Synthesis, crystal structure and anticancer activity of the dibutyltin(IV)oxide complexes containing substituted salicylaldehyde-o-aminophenol Schiff base with appended donor functionality

Article abstract of DOI:10.1080/24701556.2019.1571513

Schiff base butyltin complexes C1 ～ C3 have been synthesized via the reaction of dibutyltin oxide with the substituted salicylaldehyde-o-aminophenol Schiff base ligands (L1 ～ L3), respectively. The complexes have been characterized by elemental analysis,

Full text of DOI:10.1080/24701556.2019.1571513

Inorganic and Nano-Metal Chemistry
ISSN: 2470-1556 (Print) 2470-1564 (Online) Journal homepage: https://www.tandfonline.com/loi/lsrt21
Synthesis, crystal structure and anticancer activity
of the dibutyltin(IV)oxide complexes containing
substituted salicylaldehyde-o-aminophenol Schiff
base with appended donor functionality
Zhi-Jian Zhang, Hui-Ting Zeng, Yang Liu, Dai-Zhi Kuang, Fu-Xing Zhang, Yu-
Xing Tan & Wu-Jiu Jiang
To cite this article: Zhi-Jian Zhang, Hui-Ting Zeng, Yang Liu, Dai-Zhi Kuang, Fu-Xing Zhang,
Yu-Xing Tan & Wu-Jiu Jiang (2019): Synthesis, crystal structure and anticancer activity of
the dibutyltin(IV)oxide complexes containing substituted salicylaldehyde-o-aminophenol
Schiff base with appended donor functionality, Inorganic and Nano-Metal Chemistry, DOI:
10.1080/24701556.2019.1571513
To link to this article: https://doi.org/10.1080/24701556.2019.1571513
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INORGANIC AND NANO-METAL CHEMISTRY
https://doi.org/10.1080/24701556.2019.1571513
Synthesis, crystal structure and anticancer activity of the dibutyltin(IV)oxide
complexes containing substituted salicylaldehyde-o-aminophenol Schiff base
with appended donor functionality
Zhi-Jian Zhanga, Hui-Ting Zengb, Yang Liua, Dai-Zhi Kuanga, Fu-Xing Zhanga, Yu-Xing Tana, and Wu-Jiu Jianga
aKey Laboratory of Functional Metal-Organic Compounds of Hunan Province Key Laboratory of Functional Organometallic Materials,
b
University of Hunan Province, College of Chemistry and Materials Science, Hengyang Normal University, Hengyang, Hunan, China; Hunan
Polytechnic of Environment and Biology, School of Medicine Technology, Hengyang, Hunan, China
ABSTRACT
ARTICLE HISTORY
Received 10 December 2017
Accepted 2 January 2019
Schiff base butyltin complexes C1 ꢀ C3 have been synthesized via the reaction of dibutyltin oxide
with the substituted salicylaldehyde-o-aminophenol Schiff base ligands (L1 ꢀ L3), respectively.
1
The complexes have been characterized by elemental analysis, IR, UV-Vis, H NMR, 13C NMR spec-
KEYWORDS
tra and the crystal structures have been determined by X-ray diffraction. The anticancer activity of
the Schiff base ligands L1 ꢀ L3 and complexes C1 ꢀ C3 against five species of cancer cells which
are MCF7, Colo205, NCI-H460, Hela and HepG2 were tested respectively, the tests showed that C3
exhibited significant anticancer activity for the cancer cells in comparison with other complexes.
The interaction between C3 and calf thymus DNA were studied by fluorescence, UV-Vis and
Viscosity experiment, the results show that the interaction of C3 with calf thymus DNA was
intercalation.
organotin; Schiff base;
synthesis; crystal structure;
anticancer activity
Introduction
was tested. And the interaction between the complex with
the strongest anticancer activity and calf thymus DNA were
studied by fluorescence, utilization of UV-Vis and Viscosity
experiment. It provide theoretical basis for the application of
this substance to anticancer drugs.
Since the last century, a large number of organotin Schiff
base complexes have been reported.[1–4] Many organotin
Schiff base complexes have attracted wide attention because
of their good anticancer,[5,6] bactericidal,[7,8] antifungal
activities and so on.[9–11] The salicylaldehyde Schiff bases
possess O, N multiple sites, so it is a kind of meaningful
biological ligand. Their complexes have a rich variety of
coordination modes so that it makes the property diversi-
fied. To fully understand the mechanism and explore the
potential of organotin Schiff base complexes as anticancer
drugs, more experimental data and studies are necessary.
However, based on our previous work,[12–17] a series of the
salicylaldehyde-o-aminophenol Schiff base with appended
donor functionality and their organotin complexes have
been synthesized, the mechanism of fluorescence emission
of complexes was discussed, the anticancer activity and the
its interaction with DNA were tested. In order to explore
the structure-activity relationship of Schiff base organotin,
we further study the anticancer activity of salicylaldehyde-o-
aminophenol Schiff base organotin complexes in vitro, three
kinds of substituted salicylaldehyde-o-aminophenol and their
butyltin complexes were synthesized and characterized in
this paper (see Scheme 1). The inhibitory activity of the
complexes on cancer cells (MCF7, Colo205, NCI-H460, Hela
Experimental
Materials and measurements
All reagents and solvents were available from commercial
sources and used as received without further purification.
FT-IR spectrum was obtained for KBr pellets on Shimadzu
Prestige-21 spectrophotometer in the 4000–400 cmꢁ1 1H
.
and 13CNMR analysis was performed on a Bruker AVANCE
NMR spectrometer. Elemental analyses for C, H, and N
were determined on a PE-2400 (II) analyzer. Crystal struc-
ture was determined on a CCD area detector X-ray diffract-
ometer. Fluorescence spectra was obtained with a Hitachi
F-7000 spectrophotometer with quartz cuvette (path length ¼
1cm). UV-Vis absorption spectra was measured by UV-2550
spectrometer. Viscosity experiments were conducted on an
Ubbelodhe viscometer. Melting point measurement was exe-
cuted on an X-4 binocular micromelting point apparatus with
the temperature unadjusted.
Tris-HCl (0.01 molꢂLꢁ1) buffer solution was prepared by
and HepG2) and the human normal cell (HL7702) in vitro a certain amount of Tris dissolved in super pure water
CONTACT Yu-Xing Tan
tanyuxing@hynu.edu.cn Wu-Jiu Jiang
jwj_china@163.com
Key Laboratory of Functional Metal-Organic Compounds of Hunan
Province Key Laboratory of Functional Organometallic Materials, University of Hunan Province, College of Chemistry and Materials Science, Hengyang Normal
University, Hengyang, Hunan, 421008, China.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsrt.
ß 2019 Taylor & Francis Group, LLC

2
Z.-J. ZHANG ET AL.
Scheme 1. Synthesis of complexes.
before using, the pH of the solution was adjusted to 7.40 (KBr, cmꢁ1): 3445 (w), 3086 (w), 2945 (w), 1627 (s), 1519
1
with hydrochloric acid solution (0.1 molꢂLꢁ1). The purity of (s), 1395 (s), 1251 (s), 1032 (m), 797 (s). H NMR (CDCl3,
calf thymus DNA was determined by comparing the absorb- 400 MHz, d/ppm):12.41 (s, 1H), 8.61 (s, 1H), 7.33-7.40 (m,
ance at 260 and 280 nm (A260/A280 ¼ 1.8 ꢀ 1.9/1). The con- 2H), 6.90-7.05 (m, 4H), 5.56 (s, 1H), 2.33 (s, 3H).
5-BrC6H3(OH)C ¼ NC6H3(OH)-4-NO2
(L3):
Yield:
centration of calf thymus DNA was calculated by measuring
the absorbance at 260 nm (e260 ¼ 6600 Lꢂmolꢁ1ꢂcmꢁ1). The
reserve liquid was stored at 4 ꢃC. The ethidium bromide
solution was prepared by a certain amount of ethidium
bromide solid dissolved in Tris-HCl (0.01 molꢂLꢁ1) buf-
fer solution.
77.6%. m.p.: 300–301 ꢃC. Anal. Calc. for (C13H9BrN2O4): C
46.32, H 2.69, N 8.31%. Found: C 49.30, H 2.70, N 8.31%.
IR (KBr, cmꢁ1)： 3454 (w), 3077 (w), 1619 (s), 1512 (w),
1375 (s), 1288 (s), 1033 (m), 742 (m). 1H NMR (CDCl3,
400 MHz, d/ppm): 13.15 (s,1H), 11.43 (s, 1H), 9.14 (s, 1H),
8.14 (d, J ¼ 8.8 Hz, 1H), 8.13 (s, 1H), 8.00, (s, 1H), 7.62
(d, J ¼ 8.4 Hz, 1H), 7.17 (d, J ¼ 8.8 Hz, 1H), 7.00
(d, J ¼ 8.8 Hz, 1H).
Synthesis of ligands (L1 ꢀ L3)
According to literatures,[12] a mixture of substituted salicyal-
dehyde (10 mmol), absolute ethanol (20 mL) and substituted
o-aminophenol (10 mmol) were added to microwave reactor,
the reaction continued for about 30 min at 100 ꢃC. After
that, the solvent was removed by evaporation in vacuo and
the residual solution was filtered. It was recrystallized by
absolute ethanol.
Synthesis of complexes (C1 ꢀ C3)
A mixture of dibutyltin oxide (1 mmol), absolute methanol
(20 mL) and Schiff baseligands(L1, L2 or L3) (1 mmol) were
added to microwave reactor, respectively. The reaction con-
tinued for about 30 min at 120 ꢃC. After that, the solvent
3-MeOC6H3(OH)C ¼ NC6H4(OH) (L1): Yield: 84.6%. was removed by evaporation in vacuo and the residual solu-
m.p.: 197–198 ꢃC. Anal. Calc. for (C14H13NO3): C 69.12, H tion was filtered, and the solids were recrystallized by abso-
5.39, N 5.76%. Found: C 69.15, H 5.38, N 5.75%. IR (KBr, lute methanol.
cmꢁ1): 3500(w), 3047 (w), 2988 (w), 1627 (s), 1539 (m),
{[3-MeOC6H3(O)C ¼ NC6H4(O)]n-Bu2Sn}2 (C1): The
1508 (s), 1244(s), 1168 (s), 1029 (m), 740 (s). 1H NMR
product was red-brown crystal, Yield: 73.9%. m.p.:
138 ꢀ 140 ꢃC. Anal. Calc. (C22H29NO3Sn): C 55.73, H 6.16,
(CDCl3, 400 MHz,d/ppm): 12.51 (s,1H), 8.71 (s, 1H), 7.17-
N 2.95%. Found: C 55.75, H 6.15, N 2.94%. IR (KBr, cmꢁ1):
7.26 (m, 2H), 7.02-7.09 (m, 3H), 6.91-6.99 (m, 2H), 5.87 (s,
3060 (w), 3025 (w), 2953(m), 2920(m), 1602 (s), 1584 (s),
1H), 3.94 (s, 3H).
5-ClC6H3(OH)C ¼ NC6H3(OH)-4-Me (L2): Yield: 75.9%. 1541(m), 1480 (s), 1225 (s), 1149 (s), 745 (s), 565 (m), 522
m.p.: 175–176 ꢃC. Anal. Calc. for (C14H12ClNO2)：C 64.25, (w), 469(w), 419 (w). 1H NMR(CDCl3, 400 MHz,d/ppm):
H 4.62, N 5.35%. Found: C 64.26, H 4.62, N 5.34%. IR 8.66, (s, 1H), 7.34 (d, J ¼ 7.9 Hz, 1H), 7.17 (t, J ¼ 7.6 Hz,

INORGANIC AND NANO-METAL CHEMISTRY
3
Table 1. Crystallographic data of the complexes.
Complex
Empirical formula
C1
C22H29NO3Sn
C2
C3
C54H80Cl2N2O8Sn4
C21H25BrN2O4Sn
Mr
474.15
296(2)
Monoclinic
P21/n
12.4970(4)
17.9750(6)
19.3207(6)
90
98.994(2)
90
4286.7(2)
8
1430.86
296(2)
568.03
296(2)
Temperature / K
Crystal system
Space group
a / Å
b / Å
c / Å
Triclinic
Monoclinic
P21/c
17.1353(9)
9.5197(5)
14.3022(7)
90
96.7560(10)
90
2316.8(2)
4
–
P1
11.3731(9)
11.7547(10)
12.4378(10)
100.5200(10)
100.5330(10)
107.6200(10)
1507.0(2)
1
ꢃ
ꢃ
a /
b /
c/
ꢃ
Volume / Å3
Z
Dc / Mg/m3
1.469
1.213
1936
1.577
1.776
716
1.629
2.855
1128
Absorption coefficient / mm-1
F(000)
Crystal size / mm
h range / (ꢃ)
Limiting indices
0.35 ꢄ 0.23 ꢄ 0.21
1.82 ꢀ 25.10
ꢁ14ꢅhꢅ14,
ꢁ21ꢅkꢅ21,
ꢁ22ꢅlꢅ23
23656 / 7628 [Rint¼ 0.0175]
99.9 %
0.21 ꢄ 0.19 ꢄ 0.18
2.77 ꢀ 25.10
ꢁ13ꢅhꢅ13,
ꢁ14ꢅkꢅ14,
ꢁ14ꢅlꢅ14
0.23 ꢄ 0.21 ꢄ 0.18
2.45 ꢀ 25.10
ꢁ20ꢅhꢅ20,
ꢁ11ꢅkꢅ5,
ꢁ17ꢅlꢅ17
Reflections collected / unique
Completeness
15586 / 5338 [Rint ¼ 0.0231]
99.5 %
12448 / 4132 [Rint ¼ 0.0187]
100.0 %
Max. and min. transmission
Data / restraints / parameters
Goodness-of-fit on F2
0.7848 and 0.6762
7628 / 14 / 564
1.031
0.7405 and 0.7067
5338 / 69 / 394
1.079
0.6275 and 0.5597
4132 / 20 / 281
1.025
Final R indices [I > 2d(I)]
R1¼0.0263, wR2¼0.0632
R1¼0.0323, wR2¼0.0659
0.663 and -0.558
R1¼0.0409, wR2 ¼ 0.1225
R1¼0.0626, wR2 ¼ 0.1341
0.708 and -0.588
R1¼0.0314, wR2 ¼ 0.0763
R1¼0.0565, wR2 ¼ 0.0833
0.393 and -0.231
R indices (all data)
Dqmax and Dqmin (e. Å-3)
1H), 6.95 (d, J ¼ 7.9 Hz, 1H), 6.84–6.89 (m, 2H), 6.65-6.71 125.38, 123.97, 119.65, 117.51, 113.07, 105.91, 26.53, 25.50,
25.13, 13.17.
(m, 2H), 3.86 (s, 3H), 1.52-1.62 (m, 8H), 1.26-1.35 (sext,
J ¼ 7.3 Hz, 4H), 0.82 (t, J ¼ 7.3 Hz, 6H). 13C NMR (CDCl3,
100 MHz,d/ppm): 161.81, 160.63, 159.72, 151.78, 131.79,
130.00, 126.60, 118.54, 117.83, 116.93, 116.19, 115.96,
114.75, 56.36, 26.95, 26.53, 22.28, 13.47.
X-ray crystallography diffraction
X-ray diffraction data for crystals were performed with
graphite monochromated Mo-Ka radiation (k ¼ 0.71073 Å)
on a Bruker Smart Apex II CCD diffractometer, and col-
lected by the u ꢀ x scan technique at ambient temperature.
Multi-scan absorption correction was applied to the data.
The crystal structures were solved by direct methods and
(l3-O)2(l2-OCH3)2[5-ClC6H3(O)C ¼ NC6H3(O)-4-
Me]2(n-BuSn)2(n-Bu2Sn)2 (C2): The product was red-brown
crystal, Yield: 72.8%. m.p.: 130 ꢀ 133 ꢃC. Anal. Calc.
(C54H80Cl2N2O8Sn4): C 45.33, H 5.64, N 1.96%. Found: C
45.30, H 5.64, N 1.95%. IR (KBr, cmꢁ1)： 3040 (w), 3025
(w), 2953(m), 2920(m), 1604 (s), 1523 (s), 1490(s), 1458 (s), refined by full-matrix least-squares on F2. All the non-
hydrogen atoms were located in successive difference
Fourier syntheses and then refined anisotropically.
Hydrogen atoms were placed in calculated positions or
located from the Fourier maps, and refined isotropically
with the isotropic vibration parameters related to the non-
hydrogen atom to which they are bonded. All calculations
were performed with SHELXL-97 programs within
WINGX.[18,19] The crystal data and structure refinement
parameters of complexes are listed in Table 1.
1261 (s), 1165 (s), 765 (s), 607(m), 557 (m), 476 (w), 408
(w). H NMR(CDCl3, 400 MHz,d/ppm): 8.39 (s, 1H), 7.20-
1
7.23 (m,2H), 7.14(s, 1H), 7.00 (d, J ¼ 7.3 Hz, 1H), 6.75-6.79
(m, 2H), 2.29 (s, 3H), 1.26-1.32 (m, 10H), 1.13-1.14 (m,
4H), 0.89-0.92 (m, 10H), 0.70 (t, J ¼ 7.0 Hz, 3H). 13C NMR
(CDCl3, 100 MHz,d/ppm): 159.70, 136.19, 134.86, 133.23,
133.04, 131.52, 125.81, 124.46, 124.09, 120.94, 119.59,
118.50, 114.97, 50.45, 27.59, 27.01, 26.61, 26.45, 22.13, 20.78,
20.72, 13.72, 13.50.
[5-BrC6H3(O)C ¼ NC6H3(O)-4-NO2]n-Bu2Sn (C3): The
product was orange crystal, Yield: 75.5%. m.p.: 120 ꢀ 123 ꢃC.
Anal. Calc. (C21H25BrN2O4Sn): C 44.40, H 4.44, N 4.93%.
Found: C 44.41, H 4.44, N 4.94%. IR (KBr, cmꢁ1): 3053 (w),
2955 (w), 29894 (w), 1604 (s), 1519 (s), 1490 (s), 1316 (s),
1302(s), 1157(s), 648 (m), 580 (w), 511 (w), 472 (m), 418
(m). 1H NMR(DMSO-d6, 400 MHz,d/ppm): 9.26 (s, 1H),
8.63 (s, 1H), 8.04 (d, J ¼ 7.9 Hz, 1H), 7.84 (s, 1H), 7.49 (d,
J ¼ 7.9 Hz, 1H), 6.78 (d, J ¼ 8.8 Hz, 1H), 6.95 (d, J ¼ 8.8 Hz,
1H), 1.36-1.43 (m, 8H), 1.17-1.22 (m, 4H), 0.73 (t,
J ¼ 7.0 Hz, 3H). 13C NMR (DMSO-d6, 100 MHz, d/ppm):
UV-Vis property
The solutions of C1 ꢀ C3 were prepared with acetone at
room temperature, respectively, and their concentration was
1 ꢄ 10ꢁ5 mol/L. The scan range is from 340 to 600 nm, and
the width of slit scanning is 5.0 nm.
Anticancer activity studies
Primary human liver HL-7702 cells were purchased from
168.00, 166.45, 164.50, 138.82, 137.74, 135.98, 131.89, institute of Biochemistry and Cell Biology, Chinese

4
Z.-J. ZHANG ET AL.
Academic of science. MCF7, Colo205, NCI-H460, Hela and
HepG2 cells were obtained from American Tissue Culture
Collection (ATCC). HL-7702 cells were cultured in
Dulbecco’s modified Eagle’s medium (Thermo Fischer
Results and discussion
FT-IR spectra
Since all absorption peaks follow the same pattern, we pre-
Scientific) containing 4500 mg/L glucose, supplemented with sent the data of L1 and C1 as examples. In contrast to the
FT-IR spectra of L1 and C1, the presence of a single band
in the 3500 cmꢁ1 (L1) was assigned to phenolic hydroxyl,
but this peak disappears in the C1, it indicated that the
phenolic hydroxyl group have lost hydrogen protons to
coordinate with the dibutyltin oxide. Besides, a series of new
absorption peak appeared in the low frequency region, the
absorption bands at the 522 cmꢁ1 and 469 cmꢁ1 correspond
to the ꢀ(Sn–O) and ꢀ(Sn–N),[22,23] respectively. There is a
good indication of complex formation.
To summarize, the FT-IR spectra of ligands (L1 ꢀ L3)
show broad bands at 3445–3500 cmꢁ1 assignable to
ꢀ(OH),[6] and this peak disappears after coordinating.
Characteristic bands at 1508–1541 cmꢁ1 are assigned to
stretching vibration of the ꢀ(C ¼ N).[24,25] The bands at
1149– 1288 cmꢁ1 are assigned to the ꢀ(C–O).[26] Some new
bands in the ranges from 511 to 557 cmꢁ1 and 469 to
478 cmꢁ1 which appeared in the spectra of the synthesized
metal complex were probably due to (Sn–O) and (Sn–N)
bond vibration frequencies.[23, 27]
10% fetal bovine serum (GIBICO, Invitrogen) and L-glutam-
ine. The other cells were maintained at 37 ꢃC in a 5% CO2
incubator in RPMI 1640 (GIBICO, Invitrogen) containing
10% fetal bovine serum (GIBICO, Invitrogen). The test drug
was added from a stock solution in DMSO to result in a
final DMSO concentration of less than 0.1%. Cell prolifer-
ation was assessed by MTT assay. The cells were exposed to
treatment for 24 hrs, and the number of cells used per
experiment for each cell line was adjusted to obtain an
absorbance at 570 nm. Six concentrations (0.1 nM–10 lM)
were set for the compounds and at least 3 parallels of every
concentration were used. All experiments were repeated at
least three times. The data was calculated using Graph Pad
Prism version 7.0. The IC50 were fitted using a non-linear
regression model with a sigmoidal dose response.
Interaction with DNA studies
A mixture of the thymus DNA, EB and complex solution of
different concentration was placed in a 5 mL volumetric
flask. After 3 h, the fluorescence spectra were scanned at
25 ꢃC respectively, the emission wavelength was 258 nm, and
the excitation wavelength was shown in the spectrum. The
emission and excitation slit scanning width was 5.0 nm.
In order to accurately express the strength of the inter-
action between the complex and the DNA, the binding con-
stant (Kb) can be obtained according to the following
formula:[20]
NMR spectra
1
The H NMR spectrum show the ratio of the integral area
of each group is consistent with the expected number of
protons in each group.[28,29] Two phenolic hydroxy peaks at
12.41–13.15 and 8.61–11.43 ppm of the ligand disappeared
in the complex, and the hydrogen absorption peaks of butyl
groups were found in the high field, thus it can reasonably
be assumed that the Schiff bases ligand have bonded
with organotin.
cDNA= e ꢁ e
¼ cDNA= e ꢁ e þ 1=K e ꢁ e
FÞ bð FÞ
In the 13C NMR spectrum of C1 ꢀ C3, the absorption
peaks of carbon linked to nitrogen was at 161.81, 159.70,
168.00 ppm,[30] respectively. The peak positions of all carbon
atoms were basically consistent with the theoretical predic-
tion structure. And the conclusions are supported by the
results of X-ray diffraction studies.
ð
FÞ
ð
A
B
B
where cDNA is the concentration of CT-DNA, eA is the
observed extinction coefficient at arbitrary DNA concentra-
tion, eF is the extinction coefficient of the free complex, eB is
the extinction coefficient of the complex when fully combi-
nate to CT-DNA. Data was presented as cDNA/(eA ꢁ eF) ver-
sus cDNA, and the ratio of the slope to the intercept is the
binding constant (Kb). The mixture of the complex (50 lM)
and different concentration CT-DNA (0–50 lM) was added
in a 5 mL volumetric flask. After 3 hrs, the absorption spec-
tra were scanned at 25 ꢃC, respectively.
The viscosity tests were executed in the Ubbelodhe visc-
ometer, and it was keep in the 25.0 0.1 ꢃC with water bath.
The different concentration complex (0–50 lM) and CT-
DNA solution (50 lM) were added in the viscometer,
respectively. The values of viscosity were calculated from the
flow times of CT-DNA containing solutions corrected for
the flow time of buffer alone (t0), g ¼ (t ꢁ t0)[21] Data was
presented as (g/g0)1/3 versus (ccomplex/cDNA), where g is the
viscosity of CT-DNA in the presence of the complex, g0 is
the viscosity of CT-DNA alone, ccomplex is the concentration
of the complex and cDNA is the concentration of CT-DNA.
Description of the structures
The structures of C1 ꢀ C3 are illustrated in Figures 1–3.
Selected bond distances and angle are list in Table 2. From
the Figure 1, it can be seem that there are two independent
dinuclear molecule. The coordinated environment of their
central tin atom is similar. In an independent molecule con-
taining Sn1 and Sn1ii, a Sn2O2 planar four-membered ring
was constituted through Sn1, Sn1ii bridging the two phenol
oxygen atoms O2 and O2ii. The center of the Sn2O2 ring is
the symmetry center of this independent molecule. The dis-
tance of Sn1–O2 is 2.126 Å and the Sn1–O2ii is 2.862 Å, it
has subtle difference with the literature.[31,32] The central tin
atom is six-coordinate octahedral geometry, the O1, O2, N1
and O2ii were placed in equatorial sites, the axis position
were occupied by two carbon (C15 and C19) from butyl

INORGANIC AND NANO-METAL CHEMISTRY
5
Figure 1. Molecular structure of C1. (Symmetry codes: i 1ꢁx, 2ꢁy, 2ꢁz; ii1ꢁx, 1ꢁy, ꢁz.).
Figure 2. Molecular structure of C2. (Symmetry code: i ꢁx þ 1, ꢁy þ 1, ꢁz þ 1).
group. The angles [C19–Sn1–O2ii 75.90ꢃ, C19–Sn1–O2
97.75ꢃ, C19–Sn1–N1 109.47ꢃ, C19–Sn1–O1 87.81ꢃ,
Figure 3. Molecular structure of C3.
C15–Sn1–O2ii79.59ꢃ, C15–Sn1–O2 92.1ꢃ, C15–Sn1–N1
103.0ꢃ, C15–Sn1–O1 95.8ꢃ] are obviously deviated from 90ꢃ,
and the angle of C15–Sn1–C19 is 147.5ꢃ, which are also
deviated from linear angle 180ꢃ. In addition, the angle of
four atoms at the equatorial sites [O1–Sn1–O2ii 136.70ꢃ,
O1–Sn1–N1 80.88ꢃ, O2ii–Sn1–O267.37ꢃ, O2–Sn1–N1 74.96ꢃ]
are greatly deviated from 90ꢃ. Above description indicated
that the central tin atom is six-coordinate in distorted octa-
hedron geometry. The coordination environment of Sn1ii,
Sn2 and Sn2i is consistent with Sn1.
tin atom and l-O atom connected Sn2O2 four-membered
rings, respectively. Thus it made C2 present a ladder struc-
ture. The Sn2 is surrounded by two carbon atoms (C20 and
C24) from the two different butyl, one oxygen atoms (O3)
from methanol molecule and two l-O atoms. The four-
membered ring in the middle can be viewed as the center
of molecule.
For the structure of C3, it is a monomer structure, the
central tin atom is five-coordinate in distorted trigonalbipyr-
amid geometry, it is similar to the complex.[34,35] In the
crystal of C3, there are rich intermolecular hydrogen bond-
ing interaction. The dimer structure was formed by O-
H … O hydrogen bonds (H6 … O2i 2.427Å, /O6–H6 … O2i
176.55ꢃ; H7 … O3i 2.651Å, /O7–H7 … O3i 163.02ꢃ;
H10 … O3i 2.672Å, /O10–H10 … O3i 127.58ꢃ; i: 2-x, 2-y,
1-z) (Figure 4).
The ladder structure of C2 was constituted by three
Sn2O2 four-membered rings, and the three four-membered
rings are coplanar. In this ladder structure, the geometries
of all the tin atoms can be classified into two types, the first
type of tin atom (Sn1) is six-coordinate geometry, and it
occupied the top of the ladder. Besides, the de-alkylation
reaction have occurred,[33]and one butyl was laid off on the
Sn1. It can been seem that the Sn1 is surrounded by two
oxygen atoms (O1 and O2) and one nitrogen atom (N1)
from the ligand, one carbon atom (C16) from butyl, one
oxygen atoms (O3) from methanol molecule and one l-O
atom. The second type of tin (Sn2) located in the middle of
UV-Vis
The UV-Vis absorption spectra of C1 ꢀ C3 were shown in
the ladder, it is five-coordinate geometry, and this kind of Figure 5. It is obvious that the C1 ꢀ C3 have a large

6
Z.-J. ZHANG ET AL.
Table 2. Parts of bond lengths (Å) and bond angles (ꢃ) of C1 ꢀ C3.
C1
Bond
Sn1–C19
Sn1–C15
Sn1–N1
Sn2–C37
Angle
2.116(3) Sn2–O5
2.148(19) Sn2–C41
2.225(2) Sn2–O4
2.119(3) Sn2–N2
2.124(2) Sn1–O1
2.146(2)
2.126(2)
2.862(2)
2.866(2)
2.07(3)
Sn1–O2
2.1762(19) Sn1–O2ii
2.215(2) Sn2–O5i
C19–Sn1–O2 97.75(11) C41–Sn2–C37 142.8(10) C19–Sn1–O1 87.81(11)
C19–Sn1–N1 109.47(12) C41–Sn2–N2 107.1(10) O1–Sn1–N1 80.88(8)
C19–Sn1–C15 147.5(4) C41–Sn2–O5 96.4(8)
O2–Sn1–N1 74.96(8) C37–Sn2–N2 109.64(10) O2–Sn1–C15 92.1(4)
C15–Sn1–O1 95.8(5) O5–Sn2–O4 155.09(7) C15–Sn1–N1 103.0(4)
C19–Sn1–O2ii 75.905(91) C37–Sn2–O5i 76.722(81) C15–Sn1–O2ii 79.591(514)
O2–Sn1–O1 155.70(8)
C41–Sn2–O4 92.3(8)
C37–Sn2–O4 88.45(10) O5–Sn2–N2 75.26(8)
O4–Sn2–N2 79.88(8) C37–Sn2–O5 98.33(10) C41–Sn2–O5i 78.942(702)
Figure 4. The dimer structure of C3 constructed by intermolecular hydro-
gen bonding.
C2
Bond
Sn1–O1
Sn1–N1
Sn1–O5
Sn2–C24
Angle
1.889(9) Sn2–O5
2.298(5) Sn2–C20
2.029(3) Sn2–O5i
2.121(5) Sn2–O3
2.027(3) Sn1–O3
2.113(6) Sn1–O2
2.127(5) Sn1–C16
2.170(3)
2.090(3)
2.040(11)
2.152(6)
O1–Sn1–O5 110.0(3) O1-Sn1–N1
84.4(3)
O1–Sn1–O3 86.5(3)
O1–Sn1–C16 97.8(4)
O2–Sn1–N1 64.6(3)
O2–Sn1–O3 82.1(3)
O5–Sn2–C24 117.1(2) O3–Sn1–C16 171.6(2)
C20–Sn2–O3 96.72(18) O5–Sn1–O2 96.1(3)
C24–Sn2–O5i 98.90(19) O2–Sn1–C16 97.7(4)
O5–Sn1–N1 154.36(14) O5–Sn2–C20 117.73(19) C16–Sn1–N1 101.8(2)
O1–Sn1–O2 147.6(4) O5–Sn2–O3 72.82(11) O5–Sn1–O3 74.49(12)
O5–Sn1–C16 97.2(2)
O3–Sn1–N1 85.74(15) C20–Sn2–O5i 98.6(2)
C20–Sn2–C24 125.0(3) O5–Sn2–O5i 75.33(11) O5i–Sn2–O3 148.14(12)
C24–Sn2–O3 94.8(2)
C3
Bond
Sn1–O4
Sn1–C14
Angle
2.087(3) Sn1–C18
2.120(4) Sn1–N2
2.111(5) Sn1–O1
2.197(3)
2.122(3)
O4–Sn1–C18 95.08(19) O4–Sn1–C14 90.56(17) O4–Sn1–O1 157.49(11)
O4–Sn1–N2 82.46(11) C18–Sn1–N2 111.59(16) O1-Sn1–N2 75.69(10)
C18–Sn1–C14 128.9(2) C14–Sn1–N2 119.46(15) C18–Sn1–O1 97.89(19)
C14–Sn1–O1 95.45(17)
Figure 5. UV-Vis spectrum of the complexes.
Also, it have discovered that the organotin Schiff base
complexes (C1 ~ C3) exhibited better anticancer activity for
the five kinds of cancer cells in comparison with the Schiff
base ligand, and some of these compounds has greater effect
than carboplatin on the specified cancer cell. Especially, the
effect of C3 on Hela cancer cells is stronger than carboplatin
and other complexes, So C3 may become candidate com-
pound for treatment of cervical cancer after further chemical
optimization. From the structure of the complexes, it can be
found that C1 ~ C3 are butyl tin compounds, but the sub-
stituents on the Schiff base are different. The difference
activity of complexes may be caused only by a substituent
on the Schiff base ligand, it can infer that ligand has a great
influence on the anticancer activity of complexes from
Table 3, especially for compounds containing electron with-
drawing group (e.g. –X or –NO2), the activity of C3 is obvi-
ously better than C1 and C2. In C3, the bromine atom and
the nitro group on the Schiff base are electron withdrawing
groups. Those results suggest that the anticancer activity of
the complex is related to the electrical effect of the substitu-
ent on the Schiff base ligand.
absorption at about 460 nm, the reason for this may be that
the nitrogen atoms on the ligands are coordinated with tin,
and the electrons transfer from the ligand to the Sn atom,
the C ¼ N bond polarized so that the energy of the related
conjugated molecular orbital were affected.[12, 36] It further
confirmed that Schiff base ligand have coordinated dibutyl-
tin oxide, and the Schiff base organotin(IV) complexes were
synthesized. Besides, as can be seen from the Figure 5, a
absorption were presented at about 350 nm for C3, it may
ꢆ
be surmised that the transition of n!p on the nitro group
have occurd, and the nitro is a chromophoric group so that
it has a slight red shift.[37]
Anticancer activity
Table 3 lists the half inhibitory concentration of the com-
plexes and carboplatin on cultured cancer cells (MCF7,
Colo205, NCI-H460, Hela, HepG2) and the human normal
cell (HL7702) in vitro. In the toxicity test for HL7702, it
have found that all Schiff base ligands are relatively low-
toxic for the human normal cell HL7702, the activity
decreased in the following order: L2 >L3 >L1, which corre-
sponds to IC50 value at 22.36, 24.23, and 34.15 uM respect-
ively, and the toxicity activity of complexes (C1 ~ C3) are
greater than the corresponding Schiff base ligands.
Interaction with DNA
Ethidium bromide (EB) is a fluorescent dye, but its fluores-
cence is very weak. In DNA solution, EB can be inserted in
the base of double helix DNA in parallel to enhance its
fluorescence. Competitive reaction would take place when

INORGANIC AND NANO-METAL CHEMISTRY
7
Table 3 Inhibition action of ligands and complexes to cancer cell in vitro.
IC50 (uM)
Complex
MCF7
Colo205
NCI-H460
Hela
HepG2
HL7702
L1
L2
L3
C1
C2
C3
23.55 1.07
17.50 1.46
16.31 0.70
7.24 1.34
9.37 1.05
5.45 0.47
8.22 1.29
17.53 1.11
18.33 1.22
19.65 1.31
6.02 0.91
6.85 0.88
6.47 0.54
3.88 0.61
26.62 2.13
15.18 0.92
16.00 2.74
7.86 0.26
9.25 0.37
7.25 1.02
6.26 1.02
17.61 1.39
10.80 0.50
11.06 1.60
9.25 0.44
8.56 1.24
3.23 1.74
22.56 1.79
20.06 0.77
14.72 1.80
14.14 0.48
9.88 0.31
10.87 0.29
9.56 1.52
1.70 0.32
34.15 1.75
22.36 1.19
24.23 1.81
20.29 0.49
13.41 1.30
16.85 1.30
21.38 2.41
Carboplatin
Figure 7. Electronic spectra of C3 in Tris-HCl buffer upon addition of CT-DNA.
Figure 6. Effects of C3 on the fluorescent spectra of EB-DNA system. (cDNA
¼
(ccomplex ¼ 50 lmolꢂLꢁ1; from a to f, cDNA ¼ 0, 10, 20, 30, 40, 50 lmolꢂLꢁ1
,
30 lmolꢂLꢁ1; cEB ¼ 3 lmolꢂLꢁ1; from a to h, ccomplex ¼ 0, 10, 20, 30, 40, 50, 60,
70 lmolꢂLꢁ1, respectively; Inset: plot of F0/F vs ccomplex; kex ¼ 258 nm).
respectively. Arrow shows the absorbance changing upon the increase of DNA
concentration; Inset: plots of cDNA/(eA ꢁ eF) vs. cDNA).
the complex was added to the EB-DNA system solution, less than 10%, it is considered that the complex has a weak
complex can squeeze EB out of the DNA double helix,
resulting in quenching of fluorescence intensity. Thus, EB
could be used as a fluorescent probe of DNA structure.[38]
Figure 6 is fluorescence quenching curve of different con-
centration complex on the EB-DNA system. The fluores-
cence of EB-DNA system was obviously declined along with
increasing the concentration of C3. It indicated that the
complex involved in the coordination with the base pairs of
DNA and it squeezed EB out of the DNA double helix, so
the presence of complex makes the fluorescence of EB-DNA
system quenched. From the curve in figure6, it can inferred
that the interaction of C3 with DNA was intercalation
model and the way of quenching is static quenching. The
interaction with DNA. The higher the color reduction rate,
the stronger the interaction between the complex and DNA.
From the absorption spectroscopy tests, Kb values of C3
were calculated as 2.8 ꢄ 103 Lꢂmolꢁ1 (r2 ¼ 0.996). This value
is similar to the reported values in the literature.[41] It dem-
onstrated the interaction between complex and DNA is rela-
tively strong.
It shows the viscosity of DNA raises steadily with increas-
ing the concentration of the complexes C3 and Ligand L3 in
Figure 8. This may be explained by the complexes intercalat-
ing the adjacent DNA base pairs, and it leads an increase in
the separation of base pairs at intercalation sites. Thus, the
contour length of DNA was increased. The result is consist-
ent with fluorescence studies. The interaction of C3 with
calf thymus DNA was intercalation. So the results demon-
strated that the C3 and L3 could bind to DNA by intercal-
ation, but the order of the intensity of the action is C3 > L3,
it is consistent with the absorption spectroscopic studies.
quenching constant was calculated using the Stern-Volmer
[39]
equation: I0/I ¼ 1þKSVꢄccomplex,
the KSV was calculated as
1.56 ꢄ 104 Lꢂmolꢁ1, this value is similar to that reported in
the literature.[27,
It indicated that the C3 has a strong
40]
intercalation with DNA, and can be assumed that the tin
atom of C3 combined the base pairs of DNA, the terminal
ligands inserted into the DNA base pairs to compete with
EB, so that EB was squeeze out the DNA double helix
by C3.
Conclusion
Schiff base organotin (IV) complexes C1 ꢀ C3 have been
synthesized. There are two independent dinuclearmolecule
in C1, the central tin atom is six-coordinate in distorted
octahedron geometry. For C2, it exhibit a ladder structure.
The C3 is a monomer structure, the central tin atom is five-
The electronic absorption spectra of C3 in the absence
and presence of CT-DNA are shown in Figure 7. With the
addition of DNA, the absorbance has decreased, this absorp-
tion bands exhibited hypochromism of 20.1%. The hypo-
chromism value reflected the interaction force of complexes
with DNA at a certain extent. If the color reduction rate is coordinate in distorted trigonalbipyramid geometry. The

8
Z.-J. ZHANG ET AL.
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Funding
This work was supported by the Hunan Provincial Natural
Science Foundation of China (Nos. 2017JJ3003, 2016JJ5004)
and Foundation of Key Laboratory of Functional Metal-
Organic Compounds of Hunan Province (No. MO18K01).
15. Tan, Y.-X.; Zhang, Z.-J.; Feng, Y.-L.; Yu, J.-X.; Zhu, X.-M.;
Zhang, F.-X.; Kuang, D.-Z.; Jiang, W.-J. Syntheses, Crystal
Structures and Biological Activity of the 1D Chain Benzyltin
Complexes Based on 2-Oxo-Propionic Acid Benzoyl Hydrazone.
J. Inorg. Organomet. Polym. 2017, 27, 342–352. P. DOI:
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