Spectral, antimicrobial, and thermal studies of some transition metal complexes derived from bidentate ligands containing N and S donor atoms

Article abstract of DOI:10.1080/10426507.2012.692128

Bidentate ligands have been synthesized by the reaction of 2,4-dichlorobenzaldehyde with 4-amino-5-mercapto-1,2,4-triazole and 4-amino-5-mercapto-3-propyl-1,2,4-triazole. The ligands react with acetates of Co(II), Ni(II), Cu(II), and Zn(II) to yield 1:2 [metal:ligand] complexes. The newly synthesized compounds were characterized by elemental analyses, spectral (UV-Vis, IR, ¹H NMR, fluorescence, ESR) studies, thermal techniques, and magnetic measurements. Thermal studies of the complexes showed a multistep decomposition pattern. A square planar geometry for Cu(II) and octahedral geometry for Co(II), Ni(II), and Zn(II) complexes have been proposed. The synthesized complexes exhibit enhanced antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, Aspergillus niger, and A. flavus compared to parent ligands. However, tested compounds did not exhibit any activity against Escherichia coli and Pseudomonas aeruginosa. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Full text of DOI:10.1080/10426507.2012.692128

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Spectral, Antimicrobial, and Thermal
Studies of Some Transition Metal
Complexes Derived from Bidentate
Ligands Containing N and S Donor Atoms
Kiran Singh a , Yogender Kumar a , Parvesh Puri a , Chetan Sharma b
& Kamal Rai Aneja b
a Department of Chemistry , Kurukshetra University , Kurukshetra ,
136 119 , Haryana , India
b Department of Microbiology , Kurukshetra University ,
Kurukshetra , 136 119 , Haryana , India
Accepted author version posted online: 17 May 2012.Published
online: 10 Sep 2012.
To cite this article: Kiran Singh , Yogender Kumar , Parvesh Puri , Chetan Sharma & Kamal Rai Aneja
(2012) Spectral, Antimicrobial, and Thermal Studies of Some Transition Metal Complexes Derived from
Bidentate Ligands Containing N and S Donor Atoms, Phosphorus, Sulfur, and Silicon and the Related
Elements, 187:12, 1498-1509, DOI: 10.1080/10426507.2012.692128
To link to this article: http://dx.doi.org/10.1080/10426507.2012.692128
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Phosphorus, Sulfur, and Silicon, 187:1498–1509, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.692128
SPECTRAL, ANTIMICROBIAL, AND THERMAL STUDIES
OF SOME TRANSITION METAL COMPLEXES DERIVED
FROM BIDENTATE LIGANDS CONTAINING
N AND S DONOR ATOMS
Kiran Singh,1 Yogender Kumar,1 Parvesh Puri,1
Chetan Sharma,2 and Kamal Rai Aneja2
1Department of Chemistry, Kurukshetra University, Kurukshetra 136 119,
Haryana, India
2Department of Microbiology, Kurukshetra University, Kurukshetra 136 119,
Haryana, India
GRAPHICAL ABSTRACT
Abstract Bidentate ligands have been synthesized by the reaction of 2,4-dichlorobenzaldehyde
with 4-amino-5-mercapto-1,2,4-triazole and 4-amino-5-mercapto-3-propyl-1,2,4-triazole. The
ligands react with acetates of Co(II), Ni(II), Cu(II), and Zn(II) to yield 1:2 [metal:ligand] com-
plexes. The newly synthesized compounds were characterized by elemental analyses, spectral
(UV-Vis, IR, 1H NMR, fluorescence, ESR) studies, thermal techniques, and magnetic measure-
ments. Thermal studies of the complexes showed a multistep decomposition pattern. A square
planar geometry for Cu(II) and octahedral geometry for Co(II), Ni(II), and Zn(II) complexes
have been proposed. The synthesized complexes exhibit enhanced antimicrobial activity against
Staphylococcus aureus, Bacillus subtilis, Aspergillus niger, and A. flavus compared to parent
ligands. However, tested compounds did not exhibit any activity against Escherichia coli and
Pseudomonas aeruginosa.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
Received 24 February 2012; accepted 6 May 2012.
Yogender Kumar is highly thankful to University Grant Commission, New Delhi for providing Senior
Research Fellowship (SRF) and Department of Chemistry, Kurukshetra University, Kurukshetra, for providing
facilities to carry out this research work.
Address correspondence to Kiran Singh, Department of Chemistry, Kurukshetra University, Kurukshetra
136 119, Haryana, India. E-mail: knsingh@kuk.ac.in
1498

SPECTRAL, ANTIMICROBIAL, AND THERMAL STUDIES
1499
Keywords N and S donor atoms; octahedral geometry; 1,2,4-triazole; 2,4-dichloro-
benzaldehyde; thermal studies
INTRODUCTION
The chemistry of compounds containing N and S donor atoms is of special interest
since they display a broad spectrum of physicochemical properties and biological activi-
ties.1,2 The coordination chemistry of such ligands has also attracted considerable attention
due to the variety of coordination possibilities associated with them. It is known that
metal complexes of biologically active compounds may have enhanced activities compared
to the noncoordinated ligands.3–5 Among N, S donor ligands, molecules containing the
1,2,4-triazole ring are known to possess a wide range of biological properties, including an-
timicrobial and antiinflammatory activities among others.6–10 The 1,2,4-triazole nucleus has
been incorporated into a wide variety of therapeutically interesting molecules to transform
them into better drugs.11–13 Further, they show a versatile coordinating ability, especially
when the triazole nucleus is substituted with additional donor groups.14
Schiff bases derived from 3-substituted-4-amino-5-mercapto-1,2,4-triazoles show
analgesic, antimicrobial, antiinflammatory, and antidepressant activities.15 Metal complexes
of Schiff bases derived from triazoles are biologically important compounds;16,17 some
complexes containing substituted 1,2,4-triazole ligands have spin-crossover properties and
can be used as molecular-based memory devices, display, and optical switches.18,19
Since 3-substituted-4-amino-5-mercapto-1,2,4-triazoles Schiff bases constitute an
interesting class of chelating agents, their metal complexes may have potential use in
biological fields. Accordingly, a number of bivalent Co(II), Ni(II), Cu(II), and Zn(II) metal
complexes with Schiff bases derived from 4-amino-5-mercapto-1,2,4-triazole and 4-amino-
5-mercapto-3-propyl-1,2,4-triazole and 2,4-dichlorobenzaldehyde (HIMEDIA, India) have
been synthesized, characterized, and studied for their biological activity.
RESULTS AND DISCUSSION
The synthesis of Schiff bases (HL1-2) is schematically represented in Figure 1. Ele-
mental analyses indicated the formation of metal complexes (1:2; metal:ligand) of HL with
Co(II), Ni(II), Cu(II), and Zn(II) metal ions (Table 1). The complexes are powdery solids,
colored, nonhygroscopic in nature and decomposed at higher temperature. The molar con-
ductance values of the complexes (measured in 10–3 M dimethylformamide (DMF)) are in
the range 7.4–12.5 ohm–1 cm2 mol–1 indicating their nonelectrolytic nature.20,21 The purity
of the ligands and their metal complexes has been checked by thin layer chromatography.
1H NMR Spectra
The 1H NMR spectral data of Schiff bases (HL1-2) and their diamagnetic Zn(II) com-
plexes are given in Table 2. In the spectra of Schiff bases signal observed at δ 10.26 (HL1)
and 10.51 (HL2) ppm is assigned to the azomethine proton. This signal due to the azome-
thine proton shifted downfield in the spectra of metal complexes indicates participation of
the azomethine nitrogen in coordination.22,23 The peak corresponding to –SH at 11.12 and
14.10 ppm in the free ligands is not observed in the spectra of the metal complexes.17 This
clearly shows deprotonation of –SH during complex formation. The triazole proton in the

1500
K. SINGH ET AL.
Figure 1 Scheme for the syntheses of Schiff bases.
ligand (HL1) is observed at 8.94 ppm as a singlet. The propyl group protons of HL2 Schiff
base appeared as triplet δ 1.03 ( CH3), triplet δ 2.80 ( CH2 ), and multiplet at δ 1.76
( CH2 ). The aromatic protons of Schiff bases appeared as a singlet and two doublets in
the range δ 7.36–8.07 ppm. These aromatic protons signals of Schiff bases show a slight
shift upon coordination with the metal ions.
IR Spectra
The IR spectra provide valuable information regarding the nature of the functional
group attached to the metal atom. The comparative analysis of IR spectra of the complexes
and the free ligands (Table 3) reveals that the absorption band characteristic of the stretching
Table 1 Analytical data of Schiff bases and their metal complexes
% found (Calculated)
Serial
Number
Empirical
formula
Compound
HL1
C
H
N
M
1.
2.
3.
4.
5.
6.
7.
8.
9.
C9H6Cl2N4S
42.50 (42.87) 3.01 (3.08) 19.04 (19.04)
–
Co(L1)2·2H2O C18H14Cl4CoN8O2S2 33.58 (33.82) 2.17 (2.21) 17.43 (17.53)
9.01 (9.22)
9.06 (9.19)
Ni(L1)2·2H2O C18H14Cl4N8NiO2S2 33.60 (33.83) 2.12 (2.21) 17.33 (17.54)
Cu(L1)2
C18H10Cl4CuN8S2
35.45 (35.57) 1.67 (1.66) 18.31 (18.44) 10.40 (10.45)
Zn(L1)2·2H2O C18H14Cl4N8O2S2Zn 33.41 (33.48) 2.05 (2.19) 17.28 (17.35) 10.08 (10.13)
HL2
C11H10Cl2N4S
43.82 (43.86) 3.33 (3.35) 18.40 (18.60)
–
Co(L2)2·2H2O C24H26Cl4CoN8O2S2 39.73 (39.85) 3.60 (3.62) 15.23 (15.49)
8.01 (8.15)
8.01 (8.12)
8.99 (9.18)
8.46 (8.96)
Ni(L2)2·2H2O C24H26Cl4N8NiO2S2 39.65 (39.86) 3.51 (3.62) 15.32 (15.50)
Cu(L2)2
C24H22Cl4CuN8S2
41.52 (41.66) 3.18 (3.20) 16.03 (16.19)
10.
Zn(L2)2·2H2O C24H26Cl4N8O2S2Zn 39.41 (39.50) 3.48 (3.59) 15.15 (15.35)

SPECTRAL, ANTIMICROBIAL, AND THERMAL STUDIES
1501
Table 2 1H NMR spectral data of Schiff bases and their metal complexes
Compounds
1H NMR (CDCl3/DMSO-d6) (ppm)
HL1 [C9H6Cl2N4S]
7·59 (d, 1H, Ar-H), 7.82 (s, 1H, Ar-H), 8.07 (d, 1H, Ar-H),
8.94 (s, triazole-H), 10.26 (s,1H, -N=CH-), 14.10 (s, 1H,
-SH)
Zn(L1)2·2H2O
7.58 (d, 2H, Ar-H), 7.83 (s, 2H, Ar-H), 8.07 (d, 2H, Ar-H),
9.23 (s, 2H, triazole-H), 10.68 (s, 2H, -N=CH-)
1.03 (t, 3H, -CH3), 1.76 (m, 2H, -CH2-), 2.80 (t, 2H, -CH2-),
7.36 (d, 1H, Ar-H), 7.52 (s, 1H, Ar-H), 8.06 (d, 1H,
Ar-H),10.51 (s,1H, -N=CH-), 11.12 (s, 1H, -SH)
0.88 (t, 6H, -CH3), 1.53 (m, 4H, -CH2-), 2.72 (t, 4H, -CH2-),
7.51 (d, 2H, Ar-H), 7.73 (s, 2H, Ar-H), 8.13 (d, 2H, Ar-H),
10.80 (s, 2H, -N=CH-)
[C18H14Cl4N8O2S2Zn]
HL2 [C12H12Cl2N4S]
Zn(L2)2·2H2O
[C24H26Cl4N8O2S2Zn]
vibrations of C N (azomethine group) is shifted toward lower wave number from 1610
(HL1) cm–1 and 1614 (HL2) cm–1 in the spectra of the ligands to 1582–1596 cm–1 in the
complexes.16,17,24 This indicates the coordination of the nitrogen of this group with the
metal ions. Further coordination of metal to azomethine nitrogen is confirmed by a new
band at 483–515 cm–1 due to ν(M N).25 The ligands show a weak absorption band at
∼2690 cm–1 due to ν(S H). This band due to ν(S H) completely disappeared in the case of
metal complexes indicating deprotonation of thiophenolic protons prior to coordination.16,17
Coordination of metal to sulfur is further confirmed by a band at 343–358 cm–1 in the far
IR spectra due to ν(M S).26 The new band in the region of 717–733 cm–1 in the metal
complexes is due ν(C S) bond. A broad band in the region 3382–3492 cm–1, assigned as
ν(OH), indicted the presence of coordinated water molecules in the complexes.27
Magnetic Susceptibility and Electronic Spectral Studies
In order to obtain further structural information, the electronic spectra and magnetic
moments of the complexes have been measured (Table 4). At room temperature, Co(II)
complexes show magnetic moments 4.16 and 4.21 Bohr magneton (BM), indicating three
unpaired electrons. The electronic spectra of Co(II) complexes, exhibit two absorption
band in the region 10555–11009 cm–1, and 20585–20798 cm–1. The bands observed are
Table 3 Important IR spectral bands (cm–1) of Schiff bases and their metal complexes
Compound
ν(N CH)
ν(C-S)
ν(S-H)
ν(H2O/OH)
ν(M-S)
ν(M-N)
HL1
1610
1582
1588
1583
1590
1614
1596
1592
1588
1592
—
2692
—
—
—
—
2690
—
—
—
—
—
3410
3492
-
3410
—
3410
3391
—
—
—
Co(L1)2·2H2O
Ni(L1)2·2H2O
Cu(L1)2
725
717
720
726
—
725
728
726
733
353
357
352
357
—
353
358
358
343
509
503
515
500
—
483
497
509
500
Zn(L1)2·2H2O
HL2
Co(L2)2·2H2O
Ni(L2)2·2H2O
Cu(L2)2
Zn(L2)2·2H2O
3382

1502
K. SINGH ET AL.
Table 4 Electronic spectral data of metal complexes
Transitions (cm–1
)
Compound
ν1
ν2
ν3
Dq cm–1
B cm–1
ν2/ν1
β
β%
µeff (BM)
Co(L1)2·2H2O
Co(L2)2·2H2O
Ni(L1)2·2H2O
Ni(L2)2·2H2O
Cu(L1)2
10555
11009
9985
9801
18998
19223
22337a
23227a
16213
16303
20798
20585
24588
24015
1178.2
1221.8
998.5
980.1
—
764.6
719.0
723.0
727.6
—
2.11
2.10
1.62
1.66
—
0.787
0.740
0.694
0.699
—
21.3
26.0
30.6
30.1
—
4.21
4.16
3.82
3.81
1.81
1.80
Cu(L2)2
—
—
—
—
—
aCalculated value.
4
4
4
4
assigned to the transitions T1g(F)→ T2g(F) (ν1) and T1g(F)→ T1g(P) (ν3), suggesting
that there is an octahedral geometry around Co(II) ion (Figure 2).28,29 The ν2 transition is
not observed due to very weak intensity.30 The Ni(II) complexes reported herein is found
to have room temperature magnetic moment values 3.82 and 3.81 BM, corresponding to
two unpaired electrons. The electronic spectra of Ni(II) complexes display three absorption
bands in the range 9801–9985 cm–1, 16213–16303 cm–1, and 24015–24588 cm–1, which are
Figure 2 Proposed structures of metal complexes.

SPECTRAL, ANTIMICROBIAL, AND THERMAL STUDIES
1503
3
3
3
3
assigned to three spin allowed transitions A2g(F)→ T2g(F) (ν1), A2g(F)→ T1g(F) (ν2),
3
3
and A2g(F)→ T1g(P) (ν3), respectively. These are the characteristic bands of octahedral
geometry around the Ni(II) complexes (Figure 2).26,30 The ligand field parameters (Dq, B, β,
β%) havealso beencalculated (Table4) for Co(II) andNi(II) complexes byusingband-fitting
equation.30 These parameters indicated significant covalent character of the metal–ligand
bonds and an overlapping of ligand–metal orbitals. The magnetic moments of the Cu(II)
complexes at room temperature corresponds to µeff value for one unpaired electron (1.81 and
1.80 BM ). The band observed for Cu(II) complexes (18998 and 19223 cm–1) attributable
to 2B1g→ A1g transition strongly favors the square planar geometry (Figure 2) around the
2
central metal ion.31
Photoluminescence Properties
In order to investigate the effect of Co(II), Ni(II), Cu(II), and Zn(II) ions on the
fluorescence of ligand, the fluorescence spectra of the ligands (HL1-2) and their metal
complexes are recorded in DMF at room temperature. The overlapping spectrum of the
HL1 and its Co(II), Ni(II), Cu(II), and Zn(II) compounds is given in Figure 3. HL1 exhibits
two weak fluorescence emission bands at 316 and 477 nm (EX 265 nm); in contrast to
this, enhancement of fluorescence intensity are observed in its metal complexes with the
fluorescence emission bands at 337, 543 nm for Co(II), 332, 467 nm for Ni(II), 334, 543,
592 nm for Cu(II), and 469 nm for Zn(II) complexes. HL2 shows a weak fluorescence
band at 337 nm (EX 280 nm) and its complexes exhibit higher intensity emission bands at
332 nm (Co), 461 nm (Ni), 336 and 544 nm (Cu), and 331 and 539 nm (Zn), respectively. It
is evident from the fluorescence spectra that the fluorescence intensity of metal complexes,
relative to that of the free ligand, is dramatically enhanced, which may be due to the
formation of coordination bonds between the ligands and metal ions.28
Thermal Studies
The thermogravimetric analysis were carried out for Co(L2)2.2H2O and Ni(L2)2.2H2O
(Figure S1, online Supplementary Materials). The correlation between the different decom-
position steps of the complexes with corresponding weight losses are discussed in terms of
the proposed formulae of the complexes.22,32,33 The thermogram of these complexes are al-
most similar and show three decomposition stages within the temperature range from 50 ◦C
to 800 ◦C. The first stage takes place in temperature range 50 ◦C–200 ◦C and 50 ◦C–195 ◦C,
corresponding to loss of two water molecules. The mass loss observed in this step is 5.12%
and 5.09% against the calculated loss of 4.99% and 5.0%, respectively. The second◦decom-
◦
◦
◦
position stage of the complexes takes place in 200 C–385 C and 195 C–380 C with
weight losses of 44.21% and 45.0% against the calculated losses of 43.82% and 43.76%
that correlate with the elimination of the organic moiety. The final decomposition stage of
the complexes with metal oxide formation occurs in the 385 ◦C–800 ◦C and 380 ◦C–800 ◦C
ranges with weight losses of 43.09% and 41.0% against the calculated weight losses of
41.91% and 41.0 % due to elimination of triazole molecules. These results show good
agreement with the formulae suggested from the analytical data.

1504
K. SINGH ET AL.
Figure 3 Fluorescence emission spectra of Schiff base [HL1] and its metal complexes.
ESR Spectral Studies
The electronic paramagnetic resonance spectra of Cu(L1)2 and Cu(L2)2 (Figure S2,
online Supplementary Materials) were recorded in the solid state at room temperature to
obtain further information about their stereochemistry. The g-tensor values of the Cu(L1)2
(g = 2.17, g = 2.06, gav = 2.09, G = 2.89) and Cu(L2)2 (g = 2.12, g = 2.06, gav = 2.08,
ꢁ
⊥
ꢁ
⊥
G = 2.03) complexes can be used to derive the ground state. In square planar complexes,

SPECTRAL, ANTIMICROBIAL, AND THERMAL STUDIES
1505
the unpaired electron lies in dx2-y2 orbital giving 2B1g as the ground state with g > g > 2,
ꢁ
⊥
while the unpaired electron lies in the dz2 orbital giving 2A1g as the ground state with g >
⊥
g > 2. In the present case, the g > g > 2, therefore the unpaired electron is likely to be in
ꢁ
ꢁ
⊥
the dx2-y2 orbital indicates square planar geometry around the Cu(II) ion.34,35 No signal at
half field was observed in the spectrum, ruling out the possibility of a dimeric form.36 This
is also supported by the magnetic moments of Cu complexes (1.81 and 1.80 BM) which
confirm the mononuclear nature of the complexes.
Antimicrobial Discussion
The ligands (HL1-2), metal complexes, standard drugs, and dimethyl sulfoxide
(DMSO) solvent (Spectrochem, India) were screened separately for their antibacterial ac-
tivity against Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative
(Escherichia coli, Pseudomonas aeruginosa) bacteria and antifungal activity against As-
pergillus niger and Aspergillus flavus. However, tested compounds did not exhibit any
activity against Gram-negative (E. coli and P. aeruginosa) bacteria. The microbial results
and discussion are summarized in the online Supplementary Materials (Tables S1–S3).
Positive controls (standard drug) produced significantly sized inhibition zones against the
tested bacteria and fungi; however, negative control (DMSO) produced no observable
inhibitory effect against any of the test organisms. Overtone’s concept37 and Tweedy’s
chelation theory38 can be used to explain the enhanced antimicrobial activity of the metal
complexes.
In the whole series, the minimum inhibitory concentration (MIC) of synthesized
compounds ranged between 32 µg mL–1 and 512 µg mL–1 against Gram-positive bacteria.
MIC results revealed that the metal complexes are more effective against the antibacterial
strains as compared to the Schiff bases. Ni(L2)2.2H2O was found to be the best antibacterial
agent and exhibited the lowest MIC of 32 µg mL–1 and 64 µg mL–1 against B. subtilis
and S. aureus, respectively (Table S2, online Supplementary Materials). The results of our
study are in accordance with the reports of earlier workers,22,26,39 which also showed that
the antibacterial activity of ligands is greatly enhanced when it is coordinated to metal ions.
CONCLUSIONS
In this paper, a number of bivalent Co(II), Ni(II), Cu(II), and Zn(II) metal complexes
with Schiff bases of 4-amino-5-mercapto-1,2,4-triazole and 4-amino-5-mercapto-3-propyl-
1,2,4-triazole and 2,4-dichlorobenzaldehyde have been synthesized. The synthesized Schiff
bases act as bidentate ligands and coordinated to metal ion through nitrogen and sulphur of
thiol group. In the electron spin resonance (ESR) spectra of copper complexes, no signal
at half field was observed, ruling out the possibility of a dimeric form. A square planar
geometry for Cu(II) and octahedral geometry for Co(II), Ni(II), and Zn(II) complexes have
been proposed. The synthesized complexes exhibit enhanced antibacterial activity against
S. aureus and B. subtilis and antifungal activity against A. niger and A. flavus compared
to parent ligands. However, tested compounds did not exhibit any activity against E. coli
and P. aeruginosa. Thus, exhibiting their broad spectrum nature and can become a new
antimicrobial agent, after further biological studies.

1506
K. SINGH ET AL.
EXPERIMENTAL
Materials
All the chemicals used in the present study were of analytical grade and used without
further purification. All metal (II) salts used as their acetates. 4-amino-5-mercapto-1,2,4-
triazole and 4-amino-5-mercapto-3-propyl-1,2,4-triazole were prepared by a reported liter-
ature method.40
Syntheses of Schiff Bases
4-(2,4-Dichlorobenzylideneamino)-5-mercapto-1,2,4-triazole (HL1). An
ethanolic solution (40 mL) of 4-amino-5-mercapto-1,2,4-triazole (0.69 g, 6.03 mmol) and
2,4-dichlorobenzaldehyde (1.05 g, 6.03 mmol) was refluxed for ca. 4 h. The resultant
solution was cooled to room temperature. The yellow solid formed was filtered and
recrystallized in ethanol. M.p. 238 ◦C–240 ◦C.
4-(2,4-Dichlorobenzylideneamino)-5-mercapto-3-propyl-1,2,4-triazole
(HL2). A solution of 4-amino-5-mercapto-3-propyl-1,2,4-triazole (1.04 g, 6.58 mmol) in
ethanol (40 mL) was treated with 2,4-dichlorobenzaldehyde (1.51 g, 6.58 mmol). The
reaction mixture was refluxed for 6 h and the solid crude was filtered off and washed with
cold ethanol, dried, and recrystallized in ethanol. M.p. 165 ◦C–168 ◦C.
Syntheses of Metal Complexes
Metal Complexes of 4-(2,4-Dichlorobenzylideneamino)-5-mercapto-
1,2,4-triazole (HL1). The aqueous ethanolic solutions (30 mL) of acetates of Co(II)
(0.16 g, 0.62 mmol), Ni(II) (0.15 g, 0.62 mmol), Cu(II) (0.13 g, 0.62 mmol), and ◦Zn(II)
(0.14 g, 0.62 mmol) were treated with the hot ethanolic solutions (40 mL, ∼60 C) of
the HL1 (0.34 g, 1.25 mmol), which resulted in the immediate precipitation of the metal
derivatives.◦The solid complexes were filtered, washed several times with warm water
◦
(60 C–70 C), aqueous ethanol to remove unreacted metal acetates (CDH Chemicals,
India) or ligands and finally with acetone, and vacuum dried.
Metal Complexes of 4-(2,4-Dichlorobenzylideneamino)-5-mercapto-3-
propyl-1,2,4-triazole (HL2). The metal acetates of Co(II) (0.14 g, 0.55 mmol), Ni(II)
(0.14 g, 0.55 mmol), Cu(II) (0.11 g, 0.55 mmol), and Zn(II) (0.12 g, 0.55 mmol) in aqueous
◦
ethanol (30 mL) were treated with hot ethanolic solution (40 mL, ∼60 C) of the HL2
(0.35 g, 1.11 mmol), which resulted in the immediate precipitation of metal derivatives.
The solid complexes formed were filtered off, washed several times with warm water
(60 ◦C–70 ◦C), aqueous ethanol to remove unreacted metal acetates or ligands and finally
with acetone, and vacuum dried.
Analyses and Instrumentation
The elemental analyses (C, H, and N) were carried out at SAIF, Punjab University,
Chandigarh by using Perkin-Elmer 2400 Elemental Analyzer. The metal contents were
determined gravimetrically by a literature procedure41 after digesting the organic matter
with aqua regia. IR spectra of neat samples of the ligands and their metal complexes
were performed in the range 4000–250 cm–1 on a MB-3000 ABB Spectrometer. The
electronic spectra of solid complexes were recorded on T 90 (PG Instruments ltd) UV/Vis

SPECTRAL, ANTIMICROBIAL, AND THERMAL STUDIES
1507
spectrophotometer in the region 1100–200 nm. 1H NMR spectra were recorded in DMSO-
d6 (Acros Organics, Belgium) on a Bruker ACF 300 spectrometer at 300 MHZ using
“tetramethyl silane” as the internal standard. Magnetic moments were measured at Institute
Instrumentation Centre, IIT Roorkee, on vibrating sample magnetometer (Model 155). The
Perkin Elmer (Pyris Diamond) instrument was used to carry out the thermal analyses of
metal complexes in atmospheric air (50 ◦C–800 ◦C) at a heating rate of 10 ◦C min–1 using
a reference to alumina powder. The fluorescence studies of Schiff bases and their metal
complexes were recorded on SHIMADZU RF-5301PC spectrophotometer. Solutions of
10–3 M concentration were prepared in high-performance liquid chromatography grade
DMF and the experiment was carried out at room temperature. ESR spectra were recorded
on X-Band at frequency of 9.1 GHz under the magnetic field 3000 Gauss on a Varian E-112
ESR spectrometer at SAIF, IIT Bombay.
Pharmacology
Antibacterial Activity (In Vitro). All the newly synthesized ligands [HL1-2] and
their metal complexes were screened in vitro for their antibacterial activity against two
Gram-positive (S. aureus Microbial Type Culture Collection (MTCC) 96, B. subtilis MTCC
121) and two Gram-negative (E. coli MTCC 1652, P. aeruginosa MTCC 741) bacterial
strains by agar well diffusion method as reported in our previous paper.22 All the bacterial
cultures were procured from MTCC, IMTECH, Chandigarh and subcultured on nutrient
agar (HIMEDIA). DMSO was used as a negative control whereas ciprofloxacin was used
as positive control. This procedure was performed in three replicate plates for each organ-
ism and the mean values of the diameter of inhibition zones standard deviations were
calculated.42
Antifungal Activity (In Vitro). All the newly synthesized ligands [HL1-2] and
their metal complexes were screened in vitro for their antifungal activity against two fungi,
A. niger and A. flavus, the ear pathogens isolated from the patients of Kurukshetra43 and
evaluated by poisoned food technique.22 The molds were grown on Sabouraud dextrose agar
(HIMEDIA) at 25 ◦C for 7 days and used as inocula. DMSO was used as the negative control
whereas fluconazole was used as the positive control. The experiments were performed in
triplicates. Diameters of fungal colonies were measured and expressed as percent mycelial
inhibition.
Percent inhibition of mycelial growth = (dc − dt)/dc × 100,
where dc is the average diameter of fungal colony in negative control sets and dt is the
average diameter fungal colony in experimental sets.
Determination of MIC
MIC is the lowest concentration of an antimicrobial compound that will inhibit
the visible growth of a microorganism after overnight incubation. MIC of the various
compounds against bacterial strains was tested through a modified agar well diffusion
method.22,42 MIC showed by a clear zone of inhibition, was recorded for each test organism.
Ciprofloxacin was used as positive control.

1508
K. SINGH ET AL.
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