Symmetry-Supported Magnetic Blocking at 20 K in Pentagonal Bipyramidal Dy(III) Single-Ion Magnets

Single-molecule magnets (SMMs) that
can be trapped in one of the
bistable magnetic states separated by an energy barrier are among
the most promising candidates for high-density information storage,
quantum processing, and spintronics. To date, a considerable series
of achievements have been made. However, the presence of fast quantum
tunnelling of magnetization (QTM) in most SMMs, especially in single-ion
magnets (SIMs), provides a rapid relaxation route and often sets up
a limit for the relaxation time. Here, we pursue the pentagonal bipyramidal
symmetry to suppress the QTM and present pentagonal bipyramidal Dy­(III)
SIMs [Dy­(Cy3PO)2(H2O)5]­Cl3·(Cy3PO)·H2O·EtOH
(1) and [Dy­(Cy3PO)2(H2O)5]­Br3·2­(Cy3PO)·2H2O·2EtOH (2), (Cy3PO = tricyclohexyl
phosphine oxide). Magnetic characterizations reveal their fascinating
SMM properties with high energy barriers as 472(7) K for 1 and 543(2) K for 2, along with a record magnetic hysteresis
temperature up to 20 K for 2. These results, combined
with the ab initio calculations, offer an illuminating
insight into the vast possibility and potential of what the symmetry
rules can achieve in molecular magnetism.