Impact of paramagnetic CuII and diamagnetic ZnII ions on single-molecule magnetism in heterodinuclear 3d–4f complexes displaying slow relaxation of magnetization

Abstract

The fascinating field of 3d–4f single-molecule magnets (SMMs) has gained considerable attention since the breakthrough work of slow relaxation of magnetization in a Cu^II–Tb^III system. In this report, we present the synthesis of three new isostructural and isomorphous [CuLn(L)(NO₃)₃(H₂O)] complexes (Ln = Gd (1), Tb (2), and Dy (3)), derived from a compartmental Schiff base ligand, H₂L. To further unravel the magnetic dynamics, we also developed two closely related Zn^II–Dy^III complexes, [ZnDy(L)(NO₃)₃(py)] (4) and [ZnDy(L)(OAc)(piv)(NO₃)] (5), with py, OAc, and piv representing pyridine, acetate, and pivalate ions, respectively. These complexes offer an opportunity to explore the influence of paramagnetic Cu^II and diamagnetic Zn^II ions on dynamic magnetic behaviors. Magnetic susceptibility measurements indicate a dominant Stark sublevel depopulation effect for the Dy^III ions in complexes 4 and 5, alongside pronounced ferromagnetic interactions between the Cu^II ion and the respective Ln^III ions in 1–3, as commonly observed for ≥4f⁷ ions. Intriguingly, all synthesized complexes exhibit dynamic magnetic behavior in the presence of an applied magnetic field, indicating that the ferromagnetic influence of Cu^II ions and the charge polarization from the Zn^II ion play crucial roles in shaping their magnetic properties. The most important achievement of this study is the observation of field-induced slow relaxation of magnetization in complex 1, despite the isotropic nature of the Gd^III ion. Given the scarcity of Cu^II–Gd^III systems demonstrating single-molecule magnet behavior, this work adds a remarkable contribution to the expanding field of Gd^III-based SMMs, offering fresh insights and broadening the horizons of future research in this promising area.