The Raman and infrared spectra of the series (CH3)nSnCl(4−n)

JOURiXAL

OF MOLECCLAR

SPECTROSCOPY

The Raman

343-364 (1962)

and Infrared Spectra (CH&nCL,*

WALTER Department

8,

I?. EUGELL

of C’hemistry, Purdue

AND C.

H.

University,

of the Series

WARD? Lafayette,

Indiana

The Raman and infrared spectra of CH,SnCl,, (CHB)2RnCl,, (CH3)&CI, and Sn(CHI)< w-ere observed. For each of these molecules, the observed wave numbers were assigned to the fundamental modes of vibration or to combinations, and overtones of the fundamental frequencies. Key features of the assignments for the molecules of this series are the apparent decoupling of the CHI group vibrations, the coincidence of the S-C stretching vibrations, and the superposition of the low-lying fundamentals. The results for this series of tin compounds have been compared to the results for the corresponding carbon and silicon series. I. ISTRODUCTIOX

The spectral series (CH,).SnC1~4_,j is of considerable interest in that it represents the first complete series of tin compounds to be investigated in both the Raman and infrared effect and for which complete frequency assignments have been made.’ The resultIs thereof, by comparison t’o the corresponding carbon and silicon series, provide an excellent approach to the problem of central atom mass and size effects on vibrational spectra. II. EYPPRIMFNTAI Li 2 A.

PREPARATION

J

OF COMPOUNDS

Methyl tin trichloride was prepared by bubbling met’hyl chloride through fused anhydrous stannous chloride at 365°C (2, Y). The compound was purified by sublimation at 35°C under 0.2-mm pressure. The purified compound melted at 47-50°C. Only one or two very weak infrared bands were observed which may be due to impurities. Dimethyl t,in dichloride2 was purified by sublimation at 55°C under 02mm * Based upon a portion of the Ph.D. thesis of C. H. Ward, Purdue University,

September,

1953. t Present address, School of Chemistry, Auburn University, Auburn, Alabama. 1The series &SnClcI_,,, has been studied in the infrared by Grifhths and Dervish (1) and the series Et,SnMec,_,,, has been studied in both the Raman and infrared by Dillard and Lawson (1)) but complete assignments w-ere not made. 2 Research sample kindly supplied by Metal and Thermit Corporation.

344

EDGELL

AND

WARD

so* 5.C

C H, SnClj

0

FIG. 1. The

600

400

200

Rnman

spectrunl

cm-’

of CHa8nCI:I

pressure. After two sublimaGons, t,he purified compound of mp 108-l 11°C’ showed no infrared bands due to impurities. Trimethyl tin chloride was prepared by passing methyl chloride over st#annous oxide at 325°C (9, 3). The crude (CH,),SnCl, as obtained directly from t#hc react,ion, was contaminated wit,h small amounts of (CH,)2SnC12. Separation and purification of the (CH&SnCl was effected by a fractional sublimation process. Such a purification process is feasible because of the ohsrr\red marked different in sublimation behavior of the two compounds, i.e., (CH3)&Clt sublimes appreciably under 0.2 mm pressure at about .iO”C, while (CH,),SnCl suhlimev fairly rapidly at room temperature, or slight,ly below, even under pressures rip to 0..5 mm. The separation and purification process was followed by obscrvatioll of thtx melting point, chlorine analysis,3 and infrared speWurn of each frwtion. The fraction used for spectroscopic study melt,ed at X8-10°C. 0nly one very we:~k infrared band was observed whirh may be due t)o impurities. Tin t.etramethyl was prepared by t,he met.hod of Waring and Horton (:j) a11d 2 A method simi1s.r to that used developed (see Kochow (4) 1.

for corresponding

silicon

compounds

was successfnll~-

SPECTRA

OF METHYL

TIN

CHLORIDES

X.5

by the method of Edge11 and Ward (6). The Sn(CHJ4 was purified by fractionation through a Todd column (40-50 plates). The fraction distilling at 76.6% (748 mm) was used in the spectroscopic work. No infrared bands due to impurities were observed. B. RAMAN

SPECTRA

The equipment and techniques employed in observing the Raman spectra of these compounds has been described previously (7). The Raman spectrum of CH3SnC13, in the liquid state, was observed at 60& 5°C. The photoelectrically recorded Raman spect,rum of CH$nC& (below 600 cm-l) is shown in Fig. 1. The complete Raman spectrum is listed in Table I. The Raman spectrum of (CH,)zSnClz was observed fo both the liquid and solid state. In liquid state measurements, the sample was maintained at 120 f 5°C by means of a Variac controlled Pyrex glass furnace. The solid state spectrum was observed at 50 f .!i°C. Excessive background radiation, apparently due to slight decomposition of the sample by ultraviolet radiation during long exposures, prevented the measurement of polarization factors. The observed Raman bands are listed in Table VIII. TABLE

I

THE RAMAN SPECTRUM OF CHBSnCll Wave number (cm-l)

Relative intensity

Polarization factor

3024 2932 1200 550 3ti3 142 112

2 3 3 5.5 10 G. 1 G.4

Depol. Pol.

Assignment

vi (El VI (Ad

~2(A,)

PO1

0.43 0.2G 0.8G 0.7G

v:j (A,) ~1 (A,), ~5 (A,), WC (E)

~10 (E) ~11(E)

Hg 4916

J 0

500

1000

1500

FIG. 2. The Raman

spectrum

2000

2500

of (CH:s)$nCl

L 3000

cm-’

346

EDGELL

AND

WtZRD

The Raman spectrum of (CH3)$nC1, in t’he liquid state, was observed at’ 50 f 5°C. The Raman spectrum of (CH3)$nCI, photoelectrically recorded, is shown in Fig. 2. The complete Raman spectrum, including very weak lines only observed by photographic methods, is list’ed in Table XIII. The Raman spectrum of tin tetramethyl has been report’ed elsewhere (7). The compounds of this series are excellent Raman scatt,erers. For esampk~, a I.>-set photographic exposure is sufficient t,o observe nearly all of the fundamental hands of Sn(CHJ4. c‘.

IXFRARED

SPECTRA

A double beam recording infrared spect’rophotometer (Perkin-Elmer Model 21) n-as used. KaCl optics were used in the range 2-15 p and IiBr optics for the range 15-25 p. Specially designed cells (8) were employed for the infrared study in the liquid stat,e. The infrared of CH3SnC13, (CHJ&nC12, and (CHJ$nCl spect,rum of CH3SnC13 was observed at 60 f- ;i”C, of (CH,)BnC& at 120 & 5”c’, and of(CH,)$nCl at 50 f 5°C. Infrared spectra for these three rompounds are shown in Figs. 3-5 and are tabulated in Tables II, IX, and XIV. The infrared spcc+rum of Sn(CH3)4 has been reported in a separat,e paper (7). CH, XI,

2

3

9

4

6

liquid

7

9

8

FIG.

3. The

“HJ,SnCI,

O.IZZmm

IO

12

II

infrared liquid

~053°C

I3

IS

14

spectrum

I6

I7

0.025

mm

I8

I9

20

2%

of CH,&K& 120*5*c

-0.05mm CH$N

d-t.

L

2

2.

4

5

6

7 FIG.

9 4.

9

The

IO

II

infrared

12

I3

spect,rnrn

I4

I5

I6

I7

of (CHs)?8nC15

19

I9

20

21

22F

SPECTRA

OF METHYL

3-17

TIN CHLORIDES

III. INTERPRETATION

OF SPECTRA

A. CH3SnC13 The CH$nC& molecule belongs to the point group C3”. The number, character, and Raman and infrared activity of the fundamental vibrations of t’he CH,SnCl, molecule were determined by group theory calculations (9, 10) and are listed in Table III. Approximate descriptions of the permitted fundamentals are given in Table IV. The pertinent rules for determining the species of combination bands and overtones are: AI-A,

= A?.A? = Al,

AI-AZ = Al, ill.E

= A2.E

= E,

E.E

= Al+A2+E,

E” = A1+E. Five of the eleven active fundament#als may be considered to he due t’o vibrations of the CH, groups, and correspondingly, five arise from vibrations of the SnC13 group. The remaining fundamental arises from the &-C stretching mode. The CH, group vibrat,ions are readily assigned on the basis of observed polarization dat,a and the reported freyuency assignments for the methyl halides (11), the corresponding I, 1, I-trihaloethanes (12) and methyl silicon trihalides (12-14). The Raman lines at 30% crnl, 2932 cm-l, and 1200 cm-’ have been assigned to ZJ~,vl: and v~,respe&ively. Infrared bands corresponding to t,hese Raman lines were observed at 3033 cm-‘, 2940 cm-‘, and 1200 cm-l. The skong infrared band at, l-102 cm-1 must, be assigned to the CH, asymmetrical deformation, us, even (CH&%Cl

2

3

,

4

,

5

I

6

liquid

(

.

7

8

9

IO

0.122 mm

II

12

509 sac

c

.

*

13

14

15

L

16

17

FIG. 5. The infrared spectrum of (CH&SnCl

I8

19

20

21

22

23/u

:24s

ISIX :ELL

AND

TABLE; THE

INFRARED

WARD II

sPE(‘TRITM

OF

CH:$d$

Interpretation

Description

3033 3033 3033 940

+ 1402 = 4435 + 1200 = 4233 + 800 = 3833 + 800 = 3i-10

L'S40 + 2IXM) = 3XiO or Inlpur.il!_? :HM + 548 = 3581 or Inlpurit y ? 1,: i1*:i Y, (A, 1 211402) = 2804 L’c1‘200) = 2400 1402 + 800 = 2’202 1200+ 800 = 2000 1200 + 548 = 1748 2(80(l) = lliO0 1200 + 363 = 1563 1402 + 112 = 1544 Y$ 112) 1200 + 142 = 1342 Y:! (‘1,) “(548) = IO!lCi Pi, iI51

1200- 548 = ti5201'363 + 2C142) = Ii-IT 1:02 - XI)0 = cm :triY + 2(112) = 587

Ii!)!)

58s

jli” 548; .5"5

I~‘unclamental type

v:< (A,

No. of fundamentals 5 1 ti

.I,

A, 14:

Kaman

I

activity

Infrared

B., 1101. i. a. :t., tlcpol

activit!

:I i. :1.

:1

though no corresponding Raman line is observed. Similarly, the very strong infrared hand at SO0 cm-’ was assigned to the CH, rocking vibration, vg. Estrcmely low inten&ies of &man bands due to asymmetrical CH, deformations and CHzc rocks

appears

to he characteristic

of the present

series

of moleclllrs.

SPECTRA

OF METHYL TABLE

TIN

349

CHLORIDES

IV

DESCRIPTION OF FUNDAMENTAL VIBRATIONS OF CH3SnCli Description CHJ symmetrical CH3 asymmetrical CH, symmetrical CH, asymmetrical CH, rocking Sn-C stretch SnCL symmetrical SnC13 asymmetrical SnC13 symmetrical SnCl:, asymmetrical SnClP rocking CH, torsion

A,

AZ

E

stret,ch stretch deformation deformation

stretch stretch deformation deformation

TABLE

V

THE FUNDAMENTAL FREQUENCIES OF CH,$nCl:, Fundamental type ~1 Y? ~3

Raman 2932 cm-l 1200 550 303 142 i. a. 3024

(AI) (AI) (A,)

(AI) (AI) ~6 (Ad ~7 (El ~8(El VI

~6

v9

(E)

~10

(El

YlI

(El

Y,P

03)

Infrared 2940 cm-l 1200 548 i. a. 3033 1402 800

363 142 112

Similar observations have been reported for corresponding silicon and lead compounds (13-16). The sharp, strong Raman band at ,550 cm-’ was assigned to the Sn-C sketching fundamental, v3. This assignment is substantiated by t#he observed polarization fact’or. was also observed as an infrared band at 548 cm-l. Two Raman bands arising from Sn-Cl stretching vibrations were expect’ed in the region 200 to 500 cm-l. However, only one very strong Raman band was observed in this region, at 363 cm-l. The observed band has a somewhat diffuse character, which might seem to indicat’e that it is of E type. However, the band is very strongly polarized and therefore must be of A1 type. On the basis of these observations, it is believed that accidental degeneracy of the symmetrical and v3

EDGELL

:kio

ASD

WARD

asymmetrical &-Cl &etching fundamentals occurs. The Raman line at, 36X (7+ was therefore assigned t,o both Sn-Cl stretching vibrat,ions, v4 and v,,~. AUthough t,his assignment fits the observed spectral data, there remains the possibility that’ t,his band is of pure A1 character and that the E-type hand is of extrcmcly low intensity and was not observed. The two &Cl, deformation and t’he single SnC13 rocking fundamentals aw yc*t to b(t assigned. Two strong Ramnn lines at, 112 csrnpl, and at 14% c*m-’ ww observed. Roth are diffuse, and neither are polarized. The lowest Raman line at 1 I:! (*npl was assigned t,o the SnCl, asymmetrical deformat,ion vibration, vl,, by comparison to the c*orrcsponding CH,CCl, and CH3SiC1, molecules (12). Awclc~ntal degeneracy of the remaining t’wo fundamentals of AI and E t,ype appears to o(wlr. The assignmentj of fundamental vibrat,ions of t.he CH,SnCl, In(JkUtP is thus complet,ed by attributing the Raman lint at 142 (sm-’ to bot’h the SnCl:+ symmetricA deformation, v5, and the SnCI,, rocaking mod?, IQ. The fundan~ct~tal frec~ucqlc*iesare listed in Table V. The flmdamental freqwncy assignmcnt~s for t)he series CH:JXI:j, CHaSi(‘lzl, (‘H3(K13, and (:H38nC1, are shown in lcig. 6. The assignmrntjs for thr (‘f-T:, (‘(‘I:] and CH, SiCl,, molecules are those proposed by Tobin (12). cm-’

0

moo

500

l500,‘

3000

I

I~‘undamental type

No. of fundamentals

Kaman activitl

Infrared activit!

SPECTRA

OF METHYL

TIN

CHLORIDE8

351

B. (CH&SnCl? The (CH&SnC12 molecule belongs to the point group Czv. The number and nature of the fundamental modes, as deduced from group theory calculations (9 IO), is given in Table VI. An approximate descript,ion of the permitted fundamentals is given in Table VII. The pertinent select,ion rules for determining the species of combination bands and overtones are: A,.AI

= Az.AI = B1.B2.B2.B2

Al.Az

= BI.B2

= A2,

A,.BI

= A,.Bx

= B1,

AI+B? = A,.B1

= BP,

= A1,

A1’ = A22 = B1” = B22 = A1. Several important aspects of the observed spectral data are easily deduced by inspection, one being that the number of observed lines which can reasonably be assigned to fundamental modes is markedly less than the number of fundamentals permitted by selection rules. Considerable piling up of fundamental frequencies is thus expected. This tendency has previously been observed for the (CH,),CC12 and (CH&SiCL molecules (1.2). A second outstanding feature of the spectrum of (CH&3nC12 is that the number of lines which can be reasonably assigned to extra-skeletal fundamental modes is five. This is, of course, the same number expected and observed for the CH,SnCl, molecule. This observation seems to indicate that in the (CH&3nC12 molecule, the CH, group tends to behave as if it were attached to some heavy point mass and thus only five fundamentals of the CH, group itself could be expected. Thus it appears that t(here is very little TABLE

VII

DESCRIPTIONOF FUNDAMEXTAL VIBRATIONS OF (CH,)$AnCIZ Description CH, asymmetrical stretch CH, symmetrical stretch CH, asymmetrical deformation CH, symmetrical deformat.ion CH, rocking Sn-C stretch SnCL stretch Sn--Cz bending SnCl! deformation SnClz rocking SnCl2 torsion CH, torsion

4

A2

B,

B2

VI

Vlil

Y15

Y?,

EI>(;ELI,

352

AND

WARD

interaction\

hetmeen the CH, groups and the rest of t,he molecule and would indirat,e that the CH, group would behave similarly regardless of the symmct,ry of t,he rest of the molecule if the attached group or groups is of very large mass. That coupling forces between the CHa groups themselves and the rest, of the molecule are small may he illustrated by considering the CH,, &etching modes, I;? and L+ These are hot.h symmetrical modes and difl‘er only in that, for ~2 only \-ihrations in phase are taking plaw while for yY2only out of phase \-ihraGons arc occuring. If the two modes are coupled through interaction forces, or otjhwLvisc, therct will he a frequency difference hetwecn V?and pz2and the diffcrcttw in frcquenc*y will he a measure of t#he coupling. Experimentally, t,here is observed only one hand in the region of CHB stret.ching vibrations which can he rcasonahlp intcrpretcd as being of symmetrical type. This hand is found at approximatrly the same place as t,he single CH:( symmetric*al st,retch of CH:$3nCl:~. In vie\\- of these ohscrvat,ions, the most plausible interprct,ation is that, these two modem arc tutcoupled and hence v2 and pz2 have t,he same frequetwy value. A similar argumrttt is valid for the CH, asymmetrical st,ret>ching modes, ~1, VI,,, y15, and Y?~,aIt,hortgh not so readily apparent as in the case of t.he symmet.rical modw. _1tt alternate possibility is that sinw only tjwo stretching futtdamcntals arc observed, the remaining four, alt,hough appearing at difYerent, frequcncics, :w too weak to he observed. However, this possibility dots not’ appear likely in \icw of the high intcttsit8y of the t,wo observed hand s, nonappearance of comhittatiott hands ittvolving these fottr fundamctttals, and the ohser\~ed intrnsit,y wlatiottships to hc discussed later. The fmtdamental frequetwics tnay now hc assigned in a very straightforwwd mannw. In view of the foregoing discussion and by cwmpsrison t,o the (‘H:$IICI:~ assignmcwts, the fire highest fm~damentals arc’ assigned to the CH, group. AA.wignmcwt of these hands is shown in Tables VIII&S. It, should he noted that, as in t,ht>caase of CHaSnC13, ltamatt bands corresponding t.n the CH:, asymmc~t.ric*al modt+ and to CH:, rocking rnodcs were not ohswwd. TABLE: THE

2928 1211 566 521 31-I 185

VIII

RAMAN SPECTRUM OF (CH,)$-3nCIz

111 111 111 “S

s “S

SPECTRA

OF METHYL TABLE

TIN

3.53

CHLORIDES

IX

THE INFRARED SPECTRUM OF (CH,)2SnC12 Wave number (cm-‘) 4392 4200 3782 3726 3009 2926 2786 2377 2177 1996 1763 1718 1547 1402 1201 1072 792 563 524

Description

s

sh, br br sh, br s s

Intensity m um m S S a

R, vbr

m VW

Vh

VW

S

m

s

br br S

m w S S

Vhr

VW

vvbr

vvs

br

S

br

S

Interpretation

3009 3009 3009 2926

+ 1402 = 4411 + 1201 = 4210 + 792 = 3801 + 792 = 3718

niA1), vp(Al), 2(1402) 2(1201) 1402 + 1201 + 1201 + 1201 + 1201 +

~1dBd, m(Bz) v?.,(Bz) = 2804 = 2402 792 = 2194 792 = 1993 563 = 1764 524 = 1725 344 = 1545

w(A,), ~ls(B,), o;(Br) Q(AJ, w(Bd 563 + 524 = 1087 vs(Ad, Y,~(B,), I vzs(Bd I

The so-called skeletal frequencies remain to be assigned. The Sn-C stretching fundamentals, ~6 and yz6,are observed as Raman lines at 521 cm-l and 566 cm-l with corresponding infrared bands at 524 cm-l and 563 cm-l. The lower of these two frequencies is assigned t’o the AI-type vibration, ~6, by comparison to the other members of this series and because of its great Raman intensity. The higher of the two must then be assigned to the Bs-t,ype vibration, ~26.Accidental degeneracy of the two Sn-Cl stretching vibrations, as was previously observed for the CH3SnC1, molecule, appears to occur. Consequently, the strong Raman line at 344 cm-l has been assigned to both of the Sn-Cl stretching fundamentals, v7 and v18. Five fundamentals are yet unassigned and although all five are to he expected to appear below the &-Cl stret’ching frequencies, only one strong, very broad Raman line is observed in this region. This observed band is much broader than any other Raman band of (CHJ2SnC12, which tends to indicate that the band is composed of more than one band. Accidental degeneracy of low-lying fundamentals is also to be expected by comparison to the CH,SnCl, molecule and other similar molecules having heavy central atoms (19). Although the possibility that only one fundament,al was observed, while the remaining four are too weak to be observed, is plausible, this does not appear too likely in view of the high intensity of the observed band (especially since at least four of the corresponding

3010 cn-1

2928 1211 521 344 135 135 3010 (1402) 1702) 135

i. a. i. a. i. :I. i. a. i. a. 3009 1402 792 -

3010

344 135 3010 2028 1211 5Mi 13.5

fundamcwtals

of (CH,)$3iCl~

of the ;tJ~ovc discussion. remaining

fundamrntal

are of almost

The Raman modes,

equal intensity

band at, 135 cn?

(IJ,

I./,)) and in vie\\

is thus assigned

to the

vg, ~9, yt’?, v13, and vx.

C‘ompariwn of frcqucncy assignment,s for t’hc C, Si, (:c, and 8n series is show1 i11 Fig. 7. Thr proposed assigmncrlt, of Tohin (12) for (CH&W12 and ( C’FT:j)2Si($

ww Iwcd. :I st#ud.y of t,his figure leads one to suggest’ that

of I+, and v4 of the (CH,),CCl,

molwule

the assignrrwntj

may he in error.

(‘. (CH:,),Sn<.‘l Tht ((‘H:J$M’l molw~~l~~, like the CH:jSnC’l:, n~olcc~ul~, belongs t)o t,hc point, group (‘3,. Howevrr, the grcat,cr numhrr of atoms of (CH&SnCl (wwider:dJy incrrarrs the llumher of fundamcnt,al vibrations over that, of CH$n<‘l!. Thv nlunhrr and nature of the fundamental vihratjionnl modes of (CHJ3SnC1 is gi\wr in Tal)lt> XI and an npprosimatt> dwcription of the fundamcnt~al modes ilr Table

SPECTRA

OF METHYL

FIG. 7. Fundamental

frequencies TABLE

FUNDAMENTAL

TIN

CHLORIDES

of (CH,)?MCl,

3.55

molecules

XI

VIBRATIONS

OF

(CH8)1SnCl

Fundamental type

No. of fundamentals

Raman activity

Infrared activity

4, A? E

8 4 12

a. pol. i. a. a. depol.

a. i. a. a.

XII. The selection rules for combinat,ion bands and overtones are the same as those for CH3SnCl~. The general aspect,s of the spectrum of t,he (CHJ$nCl molecule are the same as those observed for (CH,)$nCl?, i.e., the vibrations of the CH, groups are little coupled to each other thus giving rise to only five fundamental frequencies and again considerable piling up of skeletal frequencies occurs. The five highest fundamentals are thus readily assigned t,o vibrations of t’he CH, group. Comparison t,o the assignments for CH,SnCl, and (CH,)$3nCl, molecules and a study of t,he observed polarization data leads to an unambiguous assignment as given in Tables XIII-XV. It should be noted that very weak Raman lines corresponding to CH, asymmet’rical deformation and CH, rocking modes were observed in contrast to observations for the other methyl tin chlorides. y6 and vZ1are assigned to the polarized Raman line at 518 cm-l and the Raman line at 548 cm-l, respectively. v6is also observed as an infrared band at 514 cm-‘, while Y:~ appears at 545 cm+ in the infrared. The Al-type Sn-Cl stretching fundamental, y7, appears as a polarized Raman band at 318 cm-‘.

:+x

EDGELL

AKD

TABLE DESCRIPTION

WARD

XII

OF FUNDAMENTAL

VIBRATIONS

Description

OF

(CH,)$nCl

A,

CH, asymmetrical stretch CH:, symmetrical stretch CH, asymmetrical deformation CH, symmetrical deformation CH:, rocking Sn-C stretch Sn-Cl stretch SIIF C:{ deformat,ion C, -911 --Cl bend C’H, torsion

TABLP:

irave number (cm-‘)

Relative intensit!

Three

fundamentals, broad Raman

u,(r2,), v,,(E), v,,iE) vz(A,), vl~(E) 211202) = 2402 1202 + 518 = 1720

0.79

0.23

v:r(A,), 06(E), v,(.4,), Q(E) vj(A,), ulyiE), Y”1(E 1

0.50 0.74

0.24 0.45 0.88

v8, ~2, and vzR,remain band was observed

any of t’hese three fundamentals. for the low-lying fundamentals

Assignment

Polarization factor

3001 2923 237-l 1712 1401 1202 790 548 51fi 318 150

strong

XIII

vz,,(b:l

Y6(A,1 w(A,) va(.2,),

to be assigned.

vrr(E),

v,:i(l~;,

However,

whirh could reasonably

Apparently of CH,SnCl,

Y,,~I+:)

only one

be assigned

to

a situation similar to t’hat observed and (CH3)SnC12 owurs here also.

The possibility that one fundamental is strong, while the other two are wry weak, is not excluded. However, on the basis of argument,s similar to t,hose for CH$nCl:~

and (CH,)$nC12,

piling up of these

three

fundamentals

t,o give riscb

to a single Raman band was considered more likely. Consequently, the observed strong Raman band at 150 cm-l was assigned to the remaining fundamentals, ~8, ~2, and ~23. Graphical comparison of the fundamental frequencies of the C, Si, Ge, and Hn series is shown in Fig. 8. It should be not#ed that the assignment of v:( of

SPECTRA

OF METHYL TABLE

TIN

357

CHLORIDES

XIV

THE INFRARED SPECTRUM OF (CH&SnCl Wave number (CM’)

4396 4195 3989 3799 3727 3652 3535 3002 2925 2786 25SF 2368 2165 1988 1740 1706 1600 1484 1400 1193 1082 1052 787 619 587 5611 545) 523) 511 472 458 419

Description

Intensity 3002 3002 2925 3002 2925 3002 3002

s s

br br br sh, br sh, hr s R sh, s br

+ + + + + + +

w(AI), ~z(Al), 2(1400) 1400 + 2(1193) 1400 + 1193 + 1193 + 1193 + 2(787) 1193 +

S

vbr hr 8 s

sh, br sh, br br

1400 = 4402 1193 = 4195 545 + 514 = 3984 787 = 3789 787 = 3712 514 + 150 = 3666 545 = 3547 VIZ(E), Y,~(E) vlj(E) = 2800 1193 = 2593 = 2386 787 = 2187 787 = 1980 545 = 1738 514 = 1707 = 1574 318 = 1511

YS~A,), w,(E), y,,(E) v,(A,), Y,~(E) 2(545) = 1090 545 + 514 = 1059

S

vbr br vvbr hr sh, br br sh, br br br br

Interpretation

v:(A,), w(E), w(E) l-100 - 787 = G13 -

VW VW

787 - 318 = 469 318 + 150 = 468

(CH,)$iCl does not appear to be in harmony with the series and may possibly be in error. D. Sn(CHJ4 The Sn(CHJ4 molecule, like the other tetramethyl compounds of Group IV A elements, belongs to the point group Ta. The Raman and infrared spectrum of Sn(CH3)4 and assignment of observed lines and bands has been reported previously (7). The fundamental frequencies and their description are listed in

EI>(;ELI,

:C%

All’D

1’ABLE THE FUNDAMENTAL Fundamental type

WARD

XV

FREQUENCIES

OF (CH,),SnCI

Raman

Infrared

3001 cn-’ 2923 1401 1202 ioo 518 31s 150 (3001 1 (14011

3002 rtn -’ 2925 1400 1193 787 514

(700I i. a. 3001 3001 292:i 1401 1401 1202 790 790 548 150 150

FIG. 8. Fundamental

frequencies

(8002 ) 114001 (757 i i. a. 3002 3002 2w5 1400 1400 1193 737

7% 54.3

of (CH,),MCI

molecules

SPECTRA

OF METHYL TABLE

TIS

CHLORIDES

359

XVI

THE FUNDAMENTALFREQUENCIESOF Sn(CH,), Fundamental

type

Description CH, symmetrical stretch CH, symmetrical deformation Skeletal stretching CH, torsion CH, asymmetrical stretch CH, asymmetrical deformation CH, rocking Skeletal deformation CH, asymmetrical stretch CH, asymmetrical deformation CH, rocking CH, torsion CH:T asymmetrical st,retch CH, symmetrical stretch CH, asymmetrical deformation CH, symmetrical deformation CH, rocking Skeletal stretching Skeletal deformation

Table XVI. Graphical comparison of the fundamental Ge, and Sn series is shown in Fig. 9. IV.

GENERAL

Wave number (cm-‘) 2915 1205 508 i. a. 2987 (1445) 788 157 (2987) (1445) (768) i. a. 2987 2915 (1445) 1194 768 530 157

frequencies of the C, Si,

DISCUSSION

The fundamental frequencies for the spectral series studied, i.e., Sn(CHJ4, (CH,)$nCl, (CHJ2SnC12, and CH$nC&, are graphically shown in Fig. 10. The data for SnCl4 have been added in order to complete the series (Ref. 11, p. 167). The spect,ral range has been divided into six regions for purposes of clarity and discussion. The highest region, labelled C-H stretch, is the region in which fundamentals arising from CH, stretching motions are observed. Corresponding regions represent CHs deformation frequencies, CH, rocking frequencies, Sn-C stretching frequencies, and Sn-Cl stretching frequencies. The remaining lowest region is approximately described as the region of skeletal deformation and rocking frequencies. This graph clearly shows that increasing mass produced by successive substitution of CH, groups by Cl atoms has relatively little effect on the observed frequencies. This effect was expected in view of the small change in total mass of the molecule brought about by this successive substitution. That t,he interactions between methyl groups and the rest of the molecule is small is clearly indicated by this graph. With the single exception of the CH, symmetrical deformat,ions of Sn(CH,)4, only five fundamentals of the so-called

300

EDGELL

cm-’

0

AND WARD

500

I

1000

1500,

3.000

9 , c3

I I

(C H&C

(CH,),Si i/ KH&Ge

1 I 1

CH&Sn

I 1

(CH3b Pb

FIG. 9. Fundamental cm-’

0

500

of M(CH,),

molecules

1000

I500

5

3oqo

I

II

II

SnCI )

II

1

I

I

I

I I

I

I

I

I

I

I

I

I

I

1C H,),Sn

(CH,),

frequencies

I sq

II

II

s k&al

%-Cl

def.+ rock

FIG.

10. Fundanlental

Sn-C

frequencies

CH3 rock

of the series

cu3

I

def.

I

I

,‘-Ii

;trotch

(CH~),,SI~CI~~-,,

inner vihrst’ions of CH, group are obserrtd. It would thus appear that all molec-ulrs of this series tend to behave as if composed of a CH, group attached to some heal-y point mass. It should he noted t,hat t’he only region in which the number of observed fundamentals is the same as the number permitted by selection rules is that of

SPECTRA

OF METHYL

TIN

CHLORIDES

361

the Sn-C stretching frequencies. The number of fundamentals observed in all other regions is less than t,he permitted number. As will be not,ed below, this effect is not nearly so pronounced in the corresponding spectral series having the light,er central atoms, Si and C. The intensity of various fundamentals is of interest. The skeletal deformation and rocking fundamentals are observed, in each compound, as very strong diffuse Raman bands. The CH, rocking fundamentals are observed as extremely strong and very broad infrared bands, while being of very low intensity or not observable in the Raman effect. The CH, symmetrical deformation frequencies occur as sharp, well-defined bands in both the Raman and infrared. However, t’he CH, asymmetrical deformation fundamentals are extremely weak or not observed in bhe Raman effect. The CH, stretching fundamentals are observed as strong bands in both the Raman and infrared spectrum. The asymmetrical and symmetrical frequencies are of nearly equal intensity as observed in the infrared spectrum as contrasted to that observed in the Raman spectrum in which the CH, symmetrical stretching fundamentals are considerably stronger than the asymmetrical mode. The alteration in infrared intensity of the CH, stretching fundamentals as the number of Cl at,oms in the molecule is increased is very st,riking. The intensity is markedly decreased as the number of Cl atoms is increased. The intensities appear t*o be almost in a rat,io of 3, 2, and 1 for the series of (CHJ$nCl, (CH&SnC$, and CH3SnClz. It should be noted that a 3 to 2 to 1 ratio is easily interpreted in terms of litt,le or no coupling between CH, groups of the methyl tin chlorides. Although all Sn-C stretching fundamentals appear as strong Raman lines, the Al-type fmldamentals are much stronger than fundamentals of other species. These fundamentals are also observed as strong lines in infrared spectra. The number of Cl atoms per molecule of the methyl tin chlorides greatly influences the Raman intensity of t’he Sn-Cl stretching frequencies. The Sn-Cl stretching fundamental is relatively weak in the case of (CHJ$nCl, is much stronger for (CH,)2SnC12, and is very intense in the case of CHzSnCls-in fact is the strongest Raman line of CH$nCl.,. The spectral series of C and of Si compounds corresponding to the Sn series are shown in Figs. 11 and 12. The pattern formed by the C-Cl, Si-Cl, and Sn-Cl stretching fundamentals appears to be of considerable importance. A wedge shaped pattern is formed by the C-Cl stretching fundament#als. A similar wedge, but much smaller, is formed by the Si-Cl stretches. One would then predict that the wedge would be smaller for the corresponding Ge compounds and even smaller for the Sn compounds. Thus the pattern actually observed in this work is as predicted from the above considerations and furthermore, provides additional evidence that the frequencies of the &-Cl symmetrical and asymmetrical stretching fundamentals of (CH&SnCL and of CH,SnCl, coincide.

EDGELL

3(i2 ;m- f

II

II

(CH&Si

1

II

Cl

(CH&SiCI,

KHJ

1000

500

0

(C H&&i

AND W.4RD

11 11

SKI,

1

1 1

I

I I

II

I

I! \ I\

II

I

1’ I II

ISOQ.

3000

Ill

II

I I

III

II

I I

I

II

I I

I

I

I I

\

1 1

SiCI,

skeletal def.+rock

FIG.

Il.

Fund:tmmtal

Gsi

I

I

.cn3

rock

i

CHJ def.

C-H

1 stretcl

frequencies of the series (CHa),,t;iC1~1_,,) 500

!,

.m-I

si-Ci

\ ‘1

1000

I5PO.,

3000

I

I I I I

C-H ,tretch

Flc. 13. Fundamental frequencir3 of the r~riw rCH:,),,CC’IIr_,,, The

freqncncay

assignments

ponnds is thus further

previously

made

in this work for the?c

t\vo

C’Onl-

xuhstIant~iat~cd.

*%nothcr observation drawn from comparison of the graphs of (1, Si, and Sn fnndamentals ia that, the number of observed fnndamentnls more nearly approaches t,he permitt#ed number wit*h C and Si as the central atom than with Sn. Iwrensing t,he mass of the ventral atom thus appears to incwase the twrdcllc*y toxxrd

awidental

degenerary

or piling np of fmndament~al frequencies.

SPECTRA

OF METHYL TABLE

COVAI.ENT RADII

TIN

CHLORIDES

363

XVII

OF VARI~TX

Element

EI,EMENTS Atomic radius (A)

c

0.77 1 .I7 1.22 1.10 1.46 0.30 ct.99

Si Ge

Sn Ph H Cl

The piling up of fundamental frequencies is indicative of uncoupled vibrational modes and may be interpreted in terms of central atom size and mass. I?or example, as the mass of the central atom is increased (C t.o Si t,o Ge to Sn), vibrations of the CH2 group become “purer”, i.e., the central atom moves less and less during a vibration primarily of the CH, group and hence less coupling is present. With C as the central atom, coupling is present as evidenced by the small amowt of piling up. Thus it appears that forces are operative in compounds of the C series which are not in the Sn series and that these forces appear to be very small. The idealized case of uncoupling due to mass effects would hr realized only if the central atom was of infinite mass. The second factor, t’hat of central atom size, may be illustrat.ed in terms of covalent radii of the various atoms as listed in Table XVII. For example, as the size of the central atom increases, t,he distance between CH, groups increases and hence less interference and interaction between CH, groups is expected. Less coupling of vibrational modes is then certainly to he expected. Mass changes brought, about by successive substitution of Cl atoms for CH, groups have much less influence on the observed fundamental frequencies with Sn as the central atom than with C or Si. This effect is readily understood in view of the smaller mass ratio changes in the case of Sn as the central atom. RECEIVEI)

: Sept,ember 1 I, 1961 REFERENCES

1. V. S. GRIFBITHG AND G. A. W. DERWISH, J. Mel Spectroseop~ 5, 148 (1060); C. R.. DIM~ARI) AND d. R. LAWSON, J. Opt. Sot. dn~. 60, 1270 (1960). 2. A. C. SMITH, JR., PH.D. thesis, Harvard University, 1951. 3. A. C. SMITH, JR., ANU E. G. RQCHO~, J. _4t)t. Che+x. Sot. 76,4105 (1953). 4. E. G. Ro~Ho~, “An Introduction to the Chemistry of the Silicones,” 2nd ed., p. 165. Wiley, New York, 1951. 5. C. F,. W.s~r~;o ANI) W. P. HORTON, J. ilm. C’hena. Sot. 67, 540 (1945). 6. W. F. EuG~:I,I, ANI) C. H. WARL), J. 11~)~.C’hm. Sot. 76, 1169 (1954). 7. W. F. E:DGEI.I, AND C. H. WARD, J. .,lni. C’heul. SM. 77, 6486 (1955).

M4

EDC:EI JL AND W I4RI)

8. W. F. EI)GEI,I, AND C. H. W.~RLI (t,o t,e published). 9. J. E. ROSENTHAL AND G. M. ML-RPHY, Revs. Modern Phys. 8, 317 (19%). 10. A. G. MEISTER, F. F. Cleveland, and M. J. MURRAY, .‘lm. J. Ph?/s. 11, 239 (19-43). 11. (;. HERZBERG, “Infrared and Rarnnn Spectra, of Potyatomic Molecules”, p. 315. V:tll Nostrand, New York, 1945. 12. M. C. T~BIS, J. ;lm. Chem. Sot. 76, 1788 (1953). 18. VON J.(:~uRE~~, H. SIEBERT, ANI) M. W. WINTERW.ERB, Z. .lnorg. U. allgetu. (‘hvvt. 269, 240 (1949). 14. H. MUR.~TA, J. Chem. Sot. Japan, Pure Chem. Sect. 73, 4G5, (1952). 15. It. JX. SHELINE AXD IX. 8. PITZER, J. Chem. Phys. 18, 595 (1950). 16. H. SIEBERT, Z. Anorg. I(. al/gem. Chern. 263, 82 (1950).