Organotin(IV) derivatives of o-isobutyl carbonodithioate: Synthesis, spectroscopic characterization, X-ray structure, HOMO/LUMO and in vitro biological activities

Article abstract of DOI:10.1016/j.poly.2015.11.041

A series of organotin(IV) complexes have been synthesized by reacting potassium o-isobutyl carbonodithioate with di- and triorganotin halides in methanol under stirring conditions. The newly synthesized complexes have been characterized by elemental analysis, FT-IR, NMR (¹H and ¹³C) and X-ray crystallography. The FT-IR results show that the ligand acts as bidentate in complexes 1-3 and monodentate in complexes 4 and 5, which were also confirmed by theoretical calculations. The NMR data reveal four and six coordinated geometries in solution. A HOMO-LUMO study shows that all the complexes are stable. Biological screenings demonstrate that, with a few exceptions, all the complexes show significant activity against various bacterial and fungal strains. The synthesized complexes were also found to be effective antioxidants of the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH). All the complexes have been assayed for antileishmanial activity in vitro and found some promising results. The UV-Vis studies confirmed that the ligand and its complexes bind to DNA via intercalative interactions, resulting in hypochromism and minor red shifts.

Full text of DOI:10.1016/j.poly.2015.11.041

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Polyhedron 104 (2016) 80–90
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Organotin(IV) derivatives of o-isobutyl carbonodithioate: Synthesis,
spectroscopic characterization, X-ray structure, HOMO/LUMO and
in vitro biological activities
a,
c
d
Fatima Javed a, Muhammad Sirajuddin b, , Saqib Ali , Nasir Khalid , Muhammad Nawaz Tahir ,
⇑
⇑
Naseer Ali Shah e, Zahid Rasheed a, Muhammad Rashid Khan f
a Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan
b Department of Chemistry, University of Science & Technology, Bannu, Pakistan
c Chemistry Division, Pakistan Institute of Nuclear Science and Technology, P.O. Nilore, Islamabad, Pakistan
d Department of Physics, University of Sargodha, Pakistan
e Department of Biosciences, COMSATS Institute of Information Technology, Islamabad, Pakistan
f Department of Biochemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of organotin(IV) complexes have been synthesized by reacting potassium o-isobutyl car-
bonodithioate with di- and triorganotin halides in methanol under stirring conditions. The newly synthe-
sized complexes have been characterized by elemental analysis, FT-IR, NMR (1H and 13C) and X-ray
crystallography. The FT-IR results show that the ligand acts as bidentate in complexes 1–3 and monoden-
tate in complexes 4 and 5, which were also confirmed by theoretical calculations. The NMR data reveal
four and six coordinated geometries in solution. A HOMO–LUMO study shows that all the complexes are
stable. Biological screenings demonstrate that, with a few exceptions, all the complexes show significant
activity against various bacterial and fungal strains. The synthesized complexes were also found to be
effective antioxidants of the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH). All the complexes have been
assayed for antileishmanial activity in vitro and found some promising results. The UV–Vis studies con-
firmed that the ligand and its complexes bind to DNA via intercalative interactions, resulting in hypochro-
mism and minor red shifts.
Received 17 September 2015
Accepted 15 November 2015
Available online 2 December 2015
Keywords:
Organotin(IV) complex
HOMO–LUMO calculation
DNA interaction
In vitro biological application
Protein kinase inhibition
Ó 2015 Published by Elsevier Ltd.
1. Introduction
which showed that these ligands can coordinate to metal atoms
in monodentate, isobidentate or anisobidentate fashions. More
The multifunctional approaches of dithiocarbonates make its
chemistry more impressive due to its chemical interaction with a
variety of biomolecules, such as proteins, DNA and drugs etc.
One of the important structural consequences of dithio ligands lead
to the preferential stabilization of specific stereochemistries in
their metal complexes. Dithio ligands are considered as soft
donors, showing excellent coordination ability. They form stable
complexes with transition as well as non-transition metal ions
[1,2] and exhibit a variety of coordination modes in homo and
heteronuclear complexes, depending on the binding modes of the
ligands toward the metal center [3–7]. Subsequently, extensive
structural analyses were performed by Tiekink and Haiduc [8]
recent applications of xanthates and other thio-compounds are in
the production of nanoparticles of metal sulfides [9,10] and for
the use of their non-linear optical properties [11,12]. Metal xan-
thates are extensively used as pesticides [13], corrosion inhibitors
[14], agricultural reagents [15] and quite recently in therapy for
HIV infections [16]. Moreover, xanthates are also known to show
antitumor properties [17,18] and their antioxidant properties
could be of importance for treating Alzheimer’s disease [19].
The chemistry of organotin compounds is gaining attention on
account of their interesting structural features, schizonticidal, anti-
malarial, fungicidal activities and their potential as agricultural
biocides [20]. Recent studies have shown very promising in vitro
antitumor properties of organotin compounds against a wide panel
of tumor cell lines of human origin. In some cases, organotin(IV)
derivatives have also shown acceptable antiproliferative in vivo
activity as new chemotherapy agents. The biological activity of
⇑
Corresponding authors. Tel.: +92 5190642130; fax: +92 5190642241.
E-mail addresses: m.siraj09@yahoo.com (M. Sirajuddin), drsa54@hotmail.com
(S. Ali).
http://dx.doi.org/10.1016/j.poly.2015.11.041
0277-5387/Ó 2015 Published by Elsevier Ltd.

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F. Javed et al. / Polyhedron 104 (2016) 80–90
81
organotin compounds is basically determined by the number and
nature of the organic groups bound to the central tin atom. [R3Sn
(IV)]+ and [Ar3Sn(IV)]+ derivatives exert powerful toxic action on
the central nervous system. Within the series of [R3Sn(IV)]+ com-
pounds, the lower homologs (Me, Et) are the most toxic when
administrated orally, and the toxicity reduces progressively on
going from propyl to octyl, the latter not being toxic at all. The
presence of easily hydrolysable groups (easily dissociable chelating
ligands), producing intermediates such as RnSn(4ꢀn)+ (n = 2 or 3)
moieties which may bind with DNA or the high affinity site of
ATPase (histidine only), the low-affinity site of ATPase and hemo-
globins (histidine and cystine), play an important role in the deter-
mination of the biological activity of the organotin compounds.
Therefore, substantial attempts have been made to characterize
model organotin compounds of ligands having hetero donor atoms
2.2. Synthesis
2.2.1. Synthesis of the ligand (KL)
Potassium o-isobutyl carbonodithioate was prepared by stirring
equimolar amounts (1 mmol) of isobutanol, potassium hydroxide
and carbon disulfide (1 mmol) with continuous stirring at ambient
temperature (23 1 °C) for 4 h. The precipitates obtained were fil-
tered off and dried in air.
Yield: 92%. M.p.: 205–206 °C. Mol. Wt.: 187.97. Anal. Calc. for
C5H9KOS2: C, 31.88 (31.84); H, 4.82 (4.85); S, 34.05 (34.02). IR
(cmꢀ1): 997
m(CAO); 1396 m(CSSasym); 1124 m(CSSsym); 272
(Dm
); 1H NMR (DMSO-d6, 300 MHz) d (ppm): 0.87 (d, 6H, H1, 3J
[1H,1H] = 6.6 Hz); 1.90 (m, 1H, H2); 3.96 (d, 2H, H3, 3J[1H, 1H]
= 6.6 Hz). 13C NMR (DMSO-d6, 75 MHz) d (ppm): 19.9 (C1); 27.9
(C2); 77.6 (C3); 230.5 (C4).
S
KOH
H3C
H3C
H2
C
H3C
H3C
H
C
H2
C
H
C
CS2
OH
O
SK
4h stirring at
room temperature
(O, N and S), and simultaneously several studies have been focused
on structure-activity correlations during the last two decades [21].
In the present study we have synthesized some novel organotin
complexes by the reaction of di- and triorganotin(IV) halides with a
sulfur donor ligand. The complexes have been characterized by
FT-IR, NMR (1H and 13C), X-ray crystallography and a computa-
tional study. A HOMO/LUMO study was performed to establish
the stability of the complexes. Biological screening, i.e. antibacte-
rial, antifungal, antileishminial, antioxidant, toxicity, protein
kinase inhibition and DNA binding studies, have been performed
to establish the significance of the synthesized complexes.
2.2.2. Synthesis of the organotin(IV) complexes
Potassium o-isobutyl carbonodithioate (2 mmol) was dissolved
in methanol (20 mL) in a round bottom two-necked flask (100 mL)
with continuous stirring at ambient temperature. Then to this solu-
tion, R2SnCl2/R3SnCl (1 mmol/2 mmol) was added. The reaction
mixture was continuously stirred for 4 h at room temperature.
The solvent was evaporated slowly at room temperature. The solid
product obtained was dried in air and recrystallized from an ace-
tone:ether mixture (1:1). The synthesis of the organotin(IV) com-
plexes have been shown as a generalized chemical equation in
Scheme 1, whereas the numbering patterns of KL and the alkyl
groups attached to the Sn atom for NMR interpretation are
depicted in Scheme 2.
2. Experimental
2.2.3. Dimethylstannanediyl bis (o-isobutyl dicarbonodithioate) (1)
Yield: 86%. M.p. 105–106 °C. Mol. Wt.: 447.97. Anal. Calc. for
2.1. Materials and methods
C
12H24O2S4Sn: C, 32.22 (32.19); H, 5.41 (5.38); S, 25.68 (25.65).
IR (cmꢀ1): 961
(CAO); 1259 (CSSasym); 1078 (CSSsym); 181
); 377 (SnAS); 557
(SnAC). 1H NMR (DMSO-d6, 300 MHz) d
(ppm): 1.01 (d, 12H, H1, 3J[1H, 1H] = 6.6 Hz); 2.15 (m, 2H, H2);
4.23 (d, 4H, H3, 3J[1H, 1H] = 6.6 Hz), 1.51 (s, 6H,
m
m
m
All the organotin(IV) halides, Ph3SnCl, isobutanol, potassium
hydroxide and carbon disulfide were obtained from Aldrich (USA)
and were used without further purification. All the solvents pur-
chased from E. Merck (Germany) were dried before use according
to literature procedures [22]. Melting points were recorded with
a Bio-Cote Model SMP10 melting point apparatus and are uncor-
rected. FT-IR spectra were recorded in the range 4000–250 cmꢀ1
with a Thermo Scientific Nicolet-6700 FTIR spectrometer and
NMR spectra were obtained with a Bruker Avance 300 MHz NMR
spectrometer. Absorption spectra were measured on a double
beam UV–Vis spectrometer, Shimadzu 1800, at 25 1 °C. The
sodium salt of DNA (Acros) was used as received. The quantitative
determination of C, H and S was carried out using a LECO CHNS-
932 analyzer. The X-ray diffraction data were collected on a Bruker
SMART APEX CCD diffractometer, equipped with a 4 K CCD detec-
tor set 60.0 mm from the crystal. The crystals were cooled to
100 1 K using a Bruker KRYOFLEX low temperature device and
intensity measurements were performed using graphite
(D
m
m
m
Ha)
[
119/117SnA1H] = 79, 76 Hz). 13C NMR (DMSO-d6, 75 MHz)
d
(ppm): 19.0 (C1); 27.7 (C2); 82.3 (C3); 222.2 (C4); 10.5 (C
a
,
1J
[
119/117SnA13C
a] = 599, 573 Hz).
2.2.4. Dibutylstannanediyl bis (o-isobutyl dicarbonodithioate) (2)
Yield: 85%. M.p. oily. Mol. Wt.: 532.06. Anal. Calc. for
18H36O2S4Sn: C, 40.68 (40.65); H, 6.83 (6.80); S, 24.13 (24.10).
C
monochromated Mo Ka radiation from a sealed ceramic diffraction
tube (SIEMENS). The structure was solved by the Patterson method
and extension of the model was accomplished by the direct
method using the program DIRDIF or SIR2004. Final refinement on
F2 was carried out by full matrix least squares techniques using
SHELXL-97, a modified version of the program PLUTO (to prepare illus-
trations) and the PLATON package.
Scheme 1. Generalized chemicals equations for the synthesis of the organotin(IV)
derivatives.

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82
F. Javed et al. / Polyhedron 104 (2016) 80–90
Scheme 2. Numbering patterns of KL and the organic moieties attached to the Sn atom for NMR interpretation.
IR (cmꢀ1): 967
m
(CAO); 1267
m
(CSSasym); 1067
m
(CSSsym); 200
symmetry restrictions were imposed on any complex. The Hessian
calculations confirmed that the optimized structures are local min-
ima on the potential energy surface as no imaginary frequencies
were found in any case. The plots of the optimized structures
and the HOMO–LUMO were realized, respectively, with Molden
[24] and CCP1-GUI [25] programs.
(D
m
); 369
(ppm): 0.99 (d, 12H, H1); 2.14 (m, 2H, H2); 4.24 (d, 4H, H3, 3J[1H,
1H] = 6.6 Hz), 2.03 (m, 4H, H
), 1.88 (m, 4H, Hb); 1.43 (m, 4H,
); 0.93 (m, 6H, Hd, 3J[1H, 1H] = 7.2 Hz). 13C NMR (DMSO-d6,
75 MHz) d (ppm): 19.2 (C1); 26.4 (C2); 82.1 (C3); 223.2 (C4);
30.5 (C
1J[119/117SnA13C ] = 542, 518 Hz); 29.0 (Cb, 2J
119SnA13Cb] = 39 Hz); 27.7 (C 3J[119/117SnA13C
] = 39, 35 Hz);
13.7 (Cd).
m(SnAS); 558 m
(SnAC): 1H NMR (DMSO-d6, 300 MHz) d
a
Hc
a,
a
[
c,
c
2.4. Biological screenings
DNA interaction assay by UV–Vis spectroscopy, antibacterial,
antifungal, antileishmanial, antioxidant, cytotoxicity and protein
kinase inhibition studies were performed using the same proce-
dures as reported earlier [26,27].
2.2.5. Diphenylstannanediyl bis (o-isobutyl dicarbonodithioate) (3)
Yield: 76%. M.p. 90–91 °C. Mol. Wt.: 572.0. Anal. Calc. for
C
22H28O2S4Sn: C, 46.24 (46.21); H, 4.94 (4.90); S, 22.45 (22.42).
IR (cmꢀ1): 944
(CAO); 1251 (CSSasym); 1045 (CSSsym); 206
); 370 (SnAS); 283
(SnAC). 1H NMR (DMSO-d6, 300 MHz) d
(ppm): 0.89 (d, 12H, H1, 3J[1H, 1H] = 6.6 Hz); 1.90 (m, 2H, H2);
4.15 (m, 4H, H3); 7.74 (m, 4H, Hb); 7.49 (m, 4H, H ); 7.47 (m,
2H, Hd). 13C NMR (DMSO-d6, 75 MHz) d (ppm): 19.0 (C1); 27.5
(C2); 82.7 (C3); 215.7 (C4); 130.0 (C ] = 828,
1J[119/117SnA13C
793 Hz), 128.7 (Cb, 2J[119/117SnA13Cb] = 71, 68 Hz); 135.5 (C 3J
119/117SnA13C ] = 55, 52 Hz); 131.0 (Cd, 4J[119SnA13Cd] = 15 Hz).
m
m
m
(D
m
m
m
3. Results and discussion
c
The proposed chemical structures of the synthesized complexes
are given in Supplementary data Table S1.
a
,
a
c,
3.1. FT-IR spectra
[
c
The characteristic IR frequencies (cmꢀ1) of the ligand (KL) and
its organotin(IV) complexes (1–5) are listed in the experimental
part. Several significant changes on complexation with respect to
the bands of the free ligand suggest coordination through the thio-
carboxylate group of the ligand. In the spectra of the investigated
complexes, the vibrational modes of CS2 are of particular interest
to differentiate between monodentate and bidentate coordination
of the dithiolate moiety. The FT-IR spectra of complexes 1–5 gave
2.2.6. Tributylstannyl o-isobutylcarbonodithiate (4)
Yield: 80%. M.p. oily. Mol. Wt.: 440.12. Anal. Calc. for C17H36OS2Sn:
C, 46.48 (46.45); H, 8.26 (8.24); S, 14.60 (14.56). IR (cmꢀ1): 960
(CAO); 1288 (CSSasym); 1021 (CSSsym); 267 ( ); 366 (SnAS);
592
(SnAC): 1H NMR (DMSO-d6, 300 MHz) d (ppm): 0.98 (d, 6H,
H1, 3J[1H, 1H] = 6.6 Hz); 2.12 (m, 2H, H2); 4.23 (m, 4H, H3, 3J[1H,
1H] = 6.6 Hz); 1.61 (m, 6H, H
), 1.38 (m, 6H, Hb); 1.33 (m, 6H,
); 0.91 (m, 9H, Hd, 3J[1H, 1H] = 7.2 Hz). 13C NMR (DMSO-d6,
75 MHz) d (ppm): 19.2 (C1); 27.6 (C2); 81.3 (C3); 218.3 (C4);
15.8 (C
1J[119/117SnA13C ] = 337, 322 Hz), 29.0 (Cb, 2J
119SnA13Cb] = 22 Hz); 27.0 (C 3J[119/117SnA13C
] = 66, 63 Hz);
13.6 (Cd).
m
m
m
D
m
m
m
a
strong peaks at 1251–1297 cmꢀ1, attributed to the asymmetric
m
m
H
c
(CS2)as absorption, and 1021–1078 cmꢀ1, assigned to symmetric
a,
a
(CS2)s absorption frequencies. The differences between
m(CS2)as
(CS2)s are 181, 200 and 206 cmꢀ1 for complexes 1–3, respec-
[
c
,
c
and
m
tively, which indicate a bidentate binding mode of the ligand to the
central tin atom. For complexes 4 and 5, the differences are 267
and 253 cmꢀ1, which indicate a monodentate mode, probably
due to steric effects [28]. The binding modes of the complexes were
also confirmed by a theoretical study. The FT-IR results of complex
1 are consistent with the X-ray crystallographic data. The IR bands
observed in the range 366–377 cmꢀ1 in the spectra of the com-
plexes are assigned to SnAS bonding [29]. The absorptions at
2.2.7. Triphenylstannyl o-isobutylcarbonodithiate (5)
Yield: 91%. M.p. 111–112 °C. Mol. Wt.: 500.03. Anal. Calc. for
C
23H24OS2Sn: C, 55.33 (55.31); H, 4.85 (4.80); S, 12.84 (12.81). IR
(cmꢀ1): 996
m
(CAO); 1297
m(CSSasym); 1044 m(CSSsym); 253
(D
m
); 375
m
(SnAS); 279 m
(SnAC). 1H NMR (DMSO-d6, 300 MHz) d
(ppm): 0.90 (d, 6H, H1, 3J[1H, 1H] = 6.6 Hz); 1.90 (m, 2H, H2);
4.09 (m, 4H, H3, 3J[1H, 1H] = 6.6 Hz); 8.02 (m, 6H, Hb); 7.51 (m,
557, 558 and 592 cmꢀ1 are assigned to
plexes 1, 2 and 4, respectively whereas for the di- and triph-
m(SnAC) bands for com-
6H, H
19.3 (C1); 29.7 (C2); 83.0 (C3); 218.7 (C4); 139.0 (C
119/117SnA13C ] = 566, 543 Hz), 128.6 (Cb, 2J[119/117SnA13Cb] = 59,
57 Hz); 136.6 (C
3J[119SnA13C ] = 44 Hz); 129.4 (Cd, 4J
119SnA13Cd] = 13 Hz).
c
); 7.49 (m, 3H, Hd). 13C NMR (DMSO-d6, 75 MHz) d (ppm):
a,
1J
enyltin(IV) derivatives (3 and 5), the m(SnAC) bands are observed
at 283 and 279 cmꢀ1, respectively. These values are in close agree-
ment with those observed for a number of organotin(IV) deriva-
tives of sulfur donor ligands [28]. Based on the infrared analyses,
it is suggested that the ligand is coordinated to the tin(IV) moiety
through the thiolato sulfur atoms.
[
a
c
,
c
[
2.3. Theoretical study
All the calculations were performed using the 6-31G* basis set
for H, C, O and S. This is a split valence double-zeta basis set which
adds d-type polarization functions on the first and second row ele-
ments. For the Sn atom, the LANL2DZ basis set was used, which
uses the Los Alamos effective core potential on the metal atom.
The geometries of complexes 1–5 were optimized with the DFT/
B3LYP method as implemented in the Gaussian-09 quantum chem-
istry package [23]. In the geometry optimization procedure, no
3.2. 1H and 13C NMR spectra
In the 1H NMR spectra, the chemical shifts were identified from
their relative intensities and multiplicity patterns. The total num-
bers of protons, calculated from the integration curves, are com-
patible with the proposed structures. The protons H1, H2 and H3
of the ligand appeared at 0.87, 1.90 and 3.96 ppm and these peaks
exhibited a downfield shift in the complexes (1–5) in the range

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F. Javed et al. / Polyhedron 104 (2016) 80–90
83
Table 1
the coordination of the ligand to the metal center via the ACSS
moiety [30]. Coordination of the Sn atom in the di- and triorgan-
otin complexes has been further supported by the 1J(119SnA13C)
coupling constants and the CASnAC angles (108–129°), calculated
by Lockhart’s equation (Table 1) [32]. In complexes 1–3, the 1J
(CASnAC) angles (°) based on NMR parameters of complexes 1–5.
Compd. no.
1J [119Sn,13C] (Hz)
2J[119Sn, 1H] (Hz)
Angles (°)
1J
2J
1
2
3
4
5
599
542
828
337
566
80
–
–
–
–
129
128
128
108
111
126
–
–
–
–
(
119SnA13C) coupling constants observed and CASnAC angles cal-
culated were 599 Hz (129°), 542 Hz (128°) and 828 Hz (128°),
which are attributed to a six coordinated geometry, while a four
coordinated geometry is inferred for complexes 4 and 5, having
coupling constants and angles of 337 Hz (108°) and 566 Hz
(111°) [33]. This was further confirmed by theoretical calculations.
The results are also consistent with the X-ray crystallographic
structure for complex 1.
0.89–1.01 for H1, 2.12–2.15 for H2 and 4.09–4.24 ppm for H3. This
downfield shift is due to the deshielding of these protons due to
deprotonation of the ligand and coordination of the CS2 group to
the tin moiety. These observations are in agreement with the
reported triphenyltin(IV) dithiocarboxylates [30]. The coupling
constant [2J(119Sn, 1H)] for 1 was 79 Hz, which is in the expected
range for a six-coordinated Sn center and is consistent with a
CASnAC angle of 126°. The coupling constants, [2J(119Sn, 1H)], for
the n-butyl-, di-, and triphenyltin(IV) complexes could not be
determined owing to their complex patterns. The geometry of
the triphenyltin(IV) complex was calculated from the difference
in the chemical shift resonances of the ortho to meta and para pro-
tons (0.5 ppm), which matched well with the bidentate bonding of
the 1,1-dithiolate moiety in solution [31].
3.3. Crystal structure of complex 1
The structure of complex 1 and its packing diagrams are shown
in Figs. 1–3. The crystal and structural refinement data and
selected interatomic parameters are summarized in Tables 2 and
3, respectively. The Sn atom is coordinated by two methyl groups
and two dithiocarboxylate ligands, with the latter adopting similar
behavior with regard to their coordination modes. The two ligands
are anisobidentically chelated to Sn, with one longer SnAS2 and
one shorter SnAS1 bond (3.125(15) and 2.481(14) Å). The longer
SnAS distances are significantly less than the sum of the van der
Waal’s radii (4.0 Å), and the coordination number of Sn is unam-
biguously assigned as six. The overall geometry at Sn is, however,
highly distorted from trans octahedral: the C6ASnAC7 angle is
only 134.5(5)°, the Sn and four sulfur atoms of the dithiocarboxy-
late ligands are nearly coplanar, but are badly distorted from a
square-planar geometry (the cis (SASnAS) angles range from 85.7
(6) [S1ASnAS1A] to 146.9(1)° [(S2ASnAS2A]). In both anisobiden-
tate ligands, each shorter SnAS bond is associated with a longer
The 13C NMR spectral data, along with the assignment of char-
acteristic peaks of the ligand and the organotin(IV) complexes, are
described in the experimental section. An important chemical shift
of a carbon atom in the dithiocarbonate complex is that of the
thione carbon (CS2). The signal due to the CS2 carbon atom in
the free ligand appears at 230.5 ppm. However, in the spectra of
the corresponding tin complexes, this appears at 222.2 in complex
1, 223.2 in 2, 215.7 in 3, 218.3 in 4 and 218.7 ppm in 5, indicating
Fig. 1. Crystal structure of complex 1.
Fig. 2. Packing diagram of complex 1 viewed along the a-axis.