КООРДИНАЦИОННАЯ ХИМИЯ, 2009, том 35, № 5, с. 336-340
УДК 541.49
SYNTHESIS, SPECTROSCOPIC, AND ANTIMICROBIAL STUDIES OF THE BIVALENT ZINC AND MERCURY COMPLEXES OF THIOSEMICARBAZIDE
© 2009 S. Chandra1, S. Parmar2*, and Y. Kumar2
1 Department of Chemistry, Zakir Husain College, University of Delhi, Jawaharlal Nehru Marg, New Delhi 110002, India 2 I T S. Paramedical College (Pharmacy), Delhi Meerut Road, Muradnagar, Ghaziabad 201206, India * E-mail: parmarshikha@yahoo.com, its.phmc@gmail.com, schandra_00@yahoo.com
Received June 11, 2008
A series of metal complexes of Zn(II) and Hg(II) having the general composition [ML2]X2 with thiosemicarbazide have been prepared and characterized by elemental chemical analysis, molar conductance, and spectral (IR and mass) studies. The IR spectral data suggest the involvement of sulfur and terminal amino nitrogen in coordination to central metal ion. On the basis of spectral studies, a tetrahedral geometry has been assigned for the Zn(II) and Hg(II) complexes. Thiosemicarbazide and its metal complexes have been tested in vitro against a number of microorganisms in order to assess their antimicrobial properties.
INTRODUCTION
Sulfur compounds have been the subject of interest in coordination chemistry. Thiosemicarbazide-based compounds have been extensively studied over the last couple of decades [1-3]. The various Schiff bases of thiosemicarbazide (thiosemicarbazones) and their corresponding complexes have attracted much attention due to their wide biological activities, such as antitumor [4], antibacterial [5], and antifungal activities [6]. Coordination of these com-
pounds with metal ions, such as copper, nickel, and iron, often enhances their activity [7-9]. Although in recent years a number of structures of thiosemicarbazone complexes have been reported, there have been few structures of the precursor thiosemicarbazides or their complexes [10]. Thiosemicarbazide is an ambidentate ligand capable of forming five-membered metallocycles (A, B) during coordination or monodentate bonding (C) through sulfur as shown below [11]:
H_ N
/
H2N
NH2
I 2
-C
»
S
-C
M
(A)
/ \
M
NH
NH2
II 2
C
H2N
/ w
S
(B)
M
(C)
In view of the above applications, the present work relates to the synthesis, spectroscopic, and antimicrobial studies of the Zn(II) and Hg(II) complexes of thiosemicarbazide.
EXPERIMENTAL
All the chemicals were of analytical grade and were procured from Sigma Aldrich and Fluka. Metal salts were purchased from E. Merck and used as received.
Synthesis of complexes. A hot ethanolic solution (20 ml) of thiosemicarbazide (1.8 g, 0.02 mol) and a hot ethanolic solution (20 ml) of the corresponding metal salt (0.01 mol) were refluxed for 3-4 h at 60°C. On cooling colored complexes were precipitated out. They were fil-
tered off, washed with 50% ethanol, and dried under vac-cum over P4O10.
The C, H, and N were analyzed on a Carlo-Erba 1106 elemental analyzer. The nitrogen content of the complexes was determined using Kjeldahl's method.
Molar conductance was measured with the ELICO (CM82T) conductivity bridge. The electronic impact mass spectrum was recorded on a JEOL, JMS-DX-303 mass spectrometer. IR spectra (KBr) were recorded on a FTIR spectrum BX-II spectrophotometer. The molecular weights of the complexes were determined cryoscopically in benzene.
In vitro antimicrobial screening was performed by the agar disc diffusion method [12, 13]. All the test organisms were obtained from Microbial Type Culture
S
SYNTHESIS, SPECTROSCOPIC, AND ANTIMICROBIAL STUDIES OF THE BIVALENT ZINC Table 1. Elemental analysis data and physical properties of the complexes
Complex
Atomic mass found (calcd)
Yield,%
Color
M.p.,°C
Contents (found/calcd), %
C
[Zn(L)2]Cl2 318(320) 74 White 185 7.54/7.35 3.14/3.32 26.41/25.31 20.40/20.55
[Zn(L)2](NO3)2 372(371) 60 White 240 6.45/6.56 2.68/2.51 30.10/30.27 17.47/17.40
[Zn(L)2]SO4 344(345) 61 White 180 6.97/6.80 2.90/2.97 24.41/24.63 18.89/18.79
[Hg(L)2]Cl2 453(454) 80 White 220 5.29/5.33 2.20/2.12 18.54/18.58 44.37/44.39
[Hg(L)2](NO3)2 507(506) 60 Brown 190 4.73/4.65 1.97/1.91 22.09/22.20 39.64/39.71
[Hg(L)2]SO4 479(478) 54 Mustard 180 5.01/5.12 2.08/2.04 17.53/17.64 41.96/41.81
H
N
M
Table 2. IR spectral data of the metal complexes
Compound Vas(NH2) Vs(NH2) S(NH2) v(C=S) v(M-N) v(M-S)
CH5N3S (L) 3365 3263 1642 800
[Zn(L)2]Cl2 3338 3247 1633 675 430 350
[Zn(L)2](NO3)2 3355 3158 1632 700 431 360
[Zn(L)2]SO4 3300 3153 1617 700 486 380
[Hg(L)2]Cl2 3330 3255 1628 700 443 390
[Hg(L)2](NOs)2 3341 3258 1624 678 458 390
[Hg(L)2]SO4 3344 3342 1623 699 408 340
Collection and Gene Bank (Institute of Microbial Technology, Chandigarh, India). The sterile discs impregnated with the test compounds were placed on the seeded plates. The zone of inhibition around the disc indicated the antimicrobial activity of the test compounds.
RESULTS AND DISCUSSION
The complexes were synthesized by reacting thiosemi-carbazide with metal ion in a 2 : 1 molar ratio in an ethan-olic medium. The ligand behaves as bidentate and coordinates through the terminal N and S atoms. Elemental anal-
ysis of the complexes corresponds to the composition as shown in Table 1. The molar conductance measurements of the complexes in DMF lie in a range of 116— 138 Ohm1 cm2 mol1, indicating their 1 : 2 electrolytic behavior. Thus, the complexes may be formulated as [M(L)2]X2, (where M = Zn(II) and Hg(II); L = thio-
semicarbazide, X = Cl-, NO3 and 1/2 SO^- ). The
complexes containing SO;j- and NO3 are produced in the cis form (D), while the trans form (E) is obtained when Cl- is the anion as shown below:
H2 H2
HN N NH
I M I
H2N
(D)
NH2
X9
H2NWS^
H2 .Ns
Cr ^ ^ NH
C M I H2
(E)
X9
All complexes are diamagnetic.The assignments of the significant IR spectral bands of thiosemicarbazide and its metal complexes are presented in Table 2. Ideally, five N-H stretching frequencies would be expected in thiosemicarbazide in a high-frequency region of 3400-3000 cm-1. The band due to vas(NH2) at 3365 cm1 in thiosemicarbazide is shifted to lower frequencies in the complexes. Thiosemicarbazide has two bands at 1642 and
1619 cm-1. The former is the deformation mode, 5(NH2), of the amine in the hydrazine residue, and the latter is the amide II band of the primary amine. These bands shift toward lower frequencies due to the involvement of one of the group NH2 in coordination. Strong evidence is the appearance of a 430-459 cm-1 band due to v(M-N). Strong band at 800 cm-1 assigned to C=S stretching vibration shifts to lower frequencies in the complexes, indicating the
2 KOOP,n,HHAU,HOHHAü XHMHü tom 35 < 5 2009
65 60 55 50 ^ 45 40 35 30
26.5
4400
3000
2000
1500
1000
v, cm
400
1
Fig. 1. IR spectra of cis-[Zn(L)2]SO4
75 70 65 60
- 55 -
50 45 40
35
31.1
4400
3000
2000
1500
1000
400
v, cm
-1
Fig. 2. IR spectra of trans-[Zn(L)2]Cl2.
involvement of thioketo sulfur in complex formation. In each complex, two thiosemicarbazide ligands coordinate to the central metal ion through two terminal hydrazine N atoms and two S atoms. Thus, it is concluded that the ligand acts as a bidentate chelating agent.
The infrared spectra of the cis and trans complexes show marked differences in certain regions of the spectrum (Figs. 1 and 2). The trans isomers show two sharp strong bands in a frequency region of 3400-3000 cm-1. The cor-
responding cis isomers show only broad bands throughout this region. In the region around 1600 cm-1 corresponding to NH2 bending modes, two sharp bands are observed for the trans isomer, while a single broad band is observed for the cis isomers [14].
The infrared spectra of the nitrate complexes show a sharp band at 1384 cm-1 characteristic of the uncoordinated nitrate group [15]. The IR bands in the region of 1408-1426 and 615-622 cm-1 characteristic of the unco-
КООРДИНАЦИОННАЯ ХИМИЯ том 35 № 5 2009
SYNTHESIS, SPECTROSCOPIC, AND ANTIMICROBIAL STUDIES OF THE BIVALENT ZINC 339 Table 3. Antibacterial screening data of thiosemicarbazide and its complexes
Diameter of zone of inhibition, mm
Compound Mg/disc gram positive gram negative
Staphylococcus aureus Staphylococcus epidermidis Escherichia coli Pseudomonas aeruginosa
CH5N3S (L) 100
[Zn(L)JCl2 100 10 08 09
[Zn(L)2](NO3)2 100 09 08 08 07
[Zn(L)2]SÜ4 100 09 07
[Hg(L)JCl2 100 26 24 22 22
[Hg(L)2](NÜ3)2 100 24 25 18 20
[Hg(L)2]SÜ4 100 23 22 16 14
Amikacin 30 26 22 21 20
ordinated sulfate group are seen in the infrared spectra of the sulfate complexes [16]. However, no v(M-Cl) band is observed in the spectrum of the [M(L)2]Cl2 complexes, suggesting that the chloride is ionic [17].
The antimicrobial screening data show that thiosemicarbazide does not exhibit antimicrobial properties. From Tables 3 and 4, it is clear that the Zn(II) and Hg(II) complexes exhibit antibacterial and antifungal activities. The antimicrobial data of the Hg(L)2Cl2 complexes are very similar to those of standard antibacterial amikacin and an-tifungal nystatin. The increased activity of the metal che-lates can be explained on the basis of the chelation theory [18]. It is known that chelation tends to make the ligand act as more powerful and potent bactericidal agents. It is observed that in a complex the positive charge of metal is partially shared with the donor atoms present in the ligands and there may be n-electron delocalization over the whole chelating. This increases the lipophilic character of the metal chelate and favors its permeation through the lipoid layer of the bacterial membranes. There are other factors which also increase the activity, namely, solubility, conductivity, and bond length between the metal and ligand.
Table. 4. Antifungal screening data of thiosemicarbazide and its complexes
Compound Mg/disc Diameter of zone of inhibition, mm
Candida albicans Aspergillus niger
CH5N3S ligand(L) 200
[Zn(L)2]Cl2 200 08
[Zn(L)2](NÜ3)2 200 08 08
[Zn(L)2]S
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