Structure-activity studies of ferroelectric and antiferroelectric imine ligands and their palladium(II) complexes. An antiferroelectric metallomesogen

Article abstract of DOI:10.1039/b310955k

The synthesis and characterization of the mesomorphic and dielectric properties of new imine-based liquid crystalline compounds that exhibit tilted SmC* phases is reported. The presence of an imino linkage within the mesogenic nucleus of these compounds is significant due to the ability of benzaldimines to coordinate to metals. Complexation to a divalent metal such as Pd(II) has been studied in order to assess the effects of antiparallel dimerization of organic ligands, through metal-coordination, on the appearance of antiferroelectric order in the mesophase. An organometallic palladium(II) complex has been prepared and this shows antiferroelectric behaviour over the whole range of the tilted smectic mesophase. Structure-activity studies have also been carried out by varying structural elements in the composition of the ligands. The changes include the disposition of the linking groups within the mesogenic core, and presence of a lateral hydroxy group.

Full text of DOI:10.1039/b310955k

View Article Online / Journal Homepage / Table of Contents for this issue
A R T I C L E
Structure–activity studies of ferroelectric and antiferroelectric
imine ligands and their palladium(II) complexes. An
antiferroelectric metallomesogen
Delia Lo´pez de Murillas,a Rafael Pin˜ol,a M. Blanca Ros,a Jose´ Luis Serrano,*a
Teresa Sierraa and M. Rosario de la Fuenteb
aQu´ımica Orga´nica, Facultad de Ciencias-I.C.M.A., Universidad de Zaragoza-C.S.I.C.,
50009-Zaragoza, Spain
bDept. F´ısica Aplicada II, Facultad de Ciencias, Universidad del Pa´ıs Vasco, Aptdo. 644,
48080-Bilbao, Spain
Received 8th September 2003, Accepted 7th January 2004
First published as an Advance Article on the web 20th February 2004
The synthesis and characterization of the mesomorphic and dielectric properties of new imine-based liquid
crystalline compounds that exhibit tilted SmC* phases is reported. The presence of an imino linkage within the
mesogenic nucleus of these compounds is significant due to the ability of benzaldimines to coordinate to metals.
Complexation to a divalent metal such as Pd(II) has been studied in order to assess the effects of antiparallel
dimerization of organic ligands, through metal-coordination, on the appearance of antiferroelectric order in the
mesophase. An organometallic palladium(II) complex has been prepared and this shows antiferroelectric
behaviour over the whole range of the tilted smectic mesophase. Structure–activity studies have also been
carried out by varying structural elements in the composition of the ligands. The changes include the
disposition of the linking groups within the mesogenic core, and presence of a lateral hydroxy group.
molecules. Furthermore, these imino compounds possess the
Introduction
ability to coordinate to metals. The aforementioned anti-
parallel arrangement in the crystal is reminiscent of the ligand
disposition in the square-planar dimeric metal complexes
derived from Schiff bases (Fig. 1), investigated in depth by
our group.5 On the basis of this structural similarity we were
tempted to investigate the possibilities for metal complexation
of our chiral imines with the aim of inducing or stabilizing
antiferroelectric order in metallomesogens. Such structures
Interest in Antiferroelectric Liquid Crystals (AFLCs) is based
on their characteristic features and, in particular, on new
effects, such as thresholdless antiferroelectricity or V-shaped
switching – properties that make these systems suitable
materials for flat panel displays.1 Since the first confirmation
of this property,2 the need for suitable materials has led to the
design and synthesis of many calamitic molecules, most of
which are structurally related to the first AFLC, MHPOBC.
Structure–activity studies have been carried out in an attempt
to establish the molecular characteristics required for the
appearance of antiferroelectric order in the mesophase. The
most significant conclusions indicate a molecule consisting of a
three-ring core, with at least two aromatic rings that are not
directly connected, and a chiral tail with a transversal disposi-
tion with respect to the long molecular axis and connected to
the rigid core through a carboxylate linkage.3 The main types
of connectors within the core have been dipole-associated
functional groups such as ester or amido groups.
Examination of the crystalline structures of mesogenic
compounds exhibiting antiferroelectric behavior4 shows that
molecules adopt a herringbone crystal packing with a layer-like
organization. Within each layer, mesogenic moieties adopt an
antiparallel arrangement with the chiral tail almost perpendi-
cular to the core moiety. Additionally, two ester groups of each
molecule are oriented in the same direction transversal to the
long molecular axis, making the layer highly polar with
additional ester–ester interactions. These structures have been
interpreted as being responsible for antiferroelectric ordering
within the liquid crystal phase, a situation in which interlayer
interactions would be stabilized by an alternating arrangement
of highly polar layers.
Fig. 1 a) Schematic representation of the crystal structure of a typical
antiferroelectric liquid crystal according to ref. 4d. b) The antiparallel
disposition of the molecules is reminiscent of the ligand orientation in
square-planar dimeric Schiff base complexes. As an example, the
general structure of a salicylaldiminate is represented in the figure.
The work described here deals with the synthesis and the
liquid crystal and dielectric characterization of different imine
derivatives whose molecular structure is based on the generally
accepted formula reported for antiferroelectric mesogenic
T h i s j o u r n a l i s ß T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 1 1 7 – 1 1 2 7
1 1 1 7

View Article Online
and an ester group – the former has scarcely been employed
in the design of antiferroelectric liquid crystals.6 Structural
modifications were also undertaken, and these included: (i) the
relative orientation of the dipoles along the longitudinal
molecular axis (L1 vs. L2), (ii) the presence of lateral polar
groups such as a hydroxy group, which can affect the rigidity
and polarisability of the mesogenic nucleus by means of
intramolecular hydrogen-bonding (L3 vs. L1) and will allow a
different way of chelation to the metal atom.
Coordination of salicylaldimine L3 to Pd(II) gives rise to a
square-planar dimeric complex through chelation of the N
(imine) and O (hydroxy group) heteroatoms to the metal. The
resulting molecular structure consists of two ligands whose
mesogenic moieties face each other and adopt an antiparallel
disposition of their mesogenic nuclei fixed by coordination to
the metal. Likewise, orthopalladation complexes derived from
benzaldimines L1 and L2 and their reaction with palladium(II)
acetate, and these with palladium(II) chloride, give rise to
dimeric dinuclear complexes. In this case the antiparallel
orientation of the ligands is only achieved if the coordination to
the metal occurs with a trans configuration of the chelating
atoms. This situation can be readly confirmed by 1H NMR, as
already reported for various examples.7 Taking into account
the conformation of this type of ligand in which the chiral tail
adopts a disposition almost perpendicular to the rest of the
molecule,4 the final molecular shape of all these complexes is
reminiscent of the crystal packing described for some liquid
crystals that exhibit the antiferroelectric SmC*A mesophase, as
mentioned above.
Chart 1
have no precedents in the literature. Metal complexation could
well prove to be a convenient approach to new antiferroelectric
materials.
For this purpose, we designed organic ligands that struc-
turally have the capability to coordinate to metal atoms and
also incorporate a chiral tail and linkages that favor highly
polar layers and, hence, promote antiferroelectric order within
the mesophase (Chart 1). From these ligands, we selected diffe-
rent square-planar dimeric structures, namely palladium(II)
salicylaldiminates and acetato- and chloro-bridged-ortho-
palladated structures that ensure a fixed antiparallel, i.e.
trans, disposition of the ligands within the complex (Chart 2).
In order to gain an insight into the molecular structural
factors that influence the appearance of either ferro- or
antiferro-electric order, or both, in the ligands and the metal
complexes, we prepared three types of chiral Schiff base ligand.
All of them consist of a three-ring mesogenic core in which the
aromatic rings are linked by two different groups, i.e. an imino
All of the compounds were studied by optical microscopy,
DSC and broadband dielectric spectroscopy. The spontaneous
polarisation values were evaluated by means of the triangular
wave method, wherever possible.
Chart 2
1 1 1 8
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 1 1 7 – 1 1 2 7

View Article Online
Scheme 1
over a wide temperature range (Table 1). Moreover, three of
them show the potentially ferroelectric SmC* mesophase. The
antiferroelectric mesophase was detected by both optical
microscopy and DSC for compound L2 but only by observa-
tion of textures through polarising optical microscopy for
L1 and L3. In all three ligands the SmC*A mesophase was
further confirmed by dielectric spectroscopy studies, as will be
discussed below.
Two structural factors will be considered as far as their influ-
ence on the mesomorphic behaviour is concerned: (i) relative
orientation of the dipoles along the long molecular axis; and (ii)
presence of lateral polar groups such as a hydroxy group, which
can affect the rigidity and polarisability of the mesogenic nucleus
by means of intramolecular hydrogen bonding.
Comparison of the mesomorphic behaviour of compounds
L1 and L2 shows that there is a significant effect when the
orientation of dipoles along the molecular long axis is modified.
Thus, dipoles in L1 are all oriented head-to-tail whereas the
sense of the imino linkage has been reversed in L2. One of the
consequences of the inversion of this linking group is a marked
decrease in the melting point without significantly affecting the
clearing temperature. Furthermore, smectic polymorphism is
significantly favoured; and an enantiotropic antiferroelectric
SmC*A is observed below the SmC* phase as well as an interval
of coexistence of ferroelectric and antiferroelectric behaviour
being deduced from dielectric spectroscopy and spontaneous
polarisation studies. Below the antiferroelectric mesophase, a
monotropic SmI*A mesophase appears, and this behaves in an
antiferroelectric manner under an electric field. The compound
does not crystallize on cooling till room temperature but
undergoes a cold crystallization during the subsequent heating
process (see Fig. 2).
As a general trend, the mesomorphic interval increases when
the rigidity of the mesogenic nucleus and its polarisability are
enhanced by intramolecular hydrogen bonding. This situation
is as one would expect for mesogenic molecules derived from
salicylaldimines.8 Thus, compound L3 shows a mesophase
interval 24 uC wider than its analogue L1, which does not
have the possibility of intramolecular H-bond. The melting
temperatures are similar but the clearing point is 22 uC higher
Results and discussion
Study of the ligands
Synthesis. The synthetic route used to prepare the ligands
is shown in Scheme 1. The final step is, in all cases, the
condensation of the aniline and the corresponding aldehyde to
form the imine linkage.
The chiral tail, (2R)-2-octanol, was coupled with benzyl-
protected 4-hydroxybenzoic acid using dicyclohexylcarbodi-
imide as esterification agent. The chiral phenol (2) was coupled
either with p-nitrobenzoic acid (the nitro group was sub-
sequently reduced to amino) or p-formylbenzoic acid to yield
the corresponding chiral moieties (3 and 4) of the final ligands.
These chiral moieties were coupled with the corresponding
4-alkoxybenzaldehyde (5) and p-alkoxyaniline (8) respectively,
in ethanol with acetic acid as catalyst. These reactions gave the
target Schiff bases.
Mesomorphic properties. The thermal properties of the
ligands were investigated by polarising microscopy and diffe-
rential scanning calorimetry. Results are given in Table 1.
All of the ligands prepared show mesomorphic behaviour
Table 1 Thermal properties of the ligands and their palladium
complexes
Transition temperature/uC [transition enthalpy,
Compound
DH/kJ mol21
]
L1
L2
L3
Cr 110 [37.9] (SmC*A 108a) SmC* 125 [0.1]
SmA 151[4.2] I
Cr 74 [27.1] (SmI*A 56 [1.9]) SmC*A 114 [0.1]
SmC* 123 [0.4] SmA 158 [4.7] I
Cr 108 [32.5] SmC*A 112a SmC* 139a
SmA 173 [4.5] I
L1–PdAc
L1–PdCl
L2–PdAc
L2–PdCl
L3–Pd
Cr 201 [37.9] SmA 205 dec
Cr 188 [37.3] (SmC* 185a) SmA 240 dec
Cr 164 [4.7] SmA 196 dec
Cr 162 [23.3] SmC*A 198a SmA 250 dec
Cr 225 [59.7] SmA 270 dec
a Transition temperatures taken from optical microscopy observations.
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 1 1 7 – 1 1 2 7
1 1 1 9

View Article Online
Fig. 2 DSC scans of compound L2 during the second heating and cooling processes. Inset: expansion of the temperature interval in which
transitions between SmA, SmC* and SmC*A appear.
than that of L1. This extension of mesomorphic behaviour
drastically affects the SmC* mesophase and gives rise to
polymorphism. An enantiotropic antiferroelectric SmC*A
mesophase appears along with an interval of coexistence of
ferroelectric and antiferroelectric behaviour (deduced from
dielectric and spontaneous polarisation studies).
This observation is in contrast to that occurring in the
ferroelectric SmC* phase, whose helix becomes tighter as the
temperature decreases. This phenomenon, which is clearly
detectable, allowed confirmation of antiferroelectric ordering
in these compounds. Moreover, at a temperature close to the
transition to the antiferroelectric mesophase, both compounds
show an iridescent petal texture due to a helix pitch in the
visible region of the spectrum, with the visible light being blue-
green. In the case of compounds L2 and L3, the dechiralization
lines visible in the ferroelectric SmC* mesophase disappear on
reaching the antiferroelectric ordering. The SmI*A mesophase
of compound L2 was identified by its bubble texture on cooling
from the SmC*A mesophase. Confirmation of this mesophase,
as opposed to SmF*, came from the observation of its Schlieren
texture (arising from the pseudohomeotropic zones of the
SmC*A), which was difficult to be focused. Dechiralization
lines related to the helix of the phase reappear when this
mesophase forms.
Texture analysis. Analysis of the textures allowed the
identification of the type of smectic mesophase appearing in
each compound. The change to antiferroelectric ordering in
the tilted smectic mesophase in L1, L2 and L3 was particularly
clear.
The natural texture of the SmA mesophase, on cooling from
the isotropic state, is fan-shaped with black zones correspond-
ing to homeotropic alignment of the molecules. Further cooling
yields a broken fan-shaped texture corresponding to the tilted
SmC* and this shows dechiralization lines at certain tempera-
ture intervals within the ferroelectric SmC* mesophase. In L1
and L2, the pseudohomeotropic texture of the SmC* phase
arising from the homeotropic alignment in the SmA mesophase
appears red initially (Fig. 3a) and then turns green on cooling
(Fig. 3b and 3c). At a given temperature the colour again
becomes red (Fig. 3d), which signifies unwinding of the helix.9
Ferroelectric properties of the ligands. All the three ligands
were studied under the influence of an alternating electric field
in 5 mm cells with polyimide coating (to achieve homogeneous
alignment) and inner ITO electrodes. The spontaneous
Fig. 3 Photomicrographs of L2 in its SmC* and SmC*A mesophases. The pseudohomeotropic texture of the SmC* appears red (a) and turns green
on cooling (b and c). At the transition to the antiferroelectric mesophase, it becomes red again (d).
1 1 2 0
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 1 1 7 – 1 1 2 7

View Article Online
Fig. 4 Plot of the spontaneous polarisation values against the electric field at different temperatures for L2. Measurements were carried out in a
5 mm Linkam cell.
polarisation (Ps) was evaluated by means of the triangular
wave method.10 The maximum value reached in all cases
was around 80 nC cm22 (85 nC cm22 for compound L1 and
80 nC cm22 for L2 and L3). The sign of the Ps was negative in
all the three cases. Measurements were made at 8.5 Vpp mm21
and 50 Hz (Vpp ~ voltage peak to peak). For L2, it was
necessary to employ 20 Vpp mm21 in order to induce ferro-
electric switching over the whole range of ferro- and antiferro-
electric mesophases. L1 and L3 show a dependence of the
spontaneous polarisation values on the applied electric field as
one would expect for a ferroelectric behaviour. L2 was an
exception to this trend. Fig. 4 shows the measured polarisation
for different values of the maximum field of the triangular wave
(50 Hz) for different temperatures, both in the SmC* phase and
in the SmC*A phase. For the last mesophase, although the
switching current shows only a peak for each half period, the
behaviour is clearly antiferroelectric with a very clear threshold
field that increases as temperature decreases.11
1 kHz in a metallic cell (50 mm) for compound L2. Fig. 6 shows
the corresponding results for compound L3 at 125 Hz in a
metallic cell (50 mm). All the samples were studied on cooling.
The huge increase corresponds to the SmA–SmC* phase
transition and the step decrease to the SmC*–SmC*A
transition. For L1 (not shown) the decrease coincides with
the change in texture but the compound crystallizes immedi-
ately, making it impossible to perform any study in the
antiferroelectric mesophase. For L3 the SmC*A phase persists
over several degrees but any attempt to measure the
spontaneous polarisation during this period was unsuccessful
because of field-induced crystallization. In Linkam cells the
interval over which the antiferroelectric mesophase exists
almost disappears. The temperature interval associated with
the large value of the permittivity (for the three compounds)
does not correspond to pure ferroelectric behaviour, probably
due to the coexistence of ferro- and antiferroelectric behaviour.
In Fig. 5 one can also see that for L2 the transition from the
ferroelectric to the antiferroelectric mesophase is sharper in the
metallic cell than in the Linkam cell. Similar effects have also
been observed by other authors.12
The formation of antiferroelectric order below the ferro-
electric mesophase, which would be the responsible for the
special textural appearance observed for L1, L2 and L3, was
confirmed by means of dielectric spectroscopy. Fig. 5 shows the
dielectric permittivity at 125 Hz in a Linkam cell (5 mm) and at
As far as the structural modifications influencing ferro-
electric properties are concerned (i.e. Ps), significant effects
Fig. 5 Plots of the dielectric permittivity against temperature for compound L2 measured at 125 Hz in a 5 mm Linkam cell and at 1 kHz in a 50 mm
thick metallic cell on cooling.
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 1 1 7 – 1 1 2 7
1 1 2 1

View Article Online
Fig. 6 Plot of the dielectric permittivity against temperature for compound L3 measured at 125 Hz in a 50 mm thick metallic cell on cooling.
were not detected compared to those observed for meso-
morphic behaviour. Neither reversing dipoles along the mole-
cular long axis nor having a lateral hydroxy group in the
mesogenic core showed any influence on the Ps values, which
compound also showed decomposition on reaching the clearing
temperature.
On the basis of all the experimental results, it can be seen that
all the complexes organized themselves into the orthogonal
SmA mesophase up to decomposition, irrespective of the
planarity of their structures. However, the appearance of the
tilted chiral SmC mesophases is basically observed for planar
structures only. Furthermore, the targeted antiferroelectric
SmC*A order is exclusive for compound L2–PdCl and is seen
over a range of 40 uC, with complete absence of the ferroelectric
SmC* mesophase.
Comparison of the types of mesophase and their temperature
ranges of both the ligands and their related complexes (see
Table 1) shows that, along with the expected increase of the
transition temperatures and stabilization of the liquid crystal
order for the complexes, no dramatic modifications of the
mesophase range occur on going from the ligand to the
complex. However, a significant change in the mesomorphic
order is clear. For example, the orthogonal SmA is favoured
for the metal-containing molecules, while the decrease or total
suppression of tilted SmC* phases are apparent.
are in all cases around 80 nC cm22
.
Study of the complexes
The metal complexes were prepared by coordination of both
benzaldimine ligands (L1 and L2) and the salicylaldimine
ligand (L3) with palladium(II). The metal was coordinated to
the corresponding ligands according to their nature. Thus, L1
and L2 give rise to dinuclear-ortho-palladated complexes, in
which bridges between palladium atoms are either acetate or
chlorine. On the other hand, ligand L3 gives rise to a N,O-
chelated mononuclear palladium(II) complex. By means of
both strategies, dimeric molecules have been built with an
antiparallel orientation of their corresponding mesogenic chiral
ligands.
Synthesis of the complexes. The preparation of the ortho-
palladated complexes was carried out by reaction of the ligand
with palladium(II) acetate in glacial acetic acid. Two acetate-
bridged complexes, L1–PdAc and L2–PdAc, were obtained in
this way. In both cases the trans isomer was only observed by
1H NMR studies. The chloro-bridged complexes, L1–PdCl and
L2–PdCl, were prepared from the corresponding acetate
derivatives by reaction with HCl in methanol (see Scheme 2a).
The presence of only one isomer, i.e. trans, was again indicated
Ferroelectric properties of the complexes. Maximum sponta-
neous polarisation values were measured for the complexes dis-
playing an enantiotropic SmC* phase, i.e. L3–Pd (36 nC cm22
,
measured under 10 Vpp mm21 and a frequency of 50 Hz), or the
antiferroelectric SmC*A mesophase, L2–PdCl (15 nC cm22
,
measured under 35 Vpp mm21 and a frequency of 50 Hz). During
the study of the mesophase of L2–PdCl, even though only a single
current peak was observed upon application of a triangular-wave
electric field, a threshold voltage around 30 V mm21 was clearly
detected. Such a result is indicative of the existence of antiferro-
electric ordering within the mesophase. This phenomenon
occurred over the whole range of the tilted mesophase. The
dielectric studies also confirm the antiferroelectric nature of the
tilted phase. Fig. 7 shows the dielectric permittivity at 1 kHz on
cooling (the value measured almost corresponds to the static
value because all the relaxations present occur at higher fre-
quencies) and this shows typical soft mode behaviour. A mode
that could be described as a ferroelectric Goldstone mode was not
observed.
1
by H NMR studies.
Mesomorphic behaviour. The transition temperatures and
enthalpies corresponding to the complexes studied are gathered
in Table 1.
Textures for ortho-palladated compounds were observed on
cooling from the SmA mesophase as decomposition was
detected at around 200 uC. The SmA showed a homeotropic
texture that turned into a Schlieren, pseudohomeotropic,
texture corresponding to the SmC* phase for L1–PdCl. In
the case of L2–PdCl the homeotropic SmA texture gave rise to
a grey marbled appearance below the transition to the anti-
ferroelectric SmC*A mesophase. Similarly, usual fan-shaped
and homeotropic textures were observed for the SmA meso-
phase of the salicylaldiminate complex L3–Pd. However, this
One of the targets of our work was the induction or stabiliza-
tion of the antiferroelectric ordering upon dimerization
1 1 2 2
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 1 1 7 – 1 1 2 7

View Article Online
Scheme 2
through complexation. Although induction of this mesophase
was not observed in any case, the appearance of antiferro-
electric switching in a metallomesogen has been accomplished.
Thus, the ligand L2, which shows SmC* and SmC*A meso-
phases, gives rise to a chloro-bridged complex, L2–PdCl, that
shows enantiotropic antiferroelectric behaviour over a range of
40 uC, up to 190 uC. This phase appears below the SmA phase,
as confirmed by dielectric studies (Ps measurements and
broadband dielectric spectroscopy). In fact, we can propose
this type of dimerization as an approach for the design of
antiferroelectric liquid crystals that ensures an antiparallel
disposition of the linked monomers. This strategy can be
considered as an alternative to previously reported strategies
based on twining calamitic molecules, either by terminally
attached or laterally connected monomers, which have
afforded antiferrroelctric liquid crystalline materials.13
However, even though the restricted antiparallel arrange-
ment of the chiral ligands has been ensured by means of metal
coordination, trans complexation only maintains the highly
polar character in the smectic layers of the ligands in one case,
L2–PdCl. Thus, from ligands that show an enantiotropic
antiferroelectric mesophase, i.e. L3 and L2, only an antiferro-
electric mesophase has been achieved for the dinuclear ortho-
palladated complex L2–PdCl. In contrast, L3–Pd does not
Fig. 7 Plot of the dielectric permittivity against temperature for complex L2–PdCl measured at 1 kHz in a 50 mm thick metallic cell on cooling.
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 1 1 7 – 1 1 2 7
1 1 2 3

View Article Online
maintain the antiferroelectric behaviour shown by the ligand
itself. This is related to recent results of metal-complexation
experiments of salicylaldimine banana-shaped ligands, in which
disappearance of the switchable B2 mesophase occurs for metal
complexes prepared from ligands that show the mesophase in a
wide temperature interval.14
Synthesis of 4-[(1R)-1-methylheptyloxycarbonyl]phenyl
4-nitrobenzoate (3)
The esterification of p-nitrobenzoic acid with the correspond-
ing phenol (2) was carried out with dicyclohexylcarbodiimide
(DCC) and dimethylaminopyridine (DMAP) in dichloro-
methane, in a similar way to that described for (1R)-1-
methylheptyl 4-benzyloxybenzoate (1). The reaction was
carried out at room temperature. The crude product was
purified by flash chromatography on silica gel using a mixture
of hexanes/ethyl acetate (1:7) as eluent. Yield: 68% of a white
solid. Rf: 0.61 (8:2 hexanes/ethyl acetate). Mp: 36 uC. 1H-RMN
(300 MHz, CDCl3): d 0.86 (t, J ~ 6.6 Hz, 3 H), 1.27 (m, 8 H),
1.33 (d, J ~ 6.3 Hz, 3 H), 1.60 (m, 1 H), 1.71 (m, 1 H), 5.15 (m,
1 H), 7.30 (d, J ~ 8.7 Hz, 2 H), 8.13 (d, J ~ 8.7 Hz, 2 H), 8.37
(s, 4 H). 13C-RMN (300 MHz, CDCl3): d 14.0, 20.0, 22.6, 25.4,
29.1, 31.7, 36.0, 72.1, 121.4, 123.8, 129.1, 131.2, 131.3, 134.5,
150.9, 153.8, 162.8, 165.2. IR (Nujol) n/cm21: 1746, 1712, 1528,
1349, 1261, 1201, 1162, 1110.
Conclusion
We have described the synthesis and mesomorphic and dielectric
characterization of a series of new imine-based liquid crystal-
line compounds that exhibit tilted SmC* phases. These
compounds have offered the possibility of analysing and
establishing the effect of different structural modifications on
mesomorphism and dielectric behavior. In addition, these
imines have allowed a new approach to the design of anti-
ferroelectric liquid crystals to be investigated. The complexa-
tion of these ligands to palladium(II) gives rise to new
ferroelectric materials. It is worth noting that transfer of the
tendency to form antiferroelectric order from the ligand to the
metal derivative has been accomplished for a chloro-bridged-
ortho-palladated compound. This represents an alternative
strategy to a more general approach to the design of anti-
ferroelectric materials based on dimerization of chiral smecto-
genic molecules.
Synthesis of 4-[(1R)-1-methylheptyloxycarbonyl]phenyl
4-formylbenzoate (4)
The esterification of p-formylbenzoic acid with the correspond-
ing phenol (2) was carried out with dicyclohexylcarbodiimide
(DCC) and dimethylaminopyridine (DMAP) in dichloro-
methane, in a similar way to that described for (3). The
crude product was purified by flash chromatography using a
mixture of hexanes/ethyl acetate (9:1) as eluent. Yield: 69%. Rf:
0.54 (8:2 hexanes/ethyl acetate). 1H-RMN (300 MHz, CDCl3):
d 0.86 (m, 3 H), 1.26 (m, 8 H), 1.33 (d, J ~ 6.2 Hz, 3 H), 1.59
(m, 1 H), 1.71 (m, 1 H), 5.15 (m, 1 H), 7.27 (d, J ~ 8.7 Hz, 2 H),
8.02 (d, J ~ 8.4 Hz, 2 H), 8.12 (d, J ~ 8.7 Hz, 2 H), 8.35 (d, J ~
8.4 Hz, 2 H), 10.13 (s, 1 H). 13C-RMN (300 MHz, CDCl3): d
14.1, 20.1, 22.6, 25.4, 29.2, 31.8, 36.1, 72.1, 121.5, 129.0, 129.7,
130.9, 131.3, 134.1, 139.7, 154.1, 163.7, 165.3, 191.5. IR (Nujol)
n/cm21: 2856, 1746, 1712, 1260, 1199.
Experimental
Synthesis of (1R)-1-methylheptyl 4-benzyloxybenzoate (1)
To a solution of 15 mmol of (2R)-2-octanol in 150 mL of
distilled dichloromethane were added 15 mmol of 4-benzyloxy-
benzoic acid and 1.5 mmol of dimethylaminopyridine (DMAP)
under an argon atmosphere. The mixture was cooled in an ice/
water bath and, after 10 min, 15 mmol of dicyclohexylcarbodi-
imide (DCC) were added under an argon atmosphere. The
mixture was stirred overnight at room temperature, the salts
were filtered off and the solvent was evaporated. The crude
product was purified by flash chromatography using a mixture
of hexanes/ethyl acetate (7:1) as eluent. Yield: 68% of a yellow
Synthesis of 4-octyloxy-2-hydroxybenzaldehyde (5, X ~ OH)
A mixture of 14 mmol of 2,4-dihydroxybenzaldehyde, 14 mmol
of n-octyl bromide and 14 mmol of dry potassium bicarbonate
in 60 mL of dry acetone was refluxed for 90 h under an argon
atmosphere. The reaction advanced slowly and was checked by
TLC. The reaction was stopped when the TLC plate showed
that the diether compound began to appear. The mixture was
filtered through a pad of Celite1 to remove the inorganic salts
and the solvent was evaporated. The crude product was
purified by flash chromatography using a mixture of hexanes/
ethyl acetate (3:1) as eluent. Yield: 54% of an orange oil. Rf:
0.76 (8:2 hexanes/ethyl acetate). 1H-RMN (300 MHz, CDCl3):
d 0.88 (t, J ~ 6.2 Hz, 3 H), 1.2–1.5 (m, 10 H) 1.81 (t, J ~
6.6 Hz, 2 H), 6.38 (d, J ~ 2.2 Hz, 1 H) 6.5 (dd, J ~ 2.2 Hz, J ~
8.8 Hz, 1 H), 7.37 (d, J ~ 8.8 Hz, 1 H) 9.69 (s, 1 H). IR (Nujol)
n/cm21: 3037 (w), 1643, 1630, 1221.
1
oil. Rf: 0.72 (8:2 hexanes/ethyl acetate). H-RMN (300 MHz,
CDCl3): d 0.87 (t, J ~ 7.0 Hz, 3 H), 1.27 (m, 8 H), 1.31 (d, J ~
6.2 Hz, 3 H), 1.57 (m, 1 H), 1.69 (m, 1 H), 5.1 (m, 3 H), 6.98 (d,
J ~ 8.9 Hz, 2 H), 7.32–7.44 (m, 5 H), 7.99 (d, J ~ 8.9 Hz, 2 H).
13C-RMN (300 MHz, CDCl3): d 14.1, 20.1, 22.6, 25.4, 29.2,
31.7, 36.1, 70.1, 71.4, 113.4, 123.6, 127.5, 128.2, 128.7, 131.5,
136.4, 162.3, 166.0. IR (Nujol) n/cm21: 1708, 1276, 1251, 1167,
1105.
Synthesis of (1R)-1-methylheptyl 4-hydroxybenzoate (2)
To
a
mixture of 7.34 mmol of (1R)-1-methylheptyl
Synthesis of 4-octyloxybenzaldehyde (5, X ~ H)
4-benzyloxybenzoate (1), were added 30 mL of cyclohexene
and 60 mL of ethanol under an argon atmosphere. 0.5 g of
Pd(OH)2/C (20%) was then added in small portions. The
mixture was refluxed for 24 h. The mixture was filtered through
a pad of Celite1 and the solvent was evaporated. The crude
product was purified by flash chromatography using dichloro-
methane as eluent. Yield: 97% of a yellow oil. Rf: 0.43 (8:2
hexanes/ethyl acetate). 1H-RMN (300 MHz, CDCl3): d 0.85 (t,
J ~ 7.1 Hz, 3 H), 1.25 (m, 8 H), 1.30 (d, J ~ 6.2 Hz, 3 H), 1.59
(m, 1 H), 1.69 (m, 1 H), 5.1 (m, 1 H), 6.84 (d, J ~ 8.9 Hz, 2 H),
7.94 (d, J ~ 8.9 Hz, 2 H). 13C-RMN (300 MHz, CDCl3): d
14.0, 20.0, 22.5, 25.3, 29.1, 31.7, 36.0, 72.1, 115.3, 122.2, 131.9,
160.9, 167.3. IR (Nujol) n/cm21: 3351(w), 1709, 1678, 1284,
1231, 1166, 1115.
A mixture of 34 mmol of 4-hydroxybenzaldehyde, 34 mmol of
n-octyl bromide and 34 mmol of potassium carbonate in 30 mL
of dimethylformamide was heated at 80 uC under an argon
atmosphere for 8 h. The mixture was poured into 60 mL of
water and then the aqueous layer was extracted several times
with a mixture of hexanes/ethyl acetate (1:1), the combined
organic layers were extracted with 2 M sodium hydroxide,
washed with brine, water, dried over magnesium sulfate and
then the solvent was evaporated. The compound was purified
by flash cromatography using a mixture of hexanes/ethyl
acetate (4:1) as eluent. Yield: 48% of yellowish oil. Rf. 0.68 (8:2
hexanes/ethyl acetate). 1H-RMN (300 MHz, CDCl3): d 0.86 (t,
J ~ 6.9 Hz, 3 H), 1.26–1.46 (m, 10 H) 1.79 (m, 2 H), 4.01 (t,
1 1 2 4
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 1 1 7 – 1 1 2 7

View Article Online
J ~ 6.6 Hz, 2 H), 6.97 (d, J ~ 8.8 Hz, 2 H), 7.78 (d, J ~ 8.6 Hz,
1 H), 9.85 (s, 1 H). IR (Nujol): n/cm21: 2733, 1690, 1601, 1259,
1159, 1140.
Synthesis of N-{4’-[4@-[(1R)-1-methylheptyloxycarbonyl]-
phenoxycarbonyl]benzylidene}-4-octyloxyaniline, L2
The compound was synthetized from 4 and 8 using the same
synthetic method as described for compound L1. Yield: 63% of
a yellowish solid. 1H-RMN (300 MHz, CDCl3): d 0.86 (s, 6 H),
1.27–1.34 (m, 21 H), 1.46–1.53 (m, 1 H), 1.74–1.80 (m, 3 H),
3.97 (t, J ~ 6.9 Hz, 2 H), 5.11 (m, 1 H), 6.93 (d, J ~ 8.7 Hz,
2 H), 7.28 (m, 4 H), 8.02 (d, J ~ 8.1 Hz, 2 H), 8.12 (d, J ~
8.7 Hz, 2 H), 8.27 (d, J ~ 8.1 Hz, 2 H), 8.57 (s, 1 H). 13C-RMN
(300 MHz, CDCl3): d 14.1, 20.1, 22.6, 22.7, 25.4, 26.0, 29.1,
29.2, 29.4, 30.9, 31.7, 31.8, 36.1, 68.3, 72.0, 115.1, 121.6, 122.5,
128.5, 128.7, 130.6, 130.8, 131.7, 141.2, 143.8, 154.3, 156.2,
158.5,164.2, 165.4. IR (Nujol) n/cm21: 1733, 1716, 1255. Anal.
Calc. for C37H47NO5: C 75.86, H 8.09, N 2.39; Found: C 75.84,
H 8.14, N 2.43%. MS (FAB1) m/z: (M 1 1) 586, 472, 336
(100%).
Synthesis of 4-(1-methylheptyloxycarbonyl)phenyl
4-aminobenzoate (6)
To 1 mmol of 3 (obtained as described the previous steps) in
16 mL of a mixture cyclohexene/absolute ethanol (1:1), was
added 68 mg of Pd(OH)2/C in small portions under an argon
atmosphere. The suspension was refluxed for 90 min. The
mixture was cooled down, filtered through a pad of Celite1,
and the crude product was used in the next reaction without
further purification. The pure compound was obtained by
recrystallization from ethanol/water (3:1). Yield: 98% of a
white solid. Rf: 0.17 (8:2 hexanes/ethyl acetate). Mp: 77 uC.
1H-RMN (300 MHz, CDCl3): d 0.85 (t, J ~ 7.1 Hz, 3 H), 1.26
(m, 8 H), 1.32 (t, J ~ 6.2 Hz, 2 H), 1.59 (m, 1 H), 1.66 (m, 1 H),
4.16 (s, 2 H) 5.13 (m, 1 H), 6.67 (d, J ~ 8.8 Hz, 2 H), 7.24 (d,
J ~ 8.8 Hz, 2 H), 7.98 (d, J ~ 8.8 Hz, 2 H), 8.08 (d, J ~ 8.8 Hz,
2 H). 13C-RMN (300 MHz, CDCl3): d 14.1, 20.1, 22.6, 25.4,
29.1, 31.7, 36.1, 71.9, 113.8, 118.1, 121.8, 128.1, 131.0, 132.5,
151.8, 154.9, 164.7, 165.6. IR (Nujol) n/cm21: 3460, 3362, 3224,
1703, 1279, 1205, 1171, 1064.
Synthesis of 4-[(1R)-1-methylheptyloxycarbonyl]phenyl N-(4’-
octyloxy-2’-hydroxybenzylidene)-4-aminobenzoate, L3
A mixture of 1 mmol 4-octyloxy-2-hydroxybenzaldehyde (5,
X ~ OH) and 1 mmol of 4-(1-methylheptyloxycarbonyl)-
phenyl 4-aminobenzoate (6) and 5 drops of acetic acid in 10 mL
of absolute ethanol was refluxed for 4 h, cooled down and then
stirred at room temperature overnight. The solid was collected
and recrystallized from technical ethanol . Yield 45% of a
1
yellow solid. H-RMN (300 MHz, CDCl3): d 0.86 (m, 6 H),
Synthesis of 4-octyloxynitrobenzene (7)
1.23–1.45 (m, 21 H), 1.56–1.66 (m, 1 H), 1.66–1.84 (m, 3 H),
3.99 (t, J ~ 6.6 Hz, 2 H), 5.16 (m, 1 H), 6.50 (m, 2 H), 7.20–7.38
(m, 5 H), 8.1 (d, J ~ 8.7 Hz, 2 H), 8.22 (d, J ~ 8.4 Hz, 2 H),
8.55 (s, 1 H), 13.3 (s, 1 H). 13C-RMN (300 MHz, CDCl3): d
14.0, 20.0, 22.6, 25.4, 25.9, 29.00, 29.2, 29.3, 29.4, 29.6, 31.7,
36.0, 68.3, 71.9, 101.5, 108.1, 112.7, 121.2, 121.6, 126.5, 128.5,
131.1, 131.7, 134.0, 153.4, 154.4, 163.1, 164.1, 164.2, 164.3,
165.4. IR (Nujol) n/cm21: 3433 (w), 1728, 1714, 1627, 1272,
1210, 1195. Anal. Calc. for C37H47NO6: C 73.87, H 7.8, N 2.32;
Found: C 73.87, H 7.8, N 2.27%. MS (FAB1) m/z: (M 1 1)
602, 490, 352 (100%).
The compound was synthesized using the same synthetic
method as described for 4-octyloxybenzaldehyde (5), and was
used in the next step without further purification. Yield: 70%.
Rf: 0.75 (8:2 hexanes/ethyl acetate). 1H-RMN (300 MHz,
CDCl3): d 0.86 (m, 3 H), 1.27–1.55 (m, 10 H), 1.75–1.82 (m,
2 H), 4.02 (t, J ~ 6 Hz, 2 H), 6.91 (d, J ~ 9 Hz, 2 H), 8.16 (d,
J ~ 9 Hz, 2 H).
Synthesis of 4-octyloxyaniline (8)
The compound was synthesized using the same synthetic
method as that described for compound 6. The product was
used in the next step without further purification.
Preparation of the acetato-bridged complexes. General
procedure
1
The palladium complexes were prepared from the metal salt
palladium(II) acetate. The metal salt (236 mg, 1 mmol) was
added to a solution of the ligand (600 mg, 1 mmol) in acetic
acid (30 mL). The reaction mixture was stirred at 40 uC for 8 h
and then cooled. The precipitate was filtered off and dissolved
in dichloromethane. The resulting solution was filtered on
Celite1 and the complex was re-precipitated by addition of
acetone.
Yield: 98%. H-RMN (300 MHz, CDCl3): d 0.87 (m, 3 H),
1.22–1.41 (m, 8 H), 1.69–1.74 (m, 4 H), 3.12 (s, 2 H), 3.85 (t, J ~
9 Hz, 2 H), 6.61 (d, J ~ 9 Hz, 2 H), 6.72 (d, J ~ 9 Hz, 2 H). IR
(Nujol) n/cm21: 3408, 3315, 3221, 2952, 1631, 1511, 1233.
Synthesis of 4-[(1R)-1-methylheptyloxycarbonyl]phenyl
N-(4’-octyloxybenzylidene)-4-aminobenzoate, L1
Analytical data. L1–PdAc. Yield 30%. 1H-RMN (300 MHz,
CDCl3): d 0.85 (m, 12 H), 1.19–1.34 (m, 42 H), 1.58–1.75 (m,
8 H), 1.93 (s, 6 H), 3.48 (m, 2 H), 3.74 (m, 2 H), 5.15 (m, 2 H),
5.97 (d, J ~ 2.1, Hz, 2 H), 6.60 (dd, J ~ 2.1 Hz, J ~ 8.7 Hz,
2 H), 6.87 (d, J ~ 8.7 Hz, 2 H), 7.23 (d, J ~ 8.4 Hz, 4 H), 7.30
(d, J ~ 8.7 Hz, 4 H), 7.64 (s, 2 H), 7.93 (d, J ~ 8.4 Hz, 4 H),
8.11 (d, J ~ 8.7 Hz, 4 H). 13C-RMN (300 MHz, CDCl3): d
14.1, 20.1, 22.5, 22.6, 24.4, 25.4, 25.9, 29.1, 29.2, 29.3, 31.7,
31.8, 36.1, 68.0, 72.0, 111.7, 117.0, 121.5, 123.2, 127.0, 128.6,
129.9, 130.0, 130.1, 131.1, 137.8, 152.1, 154.3, 159.1, 160.7,
163.9, 165.4, 172.1, 180.4. IR (Nujol) n/cm21: 1727, 1586, 1573,
1531. Anal. Calc. for (C39H49NO7Pd)2: C 62.44, H 6.58, N 1.87;
Found: C 62.39, H 6.20, N 2.09%. MS (FAB1) m/z: (M) 1444,
788, 576, 472 (100%).
A mixture of 1 mmol of 4-octyloxybenzaldehyde (5, X ~
H) and
1 mmol of 4-(1-methylheptyloxycarbonyl)phenyl
4-aminobenzoate (6) and 5 drops of acetic acid in 20 mL of
absolute ethanol was stirred for 4 h at room temperature
under an argon atmosphere. The solid was collected and
recrystallized from technical ethanol . Yield: 60% of a white
solid. 1H-RMN (300 MHz, CDCl3): d 0.87 (m, 6 H), 1.28–1.33
(m, 21 H), 1.54–1.60 (m, 1 H), 1.70–1.82 (m, 3 H), 4.02 (t,
J ~ 6.3 Hz, 2 H), 5.15 (m, 1 H), 6.97 (d, J ~ 8.4 Hz, 2 H),
7.24 (d, J ~ 8.7 Hz, 2 H), 7.29 (d, J ~ 8.7 Hz, 2 H), 7.84 (d,
J ~ 8.4 Hz, 2 H), 8.11 (d, J ~ 8.7 Hz, 2 H), 8.20 (d, J ~
8.7 Hz, 2 H), 8.36 (s, 1 H). 13C-RMN (300 MHz, CDCl3): d
14.0, 14.1, 20.1, 22.5, 22.6, 25.4, 25.9, 29.1, 29.2, 29.3, 31.7,
31.8, 36.0, 68.3, 71.9, 114.8, 121.0, 121.7, 125.7, 128.5, 130.9,
131.1, 131.6, 154.5, 157.3, 161.2, 162.2, 162.4, 164.5, 165.5. IR
(Nujol) n/cm21: 1733, 1712, 1621, 1593, 1573, 1277. Anal. Calc.
for C37H47NO5: C 75.86, H 8.09, N 2.39; Found: C 75.82;
H 8.12; N 2.49%. MS (FAB1) m/z: (M 1 1) 586, 474, 360,
336 (100%).
1
L2–PdAc. Yield 28%. H-RMN (300 MHz, CDCl3): d 0.86
(m, 12 H), 1.28–1.34 (m, 42 H), 1.39–1.60 (M, 8 H), 1.96 (s,
6 H), 3.68 (t, J ~ 6 Hz, 4 H), 5.15 (m, 2 H), 6.60 (d, J ~ 9 Hz,
4 H), 6.71 (d, J ~ 9 Hz, 4 H), 7.31 (m, 8 H), 7.69 (s, 2 H), 7.85
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 1 1 7 – 1 1 2 7
1 1 2 5

View Article Online
(d, J ~ 9 Hz, 2 H), 8.10 (d, J ~ 9 Hz, 4 H). 13C-RMN
(300 MHz, CDCl3): d 14.0, 14.1, 20.1, 22.6, 22.7, 24.3, 25.4,
25.8, 29.1, 29.2, 29.3, 31.7, 31.8, 36.1, 68.2, 71.9, 113.6, 121.5,
123.9, 126.1, 126.6, 128.4, 129.0, 131.0, 133.2, 140.4, 149.9,
154.3, 154.4, 159.2, 164.1, 165.4, 170.0, 180.7. Anal. Calc. for
(C39H49NO7Pd)2: C 62.44, H 6.58, N 1.87; Found: C 62.50, H
6.17, N 2.05%. MS (FAB1) m/z: (M) 1444, 586, 472, 336
(100%).
167.1. IR (Nujol) n/cm21: 1727, 1713, 1266. Anal. Calc. for
(C37H46NO6Pd)2: C 67.9, H 7.0, N 2.15; Found: C 67.55, H
6.20, N 2.14%. MS (FAB1) m/z: (M) 1306, 602, 352 (100%).
Techniques
Infrared spectra for all the complexes were obtained by using a
Perkin-Elmer 1600 (FTIR) spectrophotometer in the 400–
4000 cm21 spectral range. NMR spectra were recorded on a
Bruker ARX 300 spectrometer in CDCl3 solutions. Microanalysis
was performed with a Perkin-Elmer 240 B microanalyser.
The textures of the mesophases were studied using an optical
microscope (Olympus) with crossed polarisers and connected
to a Linkam THMS 600 hot stage and a Linkam TMS 91
central processor. Microphotographs were taken with a DP12
Olympus camera, adapted to the microscope. Measurements of
the transition temperatures were made using a TA2910
differential scanning calorimeter with a heating or cooling
rate of 10 uC min21. The apparatus was calibrated with indium
(156.6 uC, 28.44 J g21).
The complex permittivity was measured over 11 decades of
frequency (1022 to 109 Hz) using three different measuring
systems: a Schulmberger 1260 frequency response analyser
fitted with a high-impedance preamplifier of a variable gain
(1022 to 106 Hz), and two impedance analysers, the HP 4191A
(102 to 107 Hz) Hz and the HP 4192A (106–109 Hz).
The spontaneous polarisation was measured using the tri-
angular wave method. In the experimental set-up the triangular
wave voltage was supplied by a HP3245A Function Generator.
The current–voltage cycles were recorded by a digital acquisi-
tion system, tech ADC488/16A. All equipment was interfaced
to a computer.
Preparation of the chloro-bridged complexes. General procedure
The complexes with chloro bridges were prepared from the
corresponding acetate-bridged derivatives. A 0.61 N solution
of hydrochloric acid in methanol (0.17 mmol) was added to a
solution of the acetato-bridged complex (0.084 mmol) in
dichloromethane (4 mL). The reaction mixture was stirred at
room temperature for 1 h. The solvent was removed under
reduced pressure and the crude product was purified by flash
chromatography on silica gel eluting with dichloromethane.
The product was re-precipitated by adding acetone to a
concentrated solution of the product in dichloromethane.
Analytical data. L1–PdCl. Yield 60%. 1H-RMN (300 MHz,
CDCl3): d 0.85 (m, 12 H), 1.19–1.34 (m, 42 H), 1.53–1.72 (m,
8 H), 3.93–3.98 (m, 4 H), 5.12–5.16 (m, 2 H), 6.59 (d, J ~
7.5 Hz, 2 H), 6.78 (d, J ~ 2.1 Hz, 2 H), 7.25 (d, J ~ 8.4 Hz, 4
H), 7.38 (d, J ~ 8.4 Hz, 4 H), 7.5 (dd, J ~ 2.1 Hz, J ~ 7.5 Hz,
4 H), 7.90 (s, 2 H), 8.12 (d, J ~ 8.4 Hz, 4 H), 8.24 (d, J ~
7.5 Hz, 4 H). 13C-RMN (300 MHz, CDCl3): d 14.1, 20.1, 22.6,
25.4, 25.9, 29.0, 29.2, 29.3, 31.7, 31.8, 36.1, 68.3, 71.9, 111.5,
119.6, 121.6, 123.6, 128.0, 128.6, 130.7, 131.1, 138.3, 153.0,
154.4, 156.7, 160.8, 163.9, 165.4, 173.9. IR (Nujol) n/cm21
:
1733, 1712, 1621, 1593, 1573, 1277. Anal. Calc. for
(C37H46NO5PdCl)2: C 61.16, H 6.38, N 1.93; Found: C
61.26, H 6.20, N 2.09%. MS (FAB1) m/z: 586, 474, 360, 336
(100%).
Acknowledgements
This work was supported by the C.I.C.Y.T. (MAT 2000-1293-
CO2).
1
L2–PdCl. Yield 48%. H-RMN (300 MHz, CDCl3): d 0.87
(m, 12 H), 1.23–1.34 (m, 42 H), 1.55–1.70 (m, 8 H), 3.81 (t, J ~
5.7 Hz, 4 H), 5.13 (m, 2 H), 6.85 (d, J ~ 8.1 Hz, 4 H), 7.24–7.27
(m, 8 H), 7.34 (d, J ~ 7.5 Hz, 2 H), 7.39 (d, J ~ 8.1 Hz, 2 H),
7.87 (d, J ~ 7.5 Hz, 2 H), 7.99 (s, 2 H), 8.09 (d, J ~ 8.1 Hz,
4 H). 13C-RMN (300 MHz, CDCl3): d 14.0, 14.1, 20.1, 22.5,
22.6, 25.4, 26.0, 29.1, 29.2, 29.3, 31.7, 31.8, 36.1, 38.1, 68.3,
71.9, 114.5, 121.6, 124.4, 127.0, 127.5, 128.5, 129.3, 131.1,
134.3, 141.2, 150.7, 152.9, 154.5, 157.5, 159.5, 164.0, 165.4,
172.3. IR (Nujol) n/cm21: 1739, 1716, 1268. Anal. Calc. for
(C37H46NO5PdCl)2: C 61.16, H 6.38, N 1.93; Found: C 61.05,
H 6.28, N 1.99%. MS (FAB1) m/z: (M 2 Cl) 1417, 586, 472,
336 (100%).
References
1
K. Miyachi and A. Fukuda, in Handbook of Liquid Crystals,
D. Demus, J. W. Goodby, G. W. Gray, H.-W. Spiess and V. Vill,
ed., Wiley-VCH, Weinheim, 1998, vol. 2B, pp. 665–691;
S. T. Lagerwall, Ferroelectric and Antiferroelectric Liquid Crystals,
Wiley-VCH, Weinheim, 1999.
2
3
A. D. L. Chandani, E. Gorecka, Y. Ouchi, H. Takezoe and
A. Fukuda, Jpn. J. Appl. Phys., 1989, 29, L1265–L1268.
Y. Suzuki, O. Nonaka, Y. Koide, N. Okabe, T. Hagiwara,
I. Kawamura, N. Yamamoto, Y. Yamada and T. Kitazume,
Ferroelectrics, 1993, 147, 109–119.
4
(a) K. Hori and K. Endo, Bull. Chem. Soc. Jpn., 1993, 66, 46–50;
(b) H. Hori, Y. Yamahara and K. Ito, Ferroelectrics, 1993, 147,
91–94; (c) K. Okuyama, N. Kawamano, S. Uehori, K. Noguchi,
N. Okabe, Y. Suzuki and I. Kawamura, Mol. Cryst. Liq. Cryst.,
1996, 276, 193–201; (d) K. Hori and S. Kawamura, Liq. Cryst.,
1996, 20, 311–319; (e) H. Allouchi, H.-T. Nguyen and M. Cotrait,
Mol. Cryst. Liq. Cryst., 1999, 328, 375–382.
Preparation of L3–Pd
To a solution of 500 mg (0.83 mmol) of the imine ligand, L3, in
40 mL of absolute ethanol, a suspension of 93 mg (0.41 mmol)
of palladium(II) acetate in ethanol was added dropwise. The
reaction mixture was refluxed for 2 h, and then stirred at
room temperature for 8 h. The precipitate was filtered off
and dissolved in dichloromethane. The resulting solution was
filtered on Celite1 and the complex was precipitated by pour-
ing the solution into cold ethanol. Yield 62%.
1H-RMN (300 MHz, CDCl3): d 0.84 (m, 12 H), 1.22–1.34 (m,
42 H), 1.55–1.70 (m, 8 H), 3.77 (t, J ~ 6.6 Hz, 4 H), 5.15 (m,
2 H), 5.52 (d, J ~ 2.1 Hz, 2 H), 6.18 (dd, J ~ 9 Hz, J ~ 2.1 Hz,
2 H), 7.06 (d, J ~ 9 Hz, 2 H), 7.29 (d, J ~ 8.7 Hz, 4 H), 7.47 (d,
J ~ 8.7 Hz, 4 H), 7.58 (s, 2 H), 8.12 (d, J ~ 8.7 Hz, 4 H), 8.25
(d, J ~ 8.7 Hz, 4 H). 13C-RMN (300 MHz, CDCl3): d 14.0,
20.1, 22.5, 22.6, 25.4, 25.9, 28.9, 29.1, 29.3, 31.7, 31.8, 36.1,
38.1, 67.8, 71.9, 102.1, 107.3, 114.5, 121.6, 125.4, 127.0, 128.5,
130.4, 131.1, 135.8, 154.4, 154.5, 161.0, 164.2, 165.4, 165.7,
5
M. Marcos, J. L. Serrano, T. Sierra and M. J. Gime´nez, Angew.
Chem., Int. Ed. Engl., 1992, 31, 1471–1472; M. Marcos,
J. L. Serrano, T. Sierra and M. J. Gime´nez, Chem. Mater.,
1993, 5, 1332–1337; M. J. Baena, J. Barbera´, P. Espinet,
A. Ezcurra, M. B. Ros and J. L. Serrano, J. Am. Chem. Soc.,
1994, 116, 1065; R. Iglesias, M. Marcos, J. L. Serrano, T. Sierra
and M. A. Pe´rez-Jubindo, Chem. Mater., 1996, 8, 2611–2617; For
studies concerning achiral Schiff base complexes, see: J. L. Serrano
and T. Sierra, in Metallomesogens. Synthesis, Properties and
Applications, Wiley-VCH, Weinheim, 1996, ch. 3,.
6
7
G. Heppke, P. Kleineberg and D. Lo¨tzsch, Liq. Cryst., 1993, 14,
67–71.
P. Espinet, E. Lalinde, M. Marcos, J. Pe´rez and J. L. Serrano,
Organometallics, 1990, 9, 555–560; J. Barbera´, P. Espinet,
E. Lalinde, M. Marcos and J. L. Serrano, Liq. Cryst., 1987, 2,
833–842; M. Lehmann, M. Marcos, J. L. Serrano, T. Sierra,
C. Bolm, K. Weickhardt, A. Magnus and G. Moll, Chem. Mater.,
2001, 13, 4374–4381.
1 1 2 6
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 1 1 7 – 1 1 2 7

View Article Online
8
9
J. Barbera´, E. Mele´ndez, J. L. Serrano, T. Sierra, A. Ezcurra and
M. A. Pe´rez-Jubindo, Mol. Cryst. Liq. Cryst., 1989, 170, 151–
157; T. Sierra, E. Mele´ndez, J. L. Serrano, A. Ezcurra and
M. A. Pe´rez-Jubindo, Chem. Mater., 1991, 3, 157–163.
J. W. Goodby, J. S. Patel and E. Chin, J. Mater. Chem., 1992, 2,
197–207.
F. Gießeslmann, Liq. Cryst., 2003, 30, 399–414; J. P. F. Lagerwall,
D. D. Parghi, D. Kru¨erke, F. Gouda and P. Ja¨gemalm, Liq. Cryst.,
2002, 29, 163–178.
13 D. R. Medeiros, M. A. Hale, J. K. Leitko and C. G. Willson,
Chem. Mater., 1998, 10, 1805–1813; M. A. Hale, D. R. Medeiros,
K. D. Dombrowski and C. G. Willson, Chem. Mater., 1999, 11,
2515–2519; I. Nishiyama, J. Yamamoto, J. W. Goodby and
H. Yokoyama, Liq. Cryst., 2002, 29, 1409–1423; Y.-I. Suzuki,
T. Isozaki, S. Hashimoto, T. Kusumoto, T. Hiyama, Y. Takanishi,
H. Takezoe and A. Fukuda, J. Mater. Chem., 1996, 6, 753–760.
14 C. V. Yelemaggad, S. A. Nagamani, G. G. Nair, D. S. S. Rao,
K. Prasad and A. Jakli, Liq. Cryst., 2002, 29, 1181–1185.
10 M. A. Pe´rz-Jubindo, M. J. Tello and J. Ferna´ndez, J. Phys. D,
1981, 14, 2305–2308.
11 S. Merino, M. R. de la Fuente, Y. Gonza´lez, M. A. Pe´rez Jubindo,
B. Ros and J. A. Pue´rtolas, Phys. Rev. E, 1996, 54, 5169–5177;
M. C. Artal, B. Ros, J. L. Serrano, M. R. de la Fuente and
M. A. Pe´rez Jubindo, Chem. Mater., 2001, 13, 2056–2067.
12 J. P. F. Lagerwall, P. Rudquist, S. T. Lagerwall and
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 1 1 7 – 1 1 2 7
1 1 2 7