The first phenalenyl-based neutral radical molecular conductor

We report the preparation, crystallization, and solid-state characterizatio n of a spiro-biphenalenyl radical. The crystal structure shows that the rad ical is monomeric in the solid state and without intermolecular contacts th at fall within the van der waals atomic separation. Magnetic susceptibility measurements show Curie behavior (1 spin per molecule) throughout the temp erature 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 t he ground state of the radical corresponds to a degenerate Mott-Hubbard ins ulator. We postulate the presence of delocalized energy bands that are resp onsible for the transport properties but that are separated from the insula ting ground state by an energy gap corresponding to the on-site Coulombic c orrelation 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.