Synthesis, characterization and biological activities of 2-((E)-(benzo[d][1,3]dioxol-6-ylimino)methyl)-6-ethoxyphenol and its metal complexes

Article abstract of DOI:10.1016/j.saa.2014.01.065

Metal complexes of Zn(II), Cd(II), Ni(II), Cu(II), and Fe(III) have been synthesized from the Schiff base ligand derived by the condensation of 3,4-(methylenedioxy)aniline and 3-ethoxy salicylaldehyde. The compounds have been characterized by using elemen

Full text of DOI:10.1016/j.saa.2014.01.065

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 125 (2014) 104–113
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization and biological activities of 2-((E)-(benzo
[d][1,3]dioxol-6-ylimino)methyl)-6-ethoxyphenol and its metal
complexes
⇑
M.L. Sundararajan, J. Anandakumaran, T. Jeyakumar
Chemistry Section (Faculty of Engineering and Technology), Annamalai University, Annamalai Nagar 608002, Tamilnadu, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
Schiff base and its metal complexes
have been synthesized.
The synthesized compounds were
characterized by spectral and thermal
analysis.
O
N
O
OH
O
2-((E)-(benzo[d][1,3]dioxol-6-ylimino)methyl)-6-ethoxyphenol
Fe Cl3 6H2
O
Metal (II)
Chloride (or)
Nitrate (or)
Acetate
ꢀ
All the compounds were tested for
their antimicrobial activities.
Methanol
Reflux 4h, Metal-ligand (1:1),
O
O
N
O
O
N
O
n H2
O
HX
O
O
4 H2O
HCl
M
H2
O
O
X
OH2
Fe
OH2
Cl
Cl
M
X
n
Zn
Cd
Ni
NO
OOCCH
OOCCH
Cl
1
1
3
1
3
3
3
Cu
a r t i c l e i n f o
a b s t r a c t
Article history:
Metal complexes of Zn(II), Cd(II), Ni(II), Cu(II), and Fe(III) have been synthesized from the Schiff base
ligand derived by the condensation of 3,4-(methylenedioxy)aniline and 3-ethoxy salicylaldehyde. The
compounds have been characterized by using elemental analysis, molar conductance, IR, UV–Visible,
1H NMR, 13C NMR, mass spectra and thermal analysis (TG/DTA). The elemental analysis suggests the
stoichiometry to be 1:1 (metal:ligand). The IR, 1H NMR, 13C NMR and UV–Visible spectral data suggest
that the ligand coordinate to the metal atom by imino nitrogen and phenolic oxygen as bidentate manner.
The mass spectral data also strengthen the formation of the metal complexes. The thermal behaviors of
the complexes prove the presence of lattice as well as coordinated water molecules in the complexes. The
in vitro biological screening effects of the synthesized compounds are tested against five bacterial species
and three fungal species by well diffusion method. Antioxidant activities have also been performed for all
the compounds. Metal complexes show more pronounced biological activity than the free ligand.
Ó 2014 Elsevier B.V. All rights reserved.
Received 12 November 2013
Received in revised form 12 December 2013
Accepted 10 January 2014
Available online 25 January 2014
Keywords:
3,4-(Methylenedioxy)aniline
3-Ethoxy salicylaldehyde
Schiff base metal complexes
Introduction
agents [2], as antivirus agents [3], as fungicide agents [4] and other
biological properties [5]. The interaction of Schiff bases derived
The bioinorganic chemistry field has increased the interest in
Schiff base complexes. These compounds have numerous applica-
tions, such as, in the treatment of cancer [1], as anti bactericide
from salicylaldehyde moiety and primary amines, especially amino
acids with variety of transition metals have been reported [6–9].
Methylenedioxy is the functional group in organic chemistry,
which is generally found attached to an aromatic structure such
as phenyl, where it forms the methylenedioxy or benzodiazole
functional group. Organic compounds with methylenedioxy
⇑
Corresponding author. Tel.: +91 9442155978.
E-mail address: jeyasundarligand@rediffmail.com (T. Jeyakumar).
http://dx.doi.org/10.1016/j.saa.2014.01.065
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

M.L. Sundararajan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 125 (2014) 104–113
105
Table 1
Elemental analysis, percentage of metal, color and molecular weight of Schiff base metal complexes.
Ligand/complexes
Empirical formula
Color
Mol. wt
Yield (%)
Elements found (calc)
% of metal found (calc)
C
H
N
A1E
C
C
C
C
C
C
16H15NO4
Brown
Grey
Grey
Green
Brown
Brown
285.29
447.71
491.77
474.08
419.31
519.13
68
57
68
68
90
80
67.18 (67.35)
43.02 (42.92)
44.08 (43.96)
45.44 (45.57)
45.70 (45.83)
37.01 (37.08)
5.25 (5.29)
3.92 (4.05)
4.13 (4.3)
5.23 (5.31)
4.39 (4.32)
5.14 (5.05)
5.05 (4.91)
6.37 (6.25)
2.78 (2.84)
2.85 (2.95)
3.27 (3.34)
2.72 (2.69)
A1E–Zn
A1E–Cd
A1E–Ni
A1E–Cu
A1E–Fe
16H18ZnN2O9
18H21CdNO8
18H25NiNO10
16H18ClCuNO6
16H26Cl2FeNO10
14.48 (14.60)
22.92 (22.85)
12.42 (12.37)
15.23 (15.15)
10.66 (10.75)
moiety is widely found in natural products, including Safrole, drugs
and chemicals such as tadalafil, MDMA (3,4-methylenedioxymeth-
amphetamine), and piperonyl butoxide [10–13]. Moreover, methyl-
enedioxy functional group in organic compounds posses biological
activities [14–18]. Metal ions play a vital role in a vast number
of biological processes [19–21]. Keeping in view of the pro-
nounced biological activity of the metal complexes of Schiff bases
derived from salicylaldehyde based compounds, it was thought of
worthwhile to synthesize and characterize some Schiff base metal
complexes of Zn(II), Cd(II), Ni(II), Cu(II), and Fe(III) derived from
3,4-(methylenedioxy)aniline and 3-ethoxy salicylaldehyde. The
biological screening of free ligand and its metal complexes against
different bacteria, fungi and antioxidant activities are reported.
determined by atomic absorption spectrophotometer (Perkin El-
mer 5000). Infrared spectra of ligand and its metal complexes were
recorded on Avatar 330FT-IR, in the range of 4000–400 cmꢂ1 using
KBr pellets. The UV–Visible spectra of the ligand and the metal
complexes were recorded on a Shimadzu UV-1650PC spectropho-
tometer in the range of 200–800 nm. 1H NMR and 13C NMR spectra
(at room temperature) were recorded on a Bruker magnet system
(400 MHz/54 mm) ultra shield plus using CDCl3 as a solvent and
TMS as internal standard. Thermal analysis (TG/DTA) was carried
out on TA instruments, Model: Q600SDT TG/DTA in the tempera-
ture range 20–1000 °C, in nitrogen atmosphere at a heating rate
of 20 °C/min. The Mass spectra were recorded by using JEOL
GCMATE II GC–MS. Melting points were determined using Gallenk-
amp melting point apparatus. Molar conductance of the Schiff-base
ligand and its transition metal complexes were determined in
CHCl3 at room temperature using a CMD 750 WPA conductivity
meter.
Materials and instrumentation
All chemicals used in the present work viz., 3-ethoxysalicylalde-
hyde, 3,4-(methylenedioxy)aniline, Zn(NO3)26H2O, Cd(CH3COO)22-
H2O, Ni(CH3COO)24H2O, CuCl2ꢁ2H2O, FeCl36H2O, ethanol and
methanol were analytical reagent grade (Aldrich) and used without
further purification.
Antibacterial activity
Antibacterial activity of acetone, methanol, ethanol and chloro-
form extracts of five different marine microalgal strains was eval-
uated. All the synthesized compounds were screened for their
in vitro antibacterial activity by agar well diffusion method [22]
against bacterial strains such as Escherichia coli, Staphylococcus aur-
eus, Enterococcus faecalis, Pseudomonas fluorescens, and Klebsiella sp.
Instrumentation
The microanalysis of C, H, and N were estimated by Perkin El-
mer 240 (USA) elemental analyzer and the metal content were
O
O
NH
O
O
N
2
HO
Reflux 6h
Methanol
O
OH
O
OHC
3,4-(methylenedioxy)aniline
3-Ethoxy salicylaldehyde 2-((E)-(benzo[d][1,3]dioxol-6-ylimino)methyl)-6-ethoxyphenol
Fe Cl3 6H2 O
Metal (II)
Chloride
(or)
Nitrate
(or)
Reflux 4h
Methanol
Metal-ligand (1:1)
O
N
O
4 H2O
HCl
H2O
Cl
O
Acetate
Fe
OH2
O
Cl
O
O
N
O
n H2O
HX
O
M
X
OH2
M
X
n
Zn
Cd
Ni
-
-
-
-Cl
NO3
OOCCH3
OOCCH3
1
1
3
1
Cu
Scheme 1. Synthesis of Schiff base and its metal complexes.

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M.L. Sundararajan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 125 (2014) 104–113
Table 2
was poured onto a pre-sterilized petri dish and test microorgan-
isms were spread on the plates using sterile L-rod. Five wells were
punched using a sterile cork borer and filled with 100 lL test sam-
ple. The inoculated plates were incubated for 24 h at 37 °C. After
incubation, the diameter of the inhibition zone was measured
and the results were recorded in millimeters. Each solvent extracts
were tested separately in triplicates.
UV–Vis spectral data, molar conductivity and melting point of Schiff base metal
complexes.
Ligand/
complexes
UV–Visible bands
(nm)
j
m Ohmꢂ1
Melting point
°C
cm2 molꢂ1
A1E
266, 356, 402
264, 360, 420
263, 359, 414
264, 362, 436
266, 387, 426
263, 360, 453
3.42
5.57
6.19
5.67
5.27
6.00
108
224
92
>300
128
>300
A1E–Zn
A1E–Cd
A1E–Ni
A1E–Cu
A1E–Fe
Antifungal activity
The free ligand, its metal complexes (10 mg/ml) and control-
solvent mixture were screened for their antifungal activity against
various fungi viz., Candida albicans, Fusarium sp. and Trichosporon
sp. Each fungal inoculum was swab spread on Muller Hinton agar.
Five wells of 4 mm diameter were cut into agar plates and 50 lL
A1E
(MIC) of microalgal extracts and positive control (Streptomycin)
were added to each well. The inoculated plates were incubated
for 3 days at 30 °C. The growth inhibition zone was measured in
millimeters. Tests were carried out in triplicate [23].
A1E – Ni
A1E – Cu
A1E – Cd
Antioxidant activity
Antioxidant activities of the synthesized compounds (10 mg/
ml) were expressed from their radical scavenging ability against
the stable free radical, 2,2-diphenyl-1-picryl hydrazyl (DPPH ).
A1E – Zn
A1E – Fe
Å
´
The DPPHÅ scavenging capacity was determined spectrophotomet-
rically [24]. DPPH (0.004%) was prepared in methanol and 1 ml of
0.004% DPPH-methanol solution was mixed with 2 ml of metha-
nol-compound mixture. The reaction tubes were wrapped in
aluminium foil and kept in dark for 30 min. The reduction of the
DPPHÅ was monitored by observing the decrease in absorbance at
517 nm using UV–Vis spectrophotometer with solvent and DPPH
as blank. The percentage inhibition was calculated using the
formula
4000
3500
2500
2000
1500
1000
500
3000
Wavenumber (cm-1)
Fig. 1. IR spectra of Schiff base metal complexes.
Standard antibiotics, ampicillin was used as control. Stock
solutions (100 mg/ml) of each compound were diluted in DMSO
to produce 10 mg/ml. Schiff base and its metal complexes were
tested against different concentrations in DMSO solution range
Acontrol ꢂ Asample
Percent ð%Þ inhibition of DPPH activity ¼
ꢃ 100
Acontrol
from 20
tion concentrations (MIC). From the results we concluded that
100 L is suitable for all the test samples. 20 ml of nutrient agar
lL to 200
lL (10 mg/ml) to find out the minimum inhibi-
where Acontrol is the absorbance of DPPHÅ in methanol without an
antioxidant and Asample the absorbance of DPPHÅ in the presence
of an antioxidant.
l
Table 3
IR spectral data of Schiff base metal complexes.
Ligand/complexes
m
(OH)/(H2O) (cmꢂ1
)
m
asym(CAH)a (cmꢂ1
)
m
sym(CAH)b (cmꢂ1
)
m
(C@N) (cmꢂ1
)
m
(CAOH) (cmꢂ1
)
m )
(AOACH2AOA) (cmꢂ1
A1E
3438
3446
3432
3407
3446
3433
2976
2975
2978
2980
2980
2969
2883
2917
2920
2893
2921
2922
1629
1635
1630
1603
1601
1614
1248
1245
1246
1242
1243
1250
931
929
929
935
929
948
A1E–Zn
A1E–Cd
A1E–Ni
A1E–Cu
A1E–Fe
a
Asymmetric stretching.
Symmetric stretching.
b
Table 4
1H NMR and 13C NMR spectral data of Schiff base and its Zn (II), Cd(II) metal complexes.
Compounds
ACH3
ACH2
AOACH2AOA
Aromatic proton/Aromatic carbon
AHC@NA
AOH
1H NMR functional groups with chemical shift in (d, ppm)
A1E
A1E–Zn
A1E–Cd
1.504
1.509
1.509
4.135
4.139
4.138
6.011
6.020
6.019
6.794–7.000
6.825–7.265
6.803–7.266
8.575
8.583
8.583
13.742
13C NMR functional groups with chemical shift in (d, ppm)
A1E
A1E–Zn
A1E–Cd
14.93
14.94
14.93
64.62
64.62
64.62
101.47
101.47
101.47
101.65–151.45
101.65–151.47
101.65–151.44
160.59
160.59
160.59

M.L. Sundararajan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 125 (2014) 104–113
107
Synthesis of Schiff base (A1E)
until the washing becomes colorless. The product was dried in vac-
uum over CaCl2. All the metal complexes are colored and stable to
air and moisture. The elemental analysis data, color, percentage of
metal and molecular weight of Schiff base (A1E) and its metal com-
plexes (A1E–Zn, A1E–Cd, A1E–Ni, A1E–Cu, and A1E–Fe) are given
in Table 1.
The Schiff base was prepared by refluxing of 3-ethoxy salicylal-
dehyde (3.32 g; 0.02 mol) with 3,4-(methylenedioxy)aniline
(2.74 g; 0.02 mol) in methanol solution (50 ml) for 6 h. The result-
ing solution was evaporated under vacuum to remove the solvent.
The product was collected by filtration, washed several times with
methanol and recrystallized from hot methanol. The recrystallized
product was dried under vacuum.
Results and discussions
Synthesis of complexes
The condensation reaction of 3-ethoxy salicylaldehyde with 3,4-
(methylenedioxy)aniline in a 1:1 M ratio yields 2-((E)-(benzo[d]
[1,3]dioxol-6-ylimino)methyl)-6-ethoxyphenol which further re-
act with the metal salts [Zn(NO3)26H2O, Cd(CH3COO)22H2O,
Ni(CH3COO)24H2O, CuCl22H2O, FeCl36H2O] in metal–ligand ratio
1:1 yielded the corresponding complexes. The general reaction
A methanolic (50 ml) solution of Schiff base (0.002 mol) was
mixed with metal chloride or nitrate or acetate (0.002 mol) in
methanol (50 ml) solution keeping metal–ligand ratio 1:1. The
mixture was refluxed for 4 h. The solid product precipitated on
cooling was collected by filtration and washed with hot methanol
Fig. 2. (a) 1H NMR and (b) 13C NMR spectra of Schiff base ligand (A1E).

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M.L. Sundararajan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 125 (2014) 104–113
performed in synthesis of the title compound and its metal com-
plexes are shown in the following scheme (Scheme 1).
exhibits two bands at 266 nm and 402 nm attributed to p–
p* and
n–p* transition within the Schiff base ligand. In the spectra of the
complexes, the band at 266 nm remains as such, in agreement with
Physical properties
the p–p
* transition of the Schiff base ligand. The band observed at
402 nm in the spectrum of the free ligand (A1E) is red shifted to
414–453 nm in complexes in the form of ligand to metal charge
transfer (LMCT) transition. The spectra of the entire complexes
showed intense band at 414–453 nm, which could be assigned to
the charge transfer of ligand–metal charge transfer [25]. Since it
is masked by the high-intensity charge transfer transitions, the
d–d transition could not be observed in the visible region for com-
plexes with aromatic imines [26]. The UV–Vis spectral data, melting
point of the ligand and their complexes are given in Table 2.
The observed molar conductance of the complexes in chloro-
form (Table 2) for ꢄ 10ꢂ3M solutions at room temperature are
consistent with the non-electrolytic [27] nature of the complexes
due to no counter ions in the proposed structure of the Schiff base
Elemental analysis
The elemental analysis results are agree with the calculated val-
ues (Table 1) showing that the complexes have 1:1 metal/ligand
ratios and the Schiff base ligand is formed by the condensation of
0.02mol of 3,4-(methylenedioxy)aniline with 0.02mol of 3-ethoxy
salicylaldehyde.
UV–Vis spectra, molar conductance of ligand and its complexes
UV–Vis spectra provide the most detailed information about the
electronic structure of a compound. The UV–Vis spectra of the li-
gand and all the complexes were recorded in CHCl3 at room tem-
perature. The UV–Vis spectrum of the Schiff base ligand (A1E)
Fig. 3. 1H NMR spectra of Schiff base metal complexes (a) A1E–Zn and (b) A1E–Cd.

M.L. Sundararajan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 125 (2014) 104–113
109
metal complexes. From the electronic spectra and molar conduc-
IR Spectra
tance results, A1E–Zn, A1E–Cd, A1E–Ni, A1E–Cu complexes are
found to be tetrahedral structure and A1E–Fe is in octahedral
structure (Scheme 1).
The IR spectra of the complexes are compared with that of the
free ligand to determine the changes that might have taken place
during complexation (Fig. 1). IR spectra of the ligand exhibit
m
(C@N) vibration at 1629 cmꢂ1
.
The absorption bands at
3066 cmꢂ1, 2976 cmꢂ1 and 2883 cmꢂ1 is attributed to aromatic
(CAH), aliphatic asym(CAH), and sym(CAH) respectively. A sharp
band observed at 931 cmꢂ1 assigned due to
(AOACH2AOA)meth-
ylenedioxy moiety [28], medium to sharp band appeared at
1248 cmꢂ1 [29] is due to
(CAOH) stretching vibration of phenol.
This
(CAOH) stretching vibration of phenol shifted to 1–5 cmꢂ1
Table 5
Mass spectral data of Schiff base metal complexes.
m
m
m
m
Ligand/complexes
Calculated m/z
Found m/z
Peak
assignment
m
A1E
285.29
447.71
491.77
474.08
419.31
519.13
285.68
448.86
492.78
474.27
420.89
519.29
Ligand
[M + 1]
[M + 1]
[M]
[M + 1]
[M]
m
[A1E–Zn(NO3)(H2O)] H2O
[A1E–Cd(COOCH3)(H2O)]H2O
[A1E–Ni(COOCH3)(H2O)]3H2O
[A1E–Cu(Cl) (H2O)] H2O
[A1E–Fe(Cl2)2H2O]4H2O
on complexation, which indicates that phenolic group (OH) in-
volved in the complex formation.
All the metal complexes show a broad band at 3446 cmꢂ1
(A1E–Cu), 3407 cmꢂ1(A1E–Ni), 3446 cmꢂ1(A1E–Zn), 3432 cmꢂ1
Fig. 4. Mass spectra of (a) Schiff base (A1E) and (b) metal complex (A1E–Cu).

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M.L. Sundararajan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 125 (2014) 104–113
(A1E–Cd), and 3433 cmꢂ1(A1E–Fe), may be due to
m(OH) of
shifted to downfield in the complexes indicates the formation of
metal nitrogen bond. The signal at d13.742 ppm in ligand is disap-
peared in metal complexes A1E–Zn and A1E–Cd confirms that the
phenolic proton (AOH) is involved in coordination with Zn (II) and
Cd (II). Thus the 1H NMR spectral observations supported the
bidentate nature of ligand in coordination with metal salts.
13C NMR spectra of the Schiff base (A1E) and its two complexes
A1E–Zn, A1E–Cd were recorded in CDCl3 solution, using tetrameth-
ylsilane (TMS) as internal standard. 13C NMR spectrum of ligand
displayed characteristic signals at d14.93 ppm, d64.62 ppm,
d101.47 ppm, d101.65–151.45 ppm and d160.59 ppm are due to
the ACH3, ACH2, AOACH2AOA, aromatic carbons and azomethine
(AHC@NA) carbon respectively [34]. The 13C NMR spectra of com-
plexes A1E–Zn and A1E–Cd shows no appreciable changes com-
pared with ligand. The spectral data are presented in Table 4. The
1H NMR and 13C NMR spectra of ligand (A1E) and 1H NMR spectra
of A1E–Zn and A1E–Cd are given in Figs. 2 and 3.
water molecule. The band at 1629 cmꢂ1 due to azomeꢂth1ine group
of Schiff base shifted to 1–28 cmꢂ1 [1601 cm (A1E–Cu),
1603 cmꢂ1(A1E–Ni), 1635 cmꢂ1(A1E–Zn), 1630 cmꢂ1(A1E–Cd),
1614 cmꢂ1 (A1E–Fe)] on complexation suggesting the coordination
of azomethine nitrogen with the metal atoms. This shifting can be
explained by the donation of electron from lone pair of azomethine
nitrogen to the empty d-orbital of the transition metal atom. How-
ever, shifting of band for azomethine and phenolic group to both
higher and lower frequencies have been well documented in liter-
ature [30]. Moreover A1E–Cd and A1E–Ni complexes showed the
coordination of acetato group by the appearance of new bands
due to masym(COO), and m
sym(COO) at 1563–1588 cmꢂ1and 1338–
1342 cmꢂ1respectively [31] and A1E–Zn complex shows three
new bands at 1460 cmꢂ1, 1385 cmꢂ1 and 1087 cmꢂ1 due to the
coordination of nitrato group in the coordination complex [32].
Furtherꢂm1ore, new band appeared at the lower frequency region;
614 cmꢂ1(A1E–Zn), 625 cmꢂ1 (A1E–Cd), 619 cmꢂ1(A1E–Ni),
510 cm (A1E–Cu), 575 cmꢂ1 (A1E–Fe) and 508 cmꢂ1 (A1E–Zn),
549 cmꢂ1 (A1E–Cd), 503 cmꢂ1 (A1E–Ni), 475 cmꢂ1 (A1E–Cu),
482 cmꢂ1 (A1E–Fe) is due to the metal nitrogen (M–N) and metal
oxygen (M–O) coordination respectively. Therefore from the above
details it is concluded that the ligand acts as a bidentate and coor-
dinate to the empty d-orbital of metal ion through the azomethine
nitrogen and phenolic oxygen atom. The IR spectral details are pre-
sented in Table 3.
Mass spectra
The mass spectra of the ligand and its transition metal com-
plexes are recorded at ambient temperature. Mass spectra are a
useful technique to interpret the stoichiometric composition of
ligand and its complexes. The Schiff base ligand (A1E) shows a
molecular ion peak at m/z 285.68, which is very close to the calcu-
lated values of m/z 285.29. The peak assignment in mass spectra
observed for ligand and the metal complexes are presented in
Table 5. The mass spectral evidence reveals that the metal com-
plexes have equimolar ratio of metal and ligand, as prescribed in
Scheme 1. A representative mass spectrum is given in Fig. 4.
1H and 13C NMR spectra
NMR spectroscopy is a useful tool to establish the structure and
nature of many Schiff bases and their metal complexes. The 1H
NMR spectra of Schiff base (A1E) and its diamagnetic complexes
A1E–Zn and A1E–Cd were recorded in CDCl3, using tetramethylsil-
ane (TMS) as internal standard and are presented in Table 4. 1H
NMR spectrum of ligand (A1E) showed signal at d1.504 ppm corre-
sponding to CH3 proton. A sharp signal observed at d4.135 ppm is
due to CH2 proton and a sharp singlet appeared at d6.011 ppm is
attributed to methylene dioxy moiety (AOACH2AOA). The multi-
ple signals observed between d6.794 and d7.00 ppm are related
to the aromatic protons. The peak at d8.575 ppm is assigned to azo-
methine (AHC@NA) with an integration corresponding to 1 proton
in the ligand. The sharp singlet observed at d13.742 ppm is due to
phenolic proton of the ligand [33]. 1H NMR spectra of the
complexes (A1E–Zn and A1E–Cd) was also recorded in CDCl3. In
the 1H NMR spectra of the Zinc (II) and Cadmium (II) complexes,
the signal for imine proton in the free ligand at d8.575 ppm is
Thermal analysis
Thermo gravimetric analysis (TGA) and differential thermal
analysis (DTA) are useful technique to determine the thermal sta-
bility of the metal complexes. In the present study, heating rates
were suitably controlled at 20 °C/min, under nitrogen atmosphere
and the loss in weight was measured up to 1000 °C. The stages of
decomposition temperature range, decomposition product and
weight loss percentage of complexes are given in Table 6. The first
step at 30–125 °C with a weight loss (found) of 4.00% for A1E–Zn,
3.70% for A1E–Cd, 11.50% for A1E–Ni, 4.40% for A1E–Cu and 13.80%
for A1E–Fe is attributed to lattice water molecule. The second step
weight loss at 125–280 °C corresponds to removal of coordinated
water molecule from the metal complexes of A1E–Zn, A1E–Cd,
A1E–Ni, A1E–Cu, and A1E–Fe. Moreover, the third step observed
Table 6
Thermal analysis of metal complexes.
Complexes
TG range in °C
Mass loss in % Found(calc)
Assignment
[A1E–Zn(NO3)(H2O)] H2O
30–210
210–250
275–1000
4.00(4.02)
4.00(4.02)
63.70(63.72)
Loss of 1 lattice H2O molecule
Loss of 1 coordinated H2O molecule
Decomposition of the ligand
[A1E–Cd(COOCH3)(H2O)]H2O
[A1E–Ni(COOCH3)(H2O)]3H2O
[A1E–Cu(Cl) (H2O)] H2O
50–225
225–275
300–1000
3.70 (3.66)
3.70(3.66)
58.00 (58.02)
Loss of 1 lattice H2O molecule
Loss of 1 coordinated H2O molecule
Decomposition of the ligand
30–225
225–280
310–1000
11.50(11.39)
3.80 (3.79)
60.20 (60.17)
Loss of 3 lattice H2O molecule
Loss of 1 coordinated H2O molecule
Decomposition of the ligand
50–125
125–225
325–1000
4.40(4.29)
4.40(4.29)
68(68.03)
Loss of 1 lattice H2O molecule
Loss of 1 coordinated H2O molecule
Decomposition of the ligand
[A1E–Fe(Cl2)2H2O]4H2O
50–125
125–225
250–1000
13.80(13.86)
7.00(6.93)
55.00(54.95)
Loss of 4 lattice H2O molecule
Loss of 2 coordinated H2O molecule
Decomposition of the ligand

M.L. Sundararajan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 125 (2014) 104–113
111
Fig. 5. Thermo gravimetric analysis of (a) A1E–Zn and (b) A1E–Cu Schiff base complexes.
at 250–1000 °C involved the ligand decomposition. The results ob-
tained from thermal analysis suggest that all the complexes are
more stable and also nonvolatile. A representative TG/DTA diagram
is given in Fig. 5.
bacteria (E. coli, S. aureus, E. faecalis sp., P. florescens sp., and
Klebsiella sp.,) by well diffusion method using ampicillin as
standard. The susceptibility of the strain of bacteria towards the
compounds is judged by measuring the size of inhibition diameter
(Fig. 6). The inhibition zones of bacteria in the compounds are
given in Table 7. The obtained results suggest that the metal com-
plexes are more active than the ligand, as well as more active than
the standard against all the bacteria tested. A1E–Ni, A1E–Zn and
A1E–Fe are found to have moderate activity towards the bacteria
Antibacterial activity
The in vitro antibacterial activities of the ligand and its com-
plexes were screened separately against five human pathogenic
Fig. 6. Antibacterial activities of Schiff base metal complexes.

112
M.L. Sundararajan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 125 (2014) 104–113
Table 7
Antimicrobial activity and antioxidant of Schiff base metal complexes.
Compound
Anti-Bacterial Activity Zone of inhibition (mm)
Anti fungal activity Zone of inhibition (mm)
Antioxidant Acitivity (%)
a
b
c
d
e
f
g
h
Control
A1E
7
5
9
11
9
9
15
9
6
8
5
9
9
8
9
9
8
5
5
3
3
2
4
2
1
6
1
2
1
5
1
1
1
2
2
1
4
1
1
10
11
12
10
11
9
10
10
16
10
12
10
25.7
76.4
68.5
32.8
45.4
40.0
A1E–Zn
A1E–Cd
A1E–Ni
A1E–Cu
A1E–Fe
10
12
10
10
9
a – Escherichia coli, b – Staphylococcus aureus, c – Enterococcus faecalis, d – Pseudomonas fluorescens, e – Klebsiella sp. f – Candida albicans, g – Fusarium sp. h – Trichosporon sp.
Fig. 7. Antifungal activities of Schiff base metal complexes.
tested whereas, A1E–Cd posses’ higher activity towards Klebsiella
sp., E. faecalis sp., E. coli and S. aureus, than the other metal com-
plexes. S. aureus and Klebsiella sp., have higher activity for A1E–Cu.
The variation in the antimicrobial activity of different metal
complexes against different microorganisms depends on their
impermeability of the cell or the differences in ribosome in
microbial cell [35]. Chelation reduces the polarity of the metal
ion in the complexes considerably, mainly due to the partial
sharing of its positive charge with the donor group. The possible
electron delocalization over the chelate ring system in turn
increases the hydrophobic character of the metal chelate thus
favoring its permeation through lipoid layer of microorganism.
Also the normal cell process may be affected by the formation of
hydrogen bond through the azomethine nitrogen atom with the
active centers of cell constituent [36]. Thus lipophilicity is an
important factor controlling antimicrobial activity [37].
Antifungal activity
Antifungal activities of the synthesized compounds were tested
against C. albicans, Fusarium sp., and Trichosporon sp., by well diffu-
sion method. The growth inhibition zone of the compounds against
microorganism are summarized in Table 7. The experimental re-
sults were compared with the standard antifungal drug streptomy-
cin at the same concentration. All the metal complexes exhibited
greater antifungal activity against C. albieans. However, they show
Fig. 8. Antioxidant activities of Schiff base metal complexes.

M.L. Sundararajan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 125 (2014) 104–113
113
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We synthesized Schiff base [2-((E)-(benzo[d][1,3]dioxol-6-yli-
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their structure and physical properties. The spectral studies sug-
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complexes are in tetrahedral structure and Fe(III) is in octahedral
structure. The ligand and their metal complexes are tested for their
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