An H O Molecule Stabilized inside Open-Cage C Derivatives by a Hydroxy Stopper.

An H O molecule was isolated inside hydroxylated open-cage fullerene derivatives by mixing an H O solution with a precursor molecule followed by reduction of one of carbonyl groups on its orifice. Depending on the reduction site, two structural isomers for H O @open-fullerenes were obtained. A high encapsulation ratio of 81 % was attained at low temperature. The structures of the peroxosolvate complexes thus obtained were studied by H NMR spectroscopy, X-ray analysis, and DFT calculations, showing strong hydrogen bonding between the encapsulated H O and the hydroxy group located at the center of the orifice. This OH group was found to act as a kinetic stopper, and the formation of the hydrogen bonding caused thermodynamic stabilization of the H O molecule, both of which prevent its escape from the cage. One of the peroxosolvates was isolated by HPLC, affording H O @open-fullerene with 100 % encapsulation ratio, likely due to the intramolecular hydrogen-bonding interaction.