Synthesis and characterization of bis [ n -(4-benzoyloxy) Benzylidene{ n (n -di-/tri-alkoxy)benzoyl}-hydrazinato]nickel(II) complexes displaying liquid crystalline columnar phases

Article abstract of DOI:10.1080/15421406.2012.726008

A series of materials based on the aroylhydrazinatonickel (II) complex is synthesized and characterized. The molecule in the materials consist of two 4-benzoyloxy-benzene groups and two benzene rings having two or three alkoxy chains containing 6, 8, 10,

Full text of DOI:10.1080/15421406.2012.726008

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Synthesis and Characterization of bis[n-
(4-benzoyloxy) Benzylidene{n(n-di-/tri-
alkoxy)benzoyl}-hydrazinato]nickel(II)
Complexes Displaying Liquid Crystalline
Columnar Phases
M. Nurul Abser a , M. Manzurul Karim a , Abu Kauser a , Rabeya
Parvin a , M. Elias Molla a , Zenifer Yeasmin a , Wajdi Michel Zoghaib
b , Zainab Al-Rawahi b , Carlo Carboni c & Ghalib Al-Saidi d
a Department of Chemistry, Jahangirnagar University, Savar, Dhaka,
Bangladesh
b Department of Chemistry, Sultan Qaboos University, Al-Khod,
Sultanate of Oman
c Department of Physics, Sultan Qaboos University, Al-Khod,
Sultanate of Oman
d Department of Food Science & Nutrition, Sultan Qaboos University,
Al-Khod, Sultanate of Oman
To cite this article: M. Nurul Abser , M. Manzurul Karim , Abu Kauser , Rabeya Parvin , M. Elias Molla ,
Zenifer Yeasmin , Wajdi Michel Zoghaib , Zainab Al-Rawahi , Carlo Carboni & Ghalib Al-Saidi (2013)
Synthesis and Characterization of bis[n-(4-benzoyloxy) Benzylidene{n(n-di-/tri-alkoxy)benzoyl}-
hydrazinato]nickel(II) Complexes Displaying Liquid Crystalline Columnar Phases, Molecular Crystals
and Liquid Crystals, 571:1, 9-18, DOI: 10.1080/15421406.2012.726008
To link to this article: http://dx.doi.org/10.1080/15421406.2012.726008
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Mol. Cryst. Liq. Cryst., Vol. 571: pp. 9–18, 2013
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.726008
Synthesis and Characterization of
bis[n-(4-benzoyloxy) Benzylidene{n(n-di-/tri-
alkoxy)benzoyl}-hydrazinato]nickel(II) Complexes
Displaying Liquid Crystalline Columnar Phases
M. NURUL ABSER,1 M. MANZURUL KARIM,1 ABU
KAUSER,1 RABEYA PARVIN,1 M. ELIAS MOLLA,1 ZENIFER
YEASMIN,1 WAJDI MICHEL ZOGHAIB,2,∗ ZAINAB
AL-RAWAHI,2 CARLO CARBONI,3 AND GHALIB AL-SAIDI4
1Department of Chemistry, Jahangirnagar University, Savar, Dhaka, Bangladesh
2Department of Chemistry, Sultan Qaboos University, Al-Khod, Sultanate of
Oman
3Department of Physics, Sultan Qaboos University, Al-Khod, Sultanate of Oman
4Department of Food Science & Nutrition, Sultan Qaboos University, Al-Khod,
Sultanate of Oman
A series of materials based on the aroylhydrazinatonickel (II) complex is synthesized
and characterized. The molecule in the materials consist of two 4-benzoyloxy-benzene
groups and two benzene rings having two or three alkoxy chains containing 6, 8, 10,
and 12 carbon atoms attached at the azomethine moiety. The synthesis, characterization
by NMR and the phase sequence observed by DSC and polarized light microscopy are
presented. Most of the compounds in the series display columnar phases in the tem-
perature range between 100◦C and 200◦C. The phases observed and their temperature
ranges are discussed in terms of the number and position of attached alkoxy chains.
Keywords Columnar; dendritic growth; discotic; metallomesogen
1. Introduction
The incorporation of heterocyclic rings as core centers in the generation of mesogenic ma-
terials has been widely investigated during the more than 30 years of discotic liquid crystal
research [1,2]. Five- or six-membered heterocyclic rings have been studied extensively due
to their structural variety and known chemistry. Good mesomorphic behavior often resulted
from such structures which can be attributed to their electronic properties and polarizability
[3].
In parallel to the use of heterocyclic rings, metal-containing liquid crystals (metallome-
sogens) have received considerable attention for more than a decade now [4,5]. Numerous
∗Address correspondence to Wajdi Michel Zoghaib, Department of Chemistry, Sultan Qaboos
University, P.O. Box 36, Al-Khod 123, Sultanate of Oman. Tel.: +968-24142472; Fax.: +968-
24141469. E-mail: zoghaibw@squ.edu.om
9

10
M. N. Abser et al.
Figure 1. The general schematic diagram of the molecules in the series of materials synthesized.
transition metal-containing liquid crystalline materials with varying molecular structures
were synthesized and their mesomorphic properties investigated.
Numerous metallomesomorphic materials with varying length branched chains (ethers
or esters) attached to the rigid core were prepared and investigated [6]. In the case of
rod-like liquid crystals, an increase in the chain length leads to more organized mesophase
structures [7,8]. Thus nematic phases are more stable with short chains, while smectic
phases are thermodynamically favored when longer chains are present; compounds with
intermediate chain length sometimes show polymorphism.
The present paper is an investigation of the formation of discotic liquid–crystal phases
with molecules based on the aroylhydrazinatonickel (II). The general schematic diagram
of molecules in the series presented here is given in Fig. 1. The molecule consists of the
aroylhydrazinatonickel (II) complex with two 4-benzoyloxy-benzene groups; benzene rings
attached at the azomethine moiety have either two alkoxy chains at either positions 3 and
4 or 3 and 5 or three alkoxy chains at positions 3, 4, and 5. Individual alkoxy chains are
composed of 6, 8, 10, or 12 carbon atoms.
The position and length (6, 8, 10, and 12 carbon atoms) of the alkoxy chains are the
parameters varied in the present study. Throughout this study, materials in the series will
be labeled by the number and position of the alkoxy chain and the number of carbon atoms
in the chain.
2. Synthesis
The complexes have been synthesized following the method summarized in Scheme 1
and details provided in references [9–13]. The reaction of benzoic acid with

Novel Benzoylhydrazinato Nickel(II) Complexes
11
H/HO
H/HO
O
+ RBr
OEt
HO
O
O
H
K2CO3, KI
Cyclohexanone
reflux, 24 hours
OH
+
HO
H/RO
O
H/RO
DCC, DMAP
Dichloromethane
rt, 24 hours
OEt
RO
(4)
NH2NH2. H2O
1-propanol
reflux, 36 hours
O
H/RO
O
H
O
O
H/RO
(3)
NHNH2
RO
(5)
1-Propanol
Reflux, 2 hours
H/RO
O
H/RO
O
HN
N
RO
O
(6)
Ni(OOCCH3)2.4H2O
1-Propanol
Reflux, 4 hours
O
O
OR/H
H/RO
RO
H
O
N
N
Ni
N
N
O
H
O
O
OR
OR/H
H/RO
(7
)
Scheme 1. Generalized synthesis of title compounds.

12
M. N. Abser et al.
Table 1. Calculated and experimental C, H, and N elemental analysis
Structure
3,4-C6
Calculated C, H, and N
Experimental C, H, and N
C66H78N4NiO10
C66H78N4NiO10
C: 69.17; H: 6.86; N: 4.89
C66H78N4NiO10
C: 69.12; H: 6.83; N: 4.85
C66H78N4NiO10
3,5-C6
C: 69.17; H: 6.86; N: 4.89
C78H102N4NiO12
C: 69.58; H: 7.64; N: 4.16
C74H94N4NiO10
C: 69.10; H: 6.82; N: 4.86
C78H102N4NiO12
C: 69.51; H: 7.58; N: 4.13
C74H94N4NiO10
3,4,5-C6
3,4-C8
C: 70.64; H: 7.53; N: 4.45
C74H94N4NiO10
C: 70.45; H: 7.45; N: 4.38
C74H94N4NiO10
3,5-C8
C: 70.64; H: 7.53; N: 4.45
C90H126N4NiO12
C: 71.37; H: 8.38; N: 3.70
C82H110N4NiO10
C: 71.86; H: 8.09; N: 4.09
C82H110N4NiO10
C: 71.86; H: 8.09; N: 4.09
C102H150N4NiO12
C: 72.79; H: 8.98; N: 3.33
C90H126N4NiO10
C: 72.91; H: 8.57; N: 3.78
C90H126N4NiO10
C: 72.91; H: 8.57; N: 3.78
C114H174N4NiO12
C: 70.41; H: 7.44; N: 4.36
C90H126N4NiO12
C: 71.14; H: 8.31; N: 3.59
C82H110N4NiO10
C: 71.75; H: 8.07; N: 4.05
C82H110N4NiO10
C: 71.75; H: 8.07; N: 4.05
C102H150N4NiO12
C: 72.59; H: 8.90; N: 3.30
C90H126N4NiO10
C: 72.55; H: 8.51; N: 3.75
C90H126N4NiO10
C: 72.61; H: 8.50; N: 3.81
C114H174N4NiO12
3,4,5-C8
3,4-C10
3,5-C10
3,4,5-C10
3,4-C12
3,5-C12
3,4,5-C12
C: 73.96; H: 9.47; N: 3.03
C: 73.66; H: 9.42; N: 3.01
4-hydroxybenzaldehyde in the presence of dicyclohexylcarbodiimide (DCC) and
dimethylaminopyridine (DMAP) in dichloromethane at room temperature for 24 hours
gave 4-benzoyloxybenzaldehyde 3 as a white solid. Alkylation (using 1-bromo alkanes) of
di-/tri-hydroxybenzoates was performed in refluxing cyclohexanone by using anhydrous
K2CO3 as the base and KI as a catalyst. The di-/tri-alkoxybenzoates 4 were converted to
the corresponding hydrazines 5 by reacting with excess hydrazine hydrate in refluxing 1-
propanol. The Schiff bases 6 of the hydrazines were generated by condensation of 5 with 3
in refluxing 1-propanol and were used in situ for complexation with nickel (II) acetate. The
nickel (II) complexes 7 were isolated in good yield as orange–red solid by recrystallization
from dichloromethane/acetone mixture and their purity was confirmed by the 1H NMR
and C, H, and N elemental analysis (Table 1). All the isolated nickel complexes have good
solubility in common organic solvents.
The 1-bromoalkanes, ethyl 3,4-di-hydroxybenzoate, methyl 3,5-di-hydroxybenzoate,
ethyl 3,4,5-tri-hydroxybenzoate, benzoic acid, 4-hydroxybenzaldehyde DCC, and DMAP
were obtained from ACROS Organics chemicals (Geel, Belgium) and were used as pur-
chased so were the other conventional reagents. 1-Propanol was distilled over calcium
oxide. A precoated silica gel aluminum plate (Silica gel 60, F-254, 0.25 mm) from E-
Merck was used for analytical TLC, while flash column chromatography was done over
silica gel Merck 60 (230–400 mesh) for purification.

Novel Benzoylhydrazinato Nickel(II) Complexes
2.1. 4-Benzoyloxybenzaldehyde (3)
13
Equimolar quantities of benzoic acid and 4-hydroxybenzaldehyde in the presence of DCC
and a catalytic amount of DMAP (0.1 gm) in dichloromethane (25 mL) were stirred for
24 hours at room temperature. After filtration and evaporation a white solid was obtained,
which was recrystallized from methanol.
IR (KBr); ν, cm−1: 2847, 2811 (aliphatic, C–H), 1736 (C O, ester), 1697 (C O,
aldehyde), 1595, 1502, 1450 (aromatic, C=C), 1207, 1157, 1058 (C–O), 878, 816, 708,
677, 517.
1H-NMR (CDCl3); δ, ppm: 10.01 (1H, s, CHO), 8.19 (2H, dd, 7.2 Hz, 1.2 Hz, C6H5),
7.96 (2H, d, C6H4, 8.4 Hz, C6H4), 7.66 (1H, dd, J = 7.2, 1.2 Hz, C6H5), 7.53 (2H, dd, J =
7.2, 7.2 Hz, C6H5), and 7.38 (2H, d, 8.4 Hz, C6H4).
2.2. Alkylation of Di-/tri-hydroxybenzoates: Synthesis of Compounds (4)
Alkylation of di-/tri-hydroxybenzoates was achieved by following a general procedure. De-
tails of methyl 3,5-di-decyloxybenzoate are given here. While for 3,5-dialkoxy derivatives
the methyl ester (methyl 3,5-di-hydroxybenzoate) was used, for 3,4-dialkoxy and 3,4,5-
trialkoxy derivatives, ethyl 3,4-di-hydroxybenzoate and ethyl 3,4,5-tri-hydroxybenzoate
were used, respectively.
A mixture of methyl 3,5-di-hydroxybenzoate (9.2 g, 55 mmol), 1-bromodecane (24.8 g,
112 mmol), anhydrous potassium carbonate (23 g, 165 mmol), and catalytic amount of KI
(ca. 1 g) in cyclohexanone (100 mL) was refluxed for 24 hours. Solvent was removed under
reduced pressure and the residual mass was treated with water (75 mL), extracted with
dichloromethane (4 × 30 mL), dried over anhydrous MgSO4, and evaporated in vacuo.
Crystallization of the crude product from hexane/dichloromethane (2:1) gave the pure
methyl 3,5-di-decyloxybenzoate as white solid. Yield: 90%.
IR (KBr); ν, cm−1: 2923(s), 2851(m) (saturated, C–H), 1723(s) (C O), 1601(m), (aro-
matic, C=C), 1472(w), 1443(m), 1393(w), 1325(m), 1240(m), 1165(s), 1129(w), 1055(m),
1007(w), 860(w), and 762(w).
1H-NMR (CDCl3); δ, ppm: 7.16 (2H, d, J = 2.2 Hz, C6H3), 6.63 (1H, dd, J =
2.2 Hz, C6H3), 3.96 (4H, t, J = 6.5 Hz, –OCH2CH2–), 3.9 (3H, s, OCH3), 1.77 (4H, m,
–OCH2CH2CH2), 1.44–1.26 (36H, m, –O(CH2)2(CH2)7CH3), and 0.88 (6H, t, J = 6.5 Hz,
–O(CH2)9CH3).
2.3. Synthesis of Acid Hydrazides (5)
The acid hydrazides were synthesized by following a general procedure; representative
details for 3,5-di-decyloxybenzoylhydrazine are given here.A mixture of methyl 3,5-di-
decyloxybenzoate (10 g, 22.3 mmol) and hydrazine hydrate (10 g, 200 mmol) was refluxed
in 1-propanol (50 mL) for 36 hours. The reaction mixture was cooled to room temperature
and treated with water (100 mL). The white solid thus formed was filtered and dried under
suction. It was then recrystallized from ethanol to give the title compound as a white solid.
Yield: 75%.
IR, (KBr); υ, cm−1: 3370(w), 3312(w) (N–H), 2920(s), 2851(s) (saturated, C–H),
1642(s) (C O), 1595(s), 1518(s) (aromatic, C=C), 1470(w), 1390(w), 1358(m), 1304(w),
1179(s), 1055(w), 874(w), 837(w), 766(w), 685(w), 517(w).
1H-NMR (CDCl3); δ, ppm: 7.41 (1H, bs, –CONHNH2), 6.83 (2H, d, J = 2 Hz,
C6H3), 6.57 (1H, dd, J = 2 Hz, C6H3), 4.1 (2H, bs, –CONHNH2), 3.95 (4H, t,
J = 6.5 Hz, –OCH2CH2–), 1.76 (4H, m, –OCH2CH2CH2–), 1.20–1.40 (28H, m,
–OCH2CH2(CH2)7CH3 ), and 0.88 (6H, t, J = 6.5 Hz, –O(CH2)9CH3).

14
M. N. Abser et al.
2.4. Synthesis of the Complex (7)
A mixture of 4-benzoyloxybenzaldehyde (3) and appropriate alkyloxybenzoylhydrazine
(5) in 1:1 molar ratio was refluxed in 1-propanol (20 mL) for 2 hours, after which nickel (II)
acetate (0.5 mol equivalent) was added to the reaction mixture, and refluxing was continued
for another 4 hours. The reaction mixture was cooled to room temperature and the resulting
yellow solid was collected by filtration; washed thoroughly with water and ethanol. The
crude product was dissolved in dichloromethane and passed through a short column of
silica eluting with hexane/dichloromethane (2:1, v/v), and subsequently re-crystallized
from dichloromethane/acetone to afford the complexes 7 as orange–red solids.
Complex 3,4-C10:
Yield: 59%.
1H-NMR (CDCl3); δ, ppm: 8.43 (2H, d, 8.8 Hz, C6H4), 8.22 (2H, d, J = 7.6 Hz, 1 Hz,
C6H5) 7.67 (1H, dd, J = 7.6 Hz, 1 Hz, C6H5), 7.59–7.47 (4H, overlap peaks), 7.37 (2H, d,
J = 8.8 Hz, C6H4), 7.26 (1H, s, N CH) 6.88 (2H, d, J = 8.8 Hz, C6H3), 4.0 (4H), 1.84
(4H), 1.48 (4H), 1.25 (24H), and 0.87 (6H).
Complex 3,5-C10:
Yield: 56%.
1H-NMR (CDCl3); δ, ppm: 8.43 (2H, d, 8.8 Hz, C6H4), 8.22 (4H, dd, 8.5 Hz, 1.3 Hz,
C6H5), 7.65 (1H, d, J = 7.4 Hz, 2 Hz, C6H5), 7.54 (2H, dd, J = 7.6 Hz, J = 7.0, C6H5),
7.36 (2H, d, 8.8 Hz, C6H4), 7.27 (1H, s, N CH), 7.11 (2H, d, 2 Hz, C6H3), 6.56 (1H, dd,
2 Hz, 2 Hz, C6H3), 3.99 (4H), 1.79 (4H), 1.46 (4H), 1.37 (24H), and 0.92 (6H).
Complex 3,4,5-C10:
Yield: 47%.
1H-NMR (CDCl3); δ, ppm: 8.40 (2H, d, 8.8 Hz, C6H4), 8.23 (4H, dd, 8.0 Hz, 1.0 Hz,
C6H5), 7.6 (1H, dd, J = 7.4 Hz, 2 Hz, C6H5), 7.50 (2H, dd, J = 7.4 Hz, J = 1.2 Hz, C6H5),
7.36 (2H, d, 8.8 Hz, C6H4), 7.25 (1H, s, N CH), 7.21 (2H, s, C6H2), 4.0 (6H), 1.88–1.72
(6H), 1.54–1.47 (6H), 1.34–1.31 (36H), and 0.93–0.88 (9H).
3. Structural Characterization of the Complexes by 1H-NMR
The H1 NMR spectra were obtained on a Bruker Avance 400 MHz spectrometer (Bruker
1
Biospin, Switzerland). For the H-NMR measurements, residual CHCl3 in CDCl3 was
employed as the internal standard and assigned as 7.26 ppm downfield from TMS. Assign-
ments were made on the basis of chemical shift, multiplicity, and ortho, meta, and para
substitution patterns.
All the complexes displayed sharp peaks in their 1H-NMR spectra and are consistent
with their structure.
Complexes 3,4,5-Cn: The protons of the C6H2 ring give a singlet at around δ 7.21 for
proton a; the protons of the C6H4 ring give two separate doublets of equal intensity and
coupling constant 8.8 Hz at around δ 8.40 and δ 7.36; the protons of the C6H5 ring give
three separate signals, two double doublets at δ 8.23 for proton b and δ 7.50 for proton b,
while the proton d resonates at δ 7.60.
Complexes 3,5-Cn: The protons of the C6H3 ring give a double doublet at δ 6.56 for
proton a, while proton b resonates as a doublet at δ 7.11; the protons of the C6H4 ring give
two separate doublets of equal intensity and coupling constant 8.8 Hz at δ 8.43 and δ 7.36;
the protons of the C6H5 ring give three separate signals, two double doublets at δ 8.22 for
proton c and δ 7.55 for proton d, while the proton e resonates at δ 7.36.

Novel Benzoylhydrazinato Nickel(II) Complexes
15
Complexes 3,4-Cn: The proton c of the ring C6H3 gives a doublet at around δ 6.88,
the other two protons a and b of this ring give overlapped peak with that of proton e of
the ring C6H5; the protons of the C6H4 ring give two separate doublets of equal intensity
and coupling constant 8.8 Hz at δ 8.43 and δ 7.36; the protons d of the C6H5 ring give a
doublet at δ 8.22; proton f resonates at δ 7.55, while the signal from proton e overlaps that
of protons a and b at δ 7.59–7.47.
Table 1 displays the calculated versus experimental C, H, and N elemental analysis for
all 12 compounds in thestudy.
4. Phase Sequences
The transition temperatures on heating were observed by Differential Scanning Calorimetry
(DSC); phase identification was done on cooling by using a polarized light microscope.
The phase changes were observed by varying the temperature at a rate of 0.5◦C per minute.
For the polarized light microscopy observations, the specimen was placed between a clean
microscope slide and a cover slip; no alignment treatment was applied to the glass. The
specimen was seared by applying a force parallel to the plane of the cell on the cover slip.
A summary of the observed phase sequences is given in Table 2, while Table 3 specifically
shows the transition to isotropic for each of the materials. In Table 2, the symbol Cr is
loosely used to refer to the solid phase observed at room temperature, it was not always
possible to ascertain from the optical observations if the phase is crystalline or glass. The
label X is used for a mesophase that can be easily sheared but could not be unequivocally
identified from the observed texture between crossed polarizers. We have labeled Col? as a
columnar phase where there is no well-defined symmetry in the observed dendritic growth
on cooling from the isotropic phase.
Table 2. Phase sequences of the compounds in the series. The uncertainty on transition
temperatures is of the order of 2◦C
Label
R
Phase sequence on heating
196
250
3,4-C6
C6H13O
C8H17O
C10H21O
C12H25O
C6H13O
C8H17O
C10H21O
C12H25O
C6H13O
C8H17O
C10H21O
C12H25O
Cr −→ Colh ←→ I
76 98 208
3,4-C8
Cr −→ X −→ Colh ←→ I
104 198
3,4-C10
3,4-C12
3,5-C6
Cr −→ X←→ I
124 184
Cr −→ X←→ I
187
190
282
Cr1 −→ Cr1 −→ Colh ←→ I
159
260
3,5-C8
Cr −→ Colh ←→ I
122 182
242
3,5-C10
3,5-C12
3,4,5-C6
3,4,5-C8
3,4,5-C10
3,4,5-C12
Cr −→ Cr1 −→ Colh ←→ I
118 137 224
Cr −→ Cr1 −→ Colh←→ I
257
259
Cr −→ Col? ←→ I
152
233
Cr −→ Col? ←→ I
106
222
Cr −→ Col? ←→ I
50
207
Cr −→ Col? ←→ I

16
M. N. Abser et al.
Table 3. Transition temperatures to isotropic phase
Transition
Transition
to isotropic
(◦C)
Transition
to isotropic
(◦C)
to isotropic
Label
(◦C)
Label
Label
3,4-C6
3,4-C8
3,4-C10
3,4-C12
250
208
198
184
3,5-C6
3,5-C8
3,5-C10
3,5-C12
282
260
242
224
3,4,5-C6
3,4,5-C8
3,4,5-C10
3,4,5-C12
259
233
222
207
As for most discotic materials, the spontaneous alignment of the columnar phase on
slow cooling from the isotropic phase between glass plates is homeotropic with the axis of
the columns perpendicular to the cover slip. Plate 1 shows some of the textures observed.
The typical dendritic growth of the columnar phase was better observed with slightly
uncrossed polarizers.
The 3,4-Cn materials with n = 6 and n = 8 display a Colh phase on cooling from the
isotropic phase. Dendritic growth with the well-defined hexagonal symmetry characteristic
of the Colh phase [14,15] is observed (insert in photo A, plate 1). The Colh phase grows with
Plate 1. Some of the textures observed in the series of materials. A: 3,4-C6 at 248◦C after shearing.
The insert shows the dendritic growth at 258◦C; B: the crystal transition in 3,4-C10, above the transition
at 110◦C and below the transition at 93◦C; C: 3,4-C12 growing in the isotropic liquid at 184◦C, D:
Hexagonal dendritic growth of 3,5-C10 at 244◦C. E: 3,4,5-C10 growth from isotropic phase 222◦C.
F: 3,4,5-C10 homeotropic alignment at T = 177◦C; the insert shows the conoscopic figure obtained
from the texture by using a Bertrand lens. G: 3,4,5-C10 texture obtained after shearing at 177◦C. H:
3,4,5-C10 at 100◦C, the texture cannot be sheared.

Novel Benzoylhydrazinato Nickel(II) Complexes
17
the axis of the column normal to the glass plates giving a dark orange uniform color to the
sample. However, if a gentle shear is applied to the sample, the orientation of the columns
and, therefore, the optical axis can be altered. Bright birefringence colors are observed after
shearing the material in the columnar phase (photo A, plate 1). The 3,4-Cn materials with
n = 10 and n = 12 appear to melt directly from the room temperature phase to the isotropic
phase; however, on cooling from the isotropic phase the materials go through a mesophase
that could not be identified and then crystallize at a lower temperature (photo B, plate 1).
No dendritic growths are observed on cooling from the isotropic, the optical axis is not
normal to the glass plate (photo C, plate 1); the mesophase can be sheared if pressure is
applied to the cover slip. This mesophase that does not appear to be a columnar phase is
labeled X in Table 2.
All the 3,5-Cn materials display a Colh phase. The characteristic hexagonal nucleation
evolving in the dendritic growth [14] was observed on cooling from the isotropic phase in
all the 3,5-Cn materials (photo D, plate 1). Except for 3,5-C8, a solid phase that cannot
be sheared is observed on cooling from the Colh phase. A rapidly growing crystallization
nucleates at lower temperatures. The solid phase observed below the Colh phase is labeled
Cr1 in Table 2. The Cr1 phase is also observed in the DSC scans.
In the 3,4,5-Cn materials, the columnar phase grows from the isotropic melt as a pro-
gressing front with dendrites (photo E, plate 1). No nucleations with hexagonal symmetry
were observed; therefore, it is not possible to ascertain whether the columnar phase is
rectangular or hexagonal. This columnar phase is labeled Col? in Table 2. The columns
axes are well aligned perpendicular to the cell glass giving a clear conoscopic figure (photo
F, plate 1). The fact that the material with three alkoxy chains does not display hexagonal
nucleation, when the columnar phase grows from the isotropic melt indicates that this com-
plex has significantly different surface tension anisotropy than the complexes with only two
alkoxy chains [16–19].
Figure 2. The clearing temperatures of the materials against chain length.

18
M. N. Abser et al.
The clearing temperatures of the materials as a function of the alkoxy chain-length are
plotted in Fig. 2. It can be seen that as is expected, increasing the chain length reduces the
clearing temperature in all cases. The 3,4-Cn materials have the lowest clearing temperatures
and the 3,5-Cn have the highest. The fact the clearing temperature of the 3,4,5-Cn analogues
is between that of the 3,4-Cn and the 3,5-Cn isomers is somehow unexpected. The unusual
behavior together with the surface tension anisotropy of these tri-alkoxy analogues is the
subject of further investigation.
Acknowledgments
The authors gratefully acknowledge research grants from the Third World Academy of
Sciences (TWAS), Italy, the Ministry of Science and Technology, Bangladesh, and the
financial support from Sultan Qaboos University, Sultanate of Oman.
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