Chemical shielding of H2O and HF encapsulated inside a C60 cage

Abstract

Molecular surgery provides the opportunity to study 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 and molecular dynamics simulations, we show that both H2O and HF are located at an off-centre position within the fullerene cage, caused by substantial intra-cage electrostatic fields generated by surface adsorption of the fullerene. The atomistic and electronic structure simulations also reveal significant internal rotational motion consistent with the NIXSW data. Despite this substantial intra-cage interaction, we find that neither HF or H2O contribute to the endofullerene frontier orbitals, confirming the 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.

Unraveling the Origin of Symmetry Breaking in H2O@C60 Endofullerene Through Quantum Computations

“…Such data from experimental observations are available only for the ground 1 ortho‐H 2 O state, while the theoretical studies predict the lifting of degeneracy for higher excited rotationally states, too. Just recently, an energy splitting of 2.9 cm −1 has been also reported [16] for the translational transition of ortho‐H 2 O from IR absorption spectroscopy experiments, while X‐ray experiments coupled with DFT and molecular dynamics simulations have just shown that H 2 O is located at an off‐center position inside the C 60 [34] . Definitely, the observation of such phenomena requires deeper investigation from both theory and experiment.…”

“…As emphasized earlier, [27] in lack of full dimensional firstprinciples/ab initio interaction energies, we may speculate for various possible interaction terms in the potential and/or nuclear motion couplings, that could be able to match experimental evidences. In this vein, by introducing anisotropy in the n-mode potential expansion, [27] according to recent electronic structure calculations [33] and X-ray experimental evidences, [34] due to noncolavent interactions in interfullerene environment, [33,[35][36][37][38][39][40] we have also computed rotational states splitting patterns in qualitative accord to those observed experimentally. [3,10] Theoretical investigations of such unconventional features require fully coupled quantum treatments.…”

“…position inside the C 60 . [34] Definitely, the observation of such phenomena requires deeper investigation from both theory and experiment. As the nature of the observed symmetry breaking can have a very subtle origin, apart of decisive experimental measurements of higher lying states for the H 2 O@C 60 endofullerene, theoretical treatments especially on the electronic structure many-body interactions are highly demanded in order to provide conclusive insights on the symmetry-lowering effects.…”

“…Both models are alternative potential models, that are logically supported, and have been introduced by the need to understand complementary reasons (such as inter-and intra-fullerene interactions) about the origin of the symmetry breaking observed in the H 2 O@C 60 . Model (1) scenario considers anisotropy in the interfullerene interactions due to the change of water molecule configuration, e. g. such as an off-center position within the fullerene cage, [33,34] caused by the presence of significant electronic (noncovalent) intermolecular anisotropic interactions between it and the cage or neighbor ones. Model (2) incorporates anisotropy due to an uniaxial cage distortion.…”

“…Model (1) scenario considers anisotropy in the interfullerene interactions due to the change of water molecule configuration, e. g . such as an off‐center position within the fullerene cage, [33,34] caused by the presence of significant electronic (noncovalent) intermolecular anisotropic interactions between it and the cage or neighbor ones. Model (2) incorporates anisotropy due to an uniaxial cage distortion.…”