Planar Tetranuclear Dy(III) Single-Molecule Magnet and Its Sm(III), Gd(III), and Tb(III) Analogues Encapsulated by Salen-Type and β-Diketonate Ligands

The syntheses, structures, and magnetic properties are reported for four new lanthanide clusters [Sm-4(mu 3OH)(2)L-2(acac)(6)] center dot 4H(2)O (1), [Gd-4(mu(3)-OH)(2)L-2(acac)(6)]center dot 4CH(3)CN (2), and [Ln(4)(mu(3)-OH)(2)L-2(acac)(6)]center dot 2H(2)L center dot 2CH(3)CN (3, Ln = Tb; 4, Ln = Dy) supported by salen-type (H2L = N,N'-bis(salicylidene)-1,2-cyclohexanediamine) and beta-diketonate (acac = acetylacetonate) ligands. The four clusters were confirmed to be essentially isomorphous by infrared spectroscopy and single-crystal X-ray diffraction. Their crystal structures reveal that the salen-type ligand provides a suitable tetradentate coordination pocket (N2O2) to encapsulate lanthanide(III) ions. Moreover, the planar Ln(4) core is bridged by two mu(3)-hydroxide, four phenoxide, and two ketonate oxygen atoms. Magnetic properties of all four compounds have been investigated using dc and ac susceptibility measurements. For 4, the static and dynamic data indicate that the Dy-4 complex exhibits slow relaxation of the magnetization below 5 K associated with single-molecule magnet behavior.