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]­[Ln4{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.