Metal-Organic Framework with Space-Partition Pores by Fluorinated Anions for Benchmark C2H2/CO2 Separation.

The efficient separation of C2H2 from C2H2/CO2 or C2H2/CO2/CH4 mixtures is crucial for achieving high-purity C2H2 (>99%), essential in producing contemporary commodity chemicals. In this report, we present ZNU-12, a metal-organic framework with space-partitioned pores formed by inorganic fluorinated anions, for highly efficient C2H2/CO2 and C2H2/CO2/CH4 separation. The framework, partitioned by fluorinated SiF62- anions into three distinct cages, enables both a high C2H2 capacity (176.5 cm3/g at 298 K and 1.0 bar) and outstanding C2H2 selectivity over CO2 (13.4) and CH4 (233.5) simultaneously. Notably, we achieve a record-high C2H2 productivity (132.7, 105.9, 98.8, and 80.0 L/kg with 99.5% purity) from C2H2/CO2 (v/v = 50/50) and C2H2/CO2/CH4 (v/v = 1/1/1, 1/1/2, or 1/1/8) mixtures through a cycle of adsorption-desorption breakthrough experiments with high recovery rates. Theoretical calculations suggest the presence of potent "2 + 2" collaborative hydrogen bonds between C2H2 and two hexafluorosilicate (SiF62-) anions in the confined cavities.

Covalent Organic Framework/Graphene Hybrids: Synthesis, Properties, and Applications.

To address current energy crises and environmental concerns, it is imperative to develop and design versatile porous materials ideal for water purification and energy storage. The advent of covalent organic frameworks (COFs), a revolutionary terrain of porous materials, is underscored by their superlative features such as divinable structure, adjustable aperture, and high specific surface area. However, issues like inferior electric conductivity, inaccessible active sites impede mass transfer and poor processability of bulky COFs restrict their wider application. As a herculean stride forward, COF/graphene hybrids amalgamate the strengths of their constituent components and have in consequence, enticed significant scientific intrigue. Herein, the current progress on the structure and properties of graphene-based materials and COFs are systematically outlined. Then, synthetic strategies for preparing COF/graphene hybrids, including one-pot synthesis, ex situ synthesis, and in situ growth, are comprehensively reviewed. Afterward, the pivotal attributes of COF/graphene hybrids are dissected in conjunction with their multifaceted applications spanning adsorption, separation, catalysis, sensing, and energy storage. Finally, this review is concluded by elucidating prevailing challenges and gesturing toward prospective strides within the realm of COF/graphene hybrids research.

Dual-Emitting Mixed-Lanthanide Metal-Organic Framework for Ratiometric and Quantitative Visual Detection of 2,6-Pyridine Dicarboxylic Acid.

The detection of the major biomarker of Bacillus anthracis, 2,6-dipicolinic acid (DPA), has attracted great interest in recent years. In this work, mixed-lanthanide metal-organic frameworks (M'LnMOFs), TbxEu1-x-cppa (cppa = 5-(5-carboxypyridin-3-yl)isophthalic acid), with different Tb/Eu ratios, were solvothermally synthesized. The results reveal that ratiometric fluorescent probe [Tb0.533Eu0.467-(Hcppa)1.5(H2O)(DMF)]·3H2O is water and acid-base stable and exhibits excellent sensitivity (LOD = 2.286 µM), high selectivity, and fast response (<2 min) for the detection of DPA. Due to the blocked energy transfer from Tb3+ to Eu3+ and the inner filter effect upon the addition of DPA, the fluorescent probe shows a distinct color change from orange-red to green. Furthermore, the visual detection of DPA was realized by identifying the RGB values of MOF-based agarose hydrogel films via a smartphone, highlighting the practical application of the fluorescent probe for DPA detection under aqueous solution conditions.

Integrating Self-Partitioned Pore Space and Amine Functionality into an Aromatic-Rich Coordination Framework with Ph Stability for Effective Purification of C2 Hydrocarbons.

A great demand for high-purity C2 hydrocarbons calls for the development of chemically stable porous materials for the effective isolation of C2 hydrocarbons from CH4 and CO2. However, such separations are challenged by their similar physiochemical parameters and have not been systematically studied to date. In this work, we reported a cadmium-based rod-packing coordination framework compound ZJNU-140 of a new 5,6,7-c topology built up from a custom-designed tricarboxylate ligand. The metal-organic framework (MOF) features an aromatic-abundant pore surface, uncoordinated amine functionality, and self-partitioned pore space of suitable size. These structural characteristics act synergistically to provide the MOF with both selective recognition ability and the confinement effect toward C2 hydrocarbons. As a result, the MOF displays promising potential for adsorptive separation of C2-CH4 and C2-CO2 mixtures. The IAST-predicted C2/CH4 and C2/CO2 adsorption selectivities, respectively, fall in the ranges of 7.3-10.2 and 2.1-2.9 at 298 K and 109 kPa. The real separation performance was also confirmed by dynamic breakthrough experiments. In addition, the MOF can maintain skeleton intactness in aqueous solutions with a wide pH range of 3-11, as confirmed by powder X-ray diffraction (PXRD) and isotherm measurements, showing no loss of framework integrity and porosity. The excellent hydrostability, considerable uptake capacity, impressive adsorption selectivity, and mild regeneration make ZJNU-140 a promising adsorbent material applied for the separation and purification of C2 hydrocarbons.

A Multimodal Ratiometric Luminescent Thermometer Based on a Single-Dysprosium Metal-Organic Framework.

The design of high-performance luminescent MOF thermometers with multi-operation modes has been long sought but remains a formidable challenge. In this work, for the first time, we present a multimodal luminescent ratiometric thermometer based on the single-lanthanide metal-organic framework (MOF) DyTPTC-2Me (H4TPTC-2Me = 2',5'-dimethyl-[1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid). It not only has the characteristic luminescence of Dy3+ in which the atomic transitions from the 4I15/2 and 4F9/2 states (thermally coupled energy levels, TCELs) are included but also emits ligand fluorescence due to the efficient energy back-transfer of Dy3+ to the ligand, thus allowing accurate non-invasive determination of temperature by different modes. In particular, the TCEL-based emissions of the Dy3+ ions give ideal signals for measuring the temperature in the 303-423 K range. The emissions of the ligand and Dy3+ (4F9/2 → 6H13/2) are used for temperature sensing in the range of 423 to 503 K. Both two modes feature promising thermometric performance, including high relative sensitivity, high temperature resolution, and excellent repeatability. Their combination is thus beneficial to achieve more accurate temperature detection over a broad temperature range, which can broaden the application scope of the ratiometric luminescent thermometers.

Ligand Conformation Fixation Strategy for Expanding the Structural Diversity of Copper-Tricarboxylate Frameworks and C2H2 Purification Performance Studies.

Structural and functional expansion of metal-organic frameworks (MOFs) is fundamentally important because it not only enriches the structural chemistry of MOFs but also facilitates the full exploration of their application potentials. In this work, by employing a dual-site functionalization strategy to lock the ligand conformation, we designed and synthesized a pair of biphenyl tricarboxylate ligands bearing dimethyl and dimethoxy groups and fabricated their corresponding framework compounds through coordination with copper(II) ions. Compared to the monofunctionalized version, introduction of two side groups can significantly fix the ligand conformation, and as a result, the dual-methoxy compound exhibited a different network structure from the mono-methoxy counterpart. Although only one almost orthogonal conformation was observed for the two ligands, their coordination framework compounds displayed distinct topological structures probably due to different solvothermal conditions. Significantly, with a hierarchical cage-type structure and good hydrostability, the dimethyl compound exhibited promising practical application value for industrially important C2H2 separation and purification, which was comprehensively demonstrated by equilibrium/dynamic adsorption measurements and the corresponding Clausius-Clapeyron/IAST/DFT theoretical analyses.

Amino-Functionalized Single-Lanthanide Metal-Organic Framework as a Ratiometric Fluorescent Sensor for Quantitative Visual Detection of Fluoride Ions.

Excessive content of fluoride ions (F-) in water will lead to water pollution and endanger human health, so the research on the method of low-cost, rapid, and efficient detection of F- is of particular significance. In this work, an amino-functionalized ligand with an appropriate triplet energy excited state, 2'-amino-[1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid (H4TPTC-NH2), was selected to construct a luminescent single-lanthanide metal-organic framework, EuTPTC-NH2, with uncoordinated amino groups for the detection of F-. Based on host-guest interactions, that is, hydrogen bonds formed between the free amino groups and F- ions, EuTPTC-NH2 was developed as a ratiometric fluorescence probe for F- detection with good anti-interference ability, low detection limit, high water stability, and selectivity. It was found that EuTPTC-NH2 has an excellent linear response to F- in the concentration range of 0-80 µM with high sensitivity and a low detection limit of 11.26 µM. A hydrogel membrane based on the combination of EuTPTC-NH2 and agarose was also prepared for the quantitative visual detection of F- in water.

Water-Stable Eu6-Cluster-Based fcu-MOF with Exposed Vinyl Groups for Ratiometric and Fluorescent Visual Sensing of Hydrogen Sulfide.

Detection of H2S in the biological system has attracted enormous attention in recent years. In this work, a new vinyl-functionalized metal-organic framework (MOF), [(Me2NH2)2] [Eu6(µ3-OH)8(BDC-CH═CH2)6(H2O)6] (Eu-BDC-CH═CH2, BDC-CH═CH2 = 2-vinylterephthalic acid), was synthesized under solvothermal conditions. The vinyl groups in the ligands can not only modulate the "antenna effect" of the ligand on Eu3+ ions but also serve as an exposed reactive site to allow for the quantitative detection of H2S by Eu-BDC-CH═CH2. The ratiometric fluorescent probe has the advantages of water stability, acid-base stability (pH = 2-11), fast response (<2 min), high selectivity, and sensitivity (LOD = 38.4 µM). We also used Eu-BDC-CH═CH2 to detect and analyze H2S in tap and lake waters, demonstrating the potential of the probe for biological and environmental applications. In addition, the MOF-based agarose hydrogel film allows for the visual detection of H2S via a smartphone by identifying the RGB values. The vinyl-functionalized MOF can thus be a powerful sensing platform for H2S.

Substituent Engineering-Enabled Structural Rigidification and Performance Improvement for C2/CO2 Separation in Three Isoreticular Coordination Frameworks.

Construction of porous solid materials applied to the adsorptive removal of CO2 from C2 hydrocarbons is highly demanded thanks to the important role C2 hydrocarbons play in the chemical industry but quite challenging owing to the similar physical parameters between C2 hydrocarbons and CO2. In particular, the development of synthetic strategies to simultaneously enhance the uptake capacity and adsorption selectivity is very difficult due to the trade-off effect frequently existing between both of them. In this work, a combination of the dicopper paddlewheel unit and 4-pyridylisophthalate derivatives bearing different substituents afforded an isoreticular family of coordination framework compounds as a platform. Their adsorption properties toward C2 hydrocarbons and CO2 were systematically investigated, and subsequent IAST and density functional theory calculations combined with column breakthrough experiments verified their promising potential for C2/CO2 separations. Furthermore, the substituent engineering endowed the resulting compounds with simultaneous enhancement of uptake capacity and adsorption selectivity and thus better C2/CO2 separation performance compared to their parent compound. The substituent introduction not only mitigated the framework distortion via fixing the ligand conformation for establishment of better permanent porosity required for gas adsorption but also polarized the framework surface for host-guest interaction improvement, thus resulting in enhanced separation performance.

Hydrogen Bond Organic Frameworks as a Novel Electrochemiluminescence Luminophore: Simple Synthesis and Ultrasensitive Biosensing.

Nowadays, continuous efforts have been devoted to searching highly efficient electrochemiluminescence (ECL) emitters for applications in clinical diagnosis and food safety. In this work, triazinyl-based hydrogen bond organic frameworks (Tr-HOFs) were synthesized by N···H hydrogen bond self-assembly aggregation, where 6,6'-(1,4-phenylene)bis(1,3,5-triazine-2,4-diamine) (phenyDAT) was prepared via the cyclization reaction and behaved as a novel ligand. Impressively, the resulting Tr-HOFs showed strong ECL responses with highly enhanced ECL efficiency (21.3%) relative to the Ru(bpy)32+ standard, while phenyDAT hardly showed any ECL emission in aqueous phase. The Tr-HOFs innovatively worked as a new ECL luminophore to construct a label-free biosensor for assay of kanamycin (Kana). Specifically, the ECL response greatly weakened upon assembly of captured DNA with ferrocene (cDNA-Fc) onto the Tr-HOFs-modified electrode, while the ECL signals were adversely recovered by releasing linked DNA (L-DNA) from double-stranded DNA (dsDNA, hybridization of aptamer DNA (aptDNA) with L-DNA) due to the specific recognition of Kana with the aptDNA combined by the linkage of L-DNA and cDNA-Fc on the electrode. The as-built sensor showed a broadened linear range (1 nM-10 µM) and a limit of detection (LOD) down to 0.28 nM, which also displayed satisfactory results in the analysis of Kana in the milk and diluted human serum samples. This work offers a novel pathway to design an ECL emitter with organic molecules, holding great promise in biomedical analysis and food detection.

A Microporous MOF Constructed by Cross-Linking Helical Chains for Efficient Purification of Natural Gas and Ethylene.

Natural gas (NG) and ethylene (C2H4) are two raw materials of significant value for manufacturing versatile fine chemicals and/or polymers, and thus the development of solid adsorbing agents such as metal-organic frameworks (MOFs) applied to their depuration is very crucial but remains highly challenging. In this research, we designed and synthesized a ligand containing mixed N and O coordination donors, which was solvothermally assembled with Cu(II) ions to generate a microporous MOF. X-ray crystallography revealed that the title MOF incorporates one-dimensional (1D) homochiral helical chains that are datively cross-linked to form open channels in the three-periodic coordination framework. Furthermore, the behaviors of C1-C2 hydrocarbons and carbon dioxide (CO2) adsorbed in the title MOF were systematically investigated, revealing its promising potential for the purification of both NG and C2H4. At 109 kPa and 298 K, the C2/methane (CH4), CO2/CH4, and acetylene (C2H2)/C2H4 adsorption selectivities are impressive, reaching as high as 62.9, 28.6, and 3.5, respectively. This work represents a unique MOF based on cross-linked homochiral helical chains exhibiting dual-function separation potentials for NG and C2H4 purifications.

Lanthanide-Organic Frameworks Featuring Three-Dimensional Inorganic Connectivity for Multipurpose Hydrocarbon Separation.

Implementation of lanthanide-organic frameworks (LOFs) as solid adsorbents has been frequently handicapped by their permanent porosity being difficult to establish owing to the remarkable flexibility and diversity of lanthanide ions in terms of coordination number and geometry. Construction of robust LOFs with permanent porosity for industrially important hydrocarbon separation will greatly expand their application potential. In this work, by distributing N and O donors into an m-terphenyl skeleton, we rationally synthesized a heterofunctional linker, and constructed a pair of isostructural LOFs. Due to the inclusion of a rarely observed three-dimensional metal-carboxylate backbone serving as a highly connected inorganic secondary building unit, their permanent porosities were successfully established by diverse gas isotherms. They can be applied as separating media not only for natural gas purification and removal of carbon dioxide from C2 hydrocarbons but also more importantly for single-step ethylene (C2H4) purification from a three-component C2Hn mixture during the adsorption process. The latter separation is very challenging and has been less reported in the literature. This work provides a unique example of LOFs featuring three-dimensional inorganic connectivity applied to multipurpose hydrocarbon separations.

Rational Construction and Performance Regulation of an In(III)-Tetraisophthalate Framework for One-Step Adsorption-Phase Purification of C2H4 from C2 Hydrocarbons.

The development of porous materials for ethylene (C2H4) separation and purification, a very important separation process in the chemical industry, is urgently needed but quite challenging. In particular, the realization of selectivity-reversed adsorption (namely, C2H4 is not preferentially adsorbed) and the simultaneous capture of multinary coexisting impurities such as ethane (C2H6) and acetylene (C2H2) will significantly simplify process design and reduce energy and cost consumption, but such porous materials are quite difficult to design and have not yet been fully explored. In this work, by employing an aromatic-rich bithiophene-based tetraisophthalate ligand, we solvothermally fabricated an anionic In(III)-based framework termed ZJNU-115 featuring In(COO)4 as an inorganic secondary building unit as well as one-dimensional channels. Due to the absence of unsaturated metallic sites, together with aromatic-rich channel surface decorated with abundant hydrogen-bonding acceptors of carboxylate oxygen and thiophene sulfur atoms, desolvated ZJNU-115 exhibited an unusual adsorption relationship with respect to C2 hydrocarbons, namely, simultaneous and preferable capture of C2H6 and C2H2 over C2H4 at the temperatures investigated, thus representing a rare metal-organic framework (MOF) with the promising potential for one-step adsorption-phase purification of C2H4 from a trinary C2 hydrocarbon mixture. Compared to a few of the MOFs reported for such an application, ZJNU-115 displayed simultaneously good adsorption selectivities of both C2H2 and C2H6 over C2H4. Furthermore, its separation potential can be postsynthetically tailored by substituting dimethylammonium (Me2NH2+) counterions with tetraalkyl ammonium ions (NR4+; R = Me, Et, or n-Pr). More importantly, ZJNU-115 was stable in various organic solvents as well as aqueous solutions with pH values ranging from 5 to 9, thus laying a solid foundation for its practical applications. The design principle and the performance regulation strategy adopted in this work will offer valuable guidance for the contrapuntal construction of porous MOFs employed for direct multicomponent purification of C2H4 with improved performance.

A Series of Metal-Organic Framework Isomers Based on Pyridinedicarboxylate Ligands: Diversified Selective Gas Adsorption and the Positional Effect of Methyl Functionality.

Solvothermal assembly of copper(II) cations and 5-(pyridine-3-yl)isophthalate linkers bearing different position-substituted methyl groups afforded four ligand-induced metal-organic framework (MOF) isomers as a platform for investigating diverse selective gas adsorption properties and understanding the positional effect of methyl functionality. Single-crystal X-ray diffraction (SCXRD) analyses showed that, when the methyl substituent is at the para position with respect to the pyridinic N atom, the resultant framework compound ZJNU-27 features an eea-type topology, while the other three solids possess an isoreticular structure with an rtl-type topology when the methyl group is situated at the other positions. As revealed by N2 physi-adsorption measurements at 77 K, they exhibit moderate specific surface areas ranging from 584 to 1182 m2 g-1 and distinct degrees of framework flexibility, which are heavily dependent on the methyl position. Comprehensive gas adsorption studies show that they are capable of effectively separating three pairs of binary gas mixtures including C2H2-CH4, CO2-CH4, and CO2-N2 couples. Moreover, their uptake capacities and adsorption selectivities can be tailored by altering the methyl position. In addition, their framework hydro-stability is also influenced by the methyl position. Compared to ZJNU-27 and ZJNU-28, ZJNU-26 and ZJNU-29 exhibit poorer stability against H2O, although the methyl group is more close to inorganic secondary building units (SBUs), which are believed to originate from the steric effect of the methyl group. Overall, the four MOFs display the methyl position-dependent network architectures, framework flexibilities, and selective gas adsorption properties as well as hydrostabilities. The findings observed in this work not only demonstrate the importance of the positional effect of the functional group but also highlight that engineering the substituent position is a potential strategy for achieving the modulation of MOF structures and properties.

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.

Interpenetration Symmetry Control Within Ultramicroporous Robust Boron Cluster Hybrid MOFs for Benchmark Purification of Acetylene from Carbon Dioxide.

The separation of C2 H2 /CO2 is an important process in industry but challenged by the trade-off of capacity and selectivity owning to their similar physical properties and identical kinetic molecular size. We report the first example of symmetrically interpenetrated dodecaborate pillared MOF, ZNU-1, for benchmark selective separation of C2 H2 from CO2 with a high C2 H2 capacity of 76.3 cm3 g-1 and record C2 H2 /CO2 selectivity of 56.6 (298 K, 1 bar) among all the robust porous materials without open metal sites. Single crystal structure analysis and modeling indicated that the interpenetration shifting from asymmetric to symmetric mode provided optimal pore chemistry with ideal synergistic "2+2" dihydrogen bonding sites for tight C2 H2 trapping. The exceptional separation performance was further evidenced by simulated and experimental breakthroughs with excellent recyclability and high productivity (2.4 mol kg-1 ) of 99.5 % purity C2 H2 during stepped desorption process.

Multifunctional porous hydrogen-bonded organic framework materials.

Hydrogen-bonded organic frameworks (HOFs) represent an interesting type of polymeric porous materials that can be self-assembled through H-bonding between organic linkers. To realize permanent porosity in HOFs, stable and robust open frameworks can be constructed by judicious selection of rigid molecular building blocks and hydrogen-bonded units with strong H-bonding interactions, in which the framework stability might be further enhanced through framework interpenetration and other types of weak intermolecular interactions such as ππ interactions. Owing to the reversible and flexible nature of H-bonding connections, HOFs show high crystallinity, solution processability, easy healing and purification. These unique advantages enable HOFs to be used as a highly versatile platform for exploring multifunctional porous materials. Here, the bright potential of HOF materials as multifunctional materials is highlighted in some of the most important applications for gas storage and separation, molecular recognition, electric and optical materials, chemical sensing, catalysis, and biomedicine.

Fine Tuning of MOF-505 Analogues To Reduce Low-Pressure Methane Uptake and Enhance Methane Working Capacity.

We present a crystal engineering strategy to fine tune the pore chemistry and CH4 -storage performance of a family of isomorphic MOFs based upon PCN-14. These MOFs exhibit similar pore size, pore surface, and surface area (around 3000 m2 g-1 ) and were prepared with the goal to enhance CH4 working capacity. [Cu2 (L2)(H2 O)2 ]n (NJU-Bai 41: NJU-Bai for Nanjing University Bai's group), [Cu2 (L3)(H2 O)2 ]n (NJU-Bai 42), and [Cu2 (L4)(DMF)2 ]n (NJU-Bai 43) were prepared and we observed that the CH4 volumetric working capacity and volumetric uptake values are influenced by subtle changes in structure and chemistry. In particular, the CH4 working capacity of NJU-Bai 43 reaches 198 cm3 (STP: 273.15 K, 1 atm) cm-3 at 298 K and 65 bar, which is amongst the highest reported for MOFs under these conditions and is much higher than the corresponding value for PCN-14 (157 cm3 (STP) cm-3 ).

A Porous Zirconium-Based Metal-Organic Framework with the Potential for the Separation of Butene Isomers.

By using a novel C3 -symmetrical tricarboxylate (4,4',4''-benzene-1,3,5-triyl-1,1',1''-trinaphthoic acid), a novel zirconium-based metal-organic framework ZJNU-30 was solvothermally synthesized and structurally characterized. Single-crystal X-ray structural analyses show that ZJNU-30 consists of Zr6 -based nodes connected by the organic linkers to form a (3,8)-connected network featuring the coexistence of two different polyhedral cages: octahedral and cuboctahedral cages with the dimensions of about 14 and 22 Å, respectively. Remarkably, ZJNU-30 is very stable when exposed to air for one month. More importantly, with a moderately high surface area, hierarchical pore structures, and an aromatic-rich pore surface in the framework, ZJNU-30, after activation, exhibits a promising potential for the selective adsorptive separation of industrially important butene isomers consisting of cis-2-butene, trans-2-butene, 1-butene, and iso-butene at ambient temperature. This separation was established exclusively by gas adsorption isotherms and simulated breakthrough experiments. To the best of our knowledge, this is the first study investigating porous metal-organic frameworks for butene-isomer separation.

A Chemically Cross-Linked NbO-Type Metal-Organic Framework: Cage or Window Partition?

By using a presynthetically cross-linked octacarboxylate ligand, a chemically cross-linked version of the NbO-type metal-organic framework (MOF) NOTT-101 (ZJNU-80) was prepared. Single-crystal X-ray structure analysis showed that ZJNU-80 adopts the same topology as the parent compound NOTT-101, and the tethering groups take part in the window partition, not the cage partition. The gas adsorption studies showed that, despite the lower porosity, ZJNU-80a exhibits low-pressure gas adsorption behavior similar to that of the parent MOF NOTT-101a toward CO2, CH4, and N2 at ambient temperature because of the fact that the window partition as a result of chemical cross-linking does not almost alter the pore-size distributions. However, different adsorption behaviors toward 1-butene, a molecule with even larger kinetic diameter than that of the aforementioned adsorbates, were observed because the window partition alters the efficiency with which 1-butene molecules pack within ZJNU-80a and NOTT-101a at conditions close to saturation. This work provides a fundamental understanding on the effect of chemical cross-linking on the MOF's structure and gas adsorption properties.