Synthesis, crystal structure and characterization of a three-dimensional CdII coordination polymer constructed from 2,5-bis(1H-1,2,4-triazol-1-yl)terephthalate

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-.

A two-dimensional cadmium(II) coordination polymer constructed from 4-carboxy-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-5-carboxylate and 1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-4-carboxylate ligands

Crystals of poly[[aqua[μ₃-4-carboxy-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-5-carboxylato-κ⁵O¹O^1':N³,O⁴:O⁵][μ₄-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-4-carboxylato-κ⁷N³,O⁴:O⁴,O^4':O¹,O^1':O¹]cadmium(II)] monohydrate], {[Cd₂(C₁₅H₁₄N₂O₄)(C₁₆H₁₄N₂O₆)(H₂O)]·H₂O}_n or {[Cd₂(Hcpimda)(cpima)(H₂O)]·H₂O}_n, (I), were obtained from 1-(4-carboxybenzyl)-2-propyl-1H-imidazole-4,5-dicarboxylic acid (H₃cpimda) and cadmium(II) chloride under hydrothermal conditions. The structure indicates that in-situ decarboxylation of H₃cpimda occurred during the synthesis process. The asymmetric unit consists of two Cd²⁺ centres, one 4-carboxy-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-5-carboxylate (Hcpimda^2-) anion, one 1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-4-carboxylate (cpima^2-) anion, one coordinated water molecule and one lattice water molecule. One Cd²⁺ centre, i.e. Cd1, is hexacoordinated and displays a slightly distorted octahedral CdN₂O₄ geometry. The other Cd centre, i.e. Cd2, is coordinated by seven O atoms originating from one Hcpimda^2- ligand and three cpima^2- ligands. This Cd²⁺ centre can be described as having a distorted capped octahedral coordination geometry. Two carboxylate groups of the benzoate moieties of two cpima^2- ligands bridge between Cd2 centres to generate [Cd₂O₂] units, which are further linked by two cpima^2- ligands to produce one-dimensional (1D) infinite chains based around large 26-membered rings. Meanwhile, adjacent Cd1 centres are linked by Hcpimda^2- ligands to generate 1D zigzag chains. The two types of chains are linked through a μ₂-η² bidentate bridging mode from an O atom of an imidazole carboxylate unit of cpima^2- to give a two-dimensional (2D) coordination polymer. The simplified 2D net structure can be described as a 3,6-coordinated net which has a (4³)₂(4⁶.6⁶.8³) topology. Furthermore, the FT-IR spectroscopic properties, photoluminescence properties, powder X-ray diffraction (PXRD) pattern and thermogravimetric behaviour of the polymer have been investigated.