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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, HClsal=5‐chlorosalicylaldehyde) wherein a square planar NiII 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 (HClsaldt=4‐chloro‐2‐(1,3‐dithiolan‐2‐yl)phenol). Thanks to the additional ligations of thioacetal onto the NiII 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. [ABSTRACT FROM AUTHOR]

The relaxation time under zero field reflects the memory retention capabilities of single‐molecule magnets (SMMs) when used as storage devices. Intermolecular magnetic dipole interaction is ubiquitous in aggregates of magnetic molecules and can greatly influence relaxation times. However, such interaction is often considered harmful and challenging to manipulate in molecular solids, especially for high‐performance lanthanide single‐ion magnets (SIMs). By an elaborately designed combination of ion pairing and hydrogen bonding, we have synthesized two pseudo‐D5h SIMs with supramolecular arrangements of magnetic dipoles in staggered and side‐by‐side patterns, the latter of which exhibits a 104‐fold slower zero‐field relaxation time at 2 K. Intriguingly, the side‐by‐side complex exhibits a significantly accelerated magnetic relaxation upon diamagnetic dilution, contrary to the general trend observed in the staggered complex. This strongly reveals the presence of aggregation‐induced suppression of quantum tunneling in a side‐by‐side arrangement, which has not been observed in mononuclear SMMs. By leveraging ion‐pairing aggregation and converting to a side‐by‐side pattern, this study successfully demonstrates an approach to transform a harmful intermolecular dipole interaction into a beneficial one, achieving a τQTM of 980 s ranking among the best‐performance SMMs. [ABSTRACT FROM AUTHOR]

Here we reported the deuteration of the metal‐binding equatorial water molecules in a reported HoIII single‐molecule magnet (SMM) with pentagonal‐bipyramidal geometry, from [Ho(CyPh2PO)2(H2O)5]3+ to [Ho(CyPh2PO)2(D2O)5]3+. The hyperfine structures originating from the nuclear spin of 165HoIII can be clearly observed. Moreover, the resulting magnetization dynamics revealed the switch of the relative relaxation rates for the two isotope‐isomorphic complexes—respectively faster/slower at low/high temperature. The noticeable isotope effect arises from not only the paramagnetic metal center but also the diamagnetic ligands, which can be explained by the ab initio calculated tunnel splitting and the involvement of the super‐hyperfine interaction related to the difference in the nuclear spin number of protium (1H, I=1/2) and deuterium (2H, I=1). [ABSTRACT FROM AUTHOR]

Keywords: hyperfine interaction; isotope effect; magnetization dynamics; single-molecule magnets; super-hyperfine interaction EN hyperfine interaction isotope effect magnetization dynamics single-molecule magnets super-hyperfine interaction 27074 27074 1 12/15/21 20211220 NES 211220 B Das Zusammenwirken b von kernspingetriebener Relaxation und den Liganden in Lanthanoid-Einzelmolekülmagneten (SMMs) ist nicht vollständig geklärt. Hyperfine interaction, isotope effect, magnetization dynamics, single-molecule magnets, super-hyperfine interaction Innentitelbild: Magnetization Dynamics on Isotope-Isomorphic Holmium Single-Molecule Magnets (Angew. [Extracted from the article]

Hyperfine interaction, isotope effect, magnetization dynamics, single-molecule magnets, super-hyperfine interaction Inside Cover: Magnetization Dynamics on Isotope-Isomorphic Holmium Single-Molecule Magnets (Angew. Keywords: hyperfine interaction; isotope effect; magnetization dynamics; single-molecule magnets; super-hyperfine interaction EN hyperfine interaction isotope effect magnetization dynamics single-molecule magnets super-hyperfine interaction 26870 26870 1 12/15/21 20211220 NES 211220 B Nuclear-spin driven relaxation b collaborating with the ligands in lanthanide single molecule magnets (SMMs) remains ambiguous. [Extracted from the article]