A series of three-dimensional lanthanide MOFs: Observation of reversible structural changes controlled by solvent desorption–adsorption, and magnetic properties

High-performance lanthanum-based metal-organic framework with ligand tuning of the microstructures for removal of fluoride from water

Excess fluoride in water poses a threat to ecology and human health, which has attracted global attention. In this study, a series of lanthanum-based metal-organic frameworks (La-MOFs) were synthesized by varying the organic ligands (i.e., terephthalic acid (BDC), trimesic acid (BTC), biphenyl-4,4-dicarboxylic acid (BPDC), 2,5-dihydroxyterephthalic acid (BHTA), and 1,2,4,5-benzenetetracarboxylic acid (PMA)) to control the microscopic structure of the MOFs and subsequently apply them for the removal of fluoride in water. The maximum capture capacities of La-BTC, La-BPDC, La-BHTA, La-PMA, and La-BDC at 298 K are 105.2, 125.9, 145.5, 158.9, and 171.7 mg g^-1, respectively. The adsorption capacity is greater than most reported adsorbents. The adsorption isotherms of La-MOFs for fluoride are well fit to the Langmuir isotherm model. In addition, the adsorption kinetics of La-BTC, La-BPDC, La-BHTA, La-PMA, and La-BDC follows the pseudo-second-order kinetic model, and the kinetic rate-limiting step of adsorption is chemical adsorption. Thermodynamics revealed that temperature is favorable for the adsorption of fluoride. Meanwhile, La-BTC, La-BPDC, La-BHTA, La-PMA, and La-BDC are suitable for the removal of fluoride in a relatively wide pH range (4.0-9.0). Simultaneously, from X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis, electrostatic attraction and ligand exchange are identified as the main action mechanisms for the adsorption of fluoride of La-MOFs. The prepared La-MOFs are used as efficient adsorbents for removal of fluoride in actual water, indicating that they have great potential in removing fluoride in real and complex environmental water. This work provides a new strategy for designing adsorbents with adjustable microstructure and expected function to effectively recover fluorosis in water.

Synthesis, crystal structures and, magnetic and photoluminescence properties of lanthanide-based metal-organic frameworks constructed with 2,5-dihydroxybenzene-1,4-dicarboxylic acid

Four new lanthanide(iii) coordination polymers (1-4) have been synthesized by using 2,5-dihydroxybenzene-1,4-dicarboxylate (Dhbdc, C8H6O6 2-) as a ligand and characterized by elemental analysis, infrared spectroscopy, TGA-DSC (Thermogravimetric Analysis-Differential Scanning Calorimetry) and single crystal X-ray diffraction studies. The isolated complexes include; [Ce(Dhbdc)(H2O)3Cl] n (1) and [Ln(Dhbdc)1.5(H2O)2] n ·3n(C2H6O)·nH2O [Ln = Eu (2), Gd (3) and Tb (4)]. The structural analysis reveals that compound 1 is a two-dimensional polymer in which the cerium atoms are coordinated by six oxygen and two bridging chloride ions adopting a dodecahedral geometry. The compounds 2-4 are isomorphous and their extended structures consist of three-dimensional supramolecular frameworks encapsulating [001] channels occupied by the guest water and ethanol molecules. The metal atoms in 2-4 exhibit a square antiprism geometry. All these compounds have O-H⋯O hydrogen bonds originating from the coordinated water and solvent molecules that help to consolidate the structures. The compounds 1, 3 and 4 were investigated for magnetic properties and they exhibited weak antiferromagnetic coupling interactions between the lanthanides as per the Curie Weiss law. Anisotropic nature of 3 and 4 has been depicted as per magnetization versus field plots. Complex 4 behaves as a soft magnetic material as compared to 3. The luminescence studies indicate that compounds 2, 3 and 4 show ligand-centred fluorescence, which is significantly enhanced in the case of 4.

From partial to complete neutralization of 2,5-dihydroxyterephthalic acid in the Li–Na system: crystal chemistry and electrochemical behavior of Na2Li2C8H2O6vs.Li

The 2,5-dihydroxyterephthalic acid (H₄-p-DHT) is of special interest in the field of materials science because of the two symmetric sets of oxygen donor functional groups (i.e., β-hydroxy acid moieties).

Single-crystal-to-single-crystal post-synthetic modifications of three-dimensional LOFs (Ln = Gd, Eu): a way to modulate their luminescence and thermometric properties

Single-crystal-to-single-crystal post-synthetic modifications of {[Ln₂(H₂L)₃(DMF)₄]·2DMF}_n LOFs (Ln = Gd, Eu) to modulate their luminescence and thermometric properties.

Rare-earth metal–organic frameworks: from structure to applications

In the past 30 years, rare-earth metal–organic frameworks (MOFs) have been gaining attention owing to their diverse chemical structures, and tunable properties.

Solvent-Triggered Reversible Phase Changes in Two Manganese-Based Metal-Organic Frameworks and Associated Sensing Events

A flexible Mn-based MOF, Mn-sdc-1, has been successfully synthesized by using the ligand 4,4'-stilbenedicarboxylic acid (H₂ sdc). Attributed to the flexibility of the framework, Mn-sdc-1 can transform into a new phase (Mn-sdc-2) with completely different structural geometry; this is induced by trace levels of H₂ O at room temperature. Reversibly, the transformation from Mn-sdc-2 to Mn-sdc-1 can be triggered by DMF upon heating beyond 100 °C. These results inspired a study of the influences of temperature and H₂ O volume in the solid-state transformation of two MOF phases and, for the first time, a phase diagram of MOFs has been depicted. This phase diagram reflects the gradual H₂ O-/temperature-dependent changes between Mn-sdc-1 and Mn-sdc-2, which is very meaningful in achieving the controllable synthesis of these two MOFs and lead to targeting the desired water-stable structure. As a result, the obtained water-stable Mn-sdc-2 can be developed as an excellent Pb²⁺ sensor in aqueous solution through the luminescence quenching effect with a limit of detection of 31.4 nm.

Synthesis, Structures and Luminescence Properties of Metal-Organic Frameworks Based on Lithium-Lanthanide and Terephthalate

Metal-organic frameworks assembled from Ln(III), Li(I) and rigid dicarboxylate ligand, formulated as [LiLn(BDC)₂(H₂O)·2(H₂O)] (MS1-6,7a) and [LiTb(BDC)₂] (MS7b) (Ln = Tb, Dy, Ho, Er, Yb, Y_0.96Eu_0.04, Y_0.93Tb_0.07, and H₂BDC = terephthalic acid), were obtained under hydrothermal conditions. The isostructural MS1-6 crystallize in monoclinic P2₁/c space group. While, in the case of Tb³⁺ a mixture of at least two phases was obtained, the former one (MS7a) and a new monoclinic C2/c phase (MS7b). All compounds have been studied by single-crystal and powder X-ray diffraction, thermal analyses (TGA), vibrational spectroscopy (FTIR), and scanning electron microscopy (SEM-EDX). The structures of MS1-6 and MS7a are built up of inorganic-organic hybrid chains. These chains constructed from unusual four-membered rings, are formed by edge- and vertex-shared {LnO₈} and {LiO₄} polyhedra through oxygen atoms O3 (vertex) and O6-O7 (edge). Each chain is cross-linked to six neighboring chains through six terephthalate bridges. While, the structure of MS7b is constructed from double inorganic chains, and each chain is, in turn, related symmetrically to the adjacent one through the c glide plane. These chains are formed by infinitely alternating {LiO₄} and {TbO₈} polyhedra through (O2-O3) edges to create Tb–O–Li connectivity along the c-axis. Both MS1-6,7a and MS7b structures possess a 3D framework with 1D trigonal channels running along the a and c axes, containing water molecules and anhydrous, respectively. Topological studies revealed that MS1-6 and MS7a have a new 2-nodal 3,10-c net, while MS7b generates a 3D net with unusual β-Sn topology. The photoluminescence properties Eu- and Tb-doped compounds (MS5-6) are also investigated, exhibiting strong red and green light emissions, respectively, which are attributed to the efficient energy transfer process from the BDC ligand to Eu³⁺ and Tb³⁺.

Microwave-assisted ionothermal synthesis of a water-stable Eu-coordination polymer: a Ba2+ ion detector and fluorescence thermometer

Presented is a water-stable Eu-coordination polymer, namely [HMIm]Eu(DHBDC)₂, capable of detecting Ba²⁺ in aqueous solution and acting as a two-PL transition fluorescence thermometer.