Isotropic Three-Dimensional Molecular Conductor Based on the Coronene Radical Cation

In this study, we obtained the first cation radical solid of a highly symmetric (D_6h) polyaromatic hydrocarbon, coronene, by electrooxidation. The (coronene)₃Mo₆Cl₁₄ salt, which is formed with an O_h-symmetric molybdenum cluster unit Mo₆Cl₁₄^2-, has an isotropic cubic structure with Pm3¯m symmetry. The presence of two orientations for the coronene molecules related by an in-plane 90° rotation (merohedral disorder) allows for fourfold symmetry along the <100> direction. The disorder has dynamic features because ²H NMR spectroscopic studies revealed that the coronene molecules undergo an in-plane flipping motion. The observation of two motional sites with significantly different rotational rates (300 Hz and 5 MHz at 103 K) in an approximate 2:1 ratio appears to be consistent with the splitting of a Raman-active A_1g mode, confirming a random charge-disproportionated state instead of a uniform partially-charged state. The slower- and faster-rotating species are assigned to charge-rich and charge-poor coronenes, respectively, with respect to C-H···Cl hydrogen bonds with neighboring Mo₆Cl₁₄^2- cluster units. The electrical conductivity of the salt is rather high but is well-described by a three-dimensional (3D) variable-range hopping mechanism, which is possibly associated with the random charge disproportionation. These results provide a significant step forward in developing an isotropic 3D π-conducting system composed of planar π-conjugated molecules.