Synthesis, protonation and co-ordination abilities of the open-chain polyamine 4,8,11,15-tetraazaoctadecane-1,18-diamine

Abstract

The new open-chain polyamine 4,8,11,15-tetraazaoctadecane-1,18-diamine has been synthesised and characterized. The acid–base behaviour and the co-ordination abilities towards Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ have been studied by potentiometry at 298.1 K in 0.15 mol dm^–3 NaClO₄, as well as by ¹H and ¹³C NMR spectroscopy. The protonation pattern shows the effects produced by the presence of primary and secondary nitrogen atoms as well as ethylenic and propylenic hydrocarbon chains within the molecule. The stability and spectroscopic data show that at most four of the six nitrogens present are involved in co-ordination to the different metal ions. The contrast to other hexaamines, this compound is able to form binuclear species with all the metal ions studied. Formation of predominant binuclear hydroxo species has been detected in a number of systems.