Lanthanide azolecarboxylate compounds: Structure, luminescent properties and applications

Integrated Solution for As(III) Contamination in Water Based on Crystalline Porous Organic Salts

A stable crystalline organic porous salt (CPOSs-NXU-1) with 1D apertures has been assembled by the solvothermal method, which shows high-sensitivity "turn-on" fluorescence detection and large-capacity adsorption of As(III) ions in water. The detection limits, saturated adsorption capacity, and removal rate of CPOSs-NXU-1 for As(III) ions in an aqueous solution can reach 74.34 nm (5.57 ppb), 451.01 mg g-1, and 99.6%, respectively, at pH = 7 and room temperature. With the aid of XPS, IR, Raman, and DFT theoretical calculations, it is determined that CPOSs-NXU-1 adsorbed As(III) ions in the form of H2AsO3 - and H3AsO3 through hydrogen bonding between the host and guest. The mechanism for fluorescence sensitization of As(III) ions to CPOSs-NXU-1 is mainly to increase the energy level difference between the ground state and excited state investigated by UV-vis absorption spectra, UV-vis diffuse reflectance spectra, and theoretical calculations. By constructing fluorescent CPOSs, an integrated solution has been achieved to treating As(III) contamination in the water that is equipped with detection and removal. These results blaze a promising path for addressing trivalent arsenic contamination in water efficiently, rapidly, and economically.

Eu3+-Doped Anionic Zinc-Based Organic Framework Ratio Fluorescence Sensing Platform: Supersensitive Visual Identification of Prescription Drugs

Advanced techniques for both environmental and biological prescription drug monitoring are of ongoing interest. In this work, a fluorescent sensor based on an Eu3+-doped anionic zinc-based metal-organic framework (Eu3+@Zn-MOF) was constructed for rapid visual analysis of the prescription drug molecule demecycline (DEM), achieving both high sensitivity and selectivity. The ligand 2-amino-[1,1'-biphenyl]-4,4'-dicarboxylic acid (bpdc-NH2) not only provides stable cyan fluorescence (467 nm) for the framework through intramolecular charge transfer of bpdc-NH2 infinitesimal disturbanced by Zn2+ but also chelates Eu3+, resulting in red (617 nm) fluorescence. Through the synergy of photoinduced electron transfer and the antenna effect, a bidirectional response to DEM is achieved, enabling concentration quantification. The Eu3+@Zn-MOF platform exhibits a wide linear range (0.25-2.5 μM) to DEM and a detection limit (LOD) of 10.9 nM. Further, we integrated the DEM sensing platform into a paper-based system and utilized a smartphone for the visual detection of DEM in water samples and milk products, demonstrating the potential for large-scale, low-cost utilization of the technology.

Novel stable ytterbium acetylacetonate-quinaldinate complexes as single-molecule magnets and surprisingly efficient luminophores

The first Yb complexes comprising a quinoline-2-carboxylate (quinaldinate, Q-) ligand, namely 1D-polymeric [Yb(acac)2(Q)]n (1, acac- is the acetylacetonate (pentane-2,4-dionate) anion) and mononuclear [Yb(acac)2(Q)(Phen)] (2, Phen is 1,10-phenanthroline), are reported. The bifunctionality of both complexes as field-induced single-molecule magnets (SMMs) and near IR luminophores has been revealed. The SMM properties of 1 and 2 have been discussed in terms of the geometry and composition of the coordination environment. Also, 1 is the first example of 1D-polymeric SMMs with the capped octahedral surrounding of Yb3+. The photoluminescence quantum yields (PLQYs) of 1 and 2 are 2 and 4%, respectively. The origins of this difference are discussed. Surprisingly, the PLQY value of 2 is high for compounds comprising a lot of C-H vibrational quenchers, being the highest one for reliably characterized Yb β-diketonate complexes, and surpassing those for complexes with a broad range of anionic ligands. In this respect, the role of the Phen ligand is to tune the coordination mode of Q- thereby decreasing the energy of coordinating C-O oscillators rather than to act as a typical antenna ligand. These results can give rise to an alternative route to elaborate efficient Yb-based luminophores via the substitution of the β-diketonate ligands controlled by the introduction of appropriate neutral ligands.

Stacking Lanthanide-MOF Thin Films to Yield Highly Sensitive Optical Thermometers

Easy-to-integrate, remote read-out thermometers with fast response are of huge interest in numerous application fields. In the context of optical read-out devices, sensors based on the emission of lanthanides (Eu(III), Tb(III)) are particularly promising. Here, by using a layer-by-layer (LbL) approach in the liquid-phase epitaxy process, a series of continuous, low-thickness lanthanide-MIL-103 SURMOFs were fabricated to yield highly sensitive thermometers with optical readout. These Ln-SURMOFs exhibit remarkable temperature-sensing photoluminescence behavior, which can be read out using the naked eye. High transmittance is realized as well by precisely controlling the film thickness and the quality of these Ln-SURMOF thermometers. Moreover, we demonstrate that the thermal sensitivity can be improved in the temperature regime above 120 K, by controlling the energy transfer between Tb(III) and Eu(III). This performance is achieved by employing a sophisticated supramolecular architecture, namely MOF-on-MOF heteroepitaxy.

Thermal, structural, optical, and photon shielding studies of cerium-doped barium tellurite glasses

A series of tellurite-based glasses are prepared by using a melt-quenching method. The effect of cerium on the physical, thermal, structural, optical, spectroscopic, and shielding properties of barium tellurite glass samples is studied. It has been observed that the thermal stability factor increases with increasing cerium ion (Ce³⁺ ) concentration. The density and other physical parameters such as ion concentration and molar volume are calculated using the Archimedes principle. An increase in optical band gap and density suggests a decrement in non-bridging oxygens. These results are in accordance with Raman results. The blue emission in prepared glasses is studied in terms of International Commission on Illumination chromaticity coordinates. Moreover, various shielding properties such as mass attenuation coefficient, linear attenuation coefficient, effective atomic number, half-value layer, and tenth-value layer have also been determined to understand the photon shielding characteristics of as-prepared glass samples.

Metal Complexes with Naphthalene-Based Acetic Acids as Ligands: Structure and Biological Activity

Naproxen (6-methoxy-α-methyl-2-naphthaleneacetic acid), 1-naphthylacetic acid, 2-naphthylacetic acid and 1-pyreneacetic acid are derivatives of acetic acid bearing a naphthalene-based ring. In the present review, the coordination compounds of naproxen, 1- or 2-naphthylacetato and 1-pyreneacetato ligands are discussed in regard to their structural features (nature and nuclearity of metal ions and coordination mode of ligands), their spectroscopic and physicochemical properties and their biological activities.

Self-Assembly of a Two-Dimensional Coordination Polymer Based on Silver and Lanthanide Tetrakis-Acylpyrazolonates: An Efficient New Strategy for Suppressing Ligand-to-Metal Charge Transfer Quenching of Europium Luminescence

A new strategy for the easy polymerization of anionic [Ln(Q^cy)₄]^- (HQ^cy-4-(cyclohexanecarbonyl)-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one) into two-dimensional layers of [AgLn(Q^cy)₄]_n (Ln = Sm, Eu, Gd, Tb and Dy) is proposed by binding the single molecular anions [Ln(Q^cy)₄]^- to silver cations through the coordination of the pyridinic nitrogen atoms of the pyrazolonate rings. The luminescent properties of [AgLn(Q^cy)₄]_n have been studied in detail, and it was shown that the previously described low photoluminescence quantum yield (PLQY) of [Eu(Q^cy)₄]^- is due to Ligand-To-Metal Charge Transfer (LMCT) quenching, which is effectively suppressed in the heterometallic [AgEu(Q^cy)₄]_n polymer. Sensibilization coefficients for H₃O[Eu(Q^cy)₄], [AgEu(Q^cy)₄]_n, and H₃O[Sm(Q^cy)₄] complexes (n ≈ 1) were estimated via theoretical analysis (also by using Judd-Ofelt theory for Sm³⁺) and PLQY measurements.

Samarium-Based Turn-Off Fluorescence Sensor for Sensitive and Selective Detection of Quinolinic Acid in Human Urine and Serum

Quinolinic acid (QA) is an index for some diseases, whose detection is of importance. This work presents a samarium metal-organic framework (Sm-MOF) containing 5-sulfoisophthalate ligand (SIP^3-). The fluorescence of Sm-MOF integrates the emission at 339 nm from the SIP^3- ligand and four characteristic ⁴G_5/2 → ⁴H_j (j = 5/2, 7/2, 9/2, and 11/2) transitions at 559, 596, 642, and 701 nm from Sm(III). Sm-MOF as a turn-off fluorescence sensor to QA exhibits high sensitivity, selectivity, and durability. The fluorescence quenching response to QA shows a linear relationship of I₀/I = 0.00496·C_QA + 1.12474 in the QA concentration of 0-500 μM and a limit of detection calculated as 4.11 μM. Sm-MOF shows the structural and fluorescent stabilities in five quenching-recovery cycles. The recoveries of close to 100% in human urine and serum indicate high reliability. The paper-based Sm-MOF sensor displays a rough QA quantitative analysis by recognizing red values in the on-site QA detection.

Dual-Color 2D Lead-Organic Framework with Two-Fold Interlocking Structures for the Detection of Nitrofuran Antibiotics and 2,6-Dichloro-4-nitroaniline

The misuse of organic pollutants such as nitrofuran antibiotics (NFAs) and 2,6-dichloro-4-nitroaniline (DCN) has become a hot topic of global concern, and developing rapid, efficient, and accurate techniques for detecting NFAs and pesticides in water is a major challenge. Here, we designed a novel lead-based anion 2D metal-organic framework (MOF){[(CH₃)₂NH₂]₂[Pb(TCBPE)(H₂O)₂]}_n (F3) with interlocking structures, in which TCBPE stands for 1,1,2,2-tetra(4-carboxylbiphenyl)ethylene. Powder X-ray diffraction and thermogravimetric analysis revealed that F3 has excellent chemical and solvent stability. It is worth noting that F3 has a grinding discoloration effect. The solvent-protected grinding approach achieved F3B with a high quantum yield (QY = 73.77%) and blue fluorescence, while the direct grinding method produced F3Y with a high quantum yield (QY = 37.27%) and yellow-green fluorescence. Importantly, F3B can detect NFAs in water rapidly and sensitively while remaining unaffected by other antibiotics. F3Y can identify DCN in water quickly and selectively while remaining unchanged by other pesticides. F3B demonstrated high selectivity and rapid response to NFAs at a limit of detection (LOD) as low as 0.26 μM, while F3Y indicated high selectivity and responded quickly to DCN in water at an LOD as low as 0.14 μM. The method was successfully applied to detect NFAs in actual water samples of the fish tanks and ponds as well as the pesticide DCN in soil samples. The recovery rates were 97.0-105.15% and 102.2-106.48%, and the relative standard deviations were 0.63-1.45% and 0.29-1.69%, respectively. In addition, F3B and F3Y can be made into fluorescent test papers for the visual detection of NFAs and DCN, respectively. Combined with experiments and density functional theory calculations, the mechanism of fluorescence quenching of MOFs by target analytes was also revealed.

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.

Aliphatic-Bridged Early Lanthanide Metal–Organic Frameworks: Topological Polymorphism and Excitation-Dependent Luminescence

Six new three-dimensional metal–organic frameworks based on early lanthanide(III) cations and trans-1,4-cyclohexanedicarboxylic acid (H2chdc) were obtained. Their crystal structures were determined by single-crystal X-ray diffraction analysis. The structure of [La2(H2O)4(chdc)3]·2DMF·H2O (1; DMF = N,N-dimethylformamide) contains one-dimensional infinite La(III)-carboxylate chains interconnected by cyclohexane moieties to form a highly porous polymeric lattice with 30% solvent accessible volume. Compounds [Ln2(phen)2(chdc)3]·0.75DMF (2Ln; Ln3+ = Ce3+, Pr3+, Nd3+ and Sm3+; phen = 1,10-phenanthroline) are based on binuclear carboxylate building blocks, which are decorated by chelate phenanthroline ligands and interconnected by cyclohexane moieties to form more dense isostructural coordination frameworks with primitive cubic pcu topology. Compound [Nd2(phen)2(chdc)3]·2DMF·0.67H2O (3) is based on secondary building units similar to 2Ln and contains a coordination lattice isomeric to 2Ln with a rare hexagonal helical snz topology. Thermal stability and luminescent properties were investigated. For 2Sm, a strong and nonmonotonous dependence of the luminescence color on the variation of excitation wavelength was revealed, changing its emission from pinkish red at λex = 340 nm to white at λex = 400 nm, and then to yellow at lower excitation energies. Such nonlinear behavior was rationalized in terms of the contribution of several different luminescence mechanisms. Thus, 2Sm is a rather rare example of a highly tunable monometallic lanthanide-based luminophore with possible applications in light-emitting devices and optical data processing.

2,3,4,5,6-Pentabromobenzoic Acid

Pentabromobenzoate is a useful fragment in organic synthesis and in coordination chemistry. Among known synthetic approaches to pentabromobenzoic acid (PBA), we have assessed and identified exhaustive bromination of benzoic acid by using 1.3-dibromoisocyanuric acid in concentrated H2SO4 solution as the most efficient method for the preparation of PBA on a multigram scale. As the crude bromination product is typically contaminated with 3,4,5,6-tetrabromobenzoic acid (TBA) and pentabromobenzene, C6Br5H, a simple purification protocol for preparation of analytically pure PBA has been developed. The molecular structure and crystal packing of PBA established by single-crystal X-ray diffractometry suggests a pattern of H-bonding and halogen bonding in solid state.

(Diaqua)hexakis(4,4,4-trifluoro-1-(1-methyl-1H-pyrazol-4-yl)butane-1,3-dionato-κ2O,O’)(μ-(1,4-dioxane))digadolinium (III), Solvate with Two Molecules of 1,4-Dioxane

A binuclear gadolinium (III) complex was obtained through the interaction of GdCl3·6H2O, 4,4,4-trifluoro-1-(1-methyl-1H-pyrazol-4-yl)butane-1,3-dione and NaOH in MeOH solution. Molar ration of reagents equal to 1:3:3 was used. Upon recrystallization of wet 1,4-dioxane, an intermediate hydrated complex formed stable crystalline solvate with the composition [(Gd2(L)3(H2O))2(C4H8O2)]•2(C4H8O2). The structured of complex was established by single crystal XRD experiment. Furthermore, some photophysical properties of the complex were measured. Thus, the energy of the first exited triplet state for the diketonate ligand was found to be 22400 cm−1, which makes 4,4,4-trifluoro-1-(1-methyl-1H-pyrazol-4-yl)butane-1,3-dione a promising ligand for the preparation of highly luminescent Eu3+ and Sm3+ complexes.

New Carboxylate Anionic Sm-MOF: Synthesis, Structure and Effect of the Isomorphic Substitution of Sm3+ with Gd3+ and Tb3+ Ions on the Luminescent Properties

Two new compounds, namely {(NMe2H2)}[Ln(TDA)(HCOO)] 0.5H2O, Ln = Sm3+ (Sm-TDA) and Gd3+ (Gd-TDA), where TDA3− is the anion of 1H-1,2,3-triazole-4,5-dicarboxylic acid (H3TDA), were synthesized by the solvothermal method in a DMF:H2O mixture. According to single-crystal X-ray diffraction data, the compounds are 3d-MOFs with an anionic lattice and dimethylammonium cations occupying part of the cavities. Based on these compounds, two series of mixed-metal complexes, [NMe2H2][SmxLn1-x(TDA)(HCOO)], (x = 0.9 (Sm0.9Ln0.1-TDA), x = 0.8 (Sm0.8-Ln0.2-TDA)…Sm0.02Ln0.98-TDA, Ln = Tb, Gd), were also obtained and characterized by powder XRD. The luminescent properties of the compounds were studied and it was shown that the resulting compounds are two- or three-component emitters with the possibility of fine color tuning by changing the intensities of fluorescence and phosphorescence of the ligand, as well as the luminescence of Sm3+ and Tb3+ f-ions.

Polyaromatic Carboxylate Ligands Based Zn(II) Coordination Polymers for Ultrasound-Assisted One-Pot Tandem Deacetalization–Knoevenagel Reactions

Solvothermal reactions between the polyaromatic group containing carboxylic acid pro-ligands 5-{(pyren-1-ylmethyl)amino}isophthalic acid (H2L1) and 5-{(anthracen-9-ylmethyl)amino}isophthalic acid (H2L2) with Zn(NO3)2·6H2O led to the formation of the new 1D coordination polymer [Zn(L1)(NMF)]n (1) and four other coordination polymers, [Zn(L1)(DMF)]n (2), [Zn(L1)(4,4′-Bipy)]n (3), [Zn(L2)(DMF)(H2O)2]n·n(H2O) (4) and [Zn2(L2)2(DMF)(CH3OH)]n (5), which were previously reported by our group. Single crystal X-ray diffraction analyses revealed that the CP 1 has a one-dimensional (1D) double-chain-type structure similar to that of CP 2. For CP 3, the assembly of the Zn(II) ion with a deprotonated L12− ligand and 4,4′-bipyridine produces a 3D network. CP 4 and 5 exhibit 1D linear and 2D layered-type structures. The ultrasound-assisted tandem reactions promoted by CPs have not yet been well studied. Thus, in the present work, we have investigated the catalytic activities of the newly synthesized CP 1, as well as of the other CPs 2–5, towards the tandem deacetalization–Knoevenagel condensation reactions of various acetals under ultrasonic irradiation. They proved to be highly efficient, with special emphasis on catalyst 1, which completely converted the substrate (benzaldehyde dimethyl acetal) into the desired product (2-benzylidenemalononitrile) after 2 h. The stability of the catalysts, namely regarding the action of ultrasonic radiation, was demonstrated by their reuse, where only a slight loss of activity was observed after four cycles. Heterogeneity was also demonstrated, and no leaching was detected over the various cycles.

Study on the synthesis and host–guest luminescence properties of a novel Cd(ii)-picolinate coordination polymer

A coordination polymer with guest-molecule-based luminescence is flexible in preparation and shows greater controllability.

Crystal Structures, Thermal and Luminescent Properties of Gadolinium(III) Trans-1,4-cyclohexanedicarboxylate Metal-Organic Frameworks

Four new gadolinium(III) metal-organic frameworks containing 2,2′-bipyridyl (bpy) or 1,10-phenanthroline (phen) chelate ligands and trans-1,4-cyclohexanedicarboxylate (chdc2−) were synthesized. Their crystal structures were determined by single-crystal X-ray diffraction analysis. All four coordination frameworks are based on the binuclear carboxylate building units. In the compounds [Gd2(bpy)2(chdc)3]·H2O (1) and [Gd2(phen)2(chdc)3]·0.5DMF (2), the six-connected {Ln2(L)2(OOCR)6} blocks form a 3D network with the primitive cubic (pcu) topology. In the compounds [Gd2(NO3)2(phen)2(chdc)2]·2DMF (3) and [Gd2Cl2(phen)2(chdc)2]·0.3DMF·2.2dioxane (4), the four-connected {Ln2(L)2(X)2OOCR)4} units (where X = NO3− for 3 or Cl− for 4) form a 2D square-grid (sql) network. The solid-state luminescent properties were investigated for the synthesized frameworks. Bpy-containing compound 1 shows no luminescence, possibly due to the paramagnetic quenching by Gd3+ cation. In contrast, the phenathroline-containing MOFs 2–4 possess yellow emission under visible excitation (λex = 460 nm) with the tuning of the characteristic wavelength by the coordination environment of the metal center.

Synthesis, Crystal Structure, and Luminescence of Cadmium(II) and Silver(I) Coordination Polymers Based on 1,3-Bis(1,2,4-triazol-1-yl)adamantane

Coordination polymers with a new rigid ligand 1,3-bis(1,2,4-triazol-1-yl)adamantane (L) were prepared by its reaction with cadmium(II) or silver(I) nitrates. Crystal structure of the coordination polymers was determined using single-crystal X-ray diffraction analysis. Silver formed two-dimensional coordination polymer [Ag(L)NO₃]_n, in which metal ions are linked by 1,3-bis(1,2,4-triazol-1-yl)adamantane ligands, coordinated by nitrogen atoms at positions 2 and 4 of 1,2,4-triazole rings. Layers of the coordination polymer consist of rare 18- and 30-membered {Ag₂L₂} and {Ag₄L₄} metallocycles. Cadmium(II) nitrate formed two kinds of one-dimensional coordination polymers depending on the metal-to-ligand ratio used in the synthesis. Coordination polymer [Cd(L)₂(NO₃)₂]_n was obtained in case of a 1:2 M:L ratio, while for M:L = 2:1 product {[Cd(L)(NO₃)₂(CH₃OH)]·0.5CH₃OH}_n was isolated. All coordination polymers demonstrated ligand-centered emission near 450 nm upon excitation at 370 nm.

Cinnamal Sensing and Luminescence Color Tuning in a Series of Rare-Earth Metal-Organic Frameworks with Trans-1,4-cyclohexanedicarboxylate

Three isostructural metal-organic frameworks ([Ln2(phen)2(NO3)2(chdc)2]·2DMF (Ln3+ = Y3+ for 1, Eu3+ for 2 or Tb3+ for 3; phen = 1,10-phenanthroline; H2chdc = trans-1,4-cyclohexanedicarboxylic acid) were synthesized and characterized. The compounds are based on a binuclear block {M2(phen)2(NO3)2(OOCR)4} assembled into a two-dime nsional square-grid network containing tetragonal channels with 26% total solvent-accessible volume. Yttrium (1)-, europium (2)- and terbium (3)-based structures emit in the blue, red and green regions, respectively, representing the basic colors of the standard RGB matrix. A doping of Eu3+ and/or Tb3+ centers into the Y3+-based phase led to mixed-metal compositions with tunable emission color and high quantum yields (QY) up to 84%. The bright luminescence of a suspension of microcrystalline 3 in DMF (QY = 78%) is effectively quenched by diluted cinnamaldehyde (cinnamal) solutions at millimolar concentrations, suggesting a convenient and analytically viable sensing method for this important chemical.