Synthesis and characterization of two discrete Ln₁₀ nanoscopic ladder-type cages: magnetic studies reveal a significant cryogenic magnetocaloric effect and slow magnetic relaxation.

Two unique lanthanide-based cages [Ln10(L)5(μ2-OH)6(H2O)22](Cl)4⋅7 H2O ([Gd10] and [Dy10]) have been synthesized by using a hydrazone-based ligand H4L (H4L=2,6-bis[(3-methoxysalicylidene)hydrazinecarbonyl]pyridine) and LnCl3⋅x H2O. Structural characterization of [Gd10] reveals an aesthetically pleasing self-assembly of five L(4-) and ten Gd(3+) ions forming a 2×[1×5] rectangular array. The ladder-shaped cage consists of three "rungs" and two "rails" that are occupied by five ligands. Six out of ten gadolinium centers act as rung locks. Further analysis revealed that three chloride ions are encapsulated inside each discrete [Gd10] molecule through hydrogen bonding and other noncovalent interactions. Both the complexes ([Gd10] and [Dy10]) were characterized by powder X-ray diffraction and thermogravimetric analysis, which shows that they are isostructural in nature. Magnetic investigations reveal that [Gd10] is a good candidate for magnetic refrigeration with a significant entropy change (-ΔS(m)) of 37.4 J kg(-1) K(-1) for an applied field of 7 T and at 3 K. Whereas [Dy10] shows single-molecule-magnet-like behavior.