Cationic π-Stacking Columns of Coronene Molecules with Fully Charged and Charge-Disproportionated States

Electrochemical oxidation of a polycyclic aromatic hydrocarbon, coronene, with D_6h symmetry in the presence of tetrahedral GaCl₄^- anions gave two cation salts, (coronene)(GaCl₄) (1) and (coronene)₅(GaCl₄)₂ (2), with unprecedented charge arrangements. Salt 1 involves π-stacking columns in a zigzag manner, which are composed of the crystallographically equivalent coronene monocations. First-principle calculations revealed that the dimerization of coronene cations gives rise to a band gap opening at the Fermi level, and thus, semiconducting behavior. On the other hand, in salt 2, two crystallographically independent coronene molecules (A and B) form π-stacking columns with an AABB repeating unit, which are flanked by another coronene molecule (C). The crystallographic features, such as interplanar distances and in-plane molecular distortions arising from the Jahn-Teller effect, as well as the first-principle calculations, strongly suggested the emergence of charge disproportionation within the π-stacking columns. As in the case of 1, the calculated band structure exhibits a band gap opening at the Fermi level, which corresponds to the observed semiconducting behavior.