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Illuminating the nature of f-element bonding
with ‘soft’ ligands
Preparation of sulfur and selenium donor complexes advances
actinide science and separations continued
This work opens up a new area of study in actinide chemistry in the preparation
of a series of discrete actinide-chalcogen complexes with particular emphasis
on comparison of isostructural An(III) and Ln(III) complexes of similar
ionic radii to examine for subtle differences in the nature of the bonding.
Initial results support the hypothesis that An(III) ions have a stronger
interaction than Ln(III) ions for ligands bearing softer donor atoms.
Future directions
We are preparing a series of uranium
compounds with nitrogen, sulfur, and selenium donor atoms. The characterization
of these complexes, which contain only
uranium-chalcogen bonds and solvent molecules in the inner coordination
sphere, will greatly enhance our understanding of structural preferences
and bonding types in these
systems. In addition to the characterization techniques described
in this article, future studies will include X-ray photoelectron
spectroscopy to probe the energies of the molecular orbitals involved
in bonding and ligand-metal orbital interactions.
We are also measuring the magnetic properties of the compounds to
better quantify the delocalization of the electrons away from the
actinide ion. As the number of complexes synthesized increases and
more comparisons to lanthanides are drawn, we may see a trend emerge
from which subtle differences between actinide and lanthanide bonding with
soft-donor ligands can be elucidated.
The preparation of An(III) and (IV) complexes with “soft” donor
atom ligands requires inert atmosphere techniques such as the use of
this helium-filled glovebox at the Actinide Research Facility at TA-48.
The glovebox is maintained at a pressure slightly negative relative
to atmospheric pressure, the inlets/outlets are HEPA filtered, and the
antechamber opens directly into a HEPA-filtered fume hood. This configuration
allows transuranic isotopes such as plutonium-239 to be safely handled
and manipulated. Seaborg postdoctoral researcher Andrew Gaunt cogitates
over a reaction (inset).
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A principal component of future research will
focus on extending this chemistry to plutonium(III). Because of
the actinide contraction, trivalent plutonium is more stable, with respect
to oxidation, than trivalent uranium and therefore is attractive to use
for the study and comparison of An(III) and Ln(III) complexes with soft-donor
atom ligands. In addition, very few coordination chemistry studies and structural
characterizations have been conducted for the transuranic elements because
the high specific activity renders their manipulation challenging and requires
specialist radiological facilities. For this reason, the isolation of Pu(III)
complexes with soft donors will not only contribute to a general picture
of 5f element bonding but will also offer a unique insight into the chemistry
of this fascinating, yet inadequately understood, element. next
article... "Tuning plutonium superconductors" |
 The UV–vis
spectrum (above) of U[N(SePPh2)2]3 (2), in benzene solution displays
the 5f-5f and 5f-6d transitions of U(III), which is isolated as a
gray/brown
powder in the solid state (below).
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