Synthesis and Characterization of Two Discrete Ln₁₀ Nanoscopic Ladder‐Type Cages: Magnetic Studies Reveal a Significant Cryogenic Magnetocaloric Effect and Slow Magnetic Relaxation

Abstract

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.

Europium‐Based Dinuclear Triple‐Stranded Helicate vs. Tetranuclear Quadruple‐Stranded Helicate: Effect of Stoichiometric Ratio on the Supramolecular Self‐Assembly

“…However, a new strong band centered at ca. 1637 cm –1 is observed, which confirms the coordination of Eu 3+ to ligand H 2 L 23b,23c. To ensure the phase purity of both the complexes, the bulk‐phase powder X‐ray diffraction patterns (PXRD) of the complexes were measured and found to be in good agreement with the simulated one based on the single‐crystal structure data (Figure S1).…”

Hydrazone-Based Lanthanide Single-Molecule Magnets

“…Furthermore, the application of an 1800 Oe dc field allowed the observation of χ″ peaks, and an effective barrier was given to be 14 K. Remarkably, a Dy 10 compound with a double rectangular grid-like structure (Fig. 5.32b) was constructed through applying ligand H 4 L 25 containing o-vanillin moieties [34]. Here, two Dy 5 subunits, where five Dy ions occupy all coordination pockets within a single ligand, are further linked by three terminally bound ligands in a syn conformation.…”

Coordination‐Cluster‐Based Molecular Magnetic Refrigerants

“…Among Ln ions, the Gd III ion is usually chosen to construct molecular magnetic refrigerants; this may be attributes to the Gd III ion having a large single‐ion spin ( S =7/2) and negligible anisotropy, resulting from the lack of orbital contribution. Furthermore, the coupled interactions between Gd III ions are always weak, which is fit for acquiring a large MCE to work as an ideal molecular magnetic refrigerant (Tables and ) 25,27,39–57…”

“…In the same year, Konar et al also harvested a discrete {Gd 10 } nanoscopic ladder‐type cage (Figure ),45a 31 . Structural analysis of 31 shows an aesthetically interesting self‐assembly of 5 bmsdp 4– and 10 Gd III ions generating a rectangular array.…”