NOTES
August, 1961 TABLE I
1447
SO],} [CoCI4] is not unambiguous. Table I1
contains the results published2 on this experiment. COMPI,F,XF;S IN XITROMCTHANE SOLUTION TABLE I1 s-0 CHs rock INFRARED SPECTR.4 REPORTED^ O N DEUTERATED DIMETHYL { l?lln[(CH3)2S0]6} [hlnC141 1004i,s 955i,s SULFOXIDE COMPOUNDS ~ C O [ ( C H ~ ) Z[cOc14] SO~~~ 994i,e 950i,s I C o [ (CH$zS0lsl-CO[ ( C D W 0 1 6 $ssignment {Si[(CH3)2SO]61 [SiC14]" 10OOi,s 950i,s [ CoCla] [CoClr] 1Cu [(CH~),SO141 [CuBrrl 988i,s 940i,br 3002m 2240m ilsym C-H, C-D stretch {Cu[(CH3)?SOIrl[ C ~ C l r l 987i,s 937i,br 2906m 2120w Sym C-H, C-D stretch Hg( SCS)z'2(CH3)zSO 1010i,br 950i,s 1416in 1015s Asym CHD,CD,, defor1025i,m 950m,s mation (CH&SO.I~ 1039ni Sym CH8,CDa,drformaa There is evidence for some dissociation of the complex in this instance. b Spectrum was obtained on a smear of tion 1292w l3 a dimethyl sulfouide-iodine mixture. The first symbol 1009s,sh 819111 listed refers to the intensity of absorption: i, intense; CH3, CD, rovk 999s m, medium, the second to the width of the peak; s, sharp; 760w lir, broad; m,medium. 775w S-0 stretch 950vs 970vs
INFRARED SPECTRA OF
THE
14w1
1
1
The high intensity observed in the deuterated cm. -l in the dimethyl sulfoxide-iodine complex, a pronounced increase in intensity but no change complex for the 1015 and 1039 cm.-' peak is in frequency is observed for the 950 cm.-l peak. surprising in view of the assignments made. In the CoC12, TvlnCl., and Hg(SCN)Z complexes the The frequency shift of the S-0 stretch upon deuterpeak in the 1000 cm.-l region occurs a t slightly ation is also surprising. An alternate explanation of the data (Table 11) different frequencies and is still the more intense peak in the spectra. HoTvever, the relative in- can be proposed which explains the observed fretensity of the 950 em.-' peak is increased con- quencies and intensities and is also compatible siderably over that in the iodine complex but the with our assignment of the S-0 stretching frefrequency of' this peak varies very little. The quency. The peak at 999 cm.-' in the undeuterweak peak at 915 em.-' in free dimethyl sulfoxide ated complex which we attribute to S-0 stretch disappears in the complexes and probably becomes occurs a t 1015 cm.-l in the deuterated complex. The 970 cm.-l peak in the deuterated complex the shoulder on the 950 em.-' peak. There is n o unique explanation for the de- can be attributed to either the symmetric or asymscribed spectral changes. However a tentative metric deformation. Assignment of the peaks explanation can be proposed which is consistent in this way does little to improve the earlier with the information now available. The series criticism about the intensity of the peaks atof compounds contained in Table I indicates an tributed to the various vibrational modes. However, it can now be proposed that considerable increase in the relative intensity of the 950 cm.-' peak without much change in frequency as the interaction is operative in the deuterated complex peak in the 1000 cm.-l region approaches the 950 between the S-0 stretch and either the asymmetric cm.-l peak. The variation in the frequency of the or symmetric deformation to account for the repeak in the 1000 cm.-' region as the metal ion is sulting frequencies and intensities. In the absence raried leads us to believe that this is the S-0 of this interaction the peaks corresponding to the stretching frequency. The constancy of the peak group frequency vibrations might be expected to a t 950 cm.-' supports an assignment of methyl occur a t about 1000 cm.-' for S-0 stretch and in rock. There is considerable coupling and this the same region for a n-eak methyl deformation assignment should not be construed to indicate a absorption. The considerations described above, though pure S-0 group frequency vibration. The increase in the intensity and the broadening of the qualitative in nature, do indicate the complexity lorn frequency peak can be attributed to a "bor- of this problem. The explanation proposed favors rowing of intensity"3 by an interaction between an assignment of the high frequency peak (1000 the pure groiip frequency vibrations producing cm.-') to a S-0 stretching frequency and accounts the -1000 and 950 em.-' peak.4 The extent for the observed peak intensities. of the interaction increases as the frequencies Acknowledgments.-The authors wish to acknowlcome closer together. edge the financial assistance of the Atomic Energy When the S-0 peak is shifted below 990 em.-', Commission (Contract No. AT(11-1)-758). as in the CuCll and CuBr2complexes, the interaction between the two peaks now causes the low frequency peak to broaden and become the most intense SOLUBILITY AND CONDUCTIT'ITY OF peak in the spectra. An assignment now becomes SCBSTITCTED - x m t o m x IODIDES IN very difficult. PESTABORBNE The interpretation of the spectral results reBY HENRYE. FIRTH AND PAUL I. SLICK ported? on the deuterated complex, { Co[(CD&(3) G . Hereberg, "Infrared and Raman Spectra," D. Van Nostrand Co., New York, N. Y.. 1951, p. 265. (4) It is possible t h a t t h e 915 c m - 1 peak would be involved in this interaction instead of the 950 om.-' peak,
Department of Chemtstru. Syracuss Unzversity, Syracuse, zi. Y . Recazked February 1 , 1961
Since pentaborane has a dielectric constant of
20.8 a t 2501 it was ef interest to determine its sol-
1448
T'ol. 65
SOTES
vent properties for electrolytes. A conductance method was used, as all manipulations had to be performed out of contact with air. Experimental Apparatus.-The conductivity cell had a cell constant of 0.4 at 25", and required approximately 5 g. of pentaborane to cover the electrodes. The salt to be investigated was weighed, pentaborane was distilled into the cell, the cell assembly was removed from the vacuum system and weighed to determine the concentration. A magnetic stirrer was placed in the bottom of the cell to speed attainment of equilibrium. The cell was calibrated with standard KCI solutions in the usual manner. The conductance W M measured with the bridge described by Orr and Wirth.2 The bath temperature was maintained constant at selected temperatures between 0 and 25' to within & 0.05'. The density of' solutions of tetra-n-butylammonium iodide was determined in a dilatometer which was sealed off under vacuum after introduction of the pentaborane. Materials.-Pentaborane was purified by repeated freexing with a Dry Ice-acetone mixture and removal of the noncondensable gases. The specific conductivity of the pentaborane was ca. 1 X 10-8 mhos. The substituted ammonium salts used were Eastman reagent grade. The tetra-n-butylammonium iodide was 99.3y0 pure by analysis.
mum as the concentration was increased. Since this maximum is close to the conductivity of the saturated solutions in the temperature range 0-15", the solubility was checked by determining the vapor pressure of solutions a t constant temperature as known amounts of solveut were removed. The intersection of the vapor pressure curve for the unsaturated solutions with that of saturated solution permitted the estimation of the solubility. The solubilitv was found to varv from 40.5 i. 0.4 E. a t 0" to'61.0 =t0.4 g. of (k-C411y)4?;Iper 100 of B6H9a t 25". The densitv of solutions of ( T L - C ~ H ~was ) ~ Nfound I to vary lineaf;lywith the square root of the molality a t constant temperature. Our results combined with the results of Smith and Miller3 for piire pentaborane lead to the equation
g.
d~ = 0.8674
- 0.00082,T + 0.00023501'm'/~
which represents the data to j=0.002 g./ml. The equivalent conductivity of (n-C4H9)4NI (Fig. 1) was not determined in sufficiently dilute solutions to permit the precise evaluation of values Results of both A' and of the dissociation constant. Since LiC1, LiH, NaBH4, KBH4 and LiAlH4 were pentaborane has practically the same dielectric found to be insoluble in pentaborane; tetra-n- constant1 and viscositya as acetone4 (20.8 and 3.03 butyl- and te tra-n-propylammonium iodides were millipoise as compared with 20.47 and 3.040 appreciably soluble, and tetraethylammonium io- millipoise, respectively) it was assumed that Ao dide was slightly soluble. for (n-C4Ho)4NI would have the same value in Tetra-n-butylammonium Iodide.-The specific pentaborane as in acetone. Assuming this value conductivity (Fig. 1) was found to reach a mnxi- (1804) the method described by Wirth5 was applied to estimate the value of the dissociation constant (see Fig. 2 ) . At other temperatures, Wal-
0.015
8
4 h s& 0.010
6 m-
2 X
4G 0.005 0
2
U
u.2
0.4
0.6
0.8
di Fig. 1.--Specific conductance ( L ) and equivalent conductance ( A ) of (n-CIH9)NI.in BsH9 as a fuiiction of the square root of the concentration. (1) 13. E. Wirth and E. D. Palmer, J . Phy.8,. Chem., 60, 914 (1956). ( 2 ) C. 11. Orr snd. H. E. Wirth, ibid., 63, 1147 (1959).
0.5
1.u
CAY*~/W(Z). Fig. %.-Estimation of the dissociation constants of (nC4H9)NIin pentaborane.
den's rule was used to estimate the value of A". The results are given in Table I. The dissociation constant decreases with increasing temperature as has been found by Sears, Wilhoit and Dawson6 for (n-C4H9)4XIin acetone. This effect is attributed to the rapid decrease of dielectric constant with increasing temperature. (3) S. H. Smith, J r . , and R. R. Miller, J . Am. Chem. Soc., 72, 1 4 X (1950).
(4) M. B. Reynolds and C. A. Kraus, ibid., 70, 1709 (1948). ( 5 ) €1. E. Wirth, J . P k y s . Chem., 65, 0000 (1961). (6) P. G. Sears, E. I). Wilhoit and L. R . Dawson, ibid., 6 0 , 109 (1956).
NOTES
F\TIMATED
"C.
0 10
20 25
TABLEI TABLEI1 CONSTANT O F TETRABUTYLAMSOLUBILITY OF SUBSTITUTED AMMONIUMT o n r ~ ~TsU IODIDE IN PENTABORANE VARIOUSSOLVENTS AT 25'
nI'3SUCIATION
MVNIUM
Temp.,
1449
A0
(assumed)
a X 108
138
5.94
155 170 180
5.78 5.63 5.55
K X 10'
7.7 (i . 4 5.3 4.6
K X 10' (in acetone)e
8.5 7.7 6.8 6.1
The equilibrium constant is only slightly less in pentaborane than in acetone, which may indicate that the interaction between the solvent and the ions (in the ion pairs) is about the same in the two solvents (cf., ref. 4). The value of "a" required to give a straight line a t 25" is the same as that found by Fuoss and I
