The infrared spectra of the trimethylplatinum compounds

JOVRNAL

OF MOLECULAR

The Infrared

SPECTROSCOPY

Spectra

13,

of the Trimethylplatinum

MICHAEL Chemistry

Department,

407417 (1964)

Michigan

N.

Compounds*

HOECHSTETTEH. t

State Cnirersity,

East Lansing,

Michigan

The infrared spectra of the trimethylplatinum compounds were studied in order to correlate the observed spectra with the known structures of these compounds. However, this could not be done because the spectra consisted entirely of the CH stretching and bending vibrations of the methyl group and the hydroxyl group in the case of the halides and hydroxide, and the methyl group and uncoupled ligand vibrations in the case of the ammonia and pyridine complexes. No bands were observed which could be classed as vibrations of the molecule as a whole. The spectra of the halotrimethylplatinum compounds showed similarities to those of the methyl halides. I. INTRODUCTION Tkle cubic tetrameric structure of the halotrimethylplatinum compounds was first elucidated by Rundle (1) who found that each platinum was surrounded octahcdrally by three mutually perpendicular methyl groups and three halogens which also acted as bridging agents between the platinum atoms. The analogous hydroxy compound is believed to have a similar structure according to a conlparison of x-ray powder patterns. Such a molecule has DB or F’ symmetry and would he expected to give a large number of vibrations (2): 42 totally symInctric ,4 vibrations and 40 each of the B1 ,B2 ,and BB type, each mode of which is sylrlmetric to one axis but antisymmetric to the other two axes. This means thcrc is a total of 162 vibrations which are possible for this type of molecule. The hydroxy colllpound would have 45 A vibrations, and 43 each of the B, , Bz , and Ra tfype for a total of 174 vibrations. If all of these vibrations were infrared active, the spectra would be so complicated as to be virtually impossible to interpret E‘ortunately most of these vibrations are inactive so that the spectra are remarkably simple, and the assignments for both the methyl and methyl-ds compounds were easily Inade. ThP molec*ular structure of the [(CH,),Pt(NH,)J +l ion is believed to consist of three mutually perpendicular methyl groups and three mutually perpendicular

* This work was supported by t’he U. S. Atomic Energy Commission under Contract. AT ill-lj-399. i Present address: The Chemical Abstracts Service, The Ohio State University, Columbus 10, Ohio.

408

HOECHSTETTER

ammonia groups in an octahedral configuration around the platinum. The alternate possibility of an octahedral configuration with planar arrangements of both ammonias and methyls is believed not to form upon reaction of gaseous NH3 with (CHs)gPtI (3). The reason for this is based on the fact that all structural investigations thus far on compounds containing the trimethylplatinum group have shown that the methyl groups are always mutually perpendicular (1,4). In addition Foss and Gibson (6) were unable to prepare any methylplatinum compounds from tlans-(pyridine),PtCh while the cis isomer reacts readily with CHJlgI to produce [(CHB)BPt(py)I] 2 f rom which (CH3)sPtI can be obtained. Therefore, the configuration containing the mutually perpendicular groups would have a Ctv space group and would give 14 totally symmetric Al vibrations, nine A, vibrations which are symmetric to the single threefold axis of symmetry but antisymmetric to the vertical plane of symmetry, and 23 doubly degenerate E vibrations which are antisymmetric to the rotational axis (2). This would give a. total of 69 vibrations if all were infrared active. However, as in the case of the halotrimethylplatinum compounds, the spectra of [(CH3)sPt(NH,)s]I and its methyl-& counterpart are very simple so that assignments are easily made. (CHl)sPt(py)J is believed to contain three mutually perpendicular methyl groups. Other configurations are ruled out for the same reasons which were presented for eliminating the nonmutually perpendicular methyl configurations of the ammine complex. The only element of symmetry possible for such a configuration is a plane which can be passed through the I, the Pt and the methyl group opposite to the I, and which reflects the pyridines and the other two methyls. Such an arrangement has a Cs space group which would have 25 vibrations of the A type or symmetric to the plane of symmetry and 17 vibrations of the A’ type or antisymmetric to the plane. A total of 42 vibrations is possible for the molecule as a whole if the pyridines are considered as point masses and also excluding the pyridine vibrations themselves (2). However, the actual spectra are very much simpler than expected. II. EXPERIMENTAL

Preparation of iodotrimethylplatinum. This compound was prepared by the method of Pope and Peachy (6). Analysis: ca1cd.l for (CH&PtI: C, 9.82%; H, 2.45%; Pt, 53.16 %. Found: C, 10.01%; H, 2.46%; Pt, 53.55%. Preparation of chlorotrimethylplatinum. This compound was prepared from hydroxytrimethylplatinum by the method of Pope and Peachy (6). Analysis: calcd. for (CH&PtCl: C, 13.08%; H, 3.29 %; Pt, 70.73%; Cl, 12.90%. Found: C, 13.15%; H, 3.17%; Pt, 71.86%; Cl, 13.01%. Preparation of bromotrimethylplatinum. This compound was produced either by a method analogous to that for (CH,)3PtC1 or by the reaction of PtCh with a 1 Analyses were carried out by Microtech Microanalytical of Ann Arbor, Mich.

Laboratories

of Skokie,

Ill. and by Spang

INFRARED

SPECTRA

OF TRIMETHYLPLATINUM

COMPOUNDS

409

grignard reagent prepared from CH3Br. The preparation otherwise is similar to that for (CH3)J’tI (6). Analysis: calcd. for (CH3)3PtBr: C, 11.25%; H, 2.83%;‘; Pt, 61.00 %,. Found: C, 11.08%1; H, 2.84%; Pt, 60.845‘;. Preparation of hydroxytrimethylplatinum. This compound was prepared by the method of Pope and Peachy (6). Analysis: calcd. for (CH&PtOH: C, 13.96’:;.; H, 4.19%; Pt, 75.65%. Found: C, 14.17%; H, 4.36%; Pt, 79.37% (compound explodes on analysis). Preparation of triamminetrimethylplatinum iodide. This compound was prepared by the method of Gel’man and Gorushkina (3) in which gaseous XII3 is passed through a benzene solution of (CH,),PtI. The product precipitates and is collected by filtration. Analysis: calcd. for [(CHa)aPt(NHs)a]I: C, 8.61“; ; H, 4.34 “;3; I%, 46.47 ‘?‘,a;K, 10.04 $1). Found: C, 8.73%; H, 4.27?; Pt, 47.10:;; K, 9.98 %. Preparation of iodotrimethylbis(pyridine)platinum. This compound was prcpared by the method of Lile and Rlenzies (7) in which about 0.25 gm of white (CH3)3PtI was dissolved in 25 ml of benzene containing 2 ml of pyridine. The solution was evaporated to dryness, and the resulting white crystalline product was washed with ether and air dried without any further treatment. Analysis: calcd. for (CH&Pt(py)J: C, 29.71 ‘X; H, 3.64%; N, 5.33 %; Pt, 37.15’; ; I, 24.15%. Found: C, 30.11 “I,; H, 3.67%; N, 5.08%; Pt, 38.99%); I, 23.89*;. Preparation of cis-tetrachlorobis(pyridine)platinum. This compound was prcpared according to the method of Foss and Gibson (n’) in which SazPtCl,i w acted with pyridine in warm aqueous solution. Analysis: calcd. for (pyjsPtul: C, 24.257’; H, 2.03 ‘;; ; N, 5.66%; Pt, 39.42%; Cl, 28.64%. Found: C, “4.65”; ; H, 1.82 %; X, 5.46 %; Pt, 38.40 7L’; Cl, 28.88 %. Preparation of iodotri(methyl-d3)platinum. This compound was prepared in the same manner as the normal (CH,)aPtI except that the grignard reagent was prepared with 3.0 gm of CD,1 (used as obtained from Tracerlab Inc.). The IXaction is extremely wasteful giving only a 26 % yield of (CDs)sPtI. This resulted in barely enough sample heing available for analysis of some of the derivatives. In addition hydrogen analyses are not listed for the methyl-d, compounds bccause of uncertainties in the deuterium content. Analysis: calcd. for (CD+),PtI : C, Y.5i 5 ; I%, 51.88 %. Found: C, 9.70 c/; Pt, 51.67 ‘S. Preparation of chlorotri(methyl-&)platinum. This compound was preparK from (CD,)sPtOH in the same manner as the normal methyl compound. Analysis: calcd. for (CD,),PtCl: C, 12.655). Found: C, 13.24“<. (Insuffici~~nt sample for 1% analysis.) Preparation of bromotri(methyl-d,)platinum. This compound was prepared front (CD,,,PtOH in the same manner as the normal methyl compound. Analysis: calcd. for (CD&PtBr: C, 10.94%. Found: C, 11.24 ‘Z. (Insuflicic~nt~ sample for I’t analysis.) Preparation of hydroxytri(methyl-&)platinum. This compound was prepared

410

HOECHSTETTER

by the method of Pope and Peachy (8) using (CD3)3PtI as the starting material. Analysis: calcd. for (CD&PtOH: C, 13.53 %; Pt, 73.30%. Found: C, 13.94%; Pt, 72.71%. Preparation of hydroxy-d-trimethylplatinum. The apparatus and method used were the same as those used for the normal hydroxide except that the silver oxide was rinsed with abs. EtOH and ether in order to remove most of the water present. The 0.20 gm of (CH3)3PtI starting material was then treated with a mixture of 100 ml of dry benzene, 20 ml of dry acetone, 0.50 gm of the previously described Ag,O, 5 ml of DzO and reacted as previously outlined. The product was a mixture of both the normal and hydroxide-d according to the infrared spectrum. Several other attempts to produce the pure (CH,)3PtOD resulted in failure, apparently from rapid D-H exchange on the hydroxide group. Preparation of hydroxy-d-tri(methyl-ds)platinum. This compound was prepared in a similar manner to that for (CH,),PtOD only the starting material was (CD3),PtI. The Age0 was prepared by reacting AgN03 with NaOD in DzO. The NaOD in turn was prepared by direct reaction of Na with D20. In spite of these precautions the product was a mixture of both the normal hydroxide and the hydroxide-d according to the infrared spectrum. Preparation of triamminetri(methyl-d3)platinum iodide. This compound was prepared from (CDB)3PtI and gaseous NH3 in the same manner as for the normal compound. Analysis: calcd. for [(CD&Pt(NH,),]I: C, 8.43%; Pt, 45.68%; N, 9.83%. Found: C, 8.10%; Pt, 45.02%; N, 10.02%. Preparation of iodotri(methyl-da)bis(pyridine)platinum. This compound was prepared from (CDB)BPtI in the same manner as the normal methyl compound. Analysis: calcd. for (CD&Pt(py)J: C, 29.21%; Pt, 36.53 %; N, 5.24%. Found: C, 29.06 %; Pt, 36.70 %; N, 5.74 %I. All spectral samples were prepared by the KBr disc technique. Also samples in CC& and CS2 solutions were run as a check on the disc method. No differences were noted Fetween the two methods. The measurements were made on a Perkin-Elmer hIode 21 recording spectrophotometer using NaCl optics for the 2 to 14.5~ range. A Perkin-Elmer Infracord with KBr optics was used for the 14.5 to 25~ range; only the pyridine complex absorbed in that part of the spectrum. III. RESULTS

The experimental results are listed in Tables I-VI. IV. DISCUSSION

The spectra of all the trimethylplatinum compounds studied exhibited methyl group CH stretching and bending vibrations which were similar in character to those of the methyl halides (2). The assignments were made by comparisons with these latter spectra. The methyl-platinum group, like a methyl halide molecule, has Csv site sym-

INFRARED SPECTRAOF

TRIMETHYLPLATINUM

COMPOUNDS

411

Table I Vibrational Frequencies in cm-l of (CHsj9PtI and (CDs)sPtIa jCHe)sPtI

lCDs)sPtI

Assignment

2950

m

2203

2874

m

2096 m

Symmetric CH stretching

2755

w

2041 m

Overtone from unsymmetric CH bending

lJ406m

1027 m

Unsymmetric CH bending

m

Unsymmetric CH stretching

s

962

s

Methyl rocking CH bending

1218 s

936

s

Symmetric CH bending

1253

aThe following abbreviations for intensity have been used: s strong, m medium, w weak, v very, and sh shoulder. Table II Vibrational Frequencies in cm-' of (CHs)sPtBr and (CDb)sPtBra Assignment

(CHsjaPtBr

JCDs)sPtBr

2941 s

2208 s

Unsymmetric CH stretching

2874 s

2101 s

Symmetric CH stretching

2770 m

2045 m

Overtone from unsymmetric CH bending

407 s

1030 m

Unsymmetric CH bending

12.59 s

968

m

Methyl rocking CH bending

1222 vs

942

s

Symmetric CH bending

a See footnote to Table I for meanings of abbreviations used. metry,so that therewould be threetotally symmetric and three unsymmetric vibrations: sym. CH stretching (Al), unsym. CH stretching (E), unsym. CH bending (E), methyl rocking CH bending (E), sym. CH kending (AI), and PtC stretching (A 1).

412

HOECHSTETTER Table III

Vibrational

Frequencies in cm-' of (CHs)~.Ptcland (CDB)sPtCla Assignment

(CH3)aPtC1

jCD&PtCl

2950

m

2208

m

Unsymmetric

2874

m

2101

s

Symmetric

2770

w

204.5 m

Overtone

1406

m

1032

w

Unsymmetric

1259

m

972

w

Methyl rocking CH bending

1225

s

94s

s

Symmetric CH bending

CH stretching CH stretching

from

unsymmetric

CH bending

CH bending

a See footnote to Table I for meanings of abbreviations used. The two CH stretching and the unsymmetric CH bending vibrations were very close to those of methyl iodide (2) and were assigned accordingly. The symmetric CH bending was assigned on the basis of its great intensity and the fact that other organometallic compounds show an intense symmetric CH bending peak between 1100 and 1250 cm-l (9-11). The intensity of this peak did not appear to be altered appreciably by the atom or group attached to the platinum. This was not true of the methyl rocking frequency which was assigned partly on this basis and also on the fact that the frequency of this vibration appears to be grossly affected by the electronegativity of the group attached to the carbon atom as in the methyl halides. In the case of the trimethylplatinum compounds, the methyl groups are attached only to platinum and the different halides or other ligands have little effect on the frequency of this vibration, but instead change only the intensity. The only vibration not present or accounted for is the PtC stretching frequency which would be expected to appear in the region of 500 to 700 cm-l (12). Such metal-carbon vibrations are present in molecules like (CH&Zn, (CH3)zHg, (CH&Pb, and (CH&Sn (g-11). Also Chatt (13) observed PtC vibrations in the 500 to 600 cm-l region in a series of methyl and dimethyl platinum complexes with tertiary phosphines. On the other hand, Gel’man (14) reported a PtC vibration at 562 cm-l and a methyl rocking CH bending at 852 cm-l in the spectrum of (CH3)3PtI. These and other data on the spectrum of this compound are completely at variance with this author’s observations. During the course of this investigation the spectrum of (CH,),PtI was run many times as were those of other trimethylplatinum compounds, and at no time was there the slightest indication of the PtC stretching frequency which Gel’man claims.

INFRARED SPECTRA OF TRIMETHYLPLATINUM

COMPOUNDS

413

Table IV Vibrational Frequencies in cm-' of (CHs)sPtOH and (CDs)3PtODa ICH3)sPtOH

1 CD=) SP tOD

3559

2639

8

m

Assignment OH stretching

2941 s

2198 vs

Unsgmmetric CH stretching

2865 s

2105 s

Symmetric CH stretching

2778 s

2045 m

Overtone from unsymmetric CH bending

1410 m

1414 m

Overtone from PtO stretching

1399 m

1027 m

Unsgmmetric CH bending

1368 m

1337 w

Unidentified

1271 m

970 W-J

Methyl rocking CH bending

1238 vs

957

Symmetric CH bending

873 m

660 w

Unidentified CH bending

858 msh

65'3 w

Unidentified CH bending

719 v.¶

712

PtO stretching

s

9

a See footnote to Table I for m3ahings of abbreviations used. Theredoesnotappear to be any reasonable explanation forthedifference inbehaviorbetweenthe nlethyl conlpounds of Pt(I1) and Pt(IV). The lack of PtC stretching inodes appears to be an unexplained tnystery. The spectrum of hydroxytrirnethylplatinurn exhibits the same type of Inethyl group vibrations as those of the corresponding halo compounds, and these assignulents are made accordingly. The notable exceptions are the two peaks at 873 and 858 cm-’ which are undoubtedly CH defornlation vibrations since they shift to 660 and 6.53 enI-’ upon deuteration of the methyl group. However, the nlodes of these vibrations can not Fe accounted for on the basis of a (la? space group for the CH3-Pt group; so the nlodes of these CH bending vibrations are unidentified. The OH stretching vibration is easily identified and assigned since it is well known to occur in the 3400 to 3700 cm+ region (16). Also deuteration of the OH group caused the expected shift to 26.39 cnl-‘.

Overtone from unsymmetric CH bending Unsymmetric NH bending Unsymmetric CH bending Methyl rocking CR bending

2096 s m m

2045

1587

1031 w

959 w

s

2865

2778 w

1590 m

1410 w

1261 m

1212 vs

1209

Symmetric NH bending

Symmetric CH bending

a See footnote to Table I for meanings of abbreviationsused.

vs

935

1227 msh

m

Unsymmetric CR stretching

m

2193

2933 m

Symmetric CH stretching

Overtone from unsymmetric NH bending

m

Symmetric NH stretching

Unsymmetric NH stretching

3155

8

3165 w

3300

Assignment

[(CIb)&WNH&dIa

3226 m

9

~(CD&Pt(_NHe)e]I

and

3226 m

3289

[(CHe)sPt(NHe)&

VibrationalFrequencies in cm-' of [(CH&Pt(NH&lI

Table V

i 2 g Lz Y

2

Table VI

Pyridine ring C:C or CXJ atretching

477 m

2706 m 1592 s 1477 s

----

NW__

1600 s

w--w

-w-B

1587 m 1572 8I

Pyridine ring CC stretching Pyridine CR wagging

1009 m

752 8

1037 8 1009 s

1093 w

1067 s

1016 m

756 vs

W-W-

1139 m

1064 m

1026 m

987 m

746

656 m

672 ash

vs

633 s

691

Pyridine CH wagging Pyridine CH wagging

631 m

Pyridine CH wagging

1063 a

691 va

Pyridine CH rocking

1145 m

Methyl symmetric CH bending

a see footnote to Table I for meanings of abbreviationsused.

676 vs

s

750 8

144m

m

1206 s

W-e939

Pyridine CH rocking

1214 m

1215 s

1200 s

700 vs

a

Pyridine CCC ring bending

1037 m

1063

1145 w

1211 m

Methyl rocking CH bending Overtone from 633 cm" peak

w

1229 w

1229 m

964

1255 m

1241 m

__I_

Overtone from 691 cm" peak

-__.a

1346 m

1348 m

1340 w

Pyridioe ring Cm0 or CXV stretching

1437 vs

1437 vs

1447 s

or C=N stretching

-m-w

llc2qs B-s_

8

Pyridine ring CX

1592 8

2874 s

-S-S

$2

Overtone from methyl unsym. CH stretching

2045 s

2941 s

3058 w

2994 m __s_

1473 m

Methyl symm?trIc CK stretching

2101 s

--__

3106 w

3040 m

Methyl unsymmvtric CH stretching

Pgridine CH stretching

---_

--_-

2203 s

Pgridine CH stretching

~CD.).Pt(py)eI '____

jCHe).Pto,I

Assignment

(CHe)ePt(py)eIand (CDe)ePt(py)eI'

bjpPtC1*

of Pyridine (fi),a-(Py)ePtClr,

Pgridlne

VibrationalFrequencies in cm"

416

HOECHSTETTER

The bending vibrations of the OH group might be expected in a molecule such as (CH,),PtOH since alcohols and phenols exhibit such vibrations although there is some uncertainty concerning their location (15). None were observed for (CH,)sPtOH although the peak at 1337 cm-’ was first thought to he such a vibration. However, deuteration of the OH or methyl groups caused an insignificant shift. An expected shift to the lOOO-cm-’ region for an OH bending was not observed; so the peak is unidentified. The assignment of the PtO stretching vibration at 719 cni-l is lased on the shift which occurs only with deuteration of the OH group while none occurs with deuteration of the methyl group. The observed shift is within the range expected for a PtO vibration in which the OH or OD group is considered as a point mass. Such approximations have been found to be very good (2). The most significant observation in the spectrum of (CH3)3PtOH is the occurrence of the very intense PtO vibration and the absence of the PtC vibration. Both PtC and PtO vibrations would be expected to occur in the 500- to 700-cm-l region because the masses and electronegativities of both the carbon and the oxygen atoms are of the same orders of magnitude (16). The spectra of [(CH,),Pt(NH,),]I and its methyl-& counterpart consist only of the already assigned methyl group vibrations and the NH stretching and bending vibrations of NH, without any coupling between them. These latter vibrations are essentially those of free ammonia because, with its Csv symmetry, two symmetric and two doubly degenerate modes are possible, and are observed in this case. The NH stretching modes have been well characterized (2, 15) and are assigned accordingly. Unsymmetric (degenerate) NH bending modes appear to vary somewhat depending on the symmetry of the molecule and also upon the atom to which the NH, is attached. Degenerate NH bending in the 1540- to 1670-cm-’ region has been reported for cis- and t~ans-[Pt(NH~)zC12] (16, 17’). Also the degenerate mode for free NH, appears at 1626 cnl-l so that the assignment in this case is certain. Symmetric NH bending modes can vary in much the same manner as the symmetric CH bending of the methyl group; namely, that the frequency can shift very drastically depending upon what atom or group the ammonia is attached to. Ammonia exhibits this mode at 943 cnr-‘, while several cobalt and platinum ammine complexes exhibit this mode in the 1170- to 1300-cm-’ region (16, I?‘). The assignment of the symmetric NH bending is made on the basis of the above information. No bands were observed which could be classified as PtC or PtN vibrations, again the unexplained mystery. Also there was no coupling between the CH and NH vibrations so that the spectra consist of only these vibrations rather than vibrations of the molecule as a whole plus those of the methyl and ammonia groups. The lack of a PtC vibration is again at variance with the spectrum for

INFRARED

SPECTRA

OF TI~l~lET~~LPI,ATI~U~f

CORIPOK?UP

-117

[(CH~)J’t(KH,)3]I reported by Gel’man (14) who also reported ammonia and methyl rocking frequencies at 720 and 881 m-l respectively. During the course of this work, neither of the above two vibrations nor the previously mentioned Pt,C peaks which Gel’man claims could be detected. Thespectra of (CH3)sYt(py)zI and its methyl-d3 counterpart consist only of t,hc already assigned methyl group vibrations and those of the pyridine with no coupling between them as in the cast of the previous compound. This may be relat.ed to the unexplained absence of PtC and PtN vibrations in the trimrthylplatiI~u~~~ col~~pounds. Sonre of the pyridine bands undergo shifts upon complex formatiou, but in an unexplainable manner. The use of the electron-pair on the nitSroger of that pyridine for complex formation mitb the platinunl would teud to reduce the aromatic character of the pyridine somewhat, resulting in slightly weakened and longer bonds throughout the entire pyridine ring. Accordingly the pyridine bands would be expected to shift to lower frequency. The actual spectra showed shifts to higher frequency with the exception of two CH wagging modes at, the long wavelength tnd of the spectrum. Also the pyridine CH stretching peaks virtually disappear. The explanation for the observed phenomena is not knowvn.

The author wishes to t~hankProf. C. H. f-&+ubakerand other department,al staff members fr)r many helpful suggestions, and the U. S. Atomic Energy Commission for financial Support of t,his work. RECEIVED

: December

26, 1963 REFERENCES

1. I%. E. RI.NDLE AND J. H. STURDIVANT,J. An2. C’hem. Sot. 69, 1561 (1917). 2. U. HERZBEIZG,“Infrared and Ramlzn spectra of Polyatomic Molecules.” Van Nostrand, sew Tork, 1945. 3. A. I). GEL’MAN AND E. GORUSHKINA,Doll. dkacl. lyuuk SSSR 57, 43-4 (1947). 4. A. (1. HAZELL, A. G. SWALLOW, AXD M. R. TRVTER, (‘hem. and Id, pp. 564-5 (1959). 5. Al. E. Foss AXU C. P. GISSOX, 6. Chem. Sot. p. 299 (1951). 6. W.J. POPE AND S. J. PEACHY,J. Chew See. 96,571 (1909). 7. W. J. LIZE AND R. C. MENZIES, J. Ckent. Xoc, p. 1168 (1949). 8. H. W. RANDALL, N. FZSON, K. G. FOWLER, AND J. R. DANGL, “Infrared ~~terrni~~ati~tll of Organic Structures.” Vau Nostrand, New York, 1949. 9. fI. S. &~TOWSKY, J. Am. Clzem. sot. 71, 3194 (1939). IO. H. S. C:IXJ\\‘SKY,J. C’hem. t’hys. 17, 128--38 (1949). 1f. IL K. SHEUNE AND K. S. PITZER, J. C’hen~.Yhys. 18, 595 (1950). 18. J. W. LINNET~I’,Quart. Rem. 1, 73-!)O (1947). 13. L). n1. ADAMS, J. CHATT, ANU B. L. SHAW, J. (‘hem. Sot. p. 2047-53 (1960). 14. A. 1). GEL’MAN, L. A. GRIBO~, F. A. ZAKHABOVA, ANTI51. K. ORLOVA, Zhur. ATeorg. Khim. 5, 987-9 (1960). iii. L. J. BELI,AMY, “The Infrared Spectra of Comples Molecules.” Wiley, Piew k’ork, 1958. 16. ,J. V. @TA