Three Series of 3d–4f Heterometallic Polymers Based on [LnCu6] or [Ln6Cu24] Clusters and Formate Bridges: Displaying Significant Magnetocaloric Effect

The syntheses, structures, and characterization of three series of one-dimensional (1D) and three-dimensional (3D) 3d–4f cluster-based polymers with AA (HGly or HAla) and formate as mixed ligands are described. Under the pH values of 6.0 and 5.2, respectively, three 1D undulating chains [Ln = Gd, (1); Tb, (2); and Dy(3)] and two 3D frameworks [Ln = Gd, (4) and Tb, (5)] with a 3-connected pcu-h network were obtained. Both of them use Gly-based heptanuclear trigonal prism [LnCu6] clusters and mononuclear Ln3+ as nodes linked by syn–anti formate ligands. Moreover, three 3D polymers [Ln = Gd, (6); Tb, (7); and Dy (8)] with a 6-connected pcu network were built from Ala-based [Ln6Cu24] clusters and formate bridges. The formate ligand played an important role not only for the construction of the cluster units but also for their further linkage to extended arrays. Magnetic analyses indicate the three Gd3+-containing compounds bear an interesting magnetocaloric effect, and the −ΔSm(T) values are 5.8, 6.0, and 18.8...