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Vibrational spectra of bis(ammonia)- and bis(trimethylamine)-boronium iodide
Z inorg, nucl, Chem., 1975, VoL 37, pp. 887-889. Pergamon Press. Printed in Great Britain
VIBRATIONAL SPECTRA OF BIS(AMMONIA)- AND BIS(TRIMETHYLAMINE)-BORONIUM IODIDE PETER J. BRATT, MICHAELP. BROWN and KENNETH R. SEDDON* DonnanLaboratories,The University,P.O. Box 147,LiverpoolL69 3BX (First received6 May 1974;in revisedfonn 1August 1974) Abstract--The i.r. and Raman spectra of [(NH~)2BI-I~]Iand the i.r. spectrum of [(Me~N)2BH2]Iare reported. Vibrational assignments are proposed, using the group vibration approximation. INTRODUCTION ALTHOUGHthere have been a number of partial i.r. studies of boronium compounds [1-7], these have been restricted either just to reporting the spectra, or simply to assignment of the -BHz frequencies. We report here the Raman and i.r. spectra of bis(ammonia)boronium iodide. We failed to record a Raman spectrum of bis(trimethylamine)boronium iodide, owing to its fluorescence in the laser beam. Assignments of these spectra have been made using the group vibration approximation, which has previously been successfully applied to the related boron amines, Me3N.BX3[8], Me3N.BHX2[9] and Me3N.BH2X[9] (where X = CI, Br, I). EXPERIMENTAL
Both [(NH3)aBH2]Iand [(Me3N)~BH2]Iwere prepared and purified by methods described elsewhere[13]. The i.r. spectra were recorded on a Perkin-Elmer 225 spectrophotometer. The Raman spectrawere recordedon a powdered sampleusing a Spex 1401 spectrometer and the 514.5nm line of an Ar+ laser at 300 roW. RESULTS AND DISCUSSION Bis(trimethylamine)boronium iodide The Me3N group has C3~ symmetry, and gives 18 i.r. active bands (7at+lie), eleven of which are doubly degenerate. A list of these bands, together with their description and frequency numbers, has been published elsewhere [9]. The H2BNz group has C2~ symmetry, and gives 8 i.r. active bands (4al + 2bj + 2b:), which are listed and described in Table 1. The i.r. spectrum of [(Me3N)2BH2]I, together with assignments, is listed in Table 2. The assignments of the bands due to Me3N were straightforward, and analogous to those found in related trimethylamine adducts. The bands assigned to v(BH2)~[2460cm-~], v(BH~)~y~[2375, 2325cm-'], 8(BH2)~s[1198, 1194cm-~] and 8(BH2)~y~[1103cm-~] occur in the same region as found for compounds of the type Me3N.BHzX[9] and py.BH2Ph[10]; the bands are either asymmetric or split by the ~°B-nB isotope effect. The assignments of the BH2 deformation modes, however, differ quite considerably from those found for I.I.N.C.~ Vol. 37, No. 4--C
887
Et3NBH2X [I1]. v(BN)~d748cm-I] and u(BN),ym[690 cm-~] also occur in the region found for the complexes, Me3N.BH:X. It is of interest to note that, despite the contrast in boron species in comparing the neutral molecule LBH2X with the charged cationic species [L2BH2]+, there has been very little change in the position of either the v(BH2), 8(BH2) or v(BN2) bands. Bis (ammonia )boronium iodide The i.r. and Raman spectra of [(NH3)2BH2]I,together with assignments, are reported in Table 3. The region of the boron-hydrogen stretching frequencies in the i.r. spectrum is very complex (see Fig. I). This apparently is due to overtones and combination bands arising from the BH2 deformation modes falling in the same region of the spectrum, and gaining in intensity by a Fermi resonance effect. The same region in the Raman spectrum is far simpler, showing only two strong bands, split by the I°B-'B isotope effect, and one weak overtone. This permitted unambiguous assignment of v(BH2),~ and v(BH2),y~. The pattern in the i.r. spectrum is quite distinctive, and appears to be characteristic of boronium ions. Although neutral molecules containing -BH2 and -BH3 groupings do show weak overtone and combination
2500
2000
Fig. 1, I.R. (2600-2000crn-') of [(NH3)2BH2]I.
888
P.J. BRATr, M. P. BROWNand K. R. SEDDON Table 1. DescriptionofvibrationalmodesforH2BN2(C2~)
No.
Symmetry
F~o ~'2, v2z ~z3 vz, vz, vz6
al al a, b~ b~ b2 b2
Table 3. I.R. and Raman spectra of [(NH3)zBH2]I
Description symmetrical BH: stretch u(BNz)~m symmetrical BN2 stretch 8(BH2),y~ symmetrical BHz deformation 8(BN2)~ym symmetrical BN: deformation v(BHz).~ asymmetrical BH: stretch u(BNz).~ asymmetrical BN2 stretch 8(BHz),~ asymmetrical BH2 deformation 8(BNz)~, asymmetrical BNz deformation
Table 2. I.R. spectrum of [(MesN)2BH2]I('unitsof cm -1)
I.R.
R
3150 s,v br
3195 vs,br
v(NH3)
2405 sh
2402 w
*
2360 sh /
2350 sh 1
~(B~2)~,~
2330 m J 2250 w 2178 w 2115vw 1591 s ] 1557 m)
2334 m )
-
Band
Assignment
Band
3025 sh 3015 w,sh 3009 w,sh 2994 m 2949 m 2910 w,sh 2880 vw,sh 2850 w
v. * * v~ v~ ~qo 1/2 *
2815 w 2700 w 2460 s 2442 w,sh 2412 w,sh 2375 m ] 2325 mJ 2290 w,sh 2255 w 1497 w 1480 s 1467 w 1456 m 1437 m 1419 m 1380 w,sh
* * v2s * *
1348 vw 1265 w,sh 1250 s ~ 1240 s J 1198 sh~ ' 1194 s J 1179 w 1144 w 1132w] 1122 mJ 1103 m 1062 vw 999 s~ 981 sJ 878 w 867 w 851 s 748 m 690 vw 539w 499 m 443 vw~ 410 m J 387 m
v,~ * * * v~ v12 v3 1/13
u, *
* Vt4
u~
~'25
v~ v21
v~
u~ v24 ~'~o
v26 vn
*Combination or overtone bands, s, strong; m, medium; w, weak; v, very; sh, shoulder. bands in this region, Fermi resonance does not appear to enhance their intensity to the same extent as with the boronium compounds. The assignments of 8(BH2) and v(BN2) are consistent with the assignments for [(Me3N)2BH2]I and Me3N.BHzX,
-
1405 s 1382 sh 1240 vw 1208 w
Assignment
Assignments
* * * 1591 sh ) 1571s ~ 1542 shJ 1404 m
8(NH3) 8(NH3)
.9,m} 1182
1211 s
8(BH2)~
l150w,sh ll07w,shl 1093 s / 1016 s 850 sh 840 m 776 w 729 vw'~ 697m J 372 m
1083w 1021 m 856 vw 846 vw 781 m 730 w~ 6%w) 382 m
8(BH2)~,m p(NH3)
v(BN2),, v(BN2),~,~ 6(BN2)~
and the bands show the expected boron-isotope effect. The frequency assignments of the bands due to ammonia are consistent with those for other ammonia adducts. General discussion Table 4 compares the important features of the i.r. spectra of [(Me3N)2BH2]I, [(NH3)2BH2]I, Me3N.BH2X and NH3.BH3. Although, individually, the assignments of 6(BH2) and v(BN2) may have been open to doubt (especially in view of the number of trimethylamine bands in the region), the positions are all internally consistent. This, taken with the simplicity of the Raman and i.r. spectra of [(NH3)2BH2]I, and the splitting or asymmetry (due to the boron-isotope effect) of the bands, adds weight both to the present assignments, and to those already in the literature. Acknowledgements--We would like to express our gratitude to
Table 4. Principal i.r. bands for L BHzX and [LzBHz]X (units of cm-1) v(BHz),s [(Me3N)2BH:]I [(NHs)zBH2]I Me3N-BH2C1 MesN.BHzBr Me3N.BH21 H~N.BH3
v(BHz),~m ~(BH2)as
2460, 2442 2375, 2325 2442 2360, 2330 2443, 2414 2346 2475, 2425 2337 2480, 2437 2328 . . .
1198,1194 1198,1182 1186 1175 1171 .
8(BH2),ym v(BN) 1103 1107, 1093 1094, 1083 1080, 1067 1057, 1040
--705,693 710,698 717, 703 787
v(BNz)a~ 748 776 -----
v(BN2)~ym 690 729, 697 -----
Ref.
[9] [9] [9] [12]
I.R. and Raman studies of boronium salts Professor D. A. Long and his staff for the use of Raman facilities at the University of Bradford. We would also like to thank the S.R~C. for a maintenance grant (to P.J.B.) and I.C.I. for the award of a fellowship (to K.R.S.). REFERENCES 1. G. E. Ryschkewitsch and K. Zutshi, Inorg. Chem. 9, 411 (1970). 2. G. E. Ryschkewitsch and T. E. Sullivan, Inorg. Chem. 9, 899 (1970). 3. V. R. Miller, G. E. Ryschkewitsch and S. Chandra, lnorg. Chem. 9, 1427 (1970). 4. K. C. Nainan and G. E. Ryschkewitsch, J. Am. chem. Soc. 91, 330 (1969).
889
5. N. E. Miller and D. L. Reznicek, Inorg. Chem. 8,275 (1%9). 6. K. C. Nainan and G. E. Ryschkewitsch, Inorg. Chem. 7, 1316 (1%8). 7. D. L. Reznicek and N. E. Miller, Inorg. Chem. 11,858 (1972). 8. R. L. Amster and R. C. Taylor, Spectrochim. Acta 20, 1487 (196#). 9. P. J. Bratt, K. R. Seddon and I. A. Steer, Inorg. Chim. Acta to be published. 10. J. F. Douglass, J. Am. chem. Soc. 84, 121 (1962). 11. J. N. G. Faulks, N. N. Greenwood and J. H. Morris, J. inorg. nucl. Chem. 29, 329 (1%7). 12. R. C. Taylor and C. L. Cluff, Nature, Lond. 182,390 (1958). 13. P. J. Bratt and M. P. Brown, J. Chem. Soc. Dalton, to be published.
VIBRATIONAL SPECTRA OF BIS(AMMONIA)- AND BIS(TRIMETHYLAMINE)-BORONIUM IODIDE PETER J. BRATT, MICHAELP. BROWN and KENNETH R. SEDDON* DonnanLaboratories,The University,P.O. Box 147,LiverpoolL69 3BX (First received6 May 1974;in revisedfonn 1August 1974) Abstract--The i.r. and Raman spectra of [(NH~)2BI-I~]Iand the i.r. spectrum of [(Me~N)2BH2]Iare reported. Vibrational assignments are proposed, using the group vibration approximation. INTRODUCTION ALTHOUGHthere have been a number of partial i.r. studies of boronium compounds [1-7], these have been restricted either just to reporting the spectra, or simply to assignment of the -BHz frequencies. We report here the Raman and i.r. spectra of bis(ammonia)boronium iodide. We failed to record a Raman spectrum of bis(trimethylamine)boronium iodide, owing to its fluorescence in the laser beam. Assignments of these spectra have been made using the group vibration approximation, which has previously been successfully applied to the related boron amines, Me3N.BX3[8], Me3N.BHX2[9] and Me3N.BH2X[9] (where X = CI, Br, I). EXPERIMENTAL
Both [(NH3)aBH2]Iand [(Me3N)~BH2]Iwere prepared and purified by methods described elsewhere[13]. The i.r. spectra were recorded on a Perkin-Elmer 225 spectrophotometer. The Raman spectrawere recordedon a powdered sampleusing a Spex 1401 spectrometer and the 514.5nm line of an Ar+ laser at 300 roW. RESULTS AND DISCUSSION Bis(trimethylamine)boronium iodide The Me3N group has C3~ symmetry, and gives 18 i.r. active bands (7at+lie), eleven of which are doubly degenerate. A list of these bands, together with their description and frequency numbers, has been published elsewhere [9]. The H2BNz group has C2~ symmetry, and gives 8 i.r. active bands (4al + 2bj + 2b:), which are listed and described in Table 1. The i.r. spectrum of [(Me3N)2BH2]I, together with assignments, is listed in Table 2. The assignments of the bands due to Me3N were straightforward, and analogous to those found in related trimethylamine adducts. The bands assigned to v(BH2)~[2460cm-~], v(BH~)~y~[2375, 2325cm-'], 8(BH2)~s[1198, 1194cm-~] and 8(BH2)~y~[1103cm-~] occur in the same region as found for compounds of the type Me3N.BHzX[9] and py.BH2Ph[10]; the bands are either asymmetric or split by the ~°B-nB isotope effect. The assignments of the BH2 deformation modes, however, differ quite considerably from those found for I.I.N.C.~ Vol. 37, No. 4--C
887
Et3NBH2X [I1]. v(BN)~d748cm-I] and u(BN),ym[690 cm-~] also occur in the region found for the complexes, Me3N.BH:X. It is of interest to note that, despite the contrast in boron species in comparing the neutral molecule LBH2X with the charged cationic species [L2BH2]+, there has been very little change in the position of either the v(BH2), 8(BH2) or v(BN2) bands. Bis (ammonia )boronium iodide The i.r. and Raman spectra of [(NH3)2BH2]I,together with assignments, are reported in Table 3. The region of the boron-hydrogen stretching frequencies in the i.r. spectrum is very complex (see Fig. I). This apparently is due to overtones and combination bands arising from the BH2 deformation modes falling in the same region of the spectrum, and gaining in intensity by a Fermi resonance effect. The same region in the Raman spectrum is far simpler, showing only two strong bands, split by the I°B-'B isotope effect, and one weak overtone. This permitted unambiguous assignment of v(BH2),~ and v(BH2),y~. The pattern in the i.r. spectrum is quite distinctive, and appears to be characteristic of boronium ions. Although neutral molecules containing -BH2 and -BH3 groupings do show weak overtone and combination
2500
2000
Fig. 1, I.R. (2600-2000crn-') of [(NH3)2BH2]I.
888
P.J. BRATr, M. P. BROWNand K. R. SEDDON Table 1. DescriptionofvibrationalmodesforH2BN2(C2~)
No.
Symmetry
F~o ~'2, v2z ~z3 vz, vz, vz6
al al a, b~ b~ b2 b2
Table 3. I.R. and Raman spectra of [(NH3)zBH2]I
Description symmetrical BH: stretch u(BNz)~m symmetrical BN2 stretch 8(BH2),y~ symmetrical BHz deformation 8(BN2)~ym symmetrical BN: deformation v(BHz).~ asymmetrical BH: stretch u(BNz).~ asymmetrical BN2 stretch 8(BHz),~ asymmetrical BH2 deformation 8(BNz)~, asymmetrical BNz deformation
Table 2. I.R. spectrum of [(MesN)2BH2]I('unitsof cm -1)
I.R.
R
3150 s,v br
3195 vs,br
v(NH3)
2405 sh
2402 w
*
2360 sh /
2350 sh 1
~(B~2)~,~
2330 m J 2250 w 2178 w 2115vw 1591 s ] 1557 m)
2334 m )
-
Band
Assignment
Band
3025 sh 3015 w,sh 3009 w,sh 2994 m 2949 m 2910 w,sh 2880 vw,sh 2850 w
v. * * v~ v~ ~qo 1/2 *
2815 w 2700 w 2460 s 2442 w,sh 2412 w,sh 2375 m ] 2325 mJ 2290 w,sh 2255 w 1497 w 1480 s 1467 w 1456 m 1437 m 1419 m 1380 w,sh
* * v2s * *
1348 vw 1265 w,sh 1250 s ~ 1240 s J 1198 sh~ ' 1194 s J 1179 w 1144 w 1132w] 1122 mJ 1103 m 1062 vw 999 s~ 981 sJ 878 w 867 w 851 s 748 m 690 vw 539w 499 m 443 vw~ 410 m J 387 m
v,~ * * * v~ v12 v3 1/13
u, *
* Vt4
u~
~'25
v~ v21
v~
u~ v24 ~'~o
v26 vn
*Combination or overtone bands, s, strong; m, medium; w, weak; v, very; sh, shoulder. bands in this region, Fermi resonance does not appear to enhance their intensity to the same extent as with the boronium compounds. The assignments of 8(BH2) and v(BN2) are consistent with the assignments for [(Me3N)2BH2]I and Me3N.BHzX,
-
1405 s 1382 sh 1240 vw 1208 w
Assignment
Assignments
* * * 1591 sh ) 1571s ~ 1542 shJ 1404 m
8(NH3) 8(NH3)
.9,m} 1182
1211 s
8(BH2)~
l150w,sh ll07w,shl 1093 s / 1016 s 850 sh 840 m 776 w 729 vw'~ 697m J 372 m
1083w 1021 m 856 vw 846 vw 781 m 730 w~ 6%w) 382 m
8(BH2)~,m p(NH3)
v(BN2),, v(BN2),~,~ 6(BN2)~
and the bands show the expected boron-isotope effect. The frequency assignments of the bands due to ammonia are consistent with those for other ammonia adducts. General discussion Table 4 compares the important features of the i.r. spectra of [(Me3N)2BH2]I, [(NH3)2BH2]I, Me3N.BH2X and NH3.BH3. Although, individually, the assignments of 6(BH2) and v(BN2) may have been open to doubt (especially in view of the number of trimethylamine bands in the region), the positions are all internally consistent. This, taken with the simplicity of the Raman and i.r. spectra of [(NH3)2BH2]I, and the splitting or asymmetry (due to the boron-isotope effect) of the bands, adds weight both to the present assignments, and to those already in the literature. Acknowledgements--We would like to express our gratitude to
Table 4. Principal i.r. bands for L BHzX and [LzBHz]X (units of cm-1) v(BHz),s [(Me3N)2BH:]I [(NHs)zBH2]I Me3N-BH2C1 MesN.BHzBr Me3N.BH21 H~N.BH3
v(BHz),~m ~(BH2)as
2460, 2442 2375, 2325 2442 2360, 2330 2443, 2414 2346 2475, 2425 2337 2480, 2437 2328 . . .
1198,1194 1198,1182 1186 1175 1171 .
8(BH2),ym v(BN) 1103 1107, 1093 1094, 1083 1080, 1067 1057, 1040
--705,693 710,698 717, 703 787
v(BNz)a~ 748 776 -----
v(BN2)~ym 690 729, 697 -----
Ref.
[9] [9] [9] [12]
I.R. and Raman studies of boronium salts Professor D. A. Long and his staff for the use of Raman facilities at the University of Bradford. We would also like to thank the S.R~C. for a maintenance grant (to P.J.B.) and I.C.I. for the award of a fellowship (to K.R.S.). REFERENCES 1. G. E. Ryschkewitsch and K. Zutshi, Inorg. Chem. 9, 411 (1970). 2. G. E. Ryschkewitsch and T. E. Sullivan, Inorg. Chem. 9, 899 (1970). 3. V. R. Miller, G. E. Ryschkewitsch and S. Chandra, lnorg. Chem. 9, 1427 (1970). 4. K. C. Nainan and G. E. Ryschkewitsch, J. Am. chem. Soc. 91, 330 (1969).
889
5. N. E. Miller and D. L. Reznicek, Inorg. Chem. 8,275 (1%9). 6. K. C. Nainan and G. E. Ryschkewitsch, Inorg. Chem. 7, 1316 (1%8). 7. D. L. Reznicek and N. E. Miller, Inorg. Chem. 11,858 (1972). 8. R. L. Amster and R. C. Taylor, Spectrochim. Acta 20, 1487 (196#). 9. P. J. Bratt, K. R. Seddon and I. A. Steer, Inorg. Chim. Acta to be published. 10. J. F. Douglass, J. Am. chem. Soc. 84, 121 (1962). 11. J. N. G. Faulks, N. N. Greenwood and J. H. Morris, J. inorg. nucl. Chem. 29, 329 (1%7). 12. R. C. Taylor and C. L. Cluff, Nature, Lond. 182,390 (1958). 13. P. J. Bratt and M. P. Brown, J. Chem. Soc. Dalton, to be published.