Dialkyl (alkylene) dithiophosphate adducts of anhydrous stannous chloride: Synthesis, characterization, and biological activities

Article abstract of DOI:10.1080/10426507.2012.681406

Dialkyl (alkylene) dithiophosphate adducts of stannous chloride were synthesized by the reaction of anhydrous tin(II) chloride (SnCl₂) and dialkyl (alkylene) dithiophosphoric acid in a 1:1 molar ratio, under anhydrous reaction conditions, below 5 °C in a closed vessel. The newly synthesized adducts were characterized by physicochemical and spectroscopic techniques [FT-IR, NMR (¹H, ³¹P, and ¹¹⁹Sn), and mass spectrometry]. Coordination modalities have indicated a donor-acceptor interaction between sulfur and tin(II) moieties, where tin(II) acts as a Lewis acid. The adducts were found to have significant antibacterial activity against Escherichia coli and Pseudomonas aeruginosa, and antifungal activity against Aspergillus niger and Candida albicans. 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:10.1080/10426507.2012.681406

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Dialkyl (Alkylene) Dithiophosphate
Adducts of Anhydrous Stannous Chloride:
Synthesis, Characterization, and
Biological Activities
Mohammed Mohsin a , Meena Nagar a & Alka Choudhary a
a Department of Chemistry, University of Rajasthan, Jaipur, 302004,
India
Accepted author version posted online: 13 Apr 2012. Version of
record first published: 06 Aug 2012
To cite this article: Mohammed Mohsin, Meena Nagar & Alka Choudhary (2012): Dialkyl (Alkylene)
Dithiophosphate Adducts of Anhydrous Stannous Chloride: Synthesis, Characterization, and Biological
Activities, Phosphorus, Sulfur, and Silicon and the Related Elements, 187:11, 1331-1338
To link to this article: http://dx.doi.org/10.1080/10426507.2012.681406
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Phosphorus, Sulfur, and Silicon, 187:1331–1338, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.681406
DIALKYL (ALKYLENE) DITHIOPHOSPHATE ADDUCTS
OF ANHYDROUS STANNOUS CHLORIDE: SYNTHESIS,
CHARACTERIZATION, AND BIOLOGICAL ACTIVITIES
Mohammed Mohsin, Meena Nagar, and Alka Choudhary
Department of Chemistry, University of Rajasthan, Jaipur-302004, India
GRAPHICAL ABSTRACT
RO
S
6
8 h stirring
below 5 oC
RO
RO
S
P
SnCl2
+
P
SnCl2
C2H5OH
RO
SH
(As solvent)
SH
Abstract Dialkyl (alkylene) dithiophosphate adducts of stannous chloride were synthesized
by the reaction of anhydrous tin(II) chloride (SnCl2) and dialkyl (alkylene) dithiophosphoric
acid in a 1:1 molar ratio, under anhydrous reaction conditions, below 5 ◦C in a closed vessel.
The newly synthesized adducts were characterized by physicochemical and spectroscopic tech-
niques [FT-IR, NMR (1H, 31P, and 119Sn), and mass spectrometry]. Coordination modalities
have indicated a donor–acceptor interaction between sulfur and tin(II) moieties, where tin(II)
acts as a Lewis acid. The adducts were found to have significant antibacterial activity against
Escherichia coli and Pseudomonas aeruginosa, and antifungal activity against Aspergillus
niger and Candida albicans.
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 Adducts; anhydrous stannous chloride; dialkyl (alkylene) dithiophosphoric acid;
antifungal activity; antimicrobial activity
INTRODUCTION
In the last two decades, dialkyl (alkylene) dithiophosphate derivatives have played
a key role in the advancement of organophosphorus chemistry.1–7 Metal- and metalloid-
based dithiophosphates have shown various applications in diversified technical areas, viz.,
Received 18 January 2012; accepted 28 March 2012.
The authors are highly thankful to the Department of Chemistry, University of Rajasthan, Jaipur, India for
providing the necessary facilities for experimentation. They express their sincere thanks to Defence Institute of
Bio-Energy Research, Haldwani, India to support this study, and Institute of Microbial Technology, Chandigarh,
India for providing the microbial culture. One of the authors, Mohammed Mohsin is also thankful to Council
of Scientific and Industrial Research (CSIR), New Delhi, India for providing the Research Fellowship for his
research activities. This article is dedicated to Late Dr. P. N. Nagar, Professor, Department of Chemistry, U.O.R.
Jaipur.
Address correspondence to Mohammed Mohsin, Department of Chemistry, University of Rajasthan, Jaipur-
302004, India. E-mail: mmchem@yahoo.com
1331

1332
M. MOHSIN ET AL.
antioxidants, additives in oil and petroleum industries,8 agricultural insecticide and pesticide
derivatives,9 and metal ore extraction procedures.10,11 In recent years, these compounds
have been implemented in electrochemistry, microelectronics, catalysis, ion exchange,
photophysics, and material science, because of their structural and bonding patterns.12 More
recently, attempts have been made to utilize these compounds to form liquid transition metal
complexes, especially of platinum, for use in the preparation of thin layers by chemical
vapor deposition (CVD) or of polymer–inorganic nanocomposites.13
Structural investigations have revealed a variety of coordination patterns and
metal–sulfur bonding interaction in dithiophosphonato ([(RO)2PS(S)]M) and dithiophos-
phinato complexes ([R2PS(S)]M), where M is a transition metal or heavier main group
element.14 Furthermore, related metal complexes also play an important role in material
sciences,15 crystal engineering, supramolecular network, and tuning electronic properties
leading to luminescent or electron-transferring reagents.16
A number of research papers have been published from our laboratory on the reaction
of dialkyl (alkylene) dithiophosphates with metals,17,18 organometals, transition metals,
and their organic derivatives,19,20 which indicate a variety of coordination tendencies and
biological/pesticidal significance of these complexes.
The synthesis and properties of organogermanium and organotin dithiophosphonate
complexes, and the several X-ray crystal structures have been reported in the literature.21–25
The present investigation is aimed to synthesize and characterize the dialkyldithiophosphate
adducts of anhydrous tin(II) chloride, and attempts have been made for the biocidal activity
evaluation of these adducts.
RESULTS AND DISCUSSION
The reaction of anhydrous tin(II) chloride (SnCl2) with dialkyl◦(alkylene) dithiophos-
phoric acid, in 1:1 molar ratio, in an anhydrous ethanol, below 5 C, with a continuous
stirring for 6–8 h in a closed vessel yielded the dithiophosphate adduct of tin(II) chloride
(Schemes 1 and 2).
For dialkyldithiophosphates
RO
RO
S
6
8 h stirring
below 5 oC
RO
RO
S
P
SnCl2
+
P
SnCl2
C2H5OH
SH
(As solvent)
SH
Scheme 1
where R CH3, C2H5, n-C3H7, i-C3H7, and CH2 CH CH2-.
The dialkyldithiophosphate adducts of tin(II) chloride have been assigned with fol-
lowing numbering:
Compound
Alkyl group R=
Compound
Alkyl group R=
1
2
3
CH3
C2H5
n-C3H7
4
5
i-C3H7
CH2 CH-CH2-

DIALKYL (ALKYLENE) DITHIOPHOSPHATE ADDUCTS
1333
For alkylenedithiophosphates
6
8 h stirring
below 5oC
O
O
S
O
O
S
SnCl2
G
P
+
G
P
SnCl2
C2H5OH
SH
SH
(As solvent)
Scheme 2
where G= CH2 CH2 and CH (CH3) CH2
The alkylenedithiophosphate adducts of tin(II) chloride have been assigned with
following numbering:
.
Compound
Alkylene group G=
CH2 CH2
Compound
Alkylene group G=
CH (CH3) CH2
6
7
These adducts were light yellow colored viscous liquids, immiscible in n-hexane, and
decomposed on heating under reduced pressure. These adducts were soluble in chloroform,
dichloromethane, and THF, and showed stability in solution even at their boiling points.
Although, these complexes showed stability toward atmospheric oxygen and moisture, they
converted into white glassy solids on mild heating by eliminating hydrogen chloride, and
formed a polymeric black residue along with SnO2 on vigorous heating. This residue was
insoluble in THF and other common organic solvents. When the addition complexes of
dialkyl (alkylene) dithiophosphate with tin(II) chloride reacted with Et3N, in anhydrous
THF, in 1:1 ratio, triethylammonium salts of addition complexes were formed (Scheme 3).
S
S
H
RO
RO
THF
Sn
P
(RO)2P(S)SSnCl2
(White ppt)
(C2H5)3NH
Cl
Reflux
Cl
(C2H5)3N
Scheme 3
Alkylenedithiophosphate adducts of tin(II) chloride also had the same characteristic
features.
The complexes were characterized by physicochemical and spectroscopic techniques,
viz. [FT-IR and NMR (1H, 31P, and 119Sn)], and are discussed below.
FT-IR SPECTRA
The FT-IR spectra of adducts (Table 1) are comparable with the corresponding free
dithiophosphoric acids and their metal derivatives. All assignments have been made on the

1334
M. MOHSIN ET AL.
Table 1 FT-IR spectral data of dialkyl (alkylene) dithiophosphate adducts of tin(II) chloride
S.N.
Compounds
ν(P)
O
C
νP
O
(C)
νP
S
νP
S
νS
H
νSn Cl
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1085–1025 vs
1070–1015 vs
1075–1015 vs
1130–1065 vs
1125–1065 vs
1105–1055 vs
1095–1025 vs
996 s
985 s
974 s
982 vs
970 b
990 s
984 s
635 s
645 s
650 s & b
640 vs
670 vs
655 s
548 m
552 m
535 m
548 m
542 b
2462 m
2476 m
2478 br
2495 m
2505 m
2472 m
2492 m
415 w
410 w
408 m
415 w
412 w
410 w
405 w
530 m
540 m
648 s
ν was measured as wave number in cm–1
Here, abbreviations are used: vs = very strong, m = medium, w = weak, b = broad, s = strong.
.
basis of literature.17–20 The absorption bands present in the region 1130–1015 cm–1 and
985 12 cm–1 have been assigned to (P) O C and P O (C) vibrations, respectively. In
some instances ν(P)–O–C is found to be coupled with symmetric and asymmetric P O (C)
vibrations. The absorption band present in the region of 552–530 cm–1 has been assigned
to νP-S stretching band. The absorption band present in the region of 415–405 cm–1 has
been assigned to Sn Cl band. The sharp and strong phosphoryl (P S) absorption band
observed at 670–635 cm–1. Stretching vibration for νS H has been shifted up to 40 cm–1
toward lower wave number (red shift). Spectral observations for νS H and νP S suggest
that the dimethyldithiophosphoric acid is more efficient for this type of adduct formation.
NMR (1H, 31P, a n d 119Sn) SPECTRA
The NMR (1H, 31P, and 119Sn) spectra of these adducts have been recorded in CDCl3,
and the spectral data are summarized in Table 2. Representative spectra for compounds 3
and 6 are shown in Figures S1–S6 (Supplemental Materials).
Table 2 NMR (1H, 31P, and 119Sn) spectral data of dialkyl (alkylene) dithiophosphate adducts of tin(II) chloride
S.N.
Compounds
1H (δ, ppm)
31P (δ, ppm)
91.6
119Sn (δ, ppm)
1
2
3
1
2
3
3.95, d, 6H, JPH = 18.2 Hz (OCH3); 3.58,
s, 1H (S H)
–
–
1.34, t, 6H, JHH = 7.3 Hz (CH3); 4.08, m,
4H (OCH2); 3.39, s, 1H (S H)
0.89, t, 6H, JHH = 7.8 Hz (CH3); 1.51, m,
4H (CH2); 4.15, m, 4H (OCH2); 3.32, s, 1H
(S H)
90.5
87.0
456.4
4
5
4
5
1.38, d, 12H, JHH = 7.5 Hz (CH3); 3.89, m,
2H (OCH ); 3.42, s, 1H (S H)
5.92, m, 2H ( CH ); 4.98, m, 4H
88.7
90.1
438.6
418.8
(
CH2); 4.15, m, 4H (OCH2); 3.32, s,
1H (SH)
6
7
6
7
4.08, d, 4H, JPH = 16.9 Hz (OCH2); 3.46,
89.8
87.8
428.2
–
s, 1H (S H)
1.32, d, 3H, JHH = 7.8 Hz (CH3); 3.86, m,
3H (O CH2 CH O); 3.36, s, 1H (S H)

DIALKYL (ALKYLENE) DITHIOPHOSPHATE ADDUCTS
1335
Table 3 Mass spectrum data of compounds 3 and 6 (relative abundances have been indicated in parentheses)
Compound
m/z (%)
3
6
406 (M++4, 6%), 402 (M+, 17%), 401 (22%), 214 (28%), 213 (32%), 188 (14%),
95 (6%), 57 (8%), 43 (10%), 29 (100%), 15 (8%)
348 (M++4, 5%), 344 (M+, 16%), 343 (21%), 188 (18%), 156 (9%), 95 (6%),
61 (15%), 33 (32%), 31 (100%), 29 (8%), 18 (9%), 15 (5%)
The spectra show a multiplet for OCH2 and OCH protons in the region
δ 3.86–4.15 due to long-range coupling of protons with magnetically active phosphorus-31
atom. In addition to this, the usual patterns of splitting of resonance signal in the 1H NMR
spectra have also been observed for alkyl, alkylene, and allyl protons. S H protons have
been observed in the slightly deshielded region (δ 3.32–3.58) in these adducts in comparison
to free ligands.17–20
31P NMR spectra show a single resonance signal in the range δ 87.0–91.6 ppm,
showing the retention of the dithiophosphate moieties in the adducts, and purity of the
complexes.20–24 31P resonance signals are slightly deshielded in these adducts as compared
to the dialkyldithiophosphate ligands (82 5 ppm). The deshielding of 31P signal is due to
the possible coordination of sulfur atom to the tin(II).
119Sn NMR signals have been observed in the range of δ 438.6–456.4 ppm, which
are slightly up fielded than the tin(II) chloride (δ 510 ppm). This is due to the increase of
electron density in the vicinity of tin(II) atom due to dithiophosphate ligands.
MASS SPECTRUM
Mass spectra of two compounds (3 and 6) were recorded. In compound 3 the molecular
ion peak with an (M+4) peak was observed at m/z 402 (17%) and 406 (6%). A radical ion
peak of m/z 29 showed 100% abundance. Compound 6 also showed M and M+4 peak at
344 and 348 with 16% and 5% abundance, and m/z 31 with 100% abundance. All signals
showed the presence of two chlorine atoms (Table 3).
Tin(II) in SnCl2 is electron deficient, which accepts the lone pair from sulfur atom
of thiol ( SH) group of dialkyl (alkylene) dithiophosphates. Based on their physicochem-
ical properties and spectroscopic investigations, it is concluded that these adducts are
monomeric in nature, and have a trigonal base pyramidal structure.
S
S
H
RO
RO
Sn
P
Cl
Cl
MICROBICIDAL ACTIVITY
Adducts were screened for their antibacterial and fungicidal activities.

1336
M. MOHSIN ET AL.
Antibacterial Activity
The newly formed adducts were screened for their antibacterial activities against
Escherichia coli (MTCC-40) and Pseudomonas aeruginosa (MTCC-424) using the filter
paper scrap disc method.26
Fungicidal Activity
Adducts were also evaluated for their Minimum Inhibitory Concentrations (MIC)
against A. niger and C. albicans using agar dilution assay. The MIC values were determined
as the lowest concentration of the targeted compounds preventing visible growth of A. niger
and C. albicans.27
The results of antibacterial and antifungal activities have been summarized in
Table S1. Results have shown the high potency of microbicidal activities for adducts,
in comparison to SnCl2 and dialkyl (alkylene) dithiophosphoric acids.
EXPERIMENTAL
Reactions were carried out in inert atmosphere and reagents were purified by standard
methods. Dialkyldithiophosphoric acids were synthesized by the reaction of P2S5 and
alcohol in 1:4 ratios in refluxing anhydrous benzene and the resulting dithiophosphoric acids
were purified by distillation under reduced pressure.28 The estimation of tin (Sn), chlorine
(Cl), and sulfur (S) was carried out gravimetrically using standard methods reported in the
literature.29 Molecular weights were determined by the Knaur Vapor Pressure Osmometer
using a chloroform solution at 45 ◦C.
FT-IR spectra were recorded in Nujol mull on FTIR 8400S SHIMADZU JAPAN spec-
trophotometer. Carbon and Hydrogen analysis was preformed on Perkins Elmer CHN/O
1
analyzer. H NMR spectra were recorded in CDCl3 solution on 300 MHz JEOL FX 300
spectrometer using TMS as an internal reference. 31P NMR spectra were recorded in CDCl3
solution using H3PO4 (85%) as an external reference. Tetramethyl tin (Me4Sn) was used as
reference for 119Sn NMR. Fast atomic bombardment (FAB) mass spectrum was recorded on
a Jeol SX 102/DA-6000 mass spectrometer/data system. Argon/Xenon (6.0KV, 10.0 mA)
were used as FAB gases.
Preparation of Dimethyldithiophosphate Adduct of Tin(II) Chloride
Dimethyldithiophosphoric acid (10.0 mmol) in anhydrous ethanol (10.0 mL)
was mixed with SnCl2 (10.0 mmol) in anhydrous ethanol (20.0 mL) in a dropwise
manner, and was continuously stirred for 6–8 h below 5 ◦C in a closed vessel
(1:1 molar ratio). The product obtained after the removal of solvent under reduced
pressure, i.e., [(CH3O)2P(S)SH]SnCl2 was a light yellow viscous liquid (3.24 g,
93.5%).
Other complexes were also synthesized by following the same experimental
procedure. The analytical results for the synthesized adducts are summarized in
Table 4.

1337

1338
M. MOHSIN ET AL.
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