Vol. 65
1446
with the value of 72 kcal./mole for D(0-KO) tabulated by C ~ t t r e l l . ~ ~ We observe that the results reported by us for IP(NOz+) and ,4P(NO+) from NO2 differ significantly from results reported by a number of inv e s t i g a t o r ~ ~ ,but ~ - ~agree closely with those reported by Stueckelberg and SmythI8 and others. 19-20 We suggest that additional detailed experimental determinations of KO2 be undertaken in an effort to fix these potentials.
20.0
c
1
10.0 8.0 L
(21) G. G. Cloutier and H. I. Sohiff, i b i d . , 31, 793 (1959). (22) H. Huraeler, M. G. Inghram and J. D. Morrison, ibid., 28, 70
(1958). (23) T. L. Cottrell, "The Strengths of Chemical Bonds," Second Edition, Butterworths Scientific Publications, London, 1958, pp. 210 and 278.
T H E INFRSRED SPECTRA OF SOME DIMETHYL SULFOXIDE COMPLEXES
O ' I /// 0.4
BY RUSSELLS. DRAGO AND DEVON MEEK
-
0,2F I 0.1 13
I
10
12
14
16
18
20
Electron energy, uncorr. (e.v.). Fig. 1.--Ionization efficiency curves for NOz+ and N O + from NOz,using krypton for the electron energy calibration.
and others.2-6 Since the i.e. curves for KO,+from SO2 should be of the norim1 form, the various methods of determining the electron impact ionization potential should all give essentially identical results. Table I show, that this is the case, and a simple average of these values gives the yalue of 11.27 =t 0.19 e.v. That the i.e. curve for SO2+ is of the normal form is readily seen from Fig. 1. During our studies of SO2 we never observed any peaks due to S03+ or N204+. NO+.- The ion of m/e 30 is NO+. It was found to have an appearance potential of 12.48 i= 0.43 e.v. I n addition, individual determinations of the ionization efficiency curves of S O + and NO2+ resulted in hP(NO+) - IP(KO*+) = 1.16 h 0.08 e.v. This coupled with IP(T\;O2+) = 11.27 =t 0.17 e.v. from above gives A P ( N 0 f ) = 12.43 =t 0.19 e.v., in agreement with the value of 12.48 f 0.43 e.v. determined directly. We attempted to determine the appearance potential of SO+from N O with little success. We consistently obtained values about 1.3 v. too high, for which mc= can offer no explanation. We are presently repeating this determination. It may be noted from Fig. 1 that there is a rather sudden change in slope iii the X O + i. e. curve a t approximately 14 v. The latter was also observed in the deterniinatioiis of S O + from NO. Using the value of 12.48 e.v. for AP(NO+) from NO2 and the literature value of IP(NO+) = 9.25 e.v.,21-22we calculated the nitrogen-oxygen bond energy in nitrogen dioxide. D(0-NO) = 3.2 e.v. nr 74 kcal./mded This is in reasonable agreement
W m . A . S o u e s L a b o i a t o ~ y ,Chemistry Department, Lrnieeraity of Illinois, Urbana, Illinois Received Ja?iuary 81, 1961
The preparation of a series of dimethyl sulfoxide complexes has been carried out in this Laboratory and assignments were made for the S-0 st'retching frequency.'& Subsequent to reading proof of the art'icle on this research, assignments which differed from ours were published.2 The purpose of this article is to provide additional data to support some of our original assignments and to aid in solving a problem which is more complex than the present published information would indicate. Results and Discussion The preparation of the complexes and conditions employed to obtain the spectra have been reported,' There is agreement on the assignment of the S-0 stretching frequency for dimethyl sulfoxide (1045 cm.-l in CH3S02 solution), There is also agreement on a very sharp, much less intense absorption a t 950 cm.-l, and a, weaker, broader peak a t 915 cm,-' assigned2 to -CH3 rock. In the complexes there is a discrepancy in the assignments. The addit,ional information we have to offer involves a detailed description of the above two absorption peaks in the complexes as measured in nitromethane solution. Sharper, more easily interpreted spectra are obtained in solution than on Nujol mulls of the solids. Table I contains data for the peaks in the 1000 and 950 cm.-l region. The 1000 crn.-' peak is the one in the complexes that n-e assigned to S-0 stretch and the latter is the oiie assigned by Cotton, et aL2 Some very significant information regarding t8hese spectra entails a qualitative description of the relative intensity of the peaks measured in solution. As the peak in the 1000 cm.-' region moves from 104.7 cm.-l in free sulfoxide to 1025
-
(1) (a) D. W.Meek. D. K. Straub a n d R. S. Drago, J . A m . Chem. SPC,,82, 6013 (1980). (b) For the preparation of these complexes also see F. A . Cotton and R. Francis, abid., 82, 2986 (1960) and H. I,. Schliifer and W. Schaffernioht, Angew. Chsm., 72, 618 (1960). (2) F. A . CotOon, R. Francis and W. D. Horrocks, Jr., J. Phvs. Chem., 6 4 , 1634 (1900).
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-
