Immobilisation of a molecular epoxidation catalyst on UiO-66 and -67: the effect of pore size on catalyst activity and recycling

Amino-induced cadmium metal-organic framework based on thiazole ligand as a heterogeneous catalyst for the epoxidation of alkenes

Selective epoxidation of olefins is of high interest in the chemical industry due to the many applications of epoxides. This study reports on the synthesis of Cd-MOF, [Cd(DPTTZ)(5-AIP)] (IUST-1) (where DPTTZ = 2, 5-di (pyridine-4-yl) thiazolo [5, 4-d] thiazole, 5-AIP = 5-Aminoisophthalic acid), by a reflux method, which can be considered as a fast and simple process. The morphology and structure of the synthesized IUST-1 were determined by using FE-SEM (Field Emission Scanning Electron Microscopy), EDX (Energy Dispersive Analysis of X-ray), Mapping (Elemental Mapping), CHNS (Elemental analysis), XRD (X-Ray Diffraction), FT-IR (Fourier Transform Infrared), and TGA (Thermo Gravimetric Analysis). The epoxidation of cyclooctene was investigated using the activity of catalytic IUST-1. The results showed that in the presence of tert-butyl hydroperoxide and CCl4 in a 1:2 alkene/oxidant ratio, a high epoxide yield (99.8%) was obtained. In addition, IUST-1 can be easily separated by simple filtration and recycled five times successfully with a slight decrease in activity. This compound has some advantages such as high yield, short reaction time, and ease of reuse, which make it a suitable heterogeneous catalyst for the epoxidation of cyclooctene.

Aligning Metal Coordination Sites in Metal-Organic Framework-Enabled Metallaphotoredox Catalysis

Construction of catalytic metal centers, the key modules in artificial photosynthetic systems, lies at the heart to explore unpaved reactivity patterns powered by light. Here, we disclose that the amino (-NH₂) and carboxylic (-COO) functionalities, aligned in various visible-light-harvesting metal-organic frameworks (MOFs) (NH₂-UiO-66, (NH₂)₂-UiO-67, and NH₂-MIL-125), provide N/O-ligated Ni featuring different configurations and valence states. Of note, these Ni centers, in situ formed or preimplanted, demonstrated coordination units' spatial arrangement-dependent activity in cross-coupling of aryl halides and various nucleophiles. Our work provides a novel approach to construct and to regulate metal center(s) by MOFs' skeleton defined coordination environments, highlighting exclusive potential in exploring the reactivity pattern of the hosted metals.

Capture of Gaseous Iodine in Isoreticular Zirconium-Based UiO-n Metal-Organic Frameworks: Influence of Amino Functionalization, DFT Calculations, Raman and EPR Spectroscopic Investigation

A series of Zr-based UiO-n MOF materials (n=66, 67, 68) have been studied for iodine capture. Gaseous iodine adsorption was collected kinetically from a home-made set-up allowing the continuous measurement of iodine content trapped within UiO-n compounds, with organic functionalities (-H, -CH₃ , -Cl, -Br, -(OH)₂ , -NO₂ , -NH₂ , (-NH₂ )₂ , -CH₂ NH₂ ) by in-situ UV-Vis spectroscopy. This study emphasizes the role of the amino groups attached to the aromatic rings of the ligands connecting the {Zr₆ O₄ (OH)₄ } brick. In particular, the preferential interaction of iodine with lone-pair groups, such as amino functions, has been experimentally observed and is also based on DFT calculations. Indeed, higher iodine contents were systematically measured for amino-functionalized UiO-66 or UiO-67, compared to the pristine material (up to 1211 mg/g for UiO-67-(NH₂ )₂ ). However, DFT calculations revealed the highest computed interaction energies for alkylamine groups (-CH₂ NH₂ ) in UiO-67 (-128.5 kJ/mol for the octahedral cavity), and pointed out the influence of this specific functionality compared with that of an aromatic amine. The encapsulation of iodine within the pore system of UiO-n materials and their amino-derivatives has been analyzed by UV-Vis and Raman spectroscopy. We showed that a systematic conversion of molecular iodine (I₂ ) species into anionic I^- ones, stabilized as I^- ⋅⋅⋅I₂ or I₃ ^- complexes within the MOF cavities, occurs when I₂ @UiO-n samples are left in ambient light.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

An efficient and recyclable Cu@UiO-67-BPY catalyst for the selective oxidation of alcohols and the epoxidation of olefins

A novel CuCl2-UiO-67-BPY catalyst was synthesized for catalytic oxidation with up to 99% yield and 99% selectivity.

Host-Guest Interactions in a Metal-Organic Framework Isoreticular Series for Molecular Photocatalytic CO2 Reduction

A strategy to improve homogeneous molecular catalyst stability, efficiency, and selectivity is the immobilization on supporting surfaces or within host matrices. Herein, we examine the co‐immobilization of a CO₂ reduction catalyst [ReBr(CO)₃(4,4′‐dcbpy)] and a photosensitizer [Ru(bpy)₂(5,5′‐dcbpy)]Cl₂ using the isoreticular series of metal–organic frameworks (MOFs) UiO‐66, ‐67, and ‐68. Specific host pore size choice enables distinct catalyst and photosensitizer spatial location—either at the outer MOF particle surface or inside the MOF cavities—affecting catalyst stability, electronic communication between reaction center and photosensitizer, and consequently the apparent catalytic rates. These results allow for a rational understanding of an optimized supramolecular layout of catalyst, photosensitizer, and host matrix.

Metal-Organic Frameworks: Synthetic Methods and Potential Applications

Metal-organic frameworks represent a porous class of materials that are build up from metal ions or oligonuclear metallic complexes and organic ligands. They can be considered as sub-class of coordination polymers and can be extended into one-dimension, two-dimensions, and three-dimensions. Depending on the size of the pores, MOFs are divided into nanoporous, mesoporous, and macroporous items. The latter two are usually amorphous. MOFs display high porosity, a large specific surface area, and high thermal stability due to the presence of coordination bonds. The pores can incorporate neutral molecules, such as solvent molecules, anions, and cations, depending on the overall charge of the MOF, gas molecules, and biomolecules. The structural diversity of the framework and the multifunctionality of the pores render this class of materials as candidates for a plethora of environmental and biomedical applications and also as catalysts, sensors, piezo/ferroelectric, thermoelectric, and magnetic materials. In the present review, the synthetic methods reported in the literature for preparing MOFs and their derived materials, and their potential applications in environment, energy, and biomedicine are discussed.

Alkaline earth-organic frameworks with amino derivatives of 2,6-naphthalene dicarboxylates: structural studies and fluorescence properties

Alkaline earth metal ion organic frameworks (AEMOFs) represent a relatively underexplored subcategory of metal-organic frameworks (MOFs). In this contribution, we present the synthesis and structural study of the new MOFs 1-8 based on the alkaline earth ions Mg2+, Ca2+, Sr2+ and Ba2+ and the amino substituted bridging ligands 4-aminonaphthalene-2,6-dicarboxylate (ANDC2-) and 4,8-diaminonaphthalene-2,6-dicarboxylate (DANDC2-). Compounds 1, 5, 6, 7 and 8 constitute rare examples of three-dimensional MOFs which feature square planar M4 secondary building units (SBUs) surrounded by eight bridging ditopic ligands. The underlying topology of MOFs 1, 5, 7 and 8 conforms to the 4-c pcb net which can be simplified to the 8-c bcu net, while 6 adopts the 4-c lta net which simplifies to the 8-c reo net. To the best of our knowledge these are the first examples of MOFs of their structural types formed by linear dicarboxylates instead of trigonal tricarboxylates or tetrahedral tetracarboxylates. Compounds 2, 3 and 4 also feature three dimensional networks with linear rod-shaped SBUs with the Ba2+ MOF 3 displaying an sra rod-net and MOFs 2 and 4 showing very complex rod-nets with so far unique topologies. Fluorescence studies revealed that the free ligands exhibit strong blue-green emission displaying considerable positive solvatochromism thereby pointing towards charge transfer excited states involving the shift of electron density from the amino groups to the aromatic core. Correspondingly, the MOFs display ligand based fluorescence with small differences in emission maxima possibly attributable to the difference in the charge density of the metal ions combined with the different environments around ligands in the crystal structures.

Interpenetration isomers in isoreticular amine-tagged zinc MOFs

Subtleties of interpenetration are exposed and classified in the IRMOF-9 system.

Catalysis and photocatalysis by metal organic frameworks

This review aims to provide different strategies employed to use MOFs as solid catalysts and photocatalysts in organic transformations.

Stable metal–organic frameworks as a host platform for catalysis and biomimetics

Recent years have witnessed the exploration and synthesis of an increasing number of metal–organic frameworks (MOFs). The utilization of stable MOFs as a platform for catalysis and biomimetics is discussed.