Synthesis, characterization and preliminary in vitro antibacterial screening activity of organotin(IV) complexes derivatives of 2-amino-3-nitrobenzoic acid

Article abstract of DOI:10.14233/ajchem.2014.16576

A total of four organotin(IV) carboxylate complexes have been synthesized and characterized quantitatively and qualitatively. Spectroscopy studies indicated that the coordination took place via oxygen atoms from the carboxylate anions. Moreover, all the complexes obtained as simple monomeric structure except complex 3 which was obtained as organodistannoxane dimer types. From the preliminary in vitro antibacterial screening activity, triphenyltin(IV) (complex 4) showed significant activity against Bacillus subtilis, Pseudomonas aeruginosa and Staphylococcus aureus and complex 2 only possessed better activity against Pseudomonas aeruginosa.

Full text of DOI:10.14233/ajchem.2014.16576

Asian Journal of Chemistry; Vol. 26, No. 21 (2014), 7235-7238
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.16576
Synthesis, Characterization and Preliminary in vitro Antibacterial Screening Activity of
Organotin(IV) Complexes Derivatives of 2-Amino-3-nitrobenzoic Acid
*
CHEN-SHANG CHOONG, SIE-TIONG HA, MEI-HSUAN HENG andYIP-FOO WIN
Faculty of Science, Universiti Tunku Abdul Rahman, Perak Campus, Jalan Universiti, Bandar Barat, 31900 Kampar, Perak, Malaysia
*Corresponding author: Fax: +60 5 4661676; Tel: +60 5 4688888; E-mail: williamyfw@yahoo.com
Received: 24 October 2013;
Accepted: 18 March 2014;
Published online: 30 September 2014;
AJC-16109
A total of four organotin(IV) carboxylate complexes have been synthesized and characterized quantitatively and qualitatively. Spectroscopy
studies indicated that the coordination took place via oxygen atoms from the carboxylate anions. Moreover, all the complexes obtained as
simple monomeric structure except complex 3 which was obtained as organodistannoxane dimer types. From the preliminary in vitro
antibacterial screening activity, triphenyltin(IV) (complex 4) showed significant activity against Bacillus subtilis, Pseudomonas aeruginosa
and Staphylococcus aureus and complex 2 only possessed better activity against Pseudomonas aeruginosa.
Keywords: Organotin(IV) carboxylate, 2-Amino-3-nitrobenzoic acid.
The preliminary in vitro antibacterial screening activity
was carried out against two Gram-negative [Escherichia coli
(ATCC 25922) and Pseudomonas aeruginosa (ATCC 27853)]
and two Gram-positive [Bacillus subtilis (ATCC 38583) and
Staphylococcus aureus (ATCC 25923)] bacterial strains by
inhibition zone method using paper disc diffusion method14.
The seeded agar (nutrient agar medium) was prepared by cooling
the molten agar to 40 °C and then adding bacterial inoculums
containing approximately 1 × 104-108 colony forming units
(CFU)/mL. The bacterial inoculums were spread on the plate
containing agar medium and even coverage was ensured before
the agar solidified. The complexes were dissolved in DMSO
to prepare 1 mg/mL concentration. Later, small filter paper discs
(6 mm) containing 1 mg/mL of the samples were laid on the
growth medium. The plates were incubated immediately at
37 °C for 20-24 h. The activity was determined by measuring
the diameter of the inhibition zone (in mm).
INTRODUCTION
The coordination chemistry of organotin(IV) complexes
are extensively studied due to its structural diversity from a
simple monomer until polymeric structures1-8. In addition, in
some studies showed that the overall structure of organotin(IV)
complexes including its 3D crystal structure packing also
influenced by the participation of coordinating solvent
molecules such as water, acetone, methanol and ethanol to
tin(IV) atoms moieties5-8. The biological properties of organo-
tin(IV) complexes also have been extensively studied in order
to explore its structural-activity relationship9-13
.
In this paper, we report the synthesis, characterization and
preliminary in vitro antibacterial screening activity of organo-
tin(IV) complexes derivatives of 2-amino-3-nitrobenzoic acid.
EXPERIMENTAL
All the reagents, starting materials as well as the solvents
were purchased commercially and used without any further
purification. The melting points were determined in an open
capillary and were uncorrected. Elemental C, H and N analyses
were carried out on a Perkin-Elmer 2400 CHN elemental
analyzer. The infrared spectra were recorded using a Perkin-
Elmer System 2000 FTIR Spectrophotometer as a KBr disc in
the frequency range of 4000-400 cm-1. The spectra for 1H, 13C,
1H-13C HMQC and 119Sn NMR were recorded on a JEOL JNM-
ECX 400 FT-NMR Spectrometer using deuterated CDCl3 and
DMSO-d6 as the solvent and tetramethylsilane, TMS as the
internal standard.
2-Amino-3-nitrobenzoic acid (HL): The parent acid, 2-
amino-3-nitrobenzoic acid (HL) was purchased from Aldrich
Chemical Company (USA) and used without any further
purification. In the early stage of synthesis, the attempt to pre-
pare organotin(IV) complexes with dimethyltin(IV) oxide in
methanol was unsuccessful. The resulting orange solution was
filtered and orange crystals were collected. Unfortunately, the
crystals obtained were found to be the starting material (acid
itself) with the melting point of 209 °C and the crystal structure
of the acid has been report15. FTIR as KBr disc (cm-1): Selected
data: ν(OH) 2868-2561, ν(COO)as 1668, ν(COO)s 1251, ∆ν
= 417. 1H NMR (ppm) (DMSO-d6): δ benzene protons 6.68 (t,

7236 Choong et al.
Asian J. Chem.
7.4 Hz, 1H); 8.18 (d, 7.3 Hz, 1H); 8.26 (d, 7.8 Hz, 1H). 13C
NMR (ppm) (DMSO-d6): δ benzene carbons 113.98, 114.79,
131.77, 132.53, 139.81, 146.86; COO 168.86.
ν(COO)as 1654, 1632, ν(COO)s 1247, 1309, ∆ν = 407, 323;
ν(Sn-O-Sn) 629, ν(Sn-C) 577, ν(Sn-O) 490. 1H NMR (ppm)
(CDCl3): δ benzene protons 6.56 (s, 4H); 8.14 (s, 4H); 8.29
(d, 7.8 Hz, 4H); butyl, CH3 0.88-0.98 (m, 24H); CH2 1.20-
1.54 (m, 16H); CH2 1.59-1.73 (m, 32H). 13C NMR (ppm)
(CDCl3): δ benzene carbons 113.23, 119.16, 130.67, 132.87,
139.47, 147.74; butyl 13.68, 23.70, 25.84, 26.87, 27.08, 27.44,
27.61; COO 172.40. 119Sn-NMR (ppm) (CDCl3): δ = -173.34,
-211.45.
Preparationofdimethyltin(IV)oxide, Me2SnOandsodium
salt: Dimethyltin(IV) dichloride was dissolved in distilled
water and stirred for 16 h. Colourless solution was obtained.
Ammonia solution (60 %) was added into the colourless
solution and finally white precipitate was obtained. The preci-
pitate was placed in an oven (60 °C) for a few days to dry. The
sodium salt was obtained by heating under reflux a 1:1 molar
mixture of sodium hydroxide, NaOH and 2-amino-3-nitro-
benzoic acid in ethanol (50 mL) for two hours. After a few
days, yellow precipitates were obtained. Sodium salt of 2-amino-
3-nitrobenzoic acid: FTIR as KBr disc (cm-1) selected data:
ν(COO)as 1601, ν(COO)s 1263, ∆ν = 338.
Preparation of 2-NH2-3-NO2-C6H3COO(C6H5)3Sn (4):
The complex 4 was obtained by heating under reflux a 1:1
molar mixture of triphenyltin(IV) hydroxide (0.73 g, 2 mmol)
and 2-amino-3-nitrobenzoic acid (0.36 g, 2 mmol) in methanol
(60 mL) for 2 h. A clear yellow transparent solution was
isolated by filtration and kept in a bottle.After few days, yellow
crystals (0.46 g, 86 % yield) were collected. m.p: 155-156 °C.
Analysis for C25H20N2O4Sn: C, 56.72; H, 3.73; N, 5.24 %.
Calculated for C25H20N2O4Sn: C, 56.53; H, 3.80; N, 5.27 %.
FTIR as KBr disc (cm-1): ν(COO)as 1635, ν(COO)s 1248, ∆ν
Preparation of (2-NH2-3-NO2-C6H3COO)2(CH3)2Sn
(1): Complex 1 was obtained by heating under reflux a 1:2
molar mixture of dimethyltin(IV) oxide (0.33 g, 2 mmol) and
2-amino-3-nitrobenzoic acid (0.73 g, 4 mmol) in ethanol (50
mL) for 2 h. A yellow transparent solution was separated by
filtration and kept in a bottle. After few days, yellow preci-
pitates (0.78 g, 76.5 % yield) were collected. m.p.: 196-198 °C.
Analysis for C16H16N4O8Sn: C, 36.98; H, 3.08; N, 10.06 %.
Calculated for C16H16N4O8Sn1: C, 37.61; H, 3.16; N, 10.97 %.
FTIR as KBr disc (cm-1): ν(COO)as 1686; ν(COO)s 1252, ∆ν
= 434; ν(O-Sn-O) 601, ν(Sn-C) 538, ν(Sn-O) 491. 1H NMR
(ppm) (CDCl3): δ benzene protons 6.71 (t, 8.2 Hz, 2H); 8.35
(dd, 1.4 Hz, 7.8 Hz, 2H); 8.43 (dd, 1.4 Hz, 8.2 Hz, 2H); methyl
1.19 (s, 6H). 13C NMR (ppm) (CDCl3): δ benzene carbons
113.51, 114.21, 133.22, 133.38, 140.69, 147.60; methyl 5.10,
COO 172.32. 119Sn-NMR (ppm) (CDCl3): δ = -103.44.
Preparation of (2-NH2-3-NO2-C6H3COO)2(C4H9)2Sn
(2): Complex 2 was obtained by heating under reflux a 1:2
molar mixture of dibutyltin(IV) oxide (0.50 g, 2 mmol) and
2-amino-3-nitrobenzoic acid (0.73 g, 4 mmol) in ethanol (50
mL) for 4 h. A clear yellow transparent solution was separated
by filtration and kept in a bottle. After few days, yellow preci-
pitates (0.86 g, 67.8 % yield) were collected. m.p.: 189-190
°C. Analysis for C22H28N4O8Sn: C, 43.77; H, 5.17; N, 8.21 %.
Calculated for C22H28N4O8Sn: C, 44.40; H, 4.74; N, 9.41 %.
FTIR as KBr disc (cm-1): ν(COO)as 1631, ν(COO)s 1247, ∆ν
= 371; ν(O-Sn-O) 622, ν(Sn-C) 536, ν(Sn-O) 445. 1H NMR
(ppm) (DMSO-d6): δ benzene protons 6.69 (t, 7.8 Hz, 2H);
8.22 (d, 4.6 Hz, 2H); 8.25 (d, 4.6 Hz, 2H); butyl, CH3 0.79 (t,
7.3 Hz, 6H); CH2 1.27 (sx, 7.3 Hz, 4H); CH2 1.52-1.64 (m,
8H). 13C NMR (ppm) (DMSO-d6): δ benzene carbons 113.87,
117.54, 130.88, 132.40, 140.04, 146.69; butyl 13.58, 25.64,
26.89, 30.38; COO 172.46. 119Sn-NMR (ppm) (DMSO-d6): δ
= -317.60.
1
= 387; ν(Sn-O) 446. H NMR (ppm) (DMSO-d6): δ phenyl
protons 7.41-7.48 (m, 9H); 7.76-7.94 (m, 6H); benzene 6.61
(t, 8.3 Hz, 1H); 8.15 (dd, 1.8 Hz, 8.7 Hz, 1H); 8.19 (dd, 1.8
Hz, 7.8 Hz, 1H). 13C NMR (ppm) (DMSO-d6): δ phenyl carbons
Cipso 142.97, Cortho 136.18 (45.8 Hz), Cmeta 128.51 (69.6 Hz),
Cpara 129.07; benzene 113.70, 119.09, 130.12, 132.13, 139.80,
146.83; COO 169.99. 119Sn-NMR (ppm) (DMSO-d6): δ =
-263.25.
RESULTS AND DISCUSSION
In this study, all the four complexes (1-4) have been succe-
ssfully obtained in solid state. Only complex 4 was obtained
as crystal form and the crystal structure has been reported16.
The micro-elemental analysis for C, H and N data obtained
were in agreement with the predicted formula for complexes
1-4 together with the respective sharp melting points indicating
the isolation of fairly pure complexes. An outline of the
proposed structure for complexes 1-4 were depicted in Fig. 1.
The ν(O-H) bands of the acid, HL was absent in the
infrared spectra of salt and complexes 1-4 showed that the
deprotonation and coordination of the carboxylate anion. In
addition, complexes 2-4 revealed that the ν(COO)as was shifted
to a lower wavelength number compared to the acid, HL which
signified that the coordination took place via the oxygen atoms
of the carboxylate anion. The magnitude of ∆ν = [ν(COO)as -
ν(COO)s] is an useful indicator in the correlation of the coor-
dination modes of the carboxylate anion to the tin(IV) atom
in the organotin(IV) carboxylate complexes17. In general, if
the ∆ν value of complexes is greater by 65-90 cm-1 compared
to their sodium salts indicating either asymmetric or mono-
dentate bonding of the carboxylate anions and if the ∆ν values
being comparable or slightly higher by at most 50 cm-1 than
those of the sodium salts, the carboxylate anions chelate biden-
tately to the tin(IV) atom17. Based on the comparison of ∆ν
values of complexes 1-4 and sodium salt, the carboxylate anion
were bonded to tin(IV) atom in monodentate manner in
complex 1; bidentate manner in complex 2; and exhibited
monodentate and bidentate bonding manner in complex 3. For
complexes derivatives of triphenyltin(IV) carboxylate, ∆ν
greater than 200 cm-1 would be expected for the monodentate
Preparation of [{2-NH2-3-NO2-C6H3COO(C4H9)2Sn}2O]2
(3): Complex 3 was obtained by heating under reflux a 1:1
molar mixture of dibutyltin(IV) oxide (0.50 g, 2 mmol) and
2-amino-3-nitrobenzoic acid (0.36 g, 2 mmol). The reaction
was carried out in a mixture of ethanol (60 mL) for 3 h. A
clear yellow solution was isolated by filtration and kept in a
bottle. After few days, yellow crystals (0.73 g, 83.7 % yield)
were collected. m.p.: 140-142 °C.Analysis for C60H92N8O18Sn4:
C, 41.23; H, 6.62; N, 4.26 %. Calculated for C60H92N8O18Sn4:
C, 42.69; H, 5.49; N, 6.64 %. FTIR as KBr disc (cm-1):

Vol. 26, No. 21 (2014)
Synthesis, Characterization and Antibacterial Activity of Organotin(IV) Complexes 7237
Me
O
O
O
O
Sn
C
+ H2O
C
2 HOOC
Me2SnO
+
NO2
Me
H2N
O2N
NH2
NO2
H2N
1
Bu
O
O
O
O
Sn
+ H2O
O2N
O2N
C
C
Bu2SnO
+
2 HOOC
Bu
NO2
NH2
H2N
H2N
NO2
2
Bu Bu
Sn
NO2
O2N
NH2
H2N
O
C
O
C
O
O
O
O
Bu
Bu
Bu
Sn
Sn
+ 2H O
2
Bu
4 HOOC
+
4 Bu2SnO
O
C
H2N
NO2
O
C
Sn
O
O
NO2
H2N
O2N
NH2
Bu
Bu
3
Ph
O
Ph Sn
Ph
+ H2O
C
HOOC
+
Ph3SnOH
O
NO2
Me= methyl, Bu= butyl & Ph= phenyl
Fig. 1. Proposed structure of complexes 1-4
H2N
NO2
H2N
4
bonding carboxylate anions18. Hence, the carboxylate anion
in complex 4 would be expected to bond to the tin(IV) atom
in monodentate manner since the ∆ν above 200 cm-1. For
further evidence of the coordination of carboxylate anion, this
can be revealed by the presence of ν(O-Sn-O)/ν(Sn-O-Sn) and
ν(Sn-O) stretching bands in the wavelength number at 629-
601 and 491-445 cm-1 in the spectra of complexes 1-4.
ppm indicating the presence of the butyl groups of the SnBu2
moiety. Moreover, complex 3 was derivatives of organodistann-
oxane dimer types exhibited two sets of signals corresponding
to the butyl groups linked to the exo- and endo-cyclic tin(IV)
atoms, respectively20. Complex 4 revealed the chemical shift
of the δ(13C)ipso at 142.97 ppm indicative of a five-coordinated
tin(IV) atom21. Thus, indicating that the tin(IV) atom in
complex 4 was five-coordinated and has a trigonal bipyramid
geometry21.
The δ(119Sn) values of the five-coordinated diorganotin(IV)
complexes fall in the range between -90 to -190 ppm and the
six-coordinated complexes between -210 to -400 ppm22. The
δ(119Sn) values of complexes 1 and 2 were -103.44 and -317.60
ppm, respectively indicating that the tin(IV) atom in complex
1 was five-coordinated whereas the tin(IV) atom in complex
2 was six-coordinated. Complex 3 exhibited two well resolved
δ(119Sn) signals at -173.34 and -211.45 ppm indicating two
tin(IV) atoms were five-coordinated and another two tin(IV)
atoms were six-coordinated. In general, the δ(119Sn) value
of triphenyltin(IV) complexes lie in the range between -180
to -260 ppm was believed to be five-coordinated and in the
distorted trigonal bipyramid geometry. Complex 4 showed that
1
The H NMR spectra of complexes 1-4 exhibited simi-
larities to the acid, HL. The only exceptional and predictable
observation were the occurrence of the methyl and butyl
protons signals of complexes 1-3 at 1.19 ppm and in the range
of 0.79-1.73 ppm, respectively. The appearance of two well
separated sets of multiplets in the regions centering around δ
≈ 7.45 and 7.85 ppm (downfield) ascribed to the phenyl protons
of complex 419.
The 13C NMR spectra of complexes 1-4 showed that the
δ(COO) signals shifted to the downfield region which was
lower compared to that of the acid, HL indicating the
carboxylate anions were bonded to tin(IV) atoms. Complex 1
exhibited a sharp signal at 5.10 ppm indicating the presence
of the methyl groups in the SnMe2 moiety whereas complex 2
exhibited four sharp signals at 13.58, 25.64, 26.89 and 30.38

7238 Choong et al.
Asian J. Chem.
the δ(119Sn) value at -263.25 ppm indicated the tin(IV) atom
was five-coordinated and possessed a trigonal bipyramid
geometry21. From the 119Sn NMR study, it is strongly to conclude
that the all the carboxylate anions were bonded to the tin(IV)
atoms in bidentate manner. This phenomenon may due to upon
in solution form, the organic groups of complexes 1-4 were
undergo self-arrangement and in the dynamic state resulting
the carboxylate anions were closer to the tin(IV) atoms moieties
to exhibit dative bonding.
atoms moieties have been characterized quantitatively and
qualitatively. Based on the preliminary in vitro antibacterial
screening activity, complex 4 [triphenyltin(IV)] showed better
activity compared to complexes 1-3 [diorganotin(IV)] against
Gram-positive bacterial strains but its activities are lower com-
pared to the reference drugs.
ACKNOWLEDGEMENTS
The authors thank Malaysian Ministry of Higher Education,
MOHE (Project No.: FRGS/1/2012/SG01/UTAR/02/1) and
Universiti Tunku Abdul Rahman, UTAR (Project No.: IPSR/
RMC/UTARRF/C1-11/C07) for financial support as well as
technical assistance and facilities.
The preliminary in vitro antibacterial screening activity
of acid, HL and complexes 1-4 were given in Table-1. Inhibi-
tion zones with a diameter less than 10 mm are considered as
weak; larger than 10 mm but less than 16 mm are considered
as moderate and finally larger than 16 mm and above are active.
Based on the study, acid, HL was found to be inactive and
complex 1 showed a weak activity to all the tested bacterial
strains. In addition, complex 4 was found to show selective
activity against Bacillus subtillis, Pseudomonas aeruginosa
and Staphylococcus aureus at 1 mg/mL with the inhibition
zones of 20, 19 and 20 mm, respectively indicating the
activities were in the active mode. Among the dibutyltin(IV)
complexes, complex 2 only showed significant activity against
Pseudomonas aeruginosa with the inhibition zone of 22 mm.
Overall, in this study the triphenyltin(IV) complexes is
pronounced to be more active against three bacterial strains
compared to diorganotin(IV) complexes and this was due to
complex 4 was derivatives of triorganotin(IV) which is known
to possess higher biological activity compared to diorgano-
tin(IV)20. Although complex 4 showed significant in vitro
antibacterial activity against Gram-positive bacterial strains but
the value obtained were lower compared to the reference drugs.
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Conclusion
Complexes 1-4 have been successfully synthesized and
their structures as well as the coordination number of tin(IV)