Thermal decomposition kinetics of the synthetic complex Pb(1,4-BDC)?(DMF)(H2O)

Article abstract of DOI:10.1007/s10973-007-8494-9

Pb(1,4-BDC)?(DMF)(H₂O) (1,4-BDC=1,4-benzenedicarboxylate; DMF=dimethylformamide) has been synthesized and investigated by elemental analysis, FTIR spectroscopy, thermogravimetry (TG), derivative thermogravimetry (DTG). TG-DTG curves show that t

Full text of DOI:10.1007/s10973-007-8494-9

Journal of Thermal Analysis and Calorimetry, Vol. 91 (2008) 1, 189–193
THERMAL DECOMPOSITION KINETICS OF THE SYNTHETIC
COMPLEX Pb(1,4-BDC)×(DMF)(H2O)
J. Zhang1,2, J. L. Zeng1,2, Y. Y. Liu1,2, L. X. Sun1*, F. Xu1, W. S. You3 and Y. Sawada4
1Materials and Thermochemistry Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences
Dalian 116023, P.R. China
2Graduate School of the Chinese Academy of Sciences, Beijing 100049, P.R. China
3Liaoning Nomal Univ., Fac. Chem. and Chem. Engn., Dalian 116029, P.R. China
4Department of Nanochemistry, Faculty of Engineering, Tokyo Polytechnic University, 1583 Iiyama, Atsugi,
Kanagawa, 243-0297 Japan
Pb(1,4-BDC)×(DMF)(H2O) (1,4-BDC=1,4-benzenedicarboxylate; DMF=dimethylformamide) has been synthesized and investi-
gated by elemental analysis, FTIR spectroscopy, thermogravimetry (TG), derivative thermogravimetry (DTG). TG-DTG curves
show that the thermal decomposition occurs in four stages and the corresponding apparent activation energies were calculated with
the Ozawa–Flynn–Wall (OFW) and the Friedman methods. The most probable kinetic model function of the dehydration reaction of
the compound has been estimated by the Coats–Redfern integral and the Achar–Bridly–Sharp differential methods in this study.
Keywords: apparent activation energy, kinetic model, TG-DTG, thermal decomposition
Introduction
Friedman [14] were used in this study to evaluate the ap-
parent activation energy. The most probable kinetic
model of thermal dehydration of the compound has been
suggested according to Coats–Redfern integral method
and Achar–Bridly–Sharp differential method.
1,4-benzenedicarboxylic acid (1,4-H2BDC) with a 180º
separation between the two carboxylic groups can be
coordinated with many transition and non-transition
metals , which is an ideal ligand to design novel coordi-
nation polymers and metal organic open framework
structures [1–4]. A series of transition-metal complexes Experimental
with 1,4-benzenedicarboxylate (1,4-BDC) and its deriv-
Sample preparation
atives have been reported and investigated due to their
potential applications in separations, hydrogen sorption,
All materials were commercially available and were of
non-linear optics, magnetism and catalysis [4–8]. In
contrast to other transition-metal 1,4-benzenedi-
carboxylate complexes, lead complexes with 1,4-BDC
are much less studied. Recently, Yaghi et al. reported
Pb(1,4-BDC)(C2H5OH)×(C2H5OH), which becomes un-
stable exposure to air [4]. In addition, some thermal be-
haviors of metal complexes have been already investi-
gated by a number of researchers [9–11], but there has
been very little report on thermal decomposition kinetics
in literature up to now. Kinetic analysis of thermal anal-
ysis data is an important tool for estimating the thermal
stability and allows obtaining some information on ther-
mal decomposition mechanisms at high temperature.
In the present work, Pb(1,4-BDC)×(DMF)(H2O)
(DMF=dimethylformamide) has been synthesized and
characterized by elemental analysis, FTIR spectroscopy
and thermogravimetric (TG) analysis. Kinetic methods,
such as the Ozawa–Flynn–Wall (OFW) [12, 13] and
analytical grade unless stated elsewhere. The lead com-
plex was synthesized using solvothermal method.
Lead(II) nitrate (1.66 g, 5.0 mmol) and 1,4-H2BDC
(0.83 g, 5.0 mmol) were dissolved in DMF/1,4-dioxane
(5:2 by volume, 70 mL). The clear solution was then re-
moved in a Teflon bomb. The bomb was heated
to 393 K and maintained at this temperature for 3 days.
After slowly cooling down to the room temperature, the
final product obtained as yellowish crystals was col-
lected by filtration and washed three times with DMF
(50 mL) and dried in air. This lead complex is air stable
and is insoluble in water and most of the common or-
ganic solvents.
Elemental analyses for C11H13NO6Pb found (%):
C, 28.58; H, 2.24; N, 3.16; calc. (%): C, 28.55;
H, 2.81; N, 3.03. The content of lead was determined
by thermogravimetry analysis. The purity of the sam-
ple was >99.0%.
*
Author for correspondence: lxsun@dicp.ac.cn
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2008 Akadémiai Kiadó, Budapest

ZHANG et al.
FTIR (KBr pellet, 4000–400 cm–1 ): 3450(br),
(calcd. 3.89%) likely due to the loss of a molecule of
water. The second stage takes place between 468
and 644 K and is accompanied by 13.94% mass loss
which roughly coincides with the calculated value
of 15.81%. It is attributed to the loss of a molecule of
DMF. Subsequently, the decomposition of the ligand
(1,4-BDC) is followed. Two well-separated peaks are
presented on the DTG curve, this indicates that the
decomposition of the ligand (1,4-BDC) is divided
into two steps. The third rapid loss of 18.26%
(calcd. 17.33%) and the fourth slow loss of 8.47%
(calcd. 6.92%) are observed in the region
of 644–815 K, and there is probably some complex of
lead carbonate and carbon between the two processes
(PbCO3·2C). The overall mass loss of the sample is
about 44.50% in accord with the calculated percent-
age (43.95%). Heating the black residue in air on an
electric stove, the sample mass lost and the color be-
came yellow. So the final black residue was estimated
as inorganic mixture of lead monoxide and carbon un-
der nitrogen atmosphere.
3049(w), 2929(w), 2881(w), 1645(s), 1547(s),
1500(w), 1437(w), 11371(s), 1315(w), 1296(w),
1256(w), 11460(w), 1103(m), 1063(w), 1016(m),
982(w), 885(m), 864(w), 835(w), 746(s), 660(m),
519(s), 410(w). FTIR spectroscopy shows that the
carboxyl groups of the ligand have been coordinated
to the metal ion.
Methods
Elemental analysis was carried on PE-2400 II Se-
ries CHNS/O analyzer. FTIR spectrum was recorded
on Bruker Equinox 55 infrared spectrometer using
KBr pellet in the range of 4000–400 cm–1.
Thermal analysis
A thermogravimetric analyzer (Model: Setsys 16/18,
Setaram Co., France) was used for TG measurement
of this sample under nitrogen atmosphere (99.999%).
Several experiments were carried out at heating rates
of b=5, 10, 15, 20 K min–1 and the flow rate of nitro-
gen was 45 cm3 min–1. The mass of the sample was
ca. 10 mg. Two Al2O3 crucibles were used (capac-
ity: 100 mL). The reference crucible was filled with
a-Al2O3. The TG equipment was calibrated by the
CaC2O4×H2O (99.9%).
The possible mechanism of the thermal decom-
positions was deduced as follows:
Pb(1,4-BDC)×(DMF)H2O
¯363–468 K
Pb(1,4-BDC)×(DMF)
¯468–520 K
Pb(1,4-BDC)
¯644–745 K
PbCO3+2C
Results and discussion
¯745–815 K
PbO+3C
Thermal analysis
Figure 1 displays the TG and DTG curves obtained at
heating rate of 5 K min–1 under nitrogen atmosphere.
The curves exhibit that the non-isothermal decompo-
sition of the compound undergoes four stages in the
temperature range of 300 to 900 K. The first mass loss
starts at about 363 K and is about 3.83%
Kinetic methods
Model-free estimation of activation energy
Two typical isoconversional methods of integral
Ozawa–Flynn–Wall and differential Friedman have
been widely applied to estimate the apparent activa-
tion energy without having to presuppose a certain ki-
netic model. Figure 2 shows the TG curves of
Pb(1,4-BDC)×(DMF)(H2O) measured in N2 atmo-
sphere from 300 to 900 K with the heating rate
of 5, 10, 15, 20 K min–1, respectively. The basic data
(b, a, T) taken from the TG curves are used in the
following equations:
DTG
0
–10
–20
–30
–40
–50
0
3.83%
13.94%
–2
18.26%
8.47% –4
TG
Ozawa–Flynn–Wall equation [12, 13]:
AE
R
1.052Ea
æ
ç
è
ö
÷
ø
a
lnb = ln
– ln g(a ) – 5.3305 –
(1)
RTa
300
400
500
600
700
800
900
Temperature/K
where b is heating rate, a extent of conversion, g(a)
integral expression of kinetic function, E apparent ac-
tivation energy, A pre-exponential factor and R gas
Fig. 1 TG-DTG curves of Pb(1,4-BDC)×(DMF)(H2O) under high
purity nitrogen atmosphere at heating rate of 5 K min–1
190
J. Therm. Anal. Cal., 91, 2008

SYNTHETIC COMPLEX Pb(1,4-BDC)×(DMF)(H2O)
400
300
200
100
0
0
–10
–20
–30
–40
–50
step 1
step 2
step 3
step 4
–1
b=5 K min
–1
b=10 K min
–1
b=15 K min
–1
b=20 K min
300
400
500
600
700
800
900
1000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Temperature/K
a
Fig. 4 Apparent activation energy in relation to the conversion
for the four steps based on the OFW method
Fig. 2 TG curves of Pb(1,4-BDC)×(DMF)(H2O) under high
purity nitrogen atmosphere at 5, 10, 15, 20 K min–1
3.2
2.8
2.4
400
step 1
step 2
step 3
300
200
100
0
step 4
0.2
0.8
2.0
1.6
2.08 2.12 2.16 2.20 2.24 2.28 2.32 2.36 2.40 2.44
1000/T/K–1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
a
Fig. 3 OFW analysis of the thermal decomposition of
Pb(1,4-BDC)×(DMF)(H2O) for the first step at 5, 10,
15, 20 K min–1
Fig. 5 Apparent activation energy in relation to the conversion
for the four steps based on the Friedman method
For four decomposition stages, the apparent activa-
tion energy can be calculated at different extent of con-
version (in the range 0.2£a£0.8) using both Eqs (1)
and (2), and the results are presented in Figs 4 and 5, re-
spectively. The average value and standard deviation of
the activation energies are tabulated in Table 1.
Comparing the results from two isoconversional
methods, the apparent activation energies values cal-
culated by Friedman method are larger than those of
OFW method for the first and third steps. However,
the reverse results are obtained for the other steps. It
is well known that Friedman method is very sensitive
to experimental noise, and tends to be numerically un-
stable because of employing instantaneous rate value.
But OFW method produces a systematic error in Ea
constant. The subscript a indicates the values related
to a particular extent of conversion. For constant val-
ues of a, plots of lnb vs. 1/Ta should fit to a straight
line with a slope of –1.052Ea/R. Such plots for the de-
hydration step of the complex at different a
(0.2£a£0.8) are exhibited in Fig. 3.
Friedman equation [14]:
Ea
da
dt
æ
ç
ö
÷
ln
= ln[Af (a )] –
(2)
RTa
è
øa
where da/dt is the rate of conversion and f(a) differen-
tial expression of kinetic function. A plot of ln(da/dt)a
vs. 1/Ta gives a straight line with a slope of –Ea/R.
Table 1 Apparent activation energy obtained from the OFW and Friedman methods for four steps
Ea/kJ mol–1
Method
step 1
step 2
step 3
step 4
OFW
104.42±4.70
118.46±16.33
217.27±12.82
206.29±18.33
245.66±11.19
275.62±14.73
209.24±7.42
185.53±5.03
Friedman
J. Therm. Anal. Cal., 91, 2008
191

ZHANG et al.
when the activation energy varies with a. This error
does not appear in Friedman method [15].
é
ù
1
da
E
ln
= ln(A / b) –
(4)
ê
ú
f (a ) dt
RT
ë
û
Plotting ln{[1/f(a)][da/dt]} vs. 1/T, a straight
line is given. The activation energy E and pre-expo-
nential factor A can be obtained from the slope –E/R
and the intercept ln(A/b).
The basic data a, T and da/dt of the four decom-
position steps and fifteen reaction models commonly
used in solid-state reaction kinetics [19] were inserted
into Eqs (3) and (4).
Determination of the most probable kinetic model
Coats–Redfern integral equation [16, 17]
g(a )
T 2
AR
E
ln
= ln
–
(3)
bE RT
The values of E, lnA and the linear correlation
coefficients r are calculated from the linear least-
squares plot of ln[g(a)/T 2] vs. 1/T, which the slope is
equal to –E/R and the intercept is equal to ln(AR/bE).
Achar–Bridly–Sharp differential equation [18]
For the first step of dehydration, the results and
the reaction model are listed in Table 2. Comparing the
activation energies data in Tables 1 and 2, the possible
Table 2 Non-isothermal kinetic parameters obtained from Coats–Redfern equation and Achar–Brindley–Sharp equation for
b=5 K min–1 for the first step
Achar–Brindley–Sharp
Coats–Redfern
Mechanism
E/kJ mol–1
lnA/s–1
r
SD
E/kJ mol–1
lnA/s–1
r
SD
A2
A3
A4
38.75
25.62
19.05
8.41
4.46
2.40
–0.9767
–0.9481
–0.9108
0.0632
0.0638
0.0641
32.15
19.03
12.46
6.35
2.28
0.09
–0.9994
–0.9993
–0.9991
0.0082
0.0053
0.0039
D1
D2
D3
D4
82.80
105.28
131.46
114.26
20.18
26.02
32.11
27.12
–0.9701
–0.9886
–0.9967
–0.9926
0.1537
0.1189
0.0797
0.1038
105.34
118.27
133.85
123.42
26.35
29.55
32.70
29.59
–0.9972
–0.9988
–0.9997
–0.9993
0.0588
0.0425
0.0250
0.0353
F1
F2
78.13
129.74
19.73
34.71
–0.9943
–0.9933
0.0624
0.1120
71.54
100.67
17.78
26.56
–0.9995
–0.9949
0.0168
0.0758
PL2
PL3
PL4
–1.63
–11.01
–15.70
–3.30
–6.16
–7.67
0.1035
0.5885
0.7262
0.1161
0.1122
0.1103
20.91
11.53
6.84
2.65
–0.40
–2.15
–0.9953
–0.9929
–0.9882
0.0151
0.0103
0.0079
R1
R2
R3
26.52
52.32
60.92
4.76
11.55
13.64
–0.8377
–0.9760
–0.9863
0.1282
0.0867
0.0756
49.06
59.47
63.31
10.86
13.40
14.17
–0.9967
–0.9993
–0.9996
0.0297
0.0160
0.0126
Table 3 The kinetics parameters from differential method and integral method for the possible four kinetic models at the four
heating rates for the first step
Achar–Brindley–Sharp
Coats–Redfern
Heating rate/K min–1 Model
E/kJ mol–1
lnA/s–1
r
E/kJ mol–1
lnA/s–1
r
D2
D3
D4
F2
105.28
131.46
114.26
129.74
26.02
32.11
27.12
34.71
–0.9886
–0.9967
–0.9926
–0.9933
118.27
133.85
123.42
100.67
29.55
32.70
29.59
26.56
–0.9988
–0.9997
–0.9993
–0.9949
5
D2
D3
D4
F2
114.44
139.76
123.12
136.38
28.52
34.21
29.48
36.36
–0.9975
–0.9993
–0.9988
–0.9885
117.39
132.50
122.39
98.64
28.49
31.40
28.45
25.28
–0.9999
–0.9995
–0.9999
–0.9904
10
D2
D3
D4
F2
118.51
143.69
127.14
139.81
29.59
35.13
30.50
37.17
–0.9996
–0.9980
–0.9994
–0.9808
117.61
132.63
122.58
98.43
28.04
30.88
27.98
24.80
–0.9999
–0.9990
–0.9997
–0.9878
15
D2
D3
D4
F2
122.59
147.77
131.22
143.09
30.77
36.26
31.66
38.08
–0.9992
–0.9964
–0.9984
–0.9769
119.22
134.27
124.20
99.21
28.24
31.05
28.17
24.80
–0.9999
–0.9988
–0.9996
–0.9871
20
192
J. Therm. Anal. Cal., 91, 2008

SYNTHETIC COMPLEX Pb(1,4-BDC)×(DMF)(H2O)
5 H. J. Choi, T. S. Lee and M. P. Suh, Angew. Chem. Int. Ed.,
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four kinetic models and respective kinetic parameters
at various heating rates are tabulated in Table 3.
From Table 3, we can see that function D4
(G-B equation), namely, f(a)=(3/2)[(1–a)–1/3–1]–1
and g(a)=1–2/3a–(1–a)2/3, is the most probable
mechanism function of the dehydration of
Pb(1,4-BDC)×(DMF)H2O.
6 J. S. Seo, D. M. Whang, H.-Y. Lee, S. I. Jun, J. H. Oh,
Y. J. Jeon and K. M. Kim, Nature, 404 (2000) 982.
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8 S. Kitagawa, R. Kitaura and S. Noro, Angew. Chem. Int. Ed.,
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However, no reasonable kinetic model can be ob-
tained for other three steps by means of above model-fit-
ting methods. The results suggest that these three steps
could not be interpreted by the fifteen reaction models in
this study, or every single thermal decomposition step of
them could be multi-step kinetics [20].
9 J.-H. Liao, T.-J. Lee and C.-T. Su, Inorg. Chem.
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10 H. Park, D. M. Moureau and J. B. Parise, Chem. Mater.,
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11 L. Huang, H. Wang, J. Chen, Z. Wang, J. Sun, D. Zhao
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The authors gratefully acknowledge the National Nature Sci-
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under Grant No. 20473091, 20573112 and 50671098.
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Received: April 3, 2007
Accepted: April 5, 2007
OnlineFirst: July 12, 2007
DOI: 10.1007/s10973-007-8494-9
J. Therm. Anal. Cal., 91, 2008
193