Rhenium(I) tricarbonyl complexes appended to oxathiacrown ethers as selective optical sensing probes for mercury(II) ions

The photophysical properties of thiacrown ether-based complexes permit their potential application in detecting heavy metals. In this paper, we report the recognition properties of various thiacrown ethers appended to rhenium(I) tricarbonyl signaling moiety (C1-C3) towards Cd2+, Hg2+, and Pb2+ ions using absorbance, luminescence, and electrochemical titration techniques. Upon sequential addition of Hg2+ ions to C1-C3, their absorbance and emission spectra display a quenching of their peaks up to a 1:1 stoichiometric ratio. The binding constant values (log Ka) from C1-Hg2+, C2-Hg2+, and C3-Hg2+ absorbance data range between 4.34 and 5.42, while the LOD ranges between 123 and 209 ppm. Similar calculations from their emission data show log Ka values ranging between 4.58 and 5.36, while the LOD values range between 39 and 51 ppm. The absorbance and emission spectra of C1-C3 are, however, not perturbed by the presence of Cd2+, Pb2+, Li+, Na+, K+, Mg2+, Ca2+, and Zn2+ ions except for Cu2+ and Ag+ ions which display very minimal perturbation. The electrochemical responses of C1-C3 to the presence of Cd2+, Hg2+, and Pb2+ ions are negligible since their cyclic voltammograms do not undergo any anodic or cathodic change upon adding these ions. These results demonstrate that the rhenium(I) oxathiacrown ether complexes could be fabricated as optical probes for detecting Hg2+ ions.