In vitro biological studies and structural elucidation of organotin(IV) derivatives of 6-nitropiperonylic acid: Crystal structure of {[(CH2O2C6H2(o-NO2)COO)SnBu2]2O}2

Article abstract of DOI:10.1016/j.poly.2009.07.039

Six organotin(IV) compounds with general formulae R₃SnL, R = Me (2), Ph (6), R₂SnL₂, R = Me (1), Et (3), n-Oct (5), [((R₂SnL)₂O)₂], R = Bu (4), L = 6-nitropiperonylate, have been prepared. The newly synthesized compounds have been characterized by elemental analysis, FT-IR and multinuclear NMR (¹H, ¹³C and ¹¹⁹ Sn). The structure of 4 has been determined by single crystal X-ray crystallography which is triclinic with the space group P over(1, ?). The crystal structure contains centrosymmetric dimer distannoxane with planar central four-membered Sn₂O₂ core. The 6-nitropiperonylate ligand shows different modes of coordination with Sn, as a result the central Sn₂O₂ core is fused with two four-membered (Sn(1)-O(1)-Sn(2)-O(13)) and two six-membered (Sn(1)-O(13)-Sn(2)-O(8)-C(9)-O(7)) rings. The endocyclic Sn(2) is six coordinated in a skew trapezoidal bipyramidal environment while exocyclic Sn(1) is five coordinated with distorted trigonal bipyramidal geometry. The ligand acid and synthesized organotin compounds were also screened for antibacterial, antifungal, brine-shrimp lethality and potato disc antitumor activities. Results of bioassay demonstrate that organotin derivatives are in general more active than the ligand acid.

Full text of DOI:10.1016/j.poly.2009.07.039

Polyhedron 29 (2010) 613–619
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
In vitro biological studies and structural elucidation of organotin(IV)
derivatives of 6-nitropiperonylic acid: Crystal structure of
{[(CH2O2C6H2(o-NO2)COO)SnBu2]2O}2
b,
c
Muhammad Hanif a, Mukhtiar Hussain a, Saqib Ali a, , Moazzam H. Bhatti , Muhammad Sheeraz Ahmed ,
*
*
Bushra Mirza c, Helen Stoeckli-Evans d
a Department of Chemistry, Quaid-i-Azam University, Islamabad-45320, Pakistan
b Department of Chemistry, Allama Iqbal Open University, H/8, Islamabad, Pakistan
c Department of Biochemistry, Faculty of Biological Sciences, Quaid-i-Azam University, Islamabad, Pakistan
d Institute of Physics, University of Neuchatel, Rue Emile-Argand 11, CH-2009 Neuchatel, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 26 July 2009
Six organotin(IV) compounds with general formulae R3SnL, R = Me (2), Ph (6), R2SnL2, R = Me (1), Et (3), n-
Oct (5), [((R2SnL)2O)2], R = Bu (4), L = 6-nitropiperonylate, have been prepared. The newly synthesized
compounds have been characterized by elemental analysis, FT-IR and multinuclear NMR (1H, 13C and
119
Keywords:
Sn). The structure of 4 has been determined by single crystal X-ray crystallography which is triclinic
Organotin(IV) compounds
6-Nitropiperonylic acid
Multinuclear NMR
Crystal structure
Distannoxane
ꢀ
with the space group P1. The crystal structure contains centrosymmetric dimer distannoxane with planar
central four-membered Sn2O2 core. The 6-nitropiperonylate ligand shows different modes of coordina-
tion with Sn, as a result the central Sn2O2 core is fused with two four-membered (Sn(1)–O(1)–Sn(2)–
O(13)) and two six-membered (Sn(1)–O(13)–Sn(2)–O(8)–C(9)–O(7)) rings. The endocyclic Sn(2) is six
coordinated in a skew trapezoidal bipyramidal environment while exocyclic Sn(1) is five coordinated
with distorted trigonal bipyramidal geometry. The ligand acid and synthesized organotin compounds
were also screened for antibacterial, antifungal, brine-shrimp lethality and potato disc antitumor activi-
ties. Results of bioassay demonstrate that organotin derivatives are in general more active than the ligand
acid.
Bioassay
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
by the oxidation of piperonal with KMnO4 [13c]. To the best of our
knowledge no metal complexes has been reported for Piperonylic
Organotin(IV) carboxylates are being extensively studied with
special reference to their methods of synthesis, structural elucida-
tion and biological activities [1–7]. Generally these compounds are
well characterized by FT-IR, multinuclear NMR (1H, 13C, 119Sn), X-
ray and 119mSn Mössbauer spectroscopy [8–12]. In addition exten-
sive biocidal applications utilizing the antitumor and anticancer
activities of such compounds has made them significantly impor-
tant [5,6]. Another aspect of major interest in organotin carboxyl-
ates is of their structural diversity. Both diorganotin(IV) and
triorganotin(IV) esters show rich and diverse structural chemistry
as citied in recent reviews [7,9].
acid until we reported first time organotin(IV) complexes of piper-
onylic acid with structural and biological activities [14]. On the basis
of our previous investigation on structural and biological activities
organotin(IV) complexes of piperonylic acid [14–18], we extended
our work to synthesis organotin(IV) derivatives of 6-nitropiperony-
lic acid (Fig. 1) and to establish their biological role [14–18].
2. Experimental
2.1. Materials
Piperonylic acid is a natural molecule bearing a methelenedioxy
function that closely mimics the structure of trans-cinnamic acid
[13a] and possess antimicrobial properties [13b]. It is extracted
from the bark of Paracoto tree. It can also be prepared in laboratory
All the organotin precursors and chemicals used were procured
from Aldrich or Fluka. All the solvents were dried before use by the
literature methods [19].
2.2. Instrumentation
* Corresponding authors. Tel.: +92 5190642130; fax: +92 5190642241 (S. Ali),
tel.: +92 519057262; fax: +92 519250081(M.H. Bhatti).
E-mail addresses: drsa54@yahoo.com (S. Ali), moazzamhussain_b@yahoo.com
(M.H. Bhatti).
Melting points were determined in a capillary tube using a MPD
Mitamura Riken Kogyo (Japan) electrothermal melting point
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.07.039

614
M. Hanif et al. / Polyhedron 29 (2010) 613–619
1H NMR data (CDCl3, ppm, 2J[119Sn,1H] in Hz); 7.46 (s, 2H, aro-
O
matic protons), 7.25 (s, 2H, aromatic protons), 6.31 (s, 4H, O–
CH2–O), {1.26 (s, 6H, [79], SnCH3)}.
2
13C NMR data (CDCl3, ppm); 129.0 (C1), 108.5 (C2), 151.3 (C3),
149.8 (C4), 105.0 (C5), 143.2 (C6), 103.6 (C7), 174.3 (C8), {4.6
(SnCH3)}.
O
O
3
4
1
6
8
OH
7
119Sn NMR data (CDCl3, ppm); ꢀ172.0.
NO2
2.3.3.1.2. Compound (2) Me3SnL. Prepared by method A by adding
sodium salt of ligand (1 g, 4.29 mmol) and Me3SnCl (0.86 g,
4.29 mmol) in 1:1 ratio, respectively.
5
Fig. 1. Numbering scheme and structure of the 6-nitropiperonylic acid (HL).
Physical data; Yield 76%, m.p. 188–191 °C, CHN Anal. Calc.: C,
35.36; H, 3.48; N, 3.74. Found: C, 35.24; H, 3.51; N, 3.65%.
apparatus and are uncorrected. Multinuclear NMR (1H, 13C and
119Sn) spectra were recorded on a Bruker ARX 300 MHz-FT-NMR
spectrometer using CDCl3 as an internal reference for [d 1H
(CDCl3) = 7.25 and d 13C (CDCl3) = 77.0]. 119Sn NMR spectra were
FT-IR data (KBr, cmꢀ1);
t
(COO)Asym 1624,
t(COO)sym 1424, Dt
200, t(Sn–C) 550, t(Sn–O) 450.
1H NMR data (CDCl3, ppm, 2J[119Sn, 1H] in Hz); 7.33 (s, 1H, aro-
matic protons), 7.26 (s, 1H, aromatic protons), 6.13 (s, 2H, O–CH2–
O), {1.25 (s, 9H, [57], SnCH3)}.
obtained
with
Me4Sn
as
an
external
reference
[(119Sn) = 37.290665]. Chemical shifts (d) are given in ppm and
coupling constants J are given in Hz. The multiplicities of signals
in 1H NMR are given with chemical shifts; (s = singlet, t = triplet,
q = quartet, m = multiplet).
13C NMR data (CDCl3, ppm, 1J[117/119Sn, 13C] in Hz); 128.5 (C1),
110.7 (C2), 153.4 (C3), 150.2 (C4), 106.9 (C5), 144.4 (C6), 105.6
(C7), 173.6 (C8), {0.1 (SnCH3, [388, 400])}.
119Sn NMR data (CDCl3, ppm); 128.5.
2.3.3.1.3. Compound (3) Et2SnL2. Prepared by method A by adding
sodium salt of ligand (1 g, 4.29 mmol) and Et2SnCl2 (0.53 g,
2.15 mmol) in 2:1 ratio, respectively.
2.3. Synthesis
2.3.1. Synthesis of the ligand LH
Physical data; Yield 80%, m.p. 200–202 °C, CHN Anal. Calc.: C,
40.2; H, 3.02; N, 4.69. Found: C, 40.13; H, 2.961; N, 4.53%.
The ligand acid was synthesized by the method reported else-
FT-IR data (KBr, cmꢀ1);
t
(COO)Asym 1610,
t(COO)sym 1414, Dt
where [14]. In
1.32 mmol) and 41.6 g (2.64 mmol) of potassium permanganate
were added in mixture of water (300 mL) and acetone
(200 mL). The mixture was mechanically stirred and reflux for
4 h. After reflux acetone was distilled off, the flask was cooled
and MnO2 precipitate was filtered off, washed with 100 mL (in
two 50 mL portions) of hot water. The filtrate was ice cooled in
an ice bath and acidified to produce analytically pure yellow solid.
M.p. 166–167 °C. Yield 68%.
a typical procedure 6-nitropiperonal (25.7 g,
196, t(Sn–C) 545, t(Sn–O) 465.
1H NMR data (CDCl3, ppm, nJ(1H, 1H), 2J[119Sn, 1H] in Hz); 7.36 (s,
2H, aromatic protons), 7.16 (s, 2H, aromatic protons), 6.19 (s, 4H,
O–CH2–O), {1.94 (q, 4H, (8.1), [75]), 1.47 (t, 6H, (8.0), SnCH2CH3)}.
13C NMR data (CDCl3, ppm, nJ[119Sn, 13C] in Hz); 129.1 (C1),
108.8 (C2), 151.0 (C3), 149.6 (C4), 104.9 (C5), 143.4 (C6), 103.5
(C7), 174.4 (C8), {17.7 [580], 9.0 [43] (SnCH2CH3)}.
a
119Sn NMR data (CDCl3, ppm); ꢀ157.7.
2.3.3.1.4. Compound (4) [(n-Bu2SnL)2O]2ꢁCHCl3. Prepared by method
B by adding ligand acid (1 g, 4.74 mmol) and n-Bu2SnO (0.59 g,
2.37 mmol) in 2:1 ratio, respectively.
2.3.2. Synthesis of the ligand NaL
The sodium salt of the ligand acid was prepared by adding drop
wise an equimolar amount of sodium hydrogen carbonate dis-
solved in distilled water to the ligand acid dissolved in ethanol.
The clear solution obtained was concentrated under reduced pres-
sure. The solid obtained was dried over CaO/P2O5.
Physical data; Yield 65%, m.p. 196–198 °C, CHN Anal. Calc.: C,
38.77; H, 4.4; N, 2.74. Found: C, 38.02; H, 4.22; N, 2.62%.
FT-IR data (KBr, cmꢀ1);
t(COO)Asym 1609,
t(COO)sym 1420, Dt
189,
t
(Sn–O-Sn–O) 686,
t
(Sn–C) 563, (Sn–O) 445.
t
1H NMR data (CDCl3, ppm, nJ(1H, 1H), 2J[119Sn, 1H] in Hz); 7.3 (s,
4H, aromatic protons), 6.91 (s, 4H, aromatic protons), 6.15 (s, 8H,
O–CH2–O), {1.82 (t, 16H, (8), [73]), 1.51–1.38 (m, 32H), 0.91 (t,
24H, (7.4), SnCH2CH2CH2CH3)}.
2.3.3. Synthesis of organotin derivatives
2.3.3.1. General procedure. Two different methods have been em-
ployed for the synthesis of the organotin derivatives of the 6-nitro-
piperonylic acid. In method A the organotin chloride was refluxed
with sodium salt of the acid in dry toluene for 5–6 h in 1:2 (dior-
ganotin dichloride) or 1:1 (triorganotin chloride) molar ratio. After
reflux the insoluble material were filtered off and solvent was
evaporated under reduce pressure. The resultant solid masses were
recrystallized from chloroform and n-hexane mixture. In method B
appropriate R2SnO and ligand were refluxed for 6 h in 1:2 molar ra-
tios in dry toluene (100 mL) using Dean-stark apparatus for azeo-
tropic removal of water formed during the condensation
reaction. The reaction mixture was then cooled to room tempera-
ture and the solvent was rotary evaporated. The solid product
obtained was recrystallized from a mixture of chloroform and
n-hexane.
13C NMR data (CDCl3, ppm); 127.2 (C1), 107.8 (C2), 151.1 (C3),
148.8 (C4), 104.6 (C5), 142.3 (C6), 103.3 (C7), 170.2 (C8), {26.8,
27.4, 27.8, 13.7 (SnCH2CH2CH2CH3)}.
119Sn NMR data (CDCl3, ppm); ꢀ198.2, ꢀ199.8.
2.3.3.1.5. Compound (5) n-Oct2SnL2. Prepared by method B by add-
ing ligand acid (1 g, 4.74 mmol) and n-Oct2SnO (0.86 g, 2.37 mmol)
in 2:1 ratio, respectively.
Physical data; Yield 77%, m.p. 134–137 °C, CHN Anal. Calc.: C,
50.19; H, 5.49; N, 3.66. Found: C, 50.09; H, 5.40; N, 3.86%.
FT-IR data (KBr, cmꢀ1);
t
(COO)Asym 1619,
t(COO)sym 1427, Dt
192, t(Sn–C) 564, t(Sn–O) 480.
1H NMR data (CDCl3, ppm, nJ(1H, 1H) in Hz); 7.45 (s, 2H,
aromatic protons), 6.88 (s, 2H, aromatic protons), 6.04 (s, 4H,
O–CH2–O), {1.65–1.1 (m, 28H), 0.86 (t, 6H, (8), Sn CH2CH2CH2CH2-
CH2CH2CH2CH3)}.
2.3.3.1.1. Compound (1) Me2SnL2. Prepared by method A by adding
sodium salt of ligand (1 g, 4.29 mmol) and Me2SnCl2 (0.47 g,
2.15 mmol) in 2:1 ratio, respectively.
13C NMR data (CDCl3, ppm); 127.1 (C1), 107.9 (C2), 151.0 (C3),
148.8 (C4), 104.6 (C5), 142.4 (C6), 103.3 (C7), 170.2 (C8), {25.3,
22.7, 34.1, 29.5, 29.4, 32.0, 25.5, 14.1, (SnCH2CH2CH2CH2-
CH2CH2CH2CH3)}.
Physical data; Yield 82%, m.p. 229–231 °C, CHN Anal. Calc.: C,
37.96; H, 2.46; N, 4.92. Found: C, 38.06; H, 2.51; N, 4.86%.
FT-IR data (KBr, cmꢀ1);
t
(COO)Asym 1602,
t(COO)sym 1412, Dt
190,
t
(Sn–C) 577,
t
(Sn–O) 445.
119Sn NMR data (CDCl3, ppm); ꢀ199.1.

M. Hanif et al. / Polyhedron 29 (2010) 613–619
615
2.3.3.1.6. Compound (6) Ph3SnL. Prepared by method B by adding
ligand acid (1 g, 4.74 mmol) and Ph3SnOH (1.74 g, 4.74 mmol) in
1:1 ratio, respectively.
was added to the 75 mL of nutrient agar medium at 45 °C, mixed
well, and then poured into a 14 cm sterile petri plate. The media
was allowed to solidify, and 8 mm wells were dug with a sterile
Physical data; Yield 83%, m.p. >300 °C, CHN Anal. Calc.: C, 55.71;
H, 3.4; N, 2.50. Found: C, 55.63; H, 3.28; N, 2.51%.
metallic borer. Then a DMSO solution of test sample (100 lL) at
1 mg/mL was added to the respective wells. DMSO served as neg-
ative control, and the standard antibacterial drugs Roxyithromycin
(1 mg/mL) and Cefixime (1 mg/mL) were used as positive control.
Triplicate plate of each bacterial strain was prepared. The plates
were incubated aerobically at 37 °C for 24 h. The activity was
determined by measuring the diameter of zone showing complete
inhibition (mm). Thereby zones were precisely measured with the
aid of a vernier caliper (precision 0.1 mm). The growth inhibition
was calculated with reference to the positive control. For individ-
ual compounds that showed inhibition >10 mm, MIC values were
determined by using agar well-diffusion method [21].
FT-IR data (KBr, cmꢀ1);
t(COO)Asym 1608, t(COO)sym 1413, Dt
195, t(Sn–O) 449.
1H NMR data (CDCl3, ppm); {7.73–7.49 (m, 15H, SnPh)}, 7.31 (s,
1H, aromatic protons), 7.26 (s, 1H, aromatic protons), 6.27 (s, 2H,
O–CH2–O).
13C NMR data (CDCl3, ppm); 128.9 (C1), 109.2 (C2), 150.6 (C3),
149.4 (C4), 104.6 (C5), 137.5 (C6), 103.3 (C7), 173.1 (C8), {129.6,
136.9, 130.4, 129.3, (SnPh)}.
119Sn NMR data (CDCl3, ppm); ꢀ125.1.
2.4. X-ray crystallography
2.5.2. Antifungal assay
All X-ray crystallographic data were collected on a Stoe Imaging
Plate Diffractometer System. Correction for semi-empirical from
equivalents was applied, and the structure was solved by direct
methods and refined by a full-matrix least squares procedure
based on F2 using the SHELXS-97 and SHELXL-97 Program System
[20]. All data were collected with graphite-monochromated Mo
Antifungal activity against six fungal strains [Fusarium monili-
formis, Alternaria specie, Aspergillus niger, Fusarium solani, Mucor
specie and Aspergillus fumigatus] was determined by using Agar
tube dilution method [21]. Screw caped test tubes containing Sab-
ouraud dextrose agar (SDA) medium (4 mL) were autoclaved at
121 °C for 15 min. Tubes were allowed to cool at 50 °C and non
Ka radiation (k = 0.71073 Å) at 173 K. Table 1 present the crystallo-
graphic data for the compound 4.
solidified SDA was loaded with 66.6
stock solution (12 mg/mL in DMSO) to make 200
l
L of compound from the
lL/mL final con-
centration. Tubes were then allowed to solidify in slanting position
at room temperature. Each tube was inoculated with 4 mm diam-
eter piece of inoculum from seven days old fungal culture. The
2.5. Biological activity
2.5.1. Antibacterial assay
media supplemented with DMSO and Turbinafine (200 lL/mL)
All these synthesized compounds and their acid were tested
against six bacterial strains; three Gram-Positive [Bacillus subtilis
(ATCC6633), Micrococcus luteus (ATCC10240) and Staphylococcus
aureus (ATCC6538)] and three Gram-negative [Escherichia coli
(ATCC15224), Enterobactor aerogenes (ATCC13048), Bordetella bron-
chiseptica (ATCC4617)]. The agar well-diffusion method was used
for the determination of inhibition zones and minimum inhibitory
concentration (MIC) [21]. Briefly 0.75 mL of the broth culture con-
taining ca. 106 colony forming units (CFU) per mL of the test strain
were used as negative and positive control, respectively. The tubes
were incubated at 28 °C for 7 days and growth was determined by
measuring linear growth (mm) and growth inhibition was calcu-
lated with reference to the negative control.
2.5.3. Cytotoxicity
The cytotoxicity was studied by the brine-shrimp lethality as-
say method [21,22]. Brine-shrimp (Artemia salina) eggs were
hatched in artificial sea water (3.8 g sea salt/L) at room tempera-
ture (22–29 °C). After two days these shrimps were transferred
to vials containing 5 mL of artificial sea water (30 shrimps per vial)
with 10 100 and 1000 ppm final concentrations of each compound
taken from their stock solutions of 12 mg/mL in DMSO. After 24 h
number of surviving shrimps was counted. Data was analyzed with
a finny computer programme (Probit analysis) to determine LD50
values.
Table 1
Crystal Data and structure refinements for compound 4.
Compound 4
Empirical formula
Formula weight
Crystal shape (color)
Crystal system
C32H44N2O13Sn2ꢁCHCl3
1021.44
block (yellow)
triclinic
ꢀ
Space group
P1
Unit cell dimension
2.5.4. Antitumor activity
0
12.3636(14)
13.0105(16)
13.4017(15)
a(AÅ)
Antitumor Potato Disc Assay [21] was also performed for all
these synthesized compounds. Potato discs (0.5 cm thickness)
were obtained from surface sterilized potatoes by using metallic
cork borer and special cutter under complete aseptic conditions.
These potato discs were then transferred Petri plates each contain-
ing 25 mL of 1.5% agar solution. Then 0.5 mL of stock (10 mg/mL) of
the test sample was added to 2 mL of a broth culture of Agrobacte-
rium tumefaciens (At10, a 48 h culture containing 5 ꢂ 109 cells/mL)
and 2.5 mL of autoclaved distilled water was added to make
1000 ppm concentration. One drop of these cultures was poured
on each potato disc. The petri plates were incubated at 28 °C. After
21 days incubation, the number of tumors was counted with the
aid of dissecting microscope after staining with Lugol’s solution.
0
b (ÅA)
0
c (AÅ)
a
(°)
90.164(14)
98.435(13)
100.292(14)
2097.2(4)
b (°)
c
(°)
0
3
V (AÅ
)
Z
2
Dcalc (g cmꢀ3
)
1.618
Crystal size (mm)
F(0 0 0)
Total reflections
Independent reflections
Observed reflections
All indices (all data)
0.50 ꢂ 0.50 ꢂ 0.50
1024
15 415
7458
6084
R1 = 0.0672
wR2 = 0.1802
R1 = 0.0818
wR2 = 0.1984
1.054
Final R indices [I > 2r(I)]
3. Result and discussion
Goodness-of-fit
h Range for data collection (°)
The synthesis of organotin derivatives of 6-nitropiperonylic acid
may be represented by the following equations:
2.4–25.8

616
M. Hanif et al. / Polyhedron 29 (2010) 613–619
sharp singlet with 2J[119Sn,1H] coupling of 79 and 57 Hz, respec-
R3SnCl þ NaL ! R3SnL þ NaCl
R¼Með2Þ
tively. The protons of SnCH2CH3 group in 3 appear at 1.94 and
1.47 ppm with distinct quartet and triplet, respectively. Both
methylene and methyl protons show well resolved 3J[1H,1H] cou-
plings and methylene protons show 2J[119Sn,1H] coupling of
75 Hz. In complex 4 the protons of n-butyl group show complex
pattern due to –CH2–CH2– skeleton in the range 1.38–1.51 ppm
and clear triplet for Sn–CH2 (at 1.82 ppm) and terminal CH3 (at
0.91 ppm) with 2J[119Sn,1H] and 3J[1H,1H] couplings. The methy-
lene protons (CH2)7 n-octyl moiety of 5 exhibit a somewhat differ-
ent behavior and appear as broad signals in the range 1.1–
1.65 ppm comparable with analogues compounds [14]. However,
terminal CH3 protons give a triplet at 0.86 ppm with 3J[1H,1H] cou-
pling of 8 Hz. A complex pattern for aromatic protons in case of tri-
phenyltin 6 has also been observed in the expected region.
R2SnCl2 þ 2NaL ! R2SnL2 þ 2NaCl
R¼Með1Þ;Etð3Þ
R2SnO þ 2LH ! R2SnL2 þ H2O
R¼Octð5Þ
R3SnOH þ LH ! R3SnL þ H2O
R¼Phð6Þ
In an attempt to prepare diorganotin dicarboxylate with general
formula Bu2SnL2, only the compound {[(LSnBu2]2O}2 4 was isolated
after recrystallization as evident by the observed two 119Sn NMR
resonances of almost equal intensity and X-ray crystal structure.
Apparently, either only one equivalent of acid can be consumed
or the diorganotin dicarboxylates formed can undergo a hydrolysis
to yield the dimeric distannoxanes as shown below [23].
13C NMR spectral data for ligand acid and its organotin(IV) deriv-
atives are listed along their synthesis in the experimental section.
The assignment of 13C signals for ligand and its organotin deriva-
tives are assigned by comparison with related compounds, by re-
sults obtained from incremental methods and by nJ[119Sn,13C]
couplings [26]. The chemical shift of carboxylate carbon shifts to
a lower field region in almost all the organotin(IV) derivatives indi-
cating participation of the carboxyl (COO) group in coordination to
tin atom [14]. The chemical shift of the methylene and aromatic
carbons undergo minor variation in the complexes, as compare to
those observed in the free acid. The organic moiety attached to
tin atom display the expected carbon signals [27]. In addition
nJ[119Sn,13C] couplings are also observed in some complexes.
nJ[119Sn,13C] satellites are important indicators for structural evalu-
ation of organotin carboxylates. Holecek and coworkers have
shown that for four coordinated trialkyltin and triphenyltin com-
pounds, the coupling constants 1J[119Sn,13C] occur in the range of
325–400 and 550–670 Hz, respectively, while five coordinated tin
compounds exhibit couplings in the range of 440–540 and 750–
850 Hz, respectively. In the present investigation the trimethyltin
2 compound show tin-carbon satellite of 400 Hz in solution (CDCl3),
characteristic of the tetrahedral geometry around tin atom. Thus
bidentate nature of the ligand acid resulting in penta-coordination
in solid state (FT-IR) is therefore lost in solution to generate a mono-
mer four coordinated tetrahedral structure for 2 [28]. Unfortunately
we are not able to record the tin–carbon satellite for triphenyltin
derivative. In diorganotin compounds, 1J[119Sn,13C] satellites are
observed for diethyltin 3 compound, which suggest coordination
number higher than four in comparison with the reported values
[29]. However, it is not defined with certainty because of the flux-
ional behavior of the carboxylate oxygen in their coordination with
the tin atom but most of alkyl diorganotin(IV) carboxylates appear
as skew trapezoidal geometry which is in between five and six coor-
dination numbers [30]. We emphasized, therefore, on the 119Sn
NMR (see synthesis part in Section 2) in order to deduce the coordi-
nation of tin atom in diorganotin compounds as well as triorganotin
compounds. Compounds 1, 3 and 5 exhibit a single 119Sn chemical
shift at ꢀ172.0, 157.7 and ꢀ199.1 ppm, respectively, characteristic
of penta-coordinated tin atom as earlier reports manifested [14–
18]. On the other hand trimethyltin 2 give a single resonance peak
in the range characteristic for tetrahedral compounds. Triphenyltin
6 show 119Sn chemical shift at ꢀ125.1 ppm which is very close to
the reported four coordinated triphenyltin compounds and less
than the maximum value of ꢀ128.1 ppm for four coordinated tetra-
phenyltin compound [27]. For compound 4 two 119Sn resonances of
almost equal intensities are observed (ꢀ198.2 and ꢀ199.8 ppm)
and assigned to the five coordinated endocyclic and exocyclic tin
atoms. These values are in agreement with the literature values re-
ports for similar distannoxanes [23,31].
4Bu2SnO þ 4LH ! fðBu2SnLÞ2Og2 þ2H2O
ð4Þ
4Bu2SnL2 þ 2H2O ! fðBu2SnLÞ2Og2 þ4LH
ð4Þ
All the newly synthesized compounds are air stable, crystalline sol-
ids and soluble in common organic solvents. These newly synthe-
sized compounds were characterized by FT-IR, and multinuclear
NMR (1H, 13C and 119Sn) spectroscopy. Further single crystal X-ray
structure of compound 4 is also determined.
3.1. Infrared spectroscopy
The absorption frequencies of interest are
(Sn–O). The absence of a broad band in the range 3100–
2500 cmꢀ1 appearing in the ligand acid, as
(OH) vibrations, indi-
t(COO), t(Sn–C) and
t
t
cating metal–ligand bond formation through this site. Similarly,
absorption bands in the range 577–545 and 485–445 cmꢀ1, as-
signed to Sn–C and Sn–O bonds, respectively, also support the for-
mation of complexes [24]. Bands due to nitro group are also
observed in the complexes at the same frequencies as observed
in the free ligand, indicating that nitro group is not coordinated
to tin(IV). The shift in
compare to ligand acid and magnitude of
t
(COO) vibrations to lower frequencies as
(COO) in the range
D
t
of 189–200 cmꢀ1 indicating a bidentate nature of the carboxylate
towards the Sn atom [25]. Thus according to the earlier reports fea-
turing the same results and crystallographic data [14,18], it is most
likely that in diorganotin(IV) compounds, the tin atom approaches
six coordination based on skew trapezoidal planar geometry and
the carboxylate group acts as chelating bidentate ligand while in
triorganotin(IV) compounds, the tin atom approaches five coordi-
nation and carboxylate group acts as bridiging bidentate ligand
leading to trigonal bipyramidal with trans-R3SnO2 geometry [25].
The IR spectrum of compound 4 is almost similar to diorganotin
compounds except for a very sharp band at 686 cmꢀ1, characteris-
tic for Sn–O–Sn–O four-membered rings as dimeric dicarboxyla-
totetraorgano distannoxane [23].
3.2. Multinuclear (1H, 13C, 119Sn) NMR spectroscopy
Multinuclear NMR spectra (1H, 13C, 119Sn) for new compounds
and free acid have been recorded in CDCl3 and DMSO-d6 solution,
respectively, and are given in experimental part along the synthe-
sis of compounds. The single resonance at 10 ppm due to carbox-
ylic acid proton is absent in the 1H NMR spectra of the
complexes indicating the replacement of the carboxylic acid pro-
ton with organotin(IV) moieties. In the spectrum of ligand acid
the methylenedioxy protons (O–CH2–O) at 6.33 ppm and aromatic
protons at 7.37 and 7.66 ppm are appeared as singlet and a set of
similar pattern has been observed in the complexes. The methyl
protons in dimethyltin 1 and trimethyltin 2 derivatives appear as
Various literature methods have been applied to calculate C–
Sn–C bond angles in solution, based on 2J[119Sn,1H] and

M. Hanif et al. / Polyhedron 29 (2010) 613–619
617
1J[119Sn,13C] coupling constants [32,33]. By the use of Lockhart and
Table 2
Selected bond lengths (Å) and bond angles (°) for compound 4.a
Holecek equations, the values obtained are 111.8° and 127.6° for
compounds 2 and 3, respectively on the basis of 1J[119Sn,13C] cou-
plings. The geometrical data calculated are consistent with tetrahe-
dral and skew trapezoidal geometry, respectively, for tri- and
diorganotin compounds.
Bond lengths (Å)
C(1)–O(2)
C(9)–O(8)
C(17)–Sn(1)
C(25)–Sn(2)
O(1)–Sn(1)
O(8)–Sn(2)
O(13)–Sn(2)
O(13)i–Sn(2)
1.218(11)
1.242(10)
2.143(9)
2.121(9)
2.190(5)
2.287(6)
2.046(5)
2.155(5)
C(1)–O(1)
C(9)–O(7)
1.321(10)
1.272(10)
2.116(9)
2.125(8)
2.286(6)
2.038(5)
2.155(5)
C(21)–Sn(1)
C(29)–Sn(2)
O(7)–Sn(1)
O(13)–Sn(1)
O(13)–Sn(2)i
3.3. Crystal structure of 4
The molecular structure of 4 is shown in Fig. 2 and selected
interatomic parameters are given in Table 2. The compound 4 is
crystallized with a solvent molecule of CHCl3 which is disordered
over two orientations with site occupancy ratio of 0.5:0.5. The
structure of 4 is composed of a tetranuclear centrosymmetric di-
mer of oxoditin unit with a central four-membered ring defined
by Sn(2)–O(13)–Sn(2)i–O(13)i (i symmetry transformations used
to generate equivalent atoms: ꢀx, ꢀy + 1, ꢀz). This central Sn2O2
core is fused with two four-membered (Sn2O2, i.e., O(13)–Sn(1)–
O(1)–Sn(2)i) and two six-membered (Sn2O3C, i.e., Sn(1)–O(13)–
Sn(2)–O(8)–C(9)–O(7)) rings. The each endocyclic Sn(2) atom of
the central Sn2O2 core is six coordinated in C2SnO4 skew trapezoi-
dal bipyramidal geometry, wherein Sn(2) is coordinated to O(8) of
bidentate ligand acid anion bridging endocyclic Sn(2) with exocy-
Bond angles (°)
O(2)–C(1)–O(1)
123.7(7)
114.3(3)
136.5(4)
96.5(3)
91.0(2)
87.6(3)
103.9(4)
144.9(4)
99.7(3)
89.8(2)
84.6(3)
134.8(2)
104.3(2)
O(8)–C(9)–O(7)
126.5(7)
108.7(3)
77.78(19)
98.8(3)
O(13)–Sn(1)–C(21)
C(21)–Sn(1)–C(17)
C(21)–Sn(1)–O(1)
O(13)–Sn(1)–O(7)
C(17)–Sn(1)–O(7)
O(13)–Sn(2)–C(25)
C(25)–Sn(2)–C(29)
C(25)–Sn(2)–O(13)i
O(13)–Sn(2)–O(8)
C(29)–Sn(2)–O(8)
Sn(1)–O(13)–Sn(2)
Sn(2)–O(13)–Sn(2)i
O(13)–Sn(1)–C(17)
O(13)–Sn(1)–O(1)
C(17)–Sn(1)–O(1)
C(21)–Sn(1)–O(7)
O(1)–Sn(1)–O(7)
O(13)–Sn(2)–C(29)
O(13)–Sn(2)–O(13)i
C(29)–Sn(2)–O(13)i
C(25)–Sn(2)–O(8)
O(13)i–Sn(2)–O(8)
Sn(1)–O(13)–Sn(2)i
85.3(3)
168.4(2)
110.4(3)
75.7(2)
95.8(3)
88.3(3)
164.7(2)
120.3(2)
a
Symmetry transformations used to generate equivalent atoms: i ꢀx, ꢀy + 1, ꢀz.
clic Sn(1) through O(8)–C(9)–O(7), two a-carbon atoms of n-butyl
groups and O(1) of monodenate ligand acid also bridging Sn(1)
forming four-membered ring. The bidentate bridging ligand forms
almost equivalent interactions with tin, i.e., Sn(2)–O(8) = 2.287(6)
and Sn(1)–O(7) = 2.286(6) Å. The other endocyclic Sn–O distances
in the Sn2O2 core, Sn(2)–O(13) = 2.046(5) and Sn(2)–
O(13)i = 2.155(5) Å, are quite close to other related compounds
[34]. The sixth position of the skew trapezoidal geometry is
occupied by Sn(2)–O(1) bond with Sn–O distance Sn(2)–
O(1) = 2.722(6) Å. This indicates a quite long and weaker Sn–O
interaction. This longer Sn–O bond is much longer than the sum
of the covalent radii of the tin and oxygen (2.13 Å) but significantly
below the sum of the van der Waal’s radii of these atoms (3.68 Å)
[14].
intramolecular Sn–O contacts in the range of 2.61–3.02 Å have
been confidently reported for intramolecular Sn–O bonding. In this
case, the O(1) acts as monoatomic bridging atom (l2) and connect
the endocyclic and exocyclic tin centers thus making endocyclic
Sn(2) six coordinated [37]. However the distance Sn(1)–
O(2) = 3.020(6) Å is considered to be very weak intramolecular
interaction when compare to Sn(2)–O(1) distance and could not
be considered for any coordination with Sn(1) [9]. The axial C–
Sn–C angle, C(25)–Sn(2)–C(29) = 144.9(4)° is distorted from ideal
value of 180° by nearly 35° so as to better occupy the open space
left by the skew trapezoidal arrangement of the equatorial ligands
[37].
The exocyclic Sn(1) atoms are five coordinated and show dis-
torted trigonal bipyramidal geometry. Sn(1) atom is coordinated
with O(7) of bidentate briding ligand anion, O(1) of monatomic
It is worth noted that some reports do not consider such long
interactions as significant bonding contacts [35,36]. However, such
briding ligand, O(13) of central Sn2O2 core and two a-carbon atoms
of n-butyl groups. The axial C–Sn–C angle, C(17)–Sn(2)–
C(21) = 136.5(4)°.
The Sn–C distances, which are almost identical, lie within the
narrow range of 2.116(9)–2.143(9) Å and are in agreement with
the values reported for related structures [9]. It is interesting to
note that one of the ligand acid is coordinated to both Sn atoms
with
C–O
distances,
C(9)–O(7) = 1.272(10)
and
C(9)–
O(8) = 1.242(10) Å, and lying between a single and double bond
representing a delocalized system. In other ligand the C–O dis-
tances, C(1)–O(1) = 1.321(10) and C(1)–O(2) = 1.218(11) Å, clearly
indicate a single and a double bond.
The ligand acid shows different modes of coordination with tin.
It acts as a monodentate bridging ligand, bridging the two exo and
endo Sn atoms via O(1) forming four-membered rings. The ligand
also bridges two Sn atoms in bidentate coordination mode via
O(7) and O(8) thus resulting in six-membered rings.
3.4. Biological activity
In vitro biocidal screening tests of synthesized organotin com-
pounds and their acid were carried out for antibacterial, antifungal,
cytotoxicity and antitumor activity. The antibacterial activity was
tested against six bacterial strains; three Gram-positive [S. aureus
(ATCC6538), B. subtilis (ATCC6633), M. luteus (ATCC10240)] and
three Gram-negative [E. aerogenes (ATCC13048), E. coli
Fig. 2. Molecular structure of compound 4. The displacement ellipsoids are drawn
at the 30% probability level. Atoms labeled with a superscript (i) are related to the
others by an inversion center (hydrogen atoms and solvent molecules have been
removed for clarity).

618
M. Hanif et al. / Polyhedron 29 (2010) 613–619
(ATCC15224) and B. bronchiseptica (ATCC4617)]. The agar well-dif-
fusion method [21] was used in these assays and each experiment
was performed in triplicate. Readings of the zone of inhibition rep-
resents the mean value of three readings with standard deviation
(STDEV), which are shown in Table 3. Roxyithromycin and Cefix-
ime were used as standard drugs in these assays. Criteria for activ-
ity is based on inhibition zone (mm); inhibition zone more than
12 mm shows significant activity, for 10–12 mm inhibition activity
is good, 7–9 mm is low, and below 7 mm is non-significant activity.
The antibacterial studies demonstrated that all complexes have
activity toward tested bacteria than their ligand acid which show
no activity [13,14]. The values obtained for activity for compounds
1–4 and 6 falls in criteria of significant activity except for com-
pound 5 which show low activity against two pathogenic strains,
S. aureus and M. luteus and non-significant activity against the rest
four pathogenic strains. Compound 6 (triphenyltin derivative) have
the highest activity among all synthesized compounds and compa-
rable with one of the reference drug Roxyithromycin. Compound 4
also show non-significant activity against B. subtilis.
cies, A. niger, F. solani, Mucor species and A. fumigatus] by using
Agar tube dilution method [21]. The results are shown in Table
4. Terbinafine was used as standard drug in this assay. Criteria
for activity is based on percent growth inhibition; more than
70% growth inhibition shows significant activity, 60–70% inhibi-
tion activity is good, 50–60% inhibition activity is moderate and
below 50% inhibition activity is non-significant. The investiga-
tion shows that all the synthesized organotin compounds in
general have more activity than the parent acid except few
cases but less than the reference drug Terbinafine. Compound
4 show 100% growth inhibition against F. moniliforme. Ligand
acid and compounds 1 and 5 show no activity against some
fungal strains.
The cytotoxicity was studied by the brine-shrimp bioassay
lethality method [21,22] and the results are summarized in Table
5. The LD50 data show that all the tested compounds even the li-
gand acid are toxic with LD50 values in the range 0–230.78
mL in comparison to reference drug MS-222 (Tricaine Methanesul-
fonate) with LD50 value 4.3 g/mL. Triphenyltin 6 and distannox-
lg/
l
All synthesized compounds were also subjected to antifungal
activity against six fungal strains [F. moniliforme, Alternaria spe-
ane 4 are the most toxic as compare to tested compounds and
ligand acid.
Table 3
Antibacterial activities of 6-nitropiperonylic acid and its organotin(IV) derivatives.a
Compound no.
Mean zone of inhibition (mm) SD
S. aureus
B. subtillus
M. luteus
E. aerogenase
E. coli
B. bronchiseptica
(ATCC6538)
(ATCC6633)
(ATCC10240)
(ATCC13048)
(ATCC5224)
(ATCC4617)
1
2
3
4
5
6
22.3 0.20
20.6 0.15
21.0 0.28
20.0 0.39
8.5 0.28
22.1 0.23
22.4 0.66
20.8 0.23
1.88 0.23
2.4 0.66
20.8 0.37
21.7 0.05
18.6 0.20
12.6 0.14
11.6 0.23
23.3 0.20
21.3 0.34
18.4 0.13
22.3 0.38
21.3 0.26
3.1 0.45
19.2 0.70
19.8 0.15
21.0 00
18.5 0.20
5.7 0.12
24.0 0.00
22.4 0.45
23.5 0.98
20.6 0.07
20.2 0.30
2.7 0.40
23.5 0.37
24.0 0.00
24.4 0.26
24.2 0.10
HL
0
0.00
0
0.00
0
0.00
0
0.00
0
0.00
0
0.00
Roxyithromycin 23.5 0.50
Cefixime 27.2 0.70
24.0 0.00
27.6 0.75
23.3 0.26
22.7 0.30
24.4 0.05
25.3 0.45
24.33 0.20
27.6 0.00
24.2 0.25
27.8 0.56
a
In vitro, agar well-diffusion method, concentration: 1 mg/mL of DMSO, reference drugs, Roxyithromycin and Cefixime, concentration: 1 mg/mL of DMSO.
Table 4
Antifungal activities of 6-nitropiperonylic acid and its organotin(IV) derivatives.a
Compound no.
Mean value of percent growth inhibition SD
F. moniliformis
A. specie
A. niger
F. solani
M. specie
A. fumigatus
1
2
3
4
5
6
HL
70.73 1.88
60.23 1.27
55.46 1.41
100 0.00
80.24 0.49
74.79 0.70
21.95 2.12
100 0.00
0
0.00
29.04 0.25
77.56 1.41
73.69 0.30
90.95 0.46
42.01 0.28
86.17 0.46
57.65 2.82
100 0.00
14.35 0.49
27.87 4.94
36.57 0.46
45.64 0.70
37.43 1.41
32.82 3.53
0
0.00
1.93 2.12
20.95 0.14
27.46 0.17
0.72 0.17
5.31 1.41
66.6 0.25
19.56 0.37
100 0.00
54.98 0.16
65.33 0.75
87.69 0.16
05.02 1.41
87.48 1.88
48.71 5.65
100 0.00
30.85 2.12
37.68 0.70
73.33 3.53
0
0.00
66.6 5.65
0.00
100 0.00
0
0.00
0
Terbinafine
100 0.00
a
In vitro, agar tube dilution method, concentration: 200 lg/mL of DMSO, percent inhibition (standard drug) = 100%, reference drug, Terbinafine.
Table 5
Cytotoxicity and antitumor activities of 6-nitropiperonylic acid and its organotin(IV) derivatives.a,b
Compound no.
LD50
(lg/mL)
Average number of tumors SE
% Inhibition of tumors
1
2
3
149.37
–
–
3.7 0.36
1.3 1.13
2.4 0.61
61.1
87.3
74.7
4
5
6
HL
0
0
0.00
3.0 0.51
0.00
9.3 0.69
100.0
51.6
100.0
31.5
75.47
0
230.78
0
a
In vitro, against brine-shrimps, reference drug MS-222 (Tricaine Methanesulfonate).
Potato disc antitumor assay, concentration: 1000 ppm in DMSO, more than 20% tumor inhibition is significant, data represents mean value of 15 replicates, reference
b
drug, Vincristine.

M. Hanif et al. / Polyhedron 29 (2010) 613–619
619
Organometallic Chemistry Research, Nova Science Publisher, USA, 2007, p. 139
(Chapter 6);
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Potato Disc Antitumor assay was also performed for all these
synthesized compounds by using Agrobacterium tumefaciens
(At10) [21] (Table 5). All the compounds showed significant level
of tumor inhibition in comparison to reference drug (Vincristine)
with 100% tumor inhibition, as shown in Table 5. Activity of the
synthesized organotin series was observed more than their parent
acid. Furthermore, compounds 4 and 6 showed 100% tumor
inhibition.
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Six new organotin compounds of 6-nitropiperonylic acid were
synthesized by reacting either sodium salt with organotin chlo-
rides or ligand acid with organotin oxides and were characterized
by FT-IR and 1H, 13C and 119Sn multinuclear NMR. Single crystal X-
ray analysis of compound 4 showed distannoxane with two types
of tin atoms. Endocyclic Sn is six coordinated with skew trapezoi-
dal bipyramidal geometry while exocyclic Sn is five coordinated
with distorted trigonal bipyramidal geometry. All the synthesized
organotin compounds revealed better in vitro biological activities
than their parent acid when screened for antibacterial, antifungal,
cytotoxicity and potato disc antitumor studies.
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M. Hanif is indebted to Pakistan Atomic Energy Commission
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Hussain highly acknowledge the financial grant from the Higher
Education Commission, Pakistan.
Appendix A. Supplementary data
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