Three [Ln2Co2] cluster-based three-dimensional frameworks: Syntheses, structure, and magnetocaloric effect

Abstract

The heterometallic 3d-4f clusters are being researched, for some time now, as being applicable to molecular magnetism. Especially, the Gd3+-containing multi-nuclear clusters attract wide study attention, on account of the significant magnetocaloric effect (MCE). Herein, three-dimensional (3D) 3d-4f heterometallic clusters are successfully gained via solvothermal conditions, formulated as {[Ln2Co2Na2(L)2(C2O4)2(H2O)4]·(H2O)2}n (abbreviated as Ln2Co2, Ln = Gd for 1; Ln = Tb for 2, and Ln = Dy for 3; L = ethylenediaminetetraacetic acid disodium salt). Structural analysis shows that Ln2Co2 clusters are mainly consistent of the [Ln2Co2Na2(L)2(C2O4)2(H2O)4] metal frames, which are the asymmetric building units. Interestingly, [Ln2Co2Na2(L)2(C2O4)2(H2O)4] metal frames can be constructed by one chain-shaped [Ln2(C2O4)2], one [Na2(H2O)2] dimer, and two [CoL(H2O)] units. Tree building units are connected to constitute 3D structure of Ln2Co2. In addition, the metal ions make Gd2Co2 exhibit the magnetic entropy change (-∆Sm = 31.17 J kg−1 K−1 at 2.0 K and 7.0 T) and ideal -∆Sm value at low-field condition (20.18 J kg−1 K−1 at 2.0 K and 2.0 T).