Synthesis and characterization of schiff base complexes of o-vanillin and anthranilic acid and their biological evaluation

Article abstract of DOI:10.14233/ajchem.2018.21362

Complexes of Schiff base derived from o-vanillin (2-hydroxy-3-methoxybenzaldehyde) and anthranilic acid (2-aminobenzoic acid) has been used for complexation with Mn(II), Fe(II) and Co(II). The complexes have been formulated as [ML2X2] where X = pyridine or α-picoline on the basic of their microanalysis. Infrared spectral study has been made to confirm the coordination sites of the Schiff base. The magnetic susceptibility and electronic spectral study leads to tetragonally distorted octahedral symmetry (T4h) of complexes. Their biological evaluation with different strains of bacteria suggest that the complexes are more active than the ligand against both Gram-positive and Gram-negative bacteria.

Full text of DOI:10.14233/ajchem.2018.21362

Asian Journal of Chemistry; Vol. 30, No. 9 (2018), 1989-1993
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2018.21362
Synthesis and Characterization of Schiff Base Complexes of o-Vanillin
and Anthranilic Acid and Their Biological Evaluation
1
2
2
2
2,*
RAJEEV PRADHAN , SUMIT KUMAR SINHA , PUNAM VERMA , SUNNY KUMAR and SHIVADHAR SHARMA
1Department of Chemistry, P.K. Roy Memorial College, Dhanbad-826 004, India
2Department of Chemistry, Magadh University, Bodh Gaya-824 234, India
*Corresponding author: Tel: +91 631 2220039; E-mail: sharma.shivadhar@gmail.com
Received: 2 April 2018;
Accepted: 10 May 2018;
Published online: 31 July 2018;
AJC-19007
Complexes of Schiff base derived from o-vanillin (2-hydroxy-3-methoxybenzaldehyde) and anthranilic acid (2-aminobenzoic acid) has
been used for complexation with Mn(II), Fe(II) and Co(II). The complexes have been formulated as [ML2X2] where X = pyridine or α-
picoline on the basic of their microanalysis. Infrared spectral study has been made to confirm the coordination sites of the Schiff base. The
magnetic susceptibility and electronic spectral study leads to tetragonally distorted octahedral symmetry (T4h) of complexes. Their biological
evaluation with different strains of bacteria suggest that the complexes are more active than the ligand against both Gram-positive and
Gram-negative bacteria.
Keywords: Magnetically dilute, Distorted octahedral, Escherichia colii, Bacillus subtilis, Schiff bases, Transition metal complexes.
lexes, we made the study of synthesis, characterization and
biological evaluation of some transition metal complexes with
Schiff base ligand derived from o-vanillin and anthranilic acid
i.e., N-(2'-benzoic acid)-2-hydroxy-3-methoxy benzalidine
(BHMBH).
INTRODUCTION
The condensation of o-vanillin (2-hydroxy-3-methoxy-
benzaldehyde) with biologically active anthranilic acid (2-
aminobenzoic acid) leads to the formation of a stable Schiff
base. It is an interesting and fascinating member of the family
of Schiff bases containing two aromatic rings with –OH group
at ortho position. The amino acids on condensation with an
aldehyde group has shown conserved activity upon inactivation
of the –NH2 group of the parent anthranilic acid [1-4]. Different
types of Schiff base ligands and their transition metal complexes
have been widely studied for biological [5-8], material [9-12]
and industrial applications [13,14]. In the field of coordination
chemistry the Schiff base ligand have received special attention
as polyfunctional ligands in metal complexes which exhibit a
variety of pharmaceutical activities like antimicrobial, anti-
tuberculosis, antitumoral and antioxidant agents [15-17].
Because of the biological relevance a large no. of transition
metal complexes have been synthesized and explored as model
system in bio-inorganic chemistry [18]. Generally Schiff base
ligands act as chelating ligands and the biological activities of
Schiff base ligands on coordination get enhanced [19-21].
From the fascinating biological activities of Schiff base comp-
EXPERIMENTAL
All the reagents used for present work of Anal-R grade,
o-vanillin was procured from Aldrich was used without further
purification. Anthranilic acid was prepared by Hoffmann
bromamide method [22] that involves the oxidation of phthal-
imide with aquous sodium hypochloride followed by treatment
with HCl as given in Scheme-I.
The Schiff base was prepared by the condensation of 0.01
M (1.52 g) of o-vanillin and 0.01 M (1.37 g) of anthranilic
acid in ethanolic medium with pH in slightly acidic range
(Scheme-II).
The metal complexes were prepared by refluxing 0.01 M
of metal salt of Mn(II), Fe(II) and Co(II) with 0.02 M (5.42 g)
of Schiff base BHMBH in ethanolic medium for 3-4 h.A little
of sodium acetate was added to make the medium slightly
alkaline followed by the addition of 0.02 M of pyridine or
α-picoline slowly to the boiling solution. The solution was cooled
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1990 Pradhan et al.
Asian J. Chem.
O
O
NH2
OsNa
NH2
OH
NH2
NaOH
NaOCl
HCl
N–H
r
r
OsNa
O
O
O
O
Scheme-I
OH
COOH
any change in the IR-spectra of complexes showing its non-
involvement in coordination. This medium band appearing at
3000 cm-1 is assigned to new C-H of phenyl group [29]. The
bands at 1610 and 1525 cm-1 taken in conjugation with new
C-H stretching band affords a ready means of recognition of
aromatic ring in the ligand [30,31]. The medium band appearing
at 2820 cm-1 in the spectra of free ligand is assigned to stret-
ching vibration of C-H bond of methyl group of the ligand [32].
The presence of methoxy group in the ligand is further subs-
tantiated by a medium band at 1160 cm-1 in the IR-spectra of
free ligand due to ν(C-O-C) stretching vibration. This band
also does not suffer any change after complexation which is
indicative of its non-participation in coordination. The weak
band at 2730 cm-1 may be assigned to ν(CH=) moiety of
the free ligand. The sharp band appearing at 1640 cm-1 is
assigned to ν(CH=N) (azomethine group) vibration which
undergoes shift by 30-35 cm-1 in complexes [33,34]. This
indicates the coordination of azomethine nitrogen to the metal
ion in complexes. The band at 1720 cm-1 in the IR spectra of
free ligand is indicative of the presence of aro-COOH group
in the free ligand. In complexes this band gets split into two
bands and appears at 1570-1560 cm-1 and 1410-1400 cm-1 due
to antisymmetric and symmetric stretching of ν(C-O) of
H+
H3CO
C
O
H2N
+
H
OH
COOH
H3CO
C
H
N
Scheme-II
to room temperature and was stirred for 20 min where by the
precipitate of complexes appeared which was filtered on
suction and washed with ethanol. It was dried in an electric
oven at 100 °C. Their yield and melting points were recorded.
The % of C, H and N was determined Perkin-Elmer 2400 CHN
elemental analyzer and their molar conductivities were deter-
mined in 10-3 M solution in DMF on conductivity meter CG-
857 Schott-Grate G-mbH. The IR spectra of the ligand and
complexes were recorded on Shimadzu FTIR-8400 spectro-
photometer using KBr disc. Their magnetic susceptibility was
determined at room temperature using Gouy balance while
their electronic spectra were recorded on Perkin-Elmer UV/
vis spectrophotometer Lambda in D.M.F. solution. The %
composition, molar conductivity and magnetic susceptibility
have been given in Table-1.
O
C
. It shows that during complexation the deprotonation
O
of acid group has occurred followed by its coordination through
oxygen [35,36]. The separation between νassym and νsym of
–COO– group is about 160 cm-1which is indicative of mono-
dentate coordination of the carboxylate ion [37,38]. The IR-
spectra of complexes 1, 3 and 5 display a new band at 760-
750 cm-1 due to the coordination of pyridine through nitrogen
and the complexes no. 2, 4 and 6 show the appearance of a
new band at 810-800 cm-1 due to co-ordination of α-picoline
through nitrogen [39,40]. The new band appearing at 425-
410 and 510-500 cm-1 are safely assigned to ν(M-O) and ν(M-
N) stretching vibration further conform our above assertion
of the coordination mode of the ligand [41].
RESULTS AND DISCUSSION
The molar conductivities values for all the complexes are
around 15 ohm-1 cm2 mol-1 which indicate their non-electrolytic
nature [23-26]. On the basis of % composition and molar con-
ductivity values, complexes are formulated as [ML2X2] where
L = BHMBH and X = pyridine or α-picoline.
Infrared spectra: The important IR-bands of ligands
and complexes have been assigned and interpreted. The free
ligand absorbs strongly at 3540 cm-1 due to phenolic –OH
group stretching vibration [27,28]. This band does not undergo
TABLE-1
PERCENTAGE COMPOSITION, MOLAR CONDUCTANCE AND MAGNETIC MOMENT (FOUND/CALCULATED)
λm (ohm-1
Complexes
Colour
m.p. (°C)
M
–
C
H
N
µeff (B.M.)
cm2 mol-1)
–
Schiff base (BHMBH)
[MnL2(py)2]
[MnL2(α-pico)2]
[FeL2(py)2]
[FeL2(α-pico)2]
[CoL2(py)2]
[CoL2(α-pico)2]
Light yellow
Light orange
Orange
192
278
280
292
298
310
315
66.68 (66.42) 4.43 (4.40)
5.00 (5.17)
7.33 (7.42)
7.00 (7.15)
7.32 (7.40)
6.95 (7.14)
7.16 (7.38)
6.52 (6.73)
–
7.12 (7.28) 63.72 (63.58) 4.48 (4.77)
6.92 (7.02) 64.58 (64.36) 4.88 (5.11)
7.28 (7.40) 63.72 (63.49) 4.45 (4.76)
7.00 (7.14) 64.46 (64.28) 4.96 (5.10)
7.52 (7.77) 63.46 (63.24) 4.51 (4.74)
7.31 (7.50) 64.34 (63.04) 6.91 (5.08)
15.30
10.60
13.23
14.45
11.51
15.10
5.86
5.82
5.10
5.12
4.80
4.83
Green
Light green
Light pink
Light pink

Vol. 30, No. 9 (2018)
Synthesis and Characterization of Schiff Base Complexes of o-Vanillin and Anthranilic Acid 1991
TABLE-3
Complexes
Dq (cm-1)
B (cm-1)
C (cm-1)
C/B
β (%)
0.1136
0.137
[Mn(BHMBH)2(py)2]
[Mn(BHMBH)2(α-pico)2]
1034.47
1063.63
862.06
844.15
3084.98
3029.89
3.579
3.589
Magnetic moment and electronic spectra
TABLE-5
Mn(II) complexes: The magnetic moment of Mn(II) com-
plexes lies between 5.82-5.86 B.M. which is very close to the
µs value corresponding to five unpaired electrons. It shows
that these complexes are spin free octahedral magnetically
dilute [42]. The electronic spectra of Mn(II) complexes display
three bands which has been given in Table-2 below with their
assignments.
Complexes
Dq(xy)
Dq(z)
Ds
Dt
(cm–1)
(cm–1)
(cm–1)
1557
1488
(cm–1)
[Fe(BHMBH)2(py)2]
[Fe(BHMBH)2(α-pico)2]
1170
1140
5709
5746
2594
2632
Co(II) complexes: The magnetic moment of Co(II) comp-
lexes have been found 4.80 and 4.83 B.M. These values are in
good agreement with the values reported for octahedral comp-
lexes of Co(II) [47,48]. Cobalt(II) complexes display three
bands in their electronic spectra. The spectral band with their
assignment have been displayed in Table-6.
TABLE-2
Electronic spectral bands (cm-1)
Complexes
ν1
ν2
ν3
[Mn(BHMBH)2(py)2]
[Mn(BHMBH)2(α-pico)2]
Assignments:
20000
19500
24000
23480
30080
29500
TABLE-6
Electronic spectral bands (cm-1)
Complexes
ν1: 6A1g → 4T1g (4G) = 20000 & 19500 cm-1
ν2: 6A1g → 4T2g (4G) = 24000 & 23480 cm-1
ν3: 6A1g → 4Eg (4D) = 30080 & 29500 cm-1
ν1
7200
7300
ν2
15250
15360
ν3
19300
19450
[Co(BHMBH)2(py)2]
[Co(BHMBH)2(α-pico)2]
Assignments:
4E1g → 2T2g (ν1); 4T1g → 4A2g (ν2); 4T1g → 4T1g(P) (ν3)
The low intensity of these bands may be attributed to the
spin forbidden transition [43]. The values of different crystal
field parameters have been derived using Tanabe-Sugano
diagram and the values have been displayed in Table-3.
The value of C/B derived for Mn(II) complexes (3.579
and 3.589) is very close to the theoretical value 3.8. The greater
value of Dq for the second complex is due to the effect of the
secondary ligand α-picoline which is a better donor than the
pyridine due to +I effect of –CH3 group at α-position. The values
are in good agreement with those reported for octahedral com-
plexes of Mn(II) [44-46].
Various crystal field parameters have been derived by
using reported equations [49] and the values have been shown
in Table-7.
TABLE-7
10 Dq
Complexes
B (cm–1)
ν2/ν1
β (%)
(cm–1)
10605
11992
[Co(BHMBH)2(py)2]
[Co(BHMBH)2(α-pico)2]
2.12
2.104
731.4
648.24
24.59
33.17
Fe(II) complexes: The magnetic moment of Fe(II) comp-
lexes are 5.10 and 5.12 B.M. The values are greater than expected
for 4 unpaired electrons, t2g4 eg2 (4.898 B.M.) which may be
due to the strong contribution from triply degenerate ground
Values of different crystal field parameters are in good
agreement with the reported values for octahedral values for
octahedral Co(II) complexes with slight distortion [50,51]. The
tentative structure of the metal complexes may be given as:
5
term, T2g in octahedral symmetry. Their electronic spectra
display three bands which indicate the further splitting of both
ground state 5T2g and excited state 5Eg under the influence of
tetragonal distortion. The bands and their assignments have
been given in Table-4.
H3CO
OH
CH
N
X
TABLE-4
O
C
Electronic spectral bands (cm-1)
(II)
M
O
Complexes
C
O
O
ν1
8300
8700
ν2
17400
18380
ν3
20000
20100
[Fe(BHMBH)2(py)2]
[Fe(BHMBH)2(α-pico)2]
Assignments:
N
X
5Eg → 5B2g (ν1); 5Eg → 5A1g (ν2); 5Eg → 5B2g (ν3)
CH
Various crystal field parameters have been derived from
the electronic spectral bands and values have been displayed
in Table-5.
The values obviously show that there is appreciable
amount of distortion in octahedral symmetry of Fe(II) comp-
lexes.
HO
OCH3
M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II)
X = pyridine and α-picoline
Biological evaluation: The ligand as well as complexes
were screened for their in vitro antibacterial activity against

1992 Pradhan et al.
Asian J. Chem.
TABLE-8
ANTIBACTERIAL SCREENING OF LIGAND AND ITS COMPLEXES-DIAMETER OF
INHIBITION ZONE (mm) AND ACTIVITY INDEX (%)
Gram-positive bacteria
Inhibition
Gram-negative bacteria
Inhibition
zone
50 100
Inhibition
zone
50 100
Inhibition
zone
Activity zone
Activity zone
50 100
Activity zone
50 100
Activity zone
zone
Concentration
Schiff base (BHMBH)
[MnL2(py)2]
[MnL2(α-pico)2]
[FeL2(py)2]
[FeL2(α-pico)2]
[CoL2(py)2]
[CoL2(α-pico)2]
Streptomycin
50
100
50 100
50 100
50
100
12
17
17
16
16
15
15
18
15
21
21
19
19
18
18
22
66.66 68.18 11
94.44 95.45 16
94.44 95.45 16
88.88 86.36 15
88.88 86.36 15
83.33 81.81 14
83.33 81.81 14
16
23
23
21
21
20
20
24
64.70 66.66 12
94.11 95.83 17
94.11 95.83 17
88.23 87.50 16
88.23 87.50 16
82.35 83.33 15
82.35 83.33 15
19
27
27
24
24
23
23
28
66.66 67.85 11
94.44 96.42 15
94.44 96.42 15
88.88 85.71 14
88.88 85.71 14
83.33 82.14 13
83.33 82.14 13
15
21
21
19
19
18
18
22
68.75 68.18
93.75 95.45
93.75 95.45
87.50 86.36
87.50 86.36
81.25 81.81
81.25 81.81
100
100
17
100
100
18
100
100
16
100
100
TABLE-9
ANTIFUNGAL SCREENING OF LIGAND AND ITS COMPLEXES-DIAMETER OF INHIBITION ZONE (mm) and ACTIVITY INDEX (%)
Asepergillus flavu Fusariumoxy
Inhibition zone Activity zone
50
Inhibition zone
50 100
Activity zone
Concentration
Schiff base (BHMBH)
[MnL2(py)2]
[MnL2(α-pico)2]
[FeL2(py)2]
[FeL2(α-pico)2]
[CoL2(py)2]
[CoL2(α-pico)2]
Clotrimazole
100
19
27
27
24
24
23
23
28
50
100
50
100
14
19
19
17
17
16
16
20
70.00
95.00
95.00
85.00
85.00
80.00
80.00
100
67.85
96.42
96.42
85.71
85.71
82.14
82.14
100
13
18
18
16
16
15
15
19
19
27
27
24
24
23
23
28
68.42
94.73
94.73
84.21
84.21
78.94
78.94
100
67.85
96.42
96.42
85.71
85.71
82.14
82.14
100
Gram-positive bacteria Bacillus subtilis, Staphylococcus aureus
and Gram-negative bacteria Escherichia coli and Klebsilla
pneumonia by disc diffusion method using nutrient Agar as
medium and streptomycin as control. The in vitro antifungal
activities of the ligand and its metal complexes have been tested
against the fungi Asepergillus flavu and Fusariumoxy by well
diffusion method on potato dextrose agar as the medium and
clotrimazole as control. The compounds were dissolved in
DMSO and solution of different concentration like 50 ppm
and 100 ppm were prepared separately. The well mode on agar
medium was inoculated with microorganism. The well was
filled with the test solution using a micro pipette and the plate
was incubated 24 h for bacteria at 35 °C and 72 h for fungi at
30 °C. During this period the test solution got diffused and the
growth of inoculated microorganism was effected. The
inhibition zone was developed at which the concentration was
noted down. All the determinations were performed thrice and
activity index of compounds was determined using the expression:
Inhibition zone by test compound
of complexes due to chelation [52].All Mn(II) complexes show
the highest activity which may be due to its toxic nature [53].
Conclusion
On the basis of forgoing study of the transition metal
complexes it may be concluded that the ligand acts as mono
anionic bidentate coordinating through azomethine nitrogen
and deprotonated carboxylic acid oxygen forming a six
membered chelate. The complexes are octahedral with slightly
tetragonal distortion. The ligand as well as its complexes are
active against Gram-positive and Gram-negative bacteria and
also against both the fungi. The biological activity of ligand
gets enhanced after complexation with transition metal ions.
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests
regarding the publication of this article.
REFERENCES
(diameter in mm)
1. A. Zubrys and C.O. Siebenmann, Can. J. Chem., 33, 11 (1955);
https://doi.org/10.1139/v55-003.
2. R. Maccari, R. Ottana and M.G. Vigorita, Bioorg. Med. Chem. Lett., 15,
2509 (2005);
Activity index (%) =
×100
Inhibition zone by control compound
(diameter in mm)
The results have been displayed in Tables 8 and 9. It is
obvious from the results that the ligand and its metal complexes
show positive activity towards Gram-positive and Gram-
negative bacteria and also to the fungi. It is also clear that the
biological activity of the ligand gets enhanced appreciably
in complexes. The activity of the ligand may be attributed to
azomethine linkage in it. The increased activity of the metal
complexes can be ascribed to the increase in lipophilic nature
https://doi.org/10.1016/j.bmcl.2005.03.065.
3. B. Villemagne, C. Crauste, M. Flipo, A.R. Baulard, B. Deprez and N.
Willand, Eur. J. Med. Chem., 51, 1 (2012);
https://doi.org/10.1016/j.ejmech.2012.02.033.
4. M.A. Bhat and M.A. Al-Omar, Med. Chem. Res., 22, 4522 (2013);
https://doi.org/10.1007/s00044-012-0458-3.
5. A.M. Abu-Dief and I.M.A. Mohamed, Beni-Suef Univ. J. Basic Appl.
Sci., 4, 119 (2015);
https://doi.org/10.1016/j.bjbas.2015.05.004.

Vol. 30, No. 9 (2018)
Synthesis and Characterization of Schiff Base Complexes of o-Vanillin and Anthranilic Acid 1993
28. S. Manivannan, A. Manimaran, S. Arunachalam, C. Jaibalkrishnan and
V. Chinnusamy, J. Indian Chem. Soc., 85, 988 (2008).
29. S. Mallik, N. Kumari and D.K. Sharma, J. Indian Chem. Soc., 87, 539
(2010).
30. B.B. Mahapatra and N. Patel, J. Indian Chem. Soc., 86, 518 (2009).
31. A. Joseph, B. Joseph and B. Narayana, J. Indian Chem. Soc., 85, 479
(2008).
32. L.K. Mishra and B.K. Keshri, Indian J. Chem., 28A, 883 (1981).
33. A. Karim, R. Rani, R. Ranjan, U. Kumar, V. Kumar and S. Sharma,
Asian J. Chem., 29, 626 (2017);
6. W. Al Zoubi, Int. J. Org. Chem., 3, 73 (2013);
https://doi.org/10.4236/ijoc.2013.33A008.
7. C.M. da Silva, D.L. da Silva, L.V. Modolo, R.B.Alvesa, M.A. de Resende,
C.V.B. Martins and Â. Fátima, J. Adv. Res., 2, 1 (2011);
https://doi.org/10.1016/j.jare.2010.05.004.
8. G. Levy and T. Tsuchiya, N. Engl. J. Med., 287, 430 (1972);
https://doi.org/10.1056/NEJM197208312870903.
9. G. Gran, Analyst, 77, 661 (1952);
https://doi.org/10.1039/an9527700661.
10. D.B. Watlaufer, S.K. Malik, L. Stoller and R.L. Coffin, J. Am. Chem.
Soc., 86, 508 (1964);
https://doi.org/10.1021/ja01057a045.
11. G. Gran, Anal. Chim. Acta, 206, 111 (1988);
https://doi.org/10.1016/S0003-2670(00)80835-1.
12. R.S. Rao and G.N. Rao, Computer Applications in Chemistry,
Himalaya Publishing House, Mumbai, India, p. 302 (2005).
13. V.G. Kumari, M. Ramanaiah and B.B.V. Sailaja, Chem. Spec. Bioavail.,
27, 121 (2015);
https://doi.org/10.1080/09542299.2015.1087159.
14. C.N. Rao, M. Ramanaiah and B.B.V. Sailaja, Bull. Chem. Soc. Ethiop.,
30, 71 (2016);
https://doi.org/10.14233/ajchem.2017.20286.
34. J. Devi and M. Yadav, Asian J. Chem., 29, 551 (2017);
https://doi.org/10.14233/ajchem.2017.20236.
35. K. Nakamoto, Infrared Spectra of Inorganic and Coordination Comp-
ounds, John Wiley & Sons, Inc., New York, pp. 198-199 (1963).
36. R.N. Pandey and K. Sahi, Asian J. Chem., 23, 4508 (2011).
37. K.R.N. Bhowimik, A.K. De and R.N.D. Purkayastha, J. Indian Chem.
Soc., 89, 177 (2012).
38. C.T. Yang, M. VetricheIvan, X. Yang, B. Moubaraki, K.S. Murry and J.J.
Vittal, J. Chem. Soc., Dalton Trans., 113 (2014);
https://doi.org/10.1039/B310262A.
39. M.K. Singh, A.D.R. Laskar and B. Paul, J. Indian Chem. Soc., 85, 485
(2008).
https://doi.org/10.4314/bcse.v30i1.6.
15. R. Maccari, R. Ottanà, B. Bottari, E. Rotondo and M.G. Vigorita, Bioorg.
Med. Chem. Lett., 14, 5731 (2004);
40. S. Chandra, D. Jain, A. Sarkar and Anupama, J. Indian Chem. Soc., 86,
220 (2009).
41. N. Raman, J. Indian Chem. Soc., 85, 1082 (2008).
42. B.C. Guha, Proc. R. Soc. Lond. A Math. Phys. Sci., 206, 353 (1951);
https://doi.org/10.1098/rspa.1951.0075.
43. I.S. Ahuja, Indian J. Chem., 22A, 262 (1983).
44. V.P. Singh, S. Singh and A. Katiyar, J. Enzym. Inhib. Med. Chem., 24,
577 (2009);
https://doi.org/10.1016/j.bmcl.2004.09.052.
16. M.L. Ferreira, R.S.B. Gonçalves, L.N.F. Cardoso, C.R. Kaiser, A.L.P.
Candéa, M.G.M.O. Henriques, M.C.S. Lourenço, F.A.F.M. Bezerra and
M.V.N. de Souza, Sci. World J., 10, 1347 (2010);
https://doi.org/10.1100/tsw.2010.124.
17. P. Krishnamoorthy, P. Sathyadevi, A.H. Cowley, R.R. Butorac and N.
Dharmaraj, Eur. J. Med. Chem., 46, 3376 (2011);
https://doi.org/10.1080/14756360802318662.
45. T.T. Al-Nahary, J. Saudi Chem. Soc., 13, 253 (2009);
https://doi.org/10.1016/j.jscs.2009.10.004.
46. E. Soleimani, J. Chin. Chem. Soc., 57, 653 (2010);
https://doi.org/10.1002/jccs.201000091.
47. A.K. Singh, S.P. Sinha,V. Kumar, S.S. Rai and S. Sharma, Asian J. Chem.,
23, 4347 (2011).
48. B.K. Rai and R. Kumari, Asian J. Chem., 23, 4625 (2011).
49. A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Amsterdam,
edn 2, p. 818 (1984).
https://doi.org/10.1016/j.ejmech.2011.05.001.
18. M. Balakrishna, G.S. Rao, M. Ramanaiah, G.N. Rao and B. Ramaraju,
Res. J. Pharm. Biol. Chem. Sci., 6, 1430 (2015).
19. P. Bindu, M.R.P. Kurup and T.R. Satyakeerty, Polyhedron, 18, 321 (1998);
https://doi.org/10.1016/S0277-5387(98)00166-1.
20. R.V. Singh, N. Fahmi and M.K. Biyala, J. Iran. Chem. Soc., 2, 40 (2005);
https://doi.org/10.1007/BF03245778.
21. D.K.A. Kumar, A.P. Sangamesh and S.B. Prema, Int. J. Electrochem. Sci.,
4, 717 (2009).
50. B.K. Rai, J. Indian Chem. Soc., 90, 105 (2013).
51. K. Anbalagan and A.S. Ganesh Raja, J. Indian Chem. Soc., 90, 133
(2013).
52. N. Soltani, M. Behpour, S.M. Ghoreishi and H. Naeimi, Corros. Sci., 52,
1351 (2010);
22. I.L. Finar, Organic Chemistry, The English Language Book Society and
Longmann Group Limited, London, edn 6, vol. 1, pp. 764-765 (1982).
23. J.T. Makode and A.S. Aswar, Indian J. Chem., 43A, 2120 (2004).
24. K. Siddappa, P.C. Reddy, M. Kote, T. Reddy, M. Tambe and M. Mitra,
Asian J. Chem., 23, 4511 (2011).
https://doi.org/10.1016/j.corsci.2009.11.045.
53. M. Selvaganapathy and N. Raman, J. Chem. Biol. Ther., 1, 108 (2016);
https://doi.org/10.4172/2572-0406.1000108.
25. P. Kumari, S. Prakash and D. Prakash, J. Indian Chem. Soc., 89, 19 (2012).
26. R. Rani, R. Ranjan, N.C. Bhattacharzee, S. Sharma and F. Suraiya, J.
Indian Chem. Soc., 90, 331 (2013).
27. R. Prabhakaran, V. Krishnan, A. Geetha, H. Bertagnolli and K.
Natarajan, Inorg. Chim. Acta, 359, 1114 (2006);
https://doi.org/10.1016/j.ica.2005.11.028.