Naked Eye Cd²⁺ Ion Detection and Reversible Iodine Uptake by a Three-Dimensional Pillared-Layered Zn-MOF

A novel metal-organic framework (MOF), [Zn₂(tdca)₂(bppd)₂]·2DMF, has been synthesized solvothermally using the ligand thiophene-2,5-dicarboxylic acid (H₂tdca), coligand N,N'-bis(4-pyridylmethylene)-1,4-benzenediamine (bppd), and Zn(NO₃)₂. Single crystal X-ray crystallography reveals that the titled MOF is a three-dimensional pillared-layered MOF. A layer is constituted by a Zn(tdca) unit, and the layers are stabilized by the long hydrocarbon coligand, bppd, which acts as a pillar. A rectangular pore size of 11.42 × 8.12 Ų is found in the framework. The porous framework is found to be an excellent fluorescence sensor for the detection of toxic Cd²⁺ ion. The sensor shows high selectivity and sensitivity and a quick response toward Cd²⁺. The synthesized MOF is able to not only detect cadmium ions but also adsorb iodine in the gas phase. The MOF can adsorb ∼66% iodine, verified by thiosulfate-iodine titration and TG analysis. Adsorbed iodine can also be removed easily in acetonitrile as well as in n-hexane, which shows that iodine can be reversibly loaded as well as unloaded into the framework.