Switchable Multiple Spin States in the Kondo description of Doped Molecular Magnets

Air-stable redox-active nanomagnets with lanthanide spins radical-bridged by a metal-metal bond

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 Ln₂@C₈₀(CH₂Ph) dimetallofullerenes (Ln₂ = Y₂, Gd₂, Tb₂, Dy₂, Ho₂, Er₂, 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. Tb₂@C₈₀(CH₂Ph) 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 Ln₂@C₈₀(CH₂Ph) is redox active, enabling electrochemical tuning of the magnetism.

Dilanthanide complexes that possess radical bridges exhibit enhanced magnetic exchange coupling, affording molecular magnets with high blocking temperatures. Here, the authors explore a series of dilanthanide-encapsulated fullerenes where the radical bridge is taken to its limit and the role is played by a single unpaired electron.