Spin‐State Control in Dysprosium(III) Metallacrown Magnets via Thioacetal Modification

Integrating controllable spin states into single-molecule magnets (SMMs) enables precise manipulation of magnetic interactions at a molecular level, but remains a synthetic challenge. Herein, we developed a 3d-4f metallacrown (MC) magnet [DyNi₅(quinha)₅(^Clsal)₂(py)₈](ClO₄) ⋅ 4H₂O (H₂quinha=quinaldichydroxamic acid, H^Clsal=5-chlorosalicylaldehyde) wherein a square planar Ni^II is stabilized by chemical stacking. Thioacetal modification was employed via post-synthetic ligand substitutions and yielded [DyNi₅(quinha)₅(^Clsaldt)₂(py)₈](ClO₄) ⋅ 3H₂O (H^Clsaldt=4-chloro-2-(1,3-dithiolan-2-yl)phenol). Thanks to the additional ligations of thioacetal onto the Ni^II site, coordination-induced spin state switching (CISSS) took place with spin state altering from low-spin S=0 to high-spin S=1. The synergy of CISSS effect and magnetic interactions results in distinct energy splitting and magnetic dynamics. Magnetic studies indicate prominent enhancement of reversal barrier from 57 cm^-1 to 423 cm^-1, along with hysteresis opening and an over 200-fold increment in coercive field at 2 K. Ab initio calculations provide deeper insights into the exchange models and rationalize the relaxation/tunnelling pathways. These results demonstrate here provide a fire-new perspective in modulating the magnetization relaxation via the incorporation of controllable spin states and magnetic interactions facilitated by the CISSS approach.