Lanthanide and Actinide Chemistry and Spectroscopy - American

3 Organic Derivatives of the ƒ-Block Elements: A Quest

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 10, 2016 | http://pubs.acs.org Publication Date: September 23, 1980 | doi: 10.1021/bk-1980-0131.ch003

for ƒ-Orbital Participation and Future Perspective TAKESHI MIYAMOTO (1) and MINORU TSUTSUI Department of Chemistry, Texas A&M University, College Station, TX 77843

Summary The long-term quest for f-orbital participation in bonding is described along with progress in organometallic chemistry of f-block elements. A wide variety of sigma-bonded organolanthanide compounds have been synthesized with the expectation of the f-orbital participation in metal-carbon bonding. To our dis appointment, visible spectra, magnetic properties and x-ray analyses did not show any definite evidence of f-orbital parti cipation in bonding. However, recent ESCA studies have revealed unique electronic structures of a series of f-block phthalocyanine and porphyrin complexes in which f-orbitals play an im portant role in the core ionization process. Plets' first attempt to prepare organolanthanide compounds marked the dawn of a new area of chemistry (2). Since then, a wide variety of complexes of f-block elements have been synthe sized and their structures have been satisfactorily explained in terms of "steric congestion" of ligands around f-metal ions (3,4,5,6). However, the question of whether the 4f valence orbitals participate in bonding has not as yet been answered. The purpose of this article is to review the recent progress in some of the f-element chemistry which is related to the possible f-orbital participation in bonding. Tsutsui and co-workers have continued to explore a series of σ-bonded organic derivaties of 4f-elements in order to search for possible participation of 4forbitals in the bonding (7,8). Below their expectation, x-ray analyses, the visible spectra and magnetic susceptibilities have not shown any evidence of f-orbital participation, until a few years ago. However, they have recently found unique electronic structures of known lanthanide complexes by ESCA, which yields

0-8412-0568-X/80/47-131-045$05.00/0 © 1980 American Chemical Society Edelstein; Lanthanide and Actinide Chemistry and Spectroscopy ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

46

LANTHANIDE AND ACTINIDE CHEMISTRY AND

SPECTROSCOPY

evidence f o r f-orbital p a r t i c i p a t i o n i n the bonding. T h i s artic l e deals with the current developments of t h e i r s t u d i e s on t h i s subject i n a d d i t i o n to t h e i r past e f f o r t s .


H i s t o r i c a l Background The f i r s t TT-bonded organometallic compounds of the f - b l o c k elements were prepared by Wilkinson e t . a l . (Ln(C H.)., Ln=La, Ce, Pr, Nd, Sm. Gd, Dy, E r , or Yb, and U(C H ^ C l ) i n mid-1950 (9,10). The pentahapto c o o r d i n a t i o n of the c y c l o p e n t a d i e n y l r i n g i n U ( C H ) C 1 (11) was shown by x-ray a n a l y s i s . The U(C H^Cl complex i s d i f f e r e n t from L^C^H,.)^ w i t h respect to the r e a c t i o n with F e C l . The L n ( C X ) complex reacted r e a d i l y with F e C l to give ferrocene while the 'd(C^R^) CI complex d i d not y i e l d C p L n CI

3

5

LnCl + R L i

2

- C H 5

5

™ ^

L n = Sm - Lu > Cp

2

Ln R

L n = Sm, Gd, E r , Yb R = CH > -C=C - ® , - ® > a l l y l 3

Edelstein; Lanthanide and Actinide Chemistry and Spectroscopy ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

3.

MIYAMOTO

Derivatives

AND TSUTSUI

of the {-Block

Elements

51

By a s i m i l a r procedure, E l y and T s u t s u i synthesized and chara c t e r i z e d a monocyclopentadienyl b i s p h e n y l a c e t y l i d e complex (40). Visible s p e c t r a of a l l the Cp^Ln-R complexes (except the Yb ones, which were not studied) show a c h a r g e - t r a n s f e r band which i s

5

(Tl -C H )HoCl -3THF 5

5

2

+ 2LiC=CC H 6

5

—

5

> (n -C H )Ho ( C S C C ^ ) 5

5

2


(4) + 2LiCl absent i n the s t a r t i n g Cp LnCl complex. T h i s band s h i f t s to lower energy as the reducing s t r e n g t h of the R moiety i s i n c r e a s ed, an e f f e c t c o n s i s t e n t w i t h i t s f o r m u l a t i o n as l i g a n d to metal charge t r a n s f e r (41). A l s o , i n the complexes Cp Ho(C=CPh) and CpHo(C=CPh) , the c h a r g e - t r a n s f e r band i s s h i f t e d to lower energy i n the spectrum of the complex with two R m o i e t i e s , i n d i c a t i n g that the charge t r a n s f e r i n v o l v e s l i g a n d to metal i n t e r a c t i o n s . A number of the s p e c t r a d i s p l a y e d h y p e r s e n s i t i v e (42,43) t r a n s i t i o n s f o r some of the bands observed (39). Although hypers e n s i t i v i t y has been r e l a t e d to e i t h e r increased i n t e r a c t i o n , the polarizabilj'tyof l i g a n d or symmetry changes around the metal i o n , the symmetry might remain e s s e n t i a l l y the same on going from the C p L n C l complex to the Cp Ln-R complex. Therefore, the appearance of h y p e r s e n s i t i v i t y i n the s p e c t r a of some of the Cp~Ln-R complexes may r e f l e c t enhanced i n t e r a c t i o n between metal tLn) and l i g a n d (R), or increased p o l a r i z a b i l i t y of l i g a n d (R). Magnetic s u s c e p t i b i l i t y s t u d i e s of these complexes were p e r formed, and the values of u £ f were found to decrease on lowering temperature, u n l i k e the m a g n e t i c a l l y more w e l l behaved c h l o r i d e analogues C p L n C l . The temperature dependence of u f f the Cp Ln-R complexes appears to a r i s e from the d i f f e r e n c e of s i t e symmetry and the strength^of the c r y s t a l f i e l d i n t e r a c t i o n s . Ann (a) carbanion such as CH^- has i t s e l e c t r o n d e n s i t y concentrated on one carbon atom where i t could be more r e a d i l y a v a i l a b l e f o r some type of l o c a l i z e d i n t e r a c t i o n with the metal and thus may lead to the unusual o p t i c a l and magnetic e f f e c t s . S t r u c t u r a l s t u d i e s by Baker, Brown, and Raymond (42) have shown the dimeric nature of lanthanide d i c y c l o p e n t a d i e n y l halides. They reported that the molecular s t r u c t u r e of [Y^(C^H^CH^)oCl] c o n s i s t s of two ytterbium atoms, each with two n -bound methylc y c l o p e n t a d i e n y l r i n g s , which are n e a r l y symmetrically bridged by the two c h l o r i n e atoms. The c r y s t a l s t r u c t u r e of Yb(C^H^) Me was reported by Halton et a l . (43). The complex a c t u a l l y has a dimeric s t r u c t u r e , Cp YbMe YbCp , remarkably s i m i l a r to Me ALMe AlMe « The o v e r a l l molecular geometry i s i d e n t i c a l with that or the c h l o r i d e analogue Yb(C H^CH ) C1. In an e f f o r t to prepare a a-bonded a l l y l d e r i v a t i v e analogous to C p U C H , T s u t s u i and E l y (38) prepared CpJLnC^(Ln=Sm,Er,Ho) by r e a c t i n g C p L n C l with allylmagnesium bromide i n THF-ether s o l u t i o n at -7o°C. C h a r a c t e r i z a t i o n of these new a l l y l d e r i ?

2

2

2

e

2

i

e

n

2

2

2

2

2

2

2

2

5

3

3

3

2

5

?


2


52

LANTHANIDE AND ACTINIDE CHEMISTRY AND SPECTROSCOPY

v a t i v e s revealed t h j formation of an n - a l l y l - l a t h a n i d e bond i n preference to the n - a l l y l bond observed i n the analogous a c t i nide d e r i v a t i v e s . The s i z e of the c o o r d i n a t i o n s i t e a v a i l a b l e i s an important f a c t o r which governs the molecular geometry. One example i s that sigma-bonded a l k y l d e r i v a t e s of the type (Cp^LnR) have been synthesized f o r only the l a t e lanthanides elements. Those of e a r l y lanthanides s e r i e s ; L a , Ce, Pr and Nd have conspicously been absent due to t h e i r low thermal s t a b i l i t y . The d i f f e r e n c e between the l a t e and the e a r l y lanthanides may be a f e a t u r e of the lanthanide c o n t r a c t i o n , and c o o r d i n a t i o n s a t u r a t i o n may be the key f a c t o r i n c o n t r o l l i n g the s t a b i l i t y and/or r e a c t i o n p a t t e r n of the organolanthanindes. John and T s u t s u i r e c e n t l y have prepared the s t a b l e a -bonded organometallic compounds of the e a r l y lanthanides, using trimethylene bridged b i s c y c l o p e n t a d i e n y l l i g a n d (eq.5) (44) ,which i s much more s t e r i c a l l y bulky than the Cp l i g a n d .

Ln = La, Ce

R = - ®

, -C=C

-

®

V i s i b l e s p e c t r a of the Ln[Cp(CR^)^Cp]C=CPh complexes show a charge t r a n s f e r band which i s absent i n the s t a r t i n g L n C p t e H ^ ) ^ CpCl, again i n d i c a t i n g that the charge t r a n s f e r can be a t t r i b u t able to l i g a n d to metal i n t e r a c t i o n s or the p o l a r i z a b i l i t y of C=CPh group. During syntheses and c h a r a c t e r i z a t i o n of organolanthanum compounds, the data of magnetic p r o p e r t i e s , o p t i c a l s p e c t r a and x-ray analyses have been i n e f f e c t i v e to c l a i m the existence of f - o r b i t a l p a r t i c i p a t i o n i n bonding. The i o n i c model v e r s i o n s a t i s f a c t o r i l y e x p l a i n s these data. A c c o r d i n t l y , i t i s b e l i e v e d f o r the l a n t h a nide compound, that the 4f o r b i t a l s d i d not extend f a r enough spati a l l y to enter i n t o covalent bonding or to be s p l i t by l i g a n d f i e l d s to any great extent. In the a c t i n i d e s , the 5f o r b i t a l s are much l e s s s h i e l d e d than the 4f o r b i t a l s and the b i n d i n g energies are lower than the l a n t h a n i d e s . These f a c t o r s have been a t t r i buted to an increase i n covalent bonding f o r the a c t i n i d e s . Indeed, Raymond and co-workers have presented extensive c o r r e l a tions of the c r y s t a l l o g r a p h i c data on the organolanthanide and


3.

MIYAMOTO AND TSUTSUI

Derivatives

of the

{-Block

Elements

53

organoactinide complexes on the b a s i s of an i o n i c model (7,8). They concluded that there might be some appreciable f - o r b i t a l cont r i b u t i o n to the bonding i n the e a r l y a c t i n i d e (IV) complexes, but there i s e s s e n t i a l l y none i n the a c t i n i d e ( I I I ) or lanthanide (III) complexes.


f-Orbital Participation For the lanthanide complexes, even i f the amount of covalent i n t e r a c t i o n i s very small, we might have a chance to get the e v i dence of f - o r b i t a l p a r t i c i p a t i o n i n bonding (Figure 4 ) . Recently, T s u t s u i and co-workers have shown some i n t e r e s t i n g r e s u l t s from ESCA s t u d i e s on a s e r i e s of Ln(OH) (Ln-La, Ce, Pr, Nd, Sm, Eu, Gd), H [ L n P c ] , Pc=phthalocyanine and AnPc (45,46). From an i n v e s t i g a t i o n of s a t e l l i t e s t r u c t u r e s of Ln3d5/2 and An4d5/2 peak (Figure 5 ) , a p u z z l i n g question arose as to the shake-up s a t e l l i t e of l i g a n d f - o r b i t a l s charge-transfer type. 2 The l i g a n d 4-f shgke-up s a t e l l i t e was not observed i n P r ( I I I ) (f ) and Nd ( I I ) ( f ) complexes which have s u f f i c i e n t vacant f - o r b i t a l s to r e c e i v e e l e c t r o n s from l i g a n d s , whereas La(III)(f°) complex has a propensity to show the s a t e l l i t e s . (Figure 5) The a n a l y s i s of the date shows that f - o r b i t a l s (both h a l f - o c c u p i e d and vacant) play an important r o l e i n the c o r e - i o n i z a t i o n process to give the sharp v a r i a t i o n i n i n t e n s i t y to the s a t e l l i t e s . The above r e s u l t may not r e l a t e d i r e c t l y to the f - o r b i t a l p a r t i c i p a t i o n i n r e a c t i o n s of f-elements, but i s i n d i c a t i v e of important r o l e of f - o r b i t a l s (or f - e l e c t r o n s ) f o r bonding s i g n i ficance. ESCA s t u d i e s are a l s o e f f e c t i v e f o r the e l u c i d a t i o n of s t r u c ture. The N Is spectrum of Pc^NdH (Figure 6) shows a sharp s i n g l e peak (Figure 7), while that ox a phthalocyanine f r e e base has two types of peak based on aza n i t r o g e n atoms and p y r r o l e n i t r o g e n atoms* The date i m p l i e s that e i g h t c e n t r a l n i t r o g e n atoms are chemically equivalent to each other, and thereby the a c i d i c hydrogen does not bind s t r o n g l y to any of n i t r o g e n atoms i n the complex (47). 3

2

?

The n i t r o g e n Is s p e c t r a have been a l s o i n v e s t i g a t e d f o r a s e r i e s of o c t a e t h y l p o r p h y r i n and tetraphenylporphine complexes of lanthanides Ln(DEP) (OH) and Ln (TPP)(acac) [Ln=Sm,Gd,Er and Yb; acac = acetylacetove] (48). The p r o f i l e of N Is spectrum f o r each lanthanide porphyrin showed that the four n i t r o g e n atoms were equivalent i n the complex. No s i g n i f i c a n t change was detected between the N Is b i n d i n g energies of the lanthanide porphyrins. A good c o r r e l a t i o n between N Is l i n e width (FWHM) and a number of unpaired e l e c t r o n s i n the complex was found. T h i s r e s u l t implies the presence of unpaired valance e l e c t r o n s on the n i t r o g e n atoms, which are induced through an i n t e r a c t i o n between n i t r o g e n valence o r b i t a l s and h a l f - o c c u p i e d 4f o r b i t a l s of lanthanides. Although the ESCA r e s u l t s c l e a r l y demonstrate the evidence f o r covalency i n c l u d i n g f - o r b i t a l p a r t i c i p a t i o n , at the present stage, i t i s d i f f i c u l t to estimate t h e i r extents.




Figure 5. Photoelectron spectra of the Ln3d and An4d. levels of H[LnPc ](Ln = La, Ce, Pr, and Nd) and AnPc (An = Th and U). Deconvolution of the satellite structure is given by the dotted line. 5/2

J/2

2


2


3.

MIYAMOTO A N D TSUTSUI

Derivatives

of the {-Block

Elements

Journal of the American Chemical Society

Figure 6.

Structure of [Pc Nd(ni)]-H+ 2

400

(47)

395 Binding Energy (ev)

Figure 7. N Is signals of Pc NdH 2


55

56



Future P e r s p e c t i v e Up to the present time, s t u d i e s on organo-lanthanide complexes have f a l l e n almost e x c l u s i v e l y under the category of t r i v a l e n t - l a n t h a n i d e chemistry. When the o x i d a t i o n s t a t e o f organolanthanides i s reduced to 0, 1, o r 2, the s i z e of c o o r d i n a t i o n sphere and f - o r b i t a l p a r t i c i p a t i o n i n bonding would be a l t e r e d . Due to these e f f e c t s , low-valent organo-lanthanides w i l l show an increased v a r i e t y i n t h e i r r e a c t i o n f a c e t s and c a t a l y t i c a c t i v i ties . In s p i t e o f t h i s p o t e n t i a l f o r unusual chemistry, i n v e s t i gations of the r e d u c t i v e lanthanide chemistry has j u s t been s t a r t e d by one group (49). Co-condensation of 1,3-butadiene with lanthanides (Er, Nd, Sm or La) gave a v a r i e t y o f new organolanthanides; Er(1,3-butadiene) , E r ( 2 , 3 - d i m e t h y l - l , 3 b u t a d i e n e ) , Nd (1, 3butadiene)^, Sm(l,3-butadiene)^. The o p t i c a l s p e c t r a of these complexes do not c o n t a i n the u s u a l sharp absorption bands chara c t e r i s t i c of t r i v a l e n t l a n t h a n d i e s . The room temperature magn e t i c s u s c e p t i b i l i t i e s of these compounds are somewhat d i f f e r e n t from s u s c e p t i b i l i t i e s p r e v i o u s l y measured f o r t r i v a l e n t lanthanide s p e c i e s . The most s t r i k i n g d i f f e r e n c e s were observed f o r Sm(C^H^) and La[ ( C H ^ ^ C ^ H ^ ^ where the l a t t e r compound was the f i r s t r e ported paramagnetic organo-lathanum complex. A v a r i e t y of the metal-metal bonded complexes or c l u s t e r s a l s o provide a f o o t h o l d f o r the s t u d i e s of f - o r b i t a l p a r t i c i p a t i o n . Examples of such organo-lanthanide complexes i n c l u d e c y c l o p e n t a d i e n y l lanthanides with l a n t h a n i d e - t o - t r a n s i t i o n metal bonding C (n -C H ) LnW (n -C H ) (CO) (n -C H ) LnMo(n H ) (CO) (n -C H ? £nFe(n -C H )XC0) , ( n-C H ) ^ £ n 6 o ( C O ) , Ln = Dy, No, E r , Y b ^ \39); b i s c y c l o p e n t a d i e n y l erbium-triphenylgermane, -triphenylstannane and b i s c y c l o p e n t a d i e n y l y e t t e r b i u m - t r i p h e n y l stannane (50, 51). While s u b s t a n t i a l progress has been made i n e l u c i d a t i n g the nature of the f - e l e c t r o n p a r t i c i p a t i o n i n bonding, a number of problems remain. F i r s t , the question of whether 4f valence o r b i t a l s p a r t i c i p a t e i n bonding i n the ground s t a t e has not y e t been answered. More d e f i n i t i v e data a r e needed to r e s o l v e the question. A thorough examination of the s p e c t r o s c o p i c data of a s e r i e s of lanthanide complexes, together with a w e l l q u a l i f i e d M.O. approach, might provide the necessary i n s i g h t by which the question of f - o r b i t a l p a r t i c i p a t i o n i n bonding might u l t i m a t e l y be r e s o l v e d . We are g r a t e f u l f o r support by the Robert A. Welch Foundation (Grant No. A420) f o r the p r e p a r a t i o n of t h i s a r t i c l e . 2

3

4


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Literature Cited 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.

On leave from the University of Tokyo. V.M. Plets, Compt. Rend. Acad. S c i . , 1938, 20, 27. T . J . Marks, Prog. Inorg, Chem., 1978, 24, 51. T . J . Marks, Prog. Inorg. Chem., 1979, 25, 224. K.N. Raymond in "Organometallics of the f-elements," T.J. Marks and R.D. Fischer; E d . , Reidel Publishing Co., Dordrecht, Holland 1979, pp. 249-280. E . C . Baker, G.W. Halstead and K.N. Raymond, Struct. Bonding (Berlin), 25, 23 (1976). M. Tsutsui, N. Ely and R. Dubois, Acc, Chem. Res., 1976, 9, 217. H. Gysling and M. Tsutsui, Adv. Organomet, Chem., 1970, 9, 361. J.M. Birmingham and G. Wilkinson, J. Am. Chem. Soc., 1956, 78, 42. L . Reynold and G. Wilkinson, J. Inorg. Nucl. Chem., 1956 2, 246. C. Wong, T. Yen and T. Lee, Acta Cryst., 1965, 18, 340. E.O. Fischer and H. Fischer, J. Organomet. Chem., 1965, 3, 181. S. Manastyrskyj and M. Dubeck, Inorg. Chem., 1964, 3, 1697. M. Tsutsui, T. Takino, and D. Lorenz, Z. Naturforsch, 1965, 21B, 1. F. Baumgartner, E.O. Fischer, B. Kanellakopulos and P. Laubereau, Angew, Chem., 1965, 77, 866. F. Baumgartner, E.O. Fischer, B. Kanellakopulos and P. Laubereau, Angew, Chem. Int. Ed. in English, 1966, 5, 134. A. streitwieser, Jr., and U. Muller-Westerhoff, J . Am. Chem. S o c . 1968, 90, 7364. R.G. Hayes and J.L. Thomas, J . Am. Chem. Soc., 1969, 91,6876. K.O. Hodgson, F. Mares, D.F. Starks and A. Streitwieser, Jr., J . Am. Chem. Soc., 1973, 95, 8650. C.W. Dekock, S.R. E l y , T . E . Hopkins and M.A. Brantt, Inorg. Chem., 1978, 17, 625. A. Creco, S. Cesca, and G. B e r t o l i n i , J. Organomet. Chem., 1976, 113, 321. M. Tsutsui and H . J . Gysling, J . Am. Chem. Soc., 1969, 91, 3175. A. Gebala and M. Tsutsui, J . Am. Chem. Soc., 1975, 14, 78. J . L . Atwood, J . H . Burns, and P.G. Laubereau, J. Am. Chem. Soc., 1973, 95, 1830. S.A. Cotton, F.A. Hart, M.B. Hursthouse and A . J . Welch, J . Chem. Soc., Chem. Commun., 1972, 1225. M. Tsutsui, N. Ely and A. Gebala, Inorg. Chem., 1975, 14, 78. T. Marks, A.M. Seyam and J.R. Kolb, J . Am. Chem. Soc., 1973, 95, 5529 G. L u g l i , W. Marconi, A. Mazzei, N. Paladino and U. Pedretti, Inorg. Chim. Acta, 1969, 3, 253.


58 29. 30. 31.


32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47.

48. 49. 50. 51.


J . L . Atwood, C . F . Hains, Jr., M. Tsutsui and A . E . Gebala, J.C.S. Chem. Commun., 1973, 452. J . L . Atwood, M. Tsutsui, N. Ely and A . E . Gebala, J. Coord. Chem., 1976, 5, 209. A. Streitwieser, Jr., D. Dempf, G.N. LaMar, D.G. Karraker and N. Edelstein, J . Am. Chem. Soc., 1971, 93, 7343. G.W. Halstead, E . C . Baker and K.N. Raymond, J. Am. Chem.Soc., 1975, 97, 3049. J . H . Burns, J. Organomet. Chem., 1976, 69, 225. T . J . Marks and W.A. Wachter, J . Am. Chem. Soc., 1976, 98,703. M. Tsutsui and N. E l y , J. Am. Chem. Soc., 1974, 96, 3650. E . C . Baker, K.N. Raymond, T.J. Marks and W.A. Wachter, J.Am. Chem. Soc., 1974, 96, 7586. M. Tsutsui and N. E l y , J. Am. Chem. Soc., 1974, 96, 4042. M. Tsutsui and N. E l y , J. Am. Chem. Soc., 1975, 97, 3551. N. Ely and M. Tsutsui, J. Am. Chem. Soc., 1975, 97, 1280. N. Ely and M. Tsutsui, Inorg. Chem., 1975, 14, 2680. J . C . Burnes, J . Chem. Soc., 1964, 3880. E . C . Baker, L . D . Brown and K.N. Raymond, Inorg. Chem., 1975 14, 1376. J . Halton, M.F. Lappert, D.G.H. Ballard, R. Pearce, J.L. Atwood and W.E. Hunter, J.C.S. Dalton, 1979, 54. J . John and M. Tsutsui, to be submitted to J. Am.Chem. Soc. K. Tatsumi, M. Tsutsui, G.M. Beall, D.F. Mullica and W.O. Milligan, J . Elec. S p e c . 1979, 16, 113. K. Tatsumi, K. Kasuga and M. Tsutsui, J. Am. Chem. Soc., 1979, 101, 484. K. Kasuga, M. Tsutsui, R.C. Petterson, K. Tatsumi, N. Van Opdenbosch, G. Pepe and E . F . Meyer, Jr., to be submitted to J. Am. Chem. Soc. K. Tatsumi and M. Tsutsui, J . Am. Chem. Soc., In Press. W.J. Evans, S.C. Engerer and A . C . Neville, J . Am. Chem. Soc., 1978, 100, 331. A . E . Crease and P. Legzdins, J.C.S., Chem. Commun., 1972,268. A . E . Crease and P. Legzdins, J . Chem. Soc., Dalton Trans., 1973, 1501.

RECEIVED December 26, 1979.


Lanthanide and Actinide Chemistry and Spectroscopy - American

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