Facile syntheses of pure uranium halides: UCl4, UBr4 and UI4

Article abstract of DOI:10.1039/c7dt00726d

Herein we describe convenient lab scale syntheses of several uranium(iv) halides of high purity by reaction of AlX₃ (X = Cl, Br and I) with UO₂, which is readily available by reduction of uranyl salts like UO₂(NO₃

Full text of DOI:10.1039/c7dt00726d

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Facile syntheses of pure uranium halides:
UCl , UBr and UI †
4
4
4
Cite this: DOI: 10.1039/c7dt00726d
a,b
a,b
Stefan S. Rudel and Florian Kraus
*
Herein we describe convenient lab scale syntheses of several uranium(IV) halides of high purity by reaction
of AlX (X = Cl, Br and I) with UO , which is readily available by reduction of uranyl salts like
UO (NO ·6H O. UCl , UBr , and UI are obtained in the form of aggregates of large single crystals. Their
3
2
2
3
)
2
2
4
4
4
Received 27th February 2017,
Accepted 1st April 2017
identities and purity were checked by powder X-ray diffraction, IR spectroscopy and elemental analysis.
The syntheses introduced here avoid the need for pure metallic uranium and are based on more readily
DOI: 10.1039/c7dt00726d
2
available starting materials, UO , which does not even have to be pure, and the respective aluminium
rsc.li/dalton
halide. Chemical vapor transport (CVT) is applied in situ for purification of the products.
2
2
made accessible in the form of its pyridine adduct. And, very
recently, a facile synthesis of phosphine oxide stabilized UCl
Uranium chemistry has experienced a renaissance over the was presented. Other uranium halides usually require much
Introduction
4
2
3
past 10 years – which is expressed in half of the uranium less convenient conditions for their preparation.
1
,2
related CSD entries added during this period of time.
However in solid state chemistry, or for instance for the
Following the syntheses of famous compounds like uranocene exploration of reactions with weakly coordinating ligands like
8
3
4,5
10
[
U(η -C H ) ], the first actinide carbonyl complex,
or the heavier pnictogen donors, pure and solvent-free starting pro-
8
8 2
6
first dinitrogen complex of an f element, remarkable com- ducts are strongly preferable. Besides this requirement, the
pounds have been synthesized in recent years. Amongst many reactants being oxygen or moisture free, as well as the exclu-
others, apparently simple molecules like the first uranium nitro- sion of air, is essential to avoid unwanted side products,
7
8
3 2 4
syl complex, amides like [U{N(SiMe ) } ], and even a terminal especially in the case of small scale batches. The oxophilicity
9
nitride complex have been discovered. Coordination by heavier of uranium otherwise will inevitably lead to oxygen containing
pnictides has been scarcely explored, yet there are examples of byproducts. In previous experiments on the ammonolysis reac-
phosphino and arsino complexes, as well as phosphini- tions of uranium halides in liquid ammonia, for example, we
1
0,11
denes.
Uranium has been proven to be stable in the encountered oxo-bridged complexes as well as products con-
unusual oxidation state +II while the long accepted existence of taining uranyl cations as side products. These will be pub-
1
2–14
a U(0) complex has been questioned.
Enormous progress lished elsewhere.
1
5
has been made in the fields of electrocatalytic H production,
The halides of uranium(IV) have been known since the very
2
16,17
18
small molecule activation,
and single molecule magnets.
This progress had been spurred by the development of a in 1842 by reacting a mixture of UO
beginnings of uranium chemistry when Péligot produced UCl
4
4
2
2 2
and carbon with Cl .
synthesis of the easily accessible [UI (THF) ], which is largely Thus, a large variety of syntheses have evolved over time.
3
4
used as a readily soluble starting material for coordination Especially in the efforts to create a nuclear weapon (the
1
9
25
chemistry. In 2008 UI
4 2 2
(OEt ) was made accessible by soni- Manhattan project), a lot of knowledge on the basic chem-
2
0
cation of a mixture of I and uranium in Et O. Similar syn- istry of uranium was gathered, most of which was connected
2
2
2
6
thons with improved stability and ligands with weaker donor to the separation, purification and enrichment of uranium.
characteristics – [UI (1,4-dioxane) ], [UCl (1,4-dioxane) ], and The most important lab scale syntheses will be discussed in
UI (1,4-dioxane)1.5] – were introduced in 2011. UCl3 was the following: as UCl was initially used for isotope separation
4
2
4
2
2
1
[
3
4
2
7
in the electromagnetic isotope separation process, a large
variety of methods for its synthesis were investigated. An over-
view of the available reactions is presented in the literature.
The method most commonly used in the laboratory is reflux-
3
ing UO or its hydrate in hexachloropropene at 190 °C.
a
26
Fachbereich Chemie Philipps-Universität Marburg, Hans-Meerwein-Str. 4,
5032 Marburg, Germany. E-mail: florian.kraus@chemie.uni-marburg.de;
3
Fax: +49 6421 28 25669
28
b
WZMW, Hans-Meerwein-Straße, 35032 Marburg, Germany
Purification can be achieved by high vacuum sublimation or
chemical vapor transport.
†
Electronic supplementary information (ESI) available: Infrared spectra of UCl
4
,
2
9,30
UBr , and UI . See DOI: 10.1039/c7dt00726d
4
4
The crystal structure of UCl was
4
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revised by Meyer and Schleid using a novel synthesis from UH
3
excess of AlCl
3
is reacted ensures that the bursting pressure of
3
1
39
and NH Cl by decomposing the intermediate (NH ) UCl .
the ampoule will not be exceeded. The excess of AlCl3 is
4
4 2
6
UBr
of UO
metal, UH , or many other uranium compounds such as UN, UC, that all Al is present in the form of Al Cl and complying with
4
can be prepared by reaction of a red glowing mixture chosen such that a pressure of approximately one bar of Al
and an excess of carbon with bromine. Also, uranium is generated at the transport temperature of 350 °C, assuming
2
Cl
6
32
2
3
2
6
or US
their conditions, refer to ref. 26. Purification of UBr
achieved by sublimation in a stream of dry nitrogen at a chemical vapor transport reaction, see the literature.
2
can be reacted with bromine. For further reactions and the ideal gas law. For calculations of the appropriate amount of
4
may be the transport reagent and for information on the conduction of
30
26,32
7
00–800 °C, but it also leads to partial decomposition to UBr
Least work is reported for the preparation of uranium in the form of green lustrous single crystals of several milli-
iodides. UI easily decomposes into UI and I even at room meters edge length, which can be seen in Fig. 1. The synthesis
3
.
4
With this one batch reaction, highly pure UCl is obtained
4
3
2
temperature, so a sufficiently high pressure of I
ensured during its synthesis. Both, UI and UI , are usually is essentially quantitative. In the source side, only the colorless
synthesized by reaction of uranium metal with iodine at a powder of AlOCl, and the excess of AlCl remain.
2 4
must be and transport of 8 g of UCl takes two to three days. The yield
3
4
3
2
6,33
temperature of 530 °C.
2
The synthesis tolerates partially oxidized UO . Uranyl chlo-
However, uranium metal as a starting material, at least in ride is formed in this case, which is not as volatile as UCl
4
Germany and the EU, is nowadays not easily available, under the applied conditions. For batches larger than about
especially not in a pure state. Also to our knowledge, there is one gram, we recommend shaking the ampoule from time to
no convenient lab scale method for the purification of either time in order to break up the sintered AlOCl/UCl
4
mixture.
uranium metal, uranium oxides or UH . For this reason, we Using a vortex mixer commonly used in biochemical labs
3
were searching for alternative syntheses of uranium halides.
proved to be suitable for this task.
Fig. 2 shows the powder X-ray diffraction pattern of ground
crystals of UCl , obtained by the described method. The
4
refined lattice parameters a = 8.30361(2) and c = 7.48498(2) Å
Results and discussion
Preparation of UCl4
of the tetragonal lattice are in accordance with the results of
31
Meyer and Schleid (a = 8.3018(4), c = 7.4813(6) Å).
When we first tried to synthesize pure UCl , we used the reac-
The ATR IR spectrum (Fig. S1†) shows no intensity from
4
2
8
−1
tion of UO
3
with C
3
Cl
6
.
However, we always observed some 4000 to 400 cm . IR bands of UCl should be observed at 270,
4
−
1
unknown crystalline impurity in the resulting greenish UCl
powder. We achieved even worse results via the carbochlorina- the measured region.
tion of UO , as often, UO or carbon remained in the product.
Also, there is no hint of characteristic bands of common
4
240, 153, and 102 cm , so there is no IR activity expected in
4
0
2
2
In an attempt to purify this product by an endothermic station- impurities like the uranyl cation (asymmetric stretching:
ary chemical vapor transport reaction from 350 to 250 °C ∼911–960 cm−
1 41
)
or hydrolysis products that would be indi-
using AlCl
3
as the transport agent, single crystalline UCl
4
was cated by bands in the hydroxyl stretching region. The purity of
being con- the product is further shown by elemental analysis.
3
0
obtained. Additionally, we found all residual UO
2
verted to UCl , leaving AlOCl as a byproduct in the source side
of the ampoule, according to eqn (1).
In some experiments, a small amount of a white nonvolatile
byproduct covered the wall of the ampoules and also parts of
the product. We assumed this to be AlOCl from a reaction of
4
UO2 þ 2AlCl3 ! UCl4 þ 2AlOCl
ð1Þ
AlCl
Etching of fused silica was reported for transport reactions
at 250 °C, but isolation of the product did not succeed, pre- with AlCl , whereas in this case, kinetic hindrance prevents
3
with the glass wall which is formally shown in eqn (2).
UO
2
had been reported previously to react readily with AlCl
3
3
4
2
sumably because the chemical transport of UCl
4
with AlCl
3
this below 600 °C.
2
6,30,34–37
had not been studied until later.
Using the method presented here, the synthesis and purifi-
cation of UCl can be significantly shortened and simplified:
UO is directly reacted with AlCl according to eqn (1) at a
temperature of 200–250 °C in a flame sealed glass ampoule
regular borosilicate lab glass) under vacuum. The reaction is
SiO2 þ 2AlCl3 ! SiCl4 þ 2AlOCl
ð2Þ
4
2
3
(
carried out until the color of this mixture changes from brown
to green (at room temperature; UCl turns brownish at reaction
4
2
9
temperature).
Four hours of reaction time are usually
sufficient. Subsequently, the ampoule is placed in a tempera-
ture gradient from 350 to 250 °C to perform the endothermal
3
0
chemical transport with an excess of AlCl
pressure of AlCl was reported to be 7.25 bar at 256 °C. Thus,
keeping the temperature at 200–250 °C before all but the thesis method. The height of the picture corresponds to ∼15 mm.
3
.
The vapor
3
8
3
4
Fig. 1 Photography of crystals of UCl , obtained by the described syn-
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Fig. 2 Powder X-ray diffraction pattern of UCl
4
with Le Bail fitting. The calculated reflection positions are represented by strokes below the
p p
observed and calculated powder pattern. The difference curve is plotted underneath. Profile R factors: R = 2.30%, wR = 3.02%, GOF = 1.11.
As the amount was too small to prove this by powder X-ray
diffraction, we reacted borosilicate glass powder with AlCl
the transport temperature. A liquid, assumed to be SiCl4 or
BCl condensed on the glass wall after cooling a spot with a
3
at
3
dry ice pellet. The presence of AlOCl in the solid residue was
shown by powder X-ray diffraction.
Preparation of UBr4
2 3
The reaction of UO with AlBr proceeds in a similar way. The
ideal temperature gradient for the endothermic transport reac-
tion is 350 to 230 °C. However, due to the higher reactivity of
Fig. 3 Photography of UBr
height of the picture corresponds to ∼15 mm.
4
-crystals inside the transport ampoule. The
AlBr
reaction (2)), which only marginally occurs in the case of AlCl3,
becomes strongly noticeable. In many cases, the sink of the refined lattice parameters a = 11.0665(2), b = 8.8128(2), c =
3
, the side reaction with the glass ampoule (analogous to
3
transport ampoule not only contained UBr
mostly in the form 7.0794(2) Å, β = 94.450(2)°, and V = 688.34(3) Å of the mono-
4
of crooked, large orange brown, plate like crystals (Fig. 3), but clinic lattice are in accordance with the results of Taylor and
also white powder of AlOBr.
Wilson (a = 11.04(2), b = 8.76(2), c = 7.04(1) Å, β = 94.05(8)°,
For this reason, we reduced the pressure of excess Al Br
2 6
to and V = 679.1 Å ).
3
43
1
00–200 mbar (calculated as before), which results in a
The ATR IR spectrum (Fig. S2†) shows no intensity from
reduced transport rate, but improved purity of the product. 4000 to 400 cm− . The antisymmetrical U–Br stretching band
1
The transport of 8 g UBr
4
takes about one week. The yield of UBr
4
should be observed at 233 cm− , so there is no IR
1
4
4
varies depending on the side reaction. Practically, the reaction activity to be expected in the measured region. Also, there is
is quantitative. In some cases, the transport reagent is con- no hint of characteristic bands of common impurities like the
−
1 41
sumed by the side reaction, before all UBr
4
is transported from uranyl cation (asymmetric stretching: ∼911–960 cm
)
or
the source to sink. In such cases, the left-overs in the source hydrolysis products that would be indicated by bands in the
side of the ampoule can be collected and recycled in another hydroxyl stretching region.
batch. The synthesis tolerates partially oxidized UO
bromine is then formed as a byproduct. This reduces the
amount of available AlBr
Fig. 4 shows the powder X-ray diffraction pattern of ground vapor transport of uranium with iodine via UI
2
, but
Preparation of UI
Some investigations had been carried out on the chemical
in the iodine
crystals of UBr , produced by the described method. The (van Arkel–de Boer) process. Further interest lay in the field
4
3
.
4
4
5
4
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Fig. 4 Powder X-ray diffraction pattern of UBr
4
with Le Bail fitting. The calculated reflection positions are represented by strokes below the
p p
observed and calculated powder pattern. The difference curve is plotted underneath. Profile R factors: R = 1.33%, wR = 1.82%, GOF = 1.42.
of UI gas discharge lamps. Within this scope, the reaction of
7Al3O4X ! Al5O7X þ AlX3
ðX ¼ Br : T > 580 ꢀ 720 °C; X ¼ I : T , 480 °CÞ
4
ð6Þ
ð7Þ
uranium oxide with AlI at 450 °C was used for the synthesis of
3
UI
vacuum.
4
, which was subsequently isolated by sublimation in a high
4
6–48
3
Al5O7X ! 7Al2O3 þ AlX3
Since UI is prone to decomposition even at room tempera-
4
ðX ¼ Br : T > 720 °C; X ¼ I : T > 540 °CÞ
ture according to eqn (3), sublimation in a vacuum is not the
preferable purification method on a preparative scale. We
added an excess of iodine to the chemical transport reaction
in order to prevent the decomposition.
4 3
As is the case for UBr , the excess of AlI has to be reduced
to prevent impurities from the reaction of AlI with borosilicate
3
glass. The best results were achieved with a pressure of
∼
50 mbar of Al
2 6
I (calculated as before) and a pressure of 1 bar
2UI4 ! 2UI3 þ I2
ð3Þ
of I at 430 °C. A large batch of 8 g of UI thus takes about two
2
4
For the chemical vapor transport of UI
4
, a higher tempera- weeks for transport. Just like the yield of the UBr synthesis,
4
ture of 430 °C is necessary compared to UCl
temperature, the metathesis reaction does not form AlOI, but to side reactions. Residues can be fed back into new batches,
Al I, so the composition of the reactants has to be adapted which results in an overall quantitative yield with respect to
to the stoichiometry shown in eqn (4).
4 4
4
and UBr . At this the yield of UI is also quantitative in principle, but varies due
3 4
O
4
9
uranium. The synthesis tolerates partially oxidized UO , but
2
iodine is then formed as a byproduct. This reduces the
2
UO2 þ 3AlI3 ! 2UI4 þ Al3O4I
ð4Þ
amount of available AlI . AlI can also be produced in situ
3
3
The reactivity of the aluminium oxyhalides (eqn (5)–(7))
might be the reason why former attempts to produce UX from
4
UO and AlX did not result in pure products. These authors
2
3
assumed Al
2
O
3
to be the byproduct of the metathesis reactions
(
(
eqn (1) and (4)) which only is formed at high temperatures
26,49
>540 °C for AlOI; >720 °C for AlOBr and AlOCl).
This
incorrect assumption results in a lack of aluminium halide for
the full conversion of the uranium oxide.
4
AlOX ! Al3O4X þ AlX3
ðX ¼ Br : T ¼ 460 ꢀ 580 °C; X ¼ I : T ¼ 280 °CÞ
ð5Þ Fig. 5 Photography of UI -crystals inside the transport ampoule. The
4
height of the picture corresponds to ∼15 mm.
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Fig. 6 Powder X-ray diffraction pattern of UI
4
with Le Bail fitting. The calculated reflection positions are represented by strokes below the observed
and calculated powder pattern. The difference curve is plotted underneath. Profile R factors: R
p
= 1.04%, wR
p
= 1.33%, GOF = 1.86. Phase #1 =
5
0
51
monoclinic UI
4
,
4
phase #2 = triclinic modification of UI ,
presumably formed upon grinding the monoclinic phase.
from the elements. A photograph of the obtained black, lath-
Conclusions
like UI
Fig. 6 shows the powder X-ray diffraction pattern of coarsely Uranium(IV) halides UX4 (X = Cl, Br and I) were synthesized
ground crystals of UI , produced by the described method. We from easily available uranium dioxide and the respective alu-
observed reflections of two modifications of UI in the diagram. minium halides in a one-pot synthesis in the form of large
4
crystals is shown in Fig. 5.
4
4
The refined lattice parameters of the monoclinic main phase crystalline aggregates in amounts of up to eight grams. This
a = 13.9582(2), b = 8.4708(2), c = 7.5134(2) Å, β = 90.644(2)°, and method avoids the need for uranium metal or uranium
3
V = 888.3 Å are in accordance with the results of Levy and co- hydride as well as complex apparatus.
workers (a = 13.967(6), b = 8.472(4), c = 7.510(3) Å, β = 90.54(5)°,
3
50
and V = 888.7 Å ). The nature of the triclinic second phase
with lattice parameters a = 7.6200(3), b = 7.6706(3), c = 7.5841(3)
Å, α = 96.161(4)°, β = 102.772(3)°, γ = 89.461(3)° and V = 429.8 Å
Experimental section
3
4
is unknown, yet it is listed as a modification of UI in the ICDD All the work was carried out excluding humidity and air under
powder database (a = 7.6120(10), b = 7.6570, c = 7.5770(10), α = an atmosphere of dried and purified argon (5.0, Praxair) using
51
9
6.440(10), β = 102.720(10) and γ = 89.350(10)). Since we only high-vacuum glass lines or a glovebox (MBraun), if not stated
observed the monoclinic phase when we examined single crys- otherwise. Aluminium chloride and bromide (Merck, 98%/Alfa
tals, we assume that this second phase is formed during the Aesar, 98%) were purified by sublimation in vacuo. Iodine was
grinding of the sample, as the chain structure of the main sublimed in vacuo twice, the first time from phosphorous pent-
phase can easily be deformed. The growing intensities of the oxide. Aluminium (Fluka, purum >99%), as well as uranyl
corresponding reflexions upon grinding with additives like nitrate (Riedel de Haën, zur Analyse), was used as supplied.
diamond powder support this conjecture.
All glass vessels were made of borosilicate glass and flame-
The ATR IR spectrum (Fig. S3†) shows no intensity from dried under vacuum before use.
000 to 400 cm− . To our knowledge, no IR spectrum of UI
1
For the syntheses, glass ampoules were used as shown in
4
4
has been reported yet. However, no U–I stretching band is to Fig. 7. These ampoules are equipped with a NS14.5 ground
be expected in the measured region, which is also shown by joint and a constriction at position a for easy flame sealing. A
the measurement. Also, there is no hint of characteristic constriction at position b at one-third of the ampoule length is
bands of common impurities like the uranyl cation (asym- used for facilitated breakup of the ampoule and prevents the
−
1 41
metric stretching: ∼911–960 cm
)
or hydrolysis products mixing of loose crystals in the sink with the residual powder in
that would be indicated by bands in the hydroxyl stretching the source of the transport ampoule. The length of the sealed
region.
ampoule is 16 cm and the outer diameter is 19 mm with
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Fig. 7 Ampoule used for the synthesis and purification of uranium(IV) halides.
–3
1
.3 mm wall thickness, resulting in approximately 34 ml of and flame sealed under vacuum (1 × 10 mbar). The starting
volume. The pressure resistance according to Schott Duranglas products were reacted at 250 °C for 12 hours before the trans-
3
9
GmbH is 10.3 ± 0.8 bar. The ampoules are filled inside a port reaction was conducted with a source temperature of
glove box with a long funnel to prevent the contamination of 350 °C and a sink temperature of 230 °C. 991 mg (2.2 mmol,
the sink and the sealing constraint with nonvolatile sub- 88%) of large brown plate-shaped crystals were extracted after
stances, which is problematic for flame sealing. A stopcock 6 days.
attached to the ground joint allows the transfer to a Schlenk
Large batch. An ampoule was charged with 4.000 g UO2
line. There the content of the ampoule is cooled with liquid (15 mmol) and 8.000 g AlBr (30 mmol) and treated as above.
3
nitrogen and the ampoule is flame sealed under vacuum after After eight days 7.992 g (14 mmol, 97%) UBr
4
were extracted.
pumping off the argon. The batch size is limited due to Typical elemental analysis: U: 42.4%, Br: 57.2% (calculated:
diffusion problems. Batches, larger than ∼1 g of UO2 often U: 42.7%, Br: 57.3%).
lead to reduced yield due to a clogged ampoule. For the larger
batches described in the following, we used ampoules of the Preparation of UI4
same length, but with an outer diameter of 24 mm and a wall
Small batch. An ampoule was charged with 270 mg UO
2
thickness of 2 mm. The reaction, as well as the chemical trans-
port, was performed in standard single zone tubular furnaces,
using their natural temperature gradient. The ampule length
and thus calculation of the amount of the transport reagent
have to be adjusted to the temperature gradient in the respect-
ive furnace.
(
1 mmol), 65 mg Al (2.4 mmol), and 2670 mg I (10.5 mmol)
2
–3
and flame sealed under vacuum (1 × 10 mbar). The starting
products were reacted at 150 °C for 1 hour to prevent a too vig-
orous reaction of Al and I2 followed by 350 °C for 6 hours
before the transport reaction was conducted with a source
temperature of 450 °C and a sink temperature of 300 °C.
6
07 mg (0.8 mmol, 81%) of black lath-like crystals were
Preparation of UO
2
extracted after eight days.
2
6.2 g of UO
2 3 2 2
(NO ) ·6H O (52 mmol) were decomposed to
Large batch. An ampoule was charged with 3.000 g UO
2
1
4.5 g U (17 mmol) by heating to 700 °C in air for 7 h
3 8
O
(
11 mmol), 0.485 g Al (18 mmol) and 7.150 g I (28 mmol) and
2
inside an open fused silica test tube. The black product was
powdered in air and reduced in a stream of hydrogen at 800 °C
for 8 h to obtain 13.8 g (51 mmol, 98%) of phase pure UO .
2
treated as above. After 17 days 7.459 g (10 mmol, 90%) UI
were extracted.
Typical elemental analysis: U: 31.9%, I: 67.9% (calculated:
U: 31.9%, I: 68.1%).
4
Preparation of UCl4
Small batch. An ampoule was charged with 1.080 g UO
4 mmol) and 1.066.7 + 0.177 g AlCl3 (8 mmol + transport
agent) and flame sealed under vacuum (1 × 10 mbar). The
starting products were reacted at 250 °C for 5 hours before the
transport reaction was conducted with a source temperature of
2
Powder X-ray diffraction
(
–
3
Powder X-ray diffraction was conducted at room temperature
with a STOE Stadi MP powder diffractometer using Cu-Kα1
radiation, a Ge monochromator and a Mythen1K detector.
Samples were powdered in agate mortars under a glovebox
atmosphere, and sealed inside 0.3 mm capillaries made out of
borosilicate glass, which were flame-dried in a vacuum before
use.
3
9
50 °C and a sink temperature of 250 °C. 1.476 g (3.9 mmol,
7%) of dark green crystals of UCl were extracted after three
4
days of transport.
Large batch. An ampoule was charged with 6.000 g UO
22 mmol) and 6.270 g AlCl (48 mmol) and treated as above.
After three days 8.336 g (22 mmol, 99%) UCl were extracted.
2
5
2
Phase analysis was carried out with WinXPOW, using the
(
3
5
3
54
ICDD-Database. Le Bail fitting was done in JANA 2006.
4
Typical elemental analysis: U: 62.4%, Cl: 37.0% (calculated:
U: 62.7%, Cl: 37.3%).
IR spectroscopy
IR-spectra were recorded with a Bruker alpha FT-IR-spectro-
meter using a Diamond ATR unit with a resolution of 4 cm
Preparation of UBr4
−1
Small batch. An ampoule was charged with 544 mg UO
2
inside a glovebox. Spectra were processed with the OPUS soft-
5
5
(
2 mmol) and 1075 + 65 mg AlBr (4 mmol + transport agent) ware package.
3
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Elemental analysis
13 H. S. La Pierre, A. Scheurer, F. W. Heinemann,
W. Hieringer and K. Meyer, Angew. Chem., Int. Ed., 2014,
All samples were weighed on a microbalance (Mettler-Toledo
WXT26T) inside a glove box and filled into small PTFE vials.
Water was introduced with a syringe through a tightly fitting
hole in the lid to prevent the loss of material during hydrolysis.
The uranium content was determined by atomic emission
spectroscopy (Agilent 4200 MP-AES) using the 424.166 nm
spectral line. Samples were acidified with sulfuric acid. The
chloride content was determined by potentiometric titration
with silver nitrate (Metrohm 803 Titrando + Mettler Toledo
DM141-SC Silver electrode). Bromide and iodide contents were
determined by titration with silver nitrate solution according
53, 7158, (Angew. Chem., 2014, 126, 7286).
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to the method of Fajans.
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a Heisenberg professorship. We thank Heike Mallinger,
Clemens Pietzonka, and Uwe Linne for conducting the
elemental analyses as well as our master’s students Maik
Assmann and Eike Dornsiepen for doing some of the experi-
mental work.
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