The distinguishing effect of the magnetic states of cobalt on the performance of single-molecule magnet behaviors in closely related CoIIIDyIII and CoIIDyIII complexes

Abstract

This report details the synthesis and characterization of heterobimetallic 3d–4f complexes, labeled as 1 and 2, utilizing a new Schiff base ligand derived from the condensation of 2-aminobenzyl alcohol with a methyl-substituted o-vanillin. A comprehensive structural analysis reveals that complex 1 comprises a Co^III–Dy^III assembly, bridged by two alkoxide groups, in which the Co^III center adopts an octahedral geometry, and the Dy^III ion is situated within a DyO₉ coordination sphere. Under nearly identical reaction conditions, an intramolecular nucleophilic attack led to a subtle modification of approximately one-half of the ligand from H₂L to HL′, resulting in the isolation of complex 2. This complex features a Co^II–Dy^III core, bridged by a pivalate ion along with phenoxide groups. To the best of our knowledge, this is a rare instance of dinuclear Co–Dy systems exhibiting variable oxidation states of the cobalt center within a similar ligand framework. Both complexes 1 and 2 exhibit field-induced slow relaxation of magnetization, and theoretical analysis revealed that in complex 1, the principal magnetic axis aligns with the shortest Dy–O bond, underscoring the charge polarization effect exerted by the diamagnetic Co^III ion in tuning the crystal field around the Dy^III ion, thereby influencing its magnetic anisotropy. Conversely, in complex 2, the ferromagnetic interaction between the Co^II and Dy^III ions significantly reduces quantum tunneling of magnetization (QTM). Additionally, we employed quantum theory of atoms in molecules (QT-AIM) calculations to investigate the nature of the coordination bonds in these 3d–4f complexes, which provided insights into the crystal field strength around the Ln^III ions and their subsequent magnetic anisotropy. This study broadens the exploration of Schiff base-derived 3d–4f complexes and their magnetic properties, highlighting the potential for further advancements in this field.