Tetranuclear Lanthanide (III) Complexes Containing Dimeric Subunits: Single-Molecule Magnet Behavior for the Dy4 Analogue

The reaction of the lanthanide(III) salts [Dy(III), Tb(III), and Gd (III)] with a hetero donor chelating ligand N'-(2-hydroxy-3-methoxybenzylidene)-6-(hydroxymethyl) picolinohydrazide (LH3) and pivalic acid (PivH) in the presence of tetra-n-butylammonium hydroxide (TBAH) afforded the tetranuclear Ln(III) coordination compounds, [Ln(4)(LH)(2)(LH2)(2)(mu(2)-eta(1)eta(1)Piv)(2)(eta(1)Piv)(4)]center dot 2CHCl(3) [Ln = Dy(1), Tb(2), and Gd(3)]. The molecular structure of these complexes reveals that the tetranuclear derivatives are composed of two dinuclear subunits which are interconnected through the coordination action of the picolinoyl hydrazine ligand. Within each subunit two different types of Ln(III) ions are present. One of these is eight-coordinate in a distorted triangular dodecahedral geometry while the other is nine-coordinate in a distorted spherical capped square antiprism geometry. Alternating current (ac) susceptibility measurements of complex 1 reveal a frequency- and temperature-dependent two step out-of-phase signals under 1kOe DC field which is characteristic of a single-molecule magnet (SMM) behavior. Analysis of the magnetic data afforded the anisotropic barriers and relaxation times: Delta/k(B) = 62.6 K, tau(0) = 8.7 x 10(-7) s; Delta/k(B) = 26.3 K, tau(0) = 1.26 X 10(-6) s for the slow and fast relaxations respectively.