Vibrational spectra and conformational analysis of chloromethylformate

Journal

ofMolecular

Structure,

213 (1989) 97-116

Elsevier Science Publishers B.V., Amsterdam -

97

Printed in The Netherlands

VIBRATIONAL SPECTRA AND CONFORMATIONAL OF CHLOROMETHYLFORMATE

ANALYSIS

F. DAEYAERT and B.J. VAN DER VEKEN Laboratorium

voor Anorganische

B 2020 Antwerpen

Scheikunde,

R. U.C.A., Groenenborgerlaan

171,

(Belgium)

(Received 8 February 1989 )

ABSTRACT The results of an IR and Raman study of normal chloromethylformate, HCOOCH,Cl, and the deuterated derivative HCOOCD,Cl are reported. A minor alteration to the assignments previously published is proposed. It was observed that this molecule exhibits two different crystalline phases, the IR spectra of which show pronounced polarisation effects. These dichroic spectra, however, give no information on the molecular conformation of crystalline chloromethylformate. The (s-c&gauche) conformation of gaseous CMF was established by harmonic rigid rotor asymmetric top simulation of the IR vapour phase contours. No evidence was found for free or nearly free internal rotation of the CH,Cl group, which was suggested by previous ab initio calculations.

INTRODUCTION

Chloromethylformate (HCOOCH,Cl, CMF) has been the subject of a series of investigations by Dahlqvist and co-workers [l-4]. The IR spectra of the normal compound and its deuterated derivatives in different aggregation states were recorded and an assignment was proposed [ 11. It was observed that the carbonyl band of HCOOCH,Cl in the liquid phase and in CH,CN solution has a high frequency shoulder, which disappears in Ccl, solution and in the solid phase. It was concluded that this shoulder originates from a more polar second conformer with an s- truns (E ) ester skeleton, while the dominating conformer then has an s-cis (Z) ester conformation. As to the conformation of the OCH,Cl grouping of CMF, it was suggested that the C-Cl bond oscillates between the antiperiplanar (tram) and synclinal (gauche) positions. This conclusion was based upon the high UC-Cl frequency of CMF, which was assumed to be indicative of a truns OCH,Cl conformation. However, since the IR vapour phase contours indicated that no plane of symmetry is present in the molecule, it was suggested that the tram conformation is not rigid. In a second publication [ 21, a normal coordinate calculation of CMF and its deuterated derivatives was

0022-2860/89/$03.50

0 1989 Elsevier Science Publishers B.V.

98

described. A Urey-Bradley force field was calculated, using an (s-c& tram) geometry. In a first ab initio study of CMF [ 31 the calculated potential energy showed a minimum for the s-cis ester conformation. The calculated potential energy curve as a function of the 0-CH.$l torsional angle was very flat, suggesting that the internal rotation from gauche to truns conformations is essentially free. More elaborate ab initio calculations [4] show a minimum in the potential energy for the (c-cis, gauche) conformation, with a barrier between the gauche and trans conformations not exceeding 2 kJ mol-’ (167 cm-‘). The latter study accompanied a matrix isolation study of CMF, including photorotamerisation experiments during which the less stable (s-truns, gauche) conformer could be isolated. Recently, we investigated the vibrational spectra of a series of three chloromethyl esters [ 5-71. In none of these investigations were spectroscopic indications found for free or nearly free internal rotation of the CH,Cl group, as suggested by the calculated barrier and the torsional frequency of 70 cm- ’ [ 11. This can be inferred from the observation in the CHDCl derivatives of these compounds of two distinct C-H stretching fundamentals: if in these molecules the internal rotation of the CHDCl group were free, clearly a much less well defined vi*(C-H) pattern would be observed, as in the case of, for example, methylnitrite [8]. In the normal derivative, the observed CH, stretching vibrations of these chloromethylesters give rise to simple AC hybrid band contours with one single Q-branch, which can be neatly reproduced with the contours calculated for the (s-c& gauche) conformer. This again is evidence for the non-free CH,Cl rotation in these compounds. Since no a priori reasons exist why chloromethylformate should show conformational behaviour different from its acetate, chloroformate and fluoroformate analogues, it was judged useful to expand the available vibrational data and to carefully investigate the vapour phase contours in order to find evidence for free internal rotation of the CH,Cl group, or to establish the vapour phase conformation of this molecule. The results of a low temperature study of CMF are also reported. EXPERIMENTAL

Normal CMF and HCOOCD,Cl were prepared by the reaction of methylformate vapour with chlorine gas. Equal amounts of both reagents were brought together in a glass reaction vessel connected to a vacuum manifold, and illuminated with a 500 W tungsten lamp. The yield of the reaction was lowered by the formation of an appreciable amount of methylchloroformate, C1COOCH3, while chloromethylchloroformate (ClCOOCH,Cl) was also spectroscopically detected in the reaction mixture. A first purification was carried out by distillation at atmospheric pressure on a Widmer column, and the resulting product was further purified on a low temperature, low pressure fractionating column. The deuterated methylformate required for the synthesis of HCOOCD&l was prepared by the reaction of deuterated methanol with an excess of formic acid.

99

Fig. 1. Mid-IR spectra of HCOOCH,Cl both crystalline phases (C and D ) .

in the vapour phase (A), amorphous

solid phase (B) and

All IR spectra were recorded on a Bruker IFS 113~ Fourier transform spectrometer. For the mid-IR region the instrument was equipped with a globar source, a Ge/KBr beamsplitter and an LN2 cooled MCT detector. For the far IR region a high pressure Hg lamp, Mylar beamsplitters of 3.5 and 12 pm and a DTGS detector were used. Mid-IR vapour phase spectra were obtained with a 30 cm cell equipped with KBr windows. Spectra were recorded with pressures of 1.5,5 and 40 mbar, with a resolution of 0.5 cm-l. For the far IR vapour phase

Fig. 2. Raman spectra of HCOOCH&l in the vapour phase (A), liquid phase (B), amorphous solid phase (C ) and crystalline solid phase (D ) .

spectra of the region between 600 and 50 cm-’ an identical cell, equipped with PE windows, was used. The pressure in the cell was 32 mbar, and the resolution was 0.25 cm-‘. Spectra of solid CMF were obtained by depositing the samples onto an LN2 cooled Csl window for the mid-IR spectra, or a wedged Si single crystal for the far-IR spectra. The amorphous films thus obtained were crystallised by annealing. A first crystalline phase was obtained by annealing at ca. - 110’ C, while annealing at higher temperatures led to the formation of a

101

Y I

I

600

500

400

I

I

I

300

200

100 r/CM-l

Fig. 3. Far-IR spectra of HCOOCH&l both crystalline phases (C and D).

in the vapour phase (A), amorphous

solid phase (B) and

second crystalline phase. To record the IR spectra of the annealed solids the cell was retooled to - 196°C. The resolution of all low temperature spectra is 0.5 cm-‘. Polarised mid-IR spectra of solid CMF were obtained using a gold wire grid polariser. To neutralise possible polarisation effects of the interferometer, separate background spectra were taken for each polarisation angle at which measurements were made. Raman spectra were recorded with a Spex 1403 0.85 m double monochrom-

102

ator, using the 514.5 nm line from a Spectra Physics model 2020 Ar+ laser. Vapour phase spectra were obtained with a quartz cell fitted into a standard multipass accessory. The pressure in the cell was 40 mbar. Liquid phase Raman spectra were taken from sealed glass capillaries. Low temperature spectra were recorded by cooling the capillaries in a Miller-Harney set-up [91. By cooling the samples to - 16O”C, an amorphous solid phase was obtained. Upon annealing at ca. - 110” C the samples crystallised. The resolution of all Raman spectra is 3 cm-‘. Typical IR and Raman spectra are shown in Figs. 1-3. VIBRATIONAL SPECTRA

As has already been observed by Dahlqvist [ 11,the IR vapour phase contours indicate the presence of a non-planar heavy atom conformation of CMF. Indeed, the vibrations that in the case of a symmetric conformation would belong to the a” irreducible representation of the C, molecular point group do not give rise to the expected type C band contours. A division into a’ and u” modes would also show up in the Raman spectra of the liquid products. Since no such division is observed, it can be stated that in the liquid phase also the conformer present has a non-planar heavy atom arrangement. A thorough vibrational assignment of CMF and its deuterated derivatives was carried out by Dahlqvist [ 1,2]. At one point however, it seems appropriate to us to alter this assignment. In ref. 2, the CO torsion and the COC skeletal deformation of HCOOCH&l were assigned at 325 and 240 cm-‘, respectively. This assignment was based upon the normal coordinate analysis and is seemingly in agreement with the fact that also in the methylester, HCOOCHB, the CO torsion falls at a higher frequency than the COC deformation [lo]. However, in our study of other chloromethylesters [ 5-71 it was noticed that in each case the CO torsion frequency drops considerably when going from the methyl to the chloromethyl esters, with the COC deformation frequency remaining nearly constant. The rC0 and 6COC frequencies of methylformate are 341 and 325 cm-‘, respectively, while in the spectrum of CMF bands are observed at 323 and 225 cm-‘. When it is assumed that for the formate the 6COC frequency also remains constant and the CO torsion frequency drops upon chlorination of the methyl ester, it is clear that the assignment in ref. 2 is to be reversed. As stated in the Introduction, Dahlqvist observed a shoulder on the high frequency side of the carbonyl band in the IR spectrum of liquid CMF, which was assigned to a second conformer [ 11. This shoulder is also observed in the Raman spectrum of liquid HCOOCH,Cl, and its disappearance upon cooling the product to an amorphous solid phase confirms the above mentioned assignment. An attempt to measure the AH in a Raman temperature study failed because of the strong overlap of the bands and the weakness of the conformer

103

band. The high frequency shoulder on the carbonyl band of liquid CMF-d, is an overtone band [ 11. A remarkable feature is observed in the Raman spectra between 650 and 750 cm-l, where the G-Cl and 6OCO transitions appear. In the d, spectra the relative intensity of both bands is reversed upon going from the vapour phase to the liquid and solid phases (Fig. 3 ) . This can be explained by the frequency drop of vC-Cl when passing to the condensed phases, which was also observed in other chloromethylesters [ 5-71: in the vapour phase the vC-Cl band, which is the most intense, lies at a higher frequency than the 6OCO band, while upon condensation it drops below the 6OCO frequency. The same phenomenon is observed in the d, spectra. As already mentioned in the experimental section, two different crystalline phases of CMF were found to exist. A first one (I) is formed when the amorphous films deposited on the CsI and Si windows of the low temperature IR cells used are warmed up from - 196 to approximately - 110°C. This first crystalline phase transforms into a second one (II) when the samples are further annealed at approximately - 90’ C. This phase change is accompanied by large changes in the IR spectra, as is shown in Fig. 1. Comparison of the low temperature IR band Raman spectra indicates that the crystalline phase formed in the Miller-Harney cells is phase II. This is also the crystalline phase which was obtained by Dahlqvist [ 1 ] by cooling the liquid products between CsI windows, as is revealed upon comparison of our data with the spectra published in ref. 1. Dahlqvist did not observe any polarisation effects in the IR spectra of crystalline CMF [ 11,In our spectra, however, pronounced polarisation effects are present in both crystalline phases. In favourable cases, polarisation data can be used to establish the symmetry of the species in the solid phase, as was shown for instance in the case of methylchloroformate [ 111. Therefore these polarisations were investigated in some detail. As an example, the intensity variation with the polarisation angle of the IR beam for some transitions of HCOOCD&l in phase II are shown in Fig. 4. To have a more pictorial view of the intensity variations, the observed integrated intensities, or, for overlapping transitions, the peak heights, were fitted by a least-squares method to the equation

In this equation, I0 is the observed intensity and 8 measures the orientation of the plane of polarisation of the IR beam with respect to an arbitrary zero position. Ib and 1, are constants, while (b is the phase angle. The result of this fit for the transition depicted in Fig. 4 is presented in Fig. 5, the solid line in each case showing the calculated IB. It is clearly seen that 4 of the transitions considered show identical intensity variation with the polariser angle, while 4

23i0

CM-1

300

450

60'

750

9o"

105O

120°

135O

J

Fig. 4. IR absorption bands as a function of the polarisation angle of the IR beam in the spectrum of HCOOCH,Cl in the second crystalline phase. The polarisation angle increases linearly from left to right; some of its values are indicated in the bottom line of the figure.

WRVENUHRERS

30~-HJuuuuurJL~

2340

0"

30"

60"

90"

120"

0"

30"

60"

90"

120"

Fig. 5. Intensity (in ordinate) variation as a function of the polarisation angle of the IR beam of the transitions in Fig. 4. The abscissa values correspond to the polarisation angles in Fig. 4.

106

others have a phase difference of 90” with the former. This indicates that the @/dQ vector giving rise to the first 4 transitions is oriented perpendicular to the dji/dQ of the latter 4. The fact that this 90” shift is observed between, for example, the antisymmetric CD, stretch and the out-of-plane C-H deformation bands indicates that this behaviour does not find its origin in a C, symmetry of the individual molecules. If this were the case, both vibrations would be u”, would show an in-phase intensity variation, and would both show a 90” phase difference with the in-plane C-H stretch band. It was observed that in the spectra of both crystalline phases several of these 90” phase differences occur within doublets due to crystal effects. This behaviour indicates that the observed polarisations reflect the symmetry of the unit cell of the crystals, and not the symmetry of the individual molecules. Therefore, the polarised IR spectra of CMF do not allow us to draw conclusions about the conformation of the compound in these solid phases. INFRARED VAPOUR PHASE CONTOURS

As described in the Introduction, the ab initio calculations [4] predict CMF to be a floppy molecule, due to a low barrier between (s-c& gauche) and TABLE 1 Structural parameters and rotational constants for chloromethylformate Structural parameters” r((O)C-I-I) 1.10 r(C=O) 1.20 r( (OK-0) 1.33 r(O-CH,Cl) 1.44 r(C-Cl) 1.74 r(C-H) 1.09

(r(H-C=O) cx(O=C-0) (Y(C-O-C)

124.8 125.9 114.8

CH&l

tetrahedral

180

(s-trans, gauche ) 180 60

180 180

Rotational constantsb HCOOCH,Cl A 0.2573 B 0.1085 C 0.0843

0.6678 0.0601 0.0557

0.3722 0.0734 0.0639

0.9750

HCOOCD,Cl A B C

0.5793 0.0598 0.0553

0.3264 0.0723 0.0624

0.7581 0.0515 0.0491

7HC(O)OC 7(O)OCCl

(s-k, gauche) 0 60

0.2340 0.1061 0.0823

(s-ck, truns) 0

“Bond lengths are in A, and angles in degrees. bRotational constants are in cm-‘.

(s-tram,

0.0518 0.0497

tram)

s-‘IS.

tram

I

x)00

2900

300

v/cm-

2900

Fig. 6. IR vapour phase band contour simulation of u,CH, (3000 cm-‘) and K-H (2950 cm-‘) in the spectrum of HCOOCH&l. The calculated contours of both transitions are extra convolved with a Lorentzian slit function with a FWHH of 2 cm-‘.

trans) conformers. It is extremely difficult however to include the effects of a large amplitude motion in an asymmetric top simulation of IR contours. Therefore we have attempted a rigid top simulation, assuming the molecule is tightly locked in each of the conformers investigated. Evidence for a floppy molecule must then come from an inability to reproduce the experimental contours. Using the structural parameters displayed in Table 1, the pure type contours for the (s-c& gauche), (s-c& tram), (s-tram, gauche) and (s-tram, tram) conformations of HCOOCH,Cl and HCOOCD&l were calculated up to a maximal J value of 150 [ 121. These were used to predict the band contours of the v,C!H~, vC-H and vC=O fundamentals of the do compound, and the v,CD~, vC-H and vC-Cl fundamentals of the d, derivatives. Hereby it is assumed that the $/dQ vectors of the C-X stretchings lie along the moving C-X bond, while for the v,CH, vibration the vector is assumed parallel with the bisector of the HCH angle [ 121. The IR vapour phase contours of &-Cl of the normal and (s-c&

108

I

I

1000

I

2950

I

2900

I

I

3000

2950

E/m-’

2900

Fig. 7. IR vapour phase band contour simulation of K-H in the spectrum of HCOOCD,Cl. The calculated contours are extra convolved with a mixed Gaussian/Lorentzian slit function (50% Gauss) with a FWHH of 3.25 cm-‘.

vC=O of the deuterated compound are distorted by the presence of another fundamental (6OCO ) in the former and a combination band in the latter case, and are not fit for simulation. The observed and calculated contours are compared in Figs. 6-10. The isolated C-H stretching experiments in similar chloromethylesters [ 571 indicate variation in C-H bonding with orientation. In the case of a large amplitude motion between (s-cis, gauche) and (s-c& truns) conformers as predicted by ab initio calculations [ 41, in the first place a substantial broadening of the v,CH~ contour, Fig. 6, can be expected. Moreover, the observed contour should be some average of the contours predicted for the (s-c& gauche) and (s-c& trcms) conformers. It can be seen from Fig. 6 that not only the experimental v&H2 contour shows a sharp Q branch, but also the contour is neatly reproduced by the (s-k, gauche) conformer. The same behaviour is observed

,

I

1

2250

2200

22%

I

Df CPA-’

2200

Fig. 8. IR vapour phase band contour simulation of v,CD, in the spectrum of HCOOCD&l. The calculated contours are extra convolved with a Lorentzian slit function with a FWHH of 1.75 cm-‘.

for Y$D~, as is shown in Fig. 8. These observations can thus be regarded as evidence against a very low rotational barrier between the above conformers. From Fig. 6 it is clear that the S-H contour of HCOOCH,Cl is about equally well reproduced by the contours calculated for the (s-k, gauche) and (s-trans, gauche) conformers, but that it is certainly incompatible with a trans conformation. The same is true for the corresponding vC-H contour of the deuterated compound (Fig. 7). Although the experimental vC=O contour is slightly deformed by anharmonicity, from Fig. 9 it is still evident that the contour calculated for the (s-c& gauche) conformer gives the best agreement with experiment. The K-Cl band of CMF-d2 also clearly points at the presence of the (c-c& gauche) conformer, the observed Q branch being too intense to originate from the (s- trcnw,gauche) conformer. This band is characterised by the presence of some hot bands, that presumably arise from a torsional series, which would lend support to the presence of a non-negligible rotational barrier.

Fig. 9. IR vapour phase band contour simulation of vC=O in the spectrum calculated contours are extra convolved with a mixed Gaussian/Lorentzian Gauss) with a FWHH of 3 cm-‘.

of HCOOCH,Cl. The slit function (50%

We may thus conclude that no evidence is found for a large amplitude motion between two conformers, and that the vapour phase conformation of CMF is (s-cis, gauche ) . This conformation was predicted to have the lowest energy by the ab initio calculations in ref. 4, and is also the conformation of the acetate, chloroformate and fluoroformate chloromethylesters [ 5-71. NORMAL

COORDINATE

CALCULATIONS

A normal coordinate analysis of CMF-d, and d, was carried out using the transferable simplified valence force field that was set up for chloromethylacetate, chloroformate and -fluoroformate [6,7 1. In contrast to the normal coordinate analysis of Dahlqvist [ 21, our calculations are based upon the nonsymmetric (s-cis, gauche) conformer of CMF, which has been shown to be the one actually present. For more details on the force field calculations we refer to refs. 6 and 7. In Table 2 the diagonal force constants of the formate part of

I 750

I 700

I 17/CK1

650

Fig. 10. IR vapour phase band contour simulation of K-Cl in the spectrum of HCOOCH&l. The calculated contours are extra convolved with a mixed Gaussian/Lorentzian slit function (50% Gauss) with a FWHH of 2 cm-‘. TABLE 2 Diagonal internal force constants of chloromethylformate Constant

Value

Constant

Value

KD

13.142

f@

KS,

5.032

HE

0.992 1.624

4.710

HY HT

0.106

KR H6

1.195

0.548

the molecule are displayed. All other force constants are transferred from refs. 7 and 10. The observed and calculated fundamental frequencies of CMF and their PED are shown in Tables 3 and 4. It may be noted that the assignment of 6COC and ZCO, mentioned in a former paragraph, is confirmed by the calculated PED of these vibrations, although the strong coupling between the low frequency skeletal deformations of CMF shows that the assignment of these

13436 1335P 1273R 12676 1260P

1348R

13686

1442P

1451Q 14456

1456R

1763PQ

1770ctr

2947P 1775QR

2960R 29546

2998Q 2993P

3003R

m

1735vs

1717vs

2995vw,sh

3000~

m

m

1 1

vw

1263m/s

1339m

1379m/w

1443m

1344s

1263m/s

1274mJw 1264s 1263m/s

1338m

1

1349w 1345w

1337s

1384m/s 138Om/s

1

1387m

1441s

1406m 1401m/w

1442m

1453s

1728~s

1742~s

2986m/w

3019m

3089m/s

1m/w1

vs

2975m/w

2996m/w

3064m/w

1m/w 1 1

3076mJw

clyst. solid (II)

1

1

1369m

1

1452m/w

1771mJs

2954~s

2999vs

3059w

Vapour

Cryst. solid(I)

Vapour

Amorph. solid

Baman

IR

IR and Baman fundamental frequencies and PED for HCOOCHaCl

TABLE 3

1264m/w

1340w

1376m

1446m

1738m/s

2970m/s

2996vs

3066m

Liquid

3000s

3075m

P

1263m Jw

1540m

1378m

1443m

1725m/s

p -2975sh

P

d

Amorph. solid

1263m

1338mJw

1380m/s

1441m/s

1715s

1731~ 1726m Jw

1743vw

2986m/s

3018s

3089m

clyst. solid(I1)

98 us C-H

99 v. CH,

99 u.CH,

78 &ICO+34

6OCO+7

&ICO+6

1273 88 rCH2+5pCH,

1335 86 c&H,+9 6OCO+7 76Hco + 5 K-Cl

1372

1450 98 SCH,

1769 98 vC=O+ll

1

2955

2998

3061

Calc. PED

6OCO+

c&H2

UC-O

=: N

2256 2246

3206 226Q

3236 322Q

3246

4236

428Q 4256

745P

7546 7526

7566

759R

9476

1OOlP 951R

lOO8Q

1014R

1118P

11266

1131R

m

m

m

m/s

m

m/w

VS

247m/w

335m

427mJs

716s,br

755m/s

941m/s

1005m/w

103ow

1119vs,br

279m /w

432m/s 345m

439m/s

724s 711m/w

762m 757s

936m/s 920w

947m

1007m

1032~~

1123~

1167s

J

1

1

245m

336m/w

341m/w

429m/s

717s

724~s

749s

923m

934m

940vs

1001s

1033m

;:;:m,s

1

1

]

1

1

225s

322m

425m

739s

753~1~s

947m/s

1127m

1

J

]

241s

326m/s

423s

722~s

749sh

941s

1005w

1026~

1120m/w,br

249s

334m/s

426s

714vs

754m

942s

1002w

1027~

112Ow,br

238m/s

247s

336m/s

427m/s

715vs

724m/s

748m/s

938s

1OOOm

1032m

1126m

1

1

6OCO-t

65 vO-C + 17 UC-O+ 5 6OCC1

rCH2+9 6COC+

vO-C+27

zCO+7

76COC

229 54 socc1+33

?-Co+13

311 6OSCOC+15 ~C0+15 13 cSoco+7 6Hco

428 62 6OCC1+48

743 39 vc-cl+296coc+22 1760c0+1060cc1

UC-cl+

6OCCl+

d-Cl

UC-o+

753 93 UC-Cl+ 27 vO-C + 8 UC-O

943

7vc-0

1009 73pCHZ+ll

1020 94 yC=o

15 wCH,

1125 43 K-O+38

10836 1076P

1146P 1088R

11536

1159R

1375R 1369Q 1363P

1769Q 1762P

1773R

2221R 22166 2211P

29566 2949P

I m/s

vs

VW

vs

w

1 1 1 1

m/s

1400m

1406m/s

1715vs

1078m/s

1082sh 1079m/w

1211sh 1153vs,br 1189s

1378m/w

173ovs

2213~

2312~

2320~

2215~

2997vw

2975w

1

1 1075m/s 1066w

1077sh

118lm/s,br 1151s

1196w

1386m/s 1382m/s

- 1735sh 1725~s

2231~ 2223~

2330m/w

2987m/w

solid(D)

Clyst.

1083m

1

1153m

1369m

1 1

1763m

1770m/s

2217~s

1 1

2965vs

Vapour

Clyst. solid(I)

Vapour

Amorph. solid

Raman

IR

IR and Raman fundamental frequencies and PED for HCOOCD,Cl

TABLE 4

1079m

1152w,br

1375m

1734m

2214~s

2313m

2969m/s

Liquid

p 1078m

p 1152m/w

p 1378m

p 1723m/s

p 2216s

d 2319m/s

p 2980m/s

Amorph. solid

1076m

1168m

1386m 1381m/s

1713s

1723m/s

2230m 2223m/s

2330m/s

2987vs

Cryst. solid (II)

J

98 V&D,

98 K-H

&ICO+6

1074 88SCD,+8

1157 47 vC-0+24 wCD,

vc-Cl-t5

60CO+18

1368 86 &ICO + 42 6OCO

1769 98 uC=O+ll

2191 98 u.CD,

1 1

2286

2955

Calc. PED

vo-c

v0-C+7

vC-0

vw

I m

4266 422Q

m

2886 2246

223Q 2226 2216

m

4206 2916

1

1

VW

6829

1

1

s

243m/w

308m

427m/s

678m/s

698s

804~

271m/w

327m/w

432m

675sh 437m

678m/s

704s

801m

802m

1

1 1

m/w 1

689Q

709P

720R 714Q

806vw

895P

900Q

9016

904R

986m/s

304sh 243m

306m

428mfs

677s

683m/s

702sh 693s

803~ 800~

804~

897s 890w

1

985s

1013m/s

987s/vs

m

1014m

1032m 1017sh

994R 989Q

1004s

1029w

1003m/s

m/s

‘1025w,sh

J

1

1015P

10206

1026R

A

1

1 1

900s

220m/s

420m

684m

714vs

1

1

1

1021m

238s

300m

420m/s

682s

696vs

804m/w

897s

984w

1008m/w

1022sh

d

p

p

p

p

d

p

d

244s

307m/s

425s

679vs

698s/vs

804m

899m

984m

p 1005m

1028m/w

236m/s

244s

303m

426m

690vs 68Ovs

702m/s

800s

897s

996m 988w

1014w

1031m/w

1

1

1 &D,+9

YO-c

7 UC-O

53 rCD2+31 &D,+lZ

66CD*

47 uO-C+10

14 cc-o+5

iiCOC+

G-O+

36 rCD2 + 18 pCD2 + 146COC +

100 wC!D, + 37 vO-C + 20 K-Cl

yc=o

616OCC1+47

546COC+23

56COC

UC-Cl+

7CO+2160CCl+

rC0+9

10 6OCO +6 UC-Cl 223 496OCC1+26rC0+136COC+ 12 UC-Cl

291

420

710 69 AI-Cl+ 16 u0-C + 13 pCDz+ 5 UC-0 UC-O+ 684 36 vC-C1+26&D,+16 136OCO + 12 xoc

817

a97

982

1016

1021 95

116

modes to one single symmetry coordinate is clearly an oversimplification. Especially the 6OCCl and Z-COmodes are highly coupled. ACKNOWLEDGEMENT

The authors are grateful to Prof. Dr. H.O. Desseyn for his continued interest and support of the present research. Frits Daeyaert is indebted to the I.W.O.N.L. for financial support (ref. 85120).

REFERENCES

6 7 8 9 10 11 12

M.G. Dahlqvist, Spectrochim. Acta, Part A, 36 (1980) 37. M.G. Dahlqvist, Acta Chem. Stand., Ser. A, 38 (1984) 429. M. Hotokka and M.G. Dahlqvist, J. Mol. Struct., 63 (1980) 287. M. Rasanen, H. Kunttu and J. Murto, M.G. Dahlqvist, J. Mol. Struct., 159 (1987) 65. F. Daeyaert, H.O. Desseyn and B.J. Van der Veken, Spectrochim. Acta, Part A, 44 (1988) 1165. F. Daeyaert and B.J. Van der Veken, J. Mol. Struct., 198 (1989) 239. F. Daeyaert and B.J. Van der Veken, Spectrochim. Acta, (1989) in press. R. Maas, personal communication. F.A. Miller and B.M. Harney, Appl. Spectrosc., 24(2) (1970) 291. H. Hollenstein and Hs.H. Gtinthard, J. Mol. Spectrosc., 84 (1980) 457. J.E. Katon and M.G. Griffin, J. Chem. Phys., 59 (1973) 5868. B.J. Van der Veken, in J.R. Durig (Ed.), Vibrational Spectra and Structure, Vol. 15, Elsevier, Amsterdam, 1986, p. 313.