Metal template synthesis of a tripodal tris(bipyridyl) receptor that encapsulates a proton and an iron(ii) centre in a pseudo cage

The Fe(ii) template synthesis of the first member of a new category of tripodal tris-bipyridine ligands incorporating a nitrogen bridgehead is reported. The X-ray structure of the reaction product shows that the ligand adopts a pseudo cage-like structure that encapsulates both a proton and an Fe(ii) ion in its cavity. The complex shows an extended helical arrangement that is effectively 'capped' at its open end by a hydrogen bonded PF6– counter ion that is symmetrically aligned with the 3-fold axis of the helix. A 1H NMR study demonstrated that the encapsulated proton can be reversibly exchanged under acid/base conditions in CD3CN