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

Heterotrinuclear [(Ni^IIL)₂Ln^III(NO ₃)] complexes (where H₃L = l,l,l-tris[(salicylideneamino) methyl]ethane and Ln = Gd (1), Eu (2), Tb (3), and Dy (4)) were prepared by treating [Ni(H_1.5L)]Cl_0.5 with Ln(NO₃) ₃·6H₂O in the presence of triethylamine. Complexes l·2CH₃OH, 3·2CH₃OH, and 4·C ₂H₅OH·0.5H₂O crystallized in the triclinic space group, P1̄ (No. 2), with Z = 2, while 2·CH ₃OH·0.5H₂O crystallized in the tetragonal space group, I4₁/a (No. 88), with Z = 8. All the complexes had very similar structures. Each complex was a doubly face-sharing trinuclear molecule. The Ni^II ion is coordinated by the L^3- ligand in an N ₃O₃ 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 six phenolate oxygen atoms of the two L^3- ligands and two oxygen atoms of NO₃^-. Coordination of the NO₃^- group entails a bending of the Ni⋯Ln⋯Ni angle (ca. 140°). All the complexes involve π-π and CH-π interactions between the neighboring molecules to form a three dimensional structure. Temperature-dependent magnetic susceptibility and field-dependent magnetization measurements on 1 showed a ferromagnetic interaction between the Ni^II and Gd^III atoms. A ferromagnetic interaction was also suggested for Ni^II-Tb ^III (3) and Ni^II-Dy^III (4).