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.

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.

Luminescent and magnetic bifunctional coordination complex based on a chiral tartaric acid derivative and europium

A new mononuclear europium complex incorporating the (+)-di-p-toluoyl-D-tartaric acid (D-H2DTTA) ligand, namely, catena-poly[tris{μ2-3-carboxy-2,3-bis[(4-methylphenyl)carbonyloxy]propanoato}tris(methanol)europium(III)], [Eu(C20H17O8)3(CH3OH)3] n , (I), has been synthesized and characterized by IR spectroscopy, elemental analysis, powder X-ray diffraction and single-crystal X-ray diffraction analysis. The structure analysis indicates that complex (I) crystallizes in the trigonal space group R3 and exhibits an infinite one-dimensional chain structure, in which the Eu3+ ion is surrounded by six O atoms from six D-HDTTA− ligands and three O atoms from three coordinated methanol molecules, thus forming a tricapped trigonal prism geometry. The D-H2DTTA ligand is partially deprotonated and adopts a μ1,6-coordination mode via two carboxylate groups to link adjacent Eu3+ ions, affording an infinite one-dimensional propeller-shaped coordination polymer chain along the c axis, with an Eu...Eu distance of 7.622 (1) Å. Moreover, C—H...π interactions lead to the formation of helical chains running along the c axis and the whole structure displays a snowflake pattern in the ab plane. The circular dichroism spectrum confirms the chirality of complex (I). The solid-state photoluminescence properties were also investigated at room temperature and (I) exhibits characteristic red emission bands derived from the Eu3+ ion (CIE 0.63, 0.32), with a reasonably long lifetime of 0.394 ms, indicating effective energy transfer from the ligand to the metal centre. In addition, a magnetic investigation reveals single-ion magnetic behaviour. The spin-orbit coupling parameter (λ) between the ground and excited states is fitted to be 360 (2) cm−1 through Zeeman perturbation. Therefore, complex (I) may be regarded as a chiral optical-magneto bifunctional material.

Cadmium(II) three-dimensional coordination polymers constructed from 1,3,5-tris(4-carboxyphenoxy)benzene: synthesis, crystal structure, fluorescence and I2 sorption characterization

Two three-dimensional (3D) CdII coordination polymers, namely poly[[di-μ-aqua-diaquabis{μ5-4,4′,4′′-[benzene-1,3,5-triyltris(oxy)]tribenzoato}tricadmium(II)] dihydrate], {[Cd3(C27H15O9)2(H2O)4]·2H2O} n , (I), and poly[[aqua{μ6-4,4′,4′′-[benzene-1,3,5-triyltris(oxy)]tribenzoato}(μ-formato)[μ-1,1′-(1,4-phenylene)bis(1H-imidazole)]dicadmium(II)] dihydrate], {[Cd2(C27H15O9)(C12H10N4)(HCOO)(H2O)]·2H2O} n , (II), have been hydrothermally synthesized from the reaction system containing Cd(NO3)2·4H2O and the flexible tripodal ligand 1,3,5-tris(4-carboxyphenoxy)benzene (H3tcpb) via tuning of the auxiliary ligand. Both complexes have been characterized by single-crystal X-ray diffraction analysis, elemental analysis, IR spectra, powder X-ray diffraction and thermogravimetric analysis. Complex (I) is a 3D framework constructed from trinuclear structural units and tcpb3− ligands in a μ5-coordination mode. The central CdII atom of the trinuclear unit is located on a crystallographic inversion centre and adopts an octahedral geometry. The metal atoms are bridged by four syn–syn carboxylate groups and two μ2-water molecules to form trinuclear [Cd3(COO)4(μ2-H2O)2] secondary building units (SBUs). These SBUs are incorporated into clusters by bridging carboxylate groups to produce pillars along the c axis. The one-dimensional inorganic pillars are connected by tcpb3− linkers in a μ5-coordination mode, thus forming a 3D network; its topology corresponds to the point symbol (42.62.82)(44.62)2(45.66.84)2. In contrast to (I), complex (II) is characterized by a 3D framework based on dinuclear cadmium SBUs, i.e. [Cd2(COO)3]. The two symmetry-independent CdII ions display different coordinated geometries, namely octahedral [CdN2O4] and monocapped octahedral [CdO7]. The dinuclear SBUs are incorporated into clusters by bridging formate groups to produce pillars along the c axis. These pillars are further bridged either by tcpb3− ligands into sheets or by 1,4-bis(imidazol-1-yl)benzene ligands into undulating layers, and finally these two-dimensional surfaces interweave, forming a 3D structure with the point symbol (4.62)(47.614). Compound (II) exhibits reversible I2 uptake of 56.8 mg g−1 with apparent changes in the visible colour and the UV–Vis and fluorescence spectra, and therefore may be regarded as a potential reagent for the capture and release of I2.

Irreversible solvent-assisted structural transformation in 3D metal-organic frameworks: Structural modification and enhanced iodine-adsorption properties

In this work, we demonstrate a solvent-assisted structural transformation between two 3D metal-organic frameworks (MOFs) ([Zn₄(α-bptc)₂(H₂O)₃]_n (1) → {[Zn₂(α-bptc)(H₂O)₄]·(pra)}_n (2)) (α-H₄bptc = 2,3,3',4'-biphenyl tetra-carboxylic acid and pra = pyridin-2-amine) at room temperature by immersing complex 1 in a mother solution. The structural transformation involves not only solvent exchange but also the cleavage and formation of coordination bonds, which is confirmed by infrared spectroscopy, single-crystal X-ray diffraction analysis, powder X-ray diffraction patterns, and thermogravimetric analysis. Structural analyses revealed that significant modifications occurred during the transformation including the changes in lattice parameters, unit cell volume, space group, coordination number, secondary building units, and topological type. In the case of drastic structural transitions, significant changes in properties were also observed. Complex 2 displayed the interesting uptake and release of iodine with the changes in visible color, UV and fluorescence spectra, and fully reversible I2 uptake of 8.5 mg g-1, which further suggested about its future application as iodine absorbing material.

Synthesis, Crystal Structure, and Properties of a Zn(II) Coordination Polymer Based on a Difunctional Ligand Containing Triazolyl and Carboxyl Groups

A new compound, namely, [Zn(L)2]n (1) was obtained by the reaction of 2-methyl-4-(4H-1,2,4-triazol-4-yl) benzoic acid (HL) with ZnSO4·7H2O, and the compound was characterized by single-crystal X-ray diffraction, infrared spectroscopy, elemental analysis, powder X-ray diffraction (PXRD), and thermogravimetric analysis. The linear HL ligands were deprotonated to be L− anions and act as two-connectors to link Zn2+ to form a two-dimensional (2D) lay structure with (4, 4) topology. The large vacancy of 2D framework allows another layer structure to interpenetrate, resulting in the formation of 2D + 2D → 2D parallel interpenetration in 1. The weak interactions, such as hydrogen bonding and π–π stacking interactions, connect the adjacent 2D layers into a three-dimensional (3D) coordination polymer. The solid-state UV-visible spectroscopy and luminescent property have also been studied.

Pseudopolymorphism based on 1D metallacyclic chains constructed from an angular zwitterionic ditopic diacid organic linker

Two pseudopolymorphs based on one dimensional metallacyclic chains display crystalline-form-dependent optical properties.

A new family of 1D, 2D and 3D frameworks aggregated from Ni5, Ni4 and Ni7 building units: synthesis, structure, and magnetism

Three polynuclear nickel(ii) complexes with 1D, 2D and 3D structures are controlled by carboxylate bridges of biphenyl-3,4′,5-tricarboxylic acid. Magnetic studies reveal that the polymers have ferromagnetic coupling features for 1 and 2 and an alternating magnetic chain behavior for 3.