Heterometallic Octanuclear NiII4LnIII4 (Ln = Y, Gd, Tb, Dy, Ho, Er) Complexes Containing NiII2LnIII2O4 Distorted Cubane Motifs: Synthesis, Structure, and Magnetic Properties

The reaction of 2-methoxy-6-[{2-(2-hydroxyethylamino)ethylimino}methyl] phenol (LH 3 ) with lanthanide metal salts followed by the addition of nickel acetate allowed isolation of a family of octanuclear complexes, [Ni 4 Ln 4 (μ 2 -OH) 2 (μ 3 -OH) 4 (μ-OOCCH 3 ) 8 (LH 2 ) 4 ]·(OH) 2 · x H 2 O. Single crystal X-ray diffraction studies of these complexes reveal that their central metallic core consists of two tetranuclear [Ni 2 Ln 2 O 4 ] 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 J = +0.86 cm -1 . The magneto caloric effect, studied for the Ni II 4 Gd III 4 complex, shows a maximum of magnetic entropy change, -Δ S m = 22.58 J kg -1 K -1 at 3 K for an applied external field of 5 T.