Tetracarboxylate Ligand Research Articles

Fabrication of a novel Eu3+-functionalized Mn-MOF based on the X-type tetracarboxylate ligand for efficient temperature sensing

In this work, by utilizing an X-type tetracarboxylate ligand (1,2,4,5-tetrakis(4-carboxyphenyl)benzene, H4TCPB), a novel Mn-organic framework, namely, [(CH3CH2)2NH2]2[Mn(TCPB)(H2O)2] (SQNU-25, SQNU = Shangqiu Normal University), was prepared under a DEF/HAc solm. Due to the structural advantage of SQNU-25, the Ln3+ ions (Eu3+ and Gd3+) have been successfully introduced into the framework by post-synthetic modification. The result of the energy levels of the H4TCPB ligand and Eu3+ ion shows that the H4TCPB ligand as a chromophore can effectively sensitize Eu3+ ions. Moreover, the Eu@SQNU-25 not only shows a typical Eu3+ ion red emission but also exhibits good temperature sensing in the wide temperature range (80 to 300 K).

Investigations of magnetic and thermal expansion properties of two cobalt(II) metal-organic frameworks constructed by mixed bipyridyl-tetracarboxylate strategy

We report the syntheses, crystal structures, adsorption behavior, thermal expansion behavior, and magnetic properties of two cobalt(II) metal-organic frameworks (MOFs), {[Co(btca)1/2(bpe)(H2O)2]·bpe}n (1) and {Co(btca)1/2(bpe)(DMF)}n (2, H4btca = 1,2,4,5-benzenetetracarboxylic acid; bpe = 1,2-di(4-pyridyl)ethane), constructed using mixed bipyridyl and tetracarboxylate ligands. Single-crystal X-ray diffraction (SC-XRD) indicates that the change of synthetic solvents leads to a significant tuning of structural dimensionality from 2D to 3D framework. Temperature-dependent SC-XRD reveals anisotropically negative and positive thermal expansion of the compounds identified along different crystallographic axes within the frameworks over a 120–400 K temperature range. N2 adsorption measurements indicate a nonporous and ultramicroporous framework for 1 and 2, respectively. Magnetic measurements indicate an easy-plane magnetic anisotropy of the Co2+ ions in the MOFs, with experimental D values of 63.1 and 87.1 cm−1. The ac susceptibility measurements of 1 and 2 show field-induced slow magnetic relaxation below 6 K through different relaxation dynamics. This work not only provides two new cobalt(II) SIM-MOFs, but also presents an effective bipyridyl-tetracarboxylate strategy for designing and building framework materials with interesting magnetic and mechanical properties.

Highly stable rare earth metal-organic frameworks for proton conduction and magnetic refrigeration

Four isomorphic rare earth metal-organic frameworks designated as {[(CH3)2NH2]0.7[RE2(BTDBA)1.5(lac)0.7(H2O)2]·solvent}n (RE = Tb (JXUST-19), Eu (JXUST-29), Gd (JXUST-42), and Dy (JXUST-43), where JXUST denotes Jiangxi University of Science and Technology) have been synthesized derived from a benzothiadiazole tetracarboxylate ligand (4′,4'''-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis([1,1′-biphenyl]-3,5-dicarboxylic acid), H4BTDBA). They present chain-based three-dimensional structures with one-dimensional channels extending along the b-axis. Notably, the free [(CH3)2NH2]+ cations within the channels serve as proton carriers during proton conduction. All complexes demonstrate significant proton conductivity dependent on relative humidity and temperature. Among them, JXUST-43 displays the peak conductivity achieved 7. 38 × 10–5 S·cm-1. In terms of magnetic research, JXUST-42 exhibits potential as a magnetorefrigerant, reaching a maximum entropy change (-ΔSmmax) of 16.63 J kg-1 K-1 at 3.5 K with ΔH = 7 T. And the presence of field-induced slow magnetic relaxation behavior with antiferromagnetic coupling is observed in JXUST-43.

Assembly of unique interpenetrated metal–organic frameworks based on flexible tetra-carboxylate ligands

Entangled metal–organic frameworks (MOFs) are attracting more and more attentions attributed to their special performances, such as adsorption, fluorescence and catalysis. It is still of significant to synthesize new MOF with unique interpenetrating motif. In this work, two new MOFs, namely [(Me2)NH2]·[In(TCM)]·4DMF (JOU-32), and [Cd2(TCM)(DMF)2]·5DMF (JOU-33), have been successfully synthesized using flexible tetra-carboxylate ligand tetrakis(4-carboxyphenoxymethyl)methane (H4TCM). The structures of JOU-32 and JOU-33 were well characterized by single-crystal X-ray diffraction. It is shown that JOU-32 reveals a rare example of interpenetrating MOF with two different networks disorderedly distributed within the same crystal. JOU-33 is a (4,8)-connected flu topological structure based on [Cd4(COO)8(DMF)2] cluster. The fluorescent properties for both JOU-32 and JOU-33 have also been tested. The average life times for JOU-32 and JOU-33 were detected to be 2.39 and 2.42 ns, respectively. In addition, both JOU-32 and JOU-33 can be utilized as fluorescent probes for detection of NB. This work provides valuable clues for preparing new fluorescent MOFs with attractive structures.

Assembly of zeolite-like anionic indium-organic frameworks based on flexible tetra-carboxylate ligands for organic dyes separation

Zeolite-like metal-organic frameworks (ZMOFs) have attracted a great attention because of their special performances in adsorption and separation. It is still of significant to synthesize new ZMOFs with attractive structural features. In this work, two new anionic MOFs, namely [(Me2)NH2]·[In(TCM)]·4DMF (JOU-13), and [(Me2)NH2]·[In(TCM)]·DMF (JOU-14), have been successfully synthesized based on [In(COO)4]- units and flexible tetra-carboxylate ligand (H4TCM = Tetrakis(4-carboxyphenoxymethyl)methane). The structures of JOU-13 and JOU-14 were well characterized by single-crystal X-ray diffraction. It is shown that JOU-13 represents a rare example of interpenetrating framework with gis topology, while JOU-14 is a (4,4)-connected dia topological structure. Notably, JOU-13, owning to its porous and anionic skeleton, exhibits outstanding performance in selectively adsorbing and separating cationic dye methylene blue, displaying reversible capabilities in dye adsorption and release. This work provides valuable clues for preparing new anionic zeolite-like MOFs with special properties.

Selective Xenon Recovery Using Aluminum-Based Metal-Organic Frameworks with Conserved Pore Topology.

Xenon (Xe) is a commercially valuable element found in trace amounts in the off-gas from used nuclear fuel. Recovering Xe from these streams provides a cost-effective means to increase its supply. However, achieving high-purity Xe recovery is challenging due to the need for separation from nearly identical krypton (Kr). Metal-organic frameworks (MOFs), a class of crystalline porous materials, show potential to separate Xe and Kr by utilizing differences in their kinetic diameters, allowing for selective separation. In this work, we study the impact of pore aperture and volume on selective Xe recovery using four robust aluminum MOFs: Al-PMOF, Al-PyrMOF, Al-BMOF and MIL-120, all with conserved structural topology. The pore topology in each MOF is dictated by the dimensions of the tetracarboxylate ligand employed, with larger ligands leading to MOFs with increased pore size and volume. Our experimental and computational investigations revealed that MIL-120 exhibits the highest affinity (21.94 kH(Xe) = 21.94 mmol g-1 bar-1) for Xe among all MOFs, while Al-BMOF demonstrates the highest Xe/Kr selectivity of 14.34. We evaluated the potential of both MIL-120 and Al-BMOF for Xe recovery through breakthrough analysis using a mixture of 400 ppm Xe:40 ppm Kr. Our results indicate that due to its larger pore volume, Al-BMOF captured more Xe than MIL-120, demonstrating superior Xe/Kr separation efficiency.

A multifunctional Er-MOF for Methylene Blue adsorption and CO2 cycloaddition catalysis

With the acceleration of industrialization and energy consumption, global concerns for the safety of ecological system and sequent human health have attracted consideration attention increasingly in view of the severe contamination both in aqueous environment and aerosphere. Therefore, the development of multifunctional species for efficient adsorption of pollutants and chemical fixation of CO2 receives increasing attention. Herein, an anionic ErIII metal organic framework (Er-MOF) with large hexagonal channels, is obtained based on a benzene-spaced tetracarboxylate ligand, H4L (H4L = 1,4-bis(2′,2′′,6′,6′′-tetracarboxy-1,4′:4,4′′-pyridyl) benzene). Adsorption analysis indicates that Er-MOF behaves as an excellent adsorbent for selectively absorbing MB in water with a maximum adsorption capacity of 494.1 mg·g‒1. The adsorption mechanism could be a combination of size matching, electrostatic interaction, π···π stacking and hydrogen bonding. In addition, Er-MOF is demonstrated to be an efficient catalyst in the cycloaddition of CO2 with epoxides under mild conditions due to its excellent stability, substantial specific surface area, confined space and well-exposed Lewis acid/base sites. The findings presented herein had great significance for enriching the multifunctional lanthanide MOFs in environmental applications.

New Mn-CP as a multi-responsive fluorescent probe for ratiometric sensing toward ascorbic acid and turn-off sensing toward nitrofurazone and acetylacetone

The abuse of environmental and biological related molecules, such as small biomolecules, pharmaceutical antibiotics and volatile organic chemicals has become a hotspot issue of global concern. Thus, exploring accurate and effective techniques for monitoring these species remains a major challenge. Here, by employing semi-rigid tetracarboxylate ligand H4edda, one new 2D Mn-based coordination polymer with formula of [Mn2(edda)(phen)2(H2O)2]n (Mn-CP; H4edda = 5,5′-(ethane-1,2-diylbis(oxy)) diisophthalic acid); phen = 1,10-phenanthroline) has been hydrothermally fabricated. The prepared Mn-CP possesses a sql topology with Schläfli symbol of (44·62). Stability research for Mn-CP reveals that it maintains structural stability and initial fluorescence intensity after soaking in water for one week. Moreover, Mn-CP also displays high structural stability in acidic-basic aqueous solution of broad pH scope (1–13) for 48 h. Importantly, photoluminescence measurements indicate that it shows ratiometric fluorescence response to ascorbic acid (AA) as well as turn-off response toward nitrofurazone (NFZ) and acetylacetone (ACAC). The developed fluorescence probe based on Mn-CP shows merits of high selectivity and low detection limits (33.67 nM, 1.43 nM and 2.29 μM for AA, NFZ and ACAC, respectively). The possible mechanisms have been thoroughly explored through exhaustive experimental surveys and theories calculations. The CP-based multi-responsive fluorescent probe designed in this work extends the application of such materials in environmental and biological related fields.

Aromatimide tetracarboxylate metal-framework materials: Fluorescence sensing application towards NACs and small drug molecules

Three multifunctional fluorescent Metal-Organic Framework (MOF) sensors are synthesized based on N, N’-bis(3, 5-dicarboxyphenyl)isophthalic diimide (H4BDCPPI) with Zn, Cu, and Cd ions. Structural analysis shows that although using the same organic conjugated aromatic imide tetracarboxylic acids ligand, their corresponding structures are different. Based on luminescence characteristics of the organic components, they exhibit good luminescent properties. They can sensitively detect nitro aromatic compounds (p-nitrophenol (PNP), 2,4-dinitrophenol (DNP) and 2,4,6-trinitrophenol (TNP)) and small drug molecules (colchicine and balsalazide disodium) with low limit of detection. The complex 1 is more sensitive for detection of TNP, compared to the other complexes. The mechanism of fluorescence sensing is proposed in detail based on analyses of PXRD, fluorescence lifetimes, and UV–vis spectra. This study explores the potential of MOFs based on H4BDCPPI in the field of fluorescence sensing for the first time, laying the theoretical foundation for application of complexes with conjugated aromatic imide tetracarboxylic acids.

A stable Zr(IV)-MOF for efficient removal of trace SO2 from flue gas in dry and humid conditions

Obtaining suitable adsorbents for selective separation of SO2 from flue gas still remains an important issue. A stable Zr(IV)-MOF (Zr-PTBA) can be conveniently synthesized through the self-assembly of a tetracarboxylic acid ligand (H4L = 4,4',4'',4'''-(1,4-phenylenebis(azanetriyl))tetrabenzoic acid) and ZrCl4 in the presence of trace water. It exhibits a three-dimensional porous structure. The BET surface area is 1112.72 m2/g and the average pore size distribution focus on 5.9, 8.0 and 9.3 Å. Interestingly, Zr-PTBA shows selective adsorption of SO2. The maximum uptake reaches 223.21 cm3/g at ambient condition. While it exhibits lower adsorption uptake of CO2 (30.50 cm3/g) and hardly adsorbs O2 (2.57 cm3/g) and N2 (1.31 cm3/g). Higher IAST selectivities of SO2/CO2 (21.9), SO2/N2 (912.7), SO2/O2 (2269.9) and SO2/CH4 (85.0) have been obtained, which reveal its’ excellent gas separation performance. Breakthrough experiment further confirms its application for flue gas deep desulfurization both in dry and humid conditions. Furthermore, the gas adsorption results and mechanisms have also been studied by theoretical calculations.

High adsorption of ammonia in a titanium-based metal-organic framework.

We report the high adsorption of NH3 in a titanium-based metal-organic framework, MFM-300(Ti), comprising extended [TiO6]∞ chains linked by biphenyl-3,3',5,5'-tetracarboxylate ligands. At 273 K and 1 bar, MFM-300(Ti) shows an exceptional NH3 uptake of 23.4 mmol g-1 with a record-high packing density of 0.84 g cm-3. Dynamic breakthrough experiments confirm the excellent uptake and separation of NH3 at low concentration (1000 ppm). The combination of in situ neutron powder diffraction and spectroscopic studies reveal strong, yet reversible binding interactions of NH3 to the framework oxygen sites.

Structural diversity and solvent-induced transformations of a copper-based metal-organic framework with highly aromatic ligands.

A newly designed tetracarboxylic acid ligand precursor 5,5'-([9,9'-bianthracene]-10,10'-diyl)diisophthalic acid (H4BADI) has been used to prepare a series of copper-based metal-organic frameworks (MOFs) with the formula [Cu2(BADI)(S)2]·xS (denoted as 1-S, where S = solvent) and exhibiting solvent-induced structural transformations. Single-crystal-to-single-crystal transformation occurs upon exchanging 1-DMF (DMF = N,N-dimethylformamide) with DMSO (DMSO = dimethylsulfoxide). 1-DMF exhibits reversible structural transformation upon treatment with a variety of solvents; of particular interest is the reversible crystalline-to-amorphous phase transformations observed upon exchange with volatile, polar solvents. A thorough structural investigation of the three framework isomers characterized via single-crystal X-ray diffraction experiments is reported and compared to several other tetracarboxylate-based MOFs composed of dimetal secondary building units.

Effects of solvents and metal ions on the synthesis, structural diversity and magnetic properties of the 5′-nitro-[1,1′:3′,1′′-terphenyl]-3,3′′,5,5′′-tetracarboxylic acid ligand and a highly sensitive sensor for Fe3+

Solvents and metal ions play an important role in the construction of metal–organic frameworks (MOFs).

A 3D photoluminescent Eu(iii)-MOF sensor supported by a tetracarboxylate ligand for the sensitive and selective detection of Cd2+ and o-nitrophenol

A novel 3D luminescent metal–organic framework (MOF) denoted as [Eu(BTA)0.5(H2BTA)0.5(H2O)]n (Cj-2) has been constructed from a π-conjugated ligand with a tetracarboxylate group, 1,2,4,5-benzenetetracarboxylic acid (BTA), via solvothermal synthesis.

Fabrication, Crystal Structures, Catalytic, and Anti-Wear Performance of 3D Zinc(II) and Cadmium(II) Coordination Polymers Based on an Ether-Bridged Tetracarboxylate Ligand

Two 3D Zn(II) and Cd(II) coordination polymers, [Zn2(µ4-dppa)(µ-dpe)(µ-H2O)]n·nH2O (1) and [Cd2(µ8-dppa)(µ-dpe)(H2O)]n (2), have been constructed hydrothermally using 4-(3,5-dicarboxyphenoxy)phthalic acid (H4dppa), 1,2-di(4-pyridyl)ethylene (dpe), and zinc or cadmium chlorides. Both compounds feature 3D network structures. Their structure and topology, thermal stability, catalytic, and anti-wear properties were investigated. Particularly, excellent catalytic performance was displayed by zinc(II)-polymer 1 in the Knoevenagel condensation reaction at room temperature.

Multi-responsive fluorescent sensitivities of a novel 2D Cu-CP with visual turn-off sensing toward nitrofuran antibiotics, Cr(VI) and MnO4− in aqueous solutions

Herein, a novel fluorescent coordination polymer [Cu2(edda)(bpy)2]·6H2O (Cu-CP; H4edda = 5,5′-(ethane-1,2-diylbis(oxy)) diisophthalic acid; bpy = 2,2′-bipyridine) was designed and successfully architected using semi-rigid tetracarboxylic acid ligand H4edda combined with N,N′-donor linker bpy through a hydrothermal method. Single-crystal structural analysis reveals that the adjacent Cu1 centers are linked by 3′- and 5- carboxyl groups of edda4− linker to form a one-dimensional Cu(II)-edda4− chain, which is further strutted by 3- and 5′- carboxyl groups in edda4− ligand to generate a two-dimensional (2D) network with sql topology. Notably, bpy molecules do not actually dedicate to the formation of this 2D network, which merely saturate the configuration of Cu ions. Apart from the great thermal and acid/base stabilities, the π-conjugated nature of H4edda endows Cu-CP with the traits of strong fluorescent emission in both solid state and aqueous solution. Interestingly, Cu-CP can act as a multifunctional platform for effectively detecting nitrofurazone (NFZ), nitrofurantoin (NFT), Cr2O72−, CrO42− and MnO4− via fluorescence quenching effects in an aqueous system. The fabricated Cu-CP fluorescent sensor shows distinguished sensitivity and anti-interference performance as well as low detection limits (3.55 nM for NFZ; 1.02 nM for NFT; 0.58 μM for Cr2O72−, 0.68 μM for CrO42− and 4.59 μM for MnO4−). The underlying quenching mechanisms have been studied through in-depth experimental and computational researches.

A pH-Stable Tb-MOF as Luminescence Sensor for Highly Sensitive Detection of Amino Acids through Diverse Sensing Mechanism.

A luminescent Tb-MOF with excellent stability and dual-emitting properties was constructed with an amide-functionalized tetracarboxylate ligand. Tb-MOFs were initially assembled on one-dimensional Tb3+ chains, then formed a two-dimensional double-decker layer through the synergistic linking of organic ligands and bridging formic acid anions, and further fabricated the final three-dimensional structure through the connection of the organic ligands. Powder X-ray diffraction experiments revealed that Tb-MOFs not only exhibited excellent stability in water but also maintained structural integrity in the pH range of 2-12. Importantly, this Tb-MOF provided the first example of a metal-organic framework (MOF)-based luminescence sensor that can simultaneously detect two acid amino acids (aspartic and glutamic acids) through a turn-off sensing mechanism and two basic amino acids (lysine and arginine acids) through unusual turn-on and turn-off-on sensing mechanisms. Moreover, high sensitivity, low detection limit, and excellent recyclability of this sensor endow Tb-MOFs with great potential as a highly efficient amino acid fluorescence sensor in chemical detection and biological environments.

An anionic In(III)-MOF for efficient adsorption of CO2 from CO2/N2 mixture and dye removal

Efficient adsorption of CO2 and dye molecules is crucial for reducing carbon emission and environmental pollution. Metal-Organic Frameworks (MOFs) are considered to be the ideal candidates for gas adsorption material because of their designability. In this work, a new In(III)-MOF (HBU-22) was synthesized by the reaction of a tetracarboxylic acid ligand (H4L, 9,9′-bicarbazole-3,3′,6,6′-tetracarboxylic acid) with In3+ ions, which shows a three-dimensional (3D) coordination network. The saturated adsorption capacity of CO2 and N2 are 21.11 cm3‧g−1 and 0.66 cm3‧g−1 at ambient condition (298 K, 100 kPa). And the higher IAST selectivity of CO2/N2 (v/v, 15:85) reaches 347.37, exceeding that of most MOFs. Furthermore, it can also capture C2H2 with the maximum uptake of 42.80 cm3 g−1. More interestingly, HBU-22 as an anionic framework, which can selectively adsorb Rhodamine B (RhB) within 250 s with the maximum adsorption capacity of 105.04 mg‧g−1. Further studies show that higher gas adsorption capacity is mainly related to the larger Qst of the gas, while its adsorption of Rhodamine B (RhB) is mainly due to ion exchange mechanism.

A zinc coordination compound showing green photoluminescence

Abstract A novel three-dimensional coordination compound has been solvothermally synthesized based on a tetracarboxylate ligand H4L (H4L = 1,3,6,8-tetrakis(4-carboxylphenyl)pyrene), Zn2L(H2O)2·2DEF (1) (DEF = N,N′-diethylformamide). Each Zn ion is coordinated by four carboxylate oxygen atoms from four L4− ligands and one oxygen atom from a water molecule to provide a distorted square-pyramidal geometry. Pairs of adjacent Zn cations are bridged by four carboxylate groups of four different L4− ligands to generate a paddle-wheel [Zn2(COO)4(H2O)2] secondary building unit (SBU). Each SUB is further linked to four L4− ligands to give a three-dimensional framework with cds-type (CdSO4-type) topology. The crystal structure has been determined via single-crystal X-ray diffraction, and the compound was characterized by elemental and thermal analysis, infrared spectroscopy, powder X-ray diffraction, and solid-state photoluminescence measurements.

Triazine‐based multicomponent metallacages with tunable structures for SO2 selective capture and conversion

AbstractThe design of novel materials for sulfur dioxide (SO2) capture and conversion with considerable efficiency under mild conditions is of great significance for human health and environmental protection yet highly challenging. Herein, we report a series of triazine‐based multicomponent metallacages via coordination‐driven self‐assembly of 2,4,6‐tri(4‐pyridyl)‐1,3,5‐triazine, cis‐Pt(PEt3)2(OTf)2 and different tetracarboxylic ligands. As the increase of the length of the tetracarboxylates, the structures of the metallacages change from pyramids to extended octahedrons. Owing to their N‐rich structure, these metallacages are further used for selective SO2 capture, showing good adsorption capacity and remarkable SO2/CO2 selectivity in ambient conditions, suggesting their potential applications toward real flue gas desulfurization. The metallacages are further employed for the conversion of SO2 into value‐added compounds, showing exceptional efficiency even dilute SO2 is used as the reactant. This study represents a type of structure‐tunable triazine‐based metallacages for SO2 capture and conversion, which will pave the way on the applications of metal‐organic complexes for gas adsorption.