Characterization and thermal analysis of thiourea and bismuth trichloride complex

Article abstract of DOI:10.1007/s10973-009-0006-7

A complex of thiourea and bismuth trichloride has been synthesized. Its composition is Bi₃Cl₉[SC (NH₂) ₂]₇. Crystallographic data are a = 7.141(2) A , b = 8.820(3) A , c = 16.365(5) A , α = 99.389(4)°, β = 95.422 (4)°, γ = 106.177(4)°, triclinic system. There are the mononuclear anion [BiCl₅SC(NH₂)₂]^2- and the dinuclear cation {Bi₂Cl₄[SC(NH₂) ₂]₆}²⁺ with the Bi-Cl-Bi bridge bonds in the complex. The electric conductance of the absolute methanol solution contained the complex indicates that the complex is an ionic compound. Raman spectra indicate that the bismuth ion is coordinated by the sulfur atoms of the thiourea. The thermal analysis verifies the structure of complex. The TG-MASS curves show the structure rearrangement in the complex at about 118 °C. The DSC curves and calculation means that the structure rearrangement is irreversible. Akademiai Kiado, Budapest, Hungary 2009.

Full text of DOI:10.1007/s10973-009-0006-7

J Therm Anal Calorim (2010) 99:523–530
DOI 10.1007/s10973-009-0006-7
Characterization and thermal analysis of thiourea and bismuth
trichloride complex
Shao Rong Luan Æ Yi Hua Zhu Æ Yu Qing Jia Æ
Qing Cao
Received: 1 May 2009 / Accepted: 7 May 2009 / Published online: 8 July 2009
´
´
Ó Akademiai Kiado, Budapest, Hungary 2009
Abstract A complex of thiourea and bismuth trichloride
has been synthesized. Its composition is Bi3Cl9[SC
˚
(NH2)2]7. Crystallographic data are a = 7.141(2) A, b =
Keywords Ionic compounds Á Bismuth(III) chloride Á
Thiourea Á Crystal structure Á Raman spectroscopy Á
Thermal analysis Á TG–DTA–MS Á DSC
˚
˚
8.820(3) A, c = 16.365(5) A, a = 99.389(4)°, b = 95.422
(4)°, c = 106.177(4)°, triclinic system. There are the
mononuclear anion [BiCl5SC(NH2)2]2- and the dinuclear
cation {Bi2Cl4[SC(NH2)2]6}2? with the Bi–Cl–Bi bridge
bonds in the complex. The electric conductance of the
absolute methanol solution contained the complex indi-
cates that the complex is an ionic compound. Raman
spectra indicate that the bismuth ion is coordinated by the
sulfur atoms of the thiourea. The thermal analysis verifies
the structure of complex. The TG–MASS curves show the
structure rearrangement in the complex at about 118 °C.
The DSC curves and calculation means that the structure
rearrangement is irreversible.
Introduction
The VA main group metal compounds including inorganic
and metallorganic complexes have been studied for dec-
ades owing to the interesting physical properties, medical
and material functions [1–8]. Bismuth nitrate and bismuth
acetate of thiourea crystal complexes were reported
with formula Bi2(CH3COO)6 Á 3SC(NH2)2 Á H2O, Bi(CH3
COO)3 Á 3SC(NH2)2, [Bi(NO3){SC(NH2)2}5](NO3)2 Á H2O
and [Bi(NO3)3{SC(NH2)2}3] [9, 10]. Two kinds single
crystal of bismuth thiourea chloride were synthesized with
different formula. One of them was [Bi(tu)6][Bi{(tu)1.5
Cl1.5}Cl3]2, which included the [Bi(tu)6]3? cations and
3-
[Bi{(tu)1.5Cl1.5}Cl3]2
anions group [11]. Another of
them was Bi(tu)3Cl3 [12]. Some bismuth complexes can be
used in medicine, microbiology and pharmacology because
of their special biological or medicinal functions [13–23].
With its features of highly variable coordination numbers
and irregular coordination geometry, bismuth can form
compounds with various structures and chemical bonding
[24, 25]. Because inorganic salts of bismuth can be easily
hydrolyzed in the aqueous solution [26], it is rather difficult
to synthesize the solid complexes of the bismuth in the
aqueous solution. We have found that some solid com-
plexes of bismuth can be prepared easily through solid–
solid reaction [27, 28]. Thermal analysis is important to
study the chemical structure and the reaction course of the
complex [29, 30]. This paper reports the complex of
bismuth chloride and thiourea in the absolute methanol
solution. The characterizations can demonstrate that the
S. R. Luan (&) Á Q. Cao
Research Center of Analysis and Test, School of Chemistry
and Molecular Engineering, East China University of Science
and Technology, Shanghai 200237, People’s Republic of China
e-mail: srluan@ecust.edu.cn
S. R. Luan Á Y. H. Zhu (&)
Key Laboratory for Ultrafine Materials of Ministry of Education,
School of Materials Science and Engineering, East China
University of Science and Technology, Shanghai 200237,
People’s Republic of China
e-mail: yhzhu@ecust.edu.cn
Y. Q. Jia
Department of Chemistry, School of Chemistry and Molecular
Engineering, East China University of Science and Technology,
Shanghai 200237, People’s Republic of China
123

524
S. R. Luan et al.
new complex is an ionic compound and possesses an
interesting formula with the special cations and anions
structure. We verify the structure of complex by thermal
analysis. From the TG–MASS curves and DSC calcula-
tions, we find there is an irreversible structure rearrange-
ment in the complex at about 118 °C.
least-squares on F2. In all cases a semi-empirical absorption
correction from equivalents was made. Hydrogen atoms
were included at the calculated positions. The powder
X-ray diffraction pattern of the sample which was obtained
from annealing sample at 120 °C for 20 min was recorded
by a D/max-2550 VB/PC X-ray powder diffractometer at
room temperature. CuKa1 radiation was used for the XRD
measurement. Data were collected with a scan step of
12°min-1 between 5° and 75°. The method for indexing is
the least-square fitting. Electric conductance of the abso-
lute methanol solution contained the complex was mea-
sured by DDS-307 Conductometer at 17 °C using DJS-1C
electrode. Raman spectra of the complex, BiCl3 and
SC(NH2)2 were measured by a Renishaw in Via Reflex
Laser Raman spectrometer (785 nm excitation). Thermal
studies for the complex were performed by a NETZSCH
STA 449C TG–DTA–MS Thermal Analyzer under argon
atmospheric with a heating rate of 10 °C min-1. The mass
of the sample is 15.020 mg. TG–DTA, MS, DSC curves of
the complex are shown in Figs. 4, 5 and 6, respectively.
The experimental and calculated results for the thermal
analysis are summarized in Table 3.
Experimental
The bismuth trichloride and thiourea used were of analyt-
ical reagent and commercially purchased. Firstly, 3.0812 g
(9.8 mmol) BiCl3 were dissolved in 80 mL absolute
methanol in a beaker. Then 2.236 g (29.4 mmol) thioureas
were slowly added. The mixture was stirred for 2 h at room
temperature. The solvent in the resultant solution was
vaporized slowly in air for a week. Finally, the light yellow
transparent crystal was obtained. The crystal is stable in the
air (Table 1).
Carbon, hydrogen, nitrogen and sulfur in the complex
were analyzed by an Elementar Vario El III elemental
analyzer. XRD of the single crystal sample was carried out
and the data were collected by SMART APEXCCD
diffractometer. The refinement method was full-matrix
Results and discussion
The results of the element analysis for the product show
that C(exp.) is 5.71%, H(exp.) is 1.90%, N(exp.) is 13.27% and
S(exp.) is 15.22%. Therefore, the most possible formula of
the resultant is Bi3Cl9[SC(NH2)2]7. In this case, the relative
Table 1 Crystallographic data for complex
Empirical formula
Formula weight
Temperature (K)
Crystal system
C7H28Bi3Cl9N14S7
1478.84
293(2)
content of C, H, N and S in Bi3Cl9[SC(NH2)2]7 is C(cal.)
:
Triclinic
P-1
5.69%, H(cal.): 1.91%, N(cal.): 13.26% and S(cal.): 15.15%.
The calculated results are very close to the measured ones.
As is shown in Figs. 1 and 2, the single-crystal X-ray
diffraction of the complex indicates that the crystal struc-
ture of the complex belongs to triclinic system. There
Space group
Unit cell dimensions
´
˚
a (A)
7.141(2)
´
˚
b (A)
8.820(3)
´
˚
c (A)
16.365(5)
a (°)
b (°)
c (°)
99.389(4)
95.422(4)
106.177(4)
´
3
˚
Volume (A )
965.9(6)
Z
1
Density, q (cal.) (Mg m-3
)
2.542
´
˚
k (Mo Ka) (A)
0.71073
Crystal size (mm3)
0.15 9 0.10 9 0.10
1.28 to 25.5
-8 B h B 8
-10 B k B 10
-19 B l B 11
4278/3538 [R(int) = 0.0484]
R1 = 0.0481, wR2 = 0.1240
R1 = 0.0527, wR2 = 0.1262
Theta range for data collection (°)
Index ranges
Reflections collected/unique
Final R indices [I [ 2r(I)]
R indices (all data)
Fig. 1 The structure of the mononuclear [BiCl5SC(NH2)2]2- group
123

Characterization and thermal analysis of thiourea and bismuth trichloride complex
525
Fig. 2 The structure of the dinuclear [Bi2Cl4(SC(NH2)2)6]2? group
Fig. 3 Raman spectrum of SC(NH2)2, BiCl3 and Bi3Cl9[SC(NH2)2]7
are mononuclear BiCl5SC(NH2)2 and dinuclear Bi2Cl4
(SC(NH2)2)6 group with two negative and positive charges.
The metal ion is coordinated by the sulfur atom in most
metal thiourea complexes and by the nitrogen atom in a
few metal thiourea complexes [31, 32]. In the new com-
plex, the bismuth ion is coordinated by the sulfur atom of
thiourea.
Generally, the stretching vibrations produce stronger
Raman bands than the deformation vibrations, the chemical
bonds containing heavier atoms produce stronger Raman
bands than those containing lighter atoms, and the intensity
of Raman scattering from the vibration of the double bond
is much stronger than that from the single bond [33]. So, in
Raman spectrum of thiourea Fig. 3(1), we assign the peak
at 1387 cm-1 to the stretching vibration of the N–C–N
bond, the peak at 478 cm-1 to the deformation vibration of
the N–C–N bond and the peak at 1096 cm-1 to the rocking
vibration of the NH2 group. The intense peak at 735 cm-1
may be from the stretching vibration of the C=S double
bond. The peak at 117 cm-1 may be from the lattice
vibrations in the solid sample. As shown in Fig. 3(2), there
are four peaks in Raman spectrum of bismuth trichloride:
the symmetric or antisymmetric stretching vibration and
the symmetric or antisymmetric deformation vibration.
Usually, the symmetric vibration will produce stronger
Raman band than antisymmetric vibration. In this case,
we assign the peak at 282 cm-1 and peak at 241 cm-1 to
the symmetric and asymmetric stretching vibration of the
Bi–Cl bond, respectively, and the peak at 180 cm-1 to the
symmetric deformation vibration of the Cl–Bi–Cl bond in
bismuth trichloride. As for the peak at 144 cm-1, perhaps,
it can be attributed to the overlap of the peak from the
antisymmetric deformation vibration of the Cl–Bi–Cl bond
and the peak from the lattice vibration in the crystal, since
it seems to be impossible that the strongest peak with a
very low frequency is only from the antisymmetric defor-
mation vibration of the Cl–Bi–Cl bond.
The conductance measurement indicates that the con-
ductivity of the absolute methanol solution contained the
complex with the concentration 1.0 9 10-3 mol L-1 is
172.3 lS cm-1 at 17 °C. Obviously the conductivity of the
complex solution is much higher than that (4.54 lS cm-1
)
of the pure absolute methanol. The conductivity of the
absolute methanol solution contained BiCl3 with the con-
centration of 3.0 9 10-3 mol L-1 is 358 lS cm-1 at 17 °C.
Each complex molecule contains three BiCl3 and
seven SC(NH2)2 molecules. Although the conductivity
(358 lS cm-1) of the BiCl3 solution with the concen-
tration 3.0 9 10-3 mol L-1 is much higher than that
(172.3 lS cm-1) of the complex solution, still much less
than the three multiple values (516.9 lS cm-1) of that
(172.3 lS cm-1) of the complex solution with the con-
centration of 1.0 9 10-3 mol L-1. The conductivity of
thiourea in the absolute methanol solution with the con-
centration of 7.0 9 10-3 mol L-1 is 4.9 lS cm-1. This is
very close to the conductivity (4.54 lS cm-1) of the pure
absolute methanol at 17 °C. So, we consider that the
[Bi2Cl4(SC(NH2)2)6]2? cation and [BiCl5SC(NH2)2]2-
anion in the complex might have made certain contribution
to the conductance of the complex. The conductance
results show that the complex is an ionic one.
As is shown in Figs. 1 and 2, the mononuclear
[BiCl5SC(NH2)2]2- group and the dinuclear [Bi2Cl4(SC
(NH2)2)6]2? group are different both in coordination
structure and symmetry. In the mononuclear [BiCl5SC
(NH2)2]2- group, five Cl atoms and one S atom coordinate
Raman spectroscopy of thiourea, bismuth trichloride and
complex are shown in Fig. 3. The symmetry of the thiourea
molecule belongs to C2v group. Many vibration modes in
the molecule with C2v symmetry are Raman active [33].
123

526
S. R. Luan et al.
with the Bi ion. The Bi ion is at the center of octahedra
composed of the Cl and S atoms. From the corresponding
bond lengths and bond angles in Table 2, we can find that
the BiCl5S group is very similar to an octahedral MX5Y-
type molecule, to which, various vibration modes have been
given [33]. In the dinuclear [Bi2Cl4(SC(NH2)2)6]2? group,
there are two Bi–Cl–Bi bridge bonds. Two Cl bridge atoms,
one Cl anion and three S atoms from the thiouea molecules
will bond to each Bi ion. According to the corresponding
bond lengths and angles in Table 2, we can consider that the
two Bi atoms and two Cl atoms in the two Bi–Cl–Bi bridge
bonds are coplanar and the symmetry of the S3ClBi–(Cl)2–
BiClS3 group approximately belongs to C2 group. Thus, we
give the assignments for the peaks in Raman spectrum of
the complex. In Fig. 3(3), some peaks from thiourea also
appear in that of the complex, but will shifts. In Raman
spectrum of the complex, there are some new peaks, such as
peaks at 237, 396 and 466 cm-1. It has been reported that
the frequency of the stretching vibration of the M–S bond in
the thiourea complexes of various metal ions is between 200
and 300 cm-1. Therefore, the new peak with highest
intensity at 237 cm-1 might be the stretching vibration of
the Bi–S bond. The peaks at 396 and 418 cm-1 may be from
various stretching vibrations of the Bi–Cl bonds with dif-
ferent bond lengths in the complex. As for the peak at
466 cm-1, this may be from the ‘‘breathing’’ vibration of
the four-member ring composed of two Bi–Cl–Bi bridge
bonds. The symmetric ‘‘breathing’’ vibration can produce
stronger Raman peak. The peak at 704 cm-1 can be
assigned to the stretching vibration of the C=S bond. Due to
the bonding between the S and Bi atoms, the effective mass
of the S atom in the C=S bond may appear slightly larger.
Therefore, the frequency (704 cm-1) of the stretching
vibration of the C=S bond in the complex molecule must be
lower than that (733.5 cm-1) of the C=S bond in the thiouea
molecule. The peak at 1108 cm-1 and the peak at
1389 cm-1 in Raman spectrum of the complex may be from
the rocking vibration of the NH2 group and the stretching
vibration of the N–C–N bond, respectively. However, due
to the induction effect of the Bi–S bond, the peaks in
the complex also shift. For example, the frequency
(1096 cm-1) of the rocking vibration of the NH2 in thiouea
is lower than that (1108 cm-1) in the complex. In Fig. 3(3),
the peaks at 1416, 1512 and 1621 cm-1 may be assigned to
various stretching and deformation vibrations in the N–C–N
bond and the NH2 group, respectively. For the peak at
135 cm-1, this may be from the lattice vibration in the
complex crystal.
Table 3 lists the possible thermal decomposition reac-
tions of the complex. As is shown in Fig. 4, there is a small
endothermic peak at 118.08 °C in DTA curve of the
complex. However, there is not any corresponding weight
Table 2 Selected bond lengths
(A) and angles (°) in the
complex
Bi(1)–Cl(5)
2.6712(10)
2.6761(9)
2.6871(9)
2.7925(11)
2.9189(10)
2.9369(10)
99.76(2)
Bi(2)–Cl(7A)
2.6987(10)
2.6987(10)
2.7151(10)
2.7151(10)
2.7564(10)
2.7564(10)
180.00(2)
90.20(2)
89.80(2)
89.80(2)
90.20(2)
180.00(2)
87.89(2)
92.11(2)
89.54(2)
90.46(2)
87.89(2)
92.11(2)
89.54(2)
92.11(3)
89.54(2)
90.46(2)
´
˚
Bi(1)–S(3)
Bi(2)–Cl(7)
Bi(1)–S(1)
Bi(2)–Cl(8A)
Bi(1)–S(2)
Bi(2)–Cl(8)
Bi(1)–Cl(4)
Bi(2)–Cl(6A)
Bi(1)–Cl(4A)
Bi(2)–S(6A)
Cl(5)–Bi(1)–S(3)
Cl(5)–Bi(1)–S(1)
S(3)–Bi(1)–S(1)
Cl(5)–Bi(1)–S(2)
S(3)–Bi(1)–S(2)
S(1)–Bi(1)–S(2)
Cl(5)–Bi(1)–Cl(4)
S(3)–Bi(1)–Cl(4)
S(1)–Bi(1)–Cl(4)
S(2)–Bi(1)–Cl(4)
Cl(5)–Bi(1)–Cl(4A)
S(3)–Bi(1)–Cl(4A)
S(1)–Bi(1)–Cl(4A)
S(2)–Bi(1)–Cl(4A)
Cl(4)–Bi(1)–Cl(4A)
Bi(1)–Cl(4)–Bi(1A)
Cl(7)–Bi(2)–S(6)
Cl(7A)–Bi(2)–Cl(7)
Cl(7A)–Bi(2)–Cl(8A)
Cl(7)–Bi(2)–Cl(8A)
Cl(7A)–Bi(2)–Cl(8)
Cl(7)–Bi(2)–Cl(8)
Cl(8A)–Bi(2)–Cl(8)
Cl(7A)–Bi(2)–Cl(6A)
Cl(7)–Bi(2)–Cl(6A)
Cl(8A)–Bi(2)–Cl(6A)
Cl(8)–Bi(2)–Cl(6A)
Cl(7A)–Bi(2)–S(6A)
Cl(7)–Bi(2)–S(6A)
Cl(8A)–Bi(2)–S(6A)
Cl(7A)–Bi(2)–S(6)
Cl(8)–Bi(2)–S(6)
Cl(8A)–Bi(2)–S(6)
89.56(2)
85.49(3)
175.19(2)
83.964(19)
93.79(2)
90.89(2)
84.88(3)
170.290(18)
86.39(2)
87.72(2)
168.118(17)
103.92(3)
88.130(19)
85.79(2)
94.21(2)
87.89(2)
123

Characterization and thermal analysis of thiourea and bismuth trichloride complex
527
loss in TG curve of the complex and no ion current in mass
curves at 118.08 °C in Fig. 5. Therefore, the small endo-
thermic peak could be attributed to the structure rear-
rangement in the coordination sphere of the complex or the
possible phase transformation in the crystal. To check
whether the structure rearrangement or the phase trans-
formation in the crystal occurs at about 118 °C, a certain
amount (about 500 mg) of the solid complex was placed in
an alumina crucible and heated at 120 °C for 20 min in a
muffle furnace, and then, measure the powder X-ray dif-
fraction pattern of the heat-treated sample. All the peaks in
the X-ray diffraction pattern of the heat-treated sample can
be very readily indexed by a set of lattice parameters and
the relative deviations between the calculated and experi-
mental dhkl are \0.5%. It is obvious that the sample is
a single-phase compound. The crystal structure of the
heat-treated sample still belongs to the triclinic system with
the lattice parameters: a = 0.7158 nm, b = 0.8850 nm,
c = 1.6431 nm, a = 99.30°, b = 95.41° and c = 106.14°.
The lattice parameters of the heat-treated sample are very
close to that of the single crystal of the complex. This
shows that the change on the cell of the complex crystal is
very small. Besides, the DSC measurement indicates that
the reaction heat for the change of complex at 118.08 °C is
6.542 kJ mol-1. This is much less than the phase trans-
formation heat of the solid compound. General speaking,
the reaction heat for the phase transformation in most solid
compounds is tens to several hundred kJ mol-1. In this
case, we can consider that the endothermic peak at
118.08 °C in DTA curve of the complex can be attributed
to the structure rearrangement in the complex, not to the
phase transformation in the crystal. We measured the DSC
Table 3 Thermal decomposition data of Bi3Cl9[SC(NH2)2]7
Reaction
T(DTA) (°C)
Mass loss (%)
Wexp.
Wtheor.
Bi3Cl9[SC(NH2)2]7
; Structural rearrangement
Bi3Cl9[SC(NH2)2]7
; Softening of crystal
Bi3Cl9[SC(NH2)2]7
; –2SC(NH2)2
; –NH2, –S
118.08 (endo.)
170.37 (endo.)
214.89 (exo.)
299.17 (endo.)
13.85
10.60
13.55
10.79
Bi3Cl9[SC(NH2)2]4(CNH2)
; –SC(NH2)2
; –NH2, –S
; –Cl
Bi3Cl8[SC(NH2)2]2
; –CNH2
; –S, –NH2
; –4Cl, –Cl2
20.85
5.08
20.62
4.95
Bi3Cl2(CCNH2)SC(NH2)2
; –2HCl
Bi3C(CNH2)SC(NH2)2
; –SC(NH2)2
; –C(CNH2)
; -0.53Bi
649.13 (endo.)
15.30
15.34
2.47Bi
; -0.22Bi
3.13
31.19a
3.11
31.80b
2.25Bi
a
The experimental percentage mass of the residue in the sample
The calculated percentage mass of the residue in the sample
b
Fig. 4 TG–DTG–DTA
curves of the complex
Bi3Cl9[SC(NH2)2]7
DTG /(%/min)
DTA /(uV/mg)
TG /%
100
exo
↓
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
-0.2
0
-13.85 %
90
80
70
60
50
40
-10.60 %
-1
-2
-3
-4
295.7 °C
299.2 °C
-20.85 %
649.1 °C
170.4 °C
118.1 °C
367.0 °C
208.3 °C
-5.08 %
641.7 °C
-15.30 %
-3.13 %
214.9 °C
100
200
300
400
Temperature /°C
500
600
700
123

528
S. R. Luan et al.
Fig. 5 MS curve of the
complex Bi3Cl9[SC(NH2)2]7
corresponding to an exothermic peak at about 214 °C in
DTA curve. In MS curves of the pyrolysis products, there
are the peaks of the species: SC(NH2)2 (m/z = 76), CS
(m/z = 44), S (m/z = 32) and NH2 (m/z = 16). If two
SC(NH2)2 molecules, one S atom and one terminal NH2
group of the thiourea molecule are eliminated from the
sample at this step, the theoretical weight loss (13.55%) is
close to the experimental one (13.85%). Usually, the
thermal decomposition process of the complex in the inert
gas always leads to the endothermic peak in DTA curve, as
the breaking of chemical bond needs certain energy.
However, why is there an exothermic peak at about 214 °C
in DTA curve of the new complex? Perhaps, the elimina-
tions of the SC(NH2)2, S atom and terminal NH2 group
from the solid complex will lead to the structure rear-
rangement and to the formation of new chemical bonds in
the residual sample. If the total bond energy of the formed
chemical bonds is larger than that of the broken chemical
bonds, this can also lead to an exothermic peak in DTA
curve of the sample. Soon afterwards, the sample will lose
one SC(NH2)2 molecule, one S atom and one terminal NH2
group, again. Meanwhile, one Cl atom is also eliminated
from the complex molecule. The above conclusion can also
be supported by MS curves of the pyrolysis products. In
this case, the calculated theoretical weight loss (10.80%)
matches very well with the experimental one (10.60%).
Then, there is a larger weight loss (20.85%) in the range
from 320 to 480 °C in TG curve of the sample. In this
stage, a lot of Cl atoms will be eliminated from the com-
plex. In addition, one SC(NH2)2 molecule and two terminal
Fig. 6 DSC curves of the complex Bi3Cl9[SC(NH2)2]7
of complex by the first heating, the first cooling and the
second heating progress. In Fig. 6, we noted that there is an
endothermic peak at 115.8 °C in the first heating, but no
corresponding exothermic peak in the first cooling. Com-
pared with the first heating, there is no endothermic peak in
the second one. This means that structure rearrangement in
the complex crystal is irreversible. Then, an apparent
endothermic peak in DTA curve appears at 170.37 °C,
again, before the thermal decomposition of the complex
begins. Since there is not any corresponding weight loss of
the sample in the TG curve at about 170 °C, this may be
due to softening of the solid sample. In fact, to heat the
crystal sample in capillary can demonstrate that the soft-
ening point of the solid complex is at about 170 °C. The
first weight loss of the sample happens at about 200 °C
123

Characterization and thermal analysis of thiourea and bismuth trichloride complex
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NH2 group will also be eliminated. We have noted that the
pyrolysis products contain both four free Cl atoms and one
Cl2 molecule. Why are there two kinds of chlorines in the
pyrolysis products? As is mentioned above, there are a lot
of hydrogen bonds (N–HÁÁÁCl) in the lattice of the complex.
Therefore, some Cl atoms exist in the solid complex in the
form of the ClÁÁÁHNHÁÁÁCl groups, and some in the form of
the Bi–Cl–Bi bridge bonds. Perhaps, different Cl atoms in
the lattice of the complex will produce the different
pyrolysis products. And above 500 °C, the sample loses the
two residual Cl atoms. Finally, the sample loses the last
thiourea ligand and becomes the metal Bi. When temper-
ature is over 600 °C, the metal Bi will gradually volatilize.
The volatilization of the metal needs certain energy; hence,
there is an apparent endothermic peak at 649.13 °C in DTA
curve. The thermal decomposition product is the black
residue with metallic luster.
´
9. Jameson GB, Blaszo E, Oswald HR. Nitratopentakis(thiourea)
bismuth(III) nitrate monohydrate, [Bi(NO3){SC(NH2)2}5]
(NO3)2ÁH2O, and trinitratotris (thiourea) bismuth(III), [Bi(NO3)3
{SC(NH2)2}3]. Acta Crystallogr Sect C. 1984;40:350–4.
´
10. Bensch W, Blazso E, Dubler E, Oswald HR. The structures of
Bi2(CH3COO)6.3SC(NH2)2ÁH2O and Bi(CH3COO)3Á3SC(NH2)2.
Conclusions
Acta Crystallogr Sect C. 1987;43:1699–704.
11. Battaglia LP, Corradi AB, Pelizzi G, Tani MEV. Cationic and
anionic bismuth(III) in chloro-thiourea complexes: crystal struc-
ture of [Bi(tu)6][Bi{(tu)1.5Cl1.5}Cl3]2 (tu = thiourea). J Chem Soc
Dalton Trans. 1977;1141.
12. Bhat SG, Dharmaprakash SM. New metal-organic crystal: bis-
muth thiourea chloride. Mater Res Bull. 1998;33:833–40.
13. Williams DJ, Hutchings AM, McConnell NE, Faucher RA, Huck
BE, Brevett CAS, et al. Main group metal halide complexes part
XVIII: the synthesis, characterization, with sterically hindered
thioureas and X-ray crystallographic study of a BiCl3 complex
with 1-methyl-2(3H)-imidazolethione. Inorg Chim Acta. 2006;
359:2252–5.
14. Vaira MD, Mani F, Stoppioni P. Lead(II) and bismuth(III)
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15. Golovnev NN, Novikova GV, Vershinin VV, Churilov TD,
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The complex of bismuth and thiourea is synthesized
through a liquid reaction in the absolute methanol solution
of thiourea and bismuth trichloride. The complex is com-
posed of a mononuclear [BiCl5SC(NH2)2]2- anion and a
dinuclear [Bi2Cl4(SC(NH2)2)6]2? cation group. The con-
ductance of the absolute methanol solution contained the
complex shows that the complex is an ionic compound.
The thermal analysis verifies the structure of complex.
From the TG–MASS curves, there is a structure rear-
rangement in the complex at about 118 °C. The DSC
curves and calculation shows that the structure rearrange-
ment is irreversible.
Acknowledgements The authors gratefully acknowledge the
National Natural Science Foundation of China (20676038), the Key
Project of Science and Technology for Ministry of Education
(107045) and the Shanghai Leading Academic Discipline Project
(Project Number: B502) for financial supports.
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