Geometry Mismatch and Reticular Chemistry: Strategies To Assemble Metal–Organic Frameworks with Non-default Topologies

Construction of Four 3D Isostructural Rare Earth-Tetrabromoterephthalate Frameworks with stp Topology: Synthesis, Crystal Structure, and CO2 Sorption Properties

The 3D rare earth metal-organic frameworks containing tetrabromoterephthalate (Br4tp) linkers with square trigonal prism (stp) topological network, [RE(Br4tp)1.5]·3H2O (RE-MOF; RE = Er, Tm, Yb, and Lu), were synthesized through the covalently linking geometrically matching molecular building blocks and cooperative intermolecular interactions. The stp type network exhibits 1D microporous structures that are capable of accommodating hexameric tubular water (H2O)6 clusters. The adsorption-desorption isotherms of CO2, CH4, and N2 gases on a typical sample of RE-MOF were analyzed. The binding mechanism of CO2 with the MOF frameworks was analyzed utilizing density functional theory (DFT) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS).

Tetrathienylethene-based porous framework composites for boosting photocatalytic antibacterial activity

In order to reduce the risk of high-threat pathogens, a photocatalytic antibacterial method with a reputation for high efficiency and sustainability has attracted widespread attention. Recently, metal-organic frameworks (MOFs) have emerged as desirable platforms for photocatalytic applications by virtue of their structural diversity and functional adjustability. Herein, we report that we have synthesized a stable and photosensitive zirconium-based MOF (Zr-MOF) with a photoactive tetrathienylethene-based organic linker, Zr-TSS-1. Compared with all-carbocyclic Zr-MOF counterparts, Zr-TSS-1 shows a substantial improvement in visible-light harvesting and free-carrier generation, enabling it to be a promising candidate for photocatalytic antibacterial applications. In order to validate the advantages of this framework as an antibacterial protective material, a composite was fabricated by incorporating robust Zr-TSS-1 onto sustainably accessible bacterial cellulose (BC) using an in situ growth method. This composite exhibits near-complete lethality toward typical Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus within 1 h under mild irradiation and preserves outstanding antibacterial capability after five cycles of reutilization. In addition, the high biocompatibility is confirmed by the low cytotoxicity toward human skin fibroblast, suggesting its potential for biomedical and healthcare applications. This research demonstrates the efficacious integration of a purposely designed photosensitive porous framework onto a sustainable substrate for synergistic functionality, paving a practical way for the development of the next-generation high-efficiency antimicrobial technology.

A lanthanide MOF with nanostructured node disorder

Structural disorder can be used to tune the properties of functional materials and is an important tool that can be employed for the development of complex framework materials, such as metal-organic frameworks. Here we show the synthesis and structural characterization of a metal-organic framework, UoB-100(Dy). Average structure refinements indicate that the node is disordered between two orientations of the nonanuclear secondary building unit (SBU). By performing 3D diffuse scattering (DS) analysis and Monte Carlo (MC) simulations, we confirm the presence of strong correlations between the metal clusters of UoB-100(Dy). These nodes assemble into a complex nanodomain structure. Quantum mechanical calculations identify linker strain as the driving force behind the nanodomain structure. The implications of such a nanodomain structure for the magnetic, gas storage, and mechanical properties of lanthanide MOFs are discussed.

Linkage Position-Controlled Synthesis of Diverse Zirconium Metal-Organic Frameworks with Prominent Intrinsic Proton Conductivities

Herein, by engineering the geometries of the organic linkers, two pyrrolo-pyrrole-based low-symmetry tetracarboxylate linkers (TAPPs) were successfully designed and subsequently used for the construction of two new zirconium-based metal-organic frameworks (Zr-MOFs) (IAM-10 and IAM-11). The reduction of the linker symmetry arises from both the asymmetric pyrrolo-pyrrole core and the integration of both the para- and meta-benzoate coordination groups on the linkers. Both MOFs are composed of 8-connected Zr6 nodes and 4-connected highly deformed TAPP4- linkers with the same scu topology, but distinct linker arrangements can be observed in two structures. The specific rhomb-shaped geometry together with the flexible m-benzoate groups through the rotation of the peripheral phenyl rings allows this type of TAPP linker to generate unique conformations and arrangements in MOF structures to optimize the coordination bonds with the inorganic building blocks and adapt to the final topologies. Furthermore, the presence of well-defined hydrophilic channels in the reported MOFs allowed us to evaluate the potential for proton conduction. Both IAM-10 and IAM-11 show the prominent intrinsic proton conductivities of 1.13 × 10-2 and 2.69 × 10-3 S cm-1 at 90 °C and 95% RH, making them the top-performing proton-conductive Zr-MOFs.

Leveraging Ligand Desymmetrization to Enrich Structural Diversity of Zirconium Metal-Organic Frameworks for Toxic Chemical Adsorption

The discovery of metal-organic frameworks (MOFs) with novel structures provides significant opportunities for developing porous solids with new properties and enriching the structural diversity of functional materials for various applications. The rational design of building units with specific geometric conformations is essential to direct the construction of MOFs with unique properties. Herein, we leverage a ligand desymmetrization approach to construct a series of new MOFs. A flexible tetratopic carboxylate ligand with a tetrahedral geometry was designed and assembled with a Zr6 cluster, generating four Zr-based MOF structures: NU-2600, NU-2700, NU-2800, and NU-1802, in which the ligand configurations and Zr6 cluster connectivities can be controlled by varying solvents and modulators during synthesis. Except for NU-1802, these represent entirely new topologies. Notably, NU-1802 exhibits structural flexibility, with up to a 74 % reduction in the unit cell volume as confirmed by single-crystal X-ray diffraction studies. Given their microporous structures, we studied the adsorption behaviors of n-hexane and 2-chloroethyl ethyl sulfide to explore the structure-property relationships of these MOFs. Overall, this work highlights ligand desymmetrization as a powerful method to enrich MOF structural diversity and access complex MOFs with non-default topologies suitable for applications such as toxic gas capture.

Structural Control of Photoconductivity in a Flexible Titanium-Organic Framework

The soft nature of Metal-Organic Frameworks (MOFs) sets them apart from other non-synthetic porous materials. Their flexibility allows the framework components to rearrange in response to environmental changes, leading to different states and properties. The work extends this concept to titanium frameworks, demonstrating control over charge transport in porous molecular crystals. MUV-35 is a two-fold catenated framework composed of heterometallic TiMn2 trimers and electron donor 4,4',4″-(benzo[1,2-b:3,4-b':5,6-b″]trithiophene-2,5,8-triyl)tribenzoic acid (H3BTTTB) linkers, forming a rare sit-c net topology that can fold to reduce its volume by ≈40% through a single-crystal transformation controlled by linker conformation in open, intermediate, and closed states. This process, driven by a free energy difference of ≈300 kJ mol-1, originates from the formation of a continuous network of non-covalent interactions that force the spontaneous loss of the solvent in the pores of the framework to establish charge transport pathways that afford photocurrents of 2.5 × 10-3 S m-1 under visible light for an ON/OFF ratio (∆R) of four orders of magnitude. This photoconductivity rivals the best conductivity values described for though-transport conductive MOFs while maintaining a porosity of ≈1.000 m2 g-1.

Merging and Clipping Nets for the Synthesis of Three- and Two-Merged Net Metal-Organic Frameworks

Herein, we report how merging and clipping nets in metal-organic frameworks (MOFs) can be controlled in a single-crystal-to-single-crystal fashion using three different approaches─the merged net, clip-off chemistry, and linker reinstallation─to design and synthesize three- and two-merged net MOFs. Initially, we show the formation of three isoreticular three-merged net MOFs by linking a trimeric Sc3+ cluster, Sc3(μ3-Ο)(-COO)6, with ditopic zigzag and tritopic linkers. The resulting MOFs exhibit three-merged edge-transitive nets─kgd + hxl + pcu─for the first time. Then, using these three-merged net MOFs as precursors, we selectively remove one of these subnets, the hxl net, via clip-off chemistry to form two-merged net MOFs. This process involves the cleavage of olefinic groups via ozonolysis, providing the resulting two-merged net MOFs with free carboxylic acid groups that can be used to tune their sorption properties such as the removal of cationic organic pollutants. Finally, we use the linker reinstallation approach to convert the two-merged net MOFs back to the three-merged net MOFs. This approach allows for the postsynthetic addition of the previously removed hxl merged net, enabling recovery of the initial three-merged net MOFs or synthesis of new ones using novel ditopic zigzag linkers.

Computational Modeling of Reticular Materials: The Past, the Present, and the Future

Reticular materials rely on a unique building concept where inorganic and organic building units are stitched together giving access to an almost limitless number of structured ordered porous materials. Given the versatility of chemical elements, underlying nets, and topologies, reticular materials provide a unique platform to design materials for timely technological applications. Reticular materials have now found their way in important societal applications, like carbon capture to address climate change, water harvesting to extract atmospheric moisture in arid environments, and clean energy applications. Combining predictions from computational materials chemistry with advanced experimental characterization and synthesis procedures unlocks a design strategy to synthesize new materials with the desired properties and functions. Within this review, the current status of modeling reticular materials is addressed and supplemented with topical examples highlighting the necessity of advanced molecular modeling to design materials for technological applications. This review is structured as a templated molecular modeling study starting from the molecular structure of a realistic material towards the prediction of properties and functions of the materials. At the end, the authors provide their perspective on the past, present of future in modeling reticular materials and formulate open challenges to inspire future model and method developments.

From Elementary to Advanced Design of Functional Metal-Organic Frameworks: A User Guide to Deciphering the Reticular Chemistry Toolbox

Here, the fundamental requirements are described for understanding and using topology tools in the design of porous materials, emphasizing the relationships between nets, metal-organic framework (MOF) structures, nodes, and building blocks. Common design approaches are discussed, highlighting prerequisites for the rational design of MOFs, such as those with simple pcu topology through the molecular building block approach, or axial-to-axial pillaring. The importance of highly connected nets and building units is emphasized for achieving structural predictability. The geometrical requirements are detailed for designing highly connected MOFs using more elaborate strategies: MOFs with rht topology through the supermolecular building block approach, tbo topology through the supermolecular building layer approach, and sph topology through a merged net approach The potential for innovation through deviations from default nets, such as introducing a geometry mismatch is addressed, which can lead to novel materials with unique zeolitic structures. Examples include MOFs with sodalite (sod) topology, developed through cantellation or mixed-ligand approaches inspired by ancestral architectural methods, utilizing centring structure-directing agents. Key insights for researchers are provided to facilitate the application and expansion of design strategies to new chemical systems. The only limit is imagination, along with some chemical, physical, and thermodynamical principles, of course.

Porous MOFs with geometric mismatch between trimers and octatopic pyrene-based ligands for low-temperature methane storage

Natural gas is recognized as a transitional clean energy fuel to address a variety of environmental problems. Identifying porous adsorbents with high-capacity low-temperature methane adsorption performances is crucial for advancing next-generation technologies for efficiently utilizing boil-off gas, inevitablely generated from liquefied natural gas systems. Herein, we synthesized highly porous metal-organic frameworks (MOFs)-TBPP-MOFs with a geometric mismatch strategy by combining seemingly incompatible trinuclear clusters with octatopic pyrene-based ligands. The Cr-TBPP-MOF achieves a high apparent Brunauer-Emmett-Teller (BET) surface area of 3700 m2 g-1 and demonstrates pore volumes of 1.31 cm3 g-1 at P/P0 = 0.9. Consequently, under the LNG-ANG coupling operation conditions, Cr-TBPP-MOF exhibits a high low-temperature methane uptake of 335 cm3 (STP) cm-3 at 159 K and 10 bar with a working capacity of 302 cm3 (STP) cm-3 between 6 bar and 159 K to 5 bar and 298 K, positioning it as a promising candidate material for low-temperature methane adsorption.

Promoting photoswitching in mismatching mixed-linker multivariate Zr6 MOFs

Multivariate metal-organic frameworks (MTV MOFs) have emerged as promising materials due to their ability to combine properties that enhance features beyond those of their pristine counterparts. Despite the potential for tailoring electronic properties through structural distortions and defects introduced by linkers of variable lengths, examples remain scarce, and information on the electronic structure is limited. Here, we present the multivariate mismatching linker approach to generate photoswitching nanoparticulated MOFs with variable lattice parameters and porosity features controlled by mixed-linker composition. Structural defects, such as dangling linkers, are generated due to mismatching crystal lattices, tuning the electronic structure. Combining biphenyl and azobenzene ditopic linkers promotes cis-trans photoswitching of dangling azobenzene linkers, which is constrained in Zr6-azobenzene MOFs. Moreover, introducing low quantities of azobenzene drastically reduces the bandgap of the materials due to the contribution of the azo group, which is supported by first-principles calculations. This paves the way for new photo-responsive materials for photo-switching applications.

Reticular Chemistry and In Situ "One-Pot" Strategy: A Dream Combination to Construct Metal-Organic Frameworks

The establishment of reticular chemistry has significantly facilitated the development of porous materials, especially for metal-organic frameworks (MOFs). On the other hand, as an alternative approach, in situ "one-pot" strategy has been explored as a promising approach to constructing MOFs, in which the synthesis of organic linkers and the sequential construction of MOFs are integrated into one solvothermal condition. This strategy can efficiently avoid the limitations faced in the traditional construction method, such as time-consuming organic synthesis and multiple separation and purification. Herein, inspired by the reaction of aldehydes and o-phenylenediamine and deep structural analysis of UiO-68, a series of tetra-, hexa-, and octa-topic carboxylic acids are synthesized using 2',3'-diamino-[1,1':4',1'"-terphenyl]-4,4'"-dicarboxylic acid and di-, tri-, and tetra-topic aldehydes as precursor. Then nine multicarboxylate-based zirconium MOFs (Zr-MOFs) are successfully constructed via the combination of reticular chemistry and in situ "one-pot" strategy. The resultant Zr-MOFs can be regarded as the partial face decoration of UiO-68. More importantly, the emission properties of resultant Zr-MOFs can be well controlled using aldehydes with tunable electronic structures. This work provides a new path to rational design and construction of porous materials with specific structures guided by reticular chemistry and conducted using in situ "one-pot" strategy.

Yttrium-based metal-organic frameworks built on hexanuclear clusters

Yttrium-based metal-organic frameworks built on hexanuclear clusters (Y6-MOFs) represent an important subgroup of MOFs that are assembled from Y6 clusters and diverse organic linkers, featuring a variety of topologies. Due to the robust Y-O bonds and high connectivity of hexanuclear SBUs, Y6-MOFs are generally thermally stable and resistant to water. Additionally, their pore structures are highly tunable through the practice of the reticular chemistry strategy, resulting in excellent performance in gas adsorption and separation related applications. Y6-MOFs are structurally analogous to Zr6-MOFs; however, the existence of charge-balancing cations in Y6-MOFs serves as an additional pore structure regulator, enhancing their tailorability with respect to pore shape and dimensions. In this Frontier article, we summarize the main advances in the design and synthesis of Y6-MOFs, with a particular focus on the precise engineering of their pore structure for gas separation. Future directions of research efforts in this field are also discussed.

In Situ Observation of Topotactic Linker Reorganization in the Aperiodic Metal-Organic Framework TRUMOF-1

We use in situ synchrotron X-ray diffraction measurements to monitor the solvothermal crystallization mechanism of the aperiodic metal-organic framework TRUMOF-1. Following an initial incubation period, TRUMOF-1 forms as a metastable intermediate that subsequently transforms into an ordered product with triclinic crystal symmetry. We determine the structure of this ordered phase, which we call msw-TRUMOF-1, and show that it is related to TRUMOF-1 through topotactic reorganization of linker occupancies. Our results imply that the connectivity of TRUMOF-1 can be reorganized, as required for data storage and manipulation applications.

Reticular Chemistry Directed "One-Pot" Strategy to in situ Construct Organic Linkers and Zirconium-Organic Frameworks

Zirconium-based metal-organic frameworks (Zr-MOFs) have emerged as one of the most studied MOFs due to the unlimited numbers of organic linkers and the varying Zr-oxo clusters. However, the synthesis of carboxylic acids, especially multitopic carboxylic acids, is always a great challenge for the discovery of new Zr-MOFs. As an alternative approach, the in situ "one-pot" strategy can address this limitation, where the generation of organic linkers from the corresponding precursors and the sequential construction of MOFs are integrated into one solvothermal condition. Herein, inspired by benzimidazole-contained compounds synthesized via reaction of aldehyde and o-phenylenediamine, tri-, tetra-, penta- and hexa-topic carboxylic acids and a series of corresponding Zr-MOFs can be prepared via the in situ "one-pot" method under the same solvothermal conditions. This strategy can be utilized not only to prepare reported Zr-MOFs constructed using benzimidazole-contained linkers, but also to rationally design, construct and realize functionalities of zirconium-pentacarboxylate frameworks guided by reticular chemistry. More importantly, in situ "one-pot" method can facilitate the discovery of new Zr-MOFs, such as zirconium-hexacarboxylate frameworks. The present study demonstrates the promising potential of benzimidazole-inspired in situ "one-pot" approach in the crystal engineering of structure- and property-specific Zr-MOFs, especially with the guidance of reticular chemistry.

Leveraging Isoreticular Principle to Elucidate the Key Role of Inherent Hydrogen-Bonding Anchoring Sites in Enhancing Water Sorption Cyclability of Zr(IV) Metal-Organic Frameworks

Water adsorption/desorption cyclability of porous materials is a prerequisite for diverse applications, including atmospheric water harvesting (AWH), humidity autocontrol (HAC), heat pumps and chillers, and hydrolytic catalysis. However, unambiguous molecular insights into the correlation between underlying building blocks and the cyclability are still highly elusive. In this work, by taking advantage of the well-established isoreticular synthetic principle in Zr(IV) metal-organic frameworks (Zr-MOFs), we show that the inherent density of hydrogen atoms in the organic skeleton can play a key role in regulating the water sorption cyclability of MOFs. The ease of isoreticular practice of Zr-MOFs enables the successful syntheses of two pairs of isostructural Zr-MOFs (NU-901 and NU-903, NU-950 and SJTU-9) from pyrene- or benzene-cored carboxylate linkers, which feature scu and sqc topological nets, respectively. NU-901 and NU-950 comprised of pyrene skeletons carrying more hydrogen-bonding anchoring sites show distinctly inferior cyclability as compared with NU-903 and SJTU-9 built of benzene units. Single-crystal X-ray crystallography analysis of the hydrated structure clearly unveils the water molecule-involved interactions with the hydrogen-bonding donors of benzene moieties. Remarkably, NU-903 and SJTU-9 isomers exhibit outstanding water vapor sorption capacities as well as working capacities at the desired humidity range with potential implementations covering indoor humidity control and water harvesting. Our findings uncover the importance of hydrogen-bonding anchoring site engineering of organic scaffold in manipulating the framework durability toward water sorption cycle and will also likely facilitate the rational design and development of highly robust porous materials.

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

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

Breathing Metal-Organic Frameworks Supported by an Arsenic-Bridged 4,4'-Bipyridine Ligand

Bent ligands bridged by heteroatoms have drawn significant interest as supramolecular coordination architectures. Traditionally, divalent group 16 elements are preferred over trivalent group 15 elements because of the anticipated steric hindrance. In this study, we explore metal-organic frameworks (MOFs) based on dipyridinoarsoles (DPAs), 4,4'-bipyridines bridged with an arsenic atom. An MOF with methyl-substituted DPA collapsed upon solvent removal, whereas that with phenyl-substituted DPA demonstrated breathing behavior due to guest molecule adsorption/desorption. In contrast, MOFs using the phosphorus analogue dipyridinophosphole exhibit inferior adsorption and lack breathing behavior. This is the first study to investigate the interplay among substituents, bridging elements, and dynamic behavior in MOFs using bent group 15 ligands.

Reticular chemistry guided precise construction of zirconium-pentacarboxylate frameworks with 5-connected Zr6 clusters

Zirconium-based metal-organic frameworks (Zr-MOFs) have been extensively studied due to their very rich structural chemistry. The combination of nearly unlimited carboxylic acid-based linkers and Zr6 clusters with multiple connectivities has led to diverse structures and specific properties of resultant Zr-MOFs. Herein, we demonstrate the successful use of reticular chemistry to construct two novel Zr-MOFs, HIAM-4040 and HIAM-4040-OH, with zfu topology. Based on a thorough structural analysis of (4,4)-connected lvt-type Zr-tetracarboxylate frameworks and a judicious linker design, we have obtained the first example of a Zr-pentacarboxylate framework featuring unprecedented 5-connected organic linkers and 5-connected Zr6 clusters. Compared with HIAM-4040, a larger Stokes shift is achieved in HIAM-4040-OH via hydroxyl group induced excited-state intramolecular proton transfer (ESIPT). HIAM-4040-OH exhibits high chemical and thermal stability and is used for HClO detection in aqueous solution with excellent sensitivity and selectivity.

Torsional flexibility in zinc-benzenedicarboxylate metal-organic frameworks

We explore the role and nature of torsional flexibility of carboxylate-benzene links in the structural chemistry of metal-organic frameworks (MOFs) based on Zn and benzenedicarboxlyate (bdc) linkers. A particular motivation is to understand the extent to which such flexibility is important in stabilising the unusual topologically aperiodic phase known as TRUMOF-1. We compare the torsion angle distributions of TRUMOF-1 models with those for crystalline Zn/1,3-bdc MOFs, including a number of new materials whose structures we report here. We find that both periodic and aperiodic Zn/1,3-bdc MOFs sample a similar range of torsion angles, and hence the formation of TRUMOF-1 does not require any additional flexibility beyond that already evident in chemically-related crystalline phases. Comparison with Zn/1,4-bdc MOFs does show, however, that the lower symmetry of the 1,3-bdc linker allows access to a broader range of torsion angles, reflecting a greater flexibility of this linker.

Rational Design and Reticulation of Infinite qbe Rod Secondary Building Units into Metal-Organic Frameworks through a Global Desymmetrization Approach for Inverse C3 H8 /C3 H6 Separation

The development of reticular chemistry has enabled the construction of a large array of metal-organic frameworks (MOFs) with diverse net topologies and functions. However, dominating this class of materials are those built from discrete/finite secondary building units (SBUs), yet the designed synthesis of frameworks involving infinite rod-shaped SBUs remain underdeveloped. Here, by virtue of a global linker desymmetrization approach, we successfully targeted a novel Cu-MOF (Cu-ASY) incorporating infinite Cu-carboxylate rod SBUs with its structure determined by micro electron diffraction (MicroED) crystallography. Interestingly, the rod SBU can be simplified as a unique cylindric sphere packing qbe tubule made of [43 .62 ] tiles, which further connect the tritopic linkers to give a newly discovered 3,5-connected gfc net. Cu-ASY is a permanent ultramicroporous material featuring 1D channels with highly inert surfaces and shows a preferential adsorption of propane (C3 H8 ) over propene (C3 H6 ). The efficiency of C3 H8 selective Cu-ASY is validated by multicycle breakthrough experiments, giving C3 H6 productivity of 2.2 L/kg. Density functional theory (DFT) calculations reveal that C3 H8 molecules form multiple C-H⋅⋅⋅π and atypical C-H⋅⋅⋅ H-C van der Waals interactions with the inner nonpolar surfaces. This work therefore highlights the linker desymmetrization as an encouraging and intriguing strategy for achieving unique MOF structures and properties.

Modulator-Dependent Dynamics Synergistically Enabled Record SO2 Uptake in Zr(IV) Metal-Organic Frameworks Based on Pyrene-Cored Molecular Quadripod Ligand

Developing innovative porous solid sorbents for the capture and storage of toxic SO2 is crucial for energy-efficient transportation and subsequent processing. Nonetheless, the quest for high-performance SO2 sorbents, characterized by exceptional uptake capacity, minimal regeneration energy requirements, and outstanding recyclability under ambient conditions, remains a significant challenge. In this study, we present the design of a unique tertiary amine-embedded, pyrene-based quadripod-shaped ligand. This ligand is then assembled into a highly porous Zr-metal-organic framework (MOF) denoted as Zr-TPA, which exhibits a newly discovered 3,4,8-c woy net structure. Remarkably, our Zr-TPA MOF achieved an unprecedented SO2 sorption capacity of 22.7 mmol g-1 at 298 K and 1 bar, surpassing those of all previously reported solid sorbents. We elucidated the distinct SO2 sorption behaviors observed in isostructural Zr-TPA variants synthesized with different capping modulators (formate, acetate, benzoate, and trifluoroacetate, abbreviated as FA, HAc, BA, and TFA, respectively) through computational analyses. These analyses revealed unexpected SO2-induced modulator-node dynamics, resulting in transient chemisorption that enhanced synergistic SO2 sorption. Additionally, we conducted a proof-of-concept experiment demonstrating that the captured SO2 in Zr-TPA-FA can be converted in situ into a valuable pharmaceutical intermediate known as aryl N-aminosulfonamide, with a high yield and excellent recyclability. This highlights the potential of robust Zr-MOFs for storing SO2 in catalytic applications. In summary, this work contributes significantly to the development of efficient SO2 solid sorbents and advances our understanding of the molecular mechanisms underlying SO2 sorption in Zr-MOF materials.

Net-clipping as a top-down approach for the prediction of topologies of MOFs built from reduced-symmetry linkers

Reticular materials constructed from regular molecular building blocks (MBBs) have been widely explored in the past three decades. Recently, there has been increasing interest in the assembly of novel, intricate materials using less-symmetric ligands; however, current methods for predicting structure are not amenable to this increased complexity. To address this gap, we propose herein a generalised version of the net-clipping approach for anticipating the topology of metal-organic frameworks (MOFs) assembled from organic linkers and different polygonal and polyhedral MBBs. It relies on the generation of less-symmetric nets with less-connected linkers, via the rational deconstruction of more-symmetric and more-connected linkers in edge-transitive nets. We applied our top-down strategy to edge-transitive nets containing 4-c tetrahedral, 6-c hexagonal, 8-c cubic or 12-c hexagonal prism linkers, envisaging the formation of 102 derived and 46 clipped nets. Among these, we report 33 new derived nets (icn7-icn39) and 6 new clipped nets (icn1-icn6). Importantly, the feasibility of using net-clipping to anticipate clipped nets is supported by literature examples and new experimental additions. Finally, we suggest and illustrate that net-clipping can be extended to less-regular, non-edge transitive nets as well as to covalent-organic frameworks (COFs), thus opening new avenues for the rational design of new reticular materials exhibiting unprecedented topologies.

Ortho Effects of Tricarboxylate Linkers in Regulating Topologies of Rare-Earth Metal-Organic Frameworks

A linker design strategy is developed to attain novel polynuclear rare-earth (RE) metal-organic frameworks (MOFs) with unprecedented topologies. We uncover the critical role of ortho-functionalized tricarboxylate ligands in directing the construction of highly connected RE MOFs. The acidity and conformation of the tricarboxylate linkers were altered by substituting with diverse functional groups at the ortho position of the carboxyl groups. For instance, the acidity difference between carboxylate moieties resulted in forming three hexanuclear RE MOFs with novel (3,3,3,10,10)-c wxl, (3,12)-c gmx, and (3,3,3,12)-c joe topologies, respectively. In addition, when a bulky methyl group was introduced, the incompatibility between the net topology and ligand conformation guided the co-appearance of hexanuclear and tetranuclear clusters, generating a novel 3-periodic MOF with a (3,3,8,10)-c kyw net. Interestingly, a fluoro-functionalized linker prompted the formation of two unusual trinuclear clusters and produced a MOF with a fascinating (3,8,10)-c lfg topology, which could be gradually replaced by a more stable tetranuclear MOF with a new (3,12)-c lee topology with extended reaction time. This work enriches the polynuclear clusters library of RE MOFs and unveils new opportunities to construct MOFs with unprecedented structural complexity and vast application potential.

Nanosized metal-organic frameworks as unique platforms for bioapplications

Metal-organic frameworks (MOFs) are extremely versatile materials, which serve to create platforms with exceptional porosity and specific reactivities. The production of MOFs at the nanoscale (NMOFs) offers the possibility of creating innovative materials for bioapplications as long as they maintain the properties of their larger counterparts. Due to their inherent chemical versatility, synthetic methods to produce them at the nanoscale can be combined with inorganic nanoparticles (NPs) to create nanocomposites (NCs) with one-of-a-kind features. These systems can be remotely controlled and can catalyze abiotic reactions in living cells, which have the potential to stimulate further research on these nanocomposites as tools for advanced therapies.

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.

Truchet-tile structure of a topologically aperiodic metal-organic framework

When tiles decorated to lower their symmetry are joined together, they can form aperiodic and labyrinthine patterns. Such Truchet tilings offer an efficient mechanism of visual data storage related to that used in barcodes and QR codes. We show that the crystalline metal-organic framework [OZn₄][1,3-benzenedicarboxylate]₃ (TRUMOF-1) is an atomic-scale realization of a complex three-dimensional Truchet tiling. Its crystal structure consists of a periodically arranged assembly of identical zinc-containing clusters connected uniformly in a well-defined but disordered fashion to give a topologically aperiodic microporous network. We suggest that this unusual structure emerges as a consequence of geometric frustration in the chemical building units from which it is assembled.

Tröger's Base Chemistry in Solution and in Zr(IV)-Based Metal-Organic Frameworks

Tröger's base (TB) and its derivatives have been studied extensively due to their unique concave shape stemming from the endomethylene strap. However, the strap-clipped TB chemistry has been largely overlooked in metal-organic framework (MOF) solids, leading to a gap in our knowledge within this field. In this work, we report the in situ strap elimination of a carboxylate-carrying TB in the presence of formic acid, both in solution and in Zr(IV)-based MOFs. In the solution system, the methanodiazocine nucleus can be exclusively transformed into an N,N'-diformyl-decorated phenhomazine derivative, regardless of the solvent used (DMF, DMA, or DEF), as unambiguously uncovered by single crystal X-ray crystallography. In contrast, while in the MOF synthetic system, the degree of derivatization reaction can be effectively controlled to give either the secondary diamine or formyl-decorated diamine, depending on the solvent used (DMF or DEF), resulting in the formation of two Zr-MOFs with 8-connected bcu (NU-1900) and 12-connected fcu (NU-407) topologies, respectively. The derivatization mechanism is proposed to be topology-guided and dependent on the local acid concentration during the MOF formation processes. Moreover, we discovered a novel post-synthetically water-induced in situ linker formylation process in NU-1900 through sequential formic acid elimination, migration, and condensation processes, affording an isostructural framework with the same linker as in NU-407, which further corroborates our proposed mechanism. Additionally, the highly defective NU-1900 with abundant accessible Zr sites was demonstrated to be an outstanding catalyst for the detoxification of a nerve agent simulant with a half-life of less than 1 min.

Reticular Chemistry with Art: A Case Study of Olympic Rings-Inspired Metal-Organic Frameworks

Herein, we demonstrate the successful utilization of reticular chemistry as an excellent designing strategy for the deliberate construction of a zirconium-tetracarboxylate metal-organic framework (MOF) inspired by the Olympic rings. HIAM-4017, with an unprecedented (4,8)-c underlying net topology termed jcs, was developed via insightful reconstruction of the rings and judicious design of a nonsymmetric organic linker. HIAM-4017 exhibits high porosity and excellent chemical and thermal stability. Furthermore, excited-state intramolecular proton transfer (ESIPT) was achieved in an isoreticular MOF, HIAM-4018, with a large Stokes shift of 155 nm as a result of introducing the hydroxyl group to the linker skeleton to induce OH···N interactions. Such interactions were analyzed thoroughly by employing the time-dependent density functional theory (TD-DFT). Because of their good thermal and chemical stability, and strong luminescence, nanosized HIAM-4017 and HIAM-4018 were fabricated and used for Cr₂O₇^2- detection. Both MOFs demonstrate excellent sensitivity and selectivity. This work represents a neat example of building structure- and property-specific MOFs guided by reticular chemistry.

Computer simulation of the early stages of self-assembly and thermal decomposition of ZIF-8

We employ all-atom well-tempered metadynamics simulations to study the mechanistic details of both the early stages of nucleation and crystal decomposition for the benchmark metal–organic framework (MOF) ZIF-8. To do so, we developed and validated a force field that reliably models the modes of coordination bonds via a Morse potential functional form and employs cationic and anionic dummy atoms to capture coordination symmetry. We also explored a set of physically relevant collective variables and carefully selected an appropriate subset for our problem at hand. After a rapid increase of the Zn–N connectivity, we observe the evaporation of small clusters in favor of a few large clusters, which leads to the formation of an amorphous highly connected aggregate. [Formula: see text] and [Formula: see text] complexes are observed with lifetimes in the order of a few picoseconds, while larger structures, such as four-, five-, and six-membered rings, have substantially longer lifetimes of a few nanoseconds. The free ligands act as “templating agents” for the formation of sodalite cages. ZIF-8 crystal decomposition results in the formation of a vitreous phase. Our findings contribute to a fundamental understanding of MOF’s synthesis that paves the way to controlling synthesis products. Furthermore, our developed force field and methodology can be applied to model solution processes that require coordination bond reactivity for other ZIFs besides ZIF-8.

Unique Fluorescence Turn-On and Turn-Off-On Responses to Acids by a Carbazole-Based Metal-Organic Framework and Theoretical Studies

Distinct from predominately known fluorescence quenching (turn-off) detection, turn-on response to hazardous substances by luminescent metal-organic frameworks (LMOFs) could greatly avoid signal loss and susceptibility to environmental stimulus. However, such detection rarely occurs and lacks theoretical elucidations. Here, we present the first example of unique turn-on and unprecedented turn-off-on responses to a variety of acids by a stable 12-connected hexanuclear Y(III)-cluster-based LMOF material─JLU-MOF111, featuring the nondefault pcu topology. Benefiting from the "pocket" structures formed by the carbazole-containing ligands, JLU-MOF111 can sense multiple inorganic and organic acids via different degrees of fluorescence turn-on behaviors. Particularly, turn-on sensing of HNO₃, HCl, HBr, and TFA is hypersensitive with LODs as low as the ppb level. Theoretical calculations confirm weak interactions in acid-ligand complexes, which lead to constrained rotations of benzene moieties of the ligands when the complexes decay from excited states. These account for the turn-on response through reduced nonradiative energy consumption that competes with emissive decay. The turn-off-on response to 4-NBA and 3,5-DNBA involves an excited-state electron transfer process that dominates the turn-off stage and prohibited nonradiative decay that competes with the intrinsic emission of the ligand and dominates the turn-on stage. This work has a guiding significance for the full-scale understanding of turn-on and turn-off-on sensing performance in LMOF materials and beyond.

A microporous Zr6@Zr-MOF for the separation of Xe and Kr

We report here the self-assembly of a she-type zirconium-based metal-organic framework with discrete hexanuclear Zr-oxo clusters residing inside its pore windows. The overall structure features microporosity showing preferential adsorption of Xe over Kr.

A Microporous Metal-Organic Framework Incorporating Both Primary and Secondary Building Units for Splitting Alkane Isomers

We demonstrate the assembly of a mononuclear metal center, a hexanuclear cluster, and a V-shaped, trapezoidal tetracarboxylate linker into a microporous metal-organic framework featuring an unprecedented 3-nodal (4,4,8)-c lyu topology. The compound, HIAM-302, represents the first example that incorporates both a primary building unit and a hexanuclear secondary building unit in one structure, which should be attributed to the desymmetrized geometry of the organic linker. HIAM-302 possesses optimal pore dimensions and can separate monobranched and dibranched alkanes through selective molecular sieving, which is of significant value in the petrochemical industry.

High-Throughput Discovery of a Rhombohedral Twelve-Connected Zirconium-Based Metal-Organic Framework with Ordered Terephthalate and Fumarate Linkers

We report a metal-organic framework where an ordered array of two linkers with differing length and geometry connect [Zr6 (OH)4 O4 ]12+ clusters into a twelve-connected fcu net that is rhombohedrally distorted from cubic symmetry. The ordered binding of equal numbers of terephthalate and fumarate ditopic carboxylate linkers at the trigonal antiprismatic Zr6 core creates close-packed layers of fumarate-connected clusters that are connected along the single remaining threefold axis by terephthalates. This well-defined linker arrangement retains the three-dimensional porosity of the Zr cluster-based UiO family while creating two distinct windows within the channels that define two distinct guest diffusion paths. The ordered material is accessed by a restricted combination of composition and process parameters that were identified by high-throughput synthesis.

The Importance of Highly Connected Building Units in Reticular Chemistry: Thoughtful Design of Metal-Organic Frameworks

The prediction of crystal structures assembled in three dimensions has been considered for a long time, simultaneously as a chemical wasteland and a certain growth point of the chemistry of the future. Less than 30 years after Roald Hoffmann's statement, we can categorically affirm that the elevation of reticular chemistry and the introduction of metal-organic frameworks (MOFs) significantly tackled this tridimensional assembly issue. MOFs result from the assembly of organic polytopic organic ligands bridging metal nodes, clusters, chains, or layers together into mostly three-periodic open frameworks. They can exhibit extremely high porosity and offer great potential as revolutionary catalysts, drug carrier systems, sensors, smart materials, and, of course, separation agents. Overall, the progressive development of reticular chemistry has been a game changer in materials chemistry during the last 25 years.Such diverse properties often result not only from the selected organic and inorganic molecular building blocks (MBBs) but also from their distribution within the framework. Indeed, the size and shape of the porous system, as well as the location of active sites influence the overall properties. Therefore, in the continuity of achieving the crystallization of three-periodic structures, chemists and crystal engineers faced the next challenge, as summarized by John Maddox: "it remains in general impossible to predict the structure of even the simplest crystallographic solids from knowledge of their chemical composition". This is where rational design takes place.In this Account, we detail three specific approaches developed by our group to facilitate the design and assembly of finely tuned MOFs. All are based on careful geometrical consideration and a deep study and understanding of the existing nets and topologies. We recognized that highly connected nets, if possible, edge-transitive, are ideal blueprints because their number is limited in contrast to nets with lower connectivity. Therefore, we embarked on taking advantage of existing highly connected MBBs, or, in parallel, promoting their formation to meet our requirements. This is achieved by utilizing externally decorated metal-organic polyhedra as supermolecular building blocks (SBBs), serving as a net-coding building unit, comprising the requisite connectivity and directional information coding for the chosen nets. The SBB approach allowed the synthesis of several families of SBB-based MOFs, including fcu, rht, and gea-MOFs, that are detailed here.The second strategy is directly inherited from the success of the SBB approach. In seeking highly connected building units, our group naturally expanded its research focus to nets that can be deconstructed into layers, pillared in various ways. In the supermolecular building layer (SBL) approach, the layers have an almost infinite connectivity, and the framework backbone is fixed in two dimensions while the third is free for pillar expansion and functionalization. The cases of trigonal pillaring leading to rtl, eea, and apo MOFs as well as the quadrangular pillaring leading to a family of tbo-MOFs are discussed here, along with recent cases of highly connected pillars in pek and aea-MOFs.Finally, our experience with highly coordinated MBBs led us to develop a novel way to use them as secondary building units of lower connectivity and unlock the possibility of assembling a novel class of zeolite-like MOFs (ZMOFs). The case of the Zr-sod-ZMOFs designed through a cantellation strategy is described as a future leading direction of MOF design.

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.

Construction of Highly Proton-Conductive Zr(IV)-Based Metal-Organic Frameworks From Pyrrolo-pyrrole-Based Linkers with a Rhombic Shape

To date, numerous zirconium cluster-based metal-organic frameworks (Zr-MOFs) with attractive physical properties have been achieved thanks to tailorable organic linkers and versatile Zr clusters. Nevertheless, in comparison with the most-used high-symmetry organic linkers, low-symmetry linkers have rarely been exploited in the construction of Zr-MOFs. Despite challenges in predicting the structure and topology of the MOF, linker desymmetrization presents opportunities for the design of Zr-MOFs with unusual topologies and unexpected functionalities. Herein, we report for the first time the construction of two robust Zr-MOFs (IAM-7 and IAM-8) from two pyrrolo-pyrrole-based low-symmetry tetracarboxylate linkers with a rare rhombic shape. The low symmetry of the linkers arises from the asymmetric pyrrolo-pyrrole core and the varying branch lengths, which play a critical role in the structural diversity between IAM-7 and IAM-8 seen from the structural analysis and lead to hydrophilic channels that contain uncoordinated carboxylate groups in the structure of IAM-7. Furthermore, the proton conductivity of IAM-7 displays a high temperature and humidity dependence where the proton conductivity increases from 2.84 × 10^-8 S cm^-1 at 30 °C and 40% relative humidity (RH) to 1.42 × 10^-2 S cm^-1 at 90 °C and 95% RH, making it among one of the most conductive Zr-MOFs. This work not only enriches the library of Zr-MOFs but also offers a platform for the design of low-symmetry linkers toward the structural diversity or irregularity of MOFs as well as their structure-related properties.

Ligand-Conformer-Induced Formation of Zirconium-Organic Framework for Methane Storage and MTO Product Separation

In pursuit of novel adsorbents with efficient adsorptive gas storage and separation capabilities remains highly desired and challenging. Although the documented zirconium-tricarboxylate-based metal-organic frameworks (MOFs) have displayed a variety of topologies encompassing underlying and geometry mismatch ones, the employed organic linkers are exclusively rigid and poorly presenting one type of conformation in the resultant structures. Herein, a used and semirigid tricarboxylate ligand of H₃ TATAB was judiciously selected to isolate a zirconium-based spe-MOF after the preliminary discovery of srl-MOF. Single-crystal X-ray diffraction reveals that the fully deprotonated TATAB linker in spe-MOF exhibits two distinct conformers, concomitant with popular O_h and rare S₆ symmetrical Zr₆ molecular building blocks, generating an unprecedented (3,3,12,12)-c nondefault topology. Specifically, the spe-MOF exhibits structurally higher complexity, hierarchical micropores, open metal sites free and rich electronegative groups on the pore surfaces, leading to relatively high methane storage capacity without considering the missing-linker defects and efficient MTO product separation performance.

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.

Modulation of Topological Structures and Adsorption Properties of Copper-Tricarboxylate Frameworks Enabled by the Effect of the Functional Group and Its Position

To push forward the structural development and fully explore the potential utility, it is highly desired but challenging to regulate in a controllable manner the structures and properties of MOFs. In this work, we reported the structural and functional modulation of Cu(II)-tricarboxylate frameworks by employing a strategy of engineering the functionalities and their positions. Two pairs of unsymmetrical biaryl tricarboxylate ligands modified with a methyl group and a pyridinic-N atom at distinct positions were logically designed and synthesized, and their corresponding Cu(II)-based MOFs were solvothermally constructed. Diffraction analyses revealed that the variation of functionalities and their positions furnished three different types of topological structures, which we ascribed to the steric effect exerted by the methyl group and the chelating effect involving the pyridinic-N atom. Furthermore, gas adsorption studies showed that three of them are potential candidates as solid separation media for acetylene (C₂H₂) purification, with the separation potential tailorable by altering functionalities and their locations. At 106.7 kPa and 298 K, the C₂H₂ uptake capacity varies from 64.1 to 132.4 cm³ (STP) g^-1, while the adsorption selectivities of C₂H₂ over its coexisting components of CO₂ and CH₄ fall in the ranges of 3.28-4.60 and 14.1-21.9, respectively.