Cd^II-based compound as a multi-responsive fluorescent probe for sensing Fe^III cations and Cr^VI oxyanions

A new luminescent Cd^II compound, poly[[μ₂-1,4-bis(1H-imidazol-1-yl)benzene]{μ₂-5-[(3-carboxylphenoxy)methyl]isophthalato}cadmium(II)], [Cd(C₁₆H₁₀O₇)(C₁₂H₁₀N₄)]_n or [Cd(HL)(1,4-bib)]_n {H₃L is 5-[(3-carboxyphenoxy)methyl]isophthalic acid and 1,4-bib is 1,4-bis(1H-imidazol-1-yl)benzene}, I, has been synthesized successfully from Cd^II and a semirigid tricarboxylic ligand under hydrothermal conditions. Structure analysis shows that I is a two-dimensional structure with the point symbol {4⁴.6²}. The three-dimensional framework is constructed by O-H...O hydrogen bonds and π-π stacking interactions. Furthermore, the obtained Cd^II compound displays high solvent stability and excellent thermal stability, as shown by powder X-ray diffraction and thermogravimetry measurements. Studies of the luminescence properties reveal that compound I can act as a promising luminescent sensor for detecting Fe^III cations and Cr^VI oxyanions with high selectivity and low detection limits (0.19 µM for Fe³⁺ and 1.13 µM for Cr₂O₇^2-), and is additionally free from the interference of other ions. The mechanism of selective quenching was studied by measuring the UV-Vis absorption of the host compound and the target analytes.