Synthesis, spectra, crystal structures and anticancer studies of 26-membered macrocyclic dibutyltin(IV) dithiocarbamate complexes: Single-source precursors for tin sulfide nanoparticles

Article abstract of DOI:10.1002/aoc.5089

Four new macrocyclic dinuclear dibutyltin(IV) dithiocarbamate complexes of the type [Bu₂Sn(dtc)]₂, where dtc?=?hexane-1,6-diylbis(4-fluorobenzyldithiocarbamate) anion (1), hexane-1,6-diylbis(4-chlorobenzyldithiocarbamate) anion (2), hexane-1,6-diylbis(furfuryldithiocarbamate) anion (3) and hexane-1,6-diylbis(pyrrole-2-ylmethyldithiocarbamate) anion (4), have been prepared. The dithiocarbamate ligands efficiently self-assemble with Bu₂Sn(IV) to form bimetallic 26-membered macrocycles. All the complexes have been characterized using elemental analysis, infrared and NMR (¹H and ¹³C) spectroscopies and X-ray crystallography. Single-crystal X-ray diffraction analysis of all the complexes confirms the formation of the dinuclear metallomacrocycles in which dithiocarbamate ligands are asymmetrically bound to the tin atoms. The coordination sphere around the tin atom in 1–4 can be described as a skew trapezoidal bipyramid. The dimensions of the cavity of the macrocycles of 1–4 are ca 8.0?×?9.0??². Complexes 1–4 were evaluated for their in vitro anticancer activity against MCF-7 and HL-60 cells. Complexes 1 and 2 are more active against MCF-7 and HL-60. Thermal decomposition of 1 and 4 yielded tin sulfides. They were characterized using powder X-ray diffraction (PXRD), high-resolution transmission electron microscopy and UV diffuse reflectance and energy-dispersive X-ray spectroscopies. PXRD studies reveal that the as-prepared tin sulfides are composed of orthorhombic phase of SnS.

Full text of DOI:10.1002/aoc.5089

Received: 26 December 2018
DOI: 10.1002/aoc.5089
Revised: 29 May 2019
Accepted: 7 June 2019
F U L L P A P E R
Synthesis, spectra, crystal structures and anticancer studies
of 26‐membered macrocyclic dibutyltin(IV) dithiocarbamate
complexes: Single‐source precursors for tin sulfide
nanoparticles
Pandurangan Selvaganapathi1 | Subbiah Thirumaran1
| Samuele Ciattini2
1 Department of Chemistry, Annamalai
Four new macrocyclic dinuclear dibutyltin(IV) dithiocarbamate complexes
University, Annamalinagar 608 002,Tamil
Nadu, India
2 Centro di Cristallografia Strutturale, Polo
Scientifio di Sesto Fiorentino, Via della
Lastruccia 3, 50019 Sesto Fiorentino,
Florence, Italy
of the type [Bu2Sn(dtc)]2, where dtc
=
hexane‐1,6‐diylbis(4‐
hexane‐1,6‐diylbis(4‐
hexane‐1,6‐diylbis
fluorobenzyldithiocarbamate)
chlorobenzyldithiocarbamate)
anion
anion
(1),
(2),
(furfuryldithiocarbamate) anion (3) and hexane‐1,6‐diylbis(pyrrole‐2‐
ylmethyldithiocarbamate) anion (4), have been prepared. The dithiocarbamate
ligands efficiently self‐assemble with Bu2Sn(IV) to form bimetallic 26‐
membered macrocycles. All the complexes have been characterized using ele-
mental analysis, infrared and NMR (1H and 13C) spectroscopies and X‐ray crys-
tallography. Single‐crystal X‐ray diffraction analysis of all the complexes
confirms the formation of the dinuclear metallomacrocycles in which dithiocar-
bamate ligands are asymmetrically bound to the tin atoms. The coordination
sphere around the tin atom in 1–4 can be described as a skew trapezoidal bipyr-
amid. The dimensions of the cavity of the macrocycles of 1–4 are ca 8.0 × 9.0 Å2.
Complexes 1–4 were evaluated for their in vitro anticancer activity against MCF‐
7 and HL‐60 cells. Complexes 1 and 2 are more active against MCF‐7 and HL‐60.
Thermal decomposition of 1 and 4 yielded tin sulfides. They were characterized
using powder X‐ray diffraction (PXRD), high‐resolution transmission electron
microscopy and UV diffuse reflectance and energy‐dispersive X‐ray spectros-
copies. PXRD studies reveal that the as‐prepared tin sulfides are composed of
orthorhombic phase of SnS.
Correspondence
S. Thirumaran, Department of Chemistry,
Annamalai University, Annamalainagar
608 002, Tamil Nadu, India.
Email: sthirumaran@yahoo.com
KEYWORDS
anticancer studies, single‐source precursors, tin(IV) dithiocarbamates, tin sulfide nanoparticles
1 | INTRODUCTION
and coordination geometries.[3–5] Complexes of dithiocar-
bamate ligands have various applications in vulcanization
In recent years coordination compounds containing sulfur
donor ligands have received considerable attention.[1,2]
Among these ligands, dithiocarbamates have attracted
attention owing to their importance in the preparation of
a variety of metal complexes in various oxidation states
accelerators, analysis, radiation protectors and as precur-
sors for the preparation of metal sulfide and metal oxide
nanoparticles.[6–10] Interest in organotin dithiocarbamate
complexes arises because of their variety of structures
and wide range of applications in fields such as agriculture,
Appl Organometal Chem. 2019;e5089.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5089

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SELVAGANAPATHI ET AL.
biology, organic synthesis and catalysis.[11–13] The prod-
ucts obtained from the reaction of organtin(IV) halides
with dithiocarbamates show substantial tendency to gen-
erate self‐assembled supramolecular architectures[14,15]
and can also offer a platform for the formation of
macrocyles[16–18] due to the Lewis acidity of organotin(IV)
chlorides. In terms of crystallographic analyses, the
diorganotin(IV) dithiocarbamates are the best studied
and arguably the most interesting in terms of the observed
structural diversity. These complexes show that there are
four distinct structural motifs.[19–23] Recent studies have
shown very promising in vitro antitumour properties of
organotin compounds against a wide panel of tumour cell
lines of human origin. In some cases, diorganotin(IV)
derivatives have also shown acceptable in vivo antiprolifer-
ative activity as new chemotherapy agents.[13,24,25] In addi-
tion, these complexes have been found to be efficient and
somewhat selective anion and cation receptors.[26–30]
Recently, investigations in the field of photovoltaics have
been directed towards the development of cost‐effective
and non‐toxic materials for solar cell fabrication. Tin
sulfide is one such compound that belongs to the group
IV–VI semiconductors. It has attracted particular
attention as a low‐toxicity solar energy absorber,[31,32] in
halographic recording[33,34] and for infrared detection.[35]
Organotin(IV) dithiocarbamates are widely used as
single‐source precursors for the preparation of tin sulfide
nanomaterials (SnS, SnS2 and SnS3).[36–38] The organic
substituents on the dithiocarbamate ligands play an impor-
tant role in determining the biological activities of the
organotin dithiocarbamate complexes[11,13] and the phase,
size and shape of metal sulfides prepared from such metal
dithiocarbamate complexes.[10,36–38]
in atmospheric air. Melting points were determined using
an electro‐thermal melting point apparatus and are
uncorrected. Microanalysis for carbon, hydrogen and
nitrogen in the synthesized complexes was conducted
with a Vario MICRO V2.2.0 elemental analyser. Fourier
transform infrared (FT‐IR) spectra were recorded with a
PerkinElmer FT‐IR spectrometer. NMR spectra were
recorded with Bruker 400 MHz (1H and 13C) and Bruker
500 MHz (119Sn) spectrometers at room temperature in
CDCl3 as a solvent, using tetramethylsilane as an internal
standard. Thermogravimetric analysis (TGA) was
performed using a NETZSCH 5 thermal instrument. Sam-
ples were heated at a rate of 10°C min−1. Powder X‐ray
diffraction (XRD) patterns were recorded using
an EQUINX 1000. High‐resolution transmission electron
microscopy (HRTEM) images were recorded using a
Jeol JEM2100 (200 keV and LaB6 filament) and energy‐
dispersive X‐ray spectroscopy (EDS) was conducted
using INCA energy software. Diffuse reflectance
spectra were recorded using a JASCO V‐670 UV–visible
spectrophotometer.
2.2 | X‐ray crystallography
Single‐crystal X‐ray diffraction data for complexes 1 and 2
were obtained with an Xcalibur Onyx (Cu Kα radiation
(λ = 1.54184 Å)) diffractometer and those for complexes
3 and 4 with an Xcalibur Sapphire 3 (Mo Kα radiation
(λ = 0.71073 Å)) diffractometer. The structures were
solved and refined by direct method using SHELXL‐
2014/7.[39] Details of the data collection, crystal data and
structure refinement parameters for 1–4 are given in
Table 1.
In consideration of all the above facts, our aim was to
prepare macrocyclic diorganotin(IV) dithiocarbamate
complexes containing various N‐bound organic moieties
(fluorobenzyl, chlorobenzyl, furfuryl and pyrrole) to
study the effect of such organic moieties on anticancer
activity of the complexes and properties of tin sulfide
nanoparticles prepared from the complexes. In this paper,
the preparation, spectral and structural characterization
and anticancer activity of four 26‐membered macrocyclic
diorganotin(IV) bis(dithiocarbamate) complexes are
reported. In addition, tin sulfide nanoparticles were pre-
pared from two of the complexes.
2.3 | Anticancer activity (procedure for
sulforhodamine B (SRB) assay)
Cell lines were grown in RPMI 1640 medium containing
10% foetal bovine serum and 2 mM L‐glutamine. For
screening experiments, cells were inoculated into 96‐well
microtiter plates in 100 μl at plating densities as shown in
the study details above, depending on the doubling time
of individual cell lines. After cell inoculation, the microti-
ter plates were incubated at 37°C, 5% CO2, 95% air and
100% relative humidity for 24 h prior to addition of exper-
imental drugs.
Experimental drugs were initially solubilized in
dimethylsulfoxide at 100 mg ml−1 and diluted to
1 mg ml−1 using water and stored frozen prior to use.
At the time of drug addition, an aliquot of frozen concen-
trate (1 mg ml−1) was thawed and diluted to 100, 200, 400
and 800 μg ml−1 with complete medium containing test
2 | EXPERIMENTAL
2.1 | Materials and methods
All reagents and solvents were used as received without
further purification and all experiments were carried out

SELVAGANAPATHI ET AL.
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SELVAGANAPATHI ET AL.
sample. Aliquots of 10 μl of these different drug dilutions
were added to the appropriate microtiter wells already
containing 90 μl of medium, resulting in the required
final drug concentrations, i.e.10, 20, 40 and 80 μg ml−1
.
After compound addition, plates were incubated at stan-
dard conditions for 48 h and assay was terminated by
the addition of cold TCA. Cells were fixed in situ by the
gentle addition of 50 μl of cold 30% (w/v) TCA (final con-
centration, 10% TCA) and incubated for 60 min at 4°C.
The supernatant was discarded; the plates were washed
five times with tap water and air dried. SRB solution
(50 μl) at 0.4% (w/v) in 1% acetic acid was added to each
of the wells, and plates were incubated for 20 min at
room temperature. After staining, unbound dye was
recovered and the residual dye was removed by washing
five times with 1% acetic acid. The plates were air‐dried.
Bound stain was subsequently eluted with 10 mM trizma
base, and the absorbance was read on a plate reader at a
wavelength of 540 nm with 690 nm reference wavelength.
Percent growth was calculated on a plate‐by‐plate
basis for test wells relative to control wells. Percent
growth was expressed as the ratio of average absorbance
of the test well to the average absorbance of the control
wells × 100. Using the six absorbance measurements
(time zero (Tz), control growth (C) and test growth in
the presence of drug at the four concentration levels
(Ti)), the percentage growth was calculated at each of
the drug concentration levels. Percentage growth inhibi-
tion was calculated as: [Ti/C] × 100%.
2.4 | Preparation of macrocyclic
dibutyltin(IV) dithiocarbamate complexes
2.4.1 | Preparation of N,N′‐disubstituted
hexamethylene‐1,6‐diamines
1,6‐Hexamethylenediamine (4.6 mmol) and two
equivalents of aldehyde (4‐fluorobenzaldehyde, 4‐
chlorobenzaldehyde, furfuraldehyde and pyrrole‐2‐
carboxaldehyde) (10.6 mmol) were dissolved in ethanol
(30 ml) and the reaction mixture was refluxed for 2 h.
After evaporation of the solvent the diimine was obtained
in the form of a yellow liquid. The N,N′‐disubstituted
hexamethylene‐1,6‐diimine was dissolved in methanol
and kept in an ice bath to which a solution of NaBH4
(27.6 mmol) in methanol (30 ml) was added dropwise
with stirring. Stirring was continued for 12 h. After the
removal of the solvent by evaporation, the resulting
viscous liquid was washed with water. The product was
extracted using dichloromethane. Evaporation of dichlo-
romethane afforded N,N′‐disubstituted hexamethylene‐
1,6‐diamine as yellow oil.[18]

SELVAGANAPATHI ET AL.
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(CH2CH2Sn); 34.0 (CH2Sn); 53.9 (CH2N); 56.6
(4FC6H4CH2N); 115.5, 115.7, 129.3, 131.5 (phenyl ring
carbons); 161.2, 163.6 (4F─Ar); 202.1 (NCS2).
2.4.2 | Preparation of bis(μ2‐hexane‐1,6‐
diylbis((4‐fluorobenzyl)
dithiocarbamato)‐κ4S,S′,S″,S″′)tetra‐n‐
butylditin(IV) (1)
N,N′‐Di(4‐fluorobenzyl)hexamethylene‐1,6‐diamine
(4.0 mmol) and two equivalents of triethylamine
(8.0 mmol) were dissolved in ethanol (30 ml) whereupon
an excess of carbon disulfide (12.0 mmol) was added.
After the mixture was stirred for 2 h at room temperature,
a solution of one equivalent of dibutyltin dichloride
(4.0 mmol) in methanol (20 ml) was added giving almost
immediately a white precipitate. The precipitate was
separated by filtration and washed with water (Scheme 1).
Yield: 75%; m.p. 146–148°C. Anal. Calcd for
C60H84F4N4S8Sn2 (%): C, 50.35; H, 5.92; N, 3.91. Found
(%): C, 50.14; H, 5.93; N, 3.87. FT‐IR (cm−1) with KBr
disc: 1478 (νC–N), 981 (νC–S). 1H NMR (400 MHz,
2.4.3 | Preparation of bis(μ2‐hexane‐1,6‐
diylbis((4‐chlorobenzyl)
dithiocarbamato)‐κ4S,S′,S″,S″′)tetra‐n‐
butylditin(IV) (2)
A method similar to that described for the synthesis
of 1 was adopted; however, N,N‐di(4‐chlorobenzyl)
hexamethylene‐1,6‐diamine was used instead of N,N‐
di(4‐fluorobenzyl)hexamethylene‐1,6‐diamine.
Yield:
76%; m.p. 142–144°C. Anal. Calcd for C60H84Cl4N4S8Sn2
(%): C, 48.14; H, 5.66; N, 3.74. Found (%): C, 47.99; H,
5.63; N, 3.72. FT‐IR (cm−1) with KBr disc: 1477 (νC–N),
1
CDCl3, δ, ppm): 0.95 (t, 12H,
J
=
7.6 Hz,
980 (νC–S). H NMR (400 MHz, CDCl3, δ, ppm): 0.95 (t,
CH3CH2CH2CH2Sn); 1.22 (b, 8H, CH2CH2CH2N); 1.39–
1.51 (m, 8H, CH2CH2CH2Sn); 1.68 (b, 8H, CH2CH2N);
1.91–1.99 (m, 8H, CH2CH2Sn); 2.12 (t, 8H, J = 8.8 Hz,
CH2Sn); 3.63 (t, 8H, J = 8.4 Hz, CH2N); 5.14 (s, 8H,
4FC6H4CH2N); 7.00–7.28 (phenyl ring protons). 13C
NMR: 13.9 (CH3CH2CH2CH2Sn); 26.4 (CH2CH2CH2Sn);
12H, J = 7.2 Hz, CH3CH2CH2CH2Sn); 1.23 (b, 8H,
CH2CH2CH2N); 1.44–1.51 (m, 8H, CH2CH2CH2Sn); 1.69
(b, 8H, CH2CH2N); 1.88–1.95 (m, 8H, CH2CH2Sn); 2.11
(t, 8H, J = 5.6 Hz, CH2Sn); 3.63 (t, 8H, J = 8.0 Hz, CH2N);
5.13 (s, 8H, 4ClC6H4CH2N); 7.20–7.36 (phenyl ring pro-
tons). 13C NMR: 14.0 (CH3CH2CH2CH2Sn); 26.4
(CH2CH2CH2Sn); 26.8 (CH2CH2CH2N); 28.6 (CH2CH2N);
29.7 (CH2CH2Sn); 33.9 (CH2Sn); 54.1 (CH2N); 56.7
(4ClC6H4CH2N); 127.6, 127.8, 128.8, 128.9, 133.6, 134.1,
134.3, 135.7 (phenyl ring carbons), 202.3 (NCS2).
26.8
(CH2CH2CH2N);
28.6
(CH2CH2N);
29.7
2.4.4 | Preparation of bis(μ2‐hexane‐1,6‐
diylbis((furfuryl)dithiocarbamato)‐κ4S,S′,S
″,S″′)tetra‐n‐butylditin(IV) (3)
A method similar to that described for the synthesis of 1
was adopted; however, N,N‐di (furfuryl)hexamethylene‐
1,6‐diamine was used instead of N,N‐di(4‐fluorobenzyl)
hexamethylene‐1,6‐diamine. Yield: 79%; m.p. 128–130°C.
Anal. Calcd for C52H80N4O4S8Sn2 (%): C, 47.35; H, 6.11;
N, 4.25. Found (%): C, 47.21; H, 6.07; N, 4.26. FT‐IR
1
(cm−1) with KBr disc: 1473 (νC–N), 980 (νC–S). H NMR
(400 MHz, CDCl3, δ, ppm): 0.92 (t, 12H, J = 7.2 Hz,
CH3CH2CH2CH2Sn); 1.25 (b, 8H, CH2CH2CH2N); 1.41–
1.46 (m, 8H, CH2CH2CH2Sn); 1.66 (b, 8H, CH2CH2N);
1.89–1.95 (m, 8H, CH2CH2Sn); 2.07 (t, 8H, J = 8.0 Hz,
CH2Sn); 3.72 (t, 8H, J = 8.0 Hz, CH2N); 5.07 (s, 8H,
(furfuryl)CH2N); 6.34–7.37 (furyl ring protons). 13C NMR:
13.9 (CH3CH2CH2CH2Sn); 26.5 (CH2CH2CH2Sn); 26.9
(CH2CH2CH2N); 28.6 (CH2CH2N); 29.7 (CH2CH2Sn);
33.8 (CH2Sn); 54.4 (CH2N); 50.3 ((furfuryl)CH2N); 109.6,
110.7, 142.3, 149.3 (furyl ring carbons); 201.6 (NCS2).
SCHEME
complexes 1–4
1
Preparation of dibutyltin(IV) dithiocarbamate

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SELVAGANAPATHI ET AL.
ligands in 1–4 gave bands at positions intermediate
between those of a single and a double bond (1473–
1482 cm−1), which can be attributed to the delocalization
of π‐electron density within the NCS2 group of atoms.[40]
In the spectra of the investigated complexes, the vibra-
tional modes of CS2 are of particular interest to differen-
tiate between monodentate and bidentate coordination
of the dithiocarbamate moiety. A single band which
appeared around 980 cm−1 for complexes 1–4 corre-
sponds to vC–S vibration and indicates bidentate coordina-
tion mode of the dithiocarbamate moiety through the two
S donor atoms.[41]
2.4.5 | Preparation of bis(μ2‐hexane‐1,6‐
diylbis((pyrrole‐2‐ylmethyl)
dithiocarbamato)‐κ4S,S′,S″,S″′)tetra‐n‐
butylditin(IV) (4)
A method similar to that described for the synthesis of 1
was adopted; however, N,N‐di(pyrrole‐2‐ylmethyl)
hexamethylene‐1,6‐diamine was used instead of N,N‐
di(4‐fluorobenzyl)hexamethylene‐1,6‐diamine.
Yield:
73%; m.p. 148–150°C. Anal. Calcd for C52H84N8S8Sn2
(%): C, 47.49; H, 6.44; N, 8.52. Found (%): C, 47.38; H,
6.44; N, 8.50. FT‐IR (cm−1) with KBr disc: 1482 (νC–N),
1
977 (νC–S). H NMR (400 MHz, CDCl3, δ, ppm): 0.95 (t,
The 1H NMR spectra for the Bu4Sn2L2 (L = dithiocarba-
mate ligand) macrocycle show both L2− units to be mag-
netically equivalent; moreover, the two halves in each
L2− are also equivalent, showing one set of signals for
12H, J = 7.6 Hz, CH3CH2CH2CH2Sn); 1.27 (b, 8H,
CH2CH2CH2N); 1.44–1.49 (m, 8H, CH2CH2CH2Sn); 1.70
(b, 8H, CH2CH2N); 1.89–1.96 (m, 8H, CH2CH2Sn); 2.11
(t, 8H, J = 9.2 Hz, CH2Sn); 3.65 (t, 8H, J = 8.4 Hz,
CH2N); 4.98 (s, 8H, (pyrrole)CH2N); 6.10–6.76 (pyrrole
ring protons); 9.40 (s, 4H, pyrrole NH). 13C NMR: 13.9
(CH3CH2CH2CH2Sn); 26.4 (CH2CH2CH2Sn); 26.9
(CH2CH2CH2N); 27.0 (CH2CH2N); 28.6 (CH2CH2Sn);
33.5 (CH2Sn); 54.2 (CH2N); 50.9 ((pyrrole)CH2N); 107.5,
108.8, 118.7, 126.9 (pyrrole ring carbons); 200.7 (NCS2).
1
one‐fourth of the complex. The H NMR spectra of all
four complexes exhibit a triplet and a singlet in the ranges
3.63–3.72 and 4.98–5.14 ppm for NCH2 of hexamethylene
group and another NCH2 group attached to the aromatic
ring, respectively. Two broad signals observed around
1.25 and 1.68 ppm are assigned to CH2CH2CH2N and
CH2CH2CH2N, respectively. The methylene group
attached to tin atom shows a triplet at around 2.10 ppm.
Another triplet observed at around 0.95 ppm and two
multiplets in the ranges 1.39–1.51 and 1.89–1.99 ppm
are due to methyl protons and the remaining two methy-
lene protons of butyl group, respectively. Aromatic pro-
tons exhibit signals in the region 6.10–7.37 ppm. In the
case of 4, NH proton of pyrrole group appeared at
9.40 ppm.
2.5 | Preparation of tin sulfide
nanoparticles
Tin sulfide nanoparticles obtained from complexes 1 and
4 are represented by SnS‐1 and SnS‐2.
In the 13C NMR spectra, the assignment of the 13C sig-
nal for CS2 group in all the complexes is quite straightfor-
ward and is observed in the range 200.7–202.3 ppm
indicating the coordination of sulfur atoms with the tin
atom.[42,43] The methylene carbon attached to the tin
atom gave signals in the range 33.5–34.0 ppm. The com-
plexes exhibit 13C NMR signals for NCH2 carbon attached
to aromatic ring at 56.6, 56.7, 50.3 and 50.9 ppm for 1–4,
respectively, while the NCH2 carbons bound to the
hexamethylene chain are found to resonate at around
54.0 ppm. Signals of the butyl carbon atoms appeared at
around 13.9, 26.4, 29.0 and 34.0 ppm. The signals
observed in the region 107.5–163.6 ppm are assigned to
the aromatic carbons.
In order to study the coordination environment
around tin in solution, 119Sn NMR spectra for complexes
1 and 2 were recorded in CDCl3 solution at room temper-
ature. For 1 and 2, 119Sn chemical shifts appeared at
−332.3 and −331.9 ppm, respectively. As reported previ-
ously, four‐, five‐ and six‐coordinated tin compounds
have 119Sn chemical shifts in the ranges +200 to
−60 ppm, −90 to −190 ppm and −210 to −400 ppm,
2.5.1 | Preparation of SnS‐1
An amount of 1.5 g of complex 1 was placed in a muffle
furnace at 330°C for 30 min in the presence of air atmo-
sphere. The final residue was analysed to SnS‐1.
2.5.2 | Preparation of SnS‐2
An amount of 1.5 g of complex 4 was placed in a muffle
furnace at 250°C for 30 min in the presence of air atmo-
sphere. The final residue was analysed to SnS‐2.
3 | RESULTS AND DISCUSSION
3.1 | Spectral studies and TGA
FT‐IR and NMR (H1, 13C and 119Sn) spectra of complexes
1–4 are shown in Figures S1–S14. The FT‐IR spectra of
complexes 1–4 exhibit bands characteristic for tin‐
coordinated dithiocarbamate group. The vibrations for
the N─C (thioureide) bonds of the dithiocarbamate

SELVAGANAPATHI ET AL.
7 of 14
respectively.[44] Therefore, 119Sn chemical shifts of 1
(−332.3 ppm) and 2 (−331.9 ppm) show that Sn atoms
in complexes 1 and 2 are hexa‐coordinated.
Thermal decomposition of complex 1 was studied using
TGA. The overlapped TG/DTG curves are shown in
Figure 1. Two‐step decomposition in the ranges 240–325
and 420–560°C was observed. The first decomposition step
occurred with weight loss of 65.3%. This weight loss corre-
sponds to the decomposition of the organic moiety in the
complexes and the formation of metal thiocyanate interme-
diate (% of residue: expt. 34.7 and calcd 32.0%). This inter-
mediate decomposed in the range 420–560°C. The final
residue is 19.6% which is in good agreement with calculated
value of 20.5% for SnS. TGA studies of similar [Bu2Sn(dtc)2]
were carried out under air and nitrogen atmosphere. In
these cases also, the final residue is SnS.[45–47]
FIGURE 1 TG and DTC curves of 1
FIGURE 2 ORTEP diagrams of 1–4

8 of 14
SELVAGANAPATHI ET AL.
a monodentate fashion. Several organotin complexes con-
taining one or more dithiocarbamates are known which
reveal that these ligands are rarely symmetrically bound to
the tin.[42,43] In these complexes one sulfur atom of each
dithiocarbamate forms a normal covalent bond with Sn
(Sn–S = 2.4911(10)–2.5317(16) Å). The distances between
the Sn atom and the other sulfur atoms of dithiocarbamate
ligands are in the range 2.985(1)–3.138(1) Å, which are lon-
ger than the covalently bonded Sn–S distance and signifi-
cantly less than the sum of van der Waals radii of
3.2 | Single‐crystal X‐ray structural
analysis of 1–4
ORTEP diagrams of 1–4 with numbering scheme are shown
in Figure 2. Selected bond lengths and bond angles are
given in Table 2. Complexes 1–4 have dinuclear 26‐
membered macrocyclic structures and display symmetry,
each being disposed about a crystallographic centre of
inversion. As can be seen from the structures (Figure 2),
the dithiocarbamate ligands bind to the metal primarily in
TABLE 2 Selected bond distances and bond angles for 1–4
1
2
3
4
Bond distance (Å)
Bond distance (Å)
Bond distance (Å)
Bond distance (Å)
XRD
XRD
XRD
XRD
Sn1–C12
Sn1–C16
Sn1–S2
2.146(7)
2.159(7)
2.5156(18)
2.5265(18)
2.933(2)
2.962(2)
1.705(7)
1.750(7)
1.760(7)
1.700(7)
1.318(9)
1.322(9)
Sn1–C27
Sn1–C23
S1–Sn1
2.153(7)
2.162(7)
2.943(2)
2.5181(17)
2.9199(18)
2.5317(16)
1.703(6)
1.738(7)
1.699(6)
1.744(6)
1.349(9)
1.330(8)
Sn1–C19
Sn1–C23
Sn1–S1
1.972(13)
2.256(8)
2.4911(10)
2.936(2)
2.5041(13)
3.138(1)
1.739(4)
1.682(4)
1.736(4)
1.693(4)
1.339(5)
1.344(5)
Sn1–C19
Sn1–C23
Sn1–S1
2.141(3)
2.143(3)
2.5203(6)
2.9854(7)
2.5210(6)
3.0473(7)
1.742(2)
1.696(2)
1.735(2)
1.709(2)
1.337(3)
1.339(3)
Sn1–S3
Sn1–S2
Sn1–S2
Sn1–S2
Sn1–S1
Sn1–S3
Sn1–S3
Sn1–S3
Sn1–S4
Sn1–S4
Sn1–S4
Sn1–S4
S1–C8
S1–C1
S1–C1
S1–C1
S2–C8
S2–C1
S2–C1
S2–C1
S3–C20
S4–C20
N1–C8
S3–C15
S3–C13
S3–C13
S4–C15
S4–C13
S4–C13
N1–C1
N1–C1
N3–C13
N1–C1
N2–C20
Bond angle (°)
N2–C15
Bond angle (°)
N2–C13
Bond angle (°)
Bond angle (°)
C12–Sn1–C16
C12–Sn1–S2
C16–Sn1–S2
C12–Sn1–S3
C16–Sn1–S3
S2–Sn1–S3
S1–Sn1–S2
S3–Sn1–S4
S1–C8–S2
137.9(3)
105.9(2)
104.6(2)
109.9(2)
102.1(2)
83.06(6)
65.66(6)
65.21(6)
118.8(4)
118.9(4)
123.8(5)
117.4(5)
123.4(5)
117.7(5)
C27–Sn1–C23
C27–Sn1–S2
C23–Sn1–S2
C27–Sn1–S4
C23–Sn1–S4
C27–Sn1–S3
C23–Sn1–S3
S2–Sn1–S3
S4–Sn1–S3
S2–Sn1–S1
S2–Sn1–S4
S1–C1–S2
142.0(3)
107.1(2)
103.1(2)
102.19(19)
103.3(2)
81.7(2)
C19A–Sn1–C23A
C19A–Sn1–S1
C23A–Sn1–S1
C19A–Sn1S1
C23A–Sn1–S3
S2–Sn1–S1
134.2(5)
113.5(4)
104.6(2)
100.6(2)
96.4(2)
C19–Sn1–C23
C19–Sn1–S1
C23–Sn1–S1
C19–Sn1–S3
C23–Sn1–S3
S1–Sn1–S3
S3–Sn1–S4
S2–Sn1–S1
S2–C1–S1
136.91(10)
109.18(7)
103.92(8)
106.41(8)
104.35(7)
82.85(2)
65.21(4)
62.53(3)
80.89(4)
119.0(2)
120.5(2)
123.9(3)
117.1(3)
124.1(3)
115.4(3)
83.6(2)
S3–Sn1–S4
64.12(2)
149.97(5)
65.74(5)
65.62(5)
84.25(5)
120.0(4)
119.7(4)
122.2(5)
117.8(5)
117.5(5)
122.8(5)
S1–Sn1–S3
64.65(2)
S2–C1–S1
119.53(14)
120.47(14)
122.29(18)
118.16(17)
121.77(18)
117.76(17)
S4–C20–S3
N1–C8–S1
S4–C13–S3
S4–C13–S3
N1–C1–S2
N1–C1–S2
N1–C8–S2
N1–C1–S1
N1–C1–S1
N2–C20–S4
N2–C20–S3
S3–C15–S4
N1–C1–S1
N2–C13–S4
N2–C13–S3
N3–C13–S4
N3–C13–S3
N1–C1–S2
N2–C15–S4
N2–C15–S3

SELVAGANAPATHI ET AL.
9 of 14
3.97 Å.[48] The Sn–C bonds (Sn–C = 2.141(3)–2.162(7) Å)
are well within the usually observed Sn–C distances in
organotin compounds. The coordination sphere around
the tin atoms in these complexes can be described as a
slightly distorted tetrahedron. However, if the two long
Sn–S bonds are taken into account, tin atoms have skewed
trapezoidal bipyramidal coordination environments. The
four sulfur atoms constitute a trapezoid and the two carbon
atoms of butyl occupy the axial positions to complete the
six‐coordination of the tin atom. The effective cavity size
of 1–4 is ca 8.0 × 9.0 Å2 (Figure 3). The length of the C–S
bond is inversely correlated with the Sn–S bond; thus short
S–C bonds (C–S = 1.682(4)–1.709(2) Å) and long S–C bonds
(C–S = 1.735(2)–1.760(7) Å) correlate with long and short
Sn–S bonds, respectively. All C–S bond lengths are signifi-
cantly shorter than the C–S single bond (ca 1.81 Å) due to
π‐delocalization over the NCS2 units.[19–23] Within the
dithiocarbamate function, the C–Ndtc bond lengths in the
range 1.318(9)–1.349(9) Å indicate a substantial delocaliza-
tion of π‐electron density in this bond.[14–18]
The crystal structure of 1 is further stabilized through
two C–H⋅⋅⋅F interactions (Figure 4). Intramolecular weak
C–H⋅⋅⋅S interactions are present in this compound which
can be seen in Figure S15. Complex 2 is stabilized by C–
H⋅⋅⋅Cl intermolecular interactions with H⋅⋅⋅Cl = 2.827 Å,
which gives rise to a supramolecular network in the solid
state (Figure 5). The supramolecular structure is further
stabilized by C–H⋅⋅⋅S interactions (Figure S16). Complex
FIGURE 3 Space filling model of (a) 1 and (b) 2 showing the macrocyclic cavity
FIGURE 4 Intermolecular C–H…F
interactions in 1
FIGURE 5 Intermolecular C–H…Cl interactions in 2

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SELVAGANAPATHI ET AL.
TABLE 3 Geometric details of hydrogen bonding (Å, °) in complexes 1–4
Interaction
D–H
H···A
D···A
D–H···A
Interaction
D–H
H···A
D···A
D–H···A
1
3
C19–H19C…F2a
C27–H27…F2a
C7–H7A…S1b
C9–H9A…S2b
C21–H21B…S3b
C24–H24B…S4b
2
C29–H29A…Cla
C9–H9A…S3a
C2–H2A…S1b
C9–H9A…S2b
C16–H16A…S3b
C14–H14A…S4b
0.96
0.93
0.97
0.97
0.97
0.97
2.607
2.587
2.540
2.498
2.562
2.583
3.529
3.463
3.060
2.963
2.946
3.081
160.77
157.07
113.50
109.23
103.70
111.97
C7–H7A…S1a
C2–H2A…S2a
C12–H12A…S3a
C14–H14B…S4a
0.97
0.97
0.97
0.97
2.565
2.526
2.480
2.541
4
2.936
3.042
2.901
3.075
102.78
113.27
105.88
114.65
C23–H23B…S2a
C7–H7A…S1b
C2–H2B…S2b
C12–H12A…S3b
C14–H14A…S4b
0.84
0.93
0.95
0.96
1.01
2.994
2.558
2.640
2.484
2.598
3.396
2.971
3.031
2.953
3.017
111.82
107.58
105.33
109.94
104.57
0.97
0.97
0.97
0.97
0.97
0.97
2.827
2.859
2.518
2.506
2.568
2.588
3.644
3.544
3.031
2.938
3.038
2.969
142.59
128.53
112.93
106.98
109.86
103.58
aIntermolecular C–H…S interaction.
bIntramolecular C–H…S interaction.
2 has four more intramolecular C–H⋅⋅⋅S interactions
(Figure S17). In complex 3, there are no significant inter-
molecular interactions. However, intramolecular C–H⋅⋅⋅S
interactions are observed (Figure S18; Table 3). The
neighbouring molecules are linked by intermolecular C–
H⋅⋅⋅S interactions between H23B (methylene proton of
butyl group) and S2 atom, generating a linear chain.
These interactions also form a 12‐membered macrocyclic
ring (Figure 6). All the S atoms of CS2 group are involved
in the formation of intramolecular C–H⋅⋅⋅S bonds with H
atoms of methylene groups adjacent to N atom of dithio-
carbamate ligand (Figure S19; Table 3).
produces 50% inhibition of cells), TGI (concentration of
drug that produces total inhibition of cells) and LC50
(median lethal concentration) using SRB assay. The growth
rate curves are shown in Figure 7. The observed results
revealed that complexes 1 and 2 show pronounced GI50
values <10 μg ml−1 towards both the tested cell lines
(Table S1). Complex
3
shows lower activity
(GI50 > 80 μg ml−1) against both cell lines than the other
complexes, while complex 4 reveals moderate activity
against MCF‐7 and better activity against HL‐60.
3.4 | Characterization of tin sulfide
nanoparticles
3.3 | Anticancer activity
Figure 8 shows the XRD patterns of SnS‐1 and SnS‐2 pre-
pared by thermal decomposition of complexes 1 and 4,
respectively. The XRD patterns exhibit multiple intense
peaks that are clearly distinguishable. The diffraction
The in vitro anticancer activity of complexes 1–4 was
analysed against MCF‐7 and HL‐60 cells and was
evaluated in terms of GI50 (concentration of drug that
FIGURE 6 Intermolecular C–H…S interactions in 4

SELVAGANAPATHI ET AL.
11 of 14
FIGURE 7 Growth curve showing control growth versus drug concentration against MCF‐7 and HL‐60 cell lines
FIGURE 8 Powder XRD patterns of (a)
SnS‐1 and (b) SnS‐2
peaks for both samples are indexed and assigned to SnS of
orthorhombic structure with lattice parameters
a = 0.4328 nm, b = 0.1119 nm and c = 0.3978 nm (JCPDS
39‐0354; herzenbergite). The diffraction peaks at 22.43°,
26.38°, 27.89°, 32.24°, 39.77°, 42.77°, 45.40°, 46.35°,
49.18°, 51.26°, 54.08°, 57.47°, 65.01° and 67.28° corre-
spond to the (1 1 0), (1 2 0), (0 2 1), (1 1 1), (1 3 1),
(2 1 0), (1 4 1), (0 0 2), (2 2 1), (1 5 1), (1 2 2), (0 4 2),
(2 5 1) and (0 8 1) planes of orthorhombic SnS. In the
XRD patterns of both samples, no characteristic peaks
was observed for other phases of SnS and impurities such
as Sn metal and SnS2, which indicates that the products
are single‐phase SnS. HRTEM images of SnS‐1 and SnS‐
2 are displayed in Figure 9. SnS‐1 and SnS‐2 samples
are composed of large numbers of spherical particles with
an average size of ca 5 and ca 2 nm, respectively. The
HRTEM image of SnS‐1 (Figure 9(b)) exhibits well‐
defined lattice fringes with a lattice spacing of 0.28 nm,
which corresponds to the (1 1 1) plane of orthorhombic
SnS. The selected area electron diffraction spots
(Figure 9) of both SnS‐1 and SnS‐2 indicate the crystalline
nature of as‐prepared SnS nanoparticles.
The formation of SnS was confirmed using EDS analy-
sis. The EDS spectra of SnS‐1 and SnS‐2 are displayed in
Figure S20. The EDS analysis of both the samples con-
firms the presence of Sn and S in the products. The
atomic ratio of Sn and S for SnS‐1 (1.0:1.2) and SnS‐2
(1.0:1.1) shows that there are some vacancies of Sn2+
ion positions or some sulfur dangling bonds are present
in SnS‐1 and SnS‐2.
The Kubelka–Munk method based on diffuse reflec-
tance spectra was employed to determine the band
gaps of the samples. Plots of ( F(R)hv)2 versus photon
energy (hv) are shown in Figure 10. The optical band gaps
of the SnS‐1 and SnS‐2 nanoparticles were estimated from
the intercept of the straight part of the curves with the x‐
axis. The band gap energy values for SnS‐1 and SnS‐2 are
3.5 and 2.2 eV, which are higher compared to the bulk

12 of 14
SELVAGANAPATHI ET AL.
FIGURE 9 HRTEM images and selected area electron diffraction patterns (insets) of SnS‐1 and SnS‐2
FIGURE 10 UV diffuse reflectance spectra of (a) SnS‐1 and (b) SnS‐2
SnS band gap (1.3 eV).[49] This indicates quantum confine-
ment effects in the nanoparticles, i.e. when the electron–
hole pair is squeezed below the dimensions approaching
the exciton Bohr radius.
trapezoidal bipyramid. The anticancer activity of 1–4
decreases in the following order:1 ≈ 2 > 4 > 3. Complexes
1 and 3 were used as single‐source precursors for the
preparation of SnS. Anticancer studies of complexes 1–4
showed that 1 and 2 exhibit better anticancer activity
than 3 and 4. This indicates that the halogen‐containing
nitrogen‐bound organic moiety present in dithiocarba-
mate ligands increases the anticancer activity of 1 and 2.
This study shows that increasing the number of halogen
atoms on organic moiety of dithiocarbamate may increase
the anticancer activity of the complexes. The thermal
decomposition of complexes 1 and 3 yielded spherical
3.5 | CONCLUSIONS
Four dinuclear macrocyclic complexes, [Bu2Sn(dtc)]2,
have been synthesized. The structures of 1–4 were
determined by single‐crystal X‐ray crystallography. The
coordination geometry about the tin atom is skew

SELVAGANAPATHI ET AL.
13 of 14
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tin sulfide nanoparticles. The size of tin sulfide nanopar-
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ence in band gap between SnS‐1 and SnS‐2 is 1.3 eV.
These results indicate that various sizes of tin sulfides
with different band gap energy can be prepared using
tin dithiocarbamate complexes.
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5328
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How to cite this article: Selvaganapathi P,
Thirumaran S, Ciattini S. Synthesis, spectra, crystal
structures and anticancer studies of 26‐membered
macrocyclic dibutyltin(IV) dithiocarbamate
complexes: Single‐source precursors for tin sulfide
nanoparticles. Appl Organometal Chem. 2019;e5089.
https://doi.org/10.1002/aoc.5089
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