4f-Metal Clusters Exhibiting Slow Relaxation of Magnetization: A {Dy7} Complex with An Hourglass-like Metal Topology.

The reaction between Dy(NO3)3∙6H2O and the bulky Schiff base ligand, N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2), in the presence of the organic base NEt3 has led to crystallization and structural, spectroscopic and magnetic characterization of a new heptanuclear [Dy7(OH)6(OMe)2(NO3)1.5(nacb)2(nacbH)6(MeOH)(H2O)2](NO3)1.5 (1) compound in ~40% yield. Complex 1 has a unique hourglass-like metal topology, among all previously reported {Dy7} clusters, comprising two distorted {Dy4(μ3-OH)3(μ3-OMe)}8+ cubanes that share a common metal vertex (Dy2). Peripheral ligation about the metal core is provided by the carboxylate groups of four η1:η1:η1:μ single-deprotonated nacbH- and two η1:η1:η2:η1:μ3 fully-deprotonated nacb2- ligands. Complex 1 is the first structurally characterized 4f-metal complex bearing the chelating/bridging ligand nacbH2 at any protonation level. Magnetic susceptibility studies revealed that 1 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 nacbH2 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.