A Stable, Soluble, and Crystalline Supramolecular System with a Triplet Ground State.

A supramolecular complex was constructed by encapsulation of a (3) O2 molecule inside an open-cage C60 derivative. Its single-crystal X-ray diffraction analysis revealed the presence of the (3) O2 at the center of the fullerene cage. The CV measurements suggested that unprecedented dehydrogenation was promoted by the encapsulated (3) O2 after two-electron reduction. The ESR measurements displayed the triplet character as well as the anisotropy of the (3) O2 . Additionally, the SQUID measurements also demonstrated the paramagnetic behavior above 3 K without an antiferromagnetic transition. Upon photoirradiation with visible light, three phosphorescent bands at the NIR region were observed, arising from the exited (1) O2 generated by self-sensitization with the outer cage, whose lifetimes were not affected by the environments. These studies confirmed that the complex is a crystalline triplet system with incompatible "high spin density" but "small interspin interaction" properties.