Recent development on the alkaline earth MOFs (AEMOFs)

Synthesis of anionic alkaline earth metal methanesulfonates bearing photo-responsive methylviologen

Anionic coordination frameworks stabilized by methylviologen (MV2+; 1,1'-dimethyl 4,4'-bipyridinium) as a photochromic module are a distinct class of functional materials. Herein, we report the first examples of alkaline earth metal methanesulfonates [MV{Mg(OSO2Me)3(H2O)2}2] (1), [MV{Ca(OSO2Me)3(H2O)2}2] (2), [2{Mg(OSO2Me)2(H2O)4}MV·2OSO2Me] (3), and [Me4-pip{Ca2(OSO2Me)6(H2O)2}]n (4) incorporating methylviologen or tetra-N-methylpiperazinium (Me4-pip) as a charge-balancing cation. X-ray crystallographic studies of 1-3 emphasize the role of isolated ion-pairs for the construction of hydrogen-bonded supramolecular assemblies and the ability of methanesulfonates to donate electrons (centroid⋯O = 3.09-3.15 Å) to promote photoinduced one-electron reduction of MV2+ to an MV˙+ radical cation in the solid state. The inorganic framework in 4 adopts a layered motif with an inter-lamellar spacing of 11.8 Å, providing spatial expanse to accommodate the organic cations.

A new three-dimensional barium(II) coordination polymer constructed from N,N'-bis(glycinyl)pyromellitic diimide: microwave-assisted synthesis, structure, Hirshfeld surface analysis and properties

A new three-dimensional (3D) coordination polymer, namely, poly[diaqua[μ5-2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetato]barium(II)], [Ba(C14H6N2O8)(H2O)2]n, (I), has been synthesized by the microwave-irradiated reaction of Ba(NO3)2 with N,N'-bis(glycinyl)pyromellitic diimide {BGPD, namely, 2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetatic acid, H2L}. The title compound was structurally characterized by single-crystal X-ray diffraction analysis and powder X-ray diffraction analysis, as well as IR spectroscopy. In the crystal structure of (I), the BaII ion is nine-coordinated by six carboxylate O atoms from five symmetry-related L2- dianions and one imide O atom, as well as two water O atoms. The coordination geometry of the central BaII ion can be described as a spherical capped square antiprism. One carboxylate group of the ligand serves as a μ3-bridge linking the BaII cations into a one-dimensional polynuclear secondary building unit (SBU). Another carboxylate group of the ligand acts as a μ2-bridge connecting the 1D SBUs, thereby forming a two-dimensional (2D) SBU. The resulting 2D SBUs are extended into a 3D framework via the pyromellitic diimide moiety of the ligand as a spacer. The 3D Ba framework can be simplified as a 5-connected hexagonal boron nitride net (bnn) topology. The intermolecular interactions in the 3D framework were further investigated by Hirshfeld surface analysis and the results show that the prominent interactions are H...O (45.1%), Ba...O (11.1%) and C...H (11.1%), as well as H...H (11.1%) contacts. The thermal stability, photoluminescence properties and UV-Vis absorption spectra of (I) were also investigated. The coordination polymer exhibits a fluorescence emission with a quantum yield of 0.071 and high thermal stability.

Three-dimensional alkaline earth metal-organic framework poly[[μ-aqua-aqua-bis-(μ3-carba-moyl-cyano-nitro-somethanido)barium] monohydrate] and its thermal decomposition

In the structure of the title salt, {[Ba(μ3-C3H2N3O2)2(μ-H2O)(H2O)]·H2O} n , the barium ion and all three oxygen atoms of the water mol-ecules reside on a mirror plane. The hydrogen atoms of the bridging water and the solvate water mol-ecules are arranged across a mirror plane whereas all atoms of the monodentate aqua ligand are situated on this mirror plane. The distorted ninefold coord-ination of the Ba ions is completed with four nitroso-, two carbonyl- and three aqua-O atoms at the distances of 2.763 (3)-2.961 (4) Å and it is best described as tricapped trigonal prism. The three-dimensional framework structure is formed by face-sharing of the trigonal prisms, via μ-nitroso- and μ-aqua-O atoms, and also by the bridging coordination of the anions via carbonyl-O atoms occupying two out of the three cap positions. The solvate water mol-ecules populate the crystal channels and facilitate a set of four directional hydrogen bonds. The principal Ba-carbamoyl-cyano-nitro-somethanido linkage reveals a rare example of the inherently polar binodal six- and three-coordinated bipartite topology (three-letter notation sit). It suggests that small resonance-stabilized cyano-nitroso anions can be utilized as bridging ligands for the supra-molecular synthesis of MOF solids. Such an outcome may be anti-cipated for a broader range of hard Lewis acidic alkaline earth metal ions, which perfectly match the coordination preferences of highly nucleophilic nitroso-O atoms. Thermal analysis reveals two-stage dehydration of the title compound (383 and 473 K) followed by decomposition with release of CO2, HCN and H2O at 558 K.

Metal-Organic Frameworks (MOFs): Classification, Synthesis, Modification, and Biomedical Applications

Metal-organic frameworks (MOFs) are a new variety of solid crystalline porous functional materials. As an extension of inorganic porous materials, it has made important progress in preparation and application. MOFs are widely used in various fields such as gas adsorption storage, drug delivery, sensing, and biological imaging due to their high specific surface area, porosity, adjustable pore size, abundant active sites, and functional modification by introducing groups. In this paper, the types of MOFs are classified, and the synthesis methods and functional modification mechanisms of MOFs materials are summarized. Finally, the application prospects and challenges of metal-organic framework materials in the biomedical field are discussed, hoping to promote their application in multidisciplinary fields.

Pd NPs decorated on crosslinked sodium alginate modified iron-based metal-organic framework Fe(BTC) as a green multifunctional catalyst for the oxidative amidation

The primary objective of this investigation was to develop a new nanocatalyst that could produce amides by oxidative amidation of benzyl alcohol, thereby reducing its environmental harm. To achieve this, Pd nanoparticle-immobilized crosslinked sodium alginate-modified iron-based metal-organic framework Fe(BTC) (Fe(BTC)@SA/ED/Pd), with excellent activity and selectivity in modified oxidative amidation of benzyl alcohol with amines, has been described. Crosslinked sodium alginate was modified on iron-based metal-organic framework Fe(BTC). It is worth noting that Pd nanoparticles were immobilized for the first time on a novel nanocomposite based on the Fe(BTC) MOF and crosslinked sodium alginate for tandem oxidative amidation to improve the eco-friendliness and economic efficiency of the process. The synergic effects of Fe(BTC), sodium alginate, and Pd NPs are important factors influencing the catalytic activity. Easy and green synthesis methods, availability of materials, high Pd loading, available catalytic sites, high surface area, high selectivity, and simple separation from the reaction medium are effective properties in catalytic activity.

2D/2D coupled MOF/Fe composite metamaterials enable robust ultra-broadband microwave absorption

The combination between macroscopic structure designs and microscopic material designs offers tremendous possibilities for the development of advanced electromagnetic wave (EMW) absorbers. Herein, we propose a metamaterial design to address persistent challenges in this field, including narrow bandwidth, low-frequency bottlenecks, and, particularly, the urgent issue of robustness (i.e., oblique, and polarized incidence). Our absorber features a semiconductive metal-organic framework/iron 2D/2D assembly (CuHT-FCIP) with abundant crystal/crystal heterojunctions and strong magneto-electric coupling networks. This design achieves remarkable EMW absorption across a broad range (2 to 40 GHz) at a thickness of just 9.3 mm. Notably, it maintains stable performance against oblique incidence (within 75°) and polarizations (both transverse electric and transverse magnetic). Furthermore, the absorber demonstrates high specific compressive strength (201.01 MPa·cm3·g-1) and low density (0.89 g·cm-3). This advancement holds promise for developing robust EMW absorbers with superior performance.

Square-planar Tetranuclear Cluster-based Alkaline Earth Metal-organic Frameworks with Enhanced Proton Conductivity

Alkaline earth (AE) metal complexes have garnered significant interest in various functional fields due to their nontoxicity, low density, and low cost. However, there is a lack of systematic investigation into the structural characteristics and physical properties of AE-metal-organic frameworks (MOFs). In this research, we synthesized isostructural MOFs consisting of AE4(μ4-Cl) clusters bridged by benzo-(1,2;3,4;5,6)-tris(thiophene-2'-carboxylic acid) (BTTC3-) ligands. The resulting structure forms a truncated octahedral cage denoted as [AE4(m4-Cl)]6(BTTC)8, which further linked to a porous three-dimensional framework. Among the investigated AE ions (Ca, Sr, and Ba), the Ca4-MOF demonstrated good chemical stability in water compared to Sr4-MOF and Ba4-MOF. The N2 adsorption and solid-state UV-vis-NIR absorption behaviors were evaluated for all AE4-MOFs, showing similar trends among the different metal ions. Additionally, the proton conduction study revealed that the Ca4-MOF exhibited ultra-high proton conductivity, reaching 3.52×10-2 S cm-1 at 343 K and 98 % RH. Notably, the introduction of LiCl via guest exchange resulted in an improved proton conduction of up to 6.36×10-2 S cm-1 under similar conditions in the modified LiCl@Ca4-MOF. The findings shed light on the regulation of physical properties and proton conductivity of AE-MOFs, providing valuable insights for their potential applications in various fields.

Current Status and Challenges for Metal-Organic-Framework-Assisted Conversion of Biomass into Value-Added Chemicals

Owing to the abundance of availability, low cost, and environmental-friendliness, biomass waste could serve as a prospective renewable source for value-added chemicals. Nevertheless, biomass conversion into chemicals is quite challenging due to the heterogeneous nature of biomass waste. Biomass-derived chemicals are appealing sustainable solutions that can reduce the dependency on existing petroleum-based production. Metal-organic frameworks (MOFs)-based catalysts and their composite materials have attracted considerable amounts of interest in biomass conversion applications recently because of their interesting physical and chemical characteristics. Due to their tunability, the catalytic activity and selectivity of MOF-based catalyst/composite materials can be tailored by functionalizing them with a variety of functional groups to enhance biomass conversion efficiency. This review focuses on the catalytic transformation of lignocellulosic biomass into value-added chemicals by employing MOF-based catalyst/composite materials. The main focus is given to the production of the platform chemicals HMF and Furfural from the corresponding (hemi)cellulosic biomass, due to their versatility as intermediates for the production of various biobased chemicals and fuels. The effects of different experimental parameters on the conversion of biomass by MOF-based catalysts are also included. Finally, current challenges and perspectives of biomass conversion into chemicals by MOF-based catalysts are highlighted.

A Robust Strontium Coordination Polymer with Selective and Sensitive Fluorescence Sensing Ability for Fe3+ Ions

Exploration of sensitive and selective fluorescence sensors towards toxic metal species is of great importance to solve metal pollution issues. In this work, a three-dimensional (3D) strontium coordination polymer of Sr₂(tcbpe) (H₄tcbpe = 1,1,2,2-tetrakis(4-(4-carboxy-phenyl)phenyl)ethene) has been synthesized and developed as a fluorescent sensor to Fe³⁺ ions. Sr₂(tcbpe) shows a mechanochromic fluorescence with emission shifting from blue of the pristine to green after being ground. Notably, based on a fluorescence quenching mechanism, Sr₂(tcbpe) displays a sensitive and selective fluorescent sensing behavior to Fe³⁺ ions with a detection limit of 0.14 mM. Moreover, Sr₂(tcbpe) exhibits high tolerance to water in a wide pH range (pH = 3-13), demonstrating that Sr₂(tcbpe) is a potential fluorescent sensor of Fe³⁺ in water.

A series of naphthalenediimide-based metal-organic frameworks: synthesis, photochromism and inkless and erasable printing

Three new three-dimensional metal-organic frameworks were synthesized based on a naphthalenediimide derivative ligand, all of which exhibit photochromic behaviour due to the presence of the naphthalenediimide core. Interestingly, two of them possess significant colour changes under light, excellent stability, and appropriate photochromic lifetimes, thus showing potential for application in inkless and erasable printing media.

The use of metal-organic frameworks as heterogeneous catalysts

This article presents an overview of some of the available research studies of MOFs as catalysts. Catalytic studies of magnetic iron oxide nanoparticles with modified surfaces, MOFs with precious metals such as palladium, platinum, and silver, with zirconium, hafnium, copper, alkaline earth metals, lanthanides are generalized. The studies of the catalytic activity of micro- and mesoporous MOF structures are described.

Biobased hydrogels and their composite containing MgMOF74 for the removal of textile dyes and wastewater treatment

In this work, we report the synthesis of a biobased hydrogel comprised of collagen, chitosan, and polyurethane for the removal of textile dyes. The adsorption capacity of this hydrogel was improved by adding a magnesium metal-organic framework to the semi-interpenetrating polymer matrix yielding a composite hydrogel. Removal of Bismarck Brown and Congo red was studied, and the experimental results fit Freundlich's model. Both hydrogel formulations were tested for the removal of textiles dyes from wastewaters. The magnesium-metal organic framework improved the efficiency of the biobased hydrogel for the removal of direct and mordant dyes reaching up to 89 ± 2%. The composite hydrogel was tested for the removal of Congo Red in a fixed bed column observing the breakthrough point after 168 min. Also, a flocculant material was prepared from collagen and chitosan and was tested for the removal of direct red dye from wastewater removing up to 80 ± 1%. The pretreated wastewater by coagulation-flocculation was treated by adsorption yielding a global removal efficiency of 99%. Finally, the studied hydrogels are potentially biodegradable being completely degraded by the proteolytic action after 22 days. PRACTITIONER POINTS: Composite hydrogels of collagen, chitosan, and MgMOF74 removed efficiently textile dyes from wastewater in batch systems and fixed bed columns. A biobased flocculant of collagen and chitosan significantly improved water quality after coagulation flocculation. Hydrogels were reusable for four cycles, and they can be proteolytically degraded after 22 days.

Synthesis of a Heterometallic [Zn2Ca] Pinwheel Array Stabilized by Amide-Amide Synthons

The rational design of heterometallic compounds bearing s-block metal ions have been a difficult task for chemists owing to their lack of preferential geometries. However, some strategies, such as the design of coordinating pockets with different sizes and/or donor atoms, have offered great results. In this work, this strategy has been tested using Ca(II) as an s-block metal ion and a compound previously obtained by our group with the formula [Zn3(μ-ACA)6(4-phpy)2], which contains tetrahedral N,O- and octahedral O-coordinating pockets as a model structure. From this work, the corresponding heterometallic compound with the formula [Zn2Ca(μ-ACA)6(4-phpy)2]·EtOH (1) has been successfully synthesized, and fully characterized, and its crystal structure has been elucidated. Furthermore, we have compiled all the crystal structures containing [Zn2M] pinwheel secondary building units (SBUs), where M stands for an s-block metal ion, and the observed tendencies, as well as the promising applications as template SBUs for the preparation of 1D–3D coordination polymers, have been discussed. Finally, solid-state UV-Vis and photoluminescence have been recorded and compared with the homometallic [Zn3(μ-ACA)6(4-phpy)2] compound.

Structural characterization of sodium and potassium 3-nitrohydrogenphthalate coordination polymers

The synthesis, crystal structures and properties of two alkali metal 3-nitrohydrogenphthalates obtained by a 1:2 reaction of M2CO3 (M = K or Na) with 3-nitrophthalic acid (LH2) are reported. In the anhydrous potassium coordination polymer [K(LH)] (LH = 2-carboxy-3-nitrobenzoate) 1, the K+ cation is bonded to nine oxygen atoms from six symmetry related (LH)– ligands resulting in a distorted {KO9} coordination polyhedron. Five of the six oxygen atoms including a nitro oxygen atom of the crystallographically unique 2-carboxy-3-nitrobenzoate are involved in metal binding. The μ6-bridging mode of (LH)– places the K+ cations into the layers of the two-dimensional (2D) coordination polymer. Each {KO9} polyhedron in 1 shares edges with two other polyhedra along the b and c axes. A low temperature structure redetermination of [Na(L#H)(H2O)3]·H2O (L#H = 2-carboxy-6-nitrobenzoate) 2 has revealed that the (L#H)− anion is bonded to the Na+ cation in a monodentate fashion via the carbonyl oxygen atom of the –COOH group and two of the three unique aqua ligands exhibit a bridging bidentate mode stabilizing a chain polymer. The structure of compound 2 thus consists of chains of edge-sharing {NaO6} octahedra. Thermal decomposition of 1 or 2 results in the formation of metal carbonate residues.

Ionothermal synthesis of calcium-based metal–organic frameworks in a deep eutectic solvent

The ionothermal synthesis of Ca-MOFs has been performed using the 1 : 2 choline chloride : e-urea deep eutectic solvent, allowing the preparation of water sensitive materials.

Three-fold interpenetrated metal–organic framework as a multifunctional fluorescent probe for detecting 2,4,6-trinitrophenol, levofloxacin, and l-cystine

A robust Zn(ii) MOF with good chemical and thermal stability, was prepared as an effective fluorescent probe for 2,4,6-trinitrophenol (TNP), levofloxacin (LVX) and l-cystine (l-Cys) with recyclability.