High Proton Conductivity by a Metal–Organic Framework Incorporating Zn8O Clusters with Aligned Imidazolium Groups Decorating the Channels

Close-packing effect of water clusters within metal-organic framework pores on proton conductivity: a dielectric relaxation phenomenon in loose space and colossal dielectric permittivity

Proton-conducting metal-organic frameworks (MOFs) have attracted tremendous attention for their promising application in proton-exchange membrane fuel cells. Water clusters play an extremely important role in the proton-conduction process and affect the proton conductivity of host materials. To date, the close-packing effect of water clusters within pores on proton conductivity due to the amorphous structure of commercial proton-exchange membranes is unclear. Herein, we prepared two crystalline MOFs containing different water clusters, namely, [Sm2(fum)3(H2O)4]·3H2O (Sm-fum-7H2O) and [Er2(fum)3(H2O)4]·8H2O (Er-fum-12H2O) (H2fum = fumaric acid), and regulated their proton conductivities by changing the water clusters. As expected, Sm-fum-7H2O showed a high proton conductivity of 6.89 × 10-4 S cm-1 at 333 K and ∼97% RH because of the close packing of the water clusters within the pores triggered by a lanthanide contraction effect, outperforming that of Er-fum-12H2O and some previously reported MOFs. Additionally, Sm-fum-7H2O and Er-fum-12H2O demonstrated high dielectric functions, reaching 2.22 × 103 and 1.42 × 105 at 102.5 Hz, respectively, making Er-fum-12H2O a highly dielectric material. More importantly, broadband dielectric spectroscopy measurements indicated that there was a dielectric relaxation process in Er-fum-12H2O with an activation energy of 0.59 eV. The present findings provide a better understanding of the crucial role of confined water clusters in proton conductivity and the novel phenomenon of the coexistence of proton conduction and dielectric relaxation in crystalline MOF materials.

Symmetry related proton conductivity tunability via aliovalent metal substitution in imidazolium templated stable metal-organic framework hybrid membranes

Proton-conducting materials have gained popularity owing to their extensive applications in biologic/chemical sensors, supercapacitors, proton sieving, and proton-exchange-membrane fuel cells. To date, the most commercially used polymer membrane has been the Nafion series that exhibits conductivity exceeding 0.1 S cm-1, however, this series is expensive, has poor dimensional stability, and requires a complex synthesis process. The key criterion for selecting Nafion alternatives is to achieve the systematic integration of high proton conductivity with high stability through a simple and efficient approach. In this study, we used an aliovalent metal substitution strategy to design serial metal-organic frameworks (MOFs), including tetragonal T-Cd-BTC (CH3NH2CH3)2[Cd(BTC)](H2O) and quasi-cubic quasi-C-In-BTC (C4H7N2)[In(BTC)] and Im@quasi-C-In-BTC (C3H5N2)2[In(BTC)] frameworks, with 2-methylimidazolium and imidazolium cations as templates, respectively. Because of the aliovalent substitution of In(III) for Cd(II), both the metal-oxygen bond strength and unit cell symmetry gradually increased, resulting in an increase in the thermal stability of quasi-C-In-BTC and Im@quasi-C-In-BTC at temperatures of up to 700 K. Compared with in situ loaded 2-methylimidazolium quasi-C-In-BTC, Im@quasi-C-In-BTC prepared by incorporating the imidazolium cation into the pores of activated quasi-C-In-BTC exhibited a higher proton conductivity of 7.1 × 10-2 S cm-1 at 338 K and 95 % relative humidity. Thus, Im@quasi-C-In-BTC demonstrated real-life application. This result was confirmed by integrating Im@quasi-C-In-BTC with a poly(vinyl pyrrolidone)-poly(vinylidene fluoride) polymer matrix. Density functional theory simulations indicated that Im@quasi-C-In-BTC was strongly acidic and had high water-adsorption capacities, which contributed to extensive hydrogen-bond networks and strong host-guest interactions, in accordance with the experimental finding.

Proton Conduction via Water and Ammonia Coordinated Metal Cationic Species in MOF and MHOF Platforms

Although metal-organic frameworks (MOFs) and metalo hydrogen-bonded organic frameworks (MHOFs) are designed as promising solid-state proton conductors by incorporating various protonic species intrinsically or extrinsically, design and development of such materials by employing the concept of proton conduction through coordinated polar protic solvent is largely unexplored. Herein, we have constructed two proton-conducting materials having different solvent coordinated metal cationic species: In-H2O-MOF, ({[In(H2O)6][In3(Pzdc)6] ⋅ 15H2O}n; H2Pzdc: pyrazine-2,3-dicarboxylic acid) with coordinated water molecules from hexaaquaindium cationic species, and MHOF-4, ([{Co(NH3)6}2(2,6-NDS)2(H2O)2]n; 2,6-H2NDS: 2,6-naphthalenedisulfonic acid) with coordinated ammonia from hexaammoniacobalt cationic species. Interestingly, higher proton conductivity was achieved for In-H2O-MOF (1.5×10-5 S cm-1) than MHOF-4 (6.3×10-6 S cm-1) under the extreme conditions (80 °C and 95 % RH), which could be attributed to enhanced acidity of coordinated water molecules having much lower pKa value than that of coordinated ammonia. Greater charge polarization on hydrogen atoms of In3+-coordinated water molecules than that of Co2+-coordinated ammonia led to the high conductivity of In-H2O-MOF, as evident by quantum chemical studies. Such a comparative study on metal-coordinated protic polar solvents in achieving proton conduction in crystalline solids is yet to be made.

Room-Temperature Superprotonic Conductivity beyond 10-1 S cm-1 in a Co(II) Coordination Polymer

An efficient design of crystalline solid-state proton conductors (SSPCs) is crucial for the progress of clean energy applications. Developing such materials to make them work at room temperature with a conductivity of ≥10-1 S cm-1 is of significant interest in terms of technical and commercial aspects. Utilizing the recently highlighted "coordinated-water-driven proton conduction" approach, herein, we have rationally synthesized two highly stable and scalable 1D Co(II) coordination polymers (CPs) as SSPCs, PCM-2 {[Co(bpy)(H2O)2(NO3)2]·H2O}n and PCM-3 {[Co2(bpy)2(SO4)2(H2O)6].4H2O}n, with distinct alignments in coordinated water and coordinated oxo-anions (nitrate and sulfate, respectively). The acidity of the metal-bound water molecules in PCM-2 is further enhanced through cooperative long-range continuous H bonds with coordinated Brønsted basic nitrates (proton acceptors), leading to ultrahigh superprotonic conductivities even at 25 °C (1.03 × 10-1 S cm-1 under 95% RH), and reached a maximum of 2.99 × 10-1 S cm-1 at 85 °C (95% RH). The conductivity at 25 °C is even higher than that of commercial Nafion 117 (6.74 × 10-2 S cm-1 at 100% RH). The absence of such an H-bonding interaction in PCM-3 (closed loops) resulted in a lesser conductivity of 5.87 × 10-5 S cm-1 (95% RH, 85 °C). PCM-2 represents the first example of SSPC exhibiting conductivity in the order 10-1 S cm-1 at ambient temperature (25 °C) with excellent recyclability.

Super Proton Conductivity Through Control of Hydrogen-Bonding Networks in Flexible Metal-Organic Frameworks

Metal-organic frameworks (MOFs) have received much attention as a solid-state electrolyte in proton exchange membrane fuel cells. The introduction of proton carriers and functional groups into MOFs can improve the proton conductivity attributed to the formation of hydrogen-bonding networks, while the underlying synergistic mechanism is still unclear. Here, a series of flexible MOFs (MIL-88B, [Fe3 O(OH)(H2 O)2 (O2 C-C6 H4 -CO2 )3 ] with imidazole) is designed to modify the hydrogen-bonding networks and investigate the resulting proton-conducting characteristics by controlling the breathing behaviors. The breathing behavior is tuned by varying the amount of adsorbed imidazole into pore (small breathing (SB) and large breathing (LB)) and introducing functional groups onto ligands (-NH2 , -SO3 H), resulting in four kinds of imidazole-loaded MOFs-Im@MIL-88B-SB, Im@MIL-88B-LB, Im@MIL-88B-NH2 , and Im@MIL-88B-SO3 H. Im@MIL-88B-LB without functional groups exhibits the highest proton conductivity of 8.93 × 10-2  S cm-1 at 60 °C and 95% relative humidity among imidazole-loaded proton conductors despite the mild condition, indicating that functional groups may not be always required to enhance proton conductivity. The elaborately controlled pore size and host-guest interaction in flexible MOFs through imidazole-dependent structural transformation are translated into the high proton concentration without the limitation of proton mobility, contributing to the formation of effective hydrogen-bonding networks in imidazole conducting media.

Phase Purity Regulated by Mechano-Chemical Synthesis of Metal-Organic Frameworks for the Electrocatalytic Oxygen Evolution Reaction

Three new metal organic frameworks (ZnTIA-1mc, CuTIA-1mc, and CoTIA-1mc) were synthesized by the mechanochemical grinding (mc) method in the unadulterated form. They compared with their solvothermally synthesized (st) counterparts, where the mixtures of isomeric forms have been isolated. Kinetics study with the function of grinding time during the mechanosynthesis process revealed the formation of new metastable phases. Less crystallinity and short of mechanical defects in the structure of synthesized mc metal organic frameworks showed enhanced electrocatalytic activity toward oxygen evolution reaction (OER). Among all, CoTIA-1mc showed high OER activity with 289 mV overpotential, 10 mA cm^-2 current density, and 55.4 mV dec^-1 Tafel slope in 1 M KOH which is close to the commercially used RuO₂.

Ionic metal-organic frameworks (iMOFs): progress and prospects as ionic functional materials

Metal-organic frameworks (MOFs) have been a research hotspot for the last two decades, witnessing an extraordinary upsurge across various domains in materials chemistry. Ionic MOFs (both anionic and cationic MOFs) have emerged as next-generation ionic functional materials and are an important subclass of MOFs owing to their ability to generate strong electrostatic interactions between their charged framework and guest molecules. Furthermore, the presence of extra-framework counter-ions in their confined nanospaces can serve as additional functionality in these materials, which endows them a significant advantage in specific host-guest interactions and ion-exchange-based applications. In the present review, we summarize the progress and future prospects of iMOFs both in terms of fundamental developments and potential applications. Furthermore, the design principles of ionic MOFs and their state-of-the-art ion exchange performances are discussed in detail and the future perspectives of these promising ionic materials are proposed.

Imidazolium Salt for Enhanced Interfacial Shear Strength in Polyphenylene Sulfide/Ex-PAN Carbon Fiber Composites

Processing structural or semi-structural thermoplastic-based composites is a promising solution to solve the environmental issues of the aeronautic industry. However, these composites must withstand high standard specification to ensure safety during transportation. For this reason, there is a real need to develop strong interactions between thermoplastic polymers and reinforcement fibers. This paper investigates relationships between the surface chemistry, microstructure and micromechanical properties between polyphenylene sulfide and ex-PAN carbon fibers. The incorporation of ionic salt such as 1,3-Bis(4-carboxyphenyl)imidazolium chloride into neat polyphenylene sulfide was able to significantly increase the interfacial shear strength measured by microbond micromechanical test combined with different carbon fiber surfaces treatment.

Strategic design of a bifunctional Ag(i)-grafted NHC-MOF for efficient chemical fixation of CO2 from a dilute gas under ambient conditions

Facile grafting of catalytically active Ag(i) into CO2-philic NHC-MOF for simultaneous capture and conversion of CO2 from dilute gas to value-added α-alkylidene cyclic carbonate and oxazolidinones under mild conditions is demonstrated.

N-Heterocyclic carbenes and their precursors in functionalised porous materials

Though N-heterocyclic carbenes (NHCs) have emerged as diverse and powerful discrete functional molecules in pharmaceutics, nanotechnology, and catalysis over decades, the heterogenization of NHCs and their precursors for broader applications in porous materials, like metal-organic frameworks (MOFs), porous coordination polymers (PCPs), covalent-organic frameworks (COFs), porous organic polymers (POPs), and porous organometallic cages (POMCs) was not extensively studied until the last ten years. By de novo or post-synthetic modification (PSM) methods, myriads of NHCs and their precursors containing building blocks were designed and integrated into MOFs, PCPs, COFs, POPs and POMCs to form various structures and porosities. Functionalisation with NHCs and their precursors significantly expands the scope of the potential applications of porous materials by tuning the pore surface chemical/physical properties, providing active sites for binding guest molecules and substrates and realizing recyclability. In this review, we summarise and discuss the recent progress on the synthetic methods, structural features, and promising applications of NHCs and their precursors in functionalised porous materials. At the end, a brief perspective on the encouraging future prospects and challenges in this contemporary field is presented. This review will serve as a guide for researchers to design and synthesize more novel porous materials functionalised with NHCs and their precursors.

Two mesoporous anionic metal-organic frameworks for selective and efficient adsorption of a cationic organic dye

Anionic metal-organic frameworks (MOFs) are beginning to have a great impact in the field of absorption and separation of ionic organic molecules due to the enhanced electrostatic interactions between their anionic frameworks and counter-ionic guests. Herein, the rational design and synthesis of two mesoporous anionic MOFs, [Zn₃(ITTC)₃](Me₂ NH₂)₃·3DMF·H₂O (1) and [Cd₂(ITTC)₃](Me₂NH₂)₅·2DMF (2), where H₃ITTC = 4,4',4''-(1H-imidazole-2,4,5-triyl) tribenzoic acid, is reported. Structural analysis revealed that both materials are anionic MOFs with a 2-fold interpenetrating three dimensional (3D) framework. The cross sectional area of the open one-dimensional rectangular channels is 31.7 Å × 15.6 Å for 1, of which the architecture is indicative of an unprecedented (3,3,4,5)-connection topology. For 2, the diameter of the open one-dimensional regular hexagonal channel is about 34.1 Å, decorated with uncoordinated carboxyl O atoms, and the framework exhibits a (3,4)-connected fcu network. Due to their anionic frameworks and bulky pore window sizes, both MOFs can be employed for absorbing and separating the cationic organic dye methylene blue (MB). The results reveal that both MOFs have better dye adsorption selectivity for MB, than for MO and SDI, because of charge and size-matching effects, enabling them to be potential candidates for use in environmental cleaning. By comparison, 2 presents superior selectivity and adsorptivity for cationic MB which depends on the presence of a basic functionalized pore surface.

MOF-Zn-NHC as an efficient N-heterocyclic carbene catalyst for aerobic oxidation of aldehydes to their corresponding carboxylic acids via a cooperative geminal anomeric based oxidation

As an efficient heterogenous N-heterocyclic carbene (NHC) catalyst, MOF-Zn-NHC was used in the aerobic oxidation of aryl aldehydes to their corresponding carbocyclic acids via an anomeric based oxidation. Features such as mild reaction conditions and no need for a co-catalyst or oxidative reagent can be considered as the major advantages of the presented method in this study.

As an efficient heterogenous N-heterocyclic carbene (NHC) catalyst, MOF-Zn-NHC was used in the aerobic oxidation of aryl aldehydes to their corresponding carbocyclic acids via an anomeric based oxidation.

Double-Walled Metal-Organic Framework with Regulable Pore Environments for Efficient Removal of Radioactive Cesium Cations

An anion double-walled metal-organic framework [Co₂Li₄(BTC)₃(DMF)(H₂O)·(CH₃)₂N]_n (1) based on heterobimetallic Li⁺ and Co²⁺ ions was successfully constructed. Utilizing selective destruction and formation of Co-O/Co-N bonds in the metal chains, [Co₂Li₄(BTC)₃(py)(H₂O)·(CH₃)₂N]_n (2) and [Co₂Li₄(BTC)₃(pi)(H₂O)·(CH₃)₂N]_n (3) with the same skeleton but distinct pore structures can be surprisingly obtained. Additionally, compounds 2 and 3 can be transformed into [Co₂Li₄(BTC)₃(H₂O)₂·(CH₃)₂N]_n (4) by soaking them in an ethanol solution. This kind of single-crystal-to-single-crystal transformation successfully regulates the pore structure of MOFs and enriches the diversity of the pore wall on the premise of retaining the original framework. Most impressively, compound 1 shows high adsorption capacity for Cs⁺ cations and is a good candidate to selectively accommodate Cs⁺ among the common alkali metal ions, which is future identified by single-crystal X-ray diffraction and inductively coupled plasma mass spectrometry (ICP-MS) test. Meanwhile, compound 1 can selectively adsorb methylene blue (MB) and crystal violet (CV) molecules over Rhodamine B (RMB).

A Series of Mesoporous Rare-Earth Metal-Organic Frameworks Constructed from Organic Secondary Building Units

Further development of metal-organic frameworks (MOFs) requires an establishment of hierarchical interaction within the framework. Herein, we report a series of mesoporous rare-earth (RE) MOFs that are constructed from an unusual 12-connected π-stacked pyrene secondary building unit (SBU) and a typical 12-connected RE₆ cluster (RE=Eu, Y, Yb, Tb, Ce). The judicious design of a butterfly-shape pyrene ligand with a tert-butyl substituent enables the formation of the disordered 12-connected organic SBUs on its strong intermolecular π-π interactions. The assembly of 12-connected inorganic cuboctahedron SBUs and 12-connected organic distorted hexagonal prism SBUs generates an unprecedented network that can be further simplified into a 4,4-connected pts net linked from planar square and tetrahedra. This work provides fresh insights into the design and synthesis of frameworks constructed from coordinatively, covalently, and noncovalently linked building units.

Linker Desymmetrization: Access to a Series of Rare-Earth Tetracarboxylate Frameworks with Eight-Connected Hexanuclear Nodes

The exploration of metal-organic frameworks (MOFs) through the rational design of building units with specific sizes, geometries, and symmetries is essential for enriching the structural diversity of porous solids for applications including storage, separation, and conversion. However, it is still a challenge to directly synthesize rare-earth (RE) MOFs with less connected clusters as a thermodynamically favored product. Herein, we report a systematic investigation on the influence of size, rigidity, and symmetry of linkers over the formation of RE-tetracarboxylate MOFs and uncover the critical role of linker desymmetrization in constructing RE-MOFs with eight-connected hexanuclear clusters. Our results on nine new RE-MOFs, PCN-50X (X = 1-9), indicate that utilization of trapezoidal or tetrahedral linkers provides accesses to traditionally unattainable RE-tetracarboxylate MOFs with 8-c hexanuclear nodes, while the introduction of square or rectangular linkers during the assembly of RE-MOFs based on polynuclear clusters typically leads to the MOFs constructed from 12-c nodes with underlying shp topology. By rational linker design, MOFs with two unprecedented (4, 8)-c nets, lxl and jun, can also be obtained. This work highlights linker desymmetrization as a powerful strategy to enhance MOFs' structural complexity and access MOF materials with nondefault topologies that can be potentially used for separation and catalysis.

Effect of pyridyl donors from organic ligands versus metalloligands on material design

This review illustrates designs and structures of various coordination frameworks constructed using assorted organic ligands and metalloligands offering pyridyl donors to evaluate the impact of flexibility versus rigidity on material design.

Two imidazole multicarboxylate-based MOFs: syntheses, structures and proton conductive properties

Two highly water-stable MOFs exhibited optimal σ values of around 10−4 S cm−1 at 98% RH and 100 °C, which can be compared to the values of previous MOFs.

Dual-Functional Proton-Conducting and pH-Sensing Polymer Membrane Benefiting from a Eu-MOF

Porous metal-organic frameworks (MOFs) have demonstrated a great potential in proton conduction and luminescence sensing due to functionalized nodes, ligands and channels, or pores. Herein, we prepared a hydrothermally stable Eu-MOF that also resisted acid and base using a bifunctional organic ligand containing carboxylic acid groups, which are easily coordinated to Eu ions, and Eu-phobic tetrazolyl groups as potential proton-hopping sites. The hydrogen bond network, which was constructed by the uncoordinated anionic tetrazolium and the coordinated and free water molecules, endowed this Eu-MOF with the highest proton conductivity of 4.45 × 10^-2 S/cm at 373 K and 93% relative humidity. The proton conductivity of the Nafion membrane containing this Eu-MOF increased 1.74 times. More interestingly, the hybrid membrane displayed luminescence pH sensing because the changeable protonation levels of uncoordinated tetrazolium groups along with the pH tuned the emission of embedded Eu-MOFs. Such a dual-functional MOF-based hybrid membrane including proton conduction and pH sensing is reported for the first time, which could open an avenue to the more practical application for functional MOFs.

A hydrazine functionalized UiO-66(Hf) metal–organic framework for the synthesis of quinolines via Friedländer condensation

A hydrazine functionalized Hf MOF was used as a heterogeneous catalyst for the synthesis of quinolone scaffolds with high yields. The catalyst showed a broad substrate scope and excellent recyclability.

The construction of a multifunctional metal–organic framework for targeting tumors and bioimaging

A simple one-pot process has been developed for the synthesis of multifunctional MOFs for targeting tumors and bioimaging.

MOF nanoparticles with encapsulated dihydroartemisinin as a controlled drug delivery system for enhanced cancer therapy and mechanism analysis

Schematic illustration of (a) the preparation of DHA@ZIF-8 NPs and (b) their application for cancer therapy.

Polyoxometalate-based hydrogen-bonded organic frameworks as a new class of proton conducting materials

To develop new types of crystalline proton conducting materials for fuel cells, a polyoxometalate-based hydrogen-bonded organic framework (PHOF) based on Keggin-type [PMo₁₂O₄₀]³⁻ and phenylimidazole (PHOF 1) has been prepared.

Structural features of proton-conducting metal organic and covalent organic frameworks

Proton conductivity in MOFs and COFs have been attracted due to their applicability as electrolytes in proton exchange membrane fuel cells. A short overview with recent updates on the structural features of MOFs and COFs for proton conduction are presented here.

Ln(iii)–Ni(ii) heteropolynuclear metal organic frameworks of oxydiacetate with promising proton-conductive properties

Heteropolynuclear metal organic frameworks (MOFs) of the general formula [Ln₂Ni₃(oda)₆(H₂O)₆]·xH₂O (oda = oxydiacetate, Ln = +3 rare earth ion) were synthesized and characterized.

Series of Water-Stable Lanthanide Metal-Organic Frameworks Based on Carboxylic Acid Imidazolium Chloride: Tunable Luminescent Emission and Sensing

A series of isomorphic lanthanide metal-organic frameworks (Ln-MOFs), {[Ln(L)(H₂O)₂]·5H₂O}_n (1-Ln, where Ln = Eu, Tb, Gd, and Eu_xTb_1-x), have been synthesized by a rigid 1,3-bis(3,5-dicarboxyphenyl)imidazolium chloride (H₄L⁺Cl^-) ligand and Ln³⁺ ions via a solvothermal method. Single-crystal X-ray diffraction indicated that 1-Ln exhibited similar three-dimensional porous frameworks with one-dimensional channels decorated by the uncoordinated carboxylate oxygen atoms. The luminescent sensing studies indicated that 1-Eu is an outstanding reusable luminescent probe suitable for the simultaneous detection of Cr₂O₇^2-, CrO₄^2-, and MnO₄^- ions in an aqueous solution. Remarkably, the different proportions of Eu³⁺ and Tb³⁺ can be combined into the same Ln-MOF to yield a new series of differently doped 1-Eu_xTb_1-x MOFs. At the same excitation wavelength, they generated dual-emission peaks of Eu³⁺ and Tb³⁺ to show a gradual change in luminous color between yellow-green, yellow, orange, orange-red, and red. On the basis of the excellent optical properties of 1-Ln complexes, they can be employed as promising luminescent probe and multicolor tunable photoluminescence materials.

Three Anionic Indium-Organic Frameworks for Highly Efficient and Selective Dye Adsorption, Lanthanide Adsorption, and Luminescence Regulation

Through solvothermal reaction of InCl₃ and tetracarboxylate ligands with different substituent groups on diphenyl ethers, three new anionic indium-organic frameworks have been successfully prepared. They are {[(CH₃)₂NH₂]In(G-1)(H₂O)}·9DMF (1), {[(CH₃)₂NH₂]In(G-2)}·15DMF (2), and {[(CH₃)₂NH₂]₂In₂(G-3)₂}·16DMF (3) {DMF = N, N'-dimethylformamide; H₄(G-1) = 5',5″″-oxybis(2'-methoxy[1,1':3',1″-terphenyl]-4,4″-dicarboxylic acid); H₄(G-2) = 5',5″″-oxybis(2'-amino[1,1':3',1″-terphenyl]-4,4″-dicarboxylic acid); H₄(G-3) = 5',5″″-oxybis([1,1':3',1″-terphenyl]-4,4″-dicarboxylic acid)}. Compounds 1-3 can be simplified as unimodal 4-connected frameworks with different topological types: lon, cag, and dia, respectively. Compounds 1 and 3 display 2-fold interpenetrating nets, while compound 2 is non-interpenetrating. Compounds 1 and 3 can adsorb cationic methylene blue (MB) with good capacity and a high adsorption rate due to their anionic frameworks and channel-type voids. In particular, compound 1 exhibits great selectivity for cationic MB in the mixtures of MB and methyl orange. In addition, the adsorption behavior of rare earth ions (Eu³⁺ and Tb³⁺) on compounds 1 and 3 has also been studied. Due to the different structural features and channel sizes of compounds 1 and 3 caused by different substituents on the ligands, the adsorption properties of rare earth ions on the two compounds are different.

An NHC-CuCl functionalized metal-organic framework for catalyzing β-boration of α,β-unsaturated carbonyl compounds

A microporous metal-organic framework functionalized with in situ generated NHC-CuCl units (1) has been successfully synthesized from a novel imidazolium-containing ligand. In particular, the MOF 1 can catalyze β-boration of α,β-unsaturated carbonyl compounds, while the isoreticular version of 1 (1-im) modified with only imidazolium moiety cannot. This work demonstrates for the first time the heterogeneous catalysis of NHC-Cu(i)Cl within a MOF solid.