Anion-Directed Assemblies of Cationic Metal–Organic Frameworks Based on 4,4′-Bis(1,2,4-triazole): Syntheses, Structures, Luminescent and Anion Exchange Properties

Two-Fold Interlocking Cationic Metal-Organic Framework Material with Exchangeable Chloride for Perrhenate/Pertechnetate Sorption

Albeit reported substantial sorbents for elimination of TcO₄^-, the issue of secondary contamination caused by released counterions (such as NO₃^-) from the cationic metal-organic framework (MOF) has not come into the sufficient limelight for researchers. Herein, our efforts are dedicated to settle the matter through synthesis of NiCl₂ based on the cationic MOF (ZJU-X4). Less harmful chlorides are used as exchangeable anions for replacing hazardous anions. Notably, ZJU-X4 exhibited fast sorption kinetics, high sorption capacity of 395 mg/g, decent selectivity, and excellent reusability in four recycles. The results of ion chromatography revealed that the released chloride ion was equal to sorption of target ions, and pair distribution functions were employed to analyze the changes in ZJU-X4 after sorption of ReO₄^-, clearly elucidating the anion-exchange mechanism. Furthermore, in the dynamic sorption experiments, ReO₄^- could be facilely and effectively removed and recovered, showing the value of practical applications. This work indicated that cationic MOF-based metal chloride salts would be a better choice for anionic sorbents.

Face-Directed Construction of a Metal-Organic Isohedral Tetrahedron for the Highly Efficient Capture of Environmentally Toxic Oxoanions and Iodine

Geometric analysis has been guiding the design and construction of metal-organic polyhedra. Here, a series of isohedral tetrahedra ZrIT-1 and -2 and VIT-1 and -2 were synthesized by a one-pot method relying on trivalent molecular building blocks. Structural analysis shows that the isohedral tetrahedra constructed with {V₆(SO₄)(CO₂)₃} have three different sets of prism lengths, while those constructed with {Zr₃O(CO₂)₃} have two different sets of prism lengths. Comparison of two types of polyhedra reveals that the different sizes and coordination flexibilities of the two MBBs result in different cavity volumes. The environmentally toxic oxoanion trapping ability of ZrIT-1 was explored due to its structural stability and cation cage properties. The results show that ZrIT-1 can capture permanganate and dichromate anions in water with high efficiency and selectivity. Notably, the permanganate adsorption capacity can reach ∼276.6 mg/g, which exceeds those of most metal-organic framework materials. In addition, the adsorption and desorption of iodine showed that ZrIT-1 has a reversible adsorption capacity for iodine.

Contiguous layer based metal-organic framework with conjugated π-electron ligand for high iodine capture

Herein, a novel 3-dimensional (3D) Cu(II) metal-organic framework (MOF), [Cu₃(μ₂-O)₂(p-tr₂Ph)₂(HCOO)][NO₃]·3DMF·3H₂O (compound 1), which is constructed by directly interlocking regionalized hollow two-dimensional (2D) layers, has been conceived and solvothermally synthesized. Such a distinctive regionalized pore system effectively maintains the uniformity of the pore structure, isolates the counterions and bridging ligands in the partition layer, and endows compound 1 with high porosity. In consequence, compound 1 exhibits excellent adsorption ability of iodine in cyclohexane. The removal efficiency in cyclohexane solution (0.01 mol L^-1) can reach up to 80% in 8 min, and the absorption ability towards iodine can reach about 1.15 g g^-1. Moreover, iodine can also be controllably released in ethanol. The release rate was up to 4 × 10^-5 mol L^-1 min^-1. Furthermore, compound 1 also showed prominent recyclability due to the high stability, and the maximum sorption amount could be retained after 3 cycles. This study paves a new way towards opening up MOFs' potential application in capturing radioactive iodine to protect the environment.

Single crystal growth of water-soluble metal complexes with the help of the nano-crystallization method

Let pipetting robots set up nano crystallization trials of water-soluble metal complexes in order to obtain single crystals!

Luminescent metal–organic framework-based phosphor for the detection of toxic oxoanions in an aqueous medium

Compound 1 has been utilized for the luminescence based visible detection of chromate, permanganate and phosphate ions in aqueous medium.

A Cationic Silver Pyrazine Coordination Polymer with High Capacity Anion Uptake from Water

We report the first example of linker modification for an N-donor Ag-based cationic material while maintaining and in some cases increasing the anion exchange capacity. Cationic silver(I) pyrazine nitrate selectively traps harmful oxo-anions from water such as permanganate, perrhenate and a variety of α,ω-alkanedicarboxylates. We chose these anions as initial examples of exchange for potential water purification. The host-guest interaction between the cationic layers of π-stacked silver pyrazine polymers and the incoming/outgoing interlamellar anions allows for the exchange. The exchange capacity over 24 h reached 435 and 818 mg/g for permanganate and perrhenate, respectively, a record for a crystalline metal-organic material and over five times the exchange capacity compared to commercial resin. The material also undergoes organic exchange as an analog for pharmaceutical waste, some of which have a carboxylate functionality at the neutral pH range typical of natural water sources. Both the as-synthesized and exchanged materials are characterized by a variety of analytical techniques.

Metal-organic framework-based materials: superior adsorbents for the capture of toxic and radioactive metal ions

Highly efficient removal of metal ion pollutants, such as toxic and nuclear waste-related metal ions, remains a serious task from the biological and environmental standpoint because of their harmful effects on human health and the environment. Recently, highly porous metal-organic frameworks (MOFs), with excellent chemical stability and abundant functional groups, have represented a new addition to the area of capturing various types of hazardous metal ion pollutants. This review focuses on recent progress in reported MOFs and MOF-based composites as superior adsorbents for the efficient removal of toxic and nuclear waste-related metal ions. Aspects related to the interaction mechanisms between metal ions and MOF-based materials are systematically summarized, including macroscopic batch experiments, microscopic spectroscopy analysis, and theoretical calculations. The adsorption properties of various MOF-based materials are assessed and compared with those of other widely used adsorbents. Finally, we propose our personal insights into future research opportunities and challenges in the hope of stimulating more researchers to engage in this new field of MOF-based materials for environmental pollution management.

A one-dimensional silver(I) coordination polymer based on 5-methyl-1,3,4-thiadiazol-2-amine and pyridine-2,3-dicarboxylate

The bifunctional pyridine-2,3-dicarboxylic acid (H2pdc) ligand has one N atom and four O atoms, which could bind more than one AgI centre with diverse binding modes. A novel infinite one-dimensional AgI coordination polymer, namely catena-poly[[silver(I)-(μ2-pyridine-2,3-dicarboxylato-κ2 N:O 3)-silver(I)-tris(μ2-5-methyl-1,3,4-thiodiazol-2-amine-κ2 N:N′)] monohydrate ethanol monosolvate], {[Ag2(C7H3NO4)(C3H5N3S)3]·H2O·C2H5OH} n , has been synthesized using H2pdc and 5-methyl-1,3,4-thiadiazol-2-amine (tda), and characterized by single-crystal X-ray diffraction. One AgI atom is located in a four-coordinated AgN4 tetrahedral geometry and the other AgI atom is in a tetrahedral AgN3O geometry. A dinuclear AgI cluster formed by three tda ligands with a paddelwheel configuration is bridged by the dianionic pdc2− ligand into a one-dimensional coordination polymer. Interchain N—H...O hydrogen bonds extend the one-dimensional chains into an undulating two-dimensional sheet. The sheets are further packed into a three-dimensional supramolecular framework by interchain N—H...O hydrogen bonds.

Efficient and Selective Uptake of TcO4- by a Cationic Metal-Organic Framework Material with Open Ag+ Sites

⁹⁹Tc is one of the most problematic radioisotopes in used nuclear fuel owing to its combined features of high fission yield, long half-life, and high environmental mobility. There are only a handful of functional materials that can remove TcO₄^- anion from aqueous solution and identifying for new, stable materials with high anion-exchange capacities, fast kinetics, and good selectivity remains a challenge. We report here an 8-fold interpenetrated three-dimensional cationic metal-organic framework material, SCU-100, which is assembled from a tetradentate neutral nitrogen-donor ligand and two-coordinate Ag⁺ cations as potential open metal sites. The structure also contains a series of 1D channels filled with unbound nitrate anions. SCU-100 maintains its crystallinity in aqueous solution over a wide pH range from 1 to 13 and exhibits excellent β and γ radiation-resistance. Initial anion exchange studies show that SCU-100 is able to both quantitatively and rapidly remove TcO₄^- from water within 30 min. The exchange capacity for the surrogate ReO₄^- reaches up to 541 mg/g and the distribution coefficient K_d is up to 1.9 × 10⁵ mL/g, which are significantly higher than all previously tested inorganic anion sorbent materials. More importantly, SCU-100 can selectively capture TcO₄^- in the presence of large excess of competitive anions (NO₃^-, SO₄^2-, CO₃^2-, and PO₄^3-) and remove as much as 87% of TcO₄^- from the Hanford low-level waste melter off-gas scrubber simulant stream within 2 h. The sorption mechanism is well elucidated by single crystal X-ray diffraction, showing that the sorbed ReO₄^- anion is able to selectively coordinate to the open Ag⁺ sites forming Ag-O-Re bonds and a series of hydrogen bonds. This further leads to a single-crystal-to-single-crystal transformation from an 8-fold interpenetrated framework with disordered nitrate anions to a 4-fold interpenetrated framework with fully ordered ReO₄^- anions. This work represents a practical case of TcO₄^- removal by a MOF material and demonstrates the promise of using this type of material as a scavenger for treating anionic radioactive contaminants during the nuclear waste partitioning and remediation processes.

Tracking the Superefficient Anion Exchange of a Dynamic Porous Material Constructed by Ag(I) Nitrate and Tripyridyltriazole via Multistep Single-Crystal to Single-Crystal Transformations

To avoid the instability and inefficiency for anion-exchange resins and layered double-hydroxides materials, we present herein a flexible coordination network [Ag(L²⁴³)](NO₃)(H₂O)(CH₃CN) (L²⁴³ = 3-(2-pyridyl)-4-(4-pyridyl)-5-(3-pyridyl)-1,2,4-triazole) with superefficient trapping capacity for permanganate, as a group-7 oxoanion model for radiotoxic pertechnetate pollutant. Furthermore, a high-throughput screening strategy has been developed based on concentration-gradient design principle to ascertain the process and mechanism for anion exchange. Significantly, a series of intermediates can be successfully isolated as the qualified crystals for single-crystal X-ray diffraction. The result evidently indicates that such a dynamic material will show remarkable breathing effect of the three-dimensional host framework upon anion exchange, which mostly facilitates the anion trapping process. This established methodology will provide a general strategy to discover the internal secrets of complicated solid-state reactions in crystals at the molecular level.

Metal–organic frameworks: functional luminescent and photonic materials for sensing applications

This review summarizes the diverse routes to derive sensing applications from suitably functionalized and crystal-engineered metal–organic framework (MOF) materials, either by fluorometric responses, or based on photonic crystal-based signal transduction.

A Simple and Efficient Synthesis of Novel Aryloxy-Functionalised 4,4′-bi-1,2,4-Triazoles

A simple and efficient strategy for the synthesis of novel aryloxy-functionalised 4,4′-bi-1,2,4-triazoles was successfully explored by nucleophilic aromatic substitution of tetrachloro-4,4′-bi-1,2,4-triazole by various phenols using Cs2CO3 as catalyst. The syntheses were achieved in 25–94% yields.

Triazole based Ag coordination clusters: synthesis, structural diversity and anion exchange properties

In this work three novel triazole based cluster-based silver(i) clusters have been isolated. 2 and 3 can effectively capturing the anion pollutants Cr₂O₇²⁻, MnO₄⁻ in water solutions and Congo Red in methanol solutions.