Radical‐Bridged Ln₄ Metallocene Complexes with Strong Magnetic Coupling and a Large Coercive Field

Abstract

Inducing magnetic coupling between 4f elements is an ongoing challenge.T oo vercome this formidable difficulty, we incorporate highly delocalized tetrazinyl radicals,w hich strongly couple with f-blockm etallocenes to form discrete tetranuclear complexes.S ynthesis,s tructure,a nd magnetic properties of two tetranuclear [(Cp* 2 Ln) 4 (tzC) 4 ]•3(C 6 H 6 ) (Cp* = pentamethylcyclopentadienyl;t z = 1,2,4,5-tetrazine; Ln = Dy,G d) complexes are reported. An in-depth examination of their magnetic properties through magnetic susceptibility measurements as well as computational studies support ah ighly sought-after radical-induced "giant-spin" model. Strong exchange interactions between the Ln III ions and tzC radicals lead to as trong magnet-like behaviour in this molecular magnet with alarge coercive field of 30 kOe.

New members of radical bridged Ln2metallocene single-molecule magnets based on the unsubstituted 1,2,4,5-tetrazine ligand

“…Ln-N tz : 2.601(4) Å). 20 These Ln-N tz bond distances are also similar to those observed for bipyrimidyl radical-bridged complexes (2.424(6)-2.440(6) Å), 18,25 but, as expected, they are larger upon comparison to the N 2…”

“…The U eff that were obtained for 2 and 3 (Table S8 †) are higher compared to other tetrazine-based radical bridged lanthanide systems 15,16,27 but are modest in comparison to the "Ln 4 " tetranuclear tz • -bridged system 20 or other radical bridged systems. 14,18,19 This is probably attributed to the presence of the coordinated THF.…”

“…Such N-N bond elongations have been previously reported for tz •− -based ligands. 20,27 Inspection of the packing arrangement of all three compounds reveals that these dimers are in relatively close proximity (Fig. S3 †).…”

“…2, insert). 20,23,25 In other words, the antiferromagnetic metal-radical coupling leads to a ferrimagnetic ground state where the magnetic moments of the lanthanides are aligned in the same direction, leading to an increase in the susceptibility at low temperatures. Bellow this temperature, the χT value decreases slowly for 1 and rapidly for 2 and 3 with the temperature drop until it reaches a value of 24.02 cm 3 K mol −1 , 29.15 cm 3 K mol −1 and 40.93 cm 3 K mol −1 at 1.8 K, respectively.…”

“…Recently, we demonstrated that the incorporation of the 1,2,4,5-tetrazine radical anion (tz •− ) into tetranuclear "Ln 4 " metallocenes ([(Cp* 2 Ln) 4 (tz •− ) 4 ]•3(C 6 H 6 ), where Ln = Dy and Gd; Cp* = pentamethylcyclopentadienyl), can lead to strong magnetic coupling and significant magnetic hardness (H c = 3 T). 20 Apart from the synthetic advances over the N 2…”