The diversity of five metal–organic complexes based on an unsymmetrical biphenyl tetracarboxylate: Synthesis, structures, magnetism and luminescence

Syntheses, Crystal Structures, and Catalytic Properties of Three Cu(II) and Cobalt(II) Coordination Compounds Based on an Ether-Bridged Tetracarboxylic Acid

Three new products, [Cu2(μ3-dppa)(2,2'-bipy)2(H2O)]n·2nH2O (1), [Co4(μ4-dppa)2(phen)4(H2O)4]·2H2O (2), and [Co2(μ6-dppa)(μ-4,4'-bipy)(H2O)2]n·3nH2O (3) were synthesized using a hydrothermal method from Cu(II) and Co(II) metal(II) chlorides, 3-(3,4-dicarboxyphenoxy)phthalic acid (H4dppa), and different auxiliary ligands, namely 2,2'-bipyridine (2,2'-bipy),1,10-phenanthroline (phen), and 4,4'-bipyridine (4,4'-bipy). Products 1-3 were characterized by elemental analysis, FTIR, TGA, PXRD, SEM, and single-crystal X-ray crystallography. The structure of 1 features a 1D chain of the 2C1 topological type. Compound 2 shows a discrete tetrameric complex. Product 3 demonstrates a 3D metal-organic framework (MOF) with the new topology. Their structure and topology, thermal stability, and catalytic activity were studied. In particular, excellent catalytic activity was demonstrated for copper(II)-polymer 1 in the cyanosilylation reaction at 35 °C.

Synthesis, Crystal Structure and Catalytic Activity of Tri-Nuclear Zn(II) Complex Based on 6-Phenylpyridine-2-carboxylic Acid and Bis(4-pyridyl)amine Ligands

A new trinuclear Zn (II) complex, [Zn3(L1)4(L2)2(CH3COO)2] (1) (HL1 = 6-phenylpyridine-2-carboxylic acid, L2 = bis(4-pyridyl)amine) has been synthesized by 6-phenylpyridine-2-carboxylic acid, NaOH, bis(4-pyridyl)amine and Zn(CH3COO)2•2H2O. The complex 1 has also been structural characterized by elemental analysis and single crystal X-ray diffraction. The results reveals that complex 1 is made up of three Zn(II) ions, four L1 ligands, two L2 ligands and two CH3COO- anions. In 1, both Zn1 ion and Zn1a ion are five-coordinated with two O atoms from two different L1 ligands, two N atoms from two different L1 ligands, and one N atoms from bis(4-pyridyl)amine ligand, respectively, and forms a distorted trigonal biyramid geometry. And Zn2 ion is four-coordinated with two O atoms from two different CH3COO− anions and two N atoms from two different L2 ligands, forming a distorted tetrahedral geometry. Complex 1 displays a 3D network structure by the intermolecular N−H···O hydrogen bonds. The catalytic performance for oxidation of benzyl alcohol with O2 was studied under mild reaction conditions using complex 1 as catalyst. The results demonstrated that the catalysts were very active, and the yield of benzaldehyde was 50.8% at 90 °C with THF as solvent under 0.5 MPa O2 within 3 h. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

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 Multistimuli Responsive Crystalline Cd(II)-Viologen Coordination Polymer with Single-Crystal-Single-Crystal Transformation

It is necessary to develop stable and fast multistimuli responsive materials due to the growing demand in our daily life. In this work, a new viologen-based Cd-complex (1) exhibits multiple thermochromic and photochromic behaviors through 10 states with 7 colors. For example, it responds to both Cu Kα/Mo Kα X-ray sources and UV dual light quickly with a color change from colorless to dark blue (1X) (Cu Kα/Mo Kα X-ray sources) and cyan (1-UV) (UV light), respectively. Interestingly, it exhibits a three-step coloration phenomenon when heated, which is unprecedented in viologen compounds. Crystal 1 undergoes a color change to pink, blue, and brown under 130, 180, and 240 °C, respectively. In addition, upon fumigation, both 1P and 1Q undergo a decoloration process to colorless (1K) and yellow (1T), respectively. Four more states (1P, 1K, 1T, and 1O) obtained via dehydration-hydration treatment are all photochromic. More importantly, via single-crystal-single-crystal transformation (SC-SC), the photochromic and thermochromic behaviors of 1 were investigated from the molecular level, which is also rather rare for thermochromic species. The detailed electron donor and the pathways for electron transfer were clearly given according to the results of crystal structure. The colorful states upon external stimuli may be attributed to the multiple pathways for electron transfer.

Hydrothermal synthesis of two-dimensional cadmium(II) micro-porous coordination material based on Bi-functional building block and its application in highly sensitive detection of Fe3+ and Cr2O72

Metal-organic framework (MOFs), also known as porous coordination polymers (PCPs), is a new kind of crystalline porous materials, which has received extensive attention in the past few decades. As a new type of sensing material, MOFs stand out from many other traditional fluorescence sensors because of its crystal characteristics, structural diversity, stable porosity and adjustable functional characteristics. In this work, the bi-functional building block containing aromatic carboxylic acid and triazole moieties, namely 3-(1H-1,3,4-triazol-1-yl) benzoic acid, was selected as the linker to synthesize {[Cd(µ₅-L)⋅I}_n (1, HL = 3-(1H-1,3,4-triazol-1-yl)benzoic acid) by hydrothermal method with transition Cd^II metal centers. Firstly, the preliminary characterization of 1 was carried out by means of PXRD, FT-IR, and then the UV and fluorescence tests were conducted to study the fluorescence properties of 1. The crystal structure analysis indicates that Cd^II is the center and the ligand is bridged to form a two-dimensional porous structure. In addition, 1 has good selectivity for Fe³⁺ and Cr₂O₇^2-, meanwhile, it has high detection sensitivity (K_sv quenching efficiency for Fe³⁺: 1.2 × 10⁴ M^-1 and Cr₂O₇^2- 1.85 × 10⁴ M^-1) and low detection limit (Fe³⁺: 19.21 μM and Cr₂O₇^2-: 12.46 μM). The results of photoluminescence test show that 1 can detect cations and anions with high sensitivity, resist the interference of other ions, and have good reusability. As far as we know, 1 is the first example of ultra-stable two-dimensional (2D) Cadmium (II) microporous coordination material as a fluorescence sensor for Fe³⁺ and Cr₂O₇^2-.

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.

A new 3D four-fold interpenetrated dia-like luminescent Zn(ii)-based metal–organic framework: the sensitive detection of Fe3+, Cr2O72−, and CrO42− in water, and nitrobenzene in ethanol

A four-fold interpenetrating Zn-MOF as a multi-responsive fluorescent sensor for Fe³⁺, Cr₂O₇²⁻, and CrO₄²⁻ ions in water, and NB in ethanol is reported.

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.

Binuclear Mn2+ complexes of a biphenyltetracarboxylic acid with variable N-donor ligands: syntheses, structures, and magnetic properties

A series of manganese(ii) coordination polymers show a variety of features due to the recognition and assembly processes of the N-donor ligands.