Coordination Chemistry of Mixed-Donor Pyridine-Containing Macrocyclic Ligands: From Optical to Redox Chemosensors for Heavy Metal Ions.

2,8-Dithia-5-aza-2,6-pyridinophane () has been used as a receptor unit in the construction of the conjugated redox chemosensor 5-ferrocenylmethyl-2,8-dithia-5-aza-2,6-pyridinophane (). In order to further explore the coordination chemistry of , and comparatively, that of its structural analogue 2,11-dithia-5,8-diaza-2,6-pyridinophane (), featuring two secondary nitrogen atoms in the macrocyclic unit, the crystal structures of the new synthesised complexes [Pb()(ClO)]·½CHCN, Cu()·CHCN and [Cd()(NO)]NO were determined by X-ray diffraction analysis. The electrochemical response of towards the metal ions Cu, Zn, Cd, Hg, and Pb was investigated by cyclic voltammetry (CV) in CHCl/CHCN 0.25:1 (/) mixture. Upon addition to of increasing amounts of the aforementioned metal cations, the wave corresponding to the Fc/Fc redox couple of the un-complexed was gradually replaced by a new reversible wave at more positive potentials and corresponding to the Fc/Fc redox couple of the complexed ligand. The maximum anodic shift of the ferrocene oxidation wave is observed in the presence of Pb (230 mV), to which corresponds a reaction coupling efficiency (RCE) value as large as 7.9 × 10. The response selectivity of is discussed in reference to the optical selectivity observed for conjugated chemosensors featuring as receptor unit and different fluorogenic fragments as signalling units.