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

Abstract

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, E_½ is pH-dependent and from the E_½vs. pH curve the protonation constants of oxidized L¹(Fe^III) were determined. Similar electrochemical experiments were carried out for L¹–H⁺–M²⁺ systems. The good agreement between the E_½vs. pH and z vs. pH curves (z= average charge calculated from potentiometric data) appears to suggest that the ferrocene–substrate interaction is mainly electrostatic.