Guest selectivity of [Ni2] supramolecular helicates

Two new paramagnetic supramolecular helicates with formula (X@[Ni2L3])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 host of anionic species. The persistence in solution of the new assemblies has been demonstrated unambiguously by mass spectrometry and paramagnetic NMR. This has allowed to establish the preference of the coordination [Ni2] host for Cl− over Br−, in agreement DFT calculations. These results show the promise of the use of metallohelicates as suitable systems for the selective encapsulation of specific anions in solution.