Thermodynamic properties of α-platinum dichloride

Article abstract of DOI:10.1007/s11172-008-0143-3

The heat capacity of crystalline α-platinum dichloride was measured for the first time in the temperature intervals from 11 to 300 K (vacuum adiabatic microcalorimeter) and from 300 to 620 K (differential scanning calorimetry). In the 300-620 K temperatur

Full text of DOI:10.1007/s11172-008-0143-3

Russian Chemical Bulletin, International Edition, Vol. 57, No. 6, pp. 1157—1159, June, 2008
1157
Thermodynamic properties of αꢀplatinum dichloride
Z. I. Semenova and T. P. Chusova
A. V. Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences,
3 prosp. Akad. Lavrent´eva, 630090 Novosibirsk, Russian Federation.
Eꢀmail: chu@che.nsk.su
The heat capacity of сrystalline αꢀplatinum dichloride was measured for the first time in
the temperature intervals from 11 to 300 K (vacuum adiabatic microcalorimeter) and from 300 to 620 K
(differential scanning calorimetry). In the 300—620 K temperature interval, the C° values for
p
αꢀPtCl2 (cr) coincide with the heat capacity of CrCl2 (cr) within the limits of experimental error,
which made it possible to estimate the heat capacity of αꢀPtCl2 (cr) at higher temperatures.
The approximating equation of the temperature dependence of the heat capacity in the interval from
298 to 900 K C° ( 0.8) = 63.5 + 21.4•10–3T + 0.883•105/Т2 (J mol–1 K–1) was derived using
p
the experimental values, as well as the literature data on the heat capacity of CrCl2 (cr). For
the standard conditions, the C°p,298.15 and S°298.15 values are 70.92 0.08 and 100.9 0.33 J mol–1 K,
respectively; H°298.15 – Н° = 14 120 42 J mol–1
.
0
Key words: lowꢀtemperature calorimetry, differential scanning calorimetry, platinum dichloride,
heat capacity, entropy, enthalpy.
The reduction was carried out as follows. A weighed sample of
the substance (0.08—0.15 g) was loaded into a quartz beaker, whose
weight was brought to a constant value, and the beaker was mounted
in a quartz reactor. The system was purged with hydrogen for
10 min. Then, using a special heater, the temperature in the sample
zone was gradually increased with a rate of 50 K h–1 to 473 K, and
the reaction was carried out for 40 min. Hydrogen chloride that
formed was absorbed at the reactor outlet in two consecutively
connected vessels filled with distilled water. The apparatus was
cooled to room temperature in hydrogen flow, the quartz beaker
was taken out and calcined to 1073 K to remove the adsorbed
hydrogen. The amount of platinum formed was determined by the
difference in weights. Weighing was carried out on an analytical
balance with an accuracy of 0.00005 g. The error in platinum
determination was 0.2—0.5%, depending on the sample weight.
The content of chloride ions was determined by potentiometric
titration with a 0.05 M AgNO3 solution under standard conditions
with a relative error of 0.5%. Found (%): Pt, 73.26; Cl, 26.67.
PtCl2. Calculated (%): Pt, 73,34; Cl, 26.66.
Xꢀray diffraction study of αꢀplatinum dichloride was carried
out on a DRONꢀ2 diffractometer with filtered copper radiation
(CuꢀKα radiation, Ni filter). The interplanar spacings coincided
satisfactorily with the values published1 for αꢀPtCl2. All reflections
in the Xꢀray diffraction pattern were indexed in the monoclinic unit
cell with the parameters a = 13.49 Å, b = 3.18 Å, c = 6.85 Å,
β = 107.75°, and Z = 4. These values agree well with the results
(space group С2/m, unit cell parameters a = 13.258 Å, b = 3.194 Å,
c = 6.802 Å, β = 107.75°, Z = 4) obtained in singleꢀcrystal Xꢀray
diffraction study.1
The purpose of this work is to measure the heat capacꢀ
ity of crystalline αꢀplatinum dichloride in the temperaꢀ
ture interval from 11 to 620 K and to calculate the entropy
and the enthalpy difference using the results obtained.
No experimental data on the heat capacity of crystalline
platinum chlorides have been reported so far.
Experimental
Synthesis of αꢀPtCl2. The synthesis is based on the data1 that
αꢀPtCl2 is formed by heating of βꢀPtCl2 at 773 K in an evacuated
ampule for 2 days. A weighed sample (0.5—0.8 g) of βꢀPtCl2,
which was synthesized using a standard procedure2 by thermal
decomposition of H2PtCl6•6H2O in a chlorine flow (РCl = 1 atm),
was loaded into a quartz ampule 15—18 mL in volume. T2he ampule
was evacuated at room temperature for 1 h, sealed, and heated in
a gradient furnace. The substance transfer (∼2/3 of the sample over
a period of 10 days) occurred from the "hot" (873 K) to "cold" zone
(773 K). The product precipitated represented dark violet dendrites
0.5—1.0 cm in size.
The substance synthesized was identified by elemental, Xꢀray
phase, and spectral analyses and by IR spectroscopy.
Elemental analysis was based on a method of platinum and
chlorine determination by separation of the metal from chlorine by
the reduction
PtClx (cr) + x/2 H2 (g) = Pt (cr) + x HCl (g)
with simultaneous uptake of hydrogen chloride by water. The optiꢀ
mal conditions for the reduction reaction to occur were preliminarꢀ
ily determined using a Paulik—Paulik—Erdey derivatograph.
The quantitative reduction of platinum dichloride was shown to start
above 340 K, and the rate maximum was observed at 403 K.
IR spectra were recorded on a Perkin—Elmer 325 instrument in
the region 200—400 cm–1 using СsI windows. Samples were preꢀ
pared as suspensions in anhydrous Nujol. Two strong absorption
bands were observed at 326 and 344 cm–1, which agreed with the
published data.3
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1136—1138, June, 2008.
1066ꢀ5285/08/5706ꢀ01157 © 2008 Springer Science+Business Media, Inc.

1158
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 6, June, 2008
Semenova and Chusova
Spectral analysis of the sample studied showed the presence of
Pd (3•10–2 wt.%) and Rh (1•10–2 wt.%) admixtures. No Ir, Ru, Os,
Fe, and Ni admixtures were found within the analysis accuracy
(10–3—10–4 wt.%).
Table 1. Experimental heat capacity values for αꢀPtCl2 in
the temperature interval from 11 to 300 K
Т/K
С° /J mol–1 K–1
Т/K
С° /J mol–1 K–1
р
р
Experimental procedure. The heat capacity of αꢀPtCl2 was meaꢀ
sured in a vacuum adiabatic microcalorimeter.4 A nickel ampule for
the substance had a useful volume of ∼10 cm3, and the sample weight
was 1.0368 g. The heat capacity (thermal value) of the empty ampule
was determined in the 10.7—311.30 K interval at 99 experimental
points. The smoothed (Cp)empty = f(T) values calculated using these
data were then used to determine the heat capacity of the substance.
To check this procedure, the heat capacity of benzoic acid (BnOH)
was determined at 32 experimental points in the interval from 14 to
273 K. The results obtained agree satisfactorily with the standard
data5 (1% for temperatures from 11 to 30 K and 0.2% for the interval
30—273 K).
The heat capacity of αꢀplatinum dichloride under constant
pressure was determined in the temperature interval from 10.7 to
311.30 K in 96 calorimetric experiments. The average deviation of
the experimental values from the smoothed Ср(Т) curve was 0.8% at
11—30 K and only 0.14% at 30—300 K.
10.74
11.21
11.80
12.28
12.79
13.31
13.79
14.29
14.84
15.60
16.64
17.68
18.69
19.68
20.71
21.78
23,19
24.44
25.57
26.62
27.89
29.90
31.80
33.84
36.00
39.25
40.75
44.13
45.52
48.90
50.11
53.15
56.81
61.28
61.91
65.72
66.07
69.36
69.89
70.67
71.98
72.93
73.68
74.36
75.02
75.85
77.98
80.68
2.063
2.238
2.460
2.720
2.950
3.297
3.515
3.807
4.105
4.347
4.891
5.481
6.025
6.563
7.071
7.657
8.410
9.079
9.665
10.25
10.88
12.05
13.07
14.23
15.39
17.05
17.97
19.63
20.26
21.85
22.47
23.72
25.11
26.74
27.782
28.65
29.52
30.11
31.27
31.40
31.88
32.10
32.24
33.35
33.11
33.50
33.66
35.32
82.91
83.26
85.56
86.97
90.54
93.32
98.04
36.13
36.30
37.02
37.59
38.81
39.70
41.29
42.51
43.81
46.32
47.28
48.41
49.91
50.71
51.13
52.43
53.85
54.77
55.90
56.82
57.66
58.49
59.45
60.29
61.67
62.38
62.97
63.51
64.14
64.85
65.44
65.77
66.45
66.61
67.15
67.57
68.49
68.87
69.62
69.87
70.08
70.42
70.75
71.09
71.13
70.79
71.29
71.59
101.84
105.84
114.38
118.00
122.25
128.02
131.67
133.27
138.78
145.43
149.72
155.56
160.44
165.16
170.22
176.47
182.00
192.70
197.86
202.99
208.07
213.46
220.72
226.07
231.18
234.95
239.38
246.46
251.95
264.25
269.63
276.45
279.50
283.24
288.22
294.03
299.57
299.65
300.62
305.72
311.30
At medium temperatures (300—620 K), the heat capacity
of αꢀPtCl2 (cr) was measured using a differential scanning calorimꢀ
eter (Setaram). The sample weight was 0.1560 g. The limiting error
of the method in heat capacity determination was 10%.6
Results and Discussion
The experimental values of the heat capacity of
αꢀPtCl2 are presented in Table 1. Table 2 lists the
smoothed values of the heat capacity, enthalpy differencꢀ
es (Н°T – Н°0), and entropies (S°T) of αꢀPtCl2 (cr) at the
temperatures recommended for the tables of smoothed
values. The contributions of the thermodynamic values at
temperatures from 0 to 11 K were calculated assuming
that the heat capacity in this interval is proportional to
Т3. Under these conditions, S°(11 K) = 0.75 J mol–1 K–1
or ∼0.8% of the entropy value at 298.15 K.
,
For the standard conditions, C°p,298.15 and S°298.15 are
70.92 0.08 and 100.9 0.33 J mol–1 K–1, respectively;
Н°298.15 – Н°0 = 14120 42 J mol–1. It was accepted in the
calculations that 1 gꢀmole of αꢀPtCl2 was 265.996 g.
The errors of the calculated enthalpy differences and
the entropies were estimated with allowance for the deviꢀ
ation of the experimental points from the smoothed curve
and the calibration accuracy of the empty calorimeter
assuming that the С°р(Т) curve had no anomalies below
11 K. The entropies and enthalpy differences of αꢀPtCl2
under standard conditions were obtained by numerical
integration of the С°р(Т)/Т and С°р(Т) functions.
The heat capacity values of αꢀPtCl2 obtained by difꢀ
ferential scanning calorimetry in the 300—620 K interval
are given in Table 3.
The experimental data in the whole temperature range
(10.7—620 K) are shown in Fig. 1. The results obtained
by lowꢀtemperature calorimetry and DSC are well conꢀ
sistent. Figure 1 also presents the previously published
data on the heat capacity of CrCl2 (cr). Based on the
results obtained in this work and on the published data,
we calculated coefficients for the equation approximatꢀ
ing the temperature dependence of the heat capacity of
crystalline αꢀPtCl2 in the temperature interval from 298
to 900 K.

Thermodynamics of αꢀplatinum dichloride
Table 2. Thermodynamic characteristics of αꢀPtCl2
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 6, June, 2008
1159
Table 3. Experimental heat capacity values for αꢀPtCl2 in
the temperature interval from 300 to 620 K
Т/K
С°
S°
Н°Т – Н°
0
р
T
/J mol–1
Т/K
С° /J mol–1 K–1
Т/K
С° /J mol–1 K–1
р
р
J mol–1 K–1
301.1
340.4
340.8
380.6
420.3
420.3
70.3
68.8
69.4
75.0
75.0
73.8
460.1
499.8
539.6
579.3
619.1
73.6
74.6
75.3
75.0
76.4
11
12
13
14
15
16
18
20
25
30
35
40
45
50
55
60
2.163
2.615
3.092
3.586
4.096
4.602
5.690
6.736
9.372
12.07
14.82
17.51
20.03
22.36
24.63
26.88
29.14
31.14
6.109
8.494
11.38
14.69
18.53
22.89
33.18
45.61
85.77
139.4
206.6
287.5
381.4
487.4
605.0
733.9
873.6
1025
1185
1356
1725
2128
2563
3027
3519
4034
4573
5129
5707
62970
6904
7527
8159
8799
9452
10110
10790
11460
12150
12410
12840
13540
14120
14250
0.741
0.950
1.176
1.423
1.955
1.971
2.573
3.226
5.021
6.958
9.025
11.18
Cp//J mol–1 K–1
80
60
40
20
0
13.39
15.62
17.86
20.10
22.34
24.58
26.790
29.00
33.34
37.58
41.73
45.77
49.71
53.51
57.03
60.83
64.31
67.70
70.96
74.14
77.24
80.25
83.14
85.94
88.70
91.34
93.93
94.73
96.44
98.91
100.9
101.3
1
2
3
4
65
70
75
80
33.17
35.21
38.61
41.92
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
260
270
273.15
280
290
298.15
300
45.020
47.823
50.375
52.677
54.810
56.735
58.450
59.999
61.379
62.592
63.764
64.810
65.731
66.610
67.404
68.199
68.994
69.287
69.873
70.500
70.919
71.002
0
100 200 300 400 500 600 700 800 T/K
Fig. 1. Temperature dependences of the heat capacities of platinum
and chromium dichlorides: our experimental data on the heat caꢀ
pacity of αꢀPtCl2 obtained in vacuum adiabatic microcalorimeter
(1) and in differential scanning calorimeter (2); published data on
the heat capacity of CrCl2 (3); heat capacity of αꢀPtCl2 calculated by
the approximating equation (4).
values of αꢀPtCl2 are most similar to the published data on
the heat capacity of chromium dichloride.7
References
1. B. Krebs, C. Brendel, H. Schafer, Z. anorg. allgem. Chem., 1988,
561, 119.
2. G. Brauer, Handbuch der Preparativen Anorganischen, Chemie
Ferdinand Enke Verlag, Stuttgart, 1954.
3. R. Mattes, Z. anorg. allgem. Chem., 1969, 364, 290.
4. K. S. Sukhovei, V. F. Anishin, I. E. Paukov, Zh. Fiz. Khim., 1974,
48, 1589 [J. Phys. Chem. USSR, 1974, 48 (Engl. Transl.)].
5. N. P. Rybkin, M. P. Orlova, A. K. Baranyuk, N. G. Nurullaev,
L. N. Rozhnovskaya, Izmerit. Tekhnika [Measurement Techꢀ
nique], 1974, No. 7, 29 (in Russian).
С° ( 0.8) = 63.5 + 21.4•10–3T +
р
+ 0.883•105/Т2 (J mol–1 deg–1).
6. L. N. Zelenina, T. P. Chusova, Yu. G. Stenin, V. V. Bakovets,
Zh. Fiz. Khim., 2006, 80, 199 [Russ. J. Phys. Chem., 2006, 80
(Engl. Transl.)].
7. О. Knacke, O. Kubaschewski, K. Hesselmann, Thermochemical
Properties of Inorganic Substances, Springer, Berlin, 1991, p. 426.
When estimating the heat capacity of αꢀPtCl2 in the
620—900 K temperature interval, we based on the fact
that the heat capacities of transition metal dichlorides
(CrCl2, TiCl2, ZrCl2, and FeCl2) are close to each other
and their temperature runs are parallel according to availꢀ
able literature data.7 In the region 300—620 K, the Ср
Received November 20, 2007;
in revised form April 9, 2008