•Three three-dimensional (3D) Ln2Co2 clusters were successfully synthesized.•Three clusters are assembled via butterfly-shaped Ln2Co2Na2(L)2(C2O4)2(H2O)4 frames.•Gd2Co2 shows the large -∆Sm values at 2.0 K (31.17 J kg−1 K−1 at 7.0 T; 20.18 J kg−1 K−1 at 2.0 T). 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). Three 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, Tb or Dy). Structural analysis shows that the Ln2Co2 clusters are mainly consistent of the butterfly-shaped Ln2Co2Na2(L)2(C2O4)2(H2O)4 metal frames. In addition, Gd2Co2 exhibits the large MCE (-∆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). Display omitted