Room-temperature chemical synthesis of C 2

Diatomic carbon (C 2 ) is historically an elusive chemical species. It has long been believed that the generation of C 2 requires extremely high physical energy, such as an electric carbon arc or multiple photon excitation, and so it has been the general consensus that the inherent nature of C 2 in the ground state is experimentally inaccessible. Here, we present the chemical synthesis of C 2 from a hypervalent alkynyl-λ 3 -iodane in a flask at room temperature or below, providing experimental evidence to support theoretical predictions that C 2 has a singlet biradical character with a quadruple bond, thus settling a long-standing controversy between experimental and theoretical chemists, and that C 2 serves as a molecular element in the bottom-up chemical synthesis of nanocarbons such as graphite, carbon nanotubes, and C 60 .