Low-temperature heat capacity and thermodynamic properties of crystalline lead formate

Article abstract of DOI:10.1007/s10973-006-7510-9

As one 3-D coordination polymer, lead formate was synthesized; calorimetric study and thermal analysis for this compound were performed. The low-temperature heat capacity of lead formate was measured by a precise automated adiabatic calorimeter over the temperature range from 80 to 380 K. No thermal anomaly or phase transition was observed in this temperature range. A four-step sequential thermal decomposition mechanism for the lead formate was found through the DSC and TG-DTG techniques at the temperature range from 500 to 635 K.

Full text of DOI:10.1007/s10973-006-7510-9

Journal of Thermal Analysis and Calorimetry, Vol. 89 (2007) 2, 643–647
LOW-TEMPERATURE HEAT CAPACITY AND THERMODYNAMIC
PROPERTIES OF CRYSTALLINE LEAD FORMATE
1
J. Zhang , Y. Y. Liu , Z. H. Zhang , X. C. Lv , L. X. Sun , F. Xu , Z. C. Tan , T. Zhang
,2
1,2
1,2
1,2
1*
1
1
1
3
and Y. Sawada
1
Materials and Thermochemistry Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences,
Dalian 116023, P.R. China
2
Graduate School of the Chinese Academy of Sciences, Beijing 100049, P.R. China
Department of Nanochemistry, Faculty of Engineering, Tokyo Polytechnic University, 1583 Iiyama, Atsugi,
Kanagawa 243-0297, Japan
3
As one 3-D coordination polymer, lead formate was synthesized; calorimetric study and thermal analysis for this compound were
performed. The low-temperature heat capacity of lead formate was measured by a precise automated adiabatic calorimeter over the
temperature range from 80 to 380 K. No thermal anomaly or phase transition was observed in this temperature range. A four-step
sequential thermal decomposition mechanism for the lead formate was found through the DSC and TG-DTG techniques at the
temperature range from 500 to 635 K.
Keywords: adiabatic calorimetry, coordination polymers, DSC, heat capacity, lead formate, phase transition, TG-DTG
Introduction
Experimental
Sample preparation
The construction of infinite frameworks by linking
metal ions with small organic multifunctional ligands
is an attractive topic on the interface between chemis-
try and materials science. The most promising applica-
tions of coordination polymers may include magnetic
exchange, non-linear optical (NLO), catalysis, or hy-
drogen storage [1, 2].
All materials were commercially available and were
of analytical grade unless stated elsewhere. Lead
nitrate (3.3 g, 10.0 mmol) was dissolved in DMF/1,
4-dioxane (2:1 by volume, 360 mL). The mixture was
stirred at room temperature until lead nitrate entirely
dissolved. Then, formic acid (920 mg, 755 mL,
Lead formate [Pb(HCOO)
No. 811-54-1] with simple component, comprises a
-D polymeric network [3, 4], which has been referred
2
; CA registry
2
0.0 mmol) was slowly added to the above
transparent mixed solution. Then, the solution was
distributed to twenty vials of 20 mL. The vials were
open, and the solvent was slowly volatilized. After
four weeks, polyhedral crystals were produced,
collected, and washed three times with DMF (50 mL).
3
to as a new material in the field of non-linear optical ap-
plications [5]. Some thermal behaviors of lead formate
have been already investigated by a number of research-
ers [6, 7]. To our best knowledge, there has been no re-
port on molar heat capacity of lead formate in literature.
Heat capacities determinations of various compounds
have attracted many researchers’ attention [8–11]. For
the application of the compound, thermodynamic prop-
erties of this substance are urgently required.
In the present work, the low-temperature heat ca-
pacity of lead formate has been measured over the tem-
perature range from 80 to 380 K. The thermal decom-
position characteristics of this compound were investi-
gated by differential scanning calorimetry (DSC) and
thermogravimetric analysis (TG-DTG).
Elemental analyses for C
C, 7.78; H, 0.43; calc. (%): C, 8.08; H, 0.68; FTIR
H O Pb found (%):
2 2 4
–1
(
KBr pellet, 4000–400 cm ): 1629 and 1562 (OCO,
str., asym.), 1352 (OCO, deform., asym.), 1338s
OCO, str., sym.), 778 and 764 (OCO, deform., sym.).
(
The content of lead was determined by atomic absorp-
tion spectrometer.
The crystal structure of lead formate was
determined by the single crystal X-ray diffraction.
Crystal data: C H O Pb, orthorhombic, P2 2 2 ,
2 2 4 1 1 1
a=6.4934(6) , b=7.4232(7) , c=8.7240(8) ,
3
V=420.51(7)  , Z=4. The values are in excellent
agreement with earlier published values [4].
*
Author for correspondence: lxsun@dicp.ac.cn
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2007 Akadémiai Kiadó, Budapest

ZHANG et al.
–
3
–4
–1
All chemical and elemental analyses showed that
the purity of the sample prepared was enough high to
the heat capacity measurements.
generally within 10 to 10 K min during the acqui-
sition of all heat capacity data. The sample mass of
lead formate used for heat capacity measurement
was 13.9626 g, which was equivalent to 0.0470 mol,
–1
based on its molar mass of 297.24 g mol .
Methods
Elemental analysis was carried on PE-2400 II Series
CHNS/O analyzer. FTIR spectra was recorded on
Bruker Equinox 55 infrared spectrometer using KBr
pellet in the range of 4000–400 cm . Atomic absorption
spectra was performed by AA6650 Shimadzu atomic
absorption spectrometer. The crystal data were collected
with a Bruker Smart CCD area diffractometer equipped
Thermal analysis
DSC analysis was performed using a differential
scanning calorimeter (Model: DSC 141, Setaram Co.,
France) with a heating rate of 10 K min . Dry high
purity nitrogen (99.999%) was used as a purge gas at
–1
–
1
3
–1
a flow rate of 50 cm min . The mass of the sample
used for DSC analysis was 9.0 mg. Two aluminum
crucibles were used (capacity: 30 mL) and the
reference crucible was empty. The calibrations for the
temperature and heat flux of the calorimeter were
performed before the determination of the sample.
The temperature and heat flux were calibrated by
measuring the melting points of Hg (99.99%),
In (99.99%), Sn (99.99%), Pb (99.99%) and
Zn (99.99%), at different heating rates.
with graphite monochromated MoK
a
radiation
(l=0.71073 ) by the w–2q scan technique at 187(2) K.
Adiabatic calorimetry
The heat capacity measurements were carried out in a
high-precision automated adiabatic calorimeter over
the temperature range from 80 to 380 K. The calorime-
ter was established by Thermochemistry Laboratory of
Dalian Institute of Chemical Physics, Chinese Acad-
emy of Sciences in PR China. The structure and princi-
ple of the calorimeter have been described in detail in
the literature [12, 13]. Briefly, the automatic adiabatic
calorimeter mainly consisted of a sample cell, a minia-
ture platinum resistance thermometer, an electric
heater, an adiabatic (or inner) shield, a guard (outer)
shield, two sets of six-junctions chromel–copper
A
thermogravimetric analyzer (Model:
Setsys 16/18, Setaram Co., France) was used for TG
measurement of this sample under nitrogen atmo-
sphere (99.999%). The heating rate was 10 K min
and the flow rate of nitrogen was 30 cm min . The
mass of the sample was 7.9 mg. Two Al crucibles
were used (capacity: 100 mL). The reference crucible
was filled with a-Al . The TG equipment was cali-
brated by the CaC ·H O (99.9%).
–
1
3
–1
O
3
2
O
3
2
(Ni: 55%, Cu: 45%) thermopiles installed between the
2
O
4
2
calorimetric cell and the inner shield and between the
inner and outer shields, respectively, and a high vac-
uum can. The evacuated chamber was kept within
ca. 1 mbar during the heat capacity measurement so as
to eliminate the heat loss owing to gas convection.
Liquid nitrogen was used as the cooling medium.
Prior to the heat capacity measurement of the
sample, the reliability of the calorimetric apparatus
was verified by heat capacity measurements of the
Results and discussion
Heat capacity
The low-temperature experimental molar heat
capacities of the solid compound are shown in Fig. 1
and tabulated in Table 1. The molar heat capacities of
the sample are fitted to the following polynomial
standard reference material-a-Al O (NBS SRM-720).
2 3
The results showed that the deviation of our calibration
data from the recommended value of the former Na-
tional Bureau of Standards [14] over the whole temper-
ature range was within ±0.3%. The electrical energy
introduced into the sample cell and the equilibrium
temperature of the cell after the energy input were au-
tomatically collected by use of a Data Acquisi-
tion/Switch Unit (Model: 34970A, Agilent, USA) and
processed by a computer on line.
The heat capacity measurements were continu-
ously and automatically carried out by the standard
procedure of intermittently heating the sample and al-
ternately measuring the temperature. The heating dura-
tion was 10 min, and the temperature drift rates of the
sample cell measured in an equilibrium period were
Fig. 1 Experimental molar heat capacities (Cp,m) of lead
formate as a function of the temperature (K)
644
J. Therm. Anal. Cal., 89, 2007

THERMODYNAMIC PROPERTIES OF CRYSTALLINE LEAD FORMATE
–
, molar mass: 297.24 g mol )
1
Table 1 The experimental molar heat capacities of lead formate (molecular formula: Pb(HCOO)
2
–
1
–1
K
–1 –1
K
–1 –1
p,m/J mol K
Temperature/K
Cp,m/J mol
Temperature/K
Cp,m/J mol
Temperature/K
C
8
8
8
9
9
0.87
4.38
8.30
2.28
6.22
87.326
90.585
183.26
187.16
191.12
195.08
199.02
202.92
206.79
210.64
214.52
218.45
222.35
226.23
230.09
234.08
238.10
242.05
245.99
249.94
253.87
257.85
261.86
265.86
269.83
273.79
277.72
281.69
138.825
140.340
141.212
142.047
142.813
143.663
144.586
145.414
146.367
147.233
148.432
149.632
150.636
151.038
152.060
153.192
153.667
154.519
155.355
156.181
157.001
157.952
158.922
159.730
160.568
161.649
285.70
289.68
293.62
297.55
301.46
305.36
309.29
313.26
317.21
321.12
324.98
328.76
332.49
336.29
340.12
343.99
347.84
351.69
355.51
359.31
363.09
366.91
370.77
374.60
378.42
382.22
162.748
163.689
164.638
165.497
166.333
166.939
167.868
168.586
169.164
169.865
170.991
171.722
172.525
173.985
174.734
175.740
176.450
177.684
178.428
179.473
180.523
181.554
182.465
183.328
184.288
185.254
94.110
97.518
100.598
103.500
106.272
108.843
111.292
113.579
115.833
117.956
119.804
121.547
123.233
124.873
126.641
128.190
129.479
130.839
132.045
133.135
134.307
135.609
136.686
137.686
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
00.13
04.12
08.10
12.06
16.02
19.98
23.95
27.92
31.91
35.83
39.76
43.72
47.69
51.69
55.63
59.54
63.47
67.44
71.36
75.32
79.31
equation of heat capacities (Cp,m) with reduced
temperature (X) by means of the least square fitting:
From T=(80 to 380) K
–
p,m [J mol K ]=150.1516+33.9162X
1
–1
C
2
3.5641X +7.2381X –9.4935X
3
4
–
5
8.0777X –1.4893X
6
+
(1)
where X=(T–230)/150, and T is the experimental tem-
perature, 230 is obtained from polynomial
(Tmax+Tmin)/2, 150 is obtained from polyno-
mial (Tmax–Tmin)/2, Tmax is the upper limit (380 K) of
the above temperature region, Tmin is the lower
limit (80 K) of the above temperature region. The cor-
2
relation coefficient of the fitting, R =0.9999. Based
on Eq. (1), the heat capacity of the sample at 298.15 K
Fig. 2 The plot of relative deviations of the experimental heat
capacity values [Cp,m(exp)] from the fitting heat capac-
ity values [Cp,m(fit)] vs. the absolute temperature (T).
DCp,m=[Cp,m(exp)–Cp,m(fit)]
–
1
was calculated to be 165.243 J mol K .
–1
From Fig. 1, it can be seen that the heat capacity
of the sample increases with increasing temperature
in a smooth and continuous manner in the temperature
range from 80 to 380 K. In this temperature range, no
phase transition or thermal anomaly was observed,
which indicates that this sample is stable in the above
temperature range.
Figure 2 gives the plot of relative deviations of
the experimental heat capacity values of the sample,
C
p,m(exp), from the fitting heat capacity values,
J. Therm. Anal. Cal., 89, 2007
645

ZHANG et al.
T
Cp,m(fit), vs. the absolute temperature (T). It can be
Cp,m
T
ST – S298.15
=
dT
(3)
seen from Fig. 2 that relative deviations of all the ex-
perimental points from the fitting heat capacity values
are within ±0.30%.
ò
2
98.15
The values of thermodynamic function H
ST–S298.15 are listed in Table 2.
–H298.15,
T
Thermodynamic functions of lead formate
DSC and TG results
Enthalpy and entropy of substances are basic thermody-
namic functions. Through the polynomial representing
heat capacity and the relationship between thermody-
namic functions and heat capacity, the thermodynamic
functions relative to the reference temperature of
298.15 K were calculated in the temperature ranges
from 80 to 380 K with an interval of 5 K. The thermody-
namic relationships are as follows:
The DSC curve of lead formate in Fig. 3 exhibited four
sharp endothermic peaks in the temperature range
from 500 to 635 K. Based on the DSC curve, there was
no phase transition or other thermal event which was
observed below 500 K. Above 500 K, the first signifi-
cant sharp endothermic peak started at 500 K and
ended at 543 K with the peak temperature at 539.0 K.
Next to the first peak, immediately, the second peak
temperature was 551.9 K and the third peak tempera-
ture was 556.9 K. Since two intense endothermic de-
T
H – H
=
òCp,m dT
(2)
T
298.15
2
98.15
Table 2 Calculated thermodynamic function data of lead formate
C
J mol
p,m
–1 –1
/
K
H
T
–H298.15
kJ mol
/
S
J mol
T
–S298.15
/
C
J mol
p,m
–1 –1
/
K
H
T
–H298.15
–1
/
S
J mol
T
–S298.15
/
T/K
–1
–1 –1
T/K
–1 –1
K
kJ mol
–9.995
–9.236
–8.471
–7.701
–6.925
–6.144
–5.357
–4.564
–3.766
–2.963
–2.154
–1.339
–0.519
0.000
K
8
8
9
9
0
5
0
5
86.373
–29.760
–29.316
–28.849
–28.360
–27.852
–27.326
–26.784
–26.226
–25.653
–25.068
–24.470
–23.861
–23.241
–22.611
–21.971
–21.323
–20.666
–20.001
–19.329
–18.649
–17.962
–17.269
–16.569
–15.862
–15.150
–14.431
–13.706
–12.976
–12.239
–11.497
–10.749
–169.04
235
240
245
250
255
260
265
270
275
280
285
290
295
298.15
300
305
310
315
320
325
330
335
340
345
350
355
360
365
370
375
380
151.278
–37.61
91.174
95.597
–163.65
–158.31
–153.04
–147.83
–142.70
–137.66
–132.70
–127.82
–123.04
–118.35
–113.75
–109.24
–104.82
–100.48
–96.23
–92.06
–87.97
–83.96
–80.02
–76.15
–72.35
–68.62
–64.95
–61.34
–57.79
–54.29
–50.86
–47.47
–44.13
–40.85
152.399
153.514
154.625
155.732
156.837
157.940
159.042
160.143
161.243
162.343
163.445
164.547
165.243
165.652
166.759
167.871
168.987
170.110
171.241
172.381
173.532
174.697
175.878
177.077
178.298
179.543
180.815
182.119
183.458
184.837
–34.41
–31.26
–28.15
–25.08
–22.04
–19.05
–16.09
–13.16
–10.26
–7.40
–4.56
–1.75
0.00
99.674
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
00
05
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
00
05
10
15
20
25
30
103.432
106.901
110.106
113.071
115.818
118.369
120.742
122.956
125.027
126.971
128.800
130.529
132.168
133.728
135.220
136.651
138.030
139.363
140.657
141.918
143.150
144.358
145.546
146.716
147.872
149.017
150.152
0.306
1.02
1.137
3.78
1.974
6.50
2.816
9.20
3.664
11.86
14.50
17.10
19.66
22.18
24.65
27.07
29.41
31.68
33.86
35.93
37.87
39.66
4.517
5.376
6.241
7.111
7.988
8.870
9.759
10.653
11.554
12.461
13.375
14.296
646
J. Therm. Anal. Cal., 89, 2007

THERMODYNAMIC PROPERTIES OF CRYSTALLINE LEAD FORMATE
fourth slow loss of 2.9% were observed above 552 K,
and there was some complex of lead monoxide and
lead (PbO·Pb) between the two processes. The overall
mass loss of the sample was ca. 29.6% in accord with
the calculated percentage (30.3%). Furthermore, the
brown residue was found in the crucible after the ex-
periment was completed. We considered that the
brown residue should be the metal with a little amount
of lead monoxide under nitrogen atmosphere.
The further investigation of hydrogen storage
performance for the compound is in process of study
in our laboratory.
Fig. 3 DSC curve of lead formate under high purity nitrogen
atmosphere
Acknowledgements
The authors gratefully acknowledge the National Nature
Science Foundation of China for financial support to this work
under Grant No. 20473091.
References
1
2
3
J. L.C. Rowsell and O. M. Yaghi, Micropor. Mesopor. Mater.,
3 (2004) 3.
S. Kitagawa, R. Kitaura and S. Noro, Angew. Chem. Int. Ed.,
3 (2004) 2334.
7
4
P. G. Harrison and A. T. Steel, J. Organomet. Chem.,
239 (1982) 105.
4 R. C. Weast, CRC Handbook of Chemistry and Physics,
Fig. 4 TG-DTG curves of lead formate under high purity ni-
trogen atmosphere
nd
6
2 Ed. (Chemical Rubber, Boca Raton, FL 1981).
composition processes occurred successively, one de-
composition process did not finish, and another
occurred. The endothermic peak could not be sepa-
rated, which formed a wide exothermic peak. Between
595 and 635 K range, the fourth peak was observed
with the peak temperature at 601.1 K.
From the TG-DTG curve (Fig. 4), TG analysis of
lead formate showed that the four-step mass loss
occurred in the 500 to 635 K temperature range. The
decomposition taking place during heating can be
traced as follows:
5
K. Betzler, H. Hesse, R. Jaquet and D. Lammers,
J. Appl. Phys., 87 (2000) 2.
6 P. Baraldi, Spectrochim. Acta A, 37 (1981) 99.
7 M. N. Ray and N. D. Sinnarkar, J. Inorg. Nucl. Chem.,
35 (1973) 1373.
8
9
V. G. Bessergenev, Y. A. Kovalevskaya, L. G. Lavrenova
and I. E. Paukov, J. Therm. Anal. Cal., 75 (2004) 331.
J. Boerio-Goates, R. Stevens, B. Lang and B. F. Woodfield,
J. Therm. Anal. Cal., 69 (2002) 773.
1
0 V. A. Drebushchak, E. V. Boldyreva, Y. A. Kovalevskaya,
I. E. Paukov and T. N. Drebushchak, J. Therm. Anal. Cal.,
79 (2005) 65.
11 V. Rohac, M. Fulem, H. G. Schmidt, V. Ruzicka, K. Ruzicka
and G. Wolf, J. Therm. Anal. Cal., 70 (2002) 455.
1
0.1% (calcd.), 11.0% (exp); 500–540 K
Pb(HCOO) ¾¾¾¾¾¾¾¾¾¾®
2
9.9% (calcd.), 8.8% (exp); 540–552 K
PbCO ¾¾¾¾¾¾¾¾ ¾¾ ®
3
12 L. Wang, Z. C. Tan, S. H. Meng, D. B. Liang, S. T. Ji and
Z. K. Hei, J. Therm. Anal. Cal., 66 (2001) 409.
7
.6% (calcd.), 6.9% (exp); 552–565 K
PbCO ×2PbO¾¾¾¾¾¾¾¾ ¾¾ ®
3
2.7% (calcd.), 2.9% (exp); 565–635 K
13 Z. C. Tan, B. Xue, S.W. Lu, S. H. Meng, X. H. Yuan and
Y. S. Song, J. Therm. Anal. Cal., 63 (2000) 297.
PbO×Pb¾¾¾¾¾¾¾¾ ¾¾ ®Pb
The first mass loss was about 11.0% likely due to
the decomposition from lead formate to lead carbonate,
which roughly coincides with the calculated value
of 10.1% in the 500–540 K range. Further decomposi-
tion of lead carbonate occurred in the region
of 540–552 K and the mass loss was 8.8%, which was
probably decomposed to the complex of lead carbonate
1
4 D. A. Ditmars, S. Ishihara, S. S. Chang, G. Bernstein and
B. D. West, J. Res. Natl. Bur. Stand., 87 (1982) 159.
Received: January 16, 2006
Accepted: January 31, 2006
OnlineFirst: May 23, 2006
and lead monoxide (PbCO ·2PbO). These two steps
3
DOI: 10.1007/s10973-006-7510-9
were in agreement with that reported in literature [5].
Subsequently, the third rapid loss of 6.9% and the
J. Therm. Anal. Cal., 89, 2007
647