Synthesis and Characterization of Electroactive Ferrocene Derivatives: Ferrocenylimidazoquinazoline as a Multichannel Chemosensor Selectively for Hg2+ and Pb2+ Ions in an Aqueous Environment

The synthesis and characterization of ferrocene (Fc) derivatives 4-[2,5-diferrocenyl-4-(4-pyridyl)­imidazolidin-1-ylmethyl]­pyridine (1), ferrocenylmethylenepyridin-3-ylmethylamine (2), N,N′-bis­(ferrocenylmethylene)-2,4,6-trimethylbenzene-1,3-diamine (3), and 6-ferrocenyl-5,6-dihydro­[4,5]­imidazo­[1,2-c]­quinazoline (4) have been described. Structures of 1, 2, and 4 have been determined by single-crystal X-ray diffraction analyses. At 25 °C, 1–3 are nonfluorescent, while 4 displays moderate fluorescence and chromogenic, fluorogenic, and electrochemical sensing selectively toward Hg2+ and Pb2+ ions. Association constants (Ka) for Hg2+ and Pb2+ have been determined by the Benesi–Hildebrand method. Job’s plot analysis supported 1:1 and 1:2 stoichiometries for Hg2+ and Pb2+ ions. Cyclic voltammograms of 1–4 exhibited reversible waves corresponding to a ferrocene/ferrocenium couple. The wave associated with 4 (+0.0263 V) exhibited positive (ΔEpa = 0.136 V) and negative (ΔEpa = 0.025 V) shifts in the presence of Hg2+ and Pb2+ ions, respectively. The mode of interaction between metal ions and 4 has been supported by 1H NMR spectroscopy and mass spectrometry studies and verified by theoretical studies. It presents the first report dealing with ferrocene-substituted quinazoline as a multichannel chemosensor for Hg2+/Pb2+ ions.