Two Cd(II) MOFs of Flexible Aliphatic Dicarboxylate Ligands and 1,4-Bis[(2-methyl-1H-imidazol-1-yl)-methyl]benzene: Synthesis, Crystal Structures and Selective Sensing of Fe3+.

Two Cd(II) MOFs based on the 1,4-bis[(2-methyl-1H-imidazol-1-yl)-methyl]benzene (1,4-mbix) and succinate (Suc2−) or azelate (Aze2−) ligands have been hydrothermally synthesized, namely, {[Cd2(Suc)2(1,4-mbix)2]·5H2O}n (1) and [Cd(Aze)(1,4-mbix)]n (2). Both MOFs were structurally characterized by single-crystal X-ray diffraction. In MOF 1, the Cd(II) centers are connected by Suc2− and 1,4-mbix to generate a two-dimensional (2D) sql layer with (H2O)5 water cluster. Each 2D layer is further interlocked with two adjacent layers to form a 2D + 2D → 3D parallel polycatenated structure. In MOF 2, when the Suc2− was placed by Aze2−, the Cd(II) centers are connected by Aze2− and 1,4-mbix into a 2D sql layer but without any water molecules. And two 2D sql layers interpenetrate with each other to generate a twofold 2D + 2D → 2D sheet. MOFs 1 and 2 display photoluminescence at 343 nm (λex = 288 nm) and 298 nm (λex = 271 nm), respectively. Luminescent quenching experiments show that 1 and 2 have good ability for detection of Fe3+ in deionized water with low detection limits as 0.58 μM for 1 and 0.54 μM for 2, respectively. Two MOFs also can serve as luminescent sensors for Fe3+ in real tap water and river water. The luminescent quenching of 1 and 2 toward Fe3+ can be attributed to the competition among the absorption of Fe3+ with the excitation and emission of two MOFs. [ABSTRACT FROM AUTHOR]