Novel macro metallomesogens derived from simple dihydroxy benzenes

Article abstract of DOI:10.1016/j.ica.2012.12.001

A series of tetradentate Schiff base metallomesogenic diols and their model compounds were synthesized from two simple dihydroxy benzenes. The metallomesogenic diol was constructed from three ring containing mesogen linked through ester and azomethine with terminal hydroxy group. This upon complexation with copper(II) formed metallomesogenic diol with varing terminal chain length. The related model metallomesogenic compounds were also synthesized with varying chain length with terminal methyl group and compared the properties with metallomesogenic diols. Extensive characterization of all metallomesogenic compounds and intermediates were carried out by FT-IR, ¹H & ¹³C NMR, EPR, VSM, Mass (EI and FAB) and UV-Vis spectroscopy. Hot stage polarizing microscope, Differential scanning calorimetry was used to ensure the phase characteristics such as nature of phase, melting and clearing temperatures and phase range. The appearance of enantiotropic smectic A phases indicated high molecular polarizability of the core due to the metal ion. The role of copper(II) ion on mesogens were discussed.

Full text of DOI:10.1016/j.ica.2012.12.001

Inorganica Chimica Acta 397 (2013) 129–139
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Inorganica Chimica Acta
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Novel macro metallomesogens derived from simple dihydroxy benzenes
b
c
a
Natarajan Senthilkumar a,b, , Aravamudhan Raghavan , Tanneru Narasimhaswamy , Il-Jin Kim
⇑
a Production Technology Research Center, Samsung Cheil Industries, 62 Pyeongyeo-dong, Yeosu-si, JeonNam 555-210, South Korea
b Department of Polymer Science, University of Madras, Guindy Campus, Chennai 600 025, India
c Polymer Laboratory, Central Leather Research Institute, Chennai 600 020, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of tetradentate Schiff base metallomesogenic diols and their model compounds were synthesized
from two simple dihydroxy benzenes. The metallomesogenic diol was constructed from three ring con-
taining mesogen linked through ester and azomethine with terminal hydroxy group. This upon complex-
ation with copper(II) formed metallomesogenic diol with varing terminal chain length. The related model
metallomesogenic compounds were also synthesized with varying chain length with terminal methyl
group and compared the properties with metallomesogenic diols. Extensive characterization of all met-
allomesogenic compounds and intermediates were carried out by FT-IR, 1H & 13C NMR, EPR, VSM, Mass
(EI and FAB) and UV–Vis spectroscopy. Hot stage polarizing microscope, Differential scanning calorimetry
was used to ensure the phase characteristics such as nature of phase, melting and clearing temperatures
and phase range. The appearance of enantiotropic smectic A phases indicated high molecular polarizabil-
ity of the core due to the metal ion. The role of copper(II) ion on mesogens were discussed.
Ó 2012 Elsevier B.V. All rights reserved.
Received 24 February 2012
Received in revised form 30 October 2012
Accepted 3 December 2012
Available online 8 December 2012
Keywords:
Metallomesogen
Copper(II) complex
Liquid crystal
Schiff base
SmA phase
1. Introduction
their inclusion opens up the possibilities of the incorporation of
new physical properties into the liquid crystals [12].
Liquid crystalline materials containing metal ions are known as
metallomesogens [1–4]. The interest on a study of these systems
arises from the fact that the combination of the properties of or-
ganic liquid crystals and of transition-metal ions can produce
new materials exhibiting unique assembly structures, and unique
optical, magnetic and electronic properties [5–7]. Although cala-
mitic liquid crystals are based on organic moieties, when heteroat-
oms which can bind to metals are incorporated into them,
metallomesogens can be realized [8–10]. In other words, the
dipole–dipole and dispersion forces which had liquid crystals in
anisotropic supramolecular arrays are not destroyed by the intro-
duction of the metals. The metallomesogens combine the known
properties of organic liquid crystals with those introduced by the
presence of one or more metals (color, magnetism, polarizability,
multiple localized charges) and provide new geometrical shapes
including linear, square planar, trigonal, tetrahedral, octahedral,
and square pyramidal, lantern structures which are unobtainable
in pure organic compounds [1]. Furthermore, with the large and
polarizable electron density which is a feature of many metal ions
of the d and f block elements (with unpaired electrons) giving rise
to interesting spectroscopic and magnetic properties [11]. And
In this work, the hydroxy terminated metallomesogens were
designed and synthesized from two simple dihydroxy benzenes
(resorcinol and hydroquinone), which were linked through multi-
functional groups such as ether, ester and azomethane. These hy-
droxy metallomesogens exhibit liquid crystalline behavior with a
better aspect ratio (length to breadth ratio) through the intermo-
lecular H-bonding [13–15]. The related model metallomesogenic
compounds were also synthesized with varying chain length with
terminal methyl group and their properties were compared with
that of hydroxy metallomesogens. A three ring based core was
used in the present investigation as its aspect ratio would be ex-
pected to be high in contrast to two ring systems. In calamitic mes-
ogens, in addition to molecular polarizability and linearity, the
aspect ratio of the mesogen is a crucial factor [16–18]. Moreover,
the introduction of hydroxy group adjacent to ortho to azomethine
link which is essential for complexing metal ion, enhances the
breadth of the molecule [19–23]. The introduction of reactive ter-
minal hydroxy group in metallomesogen enables them to undergo
radical or condensation polymerization to form liquid crystalline
polymers [24,25].
2. Experimental
2.1. Materials and methods
⇑
Corresponding author at: Production Technology Research Center, Samsung
Cheil Industries, 62 Pyeongyeo-dong, Yeosu-si, JeonNam 555-210, South Korea. Tel.:
+82 10 6265 7146; fax: +82 61 689 1568.
Resorcinol (Aldrich), hydroquinone (Aldrich), 2-bromoethanol
(Lancaster), 1,6-hexanediol (Lancaster), 1,8-octanediol (Lancaster),
E-mail address: nskumar77@yahoo.com (N. Senthilkumar).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.12.001

130
N. Senthilkumar et al. / Inorganica Chimica Acta 397 (2013) 129–139
1,10-decanediol (Lancaster), sodium hydroxide pellets (Loba Che-
mie), 4-nitrobenzoic acid (Lancaster), N,N0-dicyclohexyl carbodiim-
ide (DCC) (Fluka), 4-dimethylaminopyridine (DMAP) (Fluka),
phosphorus oxy chloride (POCl3) (CDH), hydrobromic acid
(Aldrich), p-toluenesulfonic acid (PTSA) (Aldrich), palladium on
carbon 10%(Pd/C) (Aldrich), copper acetate (Lancaster) were used
as received. The solvent N,N0-dimethyl formamide (DMF) was stir-
red with calcium hydride and distilled under reduced pressure be-
fore use. Ethanol and methanol were purified by refluxing with
lime followed by distillation. n-Butanol (Qualigens), Toluene
(Merck), THF (Merck), dichloromethane (Merck), ethyl acetate
(Qualigens), hexane (Qualigens) and petroleum ether (S.D. Fine
Chemicals) were used as received.
101.09, 108.76, 118.92, 135.22, 164.54, 166.49, 194.30. MS (EI)
m/z: 222 (M+).
2.2.2. 4-(Decyloxy)-2-hydroxybenzaldehyde (3b)
Yield: 3.17 g (38%). a colorless liquid. IR (KBr, cmꢀ1): 2924, 2952
and 2850 (C–H), 2746 (CHO), 1644 (C@O), 1219 (C–O–C). 1H NMR
(400 MHz, CDCl3): d 0.88 (t, 3H, J = 6.35 Hz, CH3), 1.27–1.43 (m,
14H, CH2), 1.73–1.80 (m, 2H, CH2), 3.96 (t, 2H, J = 6.53 Hz, CH2),
6.37 (d, 1H, J = 1.72, Ar–H), 6.49 (d, 1H, J = 6.96 Hz, Ar–H), 7.35
(d, 1H, J = 8.64 Hz, Ar–H), 9.65 (s, 1H, CHO), 11.46 (s, 1H, Ar–-
OH). 13C NMR (100 MHz, CDCl3): d 15.49, 24.11, 27.36, 30.37,
30.55, 30.76, 30.99, 31.07, 69.75, 71.98, 102.46, 110.32, 116.45,
136.51, 165.92, 167.82, 195.53. MS (EI) m/z: 278.2 (M+).
Infrared (IR) spectra were recorded by the KBr pellet method in
a Thermo Mattson Satellite model FTIR spectrophotometer. 1H and
13C NMR spectra were recorded using a JEOL GSX 400 MHz NMR
instrument. The EI mass spectra were recorded using a JEOL DX-
303 mass spectrometer. Elemental analyses were performed on a
Perkin-Elmer 240B elemental analyzer. The electronic spectra were
recorded on a Shimadzu 160A spectrometer. The solution state EPR
spectra were recorded on a Bruker EMX, X-band EPR spectrometer
using diphenylpicrylhydrazine (DPPH) as the reference. The mag-
netic studies of the complexes were performed on a PAR model
155 Vibrating Sample Magnetometer at the field strength of
5000G, at room temperature, and the instrument was calibrated
using metallic nickel supplied with the instrument. The FAB-MS
spectra were recorded on a JEOL SX 102/DA-6000 mass spectrom-
eter using a p-nitrobenzyl alcohol (NBA) matrix. The estimation of
metal content was carried out with (approximately 1 ppm metal-
content) concentrated nitric acid solution using a GBC-Avanta
1.33 Atomic Absorption Spectroscopy (AAS). Thermogravimetric
analyses (TGA) were carried out using Mettler Toledo TGA/SDTA
851e analyzer, from 50 to 800 °C under nitrogen atmosphere at a
heating rate of 10 °C minꢀ1. The gas flow rate was 50 mL minꢀ1
and the amount of sample used was 10–15 mg. DSC was performed
using a NETZSCHGeratebau Gmbh Thermal Analyzer from 25 to
2.2.3. 4-(Dodecyloxy)-2-hydroxybenzaldehyde (3c)
Yield: 3.59 g (39%). a colorless liquid. IR (KBr, cmꢀ1): 2956, 2924
and 2850 (C–H), 2744 (CHO), 1644 (C@O), 1215 (C–O–C). 1H NMR
(400 MHz, CDCl3): d 0.88 (t, 3H, J = 6.2 Hz, CH3), 1.26–1.55 (m, 18H,
CH2), 1.77–1.84 (m, 2H, CH2), 3.99 (t, 2H, J = 6.5 Hz, CH2), 6.39 (d,
1H, Ar–H), 6.51 (d, 1H, J = 6.81 Hz, Ar–H), 7.39 (d, 1H, J = 3.4 Hz,
Ar–H), 9.69 (s, 1H, CHO), 11.46 (s, 1H, Ar–OH). 13C NMR
(100 MHz, CDCl3): d 14.14, 19.43, 22.74, 28.25, 28.85, 29.42,
29.52, 29.64, 29.85, 32.92, 68.60, 70.66, 101.08, 108.75, 115.06,
135.15, 164.60, 166.48, 194.20. MS (EI) m/z: 306.2 (M+).
2.2.4. 4-(6-Hydroxyhexyloxy)-2-hydroxybenzaldehyde (3d)
Yield: 2.72 g (38%). a white solid. m.p. 73 °C. IR (KBr, cmꢀ1):
3364 (aliphatic OH), 3284 (phenolic OH), 2944 and 2858 (C–H),
2752 (CHO), 1627 (C@O), 1228 (C–O–C). 1H NMR (400 MHz,
CDCl3): d 1.44 (s(broad), 1H, OH), 1.45–1.63 (m, 6H, CH2), 1.79–
1.83 (m, 2H, CH2), 3.66 (t, 2H, J = 6.6 Hz, CH2), 4.01 (t, 2H,
J = 6.6 Hz, CH2), 6.40 (d, 1H, J = 2.4 Hz, Ar–H), 6.52 (d–d, 1H,
J = 8.8 Hz, Ar–H), 7.41 (d, 1H, J = 8.8 Hz, Ar–H), 9.70 (s, 1H, CHO),
11.47 (s, 1H, Ar–OH). 13C NMR (100 MHz, CDCl3): d 24.81, 25.10,
28.23, 31.93, 62.10, 67.79, 100.49, 108.05, 114.44, 134.55, 163.86,
165.76, 193.61. MS (EI) m/z: 238.7 (M+).
250 °C, cooled rapidly and re-heated at
a heating rate of
10 °C minꢀ1 under nitrogen atmosphere with a purge rate of
60 mL minꢀ1. The sample size used was 8–18 mg in a sealed alu-
minium pan. LC phase transitions were studied with an Olympus
BX 50 polarizing microscope equipped with a linkam THMS 600
heating stage.
2.2.5. 4-(8-Hydroxyoctyloxy)-2-hydroxybenzaldehyde (3e)
Yield: 2.80 g (35%). a white solid. m.p. 63 °C. IR (KBr, cmꢀ1):
3458 (aliphatic OH), 3384 (phenolic OH), 2915 and 2846 (C–H),
2749 (CHO), 1644 (C@O), 1224 (C–O–C). 1H NMR (400 MHz,
CDCl3): d 1.36 (s(broad), 1H, OH), 1.45–1.58 (m, 10H, CH2), 1.75–
1.80 (m, 2H, CH2), 3.63 (t, 2H, J = 6.6 Hz, CH2), 3.99 (t, 2H,
J = 6.6 Hz, CH2), 6.40 (d, 1H, J = 4.4 Hz, Ar–H), 6.52 (d–d, 1H,
J = 8.4 Hz, Ar–H), 7.41 (d, 1H, J = 8.4 Hz, Ar–H), 9.70 (s, 1H, CHO),
11.47 (s, 1H, Ar–OH). 13C NMR (100 MHz, CDCl3): d 25.68, 25.84,
28.87, 29.25, 29.30, 32.67, 62.74, 68.55, 101.04, 108.73, 114.97,
135.26, 164.42, 166.44, 194.37. MS (EI) m/z: 266.1 (M+).
2.2. Synthesis of O-alkylated benzaldehyde (3a–f)
A 30 mmol of 2,4-dihydroxy benzaldehyde 2 (which was pre-
pared from 2,4-dihydroxy benzene 1 as reported in the literature
[26]) and 30 mmol of sodium hydroxide were dissolved in 50 mL
of n-butanol, stirred under nitrogen atmosphere at room tempera-
ture for 30 min and then the temperature was raised to reflux
temperature. 30 mmol of corresponding bromoalkanes or
bromoalkanols dissolved in 25 mL of n-butanol was slowly added
into the reaction mixture and the refluxing was continued for
60 h. Evaporation of solvent from the n-butanol solution yielded
crude compound. Column chromatography (SiO2; hexane/EtOAc,
7:2 v/v) gave corresponding O-alkylated aldehyde 3a–f as a liquid
and solid at 31–43% yield.
2.2.6. 4-(10-Hydroxydecyloxy)-2-hydroxybenzaldehyde (3f)
Yield: 2.74 g (31%). a white solid. m.p. 60 °C. IR (KBr, cmꢀ1):
3437 (aliphatic OH), 3278 (phenolic OH), 2940 and 2850 (C–H),
2749 (CHO), 1644 (C@O), 1211 (C–O–C). 1H NMR (400 MHz,
CDCl3): d 1.31 (s(broad), 1H, OH), 1.41–1.58 (m, 14H, CH2), 1.75–
1.82 (m, 2H, CH2), 3.63 (t, 2H, J = 6.6 Hz, CH2), 4.00 (t, 2H,
J = 6.5 Hz, CH2), 6.41 (d, 1H, J = 2 Hz, Ar–H), 6.52 (d–d, 1H,
J = 8.68 Hz, Ar–H), 7.41 (d, 1H, J = 8.64 Hz, Ar–H), 9.69 (s, 1H,
CHO), 11.48 (s, 1H, Ar–OH). 13C NMR (100 MHz, CDCl3): d 25.73,
25.89, 28.89, 29.27, 29.39, 29.44, 29.50, 32.75, 62.94, 68.58,
101.04, 108.78, 114.98, 135.23, 164.48, 166.46, 194.34. MS (EI)
m/z: 294.1 (M+).
2.2.1. 4-(Hexyloxy)-2-hydroxybenzaldehyde (3a)
Yield: 2.87 g (43%). a colorless liquid. IR (KBr, cmꢀ1): 2952, 2932
and 2858 (C–H), 2744 (CHO), 1648 (C@O), 1224 (C–O–C). 1H NMR
(400 MHz, CDCl3): d 0.91 (t, 3H, J = 3.26 Hz, CH3), 1.31–1.47 (m, 6H,
CH2), 1.77–1.80 (m, 2H, CH2), 3.99 (t, 2H, J = 6.96 Hz, CH2), 6.40 (d,
1H, J = 1.71, Ar–H), 6.52 (d, 1H, J = 3.48 Hz, Ar–H), 7.39 (d, 1H,
J = 8.68 Hz, Ar–H), 9.69 (s, 1H, CHO), 11.48 (s, 1H, Ar–OH). 13C
NMR (100 MHz, CDCl3): d 14.02, 22.58, 25.61, 28.99, 31.51, 68.61,
2.3. Synthesis of O-alkylated hydroquinones (5a–c)
A mixture of hydroquinone 4 (33.03 g, 300 mmol) and sodium
hydroxide (12 g, 300 mmol) were dissolved in 150 ml of n-butanol,

N. Senthilkumar et al. / Inorganica Chimica Acta 397 (2013) 129–139
131
stirred under nitrogen atmosphere at room temperature for
30 min, and then the temperature was raised to 100 °C. 300 mmol
of corresponding bromoalkanes dissolved in 70 ml of n-butanol
was slowly added into the reaction mixture and the reaction was
continued for 60 h. Evaporation of solvent from the butanol solu-
tion under rotary evaporator yielded crude compound. Column
chromatography (SiO2; petroleum ether/EtOAc, 93:7 v/v) gave cor-
responding mono O-alkylated product 5a–c as a pale yellow solid.
2.4.2. 4-(Decyloxy)phenyl 4-nitrobenzoate (6b)
Yield: 5.83 g (73%). m.p. 73 °C. IR (KBr, cmꢀ1): 3096, 3065 and
3042 (NO2), 2940, 2915 and 2850 (C–H), 1749 (C@O), 1533 and
1350 (NO2), 1278 and 1194 (C–O). 1H NMR (400 MHz, CDCl3): d
0.89 (t, 3H, J = 6.84 Hz, CH3), 1.28–1.61 (m, 14H, CH2), 1.76–1.81
(m, 2H, CH2), 3.95 (t, 2H, J = 6.56 Hz, CH2), 6.94 (d, 2H,
J = 8.96 Hz, Ar–H), 7.13 (d, 2H, J = 9.08 Hz, Ar–H), 8.36 (d, 4H,
J = 3.16 Hz, Ar–H). 13C NMR (100 MHz, CDCl3): d 14.13, 22.69,
26,05, 29.26, 29.33, 29.40, 29.57, 29.59, 31.91, 68.49, 115.23,
122.11, 123.70, 131.26, 135.12, 143.80, 150.86, 157.28, 163.70.
MS (EI) m/z: 399 (M+).
2.3.1. 4-(Heptyloxy)phenol (5a)
Yield: 22.50 g (36%). m.p. 81 °C. IR (KBr, cmꢀ1): 3433 (OH),
2952, 2932 and 2858 (Ali–C–H), 1513 (Ar–C–H), 1244 (C–O–C).
1H NMR (400 MHz, CDCl3): d 0.88 (t, 3H, J = 6.81 Hz, CH3), 1.29–
1.44 (m, 8H, CH2), 1.71–1.76 (m, 2H, CH2), 3.89 (t, 2H, J = 6.71 Hz,
CH2), 5.43 (s(broad), 1H, OH), 6.7–6.8 (m, 4H, Ar–H). 13C NMR
(100 MHz, CDCl3): d 13.80, 22.36, 25.77, 28.83, 29.15, 31.56,
68.76, 115.6, 115.87, 149.28, 153.03. MS (EI) m/z: 208.1 (M+).
2.4.3. 4-(Dodecyloxy)phenyl 4-nitrobenzoate (6c)
Yield: 5.90 g (69%). m.p. 71 °C. IR (KBr, cmꢀ1): 3111, 3079 and
3051 (NO2), 2944, 2924 and 2850 (C–H), 1733 (C@O), 1529 and
1346 (NO2), 1272 and 1191 (C–O). 1H NMR (400 MHz, CDCl3): d
0.90 (t, 3H, J = 6.7 Hz, CH3), 1.27–1.62 (m, 18H, CH2), 1.73–1.83
(m, 2H, CH2), 3.96 (t, 2H, J = 6.58 Hz, CH2), 6.95 (d, 2H,
J = 6.88 Hz, Ar–H), 7.14 (d, 2H, J = 6.76 Hz, Ar–H), 8.36 (d, 4H,
J = 2.04 Hz, Ar–H). 13C NMR (100 MHz, CDCl3): d 14.13, 22.71,
26.05, 29.27, 29.37, 29.41, 29.60, 29.65, 29.68, 29.80, 31.94,
68.49, 115.22, 122.11, 123.70, 131.25, 135.13, 143.80, 150.86,
157.28, 163.70. MS (EI) m/z: 427.2 (M+).
2.3.2. 4-(Decyloxy)phenol (5b)
Yield: 25.54 g (34%). m.p. 80 °C. IR (KBr, cmꢀ1): 3429 (OH),
2952, 2932 and 2858 (Ali–C–H), 1517 (Ar–C–H), 1240 (C–O–C).
1H NMR (400 MHz, CDCl3): d 0.88 (t, 3H, J = 6.84 Hz, CH3), 1.27–
1.45 (m, 14H, CH2), 1.70–1.79 (m, 2H, CH2), 3.89 (t, 2H,
J = 6.71 Hz, CH2), 4.9 (s(broad), 1H, OH), 6.73–6.79 (m, 4H, Ar–H).
13C NMR (100 MHz, CDCl3): d 14.04, 22.64, 26.03, 29.19, 29.28,
29.37, 29.52, 29.55, 31.87, 68.87, 115.73, 116.01, 149.43, 153.34.
MS (EI) m/z: 250.2 (M+).
2.5. Synthesis of 4-(alkyloxy)phenyl 4-aminobenzoate (7a–c)
A mixture of 10 g of nitro compound 6a–c, 0.36 g of 10% palla-
dium carbon and 120 ml of a 1/1 (by volume) mixture of THF/eth-
anol was vigorously stirred under hydrogen pressure at room
temperature for 24 h. After filtration through Celite 540, palladium
carbon was removed. The filtrate was concentrated by rotary evo-
parator and poured into hexane to precipitate the product. The pre-
cipitate was collected by filtration, and recrystallized from acetone
at 0 °C, which was filtered and dried in vacuum. The amino prod-
ucts 7a–c were obtained as white solids.
2.3.3. 4-(Dodecyloxy)phenol (5c)
Yield: 32.58 g (34%). m.p. 78 °C. IR (KBr, cmꢀ1): 3429 (OH),
2952, 2911 and 2846 (Ali–C–H), 1517 (Ar–C–H), 1240 (C–O–C).
1H NMR (400 MHz, CDCl3): d 0.88 (t, 3H, J = 6.67 Hz, CH3), 1.26–
1.44 (m, 18H, CH2), 1.71–1.76 (m, 2H, CH2), 3.89 (t, 2H,
J = 6.58 Hz, CH2), 4.9 (s(broad), 1H, OH), 6.73–6.82 (m, 4H, Ar–H).
13C NMR (100 MHz, CDCl3): d 14.02, 22.67, 26,07, 29.22, 29.26,
29.33, 29.47, 29.53, 29.56, 31.81, 31.89, 68.86, 115.73, 116.03,
149.41, 153.37. MS (EI) m/z: 278.2 (M+).
2.5.1. 4-(Heptyloxy)phenyl 4-aminobenzoate (7a)
Yield: 8.52 g (93%). m.p. 149 °C. IR (KBr, cmꢀ1): 3409, 3340 and
3234 (NH2), 2952, 2932 and 2854 (C–H), 1701 (C@O), 1281 and
1171 (C–O). 1H NMR (400 MHz, CDCl3): d 0.89 (t, 3H, J = 6.26 Hz,
CH3), 1.31–1.43 (m, 8H, CH2), 1.72–1.75 (m, 2H, CH2), 3.89–3.93
(m, 2H, CH2), 4.16 (s(broad), 2H, NH2), 6.65 (d, 2H, J = 8.39 Hz,
Ar–H), 6.82 (s, 2H, Ar–H), 6.91 (d, 1H, J = 8.83 Hz, Ar–H), 7.07 (d,
1H, J = 8.74 Hz, Ar–H), 7.99 (d, 2H, J = 8.39 Hz, Ar–H). 13C NMR
(100 MHz, CDCl3): d 14.10, 22.62, 26.03, 29.29, 29.41, 31.80,
68.64, 113.80, 115.01, 115.38, 118.73, 122.55, 132.26, 144.50,
151.48, 153.17, 156.65, 165.65. MS (EI): m/z = 327.3 (M+).
2.4. Synthesis of 4-(alkyloxy)phenyl 4-nitrobenzoate (6a–c)
A mixture of corresponding 4-alkoxy phenol 5a–c (20 mmol), 4-
nitrobenzoic acid (5 g, 20 mmol) and 4-(dimethyl amino) pyridine
(DMAP) (0.24 g, 2 mmol) was dissolved in 25 ml of dry DMF/DCM
mixture (1:1) and stirred using mechanical stirrer at 0 °C under
N2-atmosphere. To this solution, dicyclohexyl carbodiimide (DCC)
(4.07 g, 20 mmol) dissolved in 20 ml of DCM was added dropwise
and stirred at 0 °C for 1 h and then at room temperature for 12 h.
Finally, the reaction mixture was filtered and DCM removed from
the filtrate by evaporation. The solution was then poured into
water to precipitate the product. The crude product was purified
by column chromatography (SiO2; petroleum ether/EtOAc,
97:3 v/v) to give corresponding esterified product 6a–c as a yellow
solid.
2.5.2. 4-(Decyloxy)phenyl 4-aminobenzoate (7b)
Yield: 8.32 g (90%). m.p. 145 °C. IR (KBr, cmꢀ1): 3409, 3340 and
3234 (NH2), 2952, 2920 and 2850 (C–H), 1705 (C@O), 1280 and
1171 (C–O). 1H NMR (400 MHz, CDCl3): d 0.88 (t, 3H, J = 6.25 Hz,
CH3), 1.27–1.43 (m, 14H, CH2), 1.72–1.75 (m, 2H, CH2), 3.86–3.94
(m, 2H, CH2), 4.15 (s(broad), 2H, NH2), 6.63 (d, 2H, J = 8.37 Hz,
Ar–H), 6.81 (s, 2H, Ar–H), 6.89 (d, 1H, J = 8.82 Hz, Ar–H), 7.07 (d,
1H, J = 8.74 Hz, Ar–H), 7.97 (d, 2H, J = 8.37 Hz, Ar–H). 13C NMR
(100 MHz, CDCl3): d 14.10, 22.70, 26.06, 29.30, 29.34, 29.42,
29.58, 29.61, 31.92, 68.64, 113.79, 115.00, 115.37, 118.65, 122.56,
132.25, 144.51, 151.55, 153.18, 156.66, 165.67. MS (EI) m/z: 369
(M+).
2.4.1. 4-(Heptyloxy)phenyl 4-nitrobenzoate (6a)
Yield: 5.10 g (71%). m.p. 74 °C. IR (KBr, cmꢀ1): 3107, 3079 and
3047 (NO2), 2952, 2931 and 2850 (C–H), 1741 (C@O), 1525 and
1341 (NO2), 1244 and 1191 (C–O). 1H NMR (400 MHz, CDCl3): d
0.90 (t, 3H, J = 6.70 Hz, CH3), 1.32–1.48 (m, 8H, CH2), 1.77–1.81
(m, 2H, CH2), 3.96 (t, 2H, J = 6.54 Hz, CH2), 6.94 (d, 2H,
J = 8.98 Hz, Ar–H), 7.13 (d, 2H, J = 8.97 Hz, Ar–H), 8.34 (m, 4H,
Ar–H). 13C NMR (100 MHz, CDCl3): d 14.11, 22.63, 26.01, 29.07,
29.26, 31.80, 68.45, 115.18, 122.18, 123.68, 131.24, 135.09,
143.78, 150.82, 157.26, 163.68. MS (EI) m/z: 357.4 (M+).
2.5.3. 4-(Dodecyloxy)phenyl 4-aminobenzoate (7c)
Yield: 8.46 g (91%). m.p.139 °C. IR (KBr, cmꢀ1): 3413, 3340 and
3234 (NH2), 2956, 2920 and 2850 (C–H), 1701 (C@O), 1280 and
1171 (C–O). 1H NMR (400 MHz, CDCl3): d 0.89 (t, 3H, J = 6.25 Hz,
CH3), 1.26–1.45 (m, 18H, CH2), 1.72–1.77 (m, 2H, CH2), 3.87–3.95

132
N. Senthilkumar et al. / Inorganica Chimica Acta 397 (2013) 129–139
(m, 2H, CH2), 4.16 (s(broad), 2H, NH2), 6.65 (d, 2H, J = 8.58 Hz, Ar–
H), 6.81 (s, 2H, Ar–H), 6.90 (d, 1H, J = 8.92 Hz, Ar–H), 7.07 (d, 1H,
J = 8.91 Hz, Ar–H), 7.98 (d, 2H, J = 8.49 Hz, Ar–H). 13C NMR
(100 MHz, CDCl3): d 14.14, 22.70, 26.05, 29.29, 29.37, 29.42,
29.60, 29.62, 29.65, 29.68, 31.93, 68.65, 113.81, 115.01, 115.37,
118.74, 122.55, 132.26, 144.49, 151.48, 153.18, 156.66, 165.65.
MS (EI) m/z: 397.1 (M+).
C44H63NO5 (685.99): C, 77.03; H, 9.28; N, 2.04. Found: C, 77.31;
H, 9.07; N, 2.11%.
2.7. Synthesis of ligands (8d–h)
A mixture of corresponding aldehyde 3d–f (10 mmol) and
amine 7a–c (10 mmol) in dry ethanol (120 ml) was refluxed for
6 h. The product precipitated out as a yellow solid when cooled
to room temperature. The precipitate was filtered, washed with
methanol and dried under vacuum. The solid product was recrys-
tallized from chloroform.
2.6. Synthesis of ligands (8a–c)
A mixture of corresponding aldehyde 3a–c (10 mmol), amine 7–
c (10 mmol) and para toluene sulfonic acid in dry ethanol (120 mL)
was refluxed for 5 h. The product precipitated out as a yellow solid
when cooled to room temperature. The precipitate was filtered,
washed with methanol and dried under vacuum. The solid product
was recrystallized from chloroform to afford pure yellow solid.
2.7.1. (E)-4-(heptyloxy)phenyl-4-(4-(6-hydroxyhexyloxy)-2-
hydroxybenzylideneamino)benzoate (8d)
Yield: 4.22 g (77%). m.p. 129 °C. IR (KBr, cmꢀ1): 3417 (aliphatic
OH), 3285 (phenolic OH), 2952, 2936 and 2858 (C–H), 1733 (C@O),
1631 (C@N), 1285 and 1195 (C–O). 1H NMR (400 MHz, CDCl3): d
0.90 (t, 3H, J = 6.64 Hz, CH3), 1.26 (s(broad), 1H, OH), 1.32–1.62
(m, 14H, CH2), 1.77–1.83 (m, 4H, CH2), 3.67 (t, 2H, J = 6.38 Hz,
CH2), 3.96 (t, 2H, J = 6.52 Hz, CH2), 4.02 (t, 2H, J = 6.46 Hz, CH2),
6.51 (s, 2H, Ar–H), 6.93 (d, 2H, J = 8.96 Hz, Ar–H), 7.12 (d, 2H,
J = 8.84 Hz, Ar–H), 7.29–7.35 (m, 3H, Ar–H), 8.23 (d, 2H,
J = 8.44 Hz, Ar–H), 8.57 (s, 1H, imine C–H), 13.39 (s, 1H, Ar–OH).
13C NMR (100 MHz, CDCl3, 50 °C): d 11.80, 20.34, 23.24, 23.56,
23.73, 26.75, 26.79, 27.01, 29.52, 30.38, 60.61, 65.90, 66.18,
99.29, 105.78, 110.55, 112.85, 118.88, 120.09, 124.97, 126.03,
129.35, 131.72, 141.97, 150.83, 154.65, 160.72, 161.82, 161.90.
MS (EI) m/z: 548.8 (M+). Anal. Calc. for C33H41NO6 (547.69): C,
72.36; H, 7.56; N, 2.56. Found: C, 72.72; H, 7.93; N, 2.44%.
2.6.1. (E)-4-(heptyloxy)phenyl 4-(4-(hexyloxy)-2-
hydroxybenzylideneamino)benzoate (8a)
Yield: 4.14 g (78%). m.p. 96 °C. IR (KBr, cmꢀ1): 3441 (OH), 2956,
2919 and 2854 (C–H), 1741 (C@O), 1631 (C@N), 1284 and 1195 (C–
O). 1H NMR (400 MHz, CDCl3): d 0.90 (t, 6H, J = 6.34 Hz, CH3), 1.25–
1.46 (m, 14H, CH2), 1.77–1.82 (m, 4H, CH2), 3.95 (t, 2H, J = 6.58 Hz,
CH2), 4.00 (t, 2H, J = 6.6 Hz, CH2), 6.50–6.52 (m, 2H, Ar–H), 6.93 (d,
2H, J = 8.96 Hz, Ar–H), 7.12 (d, 2H, J = 8.96 Hz, Ar–H), 7.25–7.34 (m,
3H, Ar–H), 8.22 (d, 2H, J = 8.52 Hz, Ar–H), 8.55 (s, 1H, imine C–H),
13.39 (s, 1H, Ar–OH). 13C NMR (100 MHz, CDCl3, 50 °C): d 13.34,
13.41, 21.93, 21.97, 25.02, 25.38, 28.42, 28.68, 29.06, 30.90,
31.16, 67.76, 67.89, 101.02, 107.44, 112.23, 114.55, 120.51,
121.88, 126.67, 130.97, 133.36, 143.71, 152.53, 156.33, 162.36,
163.52, 163.69, 164.43. MS (EI) m/z: 530.7 (M+). Anal. Calc. for
2.7.2. (E)-4-(decyloxy)phenyl 4-(4-(6-hydroxyhexyloxy)-2-
hydroxybenzylideneamino)benzoate (8e)
C33H41NO5 (531.69): C, 74.54; H, 7.79; N, 2.63. Found: C, 74.72;
H, 7.83; N, 2.49%.
Yield: 4.36 g (74%). m.p. 129 °C. IR (KBr, cmꢀ1): 3384 (aliphatic
OH), 3283 (phenolic OH), 2956, 2916 and 2850 (C–H), 1733 (C@O),
1627 (C@N), 1281 and 1195 (C–O). 1H NMR (400 MHz, CDCl3): d
0.89 (t, 3H, J = 6.80 Hz, CH3), 1.28 (s(broad), 1H, OH), 1.31–1.62
(m, 20H, CH2), 1.79–1.83 (m, 4H, CH2), 3.68 (t, 2H, J = 6.38 Hz,
CH2), 3.96 (t, 2H, J = 6.54 Hz, CH2), 4.03 (t, 2H, J = 6.48 Hz, CH2),
6.51–6.53 (m, 2H, Ar–H), 6.93 (d, 2H, J = 9.04 Hz, Ar–H), 7.12 (d,
2H, J = 9.04 Hz, Ar–H), 7.26–7.35 (m, 3H, Ar–H), 8.23 (d, 2H,
J = 8.56 Hz, Ar–H), 8.57 (s, 1H, imine C–H), 13.45 (s, 1H, Ar–OH).
13C NMR (100 MHz, CDCl3, 50 °C): d 13.99, 22.64, 25.57, 25.62,
25.88, 26.09, 26.17, 29.09, 29.29, 29.40, 29.58, 31.90, 32.74,
62.85, 68.32, 68.37, 101.91, 108.07, 113.10, 115.37, 121.14,
122.36, 127.55, 131.61, 132.57, 134.03, 144.59, 153.29, 157.10,
162.99, 164.37, 164.99. MS (EI) m/z: 589 (M+). Anal. Calc. for
2.6.2. (E)-4-(decyloxy)phenyl 4-(4-(decyloxy)-2-
hydroxybenzylideneamino)benzoate (8b)
Yield: 4.98 g (79%). m.p. 95 °C. IR (KBr, cmꢀ1): 3441 (OH), 2956,
2919 and 2850 (C–H), 1737 (C@O), 1631 (C@N), 1281 and 1199 (C–
O). 1H NMR (400 MHz, CDCl3): d 0.81 (t, 6H, J = 6.34 Hz, CH3), 1.20–
1.40 (m, 28H, CH2), 1.67–1.74 (m, 4H, CH2), 3.86–3.94 (m, 4H, CH2),
6.43 (d, 2H, J = 6.56 Hz, Ar–H), 6.85 (d, 2H, J = 9.04 Hz, Ar–H), 7.04
(d, 2H, J = 8.00 Hz, Ar–H), 7.17–7.26 (m, 3H, Ar–H), 8.14 (d, 2H,
J = 8.40 Hz, Ar–H), 8.47 (s, 1H, imine C–H), 13.31 (s, 1H, Ar–OH).
13C NMR (100 MHz, CDCl3, 50 °C): d 14.06, 14.09, 22.67, 22.69,
25.63, 25.98, 26.05, 26.31, 29.06, 29.11, 29.19, 29.31, 29.35,
29.41, 29.56, 29.58, 31.56, 31.89, 68.46, 68.68, 101.59, 108.08,
115.12, 115.41, 121.14, 122.36, 127.23, 131.60, 133.99, 144.27,
153.11, 153.22, 156.93, 162.98, 164.27, 165.08. MS (EI) m/z:
629.5 (M+). Anal. Calc. for C40H55NO5 (629.88): C, 76.27; H, 8.82;
N, 2.22. Found: C, 75.84; H, 8.96; N, 2.31%.
C36H47NO6 (589.78): C, 73.31; H, 8.05; N, 2.38. Found: C, 72.96;
H, 8.01; N, 2.41%.
2.7.3. (E)-4-(dodecyloxy)phenyl 4-(4-(6-hydroxyhexyloxy)-2-
hydroxybenzylideneamino)benzoate (8f)
2.6.3. (E)-4-(dodecyloxy)phenyl 4-(4-(dodecyloxy)-2-
hydroxybenzylideneamino)benzoate (8c)
Yield: 4.51 g (73%). m.p. 128 °C. IR (KBr, cmꢀ1): 3417 (aliphatic
OH), 3267 (phenolic OH), 2956, 2920 and 2850 (C–H), 1733 (C@O),
1627 (C@N), 1281 and 1195 (C–O). 1H NMR (400 MHz, CDCl3): d
0.88 (t, 3H, J = 6.52 Hz, CH3), 1.26 (s(broad), 1H, OH), 1.27–1.62
(m, 24H, CH2), 1.79–1.83 (m, 4H, CH2), 3.67 (t, 2H, J = 6.34 Hz,
CH2), 3.96 (t, 2H, J = 6.48 Hz, CH2), 4.03 (t, 2H, J = 6.44 Hz, CH2),
6.50–6.52 (m, 2H, Ar–H), 6.93 (d, 2H, J = 8.96 Hz, Ar–H), 7.12 (d,
2H, J = 8.92 Hz, Ar–H), 7.29–7.35 (m, 3H, Ar–H), 8.23 (d, 2H,
J = 8.32 Hz, Ar–H), 8.57 (s, 1H, imine C–H), 13.39 (s, 1H, Ar–OH).
13C NMR (100 MHz, CDCl3, 50 °C): d 14.06, 22.71, 25.61, 25.73,
25.93, 26.14, 29.13, 29.37, 29.42, 29.45, 29.65, 29.68, 29.81,
29.97, 32.77, 62.89, 68.34, 68.73, 101.91, 108.12, 113.15, 115.38,
121.19, 122.40, 127.55, 131.66, 132.63, 134.08, 144.60, 153.29,
157.12, 163.02, 164.39, 165.06. MS (EI) m/z: 617.4 (M+). Anal. Calc.
Yield: 5.10 g (74%). m.p. 94 °C. IR (KBr, cmꢀ1): 3417 (OH), 2956,
2915 and 2846 (C–H), 1737 (C@O), 1623 (C@N), 1281 and 1195 (C–
O). 1H NMR (400 MHz, CDCl3): d 0.88 (t, 6H, J = 6.48 Hz, CH3), 1.27–
1.56 (m, 36H, CH2), 1.76–1.84 (m, 4H, CH2), 3.94 (t, 2H, J = 6.28 Hz,
CH2), 4.01 (t, 2H J = 6.42 Hz, CH2), 6.50 (m, 2H, Ar–H), 6.93 (d, 2H,
J = 8.68 Hz, Ar–H), 7.12 (d, 2H, J = 8.56 Hz, Ar–H), 7.28–7.34 (m, 3H,
Ar–H), 8.23 (d, 2H, J = 8.08 Hz, Ar–H), 8.56 (s, 1H, imine C–H), 13.38
(s, 1H, Ar–OH). 13C NMR (100 MHz, CDCl3, 50 °C): d 14.05, 14.08,
22.63, 22.68, 25.59, 25.89, 26.11, 26.23, 26.29, 26.34, 26.41,
29.02, 29.14, 29.20, 29.37, 29.44, 29.51, 29.59, 29.63, 29.72,
31.59, 31.96, 68.52, 68.72, 101.66, 108.11, 115.17, 115.47, 131.16,
122.41, 127.33, 131.56, 133.87, 144.31, 153.07, 153.27, 156.95,
162.96, 164.30, 164.98. MS (EI) m/z: 685 (M+). Anal. Calc. for

N. Senthilkumar et al. / Inorganica Chimica Acta 397 (2013) 129–139
133
for C38H51NO6 (617.83): C, 73.87; H, 8.34; N, 2.27. Found: C, 73.98;
2.8.3. Bis[(E)-4-(dodecyloxy)phenyl 4-(4-(dodecyloxy)-2-
H, 8.46; N, 2.24%.
hydroxybenzylideneamino)benzoate]copper(II) (9c)
Yield: 1.12 g (78%). a brown color solid. m.p. 209 °C. IR (KBr,
cmꢀ1): 2957, 2919 and 2850 (C–H), 1725 (C@O), 1611 (C@N),
1248 and 1191 (C–O). MS (FAB) m/z: 1433 (M+). Anal. Calc. for
2.7.4. (E)-4-(dodecyloxy)phenyl 4-(4-(8-hydroxyoctyloxy)-2-
hydroxybenzylideneamino)benzoate (8g)
C88H124N2O10Cu (1433.51): Cu, 4.43; C, 73.73; H, 8.74; N, 1.95.
Yield: 4.78 g (74%). m.p. 128 °C. IR (KBr, cmꢀ1): 3419 (aliphatic
OH), 3281 (phenolic OH), 2956, 2936 and 2855 (C–H), 1733 (C@O),
1627 (C@N), 1281 and 1195 (C–O). 1H NMR (400 MHz, CDCl3): d
0.88 (t, 3H, J = 6.58 Hz, CH3), 1.25 (s(broad), 1H, OH), 1.26–1.58
(m, 28H, CH2), 1.79–1.82 (m, 4H, CH2), 3.64 (t, 2H, J = 6.6 Hz,
CH2), 3.96 (t, 2H, J = 6.52 Hz, CH2), 4.02 (t, 2H, J = 6.5 Hz, CH2),
6.50–6.52 (m, 2H, Ar–H), 6.93 (d, 2H, J = 9.04 Hz, Ar–H), 7.12 (d,
2H, J = 9.03 Hz, Ar–H), 7.29–7.35 (m, 3H, Ar–H), 8.23 (d, 2H,
J = 8.48 Hz, Ar–H), 8.57 (s, 1H, imine C–H), 13.41 (s, 1H, Ar–OH).
13C NMR (100 MHz, CDCl3, 50 °C): d 14.17, 22.84, 25.63, 25.73,
25.89, 26.12, 26.16, 29.24, 29.42, 29.50, 29.64, 29.68, 29.81,
29.95, 31.85, 32.10, 33.02, 63.20, 68.59, 68.86, 101.87, 108.28,
113.07, 115.51, 121.32, 122.52, 127.68, 131.80, 132.63, 134.19,
144.71, 153.47, 157.25, 163.17, 164.41, 165.12. MS (EI) m/z:
645.4 (M+). Anal. Calc. for C40H55NO6 (645.88): C, 74.38; H, 8.60;
N, 2.17. Found: C, 74.12; H, 8.73; N, 2.19%.
Found: Cu, 4.27; C, 73.56; H, 8.92; N, 1.97%.
2.9. Synthesis of metallomesogenic diols (9d–h)
The corresponding ligand 8d–h (2 mmol) and copper acetate
(1 mmol) were taken in methanol (40 ml) and refluxed for 5 h in
an oil bath. The solid formed was filtered, washed with methanol
and dried under vacuum. Recrystallization of the product in chlo-
roform gave the copper complexes 9d–h at 79–83% yield.
2.9.1. Bis[(E)-4-(heptyloxy)phenyl-4-(4-(6-hydroxyhexyloxy)-2-
hydroxybenzylideneamino)benzoate]copper(II) (9d)
Yield: 0.96 g (83%). a light brown solid. m.p. 209 °C. IR (KBr,
cmꢀ1): 3368 (OH), 2936 and 2858 (C–H), 1725 (C@O), 1611
(C@N), 1252 and 1187 (C–O). MS (FAB) m/z: 1157 (M+). Anal. Calc.
for C66H80N2O12Cu (1156.91): Cu, 5.49; C, 68.52; H, 6.98; N, 2.42.
Found: Cu, 5.41; C, 68.66; H, 7.03; N, 2.39%.
2.7.5. (E)-4-(dodecyloxy)phenyl 4-(4-(10-hydroxydecyloxy)-2-
hydroxybenzylideneamino)benzoate (8h)
2.9.2. Bis[(E)-4-(decyloxy)phenyl 4-(4-(6-hydroxyhexyloxy)-2-
hydroxybenzylideneamino)benzoate]copper(II) (9e)
Yield: 4.85 g (72%). m.p. 128 °C. IR (KBr, cmꢀ1): 3433 (aliphatic
OH), 3287 (phenolic OH), 2956, 2920 and 2850 (C–H), 1737 (C@O),
1631 (C@N), 1281 and 1199 (C–O). 1H NMR (400 MHz, CDCl3): d
0.88 (t, 3H, J = 6.56 Hz, CH3), 1.26 (s(broad), 1H, OH), 1.27–1.61
(m, 32H, CH2), 1.79–1.83 (m, 4H, CH2), 3.66 (t, 2H, J = 6.34 Hz,
CH2), 3.96 (t, 2H, J = 6.48 Hz, CH2), 4.03 (t, 2H, J = 6.5 Hz, CH2),
6.50–6.52 (m, 2H, Ar–H), 6.93 (d, 2H, J = 8.92 Hz, Ar–H), 7.12 (d,
2H, J = 8.92 Hz, Ar–H), 7.29–7.35 (m, 3H, Ar–H), 8.23 (d, 2H,
J = 8.48 Hz, Ar–H), 8.57 (s, 1H, imine C–H), 13.37 (s, 1H, Ar–OH).
13C NMR (100 MHz, CDCl3, 50 °C): d 14.07, 22.74, 25.61, 25.72,
25.78, 26.07, 26.16, 26.37, 29.34, 29.42, 29.48, 29.54, 29.67,
29.76, 29.83, 29.97, 31.83, 32.14, 33.07, 62.98, 68.39, 68.76,
101.90, 108.12, 113.13, 115.46, 121.24, 122.43, 127.39, 131.77,
132.56, 134.22, 144.69, 153.31, 157.16, 163.12, 164.39, 165.18.
MS (EI) m/z: 674 (M+). Anal. Calc. for C42H59NO6 (673.94): C,
74.85; H, 8.84; N, 2.08. Found: C, 74.69; H, 8.97; N, 2.03%.
Yield: 0.98 g (79%). a light brown solid. m.p. 186 °C. IR (KBr,
cmꢀ1): 3441 (OH), 2924 and 2854 (C–H), 1725 (C@O), 1607
(C@N), 1252 and 1191 (C–O). MS (FAB) m/z: 1240 (M+). Anal. Calc.
for C72H92N2O12Cu (1241.09): Cu, 5.12; C, 69.67; H, 7.49; N, 2.26.
Found: Cu, 4.96; C, 69.81; H, 7.37; N, 2.22%.
2.9.3. Bis[(E)-4-(dodecyloxy)phenyl 4-(4-(6-hydroxyhexyloxy)-2-
hydroxybenzylideneamino)benzoate]copper(II) (9f)
Yield: 1.06 g (82%). a light brown solid. m.p. 182 °C. IR (KBr,
cmꢀ1): 3441 (OH), 2920 and 2850 (C–H), 1725 (C@O), 1611
(C@N), 1252 and 1199 (C–O). MS (FAB) m/z: 1353 (M+). Anal. Calc.
for C76H100N2O12Cu (1297.19): Cu, 4.90; C, 70.36; H, 7.79; N, 2.16.
Found: Cu, 4.66; C, 70.12; H, 7.86; N, 2.13%.
2.9.4. Bis[(E)-4-(dodecyloxy)phenyl 4-(4-(8-hydroxyoctyloxy)-2-
hydroxybenzylideneamino)benzoate]copper(II) (9g)
2.8. Synthesis of model metallomesogens (9a–c)
Yield: 1.12 g (83%). A light brown solid. m.p. 191 °C. IR (KBr,
cmꢀ1): 3443 (OH), 2920 and 2855 (C–H), 1725 (C@O), 1607
(C@N), 1252 and 1190 (C–O). MS (FAB) m/z: 1295 (M+). Anal. Calc.
for C80H108N2O12Cu (1353.44): Cu, 4.70; C, 70.99; H, 8.06; N, 2.07.
Found: Cu, 4.56; C, 71.16; H, 8.13; N, 2.11.
The corresponding ligand 8a–c (2 mmol) and copper acetate
(1 mmol) were taken in methanol (40 ml) and refluxed for 5 h in
an oil bath. The solid formed was filtered, washed with methanol
and dried under vacuum. Recrystallization of the product in chlo-
roform gave the copper complexes 9a–c at 78–83% yield.
2.9.5. Bis[(E)-4-(dodecyloxy)phenyl 4-(4-(10-hydroxydecyloxy)-2-
hydroxybenzylideneamino)benzoate]copper(II) (9h)
2.8.1. Bis[(E)-4-(heptyloxy)phenyl 4-(4-(hexyloxy)-2-
hydroxybenzylideneamino)benzoate]copper(II) (9a)
Yield: 1.14 g (81%). a light brown solid. m.p. 187 °C. IR (KBr,
cmꢀ1): 3441 (OH), 2919 and 2850 (C–H), 1725 (C@O), 1607
(C@N), 1252 and 1191 (C–O). MS (FAB) m/z: 1407 (M+). Anal. Calc.
for C84H116N2O12Cu (1409.56): Cu, 4.51; C, 71.57; H, 8.31; N, 1.99.
Found: Cu, 4.33; C, 71.46; H, 8.57; N, 2.03%.
Yield: 0.92 g (82%). a maroon color solid. m.p. 234 °C. IR (KBr,
cmꢀ1): 2952, 2932 and 2854 (C–H), 1725 (C@O), 1607 (C@N),
1248, 1191 (C–O). MS (FAB) m/z: 1124 (M+). Anal. Calc. for C66H80
N2O10Cu (1124.91): Cu, 5.65; C, 70.46; H, 7.18; N, 2.49. Found: Cu,
5.62; C, 70.41; H, 7.31; N, 2.48%.
3. Results and discussion
2.8.2. Bis[(E)-4-(decyloxy)phenyl 4-(4-(decyloxy)-2-
3.1. Synthesis and characterization
hydroxybenzylideneamino)benzoate]copper(II) (9b)
Yield: 1.10 g (83%). a brown color solid. m.p. 226 °C. IR (KBr,
cmꢀ1): 2952, 2919 and 2850 (C–H), 1725 (C@O), 1607 (C@N),
1248 and 1191 (C-O). MS (FAB) m/z: 1320 (M+). Anal. Calc. for
With a view to understand the mesophase characteristics of
metallomesogenic diols, model compounds with terminal methyl
groups (i.e., without terminal hydroxy) were synthesized. The
model metallomesogenic compounds were synthesized from tria-
romatic ring core linked through ester, azomethine and alkoxy
C80H108N2O10Cu (1321.29): Cu, 4.81; C, 72.72; H, 8.26; N, 2.12.
Found: Cu, 4.69; C, 72.58; H, 8.33; N, 2.06%.

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N. Senthilkumar et al. / Inorganica Chimica Acta 397 (2013) 129–139
OH
OH
O
OH
NaOH
+
Br
CH3
(
)
m-1
n-Butanol
OH
OH
4
CH3
(
)
1
m-1
5a-c
POCl3
DMF
DCC/DMAP
O2N
COOH
CHO
DCM:DMF
OH
+
Br-(CH2)n-1CH3
CH3
O
O2N
COO
6a-c
(
)
m-1
OH
2
NaOH
n-Butanol
Pd/C, H2
THF:EtOH
CHO
OH
CH3
O
H2N
COO
+
(
)
m-1
7a-c
CH3
O
( )
n-1
EtOH
Reflux
PTSA
3a-c
H
H3C
O
n-1
C
(
)
CH3
N
O
COO
(
)
m-1
OH
8a-c
Cu(OAc)2.H2O
MeOH
Reflux
H
C
H3C
O
(
)
n-1
N
COO
CH3
O
(
)
m-1
O
Cu2+
O
OOC
N
O
H3C
9a: n=6, m=7
9b: n=10, m=10
9c: n=12, m=12
(
)
m-1
C
H
O
CH3
(
)
n-1
n= 6, 10, 12
m= 7, 10, 12
9a-c
Scheme 1. Synthesis of model metallomesogens.
groups of different chain length. Scheme 1 shows the overall
synthetic route for the preparation of model metallomesogens.
2,4-Dihydroxy benzaldehyde was synthesized using resorcinol 1
based on Vilsmeier-Haack reaction [26]. The O-alkylation of 2,4-
dihydroxy benzaldehyde 2 and hydroquinone 4 were carried out
with various bromo alkanes (n-bromoheptane, n-bromodecane,
n-bromododecane) in the presence of sodium hydroxide as de-
scribed in the experimental section. The alkylated products 3a–c
were obtained as colorless liquid, after purification by column
chromatography. The alkylated products 5a–c were obtained as
pale yellow solids, which were treated with 4-nitro benzoic acid
in the presence of DCC/DMAP. The resulting esters (yellow solids
6a–c) were selectively reduced to amines in the presence of Pd/C
as a catalyst in THF/ethanol mixture. The amines 7a–c were further
treated with substituted 2,4-dihydroxy benzaldehyde 3a–c in the
presence of catalytic amount of para toluene sulfonic acid to get
the Schiff base ligand 8a–c as yellow solid in high yield. All the li-
gands and intermediate products were well characterized with FT-
IR, 1H & 13C NMR, EI-MS and elemental analysis. These three ring
containing mesogenic ligands were further reacted with copper(II)
acetate and afforded model metallomesogenic compounds 9a–c as
brown solid with high yield.
The core metallomesogen was also constructed from three phe-
nyl rings, which were linked through ester and azomethine groups
at 1,4-positions. The terminal groups were designed in such a way
that one end is functionalized with alkoxy groups, while the other

N. Senthilkumar et al. / Inorganica Chimica Acta 397 (2013) 129–139
135
CHO
CHO
OH
OH
NaOH
+
Br-(CH2)xOH
CH3
+
O
H2N
COO
(
)
n-Butanol
m-1
7a-c
OH
O
OH
( )
x
EtOH
2
Reflux
3d-f
H
O
C
HO
(
)
CH3
N
O
COO
x
(
)
m-1
OH
8d-h
Cu(OAc)2.H2O
MeOH
Reflux
H
C
HO
O
(
)
x
N
COO
CH3
m-1
O
(
O
N
Cu2+
O
OOC
O
H3C
9d: x=6, m=7
9e: x=6, m=10
9f: x=6, m=12
9g: x=8, m=12
9h: x=10, m=12
(
)
m-1
C
H
O
OH
(
)
x
x= 6, 8, 10
9d-h
m= 7, 10, 12
Scheme 2. Synthesis of metallomesogenic diols.
end was functionalized with hydroxyalkoxy group as shown in
Scheme 2. Based on the mesophase characteristics of the model
compounds, the terminal hydroxy groups were selectively intro-
duced [27]. The O-alkylation of 2,4-dihydroxy benzaldehyde was
achieved by treating with bromoalkanols (6-bromohexanol, 8-
bromooctanol, 10-bromodecanol) in the presence of sodium
hydroxide. The relevant bromoalkanols were also prepared from
corresponding alkyl diols, followed by purified with column chro-
matography and were well characterized according to the litera-
ture procedure [28]. The alkylated products 3d–f were obtained
as white solids, after purification by column chromatography.
These molecules subsequently react with amino compounds 7a–c
to afford Schiff base ligand 8d–h as yellow solids in high yield.
The synthesis of metallomesogenic diols was achieved by complex-
ing the hydroxy terminal three ring containing mesogenic ligands.
These mesogenic ligands, by virtue of the presence of hydroxy
group adjacent to imine link act as coordinate centers and form
complexes with metal ions. These copper(II) complexes were con-
firmed by FT-IR, UV–Vis, EPR, AAS, VSM, FAB-mass and elemental
analysis. The infrared spectrum of one of the metal complexes
showed bands at 3368 cmꢀ1 due to –OH stretching (terminal hy-
droxyl), –C–H symmetric and asymmetric stretching at 2858 and
2936 cmꢀ1, ester carbonyl (–C@O) stretching at 1725 cmꢀ1, –C@N
stretching at 1611 cmꢀ1 and the aryl–alkyl ether and ester –C–
O– stretching at 1252 and 1187 cmꢀ1, respectively.
Fig. 1. Electronic spectra of metallomesogenic diols, (a) Cu6OH7CH3 (9d); (b)
Cu6OH10CH3 (9e); (c) Cu6OH12CH3 (9f).
observed in the earlier studies of metallomesogens [29]. A moder-
ate intense band observed at 391 nm is due to ligand to metal
charge transfer transition and the strong band observed around
307 nm is due to intra-ligand charge transfer transition (Table 1).
The low temperature solution state X-band EPR spectra of the cop-
per(II) complexes (9e–g) were recorded in CHCl3 (Fig. 3). The spec-
tra of the complexes showed four lines due to hyperfine splitting
with nuclear hyperfine spin 3/2 [31]. For the complexes, gll values
were observed in the range 2.24–2.25, g\ values were in the range
2.06–2.07, and All values were observed at 160 and 161 (G) (Ta-
ble 1). The relation gll > g\ was typical of Cu(II) having one un-
paired electron in a dx2ꢀy2 orbital [32,33]. The magnetic moment
studies of the copper(II) complexes were carried out at room
The metallomesogenic complexes were well soluble in CHCl3,
THF and DMF. The electronic spectra of the complexes in CHCl3
showed an intense absorption at 307, 391 and 678 nm (Fig. 1). Diaz
et al. [29] also observed similar features with copper(II) complexes
of mesogens. The appearance of band at 678 nm (kmax) was attrib-
uted to square pyramidal geometry due to the fifth coordination
site [30] from the neighboring carbonyl oxygen group with weak
inter-axial coordination with copper center as shown in Fig. 2. This
band was also assigned to d–d transitions of the copper(II) ion as

136
N. Senthilkumar et al. / Inorganica Chimica Acta 397 (2013) 129–139
Fig. 2. Ball-and-stick representation showing weak axial coordination (dotted line) of a carbonyl oxygen to the neighboring copper center.
Table 1
Spectral and magnetic data of metallomesogens.
S. No.
Metallomesogens
UV–Vis (wavelength, nm)
EPR
Magnetic moment (meff) B.M.
d–d
CT
gll
g\
All
9a
9b
9c
9d
9e
9f
Cu6CH37CH3
Cu10CH310CH3
Cu12CH312CH3
Cu6OH7CH3
Cu6OH10CH3
Cu6OH12CH3
Cu8OH12CH3
Cu10OH12CH3
677
677
677
678
678
678
678
677
369, 308
371, 309
369, 311
391, 307
379, 311
378, 308
389, 312
387, 308
2.24
2.25
2.21
2.24
2.25
2.24
2.25
2.25
2.07
2.08
2.08
2.06
2.06
2.07
2.07
2.06
161
161
160
160
160
161
160
161
1.71
1.71
1.71
1.71
1.71
1.71
1.72
1.71
9g
9h
temperature (25 °C). The copper(II) complexes showed leff value of
1.71 B.M., which indicates that Cu(II) complexes are paramagnetic;
and the lower magnetic moment values confirming the square
pyramidal geometry of these systems [34].
The positive ion FAB mass spectral analysis taken for all the cop-
per complexes showed the molecular ion peaks corresponding to
the respective molecular weights. All the metal complexes were
analyzed for metal and elemental composition. The metal percent-
ages were determined by atomic absorption spectroscopy. The
experimentally found metal content and other elemental composi-
tions were in good agreement with theoretical values and con-
firmed the structures of the model and dihydroxy copper(II)
complexes 9a–h.
The thermal stability of the metallomesogenic compounds
was studied by TGA (Fig. 4) [35]. The initial decomposition temper-
atures (IDT) (10% weight loss) were found in the range 386–453 °C
and the values substantiate the stability of the model compounds.
Increase in terminal alkyl chain length resulted in reduction of
thermal stability 453 > 406 > 386 °C and is due to higher flexibility
in the system. The residual weight of the model metallomesogens
b
a
c
2600
2800
3000
3200
3400
3600
Gauss
Fig. 3. EPR spectra of metallomesogenic diols, (a) Cu6OH10CH3 (9e); (b)
Cu6OH12CH3 (9f); (c) Cu8OH12CH3 (9g).

N. Senthilkumar et al. / Inorganica Chimica Acta 397 (2013) 129–139
137
as against three with other compounds. The compound 9a showed
SmA phase while heating the sample under microscope and under-
went decomposition before clearing. This is attributed to relatively
lower carbon chain length in the terminal alkoxy units (n = 6;
m = 7). The TC–SmA transition was noted at 233.9 °C while apparent
clearing was not seen because of decomposition. When the termi-
nal alkyl chain length was increased on both sides (n = 10; m = 10),
SmA phase was noticed with the formation of batonnets initially
and focal conic fan texture while cooling the isotropic liquid as
shown in Fig. 5. The DSC also showed two transitions at 225.5 °C,
272.4 °C which was assigned to TC–SmA and TSmA–I phases. The com-
pound 9c consists of 12 carbons each at the terminal positions and
showed SmC phase in addition to SmA compared to its homologue
9b. The HOPM photographs clearly show the appearance of baton-
nets and focal-conic fan texture while cooling the isotropic liquid
initially, and upon further cooling transformation to SmC was
noted. In this case, the SmC was composed of coexistence of schlie-
ren and broken-focal conic domains. The transition temperatures
and their associated enthalpy changes were listed in Table 2.
The metallomesogenic diols (9d–h) consist of terminal hydroxy
groups in contrast to the model metallomesogens. The compounds
9d–h vary in terminal chain length (x, m); for instance, in 9d–f the
terminal hydroxy chain was same (C6) while in others terminal al-
kyl chain was varied between 7–12 carbons. In the case of 9 g and
9 h, octyl and decyl chains for hydroxy terminal and dodecyl for
other terminal were introduced. The compound 9d showed polyg-
onal texture typical of smectic A phase. The transition tempera-
tures as found from DSC are TC–SmA 209.2 °C and TSmA–I 247.9 °C
and the change in enthalpy associated with these transitions were
45.09 and 7.54 kJ/mol respectively. Both 9e and 9f also showed
polygonal texture characteristic of smectic A phase as shown in
Fig. 6. The transitions temperatures were 185.7 °C and 251 °C for
9e and 182.3 °C and 255.4 °C for 9f, respectively. For 9 g also smec-
tic A phase was seen and the compound showed batonnets while
cooling the isotropic liquid and formation of focal conic fan texture
of smectic A is evident on further cooling. The TC–SmA was 191.1 °C
and TSmA–I was 244.3 °C and the transitional enthalpy was 45.22
and 13.02 kJ/mol respectively. The HOPM photographs too indicate
the appearance of smectic A phase. In this case also batonnets and
focal conic fan textures were clearly seen upon cooling the sample.
Table 2 lists the transition temperatures, phase stability, transition
enthalpy values of all the compounds (9d–h).
Fig. 4. TGA thermograms of model metallomesogens (a) Cu6CH37CH3 (9a); (b)
Cu10CH310CH3 (9b); (c) Cu12CH312CH3 (9c).
obtained at 650 °C is 61.22–85.74%, and this confirms that the met-
allomesogenic compounds show higher thermal stability.
3.2. Mesomorphic properties
The liquid crystalline properties of model metallomesogens,
terminal hydroxy metallomesogens have been investigated by
hot stage optical polarizing microscope (HOPM) and differential
scanning calorimetry (DSC). The HOPM was used to observe the
characteristic textures for identification of phase while DSC was
employed for confirming the phase observed in the microscope
by determining the transition enthalpy values. Thin samples of
the compounds sandwiched between cover slips were placed un-
der microscope and heated in a programmed manner. In this work,
core is designed to have three phenyl rings linked through ester
and azomethine groups at 1,4-positions while the terminal groups
are alkoxy groups. The length of the terminal alkoxy (n, m) units
was varied with a view to study their role on mesophase transition
temperatures.
The compounds 9a–c were classified as model metallomeso-
gens. All consist of three ring based core with ester and azomethine
linking units with varying terminal alkoxy chain length and were
coordinated with copper(II). Their structural similarity with the
metallomesogenic diols make them as models. In contrast to the
compounds described in the preceding section, the breadth of
these model mesogens is high due to the incorporation of metal
ion. In addition, the overall molecule consists of six phenyl rings
The model metallomesogens (9a–c; Table 2) show high melting
and clearing temperatures. For example, the compound 9a under-
goes decomposition before clearing (Fig. 7). Such an increase in
thermal stabilities is attributed to presence of metal ion (cop-
per(II)) which enhances the overall molecular polarisability. Metals
being electropositive in contrast to mesogenic ligands, their
Fig. 5. The HOPM photographs of model metallomesogen, 9b (while cooling) showing: (a) battonnets texture of smectic A phase at 250.1 °C; (b) focal conic fan like texture of
smectic A phase at 221 °C.

138
N. Senthilkumar et al. / Inorganica Chimica Acta 397 (2013) 129–139
Table 2
Synthesis and thermal properties of metallomesogens.
S. No.
Metallomesogens
n
m
DSC
Microscope (°C)
Transition
T (°C)
D
H (kJ molꢀ1
)
D
T (°C)
Tm
Ti
DT
Model metallomesogens
9a
9b
9c
Cu6CH37CH3
6
7
Cr ? SmA
SmA ? I
Cr ? SmA
SmA ? I
Cr ? SmC
SmC ? SmA
SmA ? I
233.9
>300(Dec.)
225.5
272.4
208.9
221.7
240
45.89
–
52.63
6.20
43.46
–
>70.00
46.9
235
220
210
308
259
248
73
39
38
Cu10CH310CH3
Cu12CH312CH3
9
10
12
11
31.13
9.04
Metallomesogenic diols
9d
9e
9f
Cu6OH7CH3
6
7
Cr ? SmA
SmA ? I
Cr ? SmA
SmA ? I
Cr ? SmA
SmA ? I
Cr ? SmA
SmA ? I
Cr ? SmA
SmA ? I
209.2
247.9
185.7
251
182.3
255.4
191.1
244.3
187.4
218.1
45.09
7.54
38.73
65.29
73.05
53.25
30.69
206
185
175
187
185
252
256
252
244
217
46
71
77
69
32
Cu6OH10CH3
Cu6OH12CH3
Cu8OH12CH3
Cu10OH12CH3
6
10
12
12
12
36.38
13.31
34.04
17.42
45.22
13.02
45.01
10.01
6
9g
9h
8
10
Fig. 6. The HOPM photographs of metallomesogenic diol, 9e (while cooling) showing: (a) focal conic texture of smectic A phase at 198.2 °C; (b) focal conic fan like texture of
smectic A phase at 158.8 °C.
c
incorporation in the molecule profoundly affects the thermal sta-
b
a
bilities which was clearly noticed in the present work. The appear-
ance of smectic phase (SmA particularly) in these compounds and
absence of nematic phase further supports the domination of lat-
eral intermolecular attractions rather than the terminal forces.
The geometry forced by the presence of metal in the molecule also
contributes to the location of intermolecular attractions. The EPR
data of the complexes was indicative of square pyramidal
geometry which favors the axial interactions between the metal
and carbonyl (ester linking unit) of two molecular entities (inter-
molecular). Similar features were also reported in the literature re-
lated to metallomesogens [30]. The introduction of terminal
hydroxy in the model metallomesogens resulted in metallomeso-
genic diols with a better aspect ratio was induced by intermolecu-
lar H-bond, which led to the formation and facilitation of
mesophases [13–15]. The data (Table 2; compounds 9d–h) show
the appearance of SmA phase in all the cases. The examination of
thermal stability values of these compounds with those of Table 2
was indicative of the influence of terminal hydroxy group. As a
result of hydroxy induced terminal attractions, the melting
temperatures have shown decreasing trend (Fig. 8). However, the
terminal forces are insufficient to induce nematic phase in these
molecules. Another interesting feature of these compounds is
elimination of SmC phase which was present in the model
T
SmA-I
T
SmC-SmA
T
C-SmC
T
SmA-I
T
C-SmA
T
d
T
C-SmA
100
150
200
Temp. 0C
250
300
Fig. 7. DSC thermograms of model metallomesogens (while heating), 9a–c.
metallomesogens (Table 2). The reasonable mesophase stability
of these compounds is clear indication of balance of polarisability,

N. Senthilkumar et al. / Inorganica Chimica Acta 397 (2013) 129–139
139
Appendix A. Supplementary material
h
g
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2012.12.001.
T
SmA-I
T
C-SmA
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T
SmA-I
f
T
C-SmA
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With judicious modification of ligand design, mesogenic moie-
ties as metallo diols have been synthesized. The metallomesogenic
diols were constructed from three ring containing mesogen linked
through ester and azomethine with terminal hydroxy group and
were complexed with copper(II). The introduction of terminal hy-
droxy group with a better aspect ratio was induced by intermolec-
ular H-bond, which led to the formation and facilitation of
mesophases. The model metallomesogenic compounds (without
hydroxy) were also synthesized with varying chain length, and
mesophase properties with metallomesogenic diols were
compared. An extensive characterization of all metallomesogens
carried out by FT-IR, 1H & 13C NMR, VSM, AAS, EPR, electronic spec-
troscopy and elemental analysis. Hot stage polarizing microscope
and differential scanning calorimetry were used to ensure the
phase characteristics such as nature of phase, phase range, melting
and clearing temperatures. Spectroscopic studies confirmed the
structure of respective compounds while EPR and VSM established
the square pyramidal geometry. The appearance of enantiotropic
smectic A phases indicated high molecular polarizability of the
mesogenic core.
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