Thermal decomposition kinetics of M (mnt) (5-NO2-phen) (M=CoII, CuII, ZnII) complexes

Article abstract of DOI:10.1016/s0040-6031(98)00428-6

Studies of the non-isothermal decomposition of M (mnt) (5-NO₂-phen) (M=Co^II, Cu^II, Zn^II) were carried out by thermogravimetry. The thermal decomposition mechanisms and associated kinetics have been investigated.

Full text of DOI:10.1016/s0040-6031(98)00428-6

Thermochimica Acta 320 (1998) 291±295
Thermal decomposition kinetics of M (mnt) (5-NO2-phen)
(MˆCoII, CuII, ZnII) complexes
Chen Donghuaa,*, Yuan Yuhonga, Peng Zhengheb, Jian Lihuaa, Pan Qingcaib, Qin Zibinb
a Department of Chemistry, South-Central University for Nationalities, Wuhan 430074, China
b Department of Chemistry, Wuhan University, Wuhan, China
Received 14 July 1997; received in revised form 19 June 1998; accepted 20 June 1998
Abstract
Studies of the non-isothermal decomposition of M (mnt) (5-NO2-phen) (MˆCoII, CuII, ZnII) were carried out by
thermogravimetry. The thermal decomposition mechanisms and associated kinetics have been investigated. The kinetic
parameters were obtained from an analysis of the TG±DTG curves by integral and differential methods. The most probable
kinetic model functions were suggested by comparison of the kinetic parameters. Mathematical expressions for the kinetic
compensation effect were derived. # 1998 Elsevier Science B.V.
Keywords: Metal complex; Mixed ligand; Non-isothermal kinetics; TG; Thermal decomposition
1. Introduction
phen) type and to provide valuable data for their
applications, we studied the thermal decomposition
processes of these complexes by TG and DTG tech-
niques and the kinetic parameters were obtained by
integral and differential methods. The possible
decomposition mechanisms are also discussed.
Recently, we have reported the synthesis and prop-
erties of cobalt (II), cupper (II) and zinc (II) complexes
of mixed ligand (Lˆmnt, L0ˆbpy) [1±3]. Subse-
quently, we have synthesized a series of complexes
of the type M (mnt) (5-NO2-phen) (MˆCoII, CuII,
ZnII) [4]. These complexes have potential electronic
application as a result of their gas-sensitivity, photo-
sensitivity and photoconductivity properties. It is
known that these complexes have potential applica-
tions as gas sensors, photovoltaic cell, non-linear
optical devices and molecular devices [5]. The aim
of this investigation was to show the in¯uence of the
nature of the metal on the thermal stability of these
complexes of the mixed ligand (Lˆmnt, L0ˆ5-NO2-
2. Experimental
2.1. Synthesis procedures
Complexes Co (mnt) (5-NO2-phen)Á0.5H2O (I), Cu
(mnt) (5-NO2-phen) (II) and Zn (mnt) (5-NO2-
phen)Á0.5H2O (III) have been synthesized by reaction
of disodum 1,2-dicyanoethlene-1,2-dithiolate [Na2
(mnt)] with the relative metal complex M (5-NO2-
phen) Cl2, respectively. The structure and properties
of the M (mnt) (5-NO2-phen) were determined by
*Corresonding author. Tel.: 0086 27 87801223; e-mail:
znmzxy@public.wh.hb.cn
0040-6031/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved
P I I S 0 0 4 0 - 6 0 3 1 ( 9 8 ) 0 0 4 2 8 - 6

292
C. Donghua et al. / Thermochimica Acta 320 (1998) 291±295
elemental analysis, molar conductivity, molar suscept-
ibility, IR, UV-VIS, EPR and ¯uorescence spectra [4].
2.2. Instrumental
Thermogravimetric analysis was performed on a
Perkin±Elmer TGS-2 thermobalance, employing the
following conditions: sample mass: 3.00 mg; heating
rate: 58C min 1; atmosphere: static air; temperature
range: 30±8308C.
All the thermogravimetric data were analysed on an
AT-486 computer.
Fig. 2. TG±DTG curves of Cu (mnt) (5-NO2-phen).
3. Result and discussion
3.2. Thermal decomposition kinetics
3.1. Thermal analysis
We used the Narahari Achar [6] and the Coats±
Redfern [7] method to derive the kinetics parameters
and a possible kinetic model function of thermal
decomposition was suggested by comparing the
kinetic parameters.
The TG±DTG curves of the complexes in
the temperature range 30±8308C are shown in
Figs. 1±3. They show that the thermal decomposition
processes of complexes I and II involve three stages
and complex III four stages. The TG±DTG data are
given in Table 1.
The stoichiometry of the thermal decompositions of
complexes I±III can be expressed by the following
schemes:
The Narahari Achar equation is:
ln‰ꢀdꢀ=dT†=fꢀꢀ†Š ˆ ln ꢀA=ꢁ† E=RT
The Coats±Redfern equation is:
(1)
ln‰gꢀꢀ†=T2Š ˆ lnꢀAR=ꢁE† E=RT
(2)
where ꢀ is the reaction fraction of decomposition, ꢁ
the heating rate, E the activation energy in J/mol, A the
frequency factor, R the gas constant in J/mol K, and
g(ꢀ) and f(ꢀ) are the most probable kinetic model
functions. We took the complex III for stage (1) as an
example to demonstrate the process.
From the TG±DTG curves of the complex III, the
base data (T, ꢀ, dꢀ/dT) for stage (1) can be obtained as
shown in Table 2.
(a) Co (C12H7N3O2) (C4S2N2)Á0.5H2O (I)!
Co(C12H7N3O2) (C4S2N2) (I0)!Co(C12H7N3O2)1/2
(C4S2N2)!CoSO4
(b) Cu (C12H7N3O2) (C4S2N2) (II)!Cu
(C12H7N3O2)2/3 (C4S2N2)!CuS2!Cu2S
(c) Zn (C12H7N3O2) (C4S2N2)Á0.5H2O (III)!Zn
(C12H7N3O2) (C4S2N2)(III0)!Zn (C12H7N3O2)1/3
(C4S2N2)!Zn(C3S2N)!ZnO
Fig. 1. TG±DTG curves of Co (mnt) (5-NO2-phen)Á0.5H2O.
Fig. 3. TG±DTG curves of Zn (mnt) (5-NO2-phen)Á0.5H2O.

C. Donghua et al. / Thermochimica Acta 320 (1998) 291±295
293
Table 1
The thermal decomposition data of three complexes by TG±DTG
Stages of
decomposition
TG
plateaux/8C
DTG
peak/8C
% mass loss found
(calculated)
Residue/%
Found
Residue
found
Colour
theory
Calc.
35.80
Co (mnt) (5-NO2-phen)Á0.5H2O
(1)
(2)
(3)
31
171
406
83
406
533
58
290
444
2.58 (2.08)
24.53 (25.98)
38.72 (36.14)
35.60
18.64
black
black
black
black
Cu (mnt) (5-NO2-phen)
(1)
(2)
(3)
162
297
486
741
275
450
651
16.59 (17.48)
53.81 (52.68)
11.19 (11.18)
297
507
18.65
Zn (mnt) (5-NO2-phen)Á0.5H2O
(1)
(2)
(3)
(4)
31
139
456
506
90
456
506
643
67
262
482
581
2.47 (2.05)
33.25 (34.17)
24.19 (23.01)
22.50 (22.30)
19.59
18.45
white
white
Thirty-one types of kinetic model functions [8]
function No. 6 whose values of E and ln A were very
close to each other with the better value of r. We
conclude that the kinetic equation of thermal decom-
position of complex III for stage (1) is dꢀ/dtˆ
were into Eqs. (1) and (2), respectively. The values
of E, ln A and the linear correlation coef®cients (r) of
different model functions were calculated from a
weighted least±squares plot of ln[(dꢀ/dT)/f(ꢀ)] vs.
1/T and of ln[g(ꢀ)/T2] vs. 1/T. The results are listed
in Table 3. Comparing the kinetic parameters from
methods, we selected the probable kinetic model
E/RT
1/3
A/ꢁÁe
Â3/2(1 ꢀ)4/3/[(1 ꢀ)
1].
It shows that the ®rst stage of decomposition for
complex III is controlled by D3 diffusion mechanism.
The calculated values of the kinetic parameters of
three complexes for each stage and their probable
kinetic model functions are summarized in Table 4.
Table 2
Data for stage (1) of Zn (mnt) (5-NO2-phen)Á0.5H2O determined by
3.3. The kinetic compensation effect
TG±DTG
Data point
T/K
ꢀ
dꢀ/dT
According to the mathematical expression for the
kinetic compensation effect ln AˆaE‡b [9], we ®tted
the kinetic parameters (E and ln A) obtained from the
differential methods by the linear least-squares
method. The obtained values of a and b are listed
in Table 4.
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
2
310.52
311.77
313.02
315.52
323.02
325.52
328.12
330.52
333.02
335.51
338.01
340.51
343.01
345.51
348.01
349.26
0.1183
0.1428
0.1673
0.2244
0.3510
0.3959
0.4408
0.4816
0.5142
0.5428
0.5877
0.6489
0.7183
0.7306
0.8244
0.8612
1.9591Â10
1.9259Â10
2.0919Â10
2.2085Â10
1.6881Â10
1.8368Â10
1.7399Â10
1.4889Â10
1.1204Â10
1.3892Â10
2.1507Â10
2.7425Â10
2.5524Â10
2.3377Â10
2.6535Â10
3.1241Â10
3
4
5
6
7
8
9
4. Conclusions
10
11
12
13
14
15
16
Thermal analysis results obtained for the complexes
I to III indicate that the complexes under study, when
thermally decomposed, release water (I and III), at
®rst, the dehydration temperature being ca. 908C; the
release of ligand is a three-stage (II, III0), two-stage (I0)

294
C. Donghua et al. / Thermochimica Acta 320 (1998) 291±295
Table 3
Results of kinetic analysis for stage (1) of Zn (mnt) (5-NO2-phen))Á0.5H2O
Function
no.
Integral method
Differential method
1
1
)
1
1
)
ln A/s
E/(kJ mol
r
ln A/s
E/(kJ mol
r
1
2
22.58
25.39
28.17
25.30
17.02
37.68
13.42
10.63
9.51
80.29
89.03
99.78
92.58
72.08
123.87
52.88
35.25
26.44
17.62
13.22
48.53
47.16
44.51
37.41
58.85
15.97
8.83
0.9757
0.9287
0.9886
0.9850
0.9704
0.9932
0.9911
0.9911
0.9911
0.9911
0.9911
0.9884
0.9872
0.9843
0.9720
0.9746
0.9616
0.9446
0.9149
0.9911
0.9926
0.9901
0.9794
0.9329
0.8807
0.8194
0.9920
0.9922
0.9924
0.9795
0.9835
11.42
16.73
22.31
17.66
4.57
49.43
64.90
83.26
71.22
37.72
119.39
42.68
23.23
13.50
3.78
0.9572
0.9654
0.9655
0.9657
0.9325
0.9818
0.8347
0.6298
0.4226
0.1279
0.0366
0.7998
0.7834
0.7387
0.3518
0.8733
0.5945
0.7212
0.7629
0.8347
0.8714
0.8898
0.9076
0.9156
0.9581
0.9569
0.9640
0.9835
0.9892
0.0150
0.1641
3
4
5
6
36.26
9.94
7
8
2.62
1.11
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
7.55
4.98
6.67
6.99
1.08
10.26
9.99
5.06
4.19
33.56
30.64
24.62
6.55
9.31
2.27
7.08
4.00
14.90
1.14
3.76
27.99
14.88
22.02
25.60
42.68
60.74
78.80
114.93
29.56
65.69
101.82
101.03
159.38
217.74
0.36
12.07
14.93
16.45
9.94
4.19
5.94
5.25
13.42
16.63
21.70
32.38
3.16
52.88
62.57
73.54
98.76
26.51
18.93
13.55
111.24
169.59
227.94
19.52
20.84
16.22
23.89
38.54
17.26
30.81
44.84
31.37
52.52
73.54
6.82
0.23
1.96
34.90
56.06
77.10
0.08
0.46
5.21
4.32
Table 4
All metal complexes stage's kinetic model functions and correspond compensation effect
Metal complex Stage Function No. Integral method
Differential method
Compensation effect
1
1
1
1
E/(kJ mol
)
ln A/s
r
E/(kJ mol
)
lnA/s
r
a
b
r
CoII
(1)
(2)
(3)
23
29
23
136.23
222.29
352.92
47.46
38.50
55.11
0.9860 136.85
0.9932 235.54
0.9820 320.16
47.82
40.98
49.47
0.8282 0.3765
0.9764 0.2124
0.9573 0.1688
6.41
8.54
7.47
0.9995
0.9972
0.9995
CuII
ZnII
(2)
(3)
1
6
135.92
292.79
15.56
30.29
0.9800 135.75
0.9744 275.65
15.55
27.77
0.9722 0.1757
0.9117 0.1353
8.03
8.38
0.9987
0.9987
(1)
(2)
(3)
(4)
6
29
21
5
123.87
154.31
497.84
307.32
37.68
22.58
74.09
34.40
0.9932 119.39
0.9946 168.70
0.9985 488.42
0.9988 327.46
36.26
25.56
72.66
37.13
0.9818 0.3699
0.9839 0.2046
0.9861 0.1612
0.9417 0.1451
6.71
8.56
6.61
7.66
0.9991
0.9937
0.9999
0.9996

C. Donghua et al. / Thermochimica Acta 320 (1998) 291±295
295
process; the initial and ®nal temperature of decom-
position of the complexes (I0, II and III0) for ®rst stage
are in the range 171±4068C, 162±2978C and 139±
4568C, respectively. It is concluded that it is possible
to establish the following relative thermal stability
order: Co (mnt) (5-NO2-phen)>Cu (mnt) (5-NO2-
phen)>Zn (mnt) (5-NO2-phen).
29471022) and the Approach Fund of State Key
Laboratory of Coordination Chemistry in Nanjing
University is gratefully acknowledge.
References
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Xuebao 10(2) (1994) 115.
From Table 4, there is no regular variation in the
values of the kinetic parameters of decomposition of
the complexes. The activation energy of the dehydra-
tion reactions for complexes I and III is in the range
113.39±136.85 kJ/mol. The activation energy of the
decomposition reaction for complexes I0, II and III0 is
in the range 135.92±497.84 kJ/mol which indicates
that the metal±ligand bond is strong.
[2] Wang Shuoxing, Peng Zhenghe, Qin Zibin, Huaxue Tongbao
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Acknowledgements
Financial support for this work from the National
Natural Science Foundation of China (Grants
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