Carbon atoms, the favorite "Lego blocks" for chemists, are known for their versatility of forming a large variety of three-dimensional configurations. For decades, scientists have been trying to create a ring-shaped molecule comprising only carbon.
This August, a collaboration between IBM Research–Zürich and Oxford University reported the first success: they have managed to synthesize a cyclo[18]carbon, a circular molecule with 18 carbon atoms, and capture its image using an atomic force microscope.
Carbon is capable of forming many allotropes—chemical entities that are elementally identical but structurally different. For example, inside diamonds, carbon atoms are tetrahedrally bonded, while graphite is made of hexagonal carbon sheets. The Nobel-worthy fullerene (also known as the "buckyball") has 60 carbons forming an icosahedral, soccer ball-like molecular structure.
Throughout the years, many allotropes of carbons have been discovered and/or synthesized, but no one has come close to making a cyclocarbon because the molecule must be highly reactive: all atoms are expected to either share double bonds with each other, or have a triple bond on one side and a single bond on the other. This unusual chemical bond formation makes the hypothetical compound extra hard to synthesize.
Led by Przemyslaw Gawel, a post-doctoral fellow at Oxford, the team of researchers adopted a unique approach for their synthesis route, or more accurately, "subtraction" route. They started with a larger molecule C24O6 (imagine a triangle carbon backbone with a couple of oxygens attached to each tip), and removed a pair of C=O at a time, using the high-vacuum chamber of an atomic-force microscope. After the removal of 6 carbon monoxide molecules, a cyclo[18]carbon emerged.
Their microscopic image showed that all the atoms in the C-18 ring are both triple- and single-bonded, which means that the carbon allotrope should be a semiconductor, like graphene. However, as emphasized by the researchers, it would take a lot more investigations and development to eventually turn this novel molecule into something practically useful like a molecular-sized transistor.
The groundbreaking study was published in the journal Science.
Making and Imaging Cyclocarbon (IBM Research)
Source: Nature News
