Windmill Co4 {Co4 (μ4 -O)} with 16 Divergent Branches Forming a Family of Metal-Organic Frameworks: Organic Metrics Control Topology, Gas Sorption, and Magnetism

Mesoporous MOF Based on a Hexagonal Bipyramid Co8-Cluster: High Catalytic Efficiency on the Cycloaddition Reaction of CO2 with Bulky Epoxides

A mesoporous cobalt-based metal-organic framework (LCU-606) was synthesized based on a hexagonal bipyramid Co8(μ4-O)3 cluster and an N,N,N',N'-tetrakis-(4-benzoic acid)-1,4-phenylenediamine ligand (H4TBAP). LCU-606 featuring large pore diameters of 21.7 Å and exposed Lewis-acid metal sites could serve as an excellent heterogeneous catalyst for CO2 cycloaddition reaction with various epoxide substrates under mild conditions (1 atm CO2, 60 °C, and solvent free). In particular, when extending the substrates to bulkier ones, LCU-606 still shows high catalytic efficiency on account of the large pore aperture. Also, LCU-606 demonstrates high recyclability and stability in consecutive catalytic runs. Therefore, the high efficiency, recyclability, and generality on CO2 catalytic cycloaddition make LCU-606 a very promising heterogeneous catalyst for CO2 chemical fixation.

Supramolecular Chemistry of Windmill-like Al10 Clusters: Adjustable Guests and Hydrogen-Bonding Networks for Enhanced Optical Limiting

The interest in cluster chemistry lies not only in the development of new types of geometric structures but also in the higher-level connectivity and assembly of clusters at the supramolecular level. Here, we report a novel windmill-like Al₁₀ cluster and consider this geometrically unique cluster as an anionic node assembled together with different cationic guests such as imidazolium and guanidinium. These guests with different hydrogen-bond angles can help to obtain a series of diverse hydrogen-bonding networks and then manipulate the stacking mode of hosts and guests. Furthermore, we realized a supramolecular approach to fine-tune the optical limiting properties of the cluster. This work not only enriches the host-guest chemistry of ionic windmill-like clusters but also opens up more possibilities for aluminum oxo cluster-based hydrogen-bonded frameworks.

Desolvation-Degree-Induced Structural Dynamics in a Rigid Cerium-Organic Framework Exhibiting Tandem Purification of Ethylene from Acetylene and Ethane

Due to the industrial requirements for high production and high quality of ethylene, efficient purification of ethylene from acetylene and ethane is of prime importance but challenging. Dynamic metal-organic frameworks (MOFs) have demonstrated intriguing structural dynamics and diverse applications recently. Among them, although a few flexible ones have exhibited interesting ethylene purification capability, rigid ones were yet barely investigated for such purpose. In this regard, a cerium(III)-based MOF was solvothermally synthesized, which is rigid and assembled from rod molecular building blocks associated with coordinative N,N-dimethylformamide (DMF) molecules. After liberating different degrees of DMF ligands via heating under vacuum or acetone exchange, both partially desolvated compounds of Ce-MOF-1 and Ce-MOF-2 were concertedly isolated in a fashion of single-crystal to single-crystal transformation. Although both newly generated materials crystallize in the same space group, they exhibit dissimilar unit cell parameters and slightly distinct ultramicropore sizes and pore microenvironments, thanks to the discrepancy in the desolvation degree. Consequently, Ce-MOF-1 and Ce-MOF-2 individually demonstrate C₂H₂- and C₂H₆-selective adsorption behavior, resulting in the potential tandem separation of C₂H₄ from C₂H₂ and C₂H₆ mixtures. The above results were successfully supported by not only single gas adsorption isotherms but also grand canonical Monte Carlo (GCMC) calculation studies and dynamic breakthrough experiments. The present work may pave the way for rigid MOFs aiming at advancing applications via solid-state structural dynamics.

Multifunctional Zr-MOF Based on Bisimidazole Tetracarboxylic Acid for pH Sensing and Photoreduction of Cr(VI)

Herein, a new luminescent zirconium MOF [Zr-BBI, BBI = 4,4',4″,4‴-(1,4-phenylenebis(1H-imidazole-2,4,5-triyl))tetrabenzoic acid] was successfully constructed by a rationally designed functionalized bisimidazole tetracarboxylic acid ligand. Zr-BBI consists of eight-connected Zr₆ clusters and four-connected BBI ligands. The high connection mode must be responsible for the high stabilities of Zr-BBI in both acidic and basic systems. Apart from the high stability, the inherent bisimidazole units endow Zr-BBI with the traits of intense fluorescent emission as well as the protonation/deprotonation behavior. Therefore, Zr-BBI could display a highly sensitive fluorescence response along with the varying pH values in the aqueous solutions and act as a pH sensing scaffold, especially in the pH value range from 4.6 to 7.12. Zr-BBI also shows good fluorescence detection performance toward Cr₂O₇^2- at a low concentration with a high K_SV value up to 6.49 × 10⁴ M^-1. Moreover, by the utilization of Zr-BBI as a catalyst, Cr(VI) could be effectively photoreduced to Cr(III) in aqueous solution under visible light irradiation, in which the introduction of a hole scavenger (benzyl alcohol) could further significantly enhance the photocatalytic efficiency. Compared to that of the recently representative MOFs, the k value of the photocatalytic reaction over Zr-BBI is as high as 0.073 min^-1. With the consideration of the presented results, Zr-BBI can serve as a multifunctional platform for efficiently sensing and photoreducing Cr₂O₇^2- in an aqueous system, which fully illustrates the feasibility that introducing specific functional groups in the framework of MOFs would enhance the related photocatalytic activity.

Octanuclear Cobalt(II) Cluster-Based Metal-Organic Framework with Caged Structure Exhibiting the Selective Adsorption of Ethane over Ethylene

A novel metal-organic framework (MOF) of [Co₈(OH)₄(TCA)₄(H₂O)₄]_n (abbreviation: JXNU-9) based on the unique octanuclear Co₈(μ₃-OH)₄ clusters linked by 4,4',4″-nitrilotribenzoate (TCA^3-) ligands featuring small caged structures and one-dimensional channels was prepared and characterized. JXNU-9 shows a high C₂H₆ uptake capacity of 3.60 mmol g^-1 (4.46 mmol cm^-3) at 298 K and 1 atm with a small isosteric heat of adsorption (23.6 kJ mol^-1) and a moderate C₂H₆/C₂H₄ adsorption selectivity of 1.7, resulting in excellent C₂H₆/C₂H₄ separation performance. The pore walls decorated by plenty of aromatic rings provide π-electron-cloud-surrounding environments to accommodate the large polarizable C₂H₆ molecules. The calculations demonstrate that the rich π-systems in JXNU-9 facilitate an adsorption affinity for large C₂H₆ molecules through multiple C-H···π interactions. Additionally, the open metal sites located in the concave pores with a close Co···Co separation (4.21 Å) in octanuclear Co₈(μ₃-OH)₄ clusters make the open metal sites inaccessible for the C₂H₄ molecule with a kinetic diameter of 4.163 Å. Thus, the annihilation of open metal sites in this structure is achieved, which further facilitates the C₂H₆-selective C₂H₆/C₂H₄ separation.

Two Metal-Organic Frameworks Based on Hexanuclear Cobalt-Hydroxyl Clusters or a Manganese-Hydroxyl Chain from Triangular [MII3(μ3-OH)] (M = Co and Mn) Units: Antiferromagnetic and Spin-Canting Antiferromagnetic Ordering with Soft-Magnetic Behavior

Three-dimensional highly connected isonicotinic acid-base metal-organic frameworks (MOFs), [Co^II₆(μ₃-OH)₂(in)₇(HCOO)₃H₂O]·4DMF (1) and [Mn^II₃(μ₃-OH)(in)₃(CH₃COO)₂] (2) (Hin = isonicotinic acid), have been successfully prepared. Compounds 1 and 2 were constructed from planar Co₆ cluster SBUs or rare 1D manganese-hydroxyl chain SBUs, respectively. Both SBUs contain triangular M^II₃(OH) (M = Co and Mn) central units, which are connected by rare syn,anti,syn,anti- and syn,syn,anti-coordinated formic acid or acetic acid. Both compounds 1 and 2 have good thermal stability, while compound 2 also exhibits an extraordinarily high moisture stability. Magnetic studies demonstrate that 1 shows antiferromagnetic behavior, and 2 exhibits spin-canting antiferromagnetic ordering with soft-magnetic behavior.

Heavy chalcogenide-transition metal clusters as coordination polymer nodes

While metal-oxygen clusters are widely used as secondary building units in the construction of coordination polymers or metal-organic frameworks, multimetallic nodes with heavier chalcogenide atoms (S, Se, and Te) are comparatively untapped. The lower electronegativity of heavy chalcogenides means that transition metal clusters of these elements generally exhibit enhanced coupling, delocalization, and redox-flexibility. Leveraging these features in coordination polymers provides these materials with extraordinary properties in catalysis, conductivity, magnetism, and photoactivity. In this perspective, we summarize common transition metal heavy chalcogenide building blocks including polynuclear metal nodes with organothiolate/selenolate or anionic heavy chalcogenide atoms. Based on recent discoveries, we also outline potential challenges and opportunities for applications in this field.

Three novel topologically different metal–organic frameworks built from 3-nitro-4-(pyridin-4-yl)benzoic acid

The design and synthesis of metal–organic frameworks (MOFs) have attracted much interest due to the intriguing diversity of their architectures and topologies. However, building MOFs with different topological structures from the same ligand is still a challenge. Using 3-nitro-4-(pyridin-4-yl)benzoic acid (HL) as a new ligand, three novel MOFs, namely poly[[(N,N-dimethylformamide-κO)bis[μ2-3-nitro-4-(pyridin-4-yl)benzoato-κ3 O,O′:N]cadmium(II)] N,N-dimethylformamide monosolvate methanol monosolvate], {[Cd(C12H7N2O4)2(C3H7NO)]·C3H7NO·CH3OH} n , (1), poly[[(μ2-acetato-κ2 O:O′)[μ3-3-nitro-4-(pyridin-4-yl)benzoato-κ3 O:O′:N]bis[μ3-3-nitro-4-(pyridin-4-yl)benzoato-κ4 O,O′:O′:N]dicadmium(II)] N,N-dimethylacetamide disolvate monohydrate], {[Cd2(C12H7N2O4)3(CH3CO2)]·2C4H9NO·H2O} n , (2), and catena-poly[[[diaquanickel(II)]-bis[μ2-3-nitro-4-(pyridin-4-yl)benzoato-κ2 O:N]] N,N-dimethylacetamide disolvate], {[Ni(C12H7N2O4)2(H2O)2]·2C4H9NO} n , (3), have been prepared. Single-crystal structure analysis shows that the CdII atom in MOF (1) has a distorted pentagonal bipyramidal [CdN2O5] coordination geometry. The [CdN2O5] units as 4-connected nodes are interconnected by L − ligands to form a fourfold interpenetrating three-dimensional (3D) framework with a dia topology. In MOF (2), there are two crystallographically different CdII ions showing a distorted pentagonal bipyramidal [CdNO6] and a distorted octahedral [CdN2O4] coordination geometry, respectively. Two CdII ions are connected by three carboxylate groups to form a binuclear [Cd2(COO)3] cluster. Each binuclear cluster as a 6-connected node is further linked by acetate groups and L − ligands to produce a non-interpenetrating 3D framework with a pcu topology. MOF (3) contains two crystallographically distinct NiII ions on special positions. Each NiII ion adopts an elongated octahedral [NiN2O4] geometry. Each NiII ion as a 4-connected node is linked by L − ligands to generate a two-dimensional network with an sql topology, which is further stabilized by two types of intermolecular OW—HW...O hydrogen bonds to form a 3D supramolecular framework. MOFs (1)–(3) were also characterized by powder X-ray diffraction, IR spectroscopy and thermogravimetic analysis. Furthermore, the solid-state photoluminescence of HL and MOFs (1) and (2) have been investigated. The photoluminescence of MOFs (1) and (2) are enhanced and red-shifted with respect to free HL. The gas adsorption investigation of MOF (2) indicates a good separation selectivity (71) of CO2/N2 at 273 K (i.e. the amount of CO2 adsorption is 71 times higher than N2 at the same pressure).

Development of a new Lindqvist-like Fe6 cluster secondary building unit for MOFs

In this work, a novel Lindqvist-like Fe6 cluster was introduced as an SBU to construct a new family of Fe-cluster organic frameworks.

Fluorescent sensing and selective adsorption properties of metal-organic frameworks with mixed tricarboxylate and 1H-imidazol-4-yl-containing ligands

Herein, two metal-organic frameworks (MOFs), [Co₄(μ₃-OH)₂(L)(BTB)₂(H₂O)₃]·5.6H₂O (1) and [Cd₃(L)₂(BTB)₂(μ₂-H₂O)]·7.4H₂O (2), based on 1,3-di(1H-imidazol-4-yl)benzene (L) and 1,3,5-tri(4-carboxyphenyl)benzene (H₃BTB), respectively, have been achieved. Compound 1 is a porous three-dimensional (3D) framework with butterfly-like tetranuclear clusters as 7-connected nodes, and compund 2 is a 3D net with a different topology. Remarkably, compounds 1 and 2 exhibit selective adsorption of CO₂ over N₂ and methyl orange (MO) dye molecules. Magnetic measurements reveal that there are antiferromagnetic interactions within the tetranuclear cluster in 1. Furthermore, 2 was well-dispersed in different solvents, and their luminescent properties were investigated, and the results indicated that 2 could be considered as a potential luminescent probe for the detection of ketone molecules.

A semiconducting metal-chalcogenide–organic framework with square-planar tetra-coordinated sulfur

A semiconducting metal-chalcogenide–organic framework with square-planar tetra-coordinated sulfur is reported.

A new series of Co, Ni, Zn, and Cd metal–organic architectures driven by an unsymmetrical biphenyl-tricarboxylic acid: hydrothermal assembly, structural features and properties

Twelve new Zn(ii), Ni(ii), Co(ii), and Cd(ii) coordination compounds with diverse dimensionalities were assembled using 3′-nitro-biphenyl-2,4,4′-tricarboxylic acid as a main building block.

An unusual zig-zag 1D copper(ii) coordination polymer displaying magnetic phase transition

A new Cu(ii)-based 1D chain was prepared and its magnetic behaviour was investigated, which indicated a magnetic phase transition below 25 K as well as long-range magnetic ordering.

A Novel, Interpenetrating Metal–Organic Framework: Synthesis, Structure, and Luminescence Detection of Nitrobenzene

A 3D heterometal–organic framework {[TbZn(BPDC)2(HCOO)(H2O)3]·2H2O}n (1) was constructed from Tb3+ and Zn2+ as metal ions and 4,4′-dicarboxylate-2,2′-dipyridine (H2BPDC) as the ligand using a solvothermal method. Single-crystal X-ray diffraction analysis revealed that compound 1 is 2-fold interpenetrating. Thermogravimetric and solvent stability analyses demonstrated that compound 1 displayed good thermal and solvent stabilities. The luminescent explorations revealed that compound 1 exhibited highly sensitive and qualitative detection of nitrobenzene at the ppm level. To our knowledge, the present study reports for the first time the use of an interpenetrating heterometallic metal–organic framework as a luminescent probe for nitrobenzene.

Assembling hierarchical metal–oxygen building units with a semirigid tetracarboxylate ligand into a three-dimensional framework for nitrobenzene sensing

A three-dimensional framework collecting hierarchical metal–oxygen multicluster, macrocyclic, and infinite chain-like building units was fabricated and investigated as efficient luminescent sensor towards nitrobenzene.