Thermal studies of Ni(II), Pd(II), Pt(II) and Ru(III) complexes of N,N-dihexyl-N′-benzoylthiourea

Article abstract of DOI:10.1016/s0040-6031(99)00338-x

Some metal complexes of N,N-dihexyl-N′-benzoylthiourea (DHBT) of the type M(DHBT)_n [ M=Ni, Pd, Pt, (n=2), Ru, (n=3)] have been synthesised and studied using DTA and TG. These complexes undergo only the pyrolytic decomposition process. The orders, n, the activation energies, E, the pre-exponential factor, A, and the entropies, ΔS of the thermal decomposition reactions have been derived from thermogravimetric (TG) and differential thermogravimetric (DTG) curves. The characterisation of the end products of the decomposition was achieved by X-ray diffraction. UV-Vis and IR spectra were used for the investigation of characteristic absorption bands and the structural characterisation of ligand and the metals, respectively. Using the Coats and Redfern and Horowitz and Metzger methods performed kinetic analysis of the thermogravimetric data.

Full text of DOI:10.1016/s0040-6031(99)00338-x

Thermochimica Acta 343 (2000) 127±133
Thermal studies of Ni(II), Pd(II), Pt(II) and Ru(III)
complexes of N,N-dihexyl-N0-benzoylthiourea
a,*
N. Ozpozan , H. Arslan , T. Ozpozan , N. Ozdes, , N. KuÈlcuÈ
b
a
a
b
È
È
È
aChemistry Department, Erciyes University, Kayseri, Turkey
bChemistry Department, Mersin University, Mersin, Turkey
Received 22 March 1999; received in revised form 30 August 1999; accepted 2 September 1999
Abstract
Some metal complexes of N,N-dihexyl-N0-benzoylthiourea (DHBT) of the type M(DHBT)n [ M ˆ Ni, Pd, Pt, (n ˆ 2), Ru,
(n ˆ 3)] have been synthesised and studied using DTA and TG. These complexes undergo only the pyrolytic decomposition
process. The orders, n, the activation energies, E, the pre-exponential factor, A, and the entropies, DS of the thermal
decomposition reactions have been derived from thermogravimetric (TG) and differential thermogravimetric (DTG) curves.
The characterisation of the end products of the decomposition was achieved by X-ray diffraction. UV±Vis and IR spectra were
used for the investigation of characteristic absorption bands and the structural characterisation of ligand and the metals,
respectively. Using the Coats and Redfern and Horowitz and Metzger methods performed kinetic analysis of the
thermogravimetric data. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: N,N-dihexyl-N0-benzoylthiourea; Ru(III)-, Ni(II)-, Pd(II)-, and Pt(II)- complexes; Thermal behaviours; Thermal decomposition
kinetic; DTA/TG/DTG
1. Introduction
Ruthenium is a good hydrogenation catalyst, the usage
of this is not common at present [3]. Some amount of
these metals remains in the medium after they are used
as catalysts. The regeneration of these metals is
achieved by employing a complexing agent. One of
such agent is of N,N-dihexyl-N0-benzoylthiourea
which can be used successfully for those metals such
as Pt, Pd, Ru and Ni [4]. Thermal properties of these
metal complexes have not been studied previously. In
this study, thermal properties and decomposition
kinetics of the metal complexes of Ru(III), Ni(II),
Pd(II), and Pt(II) are investigated. In the decomposi-
tion kinetic study, the integral method employing the
Coats±Redfern equation and the approximation
method using the Horowitz±Metzger equation are
used for the calculation of kinetic parameters such
The natural resources of the platinum group metals
in the world are very rare. Usage of these metals in
industry is increasing and is being used in electricity±
electronic industry and as an auto-exhaust catalyst in
automobile industry, petroleum±chemical industry,
and jewellery industry [1]. One of the most important
features of these metals is high-rate hydrogen absorp-
tion when they are in metallic form. Therefore, they
are used as hydrogenation catalysts [2]. Pt and Pd
catalysts are being used for more than ten years.
* Corresponding author. Tel.: ‡90-0352-4374901; fax: ‡90-
0352-4374933.
E-mail address: ozpozant@erciyes.edu.tr (N. Ozpozan).
È
0040-6031/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 6 0 3 1 ( 9 9 ) 0 0 3 3 8 - X

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N. Ozpozan et al. / Thermochimica Acta 343 (2000) 127±133
128
as the reaction order, n, the activation energy, E,
entropies, DS and the pre-exponential factor, A, from
a nonisothermal kinetic study [5,6].
435 spectrophotometer, using KBr pellets. The DTA
and TG curves are obtained with Shimadzu DT-40
model simultaneously with DTA and TG apparatus.
The measurements were performed by using a
dynamic nitrogen atmosphere at a ¯ow rate of
1
2. Experimental
60 ml min
up to 1273 K. The heating rate was
108C min 1 and the sample sizes ranged in mass from
5 to 10 mg contained in platinum crucible. a-Al2O3 is
used as a reference material. Melting points were
determined by a digital m.p. instrument from Electro-
thermal Model 9200.
2.1. Synthesis procedure
The synthesis of ligand and metal complexes is
made as given in literature [7]. 0.01 mol Ni(II), Pd(II),
Pt(II), Ru(III) solutions are prepared from NiCl2,
PdCl2 (60% Merck), K2PtCl4 (47% Sigma),
RuCl3ÁH2O (38% Sigma) respectively. Metal com-
plexes are prepared with alcoholic ligand solutions,
mixed aqueous metal solutions, and solid complexes
are ®ltered off.
3. Results and discussions
3.1. Thermal analysis
All complexes were studied by thermogravimetric
analysis from ambient temperature to 1273 K in nitro-
gen atmosphere. The temperature ranges and percen-
tage mass losses are given in Table 1, together with the
temperatures of greatest rate of decomposition
(DTGmax) and the theoretical percentage mass losses.
Thermal curves obtained for most of the compounds
were very similar in character. All complexes show
two-stage mass loss. The ®rst mass loss corresponds to
the formation of M(SCN)2 and the second mass loss is
due to the decomposition of SCN and CN radicals.
The beginning and the end products were con®rmed
2.2. Instrumentation
X- ray powder diffraction analysis of the solid metal
complexes and the ®nal residue were made with a
Phillips PW-1010 model X-ray diffractometer using
Ê
CuKa radiation (ꢀ ˆ 1.5406 A) which work in the
range of 20±50 kV and 6±50 mA. The characteristic
absorption bands of metal complexes are obtained
with Hitachi 150-20 model double beam UV±Vis
absorption spectrophotometer. Infrared spectra were
recorded in the region 4000±400 cm 1 on a Shimadzu
Table 1
Thermoanalytical results on metal complexes of N,N-dihexyl-N0-benzoylthiourea
Complexes
Stage
Temperature
range (K)
DTGmax
(K)
Mass loss (%)
TG
Evolved moiety
Theoretical
Ni(DHBT)2
Pd(DHBT)2
Pt(DHBT)2
Ru(DHBT)3
I
438±651
651±855
>855
548
75.9
11.7
12.6
76.1
11.5
12.5
2DHB
SCN ‡ CN
NiS
II
793
±
Residue
I
507±682
682±807
>807
538
738
±
71.8
10.2
18.0
71.1
10.9
17.9
2DHB
SCN ‡ CN
PdS
II
Residue
I
475±691
691±814
>814
537
723
±
62.1
11.3
26.5
63.7
9.8
2DHB
SCN ‡ CN
PtS
II
Residue
26.6
Ia
421±538
538±780
780±1113
>1113
519
738
1025
±
49.4
25.0
15.9
9.2
49.9
24.9
15.2
9.8
2DHB
DHB
3SCN
Ru
Ib
II
Residue

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N. Ozpozan et al. / Thermochimica Acta 343 (2000) 127±133
129
Fig. 1. X-ray powder diffraction pattern of PdS.
via the IR spectrometric and X-ray diffraction data. As
an example, X-ray pattern of end product of Pd(II)
complex is shown in Fig. 1. It may also be noted here
that the absence of dehydration peaks in the DTG
curves and the absence of hydroxyl band in the IR
spectra indicate that all the compounds under inves-
tigation are anhydrous. The IR spectrum of
Pd(DHBT)2 is presented in Fig. 2 and the TG and
DTG curves of Ni(DHBT)2, Pd(DHBT)2, Pt(DHBT)2
and Ru(DHBT)3 are presented in Fig. 3. The DTA
Fig. 2. IR spectra of Pd(II)-N,N-dihexyl-N0-benzoylthiourea complex.

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N. Ozpozan et al. / Thermochimica Acta 343 (2000) 127±133
130
Fig. 3. TG±DTG curves for Ru(III)-, Ni(II)-, Pd(II)-, and Pt(II)-N,N-dihexyl-N0-benzoylthiourea complexes.
pro®les of related complexes are shown in Fig. 4. In
the case of Ru(DHBT)3, however, the decomposition
of ruthenium complex to metal itself is observed to
occur in two. The ®rst mass loss corresponds to the
elimination of two dihexylbenzamid (DHB) groups
followed by the elimination of other DHB group and
the formation of metallic ruthenium after the second
mass loss.
3.2. Ni(DHBT)2
The complex is thermally stable up to 438 K and
decomposition beyond this temperature as indicated
by the ®rst loss step in the TG curve. The mass loss at
438 K corresponds to the formation of Ni(SCN)2.
Beyond 651 K, continuous mass loss in the TG curve
has been observed up to 855 K, which corresponds to
the decomposition of Ni(SCN)2 to NiS. The DTA
pro®le shows two endothermic peaks at 351 and
543 K. First peak corresponding to the melting of
the complex, second endothermic peak corresponds
to the decomposition of the complexes to form
Ni(SCN)2. Exothermic thermal effects at 571 and
674 K correspond to the dimerisation of dihexylben-
zamid (DHB) which is decomposition product of the
complex, and the other exothermic effect corresponds
to the decomposition of Ni(SCN)2 to the NiS.
Fig. 4. DTA profiles for (a) Ni(II)-, (b) Ru(III)-, (c) Pd(II)-, and (d)
Pt(II)-N,N-dihexyl-N0-benzoylthiourea complexes.

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131
Table 2
Kinetic data on metal complexes of N,N-dihexyl-N0-benzoylthiourea
Complexes
Stage
Reaction
order (n)
Parameters
From Coats±
Redfern eqn.
From Horowitz±
Metzger eqn.
Ni(DHBT)2
I
0.959
0.514
Ea
158.0
5.7 Â 1012
20.7
168.1
5.2 Â 1013
12.5
Ab
DSc
rd
0.9996
55.3
0.9987
64.0
II
Ea
Ab
DSc
rd
305
176.0
0.9940
215
186.6
0.9957
Pd(DHBT)2
Pt(DHBT)2
Ru(DHBT)3
I
0.924
0.556
Ea
36.4
5.85
44.8
43.9
Ab
DSc
rd
208.9
0.9987
52.7
218.7
0.9979
61.5
II
Ea
Ab
DSc
rd
11.3
46.4
203.4
0.8145
220.6
0.8597
I
0.966
0.534
Ea
17.9
0.059
247.1
0.9654
18.7
21.3
0.141
266.3
0.9837
28.7
Ab
DSc
rd
II
Ea
Ab
DSc
rd
2.13
255.6
0.6065
0.12
269.5
0.7785
Ia
Ib
II
0.964
0.523
0.710
Ea
153.9
2.8 Â 1013
33.8
153.5
2.7 Â 1013
7.7
Ab
DSc
rd
0.9956
33.9
0.9960
37.2
Ea
Ab
DSc
rd
0.48
1.48
229.7
0.9333
107.1
603.4
170.3
0.9898
248.2
0.9648
94.9
Ea
Ab
DSc
rd
121.3
215.2
0.9959
1
a Unit of E is in kJ mol
.
1
b Unit of A is in s
.
c Unit of DS is in J mol 1 K
.
1
d r: correlation coefficient of the linear plot.
3.3. Pd(DHBT)2
corresponds to the formation of Pd(SCN)2. The next
decomposition step occurs in the temperature range
682±807 K and corresponds to the formation of PdS.
DTA pro®le shows two endothermic and one exother-
The TG curve indicates that the mass change begins
at 507 K and continuous up to 682 K. The mass loss

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N. Ozpozan et al. / Thermochimica Acta 343 (2000) 127±133
132
mic peaks. The ®rst, at 357 K corresponds to the
melting of the complex, while the second at 521 K
corresponds to the decomposition of the complex to
Pd(SCN)2. The third broad exothermic peak corre-
sponds to the dimerisation of dihexylbenzamid and
also corresponds to the decomposition of Pd(SCN)2 to
the PdS.
of Ru(DHBT)(SCN)2. Beyond 538 K continuous mass
loss in the TG curve has been observed up to 780 K
which correspond to the decomposition of
Ru(DHBT)(SCN)2 to Ru(SCN)3. After this decom-
position, the mass loss at 780±1113 K corresponds to
the formation of ruthenium metal. The DTA pro®le
shows two endothermic and one broad exothermic
peaks at 327, 515 and 693 K. The ®rst appears at
327 K corresponding to the melting of the complex,
while the second at 515 K corresponds to the decom-
position of the complex to Ru(DHBT)(SCN)2 and the
third exothermic peak at 693 K corresponds to the
dimerisation of dihexylbenzamid and also corre-
sponds to decomposition of Ru(SCN)3 to Ru.
3.4. Pt(DHBT)2
The TG curve shows an initial mass loss in the
temperature range 475±691 K corresponding to the
decomposition of the complex to Pt(SCN)2. This is
followed by another mass loss in the temperature
range 691±814 K due to the thermal decomposition
of Pt(SCN)2 to PtS. The DTA curve shows two
endothermic, one exothermic effects at 369, 514
and 693 K. The former corresponds to the melting
of the complex, the second to its decomposition to
Pt(SCN)2, and the third to the dimerisation of dihex-
ylbenzamid which also corresponds to the decompo-
sition of Pt(SCN)2 to the PtS.
3.6. Thermal decomposition
The results of TG±DTG studies are presented in
Table 2. These results reveal that the ®rst step decom-
position of Ni(II), Pd(II) and Pt(II) complexes give
corresponding thiocyanates, Ni(SCN)2, Pd(SCN)2 and
Pt(SCN)2. The former decomposes to NiS while the
second and the third to PdS, and PtS in the ®nal step,
respectively. From the TG curves, the order, n, and the
activation energy, E, of the thermal decomposition
reaction, the pre-exponential factor, A, and the entro-
pies, DS, of the decomposition reaction have been
elucidated by the methods of Coats±Redfern and
Horowitz±Metzger. The linearisation curves are
3.5. Ru(DHBT)3
The complex is thermally stable up to 421 K and
undergoes decomposition beyond this temperature, as
indicated by the ®rst mass loss step in the TG curve.
The mass loss at 538 K corresponds to the formation
Fig. 5. Linearisation curves of Coats±Redfern method for Ru(III)-, Ni(II)-, Pd(II)-, and Pt(II)-N,N-dihexyl-N0-benzoylthiourea complexes.

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N. Ozpozan et al. / Thermochimica Acta 343 (2000) 127±133
133
Fig. 6. Linearisation curves of Horowitz±Metzger method for Ru(III)-, Ni(II)-, Pd(II)-, and Pt(II)-N,N-dihexyl-N0-benzoylthiourea complexes.
shown in Figs. 5 and 6, respectively. Among these
three complexes having the same square-planar geo-
metry and the same decomposition steps, the smaller
size of Ni(II) as compared to Pd(II) and Pt(II) permits
a closer approach of the ligand to the Ni(II) ion. Hence
the E value for the Ni(II) complex is higher than that of
Pd(II) and Pt(II). The ionic sizes (r) of the metals are
shown below [8].
decomposing in two sub-stages is higher than that
of all values found for the other complexes. The
reaction orders found for the ®rst decomposition
stages of all complexes are nearly equal to unity.
References
[1] G.J.K. Ackes, K. Swars, Gmelin Handbook of Inorganic
Chemistry, 8th ed., Springer, Berlin, 1985.
Ions
Ru(III)
69
Ni(II)
72
Pd(II)
86
Pt(II)
96
[2] Werkgruppe Metalle Precious Metal Catalyst, PCHB 10,
Hanau, Hereaus, 1977.
r (pm)
[3] P.N. Rylander, Catalytic Hydrogenation Over Platinum
Metals, Academic Press, New York, 1977.
È
[4] K.H. Konig, Z. Anal. Chem. 319 (1984) 66.
The E values for the ®rst and second thermal
decomposition with respect to the method of Coats±
Redfern can be put into a descending order as,
ENi > EPd > EPt.
The E value of the ®rst decomposition stage of
Ru(III) complex having octahedral geometry and
[5] A.W. Coats, J.P. Redfern, Nature 201 (1964) 68.
[6] H.H. Horowitz, G. Metzger, Anal. Chem. 35 (1963) 1464.
[7] M. Schuster, Ph.D. Thesis, Johann Wolfgang Goethe
È
Universitat, Germany, 1986.
È
[8] N.K. Tunali, S. Ozkar, Inorganic Chemistry, Gazi University
Publication, Publication No. 185, Ankara, 1993.