The first phenalenyl-based neutral radical molecular conductor
by Chi, X.; Itkis, M. E.; Patrick, B. O.; Barclay, T. M.; Reed, R. W.; Oakley, R. T.; Cordes, A. W.; Haddon, R. C.
We report the preparation, crystallization, and solid-state characterization of a spiro-biphenalenyl radical. The crystal structure shows that the radical is monomeric in the solid state and without intermolecular contacts that fall within the van der waals atomic separation. Magnetic susceptibility measurements show Curie behavior (1 spin per molecule) throughout the temperature range 10-400 K, confirming the presence of noninteracting spins in the solid. The compound shows a room-temperature conductivity of sigma = 0.05 S/cm, the highest yet for a neutral radical conductor. We suggest that the ground state of the radical corresponds to a degenerate Mott-Hubbard insulator. We postulate the presence of delocalized energy bands that are responsible for the transport properties but that are separated from the insulating ground state by an energy gap corresponding to the on-site Coulombic correlation energy. Given the presence of isolated molecules in the crystal lattice, the magnitude of the conductivity, the finding of band transport, and the width of the conduction band (0.5 eV) are unprecedented.