Tubes instead of spheres: Researchers have created a new type of carbon from spherical fullerenes. For this new allotrope, the 60-carbon buckyballs are partially broken open under the influence of a catalyst. As a result, new bonds form between the fullerenes, which lead to the formation of a relatively ordered, porous carbon structure. This material is conductive when it is cold and could open up new applications, the team reports in Nature.
Carbon is one of the most versatile elements on the periodic table. Its reactions with other elements form the basis of all organic chemistry. At the same time, pure carbon also shows a wealth of structural variants. The range of these allotropes extends from graphite and the single-layer “miracle material” graphene to diamond and fullerenes – hollow spheres made up of 60 carbon atoms. Only recently did chemists succeed for the first time in producing a type of polymer from such “buckyballs” – a network of interconnected fullerenes.
Buckyballs in the oven
Chemists around Fei Pan from the University of Hefei have now produced another modification of the carbon. The starting point was the hollow spherical fullerenes. In them, each atom is connected to three others and is therefore sp 2 -hybridized. Mathematically, the carbon forms two single bonds and one double bond. In practice, however, the electrons of the double bond are not localized at one point, but rather delocalized, similar to the benzene ring.
For their new structure, the chemists mixed fullerene powder with alpha-lithium nitride (α-Li 3 N), a compound that can promote the transfer of electrons and thus the rearrangement of bonds. Mixtures with different proportions of this catalyst gradually heated them up to temperatures of 600 degrees.
Fullerenes with connecting hoses
It turned out that at low temperatures of up to around 480 degrees, the fullerenes remain intact, but can clump together and form a kind of polymer crystal. At 600 degrees, the heat causes the carbon balls to completely disintegrate. But in between lies an area where something completely new is emerging, as Pan and his team observed: When a 5:1 mixture of fullerenes and alpha lithium nitride is heated to 550 gad, the spherical molecules only partially break open and form new bonds with each other .
A novel structure is created in which the half-broken fullerenes form a kind of tubular structure. They are still sp 2 -hybridized and also retain their position in the crystal lattice. At the same time, however, they are linked to their neighbors by several bonds enclosing a cavity, and not every fullerene sphere is broken open in the same way.
Novel and possibly useful
“This form of carbon is completely different and unique,” explains co-author Rodney Ruoff from the Institute for Basic Research in South Korea. He and his colleagues have dubbed this novel modification of carbon “Long-range ordered porous carbon” (LOPC). This reflects that this carbon variant still has a regular basic structure, which varies slightly at close range.
Also interesting: Measurements showed that the LOPC carbon only has a low electrical conductivity at room temperature. However, if the material is cooled down to around 30 Kelvin, it becomes an electrical conductor with metal-like electron transport, as the team reports. According to them, the properties of this material open up the possibility of using this carbon variant, for example, for storing or converting energy, for catalysis or for separating gases. (Nature, 2023; doi: 10.1038/s41586-022-05532-0 )
Source: Institute for Basic Science
