The use of ionic liquids in the synthesis of zinc imidazolate frameworks

Tunable Zeolitic Imidazolate Framework-8 Nanoparticles for Biomedical Applications

Zeolite imidazole framework-8 (ZIF-8) is the most prestigious one among zeolitic imidazolate framework (ZIF) with tunable dimensions and unique morphological features. Utilizing its synthetic adjustability and structural regularity, ZIF-8 exhibits enhanced flexibility, allowing for a wide range of functionalities, such as loading of nanoparticle components while preserving biomolecules activity. Extensive efforts are made from investigating synthesis techniques to develop novel applications over decades. In this review, the development and recent progress of various synthesis approaches are briefly summarized. In addition, its interesting properties such as adjustable porosity, excellent thermal, and chemical stabilities are introduced. Further, five representative biomedical applications are highlighted based on above physicochemical properties. Finally, the remaining challenges and offered insights into the future outlook are also discussed. This review aims to understand the co-relationships between structures and biomedical functionalities, offering the opportunity to construct attractive materials with promising characteristics.

Highly Enantioselective Catalysis by Enzyme Encapsulated in Metal Azolate Frameworks with Micelle-Controlled Pore Sizes

Encapsulating enzymes within metal-organic frameworks has enhanced their structural stability and interface tunability for catalysis. However, the small apertures of the frameworks restrict their effectiveness to small organic molecules. Herein, we present a green strategy directed by visible linker micelles for the aqueous synthesis of MAF-6 that enables enzymes for the catalytic asymmetric synthesis of chiral molecules. Due to the large pore aperture (7.6 Å), double the aperture size of benchmark ZIF-8 (3.4 Å), MAF-6 allows encapsulated enzyme BCL to access larger substrates and do so faster. Through the optimization of surfactants' effect during synthesis, BCL@MAF-6-SDS (SDS = sodium dodecyl sulfate) displayed a catalytic efficiency (Kcat/Km) that was 420 times greater than that of BCL@ZIF-8. This biocomposite efficiently catalyzed the synthesis of drug precursor molecules with 94-99% enantioselectivity and nearly quantitative yields. These findings represent a deeper understanding of de novo synthetic encapsulation of enzyme in MOFs, thereby unfolding the great potential of enzyme@MAF catalysts for asymmetric synthesis of organics and pharmaceuticals.

New heterometallic Co/Zn, Ag/Co, and Ag/Zn imidazolates: structural characterization and catalytic activity in the oxidation of organic compounds

Nanocrystalline powders of monometallic and bimetallic imidazolates of Co, Zn and Ag were produced by a reaction carried out in water. The powders were characterized by powder X-ray diffraction and the crystal structures of the new compounds Ag2ZnIm4 and Ag2CoIm4 (Im = imidazolate) were solved. Heterometallic Co/Zn imidazolates showed the known Zn-zni crystal structure while Ag/Zn and Ag/Co systems were isostructural to the copper analogs. The powders were further characterized by EDX, UV-Vis and FTIR ATR spectroscopy in the solid state. The catalytic experiments indicated that out of the studied heterometallic compounds only Ag2Co(Im)4 exhibits some catalytic activity in the oxidation reaction of 1-phenylethanol with tert-butylhydroperoxide at elevated temperatures.

ZIF-8 metal organic framework composites as hydrogen evolution reaction photocatalyst: A review of the current state

In the past decade, extensive research has been devoted to synthesis of ZIF-8 materials for catalytic applications. As physico-chemical properties are synthesis-dependent, this review explores different synthesis strategies based the solvent and solvent-free synthesis of zeolitic imidazole framework. Accordingly, the effect of several parameters on the ZIF-8 synthesis were discussed including solvent, deprotonating agents, precursors ratio is delivered. Additionally, the advantages and disadvantages of each synthesis have been discussed and assessed. ZIF-8 textural and structural properties justify its wide use as a stable high surface area MOF in aqueous catalytic reactions. This review includes the applicatios of ZIF-8 materials in photocatalytic hydrogen evolution reaction (HER). The efficiency of the reviewed materials was fairly assessed. Finally, Limitations, drawbacks and future challenges were fully debated to ensure the industrial viability of the ZIFs.

Larrea E, Bazán B, Barandika G, Urtiaga MK, Arriortua MI. Ionothermal Synthesis of Cadmium Coordination Polymers: Ionic Liquid Effects on the Synthesis, Structural, and Thermal Characterization

Ionothermal synthesis is a little used method for the preparation of coordination polymers. By this method, two cadmium compounds were synthesized, 1, with formula Cd₃(ox)F₂(Ina)₂ (Ina = isonicotinate) and 2, Cd(NO₃)₂(4,4′-Bpy) (4,4′-Bpy = 4,4′-Bipyridine). The modification of the reaction conditions has allowed to obtain 2 as a pure phase. The structure of both compounds was determined by a single-crystal X-ray diffraction. Compound 1 is isostructural to the previously reported Cd₂Zn(ox)(OH)₂(Ina)₂. It crystallizes in the monoclinic space group P2₁/n and present a three-dimensional (3D) network, built-up from [Cd₃(ox)F₂]_n²ⁿ⁺ layers, linked by isonicotinate ligands. Crystals of 2 are formed by twins of two components which are rotated ca. 180° to each other. This compound crystallizes in the triclinic P-1 space group and its structure can be describe as a two-dimensional (2D) 4 connected ‘sql’ net. The layers are composed by [Cd(NO₃)₂]_n chains linked through 4,4′-Bpy ligands, and are pillared along the [011] direction. The thermal decomposition of 2 was studied by thermogravimetric and thermodiffractiometric techniques. The compound decomposes gradually starting from 160 °C, and due to heating, the structure suffers slight reversible changes in the bond distances and angles.

New synthetic strategies to prepare metal–organic frameworks

This critical review summarizes the recent developments in the application of new synthetic strategies for preparing MOFs, including the ionothermal method, deep eutectic solvent usage, surfactant-thermal process, and mechanochemistry.

Structure-directing effects of ionic liquids in the ionothermal synthesis of metal-organic frameworks

Traditional synthesis of metal-organic frameworks (MOFs) involves the reaction of a metal-containing precursor with an organic linker in an organic solvent at an elevated temperature, in what is termed a 'solvothermal' reaction. More recently, many examples have been reported of MOF synthesis in ionic liquids (ILs), rather than an organic solvent, in 'ionothermal' reactions. The high concentration of both cations and anions in an ionic liquid allows for the formation of new MOF structures in which the IL cation or anion or both are incorporated into the MOF. Most commonly, the IL cation is included in the open cavities of the MOF, countering the anionic charge of the MOF framework itself and acting as a template around which the MOF structure forms. Ionic liquids can also serve other structure-directing roles, for example, when an IL containing a single enantiomer of a chiral anion leads to a homochiral MOF, even though the IL anion is not itself incorporated into the MOF. A comprehensive review of ionothermal syntheses of MOFs, and the structure-directing effects of the ILs, is given.

Crystal structure of catena-poly[[bis-(acetato-κO)copper(II)]-bis-[μ-4-(1H-imidazol-1-yl)phenol]-κ2N3:O;κ2O:N3]

In the title compound, [Cu(CH3COO)2(C9H8N2O)2] n , the CuII ion resides on a centre of inversion, displaying a tetra-gonally distorted octa-hedral coordination environment defined by two pairs of N and O atoms of symmetry-related 4-(1H-imidazol-1-yl)phenol ligands and the O atoms of two symmetry-related acetate ligands. The bridging mode of the 4-(1H-imidazol-1-yl)phenol ligands is associated with a very long Cu⋯O inter-actions involving the phenol O atom of the heterocyclic ligand, which creates chains extending parallel to [100]. In the crystal, the chains are arranged in a distorted hexa-gonal rod packing and are linked via C-H⋯O hydrogen bonds and by π-π stacking inter-actions involving centrosymmetrically related pairs of imidazole and phenol rings.

A facile solvent-free synthesis route for the assembly of a highly CO2 selective and H2S tolerant NiSIFSIX metal-organic framework

The development of materials for CO2 capture with high selectivity and high tolerance to H2S is of prime importance for various industrially relevant gas streams (e.g. natural gas and biogas upgrading as well as pre-combustion capture). Here, we report the successful fabrication of a MOF with combined exceptional CO2 capture properties and H2S tolerance, namely the NiSIFSIX-based MOF using both solvothermal and solvent-free methodologies.

Surfactant-directed syntheses of mesostructured zinc imidazolates: formation mechanism and structural insights

A detailed study on the formation mechanism, local and long-range structures of surfactant-directed lamellar zinc imidazolates is presented.

Zn10(Im)20·4DBF: an unprecedented 10-nodal zeolitic topology with a 10-MR channel and 10 crystallographically independent Zn atoms

Zn₁₀(Im)₂₀·4DBF has an unprecedented zeolitic topology and features 10 crystallographically independent Zn atoms and an unusual 4-connected 10-nodal net.

A single precursor approach for ZIF synthesis: transformation of a new 1D [Zn(Im)(HIm)2(OAc)] structure to 3D Zn(Im)2 frameworks

We successfully use a 1-dimensional (1D) chain structure with the formula [Zn(Im)(HIm)₂(OAc)] (Im = imidazolate, HIm = imidazole, OAc = carboxylate) as a single precursor/source of a metal and ligand to directly prepare 3-dimensional (3D) [Zn(Im)₂] frameworks.

Anisotropic thermal expansion in a metal-organic framework

Ionothermal reaction between Mn(II)(acetate)2·4H2O and 1,3,5-benzenetricarboxylic acid (H3BTC) in either of the two ionic liquids 1-ethyl-3-methylimidazolium bromide (EMIMBr) and 1-ethyl-3-methylimidazolium tosylate (EMIMOTs) resulted in the formation of the new metal-organic framework (MOF) EMIM[Mn(II)BTC] (BTC = 1,3,5-benzenetricarboxylate). The compound crystallizes in the orthorhombic space group Pbca with unit-cell parameters of a = 14.66658 (12), b = 12.39497 (9), c = 16.63509 (14) Å at 100 K. Multi-temperature single-crystal (15-340 K) and powder X-ray diffraction studies (100-400 K) reveal strongly anisotropic thermal expansion properties. The linear thermal expansion coefficients, αL(l), attain maximum values at 400 K along the a- and b-axis, with αL(a) = 115 × 10(-6) K(-1) and αL(b) = 75 × 10(-6) K(-1). At 400 K a negative thermal expansion coefficient of -40 × 10(-6) K(-1) is observed along the c-axis. The thermal expansion is coupled to a continuous deformation of the framework, which causes the structure to expand in two directions. Due to the rigidity of the linker, the expansion in the ab plane causes the network to contract along the c-axis. Hirshfeld surface analysis has been used to describe the interaction between the framework structure and the EMIM cation that resides within the channel. This reveals a number of rather weak interactions and one governing hydrogen-bonding interactions.

Real-time and in situ monitoring of mechanochemical milling reactions

Chemical and structural transformations have long been carried out by milling. Such mechanochemical steps are now ubiquitous in a number of industries (such as the pharmaceutical, chemical and metallurgical industries), and are emerging as excellent environmentally friendly alternatives to solution-based syntheses. However, mechanochemical transformations are typically difficult to monitor in real time, which leaves a large gap in the mechanistic understanding required for their development. We now report the real-time study of mechanochemical transformations in a ball mill by means of in situ diffraction of high-energy synchrotron X-rays. Focusing on the mechanosynthesis of metal-organic frameworks, we have directly monitored reaction profiles, the formation of intermediates, and interconversions of framework topologies. Our results reveal that mechanochemistry is highly dynamic, with reaction rates comparable to or greater than those in solution. The technique also enabled us to probe directly how catalytic additives recently introduced in the mechanosynthesis of metal-organic frameworks, such as organic liquids or ionic species, change the reactivity pathways and kinetics.

Poly[(μ(3)-benzene-1,3,5-tricarboxyl-ato-κO:O:O)(μ(2)-2-methyl-imidazolato-κN:N')tris-(2-methyl-imidazole-κN)dizinc(II)]

Hydro-thermal reaction involving zinc nitrate hexa-hydrate, tris-odium benzene-1,3,5-tricarboxyl-ate (Na(3)BTC) and 2-methyl-imidazole (2-MeImH) yielded the title compound, [Zn(2)(C(9)H(3)O(6))(C(4)H(5)N(2))(C(4)H(6)N(2))(3)]. In this mixed-ligand metal-organic compound, Zn(2+) ions are coordinated by N atoms from 2-MeImH mol-ecules and (2-MeIm)(-) ions, as well as by O atoms from (BTC)(3-) ions. This results in two different distorted tetra-hedra, viz. ZnN(3)O and ZnN(2)O(2). These tetra-hedra are inter-connected via (BTC)(3-) ions and N:N'-bridging (2-MeIm)(-) ions, thus forming a layered structure in the bc plane. Hydrogen bonds between the O atoms of carboxyl-ate ions and NH groups of 2-MeImH ligands link the layers into a three-dimensional structure.