An Amino-Coordinated Metal-Organic Framework for Selective Gas Adsorption

Ionic liquid post-modified carboxylate-rich MOFs for efficient catalytic CO2 cycloaddition under solvent-free conditions

The synthesis of cyclic carbonates through cycloaddition reactions between epoxides and carbon dioxide (CO2) is an important industrial process. Metal-Organic Frameworks (MOFs) have functional and ordered pore structures, making them attractive catalysts for converting gas molecules into valuable products. One approach to enhance the catalytic activity of MOFs in CO2 cycloaddition reactions is to create open metal sites within MOFs. In this study, the amino-functionalized rare earth Gd-MOF (Gd-TPTC-NH2) and its ionic liquid composite catalysts (Gd-TPTC-NH-[BMIM]Br) were synthesized using 2'-amino-[1,1':4',1''-terphenyl]-3,3'',5,5''-tetracarboxylic acid (H4TPTC-NH2) as the ligand. The catalytic performance of these two catalysts was observed in the cycloaddition reaction of CO2 and epoxides. Under the optimized reaction conditions, Gd-TPTC-NH-[BMIM]Br can effectively catalyze the cycloaddition reaction of a variety of epoxide substrates with good to excellent yields of cyclic carbonate products. Comparatively, epichlorohydrin and epibromohydrin, which possess halogen substituents, promote higher yields of cyclic carbonates due to the electron-withdrawing nature of Cl and Br substituents. Additionally, the Gd-TPTC-NH-[BMIM]Br catalyst demonstrated good recyclability and reproducibility, maintaining its catalytic activity without any changes in its structure or properties after five reuse cycles.

Trajectory in biological metal-organic frameworks: Biosensing and sustainable strategies-perspectives and challenges

The ligand attribute of biomolecules to form coordination bonds with metal ions led to the discovery of a novel class of materials called biomolecule-associated metal-organic frameworks (Bio-MOFs). These biomolecules coordinate in multiple ways and provide versatile applications. Far-spread bio-ligands include nucleobases, amino acids, peptides, cyclodextrins, saccharides, porphyrins/metalloporphyrin, proteins, etc. Low-toxicity, self-assembly, stability, designable and selectable porous size, the existence of rigid and flexible forms, bio-compatibility, and synergistic interactions between metal ions have led Bio-MOFs to be commercialized in industries such as sensors, food, pharma, and eco-sensing. The rapid growth and commercialization are stunted by absolute bio-compatibility issues, bulk morphology that makes it rigid to alter shape/porosity, longer reaction times, and inadequate research. This review elucidates the structural vitality, biocompatibility issues, and vital sensing applications, including challenges for incorporating bio-ligands into MOF. Critical innovations in Bio-MOFs' applicative spectrum, including sustainable food packaging, biosensing, insulin and phosphoprotein detection, gas sensing, CO2 capture, pesticide carriers, toxicant adsorptions, etc., have been elucidated. Emphasis is placed on biosensing and biomedical applications with biomimetic catalysis and sensitive sensor designing.

Five Porous Complexes Constructed from a Racemic Ligand: Synthesis, Chiral Self-Assembly, Iodine Adsorption, and Desorption Properties

Herein, a chiral bispyridyl ligand (L) was designed and synthesized using a Schiff base condensation reaction, followed by a 1,3-H shift. Five complexes, [Zn₂L₂(OAc)₄] (1), {[CdLCl₂(DMF)]·4H₂O}_n (2), [Cd₂L₂I₄]·4H₂O (3), {[CdL₂(H₂O)₂](NO₃)₂·2CH₃OH}_n (4), and [Hg₂L₂Cl₄]·2DMF (5), were synthesized and characterized upon its reaction with Zn(II), Cd(II), or Hg(II) ions, respectively. X-ray crystallography shows that the organic compound exists as a racemic ligand with equal amounts of its R- and S-isomers, and all of the synthesized complexes exhibit heterochiral self-assembly via a chiral self-discrimination process. Complexes 1, 3, and 5 exist as centrosymmetric binuclear metallamacrocycles, while complexes 2 and 4 exist as 1D looped-chain coordination polymers. Inspired by the assembled structures of the five complexes, I₂ adsorption/desorption measurements for the complexes were carried out. The results show that complexes 1 and 5 exhibit good adsorption capacities toward I₂ in n-hexane and in water, respectively.

Two Solvent-Induced In(III)-Based Metal-Organic Frameworks with Controllable Topology Performing High-Efficiency Separation of C2H2/CH4 and CO2/CH4

For pure acetylene manufacturing and natural gas purification, the development of porous materials displaying highly selective C₂H₂/CH₄ and CO₂/CH₄ separation is greatly important but remains a major challenge. In this work, a plausible strategy involving solvent-induced effects and using the flexibility of the ligand conformation to make two In(III) metal-organic frameworks (MOFs) is developed, showing topological diversity and different stability. The X-shaped tetracarboxylic ligand H₄TPTA ([1,1':3',1″-terphenyl]-4,4',4″,6'-tetracarboxylic acid) was selected to construct two new heteroid In MOFs, namely, {[CH₃NH₃][In(TPTA)]·2(NMF)} (MOF 1) and {[In₂(TPTA)(OH)₂]·2(H₂O)·(DMF)} (MOF 2). MOF 1 is a (4, 4)-connected net showing a pts topology with a large channel that is not conducive to fine gas separation. By contrast, with the reduction of SBU from uninucleated In to an {In-OH-In}_n chain, MOF 2 has a (4, 6)-connected net with the fsc topology with an ∼5 Å suitable micropore to confine matching small gas. The permanent porosity of MOF 2 leads to the preferential adsorption of C₂H₂ over CO₂ with superior C₂H₂/CH₄ (332.3) and CO₂/CH₄ (31.2) separation selectivities. Meanwhile, the cycling dynamic breakthrough experiments showed that the high-purity C₂H₂ (>99.8%) capture capacities of MOF 2 were >1.92 mmol g^-1 from a binary C₂H₂/CH₄ mixture, and its separation factor reached 10.

Facile preparation of oxygen-rich porous polymer microspheres from lignin-derived phenols for selective CO2 adsorption and iodine vapor capture

Lignin is a natural O-containing aromatic amorphous polymers from the residues of biorefinery and industrial papermaking, it can derive lots of aromatic phenol chemicals used as industrial raw materials by an efficient depolymerization, and then produce synthetic polymers. Here, we selected six aromatic units from the liquid products of lignin depolymerization, and tried to prepare diversified O-rich hyper-cross-linked polymers (HCPs) by one-pot Friedel-Crafts alkylation reaction for CO₂ and iodine vapor capture. HCP1, HCP2, and HCP3 microspheres possessed similar porous structure with Brunauer-Emmett-Teller (BET) surface areas (S_BET) of 14.1-20.6 m²/g and high O content (26.34-30.68 wt%), while HCP4, HCP5, and HCP6 were composed of many bulks with 3D networks structure, and showed larger S_BET of 15.4-246.9 m²/g and relatively low O content (18.48-26.38 wt%). The results indicated that the chemical position and quantities of substituent groups (methoxy and alkyl) into lignin-derived units had evident impact on their morphology and textural parameters. These HCPs exhibited considerable CO₂ uptake (64.1 mg/g) and selectivity (35.2) at 273 K， and high iodine vapor uptake (192.3 wt%). Moreover, the performance analysis implied that the S_BET and pore volume of these HCPs had not played the dominated roles in the CO₂ and I₂ adsorption, while their pore size distribution, O-functional groups, and electron density will be more important for the capture of the both. This study will offer a facile synthesis of O-rich polymer microsphere adsorbents based on the green and sustainable lignin.

Unravelling the catalytic potential of a magnetic CoFe2O4/Cu–ABDC MOF composite in the sustainable synthesis of 2H-indazole motifs

A magnetic CoFe2O4/Cu–ABDC hybrid composite was fabricated for the synthesis of biologically active and pharmacologically significant 2H-indazole scaffolds.

Construction of three new Co(ii)-organic frameworks based on diverse metal clusters: highly selective C2H2 and CO2 capture and magnetic properties

Three Co(ii)-MOFs have been synthesized. The desolvated frameworks of 2 and 3 exhibit good adsorption selectivity for C₂H₂ and CO₂ over CH₄ at 273 and 298 K. Moreover, 1–3 show that there exist antiferromagnetic interactions between metal ions.

Structural Tuning and Pore Modulation of Three Cu(II)-Organic Frameworks: Enhancement of Stability and Functionality

Through use of an irregular pentacarboxylate ligand, 2,2'-(pyridine-2,6-diyl)diterephthalic acid (H₄L), two Cu(II)-based metal-organic frameworks, {[(Me₂NH₂)_0.5][Cu_0.75(L)_0.5(DMA)_0.375]·H₂O}_n (1) and {[Cu₄(L)₂(H₂O)₄]·4DMF·8H₂O}_n (2), have been synthesized. A structural analysis demonstrates that 1 is a 2D layer and 2 shows a 3D framework, which exhibit hopeful possibilities for the selective separations of C₂H₂/CH₄ and CO₂/CH₄. To enhance the adsorption properties, 5-amino-1H-tetrazole (HAT) has been introduced in the synthesis system, and a new framework, {[Cu₄(L)₂(ATZ)₂(H₂O)]·5DMF·5H₂O}_n (3), has been obtained. 3 is a 3D framework. Especially, 3 is constructed from multiple SBUs and displays an unusual (3,4,6)-connected topology. Furthermore, especially 3 performs better than 1 and 2 in terms of uptake capacity as well as adsorption selectivity, which might be ascribed to the more proper pore space of 3.

Polar Sulfone-Functionalized Oxygen-Rich Metal-Organic Frameworks for Highly Selective CO2 Capture and Sensitive Detection of Acetylacetone at ppb Level

A rational combination of an oxygen-rich pyridyl substituted tetrapodal ligand, tetrakis(4-pyridyloxymethylene)methane (TPOM), and a polar sulfone-functionalized conjugated bent dicarboxylate linker, dibenzothiophene-5,5'-dioxide-3,7-dicarboxylic acid (H₂(3,7-DBTDC)), with d¹⁰ metal centers, Zn(II) and Cd(II), has led to the construction of two new three-dimensional (3D) metal-organic frameworks,{[Zn₂(TPOM)(3,7-DBTDC)₂]·7H₂O·DMA}_n (1) and {[Cd₂(TPOM)(3,7-DBTDC)₂]·6H₂O·3DMF}_n (2). Single-crystal X-ray analysis indicates that 1 is a 3D framework with a dinuclear repeating unit having two different Zn(II) centers (tetrahedral and square pyramidal) and 2 is a 3D framework comprised of a dinuclear repeating unit with one crystallographically independent distorted pentagonal bipyramidal Cd(II) coordinated to chelating/bridging carboxylates and nitrogen atoms of the TPOM ligand. In both cases, the pores are aligned with oxygen atoms of the TPOM ligand and decorated with polar sulfone moieties. On the basis of the stability established by thermogravimetric analysis and powder X-ray diffraction (PXRD) and the presence of large solvent accessible voids (25.4% for 1 and 40.6% for 2), gas sorption studies of different gases (N₂, CO₂, and CH₄) and water vapor have been explored for both 1 and 2. The CO₂ sorption isotherm depicts type I isotherm with an uptake of 93.6 cm³ g^-1 (for 1) and 100.6 cm³ g^-1 (for 2) at 195 K. Additionally, sorption of CO₂ is highly selective over that of N₂ and CH₄ for both 1 and 2 due to the strong quadrupolar interactions between sulfone moieties and CO₂ molecules. Configurational bias Monte Carlo (CBMC) molecular simulation has further justified the highly selective CO₂ capture. On the other hand, the luminescence nature of 1 and 2 has been employed for highly selective detection of acetylacetone in aqueous methanol with a limit of 59 ppb in 1 and 66 ppb in 2, which are among the best reported values so far in the literature. The Stern-Volmer plots, spectral overlap, density functional theory calculations, CBMC simulation, and time-resolved lifetime measurements have been utilized for an extensive mechanistic study. The exclusive selectivity for acetylacetone in 1 and 2 have been confirmed by competitive selectivity test. Both exhibited good recyclability and stability after sensing experiments analyzed by fluorescence, PXRD, and field emission scanning electron microscopy studies.

Fine-Tuning the Porosities of the Entangled Isostructural Zn(II)-Based Metal-Organic Frameworks with Active Sites by Introducing Different N-Auxiliary Ligands: Selective Gas Sorption and Efficient CO2 Conversion

Three new pairs of 2-fold interpenetrated and self-entangled three-dimensional isostructural porous metal-organic frameworks (MOFs), [Zn(L1)(x)_0.5]·0.5H₂O (x = bipy for 1, bpa for 2, and bpe for 3) and [Zn(L2)(x)_0.5]·0.5H₂O (x = bipy for 4, bpa for 5, and bpe for 6) [bipy = 4,4'-bipyridine, bpa = 1,2-bis(4-pyridyl)ethylene, and bpe = 1,2-bis(4-pyridyl)ethylene], have been created and fine-tuned via similar skeleton ligands 2-(imidazol-1-yl)terephthalic acid (H₂L1) and 2-(1H-1,2,4-triazol-1-yl)terephthalic acid (H₂L2) and N-auxiliary coligands with different linking groups. Interestingly, the porosities of the MOFs can be effectively increased via the insertion of -CH₂CH₂- or -CH═CH- spacers into the N-auxiliary bipy ligand. As a result, complexes 5 and 6 displayed highly enhanced CO₂ uptake capacities. Furthermore, complex 5 also had a higher C₂/C₁ selectivity as well as great CO₂ cycloaddition efficiency.

Triggering Lewis Acidic Nature through the Variation of Coordination Environment of Cd-Centers in 2D-Coordination Polymers

The rational design and successful synthesis of novel functional metal-organic frameworks relies on careful selection of metals and versatile organic ligands. A newly designed pyrazole-based dicarboxylate ligand, 5-(3,5-dimethyl-1H-pyrazol-1-yl) 1,3-benzenedicarboxylic acid (H₂L), was utilized to obtain two new Cd-based coordination polymers I [Cd(L)(H₂O)]·H₂O and II [Cd(L)] under similar reaction conditions via solvothermal strategy. Single-crystal X-ray data confirmed that compound I exhibits a two-dimensional (2D) skeleton comprising pentagonal bipyramidal Cd-ions and an organic ligand moiety. Compound II has also formed a two-dimensional layer arrangement with the connectivity between trigonal bipyramidal Cd-ions and the organic ligand. Topological analysis revealed that compound I has formed unique 4³.6³ net topology while compound II has displayed a 4⁴.6² sql net topology with 2D frameworks. The Lewis acidic nature of both I and II containing a Cd²⁺ metal center has been correlated with the coordination number through dye adsorption-desorption and catalysis studies. The selective adsorption of anionic dye and the extent of adsorption are interrelated with the Cd-ion geometry. For the first time, the role of coordinated water molecule has been analyzed through heterogeneous catalysis reaction (i.e., cyanosilylation) with Cd-based 2D-coordination polymers (CPs). The plausible mechanisms have been proposed to explain the subsequent role of coordination number and environment in CPs.

Constructing new metal-organic frameworks with complicated ligands from "One-Pot" in situ reactions

Metal-organic frameworks (MOFs) have emerged as one of the most fascinating libraries of porous materials. In spite of their myriad merits, practical application of most MOFs is restricted due to their high preparation cost because of the complicated organic ligands involved. To address this limitation, we propose to use simple and cheap organic precursors to synthesize MOFs with complicated ligands via "one-pot" in situ reactions of these precursors along with the formation of new MOFs. In this work, we have carefully screened several organic reactions, through which target ligands were generated in situ from easily available reactants during the MOF construction. With this "one-pot" approach, the fabrication of a series of novel MOFs by integrating the organic covalent bond and the coordinate bond has thus been realized through the judicious selection of organic reactions, which effectively simplifies the MOF synthesis process and thus reduces the cost.

Effects of synthesis methodology on microporous organic hyper-cross-linked polymers with respect to structural porosity, gas uptake performance and fluorescence properties

The structural characteristics of hyper-cross-linked polymers (HCPs) make them interesting for a wide variety of applications.

Two 2D microporous MOFs based on bent carboxylates and a linear spacer for selective CO2 adsorption

Two new 2D microporous MOFs based on bent carboxylates and an unexplored N,N-donor spacer containing imine and amide functionalities exhibited high IAST selectivity for CO₂/N₂ and CO₂/CH₄ mixtures under ambient conditions.

A robust and water-stable two-fold interpenetrated metal–organic framework containing both rigid tetrapodal carboxylate and rigid bifunctional nitrogen linkers exhibiting selective CO2 capture

A robust and water-stable two-fold interpenetrated metal–organic framework containing both rigid tetrapodal carboxylate and rigid bifunctional nitrogen linkers exhibiting selective CO₂ capture is reported.

Strategic Design and Functionalization of an Amine-Decorated Luminescent Metal Organic Framework for Selective Gas/Vapor Sorption and Nanomolar Sensing of 2,4,6-Trinitrophenol in Water

On the basis of the strategic design of a triazine-based dicarboxylate ligand with two primary amino groups and one secondary amino group, an amine-functionalized autofluorescent and polar three-dimensional metal organic framework (MOF) {[Cd(ATAIA)]·4H₂O} _n (1), where H₂ATAIA = 5-((4,6-diamino-1,3,5-triazin-2-yl)amino)isophthalic acid, has been synthesized under two different solvothermal conditions and structurally characterized. Single-crystal X-ray analysis reveals that 1 crystallizes in the orthorhombic polar space group Fdd2, where each ATAIA ligand acts as a linear linker to connect four Cd(II) centers, resulting in the formation of a three-dimensional framework with a repeat of a double helical metal chain. It has been further characterized by elemental analysis, UV-vis and Fourier transform infrared spectroscopy, and thermogravimetric analysis. Its bulk phase purity and stability in aqueous acid and base solutions are confirmed by powder X-ray diffraction. Both field emission scanning electron microscopy and high resolution transmission electron microscopy images of 1 reflect the formation of microflowers by self-assembly of nanopetals. With the dehydrated framework of 1, sorption studies of different gases (N₂, H₂, and CO₂) as well as polar and nonpolar solvents, such as water, benzene (Bz), and cyclohexane (Cy), have been performed. The CO₂ sorption isotherm depicts type I isotherm at 298 and 273 K and type IV isotherm at 195 K. Furthermore, with an uptake of 129.2 cm³ g^-1 (25.62 wt %) at 195 K, sorption of CO₂ is selective over N₂ (77 K) and H₂ (77 K) because of the strong adsorbate-adsorbent interaction as clearly evident from an isosteric heat of adsorption ( Q_st) at zero coverage of 37.5 kJ mol^-1, which is exceptionally higher than that of other functionalized MOFs. Using the ideal adsorption solution theory calculation for a CO₂/N₂ (15:85) mixture, selectivity values are found to be 54.08 (298 K) and 46.96 (273 K) at 100 kPa. For a major application, activated 1 has been utilized for selective and ultrafast detection of 2,4,6-trinitrophenol (TNP) in water with a limit of 0.94 nM (0.2 ppb), which supersedes any previous reported value. Excellent recyclability and stability of 1 for sensing experiments have been established. Time-resolved fluorescence studies and density functional theory calculations have been used to establish its mechanism of action. Furthermore, a prototype experiment for the real-time sensing of TNP in the vapor phase by fluorescence microscopy provides an easy colorimetric monitoring.

Functionalization of MOFs via a mixed-ligand strategy: enhanced CO2 uptake by pore surface modification

Two isostructural MOFs based on rare quaternary SBUs with a new (3,3,4,6)-connected topology have been assembled, which possess high porosity with highly polar pore systems, and also exhibit high uptake for CO₂ and significant selectivity for CO₂ over CH₄.

Cross-dehydrogenative coupling of coumarins with Csp3–H bonds using an iron–organic framework as a productive heterogeneous catalyst

The iron–organic framework VNU-20 was utilized as an active heterogeneous catalyst for the cross-dehydrogenative coupling of coumarins with Csp³–H bonds in alkylbenzenes, cyclohexanes, ethers, and formamides.

An Uncommon Carboxyl-Decorated Metal-Organic Framework with Selective Gas Adsorption and Catalytic Conversion of CO2

A new three-dimensional (3D) framework, [Ni(btzip)(H₂ btzip)]⋅2 DMF⋅2 H₂ O (1) (H₂ btzip=4,6-bis(triazol-1-yl)isophthalic acid) as an acidic heterogeneous catalyst was constructed by the reaction of nickel wire and a triazolyl-carboxyl linker. Framework 1 possesses intersected 2D channels decorated by free COOH groups and uncoordinated triazolyl N atoms, leading to not only high CO₂ and C₂ H₆ adsorption capacity but also significant selective capture for CO₂ and C₂ H₆ over CH₄ and CO in 273-333 K. Moreover, 1 reveals chemical stability toward water. Grand Canonical Monte Carlo simulations confirmed the multiple CO₂ - and C₂ H₆ -philic sites. As a result of the presence of accessible Brønsted acidic COOH groups in the channels, the activated framework demonstrates highly efficient catalytic activity in the cycloaddition reaction of CO₂ with propylene oxide/4-chloromethyl-1,3-dioxolan-2-one/3-butoxy-1,2-epoxypropane into cyclic carbonates.

NIR emission and luminescent sensing of a lanthanide–organic framework with Lewis basic imidazole and pyridyl sites

Three luminescent lanthanide–organic frameworks, [Ln(Himdc)(ina)(H₂O)]_n, consist of a 3D microporous lanthanide carboxylate ([Eu(COO)₃]_n) framework and imidazole and pyridyl sites for the luminescent sensor.

A microporous MOF with a polar pore surface exhibiting excellent selective adsorption of CO2 from CO2–N2 and CO2–CH4 gas mixtures with high CO2 loading

A microporous MOF (IITKGP-5) with polar pore surface exhibits highly selective sorption of CO₂ from flue gas as well as landfill gas mixture with IAST selectivity for 435.5 and 151.6 at 273 K/100 kPa respectively.