Effects of Chirality and Counter Anions on the Structures and Solid‐State Properties of Radical Cation Salts of Benzo[ b ]Phenoxazine‐Based Double Heterohelicene

Abstract In this study, we prepared stable radical cation salts of racemic and enantiopure double hetero[5]helicene ( 1 ), consisting of two benzo[ b ]phenoxazine ( BPO ) molecules, using two different counter anions (SbCl 6 − and NTf 2 − ). The effects of chirality and counter anions on the packing structure and solid‐state electronic properties were investigated. X‐ray single‐crystal analysis revealed that the SbCl 6 − anion was positioned above the midpoint of 1 ·+ in both the racemic and enantiopure crystals of 1 ·+ · SbCl 6 − . This alignment resulted from the matching between the curvature of 1 ·+ and the spherical shape of the SbCl 6 − anion, preventing the formation of continuous π–π interactions among 1 ·+ . In contrast, 1D π–stacked columns of 1 ·+ were present in both the racemic and enantiopure 1 ·+ · NTf 2 − crystals, as the NTf 2 − anions encased the π‐stacked columns of 1 ·+ . All radical cation salts exhibited distinct melting points, and the enantiopure salts of 1 ·+ · NTf 2 − had notably low melting points of 393–395 K, which was 142 K lower than that of rac ‐ 1 ·+ · NTf 2 − . ESR and SQUID measurements of the enantiopure 1 ·+ · NTf 2 − crystals revealed significant changes in their magnetic properties upon crystal melting. In contrast, rac ‐ 1 ·+ · NTf 2 − displayed an unexpected crystal–crystal phase transition near room temperature, accompanied by a thermal hysteresis loop in its magnetic susceptibility.