Isoreticular Metal-organic Frameworks Research Articles

A Comparison of Two Isoreticular Metal-Organic Frameworks with Cationic and Neutral Skeletons: Stability, Mechanism, and Catalytic Activity.

Although many ionic metal-organic frameworks (MOFs) have been reported, little is known about how the charge of the skeleton affects the properties of the MOF materials. Herein we report how the chemical stability of MOFs can be substantially improved through embedding electrostatic interactions in structure. A MOF with a cationic skeleton is impervious to extremely acidic, oxidative, reductive, and high ionic strength conditions, such as 12 m HCl (301 days), aqua regia (86 days), H2 O2 (30 days), and seawater (30 days), which is unprecedented for MOFs. DFT calculations suggested that steric hinderance and the repulsive interaction of the cationic framework toward positively charged species in microenvironments protects the vulnerable bonds in the structure. Diverse functionalities can be bestowed by substituting the counterions of the charged framework with identically charged functional species, which broadens the horizon in the design of MOFs adaptable to a demanding environment with specific functionalities.

Understanding the Loading Dependence of Adsorbate Diffusivities in Hierarchical Metal-Organic Frameworks.

Using atomistic simulations, we studied the diffusion of n-hexane in a series of isoreticular hierarchical metal-organic frameworks (MOFs) NU-100x. Nonmonotonic diffusivity-loading relationships that depend on the pore sizes were observed, which can be explained by the spatial distribution of adsorbates at different loadings. For one of the MOFs in the series, NU-1000-M, the diffusivity-loading relationship is almost identical to the previously reported results of n-hexane diffusion in the hierarchical self-pillared pentasil (SPP) zeolite. Detailed analysis revealed that the similarity results from their similar micropore and window sizes, which was confirmed by free-energy mapping. The effects of temperature and adsorbate chain length on the diffusion were also studied, which supported our conclusion that the diffusivity in hierarchical nanoporous materials is primarily controlled by the sizes of the micropores and the connecting windows, particularly at relatively low loadings.

H2/CO2 separations in multicomponent metal-adeninate MOFs with multiple chemically distinct pore environments.

Metal–organic frameworks constructed from multiple (≥3) components often exhibit dramatically increased structural complexity compared to their 2 component (1 metal, 1 linker) counterparts, such as multiple chemically unique pore environments and a plurality of diverse molecular diffusion pathways. This inherent complexity can be advantageous for gas separation applications. Here, we report two isoreticular multicomponent MOFs, bMOF-200 (4 components; Cu, Zn, adeninate, pyrazolate) and bMOF-201 (3 components; Zn, adeninate, pyrazolate). We describe their structures, which contain 3 unique interconnected pore environments, and we use Kohn–Sham density functional theory (DFT) along with the climbing image nudged elastic band (CI-NEB) method to predict potential H2/CO2 separation ability of bMOF-200. We examine the H2/CO2 separation performance using both column breakthrough and membrane permeation studies. bMOF-200 membranes exhibit a H2/CO2 separation factor of 7.9. The pore space of bMOF-201 is significantly different than bMOF-200, and one molecular diffusion pathway is occluded by coordinating charge-balancing formate and acetate anions. A consequence of this structural difference is reduced permeability to both H2 and CO2 and a significantly improved H2/CO2 separation factor of 22.2 compared to bMOF-200, which makes bMOF-201 membranes competitive with some of the best performing MOF membranes in terms of H2/CO2 separations.

Precise Control of Molecular Self-Diffusion in Isoreticular and Multivariate Metal-Organic Frameworks.

Understanding the factors that affect self‐diffusion in isoreticular and multivariate (MTV) MOFs is key to their application in drug delivery, separations, and heterogeneous catalysis. Here, we measure the apparent self‐diffusion of solvents saturated within the pores of large single crystals of MOF‐5, IRMOF‐3 (amino‐functionalized MOF‐5), and 17 MTV‐MOF‐5/IRMOF‐3 materials at various mole fractions. We find that the apparent self‐diffusion coefficient of N,N‐dimethylformamide (DMF) may be tuned linearly between the diffusion coefficients of MOF‐5 and IRMOF‐3 as a function of the linker mole fraction. We compare a series of solvents at saturation in MOF‐5 and IRMOF‐3 to elucidate the mechanism by which the linker amino groups tune molecular diffusion. The ratio of the self‐diffusion coefficients for solvents in MOF‐5 to those in IRMOF‐3 is similar across all solvents tested, regardless of solvent polarity. We conclude that average pore aperture, not solvent‐linker chemical interactions, is the primary factor responsible for the different diffusion dynamics upon introduction of an amino group to the linker.

Nanobundles of Iron Phosphide Fabricated by Direct Phosphorization of Metal-Organic Frameworks as an Efficient Hydrogen-Evolving Electrocatalyst.

Transition-metal-based phosphides (TMPs) have been considered as attractive electrocatalysts for water splitting due to their earth-abundance and remarkable catalytic activity. As a representative type of precursors, metal-organic frameworks (MOFs) provide ideal plateaus for the design of nanostructured TMPs. In this work, the hierarchically structured iron phosphide nanobundles (FeP-500) were fabricated by one-step phosphorization of an iron-based MOF (MET(Fe)) precursor. The derived FeP-500 nanobundles were constructed by quasi-paralleled one-dimensional nanorods with uneven surface, which provided channels for electrolyte penetration, mass transport, and effective exposure of active sites during the water-splitting process. With the addition of conductive Super P, the obtained FeP-500-S exhibited a good electrocatalytic performance towards the hydrogen evolution reaction in alkaline electrolyte (1 mol L-1 KOH). Furthermore, to investigate the influence of secondary metal doping, a series of isoreticular MOF precursors and bimetallic TMPs were fabricated. The results indicated that the catalytic performance is structure dominated.

Topology-Guided Design for Sc-soc-MOFs and Their Enhanced Storage and Separation for CO2 and C2-Hydrocarbons.

Evaluating the effect of ligand substitution on metal ions and/or clusters during the MOF growth process is conducive to rational design of isoreticular MOFs with improved performance. Through topological direction and ligand substitution strategy, we herein constructed two Sc-soc-MOFs (Sc-EBTC and Sc-ABTC) based on two similar rectangular-planar diisophthalate ligands, linear-shaped H4EBTC (1,1'-ethynebenzene-3,3',5,5'-tetracarboxylic acid) and zigzag-shaped H4ABTC (3,3',5,5'-azobenzenetetracarboxylic acid), under solvothermal conditions with formic acid as a modulator. {Sc[(Sc3O)(H2O)3]3(EBTC)6} (Sc-EBTC) possesses two distinct clusters as SBUs, trinuclear [Sc3O(CO2)6] (SBU1) and mononuclear cluster [ScO6] (SBU2), which maintain the soc-topology except for the mononuclear [ScO6] instead of the corresponding trinuclear [Sc3O(CO2)6] in Sc-ABTC ({(Sc3O)(H2O)3(ABTC)1.5(NO3)}). Notably, Sc-EBTC represents a rare soc-MOF with two distinct clusters as SBUs. Due to similar pore spaces, the two Sc-soc-MOF materials both exhibit enhanced and comparable gas sorption and selectivity performances. Specially, their remarkable C2H2, C2H4, and CO2 storage capacity along with prominent CO2/CH4 and C2-hydrocarbons/CH4 separations indicate that these Sc-soc-MOFs are promising adsorbents for natural gas purification under ambient conditions.

Dual sensing of copper ion and chromium (VI) oxyanions by benzotriazole functionalized UiO-66 metal-organic framework in aqueous media

A new dual chemosensor UiO-66-NH-BT (BT=1-methylenebenzotriazole) based on the UiO-66 (University of Oslo) framework, containing benzotriazole functionalized dicarboxylate struts was synthesized and characterized. This isoreticular Metal-Organic Framework (MOF) was found to be a very selective and ultrasensitive for copper ion and chromium oxyanions in aqueous media. It showed a detection limit of 16.9 ppb (0.266 μM) for Cu2+ ion, 280 ppb (1.3 μM) for Cr2O72− and 47.7 ppb (0.411 μM) for CrO42− anions. The quenching constants (Ksv) for Cu2+, Cr2O72−, CrO42− was found to be 1.1x105 M−1, 3.9x103 M−1, and 6.7x103 M−1 respectively. The covalently bonded benzotriazole moiety with the UiO-66 framework not only produces an emission peak at 491 nm but also act as an intrinsic binding site for both cations and anions. The nature of the coordinative interaction between the analytes and the UiO-66-NH-BT has also been elaborated with the help of ICP and FTIR. This chemosensor also demonstrated a regenerative property without the loss in performance for five consecutive cycles.

Understanding phonon properties in isoreticular metal-organic frameworks from first principles

Metal-organic frameworks (MOFs) are crystalline materials consisting of metal centers and organic linkers forming open and porous structures. They have been extensively studied due to various possible applications exploiting their large amount of internal surface area. Phonon properties of MOFs are, however, still largely unexplored, despite their relevance for thermal and electrical conductivities, thermal expansion, and mechanical properties. Here, we use quantum-mechanical simulations to provide an in-depth analysis of the phonon properties of isoreticular MOFs. We consider phonon band structures, spatial confinements of modes, projected densities of states, and group velocity distributions. We find that more complex linkers shift the spectral weight of the phonon density of states towards higher frequencies, while increasing the mass of the metal atoms in the nodes has the opposite effect. Due to the high porosity of MOFs, we observe a particularly pronounced polarization dependence of the dispersion of acoustic phonons with rather high group velocities for longitudinal acoustic modes. Interestingly, also for several optical phonon modes group velocities amounting to several thousand m/s are obtained. For heterogeneous systems like MOFs, correlating group velocities and the displacement of modes is particularly relevant. Here we find that high group velocities are generally associated with delocalized vibrations, while the inverse correlation does not necessarily hold. To quantify anharmonicities, we calculate mode Gr\"uneisen parameters, which we find to be significant only for phonons with frequencies below ~3 THz. The presented results provide the foundations for an in-depth understanding of the vibrational properties of MOF, and, thus, pave the way for a future rational design of systems with well-defined phonon properties.

Synthesis and Applications of Isoreticular Metal–Organic Frameworks IRMOFs-n (n = 1, 3, 6, 8)

Isoreticular metal–organic frameworks (IRMOFs) are a series of MOFs that own similar network topology. By simple substitution of organic linkers of IRMOF-1 (i.e., MOF-5), other IRMOFs can be obtain...

Fe-Substituted Isoreticular Metal–Organic Framework for Efficient and Rapid Removal of Phosphate

Excessive phosphate can cause water eutrophication. Adsorption can remove excessive phosphate in water to alleviate eutrophication effectively. Herein, an isoreticular metal–organic framework (Fe-I...

Ammonia Capture within Isoreticular Metal–Organic Frameworks with Rod Secondary Building Units

The efficient removal, capture, and recycling of ammonia (NH3) constitutes a demanding process; thus, the development of competent adsorbent materials is highly desirable. The implementation of met...

Multifunctional Fe3O4@C-based nanoparticles coupling optical/MRI imaging and pH/photothermal controllable drug release as efficient anti-cancer drug delivery platforms

Multifunctional nanomedicines featuring high drug loading capacity, controllable drug release and real-time self-monitoring are attracting increasing attention due to their potential to improve cancer therapeutic efficacy. Herein, a new kind of Fe3O4@C-based nanoparticles modified with isoreticular metal organic frameworks (IRMOF-3), folic acid (FA) and detachable polyethylene glycol (PEG) under tumor microenvironment was developed. The core-shell structured Fe3O4@C was synthesized via the one-pot solvothermal reaction and the IRMOF-3 layers were coated on the outer shell of Fe3O4@C through layer-by-layer coating method. The FA and PEG were conjugated on the surface of nanoparticles by reacting with the amine groups provided by IRMOF-3. The as-synthesized nanoparticles showed stable photothermal effect, superparamagnetic properties and blue fluorescence characteristic under 360 nm irradiation. The in vitro experiments showed that the drug loaded nanoparticles exhibit pH-dependent drug release property, and PEGylation was proved effective in suppressing burst drug release (only 8.0% of drugs were released within 95 h). The confocal laser scanning microscopy study revealed that the as-synthesized nanoparticles could serve as a cell imaging agent and the cell internalization can be significantly enhanced after FA modified. The IRMOF-3 modified nanoparticles showed negligible cytotoxicity and the drug loaded nanoparticles showed pH/photothermal-stimuli enhanced cytotoxicity in vitro. It is believed that the present smart drug delivery platforms will hold great potential in imaging guided drug delivery and cancer therapy.

High-Pressure in Situ 129Xe NMR Spectroscopy: Insights into Switching Mechanisms of Flexible Metal-Organic Frameworks Isoreticular to DUT-49.

Flexible metal–organic frameworks (MOFs) are capable of changing their crystal structure as a function of external stimuli such as pressure, temperature, and type of adsorbed guest species. DUT-49 is the first MOF exhibiting structural transitions accompanied by the counterintuitive phenomenon of negative gas adsorption. Here, we present high-pressure in situ 129Xe NMR spectroscopic studies of a novel isoreticular MOF family based on DUT-49. These porous materials differ only in the length of their organic linkers causing changes in pore size and elasticity. The series encompasses both, purely microporous materials as well as materials with both micropores and small mesopores. The chemical shift of the adsorbed xenon depends on xenon–wall interactions and thus on the pore size of the material. The xenon adsorption behavior of different MOFs can be observed over the whole range of relative pressure. Chemical shift adsorption/desorption isotherms closely resembling the conventional, uptake-measurement-based isotherms were obtained at 237 K where all materials are rigid. The comparable chemical environment of the adsorbed xenon in these isoreticular MOFs allows to establish a correlation between the chemical shift at a relative pressure of p/p0 = 1.0 and the mean pore diameter. Furthermore, the xenon adsorption behavior of MOFs is studied also at 200 K. Here, structural flexibility is found for DUT-50, a material with an even longer linker than that of the previously known DUT-49. Its structural transitions are monitored by 129Xe NMR spectroscopy. This compound is the second known MOF showing the phenomenon of negative gas adsorption. Further increase in the linker length results in DUT-151, a material with an interpenetrated network topology. In situ 129Xe NMR spectroscopy proves that this material exhibits another type of flexibility compared to DUT-49 and DUT-50. Further surprising observations are made for DUT-46. Volumetric xenon adsorption measurements show that this nonflexible microporous material does not exhibit any hysteresis. In contrast, the in situ 129Xe NMR spectroscopically detected xenon chemical shift isotherms exhibit a hysteresis even after longer equilibration times than in the volumetric experiments. This indicates kinetically hindered redistribution processes and long-lived metastable states of adsorbed xenon within the MOF persisting at the time scale of hours or longer.

Yanli Zhao.

"My biggest motivation is the discovery of new therapeutics to save lives. The most significant scientific advance of the last 100 years has been the discovery of polio vaccine …" Find out more about Yanli Zhao in his Author Profile.

Construction of mixed carboxylate and pyrogallate building units for luminescent metal–organic frameworks

A metal-organic framework, Ce-FDM-50, was constructed by employing gallic acid featuring both carboxylate and pyrogallate as the coordinating sites and Ce(III). The co-assembly of the carboxylates and pyrogallates with two metal ions have achieved a new type of paddle wheel secondary building unit. These building units were further joined by organic struts to obtain frameworks in sql topology. This synthetic approach could be expanded to five different lanthanide metals (Nd, Eu, Gd, Tb, Yb) for the construction of a series of isoreticular MOFs based on FDM-50, and even MTV-MOFs in which mixed lanthanide metals with specific ratios were distributed. In addition, featuring the lanthanide metals as the inorganic nodes in the network, Tb-FDM-50 showed distinct luminescence properties that could be furtherly tuned for variable applications.

Interface construction in microporous metal–organic frameworks from luminescent terbium-based building blocks

Interfaces between the pores and the skeletons in metal–organic frameworks (MOFs) define the places where the materials interact with the incoming guests, and constructing functionalized interfaces in MOFs is crucial for various applications. In this report, by using the platform of the well-known terbium-based 12-connected building units, four isoreticular MOFs, FDM-34–37, with fcu-a topology in single crystal form were obtained with linear organic linkers featuring diversified edge lengths (from 17.4 to 23.8 Å) and functionalities (naphthalene, bipyridine, stilbene, and rotatable triphenyl rings). With the surface areas of up to 1850 m2 g−1, these MOFs feature distinct pores with fine-tuned sizes. Furthermore, the relationship between the luminescence originated from the terbium, and the energy transfer between the metals and the linkers on the interfaces were carefully investigated. With characteristic luminescence and potentially active sites from both the metals and the linkers, these MOFs show prospects in various applications.

Solid-Solution Mixed-Linker Synthesis of Isoreticular Al-Based MOFs for an Easy Hydrophilicity Tuning in Water-Sorption Heat Transformations

The solid-solution mixed-linker approach, where a linker is partially replaced by a similar one under retention of the isoreticular metal–organic framework (MOF) structure, offers an easy and inexpensive way to fine-tune MOF properties to design tailored compounds. A total of 10 aluminum mixed-linker MOFs, [Al(OH)(X)a(Y)1–a] (X = IPA, isophthalate; Y = FDC, 2,5-furandicarboxylate) spanning between the isostructural MOFs CAU-10-H (a = 1) and MIL-160 (a = 0), were synthesized by employing different ratios of the aforementioned linkers. CAU-10-H and MIL-160 have been reported as highly promising materials for cycling water sorption for heat transformation applications. A detailed characterization with a focus on the changes in the sorption properties for water vapor showed that the hydrophilicity is readily and easily tuned through the mixed-linker approach between the limits of MIL-160 and CAU-10-H. An increasing fraction of IPA shifts the steep increase in the S-shaped water adsorption isotherm in small steps from p/p0 = ∼0.05 for MIL-160 to p/p0 = ∼0.18 for CAU-10-H. Higher coefficient of performance (COPH) values for the mixed-linker materials over MIL-160 illustrate the well-balanced hydrophobicity/hydrophilicity of the former under the exemplary calculation conditions.

Intrinsic White‐Light‐Emitting Metal–Organic Frameworks with Structurally Deformable Secondary Building Units

AbstractThe secondary building units in metal–organic frameworks (MOFs) are commonly well‐defined metal–oxo clusters or chains with very limited structural strain. Herein, the structurally deformable haloplumbate units that are often observed in organolead halide perovskites have been successfully incorporated into MOFs. The resultant materials are a rare class of isoreticular MOFs exhibiting large Stokes‐shifted broadband white‐light emission, which is probably induced by self‐trapped excitons from electron–phonon coupling in the deformable, zigzag [Pb2X3]+ (X=Cl, Br, or I) chains. In contrast, MOFs with highly symmetric, robust haloplumbate chains only exhibit narrow UV–blue photoemission. The designed MOF‐based intrinsic white‐light photoemitters have a number of advantages over hybrid inorganic–organic perovskites in terms of stability and tunability, including moisture resistance, facile functionalization of photoactive moieties onto the organic linkers, introduction of luminescent guests.

Intrinsic White-Light-Emitting Metal-Organic Frameworks with Structurally Deformable Secondary Building Units.

The secondary building units in metal-organic frameworks (MOFs) are commonly well-defined metal-oxo clusters or chains with very limited structural strain. Herein, the structurally deformable haloplumbate units that are often observed in organolead halide perovskites have been successfully incorporated into MOFs. The resultant materials are a rare class of isoreticular MOFs exhibiting large Stokes-shifted broadband white-light emission, which is probably induced by self-trapped excitons from electron-phonon coupling in the deformable, zigzag [Pb2 X3 ]+ (X=Cl, Br, or I) chains. In contrast, MOFs with highly symmetric, robust haloplumbate chains only exhibit narrow UV-blue photoemission. The designed MOF-based intrinsic white-light photoemitters have a number of advantages over hybrid inorganic-organic perovskites in terms of stability and tunability, including moisture resistance, facile functionalization of photoactive moieties onto the organic linkers, introduction of luminescent guests.

Self-assembly and optoelectronic properties of isoreticular MOF nanocrystals

Self-assembly behaviour and optoelectronic properties of IRMOF-8 nanocrystals have been studied for the first time. Utilizing a rapid and simple self-assembly directed solvothermal process, microstructures of an interpenetrated analogue of IRMOF-8 was prepared and fully characterized. The elemental composition analysis reveals that the structural formula is to be Zn4O(NDC)3, confirming the original IRMOF-8 structural formula. The powder XRD analysis along with simulated XRD traces of two known IRMOF-8 analogues (IRMOF-8 and INT-IRMOF-8 A) reveals that the crystal structure of IRMOF-8 microstructures follows the primitive cubic (pcu) unit cell topology as the two-fold interpenetrated IRMOF-8. The selective area electron diffraction (SAED) pattern further supports the interpenetrating network with off-sets layer-by-layer arrangement of NDC units. The UV–vis spectra of nanostructures show the naphthalene absorption with a pronounced excitonic transition absorption at 374 nm and 380 nm for Zn4O clusters in solution and thin films, respectively. The optical band gap of 2.84 eV and the characteristic linker-based luminescence evidence that microstructures show excellent semiconducting properties. The thin films of microstructures exhibit an electrical conductivity of 3.98 × 10−2 S/cm at room temperature.