Synthesis, thermal behavior, and antimicrobial activity of a novel macrocycle and its transition metal complexes derived from thiosemicarbazide

Article abstract of DOI:10.1080/00387010903278341

The present study reports the synthesis of Co(II), Ni(II), Mn(II), Cu(II), and Zn(II) complexes with a new macrocyclic ligand (L₂)-1,2,8,9,11,14-hexaazacyclopentadeca-12,13-dioxo-10,15-dithione-2,7-diene. The macrocycle was derived from thiosemicabazone (L₁) and diethyloxalate that were prepared by the reaction of thiosemicarbazide and glutaraldehyde in the ratio of 2:1. The synthesized complexes and ligands were characterized by elemental analysis and molar conductance, magnetic susceptibility, 1 HNMR, IR, electronic, and thermogravimetric analyses. The molar conductance values confirmed that the Ni(II), Cu(II), Zn(II), Mn(II) and Co(II) complexes were 1:2 electrolytes. On the basis of electronic spectral studies and molar conductance measurements, the authors proposed an octahedral structure for Ni(II), Mn(II), and Co(II) complexes, tetrahedral geometry for Zn(II) complex, and square planar geometry for Cu(II) complex. The thermal behavior of the compounds was studied by TGA in a nitrogen atmosphere up to 750°C at the rate of 20°C/min. The TGA results revealed that the complexes had higher thermal stability than the macrocycle. All the synthesized compounds were screened against 4 bacteria (i.e., Streptococcus aureus, Escherichia coli, Bacillus subtillis, Salmonella typhimurium) and 2 fungi (i.e., Fusarium oryzae, Candida albicans). The results showed that the metal complexes inhibited the growth of bacteria to a greater extent as compared to the ligand. Taylor & Francis Group, LLC.

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Synthesis, Thermal Behavior, and Antimicrobial
Activity of a Novel Macrocycle and its Transition Metal
Complexes Derived from Thiosemicarbazide
Nahid Nishat a , Rhis-ud-din Manisha a & Swati Dhyani a
a Department of Chemistry , Jamia Millia Islamia , New Delhi, India
Published online: 06 Aug 2010.
To cite this article: Nahid Nishat , Rhis-ud-din Manisha & Swati Dhyani (2010) Synthesis, Thermal Behavior, and Antimicrobial
Activity of a Novel Macrocycle and its Transition Metal Complexes Derived from Thiosemicarbazide, Spectroscopy Letters: An
International Journal for Rapid Communication, 43:6, 465-473, DOI: 10.1080/00387010903278341
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Spectroscopy Letters, 43:465–473, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0038-7010 print=1532-2289 online
DOI: 10.1080/00387010903278341
Synthesis, Thermal Behavior, and
Antimicrobial Activity of a Novel
Macrocycle and its Transition Metal
Complexes Derived from
Thiosemicarbazide
Nahid Nishat,
Rhis-ud-din Manisha,
and Swati Dhyani
ABSTRACT The present study reports the synthesis of Co(II), Ni(II), Mn(II),
Cu(II), and Zn(II) complexes with a new macrocyclic ligand (L2)-
1,2,8,9,11,14-hexaazacyclopentadeca-12,13-dioxo-10,15-dithione-2,7-diene.
The macrocycle was derived from thiosemicabazone (L1) and diethyloxalate
that were prepared by the reaction of thiosemicarbazide and glutaraldehyde
in the ratio of 2:1. The synthesized complexes and ligands were character-
ized by elemental analysis and molar conductance, magnetic susceptibility,
1HNMR, IR, electronic, and thermogravimetric analyses. The molar conduc-
tance values confirmed that the Ni(II), Cu(II), Zn(II), Mn(II) and Co(II)
complexes were 1:2 electrolytes. On the basis of electronic spectral studies
and molar conductance measurements, the authors proposed an octahedral
structure for Ni(II), Mn(II), and Co(II) complexes, tetrahedral geometry for
Zn(II) complex, and square planar geometry for Cu(II) complex. The ther-
mal behavior of the compounds was studied by TGA in a nitrogen atmo-
sphere up to 750ꢀC at the rate of 20ꢀC=min. The TGA results revealed that
the complexes had higher thermal stability than the macrocycle. All the
synthesized compounds were screened against 4 bacteria (i.e., Streptococcus
aureus, Escherichia coli, Bacillus subtillis, Salmonella typhimurium) and 2
fungi (i.e., Fusarium oryzae, Candida albicans). The results showed that
the metal complexes inhibited the growth of bacteria to a greater extent
as compared to the ligand.
Department of Chemistry, Jamia
Millia Islamia, New Delhi, India
KEYWORDS antibacterial and antifungal activity, macrocyclic complexes,
thiosemicabazones
Received 14 August 2008;
accepted 8 August 2009.
Address correspondence to
Nahid Nishat, Department of
Chemistry, Jamia Millia Islamia,
New Delhi-110025, India. E-mail:
nishat_nchem08@yahoo.com
465

analysis, molar conductance measurements, mag-
1
netic susceptibility measurements, HNMR spectra,
INTRODUCTION
A large number of natural macrocycles like
porphyrin and cobalamine display remarkable prop-
erties, and their coordination chemistry has been
intensely investigated.[1] Macrocyclic complexes have
attracted research interest due to their analytical,
biological, and catalytic applications.[2,3] The macro-
cyclic ligands play an important role in transition
metal complexes due to kinetic and thermodynamic
stabilities.[4,5] Interest in synthetic macrocycles
derived from Schiff base is growing due to their wide
applications in catalysts, radiopharmaceuticals, and
magnetic-imaging reagents.[6] They provide an envir-
onment of controlled geometry and ligand field
strength to the metal ions. The formation of macro-
cyclic complexes mainly depends on the internal
cavity and the rigidity of the macrocycle formed.
The macrocyclic ligand based on thiosemicarbazone
and their metal complexes have shown themselves
to be pharmacologically active against several
viruses, bacteria, and fungi and certain kinds of
tumors.[7–9] The importance of these compounds is
mainly the result of their antimicrobial activities.[10,11]
It has been observed that the pharmacological
activities are enhanced in the presence of transi-
tion metal ion.[12] The fungicidal activity of these
compounds is due to their ability to form stable
chelates with metal ions that fungi need for meta-
bolism.[13] Keeping the above views in mind, we
synthesized a series of transition metal complexes
having macrocyclic ligand based on thiosemicar-
bazone. They were characterized by elemental
IR spectra, electronic spectra, and thermogravi-
metric studies.
MATERIALS AND METHODS
Glutaraldehyde, transition metal chloride (S.D.
Fine-Chemicals, India), thiosemicarbazide (BDH)
and diethyl oxalate (Merck) were used as received.
Solvents were distilled before use. Microorganisms
were isolated in suitable environment.
Synthesis of L1
An ethanolic solution of thiosemicarbazide
(20 mmol, 1.82 g) was added to ethanolic solution
of glutaraldehyde (10 mmol, 0.942 ml) with constant
stirring in the presence of a few drops of hydrochlo-
ric acid. After addition of all the reagents, the mixture
was heated at 60ꢀC with constant stirring for 7 hr. On
keeping it overnight at room temperature, a red
colored amorphous solid was formed. It was filtered,
washed with acetone and diethyl ether, and dried in
vacuum over CaCl2. The synthesis is represented in
Fig. 1.
Synthesis of L2
An ethanolic solution of L1 (10 mmol, 2.47 g) was
added to ethanolic solution of diethyl oxalate
(10 mmol, 1.36 ml). The diethyl oxalate solution
was taken in burette and added drop-wise to the
solution of L1 in such a manner that the addition
FIGURE 1 1H NMR of L1.
N. Nishat et al.
466

would take at least 1 hr. Then, the mixture was
heated at 60ꢀC with stirring for 10 hr. After that per-
iod, the mixture was reduced by more than half of
its volume by rotatory evaporator. After that, we left
the mixture at room temperature till all the solvent
vaporized. The obtained product was washed with
acetone and diethyl ether in vacuum over CaCl2.
The synthesis is represented in Fig. 1.
nitrogen atmosphere. Chlorine was estimated
gravimetrically, and metals were determined by
EDTA complexometric titration followed by de-
composition of their complexes with fuming nitric
acid. The antibacterial and antifungal activity was
performed by agar disc diffusion method. The sam-
ples were prepared by using DMSO as solvent at a
concentration of 50 mg=ml. The test was performed
at 37ꢀC, and bacteria were incubated for 24 hr, while
fungi were incubated for 48 hr.
Synthesis of ML2
An ethanolic solution of L2 (10 mmol, 3.01 g) was
added to ethanolic solution of Ni(II) chloride
(10 mmol, 2.37 g) in 1:1 ratio with constant stirring
at 50ꢀC. The green precipitate of nickel complex
was obtained. This precipitate was washed several
times with acetone and diethyl ether and dried in
vacuum over CaCl2. The complexes from Co(II),
Mn(II), Zn(II), and Cu(II) chlorides were prepared
by the same method. Template synthesis also gave
the same products as obtained by the above
described method. Template synthesis was followed
by the addition of ethanolic solution of diethyloxa-
late to the ethanolic solution of L1 at 60ꢀC and stirred
for 10 hr. Instant precipitate was obtained by adding
metal chlorides to the above solution. All the proper-
ties of L2 and metal complexes prepared from both
the methods were found to be similar.
RESULTS AND DISCUSSION
The proposed analytical data of the complexes
with their colors are summarized in Table 1. The
thiosemicarbazone (L1) was obtained by the reaction
of glutraldehyde with thiosemicarbazide in the ratio
of 2:1. The L1 was refluxed and stirred with diethy-
loxalate (1:1 molar ratio), which yielded orange-
colored macrocyclic ligand (L2). The ligands L1 and
L2 were found to be soluble in ethanol and DMSO,
whereas all the synthesized metal complexes were
insoluble in common organic solvents except DMSO.
On heating of all the metal complexes, they under-
went decomposition and did not give a sharp melt-
ing point. The L2 and its metal complexes were
found to be stable in air. The molar conductance of
the metal complexes of Mn(II), Co(II), and Ni(II) fell
into the expected range in DMSO for nonelectro-
lytes, and that circumstance indicated the absence
of chloride ions, while the higher values of molar
conductance of Cu(II) and Zn(II) complexes showed
their electrolytic nature and confirmed the presence
of chloride ions outside the coordination sphere.
Physical Measurements
The IR spectra of the compounds were recorded
on PerkinElmer FTIR spectrometer, model 983
(PerkinElmer; United States), using KBr disc in the
range of 4000–200 cmꢁ1. The percentages of carbon,
hydrogen, and nitrogen of the ligands and the com-
plexes were determined by Elemental Analyzer
System GmBH varion, ELIII. The conductivity
measurements were carried out on a CM-82T Elico
conductivity bridge, and magnetic measurements
were done with a model 155 Allied Research vibra-
tion sample magnetometer at room temperature.
UV-visible spectra of the complexes were done on
a Lambda EZ201 spectrometer (PerkinElmer; United
IR Spectral Studies
The most relevant bands of the ligands and of their
metal complexes are tabulated in Table 2 with their
assignments. L1 and L2 exhibited strong IR bands at
1625 and 1629 cmꢁ1 (C¼N), respectively, which
were higher than those of metal complexes (1610–
1619 cmꢁ1). That is, on coordination, nC¼N shifts to
lower wavelength. The band of NH2 stretching was
found to be absent from L2 and all metal complexes,
but the band appeared in the L1 at 3280 cmꢁ1. The L1,
L2, and metal complexes exhibited a band in the
range of 3162–3150 cmꢁ1 assigned to nNH for second-
ary amine. The band’s appearance in range of
1
States) in DMSO. The HNMR spectra of L1, macro-
cyclic ligands, and the complexes were run in
DMSO-d6 on a Bruker Spectrospin DPX-300 MHz
Spectrometer (Bruker; United States). The thermo-
gravimetric analysis (TGA) of the compounds
was done by Perkin Elmer at 200-ml=min–flowing
467
Synthesis, Thermal Behavior, and Antimicrobial Activity

TABLE 1 Analytical Data, Color, Melting Point, Percentage Yield, and Molar Conductance of Ligands and the Metal Complexes
Compounds
(formula
weight)
Molar
Analysis % found (calcd.)
M.p. Yield %
Conductance ꢂ
Color
Red
(ꢀC)
(gm)
(Xꢁ1cm2 moleꢁ1
)
C
H
S
N
Cl
M
C7H14N6S2,
(L1)
230
68
—
—
34.24
5.68
25.79
33.95
—
—
(3.80)
(34.31)
(5.71) (25.95) (34.02)
(247.056)
ꢃ0.002 ꢃ0.005 ꢃ0.006 ꢃ0.002
C9H12N6O2S2, (L2) Orange
(301.258)
280
320
320
333
328
330
55
36.10
4.10
(4.01) (21.29) (27.89)
ꢃ0.008 ꢃ0.006
14.98 19.52
21.11
27.72
—
—
(2.16)
(36.18)
ꢃ0.002 ꢃ0.02
[MnL2Cl2]
(427.102)
Pale
73
12
25.70
2.80
16.49
12.76
yellow
(3.63)
(25.51)
(2.83) (15.01) (19.68) (16.60) (12.86)
ꢃ0.007 ꢃ0.010 ꢃ0.003 ꢃ0.008 ꢃ0.006 ꢃ0.007
[CoL2Cl2]
(431.097)
Dark
82
32
25.30
2.96
14.68
19.28
16.42
13.76
green
(4.41)
(25.28)
(2.80) (14.87) (19.49) (16.45) (13.67)
ꢃ0.000 ꢃ0.057 ꢃ0.012 ꢃ0.010 ꢃ0.002 ꢃ0.006
[NiL2Cl2]
(430.857)
Light
75
28
26.01
2.74
14.62
19.42
16.38
13.54
green
(4.03)
(25.29)
(2.80) (14.88) (19.50) (16.45) (13.62)
ꢃ0.028 ꢃ0.021 ꢃ0.017 ꢃ0.004 ꢃ0.004 ꢃ0.006
[CuL2]Cl2
(435.710)
Green
White
70
132
140
24.98
2.72
14.68
19.21
16.32
14.55
(3.29)
(25.01)
(2.77) (14.71) (19.29) (16.27) (14.58)
ꢃ0.001 ꢃ0.018 ꢃ0.002 ꢃ0.004 ꢃ0.003 ꢃ0.002
[ZnL2]Cl2
(437.554)
64
24.88
2.68
14.60
19.14
16.12
14.89
(2.79)
(24.90)
(2.76) (14.65) (19.20) (16.20) (14.94)
ꢃ0.000 ꢃ0.028 ꢃ0.003 ꢃ0.003 ꢃ0.005 ꢃ0.003
1655–1665 cmꢁ1 in L2 and metal complexes shows
the formation of oxamide group (NH-CO) from the
diethyloxalate.[14] The absence of NH2 group and
the presence of oxamide group in L2 are some of
the evidence for the formation of macrocycle. The
band observed at 1148 and 1153 cmꢁ1 in L1 and L2,
respectively, is attributed to nNꢁN. This band is
shifted to higher frequency in metal complexes, that
is, in the range of 1160–1163 cmꢁ1. This increase in
the frequency is due to the increase in the bond
strength and also confirms the coordination via
azomethine nitrogen.[15] The IR spectra of L1, L2,
and all the metal complexes showed a band in the
region 2920–2929 cmꢁ1 due to the CH2 stretching
frequency. The frequency of nC¼S band lies in the
range of 848–855 cmꢁ1 in L2 and metal complexes.
The band observed in the spectra of L1, L2, and
metal complexes in the range of 1313–1328 cmꢁ1
is attributed to dC¼S, that is, deformation of C¼S
group. The bands in the ranges of 440–457 cmꢁ1
and 328–350 cmꢁ1 are assigned to M-N and M-Cl,
respectively.[16]
TABLE 2 Characteristic IR Bands (cmꢁ1) of the Ligands and the Complexes
=
n(C O)
=
=
Compounds
n(N-H)
n=d(C S)
(oxalate group)
n(C–H)
n(C N)
n(N-N)
n(M–N)
n(M–Cl)
Ligand (L1)
Macrocycle (L2)
[MnL2Cl2]
[CoL2Cl2]
—
1328, 868
1326, 855
1314, 851
1316, 849
1316, 849
1314, 850
1315, 848
—
2929 s
2923
1629 s
1625 s
1615 s
1619 s
1619 s
1611 s
1610 s
1148
1153
1160
1160
1161
1163
1162
—
—
—
3162 m
3155 m
3150 m
3152 m
3158 m
3154 m
—
—
1654
1662
1657
1665
1657
2921 s
2920 s
2920 s
2920 s
2921 s
447 s
457 s
455 s
442 s
450 s
350 s
335 s
330 s
—
[NiL2Cl2]
[CuL2]Cl2
[ZnL2]Cl2
—
Note. m, medium; s, strong.
N. Nishat et al.
468

TABLE 3 1H NMR Spectra of the Ligands (L1 and L2) and the Zn Complex of L2 d (ppm)
=
Compound N CHꢀ(4H) ꢀ(CH2)2ꢀ(2H) ꢀ(CH2)ꢀ(4H) ꢀCSNH2 (2H) ꢀCONHꢀ(2H) N-NH (2H)
L1
(2.55)t
(2.54)t
(2.55)t
(3.57)m
(3.57)m
(3.58)m
(8.14)s
—
—
(9.64)s
(9.81)s
(9.94)s
(7.58)d
(7.62)d
(7.90)d
L2
(8.80)s
(8.87)s
[ZnL2]Cl2
—
Note. s, singlet; d, doublet; t, triplet; m, multiplet.
1HNMR Spectra
Electronic Spectra
1
The HNMR spectrum of L1, L2, and Zn complex
The magnetic moment and the significant electro-
nic absorption bands with various ligand field
parameters of Co, Ni, Mn, Zn, and Cu complexes
are given in Table 4. The magnetic moment for the
Co(II) complex (4.53 B.M.) was found to lie in
the range of octahedral complexes. The cobalt com-
plex displayed two bands at 8855 and 20219 cmꢀ1
and a shoulder at 14814 cmꢀ1, which may be
1
is described in Table 3. The HNMR spectra of L1
and L2 gave a CH¼N signal at 7.58 and 7.62 ppm,
which shifted downfield in the Zn complex at
7.90 ppm due to the complexation of nitrogen with
metal ions.[17] The spectra of L1 showed the –NH2
protons at 8.14 ppm,[18] which shifted downfield
in the spectra of L2 (i.e., 8.80 ppm due to the for-
mation of oxamide group).[12] In Zn complex, this
peak placed at 8.87 ppm due to the complexation
of –NH with metal. The peak of N-NH for L1, L2,
and the Zn complex appeared in the range of
9.64–9.94 ppm.[19] This peak was found to shift
downfield in case of Zn complex due to the com-
plexation of nitrogen with metal. The spectra of L1,
L2, and Zn complex displayed a quadrate in
the range of 2.55–2.56 ppm, which we attributed
to –CH2 protons. A multiplet also appeared in all
the spectra in the range of 3.57–3.58 ppm due to
the presence of -CH2, having different environment
from the former.
4
assigned to T2g(F) 4T1g (t1),4T1g(P) 4T1g (t3),
4
and A2g 4T1g (t2) transitions, respectively,[20] cor-
responding to six-coordinated octahedral geometry.
The b value indicated that the complex exhibited
61%-covalent character. The electronic spectra of
Ni(II) complex showed two bands at 12036 and
16000 cmꢀ1 and
a
charge transfer band at
24390 cmꢀ1. The bands indicated that the complex
revealed an octahedral geometry.[21] The ground
state of Ni (II) in an octahedral coordination was
found to be 3A2g. Thus, three spin-allowed transitions
3
are T2g(F) 3A2g(F) (t1),3T1g(F) 3A2g(F) (t2), and
3T1g(P) 3A2g(F) (t3). The magnetic moment of
TABLE 4 Electronic Spectral Bands and Magnetic Moments of the Macrocyclic Complexes
Compound Magnetic moment (B.M.) Electronic bands (cmꢀ1 Possible assignment ea 10 Dq (cmꢀ1
)
)
(B) (cmꢀ1
582
)
b
[MnL2Cl2]
[CoL2Cl2]
[NiL2Cl2]
[CuL2]Cl2
5.88
28655
24572
17610
4Eg(4D) 6A1g
4Eg(4G) 6A1g
4T1g(4 G) 6A1g
4T1g(P) 4T1g(F)
4A2g(F) 4T1g(F)
4T2g(F) 4T1g(F)
3T1g(P) 3A2g(F)
3T1g(F) 3A2g(F)
3T2g(F) 3A2g(F)
12
15
10
1754
1067
12011
—
0.60
4.53
20219
14814
8855
15
11
13
689
751
—
0.71
0.69
—
2.98
24390
16000
12036
18
14
15
1.73
23980
17500
11110
Charge transfer
2A1g 2B1g
2Eg 2B1g
14
12
10
[ZnL2]Cl2
Diamagnetic
—
—
—
—
—
—
ae ¼ dm3 molꢀ1 cmꢀ1
.
469
Synthesis, Thermal Behavior, and Antimicrobial Activity

TABLE 5 Thermal Properties of Ligands (L1 and L2) and Their Metal Complexes
Weight loss (%) at given temperature (ꢀC)
% wt at
Compounds
100
200
300
400
500
600
700
800ꢀC
L1
7
5
3
14
11
9
40
38
35
55
55
55
68
63
57
75
70
65
78
76
70
20
23
27
L2
[NiL2Cl2]
nickel complex was 2.95 B.M., which showed the pre-
sence of two unpaired electrons.
Mass Spectra
The FAB mass spectrum of Cu(II) complex
The Cu(II) complex exhibited bands at 11110,
17500, and 23980 cmꢁ1, corresponding to square
planar geometry.[22] The first two bands were
showed a molecular ion peak mnz at 437.34 amu,
which confirms the stoichiometry of metal com-
plex as [ML2]Cl2 type. It also showed a peak at
72.01 amu, which probably corresponding to free
chlorine. The mass spectra of other metal complexes
support the described stoichiometry. This stoichio-
metry was further supported by the elemental
analysis of the complexes. The mass spectrum of
macrocyclic ligand (L2) confirmed the probable
formula by showing a peak at 302.588 amu corre-
sponding to the molecular ion (Mþ þ 1).
2
2
assigned to Eg 2B1g and A1g 2B1g transitions,
respectively. The third band was probably envel-
oped into a strong charge transfer band. The band
at 22220–26040 cmꢁ1 in the spectra of complexes
was observed due to ligand metal charge transfer
(LMCT).[23] The Mn(II) complex showed a mag-
netic moment corresponding to five unpaired elec-
trons (5.88 B.M.), which indicated the presence of
high spin in case of Mn(II). The electronic
spectral bands of the complex possessed weak
absorption bands at 17610, 24572, and 28655 cmꢁ1.
Thermal Studies
4
These bands were assigned to T1g(4G) 6A1g,
The thermogravitric results are given in Table 5.
The thermogravimetric studies of L1, L2, and metal
complexes showed weight loss in the temperature
range of 100–200ꢀC due to the elimination of
entrapped moisture. L1 showed 7% weight loss in
this region, while L2 as well as all metal complexes
showed about 6 wt% loss in the same range.
The coordinated and noncoordinated chlorine in
all the metal complexes were eliminated in the
4
4Eg(4G) 6A1g, and Eg(4D) 6A1g, respectively.[24]
This result corresponded to octahedral geometry of
Mn(II) complex. The calculated value of b indicated
that the complex had appreciable covalent character.
The Zn(II) complex was diamagnetic as expected for
a d10 electronic configuration and was found to be
tetrahedral as indicated by elemental analysis and
spectral data.
TABLE 6 Antibacterial and Antifungal Activity of Macrocyclic Ligand and Complexes: Zone of Inhibitiona (in
mm) at 50 mg/ml Concentration
Compounds
S. aureus
E. coli
B. subtillis
S. typhimurium
F. oryzae
C. albicans
Ligand (L2)
[MnL2Cl2]
[CoL2Cl2]
[NiL2Cl2]
10 ꢃ 3
11 ꢃ 2
18 ꢃ 2
15 ꢃ 3
18 ꢃ 2
10 ꢃ 2
29
—
9 ꢃ 2
18 ꢃ 2
14 ꢃ 3
20 ꢃ 2
22 ꢃ 2
24 ꢃ 2
31
10 ꢃ 2
14 ꢃ 2
16 ꢃ 2
16 ꢃ 3
20 ꢃ 2
11 ꢃ 2
31
—
15 ꢃ 2
12 ꢃ 2
24 ꢃ 2
15 ꢃ 3
20 ꢃ 2
—
11 ꢃ 2
19 ꢃ 2
12 ꢃ 2
11 ꢃ 2
19 ꢃ 2
12 ꢃ 2
—
15 ꢃ 3
20 ꢃ 2
18 ꢃ 3
15 ꢃ 2
12 ꢃ 2
32
[CuL2]Cl2
[ZnL2]Cl2
Kanamycin
Miconazole
—
—
—
—
31
28
aIncluding disc diameter.
N. Nishat et al.
470

SCHEME 1 Synthesis of ligands (L1 and L2).
temperature range of 250–350ꢀC, which showed
approximately 16.80 wt% loss. The organic and
inorganic parts of the L2 and metal complexes
decomposed up to 700ꢀC, and after this tempera-
ture, negligible weight loss was observed. The
metal complexes decomposed to their metal oxides
in the temperature range of 780–800ꢀC. During the
study of thermogravimetric curves, we found that
L1 and L2 showed high weight loss in almost every
step in comparison to all metal complexes and that
the metal complexes were more thermally stable
than L1 and L2.
FIGURE 2 1HNMR of L2.
471
Synthesis, Thermal Behavior, and Antimicrobial Activity

FIGURE 3 1HNMR of Zn Complex.
Antimicrobial Activity
The macrocyclic ligands and its transition metal
complexes were screened against four bacteria and
two fungi with respect to kanamycin (antibacterial)
and miconazole (antifungal) as standard drug. The
antifungal and antibacterial activity was carried out
by agar disc diffusion method. The results shown
in Table 6 revealed that the metal complexes
exhibited higher activity as compared with the
macrocyclic ligand due to the chelation of the metal
ion in the complexes. The chelation was found to
enhance the lipophillic character of central metal
ion, which subsequently favored its permeation
through the lipid layer of all membrane. The maxi-
mum bacterial and fungal inhibition was exhibited
by Zn(II) complex.
FIGURE 4 TGA of L1, L2 and its Nickel complex.
CONCLUSION
A novel macrocycle derived from thiosemicaba-
zone (L1) and diethyloxalate that was prepared by
the reaction of thiosemicarbazide and glutaraldehyde
in the ratio of 2:1. The Co(II), Ni(II), Mn(II), Cu(II),
and Zn(II) complexes with a new macrocyclic ligand
(L2) – 1,2,8,9,11,14-hexaazacyclopentadeca-12,13-
dioxo-10,15-dithione-2,7-diene were characterized
by elemental analysis, molar conductance measure-
ments, magnetic susceptibility measurements,
1HNMR spectra, IR spectra, electronic spectra, and
FIGURE 5 Suggested structures of the metal complexes with
ligand [L2].
N. Nishat et al.
472

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cadmium(II), uranium(VI), thorium(IV) and silicon(IV). Ind. J. Chem.
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The authors sincerely thank Third World Academy
of Sciences, Italy, for U.V.=Visible spectrophotometer
EZ-201 (PerkinElmer, United States) through
research grant 00-047RG=CHE=AS.
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