Polymorphism and thermal decomposition of [Ni(DMSO)4]I 2

Article abstract of DOI:10.1007/s10973-008-9304-8

Tetrakis(dimethyl sulphoxide)nickel(II) bis(iodide) was studied by thermogravimetry (TG) and simultaneous differential thermal analysis (SDTA) and differential scanning calorimetry (DSC). The gaseous products of the decomposition were on-line identified by a quadrupole mass spectrometer (QMS). Thermal decomposition of the title compound proceeds in three main stages. In the first stage, which starts just above ca. 419 K, the compound loses two dimethyl sulphoxide (DMSO) molecules per one formula unit and small amount of iodide ion. In the second stage (464-552 K) the next DMSO ligands and the iodide ion simultaneously are released. In the last stage (552-900 K) NiSO4 is created which next decomposes to NiO and SO₃.

Full text of DOI:10.1007/s10973-008-9304-8

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Journal of Thermal Analysis and Calorimetry, Vol. 93 (2008) 3, 853–856
POLYMORPHISM AND THERMAL DECOMPOSITION OF [Ni(DMSO)4]I2
Anna MigdaÓ-Mikuli, Elübieta Szostak*, K. Druübicki and Diana DoÓÄga
Department of Chemical Physics, Faculty of Chemistry, Jagiellonian University, ulica Ingardena 3, 30-060 Kraków, Poland
Tetrakis(dimethyl sulphoxide)nickel(II) bis(iodide) was studied by thermogravimetry (TG) and simultaneous differential thermal
analysis (SDTA) and differential scanning calorimetry (DSC). The gaseous products of the decomposition were on-line identified
by a quadrupole mass spectrometer (QMS). Thermal decomposition of the title compound proceeds in three main stages. In the first
stage, which starts just above ca. 419 K, the compound loses two dimethyl sulphoxide (DMSO) molecules per one formula unit and
small amount of iodide ion. In the second stage (464–552 K) the next DMSO ligands and the iodide ion simultaneously are released.
In the last stage (552–900 K) NiSO4 is created which next decomposes to NiO and SO3.
Keywords: DSC, SDTA, tetrakis(dimethyl sulphoxide)nickel(II) bis(iodide), TG/QMS, thermal decomposition
Introduction
Experimental
Materials
This kind of compound has been studied regarding to
the polymorphism and thermal stability of the
compounds of the type: [M(DMSO)y](X)2, where
DMSO=(CH3)2SO; X=BF– , ClO– , NO– ; M=Mg, Mn,
Examined compound was obtained from hexa-
aquanickel(II) iodide which was earlier synthesised
4
4
3
by
the
reaction
of
nickel
carbonate
Co, Ni, Zn and Cd; y=4 or 6 [1–8]. Thermogravi-
metry (TG, DTG), simultaneous evolved gas analysis
with on-line quadrupole mass spectrometer
(SEGA/QMS) and simultaneous differential thermal
analysis (SDTA) measurements were performed for
these substances in order to enable verification of
their chemical composition and thermal 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.
The crystallization of [M(DMSO)y](X)2 undergo
in a specific way because some of the phases can be
very easily overcooled. Namely, in dependence of
those how fast and how deep was the sample cooled,
on DSC curve were observed from one to six
anomalies connected with phase transitions between
different stable and different overcooled, metastable
phases. It was concluded from the value of the
enthalpy changes, that some of these phases are
so-called ‘orientationally dynamically disordered
crystals’ (ODIC) and the others are more and less
ordered phases. The crystal structure, phase
polymorphism and mechanism of thermal decom-
position of [Ni(DMSO)4]I2 is so far unknown.
(www.sigmaaldrich.com-CAS number: 12607-
70-4) with diluted HI (in molar ratio 1:6). The hexa-
aquanickel(II) iodide was dissolved (in molar ra-
tio 1:6) while being slowly heated up in dimethyl-
sulphoxide (DMSO) which was previously purified
by vacuum distillation at low pressure. Then this
solution was chilled and the precipitated crystals of
[Ni(DMSO)4]I2 were filtered. This compound was
then dried in a desiccator over phosphorous ox-
ide(V) for few hours. After desiccation, it was put
in a sealed vessel and stored in a desiccator with
barium oxide as a desiccant.
Methods
To check the chemical composition of the synthesised
compound, the percentage content of nickel ions was
checked using a complexometric method, with a
solution of sodium salt of ethylenediaminetetraacetic
acid (EDTA) as a titrant. The content of carbon and
hydrogen in the DMSO ligand was determined using
elementary analysis in an EURO EA 3000 apparatus.
The theoretical content of nickel equalled 9.39%, and
its content found by the titration analysis amounted to
9.28±0.12%. For the carbon atoms, the difference
between the theoretical (15.37%) and test value
(15.43±0.01%) did not exceed 1%. For the hydrogen
atoms, the theoretical value was 3.87% and the test
The main aim of these studies was to establish
the mechanism of the thermal decomposition of
[Ni(DMSO)4]I2 using methods of thermal analysis
(TG, DTG, QMS, SDTA and DSC).
*
Author for correspondence: szostak@chemija.uj.edu.pl
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2008 Akadémiai Kiadó, Budapest

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
MIGDA˜-MIKULI et al.
value 3.87±0.01%. Therefore, the elementary
analysis of the title compound confirmed the presence
of the stoichiometric number of four DMSO mole-
cules in the complex cation.
Fourier transform Raman scattering measure-
ments (FTRS) were performed at room temperature
with a Bio-Rad spectrometer with a resolution of
4 cm–1. The incident radiation (l=1064 nm) was from
the Neodymium laser YAG Spectra-Physics. Fourier
transform middle-infrared absorption measurements
(FT-MIR)
were
performed
using
a
Bruker EQUINOX-55 spectrometers, with a resolution
of 2 cm–1. The FT-MIR spectrum was recorded for a
sample suspended in Nujol between KBr pellets.
The thermogravimetry (TG) and simultaneous
differential thermal analysis were performed using a
Mettler-Toledo TGA/SDTA 851e instrument.
The measurements were made in
a
flow
(80 mL min–1) of high purity dry argon (99.999%)
within temperature range 300–900 K. The TG
measurements were performed at a constant heating
rate of 10 K min–1. Additionally gas evolved during
the experiment was analyzed with on-line quadrupole
mass spectrometer (QMS) using a Balzer GSD 300T
instrument. The temperature was measured by a
Pt–Pt/Rh thermocouple with the accuracy of ±0.5 K.
The thermal decomposition measurements were made
for a sample weighing 19.42 mg which was placed in
a 150 mL open corundum a-Al2O3 crucible.
Fig. 1 Comparison of the infrared (FT-MIR) and Raman
(FT-RS) spectra of [Ni(DMSO)4]I2
The differential scanning calorimetry (DSC)
measurements were made using a Mettler Toledo
DSC 821e apparatus used in the temperature range of
300–823 K. The DSC measurements were made by
heating the sample of mass of 8.93 mg, measurements
were performed under constant flow of argon
(80 mL min–1), with the heating rate equals to
5 K min–1.
Results and discussion
In order to further identify of the synthesized com-
pound the FTRS and FTIR spectra were registered
[9, 10]. Figure 1 shows a comparison of Raman and
infrared spectra of [Ni(DMSO)4]I2 obtained at room
temperature. The cation was considered to have
tetrahedral symmetry with nearly freely rotating CH3
groups of DMSO ligands.
Fig. 2 TG, DTG, SDTA and DSC curves for [Ni(DMSO)4]I2
in the range of 300–900 K registered at a constant
heating rate of 10 K min–1 and DSC curves in the range
of 300–823 K registered at a constant heating rate of
5 K min–1
Figure 2 shows TG, DTG and SDTA curves
recorded for the sample in the temperature range of
300–900 K, and DSC curve recorded in the temper-
ature range of 300–823 K. We can see small differ-
ences between DSC and SDTA profiles because they
were performed under different conditions (masses of
samples, scanning rates, open and closed crucibles).
The DSC measurements were made in different
conditions in order to compare results obtained for
title compound with data obtained for previously
investigated compounds. As an insertion in Fig. 2
were placed the results of the DSC measurement for
854
J. Therm. Anal. Cal., 93, 2008

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
POLYMORPHISM AND THERMAL DECOMPOSITION OF [Ni(DMSO)4]I2
[Ni(DMSO)4]I2 in the temperature range 300–350 K.
As can be seen while heating sample from 300 to
350 K, an irreversible phase transition into the high
temperature phase can be observed at TC=315 K
(small anomaly on the DSC curve).
in Fig. 3. The TG, DTG and QMS curves show that
the decomposition of the sample proceeds in three
main stages (I, II and III). The mechanism of thermal
analysis of the title compound is presented in Table 1
and the thermogravimetric data are gathered in
Table 2. It can be observed that the first stage
(300–464 K) of thermolysis, which starts just above
419 K, involves release of two DMSO ligands per one
formula unit. This process undergoes very probably in
the two steps. At the end of this stage at 455 K also
small amount of iodide ion is released (the third
anomaly on the DTG curve) [11]. This ion imme-
diately reacts with CH3 radical derived from DMSO
fragmentation and [(CH3)3SO]+I– (TMSOI) is created
[12, 13]. The profile of the DSC curve shows that in
the vicinity of 455 K some exothermic process is
began. Releasing of small amount of iodide and
creation of TMSOI can explained this anomaly. In the
second stage, which occurs in the temperature range
of 464–552 K, we can observe melting and decom-
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=78, 61, 45, 127, 63, 44, 29, 15, 32, 17 and 18
representing CH2SO2 or (CH3)2SO, CHSO, C2H5O, I,
CH3SO, CO2, C2H5, CH3, O2, OH and H2O are shown
×
position of new-created TMSOI to CH3SO, CH3 and
I– and partial decomposition of resulting
×
[Ni(DMSO)2]I2
into
[Ni(CH3)2SO]I
radical
[11, 12, 14]. The profile of the SDTA curve of
[Ni(DMSO)4]I2 in this temperature range shows one
exothermic peak. It is probably because the TMSOI is
also created here but immediately decompose to
–
CH3SO, CH3 radical and I [12, 14]. In the third stage
×
(in the temperature range of 552–900 K) the DMSO
×
molecules reacts with OH radical derived from
DMSO fragmentation [15]. Created in this process
×
×
H2SO4 and CH3 can react with [Ni(CH3)2SO]I giving
trimethyl sulphoxonium iodide (TMSOI), nickel
sulphate, and hydrogen. New-created TMSOI decom-
Fig. 3 QMS curves for [Ni(DMSO)4]I2 in the range of
posed immediately to: CH3SO, CH3 and I–.
×
300–900 K
Table 1 Mechanism of thermal analysis of [Ni(DMSO)4]I2
Stage number
Reaction
[Ni((CH3)2SO)4]I2®[Ni((CH3)2SO)3]I2+(CH3)2SO
References
Ia
Ib
Ic
Id
[this work]
[this work]
[11]
[Ni((CH3)2SO)3]I2®[Ni((CH3)2SO)2]I2+(CH3)2SO
–
×
x([Ni((CH3)2SO)2]I2)®x( [Ni((CH3)2SO)]I)+x((CH3)2SO)+xI
× ×
x((CH3)2SO®x( CH3SO)+x( CH3)
[12]
–
x( CH3)+xI +x(CH3)2SO®x[(CH3)3SO] I
+ –
×
[13]
+ –
x[(CH3)3SO] I ®xCH3SO+2x( CH3)+xI
–
×
IIa
IIb
[12, 14]
[11]
–
×
(1–x)[Ni((CH3)2SO)2]I2®(1–x)( [Ni(CH3)2SO]I)+(1–x)(CH3)2SO+(1–x)I
– + –
(1–x)(CH3)2SO+(1–x)I ®(1–x)[(CH3)3SO] I ®(1–x)CH3SO+(2–2x)( CH3)+(1–x)I
–
×
[12, 14]
[15]
× ×
(CH3)2SO+ OH®CH3S(O)OH+ CH3
IIIa
×
CH3S(O)OH+ OH®CH3S(O)(OH)2+O2®CH3S(O)2OH+HO2
[15]
× ×
CH3S(O)2OH+ OH®H2SO4+ CH3
[15]
+ –
( [Ni((CH3)2SO)]I)+H2SO4+ CH3+®[(CH3)3SO] I +NiSO4+0.5H2
×
×
IIIb
IIIc
[this work]
[12, 14]
[this work]
+ –
[(CH3)3SO] I ®CH3SO+2( CH3)+I
–
×
NiSO4®NiO+SO3
J. Therm. Anal. Cal., 93, 2008
855

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
MIGDA˜-MIKULI et al.
Table 2 Parameters of [Ni(DMSO)4]I2 thermal decomposition; sample mass=19.42 mg
Stage
Temp. range/
K
Mass loss/
%
Mass after
Products of
Calc. values/%
25.0
number
decomposition/%
decomposition
×
2(CH3)2SO, x( [Ni((CH3)2SO)]I)
I
300–464
29.8
x[(CH3)3SO]+I–
(1–x)([Ni((CH3)2SO)]I), CH3SO,
II
464–552
552–900
31.5
26.5
32.8
2(CH3), I–
30.2
12.0
CH3SO , 2(CH3), 0.5H2, SO3, I–
NiO
III
12.2
The decomposition gets completed at 810 K, when
created in this stage nickel sulphate decomposes into
anhydrous nickel oxide and sulphur trioxide.
ately to CH3SO, >CH3 and I–. The decomposition
gets completed at 810 K when created in this stage
nickel sulphate decomposes into anhydrous nickel
oxide and sulphur trioxide.
Conclusions
Acknowledgements
1. The DSC measurements of [Ni(DMSO)4]I2 per-
formed in the temperature range of 300–350 K using a
Mettler-Toledo 851e apparatus allowed to detect one
phase transition at Tc=315 K (DH=2.43 kJ mol–1,
DS=7.7 J mol–1 K–1). In opposite to our previous
investigations the high temperature phase was not
orientationally disordered ones.
We are grateful to Professor E. Mikuli from our Faculty for
stimulating the discussion.
References
1 A. MigdaÓ-Mikuli, E. Mikuli, E. Szostak and
J. SerwoÕska, Z. Naturforsch., 58a (2003) 341.
2 A. MigdaÓ-Mikuli and E. Szostak, Thermochim. Acta,
426 (2005) 191.
2. The TG, DTG and QMS curves show that the
decomposition of the sample proceeds in three main
stages (I, II and III):
3 A. MigdaÓ-Mikuli and E. Szostak, Z. Naturforsch.,
60a (2005) 289.
• It can be observed that the first stage (300–464 K)
of thermolysis, which starts just above 419 K, in-
volves release of two DMSO ligands per one for-
mula unit. This process undergoes very probably in
the two steps. At the end of this stage also small
amount of iodide ion is released [11]. This ion im-
mediately reacts with >CH3 radical derived from
DMSO fragmentation and [(CH3)3SO]+I– (TMSOI)
is created [12, 13].
4 A. MigdaÓ-Mikuli, ˜. Skoczylas and E. Szostak,
Z. Naturforsch., 61a (2006) 180.
5 A. MigdaÓ-Mikuli and E. Szostak, Thermochim. Acta,
444 (2006) 195.
6 E. Szostak, W. Nitek and A. MigdaÓ-Mikuli, Acta Cryst.,
E 62 (2006) m2581.
7 A. MigdaÓ-Mikuli and E. Szostak, Z. Naturforsch.,
62a (2007) 67.
8 A. MigdaÓ-Mikuli and N. Górska, J. Therm. Anal. Cal.,
90 (2007) 833.
• In the second stage, which occurs in the tempera-
ture range of 464–552 K, we can observe melting
and decomposition of new-created TMSOI to
CH3SO>, >CH3 and I– and partial decomposition of
resulting [Ni(DMSO)2]I2 into >[Ni(CH3)2SO]I radi-
cal [11, 12, 14]. The profile of the SDTA curve of
[Ni(DMSO)4]I2 shows one exothermic peak in this
temperature range. It is probably because the
TMSOI is also created here but immediately de-
compose to CH3SO, CH3 radical and I– [12, 14].
• In the third stage (in the temperature range of
552–900 K) the DMSO molecules reacts with >OH
radical derived from DMSO fragmentation [15].
Created in this process H2SO4 and >CH3 can react
with >[Ni(CH3)2SO]I giving trimethyl sulphoxo-
nium iodide (TMSOI), nickel sulphate, and hydro-
gen. New-created TMSOI decomposed immedi-
9 Raman/IR Atlas, Verlag Chemie GmbH, Weinheim,
Bergstr., 1974.
10 K. Nakamoto, Infrared and Raman Spectra of Inorganic
and Coordination Compounds, Part B, 5th Ed., A. Wiley
Intersience Publ., NY 1997.
11 N. T. Madhu, P.K. Radhakrishnan and W. Linert,
J. Therm. Anal. Cal., 84 (2006) 607.
12 D. A. Blank, S. W. North, D. Stranges, A. G. Suits and
T. Yuan, J. Chem. Phys., 106 (1997) 539.
13 S. G. Smith and S. Winstein, Tetrahedron, 3 (1958) 317.
14 A. T. J. Klein and M. Holschbach, Appl. Radiat. Isot.,
55 (2001) 309.
15 M. Mori, K. Tanaka, H. Taoda, M. Ikedo and H. Itabashi,
Talanta, 70 (2006) 169.
DOI: 10.1007/s10973-008-9304-8
856
J. Therm. Anal. Cal., 93, 2008