Fluorimetric chemosensors. Interaction of toxic heavy metal ions PbII, CdII, and HgII with novel mixed-donor phenanthroline-containing macrocycles: Spectrofluorimetric, conductometric and crystallographic studies

The macrocycles L1-L3 incorporating N2S3-, N2S2O-, and N2S2-donor sets, respectively, and containing the 1,10-phenanthroline unit interact in acetonitrile solution with heavy metal ions such as PbII, CdII, and HgII to give 1:1 ML, 1:2 ML2, and 2:1 M2L complex species, which specifically modulate the photochemical properties of the ligands. The stoichiometry of the complex species formed during spectrofluorometric titrations and their formation constants in MeCN at 25 °C were determined from fluorescence vs MII/L molar ratio data. The complexes [Pb(L1)][ClO4]2.1/2H2O (1), [Pb(L2)][ClO4]2.MeNO2 (1a), [Pb(L3)2][ClO4]2.2MeCN (1b), and [Cd(L3)][NO3]2 (2b) were also characterized by X-ray diffraction studies. The conformation adopted by L1-L3 in these species reveals the aliphatic portion of the rings folded over the plane containing the heteroaromatic moiety with the ligands trying to encapsulate the metal center within their cavity. In 1, 1a, and 2b the metal ion completes the coordination sphere by interacting with counteranion units and solvent molecules. On the contrary, the 1:2 complex 1b shows PbII sandwiched between two symmetry-related molecules of L3 reaching an overall [4N + 4S] eight-coordination.