Design, spectral characterization, thermal, DFT studies and anticancer cell line activities of Co(II), Ni(II) and Cu(II) complexes of Schiff bases derived from 4-amino-5-(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol

Article abstract of DOI:10.1016/j.saa.2015.03.034

A series of two biologically active Schiff base ligands L¹, L² have been synthesized in equimolar reaction of 4-amino-5-(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol with thiophene-2-carbaldehyde and furan-2-carbaldehyde. The synthesized Schiff bases were used for complexation with different metal ions like Co(II), Ni(II) and Cu(II) by using a molar ratio of ligand: metal as 1:1 and 2:1. The characterization of Schiff bases and metal complexes was done by ¹H NMR, UV-Vis, TGA, IR, mass spectrometry and molar conductivity studies. The in DFT studies the geometries of Schiff bases and metal complexes were fully optimized with respect to the energy using the 6-31+g(d,p) basis set. On the basis of the spectral studies an octahedral geometry has been assigned for Co(II), Ni(II) and Cu(II) complexes. The effect of these complexes on proliferation of human breast cancer cell line (MCF-7) and human hepatocellular liver carcinoma cell line (Hep-G2) were studied and compared with those of free ligand. The anticancer cell line results reveal that all metal complexes show moderate to significant % cytotoxicity on cell line HepG2 and MCF-7.

Full text of DOI:10.1016/j.saa.2015.03.034

Accepted Manuscript
Design, spectral characterization, thermal, DFT studies and anticancer cell line
activities of Co(II), Ni(II) and Cu(II) complexes of Schiff bases derived from 4-
amino-5-(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol
Prateek Tyagi, Sulekh Chandra, B.S. Saraswat, Deepak Yadav
PII:
S1386-1425(15)00330-3
http://dx.doi.org/10.1016/j.saa.2015.03.034
SAA 13448
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
To appear in:
Received Date:
Revised Date:
Accepted Date:
18 November 2014
24 February 2015
1 March 2015
Please cite this article as: P. Tyagi, S. Chandra, B.S. Saraswat, D. Yadav, Design, spectral characterization, thermal,
DFT studies and anticancer cell line activities of Co(II), Ni(II) and Cu(II) complexes of Schiff bases derived from
4-amino-5-(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol, Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.03.034
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Design, spectral characterization, thermal, DFT studies and anticancer cell line
activities of Co(II), Ni(II) and Cu(II) complexes of Schiff bases derived from 4-amino-5-
(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol
Prateek Tyagia,b, Sulekh Chandraa,*, B S Saraswatb , Deepak Yadavc
a Department of Chemistry, Zakir Husain Delhi College, University of Delhi, JLN-Marg, New
Delhi 110002, India
b
Department of Chemistry, School of Sciences, IGNOU, Maidan Garhi, New Delhi 110068,
India
c Faculty of Medicine, Jamia Hamdard, New Delhi 110062, India
*Corresponding author
Tel.: +91-11-22911267; Fax: +91-11-23215906
Email: schandra_00@yahoo.com
Abstract
A series of two biologically active Schiff base ligands L1, L2 have been synthesized in
equimolar reaction of 4-amino-5-(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol with thiophene-2-
carbaldehyde and furan-2-carbaldehyde. The synthesized Schiff bases were used for
complexation with different metal ions like Co(II), Ni(II) and Cu(II) by using a molar ratio of
ligand : metal as 1:1 and 2:1. The characterization of Schiff bases and metal complexes was
done by 1H NMR, UV–Vis, TGA, IR, Mass spectrometry and molar conductivity studies. The
In DFT studies the geometries of Schiff bases and metal complexes were fully optimized with
respect to the energy using the 6-31+g(d,p) basis set. On the basis of the spectral studies an
octahedral geometry has been assigned for Co(II), Ni(II) and Cu(II) complexes. The effect of
these complexes on proliferation of human breast cancer cell line (MCF-7) and human
hepatocellular liver carcinoma cell line (Hep-G2) were studied and compared with those of
free ligand. The anticancer cell line results reveal that all metal complexes show moderate to
significant % cytotoxicity on cell line HepG2 and MCF-7.
Key Words: Schiff Base, Co(II), Ni(II) and Cu(II) complexes, Spectroscopic Studies, DFT,
Anticancer cell line activity.
1

1. Introduction
Cancer, a diverse group of diseases characterized by the proliferation and spread of abnormal
cells, is a major worldwide problem [1–2]. Therefore, the search and development of new
potent anticancer drugs is highly desirable today in cancer research. The biological
significance of 1,2,4-triazole derivatives is very well known because of their diverse
pharmacological properties [3–8]. A wide variety of therapeutically interesting molecule that
after inclusion of 1,2,4-triazole moiety, transforms into better drugs has also been reported in
literature. Fluconazole, a triazole derived compound is broad spectrum antifungal agent [9].
Similarly, trazodone is a very well known antidepressant [10]. 1,2,4-triazole ring substituted
chemotherapeutics, such as Vorozole, Letrozole and Anastrozole (Fig. 1), are currently being
used for the treatment of breast cancer [11]. The chemistry of 1,2,4-triazole and its fused
heterocyclic derivatives has received considerable attention owing to their synthetic and
effective biological importance. Schiff base of 1,2,4-triazole derivatives have also been found
to possess extensive biological activity.
The role of N and S atoms in the coordination of metals at the active sites of numerous
metallo-biomolecules is very well known. It has been reported in literature that binding of
drug to a metallo element enhances its activity and in some cases the complex possesses even
more healing properties than the parent drug [12]. Metal elements such has cobalt, nickel and
copper have small size, higher nuclear charge and thus have a great affinity for coordination.
A detail survey of the literature revealed that no work has been carried out on the synthesis of
metal complexes derived from 4-amino-5-(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol. The
synthesized Schiff bases have coordination sites with SNOS sequence and varied
coordination abilities. In view of the significant structural and biological applications of
triazole compounds, it is worthwhile to report the synthesis of cobalt(II), nickel(II) and
copper(II) complexes (1–12) of triazole Schiff base derivatives L1, L2, derived from the
condensation reaction of 4-amino-5-(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol with thiophene-
2-carbaldehyde and furan-2-carbaldehyde, respectively (Scheme 1). These compounds have
2

been investigated for their in vitro anticancer cell line activity against human breast cancer
cell line (MCF-7) and human hepatocellular liver carcinoma cell line (HepG2).
Insert Fig. 1.
2. Experimental
2.1 Materials and Methods
All the chemicals were used of Anala R grade and received from Sigma-Aldrich and Fluka.
Metal salts were purchased from E. Merck and used as received. MTT (3-(4,5-
dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide) and 0.25% trypsin and 0.02%
EDTA mixture was purchased from Himedia (India). Fetal bovine serum (FBS) was
purchased from Biowest (USA).
2.2 General procedure for the synthesis of Ligands L1 – L2
Intermediate triazoles 3a was synthesized from corresponding acid hydrazide (1a) through
multi-step reactions (Scheme 1) as per the reported literature [13–14]. The hydrazide was
converted to potassium salt (2a) by reacting with carbon disulphide and potassium hydroxide
in absolute ethanol. On reacting with hydrazine hydrate, the salt undergoes ring closure to
yield the triazole, 3a. The desired Schiff base L1 was obtained in good yield by refluxing
equimolar amount of 4-amino-5-(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol (3a) with thiophene-
2-carbaldehyde using acetic acid as a solvent. The mixture was stirred at room temperature
for 10 h (Scheme 1). The reaction mixture was kept overnight, pale yellow product was
precipitated out. It was filtered, washed with ice cold water, methanol and recrystallized with
a mixture of DMF & methanol. The same procedure was used for the synthesis of ligand L2.
(E)-5-(pyridin-4-yl)-4-((thiophen-2-ylmethylene)amino)-4H-1,2,4-triazole-3-thiol L1
o
Yield: 74(%). Color (pale-yellow). M.p. 254–256 C. IR (KBr, cm-1): 1618 (HC=N), , 2710
(SH), 1103 (C=S). 1H NMR (DMSO-d6, δ, ppm) 7.29–7.31 (m, 1H, Ar–H), 7.80–7.87 (m,
3H, Ar –H), 8.0 (d, 1H, J = 7.2 Hz, Ar–H), 8.75–8.81 (m, 2H, Ar –H), 9.92 (s, 1H, N=CH),
14.45 (s, 1H, triazole –SH). Anal. Calcd. for C12H9N5S2 (287.36): C: 50.16; H: 3.16; N:
24.37; Found: C: 50.19; H: 3.17; N: 24.39%. Mass spectrum (ESI) [M]+ = 287.97
3

(E)-4-((furan-2-ylmethylene)amino)-5-(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol L2
Yield: 76(%). Color (pale-yellow). M.p. >280 oC. IR (KBr, cm-1): 1616 (HC=N), 2714 (SH),
1
1107 (C=S). H NMR (DMSO-d6, δ, ppm) 6.81–6.83 (m, 1H, Ar–H), 7.42–7.43 (m, 1H, Ar –
H), 7.81–7.87 (m, 2H, Ar –H), 8.11–8.12 (m, 1H, Ar –H), 8.75–8.81 (m, 2H, Ar –H), 9.61 (s,
1H, N=CH), 14.45 (s, 1H, triazole –SH). Anal. Calcd. for C12H9N5OS (271.30): C: 53.13; H:
3.34; N: 25.81; Found: C: 53.17; H: 3.35; N: 25.83%. Mass spectrum (ESI) [M]+ = 271.88
2.3 General procedure for the synthesis of metal complexes 1-12
Preparation
of
Co(II)
complexes
with
(E)-5-(pyridin-4-yl)-4-((thiophen-2-
ylmethylene)amino)-4H-1,2,4-triazole-3-thiol L1 (1)
Hot methanolic solution (15 mL) of CoCl2.6H2O (2 mmol) was added drop wise to a
magnetically stirred solution of (E)-5-(pyridin-4-yl)-4-((thiophen-2-ylmethylene)amino)-4H-
1,2,4-triazole-3-thiol L1 (2 mmol) in methanol (20 mL) (scheme 1). The resultant mixture
was refluxed for 4 h and the clear solution was allowed
to cool at room temperature. The
solid product precipitated out which was filtered, washed with methanol, diethyl ether and
dried under vacuum over P4O10. The same method was used for the preparation of metal
complexes 2–5 in metal : ligand as 1:1. The metal complexes 6–12 was synthesized by using
the above mentioned same procedure by taking metal chloride : ligand in a 1:2 molar ratio.
Physical, analytical and spectral data of ligands and metal complexes are given in Table 1.
2.4 Analysis
The carbon and hydrogen were analyzed on Carlo-Erba 1106 elemental analyzer. The
nitrogen content of the complexes was determined using Kjeldahl’s method. Molar
conductance was measured on the ELICO (CM82T) conductivity bridge. ESI-MS spectra
were obtained using a VG Biotech Quattrro mass spectrometer equipped with an elctrospray
ionisation source in the mass range of m/z 100 to m/z 1000. IR spectra (CsBr) were recorded
on FTIR BX-II spectrophotometer. NMR spectra were recorded with a model Bruker
Advance DPX-300 spectrometer operating at 400 MHz using DMSO-d6 as a solvent and
TMS as internal standard. The electronic spectra were recorded in DMSO on Shimadzu UV
mini-1240 spectrophotometer. Thermogravimetric analysis (TGA) was carried out in
o
dynamic nitrogen atmosphere (30 ml/min) with a heating rate of 10 C/min using a
Schimadzu TGA-50H thermal analyzer. EPR spectra of the Cu(II) complexes were recorded
4

as polycrystalline sample at room temperature on E4-EPR spectrometer using the DPPH as
the g-marker.
2.5 DFT Calculations
The DFT calculations were performed using the B3LYP three parameter density functional,
which includes Becke’s gradient exchange correction [15], the Lee, Yang, Parr correlation
functional [16] and the Vosko, Wilk, Nusair correlation functional [17]. The gas phase
geometries of Ligand L1, and metal complexes (1–3) were fully optimized with respect to the
energy using the 6-31+g(d,p) basis set using the Gaussian 09W suite [18].
2.6 In vitro studies (Cell culturing)
The cell lines HepG2 (liver hepatocellular carcinoma) and MCF-7 (human breast adeno
carcinoma) were cultured as monolayers and maintained in Dulbecco’s modified Eagle
medium (DMEM) supplemented with 10% fetal bovine serum (FBS), 2 mM L-glutamine,
100 U/ml penicillin and 100 mg/ml streptomycin in a humidified atmosphere with 5% CO2 at
o
37 C in T-75 flasks and were sub cultured twice a week. For the assays, cells (2 x 103
cells/well in 200 µl of complete DMEM) were placed in each well of a 96 well flat bottom
plate. Cells were allowed to adhere for overnight, and then treated with two concentrations (1
and 10 µM) samples of each L1, L2 and metal complexes (1 – 12) for 48 h. The cell
proliferation of the control (untreated cells) was fixed to 100%. After completion of
incubation period, 20 µl MTT (5mg/ml) was added to each well for 2 h. Following which
media was removed and 100 µl of DMSO was added to each well in order to solubilize the
formazan. The plate was read using the ELISA reader at a wavelength of 540 nm.
3. Results and discussion
The Schiff base L1 (scheme 1) was prepared by refluxing in acetic acid an equimolar amount
of 4-amino-5-(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol and thiophene-2-carboxaldehyde. The
same method was used for the preparation of the ligand L2. The structure of Schiff bases thus
formed was established by IR, 1H NMR, Mass spectrometry and CHN analysis.
Insert Scheme 1
5

The synthesized Schiff bases were soluble in DMF, DMSO and methanol on heating only.
The composition of the ligands were consistent with their NMR, IR, mass spectral and CHN
data. The synthesized Schiff bases were further used for the complexation with Co(II), Ni(II)
and Cu(II) metal ions, using the following metal salt: CoCl2.6H2O for complexes 1,4, 7 and
9, NiCl2.6H2O for complexes 2, 5, 8 and 11, CuCl2for complexes 3, 6, 9 and 12. The
obtained complexes are microcrystalline solids which are stable in air and decompose above
o
280 C (Table 1). They are insoluble in common organic solvents such as acetone &
chloroform, sparingly soluble in ethanol, methanol and completely soluble in DMF and
DMSO. The molar conductance of the soluble complexes in DMF showed values indicating
that complexes 1–12 (11–17) ohm-1 cm2 mol-1) are non-electrolytes [19]. Physical
measurements and analytical data of the complexes 1–12 are given in Table 1.
Insert Table 1
3.1 Mass Spectra
The ESI mass spectrum of ligand showed a molecular ion peak at m/z = 287.97 amu
corresponding to [M]+, which confirms the proposed formula [C12H9N5S2].+ and its base peak
was observed at m/z 178.95 (Fig. 2). Similarly the molecular ion peak of ligand L2 shows a
molecular ion peak at 271.88 and its base peak was observed at m/z 178.88. The mass
spectrum of L1 shows a series of peaks at 180.81, 179.68, 177.95, 101.98, and 73.99
corresponding to various fragments. The intensities of these peaks give the idea of the
stability of the fragments. The m/z peak values of the ligand L1, L2 and the metal complexes
1–12 are given in Table 1.
Insert Fig. 2
1
3.2 H NMR Spectra
The 1H NMR spectra have been recorded for ligand L1 and L2. The spectra of ligand L1 (Fig.
3) displayed azomethine (–HC=N) proton as a singlet at 9.92 ppm. The aromatic protons
appeared as a set of doublet and multiplet in the region 8.81–7.29 ppm. The triazole –SH
proton appear as a weak singlet at 14.45 ppm for the ligand L1. Similarly, in the spectra of
the ligand L2 the azomethine (–HC=N) proton appeared as a singlet at 9.61 ppm. The signals
of all the protons of the ligand L1, L2 were found as to be in their expected region.
6

Insert Fig. 3
3.3 IR Spectra
The characteristic bands of IR spectra of ligands L1 , L2 and their metal(II) complexes (1–12)
are reported in order to confirm the binding mode of the Schiff base ligands to the
corresponding metal ion. Both ligands possessed potential donor sites like azomethine
linkage (–C=N), triazole (–SH) and S/O of thiophene/furan, which have tendency to
coordinate with metal ions (Table 2). Peak corresponding to ν(C=O) stretching vibrations
was absent in IR spectra of L1 and, instead, a new band assigned to azomethine ν(HC=N)
linkage appeared at 1618 cm-1 confirming the formation of Schiff base. Similarly, the peak at
1616 cm-1 in L2 corresponds to ν(HC=N) linkage [20]. The IR spectra of the ligands L1, L2
show characteristic bands due to ν(SH) at 2710 and 2714 cm-1, respectively [21].
The comparison of the IR spectra of Schiff base ligands with corresponding metal complexes
gave clue of binding modes of the Schiff base ligand to the corresponding metal ion. The IR
band due to azomethine C=N group shifts to lower frequency (12–18 cm-1) 1598–1606 cm-1,
representing the coordination of azomethine N in complex formation [22]. This is also
confirmed by the appearance of new band in spectra of metal complexes in the range of 462–
498 cm-1, which has been assigned to the ν(M–N) bond. The deprotonation of the thiol group
is indicated by the absence of a band in the metal complexes in range 2710–2714 cm-1,
which is due to ν(S–H) of Schiff bases, indicating that the metal is coordinated through thiol
sulphur [22]. This is supported by the lower frequency shift which appears around 680–670
cm-1 in the metal complexes due to ν(C–S). The specific band of ν(C–S–C) stretching
vibration of thiophene ring at 834 cm-1 in free ligand L1 shifts to (849–864 cm-1) in
complexes 1–3 and 7–9. This is also supported by the appearance of new band in range of
338–356 cm-1 of far IR spectra, which has been assigned to ν(M–S) bond. Similarly, the band
at 1018 cm-1 in ligand L2 corresponding to ν(C–O–C) stretching vibration of the furan ring
shifts to a lower value of 998–1004 cm-1 in metal complexes 4–6 and 10–12 [23]. The band in
complexes 4–6 and 10–12 in the region 510–534 cm-1 is due to metal–oxygen bond formation
[24].
7

Insert Table 2
The presence of coordinated water molecules in the complexes 1–6 is indicated by a broad
band in the region 3220–3412 cm-1 [21] and two weaker bands in the region 755–795 and
702–718 cm-1 due to ν(–OH ) rocking and wagging mode of vibrations [25], respectively.
Thus the IR spectral data results provide strong evidences for the complexation of the
potentially tridentate Schiff bases and also suggests that the metal(II) coordinated through
azomethine nitrogen, thiol sulphur and through sulphur/oxygen of the thiophene/furan ring.
Based on these observations it may be appreciated that the ligands L1, L2 coordinate
uninegative tridentately around the Co(II), Ni(II) and Cu(II) ion.
3.4 Conductance and magnetic susceptibility measurements
The molar conductance values of metal complexes 1–12 were obtained in DMF as a solvent
at room temperature and their results in (Ω-1cm2mol-1) are recorded as in Table 3. Generally,
higher molar conductance values are indicative of the electrolytic nature of the metal
complexes and lower values show their non-electrolytic nature. The molar conductance of the
metal complexes in DMF showed values indicating that complexes 1–12 (11–17 ohm-1 cm2
mol-1) are non-electrolytes. The magnetic moment (B.M.) values of all the metal complexes,
1–12 at room temperature were recorded in Table 3. The magnetic moment values of Co(II)
complexes were found in the range of 4.81–4.97 B.M. suggesting the Co(II) complexes as
high-spin with three unpaired electrons in an octahedral environment. The Ni(II) complexes
exhibited magnetic moment values in the range of 2.92–2.99 B.M. representative of two
unpaired electrons per Ni(II) ion suggesting these complexes to have octahedral geometry
[26]. The experimental magnetic moment values of 1.93–1.96 B.M. for Cu(II) complexes are
indicative of one unpaired electron per Cu(II) ion for d9 system suggesting spin-free distorted
octahedral geometry.
Insert Table 3
3.5 Electronic spectra
The electronic absorption spectra of the Co(II), Ni(II) and Cu(II) complexes in DMSO were
recorded at room temperature and the band positions of the absorption maxima, band
assignments and the proposed geometry are listed in Table 3. The electronic spectra of Co(II)
8

complexes generally showed three absorption bands in the region at 9,778–9,874, 17,330–
4
17,774 and 29,718–30,256 cm-1 assigned to transitions 4T1g→4T2g(F), T1g→4A2g(F) and
4T1g→4Tg(P), showing an octahedral geometry around the Co(II) ion [20]. The electronic
spectral data of Ni(II) complexes showed d-d bands in the region 10,815–11,643, 15,383–
-1
16,476 and 23,165–25,715 cm , respectively, assigned to the transitions A2g(F)
3
3
→
T2g(F),
3
3A2g(F) →3T1g(F) and A2g(F) →3T2g(F), which are characteristic of Ni(II) in octahedral
geometry [22]. Electronic spectra of Cu(II) complexes show the d–d transition bands in the
range 12,195–15,524, 18,598–19,112 and 24,435–27,465 cm-1.These bands correspond to
2
2
2B1g→2A1g (dx2–y2→dz2), B1g→2B2g (dx2–y2→dxy) and B1g→2Eg (dx2–y2→dxz, dyz) transitions,
respectively. On the basis of electronic transitions, a distorted octahedral geometry is
suggested for Cu(II) complexes.
3.6 Thermal Analysis
Thermal behaviour of the metal complexes has been studied using thermogravimetric
o
analysis from ambient temperature to 1000 C in nitrogen atmosphere. Based on the
thermograms; decomposition stages, temperature ranges, decomposition product as well as
weight loss percentages of the complexes were calculated. The TG curves were redrawn as %
mass loss vs. temperature (TG) curves. The thermal behaviour of complexes 4–6 is almost
same. Typical TGA/DTG curve for Co(II) (4) is presented in Fig. 4. The temperature ranges
and percentage mass losses of the decomposition reactions are given in Table 4 together with
evolved moiety and the theoretical percentage mass losses. The TGA curves of the complexes
4–6 undergo decomposition in two to three stages. In the first stage, a peak corresponding to
the loss of coordinated water molecule and chloride, followed with subsequent removal of the
five membered heterocyclic ring in the second stage. In the third stage, there was a loss in
mass corresponding to the decomposition of primary 1,2,4-triazole moiety and as a final
stage, it left air stable metal oxide as a residue. The three step decomposition of complexes 4–
6 as indicated by DTG peaks around 130–190, 310–385 and 570–680 oC corresponding to the
mass loss of coordinated water molecule and chloride, furan moiety and 1,2,4-triazole
moiety, respectively.
Insert fig. 4
Insert Table 4
3.7 EPR spectra
9

EPR spectra of Cu(II) complexes were recorded at room temperature as polycrystalline
sample, on X band at frequency of 9.1 GHz under the magnetic-field strength of 3000G. The
analysis of Cu complex (3) gives g∥ = 2.191, g⊥ = 2.056 and G = 3.41 (Table 3). The
observed g∥ values for the complex are less than 2.3 in agreement with the covalent character
of the metal ligand bond. The trend g∥ > g⊥ > 2.0023 observed for the complex indicates that
unpaired electron is localized in dx2-y2 orbital of the Cu(II) ion and the spectral features are a
characteristic of axial symmetry. Thus, a tetragonal geometry is confirmed for the aforesaid
complex [27]. G = (g∥ – 2)/(g⊥ – 2), which measures the exchange interaction between the
metal centers in a polycrystalline solid, has been calculated. According to Hathaway, if G >
4, the exchange interaction is negligible, but G < 4 indicates considerable exchange
interaction in the solid complexes [28]. The ‘‘G’’ value for Cu complexes reported in this
paper, is <4 indicating the exchange interaction in solid complexes. The g∥, g⊥ and G values
for complexes 3, 6, 9 and 12 are given in Table 3.
3.8 Geometry optimization
Geometry Optimization was done using B3LYP functional with 6-31+g(d,p) basis sets as
incorporated in the Gaussian 09W programme in gas phase. The fully optimized geometries
of the ligand L1 and complexes 1–3 are shown in Fig. 5. The numbering scheme for ligand
L1, and complexes 1–3 are given in Scheme 2. The molecular structure of Complex 1 shows
octahedral geometry around the Co(II) centre as revealed from the calculated bond lengths
and bond angles (Table 5). The C1–S1 , C4–S1, C5–N1, N1–N2 and C6–S2 bond lengths become
slightly longer in complexes as ligand L1 coordinates via azomethine nitrogen, deprotonated
sulphur of triazole moiety and through sulphur of thiophene. The thiophene moiety is bent
out of the coordination plane and move far from Co(II) ion, which results in the slight
elongation of Co–S bond length. Similarly, the bond length between Co and sulphur of
triazole elongates to 2.228 Ao. The Co–S1, Co–N1, Co–O1, Co–O2 and Co–Cl bond lengths
are found to be 2.224, 2.102, 2.014, 2.017 and 2.313 Ao, respectively. This elongation in Co–
S and Co–N bond lengths caused a slight distortion from the regular octahedral geometries.
The bond angles in the coordination sphere of Co(II) complexes are found approximately
near to the perpendicular value.
Insert Fig. 5
Insert Scheme 2
10

Insert Table 5
Similar bonding behaviour is observed in case of complex 2 having Ni(II) as metal centre. All
the bond lengths and bond angles have very close values as compared to complex 1.
However, complex 3 having Cu(II) metal centre shows a large degree of distortion from the
regular octahedral geometry. It is because of this distortion that the axial Cu–S1 and Cu–S1'
elongates to 2.556 and 2.634 Ao, respectively. This elongation in bond lengths causes a
change in the bond angle values of coordination sphere. The bond angles N1–Cu–N2 and N1'–
Cu–N2' reduces 69.23o and 72.12o, respectively. The bond angle N1–Cu–Cl is found to be
161.42o. The bond lengths and the bond angles within the thiophene moiety and 1,2,4-triazole
moiety do not change significantly on coordination with metal ion. On the basis of the above
discussion following (Fig. 6) structures can be proposed for the synthesized complexes.
Insert Fig. 6
3.8 Cell viability determination
The in vitro cytotoxicity of the ligand L and metal complexes (1–12) on human cell lines
HepG2 and MCF-7 was determined by a MTT based assay. The results are expressed as the
percentage of cell toxicity with respect to the control and are represented in Table 6. The in
vitro screening revealed that ligand L1, L2 and metal complexes 1–12 have very less effect on
% inhibition on cell proliferation on cell lines HepG2 and MCF-7 at concentration of 1 µM.
But at concentration of 10 µM complexes 6, 9, 11 and 12 show a significant increase in %
inhibition on cell proliferation on cell line HepG2 (Fig. 7). Similarly, the complexes 6, 10 and
11 shows a significant increase in % inhibition on cell proliferation on cell line MCF-7.
Insert Table 6
Insert Fig. 7
Conclusion
The newly synthesized Schiff base ligands L1, L2 act as tridentate ligands, and all these are
coordinated through the azomethine-N, thiol sulphur and through sulphur of
thiophene/oxygen of furan to the metal ion. All the synthesized metal(II) complexes
possessed an octahedral geometry except the Cu(II) complexes which showed a distorted
octahedral geometry. The reasonable agreement between the theoretical and experimental
11

data reflects to the great extent the suitability of the applied basis set, 6-31+g(d,p) for this
type of work and confirms the suggested structure. The findings of anticancer cell line
activity reveal that all metal complexes show moderate to significant % inhibition on the cell
proliferation on cell line HepG2 and MCF-7. Interestingly, the complexes 6 and 9 shows 38
and 49 % inhibition on cell proliferation against cell line HepG2, whereas complexes 9, 10
and 11 greatly reduce the malignant MCF-7 cell growth by 34, 38 & 33%, respectively. This
inhibition on cell proliferation might be due to azomethine (-HC=N-) linkage and/or hetero
atoms present in these compounds. Further structural optimization studies might thus
represent a rationale for further investigation.
5. Acknowledgements
We thank the Principal, Zakir Husain Delhi College for providing lab facilities, Jamia
Hamdard, New Delhi for Anticancer cell line activities. Authors are thankful to DRDO, for
financial assistance.
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13

Fig. 1. Some triazole based market available drugs
14

Scheme 1. Preparation of the ligands L1, L2 and their metal complexes 1–12
15

Fig. 2. Mass Spectrum of ligand L1
16

Fig. 3. NMR spectra of ligand L1
17

Fig. 4. Thermogravimetric (TGA/DTG) curves of Co(II) complex (4)
18

Fig. 5. Geometry Optimized structures of (a) Ligand L1, (b) Complex 1, (c) Complex 2, (d)
Complex 3 (Colour Code: H=White, C=Grey, N= Blue, O=red, Co= Grey, Ni= Silver Grey,
Cu=Pink)
19

N5
C11
C12
N5
C11
C12
C10
C9
C10
C9
C8
C7
C8
C7
N4
N3
N4
N3
C3
C5
C3
C5
N2
N2
C4
S1
C2
C4
S1
N1
C2
N1
C6
C6
C1
C1
S2
M
S2
H
H
H
O1
O2
Cl
H
H
(a)
(b)
Scheme 2. : Numbering Scheme of the optimized structures (a) Ligand L1, (b) Complexes
1–3
Fig. 6. Proposed Structure of the newly obtained metal complexes
20

Fig. 7. Ligand L1, L2 and metal complexes (1–12) inhibited the cell viability of HepG2 &
MCF-7 cells (Data were assayed by ANOVA and Student’s t-test. Differences between
means were considered significant when yielding a P < 0.05. Results are presented as means
S.D.)
21

Table 1
Physical measurements and analytical data of the ligand (L1, L2) and metal complexes(1-12).
Elemental Analysis (%) found
No
.
M. P Yield
(oC) (%)
(calc.)
Molecular mass/ molecular formula m/z
C
H
N
Ma
50.19
3.15 24.40
L1
L2
1
C12H9N5S2 [287.36]
C12H9N5OS [271.30]
287.48 254 74
271.31 >280 76
417.08 >280 64
416.67 >280 68
422.32 >280 58
400.81 >280 66
400.40 >280 56
-
(50.16) (3.16) (24.37)
53.15 3.33 25.82
(53.13) (3.34) (25.81)
34.53 2.92 16.78 14.12
(34.58) (2.90) (16.80) (14.14)
34.72 2.93 16.78 14.04
(34.60) (2.90) (16.81) (14.09)
34.14 3.93 16.55 15.02
(34.20) (2.87) (16.62) (15.08)
35.98 3.02 17.51 14.69
(35.97) (3.02) (17.48) (14.71)
35.98 3.02 17.44 14.67
(35.99) (3.02) (17.49) (14.66)
35.58 2.99 17.27 15.68
(35.56) (2.98) (17.28) (15.68)
-
[Co(L1–H )Cl(H2O)2] [416.76]
C12H12ClCoN5O2S2
[Ni(L1–H )Cl(H2O)2] [416.52]
C12H12ClN5NiO2S2
2
[Cu(L1–H )Cl(H2O)2] [421.38]
C12H12ClCuN5O2S2
3
[Co(L2–H )Cl(H2O)2] [400.70]
C12H12ClCoN5O3S
4
[Ni(L2–H )Cl(H2O)2] [400.46]
C12H12ClN5NiO3S
5
[Cu(L2–H )Cl(H2O)2] 405.32]
C12H12ClCuN5O3S
405.29 >280 60
6
22

[Co(L1–H)2] [631.64]
C24H16CoN10S4
45.67
(45.64) (2.55) (22.18) (9.33)
45.65 2.58 22.22 9.33
(45.66) (2.55) (22.18) (9.30)
45.33 2.53 22.05 10.01
(45.31) (2.53) (22.02) (9.99)
48.10 2.70 23.35 9.84
(48.08) (2.69) (23.36) (9.83)
48.09 2.71 23.35 9.80
(48.10) (2.69) (23.37) (9.79)
47.74 2.67 23.22 10.51
(47.72) (2.67) (23.19) (10.52)
2.54 22.20
9.35
631.78 >280 54
631.31 >280 56
636.42 >280 62
599.87 >280 52
598.89 >280 66
604.12 >280 65
7
8
[Ni(L1–H)2] [631.40]
C24H16N10NiO2S2
[Cu(L1–H)2] [636.25]
C24H16CuN10O2S2
[Co(L2–H)2] [599.51]
C24H16CoN10O2S2
[Ni(L2–H)2] [599.27]
C24H16N10NiO2S2
9
10
11
12
[Cu(L2–H)2] [604.13]
C24H16CuN10O2S2
a M = Co(II), Ni(II), Cu(II)
23

Table 2
Important infrared spectral bands (cm-1) and their assignments
Compound
ν(ΗC=N) ν(C-S-C) ν(C-O- ν(M-O) ν(M-N) ν(M-N)
C)
1618
1616
1599
1601
1598
1606
1599
1604
1604
1602
1598
1599
1600
1605
834
-
-
1018
-
-
-
-
L1
L2
1
854
852
849
-
-
468
476
462
480
473
470
470
465
475
462
478
465
483
498
478
498
491
492
487
485
495
484
495
488
-
-
2
-
-
3
999
1002
1004
-
522
516
510
-
4
-
5
-
6
851
864
856
-
7
-
-
8
-
-
9
998
1001
1004
528
534
524
10
11
12
-
-
24

Table 3
Conductivity, magnetic, electronic spectra and EPR spectra of metal complexes 1–12
ΩM
B.M
No.
λ
max (cm-1)
g∥
g⊥
G
(µeff)
(Ω-1cm2mol-1)
12.6
4.87
2.93
1.95
4.89
2.98
1.93
4.81
2.92
1.96
4.97
2.99
1.95
9778, 17665, 29974
10855, 15383, 25165
13468, 18598, 25378
9812, 17774, 30256
11643, 16476, 23165
15524, 19112, 27465
9874, 17330, 29718
10815, 15922, 25715
12195, 18712, 24435
9860, 17568, 30140
11434, 15960, 24546
14265, 19004, 26810
-
-
-
1
2
14.2
-
-
-
11.0
2.191
2.056
3.41
3
13.4
-
-
-
4
12.8
-
-
-
5
16.8
2.241
2.074
3.25
6
15.2
-
-
-
7
16.1
-
-
-
3.05
-
8
17.2
2.290
2.095
9
15.6
-
-
-
-
10
11
12
12.9
-
13.7
2.154
2.045
3.42
25

Table 4
Thermal Analysis data the ligand (L1) and metal complexes (4–6).
Mass Loss (%)
Found Calc.
Temp
Residual
Species
Comp. No
Molecular Formula
Stages
Possible Evolved Species
(oC)
1st 155-265
2nd 265-480
1st 130–190
2nd 310–385
3rd 570–680
1st 140-220
2nd 220-360
3rd 450-715
1st 160-465
2nd 465-675
C4H4N
C8H7N2O
H4O2Cl
L1
C12H9N5S2
-
100 100
[Co(L2–H )Cl(H2O)2]
C12H12ClCoN5O3S
C5H4N
CoO 18.81 18.69
4
C7H4N4S
H4O2Cl
[Ni(L2–H )Cl(H2O)2]
C12H12ClN5NiO3S
C5H4
NiO
18.98 18.65
5
6
C7H4N5S
C5H8O2NCl
C7H4N4S
[Cu(L2–H )Cl(H2O)2]
C12H12ClCuN5O3S
CuO 19.75 19.62
26

Table 5
Optimized geometry of the ligand L1 and metal complexes 1–3 (bond lengths in Angstroms;
bond angles in degrees).
Parametersa
C1 – S1
C4 – S1
C4 – C5
C5 – N1
N1 – N2
N2 – C6
C6 – S2
C6 – N3
M – S1
Ligand L1
Complex 1b
1.806
1.831
1.454
1.309
1.342
1.498
1.922
1.502
2.224
2.102
2.228
2.014
2.017
2.313
81.49
87.54
88.12
Complex 2c
1.805
1.833
1.456
1.311
1.345
1.497
1.927
1.506
2.237
2.117
2.231
2.234
2.232
2.324
83.71
81.24
86.43
Complex 3d
1.812
1.828
1.452
1.313
1.355
1.496
1.925
1.498
2.556
2.124
2.634
2.384
1.989
2.397
87.45
69.23
84.32
1.799
1.816
1.427
1.300
1.337
1.485
1.906
1.463
-
-
-
-
-
-
-
-
-
M – N1
M – S2
M – O1
M – O2
M – Cl
∠S1MΝ1
∠N1MS2
∠S2MO2
27

∠S1MO1
∠Ο1MCl
∠Ο2MCl
∠Ν1MCl
-
-
-
-
85.32
88.39
85.11
172.16
81.19
87.24
83.27
174.22
72.12
78.74
81.34
161.42
a Scheme 1 for numbering
b M=Co, c M=Ni, d M=Cu
28

Table 6
Effect of a ligand L1, L2 and series of metal complexes (1–12) at two concentrations of 1 and 10
µΜ οn the HepG2 and MCF-7 cell proliferation.a
Survival cell
Cell growth
Survival cell
Cell growth
Compound
fraction (%) at 1 µM inhibition (%) at 1 µΜ fraction (%) at 10 µΜ inhibition (%) at 10 µΜ
MCF-7
HepG2
MCF-7 HepG2
MCF-7
-
HepG2
MCF-7
HepG2
-
Control
100
96
97
93
95
92
94
92
91
94
90
88
92
89
87
2
100
97
98
95
96
95
96
93
90
97
96
93
94
92
91
1
100
94
96
82
78
76
83
72
1
100
95
97
89
83
2
-
-
L1
L2
1
3
3
4
1
2
3
2
6
5
2
4
3
5
3
3
5
3
2
4
5
4
3
2
4
3
3
3
4
1
2
3
2
5
3
3
3
2
3
5
3
4
2
1
4
3
4
3
7
5
18
22
24
17
28
38b
29
31b
49b
35b
24
32b
11
5
4
17
2
8
5
78 5
81
22 b
3
6
4
2
19
4
8
7
77 3
73 2
23b
27b
20
5
9
10b
62 1
6
6
3
71
69
51
2
1
3
80
73 1
66
2
7
10
12b
8
4
27
8
7
2
34b
38b
33b
24b
9
6
65 5
76 3
68 2
62 4
67 2
76 1
10
11
12
11b
13b
8
9
a
The results are expressed as the percentage of viable cells with respect to the control and are
presented as mean SD.
b Significantly different from the control
29