Direct synthesis of ordered and highly functionalized organosilicas containing carboxylic acid groups

Article abstract of DOI:10.1039/b618228c

A one step synthesis of highly carboxylic acid-functionalized silica, with lamellar structure under acidic conditions, by hydrolysis and polycondensation of a cyanolkyltrialkoxysilane was analyzed. The method consisted of hydrolysis and polycondensation of 1, 2 and 3 in sulfuric acid aqueous solution in order to transform the cyano groups into carboxylic acid groups. The in situ formation of bis-silyalated dimers by hydrogen-bond formation involved the formation of M1, M2 or M3. The hydrolysis of triethoxysilylpropyldiethylphosphonate in 12 M HCI solution was achieved under the conditions of formation of phosphonic acid groups. The longer the alkylene chains, the better the structural order, which rendered easier uptake of Eu ^III. The results show that these materials with high content of H+ per g can be used for high proton conductivity for fuel cells.

Full text of DOI:10.1039/b618228c

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www.rsc.org/materials | Journal of Materials Chemistry
Direct synthesis of ordered and highly functionalized organosilicas
containing carboxylic acid groups
Rola Mouawia, Ahmad Mehdi,* Catherine Reye´ and Robert Corriu*
Received 13th December 2006, Accepted 11th January 2007
First published as an Advance Article on the web 18th January 2007
DOI: 10.1039/b618228c
Ordered and highly functionalized organosilicas containing
carboxylic acid groups were obtained in one step by hydrolysis
and polycondensation of a cyanoalkyltrialkoxysilane (NC–
CH2–(CH2)nCH2–Si(OR)3 with n = 1, 3 and 9) under acidic
conditions; the europium ion adsorption capability of these
materials was investigated.
Scheme 1 Preparation of materials M1–3.
The study of functionalized organic–inorganic materials is an
expanding field of investigation, which should give rise to
advanced materials offering a wide range of possibilities in terms
of chemical or physical properties.1 The control of the structure of
hybrid materials during the sol–gel process is a great challenge in
view of obtaining such materials. Although the classical sol–gel
process usually results in the formation of amorphous materials,2
self-assembly during the sol–gel process of organosilanes bearing
hydrolysable groups offers an opportunity to create ordered
hybrid materials. Recently, much effort has been directed towards
the structural organization of bridged silsesquioxanes at the nano-
meter length scale.3 However, up to now, few examples of bridged
silsesquioxanes with long-range structure have been reported.4,5
We have shown that the hydrolytic polycondensation of
a,v-bis(trimethoxysilyl)alkylenes with long alkylene chains gives
rise in water to long-range ordered (lamellar) materials thanks only
to the hydrophobic interactions between the long alkylene
chains.6a We have shown that it is possible to obtain lamellar
functional (SH groups) materials by introducing an –S–S– bridge
in the core of the alkylene chains followed by reduction of the
–S–S– groups.6b The introduction of ionic interactions (ammo-
nium carbamate salts) instead of covalent –S–S– bonds led also to
lamellar amino functionalized materials.6c
cyano groups into carboxylic acid groups. The in situ formation of
bis-silylated dimers by hydrogen-bond formation involves the
formation of materials M1, M2 or M3 (Scheme 1).
Cyanopentyltriisopropoxysilane 2{ and cyanoundecyltriiso-
propoxysilane 3{ were synthesized as depicted in Scheme 2.
Hydrosilylation of the bromoalkenes gave rise to bromoalkyl-
triethoxysilanes followed by isopropanolysis reaction in order to
avoid the hydrolysis of ethoxy groups during the next step. Then,
treatment of the bromoalkyltriisopropoxysilanes with an aqueous
solution of sodium cyanide (NaCN) in the presence of NBu3
(3 wt%) afforded 2 and 3 in satisfactory yields after distillation. 2–3
were fully characterized by 1H, 13C and 29Si NMR spectroscopies
as well as by elemental analysis.
The synthesis of material M1 is given as an example. Sulfuric
acid solution (9 M; 65 mL) was added to 3.00 g of 1 (cyano-
propyltriethoxysilane, commercially available) at 30 uC. The
mixture was stirred at 30 uC for 45 min. Ethanol was removed
under vacuum from the resulting clear solution in order to avoid
subsequent esterification. Then, the solution was placed into a
Teflon bottle and kept at 150 uC for 6 hours without stirring. The
corresponding solid M1 was recovered by filtration and washed
successively with water (500 mL), acetone (20 mL) and ether
(20 mL). After drying at 120 uC under vacuum for 12 h, 1.78 g
(98%) of M1 was obtained as a white powder.
We now report a one-pot synthesis of highly carboxylic acid-
functionalized silica with lamellar structure under acidic conditions
starting from cyanoalkyltrialkoxysilanes, thanks to hydrogen-bond
formation within the material itself. The precursors 1, 2 and 3
(Scheme 1) with different chain lengths were selected for that
purpose (NC–CH2–(CH2)n–CH2–Si(OR)3 with n = 1 for 1, 3 for 2
and 9 for 3). The adsorption ability of the materials towards
europium salts was investigated. We show that the chain length
not only plays a role on the structure of the materials but has also
an effect on the complexation of lanthanides.
M2 and M3 were also obtained in high yields (98 and 96%
respectively).
The nitrogen adsorption measurements of the samples indicate
that all these materials are nonporous with a low surface area
(SBET , 10 m2 g21). The 29Si CP-MAS NMR spectra of samples
M1, M2 and M3 displayed only one signal, at 268.8, 268.0, and
Our strategy consists of hydrolysis and polycondensation of 1, 2
and 3 in sulfuric acid aqueous solution in order to transform the
Institut Charles Gerhardt, UMR 5253 CNRS, Chimie Mole´culaire et
Organisation du Solide, Universite´ Montpellier II, Place E. Bataillon,
34095, Montpellier Cedex 5, France.
E-mail: ahmad.mehdi@univ-montp2.fr; Fax: +33 4 6714 3852;
Tel: +33 4 6714 3038
Scheme 2 Preparation of cyanoalkyltriisopropoxysilanes 2 and 3.
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Fig. 1 CP-MAS 29Si NMR spectra of M1 and M1K.
Fig. 3 XRD patterns of M1, M2, M3 and M1K.
distance (d = 2p/q). The peak at q = 15.70 nm21 correspond to an
interlayer distance of 0.40 nm. This distance can be attributed to
alkylene chain packing within the layers. The X-ray powder
diffraction pattern of M2 is very similar with an interlayer distance
of about 1.57 nm. Interestingly, a higher organization was observed
for M3 (Fig. 3). The first peak at q = 1.97 nm21 with 3.19 nm as
interlayer distance corresponds almost exactly to the theoretical
distance obtained by ChemDraw 3D calculation (3.20 nm).
The formation of solids M1–M3 can be explained in the
following way: first, there is hydrolysis of alkoxy groups into
silanols at 30 uC. Then, the increase of the temperature to 150 uC
induces the hydrolysis of the cyano groups into carboxylic acid
groups, which dimerize, by hydrogen bonding.7 Finally, self-
assembly,6a thanks to hydrophobic interactions, of the bis-silylated
units formed in situ allows the polycondensation, giving rise to the
materials (Scheme 3).
Fig. 2 CP-MAS 13C NMR spectrum of M1.
265.4 ppm respectively, attributed to the T3 [C–Si(OSi)3] sub-
structure, indicating fully condensed materials. The absence
of resonance corresponding to Q substructures (region near
2100 ppm) denotes that there is no cleavage of Si–C bonds
during the sol–gel process and the hydrothermal treatment (see
Fig. 1 as example).
The CP-MAS 13C NMR spectra of M1–M3 revealed the
incorporation of the organosiloxanes units. Fig. 2 shows the
spectrum of M1 with three signals (12.00, 20.86 and 42.35 ppm)
assigned to the propyl spacer and an additional one at 180.66 ppm
attributed to carbonyl resonances of carboxylic acid groups. The
absence of a peak at 120 ppm shows clearly that there is no
residual –CN group in the obtained material. The signal at
61.13 ppm revealed the formation of a small amount of ester by
reaction of acid groups with some remaining EtOH.
It is worth noting that the hydrolysis of chloropropyltriethoxy-
silane under the same experimental conditions or that of
(EtO)2OP–(CH2)3–Si(OEt)3 (triethoxysilylpropyldiethylphospho-
nate) in an aqueous 12 M HCl solution does not allow the
formation of a material. Starting from chloropropyltriethoxy-
silane, there is no possibility of formation of a bis-silylated
derivative. The hydrolysis of triethoxysilylpropyldiethylphospho-
nate in 12 M HCl solution was achieved under the conditions of
formation of phosphonic acid groups.8 However, there is no
formation of dimers from phosphonic acids. This demonstrates
that the crucial step to get a solid starting from cyanoalkyltrialk-
oxysilanes is the in situ formation of dimers between the carboxylic
acid units by hydrogen bonds.
The C/Si ratio was inferred from elemental analysis results and
found to be 4.29 for M1, 6.10 for M2 and 12.25 for M3 while the
theoretical values were 4, 6 and 12 respectively (Table 1). This
confirms that the Si–C bonds remain intact and the high degree of
polycondensation. In addition, the absence of nitrogen revealed by
elemental analysis indicates that the hydrolysis of cyano groups
was complete.
The X-ray powder diffraction (XRD) pattern of M1 (Fig. 3)
exhibited a well-defined (100) peak at q = 4.60 nm21 as well as a
second broad and weak peak (200) at q = 8.40 nm21. These peaks
are characteristic of a lamellar structure with 1.36 nm as interlayer
The better self-assembly of M3 in comparison to M1 and M2
shows the involvement of hydrophobic interactions between the
long alkylene chains to produce a lamellar structure. This is in
Table 1 Elemental analysis data for different materials
Molar ratio
M1
M2
M3
M1K
M2K
M3K
M1Eu
M2Eu
M3Eu
C/Sia
K/Sia
Eu/Si
a
4.29(4)
0
0
6.10(6)
0
0
12.25(12)
0
0
—
0.88(1)
0
—
0.92(1)
0
—
0.93(1)
0
—
,5 6 1025
0.34;a 0.32b
—
,5 6 1025
0.32;a 0.33b
—
,5 6 1025
0.51;a 0.53b
b
Calculated from elemental analyses. Theoretical values in parentheses. Determined from titration results.
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The EuIII uptake within M3K requiring only two carboxylate
units instead of three within M1K and M2K was explained as the
consequence of a more regular packing of the organic units.
In conclusion, we have described a direct method to obtain
ordered and highly functionalized silicas containing carboxylic acid
groups. This method is based on the in situ formation of carboxylic
acid dimers followed by the polycondensation of silanols groups.
The participation of weak hydrophobic interactions between
alkylene chains in combination with hydrogen bonds was
evidenced. The longer the alkylene chains, the better the structural
order, which renders easier the EuIII uptake. These materials with
high content of H+ per g could be good candidates for high proton
conductivity, which is particularly useful in the fuel cells domain.
Acknowledgements
Scheme 3 Formation of the materials via hydrogen-bond interactions
The authors thank Dr Philippe Dieudonne´ (GDPC,
Montpellier II University, France) for XRD measurements,
the CNRS and Montpellier II University for financial support.
between monomeric species.
agreement with long-range order formed during the hydrolytic
polycondensation of bridged organosilica with long alkylene
chains [(MeO)3Si–(CH2)n–Si(OMe)3 with n = 12 and 18] in water,
thanks to hydrophobic interactions.6a The self-assembly of long
alkylene chains involves the polycondensation of silanols groups,
which come into close proximity (Scheme 3).
Notes and references
{ A mixture of 5-bromopentene (10.00 g, 67.1 mmol) and triethoxysilane
(22.00 g, 132.2 mmol) in the presence of Karsted catalyst (10%) was heated
at 80 uC for 24 h giving rise to 5-bromopentyltriethoxysilane in high yield.
The exchange of ethoxy groups into isopropoxy groups was achieved by
treatment of the obtained 5-bromopentyltriethoxysilane in anhydrous
isopropanol (100 mL) with 30 mg of p-toluenesulfonic acid at 70 uC for
12 h. 5-Bromopentyltrisopropoxysilane (8.00 g, 22.5 mmol) was added to a
solution of NaCN (5.30 g, 108.1 mmol) in water (11 mL) and 24 mg of
tributylamine. The resulting solution was stirred for 7 h at reflux. After
extraction with Et2O (150 mL), the organic layer was dried under MgSO4
and evaporated under vacuum. The crude product was purified by
distillation (100 uC at 4 6 1022 mbar) to give a colorless liquid (6.50 g,
Thus, this direct synthesis gave rise to materials containing
carboxylic acid groups in high density: 7.20 mmol g21 for M1,
6.15 mmol g21 for M2 and 4.00 mmol g21 for M3.
We investigated the adsorption capability of these materials
towards lanthanide ions. As there is no lanthanide ions uptake
from M1–M3, the carboxylic acid groups were transformed into
potassium carboxylate salts by treating M1–M3 with either a
1
t
tBuOK solution in BuOH at 25 uC or potassium acetylacetonate
21.6 mmol, 96% yield). H NMR (200 MHz, CDCl3): 0.62 (2H, m), 1.23
(18H, d, 3JH,H = 7.0 Hz), 1.49 (4H, m), 1.69 (2H, m), 2.36 (2H, t, 3JH,H
=
(K(acac)) in ethanol. In both cases, the reactions were achieved in
the presence of 1 equivalent of reagent for 1 COOH unit, giving
rise to exactly the same materials named M1K–3K. The 29Si NMR
spectra of these materials revealed the absence of signals in the Q
region (region near 2100 ppm) showing that the treatment did not
affect the siloxane bonds. The 29Si NMR spectrum of M1K is
given as an example (Fig. 1). The XRD patterns of materials
M1K–3K show that the structures were maintained after chemical
transformation. In addition, the interlayer distance increase to
1.97 nm for M1K (Fig. 3). This increase can be explained by the
intercalation of the potassium ions between the layers.
3
6.9 Hz), 4.23 (3H, sept, JH,H = 7.0 Hz). 13C NMR (50 MHz, CDCl3):
12.20, 17.43, 21.18, 22.70, 32.39, 65.28 and 120.20. 29Si NMR (40 MHz,
CDCl3): 249.27. Anal. calcd. for C15H31NO3Si:C 59.80, H 10.30, N 4.65.
Found: C 59.70, H 1.27, N 4.52%.
{ 3 was prepared in the same way as 2 and was obtained in 97% yield. 1H
NMR (200 MHz, CDCl3): 0.62 (2H, m), 1.23 (18H, d, 3JH,H = 7.0 Hz), 1.30
(16H, m), 1.85 (2H, m), 2.36 (2H, t, 3JH,H = 6.9 Hz), 4.23 (3H, sept, 3JH,H
=
6.9 Hz). 13C NMR (50 MHz, CDCl3): 12.42, 17.51, 23.37, 25.79, 25.96,
29.00, 29.10, 29.60, 29.68, 29.87, 29.89, 33.63, 65.16, 120.10. 29Si NMR
(40 MHz, CDCl3): 248.29. Anal. calcd. for C21H43NO3Si:C 65.45, H
11.16, N 3.63. Found: C 65.30, H 11.20, N 3.55%.
1 C. Sanchez, B. Julian, P. Belleville and M. Popall, J. Mater. Chem., 2005,
15, 3559.
2 C. J. Brinker and G. W. Sherer, Sol–Gel Science, Academic Press,
San Diego, CA, 1990.
3 (a) B. Boury and R. J. P. Corriu, Chem. Commun., 2002, 795; (b) B. Boury
and R. J. P. Corriu, Chem. Rec., 2003, 3, 120.
4 J. J. E. Moreau, B. Pichon, C. Bied and M. Wong Chi Man, J. Mater.
Chem., 2005, 15, 3929.
In order to test the chelating ability of M1K–M3K towards
europium salts, the solids were treated with an ethanolic solution
of EuCl3 at room temperature, arbitrarily for 12 h. The resulting
solids were copiously washed with ethanol to eliminate any non-
complexed salts and named M1Eu, M2Eu and M3Eu respectively.
The titration by EDTA of the whole filtrate containing the non-
complexed salt was done and revealed the incorporation of one
EuIII per three carboxylate units for M1K and M2K. Interestingly,
the EuIII uptake within M3K was found to be 1 EuIII per two
carboxylate units. Elemental analyses (Table 1) of Si and Eu in
M1Eu–M3Eu confirmed the content of europium obtained by
titration. Furthermore, it is worth noting that the content of
potassium in M1Eu–M3Eu was found to be very low (,50 ppm)
showing that all the carboxylate groups were operative.
5 N. Liu, K. Yu, B. Smarsly, D. R. Dunphy, Y. B. Jiang and C. J. Brinker,
J. Am. Chem. Soc., 2002, 124, 14540.
6 (a) J. Alauzun, A. Mehdi, C. Reye´ and R. J. P. Corriu, J. Mater. Chem.,
2005, 15, 841; (b) J. Alauzun, A. Mehdi, C. Reye´ and R. J. P. Corriu,
Chem. Commun., 2006, 347; (c) J. Alauzun, A. Mehdi, C. Reye´ and
R. J. P. Corriu, J. Am. Chem. Soc., 2005, 127, 11205.
7 P. H. Wine, R. J. Astalos and R. L. Mauldin, J. Phys. Chem., 1985, 89,
2620.
8 R. J. P. Corriu, L. Datas, Y. Guari, A. Mehdi, C. Reye´ and C. Thieuleux,
Chem. Commun., 2001, 763.
618 | J. Mater. Chem., 2007, 17, 616–618
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