Synthesis and Properties of Open Fullerenes Encapsulating Ammonia and Methane

We describe the synthesis and characterisation of open fullerene ( 1 ) and its reduced form ( 2 ) in which CH 4 and NH 3 are encapsulated, respectively. The 1 H NMR resonance of endohedral NH 3 is broadened by scalar coupling to the quadrupolar 14 N nucleus, which relaxes rapidly. This broadening is absent for small satellite peaks, which are attributed to natural abundance 15 N. The influence of the scalar relaxation mechanism on the linewidth of the 1 H ammonia resonance is probed by variable temperature NMR. A rotational correlation time of τ c =1.5 ps. is determined for endohedral NH 3 , and of τ c =57±5 ps. for the open fullerene, indicating free rotation of the encapsulated molecule. IR spectroscopy of NH 3 @ 2 at 5 K identifies three vibrations of NH 3 ( ν 1 , ν 3 and ν 4 ) redshifted in comparison with free NH 3 , and temperature dependence of the IR peak intensity indicates the presence of a large number of excited translational/ rotational states. Variable temperature 1 H NMR spectra indicate that endohedral CH 4 is also able to rotate freely at 223 K, on the NMR timescale. Inelastic neutron scattering (INS) spectra of CH 4 @ 1 show both rotational and translational modes of CH 4 . Energy of the first excited rotational state ( J= 1) of CH 4 @ 1 is significantly lower than that of free CH 4 .