A Stable Pentagonal Bipyramidal Dy(III) Single-Ion Magnet with a Record Magnetization Reversal Barrier over 1000 K

Single-molecule magnets
(SMMs) with a large spin reversal barrier
have been recognized to exhibit slow magnetic relaxation that can
lead to a magnetic hysteresis loop. Synthesis of highly stable SMMs
with both large energy barriers and significantly slow relaxation
times is challenging. Here, we report two highly stable and neutral
Dy­(III) classical coordination compounds with pentagonal bipyramidal
local geometry that exhibit SMM behavior. Weak intermolecular interactions
in the undiluted single crystals are first observed for mononuclear
lanthanide SMMs by micro-SQUID measurements. The investigation of
magnetic relaxation reveals the thermally activated quantum tunneling
of magnetization through the third excited Kramers doublet, owing
to the increased axial magnetic anisotropy and weaker transverse magnetic
anisotropy. As a result, pronounced magnetic hysteresis loops up to
14 K are observed, and the effective energy barrier (Ueff = 1025 K) for relaxation of magnetization reached
a breakthrough among the SMMs.