Synthesis, characterization, and in vitro antimicrobial activities of organotin(IV) complexes of Schiff bases with ONO-type donor atoms

Article abstract of DOI:10.1002/hc.20628

A new series of diorganotin complexes of the type R₂SnL (L ¹: N-(2-hydroxy-5-chlorophenyl)- 3-ethoxysalicylideneimine, R = Me, (Me₂SnL¹), R = n-Bu, (n-Bu₂SnL¹), R = Ph, (Ph₂SnL

Full text of DOI:10.1002/hc.20628

Heteroatom Chemistry
Volume 21, Number 6, 2010
Synthesis, Characterization, and In Vitro
Antimicrobial Activities of Organotin(IV)
Complexes of Schiff Bases with ONO-type
Donor Atoms
1
2
3
¨
Gu¨lgu¨n Yenis¸ehirli, Nurs¸en Altuntas¸ Oztas¸, Ertan S¸ ahin,
4
5
5
¨
Mustafa C¸ elebier, Nilgu¨n Ancın, and Selma Gu¨l Oztas¸
1Department of Microbiology and Clinical Microbiology, Faculty of Medicine,
Gaziosmanpas¸a University, 60100 Tokat, Turkey
2Department of Chemistry, Faculty of Science, Hacettepe University, 06800 Ankara, Turkey
3Department of Chemistry, Faculty of Arts and Sciences, Atatu¨ rk University,
25240 Erzurum, Turkey
4Department of Analytical Chemistry, Faculty of Pharmacy, Hacettepe University, 06100 Sihhiye,
Ankara, Turkey
5Department of Chemistry, Faculty of Science, Ankara University, 06100 Ankara, Turkey
Received 15 March 2010; revised 16 June 2010
midal and distorted square pyramidal arrangement.
ABSTRACT: A new series of diorganotin complexes
The C–Sn–C angles in the complexes were calculated
of the type R2SnL (L1: N-(2-hydroxy-5-chlorophenyl)-
1
using Lockhart’s equations with the J(117/119Sn-13C)
3-ethoxysalicylideneimine, R = Me, (Me2SnL1), R =
and 2 J(117/119Sn-1H) values from the 1H NMR and
n-Bu, (n-Bu2SnL1), R = Ph, (Ph2SnL1), L2: N-(2-
13C NMR spectra. Biocidal activity tests against sev-
hydroxy - 4 - nitro - 5- chlorophenyl) - 3- ethoxysalicyli -
eral micro-organisms and some fungi indicate that
deneimine, R = Ph, Ph2SnL2, L3: N-(2-hydroxy-
all the complexes are mildly active against Gram (+)
4-nitrophenyl)-3-methoxysalicylideneimine, R = Me,
bacteria and the fungi, A. niger and inactive against
(Me2SnL3), R = n-Bu, (n-Bu2SnL3), L4: N-(2-hydroxy-
ꢀ
C
Gram (−) bacteria.
2010 Wiley Periodicals, Inc. Het-
4 - nitrophenyl) - 3 - ethoxysalicylideneimine, R = Me,
(Me2SnL4), R = n-Bu, (n-Bu2SnL4)) were synthesized
and characterized by elemental analysis, infrared (IR),
1H, and 13C NMR mass spectroscopic techniques, and
electrochemical measurements. Ph2SnL1 and Ph2SnL2
were also characterized by X-ray diffraction analysis
and were found to show a fivefold C2NO2 coordination
geometry nearly halfway between a trigonal bipyra-
eroatom Chem 21:373–385, 2010; View this article online
at wileyonlinelibrary.com. DOI 10.1002/hc.20628
INTRODUCTION
The diorganotin(IV) complexes derived from hy-
droxyl Schiff base anions have attracted consider-
able interest [1–13]. Recent studies have focused on
their biological [14], particularly antitumor [15–18],
antibacterial [18–21], antifungal [21,22], and anti-
tubercular, properties [23,24]. Many in vitro stud-
ies have been performed to explain the mechanism
¨
Correspondence to: Selma Gu¨l Oztas¸; e-mail: goztas@science
.ankara.edu.tr.
Contract grant sponsor: Ankara University Research Fund.
Contract grant number: 2003-07-05-081.
2010 Wiley Periodicals, Inc.
c
ꢀ
373

374 Yenis¸ehirli et al.
FIGURE 1 Numbering and preparation of compounds.
responsible for the biological activity of these agents.
Although the true mechanism of biological ac-
tion is not understood completely, there appears
to be enough evidence that the activities of organ-
otin(IV) compounds are dependent on both the co-
valently bonded organic groups and the ligands. The
organotin(IV) complexes have also found applica-
tions in the fields of catalysis [25,26], fluorescence
probing of DNA traces [27], and nonlinear optics
[9,28].
In this part of our studies on the diorganotin(IV)
complexes, we report herein the synthesis, struc-
tural analysis, and electrochemical measurements
of diorganotin(IV) complexes containing tridentate
Schiff base anions derived from 3-methoxy salicy-
laldehyde, 3-ethoxy salicylaldehyde, and three dif-
ferent 2-aminophenols. All the Schiff base anions
(Fig. 1) were of ONO-type ligands. The complexes
were synthesized under mild conditions starting
from R2SnCl2 (R: Me, n-Bu, Ph) and the Schiff
base (H2L) in methanol in the presence of sodium
methoxide. The procedure is summarized in Fig. 1.
All the organotin(IV) complexes prepared are stable
under atmospheric conditions.
complexes were insoluble in water, solutions in
DMSO were used in the activity studies.
EXPERIMENTAL
Materials and Physical Measurements
All chemicals and reagents were of reagent-grade
quality. Dimethyltin dichloride, di-n-butyltin
dichloride, diphenyltin dichloride, 2-hydroxy-5-
chloroaniline, 2-hydroxy-4-nitroaniline, 2-hydroxy-
4-nitro-5-chloroaniline, 3-methoxysalicylaldehyde,
3-ethoxysalicylaldehyde, and solvents were pur-
chased from Aldrich (Steinheim, Germany) and
used without further purification.
The 1H NMR and 13C NMR spectra were ob-
tained in deuterated DMSO and CDCl3 solvents on
a Bruker-400 MHz Ultrashield NMR spectrometer
with TMS as internal standard. The IR spectra were
recorded on a Mattson-1000 FTIR spectrophotome-
ter using KBr pellets, in the range 4000–400 cm−1.
Bands were located by means of a microprocessor.
ESI-Mass spectra were recorded on an Agilent 1100
MSD LC-MS spectrometer. Melting points were de-
termined on a hot-stage Leica DM EP polarizing
microscope system. Chemical analysis of C, H, and
N were determined with Leco CHNS-932 elemental
analyzer.
Electrochemical properties of the Schiff bases
and complexes were investigated by cyclic voltam-
metry (CV) and the reduction potentials, and the
peak currents of the Schiff bases and the complexes
were compared.
Antibacterial and antifungal activities of the
novel complexes and similar compounds reported
elsewhere [29] were also investigated. As the
The X-ray intensity data for Ph2SnL1 and
Ph2SnL2 were measured at room temperature on
a four-circle Rigaku R-AXIS RAPID-S diffractome-
ter (equipped with a two-dimensional (2D) area IP
Heteroatom Chemistry DOI 10.1002/hc

Synthesis, Characterization, and In Vitro Antimicrobial Activities of Organotin(IV) Complexes of Schiff Bases 375
detector). The graphite-monochromatized Mo Kα ra-
(C-9), 118.69 (C-4), 119.56 (C-12), 119.78 (C-6),
123.56 (C-11), 124.60 (C-3), 127.83 (C-10), 136.27 (C-
13), 147.66 (C-2), 150.63 (C-8), 152.14 (C-1), 163.44
(C-7).
˚
diation (λ = 0.71073 A) and oscillation scans tech-
nique with ꢀω = 5◦ for one image were used for data
collection. The lattice parameters were determined
by the least-squares methods on the basis of all re-
flections with F2 >2σ(F2). Integration of the intensi-
ties, correction for Lorentz, and polarization effects,
and cell refinement were performed using Crystal-
Clear (Rigaku/MSC, Inc., The Woodlands, TX) soft-
ware [30]. The structures were solved by direct meth-
ods using SHELXS-97 [31] and refined by a full-
matrix least-squares procedure using the program
SHELXL-97 [31]. H atoms were positioned geomet-
rically and refined using a riding model. The final
difference Fourier maps showed no further peaks of
chemical significance.
N-(2-Hydroxy-4-nitro-5-chlorophenyl)-3-ethoxys-
alicylideneimine (H2 L2). Reddish-black crystals, mp
209–211◦C; IR (cm−1): 2890 br υ(O H); 1627 s
υ(C N). Mass spectrum (ESI) {m/z [assignment]
(%)}: 337 [M + H]+ (100). Elemental Anal.: Found C,
53.59; H, 3.97; N, 8.27%. Calcd for C15H13N2O5Cl: C,
53.50; H, 3.89; N, 8.32%.1H NMR (DMSO-d6),δ: 1.36
3
3
(t, J = 7.0 Hz, 3H, CH3), 4.08 (q, J = 7.0 Hz, 2H,
3
OCH2), 6.91 (t, J = 8.0 Hz, 1H, H-4), 7.78 (s, 1H,
H-9), 7.20 (dd, J = 8.0 Hz,4 J = 1.2 Hz, 1H, H-5),
3
7.25 (dd,3 J = 8.0 Hz,4 J = 1.2 Hz 1H, H-3), 7.61 (s,
1H, H-12), 9.05 (s, 1H, H-7), 10.99 [s, 1H (OH)a],
13.11 [s, 1H, (OH)b].13C NMR (DMSO-d6),δ: 14.71
(CH3), 64.34 (OCH2), 111.18 (C-12), 113.10 (C-11),
115.85 (C-9), 117.46 (C-5), 119.23 (C-4), 120.30 (C-
6), 124.21 (C-3), 144.96 (C-13), 147.36 (C-10), 150.12
(C-2), 150.84 (C-8), 151.50 (C-1), 165.72 (C-7).
The synthesis and the characteristics of N-
(2-hydroxy-4-nitrophenyl)-3-methoxysalicylidenei-
mine (H2L3) and N-(2-hydroxy-4-nitrophenyl)-3-
ethoxysalicylideneimine (H2L4) were published else-
where [29].
Electrochemical measurements were recorded
on a Radiometer Voltalab 80 (PGZ402): The work-
ing electrode was a glassy carbon, and the auxil-
iary electrode was a platinum wire. Ag/AgCl and
calomel reference electrodes were used as the ref-
erence electrodes, and measurements were carried
out at 25 0.2◦C and under argon atmosphere. The
ionic strength was maintained at 0.1 mol L−1 with
Bu4NBF4 as a supporting electrolyte. The concentra-
tion of all the electroactive species was 1 × 10−3 mol
L−1 in dimethylformamide.
Preparation of the Complexes
Synthesis of the Ligands
Tin(IV) complexes of the Schiff base-ligands were
prepared from the appropriate diorganotin(IV)
dichloride and the Schiff base as follows: To a so-
lution of Schiff base (2.0 mmol) in 15 mL dry
methanol, a few drops of concentrated sodium
methoxide in methanol were added, and the result-
ing sodium salt solution of the ligand was filtered to
remove any insoluble impurities.
A solution of R2SnCl2 (2.0 mmol) in 15 mL of dry
methanol was added slowly to this solution, and it
was heated to 50–60◦C. The resulting mixture was
kept at room temperature overnight. The crystals
were filtered off and recrystallized from butanol–
dichloromethane (1/1, v/v) mixture. The description
of the individual complexes was as follows:
The Schiff bases were prepared by reacting a 1:1
molar ratio mixture of appropriate salicylaldehyde
and aminophenol derivatives in methanol. The re-
action mixture was refluxed for 1 h, and the pre-
cipitate thus formed upon cooling in an ice bath
was filtered off. The powder products were crys-
tallized from methanol–dichloromethane (1/1 v/v)
mixture.
N-(2-Hydroxy-5-chlorophenyl)-3-ethoxysalicylid-
eneimine (H2L1). Reddish-orange crystals, mp 214–
216◦C; IR (cm−1): 2920 br υ(O H); 1638 s υ(C N).
Mass spectrum (ESI) {m/z [assignment] (%)}: 292
[M + H]+ (100). Elemental Anal.: Found C, 61.53; H,
4.71; N, 4.91%. Calcd for C15H14NO3Cl: C, 61.75; H,
1
4.83; N, 4.80%. H NMR (DMSO-d6), δ: 1.35 (t, 3 J =
[N-(2-Hydroxy-5-chlorophenyl)-3-ethoxysalicylid-
3
7.0 Hz, 3H, CH3), 4.07 (q, J = 7.0 Hz, 2H, OCH2),
eneiminato]dimethyltin(IV)
(Me2SnL1). Orange
6.87 (t, J = 7.9 Hz, 1H, H-4), 6.97 (d,3 J = 8.6 Hz,
crystals, mp 166–168◦C; IR (cm−1): 1599 s υ (C N),
680 υ(Sn C), 527 υ(Sn O), 497 υ(Sn N). Mass
spectrum (ESI) {m/z [assignment] (%)}: 440 [M
+ H]+(120Sn) (100.0), 438 [M + H]+(118Sn) (76.4),
436 [M + H]+(116Sn) (37.1), 359 [M-(OC2H5+
3
1H, H-9), 7.10 (dd, 3 J = 7.9 Hz,4 J = 1.2 Hz, 1H,
4
H-5), 7.16 (dd,3 J = 8.6 Hz, J = 2.5 Hz 1H, H-10),
7.19 (dd,3 J = 7.9 Hz,4 J = 1.2 Hz 1H, H-3), 7.50 (d,
4 J = 2.5 Hz, 1H, H-12), 9.00 (s, 1H, H-7), 10.05 [s,
1H (OH)a], 13.74 [s, 1H, (OH)b]. 13C NMR (DMSO-
d6),δ: 15.23 (CH3), 64.54 (OCH2), 117.36 (C-5), 118.27
Cl)]+(120Sn) (4.7), 357 [M-(OC2H5+ Cl)]+
(
118Sn)
(3.5), 355 [M-(OC2H5+ Cl)]+ (116Sn) (1.7). Elemental
Heteroatom Chemistry DOI 10.1002/hc

376 Yenis¸ehirli et al.
Hz, 1H, H-4), 6.91 (dd, 3 J = 7.9 Hz,4 J = 1.6 Hz,
1H, H-5), 7.06 (dd,3 J = 8.0 Hz,4 J = 1.6 Hz 1H,
Anal.: Found C, 46.32; H, 4.02; N, 3.28%. Calcd
1
for C17H18NO3ClSn: C, 46.57; H, 4.14; N, 3.19%. H
2
NMR (CDCl3), δ: 0.84 [s, J(117/119Sn-1H) = 78.5 Hz,
3
H-3), 7.09 (d,3 J = 8.4 Hz, 1H, H-9), 7.20 (dd, J =
3
8.6 Hz, 4 J = 2.4 Hz 1H, H-10), 7.34 (d, 4 J = 2.4
Hz 1H, H-12), 7.35–7.45 (m, 6H, H-meta-Sn-Ph,
H-para-Sn-Ph), 7.97 (m, 4H, H-ortho-Sn-Ph), 8.63
[s, 3 J(117/119Sn-1H) = 55.6 Hz, 1H, H-7].13C NMR
(CDCl3), δ: 15.13 (CH3), 65.10 (OCH2), 114.93
(C-12), 117.05 (C-4), 117.95 (C-6), 119.84 (C-9),
119.84 (C-3), 121.53 (C-11), 126.98 (C-5), 128.13
[3 J(117/119Sn-13C) = 84.3 Hz, C-meta-Sn-Ph], 129.80
(C-10), 130.39 (C-para-Sn-Ph), 131.89 (C-13), 136.51
[2 J(117/119Sn-13C) = 54.9 Hz, C-ortho-Sn-Ph], 139.26
(C-ipso-Sn-Ph), 151.28 (C-2), 157.45 (C-8), 161.11
(C-1), 162.37 (C-7).
6H, Sn(CH3)2], 1.45 (t, J = 7.0 Hz, 3H, CH3), 4.12
(q, 3 J = 7.0 Hz, 2H, OCH2), 6.70 (t, 3 J = 7.8 Hz,
1H, H-4), 6.78 (d,3 J = 8.7 Hz, 1H, H-9), 6.93 (dd,
3 J = 7.9 Hz,4 J = 1.4 Hz, 1H, H-5), 7.01 (dd,3 J =
7.8 Hz,4 J = 1.4 Hz 1H, H-3), 7.15 (dd, 3 J = 8.7
Hz, 4 J = 2.5 Hz 1H, H-10), 7.35 (d, 4 J = 2.5 Hz
1H, H-12), 8.62 [s, 3 J(117/119Sn-1H) = 48.5 Hz, 1H,
H-7].13C NMR (CDCl3), δ: 0.00 [1 J(117/119Sn-13C) =
647.0 Hz, (Sn(CH3)2)], 13.27 (CH3), 63.42 (OCH2),
113.49 (C-12), 115.13 (C-4), 116.17 (C-6), 117.80
(C-9), 118.08 (C-3), 119.49 (C-11), 125.49 (C-5),
128.16 (C-10), 130.44 (C-13), 149.31 (C-2), 155.90
(C-8), 159.17 (C-1), 161.22 (C-7).
[N-(2-Hydroxy-4-nitro-5-chlorophenyl)-3-ethoxy-
(Ph2SnL2).
[N-(2-Hydroxy-5-chlorophenyl)-3-ethoxysalicylid-
eneiminato]di-n-butyltin(IV) (n-Bu2 SnL1). Reddish
orange crystals, mp 100–102◦C; IR (cm−1): 1600
s υ(C N), 679 υ (Sn C), 529 υ (Sn O), 447 υ
(Sn N). Mass spectrum (ESI) {m/z [assignment]
(%)}: 524 [M + H]+(120Sn) (100), 522 [M + H]+(118Sn)
(73.8), 520 [M + H]+(116Sn) (34.3). Elemental Anal.:
Found C, 52.61; H, 5.83; N, 2.65%. Calcd for
C23H30NO3ClSn: C, 52.86; H, 5.79; N, 2.68%. 1H NMR
(CDCl3), δ: 0.86 (t, 3 J = 7.3 Hz, 6H, δ-CH3), 1.35 (m,
salicylideneiminato]diphenyltin(IV)
Reddish-orange crystals, mp 237–239◦C; IR (cm−1):
1603 s υ(C N), 696 υ(Sn C), 565 υ(Sn O), 448
υ(Sn N). Mass spectrum (ESI) {m/z [assign-
ment] (%)}: 609 [M + H]+(120Sn) (61.2), 607 [M
+ H]+(118Sn) (44.7), 605 [M + H]+(116Sn) (17.9).
Elemental Anal.: Found C, 53.45; H, 3.41; N, 4.72%.
Calcd for C27H21N2O5ClSn: C, 53.37; H, 3.48; N,
1
4.61%. H NMR (CDCl3), δ: 1.59 (t, 3 J = 7.0 Hz,
3H, CH3), 4.23 (q, 3 J = 7.0 Hz, 2H, OCH2), 6.77
3
3 J = 7.3 Hz, 4H, γ -CH2), 1.44 (t, J = 7.0 Hz, 3H,
3
3
(t, J = 8.0 Hz, 1H, H-4), 6.93 (dd, J = 8.0 Hz,4 J
= 1.3 Hz, 1H, H-5), 7.12 (dd,3 J = 8.0 Hz,4 J = 1.3
Hz 1H, H-3), 7.30 (s, 1H, H-9), 7.38–7.48 (m, 6H,
H-meta-Sn-Ph , H-para-Sn-Ph), 7.63 (s, 1H, H-12),
7.92 (m, 4H, H-ortho-Sn-Ph), 8.67 (s, 3 J(117/119Sn-1H)
= 48.0 Hz, 1H, H-7). 13C NMR (CDCl3), δ: 15.06
(CH3), 65.00 (OCH2), 113.78 (C-12), 115.37 (C-9),
117.55 (C-6), 117.67 (C-11), 117.72 (C-4), 120.32
(C-3), 127.16 (C-5), 128.95 [3 J(117/119Sn-13C) = 85.9
Hz, C-meta-Sn-Ph], 130.77 (C-para-Sn-Ph), 136.43
[2 J(117/119Sn-13C) = 56.0 Hz, C-ortho-Sn-Ph], 136.50
(C-13), 138.45 (C-ipso-Sn-Ph), 147.50 (C-10), 151.45
(C-2), 157.54 (C-8), 162.40 (C-1), 164.77 (C-7).
CH3), 1.46–1.56 (m, 3 J = 7.0 Hz, 4H, α-CH2), 1.63 (m,
3
3 J = 7.2 Hz, 4H, β-CH2), 4.10 (q, J = 7.0 Hz, 2H,
3
OCH2), 6.68 (t, J = 7.8 Hz, 1H, H-4), 6.78 (d,3 J =
8.7 Hz, 1H, H-9), 6.91 (dd, 3 J = 8.0 Hz,4 J = 1.4 Hz,
1H, H-5), 7.00 (dd,3 J = 7.7 Hz,4 J = 1.6 Hz 1H, H-3),
3
4
7.13 (dd, J = 8.7 Hz, J = 2.4 Hz 1H, H-10), 7.33
(d, 4 J = 2.4 Hz 1H, H-12), 8.61 [s, 3 J(117/119Sn-1H) =
44.5 Hz, 1H, H-7].13C NMR (CDCl3), δ: 13.60 (CH3),
14.93 (δ-CH3), 22.34 [1 J(117/119Sn-13C) = 601.0 Hz,
α-CH2], 26.70 [3 J(117/119Sn-13C) = 32.0 Hz, γ -CH2],
26.92 [2 J(117/119Sn-13C) = 32.0 Hz, β-CH2], 64.96
(OCH2), 115.02 (C-12), 116.38 (C-4), 117.93 (C-6),
119.33 (C-9), 119.74 (C-3), 120.77 (C-11), 127.03 (C-
5), 129.58 (C-10), 132.41 (C-13), 150.94 (C-2), 158.19
(C-8), 161.46 (C-1), 162.50 (C-7).
[N-(2-Hydroxy-4-nitrophenyl)-3-methoxysalicyli-
deneiminato]dimethyltin(IV) (Me2SnL3). Red crys-
tals, mp 176–178◦C; IR (cm−1): 1607 s υ(C N), 670
υ(Sn C), 521 υ(Sn O), 500 υ(Sn N). Mass spec-
trum (ESI) {m/z [assignment] (%)}: 436 [M]+(120Sn)
(1.2), 434 [M]+(118Sn) (0.8), 432 [M]+(116Sn) (0.8). El-
emental Anal.: Found C, 44.07; H, 3.77; N, 6.42%.
Calcd for C16H16N2O5Sn: C, 44.18; H, 3.71; N,
6.44%.1H NMR (CDCl3), δ: 0.81 [s, 2 J(117/119Sn-1H)
= 78.4 Hz, 6H, Sn(CH3)2], 3.80 (s, 3H, OCH3), 6.67
[N-(2-Hydroxy-5-chlorophenyl)-3-ethoxysalicylid-
eneiminato]diphenyltin(IV)
(Ph2SnL1). Reddish
brown crystals, mp 173–175◦C; IR (cm−1):1602 s
υ(C N), 679 υ(Sn C), 534 υ(Sn O), 448 υ(Sn N).
Mass spectrum (ESI) {m/z [assignment] (%)}:
564 [M + H]+(120Sn) (53.0), 562 [M + H]+(118Sn)
(27.2), 560 [M + H]+(116Sn) (16.8). Elemental
Anal.: Found C, 57.73; H, 4.01; N, 2.65%. Calcd
3
3
(t, J = 7.8 Hz, 1H, H-4), 6.85 (dd, J = 8.0 Hz,4 J
= 1.4 Hz, 1H, H-5), 6.93 (dd,3 J = 7.9 Hz,4 J = 1.4
Hz 1H, H-3), 7.34 (d, 3 J = 8.8 Hz 1H, H-12), 7.52
(dd, 3 J = 8.8 Hz, 4 J = 2.4 Hz 1H, H-11), 7.56
1
for C27H22NO3ClSn: C, 57.64; H, 3.94; N, 2.49%. H
NMR (CDCl3), δ: 1.56 (t, 3 J = 7.2 Hz, 3H, CH3),
4.23 (q, 3 J = 7.2 Hz, 2H, OCH2), 6.73 (t, 3 J = 7.8
Heteroatom Chemistry DOI 10.1002/hc

Synthesis, Characterization, and In Vitro Antimicrobial Activities of Organotin(IV) Complexes of Schiff Bases 377
(d,4 J = 2.4 Hz, 1H, H-9), 8.65 [s, 3 J(117/119Sn-
110.49 (C-11), 112.18 (C-12), 113.95 (C-9), 116.12 (C-
1H) = 49.2 Hz, 1H, H-7].13C NMR (CDCl3),δ: 0.00
[1 J(117/119Sn-13C) = 645.0 Hz, (Sn(CH3)2)], 53.23
(OCH3), 109.52 (C-11), 111.27 (C-12), 113.03 (C-9),
115.09 (C-4), 115.42 (C-6), 122.11 (C-3), 124.89 (C-
5), 135.89 (C-13), 146.61 (C-10), 149.88 (C-2), 157.09
(C-8), 159.50 (C-1), 162.91 (C-7).
4), 116.66 (C-6), 119.11 (C-3), 126.21 (C-5), 136.13
(C-13), 147.48 (C-10), 150.06 (C-2), 158.02 (C-8),
160.82 (C-1), 163.92 (C-7).
[N-(2-Hydroxy-4-nitrophenyl)-3-ethoxysalicylide-
neiminato]di-n-butyltin(IV) (n-Bu2SnL4). Red crys-
tals, mp 73–75◦C; IR (cm−1): 1592 s υ(C N), 669
υ(Sn C), 552 υ(Sn O), 484 υ(Sn N). Mass spec-
trum (ESI) {m/z [assignment] (%)}: 534 [M]+(120Sn)
(34.0), 532 [M]+(118Sn) (27.2), 530 [M]+(116Sn) (14.3),
477 [M-C4H9]+ (120Sn) (76.6), 475 [M-C4H9]+ (118Sn)
(55.0), 473 [M-C4H9]+(116Sn) (30.9), 421 [M + H-
2C4H9]+(120Sn) (100.0). Elemental Anal.: Found C,
51.72; H, 5.62; N, 5.20%. Calcd for C23H30N2O5Sn: C,
51.81; H, 5.67; N, 5.25%.1H NMR (CDCl3), δ: 0.85 (t,
[N-(2-Hydroxy-4-nitrophenyl)-3-methoxysalicyli-
deneiminato]di-n-butyltin(IV)
(n-Bu2SnL3). Red
crystals, mp 80–82◦C; IR (cm−1): 1605 s υ(C N), 680
υ(Sn C), 562 υ(Sn O), 490 υ(Sn N). Mass spec-
trum (ESI) {m/z [assignment] (%)}: 520 [M]+(120Sn)
(3.5), 518 [M]+(118Sn) (2.6), 516 [M]+(116Sn) (1.3),
463 [M-C4H9]+(120Sn) (10.0), 461 [M-C4H9]+(118Sn)
(7.5), 459 [M-C4H9]+(116Sn) (4.4), 407 [M + H-
2C4H9]+(120Sn) (17.2), 405 [M + H-2C4H9]+(118Sn)
(15.9), 403 [M + H-2C4H9]+(116Sn) (9.9). Elemental
Anal.: Found C, 51.01; H, 5.38; N, 5.41%. Calcd for
C22H28N2O5Sn: C, 50.90; H, 5.44; N, 5.40%.1H NMR
3
3 J = 7.2 Hz, 6H, δ-CH3), 1.35 (m, J = 7.2 Hz, 4H,
γ -CH2), 1.44 (t, 3 J = 7.0 Hz, 3H, CH3), 1.50–1.59 (m,
4H, α-CH2), 1.60–1.68 (m, 4H, β-CH2), 4.08 (q, 3 J =
7.0 Hz, 2H, OCH2), 6.69 (t, 3 J = 7.8 Hz, 1H, H-4), 6.93
(dd, 3 J = 8.0 Hz,4 J = 1.2 Hz, 1H, H-5), 7.10 (dd,3J =
7.8 Hz,4 J = 1.2 Hz 1H, H-3), 7.40 (d, 3 J = 8.8 Hz 1H,
H-12), 7.57 (dd, 3 J = 8.8 Hz, 4 J = 2.4 Hz 1H, H-11),
7.64 (d,4 J = 2.4 Hz, 1H, H-9), 8.74 [s, 3 J(117/119Sn-1H)
= 42.0 Hz, 1H, H-7].13C NMR (CDCl3), δ: 13.80 (CH3),
15.09 (δ-CH3), 22.78 [1 J(117/119Sn-13C) = 610.0 Hz,
α-CH2], 26.92 [3 J(117/119Sn-13C) = 29.7 Hz, γ -CH2],
27.09 [2 J(117/119Sn-13C) = 29.7 Hz, β-CH2], 65.12
(OCH2), 111.50 (C-11), 113.22 (C-12), 115.21 (C-9),
117.06 (C-4), 118.07 (C-6), 120.30 (C-3), 127.46 (C-
5), 137.90 (C-13), 148.50 (C-10), 151.28 (C-2), 159.87
(C-8), 159.87 (C-1), 161.04 (C-7).
3
(CDCl3),δ: 0.85 (t, J = 7.2 Hz, 6H, δ-CH3), 1.35 (m,
3 J = 7.2 Hz, 4H, γ -CH2), 1.50–1.58 (m, 4H, α-CH2),
1.60–1.69 (m, 4H, β-CH2), 3.89 (s, 3H, OCH3), 6.73
3
3
(t, J = 8.0 Hz, 1H, H-4), 6.93 (dd, J = 8.0 Hz,4 J
= 1.4 Hz, 1H, H-5), 7.02 (dd,3 J = 8.0 Hz,4 J =
1.4 Hz 1H, H-3), 7.42 (d, 3 J = 8.8 Hz 1H, H-12),
3
4
7.60 (dd, J = 8.8 Hz, J = 2.4 Hz 1H, H-11), 7.67
(d,4 J = 2.3 Hz, 1H, H-9), 8.73 [s, 3 J(117/119Sn-1H)
= 44.0 Hz, 1H, H-7].13C NMR (CDCl3), δ: 13.64
(δ-CH3), 22.82 [1 J(117/119Sn-13C) = 601.0 Hz, α-CH2],
26.68 [3 J(117/119Sn-13C) = 27.5 Hz, γ -CH2], 27.85
[2 J(117/119Sn-13C) = 27.5 Hz, β-CH2], 56.28 (OCH3),
111.28 (C-11), 113.19 (C-12), 114.94 (C-9), 116.74
(C-4), 116.80 (C-6), 117.56 (C-3), 126.89 (C-5),
137.59 (C-13), 148.50 (C-10), 151.90 (C-2), 159.80
(C-8), 161.97 (C-1), 164.72 (C-7).
Antimicrobial Studies
Antibacterial Activity. The compounds were
screened for their antibacterial activities against
standard strains of Gram-negative bacteria (Es-
cherichia coli ATCC (American Type Culture
Collection) 35218, Escherichia coli ATCC 25922, En-
terobacter cloacae ATCC 23355, Serratia marcescens
ATCC 8100, Pseudomonas aeruginosa ATCC 27853)
and Gram-positive bacteria (Enterococcus faecalis
ATCC 29212, Staphylococcus epidermidis ATCC
12228, Staphylococcus aureus ATCC 25923) by the
Kirby Bauer disk diffusion method [32]. Standard
0.5 McFarland saline suspensions of bacteria were
inoculated to the Mueller Hinton agar plates (Oxoid
Limited, Basingstoke, Hampshire, UK) by using
cotton swabs. All the compounds to be tested for
activity were dissolved at a concentration of 200
mg/L in DMSO (dimethylsulfoxide). Sterile filter
paper disks (diameter 6 mm) (Oxoid Limited,
Basingstoke, Hampshire, UK) soaked with 25 mL
of DMSO solutions of the compounds were put on
[N-(2-Hydroxy-4-nitrophenyl)-3-ethoxysalicylide-
neiminato]dimethyltin(IV) (Me2SnL4). Red crystals,
mp 208–210◦C; IR (cm−1): 1605 s υ(C N), 670
υ(Sn C), 525 υ(Sn O), 466 υ(Sn N). Mass spec-
trum (ESI) {m/z [assignment] (%)}: 450 [M]+(120Sn)
(3.1), 448 [M]+(118Sn) (1.2), 446 [M]+(116Sn) (0.8). El-
emental Anal.: Found C, 45.43; H, 4.19; N, 6.31%.
Calcd for C17H18N2O5Sn: C, 45.47; H, 4.04; N,
6.24%.1H NMR (CDCl3), δ: 0.79 [s, 2 J(117/119Sn-1H)
3
= 78.4 Hz, 6H, Sn(CH3)2], 1.36 (t, J = 7.0 Hz, 3H,
CH3), 4.03 (q, 3 J = 7.0 Hz, 2H, OCH2), 6.64 (t, 3 J
3
= 7.8 Hz, 1H, H-4), 6.85 (dd, J = 8.2 Hz,4 J = 1.4
Hz, 1H, H-5), 6.95 (dd,3 J = 7.7 Hz,4 J = 1.2 Hz 1H,
H-3), 7.34 (d, 3 J = 9.2 Hz 1H, H-12), 7.52 (dd, 3 J
4
= 9.0 Hz, J = 2.4 Hz 1H, H-11), 7.56 (d,4 J = 2.4
Hz, 1H, H-9), 8.65 [s, 3 J(117/119Sn-1H) = 46.8 Hz, 1H,
H-7].13C NMR (CDCl3), δ: 0.73 [1 J(117/119Sn-13C) =
666.0 Hz, (Sn(CH3)2)], 13.78 (CH3), 63.97 (OCH2),
Heteroatom Chemistry DOI 10.1002/hc

378 Yenis¸ehirli et al.
the agar plate’s surface. After incubation at 37◦C for
24 h, inhibition zone diameters surrounding each
disk was measured and recorded in millimeters.
Gentamicin (10 μg/disk) was used as a positive
control disk for the bacteria.
H2L3 and H2L4 were reported elsewhere [29]. The
1H NMR and 13C NMR data for H2L1 and H2L2 and
tin(IV) complexes are summarized in the Experi-
1
mental section. A representative H NMR spectrum
belonging to the complex Me2SnL4 is displayed in
Fig. 2.
1
Antifungal Activity. The in vitro antifungal ac-
tivities of compounds were tested against Aspergillus
niger, A. fumigatus, A. flavus, and Candida albicans
(clinical isolates). Each Aspergillus strain was inocu-
lated onto potato dextrose agar (Oxoid Limited, Bas-
ingstoke, Hampshire, UK) at 35◦C for 7 days. Spore
suspensions were prepared in sterile saline, adjusted
to a turbidity equivalent to that of 0.5 McFarland
corresponding to approximately 106 colony forming
units/mL, and then inoculated to the agar surface by
using cotton swabs. The agar plates were prepared
by using RPMI-1640 medium (Sigma, St. Louis, MO)
supplemented with 1.5% agar and 2% glucose and
buffered to a pH of 7.0 with 0.165 mol/L MOPS (3-
[N-morpholino] propanesulfonic acid) (Sigma, St.
Louis, MO). For C. albicans, Mueller Hinton agar
supplemented with 2% of glucose was used. Sterile
filter paper disks (diameter 6 mm) (Oxoid Limited,
Basingstoke, Hampshire, UK) soaked with 25 mL of
the DMSO solutions of the compounds were put on
the agar plate’s surface. Inhibition zone diameters
were measured following 24 h of incubation at 35◦C
in ambient air. Fluconazol (25 μg/disk) and Ampho-
tericin B (100 U/disk) were used as positive control
disks for fungi.
The H NMR spectra of all the ligands display
a single signal for the azomethine proton (H-7) at
9.00–9.05 ppm, in a good agreement with the re-
ported data for similar structures [15,19,20,33]. The
H-7 NMR signal of tin(IV) complexes downshift to
the range 8.61–8.74 ppm, reflecting the more elec-
tropositive nature of the tin atom relative to hydro-
gen. The 3 J(117/119Sn-1H) coupling (42.0–55.6 Hz) due
to NMR-active Sn isotopes is visible, and this is a
strong indication to the ligation of azomethine nitro-
gen to Sn atom. The extent of coupling is compara-
ble with the literature values [3,5,19]. In the 1H NMR
spectra of the ligands, the signals at 10.05–10.99 ppm
are assigned to the phenolic proton on the aniline
moiety ((OH)a, Fig. 1) and the one at 13.11–13.74
ppm to the other phenolic proton on the salicylalde-
hyde moiety ((OH)b, Fig. 1). Both the signals dis-
appear in the 1H NMR spectra of the corresponding
Sn(IV) complexes, indicating the engagement of phe-
nolic O atoms in complexation. For the ligands and
complexes, the signals of H-3 and H-5 protons are
labeled by the 2D heteronuclear-correlated (2D 13C-
1
1H HMBC) and 2D H-1H COSY NMR techniques.
The other protons in the phenyl rings are observed
1
in their normal δ range [34–36]. The H NMR spec-
tra of the dimethyltin(IV) complexes display addi-
tional signals due to the methyl protons ((CH3)2Sn
moiety) that appear at 0.79–0.84 ppm range. The
two methyl-group protons appear to be equivalent
and again, two-bond 1H-117Sn and 1H-119Sn couplings
(78.4–78.5 Hz) are observable. These values are typ-
ical of the five-coordinated tin(IV) species. As the
gyromagnetic ratios of 117Sn and 119Sn are almost
equal, they appear to be identical in terms of their
coupling effect on the NMR signal of the methyl pro-
tons. The total relative peak area of the split signals
reflects the total relative abundance of 117Sn (7.61%)
and 119Sn (8.58%).
RESULTS AND DISCUSSION
The structures two novel Schiff bases, the complexes
derived thereof, and the complexes of the previously
reported Schiff bases are described in Fig. 1. The
physical characteristics and the elemental analysis
of all these compounds are summarized in the Ex-
perimental section. Schiff bases and their diorgan-
1
otin(IV) complexes were characterized by H and
13C NMR, IR, and mass-spectral data. All the anal-
yses and cyclic voltammetric data are presented as
follows.
The 13C NMR spectral data also confirm the
proposed structures. The considerable shifts in the
positions of carbon atoms adjacent to the imine ni-
trogen (C-7) and phenolic oxygens (C-2, C-8) support
the proposed coordination sites in the complexes.
The shifts in the positions of carbon atoms adjacent
to the coordinating atoms clearly indicate the bond-
ing of the imine nitrogen and the two oxygen atoms
NMR Spectra
The NMR spectra of the organotin(IV) complexes
were recorded in CDCl3. 2D-COSY homonuclear,
HETCOR, and HMBC heteronuclear correlation
techniques were used of for signal assignments.
The complexes were dissolved in CDCl3. Because
of the low solubility in CDCl3, the NMR spectra of
the Schiff bases, H2L1, and H2L2 were measured in
deuterated DMSO. The NMR data for the ligands
1
to the central metal atom. The J(117/119Sn-13C) cou-
plings, in the dimethyl and dibutyltin complexes,
are clearly visible (645.0–666.0 and 601.0–610.0 Hz,
Heteroatom Chemistry DOI 10.1002/hc

Synthesis, Characterization, and In Vitro Antimicrobial Activities of Organotin(IV) Complexes of Schiff Bases 379
FIGURE 2 1H NMR spectra of Me2SnL4 in CDCl3.
equation 1 J117/119Sn-13C = 9.99( 0.73). θ(C Sn C)
−746( 100) replaces the Lockhart’s equation. The
C Sn C angles are found to be 134.8◦, 134.8◦, and
135.7◦ for n-Bu2SnL1, n-Bu2SnL3, and n-Bu2SnL4, re-
spectively.
respectively). For the diphenyltin compounds, the
13
1 J(117/119Sn− C) couplings are not observed in
the complexes. Obviously, the satellites are lost in
the background noise, as the the ipso-carbon tends
to give rise to a relatively weak signal. Indeed, in
the 13C NMR spectra of diphenyltin(IV) compounds,
the 2 J(117/119Sn-13C) (54.9 and 56.0 Hz) as well
as 3 J(117/119Sn-13C) couplings (84.3 and 85.9 Hz)
are visible. Again, on the 13C NMR spectra of the
dibutyltin(IV) compounds, the 2 J(117/119Sn-13C)
and 3 J(117/119Sn-13C) couplings are observed in the
range 27.5–32.0 Hz. The magnitude of the coupling
constants agrees well with those previously reported
for analogous five-coordinate derivatives [3,37].
For the dimethyltin(IV) complexes, the NMR-
based estimations of C Sn C angles were found
using Lockhart’s equation [38,39] {θ(C Sn C) =
Infrared Spectra
The characteristic frequencies of ligands and their
organotin(IV) complexes are presented in the Ex-
perimental section. The differences that are obvi-
ous rather than remarkable between the IR spec-
tra of the ligands and those of complexes are that
the stretching vibration bands of the phenolic O H
groups disappear from the spectra of the complexes.
This clearly reflects the deprotonation of the phe-
nolic oxygen atoms on the ligand upon complexa-
tion. This was also confirmed by the appearances
of a band at 521–565 cm−1, probably due to Sn-O
stretching vibration.
In the complexes, the υ(C N) band, occurring
between 1592 and 1607 cm−1, shifts toward lower
frequencies with respect to that of the free Schiff
bases (1627–1638 cm−1), confirming the coordina-
tion of the azomethine nitrogen to the organotin
moiety.
0.0161
×
[2 J(117/119Sn-1H)]2 − 1.32 × [2 J(117/119Sn-
1H)] + 133.4} with known 2 J(117/119Sn-1H) values
as well as with the equation { J(117/119Sn-13C) =
1
10.7θ −778} by inserting 1 J(117/119Sn-13C) values.
Calculated values are 133.2◦, 133.0◦, and 135.0◦
for Me2SnL1, Me2SnL3, and Me2SnL4, respectively.
For dibutyltin(IV) complexes, the tentative equa-
tion proposed by Holecek [40,41] was used to find
the estimates of the C Sn C angles. That is, the
Heteroatom Chemistry DOI 10.1002/hc

380 Yenis¸ehirli et al.
In the lower frequency region, the strong bands
observed in the region 447–500 and 669–696 cm−1
in the spectra of all the complexes have been as-
signed to the ν(Sn←N) and the ν(Sn C) vibrations,
respectively, lending further support to the proposed
coordination in the complexes.
C4
C5
Cl1
C3
C12
C7
C6
C11
C13
N1
C2
O3
C10
C1
O1
C14
Sn
Mass Spectra
C9
C8
C15
C16
In the ESI mass spectra of all the compounds,
the molecular ions and some of the tin-containing
fragments are clearly visible and they are summa-
rized in the Experimental section. Fragment ions,
[L]+, [RSnL]+, and [SnLH]+ were also detected in
the mass spectra of all the complexes. Remarkably,
in the mass spectra of Me2SnL3, n-Bu2SnL3, and
Me2SnL4, the base peaks correspond to the whole lig-
ands. The fragmentation patterns are also in agree-
ment with the literature reports [8,42,43].
O2
C24
C21
C17
C20
C19
C18
FIGURE 3 Molecular structure of Ph2SnL1 showing the
atom-numbering scheme. The thermal ellipsoids are plotted
at the 40% probability level.
The Sn-containing fragments display the natu-
ral abundance of the major Sn isotopes. The experi-
mental isotopic distributions of all the Sn-containing
fragment ions were compared with the theoretically
calculated one and were found in agreement with the
theoretical relative abundances. As an example, the
molecular ion peak with the characteristic tin iso-
topes of n-Bu2SnL4 was measured (theoretical rel-
ative abundances in parentheses): m/z 530, 41.9%
(41.1%); 531, 32.0% (32.4%); 532, 79.9% (75.4%);
533, 45.5% (43.0%); 534, 100% (100%); 535, 26.1%
(25.1%); 536, 16.6% (16.9%); 537, 4.0% (3.8%); 538,
16.2% (16.2%); 539, 4.4% (4.1%).
Cl1
C5
C4
C12
O5
N2
C6
C11
C7
Sn
C3
C13
N1
C2
C10
C14
C1
O1
O4
C9
C8
O2
O3
C15
C26
C21
C20
C24
C17
C18
C19
Crystal Structures of Ph2SnL1 and Ph2SnL2
FIGURE 4 Molecular structure of Ph2SnL2 showing the
atom-numbering scheme. The thermal ellipsoids are plotted
at the 40% probability level.
The ORTEP diagrams of the complexes Ph2SnL1 and
Ph2SnL2are shown in Figs. 3 and 4. Details of the
crystal data and a summary of the data collection
parameters for the complexes are given in Table 1.
Selected bond lengths and bond angles are presented
in Tables 2 and 3.
The ligand forms six- and five-membered chelate
rings with a R2Sn moiety. In the Ph2SnL1, the
organic part of the five-membered ring is nearly
planar; but the tin atom is out of this plane as
indicated by the torsion angles, Sn O2 C8 C13,
−13.5(12)◦ and N1 Sn O2 C8, −13.8(7)◦. In the
six-membered ring, N1, C7, C6, and C1 atoms
are in-plane, but oxygen and tin atoms are out
of this plane [the torsion angles, O1–C1–C6-C7:
8.9(15)◦, N1 Sn O1 C1: 21.5(9)◦, Sn O1 C1 C6:
−24.4(15)◦]. In the Ph2SnL2, the five-membered ring
is almost planar both in A- and B-type molecules. The
organic part of six-membered ring is nearly planar in
both molecules, whereas tin atom is out of this plane
[the torsion angles, (A: N1 Sn O1 C1: −22.1(5)◦,
The X-ray structural analysis of Ph2SnL1 and
Ph2SnL2 indicate that the coordination around the
tin atom is defined by the ipso-carbon atoms of the
phenyl groups, two oxygen atoms, and an imino ni-
trogen atom. As the phenolic oxygen serves as a do-
nating site, the ligand is regarded to be in phenol-
imine form. Compound Ph2SnL2crystals are in the
triclinic space group P-1 (no: 2) with four molecules
in the unit cell. The asymmetric unit cell contains
two pairs of crystallographically different molecules
with barely discernible differences in bond lengths
and bond angles (denoted by A and B in Table 3 refer-
ring to molecules with undashed and dashed atom
labels, respectively).
Heteroatom Chemistry DOI 10.1002/hc

Synthesis, Characterization, and In Vitro Antimicrobial Activities of Organotin(IV) Complexes of Schiff Bases 381
TABLE 1 Crystal Data and Structure Refinement Parameters for Ph2SnL1 (C27H22NO3ClSn) and Ph2SnL2(C27H21N2O5ClSn)
Complex
Ph2SnL1
Ph2SnL2
Empirical formula
Formula weight
Crystal system
Space group
C27H22NO3ClSn
562.6
Triclinic
P-1; (no: 2)
9.650(2)
C27H21N2O5ClSn
607.62
Triclinic
P-1; (no: 2)
9.9735(2)
11.8782(2)
23.9159(4)
91.38(3)
95.09(3)
114.29(4)
2566.6(3)
2
1.57
0.140
˚
a (A)
˚
b (A)
11.462(2)
˚
c (A)
12.306(3)
70.34(3)
85.17(3)
69.61(4)
1200.6(3)
2
1.56
1.204
2.5–26.4
α (o)
β (o)
γ (o)
Volume (A )
Z
3
˚
–3
Dcalc (g cm
μ(Mo Kα) (mm
min–θ
(◦)
)
–1
)
θ
2.1–30.5
max
F(000)
Index rangers
564
1216
−12 ≤ h ≤12, −13 ≤ k ≤ 14,
−14 ≤ h ≤ 12,
−15 ≤ l ≤ 15
25,248
299
16 ≤ k ≤ 16, 34 ≤ l ≤ 34
Reflections collected
Number of refined parameters
Number of reflection used
Observed data [ I >2σ (I )]
R [F2 >2σ( F2)]
74,687
658
4901
2136
0.075
0.190
0.988
1.974 and −1.602
15,559
6929
0.063
0.125
1.015
Rw (F2)
Goodness-of-fit on F2
–3
˚
Largest difference peak and hole (eA
)
0.743 and −0.1685
Sn O1 C1 C6: 20.1(9)◦) and (B: N1 Sn O1 C1:
−23.7(5)◦, Sn O1 C1 C6: 24.0(9)◦)].
TABLE 2 Selected Bond Lengths, Bond Angles, and Torsion
Angles (A, ) for Ph2SnL
◦
1
˚
The Sn-N, Sn-O, and Sn-C bond distances and
O-Sn-N bite angles in the coordination environ-
ment are comparable to those reported for similar
diphenyltin(IV) complexes [15,29].
Bond Lengths
Sn–O1
Sn–O2
Sn–N1
Sn–C16
Sn–C22
2.089(8)
2.093(7)
2.174(8)
2.102(9)
O1–C1
O2–C8
N1–C7
N1–C13
1.286(13)
1.311(12)
1.347(11)
1.436(10)
1.438(12)
In the both complexes, the central tin(IV) atom
has a geometry nearly halfway between distorted
square pyramid and trigonal bipyramid. To quan-
tify the extent of distortion from the ideal trig-
onal bipyramidal (τ = 1) geometry toward the
square pyramidal (τ = 0), the trigonal index, τ,
was computed [37,44]. For the complexes Ph2SnL1,
Ph2SnL2(A), and Ph2SnL2(B), τ values were found
0.44, 0.47, and 0.51, respectively. The evidence of dis-
torted conformation is also reflected in the bond an-
gles given in Tables 2 and 3. The distortion is mainly
due to the rigidity of chelate rings and the large co-
valent radius of tin(IV). These geometric results are
in agreement with the results of similar tin(IV) com-
plexes [3,15,28,29,45].
2.130(10) C6–C7
Bond Angles
O1–Sn–O2
O1–Sn–N1
N1–Sn–O2
O1–Sn–C16
O1–Sn–C22
O2–Sn–C16
O2–Sn–C22
158.4(4)
82.2(3)
76.7(3)
92.6(4)
95.5(4)
94.2(3)
95.2(4)
N1–Sn–C16
119.5(3)
108.7(3)
131.7(4)
134.0(7)
115.8(6)
128.6(6)
N1–Sn–C22
C16–Sn–C22
Sn–O1–C1
Sn–O2–C8
Sn–N1–C7
Torsion Angles
O2–C8–C13–N1 2.3(13)
O1–C1–C6–C7 8.9(15)
Sn–O2–C8–C13 −13.5(12) N1–Sn–O1–C1 21.5(9)
N1–Sn–O2–C8 −3.8(7)
Sn–O1–C1–C6 −24.4(15)
N1–C7–C6–C1 0.7(14)
In the both complexes, the four-atom plane
(C6 C7 N1 C13) across the imino double bond
is planar. The two phenyl rings in the ligand are
also near to coplanar in opposite directions with
the four-atom imino plane. The dihedral angles,
15.5(3)◦, 6,5(2)◦, and 9,2(2)◦ for Ph2SnL1, Ph2SnL2
(A), and Ph2SnL2 (B), respectively, may be given as
evidence.
Heteroatom Chemistry DOI 10.1002/hc

382 Yenis¸ehirli et al.
◦
2
˚
TABLE 3 Selected Bond Lengths, Bond Angles, and Torsion Angles (A, ) for Ph2SnL
Molecule A
Molecule B
Bond Lengths
Sn–O1
Sn–O2
Bond Lengths
Snꢁ–O1ꢁ
2.056(4)
2.079(4)
2.206(4)
2.101(5)
2.114(7)
1.308(6)
1.327(6)
1.304(6)
1.419(6)
1.408(7)
2.070(4)
2.084(4)
2.197(4)
2.110(6)
2.109(6)
1.294(6)
1.337(6)
1.318(6)
1.421(6)
1.428(7)
Snꢁ–O2ꢁ
Sn–N1
Snꢁ–N1ꢁ
Sn–C16
Sn–C22
O1–C1
O2–C8
N1–C7
N1–C13
C6–C7
Snꢁ–C16ꢁ
Snꢁ–C22ꢁ
O1ꢁ–C1ꢁ
O2ꢁ–C8ꢁ
N1ꢁ–C7ꢁ
N1ꢁ–C13ꢁ
C6ꢁ–C7ꢁ
Bond Angles
O1–Sn–O2
O1–Sn–N1
N1–Sn–O2
O1–Sn–C16
O1–Sn–C22
O2–Sn–C16
O2–Sn–C22
N1–Sn–C16
N1–Sn–C22
C16–Sn–C22
Sn–O1–C1
Sn–O2–C8
Sn–N1–C7
Bond Angles
158.15(16)
82.89(15)
76.77(15)
91.45(18)
95.6(2)
93.43(19)
97.5(2)
124.31(18)
105.93(18)
129.7(2)
132.9(3)
116.8(3)
124.5(4)
O1ꢁ –Snꢁ –O2ꢁ
O1ꢁ –Snꢁ –N1ꢁ
N1ꢁ –Snꢁ –O2ꢁ
O1ꢁ –Snꢁ –C16ꢁ
O1ꢁ –Snꢁ –C22ꢁ
O2ꢁ –Snꢁ –C16ꢁ
O2ꢁ –Snꢁ –C22ꢁ
N1ꢁ –Snꢁ –C16ꢁ
N1ꢁ –Snꢁ –C22ꢁ
C16ꢁ –Snꢁ –C22ꢁ
Snꢁ –O1ꢁ –C1ꢁ
Snꢁ –O2ꢁ –C8ꢁ
Snꢁ –N1ꢁ –C7ꢁ
158.37(16)
82.79(15)
76.75(15)
90.6(2)
96.62(19)
96.62(19)
96.51(19)
123.39(19)
108.76(18)
127.8(2)
132.5(3)
116.6(3)
126.0(4)
Torsion Angles
O2–C8–C13–N1
Sn–O2–C8–C13
N1–Sn–O2–C8
N1–C7–C6–C1
O1–C1–C6–C7
N1–Sn–O1–C1
Sn–O1–C1–C6
Torsion Angles
−0.3(8)
−0.9(7)
1.2(4)
−3.2(10)
−2.2(9)
−22.1(5)
20.1(9)
O2ꢁ–C8ꢁ–C13ꢁ–N1ꢁ
Snꢁ–O2ꢁ–C8ꢁ–C13ꢁ
N1ꢁ–Snꢁ–O2ꢁ–C8ꢁ
N1ꢁ–C7ꢁ–C6ꢁ–C1ꢁ
O1ꢁ–C1ꢁ–C6ꢁ–C7ꢁ
N1ꢁ–Snꢁ–O1ꢁ–C1ꢁ
Snꢁ–O1ꢁ–C1ꢁ–C6ꢁ
−0.9(8)
−0.1(7)
0.4(4)
−0.7(10)
−6.4(9)
−23.7(5)
24.0(9)
Cyclic Voltammetry
The electrochemical reduction of all the compounds
was studied by CV. The cyclic voltammetric curves
for the electrochemical reduction of H2L2, H2L3, and
H2L4 ligands and their complexes exhibit CV waves
dominated by the reduction of nitro groups [46]. As
the reduction wave of the nitro group obscures the
observation of that of the imine group, H2L1 and its
complexes are given a priority in the electrochem-
ical part of this work. The cyclic voltammograms
of H2L1 and Me2SnL1 are presented in Fig. 5. The
voltammograms recorded for Bu2SnL1 and Ph2SnL1
are basically the same with that of Me2SnL1. The
voltammograms of H2L1 and its complexes exhibit
two irreversible reduction peaks in DMF at room
temperature under argon gas atmosphere (scan rate
0.1 V s−1) [47]. The same behavior was observed for
a wide range of scan rates from 10 to 1000 mV s−1.
With increasing scan rates, ligand and its complexes
FIGURE 5 Cyclic voltammograms recorded for the reduction
of 1.0 mM ligand H2L1 (a) and 1.0 mM complex Me2SnL1 and
(b) at a glassy carbon electrode in DMF containing 0.10 M
Bu4NBF4. Scan rate, 0.1 V s−1
.
show a negative peak shift in peak potentials, as
well as an increase in current intensity, as shown
in Table 4. The cyclic voltammetric data show that
the reduction of the mentioned complexes is ligand
Heteroatom Chemistry DOI 10.1002/hc

Synthesis, Characterization, and In Vitro Antimicrobial Activities of Organotin(IV) Complexes of Schiff Bases 383
TABLE 4 Cyclic Voltammetric Data for Compounds in DMF
Hg/Hg2Cl2 Ag/AgCl
Compounds ν (V s−1) Epc1(V) Epc2(V) Epc1(V) Epc2(V)
Biological Activity
In this work, the in vitro antibacterial and antifun-
gal activities of the several Schiff bases and their
diorganotin(IV) complexes were investigated, and
the results are presented in Table 5.
H2L1
0.05
0.1
1
−1.84 −2.21 −1.78 −2.17
−1.87 −2.24 −1.79 −2.19
−1.96 −2.34 −1.85 −2.25
−1.80 −2.20 −1.77 −2.13
−1.83 −2.22 −1.78 −2.16
−1.90 −2.31 −1.86 −2.23
−1.82 −2.20 −1.77 −2.16
−1.85 −2.23 −1.77 −2.19
−1.89 −2.29 −1.86 −2.26
−1.80 −2.06 −1.75 −2.14
−1.81 −2.22 −1.76 −2.17
−1.88 −2.30 −1.83 −2.27
The data obtained indicate that the ligands other
than H2L3 and H2L4 have no activity against all
the test organisms. H2L3 and H2L4 had moderate
activity against Gram-positive bacteria, S. aureus
ATCC 25923 and S. epidermidis ATCC 12228 and also
against the fungus, A. niger. In general, complexes
exhibit antibacterial properties higher than those of
the corresponding ligands. Ph2SnL4 was found to be
more effective against A. niger than the standard,
Amphotericin B.
All the complexes and ligands were also screened
against the Gram-negative bacteria, E. coli ATCC
25922, E. coli ATCC 35218, E. cloacae ATCC 23355,
S. marcescens ATCC 8100, and P. aeruginosa ATCC
27853, but no antibacterial activity was observed.
Apparently, the complexes are only toxic toward
Gram (+) strains. The reason probably lies in the
difference between the structures of the cell walls.
The relatively more complex walls of Gram (−) cells
may prevent the diffusion of the chemicals into the
Me2SnL1
n-Bu2SnL1
Ph2SnL1
0.05
0.1
1
0.05
0.1
1
0.05
0.1
1
centered [48,49]. The fact that in the voltammetric
reduction of all the complexes, the reduction poten-
tials of imine group are shifted to less-negative val-
ues compared to the ligand, can be taken as a further
evidence that the ligation of the azomethine nitrogen
does occur.
TABLE 5 Antibacterial and Antifungal Activities of Compounds
Inhibition Zone (mm)
S. aureus
ATCC 25923
S. epidermidis
ATCC 12228
E. faecalis
ATCC 29212
Compounds
A. niger
A. flavus
A. fumigatus
C. albicans
H2L1
–
–
10
15
–
–
–
15
15
–
–
–
–
–
–
–
–
–
15
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
H2L2
H2L3
H2L4
aH2L5
Me2SnL1
n-Bu2SnL1
Ph2SnL1
Ph2SnL2
Me2SnL3
n-Bu2SnL3
Ph2SnL3
Me2SnL4
n-Bu2SnL4
Ph2SnL4
bPh2SnL5
G
12
10
15
15
10
–
15
–
11
21
17
22
11
13
13
15
15
12
15
–
11
21
17
25
12
–
12
–
–
12
-
12
–
–
15
–
–
15
–
–
30
25
12
–
–
15
–
–
–
–
–
18
15
12
–
–
15
–
–
–
–
–
25
15
12
–
12
17
–
–
–
–
–
–
12
16
–
18
14
20
A
F
23
–
20
–
25
–
23
25
G: Gentamicin (10 μg/disk).
A: Amphotericin B (100 U/disk).
F: Fluconazol (25 μg/disk).
a
H2L5, N-(2-hydroxy-4-nitrophenyl)-3-hydroxysalicylideneimine.
b
Ph2SnL5, [N-(2-hydroxy-4-nitrophenyl)-3-hydroxysalicylideneiminato]diphenyltin(IV).
Heteroatom Chemistry DOI 10.1002/hc

384 Yenis¸ehirli et al.
[7] Dey, D. K.; Saha, M. K.; Gielen, M.; Kemmer, M.;
Biesemans, M.; Willem, R.; Gramlich, V.; Mitra, S. J
Organomet Chem 1999, 590, 88–95.
[8] Labisbal, E.; Rodr´ıguez, L.; Sousa-Pedrares, A.;
Alonso, M.; Vizoso, A.; Romero, J.; Garcı´a-Va´zquez,
J. A.; Sousa, A. J Organomet Chem 2006, 691, 1321–
1332.
cytoplasm of the organisms, and this may not be the
case for Gram (+) cells. These antibacterial and an-
tifungal activity results are in accordance with those
found for other similar diorganotin(IV) complexes
[29, 42,50].
[9] Rivera, J. M.; Guzman, D.; Rodriguez, M.; Lamere, J.
F.; Nakatani, K.; Santillan, R.; Lacroix, P. G.; Farfan,
N. J Organomet Chem 2006, 691, 1722–1732.
[10] Samanta, B.; Chakraborty, J.; Dey, D. K.; Gramlich,
V.; Mitra, S. Struct Chem 2007, 18, 287–293.
[11] Yin, H. D.; Chen, S. W.; Li, L. W.; Wang, D. Q. Inorg
Chim Acta 2007, 360, 2215–2223.
[12] Yin, H. D.; Chen, S. W. J Organomet Chem 2006, 691,
3103–3108.
[13] Yin, H. D.; Chen, S. W. Inorg Chim Acta 2006, 359,
3330–3338.
[14] Davies, A. G. In Organotin Chemistry, 2nd ed.; Wiley–
VCH: Weinheim, Germany, 2004; pp. 383.
[15] Beltra´n, H. I.; Damian-Zea, C.; Hernandez-Ortega,
S.; Nieto-Camacho, A.; Ramiraz-Apan, M. T. Inorg
Biochem 2007, 101, 1070–1085.
[16] Al-Allaf, T. A. K.; Rashan, L. J.; Stelzner, A.; Powell,
D. R. Appl Organometal Chem 2003, 17, 891–897.
[17] Pellerito, L.; Nagy, L. Coord Chem Rev 2002, 224,
111–150.
[18] Nath, M.; Yadav, R.; Gielen, M.; Dalil, H.; de Vos, D.;
Eng, G. Appl Organometal Chem 1997, 11, 727–736.
[19] Tian, L.; Shang, Z.; Zheng, X.; Sun, Y.; Yul, Y.; Qian,
B.; Liu, X. Appl Organometal Chem 2006, 20, 74–80.
[20] Zamudio-Rivera, L. S.; George-Tellez, R.; Lo´pez-
Mendoza, G.; Morales-Pacheco, A.; Flores, E.; Ho¨pfl,
H.; Barba, V.; Ferna´ndez, F. J.; Cabirol, N.; Beltra´n,
H. I. Inorg Chem 2005, 44, 5370–5378.
CONCLUSION
Organotin(IV) complexes of N-(2-hydroxyphenyl)-
salicylideneimine derivatives were prepared and
characterized by elemental analyses, NMR, IR, and
mass spectroscopy. Five-coordinate geometry is pro-
posed for the organotin(IV) complexes. X-ray crystal
structures of the diphenyltin(IV) complexes revealed
that the central tin(IV) atom has a geometry nearly
halfway between distorted square pyramid and trig-
onal bipyramid. In the voltammetric reduction of all
the complexes, the reduction potentials of the imine
group are shifted to less negative values compared
to the ligand, due to the ligation of the azomethine
nitrogen to the central tin atom. The results of an-
tibacterial screening of the compounds indicate mild
bactericidal activities.
SUPPLEMENTARY MATERIAL
CCDC-752377 and 759324 contain the supple-
mentary crystallographic data for this paper.
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.
[21] Singh, H. L.; Varshney, A. K. Appl Organometal
Chem 2001, 15, 762–768.
[22] Ruzicka, A.; Dostal, L.; Jambor, R.; Buchta, V.;
Brus, J.; Cisarova, I.; Holcapek, M.; Holecek, J. Appl
Organometal Chem 2002, 16, 315–322.
[23] Dokorou, V.; Kovala-Demertzi, D.; Jasinski, J. P.;
Galani, A.; Demertzis, M. A. Helv Chim Acta 2004,
87, 1940–1950.
[24] Kovala-Demertzi, D.; Dokorou, V.; Ciunik, Z.; Kourk-
oumelis, N.; Demertzis, M. A. Appl Organomet Chem
2002, 16, 360–368.
ACKNOWLEDGMENT
We thank Prof. Mu¨rs¸ide Tu¨zu¨n for her helpful
suggestions.
[25] Darensbourg, D. J.; Ganguly, P.; Billodeaux, D.
Macromolecules 2005, 38, 5406–5410.
[26] Jing, H.; Edulji, S. K.; Gibbs, J. M.; Stern, C. L.; Zhou,
H.; Nguyen, S. T. Inorg Chem 2004, 43, 4315–4327.
[27] Liu, G. -D.; Liao, J. -P.; Fang, Y.-Z.; Huang, S.-S.;
Sheng, G.-L.; Yu, R.-Q. Anal Sci 2002, 18, 391–395.
[28] Reyes, H.; Garcia, C.; Farfa´n, N.; Santillan, R.;
Lacroix, P. G.; Lepetit, C.; Nakatani, K. J Organomet
Chem 2004, 689, 2303–2310.
REFERENCES
[1] Preut, H.; Huber, F.; Haupt, H. J.; Bertazzi, N. Z
Anorg Allg Chem 1974, 423, 75–82.
[2] Preut, H.; Huber, F.; Haupt, H. J.; Cefalu, R.; Barbieri,
R. Z Anorg Allg Chem 1974, 410, 88–96.
[3] Pettinari, C.; Marchetti, F.; Pettinari, R.; Martini, D.;
Drozdov, A.; Troyanov, S. Inorg Chim Acta 2001, 325,
103–114.
¨
[29] C¸ elebier, M.; S¸ ahin, E.; Ancın, N.; Altuntas¸ Oztas¸, N.;
¨
Oztas¸, S. G. Appl Organometal Chem 2007, 21, 913–
918.
[4] Luna-Garc´ıa, R.; Damia´n-Murillo, B. M.; Barba, V.;
Ho¨pfl, H.; Beltra´n, H. I.; Zamudio-Rivera, L. S. J
Organomet Chem 2009, 694, 3965–3972.
[5] Barba, V.; Vega, E.; Luna, R.; Ho¨pfl, H.; Beltra´n, H.
I.; Zamudio-Rivera, L. S. J Organomet Chem 2007,
692, 731–739.
[30] Rigaku/MSC, Inc., 9009 new Trails Drive, The Wood-
lands, TX 77381, 2005.
[31] Sheldrick, G. M. SHELXS97 and SHELXL97 pro-
grams for the solution and refinement of crys-
tal structures. University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
[6] Ram´ırez-Jime´nez, A.; Go´mez, E.; Herna´ndez, S. J
Organomet Chem 2009, 694, 2965–2975.
[32] Bauer, A. W.; Kirby, W. M.; Sherris, J. C.; Turck, M.
Am J Clin Pathol 1966, 45, 493–496.
Heteroatom Chemistry DOI 10.1002/hc

Synthesis, Characterization, and In Vitro Antimicrobial Activities of Organotin(IV) Complexes of Schiff Bases 385
[33] Tian, L.; Qian, B.; Sun, Y.; Zheng, X.; Yang, M.; Li, H.;
[42] Saxena, A.; Tandon, J. P.; Crowe, A. J. Polyhedron
1985, 4, 1085–1089.
[43] Gielen, M.; Biesemans, M.; Willem, R. Appl
Organometal Chem 2005, 19, 440–450.
[44] Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.;
Verschoor, G. C. J Chem Soc, Dalton Trans 1984,
1349–1356.
[45] Diamantis, A. A.; Gulbis, J. M.; Manikas, M.; Tiekink,
E. R. T. Phosphorus Sulfur Silicon Relat Elem 1999,
150, 251–259.
[46] Squella, J. A.; Jimenez, G.; Bollo, S.; Nu´n˜ez-Vergara,
L. J. Electrochim Acta 1997, 42, 2305–2312.
[47] Isse, A. A.; Abdurahman, A. M.; Vianello, E.; J Elec-
troanal Chem 1997, 431, 249–255.
Liu, X. Appl Organometal Chem 2005, 19, 980–987.
[34] Yeap, G. Y.; Ha, S. T.; Ishizawa, N.; Suda, K.; Boey,
P. L.; Mahmood, W. A. K. J Mol Struct 2003, 658,
87–99.
[35] Schilf, W.; Kamienski, B.; Szady-Chelmieniecka, A.;
Grech, E. J Mol Struct 2005, 743, 237–241.
[36] Wrackmeyer, B. Ann Rep NMR Spectrosc 1985, 16,
73–186.
[37] Banerjee, S.; Drew, M. G. B.; Lu, C. Z.; Tercero, J.;
Diaz, C.; Ghosh, A. Eur J Inorg Chem 2005, 2376–
2383.
[38] Lockhart, T. P.; Manders, W. F. Inorg Chem 1986, 25,
892–895.
[39] Lockhart, T. P.; Davidson, F. Organometallics 1987,
6, 2479–2483.
[40] Holecˇek, J.; Na´dvorn´ık, M.; Handl´ırˇ, K. J Organomet
Chem 1986, 315, 299–318.
[41] Beltra´n, H. I.; Zamudio-Rivera, L. S.; Mancilla, T.;
Santillan, R.; Farfa´n, N. Chem Eur J 2003, 9, 2291–
2306.
[48] Galani, A.; Kovala-Demertzi, D.; Kourkoumelis, N.;
Koutsodimou, A.; Dokorou, V.; Ciunik, Z.; Russo, U.;
Demertzis, M. A. Polyhedron 2004, 23, 2021–2030.
[49] Galani, A.; Demertzis, M. A.; Kubicki, M.; Kovala-
Demertzi, D. Eur J Inorg Chem 2003, 1761–1767.
[50] Singh, R. V.; Chaudhary, P.; Poonia, K.; Chauhan, S.
Spectrochim Acta Part A 2008, 70, 587–594.
Heteroatom Chemistry DOI 10.1002/hc