In-situ study of the solid-gas reaction of biCl3 to biOCl via the intermediate hydrate biCl3·H2O

Article abstract of DOI:10.1002/ejic.201000032

At ambient conditions the hydrolysis of BiCl₃ to BiOCl proceeds via the intermediate hydrate: BiCl₃-H₂O as has been revealed by fimo dependent in-situ X-ray powdor diffraclion as well as time; and temperature controlled TG-MS experiments. Below 50 °C the topochemical formation of the hydrate can be reversed by reduciny the H₂O vapour pressure. Above this temperature the hydrate is unstable and the mechanism of the hydrolysis changes. BiCl₃·H₂O crystallizes in the monoclinic space group C2/m with lattice parameters a = 1114.25(1) pm, b = 876.82(1) pm, C = 584.20(1) pm, and β = 106.64(1)°.

Full text of DOI:10.1002/ejic.201000032

SHORT COMMUNICATION
DOI: 10.1002/ejic.201000032
In-situ Study of the Solid-Gas Reaction of BiCl3 to BiOCl via the Intermediate
Hydrate BiCl3·H2O
Aron Wosylus,*[a][‡] Stefan Hoffmann,[a] Marcus Schmidt,[a] and Michael Ruck*[b]
Dedicated to Professor Rüdiger Kniep on the occasion of his 65th birthday
Keywords: Bismuth / Hydrates / Kinetics / Reactive intermediates / Solid-state reactions / Topochemistry
At ambient conditions the hydrolysis of BiCl3 to BiOCl pro- sure. Above this temperature the hydrate is unstable and the
ceeds via the intermediate hydrate BiCl3·H2O as has been
revealed by time dependent in-situ X-ray powder diffraction
as well as time and temperature controlled TG-MS experi-
ments. Below 50 °C the topochemical formation of the
hydrate can be reversed by reducing the H2O vapour pres-
mechanism of the hydrolysis changes. BiCl3·H2O crystallizes
in the monoclinic space group C2/m with lattice parameters
a = 1114.25(1) pm, b = 876.82(1) pm, c = 584.20(1) pm, and β
= 106.64(1)°.
at room temperature. These investigations were compli-
mented with temperature-dependent TG-MS measurements
in humid and in dry inert gas atmosphere.
Introduction
Since more than a century the precipitation of a basic
bismuth salt from an aqueous solution of BiCl3 serve as
a prime example of an inorganic hydrolysis reaction.[1] In
contrast to the nitrates of bismuth, which comprises com-
plex intermediate hydrates,[2] the hydrolysis of BiCl3 was re-
garded to be of “very high simplicity”.[3] On the other hand,
Results and Discussion
According to time-dependent X-ray powder diffraction
the existence of BiCl3 hydrates was discussed[4] and a nu- data, BiCl3 reacts at ambient conditions with air moisture
clear quadrupole resonance study of a commercially avail- to give intermediate BiCl3·H2O, which subsequently decom-
able sample of “BiCl3·H2O” was published.[5] However, the poses to BiOCl. The pattern could be indexed on the basis
proof of existence, the chemical composition and the crystal of a C-centered monoclinic lattice, and the structure was
structure of the hydrate are still missing.
solved using simulated annealing methods.[12] BiCl3·H2O
[6]
The starting material BiCl3 and the hydrolysis product has a layered crystal structure with stacking direction [001]
BiOCl[7] are widely used materials, for example in organo- (Figure 1). The primary coordination of the BiIII cation by
metallic catalyzed reactions,[8] cosmetic industry,[9] pharma- three chloride ions in a distance of about 249 pm resembles
ceutical industry,[10] and battery applications.[11] For these the “molecular” structure of BiCl3 (average Bi–Cl 250 pm).
applications it is of fundament interest to understand the The bond length to the oxygen atom of the water molecule
reaction processes involved including the “simple” hydroly- is 247 pm, i.e. only 15 pm longer than the Bi–O distance in
sis reaction. In order to shed light on this long-standing BiOCl. Three remote chloride ions, which are 306 pm
problem, we performed in-situ X-ray powder diffraction ex- (2ϫ ) and 327 pm apart, complete the sevenfold coordina-
periments, monitoring the reaction of BiCl3 with humid air tion.
There is a topological relation between the crystal struc-
tures of BiCl3 and BiCl3·H2O. For visualization, the com-
[a] Max-Planck-Institut für Chemische Physik fester Stoffe,
Nöthnitzer Str. 40, 01187 Dresden, Germany
[b] Fachrichtung Chemie und Lebensmittelchemie, Technische
Universität Dresden,
parison is restricted to the Bi cations (Figure 2), which in
both cases form inclined primitive lattice complexes. The
monoclinic angle β = 106.6° of BiCl3·H2O is also found as
ε = 106.7° in the cation skeleton of BiCl3. The uptake of
water increases the volume by 26.5ϫ106 pm3 per formula
unit BiCl3.
Although the positions of the hydrogen atoms were not
determined, the O···Cl distances (Ͼ 324 pm) allow specu-
lations about hydrogen bonds. The majority and also the
01062 Dresden, Germany
Fax: +49-351-463-37287
E-mail: michael.ruck@tu-dresden.de
[‡] Current address: Max-Planck-Institut für Kohlenforschung,
Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
E-mail: wosylus@mpi-muelheim.mpg.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000032.
Eur. J. Inorg. Chem. 2010, 1469–1471
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1469

A. Wosylus, S. Hoffmann, M. Schmidt, M. Ruck
SHORT COMMUNICATION
Thermogravimetric (TG) investigations with simulta-
neous analysis of the gas atmosphere by means of mass
spectrometry (MS) were conducted at 27, 40, 50, and 60 °C
(Figure 4). Due to the denser sample in this experimental
setup the reaction rate is about two orders of magnitude
slower than in the X-ray diffraction experiment. The mass
gain of 4.6 wt.-% at 27 °C resp. 3.8 wt.-% at 40 °C during
the purging with a stream of Ar/H2O(g) clearly evidence the
formation of the intermediate hydrate (calcd.: 5.7 wt.-%).
The following linear mass loss monitors the decomposition
to BiOCl (calcd.: 82.6 wt.-%). Especially the second reac-
tion accelerates when the temperature is increased from
27 °C to 40 °C. However, at 50 °C and above, the reaction
mechanism seems to change. Right from the start a de-
pletion of mass down to a plateau close to the expected
mass of BiOCl occurs. X-ray diffraction data of the product
confirm the formation of BiOCl.
Figure 1. Layer in the monoclinic crystal structure of BiCl3·H2O.
Interatomic distances are given in pm.
Figure 2. Lattice complexes of Bi cations in BiCl3 and BiCl3·H2O
(right) demonstrating the topological relation. The indicated angles
are ε = 106.7° and β = 106.6°; distances are given in pm.
Figure 4. Time-dependent mass change during the exposure of
BiCl3 to humid argon gas at different temperatures. The theoretical
wt.-% values of BiCl3·H2O and BiOCl are indicated as dashed grey
shortest of the possible hydrogen bridges reach out for Cl2,
which makes it quite probable that these atoms are elimin- lines.
ated as HCl during the reaction to BiOCl. The remaining
almost linear fragment Cl1–Bi–O can be identified in the
Stopping the reaction at 27 °C at the maximum weight
gain yields a three phase sample with BiCl3·H2O as main
component. A portion of this sample was heated with 10°/
min in dry (!) argon up to 500 °C (Figure 5). A step in TG
with onset at about 50 °C and a simultaneous increasing
ion current at m/z = 18 (H2O+) unambiguously evidence the
decomposition of the hydrate since none of the impurities
have gravimetrical transitions in this range. At about 250 °C
sublimation of BiCl3 starts, which is experimentally indi-
cated by a substantial mass loss and the occurrence of sev-
crystal structure of BiOCl, however, a topological relation
between the structures of BiCl3·H2O and BiOCl is not obvi-
ous.
The kinetics of the two consecutive heterogeneous solid-
gas reactions at room temperature were investigated by
quantitative analysis of the time-dependent powder diffrac-
tion patterns (Figure 3). Within the time interval necessary
for the recording of the diffractogram, BiCl3 reacts with
humid air immediately when exposed to it. According to
the Johnson–Mehl–Avrami equation[13] the induction
period is about 8 min and the half life time of the reaction
is about 45 min. The distinctly slower decomposition of
BiCl3·H2O into BiOCl is completed 99% after 622 min.
+
eral BiClx (x = 1, 2, 3) species in the MS.
Figure 3. Change of volume fractions V of BiCl3, BiCl3·H2O and
BiOCl during the hydrolysis at room temperature according to in-
situ X-ray powder diffraction.
Figure 5. TG-MS measurement of BiCl3·H2O in dry argon atmo-
sphere. The dehydratisation starts at about 50 °C, the sublimation
of BiCl3 at about 250 °C.
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Eur. J. Inorg. Chem. 2010, 1469–1471

Study of the Solid-Gas Reaction of BiCl3 to BiOCl
with adjustable intensities for the background were used. Further
details on the crystal structure investigation may be obtained from
the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leo-
poldshafen, Germany (Fax: +49-7247-808-666; E-mail: crysdata@fiz-
karlsruhe.de), on quoting the depository number CSD-421319.
Switching of the gas atmosphere from Ar/H2O(g) to dry
argon at the maximum of mass increase at 27 °C, i.e.
decreasing the partial pressure of water in the atmosphere,
the reversed reaction from BiCl3·H2O to BiCl3 is observed.
At this temperature the heterogeneous hydrate formation of
BiCl3 is reversible and, with respect to the crystal structures,
almost certainly topochemical.
TG-MS measurements were performed with
a NETZSCH
STA409C Skimmer apparatus situated in an argon-filled glove box.
The sample was spread on a flat corundum sample holder (d =
15 mm). The water partial pressure was achieved by piping argon
through a cartridge filled with moistened charcoal. For the qualita-
tive analysis of the products of the TG-MS measurements the X-
ray diffraction measurements were performed as described above,
but only the first 15 min were taken as representative.
Conclusions
Experimental results support the following reaction
scheme for the hydrolysis of BiCl3: below 50 °C, the topo-
chemical reaction of solid BiCl3 with H2O(g) yields the
monohydrate BiCl3·H2O (see also Scheme 1). Under con-
stant conditions, the subsequent slow and irreversible de-
composition of the hydrate leads to the final products
BiOCl and HCl. Alternatively, the reduction of the partial
pressure of water results in the back transformation of
BiCl3·H2O to BiCl3. At 50 °C and above no intermediate
hydrate is formed and BiOCl is obtained directly. These fin-
dings should be kept in mind evaluating catalytic activities,
battery applications and pharmaceutical usage of BiCl3
when traces of water are present.
Supporting Information (see also the footnote on the first page of
this article): Plots of the Rietveld refinements of the X-ray powder
diffraction data.
Acknowledgments
We thank Dr. H. Borrmann, S. Hückmann, G. Kadner, P. Marasas,
Dr. Yu. Prots, and S. Scharsach for experimental support.
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Scheme 1. Reaction of BiCl3 with H2O(g)
.
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Experimental Section
General: BiCl3 (Alpha Aesar, 99.99%) was purified by sublimation.
In an argon-filled glove box [MBraun, c(H2O) and c(O2) Ͻ 1 ppm]
the powdered samples were placed on a mylar foil covered with
vaseline. Another foil was used to cover the sample. X-ray powder
diffraction data were collected in time intervals of 15 min using a
Huber Guinier G670 diffractometer (Cu-Kα1 radiation,
λ =
154.06 pm, 3°Յ2θՅ100°) at 20 °C in atmosphere (humidity about
65%). The structure was solved and refined with the aid of the
FullProf package.[12] According to Rietveld refinements the struc-
ture crystallizes monoclinic in the space group C2/m, no. 12, a =
1114.25(1) pm, b = 876.82(1) pm, c = 584.20(1) pm, β = 106.64(1)°,
Z = 4. Bi on 4i: 0.2088(2), 0, –0.0081(4), Uiso = 173(6) pm2; Cl1 on
4i: 0.090(1), 0, 0.294(2), Uiso = 850(50) pm2; Cl2 on 8j: 0.3547(7),
0.1879(8), 0.245(1), Uiso = 670(40) pm2; O on 4i: 0.3710(3), 0,
–0.222(8), Uiso = 2400(200) pm2. The positions of the H atoms
could not be determined. For the modeling of the diffraction
pattern Voigt functions for the reflection profiles and 26 points
[9] G. Buxbaum, G. Pfaff, Industrial Inorganic Pigments, 2005
Wiley-VCH, Weinheim, Germany.
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[12] J. Rodriguez-Carvajal, Physica B 1993, 192, 55.
[13] M. Avrami, J. Chem. Phys. 1939, 7, 1103–1112.
Received: October 13, 2009
Published Online: February 24, 2010
Eur. J. Inorg. Chem. 2010, 1469–1471
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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