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 .
(© 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)