Thermal studies of copper(II) fumarate and copper(II) terephthalate

Article abstract of DOI:10.1016/j.tca.2005.01.039

Copper(II) fumarate (Cu(OOCC₂H₂COO)) and copper(II) terephthalate (Cu(OOCC₆H₄COO)) have been synthesized. Their heat capacity has been measured by adiabatic calorimetry between 13 and 300 K and their magnetic susceptibility determined with a SQUID magnetometer between 5 and 300 K. No phase transition has been observed in the whole temperature range covered by the experiments. The thermodynamic properties of these compounds are compared with those of copper(II) trans-1,4-cyclohexane dicarboxylate, in which a structural first-order phase transition was observed at 160 K.

Full text of DOI:10.1016/j.tca.2005.01.039

Thermochimica Acta 431 (2005) 58–61
Thermal studies of copper(II) fumarate and copper(II) terephthalate
Mikako Inoue, Hitoshi Kawaji, Takeo Tojo, Tooru Atake∗
Materials and Structures laboratory, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
Received 13 October 2004; received in revised form 19 December 2004; accepted 20 January 2005
Available online 17 February 2005
Abstract
Copper(II) fumarate (Cu(OOCC2H2COO)) and copper(II) terephthalate (Cu(OOCC6H4COO)) have been synthesized. Their heat capacity
has been measured by adiabatic calorimetry between 13 and 300 K and their magnetic susceptibility determined with a SQUID magnetometer
between 5 and 300 K. No phase transition has been observed in the whole temperature range covered by the experiments. The thermodynamic
properties of these compounds are compared with those of copper(II) trans-1,4-cyclohexane dicarboxylate, in which a structural first-order
phase transition was observed at 160 K.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Heat capacity; Magnetic susceptibility; Copper(II) fumarate (Cu(OOCC2H2COO)); Copper(II) terephthalate (Cu(OOCC6H4COO))
1. Introduction
X-ray crystallography [10]. On the other hand, the fully
absorbed sample of Cuchd has no phase transition. Re-
cently, we extended our thermodynamic studies to other com-
pounds of this family of compounds, copper(II) fumarate
(Cu(OOCC2H2COO); Cufud) and copper(II) terephtalate
(Cu(OOCC6H4COO); Cuted); their structures are shown
schematically in Figs. 1 and 2, respectively. The samples of
Cufud and Cuted have been synthesized and the heat capac-
ity and the magnetic susceptibility measured at temperatures
from liquid helium temperature to room temperature. The re-
sults are compared with those of previous studies on Cuchd
[9,10].
Highly functional microporous metal-organic frameworks
have been found in a series of organometallic compounds
constructed by co-polymerization of organic groups and
metal ions. They have been receiving widespread attention in
recent years because of their reversible absorption/desorption
of great variety and large amount of molecules. The bridg-
ing group within the framework can be replaced with various
substituent groups, and a number of functional compounds
have been successfully synthesized [1–5]. For metal-organic
frameworks, the central metal ions are linked by singly, dou-
bly, or triply coordinated ligands, such as diamines, di-, or
tri-carboxylate [6–8].
The present authors have studied thermodynamic prop-
erties of copper(II) trans-1,4-cyclohexane dicarboxylate
(Cuchd), which can reversibly absorb/desorb large amount
of benzene, toluene, and carbon tetrachloride [9]. A struc-
tural first-order phase transition has been found at 160 K for
the empty (not-absorbed) sample of Cuchd, which was de-
tected as an anomaly in the heat capacity and in the mag-
netic susceptibility. The structural change was confirmed by
2. Experimental
2.1. Sample preparation
The sample of Cu(OOCC2H2COO) (Cufud) was synthe-
sized in methanol solution as follows [11]. Methanol (Wako
Pure Chemicals; 99.9% purity, 600 cm3) solution of cop-
per(II) formate (Wako P.C.; 98%, 4.06 g) was added to an-
other methanol solution (300 cm3) of fumaric acid (Wako
P.C.; 99.9%, 3.1 g) and of formic acid (Wako P.C.; 99%,
60 cm3). The mixture was put in a sealed flask, which was al-
∗
Corresponding author. Tel.: +81 45 924 5343; fax: +81 45 924 5339.
E-mail address: ataketooru@msl.titech.ac.jp (T. Atake).
0040-6031/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2005.01.039

M. Inoue et al. / Thermochimica Acta 431 (2005) 58–61
59
tus and the operation have been described previously [12,13].
The Cufud sample of 3.6546 g (0.02057 mol) was used for the
heat capacity measurements. In the case of Cuted, the amount
of the sample was 0.9796 g (0.004302 mol).
For the magnetic measurements, the Cufud sample of
0.01102 g (0.06201 mmol) was put in a silica glass tube
(2.5 mm in inside diameter). The glass tube was connected
to a pyrex glass vacuum line, connected to a rotary pump
equipped with liquid nitrogen trap. After evacuation, a small
amount of helium gas (6 kPa at room temperature) was al-
lowed inside the tube, and then the sample part was sealed
off by a hand torch. The magnetic susceptibility was mea-
sured under a magnetic field of 1 T between 5 and 300 K
using a SQUID magnetometer (MPMS, Quantum Design).
For the measurements on Cuted, the amount of the sample
was 0.01343 g (0.05898 mmol).
After the heat capacity measurements of the empty sam-
ple of Cufud, the sample was put in vacuum, and then it
was exposed to benzene vapor saturated at room tempera-
ture. By weighing, the amount of the absorbed benzene was
determined as 0.3090 g, which represented about 96% of full
absorption.
Fig. 1. Structure of Cu(OOCC2H2COO) (Cufud).
lowed to stand for several weeks at room temperature. Thus
greenish blue fine crystals precipitated in the solution, and
were separated by filtering. The specimen was heated at
100 ◦C for 4 h in vacuum to remove the solvent. The sam-
ple of Cuted was synthesized by the same method. Chemical
analysis for the elements of C, H, and O gave good agreement
with the calculated values, which showed that the synthesis
was successful.
3. Results and discussion
The calorimeter was cooled down to the liquid helium
temperature and the adiabatic calorimetry was performed on
heating direction. However, thermal equilibration within the
calorimeter vessel was not attained rapidly enough in the
lowest temperature region, as the samples of Cufud and Cuted
absorbed the helium gas put inside the calorimeter vessel.
Thus the heat capacity measurements could be made only
above 30 K. The molar heat capacity of Cufud and Cuted
obtained, without curvature corrections, are shown in Fig. 3
together with previous data for Cuchd [9]. As clearly seen in
2.2. Heat capacity and magnetic susceptibility
measurements
The heat capacity measurements were made using a home-
made adiabatic calorimeter between 13 and 300 K. The work-
ing thermometer mounted on the calorimeter vessel (gold
plated copper) was an iron–rhodium resistance thermometer
(model 5187U; Tinsley and Co. Ltd., UK) calibrated on the
basis of ITS-90 at National Physical Laboratory and Oxford
Instruments Ltd., UK. A small amount of helium gas (6 kPa at
room temperature) was introduced in the calorimeter vessel
to improve the thermal uniformity. The details of the appara-
Fig. 3. Measured molar heat capacity of empty Cuchd (circle), Cufud (tri-
angle) and Cuted (square).
Fig. 2. Structure of Cu(OOCC6H4COO) (Cuted).

60
M. Inoue et al. / Thermochimica Acta 431 (2005) 58–61
Fig. 5. Measured molar heat capacity of empty Cufud (triangle) and of 96%
benzene absorbed Cufud (inverted triangle).
Fig. 4. Normalized heat capacity of Cuchd (circle), Cufud (triangle) and
Cuted (square).
are larger than those of the empty sample. With the assump-
tion of additivity rule, the contribution of absorbed benzene
was estimated by subtracting the heat capacity of the empty
sample from that of the absorbed sample. The heat capac-
ity of absorbed benzene determined in this way is shown
in Fig. 6 together with that of absorbed benzene in Cuchd
and that of bulk benzene. The three sets of data are in rather
good agreement, which implies that absorbed benzene be-
haves like bulk benzene. It should be noted that the absorbed
benzene shows no melting phenomenon, which might be due
to the general rule; one-dimensional system should have no
cooperative phase transition. Thus the benzene molecules in
the tunnels should be considered as isolated one-dimensional
chains. In the case of the absorbed benzene in Cuchd, 100%
benzene was absorbed and thus about 5% of benzene over-
flown from the tunnels during the cooling process for the
heat capacity measurements. The small melting anomaly is
Fig. 3, no phase transition is observed in Cufud and Cuted,
while Cuchd shows an anomaly at 160 K due to a structural
phase transition [9,10]. No anomaly in Cufud and Cuted is
also detected by the magnetic susceptibility measurements.
In Fig. 3, the molar heat capacity value of Cufud is ex-
tremely small as compared with Cuchd and Cuted. A prob-
able reason may be the difference in the number of atoms
in their chemical formulas. To see the intrinsic difference,
the normalized molar heat capacity Cp∗ is obtained by divid-
ing Cp with the number of atoms, 11, 17 and 23, for Cufud,
Cuted and Cuchd, respectively. The normalized heat capac-
ity is shown in Fig. 4. At a glance, the heat capacity curves
of Cufud and of Cuchd are very close to each other, while
that of Cuted is higher. These results imply that the lattice
vibrations of Cufud and Cuchd are very similar, and thus the
force constants of their framework should be also very sim-
ilar. On the other hand, the larger value of Cuted means that
the framework of Cuted is less stiff as compared to Cufud
and Cuchd.
It is also considered that the difference in molar heat ca-
pacity among these three compounds should be caused by
the different contribution of the different substituted groups.
For example, the heat capacity difference between Cuchd and
Cuted (see Fig. 3) is attributed to the difference between the
heat capacity of cyclohexane [14] and benzene [15].
To see the effect of absorption, the heat capacity measure-
ments were made on the 96% benzene absorbed Cufud, and
the results were compared with those of the empty sample
of Cufud. In the case of benzene absorbed sample, the he-
lium gas put in the calorimeter vessel was not absorbed into
the sample of Cufud, and thus the heat capacity measure-
ments could be made in the lowest temperature region. Both
data sets are shown in Fig. 5, where the data for benzene
absorbed sample could be obtained from the lowest tempera-
ture. Theheatcapacityvaluesofthebenzeneabsorbedsample
Fig. 6. Heat capacity of absorbed benzene in Cufud (triangle), in Cuchd
(circle), and of bulk benzene (closed circle).

M. Inoue et al. / Thermochimica Acta 431 (2005) 58–61
61
due to overflown benzene, which behaved as bulk sample of
benzene.
[2] T. Sato, W. Mori, C.N. Kato, T. Ohmura, T. Sato, K. Yokohama, S.
Takamizawa, S. Naito, Chem. Lett. 32 (2003) 854.
[3] S. Noro, R. Kitaura, M. Kondo, S. Kitagawa, T. Ishii, H. Matsuzaka,
M. Yamashita, J. Am. Chem. Soc. 124 (2002) 2568.
[4] K. Seki, S. Takamizawa, W. Mori, Chem. Lett. (2001) 122.
[5] M. Eddaoudi, H. Li, O.M. Yaghi, J. Am. Chem. Soc. 122 (2000)
1391.
[6] M. Eddaoudi, D.B. Moler, H. Li, B. Chen, T.M. Reineke, M.
O’Keeffe, O.M. Yaghi, Acc. Chem. Res. 34 (2001) 319.
[7] T. Ohmura, W. Mori, M. Hasegawa, T. Takei, A. Yoshizawa, Chem.
Lett. 32 (2003) 34.
[8] S.M-F. Lo, S.S-Y. Chui, L.-Y. Shek, Z. Lin, X.X. Zhang, G.-H. Wen,
I.D. Williams, J. Am. Chem. Soc. 122 (2000) 6293.
[9] M. Inoue, M. Moriwaki, T. Atake, H. Kawaji, T. Tojo, W. Mori,
Chem. Phys. Lett. 365 (2002) 509.
[10] M. Inoue, T. Atake, H. Kawaji, T. Tojo, Solid State Commun., in
press.
In conclusion, the samples of Cufud and Cuted were syn-
thesized and the heat capacity and the magnetic suscepti-
bility were measured. The results show that no phase tran-
sition occurs in the both sample, while a structural phase
transition has been reported for Cuchd, which is a member of
this family of compounds. Comparison between lattice heat
capacities reveals that the lattice of Cuted is less stiff than
that of either Cufud or Cuchd. The reversibility of absorp-
tion/desorption of large amount of molecules is confirmed
for benzene, toluene, and carbon tetrachloride, etc. We also
point out that the absorbed molecules can be considered as
one-dimensional molecular chains, and that no phase transi-
tion or melting phenomenon has been observed.
[11] W. Mori, F. Inoue, K. Yoshida, H. Nakayama, S. Takamizawa, M.
Kishita, Chem. Lett. (1997) 1219.
[12] T. Atake, H. Kawaji, A. Hamano, Y. Saito, Rep. Res. Lab. Eng.
Mater., Tokyo Inst. Technol. 15 (1990) 13.
[13] T. Tanaka, T. Atake, H. Nakayama, T. Eguchi, K. Saito, I. Ikemoto,
J. Chem. Thermodyn. 26 (1994) 1231.
References
[1] T. Ohmura, W. Mori, M. Hasegawa, T. Takei, T. Ikeda, E. Hasegawa,
Bull. Chem. Soc. Jpn. 76 (2003) 1387.
[14] R.A. Ruehwein, H.M. Huffman, J. Am. Chem. Soc. 65 (1942) 1620.
[15] H. Kawaji, Master Thesis, Osaka University, 1986.