X-ray crystallography exposes a long-sought structure of unusually-coupled carbon
Carbon is the amazing element that makes up everything from pencil lead to diamonds. Carbon atoms may someday help us create electrified clothing, or possibly doom us to overcooked ecosystems around the globe. The bundle of six protons and neutrons even displays some amazing versatility on a molecular level, apparently defying the few rules about how atoms bond that I still remember from high school chemistry. While carbon atoms usually form bonds with up to four partner atoms, researchers have recently documented an usual molecular structure that allows a single atom to pair off with six partners at once.
This structure was first encountered in experiments in the 1970s. Researchers were working with a compound called hexamethylbenzene, or C12H18. This molecule is composed of a ring of six carbon atoms, each with an addition carbon branching off to the sides. Hydrogen atoms then fill things out, with three attached to each branched carbon atom. The slightly floral-looking arrangement is fairly stable, but researchers working with it were able to pry two electrons atoms out of the arrangement, but at the time it wasn’t clear how the geometry and bonds must have changed in order to accommodate the change in composition.
Positioned as a pyramid
New work at the Free University of Berlin has now shed some light, or rather some x-rays, on how C12H18 was rearranged. Instead of a flat ring of six-carbon atoms, it appears that one carbon moves up to the center of a five-carbon ring, forming a five-sided pyramid shape. This elevated carbon then makes up for the missing electrons by bonding with six partners at once— five from the ring, and then one of the original CH3 branches. The bonds are longer and less stable, to the point where maintaining this version of C12H18 was difficult to do— to remain stable, the whole thing needs to be suspended in a strong acid.
This finding won’t necessarily unlock any new super-strong or conductive materials, but it helps us better understand just how versatile carbon can be.
Source: Carbon can exceed four-bond limit by Laurel Hamers, Science News