Utilizing a Bulky Ligand to Regulate Orbach, Raman, and QTM Relaxation Processes in a Series of O_h-Type Dy(III)-Based Single-Molecule Magnets

Abstract

Single-molecule magnets (SMMs) retain magnetic information at the molecular scale, enabling their application in future information storage and processing. Employing a low-coordination environment has proven to be an effective strategy for enhancing magnetic anisotropy, thereby increasing their operable temperature. Herein, three octahedral (O_h)-type Dy(III)-based SMMs [DyLCl₂(THF)₃]∙2THF (1, THF = tetrahydrofuran), [DyLCl₂(THF)₂]₂∙2Benz (2, Benz = benzene), and [DyL₂Cl (THF)₃] (3) were successfully synthesized using a bulky ligand, tris(5-m-terphenyl)methanol (HL). This series of complexes, with similar structural characteristics, offers a platform to systematically investigate the regulatory effects of local environments and weak interactions on Orbach, Raman, and quantum tunneling of magnetization (QTM) relaxation processes. For Orbach process, 3 achieves an ultra-high effective energy barrier (U_eff) of 1649 K, which demonstrates the importance of a strong axial crystal field for high U_eff. Raman relaxation is suggested to be suppressed by enhanced phonon energy, possibly arising from the synergy of rigid strong-field axial ligands and weak inter-/intra-molecular interactions. Increasing the geometric symmetry and charge-distribution uniformity helps to slow down the QTM rate, which also rationalizes the anomalous observation that 3 exhibits a higher U_eff yet faster QTM. This study offers insight into strategies for understanding the relaxation mechanisms and structural design principles of Dy(III)-based SMMs.

Keywords

octahedral local configurations / relaxation processes / single-molecule magnets / strong-field ligands

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