Dynamic Metal Organic Frameworks Research Articles

Solvent induced reversible single-crystal-to-single-crystal structural transformation in dynamic metal organic frameworks: a case of enhanced hydrogen sorption in polycatenated framework

Two MOFs are showing a low-energy solid-state transformation and a dissolution–recrystallization structural transformation respectively. The hydrogen uptake was found to be influenced by the polycatenation present in one of the frameworks.

Desolvation-Degree-Induced Structural Dynamics in a Rigid Cerium-Organic Framework Exhibiting Tandem Purification of Ethylene from Acetylene and Ethane.

Due to the industrial requirements for high production and high quality of ethylene, efficient purification of ethylene from acetylene and ethane is of prime importance but challenging. Dynamic metal-organic frameworks (MOFs) have demonstrated intriguing structural dynamics and diverse applications recently. Among them, although a few flexible ones have exhibited interesting ethylene purification capability, rigid ones were yet barely investigated for such purpose. In this regard, a cerium(III)-based MOF was solvothermally synthesized, which is rigid and assembled from rod molecular building blocks associated with coordinative N,N-dimethylformamide (DMF) molecules. After liberating different degrees of DMF ligands via heating under vacuum or acetone exchange, both partially desolvated compounds of Ce-MOF-1 and Ce-MOF-2 were concertedly isolated in a fashion of single-crystal to single-crystal transformation. Although both newly generated materials crystallize in the same space group, they exhibit dissimilar unit cell parameters and slightly distinct ultramicropore sizes and pore microenvironments, thanks to the discrepancy in the desolvation degree. Consequently, Ce-MOF-1 and Ce-MOF-2 individually demonstrate C2H2- and C2H6-selective adsorption behavior, resulting in the potential tandem separation of C2H4 from C2H2 and C2H6 mixtures. The above results were successfully supported by not only single gas adsorption isotherms but also grand canonical Monte Carlo (GCMC) calculation studies and dynamic breakthrough experiments. The present work may pave the way for rigid MOFs aiming at advancing applications via solid-state structural dynamics.

Light-Induced Color Switching of Single Metal–Organic Framework Nanocrystals

Photoinduced modulation of the optical parameters of nanomaterials underlies the operating principles of all-optical nanodevices. Here, we demonstrate the laser-induced 10% modulation of the refractive index and 16-fold modulation of the extinction coefficient of the dynamic metal-organic framework (HKUST-1) nanocrystals within the whole visible range. Using the laser-induced water sorption/desorption process inside HKUST-1, we have achieved size-dependent reversible tuning of brightness and color of its nanocrystals over the different spatial directions and color palette. The numerical analysis also confirmed the detected optical tuning through the evolution of optical spectra and directivity of the scattered light. The results of the work demonstrate the promising nature of the dynamic metal-organic frameworks for nonlinear optics and expand the library of chemically synthesized hybrid materials with light-controlled optical properties.

Dynamic metal-organic frameworks for the separation of hydrogen isotopes.

Reversible structural transformation upon exposure to external stimuli can lead to breathing effect or gate-opening phenomena for dynamic metal-organic frameworks (MOFs), which endow them with excellent gas separation performance. The separation of hydrogen isotopes remains a huge challenge due to their nearly identical physical and chemical properties. The unique feature of dynamic MOFs, especially structural transition triggered by isotopes or by temperature, maximally enhances kinetic quantum sieving and contributes to the highly selective separation of hydrogen isotopes. Herein, we present some examples for the separation of hydrogen isotopes based on dynamic frameworks, and we expect to attract increasing attention to this research field.

Functionalized Dynamic Metal-Organic Frameworks as Smart Switches for Sensing and Adsorption Applications.

Over the past two decades, metal-organic frameworks (MOFs) with flexible structures or dynamic behavior have shown great potential as functional materials in many fields. This paper presents a review of these dynamic and functional MOFs, which can undergo controllable and reversible transformation, with regard to their application as smart switches. Trigger conditions, which include physical/chemical stimuli (e.g., guest molecules, light, temperature, pressure), are also discussed. Research methods for investigating the dynamic processes and mechanisms involving experimental characterization and computational modeling are briefly mentioned as well. The emphasis is on the aspects of the design and functionalization of dynamic MOFs. The pre-design of metal nodes, organic linkers, and topology, as well as post-modification of components, increases the possibility of obtaining functionalized dynamic materials. Recent advances with regard to potential applications for dynamic frameworks as smart switches for adsorption and sensing are also reviewed.

Polarity-Induced Excited-State Intramolecular Proton Transfer (ESIPT) in a Pair of Supramolecular Isomeric Multifunctional Dynamic Metal-Organic Frameworks.

A pair of supramolecular isomers of CdII -based MOF have been synthesized by utilizing a flexible N,N'-donor linker and a dicarboxylate with ESIPT (excited-state intramolecular proton transfer) fluorophore by varying the reaction media. One of the MOFs has a 3D four-fold interpenetrating framework with guest solvent in the structure that undergoes a solvent-dependent crystalline-to-crystalline structural transformation, which has been extensively studied by powder XRD and IR spectroscopy. The other MOF is structurally rigid in nature and has a two-fold interpenetrating structure without any guest molecules. Both the compounds show moderate CO2 adsorption and one of them, the MOF with the four-fold interpenetrating structure, also shows moderately high H2 adsorption. Furthermore, both the compounds show interesting luminescence behavior. In the solid state, the two compounds show single-peak spectra, whereas upon suspension of these compounds in polar solvents, the maxima split into two peaks with a large Stokes shift. On the other hand, in nonpolar solvents, only one emission maximum is observed. This solvatochromic dual-emission phenomenon is due to ESIPT, which has been extensively studied.

Crystalline to Crystalline Phase Transformations in Six Two-Dimensional Dynamic Metal–Organic Frameworks: Syntheses, Characterizations, and Sorption Studies

Six dynamic metal–organic frameworks, namely, {[Cd(1,4-bib)(glut)]·(4H2O)}n (1), {[Zn(1,4-bib)(glut)]·(4H2O)}n (2), {[Co(1,4-bib)(3,5-pydc)]·(2H2O)}n (3), {[Mn(1,4-bib)(3,5-pydc)]·(2H2O)}n (4), {[Z...

Structure and properties of dynamic metal–organic frameworks: a brief accounts of crystalline-to-crystalline and crystalline-to-amorphous transformations

External stimuli-driven structural changes and the associated properties of dynamic MOFs are discussed with examples.

Efficient and Reusable Metal–Organic Framework Catalysts for Carboxylative Cyclization of Propargylamines with Carbon Dioxide

AbstractCarbon dioxide (CO2) capture and transformation are important for decreasing the concentration of atmospheric CO2. To effectively capture CO2 and further fix it into valuable chemical products, functionalized dynamic metal–organic frameworks (MOFs) have been utilized not only because of their inherent cavity for accommodating CO2 but also owing to their reversible structural transformations in response to external stimuli for regulating the reaction. Herein, we report a dynamic and functional MOF [Cd3(L)2(BDC)3]2⋅16 DMF (MOF‐1 a; DMF=N,N‐dimethylformamide) achieved by reaction of the amino tripodal imidazole ligand N1‐(4‐(1 H‐imidazol‐1‐yl)benzyl)‐N1‐ (2‐aminoethyl)ethane‐1,2‐diamine (L) and 1,4‐benzenedicarboxylic acid (H2BDC) with cadmium salt. MOF‐1 a not only shows unprecedented high catalytic activity [initial turnover number (TON) up to 9300] and broad substrate scope for the carboxylative cyclization of propargylamines with CO2, but also can be switched on and off upon reversible structural transformation owing to its dynamic five‐fold interpenetrating structure. Further studies demonstrate that MOF‐1 a shows selective catalytic properties depending on the size of substrates, similarly to sophisticated biological systems.

Kinetic and Thermodynamic Control of Structure Transformations in a Family of Cobalt(II)-Organic Frameworks.

Dynamic metal-organic frameworks (MOFs) that respond to external stimuli have recently attracted great attention. However, the subtle control of dynamic processes as well as the illustration of the underlying mechanism, which is crucial for the targeted construction and modulation purpose, is extremely challenging. Herein, we report the achievement of simultaneous kinetic and thermodynamic modulation of the structure transformation processes of a family of cobalt(II)-organic frameworks, through the rational combination of coligand replacement, solvent molecule substitution, and ligand-based solid solution strategies. On the basis of the systematic investigation of the structural transformation behaviors, the underlying response mechanism and principles for modulation were illustrated. It is expected that this work can provide valuable hints for the study and further development of dynamic materials.

Photochromism, photoluminescence modulation and selective recognition of small molecules of two highly stable dynamic metal-organic frameworks.

Two highly stable dynamic metal-organic frameworks exhibit photochromism, tunable photoluminescence, and selective detection of oxygen, which can be recognised by the naked eye through color changes. Furthermore, they also display selective recognition of benzyl alcohol and halogenated solvents, respectively.

Dynamic metal–organic frameworks: syntheses, characterizations, sorption studies and their hydrolytic inter-conversion

Two metal–organic frameworks of Cd(II) from 3,4-pyridinedicarboxylate (3,4-pyrdc) and 1,2-bis(4-pyridyl)ethane (bpe) ligands, {[Cd(3,4-pyrdc)(bpe)(CH3OH)]·(H2O)}n (1) and {[Cd(3,4-pyrdc)(bpe)0.5(H2O)]·(H2O)}n (2) have been synthesized by changing the reaction medium. Compound 1 exhibited a 2D structure while compound 2 showed a 3D structure, which have both been revealed by single crystal X-ray studies. Both of the compounds showed interesting solvent mediated reversible structural transformations which have been established by exhaustive X-ray powder diffraction studies, elemental analysis, IR spectroscopy and thermogravimetric analysis. The desolvated form of the 2D framework (1) undergoes an irreversible structural transformation to form the 3D framework (2) upon soaking with water. The 2D to 3D transformation occurs through precise bond rotation and bond breaking which has been established by a GC–MS study. Sorption experiments with different gases and volatiles were performed for both the metal–organic frameworks and clearly indicated the differences in their inherent flexibility and transformability.

NMR and X-ray Study Revealing the Rigidity of Zeolitic Imidazolate Frameworks

NMR relaxation studies and spectroscopic measurements of zeolitic imidazolate framework-8 (ZIF-8) are reported. The dominant nuclear spin–lattice relaxation (T1) mechanism for ZIF-8 in air arises from atmospheric paramagnetic molecular oxygen. The 13C T1 measurements indicate that the oxygen interacts primarily with the imidazolate ring rather than the methyl substituent. Similar relaxation behavior was also observed in a ZIF with an unsubstituted ring, ZIF-4. Single-crystal X-ray diffraction was used to provide data for the study of the thermal ellipsoids of ZIF-8 at variable temperatures from 100 to 298 K, which further confirmed the rigid nature of this ZIF framework. These results highlight a rigid ZIF framework and are in contrast with dynamic metal–organic frameworks based on benzenedicarboxylate linking groups, for which the relaxation reflects the dynamics of the benzenedicarboxylate moiety.

The osmotic framework adsorbed solution theory: predicting mixture coadsorption in flexible nanoporous materials

Predictive analytical methods are crucial tools in the design of adsorptive gas separation processes. While they are widely used for rigid nanoporous solids, there is a lack of flexible materials, including the very topical and promising dynamic metal-organic frameworks (MOFs), which display such eye-catching phenomena as gate opening and breathing. We present here the osmotic framework adsorbed solution theory (OFAST), which predicts the evolution of structural transitions and selectivity upon adsorption of fluid mixtures in flexible nanoporous solids, using as a sole input experimental pure component isotherms.