Synthesis and characterization of a new Schiff base and its metal complexes derived from the Mannich base, N-(1-piperidinobenzyl)acetamide

Article abstract of DOI:10.1081/SIM-200066974

New neutral Schiff base complexes of Cu(II), Co(II), Ni(II), and Zn(II) derived from 4-aminoantipyrine and N-(1-piperidinobenzyl) acetamide (Mannich base) have been synthesized. The structural features of the complexes have been characterized by microanalytical data, IR, UV-Vis, ¹H NMR, ESR, CV, TGA and powder XRD techniques. Electronic absorption spectra of the complexes indicate an octahedral geometry around the metal ion. The neutral nature of the complexes is characterized from their low molar conductance values. The cyclic voltammogram of copper complex in DMSO solution shows the process is a quasi-reversible one electron transfer. The ESR spectrum of copper complex in DMSO at 300 K and 77 K was recorded and its salient features are reported. The thermal analysis shows the absence of neither coordinated nor lattice water in all the complexes. The powder XRD pattern indicates the crystalline nature of the complexes. The antimicrobial activity of the ligand and its complexes has been extensively studied on microorganisms such as Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa and the fungi Aspergillus niger and Rhizoctonia bataicola by well-diffusion technique using DMF as the solvent. The values of zone of inhibition were found out at 37°C for a period of 24 h. It has been found that all the complexes have higher activity than the free ligand and the standard. Copyright

Full text of DOI:10.1081/SIM-200066974

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Synthesis and Characterization of a New Schiff Base
and its Metal Complexes Derived from the Mannich
Base, N-(1-piperidinobenzyl)acetamide
N. Raman a & S. Ravichandran a
a Department of Chemistry , Virudhunagar Hindu Nadars' Senthi Kumar Nadar College ,
Virudhunagar , India
Published online: 31 Jan 2012.
To cite this article: N. Raman & S. Ravichandran (2005) Synthesis and Characterization of a New Schiff Base and its Metal
Complexes Derived from the Mannich Base, N-(1-piperidinobenzyl)acetamide, Synthesis and Reactivity in Inorganic, Metal-
Organic, and Nano-Metal Chemistry, 35:6, 439-444, DOI: 10.1081/SIM-200066974
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Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 35:439–444, 2005
Copyright # 2005 Taylor & Francis, Inc.
ISSN: 0094-5714 print/1532-2440 online
DOI: 10.1081/SIM-200066974
Synthesis and Characterization of a New Schiff Base
and its Metal Complexes Derived from the Mannich
Base, N-(1-piperidinobenzyl)acetamide
N. Raman and S. Ravichandran
Department of Chemistry, Virudhunagar Hindu Nadars’ Senthi Kumar Nadar College,
Virudhunagar, India
development of coordination chemistry. The coordination
New neutral Schiff base complexes of Cu(II), Co(II), Ni(II), and chemistry of Schiff bases as multidentate ligands gained much
Zn(II)derivedfrom4-aminoantipyrineandN-(1-piperidinobenzyl)
acetamide (Mannich base) have been synthesized. The structural
features of the complexes have been characterized by micro-
importance for more than two decades because of their use as
models of biological systems (Xiu et al., 1996; Srinivasan
analytical data, IR, UV-Vis, 1H NMR, ESR, CV, TGA and
powder XRD techniques. Electronic absorption spectra of the
et al., 2001; Dharmaraj et al., 2001; Sharma et al., 2001).
Among the pyrazolone derivatives, 4-aminoantipyrine forms a
complexes indicate an octahedral geometry around the metal variety of Schiff bases with aldehydes/ketones, and are
ion. The neutral nature of the complexes is characterized from
their low molar conductance values. The cyclic voltammogram
of copper complex in DMSO solution shows the process is a
quasi-reversible one electron transfer. The ESR spectrum of
copper complex in DMSO at 300 K and 77 K was recorded and
its salient features are reported. The thermal analysis shows the et al., 2004; 2003; 2001). Earlier work reported that some drugs
reported to be superior reagents in biological, pharmacological,
clinical and analytical applications (Mohamed et al., 2004;
Harikumaran et al., 2005; Warad et al., 2000; Jeyasubramanian
et al., 1995; Havaldar et al., 2004; Paschke et al., 2003; Raman
absence of neither coordinated nor lattice water in all the com-
plexes. The powder XRD pattern indicates the crystalline nature
of the complexes. The antimicrobial activity of the ligand and its
complexes has been extensively studied on microorganisms such
as Staphylococcus aureus, Bacillus subtilis, Escherichia coli and
Pseudomonas aeruginosa and the fungi Aspergillus niger and (Raman et al., 2001; 2002; 2003; 2004), in this article we
showed increased activity when administered as metal chelates
rather than as organic compounds. Keeping the above facts in
mind, and as part of our continuing efforts to investigate tran-
sition metal(II) complexes using 4-aminoantipyrine derivatives
Rhizoctonia bataicola by well-diffusion technique using DMF as
the solvent. The values of zone of inhibition were found out at
378C for a period of 24 h. It has been found that all the complexes
have higher activity than the free ligand and the standard.
describe the synthesis, characterisation, redox and antimicro-
bial studies of Cu(II), Co(II), Ni(II) and Zn(II) complexes con-
taining tridentate Schiff base derived by condensing the
biologically active 4-aminoantipyrine with N-(1-piperidinoben-
zyl)acetamide. This ligand system coordinates to the metal ion
Keywords antimicrobial activity, Mannich base, N-(1-piperidino-
in a terdentate manner through the cyclic carbonyl group of
benzyl)acetamide, Schiff base complexes
the pyrazolone ring, azomethine nitrogen and the nitrogen
atom of piperidine. The proposed structure of the complexes
is shown below.
INTRODUCTION
From the survey of existing literature, it appears that metal
complexes of Schiff bases have played a vital role in the
Received 3 November 2004; accepted 25 March 2005.
The authors are grateful to the Head, Principal and Managing
Board of VHNSN College, Virudhunagar, for providing research
facilities. They also thank the RSIC, CDRI, Lucknow and RSIC,
IIT, Chennai and Mumbai for the use of their instrumentation facili-
ties. NR expresses his sincere thanks to UGC (SERO), Hyderabad
and SR to the Tamilnadu Government, Chennai for financial support.
Address correspondence to N. Raman, Department of Chemistry,
Virudhunagar Hindu Nadars’ Senthi Kumar Nadar College,
Virudhunagar 626 001, India. E-mail: drn_raman@yahoo.co.in
439

440
N. RAMAN AND S. RAVICHANDRAN
RESULTS AND DISCUSSION
remained at the same position as in the free ligand, indicating
that the secondary nitrogen is not coordinated.
All the metal complexes are stable at room temperature.
Physical characterization, microanalytical, molar conductance
and magnetic susceptibility data of the complexes are summar-
ized in Table 1. The ligand L, on interaction with Cu(II),
Co(II), Ni(II) and Zn(II) chlorides, yields complexes
corresponding to the general formula [ML2]. The analytical
data show that the metal to ligand ratio is 1 : 2. The low
molar conductance values of the complexes support their
neutral nature (Geary, 1970). Their magnetic susceptibilities
at room temperature (Table 1) are consistent with octahedral
geometry around the central metal ion.
Electronic Absorption Spectra
The electronic absorption spectra of the Schiff base and its
Cu(II), Co(II), and Ni(II) complexes were recorded at room
temperature using DMSO as a solvent. Only one broad band
is observed at 16638 cm21 in the electronic spectrum of the
2
2
Cu(II) complex assigned to Eg ! T2g transition, which is
in conformity with octahedral geometry (Dunn, 1960).
Though three transitions are expected in this case, they are
very close in energy and often appear in the form of one
broad band envelope. The electronic spectra of Co(II)
complex showed two spin-allowed transitions at 17856 and
Infrared Spectra
4
4
4
21734 cm21 assignable to T1g(F) ! A2g (F) and T1g
In order to study the binding mode of Schiff base to metal in
the complexes, IR spectrum of the free ligand was compared
with the IR spectra of the metal complexes. The band at
1650 cm21 is characteristic for the keto group in a pyrazolone
ring. This band is shifted to ca. 1590–1575 cm21 region in all
the complexes, which is due to enolization of the ligand, i.e.,
the carbonyl group is converted into the enolic C–O form.
Such a lowering of the frequency is due to chelation of
carbonyl group to the central metal ion (Nakamoto, 1977; Li
et al., 2005) The azomethine group appears at ca. 1600 cm21
region for the free ligand. In the complexes, the C55N band
was found invariably shifted 20–40 cm21 towards the
negative side, indicating the involvement of azomethine
nitrogen atom on coordination to metal ion, and this can be
explained by the donation of electrons from nitrogen to the
empty d-orbitals of the metal atom. The proof of N and O
coordination is demonstrated by the bands that appeared in
the far IR spectra of complexes in the regions 500–580 and
380–470 cm21 assigned to M-O and M-N modes (Ferraro,
1971), respectively. The IR band observed at 1100 cm21 has
been assigned to C-N-C of the piperidine group. In all the com-
plexes, the C-N-C of piperidine band displayed substantial
4
(F) ! T1g (P) transitions, respectively, that are in conformity
with octahedral arrangements for Co(II) ion (Lever 1968). The
appearance of a band at 19240 cm21 due to 3A2g(F) ! T1g(P)
3
transitionfavorsanoctahedralgeometry(CottonandWilkinson,
1988) for the Ni(II) complex. The absence of any band below
10000 cm21 eliminates the possibility of a tetrahedral environ-
ment in this complex.
Magnetic Susceptibility Measurements
The magnetic moment value of Cu(II) complex is 1.9 B.M.,
which suggests an octahedral geometry (Dunn, 1960) around
the metal ion. The magnetic moment of Co(II) complex is
4.5 B.M., which suggests the high spin six coordinated octa-
hedral arrangement of ligand molecules around the metal ion
(Lever, 1968). The Ni(II) complex has a magnetic moment
value of 3.8 B.M., indicating a spin free octahedral con-
figuration (Cotton, 1988). The Zn(II) complex is found to be
diamagnetic as expected for d10 configuration.
1H NMR Spectra
1
The H NMR spectra of the Schiff base ligand exhibits a
negative shifts with fairly low intensity, indicating the coordi- multiplet signal at 7.2–7.8 d (m, Ar-H) and 10.1 d (s, N-H).
nation through the nitrogen of piperidine entity present in the In Zn(II) complex, the N-H proton is shifted slightly downfield
ligand. In the spectra of all the complexes, the N-H band at 10.3 d, which reveals the bonding of the azomethine nitrogen
TABLE 1
Analytical data of the Schiff base ligand and its metal complexes
% Analysis, found (calcd)
Yield
%
meff
lm
Compound
M
C
H
N
(B.M) (mho cm2 mol21
)
Ligand
[CuL2]
[CoL2]
[NiL2]
[ZnL2]
—
71.0 (71.9) 7.1 (7.7) 15.9 (16.8)
69
57
53
51
55
—
1.9
4.5
3.8
—
—
2.8
4.1
3.6
3.8
6.7 (7.1) 66.1 (66.8) 6.2 (6.9) 15.1 (15.6)
6.2 (6.6) 66.7 (67.2) 6.3 (6.9) 15.4 (15.7)
6.5 (6.6) 66.5 (67.1) 6.7 (6.9) 14.8 (15.6)
7.0 (7.3) 66.0 (66.6) 6.1 (6.8) 15.0 (15.6)
L ¼ Schiff base ligand.

SYNTHESIS AND CHARACTERIZATION OF A NEW SCHIFF BASE
441
1
to Zn(II) ion. The H NMR spectrum of the ligand shows a The G value of 3.82 indicates negligible exchange interaction
signal at 2.4–2.6 d (piperidine N-CH2). In Zn(II) complex, of Cu-Cu in the complex. The covalency parameter a2 is calcu-
the signal due to piperidine N-CH2 protons also shifted lated (a2 ¼ 0.82) using the following equation:
slightly and appeared at 2.6–2.8 d in the complex. This is an
a2cu ¼ ꢀðAk=0:036Þ þ ðgk ꢀ 2:0023Þ þ 3=7ðg? ꢀ 2:0023Þ
1
indication of the coordination of piperidine nitrogen. The H
NMR spectra of the Schiff base ligand exhibits a signal at
þ 0:04
10.7 d and is assigned to 2C55C-OH, which was absent in
the Zn(II) complex, suggesting that the ligand is in enol
If the value of a2 ¼ 0.5, it indicates a complete covalent
bonding, while the value of a2 ¼ 1.0 suggests a complete
form, followed by coordination of carbonyl oxygen to the
metal via deprotonation.
ionic bonding. The observed value of a2 (0.82) of the complex
is less than unity, which indicates that the complex has some
covalent character in the ligand environment (Dutta and
ESR Spectra
The ESR spectrum of copper complex provides information Syamal, 1992).
that is important in studying the metal ion environment. The
ESR spectra of the Cu(II) complex were recorded (Figure 1) in
DMSO at 77 K and at 300 K. The spectrum of the copper
complex at 300 K shows one intense absorption band in the
high field region and is isotropic due to the tumbling motion of
the molecules. However, this complex at 77 K shows four well
resolved peaks with low field region. The copper complex
exhibits the g value of 2.31 and g value of 2.16. These
Cyclic Voltammetric Study
The cyclic voltammogram of Cu(II) complex (0.01 M) in
DMSO solution at room temperature in 0.8 to 21.0 V potential
range at scan rate 50 mVs21 indicating quasi-reversible one-
electron process (Tumer et al., 2001). A noteworthy feature
has been observed in the cyclic voltammogram of Cu(II)
complex (Figure 2). During the forward scan, it shows two
cathodic reduction peaks, one at þ0.23 V and another at
20.82 V, which are attributed to reduction of Cu(II) ! Cu(I)
and Cu(I) ! Cu(0), respectively. During the reverse scan, it
shows two anodic oxidation peaks, one at 20.61 V and
another at þ0.28 V which are attributed to oxidation of
Cu(0) ! Cu(I) and Cu(I) ! Cu(II), respectively.
k
?
values indicate that the unpaired electron lies predominantly
in the dx22y2 orbital (Dutta and Syamal, 1992). The spin-orbit
coupling constant, l value (2488 cm21) calculated using the
relations, gav ¼ 1/3[g þ 2g ] and gav ¼ 2(1–2l/10Dq), is
k
?
less than the free Cu(II) ion (2832 cm21), which also supports
covalent character (Yen, 1969) of M-L bond in the complex.
Thermal Study
The thermal decomposition studies of Cu(II), Co(II), Ni(II)
and Zn(II) complexes show no appreciable change at about
1708C when heated. The thermal analytical data of the Cu(II)
complex shows a 7.0% loss in weight (theor. 7.1%), Co(II)
complex shows a 6.5% loss in weight (theor. 6.6%),
Ni(II) complex shows a 6.4% loss in weight (theor. 6.6%)
and Zn(II) complex shows a 7.1% loss in weight (theor.
FIG. 1. The X-band ESR spectrum of the copper complex in DMSO at (a)
300 K and (b) 77 K.
FIG. 2. Cyclic voltammogram of copper complex in DMSO.

442
N. RAMAN AND S. RAVICHANDRAN
7.3%), indicating the absence of either coordinated or lattice Biological Activity
water molecules in these complexes.
Antibacterial activity of the ligand and its complexes have
been carried out against the Gram positive bacteria like
S. aureus, B. subtilis and Gram negative bacteria such as
E. coli, P. aeruginosa using Muller-Hinton agar by well-
diffusion method (Chakrawarti, 2001) using DMF as solvent.
Ampicillin was used as the standard for comparing the
results. Antifungal activity of the ligand and its complexes
has been carried out using the fungi such as A. niger and
R. bataicola by well-diffusion technique using DMF as
solvent. For the antifungal activity, potato dextrose agar
(PDA) medium was used. Amphotericin was used as the
standard. The zone of inhibition values were determined at
the end of an incubation period of 24 h at 358C. During this
period, the test solution diffused and the growth of the inocu-
lated microorganisms was affected. It has been observed
from the results (Tables 2 and 3) that the metal complexes
have a higher activity than that of the free ligand and the
standard. This may be due to the greater lipophilic nature of
the complexes. Such increased activity of the metal chelates
can be explained on the basis of Overtone’s concept and
Chelation theory. According to Overtone’s concept of cell per-
meability the lipid membrane that surrounds the cell favors the
passage of only lipid soluble materials due to which liposolu-
bility is an important factor that controls the antimicrobial
activity. On chelation, the polarity of the metal ion will be
reduced to a greater extent due to the overlap of the ligand
orbital and partial sharing of positive charge of metal ion
with donor groups. Further, it increases the delocalization of
p-electrons over the whole chelate ring and enhances the lipo-
philicity of the complex. This increased lipophilicity enhances
the penetration of the complexes into lipid membrane and
blocks the metal binding sites on enzymes of microorganisms.
FAB Mass Spectra
The FAB mass spectra of the Schiff base ligand and its
copper complex (Figure 3) are used to compare their stoichio-
metric composition. The Schiff base ligand shows a molecular
ion peak Mþ at m/z ¼ 417. The molecular ion peak for the
copper complex was observed at m/z ¼ 898, which confirms
the stoichiometry of metal chelates as ML2.
Powder XRD Pattern
Due to practical difficulties in obtaining good crystals,
single crystal XRD could not be employed to ultimately
confirm the structure. However, powder X-ray diffractogram
is some consolation to us. The X-ray diffraction pattern of
copper complex is in the 2u range from 3 to 658C, which
corresponds to inter-planar distance d ¼ 7.824. The pattern
was found to be similar with a sharp peak clearly indicating
the crystalline nature of the copper complex.
EXPERIMENTAL
All the chemicals used were of AnalaR grade. The solvents
were dried and distilled before use according to standard
TABLE 2
Antibacterial activity of the Schiff base ligand and its
metal complexes
Inhibition zone (mm)
No. Compound S.aureus E.coli P.auroginosa B.subtilis
1.
2.
3.
4.
5.
6.
Ligand
[CuL2]
[CoL2]
[NiL2]
11
18
16
17
18
10
13
24
20
22
23
12
12
21
19
20
25
11
12
20
17
18
21
11
[ZnL2]
Ampicillin
FIG. 3. The FAB mass spectrum of (a) the Schiff base and (b) its copper
complex.
L ¼ Schiff base ligand.

SYNTHESIS AND CHARACTERIZATION OF A NEW SCHIFF BASE
443
Synthesis of Schiff Base
TABLE 3
Antifungal activity of the Schiff base ligand and its
metal complexes
The Schiff base was synthesized by the condensation of an
ethanolic solution (50 mL) of 4-aminoantipyrene (6.09 g,
30 mmol) and the Mannich base, N-(1-piperidinobenzyl)aceta-
mide (6.96 g, 30 mmol). The reaction mixture was boiled
for ca. 2 h and it was then cooled at room temperature. The
orange solid precipitate of Schiff base obtained was filtered,
washed with distilled water, dried at room temperature and
finally recrystallized from ethanol. Yield: 8.75 g (69%);
(m.p: 1488C).
Inhibition zone (mm)
No.
Compound
A.niger
R.bataicola
1.
2.
3.
4.
5.
6.
Ligand
[CuL2]
7
10
13
11
14
9
9
13
17
14
15
11
[CoL2]
[NiL2]
[ZnL2]
Amphotericin
Synthesis of Metal Complexes
An ethanolic solution of Schiff base (5 mmol) was mixed
with metal(II) chloride (2.5 mmol) in ethanol (25 mL)
solution keeping ligand-metal ratio 2 : 1. The reaction
mixture was then refluxed for ca. 1 h on a water bath till the
complex precipitated out. The solid complex obtained was
removed by filtration, successively washed with water, dried
at room temperature and recrystallized from ethanol.
L ¼ Schiff base ligand.
procedures. The supporting electrolyte, tetramethylammo-
niamperchlorate, Me4NClO4 (TMAP) used in the voltam-
metric experiment was purchased from Sigma. IR spectra
were recorded at Pondicherry University on a Jasco FT-IR-
5300 instrument (KBr pellet technique). The 1H NMR
spectra were recorded in DMSO-d6 on a Brucker instrument
using tetramethylsilane (TMS) as internal standard. The UV-
Vis spectra of all the complexes were recorded in DMSO on
a Shimadzu UV 1601 spectrophotometer. Microanalytical
data were performed at the Regional Sophisticated Instru-
mentation Centre, Central Drug Research Institute,
Lucknow. Magnetic susceptibility measurements of the
complexes in the solid state were determined by Gouy
CONCLUSIONS
The Schiff base and its complexes have been synthesized
using the Mannich base and characterized on the basis of
analytical and spectral data. All the complexes exhibit octa-
hedral geometry. The antimicrobial activity of the complexes
is higher than the ligand and the standard. The synthesized
metal complexes may serve as a vehicle for activation of
ligand as the principle cytotoxic species.
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