The odd-number cyclo[13]carbon and its dimer, cyclo[26]carbon

Molecular rings of carbon atoms (cyclo[ ]carbons, or C ) are excellent benchmarking systems for testing quantum chemical theoretical methods and valuable precursors to other carbon-rich materials. Odd- cyclocarbons, which have been elusive to date, are predicted to be even less stable than even- cyclocarbons. We report the on-surface synthesis of cyclo[13]carbon, C , by manipulation of decachlorofluorene with a scanning probe microscope tip. We elucidated the properties of C by experiment and theoretical modeling. C adopts an open-shell configuration with a triplet ground state and a kinked geometry, which shows different extents of distortion and carbene localization depending on the molecular environment. Moreover, we prepared and characterized the C dimer, cyclo[26]carbon, demonstrating the potential of cyclocarbons and their precursors as building blocks for carbon allotropes.