Breathing Metal-organic Frameworks Research Articles

Breathing Metal-Organic Frameworks Supported by an Arsenic-Bridged 4,4'-Bipyridine Ligand.

Bent ligands bridged by heteroatoms have drawn significant interest as supramolecular coordination architectures. Traditionally, divalent group 16 elements are preferred over trivalent group 15 elements because of the anticipated steric hindrance. In this study, we explore metal-organic frameworks (MOFs) based on dipyridinoarsoles (DPAs), 4,4'-bipyridines bridged with an arsenic atom. An MOF with methyl-substituted DPA collapsed upon solvent removal, whereas that with phenyl-substituted DPA demonstrated breathing behavior due to guest molecule adsorption/desorption. In contrast, MOFs using the phosphorus analogue dipyridinophosphole exhibit inferior adsorption and lack breathing behavior. This is the first study to investigate the interplay among substituents, bridging elements, and dynamic behavior in MOFs using bent group 15 ligands.

Alignment of Breathing Metal-Organic Framework Particles for Enhanced Water-Driven Actuation.

As the majority of known metal-organic frameworks (MOFs) possess anisotropic crystal lattices and thus anisotropic physicochemical properties, a pressing practical challenge in MOF research is the establishment of robust and simple processing methods to fully harness the anisotropic properties of the MOFs in various applications. We address this challenge by applying an E-field to precisely align MIL-88A microcrystals and generate MIL-88A@polymer films. Thereafter, we demonstrate the impact of MOF crystal alignment on the actuation properties of the films as a proof of concept. We investigate how different anisotropies of the MIL-88A@polymer films, specifically, crystal anisotropy, particle alignment, and film composition, can lead to the synergetic enhancement of the film actuation upon water exposure. Moreover, we explore how the directionality in application of the external stimuli (dry/humid air stream, water/air interface) affects the direction and the extent of the MIL-88A@polymer film movement. Apart from the superior water-driven actuation properties of the developed films, we demonstrate by dynamometer measurements the higher degree of mechanical work performed by the aligned MIL-88A@polymer films with the preserved anisotropies compared to the unaligned films. The insights provided by this work into anisotropic properties displayed by aligned MIL-88A@polymer films promise to translate crystal performance benefits measured in laboratories into real-world applications. We anticipate that our work is a starting point to utilize the full potential of anisotropic properties of MOFs.

Origin of the solid-state luminescence of MIL-53(Al) and its connection to the local crystalline structure

Metal-organic frameworks (MOFs) are extensively studied due to their unique surface properties, enabling many intriguing applications. Breathing MOFs, a subclass of MOFs, have gained recent interest for their ability to undergo structural changes based on factors like temperature, pressure, adsorbed molecules. Certain MOFs also exhibit remarkable optical properties useful for applications such as sensors, light-emitting diodes, and scintillators. The most promising MOFs possess high porosity, breathing properties, and photoluminescence activities, allowing for improved device responsiveness and selectivity. Understanding the relationship between crystal structures and photoluminescence properties is crucial in these cases. As studies on this topic are still very limited, we report for the first time an exhaustive study on the solid-state luminescence of the breathing MOF MIL-53(Al), that can stabilize in three different crystalline structures: open-pore, hydrated narrow-pore and closed-pore. We unveil a fascinating solid-state luminescence spectrum, comprising three partially overlapping bands, and elucidate the intricate electronic transitions within each band as well as their intimate correlation with the local crystalline structures. Our characterizations of spectroscopic properties and decay times provide a deeper understanding of the luminescent behaviour of MIL-53(Al) and demonstrate that is possible to identify present crystalline structures by optical measurements or to modify the optical properties inducing structural transitions for this type of materials. These insights could help to design next-generation, selective sensors or smart light emitting devices.

Molecular insight into the structure of heterometallic metal-organic frameworks MIL-53-M (M = Al and Ga) and their intermolecular interaction with pyridine: A periodic density functional theory

Heterometallic metal-organic frameworks (MOFs) as part of functional materials possess interesting functionalities which may benefits for many potential applications. In this study, quantum mechanical approach was used to investigate the effect of multi metal ion nodes of Al3+ and Ga3+ in a famous breathing MOF of MIL-53. The ratio of Al3+ to Ga3+ was modulated to give bimetallic MIL-53(Al/Ga). The presence of Al3+ and Ga3+ in MIL-53(Al/Ga) induces the structural changes as evidence from the calculated unit cell parameters, where increasing the concentration of Al3+ generally reduces the size of the unit cell dimension. The electronic properties have been identified to give small fine tuning of the band gap energy where the presence of Al3+ shows a dominant factor to shift the edge of the conductance band according to the density of states plots. The band gap energy of MIL-53(Ga) was calculated to be 3.47 eV and it decreases when Ga3+ was substituted by Al3+ to give band gap energy of 3.33 eV for MIL-53(Al). Therefore, the bandgap energy can be fine-tuned by modulating the ratio of Al3+ to Ga3+ in bimetallic MIL-53(Al/Ga). The nature of the bonding within various MIL-53(Al/Ga) was also identified using electron localization maps indicating a possible ionic characteristic for metal ions to ligand interaction. In addition, the adsorption of pyridine within MIL-53(Al/Ga) provides an insight into the Bronsted acidity of MIL-53(Al/Ga) due to the presence of bridging -µOH. In this case, adsorbed pyridine in MIL-53-2Al2Ga shows the lowest adsorption energy compared to the other configurations indicating a stronger Bronsted acidity of the -µOH site. This is also in correlation with the more positively charge of pyridine molecules inside MIL-53-2Al2Ga due to the hydrogen bonding interaction with hydrogen of -µOH. This study gives an insight into the functional material design in term of the electronic properties as well as the behavior towards guest molecules.

Controlling Metal Clusters in Breathing Metal–Organic Framework Nanostructures for Boosting Visible-Light-Induced ·OH Radical Formation

Controlling Metal Clusters in Breathing Metal–Organic Framework Nanostructures for Boosting Visible-Light-Induced ·OH Radical Formation

Acoustic manipulation of breathing MOFs particles for self-folding composite films preparation

Integrating breathing metal-organic frameworks (MOFs) particles into a passive polymer matrix is a successful strategy to develop self-folding composite films. However, the folding direction of the film depends on the gradient distribution of breathing MOFs particles in the polymer matrix, which is a huge challenge. Herein, acoustic manipulation is exploited to pattern breathing MIL-53(Fe) particles in liquid photosensitive resin to control over their spatial distribution, and combined with stereolithography to prepare self-folding composite films in situ. The prepared polymer film containing the microstructure of MIL-53(Fe) particles exhibits self-folding in response to the solvent that causes breathing of MIL-53(Fe) crystals. The reported strategy provides a simple, fast and environmentally friendly platform to prepare self-folding composite films based on breathing MOFs.

Molecular Mobility of Tert-butyl Alcohol Confined in a Breathing MIL-53 (Al) Metal-Organic Framework.

We present a detailed solid-state NMR characterization of the molecular dynamics of tert-butyl alcohol (TBA) confined inside breathing metal-organic framework (MOF) MIL-53(Al). 27 Al MAS NMR has demonstrated that TBA adsorption induces the iX phase of MIL-53 material with partially shrunk channels. 2 H solid-state NMR has shown that the adsorbed alcohol exhibits anisotropic rotations of the methyl groups around two axes and librations of the molecule as a whole about the axis passing through the TBA C-O bond. These librations are realized by two distinct ways: fast molecule orientation change during the translational jump diffusion along the channel with characteristic time τD of about 10-9 s at 300 K; slow local librations at a single coordination site, representing framework hydroxyl groups, with τl ≈10-6 s at 300 K. Self-diffusion coefficient of the alcohol in the MOF has been estimated: D=3.4×10-10 m2 s-1 at 300 K. It has been inferred that both the framework flexibility and the interaction with framework hydroxyl groups define the dynamics of TBA confined in the channels of MIL-53 (Al).

Investigation of structural, electronic and magnetic properties of breathing metal-organic framework MIL-47(Mn): a first principles approach.

The structural, electronic and magnetic properties of the MIL-47(Mn) metal–organic framework are investigated using first principles calculations. We find that the large-pore structure is the ground state of this material. We show that upon transition from the large-pore to the narrow-pore structure, the magnetic ground-state configuration changes from antiferromagnetic to ferromagnetic, consistent with the computed values of the intra-chain coupling constant. Furthermore, the antiferromagnetic and ferromagnetic configuration phases have intrinsically different electronic behavior: the former is semiconducting, the latter is a metal or half-metal. The change of electronic properties during breathing posits MIL-47(Mn) as a good candidate for sensing and other applications. Our calculated electronic band structure for MIL-47(Mn) presents a combination of flat dispersionless and strongly dispersive regions in the valence and conduction bands, indicative of quasi-1D electronic behavior. The spin coupling constants are obtained by mapping the total energies onto a spin Hamiltonian. The inter-chain coupling is found to be at least one order of magnitude smaller than the intra-chain coupling for both large and narrow pores. Interestingly, the intra-chain coupling changes sign and becomes five times stronger going from the large pore to the narrow pore structure. As such MIL-47(Mn) could provide unique opportunities for tunable low-dimensional magnetism in transition metal oxide systems.

High-Performance CO2-Selective Hybrid Membranes by Exploiting MOF-Breathing Effects.

Conventional CO2 separation in the petrochemical industry via cryogenic distillation or amine-based absorber-stripper units is energy-intensive and environmentally unfriendly. Membrane-based gas separation technology, in contrast, has contributed significantly to the development of energy-efficient systems for processes such as natural gas purification. The implementation of commercial polymeric membranes in gas separation processes is restricted by their permeability-selectivity trade-off and by their insufficient thermal and chemical stability. Herein, we present the fabrication of a Matrimid-based membrane loaded with a breathing metal-organic framework (MOF) (NH2-MIL-53(Al)) which is capable of separating binary CO2/CH4 gas mixtures with high selectivities without sacrificing much of its CO2 permeabilities. NH2-MIL-53(Al) crystals were embedded in a polyimide (PI) matrix, and the mixed-matrix membranes (MMMs) were treated at elevated temperatures (up to 350 °C) in air to trigger PI cross-linking and to create PI-MOF bonds at the interface to effectively seal the grain boundary. Most importantly, the MOF transitions from its narrow-pore form to its large-pore form during this treatment, which allows the PI chains to partly penetrate the pores and cross-link with the amino functions at the pore mouth of the NH2-MIL-53(Al) and stabilizes the open-pore form of NH2-MIL-53(Al). This cross-linked MMM, with MOF pore entrances was made more selective by the anchored PI-chains and achieves outstanding CO2/CH4 selectivities. This approach provides significant advancement toward the design of selective MMMs with enhanced thermal and chemical stabilities which could also be applicable for other potential applications, such as separation of hydrocarbons (olefin/paraffin or isomers), pervaporation, and solvent-resistant nanofiltration.

Breathing metal–organic frameworks based on flexible inorganic building units

Breathing metal–organic frameworks based on flexible inorganic building units

Rational Construction of Breathing Metal-Organic Frameworks through Synergy of a Stretchy Ligand and Highly Variable π-π Interaction.

The synergy of a stretchy ligand and highly variable π-π interaction has been proposed as a rational strategy for the construction of breathing metal-organic frameworks (MOFs). Based on this strategy, a breathing MOF, {[Cd2(AzDC)2(TPT)2](DMF)3} n, was successfully constructed with stretchy 4,4'-diazene-1,2-diyldibenzoate acid (H2AzDC) and 2,4,6-tris(4-pyridyl)triazine (TPT) as a source of the π-π interaction. The MOF features structure transformation upon stimulation with solvent guests and varied temperatures, which is straightforwardly characterized by single-crystal structures. Moreover, the solvent-free framework shows breathing behaviors in response to light hydrocarbon (C2H4, C2H6, C3H6, and C3H8) sorption, which was verified by stepwise sorption isotherms and in situ powder X-ray diffraction. Additional investigation of the sorption selectivity of C3/C2 systems indicated that the selectivity can be regulated by the modulation of the dynamic breathing behaviors, which can be used for the selective separation of C3/C2 light hydrocarbons.

Predictions of Stepped Isotherms in Breathing Adsorbents by the Rigid Adsorbent Lattice Fluid

Adsorbents that undergo structural changes in the presence of adsorbate molecules are an interesting new class of materials, which could offer enhanced selectivity, purity, and recovery in separation technology. To date, however, their application in such technology is hampered by the lack of a simple, consistent thermodynamic framework, which can effectively describe and predict their adsorption behavior under a range of conditions. This becomes especially true for their behavior in multicomponent adsorbate mixtures, for which experimental data are limited and cumbersome to obtain. Here, we present how the relatively simple rigid adsorbent lattice fluid model successfully and accurately predicts stepped isotherms in the breathing metal–organic framework, MIL-53 (Al), in the presence of CO2 and CH4. Breathing transitions are predicted solely on the basis of the different densities of the material’s two structural configurations and their associated Gibbs energies. Hysteresis effects can easily be included...

Flexible and breathing metal–organic framework with high and selective carbon dioxide storage versus nitrogen

A new functionalized metal–organic framework (MOF) {[Zn2(fum)2(4-bpdb)]·2H2O}n (TMU-42) fumarate (fum) and 1,4-bis(4-pyridyl)-3,4-diaza-1,3-butadiene (4-bpdb), synthesized and characterized by single-crystal X-ray diffraction, X-ray diffraction (XRD), etc. The breathing phenomenon and azine functional group introduced 2-fold interpenetrated TMU-42 as one of the highest CO2 storage capacity and surface area in between pillared metal–organic frameworks. To reveal functionality effect on CO2 adsorption TMU-42 compared with previously reported non-functionalized MOF, {[Zn2(fum)2(dpe)]·DMF·(H2O)0.5}n (TMU-43) 2-di(4-pyridyl)ethylene (dpe).

Pillared-layered metal–organic frameworks for mechanical energy storage applications

Breathing metal–organic frameworks (MOFs) are promising candidates for mechanical energy storage. Theoretical and experimental measurements reveal the potential of pillared-layered MOFs.

Adsorbate-induced lattice deformation in IRMOF-74 series

IRMOF-74 analogues are among the most widely studied metal-organic frameworks (MOFs) for adsorption applications because of their one-dimensional channels and high metal density. Most studies involving the IRMOF-74 series assume that the crystal lattice is rigid. This assumption guides the interpretation of experimental data, as changes in the crystal symmetry have so far been ignored as a possibility in the literature. Here, we report a deformation pattern, induced by the adsorption of argon, for IRMOF-74-V. This work has two main implications. First, we use molecular simulations to demonstrate that the IRMOF-74 series undergoes a deformation that is similar to the mechanism behind breathing MOFs, but is unique because the deformation pattern extends beyond a single unit cell of the original structure. Second, we provide an alternative interpretation of experimental small-angle X-ray scattering profiles of these systems, which changes how we view the fundamentals of adsorption in this MOF series.

Molecular separations with breathing metal-organic frameworks: modelling packed bed adsorbers.

Various metal-organic framework (MOFs) adsorbents show peculiar adsorption behaviour as they can adopt different crystal phases, each phase with its own adsorption characteristics. Besides external stimuli such as temperature or light, different species of guest adsorbate can trigger a transition (breathing) of the host structure at a different pressure. Such phase transitions also occur during dynamic separations on a packed bed of adsorbent, where the concentrations of the adsorbates vary throughout axial column distance and time. This work presents a general strategy to model the adsorption behavior of such phase changing adsorbents during column separations and focuses on remarkable model predictions for pure components and binary mixtures in diluted and non-diluted conditions. During binary breakthrough experiments, the behaviour of flexible adsorbents is quite complex. A succession of complete or even partial phase transformations (resulting in phase coexistence) can occur during the adsorption process. A variety of unusual breakthrough profiles is observed for diluted binary mixtures. Simulations reveal at least five types of breakthrough profiles to emerge. The occurrence of these cases can be rationalized by the hodograph technique, combined with the phase diagram of the adsorbent. The remarkable experimental breakthrough profiles observed for ortho-xylene/ethylbenzene (diluted) and CO2/CH4 (non-diluted) separation on the flexible MIL-53 framework can be rationalized by application of the proposed model strategy.

Ultraporous, Water Stable, and Breathing Zirconium-Based Metal-Organic Frameworks with ftw Topology.

"Breathing" metal-organic frameworks (MOFs) are an emerging class of soft porous crystals (SPCs) with potential for high working capacity for gas storage applications. However, most breathing MOFs have low stability and/or low surface area. Here we report a water-stable, high surface area, breathing MOF of ftw topology, NU-1105. While Zr6-oxo clusters as nodes introduce water stability in NU-1105, its high surface area and breathing character stem from its pyrene-based tetracarboxylate (Py-FP) linkers, in which the fluorene units (F) in the FP "arms" play a key role in promoting breathing behavior. During gas sorption studies, the "closed pore" (cp) ↔ "open pore" (op) transition of NU-1105 occurs at a propane pressure of ∼3 bar. At 1 bar, NU-1105 is in its cp form and adsorbs less propane than it would in its op form, highlighting improved working capacity. In situ powder X-ray diffraction during propane sorption was used to track the cp ↔ op transition, and molecular modeling was used to elucidate the structure of the op and cp forms of NU-1105. According to TD-DFT calculations, the proposed conformations of the Py-FP linkers in the op and cp forms are consistent with the measured excitation and emission spectra of the op and cp forms of NU-1105. Similar structural transitions are also observed in the porphyrinic MOF NU-1104 depending on the identity of the porphyrin core; we observed breathing behavior if the constituent Por-PTP linker is nonmetalated.

Unusually Large Band Gap Changes in Breathing Metal–Organic Framework Materials

Many of the potential applications for metal–organic frameworks (MOFs) focus on exploiting their porosity for molecular storage, release, and separation, where the functional behavior is controlled by a subtle balance of host–guest interactions. Typically, the host structure is relatively unperturbed by the presence of guests; however, a subset of MOFs exhibit dramatic phase-change behavior triggered by the adsorption of guests or other stimuli, for which the MIL-53 material is an archetype. In this work, we use density functional approaches to examine the electronic structure changes associated with changes of phase and density and find the associated change in band gaps can be larger than 1 eV for known MIL-53-type materials and hypothecated structures. Moreover, we show that internal pressure (via guest molecules) and external pressure can exert a major influence on the band gap size and gap states. The large response in electronic properties to breathing transitions in MOFs could be exploitable in future applications in resistive switching, phase-change memory, piezoresistor, gas-sensing and thermochromic materials.

ChemInform Abstract: Approaches for Synthesizing Breathing MOFs by Exploiting Dimensional Rigidity

AbstractReview: 85 refs.

Water Adsorption in Flexible Gallium-Based MIL-53 Metal–Organic Framework

Understanding the adsorption of water in metal–organic frameworks (MOF), and particularly in soft porous crystals, is a crucial prerequisite before considering MOFs for industrial applications. We report here a joint experimental and theoretical study on the behavior of a gallium-based breathing MOF, Ga-MIL-53, upon water adsorption. By looking at the energetics and thermodynamics of Ga-MIL-53, we demonstrate why it behaves differently from its sibling Al-MIL-53, showing a different phase at room temperature (a nonporous phase) and the presence of a hydrated narrow-pore structure at gas saturation pressure. Moreover, we present a complete water vapor pressure vs temperature phase diagram of Ga-MIL-53 upon water adsorption.