Preparation of luminescent sol-gel films from europium and terbium 3-(3′-triethoxysilylpropyl)pentane-2,4-dione complexes

Article abstract of DOI:10.1070/MC2006v016n04ABEH002262

Transparent luminescent sol-gel films have been prepared from the complexes of Eu^III and Tb^III with the new ligand 3-(3′-triethoxysilylpropyl)pentane-2,4-dione synthesised by the reaction of 3-allylpentane-2,4-dione with triethoxysilane in the presence of Speier catalyst.

Full text of DOI:10.1070/MC2006v016n04ABEH002262

Mendeleev
Communications
Mendeleev Commun., 2006, 16(4), 239–241
Preparation of luminescent sol–gel films from europium and terbium
3-(3'-triethoxysilylpropyl)pentane-2,4-dione complexes
Vladimir V. Semenov,*a Nadezhda F. Cherepennikova,a Larisa G. Klapshina,a Iliya S. Grigoriev,a
Boris A. Bushuk,b Sergei B. Bushuk,b Yuliya A. Kalvinkovskayab and William E. Douglasc
a G. A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences, 603950 Nizhnii Novgorod,
Russian Federation. Fax: +7 8312 12 7497; e-mail: vvsemenov@imoc.ras.ru
b B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 220072 Minsk, Belarus
c Laboratoire de Chimie Moléculaire et Organisation du Solide, CNRS UMR 5637, Université Montpellier II,
34095 Montpellier cedex 5, France. Fax: +33 467 143 852; e-mail: douglas@univ-montp2.fr
DOI: 10.1070/MC2006v016n04ABEH002262
Transparent luminescent sol–gel films have been prepared from the complexes of EuIII and TbIII with the new ligand 3-(3'-tri-
ethoxysilylpropyl)pentane-2,4-dione synthesised by the reaction of 3-allylpentane-2,4-dione with triethoxysilane in the presence of
Speier catalyst.
The sol–gel technique allows the preparation of hybrid organo-
inorganic materials for practical applications such as hetero-
geneous catalysis,1,2 photonics,3,4 medicine, and rare metal sepa-
ration technologies.6
in the presence of Speier catalyst (Scheme 1).† Note that the
replacement of an ethoxy group and a hydrogen atom in
triethoxysilane by a hydroxy group of the ketone in the enol
form, is possible in principle (Scheme 2).
However, we found that, without the addition of H2PtCl6,
3-allylpentane-2,4-dione did not interact with triethoxysilane
even at 80–100 °C. No reaction was also observed in the case of
tetraethoxysilane or hexamethyldisilazane.
The well-known sol–gel technique is based on the carbo-
functional trialkoxysilanes (RO)3Si(CH2)n-Z.7 The latter can be
prepared by the silylation of functional organic compounds
containing C=C bonds by trialkoxysilanes (RO)3SiH, or by the
replacement of Cl atoms by alkoxy groups in Cl3Si(CH2)n-Z.
β-Diketones are used as analytical reagents in photometry.
Stable volatile transition and rare earth metal complexes have
been prepared from silicon-containing derivatives for the use
in chemical vapour deposition (CVD) processes.8,9 Here, the
preparation of europium and terbium complexes with a new
functional ligand containing a β-diketone fragment and a tri-
ethoxysilyl group is reported. Such compounds open up the
possibility of forming novel sol–gel materials (hybrid films,
fibres and porous glasses) for many practical applications.
Pentane-2,4-dione silylated at the allyl group exists mainly
in the ketone form. The very low intensity of the C–OH band in
the region 3500–3400 cm–1 shows that the proportion of the
†
3-(3'-Triethoxysilylpropyl)pentane-2,4-dione 1. To 49.3 g (0.30 mol)
of (EtO)3SiH, 15.0 g (0.107 mol) of 3-allylpentane-2,4-dione and 10 drops
of a 0.02 M H2PtCl6·6H2O solution in THF were added. After slight
heating an intense reaction took place accompanied by a darkening of
the reaction mixture. Further heating at 150 °C for 10 h followed by
distillation afforded 14.3 g of transparent yellow liquid boiling at 80–98 °C
(3 Torr). Redistillation gave 8.7 g (27%) of 1, bp 89–92 °C (3 Torr),
nD20 1.4364. IR (n/cm–1): 3420 (w, CO–H), 2975 (vs, C–H), 2940 (vs, C–H),
2895 (vs, C–H), 1730 (sh), 1700 (vs, C=O), 1670 (w, C=O), 1625 (w,
C=C), 1480 (w), 1445 (m), 1385 (s), 1355 (s), 1300 (m), 1250 (m), 1165
(vs, SiOEt), 1100 (vs, SiOEt), 960 (vs, SiOEt), 795 (vs, SiOEt), 680 (vw),
(EtO)3Si
Si(OEt)3
H2PtCl6
1
630 (vw), 475 (m), 450 (m). H NMR (200 MHz, CDCl3) d: 0.55–0.66
+ (EtO)3SiH
+
(m, 2H, CH2Si), 0.77, 0.80, 0.84, 0.88 (q, 1H, CHSi), 1.13, 1.14, 1.16,
1.20, 1.18, 1.21 (s, 9H, MeCH2O), 1.32–1.46 (m, 2H, CH2), 1.77, 1.81,
1.85, 1.89 (q, 2H, CH2), 2.06, 2.09, 2.12 [t, 3H, MeC(O)], 2.23, 2.28,
2.32 (t, 3H, MeCOO), 3.54, 3.58, 3.61, 3.65 [q, 1H, CH(COMe)2], 3.70,
3.74, 3.77, 3.79, 3.81, 3.82 (s, 6H, MeCH2O). 29Si NMR (200 MHz,
CDCl3) d: 41.2, 45.5, 45.7, 46.1. UV (film on quartz, l/nm): 227, 290.
Found (%): C, 54,93; H, 9.30; Si, 10.06. Calc. for C14H28O5Si (%):
C, 55.23; H, 9.27; Si, 9.23.
O
O
O
O
O
O
1
1'
Scheme 1
3-(3'-Triethoxysilylpropyl)pentane-2,4-dione 1 was synthesised
by the silylation of 3-allylpentane-2,4-dione by triethoxysilane
Mendeleev Commun. 2006 239

Mendeleev Commun., 2006, 16(4), 239–241
2
1
1.0
0.8
0.6
0.4
0.2
+
2 (EtO)3SiH
O
OH
+
0.0
200
+
EtOH + 1/2 H2
300
400
/nm
500
600
l
O
O
O
O
Si
Si
Figure 2 Fluorescence (1, lexc = 305 nm) and fluorescence excitation
(2, lrec = 547 nm) spectra of a film prepared from 3 (70 wt%) and APTES
(30 wt%) (10 wt% Tb).
EtO
OEt
EtO
OEt
OEt
H
Scheme 2
The formation of the lanthanoid complex causes significant
changes in the IR spectrum in the β-dicarbonyl fragment vibra-
tion region. The ν(C=O) absorption band of the starting diketone
(1700 cm–1) is shifted to the lower frequency region (1590–
1570 cm–1). The position and intensities of the triethoxysilyl
group bands in the silylated β-diketoketone ligand remain almost
unchanged on formation of complexes 2 and 3 confirming that
the inner coordination sphere of the lanthanoid cation does not
include n-donor EtO substituents. The absorption in the region
corresponding to the hydroxyl group vibration (3420 cm–1) is of
very low intensity.
enol form is very small. Silylation causes the complete disap-
pearance of the band at 3080 cm–1 (νC–H in H–C=C) and the
appearance of very intense bands of the triethoxysilyl group at
1165, 1110, 960 and 795 cm–1. 3-Allylpentane-2,4-dione shows
four bands in the region 1800–1500 cm–1; two bands at 1745
and 1700 cm–1 can be related to the C=O bond vibration and
the other two (1645, 1615 cm–1) correspond to the C=C bond
vibrations in the allyl and enol groups. The introduction of
the triethoxysilyl fragment greatly simplifies the spectrum in the
region 1800–1500 cm–1 because of the very low concentration
of the enol form and the Z- and E-isomers. Compound 1 contains
a very strong band at 1700 cm–1 and two very weak bands at 1670
and 1625 cm–1. The first absorbance corresponds to the vibration
of the ketone form C=O bond and the other two characterise the
enol components [1670 (C=O) and 1625 cm–1 (C=C)].
3 (EtO)3Si
OH
+ Ln(OPri )3
O
In the UV spectrum, two bands at 227 and 290 nm are present
(intensity ratio of 1.6:1) corresponding to the π®π* and n®π*
transitions, respectively.
(EtO)3Si
O
O
The 1H NMR spectrum of 1 shows two intense multiplets (at
1.10–1.30 and 3.70–3.90 ppm) for the Si ethoxy groups. Resonances
for the methyl protons (2.10–2.40 ppm) in the MeC(O)– and
MeC(=C)O– fragments and three multiplets (0.60–0.70, 1.35–
1.50 and 1.80–1.93 ppm) corresponding to methylene substituents
in the triethoxysilylpropyl group (EtO)3SiCH2CH2CH2 are also
observed. Two signals of much lower intensity at 0.3–0.4 and
3.65 ppm are assigned to the hydrogen atom of the allyl group
silylated at the β-position MeCH[Si(OEt)3]CH2 and to the hydro-
gen atom of the β-diketone fragment MeC(O)CHC(O)Me. The
splitting of the signal can be explained by the presence of isomers
1,1' and traces of the enol form in the Z and E positions. The
29Si NMR spectrum showed four close signals of different inten-
sities in the region –45 to –47 ppm, which confirm the presence
of four isomers (out of six possible) of 1, as confirmed by GL
chromatography.
Ln
– 3 PriOH
3
2 Ln = Eu
3 Ln = Tb
Scheme 3
The incorporation of triethoxysilyl groups into compounds
1–3 gives the possibility of forming transparent films and gels.§
Silylated β-diketone 1 can be hydrolysed with air moisture
giving viscous oligomers after 24 h. Further heating up to 100 °C
causes the evaporation of more than half of the product with the
formation of a solid film. In order to improve the optical and
mechanical quality of the films, the addition of 3-aminopropyl-
triethoxysilane (APTES, 20–30 wt%) is used affording solid films,
‡
Tris[3-(3'-triethoxysilylpropyl)pentane-2,4-dionate]europium 2. To
Lanthanoid alkoxides are the most convenient reagents for
β-diketonate lanthanoid complex preparation since they allow
the performance of the reaction in water-free media. The reaction
products contain no water but only alcohol, which can be easily
removed from the reaction mixture.
The reaction of europium(III) or terbium(III) isopropylate
gives rise to tris(β-diketonate)s 2, 3, which are coloured viscous
liquids easily hydrolysed with moist air.‡
the solution of 1.0 g (3.04×10–3 mol) of europium isopropylate in 10 ml
of diethyl ether, 3.1 g (1.02×10–2 mol) of 1 in 5 ml of diethyl ether were
added. The tube was sealed and heated at 60–70 °C for 3 h. The solvent
was removed in vacuo. The viscous orange residue was dissolved in 7 ml
of hexane, and 15 ml of acetonitrile were added. The precipitate was
washed with acetonitrile and dried in vacuo affording 2.2 g (67%) of 2
(fine orange powder). IR (n/cm–1): 1714, 1674, 1588 (O=C–C=C–O–Eu),
1345, 1285, 1254 (CH), 1168, 1107, 1082, 966, 789 (SiOEt), 885, 678,
546, 480, 455, 410. Found (%): C, 46.31; H, 7.37; Eu, 14.96; Si, 7.75.
Calc. for C42H81EuO15Si3 (%): C, 47.48; H, 7.68; Eu 14.86; Si, 7.88.
Tris[3-(3'-triethoxysilylpropyl)pentane-2,4-dionate]terbium 3. To a
solution of 1.35 g (0.004 mol) of terbium isopropylate in 10 ml of diethyl
ether 3.65 g (0.012 mol) of 1 in 5 ml of diethyl ether were added. After
7 h, the mixture was centrifuged and the solvent and isopropyl alcohol
were removed from the supernatant transparent yellow solution. The
resulting residue was taken up in 5 ml of toluene and then 10 ml of
acetonitrile were added giving a precipitate, which was separated, washed
with toluene and then dried for 1 h at 50–60 °C in vacuo. 3.22 g (0.03 mol,
75%) of light yellow powder 3 were obtained. IR (n/cm–1): 1714, 1664,
1573 (O=C–C=C–O–Tb), 1345, 1300, 1259 (CH), 1168, 1102, 1082,
961, 799 (SiOEt), 895, 673, 481. Found (%): C, 46.90; H, 7.56; Si, 8.01;
Tb, 15.05. Calc. for C42H81O15Si3Tb (%): C, 47.18; H, 7.63; Si, 7.88;
Tb, 14.86.
1.0
0.8
0.6
0.4
2
1
0.2
0.0
200 300
400
500
600 700
l/nm
Figure 1 Fluorescence (1, lexc = 398 nm) and fluorescence excitation
(2, lrec = 460 nm) spectra of a film prepared from 2 (14 wt% Eu).
240 Mendeleev Commun. 2006

Mendeleev Commun., 2006, 16(4), 239–241
which remain transparent after heating up to 150 °C demon-
spectrum dramatically. A strong decrease in the cation lumine-
scence takes place and the matrix emission at 416 nm becomes
predominant.
strating the high hydrolytic stability of 1. Complexes 2 and 3
rapidly form solid films in air. For example, the europium
derivative cast from ether solution gives a transparent yellow
film in 20–30 min. However, to form films from the terbium
complex, it is necessary to add 50 wt% APTES.
This work was supported by INTAS (grant no. 03-51-5959), the
Russian Foundation for Basic Research (grant no. 05-03-32556,
06-03-81005Bel and 06-03-08208), the President of the Russian
Federation (grant no. 8017.2006.3) and the Russian Academy of
Sciences (Nanotechnology Programme).
The fluorescence excitation spectrum of a film produced from
1 and APTES shows an intense band at 379 nm (lrec = 460 nm).
The emission spectrum consists of a wide band at 440 nm (lexc
=
= 370 nm) typical of organosilsesquioxane matrices containing
N–H bonds.10 The fluorescence and fluorescence excitaton spectra
of a film of europium complex 2 on quartz are shown in Figure 1.
The fluorescence excitation spectrum shows a single band at
377 nm (the recording wavelength is 460 nm). The change of
lrec to 617 nm results in two bands at 259 and 333 nm. The
fluorescence spectrum with excitation at 398 nm showed three
narrow lines at 593, 618 and 667 nm corresponding to the
5D0 ® 7F1, 5D0 ® 7F2 and 5D0 ® 7F3 transitions of the europium
cation and a wide intense band for the matrix emisson at 491 nm.
Reduction of the excitation wavelength to 370 nm significantly
decreases the intensity of the Eu3+ luminescence and shifts the
maximum of the emission band to 468 nm.
References
1
2
3
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Ser. IV, 2000, 1, 425.
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6
Z. Ye, M. Tan, G. Wang and J. Yuan, J. Mater. Chem., 2004, 14, 851.
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678, 15.
The fluorescence and fluorescence excitation spectra of a
film formed from terbium complex 3 on addition of APTES are
presented in Figure 2. The fluorescence excitation spectrum
(recording wavelength of 547 nm) consists of two bands in the
UV region at 230 and 308 nm. Excitation at 305 nm gives an
emission spectrum with four narrow peaks at 491, 547, 585 and
9
10 V. de Zea Bermudez, D. Ostrovskii, M. C. Goncalves, L. D. Carlos,
R. A. Sa Ferreira, L. Reis and P. Jacobsson, Phys. Chem. Chem. Phys.,
2004, 6, 638.
5
5
5
623 nm corresponding to the D4 ® 7F6, D4 ® 7F5, D4 ® 7F4
and 5D4 ® 7F3 f–f transitions of Tb3+ and a weak matrix emission
at 393 nm. The D4 ® 7F5 transition has the greatest intensity.
5
Reduction of the exciting frequency (lex = 370 nm) changes the
§
Film preparation. (a) Complex 2 was dissolved in diethyl ether (ratio
of 1:3). The solution was put on a quartz surface with a capillary tube. In
20 min, a transparent hard yellow film 28 µm in thickness was obtained.
(b) To a solution of 0.128 g of 3 in 0.3 ml of diethyl ether, 0.067 g of
APTES were added. The resulting liquid was put on a quartz surface
with a capillary tube. After 3 h, a light yellow transparent hard film
37 µm in thickness was obtained.
Received: 31st October 2005; Com. 05/2604
Mendeleev Commun. 2006 241