A Family of Binuclear
Dysprosium(III) Radical Compounds
with Magnetic Relaxation in ON and OFF States
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Abstract
Four binuclear dysprosium compounds incorporating the
radical ligand
2-(4-oxidopyridyl)-4,4,5,5-tetramethylimidazolin-1-oxyl-3-oxide (PyNONIT)
have been successfully synthesized under appropriate conditions. Centrosymmetric
bimetallic Dy<sub>2</sub>O<sub>2</sub> cores in all of the compounds
through double-μ<sub>2</sub>-oxygen atoms of the <i>N</i>-oxide groups are realized in a metal–radical approach for
the first time. Dimers <b>1</b> and <b>2</b>, of the same
formula {[Dy(hfac)<sub>3</sub>(PyNONIT)]<sub>2</sub>}<sub>2</sub> (hfac
= hexafluoroacetylacetonate) but obtained by different methods, which
contain almost identical local symmetry of <i>D</i><sub>4<i>d</i></sub> and Dy–(O)<sub>2</sub>–Dy
bridging fashion, however, display no out-of-phase alternating-current
(ac) signal for <b>1</b> and slow relaxation of the magnetization
for <b>2</b> corresponding to the difference of the crystal
packing mode. The adduct ([Dy(hfac)<sub>3</sub>(PyNONIT)]<sub>2</sub>[Dy<sub>0.5</sub>(hfac)<sub>1.5</sub>(H<sub>2</sub>O)]<sub>2</sub>) (<b>3</b>) consists of two items, the dimer [Dy(hfac)<sub>3</sub>(PyNONIT)]<sub>2</sub> and the monomer [Dy(hfac)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub>], where the symmetry of Dy<sup>III</sup> ion in Dy<sub>2</sub>O<sub>2</sub> decreases to <i>D</i><sub>2<i>d</i></sub>, showing slow relaxation of the magnetization
at lower temperature. Interestingly, a moisture-mediated reversible
solid transformation between <b>1</b> and ([Dy(hfac)<sub>3</sub>(H<sub>2</sub>O)(PyNONIT)]<sub>2</sub>) (<b>4</b>) has been
investigated. Spongelike <b>1</b> can undergo a transition from
eight to nine coordination at room temperature through hydration.
A different coordination field is mostly responsible for no ac signal
noticed for <b>4</b>. The structural diversity of the Dy<sub>2</sub> family provides an opportunity to expand the investigation
on 4f single-molecule magnets. Approaches that the relaxation of the
supramolecular dimer can be tuned to ON and OFF states modulated by
the packing mode and ligand field are presented