Allosteric deprogramming of a trinuclear heterometallic helicate

Abstract

Two multidentate ditopic ligands L¹ and L² which contain both N-donor and crown ether units have been synthesised. The potentially octadentate ligand L¹ forms a trinuclear heterometallic double helicate with Cu(I) and Zn(II) ([Zn₂Cu(L¹)₂]⁵⁺), whereas L² forms a tetranuclear heterometallic double helicate with the same metal ions ([Zn₂Cu₂(L²)₂]⁶⁺). Both species have been characterised by ¹H NMR, ESI-MS and single crystal X-ray crystallography. Reaction of [Zn₂Cu₂(L²)₂]⁶⁺ with Ba²⁺ results in the coordination of the crown ether units giving the simple barium coordinated species [Zn₂Cu₂(L²)₂Ba₂]¹⁰⁺. However, reaction of [Zn₂Cu(L¹)₂]⁵⁺ with Ba²⁺ deprograms the ligand and results in the formation of a mixture of species.