Construction of four Zn(II)/Cd(II) coordination polymers with flexible isomer ligands: Chemosensor for antibiotic

Four coordination polymers have been synthesized by using Zn(II)/Cd(II) salt and bis(imidazole) ligand in the presence of the different flexible phenylenediacetate isomers under hydrothermal conditions. The flexible transconformation pda and biyb ligands in complexes 1, 3, 4 afford the 2D (4,4)-connected layer, which are further stacked in an offset fashion with an ABAB sequence to propagate into a 3D supramolecular architecture through strong C-H center dot center dot center dot p and C-H.O interactions. Differently, the flexible cis-conformation pda and biyb ligands in 2 can be seen as "V" type building block, linking Zn(II) atoms to form a 3D helix network. The structural diversity of these complexes is mainly attributed to the different coordination modes and isomer conformations of the flexible phenylenediacetic acids and bis(imidazole) ligand. The fluorescence property application and mechanisms of four complexes for detecting antibiotic cefixime (CEF) have been researched. Compared with 1, 3, 4 complex 2 has higher quenching percentage, this may be because 2 is a 3D structure with a large hole (18.99 x 20.02 A window). The detection limits of complexes 1-4 have been measured to be 0.23 mu., 0.34 mu., 0.37 mu., 0.38 mu., respectively. The theoretic calculation and UV-vis absorption experiments confirmed that the fluorescence quenching of complexes 1-4 toward cefixime (CEF) should be attributed to the electron transfer and the fluorescence inner filter effect between the fluorescent matter and the analyte.