Spectrochimica Acta, Vol. %A, pp. 1799 to 1806. PerSamon Press 1969. Printed in Northern Ireland

The infrared and Raman spectra of Cl,SiSH, and the partial spectra of C&SiCN*

FOIL A. MILLER and DONALD H. LmfMoNt Department of Chemistry, University of Pittsburgh:

and

Mellon Institute, Pittsburgh, Pennsylvania 15213

(Received 15 November 1968)

Abstract-Infrared spectra from 35 to 4000 cm-l have been measured in the vapor and liquid phases for ClsSiSH and Cl,SiCN. Some data for solid ClsSiSH are included. Raman spectra with polarizations were obtained for the liquids.

The Cl,SiCN could not be adequately purified. A complete vibrational assignment was therefore not attempted for this compound.

For Cl,SiSH the highest possible symmetry is expected to be C,, but the ClaSiS-portion of the molecule appears to obey C’s, selection rules. The effect of the hydrogen atom, presumed to be off the three-fold axis, is not great enough to split the three degenerate modes of the C,, framework. The observed bands have been assigned on this basis. Unfortunately the S-H torsional mode was not identified, possibly due to interference by the rotational bands of the H,S which was formed by decomposition of the sample in the gas phase.

THE synthesis of CIsSiSH was first described by FRIEDEL and LADENBTJR~ in 1868 [l]. The Raman spectrum was measured by GOUBEAU and HIERSEMANN [2]. Our results agree with theirs, but we have added the polarization measurements (which also helped resolve their 409 cm-l band into two components). No previous infrared work has been reported for the compound.

The preparation of ClsSiCN was reported by KACZMARCZYK and URRY [3, 41. It has had no previous spectroscopic study.

We were interested in studying the spectra of these compounds because : (1) Only a few cyanosilane or mercaptosilane compounds have had their spectra reported. (2) We hoped to find the torsional frequency in CI,SiSH in order to calculate the barrier to internal rotation.

Both compounds are colorless liquids at room temperature. They hydrolyze very

* This work was supported by the U.S. Army Research Office-Durham under Grants DA-ARO-D-31-124-G-594 and -G-735.

t Present address: Westinghouse Research Center, Pittsburgh, Pennsylvania 15235. Taken mostly from the Ph.D. thesis of D.H.L. at the University of Pittsburgh.

$ To which correspondence should be addressed.

[l] C. FRIEDEL and A. LADENEXJRG, Ann. 145, 179 (1868); Ann. Chim. Phy8.27,416 (1872). [2] J. GOUEIEAU and W. D. HIERSE-, 2. Anorg. Allgem. C?wm. 290, 292 (1957). [3] A. KACZMARCZYK and G. URRY, J. Am. Chem. Sot. 81,4112 (1959). [4] A. KACZMAJXCZ~K, Ph.D. thesis, Washington University, St. Louis (1960). University

Microfilms Mic 60-4689.

4 1799

1800 FOIL A. MILLER and DONALD H. LE~~MON

rapidly, necessitating handling in va~uo. The reported boiling points are 95°C at 768 torr for Cl,SiSH [5], and 73°C (extrapolation) for CI,SiCN [3].

PREPARATION OF THE COMPOUNDS 1. CIaSiSH

The preparation followed that of SCHUMB and BERNARD [5] with only minor modifications. SiCl, and H,S vapors were passed through a 15 mm o.d. Vycor reaction tube heated to 75O’C along ~21 cm of its length. The SiCl, was recycled, but H,S was continuously passed through the system and allowed to escape.

The SiCI, was boiled slowly in a three-neck round bottom flask. Fittings were sealed to the necks with epoxy resin. Pyrex tubing led from one neck to the heated Vycor tube and then back through a second neck to the bottom of the flask. Past the Vycor section was a T-joint to which an upright condenser tube packed with glass helices was attached. The tube was surrounded by a glass jacket which held a dry ice bath. Its exit was protected by a tube of “Drierite”. The Vycor tube and its return were inclined above the horizontal so condensed liquid would flow back into the flask. H,S, pre-dried with P,O,, was introduced through the third neck of the flask and bubbled through the SiCl, at a rate of several bubbles per second. Over a period of 14 hr the contents of 13 lecture bottles were consumed, and 175 ml of SiCl, was employed.

The resulting milky-white liquid (containing suspended sulfur) was distilled under N, at atmospheric pressure and yielded 50 ml of Cl,SiSH (b.p. 92.5-94°C at ~750 torr). We found the compound to be stable at dry ice temperature, but it slowly decomposed at room temperature. The vapor phase far infrared spectrum showed a buildup of H,S as the infrared measurements progressed.

The infrared spectrum of CI,SiSH was checked at different stages of sample purification, and after standing for various periods of time, to identify any bands of impurities and decomposition products.

2. Cl,SiCN

We attempted to repeat the preparation described by KACZMARCZYK and URRY [3 41, which consisted of passing Si,Cl, vapor over heated Hg(CN), at 100°C. Trials were made at loo”, 120°, and 130°C. The resultant liquid was fractionated by passing its vapor through a vacuum bulb-to-bulb trap system [3, 41. No Cl,SiCN was ob- tained at lOO”C, and only minute amounts at 120” and 130”. The Hg(CN), decom- posed slowly at all these temperatures. Nearly all the Si,Cl, was recovered. The Cl,SiCN was identified by its infrared spectrum [4].

We also tried reacting Si,Cl, and Hg(CN), in sealed tubes at elevated tempera- tures. Ten grams of each compound heated together at 105°C for 16-17 hr gave the optimum yield. Lower temperatures gave negligible yield, while higher temperatures or longer times resulted in extensive blackening of the reaction mixture, and also decreased yields. At best the yields were poor, and fractionation through a trap system recovered mostly SiCl, and some Si,Cl,.

In all our experiments the Hg(CN), was pretreated by heating under vacuum

[5] W.C. SCHUMB and W.J.BERNARD,J.A~Z.C~~~.SOC. 77,862 (1955).

The infrared and Raman spectra of Cl,SiSH, and the partial spectra of CI,SiCN 1801

at 100°C for 24 hr, and the reaction system was always given a preliminary flushing with S&Cl, vapor to remove any adsorbed water.

Cyanogen is known to be a good source of CN radicals when heated. Several attempts were made to react SiCl, or Si,Cl, with (CN), in a recycling apparatus analogous to that used for the preparation of Cl,SiSH. The (CN), gas was not pre- dried. Temperatures of 290’ and 750” were tried, with folded-path reaction tubes up to 40 in. in length. A number of reaction products were isolated by vacuum line techniques ; some of these contained -CN as evidenced by its infrared stretching vibration, but no Cl,SiCN was obtained. Reaction times up to ten hours were em- ployed. The higher temperature gave more reaction products, including a small amount of paracyanogen.

We were unable to determine the purity of our Cl,SiCN.* The small yields prevented a conventional distillation. Vapor phase chromatographic analysis proved impractical due to the reactivity of the sample with the column materials and the thermal conductivity detector. Mass spectroscopic analysis was not successful because of decomposition in the instrument. A sample known to contain considerable CI,SiCN by its infrared spectrum gave no trace of the compound in the mass spectro- meter but showed mainly SiCl,. Several pre-treatments of the mass spectrometer system with S&Cl, before injection of the sample did finally permit traces of Cl,SiCN to be revealed. It was evident that perfection of a quantitative analytical technique for CI,SiCN by vapor phase chromatography or mass spectroscopic methods would be a formidable task. Since what was really needed was a more efficient synthesis, the analytical determinations were not pursued further.

Many of the impurity bands in the vapor phase infrared spectrum could be sorted out by repeated fractionation of the sample in a vacuum bulb-to-bulb trap system. The chief impurity was always SiCl,, and we were unable to remove it entirely. SiC1, is an exceptionally strong Raman scatterer. The strongest Raman line in the Cl,SiCN sample was due to SiCl,, but this does not necessarily mean that the sample was predominantly SiCl,.

Raman SPECTROSCOPIC PROCEDURES AND RESULTS

The spectra were obtained with a Cary Model 81 Raman spectrophotometer using Hg 4358 A excitation and 10 cm-l slits. Raman tubes of 7 mm dia. were used. Qualitative polarizations were obtained by the usual two-measurement method with cylinders of Polaroid concentric with the sample. The results are given in Tables 1,

3, and 4.

Infrared

Spectra were measured from 35 to 4000 cm-l with Beckman IR-9 and IR-11 grating spectrophotometers. The resolution was l-2 cm-l everywhere. The vapor phase spectra were run at equilibrium vapor pressures and 10 cm path lengths. Liquid phase spectra were recorded using cavity cells which were Glled under vacuum.

* KACZMARCZYK and URRY [3,4] established the identity of their s?mple by hydrolyzing a small amount of its vapor to measured HCI, HCN, and SiO,. We needed to determine the purity of liquid samples.

1802 FOIL A. MILLER and DONALD H. LEMMON

Table 1. CIsSiSH: Raman and infrared spectra

Liquid (cm-‘)

Reman Infrared Rel. peak Solid Liquid Vapor intensity P&Xl. (cm-‘) (on+) (cm-‘) Intensity Assignment

141 27 dp 214 28 dp

92.5 Lattloe mode? 134 b Cl, -Si-S bend? 212.5 sh -2149 SiC1, deformation (e)

214 \ Pi 217 sh dp? 219 222 222 8 Q S&l, deformation

227 sh R @I) 400 sh -17 P Si-S stretch (at)? 410 100 P 411 s 409 w SCCl stretch (a,) 586 10 b dp * 680 698 VVS Si-Cl stretch (e)

730 b 721b w 141 + 586 = 727 758 sh P

768 2 P? * 770 764 m Q 770 I _ R 1

Si-S-H in-plane bend

2581 P

2566 38 P * 2569 2585 1 w Q 2587 S-H stretch w Q

2593 VW R I

* Not examined in this region. t H,S interferes seriously. $ sh = shoulder; b = broad; s = strong; m = medium; w = weak; v = very.

-I--

l

I I I I I I I

I I I

1 1 I ( I 1

CI,Si SH

721

Ir ;5e

770 764

l--

I I I

I I I

I I

l 22; \f

2600 2560 000 750 700 650 550 240 200 cm-’

1 I I I I I

92

J 5

134 ,J C 80

1,

150 110 70

-r I I I I I I I

I

I I I

L

/ I I

sict,

L! 216 230

223

.40 20(

Fig. 1. Infrared spectrum of ClsSiSH.

(A) equilibrium vapor pressure, 10 cm path, vertical scale expanded -5 x .

(B) equilibrium vapor pressure, 10 cm path. (C) cold film at -lOOoK. The 80 cm-l band is due to the cold polyethylene plate.

SiC14: equilibrium vapor pressure, 10 cm path.

A KBr cavity cell sealed to glass tubing with epoxy resin, and a polyethylene cell sealed to glass tubing with Glyptal enamel paint, were employed. The sample was condensed into a side arm, and the cell was then removed from the vacuum line and tilted so the sample would flow into the cavity. Cl,SiSH was also run from 33 to 450 cm-l as a low temperature fdm deposited from the vapor and held at ~100“K. The results are given in Tables 1, 3, and 4, and Fig. 1.

Frequencies should be accurate to &l cm-l in the infrared and f2 cm-l in the Raman spectrum unless marked as broad or shoulder.

The infrared and Raman spectra of ClsSiSH, and the partial spectra of CI,SiCN 1803

CI,SiSH ASSIGNMENTS

Table 2 lists our assignments for Cl,SiSH. This molecule is expected to have no

more than a plane of symmetry (C, point group) because of the non-linear Si-S-H

Table 2. Fundamental vibrations and assignments for ClsSiSH

Species Activity No. Schematic description Assignment

al

a2

a1

e

R (P), 1R

R (dp), IR

R (~1, IR

R (dp), IR

-S-H portion (C, symmetry) 1 S-H stretch 2 Si-S-H bend 3 Si-S-H torsion

Cl,-Si-S portion (C,, symmetry) 4 Si-Cl stretch 5 Si-S stretch 6 SiCI, deformation 7 Si-Cl stretch 8 SiC1, deformation 9 Cl,-Si-S bend

2586 764

?

410 400? 222 598 214 141?

angle. However empirical experience has shown that the relatively light off axis hydrogen atom has little influence on the vibrations of the rest of such a molecule [6, 71. Therefore a local symmetry model was used which postulated a Cl,-Si-S framework of C,, effective symmetry to which is attached an angular S&S-H group. (The C, model gives equivalent results when three pairs of its modes are considered to be accidentally degenerate.)

S-H stretck

There is no doubt that this mode is at 2586 cm-l in the vapor. The band contour is that of a type B band as expected-a quartet with two prominent central peaks [S]. (See Fig. 1A.) In the liquid the band is 20 cm-l lower, and is strong and polarized in the Raman spectrum.

Si-S-H in-plane bend

This mode is expected to be polarized, to lie above 500 cm-l, and to be prominent in the infrared. It is surely the 764 cm-l band. No other fundamental will come in this region.

S-H torsion

We leave this unassigned. It is expected below 250 cm-l, and may have been obscured by H,S which has many bands in the 32-250 cm-l region. (The sample gradually decomposed, forming His, as mentioned earlier.) If this torsion has a rich and broad rotational structure (such as the torsional mode in CH,OH) it could be very difficult to see in the presence of H,S. There are more satisfactory explanations for the observed far infrared bands than to choose one as the torsion.

[6] R. E. DINNEY and E. L. PACE, J. Chem. phys. 31, 1630 (1959). [7] R. L. REDINGTON, J. Mol. Spectry 9, 469 (1962). [S] G. Hnazmma, Infrared and Raman Spectra of Polyatomic Molecules, p. 483. Van Nostrand

(1960).

1804 FOIL A. MILLER ctnd DONALD H. LEMMON

Si-Cl stretches

The strongest Raman line is at 410 cm-l and is polarized, so it is assigned to the a, stretch. This transition is completely absent in the infrared spectrum of the vapor although it is present in the liquid (weak) and solid (strong). A possible explanation* of this behavior is that in the gas phase the Si-S restoring force and the mass of -SH may effect pseudo-T, symmetry; the Si-Cl and Si-S stretches would then be completely mixed and the resulting symmetric stretch would be infrared-inactive under Td symmetry. The liquid and solid phases would cause increasing distortion of the pseudo-T, structure, respectively, and could permit the vibration to be, observed in the infrared. [Pseudo-T, then applies to the vapor phase, but C,, holds for the condensed phases. Intra-molecular interactions apparently alter the Si-Cl and Si-S stretching forces enough to prevent the pseudo-T, situation in the liquid and solid.] The infrared intensities are consistent with this suggestion.

The extreme intensity of the infrared band at 598 cm-l indicates that it is due to Sic1 stretching. It is depolarized in the Raman spectrum, so it is assigned to the e mode.? This mode would be fa under pseudo-T, symmetry. Because the selection rule would be unchanged from Cau, no additional evidence for T, is possible.

Si-S stretch

If the pseudo-T, symmetry is considered for the vapor phase, the Si-S stretch would be mixed in with the Si-Cl stretches. If the C,, model is assumed for the liquid phase (as discussed earlier) then the Si -S stretch would be expected to appear separately. There is a polarized Raman band at 400 cm-r which is a shoulder on the strong 410 cm-l band, and we have tentatively assigned it to the Si-S stretch in the liquid phase. The 400 cm-i band is not present in the infrared and is perhaps simply too weak to be observed there. The 400 cm-l band cannot be explained as a sum or difference tone, nor as isotopic splitting of the 410 cm-l transition (C1,35SiSH and Cl,aYYViSH have nearly equal concentrations, but the 400 cm-l band is much weaker than the 410 cm-l band.) It would be surprising, however, to have two a, fundamentals only 10 cm-l apart when the Si atom participates in both modes.

SiCl, deformations

These are expected around 225 cm-l. Smith reported 229 cm-l for accidentally degenerate SiCl, deformations in CI,SiCH, [9]. We found the deformation at 223 cm-r in the infrared vapor spectrum of SiCl, (see Fig. 1). There is an infrared band with P&R structure at 222 cm-l for C1,SiSH vapor, but there are two depolarized Raman lines in the liquid phase. We choose 222 cm-i for the a, deformation and suggest that the e deformation in the vapor is buried under the P branch at -214 cm-l.

The choice of 222 cm-l as the a, species is based on its band contour. (SMITH [9]

found for Cl,SiCH, that the a1 bands had P&R structure, whereas the e bands did not ; this appears to be true for Cl,SiSH also.) SiCl, has a band at 223 cm-l which is very similar in position and contour to the 222 cm-l band of Cl,SiSH. They are both

* TTTe are indebted to one of the referees for this interesting point. t In Cl,SiCH, the Si-Cl stretches are 458 cm-l (aI) and 577 cm-l (e) [9].

[9] A. L. SMITH, J. Chem. Phya. 21, 1997 (1953).

The infrared and Raman spectra of ClsSiSH, and the partial spectra of ClsSiCN 1805

shown in Fig. 1. The 222 cm-l band in our sample cannot be due to SiCl, because the much stronger SiCI, band at 621 cm-l was completely absent.

The species e SiCl, deformation is then attributed to 214 cm-l. It is possible that the 214 and 222 cm-l assignments should be interchanged. The Raman inten- sities suggest this, but the infrared contours oppose it.

Cl,-Si-S bend

This is taken as 141 cm-l. The only other band, 92 cm-l, was observed only for the solid and therefore appears to be a lattice mode.

Comments

It was disappointing that the torsion could not be located, for this was the datum that was most eagerly sought. Two types of experiments might be helpful in further searches for it. One is to use a flow system through the cell in order to try to eliminate the interference of the H,S decomposition product. We have not yet conceived of a way to arrange such a system at adequate sample pressure, however. The second experiment is to make CI,SiSD ; the impurity problem would still have to be solved, because D,S would interfere as much as H,S does now.

The assumption of local symmetry seems to be adequate, with the possible exception of the 410-400 cm-l pair.

Cl,SiCN ASSIGWMENTS

Table 3 lists the frequencies which are believed to be due to ClsSiCN, and some suggested assignments; all questionable bands are omitted. Table 4 lists the

Table 3. ClsSiCN: Raman and infrared spectra (incomplete)

Raman Infrared Liquid Rel. peak Liquid Vapor (cm-l) intensity* Polzn. (cm-l) (cm-r) Intensity* Assignment

476 0.5 P 475 471.5 m Si-Cl stretch (al) 546.5 545 w, b 634.5 (a) 641 vvs Si-Cl stretch (e)

735.5 731

i 1 735 m Si-C stretch

2203 18 P 2207 2210 8 C&Y stretch

* Same scale is used in Table 4. w = weak; m = medium; s = strong; v = very. (a) measured in Ccl, solution due to intensity.

questionable bands and the definite impurity bands. Smith has summarized the frequencies of SiCl, which was the major impurity [9]. The molecule probably has C,, symmetry, but we could not confirm this because of the impurity of the liquid samples.

No complete set of assignments can be made from the data. However the C&N stretch (2210 cm-l) and Si-Cl stretch (641 cm-i) are obvious, and the 733 cm-l band is reasonable for the Si-C stretch [9].

1806 FOIL A. MILLER and DONALD H. LEMMON

The weak infrared band at 2086 cm-l (Table 4) has been suggested as due to an isocyanide stretch, possibly indicating a “very rapid cyanid&socyanide equilibrium” [3]. We think the band is due to a decomposition product ; its relative intensity varied in different samples and gradually increased upon standing.

Table 4. ClsSiCN: Questionable and impurity bands in our sample

Liquid (cm-‘)

RamaIl Rel. peek intensity* P&n.

Liquid (cm-l)

Inf’rared Vapor (cm-‘) Intensity* Due to

117 28 dp

152 45 dp 183 5 dp

116

184 (b)

222 55 dp

363 2 dP 425 100 P

611 11 dp

223 (b)

364 426 sh 439 531 sh 613.5 (a) 644 sh(a) 688 714 sh

2156 2261

109 m

183 m 189 w

vs

w VW VW VW

620.5 V”8 8 w VW

2086 w VW “TV

SA, 1

?

SiCl,; me Fig. 1

? SlCl,

? ?

SiC1, Sic1 1

? 1

?

?

?

* Same scale as Table 3. m = medium; v = very; s = strong; sh = shoulder; w = week. (a) Ccl, solution. (b) Band too intense to measure accurately.

For an improved interpretation of the vibrational spectrum a purer sample will be necessary for the liquid phase spectra. An efficient synthesis is needed to produce enough sample so that a better purification method than vacuum line trapping can be used.

Acknowledgment-We wish to thank Dr. S. 0. FRANKISS for helpful discussions regarding the syntheses.