Synthesis, spectroscopic characterization and antibacterial activity of new cobalt(II) complexes of unsymmetrical tetradentate (OSN2) Schiff base ligands

Article abstract of DOI:10.1016/j.ejmech.2009.06.015

Cobalt ion complexes with the Schiff bases, (4-X-2-{[2-(2-pyridine-2-yl-ethylsulfanyl)ethylimino]methyl}phenol (X = methoxy (OMe), phenylazo (N₂Ph), bromo (Br), nitro (NO₂)),were synthesized and investigated by several techniques usi

Full text of DOI:10.1016/j.ejmech.2009.06.015

European Journal of Medicinal Chemistry 44 (2009) 4490–4495
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis, spectroscopic characterization and antibacterial activity of new
cobalt(II) complexes of unsymmetrical tetradentate (OSN2) Schiff base ligands
,
b
c
Lotf Ali Saghatforoush a , Firoozeh Chalabian , Ali Aminkhani ,
*
Ghasem Karimnezhad a, Sohrab Ershad d
a Department of Chemistry, Payame Noor University, Khoy 58168-45164, Iran
b Department of Biology, Islamic Azad University, Tehran North Campus, Tehran, Iran
c Department of Chemistry, Azad Islamic University, Khoy Branch, Khoy, Iran
d Department of Chemistry, Payame Noor University, Marand, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Cobalt ion complexes with the Schiff bases, (4-X-2-{[2-(2-pyridine-2-yl-ethylsulfanyl)ethylimino]methyl}
phenol (X ¼ methoxy (OMe), phenylazo (N2Ph), bromo (Br), nitro (NO2)),were synthesized and investigated by
several techniques using elemental analysis (C, H, N), FTIR, electronic spectra and molar conductivity. The
thermal stability of free ligands and related cobalt complexes were studied by using differential scanning
calorimetry (DSC) and thermogravimetric analyses (TGA). Cyclic voltammetry indicates that the investigated
cobalt complexes, under the experimental conditions, have irreversible redox behavior. The synthesized
compounds have antibacterial activity against the four Gram-positive bacteria: Streptococcus pyogenes, Strep-
tococcus agalactiae, Staphylococcus aureus and Bacillus anthracis and also against the two Gram-negative
bacteria: Klebsiella pneumoniae and Pseudomonas aeruginosa. The activity data show that the parent Schiff bases
are more potent antibacterials than the cobalt complexes.
Received 20 October 2008
Received in revised form
25 February 2009
Accepted 11 June 2009
Available online 21 June 2009
Keywords:
Antibacterial activity
Schiff base
Co(II) complexes
Salicylaldehyde
Ó 2009 Elsevier Masson SAS. All rights reserved.
1. Introduction
deals with the synthesis and characteristics of four new cobalt(II)
complexes of [Co(Xpesei)]Cl, where Xpesei is ¼(4-X-2-{[2-(2-pyri-
Schiff bases are considered as a very important class of organic
compounds which have wide applications in many biological
aspects. Some Schiff bases were reported to possess antibacterial,
antifungal and antitumor activities [1,2]. Due to their multiple
implications, the transition metal complexes with Schiff bases, as
ligands, are of paramount scientific interest [3]. Schiff bases with
donors (N, O, S, etc.) have structure similarities with natural bio-
logical systems and due to the presence of imine group, are utilized
in elucidating the mechanism of transformation and rasemination
reaction in biological systems [4–6]. Schiff base complexes have been
used as drugs. Moreover, it is well known that some drug activities,
when administered as metal complexes, are being increased [7], and
several Schiff base complexes have also been shown to inhibit tumor
growth [8]. The effect of the presence of various substituents in the
phenyl rings of aromatic Schiff bases on their antimicrobial activity
has been reported [9]. It was also reported that salicylaldehyde
derivatives with halo atoms in the aromatic ring, showed variety of
biological activities, like antibacterial activities [2,10]. This work
dine-2-yl-ethylsulfanyl)ethylimino]methyl}phenolato (X¼ methoxy
(OMe), phenylazo (N2Ph), bromo (Br), nitro (NO2)). The coordination
behavior of Schiff base towards cobalt(II) ionwas investigated via the
IR, molar conductivity and thermal studies. The antibacterial activity
of Schiff bases and their metal chelates are reported against the four
Gram-positive bacteria: Streptococcus pyogenes (RITCC 1940), Strep-
tococcus agalactiae (RITCC 1913), Staphylococcus aureus (RITCC 1885)
and Bacillus anthracis (RITCC 1036) and also against the two Gram-
negative bacteria: Klebsiella pneumonia (RITCC 1249) and Pseudo-
monas aeruginosa (RITCC 1547).
2. Chemistry
In this study, four Co(II) complexes with the unsymmetrical
tetradentate Schiff bases, derived from aminothioether pyridine
and salicylaldehyde derivatives, (4-X-2-{[2-(2-pyridine-2-yl-eth-
ylsulfanyl)ethylimino]methyl}phenol (X ¼ OMe, N2Ph, Br, NO2),
were synthesized and investigated by several techniques using
elemental analysis (C, H, N), FTIR, electronic spectra and molar
conductivity measurements. The elemental analyses data suggest
that the stoichiometry be 1:1 [M:L] ratio formation. All the
complexes were found to be 1:1 electrolyte systems in acetonitrile.
* Corresponding author. Fax: þ98 4612332556.
E-mail address: saghatforoush@gmail.com (L.A. Saghatforoush).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.06.015

L.A. Saghatforoush et al. / European Journal of Medicinal Chemistry 44 (2009) 4490–4495
4491
S
N
HO
EtOH
Co
+
Cl
CoCl2
O
X
+
NH2
S
N
Reflux
N
OHC
X
X=Br,NO2,OMe,N2ph
Fig. 1. Representative synthesis of cobalt(II) Schiff base complexes.
FTIR spectral data supported that the cobalt ion in all complexes has
N2OS coordination sphere, bounded by deprotonated phenolic
oxygen, imine and pyridine type nitrogens and the thioether sulfur
atoms.
(X ¼ OMe, N2Ph, Br, NO2) respectively, seems to be little influenced
by different substitutions on the salicylaldehyde moiety, and
suggests that the coordination geometry at the metal ion could be
distorted from tetrahedral [18]. The broad intense and poorly
resolved bands between 320 and 450 nm may be assigned to LMCT
or MLCT [8,15,17,18]. The high intensity band below 320 nm is of
3. Results and discussion
ligand origin assignable to intraligand n–p* p* transitions
/p–
[10,19].
XpesesiH (X ¼ NO2, Br, OMe, N2Ph) was prepared by the
condensation of Pyta with salicylaldehyde derivative in absolute
ethanol in good yield and purity. The tetra coordinated mono-
nuclear cobalt(II) complexes were prepared by the reaction of
equimolar quantities of Pyta, required salicylaldehyde, Co(II) chlo-
ride hexahydrate, and methanolic NaOH in absolute ethanol (Fig.1).
The cobalt complexes were characterized by elemental analysis,
molar conductivity, FTIR and electronic spectroscopy. These
complexes were stable at room temperature in air in the solid state.
Solution conductivity measurements were performed to establish
the electrolyte type of the complexes. The molar conductivities at
10ꢀ3 M concentration for the complexes in acetonitrile were in the
expecting range of their formulations as 1:1 electrolytes [11]. The
FTIR spectra of all complexes compared with those of the ligands,
The obtained cyclic voltammetric parameters for the complexes
in acetonitrile solution are listed in Table 1. It is noted that in the
region of potentials in which the complexes are studied, the ligands
are electroinactive. In this condition the
DE (DE ¼ Ec ꢀ Ea) value for
the reversible redox couple Fcþ/Fcꢀ, as internal standard, is equal to
91 mV. On the basis of voltammetric data, all four complexes under
experimental condition, underwent irreversible reduction processes
in potential range of ꢀ0.9 to þ0.20 V. All the complexes exhibited
one oxidation and one reduction peak related to the CoIII/CoII couple.
As shown from the obtained data in Table 1, EPa become less positive
in the sequence of NO2 < N2ph < Br < OMe. This is due to the elec-
tron withdrawing effect of the substituent at the para position of
salicylaldehyde moiety. One of the voltammograms of the cobalt
complexes is shown in Fig. 2.
indicates that the n
(C]N) band at 1634–1655 cmꢀ1 is shifted to
lower frequency by 7–39 cmꢀ1 in the complexes, indicating that the
ligands are coordinated to the metal ions through the nitrogen
atom of the azomethine group [1]. On the other hand, the disap-
pearance of the OH bands of the free ligands in the complexes
indicates that the OH group has been deprotonated and bounded to
metal ions as Oꢀ. The intense band at 1243–1315 cmꢀ1, assigned to
phenolic C–O linkage, shifted towards higher wave number of
1300–1340 cmꢀ1 confirming the involvement of OH group in bond
formation with metal ion [10,12–14]. The UV–vis absorption
spectra, performed on the complexes dissolved in acetonitrile,
show the modification of the absorption bands characteristic of the
ligands as well as the occurrence of some new bands, characteristic
of the formation of the coordinative compounds. All of the
complexes show three closely spaced bands in the visible region
and very intense bands in the UV region. In the regular tetrahedral
and and near-tetrahedral Co(II) complexes, only one d–d transition
(4A2 (F) / 4T1 (P)) is observed in the visible region [15]. Three
closely spaced bands in the spectrum of complexes are because of
the distortion in tetrahedral symmetry around the metal center.
This splitting originates from the reduction of the orbital degen-
eracy, due to the difference in the ligand field strength of imine and
pyridine N donor atoms, thiol S and phenoxide O donor atoms
[2,16]. Therefore the appearance of broad intense absorption band
at 508–515 nm in the spectra of the complexes of [Co(Xpesesi)] Cl,
Thermal studies over the some Schiff base ligands and their
cobalt(II) complexes, through the differential scanning calorimetric
(DSC) and thermogravimetric (TGA) techniques, were performed.
Transition temperatures, enthalpy changes, decomposition temper-
atures of Schiff base ligands, and related cobalt(II) complexes are
tabulated in Table 2. DSC studies presented a melting process at
54.70, 68.2, 96.3 and 140.8 for OMepesesiH, BrpesesiH, NO2pesesiH
and N2PhpesesiH, respectively, followed by decomposition
70
60
50
40
30
20
10
0
-10
-20
-30
Table 1
Cyclic voltammetry data for the cobalt(II) Schiff base complexes.
Complex
Epa (V)
Epc (V)
D
E (V)
ipc/ipa
[Co(NO2pesesi)]Cl
[Co(OMepesesi)]Cl
[Co(N2phpesesi)]Cl
[Co(Brpesesi)]Cl
ꢀ0.224
ꢀ0.064
ꢀ0.105
ꢀ0.096
ꢀ0.366
ꢀ0.073
ꢀ0.275
ꢀ0.032
ꢀ0.142
ꢀ0.137
ꢀ0.175
ꢀ0.128
0.30
0.49
0.65
0.57
-1
-0.8
-0.6
-0.4
E(V)
-0.2
0
0.2
Fig. 2. Cyclic voltammogram of [Co(NO2pesesi)]Cl.

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L.A. Saghatforoush et al. / European Journal of Medicinal Chemistry 44 (2009) 4490–4495
Table 2
(RITCC 1913), S. aureus (RITCC 1885) and B. anthracis (RITCC 1036) as
Gram-positive bacteria and K. pneumoniae (RITCC 1249) and P.
aeruginosa (RITCC 1547) as Gram-negative bacteria. Obtained data
indicate high activity of BrpesesiH Schiff base against Gram-posi-
tive bacteria, S. agalactiae, B. anthracis, S. pyogenes and S. aureus, and
moderate activity of it towards Gram-negative bacteria, K. pneu-
moniae and P. aeruginosa. Two other Schiff ligands: NO2pesesiH and
OMepesesiH, have strong activity against S. pyogenes and moderate
one towards S. agalactiae, B. anthracis and K. pneumoniae. While
NO2pesesiH ligand has moderate activity against S. aureus and P.
aeruginosa, OMepesesiH ligand against these bacteria has weak
activity. Considerable activity of Schiff base ligands may be arisen
from the presense of imine group which imports in elucidating the
mechanism of transformation reaction in biological system and
also from the presense of the hydroxyl and N-pyridyl groups, which
may play an important role in the antibacterial activity [2,21–23].
BrpesesiH ligand was found to be the most potent antibacterial
agent, indicating that bromine atom played an important role in the
antibacterial activity [2]. All the three Co(II) complexes have
moderate activity (inhibitory zones >15 mm) against all four Gram-
positive bacteria, except [Co(NO2pesesi)]Cl that has strong activity
towards B. anthracis [24]. The activity of [Co(NO2pesesi)]Cl complex
may be explained on the basis of chelation theory; chelation
reduces the polarity of the metal atom mainly because of partial
Thermoanalytical (transition temperatures, enthalpy changes and decomposition
temperatures) results of free Schiff base ligands and related Co(II) complexes.
Transitiona
Tb,c (ꢁC)
D
H
b (J gꢀ1
)
Td (ꢁC)
d
Compound
BrpesesiH
OMepesesiH
NO2pesesiH
N2PhpesesiH
[Co(Brpesesi)]Cl
[Co(OMepesesi)]Cl
[Co(NO2pesesi)]Cl
[Co(N2phpesesi)]Cl
68.2
54.7
96.3
140.8
243.4 (dec.)
196.5 (mp)
255.4 (dec.)
170.4 (mp)
ꢀ97.67
ꢀ84.34
ꢀ128.30
ꢀ69.38
186.38
ꢀ61.88
192.70
ꢀ68.46
270
279
238
253
243
218
255
234
Cr. to I. (105)
a
Cr: crystal, I: isotropic liquid.
b
c
Data obtained from first DSC cycle.
dec.: decomposed, mp: melting point.
d
Data obtained from TGA; 10 ꢁC minꢀ1 under N2 gas.
represented by exothermic processes. The TGA data indicate that the
ligands BrpesesiH, OMepesesiH, NO2pesesiH and N2PhpesesiH start
decomposition at 270, 279, 238 and 253 ꢁC, respectively. Among free
Schiff base ligands, OMepesesiH has the greatest stability. DSC data
of the cobalt(II) complexes show that the [Co(NO2pesesi)]Cl complex
has one solid–solid transition at 105 ꢁC and before melting, is being
decomposed. [Co(OMepesesi)]Cl and [Co(N2phpesesi)]Cl are melted
first at 196.5 ꢁC and 170.4 ꢁC, respectively, then during a exothermic
process they are being decomposed. [Co(Brpesesi)]Cl is being
decomposed at 243 ꢁC. The TGA data indicate that the cobalt
complexes: [Co(Brpesesi)]Cl, [Co(OMepesesi)]Cl, [Co(NO2pesesi)]Cl
and [Co(N2phpesesi)]Cl start decomposition at 243, 218, 255 and
234 ꢁC, respectively. There is no mass loss up to 200 ꢁC, indicating
that either water or solvent molecules are absent in these complexes
[20]. Among cobalt complexes, [Co(NO2pesesi)]Cl has higher thermal
stabilityand the thermal stability orderof cobalt complexes is not the
same, with the order resulted for free ligands. Final decomposition
product was cobalt chloride as confirmed by qualitative analysis. The
typical thermograms for N2PhpesesiH and related cobalt complex
are presented in Figs. 3 and 4.
sharing of its positive charge with the donor groups and possible
p
electron delocalization within the whole chelation. Also, chelation
increases the lipophilic nature of the central atom which subse-
quently favors its permeation through the lipid layer of the cell
membrane [1,25]. The collected results in Table 3, indicated that the
all three complexes are weakly active against two Gram-negative
bacteria (inhibitory zones < 15 mm), except [Co(Brpesesi)]Cl
complex that shows moderate activity towards K. pneumoniae [24].
The antibacterial activity values for the complexes are lower than
those found for the free Schiff base ligands, except for [CoN-
O2pesesi)]Cl complex that shows strong activity against B. anthracis
with respect to free NO2pesesiH Schiff base ligand. It appears that
the coordination of cobalt ion to tetradentate Schiff base ligands
diminishes the antibacterial activities of the corresponding Schiff
bases. The quantitative assays gave MIC values in the range 3.125–
100 mg mlꢀ1 (Table 4), that confirmed the above obtained results.
Antibacterial activities (zone of growth inhibition and minimal
inhibitory concentrations) of three Schiff base ligands, their related
cobalt complexes and gentamicine (as a standard compound) are
shown in Tables 3 and 4. The organisms used in the present
investigation included S. pyogenes (RITCC 1940), S. agalactiae
Fig. 3. DSC (above) and TGA (below) curves of N2PhpesesiH Schiff base ligand.

L.A. Saghatforoush et al. / European Journal of Medicinal Chemistry 44 (2009) 4490–4495
4493
Fig. 4. DSC (above) and TGA (below) curves of [Co(N2Phpesesi)]Cl complex.
Table 3
Quantitative antimicrobial assay results (zone of growth inhibition) of the free Schiff base ligands and related cobalt complexes.
Microorganism
Standard
Growth inhibitory zone [mm]
Main compounds
Gentamicine
BrpesesiH
NO2pesesiH
OMepesesiH
[Co(Brpesesi)]Cl
[Co(NO2pesesi)]Cl
[Co(OMepesesi)]Cl
Stereptococcus pyogenes (þ)
Stereptococcus agalactiae (þ)
Staphylococcus aureus (þ)
Bacillus anthracis (þ)
20
–
20
32
20
16
40
50
40
50
30
20
40
30
20
20
20
20
40
20
10
20
20
10
20
25
30
30
15
5
20
20
20
50
10
5
15
15
15
25
10
10
Klebsiella pneumonia (ꢀ)
Pseudomonas aeruginosa (ꢀ)
Table 4
Quantitative antimicrobial assay results (minimal inhibitory concentrations) of the free Schiff base ligands and related cobalt complexes.
Microorganism
Minimum inhibitory concentration(mg/ml)
Main compounds
BrpesesiH
NO2pesesiH
OMepesesiH
[Co(Brpesesi)]Cl
[Co(NO2pesesi)]Cl
[Co(OMepesesi)]Cl
Stereptococcus pyogenes (þ)
Stereptococcus agalactiae (þ)
Staphylococcus aureus (þ)
Bacillus anthracis (þ)
6.25
3.125
6.25
3.125
12.5
25
6.25
12.5
25
25
25
6.25
25
50
25
25
25
25
25
25
3.125
50
100
37.5
37.5
37.5
18.75
50
18.75
12.5
12.5
37.5
100
Klebsiella pneumonia (ꢀ)
Pseudomonas aeruginosa (ꢀ)
25
50
50
4. Conclusion
which has moderate activity against K. pneumoniae. Generally, the
antibacterial activities of free Schiff base ligands are more than
cobalt(II) complexes. The BrpesesiH exhibits most activity against
tested bacteria compared with standard antibiotic.
Cobalt(II) complexes of the tetradentate Schiff base ligands
(XpesesiH) have been synthesized and characterized by various
physicochemical studies. Conductivity measurements show that all
complexes have electrolytic nature (1:1 type) and contain one Cl
anion out of the coordination sphere. The proposed structures of
the complexes are shown in Fig. 1. The antibacterial activity results
evidently show that the cobalt(II) complexes, except [Co(N-
O2pesesi)]Cl which has strong activity against B. anthracis, have
moderate activity against Gram-positive bacteria. They have weak
activity against Gram-negative bacteria, except [Co(Brpesesi)]Cl
5. Experimental
5.1. Material
All reagents were used as supplied by Merck and Fluka without
further purification. Solvents used for reactions were purified and
dried by conventional method [26]. 5-Phenylazo-salicylaldehyde,

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L.A. Saghatforoush et al. / European Journal of Medicinal Chemistry 44 (2009) 4490–4495
1-(2-pyridyl)-3-thia-5-amino pentane (pyta) were synthesized
according to the known procedures [27,28]. 2-Vinylpyridine was
distilled in vacuum before using.
5.3.2. (4-Methoxy-2-{[2-(2-pyridine-2-yl-ethylsulfanyl)ethylimino]
methyl}phenol (2), (OMe)pesesiH
Yield 75%, Anal. Calcd for C17H20N2O2S: C 64.50, H 6.37, N 8.85.
Found: C 64.00, H 6.30, and N 8.70. 1H NMR (400 MHz CDCl3)
d 12.75
(br s, 1H, OH), 8.29 (s, 1H, iminic), [8.52 (d, 1H), 7.58 (t, 1H), 7.11–7.20
(m, 4H), 6.76(d,1H)(total 7HArH)], 3.77–2.83(m, t, CH3and4 ꢃ CH2).
5.2. Physical measurements
13C NMR (400 MHz CDCl3)
d 31.90, 33.09, 38.44, 55.93, 59.33, 114.95,
117.23, 118.30, 119.38, 121.54, 123.27, 136.48, 149.29, 152.00, 155.21,
159.77,165.55 (17 C). FTIR (KBr)
Mp 55 ꢁC. Orange microcrystal.
The elemental analyses for the compounds were carried out
using Elementar CHN Analyzer Vario El III. Melting points were
determined using an electrothermal apparatus and were uncor-
rected. The 1H and 13C NMR spectra were recorded on a Bruker
spectrospin Avance 400 MHz in CDCl3 and chemical shifts were
indicated in ppm relative to tetramethylsilane. The electronic
spectra in 200–900 nm range were obtained in acetonitrile on
a Perkin–Elmer lambda 25 spectrophotometer. Infrared (FTIR)
spectra were recorded using KBr discs on a Shimadzu FTIR model
Prestige21 spectrometer. The conductivity measurements were
carried out in acetonitrile in room temperature using a Jenway 4510
conductometer instrument. The DSC thermograms of the
compounds were obtained on a Mettler-Toledo DSC 822e module,
which was calibrated with indium metal (T ¼ 156.6 ꢂ 0.3,
n .
3447, 3053, 2850–2937,1641 cmꢀ1
5.3.3. (4-Bromo-2-{[2-(2-pyridine-2-yl-ethylsulfanyl)ethylimino]
methyl}phenol (3), (Br)pesesiH
Yield 83%, Anal. Calcd for C16H17BrN2OS: C 52.50, H 4.70, N 7.60.
Found: C 52.60, H 4.69, and N 7.66. 1H NMR (400 MHz CDCl3)
d
13.20
(br s, 1H, OH), 8.55 (d, 1H), 8.26 (s, 1H, iminic), 7.67 (t, 1H), 7.39–7.21
(m, 4H), 6.85 (d, 1H) (total 7H ArH), 3.80–2.86 (t, 8H, 4 ꢃ CH2), 13
C
NMR (400 MHz CDCl3)
d 31.82, 32.94, 38.36, 58.93, 109.95, 119.02,
119.96, 121.56, 123.25, 133.46,134.92, 136.45, 149.32, 159.66, 160.16,
164.61 (16 C). FTIR (KBr) n .
3447, 3015–3050, 2850–2930, 1634 cmꢀ1
Mp 69 ꢁC. Yellow microcrystal.
D
H ¼ 28.45 ꢂ 0.61 J gꢀ1). Samples of 2–5.8 mg in solid form were
5.3.4. (4-Phenylazo-2-{[2-(2-pyridine-2-yl-ethylsulfanyl)
ethylimino]methyl}phenol (4), (N2ph)pesesiH
placed in aluminium pans (40 ml) with a pierced lid, and heated or
cooled at a scan rate of 10 ꢁC minꢀ1 under nitrogen flow. TGA were
carried out on a Mettler-Toledo TGA 851e at a heating rate of
10 ꢁC minꢀ1 under a nitrogen atmosphere. Cyclic voltammograms
(CVs) were obtained using an Autolab modular electrochemical
system (Eco chimie, Ulterecht, The Netherlands) equipped with
a PGSTAT 20 module and driven by GPES (Eco chimie) in conjunc-
tion with a three-electrode system and a personal computer for
data storage and processing. An Ag/AgCl (saturated KCl)/3 M KCl
reference electrode, a Pt wire (counter electrode) and a glassy
carbon working electrode, (Metrohm 0.0314 cm2) were employed
for the electrochemical studies. Voltammetric measurements were
performed at room temperature in acteonitrile solution with 0.1 M
tetrabutylammonium perchlorate as the supporting electrolyte.
Yield 65%, Anal. Calcd for C22H22N4OS: C 67.70, H 5.67, N 14.35.
Found: C 67.35, H 5.85, N 14.50. 1H NMR (400 MHz CDCl3)
d
13.80
(br s, 1H, OH), 8.39 (s, 1H, iminic), [8.54 (d, 1H), 7.98 (d, 1H), 7.86–
7.89 (m, 3H), 7.61(t, 1H), 7.41–7.51 (m, 3H), 7.13–7.18 (m, 2H), 7.05
(d, 1H) (total 12H ArH)], 3.80–2.85 (t, 8H, 4 ꢃ CH2). 13C NMR
(400 MHz CDCl3) d 31.83, 32.94, 38.24, 58.38, 118.05, 118.27, 121.71,
122.53,122.53,123.45,126.96,127.50,129.09,129.09,130.45,136.77,
145.02, 149.12, 152.56, 159.54, 164.94, 165.67 (22 C). FTIR (KBr)
n
3400, 3069, 2850–2930, 1641 cmꢀ1. Mp 141 ꢁC. Red brown crystal.
5.4. Synthesis of cobalt complexes
All mononuclear type complexes were prepared from chloride
salt of cobalt(II) using 1:1:1 mol ratio of the Pyta, required salicy-
laldehyde and metal salt in ethanol [17] (Fig. 1).
5.3. Synthesis of ligands
General procedure. A solution of 1 mmol of Pyta in 5 ml absolute
ethanol was added to solution of 1 mmol of the required salicy-
laldehyde in 5 ml absolute ethanol and the mixture was refluxed for
40 min and then 1 ml of methanolic NaOH was added and refluxed
and stirring was continued for a further 5 min. Then 1 mmol of
CoCl2$6H2O in 5 ml absolute ethanol was added to the ligand
solution with stirring and the reaction mixture was stirred under
reflux for 60 min. The resultant colored solution was left at room
temperature. The product was removed by filtration, washed with
cooled absolute ethanol and recrystallized from methanol or
acetonitrile and dried in vacuo.
All unsymmetrical tetradentate Schiff base ligands were
prepared in a similar manner [17]. A solution of 1 mmol of Pyta in
5 ml absolute ethanol was added to a solution of 1 mmol of
required salicylaldehyde in 5 ml absolute ethanol to give clear
yellow or light orange solutions which were gently refluxed for
about 1 h. Evaporation of the solution in vacuum gave viscous
liquids. The ligands, (4-X-2-{[2-(2-pyridine-2-yl-ethylsulfanyl)
ethylimino]methyl}phenol which [X ¼ methoxy, nitro, bromo,
phenylazo] will be abbreviated as (OMe)pesesiH, (NO2)pesesiH,
(Br)pesesiH, (N2Ph)pesesiH, respectively, were obtained as micro-
crystals. The microcrystals were filtered off, washed with 5 ml
cooled absolute ethanol and then recrystallized from ethanol–
chloroform (2:1, v/v).
5.4.1. (4-Nitro-2-{[2-(2-pyridine-2-yl-ethylsulfanyl)ethylimino]
methyl}phenolato cobalt(II) chloride (5)
Yield 58%, Anal. Calcd for C16H16ClCoN3O3S: C 45.23, H 3.79, N
5.3.1. (4-Nitro-2-{[2-(2-pyridine-2-yl-ethylsulfanyl)ethylimino]
methyl}phenol (1), (NO2)pesesiH
9.89. Found: C 45.05, H 3.8, and N 9.80. FTIR (KBr)
1616, 1541, 1325 cmꢀ1. UV (CH3CN) lmax (nm) (log
675 (180), 620 (180), 510 (386). Mp 255 ꢁC dec. Mol. conductivity
142 S. Brown crystal.
n
3020–3100, 2920,
3
l molꢀ1 cmꢀ1
)
Yield 78%, Anal. Calcd for C16H17N3O3S: C 57.99, H 5.17, N 12.67.
Found: C 57.70, H 5.20, and N 12.50.1H NMR (400 MHz CDCl3)
d
14.55
m
(br s,1H, OH), 8.35 (s,1H, iminic), [8.55 (d,1H), 8.16-8.22 (m, 2H), 7.65
(t, 1H), 7.19 (m, 2H), 6.96 (d, 1H) (total 7H ArH)], 3.84–2.88 (t, 8H,
d 31.70, 32.72, 38.21, 57.04,
116.65, 119.02, 121.69, 123.35, 128.21, 128.41,136.62, 138.72, 149.25,
5.4.2. (4-Methoxy-2-{[2-(2-pyridine-2-yl-ethylsulfanyl)ethylimino]
methyl}phenolato cobalt(II) chloride (6)
4 ꢃ CH2). 13C NMR (400 MHz CDCl3)
Yield 62%, Anal. Calcd for C17H19ClCoN2O2S: C 49.82, H 4.67, N
159.48, 164.98, 169.22 (16 C). FTIR (KBr)
n
3447, 3053, 2922–2940,
6.83. Found: C 50.15, H 4.62, and N 6.85. FTIR (KBr)
n 3050, 2820–
1655,1325–1557 cmꢀ1. Mp 96 ꢁC. Orange microcrystal.
2980, 1629 cmꢀ1. UV (CH3CN) lmax (nm) (log l molꢀ1 cmꢀ1) 665
3

L.A. Saghatforoush et al. / European Journal of Medicinal Chemistry 44 (2009) 4490–4495
4495
(174), 590 (165), 507 (435). Mp 196 ꢁC. Mol. conductivity 144
Green-brown crystal.
mS.
Acknowledgement
We are grateful to Payame Noor University and Islamic
Azad University Research Council for financial support of this
work.
5.4.3. (4-Bromo-2-{[2-(2-pyridine-2-yl-ethylsulfanyl)
ethylimino]methyl}phenolato cobalt(II) chloride (7)
Yield 60%, Anal. Calcd for C16H16BrClCoN2OS: C 41.9, H 3.51, N 6.1.
Found: C 41.48, H 3.46, and N 5.88. FTIR (KBr)
n
3020–3070, 2850–
2937, 1626 cmꢀ1. UV (CH3CN) lmax (nm) (log
3
l molꢀ1 cmꢀ1) 670
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(230), 590 (202), 508 (357). Mp 243 ꢁC dec. Mol. conductivity
148 mS. Dark brown crystal.
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