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Spectroscopic observations on germyl isocyanate
SpeotmohimlcaActs.
Vol.268,
pp. 87S to 577.
Pergamon m
1970. Printedin NorthernIreland
Spectroscopicobservations on germyl isocyanate K. M. &UKAY and S. R. STOB~T Department of Inoqenic Chemistry, The University, Nottingham (Rec&v~ 22 lwwiKwy 1969) AbstnrCtMagnetic resonance measurements on 1H and 14N in GesNCO show no evidenoe for the isomer GeqOCN. The Raman and solid state infrared speotra support the published evidence for a non-linear skeleton and modify the assignment of some of the fundamentals.
INTRODUCTION SPECTEOSCOPIC studies of germyl isocyanate by GRIFFITES[ 1,2] indicate a nonlinear heavy atom skeleton similar to those reported recently for GeH,NCS [3] snd GeH,N, [a]. In the course of his essignment for GeH,NCO [2], Grifliths suggests thst the medium-strong band at 2374 cm-l (lying above the very strong NC0 stretch at 2271 cm-l) is due to the normal cyanate, GeH,OCN. Very weak bands at 1284 cm-1 and 394 cm-1 were also tentatively assigned as GeH,OCN modes. Similar bands have often been thought to indic&e isonitrile in cyanides and both normal and iso- forms in cyantes and thiocyanates of Group IV elements. However, the slternative assignment of suah a band to an overtone in Fermi resonance with the fundamental was proposed ht in 1937 for alkyl isothiocyanates [5] and has more recently been made for alkyl isocyanstes [6], for chloro- and methylsilylisocyanstes [7] and for GeH,NCS [8]. We have looked for independent evidence for the existence of G-eH,OCN in GeH,NCO from the lH and l*N NMR spectra of a sample prepared from germyl bromide and silver cyanate, the method used by GRIFFITE~[l, 21. The lH NMR spectrum of GeH,NCS prepared by the silver salt method has been reported to show only one peak at 4.827 (wrongly given as 6.18~ in [3]) nor was there any indication of a second GeH, resonance in species obtained from exchange reactions between GeHsF and SiH,NCO or SiH,NCS [8]. We have also measured the Raman and solid-state infrared spectra of germyl isocyanate which support the conclusions from the gas-phase infrared spectrum [2] about the non-linear skeleton but which lead to some mod&&ions in the published assignment, [I] J. E. GRIB~ITHS and A. L. BEA~E, Chem.Cvnamun.437 (1961). [2] J. E. G8, J. Ch.em.Phy8.48, 278 (1968). [3] G. DAYIDSON, L. A. WOODWARD, K. M. MA-Y and P. ROBINSON, Spectrochim. Acta aSA, 2383 (1967). [4] 5. CRADOCEand E. A. V. EBBWORTH,J. C&m. Sot. A 1420 (1968). [6] R. M. BADUER,J. Chem. Phys. 6, 178 (1937). [6] N. 8. HAM and J. B. WIIUS, Spctvochim. Acta 16, 279 (1960). [7] D. F. Kosm, fipectro&im. Acta HA, 396 (1968); J. GOWEAU, H. HENBAUE, D. PAVLIN and I. WIDMAIER, 2. Anwg. Al&em. C&m. 800,194 (1969). [S] 8. CRADOCKend E. A. V. EBSWORTH,J. Chem. Sot. A 1226 (1967). 373
K. M. MACKAY and S. R. STOBART
374
EXPERIMENT&
GeH,Br was streamed over dry silver cyanate to give GeHaNCO [9]. The product appeared as a single peak on a vapour phase chromatogram on a silicone active phase. The measured vapour pressures agreed with literature values [9]: at 0*3’C, found 29.06 mm (lit. 28.25 mm); at 16*8”C, found 69.73 mm (69.82 mm). The gas phase infrared spectrum was identical with that reported [2]. Infrared spectra were measured on a Perk&Elmer 521 grating spectrometer and Raman spectra using a Cary 81 instrument with laser excitation on the neat liquid in a capillary cell. NMR spectra were measured on benzene and cy&hexane solutions on a Varian HA 100 spectrometer. Proton measurements were run at 100 MHz, the 14Nstudies at 7.2 MHz and calibrated by replacement using saturated NH4N0, solution. RESULTS
Table 1 shows the NMR results. Table 1. NMR dattta Chemicsl shift
Solvent ‘H resonance
GeHsNCO
%Hl, C&b2
14H rcsonsnce*
CHsNCO CaHsN~ MQiNCO HsGeNCO EtsGeNCO Pr,GeNCO EtOCN
* Upfield shifts from 14N0,-in
(16%)
Wf43
(20%)
wT3
(10%)
neat nest
WI
f&J&
(16%)
CA3
(20%)
wtl
(20%)
WTI
Et,0
4.98, 4.967
PI
(20%)
(10%)
WI
1101
360 343 340 361 366 363 361 220
6.607 f 2 ppm & 2 ppm f 1 ppm f 2 ppm f 2 ppm f 2 ppm f 2 ppm f 6 ppm
aqueous NH4N0,
The lH NMR spectrum shows a single resonance in cyclohexane solution at a chemical shift identical to that reported earlier for a sample prepared by a different route [8]. A single peak was also found for a benzene solution with a rather large solvent shift. A second GeH, species would have been detected at a concentration of O-050.1% of the GeH,NCO sample unless there was a fast exchange in solution between GeH,NCO and GeH,OCN. This would be difficult to detect in the lH NMR spectrum as O-GeH, and N-GeH, resonances probably lie in overlapping regions of the spectrum. However, it has been shown that the 14Nresonances of alkyl cyanates are over 100 ppm to lower field than those of alkyl isocyanates [lo]. As the 14N resonance of GeHaNCO lies close to those of isocyanates such as CHaNCO [lo] the concentration of germyl cyanate in an exchange process must be low. The 14N shifts of the trialkyls
confirm that heavier element isocyanates
resonate
in the same region.
[9] T. N. SRIVASTAVA, J. E. GRIFI~THS and M. ONYSZCHUE, Can. J. Chem. 40, 739 (1962). [lo] F. CHEW,W. DERBYSHIRE snd N. LOGAN,to be published.
Spectroscopic observations on germyl isocyanate
376
There is thus no evidence from the NMR measurements of a significant concentration of GeH,OCN in the GeH,NCO prepared by this method and the infrared bands are more likely to be due to combinations or overtones. Table 2 shows the numbering and Table 3 the Raman spectrum of liquid GeHaNCO and the infrared spectrum of the solid, together with the infrared of the gas which is essentially the same as that reported by GRIFFITHS[2]. The most significant observation is that of two polarised Raman bands in the GeH, deformation region near 860 cm-l. A molecule with a non-linear GeNCO skeleton has the two polarised, a’, GeH, bending modes +, and Yewhile a C,, molecule (GeNC = 180’) would show only one polarised band. Although the observed bands overlap, both components are distinctly polarised with a depolarisation ratio about O-6for the component at 852 cm-l, assigned as the symmetric mode Q, and a ratio about O-7 for the 867 cm-l band vs. These ratios are only approximate as no allowance for the depolarised a” band, Q, is made. If this is fairly strong, as in the spectrum of GeHaN, [a], these depolarisation ratios would be lower. The remaining Raman observations confirm the assignments made from the gas phase spectrum, especially of the NC0 stretch at 1403 cm-l and the GeN stretch at 459 cm-l which are both strongly polarised. A careful search for low frequency skeletal modes was made but none were observed. Table 2. Description of fundrunentJs symmetry symmetry a’
class a”
Vl v2
51
v3 v4 vs
v12
vi3 v7
v13
v3
VI4
vo VlO
VlS
for GeH,NCO assuming C,
Approximate
description
NC0 pseudo antisymmetric stretch GeH, asymmetric stretch (degenerate in C3,) GeH3 symmetric stretch NC0 pseudo-symmetric stretch GeH, asymmetric deformation (degenerate in C3,) GeH, symmetric deform&ion GeH, rocks (degenerate in C3,) NC0 bend (degenerate in C3,) GeN stretch GeNC bend and GeH3 torsion (degenerate in C,,)
The infrared spectrum of the solid shows three components in the GeH, stretching and deformation regions as expected for a C, molecule, though the e modes of a C,, molecule could be split because of low site symmetry in the solid. The NC0 stretch at 1390 cm-l shows a second component and a shift to lower frequency: a similar effect was observed for the N3 stretch in GeH,N, [a]. The gas phase band at 650 cm-l was assigned by GRIFFITIIS[2] as the GeH, rook and its splitting was part of the evidence for a C, structure. Skeletal deformations were assigned at 483 cm-l [2] overlapping the GeN stretch. In the solid state, however, four strong components occur in the 600-700 cm-l region and these can be explained only if the GeH, rocks y7 and y13and the skeletal deformations ye and vr4
376
K. 111.MAOKAY
and S. R. STOBART
occur in this region and have well-separated a’ and a” components. This re-assignment of the skeletal deformations to the 660 cm-l region is in accord with the assignment in CH8NC0 [ll] and in germyl azide [4] where this point about germyl isocyauate is also made. The band at 483 om-l is then to be regarded as part of a hybrid contour for the GeN stretch, ye, as found in the case of the NC0 stretch. V*shows a Table 3. Vibrational
Raman liquid (cm-‘)
2123, Pol. “S
spectra
solid (om-I) 3620 w 3000 VW 2863 VW 2790 VW 2676 w 2370 VW 2260 ““8 2190 w 2167 YB 2148 v8 2127 “B
3660 w
y1+ VI
2766 w 2360 m 2266 vva
VI + v1or Vl
y1+ vs
2128 8 2124 vsR 2113I P
1686 VW 1403, Pal. B
867. Pol. B 862. Pol. 8
660, mw. (dP)
1419 w
1390 m 1380 w1 1200 VIV 1066 VW 870 v8 861 vs 860 vs
2 x vu vo+ v1ot *8 873 B 866 R 867I vB P 672 sh 660 m 626 ah
696 8 660 8 632 B 697 s
493 B 469, Pal. m
*4 +
vu
%a.% VI
vv vo.%a*v11 VP
413 “8 432 8 >
very marked frequency shift from gas to liquid to solid, similar to those observed for GeH,NCS [3] and GeH,N, [4] and two components appear in the solid state spectrum. This splitting may be due to the presence of more than one molecule in the unit cell. Combination bands at 2360 and 1055 cm-l may involve the low frequency deformation about 116 cm-l reported by GRIFFITHS [2]. D~s~uss~o~ No positive spectroscopic evidence was found for the presence of GeH,OCN in GeH,NCO. The vibrational spectrum is consistent with a non-linear Ge-NC0 skeleton although the evidence from the splitting of the GeH, rock in the gas phase spectrum [2] is invalidated by the reassignment of skeletal deformations to the 660 cm-l region. On the other hand, the two polarised GeH, deformations provide evidence additional to that deduced from the rotational 6ne structure [Z]. The spectra of GeH,NCO and GeH,N, show a number of close parallels, especially among the heavy atom stretching and deformation modes. As germyl isocyanate and germyl isothiocyanate have non-linear M-N-(%X R. N. [ 1l] R. P. HIRSCH~~~~LNN,
KNISELEY
rendV. A.
FASSEL,
Spect~ocoohim.Aota
21,X25 (1965).
Spwtroscopic observations on gmmyl isooyyanate
377
skeletons, in contrast to their SiH, analogues [12], the clear examples of structure changes aaoribable to 7rbonding are limited to molecules with SiH, bonded to first row elements. There is some indication of rather large GeNCX bond angles but these require verification by more direct methods. Ackmu&dgeme&--We thank the S.R.C. for a studentship (S.R.S.) end Dr. LOUAN and Mr. CHEWfor informing us of their FN results prior to publication. [12] M. L. GERRY,J. C. THOMPSON and T. M. SUUDEN,Nature $X1,1284 (1966); D. R. JENKINS, R. KEWLEY and T. M. SUUDEN,Tram. Faraday Soo. 58, 1284 (1902).
Vol.268,
pp. 87S to 577.
Pergamon m
1970. Printedin NorthernIreland
Spectroscopicobservations on germyl isocyanate K. M. &UKAY and S. R. STOB~T Department of Inoqenic Chemistry, The University, Nottingham (Rec&v~ 22 lwwiKwy 1969) AbstnrCtMagnetic resonance measurements on 1H and 14N in GesNCO show no evidenoe for the isomer GeqOCN. The Raman and solid state infrared speotra support the published evidence for a non-linear skeleton and modify the assignment of some of the fundamentals.
INTRODUCTION SPECTEOSCOPIC studies of germyl isocyanate by GRIFFITES[ 1,2] indicate a nonlinear heavy atom skeleton similar to those reported recently for GeH,NCS [3] snd GeH,N, [a]. In the course of his essignment for GeH,NCO [2], Grifliths suggests thst the medium-strong band at 2374 cm-l (lying above the very strong NC0 stretch at 2271 cm-l) is due to the normal cyanate, GeH,OCN. Very weak bands at 1284 cm-1 and 394 cm-1 were also tentatively assigned as GeH,OCN modes. Similar bands have often been thought to indic&e isonitrile in cyanides and both normal and iso- forms in cyantes and thiocyanates of Group IV elements. However, the slternative assignment of suah a band to an overtone in Fermi resonance with the fundamental was proposed ht in 1937 for alkyl isothiocyanates [5] and has more recently been made for alkyl isocyanstes [6], for chloro- and methylsilylisocyanstes [7] and for GeH,NCS [8]. We have looked for independent evidence for the existence of G-eH,OCN in GeH,NCO from the lH and l*N NMR spectra of a sample prepared from germyl bromide and silver cyanate, the method used by GRIFFITE~[l, 21. The lH NMR spectrum of GeH,NCS prepared by the silver salt method has been reported to show only one peak at 4.827 (wrongly given as 6.18~ in [3]) nor was there any indication of a second GeH, resonance in species obtained from exchange reactions between GeHsF and SiH,NCO or SiH,NCS [8]. We have also measured the Raman and solid-state infrared spectra of germyl isocyanate which support the conclusions from the gas-phase infrared spectrum [2] about the non-linear skeleton but which lead to some mod&&ions in the published assignment, [I] J. E. GRIB~ITHS and A. L. BEA~E, Chem.Cvnamun.437 (1961). [2] J. E. G8, J. Ch.em.Phy8.48, 278 (1968). [3] G. DAYIDSON, L. A. WOODWARD, K. M. MA-Y and P. ROBINSON, Spectrochim. Acta aSA, 2383 (1967). [4] 5. CRADOCEand E. A. V. EBBWORTH,J. C&m. Sot. A 1420 (1968). [6] R. M. BADUER,J. Chem. Phys. 6, 178 (1937). [6] N. 8. HAM and J. B. WIIUS, Spctvochim. Acta 16, 279 (1960). [7] D. F. Kosm, fipectro&im. Acta HA, 396 (1968); J. GOWEAU, H. HENBAUE, D. PAVLIN and I. WIDMAIER, 2. Anwg. Al&em. C&m. 800,194 (1969). [S] 8. CRADOCKend E. A. V. EBSWORTH,J. Chem. Sot. A 1226 (1967). 373
K. M. MACKAY and S. R. STOBART
374
EXPERIMENT&
GeH,Br was streamed over dry silver cyanate to give GeHaNCO [9]. The product appeared as a single peak on a vapour phase chromatogram on a silicone active phase. The measured vapour pressures agreed with literature values [9]: at 0*3’C, found 29.06 mm (lit. 28.25 mm); at 16*8”C, found 69.73 mm (69.82 mm). The gas phase infrared spectrum was identical with that reported [2]. Infrared spectra were measured on a Perk&Elmer 521 grating spectrometer and Raman spectra using a Cary 81 instrument with laser excitation on the neat liquid in a capillary cell. NMR spectra were measured on benzene and cy&hexane solutions on a Varian HA 100 spectrometer. Proton measurements were run at 100 MHz, the 14Nstudies at 7.2 MHz and calibrated by replacement using saturated NH4N0, solution. RESULTS
Table 1 shows the NMR results. Table 1. NMR dattta Chemicsl shift
Solvent ‘H resonance
GeHsNCO
%Hl, C&b2
14H rcsonsnce*
CHsNCO CaHsN~ MQiNCO HsGeNCO EtsGeNCO Pr,GeNCO EtOCN
* Upfield shifts from 14N0,-in
(16%)
Wf43
(20%)
wT3
(10%)
neat nest
WI
f&J&
(16%)
CA3
(20%)
wtl
(20%)
WTI
Et,0
4.98, 4.967
PI
(20%)
(10%)
WI
1101
360 343 340 361 366 363 361 220
6.607 f 2 ppm & 2 ppm f 1 ppm f 2 ppm f 2 ppm f 2 ppm f 2 ppm f 6 ppm
aqueous NH4N0,
The lH NMR spectrum shows a single resonance in cyclohexane solution at a chemical shift identical to that reported earlier for a sample prepared by a different route [8]. A single peak was also found for a benzene solution with a rather large solvent shift. A second GeH, species would have been detected at a concentration of O-050.1% of the GeH,NCO sample unless there was a fast exchange in solution between GeH,NCO and GeH,OCN. This would be difficult to detect in the lH NMR spectrum as O-GeH, and N-GeH, resonances probably lie in overlapping regions of the spectrum. However, it has been shown that the 14Nresonances of alkyl cyanates are over 100 ppm to lower field than those of alkyl isocyanates [lo]. As the 14N resonance of GeHaNCO lies close to those of isocyanates such as CHaNCO [lo] the concentration of germyl cyanate in an exchange process must be low. The 14N shifts of the trialkyls
confirm that heavier element isocyanates
resonate
in the same region.
[9] T. N. SRIVASTAVA, J. E. GRIFI~THS and M. ONYSZCHUE, Can. J. Chem. 40, 739 (1962). [lo] F. CHEW,W. DERBYSHIRE snd N. LOGAN,to be published.
Spectroscopic observations on germyl isocyanate
376
There is thus no evidence from the NMR measurements of a significant concentration of GeH,OCN in the GeH,NCO prepared by this method and the infrared bands are more likely to be due to combinations or overtones. Table 2 shows the numbering and Table 3 the Raman spectrum of liquid GeHaNCO and the infrared spectrum of the solid, together with the infrared of the gas which is essentially the same as that reported by GRIFFITHS[2]. The most significant observation is that of two polarised Raman bands in the GeH, deformation region near 860 cm-l. A molecule with a non-linear GeNCO skeleton has the two polarised, a’, GeH, bending modes +, and Yewhile a C,, molecule (GeNC = 180’) would show only one polarised band. Although the observed bands overlap, both components are distinctly polarised with a depolarisation ratio about O-6for the component at 852 cm-l, assigned as the symmetric mode Q, and a ratio about O-7 for the 867 cm-l band vs. These ratios are only approximate as no allowance for the depolarised a” band, Q, is made. If this is fairly strong, as in the spectrum of GeHaN, [a], these depolarisation ratios would be lower. The remaining Raman observations confirm the assignments made from the gas phase spectrum, especially of the NC0 stretch at 1403 cm-l and the GeN stretch at 459 cm-l which are both strongly polarised. A careful search for low frequency skeletal modes was made but none were observed. Table 2. Description of fundrunentJs symmetry symmetry a’
class a”
Vl v2
51
v3 v4 vs
v12
vi3 v7
v13
v3
VI4
vo VlO
VlS
for GeH,NCO assuming C,
Approximate
description
NC0 pseudo antisymmetric stretch GeH, asymmetric stretch (degenerate in C3,) GeH3 symmetric stretch NC0 pseudo-symmetric stretch GeH, asymmetric deformation (degenerate in C3,) GeH, symmetric deform&ion GeH, rocks (degenerate in C3,) NC0 bend (degenerate in C3,) GeN stretch GeNC bend and GeH3 torsion (degenerate in C,,)
The infrared spectrum of the solid shows three components in the GeH, stretching and deformation regions as expected for a C, molecule, though the e modes of a C,, molecule could be split because of low site symmetry in the solid. The NC0 stretch at 1390 cm-l shows a second component and a shift to lower frequency: a similar effect was observed for the N3 stretch in GeH,N, [a]. The gas phase band at 650 cm-l was assigned by GRIFFITIIS[2] as the GeH, rook and its splitting was part of the evidence for a C, structure. Skeletal deformations were assigned at 483 cm-l [2] overlapping the GeN stretch. In the solid state, however, four strong components occur in the 600-700 cm-l region and these can be explained only if the GeH, rocks y7 and y13and the skeletal deformations ye and vr4
376
K. 111.MAOKAY
and S. R. STOBART
occur in this region and have well-separated a’ and a” components. This re-assignment of the skeletal deformations to the 660 cm-l region is in accord with the assignment in CH8NC0 [ll] and in germyl azide [4] where this point about germyl isocyauate is also made. The band at 483 om-l is then to be regarded as part of a hybrid contour for the GeN stretch, ye, as found in the case of the NC0 stretch. V*shows a Table 3. Vibrational
Raman liquid (cm-‘)
2123, Pol. “S
spectra
solid (om-I) 3620 w 3000 VW 2863 VW 2790 VW 2676 w 2370 VW 2260 ““8 2190 w 2167 YB 2148 v8 2127 “B
3660 w
y1+ VI
2766 w 2360 m 2266 vva
VI + v1or Vl
y1+ vs
2128 8 2124 vsR 2113I P
1686 VW 1403, Pal. B
867. Pol. B 862. Pol. 8
660, mw. (dP)
1419 w
1390 m 1380 w1 1200 VIV 1066 VW 870 v8 861 vs 860 vs
2 x vu vo+ v1ot *8 873 B 866 R 867I vB P 672 sh 660 m 626 ah
696 8 660 8 632 B 697 s
493 B 469, Pal. m
*4 +
vu
%a.% VI
vv vo.%a*v11 VP
413 “8 432 8 >
very marked frequency shift from gas to liquid to solid, similar to those observed for GeH,NCS [3] and GeH,N, [4] and two components appear in the solid state spectrum. This splitting may be due to the presence of more than one molecule in the unit cell. Combination bands at 2360 and 1055 cm-l may involve the low frequency deformation about 116 cm-l reported by GRIFFITHS [2]. D~s~uss~o~ No positive spectroscopic evidence was found for the presence of GeH,OCN in GeH,NCO. The vibrational spectrum is consistent with a non-linear Ge-NC0 skeleton although the evidence from the splitting of the GeH, rock in the gas phase spectrum [2] is invalidated by the reassignment of skeletal deformations to the 660 cm-l region. On the other hand, the two polarised GeH, deformations provide evidence additional to that deduced from the rotational 6ne structure [Z]. The spectra of GeH,NCO and GeH,N, show a number of close parallels, especially among the heavy atom stretching and deformation modes. As germyl isocyanate and germyl isothiocyanate have non-linear M-N-(%X R. N. [ 1l] R. P. HIRSCH~~~~LNN,
KNISELEY
rendV. A.
FASSEL,
Spect~ocoohim.Aota
21,X25 (1965).
Spwtroscopic observations on gmmyl isooyyanate
377
skeletons, in contrast to their SiH, analogues [12], the clear examples of structure changes aaoribable to 7rbonding are limited to molecules with SiH, bonded to first row elements. There is some indication of rather large GeNCX bond angles but these require verification by more direct methods. Ackmu&dgeme&--We thank the S.R.C. for a studentship (S.R.S.) end Dr. LOUAN and Mr. CHEWfor informing us of their FN results prior to publication. [12] M. L. GERRY,J. C. THOMPSON and T. M. SUUDEN,Nature $X1,1284 (1966); D. R. JENKINS, R. KEWLEY and T. M. SUUDEN,Tram. Faraday Soo. 58, 1284 (1902).