On Approaching the Limit of Molecular Magnetic Anisotropy: A Near-Perfect Pentagonal Bipyramidal Dysprosium(III) Single-Molecule Magnet.

We report a monometallic dysprosium complex, [Dy(Ot Bu)2 (py)5 ][BPh4 ] (5), that shows the largest effective energy barrier to magnetic relaxation of Ueff =1815(1) K. The massive magnetic anisotropy is due to bis-trans-disposed tert-butoxide ligands with weak equatorial pyridine donors, approaching proposed schemes for high-temperature single-molecule magnets (SMMs). The blocking temperature, TB  , is 14 K, defined by zero-field-cooled magnetization experiments, and is the largest for any monometallic complex and equal with the current record for [Tb2 N2 {N(SiMe3 )2 }4 (THF)2 ].