Single-Molecule Magnetism in Tetrametallic Terbium and Dysprosium Thiolate Cages

Metalation of ethanethiol by [{(Me3Si)(2)N}(3)Ln(mu-Cl)Li(thf)(3)] (Ln = Gd, Tb, Dy) in thf produces the thiolate-bridged tetralanthanide compounds [Li(thf)(4)][Ln(4){N(SiMe3)(2)}(4)(mu-SEt)(8)(mu(4)-SEt)], where Ln = Gd is [Li(thf)(4)][1], Ln = Tb is [Li(thf)(4)][2], and Ln = Dy is [Li(thf)(4)][3]. Crystallographic studies reveal that the monoanions 1-3 are essentially isostructural, consisting of tetrametallic Ln(4) units in which the lanthanides are bridged by mu-ethanethiolate ligands and the individual lanthanide centers occupy distorted six-coordinate {LnNS(5)} coordination environments. The magnetic susceptibility properties of all three compounds were measured in a static (dc) field of 1000 G: the data for the gadolinium anion 1 were reproduced by a model that suggests weak antiferromagnetic and ferromagnetic exchange, with coupling constants of J = -0.09 and +0.04 cm(-1) (-2J formalism). Magnetic susceptibility measurements in a dynamic (ac) field at various frequencies on [Li(thf)(4)][2] and [Li(thf)(4)][3], in zero dc field, reveal properties characteristic of a single-molecule magnet (SMM). Analysis of the out-of-phase magnetic susceptibility for 2 in zero applied field yielded a small anisotropy barrier of U-eff = 4.6 cm(-1), and a similar analysis on 3 produced U-eff = 46 cm(-1). Compounds [Li(thf)(4)][2] and [Li(thf)(4)] [3] are rare examples of sulfur-ligated SMMs.