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129I MÖSSBAUER STUDY OF CHARGE TRANSFER COMPLEXES OF IODINE IN THE FROZEN
SOLUTION
H. Sakai, Y. Maeda, S. Ichiba, H. Negita
To cite this version:
H. Sakai, Y. Maeda, S. Ichiba, H. Negita. 129I MÖSSBAUER STUDY OF CHARGE TRANSFER
COMPLEXES OF IODINE IN THE FROZEN SOLUTION. Journal de Physique Colloques, 1979, 40
(C2), pp.C2-395-C2-397. �10.1051/jphyscol:19792137�. �jpa-00218509�
JOURNAL DE PHYSIQUE
Colloque
C2,suppl6ment au n
O 3,Tome
40,mars 1979, page
C2-395129
I M ~ S S B A U E X
STUDY OF CHARGE TRANSFER COMPLEXES OF IODINE I N THE FROZEN SOLUTIONH. Sakai, Y. Maeda, S. lchibaf and H. Negita f
Research Reactor Institute, Kyoto University, Kwnatori-cho, Sennan-gun, Osaka, 590-04, Japan
I Department of Chemistry, Faculty of Science, Hiroshima University, Hiroshima, 730, Japan
R6sumQ.- On a QtudiQ par effet ~ h s b a u e r de
' , ' I
les effets de transfert de charge de la triethy- lamine et de la pyridine dans la station gelde g 16O K de disulfure de carbone. Les spectres %ss- bauer mettent en Qvidence les deux espsces chimiques de l'iode, correspondant au pontage et aux atomes des extrQmit6s de chaine. Le taux de transfert de charge a Qtb trouvd 6galB
0,14e- pour la triethylamine et 2 0,12e- pour la pyridine.Abstract.- The MGssbauer effect of ','I was used to investigate the charge transfer complexes of triethylamine-iodine and pyridine-iodine in the carbon disulfide frozen solution at 16 K. The MESS- bauer spectra of these complexes show the two chemical species of iodine, which correspond to the bridging and terminal iodines. From the Mzssbauer parameters the degrees of the charge transfer were found to be 0.1% for the triethylamine-iodine complex and 0.06e- for pyridine-iodine.
Introduction.- Triethylamine-iodine (TEA-I,) and pyridine-iodine (Py-I,) charge transfer complexes have been extensively investigated by various spec-
troscopic methods. In the n-otype complexes like TEA-I, and Py-I, the charge transfer bond is formed with an electron transfer of the unshared pair of
the nitrogen atom in the donor molecule (D) to a vacant orbital or an anti-bonding orbital of the ac-
ceptor (A). Ground state properties of these comple- xes such as the increase of the dipole moment and decrease of the 1-1 bond stretching frequency
are almost attributed to the degree of the charge transfer. The infrared spectra, the nuclear quadru- pole resonance and the dipole moment etc. have been applied to estimate the degree of the charge trans- fer in various charge transfer complexes / I /.
The Mijssbauer spectroscopy of ','I is also very useful for this investigation, although the expe- riments are not so easy because of containing the radioisotope ','I in the samples. In previous
the MEssbauer effect studies were concerned with the crystalline charge transfer complexes of iodine and iodine monohalides / 2 / 1 3 1 . Recently, Bukshpan et
aZ. /4/
have studied several charge transfer com---
plexes of iodine and iodine monohalides in the do- nor solvents. In this study, the ','I Mzssbauer ef- fect of the charge transfer complexes of TEA-I, (I: 1) and Py-I, (I: 1) in the carbon disulfide fro- zen solution were measured and the results were com- pared with the other data.
Experimental.
-
Xolecular iodine of ','I was prepa- red by oxidizingN~','I
in Na,SO, solution with10%-X,O, and 2N-H2S0, and extracting with CS,. The sample absorbers were prepared by adding a stoichio- metric amount of the donor molecule to the iodine solution of carbon disulfide. These were rapidly coo- led in an absorber holder of Teflon by liquid nitro- gen and mounted on the cryostat. The absorber thick- nesses were about 10mg '29~/cm2. The source was pre- pared by irradiating 120 mg 6 6 ~ n 1 2 8 ~ e at a flux of 2x10'~ neutrons/cm2 s in Kyoto University Reactor for 1 hour. The source and absorber were cooled at 16 K by using a commercial refrigerator "Cryodyne 1020". The apparatus for the Y6ssbauer measurement was described elsewhere 151.
Results and discussion.- The Yzssbauer spectrum of the TEA-I, complex is shown in figure 1.
1
I I I I I I I-15 -10 - 5 0 5 10 15
VELOCITY (mmls
Fig. I : %ssbauer spectrum of the triethylamine- iodine charge transfer complex at 16 K.
The spectrum is resolved into two quadrupole split patterns (designated as IA and IB). Similarly the spectrum of the Py-I, complex also consists of two sets of the quadrupole splitting. The solid lines in
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792137
C2-396
JOURNAL DE PHYSIQUEt h e f i g u r e show t h e b e s t f i t t e d L o r e n t z i a n c u r v e s and t h e v e r t i c a l l i n e s r e p r e s e n t t h e peak p o s i t i o n s . The experimental r e s u l t s a r e p r e s e n t e d i n t a b l e I t o g e t h e r w i t h t h e r e s u l t s f o r molecular i o d i n e i n carbon d i s u l f i d e .
It i s of i n t e r e s t t h a t two k i n d s of i o d i n e c o n f i g u r a t i o n s e x i s t i n t h e s e complexes i n t h e i n e r t s o l v e n t . This f a c t may s u g g e s t t h a t i n t h e c a s e of t h e n-cJ type complex t h e i o d i n e molecule l i e s along t h e symmetry a x i s of t h e donor molecule, r e s u l t i n g i n a l i n e a r N . e . 1 - I arrangement i n i n e r t s o l v e n t a s w e l l a s i n t h e c r y s t a l l i n e charge t r a n s f e r complexes.
It may be reasonable t o a s s i g n IA a s t h e b r i d g i n g i o d i n e atom and IB a s t h e t e r m i n a l i o d i n e atom i n t h e same manner a s our p r e v i o u s paper / ? / . I n o r - d e r t o determine t h e degree of t h e charge t r a n s f e r , t h e charge d e n s i t y of each i o d i n e atom i n t h e s e corn p l e x e s was c a l c u l a t e d from t h e v a l u e of t h e quadru- p o l e coupling c o n s t a n t (e2qq ) according t o t h e
obs.
Townes and Dailey t h e o r y 161. The r a t i o e2qqObs./
/e2qqat. i s expressed approximately with t h e n a t u r e of t h e chemical bond a s
e2qqobs /e2qqat.
"
1-
s 2 fi - n,
(1) where s2 i s t h e degree of t h e s - h y b r i d i z a t i o n of t h e o-bond,i
i s t h e i o n i c c h a r a c t e r , and a i s t h e dou- b l e bond and/or t h e i n t e r m o l e c u l a r bond c h a r a c t e r s , r e s p e c t i v e l y . which i s t h e atomic quadrug?l e coupling c o n s t a n t , e q u a l s t o -2293 MHz f o r iodine -127. By assuming t h a t s2 and IT a r e n e g l i g i b l e w i t h r e s p e c t t o t h e q u a n t i t y i, t h e charge d e n s i t i e s lo- c a l i z e d on t h e i o d i n e atoms a r e c a l c u l a t e d i n t h e s e complexes a s f o l l o w s :
E S N
....
I IB. . .
I. . .
IB+0.30 +0.14 -0.44 +0.23 +0.15 -0.38
On t h e o t h e r hand, t h e isomer s h i f t i s c o r r e l a t e d w i t h t h e charge d e n s i t y of t h e i o d i n e atom.
Bukshpan et aZ. / 7 / o b t a i n e d e x p e r i m e n t a l l y t h e re- l a t i o n s h i p between t h e isomer s h i f t (6) and t h e s- and p - e l e c t r o n p o p u l a t i o n s ,
6(mm/s) = -9.2 hs + 1.5 h
-
0.54 (ZnTe),P (2)
where h and h a r e t h e numbers of t h e s- and
p-
P
e l e c t r o n h o l e s , r e s p e c t i v e l y . I n t h e s e complexes the charge d e n s i t i e s of t h e t e r m i n a l i o d i n e atoms ( I )
B were found t o be-O.37e- f o r TEA-12and -0.38e- f o r Py-I, from t h e v a l u e s of t h e isomer s h i f t s and t h e e q u a t i o n (2) by assuming no s - h y b r i d i z a t i o n i n t h e 1-1 bond. These v a l u e s o b t a i n e d a r e i n good agree- ment w i t h those from t h e quadrupole coupling cons- t a n t s . This f a c t means t h a t t h e 1-1 bonds i n t h e s e complexes c o n s i s t of a pure o-bond of t h e p-electrons
The l i n e a r r e l a t i o n of t h e e q u a t i o n ( 2 ) , how- e v e r , f a i l s under t h e c o n d i t i o n h > 1.3, i . e . ,
P
6 > 1.4 181. The isomer s h i f t s observed f o r t h e
b r i d g i n g i o d i n e atoms ( I A ) a r e both c o n s i d e r a b l y l a r g e r t h a n t h o s e expected from t h e quadrupole cou- p l i n g c o n s t a n t s i f t h e charge t r a n s f e r bonds were mainly due t o p u r e o-bond of t h e 5p v a l e n c e e l e c - t r o n s . This may suggest t h a t t h e o t h e r i n n e r s h e l l e l e c t r o n s such a s 4d-electrons c o n t r i b u t e p a r t i a l l y t o t h e charge t r a n s f e r bond between t h e n i t r o g e n atom i n t h e donor molecule and t h e b r i d g i n g i o d i n e atom. That i s , t h e charge t r a n s f e r bond i n t h e s e n-o t y p e complexes may b e formed by such a double bond Shat t h e l o n e p a i r e l e c t r o n s of t h e n i t r o g e n
atom i n t h e donor form a 0 c o o r d i n a t e bond t o t h e 5p o r b i t a l of t h e b r i d g i n g i o d i n e atom and t h e io- d i n e i n t u r n d o n a t e s a p a r t of 4d-electrons t o t h e n i t r o g e n atom o r t h e donor molecule through a a- bond.
The 4d-electron d e f e c t of i o d i n e i n c r e a s e s d r a s t i c a l l y t h e isomer s h i f t because of t h e l a r g e s h i e l d i n g c o e f f i c i e n t 0.85 i n s t e a d of 0.35 f o r t h e 5 p - e l e c t r o n d e f e c t .
Table I
Msssbauer parameters of l Z 9 1 f o r charge t r a n s f e r complexes.
I
Complex ~ ' Q ~ ( M H z )*
6 (mmls)*'
r7 RemarkI
IZ i n GS, -2242 f 20 0.93 f 0.05 1 1 2 6 t h i s work
Triet-hylamine-I, (A) -2604 f 20 1.56 f 0.05 < 6
(B) -1261
*
20 0.40 f 0.05 9 -+ 6P y r i d i n e - I , (A) -2631
+
20 1.82 f 0.05 10+
6( -2600 f 30 ) ( 1.40
+
0 . 0 7 )--
r e f . /4/(B) -1439
+
20 0.39+
0.05 < 6 t h i s work( -1300 f 15 ) ( 0 . 2 8
+
0.05 )--
r e f . / 4 /i The quadrupole coupling c o n s t a n t (e2qq) is converted t o 1 - 1 27.
**
The isomer s h i f t (6) i s r e l a t i v e t o ZnTe source.On t h e o t h e r hand, t h e v a l u e of t h e q u a d r u p o l e cou- p l i n g c o n s t a n t i s l i t t l e a f f e c t e d b y t h i s 4d-elec- t r o n d e f e c t . Assuming t h a t t h e numbers of t h e Sp- e l e c t r o n h o l e s a r e e q u a l t o 1.14 f o r TEA-I2 and 1.15 f o r Py-I, which a r e c a l c u l a t e d from t h e r a t i o s of t h e e2qqobs. /e2qqat.. t h a t i s , t h e S p - e l e c t r o n o n l y depends o n t h e
a
c o o r d i n a t e bond, one c a n e s t i m a t e f r o m t h e o b s e r v e d l a r g e isomer s h i f t s f o r t h e b r i d - g i n g i o d i n e atoms t h a t t h e amount of t h e 41-electron d e f e c t a r e 0.11 f o r TEA-I2 and 0.17 f o r Py-I2 a c c o r - d i n g t o t h e f o l l o w i n g e x p r e s s i o n ,G ( m / s ) = 1.5 h + 3.64 hd
-
0.54 (ZnTe)P ( 3 )
The c o e f f i c i e n t of t h e 4 d - e l e c t r o n d e f e c t i s o b t a i - ned from S l a t e r ' s r u l e f o r t h e s h i e l d i n g c o e f f i c i e n t
191. T h e r e f o r e , t h e c h a r g e d e n s i t i e s of t h e a c c e p t o r atoms and t h e donor m o l e c u l e s i n t h e TEA-I2 and Py-I, complexes a r e e s t i m a t e d a g a i n by c o n s i d e r i n g t h e back d o n a t i o n from t h e v a l u e s of t h e q u a d r u p o l e c o u p l i n g c o n s t a n t s and t h e isomer s h i f t s a s f o l l o w s :
I l e f e r e n c a s
F o r example, Y u l l i k e n , R. S. and P e r s o n , W.B., M o l e c u l a r Complexes ( W i l e y - I n t e r s c i e n c e , New York, 1969).
I c h i b a , S . , S a k a i , H . , N e g i t a , H. and Maeda, Y., J. Chem. Phys.
56
(1971) 1627.Wynter, C . I . , H i l l , J . , B l e d s o e , W . , Shenoy, G.K. and Ruby, S., J. Chem. Phys.
50
(1969)3872.Bukshpan, S., G o l d s t e i n , C., Sonnino, T . , Yay, L. and P a s t e r n a k , Y . , J. Chem. Phys.
62
(1975) 2606.Maeda, Y . , S a k a i , H., I c h i b a , S . , Katada, K.
and N e g i t a , H., Annu. Rep. Res. R e a c t o r I n s t . Kyoto Univ.
6
(1973) 64.Townes, C.H. and D a i l e y , B.P., J. Chem. Phys.
17 (1949) 782.
-
Bukshpan, S . , G o l d s t e i n , C. and Sonnino, T . , 3. Chem. Phys.
3
(1968) 5477.P a s t e r n a k , Y., Symp. F a r a d a y Soc.
1
(1967) 119.H a f e m e i s t e r , D.W., De P a s q u a l i , G. and DeWaard,
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