Low-temperature heat capacities and standard molar enthalpy of formation of the solid-state coordination compound trans-Cu(Ala)2(s) (Ala = l-α-alanine)

Article abstract of DOI:10.1016/j.tca.2008.02.024

Low-temperature heat capacities of the solid coordination compound trans-Cu(Ala)₂(s) have been measured by a precision automated adiabatic calorimeter over the temperature range from T = 78 K to 390 K. The experimental values of the molar heat capacities in the temperature region were fitted to a polynomial equation of heat capacities (C_p,m) with the reduced temperatures (X), [X = f (T)], by a least square method. The smoothed molar heat capacities and thermodynamic functions of the complex trans-Cu(Ala)₂(s) were calculated based on the fitted polynomial. The smoothed values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were tabulated with an interval of 5 K. Enthalpies of dissolution of {Cu(Ac)₂·H₂O(s) + 2Ala (s)} and 2:1 HAc (aq) in 100 ml of 2 mol dm^-3 HCl, respectively, and trans-Cu(Ala)₂(s) in the solvent [2:1 HAc (aq) + 2 mol dm^-3 HCl] at T = 298.15 K were determined to be Δ_S H_m ° [ Cu (Ac)₂ s? H₂ O (s) + 2 Ala (s) ] = (6.75 ± 0.04) kJ mo l^{- 1}, Δ_S H_m ° [ 2 : 1 HAc (aq) ] = - (1.63 ± 0.01) kJ mo l^{- 1}, and Δ_S H_m ° [ t r a n s -Cu (Ala)₂ (s) ] = - (10.24 ± 0.08) kJ mo l^{- 1} by means of an isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of the compound was determined as Δ_f H_m ° (t r a n s -Cu (Ala)₂ (s), 298.15 K) = - (1038.6 ± 3.5) kJ mo l^{- 1} from the enthalpies of dissolution and other auxiliary thermodynamic data using a Hess thermochemical cycle.

Full text of DOI:10.1016/j.tca.2008.02.024

Thermochimica Acta 471 (2008) 70–73
Contents lists available at ScienceDirect
Thermochimica Acta
journal homepage: www.elsevier.com/locate/tca
Low-temperature heat capacities and standard molar enthalpy of formation of
the solid-state coordination compound trans-Cu(Ala)2(s) (Ala = l-␣-alanine)
You-Ying Dia,∗, Jing-Tao Chenb, Zhi-Cheng Tanc
a College of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng 252059, PR China
b Department of Chemistry, Shaannxi Educational College, Xi-an 710061, PR China
c Thermochemistry Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences,
Dalian 116023, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 January 2007
Received in revised form 21 February 2008
Accepted 26 February 2008
Available online 14 March 2008
Low-temperature heat capacities of the solid coordination compound trans-Cu(Ala)2(s) have been mea-
sured by a precision automated adiabatic calorimeter over the temperature range from T = 78 K to 390 K.
The experimental values of the molar heat capacities in the temperature region were fitted to a polynomial
equation of heat capacities (Cp,m) with the reduced temperatures (X), [X = f (T)], by a least square method.
The smoothed molar heat capacities and thermodynamic functions of the complex trans-Cu(Ala)2(s)
were calculated based on the fitted polynomial. The smoothed values of the molar heat capacities and
fundamental thermodynamic functions of the sample relative to the standard reference temperature
298.15 K were tabulated with an interval of 5 K. Enthalpies of dissolution of {Cu(Ac)2·H2O(s) + 2Ala (s)}
and 2:1 HAc (aq) in 100 ml of 2 mol dm−3 HCl, respectively, and trans-Cu(Ala)2(s) in the solvent [2:1 HAc
(aq) + 2 mol dm−3 HCl] at T = 298.15 K were determined to be ꢀSHm◦ [Cu(Ac)2 · H2O(s) + 2Ala(s)] = (6.75
Keywords:
Trans-Cu(Ala)2(s)
Adiabatic calorimetry
Heat-capacity
Isoperibol solution-reaction calorimetry
Standard molar enthalpy of formation
UV–vis spectroscopy
0.04) kJ mol−1, ꢀSHm◦ [2 : 1 HAc(aq)] = −(1.63 0.01) kJ mol−1, and ꢀSH◦ [trans-Cu(Ala)2(s)] = −(10.24
m
0.08) kJ mol−1 by means of an isoperibol solution-reaction calorimeter. The standard molar enthalpy
of formation of the compound was determined as ꢀfHm◦ (trans-Cu(Ala)2(s), 298.15 K) = −(1038.6
3.5) kJ mol−1 from the enthalpies of dissolution and other auxiliary thermodynamic data using a Hess
thermochemical cycle.
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
ambient temperature. XRD, IR, DTA and elemental analysis were
employed to characterize their structures. However, up to now, the
Solid-state chemical synthesis is an important and promising
method in the field of synthetic chemistry. The method [1] has been
widely used to synthesize various solid-state coordination com-
pounds of many metal salts with ␣-amino acids because it avoids
complicated experimental operations and harsh reaction condi-
tions. It is well-known that ␣-amino acids are basic structural units
which constitute proteins, and copper(II) is one of the trace ele-
ments necessary for the human body. It was established early that
the complexes of ␣-amino acids with copper (II) formed some com-
pounds with cis- and trans-geometric isomers, which have exten-
sive application in food, cosmetics and medicines as a nutrient.
In 1993, Zheng and Xin [2] synthesized a series of complexes
(including trans-Cu(Ala)2(s) and others) by means of solid-state
coordination reactions of copper(II) acetate with ␣-amino acids at
enthalpies of the solid-state coordination reactions involved in the
syntheses of these complexes and their respective low-temperature
heat capacities, thermodynamic functions and standard molar
enthalpies of formation have not been reported in literature. The
purpose of the present study is to determine the dissolution
enthalpies of the reactants and the products of the solid-state
coordination reaction of copper(II) acetate with l-␣-alanine by
isoperibol solution calorimetry, and measure the low-temperature
heat capacities by adiabatic calorimetry. In addition, the thermody-
namic functions and standard molar enthalpy of formation of the
product of the solid-state coordination reaction [trans-Cu(Ala)2(s)]
were derived from these experimental results.
2. Experimental
2.1. Chemicals
∗
Corresponding author at: College of Chemistry and Chemical Engineering,
Liaocheng University, Wenhua Road 34, Liaocheng 252059, Shandong Province, PR
China. Fax: +86 635 8239121.
Copper(II) acetate [Cu(Ac)2·H2O(s)], l-␣-alanine(s) and other
E-mail addresses: yydi@lcu.edu.cn, diyouying@126.com (Y.-Y. Di).
reagents used in these experiments were of analytical grade and
0040-6031/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2008.02.024

Y.-Y. Di et al. / Thermochimica Acta 471 (2008) 70–73
71
obtained from Shanghai Reagent Factory. KCl(s) and ␣-Al2O3(s)
used for calibration of the isoperibol solution calorimeter and adi-
abatic calorimeter were of a purity greater than 99.99%, and dried
in a vacuum oven for 6 h at 210–240 ◦C prior to use. The water used
in measurements was twice distilled.
tion of Low-Temperature Metrology and Measurements, Academia
Sinica. The electrical energy introduced into the sample cell and
the equilibrium temperature of the cell after the energy input were
automatically recorded by use of a Data Acquisition/Switch Unit
(Model 34970A, Agilent, USA), and processed on line by a computer.
To verify the accuracy of the calorimeter, the heat capacities
of the reference standard material (␣-Al2O3) were measured over
the temperature range 78 ≤ (T/K) ≤ 390. The sample mass used was
1.7143 g, which was equivalent to 0.0168 mol based on its molar
mass, M(Al2O3) = 101.9613 g mol−1. Deviations of the experimental
results from those of the smoothed curve lie within 0.2%, while
the uncertainty is 0.3%, as compared with the values given
by the former National Bureau of Standards [5] over the whole
temperature range.
2.2. Sample preparations and characterization
The samples used in the present measurements were prepared
according to the method given in the literature [1,2], in which
10 mmol Cu(Ac)2·H2O(s) of 80–100 mesh was mixed and ground
with a certain amount of l-␣-alanine in a 1:2 mole ratio. These were
retained for 4 h at ambient temperature. If subsequent XRD mea-
surement showed that the refraction peaks of the two reactants
in the system of the solid-state coordination reaction had disap-
peared, the reaction was complete. The product was washed three
times with absolute ethyl alcohol, and once with ethyl ether of ana-
lytical grade. Finally, the sample was placed in a vacuum desiccator
at ambient temperature to vacuum dry for 4 h. TG/DTG, chemical
and elemental analyses (model: PE-2400, PerkinElmer, USA) have
shown that the purity of the sample prepared was higher than
99.90 mol%.
Heat-capacity measurements were continuously and automati-
cally carried out by means of the standard method of intermittently
heating the sample and alternately measuring the temperature. The
heating rate and temperature increments were generally controlled
at (0.1–0.4) K min−1 and (1–3) K. The heating duration was 10 min,
and the temperature drift rates of the sample cell measured in an
equilibrium period were always kept within (10−3 to 10−4) K min−1
during the acquisition of all heat-capacity data. The data of heat
capacities and corresponding equilibrium temperature have been
corrected for heat exchange of the sample cell with its surround-
ings [3,4]. The sample mass used for calorimetric measurements
was 3.3156 g, which was equivalent to 0.0137 mol in terms of its
2.3. Adiabatic calorimetry
A precision automatic adiabatic calorimeter was used to mea-
sure heat capacities over the temperature range 78 ≤ (T/K) ≤ 390.
The calorimeter was established in the Thermochemistry Labora-
tory of the Dalian Institute of Chemical Physics, Chinese Academy
of Sciences, China. The principle and structure of the adiabatic
calorimeter were described in detail elsewhere [3,4]. Briefly, the
calorimeter mainly comprised a sample cell, a platinum resis-
tance thermometer, an electric heater, inner and outer adiabatic
shields, two sets of six-junction chromel-constant an thermopiles
installed between the calorimetric cell and the inner shield and
between the inner and outer shields, respectively, and a high vac-
uumcan. Theminiatureplatinumresistancethermometer (IPRTNo.
2, produced by Shanghai Institute of Industrial Automatic Meters,
16 mm in length, 1.6 mm in diameter and a nominal resistance of
100 ꢁ) was applied to measure the temperature of the sample.
The thermometer was calibrated on the basis of ITS-90 by the Sta-
molar mass, M = 241.73 g mol−1
.
2.4. Isoperibol solution-reaction calorimetry
The isoperibol solution-reaction calorimeter consisted primar-
ily of a precision temperature controlling system, an electric energy
calibration system, a calorimetric body, an electric stirring system,
a thermostatic bath made from transparent silicate glass, a preci-
sion temperature measuring system and a data acquisition system.
The principle and structure of the calorimeter were described in
detail elsewhere [6].
The reliability of the calorimeter was verified by measuring
the dissolution enthalpy of KCl (calorimetrically primary stan-
dard) in double distilled water at T = 298.15 K. The mean dissolution
enthalpy was ꢀSHm◦ [KCl(s)] = (17, 553 19) J mol−1 for KCl, as
Table 1
Dissolution enthalpies of [Cu(Ac)2·H2O(s) + 2Ala(s)] and [2:1 HAc(aq)] in 2 mol dm−3 HCl and [trans-Cu(Ala)2 (s)] in [2:1 HAc (aq) + 2 mol dm−3 HCl] at 298.15 K
System
Solvent
No.
m (g)
ꢀEe (mV)
ꢀEs (mV)
Qe (J)
Qs (J)
ꢀsHmo (kJ mol−1
)
Cu(Ac)2·H2O (s) + 2Ala (s)
2 mol L−1HCl
1
2
3
4
5
0.377 5
0.377 1
0.377 9
0.377 2
0.377 2
1.25
1.15
1.14
1.16
1.15
1.60
1.57
1.61
1.57
1.60
5.28
4.84
4.85
4.96
4.86
6.76
6.76
6.62
6.86
6.72
6.78
6.61
6.84
6.71
6.77
ꢀsHm◦ [Cu(Ac)2 · H2O(s) + 2Ala(s)] = (6.75 0.04)kJ mol−1
2:1 HAc (aq)
2 mol L−1 HCl
1
2
3
4
5
0.122 1
0.122 7
0.122 3
0.122 5
0.122 0
1.47
1.42
1.42
1.41
1.40
−0.37
−0.35
−0.34
−0.34
−0.33
6.66
6.65
6.80
6.69
6.78
−1.68
−1.64
−1.63
−1.61
−1.60
−1.67
−1.63
−1.63
−1.61
−1.60
ꢀsHm◦ [HAc(aq)] = −(1.63 0.01)kJ mol−1
Trans-Cu(Ala)2 (s)
2:1 HAc (aq) + 2 mol dm−3 HCl
1
2
3
4
5
0.241 6
0.241 0
0.241 8
0.241 2
0.241 5
2.49
2.50
2.51
2.42
2.40
2.39
2.35
2.41
2.35
2.37
10.62
10.62
10.63
10.62
10.61
-10.19
- 9.98
-10.20
-10.31
-10.48
-10.20
-10.01
-10.20
-10.33
-10.48
ꢀsHm◦ trans-Cu(Ala)2(s) = −(10.24 0.08) kJ mol−1
R = 1666.0 ꢁ, I = 10.000 mA, in which m (g) is mass of sample; ꢀEe (mV), the voltage change during the electrical calibration; ꢀEs (mV), the voltage change during the sample
dissolution, Qe (J), electrical energy of electrical calibration; Qs (J), heat effect of the dissolution; ꢀsHm◦ = (ꢂEs/ꢂEe)I2Rte(M/m), where R is the electro-resistance; I, the
electrical current; M, the molar mass; te, heating period of electrical calibration.

72
Y.-Y. Di et al. / Thermochimica Acta 471 (2008) 70–73
shown in Table 1 (see supplementary data), which compared with
corresponding published data [7] (17,536 3.4) J mol−1
.
In all dissolution experiments of the sample, 100 ml of
2 mol dm−3 HCl was chosen as the calorimetric solvent for mea-
suring the dissolution enthalpies of the {Cu(Ac)2·H2O(s) + 2Ala(s)}
and the 2:1 HAc(aq) (HAc denotes the acetic acid), respectively.
But the trans-Cu(Ala)2(s) was dissolved in the solvent [2:1 HAc
(aq) + 2 mol dm−3 HCl] at T = 298.15 K.
The solid Cu(Ac)2·H2O(s) (Ac denotes the acetate) and Ala(s)
were respectively ground within an agate mortar into a fine pow-
der. The mixture of about 2 mmol Ala(s) and 1 mmol Cu(Ac)2·H2O(s)
at mole ratio of n(Cu(Ac)2·H2O(s)):n(Ala) = 1:2 was dissolved in
100 ml of 2 mol dm−3 HCl at T = (298.15 0.001) K. The final solution
obtained from five tests was designated as solution A.
About 0.12 g acetic acid solution, n(HAc):n(H2O) = 2:1, was dis-
solved in 100 ml of 2 mol dm−3 HCl at T = (298.15 0.001) K. The
final solution was named as solution A1.
The solid complex trans-Cu(Ala)2(s) was dried in a vacuum des-
iccator in order to take off some additional adsorbing water. Then,
it was ground into a fine powder. The dissolution enthalpy of about
0.24 g of trans-Cu(Ala)2(s) in about 100 ml of the solution A1 was
determined under the same condition as the above. The final solu-
tion obtained was named as solution A’.
Finally, UV–vis spectroscopy and the data of the refractive
indexes were used to confirm whether solution A was in the same
thermodynamic state as that of solution A’. These results have
indicated that the chemical components and physico-chemical
properties of solution A were consistent with those of solution A’.
Fig. 1. The curve of the experimental molar heat capacities of the complex trans-Cu
(Ala)2(s) vs. the temperature (T).
(X), X = f (T), has been obtained,
C
p,m/J K−1 mol−1 = 293.86 + 203.44X + 9.31X2−10.72X3−7.53X4
In which X = (T − 235)/157. The standard deviations of experi-
mental molar heat capacities from the smoothed heat capacities
calculated by the polynomial equation were within 0.3% except for
several points around the lower and upper temperature limits. The
correlation coefficient for the fitting R2 equals 0.99994. The uncer-
tainties of the coefficients of the equation have been determined to
be 0.09%, 0.6%, 0.75%, 0.96% and 1.5%, respectively.
3. Results and discussion
3.2. Thermodynamic functions of the complex trans-Cu(Ala)2(s)
3.1. Low-temperature heat capacities
The smoothed molar heat capacities and thermodynamic func-
tions of the complex trans-Cu(Ala)2(s) were calculated based on the
fitted polynomial of the heat capacities as a function of the reduced
temperature (X) according to the following thermodynamic equa-
tions:
All experimental results, listed in Table 2 (see supplemen-
tary data) and plotted in Fig. 1, showed that the structure of the
coordination compound was stable over the temperature range
between T = 78 K and 392 K, that is, no phase change, association
nor thermal decomposition occurred. The 106 experimental points
in the temperature region between T = 78 K and 392 K were fitted by
means of the least squares method and a polynomial equation of the
experimental molar heat capacities (Cp,m) vs. reduced temperature
ꢂ
T
H(T) − H(298.15K)
=
Cp,mdT
298.15K
ꢂ
T
S(T) − S(298.15K)
=
C
p,mT−1dT
298.15K
The polynomial fitted values of the molar heat capacities and
fundamental thermodynamic functions of the sample relative to
the standard reference temperature 298.15 K were tabulated in
Table 3 (see supplementary data) with the interval of 5 K.
Table 2
Reaction scheme used to determine the standard molar enthalpy of formation of the
complex trans-Cu(Ala)2(s) at 298.15 K
No.
Reactions
Solution
A
ꢀfHm◦ or (ꢀSHm◦ ꢃa)
(kJ mol−1
)
b
3.3. The determination of enthalpy change for the solid-state
coordination reaction of Cu(Ac)2·H2O (s) with alanine
1
{Cu(Ac)2·H2O (s) + 2Ala
(s)} + ‘s’=
(6.75 0.04), ꢀH1
2
3
4
5
2HAc (l) + H2O (l) = 2:1 HAc (aq)
2:1 HAc (aq) + ‘s’=
−3.58a, ꢀH2
The solid-state coordination reaction of Cu(Ac)2·H2O(s) with
A1
A’
−(1.63 0.01), ꢀH3
−(10.24 0.08), ꢀH4
−1193.70 [9], ꢀH5
alanine is shown as follows:
Cu(Ala)2 (s) + ‘A1’=
Cu (s) + 4H2 (g) + 5/2O2 (g) + 4 C
(s)=Cu (Ac)2·H2O (s)
Cu(Ac)2·H2O(s) + 2Ala(s) → trans-Cu(Ala)2(s) + 2HAc(l) + H2O(l)
6
3C (s) + 7/2 H2 (g) + O2 (g) + 1/2
N2 (g) = Ala (s)
−(560.0 1.7) [11], ꢀH6
(1)
7
8
9
2H2 (g) + O2 (g) + 2C (s) = HAc (l)
H2 (g) + 1/2O2 (g) = H2O (l)
Cu (s) + N2 (g) + 7H2 (g) + 2O2
(g) + 6C (s) = trans-Cu(Ala)2 (s)
−(483.52 0.36) [10], ꢀH7
−(285.83 0.04) [12], ꢀH8
−(1038.6 3.5), ꢀH9
The enthalpy change of the reaction (1) was determined by mea-
suring enthalpies of dissolution of the {Cu(Ac)2·H2O(s) + 2Ala(s)}
and the 2:1 HAc(aq) in 2 mol dm−3 hydrochloric acid, and the trans-
Cu(Ala)2·H2O(s) in the solvent [2:1 HAc(aq) + 2 mol dm−3 HCl] at
298.15 K.
Of about 0.377 g sample of the {Cu(Ac)2·H2O(s) and 2Ala(s)}
mixture at mole ratio of n(trans-Cu(Ac)2·H2O):n(Ala) = 1:2 were dis-
solved in 100 ml of 2 mol dm−3 HCl at 298.15 K.
The solvent ‘s’ is 2 mol L−1 HCla according to Ref. [8].
ꢀ
ꢁ
5
(x − x)2/n(n − 1), in which n is the experimental number; xi , a
b
ꢃa
=
i
i=1
single value in a set of dissolution measurements; x, the mean value of a set of
measurement results.

Y.-Y. Di et al. / Thermochimica Acta 471 (2008) 70–73
73
If ‘s’ = calorimetric solvent, 2 mol dm−3 HCl, then,
{Cu(Ac)2·H2O(s) + 2Ala(s)} + ‘s’ = solution
y = ax + bz, or y = ax − bz, total error (R) of y equals the algebraic sum
ꢃ
of errors of x and z, that is, R =
a2rx2 + b2ry2, in which a and b are
A
the constants, rx and ry are the errors of the variables x and y.
The results of UV–vis spectrum and refrangibility (refractive
index) were two important information used to detect whether the
structure and composition of a kind of solution was the same or
not as another. In this paper, all of the reactants and products of
the reaction (1) can be easily dissolved in the selected solvent. The
measured values of the refractive indexes of solution A and solution
A’ were (1.2786 0.0011) and (1.2782 0.0008), respectively. The
results of UV–vis spectroscopy were shown in Fig. 2. UV–vis spec-
trum and the data of the refractive indexes of solution A obtained
agreed with those of solution A’, no difference in the structure and
chemical composition existed between the two solutions. These
results have demonstrated that the physicochemical properties of
the solutions A were the same as those of the solution A’.
The dissolution enthalpies of HAc (aq) [n(HAc)/n(H2O)] = 2:1 in
100 ml of 2 mol dm−3 HCl were measured under the same condi-
tion,
2 : 1HAc(aq) + ‘s’ = solution A1.
The dissolution enthalpies of trans-Cu(Ala)2 (s) in solution A1
were measured under the same condition as the above,
trans-Cu(Ala)2(s) + solution A1 = solution A’.
The measurement results of dissolution enthalpies for the reac-
tants and products of reaction (1) are listed in Table 1. In addition,
the enthalpy change of mixing HAc (l) with H2O (l) at the mole
ratio of n(HAc)/n(H2O) = 2:1 can be obtained from the literature
[8]: ꢀSH◦ = −3.58 kJ mol−1. The enthalpy change of the solid-state
m
4. Conclusions
coordination reaction (1) can be calculated in accordance with a
thermochemical cycle and the experimental results as follows:
(1) The paper reports low-temperature heat capacities measured
by adiabatic calorimetry and the dissolution enthalpies of
the reactants and the products of the solid-state coordination
reaction of copper(II) acetate with l-␣-alanine by isoperi-
bol solution calorimetry. Additionally, the thermodynamic
functions and standard molar enthalpy of formation of the
product [trans-Cu(Ala)2(s)] were derived from these experi-
mental results.
ꢀrHm(1)=ꢀSHm◦ [Cu(Ac)2 · H2O(s)+2Ala(s)]−ꢀSHm◦ [2 : 1 HAc(aq)]
−ꢀSHm◦ [trans-Cu(Ala)2(s)] − ꢀSHm◦
= (22.20 0.09) kJ mol−1
.
3.4. The standard molar enthalpy of formation of
trans-Cu(Ala)2(s)
(2) The reliability of the designed thermochemical cycle has been
verified by UV spectroscopy and the data of the refractive
indexes. It is shown that the cycle is reasonable and can be
used to determine standard molar enthalpy of formation of
the product [trans-Cu(Ala)2(s)]. The uncertainty of the standard
molar enthalpy of formation obtained by isoperibol solution
calorimetry was estimated to be between 0.3% and 0.5%, chiefly
considering the measurements of voltage changes Es and Ee,
duration time of electric calibration t, final data processing and
so on.
A reaction scheme used to derive the standard molar enthalpy of
formation of trans-Cu(Ala)2(s) was given in Table 2. The experimen-
tal values of the dissolution enthalpies of the reactants and products
in the solid-state coordination reactions (1) were combined
with auxiliary thermodynamic data of ꢀfHm◦ [Cu(E)2 · H2O,s] =
−1193.70 kJ mol−1 [9], ꢀfHm◦ (HAc, l) = −(483.52 0.36) kJ mol−1
[10],
ꢀfHm◦ (Ala,s) = −(560.0 1.7) kJ mol−1
[11],
and
ꢀfH◦ (H2O, l) = −(285.83 0.04) kJ mol−1 [12] to derive the
m
standard molar enthalpy of formation of trans-Cu(Ala)2 (s),
ꢀfHm◦ [trans-Cu(Ala)2, s] = ꢀrHm(1) + ꢀfHm◦ [Cu(Ac)2
·
Acknowledgement
H2O, s] + 2ꢀfHm◦ (Ala, s) − 2ꢀfHm◦ (HAc, l) − ꢀfH◦ (H2O, l) =
ꢀH9 = ꢀH1 − ꢀH2 − ꢀH3 − ꢀH4 + ꢀH5 + 2ꢀHm6 − 2ꢀH7
−
This work was financially supported by the National Science
Foundation of China under the contract NSFC No. 20673050.
ꢀH8 = −(1038.6 3.5)kJ mol−1
,
in which ꢀH1 ∼ ꢀH9 are the
enthalpy changes of the reactions corresponding to No. of the
reaction in Table 1. The uncertainty 3.5 kJ mol−1 was calculated
according to the error transfer formula, such as for the equations,
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.tca.2008.02.024.
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Fig. 2. UV–vis spectra of solution A and solution A’ obtained from the dissolution of
the {Cu(Ac)2·H2O(s) + 2Ala(s)} mixture in 100 cm3 of 2 mol dm−3 HCl and the {trans-
Cu(Ala)2(s)} in the solution A1 (diluted into 1:20).