INFRARED SPECTRUMOF H2B20a 731
Vol. 8, No. 4, April 1969
CONTRIBUTION FROM THE DEPARTMENT OF CHEMISTRY, CORNELL UNIVERSITY, ITHACA, NEW YORK 14850
The Infrared Spectrum and Vibrational Assignments of H,BzOJ BY F. A. GRIMM
AND RICHARD
F. PORTER
Received September 4, 1968 The infrared spectrum of cyclic H2B203(g)has been obtained from 4000 to 250 cm-l. A number of isotopic species, including H2BzlBO3, HzB21@01802, H2Bz1803, D & Z ' ~ O ~ H210Bz1603, , and H210B11B1e03, were prepared by allowing the appropriate isotopic combinations of oxygen to react with boroxine (H3B803). A vibrational analysis indicates that the molecule exists in one major isomeric form with Czv symmetry. Certain features of the spectrum arising from the mixed isotopic species are discussed.
Introduction
oxygen mixtures and condensed HzB203 are explosive. The method has been shown to produce very pure H2B20,,which may contain The compound H2B203 is one of the few known small amounts of hydrogen due to some decomposition. The cyclic molecules containing only boron, hydrogen, and method for the preparation of the isotopic species is described below. oxygen. The infrared spectrum of gaseous H2B203 was HznB2"Oa (Where n Is Used to Indicate the Natural Abundance first observed by Ditter and Shapiro2 as an unstable of Boron-10 and Boron-1 l).-Diborane was prepared from the intermediate in the partial oxidation of pentaborane-9. reaction of anhydrous stannous chloride with sodium borohydride At room temperature the gas decomposes into H 2 and "in uacuo" a t 250°.5 Matheson reagent grade oxygen was used B203(s) with a half-life of approximately 3 days. without further purification. D2nB2'603 and HDnBZ1603.-Deuteriodiborane was prepared Microwave studies have shown the HzB203 molecule to be a planar five-membered ring with CZv~ y r n m e t r y . ~ from sodium borodeuteride which contained better than 98% deuterium. Since it was observed that hydrogen or deuterium could exchange with the appropriate isotope of H2Bz03, it was Z possible to obtain information on the mixed hydrogen-deuterium t species by adding hydrogen to D~"Bz'~03 and then observing the infrared spectrum at intervals during the exchange, which occurs slowly over a period of days. The exchange of deuterium with the hydrogen species H210B11B1603was also observed.6 Hz10B2160~.-Boron-10diborane was prepared from CaF21°BF3 (obtained from Oak Ridge National Laboratory) by heating with an excess of LiAIH4. Impurities were removed by adding The microwave study did not rule out the existence of small quantities of ammonia to form a n addition compound of a highly symmetric isomer without a permanent dipole the unreacted BF3 and HBFz and then by vacuum distillation moment. However, a detailed analysis of the infrared of the boron-10 diborane. The starting material contained 96% spectrum should reveal the importance of another boron-10. H2nB21803.-The sample of oxygen-18 used contained the isomeric form. following percentages: 86.3% 1802; 12.3% 160180; 0.4% WZ. It should be noted that although the pure isotopic H2nBz160180180 (Where the Oxygen-18 Is in the Peroxide species (Hz"B203 and H210B20J have CzV symmetry, Position).-Boroxine was prepared from oxygen-16 and then the mixed species (H2l0Bl1B03)has only C, symmetry. oxygen-18 (see percentages above) was added to produce this as Naturally occurring boron contains approximately 20% the major species. Spectra were taken on a Perkin-Elmer 521 infrared spectroboron-10 and 80% boron-11. Therefore, in the specphotometer in a 10-cm cell equipped with CsI windows from trumof H2B203 prepared from the natural isotopic abun4000 to 250 cm-l. Indene was used for wavelength calibration dance of boron, one has a combination of the pure and the position of bands exhibiting very sharp Q branches could isotopic species H211B203 and Hz10B203 and the mixed be located to better than 0.5 cm-l. Reasonable limits for the isotopic species H2loBU1'BO3in the approximate ratio center of the B-type bands would be 5 2 cm-l. Higher resolution 16 : 1 : 8. In the present study the vibrational analyses spectra were also taken in order to resolve the many Q branches found in the 700-900-cm-l region of the spectrum. These were of six pure and four mixed isotopic species have been obtained by using a programmed slit set at 200 p a t 925 cm-l. considered. Attempts to obtain higher pressures by the techniques employed were thwarted by the unstable nature of the compound. Experimental Section It was found, for example, that the decomposition rate is greatly Gaseous HzB203 was prepared, as previously reported,4 from accelerated in a metal multi-path-length cell, and no improvediborane and oxygen. I n order to produce larger quantities of ment in the intensity of the spectrum is obtained. Also, attempts the compound a 3-1. bulb was used in place of the 2-1. bulb used to obtain more material by condensing together various batches in ref 4. Caution should be exercised in the preparation as diboranealways resulted in decomposition upon warming to room temperature (noted by a flash in the storage bulb). The highest sample (1) Work supported by the Army Research Office, Durham, N. C , and the pressures (15-30 mm) were obtained by combining batches while Advanced Research Projects Agency (2) J. F. Ditter and I Shapiro, J . Am. Chem. SOC, 81, 1022 (1959) still in the gas phase. (3) W. V. Brooks, C. C. Costain, and R. F. Porter, J . Chem. Phvs., 47, 4186 (1867). (4) F. A. Grimm and R.F. Porter, Inwg. Chem., 7, 706 (1868).
(5) W. Jeffers, Chem. Ind. (London), 431 (1961). (6) The sample contained 50% Hz1nB1'B1(0a.
732 F. A. GRIMMAND R. F. PORTER
Inorganic Chemistry TABLE I
FREQUENCY LISTING (hfAXIMA LISTEDEXCEPT
FOR THE
B-TYPEBANDWHERE THE
IT.4LICIZED
FREQUENCY
IS THE CENTRAL ?dINIMUM)
H 2lOB 2
1 6 0 ~
7
....
741 726, 745>764 748
m
.... ....
sh m
w,sh
W
.... 895 Q
ni
w,sh
....
879, 899, 915 PQR
vs
...
vs
895 Q
899 Q
8
899 Q 961 Q 967 Q
979, 981, 982 m
w, sh
1114 Q .... 1127 Q 1132, 1145.5, 1154 PQR W, sh 1145.5 Q .... 1167, 1168 .... 1183, 1185 1179, 1185, 1192, 1196, 1204 vs 1192
.... .
.
I
.
1400
1417, 1.419
.... .... 1780
sh vs
vw
....
.... -2 180
w
1218 Q 1237 Q 1363, 1374, 1876 1398, 1400 1417, 1419 1735 1757 1778 2135 -2160 b 2180
m
.... ....
vw
1114Q 1127 Q
w, sh
....
s
.... ....
sh
2587, 6607, 2625 PQR 2635 (?) Q
m w,sh
....
....
6680, 2683
S
V14
VI4
V6 Y3
VI3
1192
V13
VZ
1217 Q w,sh . . . . vs 1363, 1374, 1575, 1385 vs s, sh vs 1398,1400 sh 1420 VW, sh vw 1735 vw vw 1757 vw vw .... -2135 w w 2160 w
....
2537 2575
W
.... 6663
2667
s, sh vs
2680
8,sh
W
. I . .
....
W W
vs
B-type band B-type band
V4
vz
"BZ l0B1lB 'OB, "Bz l0Bl1B log,
"Bz IOBllB O ' B2 'lB2 IOBllB O ' B2 "B, IOBllB 'OB2
....
....
.... ....
B-type band
v3
1801 Q
vw m
B-type band (broad Btype center)
Y?
V6
....
6661
V8
s, sh
.... -2535 2575 2605
maximum of P andnobscure maximum of P obscure
v4
1183
m
-2380
w
(1)
vg
vw, sh . . . . s, sh 1166, 1169, 1172
-2350 -2400
(1)
VI3
979
....
1237.6 Q
v6
VI
V4
....
....
....
V6
....
....
982
VI0
....
895, 911 QR
967 b .,..
w,sh
VB
8
.... 968
776 Q
....
829 Q S
Q branch broad
B-type band strongest Q "' branchtaken '16 l l l i as center
875 Q 883 Q
....
vl4
724, 741 763 745 749
875 Q 883 Q
..*.
V10
.... sh m sh
....
vw
and remarks
407, &26.5, 444 PQR
.... 842 (?) 875 Q
Assignment
7
Freq, cm-1
....
.... 778 b
H2nB+603c-
7 ,
Intens
....
431 Q
.... ..,.
781 Q
H ~loB11BlQ~bFreq, cm-1
42 1 412, 469.6, 447 PQR
....
730, '7.48, 768
,
Intens
Freq, em-'
"B? lOBllB 'OB*
v12 B-type band v3
~ 1 B-type 2
band 2vs (1766) 2 ~ 1 2(1790) 2vg (1798) V B - ~ V I ? (2151) va-kvio (2178) V 6 f V l ? (2200) Viz-kV14(2354) ~ 3 S v 7(2381) Viz-kV14(2401) v i z f v i 3 (2544) v 3 + ~ 5 (2583) v i z + v i 3 (2611) ? v l l B-type center Y2 yll
(?)
B-type center
a At 14 rnrn, the IO-cm cell contained 92.2% H 2 1 ~ B 2 1 ~7.794 0 3 , H,10BllB1603, and 0.1% HZ1'B216O3. At 12 mm, the 10-cm cell 25% Hz1OB216Od,and 25% H211B21B03.c At 27 mm, the 10-em cell contained 65.9% Hz"B,'~O~, 30.6% contained 50% H,10B11B1603, H ~ ~ ~ B l ~ Band l ~ 3.5% 0 3 , HpBZ16O1.
INFRARED SPECTRUM OF H&O8
VoZ. 8, No. 4) April 1969
A frequency listing of the spectra of the various isotopic species of HzBz03 is given in Tables I and 11. Included in the listing is the isotopic species to which the band is att,ributed. This information was obtained by observing the change in band intensities of spectra containing different percentages of the various isotopes. Figures 1-3 give an example of the spectra obtained showing only the major features and are intended only for display of qualitative band shapes and intensities; the actual spectra obtained are niore detailed and in some cases were more intense than those shown. No bands were observed in the region above 3000 emw1or in most cases below 400 cm-l so these regions have been omitted in the figures.
0
, , , , I , , , , ,
3000
2500
,
2000
,
,
I800
,
I
1600
, , 1200 , ,
1400
I
1000
,
I
800
733
I
600
,
400
fREOUENCY lCM-'I
Figure 1.-Spectrum of H210B2160a.The sample had a pressure of 14 mm and contained 92.2y0 H2'OBz1603, 7.7y0Hz10B11B1603, and 0.1% Hz11B~160a.
Vibrational Analysis of Species with CzvSymmetry For the isotopic species of Czv symmetry group theory predicts the following fundamental vibrations: r v i b = 6A1 2Az 2B1 5B2. All of the vibrations would be active in the infrared spectrum except the Az species, which would be active only in the Raman spectrum. The molecule has an Itsymmetric top and, except for the deuterated species, has its smallest moment of inertia coincident with the symmetry axis. From the microwave results13 sufficient information was available to estimate band shapes for the fundamental vibrations. Six isotopic species with Czv synimetry have been partially analyzed. These include Hz'0B21603,Hz"B21 6 0 3 , H21'Bz1601802, H2"BZ"03, Dz10Bz1603, and DzB211l603. For convenience in the discussion of the analysis it is necessary to choose one isotopic species as an example. The natural choice is H211Bz1603.Therefore, unless otherwise noted, all frequencies quoted below will be those of Hz"B2'603. The analysis of the pure isotopic species (CZv symmetry) was based on the following reasoning.
+
+
+
'
3im
240
2000
lkl00
1600
1400
1200
lobo
El&
660
4 L
Frequency (ern-')
Figure 2.-Spectra of H z n B P 0 8(top) and Dzn&1808(bottom). Sample pressures were 11 and 12 mnl, respectively. (For percentages of isotopic species see footnotes b and c in Table I.)
Out-of-Plane Vibrations BI Species.-The two vibrations of this symmetry were readily assigned at 883 and 425.5 an-'. Isotopic shifts using the Redlich-Teller product rule and band shapes support the assignments. The results of the product rule calculations are sunimarized in Table 111. The out-of-plane B H bending mode at 883 cm-' may be compared t o the one found at 918 cm-' in both borazine8 and boroxine.9 The ring mode at 425.5 cm-' is found to be somewhat higher than in borazine where an analogous band is found at 394 cm-'. The analogous fundamental has not been observed for boroxine. There seems to be little doubt about the assignment of the B1 species for any of the isotopic species. (7) H C Allen, Jr , and P C Cross, Molecular Vib-Rotors," John Wiley & Sons, Inc , New York, N Y , 1963 (8) K Kiedenzu, W Sawodny, I< Watanabe, J Dawson, T Totani, and W Weber, Inory Chem , 6, 1453 (1867) (9) F A Grimm, L Barton, and R F Porter, zbzd , in press
3000
2500
2000
I800
I800
1400
1200
1000
800
600
400
FREQUENCY CCd)
Figure 3.-Spectra of H z " B ~ ' ~ O ~ *(bottom) OZ and HznB2'*0a (top). Sample pressures were 15 and 13 mm, respectively. (For percentages of isotopic species see footnotes b and c in Table 11.)
In-Plane Vibrations
Bz Species.-Group theory predicts two vibrations involving predominantly BH motion and three ring motions. These bands might be expected to be more intense than the corresponding symmetric in-plane A1 vibrations. Thus, the intense band at 2653 cm-l is
734 F. A. GRIMM AND R. F. PORTER
Inorganic Chemistry TABLEI1 FREQUENCY LISTING OF MAXIMA
Freq, om-'
335, 3'59, 381 PQR 733 Q 745 Q 750 Q 757, 75gId762 i+65d Q 777d Q 785 Q 816 Q 878 Q 893.5 Q 1069 1083 1125.5, 11?2rd 1137, 115Qd 1193 Q 1208 Q 1346, 1550,d 1352 1 3 7 ~ 7 1377 ,~ 1490 1850 b 1975,1977,d 1985 2050,2067, 2085
Intens
Assignment and remarks
m
VI0
W
V16
vw, sh w,sh vw
D11B motion v4 VI4
VS
V9
VS
v12
m
v9
w, sh
vs
m vw
H11B motion HloB motion
W
v3
vw,sh
V6
8
vl8
m, sh
other maxima obscure
8
v6 other maxima obscure vz
sh
v4
VS
VI2
s, sh
va
vw
2vg (1530)
VW
Vi3
vs
Vll
W
V6
-405, 485,442 PQR 694, 714, 738
f
f
Vi4
(1884)
VI2 ( V 6
-735
v10
vI6 B-type band, center taken
as strongest Q branch
724 738, Y44, 748 PQR 874 Q 868, 886 PQ 894 Q 898 Q 954 b Q 969, 97id 1101 Q 1110 Q 1149, 1151.5,d 1154 1166d
1197 Q 1213 Q 1357, 1365, 1S66,d 1369, 1374
sh w, sh m VS VS
m vw, sh m
Vll V6
v1.3
vg position of R maxima obscure v12 v9
v4 VI4
B-type band
W
v3
vw s, sh m
VI3
8
v2
sh
v4
vs
v I 2 B-type band
(?) (H2'OB"B'601*0~) B-type band vs B-type band
a At 17.5 mm, the 10-ern cell contained 61.4% D211B21603,30.7% D z 1 0 B ~ ~ B ~ 3.8% ~ 0 3 Dz10B21603, , 2.6% DH"Bz'~O~, and
