Densely Packed Lanthanide Cubane Based 3D Metal–Organic Frameworks for Efficient Magnetic Refrigeration and Slow Magnetic Relaxation

Two isostructural densely packed squarato-bridged lanthanide-based 3D metal–organic frameworks (MOFs) [Ln5(μ3-OH)5(μ3-O)­(CO3)2(HCO2)2(C4O4)­(H2O)2] [Ln = Gd (1) and Dy (2)] show giant cryogenic magnetic refrigeration (for 1) and slow magnetic relaxation (for 2). The structural analyses reveal the presence of a self-assembled crown-shaped building unit with a cubane-based rectangular moiety that leads to a special array of metal centers in 3D space in the complexes. Magnetic investigations confirm that complex 1 exhibits one of the largest cryogenic magnetocaloric effects among the molecular magnetic refrigerant materials reported so far (−ΔSm = 64.0 J kg–1 K–1 for ΔH = 9 T at 3 K). The cryogenic cooling effect (of 1) is also quite comparable with that of the commercially used magnetic refrigerant gadolinium–gallium garnet, whereas for complex 2, slow relaxation of magnetization was observed below 10 K.