New H-bonded complexes and their supramolecular liquid-crystalline organizations

Article abstract of DOI:10.1002/ejoc.200700725

Different approaches to the design of liquid crystals by using H-bonds were analyzed. A selection of stilbazoles and pyridine compounds, with one or two chelating positions, were used as H-acceptors in mixtures with carboxylic acids. The noncovalent compl

Full text of DOI:10.1002/ejoc.200700725

FULL PAPER
DOI: 10.1002/ejoc.200700725
New H-Bonded Complexes and Their Supramolecular Liquid-Crystalline
Organizations
Ana Pérez,[a] Nélida Gimeno,[a] Francisco Vera,[a] M. Blanca Ros,*[a] José Luis Serrano,[a]
and M. Rosario De la Fuente[b]
Keywords: Supramolecular chemistry / Hydrogen bond / Liquid crystals / Bent-core liquid crystals
Different approaches to the design of liquid crystals by using
H-bonds were analyzed. A selection of stilbazoles and pyr-
idine compounds, with one or two chelating positions, were
used as H-acceptors in mixtures with carboxylic acids. The
noncovalent complexes in question afforded calamitic meso-
morphism (N, SmA and SmC) as well as a lamellar meso-
phase (SmCP). Additionally, the liquid crystalline behaviour
of the new 2-hydroxy- and 2-aminopyridine compounds as
the design and stability of noncovalent calamitic and bent-
core liquid crystals are reported. To induce the bent-core li-
quid crystalline order, the conformational flexibility around
the H-bond must be controlled. The new liquid crystals were
characterized by IR spectroscopy, optical microscopy, calo-
rimetry, X-ray diffraction and dielectric spectroscopy.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
pure materials is also discussed. Useful results concerning Germany, 2008)
Introduction
Supramolecular chemistry has found in hydrogen bonds
an extraordinary tool to generate many original and attract-
ive architectures and functionalities. Furthermore, the use
of appropriate H-donor and H-acceptor structures enables
numerous calamitic and columnar liquid-crystalline me-
sophases to be stabilized[1] (Figure 1). These soft materials
have broadened the possibilities for structural design and
macroscopic arrangement through this noncovalent interac-
tion. One particularly attractive possibility is the use of
nonmesomorphic single components to form such liquid-
crystalline systems.
Figure 1. Different liquid crystals generated by using H-bonds.
Current research in this new field is focused on numerous
areas. Some examples concern the characterization and un-
derstanding of the new types of liquid crystalline phases,
their physical properties, the exploration of their practical
applications and, of particular interest to chemists, how to
control all of these properties through suitable molecular
design.
In this respect, hydrogen bonding has proved to be a use-
ful tool to tailor properties. The use of carboxylic acids and
stilbazoles I and II (Figure 2), which act as H-donor and
H-acceptor, respectively, has afforded bent-shaped com-
plexes that arrange in these new mesophases, even with
side-chain bent-shaped liquid-crystal polymers.[4,5] The
SmCP phases are the most common and widely studied of
this new type of mesophase. This phase is characterized by
its tilted lamellar and polar packing. Depending on the di-
rection of polarization in adjacent layers, the mesophase
can have either a ferro- and/or antiferroelectric ground
state. On the other hand, depending on the tilt sense of the
molecules in adjacent layers, this supramolecular arrange-
In recent years, a new type of mesogenic material has
emerged in this field, the so-called banana-shaped liquid
crystal.[2] This name comes from the bent-shape of the
molecules involved in generating these new phases. Through
a compact arrangement that restricts their rotational free-
dom, these molecules offer new types of mesophases and
phenomena that are attracting the interest of chemists and
physicists. A large variety of columnar and lamellar molec-
ular packing arrangements, some of which exhibit supra-
molecular chirality, have been reported since the pioneering
results of Niori et al.[3]
[a] Química Orgánica, Facultad de Ciencias – Instituto de Ciencia
de Materiales de Aragón, Universidad de Zaragoza – C.S.I.C.
50009-Zaragoza, Spain
Fax: +34-976761209
E-mail: bros@unizar.es
[b] Departamento de Física Aplicada II, Facultad de Ciencias y
Tecnología,Universidad del País Vasco
Apdo. 644, Bilbao, Spain
Supporting information for this article is available on the
WWW under http://www.eurjoc.org/ or from the author.
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Supramolecular Liquid-Crystalline Organizations of H-Bonded Complexes
ment could be racemic (SmCAPF or SmCSPA phases) or
In order to assess the first possibility, stilbazoles III and
homochiral (SmCSPF or SmCAPA phases).[2] This combina- IV were prepared by taking into account our previous re-
tion of tilt and molecular tip direction in the smectic layers sults (Figure 3). Likewise, given that complexes containing
causes extraordinary properties in the SmCP phase, for ex- five aromatic rings were sufficiently large to induce bent-
ample, to exhibit electrooptic switching under an applied core liquid-crystalline arrangements,[4,5] benzoic acids A14
external field.
and B14 were chosen as H-donors. For the second ap-
proach, compounds V, VI, VII, VIII, IX and X were de-
signed and prepared for mixing with acid B14.
Results and Discussion
The new H-bonded materials reported here are identified
by using a notation corresponding to both the H-acceptor
and the H-donor, as they are labelled in Figure 3.
All of the complexes prepared were first studied by op-
tical microscopy. The solid samples should melt cleanly
without the appearance of biphasic regions, which would
otherwise have indicated the presence of nonstoichiometric
complexes. Only those mixtures that resulted in homogen-
eous materials are included in the discussion.
Figure 2. Chemical structures of the H-acceptors used in a previous
study.
The formation of hydrogen-bonding interactions in the
neat materials was investigated by infrared spectroscopy. IR
spectra show features that are characteristic of carboxylic
acid–pyridine systems. The complexes show two absorp-
tions around 1950 and 2500 cm–1, which correspond to the
N···H–O interaction, whereas carboxylic acid dimers exhi-
bit a band at 2650 cm–1 (O–H). Likewise, bands corre-
sponding to the C=O absorption of acid dimers (around
In this respect, the validity of the new banana-shaped
liquid-crystal materials prepared by the H-bonding ap-
proach was also emphasized, proving that these materials
show an electrooptic and antiferroelectric response similar
to those described for covalent bent compounds in a
SmCAPA phase.[5] Interestingly, our previous studies have
allowed us to highlight the versatility of the H-bonding ap-
proach to study new bent-core liquid crystals.
In a further step, the search for new H-acceptors that
they will allow the properties to be modulated was planned.
With this target in mind, different approaches have been
proposed in an effort to build the bent-structure of the com-
plex. The possibility of creating bent-shaped liquid crystal-
line materials by the formation of two H-bonds with bis-
(pyridine) acceptors or, alternatively, by linking a carboxylic
acid to H-acceptors through single or double chelation,
have been envisaged.
Table 1. Transition temperatures and the associated enthalpy values
(in parentheses) as determined by DSC for the H-acceptors, H-
donors and the complexes derived from them.
Compound Phase transition,[a] temperature [°C] and enthalpy [kJmol–1 [b]
]
III
C 208 [25.0] I
IV
C 192 [100.6] I
V
VI
VII
VIII
IX
C 114 [64.1] SmA 148 [7.0] I
C 87 [40.1] SmA 136 [0.54] N 142 [1.1] I
C 96 [75.4] SmA 146 [5.1] I
C 148 [25.2] SmC 230 [5.1] I
C 148 [54.6] N 156 [1.2] I
X
C 195 [43.3] SmC-N 203 [1.1][c]
C 97 SmC 139 I
I
A14[6]
B14[6]
III-A14
III-B14
IV-A14
IV-B14
C 118 SmC 209 N 214 I
C 142 [66.3] I
C 154 [33.5] SmC 172 N 176 [6.2][c]
C 174 [72.5] I
I
C 171 [27.3] SmA 205[d] [8.4] I
I 204 [4.4] SmA 180 [6.4] SmC 149 [20.1] I
C 109 [125.7] SmA 131 [0.25] N 150 [2.] I
C 104 [86.8] SmC 118 [0.76] N 147 [2.6] I
C 92 [72.2] SmC 119 [0.34] N 142 [3.2] I
V-B14
VI-B14
VII-B14
VIII-B14[e] C 123 [52.6] SmC 203.7 [16.8] I
IX-B14
C 105 [89.7] SmCP 128 [17.1] N 140 [0.77] I
C 120 C + M 150 C + I 180 I
X-B14[e]
[a] C: crystalline phase, SmCP: smectic C polar mesophase, SmC:
smectic C mesophase, SmA: smectic A mesophase, N: nematic me-
sophase, I: isotropic liquid, M: mesophase. [b] Reported are the
onset values for transitions observed for the second-scans at
10 °Cmin–1. [c] Combined enthalpies. [d] Broad peak. [e] Data cor-
responding to a homogeneous blend of the components not consis-
tent with the expected H-bonded complex.
Figure 3. Chemical structures of the H-acceptors and H-donors
used in this work.
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A. Pérez, N. Gimeno, F. Vera, M. B. Ros, J. L. Serrano, M. R. De la Fuente
FULL PAPER
1683 cm–1) were not detected for the complexes. Further- otropic alignment was detected for the SmA mesophase,
more, variable-temperature IR spectra reveal that dissoci- whereas the Schlieren textures identified the SmC phase
ation of the self-assembly is not observed either in the solid (Figure 4). These assignments were confirmed by X-ray dif-
or the mesophase.
fraction patterns.
The thermal properties of the new materials were deter-
When the transition temperatures of these materials are
mined by polarizing optical microscopy (POM), differential compared, some aspects can be pointed out. Firstly, both
scanning calorimetry (DSC) and X-ray diffraction in the of the bent stilbazols studied allow strong packing within
mesophase.
the solid, but only when the long acid B14 is present are the
The majority of the complexes synthesized form liquid intermolecular interactions sufficiently strong to give rise to
crystals (see Table 1), exhibit soft phases over temperature liquid-crystal order before melting. Secondly, for either III-
ranges that are different to those at which the individual B14 or IV-B14 these interactions stabilize the calamitic me-
components display calamitic phases (see Table 1). Several sophases by around 20–30°.
representative optical textures observed for these materials
are shown in Figure 4.
The literature on banana-shaped liquid crystals contains
many examples of bent molecules that exhibit calamitic me-
sophases.[2,7,8] Some authors have attributed this fact to
open-bent cores leading to linear molecular conformations.
This proposal could also be extended to our bis(chelating)
systems. Thus, the conformational flexibility around the hy-
drogen bond could open up the central bend angle to give
rise to linear structures rather than bent ones. This situation
would prevent the strong packing required for the forma-
tion of bent-core mesophases (Figure 5).
Figure 5. Schematic representation of the molecular packing pro-
posed for the calamitic mesophases induced by H-bonded com-
plexes with molecular conformations close to the linear materials
based on III and IV (top) and based on V-VII (bottom). Linear
structures allow the rotational freedom that leads to calamitic li-
quid crystals instead of bent-core liquid-crystal phases.
Figure 4. (a) Complex IV-B14 at 178 °C in the SmC mesophase;
(b) complex VII-B14 at 119 °C, showing the transition from the N
to the SmC phase on cooling; (c) complex VI-B14 at 144 °C in the
N mesophase; (d) complex V-B14 at 145 °C in the N mesophase;
(e) complex IX-B14 at 112 °C in the SmCP phase; (f) complex IX-
B14 at 135 °C in the N phase.
These results are in good agreement to those recently re-
ported by Bruce et al.[9] By using dipyridyloxadiazole linked
to different benzoic acids, only calamitic mesophases occur.
H-acceptors II and IV are more bent and larger than dipyr-
idyloxadiazole; however, this is still not sufficient to induce
bent-core mesophases versus calamitic ones. This is also the
case when a large number of aromatic rings (up to 9) are
present (IV-B14).
Liquid Crystals Based on Compounds III and IV as the H-
Acceptors
As reported in Table 1, only some of the materials pre-
pared by using these H-acceptors (III-A14, III-B14, IV-A14
and IV-B14) induced liquid-crystalline order and none of
the mesophases were identified as any of the typical bent-
core liquid-crystalline phases. Double complexation either
prevented mesomorphism or led to less-ordered calamitic
phases (SmC, SmA or N).
Liquid Crystals Based on Compounds V, VI and VII as H-
Acceptors
Typical marbled and Schlieren optical textures with only
By taking into account the above results, the presence of
4-brush defects were detected for the N mesophase. In the conformationally restricted structures should be more ap-
case of the lamellar phases, a high tendency to afford home- propriate to achieve bent-core mesomorphism. For this pur-
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Supramolecular Liquid-Crystalline Organizations of H-Bonded Complexes
pose, different linear pyridine derivatives such as V, VI and Liquid Crystals Based on Compounds VIII, IX and X
VII were synthesized. These pyridine H-acceptors would
constitute one of the lateral parts of the bent complexes,
where the presence of covalent bonds could tighten the cen- and to enforce the bent-shape of the complexes, pyridine
tral angle. derivatives VIII, IX and X were prepared. In all cases, bent-
To decrease the flexibility in the H-bonded environment
Sufficiently long structures are needed to induce B-type core structures should be formed on complexation with acid
mesophases,[8] but as H-bonded complexes with five-ring B14 by double H-bonding.
systems are large enough to promote the SmCP mesophase,
The 2-hydroxypyridine derivative and the two 2-amino-
acid B14 was used as an H-donor in this case.
pyridines form liquid crystalline phases by themselves, with
Compounds V, VI and VII form liquid-crystal phases in a higher stabilization of the soft order than with com-
their own right (Table 1). In all cases, the presence of a SmA pounds V, IV and VII (Table 1).
phase was detected by POM and X-ray studies. A layer
2-Hydroxypyridine systems have been widely studied in
spacing of around 38 Å, close to the molecular length esti- the solid state and in solution,[10] which is in marked con-
mated from Dreiding models (≈ 36 Å), was determined in trast to the small amount of interest in the liquid-crystal
the mesophase.
field.[11] However, a broad SmC phase was attributed to
When these pyridine compounds were mixed with acid VIII on the basis of POM, DSC and X-ray studies. From
B14 (molecular length ≈ 34 Å), three new H-bonded materi- the latter studies, a layer spacing of 46 Å within the tilted
als were obtained. All exhibit liquid-crystalline behaviour, mesophase was determined and this is larger than the mo-
but as observed from their optical textures they show cala- lecular length estimated from Dreiding stereomodels
mitic phases (Figure 4).
(around 38 Å).
All of these materials show an N phase, but whereas the
IR experiments of compound VIII in KBr at different
presence of imine groups promotes an additional tilted temperatures revealed that the raw materials did not show
smectic C order (VI-B14 and VII-B14), diester V induces any absorbance around 1660 cm–1 (which is characteristic
an orthogonal arrangement (SmA). A layer thickness of for 2-pyridone tautomers) but bands at 3100–3000 and
around 49.9 Å was determined for the mesophase formed 2600–2500 (broad) cm–1 were observed (Supporting Infor-
by this complex. Likewise, all of these materials exhibit me- mation, Figure S2). However, thermal treatment of these
sophase ranges and clearing temperatures very similar to samples led to the appearance of an intense band at
those shown by the H-acceptors. On the basis of these data, 1650 cm–1, which shifted to 1686 cm–1 upon heating to the
we propose that within the mesophases of V-B14, VI-B14 isotropic liquid. This new absorption remained when the
and VII-B14, both components adopt a linear disposition sample was cooled to room temperature. These spectro-
rather than a bent orientation upon complexation.
scopic data are in good agreement with those reported in
These results seem to confirm that conformational flexi- the literature for dimers of 2-pyridone structures in the solid
bility in the bent-core structure does not stabilize the molec- phase.[10a,10b,12]
ular packing responsible for the bent-core mesosphere (Fig-
ure 5).
The 2-aminopyridine system was successfully used to pro-
mote mesomorphism through noncovalent interactions, espe-
Interestingly, comparison of the thermal properties of the cially with melamine derivatives.[1,13] Compounds IX and X,
complexes that are similar in length (III-A14, V-B14, VI- however, are the first examples of simple structures to link
B14, VII-B14) with those of complex I-A14 (Figure 6) this family of systems. Both materials form an N mesophase
shows that, as expected, the symmetric complex has the in a narrow temperature range Ϫ in contrast to compound
most efficient packing in the solid phase but undergoes a VIII, which allows a broad and strong stabilization of the
direct transition to a liquid at 142 °C. Likewise, this tem- liquid-crystal order. Likewise, compounds VIII and IX melt
perature is very close to the clearing points of the unsym- around 150 °C, but compound X derived from the diamino-
metrical complexes but they can stabilize calamitic liquid- pyridine significantly stabilizes the solid packing.
crystal order prior to the liquid phase. However, unsymmet-
To study structural aspects of these new 2-aminopyridine
rical complex I-A14, which melts to a SmCP phase at compounds in the condensed phases, IR studies at variable
around 90 °C, exhibits the lowest stabilization of mesogenic temperatures in KBr were performed. By taking into ac-
order. It can therefore be concluded that the extension of count results reported by Abdulla et al. for 2-aminopyr-
the bent structure has an important effect on the stabiliza- idines,[14] the formation of dimers could be considered to
tion of bent-core liquid-crystalline packing.
result form the absence of absorptions at 3500 cm–1 (Fig-
ure 7; Supporting Information, Figure S5). Unfortunately,
the crystallization of X prevented further evidence from be-
ing obtained for this dimerization by X-ray diffraction on
the SmC mesophase. Additionally, for compound X, the 2-
pyridone dimer seems to be the only one present (bands at
3200–3140 cm–1; Supporting Information, Figure S5), but
associations of different tautomers can be proposed for IX
owing to the presence of an extra absorption at 3340 cm–1
(Figure 7).
Figure 6. Complex I-A14 and its liquid-crystalline properties.
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FULL PAPER
Figure 8. Chemical structure proposed for the dimers formed for
compounds VIII and X in the condensed phases.
To gain better insight into the cause of the unexpected
calamitic order afforded by VIII-B14, this material was
studied by X-ray diffraction and IR spectroscopy at vari-
able temperature. The tilted lamellar phase was assigned on
the basis of both the optical textures and the X-ray diffrac-
tion patterns, which showed a layer thickness of 42 Å Ϫ
very similar to the data measured for compound VIII.
Furthermore, IR studies at variable temperature revealed
some other noteworthy aspects. Along with the presence of
the 2-pyridone tautomer (bands around 1650 cm–1), an ab-
sorption at 1716 cm–1 corresponding to the carboxylic acid
can be observed (Supporting Information, Figure S3). This
peak is far from the one attributed to the dimeric form of
acids (around 1689 cm–1).
Similar bands have been reported for 1:1 mixtures of 2-
hydroxypyridine and carboxylic acids in the solid phase.[12]
Furthermore, X-ray data[15] for this type of material re-
vealed that carboxylic acids are not capable of breaking the
strong dimerization in this type of pyridine derivative and
the interactions between the two components are limited to
weak –N–C=O···HOOC associations. By taking all of these
results into account, the calamitic mesophase presented by
the material afforded by mixing VIII and B14 is more con-
sistent with the formation of structures similar to that
shown in Figure 9 than a bent-core complex.
Figure 7. IR spectra (KBr) of compound IX at different tempera-
tures (top) and that of complex IX-B14 and its components (B14
and IX) at room temperature (bottom).
On the basis of these results, the molecular dimerization
of compounds VIII, IX and X within the condensed phase
can be proposed as the origin of the stabilization of the
mesophase order in these materials (Figure 8). When these
three 2-substituted compounds were mixed with acid B14,
three new materials were obtained and they exhibit rather
different behaviours. The blend of X and B14 did not give
rise to an appropriate material for study. A phase sequence
in which crystalline and liquid-crystalline phases coexist
was observed by POM on repeated heating and cooling
scans (Table 1). IR studies in KBr (Supporting Information,
Figure S5) suggest incomplete complexation of the two
components. In contrast, VIII-B14 promotes a calamitic
Figure 9. Chemical structure proposed for the material afforded by
mixing VIII and B14.
This is not the case for IX-B14. IR studies, X-ray diffrac-
SmC phase and IX-B14 gives rise to an N phase at high tion and DSC measurements support the formation of a
temperature but a B-type mesophase occurs at low tempera- proper bent-core complex as the origin of a bent-core meso-
tures (Figure 4e, f).
phase. It can be seen in Figure 7 that the peaks at 3400 and
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Supramolecular Liquid-Crystalline Organizations of H-Bonded Complexes
3100 cm–1, which correspond to the amino group of IX, as crease in some spurious contribution associated with the
well as those associated to dimers of acid B14 at 2600– conductivity. At 10 kHz, the permittivity is larger in the
2500 cm–1 disappear on mixing, whereas broad absorptions SmCP phase than in the N phase, as expected for these
at 2450 and 1900 cm–1, associated with the N···H–O inter- bent-core phases because of the polar correlation between
actions, are also observed.
molecules. Although we could not measure the spontaneous
DSC studies show a large enthalpy change (17 kJmol–1) polarization, there is sufficient information to infer the
on cooling the nematic phase (Figure 10b), which gives rise SmCP structure for this mesophase.
to a lamellar mesophase for which up to three orders of
reflections (hkl, 001, 002 and 003) were detected by X-ray
studies (Figure 10a).
Figure 12. Temperature behaviour of the dielectric permittivity for
complex IX-B14.
In contrast to other H-bonded bent-core materials based
on pyridine–carboxylic acid complexation[5] this complex
exhibits a significant instability under subsequent electric
field application. This instability should be attributed to the
new H-bonded system presents in IX-B14 where different
weak bonds involving H-atoms are present. Interestingly,
few data concerning the application of electric fields on 2-
aminopyridine–carboxylic acid exist[1] so these results
Figure 10. Chemical structure proposed for complex IX-B14. X-ray
diffraction pattern of a nonoriented sample in the SmCP phase at
should be considered for future research not only for liquid
110 °C (a) and DSC traces at a scanning rate of 10 °Cmin–1 (b).
crystals but for alternative H-bonded supramolecular sys-
tems in general.
The lamellar mesophase is clearly switchable under elec-
tric fields. The texture observed under a triangular field
(50 Hz, 30 Vppµm–1) is shown in Figure 11b. Crosses with
Conclusions
the extinction brushes tilted with respect to polarizer and
In this work we showed how noncovalent interactions
analyzer can be observed. However, until this maximum
play a unique role in constructing supramolecular systems
field was applied, a depolarization current could not be ob-
with liquid-crystal order. Thus, H-bonds have offered a con-
served. Further increases in the field led to the destruction
venient and versatile approach to the design and under-
of the sample. It is also important to note that the com-
standing of liquid-crystalline behaviour in general, and
bent-core mesomorphism, in particular.
pound is not very stable under electric fields (the transition
temperatures change and many bubbles appear).
Interestingly, the stabilization of calamitic liquid-crystal
order is possible by H-bonding dimerization of single and
simple 2-hydroxy- and 2-aminopyridine compounds that
open new perspectives in the engineering of these soft mate-
rials.
On the other hand, this paper demonstrates that even
though different approaches to the design of H-bonded
bent-shaped liquid crystals exist, the conformational flexi-
bility around this noncovalent interaction must be restricted
to induce bent-core liquid-crystalline order. The formation
of single H-bonds either in the apex position or within both
lateral parts of V-shaped structures do not afford the rigid
bent-structures needed to promote B-type mesophases and
Figure 11. Optical photomicrographs obtained in the liquid-crystal
phase of complex IX-B14 at 111 °C: (a) in the absence of an electric
field; (b) upon application of a square wave (30 vppµm–1, 50 Hz).
Extinction brushes are rotated at an angle with respect to polarizer
and analyzer (in the circle).
A plot of dielectric permittivity at 1 and 10 kHz versus thus less-ordered calamitic soft phases occur. Additionally,
temperature, on both heating and on cooling, is given in the appropriate selection of the chemical structure around
Figure 12. At the N-SmCP phase transition, the low fre- the H-bonded moiety could strongly determine the stability
quency permittivity decreases. This fact is related to a de- of this kind of material in electric fields.
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Experimental Section
The synthetic routes for the H-acceptors are shown in Schemes 1
and 2. In all cases, synthetic methods reported in the literature or
adaptations of these methods were followed. The carboxylic acids
used in this research were prepared according to synthetic methods
from the literature.[5,16,17] Experimental details are reported in the
Supporting Information. The thermal properties of all these com-
pounds are gathered in Table 1.
The complexes were prepared by dissolving the precise equimolecu-
lar proportions of the corresponding components in freshly dis-
tilled THF. The blends were mechanically stirred overnight at room
temperature. In the case of compounds IX and X, the mixtures
were stirred at 60 °C for 3 d due to the low solubility of the pyridine
components. The solvent was subsequently removed under reduced
pressure in all cases. The residual solvent was removed by heating
the sample at 40 °C under vacuum overnight.
Supporting Information (see footnote on the first page of this arti-
cle): Synthetic procedures, thermal, spectroscopic and X-ray data
of different materials and techniques used in their characterization.
Acknowledgments
This work was supported by the CICYT-FEDER (project
MAT2006–13571-C02) from Spain-EU and by the Gobierno de
Aragón (Spain). F. V. thanks the Ministry of Education of Spain
for a FPI grant.
Scheme 1. Routes for synthesis for compounds III and IV.
Scheme 2. Routes for synthesis for compounds V–X.
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Supramolecular Liquid-Crystalline Organizations of H-Bonded Complexes
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Published Online: December 11, 2007
Eur. J. Org. Chem. 2008, 826–833
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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