New diorganotin(IV) complexes with some Schiff bases derived from β-diketones: Synthesis, spectral properties, thermal analysis, and antibacterial activity

Article abstract of DOI:10.1080/00958972.2011.616197

The Schiff bases H₂L^a, H₂L^b, and H₂L^c have been prepared from the reaction of 2-amino-4-chlorophenol with acetylacetone, benzoylacetone, and dibenzoylmethane, respectively. Organotin(IV) complexes [SnPh₂(L^a)] (1), [SnPh₂(L^b)] (2), [SnPh₂(L^c)] (3), and [SnMe₂(L^c)] (4) have been synthesized from the reaction of SnPh₂Cl₂ and SnMe₂Cl₂ with these Schiff bases. The synthesized complexes have been characterized by elemental analysis and FT-IR, ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy. Spectroscopic data suggest the Schiff bases are completely deprotonated and coordinated tridentate to tin via imine nitrogen and phenolic and enolic oxygen atoms; the coordination number of tin is five. Thermal decomposition of the complexes has been studied by thermogravimetry. The invitro antibacterial activities of the Schiff bases and their complexes have been evaluated against Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. H₂L^a, H₂L^c, and all complexes exhibited good activities and have potential as drugs.

Full text of DOI:10.1080/00958972.2011.616197

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New diorganotin(IV) complexes with
some Schiff bases derived from
β-diketones: synthesis, spectral
properties, thermal analysis, and
antibacterial activity
Tahereh Sedaghat a , Marjan Monajjemzadeh a & Hossein
Motamedi b
a Department of Chemistry , College of Sciences, Shahid Chamran
University , Ahvaz , Iran
b Department of Biology , College of Sciences, Shahid Chamran
University , Ahvaz , Iran
Published online: 09 Sep 2011.
To cite this article: Tahereh Sedaghat , Marjan Monajjemzadeh & Hossein Motamedi (2011) New
diorganotin(IV) complexes with some Schiff bases derived from β-diketones: synthesis, spectral
properties, thermal analysis, and antibacterial activity, Journal of Coordination Chemistry, 64:18,
3169-3179, DOI: 10.1080/00958972.2011.616197
To link to this article: http://dx.doi.org/10.1080/00958972.2011.616197
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Journal of Coordination Chemistry
Vol. 64, No. 18, 20 September 2011, 3169–3179
New diorganotin(IV) complexes with some Schiff bases
derived from b-diketones: synthesis, spectral properties,
thermal analysis, and antibacterial activity
TAHEREH SEDAGHATy*, MARJAN MONAJJEMZADEHy
and HOSSEIN MOTAMEDIz
yDepartment of Chemistry, College of Sciences, Shahid Chamran University, Ahvaz, Iran
zDepartment of Biology, College of Sciences, Shahid Chamran University, Ahvaz, Iran
(Received 4 May 2011; in final form 29 July 2011)
The Schiff bases H2La, H2Lb, and H2Lc have been prepared from the reaction of 2-amino-4-
chlorophenol with acetylacetone, benzoylacetone, and dibenzoylmethane, respectively.
Organotin(IV) complexes [SnPh2(La)] (1), [SnPh2(Lb)] (2), [SnPh2(Lc)] (3), and [SnMe2(Lc)]
(4) have been synthesized from the reaction of SnPh2Cl2 and SnMe2Cl2 with these Schiff bases.
1
The synthesized complexes have been characterized by elemental analysis and FT-IR, H, 13C,
and 119Sn NMR spectroscopy. Spectroscopic data suggest the Schiff bases are completely
deprotonated and coordinated tridentate to tin via imine nitrogen and phenolic and enolic
oxygen atoms; the coordination number of tin is five. Thermal decomposition of the complexes
has been studied by thermogravimetry. The in vitro antibacterial activities of the Schiff bases
and their complexes have been evaluated against Gram-positive (Bacillus subtilis and
Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa)
bacteria. H2La, H2Lc, and all complexes exhibited good activities and have potential as drugs.
Keywords: Diorganotin(IV); Schiff base; Diketones; Thermal analysis; Antibacterial activity
1. Introduction
Schiff bases and their complexes with transition and non-transition metal ions have
medicinal, physiological, and pharmaceutical applications, well-known as antibacterial,
antifungal, anticancer, antiviral, and herbicidal agents [1–6]. Schiff-base complexes also
provide synthetic models for active sites in biological systems [7, 8]. Furthermore Schiff
bases offer opportunities for enhancing solubility and stability of their metal complexes
and tuning metal centered electronic factors [9]. In many cases, when Schiff bases are
administered as their metal complexes, biological activity is enhanced in comparison to
the free ligand. Research dealing with complexes of Schiff bases has expanded
enormously with increasing attention devoted to Schiff-base complexes of
organotin(IV) in view of their chemical properties, biological significance, industrial
importance, and structural variety [10–12]. Organotin(IV) complexes possess physical
*Corresponding author. Email: tsedaghat@scu.ac.ir
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
DOI: 10.1080/00958972.2011.616197

3170
T. Sedaghat et al.
and chemical properties for new materials and new metal-based drugs. These chemicals
show in vitro and in vivo antitumor activity, opening a new research sub-area on
organotin(IV) compounds [13–15]. Many organotin(IV) compounds have been synthe-
sized and tested for their antitumor activity and found to be as effective as, or even
better than, traditional heavy metal anticancer drugs [16–19]. Many studies have been
carried out to explore antimicrobial activity of organotin(IV) compounds and the
search for antimicrobial agents is of current and growing interest [19–25]. Since biocidal
properties of organotin(IV) compounds are dependent on both the organic group and
the ligand attached to tin [20, 26], an interesting development is introducing ligands
which are themselves bioactive [20, 27–30]. Interaction of organotins has been
extensively studied with a variety of Schiff-base ligands due to the importance of
their medicinal assays for bactericide and antitumor purposes [17, 31–37]. However,
little attention has been paid to systems in which the Schiff bases are derived from
ꢀ-diketones. Herein, we report the synthesis and spectroscopic characterization of new
diorganotin(IV) complexes with Schiff bases derived from acetylacetone and related
ꢀ-diketones and investigate their thermal behavior and antibacterial activity.
2. Experimental
2.1. Materials and methods
All starting materials were purchased from Merck except diphenyltin dichloride which
was supplied from Acros Company; all were used as received. All solvents were of
reagent grade and used without purification. IR spectra were obtained using a FT
1
BOMEM MB102 spectrophotometer. H, 13C, and 119Sn NMR spectra were recorded
with a Bruker 400 MHz Avance Ultrashield spectrometer. Thermogravimetric analyses
(TGA) were carried out using a Perkin-Elmer Diamond thermal analyzer. The heating
rates were controlled at 5ꢀC minꢁ1 under nitrogen with a 150 mL minꢁ1 flow rate; the
weight loss was measured from ambient temperature to 1050ꢀC.
2.2. Synthesis of Schiff bases
2.2.1. 4-(2-Hydroxy-5-chlorophenylimino)-pentan-2-one
(H2La).
A
solution
of
2-amino-4-chlorophenol (2.871 g, 20 mmol) in ethanol (70 mL) was added to a solution
of acetylacetone (2.00 g, 20 mmol) in ethanol (50 mL). This solution was refluxed for
8 h. Then the volume of solution was reduced to ca 60 mL. H2La precipitates after
standing overnight at room temperature, was filtered off, and washed with ethanol
(2 ꢂ 5 mL). Finally, H2La was recrystallized from ethanol to give white-brown needle
crystals. Yield: 3.204 g (71%); m.p. 159–161ꢀC; Anal. Calcd for C11H12NO2Cl (%):
C, 58.5; H, 5.3; N, 6.2. Found (%): C, 58.9; H, 5.2; N, 6.3. FT-IR (KBr, cmꢁ1): 1547,
ꢁ(C¼C); 1603, ꢁ(C¼O); 2800–3100 br, ꢁ(C–H), ꢁ(O–H)/ꢁ(N–H). 1H NMR (DMSO-d6):
ꢂ ¼ 1.98 (s, 3H, H10), 2.03 (s, 3H, H11), 5.24 (s, 1H, H8), 6.90 (d, J ¼ 8.6 Hz, 1H, H3),
7.04 (dd, J ¼ 8.6, 2.5 Hz, 1H, H4), 7.27 (d, J ¼ 2.5 Hz, 1H, H6), 10.24 (s, 1H, Henolic),
12.15 (s, 1H, Hphenolic). 13C NMR (DMSO-d6): ꢂ ¼ 20.0, C10; 29.4, C11; 98.6, C8; 117.1,
C3; 122.6, C4; 124.1, C6; 125.6, C5; 128.1, C1; 149.3, C2; 159.5, C7; 195.3, C9.

Diorganotin(IV) complexes
3171
2.2.2. 3-(2-Hydroxy-5-chlorophenylimino)-1-phenylbutan-1-one (H2Lb). H2Lb was syn-
thesized as described for H2La from benzoylacetone (3.240 g, 20 mmol) and the product
was formed as yellow crystals. Yield: 4.60 g (80%); m.p. 186–188ꢀC; Anal. Calcd for
C16H14NO2Cl (%): C, 66.8; H, 4.9; N, 4.9. Found (%): C, 67.1; H, 4.9; N, 4.8. FT-IR
(KBr, cmꢁ1): 1576, ꢁ(C¼C); 1605, ꢁ(C¼O); 2900–3200 br, ꢁ(C–H), ꢁ(O–H)/ꢁ(N–H).
1H NMR (DMSO-d6): ꢂ ¼ 2.20 (s, 3H, H10), 6.08 (s, 1H, H8), 6.96 (d, J ¼ 8.6 Hz, 1H,
H3), 7.09 (dd, J ¼ 8.6, 2.5 Hz, 1H, H4), 7.37 (d, J ¼ 2.5 Hz, 1H, H6), 7.40–7.61 (m, 3H,
H
14,15), 7.91–7.93 (m, 2H, H13), 10.33 (s, 1H, Henolic), 12.80 (s, 1H, Hphenolic). 13C NMR
(DMSO-d6): ꢂ ¼ 20.6, C10; 94.8, C8; 117.2, C3; 122.7, C4; 124.4, C6; 126.0, C5; 127.3,
C14; 128.0, C15; 128.8, C13; 131.5, C12; 139.8, C1; 149.5, C2; 162.3, C7; 187.3, C9.
2.2.3. 3-(2-Hydroxy-5-chlorophenylimino)-1,3-diphenylpropan-1-one
(H2Lc).
Dibenzoylmethane (2.242 g, 10 mmol) was dissolved in ethanol (15 mL) at 65–70ꢀC
and mixed with a solution of 2-amino-4-chlorophenol (1.435 g, 10 mmol) in ethanol
(10 mL). Then two drops of HCl was added and the solution was refluxed for 10 h. The
product was precipitated as bright brown needles after standing overnight at room
temperature. Crystals were collected, washed with ethanol, and dried over CaCl2. Yield:
2.448 g (70%); m.p. 73–75ꢀC; Anal. Calcd for C21H16NO2Cl (%): C, 72.1; H, 4.6; N,
4.0. Found (%): C, 72.5; H, 4.5; N, 4.1. FT-IR (KBr, cmꢁ1): 1567, ꢁ(C¼C); 1607,
ꢁ(C¼O); 3000–3200 br, ꢁ(C–H), ꢁ(O–H)/ꢁ(N–H). 1H NMR (DMSO-d6): ꢂ ¼ 6.18
(s, 2H, H6,8), 6.86 (m, 2H, H3,4), 7.44–7.57 (m, 8H, H14,15 17,18,19
,
), 8.01 (d, J ¼ 7.1 Hz,
1H, H13), 10.41 (s, 1H, Henolic), 12.57 (s, 1H, Hphenolic). 13C NMR (DMSO-d6): ꢂ ¼ 94.1,
C8; 98.1, C3; 117.4, C4; 122.9, C6; 124.7, C5; 128.1-130.9, C13,14,17,18; 132.5-136.0,
C
12,15,16,19; 139.9, C1; 148.7, C2; 160.7, C7; 186.2, C9.
2.3. Synthesis of organotin(IV) complexes
2.3.1. SnPh2La (1). H2La (0.056 g, 0.25 mmol) was dissolved in methanol (10 mL) at
50–55ꢀC and KOH (0.028 g, 0.5 mmol) was added. This solution was stirred for
30 min and then SnPh2Cl2 (0.085 g, 0.25 mmol) in methanol (5 mL) was added. The
solution was refluxed for 5 h. A yellow precipitate was formed after evaporating the
solvent at room temperature. This precipitate was collected, washed with methanol, and
then treated with chloroform (10 mL). The resulted mixture was filtered to remove KCl
and then evaporated to dryness. The yellow product was collected and maintained over
dry CaCl2. Yield: 0.080 g (65%); m.p. 149–152ꢀC; Anal. Calcd for C23H20NO2ClSn
(%): C, 55.6; H, 4.0; N, 2.8. Found (%): C, 55.7; H, 4.3; N, 3.2. FT-IR (KBr, cmꢁ1):
1527, ꢁ(C¼O); 1541, ꢁ(C¼N)/ꢁ(C¼C); 512, ꢁ(Sn–O); 439, ꢁ(Sn–N). 1H NMR (CDCl3):
ꢂ ¼ 2.23 (s, 3H, H10), 2.36 (s, 3H, H11), 5.34 (s, 1H, H8), 6.98–7.01 (m, 2H, H3,6), 7.05
(dd, J ¼ 8.6, 2.3 Hz, 1H, H4), 7.36–7.48 (m, 6H, Hm,p), 7.82–7.85 [m, 4H, Ho,
3J(119Sn–1H) ¼ 84.7 Hz]. 13C NMR (CDCl3): ꢂ ¼ 24.6, C10; 28.0, C11; 102.0, C8; 118.7,
C3; 120.2, C4; 122.6, C6; 127.2, C5; 129.1, Cm [3J(119Sn–13C) ¼ 85.2 Hz]; 130.8, Cp; 133.2,
C1; 136.7, Co [2J(119Sn–13C) ¼ 52.8 Hz]; 138.8, Ci [1J(119Sn–13C) ¼ 968.2 Hz]; 157.1, C2;
172.7, C7; 188.3, C9. 119Sn NMR (CDCl3): ꢂ ¼ ꢁ302.7.
2.3.2. SnPh2Lb (2). H2Lb (0.071 g, 0.25 mmol) was dissolved in methanol (10 mL) at
45–50ꢀC and a solution of SnPh2Cl2 (0.085 g, 0.25 mmol) in methanol (5 mL)

3172
T. Sedaghat et al.
was added. This solution was stirred for 30 min and then triethylamine (0.5 mmol) was
added. An orange precipitate appeared after 1 h. The mixture was stirred for another 2 h
to ensure completion of reaction. The product was filtered, washed with warm
methanol, and dried over CaCl2. Yield: 0.097 g (70%); m.p. 169–171ꢀC; Anal. Calcd for
C28H22NO2ClSn (%): C, 60.1; H, 3.9; N, 2.5. Found (%): C, 59.8; H, 3.9; N, 2.6. FT-IR
1
(KBr, cmꢁ1): 1563, ꢁ(C¼O); 1586, ꢁ(C¼N)/ꢁ(C¼C); 544, ꢁ(Sn–O); 447, ꢁ(Sn–N). H
NMR (CDCl3): ꢂ ¼ 2.52 (s, 3H, H10), 6.09 (s, 1H, H8), 7.02-7.05 (m, 2H, H3,6), 7.08 (dd,
J ¼ 8.9, 2.1 Hz, 1H, H4), 7.36–7.43 (m, 6H, Hm,p), 7.51–7.59 (m, 3H, H14,15), 7.85–7.89
[m, 4H, Ho, 3J(119Sn–1H) ¼ 84.0 Hz], 8.04–8.07 (m, 2H, H13). 13C NMR (CDCl3):
ꢂ ¼ 25.0, C10; 98.6, C8; 118.5, C3; 119.9, C4; 122.2, C6 [3J(119Sn–13C) ¼ 23.8 Hz];
127.0, C5; 127.2, 128.7, C14; 128.8, Cm [3J(119Sn–13C) ¼ 82.5 Hz]; 129.7, 130.4, Cp
[4J(119Sn–13C) ¼ 16.8 Hz]; 131.6, C13; 132.8, C15; 135.0, C12; 136.3, Co
[2J(119Sn–13C) ¼ 52.6 Hz]; 137.8, C1; 138.3, Ci [1J(119Sn–13C) ¼ 973.8 Hz]; 156.9, C2;
172.8, C7; 179.6, C9. 119Sn NMR (CDCl3): ꢂ ¼ ꢁ303.3.
2.3.3. SnPh2Lc (3). H2Lc (0.174 g, 0.5 mmol) was dissolved in methanol (10 mL) at
45–50ꢀC and KOH (0.056 g, 1.0 mmol) was added to it. The solution was stirred for
30 min and then SnPh2Cl2 (0.171 g, 0.5 mmol) in methanol (5 mL) was added
dropwise. A red precipitate was formed immediately. After 30 min stirring at the
same temperature, the precipitate was filtered, washed with warm methanol, and dried
over CaCl2. Yield: 0.254 g (82%); m.p. 164–168ꢀC; Anal. Calcd for C33H24NO2ClSn
(%): C, 63.8; H, 3.8; N, 2.2. Found (%): C, 63.7; H, 3.9; N, 1.7. FT-IR (KBr, cmꢁ1):
1541, ꢁ(C¼O); 1584, ꢁ(C¼N)/ꢁ(C¼C); 568, ꢁ(Sn–O); 448, ꢁ(Sn–N). 1H NMR
(DMSO-d6): ꢂ ¼ 5.99 (s, 1H, H6), 6.02 (s, 1H, H8), 6.82 (d, J ¼ 8.6 Hz, 1H, H3),
6.85 (dd, J ¼ 8.6, 2.1 Hz, 1H, H4), 7.28–7.37 (m, 8H, H14,15,17,18,19), 7.44–7.57 (m, 6H,
3
Hm,p), 7.69 [d, 4H, Ho, JHH ¼ 6.7 Hz, 3J(119Sn–1H) ¼ 82.5 Hz], 8.04 (d, J ¼ 7.2 Hz,
2H, H13). 13C NMR (DMSO-d6): ꢂ ¼ 99.8, C8; 118.6, C3; 118.8, C4; 122.3, C6; 125.66,
C5; 127.5–129.4, C13,14,17,18; 128.5, Cm [3J(119Sn–13C) ¼ 82.6 Hz]; 130.5, Cp; 129.5,
132.0, C15,19; 135.6, Co [2J(119Sn–13C) ¼ 50.3 Hz]; 138.5, Ci [1J(119Sn–13C) ¼ 995.8 Hz];
134.5, 138.8, C12,16; 146.2, C1; 157.1, C2; 169.8, C7; 179.7, C9. 119Sn NMR (CDCl3):
ꢂ ¼ ꢁ297.9.
2.3.4. SnMe2Lc (4). Complex 4 was synthesized as described for 1 from H2Lc
(0.174 g, 0.5 mmol), KOH (0.056 g, 1.0 mmol) and SnMe2Cl2 (0.109 g, 0.5 mmol). The
product was obtained as red solid. Yield: 0.151 g (61%); m.p. 144–146ꢀC; Anal. Calcd
for C23H20NO2ClSn (%): C, 55.6; H, 4.0; N, 2.8. Found (%): C, 55.1; H, 4.3; N, 3.2.
FT-IR (KBr, cmꢁ1): 1538, ꢁ(C¼O); 1582, ꢁ(C¼N)/ꢁ(C¼C); 563, ꢁas(SnC); 553, ꢁ(Sn–
O); 506, ꢁs(SnC); 444 ꢁ(Sn–N). 1H NMR (DMSO-d6): ꢂ ¼ 0.71 [s, 6H, H20,
2J(119Sn–1H) ¼ 88.1 Hz], 6.00 (d, J ¼ 2.5 Hz, 1H, H6), 6.06 (s, 1H, H8), 6.59 (d,
J ¼ 8.5 Hz, 1H, H3), 6.73 (dd, J ¼ 8.6, 2.5 Hz, 1H, H4), 7.32–7.55 (m, 8H, H14,15,17,18,19),
7.93 (d, J ¼ 7.1 Hz, 2 H, H13). 13C NMR (DMSO-d6): ꢂ ¼ 4.2, C20; 99.4, C8; 118.2, C3;
118.4, C4; 123.0, C6; 125.4, C5; 128.0–129.6, C13,14,17,18; 130.6, 132.3, C15,19; 136.0,
139.2, C12,16; 139.4, C1; 157.8, C2; 170.9, C7; 182.0, C9. 119Sn NMR (CDCl3):
ꢂ ¼ ꢁ117.2.

Diorganotin(IV) complexes
3173
2.4. Antibacterial tests
The in vitro antibacterial activities of ligands and their corresponding organotin(IV)
complexes were investigated against standard strains of two Gram-positive (Bacillus
subtilis ATCC 12711 and Staphylococcus aureus ATCC 6538) and two Gram-negative
(Escherichia coli ATCC 11303 and Pseudomonas aeruginosa ATCC 27853) bacteria.
Vancomycin (30 mg/disc), Colistin (2 mg per disc), Nalidixic acid (30 mg per disc), and
Erythromycin (15 mg/disc) were used as standard antibacterial drugs. Determination of
the antibacterial activity was carried out by paper-disc diffusion. The compounds were
dissolved in DMSO at 12.5, 25, 50, and 100 mgmLꢁ1 concentration. Muller Hinton
broth was used for preparing basal media for the bioassay of the organisms. A lawn
culture from 0.5 MacFarland suspension of each strain was prepared on Muller Hinton
agar. Blank paper discs (6.4 mm diameter) were saturated with a solution of test
compounds (40 mL) and placed on the surface of the agar plates. On one paper disc only
DMSO was poured as a control. The plates were incubated at 37ꢀC for 24 h. The
inhibition zone diameters around each disc were measured in mm.
3. Results and discussion
3.1. Synthesis
The Schiff bases used in this work, H2La, H2Lb, and H2Lc, have been synthesized from
reaction of 2-amino-4-chlorophenol with acetylacetone, benzoyl acetone and dibenzoyl
methane, respectively. In these reactions only 1 : 1 condensation occurred even when an
excess of the amine was used. Structural formulae for these Schiff bases are given in
figure 1; the forms I–III may be present in tautomeric equilibria as shown. The positions
of the keto–enol or amine–imine equilibria and nature of the hydrogen bond in the six-
membered chelate ring is a consideration of these Schiff bases. The condensation
products of ꢀ-dicarbonyl compounds with mono- and diamines exist, in solid state, in
keto–amine form III; however, in solution both types of hydrogen bonds, N–H ꢃ ꢃ ꢃ O or
R
R'
R
R'
R
R'
Cl
N
O
Cl
N
O
Cl
N
O
H
H
OH
OH
OH
I
II
III
R
R'
Me
Me Ph
Ph Ph
H2La
H2Lb
H2Lc
Me
Figure 1. Tautomeric forms for Schiff for bases; I: keto-imine, II: enol-limine, III: keto-amine.

3174
T. Sedaghat et al.
N ꢃ ꢃ ꢃ H–O, have been reported [38–42]. The new organotin(IV) complexes, [SnPh2(La)] (1),
[SnPh2(Lb)] (2), [SnPh2(Lc)] (3), and [SnMe2(Lc)] (4), were synthesized by the reaction of
SnPh2Cl2 and SnMe2Cl2 with Schiff bases in the presence of a base. The composition
of complexes was confirmed by their analytical data and structures were suggested by
spectroscopic investigations.
3.2. Spectroscopic studies
In the IR spectra of ligands, the absence of a band in the free C¼O stretching region
(1700–1770 cmꢁ1) rules out keto–imine form I. The band observed at 1603–1607 cmꢁ1
has been assigned as a perturbed carbonyl stretch with the frequency lowering from a
free carbonyl, ascribed to conjugation and hydrogen-bonding in keto–amine form III
[38, 39]. In the IR spectra of 1–4, this band shifts to lower frequency providing evidence
of participation of oxygen in bonding with tin and so weakening the C¼O bond. In the
IR spectra of free ligands no band is observed at 3300–3500 cm–1 attributable to
stretching vibration of free NH or OH indicating inter-/intra-molecular hydrogen-
bonding; these bands shift to lower frequency and overlap with the ꢁ(C–H) at 2800–
3200 cmꢁ1. This broad band is absent in spectra of 1–4 supporting deprotonation of the
ligands during coordination. The appearance of new bands of the complexes at 439–448
and 512–568 cmꢁ1, assigned to ꢁ(Sn–N) and ꢁ(Sn–O), respectively, supports the
bonding of nitrogen and oxygen to tin [43–46]. The presence of both ꢁs(Sn–C) and
ꢁas(Sn–C) in the IR spectrum of 4 is consistent with a nonlinear C–Sn–C configuration
[43, 45, 47, 48].
1
In the H NMR spectra of Schiff bases the integrals of signals establishes only 1 : 1
condensation of diketone and amine. The presence of a signal at 5.2–6.2 ppm (1H)
corresponds to the vinylic hydrogen and the absence of a methylene signal near
3 ppm (2H) indicates no participation of keto–imine form I in solution. A sharp singlet
at 10 ppm related to enolic proton indicates tautomeric form II in solution; proton
transfer to imine nitrogen in form III would lead to broadening of the signal due to
interaction with the electronic quadrupole moment of nitrogen [49, 50]. In the spectra of
complexes, the absence of both phenolic and enolic signals suggests deprotonation and
coordination of dianionic ligands to tin.
1
The H NMR spectrum of 4 shows a singlet at 0.71 ppm for SnMe2 accompanied by
2
satellites with J(119Sn–1H) larger than uncomplexed SnMe2Cl2 (68.7 Hz). Generally
larger coupling constant indicates higher coordination number of tin [51]. Substitution
2
of J(119Sn-1H) in the Lockhart–Manders equation [52] gives a value of 142.2ꢀ for the
Me–Sn–Me angle. Therefore in the solution, similar to the solid phase, SnMe2 is not
linear.
13C NMR spectral data also support the proposed structures. Shifts in the positions
of carbons adjacent to imine nitrogen (C7) and phenolic and enolic oxygen atoms (C2,
C9) and also in vinylic carbon (C8) clearly indicate the bonding of the imine nitrogen
and two oxygen atoms to tin [33].
119Sn NMR spectra of all complexes show one sharp singlet at lower frequency than
the original SnMe2Cl2 (þ137 ppm) and SnPh2Cl2 (ꢁ32 ppm) [46]. 119Sn chemical shifts
are influenced by variation in coordination number, bond angles, and nature of
substituents at tin. 119Sn NMR is strongly dependent on the coordination number of
tin, and an increase in coordination number produces a large upfield shift. On the basis

Diorganotin(IV) complexes
Table 1. Thermal decomposition data for 1–4.
3175
Temperature
range (ꢀC)
DTG peak
temperature (ꢀC)
Weight loss (%)
observed (Calcd)
Complex
Evolved product
C11H10NOCl, 1.5C6H5
1
2
203–365
310
64.6 (65.1)
234–353
353–396
300
390
40.9 (42.2)
34.1 (33.6)
C10H9NO, C6H5
C6H3Cl, C6H5
3
4
181–364
364–444
340
380
41.7 (41.5)
32.0 (32.4)
C15H11NO, HCl
2C6H6, 1/3SnO
155–238
238–402
402–1050
201
320
900
7.7 (6.5)
48.9 (48.7)
35.1 (35.3)
2CH4
C15H11NO, HCl
CH4, 6C, 2/3SnO
of the chemical shift ranges for organotin(IV) derivatives, the 119Sn resonances located
between ꢁ90 and ꢁ330 ppm have been empirically related to the five-coordinated tin
[17, 43, 53–56]. Thus, it appears reasonable to assume that for all complexes the
coordination number of the tin is five in solution.
3.3. Thermogravimetric analyses
The TGA of 1–4 from ambient temperature to 1050ꢀC are summarized in table 1.
Complex 1 shows only one-step decomposition with drastic mass loss at 203–365ꢀC.
This process can be readily interpreted as loss of ligand and phenyl groups. The
following decomposition of the complex exhibits a gradual mass loss and no obvious
peaks in the DTG curve leading to 0.6SnO as final product at 1050ꢀC. Complex 2
decomposed in two steps. The initial weight loss is attributed to removal of one phenyl
and part of the ligand. The second step corresponds to the formation of SnO as residue.
The thermal degradation of 3 takes place in two stages, the first corresponds to loss of
C15H11NO and HCl, while the second may be attributed to removal of two phenyl
groups and 1/3SnO. Complex 4 shows three stages of decomposition. First, mass loss
corresponds to elimination of two methyl groups. The second step involves HCl and a
part of the ligand. The third step takes place to give 1/3SnO as residue.
3.4. Biological studies
The in vitro antibacterial activities of all Schiff bases and their organotin(IV) complexes
were studied along with four standard antibacterial drugs, Vancomycin, Colistin,
Nalidixic acid, and Erythromycin. The microorganisms used in this work include
B. subtilis and S. aureus (as Gram-positive bacteria) and E. coli and P. aeruginosa (as
Gram-negative bacteria). The results are presented in table 2. Inhibition zone diameter
over 7 mm indicates that all test compounds (except H2Lb) are active against the
bacteria under investigation [57]. Antibacterial activity of compounds is due to either
bactericide effects (killing the bacteria) or bacteriostatic effects (inhibiting multiplica-
tion of bacteria by blocking their active sites). It may be postulated that antibacterial
compounds deactivate various cellular enzymes, which play a vital role in various
metabolic pathways of these organisms. It has also been proposed that the ultimate

3176
T. Sedaghat et al.

Diorganotin(IV) complexes
3177
action of the antibacterial agent is the denaturation of one or more proteins of the cell,
which, as a result, impairs normal cellular processes [58]. On comparing the biological
activity of the Schiff bases, organotin(IV) complexes and standard drugs, the following
results are obtained:
The antibacterial data indicate that H2La has remarkable and H2Lc has moderate
activity toward all bacterial strains while H2Lb is only effective against B. subtilis. The
activity of ligands may be due to NH/OH groups inside the Schiff base [59]. According
to previous findings, compounds having halogens at different positions of the aromatic
ring showed good inhibitory effects [60]. Complexes 2, 3, and 4 exhibit more inhibitory
effects than the parent ligands. Enhancement in activity may be due to the coordination
of ligand to tin leading to electron delocalization and therefore increasing the lipophilic
character and efficient diffusion of the metal complexes into bacterial cells [5, 57,
61–65]. All compounds were more toxic toward Gram(þ) strains than Gram(ꢁ) strains
due to difference in the structures of the cell walls. The walls of Gram(ꢁ) cells are more
complex than those of Gram(þ) cells. Lipopolysaccharides form an outer lipid
membrane and contribute to the complex antigenic specificity of Gram(ꢁ) cells [66].
However, it is important to note that, all compounds (except H2Lb) have appreciable
activities against Gram(ꢁ) bacteria, the activity of 4 is significant. It is also interesting
that P. aeruginosa was inhibited by both Schiff bases (except H2Lb) and complexes
while standard drugs were found to have no activity against it.
4. Conclusion
Four new diorganotin(IV) complexes have been synthesized from the reaction of
diorganotin(IV) dichlorides with three Schiff bases derived from 1 : 1 condensation of
2-amino-4-chlorophenol with various ꢀ-diketones. On the basis of analytical and
spectral data, Schiff bases are completely deprotonated and coordinated to tin
tridentate via imine nitrogen and phenolic and enolic oxygen atoms (figure 2). The
synthesized organotin complexes inhibit both Gram-positive (B. subtilis and S. aureus)
10
CH3
R =
for 1,2
for 3, 4
18
17
16
8
R
1
R'
7
19
9
6
3
11
Cl
N
O
R' =
CH3
for 1
5
13
14
Sn
12
R''
for 2, 3, 4
15
4
2
O
R''
o
m
i
for 1,2,3
for 4
p
R'' =
20
CH3
Figure 2. Suggested structure for 1–4 with numbering for NMR assignments.

3178
T. Sedaghat et al.
and Gram-negative (E. coli and P. aeruginosa) bacterial species. Most research for new
anti-tumor drugs depends on antibiotics affecting Gram-negative bacteria [67], making
it possible that these new organotin(IV) complexes have anti-tumor effects. With regard
to data published on tin derivatives, [R2Sn(IV)]2þ compounds generally exhibit higher
antitumor activity than those of the corresponding mono-, tri- and tetraorganotin(IV)
or inorganic tin derivatives; within the diorganotin(IV) class, the highest activity is
exerted by [Et2Sn(IV)]2þ and [Ph2Sn(IV)]2þ complexes [20]. Di-phenyl-tin(IV) deriva-
tives often are less toxic than other di-organo-tin(IV) derivatives [17, 68, 69]. Therefore,
1–3 may be good candidates for cytotoxicity studies. This research shows that both the
nature of organic groups (R) bound to tin and the substituents in the donor ligand (L)
can change the biological activity of R2SnL derivatives. This study shows a further
aspect of the structural chemistry and thermal and biological properties of
organotin(IV) complexes with multidentate Schiff-base ligands.
Acknowledgments
Support of this work by Shahid Chamran University, Ahvaz, Iran is gratefully
acknowledged.
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