A novel macrocyclic organotin carboxylate containing a penta-nuclear long ladder

Article abstract of DOI:10.1016/j.jorganchem.2014.01.034

A novel macrocyclic organotin carboxylate [(n-Bu₂SnO) ₅L] (complex 1) [H₂L = (3-carboxymethoxy-phenoxy) acetic acid] was synthesized by the reaction of di-n-butyltin oxide with H₂L and is characterized by elemental analyses i.e. IR ¹H NMR and UV spectroscopies. X-ray crystallography diffraction analysis reveals that complex 1 is a centrosymmetric macrocycle and contains a penta-nuclear four-fold-ladder-like organo-oxotin cluster. All five Sn atoms are five-coordinated and the coordination environment can be considered as a trigonal bipyramidal. The luminescent property of complex 1 has also been investigated. Pilot studies have confirmed that complex 1 has shown good antitumor activity.

Full text of DOI:10.1016/j.jorganchem.2014.01.034

Journal of Organometallic Chemistry 758 (2014) 19e24
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
A novel macrocyclic organotin carboxylate containing a penta-nuclear
long ladder
Aboubacar Sidiki Sougoule a, Zemin Mei b, Xiao Xiao a, Cheick Abdoul Balde c,
,
Salematou Samoura c, Arouna Dolo a, Dongsheng Zhu a
*
a Department of Chemistry, Northeast Normal University, Changchun 130024, China
b Department of Chemistry, Baicheng Normal University, Baicheng 137000, China
c Department of Chemistry, University of Conakry, Guinea
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel macrocyclic organotin carboxylate [(n-Bu2SnO)5L] (complex 1) [H2L ¼ (3-carboxymethoxy-
phenoxy) acetic acid] was synthesized by the reaction of di-n-butyltin oxide with H2L and is charac-
terized by elemental analyses i.e. IR 1H NMR and UV spectroscopies. X-ray crystallography diffraction
analysis reveals that complex 1 is a centrosymmetric macrocycle and contains a penta-nuclear four-fold-
ladder-like organo-oxotin cluster. All five Sn atoms are five-coordinated and the coordination environ-
ment can be considered as a trigonal bipyramidal. The luminescent property of complex 1 has also been
investigated. Pilot studies have confirmed that complex 1 has shown good antitumor activity.
Ó 2014 Elsevier B.V. All rights reserved.
Received 7 December 2013
Received in revised form
5 January 2014
Accepted 17 January 2014
Keywords:
Organotin (IV) compound
Synthesis
Crystal structure
Antitumor activity
1. Introduction
As the continue study of ladder-like structure in organotin
chemistry, we projected to synthesize another “single-ladder”. In
In the recent years, the interests in organotin (IV) compounds
RnSnX(4ꢀn) (n ¼ 1e4) are increasing because of their biological ac-
tivity, reactivity, and industrial applications [1e6]. In the last few
decades, some structures of organotin (IV) carboxylates are well
recognized and a wide variety of coordination geometries have
been reported [7e9]. However, at the same time new applications
of such compounds are being discovered in industry, ecology, and
medicine. Recently, much attention has also been focused on their
use as metal-based drugs [4]. In general, the biochemical activity of
organotin (IV) compounds is mainly determined by the structure of
the molecule and the coordination number of the tin atoms [10e
17]. The latter aspect has been actively investigated by a large
number of researchers, and a multitude of structure types including
monomers, dimers, tetramers, oligomeric ladders and hexameric
drums are discovered [18]. For the ladder-like structure, as far as we
research, centrosymmetric ring with double ladders bridged by two
ligands are more common in reported literatures [19e21]. The only
single-ladder macrocycle organotin containing longest ladder
bridged by one ligand was synthesized by our group [22].
the present study, a flexible dicarboxylic acid H2L as ligand has been
chosen. Because H2L is interesting because of the following reasons:
(a) strong coordination tendency with Sn and rich coordination
modes; (b) helping to form 2D and 3D moderately robust networks;
(c) here long molecular lengths tending to construct a special
macrocycle. Herein we report the synthesis, characterization,
antitumor activity and luminescent properties of complex 1. Com-
plex 1 has been prepared by azeotropic removal of H2O from the
reaction of the di-n-butyltin oxide with H2L in the solvent mixture
of toluene and ethanol. It is a 16-membered unusual macrocycle
with a single-ladder and the organotin carboxylate containing one
penta-nuclear four-fold-ladder-like organo-oxotin unit. The pre-
liminary fluorescent properties and antitumor activity have also
been investigated. This is likely to serve as a new model for further
study on the fluorescent properties and biological activity of
complex 1.
2. Experimental
2.1. General and instrumental
The reagents and solvents were purchased as supplied and used
without further purification. Melting point was determined with
digital melting point apparatus. Elemental analyses were carried
* Corresponding author. Tel.: þ86 13009010567; fax: þ86 0431 85684009.
E-mail address: zhuds206@nenu.edu.cn (D. Zhu).
http://dx.doi.org/10.1016/j.jorganchem.2014.01.034
0022-328X/Ó 2014 Elsevier B.V. All rights reserved.

20
A.S. Sougoule et al. / Journal of Organometallic Chemistry 758 (2014) 19e24
out on a PerkineElmer PE 2400 CHN instrument and gravimetric
analysis for Sn. 1H NMR spectra were recorded in CDCl3 on a Varian
Mercury 300 MHz spectrometer. Infrared spectra (KBr pellets) were
recorded on an Alpha Centauri FI/IR spectrometer (400e4000 cmꢀ1
range). The UVevis absorption spectrum was recorded by a Varian
Cary 500i UVeviseNIR spectrophotometer. The luminescent
properties of the ligand and complex were measured on a Perkine
Elmer FLS-920 spectrometer.
acid till pH ¼ 2e3. Then a large number of solid precipitated. The
solid crude product was dissolved into the water (100 mL) and
the excess solvent was removed by filtration. Finally the filtrate
was acidified with 4 mol/L hydrochloric acid to obtain pH ¼ 2e3
and the solid precipitated. It was washed with water to obtain a
pure white powder. The powder was placed in drying oven at
150 ꢁC for 3 h before all the characterizations to remove the
water. Yield: 76%, m.p: 191.5e192.0 ꢁC. IR (KBr, cmꢀ1):
y(Oe
H/O) 3253; yas(COO) 1761; ysym(COO) 1433. 1H NMR (CDCl3,
ppm): 4.64 (m, 4H, eCH2e), 6.44e7.16 (m, 4H, Ar-H). Anal. Calc.
for C10H10O6 (226.18 g/mol): C, 53.11; H, 4.46%. Found: C, 53.07;
H, 4.42%.
2.2. X-ray crystallography
Crystals of complex 1 was grown by slow evaporation of a
mixture toluene/ethanol (10:1, 50 mL) solution at room tempera-
ture. The colorless crystals were mounted on a sealed tube and used
for data collection. Single-crystal X-ray diffraction data for the
complex were recorded on a Bruker CCD Area Detector diffrac-
2.3.2. Synthesis of complex 1
A solution of (3-carboxymethoxy-phenoxy) acetic acid (H2L)
(0.113 g, 0.5 mmol) and di-n-butyltin oxide (0.747 g, 3 mmol) was
dissolved in toluene/ethanol (5:1, 50 mL) and refluxed for 20 h
using a dean stark funnel. After cooling to room temperature, the
solvent mixture was removed by filtration and transparent color-
less crystals were obtained. The product was placed in drying oven
at 110 ꢁC for 3 h before all the characterizations to remove the
solvent. Yield: 63%, m.p: 248.2e249.5 ꢁC. Anal. Calc. for
tometer by using the
u
/4 scan technique with Mo-k
a radiation
ꢀ
(l
¼ 0.71073 A). Absorption corrections were applied by using
multiscan techniques [23]. The structures were solved by direct
methods with SHELXS-97 [24] and refined by full-matrix least
squares with SHELXL-97 [25] within WINGX [26]. All nonhydrogen
atoms were refined with anisotropic temperature parameters and
hydrogen atoms were refined as rigid groups. A summary of the
crystal data, experimental details and refinement results are listed
in Table 1.
C
50H100O11Sn5 (1470.75 g/mol): C, 40.83; H, 6.85%. Found: C, 40.88;
H, 6.79%. IR (KBr, cmꢀ1):
(CeH), 2923, 2871, 2856; yas(COO) 1607;
ysym(COO) 1396; (SneOeSn) 454;
(SneC) 578. 1H NMR (CDCl3,
y
y
y
ppm): 0.92 (t, 30H, J ¼ 6.8, eCH3), 1.05e1.68 (m, 60H,
SnCH2CH2CH2e), 4.51 (m, 24H, Ar-CH2e), 6.35e6.82 (m, 28H, Ar-H)
(Scheme 1).
2.3. Synthesis
2.3.1. Synthesis of (3-carboxymethoxy-phenoxy) acetic acid (H2L)
11.0 g (0.1 mol) of resorcinol, 200 mL of water and 20.0 g
(0.5 mol) of solid sodium hydroxide were added into the three-
necked flask. Mixed them till dissolved. Then 21.0 g (0.22 mol)
of monochloroacetic acetic was added. The mixture was stirred
for 4 h and heated between 95 and 100 ꢁC. After cooling to the
room temperature, it was acidified with 4 mol/L of hydrochloric
2.4. MTT assay
Hela cell lines were grown in culture media containing 10% NCS,
1% HEPES and 1% RPMI1640 in a 5% CO2 incubator at 37 ꢁC. The
effects of di-n-butyltin oxide and complex 1 on cell growth were
evaluated using the MTT assay [27]. A total of 2 ꢂ 103 cells were
seeded in the 96-well plate and cultured for 24 h. Thereafter, the
cells were treated with various concentrations of di-n-butyltin
oxide and complex 1 for 24 h. After exposure to the drug, the MTT
assay was carried out. All experiments were performed at least
three times and the mean percentage of proliferation was
calculated.
Table 1
Crystal data and structure refinement for complex 1.
Empirical formula
Formula weight
T (K)
C50H100O11Sn5
1470.75
293(2)
Crystal size (mm)
Wavelength (A)
0.21 ꢂ 0.16 ꢂ 0.14
ꢀ
ꢀ
0.71073 A
3. Results and discussion
Crystal system
Space group
Monoclinic
P2(1)/n
21.1335(17)
13.3934 (10)
23.4488(18)
90
106.2250(10)
90
6372.8(9)
4
1.533
1.980
2952
u
3.1. IR spectra
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
The comparative analysis for the IR spectra of the ligand H2L and
the complex 1 indicates that eOH vibration bands at 3100e
3500 cmꢀ1 are absent in that of complex 1 spectrum; hence it is
evidenced that metaleligand bond formation has taken place
through eCOO groups. The yas(COO) and ysym(COO) are at
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
3
ꢀ
V (A )
Z
Dcalc. (mg/m3)
Absorption coefficient,
F(000)
1607
[
cmꢀ1
and
1396
cmꢀ1
respectively.
The
D
m
(mmꢀ1
)
yas(COO) ꢀ ysym(COO)] value of complex 1 (211 cmꢀ1) is close to
that found in the monodentate [28,29].
Scan mode
q
Range for data collection (ꢁ)
1.53, 26.05
Reflections collected/unique [R(int)
Data/parameters
]
38,330/12,459 [R(int) ¼ 0.0220]
12,459/45/547
Final R induces [I > 2
R induces (all data)
s
(I)]
R1 ¼ 0.0477, wR2 ¼ 0.1327
R1 ¼ 0.0568, wR2 ¼ 0.1418
1.041
Goodness-of-fit (GOF) on F2
Max. and min. transmission
0.7580 and 0.6910
99.4%
Completeness to
Absorption correction
q
¼ 25
Semi-empirical from equivalents
Refinement method
Full-matrix least-squares on F2
Scheme 1.

A.S. Sougoule et al. / Journal of Organometallic Chemistry 758 (2014) 19e24
21
chelated via monodentate coordination mode. O(1), O(2) and O(5)
of the skeleton are coordinated with three Bu2Sn units. Therefore
they are three-coordinated and adopt planar trigonal geometry.
O(3) and O(5) are bound by two Bu2Sn units. All Sn atoms in
complex 1 are five-coordinated, showing a trigonal bipyramid
configuration but having two chemical environments. Sn(3)eSn(5)
are coordinated with three m3-O atoms and two C atoms from butyl
groups, while the coordinated O atoms O(6) and O(8) for Sn(1) and
Sn(2) are from the carboxylate group of ligand H2L. The CeSneC
angles are 125.9(5)ꢁ and 132.4(6)ꢁ for Sn(1) and Sn(2) respectively,
much larger than those of Sn(3)eSn(5) [123.0(3)e123.1(4)ꢁ], which
are caused by the less space congestion of terminal position in the
organooxotin unit. Axial OeSneO angles of Sn(1) and Sn(2)
[155.99(16) and 155.67(16)ꢁ] are larger than those of Sn(4)eSn(5)
[148.32(16)e149.21(17)ꢁ] for the same reason. The Sn5(m3-O)5
cluster demonstrates that along ladder consists of four twisted
Sn2(m3-O)2 distannoxane units. Excluding two end units, they are
approximate to parallelogram, proved by the SneO bond lengths of
Scheme 2.
3.2. 1H NMR spectra
In the 1H NMR spectrum of ligand, the COOH group resonance
appears at 11e12 ppm and disappears when the carboxyl group
participates in coordination to the Sn atoms in complex 1. The NMR
spectrum of complex 1 shows that multiple resonance peaks are
shown in the range of 1.05e1.68 ppm by the protons of eCH2e
CH2eCH2e skeleton while three protons of the terminal methyl
groups showed a sharp peak at 0.91 ppm. The chemical shifts of the
protons on the phenyl groups of complex 1 exhibit signals at 6.35e
6.82 ppm as multiplets, while the protons on methylene groups
show resonance at 4.51 ppm (Scheme 2).
ꢀ
Sn(4)eSn(5) range from 2.046(4) to 2.158(4) A, and the related Oe
SneO [74.20(15)e75.22(14)ꢁ] and SneOeSn [104.67(14)e
105.38(15)ꢁ] angles listed in Table 2. However, the both end units
are more twisted with the SneO bond lengths of Sn(1) and Sn(2)
ꢀ
owing larger span which range from 2.013(3) to 2.185(5) A. And the
torsion is still indicated by the smaller OeSneO [74.57e74.58(15)ꢁ]
and larger SneOeSn (100.85e110.46ꢁ) angles. All the bond lengths
and angles are in agreement to those of previously synthesized
complexes [21,30e32]. “Ladder” Sn5(m3-O)5 is almost coplanar and
because of the steric hindrance, Sn5(m3-O)5 ladder is of zig-zag
shape. Ligand H2L chelates with the organo-oxotin ladder by
3.3. Crystal structure
The molecular structure of complex 1 is shown in Fig. 1 and the
selected bond lengths and angles are listed in Table 2. The crystal
cell of complex 1 is a 16-membered macrocycle consists of a penta-
nuclear organo-oxotin skeleton [Sn5(m3-O)5] and a ligand H2L
Fig. 1. The molecular structure of complex 1.

22
A.S. Sougoule et al. / Journal of Organometallic Chemistry 758 (2014) 19e24
Table 2
monodentate coordination mode via Sn(1)eO(6) and Sn(2)eO(8)
ꢁ
ꢀ
Selected bond lengths (A) and angles ( ) for complex 1.
ꢀ
bonds with bond lengths 2.210(4) and 2.185(5) A respectively.
ꢀ
ꢀ
Although, distances Sn(1)eO(7) (3.062 A) and Sn(2)eO(9) (3.108 A)
are longer than SneO covalent bond length but are much shorter
Bong lengths
Sn(1)eO(1)
Sn(1)eO(6)
Sn(1)eO(3)
Sn(1)eO(7)
Sn(1)eC(11)
Sn(1)eC(21)
Sn(2)eC(31)
Sn(2)eC(41)
Sn(2)eO(2)
Sn(2)eO(9)
Sn(2)eO(8)
Sn(2)eO(5)
Sn(3)eC(51)
Sn(3)eO(1)
Sn(3)eC(61)
Sn(3)eO(2)
Sn(3)eO(4)
2.013(3)
2.210(4)
2.168(5)
3.062(3)
2.118(7)
2.121(14)
2.139(9)
2.100(14)
2.006(3)
3.108(5)
2.185(5)
2.159(5)
2.108(12)
2.148(3)
2.132(6)
2.151(3)
2.056(4)
Sn(4)eC(81)
Sn(4)eO(3)
Sn(4)eC(71)
Sn(4)eO(1)
Sn(4)eO(4)
Sn(5)eC(101)
Sn(5)eO(5)
Sn(5)eO(2)
Sn(5)eO(4)
Sn(5)eC(91)
C(3)eO(8)
C(1)eO(7)
C(4)eO(11)
C(3)eO(9)
C(2)eO(10)
C(1)eO(6)
2.129(6)
2.155(4)
2.137(7)
2.046(4)
2.119(3)
2.110(7)
2.158(4)
2.037(4)
2.124(3)
2.122(7)
1.264(8)
1.206(8)
1.442(11)
1.223(8)
1.438(12)
1.270(8)
ꢀ
than the sum of the van der Waals radii of tin and oxygen (3.7 A)
[33]. Therefore, the oxygen atoms O(7) and O(9) are involved in a
weak interaction with tin [34,35]. The ring is an irregular macro-
cycle resembling almost a rectangle (Fig. 2) with the probable
ꢀ
ꢀ
width 14.3 A ꢂ 4.4 A. The plane of the “ladder” cluster is almost
perpendicular to the big conjugated rigid plane of ligand H2L with
the dihedral angle of 83ꢁ (see the side view of 1 in Fig. 2). Besides
the bonds mentioned above, intermolecular hydrogen bonds O(5)e
ꢀ
ꢀ
H(2) /O(9) (1.870 A) and O(3)eH(1) /O(7) (2.019 A) help complex
1 to form a kind of intermolecular 30-membered irregular ring
(Fig. 3). And complex 1 is connected with each other forming a 2D-
network through these interactions.
3.4. Anti-tumor activity
Bond angles
O(1)eSn(1)eC(11)
O(1)eSn(1)eC(21)
C(11)eSn(1)eC(21)
O(1)eSn(1)eO(3)
C(11)eSn(1)eO(3)
C(21)eSn(1)eO(3)
O(1)eSn(1)eO(6)
C(11)eSn(1)eO(6)
C(21)eSn(1)eO(6)
O(3)eSn(1)eO(6)
O(2)eSn(2)eC(41)
O(2)eSn(2)eC(31)
C(41)eSn(2)eC(31)
O(2)eSn(2)eO(5)
C(41)eSn(2)eO(5)
C(31)eSn(2)eO(5)
O(2)eSn(2)eO(8)
C(41)eSn(2)eO(8)
C(31)eSn(2)eO(8)
O(5)eSn(2)eO(8)
O(4)eSn(3)eC(51)
O(4)eSn(3)eC(61)
C(51)eSn(3)eC(61)
O(4)eSn(3)eO(1)
C(51)eSn(3)eO(1)
C(61)eSn(3)eO(1)
O(4)eSn(3)eO(2)
C(51)eSn(3)eO(2)
C(61)eSn(3)eO(2)
O(1)eSn(3)eO(2)
O(1)eSn(4)eO(4)
O(1)eSn(4)eC(81)
110.7(2)
123.4(5)
125.9(5)
74.58(15)
96.0(3)
96.0(6)
81.86(15)
96.6(3)
O(4)eSn(4)eC(81)
O(1)eSn(4)eC(71)
O(4)eSn(4)eC(71)
C(81)eSn(4)eC(71)
O(1)eSn(4)eO(3)
O(4)eSn(4)eO(3)
C(81)eSn(4)eO(3)
C(71)eSn(4)eO(3)
O(2)eSn(5)eC(101)
O(2)eSn(5)eC(91)
C(101)eSn(5)eC(91)
O(2)eSn(5)eO(4)
C(101)eSn(5)eO(4)
C(91)eSn(5)eO(4)
O(2)eSn(5)eO(5)
C(101)eSn(5)eO(5)
C(91)eSn(5)eO(5)
O(4)eSn(5)eO(5)
O(7)eC(1)eO(6)
94.24(19)
116.3(3)
103.7(2)
The results of cytostatic activity are listed in Table 3. IC50 values
of the complex 1 are expressed in
cisplatin. Complex 1 shows higher activities than n-Bu2SnO in vitro
antitumor activity in HeLa cell line. At concentrations of 10 g/L, the
results proved that complex 1 provides 91.2% growth inhibition,
and the IC50 is 1.4 g/mL. Complex 1 presents lower IC50 values than
mM and compared with those of
123.0(3)
74.20(15)
148.32(16)
93.6(2)
97.4(2)
121.5(3)
115.4(3)
123.1(4)
75.22(14)
97.3(2)
99.2(2)
74.00(16)
97.8(2)
94.7(3)
149.21(17)
125.1(7)
124.7(7)
110.36(16)
143.04(19)
104.67(14)
110.46(17)
144.1(2)
105.11(15)
100.85(16)
105.35(15)
105.38(15)
148.6(2)
m
m
93.1(6)
that of n-Bu2SnO (IC50 ¼ 1.6) and cisplatin (IC50 ¼ 3.50) [36], which
indicates its high activity against the tumoral cell line than n-
Bu2SnO and cisplatin. Based on these preliminary results, it can be
figured out that activity of this complex 1 would be significant
against antitumor effects.
155.99(16)
119.8(5)
107.7(3)
132.4(6)
74.57(16)
98.2(6)
91.5(3)
81.11(16)
94.5(7)
3.5. Fluorescence spectra
95.2(3)
155.67(16)
114.6(5)
117.4(2)
128.0(5)
74.53(13)
97.7(5)
95.18(19)
74.26(14)
97.9(4)
O(8)eC(3)eO(9)
The luminescent properties of solid 1 and free ligand H2L have
been tested with a 150 W xenon lamp as the excitation source at
room temperature and the fluorescence emission spectra of them
are illustrated in Fig. 4. The emission peak of the free ligand H2L is at
about 378 nm with the excitation peak at 340 nm, which is
generally caused by S1 / S0 transition. On complexation of the
ligand with the Sn (IV) atom, complex 1 was red-shifted to 419 nm
Sn(1)eO(1)eSn(4)
Sn(1)eO(1)eSn(3)
Sn(4)eO(1)eSn(3)
Sn(2)eO(2)eSn(5)
Sn(2)eO(2)eSn(3)
Sn(5)eO(2)eSn(3)
Sn(4)eO(3)eSn(1)
Sn(3)eO(4)eSn(4)
Sn(3)eO(4)eSn(5)
Sn(4)eO(4)eSn(5)
Sn(5)eO(5)eSn(2)
(
lex ¼ 320 nm). The red-shift might be owing to the complexation
96.4(2)
148.64(15)
75.36(14)
120.5(2)
of the ligand H2L with the organooxotin cluster, which increases the
conformational rigidity of the complex 1 and reduces the non-
radiative decay of LMCT (Figs. 5 and 6).
100.59(17)
Fig. 2. The front and side views of complex 1, the butyl groups are omitted for clarity.

A.S. Sougoule et al. / Journal of Organometallic Chemistry 758 (2014) 19e24
23
Fig. 3. Two dimensional molecular assembly of complex 1 formed by intermolecular CeH/O interactions, the butyl groups are omitted for clarity.
Table 3
In vitro antitumor activities of n-Bu2SnO and complex 1 against Hela cell.
Compound
Dose (
m
g/mL)
Anticancer activity (%)
IC50 (mg/mL)
n-Bu2SnO
0.1
0.3
1
3
10
1.1 ꢃ 7.1
18.5 ꢃ 3.3
29.8 ꢃ 3.0
65.4 ꢃ 1.5
88.1 ꢃ 0.1
1.6
Complex 1
0.1
0.3
1
3
10
1.6 ꢃ 6.5
20.1 ꢃ 3.4
32.3 ꢃ 2.7
67.9 ꢃ 1.2
91.2 ꢃ 0.1
1.4
4. Conclusion
In conclusion, this paper describes the synthesis, characteriza-
tion and antitumor activity of a novel macrocyclic organotin
carboxylate containing one penta-nuclear four-fold-ladder orga-
nooxotin unit. Complex 1 shows fluorescence activity and the result
of antitumor study is excellent. This study will be helpful in
exploring various structures of organotin carboxylate and
designing novel biological metal-based drugs.
Fig. 5. IR spectrum of ligand.
Fig. 4. Fluorescence emission spectra of ligand and 1.
Fig. 6. IR spectrum of 1.

24
A.S. Sougoule et al. / Journal of Organometallic Chemistry 758 (2014) 19e24
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Acknowledgments
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