Polymeric seven-coordinated organotin(IV) complexes derived from 5-amino-2-chlorobenzoic acid and in vitro anti-cancer studies

Article abstract of DOI:10.1080/00958972.2014.963571

Cancer cases are alarmingly increasing worldwide, and newer chemotherapeutic agents are needed. Recent analogs of cisplatin (carboplatin, lobaplatin, nedaplatin and oxaliplatin) and their marketing as advanced chemotherapeutic drugs have furthered the interest in metal-based anti-cancer drugs. In the current study, two new polymeric organotin(IV) carboxylate complexes (1 and 2) have been synthesized and characterized. Spectroscopic studies showed that coordination took place via carboxylates. Furthermore, X-ray crystallographic study on 1 indicated that it possesses a monomeric structure and exists in polymeric formation due to additional Sn-N coordination, assigning seven coordinations to each metal ion. Both the complexes were tested against three cancerous (human colon cancer, HCT 116; breast cancer, MCF-7; and leukemia, K562) and one non-cancerous (3T3-L1) cell lines. Complex 1 showed exceptional cytotoxicity against cancerous cell lines (IC50 = 1.0 M for HCT 116; 258.7 nM for MCF-7; and 46.7 nM K562) and remained comparatively non-toxic against normal cells (IC50 = 37.0 M). This shows that both complexes have selective cytotoxicity against cancer cells.

Full text of DOI:10.1080/00958972.2014.963571

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Polymeric seven-coordinated
organotin(IV) complexes derived from
5-amino-2-chlorobenzoic acid and in
vitro anti-cancer studies
a
a
a
Yip-Foo Win , Chen-Shang Choong , Jia-Chin Dang , Muhammad
b
c
d
Adnan Iqbal , Ching Kheng Quah , Amin Malik Shaw Abdul Majid &
b
Siang-Guan Teoh
a
Faculty of Science, Department of Chemical Science, Universiti
Tunku Abdul Rahman, Kampar, Malaysia
b
School of Chemical Sciences, Universiti Sains Malaysia, Pulau
Click for updates
Penang, Malaysia
c
X-ray Crystallography Unit, School of Physics, Universiti Sains
Malaysia, Pulau Penang, Malaysia
d
Eman Testing and Research Laboratory, School of Pharmaceutical
Sciences, Universiti Sains Malaysia, Pulau Penang, Malaysia
Accepted author version posted online: 09 Sep 2014.Published
online: 29 Sep 2014.
To cite this article: Yip-Foo Win, Chen-Shang Choong, Jia-Chin Dang, Muhammad Adnan
Iqbal, Ching Kheng Quah, Amin Malik Shaw Abdul Majid & Siang-Guan Teoh (2014) Polymeric
seven-coordinated organotin(IV) complexes derived from 5-amino-2-chlorobenzoic acid
and in vitro anti-cancer studies, Journal of Coordination Chemistry, 67:20, 3401-3413, DOI:
10.1080/00958972.2014.963571
To link to this article: http://dx.doi.org/10.1080/00958972.2014.963571
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Journal of Coordination Chemistry, 2014
Vol. 67, No. 20, 3401–3413, http://dx.doi.org/10.1080/00958972.2014.963571
Polymeric seven-coordinated organotin(IV) complexes derived
from 5-amino-2-chlorobenzoic acid and in vitro anti-cancer
studies
YIP-FOO WIN*†, CHEN-SHANG CHOONG†, JIA-CHIN DANG†,
MUHAMMAD ADNAN IQBAL‡, CHING KHENG QUAH§,
AMIN MALIK SHAW ABDUL MAJID¶ and SIANG-GUAN TEOH*‡
†Faculty of Science, Department of Chemical Science, Universiti Tunku Abdul Rahman, Kampar,
Malaysia
‡School of Chemical Sciences, Universiti Sains Malaysia, Pulau Penang, Malaysia
§X-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, Pulau Penang, Malaysia
¶Eman Testing and Research Laboratory, School of Pharmaceutical Sciences, Universiti Sains
Malaysia, Pulau Penang, Malaysia
(
Received 8 March 2014; accepted 1 August 2014)
Cancer cases are alarmingly increasing worldwide, and newer chemotherapeutic agents are needed.
Recent analogs of cisplatin (carboplatin, lobaplatin, nedaplatin and oxaliplatin) and their marketing as
advanced chemotherapeutic drugs have furthered the interest in metal-based anti-cancer drugs. In the
current study, two new polymeric organotin(IV) carboxylate complexes (1 and 2) have been synthe-
sized and characterized. Spectroscopic studies showed that coordination took place via carboxylates.
Furthermore, X-ray crystallographic study on 1 indicated that it possesses a monomeric structure and
exists in polymeric formation due to additional Sn–N coordination, assigning seven coordinations to
each metal ion. Both the complexes were tested against three cancerous (human colon cancer, HCT
116; breast cancer, MCF-7; and leukemia, K562) and one non-cancerous (3T3-L1) cell lines.
*
Corresponding authors. Email: yipfw@utar.edu.my (Y.-F. Win); sgteoh@usm.my (S.-G. Teoh)
2014 Taylor & Francis
©

3
402
Y.-F. Win et al.
Complex 1 showed exceptional cytotoxicity against cancerous cell lines (IC50 = 1.0 μM for HCT
116; 258.7 nM for MCF-7; and 46.7 nM K562) and remained comparatively non-toxic against normal
cells (IC50 = 37.0 μM). This shows that both complexes have selective cytotoxicity against cancer
cells.
Keywords: Organotin(IV) carboxylate complexes; 5-Amino-2-chlorobenzoic acid; Cytotoxicity;
Anti-cancer
Introduction
Tin is a biocompatible metal [1–3]. In recent years, a number of organotin complexes have
been screened for possible anti-microbial [4–17] and anti-cancer [8, 18–23] activities.
Organotin complexes offer unique coordination chemistry as well as structural diversity
which could expand from simple monomeric to polymeric structures [4, 24–31] and may
give biological adoptability to these complexes.
Organotin(IV) complexes, possessing various coordination features, have been studied
against a range of cancerous cell lines like human lung tumor (A549), cervix tumor (HeLa),
kidney cancer (A498), breast cancer (EVSA-T, MCF-7), lung cancer (H226), ovarian ade-
nocarcinoma (IGROV, A2780), melanoma (M19 MEL), colon cancer (WIDR, SW480),
hepatocellular liver carcinoma (HepG2), endometrial cancer (HEC-1B), and bladder
carcinoma (T24) [18, 19, 21, 23, 31, 32].
In the current study, we report the synthesis of two new organotin(IV) carboxylate
complexes (1 and 2, scheme 1) derived from 5-amino-2-chlorobenzoic acid (HL) and
their cytotoxicity against three cancerous cell lines (breast cancer MCF-7, human colorec-
tal cancer HCT 116, and leukemia HL-60) and one non-cancerous cell line (3T3-L1) to
study the effect of synthesized compounds on cancerous and non-cancerous cells. The
complexes have seven coordinations which have been rarely reported for tin complexes
[
33, 34].
Experimental
General and instrumental
Chemicals were purchased commercially and used without purification. Elemental analyses
were carried out on a Perkin-Elmer 2400 CHN Elemental Analyzer. Tin was assessed gravi-
metrically by igniting a known quantity of each complex to SnO . The melting points were
2
determined in an open capillary tube. Infrared spectra were recorded using a Perkin-Elmer
−
1
1
13
System 2000 FTIR spectrophotometer as KBr disks from 4000 to 400 cm . H, C, and
119
Sn NMR spectra were recorded on a Joel JNM-ECX 400 FT NMR spectrometer using
deuterated d -DMSO as the solvent and tetramethylsilane, TMS, as the internal standard.
6
Single-crystal X-ray diffraction data were collected on an APEX II Duo CCD area-detec-
tor diffractometer operating at 50 kV and 30 mA using Mo Kα radiation (λ = 0.71073 Å).
Diffraction data for 1 was collected with the Oxford Cryosystem Cobra low-temperature
attachment at 100 K [35]. Data collection and reduction were performed using APEX2 and
SAINT software. SADABS was used for absorption correction. All structures were solved
2
by direct methods, and refinement was carried out by full-matrix least squares on F using
SHELXTL [36]. All non-hydrogen atoms were refined anisotropically, whereas hydrogens
were refined isotropically. All N-bound hydrogens were located in different Fourier

Seven-coordinated organotin(IV)
3403
maps and fixed at their found positions and refined with Uiso (H) = 1.2 Ueq (N). Hydrogens
bound to carbon were positioned geometrically with Uiso (H) = 1.2 or 1.5 Ueq (C). A
rotating-group model was applied for the methyl groups.
5
-Amino-2-chlorobenzoic acid (HL)
HL was purchased from Acros Organics and was used without purification. FTIR as KBr
−
1
disk (cm ): selected data: ν(OH) 2923–2597, ν(COO) 1624, ν(COO) 1371, and Δν =
as
s
1
2
(
53. H NMR (ppm) (d -DMSO): δ: benzene protons 6.64 (dd, 2.4 Hz, 8.6 Hz, 1H); 6.91
d, 3.0 Hz, 1H); and 7.06 (d, 9.2 Hz, 1H). C NMR (ppm) (d -DMSO): δ: benzene carbons
6
1
3
6
115.8, 117.6, 118.1, 131.3, 131.9, and 147.9; COO 166.9.
Preparation of dimethyltin(IV) oxide, Me SnO
2
Dimethyltin(IV) dichloride was dissolved in distilled water and stirred for 16 h. Colorless
solution was obtained. White precipitates formed after the addition of ammonia solution
(60%). The precipitates were placed in an oven (60 °C) for a few days to dry.
Preparation of sodium salt (NaHL)
The sodium salt of the acid was obtained by refluxing a 1 : 1 M mixture of sodium hydrox-
ide and 5-amino-2-chlorobenzoic acid in ethanol (50 mL) for 2 h. After a few days, white
−
1
precipitate of sodium 5-amino-2-chlorobenzoate was obtained. FTIR as KBr disk (cm ,
selected data): ν(COO) 1565, ν(COO) 1387, Δν = 178.
as
s
Synthesis of complexes
Preparation of (5-NH -2-Cl-C H COO) (C H ) Sn (1). Complex 2 was obtained by
2
6
3
2
4
9 2
refluxing a 1 : 2 M mixture of dibutyltin(IV) oxide (0.75 g, 3 mM) and 5-amino-2-chloro-
benzoic acid (1.03 g, 6 mM) in methanol (50 mL) for 4 h. A transparent solution was
separated by filtration and kept in a bottle. After a few days, needle brown crystals (1.34 g,
7
8.0% yield) were collected. Melting point: 121–123 °C. Analysis for C H N O Cl Sn :
22 28 2 4 2 1
C, 45.77; H, 3.81; N, 4.06; Sn, 19.03%. Calculated for C H N O Cl Sn : C, 46.03; H,
2
2
28
2
4
2
1
−1
4
2
.91; N, 4.88; Sn, 20.68%. FTIR as KBr disk (cm ): ν(COO) 1592; ν(COO) 1385, Δν =
07; ν(O–Sn–O) 660, ν(Sn–C) 597, ν(Sn–N) 502, and ν(Sn–O) 447. H NMR (ppm)
as s
1
(d6-DMSO): δ: benzene protons 6.60 (d, 6.7 Hz, 2H); 6.90 (s, 2H); and 7.03 (d, 8.6 Hz,
2
H); butyl, CH 0.78 (t, 6.6 Hz, 6H), CH 1.24 (sx, 7.3 Hz, 4H); CH 1.43–1.49 (m, 4H);
3
2
2
1
3
and CH 1.52–1.59 (m, 4H). C NMR (ppm) (d -DMSO): δ: benzene carbons 115.9,
2
6
119
117.6, 131.1, 133.0, and 147.9; butyl 13.9, 14.0, 26.2, 27.3, and 30.8; COO 172.3. Sn
NMR (ppm) (d -DMSO): δ: −260.7.
6
Preparation of (5-NH -2-Cl-C H COO) (CH ) Sn (2). Complex 1 was obtained by
2
6
3
2
3 2
refluxing a 1 : 2 M mixture of dimethyltin(IV) oxide (0.50 g, 3 mM) and 5-amino-2-chloro-
benzoic acid (1.03 g, 6 mM) in acetonitrile (50 mL) for 4 h. A transparent solution was
separated by filtration and kept in a bottle. After a few days, white precipitates (1.25 g,

3
404
Y.-F. Win et al.
8
5.0% yield) were collected. Melting point: 204–206 °C. Analysis for C H N O Cl Sn :
1
6
16
2
4
2
1
C, 38.97; H, 3.01; N, 4.98; Sn, 24.22%. Calculated for C H N O Cl Sn : C, 39.23; H,
1
6
16
2
4
2
1
−1
3
2
.29; N, 5.72; Sn, 24.23%. FTIR as KBr disk (cm ): ν(COO) 1594; ν(COO) 1385, Δν =
09; ν(O–Sn–O) 663, ν(Sn–C) 577, and ν(Sn–O) 448. H NMR (ppm) (d -DMSO): δ: ben-
as s
1
6
zene protons 6.58 (dd, 2.8 Hz, 8.7 Hz, 2H); 6.87 (s, 2H); and 7.02 (d, 8.7 Hz, 2H); methyl
1
3
0
.83 (s, 6H). C NMR (ppm) (d -DMSO): δ: benzene carbons 115.7, 117.4, 131.0, 133.9,
6
119
and 147.8; methyl 11.79, COO 171.79. Sn NMR (ppm) (d -DMSO): δ: −288.5.
6
In vitro anti-cancer studies
Source of cell lines, culture conditions, preparation of cell culture, and MTT assay were
performed according to our previously reported procedure for these cell lines [37–40]. The
procedure has been additionally described in the supplementary file.
Results and discussion
In this study, 1 and 2 have been obtained in the solid state. The complexes have sharp
melting points (with a range of less than 3 °C), indicating isolation of pure complexes. An
outline of the proposed structures for complexes has been depicted in scheme 1. The
micro-analytical data obtained is in agreement with the predicted formulas of 1 and 2.
1
13
119
Spectroscopy (FTIR, H, C, Sn NMR)
The ν(O–H) bands in HL were absent in the infrared spectra of salt (NaL) and 1 and 2
which indicated deprotonation and coordination of the carboxylate. Complexes revealed that
ν(COO) shifted to a lower wave number (Δν) compared to HL which signifies that coordi-
as
nation took place via the oxygens of carboxylates. Complexes 1 and 2 were isolated as
−
1
polymeric complexes, and their Δν values were 209 and 207 cm , lower than the sodium
−1
salt (Δν = 178 cm ) of 5-amino-2-chlorobenzoic acid, indicating that the carboxylates were
bidentate to tin(IV). Further evidence of the coordination to tin(IV) via oxygens was
revealed by the presence of ν(O–Sn–O)/ν(Sn–O–Sn) and ν(Sn–O) stretching bands in the
FTIR spectra of 1 and 2.
1
H NMR spectra of 1 and 2 exhibited similarities to HL. The only exceptional differ-
1
ences were the appearance of new H NMR signals for coordinated methyl and butyl moie-
ties at δ 0.83 ppm for 1 and δ 0.75–1.60 ppm for 2. Further evidence for formation of the
1
3
13
complexes was provided by C NMR studies. The C NMR spectra of 1 and 2 showed
that the δ(COO) signals shifted downfield (~172 δ ppm) from that of HL (~167 δ ppm),
indicating the carboxylate bonding to tin(IV). Also, 1 exhibited a sharp signal at 11.7 ppm,
indicating the presence of the methyl groups in the SnMe moiety, whereas 2 exhibited a
2
set of signals in the upfield region, indicating the presence of the butyl groups of SnBu .
2
119
The δ( Sn) values of four-coordinate complexes fall in the range +200 to −60 ppm; the
five-coordinate complexes fall between −90 and −190 ppm, and the six- and seven-coordi-
nate complexes fall between −210 and −400 ppm [41, 42]. The δ( Sn) values of 1 and 2
were −288.5 and −260.7 ppm, respectively, indicating that tin(IV) in both 1 and 2 remained
six-coordinate in solutions. However, the crystallographic information revealed seven coor-
dinations, which may be acquired during crystallization.
119

Seven-coordinated organotin(IV)
3405
Cl
O
O
Cl
NH2
Sn
O
O
NH2
O
O
O
H N
2
OH
O
Sn
methanol
(60 mL)
reflux (4 h)
NH2
Cl
Cl
H2N
HL
O
acetonitrile
50 mL)
Cl
O
(
Sn
O
reflux (4 h)
1
Cl
O
O
Cl H N
2
NH2
O
O
O
O
Sn
NH2
Cl
H N
2
O
Cl
O
2
Scheme 1. Synthesis of tin complexes 1 and 2. The dashed lines represent the extended units in order to generate
a polymeric formation.
Crystallography
Complex 1 was isolated, and its molecular structure was studied using single-crystal X-ray
diffraction technique. Single-crystal X-ray determination revealed that the crystal system of
the complex is triclinic with space group Pī and unit cell parameters a = 7.5585(4) Å,
b = 16.4261(9) Å, c = 20.4598(11) Å, α = 68.216(1)°, β = 89.882(1)°, and γ = 82.410(1)°.
Summary of the crystallographic data for 1 at 100.0 K is depicted in table 1 and selected
bond lengths (Å) and angles (°) are listed in table 2. The hydrogen-bond geometry (Å, °) of
1
is given in table 3. The structural elucidation provided two crystallographically different
units (A and B) having slightly different geometrical parameters. The literature shows that
in some cases, crystallographically different units of the same molecule have some signifi-
cant differences (bond distances and angles) to be discussed in detail [43–45]. However, in
the current case, both the units (A and B) have almost similar geometries (figure S1, see

3
406
Y.-F. Win et al.
Table 1. Crystallographic data of 1.
Parameter
2 6 3 2 4 9 2
(5-NH -2-Cl-C H COO) (C H ) Sn
Empirical formula
Formula weight
Temperature (K)
C
22
H
28Cl N O Sn
2 2 4
574.05
100
Radiation/wavelength
Crystal system, space group
Unit cell dimensions
Mo Kα/0.71073 Å
Triclinic, Pī
a = 7.5585(4) Å α = 68.216(1)°
b = 16.4261(9) Å β = 89.882(1)°
c = 20.4598(11) Å γ = 82.410(1)°
2335.1(2)
4, 1.633
1.350
0.53 × 0.15 × 0.14
Needle/brown
3.5–32.6
3
Volume (Å )
−
3
Z, Calculated density (Mg m
Absorption coefficient (mm
Crystal size (mm)
Crystal morphology/color
θ range for data (°)
)
−1
)
Limiting indices
Reflections collected/unique
R (int)
−9 ≤ h ≤ 9, −21 ≤ k ≤ 21, −26 ≤ l ≤ 26
41,033/10,517
0.027
Completeness
98.1%
Max and min transmission
Goodness of fit
R[F > 2σ(F )], wR(F )
Largest difference between peak and hole (e Å
0.828 and 0.534
1.12
0.029, 0.074
1.26, −1.17
2
2
2
−
3
)
online supplemental material at http://dx.doi.org/10.1080/00958972.2014.963571), except
the terminals of the alkyl chains which might have less significance in both, biological
activities and metal coordination geometries. Furthermore, there is no interconnection
between polymer chains comprised of unit A and unit B which keeps them independent
moieties. In addition, the crystal packing for both of the units is comparable where it is
reflected by the similar hydrogen-bonding geometries (table 3). Hence, only one of the units
(A) was selected to be discussed in detail. Figure 1 exhibits the molecular structure of 1
with its numbering scheme, while the molecular packing diagram is depicted in figure S2
(supplementary file).
Based on the crystal structure depicted in figure 1, the tin is seven coordinate [33, 34,
4
6], bonded to three oxygens (Sn–O) of the carboxylate anions and two bonds from bond-
ing of butyl groups to tin (Sn–C). Another two bonds attributed to Sn–N result in tin(IV)
being seven coordinate in a distorted pentagonal–bipyramidal geometry. Due to the Sn–N
bonding, 1 forms a polymeric chain propagating in [0 1 0] instead of simple monomeric as
reported earlier [24, 47].
In the crystal, the polymeric chains are further consolidated by intermolecular N–H⋯Cl,
N–H⋯O and C–H⋯O hydrogen bonds (table 3).
Based on the spectroscopic study, carboxylates are bonded bidentate to tin(IV) and the
overall structure would be simple monomeric type. However, based on the single crystal
structure determination, it was confirmed and have a clearer view that a new structure of
dibutyltin(IV) dicarboxylate has been obtained which existed in the polymeric form and
possessed distorted pentagonal bipyramidal geometry.
Anti-cancer studies
The mortality rate due to cancer is increasing worldwide due to the rapid growth of world
population as well as adoption of cancer-causing behaviors [48, 49]. According to GLOBO-
CAN 2008 estimate, 7.6 million cancer deaths occurred worldwide labeling breast cancer as

Seven-coordinated organotin(IV)
Table 2. Bond lengths (Å) and angles (°) of 1.
3407
Bond lengths
Sn(1A)–C(15A)
Sn(1A)–C(19A)
Sn(1A)–O(1A)
Sn(1A)–O(4A)
Sn(1A)–N(1A)
Sn(1A)–N(2A)
2.133(2)
2.135(2)
2.2629(16)
2.2648(16)
2.4045(18)
2.4433(18)
Sn(1B)–C(15B)
Sn(1B)–C(19B)
Sn(1B)–O(1B)
Sn(1B)–O(4B)
Sn(1B)–N(1B)
Sn(1B)–N(2B)
2.142(2)
2.143(2)
2.2495(16)
2.2521(15)
2.4012(18)
2.4339(18)
Bond angles
C(15A)–Sn(1A)–C(19A)
C(15A)–Sn(1A)–O(1A)
C(19A)–Sn(1A)–O(1A)
C(15A)–Sn(1A)–O(4A)
C(19A)–Sn(1A)–O(4A)
O(1A)–Sn(1A)–O(4A)
C(15A)–Sn(1A)–N(1A)
C(19A)–Sn(1A)–N(1A)
O(1A)–Sn(1A)–N(1A)
O(4A)–Sn(1A)–N(1A)
C(15A)–Sn(1A)–N(2A)
C(19A)–Sn(1A)–N(2A)
O(1A)–Sn(1A)–N(2A)
O(4A)–Sn(1A)–N(2A)
N(1A)–Sn(1A)–N(2A)
177.69(8)
88.43(7)
93.45(7)
93.31(7)
85.22(7)
165.06(6)
92.93(8)
88.84(8)
75.20(6)
89.89(6)
85.00(7)
92.87(7)
121.60(6)
73.73(6)
162.92(6)
103.14(13)
C(15B)–Sn(1B)–C(19B)
C(15B)–Sn(1B)–O(1B)
C(19B)–Sn(1B)–O(1B)
C(15B)–Sn(1B)–O(4B)
C(19B)–Sn(1B)–O(4B)
O(1B)–Sn(1B)–O(4B)
C(15B)–Sn(1B)–N(1B)
C(19B)–Sn(1B)–N(1B)
O(1B)–Sn(1B)–N(1B)
O(4B)–Sn(1B)–N(1B)
C(15B)–Sn(1B)–N(2B)
C(19B)–Sn(1B)–N(2B)
O(1B)–Sn(1B)–N(2B)
O(4B)–Sn(1B)–N(2B)
N(1B)–Sn(1B)–N(2B)
178.34(8)
94.02(7)
84.86(7)
88.30(7)
93.07(7)
166.74(6)
92.45(8)
88.81(8)
91.40(6)
75.45(6)
85.47(7)
93.04(7)
73.76(6)
119.46(6)
164.80(6)
129.95(13)
i
iii
C(7A) –O(1A)–Sn(1A)
C(14B) –O(1B)–Sn(1B)
Bond angles
C(14A) –O(4A)–Sn(1A)
ii
iv
103.14(13)
122.15(14)
102.8
105.9
121.40(13)
94.8
94.8
116.33(15)
108.2
108.2
117.72(15)
107.9
C(7B) –O(4B)–Sn(1B)
105.62(13)
121.41(14)
108.1
100.6
119.43(13)
97.2
106.5
114.64(15)
108.6
108.6
116.22(15)
108.2
C(6A)–N(1A)–Sn(1A)
Sn(1A)–N(1A)–H(1NA)
Sn(1A)–N(1A)–H(2NA)
C(8A)–N(2A)–Sn(1A)
Sn(1A)–N(2A)–H(3NA)
Sn(1A)–N(2A)–H(4NA)
C(16A)–C(15A)–Sn(1A)
Sn(1A)–C(15A)–H(15A)
Sn(1A)–C(15A)–H(15B)
C(20A)–C(19A)–Sn(1A)
Sn(1A)–C(19A)–H(19C)
Sn(1A)–C(19A)–H(19D)
C(6B)–N(1B)–Sn(1B)
Sn(1B)–N(1B)–H(1NB)
Sn(1B)–N(1B)–H(2NB)
C(8B)–N(2B)–Sn(1B)
Sn(1B)–N(2B)–H(3NB)
Sn(1B)–N(2B)–H(4NB)
C(16B)–C(15B)–Sn(1B)
Sn(1B)–C(15B)–H(15C)
Sn(1B)–C(15B)–H(15D)
C(20B)–C(19B)–Sn(1B)
Sn(1B)–C(19B)–H(19A)
Sn(1B)–C(19B)–H(19B)
107.9
108.2
Note: Symmetry codes: (i) −x + 1, −y + 1, −z + 1; (ii) –x + 1, −y + 1, −z + 1; (iii) –x + 1, −y + 2, −z; (iv) –x + 1, −y + 1, −z.
a leading cause of cancer deaths [48]. The discovery of cisplatin as an anti-cancer drug and
recently its improved analogs (Carboplatin, Lobaplatin, Nedaplatin, Oxaliplatin) as market-
ing chemotherapeutic drugs give interest in exploration of metal-based anti-cancer drugs
[
50–56]. Several new organometallic compounds have been reported as anti-carcinogenic
agents [8, 10, 18, 19, 21, 32, 40, 57–99], which indicate the bright future of metal-based
drugs.
The current study reports in vitro anti-cancer potential of 1 and 2. Each complex was
tested against three cancer cell lines (human colon cancer HCT 116, breast cancer
MCF-7, and leukemia K562) and one normal cell line (3T3-L1). The IC50 values are
shown in table 4 and the dose-dependent graphs as figure 2. The table shows that 1
imparted significant activity (IC50 = 1.0 μM) compared to 2 (IC50 = 177.5 μM) against
HCT 116 cell line. Such a significant difference in the IC50 values of both the complexes

3
408
Y.-F. Win et al.
Table 3. Hydrogen-bond geometry (Å, °) of 1.
D–H⋯A
D–H
H⋯A
D⋯A
D–H⋯A
i
N1A–H1NA⋯Cl1A
N1A–H2NA⋯O2A
N1A–H2NA⋯O3A
N2A–H3NA⋯O3A
0.91
0.87
0.87
0.90
0.87
0.87
0.89
0.93
0.93
2.82
2.57
2.04
2.07
2.36
2.22
2.04
2.42
2.45
3.637(2)
3.171(3)
2.831(3)
2.893(2)
3.072(3)
2.871(3)
2.889(2)
3.059(3)
3.037(3)
150
126
149
150
140
132
160
126
121
i
ii
iii
iv
N1B–H1NB⋯O2Bv
N1B–H1NB⋯O3B
vi
N2B–H4NB⋯O3B
C1A–H1AA⋯O1A
C1B–H1BA⋯O4B
Note: Symmetry codes: (i) −x + 2, −y, −z + 1; (ii) −x + 1, −y + 1, −z + 1; (iii) −x, −y + 1, −z + 1;
iv) −x + 2, −y + 1, −z; (v) −x + 1,−y + 2, −z; (vi) −x, −y + 2, −z.
(
Figure 1. Crystal structure of 1 drawn using Olex2 software and labeled according to the CIF data file. The
ORTEP picture of molecular structure (figure S4) and crystal packing (figure S2) has been additionally provided in
supplementary file.
Table 4. The IC50 values of 1 and 2.
Normal cell
Carcinoma cell lines
MCF 7
line
3T3-L1
Cell lines
HCT 116
K562
Complexes
1
2
1.0*
177.5*
5-FU
258.7**
49.7*
Tamoxifen
8.7*
46.7**
40.7*
Betulinic acid
15.0*
37.0*
136.0*
Betulinic acid
44.0*
Standards
8
.1*
*μM.
*
*nM.
may be due to the different geometrical orientations and substitutional effects. This is
further evident from their IC50 values on MCF-7 cell line where again 1 showed results
better than 2 (IC50 of 1 = 258.7 nM and 2 = 49.7 μM). This also shows that a complex

Seven-coordinated organotin(IV)
3409
Figure 2. Dose-dependent anti-proliferative effect of 1 (a) and 2 (b) on human colorectal cancer (HCT 116),
breast cancer (MCF-7), leukemia (K562), and normal cell line (3T3-L1).
may show lower cytotoxicity or may be inactive against one cell line, but may have
observable activity against the other type of cell line. Furthermore, on K562 cell line,
similar results were obtained (IC50 of 1 = 46.7 nM and 2 = 40.7 μM) which label both
the complexes as anti-carcinogenic agents with an exception of 2 as almost inactive
against HCT 116 and moderately active against the other two cell lines. Additionally,
compared to their cytotoxicity against carcinoma cell lines, each of the complexes

3
410
Y.-F. Win et al.
Figure 3. Photomicrographic images of the cell lines, taken under an inverted phase-contrast microscope at ×200
magnification using a digital camera at 48 h after treatment with the vehicle/negative control (0.1% DMSO), 1, and
controls/standards (5-FU for HCT 116, Tamoxifen for MCF-7, Betulinic acid for K562 and 3T3-L1 cells). All the
cells treated with the vehicle (0.1% DMSO) showed confluent layer of aggressively proliferating cells for all four
cell lines, whereas treatment with 1 showed significant (p < 0.01) inhibitory effect on proliferation of HCT 116,
MCF-7, and K562 cancer cell lines with IC50 1.0 μM, 258.7 nM, and 46.7 nM, respectively. The pictures reveal
that the population of the treated cells reduced noticeably when compared to that of negative control. However, the
complex demonstrated less cytotoxicity toward normal cell line (3T3-L1), as the selective index (SI = ratio of the
IC50 obtained from the test on normal cell (3T3-L1) vs. the IC50 for cancer cell) was more than 10 except HCT
116 (SI is 8.1). Complex 1 showed a pronounced anti-proliferative effect than the respective standard reference
drugs.
showed very low cytotoxicity against normal cells (3T3-L1, IC50 for 1 = 37.0 μM and
2
= 136.0 μM). This indicates that complexes are selectively toxic against cancer cells.
The photomicrographs of cells are shown in figure 3.
Conclusion
Complexes 1 and 2 have been synthesized, and the molecular structure of 1 has been char-
acterized by X-ray crystallographic technique, representing a seven-coordinate geometry.
The complexes were tested against three cancerous and one non-cancerous cell lines. Com-
plex 1 showed cytotoxicity significantly better than 2 which may be due to geometrical and
substitutional differences. Finally, both the complexes have selective toxicity against cancer
cells and remained safe against normal cells.

Seven-coordinated organotin(IV)
3411
Supplementary material
The article contains supplementary file. Also, CCDC 983681 contains the supplementary
crystallographic data for 1. The data can be obtained free of charge via http://www.ccdc.
cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Center, 12
Union Road, Cambridge CB2 1EZ, UK; Fax: (+44) 1223-336-033; or E-mail: deposit@
ccdc.cam.ac.uk.
Acknowledgments
The authors would like to thank Ministry of Higher Education for the Fundamental
Research Grant Scheme (Project No.: FRGS/1/2012/SG01/UTAR/02/1), Universiti Tunku
Abdul Rahman and Universiti Sains Malaysia for financial support as well as technical
assistance and facilities. Dr Muhammad Adnan Iqbal is the recipient of USM-Postdoctoral
Fellowship in research.
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