Coordination behavior of unsymmetrical ligand complexes of diorganotin and diorganosilicon derived from Schiff bases

Article abstract of DOI:10.1080/10426500601087384

Hexacoordinated organotin and organosilicon derivatives have been prepared and characterized by analytical and spectroscopic techniques including UV, IR, ¹H NMR, and ¹³C NMR spectra. The ligands used in the present account were deriv

Full text of DOI:10.1080/10426500601087384

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Phosphorus, Sulfur, and Silicon
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Coordination Behavior
of Unsymmetrical Ligand
Complexes of Diorganotin and
Diorganosilicon Derived From
Schiff Bases
Shweta Gaur a , Nighat Fahmi a & R. V. Singh a
a Department of Chemistry , University of
Rajasthan , Jaipur, India
Published online: 24 Feb 2007.
To cite this article: Shweta Gaur , Nighat Fahmi & R. V. Singh (2007) Coordination
Behavior of Unsymmetrical Ligand Complexes of Diorganotin and Diorganosilicon
Derived From Schiff Bases, Phosphorus, Sulfur, and Silicon and the Related Elements,
182:4, 853-862, DOI: 10.1080/10426500601087384
To link to this article: http://dx.doi.org/10.1080/10426500601087384
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Phosphorus, Sulfur, and Silicon, 182:853–862, 2007
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500601087384
Coordination Behavior of Unsymmetrical Ligand
Complexes of Diorganotin and Diorganosilicon
Derived From Schiff Bases
Shweta Gaur
Nighat Fahmi
R. V. Singh
Department of Chemistry, University of Rajasthan, Jaipur, India
Hexacoordinated organotin and organosilicon derivatives have been prepared and
1
characterized by analytical and spectroscopic techniques including UV, IR,
13
H
NMR, and C NMR spectra. The ligands used in the present account were derived
by the condensation of thiosemicarbazide and 1H-Indol-2,3-dione, 1,3-dihydro-3-[2-
(4-fluorophenyl)-2-oxo-ethylidene]-2H-indol-2-one, and 1,3-dihydro-3-[2-(4-fluoro-
3-methyl-phenyl)-2-oxo-ethylidene]-2H-indol-2-one under microwave irradiation as
well as by conventional heating. Newly synthesized complexes with their correspond-
ing ligands were tested for their antifungal and antibacterial activities. The aim of
the present study is to synthesize some novel ecofriendly fungicides and bactericides
that have important pharmacodynamic significance.
Keywords Antimicrobial assay; silicon (IV) and tin (IV) complexes; spectral studies;
thio-ligands
INTRODUCTION
The chemistry of Schiff base complexes attracts many researchers1,2
because of their wide application in the food industry, dyes industry,
analytical chemistry, catalysis, and many agrochemical fields. The po-
tential antitumor, antibacterial, antiviral, fungicidal, and antimalar-
ial activities of thiosemicarbazones and their metal complexes have
spurred the study of the coordination chemistry of these ligands.3−10
Organotin compounds exhibit a broad spectrum of biological activity,
which includes bactericidal, fungicidal,11 antitumor,12and acaricidal13
properties. The interest in organosilicon (IV) compounds is due to their
Received july 21, 2006; accepted September 20, 2006.
The authors are thankful to CSIR, New Delhi, India, for financial assistance in the
form of Grant No. 01(1956)/04/EMR-II.
Address correspondence to R. V. Singh, Department of Chemistry, University of
Rajasthan, Jaipur, 302004, India. E-mail: singh-rv@uniraj.ernet.in
853

854
S. Gaur et al.
versatile applicability in pharmaceutical and chemical industries. For
example, the use of very bulky silicon-containing ligands allows the
isolation of a wide range of previously inaccessible types of compounds,
and silicon-substituted methyl groups are capable of making consid-
erable adjustments, especially in the inner CSi3 skeleton in response
to the electronic demands of the adjacent element.14 Organotin com-
pounds are toxic to a variety of microorganisms and find widespread
applications in biocidal compositions.15 Keeping this in mind, it was
considered worthwhile to synthesize organotin and organosilicon com-
plexes of some stereochemical as well as biological interest.
EXPERIMENTAL
All glass apparatus used were fitted with quickfit interchangeable stan-
dard ground joints. The apparatuses were cleaned, rinsed, and well
dried in an electric oven for 2–3 h. All chemicals and solvents were
dried and purified.
Preparation of Schiff Bases
The ligands were prepared by the condensation of 2-(1,2-dihydro-
2-oxo-3H-indol-3-ylidenyl) (1.0 gm, 7.76 mmol), 1,3-dihydro-3-[2-(4-
fluorophenyl)-2-oxo-ethylidene]-2H-indol-2-one (1.0 gm, 4.02 mmol),
and 1,3-dihydro-3-[2-(4-fluoro-3-methyl-phenyl)-2-oxo-ethylidene]-2H-
indol-2-one (1.0 gm, 3.80 mmol) with thiosemicarbazide (0.71 gm,
7.79 mmol), (0.37 gm, 4.06 mmol), and (0.35 gm, 3.84 mmol), respec-
tively in a equimolar ratio in a 50 mL alcohol. The contents were re-
fluxed for 45 min at 40–50◦C. After cooling, the precipitate was fil-
tered, dried, and then recrystallized from the same solvent and again
dried under reduced pressure. The physical properties of the ligands
are recorded in Table I.
For the sake of convenience, these have been abbreviated as 2-(1,2-
dihydro-2-oxo-3H-indol-3-ylidenyl)thiosemicarbazone (HTSCZ1), 1,3-
dihydro-3-[2-(4-fluorophenyl)-2-oxo-ethylidene]-2H-indol-2-one thio-
semicarbazone (HTSCZ2), and 1,3-dihydro-3-[2-(4-fluoro-3-methyl-
phenyl)-2-oxo-ethylidene]-2H-indol-2-one thiosemicarbazone (HTSCZ3)
(Figure 1).
Preparation of the Complexes
Conventional Method
To a weighed quantity of organotin/organosilicon chloride (1.19–1.75
gm, 3.58–13.56 mmol) in methanol was added an equimolar amount of

855

856
S. Gaur et al.
FIGURE 1
sodium salt of the ligands (prepared by adding corresponding weight of
sodium [0.16–0.62 gm, 6.96–26.97 mmol] to the ligands ([0.79–4.79 gm,
3.59–13.54 mmol]). The reaction mixture was refluxed for 8–10 h. The
solid products were precipitated. These were then dried in vacuum and
recrystallized from the same solvent. The main characterstics of these
complexes are given in Table I.
Microwave Method
A mixture of Me2SiCl2 (1.36 gm, 10.54 mmol), HTSCZ1 (2.32 gm,
10.54 mmol), HTSCZ2 (3.58 gm, 10.53 mmol), and sodium (0.48,
20.88 mmol) were taken in an open borosil beaker. The reaction medium
was methanol. The mixture was irradiated inside a microwave oven un-
til completion of the reaction. The resulting products were washed and

Unsymmetrical Ligand Complexes
857
dried under vaccum. A drastic reduction in reaction time was thus ob-
served due to rapid heating capability of microwaves.
Likewise, following the same procedure, all the compounds were pre-
pared in microwaves.
Analytical Methods and Physical Measurements
The various analytical methods were adopted for the proper charac-
terization of the compounds. Nitrogen and sulphur were estimated by
Kjeldahl’s and Messenger’s methods, respectively. Tin and silicon were
determined gravimetrically as SnO2 and SiO2, respectively, and molec-
ular weights were determined by the Rast Camphor Method. UV spec-
tra were recorded on a Hitachi-U-2000 spectrophotometer. IR spectra
were recorded as KBr discs on a Perkin-Elmer 577 grating spectropho-
1
tometer. H NMR spectra were recorded on JEOL AL 300 FT NMR in
DMSO-d6with TMS as the internal standard. All chemical shifts are
reported in parts per million (ppm) relative to TMS.
RESULTS AND DISCUSSION
The reactions of Me2SnCl2 Ph2SnCl2, Me2SiCl2, and Ph2SiCl2 with
the sodium salts of monobasic bidentate thiosemicarbazones result in
the replacement of chloride and isolation of [R2M(TSCZ1)(TSCZ2)] and
[R2M(TSCZ1)(TSCZ3)] types of complexes. The reactions may be repre-
sented as follows:
R2MCl2 + HTSCZ1 + HTSCZ2 → R2M(TSCZ1)(TSCZ2) + NaCl
R2MCl2 + HTSCZ1 + HTSCZ3 → R2M(TSCZ1)(TSCZ3) + NaCl
The resulting colored solids are soluble in DMF and DMSO. Their
low molar conductivity values show that they are non-electrolytes.
SPECTRAL STUDIES
UV Spectra
In the electronic spectra of the ligands, a band arising from the >C N
chromophore at ∼370 nm shifted to a shorter wave length for the com-
plexes. Such a shift in the n-π∗ band was probably due to the donation
of the lone pair of electrons by the nitrogen of the ligand to the central
metal atom. The bands of medium intensity at s∼270 and 300 nm aris-
ing from π − π∗ transition of the ligand remained almost unchanged in
the spectra of organosilicon and organotin derivatives.

858
S. Gaur et al.
IR Spectra
In the IR spectra of the ligands, a broad band in the region 3250–
3100 cm−1 and 2700 cm−1 may be assigned to ν(NH) and ν(SH) vi-
brations, respectively. The νNH and νSH bands disappeared in the
spectra of the resulting complexes, indicating possible deprotonation
of the ligands on complexation and the formation of (M-S) and (M←N)
bonds. In the spectra of HTSCZ1, HTSCZ2, andHTSCZ3,a sharp band
due to the >C N frequency appeared in the range 1620–1630 cm−1
,
which shifted to a lower frequency16 in the silicon complexes and
to a higher frequency17 (ca. 15 cm−1) in the tin complexes, indicat-
ing coordination of the azomethine nitrogen to the silicon and tin
atoms.
Several new bands observed in the far IR region of the complexes
at ∼325 cm−1; 415 cm−1, ∼540 cm−1 and 580 cm−1 were assigned to
ν(Sn-S), ν(Sn←N), ν(Si-S), and ν(Si←N), respectively.
1H NMR Spectra
The proton magnetic resonance spectra of the ligands and their com-
plexes were recorded in DMSO-d6. The chemical shift values relative to
the TMS peak are listed in Table II. The broad signal due to the –NH
proton in the ligand disappeared in the case of the complexes, showing
the bond formation between thiolic sulphur and the metal atom. The
appearance of a signal due to a –NH2 group at about the same posi-
tion in the ligand and its metal complexes showed the non-involvement
of this group in coordination. The additional signals in the region δ
TABLE II 1H NMR Spectral Data (δ ppm) of the Ligands and
Their Corresponding Complexes
NH
(free) (ring)
NH1
NH2 or 3
(ring)
M-Ph/
Compound
NH12 aromatic
HTSCZ1
11.28 12.56
—
3.44
—
—
—
8.04–7.84
7.94–7.54
7.72–6.34
8.40–7.56
8.12–7.53
8.48–6.72
8.56–7.98
8.24–7.29
8.08–7.72
8.28–6.79
8.32–7.36
HTSCZ2
10.04
10.24
—
—
—
11.08
11.12
11.14
11.18
11.24
11.28
11.16
11.28
11.32
11.44
3.16
2.64
3.18
2.68
3.45
2.68
3.54
2.72
3.65
2.85
HTSCZ3
Me2Si[TSCZ1][TSCZ2]
Me2Si[TSCZ1][TSCZ3]
Ph2Si[TSCZ1][TSCZ2]
Ph2Si[TSCZ1][TSCZ3]
Me2Sn[TSCZ1][TSCZ2]
Me2Sn[TSCZ1][TSCZ3]
Ph2Sn[TSCZ1][TSCZ2]
Ph2Sn[TSCZ1][TSCZ3]
12.52
12.54
12.60
12.62
12.58
12.56
12.54
12.58
3.45
3.52
3.64
3.62
3.54
3.48
3.72
3.68
—
—
—
—
—
—
—

Unsymmetrical Ligand Complexes
859
TABLE III 13C NMR Spectral Data (δ ppm) of the Ligands and Their
Corresponding Complexes
Thiolo Azomethine
Aromatic
carbons
Compound
carbon
carbon
HTSCZ1
HTSCZ2
HTSCZ3
178.02
178.62
172.52
161.98
157.66
155.12
156.94
150.51
152.63
154.58
153.52
150.39
155.10
153.02
131.59, 130.78, 121.89, 120.43, 119.19
148.08, 144.05, 136.25, 135.71, 133.22, 132.13
147.24, 144.28, 136.92, 135.72, 130.22, 129.71
137.23, 122.38, 132.62, 128.51, 125.12, 162.61
136.51, 128.32, 126.58, 122.82, 124.56, 110.61
132.43, 126.51, 122.80, 119.62, 121.53, 112.30
131.19, 127.91, 131.58, 120.58, 119.56, 110.08
131.62, 125.69, 128.52, 119.61, 120.51, 119.68
129.58, 120.62, 125.81, 120.08, 120.62, 110.81
128.42, 119.51, 129.82, 120.91, 120.28, 112.62
124.41, 116.53, 125.62, 119.62, 121.83, 110.52
Me2Si[TSCZ1][TSCZ2] 161.82
Me2Si[TSCZ1][TSCZ3] 168.51
Ph2Si[TSCZ1][TSCZ2] 165.38
Ph2Si[TSCZ1][TSCZ3] 170.63
Me2Sn[TSCZ1][TSCZ2] 173.91
Me2Sn[TSCZ1][TSCZ3] 167.48
Ph2Sn[TSCZ1][TSCZ2] 168.34
Ph2Sn[TSCZ1][TSCZ3] 165.42
0.63–1.17 ppm, δ 6.34–8.56 ppm, δ 0.5–0.8 ppm, and δ 6.34–8.56 ppm are
due to (CH3Sn), (C6H5Sn)/aromatic, (CH3Si), and (C6H5Si)/aromatic
groups, respectively.
13C NMR Spectra
13C NMR spectra of the ligands and their complexes were recorded in
DMSO. The carbons attached to the thiolic sulphur and azomethine
nitrogen in the ligand underwent a marked shift, which clearly showed
TABLE IV Fungicidal Screening Data of the Ligands
and Their Corresponding Complexes (Conc. in ppm)
Fusarium oxysporum Aspergillus niger
Compound
50
100
200
50
100 200
HTSCZ1
66
70
75
76
75
77
75
76
79
76
77
86
70
75
80
82
80
85
82
82
80
82
83
100
72
80
85
86
84
89
87
91
89
88
89
100
72
74
76
77
76
78
79
86
77
76
77
90
80
79
80
81
82
82
85
91
85
82
80
100
83
80
85
86
85
87
90
96
93
89
86
100
HTSCZ2
HTSCZ3
Me2Si[TSCZ1][TSCZ2]
Me2Si[TSCZ1][TSCZ3]
Ph2Si[TSCZ1][TSCZ2]
Ph2Si[TSCZ1][TSCZ3]
Me2Sn[TSCZ1][TSCZ2]
Me2Sn[TSCZ1][TSCZ3]
Ph2Sn[TSCZ1][TSCZ2]
Ph2Sn[TSCZ1][TSCZ3]
Standard (Bavistin)

860
S. Gaur et al.
FIGURE 2
the complexation of metal through the sulphur and nitrogen atoms. The
chemical shift values are listed in Table III.
On the basis of previous discussion, the geometry shown in Figure 2
has been proposed for the complexes.

Unsymmetrical Ligand Complexes
861
TABLE V Bactericidal Screening Data of the
Ligands and Their Corresponding Complexes
Diameter of inhibition zone (mm)
Staphylococcus aureus Escherichia coli
Compound
500
1000
500
1000
HTSCZ1
5
4
5
7
7
9
3
4
5
5
5
6
HTSCZ2
HTSCZ3
Me2Si[TSCZ1][TSCZ2]
Me2Si[TSCZ1][TSCZ3]
Ph2Si[TSCZ1][TSCZ2]
Ph2Si[TSCZ1][TSCZ3]
Me2Sn[TSCZ1][TSCZ2]
Me2Sn[TSCZ1][TSCZ3]
Ph2Sn[TSCZ1][TSCZ2]
Ph2Sn[TSCZ1][TSCZ3]
6
9
7
8
12
13
11
12
9
5
7
7
8
7
9
9
10
14
13
14
15
18
10
10
13
16
15
15
16
17
9
10
11
12
17
Standard (Streptomycin) 15
MICROBIAL ASSAY
Fungicidal and bactericidal activities of the ligands and their complexes
against fungi and bacteria have been recorded in Tables IV and V by
the methods reported earlier.18
CONCLUSION
The spectral studies reasonably proved that complexation of the metal
and ligand took place. A hexacoordinated environment has been sug-
gested around a silicon and tin atom. The resulting products are
lipophilic in nature. The enhancement of the activity on complexation
can also be explained by chelation theory.19 According to this theory,
chelation reduces the polarity of the central metal atom because of par-
tial sharing of a positive charge with the donor groups and possible
π electron delocalization within the whole chelate ring. The chelation
increases the lipophilic nature of the central atom, which favors the per-
meation of the complexes in the lipid layer of the cell membrane. After
entering the cells, these compounds inhibit cell division.20 Changes in
concentration influence the antimicrobial property. These compounds,
even at lower concentration, inhibit the growth of microorganisms.
This experiment has shown good activity against pathogenic hu-
man bacteria (Staphylococcus aureus) and fungus (Aspergillus species)

862
S. Gaur et al.
because these compounds can be explored as fungicides and bacteri-
cides for human use and may come out as future pesticides. Nonethe-
less, their synthesis is a step by which making of safe biocidal drugs
may be possible.
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