Published in “Science Advances” (Online Publication, April 22, 2017).

Dissociation of an acid molecule in aqueous media is one of the most fundamental solvation processes but remains poorly understood in detail at the distinct molecular level. We conducted the high-pressure treatments of an open-cage fullerene C₇₀ derivative with HF in the presence of H₂O, and found that an unprecedented encapsulation of H₂O-HF and H₂O in addition to expected one were achieved. Restoration of the opening yielded the endohedral C₇₀s, i.e., (H₂O-HF)@C₇₀, H₂O@C₇₀, and HF@C₇₀ in macroscopic scales (Figure 1). The putting of an H₂O-HF complex into the fullerene cage was a crucial step and it would proceed by the synergistic effects of “pushing from outside” and “pulling from inside”. The structure of the H₂O-HF was unambiguously determined by the single crystal x-ray diffraction analysis. The NMR measurements revealed the formation of a hydrogen bond between the H₂O and HF molecules without proton transfer even at 140 °C.

Figure 1. Molecular structure of endohedral fullerene C₇₀ encapsulating HF, H₂O-HF, and H₂O.

Zhang, R.; Murata, M.; Wakamiya, A.; Shimoaka, T.; Hasegawa, T.; Murata, Y., Isolation of the Simplest Hydrated Acid, Science Advances, 3(4), e1602833 (2017).
DOI:10.1126/sciadv.1602833