Zwitterionic dicopper helicates: anion encapsulation and binding studies

The synthesis and spectroscopic studies of a dicopper(II) double helicate capable of binding anions is described. X-Ray crystallographic analysis of three anion variations of the complex have shown that the helicate is capable of accommodating anions with an approximate volume of 0.09 nm3 and smaller. ESI-MS revealed that the supramolecular complexes retain the 2 : 2 ligand : metal cluster in solution. Spectrometric analysis has shown the complex is capable of binding anions in a 1 : 1 ratio of helicate to anion, in the order SO42− > HPO42− > ClO4−∼ BF4−∼ NO3−. We demonstrate that coordination to the metal centre, H-bonding and electrostatic interactions all play a role in encapsulating the anions.