Three Cadmium Coordination Polymers with Carboxylate and Pyridine Mixed Ligands: Luminescent Sensors for Fe^III and Cr^VI Ions in an Aqueous Medium

Abstract

Three new water-stable luminescent Cd(II) coordination polymers (CPs), {[Cd₂(bptc)(2,2'-bipy)₂(H₂O)₂]}_n (1), {[Cd₂(bptc)(phen)₂]·4H₂O}_n (2), and {[Cd₂(bptc)(4,4'-bipy)(H₂O)₂]·4H₂O}_n (3), were solvothermally synthesized with mixed ligands of 3,3',5,5'-biphenyltetracarboxylic acid (H₄bptc) and N-donor ligands (2,2'-bipy = 2,2'-bipyridine; phen = 1,10-phenanthroline; 4,4'-bipy = 4,4'-bipyridine). The CPs 1-3 show structural diversity from a 1D ladder chain to a 2D layer to a 3D porous framework, tuned by different ancillary ligands. Topological analyses reveal that the CP 2 is a 4-connected uninodal 2D net with the Schläfli point symbol {4⁴·6²}, while the CP 3 displays a 4,6-connected 2-nodal 3D net with the point symbol {3·4²·5²·6}{3²·4²·5²·6⁴·7⁴·8}. Luminescent property studies reveal that the CPs 1-3 are promising luminescent sensors that can highly select and sensitively detect ferric and chromate/dichromate ions, in which the CP 1 with a 1D structure showed the best performance, free from the interference of other ions present in an aqueous medium. Moreover, the mechanism for the sensing properties was studied in detail.