A Zn-coordination polymer for the quantitative and selective colorimetric detection of residual tetracycline in aqueous solution and urine

A one-step solvothermal synthesis provides a functional crystalline one-dimensional Zn-coordination polymer (Zn-CP) with excellent stability in aqueous solution over a wide range of temperature and pH. Zn-CP is a rapid, highly sensitive and selective sensor for detecting tetracycline (TC). Quantitative TC detection is based on the ratio of fluorescence intensities I₅₃₀/I₄₂₀, with a limit of detection (LOD) of 5.51 nM in aqueous solution and 47.17 nM in human urine. The characteristics of colorimetric TC sensing by Zn-CP are highly favorable for application because the color of Zn-CP changes in the visible part of the spectrum from blue-purple to yellow-green upon addition of TC. Conversion of these colors into an RGB signal is simply achieved with an app for the smart phone and provides LODs of 8.04 nM and 0.13 μM TC in water and urine, respectively. Our suggested sensing mechanisms assume that the fluorescence intensity of Zn-CP@TC at 530 nm is enhanced by energy transfer of Zn-CP to TC, while the fluorescence of Zn-CP at 420 nm is quenched by photoinduced electron transfer (PET) from TC to the organic ligand in Zn-CP. These fluorescence properties make Zn-CP a convenient, low-cost, rapid and green detection device for monitoring TC under physiological conditions and in aqueous media.

Novel 2D isomorphic lanthanide complexes based on a bifunctional 5-(pyridin-3-yloxy)isophthalic acid: synthesis, structure, fluorescence and magnetic properties

The Tb(iii)-complex can be used as a multifunctional luminescent sensor presenting visual quenching responses towards acetone, Fe3+ and CrO42− in aqueous solution with high sensitivity and low detection limits.

A new two-dimensional folding sheet-like coordination polymer assembled from cadmium(II) and (S)-2-(benzylamino)succinic acid: synthesis, structure and properties

A new two-dimensional (2D) coordination polymer, namely, poly[[diaqua[μ₃-(S)-2-(benzylamino)succinato-κ⁴N,O¹:O^1':O⁴]cadmium(II)] monohydrate], {[Cd(C₁₁H₁₁NO₄)(H₂O)₂]·H₂O}_n, has been synthesized by the solvothermal reaction of Cd(CH₃COO)₂·2H₂O with the synthesized ligand (S)-2-(benzylamino)succinic acid (H₂L). The title compound has been structurally characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction analysis. In the crystal structure, each Cd^II cation binds to three carboxylate groups from three symmetry-related L^2- dianions. The tetradentate L^2- ligand links three symmetry-related Cd^II cations into a 2D folding sheet, which can be simplified as a uninodal (3,3)-connected hcb net with the point symbol (6³). In the lattice, all the folding sheets are arranged in an interdigitated fashion and aggregate into zipper-like arrays through interlayer π-π interactions. The large and nonpolar side chain may play an important role in the formation and aggregation of the 2D sheet. The thermal stability and photoluminescence properties of the title compound were investigated, and it exhibits a blue emission with a quantum yield of 8%.

An ultra-sensitive selective fluorescent sensor based on a 3D zinc-tetracarboxylic framework for the detection and enrichment of trace Cu2+ in aqueous media

Herein, a novel and fluorescent zinc-organic framework sensor [Zn₃(μ₃-Hbptc)₂(μ₂-4,4'-bpy)₂(H₂O)₄]_n·2nH₂O (1) (H₄bptc = 2,3,3',4'-biphenyl tetracarboxylic acid, 4,4'-bpy = 4,4'-bipyridine) is synthesized and characterized, demonstrating its excellent fluorescence performance for Cu²⁺ detection and the enrichment of Cu²⁺ in aqueous media. The fluorescence intensity of 1 can be selectively quenched by Cu²⁺ in a linear range of Cu²⁺ concentrations of 0-0.7 μM. The limit of detection (LOD) value is as low as 32.4 nM, which is superior to those of most of the fluorescent sensors based on metal-organic frameworks (MOFs). It is also far below the maximum allowable concentration of Cu²⁺ in drinking water as defined by the U.S. Environmental Protection Agency (EPA) and the World Health Organization (WHO), so it is employed for the detection of Cu²⁺ in actual water samples. More importantly, the nature of the interaction between the active coordination site (COO^-) of 1 and Cu²⁺ determines the quenching mechanism, that is Cu²⁺ in the analyte is captured by MOF 1, which has been investigated by ICP, luminescence, UV-vis, XPS, and lifetime studies. Besides, the chemosensor shows regeneration performance without the loss of performance in five consecutive cycles. So MOF 1 is a simple and convenient probe used not only for the rapid detection but also for the enrichment of trace amounts of Cu²⁺ in aqueous media, and the application can be further extended to a variety of environmental and biological analysis processes.

Gel self-assembly of lanthanum aminopolycarboxylates with skeleton structures and adsorptions of gases

Lanthanum aminopolycarboxylates 1–3 have been isolated by gel self-assembly and fully characterized. La-EDTA 3 possesses 5.8 Å diameter tunnels inside the crystals, which can selectively adsorb very small amount of O2 without H2, N2, CH4 and CO2.

Metal-Organic Frameworks Based on Group 3 and 4 Metals

Metal-organic frameworks (MOFs) based on group 3 and 4 metals are considered as the most promising MOFs for varying practical applications including water adsorption, carbon conversion, and biomedical applications. The relatively strong coordination bonds and versatile coordination modes within these MOFs endow the framework with high chemical stability, diverse structures and topologies, and interesting properties and functions. Herein, the significant progress made on this series of MOFs since 2018 is summarized and an update on the current status and future trends on the structural design of robust MOFs with high connectivity is provided. Cluster chemistry involving Y, lanthanides (Ln, from La to Lu), actinides (An, from Ac to Lr), Ti, and Zr is initially introduced. This is followed by a review of recently developed MOFs based on group 3 and 4 metals with their structures discussed based on the types of inorganic or organic building blocks. The novel properties and arising applications of these MOFs in catalysis, adsorption and separation, delivery, and sensing are highlighted. Overall, this review is expected to provide a timely summary on MOFs based on group 3 and 4 metals, which shall guide the future discovery and development of stable and functional MOFs for practical applications.

Structural diversity, magnetic properties and luminescence of NiII, CoII and ZnII coordination polymers derived from 3,3'-[(5-carboxy-1,3-phenylene)bis(oxy)]dibenzoic acid and 1,10-phenanthroline

Three novel coordination polymers (CPs), namely poly[[di-μ-aqua-bis{μ₄-3,3'-[(5-carboxylato-1,3-phenylene)bis(oxy)]dibenzoato-κ⁵O¹:O^1',O³:O⁵:O^5'}bis(1,10-phenanthroline-κ²N,N')trinickel(II)] dimethylformamide 1.5-solvate trihydrate], {[Ni₃(C₂₁H₁₁O₈)₂(C₁₂H₈N₂)₂(H₂O)₂]·1.5C₃H₇NO·3H₂O}_n, (I), poly[[di-μ-aqua-bis{μ₄-3,3'-[(5-carboxylato-1,3-phenylene)bis(oxy)]dibenzoato-κ⁵O¹:O^1',O³:O⁵:O^5'}bis(1,10-phenanthroline-κ²N,N')tricobalt(II)] diethylamine disolvate tetrahydrate], {[Co₃(C₂₁H₁₁O₈)₂(C₁₂H₈N₂)₂(H₂O)₂]·2C₂H₇N·4H₂O}_n, (II), and catena-poly[[aqua(1,10-phenanthroline-κ²N,N')zinc(II)]-μ-5-(3-carboxyphenoxy)-3,3'-oxydibenzoato-κ²O¹:O³], [Zn(C₂₁H₁₂O₈)(C₁₂H₈N₂)(H₂O)]_n, (III), have been synthesized by the reaction of different metal ions (Ni²⁺, Co²⁺ and Zn²⁺), 3,3'-[(5-carboxy-1,3-phenylbis(oxy)]dibenzoic acid (H₃cpboda) and 1,10-phenanthroline (phen) under solvothermal conditions. All the CPs were characterized by elemental analysis, single-crystal and powder X-ray diffraction, FT-IR spectroscopy and thermogravimetric analysis. Complexes (I) and (II) have isomorphous structures, featuring similar linear trinuclear structural units, in which the central Ni^II/Co^II atom is located on an inversion centre with a slightly distorted octahedral [NiO₆]/[CoO₆] geometry. This comprises four carboxylate O-atom donors from two cpboda^3- ligands and two O-atom donors from bridging water molecules. The terminal Ni^II/Co^II groups are each connected to the central Ni^II/Co^II cation through two μ_1,3-carboxylate groups from two cpboda^3- ligands and one water bridge, giving rise to linear trinuclear [M₃(μ₂-H₂O)₂(RCOO)₄] (M = Ni²⁺/Co²⁺) secondary building units (SBUs) and the SBUs develop two-dimensional-networks parallel to the (100) plane via cpboda^3- ligands with new (3²·4)₂(3²·8³·9)₂(3⁴·4².8²·9⁴·10³) topological structures. Zinc complex (III) displays one-dimensional coordination chains and the five-coordinated Zn atom forms a distorted square-pyramidal [ZnO₃N₂] geometry, which is completed by two carboxylate O-atom donors from two distinct Hcpboda^2- ligands, one O atom from H₂O and two N atoms from a chelating phen ligand. Magnetically, CP (I) shows weak ferromagnetic interactions involving the carboxylate groups, and bridging water molecules between the nickel(II) ions, and CP (II) shows antiferromagnetic interactions between the Co²⁺ ions. The solid-state luminescence properties of CP (III) were examined at ambient temperature and the luminescence sensing of Cr₂O₇^2-/CrO₄^2- anions in aqueous solution for (III) has also been investigated.

Three chiral one-dimensional lanthanide-ditoluoyl-tartrate bifunctional polymers exhibiting luminescence and magnetic behaviors

Since Ln-CPs have excellent optical properties (higher color purity, longer fluorescence lifetime and higher quantum yield) and magnetic properties, it is of great significance to prepare dual magneto-optical materials based on Ln(iii). Herein, we obtained three versatile Ln-CPs, [Ln(HDTTA)3(CH3OH)3] n , derived from reactions of lanthanide salts (Ln = Tb 1, Dy 2, Ho 3) and a chiral and flexible ligand, namely, (+)-di-p-toluoyl-d-tartaric acid (d-H2DTTA) in a methanol-water solution, at room temperature and pressure. The structures of these compounds have been characterized by single crystal and powder X-ray diffraction, infrared spectroscopy, elemental analyses and thermogravimetric analyses. Complexes 1-3 are isomorphic, crystallizing in the chiral trigonal R3 space group with the linkage of Ln3+ ions and featuring 1D propeller chain structures. The circular dichroism spectra confirm that the complexes maintain the chirality from the ligands. Furthermore, the luminescent and magnetic properties have been investigated, relying on intrinsic properties of the lanthanide ions. The photoluminescence measurements indicate that 1, 2 and 3 show strong green, white and blue emission bands with CIE chromaticity coordinates of (0.32, 0.56), (0.29, 0.26) and (0.21, 0.12), respectively. The decay lifetime curve of 1 shows the exponential decay with long lifetime of 1.169 ms and the relative quantum yield for 1 was 19.31%. In addition, the magnetic properties of complexes 1-3 have been investigated by measuring the magnetic susceptibility in the temperature range of 2-300 K. They are all dominated by spin-orbit coupling and ligand field perturbation, and the exchange coupling between Ln3+ ions is almost negligible. Therefore, complexes 1-3 are promising chiral, optical and magnetic multifunctional materials.

Tunable Light Emission and Multiresponsive Luminescent Sensitivities in Aqueous Solutions of Two Series of Lanthanide Metal-Organic Frameworks Based on Structurally Related Ligands

Two series of lanthanide metal-organic frameworks (Ln-MOFs) from two structurally related flexible carboxylate-based ligands were solvothermally synthesized. H₃L2 with additional -CH₂- group provides more flexibility and different coordination modes and conformations compared with H₃L1. As a result, 2-Ln MOFs are modulated from two-dimensional kgd of 1-Ln to three-dimensional rtl topological frameworks and further achieve enhanced chemical stability. The Eu- and Tb-MOFs exhibit strong fluorescent emission at the solid state because of the antenna effect of the ligands. Interestingly, the emissions can be tuned by simply doping Eu³⁺ and Tb³⁺ of different concentrations within the Eu _xTb_{1- x} MOFs. Notably, 2-Ln MOFs realize nearly white light emission by means of a trichromatic approach (red of Eu(III), green of Tb(III), and blue of the H₃L2 ligand). Furthermore, 2-Ln MOFs also exhibit water stability and demonstrate high selective and sensitive sensing activities toward Fe(III) and Cr(VI) in aqueous solutions. The results further highlight the importance of the ligand flexibility on tuning MOF structures with improved structural stability and ion-sensing properties.

Multi-responsive luminescent sensor based on three dimensional lanthanide metal–organic framework

A novel multi-functional luminescent MOF was synthesized, which shows excellent recyclable luminescent sensing for acetone, Fe³⁺, Cr₂O₇²⁻ and 4-NP.

Color tuning and white light emission by codoping in isostructural homochiral lanthanide metal–organic frameworks

Pure white-light emission and fluent light-emitting color change can be facilely obtained by codoping isostructural homochiral lanthanide metal–organic frameworks.