Structure-Property Relations in Polymers - American Chemical Society

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33 Comparative Raman and Infrared Vibrational Study of the Polymer Derived from Titanocene Dichloride and Squaric Acid Melanie Williams , Charles E . Carraher, Jr.* , Fernando Medina , and Mary Jo A l o i 1

2

2

2

Motorola, Inc., Plantation, Florida 33317 Departments of Chemistry and Physics, Florida Atlantic University, Boca Raton, Florida 33431 1

2

The vibrational bands associated with the cyclopentadiene (Cp) are similar in location and intensity to the bands found for the polymer formed from the condensation of titanocene dichloride and squaric acid. This similarity is consistent with the Cp ring remaining in the original angular sandwich structure. Bands associated with the Cp ring can be treated through the use of normal coordinate analysis on the basis of a "local" C (fivefold axis of symmetry) symmetry. Selected bands associated with the squaric acid portion are displaced from bands generally due to the presence of ring strain and delocalization of electrons. The combined use of Raman and infrared spectroscopy allows the correct assignment of these bands. 5v

C H A R A C T E R I Z A T I O N O F M A N Y M E T A L - C O N T A I N I N G POLYMERS is c o m p l i c a t e d

b y the additional avenues o f reaction that can b e taken b y the metal-contain i n g moiety, lack o f specific knowledge concerning many metal-containing candidate monomers, a n d the generally p o o r solubility a n d processability o f such products. D e t e r m i n a t i o n o f the dependence o f and relationship between m o n o m e r a n d p o l y m e r properties is h e l p f u l to ascertain the extent to w h i c h * Corresponding author 0065-2393/93/0236-0769$06.00/0 © 1993 American Chemical Society

Urban and Craver; Structure-Property Relations in Polymers Advances in Chemistry; American Chemical Society: Washington, DC, 1993.

770

STRUCTURE-PROPERTY RELATIONS IN POLYMERS

k n o w n m o n o m e r properties can be used to describe the p o l y m e r i c properties of such m o n o m e r - c o n t a i n i n g materials. T h e purpose o f the present study is t w o f o l d : (1) T o determine the extent to w h i c h vibrational b a n d assignments o f the monomers titanocene d i c h l o ride, 1, a n d squaric acid, 2, can b e a p p l i e d to the p o l y m e r i c product f o r m e d f r o m condensation o f these two reactants a n d (2)

to provide additional

structural data to allow differentiation between two basic structural possibili ties. Briefly, three major structures are possible. Structure 3 is e l i m i n a t e d based o n data presented herein; 4 is e l i m i n a t e d based o n molecular weight data. F o r the p r o d u c t studied here, a weight average molecular weight that


corresponds to an average c h a i n length of 140 was d e t e r m i n e d utilizing light scattering photometry. Finally, physical characterization data are consistent

Cp

\ / CI

Cp Ti

Cp \ Ti

/ \

H-0

X

+

CI

Cp /

Cp \

3

0

Cp \

O-H

X

ο

Ti

.Cp /

4

0

Cp /

r\

5

0

0


33.

WILLIAMS ET AL.

Vibrational Study of TiCl Squaric 2

Acid Polymer

771

w i t h 5. D a t a that ehminate 3 a n d support 5 are presented. A n additional structural question involves the type o f b o n d i n g o f the C p groups into the titanium. T h e C p ring can be b o n d e d t h r o u g h a p i b o n d as p i c t u r e d i n 6 or through a sigma b o n d as p i c t u r e d i n 7. Sigma b o n d i n g of the C p ring requires a 1, 2 migration o f the metal atom. S u c h low-energy migrations require only about 10 k c a l / m o l . Again, spectral data that are consistent w i t h the connec tion o f the C p rings to the titanium atom through sigma bonds are given (1-3). A d d i t i o n a l structural characterization is reported i n reference 1.


Experimental Details Infrared Spectra. Infrared spectra were r e c o r d e d using a F o u r i e r transform i n f r a r e d ( F T I R ) spectrometer ( M a t t s o n A l p h a - C e n t a u r i ) e q u i p p e d w i t h K B r a n d mylar optics a n d a deuterated triglycine sulfate ( D T G S ) detector. A t m o s p h e r i c water vapor was r e m o v e d f r o m the spectrometer b y p u r g i n g w i t h d r y nitrogen. T h e spectrometer was calibrated w i t h polystyrene film ( m i d - I R ) a n d water vapor (far-IR). A l l spectra i n the 5 0 0 - 2 0 0 - c m range were r e c o r d e d as m i n e r a l o i l ( N u j o l ) mulls between polyethylene plates. A l l spectra were r e c o r d e d at an instrumental resolution of 4 c m using 32 scans. _ 1

- 1

Raman Spectra. R a m a n spectra w e r e obtained w i t h the 514.5-nm line o f an argon-ion laser, a double monochromator (Spex 1403), a n d p h o t o n counting techniques. T h e instrumental resolution for a typical spectrum was 6.7 c m . A l l spectra were r e c o r d e d at r o o m temperature (23 °C). T h e region b e l o w 200 c m c o u l d not be examined due to the h i g h intensity o f the Rayleigh line. Polarization studies were attempted, b u t were unsuccessful due to the n o n o r d e r e d nature o f the polymer. - 1

- 1

Results and Discussion T h e assignment o f the bands that arise f r o m the cyclopentadienyl ( C p ) ring vibrations can be readily accomplished by comparison w i t h the m o n o m e r titanocene d i c h l o r i d e ( C p T i C l ) a n d other titanocene derivatives because 2

6

2

7



772

the frequency o f the r i n g vibrations remains relatively constant u p o n substitu tion o f the halide ligands (4-7).

T h e assignment o f the bands that arise f r o m

the cyclopentadienyl r i n g vibrations was based o n previous studies o f C p T i C l 2

2

derivatives, as w e l l as studies o n ferrocene, ruthenocene, a n d dicyclopentadienyltin derivatives

(4-9).

Previous studies o n C p T i C l 2

the basis o f a " l o c a l " C

5 u

2

showed that each r i n g c a n b e treated o n

(fivefold axis o f symmetry) symmetry. U n d e r C

5v

symmetry, each r i n g gives rise to 24 n o r m a l m o d e vibrations (the n u m b e r o f degrees o f f r e e d o m is given b y the equation 3 n - 6 , where η is the n u m b e r o f atoms) distributed as 3 A + A + 4Ε X

2

+ 6 £ , w h e r e the Ε modes are 2

λ


doubly degenerate. U n d e r symmetry considerations the A , E, a n d E are R a m a n active whereas the A a n d E 1

x

2

modes

modes are I R active. Therefore, 7

n o r m a l vibrations are expected i n the I R , whereas 13 n o r m a l vibrations are expected i n the R a m a n spectra ( 4 - 9 ) . T h e observed bands a n d their assign ments f o r the ring C p vibrations o f C p T i C l 2

2

a n d the squarate p o l y m e r are

given i n T a b l e I. M o s t o f the assignments f o r the A

l

and E

modes are consistent w i t h

1

previous assignments f o r biscyclopentadienyltitanium ( I V ) titanocene deriva tives ( 2 , 10) i n similar matrices, b u t differ somewhat f r o m the assignments o f

Table I. Observed Infrared and Raman Frequencies for ( C p T i ( C 0 ) ) and C p T i C l Obtained in This Study: Bands Arise from Cyclopentadienyl Ring Vibrations 2

2

Cp TiCl Infrared (cm- ) 2

Oescripion of Mode" CH stretch CH o . p . b e n d R i n g breathing CH CH CH CH CC CH CH CH CC CC CC 359

i.p. bend stretch i.p. bend o.p. b e n d stretch stretch i.p. bend o.p. b e n d stretch i.p. bend o.p. b e n d + 5 9 7 = 956

4

4

n

2

Symmetry Species

Ai Ai A 2

£i

Εχ Ει

Ei E E E E E E

2 2 2 2 2 2

2

Squarate Polymer

b

Infrared " (cm ~ )

Raman (cm " )

3103m 821vs 1130w 1271vw

3095 822s 1149vw 1267vw

825w 1147ms

—

—

1015s 871m

1018m 880m

1440s

1455s

1

—

1197vw 1074w 1364w 927w 597w 957w

1

— — 1084w 1360w

— 595vw

J

b

1

c

— —

1020m 880w 1460m

—

1190w 1050m 1380w

—

605w

o.p., out of plane; i.p., in plane. v, very; s, strong; m, medium; w, weak. Region above 2000 not recorded. SOURCE: Portions of the data presented in this table are reproduced with permission from reference 28. Copyright 1990 Plenum Press.

a

b 0


33.

WILLIAMS ET AL.

Vibrational Study of TiCl -Squaric Acid Polymer

773

2

B a l d u c c i et al. (6) for the matrix-isolated spectra o f biseyelopentadieny! dihalides. Tentative assignments for the E mode, therefore, have been made and are given i n T a b l e I. 2

T h e Ε modes should be forbidden i n the IR, but selection rules are not always strictly obeyed. T h u s several weak infrared bands w i t h frequencies near corresponding R a m a n frequencies are assigned to E modes. A d d i t i o n ally, weak bands at 1271 ( C p T i C l ) a n d 1267 c m (squarate polymer) are assigned to an A mode. T h i s b a n d has been observed consistently i n cyclopentadienyl derivatives even though it is forbidden i n both the infrared and R a m a n spectra (6, 8, 9). 2

2

2

- 1

2


2

T h e r e is little difference between the position and intensity o f the C p ring vibrations i n C p T i C l and i n the squarate polymer. T h i s observation suggests that the C p T i moiety retains its original angular sandwich structure, change i n structure w o u l d require a change i n the orientation o f the rings relative to one another. T h i s orientation is the same as that f o u n d i n the biscyclopentadienyltitanium ( I V ) dihalides, a n d all o f the biscyclopentadienyl derivatives o f titanium ( I I ) . T h u s the I R data are consistent w i t h C p b o n d i n g do the titanium atom through a pi-type b o n d as p i c t u r e d i n 7. 2

2

2

T h e remaining bands i n this region o f the spectrum can be assigned to the squarate p o r t i o n o f the molecule. A n u m b e r o f these assignments are facilitated by the results o f previous studies o n related molecules (7, 12-16). T h e r e are two bands i n the infrared spectrum above 1600 c m , w h i c h suggests the presence o f uncoordinated oxygens (or free carbonyls) ( 1 7 ) . T h e b a n d at 1792 c m i n the R a m a n spectrum is very strong, w h i c h is consistent w i t h a symmetric stretching m o d e because a totally symmetric fundamental generally results i n a strong R a m a n line (14, 18). T h e I R b a n d that corre sponds to this fundamental appears at 1793 c m as a moderately intense b a n d . I n contrast, the b a n d at 1690 c m is very weak i n the R a m a n spectra a n d appears as a strong b a n d i n the i n f r a r e d spectrum at 1693 c m ; this indicates an asymmetric stretching mode. T h e s e bands are assigned to C = 0 stretching modes. - 1

- 1

- 1

- 1

- 1

T h e symmetric stretch occurs at a higher frequency than the asymmetric stretch because, i n a symmetric stretch, the ring b o n d is forced to compress. T h i s compression results i n a larger force constant w i t h an accompanying vibration at a higher frequency. O n the other hand, the asymmetric stretch causes less strain, because the ring carbons can move to adjust to the m o t i o n , 9. T h e b a n d at 1555 c m i n the infrared spectrum is the second most intense b a n d i n the spectrum. T h e position a n d intensity o f this b a n d suggest a symmetric ( C = C ) stretch c o u p l e d w i t h a C —Ο stretch. T h i s b a n d appears i n the R a m a n spectrum at 1557 c m " w i t h a weak shoulder at 1565 c m " . A similar b a n d has been observed i n other metal-containing derivatives (12, - 1

1


1

774


ο

\

ο

ο

/ p

W


\

19-22)

Ο

a n d organic derivatives o f squaric acid (23),

carboxylates (14,

24).

as w e l l as many metal

T h e frequency o f the C = C stretch is lower than the

frequency o f other cycloalkenes as a result o f a longer C = C b o n d distance i n the f o u r - m e m b e r e d rings. This lower frequency results i n a decreased force constant.

F o r instance,

1680-1620cm

an isolated double b o n d usually vibrates i n the

range (as do other cycloalkenes), whereas i n cyclobutene

- 1

this stretch is observed at 1566 c m " "

1

(25).

T h e frequency of the C = C

stretch i n the p o l y m e r is greater than the corresponding frequency i n squaric acid (1513 c m

- 1

) . T h i s difference may be a result o f p-ρί-d-pi

bonding,

T h e most intense b a n d i n the infrared spectrum appears at 1405 c m

- 1

,

C —Ο stretch c o u p l e d to a C = C stretch, w h i c h is i n agreement w i t h the position a n d intensity o f the C —Ο stretch f o u n d i n organic derivatives o f squaric acid (23).

A b a n d at this position is also characteristic o f metal

carboxylates and usually is assigned to a symmetric Ο ~ C — Ο stretch (14, frequency than the asymmetric stretch at 1405 c m

- 1

is again due to the

ring

strain effects m e n t i o n e d earlier. T h e weak bands at 1067 ( I R ) a n d 1075 c m

- 1

(Raman) are assigned to C — C stretching modes, i n accordance w i t h their intensity a n d position,

A characteristic vibration i n all ring systems is the ring breathing m o d e . T h e b a n d that corresponds to this vibration is intense i n the R a m a n spectrum and is infrared active only i n molecules that do not contain a center o f symmetry (25). Because nearly all o f the bands i n the I R a n d R a m a n spectra of the p o l y m e r are coincident, no center o f symmetry is present. A

ring

breathing vibration should, therefore, be observed i n the I R spectrum. T h e ring breathing m o d e usually gives rise to a vibration i n the 9 5 0 - 1 0 0 0 c m

- 1

range i n cyclobutene derivatives, but is f o u n d at considerably lower frequen-


33.

WILLIAMS E T AL.

Vibrational Study of TiCl -Squaric 2

775

Acid Polymer

cies ( 5 5 0 - 7 5 0 c m ) i n the oxocarbons (26, 27). T h e only b a n d i n the R a m a n spectrum that can be assigned to a symmetric ring breathing m o d e is the strong b a n d at 7 5 5 c m ~ . T h e corresponding i n f r a r e d b a n d is observed as a medium-intensity b a n d at 7 4 3 c m . T h i s assignment is consistent w i t h other metal-containing derivatives o f squaric acid (see references 12, 21, and - 1

1

- 1

27).

A t least two C = 0 deformations are expected i n the 5 5 0 - 7 5 0 c m region. H o w e v e r , coincidental degeneracies may occur. Additionally, because there are several bands b e l o w 7 0 0 c m , some o f these bands may be h i d d e n . T h e one b a n d that c o u l d be attributed to a C = 0 deformation occurs at 6 8 1 cm (IR) a n d as a weak b a n d i n the R a m a n spectrum at 6 8 5 c m " " . This b a n d is assigned to an asymmetric C = 0 b e n d i n g m o d e . - 1

- 1


- 1

1

T h e vibrational frequencies o f a n u m b e r o f metal-containing-squaratecontaining complexes have b e e n studied (12, 21, 27). I n these complexes, corresponds to a combination o f C - - C + C - - 0 and C = 0 stretching modes. This b a n d is absent i n the diketosquarate derivatives and is replaced by bands that correspond to C = C , C — Ο , a n d C = 0 stretching modes. T h e positions o f the bands for the complexes listed i n references 12, 2 1 , a n d 2 7 r e m a i n fairly constant for a given vibration, w h i c h suggests similarities i n the structures o f these complexes.

R e p o r t e d i n f r a r e d frequencies for diketosquarate-metal complexes that contain uncoordinated carbonyl groups that are analogous to the structure proposed here for the squarate p o l y m e r are given i n references 19, 20, 23, are attributed to C = 0 stretching modes. A strong b a n d appears between 1500-1600 c m i n the spectra o f all o f these derivatives. T h i s b a n d corresponds to a C = C or C = C + C —Ο stretching mode. - 1

T h e presence o f bands consistent w i t h the presence o f the alkene moiety and I R information that indicates a lack o f symmetry are evidence for p o l y m e r structure as p i c t u r e d i n 5 a n d are not consistent w i t h a structure as described i n 3. F u r t h e r , the absence o f unassigned bands is consistent w i t h a product of f o r m 5 w i t h little contributions f r o m other structures. In summary, vibrational frequencies f o u n d for the titanocene-squarate p o l y m e r are analogous to frequencies f o u n d i n the respective monomers a n d are consistent w i t h the lack o f influence o f the p o l y m e r i c nature o n these vibrational modes. This finding indicates that, at least for some polymers, tional bands f o u n d i n the corresponding polymer. Also, vibrational b a n d assignments are consistent w i t h the p o l y m e r b e i n g o f a general structure as p i c t u r e d i n 5 w i t h the C p rings b o n d e d through p i bonds to the titanium metal atom.


776


References 1. 2. 3. 4. 5. 6.


7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.

Williams, M.; Carraher, C.; Medina, F.; Aloi, M . Poly. Mater. 1989, 61, 227. Semmingsen, D. Acta. Chim. Scand., Ser. A 1973, 27, 3961. Ballhausen, C. J.; Dahl, J. P. Acta. Chim. Scan., Ser. A 1961, 15, 1333. Fritz, H . P., Adv. Organomet. Chem. 1964, 1, 239. Maslowsky, E. Vibrational Spectra of Organometallic Chemistry; Wiley: New York, 1973; Chapter 3. Balducci, G.; Bencivenni, L.; DeRosa, G.; Gigli, R.; Martini, B.; Cesaro, S. N . J. Mol. Struct. 1980, 64, 163. Druce, P. M.; Kingston, B. M.; Lappert, M . F.; Spalding, T. R.; Srivastava, R. C. J. Am. Chem. Soc. 1969, 91A, 2106. Lippincott, E. R.; Nelson, R. D. Spectrochim. Acta 1958, 10, 307. Harrison, P. G.; Healy, M. A. J. Organomet. Chem. 1973, 51, 153. Seymour, R. B.; Carraher, C. E. Polymer Chemistry, An Introduction; Marcel Dekker: New York, 1968. Wailes, P. C.; Courts, R. S. P.; Weigold, H . Organometallic Chemistry of Titanium, Zirconium, and Hafnium; Academic: Orlando, F L , 1974. West, R.; Niu, Η. Υ. J. Am. Chem. Soc. 1963, 85, 2589. Habenschuss, M.; Gerstein, B. C. J. Chem. Phys. 1974, 61(3), 1. Bellamy, L. J. The Infrared Spectra of Complex Molecules; 2nd ed.; Methuen: London, 1968. Oxocarbons; West, R., Ed.; Academic: Orlando, F L , 1980. Miller, F. Α.; Kiviat, F. E.; Matsuhara, I. Spectrochim. Acta, Part A 1968, 24, 1523. Doyle, G.; Tobias, R. S. Inorg. Chem. 1968, 7(12), 2484. Tobin, M . C. Laser Raman Spectroscopy; Chemical Analysis Series 35; Wiley: New York, 1971. Long, G. Inorg. Chem. 1978, 17(10), 2702. Condren, S. M.; McDonald, H . O. Inorg. Chem. 1973, 12, 57. Schwering, H . U.; Olapinski, H.; Jungk, E.; Weidlein, J. J. Organomet. Chem. 1974, 76, 315. Wrobleski, J. T.; Brown, D. B. Inorg. Chem. 1979, 18(10), 2738. Cohen, S.; Cohen, S. G. J. Am. Chem. Soc. 1966 88, 1533. Rao, C. N . R. Chemical Applications of Infrared Spectroscopy; Academic: Or lando, FL, 1963; Chapter 7. Avram, M.; Mateesca, M . Infrared Spectroscopy; Wiley-Interscience: New York, 1972. Baglin, F. G.; Rose, C. B. Spectrochim. Acta, Part A 1970, 26, 2293. Ito, M.; West, R. J. Am. Chem. Soc. 1975, 97, 2580. Sheats, J.; Carraher, C.; Pittman, C.; Zeldin, M . ; Currell, B. Inorganic and Metal-Containing Polymeric Materials; Plenum: New York, 1990.

RECEIVED for review July 15, 1991. ACCEPTED revised manuscript September 13, 1992.


Structure-Property Relations in Polymers - American Chemical Society

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