mined and analyzed the luminescence and IR spectra of europium benzoate, ... solutions of europium nitrate and sodium benzoate, contained a small number of ...
LUMINESCENCE
SPECTRA
OF
OF
COMPOUNDS
EUROPIUM
AND
INFRARED WITH
SPECTRA AROMATIC
ACIDS V. F. Zolin, N. A. A. V. Moshinskaya, and V. I. Tsaryuk
Kazanskaya, Yu. I. Kheruze,
UDC 535.37:546. 661
P r e v i o u s studies w e r e made of the absorption s p e c t r a and sensitization of r a r e - e a r t h ion l u m i n e s cence by a r o m a t i c acids in solution [1, 2]. In o r d e r to d e t e r m i n e the e x c i t a t i o n - t r a n s f e r m e c h a n i s m , it is helpful to know the s t r u c t u r e of the c o r r e s p o n d i n g complex compounds and to t r a c e the changes in the m e t a l - l i g a n d i n t e r a c t i o n f r o m t h e l u m i n e s c e n c e s p e c t r a of the compounds. In o r d e r to a c c o m p l i s h this, we d e t e r mined and analyzed the l u m i n e s c e n c e and IR s p e c t r a of e u r o p i u m benzoate, phenylacetate, and naphthylacetate, as well as the s p e c t r a of the compound f o r m e d by e u r o p i u m with a-naphthoic acid. T h e s e compounds w e r e produced by mixing and r o o m - t e m p e r a t u r e evaporation of aqueous or alcoholic solutions of e u r o p i u m n i t r a t e and the sodium salt of the c o r r e s p o n d i n g a r o m a t i c acid. The s p e c t r a of the compounds w e r e d e t e r mined in ISP-51 and IR-27 s p e c t r o g r a p h s . T a b l e s 1 and 2 give the frequencies of the e l e c t r o n transitions in the l u m i n e s c e n c e s p e c t r a and the vibration frequencies o b s e r v e d in the IR s p e c t r a . Table 3 gives the v i b r a t i o n frequencies in the e l e c t r o n - v i b r a t i o n s p e c t r a of the europium compounds with a r o m a t i c acids. The f r e q u e n c i e s were found by subtracting the frequencies of the e l e c t r o n - v i b r a t i o n t r a n s i t i o n s f r o m that of the 5D0-TF 0 t r a n s i t i o n of the Eu 3+ ion, following Gaiduk et al. [3]. C o m p a r i s o n of these s p e c t r a m a k e s it p o s s i b l e to draw a n u m b e r of conclusions r e g a r d i n g the s t r u c t u r e of the compounds and the changes in the m e t a l - ligand interaction. The l u m i n e s c e n c e s p e c t r u m of e u r o p i u m benzoate, which was obtained by mixing concentrated aqueous solutions of europium nitrate and sodium benzoate, contained a s m a l l n u m b e r of intense lines, which indicated c o m p a r a t i v e l y high s y m m e t r y of the s h o r t - r a n g e environment of the europium ions. The e l e c t r o n - v i b r a t i o n transitions in the luminescence s p e c t r u m of this compound were weak. After the europium benzoate was heated in a Vacuum at 80~ e l e c t r o n - v i b r a t i o n t r a n s i t i o n s a p p e a r e d in the luminescence s p e c t r u m that c o r r e s p o n d e d to v i b r a t i o n s at f r e q u e n c i e s of 553, 696, and 843 c m -1 (the fan-type and s c i s s o r s d e f o r m a t i o n v i b r a t i o n s of the carboxyl and the extension v i b r a t i o n s of the C - C O 2 bond [4]). The l u m i n e s c e n c e s p e c t r a of the e u r o p i u m phenylacetate and naphthylacetate and the s p e c t r u m of the compound f o r m e d by e u r o p i u m with o~-naphthoic acid indicated low s y m m e t r y for the s h o r t - r a n g e e n v i r o n ment of the europium in these compounds. This was shown by the absence of d e g e n e r a t e ~D0-TFj t r a n s i tions with j = 1, 2, 3, 4 and the component intensities of these transitions, which w e r e roughly of the s a m e o r d e r of magnitude. Judging f r o m the splitting and the intensity of the 5D0-TF J transitions, the interaction of the europium with the surrounding c r y s t a l field b e c a m e s t r o n g e r o v e r the s e r i e s : benzoate < p h e n y l a c e t a t e < naphthylacetate < complex with a-naphthoic acid. The c o m p a r a t i v e l y small, s y m m e t r i c c r y s t a l field in e u r o p i u m benzoates was a p p a r e n t l y due to the p r e s e n c e of w a t e r in the f i r s t coordination sphere of the e u r o p i u m . The d e c r e a s e in e n v i r o n m e n t s y m m e t r y produced by r e m o v a l of the w a t e r by heating in a v a c uum or on moving to the phenylacetate and naphthylacetate led to an i n c r e a s e in the p r o b a b i l i t y of ~D0-TFj t r a n s i t i o n s . Since the naphthyl r a d i c a l has pronounced donor p r o p e r t i e s and the methylene group should to s o m e extent reduce the strength of the interaction between the carboxyl and the a r o m a t i c radical, the anion of a-naphthoic acid should have the s t r o n g e s t donor p r o p e r t i e s among the a r o m a t i c acid anions studied. T r a n s l a t e d f r o m Z h u r n a l Prikladnoi Spektroskopii, Vol. 17, No. 1, pp. 71-74, July, 1972. a r t i c l e submitted April 8, 1971.
Original
9 1974 Consultants Bureau, a division of Plenum Publishing Corporation, 227 ff/est 17th Street, New York, N. Y. 10011. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission of the publisher. A copy of this article is available from the publisher for $15.00.
886
TABLE I. Electron Transitions in L u m i n e s c e n c e Spectra of C o m pounds of E u r o p i u m with A r o m a t i c Acids c m -i Eu(C~HsCOO)z 93H20
Eu(C~HsCIIaCOO)a Eu(CloHTCHzCOO)3 Eu(C1oHrCOO)a'nH,O interpretation .2HzO ,2HzO 17250 16920 16892 16835
17256 16961 16886 16807
17249 16961 16835 16779
16313 mod 16295 mod 16239 s 16192mod 16132 mod
16319 s 16295 s 16223 s 16181 s 16132 w
16036 w? 15354 15321 15279
15385mod 15337 w
15432 mod 15387 mod 15337 rood 15314 rnod 15279 w
16359 S 16329 s 16295moc 16221 s 16129 s 16098 s 15389mod 15369~od 15323 vw " 15302modf 15274mod| 15207mod:
14524 w 14457 w 14418 s 14376 s 14286mod 14253 w 14231 w
14556 mod 14526 s 14461m0d 14388 s 14339 s 14316 s 14292 s
17271 16969 16863 16835 16325 16260 16229 16181
w w s w
14572 14486 14409 14378 14339 14286
ZDo--TFo }
~Do--TFt
~Do--TF~
~Do--rFz
14624mod~ 14583rnod t I4562mod 14503 s 14459mod! 14364modl 14327mod l 14282 s I 14237mod~ 14104 s i
s mod s mod mod s
~Do--TF4
~qote: s) Strong; rood) moderate; w) weak; vw) very weak Knes in luminescence Spectra.
TABLE matic
2.
Infrared
Acids,
Spectra
of Compounds
Eu Eu Eu Eu .(C~H~COO)e -(CBHsCH2 9(CIoH~CHz -(CloHrCOO)z .nH20 ,3HzO -COO)~.2H20 .COO)n.2HzO 1629 w 1593 s 1542 vs 1529 v~
1563 vs 1545 vs 1527 vs
1401 vs
1173 w
1196 w 1148 m 1072 m 1028m
1281 m
928 W
944 m 900 w
839 822
with Aro-
W w
837 m
1546 vs 1508 1473 1419 1404 1346 1283 1252 1232 1188 1155 1068 1015
sh w sh vs sh m m m
956 943 931 904 876 853
w w
946 w
w
929 w
1472 w 1403 vs 1335 s
708 vs
w s s s
Ring-extension vibrations Symmetric extension of CO 2" Extension of C-O bond?
1256 m 1208 m
w
w
1150 1068 1025 1007
w
w
m w w w
Planar deformation vibrations of C-H bond
w
w w
877 m 812 w
764 724 707 693
Interpretation
1595 W Ring-extension vibrations 1578 w 1559 w Asymmetric extension of CO~" group 1540 t512 vWs
1598 w
1411 vs 1315 rn 1280 sh
1068 m 1024 m
of Europium
c m -1
797 w 776 s 768 s 708 m
778 s
iNonplanar Deformationvibrationsof C-H bond
716 w
680 m 668 m
Scissors deformation vibrations ofCOl 663 w 642 m 643 m 649 m Note: vs) Very strong; s) strong; m) moderate; w) weak; vw) very weak linesin IR spectra; sh) shoulder.
Polarization complex
of the ligand should lead to an increase
compound
was the largest transitions.
[5].
observed
Actually,
the Stark
splitting
and the luminescence
in the strength
of its bonding to the europium
of the 7Fj levels
spectrum
displayed
in the crystal
the most
intense
in the
f i e l d of t h i s c o m p o u n d electron-vibration
887
TABLE 3. V i b r a t i o n F r e q u e n c i e s in E l e c t r o n - V i b r a t i o n S p e c t r a of Compounds of E u r o )ium with A r o m a t i c A c i d s , cm -I Eu(C6HsCOO)~ EU(C~H~CH2 Eu(CsH,CH~- Eu(C.HTCO0). .nH20 -3H20 .COOh.2H~O .COOh.2H20
553
508 w 62O vw 634 w
696 762 w 797 w 843
530
719 S 757 m 785 w 806 m 855 w 908 w
vw
Interpretation
552 vw
Fan-type deformationvibration of COz-
630 vw 660 m
Scissorsdeformationvibration of
586 w
764 w 785 s 823 w
C O 2"
Extension of C--CO~ bond?
871 s? 901 $?
Note: s) Strong; m) moderate; w) weak; vw) very weak transitionsin electron--vibration spectrum.
The i n f r a r e d s p e c t r a of the compounds i n v e s t i g a t e d w e r e i n t e r p r e t e d by analogy with other s t u d i e s [6, 7]. In g e n e r a l , t h e s e s p e c t r a were i d e n t i c a l to those of the c o r r e s p o n d i n g s o d i u m s a l t s (which a r e not given in T a b l e 2). Only the IR s p e c t r u m of the compound of e u r o p i u m with o~-naphthoic a c i d contained an a d d i t i o n a l (in c o m p a r i s o n with the s p e c t r u m of the s o d i u m salt) i n t e n s e band in the 1335 cm -1 region, which was a p p a r e n t l y p r o d u c e d by e x t e n s i o n v i b r a t i o n s of the C - O bond. Its a p p e a r a n c e might have b e e n due to f o r m a t i o n of c r o s s - l i n k i n g c a r b o x y l g r o u p s and m a y i n d i c a t e a d i m e r i c or p o l y m e r i c s t r u c t u r e for c o m p l e x compounds of e u r o p i u m with o~-napthoie acid. Returning to the l u m i n e s c e n c e s p e c t r u m of this compound, it should be noted that the p r e s e n c e of m o r e than 2J + 1 components for the 5D0-~F J t r a n s i t i o n s , e.g., with J = 2, i n d i c a t e s the e x i s t e n c e of nonequivalent l u m i n e s c e n c e c e n t e r s . The h y p o t h e s i s that t h e r e a r e c r o s s linking c a r b o x y l g r o u p s is a l s o s u p p o r t e d by the a p p e a r a n c e of many v i b r a t i o n s with f r e q u e n c i e s in the 500900 c m -i r a n g e in the e l e c t r o n - v i b r a t i o n s p e c t r u m of the c o m p l e x of e u r o p i u m with o~-naphthoic acid (see T a b l e 3 and [4]). The d a t a obtained thus i n d i c a t e that the m e t a l - l i g a n d i n t e r a c t i o n is m a x i m a l in c o m p l e x e s of e u r o p i u m with a - n a p h t h o i c acid. T h e s e c o m p l e x e s m a y have a d i m e r i c or p o l y m e r i c s t r u c t u r e .
LITERATURE 1,
2. 3. 4. 5.
6,
7.
888
CITED
V. L. Ermolaev, N. A. Kazanskaya, A. A. Petrov, and Yu. I. Kheruze, Opt. i Spektr., 28, 208 (1970). N. A. Kazanskaya, V. L. Ermolaev, A. V. Moshinskaya, A. A. Petrov, and Yu. I. Kheruze, Opt. i Spektr., 28, 1150 (1970). M. I. Gaidu-k, V. F. Zolin, V. A. Kudryashova, and V. I. Tsaryuk, Izv. Akad. Nauk SSSR, Ser. Fiz., 32, 1555 (1968). Z. M. Alikhanova, V. F. Zolin, P. S. Fisher, and G. V. Ellert, Zh. Neorg. I/him., 15, 3119 (1970). G. A. D o m r a c h e v , M. I. G r y a z n o v a , and V. P. Ippolitova, 2nd S e m i n a r on the S p e c t r o s c o p y and P r o p e r t i e s of L u m i n o p h o r s A c t i v a t e d by R a r e E a r t h s [in Russian], IRI~ Akad. Nauk SSSR, Moscow (1969), p. 81. K. Nakanisi, I n f r a r e d S p e c t r a and S t r u c t u r e of Organic Compounds [Russian t r a n s l a t i o n ] , Mir, M o s cow (1965). M. D. T a y l o r , C. P. C a r t e r , and C. I. Winter, J. Inorg. Nucl. Chem., 30, 1503 (1968).
