21 Vibrational Spectroscopy of High Temperature Metal-Halide Vapor Complexes G. N. PAPATHEODOROU
Downloaded by UNIV QUEENSLAND on June 18, 2014 | http://pubs.acs.org Publication Date: March 8, 1982 | doi: 10.1021/bk-1982-0179.ch021
Argonne National Laboratory, Chemical Engineering Division, Argonne, IL 60439
Raman spectra of vapor-phase compounds CuFeCl , HfCl •POCl and ΝΗ •ΑlΧ (X = Cl, Br) have been measured at~500-1000K. Resonance Raman spectra obtained from an equilibrium vapor mixture containing CuFeCl (g) showed two characteristic polarized bands at 441 and 275 cm-1, which were attributed to trigonally coordinated Cu(II) and suggested a C V symmetry for the vapor complex. Raman spectra of HfCl •POCl vapors were characterized by a super position of (1) strong bands due to POCl (g) and HfCl4(g) and (2) a few new bands (at 512, 1221, and 1263 cm ) due to the vapor complex. A comparison of the vapor-complex spectra with those of HfCl (g) and POCl3(g) as well as HfCl •POCl in the liquid and glass states indicated that the bonding of the complex with a C symmetry occurs through an oxygen bridge. Raman spectra of the vapors over liquid NH AlX (X = Cl, Br) were measured and compared with the spectra of the liquid NH AlX itself as well as NH AlCl in the vapor and liquid states. The mea surements support the view that dissociative vaporiza tion and further dissociation occur according to the reaction 5
4
3
3
3
5
2
4
3
3
-1
4
4
3
3V
4
4
4
3
ΝΗ ΑlΧ (l) 4
4
3
NH AlX (g)+HX(g)
4
3
3
NH (g)+AlX (g)+HX(g) 3
3
For NH AlCl , the C molecular symmetry of the gaseous state is not preserved in the liquid state whose structure appears to be network-like. 3
3
3v
During the past three decades, i t has been e s t a b l i s h e d that s a l t vapors a t elevated temperatures ( t y p i c a l l y T>500 K) a s s o c i a t e p a r t l y to y i e l d dimeric and/or polymeric gaseous molecules. Fur thermore, c e r t a i n vapors react with vapors and/or condensed-phase compounds to form vapor complexes. Vapor complexation appears to
0097-6156/82/0179-0309$05.00/0 © 1982 American Chemical Society In Metal Bonding and Interactions in High Temperature Systems; Gole, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
METAL BONDING AND INTERACTIONS
310
be a g e n e r a l phenomenon f o r many m e t a l - h a l i d e s a l t s as w e l l as oxides and other types o f s a l t s and i s important i n determining the r a t e s o f v a p o r i z a t i o n , vapor pressures and apparent v o l a t i l i t i e s of m a t e r i a l s (J^ l_ _3) . Most of the s t u d i e s have been focused on the formation of vapor complexes between two metal h a l i d e s GX and RX^, having a common anion X ( F , CI, Br, or I ) , which r e a c t according to the general scheme: y
y
mGX (s,£, or g) + nRX (g) + G R X y
k
m
n
( m y
+
n k )
(g)
(1)
In most cases RX i s a more v o l a t i l e h a l i d e and i s present only as a vapor whereas GXy may be i n a condensed or vapor phase depending on the temperature and t o t a l pressure o f the system. Stoichiomet r i c c o e f f i c i e n t s and thermodynamic q u a n t i t i e s f o r r e a c t i o n 1 have been measured u s i n g a v a r i e t y of experimental techniques, i n c l u d i n g mass-spectrometry, chemical t r a n s p o r t and spectrophotometry. A l a r g e number of h a l i d e vapor complexes have been reported, and extensive reviews on t h e i r systematics and thermodynamics of f o r mation are already a v a i l a b l e (4-9). However, s t u d i e s regarding the e l e c t r o n i c and v i b r a t i o n a l p r o p e r t i e s o f vapor complexes are not so e x t e n s i v e . Table I summarizes the m e t a l - h a l i d e vapor complexes which have been s t u d i e d by s p e c t r o s c o p i c methods. A major part of the work has been devoted to o b t a i n i n g e l e c t r o n i c a b s o r p t i o n s p e c t r a of complexes i n v o l v i n g t r a n s i t i o n - m e t a l h a l i d e s . A l i m i t e d amount o f matrixi n f r a r e d (IR) spectroscopy data has a l s o been r e p o r t e d . More r e c e n t l y , high-temperature Raman and fluoresence spectroscopy has been used to i n v e s t i g a t e the v i b r a t i o n a l and e l e c t r o n i c s t a t e s of these vapors. I n most cases, the s p e c t r a measured served as a means of proposing s t r u c t u r a l models f o r the vapor complexes. Conclusions regarding the molecular s t r u c t u r e and symmetry of the complexes a r e a l s o g i v e n i n Table I . The present paper i s concerned with the c h a r a c t e r i z a t i o n of the v i b r a t i o n a l p r o p e r t i e s of c e r t a i n vapor complexes a t e l e v a t e d temperatures. Raman spectroscopy i s used to study the vapor complexes CuFeCl5 and HfCl4 POCl3 as w e l l as the vapor species formed by v a p o r i z a t i o n of NH4AIX4 (X = CI, B r ) .
Downloaded by UNIV QUEENSLAND on June 18, 2014 | http://pubs.acs.org Publication Date: March 8, 1982 | doi: 10.1021/bk-1982-0179.ch021
k
#
Experimental Methods The p r e p a r a t i o n and p u r i f i c a t i o n of metal h a l i d e s f o r h i g h temperature spectroscopy present c e r t a i n d i f f i c u l t i e s which vary f o r the d i f f e r e n t s a l t s . A l l chemicals used i n the present work were "anhydrous" s a l t s purchased from Cerac/Pure Inc. AICI3, AlBr3, FeCl3, and HfCl4 were p u r i f i e d by repeated slow sublimat i o n s i n f u s e d - s i l i c a tubes under vacuum. Anhydrous CuCl2 was synthesized by r e a c t i n g AICI3 with the corresponding oxide at ^300 C. A f i n a l p u r i f i c a t i o n o f CuCl2 was made by vapor t r a n s p o r t according to r e a c t i o n 1 u s i n g AlCl3(g) as a c a r r i e r gas. Two ammonium s a l t s , NH4CI and NfyBr, were p u r i f i e d by r e c r y s t a l l i z a t i o n
In Metal Bonding and Interactions in High Temperature Systems; Gole, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
PAPATHEODOROU
TABLE 1.
Vibrational
Spectroscopy
Spectroscopic Investigations of Metal-Halide Vapor Complexes Spectroscopic
Predominant Vapor Temperature
Complex Species and
Method of
K
Molecular Symmetry
Investigation
Downloaded by UNIV QUEENSLAND on June 18, 2014 | http://pubs.acs.org Publication Date: March 8, 1982 | doi: 10.1021/bk-1982-0179.ch021
System
Reference
LiF-BeF2
900
LiBeF3; C2V
Matrix IR
(10)
CSCI-C0CI2 A F-AIF3 (A=Li to Cs)
1300
CSC0CI3; C%j(?) AAIF4; C2v
VIS-UV
(11)
800-1100
Matrix IR
(12,13)
lnCI-AICl3
800-1000
InAICU; C2v
