Aggregation-induced suppression of quantum tunneling by manipulating intermolecular arrangements of magnetic dipoles

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 tau QTM of 980 s ranking among the best-performance SMMs. By utilizing adaptive supramolecular interaction to induce aggregation of ion pairs, the arrangement of magnetic dipoles can be transformed from a staggered to a side-by-side arrangement, resulting in a significant suppression of quantum tunneling under zero external field. image