An Efficient Ferrocene Derivative as a Chromogenic, Optical, and Electrochemical Receptor for Selective Recognition of Mercury(II) in an Aqueous Environment

The synthesis, electrochemical, optical, and cation-sensing properties of two triazole-tethered ferrocenyl benzylacetate derivatives, C36H36O6N6Fe (2) and C23H23O3N3Fe (3), are presented. The binding event of both the receptors can be inferred either from a redox shift (2, Delta E-1/2 = 106 mV for Hg2+ and Delta E-1/2 = 187 mV for Ni2+; 3, Delta E-1/2 = 167 mV for Hg2+ and Delta E-1/2 = 136 mV for Ni2+) or a highly visual output response (colorimetric) for Hg2+, Ni2+, and Cu2+ cations. Remarkably, the redox and calorimetric responses toward Hg2+ are preserved in the presence of water (CH3CN/H2O, 2/8), which can be used for the selective calorimetric detection of Hg2+ in an aqueous environment over Ni2+ and Cu2+ cations. The changes in the absorption spectra are accompanied by the appearance of a new low-energy (LE) peak at 625 nm for both compounds 2 and 3 (2, epsilon = 2500 M-1 cm(-1); 3, epsilon = 1370 M-1 cm(-1)), due to a change in color from yellow to purple for Hg2+ cations in CH3CN/H2O (2/8).