Indian Journal of Chcmistry Vol. 4 1 A, September 2002, pp. 1850- 1854

Crystallographic characterization of divalent organosamarium compound

(CSHS) 2Sm(THF)2*

S Jagannatha Swamy

Dep;] rtment of Chemistry, K;]btiya University, Wamng;]1 506009

Received 20 Novell/bel' 200 I ; revised 8 April 2002

The single pot re;]c ti on between SmX2 (X = CI-, 1-) ;]nd 'B uLi in THF at -40°C, followed by the ;]ddit ion of CsHs - N;]+ results in ;] dark red solution. Leav ing the concentrated reaction mi xture at - 25°C for two days in a deep freezer results in the formati on of thc crystals of the compound, (CsHs)2Sm(THF)2. The compound is inso luble in any solven t and it has been characterized by conventi onal methods. The crystals are monocl ini c with space group C2/c, and a = 13.416( I), b = 9.644( I), c = 14.129(2) pm, ~ = 109.873(9)° and z = 4 for P ealed = 1.64 g cm-3

. Least squares refi nement 0 11 the basi s of 1804 observed reOcctions has led to a final R value of 0.037 and R", = 0.054.

The organometalli c chemi stry of the most reacti ve . . . S Ili/S II divalent lanthanide metal lon, Sm(II) , With m m

couple of -1.15 Vi , has been extensively studi ed2

since 198 1. The organometallic compounds of the other two chemicall y accessible divalent lanthanides Eu(ll ) and Yb(IJ) were familiar si nce 1964 and 1966 respectively , because of the solubility of (CsHshEu, (CsHsh Yb and other monosubstituted cyclopenta­dienyl derivati ves3-s. A number of methods have been developed subsequently for the preparation of Eu(lI ) and Yb(II) organometallic compounds6

.7

. The Sm(ll) analogue (CSHS)2Sm(THF)x was first obtained by the reduction of (CSHS)3Sm with potassium and naphthalene in THF8. The organometalli c chemistry of Sm(TI) gained momentum with the preparation of the soluble complex with permethylated cyclopenta­dienide (CsMesf, first by using metal vapourizat ion technique2, and then by solution method IU.

1'1 2 . d h Subsequently, Evans et al. ·· have obtall1e t e unsolvated arene soluble complex, (CsMeshS m.

As part of our interest in divalent organolanth­an ides, we have invest igated the solubility of bis­(pentamethylcyclopentadienyl)samarium( lI) in a solvent other than tetrahydrofuran, i.e., dimethoxy-

Ded icated to Dr. P. Lingaiah, Professor of Chemistry, Kakati ya Univers ity on hi s 60'h Birthday and retirement from the servi ce in November 200 I.

ethane(DME)13. Further, we have reported a new soluble Sm(lI) organometallic compound with a stabilizing and solubilizing ring bridged di cyclopenta­dienide ' 4

. In continuation of our efforts to obtain heteroleptic organolanthanides, we accidentally obtained the title compound in crystalline form. The sy nthetic strategy, structural parameters of (Cs HshSm(THFh (I) and a comparative account of divalent organolanthanide complexes are described in thi s note.

Experimental The complex described in this note and other

reagents used are extremely air and moisture sensiti ve. Therefore, all operations were performed under rigorously purified argon by Schlenk and vacuum-line techniques. Pre-dried THF was distilled from sodium bezophenone ketyl immedi ately before use. THF-dg was dried by refluxing over sodium metal for several hours. Anhydrous SmCb was prepared by reducing SmCI3 in THF with Li and naphthalene2s, and the solution of Smh in THF wa prepared by the reaction between excess meta1 (Auer­Remy) and 1,2-diiodoethane I9. Elemental analyses were carried out with a Perki n-Elmer CHN-analyzer 2400. Metal analys is involved complexometric titration using dithizone26. Infrared spectra were recorded in paraffin mulls between Csf plates on a Perkin-Elmer 560B (200-4000 cm- I) spectrometer. IH NMR spectra were recorded for samples in sealed 5 mm tubes on a Brucker WP80 SY instrument.

Reactions To a suspension of 1.1 g (5 mmol) of red SmCI2 in

30 ml THF or to a 30 ml of solution of Smh(THFh (2.74 g, 5 mmol), 2.94 ml of 1.7M solution of IBuli (3.2 g, 5 mmol) in pentane was added slowly at -40°C. A violet solution was obtained. Then at the same temperature 0.79 g (5 mmol) of NaCsMes, containing an adventitious amount of NaCsHs, in 20 ml of THF was added in one experiment. In another experiment a solution of 0.44 g (5 mmol) of NaCsHs in 20 ml of THF was added slowly. [n both the cases the colour of the solutions changed to dark red. The reaction mixture was stirred for another 3 hours, concentrated to 20 ml by removing the solvents under vacuum and then filtered through a fine frit. The

NOTES 1851

Table I- Crystal data and summary of intensity data co llecti on and structure refin ement for (C, H,hSm(THF)2

Formul a

Formula weight, g mol- I

Cell constants, pm

Cell vo lume, 10-30 m3

Z

PeI.e, g cm-3

F(OOO)

fl, cm- I

Crystal dimensions, mm

Crystal system

Space group

Di ffrac tometer

Rad iation, A., pm

Monochromator

Temperature, OK

Scan technique

20 limits

h, k, I - limits

Refl ec ti ons measured

Number of unique data

Number of observed refl ec tions

Maxi mum shi ftlerror

Number of refi ned parameters

Parameter/F" - proportion

R = L: II Fa 1- I Fe II 1 L: I Fo I Rw = (L:w( I F" 1- I Fe I )21 L: w I Fo 12]"2 W = g/s(Fo)2 + k(Fo)2

concentrated solution was left in a deep freezer at about -25°C. Purple crys tals were found after 2 days, which were filtered (0.26 g, 14%) and used for CHM analyses and recording IR spectra. Analytical results: Found (%) - C, 50.42, H, 6.25 , Sm, 35. 13, calculated for Ct SH260 2Sm (%) - C, 50.9, H, 6.17 , Sm, 35.4. IR (Nujol/polychlorofluoroethylene o il , cm -I) 3080, 1475, 1347 , 1308, 1263 , 1070, 1008, 775 , 740 ass ignable to v(C-H) and 8(C-H) of Cp and 2980, 2880, 1375 , 725 and 565 attributable to coordinated THF.

X- ray crystallography of( C5H5hSm(THFh A single crystal measuring 0.49 x 0 .27 x 0.23 mm

was selected from the suspension taken in a dev ice reported by Veith and Barninghauscn27

. It was fas tened to a glass fiber with grease and placed in the cold nitrogen stream in the X-ray di ffractometer, Enraf- Nonius CA D4.

The data were co llected by the C1}-28 scan technique with Mo-Ka radi ation (A., 71 .073 pm). The

C IsH260 2Sm 424.74

a = 13.4 16(1 ),b = 9.644( 1)

c = 14. 129(2), ~ = 109.873 (9)

17 19.2(3)

4

1.64

848

32.37

0.49 x 0.27 x 0.23

Monocl ini c

C2/c

CA D 4

Mo- Kw 7 1.073

Graphite

11 0(5)

(3- 28

1 :s 2(3:s 53

O:S h :s 15, 0 :s k :s I I, -1 6 :s I :s 16

20 14

1937 (Ri ot = 0.039)

1864

0.000 1

96

19.4

0.037

0.054

K = 0.001047, g = 1.0

parameters are given in Table 1. The final lattice parameters were determined from least squares refinement of intensities in the limits 0 ::: h ::: 15, 0 ::: k ::: 11, -16 ::: I ::: 16; from 28 values of 25 computer centered reflections in the range of 1 ::: 20 ::: 53°, measured at 110 K. Initial investigation showed the crystal system to be monoclinic with space group Cc, and C2/c from the systematic absent refl ections. The successive refinements confirm the C2/c space group. Three refl ections were checked every hour and the maximum fluctuation was found to be -1.7%. Thc crystal orientation was checked after each 200 intensity measurements by scanning three orientation check refl ecti ons. In case of angular change greater than 0.1 ° an alTay of 25 refl ections was re-centered. The intensities were corrected for Lorentz and polari zation effects. No absorption correc tion was made (Il = 32.37 cm- I

) .

The pos itional parameters of the samarium atom were calculated fro m the patterson map. A di fference Fourier map based on the metal atom phase revea led

1852 INDI AN J CHEM. SEC A, SEPTEMBER 2002

Table 2-Selected interatomi c distances" (pm) and angles (degrees) for (C5H5hSm(THFh. Cp denotes the centroid of the

cyc lopentad ienyl group

Bond Distance Atoms An gle

Sm - O 240.7(4) CS - Sm - 0 90.2(2)

Sm - C5 271. 1(8) C6 - Sm - O 11 7.6(2)

Sm - C6 27 1.9(7) C7 - Sm - 0 135 .8(3)

Sm - C7 266.7(8) CR - SIll - 0 11 5.0(4)

Sm - C8 268.8(8) C9 - SIll - 0 R7 .7(3)

Sm - C9 268.5(7) C I - O - Sill 13 1.8(4)

Sm - Cp 242 .2(5) C4 - 0 - Sm 120.3(4)

o - Sm - 0 R2 .0(2)

Cp - Sm - Cp 129.8( 1)

Cp - Sm - 0 I 10.4(2)

*Estimated standard dev iati ons of the last signifi ca nt digit are given in parentheses

the positions of all non-hydrogen atoms. Least squares refinement with isotropic thermal parameters led to R = L II Fo I - I Fe II / L IFo I = 0.037. The hydrogen atom positions were calcul ated (dc-I'I = 0.95 pm) and added to the structure model with constant

o 2 temperature fac tor (Uiso-H = 0.08 A ). After all atoms in the structure have been positioned, the empiri ca l absorption corrections were made (minimum and maximum correcti on factors were 0.666 and 1.736). The fin al difference Fouri er showed a max imum electron density of 1.05 e -/ A 3 near the heavy metal.

All calculati ons were perfo rmed with the programme SH ELX-7628. Atomic scattering fac tors fo r Sm were taken from ref. 29, and anomalous di spersion terms from ref. 30 (The data have been deposited at the Fachinformationxzentrum Enraie b ,

Physic, Mathemati k GmbH , D-75 14, number CS D 53204). Additional data pertaining to the crystal structure determinati on are summari zed in Table I. Selected interatomi c di stances and angles are listed in Table 2.

Resu lts and discussion Namy et al. ls , have reported the sy nthetic

applicati ons of the inso luble (CsHs)2Sm(TH F)x in Barbier type reactions between alkyl halides and aldehydes/ketones. The reac ti ons of the solu ble complex (CsMes)2Sm(TH Fh were in vestigated extensively which resulted in interesting products, (CSMeS)3SmI 6, (CsMeshSmh(N2)17 and [(CsMes)2Sm(THF)] [CoCCO)"] IS. Because of the inso lubility of the complex, (CsHshSm(THF)" it was characterized by elemental analys is, magneti c susceptibility and IR spectral data9

.19 only. Deacon

et al.2o, have obtained the soluble derivative of Sm(IT)

with cyclopentadienyl by reducti on of (CsHshSm with potassium in presence of benzophenone in TH F. They reported the DM E soluble spec ies as K+ [(CsHsh Smr.

In one of our attempts to prepare heteroleptic Sm(lI ) and Yb(II ) deri vati ves, contallllllg a pentahapto li gand, CsHs/CsMes and an alkyl group, we observed the formati on of compound, I in crysta ll ine fo rm. Earlier, we have reported the preparati on of (CsHs)YbCI(THF)/ I. The reac tion of (CsHs)YbCl (THFh with RLi did not give any characteri zable product. Then we have tri ed another route fo r the preparation of the organolanthanides .

- 40°C - 40°C SmX2 + 'BuLi THF . • 1+ Y .. . (1 )

NaCs Hs

On addition of IBuLi to the suspen ion of red Smh , a violet solution was obtained, which turned red on additi on of NaCsRs in THF. From the concentrated reaction mi xture, after removal of alkali metal halides, red crystals were obtained which analyzed for the formul a CI SH200 2Sm.The other substance Y could not be charac teri zed. Further, the IR spectrum of the product was the same as reported fo r (CsHs)2Sm(THF)x' The formation cf the compound was attributed to the presence of an adventitious quantity of NaCsHs or IBuLi , and the compound I was crystall ized from the soluti on as its solubility is very low. Then si milar reac ti ons were repeated with NaCsHs. The same colour changes were observed. The solid obtained exhibited simi lar IR spectrum and analyti cal data were also identical. Then we have tried to obta in the I H NM R spectrum of the complex as follows. A few drops of the reaction mixture was dried completely in a Schlenk fl ask to whi ch an NMR tube was fused, and TH F-ds was added to the fl ask. The solid dissolved completely. The solubility of the tit le compound in the present investigation may be attributed to the presence of a sli ght excess of IBuLi and/or NaCsHs, whi ch solubili ze th e Sm(lT) complex by fo rming an ion pair as reported by Deacon et a1. 20

.

The principal signals in the spectrum [8, ppm] are 5.5 (C sHs), 3.5 and 1.6 (TH F H's) and another signal at -18.6 was observed, which may be due to the IBu_ protons (a sati sfactory analysis could not be obtained fo r the species in the solution).

Molecular structure of (C,H5hSm(THFh The ORTEP di agram of the crystal structure of the

comp lex (CsHsh Sm(THFh is giver: in Fi g. 1. The crys tal data, atomic pos itional parameters, anisotropic

NOTES 1853

Table 3-Structural data of divalent organolanthanides , (C, R' )2M.On (0 = donor molecules, n = 2 or I)

Complex Average M- C di stance, A

(C,H,h Yb(OME) 2.72

[(MeC, H4)Yb(THF) 2.76,2 .87,2.91 (/-l-Me(CsH.j)]n

(CsMesh Yb(NC, H')2 2.74

I C, H4(C H2hCsH.j)Yb(TH Fh 2.706

(CsMe\hEu 2.79( I)

(CSM eS)2Sm 2.79

(CsHshSm(TH F)z 2.86

[(CsMe,)Sm(/-l-I)(THFhh 2.8 1 (2)

(C, Mes)S mCI (OM E).O ME 2.79

(Cs HshSm(THFh 2.69(2) [(CSMc5hSm@h(N2) 2.73(2)

# (I - Sm - I), @ Sm in +3 oxidati on state, $ Present work

Fig. I- Molec ular structure of (CSH,)2Sm(THFh and numbering scheme

temperature factors and selec ted bond lengths and bond ang les of the complex I are g i ven in Tables I and 2 respecti vely . The structural data o f a few related di va lent organolanthanides are presented in T able 3 fo r compari son.

M - O Cp- M- Cp O- M- O Ref di stance, A angle (deg) angl e (deg)

2.45(3) 0 129 67.2(9) 22 2.50(3) 0

2.53(2) 0 23

2.586(7) N 136.3(3) 82.5(2) 24 2.544(6) N

2.42( 1) 0 127 ( I) 82.4(5) 14 2.4 1( 1) 0

140.3 12

140. 1 11 , 12

2.6 1(2) 0 136.7 82.6(4) 2, 10 2.65(2) 0

2.62(2) 0 73.5 (6) 10 2.66(2) 0 82.04(5)#

2.52( I) 0 140.0 62.8(4) 13 2.6 1(2) 0

2.407(4) 0 129 .8( 1) 82 .0(2) $ 2.3 N 2.68(3 ) 16 2.4 N

The smalles t (ring centro id)-Sm-(ring centroid)

ang le of 120° was reported for the Sm(lll) complex in (Cs MeshSmI 6. T he observed ang le in the compound I, 129 .8( 1)°, is the smallest angle observed to date for a Sm(lI) complex. The ang le in other pentamethylcyc lo pentadi enyl complexes is in the

range of 136.7°- 140.1°. Thi s smallest Cp- Sm-Cp ang le indi cates less steri c interactions between the CsHs rings as compared to the CsMes rings . The smalles t (ring centro id)- Yb-(ring centro id) ang le,

127(1 )°, was fo und in the case of ring bridged complex [{ CsH~(C H 2 ) 3CsH4 1 Yb(THFh J 14 . Whi Ie in the case of an open CP2 compl ex with a chelating solvent molecul e (DME) the rings are slightly far

apart, 129°, in (CsHsh Yb(DM E)22. The O-Sm-O

angle, 82.0(2r is in the same o rder as observed in ··1 1 · h d THFO I()JO I ~ stlm ar co mp exes WI t mo no entate -.. -. or

py ridine24 coordinated to Sm(lI) and Yb(ll ).

The average Sm- C(ring) distance in I , 2.69 A, is the shortes t observed to date between ri ng carbon atoms and Sm(ll) r2.79-2 .86 A], and is c lose to that reported in cyclo pentadi enyl22 and ring bridged

1854 INDIAN J C HEM, SEC A, SEPTEMBER 2002

dicyclopentad ienyl14 complexes of Yb(U). The S m- O distance, 2.407(4) A, is al so the shortest of all the reported bond lengths between Sm(II) and coordinated oxygen atoms of the solvent mo lecul es, 2.62-2.66 A. However, O-Sm-O bond angle in I (82.0°) is in the same order as reported for

(CsMeshSm(THFh (82.6°) and larger than observed in the compl ex with che lating DM E, 62 .8° (ref. 13), and iodide bridged mo nocyclopentad ienyl complex ,

[(CsMes)S m(THFh l-l-l )h (ref. 1 0)

Acknowledgement The work was carried out In the laboratori es of

Prof. Dr. H. Schumann in Techni sche Universitat Berlin . The author thanks Prof. Dr. H. Schumann for providing facilities and also thankful to Prof. W. J. Evans, Univers ity of California, Irvine for his valuable suggestions during the preparation of the manuscript. Further, the senior fe llowship of DAAD under re-in vitation programme is acknowledged.

References I Morss L R, Chelll Rev, 76 (1976) 827. 2 Evans W J, Bloom L, Hunter W E & Atwood J L, J A lii chelll

Soc, 10 (198 1) 6507. 3 Fi scher E 0 & Fischer H, Angew Chelll , 76 ( 1964) 52. 4 Fi sc her E 0 & Fi scher H, J orgal1oll1el Chell1, 6 ( 1966) 141. 5 Calderazzo F, Pappalardo R & Losi S, J inorg nllci Chell1 , 28

( 1966) 987. 6 Evans W J, Wyda A L, Hunter W J & Atwood J L, J chelll

Soc, Chell7 COIII IllUI1 , (198 1) 292. 7 Evans W J, Dominguez R & Hanusa T P, Organomelailics, 5

( 1986) 263 . 8 Deacon G B & Newnham R H, Ausl J Chelll , 39 ( 1985)

1757.

9 Watt G W & Gi ll ow E W, J Am chem Soc. 29 ( 1969) 775 . 10 Evans W J, G rate 1 W, Choi H W, Bloom I, Hunter W E &

Atwood J L, J Alii chelll Soc, 107 ( 1985) 94 1. II Evans W J, Hughes LA & Hanusa T P, J Alii chelll Soc, 106

( 1984) 4270. 12 Evans W J, Hughes I A & Hanusa T P, Organollletallic.\'. 5

( 1986) 1285 . 13 Swamy S 1, Loebel 1, Pickardt J & Schuman n H, J

organolllel Chelll , 353 ( 1988) 27. 14 Swamy S J, Loebel J & Sch uman n H, J organomel Chelll ,

379 ( 1989) 5 1. 15 Namy 1 L, Collin J, Zhang 1 & Kagan H B, J organolllel

G elll , 328 ( 1987) 8 1. 16 Evans W J, Gonza les S L & Z ill er 1 W, J Alii chelll Soc, 11 3

( 1991 ) 7423 and re fere nces there in . 17 Evans W J, Ullibari T A & Z iller 1 W. J Alii chelll Soc, 110

( 1988) 6877. 18 Evan s W J, Bloom I , Grate 1 W, Hughes L A, Hunter W E &

Atwood J L, Inorg Chelll , 24 ( 1985) 4620. 19 Namy J L, Gira rd P & Kagan H B, NOll v .I Chemie, 5 ( 198 I)

479. 20 Deacon G B, Pain G N & Tuong T D, Polyhedron, 4 ( 1985)

11 49 2 1 Swamy S J & Schu mann H, J organomel Chelll , 334 ( 1987)

I. 22 Deacon G B, Mack innon P I, Hambley T W & Tay lor J C, .I

organolllel Chelll , 259 ( 1983) 9 1. 23 Zinnen H A, Pluth 1 J & Evans W J, J chem Soc, Chem

COIIIIllUII , ( 1980) 8 10. 24 Tilley T D, Andersen R A, Spenner B & Zalkin A, Inorg

Chem, 2 1 ( 1982) 2647. 25 Rossman ith K, Monlsch Chem, 110 (1979) 109. 26 lander G & Blasius E, Einfuhrung ill das Anorganisch­

Chemische Praklikwn , S Hirzel Verl ag, Stuttgart , 1973, pp 351.

27 Ve ith M & Barninghausen H, Acla Crysl B, 30 (1974) 1806. 28 Sheldri ck G M, SHELX- 76 System of programme, 1976 . 29 Croner D T & Mann J B, ACla Crysl A, 24 ( 1968) 321. 30 Croner D T & Libermann D], J chern Phys , 53 (J 970) 189 1.