H. L. CLEVER,E. F. WESTRUM, JR.,ASD A. W. CORDEB
1214
Heat Capacities and Thermodynamic Properties of Globular Molecules.
XIV.
Tetraphosphorus Trisulfide, Tetraphosphorus Triselenide, and
Tetraphosphorus Decasulfide between 5 and 350°K.'*
by H. Lawrence Clever, Edgar F. Westrum, Jr.,Ib Department of Chemistry, University of Michigan, Ann Arbor, Michigan
48104
and A. W. Cordes Department of Chemistry, University of Arkansaa, Fayetteuille, Arkansaa
71701 (Receiued October 6. 1964)
~~
Thermal properties of three phosphorus chalcogenides were determined by adiabatic calorimetry and yielded entropies a t 298.15OK. for P4S3,P4Se3,and P4Sl0 of 48.60, 57.26, and 91.24 cal./(mole OK.), respectively. The P4S3transforms to a plastically crystalline state a t 313.90OK. with ASt = 7.85 cal./(mole OK.)and P4Se3shows an anomalous increase in heat capacity suggesting such an effect slightly above 35OOIi. Diffraction data on P4S3 provided coefficients of thermal expansion on both phases and confirmation of the plastically crystalline nature of the Crystal I phase.
Many crystalline phases of high molecular symmetry show an apparent first-order solid-solid transition to a plastically crystalline phase* with a cubic or hexagonal structure. Compared to other molecular crystal phases this state of the compound is relatively easily deformed by pressure, has a relatively high vapor pressure, and has an entropy of fusion 55 cal./(mole O K . ) . Several of the phosphorus chalcogenides are highly symmetrical molecules and solid-solid transitions have been reported for some of these. To elucidate further the range of existence and nature of the plastic crystalline phase, heat capacity measurements were made on tetraphosphorus trisulfide (P4S3),tetraphosphorus triselenide (P4Se3),and tetraphosphorus decasulfide (P4SI"). The existence of solid-solid transitions has been reported for tetraphosphorus t r i s ~ l f i d e ~and - ~ there is some evidence that tetraphosphorus triselenide exists in two modifications6; transitions have not been reported in tetraphosphorus decasulfide. In addition, differential thermal analysis on tetraphosphorus trisulfide indicated an enthalpy of transition of 3.4 kcal./mole a t 312 f 1°1L4 Recent crystallographic studies have been made on the trisulfide,4 triselenide,' and decasulfide.s The Journal of Physical Chemistry
Experimental Cryostat and Calorimeter. A gold-plated copper calorimeter (laboratory designation W-37) had a threaded, vacuum-tight seal with a 1.4-cm. diameter aperture and an annealed, gold gasket between the screw cap and thc circular knife edge of the Monel metal top. This eliminated a soldered closure for these flammable compounds. The calorimeter, including cap and gseket, weighed 34.575 g. and had o volume of 32.45 cc. The thermometer-heater assembly was inserted in a well. Six metal vanes radiated from the central well through
(1) (a) Supported in part by the Selenium-Tellurium Development Association, Inc. (b) To whom correspondence concerning this paper should be directed. (2) J. Timmermans, Phya. Chem. Solids, 18, 1 (1961). (3) A. Stock, Ber., 43, 150 (1910).
(4) Y. C. Leung, J. Waser, S. van Houten, A. VOS, G. A . Wiegers, and E. H . Wiebenga, Acta Cryst., 10, 574 (1957). (5) (a) Y. C. Leung, J. Waser, and L. R . Roberts, Chem. Ind. (London), 948 (1955); (b) S. van Houten, A. Vos, and G . A. Wiegers, Rec. trau. chim., 74, 1167 (1955). (6) J. hlai, Ber., 59, 1888 (1926); 61, 1807 (1928). (7) E. Keulen and A. Vos, Acta Cryst., 12, 323 (1959). (8) A. Vos and E. H . Wiebenga, ibid., 8, 217 (1955).
HEATCAPACITIES ASD THERMODYNAMIC PROPERTIES OF GLOBULAR MOLECULES
Table I Sample w t . Conlid
( e . in
Molecular mass
uacuo)
d , g./cc.
H e , torr"
2. 08b 13 . 3 27.496 220,09 PIS, 19.429 360.78 3 . 17c 15 . 5 PSe3 444,54 2 . OSd 5 .35 PIS10 19.254 " Helium gas was added to aid thermal contact between calorimeter and samples. Ref. 4. Ref. 7. Ref. 8.
1215
the saniple space to ensure rapid thermal equilibration of the entire assembly and sample. The calorimeter was suspended within the Mark I11 cryostatg for the measurement of heat capacity by the quasiadiabatic technique.1° A calibrated capsule-type platinuin resistance thermometer (laboratory designation A-3) was used. Its temperature scale is considered to accord with the thermodynamic temperature scale
Table I1 : Heat Capacities of Phosphorus Chalcogenides" T
T
C,
C,
T
CI
Tetraphosphorus Trisulfide! (P4Sd Series I 5.52 0,142 5.92 0,123 6.42 0.179 6.94 0 258 7.3) 0,403 8.71 0,512 9.60 0.819 1,104 10.70 1.460 11.99 1.941 13.46 2.426 14.87 2.966 16.33 3.546 17.98 4.278 20.10 5.122 22.67 5.862 25.17 6.532 27.69 7.196 30.45 7,846 33.56 8.530 37.07 9.185 41.10 9,893 45.78 10.669 51.24 57.41 11.523 64.44 12.529 71.90 13.540 79'37 87.28
14'652 15.92
Series I1 81.06 14.926 88.86 16.16 96.73 17.29 105.32 18.58
a
114.42 123.41 132.52 141.90 151.50 161.20 170.89 180.60 190.34 199.59 208.51 217.49 226.62 235,91 245,17 254.50 263 82 273.18 287.96 301.56
19.97 313.45 1590 313.79 3272 21.35 315.53 191.4 ' 22.68 24.02 Series V 25.33 260.67 35.58 26.51 267.12 36.14 27.64 276.36 36.86 28.70 Enthalpy run E 29.76 A H t run F 30.74 3 1 . ~ 5 ~ Enthalpy run G 32.47 Series VI 33.13 300.72 39.07 33.90 305.35 41.49 34.57 309.26 50.10 35.26 312.03 128.1 35.89 AHt run H 36.63 313.71 2944 37.C4 314.23 256.9 39.12 315.24 43.57 AHt run A 316.82 43.50 326.87 43.36 321.84 43.30 336.17 43.46 330.25 43.36 345.53 43.85 338.62 43.55 Series 111 346.63 43.57 266.15 36.12 275,46 Series VI1 36.80 273.75 36.67 Enthalpy run B 282.48 37.51 AH1 run c 286.49 37.82 Enthalpy run D 290.47 38.02 292.16 37.96 Series IV 305.52 46.04 311.69 208.2
Units: cal., mole, OK.
T
C,
T
C*
T
Tetraphosphorus Triselenide (PaSe8) Series I 103.89 22.28 Series I1 86.35 19.56 93.32 20.68 102.19 22.04 111.66 23.46 119.98 24.82 130.01 26.26 139.59 27.53 148.89 28.68 158.78 29.81 169.21 30.92 179.36 31.88 189.63 32.81 197.91 33.49 34.23 207.76 34.96 217.59 35.66 227.55
237.95 248.70 259.46 270.08 279.51 289.91 300.19 310.36 320.43 330.38 339.24 346.91
36.33 36.95 37.49 38.32 38.68 39.23 39.84 40.50 41.19 42.03 42.82 43.74
Series 111 5.25 0.41 5.46 0.46 6.02 0.48 6.g4 0.68 7.85 0.g9 8,g4 1.40
10.07 11.37 12.80 14.30 15.94 17.85 20.06 22.59 25.58 28.76 31.93 35.46 39.85 44.50 48.97 53.74 59.13 65.34 72.20 79.65 88.04
1.86 2.389 2.061 3.612 4.322 5.082 5.901 6,750 7.645 8.464 9.236 10.032 10.933 11.832 12,675 13.573 14.575 15.75 16,89 18.25 19,82
Tetraphosphorus decasulfide ( P4Sl0) Series I 42.77 120.63 44.86 128.22 46.95 136.83 48.96 145.81 50.88 154.70 163.63 52.71 54.40 172.57 55.94 181.54 Series I1 81.81 31.29 88.65 33.72 95.03 35.63 101.85 37.61 109.15 39.69 117.14 41.91 125.69 44.15 134.27 46.26 Enthalpy run A 187.23 56.98
196.86 206.90 217.00 226.91 236.63 246.20 255.61 265.23 275.05 285.08 295.01 304.88 314.76 324.73 334.84 345.10
58.59 60.09 61.55 62.90 64.18 65.31 66.45 67.62 68.56 69.58 70.49 71.35 72.07 72.92 73.71 74.45
Series 111 18.79 5.172 21.93 6.452 24.52 7.499 27.05 8.531 29.91 9.698
33.34 37.38 41.80 46.90 52.79 58.88 65.20 71.54 78.15 5 6 8 9 10 11 12 13 14 16 17
11.160 12.926 14.884 17.15 19.75 22.39 25.04 27.36 29,85
Series IV 72 0 42 0 68 70 22 0 98 29 1 37 35 1 76 2 14 37 38 2 49 49 2 93 80 3 52 15 4 08 72 4 76
Volume 69, LvzdmbeT 4
April 1966
H. L. CLEVER,E. I;. WESTRUM, JK.,A N D A. W. CORDES
1216
Table 111: Thermodynamic Properties of Phosphorus Chalcogenides" -(Go
T
Ca
SO
H a - H'a
- H"a)/ T
-(Go
T
Tetraphosphorus Trisulfide PIS^) 5 10 15 20 25 30 35 40 45 50
0,080 0.902 2.486 4.234 5.813 7.109 8.144 9.003 9.769 10,498
60 70 80 90 100
11.907 13,276 14.756 16.32 17.79
110 120 130 140 150
Crystal I1 0.027 0.269 0.920 1.876 2.995 4.174 5.350 6.495 7.600 8.668
0.10 2.08 10.38 27.20 52.42 84.85 123,08 166.0 212,9 263.6
0.007 0.061 0.228 0.516 0.898 1.346 1.834 2.346 2.868 3.395
10.707 12.645 14,512 16.342 18.138
375.7 501.6 641.6 797.1 967,6
4.446 5.480 6.492 7.486 8.462
19.29 '20.81 '22.33 '23.78 25.12
19.903 21.647 23.372 25.081 26.768
1,153.0 1,353.5 1,569 1,800 2,044
9.421 10.368 11.302 12.225 13.139
160 170 180 190 200
26.35 27.51 28,65 29.75 30.79
28.429 30.062 31.67 33.25 34.80
2,302 2 571 2,852 3,144 3,447
14.042 14.937 15.82 16.70 17.56
210 220 230 240 250
31.76 i32.65 33.46 34.22 34.93
36.32 37.82 39.29 40.73 42.14
3,760 4,082 4,412 4,751 5,096
18.42 19,27 20.11 20.94 21.76
260 270 280 290 300
35.63 36.37 37.17 37.93 39.28
43.53 44.89 46.22 47.54 48.84
5,449 5,809 6,177 6 552 6,937
22.57 23.37 24.16 24.95 25.72
313,90
...
50.61b
7,475b
26, 80b
273.15
36.62
45.31
5,924
23.62
298.15
:38.87
48.60
6,865
25.58
313.90 325 350
. . ,
43.31 43.77
Crystal I 58, 46b 9,939* 59.96 10,420 63.18 11,508
S O
H o - H'a
- H'a) / T
5 10 15 20 25
Tetraphosphorus Triselenide (P,Se,) 0,305 0.101 0.38 1.785 0.690 5.05 3.921 1,814 19.28 5.883 3.219 43.94 7.471 4.709 77,47
0,025 0.185 0.529 1.022 1,610
30 35 40 45 50
8,778 9.927 10.966 11.923 12.870
6.190 7.631 9.025 10.373 11.678
2 251 2,917 3.594 4.273 4.948
60 70 80 90 100
14.742 16,56 18.34 20.05 21.71
14.190 16.601 18.931 21,194 23,397
474.6 631.2 805.9 998,2 1,207.4
6.281 7.584 8.858 10.103 11.323
110 120 130 140 150
23.30 24.83 26,24 27.57 28.80
25.544 27.639 29.682 31.68 33.62
1,432.8 1,674 1,929 2,198 2,480
12,518 13.692 14.843 15.97 17.09
160 170 180 190 200
29,94 30.99 31.96 32.85 33.67
35.52 37.36 39.16 40.91 42.62
2,774 3,079 3,393 3,717 4,050
18.18 19.25 20.31 21.35 22.37
210 220 230 240 250
34.43 35,14 35,80 36.43 37.03
44.28 45.90 47.48 49.01 50.51
4,391 4,738 5,093 5,454 5,822
23.37 24.36 25.33 26.29 27.23
260 270 280 290 300
37.60 38.16 38.71 39,26 39.83
51.98 53.40 54.80 56.17 57.51
6,195 6,574 6,958 7,348 7,743
28.15 29.06 29.95 30.83 31.70
350
44.10
63.93
9,827
35.85
273.15
38.33
53.85
6,694
29.34
298.15
39,72
57,26
7,669
31.54
118.18 165.0 217.3 274,5 336.5
26. 80b 27.90 30.31
within O . O 3 O ? X . from 10-90°1
