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 L1 and 1,1′-bis(2,5-diazahexyl)ferrocene L2, have been synthesized and characterized. Their protonation behaviour has been studied by potentiometric titrations in water (0.1 mol dm–3 KNO3, 25 °C). The co-ordination ability of L1 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 L1 has been studied in CH2Cl2 and water, E½ is pH-dependent and from the E½vs. pH curve the protonation constants of oxidized L1(FeIII) were determined. Similar electrochemical experiments were carried out for L1–H+–M2+ systems. The good agreement between the E½vs. pH and z vs. pH curves (z= average charge calculated from potentiometric data) appears to suggest that the ferrocene–substrate interaction is mainly electrostatic.