Dec., 1953
SPECTRA OB TIN AND GERMANIUM HALOGEN METALORGANIC COMPOUNDS
939
THE VIBRATIONAL SPECTRA OF SOME TIN AND GERMANIUM HALOGEN METALORGANIC COMPOUNDS BY ELLISR. LIPPINCOTT Department of Chemistry, Kansas State College, Manhattan, Kansas
PHILIP MERCIER AND MARVIN C. TOBIN Department of Chemistry, University of Connecticut, Storrs, Connecticut Received April 16, 1068
The Raman spectra of tin trimethyl iodide, tin dimethyl diiodide, germanium ethyl trichloride and germanium diethyl dichloride are reported along with the infrared spectra of tin trimethyl iodide and tin dimethyl diiodide in the region from 3 to 15 microns. Tentative assignments of frequencies to normal modes of vibration are given for tin trimethyl iodide and tin dimethyl diiodide, along with assignments of the low frequencies for germanium ethyl trichloride and germanium diethyl dichloride.
Introduction The halogen metalorganic compounds represent "hybrids" of purely inorganic compounds and metalorganic compounds. I n favorable cases, such as the compounds of the group I V elements, it is possible to make the transition stepwise. One is thus able t o follow the change in properties of a series of compounds as one substitutes halogen atoms for organic radicals on the nucleus. The type of series thus formed is of particular interest from the point of view of vibrational spectroscopy. The set MX4 MY4 contains five distinct compounds of three different symmetries. Since it is t o be expected (an expectation borne out by experience) that the vibrational force constants will not vary much from one compound to another, normal coordinate analyses using quite general potential functions may be made for the series. The interpretation of vibrational spectra for these compounds is, of course, simplest for methyl compounds. There is an enormous increase in the complexity of the observed spectra in passing from the methyl to the ethyl .compounds. Crawford and Wilson' have shown that, under the assumption of zero torsional force constants, molecules consisting of spinning tops on a rigid frame can be treated as having the symmetry of the frame, in making interpretations and normal coordinate analyses. Thus, interpretation of the observed spectra of, say, ethyl germanium trichloride might give some indication of the nature and extent of interaction between the -GeC& frame and the ethyl group. The halogen metalorganics of group I V have come in for little study by physical methods. Skinner and Sutton12 using electron diffraction techniques, have reported bond distances and angles for all of the methyl tin chlorides, bromides and iodides. Shimanouchi and others3 have reported Raman spectra for the methyl silicon chloride series. Murata and co-workers4 have reported Raman spectra for the ethyl silicon chloride and methyl silicon bromide series. To date, no spectroscopic studies of germanium, tin, or lead halogen-metalorganics have been reported.
-
( 1 ) B. Crawford and E. B. Wilson, J . Chem. Phys., 9, 323 (1941). (2) H. A. Skinner and L. E. Sutton, Trona. Faraday SOC.,40, 164 (1944).
(3) T. Shimanouchi, I. Tsuchiya and Y. Mikawa, J . Chsm. Phys., 18, 1306 (1950); 17, 245 (1949); 17, 848 (1949). (4) H. Murata, R. Okawaaa and T. Watase, i b i d . , 18, 1308 (19501.
Compounds.-Samples of ethyl germanium trichloride and diethyl germanium dichloride were kindly provided by Professor Eugene Rochow of Harvard University. Stannic iodide was prepared by reaction of the elements in the presence of a small amount of carbon disulfide. The product was recrystallized three times from benzene freshly distilled from a clean, all glass still. Tin trimethyl iodide and tin dimethyl diiodide were prepared by slowly adding three moles of methylmagnesium iodide to one mole of stannic iodide in an ether slurry. The mixture was refluxed for two hours, then all volatile products were rapidly distilled off and collected. The residue in the flask was hydrolyzed with a minimum of water and repeatedly extracted with ether. The distillate and extractate were fractionally distilled, the ether coming off at atmospheric ressure, and the products coming off under vacuum. The heaSnI came over f i s t as a liquid; then the MezSnIz crystallized in the still. It was removed by gently warmng the various parts of the still with a Bunsen burner, so as to liquefy it. The MezSnIz was purified by recrystallization from n-hexane. A red-colored impurity which came over with the MerSnI, in one run, was discharged by shaking with mercury, followed by distillation. The MesSnI was a colorless liquid with a pungent odor, b.p. 170" at 735 mm., nz6 1.5728. The MerSnIz formed colorless crystals having a faint odor of chestnuts, m.p. 41.5-42.5". No SnMer or MeSnIa was found in an appreciable quantity. The sample of MeSnI8 was obtained from the Delta Chemical Company, New York. It was purified by recrystallization from absolute ethanol. Raman Spectra.-The spectra were obtained with a Hilger E 612 glass spectrograph.6BB The spectra of EtGeCla, EtzGeClz, MerSnI and MezSnIzwere taken on Kodak 103-5 plates, using the Hg 4358 A. line for excitation, and a NaNO2 filter. The spectra of SnI4 and MeSnIa were taken on Kodak 103-Eplates using a NdC13 filter, and the Hg 5461 d. line for excitation. The techniques used in obtaining the spectra of MezSnIz, Sn14and MeSnIa require some comment. MezSnIzwhich is a solid at room temperature, was kept liquid by circulating water at 60" through the water jacket holding the Raman tube. It was found impossible to get optically blank melts, since the material slowly decomposed even at 60". However, one plate which showed six skeletal lines, and one extra-skeletal line, was obtained. The spectra of Sn14 and MeSnI, were taken in solution. The sample of SnId was recrystallized from benzene, and the sample of MeSnIs from absolute ethanol, and solutions prepared by the technique recently described.@ While optically blank solutions of SnId in benzene or carbon disulfide were easily obtained, the SnI4 decomposed RO rapidly upon exposure to the exciting light, that no spect,ra could be obtained. Using a K2Cr04filter to cut out light of shorter wave length than 5300 A. was of no avail. That. photochemical decomposition was involved was shown by exposing a sample of SnIi to ultraviolet light, part of the sample being shielded. After 12 hours, the color of the unshielded portion had changed visibly. (5) E. R. Lippincott and M. C. Tobin. "The Thermodynamic F u n r tioos of Tin Tetramethyl and Germanium Tetramethyl," ONR Report No. 2, University of Connecticut, 1951. (6) E. R. Lippincott and M. C. Tobin, J . Chem. Phys., 21,1559 (1953).
E. R. LIPPINCOTT, P. MERCIER AND M.
940
c. TOBIN
Vol. 57
Likewise, with solutions of MeSnIs in alcohol, no success was attained. No evidence of photosensitivity was visible, but background on the plate was so heavy as to completely obscure any Raman lines. I t is believed that this background was due either to fluorescence of the compound, or to some fluorescent impurity. Infrared Spectra.-Infrared spectra of MesSnI and Me&nIt were taken in the region 670-3700 cm.-i on a Beckman IR-2 recording infrared spectrometer. Spectra of MeaSnI were obtained in a 0.23-mm. cell. Strong bands were observed on a capillary film sandwiched between two rock salt plates. Spectra of MetSnIt were taken of a sample melted on a rock salt plate and allowed to solidify. Spectra in the region 670-750 cni.-l were taken of a Nujol mull, due to the intensity of the band found in this region.
Sn-I stretching and C-Sn-C bending. The E modes should correspond to Sn-C stretching, CSn-C bending and C-Sn-I bending. By analogy with SnMel and assuming both C-Sn-C vibrations to be piled up at 149 em.-', we can assign 538 cm.-l t o E , 511 cm.-l toAl and 149 cm.-l toAland E. This leaves 177 crn.-I to be assigned to the AI Sn-I stretching, and 117 cm.-l to the E GSn-I bending. The interpretation of the skeletal frequencies of MezSnIz is somewhat more difficult, as only six of the nine expected lines are observed. While a line could easily have been missed, the spectrum MesSnI and MezSnIz.-The experimental results will be interpreted on the assumption that it is comfor these compounds are shown in Tables I and 11. plete, and that the small number of lines is due t o While only the skeletal frequencies show up clearly piling up of frequencies. This assumption could in the Raman spectrum for MezSnIz, some extra- be checked either by a normal coordinate analysis, skeletal frequencies can be obtained from the infra- using, force constants obtained from MerSn and red spectrum. As may be seen from Table 111, MeaSnI, or by a comparison with the spectra of making a complete assignment of frequencies is a MezSnBrz,when such becomes available. matter of some difficulty, due to the large number By analogy with dichloromethane, there should of fundamentals in any one species. However, the be two Sn-C stretchings, one of species AI, and one skeletal frequencies of these compounds may be of species BI, and two Sn-I stretchings, of species aasigned quite readily, by analogy with the chloro- A2 and Bz. These are easily assigned as shown in methanes, etc. Table IV. TABLE I OBSERVEDRAMAN FREQUENCIES OF MesSnI
TABLE IV ASSIGNMENT OF FREQUENCIES FOR MenSnIz
Me2Sn12
AND
IN CM.-l MeaSnI
117(10) 149(10) 177( 10) 511(9) 538( 4) 704( 1) '796(1)
MezSnIa
1195(8) 1328( 1) 1402( 1) 2917(8) 2992( 8)
65(3) 145(3) 182( 10) 197( 5 ) 513( 10) 544( 8) 1191(7)
TABLE I1 OBSERVEDINFRARED FREQUENCIES OF MerSnI ANI) MezSnI, IN CM.-l
vs, very strong; s, strong; m, medium; w, weak; sh, shoulder. MeaSnI
704m 714 m 770vs 778vs 785vs 1012w 1075 vw 119Ovs
1310sh w 1335 sh w 1380 vs 1445 shrn 1600vw 1700 s 1740 s 1775 s
MezSnIa
1980 w 2770 w 2905 s 3000 s 4100 m 4350 s
700 m 715 s 770vs 775vs 787 vs 800 vs 1015 w 1042 IV
1051 w 1187 s 1385 s 1691 s 1738 s 2745 m 2900 s 3000 m
TABLE 111 SELECTION RULESFOR Me3SnI ANL, SZeeSnIL Fundsmentals Skeletal
Fundaii~entaln Total Skeletal
Total
At Ai E
MeaSnI 8 3 4 0 12 3
:I , A? BI
Bz
R?eeSIi12 0 4 5 2 7 1 6 2
The skeletal modes of MerSnI, on the basis of a Cav symmetry, should have three vibrations of species AI, and three of species E. The A, frkquencies should correspond to Sn-O stretching,
1 2 3 4 5 6 7 8 9 10 11
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Frequency, cm.-l
Type of vibration
3000 2900 1385 1187 715 513 182 145 65 3000 1385 800 65
(CHs) (CHs) 6 (CHa) 6 (CHa) CHa rocking v (SnC) Y (SnI) 6 (Sn-C2) 6 (Sn-It) v (CHa) 6 (CHa) CHa rocking Twist CHa torsion v (CH3) v (CHa) 6(Ca) 6 (CHd CH3 rocking v (Sn-C) Rocking v (CHs) 6 (CHs) CHa rocking (Sn-I ) Rocking CH3 tomiqti
..
3000 2900 1385 1187 800 544 145 2900 1187 715 197 145
..
v
v
This lectves five vibrational modes t o be assigned t,o two observed frequencies, at 65 and 145 cm.-l. The A1 I-Sn-I bending may be assigned to 65 cm.-l, and the A1 C-Sn-C bending to 145 cm.-'. This leaves three I-Sn-C bending modes, of species B1, Bz and AB to be assigned. While the assignment of these is somewhat uncertain, the APfrequency, corresponding t o torsion of the C-Sn-C and I-Sn-I planes with respect to each other, may be
Dec., 1953
SPECTRA O F
TINAND GERMANIUM HALOGEN METALORGANIC COMPOUNDS
94 1
The observed Raman spectra of EtGeCls are assigned to 85 cm.-', and the two rocking fregiven in Table VI. For comparison the observed quencies of species BI and B2, to 145 ern.-'. The assumption of this distribution of piling UP is skeletal frequencies of Gelded6 and GeC&are given supported by the spectra of CClzBrzand SiClzBrz.' in Table VII.5 In these compounds, the two lowest frequencies TABLE VI are quite close together, while the next three highOBSERVED RAMAN SPECTRA OF EtGeCla A N D ELGeClz est, while far from the two lowest, are quite close EtGeCla EtzGeCIz to each other. The separation of the two groups, 112 (0) 986 ( 1 ) 155 ( 5 ) 985 (1) however, is not quite so sharp in SiC1212. 136 ( 2 ) 1022(1) 165 ( 1 ) shoulder 1024 ( 3 ) The assignment of the extra-skeletal frequencies 1114 (0) 150 (3) 1160 ( 4 ) is more ambiguous than that of the skeletal fre174(4) 1168 (4) 288 1148 (0) 275 (3) (3) quencies, but is needed for such purposes as the cal1229 (10) 295 (6) 1228 ( 5 ) 320 (2) culation of thermodynamic functions. For such 333 (2) 1400 (1) 370-406 (8) 1385 (0) calculations we have given a tentative assignment Max. at 376 1459 (6) 397 (10) 1458 (3) of frequencies for both tin trimethyl iodide and tin 425(5) br 2925 ( 5 ) 561 ( 6 ) 2924 (8) dimethyl diiodide in Tables I V and V, respectively.8
I
TABLE V ASSIGNMENT OF FREQUENCIES FOR MerSnI Vrequency, CN.-l
1
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
2992 2917 1328 1195 704 511 177 149 (2992) (1402) (795)
..
2992 2992 2917 1402 1328 1195 795 704 538 149 117
..
Type of vibration
Assignment A1
A1 A1 AI
Ai Ai A, AI A2 A2 A2 A2
E E
E E E
E E E E E E E
(CHI) v (CH3) 6 (CH3) )%3 (6 ( CHs rocking Y (Sn-C) Y
v
(Sn-I)
6 (SnCd Y
(CH3)
6 (CH3)
CHa rocking CH3 torsion v (CHs) Y (CH3) Y ((3%) 6 (CH3) 6 (CHs) 6 (CHa) CHI rocking CHs rocking v (Sn-C) 6 (SnCd Rocking CHa torsion
EtzGeClzand EtGeC13.-As was stated above, the spectra of the ethyl germanium chlorides will be complicated by several phenomena. As a firstorder approximation, these compounds may be considered as freely rotating ethyl topsgattached to a rigid frame.l To this approximation, EtGeCl, may be considered as having C3.,, and Et2GeClz may be considered as having Czv symmetry. The degenerate modes of vibration characteristic of ethane will, of course, be split even in this approximation, although the splitting may not always be experimentally observable. A further complication arises from the fact that some of the low-lying extra-skeletal modes will lie in the region in which the skeletal modes lie, and must be sorted from these. (7) M. Delwaulle, THIS JOURNAL,66, 356 (1952). (8) M. C. Tobin, J . Am. Chem. Soc., 76, 1788 (1953). (9) The situation is further complicated, of course, by the fact that in the ethyl residue, the end methyl group can be considered as a top rotating with respect to the remainder of the molecule.
596(8) 970 ( 1 )
1
1
1
2935 ( 5 ) 2968 ( 4 )
605(4) 965 (1)
2982 (4) 2972 (7)
TABLE VI1 ASSIGNMENTOF SKELETAL FREQUENCIES OF GeCh GeMec E
F* Ai
F2
GeCL
GeMet
132 171 397 45 1
175 195 558 595
AND
The line a t 598 cm.-l may reasonably be assigned to the AI C-Ge stretching corresponding to the 595 cm.-'line in MedGe. By analogy with GeC14 we may assign 425 cm. -l to the E Ge-C1 stretching, and 397 cm.-l to the A1 Ge-Cl stretching. We may likewise assign 174 em.-' to the A1 C1-Ge-C1 bending, 136 cm.-l to the E CI-Ge-C1 bending, and 150 cm.-l, since it is intermediate between C1-Ge-Cl bending and CGe-C bending to the E C-Ge-C1 bending. This completes the assignment of the expected skeletal frequencies, but fails to account for the observed frequencies a t 112, 295 and 333 cm.-l. The assignment of these frequencies can be at best an enlightened guess. It seems reasonable to assign 333 cm.-l to C-CGe bending, by analogy with the 375 cm.-l frequency in propane. 295 em.-' may well be assigned t o the H-C-C-H torsion, estimated to lie at 275 cm.-l in ethane, while 112 cm.-l may be a C-C-Ge-C1 torsion. The observed spectra of EtsGeClz are given in Table VI. The lines at 605 and 561 cm.-l are readily assigned t o the Bl and AI C-Ge stretching frequencies, respectively. The broad line from 370406 cm.-l is definitely asymmetric, with maximum density a t 376 cm.-l. We may therefore assign the A1 Ge-C1 stretching to 378 em.-', and the B2Ge-C1 stretching to 395 cm.-'. The broad band at 155 cm.-l has a weak shoulder on the long wave length side at 165 cm.-1. To these two bands must be assigned the AI Cl-Ge-C1 and C-Ge-C bendings, and the Az, B1 and Bz C-Ge-C1 bendings. Although the assignment must of necessity be uncertain, we may tentatively assign the C1-Ge-CI bending and the Aztorsion to 155 em.-', and the CGe-C bending and the Bl and Bz rockings to 165 em.-'. This radical piling up is not unexpected, i t 1 view of the fact that, by analogy with NIe4Ge,GeC14
942
F. WM. CAQLE,JR.,AND HENRYEYRING
and EtGeC13, the expected range for the skeletal bendings of all types is 150-175 cm.-'. Again, a Raman line could be too weak t o show up. The line a t 320 cm.-1 may, as was 333 cm.-' in EtGeC4, be ascribed to C-C-Ge bending. However, instead of having a single line a t 295 cm.-', as in EtGeCl8, we now have two lines, at 275 and 288 cm.-l. These may tentatively be ascribed t o symmetric and asymmetric torsions of the H-C-C-H angles in the two ethyl groups. The non-appearance of the 112 cm.-' line in Et2GeClz may be ascribed t o the hindrance of this mode by steric effects, if it indeed corresponds to the C-CGeCl torsion. The extra-skeletal frequencies for both compounds are closely similar. They fall roughly into three classes: C-C stretching and H-C-C bending, 900-1100 cm.-l, H-C-H bending, 1100-1500 cm.-' and C-H stretching, 2900-3000 cm.-L. These assignments are tabulated in Table VIII. It seems worth while t o make some comments on the interaction of the ethyl groups with the frame of the molecules. As is apparent from the discussion above, the ethyl groups have little effect on the frame vibrations, and the skeletal spectra are readily interpreted in terms of the CGeC4 and C2GeClz frames. The symmetry of the ethyl groups, however, is reduced from the D B dsymmetry of free ethane, to C,. I n consequence, the AI, species is activated, and the degenerate modes are split. This accounts for the appearance of the line a t 295 cm.-l in EtGeCL. If the assignments proposed for the lines a t 112 and 295 cm.-l in EtGeClo are correct, we may assume that there is a small interaction between the ethyl group and the frame, on one hand and, in Et2GeCl2, between the two ethyl groups on the other hand.
VOI. 57
TABLE VI11 ASSIGNMENTOF Low FREQUENCIES FOR EtzGeC12 EtGeCla Frequency, om.-'
AND
Type .of vibration
Assignment
EtGeCla v6 vb
va
v2 Y4
VI
112 136 150 174 295 333 397 425 596
T
E E A,
(C-C-Ge-C1)
6 (Cl-Ge-CI) 6
(C-Ge-CI)
6 (Cl-GeCI) T
(H-C-C-H)
6 (C-C-Ge)
Ai E A1
(Ge-Cl) (Ge-Cl) v (Ge-C) Y
Y
Et2GeC12
Vi
155 155 165 165 165 275 288 320 376 395 561
ve
(io5
Yb
v4 V? Y3
YB
Y2
Y8
A2
Ai
B1 Ai €32
Ai J32
Ai BI
Twist 6 ( CI-GeCI) Rocking 6 (C-Ge-C) Rocking T (H-C-C-H) T (H-C-C-H) 6 (C-C-Ge) Y (Ge-CI) Y (Ge-Cl) v (C-Ge) v (C-Ge)
If this is the case, the skeletal lines in EtGeCls corresponding t o the E vibrations are in reality unresolved doublets. The breadth of the line a t 425 cm.-l suggests that this might be the case. Any definite conclusion, however, must await further study with high dispersion spectrographs. The authors wish t o acknowledge financial support from the office of Naval Research Contract M 8 onr-72700.
AN APPLICATION OF THE ABSOLUTE RATE THEORY TO PHASE CHANGES IN SOLIDS1 BY F. WM. CAGLE,JR.,AND HENRY EYRING Deparlinent of Chemistry and Institute for Rate Processes, University of Utah, Salt Lake City 1 , Utah Received April 16, 1965
A theory for phase transitions in sol'ids, based on the absolute reaction rate theoryl has been developed. It has been applied quantitatively t o the transition of white to gray tin. This theory leads to the interpretation that only where growth lines for white tin cross those for grey tin can the transition occur. As might be expected, such crossing points are exceptionally rare and account for most of the slowness of the transition. The transformation of monoclinic to orthorhombic sulfur has also been discussed in terms of the theory. The effect of external constraints, especially pressure, has been considered both upon the thermodynamics and upon the kinetics of such transformations.
Introduction Quite aside from the enormous practical interest attached to phase changes in solids, one readily observes that at least in the case of pure solids, these changes permit a study of a one-component reaction which occurs a t an interface between phases. It is, of course, of primary importance to examine care(1) This paper was presented on July 14 at the 1952 Gordon Conference on Physios and Chemistry of Metals, New Hampton, New Hampshire.
fully such systems, which on account of their relative simplicity, are able t o provide information concerning the nature of the activated complex. We consider first the p- to a-tin transition. This system undergoes transition a t a convenient temperature and therefore has been the subject of numerous investigations. While most of these investigations were undertaken t o elucidate the thermodynamic relationship of the system, some are concerned with the kinetics of the reaction.
