Triazine Poly(carboxylic acid) Metal–Organic Frameworks and the Fluorescent Response with Lead Oxygen Clusters: [Pb₇(COO)₁₂X₂] by Halogen Tuning (X = Cl, Br, or I)

Abstract

A series of novel metal–organic frameworks were synthesized by using semirigid ligand 1,1′,1″-(1,3,5-triazine-2,4,6-triyl)­tripiperidine-4-carboxylic acid (H3TTPCA) and lead halide (Cl, Br, or I). The three complexes were characterized by elemental analysis, infrared spectroscopy, ultraviolet–visible spectroscopy, powder X-ray diffraction analysis, and thermogravimetric analysis. X-ray single-crystal diffraction analysis demonstrated that all three complexes were three-dimensional inorganic–organic framework structures with Pb-X2 (X = Cl, Br, or I). However, slight differences in the chemical environment were the focus of the coordinated halogen atoms and the different compositions of metal oxygen clusters: [Pb7(COO)12Cl2], [Pb7(COO)12Br2], and [Pb7(COO)12I2]. Because of the fluorescence of the organic ligand, the three complexes showed similar photoluminescence properties at room temperature, but the intensity of emissions decreased gradually with an increase in the atomic radius of coordinated halogen atoms. Interestingly, in the fluorescence response tests, complexes 1 and 2 displayed an optical signal of fluorescence “turn-on” while complex 3 showed an optical signal of fluorescence “turn-off”. Here we aim to provide a possible mechanism to explain these unique and contradictory luminescence results.

Conductive MOFs with Photophysical Properties: Applications and Thin-Film Fabrication

“…It is proposed that the conformation of ligands mainly influences the emission band and that the luminescence intensity can be modulated by the distance between neighboring ligands. This was confirmed by the research on a series of H 3 TTPCA-based Pb-MOFs that had different compositions of metal oxygen clusters [Pb 7 (COO) 12 X 2 ] (X = Cl, Br, or I) [ 34 ]. The emission spectrums of the three MOFs and free H 3 TTPCA molecule under 371 nm excitation were compared.…”

“…b Relationship among luminescence intensity, halogen atom radius, and distance between ligands in the three Pb-MOFs. Reprinted with permission from Ref [34]…”

Three Pbx(COO)y Cluster Frameworks Based on a Flexible Triazinetricarboxylic Acid Ligand: Syntheses, Structures, and Fluorescent Sensing Application for Nitrophenols

“…The H 3 TTPCA ligand was synthesized according to a literature method . The metal salts and solvents used in this work were commercially available from Aladdin Company and used without further purification.…”

“…The synthesis of triazine ligands is simple and the ligands are easily purified, which provides more possibilities for the construction of new MOFs, and these kinds of MOFs have shown a good effect in gas adsorption and separation. , In addition, triazine-containing carboxylate groups have fluorescent characteristics, so MOFs constructed by triazine derivatives also have fluorescence properties. , Facts proved that such compounds have immense potential in terms of fluorescence sensing, small molecular detection, and so on, which makes the compounds with a triazine skeleton widely studied. − Thomas et al synthesized a sequence of polymers linked with triazines for the first time in 2008 . It became a bright new type of high-performance porous organic material. − Nowadays, 1,1′,1″-(1,3,5-triazine-2,4,6-triyl)-tripiperidine-4-carboxylic acid (H 3 TTPCA) has attracted lots of interest . It was first used by Zhou’s group to synthesize an MOF [Zn 3 (BTPCA) 2 (H 2 O) 3 ·py·3DMSO, where BTPCA = benzotriazolepyridine-2-carboxylic acid, py = pyridine, and DMSO = dimethyl sulfoxide] based on Zn 3 (BTPCA); this MOF is easy to synthesize and has uniformly sized holes .…”

“…In our previous study, we used the H 3 TTPCA ligand to synthesize a series of Pb-MOFs, and it was found that similar photoluminescence properties were regulated by halogen ions. In order to further extend studies of the structures and functional properties of compounds with the H 3 TTPCA ligand, we prepared three new Pb-MOFs, 1 – 3 , with different structures and fluorescence properties, and these MOFs could be applied first to sense nitrophenols via fluorescence response.…”