Solid-state NMR of endohedral hydrogen–fullerene complexes

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.