Synthesis, characterization and antimicrobial activity of triorganotin(IV) derivatives of some bioactive Schiff base ligands

Article abstract of DOI:10.1002/aoc.3639

Triorganotin(IV) complexes of the type Me₃Sn[OC(R¹):CH(CH₃)C:NR²OH] and Ph₃Sn[OC(R′):CH(CH₃)C:NR″OH] (R′ = ─CH₃, ─C₆H₅; R″ = ─(CH₂)₂─,

Full text of DOI:10.1002/aoc.3639

Received: 6 July 2016
DOI 10.1002/aoc.3639
Revised: 17 August 2016
Accepted: 25 August 2016
F U L L PA P E R
Synthesis, characterization and antimicrobial activity of
triorganotin(IV) derivatives of some bioactive Schiff base ligands
1
1
2
1
*
Pooja Bhatra | Jyoti Sharma | Ram Avatar Sharma | Yashpal Singh
1 Department of Chemistry, University of
Triorganotin(IV) complexes of the type Me3Sn[OC(R1):CH(CH3)C:NR2OH] and
Ph3Sn[OC(R′):CH(CH3)C:NR″OH] (R′= ─CH3, ─C6H5; R″ = ─(CH2)2─,
─(CH2)3─) have been synthesized by the reactions of trimethyl/phenyltin(IV) chlo-
ride with the sodium salt of corresponding Schiff base ligands in unimolar ratio in
refluxing tetrahydrofuran. All these compounds have been characterized using ele-
mental analyses and their probable structures have been proposed on the basis of
Rajasthan, Jaipur, India
2 Department of Botany, University of Rajasthan,
Jaipur, India
Correspondence
Yashpal Singh, Department of Chemistry,
University of Rajasthan, Jaipur, India.
Email: yashpaluniraj@gmail.com
1
infrared, H NMR, 13C NMR, 119Sn NMR and mass spectroscopic studies. In the
trimethyltin(IV) derivatives the central tin atom is tetracoordinated, whereas in the
analogous triphenyltin(IV)derivatives the central tin atom is pentacoordinated. All
these ligands, metal precursors and corresponding triorganotin(IV) complexes have
been screened for antimicrobial activities. A comparison of activities of the ligands
and their corresponding triorganotin(IV) derivatives has been made. Attempts have
also been made to relate the activity to the structure of these compounds.
KEYWORDS
1
antimicrobial activities, H, 13C, 119Sn NMR spectroscopy, mass spectral data,
tetracoordinated and pentacoordinated tin, triorganotin(IV) Schiff base derivatives
1
|
INTRODUCTION
additives for paints applied on the outer covering of vessels
to protect them from marine microorganism corrosion.[42]
Some triaryltin benzoates have also shown good anti‐tumour
activity.[43] Moreover, trialkyl and triphenyl compounds
exhibit interesting structural diversity.[44–46]
Various types of Schiff bases have been synthesized and
extensively studied because of their antifungal, antiviral,
antibacterial, anti‐tumour and anti‐inflammatory properties
as well as their industrial and medicinal utility.[1–18]
Organotin(IV) complexes of β‐diketones,[19–21] heterocyclic
β‐diketones,[22] Schiff bases,[23–25] oximes,[26,27] amino
acids,[28] sulfa drugs,[29] etc., have been reported in the liter-
ature due to their potential industrial and biological applica-
tions.[30–34] Organotin(IV) complexes of Schiff bases have
attracted considerable interest owing to their biocidal[35]
and anti‐tumour activities[36] and potential applications in
organic synthesis,[37] catalysis,[38,39] medicinal chemistry[40]
and biotechnology.[41] In general, triorganotin(IV) com-
pounds exhibit more bioefficiency than their di‐ and
monoorganotin(IV) analogues.[42] Structural modification of
organic molecules has considerable biological relevance and
coordination of metal atoms in complexes also alters their
toxicity. Triphenyltin(IV) compounds are widely used as bio-
cides in agriculture whereas tributyltin species are the best
In view of the above, we have synthesized and character-
ized some new triorganotin(IV) complexes with bioactive
Schiff bases derived from β‐diketones and amino alcohols.
These compounds have been screened for antimicrobial activ-
ities. The antimicrobial activities of these tin compounds have
been compared with those of the corresponding free Schiff
bases and metal precursors. Structural modification of organic
molecules has considerable biological relevance and coordi-
nation of metal atoms in complexes also alters their toxicity
which has also been observed in the present case.
2
| EXPERIMENTAL
All the reactions were carried out under anhydrous condi-
tions. Solvents were purified and dried by standard
Appl Organometal Chem 2016; 1–8
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
1

2
BHATRA ET AL.
procedures.[47] Schiff bases (L1H2–L4H2) were prepared
using a literature method.[48] Trimethyltin(IV) chloride and
triphenyltin(IV) chloride (Aldrich) were distilled before use.
Tin was estimated gravimetrically as oxide.[49] C, H and N
were analysed using an Eager Xperience. Melting points of
the triorganotin(IV) complexes were determined in sealed
capillaries.
Infrared (IR) spectra of the complexes were recorded with
Shimadzu 840 840 FT‐IR spectrophotometer as nujoll mull
1
on KBr disc in the range 400–4000 cm−1. H NMR and
13C NMR spectra were recorded in CDCl3 solution with a
Bruker FT 400 MHz spectrometer using tetramethylsilane
as an internal reference. 119Sn NMR spectra of the complexes
were recorded using Me4Sn as an external reference. Mass
spectra of the complexes were recorded with a Shimadzu
GC–MS QP 2010 ULTRA spectrometer.
2.1 | Syntheses of complexes
All the organotin complexes, R3SnLH, were synthesized
using the same procedure. Therefore, the synthetic procedure
for one representative compound is discussed in detail. The
analytical as well as preparative details for all of the com-
pounds are summarized in Table 1.
2.1.1
|
Synthesis of complex Me3SnL1H
Trimethyltin chloride (1.564 g, 5.15 mmol) and the freshly
prepared sodium salt of Schiff base ligand Na[OC(CH3):
CH(CH3)C:NCH2CH2OH] (1.036 g, 5.15 mmol) were mixed
in tetrahydrofuran (THF; ca 50 ml) and the reaction mixture
was refluxed for ca 6 h. NaCl thus precipitated was filtered
off. The solvent was removed under reduced pressure to yield
a
brownish viscous compound. The compound was
recrystallized from THF–n‐hexane mixture. The compound
on analyses (%) was found to have: Sn, 38.76; C, 39.24; H,
6.90; N, 4.55; calculated (%): Sn, 38.79; C, 39.25; H, 6.91;
N, 4.57.
2.2 | Antimicrobial activity
Antimicrobial activities of complexes and ligands were stud-
ied against bacterial and fungal strains. Two bacterial and two
fungal strains were selected for primary screening. Strepto-
mycin was used as positive control for antibacterial activity
and clotrimazol for antifungal activity. Dimethylsulfoxide
(DMSO) was used as negative control for antimicrobial activ-
ity of the complexes.
2.2.1
| Microorganisms used
Clinical laboratory bacterial isolates of Bacillus subtilis and
Escherichia coli and fungal isolates of Aspergillus niger
and Fusarium oxysporum were collected from stock cultures
of the Microbiology Laboratory, SMS Medical College,
Jaipur, India.

BHATRA ET AL.
3
2.2.2
|
Culture and maintenance of bacteria
3
|
RESULTS AND DISCUSSION
Pure cultures obtained from SMS Medical College were used
as indicator organisms. These bacteria were grown in nutrient
agar medium (prepared by autoclaving 8% nutrient agar of
Difeco Laboratories, Detroit, USA, in distilled water at
15 psi for 25–30 min) and incubated at 37°C for 48 h. Each
bacterial culture was further maintained on the same medium
after every 48 h of transferring. A fresh suspension of test
organism in saline solution was prepared from a freshly
grown agar slant before every antimicrobial assay.
3.1 | Syntheses of triorganotin(IV) derivatives
Ligands were synthesized by the condensation reaction of
β‐diketones and selected amino alcohols using a literature
method.[48] Sodium salts of the ligands were prepared by the
reaction of Schiff bases and freshly prepared sodium
methoxide in unimolar ratio. The reactions of R3SnCl with
sodium salts of Schiff bases (LHNa) in unimolar ratio in
refluxing THF yield triorganotin(IV) complexes (Scheme 1).
2.2.3
| Antibacterial assay
3.2 | IR spectra
In vitro antibacterial activity of the complexes was studied
against Gram‐positive and Gram‐negative bacterial strains
by the agar well diffusion method.[50] Mueller–Hinton agar
no. 2 (Hi Media, India) was used as the bacteriological
medium. The test solutions were diluted in 100% DMSO at
a concentration of 5 mg ml−1. The Mueller–Hinton agar
was melted and cooled to 48–50°C and a standardized inoc-
ulum (1.5 × 108 CFU ml−1, 0.5 McFarland) was then added
aseptically to the molten agar and poured into sterile Petri
dishes to give a solid plate. Wells were prepared in the seeded
agar plates. The test compound (100 μl) was introduced in the
well (6 mm). The plates were incubated overnight at 37°C.
The antimicrobial spectrum of the extract was determined
for the bacterial species in terms of zone sizes around each
well. The diameters of zones of inhibition produced by the
agent were compared with those produced by the commercial
control antibiotic streptomycin. For each bacterial strain, con-
trols were maintained where pure solvents were used instead
of the extract. The control zones were subtracted from the test
zones and the resulting zone diameter was measured with an
antibiotic zone reader to the nearest millimetre. The experi-
ment was performed three times to minimize the error and
the mean values are presented.
In the IR spectra of these derivatives the disappearance of the
broad band observed in the spectra of parent ligands at 2700–
3000 cm−1 and assigned[52] to enolic ─OH indicates the
deprotonation of ─OH group. This is supported by the
appearance of a new band at 512–536 cm−1 due to
ν(Sn─O) stretching vibrations.[53] In the IR spectra of free
ligands the azomethine ν(>C═N) band present at 1617–
1625 cm−1 is shifted to 1571–1602 cm−1 in the spectra of
the complexes Ph3SnL1H–Ph3SnL4H. Considerable shifts to
lower wavenumber in its position may be due to the involve-
ment of >C═N group nitrogen in coordination with tin atom.
The appearance of a new band in the region 441–448 cm−1
due to ν(Sn─N) supports the formation of Sn─N bond[54] in
complexes Ph3SnL1H–Ph3SnL4H. However, no significant
shift is observed in the position of ν(>C═N) band in the
spectra of Me3SnL1H–Me3SnL4H which rules out the
involvement of this group in the bonding. A broad band
observed for aminol group ν(C─OH) at 3300–3600 cm−1 in
the spectra of ligands does not show any appreciable shift
in its position for all the complexes which rules out the
involvement of this group in the bonding.
3.3 | 1H NMR spectra
1
2.2.4
| Antifungal assay
In the H NMR spectra (Table 2) of the ligands both enolic
and aminol ─OH signals are observed at 11.3–12.2 and
Antifungal activity of the complexes was investigated using
the agar well diffusion method.[51] The yeasts and sapro-
phytic fungi were subcultured onto Sabouraud's dextrose agar
SDA (Merck, Germany) and incubated at 37°C for 24 h and
25°C for 2–5 days, respectively. Suspensions of fungal spores
were prepared in sterile phosphate‐buffered saline and
adjusted to a concentration of 106 cells ml−1. A sterile swab
was dipped into the fungal suspension and rolled on the sur-
face of the agar medium. The plates were dried at room tem-
perature for 15 min. Wells of 10 mm in diameter and about
7 mm apart were punctured in the culture media using a ster-
ile glass tube. An amount of 0.1 ml of several dilutions of
fresh extracts was administered to fullness for each well.
Plates were incubated at 37°C. After 24 h of incubation, bio-
activities were determined by measuring the diameter of inhi-
bition zones (in millimetres). All experiments were made in
triplicate and means were calculated.
a
b
SCHEME 1 Synthetic route for bifunctional tridentate Schiff bases (L1H2–
L4H2) and their triorganotin(IV) derivatives: (A) triphenyltin(IV) complexes;
(B) trimethyltin(IV) complexes

4
BHATRA ET AL.
3.4–4.4 ppm, respectively. Absence of the signal for enolic
─OH in the spectra of all the triorganotin(IV) derivatives
reveals the deprotonation and involvement of this group in
bonding with tin atom. But the signal for aminol ─OH group
is present in the spectra of ligands as well as of complexes.
The position of the signal does not show any significant shift
even after complexation which shows that aminol group does
not take part in bonding and is present as free ─OH group.
Aromatic protons appear as a multiplet in the region 7.3–
7.9 ppm in the spectra of ligands as well as of organotin
complexes.
In the spectra of Me3SnL1H–Me3SnL4H the Sn─CH3
protons appear as a singlet in the range 0.36–0.81 ppm which
indicates that all three methyl groups are in the same chemi-
cal environment. The 2J(1H–119Sn) coupling constants,
which provide important information about the coordination
environment, were also determined and are given in
Table 2. For triphenyltin(IV) complexes it is not possible to
distinguish between signals due to aromatic ligand protons
and those linked to tin, but integration takes their presence
2
into account. The J(1H–119Sn) values are in the range 54–
56.1 Hz for Me3SnLH‐type complexes. The C─Sn─C bond
angle calculated using Lockhart and Manders equations[55,56]
is in the range 109.06–110.12° for these complexes. These
coupling constant values correspond to tetracoordination
and the bond angles clearly indicate tetrahedral geometry[55]
in complexes Me3SnL1H–Me3SnL4H.
3.4 | 13C NMR spectra
The 13C NMR spectral data for these derivatives are summa-
rized in Table 3. The spectra of all the triorganotin(IV) com-
plexes as well as their corresponding ligands exhibit a signal
for >C─O─ enolic group carbon[57] in the range 187.5–
195.8 ppm. A small downfield shift is observed in the posi-
tion of this signal as compared to the corresponding free
ligands. This shift is slightly more downfield in case of
triphenyltin(IV) complexes as compared to trimethyltin(IV)
complexes. Signal for >C═N imine group carbon is observed
in the range 162.9–165.9 ppm. A downfield shift of ca
2–5 ppm is been observed for triphenyltin(IV) complexes
(Ph3SnL1H–Ph3SnL4H) as compared to its position in the
spectra of corresponding free Schiff base ligands. However,
for trimethyltin(IV) derivatives no appreciable shift in this
signal is observed. This shift in the positions of the signal
of carbon atom adjacent to the imine group nitrogen suggests
that nitrogen is involved in coordination with tin in
triphenyltin(IV)complexes only. While in trimethyltin(IV)
complexes this group does not take part in the bonding. The
signal for CH2O─ group carbon appears in the range 60.7–
68.3 ppm in spectra of Schiff bases and the corresponding
tin complexes. The spectra of complexes Me3SnL1H–
Me3SnL4H exhibit a signal for CH3─Sn group carbon in
the range 7.4–8.1 ppm. The 1 J(119Sn–13C) coupling constant
values are found to be in the range 369.7–381.3 Hz for these

BHATRA ET AL.
5
TABLE 3 13C NMR spectral data (δ, ppm) of new triorganotin(IV) Schiff base derivatives
Ligand/compound
═C─OH
>C═N
─C6H5
Alkylene carbon
L1H2
L2H2
L3H2
L4H2
Me3SnL1H
Me3SnL2H
Me3SnL3H
Me3SnL4H
Ph3SnL1H
Ph3SnL2H
Ph3SnL3H
Ph3SnL4H
191.1
193.5
188.2
192.9
191.9
192.5
193.5
194.1
193.9
194.2
195.8
195.4
162.6
163.4
161.7
163.8
164.4
165.7
164.8
164.3
165.1
165.4
164.9
165.2
94.9 (═CH─), 62.2 (CH2O), 58.0 (CH2N), 33.9 (CH3CO), 26.3 (CH3CN)
96.6 (═CH─), 68.3 (CH2O), 51.3 (CH2N), 41.2 (CH2), 31.2 (CH3CO), 24.3 (CH3CN)
95.6 (═CH─), 67.6 (CH2O), 52.4 (CH2N), 27.4 (CH3CN)
126.1–140.4
126.4–140.2
92.2 (═CH─), 70.1 (CH2O), 59.5 (CH2N), 39.9 (CH2), 26.4 (CH3CN)
95.2 (═CH─), 63.4 (CH2O), 58.4 (CH2N), 34.6 (CH3CO), 26.7 (CH3CN)
96.9 (═CH─),68.7 (CH2O),51.6 (CH2N),41.0 (CH2),31.5 (CH3CO), 24.8 (CH3CN)
95.3 (═CH─),68.2 (CH2O),57.9 (CN),34.7 (CH3CO),28.7 (CH3CN) 20.3 (CH3)
95.8 (═CH─), 68.4 (CH2O), 52.8 (CH2N), 27.7 (CH3CN)
126.7–140.8
126.2–140.1
126.4–140.3
127.4–140.6
92.7 (═CH─), 69.3 (CH2O), 60.4 (CH2N), 38.2 (CH2), 26.6 (CH3CN)
94.3 (═CH─), 61.2 (CH2O), 52.2 (CN), 27.9 (CH3CN), 24.6–19.7 (CH3)
95.3 (═CH─),68.2 (CH2O),57.9 (CN),34.7 (CH3CO),28.7 (CH3CN) 20.3 (CH3)
95.8 (═CH─), 68.4 (CH2O), 52.8 (CH2N), 27.7 (CH3CN)
complexes, which is consistent with tetracoordination in
trimethyltin(IV) complexes.[55,56]
Molecular ion peaks and other characteristic peaks indicate
the monomeric nature of these complexes. Mass peaks indi-
cate the formation of a variety of fragments bearing tin atom
in the course of decomposition. Molecular ion peaks of com-
plexes Me3SnL1H–Me3SnL4H are observed at m/z 306, 304,
352 and 366, respectively. For complexes Ph3SnL2H and
Ph3SnL4H low abundant molecular ion peaks are observed
at m/z 490 and 538. In complexes Ph3SnL1H and Ph3SnL4H
no molecular ion peaks are observed. For all these com-
pounds molecular ion peaks are not base peaks. In all these
compounds the fragmentation initiates in same manner by
the loss of ethylenic (═CH) carbon followed by the decompo-
sition of ligand and the R─Sn]+ fragment is formed as a final
decomposition product showing strong bonding of tin atom
by alkyl/phenyl group.
3.5 | 119Sn NMR spectra
119Sn NMR spectra can be used as an indicator of coordina-
tion number of the tin atom. 119Sn chemical shift also shows
a variation with a change in coordination number. The 119Sn
NMR chemical shifts for all the organotin(IV) complexes are
given in Table 2. Holecek et al.[58] reported δ(119Sn) for four‐
coordinate and five‐coordinate compounds in the range − 40
to −120 and −180 to −260 ppm, respectively. Chemical
shifts in the range − 90 to −330 ppm in CDCl3 solution have
been reported for five‐coordinate organotin(IV) chelates by
Otera.[59] The 119Sn NMR spectra of complexes
Me3SnL1H–Me3SnL4H show only one singlet at −40.4 to
−52 ppm which is in the normal range for four‐coordinate
tin complexes,[60] further supported by a value of −47 ppm
for tetrahedral Ph3SnL (L = heterocyclic β‐diketone).[61]
The spectra of complexes Ph3SnL1H–Ph3SnL4H exhibit only
one singlet at −141 to −176.1 ppm which is in the normal
range for five‐coordinate complexes.[43,59,60]
3.7 | Antimicrobial activity
The triorganotin(IV) complexes and their corresponding free
Schiff bases (L1H2–L4H2) were screened against bacteria
(Table 5) and fungi (Table 6) to examine their growth inhib-
itory potential towards the test organisms. The results for
antimicrobial activity are summarized in the following points.
3.6 | Mass spectra
i. All the compounds (ligands as well as complexes) are
more toxic towards Gram‐positive strain (B. subtilis)
than Gram‐negative strain (E. coli).The reason probably
lies in the difference between the structures of the cell
The mass spectra of all the newly synthesized complexes
were recorded and the characteristic mass peaks of one repre-
sentative complex, Me3SnL1H, are summarized in Table 4.
TABLE 4 Fragmentation mode of complex Me3SnL1H
Fragment
m/z
Relative abundance (%)
(CH3)3Sn[OC(CH3):CH (CH3)C:N(CH2CH2)OH]+.
(CH3)3Sn[OC(CH3):C(CH3):N(CH2CH2)OH]+.
(CH3)3Sn[OC(CH3):N(CH2CH2)OH]+.
(CH3)3Sn[N(CH2CH2)OH]+.
(CH3)3Sn[CH2‐OH]+.
306
293
267
223
195
164
134
6
100
18
37
23
(CH3)3Sn]+.
(CH3)Sn]+.
19
41

6
BHATRA ET AL.
TABLE 5 Antibacterial studies of ligands and corresponding triorganotin
(IV) Schiff base derivatives
walls. The relatively more complex cell walls of Gram‐
negative strains may prevent the diffusion of chemicals
into the cytoplasm of the organisms, which may not be
the case in Gram‐positive strains.
Inhibition zone diameter (mm)
Concentration
S.
aureus
B.
subtilis
E.
coli
P.
Compound
(mg ml−1
)
aeruginosa
ii. The results indicate that the metal chelates have higher
activity than the free ligands. This increased activity of
the metal chelates can be explained by Tweedy's chela-
tion theory[62] and Overtone's concept. According to
Overtone's concept of cell permeability, the lipid mem-
brane that surrounds the cell favours passage of only
lipid‐soluble material due to liposolubility which is an
important factor that controls antimicrobial activity.
On chelation, the polarity of the metal ions is reduced
to a greater extent due to the overlap of the ligand orbital
and partial sharing of the positive charge of the metal
ion with donor group. Enhanced activity may be due
to the coordination of ligand to tin leading to electron
delocalization and therefore increasing the lipophilic
character and efficient diffusion of the metal complexes
into bacterial cells.
L1H2
2
4
7
8
6
9
6
8
5
7
L2H2
2
4
7
10
7
10
5
9
6
9
L3H2
2
4
9
12
8
11
8
10
7
10
L4H2
2
4
6
8
7
9
5
7
7
9
Me3SnL1H
Me3SnL2H
Me3SnL3H
Me3SnL4H
Ph3SnL1H
Ph3SnL2H
Ph3SnL3H
Ph3SnL4H
2
4
7
10
8
10
6
9
8
10
2
4
6
8
7
12
6
8
7
11
2
4
7
11
9
14
7
10
9
12
2
4
11
14
9
15
8
13
7
11
2
4
13
17
12
15
11
16
10
14
2
4
10
13
12
16
10
13
9
12
iii. It is important to mention that the antimicrobial activity
for ligands derived from benzoyl acetone (L3H2 and
L4H2) and their corresponding metal complexes
(Me3SnL3H, Me3SnL4H, Ph3SnL3H and Ph3SnL4H) is
greater than the ligands derived from acetyl acetone
(L1H2 and L2H2) and their corresponding metal com-
plexes (Me3SnL1H, Me3SnL2H, Ph3SnL1H and
Ph3SnL2H). Moreover, the triphenyltin(IV) complexes
of all the ligands are more active than the corresponding
trimethyltin(IV) derivatives. Thus, it may be concluded
that the presence of phenyl group in the ligand as well
as at the tin centre enhances the activity which may be
due to the electron‐withdrawing nature of the phenyl
group.
2
4
14
17
13
17
12
16
8
11
2
4
12
17
12
19
12
13
9
13
TABLE 6 Antifungal studies of ligands and corresponding triorganotin(IV)
Schiff base derivatives
Inhibition zone diameter (mm)
Concentration
F.
T.
P.
A.
Compound
(mg ml−1
)
oxysporum reesei funiculosum
niger
L1H2
2
4
7
8
6
9
6
8
5
7
iv. The concentration of compounds is another important
factor which affects the inhibition of growth. At lower
concentration (2 mg ml−1) growth will be slowed down,
while at higher concentration more enzymes will
become inhibited leading to a quicker death of the
organism.
L2H2
2
4
9
11
8
12
7
11
6
10
L3H2
2
4
11
13
10
12
9
13
8
12
L4H2
2
4
6
7
5
9
5
8
6
9
Me3SnL1H
Me3SnL2H
Me3SnL3H
Me3SnL4H
Ph3SnL1H
Ph3SnL2H
Ph3SnL3H
Ph3SnL4H
2
4
7
9
8
11
6
9
7
10
2
4
8
10
7
11
7
10
8
11
3.8 | Structural elucidation
2
4
7
11
9
12
7
12
8
10
For all the complexes, aminol ─OH is not deprotonated and
deprotonation of only enolic group indicates the
monofunctional nature of the ligands. In triphenyltin(IV)
complexes (Ph3SnL1H–Ph3SnL4H), the >C═N group takes
part in coordination as indicated by the significant shift in
the position of >C═N group carbon signal in 13C NMR spec-
tra. Thus the ligands behave as monofunctional bidentate
moieties.
2
4
8
12
7
11
8
10
9
13
2
4
10
13
9
12
14
16
13
17
2
4
11
15
13
14
11
15
14
16
2
4
12
15
15
18
16
20
17
20
2
4
11
13
11
14
13
17
14
19
In view of the above, we propose structures in which the
central tin atom acquires tetracoordination (Figure 1B) and

BHATRA ET AL.
7
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FIGURE
1
Proposed structures for the complexes: (A) Ph3SnL1H–
Ph3SnL4H; (B) Me3SnL1H–Me3SnL4H
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pentacoordination (Figure 1A) in trimethyltin(IV) complexes
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2
1
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4
| CONCLUSIONS
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In triorganotin(IV) derivatives of chelating ligands, the
denticity of ligands and geometry of complexes are found
to be different in trimethyltin(IV) and triphenyltin(IV) com-
plexes. One explanation for this behaviour may be that in
trimehtyltin(IV) complexes the central tin atom is less elec-
tron deficient due to the presence of electron‐releasing group
as compared to the triphenyltin(IV) derivatives where elec-
tron‐withdrawing phenyl groups are present. We observed
similar behaviour of ligand and different geometries around
the central tin atom for trimethyltin(IV) and triphenyltin(IV)
compounds. In the compounds Me3SnLH, the ligand, which
usually behaves as a bifunctional tridentate moiety,[63] is a
monofunctional monodentate moiety and the geometry
around the central tin atom is tetrahedral. Whereas in
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the compounds Ph3SnLH, the ligand behaves as
monofunctional bidentate moiety and the geometry of the
compounds is trigonal bipyramidal.
We have also observed a structure–activity relationship in
the ligands and the newly synthesized complexes. The pres-
ence of the phenyl group enhances the toxicity of the ligands
and the complexes.
a
3169.
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The authors are grateful to SAIF, Panjab University, Chandi-
garh for recording the C, H and N analyses, and for 1H NMR,
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