Hard single-molecule magnet behavior and strong magnetic coupling in pyrazinyl radical-bridged lanthanide metallocenes

Contemporary lifestyle is interwoven with technological achievements that implement the use of permanent magnets. Polynuclear lanthanide single-molecule magnets (SMMs) lack strong magnetic communication, which renders the design of high-performing SMMs an ongoing challenge. To overcome this, incorporation of radical pyrazine (pyz^⋅−) linkers between lanthanides is a compelling approach. Careful tuning of the synthetic conditions led to dinuclear [(Cp∗₂Ln^III)₂(pyz^⋅−)(THF)₂][BPh₄] (Ln = Gd (1), Dy (2); Cp∗ = pentamethylcyclopentadienyl; THF = tetrahydrofuran) and tetranuclear [(Cp∗₂Ln^III)₄(pyz^⋅−)₄]‧10THF (Ln = Gd (3), Dy (4)) complexes. Magnetic and computational studies reveal one of the highest exchange couplings (J_Gd-pyz = −22.2 cm⁻¹) for a radical-bridged system, achieved by two 4f-SOMO interactions. This, combined with the significant anisotropy of the Dy^III, grants 2 and 4 with slow magnetic relaxation at zero field and open hysteresis loops. A giant coercive field of 65 kOe renders 4 as the hardest radical-bridged Dy-based SMM.