Microwave-assisted synthesis, characterization and biological activities of organotin (IV) complexes with some thio Schiff bases

Article abstract of DOI:10.1016/j.saa.2008.09.017

Microwave-assisted synthesis and characterization of the organotin (IV) complexes are reported. Trigonal bipyramidal and octahedral complexes of tin (IV) have been synthesized by the reaction of dimethyltin (IV) dichloride with 4-nitrobenzanilide-S-benzyl

Full text of DOI:10.1016/j.saa.2008.09.017

Spectrochimica Acta Part A 72 (2009) 260–268
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Microwave-assisted synthesis, characterization and biological activities of
organotin (IV) complexes with some thio Schiff bases
Ran Vir Singh∗, Pratibha Chaudhary, Shikha Chauhan, Monika Swami
Department of Chemistry, University of Rajasthan, Jaipur 302004, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Microwave-assisted synthesis and characterization of the organotin (IV) complexes are reported.
Trigonal bipyramidal and octahedral complexes of tin (IV) have been synthesized by the reaction of
dimethyltin (IV) dichloride with 4-nitrobenzanilide-S-benzyldithiocarbazate (L1H), 4-chlorobenzanilide-
S-benzyldithiocarbazate (L2H), 4-nitrobenzanilidebenzothiazoline (L3H) and 4-chlorobenzani-
lidebenzothiazoline (L4H). The complexes so formed were characterized by elemental analysis,
conductance measurements, molecular weight determinations and spectral data viz. IR, UV–Visible,
1H and 13 C NMR. The anti-microbial activities of the ligands and their corresponding organotin (IV)
complexes have been screened against various strains of bacteria and fungi. Antifertility activity against
male albino rats has also been reported.
Received 27 April 2008
Received in revised form
14 September 2008
Accepted 26 September 2008
Keywords:
S-Benzyldithiocarbazate
Benzothiazoline
Spectral studies
Anti-microbial activity
Organotin (IV) complexes
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
Organotin (IV) complexes have been the subject of interest for
some time because of their biomedical and commercial applica-
Microwave-mediated synthesis is a fast growing area of research
interest as evidenced by the increasing numbers of papers and
patents published in the area [1,2]. This is because it is often possible
to reduce reaction times from many hours to a few minutes and it is
also opening up avenues for new chemistry [3]. The main advantage
of microwave heating is the almost instantaneous ‘in-core’ heating
of materials in a homogenous and selective manner.
The number and diversity of nitrogen and sulfur chelating agents
used to prepare new coordination and organometallic compounds
has increased rapidly during the past few years [4–10]. The dithio-
carbazate (NH2NHCS2-) and its substituted derivatives have been
investigated [11–20]. These compounds have received much atten-
tion and for further studies because (i) they provide an interesting
series of ligands whose properties can be greatly modified by intro-
ducing different organic substituents, thereby causing a variation
in the ultimate donor properties, (ii) the interaction of these donors
with metal ions gives complexes of different geometries and prop-
erties, and (iii) these complexes are potentially biologically active.
Keeping this in view, it was considered worthwhile to synthesize tin
complexes of some stereochemical as well as biological importance.
tions [21]. It has been observed that several organotin complexes
are effective antifouling [22], anti-microbial [23] and antiviral
agents. They are also used commercially as bactericides, fungicides,
acaricides; industrial and agriculture biocides [24]. Increasing
attention has also been devoted to the organotin (IV) complexes
with Schiff base ligands in view of their special anti-tumor activities
[25–33]. In addition to their anti-tumor activities, organotin (IV)
complexes with Schiff bases present an interesting variety of struc-
tural possibilities [34]. As an extension of the studies of organotin
(IV) complexes with Schiff bases [35,36], we have now synthesized
eight organotin (IV) complexes with Schiff bases of dithiocarbazate
and benzothiazoline. The importance of microwave-assisted syn-
thesis and versatile usage of organotin (IV) compounds prompted
us to report simple, environmentally benign and facile methodol-
ogy for the synthesis of organotin derivatives and screen them for
their antibacterial, anti-fungal and antifertility activities.
2. Experimental
2.1. Analytical methods and physical measurements
The reagents 4-nitrobenzanilide (Aldrich), 4-chlorobenzanilide
(Aldrich), 4-aminothiophenol (Merck) and dimethyltin (IV) dichlo-
ride (Merck) were commercial products and were used as received.
S-Benzyldithiocarbazate was prepared as described previously [37].
All the reagents used were of AR grade and the solvents used were
∗
Corresponding author. Tel.: +91 141 2704677/9414069753/9314109388;
fax: +91 141 2704677.
E-mail addresses: rvsjpr@hotmail.com, prats20@yahoo.co.in (R.V. Singh).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.09.017

R.V. Singh et al. / Spectrochimica Acta Part A 72 (2009) 260–268
261
dried, distilled and purified by the standard methods. The reactions
were carried out under strict anhydrous conditions and adequate
care was taken to keep the organotin (IV) complexes, chemicals
and glass apparatus free from moisture. The elemental analysis
was carried out on an Elementar Analysensysteme GmbH Varion EL
III, Germany at University Scientific Instrumentation Center, Delhi
University, Delhi. Nitrogen and Sulfur were determined by the Kjel-
dahl’s and Messenger’s method, respectively [38]. The electronic
spectra were recorded on Hitachi-U-2000 spectrophotometer. Tin
was estimated gravimetrically as SnO2 and chlorine was esti-
mated volumetrically by Volhard’s method [39]. The Rast Camphor
Method was used to carry out the molecular weight determina-
tions. IR and far IR spectra were recorded on KBr and polyethylene
discs, respectively using a PerkinElmer Spectrum 2000 FTIR spec-
trophotometer and 1H and 13C NMR spectra were recorded on a
Bruker Spectrospin Advance 300 spectrometer at Delhi University,
Delhi.
ate nutrient medium (0.5% peptone, 0.15% yeast, 0.15% beef extract,
0.35% sodium chloride and 0.13% KH2PO4 in 1000 cm3 distilled
water was autoclaved for 20 min at 15 psi before inoculation) pre-
viously seeded organisms in Petri dishes and stored in an incubator
at 28 ◦C. The inhibition zone thus formed around each disc was
measured (in mm) after 24 h.
2.2.3. Anti-fertility activity
The activity of synthetic products towards biological systems is
an important feature of current research and S and N donor Schiff
bases play a significant role in this direction. A large number of
organotin (IV) complexes have been shown to cause atrophy of the
testis, prostate and epididymis in male mice. In view of the poten-
tial interest in these biologically active compounds, the antifertility
activity of some selected Schiff bases and their corresponding
organotin (IV) complexes has been studied in male rats. The colony
bred adult male albino rats (body weight 180–200 g) were used
and 100 rats were divided randomly into 10 groups of 10 animals
each. The animals were kept in plastic cages 25 cm × 40 cm × 40 cm
and only ten animals were housed in a cage. The animals were
maintained on rat feed pellets (Hindustan Lever Ltd., India) and tap
water was provided ad libitum. Only nine compounds were used
separately and each compound was administered at a dose level of
2 mg day−1 kg−1 body weight orally by gavage tube for 60 days. One
group was served as control and each animal of this group received
0.5 mL olive oil per day orally. After 24 h of last administration 10
animals from each group were autopsied and reproductive organs
were dissected out, freed from adherent tissues and weighed up
to the nearest milligram. The sperm motility in cauda epididymis
and sperm count in cauda epididymis and testes were measured by
using Neubaur’s hemocytometer according to the reported method
[42].
2.2. Anti-microbial studies
2.2.1. Anti-fungal studies
Bioefficacies of the synthesized compounds were checked
in vitro. The in vitro anti-fungal activities of the ligands and
their complexes have been evaluated against two pathogenic
fungi, Penicillium crysogenes and Rhizoctonia phaseoli by the
agar plate technique [40]. The compounds were directly mixed
with the medium in 0.01% and 0.1% (in methanol) concentra-
tions. Controls were also run and three replicates were used
in each case. The linear growth of the fungus was obtained
by measuring the diameter of the fungal colony after four
days. The amount of growth inhibition in each of the replicate
was calculated by, percentage inhibition = (C − T) × 100/C, where
C = diameter of the fungus colony in the control plate after 96 h and
T = diameter of the fungus colony in tested plates after the same
period.
2.3. Preparation of the ligands
Two different routes were employed for the synthesis of the lig-
ands for comparison purposes. These are the microwave-assisted
synthesis and the thermal method. The microwave irradiations
were carried out in a Samsung domestic microwave oven, model
G2719N at 160 W. A comparison between thermal method and
microwave method has been given in Table 1.
2.2.2. Anti-bacterial activity
For the evaluation of degree of inhibitory effects on the growth
of a wide spectrum of microorganisms antibacterial activity was
performed against two Gram-positive (Bascillus subtills and Staphy-
lococcus aureus) and two Gram-negative (Pseudomonas aeruginosa
and Salmonella typhi) bacteria and the results are summarized in
Table 7. In order to compare the results obtained the Imipinem
was used as standard drug. Determination of the antibacterial
activity was carried out by the paper-disc plate method [41]. The
compounds were dissolved in DMF at 500 and 1000 ppm concen-
trations. All the Whatman No. 1 paper with a diameter 5 mm were
soaked in these solutions. These discs were placed on the appropri-
2.3.1. Microwave-assisted synthesis of L1H and L2H
The ligands were prepared by the condensation of S-
benzyldithiocarbazate (4.4 g, 22 mmol) with 4-nitrobenzanilide
(5.3 g, 22 mmol) in case of (L1H) and 4-chlorobenzanilide (5.0 g,
22 mmol) in case of (L2H) in presence of a few drops of ethanol
(∼4.0 mL) respectively and irradiated by the microwave irradiation
Table 1
Comparison between conventional and microwave methods of synthesis.
Compound
Yield (%)
Thermal
Solvent (mL)
Time
Microwave
Thermal
Microwave
Thermal (h)
Microwave (min)
L1H
84
81
84
80
76
73
71
73
72
73
69
70
89
90
–
100
100
100
100
40
40
40
50
40
4
3
–
–
2
3
3
2
3
2
3
2
4.5
4
3.5
4
15
16
14
13
16
13
14
17
8
6
–
–
8
6
5
5
4
6
6
4
L2H
L3H
L4H
–
Me2Sn(L1)Cl
Me2Sn(L1)2
Me2Sn(L2)Cl
Me2Sn(L2)2
Me2Sn(L3)Cl
Me2Sn(L3)2
Me2Sn(L4)Cl
Me2Sn(L4)2
84
82
87
86
85
87
85
84
50
40
50

262
R.V. Singh et al. / Spectrochimica Acta Part A 72 (2009) 260–268
Fig. 1. Synthesis of L1H and L2H.
for nearly 8 min. The resulting precipitate was then recrystal-
lized with alcohol and dried under vacuum (Fig. 1). The analytical
results came in good consistence with the proposed formulae as
follows:
2.3.3. Conventional thermal method
Similar procedure was followed for the synthesis by the thermal
method where instead of few drops of alcohol the starting materials
of the ligands were dissolved ∼100 mL of alcohol and the contents
were refluxed for nearly 4.5 h. The solution was then concentrated
under reduced pressure, which on cooling gave white or yellow
crystalline precipitates. These were recrystallized twice in alcohol.
L1H: (C21H18 N4O2S2, 422.529); yellow green; M. Pt., 144–148;
yield = 84%; C, 59.69(59.35); H, 4.29(3.98); N, 13.26(13.01); S,
15.18(14.94).
L2H: (C21H18 N3ClS2, 411.977); creamy white; M. Pt., 132–135;
yield = 81%; C, 61.22(59.97); H, 4.40(4.16); N, 10.19(9.94); S,
15.56(15.34); Cl, 8.60(8.41).
2.3.4. Preparation of the sodium salts of the ligands
Sodium metal was taken in equimolar ratio of the ligand. Now
sodium metal and ligand were dissolved in minimum amount of
methanol separately. Ultimately these two solutions had been dis-
solved to prepare sodium salt of the ligand. In this process the
sodium metal first react with methanol and form sodium methox-
ide and hydrogen gas removed. This sodium methoxide in the next
step reacts with the ligand and replaces acidic proton from the eno-
lic form of the ligand with sodium metal and forms salt of the
particular ligand. We can use the ligand as such but the rate of
reaction will be slow as compare to the sodium salt. Removal of
chloride from the metal chloride is easy with sodium as compare
to hydrogen (Fig. 3).
2.3.2. Synthesis of L3H and L4H by simple stirring method
The ligands were prepared by the condensation of ethanolic
solution of 2-aminothiphenol (3.0 g, 24 mmol) with ethano-
lic solution of 4-nitrobenzanilide (5.8 g, 24 mmol) in case
of (L3H) and ethanolic solution of 4-chlorobenzanilide (5.6 g,
24 mmol) in case of (L4H) respectively with the help of
simple stirring on magnetic stirrer for 3–4 h. The resulting
precipitate was recrystallized with alcohol and dried under
vacuum (Fig. 2).
L3H: (C19 H15N3O2S, 349.412); light yellow; M. Pt., 136–139;
yield = 84%; C, 65.31(65.09); H, 4.33(4.04); N, 12.02(11.81); S,
9.17(8.96).
2.4. Preparation of the complexes
2.4.1. Microwave method
L4H: (C19 H15N2ClS, 338.860); off-white; M. Pt., 121–124;
yield = 80%; C, 67.35(67.12); H, 4.46(4.23); N, 8.26(8.02); Cl,
10.46(10.22); S, 9.46(9.20).
The reactions of dimethyltin (IV) dichloride with the corre-
sponding sodium salt of the ligands (L1H, L2H, L3H and L4H)
were carried out in equimolar and bimolar ratios, using 2–3 mL of
Fig. 2. Synthesis of ligands L3H and L4H.

R.V. Singh et al. / Spectrochimica Acta Part A 72 (2009) 260–268
263
Fig. 3. Preparation of sodium salts of the ligands L1–4H.
Fig. 4. Preparation of 1:1 and 1:2 metal complexes.
methanol as solvent in a microwave oven for ∼8 min. The product
recovered from the microwave oven and dissolved in few milliliters
of dry methanol; the white precipitate of NaCl formed during the
course of the reaction was removed by filtration and the filtrate was
dried under reduced pressure. The resulting products were repeat-
edly washed and dried with n-hexane and petroleum ether and
finally dried at 40–60 ◦C/0.5 mmHg for3–4 h (Fig. 4).
2.4.2. Thermal method
In the thermal method instead of 4–8 min reactions were com-
pleted in 13–15 h and the reaction mixture was refluxed for about
14–17 h over a distillation assembly fitted with quick fit inter-
changeable joints, and the white precipitate of sodium chloride
obtained, was removed by filtration. The mother liquor was concen-
trated by removing the excess of solvent. Compounds were dried
under reduced pressure for 3–4 h. These were purified by the same
process as described in the above method. The purity was further
checked by thin-layer chromatography using silica gel-G.
3. Results and discussion
The observation that in microwave method the reaction time has
been drastically reduced with improved yield as compared to con-
ventional method, reason is not purely thermal [43]. The difference
was observed probably due to strong microwave effect, and the high
enhancement of reaction rate. In conclusion we have developed an
easy and convenient synthetic procedure for organotin (IV) com-
pounds by using microwave technique keeping modernization and
simplification of classical procedure.
3.1. Elemental analysis and electronic spectra
The resulting coloured complexes were found to be monomeric
in nature as evidenced by their molecular weight determinations.
All the complexes were soluble in most of the common organic
solvents. The physical properties and analytical data of the organ-
otin (IV) complexes are enlisted in Table 2. In the electronic spectra
of the ligands [44,45] a band at ∼216 nm was observed which
may be assigned to the 1B band of the phenyl ring. This shifts to

264
R.V. Singh et al. / Spectrochimica Acta Part A 72 (2009) 260–268
Fig. 5. Isomeric structures for L3H and L4H.
longer wavelength on complexation and was observed at ∼232 nm
in the complexes. Also, the ligands chromophore N, which
tion thus isomerization of the benzothiazoline into the Schiff base
in presence of tin atom (Fig. 5).
C
was observed at ∼290 nm, shifts to higher wavelength and was
observed at ∼294 nm in the complexes. In the spectra of ligands,
a band observed and which gets red shifted due to the presence
3.2. IR spectra
of
C
N-N
C
. However, it appears at ∼370 nm in the complexes
Table
3
lists the significant IR bands in the region
4000–200 cm−1 of organotin (IV) complexes that are useful
for the establishment of the mode of the coordination of dithiocar-
bazones and benzothiazolines. The IR spectra of the free ligands
L1H and L2H show bands at 1622, 1615 cm−1 and 1032, 1025 cm−1
due to ꢀ(C N) and ꢀ(C S); respectively. Ligands L1H, L2H, L3H
and L4H show strong bands in the region 3269, 3265, 3375 and
3370 cm−1 due to ꢀ(NH) vibrations, respectively. The absence of
ꢀ(SH) at 2500–2600 cm−1 and ꢀ(C N) at 1600–1650 cm−1 in the IR
spectra of ligands L3H and L4H is indicative of the benzothiazoline
[50]. A doublet at ∼2960 and ∼2900 cm−1 is assigned to symmetric
and asymmetric vibrations of S-CH2-C6H5 grouping.
possibly due to the polarization in C N bond caused by the metal-
ligand electron interaction. Three sharp bands were observed in the
region, 245–268 nm and assigned as charge transfer bands, indicat-
ing the formation of ␴ bond [46] and (d␲–p␲) [47] bonds between
p-orbitals of sulfur and vacant 5d orbitals of tin. The electronic spec-
tra of the ligands L3H and L4H consist of two bands around 250 and
315 nm remain unchanged in the electronic spectra of the com-
plexes and have been assigned ␪–␪* and ␲–␲* transitions within the
benzenoid ring and azomethine group respectively [48]. However,
an additional band is also observed in the region 390–410 nm due to
n–␲* electronic transitions of the azomethine [49] and which indi-
cates rearrangement of the ligands to the imine on complexation.
This suggests the formation of azomethine grouping on complexa-
Several significant changes with respect to the ligand bands on
complexation suggest coordination through the azomethine and
Table 3
IR spectral data (cm−1) of the ligands and their organotin (IV) complexes.
Compound
ꢀsec
(
NH)
ꢀ (Ar-NH)
ꢀ(C N)
ꢀ(S-CH2-C6H6)
ꢀ (C S)
ꢀ (N-N)
ꢀ(Sn-S)
ꢀ(Sn ← N)
ꢀ(Sn-Cl)
L1H
3269
3265
3375
3370
3340
3336
3350
3344
3335
3338
3328
3332
3343
3346
3339
3341
1622
1615
–
2960, 2900
1032
1025
–
1034
1030
–
–
–
–
–
–
–
–
–
–
–
320
–
315
–
295
–
280
–
L2H
2955–2900
L3H
–
–
–
–
–
–
–
–
–
–
L4H
–
–
–
–
–
Me2Sn(L1)Cl
Me2Sn(L1)2
Me2Sn(L2)Cl
Me2Sn(L2)2
Me2Sn(L3)Cl
Me2Sn(L3)2
Me2Sn(L4)Cl
Me2Sn(L4)2
–
–
–
–
–
–
–
–
1596
1600
1605
1609
1605
1605
1600
1600
938
942
949
954
–
–
–
–
1021
1021
1017
1017
–
326
330
332
336
345
345
330
330
424
424
418
418
450
450
390
390
–
–
–

R.V. Singh et al. / Spectrochimica Acta Part A 72 (2009) 260–268
265
Fig. 6. Tautomeric structures for L1H and L2H.

266
R.V. Singh et al. / Spectrochimica Acta Part A 72 (2009) 260–268
Table 4
sulfur of the thiolic forms of the ligands. The ꢀ(N-H) absorption
bands are absent in complexes and doublet due to S-CH2-C6H5 is
reduced to a weak doublet, thereby indicating ligand enolization,
followed by deprotonation during complexation to the metal atom
1H NMR spectral data (ı, ppm) of the ligands and their compounds.
Compound
Ar–NH
–NH
Aromatic
-S-CH2
L1H
10.65 (bs)
10.61 (bs)
10.56 (bs)
10.52 (bs)
10.81 (bs)
10.78 (bs)
10.76 (bs)
10.73 (bs)
10.64 (bs)
10.61 (bs)
10.60 (bs)
10.58 (bs)
10.10 (bs)
10.05 (bs)
4.60 (bs)
4.58 (bs)
–
–
–
–
–
–
–
–
7.98–6.70 (m)
7.50–6.38 (m)
8.00–6.29 (m)
7.18–6.38 (m)
8.10–6.85(m)
8.15–6.88(m)
7.58–6.46 (m)
7.62–6.50(m)
8.15–6.80 (m)
8.18–6.87(m)
7.36–6.45 (m)
7.40–6.49(m)
4.16(s)
4.15(s)
–
–
4.16(s)
4.16 (s)
4.15 (s)
4.15 (s)
–
–
–
–
and the ꢀ(C N) bands in complexes appear at 1609–1596 cm−1
;
L2H
L3H
significantly lower than the free ligand values indicating coordi-
nation by the azomethine nitrogen atoms of the Schiff bases. In
addition to these, the ꢀ(N-N) and ꢀ(C S) modes are also shifted to
lower frequency upon coordination. The IR spectra of the ligands
L1H and L2H do not display ꢀ(SH) band in 2600–2500 cm−1 region
suggesting that in the solid state, Schiff base remains in thio-keto
form but in solution it remains as an equilibrium mixture of both
the thio-keto and thiol tautomeric forms [48] (Fig. 6). The ꢀ(Ph-NH)
absorption bands observed at 3340, 3336, 3350 and 3344 cm−1 for
L1H, L2H, L3H and L4H, respectively remain unaltered on complex-
ation indicating noninvolvement of this group in complexation. In
the complexes formed by L3H and L4H, the bands due to NH vibra-
tions are not observed and this indicates the chelation of nitrogen
with the tin atom. A new band at ca. 1600 cm−1 in the spectra of
complexes due to ꢀ(C N) vibrations suggests that the complexes
are metal-Schiff base derivatives as the benzothiazoline ring rear-
ranges to give the Schiff base derivatives in the presence of metal
ion [51].
L4H
Me2Sn(L1)Cl
Me2Sn(L1)2
Me2Sn(L2)Cl
Me2Sn(L2)2
Me2Sn(L3)Cl
Me2Sn(L3)2
Me2Sn(L4)Cl
Me2Sn(L4)2
The proton signals of the methyl groups appear at
(ı1.08–1.12 ppm) in the organotin (IV) complexes. The 1H NMR
values for all the compounds are given in Table 4.
3.4. 13 C NMR spectra
13C NMR data have been recorded for all the four ligands and
their complexes and these spectra also support the authenticity of
the proposed structures (Table 5). The signals due to the carbon
atoms attached to the thionic and azomethine groups in ligands
(L1H and L2H) appear at 180.10–178.24 and 162.90–160.75 ppm,
respectively. However, in the spectra of the corresponding tin com-
plexes, these appear at ∼163 ppm (thionic group) and at ∼164 ppm
(azomethine group), respectively. The considerable shifts in car-
bons attached to S and N indicate the involvement of sulfur and
nitrogen atoms in coordination.
Several new bands in the spectra of tin complexes in the
regions, 390–450, 326–345, and 280–320 cm−1 may be assigned
to ꢀ(Sn ← N), ꢀ(Sn-S), and ꢀ(Sn-Cl), respectively, and this lends
further support to be the proposed coordination in these
complexes.
3.3. 1H NMR spectra
The 1H NMR spectra further support the bonding pattern as
discussed above. The 1H NMR spectral data of the ligands and
their corresponding organotin (IV) complexes were recorded in
d6-DMSO taking TMS as an internal standard. The 1H NMR spec-
tra of the ligands (L1H and L2H) exhibit –CH2– protons signals
at ı4.15–4.16 ppm and aromatic protons signals at ı6.38–7.98 ppm
and these remain at the same position in the spectra of the metal
complexes. The proton of –NH group of the ligands (L1H and L2H)
gives signal at ı10.05–10.10 ppm which is absent in the spectra of
metal complexes indicating the chelation of the ligand moiety to
tin with the sulfur atom. The signals at ı10.52–10.65 ppm observed
in the ligands (L1H, L2H, L3H and L4H) were assigned to Ar-NH
protons.
The 13C NMR spectra of the benzothiazolines (L3H and L4H) and
their 1:1 and 1:2 tin complexes were also recorded (Table 5). The
considerable shifts in the positions of carbons of the tin complexes
attached to N and S respectively, clearly indicate that the nitrogen
and sulfur of the ligands group participate in the complexation
reaction.
3.5. Anti-microbial screening
3.5.1. Anti-fungal activity
It is clear from the biological screening data given in Table 6
that all of the dimethyltin (IV) complexes were more toxic than
their parent Schiff bases. The increase in the activity of organotin
(IV) complexes may be due to the effect of central metal ion in
the normal cell process. The anti-microbial activity of these Schiff
bases and their complexes can be ascribed to the hydrogen bond
formation between the ( C N) atom of the compound and some
bioreceptors in the cells of microorganisms, which in turn block the
synthesis of protein by inhibiting the movement of ribosome along
The –NH proton signals at ı4.60 ppm (L3H) and ı4.58 ppm (L4H)
in the spectra of benzthiazolines disappear in the corresponding
tin complexes indicating deprotonation of this functional group.
The free ligands show a complex multiplet at ı6.29–8.00 ppm for
the aromatic protons and this remains more or less at the same
position in the spectra of the complexes.
Table 5
13 C NMR spectral data (ı, ppm) of the ligands and their corresponding organotin (IV) complexes.
Compound
C
S
C
N/
C
Aromatic carbon
L1H
180.10
178.24
–
–
163.2
163.1
162.9
162.8
–
162.90
160.75
148.68
144.90
164.16
164.15
164.0
163.9
164.0
164.0
163.9
151.2, 140.4, 140.1, 130.8, 128.9, 128.8, 128.7, 127.9, 127.2, 126.8, 122.1, 118.6
142.8, 140.6, 130.8, 130.1, 129.3, 128.8, 128.7, 127.8, 127.2, 126.1, 124.8, 118.1
153.8, 147.1, 141.4, 137.2, 128.8, 127.8, 127.6, 127.2, 126.2, 124.6, 122.2, 117.6, 114.8, 113.9
147.2, 146.1, 141.0, 129.8, 128.8, 127.8, 127.6, 127.2, 126.0, 124.6, 122.8, 117.4, 115.0, 113.8
156.1, 151.6, 140.2, 130.8, 128.9, 128.8, 128.7, 127.8, 127.2, 126.6, 122.4, 117.8
150.8, 140.2, 139.1, 130.2, 128.9, 128.8, 128.7, 127.8, 127.2, 126.5, 122.1, 117.6
142.5, 140.1, 130.2, 129.7, 128.9, 128.8, 128.7, 127.8, 127.2, 126.1, 124.3, 117.7
142.2, 140.0, 130.1, 129.5, 128.5, 128.4, 128.3, 127.6, 127.0, 125.9, 124.0, 117.5
158.2, 150.6, 138.8, 130.7, 130.2, 128.9, 128.7, 128.1, 126.9, 126.4, 126.1, 122.6, 121.9, 117.4
155.8, 150.7, 138.6, 133.8, 130.6, 128.9, 128.7, 128.1, 127.5, 126.5, 126.1, 122.6, 121.9, 117.6
158.2, 150.5, 138.6, 130.9, 130.4, 128.9, 128.7, 127.8, 127.1, 126.4, 126.0, 122.8, 121.9, 117.2
155.6, 142.8, 133.6, 130.6, 129.8, 129.2, 128.8, 128.4, 127.8, 126.7, 126.3, 124.2, 122.5, 117.9
L2H
L3H
L4H
Me2Sn(L1)Cl
Me2Sn(L1)2
Me2Sn(L2)Cl
Me2Sn(L2)2
Me2Sn(L3)Cl
Me2Sn (L3)2
Me2Sn(L4)Cl
Me2Sn(L4)2
–
–
–
163.9

R.V. Singh et al. / Spectrochimica Acta Part A 72 (2009) 260–268
267
Table 6
Fungicidal screening data of the ligands and their corresponding complexes.
3.5.2. Antibacterial activity
The antibacterial activity results presented in Table 7 show
clearly that the newly synthesized ligands and their metal com-
plexes containing organotin (IV) possess good biological activity.
Twelve chemically synthesized compounds viz. L1H, L2H, L3H, L4H,
[Me2SnLCl], [Me2SnL2] (where, L = L1 or L2 or L3 or L4) were tested
in vitro for their antibacterial activity against B. subtilis, S. aureus, P.
aeruginosa and S. typhi at different concentrations in methanol. All
the synthesized compounds show higher activity than the ligands
but slightly lower than the standard drug. From the bactericidal
activity, it is apparent that the complexes were more toxic towards
Gram (+) strains than Gram (−) strains. The reason is the differ-
ence in the structures of the cell walls. The walls of Gram (−) cells
are more complex than those of Gram (+) cells. Lipopolysaccha-
rides form an outer lipid membrane and contribute to the complex
antigenic specificity of Gram (−) cells. The enhanced bactericidal
activity of the ligand on complexation with organotin (IV) halide
may be explained by chelation theory [53], according to which
chelation reduces the polarity of the central metal atom because
of partial sharing of its positive charge with the donor groups and
possible ␲-electron delocalization within the whole chelate ring.
This chelation increases the lipophilic nature of the central atom,
which favours the permeation of the complexes through the lipid
layer of the cell membrane. Compounds inhibit the growth of bacte-
ria to greater extent as concentration increased. Also, the complexes
of S-benzyldithiocarbazate were found to possess higher activ-
ity than corresponding benzothiazoline. The compounds showed
good antibacterial activity against S. aureus and moderate activ-
ity against S. typhi and P. aeruginosa and poor activity against
B. subtilis.
Compound
Average % inhibition after 96 h
Rhizoctonia phaseoli
Penicillium chrysogenum
Conc. (0.01%)
Conc. (0.1%)
Conc. (0.01%)
Conc. (0.1%)
L1H
45
43
40
38
54
63
51
61
50
59
48
57
56
53
50
48
80
82
76
80
72
78
61
71
43
38
36
34
46
57
44
53
42
56
40
50
54
48
45
42
74
86
69
80
68
73
58
68
L2H
L3H
L4H
Me2Sn(L1)Cl
Me2Sn(L1)2
Me2Sn(L2)Cl
Me2Sn(L2)2
Me2Sn(L3)Cl
Me2Sn(L3)2
Me2Sn(L4)Cl
Me2Sn(L4)2
with RNA. This inhibits the synthesis of DNA in the cell nucleus. The
greater toxicity of the complexes than the bases can also explained
by the greater lipophilic character of the complexes [52]. It has
also been observed that the toxicity of Schiff bases and complexes
decreases on lowering the concentration. From the data obtained,
it is evident that some of these complexes exhibit a good activity
against the tested organisms but specially significant is the com-
plex [Me2Sn(L1)2], which showed the highest activity among the
complexes possiblydue tothedifferencein sulfur content. Thecom-
pounds containing a halogen atom attached directly to the central
atom also showed moderate activity, but the replacement of halo-
gen by another ligand moiety enhances the biochemical properties
of the whole molecules.
Table 7
Antibactericidal bioassay results for the ligands and their corresponding organotin (IV) complexes (concentration, ppm).
Compound
Diameter of inhibition zone (mm) after 24 h
Bacillus subtilis(+)
Staphylococcus aureus (+)
Pseudomonas aeruginosa (−)
Salmoneall typhi (−)
500
1000
500
1000
500
1000
500
1000
L1H
9
7
8
11
10
10
9
14
16
11
11
13
15
10
13
37
14
12
13
10
15
17
13
15
14
16
12
14
39
16
14
15
13
18
20
17
19
17
19
16
18
43
8
10
11
9
12
14
11
12
11
13
10
11
26
12
13
14
11
14
18
15
16
13
17
14
15
32
12
10
11
9
14
15
12
14
13
14
11
13
30
14
12
13
11
16
17
14
16
15
16
13
15
40
L2H
L3H
L4H
7
Me2Sn(L1)Cl
Me2Sn(L1)2
Me2Sn(L2)Cl
Me2Sn(L2)2
Me2Sn(L3)Cl
Me2Sn (L3)2
Me2Sn(L4)Cl
Me2Sn(L4)2
Imipinem
11
13
8
9
10
11
8
10
21
Table 8
Effect of ligands and organotin (IV) complexes on sperm dynamics and fertility of male rats (values are expressed as mean plus/mean minus SEM).
Group
Treatment
Sperm motality (cauda epididymis) %
Sperm density (million/mL)
Fertility %
Testes
Cauda epididymis
A
B
C
D
E
F
G
H
I
Control
85.86 3.9
6.15 0.52
64.29 2.9
46.28a 3.6
49.19a 4.2
52.31b 5.1
53.16b 2.6
23.91a 2.1
23.47a 9.4
40.32b 7.2
36.77a 4.1
32.26a 2.8
98 (+)
L1H
42.26a
46.76a
48.32b
58.90b
28.63a
26.27a
38.25b
28.34a
37.43a
3.7
2.4
3.0
1.8
2.2
1.6
2.7
2.8
3.7
4.28a 0.26
4.12a 0.28
4.31b 0.23
5.26b 0.61
0.95a 0.12
0.71a 0.14
2.95b 0.30
1.58a 0.38
2.67a 0.84
58 (−)
56 (−)
54 (−)
47 (−)
90 (−)
94 (−)
80 (−)
96 (−)
86 (−)
L2H
L3H
L4H
Me2Sn(L1)Cl
Me2Sn(L1)2
Me2Sn(L2)Cl
Me2Sn(L3)Cl
Me2Sn(L4)Cl
J
Mean SEM of 10 animals.
ap ≤ 0.001 highly significant; bp ≤ 0.01 significant; csignificant.
Dose = 2 mg/kg between day−1 for 60 days.

268
R.V. Singh et al. / Spectrochimica Acta Part A 72 (2009) 260–268
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It has been observed that the motility and count of sperm
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