Synthesis, characterization and antibacterial studies of VO(IV), Cu(II), Ni(II), Co(II) chelates of tetradentate schiff base derived from benzil and anthranilic acid

Article abstract of DOI:10.14233/ajchem.2017.20480

A novel tetradentate N₂O₂ type Schiff base, synthesized from benzil and 2-aminobenzoic acid (anthranilic acid) in the ratio 1:2, form stable complexes with transition metal ions such as VO(IV), Cu(II), Ni(II) and Co(II) in ethanol. Microanalytical data, magnetic susceptibility, molar conductance measurements, FTIR, UV-visible, ESR spectroscopic techniques and thermal analysis were used to confirm their structures. These complexes show very low conductance values supporting non-electrolytic nature. The infrared spectra supports the involvement of azomethine nitrogens and oxygen from carboxylate ion are coordinated to the metal. Electronic spectra of the complexes suggest a square pyramidal geometry for oxovanadium(IV) complex [VO(L)], distorted octahedral geometry for Cu(II) and Co(II)complexes and octahedral geometry for Ni(II) complexes with general formula [M(L)(H₂O)₂] where M = Cu(II), Ni(II), Co(II). The X-band ESR spectra of VO(IV) and Cu(II) complexes were recorded in DMSO at LNT and their parameters were calculated. All these complexes are paramagnetic and thermal studies show that in all the cases a stable metal oxide was obtained as the residue. The metal complexes have been screened for their antibacterial activity against organisms like E. coli, S. aureus, Serattai sp, P. aeruginosa and B. cereus and it was found that the complexes were more active than the corresponding ligand.

Full text of DOI:10.14233/ajchem.2017.20480

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Asian Journal of Chemistry; Vol. 29, No. 6 (2017), 1308-1312
ASIAN JOURNAL OF CHEMISTRY
https://doi.org/10.14233/ajchem.2017.20480
Synthesis, Characterization and Antibacterial Studies of VO(IV), Cu(II), Ni(II), Co(II)
Chelates of Tetradentate Schiff Base Derived from Benzil and Anthranilic Acid
*
N. GAYATHRI and M.S. SURESH
Department of Chemistry, Government Arts College, Udhagamandalam-643002, India
*Corresponding author: E-mail: mssgacooty@gmail.com; sanjeevigk@gmail.com
Received: 4 January 2017;
Accepted: 16 February 2017;
Published online: 10 April 2017;
AJC-18344
A novel tetradentate N2O2 type Schiff base, synthesized from benzil and 2-aminobenzoic acid (anthranilic acid) in the ratio 1:2, form
stable complexes with transition metal ions such asVO(IV), Cu(II), Ni(II) and Co(II) in ethanol. Microanalytical data, magnetic susceptibility,
molar conductance measurements, FTIR, UV-visible, ESR spectroscopic techniques and thermal analysis were used to confirm their
structures. These complexes show very low conductance values supporting non-electrolytic nature. The infrared spectra supports the
involvement of azomethine nitrogens and oxygen from carboxylate ion are coordinated to the metal. Electronic spectra of the complexes
suggest a square pyramidal geometry for oxovanadium(IV) complex [VO(L)], distorted octahedral geometry for Cu(II) and Co(II)complexes
and octahedral geometry for Ni(II) complexes with general formula [M(L)(H2O)2] where M = Cu(II), Ni(II), Co(II). The X-band ESR
spectra of VO(IV) and Cu(II) complexes were recorded in DMSO at LNT and their parameters were calculated. All these complexes are
paramagnetic and thermal studies show that in all the cases a stable metal oxide was obtained as the residue. The metal complexes have
been screened for their antibacterial activity against organisms like E. coli, S. aureus, Serattai sp, P. aeruginosa and B. cereus and it was
found that the complexes were more active than the corresponding ligand.
Keywords: Schiff base, Benzil, Anthranilic acid, Metal complexes, Antibacterial studies.
from Merck and used as such without any further purification.
The elemental analysis (CHNS) were performed using EL
elemental analyser at Central Electrochemical Research
Institute (CECRI). The FT infrared spectra were recorded in
the range 4000-400 cm-1 on a Schimadzu FTIR 8400S spectro-
meter using KBr pellet techniques. Electronic (UV-VIS) spectra
were recorded on a Schimadzu UVspectrophototmeter in the
range 200-1100 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
10K/min. The ESR spectra of various Schiff base complexes
were recorded on a JES-X3 series in the scan range of 2300-
4300 Gauss at LNT. The magnetic susceptibility measurements
of the complexes were carried out using Gouy balance. 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.
INTRODUCTION
Addition of an amine to a compound containing a carbonyl
functional group produces an imine (N=CH-) known as Schiff
bases. Schiff bases have been playing an important part in
the development of coordination chemistry. Schiff base metal
complexes have been studied extensively because of their
attractive chemical and physical properties and their wide range
of applications in numerous scientific areas. They play an
important role in both synthetic and structural research, because
of their preparative accessibility and structural diversity [1].
These complexes are extensively examined due to their wide
applications in various fields like biological, pharmacological,
clinical, analytical [2-4] and industrial area [5]. A search
through the literature reveals that no work has been done on
transition metal complexes of Schiff bases formed by the
condensation of benzil and anthranilic acid. So in this paper
we describe the synthesis, structural characterization and anti-
bacterial studies of Schiff base complexes derived from benzil
and anthranilic acid [N2O2 donor].
Synthesis of Schiff base of benzil and anthranilic acid
(BEA): To the ethanolic solution of benzil (4.20 g, 0.02 mol in
20 mL ethanol) an ethanolic solution of 2-anthranilic acid (5.48
g, 0.04 mol in 20 mL ethanol) was added, followed by the
addition of anhydrous sodium acetate (3 g) and the mixture
was refluxed for 1 h. The hot solution was poured into ice
EXPERIMENTAL
Benzil, anthranilic acid, VOSO4·5H2O, CuCl2·2H2O,
NiCl2·5H2O, CoCl2·6H2O, ethyl alcohol, etc. were purchased

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Vol. 29, No. 6 (2017) Studies ofVO(IV), Cu(II), Ni(II), Co(II) Chelates of Tetradentate Schiff Base Derived from Benzil andAnthranilicAcid 1309
cold water where upon a grey precipitate of the Schiff base
was separated, filtered, washed with water, and dried in vacuo
[6]. The scheme of preparation is shown in Fig. 1.
metal ion. Coordination to the metal through the nitrogen atom
is expected to reduce the bond strength of azomethine group
and lowers the ν(C=N). The spectrum of the free Schiff base
ligand BEA shows -C=N bands at region 1658 cm-1 shifted to
lower frequency in the complexes 1615-1606 cm-1 showing
the involvement of the coordination of C=N to the metal [7-10].
The frequency corresponding to ν(COO)– present in the
ligand 1480 cm-1 is shifted to lower values 1470-1450 cm-1 in
the complexes, indicating the coordination through the oxygen
atom of the carboxylate COO– anion. The ν(OH) due to water
is present in the range 3845-3308 cm-1 except vanadyl complex
indicating the presence of hydrated water [11,12]. It was further
supported by M-N peak at 483-426 cm-1 and M-O peak in the
range 592-585 cm-1 [13,14].A new peak at 998 cm-1 in vanadyl
complex is due to ν(V=O) [15]. The IR spectral data are given
in Table-2.
Synthesis of metal complexes
• The vanadium complex was prepared by refluxing 1:1
molar ethanolic mixture of the vanadium salt, VOSO4·5H2O
(2.530 g, 0.01 mol) with the ligand (4.484 g, 0.01mol) for 3 h
followed by dropwise addition of ammonia until metal chelate
separated. It was suction filtered washed with ethanol and
ether before dried in vacumm dessicator. The compound was
recrystallized from rectified spirit and dried.
• The same method was adopted for other complexes in
which CuCl2·2H2O (1.704 g, 0.01 mol), NiCl2·5H2O (2.376,
0.01 mol), CoCl2·6H2O (2.379 g, 0.01 mol), was added to the
ligand (4.484 g, 0.01 mol) in ethanol medium.
UV-visible electronic spectra and magnetic suscepti-
bility measurement: The free ligand shows absorption
maxima appearing around 38461 and 31250 cm-1 due to n→π*
and π→π* transition respectively. The electronic spectrum of
[VO(BEA)] shows peaks at 11792, 15337 and 21276 cm-1
RESULTS AND DISCUSSION
Elemental analysis and molar conductance studies: The
analytical data (Table-1) suggests 1:1 metal:ligand stoichio-
metry and the synthesized complexes have the molecular
formula [VO(BEA)] and [M(BEA)·(H2O)2] where M = Cu2+,
Ni2+ and Co2+. These complexes are stable and green in colour.
These complexes have molar conductance in the range of 12.5-
17.5 S cm2 mol-1 indicating that they are non-electrolytic in
nature. The microanalytical data and its molar conductance
are presented in Table-1.
assigned to be B2→2E, B2→2B1 and B2→2A1 transitions
respectively supports the square pyramidal structure of the
complex [16-20] and confirmed by its magnetic moment of
1.78 BM [19]. The three peaks obtained at 10869, 16666 and
2
2
2
4
19011 cm-1 in Co(II) complexes is assigned to T1g(F) →
4
4
4T2g(F)ν1, T1g(F) → 4A2g(F)ν2 and T1g(F) → 4T1g(P)ν3,
respectively suggesting a distorted octahedral geometry [17]
around Co(II) ion. It was also supported by its magnetic moment
Infrared analyses: IR spectra provide valuable informa-
tion regarding the nature of functional group attached to the
NH2
C
N
C
N
2
COOH
C
O
C
O
COOH HOOC
Fig. 1. Schematic representation of the synthesis of tetradentate ligand BEA
TABLE-1
PHYSICAL CHARACTERISATION, ANALYTICAL AND MOLAR CONDUCTANCE DATA
M (S cm2
mol-1)
Elemental analysis (%): Found (calcd.)
Yield
(%)
Λ
Compound
m.w.
Colour
C
H
N
M
C28H20N2O4(BEA)
[VO(BEA)]
448.46
515.4
Grey
Dark green
Green
80
75
75
70
70
72.79 (74.98)
65.24 (65.24)
60.55 (61.36)
60.55 (61.92)
60.90 (61.88)
4.221 (4.495)
3.9115 (3.9115)
4.257 (4.414)
4.257 (4.453)
4.233 (4.451)
6.013 (6.248)
5.411 (5.436)
5.100 (5.112)
5.100 (5.158)
4.989 (5.156)
–
–
12.90 (12.98)
11.00 (11.59)
11.00 (10.80)
11.10 (10.80)
13.5
13.5
17.5
12.5
[Cu(BEA)·(H2O)2]
[Ni(BEA)·(H2O)2]
[Co(BEA)·(H2O)2]
548.04
543.20
543.42
Green
Green
TABLE-2
INFRARED SPECTRAL DATA OF THE SCHIFF BASES AND ITS METAL COMPLEXES
ν(COO)–
ν(M–O)
ν(M–N)
ν(V=O)
Compound
ν(OH)
ν(C=N)
C28H20N2O4(BEA)
[VO(BEA)]
–
1658
1615
1606
1614
1613
1480
1450
1459
1457
1457
–
–
–
998
–
–
590
590
592
585
467
483
450
426
[Cu(BEA)·(H2O)2]
[Ni(BEA)·(H2O)2]
[Co(BEA)·(H2O)2]
3345
3305
3308
–
–

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1310 Gayathri et al.
Asian J. Chem.
[VO(BEA)]130−600 °C→½V2O5 + Gaseous products
value of 4.40 BM [21]. The electronic spectrum of Cu(II)
complex shows d-d transition band in the range 13037, 19083
and 24038 cm-1 corresponds to 2A1g→2B1g (dz2 → dx2-y2) ν1,
Thermal curve of Ni2+ complex [Ni(BEA)(H2O)2] in static
air atmosphere is given in Fig. 3. It shows an initial mass loss
of 6.5 % in the range 50-100 °C itself, due to the loss of two
water molecules from the complex. The calculated value of
6.62 % is in good agreement with this. The second stage of
decomposition starts at 100 °C and progressing till 363.56 °C
with a mass loss of 53.5 % and third stage was in the range
363.56-650 °C with a mass loss of about 25.8 % leaving behind
a residual percentage of 14.2 %. Above 650 °C a horizontal
plateau was observed. The second and third stage of decom-
position corresponds to the decomposition of bulky ligand from
the complex leaving NiO, as the stable residue. The calculated
value of the residue 13.75 % is in good agreement with the
observed value of 14.2 %.
2
2
2
B2g→2B1g (dxy → dx -y ) ν2 and Eg→ B1g (dxz, dyz → dx -y )ν3
2
2
2 2
transition respectively [17]. The spectrum is typical for a
distorted octahedral geometry. The magnetic moment of 1.86
BM, also supports this [21]. The electronic spectrum of Ni(II)
complex shows three absorption maxima at 12315, 14450 and
20283 cm-1. These are characteristic of octahedral Ni(II) comp-
lexes and assigned to be 3A2g→3T2g(F)ν1, 3A2g→3T1g(F)ν2 and
3A2g→3T1g(P)→3 transition respectively [22]. Its magnetic
moment was found to be 3.01 BM supporting octahedral
environment [21] around Ni(II) ion (Table-3).
TABLE-3
UV-VISIBLE SPECTRAL DATA AND
MAGNETIC MOMENTS OF THE COMPLEXES
heating
→
Stage I [Ni(BEA)(H2O)2]
Ni(BEA)] + 2H O
2
Absorption
max (cm–1)
µeff
(BM)
Compound
Assignments
Stage II [Ni(BEA)]
NiO + gaseous products
→
38461
31250
n→π*
π→π*
2B2→2E
2B2→2B1
2B2→2A1
C28H20N2O4(BEA)
120
100
80
60
40
20
0
11792
15337
21276
100
80
60
40
20
0
2
1
[VO(BEA)]
1.78
1.86
3.01
4.40
456.82 °C
430.4 J/g
13037
19083
24038
2A1g→2B1g (ν1)
2B2g→2B1g (ν2)
2Eg→2B1g (ν3)
3A2g→3T2g(F) (ν1)
3A2g→3T1g(F) (ν2)
3A2g→3T1g(P) (ν3)
4T1g(F)→4T2g(F)
4T1g(F)→4A2g(F)
4T1g(F)→4T1g(P)
363.56 °C
[Cu(BEA)·(H2O)2]
[Ni(BEA)·(H2O)2]
[Co(BEA)·(H2O)2]
0
570.14 °C
254.07 °C
1036 J/g
-1
12315
14450
20283
-20
0
200
400
Temperature (°C)
Fig. 3. TG/DTA curve of [Ni(BEA)·(H2O)2] in static air
600
800
1000
10869
16666
19011
ESR spectroscopy: The X-band ESR spectrum of the
complex [VO(BEA)] was recorded in DMSO at LNT (77 K),
given in Fig. 4. In the frozen state, it shows two sets of eight
lines which are due to parallel and perpendicular resonance
feature of VO2+. The eight line peaks are due to hyperfine
splitting originating from the interaction of unpaired electrons
with 51V nucleus having a nuclear spin of I = 7/2. This confirms
the presence of single oxovanadium(IV) in the complex [23,24].
The g||, g⊥, g(av), A||, A⊥ and A(av) are calculated using the
equation:
Thermal studies: From the thermogram of [VO(BEA)]
given in Fig. 2, it was observed that the compound is thermally
stable upto 130 °C indicated by a well defined horizontal
plateau. The first stage decomposition is seen starting at 130
°C and progressing till 290 °C. The weight loss during this
stage was 70 %. The second stage of decomposition starts at
290 °C itself and ends at 600 °C with mass loss of 12.5 %.
Above 600 °C the residue is seen stable at static air atmosphere,
with a mass percentage of 17.5 %. The compound was stable
upto 130 °C, indicates that there is no water molecules attached
to it. The first and second stage of decomposition was due to
the breaking of bulky tetradentate Schiff bases from the
complex, leaving behind a residue, V2O5, stable oxide of
vanadium. The calculated value of the residue 17.63 % is in
good agreement with the observed value of 17.5 %.
gβH = hν
g(av) = 1/3(g|| + 2 g⊥)
A(av) = 1/3 (A|| + 2 A⊥)
The observed values are g|| = 1.97, g⊥ = 1.99, g(av) = 1.9833;
A|| = 194 G, A⊥ = 74 G, A(av) = 114 G.
120
100
80
60
40
20
0
40
20
0
2047
2
0
-20
-40
-2048
226.638
0
200
400
Temperature (°C)
Fig. 2. TG/DTA curve of [VO(BEA)] in static air
600
800
1000
326.638
mT
426.638
Fig. 4. ESR spectrum of [VO(BEA)] in LNT

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Vol. 29, No. 6 (2017) Studies ofVO(IV), Cu(II), Ni(II), Co(II) Chelates of Tetradentate Schiff Base Derived from Benzil andAnthranilicAcid 1311
It was found that g|| < g⊥ in the complex which is in good
agreement with its square pyramidal geometry.
Conclusion
In this work, the synthesis and characterization of tetra-
The X-band ESR spectrum of [Cu(BEA)·(H2O)2] in
DMSO in the frozen state at 77 K shows four well resolved
peaks of low intensities in the low field region and one intense
peak in the high field region given in Fig. 5. It was found that
the g|| value is 2.3463, g⊥ = 2.0645 and g(av) = 1/3(g|| + 2 g⊥) =
2.1524. The g tensor values of copper(II) complex can be used
to derive the ground state of the complex. If g|| > g⊥ > 2.0023,
dentate Schiff base ligand derived from benzil and anthranilic
acid and its interaction with various transition metals likeVO2+,
Cu2+, Ni2+ and Co2+ are reported. The metal complexes formed
were non-electrolytic in nature. The synthesized systems were
characterized by micro-analysis, molar conductance values,
FTIR, ESR, UV spectroscopy and TG analyses. These analytical
and spectral data suggests that azomethine N atoms, oxygens
from carboxyl group are coordinated to oxovanadium(IV)
resulted into VO(N2O2) square pyramidal structure and due to
two molecules of coordinated water, octahedral geometry was
predicted for the others. The antibacterial screening tests were
also performed against bacteria which indicate that the
complexes exhibit good antibacterial activity than the ligand.
Based on the above results, the structure of coordination com-
pounds under investigation are formulated in Fig. 6.
2
the unpaired electron lies in the dx orbital and g⊥ > g|| >
2
-y
2
2.0023, the unpaired electron is in the dz orbital. The inter-
action term G is calculated using the equation G = (g|| - 2.0023)/
(g⊥ - 2.0023) and is greater than 4. The local tetragonal axes
are aligned parallel or only slightly misaligned, while G <
4.0, significant exchange coupling is present and the misalign-
ment is appreciable. From the observed value it was clear that
g|| (2.3463) > g⊥ (2.0645) > 2.0023 and the value of G in a
complex 5.53 suggests that the local tetragonal axes are aligned
parallel or slightly misaligned, the unpaired electron is present
2
2
in dx -y orbital [25-27] and the complex is distorted octahedral.
C
N
C
N
2047
O
V
COO
OOC
-2048
206.866
306.866
mT
406.866
C
N
C
N
Fig. 5. ESR spectrum of [Cu(BEA)·(H2O)2] in LNT
H2O
M
Antibacterial studies: The ligand and its metal complexes
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 all the
metal 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 acivity
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 charge of the metal ion with donor groups. Therefore
the delocalization of π electrons in the chelate ring increases
and enhances the penetration of the complexes into lipid mem-
branes. The antibacterial data are presented in Table-4.
COO
OOC
H2O
(M = Cu2+, Ni2+ Co2+)
Fig. 6. Proposed structure of the metal complexes
ACKNOWLEDGEMENTS
The authors are thankful to The Principal, Govt. Arts
College, Ooty; The Head, Department of Chemistry, Govt.
Arts College, Ooty; The Head, Department of Pharmaceutical
Chemistry, JSS College of Pharmacy, Ooty; The Head, SAIF,
Pondicherry University; The Head, SAIF, CECRI,Karaikudi
and The Head, SAIF, IIT-Chennai; The Head, Department of
Chemistry, SRMV College ofArts & Science, Coimbatore and
Madurai Kamaraj University, Madurai, India for recording the
spectral data and performing the antibacterial studies.
TABLE-4
ANTIBACTERIAL ACTIVITY DATA OF THE LIGAND AND ITS METAL COMPLEXES
Staphylococcus
aureus
Pseudomonas
aeruginosa
Compound
Escherichia coli
Serratia sp
Bacillus cereus
Inference
C28H20N2O4(BEA)
[VO(BEA)]
9
15
9
12
14
14
16
15
8
12
8
9
11
8
12
12
8
++
+++
++
[Cu(BEA)·(H2O)2]
[Ni(BEA)·(H2O)2]
[Co(BEA)·(H2O)2]
10
9
6
9
10
11
9
+++
++
8