Three robust luminescent Cd(II) coordination polymers as multi-responsive fluorescent sensors for Cu2+, Hg2+, levofloxacin, and acetylacetone in water

Employing coordination polymers (CPs) developing effective organic contaminants and heavy metal ions luminescent detection systems is an ongoing challenge. Three ternary Cd(II) CPs namely [Cd(MIP)(L)0.5(H2O)]n (1), [Cd2(TPA)2(L)(H2O)]n (2), and [Cd2(DCTP)2(L)(H2O)]n (3), (L = 1,6-bis(2-((1H-imidazol-1-yl)methyl)-1H-benzo[d]imidazol-1-yl)hexane, H2MIP = 5-methylisophthalic acid, H2TPA = terephthalic acid, and H2DCTP = 2,5-dichloroterephthalic acid) containing new L ligands, were hydrothermally synthesized and characterized. 1 displays a (4,4)-connected 4,4L28 layer and further extended into the 3D supramolecular framework via π−π stacking interactions. 2 exhibits a (4,4,5)-connected trinodal network with the point symbol of {42.5.62.8}{42.52.72}{42.53.62.73}2. 3 takes on a (3,5,6)-connected framework with the point symbol {3.42.52.7}{3.82}2{33.44.5.62.82.92.10}2. 1−3 show highly good thermal stability, and highly acid-base tolerance. The limits of detection (LOD) of 1−3 were calculated as follows: for Cu2+, the LODs are 8.92 × 10−8, 5.74 × 10−7, and 9.37 × 10−8 mol∙L−1, respectively; for Hg²⁺, the LOD values are 3.73 × 10−7, 5.22 × 10−7, and 8.45 × 10−7 mol∙L−1, respectively. Regarding levofloxacin (LEV), the LODs for 1−3 were found to be 5.11 × 10−8 mol∙L−1, 2.45 × 10−8 mol∙L−1, and 8.54 × 10−8 mol∙L−1, respectively. Finally, for acetylacetone (acac), the LODs of 1−3 are 5.53 × 10−6, 5.66 × 10−6, and 1.23 × 10−6 mol∙L−1, respectively. 1−3 represent the first examples of exceptional multi-responsive sensing platforms for the detecting of Cu2+, Hg2+, LEV, and acac with high sensitivity, outstanding anti-interference abilities, and low LODs. The possible sensing mechanisms were investigated in detail.