LIGAND FIELD CALCULATION FOR THE COMPLEX Fe(H2O)2+6 IN FROZEN AQUEOUS SOLUTION OF Fe(ClO4)2

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LIGAND FIELD CALCULATION FOR THE COMPLEX Fe(H2O)2+6 IN FROZEN AQUEOUS

SOLUTION OF Fe(ClO4)2

D. Nagy, J. Balogh, I. Dézsi, G. Ritter, H. Spiering, H. Vogel

To cite this version:

D. Nagy, J. Balogh, I. Dézsi, G. Ritter, H. Spiering, et al.. LIGAND FIELD CALCULATION FOR

THE COMPLEX Fe(H2O)2+6 IN FROZEN AQUEOUS SOLUTION OF Fe(ClO4)2. Journal de

Physique Colloques, 1980, 41 (C1), pp.C1-283-C1-284. �10.1051/jphyscol:19801100�. �jpa-00219581�

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JOURNAL DE PHYSIQUE Colloque C1, supplkment au n ^O1 , Tome 41, janvier 1980, page C1-283

LlCiAND FIELD CALCULATION FOR THE COMPLEX F ~ ( H ~ O ) ? I N FROZEN AQUEOUS SOLUTION OF ~ e ( c 1 0 ~ ) ~

D.L. Nagy, J. Balogh, I. DLzsi, G. ~ i t t e r ~ , H . Spiering and

+

H. vogelX

Central Research I n s t i t u t e for Physics, H-1525 Budapest, Hungary.

+

I n s t i k t fur Anorganische uvd AnaZytische Cheniie, Johannes Gutenberg-Universitiit, D-5600 Mainz, FRG.

x Physikalisches I n s t i t u t dzr Universitiit ~ r i a n ~ e n - ~ i i r n b e r , 0-8520 ErZangen, FRG.

I n t r o d u c t i o n . - Frozen aqueous s o l u t i o n s /FAS/ of f e r r o u s s a l t s have been s t u d i e d by Mossbauer spectroscopy and o t h e r meth- ods 11-61. I n t h e s e systems t h e Fe2+ i o n forms an Fe(H20)it complex. I n s p i t e of t h e g l a s s y environment / 6 / of t h e Fe2+ i o n s t h e quadrupole s p l i t l i n e s a r e r e l a t i v e l y narrow: r-0.4-0.5 m m / s / 5 / . These f a c t s

suggest t h a t t h e d i s t o r t i o n of t h e ( ~ ~ 0 ) ~ o c t a h e d r a i s mainly determined by t h e

Fe ( ~ ~ 0 )

i*

complex i t s e l f . We attempted t o determine t h e symmetry of t h i s d i s t o r t i o n by Mtissbauer measurements i n an a p p l i e d magnetic f i e l d .

Experimental.- The measurements were p e r - formed on r a p i d l y quenched 0.2 mol % FAS of 5 7 ~ e ( ~ l ~ 4 ) 2 w i t h 1 7 v o l . % g l y c e r o l . The Mbssbauer s p e c t r a were measured i n v a r i o u s

l o n g i t u d i n a l and t r a n s v e r s e magnetic f i e l d s up t o 50 kG a t 4.2 K. Some of t h e recorded

t h e s p l i t t i n g of t h e 5~ l e v e l s 6 , t h e 2 g

s p i n - o r b i t - c o u p l i n g A , t h e covalency a 2 and t h e h y p e r f i n e c o n s t a n t s HL and Hc / 7 , 8 / determine t h e s p e c t r a i n e x t e r n a l magnetic f i e l d s .

The e v a l u a t i o n of t h e l i g a n d f i e l d p a r a - meters of t h e F ~ ( H ~ O ) ; + complex i n v a r i o u s t r a n s i t i o n metal c r y s t a l l i n e h y d r a t e s from high f i e l d Mossbauer d a t a / 8 / has shown t h a t A , a 2

,

^HL and Hc a r e c h a r a c t e r i s t i c o f t h e hexaquo complex i t s e l f (A=-95 cm -1

,

a 2 =O. 9 2 , H =-5 30 kG and Hc=-2 7 5 k ~ )

,

t h e L

s p l i t t i n g 6 being s e n s i t i v e t o t h e environment of t h e complex. I n view of t h i s w e t r i e d t o d e s c r i b e t h e observed s p e c t r a supposing a t r i g o n a l d i s t o r t i o n of t h e water o c t a h e d r a w i t h an a p p r o p r i a t e d i s -

t r i b u t i o n o f 6 . To d e s c r i b e t h e asymmetric shape o f t h e outermost l i n e s we used t h e l o g a r i t h m i c Gaussian d i s t r i b u t i o n

2 2

s p e c t r a a r e shown i n F i g . l b . They resemble w(6) =

---

¹ e - ( [ l n ( 6 / 6 0 ) ] 1 2 ~ ~ 1

& c s

fi

t h e corresponding s p e c t r a of F e ( ~ ~ 0 ) ~

The s p e c t r a were c a l c u l a t e d using a pro- ( ~ 1 0 ~ ) ~ / 7 / and of o t h e r s i m i l a r c r y s t a l -

gram accounting f o r a d i s t r i b u t i o n of t h e l i n e h y d r a t e s / 8 / b u t t h e resonance l i n e s

l i g a n d f i e l d parameters and f o r p o l a r i z a - a r e much broader. This s u g g e s t s t h a t t h e

t i o n e f f e c t s / 7 , 8 , 9 / . The dependence of b a s i c p o i n t symmetry of t h e ~ e i o n ~ i s +

t h e quadrupole s p l i t t i n g AE on t h e t r i g - t r i g o n a l , i n f l u e n c e d c o n s i d e r a b l y by t h e

Q

o n a l s p l i t t i n g was taken i n t o account ac- amorphous environment.

5 c o r d i n g t o t h e method of I n g a l l s / l o / . Discussion.- I n T2g approximation f o r

The quadrupole s p l i t t i n g has been normaliz- t r i g o n a l symmetry, f i v e parameters, v i z .

ed s o t h a t GE (<6>)=3.32 m m / s which i s t h e

Q

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801100

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C1-284 JOURNAL DE PHYSIQUE

F i g . 1 : Measured / b / a n d c a l c u - l a t e d / a a n d c / ~ o k s b a u e r s p e c t r a of r a p i d l y quenched 0.2 mol % FAS o f 5 7 ~ e ( ~ 1 0 4 ) 2 w i t h 1 7 v o l . % g l y c e r o l i n some l o n g i t u d i n a l a n d t r a n s v e r s e m a g n e t i c f i e l d s a t 4.2 K .

o b s e r v e d q u a d r u p o l e s p l i t t i n g a t 4.2 K . F i g u r e l a shows some s p e c t r a c a l c u l a t e d w i t h h=-95 crn'l, 6 ~ 7 5 0 cm -I

,

0 6 = 0 . 4 . T h e s e l a s t two v a l u e s c o r r e s p o n d t o <6>=812 cm-1 a n d a FWHM o f w ( 6 ) = 6 0 0 c m - l . I n s p i t e o f t h e c o n s i d e r a b l e d i s c r e p a n c i e s , t h e main c h a r a c t e r i s t i c s / s t r u c t u r e , l i n e p o s i t i o n s ,

i n t e n s i t i e s and a p p r o x i m a t e w i d t h s / o f t h e measured s p e c t r a a r e w e l l r e f l e c t e d by t h e

c a l c u l a t i o n . Very s i m i l a r s p e c t r a c a n b e o b t a i n e d by s i m u l t a n e o u s l y c h a n g i n g

X

a n d

6 0 . F i g u r e l c shows t h i s f o r A=-70 crn-l.

s0=550 c m - l and 06=0.4 (<6>=596 cm-l).

Such a r e d u c t i o n o f h can h a r d l y be e x c l u d - e d a s a c o n s e q u e n c e o f t h e dynamic J a h n - - T e l l e r e f f e c t /11/ which i s p r o b a b l y more s e n s i t i v e t o t h e e n v i r o n m e n t t h a n t h e co- v a l e n c y a n d t h e h y p e r f i n e p a r a m e t e r s .

2

+

The b a s i c t r i g o n a l s y w e t r y o f t h e F e ( ~ ~ 0 ) ~ i o n i n FAS i s a consequence o f t h e J a h n -

- T e l l e r e f f e c t which p r e d i c t s a T~ mode d i s t o r t i o n a s e n e r g e t i c a l l y most p r e f e r r e d f o r t h i s complex 1121. The o r b i t a l g r o u n d s t a t e o f t h e F e 2 + i o n i s a s i n g l e t h e n c e V Z Z < O . The g l a s s y e n v i r o n m e n t o f t h e com-

p l e x r e s u l t s i n a d i s t r i b u t i o n o f t h e t r i g - o n a l s p l i t t i n g o f a b o u t

2

³⁰⁰cm-' w i d t h

a n d a l s o i n a s t a t i s t i c a l d e v i a t i o n o f t h e symmetry from t h e t r i g o n a l o n e

-

t h e c o r - r e s p o n d i n g e n e r g y s p l i t t i n g s b e i n g p r o b a b - l y s e v e r a l h u n d r e d s o f c m -1

.

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