolysis. ATP synthesis is limited by NADH consumption, which triggers a certain degree of tumour growth inhibition and results in starvation therapy. Potentiated 2D/3D autofluorescence imaging of NADH/FAD is also achieved in liquid nitrogen and employed to efficiently monitor tumour therapy. The developed biomimetic nanoplatform provides an approach to treat orthotopic tumours and inhibit metastasis.

Metal organic frameworks (MOF) coated with mammalian cell membranes have good biocompatibility. Here, the authors develop a cobalt based hydrogen sulphide producing MOF cloaked with a macrophage membrane and show that the subsequent system can reduce tumour growth in mice.

Anionic or neutral? the charge of Ni8 cubes in metal-organic framework compounds

The cubic SBU Ni₈X₆L₆ (X = OH^-/H₂O, L = ligand) is of great interest due to its stability and potential applications when integrated in MOFs. Here, we investigate by detailed DRIFTS measurements and exchange reactions whether it is found to be neutral in MOFs, as previously assumed in the literature, or whether it can show anionic character, as observed in complexes.

Construction and application of base-stable MOFs: a critical review

Metal-organic frameworks (MOFs) are a new class of porous crystalline materials constructed from organic ligands and metal ions/clusters. Owing to their unique advantages, they have attracted more and more attention in recent years and numerous studies have revealed their great potential in various applications. Many important applications of MOFs inevitably involve harsh alkaline operational environments. To achieve high performance and long cycling life in these applications, high stability of MOFs against bases is necessary. Therefore, the construction of base-stable MOFs has become a critical research direction in the MOF field. This review gives a historic summary of the development of base-stable MOFs in the last few years. The key factors that can determine the robustness of MOFs under basic conditions are analyzed. We also demonstrate the exciting achievements that have been made by utilizing base-stable MOFs in different applications. In the end, we discuss major challenges for the further development of base-stable MOFs. Some possible methods to address these problems are presented.

Trace removal of benzene vapour using double-walled metal-dipyrazolate frameworks

In principle, porous physisorbents are attractive candidates for the removal of volatile organic compounds such as benzene by virtue of their low energy for the capture and release of this pollutant. Unfortunately, many physisorbents exhibit weak sorbate-sorbent interactions, resulting in poor selectivity and low uptake when volatile organic compounds are present at trace concentrations. Herein, we report that a family of double-walled metal-dipyrazolate frameworks, BUT-53 to BUT-58, exhibit benzene uptakes at 298 K of 2.47-3.28 mmol g^-1 at <10 Pa. Breakthrough experiments revealed that BUT-55, a supramolecular isomer of the metal-organic framework Co(BDP) (H₂BDP = 1,4-di(1H-pyrazol-4-yl)benzene), captures trace levels of benzene, producing an air stream with benzene content below acceptable limits. Furthermore, BUT-55 can be regenerated with mild heating. Insight into the performance of BUT-55 comes from the crystal structure of the benzene-loaded phase (C₆H₆@BUT-55) and density functional theory calculations, which reveal that C-H···X interactions drive the tight binding of benzene. Our results demonstrate that BUT-55 is a recyclable physisorbent that exhibits high affinity and adsorption capacity towards benzene, making it a candidate for environmental remediation of benzene-contaminated gas mixtures.

Rapid Generation of Metal-Organic Framework Phase Diagrams by High-Throughput Transmission Electron Microscopy

Metal-organic frameworks (MOFs) constructed from Zr₆ nodes and tetratopic carboxylate linkers display high structural diversity and complexity in which various crystal topologies can result from identical building units. To determine correlations between MOF topologies and experimental parameters, such as solvent choice or modulator identity and concentration, we demonstrate the rapid generation of phase diagrams for Zr₆-MOFs with 1,4-dibromo-2,3,5,6-tetrakis(4-carboxyphenyl)benzene linkers under a variety of conditions. We have developed a full set of methods for high-throughput transmission electron microscopy (TEM), including automated sample preparation and data acquisition, to accelerate MOF characterization. The use of acetic acid as a modulator yields amorphous, NU-906, NU-600, and mixed-phase structures depending on the ratio of N,N-dimethylformamide to N,N-diethylformamide solvent and the quantity of the modulator. Notably, the use of formic acid as a modulator enables direct control of crystal growth along the c direction through variation of the modulator quantity, thus realizing aspect ratio control of NU-1008 crystals with different catalytic hydrolysis performance toward a nerve agent simulant.

Homogeneously Mixing Different Metal-Organic Framework Structures in Single Nanocrystals through Forming Solid Solutions

Pore engineering plays a significant role in the applications of porous materials, especially in the area of separation and catalysis. Here, we demonstrated a metal-organic framework (MOF) solid solution (MOSS) strategy to homogeneously and controllably mix NU-1000 and NU-901 structures inside single MOF nanocrystals. The key for the homogeneous mixing and forming of MOSS was the bidentate modulator, which was designed to have a slightly longer distance between two carboxylate groups than the original tetratopic ligand. All of the MOSS nanocrystals showed a uniform pore size distribution with a well-tuned ratio of mesopores to micropores. Because of the appropriate pore ratio, MOSS nanocrystals can balance the thermodynamic interactions and kinetic diffusion of the substrates, thus showing exceedingly higher separation abilities and a unique elution sequence. Our work proposes a rational strategy to design mixed-porous MOFs with controlled pore ratios and provides a new direction to design homogeneously mixed MOFs with a high separation ability and unique separation selectivity.

Identification of a metastable uranium metal–organic framework isomer through non-equilibrium synthesis

Since the structure of supramolecular isomers determines their performance, rational synthesis of a specific isomer hinges on understanding the energetic relationships between isomeric possibilities. To this end, we have systematically interrogated a pair of uranium-based metal–organic framework topological isomers both synthetically and through density functional theory (DFT) energetic calculations. Although synthetic and energetic data initially appeared to mismatch, we assigned this phenomenon to the appearance of a metastable isomer, driven by levers defined by Le Châtelier's principle. Identifying the relationship between structure and energetics in this study reveals how non-equilibrium synthetic conditions can be used as a strategy to target metastable MOFs. Additionally, this study demonstrates how defined MOF design rules may enable access to products within the energetic phase space which are more complex than conventional binary (e.g., kinetic vs. thermodynamic) products.

Identifying the relationship between structure and energetics in a uranium MOF isomer system reveals how non-equilibrium synthetic conditions can be used as a strategy to target metastable MOFs.

Building an emission library of donor–acceptor–donor type linker-based luminescent metal–organic frameworks

An emission library was built for donor–acceptor–donor type linker-based LMOFs, which can be used to rationally design organic linkers to prepare LMOFs with emission from deep blue to near-infrared.

State-of-the-Art Advancements in Photocatalytic Hydrogenation: Reaction Mechanism and Recent Progress in Metal-Organic Framework (MOF)-Based Catalysts

Photocatalytic hydrogenation provides an effective alternative way for the synthesis of industrial chemicals to meet the economic and environment expectations. Especially, over the past few years, metal-organic frameworks (MOFs), featured with tunable structure, porosity, and crystallinity, have been significantly developed as many high-performance catalysts in the field of photocatalysis. In this review, the background and development of photocatalytic hydrogenation are systemically summarized. In particular, the comparison between photocatalysis and thermal catalysis, and the fundamental understanding of photohydrogenation, including reaction pathways, reducing species, regulation of selectivity, and critical parameters of light, are proposed. Moreover, this review highlights the advantages of MOFs-based photocatalysts in the area of photohydrogenation. Typical effective strategies for modifying MOFs-based composites to produce their advantages are concluded. The recent progress in the application of various types of MOFs-based photocatalysts for photohydrogenation of unsaturated organic chemicals and carbon dioxide (CO2 ) is summarized and discussed in detail. Finally, a brief conclusion and personal perspective on current challenges and future developments of photocatalytic hydrogenation processes and MOFs-based photocatalysts are also highlighted.

Hexahydric Components Metal Organic Frameworks Constructed by Multiple Ligands and Mixed-Valence Ions

In this work, we report two multi-component MOFs [CH3NH2CH3]2[FeIII2MII10(tz)11(HCO2)12(btc)5/3] (MII10 = FeII10 for 1 and MII10 = FeII2CoII8 for 2) obtained by solvothermal assembling formate, benzene-1,3,5-tricarboxylate (btc) and 1,2,4 triazole...

A highly stable Zn9-pyrazolate metal–organic framework with metallosalen ligands as a carbon dioxide cycloaddition catalyst

A three-dimensional (3D) metal–organic framework constructed from unprecedented Zn9O2(OH)2(pyz)12 (pyz = pyrazolate) clusters and Ni(salen)-derived linkers was reported.

Impact of Zr6 Node in a Metal-Organic Framework for Adsorptive Removal of Antibiotics from Water

Quinolone-based antibiotics commonly detected in surface, ground, and drinking water are difficult to remove and therefore pose a threat as organic contaminants of aqueous environment. We performed adsorptive removal of quinolone antibiotics, nalidixic acid and ofloxacin, using a zirconium-porphyrin-based metal-organic framework (MOF), PCN-224. PCN-224 exhibits the highest adsorption capacities for both nalidixic acid and ofloxacin among those reported for MOFs to date. The accessible metal sites of Zr metal nodes are responsible for efficient adsorptive removal. This study offers a pragmatic approach to design MOFs optimized for adsorptive removal of antibiotics.

A switchable sensor and scavenger: detection and removal of fluorinated chemical species by a luminescent metal-organic framework

Fluorosis has been regarded as a worldwide disease that seriously diminishes the quality of life through skeletal embrittlement and hepatic damage. Effective detection and removal of fluorinated chemical species such as fluoride ions (F⁻) and perfluorooctanoic acid (PFOA) from drinking water are of great importance for the sake of human health. Aiming to develop water-stable, highly selective and sensitive fluorine sensors, we have designed a new luminescent MOF In(tcpp) using a chromophore ligand 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine (H₄tcpp). In(tcpp) exhibits high sensitivity and selectivity for turn-on detection of F⁻ and turn-off detection of PFOA with a detection limit of 1.3 μg L⁻¹ and 19 μg L⁻¹, respectively. In(tcpp) also shows high recyclability and can be reused multiple times for F⁻ detection. The mechanisms of interaction between In(tcpp) and the analytes are investigated by several experiments and DFT calculations. These studies reveal insightful information concerning the nature of F⁻ and PFOA binding within the MOF structure. In addition, In(tcpp) also acts as an efficient adsorbent for the removal of F⁻ (36.7 mg g⁻¹) and PFOA (980.0 mg g⁻¹). It is the first material that is not only capable of switchable sensing of F⁻ and PFOA but also competent for removing the pollutants via different functional groups.

A robust In-MOF, In(tcpp), demonstrates sensitive detection of the fluorinated chemical species F⁻ and PFOA via distinctly different luminescence signal change, and effective adsorption and removal of both species from aqueous solution.

Probing Molecular Motions in Metal-Organic Frameworks by Three-Dimensional Electron Diffraction

Flexible metal-organic frameworks (MOFs) are known for their vast functional diversities and variable pore architectures. Dynamic motions or perturbations are among the highly desired flexibilities, which are key to guest diffusion processes. Therefore, probing such motions, especially at an atomic level, is crucial for revealing the unique properties and identifying the applications of MOFs. Nuclear magnetic resonance (NMR) and single-crystal X-ray diffraction (SCXRD) are the most important techniques to characterize molecular motions but require pure samples or large single crystals (>5 × 5 × 5 μm3), which are often inaccessible for MOF synthesis. Recent developments of three-dimensional electron diffraction (3D ED) have pushed the limits of single-crystal structural analysis. Accurate atomic information can be obtained by 3D ED from nanometer- and submicrometer-sized crystals and samples containing multiple phases. Here, we report the study of molecular motions by using the 3D ED method in MIL-140C and UiO-67, which are obtained as nanosized crystals coexisting in a mixture. In addition to an ab initio determination of their framework structures, we discovered that motions of the linker molecules could be revealed by observing the thermal ellipsoid models and analyzing the atomic anisotropic displacement parameters (ADPs) at room temperature (298 K) and cryogenic temperature (98 K). Interestingly, despite the same type of linker molecule occupying two symmetry-independent positions in MIL-140C, we observed significantly larger motions for the isolated linkers in comparison to those reinforced by π-π stacking. With an accuracy comparable to that of SCXRD, we show for the first time that 3D ED can be a powerful tool to investigate dynamics at an atomic level, which is particularly beneficial for nanocrystalline materials and/or phase mixtures.

Functional Porphyrinic Metal-Organic Framework as a New Class of Heterogeneous Halogen-Bond-Donor Catalyst

Biomimetic metal-organic frameworks have attracted great attention as they can be used as bio-inspired models, allowing us to gain important insights into how large biological molecules function as catalysts. In this work, we report the synthesis and utilization of such a metal-metalloporphyrin framework (MMPF) that is constructed from a custom-designed ligand as an efficient halogen bond donor catalyst for Diels-Alder reactions under ambient conditions. The implementation of fabricated halogen bonding capsule as binding pocket with high-density C-Br bonds enabled the use of halogen bonding to facilitate organic transformations in their three-dimensional cavities. Through combined experimental and computational studies, we showed that the substrate molecules diffuse through the pores of the MMPF, establishing a host-guest system via the C-Br⋅⋅⋅π interaction. The formation of halogen bonds is a plausible explanation for the observed boosted catalytic efficiency in Diels-Alder reactions. Moreover, the unique capability of MMPF highlights new opportunities in using artificial non-covalent binding pockets as highly tunable and selective catalytic materials.

Anchoring Ag(I) into Nitro-Functionalized Metal-Organic Frameworks: Effectively Catalyzing Cycloaddition of CO2 with Propargylic Alcohols under Mild Conditions

Carboxylative cyclization of propargylic alcohols with CO₂ is significant in synthetic chemistry, but harsh conditions are often needed according to reported results. Herein, a new stable nitro-functionalized metal-organic framework (MOF) of {[Co₃(L)₂(bpy)₄(H₂O)₂]·DMF·H₂O·bpy}_n (1) was fabricated through the solvothermal reaction, which exhibited excellent stability in acid and basic solutions. Owing to the porous structure, unsaturated metal sites, and uncoordinated 4,4'-bpy ligands, 1 can serve as an excellent platform for catalytic applications. Hence, Ag(I) ions were incorporated in 1 through a postsynthetic method, and the as-synthesized Ag-1 catalyst with low metal loading (0.64 mol %) displayed excellent catalytic performance in the chemical fixation of CO₂ with alkynols under room temperature and atmospheric pressure. The results of ¹H NMR analyses further confirmed that Ag-1 can efficiently activate hydroxyl groups and promote the reaction. Moreover, the turnover frequency (TOF) of the Ag-1 catalyst can reach 262 h^-1 in a short period of time, which is a high TOF value among the state-of-the-art MOF-based catalysts for catalyzing cycloaddition of CO₂ with propargylic alcohols.

Double-Walled Metal-Organic Framework with Regulable Pore Environments for Efficient Removal of Radioactive Cesium Cations

An anion double-walled metal-organic framework [Co₂Li₄(BTC)₃(DMF)(H₂O)·(CH₃)₂N]_n (1) based on heterobimetallic Li⁺ and Co²⁺ ions was successfully constructed. Utilizing selective destruction and formation of Co-O/Co-N bonds in the metal chains, [Co₂Li₄(BTC)₃(py)(H₂O)·(CH₃)₂N]_n (2) and [Co₂Li₄(BTC)₃(pi)(H₂O)·(CH₃)₂N]_n (3) with the same skeleton but distinct pore structures can be surprisingly obtained. Additionally, compounds 2 and 3 can be transformed into [Co₂Li₄(BTC)₃(H₂O)₂·(CH₃)₂N]_n (4) by soaking them in an ethanol solution. This kind of single-crystal-to-single-crystal transformation successfully regulates the pore structure of MOFs and enriches the diversity of the pore wall on the premise of retaining the original framework. Most impressively, compound 1 shows high adsorption capacity for Cs⁺ cations and is a good candidate to selectively accommodate Cs⁺ among the common alkali metal ions, which is future identified by single-crystal X-ray diffraction and inductively coupled plasma mass spectrometry (ICP-MS) test. Meanwhile, compound 1 can selectively adsorb methylene blue (MB) and crystal violet (CV) molecules over Rhodamine B (RMB).

Chemically Stable Metal-Organic Frameworks: Rational Construction and Application Expansion

Metal-organic frameworks (MOFs) have been attracting tremendous attention owing to their great structural diversity and functional tunability. Despite numerous inherent merits and big progress in the fundamental research (synthesizing new compounds, discovering new structures, testing associated properties, etc.), poor chemical stability of most MOFs severely hinders their involvement in practical applications, which is the final goal for developing new materials. Therefore, constructing new stable MOFs or stabilizing extant labile MOFs is quite important. As with them, some "potential" applications would come true and a lot of new applications under harsh conditions can be explored. Efficient strategies are being pursued to solve the stability problem of MOFs and thereby achieve and expand their applications.In this Account, we summarize the research advance in the design and synthesis of chemically stable MOFs, particularly those stable in acidic, basic, and aqueous systems, as well as in the exploration of their applications in several expanding fields of environment, energy, and food safety, which have been dedicated in our lab over the past decade. The strategies for accessing stable MOFs can be classified into: (a) assembling high-valent metals (hard acid, such as Zr⁴⁺, Al³⁺) with carboxylate ligands (hard base) for acid-stable MOFs; (b) combining low-valent metals (soft acid, such as Co²⁺, Ni²⁺) and azolate ligands (soft base, such as pyrazolate) for alkali-resistant MOFs; (c) enhancing the connectivity of the building unit; (d) contracting or rigidifying the ligand; (e) increasing the hydrophobicity of the framework; and (f) substituting liable building units with stable ones (such as metal metathesis) to obtain robust MOFs. In addition, other factors, including the geometry and symmetry of building units, framework-framework interaction, and so forth, have also been taken into account in the design and synthesis of stable MOFs. On the basis of these approaches, the stability of resulting MOFs under corresponding conditions has been remarkably enhanced.With high chemical stability achieved, the MOFs have found many new and significant applications, aiming at addressing global challenges related to environmental pollution, energy shortage, and food safety.A series of stable MOFs have been constructed for detecting and eliminating contaminations. Various fluorescent MOFs were rationally customized to be powerful platforms for sensing hazardous targets in food and water, such as dioxins, antibiotics, veterinary drugs, and heavy metal ions. Some hydrophobic MOFs even showed effective and specific capture of low-concentration volatile organic compounds.Novel MOFs with record-breaking acid/base/nucleophilic regent resistance have expanded their application scope under harsh conditions. BUT-8(Cr)A, as the most acid-stable MOF yet, showed reserved structural integrity in concentrated H₂SO₄ and recorded high proton conductivity; the most alkali-resistant MOF, PCN-601, retained crystallinity even in boiling saturated NaOH aqueous solution, and such base-stable MOFs composed of non-noble metal clusters and poly pyrazolate ligands also demonstrated great potential in heterogeneous catalysis in alkaline/nucleophilic systems for the first time.It is believed that this Account will provide valuable references on stable MOFs' construction as well as application expansion toward harsh conditions, thereby being helpful to promote MOF materials to step from fundamental research to practical applications.