Rod shaped oxovanadium(IV) Schiff base complexes: Synthesis, mesomorphism and influence of flexible alkoxy chain lengths

Article abstract of DOI:10.1016/j.molstruc.2014.03.006

A series of oxovanadium(IV) complexes of bidentate [N,O] donor Schiff-base ligands of the type [VO(L)₂], [L = N-(4-n-alkoxysalicylaldimine)- 4′-octadecyloxyaniline, n = 8, 10, 12, 14, 16 and 18] have been synthesized. The compounds were characterized by elemental analyses, Fourier transform infrared spectroscopy (FTIR), ¹H, ¹³C nuclear magnetic resonance (NMR), ultraviolet-visible spectroscopy (UV-Vis), and fast atom bombardment (FAB) mass spectrometry. The mesomorphic behavior of the compounds was studied by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The ligands and complexes are all thermally stable exhibiting smectic mesomorphism. The ligands 8-OR to16-OR show SmC phase at ～113-118 °C and an unidentified SmX phase reminiscent of soft crystal at ～77-91°C whereas the complexes all showed SmA phases. Interestingly the complexes with C₁₀ and C₁₂ alkoxy chain length exhibited additionally SmC phases also. The melting points of the ligands linearly increases whereas mesophase to isotropic transition temperature decreases as a function of increasing carbon chain length of alkoxy arm while no trend was apparently noticeable for the complexes.

Full text of DOI:10.1016/j.molstruc.2014.03.006

Journal of Molecular Structure 1067 (2014) 177–183
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Rod shaped oxovanadium(IV) Schiff base complexes: Synthesis,
mesomorphism and influence of flexible alkoxy chain lengths
⇑
Bishop Dev Gupta, Chitraniva Datta, Gobinda Das, Chira R. Bhattacharjee
Department of Chemistry, Assam University, Silchar 788011, Assam, India
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
A series of oxovanadium(IV) complexes of bidentate [N,O] donor rod shaped Schiff base ligands contain-
ing flexible alkoxy arms on either side of the aromatic rings have been successfully synthesized. Of par-
ticular interest is that the ligands showed striated textures (SmX) reminiscent of soft crystal not observed
in the case of complexes. The complexes with carbon chain length (C10, C12) interestingly showed SmC
mesophase in addition to SmA phase.
ꢀ
A series of oxovanadium(IV)
complexes of bidentate [N,O] donor
Schiff-base ligands have been
synthesized.
The ligands and complexes are all
thermally stable exhibiting smectic
mesomorphism.
The ligands show SmC and an
unidentified SmX phase reminiscent
of soft crystal.
Oxovanadium complexes mostly
showed SmA phase.
ꢀ
ꢀ
C10H21O
N
O
OC18H37
O
V
O
N
C18H37O
ꢀ
ꢀ
OC10H21
Interestingly, the complexes with C10
and C12 alkoxy chain length exhibited
additionally SmC phase also.
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of oxovanadium(IV) complexes of bidentate [N,O] donor Schiff-base ligands of the type [VO(L)2],
[L = N-(4-n-alkoxysalicylaldimine)-40-octadecyloxyaniline, n = 8, 10, 12, 14, 16 and 18] have been synthe-
sized. The compounds were characterized by elemental analyses, Fourier transform infrared spectroscopy
(FTIR), 1H, 13C nuclear magnetic resonance (NMR), ultraviolet–visible spectroscopy (UV–Vis), and fast
atom bombardment (FAB) mass spectrometry. The mesomorphic behavior of the compounds was studied
by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The ligands and com-
plexes are all thermally stable exhibiting smectic mesomorphism. The ligands 8-OR to16-OR show SmC
phase at ꢁ113–118 °C and an unidentified SmX phase reminiscent of soft crystal at ꢁ77–91 °C whereas
the complexes all showed SmA phases. Interestingly the complexes with C10 and C12 alkoxy chain length
exhibited additionally SmC phases also. The melting points of the ligands linearly increases whereas
mesophase to isotropic transition temperature decreases as a function of increasing carbon chain length
of alkoxy arm while no trend was apparently noticeable for the complexes.
Received 15 January 2014
Received in revised form 3 March 2014
Accepted 3 March 2014
Available online 21 March 2014
Keywords:
Metallomesogen
Oxovanadium
Smectic mesomorphism
Soft crystal
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
nature of this field is evidenced by the pervasive nature of li-
quid–crystal science, extending from biology through chemistry
Metallomesogens incorporating Schiff base ligands have trig-
gered much research in recent years because of their potential
application in multifarious areas [1–4]. The transdisciplinary
to physics, mathematics and electronic engineering. Schiff base li-
gands due to their flexible coordination donor sites, diverse struc-
tures and properties generate a variety of stereochemistries and a
wide range of bonding interactions [4–8]. Their complexes with
various transition metals lead to a distinctive class of metallomes-
ogens with novel physical properties [7–9]. Coordination of metals
⇑
Corresponding author. Tel.: +91 03842 270848; fax: +91 03842 270342.
E-mail address: crbhattacharjee@rediffmail.com (C.R. Bhattacharjee).
http://dx.doi.org/10.1016/j.molstruc.2014.03.006
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

178
B.D. Gupta et al. / Journal of Molecular Structure 1067 (2014) 177–183
to functionalised organic liquid crystals induce color, magnetism,
polarisability and provide various new structural motifs including
square planar, octahedral, square pyramidal, lantern types often
unaccessible with conventional organic materials. Salicylaldimines
have been extensively utilized to access metal complexes through
stabilized azomethine moiety with anticipated liquid crystalline
properties [9–12]. A great potential of metallomesogens as ad-
vanced molecular materials is recognized which led to a steady in-
crease in interest towards liquid crystals incorporating transition
metal element [13–16]. Mesogens containing transition metal ions
such as copper(II), nickel(II) and palladium(II) [12,17] with salicyl-
aldimine moiety are well documented. Almost all metallic
elements of the d-block have been explored to generate metallo-
mesogens yet liquid crystals containing vanadyl(IV) have not been
adequately addressed. Owing to paramagnetism of VO(IV), such
metallomesogens show quite interesting chemical and physical
properties with potential for applications [18–20]. Oxovana-
dium(IV) complexes serve as interesting models for several bio-
chemical processes such as haloperoxidation [21,22], nitrogen
fixation [23], phosphorylation [24], glycogen metabolism [25–27]
and insulin mimicking [28,29]. To devise synthetic strategy for
the oxovanadium(IV) complexes associated with multifunctional
properties such as magnetic, electronic or mesogenic properties
desirable for technological applications is quite a challenging task.
Further, oxovanadium(IV) complexes with axial coordinative
interaction(ꢂ ꢂ ꢂV@Oꢂ ꢂ ꢂV@Oꢂ ꢂ ꢂ) often inhibit exhibition of mesomor-
phism or provide an additional control on the liquid crystalline
behavior, ferroelectric/piezoelectric and non-linear optical (NLO)
properties over and above the variation in the flexibility of ligand
tails [30–32]. Liquid crystals with transition metal core groups
such as VO(IV) are a fascinating branch of material science, because
the self-assemblies of coordinated metal complexes enhances the
physico-chemical properties with new functionalities thereby
increasing their potential range of applications [33,34]. A series
of copper(II) and vanadyl(IV) complexes of N-(4-alkoxysalicylid-
ene)-40-alkylaniline with shorter alkyl chain earlier reported by
Ghedini and co-workers shows smectic mesomorphism [8].
Recently we reported a systematic investigation on a series of
oxovanadium(IV) Schiff base complexes containing a both shorter
as well as longer alkoxy substituent on either side of the ligand
[35,36]. In the present paper we report a new series of rod-shaped
mesomorphic vanadium(IV) complexes of [N,O] donor Schiff base
ligands and the effect of flexible alkoxy chain length on the
mesomorphism.
with Instec hot and cold stage HCS302, with STC200 temperature
controller of 0.1 °C accuracy. The thermal behavior of the com-
pounds were studied using a Perkin–Elmer differential scanning
calorimeter (Perkin Elmer International, Switzerland) Pyris-1 spec-
trometer with a heating or cooling rate of 10 °C/min in the temper-
ature range from 20 to 160 °C.
Materials
The materials were procured from Tokyo Kasei, Japan and
Lancaster Chemicals, USA. All solvents were purified and dried
using standard procedures. Silica (60–120 mesh) from Spectro-
chem was used for chromatographic separation. Silica gel G
(E-Merck, India) was used for thin layer chromatography (TLC).
Synthesis and analysis
The general preparative route for salicylaldimine based Schiff
bases are presented in Scheme 1. The two step procedure involves
alkylation of 2,4-dihydroxybenzaldehyde followed by condensa-
tion with p-alkoxy substituted aniline. The vanadyl(IV) complexes,
VO(LH)2 (LH = N-(4-n-alkoxysalicylaldimine)-40-octadecyloxyani-
line, n = 8, 10, 12, 14, 16, 18) were synthesized by the interaction
of hot ethanolic solution of the ligands and vanadyl sulfate in the
presence of triethylamine under reflux.
Synthesis of n-alkoxysalicyldehyde (n = 8, 10, 12, 14, 16, 18)
Alkoxysalicyldehyde derivatives were prepared following the
general method reported in literature [32]. 2,4-Dihydroxybenzal-
dehyde (10 mmol, 1.4 g), KHCO3 (10 mmol, 1 g), KI (catalytic
amount) and 1-bromooctane (10 mmol, 1.9 g), 1-bromodecane
(10 mmol, 2.2 g), 1-bromododecane (10 mmol, 2.4 g), 1-bromotet-
radecane (10 mmol, 2.7 g), 1-bromohexadecane (10 mmol, 3.0 g)
and 1-bromooctadecane (10 mmol, 3.3 g) were mixed in 250 mL
of dry acetone. The mixture was heated under reflux for 24 h,
and then filtered, while hot, to remove any insoluble solids. Dilute
HCl was added to neutralize the warm solution, which was then
extracted with chloroform (100 mL). The combined chloroform
extract was concentrated to give a purple solid. The solid was puri-
fied by column chromatography using a mixture of chloroform and
hexane (v/v, 1/1) as eluent. Evaporation of the solvents afforded a
white solid product.
Synthesis of octadecyloxy aniline
p-Hydroxy acetanilide (5 g, 0.03 mol) is refluxed with equimo-
lar amount of octadecyl bromide (9.9 g, 0.03 mol) for 36 h in dry
acetone using K2CO3 (4.6 g) as the base and KI as the catalyst,
acetone was then dried off and the product was dissolved in
dichloromethane and the solution was washed with saturated NaCl
solution. The solution was then treated with Na2SO4 to absorb the
moisture present in the solution. Dichloromethane was then
distilled off to obtain the crude 4-octadecyloxy acetanilide.
4-Octadecyloxy acetanilide was then hydrolyzed for 4 h with 35%
HCl in ethanol. After that the solution was treated with 2 mol dmꢃ3
of NaOH solution and a large amount of water up to pH ꢁ12. The
product was then filtered, recrystallised with alcohol using animal
charcoal.
Experimental section
Physical measurements
The C, H and N analyses were carried out using a Carlo Erba
1108 elemental analyzer (USA). Molar conductance of the com-
pounds was determined in dichloromethane (ca 10ꢃ3 mol Lꢃ1) at
room temperature using MAC-554 conductometer (Macroscientific
Works, India). The 1H and 13C NMR spectra were recorded on
Bruker Avance II ꢃ400 MHz (Bruker, India) spectrometer in CDCl3
(chemical shift in d) solution with tetramethylsilane (TMS) as
internal standard. Ultraviolet–visible absorption spectra of the
compounds in dichloromethane were recorded on a Shimadzu
UV-1601PC spectrophotometer (Shimadzu, Asia pacific, Pte. Ltd.,
Singapore). Infrared spectra were recorded on a Perkin–Elmer BX
series spectrometer (Perkin Elmer, USA) on a KBr disc. Mass spectra
were recorded on a JEOL SX-102 (JEOL, Japan) spectrometer with
fast atom bombardment. The optical textures of the different phase
of the compounds were studied using a polarizing microscope
(Nikon optiphot-2-Pol, Nikon Corporation, Tokyo, Japan) attached
N-(4-n-octadecyloxysalicylidene)-40-n-octadecyloxy aniline (4-18-
OR)
An ethanolic solution of (4-n-octadecyloxy)-salicyaldehyde
(0.3 g, 1 mmol) was added to an ethanolic solution of 4-octadecyl-
oxy aniline (0.3 g, 1 mmol). The solution mixture was refluxed with
few drops of acetic acid as catalyst for 3 h to yield the Schiff base
N-(4-n-octadecyloxysalicylidene)-40-n-octadecyloxy aniline. The

B.D. Gupta et al. / Journal of Molecular Structure 1067 (2014) 177–183
179
i
C18H37Br
HO
NHAc
NHAc
C18H37
O
+
ii
H2n+1CnO
CHO
H2N
OC18H37
+
OH
n=8, 10, 12, 14, 16, 18
iii
3
2
4
7
5
6
H2n+1CnO
N
OC18H37
1
OH
iv
H2n+1CnO
N
OC18H37
O
V
O
O
N
C18H37
O
OCnH2n+1
Scheme 1. The synthetic route to the ligands, N-[(4-n-alkoxysalicylidene)-40-octadecyloxy aniline] and the mononuclear oxovanadium(IV) complexes (VO-n-OR);
n = 8,10,12,14,16,18; (OR) = OC18H37. Note: (i) Dry K2CO3, dry acetone, KI (catalyst); (ii) H+/H2O, EtOH; (iii) glacial acetic acid (catalyst), EtOH, reflux, 2 h; (iv) VOSO4ꢂ2H2O,
TEA, methanol reflux 1 h.
solid was collected by filtration and recrystallised several times
from absolute ethanol to give a pure compound.
5,6H), 7.1 (d, 8.6 Hz, 3H), 7.2 (d, 8.7 Hz, 4,7H), 8.4 (s, 1H, CH@N),
13.4 (s, 1H, OH); IR (
m
max, cmꢃ1, KBr):3435 (
as(CAH), CH2), 2869 ( s(CAH), CH3), 2845 (
C@N), 1278 ( CAO).
m
OH), 2917 (
m
m
as(CAH),
as(CAH),
Yield: 0.45 g, 75%. Anal. Calc. for C49H83NO3: C, 80.2; H, 11.4; N,
1.9. Found: C, 80.1%; H, 11.3%; N, 1.8%; FAB Mass (m/e, fragment):
m/z: calc. 733.6; found: 733 [M + H+]; 1H NMR (400 MHz, CDCl3):
0.87 (t, J = 6.3 Hz, 6H, ACH3), 1.2–1.5 (m, 56H, (CH2)28), 3.9 (q,
J = 6.3, 4H, OCH2), 6.4 (s, 1H), 6.4 (d, 8.4 Hz, 2H), 6.9 (d, 8.7 Hz,
5,6H), 7.2 (d, 8.7 Hz, 3H), 7.2 (d, 8.7 Hz, 4,7H), 8.5 (s, 1H, CH@N),
13.9 (s, 1H, OH); 13C NMR (75.45 MHz; CDCl3; Me4Si at 25 °C,
ppm) d = 102.2 (AC1), 107.1 (AC2), 131.2 (AC3), 122.9 (AC4),
CH3), 2919 (
m
m
m
CH2), 1626 (
m
N-(4-n-tetradecyloxysalicylidene)-40-n-octadecyloxy aniline (4-14-
OR)
Yield: 0.48 g, 80%. Anal. Calc. for C45H75NO3: C, 79.7; H, 11.1; N,
2.0. Found: C, 79.6%; H, 11.1%; N, 2.2%; FAB Mass (m/e, fragment):
m/z: calc. 677.5; found: 678 [M + H+]; 1H NMR (400 MHz, CDCl3):
0.89 (t, J = 6.3 Hz, 6H, ACH3), 1.2–1.4 (m, 48H, (CH2)24), 3.7 (q,
J = 6.2, 4H, OCH2), 6.1 (d, 8.5 Hz, 2H), 6.4 (s, 1H), 6.9 (d, 8.7 Hz,
5,6H), 7.1 (d, 8.6 Hz, 3H), 7.2 (d, 8.7 Hz, 4,7H), 8.5 (s, 1H, CH@N),
115.7 (AC5), 115.7 (AC6), 122.9 (AC7); IR (
OH), 2917 ( as(CAH), CH3), 2919 ( as(CAH), CH2), 2868 (
CH3), 2845 ( as(CAH), CH2), 1630 ( C@N), 1277 ( CAO).
m
max, cmꢃ1, KBr):3435
s(CAH),
(m
m
m
m
m
m
m
13.4 (s, 1H, OH); IR (
m
max, cmꢃ1, KBr):3434 (
as(CAH), CH2), 2867 ( s(CAH), CH3), 2840 (
C@N), 1276 ( CAO).
m
OH), 2916 (
m
m
as(CAH),
as(CAH),
CH3), 2918 (
m
m
m
N-(4-n-hexadecyloxysalicylidene)-40-n-octadecyloxy aniline (4-16-
OR)
CH2), 1628 (
m
Yield: 0.46 g, 78%. Anal. Calc. for C47H79NO3: C, 79.9; H, 11.2; N,
1.9. Found: C, 79.8%; H, 11.1%; N, 1.9%; FAB Mass (m/e, fragment):
m/z: calc. 705.6; found: 706 [M + H+]; 1H NMR (400 MHz, CDCl3):
0.89 (t, J = 6.3 Hz, 6H, ACH3), 1.2–1.4 (m, 52H, (CH2)27), 3.8 (q,
J = 6.2, 4H, OCH2), 6.3 (d, 8.5 Hz, 2H), 6.4 (s, 1H), 6.9 (d, 8.7 Hz,
N-(4-n-dodecyloxysalicylidene)-40-n-octadecyloxy aniline (4-12-OR)
Yield: 0.38 g, 77%. Anal. Calc. for C43H71NO3: C, 79.4; H, 11.0; N,
2.1. Found: C, 79.2%; H, 10.8%; N, 2.1%; FAB Mass (m/e, fragment):
m/z: calc. 649.5; found: 650 [M + H+]; 1H NMR (400 MHz, CDCl3):

180
B.D. Gupta et al. / Journal of Molecular Structure 1067 (2014) 177–183
0.91 (t, J = 6.2 Hz, 6H, ACH3), 1.2–1.6 (m, 44H, (CH2)22), 3.7 (q,
J = 6.2, 4H, OCH2), 6.2 (d, 8.5 Hz, 2H), 6.3 (s, 1H), 6.9 (d, 8.7 Hz,
5,6H), 7.1 (d, 8.6 Hz, 3H), 7.2 (d, 8.7 Hz, 4,7H), 8.5 (s, 1H, CH@N),
fragment): m/z: calc.1251.8; found: 1252 [M+H+]; IR (KBr, cmꢃ1):
1615 ( C@N), 1141 ( CAO, phenolic), 982 ( V@O).
m
m
m
13.4 (s, 1H, OH); IR (
m
max, cmꢃ1, KBr):3431 (
as(CAH), CH2), 2867 ( s(CAH), CH3), 2841 (
C@N), 1277 ( CAO).
mOH), 2915 (
m
m
as(CAH),
as(CAH),
Results and discussion
CH3), 2918 (
CH2), 1620 (
m
m
m
m
The synthetic protocol for the ligands N-[4-n-alkoxysalicylaldi-
mine)-40-octadecyloxyaniline] and the corresponding mononu-
N-(4-n-decyloxysalicylidene)-40-n-octadecyloxy aniline (4-10-OR)
Yield: 0.38 g, 77%. Anal. Calc. for C41H67NO3: C, 79.1; H, 10.8; N,
2.2. Found: C, 79.0%; H, 10.7%; N, 2.2%; FAB Mass (m/e, fragment):
m/z: calc. 621.5; found: 622 [M + H+]; 1H NMR (400 MHz, CDCl3):
0.87 (t, J = 6.4 Hz, 6H, ACH3), 1.2–1.5 (m, 40H, (CH2)20), 3.7 (q,
J = 6.2, 4H, OCH2), 6.2 (d, 8.5 Hz, 2H), 6.3 (s, 1H), 6.9 (d, 8.7 Hz,
5,6H), 7.1 (d, 8.6 Hz, 3H), 7.2 (d, 8.7 Hz, 4,7H), 8.5 (s, 1H, CH@N),
clear oxovanadium(IV) complexes (VO-n-OR) (AOR = OC18H37
;
n = 8, 10,12,14, 16, 18) are summarized in Scheme 1. The com-
pounds were all obtained as stable colored solids. The characteriza-
tions of the compounds were made by elemental analyses, FT-IR,
UV–VIS, 1H NMR, 13C NMR and mass spectrometry. The elemental
analyses are in good agreements with composition of the com-
pounds. The Schiff bases exhibited tCN at 1635–1625 cmꢃ1; this
band shifts to a lower wave number (1610–1620 cmꢃ1) upon che-
lation, reflecting coordination of azomethine. Occurrence of vana-
dyl (V@O) stretching mode at ꢁ975 cmꢃ1 indicates the absence
of any intermolecular (ꢂ ꢂ ꢂV@Oꢂ ꢂ ꢂV@Oꢂ ꢂ ꢂ) interaction confirming
monomeric complexes. The 1H NMR spectra of ligands show signal
at 13.4–13.8 ppm, corresponding to the AOH proton and a signal at
8.5 ppm due to the proton of imine group. FAB-mass spectra of the
compounds are concordant with their formula weights. Solution
electrical conductivities of the complexes recorded in dichloro-
13.4 (s, 1H, OH); IR (
m
max, cmꢃ1, KBr):3431 (
as(CAH), CH2), 2867 ( s(CAH), CH3), 2841 (
C@N), 1277 ( CAO).
m
OH), 2915 (
m
m
as(CAH),
as(CAH),
CH3), 2918 (
m
m
m
CH2), 1625 (
m
N-(4-n-octayloxysalicylidene)-40-n-octadecyloxy aniline (4-8-OR)
Yield: 0.37 g, 75%. Anal. Calc. for C39H63NO3: C, 78.8; H, 10.6; N,
2.4. Found: C, 78.7%; H, 10.4%; N, 2.3%; FAB Mass (m/e, fragment):
m/z: calc. 593.5; found: 594 [M + H+]; 1H NMR (400 MHz, CDCl3):
0.92 (t, J = 6.3 Hz, 6H, ACH3), 1.2–1.6 (m, 36H, (CH2)18), 3.7 (q,
J = 6.2, 4H, OCH2), 6.2 (d, 8.5 Hz, 2H), 6.3 (s, 1H), 6.9 (d, 8.7 Hz,
5,6H), 7.1 (d, 8.6 Hz, 3H), 7.2 (d, 8.7 Hz, 4,7H), 8.5 (s, 1H, CH@N),
methane (10ꢃ3 M) were found to be <10
X
ꢃ1 cmꢃ1 molꢃ1 confirm-
ing the non-electrolytic nature of the complexes.
13.4 (s, 1H, OH); IR (
m
max, cmꢃ1, KBr):3430 (
as(CAH), CH2), 2867 ( s(CAH), CH3), 2841 (
C@N), 1277 ( CAO).
m
OH), 2915 (
m
m
as(CAH),
as(CAH),
The UV–visible spectra (Fig. 1) of ligands (10-OR and18-OR) in
dichloromethane and their complexes (VO-10-OR and VO-18-OR)
CH3), 2918 (
m
m
m
CH2), 1628 (
m
exhibited two bands in the
p–
p* region. The observed bands in
the ligands were almost invariant in the corresponding complexes
and also as a function of alkoxy chain lengths of the homologues
(Table 1).
Synthesis of oxovanadium(IV) complexes
The ligands, 4-18-OR (0.7 g, 1 mmol), 4-16-OR (0.7 g, 1 mmol),
4-14-OR (0.6 g, 1 mmol), 4-12-OR (0.6 g, 1 mmol), 4-10-OR (0.6 g,
1 mmol) and 4-8-OR (0.5 g, 1 mmol) was dissolved in minimum
volume of absolute ethanol and vanadyl sulfate, VOSO4ꢂ2H2O
(0.08 g, 0.5 mmol) dissolved in methanol was added to it followed
by addition of triethylamine and refluxed for 2 h. A greenish solid
formed immediately was filtered, washed with diethyl ether and
recrystallized from chloroform–ethanol.
The phase transition behavior of the compounds was monitored
using DSC and polarizing optical microscopy (POM). Thermal
traces of the ligands and the complexes are summarized in Table 2.
Both the ligands and their complexes exhibited liquid crystalline
behavior. The ligands all showed enantiotropic SmC mesomor-
phism. Upon cooling the sample from isotropic melt, a focal conic
texture of SmC phase (Fig. 2) at ꢁ113–118 °C was observed.
Remarkably a striated focal conic texture of an unidentified smec-
tic mesophase (SmX/soft crystal) (Fig. 3) is observed at ꢁ77–91 °C
on further cooling of the compounds 8-OR to16-OR. Differential
scanning calorimetry (DSC) also supports these observations.
The DSC thermogram for a typical compound (10-OR) is
shown in Fig. 4, which exhibited two transitions in heating and
VO-18-OR. Yield: 0.58 g (75%) Anal. Calc. for C98H164N2O7V: C, 76.7;
H, 10.7; N, 1.8. Found: C, 76.6%; H, 10.6%; N, 1.8%; FAB Mass (m/e,
fragment): m/z: calc.1533.2; found: 1533 [M+H+]; IR (KBr, cmꢃ1):
1613 (mC@N), 1144 (mCAO, phenolic), 981 (mV@O).
VO-16-OR. Yield: 0.51 g (76%) Anal. Calc. for C94H156N2O7V: C, 76.4;
H, 10.6; N, 1.9. Found: C, 76.1%; H, 10.6%; N, 1.8%; FAB Mass (m/e,
fragment): m/z: calc.1477.1; found: 1477 [M+H+]; IR (KBr, cmꢃ1):
three in cooling cycle. The transition at 118 °C (D )
H = 8.2 kJ molꢃ1
is due to the isotropic–smectic
C
phase, and that at 81 °C
1610 (mC@N), 1140 (mCAO, phenolic), 980 (mV@O).
2.5
2.0
1.5
1.0
0.5
1
VO-14-OR. Yield: 0.77 g (70%) Anal. Calc. for C90H148N2O7V: C, 76.0;
H, 10.5; N, 1.9. Found: C, 75.9%; H, 10.4%; N, 1.9%; FAB Mass (m/e,
fragment): m/z: calc.1420; found: 1421 [M+H+]; IR (KBr, cmꢃ1):
1.4-10-OC18H37
2.VO-10-OC18H37
3.4-18-OC18H37
4.VO-18-OC18H37
3
2
1615 (mC@N), 1141 (mCAO, phenolic), 982 (mV@O).
VO-12-OR. Yield: 0.82 g (75%) Anal. Calc. for C86H140N2O7V: C, 75.6;
H, 10.3; N, 2.0. Found: C, 75.5%; H, 10.2%; N, 1.9%; FAB Mass (m/e,
fragment): m/z: calc. 1364; found: 1364 [M+H+]; IR (KBr, cmꢃ1):
4
1612 (mC@N), 1138 (mCAO, phenolic), 982 (mV@O).
VO-10-OR. Yield: 0.74 g (74%) Anal. Calc. for C82H132N2O7V: C, 75.2;
H, 10.1; N, 2.1. Found: C, 75.1%; H, 9.8%; N, 2.1%; FAB Mass (m/e,
fragment): m/z: calc.1307.9; found: 1308 [M+H+]; IR (KBr, cmꢃ1):
0.0
1612 (mC@N), 1139 (mCAO, phenolic), 980 (mV@O).
300
350
400
Wavelength (nm)
VO-8-OR. Yield: 0.73 g (73%) Anal. Calc. for C78H124N2O7V: C, 74.7;
H, 9.9; N, 2.2. Found: C, 74.6%; H, 9.6%; N, 2.2%; FAB Mass (m/e,
Fig. 1. UV–visible spectrum of ligands and complexes.

B.D. Gupta et al. / Journal of Molecular Structure 1067 (2014) 177–183
181
Table 1
UV–visible spectral data of ligands (4-n-OR) and complexes (VO-n-OR).
Compounds
UV–visible, kmax (nm)
, l molꢃ1 cmꢃ1) ( p* transition)
p ?
(
ꢀ
C
49H83NO3
(4-18-OC18H37
98H164N2O6V
(VO-18-OC18H37
47H79NO3
(4-16-OC18H37
94H156N2O6V
(VO-16-OC18H37
45H75NO3
(4-14-OC18H37
90H148N2O6V
(VO-14-OC18H37
43H71NO3
(4-12-OC18H37
86H140N2O6V
(VO-12-OC18H37
41H67NO3
(4-10-OC18H37
82H132N2O6V
(VO-10-OC18H37
39H63NO3
(4-8-OC18H37
78H124N2O6V
(VO-8-OC18H37
285 (9300)
)
350 (20,660)
286 (6340)
352 (13,230)
284 (9350)
350 (20,530)
284 (9250)
349 (22,500)
282 (6350)
352 (21,730)
280 (6550)
349 (27,500)
285 (6350)
350 (25,630)
280 (8450)
352 (21,450)
284 (10,505)
350 (23,595)
286 (10,900)
353 (18,483)
282 (10,515)
352 (22,595)
284 (10,800)
355 (24,483)
C
)
)
)
)
)
C
)
C
C
)
C
C
)
C
C
Fig. 2. Focal conic texture of SmC phase of 10-OR.
)
C
C
)
C
)
Table 2
DSC data of ligands (4-n-OR) and complexes (VO-n-OR).
D
H, kJmolꢃ1 H, kJ molꢃ1
Compounds Heating ( Cooling (D )
)
18-OR
Cr 100.1 (89.1) SmC 114.0
(17.4) I
I 113.3 (16.4) SmC 97.5
(88.0) Cr
16-OR
Cr 96.7 (74.4) SmC 116.8
(14.5) I
I 116.1 (13.8) SmC 91.7 (4.1)
SmX 88.3 (47.0) Cr
14-OR
Cr 95.1 (26.5) SmC 117.8 (13.7) I 115.5 (12.8) SmC 87.3 (3.7)
SmX 78.3 (40.0) Cr
Cr 92.1 (68.5) SmC 118.4 (11.3) I 117.4 (8.2) SmC 85 (3.2) SmX
68.1 (38.6) Cr
I
12-OR
I
10-OR
Cr 89.4 (57.5) SmC 118.8 (8.7) I I 118 (8.2) SmC 81 (2.6) SmX
67.4 (39.5) Cr
8-OR
Cr 87.3 (77.5) SmC 119.0
(11.8) I
I 118.2 (10.9) SmC 77.3 (5.5)
SmX 71.6 (50.1) Cr
VO-18-OR
VO-16-OR
VO-14-OR
VO-12-OR
VO-10-OR
VO-8-OR
Cr 99.1 (111.3) SmA 119.0
(19.4) I
Cr 132.5 (25.4) SmA 143.9
(6.0) I
Cr 103.2 (2.6) Cr1 127.6 (34.0) I 141.8 (2.8) SmA 80.8 (13.9) Cr
SmA 145.1 (7.8) I
Cr 131.7 (24.0) SmA 158.7
(10) I
Cr 89.7 (81.2) SmA 122.9 (9.2) I I 122.8 (12.1) SmA 64.8 (25.7)
SmC 57.5 (6.1) Cr
Cr 81.9 (2.3) Cr1 96.2 (20.0)
SmA 155.2 (5.0) I
I 118.0 (19.1) SmA 89.2
(119.9) Cr
I 143.8 (5.1) SmA 83.6 (11.7) Cr
Fig. 3. Striated focal conic texture of ‘soft crystal’ phase (SmX) of 10-OR.
50
45
40
35
30
25
I 148.8 (7.0) SmA 74.2 (8.9)
SmC 45.5 (6.8) Cr
I 154.3 (6.6) SmA 49.6 (6.7) Cr
(
D
H = 2.6 kJ molꢃ1) is due to the smectic C–smectic Xphase. The
transition from smectic X phase to the crystalline phase was ob-
served at 67.4 °C (
H = 39.6 kJ molꢃ1) during cooling. In polarizing
D
optical microscopic (POM) study, all the complexes exhibited
highly birefringent fan-like texture at ꢁ118–154 °C typical of the
SmA phase (Fig. 5). In addition to SmA mesophase, VO-10-OR
and VO-12-OR, on further cooling, also showed schlieren textures
characteristic of SmC phase (Fig. 6) at ꢁ64–74 °C. The thermal
events as observed in DSC for all the complexes are concordant
with POM observations. The compound VO-10-OR for instance,
showed two transitions in heating (Cr-SmA at 89.7 °C and SmA-I
at122.9 °C) and three on cooling cycle (I-SmA at 122.8 °C, SmA-
SmC at 64.8 °C and SmC-Cr at 57.5 °C) (Fig. 7). Reproducibility of
the thermal behavior was confirmed by several heating and cooling
runs.
60
80
100
120
140
TemperatureoC
Fig. 4. DSC thermogram of 10-OR.
Variation of carbon chain length of flexible alkoxy arms with
transition temperatures are depicted in Figs. 8 and 9. The melting
points of the ligands linearly varied as a function of increasing car-
bon chain length of alkoxy arm while no trend was apparently
noticeable for the complexes. The complexes show significantly

182
B.D. Gupta et al. / Journal of Molecular Structure 1067 (2014) 177–183
120
105
90
Cr-SmC
SmC-I
I-Smc
75
SmC-SmX
SmC-Cr
SmX-Cr
60
8
10
12
14
16
18
Chain length
Fig. 8. Variation of carbon chain length in ligands.
Fig. 5. Fan-like texture of SmA phase of VO-10-OR.
160
140
120
100
80
Cr-Cr1
Cr-SmA
Cr1-SmA
SmA-I
I-SmA
SmA-SmC
SmA-Cr
SmC-Cr
60
40
8
10
12
14
16
18
Chain length
Fig. 9. Variation of carbon chain length in complexes.
(VO-14-OR to VO-18-OR) showed similar trends as that of the li-
gands whereas quite different thermal events were noted for the
complexes of lower homologues.
Fig. 6. Schlieren texture of SmC phase of VO-10-OR.
In the present study we observed enantiotropic SmA phase for
the complexes VO-8-OR to VO-18-OR and in addition to SmA
phase, SmC phases were also encountered for VO-10-OR and VO-
12-OR only, in cooling cycle. In our earlier reports, we have found
that, the oxovanadium complexes of hexadecyloxyaniline chain,
VO-n-OC16H33 (n = 12–18) showed enantiotropic SmC phase
whereas VO-10-OC16H33 showed enantiotropic SmA phase and
VO-8-OC16H33 showed monotropic SmA phase [35] and oxovana-
dium complexes of dodecyloxyaniline chain VO-n-OC12H25
(n = 6,8,16,18) showed SmA/SmX phase [36].
40
38
36
34
32
30
28
Conclusion
A series of new oxovanadium(IV) complexes of bidentate [N,O]
donor rod shaped Schiff base ligands containing flexible alkoxy
arms on either side of the aromatic rings have been successfully
synthesized and characterized. The ligands and their complexes
both exhibited smectic mesomorphism. Of particular interest is
that the ligands showed striated textures (SmX) reminiscent of soft
crystal not observed in the case of complexes. The complexes with
carbon chain length (C10, C12) interestingly showed SmC meso-
phase in addition to SmA phase. An interesting correlation of phase
behavior with the alkoxy chain length was made. These com-
pounds are new addition to the wealth of related vanadium com-
plexes showing smectic mesomorphism.
40
60
80
100
120
140
Temperature0C
Fig. 7. DSC thermogram of VO-10-OR.
higher mesophase–isotropic transition temperatures than those
for the corresponding ligands. With increase in carbon chain length
of alkoxy arm in ligands, the mesophase to isotropic transition
temperature decreases. As for complexes, the higher homologues

B.D. Gupta et al. / Journal of Molecular Structure 1067 (2014) 177–183
183
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Acknowledgment
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The authors thank Sophisticated Analytical Instrument Facility
(SAIF), North Eastern Hill University (NEHU), Shillong and Central
Drug Research Institute (CDRI), Lucknow for analytical and spectral
data. BDG thanks Principal, Pranab Vidyapith, Dimapur for permis-
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Commission (UGC), Govt. of India for financial support. We are also
thankful to DBT e-Library Consortium (DeLCON) of bioinformatics
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