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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*₂LnIII)₂(tz˙−)(THF)₂](BPh₄), (Ln = Gd (1), Tb (2), Dy (3); THF = tetrahydrofuran; Cp* = pentamethylcyclopentadienyl). The strong magnetic exchange coupling of JGd–rad = −7.2 cm−1 observed in 1, was probed through SQUID magnetometry as well as computational studies. This, combined with the highly anisotropic TbIII and DyIII 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

Inducing magnetic coupling between 4f elements is an ongoing challenge. To overcome this formidable difficulty, we incorporate highly delocalized tetrazinyl radicals, which strongly couple with f-block metallocenes to form discrete tetranuclear complexes. Synthesis, structure, magnetic properties of two tetranuclear [(Cp*₂Ln)₄(tz•)₄]·3(C₆H₆) (Cp* = pentamethylcyclopentadienyl; tz = 1,2,4,5-tetrazine; Ln = Dy, Gd) complexes are reported. An in-depth examination of their magnetic properties through magnetic susceptibility measurements, as well as computational studies, support a highly sought-after radical-induced “giant-spin” model. Strong exchange interactions between the LnIII ions and tz• radicals lead to a strong magnet-like behaviour in this molecular magnet with a giant coercive field of 30 kOe.