Some new butylthiobenzoatotin(IV) compounds: Spectral studies and analysis of ligand's bonding

Article abstract of DOI:10.1016/j.saa.2004.11.048

Five new monorganotin(IV) compounds with thiobenzoate ligand, [BuSn(SOCPh)₂]₂O (1), [BuSn(O)(SOCPh)]₂ (2), BuSn(Cl)(SOCPh)₂ (3), BuSn(Cl)₂(SOCPh) (4) and [BuSn(OH)(Cl)(SOCPh)]₂ (5) were syn

Full text of DOI:10.1016/j.saa.2004.11.048

Spectrochimica Acta Part A 61 (2005) 3145–3149
Some new butylthiobenzoatotin(IV) compounds: spectral
studies and analysis of ligand’s bonding
Subrato Bhattacharya∗
Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005, India
Received 9 November 2004; accepted 30 November 2004
Dedicated to Professor V.D. Gupta on his 65th birthday.
Abstract
Five new monorganotin(IV) compounds with thiobenzoate ligand, [BuSn(SOCPh)2]2O (1), [BuSn(O)(SOCPh)]2 (2), BuSn(Cl)(SOCPh)2
1
(3), BuSn(Cl)2(SOCPh) (4) and [BuSn(OH)(Cl)(SOCPh)]2 (5) were synthesized and characterized by elemental analyses, IR, H and 13C
NMR spectroscopy. 119Sn NMR spectroscopy was used to determine the coordination geometry around Sn(IV) in the cases of 2 and 4. 1,
2 and 5 are dimeric while 3 and 4 are monomeric. In all these molecules the thiobenzoate ion is coordinated only through its sulfur atom.
Molecular structures of the compounds have been optimized by MM2 calculations. Semi-empirical quantum mechanical calculations (PM3
method) were performed to explain the monodentate-bonding pattern of thiobenzoate ligand.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Organotin compound; Thiocarboxylate; 119Sn NMR; Molecular structure; Semi-empirical calculations
1. Introduction
[8]. Discrete monomeric molecular units of BuSn(SOCPh)3
and Sn(Cl)2(SOCPh)2 were found in their respective crystal
lattices. More interestingly, the former molecule possesses
tetracoordinated Sn(IV) center. Recently, molecular models
of some partially substituted organotin(IV) complexes using
N, O, S donor ligands have been reported [9,10]. Interaction
modes of some of these complexes with water have also been
modeled [10].
In view of the above facts, we here report syntheses and
spectral characterization including MM2 molecular struc-
tures of a few monoorganotin(IV) thiobenzoate derivatives.
Results of semi-empirical quantum chemical calculations
performed to explain the bonding mode of the thiobenzoate
anion are also reported.
Organotin(IV) compounds interact strongly with biologi-
cal substrates giving rise to toxic effects [1]. Some of them
are also known to exert therapeutic effects on various tumor
cells [2]. Certain organotin(IV) derivatives have synthetic ap-
plications as homogeneous catalysts [3]. In past few years, a
large number of organotin(IV) complexes have been synthe-
sized and structurally characterized in solution as well as in
solid state revealing incomparable multifariousness of these
systems.
Despite considerable structural information, the factors
influencing coordination number and geometry are not well
understood in these systems [4]. Monoorganotin(IV) com-
plexes are hexacoordinated in most of the cases [4–6] and
those obtained using carboxylate ligands form clusters which
exist in two distinct structural forms [7]. On the other hand,
our own findings with thiocarboxylate ligands are different
2. Experimental
All experimental manipulations were carried out under
anhydrous conditions. Solvents were purified and dried by
standard methods. Butyltin trichloride (Aldrich) was freshly
∗
Tel.: +91 542 2323598; fax: +91 542 2368174.
E-mail address: bhatt99@yahoo.com.
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.11.048

3146
S. Bhattacharya / Spectrochimica Acta Part A 61 (2005) 3145–3149
distilled (93 ◦C/10 Torr) prior to use. Butyltin hydroxide ox-
ide (butylhydroxyoxostannane) [11], butyltin dichloride hy-
droxide (butyldichlorohydroxystannane) [12] and thioben-
zoic acid [13] were prepared by literature procedures. Potas-
sium salt of thiobenzoic acid was prepared by shaking
an aqueous solution of KOH with an ethereal solution of
thiobenzoic acid. The aqueous layer was evaporated under
reduced pressure and the residue dried in a vacuum desic-
cator over P4O10. Sulfur and chlorine were estimated gravi-
metrically as BaSO4 and AgCl, respectively. Micro analyt-
ical and mass spectral data were collected through RSIC
(Chandigarh, India). IR spectra were recorded in the region
4000–400 cm−1 using a JASCO FT-IR 5300 spectrometer as
KBr pellets and in the region 400–200 cm−1 as nujol mull
over CsI disks using a Perkin-Elmer 883 instrument. 1H and
13C NMR were recorded with a JEOL FX90Q instrument and
119Sn NMR with a Bruker 400 MHz spectrometer in CDCl3
solutions. TMS was used as an internal reference for 1H and
13C while external reference Me4Sn was used in a sealed cap-
illary for 119Sn NMR. MM2 computations were performed
using CsChem3D Ultra program package. Semi-empirical
quantum mechanical calculations by PM3 method were per-
formed using MOPAC (Ver. 6.0).
under vacuo for 6 h at 0.01 Torr/39 ◦C. The pasty product so-
lidified on refrigeration overnight.
3. Results and discussion
3.1. Synthesis of the compounds
Two butyloxotin(IV) thiobenzoates, [BuSn(SOCPh)2]2O
(1) and [BuSn(O)(SOCPh)]2 (2), two butylchlorotin(IV)
thiobenzoates,
BuSn(Cl)(SOCPh)2
(3)
and
BuSn(Cl)2(SOCPh) (4) and another hydroxochloro
derivative, [BuSn(OH)(Cl)(SOCPh)]2 (5) were prepared
(Table 1). 1 and 2 are readily formed in high yields when
butyltin hydroxide oxide was reacted with thiobenzoic acid
in 1:2 and 1:1 molar ratios, respectively. Compounds 3 and
4 were obtained from the reactions of butyltin trichloride
with potassium thiobenzoate in appropriate molar ratios
(1:2 and 1:1). The hydroxochloro compound 5 was obtained
from a reaction of [BuSn(OH)Cl2·H2O]2 and KO(S)CPh
in equimolar ratio. Attempt to replace the second chlorine
from this complex using 2 moles of thiobenzoate salt led to
the formation of the previously reported tris-thiobenzoate
compound [8]. All the compounds are quite stable in open
atmosphere in solid state as well as in solution and are solids
except 4, which is a viscous liquid.
2.1. Synthesis of [BuSn(SOCPh)2]2O and
[BuSn(O)(S(O)CPh)]2
3.2. IR spectra
A solution of thiobenzoic acid in benzene (∼10 ml) was
added to a stirred suspension of butyltin hydroxide oxide in
benzene (∼20 ml) 2:1 or 1:1 molar ratio at room temperature
(28 ◦C). Stirring was continued for 2 h during which the re-
action mixture became homogeneous. The solvent was then
evaporated under reduced pressure and the product was dried
in vacuo for 1 h at 0.05 Torr/28 ◦C. 1 was recrystallized from
a 1:1 mixture of diethyl ether/n-hexane and 2 from slow cool-
ing of a hot acetone solution.
The infrared spectrum of thiobenzoic acid displays three
characteristic bands at 1685, 1213 and 950 cm−1, respec-
tively, duetoC O, Ph CandC Sbondstretchingvibrations.
Shift in the positions of these bands can be used as a diagnos-
tic tool to detect the coordination mode of the thiobenzoate
anion [14]. In the spectra of the compounds (Table 2), the
CO stretching band is observed in a narrow range between
1595 and 1610 cm−1 providing a strong evidence for exis-
tence of a double bond between the two atoms. It implies
that the carbonyl oxygen atoms are not involved in coordina-
tion with Sn(IV) atoms. This is further substantiated by the
appearance of the ν(C–S) band between 922 and 939 cm−1
indicating presence of single bond between carbon and sul-
phur atoms. We have reported earlier that on chelation with
Sn(IV) atoms, the ν(C–S) band shifts to a higher wave num-
ber [8]. Furthermore, the ν(Ph–C) absorption in the region
1211–1219 cm−1 is also indicative of monodentate attach-
ment of the ligand, since on chelation the ␲–electron drift
as shown in Scheme 1 would shift this band to a higher fre-
quency as has been observed in Cl2Sn(SOCPh)2. In the far IR
2.2. Synthesis of BuSn(Cl)(SOCPh)2 and
BuSn(Cl)2(SOCPh)
A solution of butyltin trichloride in dichloromethane
(∼10 ml) was added to a stirred suspension of potassium
thiobenzoate in the same solvent (∼20 ml) at room tempera-
ture. After stirring for 1 h, the KCl precipitate was filtered off
and the solvent evaporated under reduced pressure. The re-
sulting residue was dried in vacuo for 1 h at 0.05 Torr/28 ◦C. 3
was recrystallized from a diethyl ether/n-hexane 1:1 mixture.
2.3. Synthesis of [BuSn(OH)(Cl)(SOCPh)]2
An acetone solution of potassium thiobenzoate was added
to a stirring suspension of [BuSn(OH)Cl2H2O]2 in acetone
(∼10 ml) at room temperature. After stirring for 1 h, the pre-
cipitated KCl was filtered off and the solvent was evaporated
under reduced pressure. The residue thus obtained was dried
Scheme 1.

S. Bhattacharya / Spectrochimica Acta Part A 61 (2005) 3145–3149
3147
Table 1
Analytical and physical data of the compounds
No.
Reactants (g)
Product (g, %)
M.P. (◦C)
Anal. found (calcd.) (%)
C
H
S
Cl
1
2
3
4
5
BuSn(O)OH
(0.25)
PhCOSH
(0.33)
[BuSn(SOCPh)2]2O
(0.42, 76)
74
47.30
(47.18)
4.07
(4.18)
14.1
(14.0)
–
–
BuSn(O)OH
(0.42)
PhCOSH
(0.28)
[BuSn(O)(SOCPh)]2
(0.65, 98)
146–48
54–55
–
39.37
(40.16)
4.47
(4.29)
10.2
(9.8)
BuSnCl3
(0.34)
PhCSOK
(0.42)
BuSn(Cl)(SOCPh)2
(0.55, 95)
44.13
(44.52)
4.02
(3.94)
–
–
–
8.1
(7.8)
BuSnCl3
(0.86)
PhCSOK
(0.54)
BuSn(Cl)2(SOCPh)
(1.16, 99)
33.91
(34.41)
4.09
(3.67)
18.2
(18.5)
BuSn(OH)Cl2H2O
(0.32)
PhCSOK
(0.20)
BuSn(OH)Cl(SOCPh)
(0.33, 91)
31–32
35.51
(36.15)
4.41
(4.14)
10.3
(9.7)
region, a strong–medium intensity band was found between
643 and 653 cm−1due to the bending mode of the SCO unit.
All these facts establish monodentate attachment of the lig-
and through sulphur. Existence of the keto (C O) form in
these compounds is in agreement with our earlier experimen-
tal findings [8] as well as theoretical calculations reported in
the literature [15].
Among the other bands, important ones are ν(Sn–S),
ν(Sn–C) and in the cases of compounds 3, 4 and 5 ν(Sn–Cl).
Another important band was observed between 617 and
609 cm−1 in 1, 2 and 5 due to ν(Sn–O) vibrations (Table 2).
3.3. Multinuclear NMR spectra
The NMR spectral data of the compounds are given in
Table 2. From the Bu:Ph proton ratios (in the 1H NMR
spectra of the compounds), the compositions of the com-
pounds are established and no other structural informa-
tion is expected. However, 119Sn NMR spectroscopy is a
very useful tool for determining the coordination environ-
ment around Sn atoms. We recorded 119Sn NMR of two
representative compounds (2 and 4). For the compound 2,
a single peak was observed at −158.53 ppm, which falls
Table 2
Spectral data of the compounds
No.
IR (cm−1
)
NMR
ν(CO)
ν(PhC)
ν(CS)
δ(SCO)
ν(SnO)
ν(SnC)
ν(SnS)
ν(SnCl)
1H
13C
Bu
119Sn
Bu
Ph
Ph
1
1610
1596
1595
1593
1599
1211
922
643
615
548
365
–
0.9–2.5
7.3–8.1
13.42
25.29
26.84
31.73
128.66
129.11
131.87
136.74
–
2
1212
1219
1213
1215
928
924
939
931
653
652
650
646
609
–
551
556
560
550
365
362
350
358
–
1.0–2.5
0.8–2.6
0.9–2.4
0.8–2.5
7.8–8.8
7.4–8.2
7.4–8.0
7.6–8.5
13.50
25.61
26.77
30.83
128.39
128.93
133.89
136.77
−158.53
3
335
338
330
13.39
25.54
26.77
31.63
128.43
128.81
131.07
136.51
–
4
–
13.33
25.31
26.76
33.20
128.47
128.79
129.58
135.72
−111.82
5
617
13.41
25.22
26.80
33.38
128.86
129.29
130.97
135.56
–

3148
S. Bhattacharya / Spectrochimica Acta Part A 61 (2005) 3145–3149
within the range for tetracoordinated distannoxanes [16].
Such a structure cannot arise in the case of a monomeric
molecule. Molecular weight of this compound (658) re-
veals that it exists as a dimer. Appearance of a single
peak indicates that both the Sn(IV) atoms are chemically
equivalent. On the other hand, a resonance signal was ob-
served in the spectrum of 4 at −111.82 ppm, which is
well within the range reported for tetracoordinated organ-
otincarboxylates and thiocarboxylates [17]. A tetrahedral
monomeric structure for this compound may, therefore, be
proposed.
3.4. Molecular structures and analysis of bonding mode
of thibenzoate anion
Fig. 2. Optimized structure of 2 showing the distannoxane ring.
In order to get finer structural details of these compounds,
we have optimized the molecular structures of 1, 2, and 5.
Molecular structure of 1 is given in Fig. 1. The two Sn
atoms are connected through an oxo bridge. The conforma-
tion about one Sn atom with respect to the other is gauche
as expected and the C1–Sn1, Sn2–C19 dihedral angle is
57◦. The geometry around each Sn atom is approximately
tetrahedral; the angles vary from 107.3 to 114.8◦. The dis-
cupying the axial positions. Though the angle between the
two axial bonds (153.9◦) is far from 180◦, the other three
atoms (C1, S1, Oꢀ) along with the central Sn1 atom consti-
tute the equatorial plane, which is almost perfect (mean de-
viation = 0.04 A). The Sn–Sn distance is larger (3.19 A) than
that in 2.
˚
˚
If we compare the structures of the compounds reported
here with the earlier reported tin(IV) thiocarboxylates [8], the
major difference that we find is the dimeric nature of these
compoundsincontrasttotheearlierreportedBuSn(SOCPh)3,
Cl2Sn(SOCPh)2 and Sn(SOCPh)4 monomeric molecules.
However, dimer formation in 1, 2 and 5 is quite expected
due to the presence of oxo groups (hydroxo in 5). On the
other hand, a comparison with organotin(IV) oxocarboxy-
lates [7] reveal more structural differences. As mentioned al-
ready, all the organotin(IV) oxocarboxylates are cluster com-
pounds with higher degrees of oligomerization (n = 3–6). For-
mation of larger clusters in the present cases is prevented due
to the following two factors. Firstly, existence of the thiol
form (–C(O)SH) rather than the thione form (–C(S)OH) in
thioformic acid has been shown by theoretical calculations
[12]. However, in free acid the bidentate mode of bond-
˚
tance between two Sn atoms in a molecule being 3.42 A is
sufficiently large to disallow any interaction between them.
Fig. 2 shows the molecular structure of 2. The molecule pos-
sesses an improper axis of rotation and as a result of this
symmetry, both the Sn centers become equivalent, and thus
only one resonance signal was observed in its 119Sn NMR
spectrum. The geometry around the tin atoms is tetrahe-
dral with somewhat larger distortion. Due to the formation
of a distannoxane ring the Sn–Sn distance is much closer
˚
(2.88 A) than that in 1, but is still larger than the sum of
their van der Waals radii. The atoms constituting the ring
are almost coplanar. The deviation from planarity is only
˚
0.03 A.
Molecular structure of 5 is shown in Fig. 3. The molecule
possesses an inversion center. Each Sn center has distorted
trigonal bipyramidal geometry with the Cl1 and O atoms oc-
Fig. 1. Optimized structure of 1.
Fig. 3. Simulated structure of 3.

S. Bhattacharya / Spectrochimica Acta Part A 61 (2005) 3145–3149
3149
ing is not expected which has been found in the case of
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