Two new MOFs based on a flexible tripod ligand, structure regulation, stability, Hirshfeld surface analysis and fluorescence properties

Abstract

In this work, two MOFs, {[Cd₃(L)₂(m-BDC)(NO₃)₄]·2(H₂O)}_n (1) and [Zn₃(L)(m-BDC)₃]_n (2), were synthesized using the hydrothermal method. Single crystal diffraction showed that the flexible tripod ligand L (1,3,5-[1-(2-methylimidazole-methylene)]benzene) delivers completely different configurations under the influence of the coordination metal [Cd(II), Zn(II)] ions, resulting in two completely different structures. In 1, the flexible tripod ligand L adopted a "chair" conformation which combined with Cd(II) ions, forming a two-dimensional structure in the orthorhombic C222₁ space group. In 2, L adopted a "bowl" conformation which combined with Zn(II) ions, forming another two-dimensional structure in the P-3m1 space group. The synthesized MOFs were characterized by PXRD, thermogravimetry (TGA), infrared spectroscopy (IR), elemental analysis, fluorescence property analysis, Hirshfeld surface analysis, and density functional theory (DFT) quantitative calculations. The fluorescence analysis displayed that the maximum emission wavelength of 1 and 2 has a blue shift. In addition, the results of thermogravimetric analysis (TGA) showed that the thermal stability of 1 is 150 °C higher than that of 2. This is probably because the energy of "chair" conformation is lower than that of the "bowl" conformation, which makes 1 more stable than that of 2.

Graphical Abstract

Keywords:

• MOFs
• flexible tripod ligand
• stability
• Hirshfeld surfaces analyses
• DFT quantitative calculation

Disclosure statement

No potential conflict of interest was reported by the authors.

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Additional information

Funding

This work was supported by the research projects of colleges and universities in Gansu Province (No. 2019A-032), Innovation and Entrepreneurship Training Program for College Students in Lanzhou Jiaotong University (No. 2020033), Tianjin university-Lanzhou Jiaotong university independent innovation fund cooperation project (No. 2020060), Natural Science Foundation of Gansu Province (20JR5RA425).