Phase transition and thermal decomposition of [Al(DMSO)6]Cl 3

Article abstract of DOI:10.1007/s10973-006-7694-z

Phase transition and thermal decomposition of hexadimethylsulfoxidealuminium chloride were studied by differential scanning calorimetry (DSC), thermogravimetry (TG) and simultaneous differential thermal analysis (SDTA). The gaseous products of the decomposition were on-line identified by a quadrupole mass spectrometer (QMS). In the temperature range of 95-300 K, [Al(DMSO)₆]Cl₃ indicates one phase transition at T _c ^h =244.96 K (on heating) and at T _c ^c =220.87 K (on cooling). Large thermal hysteresis of the phase transition (～24 K) indicates its first order character. Large value of transition entropy (ΔS≈40 J mol^-1 K^-1) suggests its configurational character. Thermal decomposition of the title compound proceeds in four main stages. In the first stage, which starts just above ca. 300 K, the compound loses two DMSO molecules per one formula unit and undergoes into [Al(DMSO)₄]Cl₃. In the second stage, the next three DMSO ligands are released and simultaneously decomposed. The third stage, which continues up to ca. 552 K, is connected with a loss of the last DMSO ligand and the formation of AlCl₃. In the fourth stage AlCl₃ reacts with carbon monoxide that originates from the decomposition of DMSO, and first aluminium oxychloride and next solid Al₂O₃ plus carbon are created.

Full text of DOI:10.1007/s10973-006-7694-z

Journal of Thermal Analysis and Calorimetry, Vol. 90 (2007) 1, 223–228
PHASE TRANSITION AND THERMAL DECOMPOSITION OF
[Al(DMSO) ]Cl
6
3
*
A. MigdaÓ-Mikuli , N. Górska and E. Szostak
Jagiellonian University, Faculty of Chemistry, Ingardena 3, 30-060 Cracow, Poland
Phase transition and thermal decomposition of hexadimethylsulfoxidealuminium chloride were studied by differential scanning calo-
rimetry (DSC), thermogravimetry (TG) and simultaneous differential thermal analysis (SDTA). The gaseous products of the decompo-
sition were on-line identified by a quadrupole mass spectrometer (QMS). In the temperature range of 95–300 K, [Al(DMSO) ]Cl
6
3
indi-
h
c
cates one phase transition at T =244.96 K (on heating) and at T =220.87 K (on cooling). Large thermal hysteresis of the phase
c
c
–1
–1
transition (~24 K) indicates its first order character. Large value of transition entropy (DS»40 J mol K ) suggests its configurational
character. Thermal decomposition of the title compound proceeds in four main stages. In the first stage, which starts just above
ca. 300 K, the compound loses two DMSO molecules per one formula unit and undergoes into [Al(DMSO)
the next three DMSO ligands are released and simultaneously decomposed. The third stage, which continues up to ca. 552 K, is con-
4 3
]Cl . In the second stage,
nected with a loss of the last DMSO ligand and the formation of AlCl
inates from the decomposition of DMSO, and first aluminium oxychloride and next solid Al
3
. In the fourth stage AlCl
3
reacts with carbon monoxide that orig-
3
plus carbon are created.
2
O
Keywords: DSC, hexadimethylsulfoxidealuminium chloride, phase transition, SDTA, TG/QMS, thermal decomposition
Introduction
parameters: a=10.3760(6) , c=22.0210(12)  and
Z=3. Six oxygen atoms of six DMSO ligands are
3+
Both stable and metastable phases have been
identified by MigdaÓ-Mikuli et al. [1–4] in their
studies of polymorphism of [M(DMSO) ](ClO )
bonded to the Al ion in the form of trigonally dis-
torted octahedron. There is a distorted rhombododeca-
–
3+
6
4 2
hedral arrangement of Cl ions around the Al ions
[5]. Furthermore, thermal decomposition of
[Ln(DMSO) ]Cl , where Ln=Dy, Ho, Er, Tm, Yb and
compounds, where DMSO=(CH ) SO and M=Cd, Co,
2
3
Mn and Zn, with DSC in the temperature range of
00–390 K. Some of these phases are orientationally
3
3
3
Lu, were studied by Matos et al. [6] using oxygen or
nitrogen dynamic atmosphere. All the compounds
first melt (at 404–428 K) and then decompose (at
472–488 K). In all cases the residues at ca. 820 K
were identified as lanthanide oxychlorides and at
ca. 1170 K as Ln O . There was no evidence of for-
dynamically disordered crystals (ODDIC) or plastic
crystals. Additionally, one low temperature
solid-solid structural phase transition was detected for
both [Cd(DMSO)
[
6
](ClO
Mn(DMSO) ](ClO ) at 225 K [2], when the com-
4
)
2
at 242 K [1] and
6
4 2
2
3
pounds were heated up. The thermogravimetry (TG,
DTG), the simultaneous evolved gas analysis with
on-line quadrupole mass spectrometer (SEGA/QMS)
and simultaneous differential thermal analysis
mation of anhydrous lanthanide chlorides [6].
The main aims of these studies were to detect the
phase polymorphism of [Al(DMSO) ]Cl by DSC and
to establish the mechanism of the thermal decomposi-
tion of this compound using methods of thermal anal-
ysis (TG, DTG, QMS, SDTA and DSC).
6
3
(
SDTA) were also performed for these substances in
order to enable verification of their chemical com-
position and stability. It has been shown that all these
compounds are stable up to temperature of ca. 380 K,
whereas just above this temperature they start to loose
DMSO molecules.
Experimental
Materials
The crystal structure, phase polymorphism and
mechanism
M(DMSO)
ever, Boström et al. [5] have determined the structure
of
thermal
decomposition
of
A few grams of [Al(H O) ]Cl were dissolved while
2
6
3
[
6
]Cl compounds is so far unknown. How-
3
being slowly heated up in dimethyl sulfoxide, later
called DMSO, of high chemical purity, which was pre-
viously purified by vacuum distillation at low pressure.
The solution was then chilled and small, white col-
of the low temperature phase of [Al(DMSO) ]Cl (at
6
3
150 K) as the trigonal (space group R3), with lattice
*
Author for correspondence: migdalmi@chemia.uj.edu.pl
1
388–6150/$20.00
2007 Akadémiai Kiadó, Budapest
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©

MIGDA˜-MIKULI et al.
oured crystals of hexadimethylsulfoxidealuminium
gas used for transfer of liquid nitrogen to the cold fin-
ger dewar was of high purity as well. Two characteris-
tic temperatures of the DSC peaks, obtained on heat-
ing, were computed: the temperature of the peak maxi-
mum (Tpeak) and the temperature calculated from the
slope of the left-hand side of the peak (Tonset). The dif-
ference between these two temperatures ranged usually
from 2 to 6 K. The enthalpy changes (DH) linked up
with observed transitions were calculated by numerical
integration of the DSC curves under the peaks of the
anomalies. A linear background was subtracted prior to
the calculations. It was done in an arbitrary manner,
however, for every sample the procedure was the same.
The entropy changes (DS) were calculated using the
chloride were precipitated, filtered and washed with
acetone. The obtained crystals were then dried in a des-
iccator over P O for a few days. After desiccation,
2
5
they were put in a sealed vessel and stored in a desicca-
tor over barium oxide as a desiccant.
Methods
Before the measurements, the composition of the inves-
tigated compound was determined on the basis of car-
bon and hydrogen content in the DMSO ligand, using
elementary analysis on a EURO EA 3000 instrument.
Elementary analysis confirmed the proper composition
of the investigated compound. The average contents of
the DMSO ligands were found to be equal to the theo-
retical values within the error limit of ca. 0.3%.
following formula: DS=DH/T . The sharp peaks of the
c
DSC curves were computed with high accuracy reach-
ing ±4%, whereas the diffuse peaks could be regarded
as mere estimates. Details of the DSC experiment are
the same as described in [7].
Fourier transform Raman scattering measure-
ments (FTRS) were performed at room temperature
with a Bio-Rad spectrometer with a resolution of
–
1
4
the Neodymium laser YAG Spectra-Physics.
cm . The incident radiation (l=1064 nm) was from
Results and discussion
Fourier transform far and middle-infrared ab-
sorption measurements (FT-FIR and FT-MIR) were
performed using a Bio-Rad FTS60V and Bruker
EQUINOX-55 spectrometers, respectively, with a
In order to further identify the synthesized compound
and certify its purity, the FTRS and FTIR spectra were
performed. Figure 1 shows a comparison of Raman
–
1
resolution of 2 cm . The FT-FIR spectrum for a pow-
dered sample suspended in polyethylene dust was re-
corded. The FT-MIR spectrum was recorded for a
sample suspended in Nujol between KBr pellets.
The thermogravimetry (TG/DTG) measurements
and infrared spectra of [Al(DMSO)
room temperature. The cation was considered to have
octahedral symmetry with nearly freely rotating CH
6 3
]Cl obtained at
3
groups of DMSO ligands. Table 1 presents a list of the
bands’ positions, observed in the FTRS and FTIR
e
were performed using a Mettler-Toledo 851 instru-
ment. Three series of measurements for three samples
of different masses were performed. The measure-
–
1
ments were made in a flow (60 mL min ) of high pu-
rity dry argon (99.999%) within temperature range
3
00–640 K. The TG measurements were performed at
–
1
a constant heating rate of 10 K min . At a constant
heating rate beside TG and DTG curves, the simulta-
neous differential thermal analysis (SDTA) curve and
the simultaneous evolved gas analysis (SEGA), with
on-line quadrupole mass spectrometer (QMS) using a
Balzer GSD 300T instrument, were also registered.
The temperature was measured by a Pt–Pt/Rh thermo-
couple with the accuracy of ±0.5 K.
The DSC measurements at 95–300 K were per-
formed with a Perkin-Elmer PYRIS 1 DSC instrument.
The powdered sample was placed in an aluminium ves-
sel and was closed by compression. Another empty
vessel was used for reference. The instrument was cali-
brated by means of the melting point of indium and
melting point of water, for the high and the low tem-
perature region, respectively. High purity dry helium
(99.999%) was used as the purging gas. As the air
shield gas, nitrogen 99.999% was used. The nitrogen
Fig. 1 Comparison of the room temperature Raman and infra-
6 3
red spectra of [Al(DMSO) ]Cl
224
J. Therm. Anal. Cal., 90, 2007

6 3
PHASE TRANSITION AND THERMAL DECOMPOSITION OF [Al(DMSO) ]Cl
Table 1 The list of bands’ positions of the Raman and infrared spectra of [Al(DMSO)
with literature data
6
]Cl
3
at room temperature, comparison
–1
Frequencies/cm
RS
IR
Assignments
DMSO [9]
this work
DMSO [9]
2997m
this work
*
[8]
2990st
2967st
2905vst
2820w
1441wv
1422m
2985st
2902st
1432st
1401st
n
n
as(CH)
as(CH)
2913vst
1420m
*
n
s(CH)
s(CH)
n
1441st
1421m
d
as(HCH)
d
as(HCH)
d
as(HCH)
1
405m
1
1
1
1
331vw
312vw
056vw
024m
1330w
1307m
1062m
1007vst
961vst
930st
d
s(HCH)
1310w
1045vs
1305m
d
s(HCH)
1048vst
n
s(SO)
s(SO)
n
9
97vw
949m
rr(CH3 )
rr(CH3 )
rr(CH3 )
953m
995m
~
930vw
928vw
7
29st
727st
n
n
as(CS)
as(CS)
6
6
98vst
75m
699st
690m
660w
670vs
n
s(CS)
5
5
44st
27st
544st
n
AlO
AlO
535sh
n
4
4
96w
71w
n
n
s(AlO)
s(AlO)
4
05m
d
s(CSO)
s(CSO)
~
380m
382m
332st
308m
392m
349m
311w
230m
~170w
123m
389m
335w
303w
378m
327m
d
3
51st
d
as(CSO)
3
2
1
1
1
20m
37w
77w
25vw
02vw
d
as(CSC)
n
d(AlO)
d(AlO)
n
n
n
L
L
(lattice)
(lattice)
*
position of Nujol bands, vw – very weak, w – weak, sh – shoulder, m – medium, st – strong, vst – very strong, br – broad
–
20 K min . One anomaly on each of these DSC
1
spectra of [Al(DMSO) ]Cl , their relative intensities
6
3
h
curves was registered at T =244.28 K (on heating)
and assignments denoted by comparing with the litera-
ture data [8–11] for several [M(DMSO) ]X2 and
peak
c
and at T =210.65 K (on cooling). The temperatures
6
peak
h
c
[
M(DMSO) ]X complexes. These assignments
6
of the phase transition T =244.96 K and T =
c c
3
proved that both the composition and the structure of
the investigated compound were as expected.
220.87 K were obtained by linear extrapolation of the
h
c
dependence of T
and T
values vs. the rate of
peak
peak
The DSC measurements were made both by
heating and cooling the samples of masses of 10.20
and 12.83 mg at constant rates of: 20 and 30, 40 and
60 K min , respectively. Figure 2 shows two temper-
ature dependencies of the heat flow (two DSC curves)
heating and cooling to the zero, respectively. Large
thermal hysteresis of the phase transition (~24 K) in-
dicates its first order character. The thermodynamic
parameters of the detected phase transition are pre-
sented in Table 2. The relatively large value of the en-
tropy change connected with the observed phase tran-
–
1
obtained on heating and cooling of [Al(DMSO) ]Cl3
6
in the range of 95–300 K at the scanning rate of
J. Therm. Anal. Cal., 90, 2007
225

MIGDA˜-MIKULI et al.
1
50 mL open corundum crucible, while the third one
was placed in a 150 mL open platinum crucible.
The results obtained for all three samples are nearly
identical. Figure 3 shows TG, DTG and SDTA curves
recorded for the sample of mass 37.0941 mg placed in
the platinum crucible in the temperature range of
3
00–640 K. During the TG experiment, the QMS
spectra of masses were followed from m/e=1 to 140,
however, for reasons of graphic readability, only the
masses of m/e=16, 64, 44, 32, 48, 14, 17, 18, 78, 63
and 36 representing CH , SO , CO , O , SO, CH ,
4 2 2 2 2
OH, H O, CH SO or (CH ) SO, CH SO and Cl are
3 2
2
2
2
3
shown in Fig. 4.
The TG, DTG and QMS curves show that the de-
composition of the sample proceeds in four main stages
Fig. 2 DSC curves registered on heating and cooling of
[
6 3
Al(DMSO) ]Cl in the range of 95–300 K at a rate of
–
1
2
0 K min
–
1
–1
sition (mean value of DS is ca. 40 J mol K ) is note-
worthy as it indicates its configurational character.
To sum up, the temperature of the phase transition
h
discovered in [Al(DMSO)6]Cl atT =244.96 K is simi-
3
c
lar to the temperature of the low temperature structural
phase transitions registered for [Mn(DMSO) ](ClO )
6
4 2
h
T =225.40 K) [2] and [Cd(DMSO) ](ClO )
(
6 4 2
c
h
T =242.0 K) [1]. However, the enthalpy and entropy
(
change values (DH and DS) for the phase transition in
c
[Al(DMSO) ]Cl are distinctly larger than the corre-
6 3
sponding values for the aforementioned compounds. It
confirms the configurational character of the discovered
in [Al(DMSO) ]Cl phase transition. So the high tem-
6
3
perature phase of the title compound is probably the
phase with a high degree of orientational dynamical dis-
order (ODDIC). Moreover, contrary to the investiga-
tions of [M(DMSO) ](ClO ) compounds to date, the
6 4 2
compound under study has no metastable phases above
room temperature.
The thermal decomposition measurements were
made for three samples with masses of 33.1555,
6 3
Fig. 3 TG, DTG and SDTA curves for [Al(DMSO) ]Cl in the
range of 300–640 K registered at a constant heating
–1
rate of 10 K min
9
1
6.2831 and 37.0941 mg, at a constant heating rate of
–
0 K min . The first two samples were placed in a
1
6 3
Table 2 Thermodynamic parameters of the phase transition of [Al(DMSO) ]Cl
–
1
Scanning rate/K min
Mass/mg
20
30
40
60
10.20
12.83
12.83
12.83
heating
9.96
–
1
DH/kJ mol
–
9.37
38.34
8.75
35.56
7.74
31.39
1
–1
DS/J mol
h
K
40.54
245.78
T /K
244.28
245.99
246.57
c
cooling
8.99
–
1
DH/kJ mol
–
10.26
48.71
7.95
38.71
7.17
35.13
1
–1
DS/J mol
c
K
41.94
214.22
T /K
210.65
205.32
204.03
c
226
J. Therm. Anal. Cal., 90, 2007

6 3
PHASE TRANSITION AND THERMAL DECOMPOSITION OF [Al(DMSO) ]Cl
6 3
Table 3 Parameters of [Al(DMSO) ]Cl thermal decomposition; sample mass=37.0941 mg
Temperature
Stage number
Mass after
decomposition/%
Calculated
values/%
Products of
decomposition
Mass loss/%
range/K
I
300–433
433–519
519–552
552–640
24.0
43.3
11.2
10.9
26.0
39.0
13.0
11.3
10.7*
2DMSO
3DMSO
1DMSO
II
III
IV
3/2Cl
2
1
0.6*
2 3
1/2Al O +3/2C
*
3
mass calculated after reaction of AlCl with CO according to Eq. (2)
to the liberation of the DMSO molecules. This process
can be described by the following reactions:
stage I
[
Al(DMSO) ]Cl ®[Al(DMSO) ]Cl +2DMSO
6 3 4 3
stage II
(1)
[
Al(DMSO) ]Cl ®[Al(DMSO)]Cl +3DMSO
4 3 3
stage III
[
Al(DMSO)]Cl ®AlCl +DMSO
3 3
At the second stage, the evolved dimethyl
sulfoxide simultaneously decomposes to mainly para-
formaldehyde. Dimethyl sulfide, dimethyl disulfide,
bis(methylthio)methane and water are other volatile
products. A small amount of dimethyl sulfone can
also be found [12]. At higher temperatures or after the
fragmentation of the above mentioned molecules,
mass spectrum of DMSO contains five main groups
of lines. The most intense lines in each group are situ-
ated at m/z values equal to: 15, 29, 45, 63 and 78.
6 3
Fig. 4 QMS curves for [Al(DMSO) ]Cl in the range of 300–640 K
They may correspond to CH
and CH SO , respectively [13, 14]. At the third stage,
, C H , C H O, CH SO
3 2 5 2 5 3
(
I, II, III and IV). It can be observed that the first stage,
which takes place in the temperature range of
00–433 K, involves release of two DMSO ligands in-
2
2
solid AlCl is also formed.
3
3
The fourth and last stage, which cannot be ob-
served in the SDTA curve, but is clearly seen in DTG
curve, can be explained by the instant reaction be-
cluded in coordination sphere of aluminium atom, per
one formula unit. In the second stage, which occurs in
the temperature range of 433–519 K, three DMSO lig-
ands are released. The third stage (in the temperature
range of 519–552 K) is connected with the loss of the
last DMSO ligand. In summary, in the temperature
range of 300–552 K, six molecules of dimethylsulfoxide
tween AlCl and CO, derived from the DMSO lig-
3
ands, according to the following reaction:
stage IV
AlCl +3/2CO®AlClO+Cl +3/2C+1/4O ®
3
2
2
are released and AlCl
minium chloride is created in the temperature range of
52–608 K (stage IV), it reacts with CO derived from
DMSO fragmentation and Al O , Cl and C are created.
3
is formed. Immediately after alu-
3
/2Cl +3/2C+1/2Al O
3
(2)
2
2
5
The above presented mechanism of thermal de-
composition of [Al(DMSO) ]Cl is highly consistent
2
3
2
6
3
After the fourth stage of the decomposition 10.6% of the
initial mass of the sample remained. The temperature
ranges, percentage of mass loss and the products of ther-
with the results which we obtained from the DSC
measurement. The DSC curve obtained for the stud-
ied compound by heating the sample in the tempera-
ture range of 300–650 K is presented in Fig. 5.
The profile of the DSC curve shows four endothermic
and one exothermic peaks. The first four endothermic
peaks can be explained by the three stages of the lib-
mal decomposition of [Al(DMSO) ]Cl at particular
6 3
stages are presented in Table 3.
The profile of the SDTA curve of [Al(DMSO) ]Cl
shows three endothermic peaks. All of them correspond
6
3
J. Therm. Anal. Cal., 90, 2007
227

MIGDA˜-MIKULI et al.
tion of AlCl with CO, which was derived from
3
DMSO decomposition.
Acknowledgements
We are grateful to Dr. hab. A. WeseÓucha-BirczyÕska,
Dr. C. Paluszkiewicz and Dr. D. Majda from the Regional
Laboratory of Physicochemical Analysis and Structural Re-
search in Kraków for FTRS, FT-FIR and TG/QMS/SDTA plus
DSC measurements, respectively.
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1
2
3
4
5
6
7
8
9
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Fig. 5 DSC curve registered on heating of [Al(DMSO) ]Cl in
–
1
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1
1
0 S. Ahrland and N. Björk, Acta Chem. Scand.,
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1 D. Dembicka and A. Bartecki, Koord. Chimia,
•
The DSC measurements of [Al(DMSO) ]Cl per-
6 3
formed in the temperature range of 95–300 K allowed
one phase transition to be discovered. The tempera-
10 (1984) 1519.
h
ture of the phase transition amounts to T =244.96 K
c
12 V. J. Traynelis and W. L. Hergenrother, J. Org. Chem.,
29 (1964) 221.
c
on heating) and T =220.87 K (on cooling). The
(
c
–1
–1
large value of transition entropy (DS»40 J mol K )
indicates its configurational character.
The phase polymorphism of the hexadimethylsulf-
13 D. A. Blank, S. W. North, D. Stranges, A. G. Suits and
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4 F. C. Thyrion and G. Debecker, Intern. J. Chem. Kinetics,
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•
•
5
oxidemetal(II)
chlorates(VII)
Mn(DMSO) ](ClO ) , [Co(DMSO) ](ClO ) ,
family:
1
[
[
6
4 2
6
4 2
Cd(DMSO) ](ClO ) and [Zn(DMSO) ](ClO ) , is
4 2
6
4 2
6
quite different than that of [Al(DMSO) ]Cl .
6
Received: May 19, 2006
Accepted: June 7, 2006
Accepted: October 20, 2006
3
The thermal decomposition of the investigated
compound proceeds in four main stages. In the first
stage two, and in the second stage three, DMSO
ligands are liberated. In the third stage, the last
molecule of DMSO is liberated and aluminium
chloride is created. In the fourth and last stage,
DOI: 10.1007/s10973-006-7694-z
Al O and carbon are formed as a result of the reac-
2 3
228
J. Therm. Anal. Cal., 90, 2007