Fluorescent Cd-MOFs for ion recognition constructed by 2, 5-dimethoxyterephthalic acid and nitrogen heterocyclic derivatives

Under solvothermal synthesis, 1,4-bis(4-methyl-1H-imidazole-1- yl)benzene(1,4-BMIB), 1,1'-(2,5-dimethyl-1,4-phenylene)bis(1H-imidazole)(1,1′- DPBI) and 1,3,5-tri(1H-imidazole-1-yl)benzene (1,3,5-TIB) were used to combine with 2,5-dimethoxyterephthalic acid (H2DTA) and Cd(Ⅱ) to obtain three luminescent complexes {[Cd(DTA)(1,4-BMIB)]‧H2O}n(1), {[Cd(DTA)(1,1′-DPBI)(H2O)] ‧H2O}n(2) and {[Cd(DTA)(1,3,5-TIB)]‧0.5H2DTA}n (3), respectively. Single-crystal diffraction tests revealed that complex 1 belongs to monoclinic crystal system with C2/c space group, where binuclear Cd2(CO2)4 units act as six-connected metal centers resulting in three-dimensional frame with topological symbol of (48.52.65). Complexes 2 and 3 crystallize in triclinic P-1 space group. Among them, complex 2 is a dia-type triple interspersed framework, while complex 3 is a 2-fold-interpenetrating structure. Comparing to the fluorescent emission spectra of ligands, the fluorescence of complexes is obviously enhanced. In addition, all complexes have good recognition capability for Fe3+ and Cr2O72− ions, and their detection curves fit with Stern-Volme equation (I0/I ​= ​1+Ksv[M]) in low concentration range. The fluorescent intensities from complexes indicate a good linear relationship with the concentration of detection ions, and the detection limit is also low. Through scanning for various ions, these complexes are expected to be fluorescent sensors for identifying Fe3+ and Cr2O72− ions.