Isolation of the simplest hydrated acid

摘要

Dissociation of an acid molecule in aqueous media is one of the most fundamental solvation processes but its details remain poorly understood at the distinct molecular level. Conducting high-pressure treatments of an open-cage fullerene C₇₀ derivative with hydrogen fluoride (HF) in the presence of H₂O, we achieved an unprecedented encapsulation of H₂O·HF and H₂O. Restoration of the opening yielded the endohedral C₇₀s, that is, (H₂O·HF)@C₇₀, H₂O@C₇₀, and HF@C₇₀ in macroscopic scales. Putting 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 single crystal x-ray diffraction analysis. The nuclear magnetic resonance measurements revealed the formation of a hydrogen bond between the H₂O and HF molecules without proton transfer even at 140°C.