Actinide Chemistry

8 Electronic Spectra of Lanthanide

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Compounds in the Vapor Phase D. M. GRUEN, C. W. DEKOCK, and R. L. McBETH Argonne National Laboratory, Argonne, Ill. The vapor phase spectra of the tribromides and triiodides of Pr, Nd, Er and Tm and of the 2,2,6,6-tetramethyl-3,5heptanedionates of Pr, Nd, Sm, Eu, Dy, Ho, Er and Tm have been measured in the range 4,000-30,000 cm. . The transition intensities of most of the f l e a n d D 1

3

x

2

1

states

2

is p a r t i c u l a r l y s t r i k i n g since these are the most intense transitions i n a q u e ous s o l u t i o n . S i n c e these transitions are not o b s e r v e d i n the vapors, a n e s t i m a t e of the m a x i m u m v a l u e f o r the τ a n d τ parameters m a y b e m a d e o n 4

6

the a s s u m p t i o n that the transitions h a v e a n oscillator strength < 1 Χ 10" . 6

O n this basis, τ a n d τ are c a l c u l a t e d to be < 3 Χ 10" . A n estimate of τ Downloaded by KUNGLIGA TEKNISKA HOGSKOLAN on March 8, 2015 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch008

4

9

6

2

c a n be m a d e f r o m the intensity of the transitions i n the 4 0 0 0 - 7 0 0 0 c m . " 1

r e g i o n w h i c h are to the indicates that τ

2

3

F j (/ =

2,3,4) states.

S u c h a n analysis a g a i n

is a p p r o x i m a t e l y 20 to 30 times larger t h a n r

4

and τ , 6

w h i c h is s i g n i f i c a n t l y larger t h a n o b s e r v e d i n m o s t s o l u t i o n spectra. S o m e of the a b s o r p t i o n i n t e n s i t y i n the 4000 to 5000 c m . " c a l c u l a t e d to arise f r o m the H - F 3

c m . " a b o v e the g r o u n d 1

3

H

4

5

3

F

3

^ 3

1

r e g i o n is

H state lies —

3

2100

5

state a n d is 2 0 % t h e r m a l l y p o p u l a t e d at the

t e m p e r a t u r e of the measurement. 3

transition. T h e

3

The [ I / ] 2

2

m a t r i x element for the H 3

5

-

t r a n s i t i o n is 0.3142 w h i c h leads to a c a l c u l a t e d oscillator strength of Χ 10" for the i o d i d e a n d 2 Χ 10" for the b r o m i d e at a n e n e r g y of 6

6

4100 c m . " . 1

20 h 15

i-

15

Tm

3 +

in IM D C I 0

4

(25°)

1.0

I

30

ι

LiA

28

26

ι

24

ι/ Ν

22

ι

20

ι

cm"

Figure

U

18 1

14

χ

I0"

4. Absorption spectrum TmBr compared with Tm 3

\J

16

3+

\ι

12

ι

10

/

i\

8

ι

LA

6

4

I

2

3

of gaseous Tml ion in lm DClO

3

and

u

In Lanthanide/Actinide Chemistry; Fields, P., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

LANTHANIDE /ACTINIDE

110

Gaseous T m B r and T m l . 3

3

T h e s p e c t r a of gaseous T m B r

CHEMISTRY

and T m l

3

a p p e a r i n F i g u r e 4 together w i t h t h e s p e c t r u m o f aqueous T m

3 +

3

. The

e x p e r i m e n t a l a n d c a l c u l a t e d oscillator strengths a p p e a r i n T a b l e IV, w h i l e the τ

λ

values a r e g i v e n i n T a b l e V . Table IV.

Oscillator Strengths of T m B r ( g ) and T m l ( g ) 3

3

Ρ X 10 Downloaded by KUNGLIGA TEKNISKA HOGSKOLAN on March 8, 2015 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch008

6

Calculated energy

»H

F

iG

4

W

Calc.

10.7

10.7 4.4

12.0 2.7

12.0 4.8

12636 14280

0.5470 0

15.3

12.2 4.7

3.3

j>

0

4.6 25.3 11.0

11.1 4.7

1.2

4.5

0.0006 0

28103

2

Expt.

0.2300 0.1073

14996 21421

2

Calc.

5508 8322

4

5

3

Expt.

1

H

3

s

3

(cm.' )

S'L'J'

Tml (g)

TmBr (g)

Table V . Values of τ χ Iodide

Bromide

Pr

T

Tm

2

T4 T6

< 3 Χ 10" < 3 X 10~

T2

2 Χ 10"

T

4

T

6

T

2

7

3 Χ 10"

7

8

1 X 10"

8

8

1 X 10"

8

1.6 ± 2 . 7 X 1 0 ~

9

1.8 ± 1.2 X 1 0 "

9

5.9 ± 1.2 Χ 1 0 " 0 . 9 ± 1.2 Χ Ι Ο " 0.5 ± 3.5 Χ 1 0 " 4.6 X 10~ 3 X 10" 3 Χ 10"

9

9

6.51 ± .16 Χ 1 0 "

-

7

< 3 Χ 10"

9

T2

4

T6 1

9

T6

T2

Tm"

1 X 10~ < 3 X 10~

8

1 X 10" 1 X 10"

T

Er

— 5 Χ 10"

1 0 . 6 ± .1 Χ 1 0 "

8

6.4 ± 1.5 Χ 1 0 "

9

-

1.6 ± 1.0 Χ 1 0 "

9

-

9.8 ± . 5 Χ 1 0 " 4 . 4 ± .6 Χ 1 0 "

8

8

8

1.3 ± .2 Χ 1 0 "

8

4.06 Χ 1 0 " 3 Χ 10"

8

8

8

8

8

9

9

3 X 10~

9

9

C a l c u l a t e d assuming T4 a n d τ% are average solution values.

The τ

λ

parameters w e r e c a l c u l a t e d b o t h b y a least-squares fit to

E q u a t i o n 3 a n d b y setting τ

and τ

4

6

e q u a l to t h e i r s o l u t i o n values a n d

c a l c u l a t i n g τ f r o m a fit to t h e F l e v e l . T h e least-squares m e t h o d is n o t 3

2

4

v e r y r e l i a b l e since o n l y five transitions are a v a i l a b l e f o r T m B r four for T m l . 3

all the υ

λ

S i n c e f o r t h e t w o most intense transitions, F 3

a n d only

3

4

and H , 3

4

m a t r i x elements are large, t h e r e l a t i o n s h i p b e t w e e n t h e τ p a λ

rameters cannot b e e v a l u a t e d .

When τ

4

and r

6

are set e q u a l to t h e i r

s o l u t i o n values, r a g a i n is a factor of 1 0 l a r g e r t h a n τ o r τ , a n d there is 2

4

6


8.

G R U E N

E T

A L .

Electronic

111

Spectra

l i t t l e loss i n the o v e r - a l l fitting of E q u a t i o n 3 except for the t r a n s i t i o n to H

3

4

for T m l . 3

Some General Remarks. T h e energies a n d intensities of the a b s o r p t i o n m a x i m a f o u n d i n r a r e - e a r t h h a l i d e v a p o r spectra are b r o u g h t t o gether i n T a b l e V I . O n l y i n the case of E r B r

3

w e r e there e n o u g h transitions a v a i l a b l e to

m a k e a r i g o r o u s analysis of t h e s p e c t r u m i n a c c o r d a n c e w i t h E q u a t i o n 3. Downloaded by KUNGLIGA TEKNISKA HOGSKOLAN on March 8, 2015 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch008

T h e c h i e f reason l i m i t i n g t h e n u m b e r of o b s e r v a b l e f

for those near t h e t a i l of the i m p u r i t y

23,000 c m . " for t h e b r o m i d e s a n d > 1

20,000 c m . " f o r the 1

i o d i d e s since i t w a s difficult to d e t e r m i n e the baselines i n these regions. Gaseous 2,2,6,6«Tetramethyl-3,5-Heptanedionates. W i t h E i s e n t r a u t a n d S i e v e r s s ( 9 ) d i s c o v e r y of a g r o u p of v o l a t i l e l a n t h a n i d e chelates, the l a n t h a n i d e 2,2,6,6-tetramethyl-3,5-heptanedionates a b b r e v i a t e d M ( t h d ) , 3

a n i n t e r e s t i n g g r o u p of c o m p o u n d s f o r v a p o r phase s p e c t r a l i n v e s t i g a t i o n became available. T h e v a p o r s p e c t r a of the M ( t h d )

3

c o m p o u n d s w i t h M == P r , N d , S m ,

E u , D y , H o , E r , a n d T m are s h o w n i n F i g u r e s 5 a n d 6.

T h e arrows

i n d i c a t e a b s o r p t i o n o w i n g to v i b r a t i o n a l overtone a n d c o m b i n a t i o n b a n d s of the o r g a n i c c h e l a t e m o i e t y . T h e r e m a i n i n g a b s o r p t i o n b a n d s arise f r o m f

f transitions of the r a r e - e a r t h constituents. T h e energies a n d m o l a r

a b s o r p t i v i t i e s of the /

/ a b s o r p t i o n m a x i m a are s h o w n i n T a b l e V I I .

T h e features of p a r t i c u l a r interest f r o m t h e p o i n t of v i e w of

the

present s t u d y are the h y p e r s e n s i t i v e transitions i n the gaseous spectra. T h e y constitute the most p r o m i n e n t features of the s p e c t r a , a n d t h e i r o s c i l l a t o r strengths are l i s t e d i n T a b l e I X .

Discussion T h e unexpected

finding

that the o s c i l l a t o r strengths of the h y p e r -

sensitive transitions i n l a n t h a n i d e v a p o r spectra are l a r g e r t h a n i n m a n y


112

L A N T H A N I D E / A C T I N I D E

Energies and Intensities of the

Table V I . PrBr cm.

C H E M I S T R Y


3

€

4103 4629 4677 5025 5150 5620 5960 6470 6850

a

α

1

17 6 10 4 3 1 1 1 0.5

Frl

3

e

4135 4350 4660sh 4680 5000 5180 5680 5950sh 6030 6100sh 6430 6780

32 3 15 18 9 7 2 2 3 2 4 3

NdBr

Ndl

e

3

10570 10990 11430 12220 14672 14900 15000 15090 16260 16469 16598 16656 16750 16806 16849 16975 18867

e

3

2 3 6 7 7 11 13 10 25 115 85 105

10560 10990 11360 12220 13160 14641 14891 14936sh 16194 16334 16469 16515

60 45 40 30 8

16611 16703 16778 16877 18900sh

2 3 2 6 2 13 32 28 90 345 250 220 175 115 85 75 64

c = liters/mole-cm.

c o n d e n s e d phases demonstrates the n e e d for a better u n d e r s t a n d i n g of the i n t e n s i t y m e c h a n i s m s i n v o l v e d i n / J

4

4

2

5 /

7

E

r

r

,n

4

f

4

Tm a

3

ρ

3

D a t a f r o m J0rgensen a n d l u d d

Table IX.

Pr Nd Dy Ho

2

3

V2 Q/2 ° F D «F *G H

17,300 14,900 6,200 21,500 7,700 22,200 26,200

/

2

2

1 1 / 2

e

3

8

ii5/2 /i5/2 H H

2

3

6

H ^ιι/2 F H 1

4

3

C

0

1

/

19,200 26,500 12,600 5,500

2

4

4

(13).

Oscillator Strengths, P, of Hypersensitive Transitions in Gaseous Lanthanide Compounds Excited State

Ion

1

4,800 4,100

1

5

0

1 5 / 2

'

F F

0

Energy cm.'

G

8

°

C H E M I S T R Y

F G «F G

3

^ Bromide

Iodide

—20 330

—40 530

— —

— —

2

4

5

5

/

2

1 1 / 2

G

Er

2

Tm

^ " / a

3

F

H

l

J

/

4

15 120 32 178 34 85 12

96

58 99 15

2

Chelate

— 25

T h e oscillator strengths of these transitions i n aqueous solutions are i n the range 1 to 10 Χ ΙΟ" . 6

Table Χ .

τ

χ

Values for E r

3 +

Solution and Vapor Spectra T\

Medium DC10 LiNO KNO, Chelate Tribromide Triiodide 4

; r

Table X I .

8

10

8

τ

τ

2

) Q ι t* S ) > Vapor )

° 1 2.2 5 6.5 10.6

2 > o l u t l o n

6

6

0

2

3

0.25 —0.3 0.16 —

Range of T - V a l u e s for Solution and Vapor Spectra

A q u e o u s solutions L i N 0 - K N 0 eutectic soins. Chelate vapors Bromide a n d iodide vapors 3

χ

2

1-2 1-2 0.5-1 0.5-3

X Χ Χ Χ

10"° 10" 10~ 10" 8

7

7


0

2

4

0.19 —0.4 0.18 —

8.

G R U E N

E T

Electronic

A L .

119

Spectra Table X I I .

Compound Pr(thd) Nd(thd) Sm(thd) Eu(thd) Dy(thd) Ho(thd) Er(thd) Tm(thd)

Experimental

Literature

°C.

3

3

3 3

3

3

s

m.p., °C. (7)

222-224 215-218 195.5-198.5 187-189 180-183.5 180-182.5 179-181 171.5-173.5

222-225 215-217.5 198.5-200 188.5-189 181-183.5 182.5-185 182.5-183.5 171-174

3


m.p.,

Experimental B r o m i d e s a n d Iodides. T h e a b s o r p t i o n spectra of t h e gaseous r a r e e a r t h h a l i d e s w e r e m e a s u r e d w i t h a C a r y 14 H spectrophotometer. The e x p e r i m e n t a l p r o c e d u r e has b e e n d e s c r i b e d p r e v i o u s l y (11). I n this s t u d y a d o u b l e f u r n a c e was u s e d , a l l o w i n g the r a r e - e a r t h h a l i d e v a p o r to b e h e a t e d to a h i g h e r t e m p e r a t u r e t h a n the s o l i d or l i q u i d a n d a l l o w i n g a b a s e l i n e d e t e r m i n a t i o n at the t e m p e r a t u r e of interest. I n a d d i t i o n , a 0 0.1 f u l l scale o p t i c a l d e n s i t y s l i d e w i r e w a s e m p l o y e d w i t h the C a r y 14 H spectrophotometer, i n c r e a s i n g its s e n s i t i v i t y b y a factor of 10. W i t h this a r r a n g e m e n t transitions w i t h o p t i c a l d e n s i t y of 0.005 c o u l d b e o b s e r v e d easily. T h e m o l a r a b s o r p t i v i t i e s for P r B r a n d P r l v a p o r w e r e d e t e r m i n e d f r o m S h i m a z a k i a n d N i w a ' s ( 2 2 ) v a p o r pressure equations for the solids a n d t h e extrapolations u s e d i n the e a r l i e r gaseous N d B r a n d N d l s t u d y . T h e h e a t capacities a n d heats of f u s i o n for P r B r a n d P r l w e r e t a k e n f r o m D w o r k i n a n d B r e d i g s (7,8) d a t a . T h e v a p o r pressure equations o b t a i n e d f o r s o l i d a n d l i q u i d P r B r are g i v e n b y E q u a t i o n s 5 a n d 6 respectively 3

3

3

3

3

3

3

log P log P

a t m

a t m

(PrBr (s) ) = 3

(PrBr (l)) = 3

and for solid a n d l i q u i d P r l

3

* ™

- 4.28 log Τ + 24.279

(5)

-

(6)

7.04 log Τ + 31.189

b y Equations 7 and 8 respectively — 17109

log P

a t m

(PrI (s) ) = 3

y

-

5.59 log Τ + 29.047

(7)

—14QR7

log P t m ( P r I ( l ) ) f - 7.05 log Τ 4- 31.322 (8) S i n c e no a c c u r a t e v a p o r pressure d a t a are a v a i l a b l e for the e r b i u m a n d t h u l i u m h a l i d e s , the m o l a r a b s o r p t i v i t i e s w e r e d e t e r m i n e d d i r e c t l y f r o m a w e i g h e d a m o u n t of the respective r a r e - e a r t h h a l i d e s . G o o d results c o u l d b e o b t a i n e d f r o m this m e t h o d i f the respective h a l o g e n , b r o m i n e , or i o d i n e w e r e a d d e d to the c e l l s u c h t h a t its pressure at 1 0 0 0 ° C . w a s — 1 a t m . T h i s p r o c e d u r e g r e a t l y r e d u c e d the r e a c t i o n of the r a r e - e a r t h a

3


120

L A N T H A N I D E / A C T I N I D E

C H E M I S T R Y

h a l i d e v a p o r w i t h the q u a r t z as e v i d e n c e d b y the fact t h a t 8 0 % of the r a r e - e a r t h h a l i d e was r e c o v e r e d after a d e t e r m i n a t i o n . I n g e n e r a l , the average of the w e i g h t s b e f o r e a n d after was u s e d to c a l c u l a t e the m o l a r a b s o r p t i v i t y . T h e values g i v e n for the m o l a r a b s o r p t i v i t y are p r o b a b l y c o r r e c t to w i t h i n ± 2 5 % .


A l l t h e r a r e - e a r t h h a l i d e s w e r e p r e p a r e d b y the a m m o n i u m h a l i d e m e t h o d d e s c r i b e d b y T a y l o r a n d C a r t e r (24) and were used without f u r t h e r p u r i f i c a t i o n . T h e r a r e - e a r t h oxides ( M i c h i g a n C h e m i c a l ) u s e d to p r e p a r e the h a l i d e s w e r e of 9 9 . 8 % p u r i t y or better. T h e absolute values of the oscillator strengths m a y b e i n error b y as m u c h as ± 2 5 % ; h o w e v e r , the r e l a t i v e intensities, w h i c h d e t e r m i n e the r e l a t i v e m a g n i t u d e s of τχ, are k n o w n to w i t h i n ± 5 % except f o r t h e v e r y w e a k transitions of the less v o l a t i l e p r a s e o d y m i u m a n d n e o d y m i u m h a l i d e s f o r w h i c h the errors m a y be as l a r g e as ± 2 5 % . 2 , 2 , 6 , 6 - T e t r a m e t h y l - 3 , 5 - h e p t a n e d i o n a t e s . T e n m i l l i m o l e s of e a c h of t h e r a r e - e a r t h chelates w e r e p r e p a r e d b y the m e t h o d of E i s e n t r a u t a n d Sievers ( 9 ) . H ( t h d ) f r o m the P i e r c e C h e m i c a l C o . , R o c k f o r d , 111. w a s u s e d w i t h o u t f u r t h e r p u r i f i c a t i o n . F i v e m m o l e s of the 9 9 . 9 % r a r e e a r t h oxide ( M i c h i g a n C h e m i c a l Corp., Saint L o u i s , M i c h . ) were dissolved i n the s t o i c h i o m e t r i c a m o u n t of 6N H N 0 , a n d a p p r o p r i a t e amounts of H 0 a n d 9 5 % E t O H w e r e a d d e d to m a k e 50 m l . of 5 0 % e t h a n o l s o l u t i o n c o n t a i n i n g the r e q u i r e d a m o u n t of r a r e - e a r t h n i t r a t e . T h e d r i e d p r o d u c t w a s s u b l i m e d at 1 8 0 ° C . in vacuo, r e c r y s t a l l i z e d f r o m n-hexane in vacuo, a n d v a c u u m d r i e d . A l t h o u g h no e l e m e n t a l analyses w e r e m a d e o n the final p r o d u c t , the m e l t i n g points w e r e t a k e n o n a F i s h e r - J o n e s m e l t i n g p o i n t a p p a r a t u s , a n d the results o b t a i n e d w e r e c o m p a r e d w i t h the l i t e r a t u r e values s h o w n i n T a b l e X I I . T h e p r o d u c t s w e r e stored i n e v a c u a t e d desiccators. 3

2

T h e g e n e r a l p r o c e d u r e for o b t a i n i n g the a b s o r p t i o n s p e c t r u m of e a c h c o m p o u n d consisted of a d d i n g a w e i g h e d a m o u n t of the c o m p o u n d to a 10 or 20 c m . c e l l w h i c h h a d b e e n e v a c u a t e d p r e v i o u s l y a n d flamed out. T h e c e l l was t h e n r e t u r n e d to the v a c u u m l i n e , e v a c u a t e d , a n d sealed off w i t h a h a n d t o r c h . A b s o r p t i o n spectra measurements w e r e m a d e u s i n g a C a r y 14 Η spectrophotometer. T h e u n i q u e characteristics of this i n s t r u m e n t , w h i c h p e r m i t s its use u p to temperatures of 2400°K. or h i g h e r , h a v e b e e n d e s c r i b e d b y G r u e n (10). T h e cells w e r e h e a t e d b y a horizontally positioned 1 2 " long M a r s h a l l furnace. T h e furnace was m a i n t a i n e d at the d e s i r e d t e m p e r a t u r e b y a n a u t o m a t i c controller. S m a l l , a u x i l i a r y , p l a t i n u m - w o u n d t u b e heaters c o n t r o l l e d b y variacs s u r r o u n d e d e a c h e n d of the o p t i c a l c e l l . T h e t e m p e r a t u r e of these furnaces w a s m a i n t a i n e d at a l e v e l just sufficient to p r e v e n t c o n d e n s a t i o n of the m e t a l chelate o n the c e l l w i n d o w s . T h e a b s o r p t i o n s p e c t r u m was r e c o r d e d at v a r i o u s temperatures u n t i l there was n o f u r t h e r increase i n the m a x i m u m of the most intense p e a k . A t this t e m p e r a t u r e , the entire s p e c t r u m f r o m 4000-30,000 c m . " w a s then recorded. 1

T h e m o l a r e x t i n c t i o n coefficients w e r e c a l c u l a t e d as o u t l i n e d b y D e K o c k a n d G r u e n (6). T h e c o n c e n t r a t i o n of the a b s o r b i n g species was c a l c u l a t e d f r o m the m e a s u r e d v o l u m e of the c e l l a n d the k n o w n q u a n t i t y of m a t e r i a l a d d e d to the c e l l .


8.

G R U E N

E T A L .

Electronic

Spectra

121

Acknowledgments W e a r e i n d e b t e d to B . G . W y b o u r n e a n d G . L . G o o d m a n f o r a n u m b e r o f f r u i t f u l discussions.


Literature Cited (1) Akishin, P. Α., Naumov, V. Α., Tatevskii, V. M., Nauch. Doklady Vysshei Shkoly, Khim. & Khim. Tekhnol. 1959, 229 (1959); Chem. Àbstr. 53, 19493e (1959). (2) Axe, J. D., Jr., J. Chem. Phys. 39, 1154 (1963). (3) Broer, L. J. F., Gorter, C. J., Hoogschagen, J., Physica 11, 231 (1945). (4) Carnall, W. T., Fields, P. R., Wybourne, B. G., J . Chem. Phys. 42, 3797 (1965). (5) Carnall, W. T., Gruen, D. M., McBeth, R. L., J. Phys. Chem. 66, 2159 (1962). (6) DeKock, C. W., Gruen, D. M., J. Chem. Phys. 44, 4387 (1966). (7) Dworkin, A. S., Bredig, Μ. Α., J. Phys. Chem. 67, 2499 (1963). (8) Ibid.,p. 697. (9) Eisentraut, K. J., Sievers, R. E., J. Am. Chem. Soc. 87, 5254 (1965). (10) Gruen, D. M., Quart. Rev. (London) 19, 349 (1965). (11) Gruen, D. M., DeKock, C. W., J. Chem. Phys. 45, 455 (1966). (12) Holleck, L., Eckardt, D., Z. Naturforsch. 9b, 274 (1954). (13) Jørgensen, C. K., Judd, B. R., Mol. Phys. 8, 281 (1964). (14) Judd, B. R., Phys. Rev. 127, 750 (1962). (15) Judd, B. R., J. Chem. Phys. 44, 839 (1966). (16) Kononenko, L. I., Poluektov, N. S., Russ. J. Inorg. Chem. (English Transl.) 7, 965 (1962). (17) Krupke, W. F., Gruber, J. B., Phys. Rev. 139, A2008 (1965). (18) Krupke, W. F., Phys. Rev. 145, 325 (1966). (19) Moeller, T., Brantley, J. C., J. Am. Chem. Soc. 72, 5447 (1950). (20) Moeller, T., Ulrich, W. F., J. Inorg. Nucl. Chem. 2, 164 (1956). (21) Ofelt, G. S., J. Chem. Phys. 37, 511 (1962). (22) Shimazaki, E., Niwa, K., Z. Anorg. Allgem. Chem. 314, 21 (1962). (23) Taketatsu, T., Banks, C. V., Anal. Chem. 38, 1524 (1966). (24) Taylor, M. D., Carter, C. P., J. Inorg. Nucl. Chem. 24, 387 (1962). (25) VanVleck, J. H., J. Phys. Chem. 41, 67 (1937). (26) Vickery, R. C., J. Chem. Soc. 1952, 421 (1952). October 17, 1966. This work was performed under the auspices of the U. S. Atomic Energy Commission. RECEIVED


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