Rhenium(I) Tricarbonyl Complexes Appended to Oxathiacrown Ethers: Selective Optical Sensing Probes for Mercury(Ii) Ions

The photophysical and electrochemical behavior of thiacrown ether based complexes permit their potential use in the detection of heavy metal ions as they bind to the crownether core. In this paper, we report the absorbance, fluorescence and electrochemical responses of various thiacrown ethers appended to rhenium(I) tricarbonyl moiety (C1 – C3) towards the presence of Hg2+, Cd2+ and Pb2+. The complexes displayed selectivity towards Hg2+ ions as the absorbance and emission peaks undergo quenching up to 1:1 stoichiometric ratio upon sequential addition of Hg2+ ions. Their absorbance data gave binding constant values between 4.34 to 5.42 and LOD between 123 to 209 ppm while their emission data showed binding constant values between 4.58 to 5.36 and LOD between 39 to 51 ppm. A Stern-Volmer plot of the emission spectral data for C1 and C3 displayed a positive deviation from the expected linear plot, while a similar plot for complex C2 gave a negative deviation. The C1 – C3 cyclic voltammograms displayed no anodic or cathodic shifts upon addition of Hg2+, Cd2+ and Pb2+ ions. The presence of various cations did not affect the absorbance and luminescence of the complexes, except for Cu2+ and Ag+ ions whose effect was found to be minimal. Results obtained demonstrated that the rhenium(I) oxathiacrown ether complexes could be fabricated as optical probes for detecting Hg2+ ions.