Synthesis of an Open-Cage C60 Derivative with a Double Stopper

The construction of a suitable stopper on a C-60 orifice is of importance to prevent the release of once-encapsulated chemical species. However, a single stopper on a large orifice is in usual not sufficient to retain a small molecule within the C-60 cavity. In this work, we introduced a double stopper, constituted of two hydroxy groups, on a huge orifice with a ring-atom count of 18 by a reduction using BH3 & sdot;THF. The resulting double stopper was demonstrated to effectively isolate an argon atom inside the cavity so that the argon was retained even under mass spectrometric conditions at 200 degrees C. The structure of the open-cage C-60 derivative with the double stopper was confirmed by X-ray diffraction analysis, showing a dimeric configuration via intermolecular hydrogen-bondings. The dimerization behavior was also studied in solution.