Crystal structure and metallization mechanism of the π-radical metal TED

Radical electrons tend to localize on individual molecules, resulting an insulating (Mott-Hubbard) bandgap in the solid state. Herein, we report the crystal structure and intrinsic electronic properties of the first single crystal of a π-radical metal, tetrathiafulvalene-extended dicarboxylate (TED). The electrical conductivity is up to 30,000 S/cm at 2 K and 2,300 S/cm at room temperature. Temperature dependence of resistivity obeys a T3 power-law above T > 100 K, indicating a new type of metal. X-ray crystallographic analysis clarifies a planar TED molecule with a symmetric intramolecular hydrogen bond that is stacked along longitudinal (the a-axis) and transverse (the b-axis) directions. The π-orbitals are distributed to avoid strong local interactions. First-principles electronic calculations reveal the origin of the metallization giving rise to a wide bandwidth exceeding 1eV near the Fermi level. TED demonstrates the effect of two-dimensional stacking of π-orbitals on electron delocalization, where a high carrier mobility of 31.6 cm2/Vs (113K) is achieved.