Solid-state NMR of endohedral hydrogen–fullerene complexes

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Abstract
We present an overview of solid-state NMR studies of endohedral H2-fullerene complexes, including 1H and 13C NMR spectra, 1H and 13C spin relaxation studies, and the results of 1H dipole–dipole recoupling experiments. The available data involves three different endohedral H2-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 H2 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 1H NMR lineshapes of endohedral H2 molecules trapped in highly symmetric cages at cryogenic temperatures. This review demonstrates the richness of NMR phenomena displayed by H2-fullerene complexes, especially in the cryogenic regime.