Synthesis and characterization of volatile mixed-metal yttrium-barium, barium-copper and yttrium-copper β-diketonatofluoroisopropoxides. Molecular structure of BaY 2[ μ-OCH(CF 3)

~ ) Pergamon 0277-5387(95)00557-9

Polyhedron Vol. 15, No. 16, pp. 2707--2718, 1996 Copyright © 1996 Elsevier Science Ltd

Printed in Great Britain. All rights reserved 0277 5387/96 815.00+0.00

S Y N T H E S I S A N D C H A R A C T E R I Z A T I O N O F V O L A T I L E

M I X E D - M E T A L Y T T R I U M - B A R I U M , B A R I U M - C O P P E R A N D

Y T T R I U M - C O P P E R , 8 - D I K E T O N A T O F L U O R O I S O P R O P O X I D E S .

M O L E C U L A R S T R U C T U R E O F BaY2[~-OCH(CF3)2]4(thd)4

FLORENCE LABRIZE and LILIANE G. HUBERT-PFALZGRAF*

Laboratoire de Chimie Mol6culaire, URA-CNRS, Universit6 de Nice-Sophia Antipolis, Parc Valrose, 06 108 Nice Cedex 2, France

and

JEAN-CLAUDE DARAN and SABINE HALUT

Laboratoire des M6taux de Transition, URA-CNRS, Place Jussieu, 75 230 Paris, France

and

PASCAL TOBALY

Laboratoire d'Ing6ni6rie des Mat6riaux, URA-CNRS, 93430 Villetaneuse, France

(Received 17 October 1995 ; accepted 22 November 1995)

Abstract--Heterometallic complexes [YBa2(HFIP)7(THF)3] (1) and [BaCu(HFIP)4(DME)2] (2); HFIP = 1,1,1,3,3,3-hexafluoro-2-propoxide) were obtained by metathesis reactions between YC13 or CuCI2 and "Ba(HFIP)2" obtained in situ or by using the isolated barium hexafluoroisopropoxide [Bas(OH)(HFIP)9(THF)a(H20)]. The fluoroisopropoxides [Y(HFIP)3(THF)3] (3) and [Yz(HFIP)2(thd)4] (4) are alternative yttrium sources. Volatile mixed-metal complexes [YzBa(HFIP)4(thd)4] (5), [BaCu2(HFIP)4(thd)2] (6) and [YCu (HFIP)(thd)] (7); thdH = 2,2,6,6-tetramethyl-3,5-heptanedione) were synthesized by reacting 1, 2 or 3 with tetramethylheptanedionates of yttrium, copper and barium or directly with Hthd for 5 and 6. An alternative route to 5 was the reaction of 4 with [Bas(OH)(HFIP)9(THF)4(H20)]. The compounds were all obtained in high yields. They were characterized by elemental analysis, mass spectrometry, NMR (IH, 19F, 13C {IH}) and ESR spectroscopy, as well as vapour pressure measurements and single-crystal X-ray diffraction for 5. The volatilities of compounds 5, 6 and 7 are in the range 150-170'~C/10 -3 Torr and are the best encountered among mixed-metal compounds containing barium, yttrium and copper. Copyright © 1996 Elsevier Science Ltd

Key words ." MOCVD, fl-diketonates, fluoroalkoxides, barium, yttrium, superconductors.

The interest in metal organic chemical vapour deposition (MOCVD) 1 for the preparation of thin films of the high-temperature superconductor YBa2

* Author to whom correspondence should be addressed.

C u 3 0 7 x has prompted intensive research into the development of new precursors for these materials. While there are satisfactory metal oxide sources for yttrium and copper, barium derivatives are less favourable in terms of vapour pressure and thermal stability. The barium fl-diketonates, which are the

2707

2708 F. LABRIZE et al.

most commonly used barium sources for the deposition of YBazCu3OT_,, display reduced volatility and poor stability. This is particularly true for the 2,2,6,6-tetramethyl-3,5-heptanedionate derivative "Ba(thd)2", whose volatility and thermal behaviour are dependent on synthesis and purification methods, on storage conditions and thus on for- mulation.

A number of barium alkoxides and/~-diketonates have been structurally characterized in the solid state recently. Their oligometric nature, allowing the metal to reach high coordination numbers, accounts for their lack of volatility. Thus, barium tetramethylheptanedionate synthesized in aqueous solution is pentanuclear [Bas(OH)(thd)9(H20)] when obtained by recrystallization in pentane according to Sievers, 2 while the tetramer [Ba(thd)2]4 was first isolated by sublimation by Gleizes. 3 Com- plexation with O- or N-Lewis bases has been con- sidered as a means of decreasing the molecular complexity of barium tetramethylheptanedionate and thus increasing its volatility. Numerous complexes of low nuclearity have emerged such as the dimers [Ba(thd)2L2]2, L = NH3, 4a E t 2 0 , 4b

[Ba(thd)z(diglyme)]2, 5 [Ba(thd)z(ArOH)2(THF)]26 and the monomers [Ba(thd)z(MeOH)3, MeOH], 7 [Ba(thd)2(triglyme)]8 and [Ba(thd)z(tetraglyme)]9 (triglyme = 2,5,8,11-tetraoxadecane ; tetraglyme = 2,5,8,11,14-pentaoxapentadecane). We have isolated and structurally characterized the dimer [Ba(thd)2(HOCHMeCH2NMe2)]210 and the monomer [Ba(thd)2(TMEDA)2] II (TMEDA = N,N,N' ,N'- tetramethylethylenediamine). However, all these complexes dissociate upon sublimation yielding oligomeric [Ba(thd)2]m and free ligand and thus do not offer a significant improvement of the transport properties. More stable adducts have been reported recently with polyamines. ~2 In the case of barium hexafluoroacetylacetonate, which adopts an infinite chain structure when coordinated to monodentate O-donors, [Ba(hfac)2L]~, L = H20, TM Et20,13b, complexation with polyden- tate ethers offers monomeric adducts Ba(hfac)2L (L = tetraglyme 9 and 18-CRW-6 = 1,4,7,10,13,16- hexaoxycyclooctadecane~4), which are retrained in the vapour phase. The effect ofintramolecular coordination has been evaluated using O-functional fl- diketonates. 15 Barium fl-ketoiminate complexes containing appended ether "lariats" have been used as a volatile source of barium oxide, although they also display a limited thermal stability. 16

Barium alkoxides are mostly non-volatile oxo or hydroxo aggregates of five, six or more barium atoms, such as [H4Ba6(u6-O)(OCzHaOMe)I4], 17 [Bas(OH)(OAr)9(THF)n], (Ar = Ph, n = 8,18~ 3,5- Bu~C6H3, // : 518b) and [H2Bas(#6-O)(OPh)I4{N-

Me2)3PO}]. J9 By choosing bulky alcohols and silan- ols, oxo- or hydroxo-free barium alkoxides of lower nuclearity such as the tetramer [Ba(OBut)2 (HOBut)2]4 .2° The trimer [Ba3(OSiPh3)6(THF)" 0.5THF], 21 the dimers [Ba2(OR)4(THF)3] (R = CPh3, SiBut3) 22 and various monomeric aryloxide complexes 23 could be stabilized, but these compounds remain non-volatile. Recently, Herrmann e t al. have used the tailored alcohol HOC(PP) (CH2OR)2 to obtain solvent-free barium alkoxide, 24 which are volatile at 170°C (R = Pr i) and 185°C/ 10 2 Torr (R = Et) and which are assumed to be dimeric by comparison with their calcium and cad- mium analogues.

Non-volatile barium-copper compounds of different stoichiometries have been published, namely [Ba2Cu2(OR)4(/~-dik)4(ROH)2] (/%dik= acac, R = C2H4OMe;/%dik = thd, R = C2H4OMe, C2H4OC2HgOMe, C3H6OMe), 25 [BaCug(OC2H4 OMe)6(thd)4], 26 [BaCu(CzH6Oz),(CzH402)2], 27 and [Ba2Cu4(OCEt3)8].28 By contrast, the fluorinated derivative [BaCuz[OCMe(CF3)2]6], obtained in moderate yield, displayed some volatility. 29 A non-volatile yttrium barium oxo-/~-diketonato- alkoxide [Y4Ba2(/~6-O)(OEt)8(thd)6] has also been reported. 3° Yttrium~zopper compounds are represented by non-volatile /%diketonatoalkoxides, [YCu3(OR)5(thd)4], [YCuz(OR)6(hfd)4] and [YzCu4(OR)6(thd)4(hfac)4] 31~ (R = CzH4OMe) and by a yt t r ium~opper(I) siloxide. 3'b

We have selected bulky alcohols (tert-butanol, 2,6-dimethylphenoxide), functional alcohols (tri- ethanolamine 32 and dimethylamino-2-propanol 1~) and fluoroalcohols as a means of building up mixed- metal species, l , l , l ,3,3,3-Hexafluoro-2-propanol (HFIPH) allowed access to volatile homometallic derivatives [Bas(OH)(HFIP)9(THF)4(H20)], TM

[Y(HFIP)3(THF)3] and [Y(HFIP)(thd)2]2, 33b previously described, as well as to volatile mixed-metal derivatives [Y2Ba(HFIP)4(thd)4], [BaCu2(HFIP)4 (thd)2] and [YCu(HFIP)2(thd)3] in high yield, which are described here. Their characterization was achieved by elemental analysis, FT-IR, N M R (1H, ~3C and 19F), ESR, mass spectrometry, TGA and single-crystal diffraction investigation for [YzBa(HFIP)4(thd)4]. Vapour pressure data have been determined. Part of this work has been published as a preliminary communication. 34

EXPERIMENTAL

All manipulations were performed under dry nitrogen using Schlenk tubes and vacuum-line tech- niques. Solvents were purified by standard methods. Fluoroisopropanol and the fl-diketone were dried over 3 A molecular sieves prior to use.

Synthesis and characterization of volatile mixed-metals

YC13 (Aldrich) was used as received. [Ba(thd)2]4,1° Y(HFIP)3(THF)3 and Y(FHIP)(thd)233b were prepared as reported. Cu(thd)2 was prepared by reacting Cu(OAc)2 and Hthd in 1 : 2 ratio in methanol and recrystallized in hexane. Y(thd)3 was isolated from reaction between YsO(Oipr)1335 and Hthd (1:15) in hexane followed by sublimation. N M R spectra were recorded on a Bruker AC-200 spectrometer. CFC13 was used as an 19F N M R internal reference, upfield chemical shifts are given negative. Molecular weights are determined using the Signer method. 36 ESR spectra were obtained using a E-200 Bruker spectrometer. IR spectra were recorded as Nujol mulls on a IR-FTS 45 spectrometer. Mass spectra were recorded on a R10-10 Ribermag spectrometer at 70 eV. Thermogravimetric analysis (TGA) data were obtained on a Shimadzu TGA- 50H at a heating rate of 5°C m" n - ~ under nitrogen at a flow rate of 50 cm 3 min -~. The volatiles were analysed for 5 using a FT-IR IFS 66 spectrometer coupled to the TGA system. Melting points were determined in capillaries and are given uncorrected. Microanalyses were performed at the centre de Microanalyses du CNRS.

Vapour pressure measurements

Description of the apparatus which allows the measurements of vapour pressure in the range 10 -2 100 mm Hg has been reported. 37 It is based on a static null-method controlled by a computer through a regulation loop. The uncertainty on temperature is 0.3°C, while the thermal stability was better than 0.1 °C. The uncertainty in the pressure measurement is of the order of 0.01 Pa.

Synthesis" of[YBa2(HFIP)7(THF)3] (1)

Barium granules (3 g, 21.84 mmol), hex- afluoroisopropanol (5 cm 3, 47.5 mmol) and T H F (60 cm 3) were stirred for 3 h, all metal was then consumed. After filtration, the solution was added to a suspension of YC13 (1.22 g, 6.24 mmol) in tolene/THF 1:2 (60 cm3). Solubilization was first observed then the medium became opaque. The suspension was stirred at room temperature for 15 h and refluxed for 2 h. After decantation, BaC12 was removed through a celite pad and washed by toluene/THF. The filtrate was stripped to dryness. After dissolution of the crude product in toluene/THF (30 cm 3, 7 : 1 in volume), crystallization of 1 occurred at - 2 0 ° C ; yield 7.59 g, 75% ; m.p. 100~C; subl. 200°C/10 -3 Torr (dec). Compound 1 is insoluble in hydrocarbons, but soluble in ether and THF. Found: C, 22.9; H, 1.7; F, 38.4; Ba, 15.5; Y, 5.5. Calc. for C33H31Fa2OIoBa2Y : C, 22.6;

2709

H, 1.8; F, 45.6; Ba, 15.7; Y, 5.1%. ~H N M R (CDC13): 5.21 [hept, J(HF) = 6.5 Hz); 4.75 [hept, J(HF) = 6.5 Hz] ; 4.54 [hept, J (HF) = 6.5 Hz] ; 4.45 m (2 : 2 : 2 : 1, 7H, CH) ; 3.7 (t, 12H, THF), 1.95 (t, 12H, THF). ~9F N M R (CDCI3): - 7 2 .3 (s, Avm = 19 Hz); -76 .1 (s, Avm = 17 Hz); - 7 6 (s, Arm= 17 Hz); - 7 7 .8 (A~/2 = 17 Hz; 2 : 2 : 1 : 2 , CF3). IR (cm-1) : 1292 m, 1265 s, 1226 m, 1215 m, l184s, l172SV(c v),V(c o);1091w, 1078s, 918w, 887 s, 844 s, [V(c c)] ; 802 s, 740, 680 ; 534 w, 521 w, 460 m, 399 w v(y_o), v(Ba-ol.

Attempts to solve the structure were unsuccessful due to disorder of the HFIP ligands at room temperature; a phase transition at - 1 0 ° C precluded data collection at low temperature.

Synthesis of[BaCu(HFIP)4(DME)2] (2)

Barium granules (2.8 g, 20.5 mmol) and hex- afluoroisopropanol (4.3 cm 3, 40.85 mmol) were allowed to react in toluene/DME 5 : 1 (60 cm3). The metal was consumed in 4 h. After filtration, the solution was added to a brown suspension of CuC12 (1.38 g, 10.25 mmol) in toluene/DME 5: l (60 cm3). The suspension was stirred for 48 h, giving a blue precipitate. Refluxing for 30 min resulted in partial solubilization, leaving a white solid in a dark blue liquor. BaC12 was removed on a celite pad and washed by toluene/DME. On cooling to -20°C, turquoise-blue crystals of 2 formed (9.4 g, 73%). Compound 2 is insoluble in hydrocarbons, but soluble in ethers ; subl. 220°C, 10 .3 Torr (dec). Found : C, 22.1 ; H, 2.2; F, 36.4; Ba, 12.8; Cu, 6.1. Calc. for C20H24F24OsBaCu : C, 22.9 ; H, 2.3 ; F, 43.9 ; Ba, 13.1; Cu, 6.0%. 19F N MR (C6D6): - 7 6 (AVl/2=660 Hz). ESR (hexane, room temperature): ( 9 ) = 2 . 0 8 . IR (cm-~): 1311, 1285, 1257, 1225, 1211, 1170 V(c_v), V(c o); 1109, 1093, 1067, 1022, 982, 966, 889, 856, 632, 588, 534, 526, 467, 434, 419 Vma o), V(cu o). #err = 1.88 B.M.

Synthesis of[Y2Ba(HFIP)a(thd)4] (5)

To a suspension of 1 (2.56 g, 1.46 mmol) in hexane (60 cm 3) was added a solution of Y(thd)3 (1.86 g, 2.92 mmol) in hexane (30 cm3). Progressive solu- bulization occurred. After filtration of the hot solution, a large crop of crystals formed on cooling the filtrate. Their sublimation (150°C/10 3 Torr) gave 2.8 g of 5; yield 74% ; m.p. 150°C; deg. 170°C. Found: C, 39.0; H, 4.5; Ba, 8.1 ; Y, 10.5. Calc. for C56HsoF24012BaY2 : C, 39.2; H, 4.7; Ba, 8.0; Y, 10.4%. ~H N M R (CDCI3) : 5.68 [s, 1H, CH(thd)] ; 4.75 [br, 1H, OCH(CF3)2] ; 1.09, [s, 18H, C(CH3)3]. 19F N M R : -- 76.14 (s, Avl/: = 26 Hz). 13C{IH} 202.3 (s, C---O) ; 121.5 [q, J(CF) = 288 Hz, CF3]; 92.4 [s,


CH(thd)]; 73.2 [hept, J(CF) = 47 Hz, CH(CF3)2] ; 40.3 [s, C(CH3)3] ; 27.2 [s, CQC_H3)3]. MS (El, 70 eV, m/z +, %): Y2Ba(HFIP)3(thd) (1), F2YBa(HFIP)3 (thd) (2), YBa(HFIP)2(thd)2 (4), YBa(HF|P)3(thd) (1), YBa(HFIP)2(thd) (1), Y(thd)3 (47), Y(HF|P) (thd)2 (6), FYBa(HFIP)(thd) (2), Y(thd)2(BuCO CHCO) (100), Y(thd)2 (72), Y(UFIP)(thd) (7), Y(HFIP)2 (3), FBa(BuCOCHCO) (5), Ba(BuCOCHCO) (7), CF 3 (4), Bu (47), |R (cm-~) : 1602 m, 1584 s, 1573 s, 1557 vs, 1544 s, 1508 vs V~c=o), V(c=c); 1271 m, 1227 vs, 1181 sh, 1161 vs, 1144 s V(c o), V(c v); 1090 S, 1022 W, 965 W, 935 W, 872 m, 845 m, 799 w, 769 w, 744 m, 686 m ; 610 w, 521 w, 493 w, 476 w, 414 sh, 393 sh, 378 sh V(Ba O),

Y(Y O)"

Compound 5 could also be obtained by reacting [Bas(OH)(HFIP)9(THF)4(H20)] (1.64 g, 0.65 mmol) and Y(HFIP)(thd)2 (1:9 molar ratio) (yield 81%) or by reacting 1 and thdH (1 : 2 stoichiometry, yield 45%). Reaction between Y(HFIP)3(THF)3 and Ba(thd)2 (1 : 1 molar ratio) also yielded 5 (64%). All reactions were in hexane.

Synthesis of BaCu2(HFIP)4(thd)2 (6)

A solution of Cu(thd)2 (1.51 g, 3.51 mmole) in hexane (40 cm 3) was added to a turquoise-blue suspension of 2 (3.68 g, 3.51 mmol) in hexane (80 cm3). The precipitate progressively dissolved while the colour changed to purple. The reaction medium was stirred for 2 h. After cooling to - 20°C, purple crystals were isolated. Their sublimation at 170°C/10 -3 Torr gave 4.1 g of 6; yield 90%, m.p. 180°C, no decomposition up to 220°C. Found : C, 31.1; H, 3.4; Ba, 10.3; Cu, 9.5. Calc. for C34H42F24OsBaCu2 : C, 31.4; H, 3.2; Ba, 10.5; Cu, 9.8%. ESR (hexane, room temperature): (g ) = 2.107, ( A) = 79.9 G. MS (El, 70 eV, m/z + %): M-2HFIP (31), M-HFIP-thd (22), M-2HFIP- thd (5), M-HFIP-2thd (4), BaCu(HFIP)2(thd) (21), BaCu(HFIP)(thd) (16), BaCu(HFIP)2 (7), BaCu(HFIP)(BuCOCHCO) (9), Cu(thd)2 (3), FBa- Cu(HFIP) (8), Cu(thd)(BuCOCHCO) (11), FBa- Cu(OCHCF3) (10), Cu(BuCOCHCO)2 (19), Ba(HFIP) (4), Cu(thd) (3), Cu(BuCOCHCO) (11), CF 3 (9), Bu (100). IR (cm i): 1608 m, 1578 m, 1559 vs, 1544 s, 1506 s v(c=o), V(c=c); 1275 s, 1244 sh, 1231 vs, 1217 sh, 1159 vs, 1142 sh V(c o), V(c F); 1090 S, 1028 W, 966 W, 937 W, 881 sh, 876 m, 854 m, 802 w, 773 w, 744 m, 687 m; 644 w, 527 m, 492 w, 439 m, 420 m Y(B a o), Y(Cu.. o). #eft = 2.78 B.M. Mol.wt (hexane) : found 1250, calc. (1298.75).

Reaction between 2 and thdH in 1:1 stoichiometry in hexane led to 6 in 70% yield with formation of insoluble by-products whose IR is consistent with "Ba(HFIP)2".

Crystals of 6 were obtained by crystallization of the sublimate in petroleum ether. Unit-cell dimensions and space group ( -100°C) : a = 10.084, b = 21.333, c = 22.851 A, /3 = 91.68 °, P21/c. The low intensities precluded useful data collection.

Synthesis' of[YCu(HFIP)2(thd)3] (7)

A solution of Cu(thd)2 (1.47 g, 3.42 mmol) in hexane (40 cm 3) was added to a suspension of 3 (1.38 g, 1.71 mmol) in hexane (40 cm3). The precipitate progressively dissolved and the reaction medium was stirred for 2 h, leaving a dark blue solution. Cooling to - 2 0 ° C gave turquoise-blue crystals (7). The last crop of crystals was a mixture of 7 and pale-blue crystals (8). Their sublimation at 160oc/10 3 Torr gave pure 7; at temperatures higher than 195'~C, decomposition of 7 occurred and the sublimate was contaminated with 8. Com- pounds 7 and 8 could be separated by crystallization in hexane, yield in 7: 68% ; m.p. 182°C. Found: C, 46.0; H, 5.9; Cu, 6.2; Y, 18.7. Calc. for C39H59FI2OsCuY: C, 45.2; H, 5.7; Cu, 6.1; Y, 18.6%. ESR (hexane, room temperature): (g ) = 2.104, ( A ) = 80.9. MS (El, 70 eV, m/z +, %): M-Bu (3), M-BuCO (1), M-CF3-Bu (7), FYCu(HFIP)(thd)3 (1 1), M-HFIP (13), M-thd (7), YCu(thd)3 (19). YCu(HFIP)(thd)2 (4), Y(thd)3 (11), Y(thd)2(BuCOCHCO) (16), YCu(HFIP)(thd) (BuCOCHCO) (4), Y(thd)2 (12), Cu(thd)2 (7), Cu(BuCOCHCO) (11), CF 3 (6), Bu (100). IR (cm ~): 1603 m, 1585 s, 1570 s, 1553 vs, 1545 vs, 1508 vs V~c_o~, V(c o~; 1294 s, 1267 m, 1248 m, 1225 s, 1204 vs, 1188 vs, 1132 vs, 1103 vs V(c o), V(c v); 1029 W, 966 W, 937 W, 899 m, 872 s, 808 m, 798 m, 746 m, 689 s; 640 w, 613 m, 530 m, 494 m, 474 m, 455 m, 419 m •(y o), Y(cu o). #eft = 1.75 B.M.

Compound 7: unit-cell dimensions ( - 100°C) : a = 10.992, b = 22.287, c = 19.433 A,/3 = 90.54 °, monoclinic.

Compound 8: IR (cm ~):1600m, 1573 vs, 1558 vs, 1541 s, 1507 vs V(c=o), V(c-o); 1292 m; 1259 m, 1222 s, 1213 s, 1178 vs, 1150 s, V(c F) 1095 S, 1027 W, 964 W, 933 W, 890 m, 872 m, 798 m, 743 m, 687 m ; 608 m, 525 w, 489 w, 476 w, 453 w V~cu o~-

Crystal structure determination of [Y2Ba[/~-HFIP]4 (thd)4] (5)

This part has been reported in a communication 34 and only limited information is given here. Crystals of 5 were obtained by crystallization of the sublimate in petroleum ether. A selected crystal was set up on an Enraf-Nonius CAD-4 diffractometer at

- 100°C. Unit-cell dimensions with estimated standard deviations were obtained from least-squares


Table 1. Crystallographic data for Y2Ba[OCH(CF3)2]4 (thd)4

Formula C56HsoBaF24O12Y 2 fw 1716.4 System Triclinic Space group P1 a (/~) 10.922 (5) b (A) 16.345 (2) c (/k) 21.926 (4)

(°) 105.92 (1) fl (°) 97.59 (3) 7 (°) 100.74 (2) V (A 3) 3628 (2) Z 2 #(Mo-K,) (cm-') 22.4 dc, l¢ (g cm 3) 1.57 20 range (°) 4 < 20 < 38 Scan type ~o/20 Scan width (°) 1.20+0.35tg0 Scan speed (° min -I) 2.4 < sp. < 16.5 Diffractometer CAD-4F No. of reflections collected 6203 No. of unique reflections 5798 Merging R factor 0.04 No. of reflections with I > 3al 3490 Absorption-coefficient correction 0.92 < coeff < 1.07 R 0.057 Rw 0.064 Weighting scheme Unity No. of variables 397

refinements of the setting of 25 well-centred reflections. Two standard deviations monitored period- ically showed no change during data collection. Crystal data and other pertinent information are summarized in Table 1.

R E S U L T S A N D D I S C U S S I O N

2711

Synthesis

Mixed-metal alkoxides are usually built up either by Lewis acid-base reactions or by metathesis reactions between halides and alkali-based heterometallic alkoxides. 38 Although a species such as [Na3Y(HFIP)6(THF)3] is available, its reactivity is dominated by the retention of sodium. 33b Barium fluoroisopropoxide appeared to be a more interesting reactant. The strategy used was based on metathesis reactions between YC% or CuC12 and barium fluoroisopropoxide "Ba(HFIP)2" obtained in situ or isolated as [Bas(OH)(HFIP)9(THF)4 (H20)]. TM These reactions were achieved in polar solvents, T H F or DME (DME = dimethoxy- ethane), the latter being required for the reactivity of CuC12 at a reasonable rate. Compounds of the formula [YBa2(HFIP)7(THF)3] (1) and [BaCu (HFIP)4(DME)2] (2) were obtained, respectively. Although these compounds were volatile, their sublimation (200-220°C/10 -3 mm Hg) occurred with notable decomposition and their chemical modification was thus required. The intro- duction of the chelating ligand, 2,2,6,6-tetramethyl- 3,5-heptanedione, in the metal coordination sphere was envisioned as a means to tailor volatility and stability. Reactions between 1 and 2 and thdH led to mixed-metal tetramethylheptanedionatofluoro- isopropoxide derivatives [Y2Ba(HFIP)4(thd)4] (5) and [BaCu2(HFIP)4(thd):] (6), but with a change of the stoichiometry between the metals. Optimization of the reactions was thus achieved. The various synthetic routes are summarized in Scheme 1.

[YzBa(HFIP)4(thd)4] was formed in good yields by the reaction between [Y2Ba(HFIP)7(THF)3] and

BaCu(HFIP)4(DME) 2 (2)

or C~(thd) 2

BaCu2(HFIP)4(thd) 2 (6)

Ha

toluane/DMEt°luene/THF°r tFIPH ygo(Oipr)13

"Ba'(HFIP)2"m sltu crystallization THF ~ THF tFIPH

CI 3 BasOH(HFIP)9(THF)4 Y(HFIP)3(THF)3

[ Y2(HFIP)2lthd)4 / I

Y2Ba(HF1P)4lthd)4 YCu(HFIP)2lthd) 3 + [Cu(HFIP)(thdI] n (s) (7) (s)

* When no indication of solvant is given, reasons were made in hexane.

Scheme 1.


Y(thd)3 or thdH in 1 : 2 stoichiometry. The reaction is evidenced by the dissolution of ! in hexane. The change in the metal ratio from [YBa2(H- FIP)7(THF)3] to [Y2Ba(HFIP)4(thd)4] implies the formation of a barium by product and the stoichiometry of these reactions is important. On vary- ing the ratio thd/FIP, two cases were observed : the formation of insoluble barium species "Ba(HFIP)f ' [or Ba(OH)2], which could be easily separated or that of soluble [Ba(thd)2]m (when excess thdH was present for example by reacting I with 4 equiv, of thdH or [Bas(OH)(HFIP)9(THF)4(H20)] with Y(thd)3 in a 1:3 ratio. Compound 5 could not be isolated pure neither by crystallization nor by sublimation when Ba(thd)2 was present in the reaction medium. Optimization of the reactions conditions required two thd ligands for one yttrium atom. [Y2Ba(HFIP)z(thd)4] corresponds to a thermo- dynamic "sink" and was also obtained by reaction between yttrium and barium derivatives, namely [Y(HFIP)3(THF)3] (3) and Ba(thd)2 (64% yield) or by self assembly between "Ba(HFIP)2" and the heteroleptic yttrium compound [Y(HFIP) (thd)2] (4).

[BaCu2(HFIP)4(thd)2] (6) was isolated in 90% yield from the self-assembly between [BaCu(HFIP)4(DME)2] (2) and Cu(thd)2. Com- pound 6 could also be obtained, together with "Ba(HFIP)2" as the only byproduct, by reacting 2 with thdH in l : l ratio. Use of excess thdH or on mixing [Bas(OH)(HFIP)9(THF)4] and Cu(thd)2 in l :4.5 ratio results in the formation of Ba(thd)2 as a byproduct, which precluded isolation of 6 in good yields, as observed for 5. Thus, the use of Y(thd)3 and Cu(thd)2 for access to 5 and 6, respectively, instead of thdH permitted a significant improvement of the yields (from 45 to 74% for 5 and from 70 to 90% for 6).

Different routes to yttrium-copper fluoroisopropoxides were explored. Surprisingly, by contrast with its barium analogue, the yttrium fluoroisopropoxide [Y(HFIP)3(THF)3] (3) did not react with CuClz, even under reflux. The mixed- metal species [YCu(HFIP)2(thd)3] (7) was obtained in 68% yield from the reaction between Y(HFIP)3 (THF)3 and Cu(thd)2 in 1:2 ratio with the formation of pale blue crystals of 8, probably with a copper fl-diketonatofluoroisopropoxide as a byproduct. The different reactivity of CuC12 and Cu(thd)2 toward 3 can be related to the observations on copper fluoroalkoxides. The complete alcoholysis of [Cu(OMe)2] ~ to Cu(HFIP)2 was not achieved in the absence of Lewis bases. 39 The thd ligand allowed the isolation of the thermodynamically stable mixed-metal species 7 and YCu(HFIP)5 is, like Cu(HFIP)2, not thermodynamically favoured. The

formation of a copper fl-diketonatofluoroisopropoxide as a byproduct confirms this hypothesis.

Different results were observed in the case of l,l,l,3,3-hexafluoro-2-methylpropan-2-ol (HFTB). The barium derivative 9 obtained from barium chips and HOCMe(CF3)2 in THF reacted with yttrium chloride giving a mixed-metal YBa species of 1 : 1 stoichiometry. Its modification by thdH or Y(thd)3 proceeded with retention of the initial metal stoichiometry. This compound, although volatile, required more drastic conditions (240°C/5 x 10 -3 mm Hg) than 5 for sublimation. Another salient features is the absence of reaction between 9 and copper tetramethylheptanedionate, even under reflux. These observations prevented a more complete investigation of the systems based on the hexa- fluorobutoxide ligand. One can also notice that while we have obtained [BaCu(HFIP)4(DME)2] in a high yield, the reaction between Ba(HFTB)2 and CuC12 afforded a mixed-metal species having a different stoichiometry, [BaCu2[OCMe(CF3)2]6], in moderate yield (27%), as reported by Purdy. 29

The different compounds were isolated from the reaction medium by crystallization. The high Lewis-acid character of all fluoroalkoxide derivatives results in easy contamination by various amounts of solvents (THF, DME) acting as O- donor ligands. The volatility of the mixed-metal heteroleptic derivatives allowed further purification by sublimation.

Spectroscopic characterization

The compounds were characterized by elemental analysis, FT-IR, NMR, mass spectrometry TGA and ESR for the mixed-metal copper derivatives. Although single crystals could be grown in solution for most compounds, X-ray data are often limited to unit-cell parameters due to disorder problems and/or destructive phase transition at low temperature. Only the structure of 5 could be com- pletely solved.

The FT-IR spectra display the characteristic absorptions of the fluoroisopropoxide ligands [V~c F~ stretch between 1350 and 1100 cm -~] and, in addition, strong ~ O and C--C absorptions bands around 1600-I 500 cm- 1 of the fl-diketonates for the heteroleptic derivatives 5, 6 and 7. The change in the surroundings of the Y(thd)3, Ba(thd)2 or Cu(thd)2 moieties is supported by an increase of the number of these vibrations, as well as by a shift in their frequencies. M--O(OR) or M--O(thd) vibrations are observed around 600-300 cm ~.J°

The solubility of the various derivatives, higher for the tetramethylheptanedionatofluoroisoprop- oxides, allowed their characterization by


N M R (IH, 13C and 19F), especially if diamagnetic. ~H NMR spectra confirmed the presence of T H F for 1 and the relative proportion of the different ligands, OCH(CP3)2 and thd for the heteroleptic derivative 5. N M R spectra were achieved in CDC13, although solubility properties were higher in CD3CN or C6D6/C6F 6. As anticipated, CD3CN acts as a donor ligand. More surprising was the reactivity in benzene, although complexation of that solvent were reported for bismuth 4° and Na-Zr fluoroalkoxides. 41 Evolution of both Y-Ba precursors, I and 5, was observed in the presence of benzene ; these reactions were, however, not further investigated and the use of that solvent was excluded for investigation of their reactivity.

~H and 19F spectra of [YBa2(HFIP)7(THF)3] in CDC13 were quite complex: all T H F ligands appeared magnetically equivalent, but four types of fluoroisopropoxide ligands were observed in the proton spectra, while four singlets (Av~/2 ~ 19 Hz) whose chemical shifts are spreading over a relatively large range ( - 7 2 . 3 to -77 .8 ppm) were observed in the ~gF spectra. Dilution experiments account for the presence of two molecular species and for partial extrusion of barium fluoroisopropoxide and thus a change in the stoichiometry between the metals. [Y2Ba(HFIP)4(thd)4] is more stable and the spectra in CDC13 account for the presence of a single molecular species having the structure found in the solid state: all fluoroisoproxide and thd ligands appear magnetically equivalent by ~H, ~9F and ~3C NMR. As for 1, the 19F N M R signal is quite broad (Av~/2 = 26 Hz) as a result either of restricted rotation around the C- -C bonds due to M - - - F interactions or to quadruplar broadening.

Although slow to hydrolyse in solution at room temperature, the Y-Ba fluoroisopropoxide derivatives are quite hygroscopic solids and water can act as a competitive ligand with respect to T H F for 1, as evidenced by the presence in the IR spectrum of an absorption due to hydroxyl stretching vibrations [Vlon13434 and 3173 cm-~]. In the case of [Y2Ba (HFIP)4(thd)4], the presence of water as an ad- ditional ligand results, after sublimation, in a non- volatile mixed-metal hydroxo /?-diketonatofluoro- alkoxide complexed by tetramethylheptanedione as evidenced by a Vlc-o~ absorption band in the IR spectrum at 1728 cm J.

The paramagnetic derivatives [YCu(HFIP)2 (thd)3] and [BaCu2(HFIP)4(thd)2] were characterized by their ESR spectra, which show a four- line pattern (I63Cu = 3/2) (hexane, room temperature). Their isotropic 9 factor and hyperfine coupling constants have values of 2.104, 80.9 G and of 2.107 and 79.9 G, respectively. These values fall

2713

in the range observed for four-coordinate copper(II) centres. No hyperfine coupling was observed for BaCu(HFIP)4(DME)2.

Molecular structure o f the mixed-metal species

Compound 5 corresponds to a trinuclear heterometallic species [Y2Ba(#-HFIP)4(thd)4], which adopts an open-shell structure with alternate yttrium and barium metals as established by X-ray diffraction. 34 Its molecular structure is represented in Fig. 1. Selected bond lengths and angles are collected in Table 2. The central barium atom is linked to the two yttrium centres by four fluoroisopropoxide bridges, while all /3-diketonates are borne by the yttrium atoms. Thus, the [(thd)2Y(/~- HFIP)zBa(#-HFIP)zY(thd)2] framework can for- mally be viewed as Ba 2+ surrounded by two Y(#-HFIP)2(thd)~- moieties and a < YBaY angle of 129.35". The molecular structure of 5 illustrates that alkoxide or fluoroalkoxide ligands are more prone to act as bridging and thus assembling ligands than /3-diketonate ones. The Ba- -O bond lengths, ranging from 2.63(1) to 2.68(1) •, are short but comparable to the values observed for #2-alkoxide Ba- -O distances in fluorinated 27 or non-fluorinated Iv derivatives. The Y - - O bond lengths are similar for alkoxide and tetramethylheptanedionate ligands, ranging from 2.21(1) to 2.25(1) /k. They fall in the range of the values observed for the Y--O(thd), 26 as well as for the iL2-alkoxide Y - - O distances. 35'42 The angles O(1)--Y(1)--O(3) and O(2)--Y(2)--O(4) of the bridges (av. 74.8') are comparable with the bite of the/3-diketonate moiety (av. 74.T), resulting in a trigonal prismatic geometry for the six-coordinated yttrium. The Y - - O - - B a angles are quite large (av. 108.8 ~) and account for Y- -Ba distances of 4.00 A. The most salient feature is the coordination polyhedron of the central barium atom. At first glance the barium atom is relatively exposed, being surrounded by four fluorisopropoxide ligands assembled via quite small O - - B - - O bridge angles (av. 62.3 and 61.4~). The coordination sphere is, however, supplemented by interactions with eight fluorine with Ba- - -F distances of 2.9-3.16 A (the sum of the van der Waals radii is 3.57 A), acting as secondary bonds, 43 thus leading finally to a 12 coordinate metal. A similar environment for barium has been observed in [BaC- u2[OCMe(CF3)2]6]. 29 Short M - - - F contacts appear to be a common feature for fluorinated alkoxides/3- diketonate derivatives, especially for large elements such as alkaline earth metals, TM bismuth 4° or lan- thanides. 44 No short contacts are observed in the solid state between the [Y2Ba(HFIP)4(thd)4] mol-

2714 F(2)

F. LABRIZEet al.

F(6, F(8)

C(23)

C(21)(

c(2o)

C(18

F(3)

F(12

F(10)

,F(21)

C(55) o,

)C(51)

)C(56)

C(S4)

~ ( O ( 5 ) ~1~C(31) C ( 7 ) ~ ~ f ~ " v ~ 0 ' ~" ..... ~C) /::f p C(47) C(30 C(9} (12) - ~ ( ~ )11 ))~ ~F C(44) (42, C(32) F(17~ ( 2 4 ) 0 ( 7 ) ~ :(41) C(48) (~ C(29) F(18) ( ) 0(9)

C(17) 1~] C(24) F(22) C(35)( C(40)bC(43) C(49)

C(27)q

C(28)

c(38)

C(39)

Fig. 1. Molecular structure of [BaY2[/~-HF1P]4(thd)4], showing the atom-labelling scheme (ellipsoids at 20% probability) ; dotted lines indicate the interactions with the fluorine atoms.

ecules. The C--F bond distances cover a large range [1.26(2)-1.41(2) A], the values corresponding to the fluorine involved in the secondary bonds being gen- erally among the largest ones.

Although the structures of [BaCu2(HFIP)4(thd)2] and [YCu(HFIP)2(thd)3] could not be solved in the solid state, molecular weight data in benzene or hexane account for discrete monomeric species. Since the fluoroalkoxide ligands are more prone to bridging coordination modes, the connectivity between the metals is thus likely to be ensured by

fluoroisopropoxides, while the fl-diketonate ligands are in chelating terminal positions. Structures of type A and B are in agreement with that and with the spectroscopic data, namely magnetically equivalent fluoroisopropoxides (19F NMR). Copper atoms are four-coordinate, while yttrium is six- coordinate. The coordination number of barium is apparently only four in structure A, but as observed for [BaCuz[OCMe(CF3)2]6] or [Y2Ba[OCH(CF3)2]4 (thd)4], secondary Ba. . .F bonds are likely to complete the metal coordination sphere.

O,,,,qO f'" Cu W"'~ oRfORf' ,,,q~ Ba u0'''~ OReop~ ~ l Cu i

A

(ORf = HFIP)

8

',, ,, ~ 1 Ill ', ))),.,O< o& , C a " ~ O - - O R f f


Table 2. Selected bond lengths (A) and angles (°) of BaYE[OCH(CFa)2]a(thd)4

2715

Ba(1 )--O(1 ) 2.67(1) Ba( 1 ) - -0(2) 2.68(1 ) Ba(1 ) - -0(3) 2.64( 1 ) Ba( 1 ) - -0(4) 2.63 (1) Y(1)--O(1) 2.25(1) Y(1)---O(3) 2.25(1) Y( 1 )--0(5) 2.24(1 ) Y(1 )---0(6) 2.23( 1 ) Y(1)--O(7) 2.21(1) Y(I)--O(8) 2.23(1) Y(2)--O(2) 2.23(1) Y(2)--O(4) 2.25(1) Y(2)--O(9) 2.23(1) Y(2)---O(10) 2.23(1) Y(2)--O(11) 2.24(1) Y(2)--O(12) 2.22(1)

Ba--F interactions Ba(1)--F(1) 3.16(1) Ba(I)--F(8) 3.11(1) Ba(1)--F(12) 3.03(1) Ba(1)--F(14) 3.07(1) Ba(1)--F(17) 3.11(1) Ba(1)--F(21) 3.04(1) Ba(1)--F(4) 2.94(1) Ba(I)--F(10) 2.90(9)

O(2)--Ba(l )--O( 1 ) 57 .4(3) O(3)--Ba(1 )--O(1 ) 173.6(3) O(3)~Ba(1)--O(2) 117.2(3) O(4)--Ba(1)--O(1) 116.7(3) O(4)--Ba(l )---0(2) 88 .8(3) O(4)--Ba(1 )---0(3) 58.2(3) O(5)--Ba(1)--O(1) 62 .3(3) O(5)--Ba(1)--O(2) 119.5(3) O(5)--Ba(1)--O(3) 122.7(3) O(5)--Ba(1)---O(4) 115.2(3) O(6)--Ba(1)--O(1) 122.9(3) O(6)--Ba(1)--O(2) 113.0(3) O(6)--Ba(1 )--0(3 ) 61.4(3 ) O(6)~Ba(1)--O(4) 119.2(3) O(6)--Ba(1)--O(5) 102.1(3)

O( 5)--Y(I )---O(1 ) 75.2(4) O(7)--Y( 1 )--O(1 ) 129.0(4) O(7)--Y(I )--0(5) 86.5 (4) O(8)--Y(1)~O(1) 88.7(4) O(8)--Y(1)--O(5) 138.9(4) O(8)--Y(1 )--0(7) 74.6(4) O(9)--Y( 1 )---O( 1 ) 141.0(4) O(9)--Y( 1 )--0(5) 90.9(4) O(9)--Y(1)--O(7) 84 .9(4) O(9)--Y(1)--O(8) 122.5(4) O(10)--Y(1)--O(1) 87 .1(4) O(10)--Y(1)--O(5) 130.9(4) O(10)--Y(1)~O(7) 136.5(4) O(10)--Y(1)--O(8) 84.4(4) O(10)--Y(1)--O(9) 74 .8(4) O(6)--Y(2)~O(3) 74.6(4) O(11)--Y(2)--O(3) 138.0(4) O(11)--Y(2)--O(6) 89.5(4) O(12)--Y(2)--O(3) 88 .5(4) O(12)--Y(2)~(6) 133.1(4) O(12)--Y(2)--O(11) 74 .3(4) O(13)--Y(2)~O(3) 87.9(4) O(13)--Y(2)--O(6) 136.7(4) O(13)--Y(2)--O(11) 126.7(4) O(13)--Y(2)--O(12) 84 .2(4) O(14)--Y(2)--O(3) 132.5(4) O(14)--Y(2)--O(6) 88 .1(4) O(14)---Y(2)--O(11) 84.1(4) O(14)--Y(2)--O(12) 131.8(4) O(14)--Y(2)--O(13) 75.1(4)

Volatility and thermal behaviour

The homoleptic and the heteroleptic mixed-metal fluorisopropoxides are all volatile, but the intro- duction of the thd ligand in the metal coordination sphere improves the stability. No disproportion- ation reactions were observed in the vapour phase. [Y2Ba(HFIP)4(thd)4] sublimed at 140°C (10 -3 m m

Hg), while that of the homoleptic derivative [YBa2(HFIP)7(THF)3] occurred only at 200°C and with extensive decomposition. The same observations are valid for [BaCu2(HFIP)4(thd)2] (170°C instead of 210°C for 2). Sublimation of [YCu(HFIP)2(thd)3] proceeded quantitatively at 16ffC ( 10 -3 m m Hg). The thermal stability among

the various novel compounds was the highest for [BaCuz(HFIP)4(thd)2], as illustrated by its high decomposition point ( > 220°C).

Pertinent mass spectra data have been obtained for compounds 5, 6 and 7 and are displayed in Fig. 2. The spectra of all mixed-metal heteroleptic species show various heterometallic fragments and thus confirm the retention of the mixed-metal Y--Ba, Ba--Cu and Y--Cu derivatives in the yap- our phase. Thus, for 5, 6 and 7 the highest fragments observed correspond, respectively, to the loss of three thd and one HFIP ligands (m/z + = 997), two HFIP ligands (m/z + = 964) and a butyl group derived from the fragmentation of the thd ligand (m/z + = 978). For the species containing barium,


Y2Ba (OR04(thd) 4

% 57

1,1 .

30 . I. I.I, t I d[ ,, , II 230 430 630

m/z

YBa(OR02(tM) Y2Ba (ORO3(thd)

F2YBa (ORO3(th,

YBa (OR02(thd) 2

YBa (ORO3(thd) /

\ 830

%1

!7 BaCu 2 (OR04(thd) 2 (M)

15 '7

~ . , ] ~.. ,[ 30 230

M-2ORf BaCu (ORO2(thd) \

BaCu (ORO BaCu (ORf) (thd) ~ t i M'ORf'thd II "

189 / J B~Cu2(OR03

240 440 640 840 m/z

YCu (OR02(thd) 3 (M)

FYCu (ORO2(thd)3-Bu M-E

M-ORF M-thd

YCu (the) 3 \ I \ I

. ,I , , , , _ h 430

ndz 630 830

Fig. 2. Mass spectra at 70 ev of 5, 6 and 7.

metal fluoride fragments are observed in appreci- able amounts. Their formation implies the cleavage of C - - F bonds with the loss of OC3FsH molecule, probably pentafluoropropane-2-one. 45 The intra- molecular Ba . . . . F interactions in the solid state, which might favour the retention of the heterometallic moieties in the vapour phase, might also assist the cleavage of the C - - F bonds. Such bond- cleavage reactions appear less favoured for the Y--Cu derivative.

Vapour pressure measurements

Vapour pressures of the mixed-metal compounds 5, 6 and 7 have been measured and compared with those of the homoleptic Y, Cu or Ba fl-diketonates, as shown in Fig. 3. The plots are given in the classi- cal form logP = f ( l / T ) . The values for the homometallic Ba, Cu and Y fl-diketonates were published

1.000 w Cu(thd) 2

100 - ° i ~ Y Y(thd) 0 .~. BaCu2(HFIP) Cu(H FIP)2(thd)3

> 0.1- Ba(thd)2CH3OH " ~ x~

/ 2 , Y2Ba(HFIP)4(thd) 4

0.0i I I I I 0.002 0.0022 0.0024 0.0026 0.0028

K/T

Fig. 3. Comparison of the vapour pressure data of the mixed-metal fluoroisopropoxides 5, 6, 7 and of the homo-

metallic tetramethylheptanedionates.

previously. 46 The precision of the temperature, pressure measurements and stability are quite good, but other effects (impurities, partial decomposition.. .) may account for the relative scattering of data. The points with the lowest vapour pressures thus rep- resent only orders of magnitude.

Table 3 gives the values of the molar enthalpies of sublimation AHsu b as well as the values of A and B for the equation: log(P/Pa) = A - B ( K / T ) , where P denotes the vapour pressure, T the temperature, Pa and K are the S.I. units Pascal and Kelvin. The values for AOsu b are derived from the equation of Clapeyron AHsub = T(dP/d T) (Vvap- Vso~) and are all of the same order of magnitude. AOsu b is computed as B.R.Ln(10), where R is the perfect gas constant.

As may be seen from Fig. 3, the vapour pressures of the Ba--Cu and Y--Ba compounds are at least one order of magnitude higher than those of [Ba(thd)z]m. Another interesting feature is that those compounds are more stable than [Ba(thd)2],, ; this is especially true for [BaCuz(HFIP)a(thd)2].

Thermal gravimetric analyses (TGA) of compounds 5, 6 and 7 have been achieved up to 460°C under nitrogen (1 atmosphere) and compared with

Table 3. Molar enthalpy of sublimation and linear regression parameters derived from the vapour pressure

measurements

Compound A B (K) AHsub (kJ/mol-~)

BaCu~(HFIP)4(thd)2 13.11 5366 102.7 Y2Ba(HFIP)4(thd)4 11.28 4433 84.8 YCu(HF|P)z(thd)3 11.50 4241 81.2


80 Ba(thd)2

< I BaCu2(OROgthd)4"~t ~ ~ ~Y(thd)3

0 I00 200 300 400 500

Temp°C

Fig. 4. Comparison of the thermogramms of the mixed- metal fluoroisopropoxides 5, 6, 7 and of the homometallic tetramethylheptanedionates under 1 atm. of nitrogen

with a temperature ramp of 5°C m.n- ~.

those of the homometallic Ba, Cu and Y/%diketonates, as shown in Fig. 4. The thermogrammes indicate ca 19% residues for [Y2Ba(HFIP)4(thd)4] and for [BaCuz(HFIP)a(thd)2] and 10% for the Y - - C u derivative [YCu(HFIP)2(thd)3]. The residues obtained for the mixed-metal species containing barium are comparable to the amount found for barium tetramethylheptanedionate. Compounds 5 and 6 display a lower percentage of residue than the barium functionalized /%keto- iminates, 16a which have been used as volatile source of barium oxide for the elaboration of BaPbO3 films. 16b The volatiles eliminated during the TGA experiments have been analysed by FT-IR for the yttrium-barium derivative 5; the fluoroalkoxide ligands are removed before the/3-diketonate ones. It should be noticed that while TGA under atmo- spheric pressure accounts for some decomposition, sublimation under vacuum shows that the transport of 5, 6 and 7 into the vapour phase can be achieved quantitatively provided the range of thermal stability, which is smallest for 5, is respected.

Thermal decomposition experiments at 285- 30ff'C of 5 in a hot wall reactor on silica as wafers led essentially to the deposition of oxides, Y203 and Ba4Y2OT, with only trace amounts of BaF2, as shown by scanning electron microscopy (SEM) and XRD.

Supplementary material. Tables of hydrogen coordinates, anisotropic temperature factors, non- essential bond lengths and angles, and observed and calculated structure factors (20 pages) ; table of vapour pressure data.

Acknowledyements--The authors are grateful to the CNRS-PIRMAT for financial support (ARC), to R.

2717

Astier (Montpellier) for the X-ray data collection and to A. Mari (Toulouse) for the magnetic measurements.

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