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.