Synthesis, Crystal Structure, and Luminescent Sensing Properties of a Supramolecular 3D Zinc(II) Metal-Organic Framework with Terephthalate and Bis(imidazol-1-yl)methane Linkers

Supramolecular 3D Zn(II) coordination polymer {[Zn(bim)(bdc)]center dot 0.8DMF center dot 0.4EtOH center dot 0.1H(2)O}(n) (Zn-MOF), constructed from Zn2+ ions, bis(imidazol-1-yl)methane (bim) and terephthalate (bdc2) anions, was synthesized and structurally characterized. Zn-MOF crystallizes in the tetragonal crystal system, space group P4(2)/n. Each Zn(II) ion coordinates two neutral bim molecules in a bridging bidentate coordination mode via nitrogen atoms at position 3 of the imidazole rings and two bdc(2) anions, with monodentate coordination of the carboxylate group for one of them and bidentate coordination for another. Zn(II) cations are in a distorted square pyramidal ZnN2O3 coordination environment. Metal cations are alternately linked by the bim and bdc(2) ligands, forming a twodimensional layered structure along the crystallographic plane ab. As a result of layer interpenetration, a supramolecular 3D network is formed. Zn-MOF demonstrated blue (aquamarine) emission with a maximum at 430 nm upon excitation at 325 nm. The luminescence lifetime of 6 ns is characteristic for ligand-centered fluorescence. The luminescent sensing properties of Zn-MOF in ethanol suspension toward inorganic cations and anions were evaluated and an emission quenching response was observed for Fe3+ and chromate/dichromate ions. Photoinduced electron transfer from Zn-MOF to Fe3+ was elucidated as a possible quenching mechanism on the basis of DFT calculations.