REDOX-ACTIVE LITHIUM-SELECTIVE IONOPHORES BASED ON NEW 2,9-BIS(FERROCENYL) SUBSTITUTED PHENANTHROLINE DERIVATIVES

A variety of new redox-active 2,9-bis(ferrocenyl)-substituted phenanthroline derivatives have been prepared, and the structure of one of them, 2,9-bis(ferrocenyl)ethenyl-1,10-phenanthroline, has been determined by an X-ray diffraction study. Solution H-1 NMR complexation studies suggest the 2,9-bis(ferrocenyl)vinylic- and amine-linked phenanthroline ligands form complexes with the ligand and Li+ in 2:1 stoichiometric ratio, whereas Schiff-base-containing ionophores produced an equilibrium mixture of 2:1 and 1:1 complexes. The 2,9-bis(ferrocenyl)amide-linked phenanthroline ligands formed solution lithium complexes of 1:1 stoichiometry. Electrochemical investigations reveal that the respective ferrocene-ferricenium redox couples of most of the ligands are shifted to more positive potentials on co-ordination of Li+, but are electrochemically insensitive to Na+ or K+ guest cations. The above lithium redox-responsive ionophores recognise Li+ electrochemically in the presence of equimolar concentrations of Na+ and K+.