Spectrochimica Actn, Vol. PlA, pp. 696 to 706. Pergnmon Prass 1908. Plinted in Northern Ireland

Low frequency vibrational spectra of group IV-A phenyl compounds

A. L. SMITH

The Dow Corning Corporation, Midland, Michigan 48640

(Received 28 September 1967)

Abstract-Vibrational spectra from 600 to 50 cm-l are reported for several families of phenylated Group IV-A compounds: Ph,SiH,,; Ph,Si(CH,),_,; Ph$i(OCHs),_,; Ph,SnCl,,; Ph,CH,,; Ph,M, and PhMCls (M = C, Si, Ge, Sn). Although in many cases, anomalous band intensities and ring-skeleton interactions lead to some uncertainty, it has been possible to make consistent assignments for the five low-frequency phenyl ring modes as well as for many of the absorptions from deformations of the tetrahedral skeleton.

DURING recent work on frequency assignments for the phenyl chlorosilanes [l],

it became apparent that convincing assignments could not be made for a single compound or series of compounds without simultaneously studying a number of related series. The complexities of the low frequency spectra, because of interacting phenyl ring and skeletal modes, are such that it is very easy to be misled unless a real effort is made to achieve internally consistent assignments throughout the entire family. Therefore, the spectra of a large number of Group IV derivatives have been studied. It is the purpose of this paper to report and interpret the molecular spectra of molecules related to the phenyl chlorosilanes.

Phenyl derivatives of Group IV-A for which at least partial low frequency data are available are listed in Table 1. Upon examining the spectra, we find, as expected that the absorption patterns for any series PhJvIX,_, (where M = Si, Ge, Sn, Pb) are very similar in general appearance. Somewhat greater changes are found in the same series on going from carbon to silicon, because the small mass and diameter of the carbon atom makes it less effective as an insulator between the vibrating phenyl groups. Its electronegativity is also somewhat different from that of the other members of Group IV-A, so vibrations sensitive to this factor are influenced in an irregular fashion.

It therefore seems reasonable to start with silicon compounds as typical rep- resentatives of the organometallics ; a large number of compounds is available, and after assigning frequencies in the silicon family, we can extrapolate forward to the corresponding germanes and stannanes. Corresponding frequencies in the carbon analogs are inferred with more difficulty.

Literature reports on the spectra of Group IV phenyl derivatives are rather fragmentary, and generally include only part, if any, of the far infrared spectra. Many of these reports contain errors which become obvious when the complete spectra of a family of compounds is studied. In this paper, only low frequency vibrations are considered ; in the higher frequency region where absorptions of

695

696 AaL*8?drrE

the phenyl group predominate, the similarity of the patterns (at least for Si com- pounds) to those of the phenyl chlorosilanes [I] makes any detailed study almost trivial.

For our purposes, the low frequency region lies below about 600 cm-r. Funda- mental vibrations found in this region include five phenyl ring vibrations, of which

Table 1. Spectra of Ph&X,, molecules below 600 cm-l

PhMX, Ph,MX, Ph,MX Ph,M

M=C X = H,Cl H E[,CI,OH X Si Cl,H, Cl,H, Cl,% X

Me,OMe Me,OMe Me,OMe,Br Ge Cl Cl Cl,H,Br X Sn CI Cl CI,F,Br, X

I,OH,H Pb X

four are designated by Whiffen as “X-sensitive” [2], that is, their frequency varies with the nature of the substituent X in the molecule PhX. (Whiffen’s notation will be used throughout this discussion.) Briefly, the ring modes are: t, an AL (local symmetry) M-Ph stretch vibration, somewhat dependent on the mass of M, that falls in the range 250-550 cm-l ; y, out-of-plane bending, usually strong in the ix. and absent or weak in the Raman spectrum, that falls between 420 and 630 cm-l;

y 119’1 t i 18’) * (201 ” 114’)

I IZO’I 8, &l P

Fig. 1. Approximate normal coordinates of ring and skeletal deformation vibrations for the molecule C,H,MX,.

a, in-plane ring rotation against M, variable intensity, that falls between 170 and 410 cm-l; x, out-of-plane ring bending, that falls between 150 and 280 cm-l; and w, not X-sensitive, very weak, that falls near 400 cm-r. They are i~u~~~d in Fig. 1. If more than one phenyl group is attached to M, these frequencies can

[l] A. L. SMITH, Spectrochh. Acta 23A, 1075 (1967). [2] D. H. WEIFFEN, J. Chem. Sot. 1350 (1966).

Low frequenoy vibrational spectra of phenyl oompounds 697

interact and split. Such separation is particularly pronounced with t ; mode y often gives a small splitting; z and u may or may not split.

There are several characteristic vibrations for the tetrahedral skeleton ; for molecules of the type PhMX, (X = Cl, CH,, etc.), they include a symmetric MX, deformation and two each of the MX, antisymmetric deformations and MX, rocking modes. If rotation of the phenyl group around the M-C bond is rapid, or if the MX, framework is insensitive to the orientation of the phenyl ring (expected for tin, but not likely for carbon), the molecular symmetry is pseudo-C, and the antisymmetric deformations will be degenerate, as will the rocking modes. For molecules Ph,MX,, we expect the skeletal modes to include scissors deformations of the MIX, and MPh, groups, twisting, wagging, and rocking modes. PhBMX molecules will have symmetric and antisymmetric Mph, deformation vibrations, and a degenerate MX deformation mode (rather than MP$ rocking). Frequency assignments for a number of triphenyl methane derivatives have been discussed by WESTON et al. [3] who show approximate normal coordinates for some of the skeletal vibrations of the planar model Ph,C. Molecules of the type Ph,SiX have been found to be propeller-shaped [4j, requiring some modification of the configura- tions illustrated by Weston et al. Tetrasubstituted derivatives PhlM should exhibit one doubly degenerate and one triply degenerate skeletal bending vibration.

In all phenyl compounds of the type discussed here, the possibility exists for interaction between ring and skeletal modes; evidence for such interaction has been found with PhSiCl, [l]. It is therefore not to be inferred from the approximate descriptions given in the tables that the frequency in question is “pure”; it would be more accurate to say that the motion described accounts for the largest part of the potential energy of the vibration.

EXPERWENTAL

Most of the compounds used in this investigation were fractionated materials, checked for purity by gm chromatography and carefully protected from hydrolysis, where necessary. They were prepared in the Research Laboratories of the Dow Corning Corporation. Samples of Ph,SnCl,, Ph,SnCl, and Ph,Sn were obtained from Matheson Scientific; PhSnCl,, Ph,C, Ph,Pb were purchased from K and K Laboratories, Inc., Plainview, N.Y. Spectra of the tetraphenyl compounds agreed well with spectra from smaller samples of these materials obtained from independent sources.

Infrared spectra were obtained using a carefully calibrated Perk&Elmer Model 521 grating spectrometer and a Beckman IR-11 far infrared spectrometer. A Hilger Model E-612 and a Perk&Elmer Model LR-1 spectrometer were used to determine the Raman spectra.

INTENSITIES

In comparing infrared intensity indications given in the figures and tables, it is important to note that the intensities are reported relative to other bands in the

[3] R. E. WESTON, JR., A. TSUEAMOTO and N. N. LICETIN, Sp&och~m. Actu 22,433 (1966). [4] M. J. ARONEY, R. J. W. LEF&~BE, G. L. D. RITCEIE and V. Ross,J. C?wm.Soc. B 188 (1966).

698 A. L. SMITH

same spectrum, and a change in the intensity scale occurs at about 300 cm-r. Above 300 cm-l, samples were run as 10% solutions in Ccl,, 0.1 mm cells, or as thin mineral oil mulls. Below 300 cm-l, solution concentrations of lO-20:/, in cycluhexane in 3 mm cells, or l-2 mm thick mulls were used. Thus, intensities of infrared bands below 300 cm-l should be mentally divided by a factor of lo-50 to bring them into proper scale with the other absorptions.

PHENYL SILICON COMPOUNDS

The phenyl &lanes Ph,SiH,_, .

Vibrational spectra for the phenyl silanes have been given by KRIECISMANN and SCHOWTKA [5] but did not include Raman polarization data nor infrared spectra below 400 cm-l. The simplest compound of this group is phenyl silane (PhSiH,)

BrSiHa ,Y Si Br

;;:;p Ia I I

an1 & I I Br4Si arl 18i lVI~% &.lSf

I I I I I 0 too 200 cm-, 300 400 500 600

PhSiH3

PhpSiHe

Ph3SiH

Ph,Si

0 100 200 300 400 500 600 cm-’

Fig. 2. Schematic diagram of the low frequency spectra for phenyl silanes. Infrared bands are indicated by triangles and Raman lines by vertical bars. Polarized Raman lines are indicated by crossed bars. The intensity scale changes at about 300 cm-l (see text). Spectra of the analogous bromosilanes are shown for

comparison.

whose SiH, deformation frequencies all lie above 500 cm-l. Thus, only ring vibra- tions should appear in the low frequency spectrum (Fig. 2). By comparison with H,SiBr [6] (the mass of a phenyl group is nearly the same as bromine) we expect to find the SiPh stretch (t) near 400 cm-r. The band at 383 cm-l shows strong i.r. and Raman activity ; it is clearly t. This assignment agrees with that of KRIEW- MANN and SCHOWTRA [5] and with the frequency predicted from the mass of the SiH, group [7]. Vibration y (out-of-plane ring bending) should be nearby at a higher frequency (predicted to lie at 485 cm-l from the correlation by HARRAH [S]) and is assigned as the weak 420 cm-l band although the intensity is anomalous. The low

[5] H. KRIEWWANN and K. H. SCHO~TKA, 2. Physik. Chem. 209, 261 (1958). [6] H. MURATA and K. KAWAI, J. Chem. Phya. 23, 2451 (1955). [7] W. S. WILCOX, C. V. STEPHENSON and W. C. COBURN, JR., WADD Tech. Rep. 60-333,

September, 1960, Office of Technical Services, Dept. of Commerce, Washington, D.C. [8] L. A. ~RAH, M. T. RYAN and C. TAMBORSKI, Spectrochim. Acta 18, 21 (1962).

Low frequency vibrational spectrta of phenyl compounds 699

Table 2. Frequency assignments for the phenyl silanes below 600 om-1

PhSiI3[, Ph,Ss Ph@iH Ph,Si Assignment I.R. Raman I.R. Rcunan I.R. R&man I.R. Rsman

6(SiH,) - - 689 s - - - - -

Y 420~ - 476 8 476 p,vw 485 s 485 vvw Eillvs -

Y’ - - - - 472~ - - -

W - - - - - - 399vw - I 383 s 38f m 421 m 420~ 422 m 425 vvw 436 m - t* - - 375 w 368 p,m 380 w 385 vw 239 m 236 p,w U 204~ - 233 m 231 p,s 244~ - 261 w - u’ - - - - 230 s 232 p,s 223vw - z 162 s 161 m 167 m 165 s I68 m 170 m 185vw - 2’

S,(SiPh,) = 1 7 - 7 - 171w -

WI20 VW 6,100, 96 - &(SiPh,) - - ? ? a,57 -

p = polarized, w = weak, s = strong, v = very, m = medium, 8 = deform&ion.

frequency out-of-plane bending x lies at 162 cm- I, but the in-plane ring “rotation” mode u is very weak and could be either 204 or 306 cm-l. The former has been chosen since no alternative explanation could be devised for it; the 306 cm-l absorption could be 2 x 161.

The compounds Ph,SiH, and Ph,SiH show strong phenyl ring absorptions, but the Ph-Si skeletal deformations expected at 80-150 cm-1 were not observed. Suggested assignments for these molecules are given in Table 2.

l’he methyl phenyl &lanes (CH,),SiPh,_,

This series of compounds shows an absorption pattern (Fig. 3) similar to that of the phenyl chlorosilanes [l]. Again, identification of skeletal modes is aided by comparison with the related series of molecules (~~~)~SiBr~*_=~ [6, 9-if]. The

P%

PhzSi(CH&

Ph3SiCH, Ph,S~ I; h;;i, ), * ;

I- VI n h*h

j i

I I I 1 I J 0 100 200 _, 300 400 500 600

Fig. 3. Low frequency spectra forcLhenyl methyl silanes, shown schematically.

[QJ H. MURATA, Sci. Id Japan 30, 164 (1956). [lo] I. F. KOVALEV, Opt. Spectvy. 13, 35 (1962). [ll] I. F. KOVALEV, ibid. 13, 185 (1962).

700 A. L. Sasr~~

assignments are reasonably straightforward above 300 cm-l and sre given in Table 3. Below 300 cm-l, appsrent interaction of ring and framework vibrstions leads to some uncertainty. For Ph,Si(CH,), and PheSiCH,, some of the Ph-Si deforma- tion absorptions were not detected, but presumably lie in the 80-150 cm-l region. Only a few of the many low frequency lines reported for PhSi(CH,), by CERATO

et al. [123 were found.

The nzeth.oxy plaenyl &lanes (MeO),SiPh,_,

Analysis of the spectra of the methoxy phenyl silanes is more di&cult than for the silanes oonsidered thus far for three reasons: The more complex substituent group gives rise to additional vibrational modes below 600 em-l; the oxygen is

Table 3. Frequency assignments for the methyl phenyl silanes below 600 cm-l

PhSiMe, PhsSiMe, Ph,SiMe Assignment I.R. R- I.R. Raman I.R. Rlml&Ul

Y Y’ W t t’ u UJ

X

?

4@w ~,~S=%.) P(S~%) r(SiMe,)

468 B

408 VW 372 s 371 p,m

300s 297 VW

218 8 140 vw 259 8 259 VW 218 s 213 m 101 VW 102 s

475 s 465 m

422 s 358 m 304 m 238 w 223 s

357 p,w

238 p,w 220 w

210 VW 226 s 225 w

155 VW 142 vw

493 8 481 m 390 w 426 m 360 m 248 w 237 w 171 m

360 p,vw

235 p,m

6 = deformation, p = rocking, 7 = twisting.

probably involved in &r-pr interaction with the silicon [13]; snd the lone-pair interactions of the oxygen probably lead to the existence of configuration isomers, analogous to the situation in (MeO),C and HC(OMe), [14].

Of the phenyl ring modes in PhSi(OMe),, x may be assigned at once to the band at 185 cm-l. The SiPh stretch, t, is most likely the band at 480 cm-l. SkeletsJ modes include an SiOC deformation which usually falls et 285-480 cm-l for Si(OC), [15] ; the 360 cm-l band is sssigned as this mode. The strong 265 cm-l absorption is attributed to the symmetric OSiO deformation ; ring mode u is probably the shoulder at 280 cm-l. The location of vibration y is uncertain ; it may be coincident with t at 480 cm-’ but is probably the weak band at 450 cm-l. Other smaller bands (Table 4) which appear s,s shoulders on the strong absorptions remain unassigned; they are probably from configuration isomers and will require a low temperature study to unravel. The fact that most (or possibly all) of the Raman lines are

[12] C. C. CERATO, J. L. LAUER and H. C. BEACHELL, J. Chem. php. 22, 1 (1954). [13] F. G. A. STONE and D. SEYFERTH, J. Inqg. Nucl. Chm. 1, 112 (1955). [la] H. LEE and J. K. W~MSEURST, Spectrochim. Acta aSA, 347 (1967). [15] A. L. S-, Spectroohim. Acta 19, 849 (1963).

Low frequency vibrational spectra of phenyl compounds 701

Table 4. Frequency assignments for the methoxy phenyl silsnes below 600 cm-l

Assignment PbSi(OMe),

I.R. Ramen P~~Si(OMe)~ Ph,SiOMe

I.R. Ram&n I.R. RSXllan

Y 46Ow,sh 492m 493p,w 520s Yf 609, t 481s 480p,m 620s 478m 48OV"W Comb. 443w Comb. 432m

$SiOC!) 388~ 390x-w 393w 388~ 360m 326~~ w336ww

420~ 419 p,w 36Ow 360 p,m ? 340 p,vw

$oSiO) 280m 278m 214m 200s 266s 271 p.m 282w 261m 278s

240~~ 233m 230~ 232 p.~ 5 1868 190~~ 186x11 189w 190m E' 1138"~ 170w G(Si0) 150m 7(Sio,) %130rn (r,(SiPbJ w76m

polarized suggests that the preferred configuration of the PhSifOMe), molecule is of low symmetry. No further oonclusions are possible at this time.

Assignments for the compounds Ph,Si(OMe), and Ph,SiOMe are tentative (Table 4). Spectra are illustrated schematically in Fig. 4.

PhSNOCHd,

Ph&i(OCW&

Ph,Si I I I I I I I 0 100 200 300 400 SO0 600

cm-’

Fig. 4. Low frequency spectra for phenyl methoxy silanes, shown schematically.

OTHEB GROUP IV-A PHECNYL COMPOUNDS

Molecular spectra of phenyl tin compounds have been reported by a number of workers [ 16-211. As might be expected in comparing the series silicon [ 11, germanium [21, 221 and tin, skeletal bands are shifted to lower frequencies, and splittings between symmetric and antisymmet~c modes shrink or disappear as one proceeds from a lighter to a heavier central atom. In PhSnCle, for example, the symmetric

[M] V. S. Gmxwms and 0;. A. W. DEXWISH, J. Mol. Xpectry. 6, 148 (1960). 1173 R. C. Poxxza, J. Imwg. Nud. Chem. $4,693 (1962). [18] R. C. PO-, ~~~~~h~~. A&a $32,935 (1960). [Is] H. fcRIEas- and H. GEISSLIER, 2. Awg. A&em. Ckem. 828, 170 (1963). [ZO] J. C. Lund, J. C~SSS;N, B. LEP&~ and J. &fAR.ROT, Coopt. Rend. %60,5290 (1966). [2X] J. R. Dumu, private communication. [22] F. W. BEHNKE and C. T~MJZIORSKI, ASD Tech. Rep. ASD-RDR-62-224, February (1962).

B

102 A. L. &KITE

arsnci, PlSrll6a ,vsnsr “I, ,V&Cl

Br.$nCl 2 ,f 7, I I I I B@Kl II II I I I

SnBr, 8~ 181 I”‘ I”0 I

0 100 200 Clll“

300 4AO 500 600

psnc,, s+ ! Y ! Yf nv0SnCI~ .Y PhSnCI,_ 0’. .I, I, i 1) * !\ 1, ) I,

I ” 1 \’ Ph,SnCI, _ ‘, ) !

‘.

Fig. 5. Low frequency spectra for phenyl chlorostannanes, shown schematically.

Table 5. Frequency assignments for the phenyl tin chlorides (below 600 cm-l)

Assignment PhSnCl, Ph,SnCl, Ph,SnCl

I.R. RtUTl8Xl* I.R. I.R.

Y

Y’

z+u vW,S*Cl# v,SnC1, t t’ u

u’ z x’

440 m

403 W

380 8 383 p,m 370 w 363 p,s 263 s 249 p,m

2188

186s

216 W

184~

132 s 1148 68 W

124 s 113s 63 In

442 m

390 VW 360 B 360 * 273 s 236 B 213 m

180s

462 m 448 w

390 VW 344 m

268 w 233 s 217 w 2108 182 s 176~ 160 m

116s 96 m

87 m 77w

l Ref. [37].

SnCl stretch appears as a poorly resolved shoulder on the side of the SnCl sntisym- metric stretch. Low frequency bands, while comparatively intense, are broad and poorly resolved. In other respects, however, the pattern of the series is very similar to that observed for the corresponding silicon and germanium compounds. Spectra are shown schematically in Fig. 6. Also shown as an aid to picking out vibrations of the tetrahedral skeleton are assignments for the compounds Br,SnCl,, [23]. The assignments given in Ta,ble 5 agree well with those of POLLER [ 181 but differ some- what from those given by other workers.

[23] M. L. DELWAULLIG and F. FRANCOIS, Corn@. Rend. 8l9,64 (1944).

Low frequency vibrational spectra of phenyl compounds 703

BrCH, ,” car

“,:$?

,Wb ,“I I”.¶ IS. $1 ,* IWQ

0r.c - I& I81 In 14

~. 0 100 200 300

cm” 403 500 600 700

/ I ’ Ph,C 1 , ,, 6r sf . 1’ “1 ” . , ___ I’ Y 1

0 100 200 300 400 500 600 7cu cm-’

Fig. 6. Low frequency spectra for phenyl methanes, shown schematically.

Table 6. Frequency assignments for the phenyl methanes below 600 cm-1

PhCH, PhsCH, PhsCH Assignment Frequency I.R. Raman I.R. Raman

t Y Y’ U,

U

t’

21’

2

XI

4 W’h,)

521 552 m 464 468 m

460 m 408 406 w

394 w 345 326 w

278 m 233 m

216 196 s

550 w 598 m 495 m

452 w 469 m 400 vw 411 w

282 p,w 232 w 200 m

145 s

294,308 m 274 w 245 m 232 m 224 w

270 p,m 2421 vw 230 w

The phenyl methanes Ph,CH,_,

The spectrum of toluene has been studied extensively and reported in detail [24-271; interpretation of the low frequency absorptions, shown in Fig. 6, is well established.

Infrared spectra of Ph,CH, and Ph,CH have been reported by MCWHINNIE and POLLER [28] for the 667 to 222 cm-i region. Their assignments, while incomplete, agree well with those given here if allowance is made for a labeling discrepancy between their rlsb (illustrated as Whiffen’s 5, but assigned as y) and ~r,~ (shown as y). Splitting of some modes complicates the spectra, but the Raman date and compari- sons with the phenyl silanes are helpful in arriving at the assignment shown in Table 6. Comparison of the series Br,CH,_, is of limited usefulness, probably

[24] R. R. RANDLE and D. H. WHIFFEN, MoZecuZur Spectroecopy (Edited by E. THORNTON and H. W. THOMPSON), p. 111. Institute of Petroleum (1955).

[26] J. K. WILBSSEURST and H. J. BERNSTEIN, Cola. J. Chem. 85,. 911 (1957). [26] H. R. WYSS, R. D. WERDER and Hs. H. G~NTEA~D, Spectrochim. Acta 20,573 (1964). [27] P. R. GRI~~ITES and H. W. THOMPSON, PTOC. Roy. Sot. -8, 61 (1967). [ZS] W. R. MCWHMNIE and R. C. POLLER, Spectrochim. Acta Z&601 (1966).

704 * A. L. S-

Table 7. Frequency assignments for tetraphenyl derivatives of group IV-A

Ph,C Ph,Si Ph,Ge Ph,Sn Ph,Pb Assignment I.R. Raman I.R. Reman I.R. Reman I.R. Reman I.R. R.WNMl

c 635 8 436 In 332 m 288 8 224 B Y 627 m 619 m 481 m 459 m 463 m Y’ 492 m ‘511”s 466 m 448 m 442 m

269 In W 399 VW 399 VW 399 W 396 VW w’ 396 390 VW 390 VW 391 W 389 VW u 332 w 261 m 232 m 226 VW u’ 292 W 223 w 2141~ 1’ 242 w 236 p,w 239 m 236 p,w 222 p,* 212 m 214 P,B 206 m 100 p,m x M 200 VW 186 * 187 w 193 In 183 ma 2’ 171 m 168m 162 mw 148 m 61 06 VW 08 w 98x7 89~ 89 w 6, 63 VW 61 VW 69 VVW 01 W 66 W

because steric and electrical effects as well as vibrational interactions rare more important when the central atom is a small, light atom such as carbon. Some of the low frequency bands of Ph,CH are obviously missing; the assignments for Ph,CH, and Ph,CH are tentative below 300 cm-l.

Tetraphenyl derivations of group IV-A

Another series is formed by the compounds in the last column of the array shown in Table 1: Ph,M (M = C, Si, Ge, Sn, Pb). Reports of molecular spectra for these compounds have appeared in the literature [8, 16, 19, 28-341 but the low frequency infrared and Raman data given in Table 7 are new.

Assignments for the series (Table 7) differ somewhat from those of OIKAWA [33]

and of BROWN et al. [32] but are consistent with those for the phenyl chlorosilanes [l]. Oikawa’s frequencies for Ph,C do not agree with those reported by other investigators; his sample must have been misidentified. As shown in Fig. 7, the spectra of the tetrs,phenyl metal compounds are, for the most part, satisfactorily interpreted in terms of vibrational splittings of the phenyl ring modes superimposed on a simple pattern arising from vibrations of the tetrahedral skeleton. The dis- crepancies between Raman and infrared frequencies for a few of the bands may be due to sampling conditions ; Raman spectra were run at 70-80°C in C&H, solution, and infrared spectra were run as mineral oil mulls.

The 269 cm-l frequency in Ph,Ge does not seem to fit the pattern of the other compounds and is not assigned. This band w&s not reported by RATSEK [29] nor by FATELEY [35] and may be from an impurity.

[29] W. J. RATSEK, M.S. Thesis, University of Wisconsin (1961). [30] J. G. NOLTES, M. C. HENRY and M. J. JANSSEN, Chem. Id. 298 (1959). [31] M. C. HENRY and J. G. NOLTES, J. Am. Chews. Sot. 82, 555 (1960). [32] D. H. BROWN, A. MOEAIQXE D and D. W. A. SHARP, Spectrochim. Acta 21, 659 (1965). [33] H. OIKAWA, Nippola Kagah Zaxwhi 84, 1 (1963). [34] H. OIKAWA, ibid. 84, 11 (1963). [35] W. G. FATELEY, private communication.

Low frequency vibrational spectra of phenyl compounds 706

Ph,C

Ph,Ge

PhdSn

Ph,Pb I I I I I

0 100 200 300 400 500 600 cm-’

Fig. 7. Low frequency spectra for tetraphenyl Group IV-A elements, shown schematically.

Intensity variations in the skeletal bending modes near 60 and 100 cm-l are noteworthy. For Ph,C, Ph,Si and Ph,Ge, the bands are so weak as to be classified as questionable. Yet for Ph,Sn and Ph,Pb, they are seen comparatively easily.

Phenyl trichloro derivatives of group IV-A

The molecular spectra of PhCCl, have been reported by STEPHENSON and

COBTJRN [36] and assignments were made for PhMCl, (M = Si, Ge and Sn) by

Table 8. Low frequency assignments for phenyl trichloro derivatives of group IV-A

Assignment

r,(MCls) v, (MC&) Y t W

u X

6, (MCI,) 6, (MC&) p(MC&)

* Ref. [36]. t Ref. [l]. $ Ref. [37].

PhCCI,+ PhSiClst PhGeCl& PhSnCl&

302 690 429 377 629 514 412 368 507 461 454 439 405 346 290 264 - 389 - 396 366 264 255 218 307 244 216 184 264 189 162 128

246,237 169 146 118 176,118 110,86 92.76 68,63

DURI~ et al. [37]. The latter authors point out several unlikely aassignments in STEPHENSON’S work [36], but some of their own low frequency assignments are unconvincing when spectra for other members of the series PhJK!l,_, are considered. Specifically, the low frequency ring deformations and the MCI, deformations seem more reasonable when assigned as indicated in Table 8 and Fig. 8.

[36] C. V. STEPHENSON and W. C. COBURN, JR., J. Chem. Phys. 42,36 (1966). [37] J. R. DURIO, C. W. SINK and 5. F. BUSH, J. Chem. Phya. 45,66 (1966).

706 A. L. SMITH

p: P 80 8s x u t Y "6 'b

PhCCl, I I I I I I I I I ,/ ’ ,, __,’ :_.--‘. ___, __ _, ; ,,,’

_____ _... --;-_________- ..-- ----.---

PhSICI, I I I P ;,’ ’ ,; ,/‘,, I

,! I ,, ,,,’ .’ ,_ ‘. . . _-.-.-:- -. PhGeCll I ;’ ,; I, , , . ’ I.1 ,I , I I 11111 I

_, ‘,, PhSnCIs

; ,,’ I IL I II 1

I I I 1 , I I 0 100 200 300 400 500 600 700 600

cm-’

Fig. 8. Assignments and correlation of corresponding frequencies for phenyl trichloro derivatives of Group IV-A elements.

CoNCLlJsIoNs

Structurally related phenyl derivatives of Group IV-A elements give unique but similar patterns in the low frequency infrared region. Whereas the frequencies of the phenyl ring vibrations fall within clearly defined limits, their exact positions are often unpredictable, apparently because of interactions with vibrations involving the tetrahedral skeleton. The intensities are even more anomalous, and may vary drastically as the central tetrahedral atom or number of phenyl substituents is changed. In any case, it is clear that complex absorption patterns such as these can be successfully interpreted only when a number of related series are compared ; it is simply not possible to make realistic assignments by considering only a single molecule or even a single series.

rl&nowZe&n~&-Faz infraxed ape&a were obtained through the cooperation of R. A. NYQUIST, and Raman data were taken by Y-S. LO and R. KAUEL, all of The Dow Chemical Company. Useful discussions were held with J. R. DTJRIG of the University of South c8rOh8.