Chemists create smaller carbon rings

Two new carbon allotropes have been developed using atomic force microscopy (AFM). Led by researchers from Dongji University Wei Chu Surface synthesis was used to form rings of 10 and 14 carbon atoms called cyclos.[10]Carbon (c₁₀) and Cyclo[14]Carbon (c₁₄). Although C₁₀ and c₁₄ Studied in the gas phase, this is the first time chemists have created and characterized them on a surface, giving a deeper insight into their bonding.

To do c₁₀ and c₁₄Xu’s group started with fully chlorinated naphthalene (c₁₀ C_l8) and anthracene (C₁₄ Cl₁₀) and used an AFM tip to gradually flush out the chlorines. Removal of chlorines induced the precursor molecules to undergo ring-opening reactions, which ultimately produced 10- and 14-carbon rings (Nature 2023, DOI: 10.1038/s41586-023-06741-x)

Package differs from Cyclo[16]Carbon (c₁₆) and Cyclo[18]Carbon (c₁₈), which used more complex precursors. Oxford University’s Harry L. Andersen, who led the synthesis of those large rings, said in an email that starting with readily available polycyclic aromatic chlorocarbons „opens up the field by facilitating the synthesis of cyclocarbons.”

AFM imaging reveals that C₁₀s and c₁₄The bond characters of are different from their larger all-carbon siblings, C₁₆ and c₁₈. The bonds in the larger rings are polycyclic, meaning they alternate between single and triple bonds. C₁₀The bonds of are cumulenic—basically continuous double bonds. C₁₄ And there are only double bonds, but not all of those bonds are identical, indicating that the molecule is somewhere between cumulenic and polyenic.

Leo Gross of IBM Research-Zurich collaborated with Andersen on the compilations of C.₁₆ and c₁₈He says it is wonderful to see C₁₀ has the cumulenic structure predicted by theory and c₁₄ A transition structure between cumulenic and polyene. „For us experimenters, it’s exciting to see cyclocarbons in different forms,” ​​he says in an email.