Mesomorphic and DFT studies of terminal ester containing salicylaldimines and their copper (II) complexes

Article abstract of DOI:10.1080/15421406.2016.1263060

In this article, we report synthesis and characterization of a novel homologous series of butyl 4-(4′-(alkoxy)-2-hydroxybenzylideneamino)benzoates, C_nLH (n = 6, 8, 10, 12, 14, 16) and their copper(II) complexes. The mesomorphic properties of th

Full text of DOI:10.1080/15421406.2016.1263060

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Mesomorphic and DFT studies of terminal ester
containing salicylaldimines and their copper (II)
complexes
Hemant Kumar Singh, Sachin Kumar Singh, Vijay Kumar, Priyanka Kanth,
Kirtika Mishra & Bachcha Singh
To cite this article: Hemant Kumar Singh, Sachin Kumar Singh, Vijay Kumar, Priyanka Kanth,
Kirtika Mishra & Bachcha Singh (2017) Mesomorphic and DFT studies of terminal ester containing
salicylaldimines and their copper (II) complexes, Molecular Crystals and Liquid Crystals, 643:1,
116-128, DOI: 10.1080/15421406.2016.1263060
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1263060
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Date: 23 February 2017, At: 21:34

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Mesomorphic and DFT studies of terminal ester containing
salicylaldimines and their copper (II) complexes
Hemant Kumar Singh, Sachin Kumar Singh, Vijay Kumar, Priyanka Kanth, Kirtika Mishra,
and Bachcha Singh
Department of Chemistry (Centre of Advanced Studies), Institute of Science, Banaras Hindu University, Varanasi,
India
ABSTRACT
KEYWORDS
Copper complexes; density
functional theory;
metallomesogens;
salicylaldimine;
structure–property
correlation
In this article, we report synthesis and characterization of a novel
homologous series of butyl 4-(4ꢀ-(alkoxy)-2-hydroxybenzylideneamino)
benzoates, CnLH (n = 6, 8, 10, 12, 14, 16) and their copper(II) complexes.
The mesomorphic properties of these compounds were investigated by
differential scanning calorimetry (DSC), polarizing optical microscopy
(POM) and powder X-ray diffraction (XRD) studies. The ligands and their
copper(II) complexes exhibit wide range of enantiotropic smectic A
mesophase as confirmed by their typical optical texture under polar-
izing microscope. Thermal stability of the compounds is determined
by thermo gravimetric analyses. DFT calculations have been performed
using GAUSSIAN-09 program at B3LYP level to obtain the stable elec-
tronic structure of the ligand and its copper(II) complex.
Introduction
The diverse mesogenic behaviour of liquid crystals (LCs) makes LCs suitable for application
in various fields and because of wide applications such as selective reflection of light and ferro-
electricity, LCs are one of the most studied systems in material science [1]. The salicylaldimine
core is recognized as a good mesogenic core in liquid crystalline materials because the azome-
thine linkage is stabilized by intra-molecular hydrogen bonding, and it has the ability to coor-
dinate metals [2–3]. The incorporation of transition metals into liquid crystals has led to the
study of interesting magnetic, electronic and optical properties in mesomorphic materials.
Metallomesogens (metal containing liquid crystals) have gained attention because of their
unusual geometries and novel properties such as colour, paramagnetism, fluidity, large bire-
fringence, polarizability, spin cross-over, ferroelectricity, photo refractivity, nonlinear optical
characteristics, large magnetic anisotropy, and luminescent mesophases [4]. Since the metal-
lomesogens are achieved through changes of molecular conformation, shape, and structure,
their physico-chemical properties can be tuned by the choice of metal ions, substituents, and
position of substituents on core moieties. In 1984 Ovchinnikov and coworkers were first to
exploit the coordination possibilities of salicylideneanilines and they reported the first imino-
derived metallomesogens [5–8]. He found that alkyl chain length is deciding factor for the
mesophase formation. When the alkyl chain length is short at both ends, the compounds are
CONTACT BachchaSingh
bsinghbhu@rediffmail.com
of Science, Banaras Hindu University Varanasi , India.
DepartmentofChemistry(CentreofAdvancedStudies),Institute
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©  Taylor & Francis Group, LLC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
117
non mesogenic in nature while by elongation of one alkyl chain length smectic A mesophase is
observed. In addition, a smectic C phase is observed for cases where both alkoxy tails are long
[9]. We have replaced one chain by −CO2CH2CH2CH2CH3 group to understand the effect
of polar group on mesogenic property. For more advanced applications of LC phases, it is
necessary to understand more deeply the structure–property correlation as well as molecular
origin of mesophases and phase behaviour. In continuation of the earlier work [10] on sys-
tematic structural studies of salicylaldimine mesogenic organic Schiff-bases and their Cu(II)
complexes, we now report here the synthesis and mesogenic properties of butyl 4-(4ꢀ-(alkoxy)-
2-hydroxybenzylideneamino)benzoate and their Cu(II) complexes.
Result and discussion
Synthesis
The synthetic route for preparation of salicylaldimine based ligands and their copper (II)
complexes is outlined in Scheme 1. Alkylation of 2,4-dihydroxybenzaldehyde with alkyl
bromide in 2-butanone using potassium hydrogen carbonate leads to formation of 4-
(alkoxy)-2-hydroxybenzaldehyde. The Schiff base was obtained by the condensation of butyl
4-aminobenzoate with appropriate aldehydes in refluxing ethanol. The metal complexes were
prepared by reaction of butyl 4-(4ꢀ-(alkoxy)-2-hydroxybenzylideneamino)benzoate with cop-
per(II) acetate in refluxing ethanol. The copper complexes were then isolated as brown solid,
by recrystallization from absolute ethanol in good yield. All the ligands and their copper(II)
complexes were characterized by standard spectroscopic techniques. The experimental proce-
dures, synthesis of the intermediates and analytical data are described in experimental section.
Mesomorphic behavior
The mesomorphic behaviour of the ligands and their Cu(II) complexes were studied by
combining thermo gravimetric analyses (TGA), differential scanning calorimetry (DSC),
polarised optical microscopy (POM) and XRD studies (in selected cases). Transition
temperatures together with associated enthalpy and entropy changes are given in Tables 1
and 2.
Scheme . Reactions and reagents: (a) RBr (. equiv.), potassium hydrogen carbonate (. equiv.), refluxing
in -butanone,  h (b) butyl -aminobenzoate (. equiv.), acetic acid (– drops), refluxing in ethanol,  h
(c) Cu(OAc).HO (. equiv.), stirring,  h.

118
H. K. SINGH ET AL.
Table . Thermal transitions and corresponding thermodynamic parameters.
Compd
Heating
Cooling
T,°C [࢞H, kJ/mol; ࢞S, J/(mol K)]
1a
1b
Cr . (.; .) Cr’. (.; .) SmA . (.; i . (−.; −.) SmA . (−.; −.) Cr
.) i
Cr . (.; .) Cr’. (.; .) SmA . (.; i . (−.; −.) SmA . (−.; −.) Cr
.) i
1c
1d
1e
1f
Cr . (.; .) SmA . (.; .) i
Cr . (.; .) SmA . (.; .) i
Cr . (.; .) SmA . (.; .) i
Cr . (.; .) SmA . (.; .) i
i . (−.; −.) SmA . (−.; −.) Cr
i . (−.; −.) SmA . (− .; −.) Cr
i . (−.; −.) SmA . (−.; −.) Cr
i . (−.; −.) SmA . (−.; −.) Cr
Abbreviations: Cr & Cr’= crystalline state, Sm A = Smectic A mesophase, i = isotropic liquid.
In the series of mesogens, 1b with the octyloxy chain length showed three endothermic
peaks at 58.0, 71.8, and 103.9°C, followed by the appearance of two exothermic peaks at
103°C and 53°C (Fig. 1).
POM observations reveal that upon heating from crystal state to 71.8°C, focal conic fan
shaped texture corresponding to SmA mesophase emerges, which further transforms to
isotropic liquid at 103.9°C. In cooling cycle, POM reveals the same textural observations from
103°C to 53°C. From POM analysis, it is clear that the two peaks observed in DSC heating
scan are due to crystal transformation from one state to another (Cr–Cr’ transition); such
polymorphism has often been observed in Schiff base-containing compounds [11]. Reheat-
ing regenerates the focal conic SmA mesophase with similar pattern; that is, the mesomor-
phism is enantiotropic (Fig. 2). A similar phase transition with a similar textural pattern is
Table . Thermal transitions and corresponding thermodynamic parameters.
Compd
Heating
Cooling
T,°C [࢞H, kJ/mol; ࢞S, J/(mol K)]
2a
2b
2c
2d
2e
2f
Cr . (.; .) Cr’. (.; .) SmA
. (.; .) i
Cr . (.; .) Cr’. (.; .) SmA
. (.; .) i
Cr . (.; .) Cr’. (.; .) SmA
. (.; .) i
Cr . (.; .) Cr’. (.; .) SmA
. (.; .) i
Cr . (.; .) Cr’. (.;.) SmA
. (.; .) i
Cr . (.; .) Cr’. (.; .) SmA
. (.; .) i
i . (−.; −.) SmA . (−.; −.) Cr
i . (−.; −.) SmA . (−.; −.) Cr
i . (−.; −.) SmA . (− .; −.) Cr
i . (−.; −.) SmA . (− .; −.) Cr
i . (−.; −.) SmA . (− .; −.) Cr
i . (−.; −.) SmA . (− .; −.) Cr
Abbreviations: Cr & Cr’= crystalline state, Sm A = Smectic A mesophase, i = isotropic liquid.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
119
Figure . DSC thermogram of (a) butyl -(ꢀ-(octyloxy)--hydroxybenzylideneamino)benzoate (b) butyl -
(ꢀ-(hexadecyloxy)--hydroxybenzylideneamino)benzoate.
shown by compound 1a. From DSC analysis, we found the two endothermic and two exother-
mic peaks in compounds 1c–1f. POM analysis reveals that the two endothermic peaks are
correspondence to crystal-to-mesophase and mesophase-to-isotropic and in cooling cycle
two peaks correspondence to isotropic-to-mesophase and mesophase-to-crystal phase. In
the series of butyl 4-(4ꢀ-(alkyloxy)-2-hydroxybenzylideneamino)benzoate, the liquid crys-
tal transition temperature decreases from the hexyloxy to tetradecyloxy derivatives and then
increases in case of hexadecyloxy derivatives in the heating cycle. In the cooling cycle, the
story is quite different as the transition temperature decreases from hexyloxy to hexadecy-
loxy derivative. Compound 1d and 1e show the SmA mesophase near to room temperature in
cooling cycle. On the basis of these observations we can say that moderate chain length of soft
alkoxy tails may be assumed as most appropriate to gain good mesophase stability. Transition
temperatures of compounds 1a–1f are given in Table 1.
Figure . Optical textures of butyl -(ꢀ-(dodecyloxy)--hydroxybenzylideneamino)benzoate under a polar-
izing optical microscopy. Heating cycle: (a) crystal phase at °C (b) SmA mesophase at °C (c) SmA
mesophase to isotropic transition at °C. Cooling cycle: (d) SmA mesophase at °C (e) SmA mesophase
to crystal transition at °C (f) Crystal phase at °C.

120
H. K. SINGH ET AL.
Figure . XRD diffractogram at °C during the cooling cycle of butyl -(ꢀ-(dodecyloxy)--
hydroxybenzylideneamino)benzoate.
In order to explain the structure of the mesophase, X-ray measurements were performed
on unaligned (powder) samples. The XRD experiments were carried out with CuKα (λ =
˚
1.54 A) radiation. The samples under investigation were heated slightly above their isotropiza-
tion temperature and filled into Lindemann capillary tubes and both the ends of the tubes
were flame sealed. The XRD patterns for the compound 1d at 60°C are shown in Fig. 3. The
diffractograms obtained at different temperatures exhibited similar characteristics; a sharp
and intense peak was seen in the small angle region while the wide angle region contained a
weak and diffuse peak. XRD patterns with the single, sharp low angle diffuse scattering accom-
panied by a high-angle diffuse peak is typical of a smectic phase wherein the constituent meso-
gens, being orientationally aligned, form a layered structure with inter-molecular separation
within the smectic layer arising due to the liquid-like positional correlation in the smectic
layer.
The copper complexes of the series also exhibit SmA mesophase, but at higher temperature
(above 148°C) in comparison to the parent ligands. In the first heating scan of 2b, three sharp
peaks appear at 93.2°C, 145.7°C, and 163.5°C. The DSC thermogram recorded in the cooling
scan exhibits two distinct peaks at 161.8°C and 106.3°C (Fig. 4). The three peaks observed
in heating cycle for this compound define the crystal-to-crystal, crystal-to-mesophase and
mesophase-to-isotropic phase transition and two peaks in cooling cycle reveal an isotropic-to-
mesophase and mesophase-to-crystal transition. POM observations reveal that upon heating
from crystal state to 145.7°C, focal conic texture corresponding to SmA mesophase emerges,
which further transforms to isotropic liquid at 163.5°C. In cooling cycle, POM reveals the
same textural observations, which emerges from 161.8°C and solidifies at 106.3°C (Fig. 5).
A similar phase transition with a similar textural pattern is shown by compound 2a and
2c.
The compound 2d with dodecyloxy chain length shows three endothermic peaks at
101.3°C, 124.1°C, and 159.1°C in the first heating scan and two exothermic peaks at
156.3°C and 74.9°C. Focal conic fan shaped texture of SmA mesophase was observed in both
the heating and cooling cycle. Same textural pattern are also found in 2e and 2f. The transition
temperature and associated entropy and enthalpy are summarized in Table 2.
The mesophase structures of copper(II) complex, 2d was confirmed by XRD studies of
unoriented samples filled in Lindemann capillaries. The XRD pattern at 130°C in the smectic

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
121
Figure . DSC thermogram of (a) copper(II) complex of butyl -(ꢀ-(octyloxy)--hydroxy benzylide-
neamino)benzoate (b) copper(II) complex of butyl -(ꢀ-(dodecyloxy)--hydroxy benzylideneamino) ben-
zoate.
˚
A phase is shown in Fig. 6. Two sharp peaks in the small angle region with d spacings 32.68 A
˚
and 15.85 A were observed in small angle region while the wide angle region contained diffuse
peak at 4.54 A. These features confirm the mesophase to be SmA in agreement with the POM
˚
observations. The wide-angle diffuse peak indicates the fluid-like correlation of the molecules
in the layers.
Computational study
The single molecular optimization has been done to investigate the molecular properties using
the DFT method. The optimized structures of the ligand and its Cu(II) complex are shown in
Fig. 7.
Figure . Optical textures of copper(II) complex of butyl -(ꢀ-(dodecyloxy)--hydroxybenzylide
neamino)benzoate under a polarizing optical microscopy. Heating cycle: (a) crystal phase at °C (b)
SmA mesophase at °C (c) SmA mesophase to isotropic transition at °C. Cooling cycle: (d) Isotropic to
SmA mesophase at °C (e) SmA mesophase at °C (f) SmA mesophase to crystal transition at °C.

122
H. K. SINGH ET AL.
Figure . XRD diffractogram at °C during the cooling cycle of butyl -(ꢀ-(dodecyloxy)--
hydroxybenzylideneamino)benzoate.
The absence of any imaginary frequency in the calculated vibrational frequencies ensures
that the optimized geometry corresponds to a true energy minimum. Some of the selective
geometrical parameters of the optimised ligand and its Cu(II) complex, evaluated by density
functional theoretical (DFT) calculations at B3LYP/6–311+G (d) basis set for the ligand while
for metal complex mixed basis set (6-311+G (d) for C,H, N atoms and LANL2DZ for copper
metal) is used, are shown in Table 3.
To investigate the different stable rotational conformers, we have calculated energy by
variation of the dihedral angle C10–N12–C16–C17 in between 0° and 180° at 10° inter-
val. The relative energy with respect to the optimised structure vs. Dihedral angle is
shown in Fig. 8. From this, we see that the most stable conformer for 1c at the poten-
tial energy surface is at a dihedral angle of 30° and there is another local minimum
at a dihedral angle of 150° with an energy difference of 0.23 kJ/mol. From this, we
conclude that most of the molecules prefer to be present in the global minima in solid
phase.
Figure . The optimized structure of (a) butyl -(ꢀ-(decyloxy)--hydroxybenzylideneamino) benzoate and
(b) copper(II) complex of butyl -(ꢀ-(decyloxy)--hydroxy benzylideneamino) benzoate molecule using DFT
method.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
123
Table . Selected bond lengths and bond angles of copper(II) complex of butyl
-(ꢀ-(decyloxy)--hydroxybenzylideneamino) benzoate.
Structure parameter
Cu-complexa
Cu–O()
Cu–O()
.
.
Cu–N()
Cu–N()
.
.
O()– Cu–O()
N()– Cu –N()
N()–Cu–O()
N()–Cu–O()
N()–Cu–O()
N()–Cu–O()
.
.
.
.
.
.
a
˚
bond lengths are reported in angstrom (A) and bond angles in degrees (°).
Figure . Potential energy vs dihedral angle (−C−C−N−C−) curve of butyl -(ꢀ-(decyloxy)--
hydroxybenzylideneamino)benzoate.
Conclusion
A novel homologous series of butyl 4-(4ꢀ-(alkoxy)-2-hydroxybenzylideneamino)benzoates,
CnLH (n = 6, 8, 10, 12, 14, 16) and their copper(II) complexes have been synthesized and the
mesomorphic behaviour have been analyzed using DSC, POM, XRD and DFT techniques. All
members show SmA mesophase with focal conic textures, having large values of enthalpy and
entropy change during the transitions. DFT calculations have been also performed to obtain
the stable electronic structure of the ligand and its copper(II) complex. This study will help
in exploring further possibilities of the synthesis of thermally stable novel liquid crystalline
compounds by variation of nature of substituents at peripheral, lateral positions and density
of alkoxy chain length.
Experimental details
Materials
The reagents were purchased from commercial sources and were used as received: 2,4-
dihydroxybenzaldehyde, butyl 4-aminobenzoate, 1-bromoalkanes and copper acetate

124
H. K. SINGH ET AL.
monohydrate are from Aldrich Chemicals, USA. All other solvents and reagents were
purchased from Merck. The solvents were dried using standard methods when required [12].
Instrumental
Structural characterization
Structural characterization of the compound was carried out through a combination of CHN
analyzer (CE-440 Exeter Analytical CHN analyzer), Infrared spectroscopy (Varian 3100 FT-
IR Excalibur series spectrophotometer) using KBr pellets, 1H and 13C NMR spectra (JEOL FT-
NMR AL 300 MHz spectrometer) in CDCl3 using tetramethylsilane as an internal standard,
UV-visible spectrometer (UV-1700 Pharma Spec. Shimadzu) in CHCl3 solution.
Thermal analysis
The DSC thermograms were recorded on Mettler Toledo TC 15 TA differential scanning
calorimeters at the rate of 5.0°C min−1 under nitrogen atmosphere using spec pure grade
indium standard and taking samples in close lid aluminium pans. The transition tempera-
tures have been determined from DSC with accuracy of 0.1°C. Thermo gravimetric analysis
(TGA) was performed using a PerkinElmer-STA 6000 apparatus under high purity nitrogen.
Polarized optical microscopic study
The mesophase type was identified by visual comparison with known phase standards using
a Nikon Eclipse LV-100 POL polarizing optical microscope (POM) fitted with a hot stage
temperature-controlled LTSE 420 heating stage (Linkam Scientific Instruments, Tadworth,
Surrey, UK) with temperature controlling accuracy of 0.1 K.
Xray diffraction study
For the temperature-dependent Xray diffraction measurements, a PAN alytical X’Pert PRO
MP X-ray diffractometer consisting of a focusing elliptical mirror and a fast high resolu-
tion detector (PIXCEL) was employed; the wavelength of the radiation in this case also was
0.15418 nm. The profiles collected using this apparatus were analyzed using Fityk profile fit-
ting software.
Density functional theory (DFT) studies
The GAUSSIAN-09 program package was employed to carry out DFT calculations at the
Becke’s three parameter functionals and Lee, Yang, and Parr correlation functionals (B3LYP).
The internal coordinates of the system, which is used as input for GAUSSIAN-09 program
was generated by the GAUSS VIEW 4.1 program [13–24].
Synthesis and analytical data
The starting material 4-(alkoxy)-2-hydroxybenzaldehyde was prepared according to literature
procedure [10].
Synthesis of butyl -(ꢀ-(hexyloxy)--hydroxybenzylideneamino)benzoate, CLH (a)
The ligand, (C6LH) was prepared by refluxing together an absolute ethanolic solution of 4-
(hexyloxy)-2-hydroxybenzaldehyde (1.11 g, 5 mmol) and butyl 4-aminobenzoate (0.97 g,
5 mmol) for 4 h with a few drops (4-5 drops) of acetic acid. The yellow precipitate that

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
125
formed on cooling was filtered off, washed with cold ethanol and recrystallized from ethanol-
chloroform mixture (1/1, v/v). All the other members of the series were prepared in a similar
manner.
Yield: 87%. IR (KBr, cm−1): 3410 (−OH), 2956, 2924, 2842 (aliphatic C-H), 1713 (ester,
1
=
C O), 1628 (C = N), 1594, 1564 (Ph), 1274, 1238 (OPh); H NMR (300 MHz, CDCl3, 25°C)
δH (ppm): 13.41 (s, 1H, −OH), 8.53 (s, 1H, −CH = N), 8.10 (d, J1 (H,H) = 8.4 Hz, 2H,
−C6H4), 7.28 (d, J1 (H,H) = 8.2 Hz, 3H, −C6H4), 6.48 (d, 2H, −C6H3), 4.35 (t, 2H, −OCH2),
4.02 (t, 2H, COOCH2), 1.80-1.43 (m, 12H, −[CH2]6), 1.01 (t, 3H, −CH3), 0.89 (t, 3H, −CH3);
13C NMR (75 MHz, CDCl3, 25°C): δc 166.18, 164.10, 164.02, 162.75, 152.43, 133.85, 130.94,
128.10, 120.87, 112.75, 107.90, 101.57, 68.32, 64.85, 31.85, 30.77, 29.53, 29.29, 29.02, 25.95,
22.65, 19.26, 14.08, 13.75; Elemental analyses: calculated for C24H31NO4 (%) C, 72.52; H, 7.86;
N, 3.52; Found C, 72.41; H, 7.81; N, 3.54.
Synthesis of butyl -(ꢀ−-(1octyloxy)--hydroxybenzylideneamino)benzoate, CLH (b)
=
Yield: 89%. IR (KBr, cm ): 3413 (−OH), 2952, 2921, 2852 (aliphatic C-H), 1710 (ester, C O),
1
1630 (C = N), 1590, 1561 (Ph), 1273, 1240 (OPh); H NMR (300 MHz, CDCl3, 25°C) δH
(ppm): 13.44 (s, 1H, −OH), 8.53 (s, 1H, −CH = N), 8.09 (d, J1 (H,H) = 8.4 Hz, 2H, −C6H4),
7.29 (d, J1 (H,H) = 8.2 Hz, 3H, −C6H4), 6.50 (d, 2H, −C6H3), 4.36 (t, 2H, −OCH2), 4.03
(t, 2H, COOCH2), 1.79-1.45 (m, 16H, −[CH2]8), 1.01 (t, 3H, −CH3), 0.89 (t, 3H, −CH3);
13C NMR (75 MHz, CDCl3, 25°C): δc 166.20, 164.12, 164.03, 162.73, 152.42, 133.83, 130.93,
128.12, 120.89, 112.74, 107.89, 101.56, 68.30, 64.84, 31.87, 30.76, 29.52, 29.28, 29.02, 25.94,
22.65, 19.26, 14.07, 13.74; Elemental analyses: calculated for C26H35NO4 (%) C, 73.38; H, 8.29;
N, 3.29; Found C, 73.32; H, 8.25; N, 3.27.
Synthesis of butyl -(ꢀ−-(1decyloxy)--hydroxybenzylideneamino)benzoate, CLH (c)
=
Yield: 90%. IR (KBr, cm ): 3408 (−OH), 2957, 2922, 2848 (aliphatic C-H), 1711 (ester, C O),
1
1629 (C = N), 1592, 1564 (Ph), 1276, 1236 (OPh); H NMR (300 MHz, CDCl3, 25°C) δH
(ppm): 13.43 (s, 1H, −OH), 8.52 (s, 1H, −CH = N), 8.09 (d, J1 (H,H) = 8.4 Hz, 2H, −C6H4),
7.28 (d, J1 (H,H) = 8.2 Hz, 3H, −C6H4), 6.49 (d, 2H, −C6H3), 4.35 (t, 2H, −OCH2), 4.01
(t, 2H, COOCH2), 1.81-1.43 (m, 20H, −[CH2]10), 1.01 (t, 3H, −CH3), 0.89 (t, 3H, −CH3);
13C NMR (75 MHz, CDCl3, 25°C): δc 166.20, 164.10, 164.03, 162.75, 152.42, 133.85, 130.93,
128.10, 120.89, 112.75, 107.89, 101.57, 68.30, 64.85, 31.87, 30.77, 29.52, 29.29, 29.02, 25.94,
22.65, 19.26, 14.07, 13.75; Elemental analyses: calculated for C28H39NO4 (%) C, 74.14; H, 8.67;
N, 3.09; Found C, 74.02; H, 8.62; N, 3.04.
Synthesis of butyl -(ꢀ−-(1dodecyloxy)--hydroxybenzylideneamino)benzoate, CLH (d)
=
Yield: 86%. IR (KBr, cm ): 3406 (−OH), 2959, 2923, 2846 (aliphatic C-H), 1712 (ester, C O),
1
1627 (C = N), 1593, 1560 (Ph), 1278, 1234 (OPh); H NMR (300 MHz, CDCl3, 25°C) δH
(ppm): 13.42 (s, 1H, −OH), 8.52 (s, 1H, −CH = N), 8.08 (d, J1 (H,H) = 8.4 Hz, 2H, −C6H4),
7.30 (d, J1 (H,H) = 8.2 Hz, 3H, −C6H4), 6.50 (d, 2H, −C6H3), 4.34 (t, 2H, −OCH2), 4.04
(t, 2H, COOCH2), 1.78-1.43 (m, 24H, −[CH2]12), 1.02 (t, 3H, −CH3), 0.88 (t, 3H, −CH3);
13C NMR (75 MHz, CDCl3, 25°C): δc 166.19, 164.10, 164.03, 162.74, 152.42, 133.85, 130.95,
128.11, 120.89, 112.73, 107.91, 101.57, 68.31, 64.85, 31.87, 30.77, 29.52, 29.29, 29.02, 25.95,
22.65, 19.27, 14.07, 13.75; Elemental analyses: calculated for C30H43NO4 (%) C, 74.81; H, 9.01;
N, 2.91; Found C, 74.73; H, 8.97; N, 2.93.

126
H. K. SINGH ET AL.
Synthesis of butyl -(ꢀ−-(1tetradecyloxy)--hydroxybenzylideneamino)benzoate, CLH (e)
=
Yield: 85%. IR (KBr, cm ): 3409 (−OH), 2957, 2920, 2850 (aliphatic C-H), 1711 (ester, C O),
1
1629 (C = N), 1591, 1563 (Ph), 1276, 1237 (OPh); H NMR (300 MHz, CDCl3, 25°C) δH
(ppm): 13.43 (s, 1H, −OH), 8.54 (s, 1H, −CH = N), 8.10 (d, J1 (H,H) = 8.4 Hz, 2H, −C6H4),
7.27 (d, J1 (H,H) = 8.2 Hz, 3H, −C6H4), 6.49 (d, 2H, −C6H3), 4.33 (t, 2H, −OCH2), 4.02
(t, 2H, COOCH2), 1.80-1.43 (m, 28H, −[CH2]14), 1.01 (t, 3H, −CH3), 0.89 (t, 3H, −CH3);
13C NMR (75 MHz, CDCl3, 25°C): δc 166.17, 164.11, 164.04, 162.75, 152.40, 133.85, 130.94,
128.10, 120.89, 112.75, 107.89, 101.57, 68.31, 64.85, 31.87, 30.77, 29.52, 29.29, 29.02, 25.94,
22.65, 19.25, 14.07, 13.76; Elemental analyses: calculated for C32H47NO4 (%) C, 75.40; H, 9.29;
N, 2.75; Found C, 75.31; H, 9.23; N, 2.72.
Synthesis of butyl -(ꢀ−-(1hexadecyloxy)--hydroxybenzylideneamino)benzoate, CLH (f)
=
Yield: 88%. IR (KBr, cm ): 3415 (−OH), 2960, 2922, 2849 (aliphatic C-H), 1715 (ester, C O),
1
1626 (C = N), 1594, 1562 (Ph), 1275, 1235 (OPh); H NMR (300 MHz, CDCl3, 25°C) δH
(ppm): 13.41 (s, 1H, −OH), 8.51 (s, 1H, −CH = N), 8.07 (d, J1 (H,H) = 8.4 Hz, 2H, −C6H4),
7.28 (d, J1 (H,H) = 8.2 Hz, 3H, −C6H4), 6.48 (d, 2H, −C6H3), 4.36 (t, 2H, −OCH2), 4.01
(t, 2H, COOCH2), 1.79-1.43 (m, 32H, −[CH2]16), 1.03 (t, 3H, −CH3), 0.88 (t, 3H, −CH3);
13C NMR (75 MHz, CDCl3, 25°C): δc 166.20, 164.10, 164.05, 162.76, 152.42, 133.85, 130.92,
128.12, 120.91, 112.74, 107.88, 101.58, 68.31, 64.84, 31.86, 30.77, 29.53, 29.29, 29.02, 25.95,
22.65, 19.25, 14.05, 13.74; Elemental analyses: calculated for C34H51NO4 (%) C, 75.94; H, 9.56;
N, 2.60; Found C, 75.84; H, 9.51; N, 2.63.
Copper(II) complex of butyl -(ꢀ-(hexyloxy)--hydroxybenzylideneamino)benzoate,
(CL)Cu (a)
To a solution of butyl 4-(4ꢀ-(hexyloxy)-2-hydroxybenzylideneamino)benzoate (0.80 g,
2 mmol) in 20 mL of hot methanol/chloroform (1/1,v/v) was added copper(II) acetate (0.20 g,
1 mmol) in 10 mL of methanol- and the mixture was stirred at room temperature for 4 h.
The brown solid was filtered off, washed with methanol and recrystallized from chloro-
form/ethanol (1/1,v/v). All the other members of the series were prepared in a similar manner.
Yield: 76% (brown solid). IR (KBr, cm-1): 2954, 2926, 2857 (aliphatic C-H), 1713 (ester,
=
C O), 1612 (C = N), 1594, 1530 (Ph), 1278, 1240 (OPh); UV–visible: λmax = 436, 390, 278,
260, 208; Elemental analyses: calculated for C48H60N2O8Cu (%) − C, 67.31; H, 7.06; N, 3.27,
Cu, 7.42; Found C, 67.21; H, 7.02; N, 3.25, Cu, 7.40.
Copper(II) complex of butyl -(ꢀ-(octyloxy)--hydroxybenzylideneamino)benzoate,
(CL)Cu (b)
-1
=
Yield: 78% (brown solid). IR (KBr, cm ): 2957, 2927, 2857 (aliphatic C-H), 1712 (ester, C O),
1611 (C = N), 1593, 1531 (Ph), 1278, 1240 (OPh); UV–visible: λmax = 442, 393, 282, 265, 212;
Elemental analyses: calculated for C52H68N2O8Cu (%) − C, 68.43; H, 7.51; N, 3.07, Cu, 6.96;
Found C, 68.35; H, 7.46; N, 3.03, Cu, 6.92.
Copper(II) complex of butyl -(ꢀ-(decyloxy)--hydroxybenzylideneamino)benzoate,
(CL)Cu (c)
-1
=
Yield: 80% (brown solid). IR (KBr, cm ): 2955, 2925, 2853 (aliphatic C-H), 1710 (ester, C O),
1611 (C = N), 1591, 1535 (Ph), 1280, 1245 (OPh); UV–visible: λmax = 432, 387, 280, 268, 209;
Elemental analyses: calculated for C56H76N2O8Cu (%) − C, 69.43; H, 7.91; N, 2.89, Cu, 6.56;
Found C, 69.38; H, 7.93; N, 2.85, Cu, 6.53.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
127
Copper(II) complex of butyl -(ꢀ-(dodecyloxy)--hydroxybenzylideneamino) benzoate,
(CL)Cu (d)
-1
=
Yield: 77% (brown solid). IR (KBr, cm ): 2950, 2926, 2855 (aliphatic C-H), 1712 (ester, C O),
1610 (C = N), 1602, 1538 (Ph), 1275, 1242 (OPh); UV–visible: λmax = 430, 391, 283, 262, 201;
Elemental analyses: calculated for C60H84N2O8Cu (%) − C, 70.32; H, 8.26; N, 2.73, Cu, 6.20;
Found C, 70.23; H, 8.20; N, 2.67, Cu, 6.14.
Copper(II) complex of butyl -(ꢀ-(tetradecyloxy)--hydroxybenzylideneamino) benzoate,
(CL)Cu (e)
-1
=
Yield: 79% (brown solid). IR (KBr, cm ): 2952, 2924, 2851 (aliphatic C-H), 1714 (ester, C O),
1612 (C = N), 1598, 1537 (Ph), 1282, 1241 (OPh); UV–visible: λmax = 438, 386, 279, 263, 207;
Elemental analyses: calculated for C64H92N2O8Cu (%) − C, 71.11; H, 8.58; N, 2.59, Cu, 5.88;
Found C, 71.02; H, 8.51; N, 2.53, Cu, 5.81.
Copper(II) complex of butyl -(ꢀ-(hexadecyloxy)--hydroxybenzylideneamino) benzoate,
(CL)Cu (f)
-1
=
Yield: 75% (brown solid). IR (KBr, cm ): 2948, 2922, 2851 (aliphatic C-H), 1711 (ester, C O),
1611 (C = N), 1601, 1540 (Ph), 1277, 1242 (OPh); UV–visible: λmax = 435, 392, 280, 261, 206;
Elemental analyses: calculated for C68H100N2O8Cu (%) − C, 71.83; H, 8.86; N, 2.46, Cu, 5.59;
Found C, 71.76; H, 8.80; N, 2.40, Cu, 5.52.
Acknowledgments
HKS (Senior Research Fellow) is grateful to Council of Scientific and Industrial Research (CSIR),
New Delhi, India, for providing research fellowship. BS is grateful to DRDO, India (Project No.
ERIP/ER/1203053/M/01/1542) for financial assistance. The authors wish to thank Dr. Sandeep kumar
and Ms. Vasuda, Raman Research Institute, Bangalore, India for the XRD analysis.
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