Synthesis, characterisation and X-ray structures of yttrium, barium and copper(II) β-ketoesterate complexes

Article abstract of DOI:10.1016/S0020-1693(00)00077-3

β-Ketoesterates derivatives M(mpa)(x) (M = Y, Ba, Cu; mpaH = methylpivaloylacetate; x = 2 or 3) were prepared by ligand exchange reactions starting from methoxides (M = Ba, Cu) or from tristrimethylsilylamide (M = Y) derivatives. Decomplexation of the oligomeric and non-volatile Ba and Y species was achieved by various Lewis bases. Adducts Y(mpa)₃L [L = tmeda (N,N,N',N'-tetramethylethane-1,2-diamine), bipy (2,2'-bipyridine)] and Ba(mpa)₂L [L = diglyme, 18-crown-6 ether; pmdta = N,N,N',N',N_-pentamethylethylenetriamine] and [Ba(mpa)₂(tmedta)₂] were obtained. All compounds were synthesised in high yield and characterised by elemental analyses, ¹H NMR, FT-IR and TGA. The structures of [Ba(mpa)₂(tmeda)₂] and [Y(mpa)₃(bipy)] were established by single crystal X-ray diffraction. The metals are eight-coordinated with a slightly distorted square antiprismatic surrounding. The yttrium complexes sublime as adducts. The barium complexes, by contrast, are dissociated in the vapour phase. Better solubility properties in polar and non-polar with respect to the 2,2,6,6-tetramethylheptane-3,5-dionates analogues were observed especially for the copper species. These compounds are thus potential metal-oxide precursors for liquid injection MOCVD using solvents such as hexane or diglyme. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00077-3

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Inorganica Chimica Acta 304 (2000) 99–107
Synthesis, characterisation and X-ray structures of yttrium, barium
and copper(II) b-ketoesterate complexes
Herve´ Guillon a, Ste´phane Daniele a, Liliane G. Hubert-Pfalzgraf a,*, Claude Bavoux b
a IRC-CNRS, 2 a6enue A. Einstein, 69626 Villeurbanne Cedex, France
b Centre de Diffractome´trie, Baˆtiment 201, Uni6ersite´ Claude Bernard Lyon I, 43 bd du 11 No6embre 1918, 69622 Villeurbanne Cedex, France
Received 24 November 1999; accepted 10 January 2000
Abstract
b-Ketoesterates derivatives M(mpa)x (M=Y, Ba, Cu; mpaH=methylpivaloylacetate; x=2 or 3) were prepared by ligand
exchange reactions starting from methoxides (M=Ba, Cu) or from tristrimethylsilylamide (M=Y) derivatives. Decomplexation
of the oligomeric and non-volatile Ba and Y species was achieved by various Lewis bases. Adducts Y(mpa)3L [L=tmeda
(N,N,N%,N%-tetramethylethane-1,2-diamine), bipy (2,2%-bipyridine)] and Ba(mpa)2L [L=diglyme, 18-crown-6 ether; pmdta=
N,N,N%,N%,N¦-pentamethylethylenetriamine] and [Ba(mpa)2(tmedta)2] were obtained. All compounds were synthesised in high
yield and characterised by elemental analyses, 1H NMR, FT-IR and TGA. The structures of [Ba(mpa)2(tmeda)2] and
[Y(mpa)3(bipy)] were established by single crystal X-ray diffraction. The metals are eight-coordinated with a slightly distorted
square antiprismatic surrounding. The yttrium complexes sublime as adducts. The barium complexes, by contrast, are dissociated
in the vapour phase. Better solubility properties in polar and non-polar with respect to the 2,2,6,6-tetramethylheptane-3,5-dionates
analogues were observed especially for the copper species. These compounds are thus potential metal-oxide precursors for liquid
injection MOCVD using solvents such as hexane or diglyme. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; MOCVD; Yttrium complexes; Barium complexes; Copper complexes; b-Ketoesterate complexes
t
2,4,6-Me3C6H2 or Bu; n=2, R=Me) [7] were devel-
oped as a means to exploit intramolecular stabilisation
of the adducts. The barium derivatives showed limited
or non-volatility. This was attributed to a low tendency
of the polyether side chain to bind to the same metal
and intermolecular bridging was favoured over in-
tramolecular chelation. The introduction of bulky end
substituents into the b-diketone framework giving lig-
1. Introduction
The research on high Tc superconductors (YBCO)
and the need to obtain these ceramics as epitaxial films
[1] for most technological applications has lead to the
quest for appropriate precursors, especially for Group 2
metals. A large platform of precursors has been consid-
ered with emphasis on fluorinated [2] or non-fluori-
nated b-diketonates [3] and their adducts, or classical or
functional metal alkoxides [4,5] for MOCVD applica-
tions. Partial dissociation of barium non-fluorinated
b-diketonates adducts with N- or O-donors makes these
compounds inappropriate for repeated use in CVD.
b-Diketones and b-ketoimines with an etheral ‘scorpion
tail’ such as tBuCOCH2CO(CH2)3OMe [6] and
RCOCH2CO(CH2)3(OC2H4)nOMe (n=1, R=Me, Ph,
i
ands of type RR%COMeCOCH2COR¦ (R%=tBu, Pr,
Ph, R=tBu, C6H10OMe) did not reduce the oligomeri-
sation of the barium derivatives in the vapour phase
and thus did not improve volatibility properties [8].
Despite that body of efforts, satisfactory volatility and
stability properties remain limited to fluorinated b-dike-
tonate complexes [2]. [Ba(tdfnd)2(H2O)]m and
[Ba(tdfnd)2(diglyme)]
(tdfndH=C3F7C(O)CH2C(O)-
C3F7=tetradecafluorononane-4,6-dione) which are liq-
uid at the temperature of use could be repeatedly
transported in the vapour without decomposition. They
allowed the growth of BaF2 as well as YBCO films [9]
* Corresponding author. Tel.: +33-4-7243 1570; fax: +33-4-7243
1568.
E-mail address: hubert@univ-lyon1.fr (L.G. Hubert-Pfalzgraf)
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00077-3

100
H. Guillon et al. / Inorganica Chimica Acta 304 (2000) 99–107
but often the drawback of fluoride residues and subse-
quent high-temperature annealing is that it leads to
poor superconducting properties. Alternative deposi-
tion techniques, able to give epitaxial layers and which
place less demands on precursor volatility properties,
have thus been considered [4,10]. Direct injection tech-
niques in which the precursors are dissolved in an
appropriate solvent, the solution being kept at room
temperature (r.t.), represent to date the most promising
alternative [11]. However, since the solvent is an unde-
sired ballast for a CVD process, solubility properties
become crucial as well as long-term stability in solution.
The introduction of polar end substituents into a b-
diketonate framework was considered as a means to
improve solubility properties especially in polar media
such as diglyme often used in ‘wet’ MOCVD processes.
b-ketoesterate ligands, which have been used for cata-
lytic applications [12] as well as in material science [13]
were thus considered.
diamine) and diglyme (Aldrich) were purified by distil-
,
lation and stored over molecular sieves (4 A). FT-IR
spectra were recorded with a Perkin–Elmer Paragon
500 spectrometer as Nujol mulls. Proton NMR and
ESR spectra were obtained using Bruker WH-200 MHz
and ER 200D-SRC spectrometers, respectively. Analyt-
ical data were obtained from the Centre de Microanaly-
ses du CNRS. TGA experiments were carried out under
argon using a Setaram system equipped with a TGA 92
thermobalance (4.5°C min−1 heating rate) and under
reduced pressure using a Mettler PA8000 system with a
1
TGA 850E thermobalance. FT-IR and H NMR data
are presented in Tables 1 and 2. Melting points were
measured in capillaries and are given uncorrected.
2.1. Syntheses
2.1.1. [Y(mpa)3]m (1)
A total of 1.40 ml of mpaH (8.76 mmol) was added
to Y[N(SiMe3)2]3 (1.66 g, 2.92 mmol) in 45 ml of
hexane. After 15 h, the medium was evaporated to
dryness and the powder was recrystallised in toluene
giving 1 (1.47 g, 90%) as colourless crystals. Anal.
Found: C, 50.95; H, 6.91. Calc. for C24H39O9Y: C,
51.40; H, 6.96%. M.p. (dec.) approximately 128°C.
We report here the synthesis and characterisation of
b-ketoesterate derivatives M(mpa)n (M=Y, Ba, Cu)
based on the readily commercially available methylpi-
t
valoylacetate BuCOCH2CO(OMe) (mpaH) and their
adducts. The various compounds were characterised by
1
elemental analyses, FT-IR, H NMR, TGA and single
crystal X-ray diffraction for [Ba(mpa)2(tmeda)2] and
[Y(mpa)3(bipy)].
2.1.2. Y(mpa)3(tmeda) (2)
A total of 0.05 ml of tmeda (0.35 mmol) was added
to 0.20 g of 1 (0.35 mmol) in 15 ml of pentane. The
solvent was evaporated after 5 h, the crude product was
recrystallised in hexanes giving 2 at −25°C (0.20 g,
83%). It sublimes at 140–145°C/10−3 Torr. Anal.
Found: C, 53.36; H, 8.15; N, 3.92. Calc. for
C30H55O9N2Y: C, 53.24; H, 8.13; N, 4.13%. M.p. 117–
118°C.
2. Experimental
All manipulations were routinely performed under
nitrogen using Schlenk tubes and vacuum line tech-
niques with solvents purified by standard methods.
Y[N(SiMe3)2]3, [Ba(OMe)2]ꢀ and [Cu(OMe)2]ꢀ were
prepared according to the literature [14,15]. Methylpi-
valoylmethane ester (mpaH), bipy (2,2%-bipyridine) and
18-crown-6 ether (Aldrich) were used without further
purification. Tmeda (N,N,N%,N%-tetramethylethane-1,2-
2.1.3. Y(mpa)3(bipy) (3)
From [Y(mpa)3]m: 46 mg of bipyridine (0.29 mmol)
were added to a solution of 0.16 g of 1 (0.28 mmol) in
Table 1
IR data of the complexes (cm−1
)
Complexes
wCO, wCꢀC
wM–O, wM–N
[Y(mpa)3]m (1)
Y(mpa)3(tmeda) (2)
Y(mpa)3(bipy) (3)
1640 s, 1627 s, 1614 s, 1591 s, 1553 s, 1537 s, 1509 s
1654 s, 1624 s, 1586 m, 1541 m, 1509
1647 m, 1626 s, 1601 m, 1585 w, 1576 w, 1541 w, 1526 w, 1505 s
594 m, 571 w, 484 m, 417 m
585 w, 482 w, 450 w, 402 w
653 w, 643 w; 625 w, 591 w, 482 m,
415 w
[Ba(mpa)2]m (4)
1625 s, 1594 m, 1560 m, 1541 m, 1512 s, 1500 s
576 w, 476 w, 409 w
[Ba2(mpa)4(diglyme)]m (5) 1652 s, 1643 s, 1619 s, 1602 m, 1592 m, 1570 w, 1558 w, 1538 m, 1503 s 577 w, 473 w, 410 w, 386 w
Ba(mpa)2(18-crown-6) (6) 1664 s, 1649 s, 1623 w, 1587 w, 1567 w, 1529 w, 1484 s
582 w, 555 w, 527 w, 470 w, 411 w
573 w, 471 w, 455 w, 430 w, 407 w,
385 w
Ba(mpa)2(tmeda)2 (7)
1636 s, 1611 w, 1579 w, 1542 w, 1495 s
Ba(mpa)2(pmdta) (8)
Cu(mpa)2 (9)
1647 s, 1635 s, 1608 w, 1578 w, 1539 w, 1492 s
1598 s, 1585 s, 1542 s, 1530 s, 1507 s
596 w, 580 w, 471 m, 455 w, 430 w
504 m, 481 w, 443 w, 394 w

H. Guillon et al. / Inorganica Chimica Acta 304 (2000) 99–107
101
Table 2
1H NMR data of the complexes 1–8
Complexes
M(mpa)xLy
l (20°C, ppm)
Solvent
CH
OMe
tBu
Lewis base (L)
mpaH
[Y(mpa)3]m (1)
CDCl3
CDCl3
3.74(CH2)
5.05, 4.93 (3H)
3.58
1.18
1.18–1.04, 1.00
(27H)
3.75, 3.66, 3.60 (9H)
Y(mpa)3(bipy) (2)
CDCl3
4.84 (3H)
3.51 (9H)
1.05 (27H)
9.32 (m, 2H), 8.05 (m, 2H),
7.90 (m, 2H), 7.43 (m, 2H)
2.60 (s, 4H), 2.40 (s, 12H)
Y(mpa)3(tmeda) (3)
[Ba(mpa)2]m (4)
CDCl3
CDCl3
4.95 (3H)
4.87, 4.82 (2H)
3.54 (9H)
3.74–3.56, 3.50 (6H)
1.07 (27H)
1.18–1.06, 1.03
(18H)
[Ba2(mpa)4(diglyme)]m (5)
Ba(mpa)2(18-crown-6) (6)
Ba(mpa)2(tmeda)2 (7)
Ba(mpa)2(pmdta) (8)
CDCl3
C6D6
CDCl3
C6D6
4.85 (4H)
5.33 (2H)
4.85 (2H)
5.36 (2H)
3.55 (12H)
3.65 (6H)
3.55 (6H)
3.49 (6H)
1.06 (36H)
1.39 (18H)
1.06 (18H)
1.31 (18H)
3.68, 3.60 (m, 8H), 3.43 (s, 6H)
3.38 (s, 24H)
2.37 (s, 8H), 2.24 (s, 24H)
2.17 (s, 12H), 2.03 (m, 4H),
1.96 (s, 3H), 1.94 (m, 4H)
10 ml of hexane. After 10 min, a white precipitate was
formed. Filtration gave 3 (0.17 g, 85%). M.p. 199°C.
From Y(NO3)3·6H2O: about 2 g of molecular sieves
7.03. Calc. for C28H50O12Ba: C, 46.97; H, 7.04%. M.p.
124–125°C.
,
(3 A) were added to 1.10 g of Y(NO3)3·6H2O (2.85
2.1.7. Ba(mpa)2(tmeda)2 (7)
mmol) dissolved in 25 ml of methanol. After 1 h, 1.37
ml of mpaH (8.55 mmol) and 0.45 g of bipy (2.85
mmol) were added; precipitation occurred rapidly.
NaOH (0.34 g, 8.50 mmol) was then added. After
dissolution, a white precipitate appeared progressively.
The solvent was evaporated after 5 h, and the solid was
extracted with 60 ml of toluene. Compound 3 crys-
tallised in hexane (1.86 g, 91%). It sublimes at 120–
125°C/10−3 Torr. Anal. Found: C, 57.00; H, 6.60; N,
3.95. Calc. for C34H47O9N2Y: C, 57.00; H, 6.56; N,
3.90%.
The same procedure as for 6 was applied to 0.70 ml
of tmeda (4.60 mmol) and 1.04 g of 4 (2.30 mmol) in 20
ml of toluene and gave 7 (1.44 g, 92%). Anal. Found: C,
48.20; H, 8.20; N, 8.66. Calc. for C28H58O6N4Ba: C,
49.20; H, 8.50; N, 8.20%. M.p. 115–116°C.
2.1.8. Ba(mpa)2(pmdta) (8)
The same procedure as for 7 was applied to 0.93 ml
of pmdta (4.46 mmol) and 2.01 g of Ba(mpa)2 (4.46
mmol) in 11 ml of toluene and gave 8 (2.62 g, 94%).
Anal. Found: C, 47.55; H, 7.65; N, 6.44. Calc. for
C25H46O6N3Ba: C, 48.00; H, 7.80; N, 6.44%. M.p.
120°C.
Compounds 1–8 are soluble in hexane and in toluene
and very soluble in polar solvents (THF, DME,
diglyme).
2.1.4. [Ba(mpa)2]m (4)
A total of 0.74 ml of mpaH (4.60 mmol) was added
to a suspension of 0.46 g of Ba(OMe)2 (2.30 mmol) in
35 ml of hexane. Precipitation occurred after solubilisa-
tion. Compound 4 (0.99 g, 95%) was isolated by filtra-
tion after 15 h. Anal. Found: C, 42.50; H, 5.84. Calc.
for C16H26O6Ba: C, 42.53; H, 5.75%. M.p. (dec.) 202°C.
2.1.9. Cu(mpa)2 (9)
A total of 1.47 ml of mpaH (9.24 mmol) was added
to a suspension of 0.58 g of Cu(OMe)2 (4.62 mmol) in
25 ml of hexane. After 8 h, the reaction medium was
filtered. Green crystals of 9 were isolated at −25°C
(1.60 g, 92%). Compound 9 is soluble in common
solvents and sublimes at 55–60°C under 10−4 Torr.
Anal. Found: C, 50.95; H, 7.20. Calc. for C16H26O6Cu:
C, 50.80; H, 7.40%. EPR (hexane, 20°C): ꢀgꢁ=2.11,
ꢀAꢁ=83.4 G.
2.1.5. [Ba2(mpa)4(diglyme)]m (5)
A total of 0.53 ml of diglyme (3.72 mmol) was added
to a suspension of 0.56 g of 4 (1.24 mmol) in 15 ml of
hexane. After dissolution a precipitate appeared. Com-
pound 5 was filtered off after 15 h and recrystallised in
toluene (0.64 g, 96%). Anal. Found: C, 43.83; H, 6.27.
Calc. for C38H66O15Ba2: C, 44.00; H, 6.27%. M.p.
124°C.
2.1.6. Ba(mpa)2(18-crown-6) (6)
2.2. X-ray crystallography of 3 and 7
The same procedure as for 5 was applied to 0.61 g of
18-crown-6 (2.33 mmol) and 1.05 g of 4 (2.33 mmol)
and gave 6 (1.30 g, 78%). Anal. Found: C, 46.79; H,
Colourless crystals of 7 and 3, suitable for X-ray
studies, were grown from hexane at −25°C and were

102
H. Guillon et al. / Inorganica Chimica Acta 304 (2000) 99–107
3. Results and discussion
mounted on glass fibres with grease. Data collection
was made at 223 K with a Nonius Kappa CCD diffrac-
tometer. The detector was positioned at 35 mm from
the crystal and €-scans of 1° for 6 s were performed to
obtain the reflections measured using the COLLECT
software [16]. Cell parameters were refined using
DENZO and data reduction was achieved with
SCALEPACK [17]. A summary of the crystallographic
information and structure solution is given in Table 3.
The structures were solved and refined by least-squares
using SHELXL-96 [18]. All non-H atoms were refined
anisotropically for 7. Hydrogen atoms were included in
calculated positions and refined isotropically riding on
carbon. The poor quality of the data for 3 due to small
crystals with low intensities lead to high values of R,
only Y and O atoms were refined isotropically and only
a partial structure report will be given. Since only atom
connectivity is important and undoubtedly correct, we
do not believe that the high R factors detract from the
overall result.
3.1. Synthesis and characterisation
Scheme 1 summarises the various synthetic routes
which were investigated for the preparation of the
methylpivaloylacetates [M(mpa)n]m (mpaH=methylpi-
valoylacetate=2-methoxy-2,6,6-trimethylheptane-3,5-
dione=MeOC(O)CH2C(O)tBu. The compounds iso-
lated were characterised by elemental analyses, FT-IR
1
and H NMR or EPR (Tables 1 and 2).
[M(mpa)n]m derivatives were obtained by reacting the
appropriate equivalent of the b-ketoester with yttrium
tristrimethylsilylamide or barium and copper methox-
ides, in hexane at r.t. Molecular weight measurements
of the yttrium derivative [Y(mpa)3]m (1) in benzene by
the Signer method gave a molecular complexity value
m=1.44. This suggests the presence of an equilibrium
between species of different nuclearity. This was confi-
1
rmed by the H NMR data. The spectra in CDCl3 at
r.t., display at least three types of magnetically non-
equivalent methylpivaloylacetate ligands whose relative
area are a function of the dilution. The major species
gives NMR shifts at 5.06 (CH), 3.60 (OMe) and 1.04
(tBu) ppm. [Y(mpa)3]m is moisture sensitive. Whereas
Y(thd)3 is transformed into an hydrate, [Y(mpa)3]m is
hydrolysed over about 3 h with liberation of the free
b-ketoester and apparition of wOH absorption bands
(3640, 3430 cm−1) in the FT-IR spectrum. These obser-
vations are in agreement with the behaviour in sol–gel
processing where b-ketoesterate ligands appeared more
sensitive to hydrolysis than b-diketonates [19]. Com-
plexation with Lewis bases was thus investigated as a
means to stabilise 1, to reduce its nuclearity and impart
volatility. Examination of the volatility data of a num-
ber of yttrium derivatives has indicated a correlation
between molecular weight and volatility [4]. It was thus
possible to select ligands which, if they would stabilise
monomeric species, should lead to volatility.
Y(mpa)3(tmeda) (2) and Y(mpa)3(bipy) (3) were ob-
tained in approximately 85% yield by adding or
N,N,N%,N%-tetramethylethylenediamine (tmeda) or 2,2%-
bipyridine (bipy) to [Y(mpa)3]m in hexane. Both adducts
are air stable and, as predicted, volatile.
Table 3
Crystal data for Y(mpa)3(bipy) (3) and Ba(mpa)2(tmeda)2 (7)
Formula
Formula weight
Unit cell dimensions
C34H47N2O9Y
716.7
C28H58N4O6Ba
684.12
,
a (A)
21.634(2)
21.634(2)
16.2460(7)
90.0
90.0
90.0
7603.6(9)
8
tetragonal
P-421c
1.584
9.887(2)
16.112(3)
22.795(5)
90.0
90.0
90.0
3631.2(13)
4
orthorhombic
P212121
1.133
,
b (A)
,
c (A)
h?(°)
i (°)
k (°)
3
,
V (A )
Z
Crystal system
Space group
Absorption coefficient
(v mm−1
)
Density (z mg m−3
)
1.252
1.251
Radiation
Mo Ka
Mo Ka
,
,
(u=0.71360 A) (u=0.71073 A)
q Limits (°)
Temperature of measurement 223(2)
(K)
1.34–21.39
1.55–22.53
223(2)
Limiting indices
0, 22; 0, 15;
−16, 16
8352
0, 10; 0, 17; 0,
24
2732
2707
1
The r.t. H NMR spectra in CDCl3 of the adducts
Number of data collected
Number of unique data
collected
Number of observed
reflections [I\2|(I)]
Refinement method
4237
indicate one type of b-ketoesterate ligands with the
signals of the Lewis base being shifted to lower field
with respect to those of the free ligand. Interestingly, 3
could also be obtained in good yield (91%) directly
from Y(NO3)3·6H2O in methanol (Eq. (1)). It is a
monomer as shown by X-ray diffraction. O-donor lig-
ands such as DME or diglyme were used as well,
especially in view of their frequent use as a solvent for
liquid injection MOCVD techniques, but no crystalline
compounds could be isolated so far.
1911
2418
full-matrix least- full-matrix least-
squares on F2
4237/1/220
0.1141
squares on F2
2707/0/220
0.0370
0.0462
0.610, −0.526
Data/restraints/parameters
Final R indices [I\2|(I)]
R indices (all data)
Largest difference peak
and hole (e A
0.2400
0.546, −0.506
−3
,
)

H. Guillon et al. / Inorganica Chimica Acta 304 (2000) 99–107
103
Scheme 1. Synthesis of the crystalline compounds 1–8.
1
,
(1) Molecular sieve (4 A)
served in solution. H NMR and FT-IR experiments
suggest that compounds 6–8 are monomeric. This was
confirmed by the X-ray structure determination of
(2) 3mpah+bipy
Y(NO3)·6H2OꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁꢂY(mpa)3(bipy)
(3) 3NaOH
MeOH
+3NaNO3
(1)
For the barium derivative [Ba(mpa)2]m, 1H NMR
data suggest also the presence of several molecular
species. Its poor solubility in non-polar solvents suggest
oligomeric species which may also explain his lack of
volatility. Decomplexation was investigated with vari-
ous O- and N-polydentate donors in toluene or hexane.
[Ba2(mpa)4(diglyme)]m (5), [Ba(mpa)2(18-crown-6)] (6),
[Ba(mpa)2(tmeda)2] (7) and [Ba(mpa)2(pmdta)] (8)
(pmdta=N,N,N%,N¦,N¦ - pentamethyldiethylenetria-
mine) were isolated in yields varying from 78 to 96%.
These complexes display comparable FT-IR spectra in
the wCꢀO and wCꢀC region (1650–1400 cm−1) (Table 1).
They differ mainly by the presence of the absorption
bands of the Lewis base. The spectrum of 5 for instance
is characterised by the presence of a wC–O band of the
glyme at approximately 1070 cm−1, a shift of approxi-
mately 70 cm−1 over the free ligand. By contrast to the
other barium ketoesterate complexes, its FT-IR spec-
trum has a very intense additional band at 1619 cm−1
suggesting the presence of bridging mpa ligands. Struc-
ture A in which barium is seven-coordinated might
account for the spectroscopic data. This bridging
polyether coordination frame has already been de-
scribed for [{Ca(hfa)2}2(heptaglyme)] (hfa=hexa-
fluoroacetylacetonate) [20] and [{Ln(thd)3}2(triglyme)]
1
(Ln=Y, Gd) [21]. The H NMR spectra display the
resonances of the mpa ligands as well as those of the
neutral ligands which were shifted to lower frequencies
with respect to the free ligand. For instance the tri-
amine complex (8) is characterised by the peaks of the
CH2, NMe and NMe2 groups at 2.03, 1.94, 1.96 and
2.17 ppm, respectively, besides the resonances of the
mpa ligand. No dissociation of the adducts was ob-
Fig. 1. X-ray structure of Ba(mpa)2(tmeda)2 (7) showing the atom
numbering scheme (thermal ellipsoids at 20% probability).

104
H. Guillon et al. / Inorganica Chimica Acta 304 (2000) 99–107
[Ba(mpa)2(tmeda)2]. The structures of 6 and 8 are prob-
ably related to those of the Ba(thd)2 [22] or Ba(hfac)2
analogues [23].
Treatment of [Cu(OMe)2]ꢀ with 2 equiv. of mpaH in
hexane afforded Cu(mpa)2 (9) in 92% yield. EPR spec-
tra in hexane at r.t. display a quadruplet [I63Cu (N=
69%) and I65Cu (N=31%)=3/2, N=natural
abundance] at ꢀgꢁ=2.11 with a coupling constant
ꢀAꢁ=83.4 G. Compound 9 is likely to be monomeric
as reported for Cu(etac)2 (etacH=ethyl-3-oxobutanate
ester) [13].
3.2. Crystal structures of [Ba(mpa)2(TMEDA)2] (7)
and [Y(mpa)3(bipy)] (3)
The structure of [Ba(mpa)2(tmeda)2] is shown in Fig.
1. Selected bond lengths and angles are collected in
Table 4. The barium atom is eight-coordinated (four
Ba–N and four Ba–O bonds) in a slightly distorted
square antiprismatic geometry. The Ba–O distances
Fig. 2. X-ray structure of Y(mpa)3(bipy) (3) showing the atom
numbering scheme (thermal ellipsoids at 20% probability).
,
range from 2.643(6) to 2.739(7) A; the Ba–N ones from
,
2.925(9) to 3.058(10) A. These values fall in the range
commonly observed for Ba–O(thd) [7,11,12] and Ba–N
coordination bonds [24]. The mpa ligands are linked to
the metal in an asymmetric manner giving raise to
slightly different Ba–O bond distances, the longest one
corresponding to the ester functionality. The C–O car-
bonyl bond distances are similar. The two mpa ligands
are in a trans position with respect to the barium
centre. The tertiobutyl substituents are on the same side
of the plane described by C(13), Ba, C(3). Hence the
molecule is not centrosymmetric. The torsion angle
between the two mpa planes is 48.34(39)°. The structure
of 7 is related to that of Ba(thd)2(tmeda)2 which has
been reported by us [25] but the poor quality of the
latter crystals and thus of the structure prevents de-
tailed comparison of bonds distances and angles. Octa-
coordination for barium has found precedent for
monomeric species such as [Ba(thd)2(triglyme)] or
[Ba(thd)2(MeOH)2(H2O)2] [26] as well as for dimeric
ones such as [Ba(m-thd)2(ArOH)2(THF)]2 (Ar=3.5-
tBu2C6H3) [27].
Table 4
,
Selected bond lengths (A) and angles (°) for Ba(mpa)2(tmeda)2 (7)
Ba(1)–O(1)
Ba(1)–O(2)
Ba(1)–O(11)
Ba(1)–O(12)
Ba(1)–N(1)
Ba(1)–N(2)
Ba(1)–N(11)
Ba(1)–N(12)
2.739(7)
2.643(6)
2.659(7)
2.725(8)
2.948(9)
2.989(9)
2.925(9)
3.058(10)
O(1)–Ba(1)–N(11)
O(1)–Ba(1)–N(1)
O(1)–Ba(1)–N(2)
O(1)–Ba(1)–N(12)
O(2)–Ba(1)–O(11)
O(2)–Ba(1)–O(12)
O(2)–Ba(1)–O(1)
O(11)–Ba(1)–O(12)
O(11)–Ba(1)–O(1)
O(12)–Ba(1)–O(1)
O(2)–Ba(1)–N(1)
O(2)–Ba(1)–N(2)
O(2)–Ba(1)–N(11)
O(2)–Ba(1)–N(12)
O(11)–Ba(1)–N(11)
O(11)–Ba(1)–N(1)
O(11)–Ba(1)–N(2)
O(11)–Ba(1)–N(12)
O(12)–Ba(1)–N(11)
O(12)–Ba(1)–N(1)
O(12)–Ba(1)–N(2)
O(12)–Ba(1)–N(12)
N(1)–Ba(1)–N(2)
N(1)–Ba(1)–N(12)
N(2)–Ba(1)–N(12)
N(11)–Ba(1)–N(1)
N(11)–Ba(1)–N(2)
N(11)–Ba(1)–N(12)
83.3(2)
126.8(2)
75.8(2)
78.7(2)
120.7(2)
153.4(2)
65.2(2)
64.7(2)
155.1(2)
122.2(2)
76.0(2)
82.2(2)
77.5(2)
127.8(3)
75.4(2)
76.6(2)
127.6(3)
79.9(2)
126.9(2)
80.7(3)
76.0(2)
78.0(3)
63.6(3)
153.3(3)
125.1(3)
123.0(3)
155.5(3)
61.3(3)
The structure of Y(mpa)3(bipy) is presented in Fig. 2.
The structure is wholly consistent with the analytical
and spectroscopic data. However, in view of the poor
quality of the X-ray data, only a partial structural
report will be given. The yttrium atom is eight-coordi-
nated, bound to six oxygen atoms and two nitrogen
atoms. The Y–O distances range from 2.25(2) to
,
2.34(2) A; the Y–N coordination bonds are longer
,
(2.515(20) A average) These values are in agreement
with the body of the literature [21,28]. The two different
ligations result in a slightly distorted square antipris-
matic surrounding of the yttrium atom. This structural
type is quite common in lanthanide b-diketonate chem-
istry with complexes such as [Ln(acac)3(phen)] (phen=

H. Guillon et al. / Inorganica Chimica Acta 304 (2000) 99–107
105
o-phenanthroline) (Ln=La, Lu [29] or Eu [30]), [La-
(acac)3(H2O)2], [Eu(thd)3(Py)2] (py=pyridine) [21].
The bite angles are quite different for the two com-
pounds with values of 75.1(7)° average for 3 and only
64.9(2)° average for 7. No intermolecular interactions
were observed in the solid state structures of 3 and 7.
heptane-3,5-dionates. The solubility of the copper-b-
diketonate, the less soluble, but also the one needed in
the largest amount due to the formulation of the mate-
rial, limits the concentration of the precursors solu-
tions. Cu(mpa)2 is about ten times more soluble than
Cu(thd)2 in hexane (0.8 and 0.09 mol l−1, respectively)
and three times more soluble in diglyme (0.23 and 0.08
mol l−1, respectively). Yttrium and barium ketoesterate
complexes have similar or better solubilities than
M(thd)x analogues.
3.3. Reacti6ity
The metal-b-ketoesterate bond proved to be quite
labile. This is illustrated by the sensitivity to moisture
of 1 as seen before. Another aspect is the facility of
ligand exchange reactions. Since the solubility of
Cu(mpa)2 in diglyme was improved with respect to that
of Cu(thd)2, it was envisioned as an alternative source
of copper in association to the usual tetramethylhep-
tanedionates of barium and yttrium. However,
Cu(mpa)2 is rapidly (approximately 30 min) converted
into Cu(thd)2 when mixed with either Ba(thd)2 or
Y(thd)3 in diglyme at r.t. as evidenced by UV–Vis
spectroscopy [4].
[Y(mpa)3]m and [Ba(mpa)2]m are non-volatile while
Cu(mpa)2 sublimes at 60°C/1.3×10−4 Torr. The bar-
ium adducts undergo actually a decomposition (with
loss of the Lewis base) prior to sublimation giving the
non-volatile [Ba(mpa)2]m oligomer. Their behaviour is
comparable to that of the Ba(thd)2 adducts [7,20]. By
contrast, Y(mpa)3(tmeda) and Y(mpa)3(bipy) sublime
at 120–125°C and 140–145°C/1.3×10−3
Torr, respec-
tively, without any loss of the neutral ligand and the
adducts are recovered (FT-IR, NMR evidence). These
b-ketoesterate adducts are, to the best of our knowl-
edge, the first volatile yttrium b-ketoesterates reported.
They have a volatility close to that of Y(thd)3.
Decomplexation and formation of adducts with
Lewis bases was observed to lower the melting point as
compared to [Ba(thd)2]4 [23] or [Ba(hfac)2]ꢀ [2]. A
similar behaviour was observed for the b-ketoesterate
barium complexes
3.4. Physical properties
3.4.1. Solubility and 6olatility properties
The systems implemented at present for the elabora-
tion of YBa2Cu3O7−x films by liquid delivery MOCVD
techniques are essentially based on 2,2,6,6-tetramethyl-
Table 5
3.4.2. Thermal beha6iour
TGA data of the complexes (N2, 1 atm)
Thermogravimetric analyses (TGA) of compounds 2,
3 and 5–9 under argon (1 atm) show that decomposi-
tion processes are complex with, in each case, a number
of thermal events (Table 5). Weight losses for
Y(mpa)3bipy occur in three stages: an initial loss of
around 46.1% up to 350°C, followed by a loss of
around 25.3% between 350 and 570°C and a further
small loss. The initial losses correspond to the elimina-
tion of bipy and of two mpaH ligands. The last step is
slow and accounts for a partial decomposition of the
third mpa ligand. The amount of residue is higher than
that expected for the oxide, it corresponds to the car-
bonate (FT-IR evidence). Four well-defined steps are
observed for Ba(mpa)2(tmeda)2 (7). The first step corre-
sponds to the elimination of the Lewis base; the other
to partial decomposition of mpa ligands. As for yt-
trium, the residue is essentially the carbonate as confi-
rmed by FT-IR. TGA experiments under reduced
pressure (5×10−2 Torr) lead to yttrium oxide at 500°C
for 3 whereas the behaviour of 7 remained unchanged.
TGA profiles of Y(mpa)3(bipy) at 1 atm and under
reduced pressure are illustrated in Fig. 3. The TGA
pattern of Cu(mpa)2 shows two well-defined steps. The
first step can be associated with the elimination of one
of the mpa ligands and a partial decomposition of the
Complexes
T (°C)
Dm (%)
Y(mpa)3(tmeda) (2)
90–280
280–530
33.1
33.1
Y(mpa)3(bipy) (3)
160–350
350–570
570–890
46.1
25.3
3.3
[Ba2(mpa)4(diglyme)]m (5)
80–160
200–280
280–560
560–960
14.1
16.9
22.2
10.5
Ba(mpa)2(18–crown–6) (6)
Ba(mpa)2(tmeda)2 (7)
Ba(mpa)2(pmdta) (8)
Cu(mpa)2 (9)
50–280
280–350
350–550
550–740
34.6
22.7
10.6
1.9
60–180
220–280
280–600
800–970
35.0
9.4
13.6
9.7
80–200
240–290
290–600
800–980
24.6
13.5
17.7
9.5
150–255
255–340
62.7
15.8

106
H. Guillon et al. / Inorganica Chimica Acta 304 (2000) 99–107
Fig. 3. TGA patterns of Y(mpa)3(bipy) under argon (—) and reduced pressure (---).
second one. The residue left at 350°C corresponds to
CuO as observed for Cu(etac)2 [13].
Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-
mail: deposit@ccdc.com.ac.uk or www: http://
www.ccdc.cam.ac.uk).
4. Conclusion
Acknowledgements
A series of novel air-stable b-ketoesterates of yttrium,
barium and copper(II) has been synthesised and fully
characterised. All complexes were stable to both air and
moisture in the solid state. These compounds, especially
the copper one, have a high solubility in polar and
non-polar solvents such as diglyme or hexane as com-
pared to the thd analogues. This can be interesting for
increasing concentration of precursor solutions in liquid
injection MOCVD techniques. Lewis base yttrium ad-
ducts and the copper derivative have good volatility
properties and could be used as well in conventional
MOCVD processes.
This work was supported by the EEC (BRE2-CT94-
0742). We thank Dr J.M. Letoffe´ (Lyon) for the TGA
experiments under reduced pressure.
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