Multifunctional Lanthanide Metal-Organic Frameworks Are Used for Fluorescence Sensing of Bi3+, HPO42-, Flu, and PNBA and Application

Using a nitrogen-containing tricarboxylic acid ligand (imidazole-1-yl) benzene-2,4,6-tricarboxylic acid (H3ttc) and lanthanide metal elements (Dy, Eu, Nd, and Gd), four lanthanide metal organic frameworks (Ln-MOFs) with the same structure, namely, {[Dy2 (Httc)3]·1.5DMF}n(1), {[Eu2 (Httc)3]·1.5DMF}n(2), {[Nd2 (Httc)3]·1.5DMF}n(3), and {[Gd2 (Httc)3]·1.5DMF}n(4), were synthesized under solvothermal conditions. The characterization analysis showed that the four isomorphic Ln-MOFs were trigonal crystals of the R3̅c space group, with good phase purity and thermal stability. Fluorescence analysis showed that complex 1 can be an excellent fluorescence sensor for Bi3+, HPO42-, and fluridine (Flu), while complex 2 can be an excellent fluorescence sensor for p-nitrobenzoic acid (PNBA). And their sensing mechanisms were discussed in detail. The fluorescent test paper and fluorescent seal were prepared by using the excellent luminescence properties of 1 and 2, and the pesticide on the surface of cherry tomato was detected. The applicability of these MOFs as fluorescence sensors was proved. Therefore, Ln-MOFs are expected to have unpredictable application prospects in the field of environmental detection.

High-Entropy Lanthanide-Organic Framework as an Efficient Heterogeneous Catalyst for Cycloaddition of CO2 with Epoxides and Knoevenagel Condensation

Multimetallic synergistic effects have the potential to improve CO2 cycloesterification and Knoevenagel reaction processes, outperforming monometallic MOFs. The results demonstrate superior performance in these processes. To investigate this, we created and characterized a selection of single-component Ln(III)-MOFs (Ln=Eu, Tb, Gd, Dy, Ho) and high-entropy lanthanide-organic framework (HE-LnMOF) using solvent-thermal conditions. The experiments revealed that HE-LnMOF exhibited heightened catalytic efficiency in CO2 cycloesterification and Knoevenagel reactions compared to single-component Ln(III) MOFs. Moreover, the HE-LnMOF displayed significant stability, maintaining their structural integrity after five cycles while sustaining elevated conversion and selectivity rates. The feasible mechanisms of catalytic reactions were also discussed. HE-LnMOF possess multiple unsaturated metal centers, acting as Lewis acid sites, with oxygen atoms connecting the metal, and hydroxyl groups on the ligand serving as base sites. This study introduces a novel method for synthesizing HE-LnMOF and presents a fresh application of HE-LnMOF for converting CO2.

Bioreaction-Compatible Bivariate Lanthanide MOF Sensor Enables Stimulus-Multiresponsive Platform for ctDNA On-Site Detection

Detection of circulating tumor DNA (ctDNA) in liquid biopsy is of great importance for tumor diagnosis but difficult due to its low amount in bodily fluids. Herein, a novel ctDNA detection platform is established by quantifying DNA amplification by-product pyrophosphate (PPi) using a newly designed bivariable lanthanide metal-organic framework (Ln-MOF), namely, Ce/Eu-DPA MOF (CE-24, DPA = pyridine-2,6-dicarboxylic acid). CE-24 MOF exhibits ultrafast dual-response (fluorescence enhancement and enzyme-activity inhibition) to PPi stimuli by virtue of host-guest interaction. The platform is applied to detecting colon carcinoma-related ctDNA (KARS G12D mutation) combined with the isothermal nucleic acid exponential amplification reaction (EXPAR). ctDNA triggers the generation of a large amount of PPi, and the ctDNA quantification is achieved through the ratio fluorescence/colorimetric dual-mode assay of PPi. The combination of the EXPAR and the dual-mode PPi sensing allows the ctDNA assay method to be low-cost, convenient, bioreaction-compatible (freedom from the interference of bioreaction systems), sensitive (limit of detection down to 101 fM), and suitable for on-site detection. To the best of our knowledge, this work is the first application of Ln-MOF for ctDNA detection, and it provides a novel universal strategy for the rapid detection of nucleic acid biomarkers in point-of-care scenarios.

Modulating confinement space in metal-organic frameworks enables highly selective indole C3-formylation

Here, Selective C3-formylation of indole was achieved under mild conditions using a metal-organic framework (MOF) catalyst. The confined reaction space within the MOF pores effectively suppressed undesired side reactions and promoted the formation of the targeted product by controlling the reaction pathway. Density functional theory (DFT) calculations corroborated the experimental observations.

Multifunctional Luminescent 3D Ln-MOFs with High Sensitivity for Trace Detection of Micronutrients

The synthesis of two versatile fluorescent metal-organic frameworks (MOFs), [Eu(4-NCP)(1,4-bdc)]n·0.5H2O (1) and [Eu(4-NCP)(4,4'-bpdc)]n·0.75H2O (2) (HNCP = 2-(4-carboxyphenyl)imidazo(4,5-f)-(1,10)phenanthroline, 1,4-H2bdc = benzene-1,4-dicarboxylic acid, 4,4'-H2bpdc = 4,4'-biphenyldicarboxylic acid), was carried out using a hydrothermal method. These MOFs were characterized through various advanced technologies to determine their structural information. The results indicate that both MOFs exhibited 3D network structures with specific topologies. Furthermore, these MOFs demonstrated exceptional thermal stabilities and adsorption capabilities. Additionally, complex 2 was utilized for studying the fluorescence sensing properties of various micronutrients including metal ions, nitro aromatic compounds, and biological small molecules. Notably, complex 2 showed promising potential as a multifunctional sensor for selectively detecting Fe3+, nitrobenzene, and ascorbic acid in aqueous solutions through fluorescence quenching with low limits of detection (LODs ∼ 10-7 M) and high quenching constants (Ksv ∼ 103 M-1). Moreover, the detection mechanism of complex 2 was further investigated by using experimental methods and DFT calculations.

Base-Directed Formation of Isostructural Lanthanide-Sulfate-Glutarate Coordination Polymers with Photoluminescence

A series of five isostructural 3D lanthanide-based coordination polymers [LnIII2(H2O)6(glu)(SO4)2]n [Ln = Pr(1), Nd(2), Sm(3), Eu(4), and Gd(5)] was effortlessly obtained within a few minutes via the microwave-heating method. The employment of auxiliary bases, that is, sodium hydroxide, 4,4'-bipyridine, and 1,4-diazabicyclo[2.2.2]octane, led to the formation of the title complex, whereas base-free synthesis yielded a three-dimensional inorganic coordination polymer, [Ln2(H2O)4(SO4)3]n·nH2O, Ln = Nd (2a). The robustness of the synthetic method was illustrated as both microwave-heating and conventional hydrothermal techniques also enabled the formation of a high-crystalline phase-pure complex 1-5. In the structure of 1-5, glutarato (glu2-) and sulfato ligands link dinuclear Ln(III) building units into three-dimensional frames. The glu2- ligands act as tethering linkers, expanding the structure into a neutral 3D coordination network. Hydrogen bonds were found to be the predominant intermolecular interactions in the crystal structures. Photoluminescence of the complex 1-5 was studied.

Synthesis and catalytic performance of wood cellulose nanofibers grafted with polylactic acid in rare-earth complexes based on tetrazole carboxylic acids

Stannous octanoate [Sn(Oct)2] and 4-dimethylamino pyridine (DMAP) were used to catalyze the synthesis of amphiphilic cellulose-based graft copolymers, but the acute toxicity of tin ions and DMAP prompts the need for the application of less harmful catalysts. Herein, green catalyst complexes 1-3 [M(H0.5L)2(H2O)5]·2(H2O) (M = Sm, 1; M = Nd, 2; M = Eu, 3; H2L = 4-(3-(tetrazol-5-yl)pyridin-5-yl)benzoic acid) were synthesized, and their properties were systematically investigated. Single-crystal X-ray diffraction showed that the complexes possessed a zero-dimensional structure, while the thermogravimetry and scanning electron microscopy results confirmed their stability after heating at 110 °C for 10 h. Using complexes 1-3 and DMAP as the catalysts, CNFs were grafted with l-lactide via homogeneous ring-opening polymerization to form wood cellulose nanofibers grafted with l-lactide (WGLAs), and the effects of the ratio of wood cellulose nanofibers (WCNFs) to l-lactide ([AGU]/[LA]) and catalyst dosage were studied. The polymerization followed the coordination-insertion mechanism. Under comparable reaction conditions, the grafting ratio of WGLA-1 reached 84.7 %, and the grafting ratio of complex 1 was found to be higher than those achieved using DMAP. WGLAs demonstrated good thermal stability without cytotoxicity, and the residual catalysts in the WGLAs exhibited fluorescence characteristics. Overall, amphiphilic cellulose-based materials with fluorescence emission offered a promising modification strategy to prepare high-performance polymer composites for agriculture and biomedical application.

Ratiometric Fluorescence Thermometry, Quantitative Gossypol Detection, and CO2 Chemical Fixation by a Multipurpose Europium (III) Metal-Organic Framework

A lanthanide-based molecular crystalline material endows metal-organic frameworks (MOFs) with many fascinating applications such as fluorescence detection and CO2 chemical fixation. Herein, we describe and study a multipurpose europium(III) MOF with the formula of {[Eu2(TATAB)2]·2.5H2O·2DMF}n (Eu-MOF) (where H3TATAB is 4,4',4″-((1,3,5-triazine-2,4,6-triyl)tris(azanediyl))tribenzoic acid ligand) for photoluminescence sensor matrix and CO2 chemical fixation. This Eu-MOF features 1D square channels along the c direction with a pore size of ca.14.07 Å × 14.07 Å, occupied by lattice water and DMF molecules. The obtained Eu-MOF can achieve simultaneous luminescence of the H3TATAB ligand and Eu3+ ions, which can be developed as the sensor matrix for ratiometric fluorescence thermometry. The luminescence of the Eu-MOF demonstrates an obvious color change from red to yellow as temperature rises from 303 to 373 K and the Eu-MOF has a satisfying relative sensitivity of 3.21% K-1 and a small temperature uncertainty of 0.0093 K at 333 K. Moreover, sensitive detection of gossypol was achieved with a quenching constant Ksv of 1.18 × 105 M-1 and a detection limit of 4.61 μM. A combination of the competitive absorption and photoinduced electron transfer caused by host-guest interactions and strengthened π-π packing effect synergistically between gossypol molecules and the Eu-MOF skeleton realizes the "turn-off" sensing of gossypol. Importantly, the nature of the Eu-MOF allows showing CO2 chemical fixation under mild conditions. Thus, the Eu-MOF can be utilized as a multipurpose material for ratiometric fluorescence thermometry, quantitative gossypol detection, and CO2 chemical fixation.

Lanthanide Coordination Polymers with Soft-Base Ditopic Bisthiazolate Ligands

In order to prepare the first lanthanide coordination polymers (CPs) based on ditopic sulfide ligands, benzo[1,2-d:4,5-d']bisthiazole-2,6(3H,7H)-dithione (H2L) was used as a linker. The reactions of lanthanide silylamides Ln[N(SiMe3)2]3 (Ln = Nd, Gd, Er, and Yb) with H2L result in the formation of soluble dimethyl sulfoxide (DMSO) ionic salts [Ln(DMSO)8][L]1.5 [Ln = Nd (1), Gd (2), Er (3), and Yb (4)]. Due to the lack of coordination of anionic ligands, compounds 1, 3, and 4 do not show sensitized metal-centered photoluminescence (PL), while Gd compound 2 shows weak phosphorescence at 77 K. It was found that the heating of 1 in a 1:9 DMSO/1,4-dioxane mixture leads to the formation of large crystals of 2D CP [Nd(DMSO)3L1.5·0.5diox]n (5), where deprotonated dithione H2L plays the role of a ditopic linker. This linker acts as an "antenna" in compound 5, providing an intense near-infrared (NIR) PL of Nd3+ ion upon near-UV and blue-light excitation. The application of a synthetic protocol similar to that of compounds 2-4 led to the formation of amorphous compounds [Ln(DMSO)3L1.5·0.5diox]n [Ln = Gd (6), Er (7), and Yb (8)], whose PL properties significantly differ from those of the parental ionic salts. In the case of Yb polymer 8, the PL excitation spectra are shifted to the red region due to a low-energy ligand-to-metal charge-transfer state. The synthesized compounds 5-8 are the first examples of lanthanide CPs using soft-base ditopic linkers in their structures.

Dual-Functional Eu-Metal-Organic Framework with Ratiometric Fluorescent Broad-Spectrum Sensing of Benzophenone-like Ultraviolet Filters and High Proton Conduction

The construction of attractive dual-functional lanthanide-based metal-organic frameworks (Ln-MOFs) with ratiometric fluorescent detection and proton conductivity is significant and challenging. Herein, a three-dimensional (3D) Eu-MOF, namely, [Eu4(HL)2(SBA)4(H2O)6]·9H2O, has been hydrothermally synthesized with a dual-ligand strategy, using (4-carboxypiperidyl)-N-methylenephosphonic acid (H3L = H2O3PCH2-NC5H9-COOH) and 4-sulfobenzoic acid monopotassium salt (KHSBA = KO3SC6H4COOH) as organic linkers. Eu-MOF showed ratiometric fluorescent broad-spectrum sensing of benzophenone-like ultraviolet filters (BP-like UVFs) with satisfactory sensitivity, selectivity, and low limits of detection in water/ethanol (1:1, v/v) solutions and real urine systems. A portable test paper was prepared for the convenience of actual detection. The potential sensing mechanisms were thoroughly analyzed by diversified experiments. The synergistic effect of the forbidden energy transfer from the ligand to Eu3+, the internal filtration effect (IFE), the formation of a complex, and weak interactions between the KHSBA ligand and BP-like UVFs is responsible for the ratiometric sensing effect. Meanwhile, Eu-MOF displayed relatively high proton conductivity of 2.60 × 10-4 S cm-1 at 368 K and 95% relative humidity (RH), making it a potential material for proton conduction. This work provides valuable guidance for the facile and effective design and construction of multifunctional Ln-MOFs with promising performance.

Solvothermal synthesis and device fabrication of a Eu3+-based metal-organic framework as a turn-on and blue-shift fluorescence sensor toward Cr3+, Al3+ and Ga3

A novel three-dimensional Eu³⁺-based metal-organic framework with the formula {[(CH₃)₂NH₂][Eu(BTDI)]·H₂O·DMF}_n (JXUST-25) was prepared by solvothermal method based on Eu³⁺ and 5,5'-(benzothiadiazole-4,7-diyl)diisophthalic acid (H₄BTDI) with benzothiadiazole (BTD) luminescent groups. Due to the presence of Eu³⁺ and organic fluorescence ligand, JXUST-25 displays turn-on and blue-shift fluorescence toward Cr³⁺, Al³⁺ and Ga³⁺ with limits of detection (LOD) of 0.073, 0.006 and 0.030 ppm, respectively. Interestingly, the alkaline environment can change the fluorescence of JXUST-25 toward Cr³⁺/Al³⁺/Ga³⁺ and the addition of HCl solution realizes the reversible change of the fluorescence of JXUST-25 toward Cr³⁺/Al³⁺/Ga³⁺. It is noteworthy that the fluorescent test paper and light-emitting diode lamp based on JXUST-25 can effectively detect Cr³⁺, Al³⁺ and Ga³⁺ by the visual changes. In addition, the turn-on and blue-shift fluorescence between JXUST-25 and M³⁺ ions may be caused by the host-guest interaction and the absorbance caused enhancement mechanism.

Brightly Luminescent (TbxLu1-x)2bdc3·nH2O MOFs: Effect of Synthesis Conditions on Structure and Luminescent Properties

Luminescent, heterometallic terbium(III)-lutetium(III) terephthalate metal-organic frameworks (MOFs) were synthesized via direct reaction between aqueous solutions of disodium terephthalate and nitrates of corresponding lanthanides by using two methods: synthesis from diluted and concentrated solutions. For (Tb_xLu_1-x)₂bdc₃·nH₂O MOFs (bdc = 1,4-benzenedicarboxylate) containing more than 30 at. % of Tb³⁺, only one crystalline phase was formed: Ln₂bdc₃·4H₂O. At lower Tb³⁺ concentrations, MOFs crystallized as the mixture of Ln₂bdc₃·4H₂O and Ln₂bdc₃·10H₂O (diluted solutions) or Ln₂bdc₃ (concentrated solutions). All synthesized samples that contained Tb³⁺ ions demonstrated bright green luminescence upon excitation into the ¹ππ* excited state of terephthalate ions. The photoluminescence quantum yields (PLQY) of the compounds corresponding to the Ln₂bdc₃ crystalline phase were significantly larger than for Ln₂bdc₃·4H₂O and Ln₂bdc₃·10H₂O phases due to absence of quenching from water molecules possessing high-energy O-H vibrational modes. One of the synthesized materials, namely, (Tb_0.1Lu_0.9)₂bdc₃·1.4H₂O, had one of the highest PLQY among Tb-based MOFs, 95%.

Cation-Exchange in Metal-Organic Framework as a Strategy to Obtain New Material for Ascorbic Acid Detection

Ascorbic acid (AA) is an important biomolecule, the deficiency or maladjustment of which is associated with the symptoms of many diseases (e.g., cardiovascular disease or cancer). Therefore, there is a need to develop a fluorescent probe capable of detecting AA in aqueous media. Here, we report the synthesis, structural, and spectroscopic characterization (by means of, e.g., XRD, XPS, IR and Raman spectroscopy, TG, SEM, and EDS analyses), as well as the photoluminescent properties of a metal-organic framework (MOF) based on Cu²⁺ and Eu³⁺ ions. The ion-exchange process of the extraframework cation in anionic Cu-based MOF is proposed as an appropriate strategy to obtain a new material with a nondisturbed structure and a sensitivity to interaction with AA. Accordingly, a novel Eu[Cu₃(μ₃-OH)(μ₃-4-carboxypyrazolato)₃] compound for the selective optical detection of AA with a short detection time of 5 min is described.

Lanthanide-Anderson Polyoxometalates Frameworks: Efficient Sulfide Photooxidation

Three polyoxometalate-based metal-organic frameworks were synthesized by the thermal reaction of pyridyl-Anderson polyoxometalate linker and lanthanide ions. With the help of [Ru(bpy)₃]²⁺ photosensitizer, these frameworks exhibited excellent photocatalytic sulfide oxidation performance with sulfoxide selectivity. The reactive oxygen species as well as the photooxidation mechanism were also explored.

Highly Active La(III)-Based Metal-Organic Framework as a Heterogeneous Lewis Acid Catalyst for Friedel-Crafts Alkylation

In this study, a novel La(III)-based two-dimensional (2D) metal-organic framework, [La_2/3 (qptca)_1/2 ] (referred to as SLX-2), from LaCl₃ and 1,1' : 4',1'' : 4'',1''' : 4''',1''''-quinquephenyl]-2,2'',2'''',5''-tetracarboxylic acid (H₄ qptca) was synthesized by conventional solvothermal method and thoroughly characterized by using X-ray single-crystal diffraction, powder X-ray diffraction, and thermogravimetric analyses. The 2D SLX-2 features a unique lanthanum center exposed to the skeleton and was used as an efficient Lewis acid catalyst for the Friedel-Crafts alkylation of indole and pyrrole with β-nitrostyrene along with a wide substrate scope, giving the desired products in good-to-high yields under the optimal reaction conditions. Furthermore, the catalyst was used for twenty cycles, with nearly no effect on its activity, and the reaction was heterogeneous in nature. Moreover, compared to the previous hydrogen-bond-donating MOF catalysts for such alkylation reactions, SLX-2 showed an excellent stability toward harsh acidic and basic environment, and gave comparable catalytic activities.

Robust acid-base Ln-MOFs: searching for efficient catalysts in cycloaddition of CO2 with epoxides and cascade deacetalization-Knoevenagel reactions

A family of microporous and robust Ln(iii)-based metal-organic frameworks (1-Ln, Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) have been obtained using 4,4',4''-nitrilotribenzoic acid (H₃NTB) in NMP-HCl solvent. Both single-crystal and powder X-ray diffraction analyses demonstrate that 1-Ln are isostructural and possess 3D frameworks with permanent porosity for Ar and CO₂ adsorption. Strikingly, the incorporation of both Lewis acidic lanthanide ions and the basic triphenylamine group into 1-Ln makes them efficient acid-base catalysts for both cycloaddition of epoxides with CO₂ and one-pot cascade deacetalization-Knoevenagel reactions. The systematic catalytic studies show that 1-Tb and 1-Yb possess the best catalytic activities for both reactions, indicating the catalytic activities of these Ln-MOFs are strongly dependent on metal Lewis acid sites embedded in the frameworks.

Variable Dimensionality of Europium(III) and Terbium(III) Coordination Compounds with a Flexible Hexacarboxylate Ligand

A reaction between 4,4',4″-(benzene-1,3,5-triyltris(oxy))triphthalic acid (H₆L) and lanthanide(III) nitrates (Ln = Eu³⁺, Tb³⁺) in water under the same conditions gave a molecular coordination compound [Tb(H_4.5L)₂(H₂O)₅]∙6H₂O in the case of terbium(III) and a one-dimensional linear coordination polymer {[Eu₂(H₃L)₂(H₂O)₆]∙8H₂O}_n in the case of europium(III). The crystal structures of both compounds were established by single-crystal X-ray diffraction, and they were further characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. The compounds demonstrated characteristic lanthanide-centered photoluminescence. The lanthanide-dependent dimensionality of the synthesized compounds, which are the first examples of the coordination compounds of hexacarboxylic acid H₆L demonstrates its potential as a linker for new coordination polymers.

Development of highly permselective Mixed Matrix Membranes comprising of polyimide and Ln-MOF for CO2 capture

Mixed Matrix Membranes (MMMs) with hybrid organic-inorganic characteristics offer a strong alternative to traditional polymer-based membranes to reduce the trade-off between gas permeability and selectivity. This work incorporated lanthanum-Metal Organic Frameworks in the Matrimid to fabricate MMMs. To understand the effects of nano-filler on membranes' morphology, porosity, thermal stability, and chemical composition, MMMs were fabricated with three different loadings of nano-filler, i.e., 10, 20 and 30 wt%. The selectivity and permeability of CH₄, CO₂, and N₂ gases through MMMs were investigated at 10 bar pressure and temperatures ranging from 25 to 55 °C. All MMMs exhibited enhanced CO₂ permeation with increased nano-filler loading because the porous nano-filler provided additional channels and fractional free volume in the polymer matrix. The 30 wt% loaded membrane showed a 183% increase in permeability of CO₂ than neat membrane. With increasing nano-filler loading, the selectivity of MMMs increased from 34.1 to 48.45 for CO₂/N₂ and from 36.2 to 54.67 for CO₂/CH₄, confirming the absence of membrane defects, improved filler/polymer interface, and excellent dispersion of nano-filler in the polymer matrix. The results proved that these membranes could be further used for gas separation industrial applications.

Blue-Emitting Ligand-Mediated Assembly of Rare-Earth MOFs toward White-Light Emission, Sensing, Magnetic, and Catalytic Studies

New lanthanide carboxylate compounds with two- (2D) and three-dimensional (3D) structures have been prepared by employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as an organic linker. The compounds, [Ln(C₁₄H₈O₆)(C₇O₃H₄)·2H₂O]·4(H₂O), Ln = Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy and [Ln(C₇O₃H₄)₃·(C₃H₇ON)·(H₂O)]·2(H₂O)(C₃H₇NO), Ln = La, Ce, Pr, have two- and three-dimensional structures, respectively. In all compounds, lanthanide ions are connected together, forming a dimer, which is connected by the 2,5-BPTA ligand. In the two-dimensional structure, there are two 2,5-BPTA moieties present, and in the three-dimensional structure, there are three 2,5-BPTA moieties present. The lanthanide centers are nine-coordinated, the 2D structure has a tricapped trigonal prismatic arrangement, and the 3D structure has a monocapped distorted square antiprismatic arrangement. The Pr compound forms in both 2D and 3D structures, whose formation depends on the time of the reaction (2 days─2D and 5-6 days─3D). The ligand emits in the blue region, and using the characteristic emission of Eu³⁺ (red) and Tb³⁺ (green) ions, we achieve white light emission in the (Y_0.96Tb_0.02Eu_0.02) compound. The overall quantum yield for the white light emission is 28%. The strong green luminescence of the Tb³⁺-containing compound was employed to selectively sense the Cr³⁺ and Fe³⁺ ions in aqueous solution with limits of detection (LODs) at 0.41 and 8.6 ppm, respectively. The Tb compound was found to be a good heterogeneous catalyst for the Ullman-type O-arylation reaction between phenol and bromoarene with yields of 95%. Magnetic studies on the Gd-, Tb-, and Dy-containing compounds showed weak exchange interactions within the dimeric Ln₂ units. The present work demonstrates the many utilities of the rare-earth-containing MOFs, especially toward white-light emission, metal-ion sensing, and heterogeneous catalysis.

A minimalist fluorescent MOF sensor array for Baijiu identification

The beverage industry is in the market tuyere, and grasps the lifeline of the social economy, so it is particularly vital to supervise it. Herein, we report a minimalist fluorescence metal-organic framework (MOF) sensor array for Baijiu identification. The original MOF was modified by rare-earth elements to obtain Eu-MOFs and Tb-MOFs. They exhibited multiple fluorescence characteristic peaks in the range of 400-700 nm when excited at 325 nm. The organic molecules in the Baijiu reacted with Eu-MOF and Tb-MOF, affecting the energy transfer of the entire system and the electronic transition of Eu³⁺ and Tb³⁺, which were accompanied by various changes in the fluorescence intensity. For each analyte, a unique fluorescence fingerprint and heat map would be formed, which could be discriminated by pattern recognition. With this method, 11 kinds of organic molecules were identified accurately. A good stepwise bilinear function between the fluorescence intensity and concentrations of ferulic acid was obtained at 0.2-3.13 μM and 6.25-100 μM. Crucially, 16 kinds of Baijius of different brands were accurately identified with an accuracy of 100%. The sensor array showed the advantages of strong maneuverability and fast response, exhibiting good application value in Baijiu detection.

Magnetic UiO-66 functionalized with 4,4'-diamino-2,2'-stilbenedisulfonic as a highly recoverable acid catalyst for the synthesis of 4H-chromenes in green solvent

According to 4H-chromenes importance, we synthesized a novel magnetic UiO-66 functionalized with 4,4′-diamino-2,2′-stilbenedisulfonic as an efficient and reusable solid acid catalyst for synthesizing 4H-chromene skeletons via a one-pot three components reaction in a green solvent. The structure of the synthesized catalyst was confirmed by various techniques including FT-IR, XRD, BET, TGA, TEM, EDX, and SEM, and also the product yields were obtained in 83–96% of yields for all the reactions and under mild conditions. The reported procedure presents an environmentally friendly approach for synthesizing a significant number of 4H-chromene derivatives. Correspondingly, MOF-based catalyst makes it easy to separate from reaction media and reuse in the next runs.

Construction of Large-Scale Conjugated Functionalized Cyclotriphosphazene Lanthanide Framework for Selective Sensing of Volatile Organic Compounds and Assembly of Color-Tunable Dye-Encapsulated Composites

A flexible functionalized cyclotriphosphazene hexacarboxylic acid, hexakis(4-carboxylatephenoxy) cyclotriphosphazene (HCPCP), is used for the synthesis of a family of fluorescent Ln-HCPCP frameworks (Ln = La, Pr, Nd, Gd, and Ho). Structural analysis shows that the compounds exhibit 3D structures with [Ln₃(COO)₁₀], secondary building units formed by Ln-O-C-O-Ln connection. Then the molecules are connected to each other through HCPCP, forming rectangular channels along the c-direction. Interestingly, the fluorescence sensing studies show that compound 1 could be used as a multifunctional fluorescence sensor toward volatile organic compounds via different fluorescence emission behaviors. Moreover, a series of Dye@La-HCPCP composites (Dye = rhodamine B, safranine T, crystal violet, and malachite green) are successfully prepared with different quantum yields by the solvothermal reaction followed by cation exchanges.

Proton Conductive Lanthanide-Based Metal-Organic Frameworks: Synthesis Strategies, Structural Features, and Recent Progress

In the fields of proton exchange membrane fuel cells as well as impedance recognition, molecular sieve, and biochemistry, the development of proton conductive materials is essential. The design and preparation of the next generation of proton conductive materials-crystalline metal-organic framework (MOF) materials with high proton conductivity and excellent water stability-are facing great challenges. Due to the large radius and high positive charge of lanthanides, they often interact with organic ligands to exhibit high coordination numbers and flexible coordination configurations, resulting in the higher stability of lanthanide-based MOFs (Ln-MOFs) than their transition metal analogues, especially regarding water stability. Therefore, Ln-MOFs have attracted considerable attention. This review offers a view of the latest progress of proton conductive Ln-MOFs, including synthesis strategy, structural characteristics, and advantages, proton conductivity, proton conductive mechanism, and applications. More importantly, by discussing structure-property relationships, we searched for and analyzed design techniques and directions of development of Ln-MOFs in the future. The latest progress of synthesis strategy, structural characteristics, proton conductive properties and mechanism and applications on Ln-MOFs. Ln-MOFS Lanthanide-based MOFs, MOF metal-organic framework, PEMFC proton exchange membrane fuel cells.

A turn-on NIR fluorescence sensor for gossypol based on Yb-based metal-organic framework

The development of analytical method for selective and sensitive detection of gossypol (Gsp), an extraction from the cotton plants, is important but still challenging in food safety and medical field. Herein, we reported a turn-on near infrared (NIR) fluorescence detection strategy for Gsp based on a metal-organic framework (MOF), QBA-Yb, which was prepared from 4,4'-(quinolone-5, 8-diyl) benzoate with Yb(NO₃)₃·5H₂O by solvothermal synthesis. The Gsp acted as another "antenna" to sensitize the luminescence of Yb³⁺, leading to the turn-on NIR emission upon 467 nm excitation. As Gsp concentration increased, the NIR emission at 973 nm enhanced gradually, thus enabling highly sensitive Gsp detection in a turn-on way. The experiment and theoretical calculation results revealed the presence of strong hydrogen bonds between Gsp molecules and the MOF skeleton. The developed QBA-Yb probe showed excellent characteristics for detection of Gsp molecules, accompanied by wide linear range (5-160 μg/mL), low detection limit (0.65 μg/mL) and short response time (within 10 min). We have further demonstrated that the QBA-Yb probe was successfully applied for the determination of Gsp in real samples of cottonseeds.

Nanocage-based {In2Tm2}-organic framework for efficiently catalyzing the cycloaddition reaction of CO2 with epoxides and Knoevenagel condensation

The combination of [In2Tm2(μ2-OH)2(CO2)10(H2O)2] clusters and H5BDCP ligand generated a highly robust nanoporous MOF with high catalytic performance in the cycloaddition reaction of epoxides with CO2 and Knoevenagel condensation.

Lanthanide-MOFs as Multifunctional luminescence Sensors

Five isostructural lanthanide metal-organic frameworks, [Ln(BDPO)(H2O)4] (Ln= Eu for CUST-623, Tb for CUST-624, Gd for CUST-625, Dy for CUST-626, Sm for CUST-627, BDPO = N, N' bis (3,5 - dicarboxyphenyl)-oxalamide)...

Covalency in Actinide(IV) Hexachlorides in Relation to Chlorine K­-Edge X­-ray Absorption Structure

Chlorine K-edge X-ray absorption near edge structure (XANES) in actinide^IV hexachlorides, [AnCl₆]²⁻ (An = Th–Pu), is calculated with relativistic multiconfiguration wavefunction theory (WFT). Of particular focus is a 3-peak feature emerging from U toward Pu, and its assignment in terms of donation bonding to the An 5f vs. 6d shells. With or without spin–orbit coupling, the calculated and previously measured XANES spectra are in excellent agreement with respect to relative peak positions, relative peak intensities, and peak assignments. Metal–ligand bonding analyses from WFT and Kohn–Sham theory (KST) predict comparable An 5f and 6d covalency from U to Np and Pu. Although some frontier molecular orbitals in the KST calculations display increasing An 5f–Cl 3p mixing from Th to Pu, because of energetic stabilization of 5f relative to the Cl 3p combinations of the matching symmetry, increasing hybridization is neither seen in the WFT natural orbitals, nor is it reflected in the calculated bond orders. The appearance of the pre-edge peaks from U to Pu and their relative intensities are rationalized simply by the energetic separation of transitions to 6d t_2gversus transitions to weakly-bonded and strongly stabilized a_2u, t_2u and t_1u orbitals with 5f character. The study highlights potential pitfalls when interpreting XANES spectra based on ground state Kohn–Sham molecular orbitals.

Chlorine K-edge XANES of An(iv) hexachlorides, calculated with multiconfiguration wavefunction theory, is interpreted in terms of similar metal–ligand covalency along the An = Th–Pu series.

Selective luminescent sensing of metal ions and nitroaromatics over a porous mixed-linker cadmium(ii) based metal–organic framework

A potential luminescent sensor based on porous metal organic framework for the detection of metal ions (Al3+, Fe3+ or Cr3+) and nitro-explosive, 2,4,6-tri-nitrophenol has been discovered. MOF is capable of detecting aqueous phase analyte through luminescent sensing.

Near-Infrared Emissive Lanthanide Metal-Organic Frameworks for Targeted Biological Imaging and pH-Controlled Chemotherapy

Near-infrared window II (NIR-II, 1000-1700 nm) imaging displays the advantages in deep-tissue high-contrast imaging in vivo on the strength of the high temporal-spatial resolution and deeper penetration. However, the clinical utility of NIR-II imaging agents is limited by their single function. Herein, for the first time, we report the design of a multifunctional drug delivery system (DDS) assembly, CQ/Nd-MOF@HA nanohybrids, with NIR-II fluorescence (1067 nm), large Stokes shifts, and ultrahigh quantum yield, which combined targeted NIR-II luminescence bioimaging and pH-controlled drug delivery. The nanoscale metal-organic framework (MOF) as a highly promising multifunctional DDS for targeted NIR-II bioimaging and chemotherapy in vitro and in vivo lays the foundation of the MOF-based DDS for further clinical diagnosis and treatment.

A series of microporous and robust Ln-MOFs showing luminescence properties and catalytic performances towards Knoevenagel reactions

A series of microporous Ln(III)-based metal-organic frameworks (1-Ln) have been hydrothermally synthesized using 4,4',4''-nitrilotribenzoic acid (H₃NTB). Single crystal X-ray diffraction analyses show that 1-Ln are isostructural and have 3D porous frameworks with remarkable stability and permanent porosity for Ar and CO₂ adsorption. In addition, 1-Ln exhibit diverse photoluminescence emissions depending on the nature of lanthanide ions. More importantly, 1-Ln are further studied in the Knoevenagel reactions of benzaldehyde derivatives and malononitrile under solvent-free conditions, and it is found that 1-Tb shows the best catalytic activities (yields up to 99%), providing a unique example to differentiate the roles of Ln ions within the frameworks in catalyzing Knoevenagel reactions.

Dye functionalized lanthanide metal-organic framework as a multifunctional luminescent hybrid material for visual sensing of biomarker 2-methoxyaceticacid and sulfide anion

Based on the anionic Slug-47 [Gd(bpdc)₂^-] [NH₂(CH₃)₂⁺], a multifunctional fluorescent material with ultra-high stability has been fabricated successfully. Firstly, Eu_0.04Tb_39.96Gd₆₀ with white light emission is prepared by adjusting the doping ratio of Eu³⁺ ions and Tb³⁺ ions. Then, the dye acriflavine (ACF) is further introduced into the framework of Eu@ Slug-47 (1) via cation exchange to obtain ACF@1, which can be used as a ratio fluorescence sensor to detect 2-methoxyaceticacid (Maa), a toxic metabolite of glycol monomethyl ether, with the limit of detection (LOD) as low as 0.27 μg/mL. It is impressive that the emissions of ACF and biphenyl-4,4'-dicarboxylicacid ligands are gradually enhanced with the gradual weakening of the emission of Eu³⁺ ions during the detection of Maa. Under the superposition of three different colors, the sensing process undergoes a distinct color change from red to white and then to blue. These rich and colorful colors provide conditions for accurate visual detection of Maa. In addition, the material can also respond well to the pollutant S^2- ions and the LOD can reach 11.3 μmol /L. It is worth mentioning that the available quenching effect can be observed even if Maa and S^2- ions are detected in urine and tap water respectively, indicating that the multifunctional material has a brilliant application prospect. Finally, the quenching mechanism of Maa, S^2- ions toward ACF@1 is discussed in detail.

Multifunctional luminescence sensing and white light adjustment of lanthanide metal-organic frameworks constructed from the flexible cyclotriphosphazene-derived hexacarboxylic acid ligand

Considering that cyclotriphosphazene polycarboxylic acid is a kind of organic ligand with fantastic structures and performances and the unique luminescence characteristics of rare earth ions, a series of porous lanthanide metal-organic frameworks (Ln-MOFs) (CH3)2NH2[Ln3(HCPCP)1.5(CH3COO)]·6DMA (Ln = Ce (1), Sm (2), Eu (3), Tb (4), HCPCP = hexa(4-carboxyphenoxy)cyclotriphosphazene, and DMA = N,N-dimethylacetamide) were synthesized with novel topological network structures. Compound 4 exhibited a sensitive recognition of -NO2, and had a fluorescence quenching phenomenon for seven kinds of nitro aromatic compounds (NACs). In particular, it showed the best fluorescence response to 2,4,6-trinitrophenol (TNP) and 2,4-dinitrophenol (DNP), and the KSV values were 2.86 × 105 M-1 and 8.21 × 104 M-1, and the limit of detection (LOD) values were 0.20 μM and 0.71 μM, respectively. At the same time, we successfully doped different concentrations of Eu3+ into compound 4 to obtain a series of doped Ln-MOF materials x%Eu3+@4 (x = 0.5, 2.5, 5, 7.5, 10, 15 and 20). With the increase of Eu3+ doping ratios, the characteristic peaks of Tb3+ and Eu3+ changed regularly, and the energy transfer from Tb3+ to Eu3+ ions occurred. By changing the excitation wavelength of the samples with different Eu3+ doping concentrations, a higher quality white light emitting material 7.5%Eu3+@4 (λex = 340 nm) was finally obtained, with a CIE coordinate of (0.3268, 0.3212).

Visible-light-responsive lanthanide coordination polymers for highly efficient photocatalytic aerobic oxidation of amines and thiols

Photoinduced activation of oxygen by visible-light-responsive CPs via electron/energy transfer and its roles on aerobic oxidation of amines and thiols.