Programmable Topology in New Families of Heterobimetallic Metal–Organic Frameworks

Considerable Piezochromism in All-Inorganic Zero-Dimensional Perovskite Nanocrystals via Pressure-Modulated Self-Trapped Exciton Emission

Piezochromic materials refer to a class of matters that alter their photoluminescence (PL) colors in response to the external stimuli, which exhibit promising smart applications in anti-counterfeiting, optoelectronic memory and pressure-sensing. However, so far, most reported piezochromic materials have been confined to organic materials or hybrid materials containing organic moieties with limited piezochromic range of less than 100 nm in visible region. Here, we achieved an intriguing piezochromism in all-inorganic zero-dimensional (0D) Cs3Cu2Cl5 nanocrystals (NCs) with a considerable piezochromic range of 232 nm because of their unique inorganic rigid structure. The PL energy shifted from the lowest-energy red fluorescence (1.85 eV) to the highest-energy blue fluorescence (2.83 eV), covering almost the entire visible wavelength range. Pressure-modulated self-trapped exciton emission between different energy levels of self-trapped states within Cs3Cu2Cl5 NCs was the main reason for this piezochromism property. Note that the quenched emission, which is over five times more intense than that in the initial state, is retained under ambient conditions upon decompression. This work provides a promising pressure indicating material, particularly used in pressure stability monitoring for equipment working at extreme environments.

Stepwise and Controllable Synthesis of Mesoporous Heterotrimetallic Catalysts Based on Predesigned Al4 Ln4 Metallocycles

The motivation for making heterometallic compounds stemmed from their emergent synergistic properties and enhanced capabilities for applications. However, the atomically precisely controlled synthesis of heterometallic compounds remains a daunting challenge of the complications that arise when applying several metals and linkers. Herein, a stepwise and controlled method is reported for the accurate addition of second and third metals to homometallic aluminum macrocycles based on the synergistic coordination and hard-soft acid-base theory. These heterometallic compounds showed a good Lewis acid catalytic effect, and the addition of hetero-metals significantly improved the catalytic effect and rate, among that the conversion rate of compound AlOC-133 reached 99.9% within half an hour. This method combines both the independent controllability of stepwise assembly with the universality of one-step methods. Based on the large family of clusters, the establishment of this method paves the way for the controllable and customized molecular-level synthesis of heterometallic materials and creates materials customized for preferential application.

Mesoporous Metal-Organic Frameworks for Catalytic RNA Deprotection and Activation

A metal-organic framework (MOF) with mespores (2 to 50 nm) allows the inclusion of large biomolecules, such as nucleic acids. However, chemical reaction on the nucleic acids, to further regulate their bioactivity, is yet to be demonstrated within MOF pores. Here, we report the deprotection of carbonate protected RNA molecules (21 to 102 nt) to restore their original activity using a MOF as a heterogeneous catalyst. Two MOFs, MOF-626 and MOF-636 are designed and synthesized, with mesopores of 2.2 and 2.8 nm, respectively, carrying isolated metal sites (Ni, Co, Cu, Pd, Rh and Ru). The pores favor the entrance of RNA, while the metal sites catalyze C-O bond cleavage at the carbonate group. Complete conversion of RNA is achieved by Pd-MOF-626, 90 times more efficiently than Pd(NO3 )2 . MOF crystals are also removable from the aqueous reaction media, leaving a negligible metal footprint, 3.9 ppb, only 1/55 of that using homogeneous Pd catalysts. These features make MOF potentially suited for bioorthogonal chemistry.

Factors Controlling Complex Morphologies of Isomorphous Metal-Organic Frameworks

We demonstrate here how nitrate salts of bivalent copper, nickel, cobalt, and manganese, along with an achiral organic ligand, assemble into various structures such as symmetrical double-decker flowers, smooth elongated hexagonal bipyramids, and hexagonal prisms. Large morphological changes occur in these structures because of different metal cations, although they maintain isomorphous hexagonal crystallographic structures. Metal cations with stronger coordination to ligands (Cu and Ni) tend to form uniform crystals with unusual shapes, whereas weaker coordinating metal cations (Mn and Co) produce crystals with more regular hexagonal morphologies. The unusual flower-like crystals formed with copper nitrate have two pairs of six symmetrical petals with hexagonal convex centers. The texture of the petals indicates dendritic growth. Two different types of morphologies were formed by using different copper nitrate-to-ligand ratios. An excess of the metal salt results in uniform and hexagonal crystals having a narrow size distribution, whereas the use of an excess of ligand results in double-decker morphologies. Mechanistically, an intermediate structure was observed with slightly concave facets and a domed center. Such structures most likely play a key role in the formation of double-decker crystals that can be formed by fusion processes. The coordination chemistry results in isostructural chiral frameworks consisting of two types of continuous helical channels. Four pyridine units from four separate ligands are coordinated to the metal center in a plane having a chiral (propeller-type) arrangement. The individual double-decker flower crystals are homochiral and a batch consists of crystals having both handedness.

Semirigid Highly Conjugated Zirconium-Organic Framework for the Capture of Micropollutants and Solar-Light Photodegradation

Micro-organic pollutants, particularly organic dyes and personal care products (PPCPs), are widely present in wastewater, and thus pose a serious risk to human health. The capture and solar-light photodegradation of micro-organic pollutants are highly challenging tasks, which require the design and synthesis of microporous materials with specific structures. As we know, organic dyes and PPCPs can be absorbed via π-π* stacking. In this paper, an iron-based metal-organic framework (Fe-UiO-68-terNap) containing semirigid conjugated aromatic ligands is prepared for the capture and solar-light photodegradation of multiple water contaminants. UiO-68-terNap was synthesized based on ternaphthalene with π-π* stacking, which would increase the adsorption capacities of organic micropollutants in wastewater. Additionally, the formation of Fe-O-Zr enhances the charge-separation ability resulting in the successful degradation of micropollutants in 240 min. The novel material has been elucidated by single-crystal X-ray diffraction and Fe K-edge XANES, which provide key insights at a molecular level for the design of novel materials for the capture and photodegradation of organic micropollutants.

Regulating Activity and Selectivity of Photocatalytic CO2 Reduction on Cobalt by Rare Earth Compounds

Cobalt-based catalysts are ideal for CO₂ reduction reaction (CO₂RR) due to the strong binding and efficient activation of CO₂ molecules on cobalt. However, cobalt-based catalysts also show low free energy of hydrogen evolution reaction (HER), making HER competitive with CO₂RR. Therefore, how to improve the product selectivity of CO₂RR while maintaining the catalytic efficiency is a great challenge. Here, this work demonstrates the critical roles of the rare earth (RE) compounds (Er₂O₃ and ErF₃) in regulating the activity and selectivity of CO₂RR on cobalt. It is found that the RE compounds not only promote charge transfer but also mediate the reaction paths of CO₂RR and HER. Density functional theory calculations verify that the RE compounds lower the energy barrier of *CO → CO conversion. On the other hand, the RE compounds increase the free energy of HER, which leads to the suppression of HER. As a result, the RE compounds (Er₂O₃ and ErF₃) improve the CO selectivity of cobalt from 48.8 to 69.6%, as well as significantly increase the turnover number by a factor of over 10.

Synthesis and Biomedical Applications of Highly Porous Metal-Organic Frameworks

In this review, aspects of the synthesis, framework topologies, and biomedical applications of highly porous metal-organic frameworks are discussed. The term "highly porous metal-organic frameworks" (HPMOFs) is used to denote MOFs with a surface area larger than 4000 m² g^-1. Such compounds are suitable for the encapsulation of a variety of large guest molecules, ranging from organic dyes to drugs and proteins, and hence they can address major contemporary challenges in the environmental and biomedical field. Numerous synthetic approaches towards HPMOFs have been developed and discussed herein. Attempts are made to categorise the most successful synthetic strategies; however, these are often not independent from each other, and a combination of different parameters is required to be thoroughly considered for the synthesis of stable HPMOFs. The majority of the HPMOFs in this review are of special interest not only because of their high porosity and fascinating structures, but also due to their capability to encapsulate and deliver drugs, proteins, enzymes, genes, or cells; hence, they are excellent candidates in biomedical applications that involve drug delivery, enzyme immobilisation, gene targeting, etc. The encapsulation strategies are described, and the MOFs are categorised according to the type of biomolecule they are able to encapsulate. The research field of HPMOFs has witnessed tremendous development recently. Their intriguing features and potential applications attract researchers' interest and promise an auspicious future for this class of highly porous materials.

Multicomponent, Functionalized HKUST-1 Analogues Assembled via Reticulation of Prefabricated Metal-Organic Polyhedral Cavities

Metal–organic frameworks (MOFs) assembled from multiple building blocks exhibit greater chemical complexity and superior functionality in practical applications. Herein, we report a new approach based on using prefabricated cavities to design isoreticular multicomponent MOFs from a known parent MOF. We demonstrate this concept with the formation of multicomponent HKUST-1 analogues, using a prefabricated cavity that comprises a cuboctahedral Rh(II) metal–organic polyhedron functionalized with 24 carboxylic acid groups. The cavities are reticulated in three dimensions via Cu(II)-paddlewheel clusters and (functionalized) 1,3,5-benzenetricarboxylate linkers to form three- and four-component HKUST-1 analogues.

The topology of crystalline matter

In this chapter an overview is given in which way framework-like crystalline compounds can be regarded as nets, how a net is derived out of a particular crystal structure, what nets actually are, how they can be appropriately described, what the characteristics of nets are, and how this topological approach helps to categorize framework compounds. Finally the term reticular chemistry is explained and a number of examples are given how the topology-guided approach opens up new possibilities to intentionally develop new framework structures on a rational basis.

Designed assembly of heterometallic zeolite-like framework materials from two different supertetrahedral metal clusters

This work demonstrates a feasible strategy for the synthesis of new zeolite-like framework materials. With the strategy of using two different supertetrahedral clusters as secondary building units, two new heterometallic zeolite-like frameworks with isomeric structures but tunable topologies were first made. Besides, the porous nature and the proton conduction performance of the new materials were further studied.

Metal-hydrogen-pi-bonded organic frameworks

We report the synthesis and characterization of a new series of permanently porous, three-dimensional metal-organic frameworks (MOFs), M-HAF-2 (M = Fe, Ga, or In), constructed from tetratopic, hydroxamate-based, chelating linkers. The structure of M-HAF-2 was determined by three-dimensional electron diffraction (3D ED), revealing a unique interpenetrated hcb-a net topology. This unusual topology is enabled by the presence of free hydroxamic acid groups, which lead to the formation of a diverse network of cooperative interactions comprising metal-hydroxamate coordination interactions at single metal nodes, staggered π-π interactions between linkers, and H-bonding interactions between metal-coordinated and free hydroxamate groups. Such extensive, multimodal interconnectivity is reminiscent of the complex, noncovalent interaction networks of proteins and endows M-HAF-2 frameworks with high thermal and chemical stability and allows them to readily undergo postsynthetic metal ion exchange (PSE) between trivalent metal ions. We demonstrate that M-HAF-2 can serve as versatile porous materials for ionic separations, aided by one-dimensional channels lined by continuously π-stacked aromatic groups and H-bonding hydroxamate functionalities. As an addition to the small group of hydroxamic acid-based MOFs, M-HAF-2 represents a structural merger between MOFs and hydrogen-bonded organic frameworks (HOFs) and illustrates the utility of non-canonical metal-coordinating functionalities in the discovery of new bonding and topological patterns in reticular materials.

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.

Synthesis, Structure and Highly Selective C3H8/CH4 and C2H6/CH4 Adsorptions of a (4,8)-c Ternary flu-Metal-organic Framework based upon both [Sc4O2(COO)8] and [Cu4OCl6] Clusters

A new ternary flu topological metal-organic framework based upon the torsional cubic 8-connected [Sc4O2(COO)8] cluster and the tetrahedral 4-connected [Cu4OCl6] cluster, namely, [Sc4O2(Cu4Cl6O)2(L)8•5H2O]•xGuest (SNNU-Bai69; SNNU-Bai = Shaanxi Normal University, Bai’s...

Metal–organic frameworks with -type connectivity: design, pore structure engineering, and potential applications

The structure, pore size regulation, and potential applications of MOFs featuring ftw-type connectivity have been reviewed.

Evolution of 14-Connected Zr6 Secondary Building Units through Postsynthetic Linker Incorporation

Two new zirconium MOFs, WSU-6 and WSU-7, were synthesized through postsynthetic modifications. In both cases, linker insertion was conducted on a MOF consisting of eight-connected (8-c) Zr6 cluster and four-connected (4-c) ETTC linker, WSU-5, which possesses the uncommon 4, 8-c scu-c topology. The insertion of 1, 4-benzenedicarboxylate into the MOF formed the new 4, 12-c mjh topology, WSU-6. Interestingly, when 2, 6-naphthalenedicarboxylate was inserted, WSU-7 can be formed, which possesses a new 4, 14-c jkz topology. WSU-7 contains very rare 14-c Zr6 secondary building units (SBUs) and is the first MOF to have a Zr6 SBUs with connectivity greater than 12. The three Zr-MOFs were structurally characterized, and the photoluminescence properties of the materials were also studied.

Metal-Organic Frameworks Featuring 18-Connected Nonanuclear Rare-Earth Oxygen Clusters and Cavities for Efficient C2H2/CO2 Separation

Two rare-earth (RE) metal-organic frameworks (MOFs) formulated as {(Me₂NH₂)₂[RE₉(μ₃-OH)₈(μ₂-OH)₃(DCPB)₆(H₂O)₃]}_n (RE = Y³⁺ and Tb³⁺; termed JXNU-10) built from a triangular 3,5-di(4'-carboxylphenyl)benzoic acid (DCPB^3-) ligand are presented. JXNU-10 features the rarely observed 18-connected nonanuclear [RE₉(μ₃-OH)₈(μ₂-OH)₃] clusters, one-dimensional-nanosized tubular channels, and trigonal-bipyramidal cavities. The presence of the high-nuclear RE-oxo clusters and the robust coordination bonds between the highly charged RE ions and the hard base of the carboxylate/hydroxyl oxygen atoms yielded the water-resistant JXNU-10 materials. JXNU-10 exhibits highly selective sorption of C₂H₂ over CO₂ and highly efficient separation of a C₂H₂ and CO₂ mixture. The carboxylate oxygen atoms and the rich π systems of the organic ligands on the pore walls are the desirable binding sites for a C₂H₂ molecule with acidic hydrogen atoms and an alkyne group, facilitating the excellent efficiency of JXNU-10 for C₂H₂/CO₂ separation demonstrated by breakthrough experiments.

Low-Valent Metal Ions as MOF Pillars: A New Route Toward Stable and Multifunctional MOFs

PCM-102 is a new organophosphine metal-organic framework (MOF) featuring diphosphine pockets that consist of pairs of offset trans-oriented P(III) donors. Postsynthetic addition of M(I) salts (M = Cu, Ag, Au) to PCM-102 induces single-crystal to single-crystal transformations and the formation of trans-[P₂M]⁺ solid-state complexes (where P = framework-based triarylphosphines). While the unmetalated PCM-102 has low porosity, the addition of secondary Lewis acids to install rigid P-M-P pillars is shown to dramatically increase both stability and selective gas uptake properties, with N₂ Brunauer-Emmett-Teller surface areas >1500 m² g^-1. The Ag(I) analogue can also be obtained via a simple, one-pot peri-synthetic route and is an ideal sacrificial precursor for materials with mixed bimetallic M^A/M^B pillars via postsynthetic, solvent-assisted metal exchange. Notably, the M-PCM-102 family of MOFs contain periodic trans-[P₂M]⁺ sites that are free of counter anions, unlike traditional analogous molecular complexes, since the precursor PCM-102 MOF is monoanionic, enabling access to charge-neutral metal-pillared materials. Four M-PCM-102 materials were evaluated for the separation of C2 hydrocarbons. The separation performance was found to be tunable based on the metal(s) incorporated, and density functional theory was employed to elucidate the nature of the unusual observed sorption preference, C₂H₂ > C₂H₆ > C₂H₄.

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.

Dual-Selective Catalysis in Dephosphorylation Tuned by Hf6-Containing Metal-Organic Frameworks Mimicking Phosphatase

Selective dephosphorylation is full of great challenges in the field of biomimetic catalysis. To mimic the active sites of protein phosphatase, Hf-OH-Hf motif-containing metal-organic frameworks (MOFs) were obtained and structurally characterized, which are assembled from [Hf48Ni6] cubic nanocages and exhibit good stability in various solvents and acid/base solutions. Catalytic investigations suggest as-synthesized Hf-Ni and Hf-Ni-NH 2 display accurate type-selectivity (selectively catalyzed P-O rather than S-O or C-O bonds) and position-selectivity (selectively catalyzed phosphomonoesters over phosphodiesters) for the hydrolysis of phosphoesters. Reaction kinetic studies further revealed the high activity of the catalytic sites in these catalysts, and the unique catalytic selectivity and high activity are comparable to phosphatase. Additionally, these MOF catalysts possess good recursivity and hypotoxicity. Control experiments (including Hf- and Zr-based isomorphous MOFs) and theoretical calculations indicate that both triplet nickel and Hf6 clusters play significant roles in the unique binding site and favorable binding energy. To our knowledge, this is the first example of selective dephosphorylation through MOF catalysts as mimic enzymes, which paves a potential way for the development of specific therapeutic MOFs.

Influence of Substituents in Terephthalate Linker on the Structure of MOFs Obtained from Presynthesized Heterometallic Complex

The synthesis of new porous materials with desired properties is a challenging task. It becomes especially difficult if you need to combine several metals in one framework to obtain a heterometallic node. The use of presynthesized complexes for obtaining of new heterometallic metal–organic frameworks could be essential to solve the problem of tailored synthesis. In our study we use presynthesized heterometallic pivalate complex [Li2Zn2(piv)6(py)2] to obtain new MOFs with heterometallic core as a node of the framework. We are managed to obtain four new heterometallic MOFs: [H2N(CH3)2]2[Li2Zn2(bdc)4]·CH3CN·DMF (1), [Li2Zn2(H2Br2-bdc)(Br2-bdc)3]·2DMF (2), [H2N(CH3)2][LiZn2(ndc)3]·CH3CN (3) and [{Li2Zn2(dmf)(py)2}{LiZn(dmf)2}2 (NO2-bdc)6]·5DMF (4). Moreover three of them contain starting tetranuclear core {Li2Zn2} and saves its geometry. We also demonstrate the influence of substituent in terephthalate ring on preservation of tetranuclear core. For compound 1 it was shown that luminescence of the framework could be quenched when nitrobenzene is included in the pores.

H2/CO2 separations in multicomponent metal-adeninate MOFs with multiple chemically distinct pore environments

Metal-organic frameworks constructed from multiple (≥3) components often exhibit dramatically increased structural complexity compared to their 2 component (1 metal, 1 linker) counterparts, such as multiple chemically unique pore environments and a plurality of diverse molecular diffusion pathways. This inherent complexity can be advantageous for gas separation applications. Here, we report two isoreticular multicomponent MOFs, bMOF-200 (4 components; Cu, Zn, adeninate, pyrazolate) and bMOF-201 (3 components; Zn, adeninate, pyrazolate). We describe their structures, which contain 3 unique interconnected pore environments, and we use Kohn-Sham density functional theory (DFT) along with the climbing image nudged elastic band (CI-NEB) method to predict potential H₂/CO₂ separation ability of bMOF-200. We examine the H₂/CO₂ separation performance using both column breakthrough and membrane permeation studies. bMOF-200 membranes exhibit a H₂/CO₂ separation factor of 7.9. The pore space of bMOF-201 is significantly different than bMOF-200, and one molecular diffusion pathway is occluded by coordinating charge-balancing formate and acetate anions. A consequence of this structural difference is reduced permeability to both H₂ and CO₂ and a significantly improved H₂/CO₂ separation factor of 22.2 compared to bMOF-200, which makes bMOF-201 membranes competitive with some of the best performing MOF membranes in terms of H₂/CO₂ separations.

Molecular Vises for Precisely Positioning Ligands near Catalytic Metal Centers in Metal-Organic Frameworks

We report the construction of a molecular vise by pairing a tritopic phenylphosphorus(III) linker and a monotopic linker in opposite positions within a metal-organic framework. The angle between these linkers at metal sites is fixed upon changing the functionality in the monotopic linker, while the distance between them is precisely tuned. This distance within the molecular vise is accurately measured by ¹H-³¹P solid-state nuclear magnetic resonance spectroscopy. This unveils the impact of the distance on catalytic performance without interference from electrostatic effects or changes in the angle of the ligand, which is unprecedented in classic organometallic complexes.

The crystal structure of 3,5-difluoroisonicotinic acid, C6H3F2NO2

C6H3F2NO2, monoclinic, P21/n (no. 14), a = 6.8050(10) Å, b = 6.8443(9) Å, c = 12.7196(14) Å, β = 94.562(4)°, V = 590.54(13) Å3, Z = 4, R gt(F) = 0.0395, wR ref(F 2) = 0.1038, T = 150(2) K.

Metal-Organic Framework-Based Catalysts with Single Metal Sites

Metal-organic frameworks (MOFs) are a class of distinctive porous crystalline materials constructed by metal ions/clusters and organic linkers. Owing to their structural diversity, functional adjustability, and high surface area, different types of MOF-based single metal sites are well exploited, including coordinately unsaturated metal sites from metal nodes and metallolinkers, as well as active metal species immobilized to MOFs. Furthermore, controllable thermal transformation of MOFs can upgrade them to nanomaterials functionalized with active single-atom catalysts (SACs). These unique features of MOFs and their derivatives enable them to serve as a highly versatile platform for catalysis, which has actually been becoming a rapidly developing interdisciplinary research area. In this review, we overview the recent developments of catalysis at single metal sites in MOF-based materials with emphasis on their structures and applications for thermocatalysis, electrocatalysis, and photocatalysis. We also compare the results and summarize the major insights gained from the works in this review, providing the challenges and prospects in this emerging field.

The crystal structure of 3-bromoisonicotinic acid, C6H4BrNO2

C6H4BrNO2, triclinic, P1̄ (no. 2), a = 7.2512(6) Å, b = 7.3916(6) Å, c = 7.4920(7) Å, α = 65.065(4)°, β = 68.858(4)°, γ = 64.919(4)°, V = 321.60(5) Å3, Z = 2, R gt(F) = 0.0369, wR ref(F 2) = 0.1017, T = 150(2) K.

Interpenetrated Metal-Organic Frameworks with Topology and Versatile Functions

Through an "isoreticular expansion" strategy, a large number of highly porous zirconium-based metal-organic frameworks (Zr-MOFs) have been achieved using extended organic linkers in the past few years. However, interpenetrated Zr-MOFs with ftw topology have scarcely been reported, mainly owing to the used bulky tetratopic linkers that effectively prevent the network interpenetration. Here, we report a new family of zirconium and lanthanide (Ln) MOFs with ftw topology, constructed by hexanuclear Zr or Ln (Ln = Eu, Tb, Gd, Dy, Tm, Yb, Nd, and Er) clusters and a spirobifluorene-center tetracarboxylate linker. Our studies reveal that the isostructural Zr and Ln MOFs are all doubly interpenetrated with ultrahigh thermal and chemical stability. The observed unusual interpenetration can be attributed to the specific geometry of the spirobifluorene-center tetratopic linker. Gas adsorption studies show that the interpenetrated Zr-MOF is still highly porous and exhibits high performance for CO₂ storage, which can be attributed to the strong CO₂ binding environment contributed by the reduced pore size. In addition, the presented MOFs display strong characteristic luminescence in the UV-vis-NIR region. Moreover, the incorporation of the spiro-center linker into the framework can efficiently produce two-photon-excited photoluminescence with a large action cross-section value, which also benefited from the high packing density of the nonlinear optical chromophore linker in the interpenetrated structure.

Tracking and Visualization of Functional Domains in Stratified Metal-Organic Frameworks Using Gold Nanoparticles

We report here a new technique for the identification and visualization of functional domains in stratified metal-organic frameworks (MOFs). The technique, namely, gold diffusion enabled domain identification, utilizes the diffusion of Au nanoparticles within MOF cavities to track and selectively stain the more Au-philic domain in an MOF particle thereby allowing direct observation of domains, determination of domain sequences, and, in certain cases, domain boundaries under transmission electron microscopy. This method is an excellent tool for studying MOF materials with complex domain hierarchy.

Two tetranuclear Cd-based metal–organic frameworks for sensitive sensing of TNP/Fe3+ in aqueous media and gas adsorption

Two Cd-MOFs were solvothermally synthesized by mixed-ligand strategy. 1 has the largest adsorption selectivity for CO₂. Furthermore, 1 and 2 present sensitive sensing for TNP/Fe³⁺ in water or soil samples.

Construction of high-nuclear 4p–4f heterometallic {Ln11Ge12} cluster-organic frameworks with high-sensitivity luminescence sensing of Fe3+ in aqueous solution

The [Pr₁₁Ge₁₂] 4p–4f cluster-organic framework shows highly selective and sensitive sensing of Fe³⁺ in aqueous solution.

Facile Synthesis of Uniform Metal Carbide Nanoparticles from Metal-Organic Frameworks by Laser Metallurgy

We report the fast and efficient conversion of metal-organic frameworks (MOFs) to phase pure transition-metal carbide (TMC) nanoparticles with uniform size using laser as the energy source, consuming only 6 W power. Nanoparticles of HfC, ZrC, TiC, V₈C₇, α-MoC, Cr₃C₂, and FeC_x with homogeneous sizes (varied between 6 and 20 nm) were successfully produced, among which HfC and ZrC nanoparticles were obtained, for the first time, with sizes less than 10 nm and in the pure phase. This method was operated directly in air, in stark contrast to traditional furnace heating and laser spray methods, where a protective atmosphere is required. The use of MOFs allowed us to precisely tune the composition of TMC nanoparticles by dialing in the right type and desirable amounts of organic linkers. FeC_x nanoparticles doped with various percentages of nitrogen atoms were synthesized for the Fischer-Tropsch reaction without any pretreatment or activation. Extremely high iron time of yield (FTY) values were observed, 415 and 550 μmol g_Fe^-1 s^-1 (with addition of K), in a 40 h test without any decay in performance. A high olefin to paraffin ratio was achieved for C₂ to C₁₁ products, where the ratio for C₃ was higher than 10.

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.

Desulfurization Efficiency Preserved in a Heterometallic MOF: Synthesis and Thermodynamically Controlled Phase Transition

Efficient removal of heterocyclic organosulfur compounds from fuels can relieve increasingly serious environmental problems (e.g., gas exhaust contaminants triggering the formation of acid rain that can damage fragile ecological systems). Toward this end, novel metal-organic frameworks (MOFs)-based sorbent materials are designed and synthesized with distinct hard and soft metal building units, specifically {[Yb6Cu12(OH)4(PyC)12(H2O)36]·(NO3)14·xS} n (QUST-81) and {[Yb4O(H2O)4Cu8(OH)8/3(PyC)8(HCOO)4]·(NO3)10/3·xS} n (QUST-82), where H2PyC = 4-Pyrazolecarboxylic acid. Exploiting the hard/soft duality, it is shown that the more stable QUST-82 can preserve desulfurization efficiency in the presence of competing nitrogen-containing contaminate. In addition, thermodynamically controlled single-crystal-to-single-crystal (SC-SC) phase transition is uncovered from QUST-81 to QUST-82, and in turn, mechanistic features are probed via X-ray diffraction, inductively coupled plasma atomic emission spectroscopy, and ab initio molecular dynamics simulations.

The chemistry of multi-component and hierarchical framework compounds

This review is expected to provide a library of multi-component hierarchically porous compounds, which shall guide the state-of-the-art design of future porous materials with unprecedented tunability, synergism and precision.