Synthesis, characterization and antimicrobial activity of new cobalt (II), nickel (II) and copper (II) complexes with 2-(2-hydroxy-1, 2- diphenylethylideneamino) benzoic acid

Article abstract of DOI:10.1016/j.inoche.2011.01.016

The new Schiff base ligand 2-(2-hydroxy-1, 2-diphenylethylideneamino) benzoic acid [HL] and its Co(II), Ni(II) and Cu(II) metal complexes were synthesized. The ligand and metal complexes were characterized by elemental analysis, UV-visible, IR, ¹H NMR spectroscopy, thermal studies and magnetic susceptibility measurement. The ligand [HL] was synthesized by condensation of benzoin and 2-amino benzoic acid. On the basis of electronic spectral data and magnetic susceptibility measurement the octahedral geometry has been proposed for Cu(II), Ni(II) and Co(II) complexes. The ligand and metal (II) complexes were also screened for their antimicrobial activity against microorganisms Staphylococcus aureus and Pseudomonas aeruginosa and antifungal activity against the fungi Candida albicans and Aspergillus niger.

Full text of DOI:10.1016/j.inoche.2011.01.016

Inorganic Chemistry Communications 14 (2011) 618–621
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis, characterization and antimicrobial activity of new cobalt (II), nickel (II)
and copper (II) complexes with 2-(2-hydroxy-1, 2-diphenylethylideneamino)
benzoic acid
⁎
A.H. Manikshete , S.K. Sarsamkar ⁎⁎, S.A. Deodware, V.N. Kamble, M.R. Asabe
Department of Chemistry, Walchand college of Arts and Science, Solapur, Maharashtra, 413006, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The new Schiff base ligand 2-(2-hydroxy-1, 2-diphenylethylideneamino) benzoic acid [HL] and its Co(II),
Ni(II) and Cu(II) metal complexes were synthesized. The ligand and metal complexes were characterized by
elemental analysis, UV-visible, IR, 1H NMR spectroscopy, thermal studies and magnetic susceptibility
measurement. The ligand [HL] was synthesized by condensation of benzoin and 2-amino benzoic acid. On the
basis of electronic spectral data and magnetic susceptibility measurement the octahedral geometry has been
proposed for Cu(II), Ni(II) and Co(II) complexes. The ligand and metal (II) complexes were also screened for
their antimicrobial activity against microorganisms Staphylococcus aureus and Pseudomonas aeruginosa and
antifungal activity against the fungi Candida albicans and Aspergillus niger.
Received 24 November 2010
Accepted 11 January 2011
Available online 22 January 2011
Keywords:
Transition metal complexes
2-Amino benzoic acid
Schiff base
© 2011 Elsevier B.V. All rights reserved.
Antifungal and antibacterial activity
Arylazo compounds are very interestingbecause they are involved in
a number of biological activities [1]; they are also used in analytical
chemistry as a complexing agent to detect various types of metal ions.
The Schiff base complexes are important as medicine and show a variety
of interesting biological activities such as antibacterial and antifungal
activity [2–4]. Benzoin and its derivatives are used as intermediates for
the synthesis of organic compounds and as a catalyst in photo
polymerization. They are used in anticratering in powder coating. It
has been reported that the benzoin can be used in skin disorders as an
antibacterial and antifungal agent. Arylamines are attractive targets for
chemical synthesis because of their wide applications in fine chemicals,
polymers and dyes. These are important components in many
important biologically active natural products as well as medicinally
important compounds. [5,6]. Transition metal complexes with various
donor groups have been used in organometallic chemistry [7]. A large
number of Schiff base compounds have been synthesized and
structurally characterized [8–14].
carry out a study on synthesis of Schiff base and its complexes with
Co(II), Ni(II) and Cu(II) metal ions.
In this paper we report the synthesis of new benzoin ligand 2-(2-
hydroxy-1,2-diphenylethylideneamino) benzoic acid [HL] and its
legation behavior with Co(II), Ni(II) and Cu(II) metals. The synthe-
sized ligand and metal complexes were characterized by elemental
analysis, UV–Vis, IR, 1H NMR, TG-DTG, magnetic susceptibility. They
are also screened for their biological activities against the microor-
ganism Staphylococcus aureus, Pseudomonas aeruginosa and fungi
Aspergillus niger and Candida albicans.
All reagents used were pure AR grade such as benzoin, 2-amino
benzoic acid, copper chloride, nickel chloride and cobalt chloride. The
solvents used were ethanol, petroleum ether, ethyl acetate etc. The
synthesis of Schiff base ligand and metal complexes is shown in
Scheme 1.
The benzoin (10.6 g, 0.05 mol) and 2-amino benzoic acid (6.85 g,
0.05 mol) were dissolved in ethanol (25 ml) separately in 1:1 molar
ratio. The ethanolic solutions were mixed together. The mixture was
refluxed on water bath for 3 h. On cooling, a crystalline complex was
separated by filtration and the crystals were washed with ethanol and
anhydrous diethyl ether and dried over anhydrous CaCl2 [21–25].
A ligand (3.31 g, 0.01 mol) [HL] was dissolved in (25 ml) ethanol
and added to a metal salt [nickel chloride (2.37 g, 0.01 mol), copper
chloride (1.70 g, 0.01 mol) and cobalt chloride (2.37 g, 0.01 mol)]
ethanolic solution (25 ml). The metal-ligand molar ratio was (1:1).
The mixture was refluxed for 2 h. On cooling, a crystalline complex
was separated by filtration and the crystals were washed and dried as
above [21–25].
The various classes of Schiff bases that can be prepared by
condensation of different types of amines and carbonyl compounds
are very popular due to diverse chelating ability. Several transition
metal complexes have been screened for their medicinal properties
[5–19]. The first row transition metals have attracted much attention
due to their biological importance [20].These factors prompted us to
⁎ Corresponding author. Tel.: +91 217 2651863, +91 9422460706 (mobile); fax: +91
217 2391849.
⁎⁎ Corresponding author. Tel.: +91 217 2651863, +91 9423069381 (mobile); fax: +91
217 2391849.
E-mail addresses: ahmanikshete@yahoo.co.in (A.H. Manikshete),
sarsamkar30@yahoo.co.in (S.K. Sarsamkar).
Analytical and physical data of the compounds studied are
reported in Table 1. The ligand and the metal (II) complexes are
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.01.016

A.H. Manikshete et al. / Inorganic Chemistry Communications 14 (2011) 618–621
619
OH
shifted to lower frequencies indicate that imine nitrogen is involved in
the co-ordination of metal ion. A very weak low intensity absorption
band associated with d-d transition for Cu(II) complexes at 465,
532 nm (typical octahedral transition) Co(II) complexes at 450 nm
O
N
OH
O
O
[4T1g(F)→4T1g(P)], 525 nm [4T1g →4A2g] and 734 nm [4T1g →4T2g
]
Refluxed
Ethanol
+
H2N
and for Ni(II) complexes at 470 nm (charge transfer), 525 nm
[3A2g(F)→3T1g(P)], 985 nm [3A2g →3T1g(F)] respectively supports
the octahedral geometry of metal complexes [26].
OH
OH
HL
The magnetic moment obtained at room temperature is as shown
in Table 2. The magnetic moment obtained at room temperature
indicates paramagnetism. The Co(II) complex shows a magnetic
moment of 4.94 B.M., the spin free octahedral complex of Co(II) is
reported to exhibit magnetic moment in the range of 4.46–5.53 B.M.
[27–30]. Hence, the observed magnetic moment for the Co(II)
complex under study indicates that it has an octahedral configuration.
The Ni(II) complex shows a magnetic moment of 3.04 B.M. The
magnetic moment of octahedral Ni(II) complexes are reported to
exhibit magnetic moment in the range of 2.80–3.40 B.M. [28–31]
indicating spin orbital coupling contribution from 3A2g and higher 3T2g
states. Hence, the observed magnetic moment for the Ni(II) complex
suggests that it may have octahedral geometry. The observed
magnetic moment of Cu(II) complex is 1.73 B.M. and it indicates an
octahedral geometry [29–32]. Thus the electronic spectral data and
magnetic moment data support the octahedral geometry of the
complexes.
+
+
M
OH
O
OH2
O
N
O
M
N
OH2
O
HO
Where M = Co2+, Ni2+ and Cu2+
Scheme 1. Synthesis of Schiff base and metal complexes.
The IR spectral data of Schiff base [HL] and their metal complexes
are presented in Table 2. The IR spectra of complexes are compared
with those of ligand in order to determine the coordination sites that
may be involved in chelation. A strong band observed at 1620 cm−1 in
a ligand [HL] is a characteristic band of (HC N) azomethine group. The
shifting of this band towards lower frequency region by 15–20 cm−1
in complexes indicates involvement of azomethine nitrogen in
coordination with metal ion [33–35]. The assignment of the proposed
coordination sites is further supported by appearance of a band at
453–462 cm−1 suggesting the υ (M―N) bond. The presence of υ
(M―O) stretching vibration at 542–588 cm−1 supports the involve-
ment of oxygen atom in complexation with metal ions. The ligand and
metal complexes were characterized mainly using the azomethine
and ―OH bands. In the complexes, the broad band in the range of
3379–3385 cm−1 is attributed to the presence of water molecules.
Presence of water molecules was also confirmed by thermal analysis.
The presence of band in the range of 1314–1393 cm−1 (OH in-plane
bending vibration of carboxylic group) in ligand and metal complexes
confirms that the carboxylic functional group remains unchanged.
Therefore, from the IR spectra, it is concluded, that the ligand
coordinated to the metal ions via azomethine nitrogen and deproto-
nated oxygen atom from benzoin.
soluble in common polar solvents like methanol, ethanol and
chloroform. They are soluble even in DMF and acetone. The ligand
and the metal (II) complexes synthesized were stable at room
temperature. The synthesized ligand and the metal complexes were
characterized by elemental and spectral analysis. Biological activity of
the ligand and the metal complexes were also studied. Based on their
elemental and spectral studies the geometry of the synthesized
compounds has been elucidated.
By the elemental analysis, the stoichiometry of ligand and their
metal complexes is confirmed. The elemental analysis of ligand and
the metal complexes are found in agreement with the proposed
structure of ligand and the metal complexes are listed in Table 1.
The electronic spectra and magnetic moment are very useful in the
evaluation of results obtained by other methods of structural
investigation. Information regarding the geometry of the complexes
around the Co(II), Ni(II) and Cu(II) ions was obtained from electronic
spectral studies and magnetic moments. The electronic spectra of
ligand and their metal complexes were recorded at room temperature
using methanol as a solvent.
The 1H NMR spectra of Schiff base are recorded in CDCl3, using
Tetramethylsilane (TMS) as an internal standard at IIT, Mumbai. The 1H
NMR spectra of benzoin show signals at δ 6.03 ppm assignable to ―OH
group, δ 6.09 ppm assignable to ―CH-group and δ 7.06-8.01 ppm
assignable to aromatic protons. In the NMR spectra of ligand, the signal
due to ―OH of benzoin shifts to δ 5.960 ppm [36]. The signal at 11 ppm
The electronic spectra of ligand show bands in the region of
204 nm and 248 nm but in the complexes they are slightly shifted to
higher frequencies. The band between 325 nm can be assigned to
n→π* of transition of azomethine group. In the spectra of complexes
the bands of azomethine chromophore n→π* transition that are
Table 1
Analytical and Physical data of the compounds studied.
Name of
compounds
Molecular formula/
formula weight
Color
M.P.
0 °C
Found (calculated) %
C
H
N
Metal
HL
C
331
21H17NO3
Faint
148
77.06
(76.12)
67.38
(66.70)
67.59
(66.78)
66.04
4.83
(5.17)
5.12
(4.80)
4.88
(4.80)
5.39
4.73
(4.23)
4.09
(3.70)
4.20
–
yellow
Yellowish
brown
Yellowish
brown
Grey
HL―Co
HL―Ni
HL―Cu
C42H36N2O8Co.2H2O
755
C
755
C
N250
N250
N250
7.66
(7.80)
7.26
(7.77)
8.45
42H36N2O8Ni.2H2O
(3.71)
4.16
42H36N2O8Cu.2H2O
760.29
(66.30)
(4.74)
(3.68)
(8.36)

620
A.H. Manikshete et al. / Inorganic Chemistry Communications 14 (2011) 618–621
Table 2
The antibacterial and antifungal activity of the Schiff bases and
IR spectral data and Magnetic moment data.
their metal complexes was tested on S. aureus, P. aeruginosa, A. niger
and C. albicans. The method used for antibacterial activity was Agar
Well-Diffusion method [38] and for antifungal activity was Agar-Ditch
method [39,40]. The stock solution 1 mg/ml was prepared and was
used to prepare concentrations of 0.8, 0.6, 0.4 and 0.2 mg/l. The
bacteria and fungi were inoculated on the surface of Nutrient agar and
Sabouraud's agar, respectively. The various concentrations of the
compounds were inoculated in the wells prepared on the agar plates.
The plates were incubated at room temperature for 24 h. In order to
clarify the effect of DMF on the biological screening, separate studies
were carried out with DMF and showed no activity against any
bacteria and fungi. The results are as summarized in the Table 3.The
ligand shows less activity against the microorganisms and fungi. The
Name of
ν
ν
ν
ν
ν
ν
μeff.
Compound (C=N) (C―O) (M―N) (M―O) (C―O―H) (H2O) B.M.
HL
1620
1600
1595
1603
1090
1112
1112
1111
_
_
1393
1314
1315
1318
3379
3385
3383
3385
_
HL―Co
HL―Ni
HL―Cu
462
453
460
588
542
560
4.94
3.04
1.73
is assignable to ―OH of carboxylic acid. Since, Co2+, Ni2+ and Cu2+
complexes are paramagnetic; their 1H NMR spectra could not be
obtained [31].
The typical thermogram of nickel complex is shown in Fig. 1.
Thermal decomposition of Co(II), Ni(II) and Cu(II) metal complexes
have been studied as a function of temperature by TGA and DTG. It
exhibited three step decomposition for the Schiff base metal (II)
complexes. The first decomposition takes place around 200 °C due to
total cleavage of the base metal complex along with hydroxide to
oxide transformation followed by concomitant release of water
molecules corresponding to loss of coordinated water molecules
(calc. 4.76%;found 5.2%). An endothermic peak of DTA confirmed the
loss of water molecules. The second decomposition takes place around
400 °C, attributed to the release of intermediate organic moiety. The
third slow and broad decomposition around 510–530 °C can be
attributed to total decomposition of organic moiety into carbon
dioxide and other gasses. The remaining 11% weight is totally due to
the presence of inorganic metal oxide [27,37].
C42H36N2O8Cu.2H2O complex shows maximum activity against
bacteria as well as fungi. The cobalt complex (C42H36N2O8Co.2H2O)
is weakly active against the microorganism but is moderately active
against fungi. The C42H36N2O8Ni.2H2O complex is highly active
against S. aureus and moderately active against P. aeruginosa and
fungi. The results were compared with standard antibiotics like
Gentamycin and Streptomycin.
The hemolytic activity of the synthesized ligand and its metal
complexes were determined using Wister rat erythrocytes. The RBCs
were prepared as follows. 2–3 ml of rat blood was drawn into 12 ml of
heparinized 5 mM HEPES buffer pH 7.4 containing 150 mM NaCl and
centrifuged at 4000 rpm for 5 min. The cell pellate was washed three
times with buffer and the buffy coat was removed. A working stock of
RBCs was made by diluting the RBCs pellate (0.5–0.8 ml) to about
15 ml with buffer. For standardization of the volume for lysis assay,
Fig. 1. Thermal analysis of nickel complex.

A.H. Manikshete et al. / Inorganic Chemistry Communications 14 (2011) 618–621
621
Table 3
Table 4
Biological activity data of complexes.
Hemolytic activity data.
Name of Conc. Staphylococcus Pseudomonas
Aspergillus
niger
Candida
albicans
Name of
compound
% RBC Lysis
Rat
compd. mg/lit. Aureus
Aeruginosa
Human
HL
0.2
0.4
0.6
0.8
Inactive
Inactive
Inactive
Inactive
Weakly active Weakly active
Weakly active Weakly active
HL
24
15
22
30
20
15
23
20
HL―Co
HL―Ni
HL―Cu
Weakly active Weakly active Weakly active Weakly active
Weakly active Weakly active Weakly active Moderately
active
Weakly active Weakly active Weakly active Moderately
active
1.0
The same procedure was repeated for human erythrocytes also
and the results are recorded in Table 4. The cobalt complex shows less
hemolytic activity. The results are very interesting and much helpful
for drug designing.
All the complexes have octahedral geometry and paramagnetic nature.
The cobalt (C42H36N2O8Co.2H2O) and the nickel complexes (C42H36N2O8-
Ni.2H2O) are moderately active against the S. aureus fungi C albicans and A.
niger, The highest activity is observed for copper complex.
HL―Co 0.2
Weakly active Inactive
Weakly active Inactive
Weakly active Inactive
Weakly active Weakly active
Weakly active Weakly active
0.4
0.6
Moderately
active
Moderately
active
0.8
1.0
Weakly active Weakly active Moderately
active
Moderately
active
Moderately
active
Moderately
active
Weakly active Moderately
active
HL―Ni
0.2
0.4
0.6
0.8
1.0
Moderately
active
Weakly active Weakly active Weakly active
Moderately
active
Weakly active Weakly active Weakly active
Acknowledgement
Moderately
active
Moderately
active
Weakly active Weakly active
We acknowledge Indian Institute of Technology, Mumbai for
providing 1H NMR facility. We also acknowledge the Department of
Microbiology, Walchand College of Biotechnology, Solapur for
providing microbial activity facility.
Highly active
Moderately
active
Moderately
active
Moderately
active
Highly active
Moderately
active
Moderately
active
Moderately
active
HL―Cu 0.2
Moderately
active
Weakly active Weakly active Weakly active
References
0.4
0.6
0.8
1.0
Moderately
active
Highly active
Weakly active Weakly active Weakly active
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ꢀ
ꢁ
H% ¼ Asample−A0 X 100=ðA100−A0Þ
where A100 and A0 are absorbance of 100% and 0% hemolysed cells
respectively.