Hydrazone-Ligand-Based Homodinuclear Lanthanide Complexes: Synthesis, Structure, and Magnetism

A series of dinuclear lanthanide complexes, [Dy-2(LH)(2)(mu(2)-Piv-O-2,O)(2)(NO3-O-2,O)(2)] (1), [Tb-2(LH)(2)(mu(2)-Piv-O-2,O)(2)(NO3-O-2,O)(2)] (2), [Gd-2(LH)(2)(mu(2)-Piv-O-2,O)(2)(NO3-O-2,O)(2)] (3), and [Ho-2(LH)(2)(mu(2)-Piv-O-2,O)(2)(NO3-O-2,O)(2)] (4) have been synthesized by the reaction of Ln(NO3)(3)nH(2)O with the multidentate hydrazone-based Schiff-base ligand, N-(2-hydroxy-3-methoxybenzylidene)acetohydrazide (LH2) in the presence of pivalic acid. X-ray crystallography data reveals that 1-4 are isostructural, neutral, and contain two mono-deprotonated ligands, two pivalates, and two chelated nitrates. Within the dinuclear assembly, the two lanthanides are bridged by two phenolate and two pivalate oxygens. Each of the two lanthanide ions is nine-coordinated and possesses a distorted monocapped square-antiprism geometry. Detailed magnetochemical analysis revealed the presence of weak antiferromagnetic coupling at low temperature for all complexes. The Dy-III analogue displayed SMM behavior in the absence of a dc field with two relaxation domains in which the thermally activated domain exhibits an energy barrier of 40 K and relaxation time of 6.5x10(-5) s.