Coupling Strategies to Enhance Single-Molecule Magnet Properties of Erbium–Cyclooctatetraenyl Complexes

Two different coupling strategies
were employed to create ErIII single-molecule magnets (SMMs)
using high blocking temperature
mononuclear precursors. The magnetic properties of three lanthanide–COT
complexes, [ErIII2(COT′′)3] (1) (COT′′ = 1,4-bis­(trimethylsilyl)­cyclooctatetraenyl
dianion) and K2(THF)4[LnIII2(COT)4] (Ln = Gd (2), Er (3);
THF = tetrahydrofuran, COT = cyclooctatetraenyl dianion), are reported.
Both ErIII complexes behave as SMMs and exhibit magnetic
hysteresis at 12 K in solid state. In solution compound 1 exhibits hysteresis up to 14 K. Ac susceptibility data indicates
a 100 s blocking temperature of 12.5 and 12.9 K for [ErIII2(COT′′)3] and K2(THF)4[ErIII2(COT)4], respectively.
Both ErIII dimers display enhanced SMM properties over
their mononuclear analogues due to their linear structure and strictly
axial anisotropy. A 4 K increase in the magnetic blocking temperature
of [ErIII2(COT′′)3]
over the double-decker analogue is attributed to an additional mechanism
of magnetization blocking arising from exchange coupling between ErIII ions.