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 [DyNi 5 (quinha) 5 ( Cl sal) 2 (py) 8 ](ClO 4 ) ⋅ 4H 2 O (H 2 quinha=quinaldichydroxamic acid, H Cl sal=5-chlorosalicylaldehyde) wherein a square planar Ni II is stabilized by chemical stacking. Thioacetal modification was employed via post-synthetic ligand substitutions and yielded [DyNi 5 (quinha) 5 ( Cl saldt) 2 (py) 8 ](ClO 4 ) ⋅ 3H 2 O (H Cl saldt=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.