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

TL;DR

This paper reports the successful synthesis and atomic-scale characterization of cyclo[18]carbon, a highly reactive carbon allotrope, using atom manipulation techniques at low temperature, revealing its polyynic structure and potential for new carbon materials.

Contribution

It is the first to isolate and structurally characterize cyclo[18]carbon, demonstrating atom manipulation methods and covalent coupling to explore new carbon allotropes.

Findings

Cyclo[18]carbon has a polyynic structure with alternating triple and single bonds.

Atom manipulation can induce covalent coupling between cyclo[18]carbon molecules.

The method opens pathways for synthesizing novel carbon-rich materials.

Abstract

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, due to 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.