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 .

The strategic design and synthesis of two isomeric Cu ^II complexes, [CuL ^A ] and [CuL ^B ], of asymmetrically dicondensed N ₂ O ₃ -donor Schiff-base ligands (where H ₂ L ^A and H ₂ L ^B are N -salicylidene- N '-3-methoxysalicylidenepropane-1,2-diamine and N -3-methoxysalicylidene- N '-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-NO ₃ )Ln(NO ₃ ) ₂ (H ₂ O)]·CH ₃ CN (for complexes 1A - 3A , L = L ^A , and for complexes 1B - 3B , 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.