Three Cadmium Coordination Polymers with Carboxylate and Pyridine Mixed Ligands: Luminescent Sensors for FeIII and CrVI Ions in an Aqueous Medium

Three new water-stable luminescent Cd(II) coordination polymers (CPs), {[Cd-2(bptc)(2,2'-bipy)(2)(H2O)(2)]}(n) (1), {[Cd-2(bptc)(phen)(2)]center dot 4H(2)O}(n) (2), and {[Cd-2(bptc)(4,4'-bipy)(H2O)(2)]center dot 4H(2)O}(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 Schlafli point symbol {4(4)center dot 6(2)}, while the CP 3 displays a 4,6-connected 2-nodal 3D net with the point symbol {3 center dot 4(2)center dot 5(2)center dot 6}{3(2)center dot 4(2)center dot 5(2)center dot 6(4)center dot 7(4)center dot 8}. Luminescent property studies reveal that the CPs 13 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.