Department of Chemistry, University of Calcutta, 92, A.P.C. Road, Kolkata, India.
Dalton Trans. 2018 Dec 4;47(47):17077-17085. doi: 10.1039/c8dt02449a.
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.
一种简单可靠的监测强酸性 pH 值的方法已经开发出来。研究发现，该传感机制涉及合成探针 HQphy（1）（N-苯基-N'-喹喔啉-2-亚甲基-腙）在 pH 值 0.7-2.7 的工作范围内质子化-去质子化平衡。最终检测到 Fe3+是由于溶液中[Fe(H2O)6]3+离子在形成[Fe(H2O)5(OH)]2+时赋予的酸度。通过 1H NMR 和单晶 X 射线衍射实验研究了 HQphy 的质子化-去质子化现象。质子化探针 H2Qphy+与 FeCl4-/ClO4-抗衡阴离子结晶为[H2Qphy][FeCl4]·H2O（2）/[H2Qphy][ClO4]·H2O（3）。还形成了含有[H2Qphy]阳离子的进一步配合物（4）。通过 SC-XRD 实验对配合物进行了表征。此外，在 1 和 3 之间观察到单晶到单晶的转变。为了理解传感机制，进行了各种分析研究，如紫外-可见滴定、ESI-MS 光谱分析和 1H NMR。理论研究与实验数据很好地相关，其中配体的π（L）→π*（L）跃迁由于喹喔啉部分的质子化而红移了 100nm。该探针能够区分三卤乙酸与其单-和二-类似物。
