Binding, electrochemical and metal extraction properties of the new redox-active polyazacycloalkane 1,4,7,10,13,16-hexa(ferrocenylmethyl)-1,4,7,10,13,16-hexaazacyclooctadecane

The redox-functionalised polyazacycloalkane receptor 1,4,7,10,13,16-hexa(ferrocenylmethyl)-1,4,7,10,13,16-hexaazacyclooctadecane (L¹) has been designed and synthesized and its binding, electrochemical and metal extraction properties studied. The results have been compared to those obtained for the parent redox-active polyazacycloalkane 1,4,8,11-tetra(ferrocenylmethyl)-1,4,8,11-tetraazacyclotetradecane, L³. The cadmium complex of L¹ and the free receptor L³ have been crystallographically characterised. The structure of [CdL¹][PF₆]₂·4CH₃CN·4H₂O consists of cationic [CdL¹]²⁺ units in which the cadmium ion exhibits a distorted octahedral environment. Solution studies by potentiometric methods have also been carried out in the presence of H⁺ and Cu²⁺ in 1,4-dioxane–water (70∶30 v/v, 25 °C, 0.1 mol dm^–3 KNO₃) for L¹ and thf–water (70∶30 v/v, 25 °C, 0.1 mol dm^–3 [NBuⁿ₄][ClO₄]) for L³. Electrochemical experiments as a function of the pH in the presence of Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ or Pb²⁺ have been carried out for L¹ and L³. The solvent extraction properties of L¹ have also been studied.