Coupling strategies to enhance single-molecule magnet properties of erbium-cyclooctatetraenyl complexes.

Two different coupling strategies were employed to create Er(III) single-molecule magnets (SMMs) using high blocking temperature mononuclear precursors. The magnetic properties of three lanthanide-COT complexes, [Er(III)2(COT'')3] (1) (COT'' = 1,4-bis(trimethylsilyl)cyclooctatetraenyl dianion) and K2(THF)4[Ln(III)2(COT)4] (Ln = Gd (2), Er (3); THF = tetrahydrofuran, COT = cyclooctatetraenyl dianion), are reported. Both Er(III) 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 [Er(III)2(COT'')3] and K2(THF)4[Er(III)2(COT)4], respectively. Both Er(III) 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 [Er(III)2(COT'')3] over the double-decker analogue is attributed to an additional mechanism of magnetization blocking arising from exchange coupling between Er(III) ions.