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Bloodworth, Sally and Gräsvik, John and Alom, Shamim and Kouril,, Karel and Elliott, Stuart J. and Wells, Neil J. and Horsewill, Anthony J. and Mamone, Salvatore and Jimenez-Ruiz, Monica and Rols, Stéphane and Nagel, Urmas and Room, Toomas and Levitt, Malcolm H. and Whitby, Richard J. (2018) Synthesis and properties of open fullerenes encapsulating ammonia and methane. ChemPhysChem, 19 (3). pp. 266-276. ISSN 1439-7641

Abstract

We describe the synthesis and characterisation of open fullerene (1) and its reduced form (2) in which CH₄ and NH₃ are encapsulated, respectively. The ¹H NMR resonance of endohedral NH₃ is broadened by scalar coupling to the quadrupolar ¹⁴N nucleus, which relaxes rapidly. This broadening is absent for small satellite peaks, which are attributed to natural abundance ¹⁵N. The influence of the scalar relaxation mechanism on the linewidth of the ¹H ammonia resonance is probed by variable temperature NMR. A rotational correlation time of τc= 1.5 ps. is determined for endohedral NH₃, and of τc=57±5 ps. for the open fullerene, indicating free rotation of the encapsulated molecule. IR spectroscopy of NH3@2 at 5 K identifies three vibrations of NH₃ (ν₁, ν₃ and ν₄) redshifted in comparison with free NH₃, and temperature dependence of the IR peak intensity indicates the presence of a large number of excited translational/ rotational states. Variable temperature ¹H NMR spectra indicate that endohedral CH4 is also able to rotate freely at 223 K, on the NMR timescale. Inelastic neutron scattering (INS) spectra of CH₄@1 show both rotational and translational modes of CH₄. Energy of the first excited rotational state (J=1) of CH₄@1 is significantly lower than that of free CH₄.

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