Isoreticular Metal-organic Frameworks Research Articles

An immobilized carboxyl containing metal-organic framework-5 stationary phase for open-tubular capillary electrochromatography

A novel capillary column with metal-organic framework-5 (MOF-5) as the stationary phase was prepared for open-tubular capillary electrochromatography (OT-CEC). To grow MOF-5, the fused-silica capillary was functionalized firstly using 3-aminopropyltriethoxysilane and glutaraldehyde as covalent linkers; and then MOF-5 would be immobilized on the inner wall of COOH-terminated capillary by epitaxial growth, to produce a MOF-5-modified capillary. The successful growth of MOF-5 has been characterized and confirmed by scanning electron microscopy, X-Ray diffraction and Fourier transform infrared spectra. The influence of pH value and methanol on electroosmotic flow (EOF) of the MOF-5-modified capillary column was investigated. The EOF showed a pH-dependent from anode to cathode. The immobilization of MOF-5 improved the interactions between analytes and layer on inner wall of the capillary. Excellent separations of substituted benzenes and acidic and basic analytes were obtained on the fabricated capillary columns. The MOF-5-modified capillary columns exhibited good repeatability, with relative standard deviations for intra-day, inter-day runs and column-to-column less than 1.87%, 3.53%, and 8.49%, respectively. Our successful application of MOF-5 paved the way for introducing series of dicarboxylate-based isoreticular MOFs to OT-CEC as novel stationary phase.

Nanoscaled Zinc Pyrazolate Metal-Organic Frameworks as Drug-Delivery Systems.

This work describes synthesis at the nanoscale of the isoreticular metal-organic framework (MOF) series ZnBDP_X, based on the assembly of Zn(II) metal ions and the functionalized organic spacers 1,4-bis(1H-pyrazol-4-yl)-2-X-benzene (H2BDP_X; X = H, NO2, NH2, OH). The colloidal stability of these systems was evaluated under different relevant intravenous and oral-simulated physiological conditions, showing that ZnBDP_OH nanoparticles exhibit good structural and colloidal stability probably because of the formation of a protein corona on their surface that prevents their aggregation. Furthermore, two antitumor drugs (mitroxantrone and [Ru(p-cymene)Cl2(pta)] (RAPTA-C) where pta = 1,3,5-triaza-7-phospaadamantane) were encapsulated within the pores of the ZnBDP_X series in order to investigate the effect of the framework functionalization on the incorporation/delivery of bioactive molecules. Thus, the loading capacity of both drugs within the ZnBDP_X series seems to directly depend on the surface area of the solids. Moreover, ligand functionalization significantly affects both the delivery kinetics and the total amount of released drug. In particular, ZnBDP_OH and ZnBDP_NH2 matrixes show a slower rate of delivery and higher percentage of release than ZnBDP_NO2 and ZnBDP_H systems. Additionally, RAPTA-C delivery from ZnBDP_OH is accompanied by a concomitant and progressive matrix degradation due to the higher polarity of the BPD_OH ligand, highlighting the impact of functionalization of the MOF cavities over the kinetics of delivery.

Tuning the adsorption behaviors of water, methanol, and ethanol in a porous material by varying the flexibility of substituted groups.

Exploring the adsorption and separation of water, methanol, and ethanol is important concerning the use of a sustainable energy source from biofuel. In this paper, the effects of the flexibility of substituted groups have been studied based on three iso-reticular metal-organic frameworks (MOFs), in which the pore surface is decorated with propargyl (-CH2-C[triple bond, length as m-dash]CH), allyl (-CH2-CH[double bond, length as m-dash]CH2), and propyl (-CH2-CH2-CH3) groups respectively. These substituted groups stretch into the channel, acting as gates, and the gate-opening for guests is controlled by the flexibility as well as host-guest interactions. Our study results indicate that (i) the adsorption capacity of water, methanol and ethanol enhances accordingly with the increase of the flexibility of substituted groups; (ii) the adsorptive discrimination of water, methanol, and ethanol on this porous sorbent could be tuned by varying the substituted groups.

Metal-organic frameworks constructed from crown ether-based 1,4-benzenedicarboxylic acid derivatives.

A series of unprecedented crown ether- and thiacrown ether-derivatized benzene dicarboxylic acid (H2bdc) ligands has been synthesized and incorporated into the prototypical isoreticular metal-organic framework (IRMOF) and UiO-66 materials. In the case of UiO-66, only MOFs comprised from a mixed-ligand composition, requiring both unsubstituted bdc and crown ether containing ligands, could be prepared. These are among the few ligand derivatives, and resulting MOFs, that incorporate a macrocyclic group directly on the bdc ligand, providing a new, modular platform for exploring new supramolecular and coordination chemistry within MOFs.

Interplay between hydrophobicity and basicity toward the catalytic activity of isoreticular MOF organocatalysts

Four MOF catalysts showing different hydrophobic characters around the basic reaction center showed subtle substrate selectivity in aldol-type condensation reaction.

Effects of Extending the π-Electron System of Pillaring Linkers on Fluorescence Sensing of Aromatic Compounds in Two Isoreticular Metal–Organic Frameworks

A new porous metal–organic framework (TMU-21) that is isostructural to our recently reported TMU-6 is introduced. The structure of this framework has been determined by X-ray crystallography and further characterized by Fourier transform infrared spectroscopy, elemental analysis, and thermogravimetric analysis. Its structural features as well as its stability and porosity were studied. These two metal–organic frameworks are interesting candidates for a comparative fluorescence study. Thus, their potential abilities to sense nitrobenzene, benzene, and polycyclic aromatic hydrocarbons, namely, naphthalene, anthracene, and pyrene, were investigated. This study clearly shows an important contribution of extending the π-electron systems of pillaring linkers in the ability of metal–organic frameworks to sense aromatic compounds.

Nanoporous Materials Can Tune the Critical Point of a Pure Substance.

Molecular simulations and NMR relaxometry experiments demonstrate that pure benzene or xylene confined in isoreticular metal–organic frameworks (IRMOFs) exhibit true vapor–liquid phase equilibria where the effective critical point may be reduced by tuning the structure of the MOF. Our results are consistent with vapor and liquid phases extending over many MOF unit cells. These results are counterintuitive since the MOF pore diameters are approximately the same length scale as the adsorbate molecules. As applications of these materials in catalysis, separations, and gas storage rely on the ability to tune the properties of adsorbed molecules, we anticipate that the ability to systematically control the critical point, thereby preparing spatially inhomogeneous local adsorbate densities, could add a new design tool for MOF applications.

Nanoporous Materials Can Tune the Critical Point of a Pure Substance

AbstractMolecular simulations and NMR relaxometry experiments demonstrate that pure benzene or xylene confined in isoreticular metal–organic frameworks (IRMOFs) exhibit true vapor–liquid phase equilibria where the effective critical point may be reduced by tuning the structure of the MOF. Our results are consistent with vapor and liquid phases extending over many MOF unit cells. These results are counterintuitive since the MOF pore diameters are approximately the same length scale as the adsorbate molecules. As applications of these materials in catalysis, separations, and gas storage rely on the ability to tune the properties of adsorbed molecules, we anticipate that the ability to systematically control the critical point, thereby preparing spatially inhomogeneous local adsorbate densities, could add a new design tool for MOF applications.

Facile synthesis of nanoscale high porosity IR-MOFs for low-k dielectrics thin films

To explore the preparation of ultra-low k MOFs material, uniform nanosized isoreticular metal−organic frameworks (IR-MOFs) nanocrystals were prepared by the optimized coordination modulation method and the IR-MOF nanocrystals were used to form IR-MOF films on an ITO glass by dip coating and secondary growth. The continuous thin MOF-3, MOF-5 and MOF-10 films supported on ITO glass had a dielectric constant of 1.2, 2.1 and 4.8 at 2 MHz respectively, and good mechanical strength, adhesion, and hydrophobicity. However, probably due to the presence of the strong polarity of NH2-BDC in MOF-3, and the presence of N–H moieties on grain boundaries, crystal surfaces, and internal crystal defects, which abundantly adsorb water, the MOF-3 film has higher low-k at 100 kHz. For the MOF-10 film with high low-k at 100 kHz, due to the low BET surface area, it could be related to the strong polarity of solvent molecular trapped in the films.

Clicked Isoreticular Metal–Organic Frameworks and Their High Performance in the Selective Capture and Separation of Large Organic Molecules

AbstractThree highly porous metal–organic frameworks (MOFs) with a uniform rht‐type topological network but hierarchical pores were successfully constructed by the assembly of triazole‐containing dendritic hexacarboxylate ligands with ZnII ions. These transparent MOF crystals present gradually increasing pore sizes upon extension of the length of the organic backbone, as clearly identified by structural analysis and gas‐adsorption experiments. The inherent accessibility of the pores to large molecules endows these materials with unique properties for the uptake of large guest molecules. The visible selective adsorption of dye molecules makes these MOFs highly promising porous materials for pore‐size‐dependent large‐molecule capture and separation.

Clicked Isoreticular Metal-Organic Frameworks and Their High Performance in the Selective Capture and Separation of Large Organic Molecules.

Three highly porous metal-organic frameworks (MOFs) with a uniform rht-type topological network but hierarchical pores were successfully constructed by the assembly of triazole-containing dendritic hexacarboxylate ligands with Zn(II) ions. These transparent MOF crystals present gradually increasing pore sizes upon extension of the length of the organic backbone, as clearly identified by structural analysis and gas-adsorption experiments. The inherent accessibility of the pores to large molecules endows these materials with unique properties for the uptake of large guest molecules. The visible selective adsorption of dye molecules makes these MOFs highly promising porous materials for pore-size-dependent large-molecule capture and separation.

Assessing the reliability of van der Waals DFT functionals to study the physisorption of molecular hydrogen on aromatic systems

The physisorption of $$\hbox {H}_2$$ on organic molecules has received much attention during the 2000s, because they are the elementary bricks of the organic linkers in isoreticular metal–organic frameworks, materials that are considered as very promising ones for hydrogen storage. Here, we have studied the physisorption of $$\hbox {H}_2$$ on a wide variety of aromatic molecules, from pure and substituted benzene to polycyclic hydrocarbons, by means of density functional theory (DFT). In performing DFT calculations, we have taken of the relatively new family of functionals that include van der Waals (vdW) effects. We have performed our calculations with two different approaches: (1) the one proposed by Grimme et al. (J Chem Phys 132:154104, 2011), DFT+D3, which corrects the total energy; (2) the one proposed by Lundqvist et al. (Phys Rev B 82:081101, 2010), vdW+DF2, which corrects the correlation energy. From the comparison between our DFT vdW energies and the ones obtained by means of ab initio theory methods [MP2 and CCSD(T)], we conclude that DFT in combination with the vdW+DF2 functional yields reliable binding energies of $$\hbox {H}_2$$ to aromatic complexes, at a much smaller computational cost. Hopefully, our results will stimulate further studies on these kinds of systems, which have been hampered due to limited computational resources.

Ten new predicted covalent organic frameworks with strong optical response in the visible and near infrared.

We use density functional theory to predict and evaluate 10 novel covalent organic frameworks (COFs), labeled (X4Y)(BDC)3, (X = C/Si; Y = C, Si, Ge, Sn, and Pb), with topology based on metal organic framework isoreticular metal-organic framework (IRMOF-1), but with new elements substituted for the corner atoms. We show that these new materials are stable structures using frequency calculations. For two structures, (C4C and Si4C) molecular dynamics simulations were performed to demonstrate stability of the systems up to 600 K for 10 ps. This demonstrates the remarkable stability of these systems, some of which may be experimentally accessible. For the C4C material, we also explored the stability of isolated corners and linkers and vacuum and started to build the structure from these pieces. We discuss the equilibrium lattice parameters, formation enthalpies, electronic structures, chemical bonding, and mechanical and optical properties. The predicted bulk moduli of these COFs range from 18.9 to 23.9 GPa, larger than that of IRMOF-1 (ca. 15.4 GPa), and larger than many existing 3D COF materials. The band gaps range from 1.5 to 2.1 eV, corresponding to 600-830 nm wavelength (orange through near infrared). The negative values of the formation enthalpy suggest that they are stable and should be experimentally accessible under suitable conditions. Seven materials distort the crystal structure to a lower space group symmetry Fm-3, while three materials maintain the original Fm-3m space group symmetry. All of the new materials are highly luminescent. We hope that this work will inspire efforts for experimental synthesis of these new materials.

Engineering Homochiral Metal-Organic Frameworks by Spatially Separating 1D Chiral Metal-Peptide Ladders: Tuning the Pore Size for Enantioselective Adsorption.

The reaction of the chiral dipeptide glycyl-L(S)-glutamate with Co(II) ions produces chiral ladders that can be used as rigid 1D building units. Spatial separation of these building units with linkers of different lengths allows the engineering of homochiral porous MOFs with enhanced pore sizes, pore volumes, and surface areas. This strategy enables the synthesis of a family of isoreticular MOFs, in which the pore size dictates the enantioselective adsorption of chiral molecules (in terms of their size and enantiomeric excess).

Methane Adsorption in a Series of IRMOFs Studied by PHSC and Sanchez–Lacombe Equations of State

In this study, the methane adsorption on several kinds of isoreticular metal organic frameworks (IRMOF) has been modeled by applying perturbed hard sphere chain (PHSC) and Sanchez–Lacombe (SL) equation of state. PHSC and SL equation of state have three characteristic parameters calculated using group contribution method. In this study, the methane adsorption on absorbents, namely, IRMOF-6, IRMOF-8, IRMOF-10, IRMOF-14 has been obtained at temperature 298 K and various pressures up to 10 MPa. Finally, results have been compared with the simulated adsorption data points to show the precision of PHSC and SL equation of state in predicting the methane sorption trend.

Phenyl Groups Result in the Highest Benzene Storage and Most Efficient Desulfurization in a Series of Isostructural Metal-Organic Frameworks.

A series of isoreticular metal-organic frameworks (MOFs; NENU-511-NENU-514), which all have high surface areas and strong adsorption capacities, have been successfully constructed by using mixed ligands. NENU-513 has the highest benzene capacity of 1687 mg g(-1) at 298 K, which ranks as the top MOF material among those reported up to now. This NENU series has been used for adsorptive desulfurization because of its permanent porosity. The results indicate that this series has a higher adsorptive efficiency in the removal of organosulfur compounds than other MOF materials, especially NENU-511, which has the highest adsorptive efficiency in the ambient atmosphere. This study proves that the design and synthesis of targeted MOFs with higher surface areas and with functional groups present is an efficient method to enhance benzene-storage capacity and the adsorption of organosulfur compounds.

A bifunctional, site-isolated metal-organic framework-based tandem catalyst.

Herein, we present the synthesis of a metal-organic framework-based tandem catalyst that contains two distinct catalytic domains. Zn(II)-based IRMOF-9-Irdcppy-NH2 (IRMOF = isoreticular metal-organic framework) has both organocatalytic amine and organometallic Ir(I) groups that were incorporated by both pre- and postsynthetic functionalization methods. The isolated amine and Ir(I) sites of IRMOF-9-Irdcppy-NH2 are shown to be independently catalytically active for performing a Knoevenagel condensation and allylic N-alkylation, respectively. More importantly, IRMOF-9-Irdcppy-NH2 can act as a tandem catalyst for both of these organic transformations in a one-pot reaction, which cannot be achieved efficiently using the combined, homogeneous analogues.

Enhanced gas sorption properties of a new sulfone functionalized aluminum metal-organic framework: Synthesis, characterization, and DFT studies

A new sulfone-functionalized analogue of DUT-5 ([Al(OH) (BPDC)], BPDC = 4,4′-biphenyldicarboxylate) microporous metal-organic framework, [Al(OH) (SBPDC)] (1) (H2SBPDC = 2,2′-sulfone-4,4′-biphenyldicarboxylate), has been synthesized in order to achieve better gas sorption properties over DUT-5. The compound was characterized by powder X-ray diffraction (PXRD), scanning electron microscopy, variable temperature PXRD, thermogravimetric analysis, FT-IR spectroscopy, NMR spectroscopy and gas adsorption measurements. The new MOF forms a 3D porous framework containing 1D inorganic chains which are formed by corner-sharing octahedral AlO6 connected through SBPDC linkers. As determined by gas sorption measurements, the compound 1 exhibits high porosity with the H2 uptake capacity of 8.58 mmol g−1 at 77 K (1 atm) and CO2 uptake of 2.51 mmol g−1 at 298 K (1 atm) or 4.40 mmol g−1 at 273 K (1 atm). The gas sorption experimental results suggested that compound 1 with sulfone functionalized ligand showed higher CO2 and H2 gas uptake than that of isoreticular MOF, DUT-5. The CO2 gas sorption behavior of 1 and DUT-5 has been analyzed with the aid of DFT studies which explained that the sulfone group can enhance the efficiency of CO2 uptake.

Understanding Gas adsorption selectivity in IRMOF-8 using molecular simulation.

Grand canonical Monte Carlo simulations were used to explore the adsorption behavior of methane, ethane, ethylene, and carbon dioxide in isoreticular metal-organic frameworks, IRMOF-1, noninterpenetrated IRMOF-8, and interpenetrated IRMOF-8. The simulated isotherms are compared with experimentally measured isotherms, when available, and a good agreement is observed. In the case of IRMOF-8, the agreement is much better for the interpenetrated model than for the noninterpenetrated model, suggesting that the experimental data was obtained on an essentially interpenetrated structure. Simulations show that carbon dioxide is preferentially adsorbed over methane, and a selective adsorption at low pressures of ethane over ethylene, especially in the case of IRMOF-8, confirm recent experimental results. Analysis of simulation results on both the interpenetrated and the noninterpenetrated structures shows that interpenetration is responsible for the higher adsorbed amounts of ethane at low pressures (<100 kPa) and for the interesting selectivity for ethane in ethane/ethylene binary mixtures. Van der Waals interactions seem to be enhanced in the interpenetrated structure, favoring ethane adsorption. This indicates that interpenetrated MOF structures may be of interest for the separation of small gas molecules.

MOF as a syringe pump for the controlled release of iodine catalyst in the synthesis of meso-thienyl dipyrromethanes

In a new concept, an iodine loaded amine functionalized MOF was employed as a syringe pump for the slow release of iodine as a catalyst in the synthesis of thienyl dipyrromethanes under ambient conditions and turned out to be successful. The catalytic activities were compared with an isoreticular non-functionalized MOF and other conventional catalysts.