Effect of hydrogen-bonded supramolecular assembling on liquid crystal properties of imidazole-containing azomethines and their chelates with copper(II)

Article abstract of DOI:10.1080/10610270802709386

A series of imidazole-containing rod-like Schiff's bases and their ionic copper(II) chelates with various lengths of the terminal alkyl chain containing 6, 8, 10, 12, 14 and 16 carbon atoms have been synthesised. The synthesised compounds were characterised by elemental analyses, ¹H NMR, IR and UV-vis and mass spectroscopies. Thermotropic smectic C mesophases in the ligands and smectic A mesophases in the copper(II) complexes were identified using POM, DSC and small-angle XRD scattering methods. X-ray diffraction patterns of the prepared imidazole imines indicate to supramolecular self-assembled structures in the liquid crystal state, which are formed by means of intermolecular hydrogen bonds. It was established that both liquid crystal arrangement and supramolecular assemblies in ligands disappeared near 190°C, mainly regardless of the lengths of the terminal alkyl chains. Contrary, assembling of the copper(II) complexes into supramolecular bilayers occurs near 200°C, which causes their transition to a smectic A mesophase.

Full text of DOI:10.1080/10610270802709386

Supramolecular Chemistry
Vol. 22, No. 1, January 2010, 1–12
Effect of hydrogen-bonded supramolecular assembling on liquid crystal properties
of imidazole-containing azomethines and their chelates with copper(II)
Oleg N. Kadkin*, Jigeon Tae, Eun Ho Kim, So Yeon Kim and Moon-Gun Choi*
Department of Chemistry and Center for Bioactive Molecular Hybrids, BK21, Yonsei University, 262 Seongsanno,
Seodaemun-Gu, Seoul 120-749, Korea
(Received 24 September 2008; final version received 5 December 2008)
A series of imidazole-containing rod-like Schiff’s bases and their ionic copper(II) chelates with various lengths of the
terminal alkyl chain containing 6, 8, 10, 12, 14 and 16 carbon atoms have been synthesised. The synthesised compounds
1
were characterised by elemental analyses, H NMR, IR and UV–vis and mass spectroscopies. Thermotropic smectic C
mesophases in the ligands and smectic A mesophases in the copper(II) complexes were identified using POM, DSC and
small-angle XRD scattering methods. X-ray diffraction patterns of the prepared imidazole imines indicate to supramolecular
self-assembled structures in the liquid crystal state, which are formed by means of intermolecular hydrogen bonds. It was
established that both liquid crystal arrangement and supramolecular assemblies in ligands disappeared near 1908C, mainly
regardless of the lengths of the terminal alkyl chains. Contrary, assembling of the copper(II) complexes into supramolecular
bilayers occurs near 2008C, which causes their transition to a smectic A mesophase.
Keywords: imidazole; liquid crystal; metallomesogen; Schiff’s base; hydrogen bond; supramolecular assembling
Introduction
electric and magnetic properties, and also the crafting of
nanostructured materials, have been constructed using the
ability of these types of heterocycles to coordinate transition
metals (10). Herein, we are reporting some new examples of
the neutral molecular compounds from the class of Schiff’s
bases containing the 1H-imidazole fragment. In addition,
prospectives of imidazole derivatives for obtaining ionic
metallomesogen systems on their basis will be shown
through the examples of the copper(II) chelates.
The heterocyclic systems of the class of imidazoles play a
significant role as building blocks in biochemical systems
such as alkaloids, histidine and histamine (1). Biological
activity of imidazole derivatives is the main motive for
their wide use in medicine, agriculture and pharmaceutical
industry (2). Moreover, they also have a great potential in
the area of optical and chemical sensors (3), fuel cell
membranes (4), luminescent materials (5), ion-conducting
electrolytes (6) and photovoltaic materials for solar cell
applications (7). Even few of these instances are enough
characterising imidazole as a fascinating chemical specie.
As for known mesogenic imidazole derivatives, most of
them belong to the class of ionic liquids, which are
attracting increasing attention in many fields, including
organic chemistry, electrochemistry and catalysis (8).
Molecular imidazoles with mesogenic behaviour are less
investigated, with the exception of several works that are
mostly connected with using the imidazole moiety for
creating supramolecular assemblies (9). Amphoteric
character of the imidazole ring normally causes associ-
ation of molecular imidazole compounds into agglomer-
ates through intermolecular hydrogen bonds. Thus,
interrelation between supramolecular organisation and
liquid crystal properties in mesogenic imidazoles is rather
interesting aspect for investigation. Besides the above-
mentioned remarkable objects, metallomesogen systems,
which are interesting from the standpoint of their optical,
Results and discussion
Syntheses and characterisation
Synthetic routes towards imidazole-containig Schiff’s
bases and their copper(II) complexes are illustrated in
Scheme 1. Reduction in nitrocompounds 1 (11) was
carried out by catalytic hydrogenation on Pd/C (10%).
The used method is the most preferable over all others
in view of the fact that resulting anilines 2 trends
towards forming coffee-coloured oxidation products
during isolation and recrystallisation procedures. Clean
and facile reduction with hydrogen allows to avoid
excessive procedural operations with the reaction
products, and to isolate easily pure amines 2.
Condensation of the obtained anilines 2 with 4(5)-
imidazolyl carbaldehyde afforded target Schiff’s bases 3
with the number of carbon atoms in the terminal alkyl
chain between 6 and 16. Combining ethanol solutions
*Corresponding authors. Email: onk@yonsei.ac.kr; choim@yonsei.ac.kr
ISSN 1061-0278 print/ISSN 1029-0478 online
q 2010 Taylor & Francis
DOI: 10.1080/10610270802709386
http://www.informaworld.com

2
O.N. Kadkin et al.
Scheme 1. Syntheses of the imidazole-containing Schiff’s bases 3 and their copper(II) complexes 4.
bonds near 1730 cm21 and CvN bonds at 1630 cm21
.
of the azomethines
3
and CuCl2·2H2O leads to
precipitation of complexes 4. It should be noted that
N–H proton of an imidazole ring easily migrates
between two nitrogen atoms, so there is always a
tautomeric equilibrium existing between the two
positional isomers.
UV–vis spectra of compounds 3 are represented by two
intensive absorption bands with maxima at about 275 and
315 nm, respectively. The first band was assigned to the
p–p electronic transitions of the imidazole ring, which is
*
red shifted due to the conjugation with the CHvN group.
The second band is seemingly associated with the
azomethine chromophore.
Elemental analyses of the complexes 4 indicate that
they contain two molecules of water in the hydrate sphere.
It seems that not only the copper(II) and chloride ions but
also the imidazole group strongly holds water molecules.
The CvN bond stretching vibrations of the ligand in 4 are
shifted bathochromically by 20 cm21 in comparison with
the uncomplexed Schiff’s bases 3. Further changes in the
positions of the IR absorption bands in the region of
1000–1300 cm21 and the appearance of new metal–
ligand vibration modes near 550 and 610 cm21 were
observed upon the complex formation. Electronic spectra
of the complexes 4 consist of two strong absorption
maxima at about 270 and 340 nm, and one intensive
1
The synthesised anilines 2 gave satisfactory H NMR
spectra. Two vibration bands near 3450 and 3350 cm21
,
which are typically characterising secondary amines and
associated with valence vibrations of the N–H bonds, were
observed in the IR spectra of the series of 2. Also, the
valence stretching of the CvO bonds of the ester links can
be straightforwardly identified at about 1720 cm21
.
New imidazole-containing Schiff’s bases 3 were
unambiguously identified by the combination of elemental
analyses, 1H NMR, IR, UV–vis and mass spectroscopical
methods. Proton signals of the imidazole ring and
1
shoulder near 320 nm. It can be concluded that the p–p
azomethine group are present in the H NMR spectra of
*
electronic transitions in the ligands at 320 nm are
supplemented with metal-to-ligand charge-transfer
absorptions at 340 nm in a series of 4. Weak absorptions
near 450 and 620 nm in the complexes were assigned to d–
d transitions in the copper(II) ions. The arrangement of the
first and second coordination spheres and geometrical
configuration of the copper(II) complexes 4 are disputable;
however, we propose octahedral surrounding with the
3 as singlets in the area of 7.5–8.5 ppm. Slight broadening
of the signals of the imidazole fragment was observed,
which allowed to allocate the azomethine proton at
7.77 ppm distinguishing it from the imidazole signals.
Apparently, signal spreading in the imidazole ring is
connected with a tautomeric equilibrium due to the high
mobility of the N–H protons. FT-IR spectra of 3 display
the characteristic valence vibrational bands of the CvO

Supramolecular Chemistry
Table 1. Types of phase transitions, temperatures and the
corresponding enthalpies from DSC thermograms for compounds
3
3 and 4.
n
Compound
Transition
T (8C)
DH (kJ mol21
)
6
3
cryst1–cryst2
cryst2–iso
iso–SmCa
115.5
195
[122]
1.2
44.4
[22.0]
8
3
3
3
cryst1–cryst2
cryst2–SmC
SmC–iso
151
184
191
3.2
32.8
3.0
10
12
cryst1–cryst2
cryst2–SmC
SmC–iso
131.5
175
189
5.35
17.9
5.6
cryst1–cryst2
cryst2–cryst3
cryst3–SmC
SmC–iso
65
3.9
12.9
20.4
7.8
127
173
196
14
3
cryst1–cryst2
cryst2–cryst3
cryst3–SmC
SmC–iso
72
3.6
15.8
17.4
8.6
130
170
196
16
6
3
4
4
cryst1–cryst2
cryst2–SmC
SmC–iso
131
167
190
20.0
17.2
8.7
cryst1–cryst2
cryst2–cryst3
cryst3–SmAb
184
200
205
5.5
33.6
20.8
8
cryst1–cryst2
cryst2–SmA
295
204
34.0
20.1
10
12
14
4
4
4
cryst–SmA
cryst–SmA
198
206
39.6
35.4
Figure 1. Optical textures observed under a polarisation
microscope: a marbled schlieren texture of smectic C of 3
(n ¼ 14) (upper microphotograph, on cooling from the isotropic
liquidstateat1858C,20£),andapolygonaltextureofsmecticAin4
(n ¼ 12) (lower microphotograph, on heating at 2108C, 50£).
cryst1–cryst2
cryst2–cryst3
cryst3–cryst4
cryst4–SmA
75
7.1
31.8
35.3
16.5
133
172
199
16
4
cryst1–cryst2
cryst2–cryst3
cryst3–cryst4
cryst4–cryst5
cryst5–SmA
101
138
142
157
204
9.6
6.3
1.1
4.1
optical microscopy (POM) and differential scanning
calorimetry (DSC). In addition, several compounds, i.e. 3
(n ¼ 12,14)and4(n ¼ 12,14),werestudiedusingthesmall-
angle X-ray diffractionmethodatvarioustemperatures. Data
of the POM and DSC examinations are given in Table 1.
All compounds in the series 3 exhibited enantiotropic
smectic C mesophases with the exception of 3 (n ¼ 6),
which displayed monotropic smectic C mesomorphism.
The compounds 3 have strong tendency towards vitrifica-
tion upon cooling from the isotropic liquid state; hence,
thermodynamics of the phase transitions on the second
heating cycles was not investigated. Characterisitic POM
textures observed in 3 on cooling from an isotropic liquid
state are shown in Figure 1. A representative marbled
schlieren texture given in the microphotograph is observed
in all the compounds 3, hence identifying a smectic C
mesophase. The enthalpy values of liquid crystal-to-
isotropic liquid transitions, which lie in a range between
3.0 and 9.0 kJ mol21 depending on the length of the
terminal alkyl chain, are also in a good agreement with this
mesophase assignment.
26.4
a Monotropic phase transition detected by POM at 1608C.
b The liquid crystal-to-isotropic liquid transitions for 4 were not detected
as they lie higher than 2908C according to POM.
imidazole ligands in the equatorial edges and two chlorine
ions in the two opposite vertexes. The last suggestion and
some other structural features of the synthesised
compounds will be interpreted lower in a close connection
with their liquid crystallinity, XRD scattering data and
supramolecular organisation by means of intermolecular
hydrogen bonds.
Liquid crystal properties and supramolecular
organisation
Thermal behaviour of both series of the ligands 3 and
complexes 4 were investigated by a thermal polarisation

4
O.N. Kadkin et al.
Table 2. Crystal structure data of 3 and 4 obtained from XRD powder measurements at 258C.
Cell parameters
Molecular model dimensionsa
XRD peak
intensity (a.u.)
Plains,
Miller index
d-Spacing
˚
(A)
˚
a (A)
˚
b (A)
˚
c (A)
˚
Length (A)
˚
Width (A)
˚
Thickness (A)
Compound
a (8)
3 (n ¼ 12)
0.03
0.11
0.13
0.02
0.02
0.02
100
010
011
111
001
101
31.8
4.76
4.59
4.36
3.78
3.52
31.8
34.8
34.5
5.94
5.89
4.72
4.71
6.84
126.8
32.5
34.9
34.8
5.0
5.0
9.5
3.5
3.5
6.0
3 (n ¼ 14)
4 (n ¼ 12)
0.18
0.06
0.12
0.05
0.08
0.02
100
010
011
110
001
101
Ab
100
200
010
34.8
4.73
4.57
4.00
3.78
3.21
126.6
115.2
0.40
0.35
, 0.01
, 0.01
0.02
66.0
34.5
17.2
11.3
6.19
4.67
3.64
12.45
001
011
0 (21)1
0.02
0.02
4 (n ¼ 14)
0.67
0.10
, 0.01
, 0.01
0.07
0.07
0.07
0.07
A
71.2
37.4
18.7
11.3
6.24
4.69
4.23
3.64
37.4
12.36
6.83
114.0
37.3
9.5
6.0
100
200
010
001
011
111
0 (21)1
a Molecular modelling was performed using a standard computer program Hyperchem-7.1 (Hypercube, Inc., Gainesville, Florida, USA); a size of the
minimal box suited to a single molecule is given.
b Compound 4 at 258C is mainly a bilayered solid partially containing monolayered microcrystalline inclusions.
Besides, additional peaks assigned to crystal-to-crystal
polymorphic transitions appeared in the DSC curves of 3.
The magnitudes of some DSC peaks of this type are not
typical to a crystal-to-crystal phase transition (Table 1).
Rather large enthalpy values indicate that they are
associated with more intense transformations in the crystal
structure. The latter statement is supported by XRD
measurements as it will be discussed in lower paragraphs.
A polygonal texture of smectic A is detected in all the
complexes 4 (Figure 1). Only crystal-to-smectic A phase
transition is given for 4 as their isotropisation points were
not observable because of thermal degradation of the
samples after heating over 270–2908C. A birefringent
texture of 4 remains at least up to these temperatures
indicating a continued existence of the smectic A
mesophase. Complexes 4 do not crystallise upon cooling
from a smectic A mesophase preserving the liquid crystal
arrangement in a solid glass state at room temperature.
That was evidently distinguished by all POM, DSC and
XRD investigations.
terminal alkyl chain. Such behaviour is typical for a
homologous series of liquid crystals in a temperature
region higher than 1008C. But it is rather unusual and
intriguing that the comparatively same level of the clearing
points were observed for all members of the series 3. The
same kind of close proximity of the phase transition
temperatures, but in this case for a crystal-to-liquid crystal
transitions, was also observed in a series of the copper(II)
complexes 4. In order to explain this phenomenon, we
assumed a close relationship between the supramolecular
organisation of 3 and 4 involving intermolecular hydrogen
bonds and their liquid crystal properties.
In case of 3, disengaging of hydrogen bonds occur
roughly at the same temperatures, so parallel phase
transformations in this connection do not depend on the
lengths of the terminal alkyl chains. The ionic compound 4
has even more numerous possibilities for the supramole-
cular association not only connected with hydrogen bonds
but also supplemented by ionic electrostatic interactions
and coordination bonds. Supramolecular assembling in
this case plays the same important role in liquid crystal
ordering as traditional anisotropic interactions. Therefore,
the formation of smectic layers in 4 involves primarily the
Generally, the melting points in a series of 3, or
otherwise transition temperatures from a crystal-to-liquid
crystal phase, are decreased with the lengthening of the

Supramolecular Chemistry
5
Figure 2. Molecular model and crystal packing of 3 (n ¼ 14).
above-mentioned intermolecular interactions, and less
depends on alterations in the anisotropy of polarisability
for different lengths of the terminal alkyl chain. As a
consequence, the mesophase transition temperatures
remain almost the same for all members of a homologous
series of 4. Small-angle XRD scattering data at different
temperatures allow to expose in some extent what kind of
structural changes may occur during the phase transitions
of 3 and 4.
A monoclinic crystal system of the P2/m space group
with the cell parameters represented in Table 2 was
determined from the analysis of XRD scattering data of 3
(n 5 12 and 14). The specified cell dimensions are in very
good agreement with the corresponding computed models
of a single molecule of 3 (Figure 2). We suppose that
basically head-to-tail orientation of molecules by their
elongated axes is realised in the long-range translational
order of 3 at room temperature. This hypothesis is
Figure 3. Molecular model and crystal packing of 4 (n ¼ 14) and packing in bilayers.

6
O.N. Kadkin et al.
Figure 4. Development of crystal polymorphic modifications, smectic C and isotropic liquid phases of 3 (n ¼ 14) on heating.
supported indirectly by the absence of the bilayers with the
XRD peak corresponding to two-fold molecular length.
Molecular models of the complex 4 were built up
presuming an octahedral coordination of copper(II) ion
with the cis-orientation of the azomethine ligands and
chlorine atoms positioned in two opposite vertexes. Plane-
to-plane interactions of aromatic rings seem to be
favourable for the proposed cis-alignment of ligands.
Two hydrate molecules are placed instantly to the
hydrophilic imidazole rings. A unit cell of the crystals of
4 conforms perfectly to this model by length in case of
head-to-tail molecular orientation (Figure 3). The
corresponding peak with a d-spacing equal to one
molecular length is revealed in the XRD patterns of 4
(Table 2). But there is another more intensive XRD peak in
a small-angle region with the layer distance almost twice
exceeding the length of a molecule of 4. An appropriate
computed model of the bilayered structure illustrated in
Figure 3 is rigorously matching by size to an interlayer
distance found from the X-ray diffraction. Low intensity of
XRD peaks in a medium angle region expose the absence
of the strong long translational order within the bilayers.
Thus, by all appearances, the copper(II) complexes 4 at
room temperature mainly consist of bilayered solid with
the close to amorphous structure and some monolayered
crystalline matter.
Subsequent metamorphoses in the XRD patterns of 3
(n ¼ 14) during thermal phase transitions are illustrated in
Figure 4. A peak in a small-angle region associated with
the packing into layers with large periodicity appears in all
crystal modifications and smectic C mesophase. No XRD
peaks were observed in an isotropic liquid state. A group
of XRD peaks in the area of d-spacings connected with
positional ordering in the layers is presented only in crystal
phases and transforms to a diffuse broad reflection in a
smectic C mesophase. A significant decrease in intensity
and sharpness of these peaks in a crystal state, which is
preceding to a mesophase indicates to significant changes
in the arrangement of the cell units, and is well correlated
with the DSC data.
Table 3. Variation in interlayer spacing upon phase transitions
in 3 and 4.
Temperature
(8C)
Interlayer spacing
˚
(A)
Compound
Phase state
3 (n ¼ 12)
25
100
150
185
crystal1
crystal2
crystal3
smectic C
32.5
33.2
37.4
49.9
3 (n ¼ 14)
25
100
150
185
crystal1
crystal2
crystal3
smectic C
34.8
35.6
39.3
51.6
4 (n ¼ 12)
4 (n ¼ 14)
25
220
crystal
smectic A
66.0a
55.4
Profound changes in a d-spacing of the long
periodicity were observed in 3 during evolution from a
crystal-to-liquid crystal phase (Table 3). Positively, a huge
increase in the interlayer distance in a smectic C
mesophase in comparison with the prior values for a
crystal state can be explained by segregation of
amphiphilic molecules of 3 and the formation of bilayer
25
90
150
175
205
crystal1
crystal2
crystal3
crystal4
smectic A
71.2
71.2
71.2
68.0
59.8
a Space distance in the bilayered structure.

Supramolecular Chemistry
7
Figure 5. A computer model of the hydrogen-bonded supramolecular assembling in 3 (n ¼ 12).
structures. Hydrogen-bonded chains provide additional
stability to this kind of smectic bilayers (Figure 5).
˚
A calculated width of the supramolecular chains of 3 (60 A
tilted structure of the latter by an angle 50–558. Hence, the
XRD data confirm additionally a smectic C mesophase
assigned earlier by the POM and DSC investigations.
A solid state of the complexes 4 has more amorphous
character than in the ligands 3. As it was postulated before,
˚
for n ¼ 12 and 65 A for n ¼ 14) exceeds an experimental
d-spacing of the smectic layer (Table 3) that indicates to
Figure 6. Development of crystal polymorphic modifications and smectic A mesophase of 4 (n ¼ 14) on heating.

8
O.N. Kadkin et al.
Figure 7. Interpenetrated double layer structure of 4 (n ¼ 14).
there are bilayered structures present in 4 with head-to-
head orientation of molecules. Gradual changes in XRD
patterns during thermal development of a smectic A
mesophase are shown in Figure 6. Small signals in a
medium-angle region disappear completely in a smectic A
state, but a small-angle peak associated with layers
remains there. The most drastic changes occur in this time
in the d-spacings of bilayers upon transition to a smectic
mesophase (Table 3). A considerable decrease in the
interlayer distance cannot be explained in a case of smectic
A mesophase by a tilted structure of the layers. Only
considering interpenetrating double layers, the calculated
distance becomes close to the experimental d-spacing
(Figure 7). A number of possibilities for electrostatic ionic
and coordination interactions beside hydrogen bonds
increase the stability of the interdigitated bilayered
superstructure of 4 over 2008C contrary to hydrogen-
bonded associates of 3. Apparently, complexes 4 in a
liquid crystal state can be classified to a certain extent as
metallopolymer networks taking into account the excep-
tional thermal stability of the observed smectic A
mesophases exceeding 2908C. Besides, a re-coordination
of the copper(II) ions with the nitrogen donors from
neighbouring molecules must be considered at the
temperatures higher than 2008C, which facilitates cross-
linking of the complexes 4.
Experimental part
General details
Reagent grade chemicals and solvents were purchased from
Aldrich (Yongin, Kyounggi-Do, Korea, Korea Branch),
TCI (Tokyo, Japan) and Fluka (Yongin, Kyounggi-Do,
Korea, Korea Branch). Solvents were dried and freshly
distilled just before use. Melting points were determined by
capillary method in a Stuart Scientific apparatus SMP3.
Bu¨chi Rotavapor R-124 was used to evaporate solvents
1
from the reaction mixtures. The H NMR spectra were
measured on a Bruker AM 400 with TMS as internal
standard. FT-IR spectra were performed on Nicolet
Abatar-360 FT-IR spectrometer. UV–vis spectra in the
region of 200–800 nm were recorded on a spectropho-
tometer Shimadzu UV-1650PC. Elemental analyses were
performed on a Fisons instrument 2A1108 at Korea
Institute of Science and Technology. DSC thermographs
were obtained on PerkinElmer Diamond DSC with a scan
rate of 108C/min. Thermo-optical observations were
carried out on a Nikon Eclipse E600 POL optical polarised

Supramolecular Chemistry
9
microscope equipped with a Mettler Toledo FP82 HT
hot-stage system and Mettler FP90 central processor.
Microphotographs were obtained with a Moticam 2300
digital camera. The X-ray scattering measurements
were performed in transmission mode with synchrotron
3442, 3367, 2955, 2928, 2851, 2849, 1728, 1606, 1512,
1471, 1319, 1255, 1198, 1170, 1085 and 1014.
4-Aminophenyl-4-decyloxybenzoate (2, n ¼ 10)
˚
radiation of 1.3051 A (E ¼ 9.5 keV) at the 3C2 X-ray
The compound was synthesised in a manner similar to 4-
aminophenyl-40-hexyloxybenzoate. Yield: 1.41 g, 95%.
White powder; mp 95–968C; dH (250 MHz; CDCl3;
Me4Si) 0.88 (t, J ¼ 7.5 Hz, 3H, CH3), 1.20–1.50 (m, 14H,
CH2), 1.79 (quintet, J ¼ 7.5 Hz, 2H, OCH2CH2), 3.65 (br
s, 2H, NH2), 4.04 (t, J ¼ 5.5 Hz, 2H, OCH2), 6.97 (d,
J ¼ 10.0 Hz, 2H, aromatic), 7.05–7.20 (m, 4H, aromatic)
beamline at the Pohang Accelerator Laboratory (Pohang,
Kyoungsangnam-Do, Korea). The sample was held in an
aluminium sample holder, which was sealed with the
window of 7-mm thick Kapton films in both sides. The
sample was heated with two cartridge heaters and the
temperature of the samples was monitored by thermo-
couple placed close to the sample.
and 8.12 (d, J ¼ 10.0 Hz, 2H, aromatic); nmax (KBr, cm21
)
3435, 3371, 2953, 2920, 2863, 2851, 1724, 1606, 1513,
1472, 1316, 1279, 1259, 1200, 1167, 1082 and 1014.
Syntheses
4-Alkyloxybenzoic acids were prepared by applying
standard Williamson procedure on ethyl-4-hydroxybenzo-
ate and subsequent hydrolysis of the obtained alkoxylated
esters as reported elsewhere (11c, e). 4-Nitrophenyl
alkyloxybenzoates were synthesised by the N,N0-dicyclo-
hexylcarbodiimide-assisted esterification of the corre-
sponding benzoic acids with 4-nitrophenol (11).
4-Aminophenyl-4-dodecyloxybenzoate (2, n ¼ 12)
The compound was synthesised in a manner similar to 4-
aminophenyl-40-hexyloxybenzoate. Yield: 1.46 g, 98%.
White powder; mp 99–1018C; dH (250 MHz; CDCl3;
Me4Si) 0.88 (t, J ¼ 7.5 Hz, 3H, CH3), 1.20–1.50 (m, 18H,
CH2), 1.82 (q, J ¼ 7.5 Hz, 2H, OCH2CH2), 3.65 (br s, 2H,
NH2), 4.04 (t, J ¼ 5.5 Hz, 2H, OCH2,), 6.97 (d,
J ¼ 10.0 Hz, 2H, aromatic), 6.90–7.00 (m, 4H, aromatic)
and 8.12 (d, J ¼ 10.0 Hz, 2H, aromatic); nmax (KBr, cm21
)
4-Aminophenyl-4-hexyloxybenzoate (2, n ¼ 6)
4-Nitrophenyl-40-hexyloxybenzoate (1.00 g, 2.91 mmol)
was dissolved in a mixture of benzene–methanol (1:1,
80 ml). Then Pd/C (10%, wet, 0.40 g) was added to an
obtained clear solution. The reaction proceeded in a
hydrogenation apparatus under 2.5 atm pressure of
hydrogen for 4 h. The resulted mixture was filtered
through a layer of Celite 545 and evaporated in a vacuum
rotary evaporator. Further purification by recrystallisation
generally is not necessary as this may lead to obtaining
brownish products. Yield: 0.89 g, 98%. White powder;
mp 88–908C; dH (250 MHz; CDCl3; Me4Si) 0.92
(t, J ¼ 7.5 Hz, 3H, CH3), 1.20–1.50 (m, 6H, CH2), 1.82
(quintet, J ¼ 7.5 Hz, 2H, OCH2CH2), 3.65 (br s, 2H, NH2),
4.04 (t, J ¼ 6.5 Hz, 2H, OCH2), 6.97 (d, J ¼ 10.0 Hz,
2H, aromatic), 7.05–7.25 (m, 4H, aromatic) and 8.12 (d, J ¼
10.0 Hz, 2H, aromatic); nmax (KBr, cm21) 3440, 3370, 2920,
2849, 1715, 1605, 1513, 1277, 1256, 1192, 1166 and 1086.
3459, 3372, 2918, 2849, 1715, 1605, 1513, 1277, 1256,
1192, 1166 and 1086.
4-Aminophenyl-40-tetradecyloxybenzoate (2, n ¼ 14)
The compound was synthesised in a manner similar to 4-
aminophenyl-40-hexyloxybenzoate. Yield: 1.48 g, 99%.
White powder; mp 98–1018C; dH (250 MHz; CDCl3;
Me4Si) 0.88 (t, J ¼ 7.5 Hz, 3H, CH3), 1.20–1.50 (m, 22H,
CH2), 1.82 (q, J ¼ 7.5 Hz, 2H, OCH2CH2), 3.65 (br s, 2H,
NH2), 4.04 (t, J ¼ 5.5 Hz, 2H, OCH2,), 6.97 (d,
J ¼ 10.0 Hz, 2H, aromatic), 7.05–7.20 (m, 4H, aromatic)
and 8.12 (d, J ¼ 10.0 Hz, 2H, aromatic); nmax (KBr, cm21
)
3455, 3347, 2917, 2849, 1728, 1606, 1512, 1255, 1203,
1171 and 1085.
4-Aminophenyl-40-hexadecyloxybenzoate (2, n ¼ 16)
The compound was synthesised in a manner similar to 4-
aminophenyl-40-hexyloxybenzoate. Yield: 1.30 g, 95%.
White powder; mp 100–1028C; dH (250 MHz; CDCl3;
Me4Si) 0.88 (t, J ¼ 7.5 Hz, 3H, CH3), 1.20–1.50 (m, 26H,
CH2), 1.82 (q, J ¼ 7.5 Hz, 2H, OCH2CH2), 3.65 (br s, 2H,
NH2), 4.04 (t, J ¼ 6.0 Hz, 2H, OCH2), 6.97 (d,
J ¼ 10.0 Hz, 2H, aromatic), 7.05–7.20 (m, 4H, aromatic)
4-Aminophenyl-4-octyloxybenzoate (2, n ¼ 8)
The compound was synthesised in a manner similar to 4-
aminophenyl-40-hexyloxybenzoate. Yield: 0.90 g, 98%.
White powder; mp 137–1408C; dH (250 MHz; CDCl3;
Me4Si) 1.07 (t, J ¼ 7.5 Hz, 3H, CH3), 1.20–1.50 (m, 10H,
CH2), 1.84 (quintet, J ¼ 7.5 Hz, 2H, OCH2CH2), 3.65 (br
s, 2H, NH2), 4.01 (t, J ¼ 5.5 Hz, 2H, OCH2), 6.97 (d,
J ¼ 10.0 Hz, 2H, aromatic), 7.05–7.25 (m, 4H, aromatic)
and 8.12 (d, J ¼ 10.0 Hz, 2H, aromatic); nmax (KBr, cm21
)
3447, 3356, 2918, 2849, 1719, 1605, 1517, 1281, 1259,
1201, 1165 and 1083.
and 8.12 (d, J ¼ 10.0 Hz, 2H, aromatic); nmax (KBr, cm21
)

10
O.N. Kadkin et al.
4(5)-[40-(400-Hexyloxybenzoyloxy)phenyliminomethyl]-
J ¼ 10.0 Hz, 2H, aromatic), 7.25 (d, J ¼ 5.0 Hz, 4H,
aromatic), 7.58 (s, 1H, imidazole), 7.77 (s, 1H, CHvN),
8.15 (d, J ¼ 10.0 Hz, 2H, aromatic) and 8.42 (s, 1H,
imidazole).
1H-imidazole (3, n ¼ 6)
4-Aminophenyl-40-(hexyloxy)benzoate
(1.00 g,
3.19 mmol) and 4(5)-imidazole-carboxaldehyde (0.31 g,
3.19 mmol) were dissolved in hot ethanol separately. Two
solutions were combined and refluxed for 30 min in the
presence of 1–2 drops of acetic acid. A white precipitate
was formed upon cooling. The product was filtered off and
recrystallised from ethanol. Yield: 0.62 g, 50% (Found: C,
70.6; H, 6.4; N, 10.7; Mþ, 391; C23H25N3O3: C, 70.6; H,
6.4; N, 10.7%; M, 391); nmax (KBr, cm21) 2919, 2842,
1731, 1632, 1601, 1506, 1251, 1193, 1161 and 1065; lmax
(CH2Cl2, nm) 270 and 315 (log 1/dm3 mol21 cm21 4.03
and 3.82); dH (250 MHz; CDCl3; Me4Si) 0.92 (t,
J ¼ 7.5 Hz, 3H, CH3), 1.20–1.50 (m, 6H, CH2), 1.83
(quintet, J ¼ 7.5 Hz, 2H, OCH2CH2), 4.05 (t, J ¼ 5.5 Hz,
2H, OCH2), 6.98 (d, J ¼ 10.0 Hz, 2H, aromatic), 7.25 (d,
J ¼ 5.0 Hz, 4H, aromatic), 7.56 (s, 1H, imidazole), 7.77 (s,
1H, CHvN), 8.15 (d, J ¼ 10.0 Hz, 2H, aromatic) and 8.40
(s, 1H, imidazole).
4(5)-[40-(400-Dodecyloxybenzoyloxy)phenyliminomethyl]-
1H-imidazole (3, n ¼ 12)
The compound was prepared as described above for 3,
n ¼ 6 starting from 4-aminophenyl-40-(dodecyloxy)-
benzoate (1.00 g, 2.52 mmol) and 1H-imidazole-4(5)-
carbaldehyde (0.24 g, 2.52 mmol). Yield: 0.80 g, 67%
(Found: C, 73.0; H, 7.9; N, 8.8; Mþ, 476; C29H37N3O3: C,
73.2; H, 7.8; N, 8.8%; M, 476); nmax (KBr, cm21) 2920,
2851, 1731, 1629, 1603, 1505, 1250, 1198, 1161 and 1063;
lmax (CH2Cl2, nm) 277 and 316 (log 1/dm3 mol21 cm21
4.49 and 3.83); dH (250 MHz; CDCl3; Me4Si) 0.88 (t,
J ¼ 7.5 Hz, 3H, CH3), 1.20–1.50 (m, 18H, CH2), 1.82
(quintet, J ¼ 7.5 Hz, 2H, OCH2CH2), 4.04 (t, J ¼ 5.5 Hz,
2H, OCH2), 6.98 (d, J ¼ 10.0 Hz, 2H, aromatic), 7.25 (d,
J ¼ 5.0 Hz, 4H, aromatic), 7.57 (s, 1H, imidazole), 7.77 (s,
1H, CHvN), 8.14 (d, J ¼ 10.0 Hz, 2H, aromatic) and 8.42
(s, 1H, imidazole).
4(5)-[40-(400-Octyloxybenzoyloxy)phenyliminomethyl]-
1H-imidazole (3, n ¼ 8)
The compound was prepared as described above for 3,
n ¼ 6 starting from 4-aminophenyl-40-(octyloxy)benzoate
(1.00 g, 2.93 mmol) and 1H-imidazole-4(5)-carbaldehyde
(0.28 g, 2.93 mmol). Yield: 0.61 g, 50% (Found: C, 71.7;
H, 7.0; N, 10.0; Mþ, 420; C25H29N3O3: C, 71.6; H, 7.0; N,
10.0%; M, 420); nmax (KBr, cm21) 2920, 2846, 1732,
1631, 1603, 1504, 1252, 1197, 1160 and 1064; lmax
(CH2Cl2, nm) 275 and 316 (log 1/dm3 mol21 cm21 4.19
and 3.96); dH (250 MHz; CDCl3; Me4Si) 0.90 (t,
J ¼ 7.5 Hz, 3H, CH3), 1.20–1.50 (m, 10H, CH2), 1.83
(quintet, J ¼ 7.5 Hz, 2H, OCH2CH2), 4.05 (t, J ¼ 5.5 Hz,
2H, OCH2), 6.98 (d, J ¼ 10.0 Hz, 2H, aromatic), 7.25 (d,
J ¼ 5.0 Hz, 4H, aromatic), 7.57 (s, 1H, imidazole), 7.75 (s,
1H, CH ¼ N), 8.15 (d, J ¼ 10.0 Hz, 2H, aromatic) and
8.42 (s, 1H, imidazole).
4(5)-[40-(400-Tetradecyloxybenzoyloxy)phenyliminomethyl]-
1H-imidazole (3, n ¼ 14)
The compound was prepared as described above for 3,
n ¼ 6 starting from 4-aminophenyl-40-(tetradecyloxy)-
benzoate (1.00 g, 2.35 mmol) and 1H-imidazole-4-carbal-
dehyde (0.23 g, 2.35 mmol). Yield: 0.84 g, 75% (Found: C,
73.85; H, 8.3; N, 8.35; Mþ, 504; C31H41N3O3: C, 73.9; H,
8.2; N, 8.3%; M, 504); nmax (KBr, cm21) 2923, 2845,
1731, 1632, 1602, 1506, 1251, 1201, 1161 and 1066; lmax
(CH2Cl2, nm) 275 and 316 (log 1/dm3 mol21 cm21 4.17
and 3.95); dH (250 MHz; CDCl3; Me4Si) 0.88 (t,
J ¼ 7.5 Hz, 3H, CH3), 1.20–1.50 (m, 22H, CH2), 1.83
(quintet, J ¼ 7.5 Hz, 2H, OCH2CH2), 4.05 (t, J ¼ 5.5 Hz,
2H, OCH2), 6.98 (d, J ¼ 10.0 Hz, 2H, aromatic), 7.25 (d,
J ¼ 5.0 Hz, 4H, aromatic), 7.58 (s, 1H, imidazole), 7.78 (s,
1H, CH ¼ N), 8.15 (d, J ¼ 10.0 Hz, 2H, aromatic) and
8.42 (s, 1H, imidazole).
4(5)-[40-(400-Decyloxybenzoyloxy)phenyliminomethyl]-
1H-imidazole (3, n ¼ 10)
The compound was prepared as described above for 3,
n ¼ 6 starting from 4-aminophenyl-40-(decyloxy)benzoate
(1.00 g, 2.71 mmol) and 1H-imidazole-4(5)-carbaldehyde
(0.26 g, 2.71 mmol). Yield: 0.62 g, 52% (Found: C, 72.4;
H, 7.5; N, 9.4; Mþ, 448; C27H33N3O3: C, 72.45; H, 7.4; N,
9.4%; M, 448); nmax (KBr, cm21) 2923, 2850, 1733, 1630,
1605, 1503, 1251, 1198, 1162 and 1064; lmax (CH2Cl2,
nm) 274 and 316 (log 1/dm3 mol21 cm21 4.30 and 4.08);
dH (250 MHz; CDCl3; Me4Si) 0.89 (t, J ¼ 7.5 Hz, 3H,
CH3), 1.20–1.50 (m, 14H, CH2), 1.83 (quintet, J ¼ 7.5 Hz,
2H, OCH2CH2), 4.05 (t, J ¼ 5.5 Hz, 2H, OCH2), 6.98 (d,
4(5)-[40-(400-Hexadecyloxybenzoyloxy)phenyliminomethyl]-
1H-imidazole (3, n ¼ 16)
The compound was prepared as described above for 4(5)-
[40-(400-hexyloxybenzoyloxy)phenyliminomethyl]-1H-
imidazole starting from 4-aminophenyl-40-(hexadecylox-
y)benzoate (1.00 g, 2.21 mmol) and 1H-imidazole-4-
carbaldehyde (0.21 g, 2.21 mmol). Yield: 0.76 g, 65%
(Found: C, 74.3; H, 8.6; N, 7.9; Mþ, 532; C33H45N3O3: C,
74.5; H, 8.5; N, 7.9%; M, 532); nmax (KBr, cm21) 2922,
2849, 1732, 1633, 1601, 1504, 1252, 1198, 1160 and 1065;

Supramolecular Chemistry
11
lmax (CH2Cl2, nm) 273 and 316 (log 1/dm3 mol21 cm21
Bis-{4-[40-(400-dodecyloxybenzoyloxy)phenyliminato-
methyl]-1-imidazolato}copper(II) dichloride dihydrate
(4, n ¼ 12)
4.39 and 4.03); dH (250 MHz; CDCl3; Me4Si) 0.88 (t,
J ¼ 7.5 Hz, 3H, CH3), 1.20–1.50 (m, 26H, CH2), 1.82
(quintet, J ¼ 7.5 Hz, 2H, OCH2CH2), 4.05 (t, J ¼ 5.5 Hz,
2H, OCH2), 6.98 (d, J ¼ 10.0 Hz, 2H, aromatic), 7.25 (d,
J ¼ 5.0 Hz, 4H, aromatic), 7.58 (s, 1H, imidazole), 7.78 (s,
1H, CH ¼ N), 8.15 (d, J ¼ 10.0 Hz, 2H, aromatic) and
8.42 (s, 1H, imidazole).
Prepared similarly as above from ligand 3, n ¼ 12
(100 mg, 0.21 mmol) and CuCl2·2H2O (18 mg,
0.11 mmol). Yield: 64 mg, 56% (Found: C, 61.1; H, 6.8;
N, 7.5; C58H78Cl2CuN6O8: C, 62.1; H, 7.0; N, 7.5%)2;
nmax (KBr, cm21) 2922, 2849, 1732, 1633, 1601, 1504,
1252, 1198, 1160 and 1065; lmax (CH2Cl2, nm) 275
(log 1/dm3 mol21 cm21 4.31), 313 sh (4.15), 338 (4.05),
450 sh (3.47) and 600 sh (3.01).
Bis-{4-[40-(400-hexyloxybenzoyloxy)phenyliminatomethyl]-
1-imidazolato}copper(II) dichloride dihydrate (4, n ¼ 6)
Bis-{4-[40-(400-tetradecyloxybenzoyloxy)phenyliminato-
methyl]-1-imidazolato}copper(II) dichloride dihydrate
(4, n ¼ 14)
Ligand 3, n ¼ 6 (100 mg, 0.26 mmol) and CuCl2·2H2O
(23 mg, 0.13 mmol) were dissolved in hot ethanol
separately. Two solutions were combined and the reaction
mixture was stirred for 30 min at 608C. A light greenish
precipitate formed upon complexation, which was
centrifugated, and then an ethanol layer was pipetted off
from a centrifuge tube. The solid layer was washed with
ethanol 2£ using the same centrifugation method. Fine
light greenish powder was dried for several days in a
vacuumed desiccator with P2O5. Yield: 95 mg, 81%
(Found: C, 57.7; H, 5.6; N, 9.0; C46H54Cl2CuN6O8:
C, 57.95; H, 5.7; N, 8.8%); nmax (KBr, cm21) 2922,
2849, 1732, 1633, 1601, 1504, 1252, 1198, 1160 and
1065; lmax (CH2Cl2, nm) 270 (log 1/dm3 mol21 cm21
4.12), 313 sh (3.65), 338 (3.92), 450 sh (3.70) and
600 sh (3.31).
Prepared similarly from ligand 3, n ¼ 14 (100 mg,
0.20 mmol) and CuCl2·2H2O (18 mg, 0.11 mmol). Yield:
110 mg, 98% (Found: C, 63.7; H, 7.3; N, 7.3; C62H86Cl2-
CuN6O8: C, 63.2; H, 7.4; N, 7.1%); nmax (KBr, cm21
)
2922, 2849, 1732, 1633, 1601, 1504, 1252, 1198, 1160 and
1065; lmax (CH2Cl2, nm) 261 (log 1/dm3 mol21 cm21
4.04), 307 sh (3.98), 333 (3.99), 450 sh (3.72) and 600 sh
(3.25).
Bis-{4-[40-(400-hexadecyloxybenzoyloxy)phenyliminato-
methyl]-1-imidazolato}copper(II) dichloride dihydrate
(4, n ¼ 16)
Prepared similarly from ligand 3, n ¼ 16 (100 mg,
0.19 mmol) and CuCl2·2H2O (16 mg, 0.09 mmol). Yield:
70 mg, 65% (Found: C, 64.1; H, 7.5; N, 6.9; C66H94Cl2-
Bis-{4-[40-(400-octyloxybenzoyloxy)phenyliminatomethyl]-
1-imidazolato}copper(II) dichloride dihydrate (4, n ¼ 8)
CuN6O8: C, 64.2; H, 7.7; N, 6.8%); nmax (KBr, cm21
)
2922, 2849, 1732, 1633, 1601, 1504, 1252, 1198, 1160 and
1065; lmax (CH2Cl2, nm) 252 (log 1/dm3 mol21 cm21
4.14), 312 sh (4.06), 342 (4.06), 450 sh (3.71) and 600 sh
(3.33).
Prepared similarly as above from ligand 3, n ¼ 8 (100 mg,
0.24 mmol) and CuCl2·2H2O (21 mg, 0.12 mmol).
Yield: 110 mg, 92% (Found: C, 60.4; H, 6.0; N, 8.4;
C50H62Cl2CuN6O8: C, 59.5; H, 6.2; N, 8.3%)1; nmax (KBr,
cm21) 2922, 2849, 1732, 1633, 1601, 1504, 1252, 1198,
1160 and 1065; lmax (CH2Cl2, nm) 273 (log 1/dm3 mol21
cm21 4.18), 308 sh (3.75), 338 (3.82), 450 sh (3.61) and 600
sh (3.21).
Conclusions
A series of imidazole-containing rod-like Schiff’s bases
and their ionic copper(II) chelates displaying, respectively,
smectic C and A mesophases have been synthesised. A
variation in the length of the terminal alkyl chains within
6, 8, 10, 12, 14 and 16 carbon atoms does not influence
significantly on the clearing points of the synthesised
azomethines and melting points of their complexes. Such
behaviour is justified herein assuming considerable
regulation of these phase transitions by assembling and
disassembling of supramolecular structures. The proposed
molecular arrangement of smectic layers in both series of
the compounds is founded on hydrogen bonds, and plus
ionic and coordination interactions in a case of the
copper(II) complexes. Related superstructures have been
Bis-{4-[40-(400-decyloxybenzoyloxy)phenyliminatomethyl]-
1-imidazolato}copper(II) dichloride dihydrate (4, n ¼ 10)
Prepared similarly as above from ligand 3, n ¼ 10
(100 mg, 0.22 mmol) and CuCl2·2H2O (19 mg,
0.11 mmol). Yield: 100 mg, 89% (Found: C, 60.5; H, 6.4;
N, 7.9; C54H70Cl2CuN6O8: C, 60.9; H, 6.6; N, 7.9%); nmax
(KBr, cm21) 2922, 2849, 1732, 1633, 1601, 1504, 1252,
1198, 1160 and 1065; lmax (CH2Cl2, nm) 269
(log 1/dm3 mol21 cm21 4.24), 306 sh (4.08), 336 (4.08),
450 sh (3.66) and 600 sh (3.32).

12
O.N. Kadkin et al.
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There is a very good resemblance between the computer
models of the proposed supramolecular assemblies and
experimental d-spacings determined from the X-ray
diffraction experiments.
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Acknowledgements
This work has been supported by the programme Brain Korea 21
(BK-21) and the Centre for Bioactive Molecular Hybrids
(KOSEP).
Notes
1. Element analyses given here and in the cases below were
slightly deviated from the acceptable range. Insolubility of
the Cu(II) complexes in common solvents does not allow to
perform their recrystallisation, while in more polar solvents
like DMF, the complexes seemed to be unstable.
2. See above.
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