Synthesis, spectroscopic, thermal and antimicrobial studies of Co(II), Ni(II), Cu(II) and Zn(II) complexes with Schiff base derived from 4-amino-3-mercapto-6-methyl-5-oxo-1,2,4-triazine

Article abstract of DOI:10.1007/s00044-011-9683-4

Coordination complexes of Co(II), Ni(II), Cu(II) and Zn(II) with Schiff base derived from syringaldehyde and 4-amino-3-mercapto-6-methyl-5-oxo-1,2,4- triazine have been synthesized. These complexes have been characterized by elemental analysis, magnetic moment, spectroscopic (IR, Electronic, ¹H NMR, ESR) and thermogravimetric analysis. Magnetic and spectral data suggest octahedral geometry for Co(II), Ni(II) and Zn(II) complexes and square planar for Cu(II) complexes. The presence of coordinated water in metal complexes was confirmed by thermal and IR data. The Schiff base and its metal complexes have been screened for antibacterial (Pseudomonas aeruginosa, Bacillus subtilis, Escherichia coli, Staphylococcus aureus) and antifungal activities (Aspergillus niger, A. flavus). A comparison is made between activities of complexes with Schiff base and with the standard antibiotics. Springer Science+Business Media, LLC 2011.

Full text of DOI:10.1007/s00044-011-9683-4

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2012) 21:1708–1716
DOI 10.1007/s00044-011-9683-4
ORIGINAL RESEARCH
Synthesis, spectroscopic, thermal and antimicrobial studies
of Co(II), Ni(II), Cu(II) and Zn(II) complexes with Schiff base
derived from 4-amino-3-mercapto-6-methyl-5-oxo-1,2,4-triazine
•
Kiran Singh Yogender Kumar Parvesh Puri
•
•
•
Chetan Sharma K. R. Aneja
Received: 2 November 2010 / Accepted: 24 May 2011 / Published online: 11 June 2011
Ó Springer Science+Business Media, LLC 2011
Abstract Coordination complexes of Co(II), Ni(II),
Cu(II) and Zn(II) with Schiff base derived from syringal-
dehyde and 4-amino-3-mercapto-6-methyl-5-oxo-1,2,4-tri-
azine have been synthesized. These complexes have been
characterized by elemental analysis, magnetic moment,
application as agrochemicals. Recent studies have shown
their ability in chelating transition metal ion to form stable
metal complexes (Samir et al., 2002, 2004). They provide a
wide range of applications in the fields of optics (Mascars
et al., 2002), herbicides (Esser et al., 1976) and pharma-
ceuticals (Courme et al., 2010). Schiff bases derived from
1,2,4 triazine are known to be biologically active. They act
as antiviral (Dandson and Boykin, 1978), antibacterial,
antimalarial and antiinflammatory agents (Heilman et al.,
1980).
1
spectroscopic (IR, Electronic, H NMR, ESR) and ther-
mogravimetric analysis. Magnetic and spectral data suggest
octahedral geometry for Co(II), Ni(II) and Zn(II) com-
plexes and square planar for Cu(II) complexes. The pres-
ence of coordinated water in metal complexes was
confirmed by thermal and IR data. The Schiff base and its
metal complexes have been screened for antibacterial
(Pseudomonas aeruginosa, Bacillus subtilis, Escherichia
coli, Staphylococcus aureus) and antifungal activities
(Aspergillus niger, A. flavus). A comparison is made
between activities of complexes with Schiff base and with
the standard antibiotics.
Synthesis of new Schiff bases and their metal complexes
still the aim of many recent investigations (Lacroxi et al.,
2004; Golcu et al., 2005; Dhar et al., 2005; Peppel and
Kockerling, 2009). Therefore, in continuation of our pre-
vious studies on characterization of transition metal com-
plexes (Singh et al., 2002, 2007), the present investigation
deals with the synthesis, characterization and thermal
studies of Co(II), Ni(II), Cu(II) and Zn(II) complexes of
Schiff base derived from 4-amino-3-mercapto-6-methyl-
5-oxo-1,2,4-triazine and syringaldehyde (4-hydroxy-3,5-
dimethoxybenzaldehyde) (Fig. 1).
Keywords Schiff base ꢀ 1,2,4-triazine ꢀ Thermal studies ꢀ
Antimicrobial activity ꢀ Octahedral complexes
Introduction
Experimental
Numerous compounds containing 1,2,4-triazine moieties
are well known in natural materials and show potential
Measurements
The IR spectra were recorded as KBr pellets on a MB-
3000 ABB infrared spectrophotometer. The electronic
spectra were measured in DMF solution on a systronics
2203 Double beam spectrometer. The magnetic suscepti-
bility measurement was carried out at room temperature
on vibrating sample magnetometer (Model 155) at IIC,
K. Singh (&) ꢀ Y. Kumar ꢀ P. Puri
Department of Chemistry, Kurukshetra University,
Kurukshetra 136119, India
e-mail: kiransinghkuk@yahoo.co.in
C. Sharma ꢀ K. R. Aneja
1
IIT Roorkee. H NMR spectra were recorded in CDCl3/
Department of Microbiology, Kurukshetra University,
Kurukshetra 136119, India
DMSO-d6 on
a Bruker ACF 300 spectrometer at
123

Med Chem Res (2012) 21:1708–1716
1709
O
Synthesis of metal complexes
H3C
OCH3
OH
1:1 Metal complexes
N
N
C
H
(Z)
N
A hot ethanolic solution of the snmmot (0.45 g, 1.3 mmol)
was added to the aqueous ethanolic solutions of acetates of
Co(II) (0.34 g, 1.3 mmol), Ni(II) (0.34 g, 1.3 mmol),
Cu(II) (0.27 g, 1.3 mmol) and Zn(II) (0.30 g, 1.3 mmol),
respectively, which resulted in the immediate precipitation
of metal derivatives. The products formed were filtered,
washed with warm water, ethanol and finally with acetone
and dried on water bath.
(E)
N
SH
H3CO
O
H3C
OCH3
OH
N
N
C
(Z)
N
H
N
H
S
H3CO
1:2 Metal complexes
snmmot
Fig. 1 Structure of Schiff base
The aqueous ethanolic solutions of acetates of Co(II)
(0.30 g, 1.24 mmol), Ni(II) (0.30 g, 1.24 mmol), Cu(II)
(0.24 g, 1.24 mmol) and Zn(II) (0.27 g, 1.24 mmol) were
treated with a hot ethanolic solutions of snmmot (0.80 g,
2.48 mmol). The solid complexes separated, were filtered,
washed with warm water, ethanol and finally with acetone
and dried on water bath.
300 MHz by taking tetramethyl silane as internal stan-
dard. Thermal studies of the solid complexes were per-
formed using a Perkin-Elmer Diamond TG/DTA analyser
from ambient to 800°C with a 10°C min-1 heating
rate using air atmosphere. ESR spectra were recorded on
X-Band at frequency of 9.1 GHz under the magnetic field
3000 Guass on a varian E-112 ESR spectrometer at SAIF
IIT Bombay. Analyses indicated by CHN were within
0.4% of the theoretical values on elemental analyser, P
U Chandigarh.
Antimicrobial assay
Test microorganisms
Four bacteria, Staphylococcus aureus (MTCC 96), Bacillus
subtilis (MTCC 121) (Gram positive), Escherichia coli
(MTCC 1652) and Pseudomonas aeruginosa (MTCC 741)
(Gram negative) were procured from Microbial Type
Culture Collection (MTCC), Chandigarh and two fungi,
Aspergillus niger and A. flavus, the ear pathogens isolated
from the Kurukshetra patients, were used in this study.
Materials
All the chemicals utilized in this investigation were of Anal
R grade. The metal acetates/salts used were in their
hydrated form. The metal contents were estimated using
standard gravimetric methods; cobalt was estimated as
cobalt pyridine thiocyanate, nickel as nickel dim-
ethylglyoximate, copper as copper thiocyanate and zinc as
zinc ammonium phosphate (Vogel, 1999).
In vitro antibacterial activity
The antibacterial activity of newly synthesized compounds
was evaluated by the agar well-diffusion method. All the
microbial cultures were adjusted to 0.5 McFarland stan-
dards, which is visually comparable to a microbial sus-
pension of approximately 1.5 9 108 cfu/ml. 20 ml of
Mueller–Hinton agar medium was poured into each Petri
plate and plates were swabbed with 100-ll inocula of the
test microorganisms and kept for 15 min for adsorption.
Using sterile cork borer of 8-mm diameter, wells were
bored into the seeded agar plates and these were loaded
with a 100-ll volume with concentration of 4.0 mg/ml of
each compound reconstituted in the dimethylsulphoxide
(DMSO). All the plates were incubated at 37°C for 24 h.
Antibacterial activity of each synthetic compound was
evaluated by measuring the zone of growth inhibition
Synthesis of 4-(4-hydroxy-3,5-
dimethoxybenzalideamino)-3-mercapto-6-methyl-5-
oxo-1,2,4-triazine(snmmot) [HL]
4-Amino-3-mercapto-6-methyl-5-oxo-1,2,4-triazine (ammot)
was prepared by reported procedure (Dornow et al., 1964).
An ethanolic solution of ammot (2.50 g, 15.82 mmol) was
added with stirring to an ethanolic solutionof 4-hydroxy-3,5-
dimethoxybenzaldehyde (2.87 g, 15.82 mmol) and refluxed
for 5 h. The product was filtered off, washed with ice cold
ethanol and a light yellow crystalline product was obtained
after recrystallization from ethanol. Yield: 82%, m.p.: 221–
225°C.
123

1710
Med Chem Res (2012) 21:1708–1716
against the test organisms with zone reader (Hi Antibiotic
zone scale). DMSO was used as a negative control,
whereas ciprofloxacin was used as positive control. This
procedure was performed in three replicate plates for each
organism (Ahmad and Beg 2001; Andrews 2001).
performed in triplicates. Diameter of fungal colonies was
measured and expressed as percent mycelial inhibition by
applying the formula (Al Burtamani et al., 2005).
Percent inhibition of myelial growth
¼ ðdc ꢁ dtÞ=dc ꢂ 100
where dc is the average diameter of fungal colony in neg-
ative control sets and dt is the average diameter fungal
colony in experimental sets
Minimum inhibitory concentration (MIC)
MIC of the various compounds against bacterial strains was
tested through a macrodilution tube method as recom-
mended by NCCLS. In this method, the various test con-
centrations of chemically synthesized compounds were
made from 128 to 0.25 lg/ml in sterile tube Nos. 1 to 9.
100-ll sterile Mueller–Hinton Broth (MHB) was poured in
each sterile tube followed by addition of 200-ll test com-
pound in tube 1. Two-fold serial dilutions were carried out
from tube 1 to the tube 9 and excess broth (100 ll) was
discarded from the last tube No. 9. To each tube, 100 ll of
standard inoculum (1.5 9 108 cfu/ml) was added. Cipro-
floxacin was used as control. Turbidity was observed after
incubating the inoculated tubes at 37°C for 24 h (NCCLS
2000).
Results and discussion
Chemistry
Analytical data of ligand and metal complexes are given in
Table 1, which indicate the formation of 1:1 and 1:2 metal
complexes of snmmot with Co(II), Ni(II), Cu(II) and Zn(II)
metal ions. The ligand was soluble in ethanol and metha-
nol. All the metal complexes are coloured, nonhygroscopic
solid stable in air, insoluble in water and many common
organic solvents, infusible at higher temperature.
In vitro antifungal activity
IR spectra
The antifungal activity of Schiff base and its metal com-
plexes were evaluated by poison food technique. The
moulds were grown on Sabouraud dextrose agar (SDA) at
25°C for 7 days and used as inocula. The 15 ml of molten
SDA (45°C) was poisoned by the addition of 100-ll vol-
ume of each compound having concentration of 4.0 mg/ml
reconstituted in the DMSO, poured into a sterile Petri plate
and allowed it to solidify at room temperature. The solid-
ified poisoned agar plates were inoculated at the centre
with fungal plugs (8-mm diameter) obtained from the
colony margins and incubated at 25°C for 7 days. DMSO
was used as the negative control whereas Fluconazole was
used as the positive control. The experiments were
The important IR frequencies which characterize the Schiff
bases and metal complexes are discussed in the following
text (Table 2).
1. The free ligand exhibits a band at 1697 cm-1, assigned
to m(C=O) at the 5 position of the six-membered
triazine ring (Silverstein and Morril, 1991). In the
metal complexes, no significant change was observed,
indicating that the carbonyl oxygen may not partici-
pate in coordination.
2. A band at 1589 cm-1 in the spectra of Schiff base has
been assigned to the azomethine group frequency
m(N=CH), which shifts towards lower frequency
Table 1 Physical and analytical data of the ligand and metal complexes
Sr. no. Compound
Colour
Yield % Elemental analysis calcd (found) %
C
H
N
M
–
1
2
3
4
5
6
7
8
9
Snmmot(HL) (C13H14N4O4S)
Light yellow
82
84
48.44 (48.14) 4.34 (4.28)
4.34 (4.33)
Co(L)(OAc)ꢀ3H2O [C15H22N4O9SCo] Dark brown
36.54 (36.52) 4.46 (4.42) 11.66 (11.64) 11.95 (11.94)
42.33 (42.32) 4.07 (4.06) 15.19 (15.15) 8.00 (8.01)
36.53 (36.52) 4.46 (4.45) 11.36 (11.33) 11.91 (11.88)
42.35 (42.33) 4.07 (4.07) 15.20 (15.18) 7.96 (7.97)
39.01 (39.00) 3.92 (3.91) 12.13 (12.11) 13.75 (13.74)
44.22 (44.21) 3.71 (3.70) 15.86 (15.85) 8.99 (8.97)
36.04 (36.02) 4.43 (4.40) 11.20 (11.10) 13.07 (13.01)
41.96 (41.88) 4.06 (4.00) 15.05 (14.98) 8.78 (8.65)
Co(L)2ꢀ2H2O [C26H30N8O10S2Co]
Ni(L)(OAc)ꢀ3H2O [C15H22N4O9SNi]
Ni(L)2ꢀ2H2O [C26H30N8O10S2Ni]
Cu(L)(OAc)ꢀH2O [C15H18N4O7SCu]
Cu(L)2 [C26H26N8O8S2Cu]
Yellowish brown 86
Brown
81
85
87
84
80
82
Blackish brown
Dark brown
Dark brown
Zn(L)(OAc)ꢀ3H2O [C15H22N4O9SZn] Yellow
Zn(L)2ꢀ2H2O [C26H30N8O10S2Zn] Light yellow
123

Med Chem Res (2012) 21:1708–1716
1711
Table 2 IR spectral data of the ligand and their metal complexes
Compound
m(C=O)
m(N=CH)
m(C=S)
m(C–S)
m(N–H)
m(S–H)
m(OOCCH3)
m(H2O/OH)
m(M–S)
m(M–N)
Snmmot(HL)
1697
1690
1690
1688
1689
1688
1686
1689
1690
1589
1576
1576
1572
1574
1572
1574
1572
1576
1165
725
717
733
733
725
725
741
717
3225
2400
–
1740
–
–
3364
3271
3271
3256
3263
–
–
349
356
354
355
361
365
360
362
–
480
485
504
502
515
513
508
506
Co(L)(OAc)ꢀ3H2O
Co(L)2ꢀ2H2O
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Ni(L)(OAc)ꢀ3H2O
Ni(L)2ꢀ2H2O
1743
–
Cu(L)(OAc)ꢀH2O
Cu(L)2
1729
–
Zn(L)(OAc)ꢀ3H2O
Zn(L)2ꢀ2H2O
1735
–
3310
3286
(Singh et al., 2002, 2007) by 15–20 cm-1 in the
spectra of the complexes, indicating coordination
through the nitrogen atom. Further coordination of
metal to azomethine nitrogen is confirmed by a new
band around 480–513 cm-1 due to m(M–N).
indicating coordination through the azomethine nitrogen.
In addition to this, snmmot shows a signal at d 13.14,
which is attributed to –SH proton. The deprotonation of the
thiol group has been supported by disappearance of –SH
proton signals in the spectra of complexes.
3. The free ligand exhibits a medium intensity band at
3225 cm-1 due to m(N–H) indicating the thione form,
while a weak broad band observed around 2400 cm-1
due to m(S–H) vibrations suggests that Schiff base
exhibits thiol-thione tautomerism (Prakash et al.,
2008a, b; Sinha et al., 1977). These bands disappeared
in the spectra of the metal complexes indicating
deprotonation and complexation through sulphur. In
the spectra of metal complexes bands appeared at 715–
735 cm-1 and 340–370 cm-1 were assigned to m(C–S)
and m(M-S), respectively.
4. The presence of coordinated water molecules in the
metal complexes is indicated by a broad trough band in
the region 3200–3400 cm-1. A strong band in the
region 1730–1740 cm-1 has been assigned to m(OO-
CCH3) in 1:1 metal complexes.
In the spectra of Schiff base singlets at d 7.13 and d 2.49
were assigned to aromatic protons and methyl group of
triazine, respectively. In the spectrum of 1:1 Zn complex
singlet at d 2.61 is assigned to methyl group of acetate ion.
ESR spectra
ESR spectra for 1:1 and 1:2 copper(II) complexes, i.e.
Cu(snmmot)(OAc)ꢀH2O and Cu(snmmot)2 (Fig. 2) have
been recorded. From the observed g values for Cu(snm-
mot)(OAc)ꢀH2O at room temperature (g = 2.15, g\
=
k
2.063, gav = 2.091, G = 2.409) and for Cu(snmmot)2 at
room temperature (g = 2.189, g\ = 2.060, gav = 2.113,
k
G = 3.701) it is evident that unpaired electron is localized in
the dx2 - y2 orbital and corresponds to square planar
geometry of the complexes. The g \ 2.3 value confirms the
k
covalent character of the metal ligand bond. The axial
symmetry parameter G is less than 4.0, indicates consider-
able exchange interaction in the solid complex (Dutta and
Syamal, 1993; Prabhugouda et al., 2000).
1H NMR spectra
1
The H NMR spectrum has been studied for Schiff base
and its Zn(II) complexes (Table 3). These spectral data
have been interpreted based on literature data (Singh et al.,
2002, 2006, 2007). In the spectra of Schiff base signal at d
8.22 is assigned to azomethine proton (–HC=N–), which
shifted downfield in the spectra of metal complexes
Electronic spectra
The electronic spectra of Co(II) complexes (Table 4)
exhibit absorption bands in the region 10000–10800 and
19500–19800 cm-1 corresponding to m1 and m3 transition,
Table 3 1HMR spectra of Schiff base and its Zn(II) complexes (d, ppm)
Compound
(–N=CH–)
Ar–H
–OCH3
–SH
–CH3
Snmmot(HL)
8.22(s,1H)
8.38(s,1H)
8.31(s,1H)
7.13(s,2H)
7.17(s,2H)
7.06(s,2H)
3.89(s,6H)
3.81(s,6H)
3.79(s,6H)
13.14(bs,1H)
2.49(s,3H)
2.19(s,3H)
2.21(s,3H)
Zn(L)(OAc)ꢀ3H2O
Zn(L)2ꢀ2H2O
–
–
123

1712
Med Chem Res (2012) 21:1708–1716
ion. Using Band-fitting equation (Lever, 1968) ligand field
parameter have been calculated for Ni(II) complexes. Ra-
chah parameter B is less than free ion value, i.e. 1041 cm-1
indicating the covalent character of metal ligand bond. The
crystal field splitting energy (Dq) value was found to be
*990 cm-1 suggested octahedral geometry for Ni(II)
complexes. The ratios m2/m1 (1.5) and b% (33.2, 34.8)
support the octahedral geometry around the Ni(II) ion
(Mohammed, 2001).
The 1:1 and 1:2 Cu(II) complexes exhibit single bands at
18456 and 18498 cm-1, respectively, which is attributed to
2B1g–2A1g (m1) transition. It is a characteristic band of
square planar geometry around the Cu(II) (Greenwood and
Eamshow, 1983; Osman et al., 2004).
Fig. 2 X-band e.s.r. spectra of Cu(snmmot)2
Magnetic data
respectively, which are attributed to the transitions
4
4T1g(F)–4T2g(F) (m1); T1g(F)–4T1g(P) (m3) (Prakash et al.,
The 1:1 and 1:2 Co(II) complexes show magnetic momen-
t(leff) 4.71 and 4.78 BM, respectively, which is within the
expected range of octahedral complex (4.3–5.2 BM) (Singh
et al., 2002, 2006; Al Burtamani et al., 2005). The 1:1 and 1:2
Nickel complexes show magnetic moment 3.11 and 3.35
BM, suggest octahedral geometry. The Cu(II) complex has
magnetic moment value 1.72 and 1.73 BM, which fall in the
normal range (1.7–2.2 BM).
2008a, b; Mohammedshafi and Shreedhar, 2009). These
bands are characteristic of high spin octahedral Co(II)
complexes; m2 is not observed, but it can be calculated
(Cotton and Wilkinson, 1988; Patra et al., 2005) using
relation m2 = m1 ? 10Dq, which is very close to (m3) tran-
sition. The ligand field parameters such as Dq, B, b and b%
have been calculated using Band-fitting equation given by
Underhill and Billing (Lever, 1968). The crystal field
splitting energy (Dq) value was found to be 1190 and
1193 cm-1. These values are well within the range repor-
ted for most of the octahedral complexes. The Rachah
parameter (B) is found to be 671 cm-1 which is less than
free ion value 971 cm-1, suggesting an orbital overlap and
delocalization of electron on the metal ion. The nephel-
auxetic ratio (b) for the 1:1 and 1:2 cobalt complexes is
0.69, which is less than one suggesting partial covalency in
the metal ligand bond. The values Dq, b%, m2/m1 (Table 4)
suggest the octahedral geometry for Co(II) complexes.
The 1:1 and 1:2 Ni(II) complexes exhibit three absorp-
tion bands in the region 9800–9975, 15500–15600 and
Thermal analysis
Thermogravimetric studies of Co(L)OAcꢀ3H2O and
Zn(L)2ꢀ2H2O complexes are discussed (Canpolat and
Kaya, 2004; Sallam, 2005) (Fig. 3). The decomposition
temperature, pyrolysed products, percentage mass loss of
the complexes and the ash (percent) are given in Table 5.
The Co(II) complex decomposes in three stages. The first
step, 50–230°C, results in a mass loss (found 9.20%, calcd.
10.95%), corresponding to a loss of three water molecules
of hydration. The anhydrous complex decomposes in a
major stage consisting of two overlapping steps. In the first
stage, the organic part started decomposing, giving metal-
triazine at 385°C with a mass loss of 45.53% on TG curve
3
24600–24690 cm-1 are assigned to A2g(F)–3T2g(F) (m1),
3
3A2g(F)–3T1g(F) (m2) and A2g(F)–3T1g(P) (m3) transitions,
respectively, indicates octahedral geometry for the Ni(II)
Table 4 Electronic spectra and ligand field parameters of metal complexes
Compound
Transitions (cm-1
)
Dq (cm-1
)
B (cm-1
)
m2/m1
b
b%
m1
m2
m3
Co(L)(OAc)ꢀ3H2O
Co(L)2ꢀ2H2O
Ni(L)(OAc)ꢀ3H2O
Ni(L)2ꢀ2H2O
10750
10780
9876
22651*
22714*
15567
19670
19720
24650
24670
1190.1
1193.4
987.6
671.4
672.9
705.9
688.6
2.10
2.10
1.57
1.56
0.691
0.693
0.668
0.652
30.9
30.7
33.2
34.8
9975
15584
997.5
* Indicate the calculated values for that particular transition, it is not experimentally observed
123

Med Chem Res (2012) 21:1708–1716
1713
Fig. 3 TG and DTG
thermograms of
Co(L)OAcꢀ3H2O and
Zn(L)2ꢀ2H2O
Table 5 Themogravimetric characteristics of metal complexes
Compound
Process
Temp. (°C)
Product
Mass%
Calcd.
No. of
moles
Residue%
Calcd.
Nature
CoO
Found
Found
17.00
Co(L)OAcꢀ3H2O
Dehydration
50–230
230–385
385–750
50–215
H2O
10.95
45.65
28.22
4.83
9.20
45.53
28.27
4.76
3
15.18
Dec. of coordination
Sphere
OAc, organic moiety
Triazine
1,1
1
Zn(L)2ꢀ2H2O
Dehydration
H2O
2
10.93
11.32
ZnO
Dec. of coordination
Sphere (L)
215–360
360–750
Organic moiety
Triazine
44.62
39.58
44.62
39.54
2
2
(calcd. 45.65). In the temperature range 385–750°C all the
triazine part get decomposed with a mass loss of 28.27%
(calcd. 28.22%). The Zn(II) complex also decomposes in
three stages. The first step 50–215°C, results in a mass loss
(found 4.76%, calcd. 4.83%) corresponding to a loss of two
water molecules of hydration. In the second step, organic
part is lost in 215–360°C range with a mass loss of 44.62%
(calcd. 44.62%), giving metal triazine. The third step cor-
responds to decomposition of triazine molecules with mass
loss 39.54% (calcd. 39.58%) in the TG curve. The
decomposition of both of the complexes ended with oxide
formation.
were found to be most effective against S. aureus with zone
of inhibition 26.0 and 26.6 mm, B. subtilis with zone of
inhibition 18.6 and 19.3 mm, E. coli with the zone
of inhibition 16.6 and 16.0 mm, P. aeruginosa with zone of
inhibition 18.3 and 21.6 mm, respectively. Whereas,
compound numbers 6–9 did not show any activity against
Gram negative bacteria (Table 6). The newly synthesized
compound shows low activity against Gram negative bac-
teria as compared to Gram positive bacteria.
In the whole series, the MIC of the newly synthesized
compounds ranged between 8 and 128 lg/ml against Gram
positive bacteria. Compounds 2 and 3 showed highest MIC
of 8 lg/ml against S. aureus. In case of Gram negative
bacteria, MIC of compounds ranged from 16 to 128 lg/ml,
compounds 2 and 3 showed highest MIC of 128 lg/ml
against E. coli and compound 3 showed highest MIC of
16 lg/ml against P. aeruginosa (Table 7). The antibacte-
rial activity results revealed that compound 3 was found to
be the best from the nine compounds in inhibiting the
growth of both the Gram positive bacteria and the Gram
negative bacteria.
Antimicrobial activity discussion
A total of nine compounds were screened for their anti-
bacterial and antifungal activities. All the tested com-
pounds were found to possess variable antibacterial activity
against both Gram positive (S. aureus, B. subtilis) and
Gram negative (E. coli, P. aeruginosa) bacteria. On the
basis of maximum inhibitory activity, compounds 2 and 3
123

1714
Med Chem Res (2012) 21:1708–1716
Table 6 In vitro antibacterial activity of synthesized compounds through agar well-diffusion method
Sr.
no.
Compound
Diameter growth of inhibition zone (mm)a
Staphylococcus
aureus
Bacillus
subtilis
Escherichia
coli
Pseudomonas
aeruginosa
1
2
Snmmot(HL)
15.6
26
15
–
–
Co(L)(OAc)ꢀ3H2O
Co(L)2ꢀ2H2O
Ni(L)(OAc)ꢀ3H2O
Ni(L)2ꢀ2H2O
18.6
19.3
17
16.6
16
–
18.3
21.6
–
3
26.6
21.6
20.6
14.3
15.6
14.3
15
4
5
16.6
15
–
16.3
–
6
Cu(L)(OAc)ꢀH2O
Cu(L)2
–
7
15
–
–
8
Zn(L)(OAc)ꢀ3H2O
Zn(L)2ꢀ2H2O
Ciprofloxacin
17.6
16.6
24.0
–
–
9
–
–
10
26.0
25.0
22.0
– No activity
a
Values, including diameter of the well (8 mm), are means of three replicates
In the case of antifungal activity, it was observed that
compound 2 showed 50% inhibition of mycelial growth
against Aspergillus niger, whereas three compounds 2, 3
and 4 showed more than 50% inhibition of mycelial growth
against A. flavus (Table 8).
Table 8 In vitro antifungal activity of synthetic chemical compounds
through poisoned food method
Compound no.
Mycelial growth inhibition (%)
Aspergillus niger
Aspergillus
flavus
The antimicrobial experiments suggested that all the
newly synthesized Schiff bases are biologically active and
the metal ions on chelation with bidentate ligands showed
increase in antibacterial and antifungal activities. It is
suggested that (Chohan and Praveen, 2001; Chohan et al.,
2004) chelation of Schiff bases with different metal ions
makes them stronger bacteriostatic agents, thus inhibiting
the growth of bacteria more than the parent Schiff bases do.
It is assumed that the increase in antimicrobial activity is
due to factors such as dipole moment, conductivity,
1
44.4
50
50
2
61.1
55.5
57.7
50
3
46.6
44.4
44.4
33.3
44.4
33.3
44.4
81.1
4
5
6
44.4
44.4
44.4
50
7
8
9
Fluconazole
77.7
Table 7 Minimum inhibitory concentration (MIC) (in lg/ml) of
compounds using macrodilution method
solubility and cell permeability mechanism influenced by
presence of metal ion.
Compound
no
Staphylococcus Bacillus Escherichia Pseudomonas
aeruginosa
aureus
subtilis coli
1
2
3
4
5
6
7
8
9
>128
8
>128
64
–
–
Conclusion
128
128
–
64
16
–
8
64
The synthesized 4-(4-hydroxy-3,5-dimethoxybenzalideamino)-
3-mercapto-6-methyl-5-oxo-1,2,4-triazine Schiff base is
bidentate ligand coordinates through azomethine nitrogen
and sulphur to the metals, as confirmed by analytical, IR,
PMR, ESR, electronic, magnetic and thermal studies. The
presence of coordinated water in metal complexes was
confirmed by thermal and IR data. All these observations put
together lead us to propose the structure shown in Fig. 4. The
antimicrobial and antifungal activities of the complexes are
64
128
128
>128
>128
128
128
5
64
–
128
–
>128
>128
>128
>128
–
–
–
–
–
–
–
Ciprofloxacin 5
– Not tested
5
5
123

Med Chem Res (2012) 21:1708–1716
1715
R
H
Acknowledgments One of the authors Yogender Kumar is highly
thankful to University Grant commission, New Delhi for providing
junior research fellowship (JRF) and Department of Chemistry, Ku-
rukshetra University Kurukshetra, for providing facilities to carry out
this research work.
C
N
O
N
H2O
OCOCH3
H3C
N
M
N
H O
2
References
S
H2O
(1:1)
Ahmad I, Beg AJ (2001) Antimicrobial and phytochemical studies on
45 Indian medicinal plants against multi-drug resistant human
pathogens. J Ethnopharmacol 74:113–123
R
H
C
O
Al Burtamani SKS, Fatope MO, Marwah RG, Onifade AK, Al-Saidi
SH (2005) Chemical composition, antibacterial and antifungal
activities of the essential oil of Haplophyllum tuberculatum from
Oman. J Ethnopharmocol 96:107–112
Andrews JM (2001) Determination of minimum inhibitory concen-
trations. J Antimicrob Chemother 48:5–16
Canpolat E, Kaya M (2004) Studies on mononuclear chelates
derived from substituted Schiff-base ligands (part 2): synthesis
and characterization of a new 5-bromosalicyliden-p-amin-
oacetophenoneoxime and its complexes with Co(II), Ni(II),
Cu(II) and Zn(II). J Coord Chem 57:1217–1223
Chohan ZH, Praveen M (2001) Synthesis, characterization, coordi-
nation and antibacterial properties of novel asymmetric 1,10-
disubstituted ferrocene-derived Schiff-base ligands and their
Co(II), Cu(II) Ni(II) and Zn(II) complexes. Appl Organomet
Chem 15:617–625
H2O
N
O
S
N
H3C
N
N
M
N
N
N
C
CH3
S
N
H2O
H
R
(1:2)
M = Co(II), Ni (II) and Zn(II)
R
H
C
N
O
Chohan ZH, Supran CT, Scozzafava A (2004) Metalloantibiotics:
synthesis and antibacterial activity of cobalt(II), copper(II),
nickel(II) and zinc(II) complexes of kefzol. J Enzyme Inhib Med
Chem 19:79–84
Cotton FA, Wilkinson G (1988) Advanced inorganic chemistry, 5th
edn. Wiley, New York
OCOCH3
H3C
N
Cu
N
N
S
H2O
Courme C, Gresh N, Vidal M, Lenoir C, Garbay C, Florent JC,
Bertounesque E (2010) Synthesis of aryl phosphates based on
pyrimidine and triazine scaffolds. Eur J Med Chem 45:244–255
Dandson WM, Boykin WD (1978) Synthesis of as-triazines as
potential antiviral agents. J Pharm Sci 67:737–739
Dhar S, Nethaji M, Chakarworty AR (2005) Synthesis, crystal
structure and photo-induced DNA cleavage activity of ternary
copper(II) complexes of NSO-donor Schiff bases and NN-donor
heterocyclic ligands. Inorg Chim Acta 358:2437–2444
Dornow A, Mengel H, Marx P (1964) Uber 1,2,4-triazine, I
Darstellung einiger neuer s-Triazolo[3.2-c-]-as-triazine. Chem
Ber 97:2173–2178
(1:1)
R
H
C
N
O
N
N
S
H3C
N
N
Cu
N
N
N
C
CH3
S
O
Dutta RL, Syamal A (1993) Elements of magnetochemistry. Affiliated
East West Press Pvt Ltd, New Delhi
(1:2)
H
R
Esser HO, Dupllis G, Vogel C, Marco GJ, Kearney PC, Kaufman DD
(1976) Herbicides chemistry, degradation and mode of action,
vol II, 2nd edn. Marcel Dekker Inc, New York, p 129
Golcu A, Tumer M, Demicell H, Wheatly RC (2005) Cd(II) and
Cu(II) complexes of polydentate Schiff base ligands: synthesis,
characterization, properties and biological activity. Inorg Chim
Acta 358:1785–1797
OCH3
OH
R =
H3CO
Greenwood NN, Eamshow A (1983) Chemistry of the elements, 1st
edn. Pergamon Press, Oxford, pp 1379–1386
Fig. 4 Proposed structures of metal complexes
Heilman PW, Gielman RD, Scozzie AJ, Wayner RJ, Gollo MJ,
Ariyan SZ (1980) Synthesis and anti-inflammatory evaluation of
3-methylthio-1,2,4-triazines, 3-alkoxy-1,2,4-triazines, and 3-a-
ryloxy-1,2,4-triazines. J Pharm Sci 69:282–287
Lacroxi PG, Averseng F, Malfant I, Nakatani K (2004) Synthesis,
crystal structures, and molecular hyperpolarizabilities of a new
Schiff base ligand, and its copper(II), nickel(II), and cobalt(II)
metal complexes. Inorg Chim Acta 357:3825–3835
higher than the parent ligand. It is suggested that chelation of
Schiff bases with different metal ions makes them stronger
bacteriostatic agents, thus inhibiting the growth of bacteria
more than the parent Schiff bases do. Based on the above
studies Schiff base is versatile ligands that can coordinate
virtually any metal ion with interesting bioactivities.
123

1716
Med Chem Res (2012) 21:1708–1716
Lever ABP (1968) Inorganic spectroscopy. Elsevier, Amsterdam
Mascars JRG, Clemente Juan JM, Dunbar KR (2002) Synthesis,
structure and magnetic properties of the one-dimensional chain
4-amino (indole-3-aldehydo)-5-mercapto-1,2,4-triazole Schiff
bases. J Coord Chem 61:1884–1896
Prakash GA, Sangmesh AP, Prema SB (2008b) Synthesis, spectral,
thermal, solid-state DC electrical conductivity and biological
studies of Co(II) complexes with Schiff bases derived from 3-
substituted-4-amino-5-hydrazino-1,2,4-triazole and substituted
salicylaldehydes. Transition Met Chem 33:275–283
Sallam SA (2005) Synthesis, characterization and thermal decompo-
sition of copper(II), nickel(II) and cobalt(II) complexes of 3-
amino-5-methylpyrazole Schiff-bases. Transition Met Chem
30:341–351
Samir SK, Gamila YA, Ali ED (2002) Cobalt(II, III) and copper(II)
complexes of 3-(2-furylidene) hydrazino-5,6-diphenyl-1,2,4-tri-
azine. Transition Met Chem 27:398–406
Samir SK, Gamila YA, Ali ED (2004) Cobalt(II) and copper(II)
complexes of (2-acetylpyridine)-(5,6-diphenyl-[1,2,4]Triazin-3-
YL) hydrazone. J Coord Chem 57:105–113
Silverstein RM, Bassler G, Morril TC (1991) Characteristic group
absorbtion of organic molecules. In: Spectroscopic identification
of organic compounds, 5th edn. Wiley, New York, pp 117–119
Singh G, Singh PA, Sen AK, Singh K, Dubey SN, Handa RN, Choi J
(2002) Synthesis and characterization of some bivalent metal
complexes of schiff bases derived from as-triazine. Synth React
Inorg Met Org Chem 32:171–187
compound
{K[Fe(1,3,5-triazine-2,4,6-tricarboxylate)(H2O)2]ꢀ
2H2O}. J Chem Soc Dalton Trans 13:2710–2713
Mohammed GG (2001) Metal complexes of antibiotic drugs studies
on dicloxacillin complexes of FeII, FeIII, CoII, NiII and CuI.
Spectrochim Acta A 57:1643
Mohammedshafi AP, Shreedhar DD (2009) Synthetic, spectroscopic,
fluorescence, and biological investigation of Co(II), Ni(II),
Cu(II), and Zn(II) complexes of Schiff bases derived from 3-
formyl-2-mercaptoquinolines (Quinol-2-thiones). J Coord Chem
62:2399–2410
NCCLS (2000) Method for dilution antimicrobial susceptibility test
for bacteria that grow aerobically, approved standards, 5th edn.
National Committee for Clinical Standards, Villanova
Osman AH, Saleh MS, Sanaa MM (2004) Synthesis, characterization,
and photochemical studies of some copper complexes of schiff
bases derived from 3-hydrazino-6-methyl[1,2,4]triazin-5(4H)one.
Synth React Inorg Met Org Chem 34:1069–1085
Patra AK, Dhar S, Nethaji M, Chakarworty AR (2005) Metal-assisted
red light-induced DNA cleavage by ternary L-methionine
copper(II) complexes of planar heterocyclic bases. Dalton Trans
5:896–902
Peppel T, Kockerling M (2009) Large 1,3,5-triazine-based ligands
coordinating transition metal ions: syntheses and structures of
the ligands and the ball shaped nanometer-scaled Co complex
[Co(2,4-R-6-R0-1,3,5-triazine)2](Br1.7(OH)0.3)ꢀ4.8H2O [R =
bis(2-diphenylmethylene) hydrazinyl; R0 = piperidin-1-yl].
J Coord Chem 62:1902–1903
Prabhugouda BM, Kalagouda BG, Timmongouda RG (2000) Thermal
studies of cobalt(II), nickel(II) and copper(II) 3-substituted-4-
salicylideneamino-5-mercapto 1,2,4-triazole complexes. Transi-
tion Met Chem 25:411–414
Singh K, Singh DP, Barwa MS, Tyagi P, Mirza Y (2006) Some
bivalent metal complexes of Schiff bases containing N and S
donor atoms. J Enz Inhib Med Chem 21:749–755
Singh K, Barwa MS, Tyagi P (2007) Synthesis and characterization of
cobalt(II), nickel(II), copper(II) and zinc(II) complexes with
Schiff base derived from 4-amino-3-mercapto-6-methyl-5-oxo-
1,2,4-triazine. Eur J Med Chem 42:394–402
Sinha BK, Singh R, Srivastava JP (1977) Substituted 1,2,4-triazoles
as complexing ligands—I Ni(II), Co(II), Cu(II), Zn(II), Pd(II),
Cd(II) and Pb(II) complexes with 4-amino-3,5-dimercapto-1,
2,4-triazole. J Inorg Nucl Chem 39:1797–1801
Vogel AI (1999) A text book of quantitative chemical analysis, 5th
edn. Addison Wesley Longman, London
Prakash GA, Sangmesh AP, Badami PS (2008a) Synthesis, spectral,
thermal, solid state d.c. electrical conductivity and biological
studies of Co(II), Ni(II) and Cu(II) complexes with 3-substituted-
123