An Efficient Ferrocene
Derivative as a Chromogenic,
Optical, and Electrochemical Receptor for Selective Recognition of
Mercury(II) in an Aqueous Environment
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Abstract
The synthesis, electrochemical, optical, and cation-sensing
properties
of two triazole-tethered ferrocenyl benzylacetate derivatives, C<sub>36</sub>H<sub>36</sub>O<sub>6</sub>N<sub>6</sub>Fe (<b>2</b>) and C<sub>23</sub>H<sub>23</sub>O<sub>3</sub>N<sub>3</sub>Fe (<b>3</b>), are presented. The binding event of both the receptors
can be inferred either from a redox shift (<b>2</b>, Δ<i>E</i><sub>1/2</sub> = 106 mV for Hg<sup>2+</sup> and Δ<i>E</i><sub>1/2</sub> = 187 mV for Ni<sup>2+</sup>; <b>3</b>, Δ<i>E</i><sub>1/2</sub> = 167 mV for Hg<sup>2+</sup> and Δ<i>E</i><sub>1/2</sub> = 136 mV for Ni<sup>2+</sup>) or a highly visual output response (colorimetric) for Hg<sup>2+</sup>, Ni<sup>2+</sup>, and Cu<sup>2+</sup> cations. Remarkably,
the redox and colorimetric responses toward Hg<sup>2+</sup> are preserved
in the presence of water (CH<sub>3</sub>CN/H<sub>2</sub>O, 2/8), which
can be used for the selective colorimetric detection of Hg<sup>2+</sup> in an aqueous environment over Ni<sup>2+</sup> and Cu<sup>2+</sup> 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 <b>2</b> and <b>3</b> (<b>2</b>, ε = 2500 M<sup>–1</sup> cm<sup>–1</sup>; <b>3</b>, ε =
1370 M<sup>–1</sup> cm<sup>–1</sup>), due to a change
in color from yellow to purple for Hg<sup>2+</sup> cations in CH<sub>3</sub>CN/H<sub>2</sub>O (2/8)