Thermal decomposition of nickel(II), palladium(II), and platinum(II) complexes of N-allyl-N′-pyrimidin-2ylthiourea

Article abstract of DOI:10.1007/s10973-010-1009-0

Thermal decomposition of Ni(II), Pd(II), and Pt(II) complexes of N-pyrimidin-2ylthiourea (AllPmTu) have been studied by TG, DTG, and DTA and by electron impact (EI) mass spectra. The complexes have the molecular formulae as [Ni(AllPmTu)Cl₂(H₂O)], [Ni(AllPmTu)₂Cl ₂(H₂O)₂], and [M(AllPmTu)Cl₂], where M = Pd^II or Pt^II, and [Pt(AllPmTu)₂]. The TG curves show that Ni(II) complexes decompose in three stages to yield NiO as a residue, while Pd(II) and Pt(II) decompose in two stages to yield MS residues. The initial mass losses correspond to elimination of allylamine for Pd(II) and Pt(II) complexes but, allyisothiocyanate for both Ni(II) complexes revealing that sulfur atom of thiourea part is involved in coordination to Pd(II) and Pt(II) but does not to Ni(II). Kinetic parameters (E ^#, n, ΔH ^#, ΔS ^#, ΔG ^#) of the decomposition stages are determined and correlated with bonding and structural properties of the complexes. The EI mass spectra of the complexes show fragments corresponding to the evolved and intermediate species.

Full text of DOI:10.1007/s10973-010-1009-0

J Therm Anal Calorim (2011) 103:647–652
DOI 10.1007/s10973-010-1009-0
Thermal decomposition of nickel(II), palladium(II),
and platinum(II) complexes of N-allyl-N0-pyrimidin-2ylthiourea
Saud M. A. Katib
Received: 31 May 2010 / Accepted: 5 August 2010 / Published online: 28 August 2010
´
´
Ó Akademiai Kiado, Budapest, Hungary 2010
Abstract Thermal decomposition of Ni(II), Pd(II), and
Pt(II) complexes of N-pyrimidin-2ylthiourea (AllPmTu)
have been studied by TG, DTG, and DTA and by electron
impact (EI) mass spectra. The complexes have the molec-
ular formulae as [Ni(AllPmTu)Cl2(H2O)], [Ni(AllPmTu)2
Cl2(H2O)2], and [M(AllPmTu)Cl2], where M = PdII or PtII,
and [Pt(AllPmTu)2]. The TG curves show that Ni(II) com-
plexes decompose in three stages to yield NiO as a residue,
while Pd(II) and Pt(II) decompose in two stages to yield MS
residues. The initial mass losses correspond to elimination of
allylamine for Pd(II) and Pt(II) complexes but, allyisothio-
cyanate for both Ni(II) complexes revealing that sulfur atom
of thiourea part is involved in coordination to Pd(II) and
Pt(II) but does not to Ni(II). Kinetic parameters (E#, n, DH#,
DS#, DG#) of the decomposition stages are determined and
correlated with bonding and structural properties of the
complexes. The EI mass spectra of the complexes show
fragments corresponding to the evolved and intermediate
species.
compounds possess a wide range of biological applications
[1–3]. As part of our efforts to explore new metal complexes
of NS chelating agents that might exhibit beneficial thera-
peutic activity, we have reported the preparation and spectral
characterization of N-allyl-N0-pyridin-2ylthiourea (All-
PmTu) complexes of nickel(II), palladium(II), and plati-
num(II) [4] but no thermal studies have been reported. The
mechanisms of thermal decomposition of some thioureas
and their metal complexes have been reported [5, 6]. In this
article, it is aimed at studying the mechanism of decompo-
sition of these complexes in both solid and vapor states using
TG, DTA, and electron impact mass spectral techniques, in
order to support the mode of coordination of AllPmTu with
Ni(II), Pd(II), and Pt(II) ions, and to assess the influence of
the structural properties on their thermal behavior.
Experimental
Synthesis of complexes
Keywords Thiourea derivative ꢀ Ni(II), Pd(II) and Pt(II)
complexes ꢀ TG–DTA ꢀ Mass spectra
The synthesis of the ligand, AllPm, and corresponding metal
complexes are made by the procedures reported earlier [4].
Nickel(II) complexes were prepared from aqueous ethanolic
solution of nickel(II)chloride and AllPmTu in mole ratios 1:1
and 1:2 (M:L). The complexes were characterized as a mix-
ture of square planar/tetrahedral for [Ni(AllPmTu)Cl2(H2O)]
and as an octahedral for [Ni(AllPmTu)2Cl2(H2O)2], in both
complexes AllPmTu binds NiII as a monodentate ligand
through a pyrimidine-N. Palladium(II) and platinum(II)
were prepared by reacting aqueous solution of [MCl4]2-
with AllPmTu dissolved in EtOH in mole ratio 1:1, and PtCl2
with AllPmTu in acetone in mole ratio 1:2. The complexes
were characterized as a square planar for [M(AllPmTu)Cl2],
M = PdII or PtII and [Pt(AllPmTu)2] where AllPmTu binds
Introduction
Extensive studies on multidentate nitrogen–sulfur donors,
especially those with NS or NNS sequence chelating agents,
and their metal complexes. Such studies have led to new
S. M. A. Katib (&)
Department of Chemistry, Faculty of Applied Science,
Umm Al-Qurra University, Makkah, P.O. Box 6831,
Kingdom of Saudi Arabia
e-mail: saudKatib@hotmail.com
123

648
S. M. A. Katib
DrTGA
Mg/min
M as a neutral bidentate through a pyrimidine-N and thiono-S,
and binds PtII through a pyrimidine-N and thiolo-S atoms,
respectively.
TGA%
100
0.10
0.00
Instrumentation
80
60
40
20
–0.10
–0.20
The TG, DTG, and DTA curves were obtained using a
Shimadzu-50 thermal analyzer. The measurements were
performed in dynamic nitrogen atmosphere at a heating
rate of 10 °C min-1, using approximately 10 mg powdered
samples contained in a platinum crucible. a-Al2O3 is used
as a reference material.
243
405
–0.30
800
0
200
400
600
Temperature/°C
The electron impact mass spectra (EIMS) of the metal
complexes were performed on a Finigan Mat 312 spec-
trometer operating at 70 eV electron energy. The ion
source was set at 25 °C and a direct insertion probe (DIP)
was gradually heated from 50 to 300 °C. The electron
amplifier was maintained at 1,500 V.
Fig. 2 TG and DTG curves of [Pd(AllPmTu)Cl2]
DrTGA
Mg/min
TGA%
100
0.20
0.10
80
60
0.00
Results and discussion
256.98 °C
420.06 °C
–0.10
Thermal analysis
40
20
–0.20
800
The thermal behavior of AllPmTu metal complexes was
studied by using TG and DTA techniques from ambient
temperature up to 800 °C in nitrogen flow, Figs. 1, 2, 3, 4,
and 5. The stages of decomposition, temperature ranges,
the temperature of the greatest rate of decomposition
(DTGmax), the evolved products, as well as the found and
calculated mass loss percentages of Ni(II), Pd(II), and
Pt(II) complexes are given in Table 1.
0
200
400
600
Temperature/°C
Fig. 3 TG and DTG curves of [Pt(AllPmTu)Cl2]
DrTGA
Mg/min
TGA%
100
0.10
0.00
–0.10
[Ni(AllPmTu)Cl2(H2O)]
80
60
[Ni(AlPmTu)Cl2(H2O)] is thermally stable up to 150 °C
and decomposes beyond this temperature in a three stages
as indicated in the TG curve. The mass loss at 292 °C
–0.20
492.46 °C
40
–0.30
800
DrTGA
Mg/min
0.20
0
200
400
600
TGA%
Temperature/°C
100
Fig. 4 TG and DTG curves of [Pt(AllPmTu)2]
0.10
0.00
80
60
corresponds to the formation of [Ni(2-amPm)(H2O)], where
2-amPm = 2-aminopyrimidine), as a result of elimina-
tion of allylisothiocyanate moiety. This is evident by the
appearance in the EIMS a reasonable abundant species
with m/z 99 corresponding to AllSCN? and a less abundant
peaks corresponding to [Ni(2-amPm)Cl2(H2O) – 3]? and
[Ni(Pm)Cl2(H2O)]?, as a result of the structural damages
implicated in EI method due to both heating of the sample
and production of ions with high internal energies. Beyond
297.36 °C
206.89 °C
451.69 °C
575.43 °C
–0.10
–0.20
40
20
0
200
400
600
800
Temperature/°C
Fig. 1 TG and DTG curves of [Ni(AllPmTu)2Cl2(H2O)2]
123

Thermal decomposition
649
two allyisothiocyanate, occurs at different temperatures
and that the mechanism of decomposition is not straight-
forward and may be speculated as:
499.03 °C
[Pt(AllPmTu)2]
N
N
H
N
H
N
H
N
H
N
All
C
S
Pm
Ni
All
C
S
252.00 °C
H2O
H2O
Cl
- AllCNS
DTA, 206 °C
H2O
H2O
Cl
Cl
Ni
Cl
S
C
[Pt(AllPmTu)Cl2]
392.17 °C
Pm
NH2
248.03 °C
N
N
N
N
H
-
All
H
H2O
H
H
N
H
N
Cl
Ni
Pm
Ni
C
S
All
O
H2N
Pm
241.86 °C [Pd(AllPmTu)Cl2]
516.98 °C
Cl
H
- AllCNS
Cl
NH2
DTA, 278 °C
278.30 °C
388.78 °C
Cl
NH2
Pm
H2O
Pm
478.06 °C
[Ni(AllPmTu)2Cl2(H2O)2]
562.19 °C
The DTA curve, Fig. 5, shows one endothermic peak at
206 °C corresponding to the elimination of one allylis-
othiocyanate moiety and no peak for elimination of H2O
molecule, suggesting that the heat consumed in elimination
of H2O is nearly cancelled out by the heat evolved on bond
formation between thioketo sulfur and nickel(II). The
second mass loss occurs in the temperature range
325–481 °C on the TG curve which corresponds to elimi-
nation of 2 HCl molecules and formation of (2-APm)2NiO.
Beyond 481 °C, a continuous mass loss is observed up to
598 °C which corresponds to the decomposition of
(2-Pm)2NiO to NiO. The DTA profile, Fig. 5, also shows
two exothermic peaks at 389 and 571 °C corresponding to
the decomposition of the intermediate species with elimi-
nation of 2 HCl and 2(2-APm) molecules, respectively, and
formation.
309.42 °C
206.64 °C
[Ni(AllPmTu)Cl2(H2O)]
0.00
200.00
400.00
600.00
800.00
Temperature/°C
Fig. 5 DTA curves of AllPm Tu metal complexes
292 °C, a second mass loss has been observed up to 472 °C
corresponds to elimination of two HCl molecules and for-
mation of NiO(2-amPm). The EIMS shows a peak at
m/z 170 corresponds to NiO(2-amPm)?. Thereafter, the
mass loss continues until a species attains a constant mass at
595 °C, which corresponds to the formation of NiO. The
DTA curve, Fig. 5, shows two endothermic peaks at
207 and 309 °C corresponding the decomposition of the
complexes to NiO(2-amPm); one strong and broad exo-
thermic peak at 562 °C corresponds to the decomposition of
NiO(2-amPm) to NiO.
[Pd(AllPmTu)Cl2]
The TG curve of [Pd(AllPmTu)Cl2], Fig. 2, shows an ini-
tial mass loss in the temperature range 221–265 °C with a
DTGmax at 257 °C corresponding to the elimination of
allylimine moiety. This is followed by another mass loss in
the temperature range 265–452 °C with a DTGmax at
405 °C due to decomposition of 2-cyanopyrimidine radical
plus 2HCl molecules and formation of PdS. The DTA
profile, Fig. 5, shows one weak endothermic peak at
242 °C corresponds to the elimination of allylimine mol-
ecule and formation of [Pd(PmNHCHS)] and one relatively
broad strong exothermic peak at 420 °C corresponding to
the decomposition of the last intermediate to PdS and
dimerization (of) PmNC radical.
[Ni(AllPmTu)2Cl2(H2O)2]
The TG curve of [Ni(AlPmTu)2Cl2(H2O)2], Fig. 1, is
similar to that of [Ni(AlPmTu)Cl2(H2O)] and indicates that
the mass change begins at 173 °C and continues up to
598 °C in three stages. The initial mass loss in the tem-
perature range 173–325 °C in the TG curve corresponds to
the formation of [Ni(2-amPm)2Cl2(H2O)] with three
DTGmax values at 207, 242, and 297 °C. The appearance of
several DTG peaks for this step indicates that the greatest
rates of decomposition of the three species, one H2O plus
123

650
S. M. A. Katib
Table 1 Thermoanalytical results of metal complexes of N-allyl-N0-pyrimidin-2-ylthiourea
Complex
Stage
Temperature DTGmax/8C Mass loss/%
range/8C
Evolved moiety
DTA peak/8C
Found
Theor.
[Ni(AllPmTu)Cl2(H2O)]
(341.7)
I
150–292
292–472
472–595
243
427
529
–
C4H5NS
2HCl
252 (exo)
359 (exo)
562 (exo)
–
29.23
21.40
27.55
21.97
29.03
21.41
27.85
21.86
II
III
2-APm
NiO
Residue [595
[Ni(AllPmTu)2Cl2(H2O)2]
(553.7)
I
173–325
207, 297
452
H2O ? 2C4H5NS 2HCl
2(2-APm)
206(endo), 278(exo)
38.70
13.10
34.25
13.95
38.06
13.18
34.31
13.49
II
III
325–481
481–598
389 (exo)
571 (exo)
–
575
–
NiO
Residue [598
[Pd(AllPmTu)Cl2] (371)
[Pt(AllPmTu)Cl2] (460)
[Pt(AllPmTu)2] (583)
a
I
221–265
265–452
243
405
–
C3H5Na 2HCl ? PmNC PdS 242(endo)
14.6
14.8
II
392(exo)
–
48.10
37.30
47.97
37.19
Residue [452
I
195–265
265–481
257
420
–
C3H5N 2HCl ? PmNC PtS 243(endo)
12.05
38.40
49.55
11.95
38.69
49.34
II
441(exo)
–
Residue [481
I
195–385
385–535
269
492
2 C3H5NH2 PmNC?
PmNCS
252(endo)
499(exo)
20.03
41.87
38.10
19.55
41.50
38.93
II
PtS
Residue [535
HN=CH–CH=CH2; Pm: pyrimidine; 2-APm: 2-aminopyrimidine
[Pt(AllPmTu)Cl2]
PmNC radical plus PmSCN molecule [5] with the forma-
tion of PtS. The DTA profile, Fig. 5, shows an endothermic
peak at 252 °C and a broad strong exothermic peak at
499 °C which correspond to decomposition of 2-cyano-
pyrimidine radical plus a PmNC radical plus pyrmidin-2-
ylisothiocyanate molecule with the formation of PtS.
In order to asses the influences of the mode of bonding
of the ligand to the metal ions and the structural properties
of the complexes on their thermal behavior, the order, n,
and the heat of activation E# of the various decomposition
stages were determined from the TG and DTG thermo-
grams using the Coats–Redfern equations [7, 8] in the
following form:
The TG curve of [Pt(AllPmTu)Cl2], Fig. 3, shows a two
steps of decomposition similar to that of [Pd(All-
PmTu)Cl2]. The initial mass loss is in the temperature
range 195–269 °C with a DTGmax at 257 °C, correspond-
ing to decomposition of allylamine moiety. The second
step of decomposition shows a mass loss, in the tempera-
ture range 269–481 °C with a DTGmax at 420 °C, which is
consistent with elimination of PmNC radical and Cl2 with
the formation of PtS as the end product at 481 °C and up to
800 °C. The DTA curve, Fig. 5, shows an endothermic
peak at 243 °C corresponding to elimination of allylimine
moiety and a broad strong exothermic one at 441 °C due to
thermal decomposition of the remaining complex to PtS.
"
ꢀ
#
1ꢁn
1 ꢁ ð1 ꢁ aÞ
M
T
ln
¼
þ B for n ¼ 1;
ð1Þ
ð1 ꢁ nÞT2
ꢁ
[Pt(AllPmTu)2]
ꢁlnð1 ꢁ aÞ
M
ln
¼
þ B for n ¼ 1
ð2Þ
T2
T
The TG curve of [Pt(AlPmTu)2], Fig. 4, shows two steps of
decomposition. The first step is in 195–385 °C range with a
DTGmax at 269 °C, which corresponds to elimination of
two allylamine molecules. The other decomposition step
occurs in the temperature range 385–535 °C with a
DTGmax at 492 °C and corresponds to elimination of
where M = E#/R and B = lnAR/UE#; E#, R, A, and U are
the heat of activation, universal gas constant, pre-expo-
nential factor, and heating rate, respectively. The correla-
tion coefficient, r, was computed using the least squares
methods for different values of n, by plotting the left-hand
123

Thermal decomposition
651
Table 2 Temperature of decomposition and activation parameters of AllPmTu metal complexes
Complex
Step
T/K
r
A/s-1
E#/kJmol-1
DH#/kJmol-1
DS#/kJmol-1
DG#/kJmol-1
[Ni(AllPmTu)Cl2(H2O]
1st
2nd
3rd
1st
516
700
802
570
725
848
516
678
516
693
542
765
0.997371
0.996741
0.995710
0.998951
0.997929
0.988911
0.981165
0.953508
0.990819
0.980238
0.998395
0.903803
4.21 9 1011
7.88 9 109
2.58 9 1012
8.83 9 109
1.46 9 1011
2.69 9 1012
3.08 9 1012
3.50 9 107
5.42 9 109
7.51 9 108
1.00 9 1011
6.56 9 108
63.55
61.69
210.86
46.58
76.40
206.07
71.44
42.68
46.31
48.11
84.55
92.38
59.26
55.87
204.18
41.84
70.37
199.02
67.15
37.04
42.02
42.35
80.04
86.02
-0.027
-0.063
-0.016
-0.091
-0.063
-0.016
-0.017
-0.107
-0.064
-0.082
-0.039
-0.084
73.16
99.66
217.02
93.14
[Ni(AllPmTu)2Cl2(H2O)2]
2nd
3rd
1st
116.05
212.28
75.92
[Pd(AllPmTu)Cl2]
[Pt(AllPmTu)Cl2]
[Pt(AllPmTu)2]
2nd
1st
109.81
74.59
2nd
1st
99.18
101.18
150.24
2nd
side of the Eqs. 1 and 2 versus 1,000/T. The n value which
gave the best fit (r % 1) was chosen as the order parameter
for the decomposition stage of interest. From the intercept
and linear slope of such stage, the A and E# values were
determined. The other kinetic parameters, DH#, DS# and
DG# were computed using the relationships: DH# = E# –
RT, DS# = R[ln(Ah/kT) – 1] and DG# = DH# – TDS#,
where k is the Boltzmann’s constant and h is the Planck’s
constant. The kinetic parameters are collected in Table 2.
The following remarks can be pointed out:
complex, [Ni(AllPmTu)Cl2(H2O)], is lower than that
the octahedral one, [Ni(AllPmTu)2Cl2(H2O)2]. This
may be attributed to the larger values of CFSE of
octahedral than that of the tetrahedral and square-
planar nickel(II) complexes. The difference in DG#
values of the subsequent steps becomes smaller,
since the structure of the intermediate complexes
becomes similar.
(v) The DG# values of [Pt(AllPmTu)2] are higher than
that of [M(AllPmTu)Cl2], reflecting a higher thermal
stability of ML2 in terms of chelate effect.
(i) The negative values of the DS# indicate a more
ordered activated state than the reactants [9].
(vi) The reaction orders for all decomposition stages of all
complexes are found to be nearly equal unity. It was
emphasized that the order of a solid-state decompo-
sition reaction has no intrinsic meaning, but is rather a
mathematical smoothing parameter [12].
(ii) The values of the DG# increases markedly for the
subsequent decomposition stages of a given complex,
though there is no obvious trends in the values of
either E# or DH#. This is due to increasing the values
of TDS# from one step to another which override the
values of DH#. Increasing the values of DG# for
the subsequent steps of a given complex reflects that
the rate of removal of the subsequent species will be
lower than that of the precedent species [10, 11]. This
may be attributed to the structural rigidity of the
remaining complex after the expulsion of one or more
species, as compared with the precedent complex.
(iii) The values of DG# of the first step of decomposition
of the two structurally analogous, square-planar d8
complexes, [M(AllPmTu)Cl2], M = PdII or PtII, are
nearly equal, since this step is metal independent, but
DG# values of the second step of the two complexes
are different (DGP#d [ DGP#t), reflecting that the rate
of decomposition of this step involves the coordina-
tion core and reveals a relatively higher thermal
stability of Pt(II) complex as compared to Pd(II) one.
(iv) The DG# value for the first step, which involves the
coordination core, of the four-coordinate nickel(II)
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