The strategic design and synthesis of two isomeric Cu complexes, [CuL], of asymmetrically dicondensed N 2 0 3 -donor Schiff-base ligands (where H 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 template method. These two complexes have been used as metalloligands for the synthesis of three pairs of Cu-Ln isomeric complexes [CuL(mu-NOrespectively), all of which have been characterized structurally. In all six isomorphous and isostructural complexes, the decacoordinated Le centers and pentacoordinated Cu 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 ener barrier originating from the magnetic anisotropy. The isostructural derivatives with the ion-anisotropic lanthanides Tb and Dy do not show slow magnetic relaxation with or without a direct-current bias field, demonstrating that the magnetic response of the isotropic system Cu occurs through different mechanisms than the rest of the Ln cations.