Synthesis, structures, and magnetic properties of face-sharing heterodinuclear Ni(II)-Ln(III) (Ln = Eu, Gd, Tb, Dy) complexes

Heterodinuclear [(Ni^IIL)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(H_1.5L)]Cl_0.5 (1) with [Ln(hfac)₃(H₂O)₂] and triethylamine in ethanol (1:1:1). All 1·Ln complexes (1·Eu, 1·Gd, 1·Tb, and 1·Dy) crystallized in the triclinic space group P1 (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 L^3- 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 L^3-, 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.