Enhancing Pore-Environment Complexity Using a Trapezoidal Linker: Toward Stepwise Assembly of Multivariate Quinary Metal–Organic Frameworks

Topological Transformation and Dimensional Reduction in Multicomponent Metal-Organic Frameworks for Gas Separations

Multicomponent MOFs have offered a wide range of opportunities to harness new properties. However, the synthesis of multicomponent MOFs remains challenging. This work demonstrates the synthesis of a family of multicomponent MOFs by topological transformation from well-established multicomponent partitioned acs (pacs) structures. Such transformation is based on the new understanding on the self-assembly process of pacs MOFs. A key to this understanding is that pacs structures, topologically regarded as the introduction of a pore-partitioning ligand into MOF-235/MIL-88 type framework, are likely to be formed in a layer-pillar-layer fashion in practical reactions. As the π-π interaction between layers and other chemical interactions during the self-assembly process are recognized, the structural transformation can be modulated from 3D pacs structures to 2D interrupted pacs structures (denoted i-pacs). It is especially noteworthy that such dimensional reduction is first observed in metal-organic frameworks and the i-pacs MOFs contain four structural modules and up to five components, which have the highest complexity among 2D MOFs. Interestingly, the i-pacs MOFs have significantly enhanced performance for CO2/N2 separation in comparison with pacs MOFs.

Sequential Linker Installation in Metal-Organic Frameworks

ConspectusMetal-organic frameworks (MOFs) represent a sophisticated blend of inorganic and organic components, promoting the development of coordination chemistry greatly and offering a versatile platform for tailored functionalities. By combining various metal nodes, organic linkers, and functional guests, MOFs provide numerous pathways for their design, synthesis, and customization. Among these, sequential linker installation (SLI) stands out as a novel and crucial strategy, enabling the precise integration of desired properties and functions at the atomic scale. SLI enhances structural diversity and stability while facilitating the meticulous construction of robust frameworks by leveraging open metal sites and functional organic linkers at targeted locations. Compared to the direct synthesis of MOFs, postsynthetic modification methods allow for precise regulation of their structures and corresponding properties. While unlike conventional postsynthetic modification methods, SLI requires the careful selection of linkers and framework design to ensure precise positioning for installation, which gives rise to the well-designed and ordered positions for the installed linkers, confirmed directly by X-ray diffraction technology.Recent advancements in MOF synthesis have led to the creation of increasingly tailored flexible matrix structures, particularly due to the diverse connection modes of multicore metal clusters, especially for the Zr6 cluster. The spatial hindrance of certain ligands has resulted in the formation of unsaturated metal clusters and various missing linker pockets. Examples of these advanced MOFs include PCN-606, PCN-608, PCN-609, PCN-700, and PCN-808, which feature specific open metal sites and certain framework flexibility conducive to SLI. Strategically positioned open metal sites within these frameworks serve as predetermined anchor points for desired functional molecules, while the frameworks' flexibility can accommodate molecules of varying sizes to a certain extent, enlarging the scopes of application greatly. This precise positioning of functional groups enables the creation of tailored sites for enhanced applications, such as adsorption, catalysis, and recognition.In this Account, we delve into the intricate process of designing and synthesizing MOFs with appropriate missing-linker pockets for the aforementioned applications. We discuss the meticulous selection of functional linkers and the methods used to insert them into the corresponding missing-linker pockets within the MOFs. Additionally, we explore the diverse properties and functionalities of the resulting MOFs, focusing on their adsorptive, catalytic, and recognition performance. Furthermore, we provide insights into the future trajectory of SLI methods, complemented by our recent works. This Account not only reviews the evolution of the SLI method but also underscores its practical applications across various functional domains, paving a rational pathway for the future development of advanced multifunctional MOFs through this method.

Efficient Nickel and Cobalt Recovery by Metal-Organic Framework-Based Mixed Matrix Membranes (MMM-MOFs)

Green energy transition has supposed to give a huge boost to the electric vehicle rechargeable battery market. This has generated a compelling demand for raw materials, such as cobalt and nickel, which are key common constituents in lithium-ion batteries (LIBs). However, their existing mining protocols and the concentrated localization of such ores have made cobalt and nickel mineral conundrums, and their supplies experience shortages, which threaten to slow the progress of the renewable energy transition. Aiming to contribute to the sustainable recycling of these valuable metals from LIBs and wastewater, in this work, we explore the use of four mixed matrix membranes (MMMs) embedding different metal-organic frameworks (MOFs), i.e., MIL-53(Al), MIL-53(Fe), MIL-101(Fe), and {SrIICuII 6[(S,S)-serimox]3(OH)2(H2O)}·39H2O (SrCu 6 Ser) in polyether sulfone (PES), for the recovery of cobalt(II) and nickel(II) metal cations from mixed cobalt-nickel aqueous solutions containing common interfering ions. Whereas the neat PES membrane slightly contributes to the adsorption of metal ions, showing reduced removal efficiency values of 10.2 and 9.5% for Ni(II) and Co(II), respectively, the inclusion of MOFs in the polymeric matrix substantially improves the adsorption performances. The four MOF@PES MMMs efficiently remove these metals from water, with MIL-53(Al)@PES being the one that presents better performance, with a removal efficiency up to 95% of Ni(II) and Co(II). Remarkably, SrCu 6 Ser@PES exhibits outstanding selectivity toward cobalt(II) cations compared to of nickel(II) ones, with removal efficiencies of 63.7 and 15.1% for Co(II) and Ni(II), respectively. Overall, the remarkable efficiencies, versatility, high environmental robustness, and cost-effective synthesis shown by this family of MOF@PES MMMs situate them among the best adsorbents for the extraction of this kind of contaminants.

Programmable Water Sorption through Linker Installation into a Zirconium Metal-Organic Framework

Hydrolytically stable materials exhibiting a wide range of programmable water sorption behaviors are crucial for on-demand water sorption systems. While notable advancements in employing metal-organic frameworks (MOFs) as promising water adsorbents have been made, developing a robust yet easily tailorable MOF scaffold for specific operational conditions remains a challenge. To address this demand, we employed a topology-guided linker installation strategy using NU-600, which is a zirconium-based MOF (Zr-MOF) that contains three vacant crystallographically defined coordination sites. Through a judicious selection of three N-heterocyclic auxiliary linkers of specific lengths, we installed them into designated sites, giving rise to six new MOFs bearing different combinations of linkers in predetermined positions. The resulting MOFs, denoted as NU-606 to NU-611, demonstrate enhanced structural stability against capillary force-driven channel collapse during water desorption due to the increased connectivity of the Zr6 clusters in the resulting MOFs. Furthermore, incorporating these auxiliary linkers with various hydrophilic N sites enables the systematic modulation of the pore-filling pressure from about 55% relative humidity (RH) for the parent NU-600 down to below 40% RH. This topology-driven linker installation strategy offers precise control of water sorption properties for MOFs, highlighting a facile route to design MOF adsorbents for use in water sorption applications.

Stepwise construction of multi-component metal-organic frameworks

Multi-component metal-organic frameworks (MC-MOFs) are crystalline porous materials containing multiple organic ligands or mixed metals, which manifest new properties beyond the linear combination of the single component. However, the traditional one-pot synthesis method for MOFs is not always applicable for synthesizing MC-MOFs due to the competitive coordination of multiple ligands and metals. Therefore, the stepwise construction of MC-MOFs has been explored, which enables more precise control of the heterogeneity within the ordered MC-MOFs. This review provides a summary of the synthesis strategies, namely, ligand exchange, coordinative modification, covalent modification, ligand metalation, cluster metalation, and use of mixed-metal precursors, for the stepwise construction of MC-MOFs. Furthermore, we discuss the applications of MC-MOFs with ordered arrangements of multiple functionalities, focusing on gas adsorption and separation, water remediation, heterogeneous catalysis, luminescence, and chemical sensing.

Anisotropic flexibility and rigidification in a TPE-based Zr-MOFs with scu topology

Tetraphenylethylene (TPE)-based ligands are appealing for constructing metal-organic frameworks (MOFs) with new functions and responsiveness. Here, we report a non-interpenetrated TPE-based scu Zr-MOF with anisotropic flexibility, that is, Zr-TCPE (H4TCPE = 1,1,2,2-tetra(4-carboxylphenyl)ethylene), remaining two anisotropic pockets. The framework flexibility is further anisotropically rigidified by installing linkers individually at specific pockets. By individually installing dicarboxylic acid L1 or L2 at pocket A or B, the framework flexibility along the b-axis or c-axis is rigidified, and the intermolecular or intramolecular motions of organic ligands are restricted, respectively. Synergistically, with dual linker installation, the flexibility is completely rigidified with the restriction of ligand motion, resulting in MOFs with enhanced stability and improved separation ability. Furthermore, in situ observation of the flipping of the phenyl ring and its rigidification process is made by 2H solid-state NMR. The anisotropic rigidification of flexibility in scu Zr-MOFs guides the directional control of ligand motion for designing stimuli-responsive emitting or efficient separation materials.

Bioinspired Framework Catalysts: From Enzyme Immobilization to Biomimetic Catalysis

Enzymatic catalysis has fueled considerable interest from chemists due to its high efficiency and selectivity. However, the structural complexity and vulnerability hamper the application potentials of enzymes. Driven by the practical demand for chemical conversion, there is a long-sought quest for bioinspired catalysts reproducing and even surpassing the functions of natural enzymes. As nanoporous materials with high surface areas and crystallinity, metal-organic frameworks (MOFs) represent an exquisite case of how natural enzymes and their active sites are integrated into porous solids, affording bioinspired heterogeneous catalysts with superior stability and customizable structures. In this review, we comprehensively summarize the advances of bioinspired MOFs for catalysis, discuss the design principle of various MOF-based catalysts, such as MOF-enzyme composites and MOFs embedded with active sites, and explore the utility of these catalysts in different reactions. The advantages of MOFs as enzyme mimetics are also highlighted, including confinement, templating effects, and functionality, in comparison with homogeneous supramolecular catalysts. A perspective is provided to discuss potential solutions addressing current challenges in MOF catalysis.

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.

Reticular Design of Precise Linker Installation into a Zirconium Metal-Organic Framework to Reinforce Hydrolytic Stability

Reticular chemistry allows for the rational assembly of metal-organic frameworks (MOFs) with designed structures and desirable functionalities for advanced applications. However, it remains challenging to construct multi-component MOFs with unprecedented complexity and control through insertion of secondary or ternary linkers. Herein, we demonstrate that a Zr-based MOF, NU-600 with a (4,6)-connected she topology, has been judiciously selected to employ a linker installation strategy to precisely insert two linear linkers with different lengths into two crystallographically distinct pockets in a one-pot, de novo reaction. We reveal that the hydrolytic stability of these linker-inserted MOFs can be remarkably reinforced by increasing the Zr₆ node connectivity, while maintaining comparable water uptake capacity and pore-filling pressure as the pristine NU-600. Furthermore, introducing hydrophilic -OH groups into the linear linker backbones to construct multivariate MOFs can effectively shift the pore-filling step to lower partial pressures. This methodology demonstrates a powerful strategy to reinforce the structural stability of other MOF frameworks by increasing the connectivity of metal nodes, capable of encouraging developments in fundamental sciences and practical applications.

Generation of Strong Basicity in Metal-Organic Frameworks: How Do Coordination Solvents Matter?

Solid strong bases with an ordered pore structure (OPS-SSBs) have attracted much attention because of their high catalytic activity and shape selectivity as heterogeneous catalysts in various reactions. Nevertheless, high temperatures are required to fabricate OPS-SSBs by using traditional methods. Herein, we report for the first time that the coordination solvents affect basicity generation in metal-organic frameworks (MOFs) greatly and that strong basicity can be formed at comparatively low temperatures. A typical MOF, MIL-53, was employed, and three different solvents, namely, water, methanol, and N,N-dimethylformamide (DMF), were coordinated, respectively, by means of solvent exchange. Thermogravimetry-mass spectrometer analysis shows that the conversion temperature of base precursor KNO₃ is quite different on MIL-53 coordinated with different solvents. The conversion of KNO₃ to basic sites takes place at 350, 300, and 250 °C on MIL-53 coordinated with water, methanol, and DMF, respectively. It is fascinating to observe the generation temperature of strongly basic sites at 250 °C, which is noticeably lower than that on various supports, such as mesoporous silica SBA-15 (600 °C), zeolite Y (700 °C), and metal oxide ZrO₂ (730 °C). This is due to the redox interaction between coordination solvents and KNO₃, leading to a significant decrease in the temperature for KNO₃ conversion. Consequently, OPS-SSBs were prepared successfully with an ordered pore structure and strong basicity. The obtained OPS-SSBs show good shape selectivity in Knoevenagel condensation of aromatic aldehydes with different active methylene compounds. Moreover, these solid bases are highly active in the synthesis of dimethyl carbonate through transesterification reaction. This work might open up a new avenue for the fabrication of various functional materials at low temperatures through redox interactions.

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 cationic thorium-organic framework with triple single-crystal-to-single-crystal transformation peculiarities for ultrasensitive anion recognition

Single-crystal-to-single-crystal transformation of metal-organic frameworks has been met with great interest, as it allows for the creation of new materials in a stepwise manner and direct visualization of structural transitions when subjected to external stimuli. However, it remains a peculiarity among numerous metal-organic frameworks, particularly for the ones constructed from tetravalent metal cations. Herein, we present a cationic thorium-organic framework displaying unprecedented triple single-crystal-to-single-crystal transformations in organic solvents, water, and NaIO3 solution. Notably, both the interpenetration conversion and topological change driven by the SC-SC transformation have remained elusive for thorium-organic frameworks. Moreover, the single-crystal-to-single-crystal transition in NaIO3 solution can efficiently and selectively turn the ligand-based emission off, leading to the lowest limit of detection (0.107 μg kg-1) of iodate, one of the primary species of long-lived fission product 129I in aqueous medium, among all luminescent sensors.

Synthesis of 5,7-diarylindoles via Suzuki-Miyaura coupling in water

The synthesis of novel 5,7-diaryl and diheteroaryl indoles has been explored via efficient double Suzuki-Miyaura coupling. The method notably employs a low catalyst loading of Pd(PPh₃)₄ (1.5 mol%/coupling) and water as the reaction solvent to obtain 5,7-diarylated indoles without using N-protecting groups in up to 91% yield. The approach is also suitable for N-protected and 3-substituted indoles and constitutes an important green and convenient arylation strategy for the benzenoid ring of indoles. The synthesized diarylindoles are fluorescent.

Snapshots of Postsynthetic Modification in a Layered Metal-Organic Framework: Isometric Linker Exchange and Adaptive Linker Installation

Terminal ligand exchange and framework linker exchange have been frequently practiced as powerful tools to functionalize reticular structures such as metal-organic frameworks (MOFs). Herein, we report the postsynthetic modification (PSM) of a 6-connected layered MOF (hxl topology) to achieve a 12-connected fcu framework. In the PSM process, isometric linker exchange in the layers and linker installation between adjacent layers by the substitution of modulating ligands happen simultaneously. Snapshots of PSM at different time points reveal that the hxl domain is adaptively reorganized to create sites for new linker installation, and gradually the fcu domain dominates the crystal. Detailed kinetic analysis suggests that, although adaptive linker installation requires interlayer expansion of stackings in situ, it is kinetically faster than isometric linker exchange in the layers.

High-Performance Lithium-Ion Capacitors Based on Porosity-Regulated Zirconium Metal-Organic Frameworks

Comprised of a battery anode and a supercapacitor cathode, hybrid lithium-ion capacitors (HLICs) are found to be an effective solution to realize both high power density and high energy density at the same time. Organic-inorganic hybrid materials with well-organized framework guided by the reticular chemistry are one of the promising anode materials for HLICs because of rich active sites and ordered porosity. Herein, metal-organic framework consisting of Zr⁴⁺ metal ions and tetrathiafulvalene-based ligands (Zr-MOF) is proposed as the pseudocapacitive anode of HLICs. The Zr-MOF possesses high stability, high crystallinity, and multiple meso-microporous channels favorable for ion transport. The as-prepared Zr-MOF||activated carbon HLICs present high energy density (122.5 Wh kg^-1 ), high power density (12.5 kW kg^-1 ), and stable cycling performance (86% capacity retention after 1000 cycles at 2000 mA g^-1 ) within the operating voltage range of 1.0-4.0 V. The results expand the direct application of MOF for bridging the performance gap between batteries and supercapacitors.

A Series of Mesoporous Rare-Earth Metal-Organic Frameworks Constructed from Organic Secondary Building Units

Further development of metal-organic frameworks (MOFs) requires an establishment of hierarchical interaction within the framework. Herein, we report a series of mesoporous rare-earth (RE) MOFs that are constructed from an unusual 12-connected π-stacked pyrene secondary building unit (SBU) and a typical 12-connected RE₆ cluster (RE=Eu, Y, Yb, Tb, Ce). The judicious design of a butterfly-shape pyrene ligand with a tert-butyl substituent enables the formation of the disordered 12-connected organic SBUs on its strong intermolecular π-π interactions. The assembly of 12-connected inorganic cuboctahedron SBUs and 12-connected organic distorted hexagonal prism SBUs generates an unprecedented network that can be further simplified into a 4,4-connected pts net linked from planar square and tetrahedra. This work provides fresh insights into the design and synthesis of frameworks constructed from coordinatively, covalently, and noncovalently linked building units.

Creative Construction of a Series of Chiral 3D Indium-Organic Frameworks with a umy Topology

Using 2,2'-R₂-biphenyl-4,4'-dicarboxylic acid to bind with a cis-[InO₄(μ₂-OH)₂] octahedron, three novel chiral 3D indium-organic frameworks, [In(μ₂-OH)L] [1, L¹, R = N(CH₃)₂; 2, L², R = OCH₃; 3, L³, R = CH₃], have been hydrothermally synthesized without chiral reagents. Crystal structure analyses reveal that 1-3 show an unprecedented 4-connected umy topology with the Schläfli symbol (4²·6⁴). 1 exhibits high water stability and good sorption selectivity of CO₂ over N₂, while 3 displays high C₂H₂, C₂H₄, and C₂H₆ uptake capacity at 273 K.

Zirconium Metal-Organic Frameworks Containing a Biselenophene Linker: Synthesis, Characterization, and Luminescent Properties

The bicyclic ditopic linker 2,2'-biselenophene-5,5'-dicarboxylic acid (H₂SpSp), specifically designed for metal-organic framework (MOF) construction, has been synthesized in good yield and fully characterized. The corresponding zirconium MOF (Zr-MOF) [Zr₆O₄(OH)₄(SpSp)_3.8Cl_4.4] (1; where missing linkers are replaced by chloride anions as shown by X-ray fluorescence and elemental analysis) is isostructural with its bithiophene and bithiazole analogues. Starting from 1, an extension of the biselenophene-based Zr-MOF family has been successfully achieved, exploiting the structural analogy of the five-membered heterocycles selenophene, thiophene, and thiazole. Thus, three mixed-linker MOFs containing variable amounts of different bis(heterocyclic) dicarboxylic acids have been prepared and fully characterized: the two double-mixed [Zr₆O₄(OH)₄(SpSp)_2.6(TpTp)_1.3Cl_4.2] (2; H₂TpTp = 2,2'-bithiophene-5,5'-dicarboxylic acid) and [Zr₆O₄(OH)₄(SpSp)₂(TzTz)_1.8Cl_4.4] (3; H₂TzTz = 2,2'-bithiazole-5,5'-dicarboxylic acid) materials, as well as the triple-mixed [Zr₆O₄(OH)₄(SpSp)_1.6(TpTp)_1.2(TzTz)_1.4Cl_3.6] (4) compound. The four MOFs are luminescent under UV irradiation, exhibiting emission wavelengths falling in the blue-green visible region, as observed for their constitutive linkers. These materials open new horizons in the preparation of porous luminescent sensors or multicolor emitters for light-emitting diodes.

Metal-Organic Frameworks Based on Group 3 and 4 Metals

Metal-organic frameworks (MOFs) based on group 3 and 4 metals are considered as the most promising MOFs for varying practical applications including water adsorption, carbon conversion, and biomedical applications. The relatively strong coordination bonds and versatile coordination modes within these MOFs endow the framework with high chemical stability, diverse structures and topologies, and interesting properties and functions. Herein, the significant progress made on this series of MOFs since 2018 is summarized and an update on the current status and future trends on the structural design of robust MOFs with high connectivity is provided. Cluster chemistry involving Y, lanthanides (Ln, from La to Lu), actinides (An, from Ac to Lr), Ti, and Zr is initially introduced. This is followed by a review of recently developed MOFs based on group 3 and 4 metals with their structures discussed based on the types of inorganic or organic building blocks. The novel properties and arising applications of these MOFs in catalysis, adsorption and separation, delivery, and sensing are highlighted. Overall, this review is expected to provide a timely summary on MOFs based on group 3 and 4 metals, which shall guide the future discovery and development of stable and functional MOFs for practical applications.

Probing Nonuniform Adsorption in Multicomponent Metal-Organic Frameworks via Segmental Dynamics by Solid-State Nuclear Magnetic Resonance

The guest adsorption phenomena in multicomponent metal-organic frameworks (MOFs) are intricate due to their structural complexities. In this work, we studied two members of the isostructural series of MUF-77 frameworks that consist of long or short alkyl groups. The adsorption of methanol, N,N-dimethylaniline (DMA) and acridine orange (AO) in two structures of MUF-77 has been investigated. ²H solid-state nuclear magnetic resonance (SSNMR) and two-dimensional ¹H-¹³C NMR spectroscopy were used to probe the dynamics of various compartments of MUF-77. Through the analyses of dynamic behavior by SSNMR and molecular dynamics simulations, we elucidate the spatial distribution of guest molecules are nonuniform around different chemical components, in different pore structures, and across different parts of MOF lattice. In addition, we reveal that the framework flexibility of MUF-77 with short alkyl groups is reduced upon guest adsorption yet the framework flexibility of MUF-77 with long alkyl groups increases upon loading with methanol.

The synthesis and applications of chiral pyrrolidine functionalized metal–organic frameworks and covalent-organic frameworks

Proline based ligands show versatile functionality to construct chiral MOFs and COFs; meanwhile, the resulted frameworks are potential materials for enantioselective adsorption and asymmetric catalysis.

Rational modifications of PCN-700 to induce electrical conductivity: a computational study

Using computational methods, rational modifications of PCN-700 are performed to newly induce electrical conductivity in a previously insulating metal–organic framework.

A mixed-ligand strategy regulates thorium-based MOFs

A thorium-based MOF formed via the synergistic construction of porphyrin and bipyridyl based on the mixed-ligand strategy has the effect of enhancing photocatalysis.

The stepwise substitution in the hierarchical building of {Co11Cd6} cluster-based MOFs from {Co14} precursor

A heterometallic aggregation of {Co₁₁Cd₆} can be hierarchical built from a {Co₁₄} precursor directly. HRESI-MS technique was used to track the stepwise Cd²⁺-capture: {Co₁₄} → {Co₈} → {Co₈Cd₂} → {Co₈Cd₃} → {Co₈Cd₄} → {Co₈Cd₅} → {Co₈Cd₆} → {Co₁₁Cd₆}.

Uncovering Structural Opportunities for Zirconium Metal-Organic Frameworks via Linker Desymmetrization

The discovery of metal-organic frameworks (MOFs) mimicking inorganic minerals with intricate topologies requires elaborate linker design guidelines. Herein, the concept of linker desymmetrization into the design of tetratopic linker based Zr-MOFs is applied. A series of bent tetratopic linkers with various substituents are utilized to construct Zr-MOFs with distinct cluster connectivities and topologies. For example, the assembly between a bent linker L-SO2 with C 2v symmetry and an 8-connected Zr6 cluster leads to the formation of an scu topology, while another flu topology can be obtained by the combination of a novel 8-connected Zr6 cluster and a bent linker L-O with C 1 symmetry. Further utilization of restricted bent linker [(L-(CH3)6)] gives rise to a fascinating (4, 6)-c cor net, originated from the corundum lattice, with an unprecedented 6-c Zr6 cluster. In addition, the removal of toxic selenite ions in aqueous solution is performed by PCN-903-(CH3)6 which exhibits rapid and efficient detoxification. This work uncovers new structural opportunities for Zr-MOFs via linker desymmetrization and provides novel design strategies for the discovery of sophisticated topologies for practical applications.

Atomic- and Molecular-Level Design of Functional Metal-Organic Frameworks (MOFs) and Derivatives for Energy and Environmental Applications

Continuing population growth and accelerated fossil-fuel consumption with recent technological advancements have engendered energy and environmental concerns, urging researchers to develop advanced functional materials to overcome the associated problems. Metal-organic frameworks (MOFs) have emerged as frontier materials due to their unique porous organic-inorganic hybrid periodic assembly and exceptional diversity in structural properties and chemical functionalities. In particular, the modular nature and modularity-dependent activity of MOFs and MOF derivatives have accentuated the delicate atomic- and molecular design and synthesis of MOFs, and their meticulous conversion into carbons and transition-metal-based materials. Synthetic control over framework architecture, content, and reactivity has led to unprecedented merits relevant to various energy and environmental applications. Herein, an overview of the atomic- and molecular-design strategies of MOFs to realize application-targeted properties is provided. Recent progress on the development of MOFs and MOF derivatives based on these strategies, along with their performance, is summarized with a special emphasis on design-structure and functionality-activity relationships. Next, the respective energy- and environmental-related applications of catalysis and energy storage, as well as gas storage-separation and water harvesting with close association to the energy-water-environment nexus are highlighted. Last, perspectives on current challenges and recommendations for further development of MOF-based materials are also discussed.

Metal-Organic Frameworks as Playgrounds for Reticulate Single-Molecule Magnets

Achieving fine control on the structure of metal-organic frameworks (MOFs) is mandatory to obtain target physical properties. Herein, we present how the combination of a metalloligand approach and a postsynthetic method is a suitable and highly useful synthetic strategy to success on this extremely difficult task. First, a novel oxamato-based tetranuclear cobalt(III) compound with a tetrahedron-shaped geometry is used, for the first time, as the metalloligand toward calcium(II) metal ions to lead to a diamagnetic Ca^II-Co^III three-dimensional (3D) MOF (1). In a second stage, in a single-crystal-to-single-crystal manner, the calcium(II) ions are replaced by terbium(III), dysprosium(III), holmium(III), and erbium(III) ions to yield four isostructural novel Ln^III-Co^III [Ln = Tb (2), Dy (3), Ho (4), and Er (5)] 3D MOFs. Direct-current magnetic properties for 2-5 show typical performances for the ground-state terms of the lanthanoid cations [⁷F₆ (Tb^III), ⁶H_15/2 (Dy^III), ⁵I₈ (Ho^III), and ⁴I_15/2 (Er^III)]. Analysis of the χ_MT data indicates that the ground state is the lowest M_J value, that is, M_J = 0 (2 and 4) and ±¹/₂ (3 and 5). Kramers' ions (3 and 5) exhibit field-induced emergent frequency-dependent alternating-current magnetic susceptibility signals, which is indicative of the presence of slow magnetic relaxation typical of single-molecule magnets.

Tuning Carbon Dioxide Adsorption Affinity of Zinc(II) MOFs by Mixing Bis(pyrazolate) Ligands with N-Containing Tags

The four zinc(II) mixed-ligand metal-organic frameworks (MIXMOFs) Zn(BPZ)_x(BPZNO₂)_1-x, Zn(BPZ)_x(BPZNH₂)_1-x, Zn(BPZNO₂)_x(BPZNH₂)_1-x, and Zn(BPZ)_x(BPZNO₂)_y(BPZNH₂)_1-x-y (H₂BPZ = 4,4'-bipyrazole; H₂BPZNO₂ = 3-nitro-4,4'-bipyrazole; H₂BPZNH₂ = 3-amino-4,4'-bipyrazole) were prepared through solvothermal routes and fully investigated in the solid state. Isoreticular to the end members Zn(BPZ) and Zn(BPZX) (X = NO₂, NH₂), they are the first examples ever reported of (pyr)azolate MIXMOFs. Their crystal structure is characterized by a three-dimensional open framework with one-dimensional square or rhombic channels decorated by the functional groups. Accurate information about ligand stoichiometric ratio was determined (for the first time on MIXMOFs) through integration of selected ligands skeleton resonances from ¹³C cross polarized magic angle spinning solid-state NMR spectra collected on the as-synthesized materials. Like other poly(pyrazolate) MOFs, the four MIXMOFs are thermally stable, with decomposition temperatures between 708 and 726 K. As disclosed by N₂ adsorption at 77 K, they are micro-mesoporous materials with Brunauer-Emmett-Teller specific surface areas in the range 400-600 m²/g. A comparative study (involving also the single-ligand analogues) of CO₂ adsorption capacity, CO₂ isosteric heat of adsorption (Q_st), and CO₂/N₂ selectivity in equimolar mixtures at p = 1 bar and T = 298 K cast light on interesting trends, depending on ligand tag nature or ligand stoichiometric ratio. In particular, the amino-decorated compounds show higher Q_st values and CO₂/N₂ selectivity vs the nitro-functionalized analogues; in addition, tag "dilution" [upon passing from Zn(BPZX) to Zn(BPZ)_x(BPZX)_1-x] increases CO₂ adsorption selectivity over N₂. The simultaneous presence of amino and nitro groups is not beneficial for CO₂ uptake. Among the compounds studied, the best compromise among uptake capacity, Q_st, and CO₂/N₂ selectivity is represented by Zn(BPZ)_x(BPZNH₂)_1-x.