2144 Inorganic Chemistry, Vol. 17, No. 10, 1978 (16) M.A. M.Meester, R. C. J. Vriends, D. J. Stukens, and K. Vrieze, Inorg. Chim. Acta, 19,95 (1976). (17) For a discussion of the bonding and electronic absorption spectrum see: (a) F. A. Cotton, W. T. E. Edwards, F. C. Rauch, M. A. Graham, R. N . Perutz, and J. J. Turner, J . Coord. Chem., 2,247 (1973); (b) M. Elian and R. Hoffmann,Inorg. Chem., 14,1058(1975);(c) J. K. Burdett, J . Chem. Soc., Faraday Trans. 2,70, 1599 (1974). (18) B.R. Higginson, D. R. Lloyd, J. A. Connor, and J. H. Hillier, J . Chem. Soc., Faraday Trans. 2,70, 1418 (1974). (19) K. N.Houk, Y . M. Chang, and P. S. Engel, J . A m . Chem. SOC.,97, 1824 (1975). (20) For a discussion of the electronic structure of diazenes see ref 1 and references cited therein. (21) This was also postulated for (arene)Cr(C0)2(2,3-diazanorbornene)22 and Fe(C0)4(2,3-dia~anorbornene).~~,~~ (22) M. Herberhold, K. Leonhard, and C. G. Kreiter, Chem. Eer., 107,3222 ( 1974). (23) A. Albini and H. Kisch, Angew. Chem., 87,206 (1975). (24) H. Kisch, unpublished results. (25) Due to the absence of C4”symmetry for the diazene complexes (see also section on IR spectra) the d,,, d, orbitals are not degenerate. (26) It is not possible to make the same plot for the chromium complexes due to overlapping bands at -185 “C. (27) The process is similar to olefin rotation in low-valent metal complexes. For an MO calculation of the total energy as function of the rotational angle of the olefin see ref 28;the temperature-dependent NMR spectra are summarized in ref 29. (28) K. S . Wheelock, J. H. Nelson, L. C. Cusachs, and H. B. Jonassen, J . A m . Chem. SOC., 92, 5110 (1970). (29) L. M.Jackmann and F. A. Cotton, Ed., “Dynamic Nuclear Magnetic
Christe, Curtis, and Jacob Resonance”, Academic Press, New York, N.Y., 1975,p 428. (30) See, e.g.: M. S . Newman, Ed., “Steric Effects in Organic Chemistry”, Wiley, New York, N.Y., 1956, p 44 (31) Due to overlapping CTML bands for both conformers (see Figure 6), it is impossible to determine the relative concentrations of A and B via amanand em. It may be estimated that the fraction of A present at roam temperature is 20-40%. The decrease to 0-20% by cooling to -185 “C should be easily observable by the UV method. (32) Due to the strong spin-orbit coupling, the classification of singlet and triplet excited states is a crude oversimplifi~ation.~~ (33) G. A. Crosby, K. W. Hipps, and W. H. Elfring, Jr., J . Am. Chem. SOC., 96,629 (1974). (34) B. J. Cohen, H. Baba, and L. Goodman, J. Chem. Phys., 43,2902(1965). (35) E. Lippert and W. Voss, Z. Phys. Chem. (Frankfurt am Main), 31,321 (1962). (36) F. A.Cotton and C. Kraihanzel, J . Am. Chem. Soc., 84,4432 (1962). (37) F.R. Young, R. A. Levenson, M. N. Memering,and G. R. Dobson, Inorg. Chim. Acta, 8,61 (1974). (38) For facilitating the discussion we still use the C,, symmetry labels but put these in quotation marks (39) K. Tortschanoff, H. Kisch, and 0.E. Polansky, Justus Liebigs Ann. Chem., 449 1975. (40) H. Kisch, J . Organomet. Chem., 30,C25 (1971). (41) S . Pietra and M. Res, Ann. Chim. (Rome),48,299 (1958). (42) P. G. Gassman and K. T. Mansfield, Org. Synth., 49, 1 (1969). (43) A. H.Cook, J . Chem. Soc., 876 (1938). (44) Analogous to the preparation of diisopropyldiazene: R. Renaud and L. C. Leitch, Can. J . Chem., 32,545 (1954). (45) For a description of the cooling device see: E. Koch, Chem.-lng. Tech., 41,916 (1969),and references therein.
Contribution from Rocketdyne, A Division of Rockwell International, Canoga Park, California 9 1304, and M.A.N., Neue Technologie, D-8000, Muenchen, West Germany
Bromyl Fluoride. Vibrational Spectra, Force Field, and Thermodynamic Properties K A R L 0. CHRISTE,* E. C. C U R T I S , and E B E R H A R D J A C O B
Received February 3, 1978 Infrared spectra are reported for FBrI8O2in the gas phase and for FBrI6O2in Ne, N2, and Ar matrices a t 3.6 K. Isotopic shifts were measured for 79Br-81Br and 160-180 and were used for the computation of a valence force field. Thermodynamic properties were computed for F B r 0 2 and FCIOz in the range 0-2000 K.
Introduction Bromyl fluoride was first synthesized by Schmeisser and Pammer’,, in 1955. Because of its low thermal stability and high reactivity, this compound had been only poorly characterized and was not further studied until 1975. In 1975, Gillespie and Spekkens published3 the Raman spectra of solid and liquid F B r 0 2 and proposed a monomeric pyramidal structure, similar to that4 of FC10,. Using Raman frequencies reported3 for liquid FBrO,, Baran calculated5 a modified valence force field and mean amplitudes of vibration for FBr02, assuming all bond angles to be 108’. Very recently, Jacob succeeded6 in obtaining good gas-phase infrared spectra for FBr0, in spite of the fact that gaseous FBrO, possesses a half-life of only 30 min at 15 OC. He also prepared a sample of FBr1802and reported preliminary infrared data for the gas and for the neat and the argon matrix isolated solid. Although the oxygen isotopic shifts were measured, no 79Br-81Brisotopic shifts were given.24 In this paper, we report higher resolution spectra and oxygen and bromine isotopic shifts for gaseous and for Ne, N,, and Ar matrix isolated FBr0,. In view of the interest3s5 in the nature of bonding in FBrO,, a new force field computation To whom correspondence should be addressed at Rocketdyne.
0020-1669/18/ 13 17-2744$01 .OO/O
appeared warranted, particularly since the previously used5 frequencies significantly differ from those of gaseous F B r 0 2 and since the previously assumed5 geometry of FBr02 was only a crude estimate. Furthermore, the availability of both oxygen and bromine isotopic shifts offered a unique opportunity to test the value of such additional data for the refinement of force fields for compounds, such as bromine oxyfluorides.
Experimental Section T h e samples of FBrOz used for recording the gas-phase spectra were prepared, as previously described,6 by low-temperature cocondensation of BrF, and H,O. The infrared spectra of gaseous FBr02 were recorded at 15 OC on a Perkin-Elmer Model 325 spectrophotometer in the range 4000-290 cm-I using a nickel cell with AgBr windows attached to an external mirror system (optical path length 110 cm). T h e samples of F B r 0 2 used for the matrix isolation study were obtained as a byproduct during a spectroscopic study’ of BrF30. The spectrometer and handling have been previously described.’
Results and Discussion Infrared Spectra of Gaseous FBr0,. A survey infrared spectrum of gaseous FBrl*O, is shown in Figure 1. The corresponding spectrum of FBr1602 has previously been re@ 1978 American Chemical Society
Inorganic Chemistry, Vol. 17, No. 10, 1978 2745
Bromyl Fluoride
Y m
94
3 3
0
5 d
a
370.4 v3
a
3
a
2 2 n
h
9
4
550.6
I
FREQUENCY, CM"
300
m W m
a
1000
Figure 1. Survey infrared spectrum of gaseous FBr1802recorded a t 15 OC in a nickel cell equipped with AgBr windows with a n optical path length of 110 cm-'. The band marked by an asterisk in due to
i
f
HF. 380 400 360\
I ,
i
m w m
o m w
m o m
r 0
I
I
Figure 2. Band contours of vl, v2, and v3 of gaseous FBr1*02recorded under higher resolution conditions with scale expansion. For u , and u2 the frequencies of the 79Br and 81BrQ-branch centers are marked. For vj, only the unresolved Q branch is shown a t the same scale as that used for v1 and v2. T h e complete band envelope is shown a t a 2.5X compressed scale.
z W
9
3 m
m
2 W
m d
8
I b l
\
I
/
d
I
8
z
s
I-
I
950 940 930 920 910 FREQUENCY, CM-l
2
I
Figure 3. Band contour of u5 of gaseous FBr1802showing the double Q branches for both bromine isotopes.
ported.6 Figures 2 and 3 show the band contours of each band recorded under higher resolution conditions and scale expansion. The observed gas-phase frequencies of FBrOz are compared in Table I to those16 previously reported for the liquid and the solid. As can be seen from Table I, the gas-phase frequencies significantly deviate from those of liquid and solid FBr02, indicating some degree of association in the condensed phases. The BrF stretching mode, u2 (A'), exhibits the most pronounced frequency change (-62 cm-') on going from the gas to the solid, whereas the mean frequency change of the two BrO, stretching modes, v, (A') and vs (A"), is only -17 cm-'. This indicates that association takes place mainly through the fluorine ligands. Preferential association through fluorine ligands has previously also been demonstrated7 for BrF30. Infrared Spectra of Matrix-Isolated FBr02. In order to obtain unambiguous bromine isotopic shifts (bromine contains two naturally occurring isotopes, 79Brand *'Br, of almost equal
F
2m
m
2
F
m
T
m
0 w m
2746 Inorganic Chemistry, Vol. 17, No. 10, 1978
Christe, Curtis, and Jacob are much less of a problem due to the smallness (0-3 cm-') of these shifts. Therefore, possible anharmonicity corrections for these shifts should not exceed the measured uncertainties (kO.1 cm-I) of these shifts. The best values for the isotopic shifts are listed in the last two columns of Table I. The agreement between the bromine isotopic shifts observed for gaseous F B r 0 2 and those observed for the matrix-isolated species is generally good if one takes into consideration that the Q-branch band contours of w1 and v2 are distorted on the P-branch side by hot bands and that for v j a double Q branch is observed for each bromine isotope. Force Field Computations. A normal-coordinate analysis was carried out for FBrO, to obtain more reliable force constants for this interesting molecule and to examine the usefulness of isotopic shifts for such an analysis. The potential and kinetic energy matrices were computed by a machine method.12 The geometry
'9656 967 2 I,
,
I,
' ,,
l , , , , l ,
,,,,,,,
5370 ,I, , , 1 , ~ , , 1 , ,
5356
1
, l I , , ~ l . l l L 1 ~ . l
V
3840
,,
1 I
I , , , , l
was assumed for this computation, based on the known geometries of FBrO3,I3 FC1O3,l4 and FC1024 and an extrapolation between BrO bond length and stretching frequency, similar to thatlj used for C10 bonds, using the data published for Br04-16,17 and FBr03.13,18This geometry appears more likely than that (a = (3 = log", r = 1.63 A) chosen5 by Baran for his computation. The symmetry coordinates used for F B r 0 2 were identical with those previously giveni0for FC102, except for the correction of the obvious typographical error in the factor of S4. The bending coordinates were weighted by unit (1 A) distance. The force constants were adjusted by trial and error with the aid of a computer to give an exact (0.1 cm-') fit between all observed and computed frequencies. The observed 79Br-81Br and 160-180 isotopic shifts were used as additional constraints. We will first discuss our choice of a force field for the A" block since it contains only one stretching and one deformation mode. The force constants of FSjand F66 were computed as a function of F56. The resulting curves are shown in Figure 5. We have also computed the bromine and oxygen isotopic shifts over the same range of F56 and have plotted their values in Figure 5 . The observed isotopic shifts, ABrVsf 0.1 cm-' and AoP5f 1.6 cm-' (see above discussion of anharmonicity corrections), were used to define the probable range of the force constants. The values thus obtained are given in Figure 5 and Table 11. Figure 5 demonstrates the importance of the anharmonicity corrections for Ao,~, Le., a better overlap with the ABrV5 force field constraint, as previously d e m o n ~ t r a t e d ' ~ by McDowell and Goldblatt for Os04. Furthermore, it shows that the preferred force field closely corresponds to F66 being a minimum, a condition previously shown19~20 to be a good approximation to the general valence force field values for similar weakly coupled systems. For the A' block of FBrO, the problem of defining a preferred force field is more difficult since this block contains two stretching and two deformation modes. Numerical experiments showed that only three of the six off-diagonal symmetry force constants were essential for fitting the isotopic data. These three off-diagonal constants were F13, F24,and F34,with Fl3 and F34 being more important then F24. This result is in good agreement with the previous findings'O for the related FC102 molecule and is not surprising in view of
Inorganic Chemistry, Vol. 17, No. 10, 1978 2747
Bromyl Fluoride
Table 11. Observed Frequencies for F79Br160z,Symmetry Force Constants? Computed and Observed 160-180 and 79Br-*1BrIsotopic Shifts, and Potential Energy Distributionb isotopic shifts, cm-' assignment approx in Doint descriotion of
calcd symmetry force constants
freq, cm-' 921.0 551.9 385.8 310
F,, = fr t,f
Fzz
F33
=fR
=f
=t
F44 F13
t fa!,
=fro
= fRQ F 3 4 = fap F,, = f,- ,f F66=fa! - f a ! , F36= fra - fra' FZ4
978.9 273
6.931 i 0.095 2.750 f 0.04 1.453 f 0.08 1.487 f 0.08 -0.40 0.19 0.095 i 0.09 0.49 i 0.07 1.037 f 0.06 0.762 i 0.004 0.14 f 0.22
*
obsd
A0
ABr
AO
ABr
PED
45.23 0.31 15.65 11.74
1.56 1.40 1.12 0.52
44.7 0.4 15.4
1.5 1.4
96 Fll 99 Fzz 76 F337 16 F34 103 F,,, 37 F,,, -41 F3,
43.28 7.21
2.70 0.33
42.4
2.7
100 F,, 100 F,,
a Stretching constants in mdyn/A, deformation constants in mdyn A/radz, and stretch-bend interaction constants in mdyn/rad. contributions. Contributions of less than 9% to the PED are not listed.
LAW
L
I
\
I
Percent
1
A0 v5
F55
F33 1.40 1
. w 1.38 fF0.04 j 1.30 -0.8.0.6.0.4-0.20 0.2 0.4 F13 -0.42f 0.19 ~
0.76
-0.4 .0.2 0 0.2 0.4 0.6 0.8 F56 0.14 f 0.22
Figure 5. Force constant display of the A'' block of FBrOz using the observed bromine (2.7 f 0.1 cm-') and oxygen (42.4 f 1.6 cm-') isotopic shifts as constraints. FS5,FM,and F56have units of mdyn/A, mdyn &'radz, and mdyn/rad, respectively. The rectangle of Aov5 marked by broken lines represents the observed anharmonic oxygen shift of v5 f 0.4 cm-I, whereas the solid rectangle assumes the observed anharmonic oxygen shift as the lower limit and a 1.6 cm-I higher value, for anharmonicity corrected, as the upper limit. The broken and the solid vertical lines indicate the plausible force constant ranges and the preferred force field, respectively.
the fact that GI3, G24, and G34 are the major off-diagonal G matrix terms in the A' block. It was also shown that the variation of F I 3 ,F24, and F34 strongly influenced only the corresponding diagonal terms. This relative independence of the interaction constants permitted us to examine each of them separately. The results of these computations were again summarized in graphical form and are presented in Figures 6-8. In this manner, t h e values of F I 3 ,F24,and F34,required to duplicate all of the observed isotopic data, were determined. These three interaction constants were then combined in a single force field, and a satisfactory fit of the isotopic data could be achieved with only minor adjustments. The resulting force field is given in Table 11. The computed oxygen shifts were intentionally kept slightly larger than those observed to leave some room for any future anharmonicity corrections. Figures 6 and 7 , dealing with the stretch-bend interaction constants F I 3and F24,respectively, are analogous to Figure 5, which has been discussed above in detail for the A" block,
Figure 6. Force constant display of the A' block. All off-diagonal constants were set to zero, except for Fl,. Only those diagonal constants are shown which were significantly influenced by changes in the interaction constant FI3. For additional explanation see caption of Figure 5 . Table 111. Internal Force Constant8 of FBrO, Compared to Those Previously Reported fr fR
frr fa!
ta! folp
fRa
fra! fra!'
this work
ref 5
b
6.984 i 0.08 2.750 f 0.04 -0.05 f 0.08 1.125 0.04 1.453 f 0.08 0.363 i 0.04 0.49 f 0.07 0.095 f 0.09 -0.07 i 0.11 t 0 . 0 7 f 0.11
6.76 2.25 0 1.090 1.664 0.344 0.01 0.034 0 0
6.78 2.24 0.14 1.066 1.485 0.288
*
a Units are identical with those of Table 11. R. Bougon, P. Joubert, and G . T a n t o t , J Chem. Phys., 66, 1562 (1977).
and therefore do not require any further comment. Figure 8 shows the dependence of the two diagonal bending constants F33 and F44 on the bend-bend interaction constant F34. In order to be able to fit the observed oxygen shift of v3, either a rather large positive or a small negative value is required for F3+ Of these two possibilities, the former is preferred, since it results in more plausible force constants. For F34 = 0.2, the potential energy distribution (PED) is essentially 100% characteristic (FU = minimum), whereas, for the extreme values of F34,u3 and v4 become about even mixtures of F33and
2748 Inorganic Chemistry, Vol. 17, No. 10, 1978
Christe, Curtis, and Jacob
Table IV. Stretching Force Constants (mdyn/A) of FBrO, Compared to Those of Other Bromine Compounds BrO; fr(BrO) fR@rF)
BrO;
5.28
* BrF,O,-
BrF,O-
6.32 1.63
6.70 2.14
6.05
BrF;
FBrO,
FBrO,e
BrF,Of
6.98
6.92
7.68 2.93
2.23
BrF
BrFag
BrFSh
3.10
3.24
4.07
4.02
BrF,Ci
BrF,'j
4.60
4.90
2.75 fR'(BrF)
3.22
3.51
4.07
a H. Siebert, "Anwendungen der Schwingungsspektroskopie in der Anorganischen Chemie", Springer-Verla , Berlin, 1966. Reference 17. K. 0. Christe, R. D. Wilson, E. C. Curtis, W. Kuhlmann, and W. Sawodny,Znorg. Chem., 1 7 , 5 3 3 (1978). JK. 0. Christe and D. Naumann, ibid., 1 2 , 5 9 (1973). e Reference 13. f K. 0.Christe, E. C. Curtis, and R. Bougon,Znorg. Chem., 1 7 , 5 3 3 (1978). Reference 9. K. 0. Christe, E. C. Curtis, C. J. Schack, and D. Pilipovich,Znor Chem., 11, 1679 (1972). K. 0. Christe and C. J. Schaclc,ibid., 9 , 2 2 9 6 (1970). K. 0. Christe and R. D. Wilson,ibid., 1 4 , 6 9 4 (1975). &R. Bougon, P. Joubert,and G . Tantot,J. Chem. Phys., 66,1562 (1977).
Table V. Thermodynamic Properties for F79Br160, cpo,
1.70 F44
,
,
I
,
1.60
1.42 t 0.01
1.50 1.40 .0.4 .0.2
0
F24
( f l T - I P o ) , _(PT--flo)/T,
T, K
cal/(mol deg)
kcal/mol
cal/(mol deg)
0 100 200 298.15 300 400 5 00 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
0 9.493 12.831 15.033 15.066 16.527 17.467 18.082 18.498 18.789 18.998 19.154 19.272 19.363 19.436 19.494 19.541 19.580 19.613 19.640 19.664 19.684
0 0.831 1.957 3.332 3.360 4.945 6.648 8.427 10.258 12.123 14.013 15.921 17.842 19.774 21.714 23.661 25.613 27.569 29.529 31.491 33.456 35.424
0 48.749 54.945 59.119 59.188 62.576 65.438 67.931 70.144 72.134 73.944 75.603 77.134 78.557 79.885 81.130 82.303 83.410 84.458 85.455 86.404 87.310
SOT,
eu
0 57.059 64.732 70.295 70.388 74.938 78.134 81.977 84.797 87.288 89.513 91.523 93.355 95.036 96.589 98.031 99.378 100.640 101.828 102.950 104.013 105.022
0.2 0.4 0.6 0.13? 0.09
Figure 7. Force constant display of the A' block showing the dependence of F2, and F4 on F2+ For additional explanation see captions of Figures 5 and 6.
1.2 0 0.1 0.2 0.3 0.4 0.5 F34 0.43 f 0.04
Figure 8. Force constant display of the A' block showing the dependence of F33 and F44on F3+
F44.The moderate amount of mixing obtained for v 3 and v4 in our preferred force field (see Table 11) is not surprising in view of their similar frequencies and motions involved. The remainder of the PED (see Table 11) is highly characteristic and supports the approximate description of the modes given in Table 11. A comparison of the internal force constants of FBrO, with those previously reported is given in Table 111. As can be seen, our force field significantly differs, particularly for f R and for@
Our results show that the BrF bond in FBrO, is significantly stronger than previously a ~ s u m e d . ~ , ~ Comparison with Similar Compounds and Bonding in FBr02. A comparison of the F B r 0 2 stretching force constants with those of other bromine oxides, fluorides, and oxyfluorides is given in Table IV. The BrF stretching force constants are separated into two groups. The lowf, force constants observed for BrF202-, BrF40-, BrF4-, and some of the bonds in BrF3 and BrF, can be attributed to significant contributions from semiionic, three-center, four-electron bonding while it is assumed that the bonds belonging to thefR' group are largely covalent. The spread within each group is caused by secondary effects, such as formal charge (anion, neutral molecule, or cation), degree of fluorine substitution, and oxidation state of the central atom. These effects have previously been discussed21,22at length for the corresponding chlorine compounds and appear to be also applicable to the bromine compounds of Table IV, although for the latter they are somewhat less pronounced. This is caused by the fact that the larger bromine central atoms are more polarizable than chlorine, thereby causing the two types of bonds to become less distinct. As far as F B r 0 2 is concerned, it can be seen from Table IV that its stretching force constants do not fit too well the general trends of Table IV, and it is therefore placed between these two groups. A similar anomaly has previously been noted for FC10, and was explained by a weak highly polar ( p - ~ * ) a bond.22 The same explanation, i.e., bonding between a 2p electron of F and an antibonding a* orbital of the B r 0 2 radical, can be invoked for FBr02. Thermodynamic Properties. The thermodynamic properties of F79Br1602were computed with the molecular geometry
Chemistry and Structure of N2F3+Salts
Inorganic Chemistry, Vol. 17, No. IO, 1978 2749 -
Table VI. Thermodynamic Properties of F35C1160,
0 8.507 11.267 13.509 13.545 15.167 16.318 17.134 17.718 18.143 18.459 18.699 18.884 19.030 19.147 19.241 19.318 19.382 19.436 19.481 19.520 19.554
0 100 200 298.15 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
0 0.805 1.790 3.012 3.037 4.478 6.055 7.730 9.474 11.268 13.099 14.958 16.837 18.733 20.642 22.562 24.490 26.425 28.366 30.312 32.262 34.216
0 46.851 52.666 56.456 56.519 59.581 62.180 64.459 66.495 68.339 70.026 71.581 73.023 74.368 75.629 76.814 77.934 78.993 80.000 80.958 81.872 82.747
0 54.898 61.618 66.559 66.643 70.775 74.291 77.342 80.030 82.425 84.581 86.539 88.330 89.979 91.507 92.930 94.260 95.509 96.686 97.798 98.852 99.854
given above and the vibrational frequencies of Table 11, assuming an ideal gas at 1 atm pressure and using the harmonic-oscillator, rigid-rotor approximati~n.~~ These properties are given for the range 0-2000 K in Table V. Since no thermodynamic data had previously been reported for FC102, we have also computed these properties for F3'Cl1602 (see Table VI) using the previously published frequencies'O and ge~metry.~
Conclusion
A force field has been computed for FBrOz using gas-phase frequency values and bromine and oxygen isotopic shifts. It was shown that the most important force constants,fBro and fBrF, can be determined with an accuracy of about 0.08 and 0.04 mdyn/& respectively. The importance of anharmonicity corrections for the oxygen shifts was demonstrated. In the absence of such anharmonicity corrections, the bromine isotopic shifts are more useful for defining the force field because of the smaller anharmonicity corrections required.
The BrF bond in FBrOz (2.75 mdyn/A) is considerably stronger than previously assumed (2.25 mdyn/A)' but is still somewhat weaker than predicted by comparison with related bromine compounds. This weakening effect might be explained by assuming a polar c bond between a 2p electron of F and an antibonding P* orbital of the BrO, radical. Acknowledgment. K.O.C. is indebted to Drs. L. R. Grant, C. J. Schack, and W. W. Wilson for helpful discussions and to the Office of Naval Research for financial support. Registry No. F79Br'602,67452-70-4; F35Cl'602,35880-03-6; FBr02, 22585-64-4; FBrIgO2,64544-65-6; IgO, 14797-71-8; 79Br, 14336-94-8; glBr, 14380-59-7.
References and Notes M. Schmeisser and E. Pammer, Angew. Chem., 67, 156 (1955). M. Schmeisser and E. Pammer, Angew. Chem., 69, 781 (1957). R. J. Gillespie and P. Spekkens, J . Chem. Soc., Chem. Commun., 314 (1975); J . Chem. Soc., Dalton Trans., 1539 (1977); Isr. J . Chem., 17, 11 (1978). C. R. Parent and M. C. L. Gerry, J. Mol. Spectrosc., 49, 343 (1974). E. J. Baran, Spectrosc. Lett., 9, 323 (1976). E. Jacob, Z . Anorg. Allg. Chem., 433, 255 (1977). K. 0. Christe, E. C. Curtis, and R. Bougon, Znorg. Chem., 17,533 (1978). R. A. Frey, R. L. Redington, and A. L. Khidir Aljibury, J . Chem. Phys., 54, 344 (1971). K. 0. Christe, E. C. Curtis, and D. Pilipovich, Spectrochim. Acta, Part A , 27a, 931 (1971). D. F. Smith, G. Begun, and W. Fletcher, Spectrochim. Acta, 20, 1763 (1964). R. S. McDowell, L. B. Asprey, and L. C. Hoskins, J . Chem. Phys., 56, 5712 (1972). E. C. Curtis, Spectrochim. Acta, Part A , 27a, 1989 (1971). E. H. Appelman, B. Beagley, D. W. J. Cruickshank, A. Foord, S. Rustad, and V. Ulbrecht, J . Mol. Struct., 35, 139 (1976). A. H. Clark, B. Beagley, D. W. J. Cruickshank, and T. G. Hewitt, J . . Chem. SOC.A , 872 (1970). E. A. Robinson, Can. J . Chem., 41, 3021 (1963). S. Siegel, B. Tani, and E. Appelman, Znorg. Chem., 8, 1190 (1969). L. C. Brown, G. M. Begun, and G. E. Boyd, J. A m . Chem. Soc., 91, 2250 (1969). H. H. Claassen and E. H. Appelman, Inorg. Chem., 9, 622 (1970). R. S. McDowell and M. Goldblatt, Znorg. Chem., 10, 625 (1971). W. Sawodny, J . Mol. Spectrosc., 30, 56 (1969). K. 0. Christe, Proc. Znt. Congr. Pure Appl. Chem., 24th, 4, 115 (1974). K. 0. Christe and C. J. Schack, Adu. Znorg. Chem. Radiochem., 18, 319 (1976). J. E. Mayer and M. G. Mayer, "Statistical Mechanics", Wiley, New York, N.Y., 1940. In a recent paper on KBrOzF2,R. Bougon, P. Joubert and G. Tantot, J . Chem. Phys., 66, 1562 (1977), also reported a force field calculation for FBrOzusing the frequencies of ref 3. Their results have been included in Table 111.
Contribution from Rocketdyne, A Division of Rockwell International, Canoga Park, California 91304
Chemistry and Structure of N2F3+Salts K A R L 0. C H R I S T E * and C. J . S C H A C K
Received February 22, 1978 The novel N2F3'salt N2F3SbF6 was prepared from NzF4 and SbFS in anhydrous HF solution. A metathetical reaction between N2F3SbF6and Cs2SnF6 in HF produced N2F4 and the novel salt N2F3SnFS. I t was shown that NzF4and BF3 do not form a stable adduct a t temperatures as low as -78 OC. The vibrational and I9FNMR spectra of the N2F3' cation were reexamined. All the experimental data are consistent with a planar structure of symmetry C, for N2F3+. The previously reported vibrational assignments, made on the basis of a nonplanar structure of symmetry Cl, are revised for six fundamental frequencies.
Introduction The first report on the formation of a stable adduct between NzF4 and a Lewis acid was published' in 1965 by Ruff. He showed'g2 that SbF5, when treated with an excess of N2F4 in AsF, solution, produced, depending on the pressure of N2F4, 0020-1669/78/1317-2749$01.00/0
either the 1:2 adduct NzF,.2SbF5 or the 1:3 adduct NzF4' 3SbF5. On the basis of the observed 19FN M R spectrum and an incomplete infrared spectrum, he assigned to N2F4.2SbF5 the ionic structure N2F3+Sb2F,1- with hindered rotation around the N-N bond in N2F3+. In 1967, Young and Moy published3 0 1978 American Chemical Society
