Transformations of Fullerene
In addition to physical robustness, fullerenes are fascinating in terms of their chemical reactivity that allows chemists to produce interesting molecules.
An example is the experiment performed by the group of Professor Koichi Komatsu at Kyoto University in Japan, in which C60, potassium cyanide, and iron balls in a steel jar were subjected to high-speed vibration at 3,500 rpm. They were trying to install a cyano group (-CßN) to a fullerene, but instead a completely new, unexpected molecule of C120 consisting of two soccer balls was created (Figure 1). Because of the visual impact, the molecule has appeared on the title page of many journals and books.
Fig 1 Bucky dumbbell
O. V. Boltalina and R. Taylor have been producing unique compounds by reacting fullerene with fluorine. The C60F20 with vertically squeezed shape has twenty fluorine atoms like a band on the gequatorh of the fullerene. They gave the compound a nickname gsaturnene,h based on its resemblance to the Saturn (Figure 2).
Fig 2 saturnene
The same team also reported the compound containing eighteen fluorine atoms instead of twenty (Figure 3). As you can see, fluorine atoms are again clustered together like a band. The band shape is considered to form when the addition of the first fluorine atom causes an electronic gdistortionh on the molecule, triggering the subsequent additions around it. Many of organic fluorine-containing compounds like Teflon are smooth and friction-less, so these researches could lead to the development of good lubricant.
The molecule has such a funny shape though. If I were to nickname it the saturnene style, how about jellyfishene?
Fig 3 jellyfishene?
More recently (2005), the fullerene containing thirty chlorine atoms (C60Cl30) instead of fluorine have been reported by the P. A. Troshin and S. I. Troyanov group. After the Saturn and jellyfish, this time itfs drum-shaped. When you think of fullerene as just a molecular ball, it lets you know itfs wrong by repeatedly showing these interesting transformations.
Fig 4 C60Cl30
Professor Komatsufs research team at Kyoto University has succeeded to make a big thirteen-membered ring hole on fullerene through three steps of chemical reaction. This hole is big enough for small molecules like a hydrogen molecule to pass through, and with positive pressure the complete inclusion of H2 is possible. The researchers were then able to restore the fullerene skeleton by four chemical reactions, with a hydrogen molecule still trapped inside. Making a hole, putting in an object, and closing the hole on fullerene molecule which has the diameter of 0.7 nanometers could be considered the tiniest craftwork in the human history. gMolecular surgeryh is the word thatfs been used to describe the experiments, which sounds very fitting.
Fig 5 Komatsu's open cage fullerene
The World of Supramolecular Chemistry
Fullerenes are contributing to the rapid development of the field of supramolecular chemistry. The exact definition of supramolecular chemistry is somewhat vague, but I would simplify it as the gstudy of unique properties of the combination of several molecules or ions which arenft seen in individual molecules or ions.h
For example, Professor Odafs group at Osaka University made this cyclic molecule nanoring, which can enclose a fullerene. Furthermore, the double-nanoring complex has also been synthesized by adding an extra large ring to it. The beautiful structure may remind you of the solar system model (Figure 6).
Fig 6 Oda's double-nanoring complex
One of the leaders of recent fullerene research is Professor Eiichi Nakamura of Tokyo University. His group has found a way to introduce five substituents circularly on fullerene skeleton by using a copper catalyst. Interesting studies have been reported based on this discovery.
Shown in Figure 4.5 is the fullerene with five benzene rings. The molecule possesses two opposite properties, as the pentagonal part (blue) surrounded by the five benzene rings are negatively charged (water-soluble), while the bottom half is lipophilic (water-insoluble). This is actually the characteristics of fatty acids, which are the constituent of biological cell membranes.
Fig 7 Ph5C60-
Just like fatty acids, the molecules were found to assemble into a tight double layer with the bottom sides of fullerene facing one another, forming a hollow spherical structure with the diameter of 34 nanometers. The observation, which was completely unexpected for fullerenes, drew a great deal of attention along with the molecular property. The computer graphics of the fullerene vesicle consisting of 12,700 molecules is nothing but spectacular, and can be seen on the title page of many scientific journals.
The door to a completely different world opens when the substituent is changed from benzene rings to biphenyl rings (two benzene rings joined together) or to long hydrocarbon chains. One molecule fits into the byphenyl umbrella of the other molecule, and it repeats to look just like stacked badminton shuttlecocks (Figure 8).
Fig 8 shuttlecock fullerene
This molecule shows liquid-crystal property. In most liquid substances molecules are moving in random directions, but in special cases molecules align themselves in the same direction more or less, displaying the property similar to solid crystal. This is the so-called liquid crystal. Todayfs mainstream monitors are liquid crystal displays, which works by controlling the direction of liquid crystals with electric field, blocking the light from the behind to show images.
Pillar-shaped and saucer-shaped liquid crystal molecules had been known, but these stacked cones were the first of its kind. Itfs always amazing to see Professor Nakamura opening up new science from one chemical reaction.
Just when I think that Ifm finally running out of the news on fullerene, they keep coming back with a new character. Fullerenes are really the great actors of the molecular world.