Solid-state NMR of endohedral hydrogen-fullerene complexes

We present an overview of solid-state NMR studies of endohedral H-2-fullerene complexes, including H-1 and C-13 NMR spectra, H-1 and C-13 spin relaxation studies, and the results of H-1 dipole-dipole recoupling experiments. The available data involves three different endohedral H-2-fullerene complexes, studied over a wide range of temperatures and applied magnetic fields. The symmetry of the cage influences strongly the motionally-averaged nuclear spin interactions of the endohedral H-2 species, as well as its spin relaxation behaviour. In addition, the non-bonding interactions between fullerene cages are influenced by the presence of endohedral hydrogen molecules. The review also presents several pieces of experimental data which are not yet understood, one example being the structured H-1 NMR lineshapes of enclohedral H-2 molecules trapped in highly symmetric cages at cryogenic temperatures. This review demonstrates the richness of NMR phenomena displayed by H-2-fullerene complexes, especially in the cryogenic regime.