Actinide Chemistry

5 Physical Characterization of the Metallic LaI and CeI and of the Phase 2

LaI

2

2.42

Downloaded by UNIV OF SYDNEY on September 1, 2014 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch005

JOHN D. CORBETT, ROBERT A. SALLACH and DONALD A. LOKKEN Institute for Atomic Research and Department of Chemistry, Iowa State University, Ames, Iowa

The specific resistance and magnetic susceptibility measured for LaI2 clearly support the metallic formulation La (I) e. A comparable temperature dependence of resistivity was obtained for a mixed phase sample of CeI . The formation of apparently metallic phases for only the iodides of five lanthanide and actinide elements is considered in terms of the stoichiometry, the electronic structure of the cation, the possible nature of the band, and the role of the anion. In contrast, the intermediate LaI phase exhibits semiconduction. Its magnetic data between 80° and 300°K. can be best accounted for if the reduced component is considered to be La , [Xe]5d ,with a T ground term, a spin-orbit coupling constant λ ~650 cm. , and only small covalency and asymmetry parameters. 3+

-

-

2

2

2.42

2+

1

2

2g

-1

Q t u d i e s of b i n a r y r a r e e a r t h m e t a l - m e t a l h a l i d e systems h a v e r e v e a l e d ^

not o n l y a c o n s i d e r a b l e n u m b e r of n e w , r e d u c e d phases, b u t also a

s u b s t a n t i a l l y n e w class of h a l i d e s possessing a m e t a l l i c r a t h e r t h a n a t r u l y r e d u c e d or l o c a l i z e d c h a r a c t e r .

T h e r e d u c t i o n p r o p e r t i e s of

the

c h l o r i d e s , b r o m i d e s , a n d i o d i d e s of the first f o u r r a r e e a r t h elements are s u m m a r i z e d as f o l l o w s i n terms of the c o m p o s i t i o n s of n e w l o w e r phases or, w h e r e absent, the l i m i t i n g s o l u t i o n c o m p o s i t i o n s i n m o l e % m e t a l i n liquid M X : 3

X

La

Ce

Pr

CI Br I

9 % soin. (21 ) 1 4 % s o i n . (30) L a l . . 2 . 4 2 (β)

9 % s o i n . (27) 1 2 % s o i n . (30) C e l . . . (β)

PrCl (12) P r B r ^ (30) P i T . , . , (6)

2

00

2

0

2

4

2 3 2

Nd

NdCl

2

2

2

00

2

Ndl

1 9 5

(11 ) --------(11 )

0 0

2

2 7

2

3 7

56

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

5.

CORBETT E T A L .

Metallic

Lal

and

2

57

Cel

2

I n most of these systems there is clear e v i d e n c e for the f o r m a t i o n of the reduced ion M

2 +

. F o r example, i n N d X

n e t i c studies ( 3 1 ) ,

salts this is o n the basis of m a g -

2

a n d w i t h the p r a s e o d y m i u m c h l o r i d e a n d

phases, f r o m q u a l i t a t i v e r e s i s t i v i t y measurements

bromide

and their structural

r e l a t i o n s h i p s to the n e o d y m i u m chlorides a c c o r d i n g to x-ray d a t a . C r y o s c o p i c d a t a for a l l the systems l i s t e d are also consistent w i t h the f o r m a t i o n of a M

2 +

, as o p p o s e d to M , solute i n d i l u t e s o l u t i o n i n M X +

3

(3, 7).

T h e u n e x p e c t e d is f o u n d w i t h the i o d i d e s of the first three i n that t h e y f o r m r a t h e r stable d i i o d i d e s , c o n g r u e n t l y m e l t i n g for L a l , w i t h a 2

structure different f r o m that of " N d l " ( S m B r or S r B r t y p e ) ( I I ) . Downloaded by UNIV OF SYDNEY on September 1, 2014 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch005

2

appearance

2

2

of the first three d i i o d i d e s i m m e d i a t e l y suggested

The

a more

m e t a l - l i k e character, a n d this was s u p p o r t e d b y p r e l i m i n a r y e l e c t r i c a l a n d m a g n e t i c measurements (6).

S u c h phases are r e l a t i v e l y rare a m o n g

h a l i d e s , i n c l u d i n g , i n a d d i t i o n , o n l y the u n i q u e A g F 2

subsequently discovered G d l

2

(26)

and T h l

2

(4).

(36, 3 7 )

a n d the

H o w e v e r , this p r o p e r t y

is k n o w n for most of the rare e a r t h elements i n the

monochalcogenides

(16, 29) a n d d i c a r b i d e s ( 3 3 ) , as w e l l as w i t h the oxides, sulfides, etc. of a n u m b e r of t r a n s i t i o n elements.

T h i s article reports m o r e c o m p l e t e l y the

e v i d e n c e for this character, e s p e c i a l l y for L a l

2

because of its f a v o r a b l e

c o n g r u e n t m e l t i n g p r o p e r t y a n d d i a m a g n e t i c core b a c k g r o u n d , a n d c o n siders some of the i m p o r t a n t c r i t e r i a for t h e f o r m a t i o n of the m e t a l l i c halides.

Some properties r e l a t e d to the c o n s t i t u t i o n of the i n t e r m e d i a t e

phase L a l

2

4 2

are also presented.

Experimental P r e p a r a t i o n s w e r e g e n e r a l l y as p r e v i o u s l y d e s c r i b e d ( 6 ) . S u b l i m a t i o n of the t r i i o d i d e s was c a r r i e d out i n glass-jacketed t a n t a l u m to a v o i d the r e a c t i o n of the m o l t e n i o d i d e s w i t h S i 0 to f o r m M O I a n d S i l . R o d s of M I i i n . d i a m e t e r w e r e g r o w n f r o m the m e l t i n t a n t a l u m t u b i n g b y m a n u a l m o v e m e n t of this t h r o u g h a g r a d i e n t f u r n a c e . T h i s w a s a s i m p l e process for the c o n g r u e n t l y m e l t i n g L a l , b u t single phase samples of the i n c o n g r u e n t l y m e l t i n g C e l a n d P r l w e r e not o b t a i n e d , e v e n w i t h m e t a l reservoirs m a i n t a i n e d o n l y a short distance f r o m the interface. Samples of L a l a n d of n e i g h b o r i n g m i x t u r e s w e r e p r e p a r e d b y q u e n c h i n g s u i t able m i x t u r e s of the components f r o m the a l l l i q u i d r e g i o n f o l l o w e d b y a n n e a l i n g at ^ ~ 7 4 5 ° C . ( m . p . 7 5 0 ° C ) . S o l u t i o n of samples for analysis was p e r f o r m e d i n closed, e v a c u a t e d containers to a v o i d loss of u p to 1 w t . % i o d i n e as H I that occurs i n o p e n containers. 2

4

2

2

2

2

2 4 2

T h e r e s i s t i v i t y a p p a r a t u s s h o w n i n F i g u r e 1 w a s c o n s t r u c t e d of L a v i t e a n d stainless steel, w i t h tungsten probes a n d s i l v e r leads. T h e size of the s a m p l e rods a c c o m m o d a t e d was l a r g e l y d i c t a t e d b y t h e i r l o w s t r e n g t h d u r i n g p e e l i n g of the t a n t a l u m c o n t a i n e r a n d d u r i n g the m e a surements. T h e o r i g i n a l intent to m a k e measurements u p to near the m e l t i n g p o i n t w a s defeated b y the r e l a t i v e l y l a r g e t h e r m a l e x p a n s i o n of the d i i o d i d e s , w h i c h c a u s e d loss of c u r r e n t contact at l o w temperatures


58

LANTHANIDE/ACTINIDE

CHEMISTRY

or c o m p r e s s i v e f r a c t u r e too far a b o v e r o o m t e m p e r a t u r e . T h e entire a p p a r a t u s was b a k e d out u n d e r v a c u u m , l o a d e d i n the d r y box, a n d j a c k e t e d i n glass u n d e r A r . D i r e c t c u r r e n t m e t h o d s w e r e a b a n d o n e d w h e n the i n s u l a t i n g L a l w a s f o u n d to f o r m at the c u r r e n t l e a d s ; e v e n w i t h a sine w a v e source some r e c t i f i c a t i o n w a s o b s e r v e d u n t i l the c u r r e n t contact w a s m a d e t h r o u g h a s m a l l w a f e r of the same m e t a l as the i o d i d e .


3

Figure 1.

The resistivity sample holder

T h e p o t e n t i a l d r o p s w e r e m e a s u r e d across the s a m p l e r o d a n d a s t a n d a r d resistor i n series w i t h a sensitive V T V M ( v a c u u m t u b e v o l t m e t e r ) w h i l e the w a v e f o r m w a s m o n i t o r e d w i t h a n oscilloscope. T w o samples of c o m p o s i t i o n L a ^ . o o * o.oi w e r e m e a s u r e d f r o m 77° to 344° a n d 186° to 408°K., r e s p e c t i v e l y , w i t h o u t i r r e v e r s i b l e t e m p e r a t u r e effects. O n e s a m p l e of c o m p o s i t i o n C e I . o 7 w a s s t u d i e d f r o m 153° to 300°K., b u t satisfact o r y P r l samples c o u l d not b e o b t a i n e d . B e c a u s e of phase r e l a t i o n s h i p s a n d the r e l a t i v e l y h i g h r e s i s t i v i t y f o u n d , L a l w a s s t u d i e d as a p e l l e t f o r m e d w i t h a " K B r " press u s i n g a V T V M i n the d r y box. T h e results f r o m one s a m p l e to another w e r e s o m e w h a t e r r a t i c , p a r t l y because of extreme s u s c e p t i b i l i t y to o x i d a t i o n , b u t w e r e sufficient to c h a r a c t e r i z e t h e c o m p o u n d as s a l t - l i k e as o p p o s e d to m e t a l l i c . S u s c e p t i b i l i t i e s w e r e d e t e r m i n e d b y the G o u y m e t h o d , e x t r a p o l a t e d to infinite H ( t h o u g h the effect was s m a l l ) , a n d c o r r e c t e d for c o r e d i a m a g n e t i s m w i t h Selwood's values. M e a s u r e m e n t s o n L a l b e t w e e n 1.2 a n d 8 0 ° K . w e r e m a d e b y the m u t u a l i n d u c t a n c e m e t h o d . 2

2

2 4 2

2 4 2

Results and Discussion T h e D i i o d i d e s . T h e resistivities o b t a i n e d f o r t w o samples of

Lal

2

b e t w e e n 77° a n d 4 0 8 ° K . are s h o w n i n F i g u r e 2 ( r i g h t o r d i n a t e ) . V a l u e s


5.

Metallic

CORBETT E T A L .

for l a n t h a n u m m e t a l ( J , 32),

Lal

and

2

59

Cel

2

w i t h its h.c.p.-c.c.p.

t r a n s i t i o n near r o o m

t e m p e r a t u r e , are also s h o w n to illustrate the r e m a r k a b l e s i m i l a r i t y . opposite c u r v a t u r e f o u n d for L a l

The

2

p o s s i b l y arises because of its a b n o r

m a l l y l a r g e t h e r m a l expansion (see

E x p e r i m e n t a l ) , g i v i n g rise to a m o r e

r a p i d decrease i n o v e r l a p v a l u e of 64 ±

(band narrowing).

The room

temperature

2 /xohm.-cm. m a y also be c o m p a r e d w i t h 68 a n d 92 /xohm.-

c m . r e p o r t e d for the m e t a l l i c L a C

2

a n d L a S ( 2 5 ) , r e s p e c t i v e l y . It is

(33)

i n t e r e s t i n g that the result of a l i n e a r e x t r a p o l a t i o n of the d a t a s h o w n to the m e l t i n g p o i n t , ^ 3 5 0 ^ o h m . c m . at 8 3 0 ° , is w i t h i n a factor of three of Downloaded by UNIV OF SYDNEY on September 1, 2014 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch005

that f r o m a s i m i l a r l y l o n g e x t r a p o l a t i o n of the melt's c o n d u c t i v i t y ( as l o g Τ vs. N

, w h i c h is n e a r l y l i n e a r )

L a

/xohm.-cm.

to p u r e L a l

(13)

2

(liq.),

330-100

Since the increase i n r e s i s t i v i t y o n f u s i o n is p r o b a b l y s m a l l ,

this suggests that the l i q u i d retains the m e t a l - l i k e p r o p e r t y , as has a l r e a d y b e e n i n f e r r e d f r o m the c r y o s c o p i c b e h a v i o r of L a l

a

in L a l

(13).

2

T h e i n c o n g r u e n t m e l t i n g c h a r a c t e r i s t i c of the c e r i u m a n d

praseo

d y m i u m d i i o d i d e s p r e v e n t e d the p r e p a r a t i o n of p u r e phase samples i n the necessary size a n d shape. composition C e l

2

0

T h e resistivities o b t a i n e d for a s a m p l e of

7 , F i g u r e 2 (left o r d i n a t e ) , are m e a n i n g f u l i n that the

t e m p e r a t u r e d e p e n d e n c e is s i m i l a r to that of L a l .

Since x - r a y p o w d e r

2

d a t a suggest that the c o n t a m i n a n t phase C e l

2 4

is i s o m o r p h o u s w i t h L a l

2 4 2

a n d p r e s u m a b l y l i k e w i s e effectively a n i n s u l a t o r o n this scale, the

(6),

i m p u r i t y w o u l d serve m a i n l y to r e d u c e the effective cross sectional area w i t h o u t m a s k i n g the a p p a r e n t m e t a l l i c i t y of C e l .

L o w e r resistivities o n

2

p u r e r samples w e r e o b t a i n e d at r o o m t e m p e r a t u r e b y p r e l i m i n a r y d.c. m e t h o d s , 300 ±

100 /Aohm. for C e l

2

0 4

a n d ^ - 3 5 0 /xohm.-cm. for a P r l 7 2 0

c o m p o s i t i o n . X - r a y p o w d e r d a t a a g a i n i n d i c a t e t h a t the first t w o d i i o d i d e s are i s o m o r p h o u s , whereas P r l m a y b e s l i g h t l y different. 2

T h e absence of l o c a l i z e d states is c l e a r l y s u p p o r t e d b y the s m a l l , P a u l i - t y p e p a r a m a g n e t i s m of L a l , 0 ± 2

mole"

1

5 a n d (30 ±

at 299° a n d 78°K., r e s p e c t i v e l y .

10)

Χ 10"

6

e.m.u.

V a l u e s of this m a g n i t u d e

characteristic of metals w h e r e t h e y are ( i d e a l l y )

are

associated w i t h

P a u l i s p i n p a r a m a g n e t i s m of the c o n d u c t i o n electrons.

the

I n the present

case the results of c o r r e c t i o n for the d i a m a g n e t i c c o n t r i b u t i o n of i o d i d e ions i n L a l

2

[ ( 1 0 4 ± 5 ) a n d (134 ±

the

10) X 1 0 ° , r e s p e c t i v e l y ] are

a g a i n r e m a r k a b l y ( a n d p r o b a b l y f o r t u i t o u s l y ) close to those for the m e t a l ( 113 a n d 139 χ

10" ) 6

(22).

T h e r e is l i t t l e d o u b t that L a l

2

is c o r r e c t l y f o r m u l a t e d as L a

3 +

(l~) e~, 2

a n d that a s i m i l a r c o n s t i t u t i o n appears l i k e l y for C e l , a n d possible for 2

Prl . 2

Lal

2

does not y i e l d s o l v a t e d electrons i n l i q u i d N H

d i v a l e n t metals e u r o p i u m a n d y t t e r b i u m (39);

3

as d o

the

the r a p i d e v o l u t i o n

h y d r o g e n is p r o b a b l y a result of s u b s t a n t i a l a m m o n o l y s i s of the L a

3 +

of

ion.

A t present five m e t a l l i c d i i o d i d e s are k n o w n — t h e a b o v e three, G d l (26),

and T h l

2

(4).

2

N o other examples of m e t a l l i c phases are f o u n d i n


LANTHANIDE /ACTINIDE

60

CHEMISTRY

the other m e t a l - m e t a l h a l i d e systems of these elements w h i c h h a v e b e e n e x a m i n e d — s p e c i f i c a l l y , the c h l o r i d e s of a l l five a n d the b r o m i d e s of a l l b u t g a d o l i n i u m . T h e o n l y other h a l i d e e x a m p l e is the e n i g m a t i c A g F .


2

100

200

300

400

T° Κ Figure 2.

The resistivities of Lal ( Ο , Δ , right scale), La metal (dashed curve, right scale), and Cel sample left scale) 2

2

07

It is w o r t h w h i l e to consider the c o n d i t i o n s a n d c r i t e r i a w h i c h a p p e a r i m p o r t a n t i n a c c o m p l i s h i n g the necessary o v e r l a p a n d d e r e a l i z a t i o n a n d i n l i m i t i n g this b e h a v i o r s u b s t a n t i a l l y to the i o d i d e s c i t e d .

These

are

classified i n terms of the s t o i c h i o m e t r y , the e l e c t r o n i c state of c a t i o n , a n d the n a t u r e of the b a n d a n d the role of the anions. S T O I C H I O M E T R Y . A t present the o b s e r v e d l i m i t of t w o h a l i d e ions p e r m e t a l does not seem p a r t i c u l a r l y i m p o r t a n t as a necessity for close a p p r o a c h of the cations a n d h e n c e s u i t a b l e b a n d f o r m a t i o n ; r a t h e r , it m o r e p r o b a b l y results f r o m other characteristics of this f o r m a l o x i d a t i o n state for these elements. O n e possible fact to the c o n t r a r y is t h a t t h o r i u m ( I I I ) i o d i d e is e v i d e n t l y not m e t a l l i c (4), second criterion below.

t h o u g h it w o u l d p r o b a b l y m e e t the

T h e g e n e r a l electronic c o n d u c t i o n i n sulfide vs.

c h l o r i d e melts i n the m e t a l - r i c h r e g i o n ( as w e l l as i n the s o l i d state ) m a y b e a t t r i b u t e d to the l o w e r a n i o n to c a t i o n r a t i o a n d therefore closer a p p r o a c h of the cations ( 5 ) , a l t h o u g h c o v a l e n c y as discussed b e l o w m a y b e m o r e significant. E L E C T R O N I C S T A T E O F C A T I O N . A m o r e i m p o r t a n t f a c t o r for the l a n t h a n i d e s appears to be the e l e c t r o n i c c o n f i g u r a t i o n of the s i m p l e , r e d u c e d ion.

A s n o t e d before (19, 26),

isolated M

2

+

i t appears necessary a n d p l a u s i b l e that the

i o n s h o u l d h a v e , or be close to the c o n f i g u r a t i o n [ X e ]


4f5d

l

5.

CORBETT E T AL.

( [Rn]6d

Metallic

Lal

and

2

61

Cel.

for T h ) i n order for o v e r l a p of some sort (vide infra)

2

2 +

to l e a d

to a s u i t a b l e c o n d u c t i o n b a n d . T h e n o r m a l , s a l t - l i k e b e h a v i o r of N d l i . , 9 5

S m l , E u l , D y l , T m l , and Y b l 2

2

2

2

2

is e n t i r e l y reasonable since the g r o u n d

states a l l d e r i v e f r o m stable, w e l l - s h i e l d e d 4f

configurations. It appears

+1

m o r e t h a n c o i n c i d e n t a l that s u c h "cT states g e n e r a l l y p e r t a i n o n l y to d i p o s i t i v e rare e a r t h m e t a l ions of l a n t h a n u m , c e r i u m , g a d o l i n i u m , t e r bium, and lutetium. examined.)

(M-MI

3

systems for the last t w o h a v e not b e e n

T h i s fact was first g e n e r a l i z e d i n spectral studies of

the

d i p o s i t i v e ions i n fluorite hosts ( 2 3 ) , a l t h o u g h i t has b e e n r e c o g n i z e d for Downloaded by UNIV OF SYDNEY on September 1, 2014 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch005

m a n y of these i n s p e c t r o s c o p i c studies of the gaseous ions as w e l l . g r o u n d state c o n f i g u r a t i o n for P r ,

3

a p p a r e n t l y m e t a l l i c character of P r l . 2

in P r

2 +

The

[ X e ] 4 / , is not consistent w i t h the

2 +

A l t h o u g h the lowest 4 f 5 c i 3

1

state

is 1.6 e.v. h i g h e r i n the gas phase ( 3 5 ) , i t is o n l y 0.4 e.v. a b o v e

ground i n a simple cubic environment i n

fluorite

( 2 3 ) , so that greater

c r y s t a l field or b a n d i n g effects c o u l d r e a d i l y result i n a n effective

"d"

state. NATURE OF T H E B A N D A N D T H E ROLE OF T H E ANIONS.

The

r o l e of

the

anions a n d the t y p e of b a n d i n g are i m p o r t a n t i n a n y c o n s i d e r a t i o n of t h e absence of m e t a l - l i k e phases for these metals w i t h other h a l i d e anions. W h i l e i t is p r o b a b l y true that the d i i o d i d e s are e l e c t r o s t a t i c a l l y the most stable to d i s p r o p o r t i o n a t i o n a m o n g the d i h a l i d e s , as w i t h n o r m a l i o d i d e salts (38),

the n a t u r e of the b a n d i n g itself appears to b e m o r e significant

i n the present d i s c u s s i o n . A c o n s i d e r a b l e a m o u n t has b e e n w r i t t e n a b o u t this p r o p e r t y of the m e t a l l i c M S ( a n d M S ) phases of the rare e a r t h 3

metals (8,24),

4

g e n e r a l l y i n terms of a n i m p l i e d o r stated c a t i o n s u b l a t t i c e

b a n d i n v o l v i n g the 5d a n d p e r h a p s the 6s o r b i t a l s . F o r the c.c.p. m o n o sulfides this c a t i o n b a n d w o u l d result f r o m a sufficient o v e r l a p of t

1

2g

the

states, w h i l e the c o r r e s p o n d i n g s u l f u r o r b i t a l s r e m a i n s u b s t a n t i a l l y

nonbonding.

A c o m p a r a b l e b e h a v i o r i n the present d i i o d i d e s

(whatever

t h e i r s t r u c t u r e ) is difficult to a c c o u n t for w i t h this p i c t u r e because they are u n i q u e l y l i m i t e d to c o m p o u n d s w i t h the largest a n i o n , w h i c h p r e s u m a b l y w o u l d b e the least f a v o r a b l e for c a t i o n - c a t i o n o v e r l a p . I n c l u d i n g p i b o n d i n g w i t h i o d i d e is m o r e c r e d i b l e since it s h o u l d b e the

most

f a v o r a b l e here w i t h r e g a r d to b o t h energy a n d o v e r l a p c r i t e r i a . D e l o c a l i z a t i o n i n this case w o u l d t h e n result f r o m the b a n d i n g of the π* o r b i t a l s i n a p e r i o d i c lattice. T h i s w o u l d result f r o m (t * )* states i n the f a m i l i a r 2g

o c t a h e d r a l e n v i r o n m e n t , b u t w i t h o n l y one accommodated,

a lower

e l e c t r o n p e r m e t a l to

be

d e g e n e r a c y w o u l d present no p r o b l e m .

Co-

v a l e n c y is c r i t i c a l for a d e q u a t e d e r e a l i z a t i o n i n s u c h a b a n d (17),

and

this is most f a v o r a b l e w i t h i o d i d e anions. O f course the i n c r e a s e d s h i e l d i n g of d orbitals so o b t a i n e d , p a r t i c u l a r l y t h r o u g h s i g m a b o n d i n g , w i l l enhance o v e r l a p i n either m o d e l [ c o m p a r e the effect of o x i d e vs. f l u o r i d e


62

LANTHANIDE/ACTINIDE

CHEMISTRY

w i t h the 3d elements (28)]. Some i d e a of possible b o n d i n g i n the other m e t a l l i c d i i o d i d e s c a n b e o b t a i n e d f r o m the s t r u c t u r e r e c e n t l y d e t e r m i n e d for T h l , w h e r e a l a y e r s t r u c t u r e s i m i l a r to that f o u n d for 8 - T a S i n d i c a t e s 2

2

d e r e a l i z a t i o n o n l y w i t h i n the sheets T h e rare e a r t h elements

(18).

under discussion appear

to b e

i n possessing sufficient r a d i a l extension i n the 5d o r b i t a l s for o v e r l a p w i t h the i o d i d e s .

unique adequate

[ T h e i n v e r s e l y r e l a t e d s m a l l v a l u e of the t h i r d

i o n i z a t i o n energy is p e r h a p s m o r e i m p o r t a n t w i t h r e g a r d to the alternate f o r m a t i o n of l o c a l i z e d states o n r e d u c e d cations ( 2 6 ) ] .

O r b i t a l contrac-


t i o n i n the h e a v i e r l a n t h a n i d e s w o u l d be e x p e c t e d to r e d u c e the l i k e l i h o o d of d e l o c a l i z e d states so t h a t l u t e t i u m ( I I ) m a y not f o r m a m e t a l l i c i o d i d e . T h e extensive d i s p r o p o r t i o n a t i o n e x p e c t e d for this state ( 7 ) m a y p r e c l u d e the f o r m a t i o n of a n y n e w phase at a l l . A l o c a l i z e d m e t a l - m e t a l b o n d i n g seems e v i d e n t i n the u n u s u a l G d C l i .

6

(26)

w h i l e the 5d

l

states of ele-

ments i m m e d i a t e l y f o l l o w i n g the l a n t h a n i d e s , h a v i n g b o t h i n c r e a s e d coo r d i n a t i o n n u m b e r a n d m o r e t i g h t l y b o u n d v a l e n c e electrons, g e n e r a l l y e x h i b i t l o c a l i z e d m e t a l - m e t a l interactions.

F o r example, h a f n i u m (III)

i o d i d e is a n i n s u l a t o r a n d e x h i b i t s o n l y a s m a l l t e m p e r a t u r e - i n d e p e n d e n t p a r a m a g n e t i s m (34),

whereas the b o n d i n g is l o c a l i z e d i n T a l

f o r m a t i o n of discrete d i m e r s ( 9 ) .

4

w i t h the

T h e r e is no h a f n i u m d i i o d i d e r e p r e -

s e n t i n g a constant s t o i c h i o m e t r y , w h i l e the m o r e n u m e r o u s a n d t i g h t l y b o u n d electrons i n the closest t h i n g to a t a n t a l u m d i i o d i d e , T a l find

2 3 3

(2),

d e l o c a l i z e d m e t a l - m e t a l - h a l o g e n b o n d i n g i n discrete clusters m u c h

m o r e profitable.

M u c h m o r e needs to be l e a r n e d a b o u t transitions of

this t y p e . T h e monosulfides of the r a r e e a r t h elements b e h a v e differently f r o m that discussed here since these are m e t a l - l i k e for a l l b u t those elements f o r m i n g the most stable d i v a l e n t states. H e r e a g e n e r a l p r o c l i v i t y t o w a r d s f o r m i n g t r i p o s i t i v e ions seems m o r e i m p o r t a n t (as i n the metals t h e m s e l v e s ) — a p r o p e r t y u s u a l l y c o n s i d e r e d to result f r o m a fortuitous b a l ance b e t w e e n i o n i z a t i o n a n d lattice or s o l v a t i o n energies.

T h e sulfides

h a v e also b e e n i n t e r p r e t e d i n terms of a degeneracy of the u p p e r 4f levels w i t h a 5d b a n d ( w h e r e a p p l i c a b l e )

(10).

I n contrast to the h a l i d e s ,

there is l i t t l e d i f f e r e n t i a t i o n of the e l e c t r i c a l properties a m o n g the m o n o sulfides, monoselenides, a n d m o n o t e l l u r i d e s The Intermediate Phase L a l

2 4 2

.

(29).

T h e c o m p o s i t i o n of this phase w a s

f u r t h e r defined w i t h p o w d e r p a t t e r n d a t a for n i n e samples ( 2.36
ff

o n t e m p e r a t u r e is

s h o w n i n F i g u r e 3, together w i t h t h e o r e t i c a l curves ( 1 5 ) for t w o extremes of s p i n - o r b i t c o u p l i n g constant, c o v a l e n c y k, a n d t e t r a g o n a l a s y m m e t r y parameter ν ( =

Δ / λ ) t h a t fit the G o u y d a t a as w e l l as possible.

Inter

m e d i a t e choices of constants λ, k, a n d v, (650, 0.8, 0.6, for e x a m p l e ) give a p p r o p r i a t e l y i n t e r m e d i a t e curves. e s t i m a t e d b y j 0 r g e n s e n for L a

2 +

T h e λ v a l u e compares to 640 c m .

(20);

- 1

i n a n y case the v a l u e is not v e r y

c r i t i c a l i n this r a n g e , a n d a d d i t i o n a l effects d e s c r i b e d e m p i r i c a l l y at this p o i n t b y k a n d ν are q u i t e s m a l l .

T h e agreement w i t h t h e o r y at l o w e r

temperatures is p o o r ; a s s u m i n g the presence of a t e m p e r a t u r e - i n d e p e n d ent c o m p o n e n t i n χ

ρ

does not h e l p , a l t h o u g h m o r e n e g a t i v e values for

Pascal's constants w o u l d . T h i s degree of agreement b e t w e e n t h e o r y a n d e x p e r i m e n t c a n n o t b e o b t a i n e d a n y w h e r e else w i t h l o w e r symmetries, l a r g e r υ values, or for other configurations ( d , f , etc. ). 2

1

M e a n i n g f u l E S R or s p e c t r a l d a t a h a v e not b e e n o b t a i n e d .

Only a

b a n d at 29800 c m . " , w i t h a s h o u l d e r at 27800 c m . " , c a n be r e s o l v e d i n 1

1

the reflectance s p e c t r u m of the b l a c k c o m p o u n d i n K I ; the energy a n d i n t e n s i t y b o t h suggest these arise f r o m charge transfer processes. T h e i n d i c a t e d o c t a h e d r a l c o o r d i n a t i o n at first m a y seem u n u s u a l w h e n c o m p a r e d w i t h the n i n e - f o l d c o o r d i n a t i o n f o u n d i n the b a r i u m h a l i d e s , N d X , etc. a n d the e i g h t - f o l d c o o r d i n a t i o n of the s m a l l e r L a 2

3 +

i o n i n its t r i h a l i d e s . H o w e v e r , the g e o m e t r y i n the latter m a y d e p e n d o n a t t a i n i n g a m a x i m u m d i s p e r s i o n energy, whereas i n the present case the d

1

state m a y b e a b l e to r e a l i z e a g o o d d e a l m o r e f r o m a c r y s t a l field effects i n a n e n v i r o n m e n t of h i g h e r s y m m e t r y . T h e t r i i o d i d e is e v i d e n t l y r e l a t i v e l y loosely b o u n d c o m p a r e d w i t h the l o w e r i o d i d e s . 5 to 5.3 g r a m c m . "

3

for L a l

2

4 2

and L a l

2

D e n s i t y estimates of

f r o m measurements b o t h

samples as p r e p a r e d a n d o n pressed pellets i n d i c a t e m o l a r v o l u m e s

on of

these t w o phases are less t h a n 5 0 % of the a p p r o p r i a t e average of those of the c o m p o n e n t s L a a n d L a l . 3


5.

C O R B E T T

E T

A L .

Metallic

Lal

2

and

Cel

2

65

Acknowledgments

T h e use of the G o u y b a l a n c e was m a d e p o s s i b l e b y P . E . R o u g h a n ,


F . J. Jelinek and B. C . Gerstein.

Literature Cited (1) Alstad, J. K., Colvin, R. V., Legvold, S., Spedding, F. H., Phys. Rev. 121, 1637 (1961). (2) Bauer, D., Schnering, H. G., Schafer, H., J. Less-Common Metals 6, 388 (1965). (3) Bredig, Μ. Α., in "Molten Salt Chemistry," M. Blander, ed., p. 408, Wiley, New York, 1964. (4) Clark, R. J., Corbett, J. D., Inorg. Chem. 2, 460 (1963). (5) Corbett, J. D., in "Fused Salts," B. R. Sundheim, Ed., Chap. 6, McGrawHill, New York, 1964. (6) Corbett, J. D., Druding, L. F., Burkhard,W.,J., Lindahl, C. B., Discus sions Faraday Soc. 32, 79 (1961). (7) Corbett, J. D., Pollard, D. L., Mee, J. E., Inorg. Chem. 5, 761 (1966). (8) Cutler, M., Fitzpatrick, R. L., Leavy, T. F., J. Phys. Chem. Solids 24, 319 (1963). (9) Dahl, L. E., Wampler, D. L., J. Am. Chem. Soc. 81, 315 (1959). (10) Didchenko, R., Gortsema, F. P.,J.Phys. Chem. Solids 24, 863 (1963). (11) Druding, L. F., Corbett, J. D., J. Am. Chem. Soc. 83, 2462 (1961). (12) Druding, L. F., Corbett, J. D., Ramsey, Β. N., Inorg. Chem. 2, 869 (1963). (13) Dworkin, A. S., Sallach, R. Α., Bronstein, H. R., Bredig, M. A., Corbett, J. D.,J.Phys. Chem. 67, 1145 (1963). (14) Figgis, Β. N., "Introduction to Ligand Fields," Chap. 10. Interscience, New York, 1966. (15) Figgis, Β. N., Trans. Faraday Soc. 57, 198 (1961). (16) Flahaut, J., Guittard, M., Patrie, M., Bull. Soc.Chim.France 1959, 1917. (17) Goodenough, J. B.,J.Appl.Phys. 37, 1415 (1966). (18) Jacobson, R. Α., Guggenberger, L. (to be published). (19) Jørgensen, C. K., Mol. Phys. 7, 420 (1964). (20) Jørgensen, C. K., "Orbitals in Atoms and Molecules," p. 137, Academic Press, New York, 1962. (21) Keneshea, F. J. Jr., Cubicciotti, D. D.,J.Chem. Eng. Data 6, 507 (1961). (22) Lock, J. M., Phil. Mag. 2, 726 (1957). (23) McClure, D. S., Kiss, Z., J. Chem. Phys. 39, 3251 (1963). (24) McClure, J.W.,J.Phys. Chem. Solids 24, 871 (1963). (25) Marchenko, V. L., Samsonov, G. V., Russ. J. Inorg. Chem. 8, 1061 (1963). (26) Mee, J. E., Corbett, J. D., Inorg. Chem. 4, 88 (1965). (27) Mellors, G.W.,Senderoff, S., J. Phys. Chem. 63, 1110 (1959). (28) Morin, F. J., J.Appl.Phys. (Suppl.) 32, 2195 (1961). (29) Reid, F. J., Matson, L. K., Miller, J. F., Himes, R. C., J. Phys. Chem. Solids 25, 969 (1964). (30) Sallach, R. Α., Corbett, J. D., Inorg. Chem. 2, 457 (1963). (31) Sallach, R. Α., Corbett, J. D., Ibid. 3, 933 (1964). (32) Spedding, F. H., Daane, A. H., Herrmann, K. W., J. Metals 9, 895 (1957). (33) Spedding, F. H., Gschneidner, K., Daane, A. H., Trans. Met. Soc. AIME 215, 192 (1959). (34) Strass, A.W.,Corbett, J. D. (to be published). In Lanthanide/Actinide Chemistry; Fields, P., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

66

LANTHANIDE/ACTINIDE CHEMISTRY

Sugar, J.,J.Opt. Soc. Am. 53, 831 (1963). Terrey, H., Diamond, H.,J.Chem. Soc. 1928, 2820. Trzebiatowski, W., Różyczka, J., Poczniki Chem. 32, 183 (1958). Van Arkel, Α., Research 2, 307 (1949). Warf, J.C.,Korst, W. L.,J.Phys. Chem. 60, 1590 (1956). RECEIVED October 17, 1966. Work performed in the Ames Laboratory of the U. S. Atomic Energy Commission. Contribution No. 1980.


(35) (36) (37) (38) (39)


Actinide Chemistry

Recommend Documents