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

• Published in: European journal of inorganic chemistry 2014-08, Vol.2014 (24), p.3871-3878
• Main Authors: Yoshida, Yukihiro, Maesato, Mitsuhiko, Kumagai, Yoshihide, Mizuno, Motohiro, Isomura, Kazuhide, Kishida, Hideo, Izumi, Masanari, Kubozono, Yoshihiro, Otsuka, Akihiro, Yamochi, Hideki, Saito, Gunzi, Kirakci, Kaplan, Cordier, Stéphane, Perrin, Christiane
• Format: Article
• Language: English
• Subjects: Anodizing; Cations; Charge transfer; Cluster compounds; Clusters; Conducting materials; Disorders; Electric charge; Magnetic properties; Molybdenum; Radicals; Solid-state structures; Symmetry
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201400119

In this study, we obtained the first cation radical solid of a highly symmetric (D6h) polyaromatic hydrocarbon, coronene, by electrooxidation. The (coronene)3Mo6Cl14 salt, which is formed with an Oh‐symmetric molybdenum cluster unit Mo6Cl142–, has an isotropic cubic structure with Pm$\bar {3}$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 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 A1g 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 Mo6Cl142– 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. The first coronene cation radical salt was electrochemically obtained by combining coronene with a highly‐symmetric Mo6Cl142– cluster unit. The salt has a cubic structure with Pm$\bar {3}$m symmetry, and merohedrally disordered coronenes undergo an in‐plane flipping rotation. The randomly charge‐disproportionated coronenes form an isotropic three‐dimensional π‐conducting network.