Synthesis, characterization, biological activities of dimethyltin(IV) complexes of Schiff bases with ONO-type donors

Article abstract of DOI:10.1016/j.saa.2008.12.023

Four different dimethyltin(IV) complexes of Schiff bases derived from 2-amino-3-hydroxypyridine and different substituted salicylaldehydes have been synthesized. The compounds, with the general formula [Me₂Sn(2-OArCH{double bond, long}NC_5<

Full text of DOI:10.1016/j.saa.2008.12.023

Spectrochimica Acta Part A 72 (2009) 929–935
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization, biological activities of dimethyltin(IV) complexes of
Schiff bases with ONO-type donors
Nurs¸ en Altuntas¸ Öztas¸ a, Gülgün Yenis¸ ehirlib, Nilgün Ancınc,∗, Selma Gül Öztas¸ c,
d
d
˙
Yusuf Özcan , Semra Ide
a Department of Chemistry, Faculty of Science, Hacettepe University, 06800, Ankara, Turkey
b Department of Microbiology and Clinical Microbiology, Faculty of Medicine, Gaziosmanpas¸a University, 60100 Tokat, Turkey
c Department of Chemistry, Faculty of Science, Ankara University, 06100, Ankara, Turkey
d Department of Physics Engineering, Faculty of Engineering, Hacettepe University, 06800 Beytepe-Ankara, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Four different dimethyltin(IV) complexes of Schiff bases derived from 2-amino-3-hydroxypyridine
and different substituted salicylaldehydes have been synthesized. The compounds, with the general
formula [Me2Sn(2-OArCH NC5H3NO)], where Ar = –C6H3(5-CH3) [Me2SnL1], –C6H3(5-NO2) [Me2SnL2],
–C6H2(3,5-Cl2) [Me2SnL3], and –C6H2(3,5-I2) [Me2SnL4], were characterized by IR, NMR (1H and 13 C), mass
spectroscopy and elemental analysis. Me2SnL3 was also characterized by X-ray diffraction analysis and
shows a fivefold C2NO2 coordination with distorted square pyramidal geometry. H3C–Sn–CH3 angles in
the complexes were calculated using Lockhart’s equations with the 1J(117/119Sn–13 C) and 2J(117/119Sn–1H)
values (from the 1H-NMR and 13 C-NMR spectra). The in vitro antibacterial and antifungal activities of
dimethyltin(IV) complexes were also investigated.
Received 30 June 2008
Received in revised form
25 November 2008
Accepted 8 December 2008
Keywords:
Diorganotin(IV)
Schiff base
Antibacterial
Antifungal
© 2008 Elsevier B.V. All rights reserved.
Crystal structure
1. Introduction
As part of our investigation dealing with the study of
dimethyltin(IV) species derived from Schiff base ligands, we
An important class of organotin(IV) complexes are those derived
from ligands containing nitrogen and oxygen donor atoms. Espe-
cially, organotin(IV) complexes of deprotonated Schiff bases are
known [1–9]. Recently organotin(IV) compounds have received
considerable attention because of their biological properties [10],
particularly antitumour [11–16], antibacterial [17–21] and antifun-
gal activity [20–22]. In addition to their biological activity, the
organotin(IV) complexes have also found application in catalysts
[23] and nonlinear optics [9,24].
Generally, tin atoms in complexes derived from ONO terdentate
ligands are penta-coordinate with a trigonal bipyramidal (TBP) or
square pyramidal (SP) geometry [3,4,6,19,24–28]. In these geome-
tries, the metal center can act as a Lewis acid, which allows to
increase its coordination number by addition of molecules hav-
ing electron donating atoms (e.g. solvent molecules) [3,4,6,25–27],
changing the geometry to distorted octahedral. For that reason,
five-coordinate tin complexes frequently form Sn· · ·O intermolecu-
lar bonds in the solid state, thus giving dimeric aggregates through
the formation of a Sn2O2 four-membered ring [24,28,29].
describe herein the synthesis and structural analysis of deriva-
tives containing terdentate ONO-donor Schiff base ligands (H2L).
The ligands are derived from four different salicylaldehyde and 2-
amino-3-hydroxypyridine. The complexes have been synthesized
under mild conditions from dimethyltin(IV) dichloride and H2L in
methanol in the presence of triethylamine, Fig. 1.
We have also investigated antibacterial and antifungal activities
of these complexes, together with those of dimethyltin(IV) com-
plexes which we synthesized and characterized in our previous
studies [30–32].
2. Experimental
2.1. Analytical methods and physical measurements
All chemicals and reagents were of reagent-grade qual-
ity.
Dimethyltin
dichloride,
2-amino-3-hydroxypyridine,
5-methylsalicylaldehyde, 5-nitrosalicylaldehyde, 3,5-dichlorosa-
licylaldehyde, 3,5-diiodosalicylaldehyde and solvents were
purchased from Aldrich and used without further purification.
The 1H-NMR and 13C-NMR spectra were obtained in deuterated
DMSO and CDCl3 solvents on a Bruker-400 MHz Ultrashield NMR
spectrometer with TMS as internal standard. The infrared spectra
∗
Corresponding author. Tel.: +90 3122126720/1389; fax: +90 3122232395.
E-mail address: nancin@science.ankara.edu.tr (N. Ancın).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.12.023

930
N.A. Öztas¸ et al. / Spectrochimica Acta Part A 72 (2009) 929–935
Fig. 1. Numbering and preparation of compounds.
were recorded on a Mattson-1000 FTIR spectrophotometer using
KBr pellets, in the range of 4000–400 cm−1. Bands were located
by means of a microprocessor. ESI-mass spectra were recorded on
a AGILENT 1100 MSD LC–MS spectrometer. Melting points were
determined with in hot-stage Leica DM EP Polarizing Microscope
System. Chemical analysis of C, H and N were determined with LECO
CHNS-932 elemental analyzer. Intensity data for Me2SnL3 were
measured at room temperature on an Enraf-Nonius CAD4 diffrac-
tometer with graphite monochromatized Mo K␣ (ꢀ = 0.71073 Å)
radiation and using the ω-2Â scan technique. Full-matrix least-
squares refinement method was carried out on F2 of the positional
and anisotropic thermal parameters of the non-hydrogen atoms
and of the positional parameters of the hydrogen atoms, which
were assigned fixed isotropic thermal parameters. SHELXS-97 and
SHELXL-97 [33] programs were used to solve and refine the struc-
ture. The molecular diagram and crystal structure showing the
crystallographic unit cell were drawn with the program ORTEPIII
[34]. A summary of crystal data and refinement results were given
in Table 1.
2.2. Antimicrobial studies
2.2.1. Antibacterial activity
The dimethyltin(IV) complexes were screened for their antibac-
terial activities against standard strains of Gram negative bacteria
(Escherichia coli ATCC (American Type Culture Collection) 35218,
E. coli ATCC 25922, Enterobacter cloacae ATCC 23355, Serratia
marcescens ATCC 8100, Pseudomonas aeruginosa ATCC 27853) and
Gram positive bacteria (Enterococcus faecalis ATCC 29212, Staphylo-
coccus epidermidis ATCC 12228, Staphylococcus aureus ATCC 25923)
by Kirby Bauer disc diffusion method [35]. All compounds were
dissolved at a concentration of 200 mg/L in methanol. 0.5 McFar-
land suspension of each strain was swabbed on Mueller Hinton agar
(Oxoid Limited, Hampshire, England). Paper discs with a diameter
of 6 mm (Oxoid Limited, Hampshire, England) were saturated with
25 mL of a solution of test compounds and placed on the surface of
the agar plates. After incubation at 37 ◦C for 24 h, inhibition zone
diameters surrounding the each disc were measured and recorded
in millimeter. Gentamicin (10 ␮g/disc) was used as a positive con-
trol disc for bacteria.
Table 1
Crystal data and structure refinement parameters for C14 H12 Cl2N2O2Sn.
2.2.2. Antifungal activity
Empirical formula
Formula weight
Crystal system
C14 H12 Cl2N2O2Sn
429.88
Monoclinic
The in vitro antifungal activities of dimethyltin(IV) complexes
were also evaluated against Aspergillus niger, Aspergillus fumiga-
tus, Aspergillus flavus, and Candida albicans (clinical isolates). Each
Aspergillus strain was inoculated onto potato dextrose agar (Oxoid
Limited, Hampshire, England) at 35 ◦C for 7 days. Spore suspen-
sions were prepared in sterile saline and adjusted to a turbidity
equivalent to that of 0.5 McFarland corresponding to approximately
106 colony forming units/mL, then inoculated to the agar sur-
face. The agar plates were prepared by using RPMI-1640 medium
(Sigma, St. Louis, USA) 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, USA). For C.
albicans, Mueller Hinton agar supplemented with 2% of glucose
was used. Paper discs with a diameter of 6 mm (Oxoid Limited,
Hampshire, England) were saturated with 25 mL of a solution of
test compounds and placed on the surface of the agar plates. Inhibi-
tion zone diameters were measured following 24 h of incubation at
35 ◦C in ambient air. Fluconazol (25 ␮g/disc) was used as a positive
control disc for fungi.
Space group
P 21/n
a = 9.6010(10) Å
b = 15.861(3) Å
c = 10.9800(10) Å
ˇ = 113.825(7)◦
Volume (Å3)
Z
1529.6(4)
4
1.867
0.27
293(2)
Prism
Transparent orange
Dcalc (g cm−3
)
ꢁ(Mo K␣) (mm−1
T (K)
)
Crystal description
Colour
Crystal sizes
0.50 × 0.25 × 0.20
Radiation Mo K␣ (ꢀ, Å)
0.71073
Âmin–Âmax (◦)
2.4–26.3
Psi-scan
840
Absorption correction
F(0 0 0)
Index rangers
−10 ≤ h ≤ 11, −19 ≤ k ≤0, −13 ≤ l ≤ 0
Reflections collected
Number of refined parameters
Number of reflection used
Observed data [I > 2ꢂ (I)]
R [F2 > 2ꢂ (F2)]
3250
194
3090
2608
0.027
0.082
2.3. Preparation of the ligands
Rw (F2)
w = 1/[ꢂ2(Fo2) + (0.0617P)2 + 0.4100P]
Where P = (Fo2 + 2Fc2)/3
0.955
0.749, −0.845
The Schiff bases were synthesized by mixing equimolar amounts
of 2-amino-3-hydroxypyridine with the appropriate salicylalde-
hyde, both dissolved in methanol. The reaction mixture was
Goodness-of-fit on F2
Largest diff. peak and hole (eÅ−3
)

N.A. Öztas¸ et al. / Spectrochimica Acta Part A 72 (2009) 929–935
931
refluxed for 1 h and the precipitate thus formed upon cooling in
an ice bath was filtered off. The solid residue was crystallized from
methanol–dichloromethane (1/1, v/v) mixture. The description of
the individual products was as follows:
N-(3-hydroxypyridine-2-yl)-5-methylsalicylideneimine,
H2L1.
Orange crystals, m.p.: 149–151 ◦C. Mass spectrum (ESI) {m/z
[assignment] (%)}: 229 [M+H]+ (100.0). Elemental anal.: found C,
68.30; H, 5.42; N, 12.33%. Calcd. for C13H12N2O2: C, 68.41; H, 5.30;
N, 12.27%. IR (cm−1): 2690 br ꢃ(O–H); 1623 s ꢃ(C N).
N-(3-hydroxypyridine-2-yl)-5-nitrosalicylideneimine, H2L2. Yel-
low crystals, m.p.: >300 ◦C. Mass spectrum (ESI) {m/z [assignment]
(%)}: 260 [M+H]+ (1.1). Elemental anal.: found C, 55.47; H, 3.55; N,
16.38%. Calcd. for C12H9N3O4: C, 55.60; H, 3.50; N, 16.21%. IR (cm−1):
2997 br ꢃ(O–H), 1612 vs. ꢃ(C N).
N-(3-hydroxypyridine-2-yl)-3,5-dichlorosalicylideneimine, H2L3.
Orange crystals, m.p.: 233–235 ◦C. Mass spectrum (ESI) {m/z
[assignment] (%)}: 283 [M+H]+ (4.9). Elemental anal.: found C,
50.90; H, 2.58; N, 10.05%. Calcd. for C12H8Cl2N2O2: C, 50.91; H, 2.85;
N, 9.89%. IR (cm−1): 3013 br ꢃ(O–H), 1625 vs. ꢃ(C N).
N-(3-hydroxypyridine-2-yl)-3,5-diiodosalicylideneimine,
H2L4.
Orange crystals, m.p.: >300 ◦C. Mass spectrum (ESI) {m/z [assign-
ment] (%)}: 467 [M+H]+ (15.0). Elemental anal.: found C, 30.77; H,
1.81; N, 6.15%. Calcd. for C12H8I2N2O2: C, 30.93; H, 1.73; N, 6.01%.
IR (cm−1): 3045 br ꢃ(O–H), 1621 vs. ꢃ(C N).
2.4. Preparation of the complexes
All the complexes were similarly prepared from dimethyltin(IV)
dichloride and the appropriate Schiff base ligands as follows. To
a solution of Schiff base (2.0 mmol) in 15 mL dry methanol, a few
drops of triethylamine were added and the resulting triethylammo-
nium salt solution of the ligand was filtered to remove any insoluble
impurities.
To this solution, a solution of (CH3)2SnCl2 (2.0 mmol) in 15 mL
of dry methanol was added slowly and heated (50–60 ◦C). The
resulting mixture was cooled at room temperature overnight. The
reddish-orange crystals were filtered off and recrystallized from
butanol–dichloromethane (1/1, v/v) mixture. The description of the
individual complexes was as follows:
[N-(3-hydroxypyridine-2-yl)-5-methylsalicylideneiminato]dimeth
yltin(IV), Me2SnL1. Red crystals, m.p.: 182–184 ◦C. Mass spectrum
(ESI) {m/z [assignment] (%)}: 377 [M+H]+
(
120Sn) (97.1), 375
[M+H]+ 118 Sn) (79.9), 373 [M+H]+ 116 Sn) (52.1), 346 [M-2CH3]+
( (
(
120Sn) (3.3), 344 [M-2CH3]+ 118 Sn) (3.0), 342 [M-2CH3]+ 116 Sn)
( (
(1.5). Elemental anal.: found C, 47.99; H, 4.39; N, 7.28%. Calcd.
for C15H16 N2O2Sn: C, 48.04; H, 4.30; N, 7.47%; IR (cm−1): 1604 s
ꢃ(C N), 621 ꢃ(Sn–C), 525, 532 ꢃ(Sn–O), 467 ꢃ(Sn–N).
[N-(3-hydroxypyridine-2-yl)-5-nitrosalicylideneiminato]dimethyl
tin(IV), Me2SnL2. Brown crystals, m.p.: 259–261 ◦C. Mass spectrum
(ESI) {m/z [assignment] (%)}: 408 [M+H]+
(
120Sn) (14.9), 406
[M+H]+ 118 Sn) (14.8), 404 [M+H]+ 116 Sn) (6.3). Elemental anal.:
( (
found C, 41.37; H, 3.35; N, 10.25%. Calcd. for C14 H13N3O4Sn: C,
41.42; H, 3.23; N, 10.35%. IR (cm−1): 1610 ꢃ(C N), 691 ꢃ(Sn–C),
525, 544 ꢃ(Sn–O), 471 ꢃ(Sn–N).
[N-(3-hydroxypyridine-2-yl)-3,5-dichlorosalicylideneiminato]dimet
hyltin(IV), Me2SnL3. Red crystals, m.p.: 226–228 ◦C. Mass spectrum
(ESI) {m/z [assignment] (%)}: 431 [M+H]+
(
120Sn) (56.8), 429
[M+H]+ 118 Sn) (35.6), 427 [M+H]+ 116 Sn) (12.7), 151 [(CH3)2SnH]+
( (
(
(
120Sn) (4.3), 149 [(CH3)2SnH]+
116 Sn) (1.8), 135 [CH3Sn]+ 120Sn) (3.1), 133 [CH3Sn]+
116 Sn) (1.8). Elemental anal.: found C, 39.25; H, 2.90;
(
118 Sn) (3.7), 147 [(CH3)2SnH]+
(
(
118 Sn) (2.8),
131 [CH3Sn]+
(
N, 6.45%. Calcd. for C14 H12Cl2N2O2Sn: C, 39.12; H, 2.81; N, 6.52%.
IR (cm−1): 1600 s ꢃ(C N), 689 ꢃ(Sn–C), 581, 542 ꢃ(Sn–O), 473
ꢃ(Sn–N).
[N-(3-hydroxypyridine-2-yl)-3,5-diiodosalicylideneiminato]dimet
hyltin(IV), Me2SnL4. Red crystals, m.p.: 216–218 ◦C. Mass spectrum

932
N.A. Öztas¸ et al. / Spectrochimica Acta Part A 72 (2009) 929–935
Table 3
13 C-NMR spectral data (ı in ppm) of the ligands and their corresponding organotin(IV) complexes.
Compound
C-1
C-2
C-3
C-4
C-5
C-6
C-7
C-8
C-9
C-10
C-11
C-12
CH3
SnMe2
H2L1
118.72
117.51
118.97
119.35
116.92
115.95
118.07
118.36
159.16
169.16
160.44
164.87
168.18
173.95
162.92
166.18
117.01
120.32
121.04
79.40
122.34
123.29
120.55
95.74
135.46
130.90
133.15
149.80
135.34
131.45
136.25
152.57
128.91
138.24
123.89
92.04
126.30
138.09
127.37
99.54
133.81
131.24
130.24
142.29
139.58
133.46
132.97
144.38
164.94
159.70
158.06
159.06
163.92
163.20
162.74
162.44
146.46
147.36
147.26
147.42
153.73
154.02
154.12
154.09
123.78
125.24
124.68
125.21
125.10
126.14
125.94
125.88
124.16
125.35
124.25
125.29
125.26
126.58
126.28
126.20
140.40
139.59
138.87
139.54
135.44
136.32
136.04
136.08
145.78
140.68
142.65
140.81
143.69
142.48
142.83
142.83
20.35
–
–
–
–
–
–
–
1.77
2.43
2.40
2.42
H2L2
H2L3
H2L4
Me2SnL1
Me2SnL2
Me2SnL3
Me2SnL4
20.09
–
–
–
(ESI) {m/z [assignment] (%)}: 615 [M+H]+ (120Sn) (61.7), 613 [M+H]+
((CH3)2Sn moiety) that appear at 0.83–0.92 ppm range. The two
methyl-group protons appear to be equivalent and again, two-bond
1H–117 Sn and 1H–119 Sn couplings (77.6–86.0 Hz) are observable.
These values are typical of the five-coordinated tin(IV) species.
13C-NMR spectral data also support the authenticity of the pro-
posed structures. The considerable shifts in the positions of carbon
atoms adjacent to the imine nitrogen (C-7) and phenolic/pyridilic
oxygen (C-2, C-8) support the proposed coordination in the com-
plexes. The shifts in the positions of carbon atoms adjacent to
the coordinating atoms clearly indicate the bonding of the imine
nitrogen and two oxygen atoms to the central metal atom. The
1J(117/119Sn–13C) couplings (629.6–658.6 Hz) are clearly visible. The
magnitude of the coupling constants agree well with those previ-
ously reported for analogous five-coordinate derivatives [4,43]. The
2J(117/119Sn–13C) couplings were not observed in the complexes, as
is the case for similar structures [4].
(
118 Sn) (49.8), 611 [M+H]+ 116 Sn) (28.3). Elemental anal.: found
(
C, 27.36; H, 2.10; N, 4.67%. Calcd. for C14 H12I2N2O2Sn: C, 27.44;
H, 1.97; N, 4.57%. IR (cm−1): 1585 s ꢃ(C N), 677 ꢃ(Sn–C), 570
ꢃ(Sn–O), 465 ꢃ(Sn–N).
3. Results and discussions
In the present work, we report the synthesis, characteriza-
tion, antibacterial and antifungal activities of R2SnL, where R = Me,
L = deprotonated Schiff bases derived from substituted salicylalde-
hydes with 2-amino-3-hydroxypyridine. Schiff bases and their
dimethyltin(IV) complexes were characterized by their elemental
analysis, 1H, 13C-NMR, IR and mass spectral data.
3.1. NMR spectra
The C–Sn–C angles were calculated using Lockhart’s equation
{Â(Me–Sn–Me) = 0.0161 × [2J(117/119Sn–1H)]2 − 1.32 × [2J(117/119Sn
–1H)] + 133.4} with known 2J(117/119Sn–1H) values as well as
Because of the low solubility in CDCl3, the NMR spectra of
the Schiff bases (except H2L1) were made in deuterated DMSO.
The NMR spectra of the organotin(IV) complexes were recorded
in CDCl3. 2D COSY homonuclear, HETCOR and HMBC heteronuclear
correlation techniques were made use of for signal assignments.
The 1H-NMR and 13C-NMR data for the ligands and their tin(IV)
complexes were summarized in Tables 2 and 3.
1
with the equation { J(117/119Sn–13C) = 10.7Â − 778} by inserting
1J(117/119Sn–13C) values [40,41]. The results of the calculation
obtained by 2J(117/119Sn–1H) values for Me2SnL3 (139.0◦), was
closer to the true value [141.28(18)◦], compared to the estimated
angle based on 1J(117/119Sn,13C) data (134.3◦). Calculated values on
the basis of the Lockhart’s equations and a sample X-ray diffraction
value for Me2SnL3 are displayed in Table 4.
In the 1H-NMR spectra of the ligands, the signals at
9.55–10.72 ppm [(OH)a proton on the pyridine moiety] and
12.01–15.70 ppm [(OH)b proton on the salicylaldehyde moiety]
disappeared in the 1H-NMR spectra of the corresponding Sn(IV)
complexes, indicating the engagement of phenolic O atoms in com-
plexations. The 1H-NMR spectra of the ligands show a single signal
for H-7 that appears between 9.36 and 9.66 ppm, as well as the cor-
responding signals for the iminic salicylidene moiety [15,18,19,36].
The H-7 signal of tin(IV) complexes appear in the range of
9.40–9.64 ppm. The 3J(117/119Sn–1H) coupling (48.6–50.5 Hz) due
to NMR-active Sn isotopes is visible and this is a strong indica-
tion to the ligation of azomethine nitrogen to Sn atom. The extent
of coupling is comparable with literature values [4,18,29]. For the
ligands and complexes, the signals of H-4 and H-6 protons (for
H2L3, H2L4 and their complexes) are confirmed by two-dimensional
heteronuclear-correlated NMR technique (2D 13C–1H HMBC) in
addition to 2D 1H–1H COSY experiments. Other protons in the
phenyl rings are found in their normal ı range [37–39]. The spectra
of the complexes display additional signals due to methyl protons
3.2. IR spectra
Selected IR data for all compounds are reported in Section 2. The
differences is obvious rather than remarkable between the IR spec-
tra of the ligands and those of dimethyltin(IV) complexes is that the
stretching vibration bands of the phenolic and pyridilic O–H groups
disappear from the spectra of the complexes. This is assigned to
deprotonation of the phenolic and pyridilic oxygen atoms of the
ligand upon complexation with the tin atom. This was also con-
firmed by the appearances of a band at 570–525 cm−1 due to Sn–O
stretching vibration.
In the complexes the ꢃ(C N) band, occurring between 1610 and
1585 cm−1, is considerably shifted towards lower frequencies with
respect to that of the free Schiff bases (1625–1612 cm−1), confirm-
ing the coordination of the azomethine nitrogen to the organotin
moiety. Also the Sn–C and Sn–N bands were observed at 691–621
Table 4
The 3J(117/119Sn–1H), 2J(117/119Sn–1H), and 1J(117/119Sn–13 C) values (Hz) and the Me–Sn–Me angles of the dimethyltin complexes.
Compound
3J(Sn–H) CH
N
2J(Sn–H) Me2Sn
Â(Me–Sn–Me)a
1J(Sn–C) Me2Sn
Â(Me–Sn–Me)b
Â(Me–Sn–Me)c
Me2SnL1
Me2SnL2
Me2SnL3
Me2SnL4
48.6
49.2
49.6
50.5
78.4
77.6
86.0
79.2
128.9◦
127.9◦
139.0◦
129.9◦
629.6
640.0
658.6
656.6
131.6◦
132.5◦
134.3◦
134.1◦
–
–
141.28◦
–
a
Calculated from Â(Me–Sn–Me) = 0.0161 × [2J(117/119Sn–1H)]2 − 1.32 × [2J(117/119Sn–1H)] + 133.4.
b
c
Calculated from 1
From X-ray data.
J
117/119Sn–13 C = 10.7Â(Me–Sn–Me) − 778.

N.A. Öztas¸ et al. / Spectrochimica Acta Part A 72 (2009) 929–935
933
Fig. 2. The molecular structure of Me2SnL3 showing the atom numbering scheme. The displacement ellipsoids are plotted at the 50% probability level.
and 473–465 cm−1 correspondingly [15]. These findings clearly sug-
gest the coordination of imino nitrogen, deprotonated phenolic
and pyridilic oxygen donor sites to the central tin atom and there-
fore terdentate dibasic nature of the coordinated ligand may be
accepted.
list of the bond lengths and angles for the complex is given in
Table 5.
The coordination around tin in the complex is defined by two
carbon atoms from methyl groups, two oxygen atoms forming a
bridge to phenyl and pyridyl rings through the tin atom and imino
nitrogen atom found in the ligand which is in phenol-imine form.
The metal atom is in a distorted square pyramidal geometry. To
quantify the extent of distortion from the ideal square pyramidal
geometry towards the trigonal bipyramidal, the trigonal index, ꢄ,
was computed [7,42,43]. The ꢄ value is defined as ꢄ = (ˇ − ˛)/60,
˛ and ˇ being the two largest donor–metal–donor angles in the
five-coordinated environment. For a perfectly square pyramidal
geometry, ꢄ should be equal to 0, while it becomes unity for a
perfect trigonal bipyramidal geometry. For the complex Me2SnL3,
ꢄ value was found 0.25. Thus for compound, square pyramidal
geometry predominates over trigonal bipyramidal geometry.
In the complex, the two carbon atoms and two oxygen atoms
constitute the square base and the imino nitrogen atom occupies
the apical position. The following bond angles may be given as an
evidence of distorted square-pyramidal conformation. O1–Sn–O2:
156.16(8); O1–Sn–N1: 80.17(9); O2–Sn–N1: 75.99(9); N1–Sn–C13:
109.46(14); N1–Sn–C14: 108.51(14); C13–Sn–C14: 141.28(18);
O1–Sn–C14: 89.77(14); O1–Sn–C13: 89.39(14); O2–Sn–C13:
97.96(14); O2–Sn–C14: 98.21(13). The distortion is mainly due
3.3. Mass spectra
The Schiff bases and their dimethyltin(IV) complexes were also
characterized by mass spectrometry using electrospray ionization
technique. The [M+H]+ ion peaks of the complexes are given in Sec-
tion 2. The Sn-containing fragments display the natural abundance
of the major Sn isotopes. The experimental isotopic distributions of
all the Sn-containing fragment ions were compared with the theo-
retically calculated one and found in agreement with the theoretical
relative abundances. As an example, the [M+H]+ ion peak with the
characteristic tin isotopes of Me2SnL1 was measured (theoretical
relative abundances in parentheses): m/z 373, 53.6% (43.1%); 374,
33.1% (29.8%); 375, 82.3% (75.5%); 376, 42.4% (37.6%); 377, 100%
(100%); 378, 20.8% (16.6%); 379, 16.7% (15.0%); 380, 3.0% (2.2%);
381, 18.8% (16.5%); 382, 4.8% (2.7%). The fragmentation pattern is in
agreement with the literature reports [5,8,11].
3.4. Crystal structure of Me2SnL3
The molecular structure and the atom numbering scheme
for compound [N-(3-hydroxypyridine-2-yl)-3,5-dichlorosalicy-
lideneiminato]dimethyltin(IV), Me2SnL3 is shown in Fig. 2. A
Table 5
Selected bond lengths and angles (Å, ◦).
Sn–O1
Sn–O2
Sn–N1
Sn–C13
2.179(2)
2.131(2)
2.213(3)
2.103(4)
2.095(3)
156.16(8)
80.17(9)
75.99(9)
89.39(14)
89.77(14)
97.96(14)
98.21(13)
O1–C1
O2–C8
N1–C7
N1–C12
1.293(4)
1.333(4)
1.295(4)
1.425(4)
1.430(5)
109.46(14)
108.51(14)
141.28(18)
132.3(2)
Sn–C14
C6–C7
O1–Sn–O2
O1–Sn–N1
N1–Sn–O2
O1–Sn–C13
O1–Sn–C14
O2–Sn–C13
O2–Sn–C14
N1–Sn–C13
N1–Sn–C14
C13–Sn–C14
Sn–O1–C1
Sn–O2–C8
Sn–N1–C7
115.3(2)
129.1(2)
Fig. 3. The packing diagram of Me2SnL3.

934
N.A. Öztas¸ et al. / Spectrochimica Acta Part A 72 (2009) 929–935
Table 6
Antibacterial and antifungal activities of compounds.
Microorganism
Inhibition zone (mm)
Me2SnL1
Me2SnL2
Me2SnL3
Me2SnL4
Me2SnL5a
Me2SnL6a
Me2SnL7a
Me2SnL8a
G
F
S. aureus ATCC 25923
S. epidermidis ATCC 12228
E. faecalis ATCC 29212
E. coli ATCC 25922
E. coli ATCC 35218
E. cloacae ATCC 23355
S. marcescens ATCC 8100
P. aeruginosa ATCC 27853
A. niger
16
12
16
16
15
14
10
–
12
13
12
–
22
22
–
–
–
–
–
–
–
32
24
15
–
–
–
–
–
15
20
20
–
–
–
–
–
–
–
–
–
–
–
–
–
17
14
15
14
11
16
11
–
10
12
12
–
–
–
–
–
–
–
–
–
–
–
–
–
18
12
14
16
15
16
13
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
22
25
14
19
–
25
24
18
–
–
–
–
A. flavus
A. fumigatus
C. albicans
–
–
–
–
–
–
25
G: gentamicin; F: fluconazol.
a
Me2SnL5, [N-(3-hydroxypyridine-2-yl)-salicylideneiminato]dimethyltin(IV); Me2SnL6, [N-(3-hydroxypyridine-2-yl)-5-bromosalicylideneiminato]dimethyltin(IV);
Me2SnL7, [N-(3-hydroxypyridine-2-yl)-5-hydroxysalicylideneiminato]dimethyltin(IV); Me2SnL8, [N-(3-hydroxypyridine-2-yl)-5-chlorosalicylideneiminato]dimethyltin(IV).
to the rigidity of chelate rings, together with the large covalent
radius of tin(IV). These geometric results are in agreement with
the results of similar tin(IV) complexes [3,4,30,31,44].
antifungal activity against all Aspergillus spp., whereas no activity
was observed against C. albicans. The change of a substituent in the
ligand may lead to enhanced antibacterial and antifungal activities
of these dimethyltin(IV) complexes. These antibacterial and anti-
fungal activity results are in accordance with those found for other
similar dimethyltin(IV) complexes [20,48].
Five- and six-membered rings form upon chelation of
the Sn atom to the ligands. The organic parts of the five-
membered and six-membered rings are nearly planar (the
torsion angles, O2–C8–C13–N1: −0.6(5)◦; C1–C6–C7–N1: −5.3(6)◦;
O1–C1–C6–C7: −1.7(6)◦) but the tin atom is out of these planes
as indicated by the torsion angles, Sn–O2–C8–C12: 10.6(4)◦;
N1–Sn–O2–C8: −11.4(2)◦; Sn–O1–C1–C6: 20.4(6); Sn–N1–C7–C6:
−5.9(6).
4. Conclusion
In summary, four new dimethyltin(IV) compounds of N-
(3-hydroxypyridine-2-yl)-salicylideneimine derivatives have been
synthesized and characterized by IR, NMR, mass spectroscopy and
elemental analysis. The crystal structure of Me2SnL3 has also been
determined by X-ray single crystal diffraction analyses. It has found
that the tin atoms are five-coordinated in a square pyramidal geom-
etry. The monomeric Me2SnL3 units are linked into dimers by
weak intermolecular interactions with Sn· · ·O bonding. The in vitro
antibacterial and antifungal tests of the synthesized dimethyltin
complexes have been carried out. Me2SnL3 showed higher activity
against S. aureus ATCC 25923 than the standard drug gentamisin.
The results of antifungal screening, indicated that Me2SnL3 also
showed more activity against all Aspergillus spp. than the other
complexes.
From Fig. 3 it can be seen that in the compound the tin atom
environment is six-coordinate in a centrosymmetric arrangement
leading to a Sn2O2 core connected by the Sn–O bond, and the
Sn· · ·O2 bond distance of 2.839(2) Å is markedly greater than the
sum of the covalent radii for Sn–O (2.13 Å), but is considerably less
than the sum of the Van der Waals radii (3.70 Å). The O· · ·Sn bond-
ing occurs with the oxygen atom at the five-membered ring. It
is shown that the O2 atom makes weak interactions with the Sn
atom of the second complex. Two molecules form a weak-bridged
dimer with weak contacts of Sn· · ·O bonding. The large C–Sn–C bond
angle (141.28(18)◦) allows for the formation of Sn· · ·O intermolec-
ular interaction, giving rise to a dimeric organization. The dimeric
assembly occurs via the formation of a Sn2O2 four-membered ring.
This fact modifies the coordination around the tin atom which show
a distorted octahedral geometry with Sn· · ·O interaction distances
[4,19,24,28,29,45,46].
5. Supplementary material
More details of the crystal structure determinations have been
deposited with the Cambridge Crystallographic Data Centre with
the deposition number: CCDC 674907.
3.5. Biological activity
In the literature, the organotin(IV) complexes of Schiff bases con-
taining pyridine moiety were tested on different microbial species
including bacteria, yeast and molds. Some of the complexes showed
appreciable antimicrobial activities and lack of genotoxicity [47].
In this work, the antibacterial and antifungal activities of the
synthesized dimethyltin(IV) complexes and the others which were
characterized our previous studies [30–32] are listed in Table 6.
The results show that Me2SnL1, Me2SnL5 and Me2SnL7 were
found effective against all bacterial strains exceptP. aeruginasa ATCC
27853 while, Me2SnL3 was only effective against Gram positive bac-
teria. Compound Me2SnL3 also showed higher activity against S.
aureus ATCC 25923 than the standard drug gentamisin. Me2SnL4,
Me2SnL6 and Me2SnL8 were found to have no activity against the
all tested strains. On the other hand Me2SnL2 showed antibacte-
rial activity only against S. aureus ATCC 25923 and S. epidermidis
ATCC 12228. The results of the antifungal disc diffusion suscep-
tibilities tests revealed that Me2SnL1, Me2SnL3 and Me2SnL5 had
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