Synthesis and characterization of diorganotin (IV) complexes with tridentate schiff base ligand pyridoxal aroylhydrazones

Article abstract of DOI:10.1080/10426507.2010.517583

Dichlorodiorganotin (IV) R2SnCl₂ (where R = Me, Bu, or Ph) on reaction with substituted hydrazones (H2L) derived from the condensation of pyridoxal hydrochloride with substituted acid hydrazides, H2pydx-inh (LI), H2pydx-th (LII), or H2pydx-nh (LIII) (pydx = pyridoxal, inh = isonicotinoyl hydrazone, th = 2-thiophene carboxyl hydrazone, nh = 1-naphthoyl hydrazone), dry benzene give pentacoordinated complexes of the type R2SnL(I-III). In the solution of isolated complexes the ligand acted in a tridentate manner (O,O,N), coordinating through a phenolic oxygen, oxygen of keto group after enolization, and nitrogen of azomethine group. The synthesized complexes were characterized by elemental analyses, molar conductance, molecular weight determination, and infrared (IR) and nuclear magnetic resonance (NMR; 1H, 13C, and 119Sn) spectral data. The ligands and their tin complexes were evaluated for antifungal and antibacterial activities, and the results indicate that they exhibit significant antimicrobial properties. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Full text of DOI:10.1080/10426507.2010.517583

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Synthesis and Characterization of
Diorganotin (IV) Complexes with
Tridentate Schiff Base Ligand Pyridoxal
Aroylhydrazones
a
a
Nidhi Sonika & Rajesh Malhotra
a
Department of Chemistry , G. J. University of Science and
Technology , Hisar , Haryana , India
Published online: 04 Aug 2011.
To cite this article: Nidhi Sonika & Rajesh Malhotra (2011) Synthesis and Characterization of
Diorganotin (IV) Complexes with Tridentate Schiff Base Ligand Pyridoxal Aroylhydrazones, Phosphorus,
Sulfur, and Silicon and the Related Elements, 186:7, 1449-1459, DOI: 10.1080/10426507.2010.517583
To link to this article: http://dx.doi.org/10.1080/10426507.2010.517583
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Phosphorus, Sulfur, and Silicon, 186:1449–1459, 2011
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ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2010.517583
SYNTHESIS AND CHARACTERIZATION OF
DIORGANOTIN (IV) COMPLEXES WITH TRIDENTATE
SCHIFF BASE LIGAND PYRIDOXAL AROYLHYDRAZONES
Nidhi Sonika and Rajesh Malhotra
Department of Chemistry, G. J. University of Science and Technology,
Hisar, Haryana, India
GRAPHICAL ABSTRACT
CH OH
2
H
C
5
N
6
R'
N
4
N
1
3
O
Sn
O
2
R
R
CH3
R = Me,Bu, Ph
R' = 2-pyridyl, 2-thenyl, 1-naphthyl
Abstract Dichlorodiorganotin (IV) R2SnCl2 (where R = Me, Bu, or Ph) on reaction with
substituted hydrazones (H2L) derived from the condensation of pyridoxal hydrochloride with
substituted acid hydrazides, H2pydx-inh (LI), H2pydx-th (LII), or H2pydx-nh (LIII) (pydx =
pyridoxal, inh = isonicotinoyl hydrazone, th = 2-thiophene carboxyl hydrazone, nh = 1-
naphthoyl hydrazone), dry benzene give pentacoordinated complexes of the type R2SnL(I-III).
In the solution of isolated complexes the ligand acted in a tridentate manner (O,O,N), co-
ordinating through a phenolic oxygen, oxygen of keto group after enolization, and nitrogen
of azomethine group. The synthesized complexes were characterized by elemental analyses,
molar conductance, molecular weight determination, and infrared (IR) and nuclear magnetic
1
13
119
resonance (NMR; H, C, and Sn) spectral data. The ligands and their tin complexes were
evaluated for antifungal and antibacterial activities, and the results indicate that they exhibit
significant antimicrobial properties.
Received 27 May 2010; accepted 18 August 2010.
The authors are grateful to the Sophisticated Analytical Instrumentation Facility (SAIF), Panjab University,
Chandigarh, India, for providing NMR facilities and elemental analyses.
Address correspondence to Nidhi Sonika, Department of Chemistry, G. J. University of Science and Tech-
nology, Hisar 125001, Haryana, India. E-mail: sc ic2001@yahoo.co.in
1
449

1450
N. SONIKA AND R. MALHOTRA
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
Keywords Diorganotin (IV) complexes; pyridoxal aroylhydrazone; Schiff base
INTRODUCTION
Schiff bases continue to be of paramount importance in coordination chemistry; in
addition to their biomedical applications, they form stable complexes with most transition
metals that can serve as models for studying a wide range of biological reactions that
are catalyzed by enzymes.1 Pyridoxal is the biological active form of vitamin B6 acting
as a coenzyme in several biosynthetic, metabolic, or regulatory processes. Schiff bases
derived from pyridoxal and amines or their derivatives are of great interest because they
have been found to be more effective than the individual pyridoxal or amino derivatives
,2
3
and are considered promising for the treatment of diabetic complications. Hydrazones of
pyridoxal (Figure 1), viz. those derived from hydrazides of benzoic, p-methoxybenzoic,
59
m-fluorobenzoic, and 2-fluroylhydrazone, were highly effective in mobilizing Fe from
5
9
4
Fe-labeled hepatocytes in vitro. It is noteworthy that the biological activity of Schiff
5,6
bases is significantly enhanced on coordination with suitable metal ions.
7
,8
Organotin compounds show a wide spectrum of biological activity, which essen-
tially is determined by the number and the nature of the donor atoms of the ligands attached
to the tin moiety. Diorganotin (IV) complexes exhibit higher biological activity than the cor-
responding mono/triorganotin (IV) complexes. The activity also depends upon the nature of
the alkyl group attached to the tin atom and the highest activity is extended when R is ethyl
or phenyl in organotin complexes.9 Keeping this in mind, we have synthesized complexes
,10
(Scheme 1) obtained by the interaction of the organotin moiety with nitrogen/sulfur donor
ligands and studied the effect of coordination on biocidal activity in order to explore their
use as potential biocidal agents.
RESULTS AND DISCUSSION
Pyridoxal-substituted hydrazones (H2LI–H2LIII) were prepared by the condensation
of pyridoxal hydrochloride with substituted acid hydrazides. The progress of the reaction
was regularly monitored by thin-layer chromatography (TLC). The reaction of dichlorodi-
organotin (IV) R2SnCl2 (R Me, Bu, and Ph) with ligands (H2LI–H2LIII) in a 1:1 molar
ratio at room temperature afforded the complexes that were characterized by elemental anal-
1
13
119
yses, infrared (IR) and H , C , and Sn-NMR. All of the complexes were obtained
as solids, insoluble in most organic solvents. The low values of molar conductivity (7.0–
− −1
1
2
1
5.0 ohm cm mol ) of the complexes in dry dimethyl formamide (DMF) indicate their
nonelectrolytic nature.
IR Spectra
Coordination sites were ascertained on the basis of shifts in the frequency of various
groups and/or from the intensity lowering on comparison of the infrared spectra of the
ligands with that of the complexes. Infrared spectra of the ligands showed two bands in the
−1
region of 3210–3250 and 1673–1678 cm assigned to ν (N H) and ν (C O), respectively,
indicating their ketonic nature in the solid state. In the complexes, the bands attributed to

DIORGANOTIN (IV) COMPLEXES
1451
CH OH
2
H
C
H
N
R'
N
R SnCl2
+
2
N
O
OH
CH3
Benzene, Et3N
Stirred, 3h
CH OH
2
H
C
5
N
N
6
R'
4
N
1
3
O
Sn
O
2
R
R
CH3
where R = Me,Bu, Ph and
R' = 2-pyridyl, 2-thenyl, 1-naphthyl
Scheme 1 Synthesis of organotin (IV) complexes.
ν NH and ν C O disappeared, and two new bands in these complexes appeared in the
−1
−1
region 1350 cm , 1220 cm due to ν (NCO) and ν (C O), which suggested enolization
of the ligand after deprotonation when coordinated to the tin atom. The C N band of
−
1
−1
the ligand at 1617–1632 cm shifts to 1603–1620 cm in the spectra of complexes and
11
suggested coordination of imine nitrogen to the tin atom. Of the two nitrogens of the
azomethine group, coordination through the N(2) nitrogen of terminal isonicotinic acid
hydrazide is suggested because it gives rise to a stable five-membered ring that would be
−1
formed on coordination through the other nitrogen. The broad band at 3240–3280 cm
assignable to the ν (OH) group disappeared in the complexes, indicating the possible loss
of protons on complexation and subsequent formation of an M O bond. Involvement of
nitrogen and oxygen in coordination was supported by the appearance of new bands in the
−1
regions 445–459 and 530–561 cm in the complexes, assigned to ν (Sn N) and ν (Sn O)
modes.
12

1452
N. SONIKA AND R. MALHOTRA
CH OH
2
H
C
H
N
R'
N
N
O
OH
CH3
Where R' =
7
'
6'
8
'
5'
10'
4'
5
'
'
6'
9'
1'
1
'
S
5'
N
1'
2
'
4
'
,
,
3'
4'
2
'
3'
3
2'
H2L
III
H2LI
H L
2 II
Figure 1 Structure of Schiff base ligands.
NMR Spectra
The coordinating modes of the ligands were confirmed by comparing H-NMR pat-
1
1
terns of the ligands and their tin complexes (Table 1). In the H-NMR spectra of ligands, the
chemical shift of the proton due to phenolic hydroxyl that appeared as a broad singlet around
δ 12.27–12.62 was absent in the spectra of complexes, thereby indicating the involvement
of pyridoxal –OH in coordination after deprotonation. The singlet at δ 8.94–9.08 showed
a significant downfield shift (ꢀδ = 0.38–0.20) relative to the corresponding ligands, con-
12
firming that the coordination has indeed taken place through azomethine nitrogen. The
absence of proton signal at 12.08 assigned to the NH group coupled with the shift of the
proton of the OH group of the CH2OH moiety from δ 5.06 to 5.59 suggested the cleavage
of hydrogen bonding between hydrogen of the NH group and oxygen of the OH group (viz.
N-H . . . O-H), and coordination occurred through an enolate oxygen atom. These results
O
R
Sn
N
R
O
ꢁ ꢁ
Figure 2 Suggested structure of the complexes and ONO donor site of the ligand.

1
453

1
454

DIORGANOTIN (IV) COMPLEXES
1455
are consistent with those reported in the literature.13 The methylene and methyl protons
of pyridoxal moiety of the ligands resonate at δ 4.68–4.69 and δ 2.51–2.57, and these
signals appeared in the complexes with slight shifts in their positions. All of these data are
consistent with the conclusions drawn from the IR spectral studies and support the dibasic
tridentate ONO coordination mode. Examples of the spectra for H2LI and Bu2Sn(LI) are
shown in the Supplemental Materials (Figures S1–S5, available online).
13
The C-NMRspectraoftheligandsandtheirorganotin(IV)complexes wererecorded
in CDCl3 and dry DMSO-d6 (Table 2). The signals due to methyl and butyl groups attached
to the tin atom appeared at 10.3–10.9 and δ 26.8, 22.6, 19.5, 13.5, respectively, and the
carbons of the phenyl group attached to tin appeared at δ 149.8, 135.5, 128.5, 130.2. The
peaks at δ 155.0–156.9 and δ 162.9–169.7 are due to the carbon of azomethine (C N)
and carbon of carbonyl (C O). The peaks observed at δ 59.1–61.5 were assignable to
the methine carbons of pyridoxal groups. The signals of aromatic carbons for pyridyl
ꢁ
ꢁ
group were observed in the range of δ 158.9–159.8 for (C2 , C6 ), δ 121.7–122.5 for
ꢁ
ꢁ
ꢁ
(
C3 , C5 ), and δ 140.3–140.9 for (C4 ). In the case of 2-thenyl these signals were in
the range of δ 153.0–153.7, 136.4–139.1, 127.3–129.2, and 134.2–135.4 for (C1 ), (C2 ),
C3 ), and (C4 ) carbons, respectively. For the 1-napthyl group it was observed in the
ꢁ
ꢁ
ꢁ
ꢁ
(
range of 151.2–151.9, 139.1–140.7, 132.4–132.9, 136.0–136.7, 124.6–125.3, 128.6–129.6,
ꢁ ꢁ
27.0–127.7, 129.2–130.2, 133.5–134.9, and 136.2–137.4 for (C1 ) to (C10 ) carbons in
1
the complexes. The spectra of all tin complexes showed a significant downfield shift of
all carbon resonances compared with the free ligand. The shift was a consequence of an
electron density transfer from the ligand to the acceptor, which is consistent with that
14
reported in the literature.
The 119Sn chemical shift values of tin complexes were found to be in the range of δ
185.3 to −207.8 for the complexes where R = methyl or butyl and δ −334.8 to −336.4
−
15
when R = phenyl. The appearance of chemical shift values in this region indicated
a penta-coordinated environment around the central tin atoms in these complexes. The
chemical shift of 1 Sn is affected by (i) the nature of the R group directly attached to the
tin atom and (ii) the type of donor atom of the ligand. In cases when R = phenyl, the
localized system of this group allows for pπ-dπ interaction to dominate shielding of the
19
1
19
16
1
119
13
Sn values. The coupling constant J( Sn
C) was observed in the range of 562–
5
98.5 Hz for methyl derivatives and for phenyl it was observed in the range of 614.4–627.6
119
Hz. The parameters of Sn NMR spectra, that is, values of the chemical shift, confirm
the five coordination of complexes.1
7,18
EXPERIMENTAL
All of the operations were carried out in an inert atmosphere using dry nitrogen on a
vacuum line. The solvent used was dried by conventional methods. Sn and Cl contents in
the complexes were estimated gravimetrically. Elements (C, H, N, and S) were analyzed on
a Perkin-Elmer 2400 instrument. The Fourier transform infrared (FTIR) spectra (4000–400
−
1
1
cm ) were obtained in KBr pellets on a Perkin-Elmer spectrum RX1 instrument. H-,
13
119
C-, and Sn NMR spectra were determined on a Bruker Avance II 400 MHz NMR
spectrometer in CDCl3 and DMSO-d6 using tetramethylsilane (TMS) as an internal standard
at Chandigarh, India. Molecular weights of the complexes were determined by cryoscopic
method in dry nitrobenzene. Molar conductance measurements were carried out using a
model 306 Systronics conductivity bridge in dimethyl sulfoxide (DMSO) solvent.

1
456

1
457

1458
N. SONIKA AND R. MALHOTRA
Preparation of Schiff Base Ligands
Pyridoxal isonicotinoyl hydrazone was synthesized by dissolving pyridoxal hy-
drochloride (3 g, 15 mmol) in distilled water (30 mL) with continuous stirring. Isonicotinic
acid hydrazide (2.1 g, 15 mmol) was separately dissolved in 50% of ethanol (30 mL). The
two reactants were mixed with continuous stirring followed by the addition of a solution
of sodium acetate (1.2 g) in distilled water (15 mL). The reaction mixture was refluxed in
a steam bath for 1 h and the solution was kept overnight at room temperature. The orange
solid product so obtained was recrystallized from the mixture of benzene and methanol in
a 2:1 ratio. A similar procedure was adopted for 2-thiophenecarboxylic acid hydrazide and
1-naphthoic acid hydrazides with pyridoxal hydrochloride.
Preparation of Complexes
A solution of dichlorodialkyltin (IV) (10 mmol) in dry benzene (20 mL) was added
dropwise with constant stirring to a solution of pyridoxal-substituted hydrazone (10 mmol)
and triethylamine (10 mmol) in the same solvent 30 mL under a dry nitrogen atmosphere
at room temperature. The reaction mixture was stirred for 3 h and the white precipitate
of triethylammonium chloride obtained was filtered off. The excess solvent was removed
under vacuum. The yellow solid complex was washed with CH2Cl2/petroleum ether (30–
◦
6
0 C) to ensure the purity of the product and finally dried under vacuum. The analytical
data of the resulting complexes are recorded in Table 3.
Biological Activities
Antibacterial and Antifungal Activity. The in vitro antibacterial and antifun-
gal activity of ligands and their organotin (IV) complexes were studied against the phy-
topathogenic fungi Candida albicans and Aspergillus niger and the bacteria Bacillus
subtilis, Escherichia coli, and Staphylococcus aureus by adopting the same procedure
as reported earlier19 by dissolving the compounds in DMSO to give a concentration of
100 µg/mL and used as a stock solution (see Supplemental Materials, Table S1).
Antimicrobial Activity. The ligands and their corresponding dichlorodiorganotin
(
IV) complexes were subjected to in vitro antimicrobial studies. Antibacterial activity was
done by the serial dilution method on the following strains: Bacillus subtilis (MTCC no.
063), Staphylococcus aureus (MTCC no. 2901), and Escherichia coli (MTCC no. 1652),
2
◦
◦
under the standard conditions of temperature of 37 C ± 1 C and relative humidity of
4
0 ± 5% for 24 h.
CONCLUSION
Dichlorodiorganotin (IV) complexes of pyridoxal aroylhydrazones were synthesized,
characterized, and screened against pathogenic bacteria and fungi. The presence of a tox-
ophorically important group -CON < & -CSN < was found to be responsible for an-
timicrobial activity of the ligands.20 Dichlorodiorganotin (IV) complexes show a higher
antimicrobial activity compared to the free ligands. On complexation, the in vitro antimi-
crobial activity of the ligands was enhanced, which may be explained on the basis of
chelation theory. This reduces the polarity of the central metal ion, thereby increasing the
lipophilic nature of the metal complex, which susequently favors its permeation through

DIORGANOTIN (IV) COMPLEXES
1459
the lipid layer of the cell membrane of the microorganism and results in interference with
normal cell processes.
REFERENCES
1
2
3
. Collinson, S. R.; Fenton, D. E. Coord. Chem. Rev. 1996, 148, 19–40.
. He, H.; Puerta, D. T.; Cohen, S. M.; Rodgers, K. R. Inorg. Chem. 2005, 44, 7431–7442.
. Leovac, V. M.; Jevtovic, V. S.; Jovanovic, L. S.; Bogdanovic, G.A. J. Serb. Chem. Soc. 2005,
70(3), 393–422.
4. Blaha, K.; Cikret, M.; Nerudova, J.; Fornuskova, J.; Ponka, P. Blood 1998, 91, 4368–4372.
5. Malhotra, R.; Singh, J. P.; Dudeja, M.; Dhindsa, K. S. J. Inorg. Biochem. 1992, 46, 119–127.
6. Malhotra, R.; Mehta, J.; Bala, K.; Sharma, A. K. Indian J. Chem. 2008, 47A, 58–61.
7. Malhotra, R.; Kumar, S.; Dhindsa, K. S. Indian J. Chem. 1997, 36A, 321–323.
8. Jain, M.; Maanju, S.; Singh, R. V. Appl. Organomet. Chem. 2004, 18, 471–479.
9. Casas, J. S.; Castineiras, A.; Condori, F.; Couce, M. D.; Russo, U.; Sanchez, A.; Seoane, R.;
Sordo, J.; Varela, J. M. Polyhedron 2003, 22, 53–65.
1
0. Barens, J. M.; Magos, L. Organomet. Chem. Rev. 1968, 3, 137–150.
11. Samanta, B.; Chakraborty, J.; Dey, D. K.; Gramlich, V.; Mitra, S. Struct. Chem. 2007, 18,
287–293.
1
1
2. Maurya, M. R.; Aggarwal, S.; Bader, C.; Rehder, D. Eur. J. Inorg. Chem. 2005, 147–157.
3. Reholledo, A. P.; Lima, G. M.; Gambi, L. N.; Speziali, N. L.; Maria, D. F.; Pinheiro, C. B.;
Ardisson, J. D.; Cortes, M. E. Appl. Organomet. Chem. 2003, 17, 945–951.
1
1
1
1
1
1
2
4. Zhang, R.; Tian, G.; Ma, C. J. Organomet. Chem. 2005, 690, 4049–4057.
5. Dey, D. K.; Samanta, B.; Lycka, A.; Dahlenburg, L. Z. Naturforsch. 2003, 58b, 336–344.
6. Malhotra, R.; Mehta, J.; Puri, J. K. Cent. Eur. J. Chem. 2007, 5, 858–867.
7. Sonika, S. S.; Gupta, S.; Narula, A. K. Indian J. Chem. 1994, 33A, 1119–1121.
8. Jain, M.; Singh, R. V. Appl. Organomet. Chem. 2003, 17, 616–622.
9. Spooner, D. F.; Sykes, G. Methods in Microbiology; Academic Press: London, 1972.
0. Sing, N. K.; Agarwal, S.; Aggarwal, R. C. Synth. React. Met.-Org Chem. 1985, 15(1), 75–92.