Strong Magnetic Coupling and Single‐Molecule Magnet Behavior in Tetrazinyl Radical‐Bridged Metallocenes

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Exchange coupling is essential in defining the magnetic behavior of polymetallic lanthanide‐based (Ln III ) single‐molecule magnets (SMMs), where, thanks to the unpaired electron(s), radical ligands show promise as magnetic bridges between the paramagnetic metal centers. Combining high‐performance lanthanide metallocene [Cp*₂Ln] + (Cp* = pentamethylcyclopentadienyl) units with the 3,6‐bis(2‐pyrimidyl)‐1,2,4,5‐tetrazine radical ligand (bmtz •− ) yielded two new radical‐bridged dinuclear lanthanide metallocenes, [(Cp*₂Ln)₂(bmtz •− )](BPh 4 )·Solvent (Ln = Gd ( 1 ), Solvent = THF; Dy ( 2 ), Solvent = toluene). The strong magnetic exchange coupling of J Gd–rad = ‐12.6 cm −1 observed in 1 , was probed via SQUID magnetometry as well as computational studies. This, combined with the highly anisotropic Dy III ions in 2 , leads to zero‐field SMM behavior and slow magnetic relaxation through thermally activated processes.