Allosteric deprogramming of a trinuclear heterometallic helicate

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.