Synthesis, structural characterization and biological activities of organotin(IV) complexes with 5-allyl-2-hydroxy-3- methoxybenzaldehyde-4-thiosemicarbazone

Article abstract of DOI:10.1007/s12039-015-0924-9

The organotin(IV) complexes [MeSnCl(L)] (2), [BuSnCl(L)] (3), [PhSnCl(L)] (4) and [Me₂Sn(L)] (5) were synthesized by reacting organotin(IV) chloride(s) with 5-allyl-2-hydroxy-3-methoxybenzaldehyde-4-thiosemicarbazone [H₂L], (1)] in p

Full text of DOI:10.1007/s12039-015-0924-9

c
J. Chem. Sci. Vol. 127, No. 9, September 2015, pp. 1589–1597. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-015-0924-9
Synthesis, structural characterization and biological activities
of organotin(IV) complexes with 5-allyl-2-hydroxy-3-
methoxybenzaldehyde-4-thiosemicarbazone
ROSENANI A HAQUE and M A SALAM∗
The School of Chemical Sciences, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
e-mail: rosenani@usm.my; salambpx@yahoo.com
MS received 15 April 2015; revised 14 June 2015; accepted 18 June 2015
Abstract. The organotin(IV) complexes [MeSnCl(L)] (2), [BuSnCl(L)] (3), [PhSnCl(L)] (4) and [Me2Sn(L)]
(5) were synthesized by reacting organotin(IV) chloride(s) with 5-allyl-2-hydroxy-3-methoxybenzaldehyde-
4-thiosemicarbazone [H2L], (1)] in presence of KOH in 1:2:1 molar ratio (metal salt: base:ligand). All the
1
complexes have been characterized by elemental analyses, UV-Vis, FT-IR, H, 13C and 119Sn NMR spectral
studies. The molecular structure of complex 5 has been confirmed by single crystal X-ray diffraction analysis.
The ligand, H2L coordinates to Sn(IV) in thiolate form through phenoxide-O, azomethine-N and thiolate-S
1
atoms. The C-Sn-C angle measured from coupling constant J(119Sn, 13C) for dimethyltin(IV) complex 5 is
2
1
123.4◦. The J(119Sn, H) coupling constant values for complex 2 and 5 are 72.4 and 76.3 Hz, respectively.
Proposed geometry for five coordinated Sn(IV) atom is a strongly distorted trigonal bipyramid. Biological
studies were preformed in vitro against four bacterial strains which have shown better activities and potential
as antibacterial agents.
Keywords. 4-thiosemicarbazone; Organotin(IV) complexes; synthesis; characterization; crystal structure;
antibacterial activity.
1. Introduction
structure revealed that tin atom is penta-coordinated in
a distorted trigonal bipyramidal geometry.20 Recently,
Mouyed et al., have reported synthesis and struc-
tural studies of molybdenum(VI) complexes with
ONS-donors thiosemicarbazone ligands. These com-
plexes have been shown to exhibit significant anti-
tumour activities.21,22 Coordination of certain metal
complexex with thiosemicarbazone derivatives have
been studied along with a structural review of the main
group metal complexes with thiosemicarbazoenes.23–25
However, most of the work that have been reported
still involves complexes of thiosemicarbazones with
transition metal ions. Though organotin(IV) complexes
with thiosemicarbazone derivatives have potential bio-
logical activities,26–28 very few reports are available
regarding the mode of interaction between organ-
otin(IV) moieties and ONS tridentate thiosemicar-
bazone ligands and the nature of these complexes
in solution and solid state. In the present work,
we report the synthesis spectroscopic characterization
and antibacterial activity of new organotin(IV) com-
plexes of 5-allyl-2-hydroxy-3-methoxybenzaldehyde-
4-thiosemicarbazone. X-ray crystal structure of one
representative complex is also reported.
Thiosemicarbazones have been the subject of inter-
est due to their medicinal and biological applications
as antioxidant, DNA binding, anti-proliferative, anti-
malarial, antitumor and antibacterial agents.1–6 Gen-
erally, the biological activity of thiosemicarbazones
is influenced significantly upon coordination to metal
ions.7,8 Organotin(IV) complexes with ligands con-
taining ON, OS, ONS and NNS donors are notable
for their wonderful biological activities as fungi-
cides, bacteriocides and anti-inflammatory agents.9,10
Tin complexes are also established for their vari-
ous biological applications as antibacterial, antifungal,
biocidal and cytotoxic agents.11–13 Mostly, biological
activity of metal-thiosemicarbazones is influenced by
the metal coordination number and structure of the
molecule.14–16 In particular, complexes with thiosemi-
carbazones derived from ONS dianionic tridentate lig-
and have been extensively reported.17–19 Sousa et al.,
have reported structural studies of organotin(IV) com-
plex with ONS-tridentate thiosemicarbazone and X-ray
∗For correspondence
1589

1590
Rosenani A Haque and M A Salam
the solution cooled down to room temperature, then
2. Experimental
filtered, washed with ethanol and dried in desiccators
over silica gel. Yield: 0.68 g, 80%: M.p.: 189-191◦C:
UV–Vis (DMSO)λmax/nm: 260, 328, 366: FT-IR (KBr)
νmax/cm−1: 3411 (s, OH), 3335 (s, NH2), 3185 (s, NH),
1620 (m, C=N), 1562 (s, Caro-O), 998 (m, N-N), 1363,
859 (w, CS). 1H NMR (DMSO-d6, ppm): 11.40 (s, 1H,
OH), 10.14 (s, 1H, NH), 9.13 (s, 2H, NH2), 8.28 (s,
1H, N=CH), 7.34 (s, 1H, PhC4-H), 7.10 (s, 1H, PhC6-
H), 5.98 (m, 1H, CH2 =CH-CH2-Ph), 5.02 (m, 2H,
CH2 =CH-CH2-Ph), 3.76 (d, 2H, CH2 =CH-CH2-Ph,
J = 6.5 Hz), 3.28 (s, 3H, OCH3). 13C NMR (DMSO-
d6, ppm): 191.23 (C=S), 152.81 (C=N), 136.14-120.28
(Ph-C), 117.40 (=CH), 115.47 (CH2 =), 113.19 (CH2-
Ph), 55.79 (O-CH3). Anal. Calc. (%) for C12H15N3O2S:
C, 54.32; H, 5.70; N, 15.84. Found: C, 54.35; H, 5.52;
N, 16.01.
2.1 Materials and methods
All reagents were purchased from Fluka, Sigma and
Aldrich. All solvents were received as reagent grade
and used without further purification. Melting point
was measured on Stuart Scientific SMP1 melting point
apparatus. UV–Vis spectra were recorded in DMSO
with a Perkin Elmer Lambda 25 UV-Vis spectropho-
tometer. FT-IR spectra were recorded on a Perkin Elmer
System 2000 spectrophotometer in KBr pellet in the
4000–400 cm−1 range at room temperature. 1H, 13C and
119Sn NMR spectra were recorded on a Bruker 500 and
400 MHz NMR spectrophotometer and δ is relative to
SiMe4 and SnMe4 in DMSO-d6. Elemental analysis was
conducted with a Perkin Elmer 2400 Series-11 CHN
analyzer. X-ray crystallographic data were recorded on
a Bruker SMART APEXII CCD area-detector diffrac-
tometer using graphite monochromated MoKα radia-
tion (λ = 0.71073 Å) at 100 K. The data were col-
lected and reduced using APEX2 and SAINT pro-
grams. The structures were solved by direct methods
and refined by full-matrix least-squares method on F2
using the SHELXTL program.29 All non-H atoms were
anisotropically refined. The molecular graphics were
created using SHELXTL-97.
2.3 Synthesis of [MeSnCl(L)] (2)
The ligand, H2L (1) (0.265 g, 1.0 mmol) was dissolved
in absolute methanol (10 mL) under a nitrogen atmo-
sphere in a round-bottomed reaction flask. Potassium
hydroxide (0.11 g, 2.0 mmol) in methanol (10 mL) was
added dropwise to the ligand solution. The reaction
mixture was refluxed for 1 h. Then, a methanolic solu-
tion of methyltin(IV) trichloride (0.24 g, 1.0 mmol) was
added dropwise and resulted in a yellow solution. The
resulting reaction mixture was refluxed with stirring
for 4 h (scheme 2). The yellow solid product was
2.2 Synthesis of 5-allyl-2-hydroxy-3-methoxybenzal-
dehyde-4-thiosemicarbazone (H2L) (1)
A solution of 5-allyl-3-methoxy-2-hydroxybenzal- obtained by slow evaporation of the resulting solution
dehyde (0.57 g, 3.0 mmol) in 10 mL absolute ethanol at room temperature. The yellow product was filtered
was treated with 10 mL absolute ethanolic solution off, washed with methanol, and dried in vacuo over
of thiosemicarbazide (0.27 g, 3.0 mmol). The result- silica gel. Yield: 0.38 g, 75%: M.p.: 232–234◦C. UV–
ing colorless solution was refluxed with stirring for Vis (DMSO)λmax/nm: 272, 337, 380, 429: FT-IR (KBr)
4 h (scheme 1). White solid product was formed when νmax/cm−1: 3285 (s, NH2), 1587 (m, C=N), 1531 (s,
H
S
H2C=HC-H2C
H2N
+
NH2
O
N
H
Thiosemicarbazide
OH
OCH3
-H2O
5-allyl-2-hydroxy-3-methoxybenzaldehyde
H
H2C=HC-H2C
H2C=HC-H2C
N
N
NH2
NH2
N
N
S
OH
SH
OH
OCH3
Thione form
OCH3
Thiol form
Scheme 1. Synthesis of 5-allyl-2-hydroxy-3-methoxybenzaldehyde-4-thiosemicarbazone [H2L, 1].

Organotin(IV) thiosemicarbazone complexes
1591
Scheme 2. Reaction scheme for synthesis of organotin(IV) complexes (2-5).
Caro-O), 1020 (w, N-N), 1329, 830 (m, C-S), 582 (w, Sn- Anal. Calc. (%) for C16H22ClN3O2SSn: C, 40.49; H,
1
C), 541 (w, Sn-O), 450 (w, Sn-N). H NMR (DMSO- 4.67; N, 8.85. Found: C, 40.76; H, 4.77; N, 8.99%.
d6, ppm): 9.08 (s, 2H, NH2), 8.17 (s, 1H, N=CH), 7.38
2.5 Synthesis of [PhSnCl(L)] (4)
(s, 1H, PhC4-H), 7.14 (s, 1H, PhC6-H), 5.95 (m, 1H,
CH2 =CH-CH2-Ph), 5.05 (m, 2H, CH2 =CH-CH2-Ph),
Yield: 0.41 g, 72%: M.p: 246-248◦C. UV–Vis
(DMSO)λmax/nm: 274, 344, 382, 422: FT-IR (KBr)
νmax/cm−1: 3288 (s, NH2), 1588 (m, C=N), 1522 (s,
Caro-O), 1026 (w, N-N), 1335, 840 (m, C-S), 588
3.70 (d, 2H, CH2 =CH-CH2-Ph, J = 6.8 Hz), 3.25 (s,
2
3H, OCH3), 1.07 (s, 3H, JSn−H = 72.4 Hz, Sn-CH3).
13C NMR (DMSO-d6, ppm): 182.11 (C=S), 161.75
(C=N), 142.32-125.62 (Ph-C), 117.45 (=CH), 115.50
(CH2 =), 113.25 (CH2-Ph), 55.75 (O-CH3), 18.31
(1JSn−C = 531.82 Hz, Sn-CH3). 119Sn NMR (DMSO-d6,
ppm): –154.48. Anal. Calc. (%) for C13H16ClN3O2SSn:
C, 36.10; H, 3.73; N, 9.72. Found: C, 36.26; H, 3.86; N,
9.87%.
1
(w, Sn-C), 561 (w, Sn-O), 443 (w, Sn-N). H NMR
(DMSO-d6, ppm): 9.10 (s, 2H, NH2), 8.23 (s, 1H,
N=CH), 7.40-7.12 (m, 7H, Ph-H), 5.90 (m, 1H,
CH2 =CH-CH2-Ph), 5.03 (m, 2H, CH2 =CH-CH2-Ph),
3.78 (d, 2H, CH2 =CH-CH2-Ph, J = 6.6 Hz), 3.27
(s, 3H, OCH3). 13C NMR (DMSO-d6, ppm): 179.72
(C=S), 162.33 (C=N), 141.22–126.40 (Ph-C), 117.32
(=CH), 114.98 (CH2 =), 113.35 (CH2-Ph), 55.85 (O-
CH3). 119Sn NMR (DMSO-d6, ppm): –167.02. Anal.
Calc. (%) for C18H18ClN3O2SSn: C, 43.71; H, 3.67; N,
8.50. Found: C, 43.88; H, 3.80; N, 8.65%.
Other organotin(IV) complexes (3-5) were synthe-
sised following the same procedure by using the appro-
priate organotin(IV) chloride(s) (scheme 2).
2.4 Synthesis of [BuSnCl(L)] (3)
Yield: 0.40 g, 73%: M.p: 240–242◦C. UV–Vis
2.6 Synthesis of [Me2 Sn(L)] (5)
(DMSO)λmax/nm: 270, 339, 387, 442: FT-IR (KBr)
νmax/cm−1: 3291 (s, NH2), 1590 (m, C=N), 1527 (s, Yield: 0.36g, 74%: M.p: 235–237◦C. UV–Vis
Caro-O), 1018 (w, N-N), 1330, 834 (m, C-S), 578 (DMSO)λmax/nm: 271, 340, 377, 418: FT-IR (KBr)
1
(w, Sn-C), 549 (w, Sn-O), 432 (w, Sn-N). H NMR νmax/cm−1: 3293 (s, NH2), 1582 (m, C=N), 1524 (s,
(DMSO-d6, ppm): 9.05 (s, 2H, NH2), 8.25 (s, 1H, Caro-O), 1030 (w, N-N), 1321, 842 (m, C-S), 591
1
N=CH), 7.39 (s, 1H, PhC4-H), 7.15 (s, 1H, PhC6- (w, Sn-C), 550 (w, Sn-O), 462 (w, Sn-N). H NMR
H), 5.93 (m, 1H, CH2 =CH-CH2-Ph), 5.10 (m, 2H, (DMSO-d6, ppm): 9.04 (s, 2H, NH2), 8.08 (s, 1H,
CH2 =CH-CH2-Ph), 3.72 (d, 2H, CH2 =CH-CH2-Ph, N=CH), 7.41 (s, 1H, PhC4-H), 7.21 (s, 1H, PhC6-
J = 6.7 Hz), 3.23 (s, 3H, OCH3), 1.61-1.55 (t, 2H, Sn- H), 5.99 (m, 1H, CH2 =CH-CH2-Ph), 5.08 (m, 2H,
CH2-CH2-CH2-CH3), 1.40-1.34 (m, 2H Sn-CH2-CH2- CH2 =CH-CH2-Ph), 3.79 (d, 2H, CH2 =CH-CH2-
CH2-CH3), 1.21-1.15 (m, 2H, Sn-CH2-CH2-CH2-CH3), Ph, J = 6.4 Hz), 3.30 (s, 3H, OCH3), 1.10 (m, 6H,
0.94-0.85 (t, 3H, Sn-CH2-CH2-CH2-CH3). 13C NMR 2JSn−H = 76.3 Hz, Sn-(CH3)2). 13C NMR (DMSO-d6,
(DMSO-d6, ppm): 177.25 (C=S), 165.82 (C=N), ppm): 178.35 (C=S), 168.72 (C=N), 140.26-133.38
140.02-124.21 (Ph-C), 117.42 (=CH), 115.40 (CH2 =), (Ph-C), 118.55 (=CH), 116.11 (CH2 =), 112.24 (CH2-
113.20 (CH2-Ph), 55.82 (O-CH3), 38.01, 32.32, 26.81, Ph), 54.83 (O-CH3), 17.87 (1JSn−C = 531.82 Hz, Sn-
22.65 (Sn-Bu). 119Sn NMR (DMSO-d6, ppm): –162.37. (CH3)2). 119Sn NMR (DMSO-d6, ppm): –171.35. Anal.

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Rosenani A Haque and M A Salam
Calc. (%) for C14H19N3O2SSn: C, 40.80; H, 4.65; N, region at 328–366 nm due to the transitions of aro-
10.20. Found: C, 40.93; H, 4.72; N, 10.33%.
matic ring, thiolate function and azomethine group,
respectively. These bands are slightly shifted in energy
after complexation. In all the complexes, a moderately
intense band was observed in the region at 442–418 nm
assigned to ligand-to-metal-charge-transfer transitions
(LMCT).31 The shift of λmax clearly indicates the coor-
dination of the ligand to metal. The UV-Vis spectra of
organotin(IV) complexes (4-5) and the ligand are shown
in figure 1.
2.7 Antibacterial test
The synthesized compounds 1–5 were screened in vitro
antibacterial activities against Staphylococcus aureus
(ATCC 6538), Enterobacter aerogenes (ATCC 13048),
Escherichia colii (ATCC 15224) and Salmonella typhi
(ATCC 10749) using the agar well diffusion method.30
Doxycycline was used as the standard drug. The bac-
teria from stock culture were lightly inoculated into
the Mueller Hinton Broth (MHB) and allowed to grow
overnight at 37◦C in an ambient air incubator. The cul- 3.3 Infrared spectra
ture was diluted with a new MHB in order to achieve
an absorbance value of 2.0 × 106 colony forming units
(CFU/mL) or 0.168 at 550 nm in the spectrophotometer.
Sterile cotton swab was dipped into the broth culture
and inoculated on the Mueller Hinton Agar (MHA).
Sterile paper discs with 6 mm diameter were placed
on the agar in equal distance. The recommended con-
centration of the test sample (2 mg/mL in DMSO) was
introduced individually to each of the discs. The agar
plates were incubated immediately at 37◦C for 20 h. For
each plate, DMSO mixture and reference antibacterial
drug such as doxycycline served as negative and posi-
tive controls, respectively. The activity was determined
by measuring the diameter of zones showing complete
inhibition (mm). Growth inhibition was calculated with
reference to the positive control.
IR spectra clarify the mode of the ligand bonded to
the tin moiety and support their proposed structures.
The free ligand (1) exhibit ν(OH) stretching vibrations
at 3411 cm−1 which was absent in the spectra of the
complexes (2–5), indicating deprotonation of pheno-
lic proton and bond formation with Sn(IV) atom. The
ν(NH) stretching vibration of free ligand was observed
at 3185 cm−1. This band disappeared in the IR spectra
of the complexes (2–5), which is attributed to the coor-
dination bond of azomethine nitrogen to Sn(V) atom.
The absence of ν(S-H) peak around 2700 cm−1 in the
spectrum of free ligand (1) indicates that ligand is in
thione form in the solid state.32,33 The ν(C=N) band
which observed at 1620 cm−1 in IR spectrum of free
ligand shifted to lower frequencies in the complexes,
in agreement with coordination of azomethine nitro-
gen to Sn(IV)−1atom.34 The ν(N-N) band in free lig-
and at 998 cm is shifted to higher wave numbers at
1030–1018 cm−1 in the complexes, indicating that the
azomethine nitrogen atom is involved in coordination.
The ν(C-S) stretching and bending vibrations observed
at 1363 and 859 cm−1 in the free ligand is shifted to
lower wave numbers at 1335–1321 and 842–830 cm−1
in the complexes, indicating bonding of thiolate sul-
phur to Sn(IV) atom.35 Absorption band of ν(Caro-O)
in free ligand appeared at 1562 cm−1 is shifted to
3. Results and Discussion
3.1 Synthesis
The ligand, 5-allyl-2-hydroxy-3-methoxybenzaldehyde-
4-thiosemicarbazone (H2L) was prepared by reaction
of 5-allyl-2-hydroxy-3-methoxybenzaldehyde with thio-
semicarbazide. It exhibits two possible tautomers either
as thione or thiol forms (scheme 1). H2L was treated
with corresponding organotin(IV) chloride(s) in pres-
ence of KOH to obtain organotin(IV) derivatives
(scheme 2). The obtained organotin(IV) compounds are
yellow solids stable in air and soluble in methanol, chlo-
roform, THF, DMSO and DMF. Elemental analysis data
confirms that the complexes are of good purity. The
physical and analytical data are reported in experimen-
tal section. The nature of bonding and structures of lig-
and and its complexes were suggested by spectroscopic
studies. The molecular structure of complex 5 is also
reported.
3.2 UV-Visible spectra
The electronic spectrum of ligand (1) has π–π*
band at 260 nm and two n–π* bands around in the
Figure 1. UV-Vis spectra of ligand (1) and its complexes
(4 and 5) in DMSO (1 × 10−4 M).

Organotin(IV) thiosemicarbazone complexes
1593
lower wave numbers at 1531–1522 cm−1 in the com-
plexes, suggesting the involvement of phenolic oxygen
in coordination.36 New bands in the region at 561–541
and 462–422 cm−1 are assigned to ν(Sn-O) and ν(Sn-
N), respectively, supporting coordination of oxygen and
nitrogen to Sn(IV) atom.37–39 The weak band assigned
to ν(Sn-C) observed at 591–578 cm−1 which confirms
that Sn–C bond in their structure.40 The IR spectral
data suggested that thiosemicarbazone ligand (H2L) act
as dinegative ONS tridentate chelating agent coordi-
nated to central tin(IV) atom through phenolic oxygen,
azomethine nitrogen and thiolate sulphur atoms. This
mode of coordination has been confirmed by the X-ray
structure studies of dimethyltin(IV) complex 5.
tin(IV). The carbon signal due to aromatic ring car-
bons at 136.14–120.28 ppm in free ligand is shifted
slightly downfield upon complexation. These observa-
tions also support coordination through phenolic oxy-
gen to tin(IV) atom. The chemical shifts due to car-
bons in allyl group (-CH2–CH=CH2) and (-OCH3) did
not change upon complexation. The signals due to butyl
carbon in complex 3 bonded to tin (Bu-Sn) appeared
at 38.01–22.65 ppm. The value of the coupling constant
1J[119Sn, 13C] for complex 5 is 531.82 Hz which con-
sistent with five-coordinate geometry around tin.42 The
determination of C–Sn–C angle using the Lockhart–
1
Manders equation41 θ (C-Sn-C) = [| J(13C −119 Sn)| +
875]/11.4 provided C–Sn–C angle of 123.4◦ for com-
plex 5. The observed value of C–Sn–C angle corre-
sponds with the Cmethyl-Sn-Cmethyl angle obtained from
X-ray crystal analysis of dimethyltin(IV) complex 5.
The 119Sn NMR spectra of complexes (2–5) showed
a sharp single resonance supported that only one sin-
gle species is present. The 119Sn NMR resonances were
found to be in the range of −154.48 to −171.35 ppm for
all complexes (2–5). The occurrences of chemical shift
values for all complexes in this region suggested that
five coordination environment around the central
Sn(IV) atom.43,44
3.4 1H, 13C and 119Sn NMR spectra
The 1H and 13C spectra of ligand (1) and its complexes
(2–5) and of the 119Sn NMR spectra of the complexes
(2–5) were recorded in DMSO. The free ligand dis-
played signal at 11.40 ppm is attributed to OH proton
and the sharp signal at 10.14 ppm is assigned to NH
proton. The absence of these two signals upon com-
plexation indicating deprotonation of these groups and
coordinated with tin(IV) atom. The appearance of a
sharp resonance peak at 9.10–9.04 ppm is due to the
NH2 group in all complexes. The chemical shifts of
3.5 Crystal structure of [Me2Sn(L)] (5)
N=CH proton for ligand appears at 8.28 ppm which Yellow crystals suitable for X-ray diffraction analysis
is shifted upfield region at 8.25–8.08 ppm due to com- of the [Me2Sn(L)] (5) were obtained by slow evapo-
plex formation. The resonance signals due to aro- ration of methanol at room temperature. The molecu-
matic 4-H and 6-H protons were found to be down- lar structure of [Me2Sn(L)] (5) along with the atomic
field region in the complexes with compared to those numbering scheme and its packing in the crystal lattice
of the free ligand. This downfield shift might be due are given in figures 2 and 3, respectively. Summary of
to the donation of electron density from ring to Sn(IV) crystal data and structure refinement results are given in
The allyl group (-CH2–CH=CH2) inside the aromatic table 1. Important bond lengths (Å) and angles (◦) are
ring exhibit three signals at the region 5.98–3.70 ppm compiled in table 2.
as multiplet and doublet. However, methyl protons of
The compound crystallizes into monoclinic crystal
both methyltin(IV) (2) and dimethyltin(IV) (5) com- system with a space group of P 21/c. The molecular
2
plexes showed a singlet at 1.10–1.07 ppm. The J structure of complex 5 revealed that the ligand (H2L)
(
119Sn,1H) coupling constant of complexes 2 and 5 are is coordinated to central tin(IV) atom through phenolic
72.4 and 76.3 Hz in agreement with five-coordinate oxygen, azomethine nitrogen and thiolate sulphur
tin(IV) centre.41 The calculated C9-Sn1–C10 angles atoms. The Sn(IV) is penta-coordinated and adopts a
by the Lockhart-Manders equations41 as 122.22◦ and distorted trigonal bipyramidal geometry, with the oxy-
126.41◦ for complexes 2 and 5, respectively, support the gen and thiol sulphur atoms occupying axial posi-
proposed geometry.
tions while azomethine nitrogen atom and two methyl
The C=S carbon signal is shifted to upfield region groups occupy the equatorial position. The two methyl
in the complexes compared with the free ligand, sup- groups and azomethine nitrogen are equatorial sites
ported coordination through thiolate sulphur to tin(IV) having angles C9–Sn1–C10 = 128.20(6)◦ C9–Sn1–N1
atom. The chemical shift due to the C=N is observed = 103.24(5)◦ and N1–Sn1–C10 = 128.47(6)◦. The sum
at downfield (168.72–161.75 ppm) in the complexes of bond angles between Sn atom and equatorial atoms is
compared with the ligand (152.81 ppm), clearly indi- 360◦ indicating that they are completely coplanar with
cate the coordination of the azomethine nitrogen to the Sn atom lying in the plane. The phenolic oxygen

1594
Rosenani A Haque and M A Salam
is smaller than 180◦. Most probably, the distortion is
owing to the participation of the N1 atom in five mem-
ber chelate rings and also large covalent radius of
Sn(IV). The C9–Sn1–C10 angle (128.20(6)◦) is slightly
larger than 120◦ indicating that the two methyl groups
also contribute for deviation. The deviation from the
ideal trigonal bipyramidal geometry can be assigned
from stretch exploited by the non-planar five mem-
ber (Sn1–S1–C8–N2–N1) and six member (Sn1–O1–
C1–C6–C7–N1) chelate rings upon complexation. The
bond angles between the planes of the two rings are
C10–Sn1–C9 (128.20◦), C10–Sn1–N1 (128.47◦) and
C9–Sn1–N1 (103.24◦) for C10, C9 and N1 placed at the
three edges of the trigonal plane which is evidence for
the distortion from the perfect TBP geometry. The Sn1-
S1 [2.5497(4) Å] and Sn1-N1 [(2.2212(11) Å] bond
lengths are similar to those of other five-coordinate dis-
torted trigonal tin complexes of tridentate ONS donors
ligand.45,46 The Sn1-O1 bond distance [2.1181(10) Å]
is almost similar to the covalent radii of Sn–O (2.10 Å),
considering significant bonding interaction and com-
parable with reported article.47 The Sn1–N1 distance
[2.2212(11) Å] is a little longer than the sum of Sn-
N covalent radii (2.15 Å),48 considered as strong bond-
ing and consistence with those reported literature.49
The bond distances of Sn1–C9 (2.1243 Å) and Sn1-C10
(2.1200 Å) are comparable with those found in other
reported organotin(IV) compounds.50,51 The packing of
the molecules in the crystal structure is stabilized by
intra and intermolecular hydrogen bonding interactions.
The most important feature of the crystal packing is the
formation of N3H· · · N2, N3H...O1 and C10–H· · · N2
hydrogen bonds. Centrosymmetric dimers in the crystal
packing are conciliated by N-H....S hydrogen bonds.
Figure 2. Molecular structure of [Me2Sn(L)] (5) showing
displacement ellipsoids at the 50% probability level.
(O1) and thiolate sulphur (S1) atoms bonded with Sn1
have axial positions O1-Sn1–S1 angle of 151.41(3)◦.
The distortion from trigonal bipyramidal geometry is
evident from the bond angle O1-Sn1–N1 79.63(4)◦ and
N1–Sn1–S1 75.95(3)◦ as the sum of bond angles is
155.58◦ significantly deviated from 180◦. Furthermore,
the bond angle of N1-Sn1-C10 is 128.47(6)◦ which
3.6 Antibacterial Activity
Antibacterial studies of all compounds were carried
out in vitro against Staphylococcus aureus, Escherichia
coli, Enterobacter aerogenes and Salmonella typhi. In
this experiments, inhibition zone in millimetre units
were presented in table 3. From table 3, it can be
concluded that all compounds showed high activity
against different bacterial strains but slightly low activ-
ity with compared to standard drug (Doxycycline). The
ligand showed moderate activity might be due to the
presence of OH/NH groups within the parent ligand.52
Comparison of the antibacterial activity of the free
ligand and its organotin(IV) complexes showed that lig-
and (H2L) exhibits less activity. The increase in activity
of the complexes might be due to the chelation of lig-
and with tin(IV) leading to electron delocalization and
Figure 3. The packing diagram of [Me2Sn(L)] (5) in the
crystal lattice, viewed along the a axis.

Organotin(IV) thiosemicarbazone complexes
1595
Table 1. Crystal data and structure refinement parameters for [Me2Sn
(L)] (5).
Compound
[Me2Sn(L)] (5)
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C14H19N3O2SSn
412.07
100
0.71073
Monoclinic
P21/c
Unit cell dimensions
a (Å)
11.5023(7)
b (Å)
13.6747(8)
c (Å)
11.1597(7)
α (◦)
90
β (◦)
100.3584(8)
γ (◦)
90
Volume (Å3)
Z
1726.71(18)
4
Calculated density (mg/m3)
Radiation type λ(Å)
F(000)
1.585
M0K/a
824
Crystal size (mm)
Crystal colour
Scan range θ (◦)
Absorption coefficient (μ) (mm−1
Max. and min. transm
Goodness-of-fit on F2
Data/Restrains/ parameters
Final R indices [I > 2σ (I)]
R indices (all data)
0.14 × 0.40 × 0.47
Orange
2.78–30.22
1.607
0.805 and 0.522
1.142
5076/0/201
)
R1 = 0.0183, wR2 = 0.0191
R1 = 0.0551, wR2 = 0.0558
potent diffusion of the metal complexes into bacterial zones in the range of 27.5–26.4 mm against all bac-
cell.53,54 Based on the results, dimethyltin(IV) complex terial strains MeSnCl(L) (2) complex exhibits higher
5 exhibits highest antibacterial activity with inhibition activity than BuSnCl(L) (3) complex against all bac-
zone rangeing 29.4–27.5 mm. Phenyltin(IV) complex teria. Therefore, nature of the organo groups (phenyl,
4 exhibits significantly better activity with inhibition methyl and butyl) attached to the tin(IV) centre might
Table 2. Selected bond lengths (Å) and angles (◦) of [Me2Sn(L)] (5).
Bond lengths (Å)
Sn1-S1
Sn1-N1
Sn1-C10
O1-C1
O2-C11
N1-C7
2.5495(5)
2.2212(11)
2.1200(16)
1.3288(16)
1.426(2)
1.3038(18)
1.336(2)
Sn1-O1
Sn1-C9
S1-C8
O2-C2
N1-N2
N2-C8
C1-C2
2.1181(10)
2.1243(16)
1.7417(14)
1.3704(18)
1.3837(17)
1.3211(18)
1.4248(19)
N3-C8
Bond angles (◦)
S1-Sn1-O1
S1-Sn1-C9
O1-Sn1-N1
O1-Sn1-C10
N1-Sn1-C10
Sn1-S1-C8
Sn1-N1-N2
N2-N1-C7
151.41(3)
102.49(5)
79.63(4)
89.93(5)
128.47(5)
96.24(5)
S1-Sn1-N1
S1-Sn1-C10
O1-Sn1-C9
N1-Sn1-C9
C9-Sn1-C10
Sn1-O1-C1
Sn1-N1-C7
N1-N2-C8
75.96(3)
93.68(4)
97.36(5)
103.24(5)
128.20(6)
123.08(8)
122.48(10)
115.94(11)
122.43(8)
114.79(11)

1596
Rosenani A Haque and M A Salam
Table 3. Antibacterial activitya of ligand (1) and its organotin(IV) complexes (2–5)
(inhibition zone in mm).
Bacterium
Compounds
S. aureus
E. coli
E. aerogenes
S. typhi
H2L (1)
14.2
23.8
23.2
26.4
27.8
31.6
12.4
24.1
20.8
25.7
28.9
33.4
–
11.8
24.3
21.2
27.5
29.4
33.1
2
3
4
5
R
25.1
22.9
26.1
27.5
32.5
aConcentration used: 2 mg/mL of DMSO, R = standard drug: Doxycycline, dash
indicate inactivity.
play an important role in growth inhibitory activity. Cambridge Crystallographic data center via www.ccdc.
The organotin(IV) derivatives remarkably inhibit gram- ac.uk/data_request/cif or from the Cambridge Crys-
negative/gram-positive bacterial growth. The enhanced tallographic data center, 12 Union Road, Cambridge
antibacterial activity of organotin(IV) derivatives com- CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
pared to the parent ligand is most possibly due to deposit@ccdc.cam.ac.uk.
the reduction in the polarity of the tin(IV) atom upon
Acknowledgment
coordination with the ligand. The antibacterial activi-
ties of the studied organotin(IV) compounds are com-
parable with other reported organotin complexes.55–57
Hence, organotin(IV) complexes studied in this work
may be good candidates to be used as new antibacte-
rial agents. Detailed studies in this research field will be
investigated in future biological applications.
R.A.H. thanks Universiti Sains Malaysia (USM) for
the Research University (RU) Grant 1001/PKIMIA/
811217. M.A.S. thanks USM and Third World Aca-
demy of Sciences (TWAS) for a post-doctoral research
fellowship. We also thank the Bangladesh Petroleum
Exploration and Production Co. Ltd. (BAPEX),
Bangladesh, for the study leave to M. A. Salam.
4. Conclusion
References
Four new organotin(IV) complexes of 5-allyl-2-hydro-
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thine nitrogen and thiolate sulphur atoms. All the syn-
thesized complexes have shown pronounced biological
activities. These organotin(IV) complexes have good
antibacterial activity and may be designed as potential
drugs in the pharmaceutical field in future
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