Anisotropic nuclear spin interactions in H 2 O@C 60 determined by solid-state NMR

We report a solid-state NMR study of the anisotropic nuclear spin interactions in H 2 O@C 60 at room temperature. We find evidence of significant dipole–dipole interactions between the water protons, and also a proton chemical shift anisotropy (CSA) interaction. The principal axes of these interaction tensors are found to be perpendicular. The magnitude of the CSA is too large to be explained by a model in which the water molecules are partially aligned with respect to an external axis. The evidence indicates that the observed CSA is caused by a distortion of the geometry or electronic structure of the fullerene cages, in response to the presence of the endohedral water.