NOTES
4139
to BTMA, has a higher moment although deviation from a smooth curve in its susceptibility-temperature characteristic may reflect relatively large changes in the effective ligand field with temperature. Indeed, the increasing divergence of the susceptibilities of all the compounds studied with increasing temperature suggest that the ligand field strength and/or symmetry is markedly temperature dependent. In view of the complexity of the crystal structure, this behavior is not surprising.
Acknowledgment. The author thanks Dr. F. W. Bultitude and Mr. W. A. Fort who provided the samples.
The Sublimation of Aluminum Trifluoride
Arthur D . Little, Inc., Cambridge, Massachusetts (Received July 21, 1967)
This note reports the mass-spectrometric determination of the heats of sublimation of gaseous aluminum trifluoride monomer and dimer, and a study of the infrared spectrum of AlF3(g). The mass-spectrometric work was carried out on a 12-in. radius, 60°-sector, magnetic-deflection instrument built by Nuclide Associates. Matheson Coleman and Bell anhydrous aluminum fluoride was used in these experiments. Samples were contained in a platinum-lined two-piece nickel crucible, especially designed2 for the accurate measurement of second-law heats of vaporization. A typical mass spectrum is shown in Table I. Data for two runs are given Table I : Mass Spectrum of Aluminum Trifluoride Vapor a t 1025°K" _r_____
Ion current a
100
4.2
+
AlF,
AlFi
68.4 5 0 . 8 66.8 f 0 . 8 9 5 . 1 rt 2 . 8
+
+
A12Fs+
Run 2 970-1077°K
67.6 =t1 . 3 66.3 =t1.8 8 6 . 5 i- 2 . 8
"Z+ is the ion current; T is the temperature, OK.
and the dimer contributing at most a few per cent to the total pressure. The difference in the AlF2+ and AIFa+ slopes is probably not significant, although some temperature dependence of the fragmentation pattern cannot be excluded. We thus take the mean values of runs 1and 2 to obtain the heats of sublimation a t 1000°K. A@(' (g)
+
AHs,lOOO = 67.3
f
3 kcal mole-'
A H , , I ~=~85.8 ~
f
3 kcal mole-'
2AlFa(c) +AU'G(g)
by Alfred Buchler, Edward P. Marram, and James L. Stauffer
AlFa
Run 1 951-1057'K
Species
AlF3(C)
and the Infrared Spectrum of AlF3(g)l
AlFs'
Table 11: Slopes of 2.303R log ( Z V ) us. 10a/T"
AhFs
'
0.57
The uncertainty of =t3kcal reflects our estimate of the accuracy of second-law heat determinations with the experimental arrangement used. The value of AHs,looo for AlF,(g) is in very good agreement with the value of 67.46 kcal mole-' a t 1000°K given by JANAF Thermochemical table^,^ on the basis of an extensive survey of the literature. The present data give a value of -48.8 f 3 kcal mole-' for the heat of dimerization of AlFa(g), in good agreement with the mass-spectrometric third-law value of -48 f 4.0 kcal mole-' reported by Porter and Zeller.3 The infrared spectrum of gaseous aluminum fluoride was obtained using a modified Perkin-Elmer Model 12C infrared spectrometer described ear1ier.j Sodium chloride, cesium bromide, and cesium iodide optics were used to scan the spectrum between 2500 and 200 cm-'. The temperature of the experiments ranged from 1000 to 1200". The observed absorption bands and their assignments are shown in Table 111. The 935-cm-' band clearly represents the asymmetric stretching vibration v3. The value obtained is in satisfactory agreement with the value of 945 cm-' reported by JIcCory, Paule, and Margrave.6 The assignment of the other
60-V ionizing electrons; ion current in arbitrary values.
in Table 11. From an inspection of these data, it is clear that the ions AlF2+ and AlF3+ must be assigned to the monomer AlFa, and the ion A12FS+to the dimer A12F6. This assignment agrees with that of Porter and Zelle~-.~It also implies that the vaporization of AlF,(c) is congruent, with the vapor mainly monomeric
(1) This work was supported by the U. S. Army Research Office with funds provided by the Advanced Research Projects Agency. (2) A. Btichler and J. B. Berkowitz-Mattuck, J . Chem. Phys., 39, 286 (1963). (3) R. F. Porter and E. E. Zeller, ibid., 33,858 (1960). (4) "JANAF Thermochemical Tables," 1st addendum, The Thermal Research Laboratory, Dow Chemical Company, Midland, Mich., 1966. The vibrational frequencies used in the AlFa(g) table are based on the present work. (5) A. Btkhler and E. P. Marram, J . Chem. Phys., 39, 292 (1963).
Volume 7 1 , Number It November 1967
Noms
4140
y-butyrolactam, have shown that this liquid has excellent solvent characteristics which appear to closely parallel those of dimethyl sulfoxide and of N,N-dimethylacetamide.' It has also been shown that Nmethyl-2-pyrrolidone can act as a ligand in the formation of inorganic complex compounds.2 The present
Table 111: Infrared Spectrum of AlF,(g) Frequency, om-'
.4asignment
297 935 263
n(A2)
va(E)
~
two bands was made by analogy with the spectra of the boron t r i h a l i d e ~ . ~The , ~ higher of the two, a t 297 cm-', was thus assigned to the out-of-plane bending vibration, v2, while the lower, a t 263 cm-l, was assigned to the in-plane bending vibration, v4. Thus three of the four fundamental vibrations of A1F3(g) are accounted for. These three bands have also been observed in matrix isolation by Lir~evsky.~The frequencies obtained in a solid argon matrix are v2 266 cm-', v3 940 cm-', ttnd v4 251 cm-l. Thus, there are only small shifts for the in-plane vibration frequencies, v3 and v4, while there is a shift of about 30 cm-1 for the out-of-plane vibration, vp. The Raman-active symmetric stretching frequency remains to be determined. Applying a valence force field7to v3 and v4] we derive a value of 642 cm-I for VI. If the same analysis is applied to "BF,, one finds that the experimental value of vl, 888 cm-', is 25% higher than the value of 710 cm-' calculated from v3 and v4. We are thus led similarly to increase the valence force field value of 642 cm-' by 25%, obtaining
-
-
-
vl(A1) = 800 cm-I (estimated) for A1F3(g). (6) L. D.McCory, R. C. Paule, and J. L. Margrave, J . Phys. Chem., 67, 1086 (1963). (7) G. Heraberg, "Infrared and Raman Spectra of Polyatomic Molecules," D. Van Nostrand, Inc., Princeton, N. J., 1945, p 178. (8) T. Wentinck, Jr., and V. H. Tiensuu, J . Chem. Phys., 28, 826 (1958). (9) M. J. Linevsky, Working Group on Thermochemistry, Proceedings of the Second Meeting, Vol. 1, Applied Physics Laboratory, Johns Hopkins University, Silver Spring, Md ., Chemical Propulsion Information Agency, June 1964,p 87.
Conductances of Some Uni-univalent Electrolytes in N-Methyl-2-pyrrolidone a t 25'
by Michael D. Dyke, Paul G. Sears, and Alexander I. Popov
~~~~
Table I : Conductances of Salts in N-Methyl-2-pyrrolidone a t 25'" 10'C
NaI 2.581 4.890 8.625 12.82 20.74 29.06 3.282 5.936 11.73 19.34 28.13
A
40.148 39.55 38.91 38.24 37.52 36.80 39.95b 39.37 38.54 37.71 36.91
NaBPhr** 2.141 25.688 3.703 25.36 6.316 25.01 10.24 24.57 15.34 24.15 21.61 23.75 1.233 25.97b 3.281 25.50 5.378 25.18 8.601 24.78 12.26 24.44 17.29 24.06
lo@
A
KI 3.190 6.102 11.67 25.35 34.57 39.61 3.319 7.055 13.27 20.06 31.48 48.17
39,748 39.17 38.42 37.09 36.47 36.16 39.73b 39.06 38.22 37.56 36.66 35.72
KClOi 3.750 6.975 11.63 18.24 26.90 39.41 2.527 4.802 8.799 14.61 22.55 33.00
40.13" 39.52 38.88 38.16 37.48 36.66 40.46b 39.97 39.24 38.55 37.80 37.09
l0'C
A
NaClO, 3.929 39.95. 6.295 39.51 10.49 38.90 18.54 38.07 27.45 37.37 39.27 36.66 4.723 39.76b 7.243 39.32 13.11 38.57 19.95 37.91 26.87 37.39 38.75 36.69 (i-Am)aBuNI 5.509 36.878 9.182 36.19 13.93 35.53 21.18 34.70 29.55 33.95 43.41 32.97 4.548 37.09 8.296 36.33 13.97 35.53 20.27 34.84 27.66 34.15 36.06 33.51
(i-Am)lBuNBPh4 4.366 22.55" 9.008 22.01 15.52 21.49 21.51 21.13 29.75 20.71 36.63 20.43 3.734 22.66b 8.829 22.00 15.43 21.48 21.06 21.13 28.80 20.74 35.63 20.45 Superscripts a and b designate series of determinations; = phenyl; i-Am = isoamyl; Bu = n-butyl.
** P h
Department of Chemistry, Michigan State University, East Lansing, Michigan 48835 (Received June 81,1967)
Previous studies on N-methyl-2-pyrrolidone, CsHeNO, a cyclic amide which is also known as N-methylThe Journal of Physical Chemzstry
(1) P. G. Sears, W. H. Fortune, and R. L. Blumenshine, J. Chem. Eng. Data, 1 1 , 406 (1966). (2) J. H. Bright, R. S. Drago, D. M. Hart, and S, K. Madan, Inorg. Chem., 4, 18 (1965).
