Synthesis, characterization, thermal, and antibacterial studies of organotin(Iv) complexes of indole-3-butyric acid and indole-3-propionic acid

Article abstract of DOI:10.1080/10426507.2013.819871

Six organotin(IV) complexes of type Me₂SnL₂, Bu ₂SnL₂, and Ph₃SnL [where L = indole-3-butyric acid (1, 2 and 3) or indole-3-propionic acid (4, 5 and 6)] have been synthesized by the reactions of the corresponding diorganotin(IV) oxide and triphenyltin(IV) hydroxide with respective indole-3-butyric acid (IBH) or indole-3-propionic acid (IPH) in the desired molar ratios of 1:2/1:1. All of the compounds have been characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR, and ¹¹⁹Sn NMR spectroscopy. Thermal studies of all synthesized complexes have been carried out using thermogravimetry (TG) technique under a nitrogen atmosphere. The thermal decompositions for compounds Me₂SnL₂ and Bu₂SnL₂ occurred in two steps, whereas in compounds Ph₃SnL, it exhibited as three steps decomposition and resulted into the formation of pure SnO₂. The complexes were also screened against three gram-positive (Staphylococcus aureus, Staphylococcus epidermidis, and Micrococcus luteus) and three gram-negative (Escherichia coli, Pseudomonas aeruginosa, and Enterobacter aerogenes) bacteria using minimum inhibition concentration (MIC) method, and all of these complexes showed significant antibacterial activity. [Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental files: Additional text, tables, and figures.]

Full text of DOI:10.1080/10426507.2013.819871

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Synthesis, Characterization,
Thermal, and Antibacterial Studies of
Organotin(Iv) Complexes of Indole-3-
Butyric Acid and Indole-3-Propionic Acid
Asha Chilwal a , Priti Malhotra b & A. K. Narula a
a School of Basic and Applied Sciences , Guru Gobind Singh
Indraprastha University , Dwarka , Delhi , India
b Department of Chemistry, Daulat Ram College , University of
Delhi , Delhi , India
Accepted author version posted online: 02 Sep 2013.Published
online: 28 Jan 2014.
To cite this article: Asha Chilwal , Priti Malhotra & A. K. Narula (2014) Synthesis, Characterization,
Thermal, and Antibacterial Studies of Organotin(Iv) Complexes of Indole-3-Butyric Acid and Indole-3-
Propionic Acid, Phosphorus, Sulfur, and Silicon and the Related Elements, 189:3, 410-421, DOI:
10.1080/10426507.2013.819871
To link to this article: http://dx.doi.org/10.1080/10426507.2013.819871
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Phosphorus, Sulfur, and Silicon, 189:410–421, 2014
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2013.819871
SYNTHESIS, CHARACTERIZATION, THERMAL,
AND ANTIBACTERIAL STUDIES OF ORGANOTIN(IV)
COMPLEXES OF INDOLE-3-BUTYRIC ACID
AND INDOLE-3-PROPIONIC ACID
Asha Chilwal,1 Priti Malhotra,2 and A. K. Narula1
1School of Basic and Applied Sciences, Guru Gobind Singh Indraprastha
University, Dwarka, Delhi, India
2Department of Chemistry, Daulat Ram College, University of Delhi, Delhi, India
GRAPHICAL ABSTRACT
NH
CH3
CH2
O
O
O
O
CH2
C
Sn
C
CH2
CH2
CH2
CH2
NH
CH3
Compound: (1)
O
CH2
C
Sn
CH2
O
NH
Compound: (6)
Abstract Six organotin(IV) complexes of type Me2SnL2, Bu2SnL2, and Ph3SnL [where L =
indole-3-butyric acid (1, 2 and 3) or indole-3-propionic acid (4, 5 and 6)] have been synthesized
by the reactions of the corresponding diorganotin(IV) oxide and triphenyltin(IV) hydroxide with
respective indole-3-butyric acid (IBH) or indole-3-propionic acid (IPH) in the desired molar
ratios of 1:2/1:1. All of the compounds have been characterized by elemental analysis, IR, 1H
NMR, 13C NMR, and 119Sn NMR spectroscopy. Thermal studies of all synthesized complexes
have been carried out using thermogravimetry (TG) technique under a nitrogen atmosphere.
The thermal decompositions for compounds Me2SnL2 and Bu2SnL2 occurred in two steps,
whereas in compounds Ph3SnL, it exhibited as three steps decomposition and resulted into
the formation of pure SnO2. The complexes were also screened against three gram-positive
(Staphylococcus aureus, Staphylococcus epidermidis, and Micrococcus luteus) and three gram-
negative (Escherichia coli, Pseudomonas aeruginosa, and Enterobacter aerogenes) bacteria
Received 18 April 2013; accepted 24 June 2013.
Address correspondence to Professor A. K. Narula, Ph.D., School of Basic and Applied Sciences, Guru
Gobind Singh Indraprastha University, Dwarka, Delhi 110078, India. E-mail: aknarula58@gmail.com
410

INDOLE-3-BUTYRIC ACID AND INDOLE-3-PROPIONIC ACID
411
using minimum inhibition concentration (MIC) method, and all of these complexes showed
significant antibacterial activity.
[Supplementary materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental
files: Additional text, tables, and figures.]
Keywords Diorganotin(IV) oxide; triphenyltin(IV) hydroxide; spectroscopic analysis; thermal
decomposition; antibacterial activity
INTRODUCTION
Organotin(IV) compounds have been receiving increasing attention owing to a va-
riety of industrial and agricultural applications.1,2 In view of the diverse fields of ap-
plications, numerous articles and reviews are available in the literature.3,4 The coordi-
nation chemistry of tin is extensive with various geometries and coordination numbers
known for both inorganic and organometallic complexes.5 Considerable efforts have been
made to synthesize and characterize organotin compounds having heterodonor atoms (O,
N, and S) which have different applications6 and stabilities depending on the number,
type, and arrangement of ligands about tin;7 many studies have been focused on their
structure-activity correlations.8,9 The organotin(IV) derivatives of donor ligands are also
of considerable interest as they have been suggested to possess mild to good biological
activities.10
Among the organotin compounds, organotin(IV) carboxylates have been widely stud-
ied due to their structural diversity2 and wide range of applications,11 such as biocides,
wood preservatives, antifouling agents, catalysts, and stabilizers.12–14 In general, the bio-
chemical activity of organotin(IV) complexes is greatly influenced by the molecular struc-
tures and coordination number of the tin atom.7,15 Tri-organotin(IV) compounds display
better biological activity than their diorganotin and mono-organotin analogs.16 This has
been attributed to their ability to bind proteins.17 Therefore, their synthesis and structural
chemistry is well documented in the literature.18 However, thermokinetic parameters re-
quired to assess the functional stability of an organotin compound for its particular end
usage are yet to be explored. The thermal properties can easily be evaluated by using
thermogravimetry analysis (TGA). TGA scans recorded at a certain heating rate and un-
der nitrogen atmosphere can be utilized for the evaluation of degradation processes of
a compound. It has further been suggested that the biological activity of organotin(IV)
compounds will be considerably enhanced if acids containing an indole ring is bound with
metals.19
Hence, it is considered worthwhile to design and synthesize new organotin carboxy-
lates using indole-3-butyric acid (IBH) and indole-3-propionic acid (IPH) as ligands and to
study their thermal stability and biological assays. In view of this, we have synthesized six
organotin(IV) complexes of dimethyltin, dibutyltin, and triphenyltin esters of IBH or IPH.
These complexes have been characterized by elemental analysis, infrared, multinuclear
(1H, 13C, 119Sn) NMR spectroscopy. Thermal analysis was performed for the complexes
to study their thermal degradation and they were also screened against three gram-positive
(Staphylococcus aureus, Staphylococcus epidermidis, and Micrococcus luteus) and three
gram-negative (Escherichia coli, Pseudomonas aeruginosa, and Enterobacter aerogenes)
bacteria to establish their antibacterial activity.

412
A. CHILWAL ET AL.
Figure 1 Structure and acronyms of indole-3-butyric acid and indole-3-propionic acid.
RESULTS AND DISCUSSION
General Procedure for the Synthesis of the Complexes 1–6
The structures and acronyms of IBH and IPH used for the preparation of complexes are
given in Figure 1. The six organotin(IV) complexes were synthesized by azeotropic removal
of water from the reaction between the diorganotin(IV) oxide/triphenyltin(IV) hydroxide
and indole-3-butyric acid and indole-3-propionic acid in 1:2/1:1 molar ratio (Scheme 1).
Some representative experiments to illustrate the synthesis of the above complexes are
given subsequently.
Scheme 1 Synthesis of organotin(IV) complexes.
Structural Characterization and Elemental Analysis
The compounds were of white to light brown in color. They were soluble in organic
solvents such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) but insoluble

INDOLE-3-BUTYRIC ACID AND INDOLE-3-PROPIONIC ACID
413
Table 1 Analytical data of organotin(IV) complexes
Elemental analysis% Found (Calc.)
Compound
Comp. designation
Molecular
formula
Yield FMW
g mol−1
%
Sn
C
H
N
1
2
3
4
5
6
Me2Sn(IB)2 C26H30N2O4Sn 71
Bu2Sn(IB)2 C32H42N2O4Sn 70
553.24 21.10 (21.45) 55.07 (56.44) 4.97 (5.46) 5.11 (5.06)
637.40 18.95 (18.62) 59.81 (60.29) 6.90 (6.64) 4.53 (4.39)
552.25 21.63 (21.49) 65.33 (65.24) 5.13 (4.92) 2.71 (2.53)
525.18 22.47 (22.60) 55.10 (54.88) 4.85 (4.98) 4.92 (5.33)
609.35 19.55 (19.48) 59.27 (59.13) 6.31 (6.28) 4.68 (4.59)
538.23 21.91 (22.05) 64.65 (64.71) 4.77 (4.68) 2.51 (2.60)
Ph3SnIB
C30H27NO2Sn
82
Me2Sn(IP)2 C24H26N2O4Sn 70
Bu2Sn(IP)2 C30H38N2O4Sn 74
Ph3SnIP
C29H25NO2Sn
80
in water, carbon tetrachloride, and hexane. The yields were in the range of 70% to 82%.
The analytical data are listed in Table 1. The calculated values of C, H, N, and Sn agreed
well with the experimentally determined values.
FTIR Spectra
The IR spectra of organotin(IV) complexes have been recorded as KBr discs in the
range of 400 to 4000 cm−1 and are summarized in Table 2. The bands in the range of 421
to 460 cm−1 and 548 to 578 cm−1 indicate the Sn–O and Sn–C bonds, respectively.17,20
A
strong band due to ν(N–H) was observed at 3370 to 3423 cm−1. The compounds 1 to 6 do
not show the broad ν(OH) band at 2600 to 3000 cm−1, indicating the deprotonations of the
carboxylic group of ligands due to the formation of the oxygen-tin bond.11
In organotin(IV) complexes, when there are interactions between the carbonyl oxy-
gen atoms of the carboxylate groups and the tin atom, the asymmetric absorption vibration
frequencies νas(COO) of carboxylate groups decreases and the symmetric absorption fre-
quencies νs(COO) increases.21 In the IR spectra of the complexes 1 to 6, the two absorption
bands in the ranges of 1585 to 1615 cm−1 and 1319 to 1458 cm−1 can be assigned to
νas(COO) and νs(COO), respectively. The ꢀν values [ꢀν = νas(COO) − νs(COO)] has
been also used to predict the bonding mode of the ligand.22 As reported earlier,23 in com-
plexes where ꢀν is below 200 cm−1, the ligand behaves as a bidentate carboxylate and in
the complexes where ꢀν is above 200 cm−1 the ligand behaves as a monodentate carboxy-
late. There is donation of charge density from C O: → to the electropositive tin metal,
which slightly increase the C O bond length, hence, the absorption frequency decreases
Table 2 FTIR spectral data of organotin(IV) complexes
Comp.
Compound designation
νas(COO)
νs(COO)
ꢀ ν
ν(NH)
ν(SnO)
ν(Sn–C)
1
2
3
4
5
6
Me2Sn(IB)2
Bu2Sn(IB)2
Ph3SnIB
Me2Sn(IP)2
Bu2Sn(IP)2
Ph3SnIP
1615 (s)
1613 (s)
1585 (s)
1610 (s)
1599 (s)
1588 (s)
1432 (s)
1433 (s)
1319 (m)
1456 (s)
1458 (m)
1330 (w)
183
180
265
154
141
258
3370 (s)
3370 (w)
3385 (m)
3400 (s)
3408 (s)
3423 (s)
421 (s)
430 (s)
438 (s)
458 (m)
460 (s)
455 (m)
563 (m)
570 (m)
564 (w)
560 (s)
578 (s)
548 (m)
ν was measured as wave number in cm−1
Abbreviations: s, strong; m, medium; w, weak.
.

414
A. CHILWAL ET AL.
and carboxylate acts as bidentate ligand in the solid state.24 Complexes 1, 2, 4, and 5 showed
that the magnitude of ꢀν is comparable to the sodium salt of the acid indicating bidentate
bonding of the carboxylate group to tin(IV) atom in the solid state. For complexes derived
from triphenyltin(IV) hydroxide, the magnitude of ꢀν below 200 cm−1 would be expected
for bridging or chelating carboxylates, but greater than 200 cm−1 is for the monodentate
bonding carboxylate anions.8,21 Hence, carboxylate group in complexes 3 (265 cm−1) and
6 (258 cm−1) would be expected to bond to the tin atom in monodentate manner since the
ꢀν is above 200 cm−1. As a result, the complexes 1, 2, 4, and 5 exhibit six-coordinated
tin atom and complexes 3 and 6 exhibit four-coordinated tin atom. The IR spectra of com-
plexes 3 and 6 are shown in Figure S1 and complex 5 is shown in Figure S2 (Supplemental
Materials).
1H NMR Spectra
1
1
The H NMR spectra of the derivatives were recorded in DMSO-d6. The H NMR
spectra of the 3-indole carboxylates, due to the protons of indole ring, exhibited the res-
onances between δ 6.51 to 7.61 ppm. The heterocyclic –NH protons appeared at δ 10.10
to 10.81 ppm and there is no appreciable change in its position in the metal complexes
confirming that heteronitrogen atom is not involved in coordination. The methylene protons
i.e. –CH2CH2CH2– of IBH and –CH2CH2– of IPH are observed in the range of δ 1.20 to
2.61 ppm. In the studied complexes, the –COOH resonance of the ligand at δ 12.00 to
13.00 ppm was absent, which suggests the replacement of the carboxylic proton by the
organotin(IV) moiety.25
1
In H NMR spectra of six complexes, all protons have been identified by intensity
1
and multiplicity patterns. The upfield regions of the H NMR spectra of the complexes 1
and 4 showed the signal of the methyl protons as singlet in the range of δ 0.89 ppm and
δ 0.91 ppm, and complexes 2 and 5 showed the signal of the butyl protons as multiplet
in the range of δ 0.81 to 1.57 ppm. The resonances due to the tin-phenyl protons in the
studied complexes 3 and 6 were observed as multiplet in the region of δ 7.18 to 7.44 ppm
with integration values of 9:6, respectively, ascribed to the aromatic protons of the phenyl
n
group.26 Generally, upon complexation, the magnitude of J(119Sn–1H) varies depending
on the stereochemistry at the tin atom and on the nature of the ligand. The larger coupling
constant indicates the higher coordination number of tin.27 The proton integration area was
1
consistent with the molecular formula. The chemical shift values of H NMR spectra are
given in Table 3.
13C NMR Spectra
The 13C NMR characteristic resonance peaks of the complexes were recorded in
DMSO-d6 and the chemical shifts of the characterized carbons of organotin(IV) derivatives
are listed in Table 4. The carboxylate carbon shifts to a lower field region in all the
complexes, indicating the participation of the carboxyl group in the coordination to tin.17
The indole ring carbons are observed in the range of δ 111.2 to 137.7 ppm and the other
resonance lines in the spectrum fall into three regions, i.e., δ 5.9 to 34.4 ppm for aliphatic
carbons, δ 127.6 to 138.2 ppm for carbons of phenyl group (3 and 6), and δ 179 2 ppm
for carbonyl carbon of the carboxyl group.

INDOLE-3-BUTYRIC ACID AND INDOLE-3-PROPIONIC ACID
415
Table 3 1H NMR data (ppm) of organotin(IV) complexes of indole-3-butyric acid and indole-3-propionic acid
1Ha
δ
–CH3/–
(CH2)3CH3
protons
Phenyl
ring
protons
Compound
Comp. designation
Indole ring
protons
–NH
–(CH2)n–
1
2
3
4
5
6
Me2Sn(IB)2 10.10 (s) 7.51–6.81 (m) 2.51 (m), 1.60 (m), 1.33 (m)
Bu2Sn(IB)2 10.81 (s) 7.55–6.96 (m) 2.60 (m), 1.53 (m), 1.20 (m) 1.57–1.33 (m), 0.82 (t, 7.3)
0.89 (s, 7.2) [78.4]b
—
—
7.44–7.18 (m)
—
Ph3SnIB
10.70 (s) 7.55–6.71 (m) 2.42 (m), 1.61 (m), 1.30 (m)
–
0.91 (s, 7.2) [68.0]
1.54–1.30 (m), 0.81 (t, 7.1)
–
Me2Sn(IP)2 10.11 (s) 7.50–6.51 (m)
Bu2Sn(IP)2 10.64 (s) 7.45–6.94 (m)
2.71 (m), 1.40 (m)
2.60 (m), 1.52 (m)
2.61 (m), 1.60 (m)
—
Ph3SnIP
10.69 (s) 7.61–6.66 (m)
7.44–7.26 (m)
aMultiplicity is given as: s, singlet; t, triplet; m, multiplet.
bChemical shifts (δ) in ppm. nJ[119Sn–1H] and 3J(1H–1H) in Hz are listed in square brackets and parenthesis,
respectively.
Table 4 13C NMR data (ppm) of organotin(IV) complexes of indole-3-butyric acid and indole-3-propionic acid
δ
13Ca
–CH3/CH2
Compound
Comp. designation
Indole ring
carbons
(CH2)2CH3
carbons
Phenyl ring
carbons
δ
–COO–
178.9
– (CH2)n–
119Sna
1
2
Me2Sn(IB)2
Bu2Sn(IB)2
136.2–112.0
136.3–111.3
32.0, 25.5,
24.1
33.8, 25.7,
24.2
5.9 [723.1]b
—
—
-349
-351
180.1
25.3 [584.0], 26.8
[38.6], 26.3 [98.3],
13.6
—
3
Ph3SnIB
181.0
136.8–111.2
33.2, 25.6,
23.7
136.2 (Cα)
[640.0],
102
136.8 (Cβ )
[48.1], 127.6
(Cγ ) [64.8],
129.1 (Cδ)
—
4
5
Me2Sn(IP)2
Bu2Sn(IP)2
179.6
178.1
135.9–112.0
136.3–111.3
34.1, 20.5
34.3, 21.0
6.0 [754.0]
25.5 [568.2], 27.1
[34.7], 26.6 [87.5],
14.0
—
—
—
6
Ph3SnIP
180.0
137.7–112.0
34.4, 20.7
—
138.2(Cα)
[647.1],
99
137.7 (Cβ )
[54.3], 129.0
(Cγ ) [69.2],
130.2 (Cδ)
aChemical shifts (δ) in ppm.
bnJ[119Sn–13C] in Hz are listed in square brackets.

416
A. CHILWAL ET AL.
Figure 2 Suggested structures of organotin(IV) complexes: (a) Octahedral geometry of complexes 1, 2, 4, and
5, and (b) Tetrahedral geometry of complexes 3 and 6.
The magnitudes of the coupling constants 1J(119Sn–13C) for tri-organotin complexes
(3 and 6) suggested the tetrahedral geometry around the tin atom in solution, diorganotin(IV)
complexes (1, 2, 4, and 5) are expected to be octahedral in solution as well as in the solid
state17 (Figure 2).
119Sn NMR Spectra
The characteristic resonance peaks in the 119Sn NMR spectra of all of the studied
derivatives were recorded in DMSO-d6. The 119Sn chemical shifts of the organotin(IV)
compounds covered a range δ 600. As the electron releasing power of the alkyl group
bonded to tin increases, the tin atom becomes progressively more shielded and the δ (119Sn)
value moves to a higher field.28 It was reported earlier that 119Sn NMR is also a powerful
technique and the value of δ (119Sn) is directly linked to the coordination number of the
central tin atom.29
The 119Sn chemical shifts of organotin(IV) derivatives are listed inTable 4 and their
values indicates that the complexes 1 and 2 were hexa-coordinated and the complexes 3 and
6 were tetra-coordinated.28 Due to insufficient solubility of the diorganotin(IV) complexes
4 and 5, it was not possible to record the 119Sn NMR spectra.

INDOLE-3-BUTYRIC ACID AND INDOLE-3-PROPIONIC ACID
417
Figure 3 TG curves of organotin(IV) complexes: (a) Bu2Sn(IB)2 (2) and (b) Ph3SnIP (6).
Thermal Analysis of Organotin(IV) Complexes
The thermogravimetric (TG) curves of the organotin(IV) derivatives were obtained
in the dynamic nitrogen atmosphere and the TG curves of complexes 4 and 6 are shown in
Figure 3. The thermogravimetric (TG) analyses were used to describe thermal behavior of
the synthesized complexes 1 to 6. The thermogravimetric analysis curves of diorganotin(IV)
complexes viz., 1, 2, 4, and 5 show two consecutive steps of decomposition. The first step
of decomposition corresponds to the loss of the two alkyl groups attached to tin in the
temperature range 210 to 345◦C. Similarly, the second step of decomposition corresponds
to the loss of ligand moiety along with the formation of SnO2 as final residue in the
temperature range 345 to 600◦C. The TG study for the complexes 3 and 6 shows three steps

418
A. CHILWAL ET AL.
of decomposition. The first step of decomposition corresponds to the loss of three phenyl
groups in the temperature range 142 to 280◦C. The second step has been attributed to the
loss of ligand moiety in the temperature range 280 to 408◦C, and third step of decomposition
corresponds to the formation of the SnO2 in the temperature range 408 to 798◦C. The end
product (SnO2) obtained by the decomposition of all of the synthesized complexes has been
analyzed by the presence of ν(Sn–O) at 620 2 cm−1 in the IR spectrum of the residue.9
The higher slope of the TG curve of 3 and 6, suggests that their decomposition rate
is higher than 1, 2, 4, and 5.
Antibacterial Activity
The antibacterial activity of synthesized organotin(IV) complexes (1–6), together
with the standard antibacterial drug, viz., chloramphenicol was evaluated against three
gram-positive (S. aureus, S. epidermidis, and M. luteus) and three gram-negative (E. coli, P.
aeruginosa, and E. aerogenes) bacterial strains, using the minimum inhibition concentration
(MIC) method and the results are listed in Table S1 (Supplemental Materials). The results
revealed that all the synthesized compounds showed moderate to good bacterial inhibition.
The screening results exhibited by triphenyltin(IV) complexes 3 and 6 showed high activities
against all the bacterial strains, due to the presence of the phenyl groups, which facilitate
binding to biological molecules by π–π interactions30 and more lipophilic character, which
favors the permeation of the complexes through the lipid layer of the cell membrane.
Compounds 1, 2, 4, and 5 displayed moderate antibacterial activity against all the strains.
It was found that the synthesized compounds were more active against gram-positive
than gram-negative bacteria and this can be attributed to the difference in the structure of the
cell walls. The walls of gram-negative cells are more complex than those of gram-positive
cells.31 The enhancement in activity upon complexation may be due to the increasing of
lipophilic nature of these complexes resulted from the metal chelation.32 The chelation of
metal ion and sharing of electrons with donor atom reduces polarity of metal ion. The
reduction of polarity causes blockage of binding sites in the enzymes of pathogens and
enhances penetration of complexes into the lipid membrane. Therefore, the presence of
different organic groups in organotin(IV) complexes has played a significant role in their
growth inhibitory activity. The phenomenon of protein synthesis is blocked by interference
of complexes with the respiration processes of cell and as a result further growth of
pathogens is restricted.33 In addition, the antimicrobial activity might be due to the presence
of the NH group in the ligand;30 this group is believed to impart the transformation reaction
in the biological system.
The antibacterial effects of these complexes have been compared with a standard
reference drug, chloramphenicol and it is concluded that the synthesized compounds showed
higher antibacterial activity than the standard reference drug.
EXPERIMENTAL
Materials and Methods
All manipulations were carried out under nitrogen atmosphere, using standard
Schlenk techniques.34 Dimethyltin dichloride, dibutyltin oxide, and triphenyltin hydrox-
ide were procured from Sigma Aldrich (New Delhi, India) and were used without further
purification. Indole-3-butyric acid and indole-3-propionic acid were purchased from Merck
(New Delhi, India) and were used as received. Acetonitrile and methanol were purchased

INDOLE-3-BUTYRIC ACID AND INDOLE-3-PROPIONIC ACID
419
from Spectrochem (New Delhi, India). Methanol was dried over sodium wire and distilled.
Acetonitrile was dried over CaCl2 for overnight followed by distillation. Ethanol was pur-
chased from Merck and dried over sodium pieces and distilled. It was followed by refluxing
with Mg turnings and a crystal of iodine and redistilled.
Preparation of Dimethyltin(IV) Oxide and Sodium Salts of Acids
Dimethyltin(IV) dichloride (Me2SnCl2) was dissolve in distilled water and stirred for
overnight. Colorless solution was obtained. Ammonia solution (60%) was added into the
colorless solution and finally fine white precipitate was obtained and filtered. The precipitate
was dried in oven (60◦C) for a day until dry white yellow precipitate of dimethyltin(IV)
oxide was obtained.
The sodium salts of acids were synthesized by heating under reflux a 1:1 molar
mixture of NaOH (0.12 g, 3 mmol) and indole-3-butyric acid (0.61 g, 3 mmol) or indole-
3-propionic acid (0.57 g, 3 mmol) in ethanol (50 mL) for 2 h. The resulting clear solution
was filtered and evaporated to dryness. Recrystallization of the light yellow residue from
alcohol gave a white solid. Yield: 86%; IR (KBr, cm−1); IBH: νas(COO) 1570 s, νs(COO)
1420 s; IPH: νas(COO) 1560 s, νs(COO) 1410 s.
Me2Sn(IB)2 and Me2Sn(IP)2 Complexes (1 and 4)
Complexes 1 and 4 were prepared by heating a 1:2 molar mixture of
dimethyltin(IV)oxide (0.49 g, 3 mmol) and indole-3-butyric acid (1.22 g, 6 mmol)
or indole-3-propionic acid (1.13 g, 6 mmol) in methanol (50 mL) under a nitrogen
atmosphere. The reaction mixture was refluxed for 2 h with a Dean-Stark apparatus, and
then allowed to cool at room temperature. A clear light yellow (1) or brown (4) transparent
solution was separated by filtration and kept in a bottle. After 4 days, pale yellow solid
(1) or brown solid (4) was obtained. The products were then recrystallized from absolute
ethanol.
Bu2Sn(IB)2 and Bu2Sn(IP)2 Complexes (2 and 5)
Complexes 2 and 5 were prepared by heating under reflux a 1:2 molar mixture
of dibutyltin(IV) oxide (0.75 g, 3 mmol) and indole-3-butyric acid (1.22 g, 6 mmol) or
indole-3-propionic acid (1.13 g, 6 mmol) in acetronitrile (50 mL) for 3 h with a Dean-
Stark apparatus. A clear light yellow (2) or brown (5) transparent solution was isolated by
filtration and kept in a bottle. After two weeks, pale yellow crystalline solid (2) or brown
solid (5) was collected. The products were then recrystallized from methanol.
Ph3SnIB and Ph3SnIP Complexes (3 and 6)
Complexes 3 and 6 were prepared by heating under reflux a 1:1 molar mixture of
triphenyltin(IV) hydroxide (1.10 g, 3 mmol) and indole-3-butyric acid (0.61 g, 3 mmol) or
indole-3-propionic acid (0.57 g, 3 mmol) in acetronitrile (50 mL) for 2 h with a Dean-Stark
apparatus. A clear transparent solution of light yellow (3) or light brown (6) was isolated
by filtration and kept in a bottle. After 8 days, white solid (3) or light brown solid (6) was
collected. The products were then recrystallized from methanol.

420
A. CHILWAL ET AL.
Characterization
The structural characterization of all six diorganotin(IV) derivatives was done by
using IR, 1H NMR, 13C NMR, and 119Sn NMR spectroscopic techniques. Elemental analysis
was carried out using EURO EA 3000 elemental analyzer. The tin content in the complexes
synthesized was determined gravimetrically as SnO2.35 IR spectra were recorded in KBr
pellets using Shimadzu FTIR 8300 spectrometer. NMR spectra were recorded on a Bruker
300 spectrophotometer in DMSO-d6 using tetramethylsilane (TMS) as an internal standard
(1H, 13C) and tetramethyltin as an external standard (119Sn).
Thermal Studies
The TG curves in the range of 25 to 700◦C were recorded using a Perkin Elmer
◦
Diamond TG/DTA instrument having TG 1500 module at a heating rate of 20 C min−1
in nitrogen atmosphere. Powdered samples having weights ranging from 8 to 10 mg were
used in each experiment.
Determination of Antibacterial Activity
The synthesized organotin(IV) complexes were tested against six bacterial strains;
three gram-positive: S. aureus, S. epidermidis and M. luteus and three gram-negative: E.
coli, P. aeruginosa, and E. aerogenes. Antibacterial activity was performed by employing
Broth Microdilution MIC method.36
CONCLUSIONS
The synthesized compounds were characterized by suitable analytical techniques,
i.e., IR, 1H NMR, 13C NMR, 119Sn NMR, and elemental analysis. The data obtained were
in full agreement with the proposed structures. The thermal stability of the complexes 3
and 6 is higher as compared to compounds 1, 2, 3, and 4. All the synthesized compounds
were screened for their in vitro antibacterial activity against standard strains of S. aureus,
S. epidermidis, M. luteus, P. aeruginosa, E. coli, and E. aerogenes, and data revealed that
compounds showed moderate to good activity. Compounds 3 and 6 were exhibited as a
strong activity against all the tested bacterial strains. The results provided evidence that
the studied compounds reported in this paper could serve as potential sources of microbial
agents.
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