Benzene Dicarboxylate Research Articles

Synthesis of MIL‐53(Fe) Metal‐Organic Framework Material and Its Application as a Catalyst for Fenton‐Type Oxidation of Organic Pollutants

The iron (III) benzene dicarboxylate metal‐organic framework material (MIL‐53(Fe)) was synthesized with either the solvent‐thermal or hydrothermal method under different conditions. The influence of the type of solvents, molar ratio of precursors and solvent, temperature, and reaction time on the structure of MIL‐53(Fe) was investigated. The material was characterized by using X‐ray diffraction (XRD), Fourier‐transform infrared spectroscopy (FT‐IR), scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HR‐TEM), X‐ray photoelectron spectroscopy (XPS), and N2 adsorption/desorption isotherm. The MIL‐53(Fe) structure formed in N′, N‐dimethylformamide (DMF) and methanol (MeOH) but not in water. In DMF, the molar ratio of precursors and solvent, temperature, and reaction time had a significant effect on the crystal structure of MIL‐53(Fe). Under optimal conditions, MIL‐53(Fe) has high crystallinity and a large specific surface area (SBET = 88.2 m2/g). The obtained MIL‐53(Fe) could serve as a potential heterogeneous catalyst to oxidize phenol (PhN), rhodamine B (RhB), and methylene blue (MtB) in the Fenton‐like reaction system at the different solution pHs.

Engineering a Highly Defective Stable UiO-66 with Tunable Lewis- Brønsted Acidity: The Role of the Hemilabile Linker.

The stability of metal–organic frameworks (MOFs) typically decreases with an increasing number of defects, limiting the number of defects that can be created and limiting catalytic and other applications. Herein, we use a hemilabile (Hl) linker to create up to a maximum of six defects per cluster in UiO-66. We synthesized hemilabile UiO-66 (Hl-UiO-66) using benzene dicarboxylate (BDC) as linker and 4-sulfonatobenzoate (PSBA) as the hemilabile linker. The PSBA acts not only as a modulator to create defects but also as a coligand that enhances the stability of the resulting defective framework. Furthermore, upon a postsynthetic treatment in H2SO4, the average number of defects increases to the optimum of six missing BDC linkers per cluster (three per formula unit), leaving the Zr-nodes on average sixfold coordinated. Remarkably, the thermal stability of the materials further increases upon this treatment. Periodic density functional theory calculations confirm that the hemilabile ligands strengthen this highly defective structure by several stabilizing interactions. Finally, the catalytic activity of the obtained materials is evaluated in the acid-catalyzed isomerization of α-pinene oxide. This reaction is particularly sensitive to the Brønsted or Lewis acid sites in the catalyst. In comparison to the pristine UiO-66, which mainly possesses Brønsted acid sites, the Hl-UiO-66 and the postsynthetically treated Hl-UiO-66 structures exhibited a higher Lewis acidity and an enhanced activity and selectivity. This is further explored by CD3CN spectroscopic sorption experiments. We have shown that by tuning the number of defects in UiO-66 using PSBA as the hemilabile linker, one can achieve highly defective and stable MOFs and easily control the Brønsted to Lewis acid ratio in the materials and thus their catalytic activity and selectivity.

Long-Term Photostability in Terephthalate Metal-Organic Frameworks.

Prolonged (weeks) UV/Vis irradiation under Ar of UiO-66(Zr), UiO66 Zr-NO2 , MIL101 Fe, MIL125 Ti-NH2 , MIL101 Cr and MIL101 Cr(Pt) shows that these MOFs undergo photodecarboxylation of benzenedicarboxylate (BDC) linker in a significant percentage depending on the structure and composition of the material. Routine characterization techniques such as XRD, UV/Vis spectroscopy and TGA fail to detect changes in the material, although porosity and surface area change upon irradiation of powders. In contrast to BCD-containing MOFs, zeolitic imidazolate ZIF-8 does not evolve CO2 or any other gas upon irradiation.

Long‐Term Photostability in Terephthalate Metal–Organic Frameworks

AbstractProlonged (weeks) UV/Vis irradiation under Ar of UiO‐66(Zr), UiO66 Zr‐NO2, MIL101 Fe, MIL125 Ti‐NH2, MIL101 Cr and MIL101 Cr(Pt) shows that these MOFs undergo photodecarboxylation of benzenedicarboxylate (BDC) linker in a significant percentage depending on the structure and composition of the material. Routine characterization techniques such as XRD, UV/Vis spectroscopy and TGA fail to detect changes in the material, although porosity and surface area change upon irradiation of powders. In contrast to BCD‐containing MOFs, zeolitic imidazolate ZIF‐8 does not evolve CO2 or any other gas upon irradiation.

Tuning Thermal Expansion in Metal-Organic Frameworks Using a Mixed Linker Solid Solution Approach.

Several metal-organic frameworks are known to display negative thermal expansion (NTE). However, unlike traditional NTE material classes, there have been no reports where the thermal expansion of a MOF has been tuned continuously from negative to positive through the formation of single-phase solid solutions. In the system Zn-DMOF-TMx, Zn2[(bdc)2-2x(TM-bdabco)2x][dabco], the introduction of increasing amounts of TM-bdc, with four methyl groups decorating the benzene dicarboxylate linker, leads to a smooth transition from negative to positive thermal expansion in the a-b plane of this tetragonal material. The temperature at which zero thermal expansion occurs evolves from ∼186 K for the Zn-DMOF parent structure (x = 0) to ∼325 K for Zn-DMOF-TM (x = 1.0). The formation of mixed linker solid solutions is likely a general strategy for the control of thermal expansion in MOFs.

Potential Application Zn-MOF/MnO<sub>2</sub> Composite as Methanol Gas Sensor

Methanol is a simple alcohol compound which is known very volatile and to be toxic inside of human’s body. Therefore, it is necessary to develop a sensor that is capable to detect the methanol vapor in indoor air. Zn-based MOF is a polymeric coordination compound made up of ZnxOyCz inorganic cluster as the secondary building unit (SBU) and benzene dicarboxylate as the bridging ligand and formed bulky and porous material. In this research, composites of manganese oxide (MnO2) and Zn-based MOF are synthesized and characterized as material sensor for its capability towards sensing of methanol gas. Diffractogram of PXRD reveals that the synthesized Zn-MOF is crystalline and become more amorphous due to MnO2 addition. The composite was made into pellets and measured of its resistivity. The addition of MnO2 to the Zn-MOF lowered the resistivity of the Zn-MOF and the composite was found to be sensitive towards methanol vapor.

Sequential Ligand Exchange of Coordination Polymers Hybridized with In Situ Grown and Aligned Au Nanowires for Rapid and Selective Gas Sensing.

Combining polymeric materials and conductive one-dimensional metal nanostructures is able to achieve enhanced chemical and electrical properties, but the control over their morphology and spatial arrangement remains a big challenge. Herein, by replacing benzenedicarboxylate (BDC) in ZnBDC nanoplates with oleylamine (OAM) in the presence of HAuCl4, Zn-OAM nanobelts with a highly ordered laminar structure were obtained, on which ultrathin Au nanowires (Au NWs) were deposited and aligned along the long axes of the nanobelts. The resulting Zn-OAM/Au NW hybrid further underwent an OAM-to-2-methylimidazole ligand exchange, resulting in the formation of porous nanobelts composed of ZIF-8 nanocrystals interwound with aligned Au NWs. Due to the synergistic effect between the polymeric and metallic structures, the Zn-OAM/Au NW hybrid nanobelts and ZIF-8/Au NW porous nanobelts demonstrated fast and selective gas sensing at ambient conditions, in sharp contrast to the nonresponsive Au NWs or Zn-based polymers alone.

OX-1 Metal–Organic Framework Nanosheets as Robust Hosts for Highly Active Catalytic Palladium Species

A catalytic system based on OX-1 metal–organic framework nanosheets is reported, incorporating catalytically active palladium (Pd) species. The Pd@OX-1 guest@host system is rapidly synthesized via a one-step single-pot supramolecular assembly, with the possibility of controlling the Pd loading. The structures of the resulting framework and of the active Pd species before and after catalytic reactions are studied in detail using a wide variety of techniques including synchrotron radiation infrared spectroscopy, inelastic neutron scattering, and X-ray absorption spectroscopy. Crystals of the resulting Pd@OX-1 composite material contain predominantly atomic and small cluster Pd species, which selectively reside on benzene rings of the benzenedicarboxylate (BDC) linkers. The composites are shown to efficiently catalyze the Suzuki coupling and Heck arylation reactions under a variety of conditions. Pd@OX-1 further shows potential to be recycled for at least five cycles of each reaction as well as an ability to recapture active Pd species during both catalytic reactions.

Syntheses, Structures, and Catalytic Properties of Three Copper(II) Coordination Polymers Based on 2,3,5,6‐Tetrafluoro‐1,4‐bis(triazole‐ylmethyl)benzene and Benzene Carboxylate Ligands

Three new mixed‐ligand coordination polymers of CuII, namely, [Cu(Fbtx)(L1)(H2O)]n (1), [Cu(Fbtx)0.5(HL2)(H2O)2]n (2), and {[Cu(Fbtx)1.5(HL3)(H2O)]·H2O}n (3) [Fbtx = 2,3,5,6‐tetrafluoro‐1,4‐bis(1,2,4‐triazole‐1‐ylmethyl)benenze, H2L1 = terephthalic acid, H3L2 = trimesic acid, NaH2L3 = 5‐sulfoisophthalic acid monosodium salt], were hydrothermally synthesized and structurally characterized by elemental analysis, IR spectra, and single‐crystal and powder X‐ray diffraction techniques. All the complexes have a two‐dimensional (2D) coordination layer structure. Of these, 1 displays a planar 44‐sql structure whereas both 2 and 3 are highly undulated 63‐hcb nets. Moreover, their thermal stability and catalytic behaviors in the aerobic oxidation of 4‐methoxybenzyl alcohol were also investigated as well. The results indicate that the benzene dicarboxylate ligands have an effective influence on the structures and catalytic properties of the resulting coordination polymers.

PolyMOF Formation from Kinked Polymer Ligands via ortho‐Substitution

AbstractReticular chemistry is an important tool in the crystal engineering of metal‐organic frameworks (MOFs). Isoreticular chemistry allows for the preparation of MOFs of the same topology from ligands with related geometries. In this work, reticular chemistry is used to explore the scope of polyMOFs, which are frameworks synthesized from polymer ligands. “Linked” ortho‐substituted benzene dicarboxylate polymer ligands with varying length alkyl spacers were used to synthesize polyMOFs and elucidate the effects of polymer architecture on resulting crystal formation. It was found that these “kinked” polymer ligands were able to form polyIRMOF architectures, but did not readily form polyUiO‐66 topologies.

Ab-initio Study of the Electron Mobility in a Functionalized UiO-66 Metal Organic Framework

This study leverages density functional theory accompanied with Boltzmann transport equation approaches to investigate the electronic mobility as a function of inorganic substitution and functionalization in a thermally stable UiO-66 metal-organic framework (MOF). The MOFs investigated are based on Zr-UiO-66 MOF with three functionalization groups of benzene dicarboxylate (BDC), BDC functionalized with an amino group ( $$\hbox {BDC} + \hbox {NH}_2$$ ) and a nitro group ( $$\hbox {BDC} + \hbox {NO}_2$$ ). The design space of this study is bound by UiO-66(M)-R, [ $$\hbox {M}=\hbox {Zr}$$ , Ti, Hf; $$\hbox {R}=\hbox {BDC}$$ , $$\hbox {BDC}+\hbox {NO}_2$$ , $$\hbox {BDC}+\hbox {NH}_2$$ ]. The elastic modulus was not found to vary significantly over the structural modification of the design space for either functionalization or inorganic substitution. However, the electron–phonon scattering potential was found to be controllable by up to 30% through controlled inorganic substitution in the metal clusters of the MOF structure. The highest electron mobility was predicted for a UiO-66( $$\hbox {Hf}_5\hbox {Zr}_1$$ ) achieving a value of approximately $$1.4\times 10^{-3}\,\hbox {cm}^2$$ /V s. It was determined that functionalization provides a controlled method of modulating the charge density, while inorganic substitution provides a controlled method of modulating the electronic mobility. Within the proposed design space the electrical conductivity was able to be increased by approximately three times the base conductivity through a combination of inorganic substitution and functionalization.

Microporous metal organic framework-based copolymers with efficient gas adsorption capability and high temporal stability

We report new microporous metal-organic 3D coordinated copolymers that exhibit both highly efficient gas adsorption capability and high temporal stability. The Zn-coordinated copolymers (MBCn) were prepared by mixing two organic ligands at various molar ratios: the widely used benzenedicarboxylate (BDC) and its analogous Cn-acid with non-polar alkoxy side chains of various lengths. All MBCn copolymers bearing alkoxy side chains exhibited identical framework structures to that of MOF-5 prepared with only the BDC ligand. Interestingly, compared to MOF-5, MBCn copolymers exhibited up to three times higher gas adsorption properties and higher temporal structural stability. Therefore, copolymerization with organic ligands bearing alkoxy side chains is a promising strategy for the development of new microporous metal-organic hybrid materials. Open image in new window

Tuning Two-Photon Absorption Cross Section in Metal Organic Frameworks

The development of alternative nonlinear optical metamaterials has attracted much attention recently due to technological demands. Upconversion emission via a simultaneous two-photon absorption process is a nonlinear process that is widely studied in synthetically challenging organic compounds. Hereby, we report 9 metal organic frameworks constructed with various combinations of the following ligands: trans,trans-9,10-bis(4-pyridylethenyl) anthracene, trans,trans-9,10-bis(4-pyridylethynyl) anthracene, 1,4-bis[2-(4′-pyridyl)ethenyl]benzene, 4,4′-stilbene dicarboxylate, 4,4′-biphenyl dicarboxylate, 4,4′-benzene dicarboxylate, and benzene-1,3,5-tricarboxylate. Altering the auxiliary carboxylate ligands not only changes the structure but also varies the two-photon excited fluorescence. The two-photon excited emission is enhanced when longer spacer ligands are used and when they are packed in more expanded structures in hms topology. Unusually, the emission becomes stronger when a pair of pyridyl type ligands ...

Fluorine Doping Strengthens the Lithium-Storage Properties of the Mn-Based Metal-Organic Framework.

The electrochemical properties of the metal-organic framework (MOF)-based composite as electrode material can be significantly improved by means of partial destruction of the full coordination of linkers to metal ions and replacing with other small ions, which make metal centers become more accostable and consequently more effective for the lithiation/delithiation process. In this paper, F- was chosen to replace some of the benzenedicarboxylate (BDC) linkers because of its better interaction with the Li+ than the oxide ion. What's more, the formed M-F bond promotes the Li+ to transfer at the active material interface and protects the surface from HF attacking. The as-synthesized F-doped Mn-MOF electrode maintains a reversible capacity of 927 mA h g-1 with capacity retention of 78.5% after 100 cycles at 100 mA g-1 and also exhibits a high discharge capacity of 716 mA h g-1 at 300 mA g-1 and 620 mA h g-1 at 500 mA g-1 after 500 cycles. Even at 1000 mA g-1, the electrode still maintains a high reversible capacity of 494 mA h g-1 after 500 cycles as well as a Coulombic efficiency of nearly 100%, which is drastically increased compared with pure Mn-MOF material as expected.

Catalytic Transfer Hydrogenation of Biomass-Derived Levulinic Acid and Its Esters to γ-Valerolactone over Sulfonic Acid-Functionalized UiO-66

Production of γ-valerolactone (GVL) from biomass-derived levulinic acid and its esters via a catalytic transfer hydrogenation (CTH) process over sulfonic acid-functionalized UiO-66, a microporous zirconium-based metal–organic framework (Zr-MOF), is reported herein. On the basis of comprehensive structural analyses by means of XRD, N2 physisorption, IR, TG, and Zr K-edge XAFS, we show that free sulfonic acid (−SO3H) groups can uniformly be tethered on a UiO-66 framework without affecting the coordination state of Zr atoms, while crystallinity and surface area decrease along with the functionalization. As a consequence, UiO-66 bearing a 60 mol % fraction of sulfonic acid-containing benzene dicarboxylate (BDC) linker and retaining a high surface area exhibits the highest catalytic activity in the CTH reaction of levulinic acid and its esters to give GVL with the maximum GVL yield of up to 85% at 140 °C. Comparative experiments, together with characterization results, reveal that the high catalytic activity is provided by the cooperative effect between Lewis-basic Zr6O4(OH)4 clusters and Brönsted-acidic −SO3H sites arranged in a confined nanospace adjacently with each other, which catalyze the CTH reaction of levulinic acid and its esters and facilitate successive intramolecular dealcoholization to afford GVL, respectively. The catalyst is reusable during repeated cycles without appreciable loss of activity and selectivity, shows broad scopes toward substrates and alcohols, and also allows direct synthesis of GVL from furfural, making this material a promising candidate for efficient GVL production from biomass resources.

Polymer-based monolithic column with incorporated chiral metal-organic framework for enantioseparation of methyl phenyl sulfoxide using nano-liquid chromatography.

A new approach to the preparation of enantioselective porous polymer monolithic columns with incorporated chiral metal-organic framework for nano-liquid chromatography has been developed. While no enantioseparation was achieved with monolithic poly(4-vinylpyridine-co-ethylene dimethacrylate) column, excellent separations of both enantiomers of (±)-methyl phenyl sulfoxide were achieved with its counterpart prepared after admixing metal-organic framework [Zn2 (benzene dicarboxylate)(l-lactic acid)(dmf)], which is synthesized from zinc nitrate, l-lactic acid, and benzene dicarboxylic acid in the polymerization mixture. These novel monolithic columns combined selectivity of the chiral framework with the excellent hydrodynamic properties of polymer monoliths, may provide a great impact on future studies in the field of chiral analysis by liquid chromatography.

Free Energy of Ligand Removal in the Metal-Organic Framework UiO-66.

We report an investigation of the “missing-linker phenomenon” in the Zr-based metal–organic framework UiO-66 using atomistic force field and quantum chemical methods. For a vacant benzene dicarboxylate ligand, the lowest energy charge-capping mechanism involves acetic acid or Cl–/H2O. The calculated defect free energy of formation is remarkably low, consistent with the high defect concentrations reported experimentally. A dynamic structural instability is identified for certain higher defect concentrations. In addition to the changes in material properties upon defect formation, we assess the formation of molecular aggregates, which provide an additional driving force for ligand loss. These results are expected to be of relevance to a wide range of metal–organic frameworks.

Insights on Capacitive Interdigitated Electrodes Coated with MOF Thin Films: Humidity and VOCs Sensing as a Case Study.

A prototypical metal-organic framework (MOF), a 2D periodic porous structure based on the assembly of copper ions and benzene dicarboxylate (bdc) ligands (Cu(bdc)·xH2O), was grown successfully as a thin film on interdigitated electrodes (IDEs). IDEs have been used for achieving planar CMOS-compatible low-cost capacitive sensing structures for the detection of humidity and volatile organic compounds (VOCs). Accordingly, the resultant IDEs coated with the Cu(bdc)·xH2O thin film was evaluated, for the first time, as a capacitive sensor for gas sensing applications. A fully automated setup, using LabVIEW interfaces to experiment conduction and data acquisition, was developed in order to measure the associated gas sensing performance.

Highly emissive platinum(II) metallacages.

Light-emitting materials, especially those with tunable wavelengths, attract considerable attention for applications in optoelectronic devices, fluorescent probes, sensors and so on. Many species evaluated for these purposes either emit as a dilute solution or on aggregation, with the former often self-quenching at high concentrations, and the latter falling dark when aggregation is disrupted. Here we preserve emissive behaviour at both low- and high-concentration regimes for two discrete supramolecular coordination complexes (SCCs). These tetragonal prismatic SCCs are self-assembled on mixing a metal acceptor, Pt(PEt3)2(OSO2CF3)2, with two organic donors, a pyridyl-decorated tetraphenylethylene and one of two benzene dicarboxylate species. The rigid organization of these fluorescence-active ligands imparts an emissive behaviour to dilute solutions of the resulting assemblies. Furthermore, on aggregation the prisms exhibit variable-wavelength visible-light emission, including rare white-light emission in tetrahydrofuran. The favourable photophysical properties and solvent-dependent aggregation behaviour provide a means to tune emission wavelengths.

Ab initio calculation of electronic charge mobility in metal-organic frameworks.

A density functional theory approach coupled with the Boltzmann transport equation within the relaxation time approximation was used to investigate the charge mobility for three MOF functionalization designs. The specific MOF investigated was a Zr-UiO-66 MOF with three functionalizations that included benzenedicarboxylate (BDC), BDC functionalized with an amino group (BDC + NH2), and BDC functionalized with a nitro group (BDC + NO2). Previous experimental studies have confirmed a 40% decrease in the optical band-gap with functionization; this study predicted an accompanying decrease in mobility by 14%. On the contrary, the charge density was found to increase with functionalization. The culmination of these two findings resulted in a predicted conductivity of approximately 3.8 × 10(-8) S cm(-1) for BDC design and decreasing less than 2% for other cases. Furthermore, band conduction was confirmed for this MOF design as a result of the de-localized π electron of the carbon atoms along the organic linker. Overall, the functionalization proved to decrease mobility; however, it was evident that the functionalization has potential for tailoring the spectral layout of low lying unoccupied orbitals and ultimately the charge concentration, which could prove to be important for increasing the overall conductivity of MOFs.