Family of Isomeric Cu^II–Ln^III (Ln = Gd, Tb, and Dy) Complexes Presenting Field-Induced Slow Relaxation of Magnetization Only for the Members Containing Gd^III

Abstract

The strategic design and synthesis of two isomeric Cu^II complexes, [CuL^A] and [CuL^B], of asymmetrically dicondensed N₂O₃-donor Schiff-base ligands (where H₂L^A and H₂L^B are <i>N</i>-salicylidene-<i>N</i>'-3-methoxysalicylidenepropane-1,2-diamine and <i>N</i>-3-methoxysalicylidene-<i>N</i>'-salicylidenepropane-1,2-diamine, respectively) have been accomplished via a convenient Cu^II template method. These two complexes have been used as metalloligands for the synthesis of three pairs of Cu-Ln isomeric complexes [CuL(μ-NO₃)Ln(NO₃)₂(H₂O)]·CH₃CN (for complexes <b>1A</b>-<b>3A</b>, L = L^A, and for complexes <b>1B</b>-<b>3B</b>, L = L^B and Ln = Gd, Tb, and Dy, respectively), all of which have been characterized structurally. In all six isomorphous and isostructural complexes, the decacoordinated Ln^III centers and pentacoordinated Cu^II centers possess sphenocorona and square-pyramidal geometries, respectively. The isomeric pair of Cu-Gd compounds shows field-induced slow relaxation of magnetization, although they present the typical isotropic behavior of Gd^III complexes, indicating that slow relaxation is not due to the usual energy barrier originating from the magnetic anisotropy. The isostructural derivatives with the ion-anisotropic lanthanides Tb^III and Dy^III do not show slow magnetic relaxation with or without a direct-current bias field, demonstrating that the magnetic response of the isotropic system Cu^II-Gd^III occurs through different mechanisms than the rest of the Ln cations.