Synergism by sublimation of volatile lanthanide β-diketonates

Article abstract of DOI:10.1016/S0925-8388(00)01047-1

The synergistic effect by sublimation manifests itself in an increase in the volatility of nonvolatile or slightly volatile compounds in the presence of highly volatile agents. In this study, manifestations of the synergistic effect are demonstrated by th

Full text of DOI:10.1016/S0925-8388(00)01047-1

Journal of Alloys and Compounds 308 (2000) 158–162
L
www.elsevier.com/locate/jallcom
Synergism by sublimation of volatile lanthanide b-diketonates
*
Natalia P. Kuzmina , Larissa I. Martynenko, Nikolai V. Chugarov, Irina G. Zaitseva,
Andrei N. Grigoriev, Andrei N. Yakushevich
Department of Chemistry, Moscow State University, 119899 Moscow, Russia
Received 10 May 2000; accepted 18 May 2000
Abstract
The synergistic effect by sublimation manifests itself in an increase in the volatility of nonvolatile or slightly volatile compounds in the
presence of highly volatile agents. In this study, manifestations of the synergistic effect are demonstrated by the evaporation of mixed
ligand complexes, derivatives of lanthanide acetylacetonates and neutral organic ligands, and by evaporation of the following mixtures:
yttrium and zirconium acetylacetonates, lanthanum and nickel dipivaloylmethanates and acetylacetonates, and lanthanum and aluminum
acetylacetonates.
 2000 Elsevier Science S.A. All rights reserved.
Keywords: Lanthanide b-diketonates; Evaporation; Synergistic effect
1
. Introduction
evaporation of mixed ligand complexes, derivatives of
lanthanide acetylacetonates and neutral organic ligands,
and by evaporation of mixtures of yttrium and zirconium
acetylacetonates [1], of lanthanum and nickel di-
pivaloylmethanates and acetylacetonates, and of lanthanum
and aluminum acetylacetonates.
The synergistic effect by sublimation manifests itself in
an increase in the volatility of nonvolatile or slight volatile
compounds in the presence of highly volatile agents. The
study of the nature of this effect is of both practical and
basic interest for lanthanide b-diketonates. On the one
hand, some of these compounds are low or nonvolatile and
an increase of their volatility could promote their wider use
in modern technology in the chemical vapor deposition of
lanthanide-containing thin films. On the other hand, lantha-
nide b-diketonates are very suitable for studying the
correlation among composition–structure–volatility–syner-
gism.
2. Experimental
The starting b-diketonates, Ln(acac) ?nH O, Ln(thd) ,
3
2
3
Al(acac) , Zr(acac) , Ni(thd) and [Ni(acac) ] , were
3
4
2
2 3
prepared and purified according to literature methods [1–
5]. Mixed ligand complexes [Ln(acac) (Q) ] [Q51,10-
3
n
The two main prerequisites for the manifestation of the
synergistic effect can be formulated as follows: (1) conver-
sion of polynuclear lanthanide b-diketonates into mononu-
clear coordinatively saturated complexes on interaction
with neutral donor ligands (intramolecular rearrangement);
phenanthroline
(Phen),
hexamethylphosphortriamide
(HMPA) or acetylacetonimine (HAcim)] were synthesized
by the general method described in Ref. [6]: interaction
between Ln(acac) ?nH O and Q in organic solvents fol-
lowed by slow crystallization of products. The data from
elemental (C, H, N), XRD and IR analyses confirmed the
formulae.
Mixtures of metal b-diketonates in different mole ratios
of components were prepared by mixing individual solid
complexes. The La(thd) –Ni(thd) mixture was obtained
3
2
(
2) formation of a new system of intermolecular interac-
tions as a result of the addition of highly volatile 3d-, 4d-
or p-metal complexes to low volatile lanthanide b-diketo-
nates (intermolecular rearrangement). In this paper, mani-
festations of the synergistic effect are demonstrated by
3
2
by stirring n-hexane solutions of [La(thd) ] and Ni(thd)
3
2
2
(
50:50 mol%) followed by solvent removal under reduced
*
Corresponding author. Tel.: 17-095-939-3836; fax: 17-095-939-
998.
E-mail address: kuzmin@inorg.chem.msu.cu (N.P. Kuzmina).
1
pressure (0.01 Torr) at room temperature. H-NMR spectra
of [La(thd) ] , Ni(thd) and the La(thd) –Ni(thd) mix-
0
3
2
2
3
2
0
925-8388/00/$ – see front matter
 2000 Elsevier Science S.A. All rights reserved.
PII: S0925-8388(00)01047-1

N.P. Kuzmina et al. / Journal of Alloys and Compounds 308 (2000) 158–162
159
ture were recorded on an AC-200P spectrometer (analytical
frequency 200 mHz) in CDCl /TMS. [La(thd) ] , 5.61
3
3 2
(
4H), 5.53 (2H); Ni(thd) , 5.42 (2H); La(thd) –Ni(thd) ,
2
3
2
5
.67 (1H), 5.60 (1H), 5.56 (2H), 5.47 (1H).
Thermogravimetric analysis in vacuum (0.01 Torr) was
carried out with a ‘‘Sinku-Riko’’ TGD-700 thermal ana-
lyzer at a heating rate of 108/min.
Isothermal evaporation experiments in vacuum were run
under the following conditions: pressure, 0.01 Torr; tem-
perature range, 170–2208C; sample weight, 50 mg; heating
time, 30 min. The total weight loss of the sample was
determined gravimetrically and values of a 5 Dm/m ?
m
0
1
00% (Dm is the total weight loss and m0 the starting
weight of the sample) were calculated. Mole contents of
lanthanide complexes in the deposited sublimates were
determined by complexometric analysis and values of
aLn 5 nsubl /nstart ? 100% (nsubl and nstart are the mole
contents of lanthanide in the sublimate and starting sample,
respectively) were calculated. The values of aLn were used
as a characteristic of the synergistic effect. Mole ratios
Fig. 1. Evolution of degree of evaporation (aLn) versus lanthanide and
neutral ligand Q for Ln(acac) (Q) . 1, Ln(acac) ?nH O at 2208C; 2,
3
n
3
2
[Ln(acac)
(HAcim) ] at 1408C; 3, [Ln(acac) HMPA] at 2008C; 4,
n 3
3
[
Ln(acac) Phen] at 2308C.
3
[La]/[Ni] in sublimates were determined by X-ray fluores-
[La(acac) (Phen)] was responsible for the observed syner-
3
cence analysis.
gistic effect.
The
conversion
of
Ln(acac) ?3H O
into
3
2
[
Ln(acac) (Phen)] leads to complete sublimation of
3
acetylacetonates for all lanthanides (Fig. 1, curve 4).
However, transformation into a mixed ligand complex
3
. Results and discussion
[
Ln(acac) (Q) ] does not necessarily result in a synergistic
3 n
3
.1. Effect of neutral ligand addition to lanthanide
effect. The effect strongly depends on the lanthanide and Q
and the stability of the complexes towards dissociation into
acetylacetonates
coordinatively unsaturated Ln(acac) and Q.
3
Lanthanide acetylacetonates are practically nonvolatile
for Lewis base-free acetylacetonate complexes Ln(acac)3,
which show a tendency towards aggregation to achieve a
coordination number greater than six [7,8]. During the
usual synthesis procedure [2], hydrates Ln(acac) ?nH O
Thus, complexes with the strong monodentate donor
ligand HMPA, [Ln(acac) (HMPA)], reveal complete
3
evaporation only for the heavier lanthanides (Fig. 1, curve
3). According to the mass spectrometry data [12], the gas
phase
above
[Ln(acac) (HMPA)]
consists
of
3
2
3
(
Ln5La, n 5 2; Ln5Pr–Lu, n 5 3) are formed. Hydroly-
Ln(acac) (HMPA), Ln(acac) and HMPA. The evaporation
3
3
sis and thermal decomposition of these complexes take
place when heated, inhibiting volatility [7]. The formation
of nonvolatile Y (acac) (OH) from Y(acac) ?3H O [8] is
scheme can be described as
Ln(acac) (HMPA)
→
Ln(acac)3(g)
1
3
(s)
150–2008C
4
10
2
3
2
one example. However, partial sublimation of anhydrous
Ln(acac) (HMPA) 1 HMPA(g) 1 Ln(acac)3(s)
3
(g)
Ln(acac)3 takes place so that Ln(acac) ?nH O can be
3
2
sublimed in the temperature range 160–2408C under low
pressure (0.01 Torr, aLn 5 15–40%). Both the value of aLn
and the temperature at which aLn reaches its maximum
value depend on the lanthanide. This dependence is
displayed as curve 1 in Fig. 1.
The contents of Ln(acac) (HMPA) and Ln(acac) in the
3
3
gaseous phase depend on the Lewis acidity of Ln(acac)3
and are higher for derivatives of heavier elements.
The influence of additional ligand donor capacity on the
The influence of highly volatile organic compound
addition on lanthanide acetylacetonate volatility was
studied in experiments with o-phenanthroline. Solid
Ln(acac) ?nH O and Phen were mixed in different mole
Table 1
Isothermal evaporation of La(acac)
Phen mixture
(aLa ) on heating a La(acac) ?2H O–
3 2
3
a
3
2
ratios (Table 1).
No.
[La]/[Phen]
mole ratio
aLa
(%)
Melting was preceded by isothermal evaporation of the
mixtures. It was shown that the addition of Phen resulted
in an increase in aLa values (Table 1). A detailed study of
La(acac) ?2H O–Phen mixtures [9–11] showed that the
1
2
3
a
1:0
1:0.5
1:1
1563
2864
5364
3
2
formation of mononuclear mixed ligand complexes
Temperature of isothermal evaporation 21708C.

1
60
N.P. Kuzmina et al. / Journal of Alloys and Compounds 308 (2000) 158–162
volatility effect is illustrated by the data for [Ln(acac)3?
HAcim) ] (n 5 2, Ln5La–Gd; n 5 1, Ln5Ho–Lu) (Fig.
(
n
1
, curve 2) [13]. [Ln(acac) (HAcim) ] evolves HAcim
3 n
molecules at rather lower temperatures and forms
Ln(acac)3:
[
Ln(acac) ? (HAcim) ]
→ [Ln(acac) ] 1 nHAcim(g)
3 (s)
90–1108C
3
n
(s)
(
1)
[Ln(acac)3](s) 1
→ [Ln(acac)3](g)
10–1308C
(2)
Stage (2) in this decomposition scheme takes place only
for complexes of heavier lanthanides (at rather low tem-
perature), before melting of [Ln(acac) ] promotes poly-
3
merization.
In general, the synergistic effect observed by addition of
highly volatile organic compounds to lanthanide
acetylacetonates is associated with the formation of mono-
nuclear coordinatively saturated mixed ligand complexes.
The value of the effect depends on the thermal stability of
Fig. 2. TG curves under vacuum (0.01 Torr) for La(acac) ?2H O (1),
3
2
Al(acac) (2) and a La(acac) 2H O–Al(acac) mixture (3) with mole ratio
3
3
2
3
[La]/[Al]51:1.
the complex towards dissociation into Ln(acac) and Q.
3
h[Zr(acac)4]12x[Y(acac) ] j → Zr(acac)
1 Y(acac)3(g)
4(g)
3
x
3
.2. The synergistic effect by sublimation of metal b-
diketonate mixtures
Intermolecular interaction between Zr(acac)4 and
Y(acac) ?3H O leads to easier dehydration of the yttrium
complex, inhibited hydrolysis and, thus, increased volatili-
3
2
The synergistic effect also emerges on addition of highly
volatile d-metal b-diketonates to lanthanide-containing
complexes. First, synergism was obtained by evaporation
ty. In the absence of Zr(acac) , hydrolysis and formation of
4
nonvolatile hydroxoaggregates took place, which de-
of Y(acac) ?3H O and Zr(acac) mixtures [1] (Table 2): it
3
2
4
pressed the volatility of Y(acac) ?3H O [8].
3
2
was demonstrated that the addition of coordinatively
saturated volatile Zr(acac) to Y(acac) ?3H O resulted in
One would expect a similar synergistic effect for a
4
3
2
mixture of slightly volatile La(acac) ?2H O with mononu-
3
2
an increase in the volatility of the latter.
clear coordinatively saturated Al(acac)3 [14]. Data from
thermal gravimetric analysis at low pressure (Fig. 2) and
isothermal evaporation (Table 3) were collected to de-
termine the temperature range of the manifestation of the
The
formation
of
the
solid
solution
h[Zr(acac)4]
12x
[Y(acac) ?3H O] j (x 5 0.01–0.20) was ob-
3
2
x
tained on cooling of the Zr(acac) –Y(acac) ?3H O melt
4
3
2
(melting took place at 160–1808C), which confirmed
synergistic effect and to estimate its value (a ) for
La
interaction between the complexes. Under a further tem-
perature increase the following processes took place:
La(acac) ?2H O.
3
2
In the temperature range 60–4008C, the weight loss of
La(acac) ?2H O occurred in three stages (Fig. 2, curve 1).
3
2
h[Zr(acac)4]12x[Y(acac)3 ?
In the first stage (60–1408C), water loss and partial
hydrolysis of the lanthanum complex takes place (the
complex melts at 1388C) and the second stage (145–
3
H O] j → h[Zr(acac) ] [Y(acac) ] j 1 3H O
2
x
4
12x
3
x
2
Table 2
Effect of the addition of Zr(acac) on the degree of evaporation (a ) of
Table 3
4
Y
a
Y(acac) ?3H O [12]
Effect of the addition of Al(acac)3 on the degree of evaporation (aLa) of
La(acac) ?2H O
3
2
3
2
No.
Y(acac) ?3H O
mole content (%)
aY
(%)
3
2
No.
La(acac) ?2H O
mole content (%)
T
(8C)
aLa
(%)
3
2
1
2
3
4
5
6
a
10
20
30
50
55
9762
9862
8264
8564
7664
1562
1
2
3
4
5
6
10
50
50
66
100
100
220
220
170
170
220
170
9862
5362
3362
2262
1861
1562
100
Temperature of isothermal evaporation 22008C.

N.P. Kuzmina et al. / Journal of Alloys and Compounds 308 (2000) 158–162
161
Table 4
2
908C) corresponds to the evaporation of La(acac) accom-
3
Effect of the addition of Ni(acac)2 to La(acac) ?H O on the degree of
3
2
panied by partial thermal destruction. The third stage
290–4008C) corresponds to greater thermal decomposi-
tion of the organic part. The maximum value of aLa for
La(acac)3 obtained by isothermal evaporation at 2208C
evaporation (aLa, aNi
)
(
No.
T
am
aLa
aNi
(
8C)
(%)
(%)
(%)
1
2
3
4
150
180
210
240
961
361
(
Table 3, No. 2) was about 18%. Al(acac)3 evaporates
2862
7662
8561
1961
5862
8065
2162
7261
9065
intact in the temperature range 120–1958C (Fig. 2, curve
2
) and melts at 1858C.
The curve obtained for the La(acac) ?2H O–Al(acac)
3
2
3
mixture (50:50 mol%) (Fig. 2, curve 3) can be described
as a superposition of curves 1 and 2 with two features: (i)
dehydration and partial hydrolysis take place at a tempera-
ture (75–1008C) lower than in the case of pure La(acac)3?
the synergistic effect for the lanthanum complex manifests
itself only as an increase of a . No effect on its
La
evaporation temperature was detected, but a considerable
decrease of the evaporation rate for the nickel complex
was observed.
2
H O; and (ii) in the second stage (100–1708C) the
2
mixture of Al(acac) with La(acac) evaporates.
3
3
About 33% of the starting lanthanum acetylacetonate
was found in the sublimate, obtained after isothermal
heating of the mixture (50:50 mol%) (Table 3, No. 4). The
value of aLa for this mixture increased to its maximum
To demonstrate the synergistic effect accompanied by a
decrease of the evaporation temperature, the La(thd)3 –
Ni(thd) mixture was chosen. Lanthanum dipivaloylmetha-
2
nate has a dimeric structure due to the formation of two
(
53%) with increase of the isothermal evaporation tem-
perature (to 2208C) (Table 3, No. 5). The heating of a
0:50 mol% mixture did not lead to complete evaporation
bridging bonds between La(thd) moieties [16]. The nickel
3
dipivaloylmethanate has a mononuclear square structure
and tends to increase the coordination number of the
central nickel ion to 6 due to the additional coordination of
two donor atoms in solution [15]. The formation of
lanthanum–nickel dipivaloylmethanate associates was as-
sumed to take place also as in the case of lanthanum and
nickel acetylacetonates. Both Ni(thd)2 and [La(thd)3]2
sublimed without melting. In order to obtain an interaction
between the components, a La(thd) –Ni(thd) mixture
5
of lanthanum acetylacetonate, although mixtures with a
lower (,10 mol%) content of the lanthanum component
give a value of aLa of 100% (Table 3, No. 6).
The data obtained demonstrate that the cause of the
synergistic effect observed for La(acac) ?2H O–Al(acac)
3
2
3
mixtures, as well as for Y(acac) ?3H O–Zr(acac) [1], lies
in the formation of solid solutions with rather low contents
3
2
4
3
2
of lanthanide acetylacetonates. Y(acac) ?3H O–Zr(acac)
(50:50 mol%) was prepared in n-hexane followed by
removal of the solvent at reduced pressure. Proton NMR
spectroscopy of the La(thd)3 and Ni(thd)2 mixture in
CDCl3 was used to detect their reactivity towards each
other, and the spectra confirmed interaction between the
components in solution. The peaks of the methine protons
in the spectrum of a solution of the mixture were shifted
with respect to the spectra of individual complexes (see
Experimental). The results of solid mixture sublimation
demonstrated the proposed synergistic effect (Table 5).
Individual complexes [La(thd) ] and Ni(thd) sublimed
3
2
4
mixtures were used for the deposition of ZrO2 films
stabilized by a small amount of Y O . The mole ratio
2
3
[
La]/[Al]51:1 in La(acac) ?2H O–Al(acac) mixtures
3 2 3
would also be preferable in terms of LaAlO3 thin film
deposition.
One of the ways suggested to achieve complete evapora-
tion of mixtures with 50% mole content of lanthanide
acetylacetonates is interaction with an unsaturated but
highly volatile complex to form a heterometallic associate.
To check this proposal, nickel acetylacetonate was
chosen as the additional agent in La(acac) ?2H O evapora-
3
2
2
completely at 185 and 1258C, respectively, but the tem-
perature of the complete sublimation of their mixture was
1608C (Table 5, No. 5). Study of the temperature depen-
dence of the sublimate composition showed that the
La(thd) –Ni(thd) mixture sublimed non-intact (Table 5,
3
2
tion. On the one hand, Lewis base-free [Ni(acac) ] dem-
2
onstrates the tendency to associate into a trinuclear species
[
Ni(acac) ] [15] and, on the other, a Ni(acac) –La(acac) ?
2 3 2 3
2
H O mixture is of interest as a prospective precursor for
2
3
2
LaNiO thin film deposition by MOCVD.
3
Isothermal evaporation experiments were performed for
Table 5
Effect of the addition of Ni(thd)2 to [La(thd)2]3 on the degree of
evaporation (aLa, aNi
a La(acac) ?2H O–Ni(acac) mixture (50:50 mol%) in the
3
2
2
temperature range 130–2408C (Table 4).
)
Under the given conditions, [Ni(acac)2] evaporated
3
No.
Complex
T
a
m
a
La
a
Ni
completely at 1508C. The La(acac) ?2H O–Ni(acac) mix-
or mixture
(8C)
(%)
(%)
(%)
3
2
2
ture melted at 1308C and then evaporated, but the weight
loss at 1508C was 9% and the value of aNi was only 3%, in
contrast to 100% evaporation of pure [Ni(acac) ] . Increas-
ing the temperature to 2408C led to an increase of aNi and
aLa to 90 and 80%, respectively (Table 4, No. 4). Thus,
1
2
3
4
5
Ni(thd)2
[La(thd)3]2
125
185
130
145
160
100
100
4062
6062
100
100
100
La(thd)
–Ni(thd)
4862
8561
100
3361
4462
100
2
3
3
2
2
2
La(thd) –Ni(thd)
3
La(thd) –Ni(thd)
3

1
62
N.P. Kuzmina et al. / Journal of Alloys and Compounds 308 (2000) 158–162
Nos. 3 and 4). This means that the mutual influence of
Ni(thd) and La(thd) results in an increase in the lan-
References
2
3
thanum component sublimation rate and a decrease in that
for Ni(thd)2.
The synergistic effect by evaporation of mixtures of
slightly and highly volatile b-diketonates is influenced by
the evaporation process of the less volatile component.
[1] N.Y. Zharkova, N.G. Dzubenko, L.I. Martynenko, Russ. J. Coord.
Chem. 23 (1997) 611.
[2] J.G. Sites, C.N. McCarthy, L.L. Quill, J. Am. Chem. Soc. 70 (1948)
3
142.
[
[
[
[
[
3] E.W. Berg, J.J.C. Acosta, Anal. Chim. Acta 60 (1972) 497.
4] H. Blitz, E. Clinch, Z. Anorg. Chem. 4 (1904) 218.
5] F.A. Cotton, I.P.J. Fackler, J. Am. Chem. Soc. 83 (1961) 2818.
6] L.I. Martynenko, Russ. J. Chem. Rev. 60 (1987) 1969.
7] M.F. Richardson, W.F. Wagner, D.E. Sands, Inorg. Chem. 7 (1968)
4
. Conclusion
2
495.
[
8] E.U. Barash, P.S. Coan, E.B. Lobkovskii, W.E. Streib, K.G. Caulton,
Volatile lanthanide b-diketonates are used extensively in
Inorg. Chem. 32 (1993) 497.
modern technology for thin film deposition and for doping
of inorganic materials. The synergistic effect, demonstrated
by evaporation of lanthanide acetylacetonates, is one of the
ways to increase the volatility of lanthanide compounds
with low volatility. Lanthanide b-diketonates are very
suitable compounds for study and the observation of
synergistic effects because these complexes are coordina-
tively unsaturated and can form additional intra- and
intermolecular bonds with neutral donor ligands or with
donor atoms of the coordination compounds. These inter-
actions are responsible for the manifestation of the syner-
gistic effect by sublimation or evaporation of lanthanide
b-diketonates.
[9] N.G. Dzubenko, L.I. Martynenko, Russ. J. Inorg. Chem. 29 (1984)
91.
10] N .V . Chugarov, N.P. Kuzmina, Russ. J. Coord. Chem. 23 (1997)
50.
11] N.P. Kuzmina, L.I. Martynenko, Z.A. Tu, A.R. Kaul, G .V . Girichev,
N.I. Giricheva, A.N. Rykov, Yu.M. Korenev, J. Phys. IV C3 (1993)
385.
6
[
[
4
[
[
[
12] N.P. Kuzmina, P.P. Semyannikov, C.T. Nguet, L.I. Martynenko,
Russ. J. Inorg. Chem. 35 (1991) 487.
13] G .V . Trembovetskii, Y .V . Smirnov, I.A. Muravieva, L.I. Martynenko,
Russ. J. Inorg. Chem. 27 (1983) 611.
14] B.W. McClelland, Acta Crystallogr. B 31 (1975) 2496.
[15] F.A. Cotton, J.J. Wise, Inorg. Chem. 5 (1966) 1200.
16] C.S. Erasmus, J.C.A. Boeyens, Acta Crystallogr. B 26 (1970) 1843.
[
Acknowledgements
The authors acknowledge the Russian Basic Research
Foundation for financial support (grant 96-03-32937a).