Single-Molecule Magnetism
in Tetrametallic Terbium
and Dysprosium Thiolate Cages
- Publication date
- Publisher
Abstract
Metalation of ethanethiol by [{(Me<sub>3</sub>Si)<sub>2</sub>N}<sub>3</sub>Ln(μ-Cl)Li(thf)<sub>3</sub>] (Ln = Gd,
Tb, Dy) in thf
produces the thiolate-bridged tetralanthanide compounds [Li(thf)<sub>4</sub>][Ln<sub>4</sub>{N(SiMe<sub>3</sub>)<sub>2</sub>}<sub>4</sub>(μ-SEt)<sub>8</sub>(μ<sub>4</sub>-SEt)], where Ln = Gd
is [Li(thf)<sub>4</sub>][<b>1</b>], Ln = Tb is [Li(thf)<sub>4</sub>][<b>2</b>], and Ln = Dy is [Li(thf)<sub>4</sub>][<b>3</b>]. Crystallographic studies reveal that the monoanions <b>1</b>–<b>3</b> are essentially isostructural, consisting
of tetrametallic Ln<sub>4</sub> units in which the lanthanides are
bridged by μ-ethanethiolate ligands and the individual lanthanide
centers occupy distorted six-coordinate {LnNS<sub>5</sub>} 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 <b>1</b> were reproduced by a model
that suggests weak antiferromagnetic and ferromagnetic exchange, with
coupling constants of <i>J</i> = −0.09 and +0.04
cm<sup>–1</sup> (−2<i>J</i> formalism). Magnetic
susceptibility measurements in a dynamic (ac) field at various frequencies
on [Li(thf)<sub>4</sub>][<b>2</b>] and [Li(thf)<sub>4</sub>][<b>3</b>], in zero dc field, reveal properties characteristic of
a single-molecule magnet (SMM). Analysis of the out-of-phase magnetic
susceptibility for <b>2</b> in zero applied field yielded a
small anisotropy barrier of <i>U</i><sub>eff</sub> = 4.6
cm<sup>–1</sup>, and a similar analysis on <b>3</b> produced <i>U</i><sub>eff</sub> = 46 cm<sup>–1</sup>. Compounds [Li(thf)<sub>4</sub>][<b>2</b>] and [Li(thf)<sub>4</sub>][<b>3</b>] are rare examples of sulfur-ligated SMMs
