Synthesis and characterization of Co(II), Ni(II), Cu(II) and Zn(II) complexes of tridentate Schiff base derived from vanillin and dl-α-aminobutyric acid

Article abstract of DOI:10.1016/j.saa.2007.09.006

Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived from vanillin and dl-α-aminobutyric acid were synthesized and characterized by elemental analysis, IR, electronic spectra, conductance measurements, magnetic measurements, powder XRD and biological activity. The analytical data show the composition of the metal complex to be [ML(H₂O)], where L is the Schiff base ligand. The conductance data indicate that all the complexes are non-electrolytes. IR results demonstrate the tridentate binding of the Schiff base ligand involving azomethine nitrogen, phenolic oxygen and carboxylato oxygen atoms. The IR data also indicate the coordination of a water molecule with the metal ion in the complex. The electronic spectral measurements show that Co(II) and Ni(II) complexes have tetrahedral geometry, while Cu(II) complex has square planar geometry. The powder XRD studies indicate that Co(II) and Cu(II) complexes are amorphous, whereas Ni(II) and Zn(II) complexes are crystalline in nature. Magnetic measurements show that Co(II), Ni(II) and Cu(II) complexes have paramagnetic behaviour. Antibacterial results indicated that the metal complexes are more active than the ligand.

Full text of DOI:10.1016/j.saa.2007.09.006

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Spectrochimica Acta Part A 70 (2008) 749–753
Synthesis and characterization of Co(II), Ni(II), Cu(II) and Zn(II)
complexes of tridentate Schiff base derived from vanillin
and dl-␣-aminobutyric acid
M. Sivasankaran Nair∗, R. Selwin Joseyphus
Department of Chemistry, Manonmaniam Sundaranar University, Tirunelveli 627012, India
Received 9 July 2007; received in revised form 16 September 2007; accepted 16 September 2007
Abstract
Co(II), Ni(II), Cu(II)andZn(II)complexesoftheSchiffbasederivedfromvanillinand dl-␣-aminobutyricacidweresynthesizedandcharacterized
by elemental analysis, IR, electronic spectra, conductance measurements, magnetic measurements, powder XRD and biological activity. The
analytical data show the composition of the metal complex to be [ML(H2O)], where L is the Schiff base ligand. The conductance data indicate
that all the complexes are non-electrolytes. IR results demonstrate the tridentate binding of the Schiff base ligand involving azomethine nitrogen,
phenolic oxygen and carboxylato oxygen atoms. The IR data also indicate the coordination of a water molecule with the metal ion in the complex.
The electronic spectral measurements show that Co(II) and Ni(II) complexes have tetrahedral geometry, while Cu(II) complex has square planar
geometry. The powder XRD studies indicate that Co(II) and Cu(II) complexes are amorphous, whereas Ni(II) and Zn(II) complexes are crystalline
in nature. Magnetic measurements show that Co(II), Ni(II) and Cu(II) complexes have paramagnetic behaviour. Antibacterial results indicated that
the metal complexes are more active than the ligand.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Schiff base metal complex; Vanillidene-dl-␣-aminobutyrate; IR; Electronic spectra; Magnetic measurements; Powder XRD; Antimicrobial activity
1. Introduction
metal complexes derived from vanillin and dl-␣-aminobutyric
acid.
Schiff bases have gained importance because of physio-
logical and pharmacological activities associated with them.
A large number of Schiff base compounds are often used as
ligands in coordination chemistry by considering their metal
binding ability. Schiff base metal complexes have ability to
reversibly bind oxygen in epoxidation reactions [1], biological
activity [2,3], catalytic activity in hydrogenation of olefins [4,5]
and photochromic properties [6]. Vanillin is most prominent
as the principal flavor and aroma compound in vanilla. Syn-
thetic vanillin is used as a flavoring agent in foods, beverages,
and pharmaceuticals [7]. However, only few transition metal
complexes of vanillin were reported [8–10]. Recently we have
studied some tridentate Schiff base metal complexes [11–13].
In this paper, we report the synthesis, characterization and bio-
logical activity of some novel tridentate Schiff base K(HL)
2. Experimental
2.1. Materials
dl-␣-Aminobutyric acid (Fluka), vanillin (Sisco Research
Lab) and metal(II) nitrates were purchased from Merck. All the
chemicals used were of Analar grade. Solvents were purified
and dried before use according to the standard method [14].
2.2. Analytical and physical measurements
Carbon, hydrogen and nitrogen were obtained using a Perkin-
Elmer elemental analyzer. The metal contents were determined
by complexometric titrations with EDTA [15]. The IR spectra
were recorded in KBr pellets on a JASCO FT/IR-410 spec-
trometer in the range 400–4000 cm−1. Electronic spectra were
recorded on a Perkin-Elmer Lambda-25 UV–vis spectrome-
ter using MeOH as solvent. Conductivity measurements were
∗
Corresponding author. Tel.: +91 462 2333887; fax: +91 462 2334363.
E-mail address: msnairchem@rediffmail.com (M.S. Nair).
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.09.006

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M.S. Nair, R.S. Joseyphus / Spectrochimica Acta Part A 70 (2008) 749–753
Table 1
Analytical and physical data of the Schiff base ligand and its complexes
Compound
Empirical formula, colour
Found (calculated) (%)
Molar conductance
μeff (μB)
(S cm2 mol−1
)
C
H
N
M
K(HL)
C12H14NO4K, yellow
C12H15NO5Co, brown
C12H15NO5Ni, pale green
C12H15NO5Cu, bluish green
C12H15NO5Zn, colourless
52.35 (52.79)
46.17 (46.31)
46.20 (46.35)
45.50 (45.64)
45.23 (45.18)
5.12 (4.63)
4.84 (4.39)
4.85 (4.40)
4.77 (4.93)
4.74 (4.98)
5.09 (5.02)
4.49 (4.90)
4.49 (4.09)
4.42 (4.39)
4.40 (4.85)
–
–
–
[CoL(H2O)]
[NiL(H2O)]
[CuL(H2O)]
[ZnL(H2O)]
18.88 (18.09)
18.81 (18.20)
20.06 (21.26)
20.52 (20.90)
19.81
10.72
13.32
11.57
3.97
2.83
1.85
Dia.
made on freshly prepared 10−3 M solutions in DMF at room
temperature with a coronation digital conductivity meter. XRD
were recorded on a Rigaku D/max X-ray diffractometer with Cu
K␣ radiation. The magnetic measurements were carried out at
room temperature using EG & G PARC vibrating sample mag-
netometer and magnetic moment calculations were done using
the method described elsewhere [16].
Kirby Bauer disc diffusion method [17]. The test solutions
were prepared in DMSO. Diffusion method [18,19] was used
to evaluate the antimicrobial activities of the tested compounds
as follows: 0.5 ml spore suspension (106 to 107 spore ml−1
)
of each of the investigated organisms was added to a sterile
agar medium just before solidification, then poured into ster-
ile Petri dishes (9 cm in diameter) and left to solidify. Using
sterile cork borer (6 mm in diameter), wells were made in each
dish, then 0.1 ml of the tested compounds dissolved in DMSO
were poured into three wells and the dishes were incubated
at 37 ◦C for 48 h (for bacteria) and 30 ◦C for 72 h (for fungi),
where clear or inhibition zones were detected around each
well.
2.3. Preparation of the potassium salt of the Schiff base
ligand
To a solution of dl-␣-aminobutyric acid (0.089 g, 1 mmol)
in MeOH (15 cm3) containing KOH (0.056 g, 1 mmol), vanillin
(0.152 g, 1 mmol) in MeOH (10 cm3) was added. The above
solution was magnetically stirred for 1 h. The volume of yellow
solution was reduced in vacuo using rotary evaporator. Anhy-
drous ether was added to deposit the yellowish precipitate and
it was recrystallized from EtOH (yield = 67%).
3. Results and discussion
The analytical and physical data of the Schiff base ligand and
its complexes are given in Table 1. The complexes are soluble
in DMF and DMSO and are insoluble in some common organic
solvents. The analytical data show that the metal to ligand ratio
is 1:1 in all the complexes. The composition of the complexes
is [ML(H2O)], where (M = Co(II), Ni(II), Cu(II) and Zn(II) and
LH2 = vanillidene-dl-␣-aminobutyrate. The low molar conduc-
tance values (Table 1) of 10−3 M solutions in DMF showed them
to be non-electrolytes [20].
2.4. Preparation of metal complexes
Metal(II) nitrates (1 mmol) was dissolved in MeOH (10 cm3)
and the solution was filtered and added dropwise into a (15 cm3)
methanolic solution of K(HL) ligand (1 mmol). The above mix-
ture was magnetically stirred for 2 h. The coloured complex
obtained was filtered off, washed with MeOH and Et2O dried in
vacuo (yield = 55–61%).
3.1. Infrared spectra
2.5. Antimicrobial activity
The IR spectral data are given in Table 2. The IR spec-
trum of the Schiff base ligand and a representative system of
Cu(II) complex are shown in Fig. 1. In the Schiff base ligand,
the strong band observed at 1644 cm−1 can be assigned to the
ν(C N) azomethine stretching vibration. On complexation, this
band was shifted to lower frequency in the 1617–1638 cm−1
range indicating the coordination of the azomethine nitrogen
atom to the central metal ion [21]. The asymmetric car-
The ligand and its complexes were tested against the bacte-
rial species Staphylococcus aureus, Escherichia coli, Klebsiella
pneumaniae, Proteus vulgaris and Pseudomonas aeruginosa,
also the antifungal activity against Candida albicans. These
studies were carried out using Amikacin as standard antibac-
terial agent and Terbinafin as standard antifungal agent by
Table 2
Infrared spectral data of Schiff base ligand and its complexes (cm−1
)
Compound
ν(C N)
ν(O H)
νasym(COO−)
νsym(COO−)
ν(M N)
ν(M O)
K(HL)
1644
1630
1635
1617
1638
3453
3405
3442
3439
3419
1584
1582
1571
1570
1583
1343
1332
1335
1383
1385
–
537
574
584
580
–
456
457
420
437
[CoL(H2O)]
[NiL(H2O)]
[CuL(H2O)]
[ZnL(H2O)]

M.S. Nair, R.S. Joseyphus / Spectrochimica Acta Part A 70 (2008) 749–753
751
Fig. 1. IR spectra of K(HL) and [CuL(H2O)] complex.
boxyl stretching νasym(COO−) is shifted to higher frequency
in the 1570–1583 cm−1 range and the symmetric carboxyl
stretching νsym(COO−) is shifted to lower frequency in the
1332–1385 cm−1 range, indicating the linkage between the
metal ion and carboxylato oxygen atom [21–23]. The differ-
ence between νasym(COO−) and νsym(COO−) for the Co(II),
Ni(II), Cu(II) and Zn(II) complexes in the present study are,
respectively 250, 236, 187 and 198 cm−1. This value compares
favorably with that of 191–225 cm−1, characteristic for the mon-
odentate coordination of the carboxylato group [24–26]. Thus,
in all the complexes, the carboxylato group is monodenatate.
The ν(C O) phenolic band in the complexes was shifted to
lower frequency in the 1224–1231 cm−1 range indicating the
coordination of the phenolic oxygen atom with the metal ion
[21]. The spectra of the complexes show broad bands in the
3405–3442 cm−1 range, which can be attributed to the stretch-
ing vibration of the O H group [21]. This indicates that a water
molecule occupies in the fourth position. In the complexes, weak
bands in the 537–580 and 420–457 cm−1 range, can be attributed
to ν(M N) and ν(M O), respectively [27–29]. From the IR
results, it may be concluded that the Schiff base ligand is triden-
tate (Scheme 1) and coordinates with the metal ion through the
phenolic oxygen, azomethine nitrogen and carboxylato oxygen
atoms.
Fig. 2. Electronic spectra of K(HL) and [CuL(H2O)] complex.
ofazomethinenitrogenwiththemetalion. Co(II)complexshows
only one absorption band in the visible region at 551 nm, which
4
is due to 4A2 (F) → T1(F) transition [30]. This indicates tetra-
hedral geometry for the complex. The electronic spectrum of
the Ni(II) complex shows an intense absorption band at 610 nm,
3
which is due to the 3T1(F) → T1(P) transition, indicating
tetrahedral geometry. For square planar Cu(II) complexes, the
2
2
expected transitions are 2B1g → A1g and 2B1g → Eg with the
respective absorption bands [30]. In general, due to Jahn–Teller
distortion, square planar Cu(II) complexes give a broad absorp-
tion band between 600 and 700 nm and the peak at 510 nm
merges with the broad band. The electronic spectrum of Cu(II)
complex (Fig. 2) exhibit a broad band centered at 683 nm indi-
cating square planar geometry.
3.3. Magnetic properties
As a representative system, the magnetic behaviour of the
Cu(II) complex is shown in Fig. 3, in which magnetization (M)
is plotted against applied field (H). The linear fit of M vs. H
values for all the systems under investigation indicate para-
magnetic behaviour of the complexes [16,31]. The magnetic
moments of the complexes determined at room temperature
are given in Table 1. The magnetic moment of Co(II) complex
is 3.97μB, which compares favorably with that of 4.1–4.8μB
expected for the Co(II) complexes with three unpaired elec-
trons [32–34]. Thus, in agreement with the electronic spectral
studies, Co(II) complex has tetrahedral geometry. The Ni(II)
complex has a magnetic moment value of 2.83μB, which is
close to that of 3.0–3.5μB for the more distorted tetrahedral
complexes [34–36]. The magnetic moment of Cu(II) complex
is 1.85μB indicating the presence of one unpaired electron
[37–41]. The electronic spectral results clearly indicated square
planar geometry for the Cu(II) system, which should con-
tain one unpaired electron, where μeff value would be in the
range 1.8–2.1μB.
3.2. Electronic spectra
The electronic spectrum of the Schiff base ligand (Fig. 2)
shows a broad band at 317 nm, which is assigned to ␲–␲* tran-
sition of the C N chromophore. On complexation, this band was
shifted to lower wavelength region, suggesting the coordination
Scheme 1. Structure of Schiff base ligand, K(HL).

752
M.S. Nair, R.S. Joseyphus / Spectrochimica Acta Part A 70 (2008) 749–753
Fig. 3. Magnetization vs. field plot of [CuL(H2O)] complex.
Fig. 5. (a). Proposed molecular structure of tetrahedral [ML(H2O)] complexes,
where M = Co(II), Ni(II) and Zn(II). (b). Proposed molecular structure of square
planar [CuL(H2O)] complex.
Zn(II) complexes show sharp peaks. This shows that the above
complexes are crystalline in nature [42]. The line broadening
of the crystalline diffraction peak in the Zn(II) complex shows
higher crystallinity than that of Ni(II) complex.
Fig. 4. XRD diffraction pattern of [NiL(H2O)] and [ZnL(H2O)] complexes.
3.4. Powder XRD
X-ray diffraction patterns of the complexes were recorded at
2θ = 20–80◦ range and Ni(II) and Zn(II) complexes are shown
in Fig. 4. The Co(II) and Cu(II) complexes did not show any
peaks, indicating their amorphous nature, but the Ni(II) and
3.5. Antimicrobial activity
The antibacterial and antifungal activities of the ligand and
its complexes are given in Table 3. The activity increases with
Table 3
Antibacterial and antifungal activities of the Schiff base ligand and its complexes
Compound
S. aureus
E. coli
K. pneumaniae
P. vulgaris
P. aeruginosa
C. albicans
K(HL)
0
0
+
+
+
+
[CoL(H2O)]
[NiL(H2O)]
[CuL(H2O)]
[ZnL(H2O)]
Terbinafina
Amikacina
0
0
+++
0
0
0
+
0
0
0
+++
0
0
0
+++
0
++
0
++
0
0
+
+
0
++
−
−
−
−
−
−
++
++
++
++
++
The test was done using the diffusion agar technique. Well diameter = 0.6 cm beyond control (+) (less active); inhibition values = 0.6–1.0 cm beyond control (++)
(moderate active); inhibition values = 1.1–1.5 cm beyond control (+++) (highly active); not active (0).
a
Standards.

M.S. Nair, R.S. Joseyphus / Spectrochimica Acta Part A 70 (2008) 749–753
753
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plexes [17]. The antibacterial results (Table 3) showed that the
metal complexes are more active than their Schiff base ligand.
Among the four complex, the Cu(II) complexes was found to
be more active towards both gram positive and gram negative
bacteria. The results of fungicidal screening (Table 3) showed
that the Ni(II) and Cu(II) complexes are moderate in active than
the Schiff base ligand, when compared to other complexes.
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Co(II), Ni(II), Cu(II) and Zn(II) form complexes of com-
position [ML(H2O)], where L is the Schiff base ligand,
vanillidene-dl-␣-aminobutyrate. The results clearly demon-
strate that L is tridentate, Co(II), Ni(II) and Zn(II) complexes
have tetrahedral geometry, while the Cu(II) complex has square
planar geometry (Fig. 5(a) and (b)). The antimicrobial activities
show that Cu(II) complex is more active than the other metal
complexes.
Acknowledgements
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We thank Miss. G. Sangeetha and Mr. C. Justin Dhanaraj of
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thank the Department of Nuclear Physics, University of Madras,
Chennai 600025, India for extending their research facilities.
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