Evolution from linear tetranuclear clusters into one-dimensional chains of Dy(III) single-molecule magnets with an enhanced energy barrier

Reactions of DyCl3 center dot 6H(2)O or Dy2O3 with 2-quinolinecarboxylic acid (H-QLC) yielded two compounds, namely, [Dy-4(QLC)(12)(H2O)(6)]center dot 4H(2)O (1) and [Dy(QLC)(3)(H2O)(2)](n) (2). Compound 1 is a linear tetranuclear structure with one central [Dy-2(QLC)(4)(H2O)(4)] subunit and two terminal [Dy(QLC)(3)(H2O)] subunits linked by bridging QLC(-) ligands. Compound 2 has a one-dimensional (1D) chain wherein the [Dy(QLC) 2] unit formed by two QLC(-) ligands chelating a Dy((III)) ion is connected by the bridging QLC(-) ligands. Compounds 1 and 2 exhibit slow magnetic relaxation behaviour in the absence of a static magnetic field, which is rarely observed in lanthanide-carboxylate compounds. During the structural evolution from a linear Dy-4 cluster of 1 into a 1D chain of 2, the anisotropy energy barrier (U-eff) is enhanced from 45.4(2) to 144.2(1) K. Though the Dy((III)) centers in 1 and 2 all are eight-coordinated with square antiprismatic coordination environments, the higher energy barrier observed for 2 could be the result of a more favorable crystal field for the Dy((III)) ions in 2.