A Series Three-Dimensional Ln(4)Cr(4) (Ln = Gd, Tb, Er) Heterometallic Cluster-Based Coordination Polymers Containing Interesting Nanotubes Exhibiting High Magnetic Entropy

A series of novel 3D 3d-4f heterometallic cluster-based coordination polymers, [Ln(4)Cr(4)(mu(3)-O)(4)(mu(4)-O)(4)(NA)(8)(H2O)(12)]center dot xH(2)O (Ln = 1-Gd, 2-Tb, 3-Er; HNA = nicotinic acid; x = 13 (1-Gd), 11.33 (2-Tb), 15 (3-Er)), have been successfully synthesized by hydrothermal method using nicotinic acid as bridging ligand. The single-crystal X-ray diffraction (SCXRD) analysis indicated that the basic unit of Ln(4)Cr(4) shows a butterfly-shaped structure. Furthermore, each Ln(4)Cr(4) cluster connects with other four Ln(4)Cr(4) clusters by bridging NA(-) ligands to form a 3D structure containing interesting 1D honeycomb-shaped coordination nanotubes. The variable temperature magnetic susceptibility measurements of compound 1 revealed that the existence of antiferromagnetic (AF) coupling between the metal ions in the Gd4Cr4 clusters. Field-dependent isothermal magnetization studies displayed that the magnetic entropy change (-Delta S-m) value of 1-Gd reached 22.05 J K-1 kg(-1).