New members of radical bridged Ln2 metallocene single-molecule magnets based on the unsubstituted 1,2,4,5-tetrazine ligand

Abstract

Magnetic coupling plays a critical role in the overall magnetic behaviour of a single-molecule magnet (SMM). Through a careful design strategy that employs the highly delocalized 1,2,4,5-tetrazinyl (tz) radical anion with lanthanide metallocenes, a new family of dinuclear complexes was isolated; [(Cp*₂Ln^III)₂(tz˙⁻)(THF)₂](BPh₄), (Ln = Gd (1), Tb (2), Dy (3); THF = tetrahydrofuran; Cp* = pentamethylcyclopentadienyl). The strong magnetic exchange coupling of J_Gd–rad = −7.2 cm⁻¹ observed in 1, was probed through SQUID magnetometry as well as computational studies. This, combined with the highly anisotropic Tb^III and Dy^III ions in 2 and 3, respectively, leads to zero-field SMM behaviour and slow relaxation of the magnetization through thermally activated processes. These dinuclear complexes serve as ideal models for understanding the magnetic interactions between 4f elements.