Heterometallic Octanuclear Ni^II₄Ln^III₄ (Ln = Y, Gd, Tb, Dy, Ho, Er) Complexes Containing Ni^II₂Ln^III₂O₄ Distorted Cubane Motifs: Synthesis, Structure, and Magnetic Properties

The reaction of 2-methoxy-6-[{2-(2-hydroxyethylamino)­ethylimino}­methyl] phenol (LH₃) with lanthanide metal salts followed by the addition of nickel acetate allowed isolation of a family of octanuclear complexes, [Ni₄Ln₄(μ₂-OH)₂(μ₃-OH)₄(μ-OOCCH₃)₈(LH₂)₄]·(OH)₂·<i>x</i>H₂O. Single crystal X-ray diffraction studies of these complexes reveal that their central metallic core consists of two tetranuclear [Ni₂Ln₂O₄] cubane subunits fused together by acetate and hydroxide bridges. The magnetic study of these complexes reveals a ferromagnetic interaction between the Ln^III and the Ni^II center. The magnitude of exchange coupling between the Ni^II and Ln^III center, parametrized from the magnetic data of the Gd analogue, gives <i>J</i> = +0.86 cm^–1. The magneto caloric effect, studied for the Ni^II₄Gd^III₄ complex, shows a maximum of magnetic entropy change, −Δ<i>S</i>_m = 22.58 J kg^–1 K^–1 at 3 K for an applied external field of 5 T