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

Abstract

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.

Supermolecular Aggregates of Mononuclear and Asymmetric Dinuclear Dysprosium Single-Molecule Magnets Assembled by Intermolecular Hydrogen Bonds

“…However, it should be pointed out that lanthanide SMM systems are not only a kind of molecule constructed by coordination bonds but also crystalline molecular aggregates containing magnetic dipole fields. The dissimilarity in aggregate states of lanthanide SMMs might result in variations of dipole interactions, having non-negligible influence on the relaxation behaviors and performance. , For example, Liu et al have synthesized two supramolecular aggregates of mononuclear Dy III -SMMs utilizing hydrogen bonds . They are all assembled from the same anionic Dy III -SMMs, but in the lattice, the magnetic dipoles (adjacent Dy III centers) are arranged in staggered and side-by-side styles, respectively.…”

“…17,18 For example, Liu et al have synthesized two supramolecular aggregates of mononuclear Dy III -SMMs utilizing hydrogen bonds. 19 They are all assembled from the same anionic Dy III -SMMs, but in the lattice, the magnetic dipoles (adjacent Dy III centers) are arranged in staggered and side-by-side styles, respectively. From the former to the latter, the U eff value increases ca.…”