Molecules bearing a redox-active spacer. Synthesis and co-ordination behaviour of 1,1'-bis(5-methyl-2,5-diazahexyl)ferrocene

New open-chain tetraamines containing ferrocene, 1,1'-bis(5-methyl-2,5-diazahexyl)ferrocene L(1) and 1,1'-bis(2,5-diazahexyl)ferrocene L(2), have been synthesized and characterized. Their protonation behaviour has 4been studied by potentiometric titrations in water (0.1 mol dm(-3) KNO3, 25 degrees C). The co-ordination ability of L(1) towards the divalent metal ions Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ has also been studied. It forms both mono- and bi-nuclear complexes with Ni2+, Cu2+, Zn2+ and Cd2+ whereas only mononuclear species were found for Pb2+. The electrochemical behaviour of L(1) has been studied in CH2Cl2 and water, E(1/2) is pH-dependent and from the E(1/2) vs. pH curve the protonation constants of oxidized L(1) (Fe-III) were determined. Similar electrochemical experiments were carried out for L(1)-H+-M(2+) systems. The good agreement between the E(1/2) vs. pH and z vs. pH curves (z = average charge calculated from potentiometric data) appears to suggest that the ferrocene-substrate interaction is mainly electrostatic.