Single-molecule magnetism in tetrametallic terbium and dysprosium thiolate cages

Metalation of ethanethiol by [{(Me3Si)2N} 3Ln(μ-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(μ-SEt) 8(μ4-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 Ln4 units in which the lanthanides are bridged by μ-ethanethiolate ligands and the individual lanthanide centers occupy distorted six-coordinate {LnNS5} 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 Ueff = 4.6 cm-1, and a similar analysis on 3 produced Ueff = 46 cm-1. Compounds [Li(thf)4][2] and [Li(thf)4][3] are rare examples of sulfur-ligated SMMs. © 2012 American Chemical Society.