Synthesis, characterization and antibacterial studies of oxovanadium complexes of tetradentate Schiff base derived from 4-aminoantipyrine, o-phenylene diamine and vanillin/furfural

Article abstract of DOI:10.14233/ajchem.2017.20227

Two new vanadyl complexes were synthesized from tetradentate Schiff bases having four nitrogens act as donor atoms using 4-aminoantipyrine, o-phenylenediamine and vanillin/furfural. These complexes were characterized by elemental analysis, FTIR, UV-visibl

Full text of DOI:10.14233/ajchem.2017.20227

Asian Journal of Chemistry; Vol. 29, No. 3 (2017), 541-546
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2017.20227
Synthesis, Characterization and Antibacterial Studies of Oxovanadium Complexes of Tetradentate
Schiff Base Derived from 4-Aminoantipyrine, o-Phenylene diamine and Vanillin/Furfural
*
N. GAYATHRI and M.S. SURESH
Department of Chemistry, Government Arts College, Udhagamandalam-643 002, India
*Corresponding author: E-mail: mssgacooty@gmail.com; sanjeevigk@gmail.com
Received: 2 August 2016;
Accepted: 23 October 2016;
Published online: 30 December 2016;
AJC-18195
Two new vanadyl complexes were synthesized from tetradentate Schiff bases having four nitrogens act as donor atoms using
4-aminoantipyrine, o-phenylenediamine and vanillin/furfural. These complexes were characterized by elemental analysis, FTIR, UV-visible,
ESR spectroscopic methods, magnetic susceptibility and molar conductivity measurements and thermal analysis. These complexes have
the general molecular formula [VOL]SO4, where L = tetradentate Schiff base. The higher molar conductivity values support the 1:1
electrolytic nature of the complexes. The infrared spectra reveals the involvement of azomethine nitrogens (-C=N-) coordinated to the
metal resulting in MN4 chromophores. The electronic spectra suggested that they were square pyramidal in shape, and the complexes are
paramagnetic in nature. The thermal decomposition of both the complexes yield V2O5 as the stable residue in static air atmosphere and
decomposition is seen taking place in two stages. The eight line hyperfine splitting in ESR spectra indicates that a single vanadium is
present in the molecule. The antibacterial properties against E. coli, S. aureus, Serratia sp, P. aeruginosa, B. cereus were performed with
the Schiff base and the metal complexes. The MIC values indicates that the complexes exhibit greater antibacterial activity than the
ligands.
Keywords: Schiff base, 4-Aminoantipyrine, Vanillin, Furfural, o-Phenylenediamine, Vanadyl complexes, Antibacterial studies.
cemia, weight gain etc. Therefore some new drugs were needed
and vanadyl complexes had been proposed to function as potent
insulin-mimetic and antidiabetic agents [7].Vanadium possesses
medicinal pharmacological and biological applications in many
enzymatic reactions [8].
Most of the Schiff bases are bidentate while some of them
are tetradentate with N2O2 chromophore. Macrocyclic tetra-
dentate Schiff bases with four nitrogens (N4) as donors, similar
to porphyrins, heme group in hemoglobin etc and their metal
complexes are very rare in coordination chemistry. As a conti-
nuation of our work [9,10], to synthesize such ligands and
their metal complexes, the present paper describes two new
vanadyl complexes and their characterization using physico-
chemical methods, molar conductance, and their antibacterial
properties.
INTRODUCTION
Schiff bases are compounds containing a –C=N–
(azomethine) group formed from condensation of an aldehyde
or ketone with primary amines. These compounds are versatile
ligands with different denticity, coordinated to various metals
resulted in to metal complexes with novel properties. The
growing importance of these ligands and their metal complexes
in modern chemistry is the recent observation about their anti-
bacterial, antifungal and oxygen carrier properties. The Schiff
base derived from the condensation of 4-aminoantipyrine with
ketones are important class of chelating ligands and their metal
complexes are of great importance due to their application in
industry, extraction properties, analytical chemistry, modelling
in biosystems, catalytic and oxygen carrying systems, etc. [1-6].
Vanadium is found to be an important element as it
exhibits variety of insulin-mimetic properties [7]. The vanadyl
complexes and microminerals derived from vanadium has been
shown effective in insulin sensitivity. The main advantage of
increased insulin sensitivity are that it could promote less fat
storage as well as that it may act as an amino acid magnets to
cells. Several pharmaceutical agents have been used in diabetic
treatment but many side effects occurred such as hypogly-
EXPERIMENTAL
Vanillin, 4-aminoantipyrine, furfural, o-phenylenediamine,
vanadylsulphate, ethanol, methanol etc. were purchased from
Merck and used as such without any further purification. The
elemental analysis (CHNS) were performed using EL elemental
analyzer at Central Electrochemical Research Institute
(CECRI). The FT infrared spectra were recorded in the range

542 Gayathri et al.
Asian J. Chem.
4000-400 cm-1 on a Shimadzu FTIR 8400S spectrometer
using KBr pellet techniques. Electronic (UV-VIS) spectra were
recorded on a Schimadzu UV- spectrophototmeter in the range
1100-200 cm-1 using DMSO solvent. The thermal analyses
were carried out using universal V4.5A thermal analysis
instrument in an atmosphere of static air with a heating rate of
10 K/min. The ESR spectra of various Schiff base complexes
were recorded on a JES-X3 series in the scan range of 2300-
4300 Gauss. The molar conductance was measured on ELICO-
CM180 using DMSO as the solvent at room temperature. The
antibacterial studies was carried out with disc diffusion method.
From 4-aminoantipyrine, furfural and o-phenylenedi-
amine (AFOP) [10]: The same method was adopted for this
in which furfural (1.52 g, 0.01 mol) in 20 mL alcohol was
used instead of vanillin in the first step. Its scheme is repre-
sented in Fig. 2.
Synthesis of vanadyl complexes:A solution of the Schiff
base was prepared by dissolving 1.493 g (0.002 mol) in 50 mL
ethanol. To this solution add an ethanolic solution of VOSO4
(2.53 g, 0.01 mol) and refluxed on a water bath for about 5 h.
Its volume was reduced to one third on a waterbath and cooled.
The dark green coloured complex was precipitated out, sepa-
rated, filtered and washed several times with distilled water
and hot ethanol [9]. The same method was used for other
complex with a solution containing 1.268 g (0.002 mol) of
the ligand AFOP in 20 mL ethanol [10].
Synthesis of tetradentate Schiff bases
From 4-aminoantipyrine, vanillin and o-phenylenedi-
amine (AVOP) [9]: The synthesis of Schiff bases can be carried
out in two different steps. An ethanolic solution of 4-amino-
antipyrine (2.03 g, 0.01 mol, 20 mL) was added to an ethanolic
solution of vanillin (1.52 g, 0.01 mol, 20 mL). This mixture
was refluxed for 5 h and allowed to cool. The resulting solution
was poured into crushed ice, a yellow coloured crystals were
formed, filtered and recrystallized from ethanol. The solid
intermediate (3.373 g, 0.01 mol in ethanol) was added to an
ethanolic solution (20 mL) of o-phenylene diamine (0.541 g,
0.005 mol) and refluxed for about 30 h. The contents were
poured into crushed ice. The brown solid was separated out,
filtered and recrystallized from hot ethanol [11-13]. The Scheme
of preparation is shown in Fig. 1.
RESULTS AND DISCUSSION
Elemental analysis and molar conductance studies:The
analytical data (Table-1) suggests 1:1 metal ligand stoichio-
metry in both the cases with SO42- as counter ion. The synthe-
sized complexes have the molecular formula [VO(AVOP)] SO4
and [VO(AFOP)]SO4 where AVOP and AFOP are the new
tetradentate Schiff bases. These complexes are stable, non-
hygroscopic and dark green colour. These complexes have
molar conductance in the range of 92.5-95.0 S cm2 mol-1
indicating that they are 1:1 electrolytes . The physical analytical
and conductivity data are presented in Table-1.
STEP-I
H
H
C
O
O
NH2
N
C
OH
O
OH
N
N
N
N
O
CH3
O
CH3
CH3
CH3
H3C
H3C
I
4-Aminoantipyrine
Vanillin
STEP-II
H3C
CH3
H3C
CH3
CH3
CH3
O
O
N
N
H
C
H
C
N
N
N
N
OH
OH
O
NH2
N
N
NH2
O
N
C
H
OH
N
C
H
OH
N
N
N
N
O
O
CH3
CH3
CH3
CH3
H3C
H3C
I
AVOP
Fig. 1. Schematic representation of synthesis of tetradentate ligand 4-aminoantipyrine, vanillin and o-phenylenediamine (AVOP)

Vol. 29, No. 3 (2017)
Synthesis and Antibacterial Studies of Oxovanadium Complexes of Tetradentate Schiff Base 543
STEP-I
H
H
C
O
O
O
O
NH2
N
C
O
N
N
N
N
CH3
CH3
H3C
Furfural
H3C
4-Aminoantipyrine
I
STEP-II
H3C
CH3
H3C
CH3
N
N
H
C
H
C
N
N
N
N
O
O
O
NH2
N
N
NH2
O
O
O
N
C
H
N
C
H
N
N
N
N
CH3
CH3
AFOP
Fig. 2. Schematic representation of the synthesis of tetradentate ligand 4-aminoantipyrine, furfural and o-phenylenediamine (AFOP)
H3C
H3C
I
Infrared spectra: The absorption at 3107-2990 cm-1
(broad peak) is assigned to ν(OH) of phenolic group ofAVOP
which also appears in the vanadyl complex. This indicates that
the deprotonation of –OH group does not take place and was
not coordinated to the metal ion. The spectrum of the ligand 1
(AVOP) shows two ν(C=N) bands observed at 1650 and 1624
cm-1 was found to be shifted to lower frequencies 1607 and 1573
cm-1, attributed to the coordination of N atom of azomethine
group to the metal ion [14-16]. This is further substantiated by
the presence of a new band around 445 cm-1 due to ν(V–N).
Another absorption band at 949 cm-1 corresponds to ν(V=O)
which was found to be absent in the IR spectrum of the ligand.
The peaks observed at 993 cm-1 (ν1), 1120 cm-1 (ν3) and 619
cm-1 (ν4) are due to tetrahedral non-coordinated sulphato ions
indicating the presence of SO42- ion outside the coordination
sphere [17,18] .
Almost the same absorption peaks were found in ligand
(AFOP) and its vanadyl complex. The ν(C=N) stretching
frequency observed at 1650, 1565 cm-1 in the free ligand was
shifted to lower frequencies 1607 and 1582 cm-1 can be attri-
buted to the coordination of N atom of azomethine group to
the metal. The new absorption at 445 cm-1 was due to ν(V–N)
and a new weak absorption peak at 969 corresponds to ν(V=O).
The peaks observed at 987 (ν1), 1122 (ν3) and 653 (ν4) are
due to non-coordinated tetrahedral SO42- ion. The decrease in
the ν(C=N) is due to the lowering of CN bond order as a result
of coordination of ligand to metal via azomethine nitrogen.
The IR data are presented in Table-2.
UV-visible electronic spectra and magnetic susceptibility
measurement: The free ligands show absorption maxima
appearing around 34482 and 29850 cm-1 for AVOP and 33557
*
*
and 27777 cm-1 for AFOP was due to n→π and π→π transi-
TABLE-1
PHYSICAL, ANALYTICAL AND CONDUCTIVITY DATA OF LIGANDS AND COMPLEXES
Elemental analysis (%): Found (calcd.)
Yield
(%)
ΛM
Compound
m.w.
Colour
(S cm2 mol–1)
C
H
N
S
V
C44H42N8O4 (AVOP) 746.77 Brown
80 71.02 (70.76)
5.52 (5.67)
4.53 (4.65)
5.30 (5.40)
4.47 (4.30)
14.80 (14.99)
13.52 (12.31)
17.55 (17.65)
13.86 (14.05)
–
–
[VO(AVOP)]SO4 909.72 Dark green 75 59.16 (58.08)
C38H34N8O2 (AFOP) 634.73 Brown 75 72.00 (71.90)
[VO(AFOP)]SO4 797.67 Dark green 70 55.05 (57.21)
3.42 (3.52)
–
4.98 (4.01)
7.34 (7.36)
–
8.40 (8.39)
95.0
92.5

544 Gayathri et al.
Asian J. Chem.
TABLE-2
INFRARED SPECTRAL DATA OF THE SCHIFF BASES AND ITS VANADYL COMPLEXES
ν(SO42-
)
Compound
ν(OH)
ν(C=N)
ν(V=O)
ν(V–N)
ν1
ν3
ν4
C44H42N8O4 (AVOP)
[VO(AVOP)]SO4
C38H34N8O2 (AFOP)
[VO(AFOP)]SO4
3107-2990 (broad)
3055-2998 (broad)
1650, 1624
1607, 1573
1650, 1565
1607, 1582
–
993
–
–
1120
–
–
619
–
–
949
–
–
445
–
987
1122
653
969
445
tion respectively. But in the complex three higher energy bands
appearing around 22471, 15151 and 11904 cm-1 assigned to
leaving behind a residue of 10 %. After 725 °C, the residue is
seen stable in static air atmosphere.
2
2
2
2
2
2B2→ A1, B2→ B1 and B2→ E for complex 1 and 22471,
On heating above 175 °C, the loss of bulky Schiff bases
takes place from the complex with a calculated value of 82 %.
But the observed value was only 72.2 % (first stage) suggested
that before the complete loss of Schiff base, the second stage,
decomposition of counter ion SO42- is taking place. The observed
mass percentage of the residue 10 % is in good agreement
with the theoritical value of 9.99 % due to the formation of
V2O5 [25].
2
2
2
15822 and 11210 cm-1 due to 2B2→ A1, 2B2→ B1 and 2B2→ E
for complexes 2, respectively. These absorption bands are
typical of square pyramidal [19-23] VO2+ species.
The magnetic moments of these complexes were seen to
be in the range 1.98-2.0 BM which are also supporting the
square pyramidal geomentry ofVO2+ complexes, a 3d1 system
[24]. The electronic spectral details and magnetic moments
were presented in Table-3.
[VO(AVOP)]SO4 → ½V2O5 + Gaseous products
The thermogram of the complex 2, [VO(AFOP)]SO4 also
show the same two stage decomposition pattern (Fig. 4). This
compound was thermally stable upto 150 °C and first stage of
decomposition is seen in the range 150-225 °C with a mass
loss of 78.5 %. The second stage starts immediately at 225 °C
and ends at 625 °C with a mass loss of 11.7 % leaving behind
a residue of 9.8 %. Here also decomposition pattern is similar
to the first compound [VO(AVOP)]SO4. At high temperature
decomposition of bulky Schiff base and SO42- takes place with
a stable residue ofV2O5 in static air atmosphere. The calculated
value of the residue was 11.3 %.
TABLE-3
UV-VISIBLE SPECTRAL DATA AND
MAGNETIC MOMENTS OF THE COMPLEXES
Absorption
Compound
Assignments
µeff (BM)
max (cm–1)
n→π*
π→π*
34482
29850
C44H42N8O4-AVOP
2B2→2A1
2B2→2B1
2B2→2E
n→π*
22471
15151
11904
[VO(AVOP)]SO4
C38H34N8O2-AFOP
[VO(AFOP)]SO4
1.98
33557
27777
π→π*
2B2→2A1
2B2→2B1
2B2→2E
22471
15822
11210
[VO(AVOP)]SO4 → ½V2O5 + Gaseous products
2.0
120
100
80
60
40
20
0
40
20
0
2
1
Thermal studies: From the thermogram of the complex
[VO(AVOP)]SO4 (Fig. 3) it was observed that the compound
is thermally stable upto 170 °C indicating a well defined hori-
zontal plateau. The first stage of decomposition is seen starting
at 175 °C and progressing till 272.63 with a mass loss of 72.2 %.
The second stage of decomposition starts immediately at
272.63 °C itself and ends at 725 °C with a mass loss of 17.8 %
46.02 °C
89.40 J/g
0
90.8 %
52.09 °C
-20
-40
-1
100
80
60
40
20
0
100
80
60
40
20
0
88.89%
3
2
1
0
0
200
400
600
800
1000
Temperature (°C)
Fig. 4. TG/DTA curve of [VO(AFOP)]SO4 in static air
484.61 °C
273.8 J/g
ESR spectra: The X-band ESR spectra of the oxovana-
329.67 °C
516.06 °C
dium complexes were recorded in DMSO solution at liquid
nitrogen temperature (Figs. 5 and 6). In the frozen state, the
complexes gave typical eight line spectra with two sets of reso-
nance peaks, one set due to parallel while the other set due to
perpendicular components, due to the interaction between the
electron and the vanadium nuclear spin (I = 7/2). The two set
of eight line patterns show that single vanadium is present in
the molecule [26,27]. The various parameters calculated from
272.63 °C
587.4 J/g
-20
0
200
400
Temperature (°C)
Fig. 3. TG/DTA curve of [VO(AVOP)]SO4 in static air
600
800
1000

Vol. 29, No. 3 (2017)
Synthesis and Antibacterial Studies of Oxovanadium Complexes of Tetradentate Schiff Base 545
2047
charge of the metal ion with donor groups. Therefore the
delocalisation of π electrons in the chelate ring increases and
enhances the penetration of the complexes into lipid memb-
ranes. The antibacterial data are presented in Table-4.
Conclusion
Two square pyramidal vanadyl complexes were synthe-
sized from tetradentate Schiff bases with four nitrogen atoms
as donar atoms (with two azomethine entity). The metal comp-
lexes formed were 1:1 electrolytic in nature. The synthesized
systems were characterized by microanalysis, molar conduc-
-2048
226.776
326.776
mT
426.776
Fig. 5. ESR spectrum of [VO(AVOP)]SO4 at LNT
tance values, FTIR, ESR, UV-visible spectroscopy and TG
analyses.
2047
The analytical and spectral data suggests that azomethine
N atoms coordinated to the metal ions generating a square
pyramidal VN4O systems. The antibacterial screening tests
were also performed against certain bacteria which indicate
that the vanadium complexes exhibit good antibacterial activity
than the ligands. Based on the above results the structure of
coordination compounds were represented in Fig. 7.
-2048
226.776
326.776
mT
426.776
H3C
CH3
CH3
O
Fig. 6. ESR spectrum of [VO(AFOP)]SO4 at LNT
N
H
C
N
the spectra are given below. The g(av) andA(av) can be calculated
using:
N
OH
N
N
gβH = hν
(1)
(2)
(3)
g(av) = 1/3(g|| + 2 g⊥)
A(av) = 1/3 (A|| + 2 A⊥)
V
O
The various spin Hamiltonian parameters evaluated are
given below:
[ VO(AVOP)]SO4
A|| = 199.13 G, A⊥ = 95.23 G, A(av) = 129.86 G
[VO(AFOP)]SO4 g|| = 1.922, g⊥ = 1.955, g(av) = 1.944
N
C
H
OH
N
g|| = 1.945 , g⊥ = 1.951, g(av) = 1.949
N
O
CH3
CH3
H3C
A|| = 209.95 G, A⊥ = 83.32 G, A(av) = 125.53 G
H3C
CH3
The g||, g⊥, g(av), A||, A⊥, A(av) values are in good agreement
with the square pyramidal shape.
N
H
C
N
Antibacterial studies: The ligands and the vanadyl comp-
lexes were assayed for their antimicrobial activities against
E. coli, S. aureus, P. aeruginosa, Serratia (sp) and Bacillus
cereus by the disc diffusion method [28,29]. It was found that
the complexes have better activity than the ligands explained
by the theory of Tweedy. This is probably due to the greater
lipophilicity nature of the complexes. Such increased activity
of metal chelates can be explained on the basis of overtones
concept and chelation theory.According to overtone’s concept
of cell permeability the lipid membrane that surrounds the
cell favours the passage of lipid soluble materials. On chelation,
the polarity of metal ion will be reduced to a greater extent due
to overlap of the ligand orbitals and partial sharing of positive
N
O
N
V
O
N
O
N
C
H
N
N
CH3
H3C
Fig. 7. The proposed square pyramidal structure of complexes
[VO(AVOP)]SO4 and [VO(AFOP)]SO4
TABLE-4
ANTIBACTERIAL ACTIVITY DATA OF THE LIGAND AND ITS COMPLEXES
Staphylococcus
Pseudomonas
aeruginosa
Compound
Escherichia coli
Serratia sp
Bacillus cereus
Inference
aureus
C44H42N8O4(AVOP)
[VO(AVOP)]SO4
C38H34N8O2(AFOP)
[VO(AFOP)]SO4
11
12
9
10
13
10
11
7
12
8
9
12
12
9
++
+++
++
12
11
11
11
11
8
+++

546 Gayathri et al.
ACKNOWLEDGEMENTS
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University, SAIF, IIT-Chennai and Madurai Kamaraj University
for recording the spectral data and performing the antibacterial
studies.
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