Tetracarboxylate Ligand Research Articles

Crystal engineering of coordination polymers using flexible tetracarboxylate linkers with embedded cyclohexyldiamine cores

Flexible amine-functionalised tetracarboxylate ligands with different length arms generate a large variety of coordination polymers which notably lack topological consistency.

Highly Stable Zr(IV)-Based Metal-Organic Frameworks for Chiral Separation in Reversed-Phase Liquid Chromatography.

Separation of racemic mixtures is of great importance and interest in chemistry and pharmacology. Porous materials including metal-organic frameworks (MOFs) have been widely explored as chiral stationary phases (CSPs) in chiral resolution. However, it remains a challenge to develop new CSPs for reversed-phase high-performance liquid chromatography (RP-HPLC), which is the most popular chromatographic mode and accounts for over 90% of all separations. Here we demonstrated for the first time that highly stable Zr-based MOFs can be efficient CSPs for RP-HPLC. By elaborately designing and synthesizing three tetracarboxylate ligands of enantiopure 1,1'-biphenyl-20-crown-6, we prepared three chiral porous Zr(IV)-MOFs with the framework formula [Zr6O4(OH)8(H2O)4(L)2]. They share the same flu topological structure but channels of different sizes and display excellent tolerance to water, acid, and base. Chiral crown ether moieties are periodically aligned within the framework channels, allowing for stereoselective recognition of guest molecules via supramolecular interactions. Under acidic aqueous eluent conditions, the Zr-MOF-packed HPLC columns provide high resolution, selectivity, and durability for the separation of a variety of model racemates, including unprotected and protected amino acids and N-containing drugs, which are comparable to or even superior to several commercial chiral columns for HPLC separation. DFT calculations suggest that the Zr-MOF provides a confined microenvironment for chiral crown ethers that dictates the separation selectivity.

Topological Strain-Induced Regioselective Linker Elimination in a Chiral Zr(IV)-Based Metal-Organic Framework

Summary Zr-carboxylate metal-organic frameworks (MOFs) are structurally robust materials, in part due to their strong coordination bonds. The regioselective Zr–O bond cleavage and formation between 3D architectures are thus challenging and are heretofore unexplored. In this work, by introducing highly flexible 18-crown-6-ether functionalities into a homochiral Zr-MOF, we report an unprecedented topology transition in which a 4,10-connected framework undergoes a rapid solid-state transition into a thermodynamically more stable 4,8-connected analog by a regioselective-linker-elimination under ambient conditions. The transition process was unambiguously unraveled by single-crystal and powder X-ray diffraction studies, and we proposed a possible transition mechanism based on various control experiments and theoretical calculations. The excellent chemical stability and substantially expanded porosity and pore apertures endowed the transformed chiral MOF with an exceptional capacity for the enantioadsorptive and solid-phase extractive separation of the racemic drug molecule of lansoprazole with 98% ee and 93% ee, respectively.

A porous Eu(III)-containing MOF: selective detection of Cr2O72– and treatment activity on the uterine fibroids by reducing TGF-β production and mmp expression

Metal–organic frameworks (MOFs) composed of metal ions and organic ligands via the coordination bonds have evolved as an emerging class of functional materials showing promising applications in the fluorescent detection and biomedicine, however, seldom reports combine the two properties in one type of MOF-based materials. Herein, a novel metal–organic framework (MOF) material containing Eu(III) of {[Eu(HL)(H2O)](DMF)3(H2O)4}n (1) based on 9-(2,6-dicarboxy-pyridin-4-yl)-9H-carbazole-3,6-dicarboxylic acid (H4L), a tetracarboxylic ligand, has been prepared under the solvothermal conditions. Furthermore, this Eu-MOF reflects strong red luminescence and outstanding water stability, which in-depth demonstrate it is a kind of luminescent sensor with highly sensitive and selective for the Cr2O72–, and it possesses low limit of detection and high coefficient of quenching. More importantly, complex 1 could be reused at least for fives without loss of the detection performance and framework integrity, which is quite rare among MOF-based sensors for Cr2O72–. In addition, the treatment effect of compound against the uterine fibroids was assessed in biological research. The detection of enzyme linked immunosorbent assay (ELISA) was firstly conducted to determine the transforming growth factor-β (TGF-β) content levels produced by the endometrial cells. Next, the mmp7 and mmp3 relative expression levels in the endometrial cells were detected via the real time reverse transcription-polymerase chain reaction (RT-PCR) method.

Cu(II)-based coordination polymers: treatment activity on Takayasu’s arteritis via regulating protein-arginine deiminase content

By applying a mixed-ligand approach, two Cu(II) coordination polymers, [Cu2(μ3-deta)(H2biim)3(H2O)2]n (1, H2biim = 2,2΄-biimidazole) and {[Cu2(μ4-deta)(phen)2(H2O)]·H2O}n (2, phen = 1,10-phenanthroline), were formed by mixing Cu(NO3)2·3H2O with ether-bridged tetracarboxylic acid ligand 2,3,3΄,4΄-diphenyl ether tetracarboxylic acid (H4deta) with N-donor ligands. The biological features of 1 and 2 were further evaluated on Takayasu's arteritis (TA). The human protein-arginine deiminase (PAD) content in the plasma was detected by ELISA detection equipment. The sensitization of the inflammatory signaling channel of vascular endothelial cells was measured via real time RT-PCR.

Synthesis, characterization and spectral properties of novel azo-azomethine-tetracarboxylic Schiff base ligand and its Co(II), Ni(II), Cu(II) and Pd(II) complexes

Novel tetracarboxylic Schiff-base ligand, namely 5,5′-((1E,1′E)-(((1E,1′E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(4-hydroxy-3,1-phenylene))bis(diazene-2,1-diyl)) diisophthalic acid (L2) was prepared by the condensation reaction of ethane-1,2-diamine with 4-((3-formyl-4-hydoxyphenyl)diazenyl) isophthalic acid (L1) in anhydrous ethanol. A prepared organic compound is potential N,O-multidentate chelating ligand, which forms stable complexes with metal(II) ions in 1:1 up to 1:5 M ratio of the metal to ligand. Its reactions with corresponding nitrate salts have synthesized the complexes of L2 with Co(II) (1), Ni(II) (2), Cu(II) (3) and Pd(II) (4) ions. The prepared dye and its metal-containing complexes were investigated by the combination of elemental and ICP-MS analyses, infrared spectroscopy, thermal analysis, powder X-ray diffraction, 1H and 13C NMR and UV/VIS spectroscopy. UV/VIS titration measurements showed the stable formation of 1:1 Schiff-based complexes with four free carboxylic groups. Prepared metal-containing complexes are suitable linkers for metal–organic frameworks preparation with promising applications in gas storage and heterogeneous redox-catalysis.

Tuning the Atrazine Binding Sites in an Indium-Based Flexible Metal-Organic Framework.

Constructing flexible metal-organic frameworks (MOFs) with targeted properties is of high interest given their demonstrated potential as smart materials that undergo structural transformations in response to external stimuli. Herein, we report a flexible and interpenetrated indium-based MOF, NU-50, comprising four-connected [In(CO2)4]- nodes and tetracarboxylate pyrene-based ligands assembled in the pts topology. The flexible framework of NU-50 exhibits intricate structural transformations upon exposure to external stimuli, namely, guest solvent molecules and elevated temperatures. The high density of pyrene moieties throughout the interpenetrated framework offers numerous sites for the adsorption of highly conjugated guest molecules such as atrazine via π-π interactions. As a result, NU-50 efficiently removes atrazine from water, achieving a maximum atrazine uptake capacity of 74 mg of atrazine per gram of NU-50. Molecular simulations reveal that the dynamic behavior of NU-50 involves the distortion of metal-ligand bonds, resulting in a narrow pore structure that affords effective adsorption of atrazine molecules in a sandwich-like geometry. Moreover, washing in acetone quickly regenerates the sorbent.

A robust indium(III)−potassium(I) MOF with high CO2/C2- hydrocarbons over CH4 separation performance

A heterometallic MOF, [NH2(Me)2]5[K3In8L8(H2O)6]·13DMA·12H2O (1), has been synthesized under solvothermal conditions by employing a pyridyl-decorated tetracarboxylate ligand, 2,2′-(pyridine-2,5-diyl)diterephthalic acid (H4L). Structural analysis demonstrates that 1 is a 3D microporous framework based on three kinds of inorganic secondary building units (SBUs), which shows an unprecedented 5-nodal (3,4,4,7,7)-connected topology. Especially, 1 possesses high chemical stability in pH ​= ​2–13 aqueous solutions. The desolvated structure of 1 contains a highly polar pore system decorated with open metal sites, diethylammonium cations, and free pyridine atoms, leading to a high CO2/C2-hydrocarbons over CH4 separation performance.

RETRACTED: Two Co(II)-based metal-organic frameworks: Catalytic Knoevenagel condensation reactions and inhibitory activity on the scar tissue hyperplasia by reducing the activity of the VEGF signaling pathway

Abstract In the current research, two porous Co(II)-containing metal–organic frameworks (MOFs) whose chemical formulae can be teamed as [Co2(bptc)(H2O)2]·5DMA (1, H4bptc = biphenyl-3,3′,5,5′-tetracarboxylic acid) and [Co2(Hatta)2·(H2O)3]·3DMA (2, H4atta = 2′-amino-[1,1′:4′,1″-terphenyl]-3,3″,5,5″- tetracarboxylic acid) have been solvothermally synthesized by using two similar tetracarboxylic ligands and structurally characterized. The complex 2 with amino-functionalized pores could be used as recoverable heterogeneous catalytic agent for Knoevenagel condensation without solvents. The inhibitory activity of compounds on the scar tissue hyperplasia was evaluated and the related mechanism was discussed as well. First of all, the proliferation of the human hypertrophic scar fibroblasts was measured after indicated treatment was measured by CCK-8 assay. Next, the real time RT-PCR was applied to determine the activation power of the VEGF signaling pathway after using compounds.

Structural diversity and photocatalytic properties of two new coordination polymers based on a semi-rigid tetracarboxylate ligand

The self-assemble of flexible ligand 5,5ˊ-(4,4ˊ-phenylenebis(methyleneoxy)) diisophthalic acid (H4L) and N-donor ligands with the different molecular size, 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (bpz) and 1,10-phenanthroline (phen), has generated two new coordination polymers, [Co(L)0.5(bpz)·2.5H2O]n (1) and [Mn(H2L)(phen)]n (2). 1 has a 3D twofold interpenetrated 2-nodal 4,4-c network with a Schläfli symbol of (64.82)(66)2 topology, while 2 exhibits a 2-D grid net, which is further afforded 3D supramolecular motif through π ̶ π interactions with 3.65 Å between adjacent phen linkers. The influences of various N-donor ligands in assembly of flexible polymers accompany with H4L are also summarized. Photocatalytic studies show that 1 and 2 exhibits efficient degradation activity of organic dye methyl violet (MV). Meanwhile, the possible mechanism of the photocatalytic property has been deduced.

A novel three-dimensional tetranuclear CoII coordination polymer with water hexamers based on the V-shaped tetracarboxylate ligand 4-(2,4-dicarboxylatophenoxy)phthalate.

A new coordination polymer (CP), namely, poly[[diaquatris[μ2-1,4-bis(1H-imidazol-1-yl)benzene]bis[μ6-4-(2,4-dicarboxylatophenoxy)phthalato]tetracobalt(II)] hexahydrate], {[Co4(C16H6O9)2(C12H10N4)3(H2O)2]·6H2O}n, has been synthesized by solvothermal reaction. The CP was fully characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, and powder and single-crystal X-ray diffraction. It presents a three-dimensional (3D) structure based on tetranuclear CoII secondary building units (SBUs) with a tfz-d net and point symbol (43)2(46·618·84). The 4-(2,4-dicarboxyphenoxy)phthalic acid (H4dcppa) ligands are completely deprotonated and link {Co4(COO)4}4- SBUs into two-dimensional (2D) layers. Furthermore, adjacent layers are connected by 1,4-bis(1H-imidazol-1-yl)benzene (bib) ligands, giving rise to a 3D supramolecular architecture. Interestingly, there are numerous elliptical cavities in the CP where isolated unique discrete hexameric water clusters have been observed. The results of thermogravimetric and magnetic analyses are described in detail.

Two New Tetranuclear Cluster‐based Coordination Polymers based on Isomorphic Semi‐rigid Tetracarboxylate Ligands: Syntheses, Structures, and Luminescent Properties

Two new tetranuclear cluster‐based compounds, namely [Cd2(L1)(H2O)(DMA)]n (1) and [Cd2Ba2(L2)(H2O)6(DMA)]n (2) [H4L1 = 3‐(3',5'‐dicarboxylphenoxy) phthalic acid, H4L2 = 6‐(3',4'‐dicarboxyl‐phenoxy) isophthalic acid, DMA = N,N'‐dimethylacetamide], were successfully synthesized under solvothermal conditions and structurally characterized by single‐crystal X‐ray diffraction analyses. Compound 1 features a two‐dimensional (2D) layered framework with tetranuclear [Cd4(COO)6] clusters as building subunits, and can be simplified into a binodal (3, 6)‐connected kgd topological network with the schläfli symbol of {43}2{46;66;83}, and compound 2 features a three‐dimensional (3D) complicated framework based on heterometallic tetranulear [Cd2Ba2(COO)8] cluster subunits, and can be simplified into a binodal (3, 6)‐connected topological network. In addition, compounds 1 and 2 not only have high thermal stabilities but also show strong luminescent emissions at room temperature.

Metal‐Organic Framework Based on an Anthracene Tetracarboxylate Ligand and Cadmium or Cobalt: Synthesis, Structure Analysis, Stability and Magnetic Properties

AbstractMetal‐organic frameworks, a class of porous polymeric materials, are presenting a development on the interface between molecular coordination chemistry and materials science and are becoming one of the hottest research topics in chemistry. Two new metal‐organic frameworks, [M’2{Co3(ACTBA)2}]n (1; M’=monocation) and [(NH2Et2)2{Cd3(ACTBA)2}]n (2) (H4ACTBA=2,6,9,10‐tetrakis(p‐carboxyphenyl)anthracene), composed of trinuclear Co or Cd moieties connected by anthracene tetracarboxylate ligands are presented here, which are highly stable on removal of solvent inside the pores. The synthesis, X‐ray structure analysis, NMR spectroscopy (for 2), chemical and thermal stability, and magnetic properties (for 1) are discussed.

Ratiometric fluorescence temperature sensing based on single- and dual-lanthanide metal-organic frameworks

The ever increasing demand for fast, noninvasive, and accurate determination of temperature at the submicrometer spatial regime, particularly in microelectronic diagnostics, is driving the development of ratiometric temperature probes. In this work, we present two types of self-calibrating metal-organic framework (MOF) thermometers with both the organic chromophore and lanthanide emissions, which proposed an elegant avenue to address these concerns. By employing the symmetric tetracarboxylate ligand [1,1':4′,1″-Terphenyl]-3,3″,5,5″-tetracarboxylic acid, we synthesized and investigated single- and dual-lanthanide MOFs, TbTPTC and GdxEu1-xTPTC, in terms of their temperature dependent luminescence. Based on the energy-back transfer of lanthanide ion to ligand, the intensity ratio between the ligand and lanthanide of both the single- and dual-lanthanide MOF systems exhibits distinctly exponential response to temperatures in the range of 313–473 K. Given their good relative sensitivities, accurate temperature resolution, and excellent repeatability, as well as sensitivity to color change, the proposed dual-emitting MOF materials can be useful for thermal mapping and hot-spot monitoring of microelectronic devices.

Two ZnII-based MOFs constructed with biphenyl-2,2′,5,5′-tetracarboxylic acid and flexible N-donor ligands: syntheses, structures and properties

Two new Zn2+-based metal-organic frameworks (MOFs) based on biphenyl-2,2',5,5'-tetracarboxylic acid, i.e. H4(o,m-bpta), and N-donor ligands, namely, poly[[(μ4-biphenyl-2,2',5,5'-tetracarboxylato)bis{[1,3-phenylenebis(methylene)]bis(1H-imidazole)}dizinc(II)] dimethylformamide monosolvate dihydrate], {[Zn2(C16H6O8)(C14H14N4)2]·C3H7NO·2H2O}n or {[Zn2(o,m-bpta)(1,3-bimb)2]·C3H7NO·2H2O}n (1) {1,3-bimb = [1,3-phenylenebis(methylene)]bis(1H-imidazole)}, and poly[[(μ4-biphenyl-2,2',5,5'-tetracarboxylato)bis{[1,4-phenylenebis(methylene)]bis(1H-imidazole)}dizinc(II)] monohydrate], {[Zn2(C16H6O8)(C14H14N4)2]·H2O}n or {[Zn2(o,m-bpta)(1,4-bimb)2]·H2O}n (2) {1,4-bimb = [1,4-phenylenebis(methylene)]bis(1H-imidazole)}, have been synthesized under solvothermal conditions. The complexes were characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction and powder X-ray diffraction analysis. Structurally, the (o,m-bpta)4- ligands are fully deprotonated and combine with Zn2+ ions in μ4-coordination modes. Complex 1 is a (3,4)-connected porous network with honeycomb-like [Zn2(o,m-bpta)]n sheets formed by 4-connected (o,m-bpta)4- ligands. Complex 2 exhibits a (2,4)-connected network formed by 4-connected (o,m-bpta)4- ligands linking Zn2+ ions in left-handed helical chains. The cis-configured 1,3-bimb and 1,4-bimb ligands bridge Zn2+ ions to form multi-membered [Zn2(bimb)2] loops. Optically, the complexes show strong fluorescence and display larger red shifts compared to free H4(o,m-bpta). Complex 2 shows ferroelectric properties due to crystallizing in the C2v polar point group.

Syntheses, Crystal Structure, and Magnetic Property of a New Mn(II) Complex with an Aromatic N-heterocyclic Tetracarboxylic Acid Ligand

A new 2D Mn(II) complex named as [Mn3(HL)2(H2O)6]n (I) (H4L = 3-(2,4-dicarboxyphenyl)-2,6-dicarboxypyridine) was synthesized and characterized by IR, elemental analysis, and single-crystal X-ray diffraction method (CIF file CCDC no. 1915189). The complex crystallizes in the monoclinic space group C2/c with Z = 4, a = 20.6597(11), b = 9.0949(5), c = 20.6041(12) A, β = 110.056(6)°. The crystal consists of trinuclear Mn(II) ion clusters {Mn3} which are linked by four independent HL3– ligands and these trimeric units are connected into 2D structure by pentadentate HL3– ligand in alternate bis(bridging) and chelated coordination modes. Thermogravimetry, powder X-ray diffraction, and magnetic measurement experiments are also carried out to determinethe thermal stability, phase purity and magnetism. The results show that weak antiferromagnetic interactions occur between the Mn(II) centers within bridging trinuclear {Mn3} cluster.

Two Robust In(III)-Based Metal-Organic Frameworks with Higher Gas Separation, Efficient Carbon Dioxide Conversion, and Rapid Detection of Antibiotics.

With the aid of a pyridyl tetracarboxylate ligand, 2,5-bis(2',5'-dicarboxylphenyl)pyridine (H4L), two indium-organic frameworks, [In2(L)(OH)2]·2DMF·2H2O (1) and [Me2NH2][In(L)]·2.5NMF·4H2O (2), with (6,8)- and (4,4)-connected nets have been constructed in different solvent systems. Both 1 and 2 exhibit high thermal and chemical stability. Gas sorption behavior of 1 and 2 for N2, C2H2, C2H4, CO2, and CH4 indicate excellent separation selectivities of C2Hx/CH4 and CO2/CH4. Furthermore, 1 possesses a high density of Brønsted sites and shows efficient catalytic conversion for CO2 cycloaddition with epoxides. Meanwhile, luminescence investigations reveal that 2 can detect nitrofurazone efficiently.

Improving the Stability and Visualizing the Structural Transformation of the Stimuli-Responsive Metal-Organic Frameworks (MOFs).

New metal-organic frameworks (MOFs) based on flexible tetra-carboxylate ligands and Cu(II) are designed to gain stimuli-responsive materials. Unstable MOFs can be more stable with unabated flexibility by replacing coordinated solvent molecules with auxiliary N-based ligands. Two of them are intensively studied by in situ single-crystal X-ray diffraction (SCXRD) analysis and the unit cell parameters during transformations have been observed in detail. They undergo exceptional structural transformations which can be divided into two processes: the thermal-responsive phase transition and the solvent-responsive phase transition. The thermal-responsive phase transition takes place in a narrow temperature interval reversibly. However, the solvent-responsive phase transition is a gradual and irreversible process. The stimuli-responsive mechanism has also been explored by comparing the parameters of the crystal structures under different temperatures. Fascinatingly, their exceptional structural transformations correlate with the flexibility of the ligand fragments and the [Cu2(RCOO)4] clusters.

A Highly Stable Triazole-Functionalized Metal-Organic Framework Integrated with Exposed Metal Sites for Selective CO2 Capture and Conversion.

A new triazole-functionalized tetracarboxylic acid ligand (H4 L) 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.

Two New Coordination Polymers with UO22+ Units and Fluorinated Aromatic Carboxylate Linkers

A new coordination polymer, namely 2∞[(UVIO2)2(L)(DMA)3] (1) (C2/c, Z = 8) with L = 4‐monofluorobiphenyl‐3,3',5,5'‐tetracarboxylate (4‐mF‐BPTC4–) was synthesized by solvothermal reaction in DMA (N,N'‐dimethylacetamide). Its crystal structure was solved and refined from single‐crystal X‐ray diffraction data. It contains two different types of UO22+ units, which are connected by fluorinated tetracarboxylate ligands to form a layered structural motif. Three DMA molecules are coordinated to one UO22+ unit (CN = 7), whereas the other is solely coordinated by oxygen atoms of the tetracarboxylate linkers (CN = 8). The layers are held together by van der Waals interactions, which do not include any hydrogen bonds. An isostructural coordination polymer is formed with L' = 4,4'‐difluorobiphenyl‐3,3',5,5'‐tetracarboxylate (4,4'‐dF‐BPTC4–), as confirmed by XRPD (X‐ray powder diffraction), IR/Raman spectroscopy and elemental analysis. The DSC/TG analyses of both compounds show that they are stable up to approx. 300 °C in an inert argon atmosphere.