Structuring of bridged silsesquioxanes via cooperative weak interactions: H-bonding of urea groups and hydrophobic interactions of long alkylene chains

Article abstract of DOI:10.1039/b504635a

Lamellar-bridged silsesquioxanes were obtained by the acid-catalysed hydrolytic condensation of a series of bissilylated organobridged molecular precursors. It was found that exploiting cooperative effects between the molecular interactions created by lon

Full text of DOI:10.1039/b504635a

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Structuring of bridged silsesquioxanes via cooperative weak interactions:
H-bonding of urea groups and hydrophobic interactions of long alkylene
chains
Joe¨l J. E. Moreau,* Benoˆıt P. Pichon, Catherine Bied and Michel Wong Chi Man
Received 4th April 2005, Accepted 27th June 2005
First published as an Advance Article on the web 19th July 2005
DOI: 10.1039/b504635a
Lamellar-bridged silsesquioxanes were obtained by the acid-catalysed hydrolytic condensation of
a series of bissilylated organobridged molecular precursors. It was found that exploiting
cooperative effects between the molecular interactions created by long hydrophobic hydrocarbon
chains and the H-bonding between urea groups in the precursors favoured the nanostructuring of
the corresponding hybrid silicas.
groups to the silicon atoms did not seem to affect the ordering
Introduction
imposed by the main organic group. However, replacing the
The sol–gel hydrolysis1 of bis-trialkoxysilyl organics2–4 repre-
propylene linker with longer alkylene bridges affected the basic
sents a fascinating bottom-up approach to hybrid organic–
properties of the molecular precursor, resulting in the facile
formation of organogels.17 Furthermore, in the case of the
inorganic materials for targeted applications exploiting the
properties of the incorporated organic fragments.5 During the
chiral diaminocyclohexyl fragment as the main organic
past decade much effort has been directed towards producing
substructure, it was shown that the molecular interactions
organised and self-assembled hybrids2,3,6 and in the past five
induced by C10 alkylene linkers play a more important
years, significant progress has been made using two synthetic
structure-directing role than the intrinsic chirality of the main
strategies. On the one hand, periodic mesoporous bridged
organic substructure for a C3 linker, modifying the helical
silsesquioxanes have been synthesized by the surfactant
fibers observed in the latter case to a lamellar form for the
templating route as bulk materials7–10 and also as thin films
former.18 Considering these observations, we focused our
and particulates.11 On the other hand, the intrinsic self-
work on the role of the alkylene linker and its contribution to
assembly of the bridging organic units allowed the preparation
controlling the structural evolution of the hybrids. Recently,
of various self-organised hybrids.12–16 Our recent work
we reported a crystalline hybrid [O1.5Si(CH2)3NHCONH–Ph–
involved the synthesis of bistrialkoxysilyl organics in which
NHCONH(CH2)3SiO1.5]n with a rigid phenylene group
the organic units consist of a main organic substructure
(chiral diaminocyclohexyl units, alkylene chains or phenyl
ring) bridging two urea groups linked through a propylene
chain (linker) to the silicon atoms on both sides.12,13 The
controlled hydrolysis of these precursors led to hybrids
structured on multiple length scales ranging from the nano-
to the macro-scale range. Nevertheless, regardless of the
method used, approaches for organising such hybrids are
limited to the use of small organic units and the introduction
of larger and more complex organic fragments remains a
significant challenge.
directly connected to the two urea groups, with C3 akylene
linkers between the urea and the silicon atoms.12 The
nanoscale ordering of the organic molecules in the silica
network were attributed to the H-bonding interaction of the
urea group, possibly combined with the p-stacking of the
rigid phenylene group. Here we describe the syntheses of a
series of silylated phenylene compounds with C3 and C10
linkers and the corresponding hybrids obtained via sol–gel
chemistry. In this work we investigated: (1) the influence of
an additional flexible linker between the rigid bridging
phenylene ring and the urea groups, changing from –Ph–12
to –(CH2)n–Ph–(CH2)n– (where n varies from 1 to 3; see
Scheme 1) and; (2) the influence of the alkylene linker (C3
and C10 linkers) between the urea groups and the silicon
atoms (see Scheme 1).
In our recent work, in addition to identifying the key role of
the H bonds between the urea groups in directing the assembly
of the molecules into well defined supramolecular architec-
tures, we also demonstrated the important role of the main
organic substructure in defining the nanostructure12 and the
overall shapes of the resulting hybrid solids. However,
significant difficulties in maintaining such ordered structures
are encountered for even slight modification of the main
organic substructure. The propylene linker connecting the urea
Experimental
Chemicals
1,4-Dibromobenzene, tris(o-tolylphosphine) (TOP), palladium
acetate, palladium activated on carbon, 1 M borane solution in
THF, (3-isocyanatopropyl)triethoxysilane and acrylonitrile
were purchased from Aldrich, while 1,4-di(cyanomethyl)ben-
zene and anhydrous sodium acetate were obtained from
Laboratoire He´te´rochimie Mole´culaire et Macromole´culaire
(UMR-CNRS 5076), Ecole Nationale Supe´rieure de Chimie de
Montpellier, 8 rue de l’e´cole normale 34296 Montpellier Cedex 5,
France. E-mail: joe¨l.moreau@enscm.fr
This journal is ß The Royal Society of Chemistry 2005
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The diffracted intensity was corrected for exposition time,
transmission and the background scattering arising from an
empty capillary.
Syntheses of molecular precursors
1,4-Di(aminoethyl)benzene19,20 (2). A solution of 780 mg
(5 mmol) 1,4-di(cyanomethyl)benzene in 40 mL THF was
introduced into a 3-necked round bottom flask under a
nitrogen atmosphere. A 1 M borane solution in THF (35 mL)
was added dropwise and the reacting mixture was refluxed
for 24 h. The heating bath was removed and the solution
was allowed to cool down to room temperature. The flask was
placed in an ice bath and 40 mL of a 1 : 1 (v : v) mixture of
THF–H2O was carefully added dropwise, leading to a white
precipitate. THF was removed in vacuo and then EtOH
(80 mL) and concentrated H2SO4 (0.5 mL) were added. The
mixture was heated under reflux for 30 min. The solvents were
removed in vacuo and a 1 M NaOH solution was added to
neutralize the acid. The amino compound was extracted with
CHCl3. After drying over Na2SO4, the solvents were removed
leading to a white solid. Yield: 84% (686 mg, 4.18 mmol); mp:
Scheme 1 Syntheses of molecular precursors P1–P6 and of the hybrid
materials M1–M6.
1
60 uC; IR (CHCl3, cm21): 3358 (nNH); H NMR (200 MHz,
Alfa Aesar. Dichloromethane was distilled over CaH2, while
pentane and dimethylformamide were distilled over LiAlH4.
Tetrahydrofuran was refluxed and distilled over LiAlH4 and
then further purified by distillation over sodium/benzophe-
none. (10-Isocyanatodecyl)triethoxysilane was synthesized in
the laboratory.18 The molecular precursors were synthesized in
Schlenk tubes under a nitrogen atmosphere.
CDCl3): d 5 1.08 (m, 4H, NH2), 2.69 (t, 4H, CH2), 2.92 (t, 4H,
NCH2), 7.11 (s, 4H, Har); 13C NMR (50 MHz, CDCl3): d 5 39.7
(CH2), 43.6 (CH2N), 128.9 (CHar) and 137.6 (Car); Mass
(FAB): m/z (%): 165 (100) [M+H]+.
1,4-Di(aminopropyl)benzene21 (3). The same procedure as
above was used with 901 mg (4.90 mmol) of 1,4-di(cya-
noethyl)benzene. Yield: 96% (900 mg, 4.69 mmol); mp: 72 uC;
1H NMR (200 MHz, CDCl3): d 5 1.22 (m, 4H, NH2), 1.72 (qt,
4H, CH2), 2.60 (t, 4H, ArCH2), 2.69 (t, 4H, NCH2) 7.07 (s, 4H,
Har); 13C NMR (50 MHz, CDCl3): d 5 32.8 (CH2), 35.4
(CH2Ar), 41.8 (CH2N), 128.3 (CHar) and 139.4 (Car); Mass
(FAB): m/z (%): 192 (100).
Techniques
Melting points determinations were performed on an
Electrothermal IA9000 Series apparatus. Elemental analyses
were performed by the Service Central de Microanalyse du
CNRS at Lyon–Vernaison. Mass spectra were measured on a
JEOL JMS-DX 300 mass spectrometer. FT-IR spectra were
recorded from KBr pellets using a PERKIN ELMER 1000.
1H, 13C and 29Si liquid NMR spectra were recorded on a
Bruker AC-200 or AC-250, with deuterated chloroform and
dimethylsulfoxide used as solvents. Chemical shifts, d, were
indexed in ppm with respect to tetramethylsilane. 13C and 29Si
CP-MAS solid state NMR spectra were recorded on a Bruker
FT AM 400. Specific surface areas were measured by nitrogen
1,4-Di(cyanovinyl)benzene (5). In
a dry tube, 11.8 g
(50 mmol) of 1,4-dibromobenzene and 8.2 g (100 mmol) of
anhydrous sodium acetate were dissolved in 40 mL of
anhydrous DMF. After 5 min stirring, 224.4 mg (1 mmol)
of palladium acetate, 1.216 g (4 mmol) of o-tolylphosphine and
14.5 mL (0.22 mmol) of acrylonitrile were added. The mixture
was frozen with liquid nitrogen and the tube was sealed. The
reaction mixture was heated at 150 uC for 20 h. The catalyst
was then removed by filtration at room temperature and
washed with dichloromethane. The resulting filtrate was
extracted with water. The organic phase was then dried over
Na2SO4 and the solvent was removed in vacuo. A yellow solid
was obtained after recrystallisation in a solution of acetoni-
trile–water. The three isomers (trans-trans, cis-cis and cis-trans)
were obtained. Yield: 84% (7.55 g, 4.19 mmol); mp: 255 uC; IR
(CHCl3, cm21): 2211 (nCN); 1H NMR (200 MHz, CDCl3):
d 5 5.54 (d, 2H, CH2 cis), 5.95 (d, 2H, CH2 trans), 7.18 (dd, 2H,
CH2 cis), 7.35 (dd, 2H, CH2 trans), 7.56 (d, 4H, CHar cis-cis), 7.81
(d, 4H, CHar trans-trans); 13C NMR (50 MHz, CDCl3): d 5 96.9
(CH2 cis), 98.2 (CH2 trans), 117.0 (CNcis), 117.7 (CNtrans),
128.0 (CHar cis), 129.6 (CHar trans), 136.0 (CHar cis-trans), 147.2
(CH2 cis), 149.1 (CH2 trans); Mass (FAB): m/z (%): 180 (86);
adsorption–desorption and by BET analysis with
a
Micrometics Gemini 2375 apparatus. Scanning electron
microscopy (SEM) images were obtained from a JEOL
6300F microscope. Transmission electron microscopy (TEM)
studies were performed on a JEOL 1200EX II. X-ray
diffraction measurements and data treatment were performed
at the Groupe de Dynamique des Phases Condense´es in
Montpellier. The X-ray diffraction experiments were carried
out on solid powders in glass capillaries (1 mm diameter) in a
transmission configuration. A copper rotating anode X-ray
source (4 kW) with a multilayer focusing ‘‘Osmic’’ mono-
chromator giving high flux (108 photons s21) and pinhole
collimation was employed. An ‘‘image plate’’ 2D detector was
used, and the data obtained were radially averaged to yield
the diffracted intensity as a function of the wave vector, q.
3930 | J. Mater. Chem., 2005, 15, 3929–3936
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Calculated elemental analysis for C12H8N2 (%): C 79.97, H
4.48, N 15.55, found: C 79.97, H 4.41, N 15.42.
(3-isocyanatopropyl)triethoxysilane leading to a pink powder.
Yield: 80% (3.31 g ; 4.83 mmol); mp: 120–121 uC; IR (KBr,
cm21): 1581 (dNH), 1625 (nCO), 3334 (nNH); 1H NMR
(200 MHz, CDCl3): d 5 0.61 (t, 4H, CH2Si), 1.16 (t, 18H,
CH3), 1.62 (t, 4H, CH2), 1.75 (t, 4H, CH2), 3.13 (qt, 8H, CH2),
3.79 (qd 12H, OCH2), 4.79 (t, 2H, NH), 4.88 (t, 2H, NH), 7.03
(s, 4H, Har); 13C NMR (50 MHz, CDCl3): d 5 7.6 (CH2Si),
18.3 (CH3), 23.7, 31.9, 32.7, 39.8 and 42.8 (CH2), 58.3 (CH2O),
128.3 (CHar) and 139.0 (Car), 159.9 (CO); 29Si NMR (50 MHz,
DMSO D6): 245.0; Mass (FAB): m/z (%): 641 (15) [M-EtO]+;
Calculated elemental analysis for C32H62N4O8Si2 (%): C 55.94,
H 9.10, N 8.15, found: C 55.73, H 9.13, N 8.28.
1,4-Di(cyanoethyl)benzene22 (6). 500 mg of Pd/C was added
to a solution of 1g (5.55 mmol) of 1,4-di(cyanovinyl)benzene 5
dissolved in 40 mL of ethanol in a beaker. The solution was
placed in an autoclave under hydrogen (5 bar) for 30 min. The
mixture was filtered and the solvent was removed in vacuo.
The remaining solid was dissolved in dichloromethane and
extracted with a 1 M HCl solution. The organic phase was
dried over Na2SO4. The solvent was removed and the resulting
powder was crystallised in an acetonitrile–water mixture to
give white crystals. Yield: 93% (950 mg, 5.16 mmol); mp: 87 uC ;
1
IR (CHCl3, cm21): 2243 (nCN); H NMR (200 MHz, CDCl3):
1,4-Bis[(triethoxysilyl)decylureidomethyl]benzene (P4). The
same procedure as for P1 was used with 560 mg (4.12 mmol)
of 1,4-di(aminomethyl)benzene and 2.98 g (8.65 mmol) of
(10-isocyanatodecyl)triethoxysilane leading to a white solid.
Yield: 75% (2.55 g ; 3.09 mmol); mp: 189–191 uC ; IR (KBr,
cm21): 1579 (dNH), 1619 (nCO), 3345 (nNH); 1H NMR
(200 MHz, CDCl3): d 5 0.61 (t, 4H, CH2Si), 1.21 (t, 18H,
CH3), 1.23–1.4 (m, 32H, CH2), 3.16 (m, 4H, CH2), 3.04 (m,
4H, CH2), 3.72 (qd 12H, OCH2), 5.97 (t, 2H, NH), 7.20 (s, 4H,
Har), 8.13 (s, 2H, NH); 13C NMR (50 MHz, DMSO): d 5 10.4
(CH2Si), 18.3 (CH3), 22.8, 27.3, 29.3, 29.4, 29.6, 30.6, 33.2 and
40.3 (CH2), 40 (CH2N), 58.3 (CH2O), 129.0 (CHar) and 137.5
(Car), 159.2 (CO); 29Si NMR (50 MHz, DMSO D6): 245.0;
Mass (FAB ): m/z (%): 826 (5); Calculated elemental analysis
for C42H82N4O8Si2 (%): C 60.98, H 10.00, N 6.78, found : C
61.02, H 9.96, N 7.07.
d 5 2.62 (t, 4H, CH2), 2.95 (t, 4H, CH2), 7.21 (s, 4H, CH2); 13
C
NMR (50 MHz, CDCl3): d 5 19.2 (CH2), 31.1 (CH2), 119.2
(CN), 128.9 (CHar), 137.1 (Car); Mass (FAB): m/z (%): 184 (36).
1,4-Bis[(triethoxysilyl)propylureidomethyl]benzene (P1).
680 mg (5 mmol) of 1,4-di(aminomethyl)benzene 1 was
dissolved in 40 mL of CH2Cl2 in a Schlenk tube under a
nitrogen atmosphere. 2.59 g (10.5 mmol) of (3-isocyanatopro-
pyl)triethoxysilane was added dropwise with a syringe and the
reacting mixture was stirred overnight. The solvent was
removed under vacuum. The solid obtained was washed with
dry pentane to remove the excess isocyanate and then dried
under vacuum to give a white powder. Yield: 85% (2.65 g;
2.05 mmol); mp: 194 uC; IR (KBr, cm21): 1583 (dNH), 1627
1
(nCO), 3334 (nNH); H NMR (200 MHz, DMSO D6): d 5 0.52
(t, 4H, CH2Si), 1.15 (t, 18H, CH3), 1,42 (qt, 4H, CH2), 2.97
(qd, 4H, CH2), 3.74 (qd, 12H, OCH2), 4.15 (d, 4H, CH2), 5.92
(t, 2H, NH), 6.21 (t, 2H, NH), 7.16 (s, 4H, Har); 13C NMR
(50 MHz, CDCl3): d 5 7.7 (CH2Si), 18.2 (CH3), 23.8, 42.8 and
44.0 (CH2), 58.2 (CH2O), 128.5 (CHar) and 137.7 (Car), 159.1
(CO); 29Si NMR (50 MHz, DMSO D6): 245.0; Mass (FAB ):
m/z (%): 585 (74) [M-EtO]+; Calculated elemental analysis
C28H54N4O8Si2 (%): C 53.30, H 8.63, N 8.88, found : C 52.97,
H 8.57, N 8.91.
1,4-Bis[(triethoxysilyl)decylureidoethyl]benzene (P5). The
same procedure as for P1 was used with 387 mg (2.36 mmol)
of 1,4-di(aminoethyl)benzene and 1.97 g (5.70 mmol) of
(10-isocyanatodecyl)triethoxysilane giving a grey solid. Yield:
87% (1.75 g ; 2.05 mmol); mp: 156–158 uC; IR (KBr, cm21):
1578 (dNH), 1619 (nCO), 3346 (nNH); 1H NMR (200 MHz,
DMSO D6): d 5 0.54 (t, 4H, CH2Si), 1.17 (t, 18H, CH3), 1.23–
1.4 (m, 32H, CH2), 2.62 (t, 4H, CH2), 2.40 (qd, 4H, CH2), 3.22
(qd, 4H, CH2), 3.73 (qd 12H, OCH2), 5.72 (t, 2H, NH), 5 .81
(t, 2H, NH), 7.10 (s, 4H, Har); 13C NMR (50 MHz, DMSO
D6): d 5 9.8 (CH2Si), 18.1 (CH3), 23.4, 27.5, 31.6, 33.6, 33.8,
34.0, 34.2, 34.4, 35.2 and 37.5 (CH2), 41.0 (CH2N), 58.8
(CH2O), 129.8 (CHar) and 138.6 (Car), 159.1 (CO); 29Si NMR
(50 MHz, DMSO d6): 245.0; Mass (FAB): m/z (%): 854 (6);
Elemental analysis for C44H86N4O8Si2 (%): C 61.78, H 10.13,
N 6.55, found: C 61.55, H 10.09, N 6.87.
1,4-Bis[(triethoxysilyl)propylureidoethyl]benzene (P2). The
same procedure as for P1 was used, with 890 mg of 1,4-
di(aminoethyl)benzene (2) (5.43 mmol) and 2.82 g (11,4 mmol)
of (3-isocyanatopropyl)triethoxysilane leading to a white
powder. Yield: 71% (2.53 g ; 3.85 mmol); mp: 188 uC; IR
(KBr, cm21): 1582 (dNH), 1626 (nCO), 3339 (nNH); 1H NMR
(200 MHz, CDCl3): d 5 0.60 (t, 4H, CH2Si), 1.20 (t, 18H,
CH3), 1.55 (qt, 4H, CH2), 2.71 (t, 4H, CH2), 3.08 (qt, 4H,
CH2), 3.34 (qd, 4H, CH2), 3.79 (qd 12H, OCH2), 4.77 (t, 2H,
NH), 4.95 (t, 2H, NH), 7.07 (s, 4H, Har); 13C NMR (50 MHz,
CDCl3): d 5 7.7 (CH2Si), 18.2 (CH3), 23.7, 36.1, 41.6 and 42.8
(CH2), 58.1 (CH2O), 128.7 (CHar) and 137.2 (Car), 159 (CO);
29Si NMR (50 MHz, DMSO D6): 245.0; Mass (FAB ): m/z
(%): 613 (100) [M-EtO]+; Calculated elemental analysis for
C30H58N4O8Si2 (%): C 54.68, H 8.87, N 8.50, found: C 54.74,
H 8.77, N 8.65.
1,4-Bis[(triethoxysilyl)decylureidopropyl]benzene (P6). The
same procedure as for P1 was used with 300 mg (1.63 mmol)
of 1,4-di(aminopropyl)benzene and 1.34 g (3.90 mmol) of
(10-isocyanatodecyl)triethoxysilane leading to a pink solid.
Yield: 76% (1.09 g ; 1.24 mmol); mp: 113–115 uC; IR (KBr,
cm21): 1578 (dNH), 1623 (nCO), 3337 (nNH); 1H NMR
(200 MHz, DMSO D6): d 5 0.54 (t, 4H, CH2Si), 1.13 (t,
18H, CH3), 1.23 to 1.4 (m, 40H, CH2), 3.00 (m, 8H, CH2), 3.72
(qd 12H, OCH2), 5.74 (t, 2H, NH), 5 .80 (t, 2H, NH), 7.08 (s,
4H, Har); 13C NMR (50 MHz, DMSO D6): d 5 9.8 (CH2Si),
18.1 (CH3), 22.2, 26.3, 28.5, 28.7, 28.8, 28.9, 29.9, 31.8, 32.0,
32.2 and 41.5 (CH2), 57.5 (CH2O), 138.9 (CHar) and 157.0
1,4-Bis[(triethoxysilyl)propylureidopropyl]benzene (P3). The
same procedure as for P1 was used with 1.16 g (6.04 mmol)
of 1,4-di(aminopropyl)benzene (3) and 3.28 g (13.3 mmol) of
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(Car), 158.4 (CO); 29Si NMR (50 MHz, DMSO d6): 244.9;
Mass (FAB): m/z (%): 883 (23) [M+H]+; Calculated elemental
analysis for C46H90N4O8Si2 (%): C 62.54, H 10.27, N 6.34,
found: C 62.28, H 10.15, N 6.75.
Hybrid silica M5. The hybrid silica M5 was obtained in the
same way as M4, with 168 mg (0.2 mmol) of 1,4-bis[(triethoxy-
silyl)decylureidoethyl]benzene (P5). white powder was
obtained. IR (KBr, cm21): 1578 (dNH), 1625 (nCO) and 3356
(nNH); 13C NMR CPMAS (ppm): 14.7, 23.9, 31.6 (10 C),
42.3, 128.7, 136.5, 160.5; 29Si NMR CPMAS (ppm): 248.5,
257.1, 267.5 (T1, T2 and T3 sites); Specific surface area:
10.2 m2 g21. Found elemental analysis: C 58.56, H 8.26, N
8.75, Si 9.19.
A
Syntheses of the hybrid materials
Hybrid silica M1. 125 mg (0.20 mmol) of 1,4-bis[(triethoxy-
silyl)propylureidomethyl]benzene P1 was dissolved in 2 mL of
ethanol. Then 2.2 mL of distilled water were added while
stirring. A white precipitate appeared. 33.4 mL of a 1 M HCl
solution was added. The following molar ratio was used:
precursor: 1, EtOH: 170, H2O: 600, HCl: 0.2. After heating the
reaction mixture at 60 uC the precipitate completely dissolved
in a few minutes. After 2 h a precipitate appeared and the
mixture was aged under static conditions. After 4.5 days, the
solvents were removed by filtration. The solid product was
washed successively with water, ethanol, acetone and finally
dried at 110 uC. A grey powder was obtained. IR (KBr, cm21):
1560 (dNH), 1654 (nCO) and 3370 (nNH); 13C NMR CPMAS
(ppm): 10.7, 25.2, 43.4 (2 C), 127.4, 139.5, 160.1; 29Si NMR
CPMAS (ppm): 257.8, 265.7 (T2 and T3 sites); specific
surface area: 8.9 m2 g21. Found elemental analysis: C 44.25, H
6.23, N 12.86, Si 12.90.
Hybrid silica M6. The hybrid silica M6 was obtained in the
same way as M4 with 176 mg (0.2 mmol) of 1,4-bis[(triethoxy-
silyl)decylureidopropyl]benzene (P6). A white powder was
obtained. IR (KBr, cm21): 1580 (dNH), 1631 (nCO) and
3353 (nNH); 13C NMR CPMAS (ppm): 13.5, 31.9 (22 C),
40.4, 128.1, 136.9, 159.3; 29Si NMR CPMAS (ppm) : 248.4,
257.0, 266.4 (T1, T2 and T3 sites); Specific surface area:
14.5 m2 g21
.
Results and discussion
Preparation of the molecular precursors and the hybrids
The molecular precursors and the corresponding hybrids
obtained by their hydrolysis are given in Scheme 1.
P1–P6 were synthesised from three different diamines
(Scheme 2). 1,4-(diaminomethyl)benzene, 1, is commercially
available and 1,4-(diaminoethyl)benzene (2) and 1,4-(diamino-
propyl)benzene (3) were synthesized according to Scheme 3
and 4, respectively.
Hybrid silica M2. The hybrid silica M2 was obtained using
the same conditions as M1 with 132 mg (0.20 mmol) of 1,4-
bis[(triethoxysilyl)propylureidoethyl]benzene P2 leading to a
white powder. IR (KBr, cm21): 1560 (dNH), 1638 (nCO) and
3423 (nNH); 13C NMR CPMAS (ppm): 10.9, 24.6, 33.5, 41.5
(2 C), 129.7, 137.4, 160.1; 29Si NMR CPMAS (ppm): 256.8,
Diamine 2 was obtained in high yield (84%) from 1,4-
di(cyanomethyl)benzene) 4 by the reduction of the two nitrile
groups with BH3?THF (Scheme 3).
265.2 (T2 and T3 sites); Specific surface area: 6.1 m2 g21
.
Diamine 3 was synthesised in three steps (Scheme 4). 1,4-
dibromobenzene was treated using Heck’s reaction with
acrylonitrile in the presence of tris(o-tolyl)phosphine (TOP)
and Pd(OAc)2 as catalysts in DMF. In this case, a mixture of
the three possible isomers 5 (cis-cis, trans-trans and cis-trans)
was obtained. Treatment of this mixture with hydrogen gas
(5 bar) in an autoclave with Pd/C as catalyst gave 6. The
latter was reduced with BH3?THF to give 3 in a good overall
yield (75%)
Hybrid silica M3. Hybrid silica M3 was obtained using the
same conditions as M1 with 138 mg (0.2 mmol) of 1,4-bis-
[(triethoxysilyl)propylureidopropyl]benzene P7 to give a white
powder. IR (KBr, cm21): 1570 (dNH), 1638 (nCO) and 3424
(nNH); 13C NMR CPMAS (ppm): 11.6, 24.1, 32.4, 35.0, 41.3,
43.5, 128.6, 139.3, 160.1; 29Si NMR CPMAS (ppm): 257.7,
266.0 (T2 and T3 sites); Specific surface area: 14.3 m2 g21
.
Hybrid silica M4. 165 mg (0.2 mmol) of 1,4-bis[(triethoxy-
silyl)decylureidomethyl]benzene P4 was dissolved in 2.6 mL of
dimethylsulfoxide by heating. A gel was obtained when the
solution was cooled down to room temperature. 1.6 mL of
distilled water was added with stirring. A white precipitate
formed, and then 33.4 mL 1 M HCl solution was added. The
following molar ratios were used: precursor: 1, DMSO: 245,
H2O: 600, HCl: 0.2. The mixture was heated at 60 uC for 2 h
and then the stirring was stopped. No solubilisation of the
precipitate was observed during the whole reaction. After
4.5 days at 60 uC, the solution was filtered and the solid
was washed successively with water, ethanol and acetone and
then dried overnight at 110 uC leading to a white powder.
IR (KBr, cm21): 1583 (dNH), 1622 (nCO) and 3354 (nNH); 13C
NMR CPMAS (ppm): 13.6, 24.3, 32.0 (9 C), 40.1, 42.6, 128.9,
138.0, 159.3; 29Si NMR CPMAS (ppm): 247.9, 257.4, 266.9
(T1, T2 and T3 sites); Specific surface area: 10.1 m2 g21; Found
elemental analysis (%): C 58.35, H 8.55, N 9.23, Si 8.90.
The reaction of 3-(isocyanatopropyl)triethoxysilane and 10-
(isocyanotodecyl)triethoxysilane with the three diamines in
CH2Cl2 yielded the six molecular precursors (Scheme 5).
Scheme 2 Starting diamines 1–3 for the synthesis of P1–P6.
Scheme 3 Synthesis of diamine 2.
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Scheme 4 Synthesis of diamine 3.
Fig. 1 Solid state 13C CP-MAS NMR of M1.
Scheme 5 Synthesis of precursors P1–P6.
Syntheses of the hybrids M1–M6
The hybrid materials with the shorter C3 linker (x 5 3)
M1–M3 (see Scheme 1) were obtained by acid-catalysed
hydrolysis in a mixture of water and ethanol with the following
molar ratio: P1–P3: 1, EtOH: 170, H2O: 600, HCl: 0.2. For
those with longer linkers (x 5 10, M4–M6) the reaction
was performed in a mixture of water and DMSO due to the
insolubility of the corresponding precursors P4–P6 in ethanol.
The molar ratio was P4–P6: 1, DMSO: 245, H2O: 600, HCl:
0.2. The reactions were all conducted at 60 uC over 4.5 days.
Solid materials were obtained after filtering the solutions,
successive washings with water, ethanol and acetone followed
by drying at 110 uC.
Fig. 2 Solid state 13C CP-MAS NMR of M4.
It can be seen that for the sample incorporating a long
alkylene linker (M4), the peak at around 30 ppm is relatively
intense, as expected, due to the greater number of carbon
atoms from the C10 alkylene chain.
The complete conservation of the C–Si bonds was confirmed
by 29Si CP-MAS NMR studies. This is exemplified by the
spectra of M1 and M4 (Fig. 3). In the case of the sample M1,
which incorporates the shorter linker, both T2 [C–Si(OSi)2OR,
Characterisations of the hybrid materials M1–M6
We studied the composition of the hybrids by elemental
analysis. Since all hybrids were synthesised under the same
conditions apart from the solvents (ethanol for M1–M3) and
DMSO for M4–M6), we examined only M1 and M4. In both
cases, a ratio Si/N of 0.48 was found, which is close to the
theoretical value of 0.5 indicating that the organic fragments
are quantitatively present in the solid materials.
We further studied these compositions by solid state NMR
(13C and 29Si). The solid state 13C CP-MAS NMR spectra
(Figs. 1 and 2) exhibit several peaks characteristic of the
organic fragments with chemical shifts at 160 (CO), 136 and
129 (aromatic ring) and from 11 to 42 ppm (CH2). The signal
at 11 ppm corresponds to the C–Si, confirming that cleavage
of the C–Si bond did not occur during hydrolysis. The 13C
CP-MAS NMR spectra of M1 (Fig. 1) and M4 (Fig. 2) are
shown as examples.
Fig. 3 Solid state 29Si CP-MAS NMR of M1 and M4.
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minor peak] and T3 units [C–Si(OSi)3, major peak] are
observed, reflecting a highly condensed material. The spectra
of M2 and M3 are similar, with a degree of condensation of
90–94%.
The spectra of the samples incorporating the longer linker
(M4–M6) are identical. As exemplified in Fig. 3 in the case
of M4, these latter solids are less condensed (degree of
condensation 5 74–80%). Three peaks can be distinguished,
corresponding to T1 [C–Si (OR)2 OSi], T2 [C–Si(OSi)2OR] and
T3 [C–Si(OSi)3] units, with the T2 unit being predominant.
The hydrophobic properties and the steric bulk of the long
C10 alkylene linker may account for the decreasing rate of
hydrolysis and condensation.
We also examined the H-bonding strength of the urea
groups by FT-IR studies of the hybrids. This can be probed by
monitoring the positions of the amide 1 (nCO # 1650 cm21
)
and amide 2 modes (dNH # 1570 cm21). The difference
between these two vibrations (Dn) gives a good indication of
the strength of the H-bonds between the urea groups,23–25 with
a low Dn value indicating strong H-bonding interactions.
Interestingly, low Dn values were obtained for M4–M6 whereas
those for the short linker hybrids M1–M3 were larger (ranging
from 68 to 94 cm21) which reflects stronger H-bonds in the
former materials. Moreover, this effect is also evident from the
amide A (nNH # 3400 cm21) vibration, where a shift towards
lower wavenumbers corresponds to stronger H-bonding
between the urea groups.23 The results are in good agreement
with those of the Dn values since the nNH values of M4–M6
range from 3353 to 3356 cm21. In contrast, those for M1–M3
are observed at higher wavenumbers (3370–3423 cm21). From
these observations it can be seen that the organic fragments in
the long linker materials are better assembled than in the short
linker hybrids. The hydrophobic interactions of the long
alkylene linkers influence the self-association of the molecules
during the hydrolysis.
Fig. 5 PXRD of M4–M6.
the case of M3 reflect a slightly better organisation in this
hybrid compared with M1 and M2 (Fig. 4).
The PXRD of hybrids M4–M6 are different (Fig. 5) with
several well-resolved peaks being observed.
These materials are more organised than the short linker
hybrids since their diffractograms exhibit sharper peaks,
particularly at low q values (Fig. 6). Indeed, three peaks are
˚
observed. The very small peak at 36.9, 37.7 and 43.7 A for
M4–M6, respectively, can be attributed to a first-order
harmonic (001) of lamellar structures since the other peaks
in the three PXRD patterns are at repetitive intervals with
respect to the first one and are assigned as the second (002) and
the third (003) harmonics.
The first-order distances in the three hybrids are comparable
to the length of the organic fragments. The hydrophobic
interactions due to the long alkylene chains here compensate
We then analysed the powder X-ray diffraction (PXRD)
patterns of these materials. The two broad peaks at around 16
˚
and 4.5 A in the diffractograms of hybrids M1–M3 signify that
these materials are amorphous, although the narrower peaks in
Fig. 4 PXRD of M1–M3.
Fig. 6 PXRD of M4–M6 at low angle.
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Fig. 9 SEM image of M4.
Fig. 7 SEM image of M1.
for the disorder created by the flexibility of the C1, C2 and C3
carbon chains between the phenylene ring and the urea groups.
Interesting features can be observed from electron micro-
scopy analyses of M1–M3, which consist of spheres with
diameters ranging from 1 to 8 mm as seen from the SEM
(scanning electron microscopy) image of M1 (Fig. 7).
From the TEM (transmission electron microscopy) image,
the sphere as represented for M1 is completely dark showing
that the hybrid is a dense material, with little electron contrast
(Fig. 8).
For these short linker materials, the hydrolysis of the
precursors took place in a homogeneous way at the beginning,
with the precursors dissolving in the solution on heating. This
leads to a conventional nucleation and growth process which
can explain the formation of spheres.
The hybrids M4–M6 are similar when observed by SEM and
they resemble flexible films, as illustrated in Fig. 9 for M4.
The TEM image of M4 is presented as an example in Fig. 10,
the hybrids M5 and M6 showing similar features. The results
from the TEM pictures confirm the lamellar structures of
hybrids M4–M6 and these results correlate with those of the
Fig. 10 TEM image of M4.
PXRD analyses. Well-aligned stripes with similar distances
with those obtained from the PXRD are observed.
Conclusion
In this work, we describe the synthesis of new lamellar hybrid
silsesquioxanes by combining two weak molecular interactions
based on H-bonding and hydrophobic effects. The latter
resulted from the incorporation of long alkylene chains and it
is shown that such hydrophobic interactions can compensate
for disordering effects arising from the presence of flexible
alkylene chain (C1, C2 and C3) directly bonded to a rigid
phenylene ring. This strategy provides a synthetic approach to
the design of nanostructured, bridged silsesquioxanes and may
offer the possibility of extending the nanostructuring of bridged
silsesquioxanes to a wide range of organic functionalities.
Acknowledgements
This work was supported by the CNRS and the Ministe`re de la
Recherche (ACI Nanosciences-Nanotechnologies).
Fig. 8 TEM image of M1.
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Soc., 2001, 123, 7957–7958; J. J. E. Moreau, B. P. Pichon, M. Wong
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