Giant coercivity and high magnetic blocking temperatures for N2 3− radical-bridged dilanthanide complexes upon ligand dissociation

Increasing the operating temperatures of single-molecule magnets—molecules that can retain magnetic polarization in the absence of an applied field—has potential implications toward information storage and computing, and may also inform the development of new bulk magnets. Progress toward these goals relies upon the development of synthetic chemistry enabling enhancement of the thermal barrier to reversal of the magnetic moment, while suppressing alternative relaxation processes. Herein, we show that pairing the axial magnetic anisotropy enforced by tetramethylcyclopentadienyl (CpMe4H) capping ligands with strong magnetic exchange coupling provided by an N2 3− radical bridging ligand results in a series of dilanthanide complexes exhibiting exceptionally large magnetic hysteresis loops that persist to high temperatures. Significantly, reducing the coordination number of the metal centers appears to increase axial magnetic anisotropy, giving rise to larger magnetic relaxation barriers and 100-s magnetic blocking temperatures of up to 20 K, as observed for the complex [K(crypt-222)][(CpMe4H 2Tb)2(μ− $${\rm{N}}_2^ \cdot$$ N 2 ⋅ )].