Simultaneous thermal analysis of a cobalt(II) complex with nicotinate

Article abstract of DOI:10.1016/j.tca.2004.02.005

Dynamic kinetic analyses were performed on Co(NIA)₂(H ₂O)₄ (NIA: nicotinate (C₅H₄NCOOH)) using thermogravimetry (TG) and differential thermal analysis (DTA) measurements in air atmosphere. The thermal behavior and the kinetics of decomposition were studied. The effect of the heating rate on the thermal decomposition process was investigated. The Friedman method was applied to estimate the activation energy of decomposition.

Full text of DOI:10.1016/j.tca.2004.02.005

Thermochimica Acta 419 (2004) 115–117
Simultaneous thermal analysis of a cobalt(II) complex with nicotinate
∗
Yanhua Liu, Jiehui Yu, Jingzhe Zhao, Hui Zhang, Yanhui Deng, Zichen Wang
Department of Chemistry, Jilin University, 119 Jie Fang Road, Changchun 130023, PR China
Received 27 August 2003; received in revised form 1 February 2004; accepted 17 February 2004
Available online 9 April 2004
Abstract
Dynamic kinetic analyses were performed on Co(NIA)
2
2 4 5 4
(H O) (NIA: nicotinate (C H NCOOH)) using thermogravimetry (TG) and dif-
ferential thermal analysis (DTA) measurements in air atmosphere. The thermal behavior and the kinetics of decomposition were studied. The
effect of the heating rate on the thermal decomposition process was investigated. The Friedman method was applied to estimate the activation
energy of decomposition.
©
2004 Elsevier B.V. All rights reserved.
Keywords: Cobalt complex; Decomposition kinetics
1
. Introduction
2. Experimental
Co(NIA)2(H2O)4 (NIA: nicotinate) is a transition metal
The synthesis of Co(NIA)2(H2O)4 is described elsewhere
[1]. The product was submitted to thermal analysis. All the
experiments were performed on a Mettler Toledo simultane-
ous thermal analyzer (TGA/SDTA851e) with system inter-
face device and a computer workstation. All samples were
placed in aluminum crucibles. Experiments were performed
using sample sizes of 3 ± 0.3 mg. All the experiments were
conducted under air as the purge gas. The flow rate of the
gas was 50 ml/min. The range of temperature studied was
organic–inorganic composite compound with a novel
three-dimensional supramolecular structure. It displays re-
markably a cavity structure and ladder-type hydrogen bond
chains of carboxylates and water molecules. The design-
ing, synthesizing and determination of the structure of the
compound has been reported [1], but no study on thermo-
chemistry, so far as we know, has been done.
Thermogravimetry (TG) and differential thermal analy-
sis (DTA) are valuable techniques for studying the thermal
properties of various compounds. Materazzi et al. [2] had
reported the thermoanalytical studies of unusual adrenaline
complexes with Co(II), Ni(II) and Cu(II). Thermogravimet-
ric analysis of complexes of Co(II) chelates with Schiff
base reagents were studied by Madhu et al. [3]. Arshad
et al. [4] reported the thermal decomposition pattern of
◦
from 50 to 700 C, at the heating rates of 20, 30, 40 and
◦
50 C/min.
3. Results and discussion
Fig. 1 represent TG-DTA curves of the compound, for an
◦
1
,2-dipiperidinoethane complexes of Co(II), Ni(II), Cu(II),
experiment carried out at 30 C/min with a sample size of
3.224 mg in air. The curves show that the non-isothermal de-
composition of the compound occurs in two separate steps.
Zn(II) and Cd(II). The present study is aimed at the ther-
mal decomposition process of Co(NIA)2(H2O)4 in air at-
mosphere. The activation energy for the decomposition of
compound was also evaluated.
◦
The first weight loss starts at about 100 C; the first de-
composition stage ends with weight loss of 20.57% due to
the loss of water (calculated value is 19.10%). The second
◦
weight loss starts at about 370 C ending with a weight loss
of 59.98% due to the loss of nicotinate and the formation of
CoO (calculated value is 61.01%). The DTA curve shows an
endothermic peak for the first weight loss and an exothermic
peak for the second weight loss.
∗
Corresponding author. Tel.: +86-431-894-9334;
fax: +86-431-894-9334.
E-mail address: wangzc@mail.jlu.edu.cn (Z. Wang).
0
040-6031/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2004.02.005

1
16
Y. Liu et al. / Thermochimica Acta 419 (2004) 115–117
0
.6
2
4
0
1
00
0.4
1
st STEP
α = 0.1
α = 0.2
α = 0.3
α = 0.4
α = 0.5
α = 0.6
α = 0.7
α = 0.8
α = 0.9
2
0
.2
.0
exo
TG
0
8
6
4
2
0
0
0
0
16
-
-
-
-
0.2
0.4
0.6
0.8
1
8
4
0
2
-1.0
DTA
300
-1.2
-1.4
-1.6
-
4
100
200
400
500
600
700
-1.8
o
Temperature / C
Fig. 1. Typical TG-DTA plot for cobalt(II) complex.
2.20
2.25
2.30
2.35
2.40
2.45
2.50
1
000K/T
Fig. 2. Illustration for determining activation energy: plots of ln(dα/dt)
vs. 1/T for the first decomposition step.
Kinetic studies have been carried out at different temper-
atures by TG techniques. The apparent activation energy
of the decomposition process in non-isothermal conditions
can be calculated by isoconversional method [5–14]. The
isoconversional method avoids the use of explicit kinetic
models. The commonly used equation in the non-isothermal
decomposition kinetics is presented as [13]:
Figs. 3 and 4 present the data on activation energies of two
stages decomposition of the compound that was evaluated by
isoconversional method. Any point in figures was obtained
from the slope of ln(dα/dt) versus 1/T plot. In Fig. 3, we
see that the activation energy assumes values varying from
about 275.69 to 159.27 kJ/mol in the range of degree of
conversion 0.1–0.9. In Fig. 4, the values of activation energy
decrease from 400.22 to 13.05 kJ/mol in the range of degree
of conversion 0.1–0.9. The above results allows to confirm
that more than one reaction occurs in the first and second
decomposition process [10].The activation energy obtained
in air atmosphere is 188.42± 22.43 kJ/mol for the first weight
loss and 114.08 ± 10.86 kJ/mol for the second weight loss.
The sequence of processes implies that the water in
compound is held less strongly than the nicotinate. But the
ꢀ
ꢁ
dα
dt
Ea
=
A exp −
f(α)
(1)
RT
where α is the fraction decomposed at time t, dα/dt the rate
of the reaction, A the pre-exponential factor, Ea the appar-
ent activation energy, and f(α) is an expression describing
the kinetic model.
Isoconversional method of Friedman [15] is applied on
TG-differential thermogravimetry (DTG) data at different
heating rates. From Eq. (1), it follows that
ꢀ
ꢁ
dα
dt
Ea
ln
= −
+ ln[Af(α)]
(2)
RT
400
300
200
Alpha (α) at a particular time or temperature is defined as:
w − wt
i
α =
(3)
w − w
i
f
where wt is the solid weight at the time t, w the initial solid
i
weight, and w is the final weight.
f
The differential form of Eq. (3) gives
dα
dt
dwt/dt
=
−
(4)
w − wf
i
The function dwt/dt can be obtained directly from the dif-
ferential thermogravimetry plot, and the rate of the reaction
can be calculated using Eq. (4). This value of dα/dt obtained
from Eq. (4) is substituted into Eq. (2).The slope of ln(dα/dt)
versus 1/T for the same value of α gives the value of appar-
ent activation energy. As an illustration, such plots for the
first decomposition step are presented in Fig. 2. The appar-
ent activation energy can be calculated for various values
of α.
100
0.0
0.2
0.4
0.6
0.8
1.0
FractionConversion / %
Fig. 3. A plot of Ea as a function of α for the first stage decomposition
of the complex in air.

Y. Liu et al. / Thermochimica Acta 419 (2004) 115–117
117
8
6
4
2
00
00
00
00
0
steps of weight loss. An endothermic peak and an exother-
mic peak corresponding to two stages of decomposition are
observed. Activation energies for the first and the second
weight loss are 188.42 ± 22.43 and 114.08 ± 10.86 kJ/mol,
respectively.
References
[
[
[
[
[
[
[
1] H.B. Jia, J.H. Yu, J.Q. Xu, L. Ye, H. Ding, W.J. Jing, T.G. Wang,
J.N. Xu, Z.C. Li, J. Mol. Struct. 641 (2002) 23–27.
2] S. Materazzi, E. Vasca, U. Tentolini, S. Aquili, R. Curini, Ther-
mochim. Acta 389 (2002) 179–184.
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0.0
0.2
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1.0
Fraction Conversion / %
(
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Fig. 4. A plot of Ea as a function of α for the second stage decomposition
of the complex in air.
3
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Acta 392–393 (2002) 55–61.
activation energy for the first stage is greater than that of the
second stage. This might be due to the second stage com-
prising of the loss of nicotinate with simultaneous oxidation
Co to CoO.
[
[
8] C.K. Hsu, Thermochim. Acta 392–393 (2002) 163–167.
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[
7
[
4
. Conclusion
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92–393 (2002) 315–321.
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[15] H.L. Friedman, J. Polym. Sci.: Part C 6 (1964) 183–195.
3
[
[
Co(NIA)2(H2O)4 is a novel organic–inorganic composite
(
compound. The decomposition of the compound has been in-
vestigated by simultaneous thermal analysis at different heat-
ing rates in air atmosphere. The compound experiences two
(