Synthesis, spectroscopy, single crystal XRD and biological studies of multinuclear organotin dicarboxylates

Article abstract of DOI:10.1016/j.poly.2016.05.045

Multinuclear organotin(IV) dicarboxylates of the general formula (Me₃Sn)₂L·H₂O (1), (Ph₃Sn)₂L (2) and Me₂SnL[Sn(Cl)₂Me₂]₂ (3) were synthesized by refluxing disodium iminodiacetate hydrate (Na₂L·H₂O) with Me₃SnCl/Ph₃SnCl/Me₂SnCl₂ in methanol. The elemental analysis (C, H and N) data agreed well with the chemical compositions of the products. IR spectroscopy demonstrated a bridging coordination mode of the carboxylate group. ¹H NMR spectroscopy suggested a penta-coordinated environment around the tin(IV) center in complexes 1 and 3. The title complex 3 represents one of the very few examples of organotin(IV) carboxylates showing simultaneously coordination with dimethyltin(IV) as well as dichlorodimethyltin(IV) moieties, by substitution and addition reactions, respectively. The ¹³C NMR spectroscopy demonstrated the carboxylate-metal linkages. EIMS and ESI spectra verified the molecular skeletons of the products 1-3. Thermogravimetric analysis revealed the bimetallic nature of 2. A single crystal XRD study of 3 has shown a predominantly square pyramidal geometry with some trigonal bipyramidal characteristics around each metal center. The novel products exhibited antibacterial/antifungal potential and their minimal inhibitory concentrations (MIC) were also evaluated. In vitro hemolytic studies on human red blood cells indicated a slightly toxic nature of the synthesized complexes.

Full text of DOI:10.1016/j.poly.2016.05.045

Polyhedron 117 (2016) 64–72
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, spectroscopy, single crystal XRD and biological studies
of multinuclear organotin dicarboxylates
c,
d
e
Shabbir Hussain a,b, Saqib Ali c, , Saira Shahzadi , Muhammad Nawaz Tahir , Muhammad Shahid ,
⇑
⇑
Khurram Shahzad Munawar c,f, Syed Mustansar Abbas g
a Department of Chemistry, GC University, Faisalabad, Pakistan
b Department of Natural and Social Sciences, Sharif College of Engineering and Technology, Raiwind Road, Lahore, Pakistan
c Department of Chemistry, Quaid-i-Azam University, 45320 Islamabad, Pakistan
d Department of Physics, University of Sargodha, Sargodha, Pakistan
e Department of Chemistry and Biochemistry, University of Agriculture, Faisalabad, Pakistan
f Department of Chemistry, School of Science, University of Management and Technology, Lahore 54770, Pakistan
g Nanoscience & Technology Department, National Centre for Physics, Islamabad, Pakistan
a r t i c l e i n f o
a b s t r a c t
Article history:
Multinuclear organotin(IV) dicarboxylates of the general formula (Me3Sn)2LꢀH2O (1), (Ph3Sn)2L (2) and
Me2SnL[Sn(Cl)2Me2]2 (3) were synthesized by refluxing disodium iminodiacetate hydrate (Na2LꢀH2O)
with Me3SnCl/Ph3SnCl/Me2SnCl2 in methanol. The elemental analysis (C, H and N) data agreed well with
the chemical compositions of the products. IR spectroscopy demonstrated a bridging coordination mode
of the carboxylate group. 1H NMR spectroscopy suggested a penta-coordinated environment around the
tin(IV) center in complexes 1 and 3. The title complex 3 represents one of the very few examples of organ-
otin(IV) carboxylates showing simultaneously coordination with dimethyltin(IV) as well as dichlorodi-
methyltin(IV) moieties, by substitution and addition reactions, respectively. The 13C NMR spectroscopy
demonstrated the carboxylate-metal linkages. EIMS and ESI spectra verified the molecular skeletons of
the products 1–3. Thermogravimetric analysis revealed the bimetallic nature of 2. A single crystal XRD
study of 3 has shown a predominantly square pyramidal geometry with some trigonal bipyramidal char-
acteristics around each metal center. The novel products exhibited antibacterial/antifungal potential and
their minimal inhibitory concentrations (MIC) were also evaluated. In vitro hemolytic studies on human
red blood cells indicated a slightly toxic nature of the synthesized complexes.
Received 19 November 2015
Accepted 13 May 2016
Available online 28 May 2016
Keywords:
Multinuclear organotin(IV)
Spectroscopy
XRD
Antibacterial/antifungal
Hemolytic
Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction
center and the electronegativity difference between the carboxyl
group and the remaining part of the ligand [5]. There are reports
Organotin carboxylates are one of the most ubiquitous com-
pounds for their structural diversities arising from different coordi-
nation behavior of their ligand precursors. The presence of more
than one donating entity in a ligand may increase the coordination
number at the tin center and may lead to a variety of coordination
geometries, such as dimeric, tetrameric, oligomeric ladder, cyclic,
drums structure and polymers etc., [1–4]. The mode of coordina-
tion may also change depending on the concentration of the solu-
tion, nature of solvent, size of organic moiety attached to the tin
on the biological activities of organtoin(IV) carboxylates [6–8].
These compounds normally exhibit high toxicity, even at a very
low concentration. Their biological activities are fundamentally
determined by the number and nature of the organic groups bound
to the central Sn atom [7]. The chemistry of organotin carboxylates
has been developed considerably because of their potential appli-
cations as antineoplastic and antituberculosism agents [9–10],
anti-tumour drugs [11] and PVC stabilizers [12].
Keeping in view the great importance of organotin(IV) chem-
istry, we report here the syntheses, spectroscopic characterization,
antibacterial/antifungal potential and hemolytic activities of mult-
inuclear tin(IV) complexes. The choice of the ligand (Na2LꢀH2O) has
been made because this ligand has simultaneous availability of an
amino and two carboxyl groups and can develop a multinuclear
coordination with organo-tin centers.
⇑
Corresponding authors. Tel.: +92 51 90642130.
E-mail addresses: saqibali@qau.edu.pk (S. Ali), sairashahzadi@hotmail.com
(S. Shahzadi).
http://dx.doi.org/10.1016/j.poly.2016.05.045
0277-5387/Ó 2016 Elsevier Ltd. All rights reserved.

S. Hussain et al. / Polyhedron 117 (2016) 64–72
65
3
3'
2. Experimental
CH2
H2C
γ
1
β
2'
2
2.1. Materials and methods
N
COO
α
OOC
α
CH3
H
δ
4
Sn
.H2O
Sn
Dimethyltin dichloride, trimethyltin chloride and triphenyltin
chloride were purchased from Sigma–Aldrich (USA) and used with-
out any further purification. Disodium iminodiacetate hydrate
(Na2LꢀH2O) was procured from Merck (Germany). AR grade sol-
vents of Merck (methanol), Lab-scan (DMSO) and Riedel-de Haen
(petroleum ether) origin were used. The methanol was dried before
use by a standard procedure [13].
Scheme 1. Numbering scheme of the free ligand skeleton (LꢀH2O) and the organotin
moieties.
(1 mmol) with Me2SnCl2 (3 mmol) (Eq. (2)) by the same procedure
formed product 3.
The samples were taken in capillary tubes and their melting
points were measured by an electrochemical melting point appara-
tus, Stuart SMP3, and are uncorrected. Elemental analyses were
performed on a CHN-932 elemental analyzer, Leco Corporation,
USA. Infrared spectra were recorded by a Perkin-Elmer-1000 FTIR
spectrophotometer in the range 4000–250 cmꢁ1. The 1H and 13C
NMR spectral measurements were made at 300 and 75 MHz,
respectively by a Bruker ARC 300 MHz-FT-NMR spectrometer.
The electron spin ionization (ESI) mass spectrum was recorded
with LTQ XLTM linear ion trap mass spectrometer (Thermo Scien-
tific); the EI mass spectroscopy was performed using a Thermo
Fisher Exactive Orbitrap instrument. The TGA spectra were
2.2.1. Na2LꢀH2O
M.p. 180 °C. IR (cmꢁ1): 3285
t
(N–H), 1659
= 247 cmꢁ1), 3439
(O–H), 897
(D2O, ppm) d: 3.03 (S, H3,3 , 4H), 4.70 (S, H4, 2H). 13C NMR (D2O,
t
(OCO)asym, 1412
tq
t
(OCO)sym, (
D
t
t
r(H2O). 1H NMR
0
0
0
ppm) d: 179.3 (C-2,2 ), 51.9 (C-3,3 ).
2.2.2. Complex 1
Yield: 79%. M.p. 267–269 °C. Anal. Calc. for C10H25NO5Sn2: C,
25.19; H, 5.29; N, 2.94. Found: C, 25.11; H, 5.09; N, 3.11%. IR
(cmꢁ1): 3271
= 183 cmꢁ1), 557
r(H2O). 1H NMR (DMSO-d6, ppm) d: 3.60 (S, H3,3 , 4H), 4.69 (s,
H4, 2H), 0.81 and 0.42 (s, H , 18H); 13C NMR (DMSO-d6, ppm) d:
t(N–H), 1589
t
(OCO)asym, 1406
t
(OCO)sym,
(D
t
t(Sn–C), 461
t
(Sn–O), 3489
t(O–H), 906
obtained by TGA-7 Perkin-Elmer USA under
atmosphere.
a
nitrogen
0
tq
a
The X-ray diffraction data were collected on a Bruker SMART
APEX CCD diffractometer, equipped with a 4 K CCD detector set
60.0 mm from the crystal. The crystals were cooled using a Bruker
0
0
171.2 (C-2,2 ), 51.3 (C-3,3 ), ꢁ1.2 (C-
a).
2.2.3. Complex 2
KRYOFLEX low temperature device to 100 1 K and intensity mea-
surements were carried out from a sealed ceramic diffraction tube
(SIEMENS) using graphite monochromated Mo Ka radiation. Gen-
erator settings were 50 kV/40 mA. The structure was solved by
the Patterson method and an extension of the model was accom-
plished by the direct method using the program DIRDIF or
SIR2004. Final refinement on F2 was carried out by the full matrix
least squares techniques using SHELXL-97, a modified version of the
program PLUTO and PLATON package.
Yield: 91%. M.p. 142–144 °C. Anal. Calc. for C40H35NO4Sn2: C,
57.80; H, 4.24; N, 1.69. Found: C, 57.34; H, 4.28; N, 1.67%. IR
(cmꢁ1): 3283
t
(N–H), 1570
t
(OCO) asym, 1419
t(OCO)sym,
(D
t
= 151 cmꢁ1), 279
t(Sn–C), 451
t
(Sn–O). 1H NMR (DMSO-d6,
0
ppm) d: 3.37 (s, H3,3 , 4H), 7.67–7.96 (m, Hb, 12H), 7.19–7.57 (m,
Hc
, 12H), 7.19–7.57 (m, Hd, 6H); 13C NMR (DMSO-d6, ppm) d:
0
0
172.7 (C-2,2 ), 51.2 (C-3,3 ), 142.7 (C-a); 129.5 (C-b); 127.6 (C-c);
128.4 (C-d).
The complexes were screened against various strains of bacteria
(Escherichia coli, Bacillus subtilis, Staphlocuccus aureus and Pasturella
multocida) and fungi (Alternaria alternata, Ganoderma lucidum, Peni-
cillium notatum, Trichoderma harzianum and Aspergillus niger) by
the disc diffusion method [14,15]. The MICs evaluations were per-
formed by a reported procedure [16] with some modifications [15].
The antimicrobial activities were performed in an incubator
(Sanyo, Germany) and petri plates were sterilized in an autoclave
(Omron, Japan). The minimum inhibitory concentrations were
2.2.4. Complex 3
Yield: 66%. M.p. 209–211 °C. Anal. Calc. for C10H23Cl4NO4Sn3: C,
16.70; H, 3.22; N, 1.95. Found: C, 16.53; H, 3.36; N, 1.99%. IR
(cmꢁ1): 3139
t(N–H), 1642 t(OCO)asym, 1410 t(OCO)sym,
(D
t
= 232 cmꢁ1), 594
t(Sn–C), 469
t(Sn–O), 420
t
(Sn–N) 293
t
(Sn–Cl). 1H NMR (DMSO-d6, ppm) d: 3.03–3.10 (m, H3,3 , 4H), 1.03
0
13
0
& 0.49 (s, H , 18H). C NMR (DMSO-d6, ppm) d: 171.1 (C-2,2 ),
a
0
51.9 (C-3,3 ), 23.5 (C-
a).
determined in
a Micro Quant apparatus (BioTek, USA). The
3. Results and discussion
in vitro hemolytic bioassays [17] of the complexes were reported
with respect to triton X-100 and phosphate-buffered saline (PBS)
as a standard.
3.1. Syntheses
Scheme 1 represents numbering in the ligand and organic
groups attached to the Sn atom for 1H and 13C NMR spectral
interpretation.
The organotin(IV) dicarboxylates 1–3 were synthesized in good
yields by refluxing iminodiacetic acid disodium salt hydrate (Na2-
LꢀH2O) with Me3SnCl/Ph3SnCl (1:2 M ratio) or with Me2SnCl2
(1:3 M ratio) in methanol (Eqs. (1) and (2)). No product was iso-
lated using the stoichiometric ratios (L:Sn) of 1:3 for the reaction
of Na2L.H2O with Me3SnCl/Ph3SnCl or 1:2 with Me2SnCl2. The for-
mation of product 3 with a L:Sn ratio of 1:3 can be justified from
the fact that there is a simultaneous effect of two electronegative
chlorine atoms which render the Sn1 center highly electropositive,
so a strong Lewis acidic character is thus developed at the metal
center enabling the tin atom to receive electron density from the
carbonyl oxygen atom as well. There are reports for the formation
of the centrosymmetric dinuclear complex [Me2Sn(L)(MeOH)]2 by
the reaction of iminodiacetic acid (H2L) with an equimolar amount
of Me2SnCl2 in the presence of KOH in methanol at 60 °C for 48 h
2.2. Syntheses of complexes 1–3
Complexes 1–2 were prepared by a reported procedure [18]. To
a solution of R3SnCl (R = Me, Ph) (2 mmol) in 60 mL dry methanol
in a quickfit two necked 250 mL round bottom flask, disodium
iminodiacetate hydrate (Na2LꢀH2O) (1 mmol) was added in por-
tions with continuous stirring, and the reaction mixture was
refluxed for 10 h (Eq. 1). The precipitated sodium chloride was
removed by filtration and the solvent was evaporated slowly at
room temperature. The final solid product (1/2) was recrystallized
in methanol:petroleum ether (2:1). The reaction of Na2LꢀH2O

66
S. Hussain et al. / Polyhedron 117 (2016) 64–72
[19]. However, mononuclear diorganotin(IV) derivatives [Bu2Sn(L)
(H2O)] and [Ph2Sn(L)(H2O)], have been formed by the interaction of
R2SnL2 (R = n-Bu, Ph) with the monohydrate disodium salt of imin-
odiacetic acid (Na2L) at a 1:1 M/L ratio under reflux conditions for
10 h [20]. Refluxing iminodiacetic acid (H2L) with piperazine (pipz)
and SnCl4ꢀ5H2O in equimolar quantities in methanol for a period of
6 h resulted in a proton transfer reaction between iminodiacetic
acid (H2L) and piperazine (pipz), and subsequent complexation
with the tin(IV) chloride salt to yield (pipzH2)[Sn(L)Cl3]ꢀCl [21].
The procedure used for the synthesis of [Bu2Sn(PhL)(H2O)] consists
of suspending N-phenyl iminodiacetic acid (PhLH2) and di-n-butyl-
tin oxide (Bu2SnO) in 200 ml of a refluxing ethanol/benzene 1/4
mixture for 6 h [22]. So it can easily be concluded that the forma-
tion of organotin(IV) derivatives of iminodiacetic acid is highly
sensitive to the reaction conditions and stoichiometric ratios; the
nature of the products is completely changed by even a slight
change in the reaction conditions.
bands occurred in the range 557–594 cmꢁ1 in complexes 1 and 3
and at 279 cmꢁ1 in complex 2. The
Sn–O frequencies were
observed at 451–469 cmꢁ1. The
Sn–C and Sn–O bands were
absent in the spectrum of the free ligand (Na2LꢀH2O).
t
t
t
The IR spectrum of the free ligand Na2LꢀH2O indicated the pres-
ence of incorporated water by a broad band at 3439 cmꢁ1 and a
medium band at 897 cmꢁ1 for stretching and bending (rocking)
vibrations. These two bands were shifted to higher frequencies of
3489 and 906 cmꢁ1 for complex 1, indicating the presence of a
coordinated water molecule [28]. These bands were absent in the
IR spectra of complexes 2 and 3, indicating the absence of water.
3.3. 1H and 13C NMR spectroscopy
The 1H and 13C NMR spectra of the ligand and the complexes
were recorded in deuterated water and DMSO, respectively at
room temperature; the data has been provided in the Experimental
Section 2.2. The absence of 1H NMR signals for the amino protons
in the ligand and complexes 1–3 may be may be explained by the
broadening of the NH signal as a result of hydrogen bonding;
another possibility is the exchange of the amino protons with deu-
terium from the solvent. A singlet resonance appeared at d
3.03 ppm for the methylene protons in Na2LꢀH2O. The –CH2– pro-
tons were deshielded (d 3.37–3.60 ppm) in complexes 1 and 2
due to the flow of electronic charge towards the carboxylic moi-
eties during coordination with the metal. However, the methylene
protons did not show any significant shift (d 3.03–3.10 ppm, mul-
tiplet) in complex 3 due to its different structural characteristics,
which have also been verified by other spectroscopic and single
crystal XRD studies. The water molecule appeared as a singlet at
d 4.70 ppm in Na2LꢀH2O and at d 4.69 ppm in complex 1. The pres-
ence of two singlet resonances at d 0.81 and 0.42 ppm in complex 1
may be caused by the presence of stereoisomers. The resonance
signal for dichlorodimethyltin(IV) moiety appeared downfield (at
d 1.03 ppm) as compared to the dimethyltin(IV) moiety in complex
3. The observed 2J[119Sn, 1H] values were used to find the Me–Sn–
Me bond angles in the solution state using the Lockhart–Manders
Equation (Eq. (3)) [29].
Ph
Ph
Me
O
C
Me
Sn
Ph
O
Sn
Me
CO2Na
H2C
O
C
O
CH2
NH
2Ph3SnCl
H2C
H2O.HN
H2C
2Me3SnCl
.H O
NH
2
10 h, -2NaCl
-H2O
10 h, -2NaCl
CH2
H2C
O
O
C
CO2Na
C
Me
Ph
Sn
Sn
Na L.H O
(
)
2
2
O
O
Me
Ph
Ph
Me
(Equation 1)
1
2
( )
( )
Me
Me
Me
Sn
Me
Sn
Sn
O
H2
C
O
C
Cl
Cl
Cl
NaO2C
NaO2C
Me
3Me2SnCl2
C
O
NH.H2O
HN
Cl
O
Me
10 h, -2NaCl
-H2O
C
H2
C
H2
C
H2
(3)
Na L.H O
(
)
(Equation 2)
2
2
The complexes 1–3 are stable in air, white in colour and have
sharp melting points. They show solubility in common organic sol-
vents (e.g. DMSO and MeOH). The elemental analysis data agree
well with the molecular composition of the products.
h ¼ 0:0105½2Jꢂ2 ꢁ 0:799½2Jꢂ þ 122:4ðfor coordinating solventsÞ
ð3Þ
Table 1 represents the coupling constants (nJ) obtained from
resolved satellites and the calculated C–Sn–C bond angles (h) in a
coordinating solvent. The 1H NMR spectroscopy strongly supports
distorted square pyramidal and trigonal bipyramidal tin centers
in each of complexes 1 and 3. However, one of the C–Sn–C bond
angles is greater than the other which is also supported by single
crystal XRD and IR studies. The results demonstrate that the coor-
dinated metal centers maintain their solid state penta-coordinated
structures, even in the solution, however there are small changes
in the C–Sn–C bond angles, as in case of complex 3 where the solid
state C–Sn–C bond angles of 152.8(2) and 134.3(4)° (as depicted by
single crystal XRD) are changed to 166.82/160.36 and 127.39°,
respectively in solution. The ortho protons absorbed downfield (d
7.67–7.96 ppm) as compared to the meta and para protons (d
7.19–7.57 ppm) in the triphenyltin(IV) derivative 2 [18].
3.2. IR spectroscopy
Infrared spectra were recorded in the range 4000–250 cmꢁ1
;
the data has been provided in the Experimental Section 2.2. A sub-
stantial lowering of the N–H stretching frequency (3285 cmꢁ1) for
Na2LꢀH2O to 3139 cmꢁ1 for complex 3 indicates a coordinated
amino group [23], which is also verified by XRD crystallography
of 3. The tN–H stretching vibration did not exhibit any significant
change in complexes 1 and 2 compared to the free ligand, indicat-
ing a non-coordinated amino group [6]. The carbonyl stretching
frequencies of the free ligand (Na2LꢀH2O) was lowered in the com-
plexes, which is ascribed to a metal carboxylate interaction [24].
The binding modes of the carboxylate groups can be predicted
from the
indicates that the carboxylate groups are coordinated more sym-
metrically. The
values of 151–183 cmꢁ1 demonstrate a chelat-
D
t
=
t
COO(asym)
ꢁ
tCOO(sym) values; a smaller Dt value
D
t
ing mode of the carboxylate group in products 1 and 2 [25,26];
this value shows a significant increase to 232 cmꢁ1 in 3, reflecting
a bridging coordination mode of the carboxylate group [27], which
was also verified by the single crystal XRD study of 3. Bridging
coordination modes are common in organotin carboxylates where
each of the carboxylate groups is simultaneous bonded with two
Table 1
(C–Sn–C) angles (°) based on 1H and 13C NMR parameters.
Comp. No
2J (119/117Sn, 1H) (Hz)
Angle (°)
h(2J)
1
3
93.64; 65.1
113.4/109.2, 81.9
139.6; 114.9
166.82/160.36, 127.39
tin centers [3], as in case of 3. The
tSn–C (tin-alkyl) vibrational

S. Hussain et al. / Polyhedron 117 (2016) 64–72
67
The 13C NMR spectrum of 3 displayed the expected signals of its
ligand skeleton and the coordinated organotin moieties. The
upfield shift of the resonance signal for the carboxylate carbon
atom of the free ligand (Na2LꢀH2O) from d 179.3 to 171.1–
172.7 ppm in complexes 1–3 can be attributed to the carboxy-
late-tin linkage and indicates that the carbon atom of carboxylate
ion bound to the tin center is more electron rich compared to that
of three methyl radicals and complete decarboxylation to generate
the [C7H12NO4Sn2]+ (m/z = 414 (37%)) and [C8H21NSn2]+ (m/z = 371
(10%)) ions, respectively. In the negative mode, the appearance of a
peak with m/z = 457 (6%) corresponds to the formation of the [C10
H
-
19NO4Sn2]ꢁ ion. The EIMS of complex 2 did not display a molec-
ular ion peak. It evolved a triphenyltin radical to generate the
[C22H20NO4Sn]+ (m/z = 482 (16%)) ion, which further loses a phenyl
radical in each successive step to yield the [C16H15NO4Sn]+ 405
(100%), [C10H10NO4Sn]+ 328 (31%) and [C4H5NO4Sn]+ 251 (35%)
ions step by step. The parent species 2 may also split into a triph-
0
bound with sodium. Also the methylene carbon atoms (C-3,3 ) in
the products 1 and 2 are more shielded (d 51.2–51.3 ppm) as com-
pared to those in the ligand precursor (d 51.9 ppm). However, the –
CH2– signal did not show any shift in complex 3 as compared to the
ligand; the appearance of this peak at the same position in the
ligand and product 3 has also been verified by 1H NMR spec-
troscopy. The carbon atoms of the methyltin(IV) and dichlorodi-
methyltin(IV) moieties in complex 3 exhibited similar nuclear
magnetic resonance behavior in solution, which is demonstrated
by the appearance of their 13C NMR chemical shifts at the same
position (d 23.5 ppm). A penta-coordinated environment around
the metal center in the triphenyltin(IV) derivative 2 was verified
through the appearance of resonance shifts at d 142.7 ppm for
the ipso-carbon atom. It is known that the chemical shifts d(13C)ipso
of the phenyl groups in the SnPh3 moiety lie in the range d 135.9–
138.7 ppm, corresponding to the value shown by tetrahedrally
coordinated Sn atom. For penta-coordinated triphenyltin(IV) car-
boxylate complexes d(13C)ipso will be observed at approximately
4 ppm higher [24].
enyltin cation (m/z = 351(24%)) whose further degradation contin-
+
ues until the formation of the Sn cation. The [C12H10
]
fragment
ion, m/z = 154 (86%), corresponds to the formation of a biphenyl
cation. Fig. 1 shows the EI-mass spectrum and the structures of
important fragment ions of coordination compound 3. The mole-
cules of 3 start to decompose through the expulsion of tetram-
ethyltin(IV) (SnMe4) to yield the [C6H11Cl4NO4Sn2]+ ion (m/
z = 541 (4%)), which first loses CO2 and then CO2 and CH2 radicals
to leave behind the deposits of the [C5H11Cl4NO2Sn2]+ (m/z = 497
(7%)) and [C3H9Cl4NSn2]+ (m/z = 439 (3%)) ions, respectively. The
dimethyltin cation (m/z = 150 (21%), may lose one or both sub-
stituents to yield [CH3Sn]+ (m/z = 135 (37%)) and [Sn]+ (m/z = 120
(13%)), respectively or it may combine with a methyl radical to
yield [C3H9Sn]+ (m/z = 165 (100%)). The peak at m/z = 185 (9%) cor-
responds to the chlorodimethyltin(IV) cation and explores the exis-
tence of a chloro-substituted tin(IV) compound, which has also
been confirmed by single crysal XRD analysis of 3.
Thermogravimetric analyses (TGA) of the ligand (Na2LꢀH2O) and
complex 2 were performed under an N2 atmosphere to compare
their degradation patterns, thermal stabilities and percentage puri-
ties. The total weight loss was theoretically calculated and com-
pared with the experimental results. The thermally decomposed
data agreed well with the expected chemical composition of the
ligand and the product complex. The data showed that while the
ligand (Na2LꢀH2O) is decomposed up to 794.12 °C, leaving behind
a final residual mass (end product) equivalent to Na2CO3, complex
2 undergoes thermal degradation up to a slightly higher tempera-
ture (800.00 °C) to evolve volatile molecules/radicals of (4Phꢀ,
SnH4, 2CO, CCHꢀ, Nꢀ) and depositing a final residue of SnO2. The
results are thus completely consistent with the molecular compo-
sition of product 2. The thermal decomposition data are summa-
rized in Table 3.
3.4. Mass spectrometry and thermogravimetric analyses
The electron ionization mass spectrum (EI-MS) was recorded for
complex 1. Product 2 was investigated by electrospray ionization
mass spectrometry (ESI-MS). The mass fragmentation data have
been summarized in Table 2. The ions containing the tin(IV) ion
appeared in the spectra as a series of peaks close to each other
due to isotopic effects. The relative intensities reported here were
qualitatively estimated from the ion current for the 120Sn peak in
each species, and must be regarded as approximate. The ESI-MS
(positive mode) of 1 shows the appearance of an M-20 peak (m/
z = 459 (19%)) corresponding to the loss of water and a hydrogen
molecule from the parent species. The evolution of H2 generates
a double bond between the imino nitrogen and methylene carbon
atoms in the ligand skeleton of the complex. Further fragmentation
of [C10H21NO4Sn2]+ (m/z = 459 (19%)) is continued by the removal
3.5. XRD crystallography
Table 4 represents the important crystallographic data of com-
pound 3; selected bond angles and bond lengths are given in
Table 5. The single crystal XRD study of 3 has proven it to be a trin-
uclear complex and one of the very few reported examples of
organotin(IV) carboxylates showing the simultaneous incorpora-
tion of dimethyltin(IV) and dichlorodimethyltin(IV) moieties.
There is evidence of intermolecular N–Hꢀ ꢀ ꢀCl interactions in the
crystal lattice (Figs. 4 and 5). Each discrete molecule (Figs. 2 and
3) consists of two kinds of tin center, i.e. Sn1 in each of the two
dichlorodimethyltin(IV) fragments and Sn2 in a dimethyltin(IV)
moiety. The ligand reacts with the metal in a pentadentate fashion,
contributing all of its four carboxylate oxygen atoms and the imino
nitrogen in coordination. A structural comparison of coordination
compound 3 with the reported complexes [Me2Sn(L)(MeOH)]2,
Table 2
Mass spectral data of complexes 1–3.
Comp.
No.
MS, m/z (%)
1
Positive mode: [C10H25NO5Sn2]+ 479 (n.o)#, [C10H21NO4Sn2]+ 459
(19), [C7H12NO4Sn2]+ 414 (37), [C8H21NSn2]+ 371 (10),
[C6H16NSn2]+ 342 (40), [C5H12NSn2]+ 326 (100), [C7H12NO4Sn]+ 294
(50), [C5H9NO2Sn]+ 236 (18), [C4H6NO2Sn]+ 220 (1).
Negative mode: [C10H25NO5Sn2]ꢁ 479 (n.o)#, [C10H19NO4Sn2]ꢁ 457
(6), [C9H19NO2Sn2]ꢁ 413 (12), [C8H19NSn2]ꢁ 369 (10),
[C6H15NSn2]ꢁ 341 (2), [C5H12NSn2]ꢁ 326 (2), [C2H6NSn2]ꢁ 284 (12),
[C6H10NO4Sn]ꢁ 280 (100), [C4H8NO2Sn]ꢁ 222 (9).
2
3
[C40H35NO4Sn2]+ 833 (n.o)#, [C22H20NO4Sn]+ 482 (16),
[C16H15NO4Sn]+ 405 (100), [C18H15Sn]+ 351 (24), [C10H10NO4Sn]+
328 (31), [C12H10Sn]+ 274 (16), [C4H5NO4Sn]+ 251 (35), [C6H5Sn
197]+ (14), [C12H10
(7).
]
+ 154 (86), [Sn]+ 120, [C6H5]+ 77 (12), [C4H3]+ 51
[Bu2Sn(L)(H2O)],
[Ph2Sn(L)(H2O)]
and
[Bu2Sn(PhL)(H2O)]
[19,20,22] of the same ligand indicates that the ligand ion (Lꢁ2
)
[C10H23Cl4NO4Sn3]+ 721 (n.o)#, [C6H11Cl4NO4Sn2]+ 541 (4),
[C5H11Cl4NO2Sn2]+ 497 (7), [C3H9Cl4NSn2]+ 439 (3),
[C6H8ClNO3Sn]+ 297 (11), [C2H6SnCl]+ 185 (9), [C3H9Sn]+ 165 (100),
[C2H6Sn]+ 150 (21), [CH3Sn]+ 135 (37), [Sn]+ 120 (13), [CO2]+ 44
(82).
acts in various multidentate modes and smaller molecules like
MeOH or H2O are also involved in coordination with the tin(IV)
ions. However, the synthesis of the investigated complex 3 does
not involve the incorporation of either water or methanol mole-
cules in its crystal lattice.
#
Molecular ion peak (M+); n.o. = not observed.

68
S. Hussain et al. / Polyhedron 117 (2016) 64–72
Fig. 1. EI-mass spectrum of coordination compound 3; the structure of each fragment ion has been described against its relevant peak in the mass spectrum.
Table 3
Thermal decomposition data of the free ligand (Na2L.H2O) and complex 2.
Comp. No
Molecular formula
Evolved components
% Loss Calculated/Found
Temperature range (°C)
Na2LꢀH2O
C4H5O4NNa2ꢀH2O
Hꢀ, HCN
CH2O, CH2OH
14.35/14.25
31.27/34.30
55.71–343.64
346.39–794.12
Residue left behind = Na2CO3
2
C40H35NO4Sn2
4Phꢀ, SnH4, 2CO, CCHꢀ, Nꢀ
Residue left behind = SnO2
81.62/81.87
50–800
Table 4
Crystal data and structure refinement parameters for complex 3.
Chemical formula
C10H23Cl4NO4Sn3
719.16
Tetragonal
Prism
Z
8
Formula mass (g molꢁ1
Crystal system
Crystal description
Crystal size (mm3)
Space group
)
Temperature (K)
296(2)
2.182
3.902
2720.0
0.71073
ꢁ13 6 h 6 18,
ꢁ18 6 k 6 18,
ꢁ22 6 l 6 23
2.708–26.00
2136
Density (calculated) (g cmꢁ3
)
Absorption coefficient (mmꢁ1
)
0.3 ꢃ 0.25 ꢃ 0.22
F(000)
I-42d
Radiation (A0) (Mo K
Index ranges
a
)
a (Å)
15.0428(7)
b (Å)
c (Å)
15.0428(7)
19.3180(10)
90
h (°) min max
Total reflections
Data/restraints/parameters
Rall, Rgt
a
(°)
2136/0/117
0.0207,
b (°)
90
0.0200
c
(°)
90
WRref, WRgt
0.0413,
0.0412
1.092
Volume (Å3)
4371.4(5)
Goodness-of-fit
A penta-coordinated configuration about each tin atom (Sn1
and Sn2) has been verified by XRD crystallography. The hydroxyl
oxygen atom from each carboxylate group of the ligand becomes
chelated to a dimethyltin(IV) cation, while the carbonyl oxygen
atom becomes bonded to a dichlorodimethyltin(IV) moiety. Actu-
ally the simultaneous effect of two highly electronegative chlorine

S. Hussain et al. / Polyhedron 117 (2016) 64–72
69
Table 5
where b is the largest and
a
is the second largest of the basal angles
Selected bond lengths (Å) and bond angles (°) for complex 3.
around the Sn atom. The angle values
square-pyramidal geometry and the value
perfectly trigonal–bipyramidal geometry. Thus, the
to zero for a perfect square-pyramid and unity for a perfect trigo-
nal-bipyramid [30]. The calculated values for the Sn1 and Sn2
atoms are 0.41 and 0.21, respectively and these values suggest that
the coordination geometry around each metal center is intermedi-
ate between square-pyramidal and trigonal bipyramidal, with a
small bias towards the former geometry. The square-pyramidal
characteristics are more dominant in case of Sn2 as compared to
a
= b = 180° correspond to a
= 120° correspond to
value is equal
a
Sn1–C1
Sn1–C2
Sn1–Cl1
Sn1–Cl2
Sn1–O1
Sn2–C5
Sn2–O2
C1–Sn1–C2
C1–Sn1–Cl1
C2–Sn1–Cl1
C1–Sn1–Cl2
C2–Sn1–Cl2
Cl1–Sn1–Cl2
C1–Sn1–O1
C2–Sn1–O1
Cl1–Sn1–O1
Cl2–Sn1–O1
C5–Sn2–C50
C5–Sn2–O2
C50–Sn2–O2
O2–Sn2–O20
2.100(6)
2.103(6)
2.4184(16)
2.4794(15)
2.503(4)
2.085(6)
2.172(3)
152.8(2)
100.40(19)
100.57(18)
98.27(19)
98.01(17)
92.40(6)
83.7(2)
Sn2–N1
O1–C3
O2–C3
N1–C4
C4–N1
C3–C4
2.270(8)
1.224(6)
1.282(6)
1.527(9)
1.474(9)
1.511(7)
s
s
C5–Sn2–N1
C50–Sn2–N1
O2–Sn2–N1
O20–Sn2–N1
N1–Sn2–N1
C3–O1–Sn1
C3–O2–Sn2
C4–N1–C4
C4–N1–Sn2
C40–N1–Sn2
O1–C3–O2
O1–C3–C4
O2–C3–C40
N1–C4–C3
99.3(3)
126.4(3)
74.3(2)
73.6(2)
27.1(4)
152.1(4)
120.3(3)
112.6(6)
110.5(5)
108.4(5)
121.9(5)
121.0(5)
117.1(4)
112.0(5)
the Sn1 center, as indicated by the relatively lower
s value (0.21)
in the former case. In case of the Sn1 atom, the apical position of
the square pyramid is occupied by a chlorine atom (Cl1), whereas
the other chlorine (Cl2), oxygen (O1) and two carbon atoms (C1
and C2) lie in the basal plane. The Cl2-Sn1–O1 bond angle of
177.73(10)° lies very close to 180°, suggesting the Cl2 and O1
atoms are in almost perfect trans positions to each other. The
two carbon atoms (C1 and C2) from the methyl groups are also
in trans positions, but they are highly distorted from the basal
80.60(19)
86.12(9)
177.73(10)
134.3 (4)
96.6(2)
96.1(2)
146.92(19)
plane in
a direction opposite to the Cl1 atom (C1–Sn1–
C2 = 152.8°), so each of these carbon atoms makes an angle greater
than the regular value of 90° with the apical chlorine atom (C1–
Sn1–Cl1 = 100.40° and C1–Sn1–Cl1 = 100.57°). The basal O1 and
Cl2 atoms are comparatively closer to the Cl1 atom, which is
demonstrated by the Cl1–Sn1–O1 and Cl1–Sn1–Cl2 bond angles
of 86.12(9) and 92.40(6)°, respectively. As for as the coordination
environment about the Sn2 atom is concerned, the nitrogen atom
(N1) from the ligand lies at the apical position, with the basal plane
being occupied by two oxygen atoms (O2 and O20) and two carbon
atoms (C5 and C5) from the methyl groups. The oxygen and carbon
atoms are displaced out of the regular basal plane and have O2–
Sn2–O20 and C5–Sn2–C50 bond angles of 146.92 and 134.3°, respec-
tively. The two oxygen atoms are slightly moved toward the apical
nitrogen atom (O2–Sn2–N1 = 74.3° and O20–Sn2–N1 = 73.6°),
while both the carbon atoms are displaced away from the apical
nitrogen atom, resulting in an expansion of the C5–Sn2–N1 and
C50–Sn2–N1 bond angles to 99.3(3) and 126.4(3)°; these bond
angles also suggest one carbon atom (C5) is comparatively closer
to the nitrogen atom (N1) than the other carbon atom (C50). The
results demonstrate that the C–Sn–C bond angle about the Sn1
Fig. 2. The asymmetric unit of 3.
atoms renders the Sn1 center highly electropositive and thus
enables the metal to receive electron density from nearby carbonyl
oxygen atom. According to Addison et al., the geometry around a
Sn atom can be characterized by the value of
s
= (b ꢁ
a)/60 [30],
Fig. 3. Molecular structure of complex 3. The thermal ellipsoids are drawn at the 50% probability level. The symmetry code i = x, 0.5 ꢁ y, 0.25 ꢁ z.

70
S. Hussain et al. / Polyhedron 117 (2016) 64–72
Fig. 4. Intermolecular NHꢀ ꢀ ꢀCl interactions in 3. The individual molecules are interlinked due to N–Hꢀ ꢀ ꢀCl interactions. The H atoms of methylene and methyl groups are
omitted for clarity.
center (152.8°) is comparatively greater as compared to the Sn2
center (134.3°). The geometry of the carboxylate carbon atom is
trigonal planar with the bond angles 121.9, 121.0 and 117.1°. There
is an asymmetric coordination mode for each COOꢁ ion, which is
confirmed by unequal C–O bond distances; O1–C3 = 1.224(6) Å
and O2–C3 = 1.282(6) Å. The two oxygen atoms of a same carboxy-
late group are bound to two different tin centers, resulting in
unequal Sn–O bond distances which are reflected in the associated
C–O bond lengths; the longer C–O bond is involved in the shorter
Sn–O interaction and vice versa [3]. The Sn–O bond distances
(Sn1–O1 = 2.503 Å and Sn2–O2 = 2.172 Å) are greater than the
covalent radii (2.13 Å) and significantly lesser than the sum of
the van der Waal’s radii (3.68 Å), indicating coordinate covalent
bonding [31,32].
Fig. 5. Packing diagram of 3 approximately viewed down the b axis. The minor components of disorder and hydrogen atoms have been omitted for clarity.

S. Hussain et al. / Polyhedron 117 (2016) 64–72
71
Table 6
Antibacterial and antifungal activities dataa (Disc diffusion method).
Comp. No.
Bacterial inhibition zone (mm)
Fungal inhibition zone (mm)
E. coli
B. subtilis
S. aureus
P. multocida
A. alternata
G. lucidum
P. notatum
T. harzianum
A. niger
Na2LꢀH2O
–
–
–
–
–
–
–
–
–
1
25c 0.22
30ab 0.11
32a 0.19
30ab 0.17
36a 0.35
31b 0.22
27c 0.11
31b 0.28
30ab 0.14
26c 0.19
30ab 0.33
31a 0.31
30a 0.26
25c 0.09
30a 0.17
29ab 0.28
23bc 0.14
32ab 0.26
20c 0.08
38a 0.29
22bc 0.16
31b 0.19
20c 0.11
41a 0.21
24bc 0.19
35ab 0.31
20c 0.19
45a 0.31
22bc 0.17
21c 0.11
30a 0.21
–
25c 0.11
30bc 0.24
26bc 0.14
37a 0.23
2
3
Standard drug
aConcentration = 1 mg/ml in DMSO; Data are expressed as the mean standard deviation of samples analyzed individually in triplicate at p < 0.1.; The letters in superscripts
in a same column indicate significant differences in activities i.e., a = maximum activity, b = intermediate activity, c = minimum activity, ab = activity between maximum and
intermediate and bc = activity between intermediate and minimum; Streptomycin and fluconazole are the standard antibacterial and antifungal drugs, respectively.
Table 7
Antibacterial and antifungal activities dataa (Minimal inhibitory concentration).
Comp. No.
MIC-bacterial (
l
g/ml)
MIC-fungal (
l
g/ml)
G. lucidum
E. coli
B. subtilis
S. aureus
P. multocida
A. alternata
P. notatum
T. harzianum
A. niger
Na2LꢀH2O
–
–
–
–
–
–
–
–
–
1
156
19.5
156
1.2
156
39
78
2.4
312
19.5
156
78
312
78
39
39
104
26
52
26
52
13
26
26
6.5
26
13
>0.4
26
13
13
–
52
26
52
416
2
3
Standard drug
a
Streptomycin and fluconazole are standard antibacterial and antifungal drugs, respectively.
Table 8
Hemolytic activities of the free ligand (Na2LꢀH2O) and complexes 1–3.
Comp. No.
Na2LꢀH2O
7.36 0.07
1
2
3
MeOH
DMSO
9.71 0.05
Triton-X 100
99.53 0.00
PBS
0.00 0.00
% of Hemolysis
9.05 0.06
9.71 0.05
10.33 0.06
10.75 0.06
3.6. Antimicrobial activities
3.7. Hemolytic activities
The ligands and the synthesized complexes were screened to
see their in vitro response against various strains of bacteria and
fungi by the disc diffusion method [14,15] and minimum inhibi-
tory concentration (MIC) evaluations [15,16]. Streptomycin and
fluconazole were used as standard drugs for the antibacterial and
antifungal screening tests, respectively. The test sample/reference
drug with a concentration of 1 mg/ml in DMSO was introduced
into the wells or discs. The wells exhibiting MICs were noted visu-
ally while the zones of inhibition of the discs were measured in
millimeters. The data have been summarized in Tables 6 and 7.
The free ligands precursor Na2LꢀH2O was found to be biologi-
cally inactive against the bacterial as well as the fungal strains
[33]. The coordination of the ligands with organotin(IV) moieties
induced appreciable antimicrobial activities in the consequent
complexes [6]. This increased activities of complexes 1–3 may be
due to the coordination and polarity of the tin(IV) atom with the
oxygen donor atoms of the ligand [34]. Most of the complexes
exhibited an antibacterial/antifungal potential very close to the
standard drugs (streptomycin and fluconazole); some complexes
were found to be even more potent than the standard antimicro-
bial drugs. This high activity of the complexes may be rendered
to the multinuclear coordination. However, the antimicrobial
potential varied from complex to complex, depending upon the
coordinated organotin(IV) moieties as well as the nature of tested
microorganism. Complex 1 is showed the best result against B. sub-
tilis with a zone of inhibition of 36 mm. The results obtained from
the minimum inhibitory concentration measurements suggest that
the complexes have generally lower MIC values against the fungi
as compared to the bacteria.
The in vitro hemolytic bioassays of the synthesized complexes
were carried out with human red blood cells and the average lysis
was reported with respect to triton X-100 as a positive control
(100% lysis) and PBS as a negative control (0% lysis). The results
obtained are summarized in Table 8.
The free ligand Na2LꢀH2O displayed 7.36% hemolytic effects as
compared to triton X-100. Among the complexes, the lowest
hemolytic activity (9.05%) was reported for complex 1 and the
highest value (10.33%) was recorded for the trimethyltin(IV) com-
plex 3. The slight increase in activities of complexes 1–3 (9.05–
10.33%) compared to their free ligand precursor (7.36%) may be
due to the change of solution medium from water (for Na2LꢀH2O)
to MeOH (for complexes 1 and 2) or DMSO (for complex 3) used
to perform the activity measurements. All the complexes 1–3 dis-
played sufficiently lower activities as compared to triton X-100
and higher than PBS. The hemolytic effects in the range 9.05–
10.33% indicated the possible safe use of these complexes for
human beings; there is need of further research in this regard.
4. Conclusion
The FTIR data of the complexes indicated a bidentate binding
mode of the carboxylate group with the metal center in the bridg-
ing and chelating modes. This type of coordination behavior was
also confirmed by single crystal XRD crystallography. The com-
plexes retain their solid state penta-coordinated geometries
around the Sn(IV) center, even in the solution. XRD-crystallogra-
phy of complex 3 demonstrated that the geometry around each

72
S. Hussain et al. / Polyhedron 117 (2016) 64–72
[12] E. Arks, D. Balko, Polym. Degrad. Stab. 88 (2005) 46.
[13] W.L.F. Armarego, C.L.L. Chai, Purification of Laboratory Chemicals, 5th Edn.,
Butterworth Heinemann, London, 2003.
[14] CLSI (The Clinical Laboratory Standards Institute), Agar dilution and disk
diffusion susceptibility testing of Campylobacter sp., J. Clin. Microbiol. 45
(2007) 2758.
[15] S. Hussain, S. Ali, S. Shahzadi, M.N. Tahir, M. Shahid, J. Coord. Chem. 68 (2015)
2369.
[16] S.D. Sarker, L. Nahar, Y. Kumarasamy, Methods 42 (2007) 321.
[17] P. Sharma, J.D. Sharma, J. Ethnophamacol. 74 (2001) 239.
[18] S. Hussain, S. Ali, S. Shahzadi, S.K. Sharma, K. Qanungo, I.H. Bukhari, J. Coord.
Chem. 65 (2012) 278.
tin center is almost midway between square-pyramidal and trigo-
nal bipyramidal. The aqua and amino moieties also participated in
coordination with the metal center in complexes in 1 and 3,
respectively. There are evidences for the presence of stereoisomers
in product 1. The elemental analysis, EI-MS, ESI and TGA studies
agree well with the molecular composition of the products. The
complexes display significant antibacterial/antifungal potential,
exhibiting slightly toxic hemolytic effects.
Acknowledgment
[19] C.D. Nicola, A. Galindo, J.V. Hanna, F. Marchetti, C. Pettinari, R. Pettinari, E.
Rivarola, B.W. Skelton, A.H. White, Inorg. Chem. 44 (2005) 3094.
[20] S. Hussain, S. Ali, S. Shahzadi, C. Rizzoli, M. Shahid, J. Chin. Chem. Soc. 62
(2015) 793.
[21] F. Arjmand, I. Yousuf, Y. Zaidi, L. Toupet, RSC Adv. 5 (2015) 16250.
[22] T. Mancilla, L. Carrillo, L.S.Z. Rivera, C.C. Camacho, D. Vos, R. Kiss, F. Darro, B.
Mahieu, E.R.T. Tiekink, H. Rahier, M. Gielen, M. Kemmer, M. Biesemans, R.
Willem, Appl. Organometal. Chem. 15 (2001) 593.
[23] M. Nath, S. Pokharia, R. Yadav, Coord. Chem. Rev. 215 (2001) 99.
[24] T.S.B. Baul, S. Dhar, S.M. Pyke, E.R.T. Tiekink, E. Rivarola, R. Butcher, F.E. Smith,
J. Organomet. Chem. 633 (2001) 7.
[25] H.D. Yin, C.H. Wang, Q.J. Xing, Polyhedron 23 (2004) 1805.
[26] M. Tariq, S. Ali, N.A. Shah, N. Muhammad, M.N. Tahir, N. Khalid, M.R. Khan,
Polyhedron 57 (2013) 127.
Shabbir Hussain (Pin No. 074-3160-Ps4-362) is thankful to the
Higher Education Commission of Pakistan for financial support
during the present study.
References
[1] E.R.T. Tiekink, Appl. Organomet. Chem. 5 (1991) 1.
[2] S.M. Abbas, S. Ali, S.T. Hussain, S. Shahzadi, J. Coord. Chem. 66 (2013) 2217.
[3] S. Hussain, S. Ali, S. Shahzadi, C. Rizzoli, Phosphorus Sulfur Silicon Relat. Elem.
188 (2013) 812.
[27] G. Eng, X. Song, A. Zapata, A.C. De Dios, L. Casabiana, R.D. Pike, J. Organomet.
Chem. 692 (2007) 1398.
[28] M.L. Dianu, A. Kriza, N. Stanica, A.M. Musuc, J. Serb. Chem. Soc. 75 (2010) 1515.
[29] T.P. Lockhart, W.F. Manders, E.M. Holts, J. Am. Chem. Soc. 108 (1986) 6611.
[30] A.W. Addison, T.N. Rao, J. Reedijk, J. Van Rijn, G.C. Verschoor, J. Chem. Soc.,
Dalton Trans. (1984) 1349.
[4] G. Matela, R. Aman, Cent. Eur. J. Chem. 10 (2012) 1.
[5] R.G. Vollano, R.O. Day, D.N. Rue, V. Chandruekhar, R.R. Holmes, Inorg. Chem. 23
(1984) 3153.
[6] S. Hussain, S. Ali, S. Shahzadi, S.K. Sharma, K. Qanungo, M. Shahid, Bioinorg.
Chem. Appl. (2014) 1. 2014.
[7] L. Pellerito, L. Nagy, Coord. Chem. Rev. 224 (2012) 111.
[8] B. Parveen, I.H. Bukhari, S. Shahzadi, S. Ali, S. Hussain, K.G. Ali, M. Shahid, J.
Serb. Chem. Soc. 80 (2015) 755.
[31] M. Tariq, S. Ali, N. Muhammad, N.A. Shah, M. Sirajuddin, M.N. Tahir, N. Khalid,
M.R. Khan, J. Coord. Chem. 67 (2014) 323.
[32] E.R.T. Tiekink, Tiekink. Trends Organomet. Chem. 1 (1994) 71.
[33] S. Hussain, I.H. Bukhari, S. Ali, S. Shahzadi, M. Shahid, K.S. Munawar, J. Coord.
Chem. 68 (2015) 662.
[9] L. Tian, Y. Sun, H. Li, X. Zheng, Y. Cheng, X. Liu, B. Qian, J. Inorg. Biochem. 99
(2005) 1646.
[10] X.Y. Zhang, H. Song, Q. Li, X. Liu, L. Tang, Polyhedron 26 (2007) 3743.
[11] A.J. Crowe, P.J. Smith, G. Atassi, Chem. Biol. Interact. 32 (1980) 171.
[34] N. Singh, S. Gupta, G. Nath, Appl. Organomet. Chem. 14 (2000) 484.