Syntheses, spectroscopic characterization, thermal study, molecular modeling, and biological evaluation of novel Schiff's base benzil bis(5-amino-1,3,4-thiadiazole-2-thiol) with Ni(II), and Cu(II) metal complexes

Article abstract of DOI:10.1016/j.saa.2014.08.046

Novel Schiff's base ligand, benzil bis(5-amino-1,3,4-thiadiazole-2-thiol) was synthesized by the condensation of benzil and 5-amino-1,3,4-thiadiazole-2-thiol in 1:2 ratio. The structure of ligand was determined on the basis of elemental analyses, IR,

Full text of DOI:10.1016/j.saa.2014.08.046

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 749–760
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Syntheses, spectroscopic characterization, thermal study, molecular
modeling, and biological evaluation of novel Schiff’s base benzil bis(5-
amino-1,3,4-thiadiazole-2-thiol) with Ni(II), and Cu(II) metal complexes
Sulekh Chandra a, , Seema Gautam , Hament Kumar Rajor , Rohit Bhatia
⇑
a
b
c
a
Department of Chemistry, Zakir Husain Delhi College, University of Delhi, JLN Marg, New Delhi 110002, India
Department of Chemistry, Ramjas College, University of Delhi, New Delhi 110007, India
b
c
University of Delhi, New Delhi 110007, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Synthesized ligand behaves as tetradentate and coordinates to metal ion through sulfur atoms of thiol
ring and nitrogen atoms of imine group. Ni(II), and Cu(II) complexes were synthesized with this nitro-
gen–sulfur donor (N S ) ligand. Geometry optimized structure of [Cu(L)Cl ] complex.
2 2 2
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Synthesis, characterization and
Molecular modeling of novel Schiff’s
base ligand and complexes.
Complexes possessed octahedral,
tetragonal, square pyramidal, and
tetrahedral geometry.
Thermal data suggested that metal
complexes were more stable than free
ligand.
In vitro antimicrobial activity of
ligand and its complexes were
screened.
Complexes were found more
biologically sensitive than ligand.
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel Schiff’s base ligand, benzil bis(5-amino-1,3,4-thiadiazole-2-thiol) was synthesized by the
condensation of benzil and 5-amino-1,3,4-thiadiazole-2-thiol in 1:2 ratio. The structure of ligand was
determined on the basis of elemental analyses, IR, 1H NMR, mass, and molecular modeling studies. Syn-
thesized ligand behaved as tetradentate and coordinated to metal ion through sulfur atoms of thiol ring
and nitrogen atoms of imine group. Ni(II), and Cu(II) complexes were synthesized with this nitrogen–
Received 24 February 2014
Received in revised form 1 July 2014
Accepted 24 August 2014
Available online 3 September 2014
2 2
sulfur donor (N S ) ligand. Metal complexes were characterized by elemental analyses, molar
conductance, magnetic susceptibility measurements, IR, electronic spectra, EPR, thermal, and molecular
modeling studies. All the complexes showed molar conductance corresponding to non-electrolytic
Keywords:
Schiff’s bases
Metal complexes
Molecular modeling
Spectral studies
Biological evaluation
nature, expect [Ni(L)](NO
)
3 2
complex, which was 1:2 electrolyte in nature. [Cu(L)(SO
4
)] complex may
possessed square pyramidal geometry, [Ni(L)](NO )
3 2
complex tetrahedral and rest of the complexes six
coordinated octahedral/tetragonal geometry. Newly synthesized ligand and its metal complexes were
examined against the opportunistic pathogens. Results suggested that metal complexes were more
biological sensitive than free ligand.
Ó 2014 Elsevier B.V. All rights reserved.
⇑
Corresponding author. Tel.: +91 9811226273.
E-mail address: schandra_00@yahoo.com (S. Chandra).
http://dx.doi.org/10.1016/j.saa.2014.08.046
386-1425/Ó 2014 Elsevier B.V. All rights reserved.
1

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S. Chandra et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 749–760
Introduction
calibrant. IR spectra were recorded on FT-IR spectrum BX-II spec-
trophotometer in CsI pellet. The electronic spectra were recorded
in DMSO on Shimadzu UV–visible mini-1240 spectrophotometer.
Electronic impact mass spectrum was recorded on JEOL, JMS-DX-
Schiff’s bases and their transition metal complexes were playing
an important role in the development of coordination chemistry
1
[
1,2]. Schiff’s base metal complexes were studied extensively
303 mass spectrometer. H NMR spectra was recorded on a Bruker
because of their attractive chemical and physical properties and
their wide range of applications in numerous scientific areas [3].
Schiff’s bases had a chelating structure and were in demand
because they were straight forward to prepare [4]. In Azomethine
derivatives, the C@N linkage was essential for biological activities
like antifungal [5], antibacterial [6], antitumour [7], antimalarial
Advanced DPX-300 spectrometer using DMSO-d
Delhi. EPR spectra of all complexes were recorded at room temper-
ature (RT) on E -EPR spectrometer using the DDPH as the g-marker
at SAIF, IIT Bombay. Thermo gravimetric analysis was carried out in
dynamic nitrogen atmosphere (30 mL/min) with a heating rate of
10 °C/min using a Shimadzu TGA-50H thermal analyzer. Molecular
modeling of ligand and its metal complexes was performed using
Hyperchem. 7.51 version.
6
as a solvent at IIT
4
[
8], antiviral [9,10], etc. The synthesis of Schiff’s base ligand incor-
porating 1,3,4-thiadiazole ring as amine was attracted widespread
attention due to their diverse pharmacological properties such as
antimicrobial, analgesic, and anti-hepatitis B viral activities [11].
Thiadiazole derived Schiff’s bases showed analgesic, and inflamma-
tory activities also [12]. In recent years, a number of research arti-
cles had been published on transition metal complexes derived
from 5-amino-1,3,4-thiadiazole-2-thiol and its derivatives which
contain aza, oxo-aza, and thio-aza donor atoms [13,14]. The pres-
ent report deals with synthesis, spectroscopic characterization,
thermal study, and biological evaluation of Ni(II), and Cu(II) com-
plexes with tetradentate ligand, which was derived from benzil
and 5-amino-1,3,4-thiadiazole-2-thiol.
Molecular modeling
3D molecular modeling of the proposed structure of ligand and
its metal complexes was performed using Hyperchem. 7.51 ver-
sion. This version was used to calculate energy and other parame-
ters like bond angles, bond lengths by Molecular Mechanics, MM
plus force field. Hydrogen atoms were omitted for the sake of clar-
ity. The correct stereochemistry was assured through the manipu-
lation and modification of the molecular coordinates to obtain
reasonable low energy molecular geometries. Several cycles of
energy minimization had to be carried for each molecule. Vibration
analysis was done to check the absence of imaginary frequencies.
Experimental details
Materials
Antibacterial screening
All chemicals used were commercial products and used as sup-
plied. 5-Amino-1,3,4-thiadiazole-2-thiol, and benzil were of AR
grade and procured from Alfa Aesar, Heysham, England and Sigma
Aldrich, Bangalore, India. Metal salts were purchased from E.
Merck, India and were used as received. All used solvents were
of spectroscopic grade.
The antibacterial screening of ligand and its metal complexes
was tested against some bacteria Escherichia coli, Staphylococcus
aureus, Pseudomonas aeruginosa, and Klebsiella pneumonia by using
paper disk diffusion method [15]. Base plates were prepared by
pouring 10 mL of autoclaved Muller Hinton agar into sterilized
Petri dishes (9 mm diameter) and allowing them to settle. Molten
autoclaved Muller Hinton that was kept at 38 °C was incubated
with a broth culture of used bacteria species. Prepared plates were
incubated for 24–30 h and the inhibition zones (mm) were mea-
sured around each disk carefully. As organism grows, it forms a
turbid layer, except in the region where the concentration of anti-
bacterial agent was above the minimum inhibitory concentration,
and a zone of inhibition was seen. The solutions of tested com-
pounds were prepared in DMSO.
Synthesis of Schiff’s base ligand
An ethanolic solution of 5-amino-1,3,4-thiadiazole-2-thiol
(
2 mol, 2.664 g) was heated for 15 min. and then added to hot eth-
anolic solution of benzil (1 mol, 2.102 g) with continuous stirring
and the reaction solution was refluxed for 5 h at 60 °C. It was
allowed to stay at room temperature and kept in refrigerator over-
night. On cooling, the yellow color solid product was precipitated
out. It was filtered off, washed several times with cold ethanol, dis-
Antifungal screening
4
tilled water and then dried in vacuum over P O10. Synthesis of
ligand is given in Scheme 1 (Supplementary Material).
The Poison food Technique was applied to examine fungicidal
investigations of synthesized ligand and its metal complexes
against some fungi Rhizoctonia solani, Sclerotium rolfsii, Macropho-
mina phaseolina, Fusarium oxysporum, and Aspergillus niger. DMSO
and Fluconazole were employed as a control and standard fungi-
cide, respectively. The inhibition of the mycelial growth of fungi
was expressed in percentage and determined from the growth in
the test plate relative to the respective control plate as given
below:
Synthesis of metal complexes
A hot ethanolic solution of the corresponding metal salt, (except
sulfate which was taken in aqueous medium) (0.001 mol) was
mixed with hot ethanolic solution of Schiff’s base ligand
(
0.001 mol) and content refluxed for 10–12 h at temp. 85–90 °C.
pH (5–7) was adjusted by adding of 2–3 drops of aqueous ammo-
nia. The corresponding colored complexes were separated out by
filtration, washed thoroughly with ethanol, distilled water and
Ið%Þ ¼ ðCTÞ=C ꢂ 100;
where I = % Inhibition, C = Radial diameters of the colony in control,
T = Radial diameter of the colony in test compound.
4 10
dried under vacuum over P O .
Analytical and physical measurements
Results and discussion
Elemental study (CHN) was analyzed on Carlo-Erba 1106 ele-
mental analyzer. Molar conductance was measured on the ELICO
Metal complexes were synthesized by mixing the hot ethanolic
solution of ligand with ethanolic solution of the corresponding
metal salt in 1:1 ratio. The Schiff’s base ligand behaved as a
(
CM82T) conductivity bridge. Magnetic susceptibilities were mea-
sured at room temperature on a Gouy balance using CuSO O as
4
ꢁ5H
2

S. Chandra et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 749–760
751
Table 1
Molar conductance and elemental analyses of the ligand and its metal complexes.
ꢃ1
cm2 molꢃ1
Compound
Mol. Wt. pH Molar conductance (
X
)
Color
Yield (%) Melting point (°C) Elemental analyses (%) found (calculated)
M
–
C
H
N
Ligand(L)
440
6
5
7
6
6
5
–
Light
Yellow
Mehendi 60
68
80
49.09
(49.5)
37.91
(37.95)
34.35
(34.35)
37.59
(37.62)
34.09
(34.10)
31.05
2.72
(2.70)
2.10
(2.02)
1.90
(1.95)
2.08
(2.04)
1.89
(1.88)
1.72
19.09
(19.7)
14.74
(14.69)
17.81
(17.79)
14.62
(14.66)
17.67
(17.66)
12.07
C
18
H
12
N
6
S
4
4
[
Ni(L)Cl
2
]
569.7
628.7
574.5
633.5
599.5
20
173
18
21
15
>250
>250
>250
>250
>250
10.30
(10.38)
9.33
(9.30)
11.05
(11.09)
10.02
(10.00)
9.13
C
18
H
12
N
6
S
Cl
2
Ni
[
Ni(L)](NO
3
)
2
Parrot
Green
Mehendi 65
Green
62
C
18
H
12
N
8
S
4
O
6
Ni
[
Cu(L)Cl
2
]
C
18
H
12
N
6
S
4
Cl
2
Cu
Cu
Cu
[
Cu(L)](NO
3
)
2
Green
65
C
18
H
12
N
8
S
4
O
6
4
[
4
Cu(L)(SO )]
Green
62
C
18
H
12
N
6
S
5
O
(10.01)
(31.05)
(1.75)
(12.09)
Fig. 1. 1H NMR spectrum of Schiff’s base ligand.
tetradentate ligand and coordinated to metal ion through nitrogen
of imine and sulfur of thiazole ring. All complexes were soluble in
DMSO. The molar conductance value of nitrato complex of Ni(II),
various fragments. These peaks (407, 323, 220, 117, and 84)
appeared to loss of following species (AS), (AC S), (AC S),
(AC N), and (SH) respectively. The intensity of these peaks gave
an idea of the stabilities of fragments. The fragmentation path of
the ligand is given in Fig. 2 (Supplementary Material).
2
N
2
7 5
H
7 5
H
ꢃ1
2
ꢃ1
and for other complexes were 173, and 10–22
X
cm mol
respectively. These values were corresponded to electrolytic and
non-electrolytic nature of the complexes. Thus the complexes
may be formulated as [Ni(L)](NO
Cu(II), L = Schiff’s base ligand, and X = Cl , NO
3
)
2
and [M(L)X
2
] (where M = Ni(II),
ꢃ
ꢃ
2ꢃ
IR spectra
3
, ½ SO
4
). The ana-
lytical data of ligand and its metal complexes, together with their
physical properties is given in Table 1.
The important IR bands of ligand and metal complexes along
with their assignment are given in Table 2. The IR spectrum of free
ꢃ1
ꢃ1
ligand displayed bands in the region 3190–3010 cm , 1618 cm
,
1
H NMR spectrum of ligand
ꢃ1
ꢃ1
7
95 cm , and 3500–3350 cm corresponding to the presence of
the aromatic CAH stretching, azomethine group (C@N), stretching
vibration of C@S group, and SH stretching vibration Fig. 3(a). On
1H NMR spectrum of Schiff’s base ligand [benzil bis(5-amino-
1
,3,4-thiadiazole-2-thiol)] in DMSO-d
6
exhibited following signals:
ꢃ1
ꢃ1
complex formation, bands at 1618 cm , and 795 cm , shifted
downward, which suggested that coordination take place through
nitrogen atom of azomethine, and sulfur atom of thiazole ring [16].
This binding of the ligand to metal ion was also supported by the
d 7.78–7.93 ppm (8H, m, ArAH), d 3.34 ppm (1H, s, SH) Fig. 1. These
signals indicate that two different types of proton are present in
ligand.
ꢃ1
ꢃ1
appearance of new IR bands at 405–428 cm and 305–32 cm
due to (MAN) and (MAS) vibrations, respectively. This discus-
Mass spectrum
t
t
sion revealed that the Schiff’s base ligand coordinates to metal ions
as tetradentate chelate to form complexes. However, a strong
absorption band at about 3350–3500 cm remained as such in
IR spectra of metal complexes, indicated that SH do not coordinate
to metal ion.
The electronic impact mass spectrum of the Schiff’s base ligand
ꢃ1
confirmed the proposed formula by showing a molecular ion peak
+
at m/z = 439, corresponds to species [C18
H
11
N
6 4
S
] . It also showed a
series of peaks i.e. 407, 323, 220, 117, and 84 corresponding to

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S. Chandra et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 749–760
N
N
N
N
C H
N
N
S
SH
SH
6
5
C H
N
N
S
S
6
5
-S
-
H
C H
S
6
5
C H
S
SH
6
5
N
N
N
N
N
N
4
40
439
C H
N
N
S
S
C H
N
N
6
5
6
5
-
C N S
-C7H5N
2
2
C H
SH
C H
S
6
5
6
5
SH
N
N
N
N
3
S
23
4
07
C H
N
S
SH
SH
6
5
-
C H N
7 5
-SH
N
N
N
N
1
17
2
20
S
N
N
8
4
Fig. 2. Mass fragmentation of Schiff’s base ligand.
Table 2
Characteristic IR bands (cm ) of Schiff’s base and its metal complexes.
ꢃ1
Compound
Assignments
(C@S)
Bands due to anions
t
t
t
(CAH)Ar
t(SAH)
(C@N)
Ligand(L)
1594
1522
1522
1514
1490
795
770
770
787
778
3064
3179
3153
3162
3163
2500
2500
2500
2500
2500
ꢃ1
[
[
[
[
Ni(L)Cl
Ni(L)](NO
Cu(L)Cl
Cu(L)(NO
2
]
Band observed at 345–325 cm indicating the presence of MACl bond
ꢃ1
3
)
2
Band appeared at 1384 cm indicating uncoordinated nature of nitrate group [17]
ꢃ1
2
]
Band observed at 345–325 cm indicating the presence of MACl bond
ꢃ1
ꢃ1
ꢃ1
ꢃ1
3
)
2
]
t
5
= 1410 cm
,
t
1
= 1320 cm
,
t
2
= 1021 cm and
D
(
t
5
ꢃ
t
1
) = 104 cm indicating unidentate nature of
nitrate group
ꢃ1
ꢃ1
[
Cu(L)(SO
4
)]
1508
786
3163
2500
t
3
Splitted at 1121 cm and 1054 cm indicating the unidentate nature of sulfate group [18]

S. Chandra et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 749–760
753
2 4
Fig. 3. IR spectrum (a) Schiff’s base Ligand, (b) [Cu(L)Cl ] and (c) [Cu(L)(SO )].

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S. Chandra et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 749–760
3 2 4
Fig. 4. UV–visible spectra of (a) [Ni(L)](NO ) and (b) [Cu(L)(SO )].
2
electrons. The electronic spectra of the [Ni(L)Cl ] complex showed
Table 3
bands in the range 9661–10,834, 11,223–18,621, and 21,739–
EPR spectral data of the Cu(II) complexes.
ꢃ1
3
2g(F) ? 3T2g(F), 3
3
2,573 cm and may be assigned to the
A
A
2g
3
3
3
Complex
g
||
g
\
g
iso
g
1
g
2
g
3
R
G
(F) ? T1g(F) and
acteristic to an octahedral geometry [19]. The electronic spectra
A2g(F) ? T1g(P) transitions, respectively, char-
[Cu(L)Cl
[Cu(L)(NO
[Cu(L)(SO
2
]
2.34
2.58
–
2.09
2.05
–
2.09
2.1
2.16
–
–
2.09
–
–
2.13
–
–
2.27
–
–
0.28
3.7
3.1
–
3
)
)]
2
]
of the [Ni(L)](NO
3
)
2
complex showed three bands in range of
ꢃ1
4
9
000–10,000, 10,000–15,000, and 15,000–25,000 cm
these
transition correspond to tetrahedral geometry Fig. 4(a) [20].
Copper(II) complexes
The value of magnetic moment indicated the presence of one
unpaired electron (1.88–2.01 BM). In electronic spectrum of chloro,
and nitrato complexes of Cu(II), bands appeared in the range of
ꢃ1
ꢃ1
9
569–12,515 cm , and 18,245–20,450 cm may be assigned to
the transitions, 2B1g ? A1g
third band at 30,769–37,174 cm may be due to charge transfer.
Therefore, the complexes may be considered to possess a tetrago-
nal geometry [21,22]. The electronic spectrum of the sulfate com-
plex showed bands at 11,709 cm , 18,621 cm and third band at
6,101 cm . Third band was appeared due to charge transfer
2
(m
1
),
2
B
1g ? B2g
2
(m
2
) respectively. The
ꢃ1
ꢃ1
ꢃ1
ꢃ1
3
Fig. 4(b). Thus complex may possess either square-pyramidal or
trigonal bipyramidal geometry.
Fig. 5. EPR spectrum of [Cu(L)(SO
4
)].
Electronic paramagnetic resonance spectra
Bands due to anion
EPR spectra of Cu(II) complexes were recorded at room temper-
ature as polycrystalline sample, on X band at frequency of 9.1 GHz
under the magnetic-field strength of 3000G. The analysis of EPR
In IR spectra of chloride complexes, bands corresponding to
ꢃ1
(
MACl) were observed at 345–325 cm Fig. 3(b). The IR spectrum
spectrum of complexes gave the value of g|| (2.34–2.58) and g
1.70–2.09) Table 3. The trend g|| > g > 2.0023, was observed, indi-
\
of the nitrate complex of Ni(II) showed
a
strong band at
384 cm corresponds to uncoordinated behavior of nitrate ion.
Spectrum of sulfate complex of Cu(II) showed that band splitted
(
\
ꢃ1
1
2 2
cated that the unpaired electron was localized in the dXꢃY , orbital
of the Cu(II) ion. Thus tetragonal geometry was confirmed for the
aforesaid complexes. The geometric parameter G was evaluated by
t
3
ꢃ1
ꢃ1
at 1121 cm and 1054 cm , corresponded to unidentate behavior
of sulfate ion Fig. 3(c).
using the following relation G = (g|| ꢃ 2)/(g ꢃ 2), which measures
\
the exchange interaction between the metal centers. If G is greater
than 4, the exchange interaction was negligible or G is less than 4
indicate considerable exchange interaction in the solid complexes.
[23]. The G value was found less than 4; it suggested that there
was exchange interaction in solid complexes. The IR spectrum of
Electronic spectra and magnetic moments
Nickel(II) complexes
The magnetic moments of Ni(II) complexes lies in the range
2
.96–2.98 BM. These values indicated the presence of two unpaired
4
[Cu(L)(SO )] complex suggested five coordinated geometry. Two
Table 4
ꢃ1
Electronic spectral bands (cm ) and ligand field parameters of the complexes.
ꢃ1
ꢃ1
ꢃ1
ꢃ1
Complexes
kmax (cm
)
leff (BM)
Dq (cm
)
B (cm
)
b
t
2
/
t
1
LFSE (kJ mol )
[
[
[
[
[
Ni(L)Cl
Ni(L)](NO
Cu(L)Cl
Cu(L)(NO
Cu(L)(SO
2
]
10101, 15432, 29498
9050, 15000, 22500
9569, 18621, 35335
9680, 18621, 36900
11709, 18621, 36101
2.96
2.97
1.88
1.96
1.92
1010
905
–
–
–
975
690
–
–
–
0.93
0.66
–
–
–
1.52
1.65
–
–
–
144
152
–
–
–
3 2
)
2
]
3
)
2
]
4
)]

S. Chandra et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 749–760
755
2 2
Fig. 6. TGA spectra of (a) Schiff’s base ligand, (b) [Ni(L)Cl ] and (c) [Cu(L)Cl ].
Ligand field parameters
Table 5
Thermal data for the ligand and its complexes.
Various ligand field parameters i.e. Dq, B and b, for the com-
plexes were calculated [25]. The value of Dq, and B were calculated
by using first and third transitions. The calculated parameters were
given in Table 4. The nephelauxetic parameter b was obtained by
using the relation: b = B(complex)/B(free-ion), where B was the
Racah inter-electronic repulsion parameter, and the value of B (free
Compound
Temperature range
°C)
TG weight loss (%)
Assignments
(
Calc
%)
Found
(%)
(
[
[
[
[
[
Ni(L)Cl
2
]
25–230
12.46
31.24
45.98
12.45
31.20
45.99
ACl
AC14
2
2
4
30–495
95–780
H
10
4 2 6 4
C H N S
ꢃ1
ion) for Ni(II) is 1041 cm . The values of b are 0.93 and 0.66. These
values indicated the covalent character in metal ligand ‘r’ bond.
Ni
A(NO
AC14
AC
Ni(L)](NO
3
)
2
25–270
19.93
28.61
36.97
19.91
28.60
36.99
3 2
)
H
10
2
5
70–510
10–750
4
H
N
2 6
S
3
Thermal analysis
Cu(L)Cl
2
]
25–220
12.35
30.98
40.03
12.28
30.90
40.00
ACl
AC14
2
The thermal stability of the complexes with ligand was investi-
gated using thermogravimetric analyses (TGA). TGA was carried
out at heating rate of 10 °C/min in nitrogen atmosphere over a
temperature range of 25–800 °C. The thermogram of the com-
plexes of Cu(II) and Ni(II) did not show any peak below 150 °C
which indicated that there was no water molecule inside or out-
side the coordination sphere. On heating, Cu(II), and Ni(II) metal
complexes decomposed in three steps. First step was due to
decomposition of coordinated anion at temperature 220 °C. Second
and third step indicated decomposition of organic moieties i.e.
2
4
20–480
80–755
H
10
4 2 6 3
C H N S
CuS
A(NO
AC14
Cu(L)(NO
3
)
2
]
25–280
19.8
19.8
3 2
)
H
10
2
5
80–508
08–750
28.38
41.78
28.39
41.76
AC
4
H
N S
2 6 4
Cu
Cu(L)(SO
4
)]
25–240
13.34
29.69
43.70
13.33
29.65
43.71
ASO
4
2
5
40–510
10–780
AC14H
10
AC
4
H
N S
2 6 4
CuO
4 2 6 4
(AC12H10) and (AC H N S ) Fig. 6(a)–(c) Table 5.
Molecular modeling
basic structures were possible for five coordinated geometry i.e. tri-
gonal bipyramidal or square pyramidal, which were characterized by
the ground states dXꢃY or d , respectively. EPR spectrum of this
Z
complex provided an excellent basis for distinguishing between
these two ground states. For this system, parameter R is calculated
Because the single crystals could not be obtained for ligand and
its metal complexes, it was thought worthwhile to obtain struc-
tural information. Geometry optimization was done by using
2
2
2
Hyperchem. 7.51 version for ligand(L), [Cu(L)Cl
Ni(L)](NO complexes Fig. 7 (Supplementary Material). In case
of ligand it was noticed that the bond length for C@N is
.3493 Å, CAS is 1.8151 Å and bond angle for C@N is 118.23°,
CAS is 91.83°. [Cu(L)Cl ] metal complex had tetragonal geometry,
while [Ni(L)Cl ] and [Ni(L)](NO complexes possessed octahedral,
2 2
], [Ni(L)Cl ], and
[
R = (g
state is predominantly to d
less than one, the ground state is predominantly to dXꢃY . EPR spec-
trum of the [Cu(L)(SO )] complex shows three g values. The values of
, g , g , and R were 2.09, 2.13, 2.27, and 0.28 respectively. As the
value of ‘R’ was less than one, ground state was predominantly dXꢃY
which was consistent with a square pyramidal geometry Fig. 5 [24].
2
ꢃ g
1
)/(g
3
ꢃ g
2
)]. If the value of ‘R’ is greater than one, ground
[
3 2
)
2
Z
. On the other hand, the value of ‘R’ is
2
2
1
4
2
g
1
2
3
2
3 2
)
2
2
and tetrahedral geometry, respectively. In case of chloride com-
plexes two axial positions were occupied by chloride ions, while

7
56
S. Chandra et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 749–760
20
1
4
15
1
1
9
21
5
7
1
6
8
4
22
1
17
23
28
27
2
3
6
26
1
1
24
8
1
25
1
2
9
0
13
(a)
1
8
21
20
8
19
17
42
2
2
2
15
16
6
43
5
1
2
3
3
24
7
29
1
1
0
1
4
14
9
28
12
13
25
2
7
26
(b)
C
C
C
S
C
Cl
C
N
C
N
C
S
N
C
C
Ni
Cl
C
C
N
C
C
C
S
C
C
C
N
N
S
C
(
c)
15
18
21
20
16
14
22
7
19
17
23
4
5
1
29
2
6
3
28
27
24
8
9
26
25
11
10
12
13
(d)
Fig. 7. Geometry optimized structure of (a) Schiff’s base Ligand, (b) [Cu(L)Cl
2 2 3 2
], (c) [Ni(L)Cl ] and (d) [Ni(L)](NO ) , [color code: C-sky blue, N-blue, S-yellow, Cu-green, Ni-pink,
Cl-white]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

S. Chandra et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 749–760
757
Fig. 8. Graph showing antipathogenic behavior of compounds against R. solani, S. rolfsii, M. phaseolina, F. oxysporum, and A. niger at concentration 200 ppm.
C H
C H
6 5
6
5
C H
C H
6 5
6
5
C H
C H
6 5
6
5
X
N
N
N
N
N
N
M
Cu
Ni
(NO )
3 2
N
N
N
N
N
N
N
N
N
N
N
N
S
X
S
S
OSO3S
S
S
SH
HS
SH
HS
SH
HS
-
-
M = Ni(II), Cu(II) X = Cl , NO
3
Fig. 9. Proposed structure of metal complexes.
C H
C H
6 5
N
N
equatorial positions by nitrogen (C@N) and sulfur (thiol ring)
atoms of the ligand. In [Cu(L)Cl ] two equatorial CuAN distances
were 1.874 Å, 1.9011 Å and CuAS distances were 2.2441 Å,
6
5
2
H N
SH
2
O
O
S
2
1
.2414 Å. In [Ni(L)Cl
.884 and NiAS distances are 1.355 Å, 2.231 Å, while in case of
two equatorial NiAN distances were 1.784, 1.788
2
] two equatorial NiAN distances were 1.856,
[
Ni(L)](NO
)
3 2
Ethanol
10hrs., pH 4
Reflexed
and NiAS distances were 2.144 Å, 2.160 Å. The important bond
angles and bond distances are summarized in Tables 6 and 7.
Attempts to optimize the sulfate complexes of Cu(II) was done
but attempts were found unsuccessful.
C H
C H
6 5
6
5
Antimicrobial activity
N
N
The antimicrobial activity of ligand and its metal complexes
[
2 4 2
Cu(L)Cl ], [Cu(L)(SO )], and [Ni(L)Cl ] were examined. A compara-
tive study of the growth inhibition zone values of ligand and its
metal complexes indicated that metal complexes exhibited higher
activity than the free ligand and the same was indicated from the
results, given in Tables 8 and 9. Higher activity of metal complex
was probably due greater lipophilic nature of the complex. It
increased activity of the metal complex, and can be explained on
the basis of Overtone’s concept and Tweedy’s chelation theory
[26,27]. According to Overtone’s concept of cell permeability, the
N
N
N
S
S
N
SH
HS
Scheme 1. Syntheses of Schiff’s base ligand benzil bis(5-amino-1,3,4-thiadiazole-2-
thiol).

7
58
S. Chandra et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 749–760
Table 6
Table 7
Optimized geometry of the Schiff’s base ligand and metal complexes (bond angles in
degrees).
Optimized geometry of the Schiff’s base ligand and metal complexes (bond lengths in
Angstroms).
Atoms
Bond angle
Atoms
Bond length
Schiff’s base ligand(L)
Schiff’s base ligand(L)
C
C
C
C
1
7
2
8
AN
AS17AC16
AN AC
AS AC10
5
AC
7
118.23
91.83
115.83
91.64
C
N
1
AN
AC
AS17
5
7
1.3493
1.3447
1.3223
1.8151
1.3497
1.3434
1.3197
1.8161
5
6
8
C
7
9
S17AC16
C
2
AN
AC
AS
AC10
6
[
S
Cu(L)Cl
18ACu
2
]
N
6
8
1
ACl43
89.049
84.142
86.188
85.532
71.339
68.636
85.461
116.2
145.795
126.135
108.721
89.306
85.736
C
8
9
Cl43ACu
Cl42ACu
Cl42ACu
N
N
Cl42ACu ACl43
1
N
N
C
C
C
C
1
1
1
AS10
AN
AN
S
9
6
7
2
[Cu(L)Cl ]
7
ACu
ACu
1
AS10
AS10
S18ACu
1
2.2441
2.2043
2.2414
2.2038
1.874
1.9011
1.745
1.7519
1.761
6
1
Cu
Cu
Cl42ACu
1
Cu
Cu
1
ACl43
AS10
1
6
ACu
ACu
1
AS10
AS18
7
1
1
AN
AN
6
2
AN
AN
AS18AC17
AS10AC11
6
AC
AC
8
1
7
3
8
9
7
9
C
S
9
AS10
10AC11
AS18
C
8
[
Ni(L)Cl
2
]
[Ni(L)Cl
Cl43ANi
Cl42ANi
2
]
Cl43ANi
S
S
1
ACl42
85.45
147.03
114.89
86.27
71.95
89.61
89.23
85.61
108.21
126.74
1
2.188
2.188
2.231
1.884
1.856
1.355
1.761
1.740
1.745
1.751
1.346
1.363
1.340
1.34
18ANi
10ANi
1
1
AN
AN
7
1
6
S10ANi
1
Cl42ANi
10ANi
Cl43ANi
1
AN
AN
AS18
AS18AC17
11AS10AC
6
Ni
1
Ni
1
Ni
1
AN
AN
AS18
7
S
1
7
6
1
C
C
C
C
8
C
S
C
S
8
AS18
18AC17
11AS10
10AC
9
9
AN
AN
7
AC
AC
3
8
6
2
9
C
N
9 7
AN
[
S
S
N
N
3 2
Ni(L)](NO )
7
AC
AN
3
6
2
17ANi29AS
17ANi29AN
9
137.27
89.80
95.57
C
8
5
N
6
AC
5
ANi29AN
ANi29AS
6
6
9
83.20
3 2
[Ni(L)](NO )
C
7
AS17ANi29
67.61
S
17ANi29
2.144
2.160
1.784
1.788
1.981
1.375
1.370
1.372
1.846
1.750
1.357
1.374
1.375
Ni29AN
Ni29AN
Ni29AN
5
AC
6
AC
6
AC
1
2
8
103.39
104.75
90.61
109.14
83.71
Ni29AS
Ni29AN
Ni29AN
9
5
6
N
6
AC
AS
AC
AN
8
AS
AC10
AC
AC
9
7
C AS17
C
C
C
8
9
N
N
N
5
AC
6
AC
6
AC
1
2
8
4
2
1
2
127.83
107.58
6
8
C
8
AS
AC10
9
S
9
C
C
C
4
1
2
AC
AC
AN
1
2
lipid membrane that surrounds the cell favors the passage of only
lipid soluble materials due to which liposolubility was considered
to be an important factor that controls the antimicrobial activity.
On chelation, the polarity of the metal ion will be reduced to a
greater extent due to the overlap of the ligand orbital and partial
sharing of positive charge of metal ion with donor groups
6
complexes and parent ligand. The order of antibacterial activity
was found in order:
[
28,29]. Further, it increases the delocalization of the p electrons
over the whole chelate ring and enhances the lipophilicity of the
complex. This increased lipophilicity enhances the penetration of
the complexes into lipid membrane and thus blocks the metal
binding sites on enzymes of micro organisms [30]. These metal
complexes also disturb the respiration process of the cell and thus
block the synthesis of proteins, which restricts further growth of
the organism [31].
against E. coli
Standard > [Cu(L)(SO
against S. aureus
Standard > [Ni(L)Cl
against P. aeruginosa
Standard > [Cu(L)(SO
against K. pneumonia
4
)] > [Ni(L)Cl
2
] > [Cu(L)Cl
)] > [Cu(L)Cl
] > [Ni(L)Cl
2
2
2
] > ligand
] > ligand
] > ligand
2
] > [Cu(L)(SO
4
)] > [Cu(L)Cl
4 2
4 2 2
Standard > [Cu(L)(SO )] > ligand > [Ni(L)Cl ] > [Cu(L)Cl ]
Antibacterial screening
Antifungal screening
Antibacterial activity was tested in vitro against E. coli, S. aureus,
P. aeruginosa, and K. pneumonia. The compounds were tested at the
concentration 200 ppm, 100 ppm, 50 ppm, 25 ppm, and 12.5 ppm.
For fungicidal activity, compounds were screened in vitro
against R. solani, S. rolfsii, M. phaseolina, F. oxysporum, and A. niger.
The compounds were tested at the concentration 200 ppm,
100 ppm, 50 ppm, 25 ppm and 12.5 ppm in DMSO. From Table 9,
4
Table 8 indicates that [Cu(L)(SO )] complex showed better activity
against E. coli, P. aeruginosa, and K. pneumonia than other

S. Chandra et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 749–760
759
Table 8
Antibacterial activity result of the Schiff’s base ligand and its metal complexes.
Compounds
Ligand(L)
Concentration (ppm)
200
E. coli
S. aureus
P. aeruginosa
K. pneumonia
MIC
19
17
15
–
20
17
13
09
05
22
19
14
10
06
25
22
19
14
11
200
1
5
2
1
00
0
5
2.5
–
[
[
[
Cu(L)Cl
2
]
200
23
21
19
16
14
22
19
17
14
11
24
21
18
16
14
19
17
14
11
07
50
1
5
2
1
00
0
5
2.5
Cu(L)(SO
4
)]
200
29
26
21
17
15
27
24
20
16
13
30
27
23
20
19
30
27
25
21
19
25
1
5
2
1
00
0
5
2.5
Ni(L)Cl
2
]
200
27
23
20
17
13
28
25
23
19
15
23
21
19
15
13
23
21
19
16
14
50
1
5
2
1
00
0
5
2.5
Standard (Gentamycin)
200
32
31
30
30
30
35
33
30
28
28
39
34
32
30
30
32
30
29
27
27
12.5
1
5
2
1
00
0
5
2.5
Table 9
Antifungal activity result of the Schiff’s base ligand and its metal complexes.
Compounds
Ligand(L)
Concentration (ppm)
200
R. solani
R. rolfsii
M. phaseolina
F. oxysporum
A. niger
62
51
42
33
23
69
57
44
38
25
70
62
57
48
39
72
63
57
49
39
59
47
40
29
15
1
5
2
1
00
0
5
2.5
[
[
[
Cu(L)Cl
2
]
200
93
89
74
65
47
89
73
53
47
35
86
79
67
43
32
87
79
66
46
38
89
74
59
42
29
1
5
2
1
00
0
5
2.5
Cu(L)(SO
4
)]
200
92
84
79
59
48
93
88
76
69
47
91
88
72
59
41
91
86
78
44
30
86
77
62
57
41
1
5
2
1
00
0
5
2.5
Ni(L)Cl
2
]
200
91
82
76
65
58
87
72
67
53
39
94
89
69
58
34
85
79
64
47
36
85
73
67
53
38
1
5
2
1
00
0
5
2.5
Standard (Fluconazole)
200
97
93
86
79
74
96
87
81
73
69
98
91
86
78
67
97
92
85
78
69
98
93
87
79
68
1
5
2
1
00
0
5
2.5
it was clear that the [Cu(L)(SO
against S. rolfsii, M. phaseolina, and A. niger Fig. 8 (Supplementary
Material).
4
)] complex shows good activity
Standard > [Cu(L)(SO
against F. oxysporum
4
)] > [Ni(L)Cl
2
] > [Cu(L)Cl
)] > [Cu(L)Cl
] > [Cu(L)Cl
2
2
2
] > ligand
] > ligand
] > ligand
2
Standard > [Ni(L)Cl ] > [Cu(L)(SO
4
Order of antifungal activity was found in order:
against A. niger
Standard > [Cu(L)(SO
4
)] > [Ni(L)Cl
2
against R. solani
Standard > [Cu(L)Cl
against S. rolfsii
Standard > [Cu(L)(SO
against M. phaseolina
2
] > [Cu(L)(SO )] > [Ni(L)Cl
4
2
] > ligand
] > ligand
Conclusion
4
)] > [Cu(L)Cl ] > [Ni(L)Cl
2
2
On the basis of the physicochemical and spectral data, we
assume that ligand behaves as tetradentate [N ]. In the light of
2 2
S

7
60
S. Chandra et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 749–760
above discussed studies, we proposed octahedral geometry for
Ni(L)Cl ], tetrahedral geometry for [Ni(L)](NO , tetragonal geom-
etry for [Cu(L)Cl ], [Cu(L)(NO ], and square pyramidal geometry
for [Cu(L)(SO )] complex Fig. 9 (Supplementary Material). Thermal
study revealed thermal stability of complexes. Ligand and its
Cu(L)Cl ] complex showed a moderate activity against all fungi
[7] M.A. Neelakantan, M. Esakkiamma, S.S. Mariappan, J. Dharmaraja, T.J. Kumar,
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2
3 2
)
[
8] G.A. Bohach, D.J. Fast, R.D. Nelson, P.M. Schlievert, J. Rodes, J.P. Benhamou, A.
Blei, J. Reichen, M. Rizzetto, The Textbook of Hepatology: from Basic Science to
Clinical Practice, Wiley Blackwell, Oxford (UK), 2007, p. 1029.
2
3 2
)
4
[
9] D. Sriram, P. Yogeeswari, N.S. Myneedu, V. Saraswat, Bioorg. Med. Chem. Lett.
16 (2006) 2127.
[
2
[
[
[
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J. Inorg. Biochem. 99 (2005) 1433.
11] N. Demirbas, S.A. Karaoglu, A. Demirbas, K. Sancak, Eur. J. Med. Chem. 39
species studied here. Among all metal complexes, [Cu(L)(SO
4
)]
complex showed an excellent inhibition.
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Acknowledgements
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The author thankful to University Grant Commission (UGC),
New Delhi, India for financial assistance, USIC, University of Delhi
for recording TGA, IR, CHN, IIT Bombay for recording EPR spectra,
and IIT Delhi for recording NMR spectra.
[17] S. Chandra, M. Tyagi, K. Sharma, J. Iran. Chem. Soc. 6 (2009) 310.
[
18] N. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, third ed., John Wiley & Sons, New York, NY, USA, 1978.
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[
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[
20] S. Chandra, A. Kumar, Spectrochim. Acta, Part A 67 (2007) 697.
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22] S. Chandra, L.K. Gupta, Spectrochim. Acta, Part A 61 (2005) 1181.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2014.08.046.
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