The influence of arylene and alkylene units on the structuring of urea-based bridged silsesquioxanes

Article abstract of DOI:10.1002/ejic.201200616

The influence of the intrinsic self-assembling properties of rigid or semirigid aromatic units as the main substructures combined with the effect of the alkylene side chains as linkers on the nanostructure of bridged silsesquioxanes was studied. The symme

Full text of DOI:10.1002/ejic.201200616

FULL PAPER
DOI: 10.1002/ejic.201200616
The Influence of Arylene and Alkylene Units on the Structuring of Urea-Based
Bridged Silsesquioxanes
Benoît P. Pichon,*[a,b] Sylvana Scampini,[a] Catherine Bied,[a] Joël J. E. Moreau,[a] and
Michel Wong Chi Man*[a]
Keywords: Silsesquioxanes / Hydrogen bonds / Nanostructures / Self-assembly / Sol–gel processes
The influence of the intrinsic self-assembling properties of
rigid or semirigid aromatic units as the main substructures
combined with the effect of the alkylene side chains as
linkers on the nanostructure of bridged silsesquioxanes was
studied. The symmetry of the organic units was found to con-
trol the dimensionality of the hybrid nanostructure. Bis(silyl-
ated) aromatic units lead to lamellar hybrids, whereas tris-
(silylated) aromatic units tend to form hexagonal structures.
The ordering of each type of structure depends directly on
the conformation of the organic units, which determines the
self-assembling of precursors through intermolecular interac-
tions.
In this field, an important breakthrough was achieved by
using organo-bridged silane precursors designed with ad-
Introduction
There has been a rapid growth in the number of reports ditional self-assembling groups, which significantly im-
on the synthesis and the use of bridged silsesquioxanes[1] proved the self-structuring of the bridged silsesquioxanes
over the past two decades. These hybrid materials are easily (Scheme 1).[10] Long alkylene chains as the main organic
obtained by the sol–gel[2] hydrolysis/condensation of hy- substructure can also influence the structuring of related
drolysable organosilanes and combine the properties of the silsesquioxanes.[11] These chains can form part of the main
organic unit with the silica matrix.[3] They can be obtained substructure as pendant chains[11a–11d,11g] and they can also
as powders, monoliths[4] or processed as films.[5] Thus, the be side chains.[11e,11f,11h] Similarly, synergetic effects can be
organic functionalities can easily provide discrete properties obtained when long alkylene side chains (n = 10, 11) are
to the resulting material according to the desired applica- combined with urea groups, which offers a rational route to
tions.[6] Subsequently, much effort is being devoted to the achieve a variety of self-structured bridged silsesquioxanes
structuring of these hybrid materials since additional inter- (Scheme 1).[12]
esting properties might also be tuned by the organisation
of the organic fragments in the hybrid silica framework.[7]
Two main routes have been exploited to achieve the nano-
structuring of these materials: (1) periodic mesoporous or-
ganosilicates (PMO) are obtained with uniform pores by
using surfactants as external structuring agents,[8] and (2)
another promising approach consists of exploiting the in-
trinsic associative interactions between the bridging organic
fragments of the organosilane precursor to self-direct the
structuring of the resulting hybrid.[9]
In the case of the main structure that consists of long
akylene groups (n Ͼ 8) and with a propylene side chain (n
= 3) between the urea groups and the silicon atoms, we
previously showed that the long-range ordering of the struc-
ture was favoured by cooperative hydrophobic and
van der Waals interactions with intermolecular hydrogen
bonds for alkylene chains that consist of at least eight car-
bon atoms.[13] The resulting self-assembly of the organic
fragments hence creates the structuring of the bridged sil-
sesquioxane. The self-structuring of the final bridged silses-
quioxane has also been conducted by replacing the alkylene
fragments by a phenylene unit as main substructure directly
linked to bis(urea) groups. Although short, its rigidity al-
lows a packing of the aromatic rings that strengthens the
self-association of organic fragments additionally to the hy-
drogen-bonding interactions between urea groups.[14]
[a] Institut Charles Gerhardt, Montpellier, UMR 5253 CNRS-
UM2-ENSCM-UM1, Architectures Moléculaires et Matériaux
Nanostructurés, Ecole Nationale Supérieure de Chimie de
Montpellier,
8 rue de l’école normale, 34296 Montpellier Cedex 5, France
Fax: +33-4-67147212
E-mail: michel.wong-chi-man@enscm.fr
Homepage: http://am2n.icgm.fr
We report here the syntheses of a new family of molecu-
lar precursors (P1–6) that is based on arylene units with an
adjustable combination of several types of weak interac-
tions. The use of the arylene–alkylene–urea groups enables
one to modulate the nanostructuring of the corresponding
[b] Institut de Physique et Chimie des Matériaux de Strasbourg,
UMR CNRS-UdS 7504,
23, rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200616.
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The Influence of Arylene and Alkylene Units
Scheme 1. Illustration of the organic units in bridged silsesquioxanes.
Scheme 2. Syntheses of precursors P1–6.
hybrid silicas (HS1–6). The organic unit was tuned accord-
ing to their main substructure by following three ap-
proaches: (1) a rigid biphenylene and a semirigid methyl-
enediphenylene unit in which π-stacking interactions and
angular and steric constraints are considered; (2) both sub-
units were associated to propylene (C3) or decylene (C10)
Results and Discussions
Synthesis of the Molecular Precursors P1–6 and the
Corresponding Hybrid Bridged Silsesquioxanes HS1–6
Bis(silylated) molecular precursors P1–4 were synthe-
side chains between the urea and the trialkoxysilyl groups; sised from commercially available diamines (benzidine and
and (3) a rigid 1,3,5-tris(urea)-based phenylene unit was 4,4Ј-methylenedianiline) by treatment with 2 mol-equiv. of
also investigated with propylene and undecylene side chains (3-isocyanopropyl)triethoxysilane or (10-isocyanodecyl)tri-
(Scheme 2). The purpose of this work was to study the role ethoxysilane (Scheme 2). Tris(silylated) precursors P5 and
of the angular constraints of the biphenylene unit relative P6 were obtained by reaction of (1,3,5-triisocyano)benzene
to the semiflexible methylenediphenylene unit; the associa- with (3-aminopropyl)triethoxysilane or (11-aminoundecyl)-
tive role of long alkylene (C10 or C11) side chains relative to triethoxysilane, respectively.[15] These reactions were per-
the shorter propylene side chain; and the role of multiple formed at room temperature in CH2Cl2 under argon and
condensation sites on the substructure with three hydrolys- led to bis- or tris(urea)-based precursors P1–6 with yields
able triethoxysilyl groups.
of up to 75%.
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B. P. Pichon, M. Wong Chi Man et al.
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Scheme 3. Syntheses of hybrid silicas HS1–6.
The corresponding hybrid silicas HS1–6 were obtained HS1 in Figure S2a of the Supporting Information. These
by an aqueous acid-catalysed hydrolysis/condensation of signals correspond to high condensation rates between 75
the corresponding precursors at 80 °C for 3.5 d (Scheme 3). and 87%, thereby indicating that the organic moieties are
The precursors with propylene (C3) side chains P1, P2 and linked to the others through an average of five Si–O–Si
P5 were first dissolved in THF, whereas those with decylene bonds. Nevertheless, HS3 and HS4 show an additional low
(C10) and undecylene (C11) side chains P3, P4 and P6 were T1-type signal at δ ≈ –48 ppm (Figure S2b) that corresponds
dissolved in DMSO due to their lower solubility.
to a lower rate of condensation and might be related to the
lower solubility of the corresponding precursors that con-
tain C10 linkers. According to hybrid silicas that contain
threefold symmetry units, HS5 is featured by a dense silica
network with the highest rate of condensation (90%). In
contrast, HS6 exhibits the highest amount of T1 signal
(11%) and the lowest amount of T3 signals (22%), which
corresponds to the lowest condensation rate (69%) ob-
served among these hybrid materials. Again, this lower con-
densation rate might be attributed to the low solubility of
P6 with long C11 linkers that is closely similar to P3 and
P4.
Characterisation of the Hybrid Materials
Elemental analyses performed on HS1, HS2, HS5 and
HS6 give for every sample an Si/N molar ratio of 0.46,
which is very close to that of their corresponding precursors
P1, P2, P5 and P6 (0.5). These results indicate that the
organic fragments were not affected by the hydrolysis/con-
densation reaction and are quantitatively present in the so-
lid material. In addition, 13C solid-state NMR spectroscopy
exemplified by HS1–3 (Figure S1 in the Supporting Infor-
mation) revealed a series of specific peaks at δ ≈ 160 ppm
(CO), at δ = 137–119 ppm (aromatic rings) and at δ = 43–
10 ppm (CH2) that correspond to the chemical shifts of the
organic units. The last peak at δ ≈ 11 ppm showed that C–
Si covalent bonds were not cleaved during the reaction. 29Si
solid-state NMR spectra were recorded to study the forma-
tion and the condensation rate of the silica network. All
spectra only exhibit Tn-type signals in the δ = –40 to
–80 ppm range, which also confirms that the organic unit
remains interconnected to the silica network through cova-
lent Si–C bonds (Table 1). Hybrids HS1–4 exhibit signals
at δ ≈ –57 ppm [T2] and δ ≈ –66 ppm [T3], as exemplified by
Table 1. Integrated surfaces of Tn (n = 1, 2 or 3) signals observed
in 29Si solid-state NMR spectra and condensation rates of hybrid
silicas.
Hybrid silica
Integrated surfaces [%]
Condensation rate [%]
T1
T2
T3
HS1
HS2
HS3
HS4
HS5
HS6
–
–
3
2
0
53
41
67
54
30
64
47
60
30
44
70
22
92
87
75
81
90
69
11
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The Influence of Arylene and Alkylene Units
Scanning electron microscopy (SEM) pictures of the ferences were observed between HS3 and HS4, both of
bridged silsesquioxanes HS1–4 typically display two-dimen- which have C10 side chains. Figure 1c and d show less de-
sional morphologies (Figure 1). However, striking differ- fined plates that look larger and more flexible. Nevertheless,
ences in the morphologies clearly demonstrate the influence the increase of the hydrophobic and van der Waals interac-
of the main organic substructure. Hybrid HS1 exhibits in- tions between C10 linkers favours the formation of the silica
terconnected and smaller plates (length: 1.5 μm; width: 0.5– network in two dimensions. C10 linkers also predominate
3 μm) in contrast with the observable longer, larger and on the arylene main subunit since both morphologies of
noninterconnected ones of HS2 (length: 5.0–50 μm; width: HS3 and HS4 are similar.[16] On the other hand, the trifunc-
0.5–5 μm), which have the highest aspect ratio (Figure 1a tional hybrid silicas exhibit completely different morpho-
and b respectively). Such different morphologies are directly logies, and the threefold symmetry of the organic fragment
related to the main substructure of the arylene group. In- does not favour anisotropic shapes. Indeed, HS5 has a
deed, biphenylene and methylenediphenylene groups in- spheroidal and isotropic shape, whereas HS6 exhibits a
fluence the formation of the silica network, which results in featureless morphology (Figure 1e and f).
different growth and morphologies. The growth of HS1
The organic subunits also influence the nanostructure of
seems to proceed by the simultaneous growth of several hybrid silica as observed by X-ray diffraction (XRD). Hy-
plates from the same nuclei, whereas HS2 grows from spe- brids HS1–4 exhibit sharp and intense Bragg peaks in the
cific and independent nuclei. In contrast, no significant dif- lower q region with regular spacing that are characteristic
of lamellar structures (Figure 2). All patterns show at least
the first three harmonics indexed as the (00l) reflections.
The d spacing calculated for the (001) reflection is related
to the period of the lamellar structure. Interestingly, these
values increase with the length of the organic unit and are
very close to the length calculated for the completely ex-
tended conformation of the molecular precursors by using
the MM2 model of Chemdraw Pro 2004 (Table 2). In ad-
dition, a comparative study of the full width at half maxi-
mum (FWHM) of each (00l) reflection in all patterns re-
vealed the long-range-ordered lamellar structure within
these hybrids. More precisely, HS2 and HS4 with the
methylenediphenylene unit display a longer-range order of
the lamellar structure (369 and 285 Å, respectively) than
HS1 and HS3 (273 and 153 Å) with the biphenylene unit
on either the C3 or C10 linker. In contrast, in the case of
C10 linkers, both hybrid silicas that contain biphenylene or
methylenediphenylene units display a lower correlation
length than C3 linkers. In these particular cases, a slight
decrease of the long-range order of the lamellar structure is
observed for those materials with C10 linkers relative to
those that bear C3 ones.
The lamellar structure of HS3 and HS4 was also ana-
lyzed by transmission electron microscopy (TEM). Figure 3
shows alternate stripes that correspond to the periodic repe-
tition of the silica network and the organic units and con-
Figure 1. SEM pictures of (a) HS1, (b) HS2, (c) HS3, (d) HS4, (e)
HS5 and (f) HS6.
Figure 2. XRD patterns of (a) HS1 and HS2, and (b), (c) HS3 and HS4.
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B. P. Pichon, M. Wong Chi Man et al.
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Table 2. Calculated length of the molecular precursors: q(001) values, d(001) distances, full width at half maximum (FWHM) and coherence
lengths (ξ) related to the (001) reflection.
Hybrid silica
Length of the molecular precursors
q
(001)Ϯ0.2
d
(001)Ϯ0.2
[Å]
FWHMϮ0.002
ξ
(001)Ϯ1
[Å]
[Å–1]
[Å–1]
HS1
HS2
HS3
HS4
27.6
27.5
43.1
44.7
0.27
0.25
0.172
0.162
23.5
24.7
36.6
38.8
0.023
0.017
0.041
0.022
273
369
153
285
firm the lamellar structure of both hybrid materials. These model. However, HS6 displays a very local ordering of
stripes could only be observed for organic units with C10 about 70 Å according to the FWHM value of the (100)
linkers. A periodicity of 38 and 40 Å was calculated from peak. Whereas threefold-symmetry precursors result in a
TEM micrographs for HS3 and HS4, respectively, which is hexagonal structure, the structuring occurs with a lower-
in full agreement with the d(100) values (36.6 and 38.8 Å, range order than for the bis(triethoxysilyl) precursors.
respectively) calculated from XRD patterns (Table 2).
Additional peaks are also observed at higher q values in
the 1.3–1.8 Å–1 region in all XRD patterns. For hybrids
HS1–4, the particular peak at 4.4–4.6 Å (clearly seen as a
sharp peak in the case of HS1 and HS2 in Figure 2a) can
be related to the distance between two urea groups linked
together by means of intermolecular hydrogen bonds as al-
ready reported.[14a,17] Splitting of this peak occurs for HS3
and HS4 (Figure 2c) and is very broad for HS5 and HS6
(Figure 4), which results in more difficult indexation. This
disordering might be attributable to the gauche conforma-
tion of alkylene side chains.[12c]
Figure 3. TEM images of (a) HS3 and (b) HS4.
Complementary insights into the composition of the or-
ganic subunit in hybrid silica can be drawn from Fourier
transform infrared (FTIR) spectroscopy. All spectra were
normalised on bands (1000–1150 cm–1) that correspond to
the νSi–O–Si stretching mode due to the formation of the
silica network. In addition, numerous characteristic vi-
bration modes of the organic units (Figure 5 and Table 3)
can be attributed in the following way: the νCH2 bands
correspond to the alkylene side chains, which are mostly
intense for organic units with C10 or C11 linkers, and the
specific amide A (νNH), amide I (νCO) and amide II
(δNH) bands of the urea groups are also observed.
In the case of the tris(silylated) systems, the threefold
symmetry of the organic unit of hybrid silicas HS5 and
HS6 dramatically influences their structure (Figure 4). The
pattern of the C3-linker-based HS5 shows very broad peaks,
which clearly indicates its amorphous structure. In contrast,
the presence of a C11 linker in HS6 results in three peaks
at low q values in the XRD pattern. Although these peaks
are broad, they can be attributed to the (100), (110) and
(200) reflections of a hexagonal structure (Figure S3 in the
Supporting Information), as confirmed by the ratios be-
tween the corresponding q values (1:1.73:2, respectively).
The hexagonal structure corresponds to a lattice parameter
FTIR spectroscopy also resulted in very useful infor-
mation about the nanostructure of hybrid silica and on the
self-assembly of the organic units.
a of 38.9 Å as calculated from the formula d(100) = αΊ3/2
for a hexagonal lattice. This value is very close to the dia-
meter (41.1 Å) of a threefold symmetry molecule in its ex-
tended conformation as calculated by a computational
Firstly, the position of νCH2 bands is indicative of the
conformation of alkylene chains, which can be correlated
to the ordering through hydrophobic and van der Waals in-
teractions.[18] Hybrids HS1 and HS2 display broad νCH2
asymmetric [νCH2(as)] and νCH2 symmetric [νCH2(s)] bands
at 2932 and 2868 cm–1. These bands are narrower and are
shifted to lower wavelengths of 2925 and 2854 cm–1 for HS3
and HS4, respectively. This result shows that replacing C3
by C10 linkers increases the ordering of the alkylene chains
in an all-trans conformation[19] on account of the higher
hydrophobic nature and the van der Waals interactions of
the long carbon chains. A similar behaviour was observed
for hybrid silicas HS5 and HS6, which contain threefold-
symmetry organic units (Table 3).
Secondly, the vibration modes of amides A and I are very
sensitive to the strength of intermolecular hydrogen bonds
between urea groups. For HS1–4 and HS6, the positions
of the νNH and νCO bands (around 3326 and 1638 cm–1,
Figure 4. XRD patterns of hybrid silica HS5 and HS6.
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The Influence of Arylene and Alkylene Units
respectively) correspond to strong hydrogen-bonding inter-
actions. In contrast, the shift to higher values (3403 and
1659 cm–1, respectively) for HS5 is characteristic of weaker
hydrogen-bonding interactions. A careful observation of
νCO bands shows that they are asymmetric and broad in
HS1 and HS3 spectra (noted by arrows in Figure 5b). Such
additional contributions correspond to weaker hydrogen
bonds that are not observed for HS2 and HS4. This obser-
vation can be correlated to the difference between biphenyl-
ene and methylenediphenylene groups. The amide II bands
are also depicted by two bands in the spectra of HS1–4 and
correspond to two different vibrations modes at about 1590
and 1560 cm–1 (more clearly seen for the methylenedipheny-
lene hybrids). In contrast, the spectra of HS5 and HS6 exhi-
bit only one broad δNH band, thus indicating the multidi-
rectionality of the hydrogen bonds (Figure 5c).
Hydrogen bonds between urea groups can be quantified
by the difference Δν between the νC=O and δNH vibration
modes (Table 3); the smaller this value, the stronger the hy-
drogen-bond strength.[20] Hybrids HS2 and HS4 display
two Δν values that are lower than those of HS1 and HS3
when comparing the hybrid silicas with the same aromatic
unit. Hence the semirigid methylenediphenylene unit en-
ables stronger hydrogen bonds between urea groups than
the rigid biphenylene unit. It results in a better structuring
for the hybrid silicas that contain methylenediphenylene
units than those that contain biphenylene units, which is in
good agreement with the better ordering observed by XRD.
On the other hand, hybrid silicas that bear C10 side chains
exhibit slightly higher Δν values than those with C3 side
chains. Although the hydrophobic and van der Waals inter-
actions increase the ordering of methylene groups in alkyl-
ene chains, the higher flexibility of the organic units cannot
counterbalance strains that result from the formation of the
silica network. Therefore, the formation of hydrogen bonds
between urea groups is disfavoured when long alkylene
chains are combined with bifunctional arylene units and
results in the lower ordering of hybrid silica. In contrast,
the length of the linker influences the structure of threefold-
symmetry organic units much more dramatically. Strong in-
teractions between C11 side chains favour a better structur-
ing of HS6 than HS5 with shorter C3 side chains, which is
amorphous (Table 3).
Figure 5. FTIR spectra of hybrid silica of (a), (b) HS1–4 and (c)
HS5–6.
The results observed in this work clearly show that or-
ganosilane precursors with different organic units dramati-
cally influence the nanostructure of the resulting bridged
silsesquioxanes. Aromatic rings that consist of a different
geometry and side chains with different lengths are very
important parameters.
The bifunctional organic units HS2 and HS4, which bear
a semirigid methylenediphenylene unit, display longer-range
ordering than HS1 and HS3 with a rigid biphenylene unit.
This is directly related to stronger intermolecular hydrogen
bonds between urea groups, which favour the self-assemb-
ling of organic units. The main difference between both or-
ganic units comes from the conformation of the aromatic
rings. Molecular modelling performed with the MM2
model of Chemdraw Pro 2004 was applied to precursors P1
Table 3. Vibration modes of alkylene and urea groups and the cor-
responding Δν values for HS1–6.
Hybrid silica
Vibration modes
Δν
νCH2(as) νCH2(s) νNH νCO δNH (νCO – δNH)
HS1
HS2
2932
2932
2868 3324 1642 1557
85
45
71
35
1597
2868 3329 1635 1564
1660
HS3
HS4
2925
2925
2854 3324 1645 1555
90
52
74
37
1593
2854 3328 1636 1562
1599
HS5
HS6
2937
2928
2880 3403 1659 1557
2853 3330 1645 1574
102
71
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B. P. Pichon, M. Wong Chi Man et al.
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Scheme 4. Molecular modelling of P1 and P2 carried out by using the MM2 model of Chemdraw Pro 2004.
and P2. Although this modelling was not applied to hybrid ences are directly correlated to the intrinsic self-assembly
materials, which are very complex structures, this infor- properties of organic units. The biphenylene unit in HS1
mation collected from precursors might be helpful in under- leads to small and interconnected plates with a low aspect
standing the formation mechanism. Different conforma- ratio of about 1, whereas the methylenediphenylene unit in
tions of the aromatic rings were obtained (Scheme 4): The HS2 induces the growth of longer and independent plates
aromatic rings of the biphenylene unit exhibit a 30° tilting, with a higher aspect ratio of about 10. This difference is
whereas they are almost coplanar in the methylenediphen- directly correlated to the variation of the aromatic unit.
ylene unit. The angular strain that exists in the biphenylene Longer plates correspond to a more anisotropic growth,
case is significantly suppressed by the presence of the meth- which is ruled by stronger interactions between organic
ylene group between both aromatic groups in the latter case. units.
The existence of coplanar aromatic rings, mainly due to the
Side chains also directly influence the structure and the
flexibility around the central methylene group, favours the morphology of the hybrid silicas. Hybrids HS3 and HS4
assembling of organic units through π stacking.[14a] In ad- display less defined platelike morphologies and lower-or-
dition, such a conformation of aromatic rings directly influ- dered lamellar structures than HS1 and HS2, respectively.
ences the formation of intermolecular hydrogen bonding Interestingly, replacing the C3 linker with a C10 linker re-
between urea groups. Indeed, the conjugation of the π or- sults in stronger hydrophobic and van der Waals interac-
bitals of the aromatic ring with the electronic doublet of the tions that are expected to increase the ordering.[12c] How-
nitrogen atom closely results in the normal direction de- ever, the flexibility of long alkylene chains has to be taken
fined by the plane of aromatic and urea groups. Therefore, into account when considering the high strains that result
coplanar aromatic rings of interacting organic units favour from the formation of the silica network, which tend to dis-
well-aligned urea groups and strong intermolecular hydro- organise the organic units.
gen bonds. Moreover, the combination of hydrogen bonds
The tris(silylated) organosilane precursors P5 and P6 re-
and π-stacking interactions favours the assembly of organo- sult in a different control of the nanostructure of hybrid
silane precursors in a specific direction, which results in the silicas HS5 and HS6. The presence of a third triethoxysilyl
anisotropic growth of the silica network upon hydrolysis/ group on the same aromatic unit directly connected by
condensation and in long-range-ordered lamellar structures means of three urea groups increases strains[21] upon the
that consist of alternate layers of organic units and silica formation of the silica network, which impacts the structur-
networks, as shown by TEM micrographs of HS3 and HS4 ing of the organic units. Indeed, side chains have a dramatic
(Figure 3). Such an anisotropic structure is directly corre- influence on the structure of hybrid silica that contains
lated to the common platelike morphology of HS1–4 hybrid threefold-symmetry organic units. Whereas HS5 with C3
silicas as obtained from other bifunctional organo- linkers consists of amorphous spheres, HS6 that bears C11
silane precursors. Nevertheless, some morphological differ- linkers features a medium-range-ordered hexagonal struc-
Scheme 5. Schematic and ideal representation of the hexagonal packing of the organic units of HS6 self-assembled into columns and
interconnected to the silica network (not represented for clarity).
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The Influence of Arylene and Alkylene Units
out any further purification for the synthesis of the hybrid silses-
quioxanes and were stored under nitrogen at 4 °C.
ture. The threefold symmetry results in a planar geometry
of organic units as we reported previously[15] on the self-
assembling of P5 in a columnar structure directed by hydro-
Techniques: Melting-point determinations were performed with an
gen bonding between urea groups and π stacking between Electrothermal IA9000 Series apparatus. Elemental analyses were
performed by the Service Central de Microanalyse du CNRS at
Lyon–Vernaison (France). Mass spectra were measured with a
JEOL JMS-DX 300 mass spectrometer. FTIR spectra were re-
corded from KBr pellets using a Perkin–Elmer 1000 instrument.
1H, 13C and 29Si liquid-phase NMR spectra were recorded with a
Bruker AC-200 or AC-250, with deuterated chloroform and
DMSO as solvents. Chemical shifts, δ, were indexed in ppm with
respect to tetramethylsilane. 13C and 29Si cross-polarisation magic-
angle spinning (CP-MAS) solid-state NMR spectra were recorded
with a Bruker FT AM 400 instrument. Condensation rates of the
coplanar aromatic rings. Such a self-assembly process re-
sults in a hexagonal structure distinguished by a cell param-
eter a, which is correlated to the diameter of a planar mole-
cule (Scheme 5). With a third urea group, organic units can-
not self-assemble along the stacking axis in the case of C3
linkers, which are too short and cannot counterbalance
strains induced by the formation of the Si–O–Si linkages.
Despite its flexibility, the C11 linker favours a better organi-
sation when combined with the threefold-symmetry arylene
groups. It might result from the presence of three urea silica network were calculated by integrating the peak area of each
Tn signal. Specific surface areas were measured by nitrogen adsorp-
groups that provide further hydrogen bonds rather than in
tion/desorption and by Brunauer–Emmett–Teller (BET) analysis
the case of the bis(functional) units. Therefore, it preferen-
with a Micrometics Gemini 2375 apparatus. SEM images were ob-
tially directs the formation of the silica network along the
stacking direction of P6. Moreover, the nanostructure of
HS6 is also favoured by a lower condensation rate of the
silica network than in the case of HS5, although both hy-
brid silicas have been synthesised under similar experimen-
tal conditions.
tained with a JEOL 6300F microscope. TEM studies were per-
formed with a JEOL 1200EX II. X-ray diffraction measurements
and data treatment were performed at the Laboratoire Charles
Coulomb in Montpellier (France). The X-ray diffraction experi-
ments 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 that produced high flux (108 photonss–1) and pinhole
collimation was employed. An “imaging 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. The dif-
fracted intensity was corrected for exposition time, transmission
and the background scattering that arises from an empty capillary.
Conclusion
We have presented six new organosilane precursors
bearing organic units with different abilities to self-organise
and to address the nanostructure of hybrid silica. Whereas
weak intermolecular interactions are known to control the
self-assembly of organic units that are interconnected to the
silica network, the formation of the silica network results
in strains that tend to disfavour the organisation of the or-
ganic units. Therefore, organic units with strong intrinsic
self-assembly properties lead to the highest ordering of hy-
brid bridged silsesquioxanes. The organisation of the or-
ganic unit is mainly controlled by the conformation of the
aromatic rings, the intermolecular hydrogen bonding be-
tween urea groups, the length of the alkylene linker and the
number of triethoxysilyl groups linked to the organic unit.
Bifunctional precursors led to the formation of long-range-
ordered lamellar structures, which are favoured by a semi-
rigid main unit that contains coplanar aromatic rings and
short alkylene chains. In contrast, a trifunctional organic
unit with a threefold symmetry favours the formation of a
hexagonal structure when long alkylene linkers are used.
The value of dhkl can be calculated from Bragg’s law [Equation (1)]
with 2θ, the diffraction angle and λCu = 1.54 Å:
2dhklsinθ = λ
(1)
The value of q is related to θ by the relation according to Equa-
tion (2):
q = 4πsinθ/λ
(2)
From Equations (1) and (2), we can deduce Equation (3), in which
qhkl is the q value that corresponds to the associated Bragg peak
position:
dhkl = 2π/qhkl
(3)
Synthesis of the Molecular Precursors
Precursor P1: 4,4Ј-Diaminobiphenyl (920 mg, 5 mmol) was dis-
solved in CH2Cl2 (40 mL) in a Schlenk tube under nitrogen. (3-
Isocyanopropyl)triethoxysilane (2.59 g, 10.5 mmol) was added
dropwise with a syringe, and the reaction mixture was stirred over-
night. The solvent was removed under vacuum. The solid obtained
Experimental Section
Chemicals: 4,4Ј-Diaminobiphenyl, 4,4Ј-methylenedianiline, (3-iso- was washed with dry pentane to remove the excess amount of iso-
cyanopropyl)triethoxysilane and (3-aminopropyl)triethoxysilane
were purchased from Aldrich. (10-Isocyanodecyl)triethoxysil-
cyanate and then dried under vacuum to give a white powder.
Yield: 75% (2.5 g, 3.69 mmol). M.p. 220 °C. H NMR (200 MHz,
1
ane,[16,22]
(11-aminoundecyl)triethoxysilane,[23]
1,3,5-triisocy-
[D6]DMSO): δ = 0.56 (t, 4 H, CH2Si), 1.15 (t, 18 H, CH3), 1.48
(qt, 4 H, CH2), 3.07 (qd, 4 H, NCH2), 3.73 (qd, 12 H, OCH2), 6.17
(m, 2 H, NH), 7.44 (s, 8 H, Har), 8.44 (m, 2 H, NH) ppm. 13C
NMR (50 MHz, CDCl3): δ = 7.2 (CH2Si), 18.1 (CH3), 23.3 (CH2),
41.7 (CH2N), 57.6 (CH2O), 117.8 and 126.0 (CHar), 132.5 and
anobenzene[21] and 1,3,5-tris{[3-(triethoxysilyl)propyl]ureido}-
benzene[15] (P5) were synthesised as reported previously. Dichloro-
methane (CH2Cl2) was distilled from CaH2 and pentane from
LiAlH4. The molecular precursors were synthesised in Schlenk
tubes under nitrogen. Distilled water, tetrahydrofuran (THF), 139.3 (Car), 155.1 (CO) ppm. 29Si NMR (50 MHz, CDCl3): δ =
dichloromethane and dimethyl sulfoxide (DMSO) were used with- –45.2 ppm. IR (KBr): ν = 563, 1592 (δNH), 1638 (νCO), 3321 (νNH
)
˜
Eur. J. Inorg. Chem. 2012, 5312–5322
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5319

B. P. Pichon, M. Wong Chi Man et al.
FULL PAPER
cm–1. MS (FAB): m/z (%) = 678 (60). C32H54N4O8Si2 (678.97):
calcd. C 56.61, H 8.02, N 8.26; found C 56.78, H 8.05, N 7.92.
washed with dry pentane to remove the excess amount of isocyan-
ate and then dried under vacuum to give a yellow powder. Yield:
72% (2.05 g, 1.7 mmol). M.p. 180 °C. 1H NMR (200 MHz, [D6]-
DMSO): δ = 0.54 (t, 6 H, CH2Si), 1.14 (t, 27 H, CH3), 1.25 (m, 54
H, CH2), 3.03 (qd, 6 H, NCH2), 3.73 (qd 18 H, OCH2), 5.94 (t, 3
H, NH), 7.09 (m, 3 H, Har), 8.25 (s, 3 H, NH) ppm. 13C NMR
(50 MHz, [D6]DMSO): δ = 9.8 (CH2Si), 18.1 (CH3), 22.2, 26.2,
28.5, 28.7, 28.8, 28.9 (2 CH2), 29.7, 32.2, 41.2 (CH2N), 57.5
(CH2O), 99.9 (CHar) and 140.8 (Car), 155.0 (CO) ppm. 29Si NMR
Precursor P2: 4,4Ј-Methylenedianiline (500 mg, (2.52 mmol) was
dissolved in CH2Cl2 (40 mL) in a Schlenk tube under nitrogen. (3-
Isocyanopropyl)triethoxysilane (1.38 g, 5.59 mmol) was added
dropwise with a syringe, and the reaction mixture was stirred over-
night. The solvent was removed under vacuum. The solid obtained
was washed with dry pentane to remove the excess amount of iso-
cyanate and then dried under vacuum to give a white powder.
Yield: 88% (1.54 g, 2.22 mmol). M.p. 194 °C. 1H NMR (200 MHz,
CDCl3): δ = 0.64 (t, 4 H, CH2Si), 1.21 (t, 18 H, CH3), 1.68 (m, 4
H, CH2), 3.24 (qd, 4 H, CH2), 3.80 (qd, 12 H, OCH2) and (m, 2
H, CH2), 5.08 (t, 2 H, NH), 6.39 (s, 2 H, NH), 7.15 (dd, 8 H, Har)
ppm. 13C NMR (50 MHz, CDCl3): δ = 7.8 (CH2Si), 18.3 (CH3),
23.6 and 42.8 (CH2), 58.4 (CH2O), 120.3 and 129.3 (CHar), 135.6
and 137.0 (Car), 156.8 (CO) ppm. 29Si NMR (50 MHz, [D6]-
(50 MHz, [D ]DMSO): δ = –45.2 ppm. IR (KBr): ν = 1572 (δNH),
˜
6
1639 (νCO), 3313 (νNH) cm–1. MS (FAB): m/z (%) = 1155 (5) [M –
EtO]+. C60H120N6O12Si3 (1201.90): calcd. C 59.96, H 10.06, N 6.99;
found C 59.32, H 10.19, N 7.53.
Syntheses of the Hybrid Bridged Silsesquioxanes
Hybrid Silica HS1: Precursor P1 (142 mg, 0.21 mmol) was dis-
solved in THF (1.1 mL). Then distilled water (2.2 mL) was added
while stirring. A white precipitate appeared. A 1 m HCl solution
(36.8 μL) was added. The following molar ratio was used: P1/THF/
H2O/HCl, 1:65:600:0.2. After heating the reaction mixture at 80 °C,
the precipitate completely dissolved in a few minutes. After 2 h, a
precipitate appeared, and the mixture was aged under static condi-
tions. After 3.5 d, the solvents were removed by filtration. The solid
product was washed successively with water, ethanol and acetone
and finally dried at 110 °C. A grey powder was obtained. 13C NMR
DMSO): δ = –45.2 ppm. IR (KBr): ν = 1567, 1594 (δNH), 1644
˜
(νCO), 3325 (νNH) cm–1. MS (FAB): m/z (%) = 647 (25) [M –
EtO]+. C33H56N4O8Si2 (693.00): calcd. C 57.19, H 8.15, N 8.08;
found C 57.22, H 8.12, N 8.32.
Precursor P3: 4,4Ј-Diaminobiphenyl (500 mg, 2.72 mmol) was dis-
solved in CH2Cl2 (40 mL) in a Schlenk tube under nitrogen. (10-
Isocyanodecyl)triethoxysilane (2.44 mg, 7.07 mmol) was added
dropwise with a syringe, and the reaction mixture was stirred over-
night. The solvent was removed under vacuum. The solid obtained
was washed with dry pentane to remove the excess amount of iso-
cyanate and then dried under vacuum to give a white powder.
Yield: 69% (1.63 g, 1.86 mmol). M.p. 233 °C. 1H NMR (200 MHz,
[D6]DMSO): δ = 0.54 (t, 4 H, CH2Si), 1.14 (t, 18 H, CH3), 1.2 to
1.4 (m, 32 H, CH2), 3.07 (t, 4 H, CH2NH), 3.72 (qd, 12 H, OCH2),
6.10 (t, 2 H, NH), 7.45 (s, 4 H, Har), 8.42 (t, 2 H, NH) ppm. 13C
NMR (50 MHz, [D6]DMSO): δ = 10.4 (CH2Si), 18.3 (CH3), 22.8
and 27.3 (CH2), 29.3 to 29.6 (5 CH2), 30.5 and 33.2 (CH2), 58.3
(CH2O), 118.2 and 126.3 (CHar), 132.0 and 139.4 (Car), 155.3 (CO)
ppm. 29Si NMR (50 MHz, [D6]DMSO): δ = –45.0 ppm. MS (FAB):
CP-MAS:
δ = 10.5, 24.2, 42.3, 119.4, 125.4, 130.0, 137.0,
158.4 ppm. 29Si NMR CPMAS: δ = –57.4, –66.0 ppm (T2 and T3
sites). N BET surface area: 17.0 m2 g–1. IR (KBr): ν = 1557, 1597
˜
2
(δNH), 1642 (νCO) and 3324 (νNH) cm–1. Elemental analysis: found
C 50.53, H 5.48, N 11.73, Si 12.70.
Hybrid Silica HS2: Precursor P2 (145 mg, 0.21 mmol) was dis-
solved in THF (1.1 mL). Then distilled water (2.2 mL) was added
while stirring. A white precipitate appeared. A 1 m HCl solution
(36.8 μL) was added. The following molar ratio was used: P2/THF/
H2O/HCl, 1:65:600:0.2. After heating the reaction mixture at 80 °C,
the precipitate completely dissolved in a few minutes. After 2 h, a
precipitate appeared, and the mixture was aged under static condi-
tions. After 3.5 d, the solvents were removed by filtration. The solid
product was washed successively with water, ethanol and acetone
and finally dried at 110 °C. A white powder was obtained. 13C
NMR CPMAS: δ = 11.9, 25.1, 36.8, 42.7, 123.4, 130.5, 132.3,
135.5, 157.9 ppm. 29Si NMR CP-MAS: δ = –57.5, –66 ppm (3 T2
m/z (%) = 875 (60). IR (KBr): ν = 1555, 1585 (δNH), 1637 (νCO),
˜
3330 (νNH) cm–1. C46H82N4O8Si2 (875.35): calcd. C 63.12, H 9.44,
N 6.40; found C 63.38, H 9.30, N 6.62.
Precursor P4: 4,4Ј-Methylenedianiline (500 mg, 2.52 mmol) was
dissolved in CH2Cl2 (40 mL) in a Schlenk tube under nitrogen. (10-
Isocyanodecyl)triethoxysilane (1.93 g, 5.59 mmol) was added drop-
wise with a syringe, and the reaction mixture was stirred overnight.
The solvent was removed under vacuum. The solid obtained was
washed with dry pentane to remove the excess amount of isocyan-
ate and then dried under vacuum to give a white powder. Yield:
and T3 sites). N2 BET surface area: 38.2 m2 g–1. IR (KBr): ν =
˜
1564, 1600 (δNH), 1635 (νCO) and 3329 (νNH) cm–1. Elemental
analysis: found C 50.66, H 5.73, N 10.91, Si 11.80.
1
Hybrid Silica HS3: Precursor P3 (148 mg, 0.17 mmol) was dis-
solved in DMSO (2.8 mL). Then distilled water (1.7 mL) was added
while stirring. A white precipitate appeared. A 1 m HCl solution
(31.3 μL) was added. The following molar ratio was used: P3/
DMSO/H2O/HCl, 1:215:600:0.2. After heating the reaction mixture
at 80 °C for 2 h, a precipitate appeared, and the mixture was aged
under static conditions. After 3.5 d, the solvents were removed by
filtration. The grey solid product was washed successively with
water, ethanol and acetone and finally dried at 110 °C. A grey pow-
der was obtained. 13C NMR CP-MAS: δ = 13.5, 31.3 (7 C), 41.0,
45.2, 119.0, 125.7, 129.9, 136.9, 157.6 ppm. 29Si NMR CP-MAS: δ
= –45.4, –56.6, –66.7 ppm (T1, T2 and T3 sites). N2 BET surface
85% (1.91 g, 2.15 mmol). M.p. 172 °C. H NMR (200 MHz, [D6]-
DMSO): δ = 0.63 (t, 4 H, CH2Si), 1.22 (t, 18 H, CH3), 1.25 to 1.4
(m, 28 H, CH2), 1.50 (m, 4 H, CH2), 3.21 (qd, 4 H, CH2), 3.70 (s,
2 H, CH2), 3.81 (qd, 12 H, OCH2), 5.68 (t, 2 H, NH), 7.02 (dd, 8
H, Har), 7.08 (s, 2 H, NH) ppm. 13C NMR (50 MHz, [D6]DMSO):
δ = 10.4 (CH2Si), 18.3 (CH3), 22.8, 27.2, 29.3, 29.5, 29.6, 29.65,
29.7, 30.4, 33.2, 40.3 (CH2), 58.3 (CH2O), 120.0 and 129.2 (CHar),
135.3 and 137.2 (Car), 157.2 (CO) ppm. 29Si NMR (50 MHz, [D6]-
DMSO): δ = –45.0 ppm. IR (KBr): ν = 1568, 1593 (δNH), 1635
˜
(νCO), 3319 (νNH) cm–1. MS (FAB): m/z (%) = 844 (57) [M –
EtO]+. C47H84N4O8Si2 (889.37): calcd. C 63.47, H 9.52, N 6.30;
found C 63.62, H 9.45, N 6.71.
area: 23.4 m2 g–1. IR (KBr): ν = 1555, 1593 (δNH), 1645 (νCO) and
˜
Precursor P6: 1,3,5-Triisocyanobenzene (240 mg, 1.23 mmol) was
dissolved in CH2Cl2 (40 mL) in a Schlenk tube under nitrogen. (11-
Aminoundecyl)triethoxysilane (1.36 g, 4.07 mmol) was added drop-
wise with a syringe, and the reaction mixture was stirred overnight.
The solvent was removed under vacuum. The solid obtained was
3329 (νNH) cm–1.
Hybrid Silica HS4: Precursor P4 (151 mg, 0.17 mmol) was dis-
solved in DMSO (2.8 mL). Then distilled water (1.7 mL) was added
while stirring. A white precipitate appeared. A 1 m HCl solution
5320
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 5312–5322

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(31.3 μL) was added. The following molar ratio was used: P4/
DMSO/H2O/HCl, 1:215:600:0.2. After heating the reaction mixture
at 80 °C for 2 h, a precipitate appeared, and the mixture was aged
under static conditions. After 3.5 d, the solvents were removed by
filtration. The solid product was washed successively with water,
ethanol and acetone and finally dried at 110 °C. A grey powder
was obtained. 13C NMR CP-MAS: δ = 13.5, 26.6, 31.6 (8 C), 41.6,
124.0, 130.4, 132.5, 135.9, 157.8 ppm. 29Si NMR CP-MAS: –48.4,
–57.2, –67.5 ppm (T1, T2 and T3 sites). N2 BET surface area:
25.6 m2 g–1. IR (KBr): ν = 1562, 1599 (δNH), 1636 (νCO) and 3328
˜
(νNH) cm–1.
Hybrid Silica HS5: Precursor P5 (125 mg, 0.14 mmol) was dis-
solved in THF (2.3 mL). Then distilled water (2.3 mL) was added
while stirring. A white precipitate appeared. A 1 m HCl solution
(43.3 μL) was added. The following molar ratio was used: P5/THF/
H2O/HCl, 1:200:900:0.3. After heating the reaction mixture at
80 °C for 2 h, a precipitate appeared, and the mixture was aged
under static conditions. After 3.5 d, the solvents were removed by
filtration. The white solid product was washed successively with
water, ethanol and acetone and finally dried at 110 °C. A white
powder was obtained. 13C NMR CP-MAS: δ = 11.6, 24.9 and 42.7
(CH2), 105.3 and 140.6 (Car), 157.1 (C=O) ppm. 29Si NMR
CPMAS: –57.3, –66.8 ppm (T2 and T3 sites). N2 BET surface area:
[7]
[8]
[9]
0.0 m2 g–1. IR (KBr): ν = 1557 (δNH), 1659 (νCO) and 3403 (νNH
)
˜
cm–1. Elemental analysis: found C 33.04, H 10.77, N 12.28, Si
12.54.
Hybrid Silica HS6: Precursor P6 (125 mg, 0.1 mmol) was dissolved
in DMSO (2.8 mL). Then distilled water (1.7 mL) was added while
stirring.
A white precipitate appeared. A 1 m HCl solution
(30.8 μL) was added. The following molar ratio was used: P6/
DMSO/H2O/HCl, 1:365:900:0.3. After heating the reaction mixture
at 80 °C for 2 h, a precipitate appeared, and the mixture was aged
under static conditions. After 3.5 d, the solvents were removed by
filtration. The solid product was washed successively with water,
ethanol and acetone and finally dried at 110 °C. A grey powder
was obtained. 13C NMR CP-MAS: δ = 14.6 (CH2), 18.5 (CH3),
30.9 (9 CH2), 40.6 (CH2), 58.3 (CH2O), 110.3 and 140.0 (Car), 157.6
(C=O) ppm. 29Si NMR CP-MAS: –45.7, –57.0, –65.6 ppm (T2 and
[10]
T3 sites). N2 BET surface area: 0.0 m2 g–1. IR (KBr): ν = 1574
˜
(δNH), 1645 (νCO) and 3330 (νNH) cm–1. Elemental analysis: found
C 57.53, H 8.77, N 8.80, Si 9.41.
Supporting Information (see footnote on the first page of this arti-
cle): 29Si solid-state NMR spectra of hybrid silica HS2 and HS4
(Figure S1) and 13C solid-state spectra NMR of hybrid silica HS1–
3 (Figure S2).
Acknowledgments
The authors would like to thank the Ministère de l’enseignement
supérieur et de la recherche for a PhD grant and also the Centre
National de la Recherche Scientifique (CNRS) for financial sup-
port.
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Received: June 6, 2012
Published Online: October 4, 2012
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