A Sodium Sodate as Precursor for Lanthanide Bis(4-R-benzoxazol-2-yl)methanide Single-Molecule Magnets.

Abstract

From the sodium sodate precursor [(Na(thf)6][Na{(4-Me-NCOC6H3)2CH}2] (1) three isostructural dinuclear lanthanide complexes [(μ-Cl)LnIII{(4-MeNCOC6H3)2CH}2]2 with Ln = Gd (2), Dy (3), and Er (4) based on the N,N'-chelating monoanionic bis(4-methylbenzoxazol-2-yl)methanide ligand (titled "Mebox") were synthesized and characterized by X-ray diffraction and magnetic measurements. The sodium precursor 1 was analyzed via X-ray diffraction and diffusion-ordered NMR spectroscopy experiments (DOSY-NMR) in order to investigate its aggregation in solution and the solid state. The sodium analog [(thf)3Na(NCOC6H4)2CH] (1') based on the bis(benzoxazol-2-yl)-methanide ligand (titled "box") was prepared and analyzed for comparison reasons. From the lanthanide derivatives 2-4, the DyIII complex 3 displays slow relaxation of magnetization at zero field, with a relaxation barrier of U = 315.7 cm-1. The coupling strength between the two lanthanide centers was estimated with the GdIII equivalent 2, giving a weak antiferromagnetic coupling of J = -0.035 cm-1.