NOTES
3059
the anion is di- or trivalent than if it is univalent. In conclusion, the nature of the similion can indeed affect the ccc of a counterion, but the effects are small when compared to the dependence of the ccc on the charge of the counterion. The extent of the similion effect depends both on the charge and the size of the hydrated ion. Acknowledgments. We wish to thank Dr. K. Uglum for several helpful comments and suggestions and Central Michigan University Research and Creative Endeavor Committee for partial support of this work.
Gas-Phase Molecular Complexes. The Furan-Iodine Charge-Transfer Complex by Edward I. Ginns' and Robert L. Strong Department of Chemistry, Rennselaer Polytechnic Institute, T r o y , N e w York 1$181 (Receiaed January $0, 1967)
Several papers have recently appeared on gas-phase charge-transfer c o m p l e x e ~ . ~ -In ~ comparison with the same complexes in the condensed phase, in general the formation constant increases, the extinction coefficient decreases, and the charge-transfer band shifts toward the blue in going from the liquid to the gas phase; these effects, however, decrease with increasing complex strength as predicted.2 A difficulty associated with the use of the usual Benesi-Hildebrand treatments for the study of complexes of this type is that an appreciable fraction of the acceptor must be complexed, requiring either a very high donor concentration (i.e., high pressure in the vapor phase) or a strong complex. With most donors, a high pressure can be attained only at elevated temperatures, thereby increasing the extent of irreversible reactions between the donor and acceptor species. With furan (bp 32")) however, it is possible to produce quite high pressures at relatively low temperatures. In the liquid phase (chloroform solvent), furan and tetracyanoethylene form a very weak 1 : l 0.29 1. mole-' at 22", essentially the complex' ( K , same as that for the benzene-TCNE complex') ; preliminary measurements in this laboratory have shown that the furan-iodine complex in n-heptane at 25" is also quite weak ( K , 0.27 1. mole-', A, 315 mp), so that a relat.ively large blue shift of the furaniodine charge-transfer band would be expected for the vapor phase. L-
-
The apparatus for the spectrophotometric measurements is essentially the same as described earlier,2 the main modifications being in the design of the 10cm cell compartment to provide higher temperatures (160") and better temperature control and uniformity ( 1 1 . 2 " at 100'). Furan and iodine react in the solid or liquid phase to produce an unidentified acidsoluble brown solid, necessitating gas-phase mixing and prevention of condensation during the spectral measurements. A metered quantity of outgassed furan was transferred under vacuum and stored behind a break-seal in a side arm to the 10-cm cylindrical quartz absorption cell (2.5-cm i.d.). The desired amount of iodine was metered into the cell by successive transfers from a known metering volume, the cell and side arm were removed from the vacuum transfer apparatus by sealing off, and the absorbance of the iodine in the cell was measured in the visible and ultraviolet regions at 86, 100, and 120". With the cell assembly at loo", the break-seal was broken, pressure and concentration equilibrium were attained, and the temperature-wavelength absorbance measurements over the visible-ultraviolet spectral region were repeated on the mixture. With this technique it was possible to reproduce measurements over this temperature range for many hours; elevation to higher temperatures led to permanent reaction of the iodine, and the dark brown solid described above appeared on condensation and did not vaporize on subsequent temperature elevation. Yo change of the iodine absorption band in the visible region occurred on mixing below the convergence limit (499.5 mp) ; the ultraviolet absorbance data for the mixture were corrected for the small iodine absorbance, measured at each temperature before mixing as described above, and absorbance by the furan as determined from independent measurements at comparable temperatures and pressures on the pure material. Absorbance measurements were made on cells with ca. 2 X M iodine and six furan concentrations ranging from 0.037 to 0.077 M (ca. 1 atm). The chargetransfer absorption curve is shown in Figure 1; the (1) National Science Foundation Undergraduate Research Participant, 1965-1966. (2) F. T. Lang and R. L. Strong, J . Am. Chem. SOC.,87,2345 (1965). (3) M. Kroll and M. L. Ginter, J . Phys. Chem., 69, 3671 (1965). (4) J. hl. Goodenow and M. Tamres, J . Chem. Phys., 43, 3393 (1965). (5) J. Prochorow, ibid., 43, 3394 (1965); J. Prochorow and A . Tramer, ibid., 44, 4545 (1966). (6) H. A. Benesi and J. H. Hildebrand, J . Am. Chem. SOC.,71, 2703 (1949). (7) A. R. Cooper, C. W. P . Crowne, and P. G. Farrell, Trans. Faraday SOC.,62, 18 (1966).
Volume 7 1 , Number 9 August 1967
NOTES
3060
I
0.24k
0.18 0
c 0
n
0.12
w
n Q
”?
‘-‘20*
0.04
01
I 260
I 270
I 280
I 290
Wavelength (
I
300
I
310
I I
320
rnp)
Reasonable values for K , and e, were obtained for the diethyl ether-iodine and benzene-iodine complexes,2 but the same limitations based on experimental conditions were also applicable; it is doubtful that conclusions as to relative stabilities for weak complexes between the liquid and vapor phase are justified from spectrophotometric data alone. Although K , and e, cannot be calculated separately, the product Kcec is obtainable from the slope only of the plot of eq 1 and therefore is reasonably accurate. Assuming e, is independent of temperature, a standard enthalpy of complex formation of -3 kcal mole-’ was evaluated from this product plotted according to the integrated form of the van’t Hoff equation. ~~
(8) W. Liptay, 2. Elektrochem., 65, 375 (1961). (9) N. J. Rose and R. S. Drago, J . A m . Chem. SOC.,81, 6138 (1959).
Figure 1. Charge-transfer band of gas-phase furan-iodine complex with 7.7 X M furan and 2.15 X 10-4 M iodine.
Mass Spectrometric Investigations of the peak at ca. 284 mp is independent of temperature or furan pressure and represents a blue shift of 31 mp from the liquid-phase complex, the two curves however being virtually ident’ical in shape, in agreement with other system^.*^^ Treatment of the data by the method of Liptays indicated formation only of a 1 : l complex. There was no attenuation or shift of the visible I, band, as would have been expected if appreciable complexation occurred. The absorbances A (corrected for free iodine and furan absorption) a t 290 mp were plotted according to the Benesi-Hildebrand equation for a 1: 1 complex
where d is the optical light path, [I21 and [D] are the iodine and furan concentrations, respectively, and K O and e, are the formation constant and molar extinction coefficient for the complex. Although reasonably straight lines were obtained, the y intercepts resulted from a long extrapolation and were very close to zero or even negative, so that e, and K , could not be obtained in the usual manner from the slopes and intercepts. This was furt,her shown by evaluating the data according to the graphical method of Rose and Drago;g the experimental conditions of low donor and acceptor concentrations dictated by gas-phase operation (and hence low percentage complex formation) and the uncertainties in the small absorbance measurements are such that the lines were essentially parallel and did not intersect within the required relatively small area. The Journal of Physical Chemistry
Synthesis, Stability, and Energetics of the Low-Temperature Oxygen Fluorides. 11. Ozone Difluoridela,b by T. J. R!Ialonelc and H. A. McGee, Jr. School of Chemical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (Received January 24! 1967)
The characteristic blood-red liquid at 90°K prepared by the electric discharge of 02-Fzmixtures has been reproduced many times and many of the characteristics of the liquid have been reported,2 but whether this red liquid is, in fact, the molecular entity 03Fz as has been proposed still is uncertain. Cryogenic mass spectrometric techniques developed in this laboratory3 have been successfully applied to OzFzand to the OzF free radical4 and hence similar experiments were performed (1) t o afford an unequivocal proof of the existence of the O3Fzentity, (2) to develop the structure ~
~~~~~
~~~~~~~
~~~
(1) (a) Based on a thesis presented by T. J. hlalone in partial fulfillment of his requirements for the Ph.D. Degree in Chemical Engineering, Feb 1966; (b) the authors gratefully acknowledge support of this research by NASA Grant NsG-657; (e) T. J. hlalone expresses thanks to the National Science Foundation, Procter and Gamble Co., and Ethyl Corp. for providing fellowships during 3 years of graduate study. (2) A. G. Streng, Chem. R e v , 63, 607 (1963). (3) H. A. McGee, Jr., T. J. Malone, and W. J. Martin, Rev. Sci. Instr., 37, 561 (1966). (4) T. J. Malone and H. A. AIcGee, Jr., J . Phys. Chem., 69, 4338 (1965); 70, 316 (1966).
