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Synthesis of cyclocarbon

Researchers for the first time create a stable ring of only carbon atoms

Carbon atoms can be organized in numerous arrangements. Every carbon atom, when bonded to three other carbon atoms, the resultant element, soft graphite, is formed. Addition of one more bond in graphite results in diamond which is the hardest known substance. Buckyballs are obtained by projecting 60 carbon atoms together in a football shape. But the best efforts of researchers of forming a ring of carbon atoms, where each atom is bonded to just two others results in gaseous carbon ring which dissipates rapidly.

A team of researchers from Oxford University and IBM Research has done an excellent and challenging job by creating a stable carbon ring. The smallest cyclocarbon, it is a ring-shaped carbon compound made from 18 carbon atoms is expected to be thermodynamically stable and its image has been obtained from the modern microscopy methods. The paper has been published in Science journal.

Cyclocarbon seems to act as semiconductor and has possible use in electronics according to the research on its structure. Its high reactivity could be used to develop other carbon allotropes and carbon-abundant elements, surprisingly the property that made cyclocarbons tough to separate in the first place. Scientists started synthesizing triangular cyclocarbon oxide C24O6  which is 18 carbon atoms, bonded to six carbon monoxide molecules, two grouped at each of the three corners of the triangle to achieve this feat.

To ensure an inert surface that keeps the structure stable, the compound was moved to a layer of sodium chloride on a copper plate, cooled in a vacuum chamber to just above absolute zero. After that, the team pulled out the carbon monoxide (CO) molecules off the structure, leaving just the ring of carbon atoms behind using the top of an atomic force microscope. The scientists couldn’t always pull all the CO off without falling the ring structure and they instead produced molecules such as C22O4 and C20O2. The scientists wrote in their paper that they detached all six CO moieties from C24O6, with 13 percent yield, generally resulting in circular molecules.

It is interesting to know that the atoms in the cyclocarbon formed a polyynic structure, with an alternating triple and single bonds answering the question whether one-dimensional carbon or a cumulenic structure, with repeated double bonds, would produce this. This reciprocating structure is expected to produce semiconductivity and also suggests that carbon chains would also be semiconductive. One ring structure can be built at a time. So, Researchers are searching for ways to build multiple cyclocarbons at once and refining the process to produce a more reliable yield.

Researchers can initiate experimenting with applications after the formation of stable cyclocarbons – understanding how the semiconductivity can be used for exploring cyclocarbon properties as a basic building block for even more complex molecules. The researchers wrote that their outcomes ensure direct experimental understandings into the structure of a cyclocarbon and clear the way to form other unachievable carbon-rich molecules by atom management.

Research Paper: https://science.sciencemag.org/content/early/2019/08/14/science.aay1914