Synthesis, structure and selective luminescence sensing for iron(III) ions of a three-dimensional zinc(II) (4,6)-connected coordination network

Coordination polymers constructed from conjugated organic ligands and metal ions with a d 10 electronic configuration exhibit intriguing properties for chemical sensing and photochemistry. A Zn-II-based coordination polymer, namely poly[aqua(mu(6)-biphenyl-3,3',5,5'-tetracarboxylato)(mu(2)-4,4'-bipyridine) dizinc(II)], [Zn-2(C16H6O8)(C10H8N2)(H2O)(2)](n) or [Zn-2(m, m-bpta)(4,4'-bipy)(H2O)(2)](n), was synthesized from a mixture of biphenyl-3,3',5,5'-tetracarboxylic acid [H4(m, mbpta)], 4,4'-bipyridine (4,4'-bipy) and Zn(NO3)(2)center dot 6H(2)O under solvothermal conditions. The title complex has been structurally characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction and powder X-ray diffraction analysis, and features a mu(6)-coordination mode. The Zn-II ions adopt square-pyramidal geometries and are bridged by two syn-syn carboxylate groups to form [Zn-2(COO)(2)] secondary buildding units (SBUs). The SBUs are crosslinked by (m, m-bpta)(4-) ligands to produce a two-dimensional grid-like layer that exhibits a stair-like structure along the a axis. Adjacent layers are linked by 4,4'-bipy ligands to form a three-dimensional network with a {4(4)center dot 6(10)center dot 8}{4(4)center dot 6(2)} topology. In the solid state, the complex displays a strong photoluminescence and an excellent solvent stability. In addition, the luminescence sensing results indicate a highly selective and sensitive sensing for Fe3+ ions.