Topology Meets Reticular Chemistry for Chemical Separations: MOFs as a Case Study

Hemilabile Binding of Acetylene in an Amide-Rich Ultramicroporous MOF Enables Strong Acetylene Selectivity

Thanks to a hemilabile amide-based binding site, a previously unreported amide-functionalized metal-organic framework (MOF) exhibits high acetylene affinity over ethylene, methane, and carbon dioxide, three-in-one.

Recent Advances in Pristine Iron Triad Metal-Organic Framework Cathodes for Alkali Metal-Ion Batteries

Pristine iron triad metal-organic frameworks (MOFs), i.e., Fe-MOFs, Co-MOFs, Ni-MOFs, and heterometallic iron triad MOFs, are utilized as versatile and promising cathodes for alkali metal-ion batteries, owing to their distinctive structure characteristics, including modifiable and designable composition, multi-electron redox-active sites, exceptional porosity, and stable construction facilitating rapid ion diffusion. Notably, pristine iron triad MOFs cathodes have recently achieved significant milestones in electrochemical energy storage due to their exceptional electrochemical properties. Here, the recent advances in pristine iron triad MOFs cathodes for alkali metal-ion batteries are summarized. The redox reaction mechanisms and essential strategies to boost the electrochemical behaviors in associated electrochemical energy storage devices are also explored. Furthermore, insights into the future prospects related to pristine iron triad MOFs cathodes for lithium-ion, sodium-ion, and potassium-ion batteries are also delivered.

Atomic-level imaging of beam-sensitive COFs and MOFs by low-dose electron microscopy

Electron microscopy, an important technique that allows for the precise determination of structural information with high spatiotemporal resolution, has become indispensable in unravelling the complex relationships between material structure and properties ranging from mesoscale morphology to atomic arrangement. However, beam-sensitive materials, particularly those comprising organic components such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), would suffer catastrophic damage from the high energy electrons, hindering the determination of atomic structures. A low-dose approach has arisen as a possible solution to this problem based on the integration of advancements in several aspects: electron optical system, detector, image processing, and specimen preservation. This article summarizes the transmission electron microscopy characterization of MOFs and COFs, including local structures, host-guest interactions, and interfaces at the atomic level. Revolutions in advanced direct electron detectors, algorithms in image acquisition and processing, and emerging methodology for high quality low-dose imaging are also reviewed. Finally, perspectives on the future development of electron microscopy methodology with the support of computer science are presented.

Two 2D Metal-Organic Frameworks Based on Purine Carboxylic Acid Ligands for Photocatalytic Oxidation of Sulfides and CO2 Chemical Fixation

Two two-dimensional (2D) layered metal-organic frameworks (MOFs), namely, {[Yb(L)(H2O)2NO3]·2H2O}n (Yb-MOF) and [Er(L)(H2O)3Cl]n (Er-MOF) (H2L = 5-((6H-purin-6-yl)amino)isophthalic acid), were constructed by a solvothermal method and characterized. The catalytic performance study showed that the Yb-MOF could efficiently catalyze the oxidation of sulfides to sulfoxides under 15 W light-emitting diode (LED) blue light irradiation. Electron paramagnetic resonance spectroscopy and free-radical trapping experiments demonstrated that the photocatalytic reaction process involved •O2-, and the corresponding mechanism was proposed. Moreover, Er-MOF exhibited good catalytic efficiency and excellent substrate tolerance in the cycloaddition reaction of CO2, and the reaction conditions were mild. After 5 cycles, the catalytic activities of two MOFs did not significantly decrease, and the framework structures remained unchanged. Therefore, the Yb-MOF and Er-MOF were considered efficient and stable heterogeneous catalysts.

Unravelling abnormal in-plane stretchability of two-dimensional metal-organic frameworks by machine learning potential molecular dynamics

Two-dimensional (2D) metal-organic frameworks (MOFs) hold immense potential for various applications due to their distinctive intrinsic properties compared to their 3D analogues. Herein, we designed a highly stable NiF2(pyrazine)2 2D MOF in silico with a two-dimensional periodic wine-rack architecture. Extensive first-principles calculations and molecular dynamics (MD) simulations based on a newly developed machine learning potential (MLP) revealed that this 2D MOF exhibits huge in-plane Poisson's ratio anisotropy. This results in anomalous negative in-plane stretchability, as evidenced by an uncommon decrease in its in-plane area upon the application of uniaxial tensile strain, which makes this 2D MOF particularly attractive for flexible wearable electronics and ultra-thin sensor applications. We further demonstrated the unique capability of MLP to accurately predict the finite-temperature properties of MOFs on a large scale, exemplified by MLP-MD simulations with a dimension of 28.2 × 28.2 nm2, relevant to the length scale experimentally attainable for the fabrication of MOF films.

Finely Tuning Metal Ion Valences of [Fe3-xMx(μ3-OH)(Carboxyl)6(pyridyl)2] Cluster-Based ant-MOFs for Highly Improved CO2 Capture Performances

Solvothermal reactions of different trinuclear precursors and 5-(pyridin-4-yl)isophthalic acid (H2L) successfully led to four anionic ant topological MOFs as Fe3-xMx(μ3-OH)(CH3COO)2(L)2·(DMA+)·DMF [M = Mn(II), Fe(II), Co(II), x = 0, 1, 2 and 3], namely, NJTU-Bai79 [NJTU-Bai = Nanjing Tech University Bai's group, Mn3(μ3-OH)], NJTU-Bai80 [Fe2Mn(μ3-OH)], NJTU-Bai81 [Fe3(μ3-OH)], and NJTU-Bai82 [Fe2Co(μ3-OH)], which possess the narrow pores (2.5-6.0 Å). NJTU-Bai80-82 is able to be tuned to the neutral derivatives [NJTU-Bai80-82(-ox), ox = oxidized] with M2+ ions oxidized to M3+ ones in the air and the OH- ions coordinated on M3+ ions. Very interestingly, selective CO2/N2 adsorptions of NJTU-Bai80-82(-ox) are significantly enhanced with the CO2 adsorption uptakes more than about 6 times that of NJTU-Bai79. GCMC simulations further revealed that neutral NJTU-Bai80-82(-ox) supplies more open frameworks around the -CH3 groups at separate spaces to the CO2 gas molecules with relatively more pores available to them after the removal of counterions. For the first time, finely tuning metal ion valences of metal clusters of ionic MOFs and making them from electrostatic to neutral were adopted for greatly improving their CO2 capture properties, and it would provide another promising strategy for the exploration of high-performance CO2 capture materials.

In-based coordination polymer-derived carbon nanoribbons with abundant CoP nanoparticles in carbon nanotubes for water oxidation

The sluggish oxygen evolution reaction (OER) in overall electrocatalytic water splitting poses a significant challenge in hydrogen production. A series of transition metal phosphides are emerging as promising electrocatalysts, effectively modulating the charge distribution of surrounding atoms for OER. In this study, a highly efficient OER electrocatalyst (CoP-CNR-CNT) was successfully synthesized through the pyrolysis and phosphatization of a Co-doped In-based coordination polymer, specifically InOF-25. This process resulted in evenly dispersed CoP nanoparticles encapsulated in coordination polymer-derived carbon nanoribbons. The synthesized CoP-CNR-CNT demonstrated a competitive OER activity with a smaller overpotential (η10) of 295.7 mV at 10 mA cm-2 and a satisfactory long-term stability compared to the state-of-the-art RuO2 (η10 = 353.7 mV). The high OER activity and stability can be attributed to the high conductivity of the carbon network, the abundance of CoP particles, and the intricate nanostructure of nanoribbons/nanotubes. This work provides valuable insights into the rational design and facile preparation of efficient non-precious metal-based OER electrocatalysts from inorganic-organic coordination polymers, with potential applications in various energy conversion and storage systems.

Recent advances in the chemistry and applications of fluorinated metal-organic frameworks (F-MOFs)

Metal-organic frameworks are a class of porous crystalline materials based on the ordered connection of metal centers or metal clusters by organic linkers with comprehensive functionalities. The interest in these materials is rapidly moving towards their application in industry and real life. In this context, cheap and sustainable synthetic strategies of MOFs with tailored structures and functions are nowadays a topic widely studied from different points of view. In this review, fluorinated MOFs (F-MOFs) and their applications are investigated. The principal aim is to provide an overview of the structural features and the main application of MOFs containing fluorine atoms both as anionic units or as coordinating elements of more complex inorganic units and, therefore, directly linked to the structural metals or as part of fluorinated linkers used in the synthesis of MOFs. Herein we present a review of F-MOFs reported in the recent literature compared to benchmark compounds published over the last 10 years. The compounds are discussed in terms of their structure and properties according to the aforementioned classification, with an insight into the different chemical nature of the bonds. The application fields of F-MOFs, especially in sustainability related issues, such as harmful gas sorption and separation, will also be discussed. F-MOFs are compounds containing fluorine atoms in their framework and they can be based on: (a) fluorinated metallic or semi-metallic anionic clusters or: (b) fluorinated organic linkers or (c) eventually containing both the building blocks. The nature of a covalent C-F bond in terms of length, charge separation and dipole moment sensibly differs from that of a partly ionic M-F (M = metal) one so that the two classes of materials (points a and b) have different properties and they find various application fields. The study shows how the insertion of polar M-F and C-F bonds in the MOF structure may confer several advantages in terms of interaction with gaseous molecules and the compounds can find application in gas sorption and separation. In addition, hydrophobicity tends to increase compared to non-fluorinated analogues, resulting in an overall improvement in moisture stability.

Metal-Organic Framework Nanoparticles with Universal Dispersibility through Crown Ether Surface Coordination for Phase-Transfer Catalysis and Separation Membranes

Dispersing metal-organic framework (MOF) solids in stable colloids is crucial for their availability and processibility. Herein, we report a crown ether surface coordination approach for functionalizing the surface-exposed metal sites of MOF particles with amphiphilic carboxylated crown ether (CEC ). The surface-bound crown ethers significantly improve MOF solvation without compromising the accessible voids. We demonstrate that CEC -coated MOFs exhibit exceptional colloidal dispersibility and stability in 11 distinct solvents and six polymer matrices with a wide range of polarities. The MOF-CEC can be instantaneously suspended in immiscible two-phase solvents as an effective phase-transfer catalyst and can form various uniform membranes with enhanced adsorption and separation performance, which highlights the effectiveness of crown ether coating.

Metal-organic frameworks functionalized biomaterials for promoting bone repair

Bone defects induced by bone trauma, tumors and osteoarthritis greatly affect the life quality and health of patients. The biomaterials with numerous advantages are becoming the most preferred options for repairing bone defects and treating orthopedic diseases. However, their repairing effects remains unsatisfactory, especially in bone defects suffering from tumor, inflammation, and/or bacterial infection. There are several strategies to functionalize biomaterials, but a more general and efficient method is essential for accomplishing the functionalization of biomaterials. Possessing high specific surface, high porosity, controlled degradability and variable composition, metal-organic frameworks (MOFs) materials are inherently advantageous for functionalizing biomaterials, with tremendous improvements having been achieved. This review summarizes recent progresses in MOFs functionalized biomaterials for promoting bone repair and therapeutic effects. In specific, by utilizing various properties of diverse MOFs materials, integrated MOFs functionalized biomaterials achieve enhanced bone regeneration, antibacterial, anti-inflammatory and anti-tumor functions. Finally, the summary and prospects of on the development of MOFs-functionalized biomaterials for promoting bone repair were discussed.

Institution of Metal-Organic Frameworks as a Highly Sensitive and Selective Layer In-Field Integrated Soil-Moisture Capacitive Sensor

The ongoing global industrialization along with the notable world population growth is projected to challenge the global environment as well as pose greater pressure on water and food needs. Foreseeably, an improved irrigation management system is essential and the quest for refined chemical sensors for soil-moisture monitoring is of tremendous importance. Nevertheless, the persisting challenge is to design and construct stable materials with the requisite sensitivity, selectivity, and high performance. Here, we report the introduction of porous metal-organic frameworks (MOFs), as the receptor layer, in capacitive sensors to efficiently sense moisture in two types of soil. Namely, our study unveiled that Cr-soc-MOF-1 offers the best sensitivity (≈24,000 pF) among the other tested MOFs for any given range of soil-moisture content, outperforming several well-known oxide materials. The corresponding increase in the sensitivities for tested MOFs at 500 Hz are ≈450, ≈200, and ≈30% for Cr-soc-MOF-1, Al-ABTC-soc-MOF, and Zr-fum-fcu-MOF, respectively. Markedly, Cr-soc-MOF-1, with its well-known water capacity, manifests an excellent sensitivity of ≈450% in clayey soil, and the analogous response time was 500 s. The noted unique sensing properties of Cr-soc-MOF-1 unveils the great potential of MOFs for soil-moisture sensing application.

Ligand-Functional Groups Induced Tuning MOFs' 2D into 1D Pore Channels for Pipeline Natural Gas Purification

The solvothermal reactions of CoCl₂  ⋅ 6H₂ O, 3,5-pyridinedicarboxylic acid (H₂ L) and isonicotinic acid (HL₁ )/3-amino isonicotinic acid (HL₂ )/3-chloro isonicotinic acid (HL₃ ) successfully led to three tfz-d topological pillar-layer [Co₄ (μ-F)₂ (COO)₆ (NC₅ H₄ )₄ ] cluster-based MOFs, namely, [Co₄ (μ-F)₂ (L)₂ (L₁ )₂  ⋅ 2DMA] ⋅ DMA ⋅ 2H₂ O (SNNU-Bai76, SNNU-Bai=Shaanxi Normal University Bai's group), [Co₄ (μ-F)₂ (L)₂ (L₂ )₂  ⋅ 2H₂ O] ⋅ 2DMA ⋅ 2H₂ O (SNNU-Bai77) and [Co₄ (μ-F)₂ (L)₂ (L₃ )₂  ⋅ 2H₂ O] ⋅ 2DMF ⋅ 2H₂ O (SNNU-Bai78). With the 2D pore channels in SNNU-Bai76 and SNNU-Bai77 being tuned to the 1D pore channel in SNNU-Bai78, C₃ H₈ and C₂ H₆ adsorption uptakes are apparently improved and the IAST selectivities of C₃ H₈ /CH₄ and C₂ H₆ /CH₄ almost remain, which indicate that SNNU-Bai78 may be one potential separation material for the pipeline natural gas purification. These were further confirmed by the breakthrough experiments for the simulated pipeline natural gas (C₃ H₈ /C₂ H₆ /CH₄  : 5/10/85 gas mixture) of three isostructural MOFs. Furthermore, GCMC simulations revealed that due to one of the pore channels blocked by Cl atoms in a couple of 3-chloro isonicotinic acid with the changed conformation as the pillar, the pore wall of the formed 1D pore channel in SNNU-Bai78 may interact with the adsorbed C₃ H₈ or C₂ H₆ molecule more strongly, for which more atoms of framework at the new adsorption site will interact with the adsorbed gas molecule by more intermolecular interactions. This was also evidenced by the increased binding energies, being consistent with the tuning of adsorption enthalpies for C₃ H₈ and C₂ H₆ gas molecules, and the reduced C₃ H₈ and C₂ H₆ gas diffusion coefficients in SNNU-Bai78. Very interestingly, this work is the first example of finely tuning the pore connectivity of MOFs toward strengthened host-guest interactions for the gas adsorption and separation.

Fluorinated metal-organic frameworks for gas separation

Fluorinated metal-organic frameworks (F-MOFs) as fast-growing porous materials have revolutionized the field of gas separation due to their tunable pore apertures, appealing chemical features, and excellent stability. A deep understanding of their structure-performance relationships is critical for the synthesis and development of new F-MOFs. This critical review has focused on several strategies for the precise design and synthesis of new F-MOFs with structures tuned for specific gas separation purposes. First, the basic principles and concepts of F-MOFs as well as their structure, synthesis and modification and their structure to property relationships are studied. Then, applications of F-MOFs in adsorption and membrane gas separation are discussed. A detailed account of the design and capabilities of F-MOFs for the adsorption of various gases and the governing principles is provided. In addition, the exceptional characteristics of highly stable F-MOFs with engineered pore size and tuned structures are put into perspective to fabricate selective membranes for gas separation. Systematic analysis of the position of F-MOFs in gas separation revealed that F-MOFs are benchmark materials in most of the challenging gas separations. The outlook and future directions of the science and engineering of F-MOFs and their challenges are highlighted to tackle the issues of overcoming the trade-off between capacity/permeability and selectivity for a serious move towards industrialization.

MOF Pillaring Method: Ligand-to-Ligand and Axial-to-Axial Cross-Linking of "Paddlewheels"

By shortening the previous shortest tetracarboxylate ligand, the first ligand-to-ligand and axial-to-axial pillaring method was realized in the prototype MOF NTUniv-56 (NTUniv = Nantong University), which exhibit a rare (2,4,6)-connected net with a new topology and interesting gas adsorption performance.

Rational design of mixed-matrix metal-organic framework membranes for molecular separations

Conventional separation technologies to separate valuable commodities are energy intensive, consuming 15% of the worldwide energy. Mixed-matrix membranes, combining processable polymers and selective adsorbents, offer the potential to deploy adsorbent distinct separation properties into processable matrix. We report the rational design and construction of a highly efficient, mixed-matrix metal-organic framework membrane based on three interlocked criteria: (i) a fluorinated metal-organic framework, AlFFIVE-1-Ni, as a molecular sieve adsorbent that selectively enhances hydrogen sulfide and carbon dioxide diffusion while excluding methane; (ii) tailoring crystal morphology into nanosheets with maximally exposed (001) facets; and (iii) in-plane alignment of (001) nanosheets in polymer matrix and attainment of [001]-oriented membrane. The membrane demonstrated exceptionally high hydrogen sulfide and carbon dioxide separation from natural gas under practical working conditions. This approach offers great potential to translate other key adsorbents into processable matrix.

Metal-Organic Frameworks in Mixed-Matrix Membranes for High-Speed Visible-Light Communication

Mixed-matrix membranes (MMMs) based on luminescent metal-organic frameworks (MOFs) and emissive polymers with the combination of their unique advantages have great potential in separation science, sensing, and light-harvesting applications. Here, we demonstrate MMMs for the field of high-speed visible-light communication (VLC) using a very efficient energy transfer strategy at the interface between a MOF and an emissive polymer. Our steady-state and ultrafast time-resolved experiments, supported by high-level density functional theory calculations, revealed that efficient and ultrafast energy transfer from the luminescent MOF to the luminescent polymer can be achieved. The resultant MMMs exhibited an excellent modulation bandwidth of around 80 MHz, which is higher than those of most well-established color-converting phosphors commonly used for optical wireless communication. Interestingly, we found that the efficient energy transfer further improved the light communication data rate from 132 Mb/s of the pure polymer to 215 Mb/s of MMMs. This finding not only showcases the promise of the MMMs for high-speed VLC but also highlights the importance of an efficient and ultrafast energy transfer strategy for the advancement of data rates of optical wireless communication.

Energy Transfer in Metal-Organic Frameworks for Fluorescence Sensing

The development of materials with outstanding performance for sensitive and selective detection of multiple analytes is essential for the development of human health and society. Luminescent metal-organic frameworks (LMOFs) have controllable surface and pore sizes and excellent optical properties. Therefore, a variety of LMOF-based sensors with diverse detection functions can be easily designed and applied. Furthermore, the introduction of energy transfer (ET) into LMOFs (ET-LMOFs) could provide a richer design concept and a much more sensitive and accurate sensing performance. In this review, we focus on the recent five years of advances in ET-LMOF-based sensing materials, with an emphasis on photochemical and photophysical mechanisms. We discuss in detail possible energy transfer processes within a MOF structure or between MOFs and guest materials. Finally, the possible sensing applications of the ET-LMOF-based sensors are highlighted.

Covalent-Linking-Enabled Superior Compatibility of ZIF-8 Hybrid Membrane for Efficient Propylene Separation

The interface is a critical issue for metal-organic-framework hybrid membranes in propylene separation. Here, a covalent-linking strategy is reported for strikingly reinforcing the interfacial compatibility in a ZIF-8-based membrane. A functionalized ZIF-8 material named ZIF-8-CN is synthesized using the mixed-ligand approach. ZIF-8-CN has an identical crystalline structure to ZIF-8, and the 4,5-dicyanoimidazole ligand is available for further functionalization. Covalent linkage of ZIF-8-CN with PIM-1 is driven by the thermal reaction of the cyano groups on both entities, which strengthens the filler-polymer connection in the ZIF-8-CN@tPIM-1 membrane. ZIF-8-CN@tPIM-1 exhibits remarkably enhanced propylene permeation property with C₃ H₆ /C₃ H₈ selectivity of ≈28, which is 350% and 180% higher than those on non-treated ZIF-8-CN/PIM-1 and non-functionalized ZIF-8@tPIM-1, respectively. Additionally, ZIF-8-CN@tPIM-1 shows the highest C₃ H₆ permeability of ≈370 Barrer among all relevant ZIF-8 membranes. This strategy opens an avenue for precise interface engineering in membranes and the resultant high performance is appealing in the propylene separation industry.

Robust Nickel-Based Metal-Organic Framework for Highly Efficient Methane Purification and Capture

Developing energy-efficient alternatives for methane (CH₄) purification from natural gas and methane capture of coal-mine gas is of great significance and challenge in the chemical industry. Herein, we report a robust nickel-based metal-organic framework (MOF), Ni-BPZ, featuring one-dimensional (1D) rhombic channels decorated with abundant pyrazole rings. Ni-BPZ exhibits excellent separation performance toward both C₂H₆/CH₄ and CH₄/N₂ binary mixtures. The C₂H₆/CH₄ selectivity of Ni-BPZ is high, up to 50.2, exceeding those of most MOF adsorbents reported, and it simultaneously possesses a remarkable C₂H₆ uptake of 2.46 mmol/g at 298 K and 0.1 bar. The CH₄/N₂ selectivity of Ni-BPZ reaches 6.6, and its high CH₄ uptake is 1.56 mmol/g, which is also superior to most high-performance CH₄ adsorbents. The molecular simulation reveals that the uniform 1D rhombic channels with abundant pyrazole rings provide a high density of potential adsorption sites for efficient C₂H₆/CH₄ and CH₄/N₂ separations.

Finely Tuning Tridentate Carboxylic Acids for the Construction of Rod Scandium Metal-Organic Frameworks with High Chemical Stability and Selective Gas Adsorption

By systematic ligand tuning for control of the secondary building units, the use of tridentate carboxylic acid to construct the rod scandium metal-organic framework NTUniv-55 (NTUniv = Nantong University) with high chemical stability and interesting selective gas adsorption was reported.

Quantitative Coassembly for Precise Synthesis of Mesoporous Nanospheres with Pore Structure-Dependent Catalytic Performance

Precise synthesis of porous materials is essential for their applications. Self-assembly is a widely used strategy for synthesizing porous materials, but quantitative control of the assembly process still remains a great challenge. Here, a quantitative coassembly approach is developed for synthesizing resin/silica composite and its derived porous spheres. The assembly behaviors of the carbon and silica precursors are regulated without surfactants and the growth kinetics of the composite spheres are quantitatively controlled. This assembly approach enables the precise control of the size and pore structures of the derived carbon spheres. These carbon spheres provide a good platform to explore the structure-performance relationships of porous materials, and demonstrate their pore structure-dependent performance in catalytic water decontamination. This work provides a simple and robust approach for precise synthesis of porous spheres and brings insights into function-oriented design of porous materials.

High Enhancement in Proton Conductivity by Incorporating Sulfonic Acids into a Zirconium-Based Metal-Organic Framework via "Click" Reaction

Taking a robust zirconium-based metal-organic framework, UiO-66, as a prototype, functional postmodification via the versatile Cu(I)-catalyzed azide-alkyne "click" reaction was carried out, and sulfonic acid groups were successfully grafted into its skeleton. Characterizations revealed that the MOF network was still well maintained after being treated by "clicked" modification. Investigations by electrochemical impedance spectroscopy measurements revealed that its proton conductivity increases exponentially up to 8.8 × 10^-3 S cm^-1 at 80 °C and 98% RH, while those of the UiO-66 and UiO-66-NH₂ are only 6.3 × 10^-6 and 3.5 × 10^-6 S cm^-1, respectively, at the same condition. Additionally, the continuous test shows it possesses long-life reusability. Such a remarkable enhancement on the proton conductivities and high performance in long-life reusability of the resultant MOF demonstrated that the "click" reaction is a facile reaction in postmodification of robust porous materials toward targeted applications, with which highly promising candidates of proton-conductive electrolytes for applying in proton-exchange-membrane (PEM) fuel cell can be achieved.

Novel Ba2+ and Pb2+ metal-organic frameworks based on a semi-rigid tetracarboxylic acid: syntheses, structures, topologies and luminescence properties

Multidentate carboxylate ligands have been widely used in the construction of metal-organic frameworks (MOFs) owing to the rich variety of their coordination modes, which can lead to crystalline products with interesting structures and properties. Two new main-group MOFs, namely, poly[[di-μ-aqua-diaqua(dimethylformamide)[μ₇-5,5'-methylenebis(2,4,6-trimethylbenzene-1,3-dicarboxylato)]dibarium(II)] trihydrate], {[Ba₂(C₂₃H₂₀O₈)(C₃H₇NO)(H₂O)₄]·3H₂O}_n or {[Ba₂(BTMIPA)(DMF)(H₂O)₄]·3H₂O}_n (1), and poly[[diaqua[μ₆-5,5'-methylenebis(2,4,6-trimethylbenzene-1,3-dicarboxylato)]dilead(II)] 2.5-hydrate], {[Pb₂(C₂₃H₂₀O₈)(H₂O)₂]·2.5H₂O}_n or {[Pb₂(BTMIPA)(H₂O)₂]·2.5H₂O}_n (2), were prepared by the self-assembly of metal salts with the semi-rigid tetracarboxylic acid ligand 5,5'-methylenebis(2,4,6-trimethylisophthalic acid) (H₄BTMIPA). Both structures were characterized by elemental analysis (EA), single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), IR spectroscopy and thermogravimetric analysis (TGA). Complex 1 reveals a three-dimensional (3D) flu network formed via bridging tetranuclear secondary building units (SBUs) and complex 2 displays a 3D framework with an sqp topology based on one-dimensional metal chains. The BTMIPA^4- ligands adopt a rare coordination mode in 2, although the ligands in both 1 and 2 are X-shaped. The luminescence properties of both complexes were investigated in the solid state.

Incorporating Photochromic Triphenylamine into a Zirconium-Organic Framework for Highly Effective Photocatalytic Aerobic Oxidation of Sulfides

A zirconium-based metal-organic framework (MOF) was successfully constructed via solvothermal assembly of a triphenylamine-based tricarboxylate ligand and Zr(IV) salt, the structure simulation of which revealed that it possesses a two-dimensional layered framework with a relatively rare dodecnuclear Zr₁₂ cluster as the inorganic building unit. The inherent photo-responsive property derived from the incorporated photochromic triphenylamine groups combined with its high stability makes the constructed MOF an efficient heterogeneous photocatalyst for the oxidation of sulfides, which is a fundamentally important reaction type in both environmental and pharmaceutical industries. The photocatalytic activity of the constructed MOF was first investigated under various conditions with thioanisole as a representative sulfide substrate. The MOF exhibited both high efficiency and selectivity on aerobic oxidation of thioanisole in methanol utilizing molecular oxygen in air as the oxidant under blue light irradiation for 10 h. Its high photocatalytic performance was also observed when extending the sulfide substrate to diverse thioanisole derivatives and even a sulfur-containing nerve agent simulant (2-chloroethyl ethyl sulfide). The high photocatalytic efficiency and selectivity to a broad set of sulfide substrates make the triphenylamine-incorporating zirconium-based MOF a highly promising heterogeneous photocatalyst.

Tuning the Structural Flexibility for Multi-Responsive Gas Sorption in Isonicotinate-Based Metal-Organic Frameworks

Flexible metal-organic frameworks (MOFs) are of high interest as smart programmable materials for gas sorption due to their unique structural changes triggered by external stimuli. Owing to this property, which leads to opportunities such as maximizing deliverable gas capacity, flexible MOFs sometimes offer more advantages in sorption applications compared to their more rigid counterparts. Herein, we elucidate the effect of transition metal identity of a series of isonicotinate-based flexible MOFs, M(4-PyC)₂ [M═Mg, Mn, and Cu; 4-PyC = 4-pyridine carboxylic acid] on the structural dynamic response to different gases (C₂H₄, C₂H₆, Xe, Kr, and SO₂). Isotherms at different temperatures show that C₂H₄, C₂H₆, and Xe can form sufficiently strong interactions with both Mg(4-PyC)₂ and Mn(4-PyC)₂ frameworks resulting in gate-opening behavior due to the rotation of the linker's pyridine ring, while Kr cannot induce this phenomenon for the two MOFs under the measured conditions. In contrast, the gate-opening behavior occurs for Cu(4-PyC)₂ solely in the presence of C₂H₄, and no other measured gas, due to the open metal sites of Cu centers. In comparison, SO₂, a strong polar molecule, triggers the gate-opening effect in all three MOFs. Interestingly, a shape memory effect is observed for Cu(4-PyC)₂ during the second SO₂ sorption cycle. When comparing the different gate-opening pressures of each gas, we observed that the structural flexibility of the three frameworks is highly sensitive to the chemical hardness of the Lewis acidic metal ions (Mg²⁺ > Mn²⁺ > Cu²⁺). As a result, the gate opening behavior is observed at lower pressures for the MOFs containing weaker M-N bonds (harder metal ions), with the exception of Cu(4-PyC)₂ toward C₂H₄. These observations reveal that different transition metals can be used to finely control the structural flexibility of the frameworks.

BN-Doped Metal-Organic Frameworks: Tailoring 2D and 3D Porous Architectures through Molecular Editing of Borazines

Building on the MOF approach to prepare porous materials, herein we report the engineering of porous BN-doped materials using tricarboxylic hexaarylborazine ligands, which are laterally decorated with functional groups at the full-carbon 'inner shell'. Whilst an open porous 3D entangled structure could be obtained from the double interpenetration of two identical metal frameworks derived from the methyl substituted borazine, the chlorine-functionalised linker undergoes formation of a porous layered 2D honeycomb structure, as shown by single-crystal X-ray diffraction analysis. In this architecture, the borazine cores are rotated by 60° in alternating layers, thus generating large rhombohedral channels running perpendicular to the planes of the networks. An analogous unsubstituted full-carbon metal framework was synthesised for comparison. The resulting MOF revealed a crystalline 3D entangled porous structure, composed by three mutually interpenetrating networks, hence denser than those obtained from the borazine linkers. Their microporosity and CO2 uptake were investigated, with the porous 3D BN-MOF entangled structure exhibiting a large apparent BET specific surface area (1091 m2  g-1 ) and significant CO2 reversible adsorption (3.31 mmol g-1 ) at 1 bar and 273 K.

The state of the field: from inception to commercialization of metal–organic frameworks

We provide a brief overview of the state of the MOF field from their inception to their synthesis, potential applications, and finally, to their commercialization.