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As a new class of porous crystalline materials, hydrogen‐bonded organic frameworks (HOFs) assembled from building blocks by hydrogen bonds have gained increasing attention. HOFs benefit from advantages including mild synthesis, easy purification, and good recyclability. However, some HOFs transform into unstable frameworks after desolvation, which hinders their further applications. Nowadays, the main challenges of developing HOFs lie in stability improvement, porosity establishment, and functionalization. Recently, more and more stable and permanently porous HOFs have been reported. Of all these design strategies, stronger charge‐assisted hydrogen bonds and coordination bonds have been proven to be effective for developing stable, porous, and functional solids called hybrid HOFs, including ionic and metallized HOFs. This Review discusses the rational design synthesis principles of hybrid HOFs and their cutting‐edge applications in selective inclusion, proton conduction, gas separation, catalysis and so forth. [ABSTRACT FROM AUTHOR]

Great efforts have been made toward the separation of CO2 from flue gas and biogas to mitigate environmental pollution and the demand for renewable fuels, respectively. Nonthermal‐based separations, such as adsorption‐based or membrane‐separation technology employing porous materials, are considered to be more promising than traditional cryogenic and absorption‐based systems. Due to several advantages of metal–organic frameworks (MOFs) over other conventional porous materials, reports on flue and biogas separation by MOFs are burgeoning (423 for adsorption and 56 for membrane‐based separations until June 2021) and demand urgent summarization. This review presents a bird's eye view on such separations while organizing the developed strategies and considering several performance parameters, such as trade‐off between sorption capacity and separation selectivity in adsorption‐based systems and permeability versus separation selectivity in membrane‐based systems. In addition, the mechanisms involving such separations at the molecular level are presented. A critical discussion section offers more crucial insights into these materials from industrial deployment viewpoints. Finally, future recommendations are made for further developments of MOF materials as flue and biogas separators and thus toward solving both the challenging universal problems of global warming and energy scarcity simultaneously. [ABSTRACT FROM AUTHOR]

In this work, a multifunctional microporous metal–organic framework (MOF), [Cu2(BPDC)2(H2O)2]·5.6H2O ·DMA (1, BPDC = 5,5′-dicarboxylate-3,3′-dipyridine anion and DMA = dimethylacetamide), has been synthesized based on the ligand BPDC under solvothermal conditions. Single crystal X-ray analysis reveals that it possesses a non-interpenetrating binodal (4,4)-connected three-dimensional PtS-type network with the Schläfli point symbol of {4² ·84 }. Remarkably, the activated 1 (1a) with dual functionalities of open metal sites (OMSs) and O-rich Lewis basic sites (LBSs) exhibits excellent CO2 adsorption (193 cm³ g−1 at 298 K) and high-effect separation ability (41.5 for CO2/N2 = 15/85 and 9.7 for CO2/CH4 = 5/95 under 1 bar at 298 K). Additionally, 1a exhibits impressive performance for I2 sorption and release in solvents. [ABSTRACT FROM AUTHOR]

A new triazole‐functionalized tetracarboxylic acid ligand (H4L) has been synthesized and utilized for the fabrication of a 3D ZnII organic framework with a Zn4(−COO)6 cluster as the secondary building unit. The framework exhibits very good thermal stability and consists of dual functionalities of exposed Lewis acidic metal sites and accessible nitrogen‐donor Lewis basic sites. The Lewis basic nitrogen sites in the framework serve as CO2 binding sites for highly selective CO2 capture and the presence of exposed Lewis acidic metal sites in the framework make it an efficient heterogeneous catalyst for the chemical fixation of CO2 into value‐added cyclic carbonates under ambient conditions. [ABSTRACT FROM AUTHOR]

Tailoring the structures and properties of metal–organic frameworks (MOFs) is very important for developing porous MOFs for targeted applications. Bent diisophthalate ligands offer a rich opportunity to construct MOFs with variable topologies because of their conformation flexibility and diversity. In this work, by employing a substituent-induced ligand conformation regulation strategy, we designed and synthesized three bent diisophthalate ligands bearing different substituents, and successfully constructed their corresponding dicopper paddlewheel-based MOFs under suitable solvothermal conditions. As revealed by single-crystal structural analyses, they feature distinct topological structures, depending on the attached substituents. Interestingly, the methoxy-functionalized MOF exhibits a novel topology, thus enriching the structural diversity of copper-bent diisophthalate frameworks. Furthermore, their gas adsorption properties with respect to C2H2, CO2, and CH4 were systematically investigated, revealing their promising potential for industrially important C2H2/CH4 and CO2/CH4 separations. More significantly, their separation performance can be greatly tailored by changing the substituents. Under ambient conditions, C2H2 and CO2 uptake capacities vary from 157.7 to 184.5 cm3 (STP) g−1, and 90.8 to 101.3 cm3 (STP) g−1, respectively, while C2H2/CH4 (50/50, v/v) and CO2/CH4 (50/50, v/v) adsorption selectivities range from 30.0 to 36.2, and 5.27 to 6.01, respectively. The amino-functionalized MOF performed better than the other two counterparts, which might be due to the synergistic effect arising from Lewis basic amino groups, higher density of open copper sites, and more suitable pore size. This work not only reported three MOFs for preferable adsorption of C2H2 and CO2 over CH4, but also demonstrated that the substituent-driven ligand conformation regulation is a facile way to modulate the structures and thus gas adsorption properties of MOFs. [ABSTRACT FROM AUTHOR]

Two new 2D MOFs, formulated as {[Cd(OBA)(L)]·DMF}n, 1 and {[Zn2(SDB)2(L)]·EtOH·3H2O·2DMF}n, 2 (L = 3-pyridinecarboxaldehyde nicotinoylhydrazone, H2OBA = 4,4′-oxybis(benzoic acid), H2SDB = 4,4′-sulfonyldibenzoic acid, DMF = N,N-dimethylformamide), have been synthesized at room temperature and characterized by elemental analyses (EA), FTIR spectra, single-crystal X-ray diffraction analyses (SCXRD), powder X-ray diffraction analyses (PXRD) and thermogravimetric analyses (TGA). The structural investigations reveal that both MOFs can be rationalized as a 4-c, uninodal net with sql topology. 1 and 2 are permanently microporous, having 1D channels with approximate sizes of 3.6 × 4.2 Å2 and 6.6 × 8.0 Å2, respectively. Furthermore, CO2, CH4 and N2 sorption studies are carried out in detail at varying temperatures, and the results show that the adsorption capacities of both 1 and 2 towards CO2 are higher than those towards CH4 and N2. Importantly, IAST calculations reveal that 1 and 2 display high separation selectivities for CO2/N2 (15 : 85) and CO2/CH4 (50 : 50) mixtures at ambient conditions. [ABSTRACT FROM AUTHOR]

A microporous metal–organic framework, {[Co2(4,4′-bpy)(L)]·H2O·0.5(DMF)}n (1), was obtained from the self-assembly of cobalt(ii) nitrate hexahydrate, rigid tetrapodal carboxylic acid 4,4′,4′′,4′′′-silanetetrayltetrabenzoic acid (H4L) and a rigid bifunctional linker 4′4′-bipyridine (4,4′-bpy) under solvothermal conditions. It was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, and powder and single crystal X-ray diffraction. Its single crystal structure reveals the presence of a Co(ii)-paddle wheel core as the SBU, which is extended to form a doubly interpenetrated 3D framework with a (4,6)-connected sqc422-type uninodal net topology with the Schläfli point symbol {42·510·72·8}{42·54}. There are two types of open channels in this framework (rhombic and trigonal), which run along all three axes. Its thermal and chemical stabilities were established based on thermogravimetric analysis and in situ variable temperature powder X-ray diffraction. The activated framework (lattice solvent free) of 1 exhibits modest uptake of CO2 (53.8 and 36.4 cm3 g−1 at 273 and 298 K at 1 bar pressure, respectively), with moderately high selectivities for CO2/N2 and CO2/CH4 gas separation under ambient conditions (298 and 273 K under 1 bar pressure). [ABSTRACT FROM AUTHOR]

Self-recognition of 3,3′,5,5′-azobenzenetetracarboxylic acid drives the formation of a grid-like anionic hydrogen-bonded framework with channels occupied by organic cations. This supramolecular solid is capable of reorganizing its connectivity in the presence of specific guests into a different crystalline architecture by sequential dissolution and recrystallization. [ABSTRACT FROM AUTHOR]

A 3D microporous luminescent metal–organic framework {[Zn(oba)(L)0.5]·dma}n (IITKGP‐9, IITKGP represents the Indian Institute of Technology Kharagpur; L = 3,3′‐azodipyridine, H2oba = 4,4′‐oxydibenzoic acid) with 1D rhombus‐shaped channels has been synthesized by employing a bent organic linker with an unexploited azo‐functionalized N,N′ spacer. The metal–organic framework (MOF) exhibits potential for highly selective sorption of CO2 with excellent selectivity of CO2 from CO2/N2 (291 at 273 K and 118 at 295 K) and CO2/CH4 (17.5 at 273 K and 4.8 at 295 K) at a pressure of 1 bar, as demonstrated by ideal adsorbed solution theory (IAST) calculations. Such high separation ability, especially at 273 K for CO2/N2, can be attributed to the microporous (5.8 × 6.6 Å2) nature of this MOF and the enhanced interactions of the adsorbed CO2 molecules with the functional azo groups decorating the pore channels. This MOF is highly emissive at 374 nm upon excitation at 310 nm. The free azo groups exposed in the channels serve as functional sites for the sensing of metal ions and the recognition of small organic molecules through the quenching of fluorescence. Fluorescence measurements revealed that this MOF can selectively sense Fe3+ and also detect toxic nitromethane with high sensitivity. Elemental mapping by energy‐dispersive X‐ray spectroscopy and powder XRD analysis of the Fe3+‐loaded MOF material, recyclability tests, and a plausible quenching mechanism are presented. Thus, this MOF demonstrates potential as a trifunctional MOF material for three different applications, namely selective gas separation, selective ion sensing, and selective recognition of organic molecules. [ABSTRACT FROM AUTHOR]

Abstract: Selective adsorption and separation of CO2 from flue gas and landfill gas mixtures have drawn great attention in industry. Porous MOF materials are promising alternatives to achieve such separations; however, the stability in the presence of moisture must be taken into consideration. Herein, we have constructed a microporous metal–organic framework (MOF) {[Co(OBA)(L)0.5]⋅S}n (IITKGP‐8), by employing a V‐shaped organic linker with an azo‐functionalized N,N′ spacer forming a 3D network with mab topology and 1D rhombus‐shaped channels along the crystallographic ‘b’ axis with a void volume of 34.2 %. The activated MOF reveals a moderate CO2 uptake capacity of 55.4 and 26.5 cm3 g−1 at 273 and 295 K/1 bar, respectively, whereas it takes up a significantly lower amount of CH4 and N2 under similar conditions and thus exhibits its potential for highly selective sorption of CO2 with excellent IAST selectivity of CO2/N2 (106 at 273 K and 43.7 at 295 K) and CO2/CH4 (17.7 at 273 K and 17.1 at 295 K) under 1 bar. More importantly, this MOF exhibits excellent moisture stability as assessed through PXRD experiments coupled with surface area analysis. [ABSTRACT FROM AUTHOR]

Ssa-type MOFs constructed from dicopper paddlewheels and bent diisophthalate ligands exhibit a promising potential for gas adsorption which benefits from their rich open copper sites and polyhedron-based cages with suitable sizes. However, the rational construction of such types of MOFs is exceedingly challenging because the bent diisophthalate ligands employed are inclined to exhibit various conformations and thus are prone to form MOFs with varied topologies. In this work, by pre-organizing the ligand's conformation, we successfully targeted an ssa-type MOF ZJNU-57 from a bent diisophthalate ligand. More significantly, ZJNU-57 exhibits excellent hydrolytic stability and high C2H2 and CO2 uptake capacities as well as impressive C2H2/CH4 and CO2/CH4 adsorption selectivities, indicating its promising potential for C2H2/CH4 and CO2/CH4 separation, which are relevant to acetylene production and natural gas purification. This work not only provides a rare water-stable MOF based on the Cu2(COO)4 cluster for highly selective adsorption of C2H2 and CO2 from CH4, but also demonstrates that the ligand conformation-controlled assembly strategy may be an efficient approach toward the construction of MOF materials with definite topologies for specific applications. [ABSTRACT FROM AUTHOR]

A microporous MOF {[Zn(SDB)(L)0.5]·S}n (IITKGP-5) with a polar pore surface has been constructed by the combination of a V-shaped –SO2 functionalized organic linker (H2SDB = 4,4′-sulfonyldibenzoic acid) with an N-rich spacer (L = 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene), forming a network with sql(2,6L1) topology. IITKGP-5 is characterized by TGA, PXRD and single crystal X-ray diffraction. The framework exhibits lozenge-shaped channels of an approximate size of 4.2 × 5.6 Å2 along the crystallographic b axis with a potential solvent accessible volume of 26%. The activated IITKGP-5a revealed a CO2 uptake capacity of 56.4 and 49 cm3 g−1 at 273 K/1 atm and 295 K/1 atm, respectively. On the contrary, it takes up a much smaller amount of CH4 (17 cm3 g−1 at 273 K and 13.6 cm3 g−1 at 295 K) and N2 (5.5 cm3 g−1 at 273 K; 4 cm3 g−1 at 295 K) under 1 atm pressure exhibiting its potential for a highly selective adsorption of CO2 from flue gas as well as a landfill gas mixture. Based on the ideal adsorbed solution theory (IAST), a CO2/N2 selectivity of 435.5 and a CO2/CH4 selectivity of 151.6 have been realized at 273 K/100 kPa. The values at 295 K are 147.8 for CO2/N2 and 23.8 for CO2/CH4 gas mixtures under 100 kPa. In addition, this MOF nearly approaches the target values proposed for PSA and TSA processes for practical utility exhibiting its prospect for flue gas separation with a CO2 loading capacity of 2.04 mmol g−1. [ABSTRACT FROM AUTHOR]

Two solvent-induced porous hydrogen-bonded organic frameworks have been obtained, and their synthesis, crystal structures, gas sorption behaviours and fluorescence sensing applications have been systematically investigated to elucidate the solvent effects on the structures and functionalities of HOFs. [ABSTRACT FROM AUTHOR]

A novel metal-organic framework {[Zn(XL)2](ClO4)2⋅6 H2O} n (XL= N, N′-bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxdiimide bi(1,2,4-triazole)) was synthesized and structurally characterized, presenting the first example of six-fold interpenetrating 3 D framework with the topology type of sqc6, which displays high thermostability and solvent stability. Additionally, the luminescence investigations reveal that this MOF can sensitively and selectively detect acetylacetone with a detection limit of 1.72 ppm. More importantly, it is rather rare for an MOF-based luminescence probe to serve as a sensor to effectively detect acetylacetone. [ABSTRACT FROM AUTHOR]

In the global transition to a sustainable low-carbon economy, CO2 capture and storage technology still plays a critical role for deep emission reduction, particularly for the stationary sources in power generation and industry. However, for small and mobile emission sources in transportation, CO2 capture is not suitable and it is more practical to use relatively clean energy, such as natural gas. In these two low-carbon energy technologies, designing highly selective sorbents is one of the key and most challenging steps. Toward this end, metal-organic frameworks (MOFs) have received continuously intensive attention in the past decades for their highly porous and diversified structures. In this review, the recent progress in developing MOFs for selective CO2 capture from post-combustion flue gas and CH4 storage for vehicle applications are summarized. For CO2 capture, several promising strategies being used to improve CO2 adsorption uptake at low pressures are highlighted and compared. In addition, the conventional and novel regeneration techniques for MOFs are also discussed. In the case of CH4 storage, the flexible and rigid MOFs, whose CH4 storage capacity is close to the target set by U.S. Department of Energy are particularly emphasized. Finally, the challenge of using MOFs for CH4 storage is discussed. [ABSTRACT FROM AUTHOR]

Permanent porosity has been realized in a hydrogen bonded framework formed by a single tripodal tricarboxylic acid molecule. The presence of three phenyl rings linked to a flexible sp3 nitrogen centre renders a near-propeller shape to the molecule generating an unusual ‘non-planar’ 3-D framework formed by highly directional planar –COOH…HOOC– hydrogen bonds, propagating in all three directions. The material shows exceptional hydrolytic, acidic and thermal stability and has a surface area of 1025 m2 g−1. Importantly, it shows preferential adsorption of CO2 over N2 with very high selectivities (350 : 1@1 bar, 303 K). DFT modeling shows the presence of stable T-shaped CO2…CO2 dimers within the channels suggesting favorable co-operativity between them. [ABSTRACT FROM AUTHOR]

A variety of strategies have been developed to adsorb and separate light hydrocarbons in metal-organic frameworks. Here, we present a new approach in which the pores of a framework are lined with four different C3 sidechains that feature various degrees of branching and saturation. These pendant groups, which essentially mimic a low-density solvent with restricted degrees of freedom, offer tunable control of dispersive host-guest interactions. The performance of a series of frameworks of the type Zn2(fu-bdc)2(dabco) (fu-bdc2-=functionalized 1,4-benzenedicarboxylate; dabco=1,4-diazabicyclo[2.2.2]octane), which feature a pillared layer structure, were investigated for the adsorption and separation of methane, ethane, ethylene, and acetylene. The four frameworks exhibit low methane uptake, whereas C2 hydrocarbon uptake is substantially higher as a result of the enhanced interaction of these molecules with the ligand sidechains. Most significantly, the adsorption quantities and selectivity were found to depend strongly upon the type of sidechains attached to the framework scaffold. [ABSTRACT FROM AUTHOR]

The reaction of N-rich pyrazinyl triazolyl carboxyl ligand 3-(4-carboxylbenzene)-5-(2-pyrazinyl)-1 H-1,2,4-triazole (H2cbptz) with MnCl2 afforded 3D cationic metal-organic framework (MOF) [Mn2(Hcbptz)2(Cl)(H2O)]Cl ⋅DMF ⋅0.5 CH3CN ( 1), which has an unusual (3,4)-connected 3,4T1 topology and 1D channels composed of cavities. MOF 1 has a very polar framework that contains exposed metal sites, uncoordinated N atoms, narrow channels, and Cl− basic sites, which lead to not only high CO2 uptake, but also remarkably selective adsorption of CO2 over N2 and CH4 at 298-333 K. The multiple CO2-philic sites were identified by grand canonical Monte Carlo simulations. Moreover, 1 shows excellent stability in natural air environment. These advantages make 1 a very promising candidate in post-combustion CO2 capture, natural-gas upgrading, and landfill gas-purification processes. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of two isoreticular metal-organic frameworks (MOFs), {[Cd(bdc)(4-bpmh)]}n·2 n(H2O) (1) and {[Cd(2-NH2bdc)(4-bpmh)]}n·2n(H2O) (2) [bdc=benzene dicarboxylic acid; 2-NH2bdc=2-amino benzene dicarboxylic acid; 4-bpmh=N,N-bis-pyridin-4-ylmethylene- hydrazine], are reported. Both compounds possess similar two-fold interpenetrated 3D frameworks bridged by dicarboxylates and a 4-bpmh linker. The 2D Cd-dicarboxylate layers are extended along the a-axis to form distorted square grids which are further pillared by 4-bpmh linkers to result in a 3D pillared-bilayer interpenetrated framework. Gas adsorption studies demonstrate that the amino-functionalized MOF 2 shows high selectivity for CO2 (8.4 wt% 273 K and 7.0 wt% 298 K) over CH4, and the uptake amounts are almost double that of non-functional MOF 1. Iodine (I2) adsorption studies reveal that amino-functionalized MOF 2 exhibits a faster I2 adsorption rate and controlled delivery of I2 over the non-functionalized homolog 1. [ABSTRACT FROM AUTHOR]

Introduction of Ag(I) ions into a sulfonic acid functionalized MOF ((Cr)-MIL-101-SO3H) significantly enhances its interactions with olefin double bonds, leading to its much higher selectivities for the separation of C2H4–C2H6 and C3H6–C3H8 at room temperature over the original (Cr)-MIL-101-SO3H and other adsorbents at room temperature. [ABSTRACT FROM AUTHOR]

Introduction of Ag(i) ions into a sulfonic acid functionalized MOF ((Cr)-MIL-101-SO3H) significantly enhances its interactions with olefin double bonds, leading to its much higher selectivities for the separation of C2H4–C2H6 and C3H6–C3H8 at room temperature over the original (Cr)-MIL-101-SO3H and other adsorbents at room temperature. [ABSTRACT FROM AUTHOR]

The introduction of the combination of open metal site (OMS) and π-complexation into MOF has led to very high ethylene–ethane adsorption selectivity at 318 K, as illustrated in the context of MIL-101–Cr–SO3Ag. The interactions with ethylene from both OMS and π-complexation in MIL-101–Cr–SO3Ag have been investigated by in situ IR spectroscopic studies and computational calculations, which suggest that π-complexation contributes dominantly to the high ethylene–ethane adsorption selectivity. [ABSTRACT FROM AUTHOR]