Recent Infrared Studies on Werner Complexes

27 Recent Infrared Studies on Werner Complexes

Downloaded by UNIV OF MICHIGAN ANN ARBOR on October 23, 2014 | http://pubs.acs.org Publication Date: January 1, 1967 | doi: 10.1021/ba-1967-0062.ch027

KAZUO N A K A M O T O Department of Chemistry, Illinois Institute of Technology, Technology Center, Chicago, Ill.

Werner proposed the structure of a number of metal com plexes on the basis of his coordination theory. Infrared spectroscopy has proved to be a powerful means of dis tinguishing various types of isomers proposed by Werner. Furthermore, recent infrared studies on Werner complexes provide detailed information about their structure and bonding.

T t is well-known that Werner determined the structure of a number of metal complexes by skillfully combining his famous coordination theory with chemical methods (30). Modern physico-chemical methods such as x-ray diffraction and infrared spectroscopy, used i n the study of Werner complexes, have paralleled the development of these techniques. The re sults of these investigations have not only confirmed the validity of Wer ner's coordination theory but have also provided more detailed structural and bonding information. In early 1932, Damaschun (13) measured the Raman spectra of seven complex ions, such as [Cu(NH )4] and [Zn(CN) ]~ , and these may be the first vibrational spectra ever obtained for Werner complexes. In these early days, vibrational spectra were mainly observed as Raman spectra because they were technically much easier to obtain than infrared spectra. In 1939, Wilson (35, 86) developed a new theory, the " G F method," which enabled him to analyze the normal vibrations of complex molecules. This theoretical revolution, coupled with rapid developments of commercial infrared and Raman instruments after World W a r I I , ushered i n the most fruitful period i n the history of vibrational studies of inorganic and coordination compounds. One of the most important and interesting results obtained from Werner's coordination theory is the prediction and verification of various types of isomerism. It is, therefore, appropriate to review recent infrared studies in this area and to show how infrared spectroscopy can be used to distinguish various types of isomers. 3

4

2

396 In Werner Centennial; Kauffman, G.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

+2

27.

NAKAMOTO

Ionization

397

Infrared Studies

Isomerism

One of the most fundamental ideas in Werner's coordination theory is the distinction of molecules or ions in the "inner sphere" and the "outer sphere." For example, there are two isomeric forms for C o ( N H ) B r S 0 ; in solution, one isomer does not react with the bromide ion but does with the sulfate ion, whereas the other does not react with the sulfate ion but does with the bromide ion. From such chemical observations, Werner (80) concluded that the former solution contains the [ C o ( N H ) B r ] ion, whereas the latter solution contains the [Co(NH ) S0 ]+ ion. He called them "ionization isomers." Nowadays, it is a rather routine procedure to differentiate these isomers from infrared spectra because the vibrations of the free and coordinated (covalently bonded) ligands are markedly dif ferent. The S 0 ion in the outer sphere is essentially regarded as a free S0 ion of T symmetry, whereas that in the inner sphere is regarded as being of C symmetry in unidentate coordination because one of the four oxygens bonded to the Co atom is different from the others. This lowering of symmetry results in changes in the infrared selection rules. Thus, the triply degenerate SO stretching vibration (F species, I R active) of the free ion splits into two peaks (A\ and E species, both I R active), and the totally symmetric SO stretching vibration (A\ species, Raman active) be comes infrared active as a result of unidentate coordination (22). This is clearly demonstrated in Figure 1, which compares the infrared spectra of [ C o ( N H ) S 0 ] B r and [ C o ( N H ) B r ] S 0 .


3

3

3

4

4

- 2

5

5

4

+2

5

4

- 2

d

Sv

2

3

5

4

3

5

4

This method is further extended to distinguish unidentate and bidentate coordination. If the S 0 ion acts as a bidentate ligand, two of its four oxygens are different from the remaining two. As a result, the symmetry of the S 0 ~ ion is further lowered to C . Thus, the triply degenerate vibration (F species) splits into three components (A B and B species), and the totally symmetric vibration (A\ species) becomes i n frared active. Therefore, it is expected that a complex ion such as [Co(en) S0 ] exhibits four SO stretching bands. In fact, [Co(en) S0 ]Br recently prepared by Barraclough and Tobe (5) exhibits four bands at 1211, 1176, 1075, and 993 c m . It is rather difficult, however, to dis tinguish from the selection rules alone bidentate S 0 groups from bridging S 0 groups, such as those in 4

4

- 2

2

2v

2

h

h

2

2

4

+

2

4

1

4

4

[(NH ) Co 3

/

NH

2

\ Co(NH ) ] /

4

3

\

S0

4

+3

4

because both S 0 groups belong to the same C point groups. The varia tion of the spectra in the OSO bending region (650-550 c m . ) is also similar to that in the SO stretching region described above. °It should be added 4

2v

-1

In Werner Centennial; Kauffman, G.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

398

WERNER CENTENNIAL


T

•

i

.

1

i

>

1100

1200

1

•

i

,

r

i

1000

I

900

V(CM~) Figure 1. Infrared spectra of ( ) and [Co(NH,) SO,]Br ( stretching region

[Co(NHz) Br]S0 ) in the SO b

b

4

that this technique has been used successfully for other acid ions such as C10 ", P 0 , C 0 " , N 0 ~ , and S 0 in determining their sites of coordination {22). 4

4

- 3

3

2

3

3

- 2

If the symmetry of the ligand is already low in the free state, the num ber of infrared bands will not change upon coordination. However, dif ferences in frequency may be used to distinguish free and coordinated ligands. For example, the free N 0 " ion (C symmetry) absorbs at 1335, 1250, and 830 c m . , whereas the coordinated N 0 group (N-bonded) absorbs at 1450-1335, 1350-1325, and 840-830 c m . If the ligand is a monoatomic ion such as C l ~ or B r ~ , it is necessary to investigate the farinfrared region where the metal-halogen stretching bands appear. For example, ionization isomers such as [ P t ( N H ) C l ] B r and [ P t ( N H ) B r ] C l can be distinguished easily because the P t - C l stretching bands appear near 340 c m . , whereas the P t - B r stretching bands appear near 240 c m . (8). It should be mentioned that the metal-halogen stretching frequencies 2v

2

-1

2

1

3

4

2

2

3

-1


4

2

2

1

27.

Infrared Studies

NAKAMOTO

399

such as these have been established recently for various metals by a number of investigators (1, 2, 11, 12). Hydrate Isomerism, Coordination Polymerization Isomerism

Isomerism,

and

Werner called ionization isomerism involving solvent molecules, such as H 0 , hydrate isomerism. A typical example of hydrate isomerism given by Werner is [ C r ( H 0 ) C l ] C l - H 0 (light green), [ C r ( H 0 ) C l ] C l - 2 H 0 (dark green), and [ C r ( H 0 ) ] C l (violet). Although the first and the second complexes are difficult to distinguish, the third can be distinguished from the others by examining the spectra in the C r - C l stretching region ( 3 5 0 - 3 0 0 c m . ) . Furthermore, the coordinated water can be distinguished easily from the crystal water because the former exhibits, in addition to the metal-oxygen stretching vibration, the rocking and wagging vibrations which correspond to rotation of the whole water molecule i n free state. For example, Nakagawa and Shimanouchi (19) have located the rocking, wagging, and C r - 0 stretching vibrations of the [ C r ( H 0 ) 6 ] ion at 8 0 0 , 5 4 1 , and 4 9 0 c m . , respectively.


2

2

5

2

2

6

2

2

4

2

2

3

-1

2

+3

-1

As stated above, coordinated ligands exhibit infrared absorptions which are different from those of free ligands. Furthermore, the frequen cies of the coordinated ligand vibrations are metal-sensitive, differing with the nature of the metal. As an example, infrared frequencies of the [Co(NH ) ]+ and [Cr(NH ) ]+ ion are compared in Table I (10, 20, 26). It is seen that both ions can be distinguished easily by comparing the N H rocking or the metal-nitrogen stretching frequencies. Table I also com pares the infrared frequencies of the [Co(CN) ]~ and [Cr(CN) ]~ ions. 3

6

3

3

6

3

3

6

Table I.

3

6

3

Infrared Frequencies of Ammine (26) and Cyano (10, 20) Complexes of Co(III) and Cr(III) (cm.- ) 1

[Co(NH )s]+>

[Cr(NH ) ]+>

3240 3170 1600 1325 820 503 325

3260 3205 1600 1310 745 470

[Co(CW).]-«

lCr(CN)s]~*

z

Assignment*

z 6

F.(NH.) F.(NH.)

5 (NH ) 5 (NH ) Pr(NH ) KM—N) 5(N—M—N) d

3

B

3 3

—

r(feN) KM—C) 8(M—C=N) Abbreviations listed below are as follows: v , antisymmetric stretching; v , sym metric stretching; 5d, degenerate deformation; 5 , symmetric deformation; p , rocking. 2118 565 414

a

2127 457

&

B

8


r

400

WERNER

Again, the metal-carbon stretching frequencies are markedly different in these two hexacyano complex ions. It is, therefore, relatively easy to dif ferentiate coordination isomers such as f C o ( N H ) ] [Cr(CN) ] and [ C r ( N H ) 6 ] [Co(CN) ]. Coordination isomers involving the same central metal may be more difficult to identify from their infrared spectra. Thus, [Pt(NH ) ] [PtCLJ and [ P t ( N H ) C l ] [ P t ( N H ) C l ] may exhibit very similar spectra. This is also expected for polymerization isomers such as [ C o ( N H ) ( N 0 ) ] and [Co(NH ) ] [ C o ( N 0 ) ] because the central metal is the same in both compounds. However, minor differences may pos sibly be seen in the far-infrared region where the skeletal vibrations of these complexes appear. 3

6

6

6

3

3

4

3


CENTENNIAL

3

3

2

3

3

3

3

6

2

3

6

Stereoisomerism One of the most fundamental results of Werner's coordination theory is the recognition of the fact that the complexes of the types [ C o ( N H ) X ] and [ C o ( N H ) X Y ] + , where X , Y = N 0 " , N C S - C l ~ , B r " , etc., must exist in two forms: cis and trans. 3

3

4

4

2

+

2

X H N- — 3

/

H N3

^X

H N^

Co

i

/

/

- NH NH

^NH

3

/ \

8

Co /

H N--

~^NH

3

3

X

3

cis isomer

3

trans isomer

Werner himself (32) isolated the two isomers of [ C o ( N H ) C l ] C l : violeo salt (cis) and praseo salt (trans). He then determined their structures by chemical methods. A number of investigations have been made to dis tinguish these and other stereo isomers by infrared spectra (22). It has been found that (1) the frequencies of some ligand vibrations are different in the cis and trans isomers, and (2) the cis isomer generally exhibits more bands than the trans isomer because the symmetry of the former is lower than that of the latter. It should be pointed out, however, that these previous investigations are largely limited to the N a C l region where the vibrations caused by the ligands appear. Infrared studies in the high frequency region sometimes fail to give a clear-cut diagnosis in dis tinguishing stereoisomers because the bands characteristic of the X group (see structure) overlap strongly with those of the N H group. Because the essential difference between cis and trans structures is in the spatial arrange ment of the coordinate bonds, more marked differences are expected in the far-infrared region where the coordinate bond stretching and bending 3

4

2

3


27.

NAKAMOTO

401

Infrared Studies

modes appear. In order to illustrate this point, the infrared spectra of cisand trans- [Co(NH )4(N0 )2]C10 are compared in Figure 2.


3

4

2

V(CM )

Figure 2.

Infrared spectra o) cis and trans [CO(NH )A(N02)2]CIOA (curve A, trans; curve B, cis) 3

Other well-known stereoisomers established by Werner (33) are the square planar complexes of the type, [ P t ( N H ) X ] , where X is a halogen. Werner again assigned the cis and trans structures using chemical methods. Figure 3 illustrates the infrared spectra of cis- and trans- [ P t ( N H ) X ] , where X = CI, B r , and I (23). As is seen above, it is easy to differentiate two isomers by means of the splitting patterns of (1) the N H deformation bands at ca. 1600 and 1300 c m . , (2) the P t - N stretching bands near 500 c m . , and (3) the N H rocking bands between 800 and 600 c m . 3

2

2

3

2

2

3

- 1

- 1

Salt

- 1

3

Isomerism

A complex of the composition [ C o ( N H ) N 0 ] C l exists i n two forms, an unstable, red form and a stable, yellow form (16). Werner (30) found that the N 0 group in the former is O-bonded (nitrito), whereas that i n the latter is N-bonded (nitro). These he called salt isomers. Using infrared spectroscopy, they can be readily distinguished because the N 0 group absorptions in each isomer are notably different, as is shown in Table I I . The nitrito complex is gradually converted into the corresponding nitro complex in the K B r pellet. It is, therefore, possible to follow the kinetics of this conversion by observing the disappearance of the 1065 c m . band as a function of time. Basolo and Hammaker (6, 7) have done this for pentammine nitrito complexes of R h ( I I I ) , Ir(III), and P t ( I V ) . 3

5

2

2

2

2

- 1


402

WERNER

(XA

t rans-

Pt(NH^CI

2

1 '

'^jl^'

'

'

1

'

1

1

'

CENTENNIAL

'

1

1

CIS-

Pt(NH^CI

2

trans-

Pt(NH^Br Downloaded by UNIV OF MICHIGAN ANN ARBOR on October 23, 2014 | http://pubs.acs.org Publication Date: January 1, 1967 | doi: 10.1021/ba-1967-0062.ch027

2

ClS-

Pt(NHiBfi trans-

Pt(NhQU 2

CIS-

Pt(NH^U

JV -A -A -A i

4000

3000

2000

1600

1400

1200

1000

800

600

400

200

v (cm ) -1

Figure 3. Infrared spectra of cis and trans [Pt(NHz) X ] where X = CI, Br, and I. Dotted lines are for the corresponding deuterated compounds 2

2

Werner (34) has discussed an example of what he believes to be salt isomerism, namely [Co(en) (NCS) ]Cl, i n which the N C S group can be N-bonded or S-bonded. It seems, however, that true salt isomers involv ing the N C S groups are not yet known for Co (III) complexes. Recently, Basolo et al (8, 9) have prepared them for the first time for Pd(II). 2

2

(CeH.),As

SCN / Pd / \ NCS As(C H )

(C H )3As 6

5

NCS

\

6

5

SCN

3

S-bonded isomer

/

\

As(C H )3 6

6

N-bonded isomer

Table I I . Nitrito and Nitro Group Frequencies in Pentammine Co(III) Complexes (cm." ) 1

[Co(NH ) (0N0)]CU 3

h

1468

[Co(NH,) (N0 )]Ch b

2

1428

1065

1310

825

824

— —

594 500

Assignment* *a(N0 ) 2

»B(N0 ) 2

S(ONO)

Pw(N0 ) „(Co—N) 2

° Abbreviations listed below are as follows: v , antisymmetric stretching; v , sym metric stretching; p , wagging. &

w


t

27.

NAKAMOTO

403

Infrared Studies

A number of other infrared works (22) have led to the conclusions that: (1) the C = N stretching frequency is higher in the S-bonded than in the N-bonded isomer, and (2) the C - S stretching frequency is higher in the N-bonded than in the S-bonded isomer. In fact, the N-bonded isomer mentioned above exhibits the C = N and C - S stretching bands at 2089 and 854 c m . , respectively, whereas the S-bonded isomer exhibits them at 2119 and 720-690 c m . , respectively. Recently, Raymond and Basolo (25) prepared a complex, [Cu(tren)(NCS)(SCN)] (tren = triaminotriethylamine, N ( C H C H N H ) 3 ) , in which M - N C S and M - S C N bonds are mixed in one complex. Its structure may be depicted as -1


-1

2

2

2

or — -NCS SCN

SCN

In fact, this complex exhibits two C = N stretching bands at 2094 and 2060, and two C - S stretching bands at 745 and 818 c m . The former frequency in each pair may correspond to the S-bonded group. Acetylacetone was the first compound employed by Werner (31) as a chelating agent. He prepared four complexes of the composition, K[Pt(acac)Cl ] (acac = acetylacetonate anion, C H C O C H C O C H ~ ) , Pt(acac) , K[Pt(acac) Cl], and Na [Pt(acac) Cl ], and formulated their structures as follows: - 1

2

3

2

2

2

CH CI

,0=C

O—C

KC1

\

3

CH

\CH,

2

3

2

CHs

HC

CHs

\j—0 ,0-c/' / \ / \ \

C=0 CH,

/

Pt

\

0

\

CH /

II CH, ,0=C

Kacac Pt CI

\

CH

O—C

CI \ NaCl

acac /

A

^acacNa

CH, III

IV


CH,

404

WERNER

CENTENNIAL

Although he did not state clearly how the acetylacetonato group denoted by acac in the above diagrams is bonded to the P t atom, it was found re cently by x-ray analysis (14) that the acac group i n I I I is C-bonded as is shown below: 0

CH

\ Downloaded by UNIV OF MICHIGAN ANN ARBOR on October 23, 2014 | http://pubs.acs.org Publication Date: January 1, 1967 | doi: 10.1021/ba-1967-0062.ch027

O K

\

C I C—CH

1

CH

3

/ CH

/

\

/

X

Pt

3

3

.CH

CI

0—c

CHs J

Recently, Lewis et al. (18) measured the infrared spectra of a number of acetylacetonato complexes of Pt(II) and have shown that the O-bonded (chelated) and C-bonded structures can be distinguished easily from their infrared and N M R spectra. We (24) have carried out normal coordinate analyses on both types of structures and have obtained the results shown in Table I I I . As is seen i n this table, these two types of coordination exhibit very different spectra. Table III.

Infrared Spectra of K[Pt(acac)Cl ] and Na [Pt(acac) ] 2 H 0 (cm.- ) 2

2

2

1

K[Pt(acac)Cl ] (O-bonded) 2

Na [Pt(acac) Cl }-2H 0 (C-bonded) 2

2

2

Assignment

1652) 1626/

„(C=0)

1563\ 1380/

—

,(C—0)

1538\ 1288/

—

,(C—C)

—

13521 1193/

1212(||) I817U)J

a

2

(C—C)

V

1193) 852/

5(C—H)

650\ 478/

__

,(Pt—0)

—

567

v(Pt—C)

II, in-plane; J_, out-of-plane.


2

27.

NAKAMOTO

405

Infrared Studies

Recently, Allen et al. (4) reported a third type of complex i n which the P t atom is bonded to the C = C bond of acetylacetone:


.0

CH

H

C

0

C—H

I \ CH \

3

o-p "-\

/

3

Pt

:CH

Cl

0—c

\ CHs VI This complex was prepared by acidifying the solution of Compound I I I (Structure V ) . This type of coordination is characterized by the presence of the O H stretching (2950-2860 cm.- ), C = 0 stretching (1627 c m - ) , and C the Pt—1| stretching bands (360 c m . ) . C 1

1

-1

Other Work on Werner Complexes It is clear from the above that infrared spectroscopy is useful i n dis tinguishing the various types of isomers proposed by Werner. Several recent works may also be cited, which provide more detailed structural and bonding information on Werner complexes. Rotation of N H Group. The question as to whether the ammonia molecule in metal complexes rotates freely about its threefold axis has not yet been settled completely. Leech et al. (17) have shown, for example, that the N H groups in trans- [ P d ( N H ) C l ] are probably not rotating appreciably at or below room temperature because rotational wings are not seen in the infrared spectrum. Nakamoto et al. (23) have also postulated that the N H groups in trans- [ P t ( N H ) C l ] and other Pt(II) ammine complexes do not rotate freely because the filled d-orbitals of the P t atom interact with one of the hydrogens of the N H group. 3

3

3

3

3

2

2

2

2

3

Conformation of Ethylenediamine. Whether the ethylenediamine chelate ring is completely planar or puckered has also been a subject of controversy. The conformation of ethylenediamine may be cis if planar and gauche if puckered. Infrared studies have proved to be very useful in distinguishing cis, trans, and gauche conformation of 1,2-substituted


406

WERNER

CENTENNIAL


ethanes like ethylenediamine (22). Thus far, the conformation of chelated (not bridging) ethylenediamine has proved to be gauche without exception. Normal Coordinate Analysis. I n order to obtain quantitative i n formation about the strength of the coordinate bond, i t is necessary to carry out normal coordinate analysis using Wilson's G F method (35, 36). Such attempts have been made recently on ammine (27, 28), halogenoammine (27, 28), halogeno (15), nitro (21), and cyano (20) complexes of Co (III) and have given the following Urey-Bradley force constants for the coordinate bond stretching vibration: C N - \ N 0 " \ N H \ CI- ~ Br- \ I " 2.31 / 1.16 / 1.05 / 0.96 ~ 1.06 / 0.62 2

3

(millidynes/A.) It is interesting that the order of stretching force constants obtained above is similar to the spectrochemical series obtained from the U V spectra of various Co (III) complexes (29). Acknowledgment The author wishes to express his sincere thanks to H . Ogoshi for aid in obtaining the infrared spectra shown i n Figures 1 and 2 of this article. Literature

Cited

(1) Adams, D. M., Chatt, J., Davidson, J. M., Gerratt, J., J. Chem. Soc. 1963, 2189. (2) Adams, D. M., Chatt, J., Gerratt,J.,Westland, A. D., J. Chem. Soc. 1964, 734. (3) Adams, D.M.,Gebbie, H. A., Spectrochim. Acta 19, 925 (1963). (4) Allen, G., Lewis, J., Long, R. F., Oldham, C., Nature 202, 580 (1964). (5) Barraclough, C. G., Tobe, M. L.,J.Chem. Soc. 1961, 1993. (6) Basolo, F., Hammaker, G. S., J. Am. Chem. Soc. 82, 1001 (1960). (7) Basolo, F., Hammaker, G. S., Inorg. Chem. 1, 1 (1962). (8) Basolo, F., Burmeister, J. L., Poe, A. J., J. Am. Chem. Soc. 85, 1700 (1963). (9) Basolo, F., Burmeister, J. L., Poe, A. J., Inorg. Chem. 3, 1202 (1964). (10) Caglioti, V., Sartori, G., Furlani, C., J. Inorg. Nucl. Chem. 13, 22 (1960). (11) Clark, R.J.H., Dunn, T. M., J. Chem. Soc. 1963, 1198. (12) Coates, G. E., Ridley, D., J. Chem. Soc. 1964, 166. (13) Damasehun, I., Z. Physik. Chem. B16, 81 (1932). (14) Figgis, B. N., Lewis, J., Long, R. F., Mason, R., Nyholm, R. S., Pauling, P. J., Robertson, G. B., Nature 195, 1278 (1962). (15) Hiraishi, J., Nakagawa, I., Shimanouehi, T., Spectrochim. Acta 20, 819 (1964). (16) Jørgensen, S.M.,Z. Anorg. Allgem. Chem. 5, 169 (1893). (17) Leech, R. C., Powell, D. B., Sheppard, N., Spectrochim. Acta 21, 559 (1965). (18) Lewis, J., Long, R. F., Oldham, C., J. Chem. Soc. 1965, 6740. (19) Nakagawa, I., Shimanouchi, T., Spectrochim. Acta 20, 429 (1964). (20) Nakagawa, I., Shimanouchi, T., Spectrochim. Acta 18, 101 (1962). (21) Nakagawa, I., Shimanouchi, T., Yamasaki, K., Inorg. Chem. 3, 772 (1964). (22) Nakamoto, K., "Infrared Spectra of Inorganic and Coordination Com pounds," John Wiley, New York, N. Y., 1963. In Werner Centennial; Kauffman, G.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.


27.

NAKAMOTO

Infrared Studies

407

(23) Nakamoto, K., McCarthyl, P.J.,Fujita, J., Condrate, R. A., Behnke, G. T., Inorg. Chem. 4, 36 (1965). (24) Nakamoto, K., Behnke, G. T., Abstract of IX. I.C.C.C., St. Moritz-Bad, Switzerland, September, 1966. (25) Raymond, K. N., Basolo, F., Inorg. Chem. 5, 1632 (1966). (26) Shimanouchi, T., Nakagawa, I., Inorg. Chem. 3, 1805 (1964). (27) Shimanouchi, T., Nakagawa, I., Spectrochim. Acta 18, 89 (1962). (28) Ibid. 22, 759 (1966). (29) Shimura, Y., Tsuchida, R., Bull. Chem. Soc. Japan 29, 311 (1956). (30) Werner, A., "Neuere Anschauungen auf dem Gebiete der anorganischen Chemie," 1905. (31) Werner, A., Ber. 34, 2584 (1901). (32) Ibid. 40, 4817 (1907). (33) Werner, A., Z. Anorg. Chem. 3, 267 (1893). (34) Werner, A., Bräunlich, Z. Anorg. Chem. 22, 95 (1900). (35) Wilson, E. B., J. Chem. Phys. 7, 1047 (1939). (36) Ibid. 9, 76 (1941). RECEIVED June 30, 1966.


Recent Infrared Studies on Werner Complexes

Recommend Documents