Synthesis, structure and selective luminescence sensing for iron(III) ions of a three-dimensional zinc(II)...

Coordination polymers constructed from conjugated organic ligands and metal ions with a d¹⁰ electronic configuration exhibit intriguing properties for chemical sensing and photochemistry. A Zn^II-based coordination polymer, namely poly[aqua(μ₆-biphenyl-3,3',5,5'-tetracarboxylato)(μ₂-4,4'-bipyridine)dizinc(II)], [Zn₂(C₁₆H₆O₈)(C₁₀H₈N₂)(H₂O)₂]_n or [Zn₂(m,m-bpta)(4,4'-bipy)(H₂O)₂]_n, was synthesized from a mixture of biphenyl-3,3',5,5'-tetracarboxylic acid [H₄(m,m-bpta)], 4,4'-bipyridine (4,4'-bipy) and Zn(NO₃)₂·6H₂O 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 μ₆-coordination mode. The Zn^II ions adopt square-pyramidal geometries and are bridged by two syn-syn carboxylate groups to form [Zn₂(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 {4⁴.6¹⁰.8}{4⁴.6²} 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.