Bioactive penta-coordinated diorganotin(Iv) complexes of pyridoxalimine schiff bases

Article abstract of DOI:10.1080/10426507.2012.692129

Diorganotin(IV) complexes of an extended system derived from the condensation of pyridoxal hydrochloride with 2-amino phenol (H2L¹), 2-amino-4-methyl phenol (H2L²), 2-amino-4-chloro phenol (H2L ³), 2-amino-4-nitro phenol (H2L⁴), 1-amino-2-naphthol hydrochloride (H2L⁵) have been synthesized by the reaction of dichlorodiorganotin(IV) in a 1:1 molar ratio with these ligands. Spectral studies (IR, ¹H, ¹³C, ¹¹⁹Sn NMR) along with physical data evidenced the formation of penta-coordinated species with the ligands acting as tridentate (ONO) with oxygen occupying the axial positions, and nitrogen at one of the equatorial positions. The ligands and their organotin complexes have been evaluated for antimicrobial activity against phytopathogenic fungi Candida albicans and Aspergillus niger at 25 1C and bacteria Bacillus subtilis, Escherichia coli, and Staphylococcus aureus at 37 1C. The activities of the ligands have been enhanced on complexation 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:10.1080/10426507.2012.692129

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Bioactive Penta-Coordinated
Diorganotin(Iv) Complexes of
Pyridoxalimine Schiff Bases
Sonika Asijaa a , Nidhi Malhotra a & Rajeh Malhotra a
a Department of Chemistry , G. J. University of Science and
Technology , Hisar , 125001 , Haryana , India
Accepted author version posted online: 17 May 2012.Published
online: 10 Sep 2012.
To cite this article: Sonika Asijaa , Nidhi Malhotra & Rajeh Malhotra (2012) Bioactive Penta-
Coordinated Diorganotin(Iv) Complexes of Pyridoxalimine Schiff Bases, Phosphorus, Sulfur, and Silicon
and the Related Elements, 187:12, 1510-1520, DOI: 10.1080/10426507.2012.692129
To link to this article: http://dx.doi.org/10.1080/10426507.2012.692129
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Phosphorus, Sulfur, and Silicon, 187:1510–1520, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.692129
BIOACTIVE PENTA-COORDINATED DIORGANOTIN(IV)
COMPLEXES OF PYRIDOXALIMINE SCHIFF BASES
Sonika Asijaa, Nidhi Malhotra, and Rajeh Malhotra
Department of Chemistry, G. J. University of Science and Technology,
Hisar 125001, Haryana, India
GRAPHICAL ABSTRACT
R
R'
CH2OH
H
C
N
N
O
R'
- H
R
H2L1 = -H
H2L2 = -CH3
H2L3 = -Cl
H2L4 = -NO2
H2L5 =
Sn
O
-H
-H
-H
R
CH3
R
R = Me, Bu, Ph
Abstract Diorganotin(IV) complexes of an extended system derived from the condensation
of pyridoxal hydrochloride with 2-amino phenol (H2L1), 2-amino-4-methyl phenol (H2L2),
2-amino-4-chloro phenol (H2L3), 2-amino-4-nitro phenol (H2L4), 1-amino-2-naphthol hy-
drochloride (H2L5) have been synthesized by the reaction of dichlorodiorganotin(IV) in a
1:1 molar ratio with these ligands. Spectral studies (IR, 1H, 13C, 119Sn NMR) along with
physical data evidenced the formation of penta-coordinated species with the ligands acting
as tridentate (ONO) with oxygen occupying the axial positions, and nitrogen at one of the
equatorial positions. The ligands and their organotin complexes have been evaluated for an-
timicrobial activity against phytopathogenic fungi Candida albicans and Aspergillus niger at
25 1 ◦C and bacteria Bacillus subtilis, Escherichia coli, and Staphylococcus aureus at 37
1 ◦C. The activities of the ligands have been enhanced on complexation 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.
Keywords Schiff base; pyridoxal hydrochloride; diorganotin (IV) complexes
Received 9 March 2012; accepted 29 April 2012.
Address correspondence to R. Malhotra, Department of Chemistry, G. J. University of Science and Tech-
nology, Hisar 125001, Haryana, India. E-mail: malhotra ksrk@yahoo.co.in
1510

DIORGANOTIN(IV) COMPLEXES OF AN EXTENDED SYSTEM
1511
INTRODUCTION
Considerable importance has been given to pyridoxal having a pyridine ring, hy-
droxyl, and hydroxymethyl substituents, which may help to balance hormonal changes
in women and aid the immune system and account of other different biological proper-
ties.1 Lack of pyridoxine may cause anemia, nerve damage, seizures, skin problems, and
sores in the mouth.2 A wide variety of biological effects have been shown by organotin
complexes including bactericidal, acaricidal, fungicidal,3,4 antiinflammatory,5 anti-HIV,6
anticancer,7 and antitumor agents.8,9 A great amount of attention has been given to the
biological activity of organotin(IV) complexes with tridentate Schiff bases which are of
particular interest for existing in lactum or lactim tautomeric forms, giving variations to
their donating properties. It has been reported that these compound showed remarkable
enhancement in biological activities when combined to organotinhalides.10 We are more
concerned with the antimicrobial activity of organotin(IV) compounds, keeping this in mind
and in continuation of our work, on the synthesis of biologically active compounds con-
taining N, O, S, and their organotin/silicon complexes.11–14 We report the synthesis of new
complexes of Schiff bases derived from the condensation of pyridoxal hydrochloride with
derivatives of aminophenol and studied the effect of introducing tin on the activity of the
ligand.
RESULTS AND DISCUSSION
Pyridoxal-substituted imines (H2L1– H2L5) have been prepared by the condensa-
tion of pyridoxal hydrochloride with substituted aminophenols. The progress of reaction
was regularly monitored by thin layer chromatography. The reaction of dichlorodiorgan-
otin(IV) R2SnCl2 (R = Me, Bu, and Ph) with ligands (H2L1– H2L5) in 1:1 molar ratio at
room temperature afforded the complexes which were characterized by elemental analy-
1
ses, IR, H, 13C, and 119Sn NMR. All the complexes have been obtained as solids, insol-
uble in most organic solvents. The low values of molar conductivity (7.0–15.0 ꢀ−1 cm2
mol−1) of the complexes in dry dimethylformamide indicate their nonelectrolytic nature (see
Scheme 1).
IR Spectra
The strong broad band due to ν(O-H) appeared at approximately 3155–3180 cm−1
in the ligands showing hydrogen bonding with the nitrogen of the azomethine group. The
intensity of which was considerably reduced in the spectra of complexes indicating the
deprotonation of hydroxyl group of the ligands and involvement of both phenolate oxygens
in bonding to tin, which was further authenticated by the appearance of new band in the
spectra of complexes at 1264–1280 cm−1 assigned to ν(C-O) band. In all the tin complexes
of pyridoxal substituted imines, the ν(C N) band, appeared at 1603–1612 cm−1 was shifted
toward lower frequencies as compared to the parent Schiff base confirming the coordination
through azomethine nitrogen to diorganotin(IV) moiety due to electron density transfer from
nitrogen to tin atom, thus resulting in the weakening of the C N bond.15 In the spectra, some
new bands assigned in the region 517–577 cm−1, 616–742 cm−1, and 446–529 cm−1 were
due to Sn-O, Sn-C, and Sn-N bonds that were absent in the precursors, further indicated
formation of complexes.12

1512
S. ASIJAA ET AL.
R
4
R'
3*
5
3
CH2OH
H
C
2
6
N
1
2*
R2SnCl2
+
N
OH
4
5
*
1
OH
R'
R
CH3
H2L1 = -H
H2L2 = -CH3
H2L3 = -Cl
H2L4 = -NO2
H2L5 =
- H
-H
-H
-H
THF, Et3N
Stirred, 6-8 h
R
R'
CH2OH
H
C
N
N
O
Sn
O
R
R
CH3
R = Me, Bu, Ph
Scheme 1
1H NMR Spectra
1
In H NMR, chemical shift assignments of ligands and their diorganotin(IV) com-
plexes were assigned on the basis of multiplicity patterns and/or resonance intensities.
Broad singlets were observed for both phenolic O-H appeared at δ 12.13–15.00 (OH-
1∗) and δ 9.54–10.14 (OH-2∗). A singlet of azomethine proton appeared in the range of δ
9.24–9.36. Alcoholic proton as a singlet of (CH2-OH) group was observed at δ 5.12–5.38 in
the ligands while methylene and methyl proton of pyridoxal moiety appeared at δ 4.60–4.79
and δ 2.45–2.54, respectively.
1
The H NMR data of the ligands and their diorganotin(IV) complexes is given in
Tables 1 and 2. The absence of the O-H(1∗ & 2∗) proton signal in the complexes showed
deprotonation when attached to tin atom. The downfield shift of ≈0.3 ppm was observed
3
1
in chemical shift values of azomethine CH N proton with J (119Sn, H) coupling con-
stant value in the range 39–47 Hz16 supported the involvement of azomethine nitrogen in
coordination. On complexation, not much variation is observed in the chemical shift value
of methylene, methyl proton, and proton of OH of CH2OH group of pyridoxal moiety.
The spectra showed that the chemical shifts of the butyl group attached to tin appeared
as a multiplet in the region δ 0.77–1.88 where as protons due to phenyl ring and methyl
appeared as a multiplet in the region δ 6.68–7.94 and a singlet in the region δ 1.34–1.51, re-
spectively. The 2J [119Sn, 1H] coupling constants were in the range (76–81 Hz) for Me2SnL
complexes and supported a trigonal bipyramidal geometry.17 The integrated proton ratio

1513

1514

DIORGANOTIN(IV) COMPLEXES OF AN EXTENDED SYSTEM
1515
Table 3 13C NMR spectral characteristics (δ) of pyridoxalimine Schiff bases
Where R'=
CH2OH
H2N
H2N
2'
H2N
2'
H
C
3'
R'
3'
5'
3'
5'
2'
N
4'
4'
4'
Cl
H
HO
HO
CH3
H2N
HO
1'
1'
N
1'
OH
6'
5'
H2L1
6'
6'
H2L3
H2L2
CH3
3'
H2N
2'
2'
3'
5'
4'
HO
1'
8'
4'
NO2
HO
1'
5'
6'
H2L4
6'
7'
H2L5
Ligand
H2L1
H2L2
H2L3
H2L4
H2L5
>C
N
−CH2OH
58.8
Aromatic C
163.7
157.7
159.5
161.0
160.4
148.8 (C1ꢀ), 136.7 (C2ꢀ), ꢀ127.8 (C3ꢀ), 124.8 (C4ꢀ),
128.6 (C5ꢀ), 118.4 (C6
)
58.8
149.1 (C1ꢀ), 137.2 (C2ꢀ), ꢀ132.5 (C3ꢀ), 128.3 (C4ꢀ),
129.3 (C5ꢀ), 119.6 (C6
)
58.5
148.5 (C1ꢀ), 137.6 (C2ꢀ), ꢀ123.3 (C3ꢀ), 127.7 (C4ꢀ),
128.1 (C5ꢀ), 119.1 (C6
)
58.4
153.6 (C1ꢀ), 138.7 (C2ꢀ), ꢀ124.6 (C3ꢀ), 145.5 (C4ꢀ),
124.6 (C5ꢀ), 119.8 (C6
)
60.1
146.7 (C1ꢀ), 138.3 (C2ꢀ), 121.5 (C3ꢀ), 133.2 (C4ꢀ),
127.5 (C5ꢀ), 124.5 (C6ꢀ), 125.9 (C7ꢀ), 126.3 (C8ꢀ),
ꢀ
130.9 (C9ꢀ), 111.0 (C10
)
for each group was in agreement with the proposed structures. All these data are consistent
with the conclusions drawn from the IR spectral studies and support the dibasic tridentate
ONO coordination mode of the ligands.
13C NMR Spectra
13C NMR spectra of ligands as well as their complexes were recorded with dimethyl
sulfoxide (DMSO)-d6 (Tables 3 and 4). The spectra of all tin complexes showed a significant
downfield shift of all carbon resonances as compared to the free ligand. The shift was a
consequence of an electron density transfer from the ligand to the acceptor, which is
consistent with that reported in literature.11
The signals due to methyl groups attached to the tin atom appeared at δ 10.3–10.9.
The butyl group can be supported via the four bands due to carbon 1 to 4 in (Sn-1CH2 2CH2
3CH2 4CH3) at δ 28.3–32.8, δ 26.2–26.9, δ 19.3–19.7, and δ 13.3–13.7. The carbons of the
phenyl group attached to tin appeared at δ 145.8–148.5, 135.2–136.7, 125.3–129.3, and
130.4–132.2. A downfield shift in the value of azomethine HC N proton from 157.7–163.7
to 162.9–169.7 was observed on complexation. The peak observed at δ 60.2–62.1 was
assignable to the carbon of CH2OH group of pyridoxal.

1516
S. ASIJAA ET AL.
Table 4 13C and 119Sn NMR characterization (δ) of diorganotin(IV) complexes of pyridoxalimine Schiff bases
Complexes >C
N
−CH2OH
Aromatic C
Sn-Me/Bu/Ph
119Sn
Me2Sn(L1)
Bu2Sn(L1)
Ph2Sn(L1)
Me2Sn(L2)
Bu2Sn(L2)
Ph2Sn(L2)
Me2Sn(L3)
Bu2Sn(L3)
Ph2Sn(L3)
Me2Sn(L4)
Bu2Sn(L4)
Ph2Sn(L4)
Me2Sn(L5)
168.6
61.2
149.2 (C1ꢀ), 138.0 (C2ꢀ), 126.7
10.3
−185.3
(C3ꢀ), 124.9 (C4ꢀ), 128.7 (C5ꢀ),
ꢀ
119.4 (C6
)
168.2
60.2
60.9
61.5
62.1
61.2
60.5
60.2
61.5
61.2
60.2
60.9
60.5
148.8 (C1ꢀ), 137.7 (C2ꢀ), 127.8
32.8, 26.5, 19.3, 13.3
−203.8
−331.6
−180.7
−190.3
−333.2
−189.3
−334.8
−335.7
−184.4
−185.3
−337.5
−189.8
(C3ꢀ), 125.0 (C4ꢀ), 128.8 (C5ꢀ),
ꢀ
118.5 (C6
)
165.5
162.9
165.8
165.9
169.3
169.7
168.3
168.6
168.2
165.5
162.9
149.0 (C1ꢀ), 136.7 (C2ꢀ), 128.0
145.8, 135.5, 127.5,
131.2
(C3ꢀ), 124.9 (C4ꢀ), 128.0 (C5ꢀ),
ꢀ
118.7 (C6
)
150.1 (C1ꢀ), 137.4 (C2ꢀ), 127.8
10.5
(C3ꢀ), 125.1 (C4ꢀ), 128.8 (C5ꢀ),
ꢀ
118.5 (C6
)
150.2 (C1ꢀ), 137.5 (C2ꢀ), 126.6
28.9, 26.9, 19.3, 13.5
(C3ꢀ), 125.2 (C4ꢀ), 128.8 (C5ꢀ),
ꢀ
119.2 (C6
)
150.5 (C1ꢀ), 136.8 (C2ꢀ), 126.6
148.5, 135.7, 125.3,
130.5
(C3ꢀ), 124.7 (C4ꢀ), 128.8 (C5ꢀ),
ꢀ
119.0 (C6
)
148.6 (C1ꢀ), 135.4 (C2ꢀ), 127.9
10.9
(C3ꢀ), 123.6 (C4ꢀ), 128.8 (C5ꢀ),
ꢀ
119.2 (C6
)
149.2 (C1ꢀ), 137.2 (C2ꢀ), 127.7
29.3, 26.2, 19.7, 13.7
(C3ꢀ), 124.8 (C4ꢀ), 128.9 (C5ꢀ),
ꢀ
119.7 (C6
)
148.3 (C1ꢀ), 136.5 (C2ꢀ), 127.8
146.5, 135.2, 126.2,
131.5
(C3ꢀ), 125.2 (C4ꢀ), 128.8 (C5ꢀ),
ꢀ
118.6 (C6
)
149.1 (C1ꢀ), 138.0 (C2ꢀ), 127.8
10.3
(C3ꢀ), 125.0 (C4ꢀ), 128.6 (C5ꢀ),
ꢀ
119.0 (C6
)
148.5(C1ꢀ), 137.0 (C2ꢀ), 127.8
28.6, 26.8, 19.5, 13.5
(C3ꢀ), 125.9 (C4ꢀ), 128.6 (C5ꢀ),
ꢀ
118.8 (C6
)
150.2 (C1ꢀ), 138.1 (C2ꢀ), 127.9
147.8, 136.5, 126.5,
132.2
(C3ꢀ), 124.8 (C4ꢀ), 128.6 (C5ꢀ),
ꢀ
118.5 (C6
)
150.4 (C1ꢀ), 137.1 (C2ꢀ), 127.8
(C3ꢀ), 124.8 (C4ꢀ), 128.6 (C5ꢀ),
118.6 (C6ꢀ) 125.9 (C7ꢀ), 126.3
(C8ꢀ), 130.6 (C9ꢀ), 111.4 (C10
150.7 (C1ꢀ), 137.7 (C2ꢀ), 127.7
10.5
ꢀ
)
Bu2Sn(L5)
Ph2Sn(L5)
165.8
165.9
61.1
61.2
28.3, 26.3, 19.3, 13.3
−210.3
−340.7
(C3ꢀ), 125.1 (C4ꢀ), 128.7 (C5ꢀ),
118.6 (C6ꢀ) 125.9 (C7ꢀ), 126.3
(C8ꢀ), 130.9 (C9ꢀ), 112.54 (C10
150.9 (C1ꢀ), 138.1 (C2ꢀ), 127.8
(C3ꢀ), 124.9 (C4ꢀ), 128.7 (C5ꢀ),
118.4 (C6ꢀ) 125.9 (C7ꢀ), 126.3
ꢀ
)
146.5, 136.7, 129.3,
130.4
(C8ꢀ), 131.9 (C9ꢀ), 111.3 (C10
)
ꢀ

DIORGANOTIN(IV) COMPLEXES OF AN EXTENDED SYSTEM
1517
O
R
Sn
N
R
O
Figure 1 Suggested structure of the complexes and
donor site of the ligand.
119Sn NMR Spectra
The chemical shift of 119Sn is affected by several factors, (i) the nature of R group
directly attached to the tin atom if R is phenyl, the localized system of this group allows for
pπ-dπ interaction to dominate shielding of the 119Sn values.18 (ii) The type of donor atom
of the ligand. (iii) The geometry around tin atom. The 119Sn NMR spectra of organotin(IV)
complexes show only one sharp singlet indicating the formation of single tin species. The
119Sn chemical shift values of tin complexes R2SnL were found to be in the range of δ –180.7
to –210.3 for the complexes, where R = methyl or butyl and δ –331.6 to –340.7, where R
= phenyl (Table 4). The parameters of 119Sn NMR spectra, i.e., values of chemical shift
confirm the penta-coordinated environment around the central tin atoms in these complexes
(see Fig. 1).
EXPERIMENTAL
All the operations were carried out in an inert atmosphere using dry nitrogen on a
vacuum line. The solvent used were dried by the conventional methods. Dimethyltindichlo-
ride, dibutyltindichloride, and diphenyltindichloride were obtained through Aldrich and
were used as such without any further purification. Tin content was estimated gravimetri-
cally. Elements (C, H, and N) were analyzed on Perkin-Elmer 2400 instrument (Waltham,
Massachusetts). The FT-IR spectra (Perkin Elmer, New Jersey) [4000–400 cm−1] were
1
obtained in KBr pellets on Perkin-Elmer spectrum RX1 instrument. H, 13C, and 119Sn
NMR spectra were determined on Bruker Avance II 400 MHz NMR Spectrometer (Bruker,
Switzerland) in DMSO-d6 using tetramethylsilane as an internal standard at SAIF Chandi-
garh. Molecular weights of the complexes were determined by cryoscopic method in dry
nitrobenzene. Molar conductance measurements were carried out using a Model-306 Sys-
tronics conductivity bridge (Mumbai, India) in DMSO solvent.
Synthesis of Schiff Base Ligands
The pyridoxal hydrochloride (2.03 g, 10 mmol) was dissolved in methanol (25 mL)
and added to a solution of sodium methoxide (0.54g, 10 mmol) in the same solvent. A
solution of 2-amino-4-methyl phenol (2.72g, 10 mmol) in methanol (10 mL) was added
dropwise to the above reaction mixture. The suspension was refluxed for 6–8 h and the
mixture was kept for overnight at room temperature. The orange to dark red solids isolated

1518

DIORGANOTIN(IV) COMPLEXES OF AN EXTENDED SYSTEM
1519
were filtered, washed with small amount of water to remove sodium chloride, followed by
diethyl ether, and then dried. A similar procedure was adopted to isolate other ligands.
Synthesis of Dimethyltin(IV) Complex of 2-Amino-4-Methyl Phenol
(H2L2)
The complexes were prepared by the reaction of diphenyltindichloride (2.03 g,
5.93 mmol) taken in dry tetrahydrofuran (20 mL) and 5-hydroxymethyl-4-[(2-hydroxy-
5-methyl-phenylimino)-methyl]-2-methyl-pyridin-3-ol] (1.61 g, 5.93 mmol) (H2L2) and
triethylamine (1.20g, 11.86 mmol) taken in a same solvent, at the room temperature under
a dry nitrogen atmosphere. The reaction mixture was stirred for 6–8 h. Triethylamine hy-
drochloride formed was filtered off and excess of the solvent was removed under vacuum.
The solid obtained was dried under reduced pressure. The compound was then washed
with a mixture of chloroform and n-hexane (50–50 v/v) and finally dried over vacuum. The
physical and analytical data of complexes are given in Table 5.
Antimicrobial Activity
Antimicrobial activity of the pyridoxalimine and their corresponding dichlorodi-
organotin(IV) complexes are given in Table S1 (online Supplementary Materials). Antibac-
terial and antifungal activity was carried out by the serial dilution method on the following
strains, i.e., Bacillus subtilis [Microbial type cultural collection (MTCC) no. 2063], Staphy-
lococcus aureus (MTCC no. 2901), Escherichia coli (MTCC no. 1652), Aspergillus niger
(MTCC no1344), and Candida albicans (MTCC no.183).
It has been observed that biocidal activity of the ligands was enhanced on complex-
ation with organotin. In general, complexes where phenyl attached to tin were found to be
more potent compared to other complexes. The order of inhibiting activity was Sn-Ph >
Sn-Bu > Sn-Me and is in agreement with the reported data. The activity of the compounds,
was compared with standard drugs and the results and additional experimental details are
presented in Figure S1 (online Supplementary Materials).4,13,19
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