Syntheses, structures of three Ln-MOFs (Ln=La, Ce, Dy), fluorescent sensing Fe³⁺ and MnO₄^- of La-MOF film, and magnetic properties of Dy-MOF

Metal-organic frameworks (MOFs) have attracted significant research interest in sensors. However, due to the poor solubility and difficulty of recovery of powdered MOFs, its practical application has been limited. Herein, the pentacarboxylic acid 3, 5-bis (2 ', 4 '-dicarboxyphenyl) benzoic acid (H5L) was selected as the ligand, three lanthanide metal-organic frameworks (Ln-MOFs) with different structures: {[La7L6(H2O)(6)]9H(3)O10DMF12H(2)O}(n)(1), {[Ce5L3]6DMF13H(2)O}(n)(2), {[Dy3L2(H2O)(3)]H3O4DMF3H(2)O}(n)(3), (DMF = N,N-dimethylformamide) have been synthesized hydrothermally. Structures were characterized and performances were tested by single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), thermogravimetric (TG), infrared (IR), fluorescence spectra, and magnetic experiments. The results show that compounds 1 and 2 crystallize in the trigonal system, R-3 space group, but compound 3 crystallizes in the monoclinic system, C-2/c space group, all of which possess novel three-dimensional structure and good thermal stability. Interestingly, the fluorescence sensing studies show that compound 1 film could be used as a selective fluorescence sensor toward Fe3+ and MnO4- with the low detection limits of 0.89 mu mol/L (for Fe3+) and 1.31 mu mol/L (for MnO4-) respectively, and can be reused more than 20 times. In addition, the result of the magnetic testing showed that 3 had antiferromagnetic properties at 1kOe.