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-yl-methyl]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 degrees 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 (Delta E-pa = 0.136 V) and negative (Delta E-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 H-1 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.