Thermal behaviours of Co(II), Ni(II), Cu(II)), and Pb(II) complexes of N,N-dipropyl-N′-benzoylthiourea

Article abstract of DOI:10.1016/s0040-6031(99)00208-7

The Co(II), Ni(II), Cu(II)), and Pb(II) complexes of N,N-dipropyl-N′-benzoylthiourea (DPBT) are synthesised. The order, the activation energies, the entropies, and the pre-exponential factors of the thermal decomposition reactions are calculated with the

Full text of DOI:10.1016/s0040-6031(99)00208-7

Thermochimica Acta 336 (1999) 97±103
Thermal behaviours of Co(II), Ni(II), Cu(II)), and Pb(II)
complexes of N,N-dipropyl-N0-benzoylthiourea
N. Ozpozana,*, T. Ozpozana, H. Arslanb, F. Karipc,inc, N. KuÈlcuÈb
aChemistry Department, Erciyes University, Kayseri, Turkey
bChemistry Department, Mersin University, Mersin, Turkey
È
Chemistry Department, Suleyman Demirel University, Isparta, Turkey
c
Received 23 April 1999; accepted 1 July 1999
Abstract
The Co(II), Ni(II), Cu(II)), and Pb(II) complexes of N,N-dipropyl-N0-benzoylthiourea (DPBT) are synthesised. The order,
the activation energies, the entropies, and the pre-exponential factors of the thermal decomposition reactions are calculated
with the thermogravimetric curves. The kinetic analysis of the thermogravimetric data was performed by using the Coats±
Redfern and Horowitz±Metzger methods. # 1999 Published by Elsevier Science B.V. All rights reserved.
Keywords: N,N-dipropyl-N0-benzoylthiourea; Co(II), Ni(II), Cu(II), and Pb(II) complexes; Thermal behaviours; DTA/TG/DTG; Decom-
position kinetics
1. Introduction
the thermal behavioural point of view in the present
study.
The natural resources of Co, Ni, Cu, and Pb are used
in bulk quantities in nature. Industrial production and
the use of these elements can cause environmental
pollution. On the other hand some of these metals are
essential elements for biological systems present in
trace quantities. In each case, trace analysis of these
elements require pre-concentration prior to their ana-
lysis. To accomplish this pre-concentration process, a
water insoluble complex of the trace metal has to be
obtained and the solvent to enrich the complex has to
be removed. In our previous studies [1,2] some N-
substituted alkylbenzoylthiourea derivatives having
such properties and their metal complexes are synthe-
sised and their thermal behaviours are examined. N,N-
dipropyl-N0-benzoylthiourea is another such example
some metal complexes of which are examined from
2. Experimental
2.1. Preparation of samples
Metal solutions of Co(II), Cu(II), Ni(II) and Pb(II)
ions are prepared from analytical purity reagents of
CoCl2.6H2O, NiCl2, CuCl2.2H2O and Pb(NO3)2 salts.
Metal complexes, M(DPBT)2, (where M = Co, Ni, Cu,
and Pb) are obtained from the reactions of the metal
solutions with the alcoholic ligand solutions and solid
complexes are ®ltered out from the liquid phase [3].
2.2. Instrumental
The TG/DTG curves and DTA pro®les were
obtained on a DT-40 Model DTA/TG simultaneous
*Corresponding author. Tel.: +352-4374901; fax: +352-4374933
0040-6031/99/$ ± see front matter # 1999 Published by Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 6 0 3 1 ( 9 9 ) 0 0 2 0 8 - 7

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N. Ozpozan et al. / Thermochimica Acta 336 (1999) 97±103
Table 1
Thermoanalytical results on metal complexes of N,N-dipropyl-N0-benzoylthiourea
Complexes
Co(DPBT)2
Stage
Temperature range (K)
DTGmax
Mass loss (%)
TG
Evolved moiety
Theoretical
1a
Ib
476±513
513±568
568±833
>833
496
547
803
-
36.0
35.4
14.2
14.5
70.2
9.9
35.1
35.1
14.4
15.4
70.1
9.7
DPB
DPB
SCN + CN
CoS
II
Residue
Ni(DPBT)2
Cu(DPBT)2
Pb(DPBT)2
I
423±559
559±700
700±958
>958
534
666
775
-
2DPB
SCN
CN
II
III
4.4
4.4
Residue
Ia
15.5
34.8
34.8
19.7
10.8
55.8
15.8
29.0
15.6
34.8
34.8
19.6
10.8
55.9
15.8
28.3
NiS
471±495
495±561
561±759
>759
484
578
640
-
DPB
DPB
2SCN
Cu
Ib
II
Residue
I
470±538
538±724
>724
505
603
-
2DPB
2SCN
Pb
II
Residue
analyser. The measurements were performed by using
a dynamic nitrogen furnace atmosphere at a ¯ow rate
percentage mass losses of the decomposition reaction
are given in Table 1, together with the temperature of
greatest rate of decomposition (DTGmax) and the
theoretical percentage mass losses. The thermal
curves obtained for most of the compounds examined
were similar in character. All the complexes show
two-stage mass loss except Ni(II) complex in their TG/
DTG curves. The ®rst mass loss corresponds to the
formation of their respective thiocyanates. While the
second mass loss is due to the decomposition of the
thiocyanates. The end products were con®rmed with
the XRD data. As an example the X-ray pattern of the
end product of Ni(II) complex can be shown in Fig. 1.
1
of 60 ml min up to 1273 K. The heating rate was
10 min 1 and the sample sizes ranged in mass from 5
to 10 mg. Platinum crucible is used as sample con-
tainer, and a Al2O3 is used as reference substance.
Infrared spectra were recorded in the region 4000±
1
400 cm
on a Shimadzu 435 spectrophotometer,
using KBr pellets. X-ray powder diffraction analyses
of the ®nal residues were made with a Siemens F
model diffractometer. X-ray generator is Phillips, PW-
1010 model and ranging from 20 to 40 kV and 6 to
50 mA while using ®ne focus CuKa radiation
Ê
(ꢀ = 1.5406 A). The analyses of the characteristic
absorption bands of the sample were made with
Hitachi 150±20 model double beam UV-VIS absorp-
tion spectrophotometer. The control of melting points
was made with the Electro Thermal 9200 model
digital melting point apparatus.
3. Results and discussions
3.1. Thermal analysis
All the complexes were studied by thermogravi-
metric analysis from ambient temperature to 1273 K
in nitrogen atmosphere. The temperature ranges and
Fig. 1. X-ray powder diffraction pattern of NiS.

N. Ozpozan et al. / Thermochimica Acta 336 (1999) 97±103
99
Fig. 2. IR spectra of Ni(II)-N-N-dipropyl-N0-benzoylthiourea complex.
It may also be noted that the absence of dehydration
peaks in the DTG curves and the absence of hydroxyl
bands in the IR spectra indicate that all the compounds
under investigation are anhydrous. The IR spectrum of
Ni(DPBT)2 is presented in Fig. 2. The TG and DTG
curves of the complexes are presented in Fig. 3. The
DTA pro®les of Co(II), Ni(II), Cu(II), and Pb(II)
complexes are shown in Fig. 4.
In general, decomposition begins between 420 and
490 K, followed by a rapid mass loss over 60%. It was
presumed that metal-thiocyanate is formed at the end
of this step for which the calculated mass losses show
close agreement with the experimental values. The
mass losses at this stage are attributed to the evolved
moieties dipropylbenzamide (DPB = PhCON(C3H7)2).
In the case of Co(DPBT)2 and Cu(DPBT)2, however,
the decomposition of metal complexes to M(SCN)2
occurs in two sub-stages. The ®rst sub-stage (Ia) mass
losses in Co(DPBT)2, Cu(DPBT)2, correspond to the
formation of M(SCN)(DPBT) while the second sub-
stage (Ib) is responsible for the mass losses due to the
decomposition of the other 1 mole of DPBT. At the
end of the second stage, the second mass loss is due to
the decomposition of the SCN radicals to the metal
sulphur or the elemental metal.
3.2. Co(DPBT)2
The complex is thermally stable up to 476 K.
The mass loss at sub-stage Ia in the temperature
ranging from 476 to 513 K corresponds to the
decomposition of the complex to Co(DPBT)(SCN).
This is followed by another mass loss at stage Ib
in the temperature range 513±568 K due to the
decomposition of Co(DPBT)(SCN) to Co(SCN)2.
The last mass loss in the temperature range 568±
833 is due to the thermal decomposition of Co(SCN)2
to CoS.
The DTA curve shows two endothermic and one
exothermic effect, at 401, 474 and 545 K. The former
corresponds to the melting of the complex, the second
to its decomposition to Co(SCN)2 and the latter

100
N. Ozpozan et al. / Thermochimica Acta 336 (1999) 97±103
Fig. 3. TG/DTG curves for Co(II)-, Ni(II)-, Cu(II)-, and Pb(II)-
N,N-dipropyl-N0-benzoylthiourea complexes.
Fig. 4. DTA profiles for (A) Co(II)-, (B) Ni(II)-, (C) Pb(II)-, and
(D) Cu(II)- N,N-dipropyl-N0-benzoylthiourea complexes.
exothermic peak corresponds to dimerisation of dipro-
pylbenzamid group.
temperature range 561±759 K and corresponds to the
formation of metallic copper.
3.3. Ni(DPBT)2
The DTA pro®le shows two endothermic and two
exothermic effects. The ®rst, at 376 K, corresponds to
the melting of the complex, while the second, at 503 K
corresponds to the decomposition of the complex to
Cu(SCN)2. Exothermic effects correspond to the
dimerisation of dipropylbenzamid group.
The TG curve shows an initial mass loss in the
temperature range 423±559 K, corresponding to
the decomposition of the complex to Ni(SCN)2.
This is followed by another mass loss in the
temperature range 561±700 K due to the thermal
decomposition of Ni(SCN)2 to NiSCN. The last
decomposition step occurs in the temperature
range 714±958 K and it corresponds to the formation
of NiS.
3.5. Pb(DPBT)2
The TG of this complex reveals a mass loss in
the temperature range 470±538 K corresponding
to the formation of Pb(SCN)2. The next decom-
position step occurs in the temperature range 538±
724 K and corresponds to the formation of metallic
lead.
The DTA curve shows two endothermic peaks at
389 and 508 K. the former corresponds to the melting
of the complex, and the latter to its decomposition to
Pb(SCN)2
3.4. Cu(DPBT)2
The TG curve indicates that the mass change begins
at 471 K and continues up to 496 K. The mass loss
corresponds to the formation of Cu(DPBT)(SCN). The
next decomposition step occurs in the temperature
range 496±561 K and corresponds to the formation of
Cu(SCN)2. The last decomposition step occurs in the

N. Ozpozan et al. / Thermochimica Acta 336 (1999) 97±103
101
4. Discussion
The results of TG and DTG evaluations are pre-
sented in Table 1. The TG studies reveal that the ®rst
step decomposition of Pb(II) and Ni(II) complexes
result in the formation of the respective thiocyanates,
Pb (SCN)2 and Ni(SCN)2. The former decomposes to
metallic lead, while the latter to NiS yielding SCN and
CN radicals in two stages. In case of Cu(II) and Co(II),
the ®rst step decompositions occurs in two sub-stages
yielding metallic Cu and CoS, respectively.
From the TG curves, the order n, activation energy
E*, entropies ÁS*, and pre-exponential factors A, of
the thermal decompositions have been elucidated by
the methods of Coats±Redfern and Horowitz±Metzger
[4,5]. The linearisation curves are shown in Figs. 5 and
6, respectively. The results of kinetic studies of TG-
DTG are presented in Table 2.
Fig. 6. Linearisation curves of the first decomposition steps of
Horowitz±Metzger Method for Co(II)-, Ni(II)-, Cu(II)-, and Pb(II)-
N,N-dipropyl-N0-benzoylthiourea complexes.
Among these four complexes having the same
square-planar geometry and the similar decomposition
steps, the smaller size of Co(II) as compared to Cu(II),
(which are these two complexes decomposed in the
two sub-stages) permits a closer approach of the
ligand to the Co(II) ion [6]. Hence the E* value for
the Co(II) complex is higher than that of Cu(II). The
same is also true for the second sub-stages.
complex both of which lose two DPB molecules at this
stage.
Finally, the positive values of entropies of activation
(except Pb(II) complex) in the ®rst decomposition step
indicates that the activated complexes have less
ordered structures than the reactants [7]. The negative
values of ÁS* in the ®rst step of the decomposition of
Pb(II) and other steps of Co(II), Ni(II), and Cu(II)
complexes indicate that the reactions are slower than
normal [8,9]. The reaction orders found at all the
decomposition stages of the complexes are nearly
In a similar way, because of smaller ionic radius
of Ni(II), the E* value for the ®rst decomposi-
tion of Ni(II) complex is higher then that of Pb(II)
Fig. 5. Linearisation curves of the first decomposition steps of Coats±Redfern Method for Co(II)-, Ni(II)-, Pb(II)-, and Cu(II)-N,N-dipropyl-
N0-benzoylthiourea complexes

102
N. Ozpozan et al. / Thermochimica Acta 336 (1999) 97±103
Table 2
Kinetic data on metal complexes of N,N-dipropyl-N0-benzoylthioureaa
Complex
Stage
Reaction
order(n)
Parameters
From Coats±
Redfern eqn.
From Horowitz±
Metzger eqn.
Co(DPBT)2
Ia
0.852
0.821
0.780
0.760
0.713
0.924
0.925
0.968
0.841
0.982
0.946
E*
A
237.1
234.6
3.5 Â 1022
182.2
7.2 Â 1022
ÁS*
R
213.9
0.9974
78.6
0.9955
83.4
Ib
II
I
E*
A
2.1 Â 105
7.6 Â 105
ÁS*
r
121.8
0.9958
93.4
137.1
0.9965
91.1
E*
A
4.9x103
3.2 Â 103
ÁS*
r
152.9
0.9478
169.9
185.8
0.9649
170.8
Ni(DPBT)2
Cu(DPBT)2
Pb(DPBT)2
E*
A
2.5 Â 1014
3.6 Â 1014
ÁS*
r
51.9
0.9853
67.0
28.7
0.9898
83.1
II
III
Ia
Ib
II
I
E*
A
612
14200
172.0
ÁS*
r
170.3
0.9879
0.9919
E*
261.5
1.74 Â 1015
68.1
270.7
6.2 Â 1015
49.3
A
ÁS*
r
0.9981
0.9975
E*
274.3
6.1 Â 1027
308.3
281.3
3.5 Â 1028
297.5
A
ÁS*
r
0.9955
0.9973
E*
92.5
1.2 Â 107
134.3
103.1
1.5 Â 108
152.6
A
ÁS*
r
0.9946
42.0
7.6
0.9948
48.5
30.1
E*
A
ÁS*
r
206.7
222.7
0.9913
77.8
0.9938
80.8
E*
A
8.4 Â 105
1.4 Â 106
ÁS*
r
110.2
131.9
0.9963
34.8
1.6
0.9976
35.8
2.4
II
E*
A
ÁS*
r
219.2
243.3
0.9920
0.9975
a Unit of parameters: E* in kJ mole 1, A in s 1, ÁS* in J mole 1 K 1, r±correlation coefficient of the linear plot, n±order of reaction.
equal to unity. The melting points of the complexes
increase in the order; Cu(II) < Pb(II) < Co(II) < Ni(II)
corresponding the numerical values in Kelvin; 376,
389, 401, 420 in the same order.
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