A potential “green” organotin: Bis-(methylthiopropyl)tin dichloride, [MeS (CH2)3]2SnCl2

Article abstract of DOI:10.1016/j.ica.2017.05.026

The tetravalent organotin compound [MeS(CH₂)₃]₂SnCl₂, 1, has been synthesized in high yield and structurally characterized as being hexa-coordinate at tin with two intramolecular Sn-S bonds. The specific structure has been shown by theoretical calculations to be the low energy geometric structure available, and the differences associated with the experimental and calculated Sn-S bond lengths ascribed to crystal packing issues. The intramolecular Sn-S bonding produces a benign organotin compound with respect to its interactions with human natural killer cells; however, this blocking of coordination sites at Sn does not reduce its capacity to act as an efficient esterification catalyst.

Full text of DOI:10.1016/j.ica.2017.05.026

Accepted Manuscript
Research paper
A potential “green” organotin: Bis-(methylthiopropyl)tin dichloride, [MeS
(CH2)3]2SnCl2.
Diana Gabriela Vargas, Alejandro Metta-Magaña, Hemant K. Sharma, Margaret
M. Whalen, Thomas M. Gilbert, Keith H Pannell
PII:
S0020-1693(17)30077-4
http://dx.doi.org/10.1016/j.ica.2017.05.026
ICA 17595
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
16 January 2017
9 May 2017
10 May 2017
Please cite this article as: D.G. Vargas, A. Metta-Magaña, H.K. Sharma, M.M. Whalen, T.M. Gilbert, K.H. Pannell,
A potential “green” organotin: Bis-(methylthiopropyl)tin dichloride, [MeS (CH2)3]2SnCl2., Inorganica Chimica
Acta (2017), doi: http://dx.doi.org/10.1016/j.ica.2017.05.026
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A potential “green” organotin: Bis-(methylthiopropyl)tin dichloride,
[MeS (CH2)3]2SnCl2.
Diana Gabriela Vargas,1 Alejandro Metta-Magaña,1 Hemant K. Sharma,1 Margaret M. Whalen,2
Thomas M. Gilbert,3 Keith H Pannell.1
2
1 Department of Chemistry, University of Texas at El Paso, El Paso, TX 79968, USA; Department
of Chemistry, Tennessee State University, Nashville, TN 37209, USA; 3 Department of Chemistry
and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA
Abstract.
The tetravalent organotin compound [MeS(CH2)3]2SnCl2, 1, has been synthesized in high yield and
structurally characterized as being hexa-coordinate at tin with two intramolecular Sn-S bonds. The
specific structure has been shown by theoretical calculations to be the low energy geometric structure
available, and the differences associated with the experimental and calculated Sn-S bond lengths
ascribed to crystal packing issues. The intramolecular Sn-S bonding produces a benign organotin
compound with respect to its interactions with human natural killer cells; however, this blocking
of coordination sites at Sn does not reduce its capacity to act as an efficient esterification catalyst.
Introduction.
Organotin materials are valuable as catalysts for, inter alia, trans-esterification, siloxane
curing, polymerization, etc.1 They were widely used as anti-fouling additives in paints, and are part
of a large class of anti-fungal agrochemicals; however, their use as anti-fouling agents in marine
paints has been restricted since the organotin compounds have been shown to bio accumulate in
shellfish and indeed the decline in abundance of both oyster and mussel has been linked to
subsequently developed growth abnormalities induced by organotin compounds.2 Despite these
negative attributes their use as catalysts remains an important aspect of tin chemistry. One of us
has established that organotin compounds have the capacity to modify and degrade the ability of
human natural killer cells (NKCs) to function, and for example, concentrations as low as 10-6 M/L
can effectively stop such functionality.3 When this latter finding is coupled to the fact that a random
human population exhibited the presence of butyltin chlorides in their blood at levels of
nanogram/dL,4 it is clear that the future of organotin derivatives in the market place may be
1

restricted. Indeed as early as 1986 it was clear that a new approach to the design of organotin
derivatives was needed and research into such a program was needed to produce useful chemical
reagents without deleterious side effects.5
The precise mechanism whereby the organotin derivatives are adverse to many living systems is
still under investigation in disparate systems, but a general concept of the initial activity of the
organotin derivatives is their capacity, as Lewis Acids, to bind to S, N, and O atoms is various
biochemically important molecules (e.g. S-Bio), thus initiating a cascade of events disrupting
normal biological behavior.6 We have suggested that if the organotin derivatives contain an organic
functionality with such a heteroatom remote from the Sn atom, but with a conformational
capacity to interact with such an atom, then possible intramolecular bonding could effectively
compete with the organotin interaction with the biological molecule, Scheme 1.7
Scheme 1. Possible intramolecular S-Sn bonding modification of organotin bioactivity
To test the validity of this concept, we now report the synthesis, structural analysis, and
evaluation of some important biological and catalytic properties of bis(methylthiopropyl)tin
dichloride, (MeSCH2CH2CH2)2SnCl2 (1). Such a structural arrangement introduces the potential for
the S atom to intramolecularly bind to tin to form a favored 5-membered chelate ring.
Results and Discussion
The synthesis was readily performed as noted in Scheme 2, via initial formation of tetra-
methylthiopropyl tin, followed by a classic in-situ redistribution reaction with SnCl4 to form 1 in
high yield, >80%. This is similar to the route used by the Pardubice group of Lébl et al. for the
2

corresponding O analog.8 New material 1 was readily purified via recrystallization from a
hexane/CH2Cl2 solvent mixture.
SnCl4
Mg/THF
S
Sn
S
Cl
S
MgCl
(
)
4
S
S
Sn
+
SnCl4
SnCl2
(
(
)
4
)
2
Scheme 2. Synthesis of (MeSCH2CH2CH2)2SnCl2 (1).
1
13
119
The use of H, C and
Sn NMR spectroscopy, see experimental section, confirmed the product
as the desired material. The 119Sn NMR spectrum of 1 exhibited a signal at -93.3 ppm in CDCl3 which
is ~ 220 ppm shifted upfield from Bu2SnCl2 (126.5 ppm),9 and is in the same general range observed
for (MeOC(O)CH2CH2)2SnCl2 (-66.0 ppm),10 (Me2NCH2CH2CH2)2SnCl2 (-184.7 ppm),11
(Ph2PCH2CH2CH2)2SnCl2 (-130.0 ppm),12 and (MeOCH2CH2CH2)2SnCl2 (-108.6 ppm).8 These data
are highly suggestive of a six-coordinate structure maintained in solution formed via intramolecular
coordination to the central tin atom via the O, S, N and P donor atoms. This hexa-coordination is
further supported by the large 1J(119Sn-13C) coupling constants for
Hz)8,
1
(763 Hz),
Hz),11
(MeOCH2CH2CH2)2SnCl2
(732
(Me2NCH2CH2CH2)2SnCl2
(903
(Ph2PCH2CH2CH2)2SnCl2 (743 Hz),12 and (MeOC(O)CH2CH2)2SnCl2 (786 Hz).10
Structural Analysis of 1.
The single crystal X-ray diffraction structural analysis of1 resulted in the structure observed in Figure
1.
3

Figure 1. Single crystal X-ray structure of 1, CCDC = 1530370; Selected
bond length in Å; Sn-C5 = 2.139(4); Sn1-C1 = 2.141(4); Sn1-Cl
=2.4652(12); Sn1-Cl2 = 2.4433(12); Sn1-S1 = 2.8945(13); Sn1-S2 =
2.9892(12).
In agreement with the NMR data the Sn center is sufficiently Lewis acidic by virtue of the
two Sn-Cl bonds to result in two important intramolecular Sn-S bonds resulting in a pseudo-
octahedral arrangement at the central Sn, similar to the O analog.8 The Sn-S interactions are cis to
each other and trans to the two Sn-Cl bonds, the same arrangement as noted for the O analog.
The two Sn-S internuclear distances of 2.8945(13) Å and 2.9892(12) Å are 76% and 78% of
the sum of the theoretical van der Waals radii (vdW), respectively. A “regular” single bond is
generally in the region of 60-70% of such radii sums, thus these Sn-S interactions are significant,
and close to that we have reported for Ph(o-MeS-C6H4CH2)SnCl2, 2.2.99Å.7 However, it has
become fashionable to use the Pauling approach to Bond Orders (BO) to assess the relative strength
of the intramolecular interaction in hypervalent main group complexes.13 Using this approach with
the “standard” and accepted value for the Sn-S single bond of 2.40 Å, we calculated the Sn-S bond
orders of 0.20 and 0.15. These BO values compare to 0.16 for the Sn-O bond in the O analog,
4

8
12
(MeOCH2CH2CH2)2SnCl2 ; a Sn-P BO of 0.37 for (Ph2PCH2CH2CH2)2SnCl2 ; and our
recalculated Sn-N BO of 0.40 for (Me2NCH2CH2CH2)2SnCl2.11 By way of comparison, the single
Sn-Cl bonds in 1 represent BO values of 0.71 and 0.78. Whilst the authors are unclear concerning
the validity of using a BO relationship based upon carbon chemistry for assessing the donor
strengths of a heteroatom toward tin in hypervalent systems, it’s common usage provides a basis for
comparison.13 Clearly the intramolecular S-Sn interactions reported herein are at the low end of the strength
scale for such bonding.
We have performed (MN12SX/3Z level) relative free energies calculations on the five
possible geometric isomers of 1, (MeSCH2CH2CH2)2SnCl2, shown in Figure 2.
Figure 2. Geometric isomers of (MeSCH2CH2CH2)2SnCl2, 1, and their abbreviations
The isomers are labeled in terms of cis vs trans positioning for identical atoms, and in molecular mass
order. So isomer cct refers to the case where the heaviest Cl ligand atoms are cis to each other, the
next heaviest S atoms are also cis with respect to each other, and the lowest mass C atoms are trans
to each other. In the process of examining relative energies of the isomers, it was discovered that the
position of the sulfur-bound methyl with respect to the ligand Cl atoms had a sizable energetic impact.
Placing the methyl substituent such that it eclipses a Cl ligand lowers the relative energy by 5–25 kJ
5

mol–1 (for example, see Figure 3). Given this, optimized structures, relative electronic energies
(∆E0K), and relative free energies (∆G298K) of a total of 10 six-coordinate isomers were
computationallyestimated (Table 1).
Figure 3. Conformational options for the S-bound methyl groups, associated abbreviations, and
–1
relative energies (kJ mol MN12SX/3Z) of the cct isomer of 1, (MeSCH CH CH ) SnCl .
,
2
2
2 2
2
Table 1. Relative computed (MN12SX/3Z level) electronic energies ∆E and free energies
0K
∆G
(kJ mol-1 ), and Sn–S distances (Å) of geometric isomers of six-coordinate
1.
298K
∆G298K
Sn–S
∆E0K
0.0
cct eclipsed
cct
0.0
15.1
58.1
75.7
35.6
40.4
26.0
23.0
18.0
26.5
3.1, 3.1
3.1, 3.2
2.8, 2.8
2.8, 2.8
3.0, 3.0
3.3, 4.1
2.9, 2.9
2.9, 2.9
2.8, 2.8
2.8, 2.8
17.1
54.3
71.5
33.6
43.3
22.3
21.9
18.8
24.9
ctc eclipsed
ctc
ccc eclipsed
ccc
tcc eclipsed
tcc
ttt eclipsed
ttt
6

The data recorded in Table 1 shows that the relative electronic and free energies differ
only slightly, so discussion below will involve only ∆G298K values. The crystallographically
observed structure (cct eclipsed) is predicted to be the most stable structure in the gas phase,
15 kJ mol–1 more stable than the non-eclipsed conformer and 18–26 kJ mol–1 more stable
than the next closest geometric isomers (tcc and ttt pairs). It is notable that the isomers
where both the chlorines and carbons are cis (ctc and ccc pairs) are significantly
destabilized compared to the cct eclipsed isomer. The overall ordering cct < ttt < tcc < ccc
< ctc does not provide an obvious interpretation of ligand impact, however, orienting
carbons cis is destabilizing. One also sees that the computational model predicts longer Sn–S
distances than those observed in the crystal structure. This is common, as crystal packing
forces often shrink distances between weakly interacting atoms. This issue was probed for
the cct eclipsed isomer in two ways. First, the potential energy surface (PES) for the Sn–S
interaction was examined using a relaxed scan over the Sn–S distance range 2.7–3.7 Å. The
electronic energy varied from 15 kJ mol–1 at 2.7 Å (the crystallographic value) to 0 kJ mol–1
at 3.1 Å (the gas phase optimized value) to 9 kJ mol–1 at 3.7 Å. The 15 kJ mol–1
difference between the first two is small enough to be countered by packing forces.
Second, we optimized the cct eclipsed isomer using polarized continuum solvent models
(PCM) for CH2Cl2 and water, as models for a solid state environment. In the former case,
the optimized Sn–S distance was 3.0 Å, while in the latter it was 2.9 Å, both smaller than
the 3.1 Å gas phase value. Again this suggests that the Sn–S distance discrepancy between
experiment and theory arises mostly from packing forces in the former.
7

Interaction of 1 with Human Natural Killer Cells.
Previous studies have shown that di-butyltin dichloride (DBT), (CH3CH2CH2CH2)2SnCl2 is
able to significantly decrease the ability of human natural killer (NK) cells to destroy tumor
target cells.3 It is hypothesized that DBT may, in part, exert its inhibitory effects on NK cells by
interacting with molecules essential to their function. Specifically the Sn atom of DBT can
potentially complex with sulfhydryl groups in proteins or other cellular molecules. As noted
above compound 1 possesses significant intramolecular Sn-S interactions that might preclude its
interaction with sulfhydryl containing molecules in the NK cells. If interaction with any such group(s)
is responsible for the inhibitory effects of DBT on NK function, then compound 1 might be expected
to have a less detrimental effect on NK-cell ability to kill tumor target cells. NK cells exposed to
control, DBT, bis-pentyltin dichloride and compound 1 were examined for their ability to kill K562
(myelogenous leukemia cells) using a 51Cr- release assay.3
Figure 4 shows that NK cells exposed to compound 1 at 500 nM for 24 h were able to
kill tumor cells at essentially the same level as control NK cells (70 - 80% of tumor cells were
destroyed). This result was in stark contrast to the tumor-killing capacity ofNK cells exposed to 500 nM
DBT for 24 h. Those NK cells were only able to destroy 18% of tumor targets. This is an
approximately 75% loss in NK tumor-lysing function. Since compound 1 may be somewhat more
hydrophobic than DBT, we also investigated the activity of bis-pentyltin dichloride, which is a
more similar to compound 1 in terms of hydrophobicity. NK cells exposed to bis-pentyltin
dichloride for 24 h lysed 33% of tumor cells. This was a 45% decrease in lytic function as
compared to NK cells treated with control or compound 1. These results are consistent with the
hypothesis that the Sn atom of organotin derivatives may be complexing with sulfhydryl
groups in essential molecules within the NK cell leading to loss of NK lytic function.
8

100
80
60
40
20
0
control
butyl
phenyl methylthiopropyl
Figure 4. Impact of R2SnCl2 (R = butyl, pentyl,
3-methylthiopropyl (1) on HNKC function
Catalytic properties of 1 for acetylation of alcohols.
Organotins are well-established, and utilized, as catalysts for numerous reactions
including, inter alia, trans-esterifications.1,14 Given the results above, we wished to see if the
benign biological activity against NKCs, obtained by virtue of potential hexa-coordinated
structure, would impact the capacity of 1 to be a useful catalyst. Is it possible that the
intramolecular Sn…S interactions could block sites needed for certain aspects of catalysis? We
evaluated 1 as a catalyst for a typical esterification reaction (Table 2) between different
alcohols and excess of acetic anhydride to yield esters, eq 1.
ROH + (CH3CO)2O
ROC(O)CH3
(1)
The same reaction was performed using the “traditional” dibutyltin dichloride, 2, as catalyst at
the same molar concentrations. The transformation with low loadings of the catalyst results
in 100% yield of the ester and indicates that 1 is equally as good a catalyst as 2, Table 2. A
typical product 13C NMR is illustrated Figure 5.
9

Figure 5: 13C NMR of benzyl acetate (purified) from the
reaction of benzyl alcohol and acetic anhydride catalyzed by 1.
Investigation of a typical trans-esterification reaction between benzyl alcohol, BzOH,
and ethylacetate, EtOAc, resulted in an equilibrium between the two esters, BzOAc and
EtOAC, a result equivalent to that using 2 as a catalyst.
Table 2. Acetylation of alcohols catalyzed by (MeSCH2CH2CH2)2SnCl2 catalyst
alcohol
PhCH2OH
CH3CH2OH
(CH3)2CHOH
PhOH
(mol %)
catalyst
0.02
Conditions
RT, 2d
RT, 2d
RT, 2d
RT, 3d
RT, 1d
Yield (%)a
100 (82)
100 (88)
100 (79)
80 (65)
0.02
0.02
0.02
0.02
100 (85)
ClCH2CH2OH
a in the parenthesis, isolated yields
Overall we have demonstrated a high yield synthetic route to produce an organotin
compound that by judicious choice of alkyl substituents to include a potentially tin-bonding
hetero atom, results in biologically inert materials with excellent catalytic functionality.
However, it is well-established that biological systems are very disparate in terms of their
1

interactions with chemical reagents and lack of bioactivity in one area does not automatically
convey to another region. We are expanding these initial studies to garner an in depth
analysis of the compound and the potential of the hypothesis behind its use. However, the
prospect of a “green” organotin reagent is enticing.
Experimental.
Isolation of NK cells
Peripheral blood from healthy adult (male and female) volunteer donors was used for
this study. Buffy coats (source leukocytes) obtained from the American Red Cross (Portland,
OR) or Key Biologics (Memphis, TN) were used to prepare NK cells. Highly purified NK
cells were obtained using a rosetting procedure. Buffy coats were mixed with 0.6 mL of
RosetteSep human NK cell enrichment antibody cocktail (StemCell Technologies,
Vancouver, British Columbia, Canada) per 45 mL of buffy coat. The mixture was incubated
for 25 min at room temperature (~ 25º C). Following the incubation, 7-8 mL of the mixture was
layered onto 4 mL of Ficoll-Hypaque (1.077 g/mL) (MP Biomedicals, Irvine, CA) and
centrifuged at 1200 g for 30-50 min. The cell layer was collected and washed twice with
phosphate buffered saline (PBS) pH 7.2 and stored in complete media (RPMI-1640
supplemented with 10% heat-inactivated BCS, 2 mM L-glutamine and 50 U penicillin G
with 50 µg streptomycin/ml) at 1 million cells/mL. The resulting cell preparation was
>95% CD16+, and CD56+, 0% CD3+ by fluorescence microscopy and flow cytometry.
Cell Viability
Cell viability was determined by trypan blue exclusion. Cell numbers and viability
were assessed at the beginning and end of each exposure period. Viability was determined
at each concentration for each of the exposure periods. The viability of treated cells was
1

compared to that of control cells at each length of exposure.15 Only those concentrations
where viability was unaffected were used at a given length of exposure.
Cytotoxicity assay
The ability of NK cells to lyse tumor cells was measured using a 51Cr release assay.4 The
target cell in all cytotoxicity assays was the NK-susceptible K562 (human chronic
myelogenous leukemia) cell line. K562 cells were incubated with 51Cr (Perkin-Elmer Life
Sciences, Boston,
MA) in 0.2- 0.5 ml of BCS for 1-1.5 h at 37 °C in air/CO2 (19:1). Following this incubation
the target cells were washed twice with cell culture media. NK (effector) cells (1.2x105/100
µL for 12:1 ratio with target cells) were added to the wells of round-bottom microwell
plates. The
effectors were diluted to 6:1 ratio (0.6x105/100 µL) and 3:1 ratio (0.3x105/100 µL); each ratio
was tested in triplicate. Target cells were added (1x104/100µL) to each well of the microwell
plate and the plate was centrifuged at 300 g for 3.5 min and incubated for 2 h at 37 °C (air/CO2
,19:1). After
incubation a 0.1 ml aliquot of the supernatant was collected and counted for radioactivity for 60
sec in a Packard COBRA gamma radiation counter (Packard Instrument Co., Meriden, CT).
Target lysis was calculated as follows: 100 x[(test c.p.m - spontaneous c.p.m.)/maximum
c.p.m.- spontaneous c.p.m.)]. Maximum release was produced by adding 100 µL of 10% Triton
X-100.
Computational Methods
Optimizations and frequency analyses were performed using the Gaussian (G09) suite.16
All molecules/isomers examined were initially optimized without constraints at the M06-
1

2X/BS1 level,17 where BS1 refers to a basis set comprised of the LANL08 basis set on Sn,18
and the 6- 31+G(d,p) basis set on all other atoms. Examination of the optimized structures by
analytical frequency analyses at this level demonstrated that they were minima (no imaginary
frequencies). The analyses also provided zero point energies (ZPEs) and thermal correction
energies that were used to calculate energies reported in Table 1. All structures were then
reoptimized at the MN12SX/3Z level,19 where 3Z refers to a basis set comprised of the SDB-
aug-cc-pVTZ basis seton Sn,20 and the 6-311+G(d,p) basis set on all other atoms. A sizable
integration grid (Gaussian keyword INT(UltraFineGrid)) was used in all cases. Solvent
models employed the standard PCM model in G09 (keyword SCRF).
Synthesis of [MeS(CH2)3]2SnCl2 (1). Approximately 10% of a solution of 3-chloropropyl
methyl sulfide21 (6.0 g, 48.4 mmol) in 15 mL of THF was added to Mg turnings (1.16g, 48.4
mmol), along with 2 drops of bromobenzene as an initiator. The remaining 3-chloropropyl
methyl sulfide
solution was then added dropwise in such a manner as to maintain the reaction mixture at
reflux. The reaction mixture was then heated under reflux for 30 min. After the mixture had
cooled to -50
°C, 1 M solution of SnCl4 in CH2Cl2 (10.7mL, 12.1 mmol) was added dropwise with
vigorous stirring. The reaction mixture was left to warm to room temperature and then heated
under reflux
for 5 h. Water (10 mL) was added and the resulting precipitate was filtered off and washed
with benzene. The THF and benzene solutions were combined and dried with Na2SO4, and the
solvents were removed by rotary evaporation giving 5.45g (95%) of the tetrakis
compound
[MeS(CH2)2]4Sn, which was used for the next step without purification. A mixture of
1

[MeS(CH2)2]4Sn (5.45g, 11.5 mmol) and 1.0 M SnCl4 solution in CH2Cl2 (5.74 mL, 5.74 mmol)
was heated at 200°C for 3 h. The solvent was then removed by distillation and the crude
material was
recrystallized from hot hexanes and cooled to -20°C to yield 1 as a white solid: Yield 1.90
g (90%), mp 138-140°C.
1H NMR (CDCl3) δ 1.11 (4H, t, -CH2Sn-, J = 7.4 Hz), 1.83 (4H, q, -CH2, J = 7.4 Hz), 1.96
(6H,
13
s, -CH3), 2.54 (4H, t, -CH2S-, J = 7.4 Hz); C NMR (CDCl3) δ 15.68 (-CH3), 21.93 (-CH2,
1
2J(13C- 119Sn) = 54 Hz), 34.70 (-CH2Sn, J(13C-119/117Sn) = 763/730 Hz), 37.16 (-CH2S,
3J(13C-
119Sn) = 43 Hz); 119Sn NMR (CDCl3) δ -93.3; Anal. Calcd for C8H18Cl2S2Sn: C, 26.11; H,
493. Found: C, 26.29; H, 5.08.
Acetylation of alcohols catalyzed by 1.
In a typical reaction, a 50-mL Schlenk flask was charged with 5.2 g (0.048 mol) of
benzylalcohol in 10 mL of acetic anhydride and 0.02 mole % of catalyst 1.The reaction mixture
was stirred for 2
d at room temperature. The progress of the reaction was periodically monitored by NMR
spectroscopy. The reaction was quenched with 10 mL with water. The organic layer was
o
washed with 5% NaHCO3 solution and dried over MgSO4 and distilled at 200-206 C to yield
5.8 g (82%) of benzyl acetate.
Trans-esterification reaction catalyzed by 1.
A 25-mL round-bottom flask was charged with 1.0 g (0.0114 mol) of ethylacetate and 5.0
g (0.0462 mol) of benzylalcohol and 0.3 mole % of catalyst 1.The reaction mixture was
refluxed for 40 h. The progress of the reaction was periodically monitored by NMR
1

spectroscopy. After 40 h of refluxing an equilibrium mixture of ethyl acetate and benzyl acetate
was obtained.
Structural analysis.
A specimen of C8H18Cl2S2Sn was used for the X-ray crystallographic analysis. The X-ray
intensity data were measured on a Bruker SMART APEX CCD system equipped with a
graphite monochromator and a MoKα fine-focus tube (λ = 0.71073 Å).
The total exposure time was 10.00 hours. The frames were integrated with the Bruker SAINT
software package using a narrow-frame algorithm. The integration of the data using an
orthorhombic unit cell yielded a total of 15907 reflections to a maximum θ angle of 27.62°
(0.77 Å resolution), of which 3330 were independent (average redundancy 4.777, completeness
= 99.6%, Rint = 1.93%, Rsig = 1.49%) and 3232 (97.06%) were greater than 2σ(F2). The final
cell constants of a = 9.2719(11) Å, b = 11.7256(13) Å, c = 13.2408(15) Å, volume = 1439.5(3)
Å3, are based upon the refinement of the XYZ-centroids of 9908 reflections above 20 σ(I) with
4.640° < 2θ < 55.12°. Data were corrected for absorption effects using the multi-scan method
(SADABS). The ratio of minimum to maximum apparent transmission was 0.903. The
structure was solved and refined using the Bruker SHELXTL Software Package, using the
space group P 21 21 21, with Z = 4 for the formula unit, C8H18Cl2S2Sn. The final anisotropic
full-matrix least-squares refinement on F2 with 122 variables converged at R1 = 2.01%, for the
observed data and wR2 = 5.52% for all data. The goodness-of-fit was 1.021. The largest peak
in the final difference electron density synthesis was 0.457 e-/Å3 and the largest hole was -
0.518 e-/Å3 with an RMS deviation of 0.052 e-/Å3. On the basis of the final model, the
calculated density was 1.698 g/cm3 and F(000), 728 e-.
Acknowledgements: We thank the R. A. Welch Foundation for support of this research via
1

grant AH-0546.
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6
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7
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8
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10
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1

11
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19
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E. Anklam, Synthesis (1987) 841-3.
1

ΔΕ 0K
ΔG 298K
Sn-S
cct eclipsed
cct
0.0
0.0
3.1, 3.1
3.1, 3.2
2.8, 2.8
2.8, 2.8
3.0, 3.0
3.3, 4.1
2.9, 2.9
2.9, 2.9
2.8, 2.8
2.8, 2.8
17.1
54.3
71.5
33.6
43.3
22.3
21.9
18.8
24.9
15.1
58.1
75.7
35.6
40.4
26.0
23.0
18.0
26.5
ctc eclipsed
ctc
ccc eclipsed
ccc
tcc eclipsed
tcc
ttt eclipsed
ttt
1

Synthesis and structural characterization of organotin containing intramolecular secondary Sn-S bonds.
Theoretical calculations confirming structure as the low energy conformation. No biocidal impact upon
human natural killer cells whilst retaining catalytic activity.
1