An H2O2 Molecule Stabilized inside Open-Cage C60 Derivatives by a Hydroxy Stopper

An H₂O₂ molecule was isolated inside hydroxylated open-cage fullerene derivatives by mixing an H₂O₂ 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 H₂O₂@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 ¹H NMR spectroscopy, X-ray analysis, and DFT calculations, showing strong hydrogen bonding between the encapsulated H₂O₂ 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 H₂O₂ molecule, both of which prevent its escape from the cage. One of the peroxosolvates was isolated by HPLC, affording H₂O₂@open-fullerene with 100 % encapsulation ratio, likely due to the intramolecular hydrogen-bonding interaction.