Structure and applications of organotin complex based on trimethyltin cation and quinaldic acid

Article abstract of DOI:10.1002/aoc.4152

The reaction between aqueous solution of Me₃SnCl and acetonitrile solution of quinaldic acid (quinH) at room temperature affords a new organotin complex, [Me₃Sn(quinH)(quin)]?6H₂O (1). Complex 1 was structurally characterized using infrared, UV–visible and NMR spectra, thermogravimetric analysis and single-crystal X-ray analysis. The network structure of 1 is developed by a limitless number of discrete mononuclear molecules forming a one-dimensional chain via hydrogen bonds. Extensive hydrogen bonds and π–π stacking associate the one-dimensional chains creating a two-dimensional array. The two-dimensional arrays are additionally associated via hydrogen bonds through the water molecules and the methyl groups forming a three-dimensional network. The cytotoxic impact of 1 on the viability of MCF-7 cells was also examined using MTT assay, exhibiting great inhibiting action against MCF-7 cells. Furthermore, the catalytic degradation performance of 1 towards methylene blue dye in the presence of H₂O₂ as oxidant was investigated. The reaction is first order with respect to methylene blue dye.

Full text of DOI:10.1002/aoc.4152

Received: 31 July 2017
DOI: 10.1002/aoc.4152
Revised: 25 September 2017
Accepted: 26 September 2017
F U L L P A P E R
Structure and applications of organotin complex based on
trimethyltin cation and quinaldic acid
Mohamed M. El‐bendary1,2
| Safaa El‐din H. Etaiw2
1 Chemistry Department, Faculty of
Science, University of Jeddah, Jeddah,
Saudi Arabia
The reaction between aqueous solution of Me3SnCl and acetonitrile solution of
quinaldic acid (quinH) at room temperature affords a new organotin complex,
[Me3Sn(quinH)(quin)]⋅6H2O (1). Complex 1 was structurally characterized
using infrared, UV–visible and NMR spectra, thermogravimetric analysis and
single‐crystal X‐ray analysis. The network structure of 1 is developed by a lim-
itless number of discrete mononuclear molecules forming a one‐dimensional
chain via hydrogen bonds. Extensive hydrogen bonds and π–π stacking associ-
ate the one‐dimensional chains creating a two‐dimensional array. The two‐
dimensional arrays are additionally associated via hydrogen bonds through
the water molecules and the methyl groups forming a three‐dimensional
network. The cytotoxic impact of 1 on the viability of MCF‐7 cells was also
examined using MTT assay, exhibiting great inhibiting action against MCF‐7
cells. Furthermore, the catalytic degradation performance of 1 towards methy-
lene blue dye in the presence of H2O2 as oxidant was investigated. The reaction
is first order with respect to methylene blue dye.
2 Chemistry Department, Faculty of
Science, Tanta University, Tanta, Egypt
Correspondence
Mohamed M. El‐bendary, Chemistry
Department, Faculty of Science,
University of Jeddah, Jeddah, Saudi
Arabia.
Email: elbendary1983@yahoo.com;
mmesmaeel@uj.edu.sa;
mohamed.ismail@science.tanta.edu.eg
KEYWORDS
catalytic activity, in vitro cytotoxicity, organotin complex, quinaldic acid, spectra
1 | INTRODUCTION
exist as dinuclear[16] one‐dimensional zigzag chains[17]
and cyclic structures.[18] Numerous organotin(IV)
Organotin complexes have attracted much consideration
attributable to their properties, structural chemistry and
potential applications in numerous scientific areas.[1,2]
Among the many potential applications are in gas
storage,[3,4] as cytotoxic agents[5] and in chemical cataly-
sis,[6,7] as well as their industrial and agricultural applica-
tions.[8,9] One of the applications of organotin compounds
is their use as anticancer agents.[10,11] The pharmaceutical
properties of organotin carboxylates have been investi-
gated for their anti‐tumour activity.[12,13] In general, the
biocidal activity of organotin complexes is greatly
influenced by the structure of the molecule and the coor-
dination number of the tin atoms.[14,15] Organotin(IV)
dicarboxylates have been examined in extensive detail,
and in general the reported organotin(IV) dicarboxylates
complexes have been found to have anticancer activity
in a variety of tumour cells; however, triorganotin(IV)
compounds show a bigger cluster of anticancer action
than their di‐ and mono‐organotin(IV) analogues due to
their ability to bind proteins.[19] Additionally, organotin
carboxylates have an extensive variety of potential
biological activities[20–22] and cytotoxicities.[23,24] The high
activities of carboxylates with respect to their parent
organotin(IV) precursors and the free carboxylic acid
ligands give the impression of being an added substance
(not a synergistic) effect of the metal ions and the carbox-
ylate groups. Biological activity is by and large connected
to the nature of the ligand[25,26] which encourages the
transportation of the complexes over the cell membrane.
It has been realized that the rigidity of a molecule not only
Appl Organometal Chem. 2017;e4152.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4152

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EL‐BENDARY AND ETAIW
has a direct influence on its structure, but also affects the
properties of the complex,[27,28] for example the viscosity,
solubility, fluorescence activity, electrical characteristics,
chemical reactivity, biological activity and so on.[29,30]
For organotin carboxylates, ligands can change the rigid-
ity and regulate the structures and properties of the
complexes.[31,32] Also, the organotin(IV) carboxylates
have been used as catalysts in the synthesis of polyesters
and polyurethanes,[33] in dye degradation[34] and in
esterification and transesterification.[35]
Recently, our work has concentrated on triorganotin(IV)
complexes of nitrogen‐containing ligands in order to
examine and analyse their anti‐tumour action against
human breast cancer cell lines and their catalytic
activities.[12,13,19,23,34] Here, we report the structure and
spectral characteristics of the organotin complex
[Me3Sn(quinH)(quin)]⋅6H2O (1), which was synthesized
from H2O–CH3CN solution containing Me3SnCl and
quinaldic acid (quinH), with a study of the in vitro anti‐
tumour activity against human breast cancer cell line
MCF‐7. Furthermore, the catalytic degradation perfor-
mance of organotin complex 1 towards methylene blue
(MB) dye in the presence of H2O2 was investigated. MB
was chosen as a model compound of an organic pollutant.
The utilization of such complexes as heterogeneous
catalytic systems should eliminate the need for use of
soluble catalytic substances.
Electronic absorption spectra were recorded with a
Shimadzu (UV‐3101 PC) spectrometer. NMR spectra were
recorded using a Bruker Avance III 400 (9.4 T,
1
400.13 MHz for H) spectrometer with a 5 mm BBFO
probe at 298 K. Chemical shifts were measured relative
to internal solvent (DMSO‐d6 (2.50 ppm) for 1H). Topspin
3.2 software was used. Thermogravimetric measurements
(25–800 °C) were recorded with a Shimadzu DTG‐50
thermogravimetric analyser at a heating rate of 10 °C
min−1 and nitrogen flow rate of 10 ml min−1. Fluores-
cence spectra of solid frameworks were measured with a
PerkinElmer (LS 50B) spectrometer.
2.2 | Synthesis of complex 1
At room temperature (25 °C) a solution of Me3SnCl
(99.6 mg, 0.5 mmol) in 30 ml of H2O–CH3CN was added
to 173.17 mg (1 mmol) of quinH in 20 ml of CH3CN,
and the mixture was gently stirred for 30 min. The
obtained solution was slowly evaporated at room temper-
ature. Then, the product formed as colourless prismatic
crystals was filtered off, washed with a small amount of
cooled water and acetonitrile and then dried overnight.
About 160.52 mg (52% yield) of colourless prismatic
crystals were obtained. The organotin complex 1 is stable
to light and air and insoluble in water but it is freely
soluble in organic solvents. Elemental analysis for 1
(C23H34N2O10Sn): calcd (%): C, 44.76; H, 5.55; N, 4.54.
Found (%): C, 44.54; H, 5.65; N, 4.46. IR (KBr pellet,
cm−1): 3555–3255br, 3115w, 3083 m, 2553w, 1655s,
1631s, 1578s, 1555s, 1225w, 1464s, 1426–1338s, 1294
m, 780 s, 682 m, 624w, 594 s, 488 m. 1H NMR (400
MHz, DMSO‐d6, δ, ppm; s = singlet, b = broad, m = com-
plex pattern): 8.44–7.65 (m, 6H, quin moiety), 3.466
(b, 2H, H2O), 0.488 (s, 9H, (Me)3Sn, 2J(1H–117Sn) = 34.0 Hz
and 2J(1H–119Sn) = 35.0 Hz). 13C NMR (400 MHz,
DMSO‐d6, δ, ppm): 166.26 (s, 1C, COOH), 119.80,
136.02, 145.52, 126.75–129.08 (s, 5C, quin moiety) (vide
infra), 0.50 (s, 9C, (Me)3Sn, J = 604 Hz).
2 | EXPERIMENTAL
2.1 | Materials and instrumentation
All chemicals used were purchased from Merck or Sigma‐
Aldrich, and used without further purification. MB dye
was obtained from Sigma‐Aldrich (Scheme 1). Organic sol-
vents used included acetonitrile and dimethylformamide
(DMF) were spectroscopically pure from BDH. Hydrogen
peroxide (H2O2; 30% w/v, Merck) was used. The initial
concentration of H2O2 was determined iodometrically
using standard Na2S2O3. Deionized water collected from
all‐glass equipment was usually used in all preparations.
Elemental analyses (C, H and N) were performed with a
PerkinElmer 2400 automatic elemental analyser. Infrared
(IR) spectra (400–4000 cm−1) as KBr discs were recorded
2.3 | Single‐crystal structure
determination
Crystal structure determinations were performed using a
Kappa CCd Enraf Nonius FR 90 four‐circle goniometer
with graphite monochromatic Mo Kα radiation
with
a Jasco FT‐IR type 4100 spectrophotometer.
(λ = 0.71073 Å) at 25
2 °C. This type of goniometer
overcomes the disadvantages of the conventional four‐
circle diffractometer which screens the incident and
diffracted X‐rays at high Bragg angles and forms a
shadow zone. The structure of 1 was resolved using
direct methods and all of the non‐hydrogen atoms were
located from the initial solution or from subsequent
SCHEME 1 Structure of MB dye

EL‐BENDARY AND ETAIW
3 of 12
electron density difference maps during the initial stages
of the refinement. After locating all of the non‐hydrogen
atoms in each structure, the models were refined against
F2, first using isotropic and finally using anisotropic
thermal displacement parameters. For structure visuali-
zations, either CERIUS2 V4.0 or Mercury 3.8 software
was applied. Structure solution, refinement and data
output were completed using SHELX‐97 and SIR92
programs.[36]
line were obtained from the American Type Culture
Collection (Manassas, VA). Cells were cultured in RPMI
1640 medium supplemented with 10% foetal bovine
serum under a humidified atmosphere of 5% CO2 at 37 °C.
Complex 1 was initially dissolved in dimethylsulfoxide
(DMSO) and then diluted to the desired concentration
by adding cell culture medium. Samples (100 μl) of 1 with
various concentrations were added to the wells of 96‐well
plates. Cells were detached with trypsin and EDTA and
seeded in each well with 5 × 105 cells per well. After
incubation for 48 h, MTT solution (20 μl, 4 mg ml−1) of
phosphate buffer saline (8 g NaCl, 0.2 g KCl, 1.44 g
Na2HPO4 and 0.24 g KH2PO4 per litre) was added into
each well. The cells were further incubated for 4 h and a
purple formazan precipitate was formed, which was
separated by centrifugation. DMSO (100 μl) was added
to each well to dissolve the precipitate. The optical density
of the solution was determined using a plate reader
(Tecan) at 540 nm. The inhibition ratio was calculated
on the basis of the optical densities obtained from three
replicate tests. The 50% inhibition concentration (IC50)
was determined by curve fitting.
2.4 | Catalytic activity measurements
The catalytic activity of the prepared organotin complex 1
was evaluated for the degradation of MB dye in the
presence of H2O2. In a typical process, 25 mg of 1 and
30% H2O2 (0.01 M) were added into 50 ml of MB aqueous
solution, and magnetically stirred at room temperature
(25 °C) to ensure the degradation of MB dye. Then, 5 ml
of transparent sample solution was removed from the
reaction vessel and analysed using a UV–visible spectrom-
eter. The decolorization was calculated using the
following equation:
A0−At
3 | RESULTS AND DISCUSSION
3.1 | Crystal structure of 1
Decolorization ð%Þ ¼
×100
A0
where A0 and At represent the initial and final absorbance
of MB dye solution, respectively.
Quinaldic acid is a flexible multi‐dentate N‐ and O‐donor
ligand which can be viewed as an important variable for
the advancement of the metal–organic engineering of 1.
Organotin complex 1 was obtained under ambient condi-
tions by reacting Me3SnCl with quinH in H2O–CH3CN
solution. The asymmetric unit of 1 is outlined in
Figure 1 and crystal data are presented in Table 1. The
2.5 | In Vitro anti‐tumour activity
The cytotoxic activity of complex 1 was determined using
3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bro-
mide (MTT) assay. Human cancer cells of the MCF‐7 cell
FIGURE 1 Asymmetric unit of 1 showing the atom labelling scheme. Thermal ellipsoids are shown at 50% probability

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EL‐BENDARY AND ETAIW
TABLE 1 Crystal data and structure refinement parameters of 1
TABLE 2 Hydrogen bond lengths (Å) and bond angles (°) of 1
D─H…A
d(D─H) d(H…A) d(D…A) ∠(DHA)
Empirical formula
C23H34N2O10Sn
617.232
298
Formula weight (g mol−1
)
O10─H10B…O6
0.961
1.226
0.960
0.960
0.960
0.960
1.226
0.961
0.960
0.961
1.962
2.434
2.455
2.470
2.500
2.530
2.582
2.679
2.804
2.865
2.943
3.072
3.088
2.909
3.168
3.363
3.203
3.337
3.259
3.663
3.494
3.544
3.735
3.733
3.809
3.423
174.10
115.98
157.75
133.08
150.15
132.78
144.85
142.83
134.55
150.98
140.50
134.59
102.19
C14─O3…H9B
C29─H29…O10
O2─H2…O9
Temperature (K)
Crystal system
Space group
a (Å)
Monoclinic
P21/c
C20─H20…O5
C26─H26…O6
C14─O3…H9A
O19─H19…O5
C27─H27…O10
C19─H19…O23
7.7612(2)
25.4684(5)
13.7383(3)
90
b (Å)
c (Å)
α (°)
β (°)
95.9622(10)
90
γ (°)
V (Å3)
C31─H31A…O10 0.961
2700.90(11)
4
C31─H31C…O9
C19─H19…O10
0.961
0.961
Z
ρcalcd (g cm–3
μ (MoKα) (m m−1
)
1.515
)
1.00
θ range for data collection (°)
Index range of hkl
2–30.05
planar conformation with C─Sn─C angle of 120.03° while
O(2) and O(7) atoms are perpendicular to the plane
defined by the methyl groups (Table S1). The Sn─O(2)
and Sn─O(7) distances are equal to 2.385 and 2.254 Å,
respectively, while the Sn─C distances are in the range
2.107–2.124 Å (Table S1), which are in accordance
with the same bond distances reported for other tin
complexes.[37–39] Complex 1 creates an extended one‐
dimensional chain structure via hydrogen bonds between
water molecules and quinH/quin (1.962–3.088 Å), as the
Me3Sn cation acts as bridge between quinH and quin
ligands (Figure 2; Table 2). The Sn─O distances are
quite close to those in related organotin carboxylates
(Table S1).[40] The angle of the axial oxygen atoms,
O(2)─Sn(1)─O(7), deviates from linearity, being
171.90(10)°. The separation distance between two adja-
cent chains is 6.81 Å. Furthermore, a detailed structural
analyses of complex 1 revealed that the one‐dimensional
chain is bonded to another chain by hydrogen bonds
down the projection of c‐axis forming two‐dimensional
sheets via hydrogen bonds with six water molecules
(1.962–3.088 Å) (Table 2; Figure 3). Then again, extensive
hydrogen bonds and face‐to‐face π–π stacking
(3.502–3.784 Å) (Table S2) connect the two‐dimensional
arrays into a three‐dimensional interwoven network
along the a‐axis (Figure 4). Thus, the water molecules
play a corresponding role by means of hydrogen bonds
for stabilizing the three‐dimensional network structure
of 1 in addition to the π–π stacking. Moreover, the shape
of the structure of the main building blocks down the pro-
jection of the c‐axis looks like a fishbone structure with
open channels, with Sn─Sn distance equal to 6.871 Å
(Figure 5).
−10 ≤ h ≤ 10, 0 ≤ k
≤ 35, −19 ≤ l ≤ 19
Goodness‐of‐fit on F2
F(000)
1.262
1264
Rint
0.073
R indices[I > 3σ(I)] R1/wR2
R indices(all data)
Collected reflections
Independent reflections
Reflection with I > 2σ(I)
0.042/0.097
0.140/0.113
7119
8162
2580
Parameters refined
325
–3
Δρmax, Δρmin (e
)
1.33/−1.73
bond distances and angles are presented in Table S1 and
those of hydrogen bonds in Table 2. The unit cell is
represented by the formula [Me3Sn(quinH)(quin)]⋅6H2O
showing Z = 4 and atom size occupancy of 1. The basic
building block of 1 contains one Me3Sn cation, one
quinH, one deprotonated quinH (quin) and six H2O
molecules (Figure 1). The charge neutrality is accom-
plished by one deprotonated carboxylate group of quinH
producing quin ligand. An X‐ray investigation confirms
the assignment of 1:2 stoichiometry for the Me3Sn:
quinaldic ligand. The tin atom is coordinatively bonded
to three methyl groups and two oxygen atoms (O(2),
O(7)) from quinH and quin ligands, respectively. The
methyl groups occupy equatorial trigonal plane while
O(2) and O(7) atoms are in axial positions via coordinate
bonds to form a trigonal bipyramidal structure around
the tin site. The methyl groups are arranged in a trigonal

EL‐BENDARY AND ETAIW
5 of 12
FIGURE 2 One‐dimensional chain of 1 formed via hydrogen bonds along the a‐axis
FIGURE 3 Visualization of the two‐dimensional network structure of 1 down the projection of c‐axis
FIGURE 4 Visualization of the three‐dimensional network structure of 1 showing π–π stacking along a‐axis
bands at 3070 cm−1 (νCHarom), 2547 cm−1 (νOH) and
752 cm−1 (γCH) correspond to the quinH ligand (Table 3;
Figure S1). These bands slightly change their positions
upon complexation. The medium band at 2553 cm−1 in
3.2 | IR spectra
The IR spectra display the vibration frequencies of quinH
ligand and complex 1 in the region 400–4000 cm−1. The

6 of 12
EL‐BENDARY AND ETAIW
FIGURE 5 View of three‐dimensional network of 1 along b‐axis showing the fishbone structure with open channels
TABLE 3 Band positions (cm−1) of various vibrational modes of 1a
νasy(COO)
ν(CH)
ν(CH)
ν(C═O) ν(C═N) νsy(COO)
δCH of
γCH of
Compound ν(H2O)
νOH
(arom) (aliph) ν(C─O) ν(C═C) δ(COO)
ligand δ(H2O) ligand ν(Sn─O) ν(Sn─N)
quinH
—
2547 m 3070w
3004w
—
1703s
1269m
1588s
1575s
1385s
701 s
1458s
1464s
—
752 s
—
—
1
3255–3555br 2553w
3115w
3083 m
2921 m 1655s
1578s
1631s
1338–1426s
682m
1631s 780 s
624w
594 s
488w
1294m 1555s
br = broad; s = strong; m = medium; w = weak.
the IR spectrum of organotin complex 1 is attributed to
193–281 cm−1 which indicates the monodentate nature
of the carboxylate group and the ligand and is ascribed
to the reduction of electron density on its oxygen atoms
upon coordination to the tin(IV) moiety. The stannoxane
structure was supported from its characteristic absorption
band of medium intensity observed at 682 cm−1 assign-
able to O─Sn─O functionality.[43] Also, the strong absorp-
tion at 594 cm−1 in the IR spectrum of 1 corresponds to
the Sn─O stretching mode[44] which is absent in the
spectrum of the ligand (quinH). All these values
are consistent with those determined for a number of
organotin(IV) derivatives.[45,46] The pyridine ring breath-
ing mode vibrations of the free ligand at 1588 and
1025 cm−1 exhibit significant shifts to lower frequencies
in the spectrum of 1. The shifts upon complexation may
ν
OH of the quinH ligand confirming its subsequent coordi-
nation to tin as Sn─OH bond.[41] The sharp band at
1703 cm−1 in the spectrum of ligand quinH corresponds
to νC═O which exhibits a shift to lower wavenumber at
1655 cm−1 in the IR spectrum of 1, due to the participa-
tion of carboxylate group in complexation. The νasy(COO)
,
νsy(COO) and νC─O bands due to the carboxylate group
appear at 1631, 1338–1426 and 1294 cm−1, respectively,
supporting coordination of the other carboxylic group to
tin atom in the carboxylate form representing the counter
ion (Table 3). The difference between these two types of
vibrations (Δν) demonstrates the mode of coordination
of the ligands to the tin centre.[42] The decrease in
the Δν values of the COO− moiety was found to be

EL‐BENDARY AND ETAIW
7 of 12
TABLE 4 Thermogravimetric data for 1
suggest that the bond formation of organotin with oxygen
atoms of the carboxylate groups increases the dipolar con-
tribution of the carboxylate group of quinH ligand. The
broad peak at 3255–3555 cm−1 indicates the presence of
the water molecules in 1 in addition to the strong band
at 1619 cm−1 corresponding to δH2O (this band overlapped
with νasy(COO)) (Table 3).
Temperature Mass loss (%):
Step
range (°C)
calcd (found)
Assignment
1st
80–125
17.4 (17.3)
−6H2O
2nd
200–300
7.2 (7.4)
55.9 (56.2)
18.9 (18.5)
−3(Me)
3rd + 4th 300–500
−(quinH + quin)
Sn
Residue Over 500
3.3 | NMR spectra
1
The H NMR spectrum of 1 shows multiplet peaks at
corresponding to the decomposition of quinH and quin
ligands (55.9%). The inorganic residue left after heating
at 500 °C is constituted of tin metal which is stable up to
1000 °C (Table 4). The TGA results of 1 demonstrate
the presence of the trimethyltin cation in addition
to the quinH and quin ligands as main units of its
structure.
7.65–8.44 ppm corresponding to the aromatic protons of
the quinaldic moiety, which were shifted downfield
because of the donation of the lone pair of electrons of
the oxygen atoms of the carboxylate group to the tin atom
(Figure S2). The methyl protons appended to the tin atom
in 1 displayed a well‐defined singlet at 0.488 ppm accom-
panied with two Sn(IV) satellites (2J(1H–117Sn) = 34.0 Hz
and 2J(1H–119Sn) = 35.0 Hz). The presence of two satellite
peaks is a good indication for the presence of Me3Sn
connecting units in the structure of 1. The broad signal
3.5 | Electronic absorption and emission
spectra
1
at 3.466 ppm in the H NMR spectrum of 1 is attributed
to water molecules.
The electronic spectra of quinH and 1 were recorded in
DMF (Table 5). The UV spectrum of the ligand reveals
three bands at 215, 250 and 320 nm. The first two
The 13C NMR spectrum of 1 shows a significant
downfield shift of all carbon resonances compared with
those of the free quinaH ligand because of electron
density transfer from the ligand to the tin atom. The
13C NMR spectrum of 1 displays three singlet peaks at
119.80, 136.02 and 145.52 ppm and a multiplet peak at
126.75–129.08 ppm due to the quinaldic ring. The
13C NMR spectrum of 1 exhibits, additionally, a peak at
166.26 ppm due to the carbon of the carboxylic group.
The Me3Sn unit gives rise to a triplet peak at 0.50 ppm with
its characteristic satellite peaks with 1J(119/117Sn–13C)
coupling constant of about 604 Hz. Thus, the NMR
spectral data of 1 are in agreement with its structure
(Figure S3).
1
1
1
1
high‐energy bands are due to La ← A and Lb ← A
transitions. The third band at 320 nm is due to π–π*
transitions of the carboxylate group. Upon complexation,
these bands are slightly shifted to longer or shorter wave-
lengths where they are observed at 210, 275 and 315 nm in
the spectrum of complex 1.[47] The solid‐state emission
data of 1 are summarized in Table 5 and the spectrum
shown in Figure 6. It is worth mentioning that quinH in
DMF solution or in the solid state does not show any
emission bands on excitation at 340 nm. This finding is
expected, as pyridine, quinoline and their derivatives
are, generally, not luminescent materials.[48] On the other
hand, the emission spectrum of 1 reveals structured
high‐energy and low‐energy bands in the visible region
at 360–430 nm upon excitation at 340 nm (Figure 6;
Table 5). The emission band centred at 368 nm
corresponds to the lowest π–π* state in the ligand. On
3.4 | Thermogravimetric analysis (TGA)
TGA is a very useful method for studying the thermal
decompositions of solid substances, including organotin
complex 1. The stages of decomposition, temperature
ranges, decomposition products as well as the weight loss
percentages of 1 are given in Table 4. A representative
TGA curve for 1 is presented in Figure S4. The TGA curve
of 1 shows four stages of decomposition. The first
step occurs at 80–125 °C with mass loss of 17.3% (calcd
17.4%) which corresponds to elimination of six water
molecules. The second step at 200–300 °C with mass loss
of 7.4% (calcd 7.2%) corresponds to the release of the three
methyl groups of trimethyltin cation. The last two
steps appear at 300–420 and 420–500 °C, respectively,
TABLE 5 Electronic absorption and emission spectral data of 1
λabs (nm)
λabs (nm)
Assignment
λem (nm)
quinH Assignment
1
1
Assignment
1
1
215
1La ← A
210 1La ← A
368 Lowest π–π*
state
1
1
250
320
1Lb ← A
275 1Lb ← A
430 MLCTa
530 MLCTa
π–π*
315 π–π*
aMetal‐to‐ligand charge transfer.

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EL‐BENDARY AND ETAIW
visible region of the spectrum of 1 is a good indication
for its application as a heterogeneous catalyst. MB dye
concentrations were estimated from the absorbance at
λmax = 665 nm. A simple experiment was conducted to
investigate the degradation of MB dye in the presence of
H2O2 without using any catalyst, where the degradation
efficiency of MB was found to be 11.14% after 300 min
(Figure S5). In this case no significant changes in the
absorption spectrum were observed even for reaction
times up to 24 h, indicating that H2O2 alone is unable to
degrade MB dye. By contrast, the absorption peaks of
MB dye decreased clearly with reaction time under the
same conditions in the presence of the catalyst 1
(Figure 8). Degradation efficiency of MB dye is 82.6% after
190 min and the complete degradation occurred after
300 min. The decrease in absorption intensity of dye
solution can be related to the degradation efficiency
(Rcolor; Figure 7), which was evaluated using the following
relationship:
FIGURE 6 Emission spectrum of 1 (λex = 340 nm)
the other hand, the emission band at 430 nm may be
attributed to metal‐to‐ligand charge transfer.[49]
Aλ0 max−Aλt max
Rcolor ð%Þ ¼
×100
Aλ0 max
3.6 | Catalytic activity
where A0 represents the initial absorbance of dye solution
and At represents the absorbance of dye solution at time t.
Chemical industry wastewaters contain a variety of
organic and inorganic compounds. Organic azo
compounds from the textile industry are considered the
most polluting of all within industrial sectors. The
presence of very small amounts of synthetic dyes in water
can cause significant damage to the environment. So,
organotin complex 1 was used as a catalyst for the degra-
dation of MB as a test pollutant at room temperature
(Figure 7). The presence of electronic transitions in the
3.7 | Kinetics of catalytic degradation
reaction
The catalytic degradation of MB was also subjected to
kinetic analysis. The kinetic study was carried out under
pseudo‐first‐order conditions with respect to MB dye,
where the initial concentration of H2O2, [H2O2]0, was at
FIGURE 8 Absorption spectra of MB dye (5 × 10−5 M) at time
intervals in presence of 0.1 M H2O2 and 0.025 mmol of catalyst 1
showing the degradation profile
FIGURE 7 Results of catalytic degradation of MB dye as a
function of time in absence and presence of catalyst 1

EL‐BENDARY AND ETAIW
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FIGURE 9 Kinetics of degradation of MB (5 × 10−5 M) in
presence of 0.1 M H2O2 and 0.025 mmol of catalyst 1
FIGURE 10 IR spectra of MB solution before (1) and after (2)
degradation
least 10‐fold excess over [MB]0. The observed rate con-
stant, kobs, was determined from the slope of a first‐order
plot as shown in Figure 9, as follows:
between side aromatic ring and nitrogen atom) stretching
vibrations at 1335 cm−1 and N─CH3 stretching vibrations
at 1279 and 1184 cm .
−1 [50] After treatment using catalyst 1
and H2O2, the disappearance of these characteristic bands
indicated complete degradation of MB molecules by
breaking of central and side aromatic rings as well as
demethylation. Meanwhile, three new intense peaks at
1450, 1380 and 1224 cm−1 appeared, which might be
A0
lnAt ¼ lnA0−kobs
t
or ln ¼ kobs
t
(1)
At
where At is the absorbance at time t and A0 is the absor-
bance at t = 0. The plot indicates a pseudo‐first‐ order rate
due to the stretching vibrations of COO−, NO3 and
−
with respect to MB dye concentration (kobs = 0.0048 min−1
;
SO42−, respectively,[50] suggesting that CO2 is the main
final product in addition to some acids. The complete
oxidative degradation of the dye led to the conversion of
organic carbon into gaseous CO2 which was trapped by
Ca(OH)2 solution and the precipitated CaCO3 was deter-
mined gravimetrically. The sulfate ions were determined
gravimetrically by precipitating them as BaSO4 using
BaCl2 solution.
Figure 9). The specific rate constant k was determined
from the relation k = kobs./[H2O2], the value of which is
equal to 0.048 l mol−1 min−1
.
3.8 | Identification of degradation
products
The decolorization of an organic dye by reaction of an
oxidant and catalyst with the dye can convert the organic
carbon into CO2. The catalytic oxidation of MB is accom-
3.9 | In Vitro effects of 1 on MCF‐7 human
breast cancer cell line viability
2−
−
panied by release of CO2, SO4 and NO3
:
MB þ 36H2O2→10CO2 þ 3NaNO3 þ 3H2SO4 þ 25H2O
þ 8CH3COOH
The organotin complex 1 was investigated for its antipro-
liferative activity in vitro against MCF‐7 human breast
cancer cell line. The results of cytotoxic activity in vitro
are expressed as IC50, the concentration of compound that
inhibits proliferation of the tumour cells by 50% as
compared to control untreated cells. The cytotoxic effect
of compound 1 on the viability of MCF‐7 cells was
determined using MTT assay. The MCF‐7 cells were incu-
bated with 1 for 24 and 48 h at increasing concentration.
The dose–response curve of 1 is shown in Figure 11. The
results indicate that complex 1 is cytotoxic to MCF‐7
(2)
The products remaining in solution after complete MB
degradation using catalyst 1 and H2O2 were monitored
with IR spectra. Figure 10 shows the IR spectra before
and after degradation. Prior to degradation, MB exhibited
prominent bands of the characteristic C═N central
ring stretching vibrations at 1586 cm−1, C═C side ring
stretching vibrations at 1527 and 1427 cm−1, multiple
ring stretching vibrations at 1362 cm−1, CAr─N (bond

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EL‐BENDARY AND ETAIW
FIGURE 11 Dose–response curve for organotin complex 1
against MCF‐7 human breast cancer cell line, using various
concentrations of 1. Untreated cells were used as control. Each data
point is an average of three independent experiments and expressed
as mean SD
FIGURE 13 In vitro cytotoxicity of 1 against MCF10A, a non‐
tumorigenic breast epithelial cell line, using various concentrations
of test compound. Each data point is an average of three
independent experiments and expressed as mean SD
cells and inhibits the growth of cells in a dose‐ and time‐
dependent manner. Moreover, based on the comparison
of IC50 values, it was observed that MCF‐7 cells are more
sensitive to complex 1. Compound 1 showed an inhibition
of cell viability giving an IC50 value of 3.1 μg ml−1
(Figure 12). To examine if the active complex 1 has a
cytotoxic effect, it was tested against non‐tumorigenic cell
line derived from breast tissue (MCF10A) versus MCF‐7
cell line as a positive cancer cell line control (Figure 13).
These results indicated that compound 1 showed no
cytotoxic effects on normal, non‐tumorigenic MCF10A
cell line, compared to MCF‐7 breast cancer cells. The
results shown in Figures 12 and 13 further confirmed
the decreased cell viability of MCF‐7 breast cancer cells
caused by 1 compared to control group and also indicated
its lower toxicity against normal cells.
4 | CONCLUSIONS
The presented procedure for synthesis of organotin
complex 1 at room temperature, in spite of being surpris-
ingly simple, affords precipitates which consist exclusively
of one discrete species and never of any mixture of differ-
ent assemblies. The outcome of the present study is that
the organotin complex 1, constituted of an infinite
number of discrete mononuclear molecules, creates a
three‐dimensional network structure through extensive
hydrogen bonding and π–π stacking. The organotin
complex 1 exhibited a decrease in cell viability of MCF‐7
human breast cancer cells. The results also indicated that
compound 1 showed no cytotoxic effects on normal, non‐
tumorigenic MCF10A cell line, compared to MCF‐7 breast
cancer cells. Complex 1 needs more investigations to
advance to pre‐clinical development and to determine
the exact mechanism of its drug action. The organotin
complex 1 is a luminescent material which can be used
in applications involving molecular sensing systems.
Complex 1 can be also considered as an efficient heteroge-
neous catalyst for elimination of MB in aqueous solution
FIGURE 12 In vitro cytotoxicity of 1 against MCF‐7 human
breast cancer cell line, using various concentrations of 1. Cell
viability was expressed as the absorbance values normalized to the
control group after subtracting the blank absorbance from samples
and control. Each data point is an average of three independent
experiments and expressed as mean SD

EL‐BENDARY AND ETAIW
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Mohamed M. El‐bendary http://orcid.org/0000-0002-8465-
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Safaa El‐din H. Etaiw
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How to cite this article: El‐bendary MM, Etaiw
SEH. Structure and applications of organotin
complex based on trimethyltin cation and quinaldic
acid. Appl Organometal Chem. 2017;e4152. https://
doi.org/10.1002/aoc.4152
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