Actinide chalcogenides
are of interest for fundamental studies
of the behavior of 5f electrons in actinides located in a soft ligand
coordination environment. As actinides exhibit an extremely high affinity
for oxygen, the synthesis of phase-pure actinide chalcogenide materials
free of oxide impurities is a great challenge and, moreover, requires
the availability and use of oxygen-free starting materials. Herein,
we report a new method, the boron–chalcogen mixture (BCM) method,
for the synthesis of phase-pure uranium chalcogenides based on the
use of a boron–chalcogen mixture, where boron functions as
an “oxygen sponge” to remove oxygen from an oxide precursor
and where the elemental chalcogen effects transformation of the oxide
precursor into an oxygen-free chalcogenide reagent. The boron oxide
can be separated from the reaction mixture that is left to react to
form the desired chalcogenide product. Several syntheses are presented
that demonstrate the broad functionality of the technique, and thermodynamic
calculations that show the underlying driving force are discussed.
Specifically, three classes of chalcogenides that include both new
(rare earth uranium sulfides and alkali–thorium thiophosphates)
and previously reported compounds were prepared to validate the approach:
binary uranium and thorium sulfides, oxide to sulfide transformation
in solid-state reactions, and in situ generation of actinide chalcogenides
in flux crystal growth reactions.
To determine the influence of the lanthanide size on the structures and properties of thiophosphates, a thiophosphate series containing different lanthanides was synthesized via high temperature flux crystal growth and their structures and physical properties analyzed and compared. Layered thiohypophosphates NaLnP 2 S 6 (Ln = La, Ce, Pr) and thiopyrophosphates CsLnP 2 S 7 (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, Y) were grown out of an iodide flux using consistent reaction conditions across both series. Under the mildly reducing iodide flux reaction conditions, a rather rare example of phosphorus reduction from the +5 to the +4 oxidation state was observed. Both resultant structure types are based on lanthanide thiophosphate sheets with the alkali cations located between them. Magnetic susceptibility measurements were conducted and revealed Curie−Weiss behavior of the samples, with a Van Vleck contribution in the CsSmP 2 S 7 sample. UV−vis data was found to be in good agreement with the literature, indicating little influence of the sulfide environment on the localized 4f orbitals.
The Boron-Chalcogen Mixture method was used to obtain single crystals of the previously extremely difficult to synthesize lanthanide orthothioborates to investigate their structures and their structurally connected optical behavior, such...
The
effect of lanthanide contraction often results in topological
and symmetry changes in compounds with the same compositions as a
function of lanthanide cation size. Here we report on the first example
of a lanthanide thiophosphate exhibiting a change in the lanthanide
cation environment without any topological or symmetry change. A series
of new lanthanide thiophosphates with mixed alkali cations were obtained
via a flux crystal growth technique using a CsI flux. The obtained
compounds Cs2NaLn(PS4)2 (Ln = La–Nd,
Sm, and Gd–Ho) were grown as large single crystals (∼0.1–1
mm3) and characterized using single-crystal X-ray diffraction
and magnetic susceptibility measurements. As we moved across the series,
the structural studies revealed a change in the lanthanide coordination
environment depending on the identity of the lanthanide. Although
all compounds in the Cs2NaLn(PS4)2 series crystallize in the same space group and have the same Wyckoff
atom positions, a slight change in size between Sm3+ and
Gd3+ causes a subtle change in coordination number from
9 (for Ln = La–Sm) to 8 (for Ln = Gd–Ho), resulting
in two distinct but virtually identical structure types. Ab initio
calculations were performed, and the observed experimental trend was
corroborated computationally. Magnetic measurements performed on the
Cs2NaLn(PS4)2 (Ln = Ce, Pr, Nd, Gd,
and Tb) compounds revealed paramagnetic behavior.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.