Heterodinuclear [((NiL)-L-II)Ln(III)(hfac)(2)(EtOH)] (H3L = 1,1,1-tris[(salicylideneamino)methyl]ethane; Ln = Eu, Gd, Tb, and Dy; hfac = hexafluoroacetylacetonate) complexes (1 . Ln) were prepared by treating [Ni(H1.5L)]Cl-0.5 (1) with (Ln(hfaC)(3)(H2O)(2)] and triethylamine in ethanol (1:11). All 1 . Ln complexes (1 . Eu, 1 . Gd, 1 . Tb, and 1 . Dy) crystallized in the triclinic space group P (1) over bar (No. 2) with Z = 2 with very similar structures. Each complex is a face-sharing dinuclear molecule. The Ni-II ion is coordinated by the L3- ligand in a N3O3 coordination sphere, and the three phenolate oxygen atoms coordinate to an Ln(III) ion as bridging atoms. The Ln(III) ion is eight-coordinate, with four oxygen atoms of two hfac-'s, three phenolate oxygen atoms of L3-, and one ethanol oxygen atom coordinated. Temperature-dependent magnetic susceptibility and field-dependent magnetization measurements showed a ferromagnetic interaction between Ni-II and Gd-III in 1 . Gd. The Ni-II-Ln(III) magnetic interactions in 1 . Eu, 1 . Tb, and 1 . Dy were evaluated by comparing their magnetic susceptibilities with those of the isostructural Zn-II-Ln(III) complexes, [(ZnL)Ln(hfac)(2)(EtOH)] (2 . Ln) containing a diamagnetic Zn-II ion. A ferromagnetic interaction was indicated in 1 . Tb and 1 . Dy, while the interaction between Ni-II and Eu-III was negligible in 1 . Eu. The magnetic behaviors of 1 . Dy and 2 . Dy were analyzed theoretically to give insight into the sublevel structures of the Dy-III ion and its coupling with Ni-II. Frequency dependence in the ac susceptibility signals was observed in 1 . Dy.