4f-Metal Clusters Exhibiting Slow Relaxation of Magnetization: A {Dy} Complex with An Hourglass-like Metal Topology.

The reaction between Dy(NO)∙6HO and the bulky Schiff base ligand, -naphthalidene-2-amino-5-chlorobenzoic acid (nacbH), in the presence of the organic base NEt has led to crystallization and structural, spectroscopic and magnetic characterization of a new heptanuclear [Dy(OH)(OMe)(NO)(nacb)(nacbH)(MeOH)(HO)](NO) () compound in ~40% yield. Complex has a unique hourglass-like metal topology, among all previously reported {Dy} clusters, comprising two distorted {Dy(μ-OH)(μ-OMe)} cubanes that share a common metal vertex (Dy2). Peripheral ligation about the metal core is provided by the carboxylate groups of four η:η:η:μ single-deprotonated nacbH and two η:η:η:η:μ fully-deprotonated nacb ligands. Complex is the first structurally characterized 4f-metal complex bearing the chelating/bridging ligand nacbH at any protonation level. Magnetic susceptibility studies revealed that exhibits slow relaxation of magnetization at a zero external dc field, albeit with a small energy barrier of ~5 K for the magnetization reversal, most likely due to the very fast quantum-tunneling process. The combined results are a promising start to further explore the reactivity of nacbH upon all lanthanide ions and the systematic use of this chelate ligand as a route to new 4f-metal cluster compounds with beautiful structures and interesting magnetic dynamics.