A novel (3,6)-connected Cd^II coordination polymer based on an ether-linked tricarboxylate ligand: synthesis, topology...

A novel three-dimensional coordination polymer, namely, poly[[diaquabis(μ-4,4'-bipyridine)bis{μ₃-5-[(2-carboxyphenoxy)methyl]isophthalato}tricadmium(III)] dimethylformamide monosolvate 2.5-hydrate], {[Cd₃(C₁₆H₉O₇)₂(C₁₀H₈N₂)₂(H₂O)₂]·2C₃H₇NO·5H₂O}_n, was obtained by the reaction of ether-linked 5-[(2-carboxyphenoxy)methyl]isophthalic acid (H₃L) with Cd^II salts in the presence of 4,4'-bipyridine (bpy) under solvothermal conditions. In this complex, the Cd^II centres are connected by the carboxylate ligands to form two-dimensional wave-like layers, which are pillared by bpy ligands and extended into a rare three-dimensional (3,6)-connected sqc27 framework. The complex demonstrated good water stability and strong luminescence emissions. It not only possesses excellent luminescence sensing activities toward Fe³⁺ and Cr₂O₇^2- in aqueous solution, but can also distinguish between Cr₂O₇^2- and CrO₄^2- by luminescence. Furthermore, it could be simply and quickly regenerated at least five times. A study of the sensing mechanism indicated that luminescence quenching may be related to the energy competition between the complex and sensing analytes.