Novel luminescent metal-organic frameworks based on rigid carboxylate ligands for highly selective sensing of Fe3+ ions

Four three-dimensional (3D) luminescent metal-organic frameworks (MOFs), Zn-2(HL1)(H2O)(0.8) (1), Cd-2(L-1)(DMF)(2) (2), [Zn-3(HL2)(2)].[(CH3)(2)NH2](4) (3), and [Cd-3(L-2)(2)] .[(CH3)(2)NH2](6) (4) (H5L1 = 3,5-di(3' 5'-dicarboxyphenyl) benzoic acid, H6L2 = 3,4-di(3,5-dicarboxyphenyl) phthalic acid, DMF = N, N-dimethylformamide), have been successfully assembled based on rigid carboxylate ligands. The four compounds have been characterized by elemental analysis, infrared (IR) spectroscopy, thermogravimetric analysis (TGA), single-crystal X-ray diffraction, powder X-ray diffraction (PXRD) and fluorescence spectroscopy. Compound 1 is a (5,5)-connected 3D framework with a {4(5).6(5)} topology. Compound 2 possesses a (5,5)-connected 3D framework with a {4(7).6(3)} topology. Compounds 3 and 4 display a (4,4,6)-connected 3D framework with a {4(2).6(4)} 2{4(4).6(11)} 2{4(4).6(2)} topology. Remarkably, the four presented compounds show luminescence changes in the presence of metal ions. Interestingly, all of them exhibit highly selective sensing of Fe3+ ions and the luminescence is quenched in a 1.1 x 10(-3) M DMF solution of Fe3+ ions. Moreover, the four compounds possess reasonable recyclability and reproducibility of luminescence after regeneration. The exceptional sensitivity and reusability of the four compounds make them excellent Fe3+ sensors in the future.