Synthesis, crystal structure and biological activities of four novel tetranuclear di-organotin(IV) carboxylates

Article abstract of DOI:10.1016/j.jorganchem.2009.03.025

Four complexes: [Bu₂(L₁)SnOSn(L₁)Bu₂]₂ (1), [Bu₂(L₂)SnOSn(L₂)Bu₂]₂ (2), [Bu₂(L₃)SnOSn(L₃)Bu₂]₂ (3), and [Bu₂(L₄)SnOSn(L₄)Bu₂]₂ (4), (HL₁ = 2-(4-methylbenzoyl)benzoic acid, HL₂ = 2-(2,4-diethylbenzoyl)benzoic acid, HL₃ = 2-(4-chlorobenzoyl)benzoic acid, HL₄ = 2-(4-isopropylbenzoyl)benzoic acid) have been prepared and structurally characterized by means of elemental analysis and vibrational, ¹H NMR and FT-IR spectroscopies. The crystal structures of all complexes have been determined by X-ray crystallography. Three distannoxane rings are present to the dimeric tetraorganodistannoxane of planar ladder arrangement. Each structure is centro-symmetric and features a central rhombus Sn₂O₂ unit with two additional tin atoms linked at the O atoms. Complex 1 exhibited good antibacterial and antitumor activities and have a potential to be used as drugs.

Full text of DOI:10.1016/j.jorganchem.2009.03.025

Journal of Organometallic Chemistry 694 (2009) 2402–2408
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, crystal structure and biological activities of four novel tetranuclear
di-organotin(IV) carboxylates q
b
a,
Wanli Kang a,b, , Xiaoyan Wu , Jianbin Huang
*
*
a College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
b EOR Research Center, China University of Petroleum, Qingdao, Shandong 266555, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Four complexes: [Bu2(L1)SnOSn(L1)Bu2]2 (1), [Bu2(L2)SnOSn(L2)Bu2]2 (2), [Bu2(L3)SnOSn(L3)Bu2]2 (3), and
[Bu2(L4)SnOSn(L4)Bu2]2 (4), (HL1 = 2-(4-methylbenzoyl)benzoic acid, HL2 = 2-(2,4-diethylbenzoyl)ben-
zoic acid, HL3 = 2-(4-chlorobenzoyl)benzoic acid, HL4 = 2-(4-isopropylbenzoyl)benzoic acid) have been
prepared and structurally characterized by means of elemental analysis and vibrational, 1H NMR and
FT-IR spectroscopies. The crystal structures of all complexes have been determined by X-ray crystallog-
raphy. Three distannoxane rings are present to the dimeric tetraorganodistannoxane of planar ladder
arrangement. Each structure is centro-symmetric and features a central rhombus Sn2O2 unit with two
additional tin atoms linked at the O atoms. Complex 1 exhibited good antibacterial and antitumor activ-
ities and have a potential to be used as drugs.
Received 5 January 2009
Received in revised form 9 March 2009
Accepted 16 March 2009
Available online 21 March 2009
Keywords:
Organotin(IV) compound
Synthesis
Crystal structure
Trigonal bipyramidal geometry
Biological activities
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
Keeping in view the structural and biological diversity of organo-
tin carboxylates and in connection with our interest in coordination
The interest in organotin compounds in general and organotin
carboxylates in particular continues to grow because of their bio-
logical activity and potential antineoplastic and antituberculosis
agents [1–11]. Among those compounds dibutyltin derivatives
have displayed both higher activity and lower toxicity [12]. So
the antitumor activity of many compounds of the type [(RCOO-
Bu2Sn)2O]2 and (RCOO)2Bu2Sn has been studied [13,14]. This may
yield new leads for the development of antitumor drugs that
may possess lower toxicity than platinum compounds [2]. Diorga-
notin carboxylates derived from carboxylic acids are among the
most extensively studied class of compounds owing to their rich
structural chemistry. The diverse structural motifs known in this
family of compounds are attributed to the ambidentate character
of the carboxylate ligands [15]. Steric and electronic attributes of
organic substituents on tin and/or the carboxylate moiety impart
significant influence on the structural characteristics in tin carbox-
ylates. Therefore, synthesis of new organotin carboxylates with dif-
ferent structural features will be beneficial in the development of
pharmaceutical organotin and in other properties and application.
chemistry of organotin compounds with different carboxylic acids,
herein we report the synthesis, characterization and biological
studies of tin(IV) derivatives with some substituted benzoic acids
to widen their scope in biological applications. Complexes 1–4 have
been prepared by azeotropic removal of H2O from the reaction (in
benzene) of the di-n-butyltin oxide with HL1–HL4 in a molar ratio
of 1:1, respectively (where, HL1 = 2-(4-methylbenzoyl)benzoic acid,
HL2 = 2-(2,4-diethylbenzoyl)benzoic acid, HL3 = 2-(4-chloroben-
zoyl)benzoic acid, HL4 = 2-(4-isopropylbenzoyl)benzoic acid). All
complexes have been structurally characterized by means of ele-
mental analysis and vibrational, 1H NMR and FT-IR spectroscopies.
Single-crystal X-ray diffraction studies revealed that all these com-
plexes contain a centrosymmetric Sn2O2 core which is connected to
two exo-cyclic tin atoms via l3-oxo O-atoms to give a R8Sn4O2 cen-
tral unit. The antibacterial and antitumor activities of complex 1
have also been preliminary tested in vitro. These are the first re-
ported complexes and crystal structures of a novel class of substi-
tuted benzoato-tetraalkyl-distannoxanes.
2. Experimental
q
Foundation item: Project (20873181) supported by the NSFC and Project
2.1. General and instrumental
(2007AA06Z214) supported by the high-tech Research and Development Programm
of China; Project (ts20070704) supported by Taishan Scholars Construction Engi-
neering.
* Corresponding authors. Address: EOR Research Center, China University of
Petroleum, Qingdao, Shandong 266555, China (W. Kang). Tel.: +86 13589332193.
E-mail addresses: kangwanli@tom.com (W. Kang), jbhuang@pku.edu.cn (J.
Huang).
2.1.1. General
The reagents were used as supplied while the solvents were
purified according to standard procedures [16]. Melting points
were determined in open capillaries and were not corrected. Ele-
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.03.025

W. Kang et al. / Journal of Organometallic Chemistry 694 (2009) 2402–2408
2403
mental analyses were carried out on a Perkin–Elmer PE 2400 CHN
instrument and gravimetric analysis for Sn. 1H NMR spectra were
recorded in CDCl3 on a Varian Mercury 300 MHz spectrometer.
Infrared spectra (KBr pellets) were recorded on an Alpha Centauri
FI/IR spectrometer (400–4000 cmÀ1 range). The ligands HL1, HL2,
HL3 and HL4 were prepared by a modified literature method [17].
3 mm diameter were made carefully and these were completely
filled with the test solutions (concentration is 200 g/mL in etha-
l
nol), other holes containing ethanol and the reference antibacterial
drug served as negative and positive controls, respectively. After
the bacterium was incubated for 24 h at ca. 37 °C, the diameter
of the inhibiting area around each hole was estimated, which is de-
scribed as the inhibiting effect against bacteria [23]. The average of
three diameters was calculated for each sample.
2.2. X-ray crystallography
Crystals of 1, 2, 3 and 4 were grown by slow evaporation of eth-
anol solution at room temperature. The colorless crystals were
mounted on a sealed tube and used for data collection. Single-crys-
tal X-ray diffraction data for these complexes were recorded on a
2.3.2. MTT assay
Hela cell lines were grown in vitro in culture media containing
10% NCS, 1% HEPES and 1% RPMI1640 in a 5% CO2 incubator at
37 °C. The effects of di-n-butyltin oxide and complex 1 on cell
growth were evaluated using the MTT assay [24]. A total of
2 Â 103 cells were seeded in the wells of 96-well plate and cultured
for 24 h. Thereafter, the cells were treated with various concentra-
tions of di-n-butyltin oxide and complex 1 for 24 h. After exposure
to the drug, the MTT assay was carried out with Tetra Color One. All
experiments were performed at least three times and the mean
percentage of proliferation was calculated.
Bruker CCD Area Detector diffractometer by using the u/
x scan
technique with Mo k radiation (k = 0.71073 Å). Absorption correc-
a
tions were applied by using multiscan techniques [18]. The struc-
tures were solved by direct methods with SHELXS-97 [19] and
refined by full-matrix least-squares with SHELXL-97 [20] within
WINGX [21]. All nonhydrogen atoms were refined with anisotropic
temperature parameters, hydrogen atoms were refined as rigid
groups. A summary of the crystal data, experimental details and
refinement results are listed in Table 1.
2.4. Synthesis
2.3. Biological studies
2.4.1. Synthesis of 2-(4-methylbenzoyl)benzoic acid (HL1)
HL1 was synthesized according to the modified literature meth-
od [17]. Benzene-1,2-dicarboxylic anhydride (5.92 g, 0.04 mol),
anhydrous aluminum chloride (10.67 g, 0.08 mol) and dry toluene
(22.11 g, 0.24 mol) were added into a three-neck flask. The reaction
mixture was stirred for 4 h at 50 °C, then poured into a beaker.
After hydrolization with cooled aqueous HCl (20%), a brownish so-
lid was precipitated, which collected by filtration. Then the solid
was dissolved by aqueous NaOH (20%), and the surplus toluene
was removed by hydrodistillation. The distilled fluid was acidified
by 20% HCl, and the crud product was precipitated, then collected
2.3.1. Antibacterial tests
The antibacterial activities were determined by using the agar
well-diffusion method [22]. Broth culture medium was prepared
by mixing 10 g of albumin, 3 g of beef cream, 5 g of sodium chlo-
ride and 1000 mL distilled water at 37 °C. Five milliliters of broth
culture medium was poured into the Petri-dishes and allowed to
solidify. 0.2 mL of broth culture medium containing approximately
10 Â 106 CFU/mL of Colon or Hay bacillus was uniformly plated on
the surface of the Petri-dishes prepared before. Then three holes of
Table 1
Crystal data and details of structure refinement parameters for complex 1, 2, 3, 4.
Complex
1
2
3
4
Empirical formula
Formula weight
T (K)
C92H116O14Sn4
1920.69
293(2)
C104H140O14Sn4
2089.00
293(2)
C88H104Cl4O14Sn4
2002.35
293(2)
C100H132O14Sn4
2032.90
293(2)
Crystal size (mm)
Wavelength (Å)
Crystal system
space group
Unit cell dimensions
a (Å)
0.346 Â 0.317 Â 0.249
0.351 Â 0.302 Â 0.261
0.357 Â 0.277 Â 0.094
0.363 Â 0.312 Â 0.275
Mo K
a
0.71073
Mo K
a
0.71073
Mo K
a
0.71073
Mo Ka 0.71073
Triclinic
Monoclinic
P2(1)/n
Triclinic
Triclinic
ꢀ
ꢀ
ꢀ
P1
P1
P1
11.586(3)
14.718(4)
14.892(4)
68.274(4)
71.677(4)
76.938(4)
2222.1(10)
1
14.5876(9)
13.8977(9)
25.1798(15)
90.00
95.9190(10)
90.00
5077.6(5)
2
1.366
11.4222(6)
14.8195(8)
14.8379(8)
68.1170(10)
72.9600(10)
77.9620(10)
2214.3(2)
1
12.9345(8)
14.3545(9)
14.6789(9)
71.4700(10)
77.9400(10)
69.2730(10)
2402.5(3)
1
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc. (mg mÀ3
)
1.435
1.502
1.405
Absorption coefficient,
(mmÀ1
F(000)
Scan mode
l
1.171
1.031
1.295
1.088
)
980
x
2152
x
1012
x
1044
x
h Range for data collection (°) 1.50, 26.08
Reflections collected/unique 12954/8581 [0.0771]
[R(int)
1.55, 26.05
28061/9994 [0.0583]
1.49, 26.02
12432/8504 [0.0725]
1.47, 26.03
13527/9219 [0.0182]
]
Data/parameters
8581/0/504
9994/0/550
8504/0/496
9219/3/532
Ranges of h, k, l
À14 6 h 6 12, À13 6 k 6 18,
À17 6 h 6 18, À17 6 k 6 17,
À14 6 h 6 12, À18 6 k 6 16,
À15 6 h 6 15, À17 6 k 6 16,
À18 6 l 6 18
À29 6 l 6 31
À18 6 l 6 14
À13 6 l 6 18
Final R induces [I > 2
R indices (all data)
r(I)]
R1 = 0.0535, wR2 = 0.0808
R1 = 0.1153, wR2 = 0.0976
0.784
R1 = 0.0405, wR2 = 0.0775
R1 = 0.0674, wR2 = 0.0853
0.907
R1 = 0.0344, wR2 = 0.0908
R1 = 0.0384, wR2 = 0.0937
1.027
R1 = 0.0487, wR2 = 0.1202
R1 = 0.0653, wR2 = 0.1324
1.021
Goodness-of-fit (GOF) on F2
Largest difference in peak/
0.755 and À0.958
0.787 and À0.626
1.347 and À1.570
1.375 and À0.624
hole (e ÅÀ3
)

2404
W. Kang et al. / Journal of Organometallic Chemistry 694 (2009) 2402–2408
by filtration and washed with water. The pure product was ob-
tained by recrystallization from ethanol as a white powder, yield:
(CDCl3, ppm): 0.75–0.82 (t, 24H, J = 6.8, –CH2CH2CH2–CH3), 1.07–
1.30 (m, 48H, SnCH2CH2CH2–), 2.61–2.68 (m, 16H, Ar–CH2–),
1.13–1.18 (m, 24H, Ar–CH2–CH3), 7.1–7.8 (m, 28H, Ar–H).
67%, m.p. 145–146 °C. IR (KBr, cmÀ1):
m
(O–HÁ Á ÁO) 3443;
mas(COO)
1710, 1680;
m
sym(COO) 1458, 1410; 1H NMR(CDCl3, d): 2.39 (s,
3H, –CH3), 7.19–7.64 (m, 8H, Ar–H), 11.65 (s, 1H, –COOH). Anal.
Calc. for C15H12O3 (240.254 g molÀ1): C, 74.99; H, 5.03. Found: C,
74.47; H, 5.09%.
2.4.7. Synthesis of [Bu2(L3)SnOSn(L3)Bu2]2 (3)
Complex 3 was synthesized by the same procedures as 1 with
di-n-butyltin oxide (0.249 g, 1 mmol) and HL3 (0.261 g, 1 mmol).
The product was colorless crystals, yield: 51%, m.p. 158–159 °C.
Anal. Calc. for C88H104Cl4O14Sn4 (2002.410 g molÀ1): C, 52.78; H,
5.24; Sn, 23.71. Found: C, 52.46; H, 5.29; Sn, 23.69%. IR (KBr,
2.4.2. Synthesis of 2-(2,4-diethylbenzoyl)benzoic acid (HL2)
HL2 was synthesized by the same procedure as HL1 with ben-
zene-1,2-dicarboxylic anhydride (5.92 g, 0.04 mol) and anhydrous
aluminum chloride (10.67 g, 0.08 mol) and dry 1,3-diethylbenzene
(32.21 g, 0.24 mol). The product was white powder, yield: 56%,
cmÀ1):
1395;
m(C–H) 2956, 2868; mas(COO) 1675, 1520; msym(COO) 1450,
m
(Sn–O–Sn) 470, 420; m ; m .
(Sn–C) 541 cmÀ1 (C–Cl) 845 cmÀ1
1H NMR (CDCl3, ppm): 0.83 (t, 24H, J = 6.7, –CH3), 1.31–1.51 (m,
m.p. 100–102 °C. IR (KBr, cmÀ1):
m(O–HÁ Á ÁO) 3436;
m
as(COO)
48H, SnCH2CH2CH2–), 7.5–7.9 (m, 32H, Ar–H).
1667, 1606; msym (COO) 1588, 1564; 1H NMR(CDCl3, d): 1.27(t,
6H, –CH3), 2.63–2.71 (m, 4H, –CH2–), 7.07–7.43 (m, 7H, –ArH),
11.65 (s, –COOH). Anal. Calc. for C18H18O3 (282.334 g molÀ1): C,
76.57; H, 6.43. Found: C, 76.61; H, 6.21%.
2.4.8. Synthesis of [Bu2(L4)SnOSn(L4)Bu2]2 (4)
Complex 4 was synthesized by the same procedures as 1 with
di-n-butyltin oxide (0.249 g, 1 mmol) and HL4 (0.268 g, 1 mmol).
The product was colorless crystals, yield: 56%, m.p. 175–177 °C.
Anal. Calc. for C100H132O14Sn4 (2032.950 g molÀ1): C, 59.08; H,
6.54; Sn, 23.36. Found: C, 59.03; H, 6.87; Sn, 23.28%. IR (KBr,
2.4.3. Synthesis of 2-(4-chlorobenzoyl)benzoic acid (HL3)
HL3 was synthesized by the same procedure as HL1 with ben-
zene-1,2-dicarboxylic anhydride (5.92 g, 0.04 mol) and anhydrous
aluminum chloride (10.67 g, 0.08 mol) and dry 1-chlorobenzene
(29.41 g, 0.24 mol). The product was white powder, yield: 54%,
cmÀ1):
1475, 1452;
m
(C–H) 2958, 2926, 2869;
m
as(COO) 1616, 1586;
m
m
.
sym(COO)
m(Sn–O–Sn) 490, 430;
(Sn–C), 570 cmÀ1
1H NMR
(CDCl3, ppm): 0.67–0.87 (t, 24H, J = 6.8, –CH3), 1.23–1.38 (m,
48H, SnCH2CH2CH2–), 2.90–2.94 (m, 4H, Ar–CH–Me2), 7.2–7.7 (m,
32H, Ar–H).
m.p. 118–120 °C. IR (KBr, cmÀ1):
1678, 1586;
m
(O–HÁ Á ÁO) 3443 cmÀ1
; mas(COO)
m
sym(COO) 1485, 1426; m
(C–Cl)845; 1H NMR(CDCl3,
d): 7.6–8.2 (m, 8H, Ar–H), 113.3 (s, 1H, –COOH). Anal. Calc. for
C14H9O3Cl (260.672 g molÀ1): C, 64.51; H, 3.48. Found: C, 64.23;
H, 3.51%.
3. Result and discussion
3.1. Synthetic aspects
2.4.4. Synthesis of 2-(4-isopropylbenzoyl)benzoic acid (HL4)
HL4 was synthesized by the same procedure as HL1 with ben-
zene-1,2-dicarboxylic anhydride (5.92 g, 0.04 mol) and anhydrous
aluminum chloride (10.67 g, 0.08 mol) and dry cumene (28.85 g,
0.24 mol). The product was white powder, yield: 63%, m.p. 118–
Ligands HL1–HL4 were synthesized according to Friedel–Crafts
acylation from benzene-1,2-dicarboxylic anhydride and the substi-
tuted aromatic compounds in the presence of anhydrous alumi-
num chloride, Scheme 1. Complexes 1–4 were obtained by
azeotropic removal of H2O from the reaction (in benzene) between
the di-n-butyltin oxide and HL1–HL4 in a molar ratio of 1:1, respec-
tively, Scheme 2.
120 °C. IR (KBr, cmÀ1):
1680;
m
(O–HÁ Á ÁO) 3440 cmÀ1
; mas(COO) 1700,
m
sym(COO) 1450, 1410; 1H NMR (CDCl3, d): 1.281 (d, J = 6.9,
6H, –CH3), 2.91–3.02 (m, 1H, Ar–CHMe2), 7.1–7.7 (m, 8H, Ar–H),
11.65 (s, 1H, –COOH). Anal. Calc. for C17H16O3 (268.307 g molÀ1):
C, 76.10; H, 6.01. Found: C, 75.97; H, 5.81%.
3.2. IR spectra
2.4.5. Synthesis of [Bu2(L1)SnOSn(L1)Bu2]2 (1)
Comparing the IR spectra of the free ligands HL1–HL4 with com-
plexes 1–4, the bands at 3100–3550 cmÀ1 which appear in the
To a suspension of di-n-butyltin oxide (0.249 g, 1 mmol) in dry
benzene (30 ml) was added HL1 (0.240 g, 1 mmol). The mixture
was heated under reflux for 10 h in a Dean-Stark apparatus for aze-
otropic removal of the water formed in the reaction. After cooling
down to room temperature, the solution was filtered and the sol-
vent of the filtrate was gradually removed by evaporation under
vacuum until solid product was obtained. The solid was then
recrystallized from ethanol to give colorless crystals of complex
1. Yield: 61.4%, m.p. 186–187 °C. Anal. Calc. for C92H116O14Sn4
(1920.737 g molÀ1): C, 57.53; H, 6.09; Sn, 24.72. Found: C, 57.46;
spectra of the free ligands as the
m(O–H) vibration, are absent in
those of complexes 1–4, thus indicating metal-ligand bond forma-
tion through these sites. The mas(COO) and msym(COO) bands appear
at 1675–1515 cmÀ1 and 1475–1350 cmÀ1, respectively. The differ-
H, 6.02; Sn, 24.69%. IR (KBr, cmÀ1):
COO) 1666, 1525; sym(COO) 1400, 1350;
(Sn–C) 544 cmÀ1 1H NMR (CDCl3, ppm): 0.74 (t, 24H, J = 6.9, –
m
(C–H) 2956, 2927, 2869;
mas(-
m
m
(Sn–O–Sn) 487, 425;
m
.
CH3), 1.07–1.30 (m, 48H, SnCH2CH2CH2–), 2.37 (S, 12H, Ar–CH3),
7.2–7.7 (m, 32H, Ar–H).
2.4.6. Synthesis of [Bu2(L2)SnOSn(L2)Bu2]2 (2)
Complex 2 was synthesized by the same procedures as 1 with
di-n-butyltin oxide (0.249 g, 1 mmol) and HL2 (0.282 g, 1 mmol).
The product was colorless crystals, yield: 53.2%, m.p. 106–108 °C.
Anal. Calc. for C104H140O14Sn4 (2089.056 g molÀ1): C, 59.79; H,
6.75; Sn, 22.73. Found: C, 59.48; H, 6.87; Sn, 22.69%. IR (KBr,
cmÀ1):
1400, 1354;
m
(C–H), 2958, 2927, 2869;
m
as(COO) 1675, 1515;
m
m
.
sym(COO)
m
(Sn–O–Sn) 475, 423;
(Sn–C) 562 cmÀ1
1H NMR
Scheme 1. The reaction scheme for synthesis of HL1, HL2, HL3 and HL4.

W. Kang et al. / Journal of Organometallic Chemistry 694 (2009) 2402–2408
2405
Scheme 2. The reaction scheme for synthesis of 1, 2, 3 and 4.
ences,
D[mas(COO)–msym(COO)] between these frequencies are close
to that found for monodentate (266 cmÀ1 for 1, 275 cmÀ1 for 2 and
225 cmÀ1 for 3) and bridging bidentate carboxylto groups
(175 cmÀ1 for 1, 161 cmÀ1 for 2 and 125 cmÀ1 for 3). The differ-
ences between these two bands for 4, i.e. 141 and 134 cmÀ1 is close
to that found for bridging bidentate carboxylato groups [25,26].
This is totally consistent with the X-ray structures. Two bands at
490–470 and 430–420 cmÀ1, are assigned to
ing nonlinear O–Sn–O moieties, while the bands at 543–562 cmÀ1
are attribute to (Sn–C) stretching modes [26,27].
mas,sym(SnO)2, indicat-
m
3.3. 1H NMR spectra
Fig. 1. Perspective view of 1 showing the atomic numbering scheme.
The 1H NMR spectra of the complexes 1–4 are given in Section
2. In the 1H NMR spectra of ligands, the COOH group resonance ap-
pear at 11–12 ppm. Whereas this resonance disappear when the
carboxyl group participated in coordination to the Sn atoms in
complexes. The n-butyl protons in the complexes show a multiple
resonance due to –CH2–CH2–CH2– skeleton in the range of 1.07–
1.51 ppm and clear triple due to the terminal methyl groups at
0.67–0.87 ppm, respectively. It is shown that the chemical shifts
of the protons on the phenyl groups of complexes 1–4 exhibit sig-
nals at about 7.1–7.9 ppm as multiplets.
3.4. Crystal structures
3.4.1. Crystal structures of {[n-Bu2Sn(L1)2]2O}2 (1), {[n-
Bu2Sn(L2)2]2O}2 (2) and {[n-Bu2Sn(L3)2]2O}2 (3)
The molecular structures of 1, 2 and 3 are shown in Figs. 1–3,
and selected bond distances and angles are listed in Tables 2–4,
respectively. Each of the three structures is centrosymmetric about
a Bu4Sn2O2 core. Attached to each bridging oxygen atom is an exo-
cyclic Bu2Sn unit leading to a three-coordinate O atom. Further
connections between the tin atoms arise as a result of bridging car-
boxylate ligands which form experimentally equivalent Sn–O
bonds distances to the endo- and exo-cyclic tin atoms, i.e. Sn(1)–
O(2) 2.275(4) Å and Sn(2)–O(1) 2.284(4) Å for 1, Sn(2A)–O(4A)
2.280(3) Å and Sn(1)–O(5A) 2.277(3) Å for 2 and Sn(1)–O(1)
2.2871(19) Å and Sn(2A)–O(2) 2.288(2) Å for 3. The remaining
independent carboxylate ligand coordinates in the monodentate
mode to the exo-cyclic tin atom exclusively with Sn(2)–O(5)
2.174(4) Å for 1, Sn(1)–O(1) 2.183(2) Å for 2 and Sn(2)–O(4)
2.170(2) Å for 3, respectively. This configuration leads to five-coor-
dinate tin centers, each existing in a distorted trigonal bipyramidal
geometry [axial angles: O(2)–Sn(1)–O(7A) 162.45(15)° and O(1)–
Sn(2)–O(5) 168.30(17)° for 1; O(4)–Sn(2)–O(7) 164.13(9)° and
O(1)–Sn(1)–O(5A) 166.62(10)° for 2; O(1)–Sn(1)–O(7) 163.11(7)°
and O(4)–Sn(2)–O(2A) 168.33(7)° for 3].
Distortions from the ideal geometries may be traced, in part, to
the presence of close intramolecular SnÁ Á ÁO interactions. Thus, the
centrosymmetrically related O(5A) atom forms a contact of 2.916 Å
with the Sn(1) atom, which opens up the C(51)–Sn(1)–C(61) angle
to 142.2(3)° from the ideal angle of 120°, and an interaction of
2.847 Å between Sn(2) and O(4) atoms results in the expansion
of the C(81)–Sn(2)–C(71) angle to 141.7(3)° in complex 1. Simi-
larly, the same SnÁ Á ÁO interactions were observed to exist in both
2 and 3. Whereas the intramolecular SnÁ Á ÁO contacts mentioned
above are well within the van der Waals distances for these atoms,
Fig. 2. Perspective view of 2 showing the atomic numbering scheme.
the relatively large separations and the minor perturbations from
the ideal trigonal bipyramidal geometries indicate that these inter-
actions must be considered as weak [28]. The molecular structures
of 1, 2 and 3 conform to the common structural motif found for
compounds with the general formula {[R2Sn(O2CR’)2]2O}2 [29].
3.4.2. Crystal structures of {[n-Bu2Sn(L4)2]2O}2 (4)
The molecular structure of 4 is shown in Fig. 4, selected bond
distances and angles are listed in Table 5. Complex 4 is also a cen-
tro-symmetric dimer built up around the planar cyclic Sn2O2 unit.
The two oxygen atoms O(7) and O(7A) are triply bridging, each
linking one exo-cyclic (Sn(1) or Sn(1A)) and two endo-cyclic
(Sn(2) and Sn(2A)) atoms. Additional links between the exo- and
endo-cyclic tin centers Sn(1) and Sn(2), respectively, are provided
by four bidentate bridging carboxylate ligands. The Sn–O bond dis-
tances involving the bridging carboxylate ligands differ by 0.174
and 0.112 Å indicating asymmetrical bridges; the variations in
the C–O bond distances are much less and suggest charge delocal-
ization over the carboxylato group COO. The coordination number
around each tin is five for Sn(1) and six for Sn(2), respectively. The

2406
W. Kang et al. / Journal of Organometallic Chemistry 694 (2009) 2402–2408
Table 3
Selected bond lengths (Å) and bond angles (°) for complex 2.
Bond lengths
Sn(1)–O(7)
Sn(1)–C(61)
Sn(1)–C(51)
Sn(1)–O(1)
Sn(1)–O(5)#1
Sn(2)–O(7)#1
Sn(2)–C(71)
Sn(2)–C(81)
Sn(2)–O(7)
2.037(2)
2.112(4)
2.116(4)
2.183(2)
2.277(3)
2.038(2)
2.110(4)
2.118(4)
2.159(2)
Sn(2)–O(4)
O(1)–C(1)
O(2)–C(1)
O(3)–C(17)
O(4)–C(2)
O(5)–C(2)
O(5)–Sn(1)#1
O(6)–C(37)
O(7)–Sn(2)#1
2.280(3)
1.293(4)
1.233(4)
1.215(5)
1.261(4)
1.260(4)
2.277(2)
1.216(5)
2.038(2)
Bond angles
O(7)–Sn(1)–C(61)
O(7)–Sn(1)–C(51)
C(61)–Sn(1)–C(51)
O(7)–Sn(1)–O(1)
110.13(14)
104.25(14)
145.01(17)
81.01(9)
O(7)#1–Sn(2)–O(4)
C(71)–Sn(2)–O(4)
C(81)–Sn(2)–O(4)
O(7)–Sn(2)–O(4)
C(1)–O(1)–Sn(1)
C(2)–O(4)–Sn(2)
C(2)–O(5)–Sn(1)#1
Sn(1)–O(7)–Sn(2)#1
Sn(1)–O(7)–Sn(2)
Sn(2)#1–O(7)–Sn(2)
O(2)–C(1)–O(1)
O(2)–C(1)–C(11)
O(1)–C(1)–C(11)
O(5)–C(2)–O(4)
O(5)–C(2)–C(31)
O(4)–C(2)–C(31)
89.99(9)
89.54(14)
83.04(13)
164.13(9)
105.0(2)
124.4(2)
128.2(3)
131.72(12)
122.61(11)
104.76(10)
122.3(4)
120.2(4)
117.3(4)
124.1(4)
117.3(4)
118.6(4)
C(61)–Sn(1)–O(1)
C(51)–Sn(1)–O(1)
O(7)–Sn(1)–O(5)#1
C(61)–Sn(1)–O(5)#1
C(51)–Sn(1)–O(5)#1
O(1)–Sn(1)–O(5)#1
O(7)#1–Sn(2)–C(71)
O(7)#1–Sn(2)–C(81)
C(71)–Sn(2)–C(81)
O(7)#1–Sn(2)–O(7)
C(71)–Sn(2)–O(7)
C(81)–Sn(2)–O(7)
92.16(13)
99.49(14)
89.25(10)
82.54(13)
91.77(14)
166.62(10)
106.76(14)
115.68(13)
136.82(16)
75.24(10)
100.13(14)
97.98(13)
Fig. 3. Perspective view of 3 showing the atomic numbering scheme.
Table 2
Selected bond lengths (Å) and bond angles (°) for complex 1.
Bond lengths
Sn(1)–O(7)
Sn(1)–C(51)
Sn(1)–C(61)
Sn(1)–O(7)#1
Sn(1)–O(2)
Sn(2)–O(7)
Sn(2)–C(81)
Sn(2)–C(71)
Sn(2)–O(5)
2.029(4)
2.106(6)
2.107(6)
2.170(4)
2.275(4)
2.035(4)
2.112(7)
2.147(8)
2.174(4)
Sn(2)–O(1)
O(1)–C(1)
O(2)–C(1)
O(3)–C(17)
O(4)–C(2)
O(5)–C(2)
O(6)–C(37)
O(7)–Sn(1)#1
2.284(4)
1.265(8)
1.247(8)
1.211(7)
1.251(8)
1.290(7)
1.220(8)
2.170(4)
Table 4
Selected bond lengths (Å) and bond angles (°) for complex 3.
Bond lengths
Sn(1)–O(7)#1
Sn(1)–C(61)
Sn(1)–C(51)
Sn(1)–O(7)
Sn(1)–O(1)
Sn(2)–O(7)
Sn(2)–C(71)
Sn(2)–C(81)
Sn(2)–O(4)
Sn(2)–O(2)#1
2.0433(18)
2.124(3)
2.124(3)
2.1641(19)
2.2871(19)
2.0275(18)
2.122(3)
2.133(3)
2.170(2)
2.288(2)
Cl(1)–C(24)
Cl(2)–C(44)
O(1)–C(1)
1.742(4)
1.749(4)
1.266(3)
1.260(3)
2.288(2)
1.211(4)
1.307(3)
1.233(4)
1.216(4)
2.0433(18)
O(2)–C(1)
Bond angles
O(2)–Sn(2)#1
O(3)–C(17)
O(4)–C(2)
O(5)–C(2)
O(6)–C(37)
O(7)–Sn(1)#1
O(7)–Sn(1)–C(51)
O(7)–Sn(1)–C(61)
C(51)–Sn(1)–C(61)
O(7)–Sn(1)–O(7)#1
C(51)–Sn(1)–O(7)#1
C(61)–Sn(1)–O(7)#1
O(7)–Sn(1)–O(2)
C(51)–Sn(1)–O(2)
C(61)–Sn(1)–O(2)
O(7)#1–Sn(1)–O(2)
O(7)–Sn(2)–C(81)
O(7)–Sn(2)–C(71)
C(81)–Sn(2)–C(71)
O(7)–Sn(2)–O(5)
C(81)–Sn(2)–O(5)
C(71)–Sn(2)–O(5)
112.6(2)
O(7)–Sn(2)–O(1)
C(81)–Sn(2)–O(1)
C(71)–Sn(2)–O(1)
O(5)–Sn(2)–O(1)
C(1)–O(1)–Sn(2)
C(1)–O(2)–Sn(1)
C(2)–O(5)–Sn(2)
Sn(1)–O(7)–Sn(2)
Sn(1)–O(7)–Sn(1)#1
Sn(2)–O(7)–Sn(1)#1
O(2)–C(1)–O(1)
O(2)–C(1)–C(11)
O(1)–C(1)–C(11)
O(4)–C(2)–O(5)
O(4)–C(2)–C(31)
O(5)–C(2)–C(31)
88.70(16)
88.6(2)
83.4(3)
104.6(2)
142.2(3)
74.86(18)
97.0(2)
99.1(2)
88.83(16)
83.1(2)
168.30(17)
125.1(4)
125.2(5)
108.7(4)
132.7(2)
105.14(18)
120.75(18)
125.3(7)
118.0(7)
116.7(7)
122.0(6)
120.1(6)
117.7(6)
Bond angles
O(7)#1–Sn(1)–C(61)
O(7)#1–Sn(1)–C(51)
C(61)–Sn(1)–C(51)
O(7)#1–Sn(1)–O(7)
C(61)–Sn(1)–O(7)
C(51)–Sn(1)–O(7)
O(7)#1–Sn(1)–O(1)
C(61)–Sn(1)–O(1)
C(51)–Sn(1)–O(1)
O(7)–Sn(1)–O(1)
O(7)–Sn(2)–C(71)
O(7)–Sn(2)–C(81)
C(71)–Sn(2)–C(81)
O(7)–Sn(2)–O(4)
C(71)–Sn(2)–O(4)
C(81)–Sn(2)–O(4)
105.31(9)
O(7)–Sn(2)–O(2)#1
C(71)–Sn(2)–O(2)#1
C(81)–Sn(2)–O(2)#1
O(4)–Sn(2)–O(2)#1
C(1)–O(1)–Sn(1)
C(1)–O(2)–Sn(2)#1
C(2)–O(4)–Sn(2)
Sn(2)–O(7)–Sn(1)#1
Sn(2)–O(7)–Sn(1)
Sn(1)#1–O(7)–Sn(1)
O(2)–C(1)–O(1)
O(2)–C(1)–C(11)
O(1)–C(1)–C(11)
O(5)–C(2)–O(4)
O(5)–C(2)–C(31)
O(4)–C(2)–C(31)
89.47(7)
88.16(10)
83.58(10)
168.33(7)
125.79(18)
125.40(19)
108.47(17)
131.34(10)
122.65(9)
104.82(8)
123.5(3)
91.1(2)
112.99(9)
140.94(11)
75.18(8)
100.13(9)
96.76(9)
89.52(7)
90.66(10)
82.48(9)
163.11(7)
104.77(10)
110.31(10)
143.80(12)
81.07(7)
162.45(15)
105.7(2)
111.4(3)
141.7(3)
81.45(16)
100.1(2)
94.3(3)
metal coordination geometry is therefore described as distorted
trigonal bipyramidal with O(1) and O(5) atoms occupying the axial
positions and O(7), C(51) and C(61), the equatorial positions for
Sn(1), and a distorted octahedral for Sn(2) center. Different to the
complexes 1, 2, and 3 mentioned above, complex 4 adopted an-
other structural type, this fact indicates that there is subtle energy
difference among these types and that the structure ultimately
adopted in the solid state may depend largely on the crystallization
conditions employed.
118.6(3)
117.9(2)
122.8(3)
120.9(2)
100.81(10)
93.25(10)
116.2(2)
teria and the results are summarized in Table 6. In order to com-
pare the results obtained, the Imipinem is used as standard drug
[30]. Complex 1 shows higher activity than n-Bu2SnO and the li-
gand HL1, but lower than the standard drug. The results also
showed that the activity of complex 1 against E. coli is better than
against B. subtilis. It is noteworthy that 1 has a better antibacterial
activity against the two bacteria than the corresponding ligand
HL1, which have shown that the complex 1 is potential bactericide
than it’s corresponding ligand compound.
4. Biological studies
4.1. Antibacterial screening
Antibacterial activity was performed against one Gram positive
(Bacillus subtilis) and another Gram negative (Escherichia coli) bac-

W. Kang et al. / Journal of Organometallic Chemistry 694 (2009) 2402–2408
2407
Table 7
The in vitro antitumor activities of complex 1 against Hela cell.
Compound
Dose (
lg/mL)
Anticancer activity (%)
IC50
1.6
2.3
(
lg/mL)
n-Bu2SnO
0.1
0.3
1
3
10
À5.5 9.0
18.7 3.0
30.8 3.2
67.0 1.6
88.7 0.1
Complex 1
0.1
0.3
1
3
10
0.0 2.8
8.5 4.4
21.8 2.1
58.4 0.6
88.0 0.2
of cisplatin for comparison. The low concentrations of complex 1
showed higher activities than of n-Bu2SnO in vitro antitumor activ-
ity in Hela cell lines, whereas the high concentrations of it dis-
played a lower activities than of n-Bu2SnO. At concentrations of
10
l
g/L, the results showed that complex 1 provides 88% growth
g/mL. Complex 1 pre-
Fig. 4. Perspective view of 4 showing the atomic numbering scheme.
inhibition, and the IC50 in vitro values is 2.3
l
sents lower IC50 values than those of cisplatin (IC50 = 3.50) [31],
which indicates their high activity against the tumoral cell lines
evaluated. As these results are preliminary, further study on the
antitumor effects of these compounds is highly recommended.
Table 5
Selected bond lengths (Å) and bond angles (°) for complex 4.
Bond lengths
Sn(1)–O(7)
Sn(1)–C(61)
Sn(1)–C(51)
Sn(1)–O(5)
Sn(1)–O(1)
Sn(2)–O(7)#1
Sn(2)–C(71)
Sn(2)–C(81)
Sn(2)–O(7)
Sn(2)–O(2)#1
2.001(3)
2.105(9)
2.121(7)
2.207(4)
2.228(4)
2.115(3)
2.120(6)
2.126(6)
2.139(3)
2.350(4)
Sn(2)–O(4)
O(1)–C(1)
O(2)–C(1)
O(2)–Sn(2)#1
O(3)–C(17)
O(4)–C(2)
O(5)–C(2)
O(6)–C(37)
O(7)–Sn(2)#1
2.481(4)
1.260(6)
1.245(6)
2.350(4)
1.222(6)
1.233(6)
1.280(6)
1.210(6)
2.115(3)
Acknowledgement
We acknowledged the Project (20873181) supported by the
NSFC and the Project (2007AA06Z214) supported by the high-tech
Research and Development Programm of China; Project is
(ts20070704) supported by Taishan Scholars Construction
Engineering.
Bond angles
Appendix A. Supplementary material
O(7)–Sn(1)–C(61)
O(7)–Sn(1)–C(51)
C(61)–Sn(1)–C(51)
O(7)–Sn(1)–O(5)
C(61)–Sn(1)–O(5)
C(51)–Sn(1)–O(5)
O(7)–Sn(1)–O(1)
C(61)–Sn(1)–O(1)
C(51)–Sn(1)–O(1)
O(5)–Sn(1)–O(1)
O(7)#1–Sn(2)–C(71)
O(7)#1–Sn(2)–C(81)
C(71)–Sn(2)–C(81)
O(7)#1–Sn(2)–O(7)
C(71)–Sn(2)–O(7)
C(81)–Sn(2)–O(7)
O(7)#1–Sn(2)–O(2)#1
119.4(3)
O(7)–Sn(2)–O(2)#1
O(7)#1–Sn(2)–O(4)
C(71)–Sn(2)–O(4)
C(81)–Sn(2)–O(4)
O(7)–Sn(2)–O(4)
O(2)#1–Sn(2)–O(4)
C(1)–O(1)–Sn(1)
C(1)–O(2)–Sn(2)#1
C(2)–O(4)–Sn(2)
C(2)–O(5)–Sn(1)
Sn(1)–O(7)–Sn(2)#1
Sn(1)–O(7)–Sn(2)
Sn(2)#1–O(7)–Sn(2)
O(2)–C(1)–O(1)
162.86(13)
162.92(12)
81.29(18)
81.57(18)
86.68(11)
110.33(13)
121.9(3)
128.8(4)
120.5(3)
123.7(4)
128.07(15)
128.02(15)
103.73(13)
124.2(5)
118.5(5)
117.3(5)
113.4(3)
127.1(4)
91.86(13)
91.0(3)
88.1(2)
92.98(13)
86.7(3)
CCDC 706617, 706619, 706618 and 706620 contains the sup-
plementary crystallographic data for 1, 2, 3 and 4. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-
tary data associated with this article can be found, in the online
version, at doi:10.1016/j.jorganchem.2009.03.025.
89.9(2)
175.16(14)
102.43(19)
99.69(18)
154.0(2)
76.27(13)
99.6(2)
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