単分子内包炭素クラスターの合成と固体物性探索

抄録

In the point of a demonstration of its fundamental properties compared with bulk water,a single water molecule within a confined subnano space is one of the important topics in both material and life sciences. However, a single molecule of H₂O, that is completely isolated without any hydrogen bonds, is rare so far because water usually exists in hydrogen-bonded environments.The inner space of the fullerene C₆₀ is suitable to entrap a water molecule.It would be possible to control the properties of the outer carbon cage as well as to study the isolated specieswhen atoms or molecules are encapsulated in fullerenes.Endohedral fullerenes encapsulating a wide variety of species, such as metal ions and rare gases, have been synthesized with physical methods under harsh conditions. However, these methods are not suitable to obtain endohedral fullerenes encapsulating small molecules.

The molecular surgical approach is a promising method to synthesize yet-unknown endohedral fullerenes, which consists of creation of an opening on the empty fullerene cage, insertion of a small guest through the opening, and closure of the opening with retention of the guest.To realize endohedral fullerenes encapsulating a water molecule, creation as well as restoration of a larger orifice is needed. With the concept of dynamic control of opening size, an open-cage C₆₀ derivative was synthesized, whose opening can be enlarged in situ, resulting in quantitative encapsulation of a molecule of H₂O under the high-pressure conditions. The easy method to restore the opening was developed to realize the organic synthesis of water-encapsulating C₆₀. The structure of H₂O@C₆₀ was clearly determined by the single crystal X-ray analysis, and the properties of the single H₂O molecule as well as the spherical π-system encapsulating the water molecule were studied.