Utilizing a Bulky Ligand to Regulate Orbach, Raman, and QTM Relaxation Processes in a Series of <i>O</i> _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 [DyLCl 2 (THF) 3 ]∙2THF ( 1 , THF = tetrahydrofuran), [DyLCl 2 (THF) 2 ] 2 ∙2Benz ( 2 , Benz = benzene), and [DyL 2 Cl(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.