Role of additives and solvents in the synthesis of chiral isoreticular MOF-74 topologies.
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ABSTRACT:
SUBMITTER: Gheorghe A
PROVIDER: S-EPMC8439144 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The synthesis of chiral metal-organic frameworks (MOFs) is highly relevant for asymmetric heterogenous catalysis, yet very challenging. Chiral MOFs with MOF-74 topology were synthesised by using post-synthetic modification with proline. Vibrational circular dichroism studies demonstrate that proline is the source of chirality. The solvents used in the synthesis play a key role in tuning the loading of proline and its interaction with the MOF-74 framework. In N,N'-dimethylformamide, proline coordinates monodentate to the Zn2+ ions within the MOF-74 framework, whereas it is only weakly bound to the framework when using methanol as solvent. Introducing chirality within the MOF-74 framework also leads to the formation of defects, with both the organic linker and metal ions missing from the framework. The formation of defects combined with the coordination of DMF and proline within the framework leads to a pore blocking effect. This is confirmed by adsorption studies and testing of the chiral MOFs in the asymmetric aldol reaction between acetone and para-nitrobenzaldehyde.
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Project description:Mechanochemical synthesis has recently emerged as a scalable "green" approach for the preparation of MOFs, but current understanding of the underlying reaction mechanisms is limited. In this work, an investigation of the reaction pathway of the mechanochemical synthesis of MOF-74 from ZnO and 2,5-dihydroxyterephthalic acid (H4HDTA), using DMF as a liquid additive, is presented. The complex reaction pathway involves the formation of four short-lived intermediate phases, prior to the crystallization of MOF-74. The crystal structures of three of these intermediates have been determined using a combination of single-crystal and powder X-ray diffraction methods and are described here. The initial stages of the reaction are very fast, with a DMF solvate of H4HDTA forming after only 2 min of milling. This is followed by crystallization, after only 4 min of milling, of a triclinic one-dimensional coordination polymer, Zn(H2DHTA)(DMF)2(H2O)2, which converts into a monoclinic polymorph on additional milling. Highly crystalline MOF-74 appears after prolonged milling, for at least 70 min.
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Project description:Supramolecular isomerism of metal-organic frameworks (MOFs) is known for several MOF structures, having direct implications on the properties of these materials. Although the synthesis of MOF isomers is mainly serendipitous in nature, achieving controlled formation of a target framework is highly relevant for practical applications. This work discusses the influence of additives and synthesis conditions on the formation of porous isomers containing Zn2+ as nodes and 2,5-dihydroxy-1,4-benzenedicarboxylate (dobdc4-) as a linker. Using solvent mixtures containing strongly coordinated molecules, e.g. N,N'-dimethylformamide (DMF) and N-methylpyrrolidone (NMP), facilitates the formation of porous structures of type [Zn2(dobdc)(S)x]·yS (S = DMF, NMP) which are built from dinuclear Zn2(O)2(CO2)3 secondary building units (SBUs) consisting of two different edge-sharing polyhedra with the Zn2+ ions in a unsaturated coordinative environment. In the presence of water, the Zn2+ dimers are converted to one-dimensional infinite Zn2+ chains, in which the number of Zn2+-linker bonds increases, therefore giving a hydrolytically more stable coordination environment. The full characterization of the isomers as well as their conversion to the most stable isomer is presented.
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Project description:In this work we present the in silico design of metal-organic frameworks (MOFs) exhibiting 1-dimensional rod topologies. We introduce an algorithm for construction of this family of MOF topologies, and illustrate its application for enumerating MOF-74-type analogs. Furthermore, we perform a broad search for new linkers that satisfy the topological requirements of MOF-74 and consider the largest database of known chemical space for organic compounds, the PubChem database. Our in silico crystal assembly, when combined with dispersion-corrected density functional theory (DFT) calculations, is demonstrated to generate a hypothetical library of open-metal site containing MOF-74 analogs in the 1-D rod topology from which we can simulate the adsorption behavior of CO2. We finally conclude that these hypothetical structures have synthesizable potential through computational identification and experimental validation of a novel MOF-74 analog, Mg2(olsalazine).
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Project description:Defects in metal-organic frameworks (MOFs) have great impact on their nano-scale structure and physiochemical properties. However, isolated defects are easily concealed when the frameworks are interrogated by typical characterization methods. In this work, we unveil the presence of solvent-derived formate defects in MOF-74, an important class of MOFs with open metal sites. With multi-dimensional solid-state nuclear magnetic resonance (NMR) investigations, we uncover the ligand substitution role of formate and its chemical origin from decomposed N,N-dimethylformamide (DMF) solvent. The placement and coordination structure of formate defects are determined by 13C NMR and density functional theory (DFT) calculations. The extra metal-oxygen bonds with formates partially eliminate open metal sites and lead to a quantitative decrease of N2 and CO2 adsorption with respect to the defect concentration. In-situ NMR analysis and molecular simulations of CO2 dynamics elaborate the adsorption mechanisms in defective MOF-74. Our study establishes comprehensive strategies to search, elucidate and manipulate defects in MOFs.
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Project description:Metal-organic frameworks (MOFs) have received wide attention for their promising applications in numerous fields due to their tailorable structure, metal centers and porosity. However, the low mass permeability, poor conductivity and blockage of active metal centers severely restrict the utilization of MOF systems in electrocatalysis. Two-dimensionalization can endow MOF materials extra unsaturated metal centers and enhanced electron-transfer ability, and could be an effective strategy to achieve high-performance MOF-based electrocatalysts. Herein, Ni-MOF-74 nanosheets are synthesized using layered double hydroxide (LDH) as a template to directly grow ultrathin structures. Benefiting from the two-dimensional structure, Ni-MOF-74 nanosheets with carbon substrate exhibit an enhanced ORR electrocatalytic property with positive half-wave potential (+0.83 V vs. RHE), a large current density (3.9 mA cm-2), four-electron selectivity and a promising long-term durability.
| S-EPMC8695273 | biostudies-literature
Project description:Vapor-assisted dry-gel synthesis of the metal-organic framework-74 (MOF-74) structure, specifically Ni-MOF-74 produced from synthetic precursors using an organic-water hybrid solvent system, showed a very high yield (>90% with respect to 2,5-dihydroxyterepthalic acid) and enhanced performance. The Ni-MOF-74 obtained showed improved sorption characteristics towards CO2 and the refrigerant fluorocarbon dichlorodifluoromethane. Unlike conventional synthesis, which takes 72 hours using the tetrahydrofuran-water system, this kinetic study showed that Ni-MOF-74 forms within 12 hours under dry-gel conditions with similar performance characteristics, and exhibits its best performance characteristics even after 24 hours of heating. In the dry-gel conversion method, the physical separation of the solvent and precursor mixture allows for recycling of the solvent. We demonstrated efficient solvent recycling (up to three times) that resulted in significant cost benefits. The scaled-up manufacturing cost of Ni-MOF-74 synthesized via our dry-gel method is 45% of conventional synthesis cost. Thus, for bulk production of the MOFs, the proposed vapor-assisted, dry-gel method is efficient, simple, and inexpensive when compared to the conventional synthesis method.
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Project description:The stability of functional materials in water-containing environments is critical for their industrial applications. A wide variety of metal-organic frameworks (MOFs) synthesized in the past decade have strikingly different apparent stabilities in contact with liquid or gaseous H2O, ranging from rapid hydrolysis to persistence over days to months. Here, we show using newly determined thermochemical data obtained by high-temperature drop combustion calorimetry that these differences are thermodynamically driven rather than primarily kinetically controlled. The formation reaction of a MOF from metal oxide (MO) and a linker generally liberates water by the reaction MO + linker = MOF + H2O. Newly measured enthalpies of formation of Mg-MOF-74(s) + H2O(l) and Ni-MOF-74(s) + H2O(l) from their crystalline dense components, namely, the divalent MO (MgO or NiO) and 2,5-dihydroxyterephthalic acid, are 303.9 ± 17.2 kJ/mol of Mg for Mg-MOF-74 and 264.4 ± 19.4 kJ/mol of Ni for Ni-MOF-74. These strongly endothermic enthalpies of formation indicate that the reverse reaction, namely, the hydrolysis of these MOFs, is highly exothermic, strongly suggesting that this large thermodynamic driving force for hydrolysis is the reason why the MOF-74 family cannot be synthesized via hydrothermal routes and why these MOFs decompose on contact with moist air or water even at room temperature. In contrast, other MOFs studied previously, namely, zeolitic imidazolate frameworks (ZIF-zni, ZIF-1, ZIF-4, Zn(CF3Im)2, and ZIF-8), show enthalpies of formation in the range 20-40 kJ per mole of metal atom. These modest endothermic enthalpies of formation can be partially compensated by positive entropy terms arising from water release, and these materials do not react appreciably with H2O under ambient conditions. Thus, these differences in reactivity with water are thermodynamically controlled and energetics of formation, either measured or predicted, can be used to assess the extent of water sensitivity for different possible MOFs.
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Project description:Separation of linear, mono-branched, and di-branched isomers is critically important in the petrochemical industry. In this computational study, we demonstrate that the ligand inserted Mg-MOF-74 structure leads to a reverse selectivity effect (i.e. phenomenon that preferentially allows larger species molecules to permeate in a gas mixture) of hexane isomers in the resulting material. Molecular dynamics simulations suggest that strong confinement of the di-branched hydrocarbons in the small pores lead to reverse selectivity. Over a magnitude difference in diffusivity between linear alkanes and their di-branched isomers was observed, clearly showing the steric effects imposed by the pore structure.
| S-EPMC9054571 | biostudies-literature
Project description:A magnesium-based metal-organic framework (Mg-MOF-74) exhibits excellent CO2 adsorption under ambient conditions. However, the photostability of Mg-MOF-74 for CO2 adsorption is poor. In this study, Mg x Cu1-x -MOF-74 was synthesized by using a facile "one-pot" method. Furthermore, the effects of synthesis conditions on the CO2 adsorption capacity were investigated comprehensively. X-ray diffraction, Fourier transform infrared, scanning electron microscopy, thermo gravimetric analysis, inductively coupled plasma atomic emission spectroscopy, ultraviolet-visible spectroscopy and photoluminescence spectroscopy, and CO2 static adsorption-desorption techniques were used to characterize the structures, morphology, and physicochemical properties of Mg x Cu1-x -MOF-74. CO2 uptake of Mg x Cu1-x -MOF-74 under visible light illumination was measured by the CO2 static adsorption test combined with the Xe lamp. The results revealed that Mg x Cu1-x -MOF-74 exhibited excellent photocatalytic activity. Furthermore, the CO2 adsorption capacity of Mg x Cu1-x -MOF-74 was excellent at a synthesis temperature and time of 398 K and 24 h in dimethylformamide (DMF)-EtOH-MeOH mixing solvents, respectively. Mg x Cu1-x -MOF-74 retained a crystal structure similar to that of the corresponding monometallic MOF-74, and its CO2 uptake under visible light was superior to that of the corresponding monometallic MOF-74. Particularly, the CO2 uptake of Mg0.4Cu0.6-MOF-74 under Xe lamp illumination for 24 h was the highest, up to 3.52 mmol·g-1, which was 1.18 and 2.09 times higher than that of Mg- and Cu-MOF-74, respectively. The yield of the photocatalytic reduction of CO2 to CO was 49.44 μmol·gcat -1 over Mg0.4Cu0.6-MOF-74 under visible light for 8 h. Mg2+ and Cu2+ functioned as open alkali metal that could adsorb and activate CO2. The synergistic effect between Mg and Cu metal strengthened Mg x Cu1-x -MOF-74 photostability for CO2 adsorption and broadened the scope of its photocatalytic application. The "bimetallic" strategy exhibits considerable potential for use in MOF-based semiconductor composites and provides a feasible method for catalyst design with remarkable CO2 adsorption capacity and photocatalytic activity.
| S-EPMC9202246 | biostudies-literature