Polyazacyclophanes. 2,6,9,13-Tetraaza[14] paracyclophane as a cationic and anionic receptor

Abstract

The synthesis and characterization of the new azacyclophane, 2,6,9,13-tetraaza[14]paracyclophane, is described. The acid–base behaviour and the metal and anion coordination capabilities of this compound have been studied by potentiometry at 298.15 K in 0.15 mol dm^–3 NaClO₄, as well as, by ¹H and ¹³C NMR spectroscopy. The protonation patterns show stabilization effects produced by the presence of the aromatic ring. The aromatic spacer prevents simultaneous involvement of all four nitrogens in the coordination to the metal ions Cu²⁺ and Zn²⁺. Stable mono-hydroxylated species have been detected for both metal ions. The triprotonated species is the main one over a wide pH range around neutrality making this ligand a good coordinating agent for such anionic species as ATP^4–and p₂O₇^4–. Formation of complexed anionic species with degrees of protonation varying from three to six has been detected.