Bis-Monophospholyl Dysprosium Cation Showing Magnetic Hysteresis at 48 K

TLDR

Single‑molecule magnets must exhibit longer relaxation times at higher temperatures to be useful for data storage, and bis‑cyclopentadienyl lanthanide sandwich complexes are leading candidates for magnetic memory at liquid‑nitrogen temperatures, though their aromatic‑ring‑mediated relaxation mechanisms remain unclear. The study aims to deepen the understanding of relaxation processes in bis‑C5/C4P sandwich lanthanide SMMs, a necessary step toward achieving higher magnetic blocking temperatures. The authors synthesized a bis‑monophospholyl dysprosium SMM, [Dy(Dtp)₂][Al{OC(CF₃)₃}₄], by reacting an in‑situ prepared [Dy(Dtp)₂(C₃H₅)] complex with [HNEt₃][Al{OC(CF₃)₃}₄]. SQUID magnetometry revealed an effective barrier of 1760 K and magnetic hysteresis up to 48 K, and ab initio calculations showed slower ground‑state transitions than the first dysprosocenium SMM but overall faster relaxation due to compressed electronic energies and resonant vibrational modes.

Abstract

Single-molecule magnets (SMMs) have potential applications in high-density data storage, but magnetic relaxation times at elevated temperatures must be increased to make them practically useful. Bis-cyclopentadienyl lanthanide sandwich complexes have emerged as the leading candidates for SMMs that show magnetic memory at liquid nitrogen temperatures, but the relaxation mechanisms mediated by aromatic C5 rings have not been fully established. Here we synthesize a bis-monophospholyl dysprosium SMM [Dy(Dtp)2][Al{OC(CF3)3}4] (1, Dtp = {P(CtBuCMe)2}) by the treatment of in-situ-prepared "[Dy(Dtp)2(C3H5)]" with [HNEt3][Al{OC(CF3)3}4]. SQUID magnetometry reveals that 1 has an effective barrier to magnetization reversal of 1760 K (1223 cm-1) and magnetic hysteresis up to 48 K. Ab initio calculation of the spin dynamics reveals that transitions out of the ground state are slower in 1 than in the first reported dysprosocenium SMM, [Dy(Cpttt)2][B(C6F5)4] (Cpttt = C5H2tBu3-1,2,4); however, relaxation is faster in 1 overall due to the compression of electronic energies and to vibrational modes being brought on-resonance by the chemical and structural changes introduced by the bis-Dtp framework. With the preparation and analysis of 1, we are thus able to further refine our understanding of relaxation processes operating in bis-C5/C4P sandwich lanthanide SMMs, which is the necessary first step toward rationally achieving higher magnetic blocking temperatures in these systems in the future.