Tetraaza[1.1.1.1]m,p,m,p‑cyclophane Diradical Dications Revisited: Tuning Spin States by Confronted Arenes

Diradical dications of two kinds of alternate-meta-para-linked tetraazacyclophanes in which p-phenylene (1) and 9,10-anthracenylene (2a) moieties are embedded in their macrocyclic backbones were successfully isolated as air-stable salts. The structures of 1²⁺ and 2a²⁺ were elucidated by X-ray analysis, and significantly different types of structural deformation led to different spin density distributions due to the steric demand of the confronted arene moieties. The singlet–triplet energy gaps were determined to be +0.3 kcal mol^–1 (+151 K) and −1.0 kcal mol^–1 (−503 K) by SQUID measurements, indicating the triplet ground state for 1²⁺ and the singlet ground state for 2a²⁺.