Di- and triorganotin(IV) complexes of 2-aminobenzoic acid with and without triphenylphosphine: Synthesis, spectroscopy, semi-empirical study, and antimicrobial activities

Article abstract of DOI:10.1080/00958972.2010.544036

Eight organotin carboxylates have been synthesized in quantitative yield by reaction of NaL (L = 2-aminobenzoate) with the di- and triorganotin chlorides and triphenylphosphine. All the complexes have been characterized by elemental analysis, IR, multinuclear NMR (¹H, ¹³C, and 119Sn), and mass spectrometry. The spectroscopic data indicate 1 : 2/1 : 1 M : L stoichiometry in 1, 3, 5, and 7 and 1 : 2 : 1/1 : 1 : 1 M : L : PPh3 stoichiometry in 2, 4, 6, and 8. FT-IR spectra clearly demonstrate metal attachment with both oxygens of the ligand and bidentate coordination in 1, 3, 5, and 7 while monodentate ligand for 2, 4, 6, and 8. In solid state, 1, 2, 5, and 6 exhibit six coordination whereas 3, 4, 7, and 8 show five coordination. The structural behavior is confirmed by semi-empirical study. NMR data reveal four-coordinate geometry in solution. These complexes were screened for antimicrobial activity invitro. The screening tests show that tributyltin carboxylates are more potent antibacterial and fungicidal agents than corresponding methyl derivatives, and triphenylphosphine enhances the antibacterial and fungicidal activities of these complexes.

Full text of DOI:10.1080/00958972.2010.544036

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Di- and triorganotin(IV) complexes
of 2-aminobenzoic acid with and
without triphenylphosphine: synthesis,
spectroscopy, semi-empirical study, and
antimicrobial activities
a
b
a
Muhammad Mohsin Amin , Saqib Ali , Saira Shahzadi , Saroj K.
c
c
Sharma & Kushal Qanungo
a
Department of Chemistry , GC University , Faisalabad, Pakistan
b
Department of Chemistry , Quaid-i-Azam University , Islamabad
5320, Pakistan
4
c
Department of Applied Science and Humanities, Faculty of
Engineering and Technology , Mody Institute of Technology and
Science , Lakshmangargh 332311, Sikar, Rajasthan, India
Published online: 04 Jan 2011.
To cite this article: Muhammad Mohsin Amin , Saqib Ali , Saira Shahzadi , Saroj K. Sharma &
Kushal Qanungo (2011) Di- and triorganotin(IV) complexes of 2-aminobenzoic acid with and without
triphenylphosphine: synthesis, spectroscopy, semi-empirical study, and antimicrobial activities,
Journal of Coordination Chemistry, 64:2, 337-350, DOI: 10.1080/00958972.2010.544036
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Journal of Coordination Chemistry
Vol. 64, No. 2, 20 January 2011, 337–350
Di- and triorganotin(IV) complexes of 2-aminobenzoic acid
with and without triphenylphosphine: synthesis, spectroscopy,
semi-empirical study, and antimicrobial activities
MUHAMMAD MOHSIN AMINy, SAQIB ALI*z, SAIRA SHAHZADI*y,
SAROJ K. SHARMAx and KUSHAL QANUNGOx
yDepartment of Chemistry, GC University, Faisalabad, Pakistan
zDepartment of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan
xDepartment of Applied Science and Humanities, Faculty of Engineering and Technology,
Mody Institute of Technology and Science, Lakshmangargh 332311, Sikar, Rajasthan, India
(
Received 18 February 2010; in final form 27 October 2010)
Eight organotin carboxylates have been synthesized in quantitative yield by reaction of NaL
L ¼ 2-aminobenzoate) with the di- and triorganotin chlorides and triphenylphosphine. All the
(
complexes have been characterized by elemental analysis, IR, multinuclear NMR ( H, C, and
1
13
1
19
Sn), and mass spectrometry. The spectroscopic data indicate 1 : 2/1 : 1 M : L stoichiometry in
, 3, 5, and 7 and 1 : 2 : 1/1 : 1 : 1 M : L : PPh stoichiometry in 2, 4, 6, and 8. FT-IR spectra
clearly demonstrate metal attachment with both oxygens of the ligand and bidentate
1
3
coordination in 1, 3, 5, and 7 while monodentate ligand for 2, 4, 6, and 8. In solid state, 1,
2, 5, and 6 exhibit six coordination whereas 3, 4, 7, and 8 show five coordination. The structural
behavior is confirmed by semi-empirical study. NMR data reveal four-coordinate geometry in
solution. These complexes were screened for antimicrobial activity in vitro. The screening tests
show that tributyltin carboxylates are more potent antibacterial and fungicidal agents than
corresponding methyl derivatives, and triphenylphosphine enhances the antibacterial and
fungicidal activities of these complexes.
Keywords: Organotin complexes; Triphenylphosphine; IR; NMR; Mass; Semi-empirical study;
Biological activity
1. Introduction
Organotin derivatives are potentially active biological agents with well-documented
applications in agriculture and industries [1–4]. Interest in the chemistry of
organotin(IV) compounds has led to extended studies on their reactions with different
biomolecules, e.g., carbohydrates [5], nucleic acid derivatives [6], amino acids [7], and
peptides [8].
*
Corresponding authors. Email: drsa54@yahoo.com; sairashahzadi@yahoo.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
DOI: 10.1080/00958972.2010.544036

3
38
M.M. Amin et al.
In general, triorganotin(IV) compounds display better biological activity than their
diorganotin and mono-organotin analogs. This has been attributed to their ability to
bind proteins [9]. Organotin(IV) carboxylates possess anticancer activity in a variety of
tumor cells and the structure of these organotin(IV) compounds have been character-
ized in solid and solution [10].
Organotin(IV) carboxylates have been of interest for some time because of their
biochemical and commercial applications [11]. In general, the biochemical activity of
organotin(IV) carboxylates is greatly influenced by the structure and the coordina-
tion number of tin [12]. Recognition of the importance between biological properties
and the structure of organotin(IV) carboxylates [13] has spurred the study of
carboxylates of tin. Organotin(IV) compounds are also used for pharmacological
applications as bactericides [14], as antitumor [15], antiinflammatory [16], and
antituberculosis agents [17].
We have synthesized some new organotin(IV) derivatives with 2-aminobenzoic acid,
with and without triphenylphosphine, in continuation of our previous work [18–21], to
study possible structure activity correlations.
2. Experimental
2.1. Chemicals and instrumentation
2-Aminobenzoic acid, triphenylphosphine, tributyltin chloride, dibutyltin dichloride,
trimethyltin chloride, dimethyltin dichloride, and sodium hydroxide were purchased
from Aldrich. All these chemicals were of analytical grade and used without
purification. Solvents were dried by standard procedures [22].
Melting points were determined by using an electromelting point apparatus model
MP-D Mitamura Riken Kogyo (Japan) and are uncorrected. Elemental analyses (for
carbon, hydrogen, and nitrogen) were done by CHN-932 elemental analyzer Lesco
1
13
Corporation, USA. The H- and C-NMR spectra were recorded on a Bruker ARC
00 MHz FT-NMR spectrometer using CDCl as an internal reference (for which
3
3
1
13
ꢀ( H) ¼ 7.25 ppm and ꢀ( C) ¼ 77.0 ppm). IR spectra were recorded as KBr pellets on a
ꢀ1
Varian 2000 Schimtar series spectrophotometer from 4000 to 400 cm . The molecules
were modeled by MOPAC 2007 [23] program in gas phase using the PM3 method
[
24, 25]. Selected parts of the complexes not containing the metal ion were preoptimized
using molecular mechanics methods. Several cycles of energy minimization had to be
carried for each molecule. The root mean square gradient for molecules was all less
than 1. Self consistent field was achieved in each case.
2
.2. Synthesis of 2-aminobenzoate (NaL)
2-Aminobenzoic acid (1 mmol) and sodium hydroxide (1 mmol) were stirred
together in distilled water in a round bottom flask at room temperature for 4 h.
Then water was evaporated using a rotary evaporator to separate sodium salt of
ligand.

Di- and triorganotin(IV) complexes
339
2
.3. General procedure for the synthesis of R SnL /R SnL (1, 3, 5, and 7)
2
2
3
Sodium salt of ligand (2/1 mmol) was suspended in dry toluene (100 mL) in a 250 mL
two-necked round bottom flask equipped with water condenser and magnetic stirring
bar. R SnCl /R SnCl (1 mmol) in dry toluene (50 mL) was added dropwise with
2
2
3
constant stirring. The reaction mixture was refluxed for 6–8 h. Sodium chloride was
filtered off and the solvent was evaporated by rotary evaporator under reduced
pressure. Purity of the product was checked by TLC. Solid obtained was recrystallized
in chloroform : n-hexane (1 : 1).
2
.4. General procedure for the synthesis of R SnL (PPh ) /R SnLPPh
2 2 3 2 2 3
(
2, 4, 6, and 8)
Sodium salt of ligand (2/1 mmol), R SnCl /R SnCl (1 mmol), and Ph P in
3
2
2
3
(2/1 mmol) were stirred together in 40 mL dry chloroform in a round bottom
flask at room temperature for 3 h. Sodium chloride was removed by filtration and
the solvent was evaporated slowly at room temperature to get a solid product.
Purity of the product was checked by TLC. The product was recrystallized in
acetone : n-hexane (1 : 2).
O
C
ONa
NH2
R SnCl +2
2
2
O
R
O
Sn
R
O
O
NH2
NH2
+2NaCl
(
R=n–CH , n–C H )
3
4 9
For 1 and 5.

3
40
M.M. Amin et al.
O
C
ONa
NH2
R SnCl +2
+PPh3
2
2
O
C
R
PPh3
O
Sn
R
O
C
O
Ph3P
NH2
NH2
+2NaCl
(
R=n–CH , n–C H )
3
For 2 and 6.
O
4 9
C
ONa
NH2
R3SnCl+
NH2
R
O
O
R
Sn
R
+
NaCl
(
R=n-CH , n-C H )
3 4 9
For 3 and 7

Di- and triorganotin(IV) complexes
341
O
C
ONa
NH2
R3SnCl+
+PPh3
NH2
PPh3
R
R
Sn
O
C
O
R
+NaCl
(
R=n–CH , n–C H )
3 4 9
For 4 and 8.
3. Results and discussion
All the compounds have sharp melting points and are soluble in common organic
solvents. Elemental analyses are in good agreement with the calculated values. Physical
and elemental data for 1–8 are given in table 1.
3
.1. Infrared spectroscopy
ꢀ1
Infrared spectra of NaL and 1–8 were recorded from 4000 to 400 cm as KBr discs
with characteristic vibrational frequencies identified by comparing spectra of the
complexes with that of L. The IR absorptions of interest are ꢁ(COO)sym, ꢁ(COO)asym
ꢁ
,
(Sn–C), and ꢁ(Sn–O).
The absence of broad band of ꢁ(OH) and the presence of ꢁ(Sn–O) at 465–450 cm
ꢀ
1
indicate deprotonation of carboxylic acid and bond formation with tin. The ꢁ(Sn–C)
ꢀ
1
were observed at 583–560 cm . The vacant 5 d orbital of tin tends toward high
coordination with ligands containing lone pairs of electrons. Based on the difference
ꢀ1
between ꢁ(COO)sym and ꢁ(COO)asym (below 200 cm
for bidentate carboxylate,

3
42
M.M. Amin et al.
Table 1. Physical data of the synthesized organotin carboxylates.
CHN analysis
Molecular
formula MW
%C Calcd
Found
%H Calcd
Found
%N Calcd
Found
ꢁ
Compound No.
% Yield
M.p. ( C)
NaL
C
1
7
H
59.12
6
NO
2
2
Na
Sn
Sn
93
76
5250
52.84
52.80
3.80
3.76
8.80
8.84
1
C
16
H
18
N
O
4
122–124
45.60
45.64
66.05
66.09
40.04
40.00
59.82
59.86
52.10
52.14
67.52
69.56
53.55
53.51
64.55
64.60
4.31
4.35
5.12
5.16
5.04
5.08
5.38
5.34
6.36
6.40
6.06
6.02
7.80
7.76
7.03
7.07
6.65
6.61
2.96
3.00
4.67
4.63
2.49
2.53
5.52
5.56
2.72
2.76
3.29
3.25
2.03
2.07
4
21.04
2
3
4
5
6
7
8
C
52
H
48
P
2
N
2
O
4
70
71
75
60
72
60
65
64–65
123–125
68–70
9
45.61
15NO
99.94
30PNO
62.23
C
10
H
2
Sn
Sn
Sn
Sn
2
C
28
H
2
5
C
22
H
32
N
2
O
4
108–110
68–70
5
07.21
C
58
H
62
P
2
N
2
O
4
1
031.78
33NO
26.18
48PNO
88.47
C
19
H
2
Sn
Sn
111–113
74–76
4
C
37
H
2
6
ꢀ
1
Table 2. IR data (cm ) of synthesized organotin carboxylates.
ꢁ
(COO)
Compound No.
ꢁ(–NH)
ꢁ(COO)asym
ꢁ(COO)sym
Dꢁ
ꢁ(Sn–C)
ꢁ(Sn–O)
NaL
3220
3222
3221
3220
3222
3222
3221
3221
3220
1585
1585
1581
1590
1595
1588
1565
1592
1590
1365
1457
1362
1453
1386
1458
1341
1480
1368
220
128
219
137
209
130
224
112
222
–
–
1
2
3
4
5
6
7
8
560
562
570
574
575
583
571
580
450
462
452
451
450
455
458
465
ꢀ
1
but greater than 200 cm for monodentate carboxylate) Dꢁ for 1, 3, 5, and 7 lie in the
range 137–112 cm , indicating bidentate carboxylate [26], while for 2, 4, 6, and 8,
ꢀ1
ꢀ
1
ꢀ1
2
Important bands of complexes along with NaL are given in table 2.
24–209 cm
indicates monodentate ligand. The ꢁ(NH ) is at 3222–3220 cm .
2
3
3
.2. NMR spectroscopy
1
.2.1. H-NMR spectroscopy. Characteristic resonances in the H-NMR spectra of
1
the complexes, recorded in CDCl , are given in table 3. A broad resonance at ꢀ 11.0 ppm
3

Di- and triorganotin(IV) complexes
Table 3. H-NMR data of synthesized organotin carboxylates.
343
1
Proton No.
1
2
3
4
5
6
7
8
a
c
d
e
5.71 s
6.67 d
(7.6)
7.34 m
7.22 m
–
5.82 s
6.72 d
(7.6)
7.39 m
7.29 m
7.31 s
5.74 s
6.66 d
(7.6)
7.35 m
7.22 m
–
5.81 s
6.71 d
(7.6)
7.39 m
7.28 m
7.32 s
5.75 s
6.67 d
(7.6)
7.33 m
7.23 m
–
5.82 s
6.73 d
(7.6)
7.38 m
7.29 m
7.31 s
5.74 s
6.67 d
(7.6)
7.34 m
7.22 m
–
5.83 s
6.74 d
(7.6)
7.38 m
7.28 m
7.30 s
f
i, j, k, l, m, n
1
2
3
4
5
6
7
8
Sn–CH
Sn–CH
Sn–CH
Sn–CH
Sn–CH
Sn–CH
Sn–CH
Sn–CH
3
3
3
3
2
2
2
2
, 1.26 s [74].
, 1.35 s [75].
, 0.99 s [57].
, 1.20 s [58].
–CH
–CH
–CH
–CH
2
–CH
2
–CH
2
–CH
2
–CH
2
2
2
2
–CH
–CH
–CH
–CH
3
3
3
3
, 0.90 t [60], 1.36–1.81 m.
, 0.98 t [60], 1.39–1.83 m.
, 0.92 t, 1.33–1.74 m.
, 0.98 t, 1.31–1.78 m.
a
NH2
P
b
c
e
O
O
i
g
h
d
n
j
f
m
k
l
due to carboxylic acid proton is absent in the complexes, indicating deprotonation of
the carboxylic oxygen. The CH protons of dimethyl- and trimethyltin(IV) derivatives
3
(
1 and 3) are sharp singlets at 1.26 and 0.99 ppm, both with well-defined satellites,
119
2
1
J[ Sn, H] ¼ 74 and 57 Hz, respectively, which demonstrate diorganotin derivatives
with coordination number greater than four, probably five or six; triorganotin
derivatives show distorted tetrahedral geometry in solution. Protons of n-butyltin
derivatives show a complex pattern and were assigned as reported earlier [27–29].
However, ꢀ-CH protons of both di-n-butyl- and tri-n-butyltin(IV) moieties, 5 and 7,
3
appear as a triplet at 0.90 and 0.92 ppm, while the ꢂ-CH , ꢃ-CH , and ꢄ-CH protons
2
2
2
are multiplets [29].
1
.2.2. C-NMR spectroscopy.
3
13
3
C resonances associated with the carboxylate ligand
are assigned by comparison with results obtained from the incremental method [30] and
earlier reports [18, 31] (table 4). The carboxylic carbon shifts downfield in the
complexes, suggesting coordination, through carboxylic oxygen, to organotin(IV).
1
119
13
The value J( Sn– C) is different in di- and tri-organotin compounds for four- and
five-coordinate tin. In diorganotin dicarboxylates, the geometry around tin could not be
determined with certainty due to the fluxional behavior of the carboxylate oxygen;
however, earlier reports suggest five or six coordination [18, 31].
1
19
119
Sn chemical shifts of organotin compound cover a range of ꢂ600 ppm. The Sn
chemical shift in CDCl is given in table 4. These values lie inside the range for
3

3
44
M.M. Amin et al.
C- and Sn-NMR data of synthesized organotin carboxylates.
1
3
119
Table 4.
Carbon No.
1
2
3
4
5
6
7
8
b
c
d
e
f
g
h
i
150.64
116.46
134.76
119.57
132.97
128.63
177.34
–
151.01
118.52
138.88
120.54
134.62
129.65
179.76
128.73
132.521
28.46
150.25
116.23
133.59
119.47
132.65
128.61
179.30
–
151.25
118.23
134.88
120.47
134.65
129.65
178.28
128.77
137.101
28.47
150.61
116.40
134.63
119.54
133.06
128.65
178.29
–
151.84
118.51
134.19
120.53
134.64
129.68
179.21
128.75
132.161
28.49
150.18
116.16
133.40
119.54
132.76
128.63
178.16
–
151.80
118.16
134.62
120.43
134.74
129.63
179.29
128.74
132.061
28.56
j, n
k, m
l
–
–
–
–
–
–
–
–
–
–
–
–
128.37
128.36
128.35
128.37
1
19
1
2
3
4
5
6
7
8
Sn–CH
Sn–CH
Sn–CH
Sn–CH
Sn–CH
Sn–CH
Sn–CH
Sn–CH
3
3
3
3
2
2
2
2
, ꢀ1.40 [536]; Sn ¼ ꢀ179.3.
119
, ꢀ1.52 [538]; Sn ¼ ꢀ180.3.
119
, ꢀ1.18 [397]; Sn ¼ þ169.6.
119
, ꢀ2.17 [394]; Sn ¼ þ169.6.
1
19
–CH
–CH
–CH
–CH
2
–CH
2
–CH
2
–CH
2
–CH
2
2
2
2
–CH
–CH
–CH
–CH
3
3
3
3
, (C-ꢂ) 29.36 [350], (C-ꢃ) 25.65 [21], (C-ꢄ) 26.70 [65], (C-ꢀ) 13.58; Sn ¼ ꢀ138.6.
119
, (C-ꢂ) 26.98 [350], (C-ꢃ) 26.79 [21], (C-ꢄ) 27.76 [69], (C-ꢀ) 14.59; Sn ¼ ꢀ138.0.
1
19
, (C-ꢂ) 27.91 [358], (C-ꢃ) 26.62 [22], (C-ꢄ) 25.53 [66], (C-ꢀ) 13.70; Sn ¼ þ155.2.
1
19
, (C-ꢂ) 27.99 [358], (C-ꢃ) 12.83 [22], (C-ꢄ) 25.83 [67], (C-ꢀ) 14.72; Sn ¼ þ156.4.
P
i
n
j
m
k
l
four-coordinate di- and tri-organotin(IV) compounds with corresponding organic
substituents. Four-coordinate structures show that no donor–acceptor connection
between tin (electron–pair acceptor) and other donors of the ligands (electron–pair
donor) occurs.
n
119
13
The coupling constants, J[ Sn, C], are important parameters for the determina-
1
tion of C–Sn–C bond angles (data are given in table 5). For 7 and 8, with J[ Sn– C]
119
13
being 358 Hz and using the literature methods [32–34], a C–Sn–C bond angle was
ꢁ
calculated as 112 , which corresponds to a quasi-tetrahedral geometry. The geometric
data are consistent with tetrahedral geometries for the triorganotin(IV) species, i.e.,
monomers in solution. For the diorganotin(IV) species, for which earlier results indicate
five coordination, the calculated C–Sn–C angles are consistent with skew-trapezoidal
geometries, with the lower apparent coordination number arising from asymmetric
coordination of the carboxylate.
3
.3. Mass spectrometry
As tin has 10 naturally occurring isotopes, each ion appears in the mass spectrum as a
series of peaks close to each other due to isotopic effects. Large organotin molecules

Di- and triorganotin(IV) complexes
345
ꢁ
Table 5. (C–Sn–C) angles ( ) based on NMR parameters.
ꢁ
Angle ( )
1
119 13
J[ Sn, C] (Hz)
2
119 1
J[ Sn, H] (Hz)
1
J
2
Compound No.
J
1
2
3
4
5
6
7
8
536
538
397
394
350
350
358
358
74
75
57
58
60
60
–
123
125
111
111
111
111
112
112
124
125
110
111
112
112
–
–
–
a
Table 6. Mass spectral data of synthesized organotin carboxylates.
Fragment ion
1 m/z (%)
286 (65)
271 (13)
150 (4)/151 (16)
135 (100)/136 (4)
120 (16)/121 (8)
3 m/z (%)
154 (19)
109 (12)
150 (6)/151 (18)
135 (100)/136 (4)
120 (14)/121 (2)
a
SnOOR ]
0
þ
[
[
[
[
[
R
2
0
þ
RSnOOCR ]
þ
þ
þ
R
2
Sn] /[R
2
SnH]
þ
RSn] /[RSnH]
Sn] /[SnH]
þ
þ
aR„=
NH2
suffer considerable fragmentation in the mass spectrometer, while small organotin
molecules often show the molecular ion peaks [35]. In 1 and 3, the base peak is due to
þ þ
RSn] with m/z value of 135 which is obtained by the loss of R from the [R Sn]
2
[
þ
þ
followed by the removal of CH radicals to give [Sn] /[SnH] fragment at m/z 120/121
3
(table 6). The fragmentation patterns of both di- and triorganotin(IV) carboxylates
obey the established routes described in earlier reports [36].
3
.4. Semi-empirical study
The two aminobenzoate ligands bind bidentate to Sn(IV) in 1. The two methyl groups
and the two benzoate ligands are octahedral. The Sn–O bond lengths are 2.03 and
˚ ˚
ꢁ
2
1
.60 A and both Sn–C bond lengths are 2.08 A. The C–O bond distances are 1.25 and
ꢁ
˚
.33 A. The Sn–O–C bond angles are 86.7 and 112.6 and O–C–O angle is 108.7 .
ꢁ

3
46
M.M. Amin et al.
˚
Table 7. Selected bond lengths (A) and angles ( ) for 1, 3, 5, and 7.
ꢁ
Compound 1
Sn1
Sn1
O2
C18
O17
O2
C22
Sn1
Sn1
Sn1
2.03
2.08
C18
O41
O41
Sn1
C28
Sn1
Sn1
Sn1
C18
C29
C22
O41
O17
2.08
1.40
99.5
52.0
108.7
149.0
76.7
O2
O26
C22
149.1
Compound 3
C13
Sn2
O11
C1
C14
1.40
2.10
C1
O26
Sn2
O11
O26
Sn2
Sn2
O26
C12
Sn2
C3
C7
Sn2
1.33
2.67
112.9
114.5
85.4
C7
Sn2
Sn2
O11
95.4
146.2
114.3
O11
C3
C12
C12
Compound 5
Sn1
Sn1
O2
C18
C31
C18
2.11
2.03
C18
O44
O59
Sn1
C36
Sn1
Sn1
Sn1
C31
C35
C31
O59
O17
2.11
1.51
100.3
150.4
149.9
O44
Sn1
Sn1
Sn1
112.5
99.2
90.8
O2
C18
C31
Compound 7
Sn2
Sn2
Sn2
C19
C32
O3
C19
C1
Sn2
Sn2
2.04
2.14
C46
C32
O18
C1
Sn2
Sn2
Sn2
C19
Sn2
C32
C1
O18
C21
2.14
2.13
94.6
85.5
113.9
111.8
114.6
89.2
O3
C19
Sn2
ꢁ
Both O–Sn–O angles are 52.0 . In 3, the three methyl groups and benzoate are distorted
˚
trigonal bipyramidal. The Sn–O bond lengths are 2.04 and 2.67 A and Sn–C 2.10, 2.10,
˚
ꢁ
ꢁ
and 2.11 A. The Sn–O–C bond angles are 114.3 and 85.4 and the O–C–O angle is
ꢁ
ꢁ
109.5 . The O–Sn–O angle is 50.8 . The butyl groups and the two benzoates are
˚
distorted octahedral in 5. The Sn–O bond lengths are 2.03 and 2.60 A and both Sn–C
˚
bond lengths are 2.11 A. The C–O bond distances are 1.33 and 1.25 A. The Sn–O–C
˚
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
bond angles are 86.9 , 86.7 , 112.5 , and 112.7 and O–C–O angles are 108.7 and
ꢁ ꢁ ꢁ
1
distorted trigonal bipyramidal in 7. The Sn–O bond lengths are 2.04 and 2.67 A and the
08.6 . The O–Sn–O angles are 52.0 and 51.9 . The three butyls and the benzoate are
˚
˚
Sn–C bond lengths are 2.14, 2.14, and 2.13 A. The C–O bond distances are 1.33 and
˚
.24 A. The Sn–O–C bond angles are 114.2 and 85.5 and O–C–O angle is 109.5 . The
ꢁ
ꢁ
ꢁ
1
O–Sn–O angle is 50.8 . All bond lengths and angles are comparable to literature values
ꢁ
[37]. Selected bond lengths and angles of the optimized structure are tabulated in
table 7. The optimized structure is shown in figures 1–4.
3
.5. Biological activity
Biological activity tests of synthesized organotin carboxylates were carried out against
two strains each of Gram-positive and Gram-negative bacteria by the agar-well
diffusion method [38], and antifungal activity was determined by the tube diffusion
ꢀ1
method [38]. Data are given in table 8. The recommended concentration (1 mg mL in
DMSO) was used for each respective test sample. The screening test shows that
tributyltin carboxylates were potent antibacterial and antifungal agents, while

Di- and triorganotin(IV) complexes
347
Figure 1. Geometry optimized structure of 1.
Figure 2. Geometry optimized structure of 3.

3
48
M.M. Amin et al.
Figure 3. Geometry optimized structure of 5.
Figure 4. Geometry optimized structure of 7.

Di- and triorganotin(IV) complexes
349
Table 8. Antibacterial and antifungal activities of organotin carboxylates.
Bacterium
1
2
3
4
5
6
7
8
Standard drug
Bacillus subtilius
Staphylococcus aureus
Escherichia coli
þ
þ
þ
þ
þþ þþ
þþ
þþ
þþþ
þþþ þþþþ
þþþ
þþþ
þþ þþ þþþ þþþ þþþþ þþþ þþþþ
þþ
þ
þþþ þþþ þþþþ þþþ þþþþ
þþþþ
þþþ
Salmonella typhi
þþ þþ þþþ þþþ þþþþ þþþ þþþþ
Fungus
Aspergillus niger
Penicillium notatum
þ
þ
þþ þþþ þþþ þþþþ þþþ þþþþ
þþþ þþþ þþþþ þþþ þþþþ
þþ
þþ
þþ þþ
þ
þþþþ ¼ highly active, þþþ ¼ moderately active, þþ ¼ low active, þ ¼ very low active.
Standard drug: Miconazole and Amphotericin B (antifungal agents); Imipenem (antibacterial agent).
triphenylphosphine further enhances their activity. There is a direct relation between
the activity and the coordination environment of the metal. The ligand supports
transport of the organotin moiety to the site of action where it is released by hydrolysis
[
39]. The anionic ligand also plays an important role in determining the degree of the
activity of organotin compounds. All complexes show tetrahedral geometry in solution
and few exceptions show significant activity, which is consistent with species generating
tetrahedral geometry in solution being more active [39].
4. Conclusions
Organotin carboxylates of 2-aminobenzoic acid have been synthesized with and without
triphenylphosphine and their coordination is interpreted from semi-empirical results
and spectroscopy. FT-IR spectra demonstrate bidentate coordination for 1, 3, 5, and 7
while monodentate in 2, 4, 6, and 8. In solid state, 1, 2, 5, and 6 are six coordinate
whereas 3, 4, 7, and 8 are five coordinate. NMR data reveal the complexes are four
coordinate in solution. Biological activities show that tributyltin carboxylates are
potent antibacterial and antifungal agents, and triphenylphosphine enhances their
activity; these complexes show potential as drugs in the pharmaceutical field.
Acknowledgments
The authors are grateful to GC University, Faisalabad, and Quaid-i-Azam University,
Islamabad for support. SKS and KQ thank the Head, Applied Science and Dean FET,
MITS for encouragement and support.
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