An efficient ferrocene derivative as a chromogenic, optical, and electrochemical receptor for selective recognition of mercury(II) in an aqueous environment

Abstract

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, ΔE_1/2 = 106 mV for Hg²⁺ and ΔE_1/2 = 187 mV for Ni²⁺; 3, ΔE_1/2 = 167 mV for Hg²⁺ and ΔE_1/2 = 136 mV for Ni²⁺) or a highly visual output response (colorimetric) for Hg²⁺, Ni²⁺, and Cu²⁺ cations. Remarkably, the redox and colorimetric responses toward Hg²⁺ are preserved in the presence of water (CH₃CN/H₂O, 2/8), which can be used for the selective colorimetric 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, ε = 2500 M^-1 cm^-1; 3, ε = 1370 M^-1 cm^-1), due to a change in color from yellow to purple for Hg²⁺ cations in CH₃CN/H₂O (2/8).