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Vibrational spectra and rotational barriers of methyl titanium halides CH3TiX3 and CD3TiX3 (X = Cl, Br, I)
~~~r~l of molecule Sfrucfure, 66 (2960) 111-115 Elsevier Scientific Publishing Company, Amsterdam
-
Printed in The Netherlands
ORATIONS SPECTRA AND ROTATIONS BARRIERS OF’ METHYL TITANIUM HALIDES CH3’I’iXs AND CD3TiX3 (X =L:Cl, Br, I)
L. BENCIVENNI, Istituto
di Chimica
A. FARlNA, Fisica,
(Received 5 December
S. NUNZIANTE
University
di Roma,
CESARO, 00185
11. TE%HIL
and M. SPOLITI
Rome ~~~~~y~
1979)
ABSTRACT The IR and Raman spectra of gaseous and solid CH,TiX, and CD,TiX, species (X = Cl, Br, I) are reported. The gas phase spectra have been recorded between 4000 and 20 cm-’ at pressures of 1 atm and 4 atm at 350 K and the Baman spectra of the solid phase recorded at 4.2 K. Internal rotation barriers and thermodynamic functions have been calculated.
INTRODUCTION
The vibrational spectra of methyl germanes have been thoroughly studied by Durig et al. [l. ] and the relative methyl torsional barriers calculated. In a recent paper 12 J we compared the spectra of cyclopentadienyl titanium trichloride [ 31 with those of the corresponding cydopentadienyl germane. The conclusions drawn were that the barriers are independent of the metal and halogen atoms, within the limits of experiment& error. To our knowledge there are no experimental data on methyl titanium trihalides. Therefore we undertook this work in order to assign the vibrational spectra of the methyl titanium trihalides and to check whether the conclusions on the cyclopentadienyl compounds hold for these systems as well. EXPERIMENTAL
The IR spectra were scanned between 20 and 4000 cm-l with a PerkinElmer 180 IR grating spectrophotometer, purged with dry nitrogen. Raman spectra were run using a Cary Raman spectrophotome~r model 81 equipped with a He-Ne laser as exciting source. Resistively heated stainless steel cells (30 cm pathlength) were employed to record the spectra of the gaseous species at 350 K. Argon at 1 atm was used as a diffusion barrier and to prevent decomposition of the samples. High pressure spectroscopic cells were used for scanning Raman spectra of the gaseous species in order to reveal forbidden absorptions and increase their intensities. Raman spectra of the solid compo~ds were run at 4.2 K employ~g suitable cryogenic apparatus.
OOZE-2860~80~000~000~$02.25
0 A.980 Elsevier Scientific Publishing
Company
112 RESULTS
AND
Vibrational
DISCUSSION
assignment
CH3TiX3 species belong to the CSV point group both in the staggered or in the eclipsed configurations. The twelve fundamental vibrations consist of five modes of Al symmetry, one IR and Raman inactive mode of A2 symmetry, and six of doubly degenerate E symmetry. According to the selection rules of CSV point group symmetry the A, and E vibrations are active both in the IR and Raman spectra. Activity considerations, isotopic shifts, band intensities and previous results [l, 4, 51 are used here to assign the observed features. The IR and Raman spectra of gaseous CH, TiX, species are shown in Figs. 1 and 2 respectively and the assignment is reported in Table 1.
3100 a00
1450
1000
500
50
cm-
Fig. 1. IR spectra
I_____-
of gaseous
._I
CH,TiX,
species:
(a) X = Ci; (b) X = Br; (c) X = I.
,
--
1450
50 cm-l
Fig. 2. Raman
spectra
of the gaseous
CH,TiX,
species:
(a) X =
Cl; (b) X = Br; (C) X = 1.
113 TABLE
1
Vibrational assignment of the fundamental vibrations in the CH,TiX,
and CD,TiX,
CH,TiCI,
CD,TiI,
CD,TiCl,
CH,TiBr,
CD,TiBr,
CH,TiI,
IR
R
IR
R
IR
R
IR
R
IR
2948
2943
2150 973 602 390 145 114= 2252 1040 635 445 178 150
2935
1259 652 393 148 160a 3000 1418 823 451 189 152
2154 973 600 390 142
2930
1254 648 391 145
1242 621 303 123
1244 619 305 125 152= 3008 1406 820 351 168 197
2136 964 575 300 120
2136 968 579 301 122 108a 2257 1030 630 350 165 103
2925 1236 602 208 98
3004 1421 826 448 190 155
2255 1038 636 444 180 151
3010 1409 821 355 170 105
2260 1030 632 351 164 103
3009 1396 818 264 151 70
R 2925
1238 605 210 98 142a 3010 1400 816 268 153 71
Assignment
IR
R
2124 960 565 206 93
2121 963 566 208 95 101a 2258 1020 629 266 143 69
2260 1019 630 263 145 69
systems
A,
v,CH
A, E
%CH, us Ti-42 v, Ti-X 6, Ti-x, torsion v,CH 6, CH, PCH, IJ, Ti-x 6, Ti-X p Ti-X,
=Observed at 4 atm.
Internal rotation
barriers
The observed Raman spectra (see Fig. 2) do not show evidence of bands which can be reasonably attributed to the torsional modes (A2 species), forbidden in both the IR and Raman spectra. These absorptions are expected between 140-150 cm-’ if the threefold rotational barriers 1.10 and 1.45 kcal mol-’ of the systems CH,GeC13 [ 51 and CH3Ge13 [l] are assumed. The F terms to be used in this rough calculation can be estimated by taking each bond length as the sum of the covalent radii of the linked atoms and tetrahedral angles. Gas phase Raman spectra however often show torsional overtones [6 3. In the present case one would expect to observe these transitions around 300 cm-‘. The present Raman spectra do in fact show feeble absorptions at 313, 298 and 278 cm-l for CH3TiC13, CH,TiBr, and CHJTiIj respectively. These absorptions can be tentatively assigned to the torsional overtones 2 + 0. This hypothesis is strengthened by the observation in the Raman spectra of the corresponding deuterated species in which the three absorptions just mentioned are shifted to 221, 212 and 197 cm-l, respectively. In Fig. 3 the Raman spectra of the gaseous methyl titanium halides are reported. Week Raman shifts are observed at 160,152 and 142 cm-l for CH3TiC13, CH3TiBrJ and CHJTi13 respectively and at 114, 108 and 101 cm-l for the deuterated samples. The height of the barrier restricting the rotation in the gaseous CH3TiX3 molecules is evaluated according to the Durig treatment for the single-top systems [6]. The results of this calculation are summarized in Table 2. The observed trend and the magnitude of the calculated barriers are in good agreement with the conclusions drawn for analogous systems [l, 5,7], including the consideration that these potential barriers depend almost exclusively on the nature of the M-CH3 bond.
114
175
100 cm-’
Fig. 3. High pressure gas phase Raman spectra (100 - 175 cm-l ) of the CH,TiX, line) and CD,TiX, (dotted line) species: (a) X = Cl; (b) X = Br; (c) X = I.
TABLE Torsional
2 constants
Constant
in the gaseous
CH,TiCI,
Gas phase V (kcal mol-’
)
F (cm-’ ) A2 (cm-‘) k (mdyn A-’ ) So lid phase V (kcal mol-’ F (cm-’ ) A 2 (cm-’ )
k (mdyn
(solid
A-’ )
)
and solid CH,TiX,
CD,TiCI,
1.5 -c 0.1 a 5.4 2.7 160 + 1 1142 1 4.7 x lo-*
1.7 2 0.1 a 5.4 2.7 170 + 1 121 f 1 5.3 x 1o-2
and CD,TiX,
species
CH,TiBr,
CD,TiBr,
C!H,TiI,
CD,TiI,
1.4 * 0.1 5.2 152 _c 1 4.4 x lo-*
a
1.3, f 0.1 4.7 142 r 1 4.2 x 1o-2
a
1.6iO.l 4.7 153 2 1 4.9 x 1o-2
=
1-6 + 0.1 5.2 164 + 1 5.1 x lo-2
2.6 108 f 1
a 2.6 1142 1
aThe reported errors are estimated taking into account the frequency ?l cm-’ and the evaluation of the geometrical parameters.
uncertainty
2.4
101 + 1
2-4 108 -c 1
of
Raman spectra of crystalline CH3TiX3 species were also investigated at 4.2 K. The values of the torsional vibrations in the solid species are not largely shifted with respect to those observed in the gas phase. The summary of the torsional potential constants of the solid methyl titanium halides is reported in Table 2. Higher barriers hinder the rotation of the methyl group in the solid species in comparison to those in the gas phase. This observation however is quite common for many other systems [6] _
115 TABLE
3
Thermodynamic
functions of the gaseous CH,TiX,
Compound
T (K)
species (cala
% (calm mol-* K-’ )
= 4.184
J)
-(G+--HO,)/T (cala mol-* K-’ )
(HOT-%) (cala mol-’ )
CH,TiCl,
298.15 300 400 500 600
81.2 81.4 89.4 96.2 102.1
64.7 64.8 70.2 74.9 79.5
4899 4974 7692 10665 13560
CH,TiBr,
298.15 300 400 500 600
89.3 89.6 97.7 104.7 110.5
71.5 71.6 77.4 82.3 86.6
5313 5374 8154 11160 14370
CH,TiI,
298.15 300 400 500 600
97.5 97.8 106.1 113.1 119.0
78.4 78.5 84.5 89.8 94.2
5695 5769 8640 11650 14850
Thermodynamic
functions
In Table 3 the thermodynamic functions of gaseous CHBTiX3 molecules are listed. The calculation was made using all the fundamentals and the estimated structural data of this work. Corrections for the restricted rotation were made according to the Pitzer theory [8,93 making use of the potential barriers calculated in the present paper.
REFERENCES J. R. Durig, C. F. Jumper and J. N. Willis Jr., J. Mol. Spectrosc., 37 (1971) 260. L. Bencivenni, A. Farina, B. Martini, S. Nunziante Cesaro, R. Teghil and M. Spoliti, J. Mol. Struct., submitted. M. Spoliti, L. Bencivenni, A. Farina, B. Martini and S. Nunziante Cesaro, J. Mol. Struct., submitted. A. P. Grey, Can. J. Chem., 41(1963) 1511. J. R. Durig, P. J. Cooper and Y. S. Li, J. Mol. Spectrosc., 57 (1975) 169. J. R. Durig, in Vibrational Spectra and Structure,Vol. I, M. Dekker, New York, 1972. V. W. Laurie, 3_ Chem. Phys., 30 (1959) 1210. K. S. Pitzer and W. Gwinn, J. Chem. Phys., 10 (1942) 42% K. S. Pitzer, J. Chem. Phys., 14 (1946) 239.
-
Printed in The Netherlands
ORATIONS SPECTRA AND ROTATIONS BARRIERS OF’ METHYL TITANIUM HALIDES CH3’I’iXs AND CD3TiX3 (X =L:Cl, Br, I)
L. BENCIVENNI, Istituto
di Chimica
A. FARlNA, Fisica,
(Received 5 December
S. NUNZIANTE
University
di Roma,
CESARO, 00185
11. TE%HIL
and M. SPOLITI
Rome ~~~~~y~
1979)
ABSTRACT The IR and Raman spectra of gaseous and solid CH,TiX, and CD,TiX, species (X = Cl, Br, I) are reported. The gas phase spectra have been recorded between 4000 and 20 cm-’ at pressures of 1 atm and 4 atm at 350 K and the Baman spectra of the solid phase recorded at 4.2 K. Internal rotation barriers and thermodynamic functions have been calculated.
INTRODUCTION
The vibrational spectra of methyl germanes have been thoroughly studied by Durig et al. [l. ] and the relative methyl torsional barriers calculated. In a recent paper 12 J we compared the spectra of cyclopentadienyl titanium trichloride [ 31 with those of the corresponding cydopentadienyl germane. The conclusions drawn were that the barriers are independent of the metal and halogen atoms, within the limits of experiment& error. To our knowledge there are no experimental data on methyl titanium trihalides. Therefore we undertook this work in order to assign the vibrational spectra of the methyl titanium trihalides and to check whether the conclusions on the cyclopentadienyl compounds hold for these systems as well. EXPERIMENTAL
The IR spectra were scanned between 20 and 4000 cm-l with a PerkinElmer 180 IR grating spectrophotometer, purged with dry nitrogen. Raman spectra were run using a Cary Raman spectrophotome~r model 81 equipped with a He-Ne laser as exciting source. Resistively heated stainless steel cells (30 cm pathlength) were employed to record the spectra of the gaseous species at 350 K. Argon at 1 atm was used as a diffusion barrier and to prevent decomposition of the samples. High pressure spectroscopic cells were used for scanning Raman spectra of the gaseous species in order to reveal forbidden absorptions and increase their intensities. Raman spectra of the solid compo~ds were run at 4.2 K employ~g suitable cryogenic apparatus.
OOZE-2860~80~000~000~$02.25
0 A.980 Elsevier Scientific Publishing
Company
112 RESULTS
AND
Vibrational
DISCUSSION
assignment
CH3TiX3 species belong to the CSV point group both in the staggered or in the eclipsed configurations. The twelve fundamental vibrations consist of five modes of Al symmetry, one IR and Raman inactive mode of A2 symmetry, and six of doubly degenerate E symmetry. According to the selection rules of CSV point group symmetry the A, and E vibrations are active both in the IR and Raman spectra. Activity considerations, isotopic shifts, band intensities and previous results [l, 4, 51 are used here to assign the observed features. The IR and Raman spectra of gaseous CH, TiX, species are shown in Figs. 1 and 2 respectively and the assignment is reported in Table 1.
3100 a00
1450
1000
500
50
cm-
Fig. 1. IR spectra
I_____-
of gaseous
._I
CH,TiX,
species:
(a) X = Ci; (b) X = Br; (c) X = I.
,
--
1450
50 cm-l
Fig. 2. Raman
spectra
of the gaseous
CH,TiX,
species:
(a) X =
Cl; (b) X = Br; (C) X = 1.
113 TABLE
1
Vibrational assignment of the fundamental vibrations in the CH,TiX,
and CD,TiX,
CH,TiCI,
CD,TiI,
CD,TiCl,
CH,TiBr,
CD,TiBr,
CH,TiI,
IR
R
IR
R
IR
R
IR
R
IR
2948
2943
2150 973 602 390 145 114= 2252 1040 635 445 178 150
2935
1259 652 393 148 160a 3000 1418 823 451 189 152
2154 973 600 390 142
2930
1254 648 391 145
1242 621 303 123
1244 619 305 125 152= 3008 1406 820 351 168 197
2136 964 575 300 120
2136 968 579 301 122 108a 2257 1030 630 350 165 103
2925 1236 602 208 98
3004 1421 826 448 190 155
2255 1038 636 444 180 151
3010 1409 821 355 170 105
2260 1030 632 351 164 103
3009 1396 818 264 151 70
R 2925
1238 605 210 98 142a 3010 1400 816 268 153 71
Assignment
IR
R
2124 960 565 206 93
2121 963 566 208 95 101a 2258 1020 629 266 143 69
2260 1019 630 263 145 69
systems
A,
v,CH
A, E
%CH, us Ti-42 v, Ti-X 6, Ti-x, torsion v,CH 6, CH, PCH, IJ, Ti-x 6, Ti-X p Ti-X,
=Observed at 4 atm.
Internal rotation
barriers
The observed Raman spectra (see Fig. 2) do not show evidence of bands which can be reasonably attributed to the torsional modes (A2 species), forbidden in both the IR and Raman spectra. These absorptions are expected between 140-150 cm-’ if the threefold rotational barriers 1.10 and 1.45 kcal mol-’ of the systems CH,GeC13 [ 51 and CH3Ge13 [l] are assumed. The F terms to be used in this rough calculation can be estimated by taking each bond length as the sum of the covalent radii of the linked atoms and tetrahedral angles. Gas phase Raman spectra however often show torsional overtones [6 3. In the present case one would expect to observe these transitions around 300 cm-‘. The present Raman spectra do in fact show feeble absorptions at 313, 298 and 278 cm-l for CH3TiC13, CH,TiBr, and CHJTiIj respectively. These absorptions can be tentatively assigned to the torsional overtones 2 + 0. This hypothesis is strengthened by the observation in the Raman spectra of the corresponding deuterated species in which the three absorptions just mentioned are shifted to 221, 212 and 197 cm-l, respectively. In Fig. 3 the Raman spectra of the gaseous methyl titanium halides are reported. Week Raman shifts are observed at 160,152 and 142 cm-l for CH3TiC13, CH3TiBrJ and CHJTi13 respectively and at 114, 108 and 101 cm-l for the deuterated samples. The height of the barrier restricting the rotation in the gaseous CH3TiX3 molecules is evaluated according to the Durig treatment for the single-top systems [6]. The results of this calculation are summarized in Table 2. The observed trend and the magnitude of the calculated barriers are in good agreement with the conclusions drawn for analogous systems [l, 5,7], including the consideration that these potential barriers depend almost exclusively on the nature of the M-CH3 bond.
114
175
100 cm-’
Fig. 3. High pressure gas phase Raman spectra (100 - 175 cm-l ) of the CH,TiX, line) and CD,TiX, (dotted line) species: (a) X = Cl; (b) X = Br; (c) X = I.
TABLE Torsional
2 constants
Constant
in the gaseous
CH,TiCI,
Gas phase V (kcal mol-’
)
F (cm-’ ) A2 (cm-‘) k (mdyn A-’ ) So lid phase V (kcal mol-’ F (cm-’ ) A 2 (cm-’ )
k (mdyn
(solid
A-’ )
)
and solid CH,TiX,
CD,TiCI,
1.5 -c 0.1 a 5.4 2.7 160 + 1 1142 1 4.7 x lo-*
1.7 2 0.1 a 5.4 2.7 170 + 1 121 f 1 5.3 x 1o-2
and CD,TiX,
species
CH,TiBr,
CD,TiBr,
C!H,TiI,
CD,TiI,
1.4 * 0.1 5.2 152 _c 1 4.4 x lo-*
a
1.3, f 0.1 4.7 142 r 1 4.2 x 1o-2
a
1.6iO.l 4.7 153 2 1 4.9 x 1o-2
=
1-6 + 0.1 5.2 164 + 1 5.1 x lo-2
2.6 108 f 1
a 2.6 1142 1
aThe reported errors are estimated taking into account the frequency ?l cm-’ and the evaluation of the geometrical parameters.
uncertainty
2.4
101 + 1
2-4 108 -c 1
of
Raman spectra of crystalline CH3TiX3 species were also investigated at 4.2 K. The values of the torsional vibrations in the solid species are not largely shifted with respect to those observed in the gas phase. The summary of the torsional potential constants of the solid methyl titanium halides is reported in Table 2. Higher barriers hinder the rotation of the methyl group in the solid species in comparison to those in the gas phase. This observation however is quite common for many other systems [6] _
115 TABLE
3
Thermodynamic
functions of the gaseous CH,TiX,
Compound
T (K)
species (cala
% (calm mol-* K-’ )
= 4.184
J)
-(G+--HO,)/T (cala mol-* K-’ )
(HOT-%) (cala mol-’ )
CH,TiCl,
298.15 300 400 500 600
81.2 81.4 89.4 96.2 102.1
64.7 64.8 70.2 74.9 79.5
4899 4974 7692 10665 13560
CH,TiBr,
298.15 300 400 500 600
89.3 89.6 97.7 104.7 110.5
71.5 71.6 77.4 82.3 86.6
5313 5374 8154 11160 14370
CH,TiI,
298.15 300 400 500 600
97.5 97.8 106.1 113.1 119.0
78.4 78.5 84.5 89.8 94.2
5695 5769 8640 11650 14850
Thermodynamic
functions
In Table 3 the thermodynamic functions of gaseous CHBTiX3 molecules are listed. The calculation was made using all the fundamentals and the estimated structural data of this work. Corrections for the restricted rotation were made according to the Pitzer theory [8,93 making use of the potential barriers calculated in the present paper.
REFERENCES J. R. Durig, C. F. Jumper and J. N. Willis Jr., J. Mol. Spectrosc., 37 (1971) 260. L. Bencivenni, A. Farina, B. Martini, S. Nunziante Cesaro, R. Teghil and M. Spoliti, J. Mol. Struct., submitted. M. Spoliti, L. Bencivenni, A. Farina, B. Martini and S. Nunziante Cesaro, J. Mol. Struct., submitted. A. P. Grey, Can. J. Chem., 41(1963) 1511. J. R. Durig, P. J. Cooper and Y. S. Li, J. Mol. Spectrosc., 57 (1975) 169. J. R. Durig, in Vibrational Spectra and Structure,Vol. I, M. Dekker, New York, 1972. V. W. Laurie, 3_ Chem. Phys., 30 (1959) 1210. K. S. Pitzer and W. Gwinn, J. Chem. Phys., 10 (1942) 42% K. S. Pitzer, J. Chem. Phys., 14 (1946) 239.