Triorganotin(IV) complexes of pyruvic acid-N(4)-cyclohexylthiosemicarbazone (HPACT): Synthesis, characterization, crystal structure and in vitro antibacterial activity

Article abstract of DOI:10.1016/j.poly.2011.11.021

The reaction of triorganotin(IV) chloride with pyruvic acid-N(4)- cyclohexylthiosemicarbazone (HPACT) afforded the complexes [Bu ₃Sn(PACT)] (1) and [Ph₃Sn(PACT)] (2). The ligand HPACT and its two triorganotin(IV) complexes 1 and 2 ha

Full text of DOI:10.1016/j.poly.2011.11.021

Polyhedron 33 (2012) 19–24
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Triorganotin(IV) complexes of pyruvic acid-N(4)-cyclohexylthiosemicarbazone
(HPACT): Synthesis, characterization, crystal structure and in vitro
antibacterial activity
a
b
c
M.A. Affan a, M.A. Salam a, , Fasihuddin B. Ahmad , Ramli B. Hitam , Fraser White
⇑
a Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia
b Faculty of Science and Mathematics, Universiti Pendidikan Sultan Idris, 35900 Tanjong Malim, Perak, Malaysia
c Agilent Technologies UK Ltd., 10 Mead Road, Oxford Industrial Park, Yarnton OX5 1QU, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of triorganotin(IV) chloride with pyruvic acid-N(4)-cyclohexylthiosemicarbazone (HPACT)
afforded the complexes [Bu3Sn(PACT)] (1) and [Ph3Sn(PACT)] (2). The ligand HPACT and its two triorga-
notin(IV) complexes 1 and 2 have been characterized by elemental analyses, UV–Vis, FT-IR, 1H and 13C
NMR spectroscopy. The structure of the tributyltin(IV) complex 1 was also investigated by X-ray crystal-
lography. The crystal structure of complex 1 revealed that the ligand is coordinated to the tin(IV) moiety
as a uninegative monodentate ligand via the carboxylato-O atom. The tin(IV) atom exists in a distorted
tetrahedral geometry defined by three ipso-C atoms of the butyl groups and a carboxylato-O atom of
the ligand. The compound crystallizes into a monoclinic lattice with the space group P21. The ligand
and its triorganotin(IV) complexes 1 and 2 were assayed for in vitro antibacterial activity against two
Gram-positive bacterial strains (Bacillis subtilis and Staphylococcus aureus) and two Gram-negative bacte-
rial strains (Escherichia coli and Salmonella typhi). The screening results have shown that the triorgano-
tin(IV) complexes 1 and 2 have better antibacterial activity than the free ligand. Furthermore, it has
been shown that the triphenyltin(IV) derivative exhibits significantly better activities than the tributyl-
tin(IV) derivative.
Received 1 September 2011
Accepted 2 November 2011
Available online 25 November 2011
Keywords:
Triorganotin(IV) complexes
Pyruvic acid-N(4)-
cyclohexylthiosemicarbazone
Spectral analysis
Crystal structure
Antibacterial activity
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
chelate rings containing ONS-donor atoms. It was found that all
the compounds were highly active against MCF-7 and T-24 cancer
Thiosemicarbazones derivatives have recently attracted consid-
erable attention because of their potential biological (viz., antibac-
terial and antitumor) activities [1–3]. Organotin(IV) complexes
have been extensively studied owing to their structural diversity
and their beneficial biological activities (viz., antiviral and antitu-
mor) as well as their wide industrial and agricultural applications
[4–6]. For the past few years, a large amount of work on the syn-
thesis and chracterization of transition metal complexes with thio-
semicarbazones has been reported [7–10] but very little work has
been reported on tin(IV) complexes with substituted thiosemicar-
bazone ligands. In addition to their biological activities, the coordi-
nation chemistry of thiosemicarbazone complexes has been
studied to some extent; the reports include monomeric, dimeric
and trimeric structures [11–14]. Usually triorganotin(IV) com-
pounds display higher biological activity than their di and mono-
organotin(IV) analogues due to their ability to bind with proteins
[15,16]. Wiecek et al. [17] have reported organotin(IV) complexes
of pyruvic acid thiosemicarbazone which have five-membered
cell lines. Our research group has published the crystal structures
of pyruvic acid-N(4)-cyclohexylethiosemicarbazone and its mono
organotin(IV) complex [18,19]. In this complex, the pyruvic acid-
N(4)-cyclohexylethiosemicarbazone ligand acted in a dinegative
tridentate nature and coordinates to the tin(IV) atom through S,
O and imine N atoms, whereas in the present triorganotin(IV) com-
plexes, it functions as a uninegative monodentate ligand with oxy-
gen as the donor atom. This is probably due to the steric and
electronic effects of the bulky alkyl/aryl groups. Herein, we report
the synthesis, spectroscopic characterization, X-ray structure of
complex 1 and the biological studies of two triorganotin(IV) com-
plexes of a substituted thiosemicarbazone. The two triorgano-
tin(IV) complexes 1 and 2 showed greater antibacterial activity
than the free ligand, but this was lower than the reference drug.
2. Experimental
2.1. Materials and methods
⇑
All reagents were purchased from Fluka, Aldrich and JT Baker.
All solvents were purified according to standard procedures [20].
Corresponding author. Tel.: +60 82583042; fax: +60 82583160.
E-mail addresses: masalam20@yahoo.com, salambpx@yahoo.com (M.A. Salam).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.11.021

20
M.A. Affan et al. / Polyhedron 33 (2012) 19–24
UV–Vis spectra were recorded in CHCl3 solution with a Perkin El-
mer Lambda 25 UV–Vis spectrophotometer. Infrared spectra were
recorded on KBr discs using a Perkin Elmer Spectrum GX Fourier-
Transform spectrometer in the range 4000–370 cmÀ1 at room
temperature. 1H and 13C NMR spectra were recorded on a JEOL
500 MHz-NMR spectrophotometer relative to SiMe4 using CDCl3
as the solvent. CHN analyses were obtained with a Flash EA 1112
series CHN elemental analyzer. Molar conductivity measurements
were carried out with a Jenway 4510 conductivity meter using a
DMF solvent mode. The crystallographic data and structure refine-
ment parameters for complex 1 are given in Table 1. A colorless
block crystal of compound 1 was measured at 150 K on a CrysAlis-
silica gel. Yield: 0.68 g, 87%; M.p.: 188–190 °C; UV–Vis (CHCl3)
kmax/nm: 327; FT-IR (KBr disc, cmÀ1
max: 3322 (br, OH), 3197
)
m
(s, NH), 2922, 2851 (s, cyclohexyl), 1702 (m, C@O), 1619 (m,
C@N), 980 (m, N–N), 1249, 870 (w, C@S); 1H NMR (CDCl3) d:
12.21 (s, 1H, COOH), 9.49 (s, 1H, N2–H), 8.08 (d, 2H, 1H of N1–H,
1H of CyC6–H), 2.21 (s, 3H, N@C–CH3), 2.05–2.03 (m, 10H, CyC–
H), 1.8 (s, 1H, SH); 13C NMR (CDCl3) d: 180.01 (NH–C@S), 165.71
(COOH), 143.05 (C@N), 52.37–25.44 (cyclohexyl), 10.24 (CH3);
Anal. Calc. for C10H17N3O2S: C, 49.36; H, 7.04; N, 17.26. Found: C,
49.31; H, 7.01; N, 17.18%.
2.3. Synthesis of the complex [Bu3Sn(PACT)] (1)
pro CCD diffractometer with graphite monochromated CuKa radi-
ation (k = 1.5418 Å). The structure was solved by direct methods
using SHELXL-97 and refined by full-matrix least-squares refinement
on F2 using SHELXL-97. Positional and anisotropic atomic displace-
ment parameters were refined for all non-hydrogen atoms. Hydro-
gen atoms were placed in calculated positions.
HPACT (0.243 g, 1.0 mmol) was dissolved in absolute methanol
(10 mL) in a Schlenk round bottom flask under a nitrogen atmo-
sphere, then a 10 mL methanolic solution of tributyltin(IV) chloride
(0.325 g, 1.0 mmol) was added dropwise. The resulting reaction
mixture was refluxed for 6 h (Scheme 2) and cooled to room tem-
perature. The microcrystals that formed were filtered off, washed
with a small amount of cold methanol and dried in vacuo over silica
gel. Colourless crystals suitable for X-ray diffraction were obtained
by slow evaporation of a chloroform/methanol (1:1 ratio) solution
after 15 days at room temperature. Yield: 0.59 gÀ, 179%; M.p.: 206–
2.2. Synthesis of pyruvic acid-N(4)-cyclohexylthiosemicarbazone
(HPACT)
Cyclohexylisothiocyanate (1.41 g, 10 mmol) in 4 mL of ether
was added dropwise into 4 mL of an ether solution of hydrazine
hydrate (2 g, 40 mmol). The mixture was stirred vigorously for
5 h, then, 5 mL petroleum ether was added into the resulting solu-
tion and stirred for another 1 h. The white product, N(4)-cyclo-
hexylthiosemicarbazide, that formed was filtered off, washed
with a small amount of cold diethyl ether and dried. N(4)-Cyclo-
hexylthiosemicarbazide (0.51 g, 3 mmol) was dissolved in absolute
methanol (10 mL) and mixed with 10 mL of an absolute methano-
lic solution of pyruvic acid (0.261 g, 3 mmol). The resulting mix-
ture was refluxed for 4 h (Scheme 1) and cooled to room
temperature. White microcrystals were formed and filtered off.
The microcrystals were washed several times with small amounts
of cold methanol and subsequently with cold hexane. The micro-
crystals were recrystallised from methanol and dried in vacuo over
208 °C; molar conductance (DMF)
X
À1 cm2 mol : 11.3; UV–Vis
max: 3190 (s,
(CHCl3) kmax/nm: 328, 368; FT-IR (KBr disc, cmÀ1
)
m
NH), 2932, 2854 (s, cyclohexyl), 1674 [m, masy (COOÀ)], 1454 [m,
msym (COOÀ)], 1626 (m, C@N), 980 (m, N–N), 1250, 868 (w, C@S),
592 (w, Sn–C), 477 (w, Sn–O); 1H NMR (CDCl3) d: 9.50 (s, 1H,
N2–H), 8.05 (d, 2H, 1H of N1–H, 1H of CyC6–H), 2.24 (s, 3H,
N@C–CH3), 2.17–2.06 (m, 10H, CyC–H), 2.05–2.01 (t, 2H, Sn–
CH2–CH2–CH2–CH3), 1.68–1.61 (m, 2H Sn–CH2–CH2–CH2–CH3),
1.55–1.29 (m, 2H, Sn–CH2–CH2–CH2–CH3), 0.88–0.85 (t, 3H, Sn–
CH2–CH2–CH2–CH3); 13C NMR (CDCl3) d: 180.88 (NH–C@S),
172.52 (COOÀ), 143.42 (C@N), 52.11–32.32 (cyclohexyl), 11.98
(CH3), 27.33, 25.98, 23.24, 17.36 [1J (13C–119Sn): 386 Hz, Sn–Bu].
Anal. Calc. for C22H43N3O2SSn: C, 49.63; H, 8.14; N, 7.89. Found:
C, 49.58; H, 8.11; N, 7.85%.
The triphenyltin(IV) complex 2 was synthesized using a similar
procedure to 1 using triphenyltin(IV) chloride.
Table 1
Crystal data and structure refinement parameters for complex 1.
2.4. Synthesis of complex [Ph3Sn(PACT)] (2)
Compound
[Bu3Sn(PACT)] (1)
Yield: 0.51 g, 81%; M.p.: 218–220 °C; molar conductance
CCDC No.
Empirical formula
Formula weight
T (K)
828342
(DMF)
X
À1 cm2 molÀ1: 14.7; UV–Vis (CHCl3) kmax/nm: 328, 372;
C
44H86N6O4S2Sn2
FT-IR (KBr disc, cmÀ1
) mmax: 3114 (s, NH), 2935, 2859 (s, cyclo-
1064.75
150
1.5418
monoclinic
P21
hexyl), 1668 [m, masy (COOÀ)], 1458 [m, msym (COOÀ)], 1622 (m,
C@N), 987 (m, N–N), 1246, 865 (w, C@S), 593 (w, Sn–C), 482 (w,
Sn–O); 1H NMR (CDCl3) d: 10.17 (s, 1H, N2–H), 8.31 (d, 2H, 1H of
N1–H, 1H of CyC6–H), 7.82–7.80 (m, 15H of phenyl ring), 2.26 (s,
3H, N@C–CH3), 2.08–2.05 (m, 10H, CyC–H); 13C NMR (CDCl3) d:
180.32 (NH–C@S), 170.55 (COOÀ), 143.33 (C@N), 51.11–28.68
(cyclohexyl), 11.71 (CH3), 144.88, 143.56, 142.36, 138.36 [1J
k (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
9.2810(5)
20.1595(10)
14.0785(7)
90.00
94.259(5)
90.00
2626.8(2)
4
1.346
a
(°)
(
13C–119Sn): 661.5 Hz, Sn–Ph]. Anal. Calc. for C28H31N3O2SSn: C,
56.77; H, 5.28; N, 7.09. Found: C, 56.72; H, 5.25; N, 7.07%.
b (°)
c
(°)
V (Å3)
Z
2.5. Antibacterial test
Dcalc (mg/m3)
Radiation type k (Å)
F(000)
CuK
a
The synthesized ligand (HPACT) and its triorganotin(IV) com-
plexes 1 and 2 were screened in vitro for their antibacterial activity
against two Gram-positive (Bacillis subtilis and Staphylococcus
aureus) and two Gram-negative (Escherichia coli and Salmonella ty-
phi) bacterial strains using the agar-well diffusion method [21].
Wells (of the size 6 mm in diameter) were dug in the media with
the help of a sterile metallic borer, with centers at least 24 mm
apart. Eight hours old bacterial inoculums containing 104–106 col-
ony forming units (CFU)/mL were spread on the surface of the
1112
Crystal size (mm)
Crystal colour
Scan range h (°)
Absorption coefficient (
0.3388 Â 0.1833 Â 0.1322
colourless
3.84–74.82
8.634
0.459 and 0.197
1.045
6889/7/526
l
) (mmÀ1
)
Maximum and minimum transmission
Goodness-of-fit (GOF) on F2
Data/restrains/parameters
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0504, wR2 = 0.1313
R1 = 0.0549, wR2 = 0.1345

M.A. Affan et al. / Polyhedron 33 (2012) 19–24
21
Scheme 1. Synthesis of the pyruvic acid-N(4)-cyclohexylthiosemicarbazone (HPACT) ligand.
Scheme 2. Synthesis of the triorganotin(IV) complexes 1 and 2.
nutrient agar using a sterile cotton swab. The recommended con-
centration of the test sample (200 mg/mL in DMSO) was intro-
duced in the respective wells. Other wells supplemented with
DMSO and reference antibacterial drug (imipenem) served as neg-
ative and positive controls, respectively. The plates were incubated
immediately at 37 °C for 20 h. Activity was determined by measur-
ing the diameter of zones showing complete inhibition (mm).
Growth inhibition was calculated with reference to the positive
control.
properties and analytical data of HPACT and its triorganotin(IV)
complexes 1 and 2 are given in the experimental section. The
ligand and its complexes 1 and 2 are stable under a N2 atmosphere
and are soluble in CHCl3, CH2Cl2, DMF, DMSO and MeCN solvents,
and are insoluble in methanol, ethanol, hexane, pentane, THF and
ether. The molar conductance values of complexes 1 and 2 are
11.3 and 14.7
the complexes behave as non-electrolytes [22].
X
À1 cm2 molÀ1, respectively, which indicate that
3.1. UV–Vis spectra
3. Results and discussion
The UV–Vis spectra of the ligand HPACT and its triorganotin(IV)
Pyruvic acid-N(4)-cyclohexylthiosemicarbazone (HPACT) was
synthesized by the condensation reaction of pyruvic acid and 4-
cyclohexylthiosemicarbazide in absolute methanol in a 1:1 mole
ratio. It has two tautomers within the structure, existing as either
the thione or thiol tautomer (Scheme 1). The present triorgano-
tin(IV) complexes (1 and 2) were obtained by the direct reaction
of tributyltin(IV)/triphenyltin(IV) chloride and HPACT in absolute
methanol under a nitrogen atmosphere (Scheme 2). The physical
complexes 1 and 2 were carried out in CHCl3 solution
(10À4 mol LÀ1) at room temperature. The UV–Vis spectra of these
compounds are shown in Fig. 1. The UV–Vis spectrum of HAPCT
exhibits only one band at 327 nm, assigned to the HOMO/LUMO
transition. The HOMO orbital has a
p bonding character located
on the S@C–NH–cyclohexyl system; The LUMO orbital is a p⁄ orbi-
tal (antibonding) located on the S@C–N–N@C–Me system. After
complexation, complexes 1 and 2 showed two absorption bands

22
M.A. Affan et al. / Polyhedron 33 (2012) 19–24
in the regions 328–335 and 368–377 nm. The absorption bands
which appeared at 328–335 nm are due to an intra ligand transi-
tion. In the spectra of complexes 1 and 2, one new absorption band
appeared at 368–377 nm which is assigned to a ligand ? metal
(Sn) charge transfer (LMCT) band [23]. The shift of the HOMO/
LUMO band from HPACT to the tin(IV) complexes is a clear indica-
tion that coordination occurred between tin(IV) and the ligand
HPACT.
found at similar positions to the ligand absorption bands, indicat-
ing the azomethine nitrogen and thione sulfur atoms are not coor-
dinate to the tin(IV) moiety. The information obtained from the
infrared spectra of complexes 1 and 2 supports the X-ray data of
complex 1.
3.3. 1H and 13C NMR spectra
The characteristic resonance peaks in the 1H and 13C NMR spec-
tra of the ligand and its triorganotin(IV) complexes 1 and 2 were
recorded in CDCl3 and interpreted based on the atomic labelling
in Scheme 2. The 1H NMR spectrum of the free ligand showed a sin-
glet at 12.21 ppm, corresponding to the resonance signal of COOH.
The resonance signal at 9.49 ppm is assigned to the N2–H proton. A
doublet at 8.08 ppm corresponded to N1–H, which overlaps with
CyC6–H. The resonance signal at 2.21 ppm is due to N@C–CH3.
The OH proton signal was absent in the spectra of complexes 1
and 2, indicating the deprotonation of the carboxylic proton and
coordination to the tin(IV) atom. The chemical shift of the N2–H
proton was observed at 9.50 and 10.17 ppm for complexes 1 and
2. The N1–H proton signals, which overlap with proton signal of
CyC6–H for complexes 1 and 2, were observed at 8.05 and
8.31 ppm, respectively. The resonance signal of the phenyl protons
in complex 2 appeared as a multiplet at about 7.80–7.82 ppm. The
azomethine proton (N@C–CH3) signal appears at 2.21 ppm in the
free ligand, and at 2.24–2.26 ppm in complexes 1 and 2. These
peaks are slightly downfield shifted in the complexes, which might
be due to electron delocalization through the S@C–NH–N@C–Me
system. The three butyl groups attached to the tin(IV) moiety in
complex 1 gave four resonance signals, namely 2.05–2.01 (triplet,
Sn–CH2–CH2–CH2–CH3), 1.68–1.61 (multiplet, Sn–CH2–CH2–
CH2–CH3), 1.55–1.29 (multiplet, Sn–CH2–CH2–CH2–CH3) and
0.88–0.85 ppm (triplet, Sn–CH2–CH2–CH2–CH3). The 1H NMR infor-
mation also support the IR data of complexes 1 and 2.
3.2. IR spectra
In its IR spectrum, HPACT displayed absorption bands at 3322
and 3197 cm-1 attributed to the OH group and the NH moiety
linked to the cyclohexyl group, respectively. The other absorption
bands observed in the spectrum at 2922 and 2851, 1702, 1619,
980, 1249 and 873 cmÀ1 are due to
(C@N), (N–N) and
absorption frequencies, e.g.,
m
(cyclohexyl),
(C@S), respectively. The characteristics
(C@O) and (Sn–O), provide valuable
m(C@O),
m
m
m
m
m
information about the formation of tin(IV) complexes and the coor-
dination mode of the ligand. The assignment of IR bands of these
triorganotin(IV) derivatives have been determined by a compari-
son with the IR spectrum of the free ligand. The free ligand shows
a broad OH absorption band at 3322 cmÀ1, which is absent in the
spectra of complexes 1 and 2, suggesting that the ligand is coordi-
nated to the tin(IV) atom through the carboxylate oxygen after
deprotonation of OH. A new absorption band at 477–482 cmÀ1 is
assigned to the stretching mode of the Sn–O linkage, indicating
the formation of a complex, and this value is comparable with
the published literature [24]. The m(C@O) band of the COOH group
is observed at 1702 cmÀ1 in the infrared spectrum of the free li-
gand, and is absent in the IR spectra of complexes 1 and 2. In the
IR spectra of complexes 1 and 2, two new absorption bands were
observed at 1668–1674 and 1454–1458 cmÀ1, which are attribut-
able to
m
asy(COOÀ) and
m
sym(COOÀ), respectively. The magnitude
of
D
[
m
asy(COOÀ)–
m
sym(COOÀ)] is 220 and 210 cmÀ1 for complexes
The 13C NMR peaks in the free ligand were observed at 180.01,
165.71, 143.05, 52.07–25.44 and 10.24 ppm due to the d(NH–C@S),
d(COOH), d(C@N), d(cyclohexyl ring) and d(CH3), respectively. After
complexation, the position of the carboxylate carbon moved to the
lower field region compared to the free ligand, being at 172.52–
170.55 ppm for complexes 1 and 2, indicating coordination of the
carboxylate group to the tin(IV) atom [26]. The chemical shifts of
1 and 2, respectively, and this can be used to determine the type
of bonding between the tin(IV) centre and the carboxyl group. This
information also indicates that the carboxylate group is monoden-
tate [25]. The absorptions at 592 and 593 cmÀ1 in the spectra of
complexes 1 and 2 are assigned to the band characteristic for
m(Sn–C). The m(NH), m(C@N) and m(C@S) absorption bands were
Fig. 1. UV–Vis absorption spectra of the HPACT ligand and its triorganotin(IV) complexes (1 and 2).

M.A. Affan et al. / Polyhedron 33 (2012) 19–24
23
Table 2
d(NH–C@S), d(cyclohexyl ring) and d(CH3) does not shift signifi-
Selected bond lengths (Å) and angles (°) of [Bu3Sn(PACT)] (1).
cantly in complexes 1 and 2 as compared to the free ligand. The
coupling constant, 1J[119Sn, 13C] is one of the key parameters in
assessing the possible coordination geometries of organotin(IV)
compounds in solution. For the tributyltin(IV) (1) and triphenyl-
tin(IV) (2) compounds, the coupling constants were found to be
386 and 661.5 Hz, respectively, which corresponds to a tetrahedral
geometry in CDCl3 solution [26,27].
Bond lengths (Å)
Sn1–O1A
Sn1–C1C
Sn1–C1D
Sn1–C1B
S9A–C8A
C3D–C2D
C3D–C4D
O1A–C2A
2.131(7)
2.154(9)
2.153(11)
2.121(10)
1.695(9)
1.541(13)
1.523(18)
1.290(11)
O3A–C2A
N6A–C4A
N6A–N7A
C4A–C2A
C4A–C5A
C8A–N10A
C8A–N7A
N10A–C11A
1.245(12)
1.298(12)
1.375(11)
1.504(14)
1.494(13)
1.311(13)
1.372(12)
1.478(11)
Bond angles (°)
O1A–Sn1–C1C
O1A–Sn1–C1D
O1A–Sn1–C1B
C1D–Sn1–C1C
C1B–Sn1–C1C
C5A–C4A–C2A
O1A–C2A–C4A
O3A–C2A–O1A
O3A–C2A–C4A
3.4. X-ray crystallography diffraction analyses
92.8(3)
100.8(4)
95.9(3)
116.2(4)
116.7(4)
118.7(8)
114.5(9)
124.1(9)
121.4(8)
C1B–Sn1–C1D
C2A–O1A–Sn1
C4A–N6A–N7A
N6A–CV4A–C2A
N6A–C4A–C5A
N10A–C8A–S9A
N10A–C8A–N7A
N7A–C8A–S9A
C8A–N10A–C11A
123.2(4)
123.0(7)
118.7(8)
124.7(9)
116.6(9)
124.5(7)
117.2(8)
118(7)
The molecular structure of complex 1 with the atomic number-
ing scheme is depicted in Fig. 2. The main crystal parameters are
reported in Table 1. Selected bond lengths and bond angles are
given in Table 2. The compound crystallizes with two molecules
per asymmetric unit into the monoclinic crystal system with a
space group of P21. From Table 2 it is clear that the two molecules
in the asymmetric unit are almost identical. So the discussion can
be limited to one of the molecules. In one of the molecules a butyl
chain was disordered. This was modelled as two parts with a 60:40
occupancy ratio. The atoms involved were refined isotropically as
the data did not support anisotropic refinement. The solid state
structure of the reported complex 1 showed that the monodeprot-
onated ligand is coordinated to the tin(IV) atom via the carboxy-
lato-O atom. Thus, the coordination geometry about the tin atom
is best described as distorted tetrahedral with one O atom and
three C atoms which exhibit an R3SnO geometry. The bond lengths
O1A–C2A and O3A–C2A are 1.290(11) and 1.245(12) Å, respec-
tively, which specify delocalized bonding at the carboxylic group,
indicating the longer separation being associated with the stronger
Sn–O1A interaction [28]. The Sn1–O1A bond distance is 2.139 Å,
which is close to the sum of the covalent radii of tin and oxygen
(2.10 Å), but is considerably less than the van der Waals radii
(2.8 Å), indicating a strong Sn–O bonding interaction. The metal-
oxygen bond distance (Sn–O) is similar to other organotin(IV)
complexes presented in the literature [29–31]. The most significant
differences in the geometric parameters about the tin atom were
found in the O–Sn–C and C–Sn–C angles. The major distortion from
an ideal tetrahedral configuration is shown by the O1A–Sn1–C1C
angle of 92.8(3)°. However it is noteworthy that the C1D–Sn1–
C1B angle of 123.2(4)° is the next major distortion from the ideal
geometry. This distortion is probably due to the bulky butyl groups
attached to the tin(IV) atom. Other bond angles around the tin(IV)
125.2(8)
centre are O1A–Sn1–C1D = 100.8(4)° and O1A–Sn1–C1B = 95.9(3)°,
which deviates from the ideal value, probably due to the ligand
constituents. The sum of the bond angles for C1B–Sn1–C1D
(123.2(4)°), C1B–Sn1–C1C (116.7(4)°) and C1D–Sn1–C1C
(116.2(4)°) is 356.1°, which indicates that the Sn–3C system
[Sn1–C(1B)–C(1C)–C(1D)] is basically planar for complex 1. The
Sn–C bond lengths are consistent with those reported in other
organotin complexes [31,32]. The N6A–N7A bond length
(1.375(11) Å) is closer to a single bond length (1.45 Å) than to a
double bond length (1.25 Å) [33]. The C8A–S9A bond distance of
1.695(9) Å is close to that expected for a C@S double bond
(1.60 Å) [31] and the C4A–N6A bond length of 1.298(12) Å is nearly
the same as that of a C@N double bond (1.28 Å) [34].
3.5. Antibacterial activity
The synthesized ligand (HPACT) and its triorganotin(IV) com-
plexes 1 and 2 were tested against B. subtilis, S. aureus, E. coli and
S. typhi bacterial strains for their antibacterial activity using the
agar-well diffusion method, and data are listed Table 3. It was con-
cluded that the triorganotin complexes are more active than the
free ligand, which indicates that the metallation increases the anti-
bacterial activity. Based on the results, the free ligand (HAPCT)
Fig. 2. Molecular structure of the complex [Bu3Sn(PACT)] (1). The hydrogen atoms on the cyclohexyl and butyl groups are omitted for clarity.

24
M.A. Affan et al. / Polyhedron 33 (2012) 19–24
Table 3
Appendix A. Supplementary data
Results of the antibacterial activity of free HPACT and its triorganotin(IV) complexes
(1 and 2) (inhibition zone in mm).
CCDC 828342 contains the supplementary crystallographic data
for compound [Bu3Sn(PACT)] (1). These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223 336 033; or e-mail:
deposit@ccdc.cam.ac.uk.
Sample
Inhibition zone diameter (mm)
Bacteria
B. subtilis
S. aureus
E. coli
S. typhi
HPACT
1
2
12.2
25.7
27.3
31.5
15.8
24.8
31.8
38.8
13.4
20.3
24.7
35.2
12.7
22.8
21.1
29.7
Imipenem
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Acknowledgements
This work was financially supported by the Ministry of Science
Technology and Innovation (MOSTI) under a research Grant (No.
06-01-09-SF0046). The authors would like to thank the Universiti
Malaysia Sarawak (UNIMAS) for facilities to carry out the research
work. The authors are also thankful to Fraser White, Agilent
Technologies UK Ltd. for the X-ray diffraction analysis.
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