Hard Single-Molecule Magnet Behavior and Strong Magnetic Coupling in Radical-Bridged Ln2 and Ln4 Metallocenes

Abstract

Contemporary lifestyle is interwoven with technological achievements which implement the use of permanent magnets. Polynuclear lanthanide single-molecule magnets (SMMs) lack strong magnetic communication which renders the design of high-performing SMMs as 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*2LnIII)2(pyz•-)(THF)2][BPh4]‧Et2O (Ln = Gd (1), Dy (2), Cp* = pentamethycyclopentadienyl; THF = tetrahydrofuran) and tetranuclear [(Cp*2Ln)4(pyz•-)4]‧10THF (Ln = Gd (3), Dy (4)) complexes. Magnetic and computational studies reveal the highest exchange coupling (JGd-pyz = -22.2 cm-1) for a monoanionic radical-bridged system, achieved by two significant 4f–SOMO interactions. This in combination with the significant anisotropy of the DyIII, grant 2 and 4 with slow magnetic relaxation at zero field and open hysteresis loops. A giant coercive field of 65 kOe for 4, renders this complex as the hardest radical-bridged Dy-based SMM.

Keywords: Radical-bridged Ln metallocenes, giant-spin, strong magnetic coupling, giant coercive field, magnetic hardness.