Guest selectivity of [Ni 2 ] supramolecular helicates.

Two new paramagnetic supramolecular helicates with the formula (X@[Ni 2 L 3 ]) 3+ (X = Cl, or Br; L = a bis-pyrazolylpyridine ligand) have been prepared and are described. Helicates of this metal are very rare with virtually no prior examples of them acting as hosts of anionic species. The persistence of the new assemblies in solution has been demonstrated unambiguously by mass spectrometry and paramagnetic 1 H NMR. This has allowed us to establish the preference of the coordination [Ni 2 ] host for Cl - over Br - , in agreement with DFT calculations. These results show the promise of the use of metallohelicates as suitable systems for the selective encapsulation of specific anions in solution.