Structural properties and antibacterial potency of new supramolecular organotin(IV) dithiocarboxylates

Article abstract of DOI:10.1016/j.poly.2011.10.025

A series of new organotin(IV) derivatives; Me₃SnL (1), Bu ₃SnL (2), Ph₃SnL (3), Me₂SnClL (4), Bu ₂SnClL (5), Ph₂SnClL (6), Et₂SnClL (7) and Et₂SnL₂ (8) where L = N-(2,3-dimethylphenyl)piperazine-1- carbodithioate have been synthesized and characterized by various analytical techniques. Among these techniques, ¹H and ¹³C NMR were carried out to asses solution structures whereas the solid state structures were confirmed by FT-IR and X-ray single crystal analysis (3, 5 and 8). Crystal structure of complex (3) and (5) showed distorted trigonal bipyramidal geometry and square pyramidal geometry, respectively. The inclination of the structure 5 towards square-pyramidal may be due to the presence of the Sn-Cl...HN- piperazine hydrogen bonds between the adjacent molecules. A supramolecular structure is shown by compound (8), with central tin atom exists in a distorted octahedral geometry. The antibacterial results indicated the profound activity of the compounds against various strains of bacteria. In addition to this, the triorganotin(IV) derivatives were found more active than diorganotin(IV) compounds.

Full text of DOI:10.1016/j.poly.2011.10.025

Polyhedron 31 (2012) 697–703
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Structural properties and antibacterial potency of new supramolecular
organotin(IV) dithiocarboxylates
a,
b
Farzana Shaheen a, Zia-ur-Rehman a, , Saqib Ali , Auke Meetsma
⇑
⇑
a Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan
b Crystal Structure Center, Chemical Physics, Zernike, Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747 AG Groningen, The Netherlands
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new organotin(IV) derivatives; Me3SnL (1), Bu3SnL (2), Ph3SnL (3), Me2SnClL (4), Bu2SnClL (5),
Ph2SnClL (6), Et2SnClL (7) and Et2SnL2 (8) where L = N-(2,3-dimethylphenyl)piperazine-1-carbodithioate
have been synthesized and characterized by various analytical techniques. Among these techniques, 1H
and 13C NMR were carried out to asses solution structures whereas the solid state structures were con-
firmed by FT-IR and X-ray single crystal analysis (3, 5 and 8). Crystal structure of complex (3) and (5)
showed distorted trigonal bipyramidal geometry and square pyramidal geometry, respectively. The incli-
nation of the structure 5 towards square-pyramidal may be due to the presence of the Sn–Clꢀ ꢀ ꢀHN-piper-
azine hydrogen bonds between the adjacent molecules. A supramolecular structure is shown by
compound (8), with central tin atom exists in a distorted octahedral geometry. The antibacterial results
indicated the profound activity of the compounds against various strains of bacteria. In addition to this,
the triorganotin(IV) derivatives were found more active than diorganotin(IV) compounds.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 29 September 2011
Accepted 24 October 2011
Available online 4 November 2011
Keywords:
Organotin(IV)
Dithiocarboxylate
NMR
X-ray
Antibacterial
1. Introduction
with the amino acids, proteins, nucleosides, carbohydrates and ste-
roids present in the cell membrane [9,10]. Another proposition re-
The coordination chemistry of sulfur-donor ligands is an area of
focusing due to their close resemblance with biomolecules like
amino acids (e.g. methionine, cysteine), peptides such as glutathi-
one, proteins, enzymes and vitamins [1]. Among the various
organosulfur systems, dithiocarboxylates and their metal com-
plexes owe special significance due to their use as catalysts, in
the rubber industry and in pesticides [2]. Antitumor and antiviral
activities have been reported for pyrrolidine dithiocarboxylates
salts [3]. Diethyldithiocarboxylate salts have been investigated
for possible application in chronic alcoholic therapy [4] and treat-
ment of HIV-patients [5]. Organotin(IV) dithiocarboxylates con-
tinue to attract significant attention because of their broad
spectrum of biological applications as fungicides, bactericides,
insecticides and antitumor agents [6]. Although number of efforts
has been made to explore the mechanism of the biological action
of organotin derivatives yet none of them is up to the mark. One
group believed that the release of K+ from cells, resulting from in-
creased cytoplasmic membrane permeability, shows the cytoplas-
mic membrane to be a possible site of action [7]. The crossing of
the cytoplasmic membrane by organotin derivatives might be a
consequence of lipid-solubility [8] affected by weak interactions
lates to the redox potential (0.154 V) for the conversion of Sn(IV) to
Sn(II) that lies within the physiological range found for several en-
zyme reactions, thus suggesting that enzymatic processes might be
involved in the biological activity of organotin compounds [11].
Our group recently reported with experimental evidences that bio-
logical action of the organotin is owing to their intercalative and
electrostatic interaction with DNA [12,13]. In order to fortify this
idea and keeping in view the antimicrobial potential of organotins,
we synthesized eight organotin(IV) N-(2,3-dimethylphenyl)pipera-
zine-1-carbodithioates having the capability of forming secondary
interactions with cell constituents (see packing diagrams). These
compounds proved to be effective antibacterial agents. This study
will be helpful in designing new organotins of pharmaceutical
value.
2. Experimental
2.1. Materials and methods
All the chemicals used in synthetic work were of high purity.
Analytical grade organotin(IV) chlorides were purchased from Al-
drich and Fluka chemical company. CS2 was obtained from Rei-
del-de-Haën. Various solvents such as chloroform, methanol,
toluene, n-hexane, ethanol, acetone and DMSO of analytical grade
⇑
Corresponding authors. Tel.: +92 051 90642245; fax: +92 051 90642241
(Zia-ur-Rehman), tel.: +92 051 90642130; fax: +92 051 90642241 (S. Ali).
E-mail addresses: hafizqau@yahoo.com ( Zia-ur-Rehman), drsa54@yahoo.com
(S. Ali).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.10.025

698
F. Shaheen et al. / Polyhedron 31 (2012) 697–703
were purchased from E-Merk and Fluka. Solvents were dried by
standard procedures [14].
Melting points were determined in capillary tube using electro-
thermal melting point apparatus model MP-D Mitamura Riken Ko-
gyo (Japan) and are uncorrected. Elemental analysis was done
using a Leco CHNS 932 apparatus. Infrared spectra were recorded
as KBr disks on Perkin Elmer spectrum 1000 (USA) in range of
4000–250 cmꢁ1 1H NMR and 13C NMR were recorded on Bruker
.
AC 300 MHFT-NMR in chloroform.
The X-ray diffraction data were collected on a Bruker SMART
APEX CCD diffractometer, equipped with a 4 K CCD detector. Data
integration and global cell refinement was performed with the pro-
gram SAINT. The program suite SAINTPLUS was used for space group
determination (XPREP). The structure was solved by Patterson
method; extension of the model was accomplished by direct meth-
od and applied to different structure factors using the program DIR-
DIF. All refinement calculations and graphics were performed with
the program PLUTO and PLATON package [15]. The hydrogen atoms
were generated by geometrical considerations, constrained to ide-
alized geometries, and allowed to ride on the carrier atoms with an
isotropic displacement parameter related to the equivalent dis-
placement parameter of their carrier atoms, with Uiso(-
H) = 1.2Ueq(C) or 1.5Ueq(methyl C). The methyl-groups were
refined as rigid groups, which were allowed to rotate freely. As-
signed values of bond distances: secondary C–H2 = 0.99 Å, methyl
C–H3 = 0.98 Å and aromatic C–H = 0.95 Å.
Scheme 1. Numbering scheme of ligand-salt and organic groups.
7.8 g, 82%. M.p. 182–185 °C. Anal. Calc. for C25H36N4S2: C, 65.75; H,
7.95; N, 12.27; S, 14.04. Found: C, 65.05; H, 8.16; N, 12.23; S,
13.92%. FT-IR (cmꢁ1): 1014
m
(C–S), 1458
m
(C–N). 1H NMR (ppm):
2.30 (s, H11,11a), 2.24 (s, H10,10a), 7.28–7.12 (m, H7,7a,
5,5a),
6,6a,
4.69–4.63, 3.22–3.19 (m, H3,3,
3a), 2.97–2.94, 2.31–2.24 (m,
3a,
H2,2,
2a), 8.46 (s, NH). 13C NMR (ppm): 213.6 (C-1), 49.9, 45.0
2a,
(C-2,20), 52.4, 51.2 (C-3,30, 3a, 30a), 151.6, 150.8, 138.0, 137.7,
131.1, 131.0, 126.3, 126.2, 125.8, 125.2, 117.3, 117.0 (Ar-C), 14.1
(C-10,10a), 20.7 (C-11,11a).
2.2.2. General procedure for synthesis of complexes
Triorganotin chloride or diorganotin dichloride and ligand salt
were added to dry toluene in appropriate molar ratio. The mixture
was allowed to reflux for 6–7 h with constant stirring. Soluble
product was isolated by filtration and the solvent was rotary evap-
orated to get the desired product, which was then recrystallized
from methanol chloroform mixture (Scheme 2). The numbering
scheme of ligand-salt and organic groups is given in Scheme 1.
2.2. Synthesis
2.2.1. Synthesis of N-(2,3-dimethylphenyl)piperazinium N-(2,3-
dimethylphenyl) piperazine-1-carbodithioic acid (L-salt)
Insertion method was utilized for the synthesis of ligand. About
1.32 mL (0.02 mol) of CS2 was added drop wise to a solution of N-
(2,3-dimethylphenyl)piperazine (0.04 mol) in dry methanol. The
reaction mixture was stirred for 4 h. Temperature was maintained
at 273 K to avoid any possible decomposition. The white precipi-
tates obtained were filtered and washed with diethyl ether. Yield:
2.2.3. Synthesis of trimethylstannyl N-(2,3-
dimethylphenyl)piperazine-1-carbodithioate (1)
Yield: 0.51 g, 68%. M.p. 111–113 °C. Anal. Calc. for
C
16H26N2S2Sn: C, 44.77; H, 6.11; N, 6.53; S, 14.94. Found: C,
Scheme 2. Synthesis of ligand-salt and their organotin(IV) compounds.

F. Shaheen et al. / Polyhedron 31 (2012) 697–703
699
45.71; H, 6.48; N, 6.47; S, 14.06%. FT-IR (cmꢁ1): 995
(CS2)asym, 1460 (C–N), 368 (Sn–S), 468
m
(CS2)sym, 1108
2.2.9. Synthesis of chlorodiethylylstannyl N-(2,3-
dimethylphenyl)piperazine-1-carbodithioate (7)
m
m
m
m
(Sn–C), 1H NMR (ppm),
2J[119Sn–1H, Hz]: 2.31 (s, H11), 2.26 (s, H10), 6.86–7.11 (m, H7, 6, 5),
3.09–3.12 (m, H03;3), 2.96–2.99 (m, H20 ;2), 0.66 [57, h = 111°] (s, H3C–
Sn) 13C NMR (ppm): 198.3. (C-1), 116.9, 117.0, 125.7, 126.0, 131.4,
138.2, 150.4 (C–Ar), 52.1 (C-2, 20), 51.6 (C-3, 30), 0.8 {(H3C–Sn),
1J[119Sn–13C = 383, h = 110°]}.
Yield: 0.56 g, 66.6%. M.p. 103–104 °C. Anal. Calc. for
C
17H27N2S2SnCl: C, 42.74; H, 5.70; N, 5.86; S, 13.42. Found: C,
42.75; H, 5.66; N, 5.94; S, 13.40%. FT-IR (cmꢁ1): 991
m
(CS2)sym
,
1114
m
(m, H7,7a,
m(C–S)asym, 1460 m(C–N), 360 m(Sn–S), 473 m(Sn–C), 265
(Sn–Cl). 1H NMR (ppm) 1H 2.31 (s, H11), 2.26 (s, H12), 6.90–7.15
5,5a), 3.01–3.04 (m, H03;3), 2.26–2.31 (m, H02;2) 2.12
6,6a,
3
3
2.2.4. Synthesis of tributylstannyl N-(2,3-dimethylphenyl)piperazine-
1-carbodithioate (2)
(q, H , JH–H = 16Hz), 1.61 (t, Hb, JH–H = 16Hz). 13C NMR (ppm):
a
197.2 (C-1), 149.8, 138.4, 131.4, 126.1, 125.6, 116.9 (C–Ar), 52.2
Yield: 0.64 g, 66%. M.p. 52–54 °C. Anal. Calc. for C25H44N2S2Sn:
C, 54.06; H, 7.98; N, 5.04; S, 11.55. Found: C, 54.68; H, 7.98; N,
(C-2, 20), 51.4 (C-3, 30), 21.3 {(C- 1J[119Sn–13C = 533 Hz,
a)
h = 123.5°]}, 10.3 (C-b).
5.16; S, 11.89%. FT-IR (cmꢁ1): 975
m
(CS2)asym, 1117
(Sn–C). 1H NMR (ppm): 2.19 (s,
11), 2.15 (s, H10), 6.89–7.14 (m, H7,
5,), 2.96–2.99 (m, H03;3),
m(CS2)asym,
1465
m
(C–N), 354
m(Sn–S), 468 m
2.2.10. Synthesis of diethylstannyl bis[N-(2,3-
dimethylphenyl)piperazine-1-carbodithioate] (8)
H
6,
2.27–2.30 (m, H20 ;2), 1.33–1.72 (m, H ,b, ,d). 13C NMR (ppm):
a
c
Yield: 0.53 g, 67.9%. M.p. 220–222 °C. Anal. Calc. for
198.9 (C-1), 116.8, 125.7, 125.9, 131.4, 138.2, 150.5 (C–Ar), 52.1
(C-2,20), 51.7 (C-3,30), 28.9 {(C- ), 1J[119Sn–13C = 349 Hz,
h = 107°]}, 27.1 (C-b), 17.8 (C- ), 20.12 (C-d).
C
30H44N4S4Sn: C, 50.92; H, 6.27; N, 7.92; S, 18.12. Found: C,
50.49; H, 6.30; N, 7.60; S, 17.89%. FT-IR (cmꢁ1): 991
(CS2)sym
1113 (CS2)sym, 1460 (C–N), 356 (Sn–S), 480
(Sn–C), 261. 1H
5,),
a
m
,
c
m
m
m
m
NMR (ppm): 2.27 (s, H11), 2.25 (s, H10), 6.90–7.15 (m, H7,
6,
3
2.2.5. Synthesis of triphenylstannyl N-(2,3-
dimethylphenyl)piperazine-1-carbodithioate (3)
Yield: 0.68 g, 62.9%. M.p. 170–172 °C. Anal. Calc. for
3.01–2.97 (m, H30 ;3), 2.31–2.28 (m, H02;2). 2.12 (q, CH2, SnEt2, JH–
3
H = 15 Hz), 1.61 (t, CH3, SnEt2, JH–H = 15 Hz). 13C NMR (ppm):
200.8 (C-1), 51.6 (C-2, 20), 50.6 (C-3, 30, 3a, 30a), 150.4, 138.2,
131.41, 126.0, 125.8, 116.9 (Ar–C), 13.9 (C-7), 20.7 (C-8), 29.7
C
31H32N2S2Sn: C, 60.50; H, 5.24; N, 4.55; S, 10.42. Found: C,
59.97; H, 5.3; N, 4.58; S, 10.19%. FT-IR (cmꢁ1): 977
(CS2)sym
(Sn–S). 1H NMR (ppm): 2.30
{(C-a
), 1J[119Sn–13C = 545 Hz, h = 124.5°]}, 10.9 (C-b).
m
,
1120 m(CS2)asym, 1460 m(C–N), 351 m
(s, H11), 2.25 (s, H10), 6.89–7.14 (m, H7, 6, 5,), 3.14–3.11 (m, H03;3),
2.2.11. Antibacterial evaluation
2.96–2.99 (m, H20 ;2) 7.38–7.88 (m, H ,b, ,d). 13C NMR (ppm):
a
c
The synthesized compounds were tested for antibacterial activ-
ity against four different bacterial strains including, Staphylococcus
aureus (G+), Bacillus subtilis (G+), Pseudomonas aeruginosa (Gꢁ) and
Escherichia coli (Gꢁ) using the agar well diffusion method [16].
Ampicillin was used as standard drug and the wells (6 mm in
diameter) were dug in the media with the help of a sterile metallic
borer. Two to eight hours old bacterial inoculums containing
approximately 104–106 colony forming units (CFU)/mL were
spread on the surface of a nutrient agar with the help of a sterile
cotton swab. The recommended concentration of the test sample
(2 mg/mL in DMSO) was introduced into the respective wells.
Other wells supplemented with DMSO and reference antibacterial
drug served as negative and positive controls, respectively. The
plates were incubated immediately at 37 °C for 20 h. The activity
was determined by measuring the diameter of the inhibition zone
(in mm), showing complete inhibition. Growth inhibition was cal-
culated with reference to the positive control.
196.4 (C-1), 116.9, 125.1, 125.9, 131.4, 138.3, 151.8 (C–Ar), 52.8
(C-2, 20), 51.6 (C-3, 30), 142.2 {(C- ), 1J[119Sn–13C = 605 Hz]},
128.6 (C-b), 136.7 (C- ), 129.2 (C-d).
a
c
2.2.6. Synthesis of chlorodimethylstannyl N-(2,3-
dimethylphenyl)piperazine-1-carbodithioate (4)
Yield: 0.49 g, 62.8%. M.p. 169–170 °C. Anal. Calc. for
C
15H23N2S2SnCl: C, 40.07; H, 5.16; N, 6.23; S, 14.26. Found: C,
39.8; H, 5.02; N, 6.12; S, 13.87%. FT-IR (cmꢁ1): 987
(CS2)sym
1116 (CS2)asym, 1462 (C–N), 364 (Sn–S), 493 (Sn–C), 267
(Sn–Cl), 1H NMR (ppm) {2J[119Sn–1H, Hz]}: 2.25 (s, H11), 2.21 (s,
m
,
m
m
m
m
m
H
10) [81, h = 126°], 6.90–7.15 (m, H7,
5,), 3.01–3.05 (m, H03;3),
6,
2.26–2.31 (m, H02;2), 1.58 (H3C–Sn) 13C NMR (ppm): 196.7 (C-1),
116.9, 126.1, 126.2, 131.4, 138.4, 149.8 (C–Ar), 52.2 (C-2, 20), 51.4
(C-3, 30), 22.7 {(C–Sn), 1J[119Sn–13C = 563 Hz, h = 126°]}.
2.2.7. Synthesis of chlorodibutylstannyl N-(2,3-
dimethylphenyl)piperazine-1-carbodithioate (5)
Yield: 0.61 g, 65.5%. M.p. 98 °C. Anal. Calc. for C21H35N2S2SnCl: C,
47.25; H, 6.61; N, 5.25; S, 12.01. Found: C, 47. 91; H, 6.44; N, 4.99;
3. Results and discussion
S, 11.12%. FT-IR (cmꢁ1): 997
m
(CS2)sym, 1115
(Sn–C), 261
(Sn–Cl), 1H NMR (ppm): 2.19 (s,
11), 2.15 (s, H12), 6.89–7.14 (m, H7, 6, 5,), 3.01–3.04 (m, H03;3), 2.27–
2.30 (m, H02;2) 0.96–1.91 (m, H ,b, ,d). 13C NMR (ppm): 197.3 (C-1),
m
(CS2)asym, 1473
m
(C–
3.1. FT-IR spectral data
N), 372
H
m(Sn–S), 418
m
m
FT-IR band values related to different functional groups have
been assigned by comparison of the FT-IR spectra of the complexes
with their related precursors. New absorption bands appeared in
the region 414–480 cmꢁ1 and 351–372 cmꢁ1 can be assigned to
Sn–C and Sn–S stretching mode of vibrations, respectively. These
values are in close agreement with that observed for a number of
organotin(IV)–sulfur donor ligands [17].
a
c
154.0, 149.8, 138.4, 131.4, 126.1, 116.9 (C–Ar), 52.2 (C-2, 20), 51.4
(C-3, 30), 26.3 (C-
), 27.8 (C-b), 29.2 (C- ), 29.7 (C-d).
a
c
2.2.8. Synthesis of chlorodiphenylstannyl N-(2,3-
dimethylphenyl)piperazine-1-carbodithioate (6)
Yield: 0.68 g, 67.5%. M.p. 147–149 °C. Anal. Calc. for
The two bands related C–S and C–N stretching vibrations give
valuable information about the coordination behavior of dithiocar-
boxylate ligand to Sn atom, and thus give a clue about structure of
complexes. FT-IR spectra of complexes 1–3 gave strong peaks at
1120–1108 cmꢁ1, that can be attributed to the asymmetric absorp-
C
25H27N2S2SnCl: C, 52.33; H, 4.74; N, 4.88; S, 11.18. Found: C,
51.88; H, 4.93; N, 4.92; S, 10.95%. FT-IR (cmꢁ1): 992
(CS2)sym
1120 (CS2)asym, 1463 (C–N), 372 (Sn–S), 263
(Sn–Cl). 1H NMR
m
,
m
m
m
m
(ppm): 2.34 (s, H11), 2.30 (s, H12), 6.89–7.15 (m, H7, 5,), 2.27–
6,
2.32 (m, H03;3), 3.02–3.05 (m, H20 ;2) 7.46–8.13 (m, H ,b, ,d). 13C
tion of
metric
and
m
m
(CS2)as and the 997–977 cmꢁ1 can be assigned to the sym-
(CS2)s absorption frequencies. The difference of (CS2)as
a
c
NMR (ppm): 195.9 (C-1), 117.0, 126.1, 126.2, 128.3, 136.2, 149.7
(C–Ar), 52.9 (C-2, 20), 51.3 (C-3, 30), 128.8 (C-
) 135.7 (C-b), 130.3
(C- ), 138.4 (C-d).
m
a
m
(CS2)s are 113–135 cmꢁ1, that is an indication of bidentate
c
binding of the ligand to the central tin atom [17]. The stretching

700
F. Shaheen et al. / Polyhedron 31 (2012) 697–703
Table 1
Crystal refinement data for complexes (3), (5) and (8).
Moiety formula
C31H32N2S2Sn (3)
C21H35S2N2SnCl (5)
(C15H22N2S2)2Sn (8)
Formula weight (g molꢁ1
)
615.45
533.81
707.68
Crystal system
Space group, no. 15
a (Å)
b (Å)
c (Å)
monoclinic
P21/c, 14
19.062(2)
7.4576(9)
20.624(2)
triclinic
P1, 2
monoclinic
C2/c, 15
28.212(2)
7.2985(6)
17.0056(14)
ꢀ
10.0753(10)
14.4811(15)
18.4442(19)
113.0520(10)
94.9270(10)
94.4040(10)
2449.1(4)
2.42–29.36
4
a
(°)
b (°)
(°)
V (Å3)
103.963(2)
113.2900(10)
c
2845.2(5)
2.54–27.39
4
3216.2(4)
2.90–28.67
4
h Range for data collections (°)
Z
Total reflections
Independent reflections
All
15273
6411
21949
11600
14109
3973
For Fo P 4.0
R(F) = (||Fo| ꢁ |Fc||)/ |Fo|
r
(Fo)
4769
0.0356
9207
0.0525
3462
0.0308
P
P
For Fo > 4.0
r (Fo)
P
P
wR(F2) = [ [w(Fo ꢁ Fc2)2]/ [w(Fo2)2]]1/2
Goodness-of-fit (GOF)
Color, habit
0.0863
1.011
colorless, needle
0.41 ꢃ 0.13 ꢃ 0.08
0.1402
1.077
colorless, cut-fragment
0.55 ꢃ 0.51 ꢃ 0.45
0.0749
1.068
colorless, block
0.34 ꢃ 0.29 ꢃ 0.22
2
Crystal size (mm)
expected regions. The coupling constant value obtained for 1 sug-
gests tetrahedral geometry in solution. Similarly the angle value
calculated from 2J(119Sn–1H) coupling constant for complex 4 cer-
tify five coordinate environment around Sn [18].
Table 2
Selected bond lengths(Å) and bond angles (°) for compound 3.
Ph3SnL (3)
Sn–S1
Sn–S2
Sn–C14
Sn–C20
3.0223(9)
2.4740(8)
2.137(3)
2.146(3)
Sn–C26
S1–C1
S2–C1
2.159(3)
1.693(2)
1.754(3)
In 13C NMR of complexes 1–7, the duplicate peak pattern due N-
(2,3-dimethylphenyl)piperazinium ion disappeared upon com-
plexation to Sn. In complexes 13C chemical shift values observed
were similar to that of the ligand except small shift in the position
of C(1), which was due to deshielding of this carbon upon coordi-
nation of both the sulfur atoms with the Sn atom. The alkyl groups
attached to Sn atom showed signals in the expected range. Cou-
pling constant values obtained in case of 1, 2, 3, 4, 7 and 8 give
information about the relevant geometry of complexes in solution.
S1–Sn–S2
64.40(2)
86.26(8)
88.84(8)
155.27(8)
115.60(8)
125.43(7)
S2–Sn–C26
C14–Sn–C20
C14–Sn–C26
C20–Sn–C26
Sn–S1–C1
91.03(8)
S1–Sn–C14
S1–Sn–C20
S1–Sn–C26
S2–Sn–C14
S2–Sn–C20
108.37(10)
108.31(11)
104.56(11)
79.91(10)
69.69(8)
Sn–S2–C1
Possible geometry of 1, evaluated by 1H NMR was confirmed by 13
C
NMR. Trimethyl-, tributyl- and triphenyltin complexes dissociated
in solution and gave a tetrahedral geometry in solution state. Com-
plex 8 dissociate in solution to give a five coordinate complex,
whereas complex 7 retains its geometry in solution [19]. In com-
pounds 5 and 6, a complex peak pattern is observed which depicts
no significant Sn satellites, and hence assignment of geometry is
not possible. The angle values calculated for 1, 2, 4, 7 and 8 verify
geometry of these complexes in solution.
vibration peaks of the C–N, were obtained at ꢂ1458–1473 cmꢁ1
and are intermediate between the values for C–N single bond
(1250–1360 cmꢁ1) and C@N double bond (1640–1690 cmꢁ1). Par-
tial double bond character for the C–N bond would result in some
partial double bond character for the C–S bonds. The analyses are
in agreement with X-ray single crystal diffraction results, obtained
for complexes 3, 5 and 8.
3.2. NMR spectra
3.3. Crystal structure analysis
In case of all the complexes, the disappearance of duplicate
peak pattern and appearance of new signals for organic group at-
tached to Sn(IV) atom confirmed the formation of complexes
1–8. The organic groups attached to Sn atom give signals in the
X-ray crystal structure provides most adequate information on
the structure of crystalline compound. Upon dissolution in polar
solvents, regular packing held together by coordination, electro-
static and H-bonds may be broken down. Therefore the results
Table 3
Selected bond lengths(Å) and bond angles (°) for two different molecules of compound 5.
X = 1
X = 2
X = 1
X = 2
Sn–Clx
2.4626(12)
2.4892(12)
2.6986(12)
2.129(6)
2.4926(11)
2.4671(13)
2.7416(11)
2.156(5)
Snx–Cx18
Sx1–Cx1
Sx2–Cx1
2.162(5)
1.743(4)
1.719(4)
2.116(5)
1.755(4)
1.709(5)
Snx–Sx1
Snx–Sx2
Snx–Cx14
Clx–Snx–Sx1
Clx–Snx–Cx2
Clx–Snx–Cx14
Clx–Snx–Cx18
Sx1–Snx–Sx2
Sx1–Snx–Cx14
85.58(4)
86.07(4)
Sx1–Snx–Cx18
Sx2–Snx–Cx14
Sx2–Snx–Cx18
Snx–Sx1–Cx1
Snx–Sx2–Cx1
Cx14–Snx–Cx18
116.90(16)
98.85(14)
87.80(11)
89.64(14)
83.46(14)
126.0(2)
117.74(14)
94.26(11)
93.11(14)
90.65(15)
82.80(14)
131.62(19)
154.55(4)
95.95(14)
100.05(12)
69.39(3)
154.90(4)
97.34(12)
95.65(14)
69.06(4)
115.46(14)
109.52(13)

F. Shaheen et al. / Polyhedron 31 (2012) 697–703
701
Table 4
Selected bond lengths(Å) and bond angles (°) for compound 8.
Sn–S1
Sn–S2
Sn–S1_a
Sn–S2_a
3.0304(7)
2.5243(6)
3.0304(7)
2.5243(6)
Sn–C14
Sn–C14a
S1–C1
2.140(2)
2.140(2)
1.689(2)
1.755(2)
S2–C1
S1–Sn–S2
64.02(2)
84.60(7)
152.80(2)
143.13(2)
84.77(7)
109.98(7)
S2–Sn–S1_a
S2–Sn–S2_a
S2–Sn–C14_a
C14–Sn–S1_a
C14–Sn–S2_a
C14–Sn–C14_a
143.13(2)
79.33(2)
105.37(6)
84.77(7)
105.37(6)
133.57(9)
S1–Sn–C14
S1–Sn–S1_a
S1–Sn–S2_a
S1–Sn–C14_a
S2–Sn–C14
are not always applicable for the complexes existing in aqueous
solutions, although many examples prove that the main binding
sites are same in crystal and in solution [20].
Crystal refinement data for complexes (3), (5) and (8) are given
in Table 1, and geometric parameters are listed in Table 2–4.
In complex (3) the geometry around tin can be best character-
ized by the
= b ꢁ /60. Here b and
around Sn. value is 1 for perfect trigonal bipyramidal and zero
for perfect square planar geometry. In case of this complex (3),
the value of is 0.49 ascertaining the structure is a mid way be-
s
value that can be calculated by using expression,
Fig. 2. Supramolecular structure of compound 3 mediated by Sꢀ ꢀ ꢀH and Hꢀ ꢀ ꢀCH2N
s
a
a, are two consecutive largest angles
interactions.
s
s
tween trigonal bipyramidal and square pyramidal [21]. At the axial
positions of this distorted structure is C26 atom of phenyl group
and S1 (Fig. 1) atom of ligand and define an angle value of
155.27(8)°. The presence of S1 at apical position is in accord with
the Bent’s rule that says the most electronegative atom should be
at the axial position, on the basis of amount of s-character of the
metal hybrid orbital used in bonding [22]. The presence of S1 at
pseudo-axial position is due to chelation restrain of the four mem-
bered CS2Sn ring. Consequently, the angle value with basal plane is
reduced to 64.40(2)°. S2 from the ligand and two a-carbons of phe-
nyl group construct an equatorial plan with S2–Sn–C14 =
115.60(8)°, S2–Sn–C20 = 125.43(7)°, C14–Sn–C20 = 108.37(10)°.
The coordination of dithiocarboxylate ligand to the Sn center is
anisobidentate 0as evident from unequal Sn–S bond lengths [Sn–
0
S1 = 3.0223(9) ÅA and Sn–S2 = 2.4740(8) ÅA]. Similarly bond distance,
0
C1–S1 = 1.693(2) ÅA, indicates strong binding of S1 than S2 [C1–
0
Fig. 3. Molecular structure of complex 5 with atomic numbering scheme.
S2 = 1.754(3) ÅA] with Sn center. The packing diagram illustrates
the supramolecular structure for 3 mediated by Sꢀ ꢀ ꢀH–Ar and
NCH2ꢀ ꢀ ꢀH non-covalent intermolecular interactions (Fig. 2). The
presence of Sꢀ ꢀ ꢀH–Ar intermolecular interactions may be the sec-
ond main cause of deviation of geometry from perfect trigonal-
bipyramidal to square-pyramidal.
molecules, together with an example of the partial atom number-
ing scheme used here is shown in Fig. 3. The configuration about
the tin atom is five-coordinate. The sum of the equatorial angles
involving the two
358.36° and 358.88°, show little deviation from the ideal angle of
360°. The value for the two independent molecules is 0.47 and
a-carbons of the butyl groups and an S atom
The asymmetric unit of complex 5 contains two different
molecules. A molecular structure for one of the two independent
s
0.38 that confirms highly distorted square-pyramidal geometry,
especially for the later one (Table 3). The tendency of going from
trigonal-bipyramidal geometry to square-pyramidal one may be
due to the intermolecular SnClꢀ ꢀ ꢀH2CN interactions (Fig. 4). These
interactions result in the supramolecular structure of the com-
pound 5. For each of the two independent molecules, the Cl atom
occupies one of the apical positions of the highly distorted trigo-
nal-bipyramid with the Cl1–Sn1–S12 and Cl2–Sn2–S22 angles of
154.55° and 154.90°, respectively. The quasi-axial S12 and S22
atoms cannot occupy exactly the position trans to Cl and Cl1–
Sn1–S12 and Cl2–Sn2–S22 angles are 154.55(4)° and 154.90(4)°.
Here again ring strain plays a significant role in an asymmetric
bonding of the ligand, with shorter Sn1–S11 and Sn2–S21 bond
0
lengths are [2.4892(12) and 2.4671(13) ÅA] and longer Sn1–S12
0
bond and Sn2–Sn22 [2.6986(12) and 2.7416(11) ÅA] respectively.
The Sn–Cl bond length [2.4626(12)°] falls in the range of covalent
0
Fig. 1. Molecular structure of complex 3 with atomic numbering scheme.
radii of the two atoms (2.37–2.60 ÅA) [23].

702
F. Shaheen et al. / Polyhedron 31 (2012) 697–703
from the regular octahedral geometry can also be explicated on
electronic and steric grounds. Thus, coordination geometry around
Sn in compound
bipyramidal.
8 is best described as skew trapezoidal
A comparison of Sn–S bond lengths among the compounds 3, 5,
and 8 show that Sn–Sshort bond distances decreases in the order of
3 < 5 < 8 while Sn–Slong bond distances decreases as 5 < 3 < 8. The
larger values of bond distances for 8 in both cases is due to two
electron donating ethyl groups which decreases the electron
accepting ability of central tin atom from the donor sulfur atoms,
thus lengthening both the Sn–Sshorter and Sn–Slonger bond distances.
As the two ethyl groups occupy trans axial positions, so impart
similar effect for shorter and longer bond distances. Complex 3
shows smaller bond length value for Sn–Sshort than 5 but the trend
is reverse in case of Sn–Slonger. This may be explained on the basis
of planarity and electron withdrawing nature of the phenyl groups
on Sn that make Sn electron greedy thus attracting the sulfur atom
more closely to form shorter Sn–Sshort than 5. The lengthening of
Sn–Slonger bond in 3 than 5 can be attributed to the involvement
of this sulfur in Sꢀ ꢀ ꢀH hydrogen bond (Fig. 2). Geometry of com-
plexes imposes some additional effects on bond length values.
Octahedral and trigonal bipyramidal geometry also contributes in
defining behavior of Sn–S bond. In complex 8, basal plan experi-
ences more electronic repulsion (due to octahedral geometry) than
trigonal plan (3 and 5), resulting in elongation of Sn–Sshorter and
Sn–Slonger bonds.
Fig. 4. Supramolecular structure of compound 5 mediated by Clꢀ ꢀ ꢀH and Cl–H2CN
interactions.
Complex (8) shows a distorted octahedral geometry in which
four S-atoms of the two chelating dithiocarboxylate ligands define
the basal plane (Fig. 5). Ethyl groups occupy axial positions with
C14–Sn–C14_a = 133.57(9)°. The value of CSnCaxial shows that
two ethyl groups do not occupy exact trans axial position thus re-
sults in distorted octahedral geometry. Likewise basal plane is also
distorted from square planar geometry as cis S1–Sn–S1a angle is
152.80(2)° and cis S2–Sn–S2a is only 79.33(2)°. The 0two Sn–S bond
lengths [Sn–S1 = 3.0304(7) and Sn–S2 = 2.5243(6) ÅA] are unequal,
attesting the asymmetric coordination of ligand to Sn atom. In
addition to0 this, Sn–S1 and Sn–S1a bond lengths are equivalent
A comparison of the
s values for the five-coordinate complexes
3 and 5 reveals the smallest value for complex 5. The inclination of
the later structure more towards square-pyramidal is because of
the involvement of Sn–Cl moiety of one molecule in hydrogen
bonding to the piperazine moiety of the molecule near by (Fig. 4).
[3.0304(7) ÅA], same is the case with Sn–S2 and Sn–Sn2a bond
0
lengths [2.5243(6) ÅA] confirming the same degree of asymmetry
in the coordination of both ligands. Each shorter C–S bond is asso-
ciated with longer Sn–S bond, further verified an asymmetric mode
of coordination. The bond angles subtended at the tin atom by the
methylene carbon with S2 and S2_a atoms are 109.98(7) and
105.37(6), respectively, which reveals that Sn–C bonds are bent to-
wards longer Sn–S as a consequence of repulsion between bonding
electron pairs around central Sn atom. Such structural deviations
3.4. Antibacterial activity
Free ligand and its organotin(IV) complexes were tested against
four different strains of bacteria by agar well diffusion method.
Fig. 5. Molecular structure of compound 8 with atomic numbering scheme.
Table 5
Antibacterial activity of organotin(IV) derivatives of S-donor ligand.
Name of bacteria
Zone of inhibition of sample (mm)
Standard druga
L
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
Staphylococcus aureus
Bacillus subtilis
Pseudomonas aeruginosa
Escherichia coli
26
31
25
33
37
42
35
44
46
32
42
26
34
39
24
17
32
37
35
41
30
30
28
35
23
22
23
19
16
19
17
18
29
16
20
17
a
Standard drug = ampicillin.

F. Shaheen et al. / Polyhedron 31 (2012) 697–703
703
making similar kind of secondary non-covalent contacts with the
cell constituents of microbes. Thus, hindering various cellular pro-
cesses and ultimately causing death of the bacterium cell.
Acknowledgements
We thank the Higher Education Commission of Pakistan for
financial support.
Appendix A. Supplementary data
CCDC 723568, 723569 and 723570 contain the supplementary
crystallographic data for 8, 5 and 3. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Fig. 6. Supramolecular structure of compound 8 mediated Hꢀ ꢀ ꢀCH2N interactions.
Antibacterial data is given in Table 5. The results obtained were
quite promising, and in general complexes are more active than
parent ligand. This shows that coordination with Sn(IV) atom is a
good measure of improving activity of the ligand. The chelation re-
duces polarity of metal ion because of partial sharing of its positive
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