Tris(4‐bromophenyl)aminium hexachloridoantimonate (`Magic Blue'): a strong oxidant with low inner‐sphere reorganization

Both the radical cation tris(4‐bromophenyl)aminium hexachloridoantimonate (`Magic Blue'), (C₁₈H₁₂Br₃N)[SbCl₆], (I), and neutral tris(4‐bromophenyl)amine, C₁₈H₁₂Br₃N, (II), show extremely similar three‐bladed propeller structures with planar N atoms. Key geometric features, such as the C—N bond distances and the angles between the planes of the aryl groups and the central NC₃ plane, are identical within experimental uncertainty in the two structures. This contrasts with the significant structural changes observed on oxidation of more electron‐rich triarylamines, where resonance contributes to the stabilization of the radical cation, and suggests that, in general, more strongly oxidizing triarylaminium cations will have lower inner‐sphere reorganization energies than their lower‐potential analogues.