Bimetallic organotin(IV) complexes with ferrocene-based azomethines: Synthesis, characterization, semi-empirical study, and antibacterial activity

Article abstract of DOI:10.1080/00958972.2011.584190

A series of bimetallic organotin(IV) complexes with ferrocene-based azomethines (Schiff bases) were synthesized by reacting sodium salt of tranexamic acid, 4-amino butanoic acid, and phenyl alanine with trimethyltin and tributyltin chloride in 1 : 1 molar ratio under inert atmosphere. The synthesized trialkyl organotin complexes condense with formyl ferrocene under inert atmosphere to yield organotin(IV) ferrocenyl Schiff bases. Composition of the organotin(IV) complexes, bonding behavior of donor groups, and structural assignments were studied by elemental analysis, FT-IR, ¹H, ¹³C, ¹¹⁹Sn NMR, and mass spectrometry. The spectral data suggest that the ligand is bidentate, coordinating through oxygens. Spectroscopic techniques reveal distorted tetrahedral geometry in solution for the complexes. As solids, the complexes are trigonal bipyramidal, confirmed by semi-empirical study. Mass spectrometric and elemental analysis data support the solid and solution spectroscopic results. Bioactivity screenings show invitro biological potential.

Full text of DOI:10.1080/00958972.2011.584190

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Bimetallic organotin(IV) complexes
with ferrocene-based azomethines:
synthesis, characterization, semi-
empirical study, and antibacterial
activity
Khizra Tahira a , Saqib Ali b , Saira Shahzadi a , Saroj K. Sharma c &
Kushal Qanungo c
a Department of Chemistry , GC University , Faisalabad , Pakistan
b Department of Chemistry , Quaid-i-Azam University ,
Islamabad-45320 , Pakistan
c Department of Applied Science and Humanity , Faculty of
Engineering and Technology, Mody Institute of Technology and
Science (Deemed University) , Lakshmangargh-332311, District
Sikar , Rajasthan , India
Published online: 20 May 2011.
To cite this article: Khizra Tahira , Saqib Ali , Saira Shahzadi , Saroj K. Sharma & Kushal Qanungo
(2011) Bimetallic organotin(IV) complexes with ferrocene-based azomethines: synthesis,
characterization, semi-empirical study, and antibacterial activity, Journal of Coordination
Chemistry, 64:11, 1871-1884, DOI: 10.1080/00958972.2011.584190
To link to this article: http://dx.doi.org/10.1080/00958972.2011.584190
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Journal of Coordination Chemistry
Vol. 64, No. 11, 10 June 2011, 1871–1884
Bimetallic organotin(IV) complexes with ferrocene-based
azomethines: synthesis, characterization, semi-empirical study,
and antibacterial activity
KHIZRA TAHIRAy, 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 Humanity, Faculty of Engineering and Technology,
Mody Institute of Technology and Science (Deemed University), Lakshmangargh-332311,
District Sikar, Rajasthan, India
(Received 11 December 2010; in final form 12 April 2011)
A series of bimetallic organotin(IV) complexes with ferrocene-based azomethines (Schiff bases)
were synthesized by reacting sodium salt of tranexamic acid, 4-amino butanoic acid, and phenyl
alanine with trimethyltin and tributyltin chloride in 1 : 1 molar ratio under inert atmosphere.
The synthesized trialkyl organotin complexes condense with formyl ferrocene under inert
atmosphere to yield organotin(IV) ferrocenyl Schiff bases. Composition of the organotin(IV)
complexes, bonding behavior of donor groups, and structural assignments were studied by
elemental analysis, FT-IR, 1H, 13C, 119Sn NMR, and mass spectrometry. The spectral data
suggest that the ligand is bidentate, coordinating through oxygens. Spectroscopic techniques
reveal distorted tetrahedral geometry in solution for the complexes. As solids, the complexes are
trigonal bipyramidal, confirmed by semi-empirical study. Mass spectrometric and elemental
analysis data support the solid and solution spectroscopic results. Bioactivity screenings show
in vitro biological potential.
Keywords: Bimetallic; Ferrocene-based azomethines; Organotin; IR; NMR; Mass; Semi-
empirical; Antibacterial activity
1. Introduction
The organometallic compounds containing lead, tin, and mercury are commercially
significant [1]. Ferrocene, being readily sublimed, can be used to deposit certain
fullerenes, especially carbon nanotubes. Some ferrocenium salts exhibit anticancer
activity and an experimental drug has been reported which is a ferrocenyl version of
tamoxifen [2].
Azomethines (Schiff bases) can be polymerized and such polymers show superior
mechanical, thermal, electrical, and dielectric properties [3]. Schiff bases are potential
*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: 10.1080/00958972.2011.584190

1872
K. Tahira et al.
pesticides and herbicidal agents [4]. Schiff bases are used in photoconductive layers
in electro photographic photoreceptors, showing improved chargeability, durability,
and sensitivity. Ferrocene-containing Schiff bases have been employed in fields such as
molecular recognition of biosensors [5], asymmetric catalyst [6], polymer science as
redox active polymers and dedrimers [7], non linear optics [8], photochemical systems
[9], and pharmacology [10]. Ferrocene-containing Schiff bases and their complexes with
different metals are useful in photochemistry, photophysics, chemiluminescence, and
electron transfer [11]. Ferrocenyl Schiff bases have shown applications in agriculture
and medicines as plant protection agent or antitumor drugs [12]. From the literature
[13–15], the replacement of aromatic groups by ferrocenyl moieties in penicillin and
cephalosporin drastically improved their antibacterial activity, due to the conforma-
tional flexibility of ferrocene backbone in the ligand so it can easily cross the cell
membrane. Mono- and di-organotin complexes are biologically less active, whereas tri-
organotin complexes are powerful biocides. For improved bactericidal activity upon
replacement with ferrocene or ferrocene-derived compounds, we synthesize a new class
of potential organometallic-based antibacterial compounds and explore the possibility
of their use as biocidal agents.
2. Experimental
2.1. Materials and methods
Sodium hydrogencarbonate, tranexamic acid purchased from the market as capsules, 4-
amino butanoic acid, phenyl alanine, formyl ferrocene, trimethyltin chloride, tributyltin
chloride were purchased from Aldrich and used without purification. Solvents were
dried by standard procedure [16]. Melting points were determined by using an
electromelting point apparatus model MP-D Mitamura Rikero Kogyo (Japan) and are
uncorrected. Elemental analyses (for carbon, hydrogen and nitrogen) were done by a
CHNS-932 elemental analyzer, Leco Corporation USA. The 1H and 13C NMR spectra
were recorded on a Bruker ARC 300-MHz-FT-NMR spectrometer using CDCl3 as an
internal reference. 119Sn NMR spectra were recorded on a Bruker AM 250 spectrometer
(Germany) with Me4Sn as external reference. FT-IR spectra were recorded by Hitachi-
270-50 IR instrument from 4000 to 400 cmꢀ1. Mass spectral data were recorded on a
MAT 8500 Finnigan 70 eV mass spectrometer (Germany). The structures of 5, 6, 8, and
9 were modeled by MOPAC 2007 [17] using PM6 method [18]. Selected parts of the
molecule not containing the metal ion were pre-optimized using molecular mechanics
method before subjecting the whole molecule to geometry optimization.
2.2. General procedure for synthesis of sodium salt of tranexamic acid/
4-aminobutanoic acid/phenyl alanine 1-3
Sodium hydrogencarbonate (1 mmol) was added in portions to the solution of
4-(aminomethyl)cyclohexanecarboxylic acid (tranexamic acid)/4-aminobutanoic acid/
phenyl alanine (1 mmol) in distilled water. The resulting mixture was stirred at
room temperature for 3 h. The solution was filtered and the solvent was
evaporated under vacuum with a rotary evaporator. The solid product was dried in

Bimetallic organotin(IV) complexes
1873
open air (equations 1–3).
H2N
ONa
O
H2N
OH
–CO2 and H 2O
3 hrs stirring
(1)
+
NaHCO3
O
1
HO
NaO
–CO2 and H2 O
3 hrs stirring
(2)
H2
N
O
+
NaHCO3
H2 N
O
2
OH
ONa
O
–CO2 and H2O
3 hrs stirring
(3)
+
NaHCO3
H2N
O
H2N
3
2.3. General procedure for synthesis of organotin(IV) derivatives 4–9
The sodium salt of 4-(aminomethyl)cyclohexanecarboxylic acid 1/4-aminobutanoic acid
2/phenyl alanine 3 was suspended in 50 mL of dried chloroform in a two-necked round-
bottom flask equipped with a magnetic bar and reflux condenser. After stirring for
10 min, 1 mmol of trimethyltin chloride/tributyltin chloride dissolved in 10 mL of dried
chloroform (10 mL) was added dropwise. The reaction mixture was refluxed for 6–8 h
on a Rota mantle with continuous stirring. The reaction mixture was cooled to room
temperature, filtered to remove NaCl, and the solvent was evaporated by rotary
evaporator. The solid mass obtained was recrystallized from chloroform : n-hexane
(1 : 1) (equations 4–6).
H2N
ONa
(4)
R3SnCl
+
O
1
chlorform
–NaCl
6-8 hrs reflux
R
R
H2N
O
Sn
R
O
R = CH3, n-Bu
4
5

1874
K. Tahira et al.
ONa
(5)
NH2
O
+
R3SnCl
2
chlorform
6-8 hrs reflux
–NaCl
R
O
Sn
R
C
H2N
R
O
R = CH3, n-Bu
6
7
R3SnCl
+
ONa
O
(6)
H2N
3
chlorform
–NaCl
6-8 hrs reflux
R
R
O
Sn
R
H2N
O
R = CH3, n-Bu
8
9

Bimetallic organotin(IV) complexes
1875
2.4. General procedure for synthesis of Schiff bases 10–15
Organotin(IV) derivatives 4–9 and formyl ferrocene were stirred together in 1 : 1 molar
ratio, in 80 mL chloroform in a three-necked round-bottom flask along with molecular
sieves. The reaction mixture was refluxed at 60ꢁC for 14–16 h under inert atmosphere
and then solvent was evaporated with a rotary evaporator under reduced pressure.
Solid product obtained was recrystallized in ethanol : n-hexane (1 : 1) (equations 7–9).
CHO
(7)
Fe
4/5
+
chlorform
–H2O
14-16 hrs reflux
R
R
CH
N
O
O
Sn
R
Fe
R = CH3, n-Bu
10 11
CHO
(8)
6/7
+
Fe
chlorform
–H2O
14-16 hrs reflux
R
O
Sn
R
C
CH
N
R
O
Fe
R = CH3, n-Bu
12 13

1876
K. Tahira et al.
CHO
8/9
+
(9)
Fe
chlorform
–H2O
14-16 hrs reflux
CH3
CH3
CH3
O
O
Sn
N
CH
Fe
R = CH3, n-Bu
14 15
3. Results and discussion
Physical data of synthesized complexes along with the sodium salts are reported in
table 1. The complexes are quite stable in air and moisture and are soluble in common
organic solvents.
3.1. Infrared spectroscopy
Infrared (IR) spectra of the complexes were recorded from 4000 to 400 cmꢀ1 and
characteristic vibrational frequencies identified. Peaks of prime importance are
ꢀCH¼N, ꢀCOO(sym), and ꢀCOO(asym) and data are given in table 2. The new bands
ꢀSn–C and ꢀSn–O appear after complex formation.
Carboxylate has two strong C¼O stretches which show a strong asymmetric
stretching absorption frequency at 1594–1523 cmꢀ1 and a weaker symmetric stretch at
1458–1409 cmꢀ1. By measuring Dꢀ ¼ ꢀasym–ꢀsym, the interaction of metal centre with
carbonyl group is defined. The coordination geometry of tin, in organotin(IV)
carboxylates, adopts a variety of motifs depending on the nature of group attached to
the metal and Dꢀ value suggests the nature of carboxylate bonding [19]. The complexes
show a difference, Dꢀ 4 200 cmꢀ1, which means bidentate carboxylate. ꢀCH¼N
appears in IR spectra of the complexes confirming synthesis of Schiff bases and it
does not shift in frequency, suggesting that nitrogen is not involved in bonding with Sn.
The appearance of new bands ꢀSn–C and ꢀSn–O at 582–525 and 455–412 cmꢀ1
,
respectively, confirms complexation.

Bimetallic organotin(IV) complexes
1877
Table 1. Physical data of 1–15.
Elemental analysis
Molecular
formula
Molecular
mass
%
Yield
m.p.
(ꢁC)
%C Calcd
(found)
%H Calcd
(found)
%N Calcd
(found)
Complex No.
1
2
C8H12NO2Na
C4H8NO2Na
177.18
125.1
65
72
79
61
60
70
71
66
69
70
64
66
73
68
60
226
271
262
122
88
54.23
(54.28)
38.40
(38.44)
58.07
(58.12)
41.55
(41.59)
54.07
(54.03)
31.86
(31.82)
49.26
(49.22)
44.21
(44.25)
55.78
(55.82)
51.20
(51.24)
57.97
(57.93)
46.80
(46.76)
55.13
(55.09)
52.72
(52.76)
59.11
(59.07)
6.83
(6.87)
6.45
(6.41)
4.87
(4.830
6.66
(6.70)
8.85
(8.81)
5.73
(5.77)
8.53
(8.49)
5.26
(5.30)
7.80
(7.84)
6.05
(6.01)
7.69
(7.65)
5.45
(5.49)
7.37
(7.33)
5.19
(5.23)
6.98
(6.94)
7.91
(7.87)
11.20
(11.16)
7.52
(7.48)
4.40
(4.44)
3.15
(3.11)
5.31
(5.35)
3.59
(3.63)
4.30
(4.34)
3.10
(3.14)
2.71
(2.75)
2.18
(2.22)
3.03
(3.07)
2.38
(2.42)
2.67
(2.63)
2.15
(2.11)
3
C9H9NO2Na
186.16
318.0
4
C11H21NO2Sn
C20H39NO2Sn
C7H15NO2Sn
5
444.24
263.91
390.15
325.98
452.22
516.04
642.28
461.95
588.19
524.02
650.26
6
132
154
112
145
116
57
7
C16H33NO2Sn
C12H17NO2Sn
C21H35NO2Sn
C22H31NO2SnFe
C31H49NO2SnFe
C18H25NO2SnFe
C27H43NO2SnFe
C23H27NO2SnFe
C32H45NO2SnFe
8
9
10
11
12
13
14
15
123
141
109
162
Table 2. FT-IR data (cmꢀ1) of synthesized complexes 1–15.
Complex No.
ꢀCH¼N
ꢀCOOsym
ꢀCOOasym
Dꢀ
ꢀSn–C
ꢀSn–O
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
–
–
–
–
–
–
–
–
–
1640
1640
1640
1640
1640
1640
1469
1472
1489
1422
1412
1424
1452
1442
1432
1403
1409
1414
1458
1418
1454
1670
1686
1695
1552
1564
1538
1560
1549
1580
1579
1594
1593
1568
1523
1592
201
214
206
130
152
114
108
107
148
176
185
182
110
105
138
–
–
–
–
–
–
525
532
539
545
551
532
572
582
525
530
540
542
416
425
434
441
448
444
442
455
412
420
431
436

1878
K. Tahira et al.
Table 3. 1H NMRa shifts (ppm) of organotin(IV) complexes.
Proton No.
4
5
6
7
8
9
2
3
2.21–2.26 m
–
1.34–1.38 m
–
1.46–1.54 m
4.81–4.92 m
2.21–2.27 m
–
1.32–1.37 m
1.37–1.39 m
1.66 d (3.2)
–
1.92 d (3.5)
–
4.83 s
–
4.26–4.35 m
1.36–1.39 m
1.66 d (3.2)
–
1.92 d (3.5)
2.26–2.33 m
1.72 d (3.3)
–
7.93–7.99 m
2.26–2.34 m
1.72 d (3.3)
–
7.94–7.97 m
–
3,30
4
4,40
5
1.46–1.55 m
4.82–4.90 m
–
4.63–4.69 m
–
4.49 s
–
4.84 s
–
–
–
7.21–7.29 m
–
7.36–7.44 m
7.15–7.21 m
8.62 s
0.88 s
–
5,50
6
–
4.62–4.67 m
7.22–7.29 m
–
7.34–7.43 m
7.18–7.25 m
8.60 s
1.34 t
[81]
1.35–1.41 m
1.21–1.26 m
0.92 t
4.27–4.36 m
–
6,60
7
–
–
4.49 s
8.62 s
0.95 s
[57]
–
–
8.62 s
0.92 s
[57]
–
–
þ
NH2
ꢁ
8.61 s
1.35 t
[81]
8.60 s
1.36 t
[81]
[57]
–
–
ꢂ
ꢃ
ꢄ
1.37–1.44 m
1.24–1.28 m
0.90 t
1.38–1.45 m
1.25–1.30 m
0.96 t
–
–
–
–
–
(7.4)
(7.4)
(7.3)
a
2J[119Sn, 1H]; 3J[1H, 1H] in hertz are listed in square brackets and parenthesis, respectively. Multiplicity is given as
s ¼ singlet, d ¼ doublet, m ¼ multiple.
Table 4. 1H NMRa shifts (ppm) of ferrocene based azomethine organotin(IV) complexes.
Proton No.
10
11
12
13
14
15
2
3
2.21–2.28 m
–
1.34 m
–
1.46 m
4.81 m
2.21–2.28 m
–
1.32 m
1.37–1.42 m
1.66 d (3.2)
–
1.92 d (3.5)
1.36–1.41 m
1.66 d (3.2)
–
1.92 d (3.5)
2.26–2.34 m
1.72 d (3.3)
–
7.93–7.97 m
2.26–2.33 m
1.72 d (3.3)
–
7.94–7.99 m
3,30
4
4,40
5
1.46 m
4.82 m
–
4.63–4.71 m
–
4.83 s
–
–
–
–
4.84 s
–
–
–
–
–
–
7.21–7.28 m
–
7.36–7.39 m
7.15–7.21 m
–
7.22–7.27 m
–
7.34–7.39 m
7.18–7.21 m
5,50
6
–
4.62–4.69 m
6,60
7
–
4.49 s
–
–
–
–
4.49 s
–
–
–
–
–
4.35–4.39 m
–
4.61–4.66 m
4.75–4.79 m
–
–
4.33–4.39 m
–
4.61–4.67 m
4.75–4.79 m
–
7,70
8
–
4.80–4.86 s
–
4.82–4.88 s
8,80
9
–
–
–
–
–
–
4.36–4.39 m
4.59–4.67 m
4.72–4.79 m
9,90
10,100
11
11,110
12
ꢁ
4.37–4.48 m
4.58–4.65 m
4.73–4.79 m
–
–
4.59–4.62 m
–
4.11–4.17 m
4.75–4.77 m
0.86 s
–
–
–
–
–
–
4.56–4.60 m
–
4.14–4.20 m
4.79–4.81 m
1.32 t
–
–
0.97 s
[57]
–
–
–
–
1.37 t
[81]
–
0.90 s
[57]
–
–
–
–
1.31 t
[81]
1.31–1.36 m
1.26–1.29 m
0.94 t
(7.4)
[57]
–
–
[81]
ꢂ
ꢃ
ꢄ
1.37–1.42 m
1.27–1.35 m
0.94 t
1.29–1.39 m
1.25–1.28 m
0.90 t
–
(7.4)
(7.3)
a
2J[119Sn, 1H]; 3J[1H, 1H] in hertz are listed in square brackets and parenthesis, respectively. Multiplicity is given as
s ¼ singlet, d ¼ doublet, m ¼ multiplet.

Bimetallic organotin(IV) complexes
1879
Table 5. 13C and 119Sn NMR shifts (ppm) of synthesized organotin(IV) complexes.
13C No.
4
5
6
7
8
9
1
2
3
173.8
43.9
–
29.3
–
30.6
38.1
–
43.9
–
169.8
38.1
–
27.8
–
29.7
30.6
–
44.0
–
168.9
29.7
27.4
–
61.3
–
–
–
–
–
167.9
32.4
27.8
–
62.2
–
–
–
–
–
162.7
75.9
36.5
–
129.5
–
167.9
76.1
37.1
–
129.5
–
3,30
4
4,40
5
–
–
5,50
6
128.2
–
128.2
–
6,60
7
126.5
126.2
26.4
[392]
22.4
[22]
14.7
[64]
13.1
107.8
129.0
125.3
16.6
[391]
–
–
–
–
–
ꢁ
18.7
[392]
–
16.9
[397]
15.4
[20]
14.3
[63]
13.2
107.8
16.8
[394]
15.1
[21]
14.6
[64]
13.4
109.9
13.1
[397]
–
ꢂ
ꢃ
ꢄ
_
–
–
_
136.1
–
136.7
–
136.9
ꢄ
119Sn
Table 6. 13C and 119Sn NMR shifts (ppm) of synthesized ferrocene based azomethine organotin(IV)
complexes.
13C No.
10
11
12
178.9
29.7
27.4
13
178.9
32.4
27.8
14
176.7
75.9
36.5
15
176.9
76.1
37.1
1
2
3
181.8
43.9
–
29.3
–
30.6
38.1
–
43.9
181.8
38.1
–
27.8
–
29.7
30.6
–
44.0
3,30
4
–
61.3
–
62.2
–
–
129.5
129.5
4,40
5
–
–
–
–
–
–
161.3
–
80.6
162.5
–
80.5
5,50
6
128.2
128.2
–
–
6,60
7
–
–
–
–
–
–
126.5
126.2
129.0
125.3
161.0
–
73.2
160.8
–
73.5
7,70
8
129.2
129.8
–
–
–
–
163.1
163.4
8,80
9
–
–
–
–
126.4
122.2
126.8
122.6
–
138.8
138.7
9,90
10
10,100
11
11,110
12
ꢁ
129.6
129.3
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
128.1
124.2
128.6
124.7
129.3
129.4
–
–
–
–
–
–
128.3
126.5
26.6 [392]
22.7 [24]
14.1 [63]
13.6
128.3
126.3
16.4 [391]
–
–
18.4 [392]
–
–
13.6 [397]
16.3 [397]
15.6 [20]
14.1 [63]
13.7
16.4 [394]
15.8 [21]
14.1 [63]
13.6
ꢂ
ꢃ
_
_
_
–
–
–
–
–
ꢄ
ꢄ
119Sn
136.3
107.4
109.4
136.2
107.5
136.4

1880
K. Tahira et al.
9
7
10
R
R
'10
11
8
CH
N
O
O
5
3
9
'
1
'
6
4
Sn
R
3
Fe
4
2
11
11
'
11
11
R
R
O
8
7
5
Sn
R
'8
6
9
4
1
CH
N
7
'
O
3
2
Fe
9
9
9
9
H
65
3
R
R
7
4
CH
O
Sn
R
'6
5'
2
1
N
O
10
11
'11
9
C
H
8
10
'
Fe
12
12
12
12
12
α
CH3
Sn
α
γ
δ
Sn
CH3
β
Scheme 1. NMR numbering scheme.
3.2. NMR spectroscopy
3.2.1. 1H-NMR. 1H NMR spectra of selected compounds have been recorded in
deuterated chloroform. The number of signals in the spectra corresponds to the number
of magnetically non-equivalent hydrogens. The numbers of protons calculatedþ by
integration [20] are in good agreement with those expected. The presence of NH2 at
8.62–8.60 ppm as singlet in the ligands and absence in complexes confirm the formation
of Schiff base. In trimethyltin(IV) compounds, CH3 protons give a sharp singlet at
0.86–0.97 ppm with 2J[119Sn–1H] of 57 Hz. The n-butyl has triplet for Sn–CH2
3
(1.35–1.21 ppm) and terminal CH3 (at 0.90–0.96 ppm) with J(1H–1H) couplings of
2
7.4–7.3 Hz with J[119Sn–1H] of 81 Hz supporting four-coordinate tin in solution [21].
1H NMR chemical shifts are given in tables 3 and 4.

Bimetallic organotin(IV) complexes
1881
ꢁ
˚
Table 7. Selected bond lengths (A) and angles ( ) for 5, 6, 8, and 9.
Compound 5
Sn1
C27
O2
O26
C27
O2
Sn1
Sn1
Sn1
Sn1
2.02
2.11
C31
C31
C35
Sn1
Sn1
Sn1
Sn1
Sn1
O26
C31
C27
C31
C35
2.72
2.10
147.0
109.8
114.2
112.3
87.0
109.8
O26
C27
C31
Compound 6
C13
Sn2
O11
C1
C14
C7
Sn2
Sn2
O11
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
95.4
146.2
114.3
O11
C3
C12
C12
Compound 8
Sn1
Sn1
O2
C18
C31
C18
O44
Sn1
Sn1
Sn1
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
112.5
99.2
90.8
O2
C18
C31
Compound 9
Sn2
Sn2
Sn2
C19
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
111.8
114.6
89.2
O3
C19
Sn2
C32
113.9
3.2.2. 13C NMR. 13C NMR spectra were recorded in CDCl3. The 13C NMR spectra
of ferrocene show only one signal at 119–121 ppm, while the substituted cyclopenta-
dienyl ring shows three signals at 129.6, 128.4, and 126.3 ppm. These signals do not
show a shift on complexation. Signals due to C¼N and COO at 160.8–163.4 and 181.8–
176.7 ppm, respectively, shift downfield by 8–14 ppm on complexation of organotin
with ferrocene. The carboxylate carbon shifts to lower field region in organotin(IV)
compounds indicating participation of COO in coordination to tin. Holecek and
ˇ
coworkers [22] have shown that for four-coordinate trialkyltin compounds, the
1J[119Sn,13C] occur from 325 to 400 Hz, while five-coordinate tin compounds exhibit
coupling of 440 to 540 Hz. Here, the trialkyltin compounds show tin–carbon satellites in
the range 391–397 Hz in solution, characteristic of tetrahedral tin. Thus bidentate ligand
resulting in five coordination in the solid state (FT-IR) is lost in solution. 13C and 119Sn
NMR data are given in tables 5 and 6.
The 119Sn chemical shift values for 4–15 are in the range 107.4–136.9 ppm,
characteristic for four-coordinate in non-coordinating solvents [23].
3.3. Mass spectrometry
The EI mass spectrum of NaL1 was studied as a representative case. Peaks of
appreciable intensity were observed at m/z values 114, 85, 72, 70, 69, 57, and 55. The
molecular ion peak was observed at m/z 177.18, in agreement with its molecular weight.
In the mass spectral data, most fragment ions occur in groups of peaks as a result of tin
isotopes. For simplicity the mass spectral fragmentation data reported here is related to

1882
K. Tahira et al.
Figure 1. Geometry optimized structures of 5, 6, 8, and 9.
the principal isotope 120Sn [24]. Molecular ion peak of low intensity was observed for
the organotin(IV) derivatives.
3.4. Semi-empirical study
The 4-(aminomethyl) cyclohexane, 4-amino butanoate, and 2-amino-3-phenylpropano-
ate bind bidentate to Sn(IV) in 5, 6, 8, and 9. The three methyl/butyl groups and the

Bimetallic organotin(IV) complexes
1883
Table 8. Antibacterial activity of ferrocene based azomethine organotin(IV) complexes.
Inhibition zone diameter (mm)
Bacterium
10
11
12
14
Standard drug
Escherichia coli
Bacillus subtilis
Shigella flexenaria
Staphylococcus aureus
Pseudomonas aeruginosa
Salmonella typhi
30
32
30
42
30
38
34
35
35
40
30
36
31
35
31
40
32
35
34
33
32
40
31
33
35
36
36
43
32
40
aIn vitro, agar well diffusion method, conc. 1 mg mLꢀ1 of DMSO.
bReference drug, Imipenum.
carboxylates are arranged in a distorted trigonal bipyramid. The Sn–O bond distances
ꢁ
˚
are 2.02 and 2.72 A in 5. O–Sn–O bond angle is 50 ꢂ 0.1 in 5, 6, 8, and 9. All bond
lengths and angles are comparable to literature values [25]. Selected bond lengths and
angles of the optimized structure are tabulated in table 7. The optimized structures are
shown in figure 1.
3.5. Biological activity
3.5.1. Antibacterial activity. Selected compounds were screened for antibacterial
activity by the agar-well diffusion method [26]. The zone of inhibition is measured in
millimeters and the reference drug used was Imipenum (table 8). All bacterial strains
have clinical implication: Escherichia coli, infection of wounds, urinary tract, and
dysentery; Bacillus subtilis, food poisoning; Shigella flexenari, blood diarrhea with fever
and severe prostration; Salmonella typhi, typhoid fever, and localized infection,
Staphylococcus aureus, food poisoning, scaled skin syndrome, endocarditic,
Pseudomonas aeruginosa, infection of wounds, eyes, septicemia, and Salmonella typhi,
typhoid fever, localized infection.
Triorganotin(IV) complexes of the ferrocenyl Schiff base, R3SnL, were more active
than their parent ligands against the same microorganisms under identical experimental
conditions. The reported bimetallic organotin(IV) complexes show enhanced anti-
bacterial activity compared to monometallic organotin(IV) complexes [27–29]. No
compound shows better inhibitory action than standard drug.
4. Conclusion
IR data suggest bidentate O-coordination of the ligands to Sn moiety, which is
confirmed by semi-empirical study. NMR data reveal distorted tetrahedral geometry in
solution. Antibacterial results show that the reported complexes do not exhibit better
inhibitory action than standard drug, but could be used as conventional bactericides.

1884
K. Tahira et al.
Acknowledgment
SA is thankful to Quaid-i-Azam University, Islamabad, for financial support as URF.
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