A Chemical Role for Trichloromethane: Room-Temperature Removal of Coordinated Solvents from Open Metal Sites in the Copper-Based Metal–Organic Frameworks

Confinement Effect in Metal-Organic Framework Cu3()2 for Enhancing Shape Selectivity of Radical Difunctionalization of Alkenes

The radical difunctionalization of alkenes plays a vital role in pharmacy, but the conventional homogeneous catalytic systems are challenging in selectivity and sustainability to afford the target molecules. Herein, the famous readily available metal-organic framework (MOF), Cu3(BTC)2, has been applied to cyano-trifluoromethylation of alkenes as a high-performance and recyclable heterogeneous catalyst, which possesses copper(II) active sites residing in funnel-like cavities. Under mild conditions, styrene derivatives and various unactivated olefins could be smoothly transformed into the corresponding cyano-trifluoromethylation products. Moreover, the transformation brought about by the active copper center in confined environments achieved regio- and shape selectivity. To understand the enhanced selectivity, the activation manner of the MOF catalyst was studied with control catalytic experiments such as FT-IR and UV-vis absorption spectroscopy of substrate-incorporated Cu3(BTC)2, which elucidated that the catalyst underwent a radical transformation with the intermediates confined in the MOF cavity, and the confinement effect endowed the method with pronounced selectivities.

Unveiling the potential of HKUST-1: synthesis, activation, advantages and biomedical applications

Metal-organic frameworks (MOFs) have emerged as a unique class of nanostructured materials, resulting from the self-assembly of metal ions or clusters with organic ligands, offering a wide range of applications in fields such as drug delivery, gas catalysis, and electrochemical sensing. Among them, HKUST-1, a copper-based MOF, has gained substantial attention due to its remarkable three-dimensional porous structure. Comprising copper ions and benzene-1,3,5-tricarboxylic acid, HKUST-1 exhibits an extraordinary specific surface area and pronounced porosity, making it a promising candidate in biomedicine. Notably, the incorporation of copper ions endows HKUST-1 with noteworthy activities, including antitumor, antibacterial, and wound healing-promoting properties. In this comprehensive review, we delve into the various synthesis methods and activation pathways employed in the preparation of HKUST-1. We also explore the distinct advantages of HKUST-1 in terms of its structural properties and functionalities. Furthermore, we investigate the exciting and rapidly evolving biomedical applications of HKUST-1. From its role in tumor treatment to its antibacterial effects and its ability to promote wound healing, we showcase the multifaceted potential of HKUST-1 in addressing critical challenges in biomedicine.

Quantitatively Visualizing the Thermal Dehydration Process and Isotope Effect in Single HKUST-1 Metal-Organic Framework Particles

Quantitatively visualizing the thermal dehydration in metal-organic frameworks (MOFs), especially at the single-particle level, is still challenging, hindering a deeper understanding of the reaction dynamics. Using in situ dark-field microscopy (DFM), we image the thermal dehydration process of single water-containing HKUST-1 (H₂O-HKUST-1) metal-organic framework (MOF) particles. DFM maps the color intensity of single H₂O-HKUST-1, which is linearly correlated with the water content in the HKUST-1 framework, enabling a direct quantification of several reaction kinetic parameters of single HKUST-1 particles. Interestingly, when H₂O-HKUST-1 is transformed into deutoxide (D₂O)-containing HKUST-1, the corresponding thermal dehydration reaction displays higher temperature parameters and activation energy but shows a lower rate constant and diffusion coefficient, revealing the isotope effect. The significant variation of the diffusion coefficient is also confirmed by molecular dynamics simulations. The present operando results are anticipated to provide valuable guidelines for the design and development of advanced porous materials.

Molecular Cleavage of Metal-Organic Frameworks and Application to Energy Storage and Conversion

The physicochemical properties of metal-organic frameworks (MOFs) significantly depend on composition, topology, and porosity, which can be tuned via synthesis. In addition to a classic direct synthesis, postsynthesis modulations of MOFs, including ion exchange, installation, and destruction, can significantly expand the application. Because of a limitation of the qualitative hard and soft acids and bases (HSAB) theory, posttreatment permits regulation of MOF structure by cleaving chemical bonds at the molecular level. Here, methods of coordination bond scission to tailor the structure are critically appraised and the application to energy storage and conversion is assessed. MOF structures synthesized by molecular-level coordination bond cleavage are described and the corresponding MOFs for electrocatalysis and renewable battery applications are evaluated. Significant emphasis is placed on various coordination bond cleavage to tune properties, including chemical groups, electronic structures, and morphologies. The review concludes with a critical perspective on practical application, together with challenges and future outlook for this emerging field.

Diamine Functionalization of a Metal-Organic Framework by Exploiting Solvent Polarity for Enhanced CO2 Adsorption

Diamine-appended metal-organic frameworks (MOFs) exhibit exceptional CO₂ adsorption capacities over a wide pressure range because of the strong interaction between basic amine groups and acidic CO₂. Given that their high CO₂ working capacity is governed by solvent used during amine functionalization, a systematic investigation on solvent effect is essential but not yet demonstrated. Herein, we report a facile one-step solvent exchange route for the diamine functionalization of MOFs with open metal sites, using an efficient method to maximize diamine loading. We employed an MOF, Mg₂(dobpdc) (dobpdc^4- = 4,4'-dioxido-3,3'-biphenyldicarboxylate), which contains high-density open metal sites. Indirect grafting with N-ethylethylenediamine (een) was performed with a minimal amount of methanol (MeOH) via multiple MeOH exchanges and diamine functionalization, resulting in a top-tier CO₂ adsorption capacity of 16.5 wt %. We established the correlation between N,N-dimethylformamide (DMF) loading and infrared peaks, which provides a simple method for determining the amount of the remaining DMF in Mg₂(dobpdc). All interactions among Mg, DMF, diamine, and solvent were analyzed by van der Waals (vdw)-corrected density functional theory (DFT) calculations to elucidate the effect of chemical potential on diamine grafting.

A Cu(ii)-MOF based on a propargyl carbamate-functionalized isophthalate ligand

A copper-based metal–organic framework (MOF) was prepared using a new linker, a 5-substituted isophthalic acid bearing a propargyl carbamate group, intended to provide a terminal alkyne function protruding from the material surface to generate supported gold species for potential catalytic applications. The novel material was fully characterized by spectroscopic analyses of different kinds: FTIR, Raman, EDX, and XPS, as well as by thermal and surface area measurements. Synchrotron X-ray diffraction data analysis, in particular, revealed that this MOF, labelled [Cu(1,3-YBDC)]·xH₂O (x ∼ 2), where Y stands for the pendant alkYne and BDC for benzene dicarboxylate, contains a complex network of 5-substituted isophthalate anions bound to Cu(ii) centers, arranged in pairs within paddlewheel (or “Chinese lantern”) fragments of Cu₂(μ-COO)₄(D)₂ formulation (D being a neutral Lewis base), with a short Cu⋯Cu distance of 2.633(4) Å. Quite unexpectedly, the apical atom in the paddlewheel structure belongs to the carbamate carbonyl oxygen atom. Such extra coordination by the propargyl carbamate groups drastically reduces the MOF porosity, a feature that was also confirmed by BET measurements. However, the MOF functionality is retained at the external crystal surface where 2% of active terminal alkynes is located.

A copper-based metal–organic framework with a novel 5-substituted isophthalic linker bearing a propargyl carbamate group protruding from the material surface.

A nickel ion-incorporating zinc-mesoporous metal organic framework thin film nanocomposite modified glassy carbon electrode for electrocatalytic oxidation of methanol in alkaline media

In this work, we have successfully synthesized a nickel ion-incorporating zinc-mesoporous metal–organic framework thin films (Zn-mMOFTFs) modified glassy carbon electrode (GCE), Ni/Zn-mMOFTFs/GCE, for electrooxidation of methanol in alkaline solution.

A historical overview of the activation and porosity of metal–organic frameworks

A historical overview of the activation and porosity of MOFs including strategies to design and preserve permanent porosity in MOFs.

Coordinatively unsaturated metal sites (open metal sites) in metal–organic frameworks: design and applications

The defined synthesis of OMS in MOFs is the basis for targeted functionalization through grafting, the coordination of weakly binding species and increased (supramolecular) interactions with guest molecules.

Achieving current rectification ratios ≥ 105 across thin films of coordination polymer

A record value of the current rectification ratio (RR ≥ 10⁵) across molecularly doped thin films of a Cu(ii)-coordination polymer is achieved.

Downsizing coordination polymers (CPs) to thin film configurations is a prerequisite for device applications. However, fabrication of thin films of CPs including metal–organic frameworks (MOFs) with reasonable electrical conductivity is challenging. Herein, thin film fabrication of a Cu(ii)-CP employing a layer-by-layer method is demonstrated whereby a self-assembled monolayer on Au was used as the functionalized substrate. Growth of the Cu(ii)-CP at the solid–liquid interface generated open-metal Cu(ii) sites in the thin film which were susceptible to activation by molecular dopant molecules. A significant enhancement in in-plane electrical conductivity and an unheralded cross-plane current rectification ratio (exceeding 10⁵ both at room-temperature and at an elevated temperature) were achieved. Such a remarkable rectification ratio was realized, similar to those of commercial Si rectifier diodes. This phenomenon is attributed to the formation of an electronic heterostructure in the molecularly doped thin film. Molecular doping additionally transformed the interfacial properties of thin films from hydrophilic to highly hydrophobic.

Exploiting Microwave Chemistry for Activation of Metal-Organic Frameworks

Microwave is thought of as a useful electromagnetic radiation tool because it is often used in real life as well as in a variety of chemical processes. Meanwhile, activation of metal-organic frameworks (MOFs), which must be essentially done to remove coordinating and pore-filling solvents before the use of MOFs for various applications, has been performed commonly with the methods of heat supply or solvent exchange. Here, we show a new methodological microwave activation (MA), realizing it with various MOFs such as HKUST-1, UiO-66, and MOF-74s. For instance, microwave irradiation to the MOF samples for 4-35 min leads to the complete activation of the MOFs without structural damage. As described below, we further demonstrate that the solvent-assisted MA, which is the MA process performed after the solvent exchange, can substantially reduce the time for the activation by 4 min.

A Reversible Phase Transition of 2D Coordination Layers by B-H∙∙∙Cu(II) Interactions in a Coordination Polymer

Materials that combine flexibility and open metal sites are crucial for myriad applications. In this article, we report a 2D coordination polymer (CP) assembled from CuII ions and a flexible meta-carborane-based linker [Cu₂(L1)₂(Solv)₂]•xSolv (1-DMA, 1-DMF, and 1-MeOH; L1: 1,7-di(4-carboxyphenyl)-1,7-dicarba-closo-dodecaborane). 1-DMF undergoes an unusual example of reversible phase transition on solvent treatment (i.e., MeOH and CH₂Cl₂). Solvent exchange, followed by thermal activation provided a new porous phase that exhibits an estimated Brunauer-Emmett-Teller (BET) surface area of 301 m² g^-1 and is capable of a CO₂ uptake of 41 cm³ g^-1. The transformation is reversible and 1-DMF is reformed on addition of DMF to the porous phase. We provide evidence for the reversible process being the result of the formation/cleavage of weak but attractive B-H∙∙∙Cu interactions by a combination of single-crystal (SCXRD), powder (PXRD) X-ray diffraction, Raman spectroscopy, and DFT calculations.

Coordinative Reduction of Metal Nodes Enhances the Hydrolytic Stability of a Paddlewheel Metal-Organic Framework

Enhancement of hydrolytic stability of metal-organic frameworks (MOFs) is a challenging issue in MOF chemistry because most MOFs have shown limitations in their applications under a humid environment. Meanwhile, inner sphere electron transfer has constituted one of the most intensively studied subjects in contemporary chemistry. In this report, we show, for the first time, a new conceptual coordinative reduction of Cu²⁺ ion, which is realized in a paddlewheel MOF, HKUST-1, with a postsynthetic manner via inner sphere "single" electron transfer from hydroquinone (H₂Q) to Cu²⁺ through its coordination bond. H₂Q treatment of HKUST-1 under anhydrous conditions leads to the single charge (1+) reduction of approximately 30% of Cu²⁺ ions. Thus, this coordinative reduction is an excellent reduction process to be self-controlled in both oxidation state and quantity. As described below, once Cu²⁺ ions are reduced to Cu⁺, the reduction reaction does not proceed further, in terms of their oxidation state as well as their amount. Also, we demonstrate that a half of the Cu⁺ ions (about 15%) remains in paddlewheel framework with pseudo square planar geometry and the other half of the Cu⁺ ions (about 15%) forms [Cu(MeCN)₄]⁺ complex in a small cage in the fashion of a ship-in-a-bottle after dissociation from the framework. Furthermore, we show that the coordinative reduction results in substantial enhancement of the hydrolytic stability of HKUST-1 to the extent that its structure remains intact even after exposure to humid air for two years.

Synthesis and Characterization of an SWCNT@HKUST-1 Composite: Enhancing the CO2 Adsorption Properties of HKUST-1

Synthesis of a new HKUST-1 composite based on single-walled carbon nanotubes (SWCNTs) was successfully achieved (SWCNT@HKUST-1). SWCNTs were used as templates to grow rod-like HKUST-1 crystals over the surface of the nanotubes. N₂ adsorption properties showed an increment on the surface area and pore volume for the SWCNT@HKUST-1 composite. Furthermore, the CO₂ capture increased, from 7.92 to 8.75 mmol g^-1 at 196 K up to 100 kPa, for the SWCNT@HKUST-1 composite. This enhancement was directly associated with the increase of the surface area of the composite. Additionally, an increase in the CO₂ heat of adsorption was estimated, from 30 to 39.1 kJ mol^-1 for the SWCNT@HKUST-1 composite. In situ Raman experiments corroborated the favored CO₂ adsorption for the composite and provided an insight into the augmented hydrophobicity of the SWCNT@HKUST-1. Ethanol adsorption isotherms corroborated an increase in the hydrophobicity of the material upon the incorporation of carbon nanotubes.

Insights into Functionalization of Metal-Organic Frameworks Using In Situ NMR Spectroscopy

Postsynthetic reactions of metal-organic frameworks (MOFs) are versatile tools for producing functional materials, but the methods of evaluating these reactions are cumbersome and destructive. Here we demonstrate and validate the use of in situ NMR spectroscopy of species in the liquid state to examine solvent-assisted ligand exchange (SALE) and postsynthetic modification (PSM) reactions of metal-organic frameworks. This technique allows functionalization to be monitored over time without decomposing the product for analysis, which simplifies reaction screening. In the case of SALE, both the added ligand and the ligand leaving the framework can be observed. We demonstrate this in situ method by examining SALE and PSM reactions of the robust zirconium MOF UiO-67 as well as SALE with the aluminum MOF DUT-5. In situ NMR spectroscopy provided insights into the reactions studied, and we expect that future studies using this method will permit the examination of a variety of MOF–solute reactions.

Recent Hydrophobic Metal-Organic Frameworks and Their Applications

The focus of discussion of this review is the application of the most recent synthesized hydrophobic metal-organic frameworks (MOFs). The most promising hydrophobic MOFs are mentioned with their applications and discussed. The various MOFs considered are sub-sectioned into the main application areas, namely alcohol adsorption and oil/water-alcohol/water separation, gas separation and storage, and other applications such as self-cleaning and liquid marbles. Again, the methods of synthesis are briefly described, showing how the features of the end product aid in their applications. The efficiency of the MOF materials and synthesis methods are highlighted and briefly discussed. Lastly, the summary and outlook section concludes the write-up giving suggestions that would be useful to present-day researchers.

High Proton Mobility with High Directionality in Isolated Channels of MOF-74

Isolated one-dimensional (1-D) proton channels in a metal-organic framework, MOF-74, have been reasonably expected to show highly directional proton conductivity, although no evidence has been provided. As a result of dimensional anisotropy of the channels evenly aligned in the c-axis of MOF-74 single crystal, highly directional proton conductivity is demonstrated by using electrochemical impedance spectroscopy. In particular, single crystals treated with sulfuric acid or ammonium hydroxide displays a maximum ∼1200-fold-enhanced c-axis proton conductivity compared to its a-axis conductivity, demonstrating highly directional proton migration through the channels. Very low activation energies (e.g., 0.12 eV) for the c-axis conductivity of MOF-74 also suggest a high proton mobility that arises via Grotthuss proton transfer parallel to the channels.

Highly Effective Removal of Metal Cyanide Complexes and Recovery of Palladium Using Quaternary-Ammonium-Functionalized MOFs

In this study, quaternary-ammonium-functionalized metal–organic frameworks (MOFs) Et-N-Cu(BDC-NH₂)(DMF), were prepared, characterized, and applied for the highly effective removal of metal cyanide complexes, including Pd(CN)₄²⁻, Co(CN)₆³⁻, and Fe(CN)₆³⁻. Batch studies were carried out, and the maximum adsorption capacities of Pd(II), Co(III), and Fe(III) reached 172.9, 101.0, and 102.6, respectively. Adsorption was rapid, and equilibrium was established within 30 min. Et-N-Cu(BDC-NH₂)(DMF) exhibited high thermal and chemical stability. Furthermore, absorbed Pd(CN)₄²⁻ was selectively recovered by two-step elution. First, Co(CN)₆³⁻ and Fe(CN)₆³⁻ were eluted with a 1.5 mol L⁻¹ KCl solution. Elution rates of Co(CN)₆³⁻ and Fe(CN)₆³⁻ were greater than 98.0%, whereas the elution percentage of Pd(CN)₄²⁻ was less than 2.0%. Second, >97.0% Pd(CN)₄²⁻ on the loaded MOFs was eluted using a 2.0 mol L⁻¹ KI solution. The recovery rate of Pd(CN)₄²⁻ was greater than 91.0% after five testing cycles. Adsorption isotherms, kinetics models, and adsorption thermodynamics of Pd(CN)₄²⁻ on Et-N-Cu(BDC-NH₂) (DMF) were also systematically investigated. The Et-N-Cu(BDC-NH₂) (DMF) absorbent exhibited a rapid, excellent ability for the adsorption of metal cyanide complexes.

Metal–Organic Framework Hybrid Materials and Their Applications

The inherent porous nature and facile tunability of metal–organic frameworks (MOFs) make them ideal candidates for use in multiple fields. MOF hybrid materials are derived from existing MOFs hybridized with other materials or small molecules using a variety of techniques. This led to superior performance of the new materials by combining the advantages of MOF components and others. In this review, we discuss several hybridization methods for the preparation of various MOF hybrids with representative examples from the literature. These methods include covalent modifications, noncovalent modifications, and using MOFs as templates or precursors. We also review the applications of the MOF hybrids in the fields of catalysis, drug delivery, gas storage and separation, energy storage, sensing, and others.

Organosoluble tetravalent actinide di- and trifluorides

Soluble molecular actinide(iv) fluorides can be prepared in high yield via redox or metathesis reactions of silver fluorides with actinide compounds containing ancillary iodide or fluorinated thiolate ligands.