Binuclear organotin(IV) complexes with adipic dihydrazones: Synthesis, spectral characterization, crystal structures and antibacterial activity

Article abstract of DOI:10.1016/j.jorganchem.2013.03.037

New organotin(IV) complexes, (R₂Sn)₂L [L = L ^a: R = Me (1), Ph (2); L = L^b: R = Me (3), Ph (4)] have been synthesized by reaction of dihydrazone ligands, bis(5-bromosalicylaldehyde) adipicdihydrazone (H₄

Full text of DOI:10.1016/j.jorganchem.2013.03.037

Journal of Organometallic Chemistry 737 (2013) 26e31
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Binuclear organotin(IV) complexes with adipic dihydrazones: Synthesis, spectral
characterization, crystal structures and antibacterial activity
,
a
b
c
Tahereh Sedaghat a , Marjan Aminian , Giuseppe Bruno , Hadi Amiri Rudbari
*
a Department of Chemistry, College of Sciences, Shahid Chamran University, Ahvaz, Iran
b Dipartimento di Chimica Inorganica, Vill. S. Agata, Salita Sperone 31, Università di Messina, 98166 Messina, Italy
c Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
a r t i c l e i n f o
a b s t r a c t
New organotin(IV) complexes, (R2Sn)2L [L ¼ La: R ¼ Me (1), Ph (2); L ¼ Lb: R ¼ Me (3), Ph (4)] have been
synthesized by reaction of dihydrazone ligands, bis(5-bromosalicylaldehyde) adipicdihydrazone (H4La)
and bis(2-hydroxynaphthaldehyde) adipicdihydrazone (H4Lb) with R2SnCl2 (R ¼ Me or Ph). The syn-
thesized compounds have been investigated by elemental analysis and IR, 1H NMR, and 119Sn NMR
spectroscopy. The structures of 1 and 4 have been also confirmed by X-ray crystallography. The results
show that the dihydrazone acts as a tetrabasic ligand in the enolic form and is coordinated to two
diorganotin moiety via the imine nitrogen and phenolic and enolic oxygen atoms. All complexes are
binuclear and the coordination number of each tin is five. The in vitro antibacterial activity of ligands and
complexes has been evaluated against Gram-positive (Bacillus subtilis and Staphylococcus aureus) and
Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria and compared with standard
drugs. All complexes exhibit more inhibitory effects than the parent ligands.
Article history:
Received 16 January 2013
Received in revised form
17 February 2013
Accepted 25 March 2013
Keywords:
Organotin(IV)
Dihydrazone
Crystal structure
Antibacterial activity
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
compounds are dependent on both the organic group and the
ligand attached to tin [8,9], an interesting development is intro-
Acylhydrazones and their metal complexes have attracted great
and growing interest due to their interesting biological properties,
such as antibacterial, antifungal and antitumor activities. These
compounds have been found to have therapeutic activity for
example in the treatment of tuberculosis and Fe overload disease.
Also, they have been used as fluorescent materials, pigments,
analytical reagents and polymer-coating [1e5]. In the field of
hydrazone chemistry, a special place is held by bis-acylhydrazones
for several reasons [6]: (i) The presence of two coordinating unit in
these ligands may yield supramolecular architectures or better
coordinative properties than those a sole coordinative unit, (ii) a
ditopic ligand enables the properties of its complexes to be
modulated by the degree of deprotonation, and (iii) metal com-
plexes of dihydrazones may be able to mimic bimetallic sites in
various enzymes. Among the research dealing with complexes of
hydrazones, increasing attention has been devoted to organotin(IV)
complexes in view of chemical properties, biological significance,
industrial importance, and structural variety of organotin(IV)
compounds [7]. Since biocidal properties of organotin(IV)
ducing ligands which are themselves bioactive [8,10e12]. Up to
now many organotin complexes with a variety of hydrazones have
been studied due to the importance of their medicinal assays for
bactericide and antitumor purposes [13e15] and also because of an
interesting variety of structural possibilities. However, less atten-
tion has been paid to organotin complexes with diacylhydrazones
as multidentate ligands [16e18].
As part of our investigation dealing with the study of dio-
rganotin(IV) complexes with Schiff bases, this paper reports the
syntheses, crystal structures, spectral properties and antibacterial
activities of diphenyl- and dimethyltin(IV) complexes with bis-
acylhydrazones derived from condensation of adipic dihydrazide
with 5-bromosalicylaldehyde and 2-hydroxynaphthaldehyde, H4La
and H4Lb, respectively, Fig. 1.
2. Experimental
2.1. Materials and methods
All starting materials were purchased from Merck while
diphenyltin dichloride was supplied from Acros Company and were
all used as received. All solvents were of reagent grade and used
* Corresponding author. Fax: þ98 611 3331042.
E-mail addresses: tsedaghat@scu.ac.ir, tsedaghat@yahoo.com (T. Sedaghat).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.03.037

T. Sedaghat et al. / Journal of Organometallic Chemistry 737 (2013) 26e31
27
OH
O
H
3
1
N
N
Br
Br
N
H
N
O
2
HO
H4La
5
OH
6
4
O
H
N
N
3
N
H
N
O
2
HO
H4Lb
1
Fig. 1. Structure of dihydrazone ligands with numbering for 1H NMR assignments.
without further purification. IR spectra were obtained using a FT
d
¼ 0.79 [s,12H, SnMe2, 2J(119Sne1H) ¼ 78.2 Hz],1.72 (t, br, 4H, CH2),
BOMEM MB102 spectrophotometer. The 1H and 119Sn NMR spectra
2.34 (t, br, 4H, CH2), 6.65 (d, 2H, H1, 3JHH ¼ 9.0 Hz), 7.21 (d, 2H, H3,
4JHH ¼ 2.5 Hz), 7.36 (dd, 2H, H2, 3JHH ¼ 9.0 Hz, 4JHH ¼ 2.5 Hz), 8.46 [s,
were recorded with
spectrometer.
a Bruker 400 MHz Avance Ultrashield
2H, HC]N, 3J(119Sne1H) ¼ 45.4 Hz]. 119Sn NMR (CDCl3):
2.5. Synthesis of (Ph2Sn)2La (2)
d
¼ ꢁ151.
2.2. Synthesis of bis(5-bromosalicylaldehyde)adipicdihydrazone
(H4La)
Complex 2 was synthesized as described for compound 1 from
Ph2SnCl2 (0.086 g, 0.25 mmol). Yield: 0.068 g (63%). Anal. Calc. for
C44H36N4O4Br2Sn2: C, 48.82; H, 3.33; N, 5.17%. Found: C, 48.12; H,
A mixture of adipic dihydrazide (0.043 g, 0.25 mmol) and 5-
bromosalicylaldehyde (0.125 g, 0.625 mmol) was refluxed in
ethanol for 3 h. After this time the white product was filtered and
washed with ethanol. Yield: 0.133 g (90%); m.p. 287 ꢀC; IR (KBr,
2.95; N, 4.67%. IR (KBr, cmꢁ1):
n
(C]N), 1607;
n(SneO), 572; n(Sne
N), 445. 1H NMR (DMSO-d6):
d
¼ 1.71 (t, br, 4H, CH2), 2.35 (t, br, 4H,
3
cmꢁ1):
NMR (DMSO-d6):
n
(NH/OH), 3100e3200 br;
n
(C]O), 1679;
n
(C]N), 1611. 1H
CH2), 6.82 (d, 2H, H1, JHH ¼ 9.0 Hz), 7.27e7.37 [m, 12H, Hm,
p
4
d
¼ 1.62 (t, br, 4H, CH2), 2.63 (t, br, 4H, CH2), 6.86
(Ph2Sn)], 7.37 (d, 2H, H3, JHH ¼ 2.5 Hz), 7.54 [m, 8H, Ho(Ph2Sn)],
3
3
3
(d, 2H, H1, JHH ¼ 8.7 Hz), 7.40 (dd, 2H, H2, JHH ¼ 8.7 Hz,
4JHH ¼ 2.4 Hz), 7.72 (d, 2H, H3, 4JHH ¼ 2.3 Hz), 8.31 (s, 2H, HC]N),
11.22 (s, 2H, NH), 11.69 (s, 2H, OH).
7.75 (d, br, 2H, H2, JHH ¼ 7.2 Hz), 8.56 [s, 2H, HC]N, 3J(119Sne
1H) ¼ 50.9 Hz]. 119Sn NMR (DMSO-d6):
2.6. Synthesis of (Me2Sn)2Lb (3)
d
¼ ꢁ425.
2.3. Synthesis of bis(2-hydroxynaphthaldehyde)adipicdihydrazone
(H4Lb)
Triethylamine (0.4 mmol) was added to a solution of H4Lb
(0.048 g, 0.1 mmol) in methanol (20 mL). This solution was stirred
for 30 min. Then a solution of Me2SnCl2 (0.055 g, 0.25 mmol) in
methanol (10 mL) was added. The solution was refluxed for 5 h.
After this time the yellow product was filtered and washed with
methanol. Yield: 0.032 g (41%); Anal. Calc. for C32H34N4O4Sn2: C,
49.5; H, 4.38; N, 7.22; Found: C, 49.64; H, 3.99; N, 7.42%. IR (KBr,
A mixture of adipic dihydrazide (0.174 g, 1 mmol) and 2-
hydroxynaphthaldehyde (0.430 g, 2.5 mmol) was refluxed in
ethanol for 5 h. After this time the milky precipitate was filtered
and washed with ethanol. Yield: 0.310 g (65%); m.p. 220 ꢀC; IR (KBr,
cmꢁ1):
n(NH/OH), 3100e3200 br; n(C]O), 1659; n
(C]N), 1615. 1H
NMR (DMSO-d6):
d
¼ 1.70 (t, br, 4H, CH2), 2.33 (t, br, 4H, CH2), 7.20
cmꢁ1):
(SneN), 459. 1H NMR (DMSO-d6):
n(C]N), 1610; nas(SneC), 637; n(SneO), 566; ns(SneC), 530;
(d, 2H, H1, 3JHH ¼ 8.7 Hz), 7.40 (t, 2H, H4, 3JHH ¼ 7.6 Hz), 7.58 (t, 2H,
H5, 3JHH ¼ 7.7 Hz), 7.87 (m, 4H, H2, 3), 8.20 (d, 2H, H6, 3JHH ¼ 8.6 Hz),
9.16 (s, 2H, HC]N), 11.75 (s, 2H, NH), 12.65 (s, 2H, OH).
n
d
¼ 0.65 [s, 12H, SnMe2,
2J(119Sne1H) ¼ 86.0 Hz], 1.67 (t, br, 4H, CH2), 2.33 (t, br, 4H, CH2),
6.88 (d, 2H, H1, 3JHH ¼ 9.1 Hz), 7.28 (t, 2H, H4, 3JHH ¼ 7.6 Hz), 7.46 (t,
2H, H5, 3JHH ¼ 7.7 Hz), 7.87 (m, 2H, H3, 3JHH ¼ 8.0 Hz), 7.83 (m, 2H,
H2, 3JHH ¼ 9.1 Hz), 8.16 (d, 2H, H6, 3JHH ¼ 8.7 Hz), 9.45 [s, 2H, HC]N,
2.4. Synthesis of (Me2Sn)2La (1)
3J(119Sne1H) ¼ 40.4 Hz]. 119Sn NMR (DMSO-d6):
2.7. Synthesis of (Ph2Sn)2Lb (4)
d
¼ ꢁ209.
Triethylamine (0.4 mmol) was added to a solution of H4La
(0.054 g, 0.1 mmol) in ethanol (20 mL). This solution was stirred for
30 min. Then a solution of Me2SnCl2 (0.055 g, 0.25 mmol) in ethanol
(10 mL) was added. The solution was refluxed for 4 h. After this time
the yellow product was filtered and washed with ethanol. Yield:
0.024 g (30%). The solid was recrystallized from chloroform/ethanol
and yellow lozenge single crystals suitable for X-ray crystallog-
raphy were formed by slow evaporation at room temperature. Anal.
Calc. for C24H28N4O4Br2Sn2: C, 34.56; H, 3.36; N, 6.72%; Found: C,
Complex 2 was synthesized as described for compound 1 from
Ph2SnCl2 (0.086 g, 0.25 mmol) and in ethanol. Yield: 0.065 g (63%).
The yellow needle single crystals suitable for X-ray crystallography
were obtained after recrystallization from chloroform/ethanol.
Anal. Calc. for C52H42N4O4Sn2: C, 60.85; H, 3.90; N, 5.46%. Found: C,
61.13; H, 3.51; N, 6.52%. IR (KBr, cmꢁ1):
n(C]N), 1603; n(SneO), 572;
34.80; H, 2.95; N, 6.95. IR (KBr, cmꢁ1):
650; (SneO), 570; ns(SneC), 528;
(SneN), 457. 1H NMR (CDCl3):
n
(C]N), 1609; nas(SneC),
n
(SneN), 465. 1H NMR (CDCl3):
d
¼ 1.98 (s, 4H, CH2), 2.51 (s, 4H,
n
n
CH2), 6.88 (d, 2H, H1, 3JHH ¼ 9.1 Hz), 7.34 (t, 2H, H4, 3JHH ¼ 7.2 Hz),

28
T. Sedaghat et al. / Journal of Organometallic Chemistry 737 (2013) 26e31
7.38e7.44 [m,12H, Hm,p (Ph2Sn)], 7.46 (t, 2H, H5, 3JHH ¼ 8.0 Hz), 7.73
(m, 2H, H3, 3JHH ¼ 7.7 Hz), 7.85 [m, 8H, H2, Ho(Ph2Sn)], 8.01 (d, 2H,
H6, 3JHH ¼ 8.6 Hz), 9.58 [s, 2H, HC]N, 3J(119Sne1H) ¼ 55.8 Hz]. 119Sn
(6.4 mm diameter) were saturated with a solution of test com-
pounds 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 37 ꢀC for 24 h. The inhibition zone diameters around each disc
were measured in mm.
NMR (CDCl3):
d
¼ ꢁ330.
2.8. X-ray structure determination
3. Results and discussion
Data were collected at room temperature with a Bruker APEX II
Bis-acylhydrazone ligands, H4La and H4Lb, were obtained from
the reaction of adipic dihydrazide with 5-bromosalicylaldehyde
and 2-hydroxynaphthaldehyde, respectively. These compounds
have four ionizable protons and can potentially act as hexadentate
ligands with two tridentate domain connected by a flexible linker
group. The dinuclear complexes 1e4 were prepared by reaction of
dihydrazone ligand, R2SnCl2 (R ¼ Me or Ph) and in presence of
triethylamine in 1:2:4 ratio with a slight excess of diorganotin
dichloride. The new complexes were characterized by elemental
analysis and IR and 1H and 119Sn NMR spectroscopy. The structure
of 1 and 4 has been also determined by X-ray diffraction.
CCD area-detector diffractometer using MoK
¼ 0.71073 A). Data collection, cell refinement, data reduction and
a
radiation
ꢀ
(l
absorption correction were performed using multiscan methods
with Bruker software [19]. The structures were solved by direct
methods using SIR2004 [20]. The non-hydrogen atoms were
refined anisotropically by the full matrix least squares method on F2
using SHELXL [21]. All the hydrogen (H) atoms were placed at the
calculated positions and constrained to ride on their parent atoms.
Details concerning collection and analysis are reported in Table 1.
2.9. Antibacterial tests
The in vitro antibacterial activity of ligands and their corre-
sponding organotin(IV) complexes was investigated against the
standard strains of two Gram-positive (Bacillus subtilis ATCC 6633
and Staphylococcus aureus ATCC 6538) and two Gram-negative
(Escherichia coli ATCC 35218 and Pseudomonas aeruginosa ATCC
27853) bacteria. In order to compare the results, Nalidixic acid (30
mg/disc) and Vancomycin (30 mg/disc) were used as standard
antibacterial drugs. Determination of the antibacterial activity was
carried out by paper-disc diffusion method. The compounds were
dissolved in DMSO at 10, 20 and 40 mg/mL 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
3.1. Spectroscopic studies
In the IR spectra of complexes the disappearance of nOeH and nNe
H shows complete deprotonation of the ligand during coordination
to the tin atoms. The absence of nC
] in complexes confirms that
O
the ligand coordinates with tin in the enol form [18]. The n(C]N)
band at 1611 and 1615 cmꢁ1 for ligands is shifted to a lower energy
in the spectra of complexes. This observation indicates that the
imine nitrogen atom is involved in coordination to the tin atom. The
appearance of new bands in the IR spectra of the synthesized
complexes assigned to n(SneN) and n(SneO) supports the bonding
of nitrogen and oxygen to the tin atom [22e25]. Presence of both
ns(SneC) and nas(SneC) in the IR spectrum of 1 and 3 is consistent
with a nonlinear MeeSneMe configuration.
The signals at 11.22e12.65 ppm in the spectra of free ligands
may be attributed to acidic protons, eNHeN] and AreOH groups.
In the 1H NMR spectra of the complexes, the complete absence of
these signals suggests the deprotonation of ligand and coordination
to the tin in the enol form. The signal attributed to imine protons in
the spectrum of free ligands is shifted downfield and accompanied
by satellites in complexes due to 3J(119SneH) coupling. This is an
indication that the two imine nitrogen atoms is coordinated to
tin(IV) centers. The 1H NMR spectrum of dimethyl complexes
shows a singlet at low frequency for SnMe2 protons accompanied
by satellites with 2J(119Sne1H) larger than uncomplexed SnMe2Cl2
(68.7 Hz) indicates the higher coordination number of tin [26].
Substitution of 2J(119Sne1H) in the LockharteManders equation
Table 1
Crystallographic and structure refinement data for 1 and 4.
1
4
Empirical formula
Formula weight
T (K)
C
24H28Br2N4O4Sn2
C52H42N4O4Sn2
1024.28
296(2)
0.71073
Monoclinic
C2/c
0.19 ꢂ 0.07 ꢂ 0.06
37.333(9)
12.410(3)
9.888(2)
833.70
293(2)
0.71073
Triclinic
ꢀ
Wavelength,
l
(A)
Crystal system
Space group
P-1
Crystal size (mm3)
0.20 ꢂ 0.18 ꢂ 0.12
ꢀ
a (A)
6.626
ꢀ
b (A)
10.030
12.089
67.42
74.67
86.04
715.0
1
1.936
1.89 to 29.00
402
ꢀ
c (A)
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
90
102.874(14)
90
4465.8(18)
4
1.523
2.64 to 27.00
2056
3
ꢀ
V (A )
Z
Dcalc. (Mg mꢁ3
)
q
Ranges for data collection (ꢀ)
F(000)
Absorption coefficient (mmꢁ1
)
4.577
1.169
Index ranges
ꢁ9 ꢃ h ꢃ 9
ꢁ13 ꢃ k ꢃ 13
ꢁ16 ꢃ l ꢃ 16
29,685
ꢁ47 ꢃ h ꢃ 47
ꢁ15 ꢃ k ꢃ 15
ꢁ12 ꢃ l ꢃ 12
39,095
Reflections collected
Independent reflections
3791
4876
[R(int) ¼ 0.0284]
3791/0/163
1.057
[R(int) ¼ 0.07361]
4876/0/280
1.026
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
s
(I)]
R1 ¼ 0.0317
wR2 ¼ 0.0873
R1 ¼ 0.0360
wR2 ¼ 0.0918
1.423 and ꢁ1.166
R1 ¼ 0.0371
wR2 ¼ 0.0586
R1 ¼ 0.0994
wR2 ¼ 0.0773
0.335 and ꢁ0.385
Fig. 2. Perspective view of compound 1 constituted by the asymmetric unit (filled
drawings) showing the numbering scheme and the centrosymmetric half part (empty
drawings). Thermal ellipsoids are drawn at the 50% probability level, while the
hydrogen size is arbitrary.
R indices (all data)
Largest diff. peak and hole (e.Aꢁ3
)

T. Sedaghat et al. / Journal of Organometallic Chemistry 737 (2013) 26e31
29
Table 3
ꢀ
ꢀ
ꢀ
Selected bond lengths (A), bond angles ( ) and torsion angles ( ) for
4.
Sn(1)eC(21)
Sn(1)eO(1)
Sn(1)eC(15)
Sn(1)eN(1)
Sn(1)eO(2)
O(1)eC(1)
C(4)eC(5)
C(4)eN(1)
N(1)eN(2)
N(2)eC(1)
C(14)eO(2)
C(1)eC(2)
C(2)eC(3)
2.100(4)
2.119(3)
2.100(5)
2.135(3)
2.082(3)
1.298(4)
1.423(5)
1.300(4)
1.404(4)
1.295(4)
1.319(4)
1.492(5)
1.528(5)
C(21)eSn(1)eO(2)
C(21)eSn(1)eC(15)
O(1)eSn(1)eC(21)
C(21)eSn(1)eN(1)
O(2)eSn(1)eN(1)
C(15)eSn(1)eN(1)
C(15)eSn(1)eO(2)
O(2)eSn(1)eO(1)
C(15)eSn(1)eO(1)
N(1)eSn(1)eO(1)
O(2)eC(14)eC(5)
O(1)-C(1)eN(2)
94.24(14)
123.64(15)
95.10(14)
119.67(13)
82.87(11)
116.54(14)
96.37(18)
156.39(10)
96.39(18)
73.82(11)
124.4(4)
125.0(4)
127.6(4)
111.0(3)
129.2(3)
116.2(2)
113.8(2)
133.4(2)
Fig. 3. View of compound 4 evidencing the 2-fold axis passing through the C3 and C30
atoms and showing the numbering scheme of the asymmetric unit denoted by filled
drawings. Thermal ellipsoids are drawn at the 30% probability level, while the
hydrogen size is arbitrary.
[27], gives a value of 128.7ꢀ and 140.0ꢀ for MeeSneMe angle in 1
and 3, respectively.
The 119Sn{1H} NMR spectra of all complexes show only one
sharp singlet significantly at lower frequency than that of the
original SnMe2Cl2 (þ137 ppm) and SnPh2Cl2 (ꢁ32 ppm) [26].
Appearance of only one signal indicates the similar environment for
two tin centers in complex. On the basis of the chemical shifts
ranges proposed empirically [28e30], the coordination number of
tin atoms is five taking into consideration that this chemical shift is
located in lower frequency of the range for phenyltin complexes
and also for complexes in DMSO.
N(1)eC(4)eC(5)
C(1)eN(2)eN(1)
C(4)eN(1)eSn(1)
N(2)eN(1)eSn(1)
C(1)eO(1)eSn(1)
C(14)eO(2)eSn(1)
Sn(1)eN(1)eN(2)eC(1)
Sn(1)eO(1)eC(1)eN(2)
Sn(1)eN(1)eC(4)eC(5)
Sn(1)eO(2)eC(14)eC(5)
ꢁ1.7(4)
3.8(5)
ꢁ1.1(6)
Table 2
5.4(6)
ꢀ
ꢀ
ꢀ
Selected bond lengths (A), bond angles ( ) and torsion angles ( ) for
1.
Sn(1)eC(12)
Sn(1)eO(1)
Sn(1)eC(11)
Sn(1)eN(1)
Sn(1)eO(2)
O(1)eC(1)
C(6)eC(7)
C(7)eN(1)
N(1)eN(2)
N(2)eC(8)
C(8)eO(2)
C(8)eC(9)
C(9)eC(10)
2.097(4)
2.096(2)
2.102(5)
2.185(3)
2.152(3)
1.313(4)
1.427(4)
1.288(5)
1.398(4)
1.304(6)
1.296(5)
1.498(5)
1.474(6)
3.2. X-ray structures
The molecular structures of 1 and 4 are given in Figs. 2 and 3.
Selected bond lengths and angles are listed in Tables 2 and 3.
Complex 1 is crystallized in the P-1 triclinic space group and one
molecule is present in a unit cell, whereas complex 4 is crystallized
in the C2/c monoclinic space group with four molecules in a unit
cell. The structure of two complexes is binuclear and complex 1 is
centrosymmetry. The alkyl linker chain shows antieantieanti
conformation in 1 while gaucheeanti-gauche in 4. Structural pa-
rameters are completely similar for two parts of one molecule. The
CeO and CeN bond lengths in the amide functionality are consis-
tent with the enolate form of the hydrazinic moiety in complexes
[18,31,32]. The Schiff base is completely deprotonated and acts as a
tetrabasic ligand in the enolic form. The each tin center is sur-
rounded by imine nitrogen, enolic oxygen and phenolic oxygen of
ligand and two carbons of organic groups, therefore the coordina-
tion number of both tin is five. To quantify the extent of distortion
from either ideal square pyramid or trigonal bipyramid, the index of
C(12)eSn(1)eO(1)
C(12)eSn(1)eC(11)
O(1)eSn(1)eC(11)
C(12)eSn(1)eN(1)
O(1)eSn(1)eN(1)
C(11)eSn(1)eN(1)
C(12)eSn(1)eO(2)
O(2)eSn(1)eO(1)
C(11)eSn(1)eO(2)
N(1)eSn(1)eO(2)
O(1)eC(1)eC(6)
O(2)eC(8)eN(2)
N(1)eC(7)eC(6)
C(8)eN(2)eN(1)
C(7)eN(1)eSn(1)
N(2)eN(1)eSn(1)
C(8)eO(2)eSn(1)
C(1)eO(1)eSn(1)
93.99(14)
134.1(2)
96.99(18)
117.04(15)
83.53(10)
108.47(17)
92.88(14)
155.58(12)
94.95(18)
72.49(11)
124.2(3)
125.6(3)
126.4(3)
110.7(3)
128.5(2)
trigonality,
s
, have been found from
s
¼ (
a
ꢁ
b)/60 [33], a and b are
the two largest bond angles around the metal atom in the five-
coordinated environment. For a perfectly square pyramidal geom-
etry,
s
should be equal to zero, while it becomes unity for ideal
value is 0.358 for 1 and
116.8(2)
114.5(2)
132.4(2)
trigonal bipyramidal geometry. The
s
therefore the metal coordination geometry is described as highly
distorted square pyramid with imine nitrogen atom occupies the
apical position. The nitrogen is chosen as apex because any the four
donor atoms which define the two largest angles
be in axial position. The value for 4 obtains 0.545 and indicates the
geometry of the complex is between square-pyramidal and
Sn(1)eO(1)eC(1)eC(6)
Sn(1)eN(1)eN(2)eC(8)
Sn(1)eN(1)eC(7)eC(6)
Sn(1)eO(2)eC(8)eN(2)
ꢁ4.9(5)
ꢁ0.1(4)
2.6(6)
a and b should not
s
1.1(6)

30
T. Sedaghat et al. / Journal of Organometallic Chemistry 737 (2013) 26e31
trigonal-bipyramidal. But with particular precision, trigonal-
bipyramidal predominates over square-pyramidal geometry.
Therefore, the geometry around the tin atom may be considered as
a highly distorted trigonal-bipyramidal with phenolic and enolic
oxygens in axial and azomethine nitrogen and two ipso-carbons
from phenyl groups in equatorial positions. This distortion from
perfect geometries is mainly due to the rigidity of chelate rings, and
facilitated by the large covalent radius of tin(IV) [34,35]. The co-
ordination part of ligand forms six and five membered chelate
rings. These chelate rings are not planar but torsion angles are very
small (Tables 2 and 3). The SneN1 bond length is 2.185(3) and
2.135(3) Ǻ for 1 and 4, respectively, which are very similar to the
sum of the covalent radii of SneN (2.15 Ǻ), but are considerably
shorter than the sum of Van der Waals radii (3.75 Ǻ). SneOphenolic
and SneOenolic distances are also similar to the sum of the covalent
radii of SneO (2.10 Ǻ). Therefore, there is very strong covalent bond
between tin with oxygen and nitrogen atoms. In complex 1, the
slight difference between the CeSneC angle from X-ray data, 134.1
(2)ꢀ, and the empirical estimation in solution (128.7ꢀ) may be
related to removing the crystal network pressure in solution.
permeability across the bacterial cell wall is prior necessity for the
effectiveness of the biocide compounds against different microor-
ganisms. Therefore the enhancement in activity of the ligand on
complexation with organotins may be due to electron delocaliza-
tion over the whole chelate ring upon complexation. Such chelation
increases the lipophilic character and enhances the permeation of
the complexes through the lipid layer of the bacterial cell mem-
brane (chelation theory) [40e43]. It is apparent that toxicity toward
Gram-positive bacteria is more than Gram(ꢁ) strains. The reason is
the difference in the structures of the cell walls. The walls of
Gram(ꢁ) cells are more complex than those of Gram(þ) cells. Lip-
opolysacharides form an outer lipid membrane and contribute to
the complex antigenic specificity of Gram(ꢁ) cells. However, it is
remarkable that the bacteria of the genus Pseudomonas are a group
of resistant microorganism that many standard drugs were found
to have no activity against it [44,45]. Therefore it is interesting that
P. aeruginosa was inhibited by these complexes.
4. Conclusion
On the basis of spectral and structural investigations, dihy-
drazones are completely deprotonated and coordinated to dio-
rganotin moiety as tetrabasic ligands via imine nitrogen and
phenolic and enolic oxygens. All complexes are binuclear and on
the basis of 119Sn NMR data, coordination number of both tin re-
tains five in solution. The synthesized organotin complexes are
evaluated in inhibiting both Gram-positive (B. subtilis and S. aureus)
and Gram-negative (E. coli and P. aeruginosa) bacteria. All com-
plexes exhibit more inhibitory effects than the parent ligands and
in some cases than the standards. Therefore these compounds have
a potential to be used as drugs.
3.3. Biological studies
The in vitro antibacterial activities of Schiff base and its com-
plexes were studied along with two standard antibacterial drugs,
viz, Nalidixic acid and Vancomycin. The microorganisms used in
this work include B. subtilis and S. aureus (as Gram-positive bac-
teria) and E. coli and P. aeruginosa (as Gram-negative bacteria). The
results are presented in Table 4. Comparing the biological activity of
the ligands, organotin(IV) complexes and standard drugs, indicate
that all complexes exhibit more inhibitory effects than the parent
ligands and complex 2 show more inhibition on bacterial growth
than others. Generally, biological activity of organotin(IV) com-
plexes is influenced both by donor ligand and by the number and
nature of the organic groups bound to tin. A mechanism postulated
for action of antibacterial compounds is deactivation of various
cellular enzymes or denaturation of one or more proteins of the
cell, which, as a result, impairs normal cellular processes and
metabolic pathways of these organisms. It may involve the hy-
drolysis of organotin compound and formation of bonds between
Sn and donor atoms at active biological centers [36e39]. However,
Acknowledgment
Support of this work by Shahid Chamran University, Ahvaz, Iran
(Grant No. 1391) is gratefully acknowledged. The authors are also
thankful to Mohammad Azarkish for cooperation in Antibacterial
tests.
Appendix A. Supplementary material
CCDC 893775 and 879031 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Table 4
Antibacterial activity data of ligands and their complexes.
Compound
Conc. (mg/mL) Inhibition zone (mm)
E. coli P. aeruginosa S. aureus B. subtilis
H4La
10
20
40
10
20
40
10
20
40
10
20
40
10
20
40
10
20
40
10
11
12
11
12
13
10
13
15
16
17
22
n.a.
12
13
10
12
13
13
24
10
12
13
n.a.
n.a.
n.a.
15
16
17
13
14
15
12
13
14
12
14
16
13
15
16
13
16
18
15
18
23
19
20
22
14
16
17
17
12
12
13
15
9
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