2019, Liu, F., Velkos, G., Krylov, D.S., Spree, L., Zalibera, M., Ray, R., Samoylova, N.A., Chen, C.-H., Rosenkranz, M., Schiemenz, S., Ziegs, F., Nenkov, K., Kostanyan, A., Greber, T., Wolter, A.U.B., Richter, M., Büchner, B., Avdoshenko, S.M., Popov, A.A.

Engineering intramolecular exchange interactions between magnetic metal atoms is a ubiquitous strategy for designing molecular magnets. For lanthanides, the localized nature of 4f electrons usually results in weak exchange coupling. Mediating magnetic interactions between lanthanide ions via radical bridges is a fruitful strategy towards stronger coupling. In this work we explore the limiting case when the role of a radical bridge is played by a single unpaired electron. We synthesize an array of air-stable Ln 2 @C 80 (CH 2 Ph) dimetallofullerenes (Ln 2 = Y 2 , Gd 2 , Tb 2 , Dy 2 , Ho 2 , Er 2 , TbY, TbGd) featuring a covalent lanthanide-lanthanide bond. The lanthanide spins are glued together by very strong exchange interactions between 4f moments and a single electron residing on the metal–metal bonding orbital. Tb 2 @C 80 (CH 2 Ph) shows a gigantic coercivity of 8.2 Tesla at 5 K and a high 100-s blocking temperature of magnetization of 25.2 K. The Ln-Ln bonding orbital in Ln 2 @C 80 (CH 2 Ph) is redox active, enabling electrochemical tuning of the magnetism.