Resonating Valence Bond Ground State in Oxygen-Functionalized Phenalenyl-Based Neutral Radical Molecular Conductors

We report the preparation, crystallization, and solid-state characterization of the first two members
of a new family of spiro-bis(1,9-disubstituted phenalenyl)boron neutral radicals based solely on oxygen
functionalization, and we show that this strategy significantly lowers the electrochemical disproportionation
potentials (ΔE), in comparison with other spiro-bis(1,9-disubstituted phenalenyl)boron salts. In the solid
state, these radicals pack in a continuous array of π−π-stacked phenalenyl units with very short
intermolecular carbon···carbon contacts. These two radicals are among the most highly conducting neutral
organic solids, with room temperature conductivities reaching 0.3 S/cm. Magnetic susceptibility measurements show that the radicals do not exist as isolated free radicals, and there is significant spin−spin
interaction between the molecules in the solid state as expected from the crystal structures and the calculated
band structures; the solid-state properties are best rationalized in terms of the resonating valence bond
model.