An sp-hybridized molecular carbon allotrope, cyclo[18]carbon

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Science  20 Sep 2019:
Vol. 365, Issue 6459, pp. 1299-1301
DOI: 10.1126/science.aay1914

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An 18-member carbon ring

Carbon's allotropes include molecular species such as C60 and C70 fullerenes. Kaiser et al. now report the assembly of a large carbon ring, cyclo[18]carbon, from organic precursors whose reactivity was controlled by adsorbing them on a sodium chloride surface at 5 kelvin (see the Perspective by Maier). Manipulation, with an atomic force microscope tip, of a cyclocarbon oxide molecule, C24O6, led to elimination of carbon monoxide molecules and formation of the desired all-carbon ring. High-resolution imaging revealed alternating single and triple bonds versus an all-double-bond structure.

Science, this issue p. 1299; see also p. 1245


Carbon allotropes built from rings of two-coordinate atoms, known as cyclo[n]carbons, have fascinated chemists for many years, but until now they could not be isolated or structurally characterized because of their high reactivity. We generated cyclo[18]carbon (C18) using atom manipulation on bilayer NaCl on Cu(111) at 5 kelvin by eliminating carbon monoxide from a cyclocarbon oxide molecule, C24O6. Characterization of cyclo[18]carbon by high-resolution atomic force microscopy revealed a polyynic structure with defined positions of alternating triple and single bonds. The high reactivity of cyclocarbon and cyclocarbon oxides allows covalent coupling between molecules to be induced by atom manipulation, opening an avenue for the synthesis of other carbon allotropes and carbon-rich materials from the coalescence of cyclocarbon molecules.

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