A layerlike MOF (MIL-124, orGa2(OH)4(C9O6H4)) has been prepared and chosen as a parent compound to encapsulate Eu3+ cations by one uncoordinated carbonyl group in its pores. The Eu3+-incorporated sample (Eu3+@MIL-124) is fully characterized, which shows excellent luminescence and good fluorescence stability in water or other organic solvents. Subsequently, we choose Eu3+@MIL-124 as sensitive probe for sensing metal ions, anions, and organic small molecules because of its robust framework. Studying of the luminescence properties reveals that the complex Eu3+@MIL-124 was developed as a highly selective and sensitive probe for detection of Fe3+ (detection limit, 0.28 μM) and Fe2+ ions through fluorescence quenching of Eu3+ and MOF over other metal ions. In connection to this, a probable sensing mechanism was also discussed in this paper. In addition, when Eu3+@MIL-124 was immersed in the different anions solutions and organic solvents, it also shows highly selective for Cr2O72–(detection limit, 0.15 μM)and a...

Eu(III)-functionalized MIL-124 as fluorescent probe for highly selectively sensing ions and organic small molecules especially for Fe(III) and Fe(II).

Advanced one- and two-dimensional high-field and ultrafast MAS NMR measurements have been conducted in tandem with DFT calculations for the NMR parameters to deeply characterize the local environment and the long-range structure order of the porous metal–organic framework (MOF) type UiO-66(Zr) (UiO for University of Oslo) functionalized by a series of polar −Br, −2OH, and −NH2 groups. Such an innovative combining approach applied to the complex architecture of MOFs has been revealed successful not only to unambiguously assign all the NMR signals to the corresponding crystallographic sites but also to validate the crystal structures for each functionalized material that were only predicted so far. A further step consisted of probing the impact of the grafted functions on the ligand dynamics of these MOFs by means of dielectric relaxation spectroscopy measurements. It has been evidenced that the rotational motion of the organic linker requires overpassing an energy barrier that strongly depends on the funct...

Structure and Dynamics of the Functionalized MOF Type UiO-66(Zr): NMR and Dielectric Relaxation Spectroscopies Coupled with DFT Calculations

The burgeoning field of metal − organic frameworks or porous coordination polymers has received increasing interest in recent years. In the last decade these microporous materials have found several applications including storage and separation of gases, sensors, catalysis and functional materials. In order to better design new metal − organic frameworks and porous coordination polymers with specific functionalities a fundamental issue is to achieve a basic understanding of the relationship between molecular parameters and structures, preferred adsorption sites and properties by using using modern theoretical methods. The focus of this mini-review is a description of the potential and emerging applications of metal − organic frameworks. © 2017 Society of Chemical Industry

/pdf/application-of-metal-organic-frameworks-1bpc5o3p2m.pdf

Application of Metal‐organic Frameworks

Nuclear Magnetic Resonance (NMR) spectroscopy is a well-established method for the investigation of various types of porous materials. During the past decade, metal–organic frameworks have attracted increasing research interest. Solid-state NMR spectroscopy has rapidly evolved into an important tool for the study of the structure, dynamics and flexibility of these materials, as well as for the characterization of host–guest interactions with adsorbed species such as xenon, carbon dioxide, water, and many others. The present review introduces and highlights recent developments in this rapidly growing field.

/pdf/solid-state-nmr-spectroscopy-of-metal-organic-framework-4dd5ar6fgl.pdf

Solid-State NMR Spectroscopy of Metal–Organic Framework Compounds (MOFs)

For applications of metal-organic frameworks (MOFs) such as gas storage and separation, flexibility is often seen as a parameter that can tune material performance. In this work we aim to determine the optimal flexibility for the shape selective separation of similarly sized molecules (e.g., Xe/Kr mixtures). To obtain systematic insight into how the flexibility impacts this type of separation, we develop a simple analytical model that predicts a material's Henry regime adsorption and selectivity as a function of flexibility. We elucidate the complex dependence of selectivity on a framework's intrinsic flexibility whereby performance is either improved or reduced with increasing flexibility, depending on the material's pore size characteristics. However, the selectivity of a material with the pore size and chemistry that already maximizes selectivity in the rigid approximation is continuously diminished with increasing flexibility, demonstrating that the globally optimal separation exists within an entirely rigid pore. Molecular simulations show that our simple model predicts performance trends that are observed when screening the adsorption behavior of flexible MOFs. These flexible simulations provide better agreement with experimental adsorption data in a high-performance material that is not captured when modeling this framework as rigid, an approximation typically made in high-throughput screening studies. We conclude that, for shape selective adsorption applications, the globally optimal material will have the optimal pore size/chemistry and minimal intrinsic flexibility even though other nonoptimal materials' selectivity can actually be improved by flexibility. Equally important, we find that flexible simulations can be critical for correctly modeling adsorption in these types of systems.

/pdf/the-influence-of-intrinsic-framework-flexibility-on-1sopl899y9.pdf

The Influence of Intrinsic Framework Flexibility on Adsorption in Nanoporous Materials.

Two gallium carboxylates of MOF-type have been hydrothermally synthesized (210 °C) by using 1,2,4,5-benzenetetracarboxylate (Ga4(OH)8[C10O8H2]·5−5.6H2O or MIL-120) or 1,2,4-benzenetricarboxylate (Ga2(OH)4[C9O6H4] or MIL-124) as linkers. The structures of both compounds solved from XRD analysis, revealed two independent crystallographic sites for the gallium atoms, which are connected to each other through μ2-hydroxo edge, generating zigzag chains with a cis−trans mode. The inorganic ribbons are linked to each other via all the carboxylate functions of the pyromellitate ligand to form a 3D framework (MIL-120) or two of the carboxylate arms of the trimellitate ligand to form a 2D structure (MIL-124). For the latter, one of the carboxylate arms is not bonded to the gallium centers, resulting in the layered aspect of the final structure. Solid-state NMR using the slow-CTMAS method has been successfully implemented for the determination of the gallium site parameters for MIL-120, allowing more resolved spectra...

Redouane Hajjar

Papers

71Ga Slow-CTMAS NMR and Crystal Structures of MOF-Type Gallium Carboxylates with Infinite Edge-Sharing Octahedra Chains (MIL-120 and MIL-124)

Determination of NMR cogwheel phase cycle with XML

NMR cogwheel phase cycling determination with web tools: amplitude-modulated z-filter MQMAS sequence.