The Infrared Absorption Spectra of Some Samarium

S. P. TANDON, P. C. MEHTA, AND R. N. KAPOOR

142

The Infrared Absorption Spectra of Some Samarium Ethylbenzoyl Acetate Complexes S. P. T a n d o n , P. C. M e h t a , and R. N. K a p o o r * Department of Physics, University of Jodhpur, Jodhpur, India (Z. Naturforsch. 25 b, 142— 145 [1970] ; eingegangen am 22. November 1969)

Infrared absorption spectra of four (ethylbenzoyl acetate) [EBA] complexes of trivalent sama rium of the general formula X pSm(EBA)g [X = isopropoxy or i-butoxy group; when p = l, q— 2 and vice versa] have been studied in the region 4000 —250 cm -1 for the first time. About twenty five bands in each complex have been observed and assigned to different modes of vibration. The separation between asymmetric and symmetric CO stretching vibrations indicates that the bonding in all the complexes is nearly the same. The spectra show that the interaction between the two ligand rings is small in five coordinated metal complexes.

Rare earth complexes are gaining importance as laser materials due to the laser action observed 1 in some of them. It is only recently that the spectral and structural studies of these complexes have been started 2~9. In an earlier paper 4 the infrared spectra of some (ethyl-1 methyl acetoacetate) complexes of samarium were investigated. The present com munication reports, for the first time, the infrared absorption spectra of four- and five coordinated diketo-ester complexes of trivalent samarium with (ethylbenzoyl acetate) as the ligand, viz., samarium di-isopropoxy mono (ethylbenzoyl acetate) (1), samarium monoisopropoxy di (ethylbenzoyl acetate) (2), samarium di-tertiary butoxy mono (ethyl benzoyl acetate) (3) and samarium monotertiary butoxy di (ethylbenzoyl acetate) (4). The results

have been discussed and an attempt has been made to probe into the nature of metal-oxygen bonding in these complexes. The present infrared study would be helpful for the interpretation of the vibronic contribution to the electronic spectra of these complexes. Experimental and Results The solid state infrared spectra of all the complexes in the region 4000 —250 cm-1 were recorded on a Perkin-Elmer model-521 double-grating spectrophoto meter in KBr phase at 25 cC. All the complexes were prepared by reacting the respective alkoxide with anhydrous ligand. The alkoxides were prepared using the methods of M is r a et al. 10. Reagents of spectrograde were used in the preparation of the complexes.

WAVELENGTH ( f i ) 2.5

4

5

75

20

Fig. 1. Infrared absorption record of samarium diisopropoxy mono (ethylbenzol acetate).

FR EQ UEN CY ( C M '1)

* Present address: Department of Chemistry, University of Georgia. Athens, USA. 1 S . P. S i n h a , in: Complexes of the Rare Earths, Pergamon Press, Oxford 1966. 2 S. P. T a n d o n and P. C. M e t h a , Spectrosc. Lett. 2, 255 11969]. 3 P. C. M e h t a , S . S . L. S u r a n a . and S. P. T a n d o n , Indian J. Pure Appl. Physics 7, 767 [1969]. 4 S . P. T a n d o n and P. C. M e h t a . Z. Naturforsdi. 25 b. 139 [1970].

40

5 6

C. Y. L i a n g , E. J. S c h i m i t s c h e k , D. H . S t e p h e n s , a n d J. A. T r i a s , J. c h e m . P h y s ic s 46, 1588 [1967]. R . C. F a y and T . J. P i n n a v a i a , Inorg. C h e m . 7, 508

[1968], 7 8 9 10

M. F. R i c h a r d s o n , W.F. W a g n e r , and D. E. S a n d s , In org. C h e m . 7, 2495 [1968]. K. C . P a t i l , G . V. C h a n d r a s h e k h a r . M. V. G e o r g e , and C . N . R . R a o , Canad. J. Chem. 46. 257 [1968]. S . P. S i n h a , Z. N a t u r f o r s d i . 20 a, 552 [1965]. S . N. M i s r a , T . N . M i s r a , R. N. K a p o o r , and R. C. M e h r o t r a , Chem. Industries 1963, 120.

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IR SPECTRA OF Sm ETHYLBENZOYL ACETATE COMPLEXES WAVELENGTH ( f i )

25

4

15

5

Fig. 3. Infrared absorption record of samarium di-f-butoxy mono (ethylbenzoyl acetate).

20

Fig. 2. Infrared absorption record of samarium mono-isopropoxy di (ethylbenzoyl acetate).

40

400 0

143

3000

1000

2000

250

FR EQ U EN C Y ( C M '1)

Fig. 4. Infrared absorption record of samarium mono-J-butoxy di (ethylbenzoyl acetate). FREQUENCY ( C M '1)

1

[cm-1] ~ 3260 (sh) 3155 (b)

— 1590 1500 1470 1452 1380 1258

(b)

(b)

(s) (sh) (w)

(s)

1172 (s) 1090 (s) 1032 (sh) 1020

— 910 830 795 770 690 635 605 510

(to)

(to) (w) (w)

(to)

(w) (w) (w) (sh)

— 350 (b) —

2 [cm-1] ~ 3210 3150 2955 1595 1500 1470 1455 1380 1255 1170 1090 1030 1018

(w) (m)

(w) (sh) (w)

(to) (sh) (w)

(s) (s) (s)

(sh) (s)

— 902 830 795 770 690 637 — 500 410 365 300

(m) (w)

(w)

(to) (to) (w)

(to) (w) (b) (w)

3 [cm-1] ~ 3205 3150 2950 1592 1500 1470 1450 1380 1260

(w) (m)

(w) (s) (to) (to) (sh) (sh) (s)

1172 (s) 1092 (s) 1032 (sh) 1020

(s)

930 910 835 794 770 692 620 — 508

(sh) (w) (w)

(s) (to) (m) (w) (w)

—

345 (b) —

4 [cm-1] ~3210 3150 2960 1610 1510 1470 1455 1380 1260

(m) (s)

(w) (s) (w)

(to) (sh) (w)

(s)

1185 (s) 1095 (s) 1035 (s) 1022

(s)

932 910 838 799

(sh) (s)

630 610 512 430 372 312

(w) (w)

(w)

(s) 772 (s) 695 (s)

(to) (w)

(s) (w)

Assignments

O —H stretching in H 2O Asym. CH3 stretching Sym. CH3 stretching Asym. C—O stretching Asym. C—C stretching Asym. CH3 deformation Sym. C—O stretching Sym. CH3 deformation Sym. C—C stretching and OH2 deformation C—H in-plane bending C—H in-plane bending C—H in-plane bending C—H in-plane bending and CH3 rocking in isopropoxy group C—H stretching in t-butoxy group C—H out-of-plane bending C—H out-of-plane bending C—H out-of-plane bending Five adjacent hydrogen atoms on the ring C—H out-of-plane-bending Sm—O stretching C—H out-of-plane bending Mono substitution in ring Sm—O stretching Sm —0 stretching Ring deformation

Table 1. Infrared frequencies, intensities and assignments of samarium complexes of (ethylbenzoyl acetate) ,1 —4. sh: shoulder, w: weak, m: medium, s: strong and b: broad.


144

IR SPECTRA OF Sm ETHYLBENZOYL ACETATE COMPLEXES

The infrared absorption records of the complexes

I —4 have been given in Figs. 1 —4 respectively. The observed vibrational frequencies of the com plexes with their intensities and assignments have been collected in Table 1. The intensities of the bands have been classified in the usual manner.

Discussion The spectra of all the four complexes resemble each other very closely. The assignments have been made in the light of theoretically calculated 5> 11 dif ferent modes of vibration which have been discussed below:

bonds become uneven, and the separation of the two CO stretching frequencies may increase. Since Av in all the complexes does not vary much with each other, it appears likely that the bonding in all these cases is nearly the same. However, the relatively high Av value in 4 indicates the slightly stronger metal-oxygen bonding in it. Thus the metal-oxygen bonding in the complexes under study increases in the order: acetate< 1 ä; 3 < 2 < 4 . The values of metal-oxygen stretching force constant, K, of the complexes 1 and 3 also indicate that the bonding in these two complexes is nearly the same 13.

Carbonyl Group Vibrations

Phenyl and Alkyl Groups Vibrations Since there are four equivalent bonds in each complex, viz., two CO bonds and two CC bonds, four stretching modes of vibration including these are expected to appear. The two C — 0 stretching fre quencies should be close to each other since the two CO bonds are separated, and interaction between the two stretching coordinates is fairly small, whereas the two C —C stretching frequencies should be far apart because the two CC bonds are close to each other and interact strongly. Consequently, the bands near 1600, 1500, 1450 and 1260 cm-1 may be as signed 4 to asymmetric C — O stretching, asymmetric C —C stretching, symmetric C —0 stretching and sym metric C —C stretching modes of vibration respec tively. The position of these frequencies depends upon the masses of the groups attached to the car bonyl groups at the ends of the ligand molecule. The asymmetric and symmetric CO stretching modes in the case of samarium acetate have been found 8 at 1550 and 1420 cm-1 respectively. But in the present case of (ethylbenzoyl acetate) complexes, these frequencies are shifted to higher wave num bers. The separation between the asymmetric and symmetric CO stretching frequencies may be taken 12 as an indication of the nature of the coordination in the complexes. It can be seen that the separations {Av) in complexes 1 —4 are 138, 140, 137, and 160 cm-1 respectively. These separations are larger than Av in samarium acetate. It is expected that as the metal-oxygen bond becomes stronger, two CO II 12

K. N a k a m o t o and A. E. M a r t e l l , J. chem. Physics 32, 588 [I960], K. N a k a m o t o , F . F u j i t a , S. T a n a k a , and M . K o b a y a s h i , J. Amer. chem. Soc. 79, 4904 [1957].

The bands due to the presence of phenyl group may be assigned by comparing the spectra with those of benzene and substituted benzenes. The in-plane C —H bending vibrations in benzene are derived14 from a?g (1340 cm-1), e=>g (1178 cm-1), 62« (1152 cm-1), and e\u (1037 cm-1) modes. The corresponding frequencies are found to remain unchanged in mono substituted benzenes. Consequently the bands between 1185 and 1030 cm -1 may be assigned to C —H in-plane bending of the ring. The C —H out-of-plane bending vibrations in sub stituted benzenes are derived14 from b*g (995 cm-1). e\g (975 cm-1), e\g (850 cm-1), and e^u (673 cm-1) modes in benzene. These modes give rise to weak infrared and R a m a n bands. In view of this, the bands between 1020 and 605 cm -1 have been as signed to C —H bending out-of-plane vibrations of the ring. A band near 770 cm -1 in all the complexes indi cates the presence of five adjacent hydrogen atoms vibrating in phase and out of plane of the ring. The band near 500 cm -1 shows the presence of mono substitution in the benzene ring. The presence of alkyl groups can have charac teristic asymmetric and symmetric stretching and bending modes of vibration. The bands near 3150 and 2950 cm-1 may be assigned4 to asymmetric and symmetric CH 3 stretching vibrations respec13 S .

14 S .

P. P.

and P. C. M e t h a (to be published). P. B h u t r a , P. C. M e h t a , and J. P. Indian J. Pure Appl. Phys. 7, 651 [1969].

Tandon

T andon, M.

Saxena,


145

ISOPOLYSÄUREBILDUNG DES MOLYBDATS

tively. The asymmetric and symmetric CH3 defor mation vibrations appear at 1470 and 1380 cm-1 respectively. The isopropoxy and f-butoxy groups absorb near 1020 and 930 cm-1 respectively. The strong band near 1260 cm-1 may also be assigned to CH2 deformation of the ethyl group. Sm — 0 Stretching Bands

The bands below 700 cm-1 are generally ascribed to metal-oxygen stretching modes, the number of which depends upon the coordination number of the metal. Among the three metal-oxygen sensitive regions4, two bands near 635 and 350cm -1 in the four coordinated complexes and three bands near 635, 410 and 370 cm-1 in the case of five co ordinated complexes have been assigned to Sm — 0 stretching mode of vibration. It is observed that the vibrational frequencies, with few exceptions, are nearly independent of the

coordination number of the metal. The carbonyl and Sm —0 stretching frequencies shift to slightly higher wave numbers as the coordination number increases from four to five. The fact that the Sm — 0 stretching bands shift only slightly with the coordination number of the metal indicates that the vibrational interactions be tween the two ligand rings through Sm — O bonds in complexes 2 and 4 is small. From the present study it may be generalised that in the region above 700 cm-1 the spetra are independent of the number of ligands attached to the metal, whereas in the region below 700 cm-1 they depend on it. The number of metal-oxygen bands depends on the coordination number of the metal. The thanks are due to C.S.I.R. and U.G.C., India, for supporting the work. Thanks are also due to Dr. S. N. M i s r a , University of Washington, Washington, Seattle, USA, for helpul discussions.

Die Untersuchung der Isopolysäurebildung des Molybdats mit Hilfe der kryoskopischen Titration G. W ie s e Institut für Anorganische und Analytische Chemie der Freien Universität Berlin (Z. Naturforsdi. 25 b, 145— -148 [1970] ; eingegangen am 20. Dezember 1969)

Mit Hilfe einer kryoskopischen Titration wird die Änderung des Kondensationsgrades bestimmt, die bei der Zugabe von H® zu einer Molybdatlösung eintritt. Als dominierende Polyanionen erwei sen sich [Mo7O 24] 6 0 und [Mo80 24]4e.

Säuert man eine Molybdatlösung an, so treten die Molybdationen unter Wasserabspaltung zu kom plexen Anionen zusammen 1. Obwohl diese Konden sationsvorgänge bereits mit den verschiedensten phy sikalischen und chemischen Methoden eingehend untersucht wurden1, herrscht immer noch Unklar heit darüber, welche der verschiedenen heute be kannten Polyanionen des Molybdats in den einzel nen Acidifikationsbereichen dominieren. Durch die Entwicklung einer hochempfindlichen Temperaturmeßtemperatur zur Durchführung kryo skopischer Messungen2 und einer neuen Arbeits technik 3, lassen sich kryoskopische Titrationen durchführen, so daß man direkt die aktuelle Teil chenzahl als Funktion der Reagenzzugabe ermitteln

kann. Da sich aus der potentiellen und aktuellen Teilchenzahl der mittlere Kondensationsgrad berech nen läßt, hat man also mit der kryoskopischen Ti tration die Möglichkeit, Aussagen über Kondensa tionsvorgänge, wie sie bei der Isopolysäurebildung des Molybdats auftreten, eingehend zu studieren.

1 K. 2 K.

3 G.

F. J a h r u . J. F u c h s,

G. W i e s e N.F. 61,73 [1968]. F. J a h r ,

u.

Angew. Chem. 78, 725 [1966]. G. S c h u c h a r d t , Z. physik. Chem.,

Experimentelles Das 2. R a o u 11sehe Gesetz: AT = k0-c

gibt den Zusammenhang zwischen der Gefrierpunkts erniedrigung AT, die ein reines Lösungsmittel oder ein eutektisches Gemisch beim Zusatz von Fremdionen er fährt und der molaren Konzentration der Fremdionen wieder (k0 = molare Gefrierpunktserniedrigung). BeW ie s e

u. G.

Sc h u c h a r d t ,

Z. physik. Chem.,

N .F .,

im

Druck.
