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Issue 47, 2018
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A versatile quinoxaline derivative serves as a colorimetric sensor for strongly acidic pH

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Abstract

A facile and reliable method to monitor strongly acidic pH was developed. The sensing mechanism was found to involve the protonation–deprotonation equilibrium of the synthesized probe HQphy (1) (N-phenyl-N′-quinoxalin-2-ylmethylene-hydrazine) within a working range of pH 0.7–2.7. The eventual sensing of Fe3+ was the outcome of acidity imparted by [Fe(H2O)6]3+ ions in solution during the formation of [Fe(H2O)5(OH)]2+. The protonation–deprotonation phenomenon of HQphy was investigated using 1H NMR and single crystal X-ray diffraction experiments. The protonated probe, H2Qphy+, was crystallized with FeCl4/ClO4 counter anions as [H2Qphy][FeCl4]·H2O (2)/[H2Qphy][ClO4]·H2O (3). A further complex containing the [H2Qphy] cation (4) was also formed. The complexes were characterized by SC-XRD experiments. Moreover, single crystal to single crystal transformation is observed between 1 and 3. In order to understand the sensing mechanism, various analytical studies, such as UV-Vis titration, ESI-MS spectrometry analysis and 1H NMR, were carried out in detail. A theoretical study correlates well with the experimental data, where the π(L) → π*(L) transition of the ligand is red shifted by 100 nm due to protonation of the quinoxaline moiety. The probe enables discrimination of trihalo acetic acid from its mono- and di-analogues.

Graphical abstract: A versatile quinoxaline derivative serves as a colorimetric sensor for strongly acidic pH

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Publication details

The article was received on 14 Jun 2018, accepted on 14 Nov 2018 and first published on 14 Nov 2018


Article type: Paper
DOI: 10.1039/C8DT02449A
Citation: Dalton Trans., 2018,47, 17077-17085
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    A versatile quinoxaline derivative serves as a colorimetric sensor for strongly acidic pH

    R. Bag, Y. Sikdar, S. Sahu, D. K. Maiti, A. Frontera, A. Bauzá, M. G. B. Drew and S. Goswami, Dalton Trans., 2018, 47, 17077
    DOI: 10.1039/C8DT02449A

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