Prediction of One-Dimensional Metallicity and π-Band Superconductivity in Rhodizonate Radical Pancakes

Computational exploration of condensed phases made of potassium and carbon monoxide leads to predictions of stable salts composed of cyclic six-membered oxocarbon anions and K⁺ cations, K_n(C₆O₆)_m. The states of reduction in these systems are wide-ranging, with C₆O₆ molecules formally reduced by -2, -3, -3.5, and -6 in semiconducting and metallic phases. Special attention is paid to K₃C₆O₆, in which triply charged radical anions stack closely and equidistantly in one dimension. Equidistant interactions of radicals are exceedingly rare and typically unstable due to spontaneous symmetry breaking, Peierls or Jahn-Teller distortion. The predicted exception of K₃C₆O₆ is explained by inter-ring multicenter bonding, also known as pancake bonding, in combination with large ionic repulsion. This fascinating interplay of interactions facilitates an exceptionally high density of states at the Fermi level and leads us to predictions of metallicity, a negative temperature coefficient of resistivity, and rare π-band superconductivity. These predictions reinvigorate the search for new organic conductors and superconductors using molecular design of metallic salts.