Chemical shielding of H₂O and HF encapsulated inside a C₆₀ cage

Molecular surgery enables the study of relatively large molecules encapsulated within a fullerene cage. Here we determine the location of an H2O molecule isolated within an adsorbed buckminsterfullerene cage and compare this to the intrafullerene position of HF. Using normal incidence X-ray standing wave (NIXSW) analysis, coupled with density functional theory (DFT) and molecular dynamics (MD) simulations, we show that both H2O and HF reside at off-centre positions within the fullerene cage, caused by substantial intra-cage electrostatic fields generated by surface adsorption of the fullerene. The atomistic and electronic structure simulations reveal significant internal rotational motion consistent with the NIXSW data. Despite this intra-cage interaction, neither HF nor H2O contribute to the endofullerene frontier orbitals, confirming chemical isolation of the encapsulated molecules. We also show that our experimental NIXSW measurements and theoretical data are best described by a mixed adsorption site model.

Samuel P. Jarvis, Hongqian Sang, Filipe Junqueira, Oliver Gordon, Jo E. A. Hodgkinson, Alex Saywell, Philipp Rahe, Salvatore Mamone, Simon Taylor, Adam Sweetman, Jeremy Leaf, David A. Duncan, Tien-Lin Lee, Pardeep K. Thakur, Gabriella Hoffman, Richard J. Whitby, Malcolm H. Levitt, Georg Held, Lev Kantorovich, Philip Moriarty, Robert G. Jones