X-ray diffraction study of CsZn2Br5

Article abstract of DOI:10.1134/S0036023609060047

CsZn₂Br₅ crystals are studied by X-ray diffraction. The compound crystallizes in the monoclinic system with the unit cell parameters a = 6.8880(12) ?, b = 10.4703(19) ?, c = 6.5197(9) ?, β = 108.25°, V = 446.55 ?³, ρ_c

Full text of DOI:10.1134/S0036023609060047

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2009, Vol. 54, No. 6, pp. 840–841. © Pleiades Publishing, Inc., 2009.
Original Russian Text © I.Ya. Zaitseva, I.S. Kovaleva, V.A. Fedorov, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 6, pp. 905–906.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
X-Ray Diffraction Study of CsZn2Br5
I. Ya. Zaitseva, I. S. Kovaleva, and V. A. Fedorov
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
Received April 17, 2008
Abstract—CsZn2Br5 crystals are studied by X-ray diffraction. The compound crystallizes in the monoclinic
system with the unit cell parameters a = 6.8880(12) Å, b = 10.4703(19) Å, c = 6.5197(9) Å, β = 108.25°, V =
446.55 Å3, ρcalcd = 4.960 g/cm3. Refractive indices are np = 1.640 and np = 1.754.
DOI: 10.1134/S0036023609060047
The phase diagram of the ZnBr2–CsBr system was
studied in [1, 2], where three compounds were found to
exist. Two of them (Cs3ZnBr5 and Cs2ZnBr4) melt con-
gruently at 530°C and 560°ë, respectively; CsZn2Br5
melts incongruently at 285°ë and has two polymorphs
with transition temperatures of 215°ë at for ZnBr2 per-
centages higher than 66.67 mol % and 225°ë when
ZnBr2 percentages are equal to or higher than 66.67 mol %.
The Cs3ZnBr5 compound crystallizes in the tetragonal
system, and Cs2ZnBr4 in the orthorhombic system [2].
The CsZn2Br5 compound was prepared for the first
time. There no data on the crystal structure of CsZn2Br5
in the literature. The aim of this work was to synthesize
CsZn2Br5, grow single crystals of the compound, and
determine its crystal structure by X-ray diffraction.
The synthesis of CsZn2Br5 was carried out in evacu-
ated (to 10–1 Pa) and sealed quartz ampules at 640°ë;
the melt was stirred for 1 day and cooled with a furnace.
The crystals were grown by zone melting in cone-
tipped quartz ampules (of the cone angle was 15°–18°).
The temperature of the molten zone was 420°ë; the
zone movement velocity was 2.7 mm/h. Two passages
were performed. As a result, a colorless, transparent
block crystal of CsZn2Br5 was grown. CsZn2Br5 was a
hygroscopic compound, and all operations with were
performed in a box filled with dry argon.
The sample obtained was studied by differential
thermal analysis (DTA) and X-ray powder diffraction;
refractive indices were measured. Differential thermal
analysis was performed on an NTR-64 pyrometer with
a Pt–Pt/Rh thermocouple and calcined Al2O3 as a stan-
dard. The heating rate was 8–10 K/min; the error of
peak temperature determination was 5 K. X-ray pow-
der diffraction studies crystals were performed for
ground crystals on a DRON-1.0 diffractometer (CuKα
radiation, Ni filter, 2θ scan, 1°/min). The error of the
X-ray diffraction measurements was 3'. To protect
hygroscopic CsZn2Br5 from air humidity, the powdered
sample was placed in a Teflon cell covered with a
Teflon film 0.01 mm thick. The refractive indices were
determined with an MIN-4 polarizing microscope in
transmitted nonpolarized light using 98 standard
immersion liquids (whose refractive indices were from
1.408 to 1.780). The Becke method was used for com-
parison of the refractive indices of liquids and
immersed grains.
EXPERIMENTAL
The compound CsZn2Br5 was synthesized from
purified cesium and zinc bromides taken in stoichio-
metric amounts. The ZnBr2 compound was synthesized
as described in [3] from zinc cuttings of high purity
grade, aqueous hydrobromic acid of pure for analysis
grade, and chemically pure grade bromine. ZnBr2 crys-
tals were recrystallized from diluted hydrobromic acid,
collected on a glass filter, and dried at 200°ë. The
cream-colored ZnBr2 crystals obtained were very
hygroscopic; because of this, all operations with this
compound were performed in a box filled with dry
argon. The synthesized ZnBr2 was purified by repeated
(four–to sixfold) sublimation under vacuum at 480°ë.
Cesium bromide of chemically pure grade was
recrystallized from an aqueous solution, which was fol-
lowed by filtration and dehydration. The impurity level
in the purified zinc and cesium bromides was less than
1 × 10–3 wt % as determined by emission spectral ana-
lysis.
RESULTS AND DISCUSSION
The DTA curve of CsZn2Br5 displays two peaks at
215 and 285°ë. The first of them is assigned to the poly-
morphic transition in CsZn2Br5, and the second corre-
sponds to incongruent melting [2].
840

X-RAY DIFFRACTION STUDY OF CsZn2Br5
841
Observed and calculated X-ray diffraction data for CsZn2Br5 (low-temperature phase)
Line no.
I, %
d, Å
sin2θobs
sin2θcalcd
∆ = sin2θobs – sin2θcalcd
hkl
1
2
39
47
47
100
28
61
47
47
24
28
25
22
28
14
13
3.9230
3.3590
3.2160
3.0890
2.9690
2.8290
2.0250
1.9180
1.8450
1.8080
1.7770
1.7130
1.6860
1.5425
1.5310
0.03856
0.05259
0.05737
0.06219
0.06731
0.07414
0.14470
0.16130
0.17431
0.18152
0.18791
0.20221
0.20874
0.24938
0.25314
0.03852
0.05259
0.05743
0.06191
0.06732
0.07424
0.14470
0.16136
0.17435
0.18152
0.18791
0.20233
0.20872
0.24935
0.25304
0.00004
0.00000
–0.00006
0.00028
–0.00001
–0.00010
0.00000
–0.00006
–0.00004
0.00000
0.00000
–0.00012
0.00002
0.00003
0.00010
101
–201
–102
002
3
4
5
012
6
–221
013
7
8
–223
–133
–303
–251
123
9
10
11
12
13
14
15
160
–431
014
Reflection positions, their intensities, and interpla-
nar distances d (Å) were found from the X-ray powder
diffraction patterns of CsZn2Br5. The unit cell parame-
ters were calculated using the strongest 15 reflections
with the TREOR program. The structure of CsZn2Br5
was indexed as monoclinic. The space group was cho-
sen from systematic extinctions. Systematic extinctions
The flotation density of CsZn2Br5 was higher than the
density of methylene iodide CH2I2 (3.3254 g/cm3), which
suggests that the number of formula units is two. Conse-
quently, the X-ray density of CsZn2Br5 is 4.960 g/cm3. The
refractive indices of CsZn2Br5 crystals are np = 1.640
and ng = 1.754.
To summarize, the conditions for the preparation
and single crystal growth of CsZn2Br5 have been found,
an X-ray diffraction study of this compound performed
for the first time. The X-ray density of CsZn2Br5 has
been calculated, and the refractive indices determined.
make the following space groups possible: C12h = P2/m,
C12 = P2, and C1s = Pm [4]. The unit cell parameters are
a = 6.8880 0.0012, b = 10.4703 0.0019, c = 6.5197
0.0009 Å; β =108.25°, and V = 446.55 Å3. The factors
M = 15 and F = 9 are indicative of a high reliability of
the results. The X-ray powder diffraction data found
experimentally and calculated for CsZn2Br5 are com-
piled in the table.
REFERENCES
1. I. Ya. Kuznetsova, I. S. Kovaleva, and V. A. Fedorov, Zh.
Neorg. Khim. 33 (8), 2109 (1988).
2. I.Ya. Kuznetsova, Candidate’s Dissertation in Chemistry
(Inst. of General and Inorganic Chemistry, Moscow,
1989).
The X-ray density of CsZn2Br5 ρcalcd (g/cm3) was
calculated as
3. Handbuch der praeparativen anorganischen Chemie,
Ed. by G. Brauer (Ferdinand Enke, Stuttgart, 1975–
1981; Mir, Moscow, 1985).
ρ
calcd = ZFWg/V,
where Z is the number of formula units per unit cell
4. L. I. Mirkin, X-ray Analysis of Polycrystals. Handbook
(two), FW stands for the formula weight of CsZn2Br5
(FIZMATGIZ, Moscow, 1961) [in Russian].
(663.1854), g is the hydrogen atom weight (1.67 × 10–24 g),
5. V. I. Pakhomov, P. M. Fedorov, and I. N. Ivanova-Kor-
and V is the unit cell volume (446.55 × 10–24 cm3).
fini, Koord. Khim. 5 (8), 1245 (1979).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 6 2009