Mixed-ligand Strategy Research Articles

Engineering New Defects in MIL-100(Fe) via a Mixed-Ligand Approach To Effect Enhanced Volatile Organic Compound Adsorption Capacity

In the development of metal–organic frameworks (MOFs), expansion of pore size and exploration of facile preparation conditions are considered as two major goals that are rarely realized together. This study develops a facile method for the room-temperature synthesis of hierarchically porous MIL-100(Fe) under HF-free conditions using a mixed-ligand strategy by simultaneously introducing p-benzoquinone and terephthalic acid (TPA). The resulting MIL-100(Fe) products exhibited abundant micropores, large mesopores (∼40 nm) and macropores, and high stability, as revealed by N2 adsorption–desorption isotherms, pore size distributions, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis. The synthesis mechanism of hierarchically porous MIL-100(Fe) elucidated that the introduced p-benzoquinone accelerated crystallization, while TPA generated crystal defects. The as-synthesized hierarchically porous MIL-100(Fe) acted as adsorbents with significantly improved performance than conventional MOFs and zeolites used for toluene and p-xylene adsorption. Furthermore, the adsorption behavior of toluene and p-xylene molecules in MIL-100(Fe) was investigated using molecular simulations. This simple and facile mixed-ligand method shows promise for the large-scale and low-cost production of various hierarchically porous MOFs in a wide range of applications.

Novel alcohol vapour sensor based on the mixed-ligand modified MOF-199 coated quartz crystal microbalance

ABSTRACT Alcohol vapour sensors can be used in many fields, such as food quality monitoring, etc. Herein, we developed an alcohol vapour sensor based on the quartz crystal microbalance (QCM) technology. A modified metal-organic frameworks (MOFs), m-MOF-199 was coated on the QCM electrode surface. The different coating methods, including drop coating, spin coating and electrospray were used for preparing a thin film on the surface of the QCM electrode. MOF-199 was modified by mixed-ligand strategy in which benzotriazole ligand was introduced into the structure of MOF-199 and characterised by FT-IR, XRD, BET and FE-SEM techniques. The smaller dimension of m-MOF199 led to a better thin film and enhanced QCM sensor efficiency. In order to evaluate the QCM sensor, ethanol was used as a model compound. The developed ethanol sensor showed two linear ranges in the concentration between of 0.5–30 mg L−1 and 30–300 mg L−1 with a 0.1 and 0.5 mg L−1, LOD and LOQ, respectively. The relative standard deviation (RSD %) of measurements was less than 10%. The developed sensor could be applied for various applications including food, environmental and bioanalysis.

Mixed-ligand strategy affording two 6-connected 3-fold interpenetrated metal-organic frameworks with binuclear CoII2/NiII2 subunits: Synthesis, crystal structures and magnetic properties

Two 6-connected (6-c) edge-transitive nets, namely, [Co2(2,6-ndc)2(4-bpdb)·2CH3OH·2H2O]n, (1), and [Ni2(2,6-ndc)2(4-bpdb)·(H2O)3·2DMF]n (2) (2,6-H2ndc = 2,6-naphthalenedicarboxylic acid, 4-bpdb = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene), were synthesized under solvothermal conditions. The structure of 1 manifests a three-fold interpenetrated 3D pcu topology based on paddle-wheel [Co2(μ2-η1:η1-COO)4] dimers. The structure of 2 possesses a three-fold interpenetrated 3D acs topology based on [Ni2(μ2-OH2)(μ2-η1:η1-COO)2(η1-COO)2] dimeric units. Magnetic analyses indicate that both two compounds show weak antiferromagnetic interactions within binuclear CoII2 and NiII2 units.

Mixed Functionalization of Organic Ligands in UiO-66: A Tool to Design Metal-Organic Frameworks for Tailored Microextraction.

The mixed-ligand strategy was selected as an approach to tailor a metal–organic framework (MOF) with microextraction purposes. The strategy led to the synthesis of up to twelve UiO-66-based MOFs with different amounts of functionalized terephthalate ligands (H-bdc), including nitro (-NO2) and amino (-NH2) groups (NO2-bdc and NH2-bdc, respectively). Increases of 25% in ligands were used in each case, and different pore environments were thus obtained in the resulting crystals. Characterization of MOFs includes powder X-ray diffraction, infrared spectroscopy, and elemental analysis. The obtained MOFs with different degrees and natures of functionalization were tested as sorbents in a dispersive miniaturized solid-phase extraction (D-µSPE) method in combination with high-performance liquid chromatography (HPLC) and diode array detection (DAD), to evaluate the influence of mixed functionalization of the MOF on the analytical performance of the entire microextraction method. Eight organic pollutants of different natures were studied, using a concentration level of 5 µg· L−1 to mimic contaminated waters. Target pollutants included carbamazepine, 4-cumylphenol, benzophenone-3, 4-tert-octylphenol, 4-octylphenol, chrysene, indeno(1,2,3-cd)pyrene, and triclosan, as representatives of drugs, phenols, polycyclic aromatic hydrocarbons, and disinfectants. Structurally, they differ in size and some of them present polar groups able to form H-bond interactions, either as donors (-NH2) or acceptors (-NO2), permitting us to evaluate possible interactions between MOF pore functionalities and analytes’ groups. As a result, extraction efficiencies can reach values of up to 60%, despite employing a microextraction approach, with four main trends of behavior being observed, depending on the analyte and the MOF.

Two Novel Self-Catenated Metal–Organic Frameworks with Large Accessible Channels Obtained by a Mixed-Ligand Strategy: Adsorption of Dichromate and Ln3+ Postsynthetic Modification

Two novel metal–organic frameworks, namely [Cd3(bdc)(HCOO)2(tipo)2(H2O)2]·2NO3·6DMF (1) and [Zn8(OH)4(bpdc)6(tipo)4]·16DMF (2) (tipo = tris[4-(1H-imidazol-1-yl)phenyl]phosphine oxide, H2bdc = phenyl-1,4-dicarboxylic acid, H2bpdc = biphenyl-4,4′-dicarboxylic acid), have been successfully synthesized. Compound 1 exhibits a cationic 4,6-connected self-catenated framework with large 1D channels. Compound 2 features a 3,4-connected self-catenated framework with potential O donors located on the surface of the channels. Compound 1 shows a high adsorption for dichromate. Postsynthetic modification of 2 by lanthanide ions (Eu3+ and Tb3+) afforded fluorescent materials.

Rational Construction of an Exceptionally Stable MOF Catalyst with Metal‐Adeninate Vertices toward CO2 Cycloaddition under Mild and Cocatalyst‐Free Conditions

CO2 is considered as the primary greenhouse gas, resulting in a series of serious environmental problems that affect people's life and health. Carbon capture and sequestration has been implemented as one of the most appealing pathways to control and use CO2 . Here, we rationally integrate various functional sites within the confined nanospace of a microporous metal-organic framework (MOF) material, which is constructed by mixed-ligand strategy based on metal-adeninate vertices. It not only exhibits excellent stability but also can efficiently transform CO2 and epoxides to cyclic carbonates under mild and cocatalyst-free conditions. Additionally, this catalyst shows extraordinary recyclability for the CO2 cycloaddition reaction.

P-Terphenyl-2,2″,5″,5‴-tetracarboxylate acid based bifunctional 1D Zinc(II) metal-organic platform for luminescent sensing and gas adsorption

Based on the mixed ligands strategy of p-terphenyl-2,2″,5″,5‴-tetracarboxylate acid (H4tptc) and 1,10-phenanthroline (phen), a novel Zinc(II) coordination polymer, {[Zn(tptc)0.5(phen)]·dioxane}n (1), has been constructed. Structural analysis revealed that complex 1 is a 1D polymeric chains based architecture, with the porosity is 25.3% after remove the solvents. The gas adsorptions reveal that complex 1 displaying high CO2 selective absorption over N2 and CH4. Besides, the luminescent sensing investigation indicating complex 1 exhibiting highly luminescent sensitive sensing of Cr(VI) anions in aqueous solution.

Ruthenium complex doped metal-organic nanoplate with high electrochemiluminescent intensity and stability for ultrasensitive assay of mucin 1

In this study, a novel Ru(bpy)2(dcbpy)-doped two-dimensional (2D) metal-organic framework (MOF) nanoplate (Ru@Zr12-BPDC, BPDC = 4,4′-biphenyldicarboxylate, bpy = 2,2'-bipyridine, H2dcbpy = 2,2'-bipyridine-5,5'-dicarboxylic acid) with outstanding ECL performance was synthesized via a mixed ligand strategy. The matching lengths between Ru(bpy)2(dcbpy) and BPDC ligands allowed the Ru(bpy)2(dcbpy) to bridge two Zr12 clusters of Ru@Zr12-BPDC nanoplate through strong coordination bonds, which not only resulted in the increase of the immobilization amount of Ru(bpy)2(dcbpy), but also prevented the leakage of the Ru(bpy)2(dcbpy) effectively. Furthermore, the high porosity and ultrathin nature of 2D Ru@Zr12-BPDC nanoplate not only allowed the electrochemical activation of the internal and external Ru(bpy)2(dcbpy), but also greatly shortened the diffusion paths of the ions, electrons, coreactant (tripropylamine, TPrA) and coreactant intermediates (TPrA• and TPrA•+), which made more interior Ru(bpy)2(dcbpy) could be excited and thus led to the increasing utilization ratio of the luminophores. Because of the above merits, the Ru@Zr12-BPDC nanoplate exhibited high and stable ECL emission, and thus was employed to construct an aptasensor for ultrasensitive detection of mucin 1 (MUC1). To further enhance the sensitivity of the proposed aptasensor and amplify signal, the target MUC1 was converted into the H1-H2 duplex with the assistance of H1, H2 and MUC1-catalyzed hairpin assembly (CHA). As expected, the proposed aptasensor exhibited remarkable stability, excellent sensitivity, high sensitivity and displayed a wide liner range from 1 fg/mL to 10 ng/mL with a low detection limit of 0.14 fg/mL. To our knowledge, it is the first example of the construction of an ECL biosensor based on ruthenium complex doped 2D MOF nanoplates. This study demonstrated that the use of ruthenium complex doped MOF nanoplates to increase the ECL stability and intensity is an efficient strategy for the construction of highly stable and sensitive ECL biosensors, and therefore may extend the applications of 2D MOF nanoplates in ECL and bioanalysis fields.

A New 3D 10-Connected Cd(II) Based MOF With Mixed Ligands: A Dual Photoluminescent Sensor for Nitroaroamatics and Ferric Ion.

The precise unification of functional groups and photoluminescence properties can give rise to MOFs that can offer diverse applications like selective detection of nitroaromatic compounds (NACs) which are considered to be an important ingredient of explosive as well as cation and anion sensing. Hence, a new 3D metal-organic framework (MOF) [Cd2(btc)(bib)(HCOO)(H2O)·H2O]n (1) has been synthesized using mixed ligand strategy by solvothermal reaction of cadmium acetate with two ligands viz. 1,3,5-benzenetricarboxylic acid (H3btc) and 1,4-bis(2-methyl-imidazol-1-yl)butane (bib). The MOF 1 possesses highly 10-connected network which is based on {Cd4(btc)2(bib)4} molecular building block. The studies showed that 1 could be taken as the fluorescent sensor for sensitive recognition of NACs, in particular 2,4,6-trinitrophenol (TNP) with notable quenching (Ksv = 5.42 × 104 M−1) and LOD of 1.77 ppm. Additionally, 1 also displayed selective sensing for Fe3+ ions with Ksv = 6.05 × 103 M− 1 and LOD = 1.56 ppm. Also, this dual sensor displayed excellent reusability toward the detection of TNP and Fe3+ ion. Theoretical calculations have been performed to propose the probable mechanism for the sensing luminescence intensity. Calculations indicated that because of the charge transfer and weak interaction that is operating between NACs and MOF, the weakening in the photoluminescence intensity resulted.

Photocatalytic properties and luminescent sensing of a new 2D layer coordination polymer

ABSTRACTA 2D coordination polymer [Zn2(betc)(bip)2]·3H2O (1) has been synthesised by deploying mixed ligand strategy . The photoluminescence properties of 1 in different solvents have been investigated and its sensing properties to detect nitroaromatic compounds (NACs) have been explored. 1 displayed selective sensing for 4- nitrotoluene (4-NT) with lower limit of detection (LOD) 0.62 ppm. The probable mechanism for sensing of NACs by 1 ha s been addressed using quantum chemical calculations. Also photocatalytic properties of 1 to photo-decompose model aromatic dyes viz. methyl violet (MV) and 20 rhodamine B (Rh B) have been evaluated. The experiments indicated that 1 displayed better photocatalytic performance in photo-degrading MV than Rh B. The plausible mechanism through which 1 displayed photocatalytic degradation of aromatic dyes had been revealed using density of states (DOS) and partial DOS calculations.The probable mechanism for the photocatalytic property and emission quenching of 1 has been proposed with the aid of density of states and partial density of states calculations.

Mixed-Ligand-Architected 2D Co(II)-MOF Expressing a Novel Topology for an Efficient Photoanode for Water Oxidation Using Visible Light.

The structural diversity of Co(II) metal centers is known to influence their physicochemical properties. A novel two-dimensional (2D) Co(II)-MOF {[Co5(HL)4(dpp)2(H2O)2(μ-OH)2]·21H2O} n has been designed and synthesized by adopting a mixed-ligand strategy, using 1,3-di(4-pyridyl)propane (dpp) colinker with a flexible spacer H3L (H3L: 5-(2 carboxybenzyloxy)isophthalic acid). Co(II)-MOF features a 2D network, which is further interpenetrated among the equivalent sets and therefore results in a 3D supramolecular network. Topologically, the entire network can be viewed as a (3,4,8)-connected three-nodal net with the extended point symbol of {4.5.7}4{412.52.710.94}{52.8.92.10}2, duly assigned to the novel topological type smm2. The functional utility of Co(II)-MOF is demonstrated by employing it toward oxygen evolution reaction (OER) in a photoelectrochemical cell, exhibiting appreciable photocurrents of up to 5.89 mA/cm2 when used as an anode in a photoelectrochemical cell, while also displaying encouraging electrocatalytic currents of 9.32 mA/cm2 (at 2.01 V vs RHE) for the OER. Moreover, detailed electrochemical impedance spectroscopy studies confirm enhanced charge-transfer kinetics and improved conductivity under illumination with minimal effect of interfacial phenomena. This work provides a reference for the expanding field of research into applications of MOF materials and establishes MOF materials as favorable candidates for sustainable and efficient design of electrodes for water splitting.

Photocatalytic performances of two new Cd(II) and Zn(II)-based coordination polymers

The solvothermal reaction of Cd(NO3)2·4H2O and Zn(NO3)·6H2O with phthalic acid (H2pa) and 1,3-bis(2-methyl-imidazol-1-yl)propane (bip) using mixed ligand strategy afforded two new coordination polymers (CPs) of [Cd (pa) (bip) (H2O)]n (1) and {[Zn2 (pa)2 (bip)2]·6H2O}n (2), which have been structurally characterized. Both CPs consist of one-dimensional chains containing two alternative type of rings. Additionally, two types of trimeric water clusters are also present in 2. The uncoordinated carboxylate oxygens of pa ligands interact with free water molecules via hydrogen bonds, which further stabilized the full network. Also, both CPs have been used as photocatalyst for degradation of model organic dyes viz. methyl violet (MV) and rhodamine B (RhB) under UV light. The results indicated that both the CPs display good photocatalytic property. The plausible mechanism associated with photocatalytic activities of 1 and 2 against MV/RhB have been proposed using density of states (DOS) and partial DOS calculations.

A Zn(ii) metal–organic framework constructed by a mixed-ligand strategy for CO2 capture and gas separation

A microporous Zn(ii) metal–organic framework has been assembled using a mixed-ligand strategy, and it exhibits high capture ability for CO2 and good selectivity for CO2/CH4, C2H6/CH4 and C3H8/CH4.

Mixed-ligand Cu(II)-containing coordination polymer based on V-shape carboxylate and pyridinyl co-linkers: structural insights, molecular docking and anti-breast cancer activity evolution

A new 2 D Cu(II)-based coordination polymer (CP) {[Cu5(Hcia)4(dpp)2(H2O)2(μ-OH)2]·2H2O}n (1) was designed and synthesized via using the mixed-ligand strategy, using 1,3-di(4-pyridyl)propane (dpp) colinker with a flexible spacer H3cia (H3cia: 5-(2-carboxybenzyloxy)isophthalic acid). Furthermore, we use the grinding method to downsize the complex 1 to nano-region (denoted as nano 1 hereafter). Furthermore, in order to determine the inhibitory effect of nano 1 on the viability of the BT474 breast cancer cells, the Cell Counting Kit-8 (CCK-8) was performed firstly. Then, the Annexin V-FITC/PI staining method was used to evaluate the BT474 breast cancer cells apoptosis levels after treated with nano 1. Next, the reactive oxygen species (ROS) detection kit was used in this study to determine the ROS level in the cancer cells after nano 1 treatment. By calculating posture scores and docking, the latent binding pattern of compound to receptor DNA were explored.

Structural diversity, magnetic properties, and luminescent sensing of four coordination polymers based on 6-(3,5-dicarboxylphenyl)nicotinic acid

Four coo;rdination polymers (CPs), namely, [Ni(HDNA)(bibp)(H2O)]n (1), [Co(HDNA)(bibp)]n (2), {[Co(HDNA)(bibp)]·H2O}n (3) and {[Zn(HDNA)(bibp)]·H2O}n (4), have been synthesized from the mixed-ligand strategy of 6-(3,5-dicarboxylphenyl)nicotinic acid (H3DNA) and 4,4′-bis(benzimidazo-1-ly)benzene (bibp). Structural analyses revealed that four CPs all feature 2D sheets with diverse nets from {44.62}-sql net (1), {Co2(COO)2} SBUs based {44.62}-sql net (2), to 4-connected {65.8} sheet (3&4). Besides, the temperature-dependent magnetic susceptibilities of CPs 1-3 were investigated. And the luminescent sensing indicated CP 4 is a good bifunctional sensor for Fe3+ and Cr2O72- ions.

RETRACTED: Mixed-ligand strategy affording two new metal-organic frameworks: Photocatalytic, luminescent and anti-lung cancer properties

Abstract Mixed-ligand strategy afforded two new metal-organic frameworks (MOFs), namely [Ni(L)0.5(4,4′-bipy)0.5(H2O)2]n (1) and [Zn2(L)(bpp)2]n (2) (H4L = 1,3-di(3′,5′-dicarboxylphenyl)benzene, 4,4′-bipy = 4,4′–bipyridine and bpp = 1,3-di(4-pyridyl)propane), which were further characterized by elemental analyses, powder X-ray diffraction analyses and single crystal X-ray diffraction analyses. Compound 1 features a 4-fold interpenetrated 3D framework with (3,4)-connected dmd-type topology, and compound 2 features a 3D complicated framework with 4-connected topology. Moreover, the photocatalytic activity of compound 1 for the degradation of methyl blue (MB) and luminescent property of compound 2 were investigated in detail. In addition, the anti-lung cancer activities of both complexes have been evaluated via the MTT assay against three human lung cancer cells A549, H1299 and PC9.

Luminescent sensing and photocatalytic degradation in a new 3D Zn(II)-based highly luminescent metal−organic framework

The intelligent blending of intriguing functionalities in ligands and incorporation of spectroscopically silent metal cations can produce metal-organic frameworks (MOFs) with multifarious applications viz. selective and specific sensing of nitroaromatic compounds (NACs) an important constituent of explosives as well as photocatalytic properties. A new 3D Zn(II)-based metal-organic framework, [Zn4(μ2-OH)2(BDC)3(bip)2] (1) have been synthesized using a mixed ligand strategy using benzene-1,3-dicarboxylic acid (H2BDC) and 1,4-bis(2-methyl-imidazole-yl)-propane (bip) and zinc nitrate via hydrothermal reaction. The framework of 1 adopts a 5-connected 3D network with the Schläfli symbol {33.4.52.62.72}. The luminescent sensing investigation indicated that 1 can behave as a luminescent sensor for highly sensitive detection of nitroaromatics (NACs) especially against 2,4,6-trinitrophenol (TNP). The possible depletion in the photoluminescence intensity of 1 in presence of NACs have been addressed using theoretical calculations which indicated that charge transfer as well as the weak interaction between NACs and MOF may be responsible for the decline in the photoluminescence intensity. The MOF have been used as the photocatalyst for the decomposition of methyl violet (MV). Also, the mechanism for the photocatalysis have been addressed using density of states (DOS) calculations.

Sensitive luminescent probes of aniline, benzaldehyde and Cr(VI) based on a zinc(II) metal-organic framework and its lanthanide(III) post-functionalizations

A novel zinc(II) metal-organic framework (MOF) {[(CH3)2NH2]2 [Zn5 (TDA)4 (TZ)4].4DMF}n (1) (H2TDA = thiophene-2,5-dicarboxylic acid and HTZ = 1H-1,2,4-Triazole) based on Zn5(COO)2 (TZ)4 pentametallic clusters and thiophene-2,5-dicarboxylic acid was synthesized and structurally characterized via the mixed-ligand strategy. This MOF exhibits a uninodal 6-connected anionic framework with pcu topology and shows solvent stability. Post-functionalization via cation exchange of 1 with Eu3+ and Tb3+ afforded two lanthanide (III) functionalized MOFs: Eu3+@1 and Tb3+@1. 1 as well as Eu3+@1 and Tb3+@1 were utilized as a highly selective and sensitive turn-off luminescent sensors for detecting aniline, benzaldehyde in DMF and Cr2O72−, CrO42− in water with low detection limits. More importantly, it is rather rare in MOF-based luminescent probes that 1 and its lanthanide (III) post-functionalized materials (Eu3+@1 and Tb3+@1) can detect aniline, benzaldehyde, Cr2O72− and CrO42−. Furthermore, the sensitivity of 1 as luminescent probes for detecting aniline and benzaldehyde could be improved via post-functionalization with Eu3+ ions.

From Metal-Organic Frameworks to Single-Atom Fe Implanted N-doped Porous Carbons: Efficient Oxygen Reduction in Both Alkaline and Acidic Media.

It remains highly desired but a great challenge to achieve atomically dispersed metals in high loadings for efficient catalysis. Now porphyrinic metal-organic frameworks (MOFs) have been synthesized based on a novel mixed-ligand strategy to afford high-content (1.76 wt %) single-atom (SA) iron-implanted N-doped porous carbon (FeSA -N-C) via pyrolysis. Thanks to the single-atom Fe sites, hierarchical pores, oriented mesochannels and high conductivity, the optimized FeSA -N-C exhibits excellent oxygen reduction activity and stability, surpassing almost all non-noble-metal catalysts and state-of-the-art Pt/C, in both alkaline and more challenging acidic media. More far-reaching, this MOF-based mixed-ligand strategy opens a novel avenue to the precise fabrication of efficient single-atom catalysts.

The mixed-ligand strategy to assemble a europium metal-organic framework with a 2-fold-interpenetrated network

A novel europium complex with the mixed ligands of 1-methyl-3,5-bis(4′-carboxy-phenyl)-1,2,4-triazole (mbcpt) and p-phthalic acid (pa), [Eu2Cl2(H3O)2(μ4-mbcpt)2(μ4-pa)]n (1), has been synthesized under the solvothermal conditions and structurally characterized by single-crystal X-ray diffraction. Complex 1 exhibits a three-dimensional (3-D) metal-​organic framework. The 3-D open framework features a 2-fold-interpenetrated network. Solid-state diffuse reflectance spectroscopy uncovers the presence of a wide optical band gap of 3.56 eV, indicating that it is a wide band gap organic semiconductor material. Solid-state photoluminescence measurement reveals that complex 1 shows red light emission bands locating at 602, 611, 642 and 690 nm, which can be assigned to the 5D0 → 7FJ (Eu3+) with the value of J = 1, 2, 3 and 4, respectively. Magnetic measurements reveal that complex 1 shows an antiferromagnetic behavior.