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Far infra-red vapour-phase spectra of some metal acetylacetonates
Spectrochimica Acts, Vol. 26A, pp, 2179 to 2182. Pergamon Press 1970.Printed in Northern Ireland
Far infra-red vapour-phase spectra of some metal
acetylacetonates
J. HAIGH and L. E. SUTTON Physical Chemistry Laboratory, South Parks Road, Oxford
and JOHN CJUMBERLAIN and H. A. GEBBIE* National Physical Laboratory, Tcddington, Middlcscx, (Received7 October1969) Ah&&--Measurements over the range 30-350 cm-l of the vapour-phase SpeCtr8 of Cr(CeH,O,)s, Fe(C,H,0,)4 and Th(C,HrO,), provide support only for the fcaturcs that am common to two previously published accounts based on the use of mulled specimens. Other features reported separately in these accounts arc not reproduced.
FAR infrared spectra of acetylecetonates of transition metals have been reported down to 100 cm-l or lower frequencies by GILLARD etal.[l] and MIKABU et al. [2] who used grating spectrometers for the spectral analysis, and specimens of the solid mulled into paraffin, Nujol or fused polythene. There are contradictions between the results. As part of a study of these complexes, we made measurements on benzene solutions between 20 and 400 cm-l using a Fourier transform spectrometer and were unable to obtain consistent or informative results. The solutions were contained between Rigidex polyethylene windows in cells giving approximately L mm specimen thickness, and we suspected that much of the irreproducible structure observed in the spectra was due to the penetration of solvent and solute into the polythene windows which we had observed on some earlier occasions, and particularly during long runs, to cause swelling. If such a process were to occur during the course of a spectral measurement, the pattern of the spectrum having contributions from the solvent, solute and window materials would change, and a meaningful spectrum would not be obtained. For a grating spectrometer different parts of the spectrum would be separately affected since the spectrum is scsnned in time. However in a Fourier transform spectrometer the effects might be more serious and diflicult to decipher since the spectrum is computed from data obtained from observations on the entire band of transmitted radiation as recorded for the whole course of the run. Slow changes in optical path length in the several media would, therefore, affect the whole derived spectrum in a complicated way. It was not possible to study the effect of changing the solvent, since the only other solvents of high enough transmission were aliphatic hydrocarbons, and the solubility of the metal acetylacetonates in these is small and would not give adequate solute absorption. Accordingly, it was decided to make measurements without solvent, using the vapour of the metal complexes, to ensure that effects due to the absorption of solvent in the cell windows were avoided. The measured spectra would have the extra advantage that possible solvent-solute effects would be eliminated. * Now at National Bureau of Standards, Boulder, Colorado 80301, U.S.A. [l] R. D. GILLARD, H. G. SILVER and J. L. WOOD, Spectrochim. Acta a&63 (1964). [Z] M. MIKABXI, I. NAKAQAWA and T. S~oucm, Qectrochim. Aota %A, 1037 (1967). 2179
2180
J. HAI~H, L. E. SU!JXON,JOHN CKAMBEELAINmd H. A. GEBBIE
The windows were made of Melinex film of thickness 13 pm. These windows were attached with silicone sealing compound to the flanged ends of a 1 m long Quick& glass tube of 50 mm intarnal diameter. This cell was placed between the interferometer and detector components of a Fourier transform in~~e~rne~~ spectrometer [3] of the type developed f&6] at NI’L (and manufactured by Grubb Parsons Ltd., Newcastle-upon-Tyne). The detector was a Golay cell (Unicam Ltd., Cambridge) fitted with a wedged diamond window. The Quiukfit cell was heated by Electrothermal heating tape and lagged with asbestos and glass wool. It was fitted with a side-arm, having a separate heating system, which contained the specimen in a brass mesh basket. The heating for the cell was so arranged that the windows were always about 10°C hotter than the main body of the oell, to prevent formation of a condensed layer of specimen on them. The side-arm was maintained at a lower temperature, so that it was this temperature that determined the vapour pressure of specimen in the tube. Powdered spe~ime~ (s~thesized in ac~rdan~ with estab~h~ [7] procedures and shown to have sharp melting points ; Ck 216-O%, Fe 179-18O*C, Th 171.5Y?) were platted in the sidearm, which was kept at room temperature. Background spectra were recorded with the cell evaouated and heated, and the windows were found to undergo no spectral change during the time necessary for a run (1 hr), The sidearm was then heated to the required temperature and the specimen spectrum obtained. The choice of specimens was limited to three; others initially ohosen were found to be unstable or involatile at the temperatures used. Vapour pressures were in the region l-5 mm Hg, that of the ferric complex being known [8] and the others being assumed to lie in the same region on aocount of the approximate equivalence of the strength of co~s~n~g bands in their spectra. The Xelinex windows which had been exposed to the vapour of the ferric oomplex were examined subsequently and shown not to have acquired any new spectral features. The (unsmoothed) transmission spectra given by the ratio of the spectra obtained with and without the specimen in the cell, are shown in Figs. l-3. Three or four runs were made consecutively with each compound and such sets of measurements were always found to be self-~ona~~nt, thus indicating that the time-de~ndent trouble with the earlier liquid-phase measurements was due to the solution-cell ensemble rather than with the complex molecule or the spectrometric system. It is olear (see Table 1) that only the very strong bands are oommon to all three sets of observations [l, 21. Certain weaker bands reported at lower wave-numbers cannot be observed in the vapour phase. The luminosity and multiplex advantages [3] give Fourier spe~trome~rs a well-known superiority that leads, with careful rise, [3] G. VAXASSEand H. SAKAI, Bog. Opt. 6, 201 (1967). [4] J. CIUXBBBLAIN, A. E. COSTLEYand R. A. GEBBIE,Spwtm~&m. Aota m, 2255 (1967). [5] G. W. CEANTRY, H. A. GEBBIE, R. J. POI?FLWWLL and H. W. THOMPSON,Proc. Roy. Sot. A994, 45 (1968). [S] G. W. CZIANTRY, H. M. EVANS, J. C%AXBBRUIN and H. A. GEBBIZ, Isfrawd Phya. 9, 86 (1969). [7] The preparationswere %&en from 8 series of volumes: f%vrga?k Syntheses. McGraw-Hill (1939ff.). [t3] E. W. EIERQand J. TRUKPER,AnuZ. Chim. Acta 99, 245 (1965).
,3g
353
(a)
I,C
(
o
)
~
~.o~o
~2
!_~_
I
5 0
I00
12
- - - ~ .......... I I 150 200 2SO Wave...num~ (cm-')
I
300
..... t: ....
3SO
J
400
Fig. 1. Transmission spectra of Cr(C6HTOs) s observed a t two v a p o u r pressures corresponding to (a) 186 and (b) 197 °C. The full markers show the features observed here together with their position and estimated strength, the broken markers indi~ t e features indicated b y other workers [1, 2]. 136
233
301
I
t
I
+
i~.o.+ s
0-~--
-
+
:!
31
• SO
I I00
;I 1 I 1 ISO 200 2'50 Wave-number (cm "l)
1 300
___[ 350
._~
Fig. 2. Transmission spectra of Fe(CsH~O2) 4 observed ~t (a) 3.9 a n d (b) 5.0 torr. K e y as in Fig. 1. 2+5 234(~)
50
lO0
150
200
250
300
Wow-humOr (cm") F i g . 3. Tremsmission spect,ra o f Th(C6TT7Og) 4 observed at, t w o v a p o u r pressures
corresponding to (a) 165 a n d (b) 172°C. 1~o other observations are available for comparison. 9181
2182
J. HAIUH, L. E. SVJYON, JOHN CEAIUEXERLAIN and H. A. GEBBIE Table 1. Far infrared features in spectra of metal acetylacetonates
Cr
Fe
Th
139 (m)
This work Other work Ref. [l] Ref. [2]
60 (m)
103 (m)
This work Other work Ref. [l] Ref. [2]
60 (m)
136 (w) 111 (m)
This work
Wave-numbers iu cm-l;
202 (m) 215 (w)
353 (vs) 355 (vs) 354 (vs) 301 (vs) 298 (vs) 298 (vs)
234 (shoulder)
w, weak; m, medium; vs, very strong.
to reliable spectra even when the bands are weak. It is possible, however, that weak bands observed at low frequencies with grating instruments may occasionally be spurious due to low signal-to-noise ratio and the possibility of overlapping orders. The present results suggest that, whatever the reason, mull measurements may give weak features that are unrepresentative of the modes of the complex molecules. It is also possible that lattice vibrations and molecular vibrations may be confused [Q]. Such weak features, should, therefore, only be used cautiously in any normal co-ordinate analysis. [9] M. L. GOOD,CEINU-CEUANCIZAN~,D. W. WERTZaud J. R. DURIO,Spectrochim.Acta %A, 1303 (1969).
Far infra-red vapour-phase spectra of some metal
acetylacetonates
J. HAIGH and L. E. SUTTON Physical Chemistry Laboratory, South Parks Road, Oxford
and JOHN CJUMBERLAIN and H. A. GEBBIE* National Physical Laboratory, Tcddington, Middlcscx, (Received7 October1969) Ah&&--Measurements over the range 30-350 cm-l of the vapour-phase SpeCtr8 of Cr(CeH,O,)s, Fe(C,H,0,)4 and Th(C,HrO,), provide support only for the fcaturcs that am common to two previously published accounts based on the use of mulled specimens. Other features reported separately in these accounts arc not reproduced.
FAR infrared spectra of acetylecetonates of transition metals have been reported down to 100 cm-l or lower frequencies by GILLARD etal.[l] and MIKABU et al. [2] who used grating spectrometers for the spectral analysis, and specimens of the solid mulled into paraffin, Nujol or fused polythene. There are contradictions between the results. As part of a study of these complexes, we made measurements on benzene solutions between 20 and 400 cm-l using a Fourier transform spectrometer and were unable to obtain consistent or informative results. The solutions were contained between Rigidex polyethylene windows in cells giving approximately L mm specimen thickness, and we suspected that much of the irreproducible structure observed in the spectra was due to the penetration of solvent and solute into the polythene windows which we had observed on some earlier occasions, and particularly during long runs, to cause swelling. If such a process were to occur during the course of a spectral measurement, the pattern of the spectrum having contributions from the solvent, solute and window materials would change, and a meaningful spectrum would not be obtained. For a grating spectrometer different parts of the spectrum would be separately affected since the spectrum is scsnned in time. However in a Fourier transform spectrometer the effects might be more serious and diflicult to decipher since the spectrum is computed from data obtained from observations on the entire band of transmitted radiation as recorded for the whole course of the run. Slow changes in optical path length in the several media would, therefore, affect the whole derived spectrum in a complicated way. It was not possible to study the effect of changing the solvent, since the only other solvents of high enough transmission were aliphatic hydrocarbons, and the solubility of the metal acetylacetonates in these is small and would not give adequate solute absorption. Accordingly, it was decided to make measurements without solvent, using the vapour of the metal complexes, to ensure that effects due to the absorption of solvent in the cell windows were avoided. The measured spectra would have the extra advantage that possible solvent-solute effects would be eliminated. * Now at National Bureau of Standards, Boulder, Colorado 80301, U.S.A. [l] R. D. GILLARD, H. G. SILVER and J. L. WOOD, Spectrochim. Acta a&63 (1964). [Z] M. MIKABXI, I. NAKAQAWA and T. S~oucm, Qectrochim. Aota %A, 1037 (1967). 2179
2180
J. HAI~H, L. E. SU!JXON,JOHN CKAMBEELAINmd H. A. GEBBIE
The windows were made of Melinex film of thickness 13 pm. These windows were attached with silicone sealing compound to the flanged ends of a 1 m long Quick& glass tube of 50 mm intarnal diameter. This cell was placed between the interferometer and detector components of a Fourier transform in~~e~rne~~ spectrometer [3] of the type developed f&6] at NI’L (and manufactured by Grubb Parsons Ltd., Newcastle-upon-Tyne). The detector was a Golay cell (Unicam Ltd., Cambridge) fitted with a wedged diamond window. The Quiukfit cell was heated by Electrothermal heating tape and lagged with asbestos and glass wool. It was fitted with a side-arm, having a separate heating system, which contained the specimen in a brass mesh basket. The heating for the cell was so arranged that the windows were always about 10°C hotter than the main body of the oell, to prevent formation of a condensed layer of specimen on them. The side-arm was maintained at a lower temperature, so that it was this temperature that determined the vapour pressure of specimen in the tube. Powdered spe~ime~ (s~thesized in ac~rdan~ with estab~h~ [7] procedures and shown to have sharp melting points ; Ck 216-O%, Fe 179-18O*C, Th 171.5Y?) were platted in the sidearm, which was kept at room temperature. Background spectra were recorded with the cell evaouated and heated, and the windows were found to undergo no spectral change during the time necessary for a run (1 hr), The sidearm was then heated to the required temperature and the specimen spectrum obtained. The choice of specimens was limited to three; others initially ohosen were found to be unstable or involatile at the temperatures used. Vapour pressures were in the region l-5 mm Hg, that of the ferric complex being known [8] and the others being assumed to lie in the same region on aocount of the approximate equivalence of the strength of co~s~n~g bands in their spectra. The Xelinex windows which had been exposed to the vapour of the ferric oomplex were examined subsequently and shown not to have acquired any new spectral features. The (unsmoothed) transmission spectra given by the ratio of the spectra obtained with and without the specimen in the cell, are shown in Figs. l-3. Three or four runs were made consecutively with each compound and such sets of measurements were always found to be self-~ona~~nt, thus indicating that the time-de~ndent trouble with the earlier liquid-phase measurements was due to the solution-cell ensemble rather than with the complex molecule or the spectrometric system. It is olear (see Table 1) that only the very strong bands are oommon to all three sets of observations [l, 21. Certain weaker bands reported at lower wave-numbers cannot be observed in the vapour phase. The luminosity and multiplex advantages [3] give Fourier spe~trome~rs a well-known superiority that leads, with careful rise, [3] G. VAXASSEand H. SAKAI, Bog. Opt. 6, 201 (1967). [4] J. CIUXBBBLAIN, A. E. COSTLEYand R. A. GEBBIE,Spwtm~&m. Aota m, 2255 (1967). [5] G. W. CEANTRY, H. A. GEBBIE, R. J. POI?FLWWLL and H. W. THOMPSON,Proc. Roy. Sot. A994, 45 (1968). [S] G. W. CZIANTRY, H. M. EVANS, J. C%AXBBRUIN and H. A. GEBBIZ, Isfrawd Phya. 9, 86 (1969). [7] The preparationswere %&en from 8 series of volumes: f%vrga?k Syntheses. McGraw-Hill (1939ff.). [t3] E. W. EIERQand J. TRUKPER,AnuZ. Chim. Acta 99, 245 (1965).
,3g
353
(a)
I,C
(
o
)
~
~.o~o
~2
!_~_
I
5 0
I00
12
- - - ~ .......... I I 150 200 2SO Wave...num~ (cm-')
I
300
..... t: ....
3SO
J
400
Fig. 1. Transmission spectra of Cr(C6HTOs) s observed a t two v a p o u r pressures corresponding to (a) 186 and (b) 197 °C. The full markers show the features observed here together with their position and estimated strength, the broken markers indi~ t e features indicated b y other workers [1, 2]. 136
233
301
I
t
I
+
i~.o.+ s
0-~--
-
+
:!
31
• SO
I I00
;I 1 I 1 ISO 200 2'50 Wave-number (cm "l)
1 300
___[ 350
._~
Fig. 2. Transmission spectra of Fe(CsH~O2) 4 observed ~t (a) 3.9 a n d (b) 5.0 torr. K e y as in Fig. 1. 2+5 234(~)
50
lO0
150
200
250
300
Wow-humOr (cm") F i g . 3. Tremsmission spect,ra o f Th(C6TT7Og) 4 observed at, t w o v a p o u r pressures
corresponding to (a) 165 a n d (b) 172°C. 1~o other observations are available for comparison. 9181
2182
J. HAIUH, L. E. SVJYON, JOHN CEAIUEXERLAIN and H. A. GEBBIE Table 1. Far infrared features in spectra of metal acetylacetonates
Cr
Fe
Th
139 (m)
This work Other work Ref. [l] Ref. [2]
60 (m)
103 (m)
This work Other work Ref. [l] Ref. [2]
60 (m)
136 (w) 111 (m)
This work
Wave-numbers iu cm-l;
202 (m) 215 (w)
353 (vs) 355 (vs) 354 (vs) 301 (vs) 298 (vs) 298 (vs)
234 (shoulder)
w, weak; m, medium; vs, very strong.
to reliable spectra even when the bands are weak. It is possible, however, that weak bands observed at low frequencies with grating instruments may occasionally be spurious due to low signal-to-noise ratio and the possibility of overlapping orders. The present results suggest that, whatever the reason, mull measurements may give weak features that are unrepresentative of the modes of the complex molecules. It is also possible that lattice vibrations and molecular vibrations may be confused [Q]. Such weak features, should, therefore, only be used cautiously in any normal co-ordinate analysis. [9] M. L. GOOD,CEINU-CEUANCIZAN~,D. W. WERTZaud J. R. DURIO,Spectrochim.Acta %A, 1303 (1969).