Synthesis and characterization of electroactive ferrocene derivatives: ferrocenylimidazoquinazoline as a multichannel chemosensor selectively for Hg²⁺ and Pb²⁺ ions in an aqueous environment

Abstract

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 (K_a) 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 (ΔE_pa = 0.136 V) and negative (ΔE_pa = 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.