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+.