Diorganotin complexes of carboxylates: Synthesis and characterization

Article abstract of DOI:10.1080/00958972.2013.775428

Diorganotin complexes of monoisopropyl and monomethyl nadiate, succinate, and phthalate were synthesized and characterized by elemental analysis, FT-IR, 1H NMR, 13C NMR, and 119Sn NMR spectroscopic techniques. The spectroscopic investigation demonstrated that carboxylate is bidentate in the diorganotin complexes. On the basis of 1J(119Sn-13C) and 2J(119Sn-1H) values, C-Sn-C bond angles were also calculated. The newly synthesized complexes were also screened for their antibacterial activities against Gram-positive and Gram-negative pathogenic strains of bacteria.

Full text of DOI:10.1080/00958972.2013.775428

Journal of Coordination Chemistry
Vol. 66, No. 6, 20 March 2013, 1046–1057
Diorganotin complexes of carboxylates: synthesis and
characterization
ASHA CHILWAL†, GAGAN DEEP*‡, PRITI MALHOTRA§ and A.K. NARULA*†
†
School of Basic and Applied Sciences, Guru Gobind Singh Indraprastha University,
Delhi, India
‡
School of Science, Department of Chemistry, Lovely Professional University, Punjab,
India
§
Department of Chemistry, Daulat Ram College, Delhi University, New Delhi, India
(
Received 12 July 2012; in final form 7 December 2012)
Diorganotin complexes of monoisopropyl and monomethyl nadiate, succinate, and phthalate were
1
13
119
synthesized and characterized by elemental analysis, FT-IR, H NMR, C NMR, and Sn NMR
spectroscopic techniques. The spectroscopic investigation demonstrated that carboxylate is bidentate
1
119
13
2
119
1
in the diorganotin complexes. On the basis of J( Sn– C) and J( Sn– H) values, C–Sn–C
bond angles were also calculated. The newly synthesized complexes were also screened for their
antibacterial activities against Gram-positive and Gram-negative pathogenic strains of bacteria.
Keywords: Synthesis; Characterization; Organotin compounds
1. Introduction
Commercial significance of organometallic complexes containing lead, tin, and mercury
has risen considerably [1]. Organotin complexes can be powerful fungicides and bacteri-
cides, depending on the constituent organic group and ligands [2–5].
Tetraorganotin complexes, tin tetrahalides, and stannanes (SnR H , where n = 1–3) are
n
4ꢀn
of synthetic value for production of complexes that have industrial value [6]. Industrial use
of less toxic organotin complexes (R SnX and RSnX ) accounts for almost two-thirds of
2
2
3
the total world's consumption of tin. Several organotin complexes such as di(n-butyl) tin
laurate have been used as hydrochloric acid scavengers in PVC. Use of their complexes as
selective biocides, insecticides, and pesticides has increased rapidly in recent years. Tribu-
tyl and triphenyltin chlorides find extensive use as biocidal additives in marine antifouling
paints [6]. Synthesis and structural studies of neutral tin complexes derived from ligands
with strategically placed donors (O, N, and S) have received attention [7–11].
Organotin carboxylates have received particular attention owing to their remarkable
structural diversity and biological importance, for example, as pesticidal, antibacterial, anti-
tumor agents, and wood preservatives [12–18]. Thus, the synthesis of organotin complexes
*
Corresponding author. Email: thareja_gagan@yahoo.co.in (G. Deep); aknarula58@gmail.com (A.K. Narula)
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online Ó 2013 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2013.775428

2
A. Chilwal et al.
having carboxylates has been a research focus [19–22]. Existing literature also proved that
the biological activities of organotin carboxylates greatly depend on their structures, which
are markedly related to properties of the carboxylic acid ligands and organic substituents
bonded to tin.
In this article, we synthesized a series of organotin complexes using carboxylates and
studied their characterization and antibacterial activities against Gram-negative and Gram-
positive bacteria.
2
2
. Experimental
.1. Materials
Manipulations of air and moisture-sensitive complexes were performed under nitrogen
using standard Schlenk techniques. Diorganotin dichlorides, R SnCl (R = Me, Bu), nadic
2
2
anhydride (NA), succinic anhydride (SA), and phthalic anhydride (PA) all were obtained
commercially from Sigma–Aldrich and used as received. Methanol and isopropanol (Spect-
rochem) were dried over sodium overnight followed by distillation. Triethyl amine (Et N)
3
dried over KOH pellets for 24 h, chloroform (spectrochem) dried over calcium chloride for
7
2 h, hexane (spectrochem) and dichloromethane (spectrochem) also dried over sodium
were distilled before use according to standard methods [23].
2
.2. Measurements
Structural characterization of ligands and diorganotin complexes was done using FT-
1
13
119
IR, H NMR, C NMR, and
Sn NMR spectroscopic techniques. Elemental analysis
was carried out using a EURO EA 3000 elemental analyzer. FT-IR spectra were
ꢀ1
recorded in KBr pellets from 4000 to 200 cm using a Shimadzu FTIR 8700 spectro-
1
13
119
photometer. H NMR, C NMR, and
Sn NMR spectra were recorded on a Bruker
3
00 MHz spectrometer using DMSO-d as solvent. Tetramethylsilane was used as an
6
1
13
internal standard for H NMR, C NMR spectra, and tetramethyltin as an internal
standard for
119
Sn NMR spectra. FAB mass spectra in 3-nitrobenzyl alcohol (NBA)
were recorded at room temperature on a JEOL SX 102/DA-6000 mass spectrometer/
data system using argon/xenon (6 kV, 10 mA) as the FAB gas. The accelerating
voltage was 10 kV.
2
2
.3. Synthesis
.3.1. Synthesis of ligands. Different carboxylates (L –L ) were prepared [24] using
1
6
Scheme 1. A 10-fold excess of dry methanol (7.35 ml) and isopropanol (13.95 ml) were
separately added to nadic anhydride, NA (3 g, 0.0182 mol) in a 250 ml round-bottom flask.
The subsequent mixtures were heated under reflux for 3 h with constant stirring according
to Scheme 1. Each reaction mixture was then evaporated under reduced pressure to remove
excess of the respective alcohols, and the products were dried in a desiccator under
reduced pressure to give 90–95% of compound. These two ligands were designated as
NM and NIP, respectively.

Diorganotin carboxylates
3
Scheme 1. Synthesis of ligands.
Scheme 2. Synthesis of diorganotin complexes.
Similarly, all other ligands were prepared by reacting succinic anhydride (SA) or
phthalic anhydride (PA) with 10-fold excess of the dry methanol (M) and isopropanol (IP).
The ligands thus obtained were designated as SM, SIP, PM, and PIP, respectively.
2.3.2. Synthesis of diorganotin(IV) complexes. Diorganotin complexes (1–12) were
prepared by treating 2 mol of half-esters (ligands) with 1 mol of dialkyltin dichloride using
Scheme 2.
A solution of NM (388 mg, 0.002 mol) in 10 ml chloroform was added to a mixture of
dimethyltin dichloride (M) (219 mg, 0.001 mol) and Et N (0.3 ml). The resultant mixture
3
was heated under reflux with stirring for 6 h (Scheme 2) and then allowed to stand at
+
ꢀ
2
5 °C for 10 h. The precipitated Et NH Cl was filtered and the filtrate was evaporated
3
under vacuum to yield a solid which was purified by recrystallization in a mixture of
dichloromethane/hexane (1 : 1). It is designated as NMM.
Similarly, all other diorganotin(IV) complexes were prepared by reacting NM, NIP, SM,
SIP, PM, and PIP with dimethyltin dichloride (M) and dibutyltin dichloride (B). Sample
designation of diorganotin(IV) complexes is given in Scheme 3.

4
A. Chilwal et al.
Scheme 3. Sample designation of organotin(IV) complexes.

Diorganotin carboxylates
5
2.4. Antibacterial studies
Screening of the complexes for their antibacterial activities was performed by employing
Broth Microdilution MIC method [25]. Using sterile microtitre plates, 0.2 ml of
Mueller–Hinton Broth was added to each of the 96 wells. Doubling dilutions of each com-
pound were made in the wells, thus, a plate contained 0.5–100 μg/ml dilutions of 12 differ-
ent complexes and of ampicillin. In each plate, one well was kept as positive control
(broth + inoculum) and another as negative control (broth only). The inoculum was
adjusted to a turbidity equivalent to McFarland 0.5 turbidity standard. The inoculum was
5
suitably diluted so as to get a final concentration of approximately 5 ꢁ 10 cfu/ml of bacte-
ria in each well. Each well was inoculated with 0.01 ml of the prepared inoculum using a
multichannel micropipette and the plates were incubated overnight at 37 °C. The MICs of
these complexes and ampicillin were determined by using the standard protocol of NCCLS
Broth Microdilution MIC method.
3
3
. Results and discussion
.1. Chemistry
Scheme 1 shows the synthesis of ligands. Dehydrochlorination occurred during the synthe-
sis (Scheme 2). The designation of the compounds is shown in Scheme 3. The analytical
data have been shown in table 1.
3
.2. IR spectra
FT-IR spectra of all the complexes have been summarized in table 2. The absence of bands
ꢀ
1
ꢀ1
at 2500–3000 cm due to O–H bond of the ligands and at 360 cm due to Sn–Cl bond
ꢀ
1
and presence of band at 650–675 cm [26] due to Sn–O bond in all the organotin com-
plexes indicated that dehydrochlorination had taken place leading to removal of proton of
ꢀ
ꢀ1
carboxyl and both Cl of Sn with formation of Sn–O bonds. The band at 450–475 cm
indicated formation of O→Sn [27]. The shifting of C=O band of carboxylic acid to lower
Table 1. Analytical data of complexes.
Found (Calcd) (%)
No.
Compound
Formula
FMW
Yield (%)
C
H
Sn
1
2
3
4
5
6
7
8
9
NMM
NMB
NIPM
NIPB
SMM
SMB
SIPM
SIPB
PMM
PMB
PIPM
PIPB
C
22
C
28
C
26
C
32
C
12
C
18
C
16
C
22
C
20
C
26
C
24
C
30
H
28
H
40
H
36
H
48
H
16
H
28
H
24
H
36
H
20
H
32
H
28
H
48
O
8
O
8
O
8
O
8
O
8
O
8
O
8
O
8
O
8
O
8
O
8
O
8
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
Sn
539
623
595
679
407
491
463
547
507
591
563
647
80
79
78
75
77
76
74
72
74
73
71
70
48.9 (49.0)
53.9 (53.9)
52.4 (52.5)
56.5 (56.6)
35.3 (35.4)
43.9 (44.0)
41.4 (41.5)
48.2 (48.3)
47.2 (47.4)
52.7 (52.8)
51.1 (51.2)
54.6 (54.9)
5.1 (5.2)
6.3 (6.5)
6.0 (6.1)
7.1 (7.1)
3.9 (3.9)
5.6 (5.7)
5.1 (5.2)
6.5 (6.6)
3.9 (4.0)
5.3 (5.4)
4.9 (5.0)
7.1 (7.4)
22.1 (22.0)
19.1 (19.0)
20.2 (20.0)
17.7 (17.5)
29.3 (29.2)
24.4 (24.2)
25.8 (25.6)
21.5 (21.7)
23.6 (23.4)
20.3 (20.1)
21.3 (21.1)
18.3 (18.1)
1
0
1
1
1
2

6
A. Chilwal et al.
ꢀ
1
Table 2. FT-IR spectral data of complexes in cm
.
No.
Compound
νasym(COO)
νsym(COO)
Δν(COO)
ν(O→Sn)
ν(Sn–O)
νasym(Sn–C) νsym(Sn–C)
1
2
3
4
5
6
7
8
9
NMM
NMB
NIPM
NIPB
SMM
SMB
SIPM
SIPB
PMM
PMB
PIPM
PIPB
1583
1583
1584
1585
1583
1583
1584
1583
1584
1584
1583
1583
1454
1452
1454
1454
1454
1456
1454
1454
1452
1454
1453
1454
129
131
130
131
129
127
130
130
132
129
130
129
463
463
464
463
461
463
460
461
450
455
455
453
674
674
675
674
672
674
671
672
650
656
655
654
648, 552
647, 551
648, 551
648, 551
636, 552
634, 553
636, 553
651, 552
650, 555
650, 554
651, 555
650, 555
1
0
1
1
1
2
frequencies was seen, due to involvement of O in coordinate bond formation. However,
bands due to ester (which is already present in the reactant) were observed at nearly the
same positions both in ligands and complex showing that ester group was not involved in
bond formation.
ꢀ
1
The bands due to νasym(COO) and νsym(COO) were observed between 1640–1575 cm
ꢀ
1
and 1420–1310 cm , respectively (table 2). The difference between νasym(COO) and
νsym(COO) was less than 200 cm , indicating that the carboxylates were chelated and
ꢀ
1
bidentate to metal [24,27].
3
.3. NMR spectra
1
The H NMR spectra of ligands showed a signal at δ 10.2 due to free –COOH group
which disappeared in complexes, further supporting the dehydrochlorination reaction. Sig-
nals due to tin-alkyl protons in dibutyltin(IV) and dimethyltin(IV) complexes were
observed at δ 0.8–1.7 [28,29]. In all diorganotin(IV) complexes, singlet due to –OCH and
3
multiplet due to protons of –OCH(CH ) group were observed at δ 3.6–3.7 and δ 4.6–4.7,
3
2
respectively.
In 1–4, multiplets of olefinic protons appeared at δ 5.6 and bridging methylene protons
were at δ 1.8 ppm. Complexes 5–8 had multiplets of methylene protons at δ 2.5–2.6 ppm
1
and in 9–12 the aromatic protons were observed at δ 7.6–8.2 ppm. Other H NMR signals
of complexes were observed at their usual positions and are summarized in table 3. The
proton integrations were consistent with molecular formulas.
1
3
C NMR signals of carboxylic carbon of carboxylic acid group in all organotin(IV)
complexes were observed downfield (δ 172.0–178.0) of their corresponding ligands
δ 167.6), suggesting bonding of ligands through both carboxylic oxygens of carboxylic
(
acid to tin [30]. However, carbons of ester group were observed at nearly the same
position (δ 180–182) in ligands and complexes, indicating non-involvement of ester in
bonding. Carbons of alkyl groups that is, methyl and butyl attached to tin atom were
observed at δ 9.4–9.6 and δ 13.6–27.4, respectively. Carbons of methyl and methine
attached to oxygen of acid were observed at δ 50–51 and δ 68–70, respectively.
In 1–4, olefinic carbons appeared at δ 135–137 and bridging carbons were observed at δ
4
3–44. Methylene carbons attached to carbonyl in 5–8 were at δ 28.7–34.0 and in 9–12
1
3
the aromatic protons were at δ 127.4–134.8. Other C NMR signals of all complexes
were observed at their usual positions and are summarized in table 4.

Diorganotin carboxylates
7

8
A. Chilwal et al.

Diorganotin carboxylates
9
1
19
The presence of a singlet in the
Sn NMR spectra from δ ꢀ290 to δ ꢀ367 indicates
six-coordinate tin in all the complexes [31–33]. The signals appeared much upfield due to
large electron density on Sn due to oxygen donors of ligand. The appearance of singlets
showed that there was only one isomer.
The C–Sn–C bond angles, h were calculated using the following two equations [34,35]
and have been summarized in table 5:
2
119
1
2
2
119
1
h ¼ 0:0105j Jð Sn ꢀ HÞj ꢀ 0:799j Jð Sn ꢀ HÞj þ 122:4
ð1Þ
ð2Þ
1
119
13
Jð Sn ꢀ CÞ ¼ 9:99h ꢀ 746
3
.4. Mass spectra
Every effort to obtain crystals did not produce a single crystal. Evidence in support of the
structures of these compounds came from FAB mass spectral studies.
Under the FAB mass condition, compounds displayed molecular ions at 539 (NMM),
6
5
23 (NMB), 595 (NIPM), 679 (NIPB), 407 (SMM), 491 (SMB), 463 (SIPM), 547 (SIPB),
07 (PMM), 591 (PMB), 563 (PIPM), and 647 (PIPB). Isotopic ions were observed corre-
sponding to the different isotopes of tin. The observation of molecular ions in the mass
spectra of the respective compounds confirmed monomers of the compounds. figures 1 and
2
show the mass spectra of PMM and NIPM, respectively.
3
.5. Antibacterial studies
Antibacterial activities were evaluated using two Gram-positive (Staphylococcus aureus,
Staphylococcus epidermidis) and two Gram-negative (Escherichia coli, Pseudomonas aeru-
ginosa) bacteria (table 6). Against both the Gram-positive and Gram-negative bacteria,
however, complexes SMB, SIPB, and PMB have the greatest effects over 24 h. This was
due to the presence of electron-withdrawing group which lowers electron density in the
compound. Comparison of electron density among various complexes could predict the
Table 5. Calculated C–Sn–C bond angles of complexes.
2
119
1
1
119
13
No.
Compound
J( Sn, H)
Bond angle
127.3
J( Sn, C)
Bond angle
1
2
3
4
5
6
7
8
9
NMM
NMB
NIPM
NIPB
SMM
SMB
SIPM
SIPB
PMM
PMB
PIPM
PIPB
69.3
610.5
605.3
608.9
608.3
608.7
610.8
135.8
135.3
135.6
135.6
135.6
135.8
70.2
72.2
70.3
75.2
78.5
126.7
125.3
126.7
123.1
120.4
10
1
1
12

1
0
A. Chilwal et al.
Figure 1. Mass spectra of NIPM.
Figure 2. Mass spectra of PMM.

Diorganotin carboxylates
11
ꢀ1
Table 6. Antibacterial activities of complexes by MIC method in μg/mL
.
No.
Compound
P. aeruginosa
E. coli
S. aureus
S. epidermidis
1
2
3
4
5
6
7
8
9
NMM
NMB
NIPM
NIPB
SMM
SMB
SIPM
SIPB
PMM
PMB
PIPM
PIPB
1000
250
1000
250
1000
31.2
500
31.2
1000
31.2
1000
62.5
250
131.2
500
250
500
31.2
500
31.2
1000
31.2
500
1000
125
1000
125
1000
31.2
500
31.2
500
1000
125
1000
125
1000
31.2
500
125
1000
31.2
250
1
0
31.2
1000
62.5
1
1
1
2
62.5
62.5
extent of interaction with the bio-receptor. The solvent used to prepare the stock solutions
DMSO) played no role in growth inhibition.
(
4. Conclusion
Organotin complexes studied here are six-coordinate. Organotin(IV) derivatives of dibutyl
tin dichloride showed best MIC against Escherichia coli, Staphylococcus aureus, Staphylo-
coccus epidermidis, and Pseudomonas aeruginosa compared to dimethyl tin dichloride
derivatives.
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