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Dibromine Monoxide Br2O and Bromine Dioxide OBrO Spectroscopic Properties Molecular Structures and Harmonic Force Fields.

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f17, 9441 -9447; E. Kimura, Y Kodama, T. Koike, M. Shiro, ibid. 1995, f f 7 ,
8304-8311; 1.0.Kady, B. Tan. 2. Ho, T. Scarborough, J. Chem. Suc. Chem.
Conmun. 1995, 1137 1138; J. R. Morrow. K. Awes, D. Eppstein, ibid. 1995,
2431 -2432.
[7] V. Jubian, R . P. Dixon, A. D. Hamilton, J. Am. Chem. Soc. 1992, 114. 11201121; J. Smith, K . Ariga, E. V. Anslyn, ibid. 1993, 1f5,362-364; V. Jubian, A.
Veronese. R. P. Dition. A. D. Hamilton, A 7 p w C h m . 1995, 107. 1343-1345;
Angen:. Chew!.Inl. Ed. Engl. 1995,34. 1237-1239. M. W. Hosseini, A. J. Blakker, J.-M. Lehn. J. Am. Cliem. Suc. 1990,112.3896-3904; B. Barbier, A. Brack,
ibid. 1992, f14,3511-3535.
[S] Complexation of phosphates by bis(guanidines) and related compounds: B.
Dietrich, D. L. Fyles. T. M. Fyles, J.-M. Lehn, Helv. Chin?. Arta 1979, 62,
2763-2787; R. P. Dixon, S. J. Geib. A. D. Hamilton, J. Am. Chrm. SOC.1992,
ff4. 365-366; D. M. Kneeland, K. Ariga, V. M. Lynch, C.-Y Huang. E. V.
Anslyn, ;hid. 1993. f f . 5 , 10042-10055: F. Chu, L. S. Flatt, E. V. Anslyn, ?hid.
1994, 116. 4194-4204;V. Kral. H. Furuta, K . Shreder, V. Lynch. J. L. Sessler,
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Lynch, J. L. Sessler, ibid. 1996, flR, 1608-1616; W. Peschke. F. P. Schmidtchen, Tetrahedron Lett. 1995. 5155-5158; G. Deslongcharnps, A. Galan, J. de
Mendoza, J. Rebek, Jr.. Anpew. Chem. 1992, 104, 5X -60; Angrii. Chcni. Znl.
Ed. Engl. 1992, 3 f , 61-63.
[9] A superposition of first and higher ordcr reaction channels was also evident in
the case of the amidinium alcohol 1. Here, k , was determined exactly by
extrapolating k,,, to ~ ( ~ (=1 0) [2d]. This has not yet been successful with 5.
[lo] F. M. Menger. M. Ladika, J. Am. Chern. SOC.1987, fU9, 3145-3146.
[ l l ] C. A. Maryanoff, J. N. Plampin, R. C. Stanzione, US 4.656.291, 1988; Chem.
Ahsrr. 1988, fU8, 21911.
[12] M. S . Bernatowica, Y Wu, G . R. Matsueda, J. Org. Chem. 1992, 57, 24972502.
Dibromine Monoxide, Br,O, and Bromine
Dioxide, OBrO : Spectroscopic Properties,
Molecular Structures, and Harmonic Force
Holger S. P. Miiller,* Charles E. Miller, and
Edward A. Cohen
The halogen oxides show great variations in structural
parameters and other physical as well as chemical properties.
Over a dozen chlorine oxides are known, and many of them are
quite well characterized. Bromine oxides are unstable at room
temperature; thus few of them are known.['] Even fewer have
been studied structurally, generally in the solid state. Structure
determinations of free molecules have been confined to the BrO
Recently the chlorine and bromine oxides have attracted considerable attention because of their implication in reaction cycles leading to the destruction of atmospheric ozone. Of particular importance are the catalytic cycles involving C10 and BrO.
Recently, bromine dioxide, OBrO, has been observed in the
bromine-sensitized photodecomposition of 0, .[3,41
Dibromine monoxide, Br,O, was obtained in low yields from
the reaction of Br, with Hg0.[51Bromine dioxide was first reported by Schwarz and Schmeisser as an egg-yellow deposit
from a Br,/O, discharge.I6] The stoichiometry of the oxide was
Dr. H. S. P. Miiller, Dr. C. E. Miller, Dr. E. A. Cohen
Jet Propulsion Laboratory
California Institute of Technology
Mail Stop 183-301
4800 Oak Grove Drive, Pasadena. CA 91 109-8099 (USA)
Fati: Int. code +(818)3548460
H. S. P. M. and C. E. M . thank the National Research Council for NRCNASA Resident Research Associateships. The research was performed at the
Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
Aizgew. Cheni. Znt. Ed. Engl. 1996, 35. No. 18
deduced by quantitative analysis. Its controlled decomposition
below 0°C enabled Schmeisser and Wiele to obtain pure
Br,O.['] Later, Schmeisser and Jorger reported that the ozonolysis of Br, in cooled CC1,F solution yielded OBrO.['] In contrast,
Seppelt et al. obtained single crystals of orange Br,0,[91 and
colorless Br,O,['ol from that reaction but found no evidence for
molecular OBrO. OBrO was detected during mass spectrometric
investigations of the 0 + Br, reaction system,[' 'I ESR studies of
X-ray irradiated perbromates,l'2] and UV/Vis spectroscopic investigations of the Br + 0, reaction system.[3.41 The v1 ['31 and
v3[13, l 4 1 stretching fundamentals of the oxide were observed in
Ar matrices.
Studies on Br,O included determination of the melting
point,L71 the solution ~ ' 1and gas-phase UV/Vis spectra,["] the
solid-state Raman spectrum,[' 'I the solid-state structure from
EXAFS (extended X-ray absorption,finestructure) data,['71and
the heat of formation." The symmetric stretching Vibration
v11141 or both stretching modes['7%' I were observed in Ar[14,18]
or N, matrices.['71
We have observed the rotational spectra of the triatomic
oxides Br,O and OBrO in the millimeter- and submillimeterwave regions using the spectrometer described in reference [19].
We report here some of the fundamental spectroscopic constants as well as derived properties such as structure and harmonic force field.
Initially, Br,O was obtained when Br, was passed through a
column of HgO at room temperature, and the products were
flowed through the microwave absorption cell. Although the
yields were low, in agreement with earlier work,[51many transitions were observed with no or little signal averaging.
OBrO was formed when the reaction products of an 0, discharge plus Br, were condensed onto the wall of the microwave
absorption cell at -20 "C. After the flow of 0, and Br, was
stopped, spectra of the vapor were recorded while pumping on
the condensate. The identity of the product on the wall is not
clear. It might be OBrO, a more complex bromine oxide, or a
mixture of oxides that decompose slowly to yield OBrO. At low
temperatures ( Z - 20 "C) and pressures ( ~ 0 . Pa)
1 essentially
all absorption features were due to OBrO, although weak features of BrO were also seen. The amount of OBrO increased at
higher temperatures because of a larger vapor pressure or an
enhanced decomposition of its precursor. The BrO/OBrO ratio
increased as well, possibly because of decomposition of OBrO.
Strong absorptions of Br,O were also seen at higher pressures
(reduced flow rate) and higher temperatures. This method was
subsequently used for further study of Br,O.
The hyperfine patterns of 79Br,0 and *'Br,O are consistent
with their C,, symmetry, whereas 79'81Br20has C9symmetry.
At low J or K, quantum numbers the splittings between single
hyperfine components can be several tens of MHz, and the patterns often are complex. At high J and K, quantum numbers
usually several components overlap and symmetric triplets or
quartets, or even single lines are seen, as shown in Figure 1.
Additional complications arise from perturbations of the
quadrupole patterns due to effects of the off-diagonal quadrupole coupling constant xab.
The OBrO rotational spectrum is that of a C,,-symmetric
molecule in the 2Bl electronic ground state, as is that of OCIO.
In general, each rotational transition is observable as a doublet
of quartets. This is illustrated. in Figure 2 for a transition with
rather small splittings. The doublets indicate the presence of an
unpaired electron, the quartets are due to one nucleus with spin
3/2 (79Br or *'Br).
A large number of lines was observed for Br,O (>700)
and OBrO (> 1400), resulting in the precise determination of
VCH Verlfi~sgesell~c/iaft
mhH. D-69451 Weinhrim, 1996
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The principal planar moments have been used to calculate the
ro structural parameters. They are given with data for the related
chlorine compounds in Table 2. The structural parameters of
Table 2. Structural parameters [pm, '1 [a] and harmonic force coiistaiits [ N n - ' 1 of
Br,O and OBrO in comparison with related chlorine compounds.
Br,O [aj
C1,O [b,c]
184.29 (20)
112.24 (20)
164.91 (15)
11 4.44 (25)
412 550
412 555
0 . .
411 66
411 hK
411 70
Fig. 2. Section from the submillimeter spectrum of the bromine dioxide radical.
The 311,30-302,29transition of 0"BrO in the ground vibrational state (filled
circles) and ofO'"Br0 in the first excited bending mode (open circles) are indicated.
In general each transition appears as a doublet of quartets; see text for details.
rotational, centrifugal distortion, fine (OBrO only), and Br hyperfine structure constants as well as distortion terms on fine
and some hyperfine constants. Rotational and quartic centrifugal distortion constants for the vibrational ground state are
given in Table 1 for "Br,O and 07'Br0.
Table I. Rotational [MHz] and quartic centrifugal distortion constants [a] [kHz] of
79Br,0 and 0 7 9 B r 0in the ground vibrational states.
33220.6172 (64)
1368.30433 (29)
1313.37607 (39)
0.285030 (82)
-19.1365 (26)
1051.31Y (126)
- 19.6723 (124)
-0.3533 (29)
1000 d ,
1000 d ,
28024.51786 (111)
8233 17265 (32)
6345.43314 (32)
7.13486 (48)
-70.6925 (33)
714.380 (27)
-2637.543 (124)
- 156 555 (53)
[a] Numbers in parentheses arc two standard deviations in units of the least significant figures. Watson's S reductioii is used in the representation I' [20].
21 30
71 1.0
[a] This work; r,, structurc with estimated upper limits for uncertainties, see text.
[b] Equilibrium structure. [c] Ref. [21]. [d] Ref$. [22,23]
Fig. 1. Section from the submillimeter spectrum of Br,O, which demonstrates significant intensity and quadrupole splitting for high J transitions. The asymmetric
pattern of the 475,,, -46,,., transition is caused by the off-diagonal quadrupole
coupling constant z.~,,. I = intensity in arbitrary units.
411 60
VCH l4icrlu~fi,gereNwhnfl
mbH D-69451 Wernlierm, 1996
different isotopomers agree well within the quoted digits. However, structural ambiguities due to vibrational effects are of up
to the order of i 0 . 2 pm and 0.2" for Br,O and i 0 . 1 5 pm and
0.25" for OBr0.[201The equilibrium ( r e )structures of Br,O and
OBrO have not been determined. For both molecules the re
bond lengths are about 0.5 pm smaller than the ro parameters,
as estimated from the changes of related molecules; the re bond
angles are expected to agree with the yo data to within the uncertainties ascribed to vibrational effects.
The present structural parameters of Br,O support the
EXAFS results (185 (1)pm and 112 (2)") for the molecular
solid.[17]However, the present values are more precise and refer
to the free molecule. The changes in structural parameters are
smaller from C1,O to Br,O than from C1,O to F,O, which is in
agreement with the corresponding results in the HOBr, HOCI,
HOF series.["
The differences in bond lengths are smaller between Br,O and
C1,O (14.2 pin) than between OBrO and OClO (17.4 pm). This
can be explained by the decreased tendency of Br compared to
CI to form double bonds. For both chlorine oxides, known re
values were employed, for the two bromine oxides the estimates
of r e .
The quartic distortion constants have been used to calculate
the harmonic force fields for both bromine oxides. Vibrational
data for Br,O were taken from reference [18]. The force constants are also given in Table 2 together with those of related
The stretching force constantsf; of Br,O and C1,O are remarkably similar, possibly a reflection of the pure single-bond
character. The larger stretching force constants and shorter
bond lengths in OBrO and OClO compared to those of Br20
and C1,O are indicative of substantial double-bond character in
the dioxides.
For Br,O both,f, andf,, and the values of the quartic centrifugal distortion constants are strongly interdependent. The
present force field indicates a value of 180 cm-I for the v2 band
center, which may be compared to 197 cm-' observed for the
We have observed the v3 band of OBrO in the gas phase
(Fig. 3). The Q-branch feature of 0 7 ' B r 0 at 848.6 cm-' and
the isotopic shift of 2.4cm-' agree well with values from the
force field (851.2 and 2.35 cm-') as does the position of the v I
band in an argon matrix (794.6 versus 794.1 c n - I from reference [13]). The calculated isotopic shift for v1 is 1.15 cm-'; an
observed splitting of 2.9 cm-' is more likely due to a matrix
effect; see for example reference [23], where these effects have
0570-0833/96/3518-2130$ 15.00+ ,2510
Angen,. Clwni. Int. Ed. Engl. 1996. 35,N o . 18
ondary chemistry that may be of atmospheric importance. We
are currently investigating the spectroscopy and kinetics of these
interesting molecules.
K S C C I \ C d ,~pl-ll
10. 1996
Re\i\cd bersioti Jiiiie 3. 1996 [ZPO5XIE]
bcrsiiin . . l i i ~ ( , i x ( % w i 1996. 10s. 77x5 22XX
Keywords: bromine oxides . halogen compounds
spectroscopy . structure elucidation
becn studied in detail for OCIO. Although the bending mode has
n o t yet becn observed directly. our calculated value of 31 1 c m for 0'"BrO is consistent with relative intensities observed for
rotational transitions i n the ground state compared to those in
the = I state (Fig. 2 ) .
Thc principal Br quadrupole constants of Br,O have been
obtained by diagonalization of the quadrupole tensor. The valLK x,< = 938 MHi. is close to that of Br2 (810 M H Z [ ' ~ ~indicat).
ing ;I prcdominantly covalent Br --0 bond.[201Contributions
from ionic tornis Br 'OBr and BrO.-Br' are about 12% and
x bonding is almost negligible (ca. 2 % ) . The ionic character is
slightly lurgcr- than i n BrCl ( 9 ( j / 0 ) ( and
~ ' ~ essentially the same as
in HOBr.['"lwhich isconsistent with the view that theOX group
( X = H. halogen) IS slightly more electronegative than the C1
atom. The qu~idrupolar:axis differs substantially from the
Br 0 bond (by cii. 2.4 ; Fig. 4). I f one would assume the z axis
t o be identical with the Br --0bond. one would derive an ionic
character of about 45% for the Br- 0 bond in BrzO, exceeding
that of B1-F. (35'h1).''-l a n d a substantial degree of n bonding.
Although a detailed discussion of the fine and hyperfine structure constants is beyond the scope of a brief communication, it
should be noted that earlier ESR results" 2 1 are consistent with
those of this study. Thus. the conclusion given in reference [I21
that. iis in OCIO. halfof the spin-density is at the halogen atom.
and essentially ;ill of' this in the /i-orbital perpendicular to the
inoiecular plane. remuins unchanged.
I11 conclusion. we h a w used the 0 + Br2 reaction system to
study BrzO and the O B r O radical. The presence of a mixture of
bromine oxides under cci-t;iin conditions indicates complex sec-
. radicals .
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obroz, properties, molecular, bromine, br2o, harmonic, dibromine, spectroscopy, structure, dioxide, monoxide, field, force
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