A sandwich complex with axial symmetry for harnessing the anisotropy in a prolate erbium(III) ion.

A mononuclear Er(III) sandwich type complex, [Li(DME)3][Er(III)(COT")2], was isolated using 1,4-bis(trimethylsilyl)cyclooctatetraenyl dianion (COT"). Remarkably, this low-symmetry complex exhibits magnet-like behavior of magnetic remanence and coercivity in the hysteresis loops up to 8 K with an energy barrier (Ueff) of 187(1) K, thus making this molecule a unique single-ion magnet.