A Local D 4h Symmetric Dysprosium(III) Single‐Molecule Magnet with an Energy Barrier Exceeding 2000 K**

Three six‐coordinate Dy III single‐molecule magnets (SMMs) [Dy(O t Bu) 2 (L) 4 ] + with local D 4h symmetry are obtained by optimizing the equatorial ligands. One of the compounds with L=4‐phenylpyridine shows an energy barrier ( U eff ) of 2075(11) K, which is the third largest U eff , and the first U eff >2000 K for SMMs with axial‐type symmetry so far. Ab initio analysis indicates that the exceptional uniaxial magnetic anisotropy is deeply related to the axially compressed octahedral geometry. This work provides a new insight into the local D 4h symmetry for high‐performance SMMs.