C20
It was known for some time that a C20 fullerene was theoretically possible -- SEED Expert Bernd Eggen predicted it 10 years ago -- but it has been hard to produce one. One reason is that since it is smaller than other Fullerenes its surface has more curvature and a greater tendency to spring open. It is also highly reactive so it tends to combine with other elements to form different molecules.
Successful production of C20 was accomplished by starting with dodecahedrane, C20H20, a stable hydrocarbon consisting of 20 carbon atoms and 20 hydrogen atoms. In a two-step process the hydrogen atoms were replaced by bromine atoms, which have a weaker bond with carbon. Then the bromine was removed leaving C20.
The C20 molecules that were produced were rather unstable, but their fleeting existence was confirmed using spectroscopy.
In addition to this tiniest Bucky Ball, the researchers also generated two other forms -- called "isomers" -- of C20, one in ring and the other shaped like a bowl.
