4f-Metal Clusters Exhibiting Slow Relaxation of Magnetization: A {Dy 7 } Complex with An Hourglass-like Metal Topology.

The reaction between Dy(NO 3 ) 3 ∙6H 2 O and the bulky Schiff base ligand, N -naphthalidene-2-amino-5-chlorobenzoic acid (nacbH 2 ), in the presence of the organic base NEt 3 has led to crystallization and structural, spectroscopic and magnetic characterization of a new heptanuclear [Dy 7 (OH) 6 (OMe) 2 (NO 3 ) 1.5 (nacb) 2 (nacbH) 6 (MeOH)(H 2 O) 2 ](NO 3 ) 1.5 ( 1 ) compound in ~40% yield. Complex 1 has a unique hourglass-like metal topology, among all previously reported {Dy 7 } clusters, comprising two distorted {Dy 4 (μ 3 -OH) 3 (μ 3 -OMe)} 8+ cubanes that share a common metal vertex (Dy2). Peripheral ligation about the metal core is provided by the carboxylate groups of four η 1 :η 1 :η 1 :μ single-deprotonated nacbH - and two η 1 :η 1 :η 2 :η 1 :μ 3 fully-deprotonated nacb 2- ligands. Complex 1 is the first structurally characterized 4f-metal complex bearing the chelating/bridging ligand nacbH 2 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 nacbH 2 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.