Synthesis, structure, characterization and study of antiproliferative activity of dimeric and tetrameric oxidomolybdenum(VI) complexes of N,N′-disalicyloylhydrazine

Article abstract of DOI:10.1016/j.poly.2014.04.007

The in situ reaction of salicyloylhydrazide and its corresponding hydrazone with [MoO₂(acac)₂] afforded two novel and unusual dimeric [(Mo^VIO₂)₂L] (1) and tetrameric [{(C ₂H₅OH)LO₃Mo₂^VI} ₂(μ-O)₂]·C₂H₅OH (2) oxidomolybdenum(VI) complexes with N,N′-disalicyloylhydrazine (H ₂L). The binucleating ligand was formed by the self-combination of the acid hydrazide or corresponding hydrazone. The complexes were characterized by various spectroscopic techniques (IR, UV and NMR) and also by electrochemical study. The molecular structures of both complexes have been confirmed by X-ray crystallography. The above studies indicate that the N,N′- disalicyloylhydrazine (H₂L) has the normal tendency to form both dimeric and tetrameric complexes coordinated through the dianionic tridentate manner. The in vitro antiproliferative activity of complexes 1 and 2 was assayed against HeLa cell line.

Full text of DOI:10.1016/j.poly.2014.04.007

Polyhedron xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, structure, characterization and study of antiproliferative
activity of dimeric and tetrameric oxidomolybdenum(VI) complexes
of N,N0-disalicyloylhydrazine
b
Sagarika Pasayat a, Subhashree P. Dash a, Sudarshana Majumder a, Rupam Dinda a, , Ekkehard Sinn ,
⇑
Helen Stoeckli-Evans c, Subhadip Mukhopadhyay d, Sujit K. Bhutia d, Partha Mitra e
a Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
b Department of Chemistry, Western Michigan University, Kalamazoo, MI 49008, USA
c Institute of Physics, University of Neuchâtel, Rue Emile-Argand 11, CH-2000 Neuchâtel, Switzerland
d Department of Life Science, National Institute of Technology, Rourkela 769008, Odisha, India
e Department of Inorganic Chemistry, IACS Kolkata, Kolkata 700032, West Bengal, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The in situ reaction of salicyloylhydrazide and its corresponding hydrazone with [MoO2(acac)2] afforded
two novel and unusual dimeric [(MoVIO2)2L] (1) and tetrameric [{(C2H5OH)LO3Mo2VI}2(
l
-O)2]ꢀC2H5OH (2)
Received 10 December 2013
Accepted 4 April 2014
Available online xxxx
oxidomolybdenum(VI) complexes with N,N0-disalicyloylhydrazine (H2L). The binucleating ligand was
formed by the self-combination of the acid hydrazide or corresponding hydrazone. The complexes were
characterized by various spectroscopic techniques (IR, UV and NMR) and also by electrochemical study.
The molecular structures of both complexes have been confirmed by X-ray crystallography. The above
studies indicate that the N,N0-disalicyloylhydrazine (H2L) has the normal tendency to form both dimeric
and tetrameric complexes coordinated through the dianionic tridentate manner. The in vitro antiprolifer-
ative activity of complexes 1 and 2 was assayed against HeLa cell line.
Keywords:
N,N0-Disalicyloylhydrazine
Oxidomolybdenum(VI)
Dimeric and tetrameric complexes
X-ray crystal structure
Antiproliferative activity
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
and breast cancer cell line (MCF-7) [13]. Recently, some new
molybdenum
g
3-allyldicarbonyl complexes [Mo(g3-C3H5)-
Molybdenum(VI) complexes have attracted considerable inter-
est due to their relevance to the active sites of the majority of
molybdo-enzymes [1,2]. Oxo-peroxo and dioxo complexes of
Mo(VI) with polydentate nitrogen, sulfur and oxygen ligands are
considered valuable models for the active site of several Mo
enzymes. Recent discovery of the antitumor effects of metal com-
plexes and their potential use in cancer diseases have received
increasing attention [3–10].
Br(CO)2(L)] and [{Mo(
g
3-C3H5)Br(CO)2}2( -L)] with the bidentate
l
nitrogen ligands (L) were reported [14] to exhibit potent antitumor
activity against HeLa cell line. A. Scorilas and co-workers [15]
described the cytotoxic activity of some 2,5-dihydroxybenzoate
molybdenum(VI) with tetraphenylphosphonium as counter ion
against two human leukaemia cell lines HL-60 and K562. Bandarra
et al. have reported [16] the in vitro cytotoxic activity of some
molybdenum(II) complexes [Mo(g3-C3H5)(CF3SO3)(CO)2(N-N)]
Some molybdenum complexes, particularly, thiosemicarbazo-
nato molybdenum(VI) complexes [11] have been found to possess
antitumor activity. Yamase et al. have reported the antitumoral
effect of polyoxomolybdates, especially [NH3Pri]6[Mo7O24]ꢀ3H2O
(PM-8) against MX-1 murine mammary cancer cell line, Meth A
against human cancer cell lines cervical carcinoma (HeLa) and
breast carcinoma (MCF-7). Very recently, Gleeson et al. [17] have
reported the cytotoxicity studies of three molybdocene dichloride
derivatives against the human renal cell line Caki-1.
On the other hand, hydrazones, –NH–N = CRR0 (R and R0 = H,
alkyl, aryl), are versatile ligands due to their applications in the
field of analytical [18] and medicinal chemistry [19–21].
Hydrazone moieties are the most important pharmacophoric
cores of several anticancer, antiinflammatory, antinociceptive,
and antiplatelet drugs [22–29]. In the context of the present
study it is relevant to mention that although the chemistry
of dioxidomolybdenum(VI)-aroylhydrazone complexes is well
´
sarcoma and MM46 adenocarcinoma [12]. Cindric et al. showed
that -octamolybdates containing aminoacids and peptides
c
showed differential cell-growth inhibition in a dose-dependent
manner selectively on hepatocellular carcinoma cell line (HepG2)
⇑
Corresponding author. Tel.: +91 661 246 2657; fax: +91 661 246 2022.
E-mail address: rupamdinda@nitrkl.ac.in (R. Dinda).
http://dx.doi.org/10.1016/j.poly.2014.04.007
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: S. Pasayat et al., Polyhedron (2014), http://dx.doi.org/10.1016/j.poly.2014.04.007

2
S. Pasayat et al. / Polyhedron xxx (2014) xxx–xxx
developed [30–36], to the best of our knowledge no information is
available concerning their anticancer properties.
2.4. Synthesis of complex [(MoVIO2)2L] (1)
However, the research on the compounds with symmetrical
diaroylhydrazine ligands is limited [37–42]. The N,N0-diacylhydra-
zines have value as structural components of heterocyclic ring
systems [43], and as tuberculostatic agents [44]. The N,N0-disal-
icyloylhydrazine [45], which had previously been known to chelate
a variety of metal ions [45,46], has been shown to exhibit potent
inhibition of the human immune deficiency virus (HIV) integrase
[47].
To the refluxing solution of 0.15 g (1.0 mmol) of salicyloylhyd-
razide in 30 mL of ethanol 0.32 g (1.0 mmol) of MoO2(acac)2 was
added [52]. The color of the solution changed to dark red. The mix-
ture was then refluxed for 3 h. After leaving the solution for 2 days
at room temperature, fine dark red colored crystals were isolated
and a suitable single crystal was selected for X-ray analysis.
[(MoVIO2)2L] (1): Yield: 0.36 g (68%). Anal. Calc. for C14H8N2O8Mo2:
C, 32.08; H, 1.53; N, 5.34. Found: C, 32.06; H, 1.55; N, 5.37%. 1H
NMR (DMSO-d6, 400 MHz): d = 7.94–7.02 (m, 4H, Aromatic). 13C
NMR (DMSO-d6, 100 MHz): d = 163.55, 162.00, 135.42, 129.87,
122.53, 120.03, 115.80.
In our effort to discover and develop apoptosis inducers as
potential new anticancer agents, we recently synthesized [48]
three highly stable, hexacoordinated nonoxidovanadium(IV),
VIV(L)2, complexes of sterically constrained hydrazone ligands
and found that these compounds could inhibit proliferation
of HeLa cells. Here in, we report the synthesis, structure and char-
acterization of two new dimeric [(MoVIO2)2L] (1) and tetrameric
2.5. Synthesis of complex [{(C2H5OH)LO3MoV2I}2(
l
-O)2]ꢀC2H5OH (2)
0.24 g (1.00 mmol) of 2-hydroxybenzoylhydrazone of acetophe-
none was dissolved in 30 mL ethanol. When 0.32 g (1.00 mmol) of
MoO2(acac)2 was added to the solution, the color changed to dark
orange [51].The solution mixture was then refluxed for 3 h. After
leaving the solution for 2 days at room temperature, fine dark
orange crystals were isolated and a suitable single crystal was
[{(C2H5OH)LO3MoV2I}2(
l
-O)2]ꢀC2H5OH (2) oxidomolybdenum(VI)
complexes synthesized from the same ligand, N,N0-disal-
icyloylhydrazine along with special reference to their antiprolifer-
ative activities.
selected for X-ray analysis. [{(C2H5OH)LO3MoV2I}2(
l
-O)2]ꢀC2H5OH
2. Experimental
(2): Yield: 0.19 g (73%). Anal. Calc. for C36H40N4O20Mo4: C, 35.06;
H, 3.27; N, 4.55. Found: C, 35.08; H, 3.25; N, 4.56%. 1H NMR
(DMSO-d6, 400 MHz): d = 8.14–7.06 (m, 8H, Aromatic), 4.36 (s,
1H, OH), 3.42 (q, 2H, CH2), 1.05 (s, 3H, CH3). 13C NMR (DMSO-d6,
100 MHz): d = 163.58, 163.46, 162.42, 162.02, 135.58, 134.67,
129.87, 128.69, 122.67, 121.22, 120.10, 118.87, 115.67, 114.96,
56.49,55.95, 19.10, 19.00.
2.1. Materials
[MoO2(acac)2] and salicyloylhydrazide were prepared as
described in the literature [49,50]. Reagent grade solvents were
dried and distilled prior to use. All other chemicals were reagent
grade, available commercially and used as received. Commercially
available TBAP (tetrabutylammonium perchlorate) was properly
dried and used as a supporting electrolyte for recording cyclic
voltammograms of the complexes.
2.6. Crystallography
The X-ray diffraction data and unit cell parameters for single
crystals of complexes 1 and 2 were collected at 293(2) K, on a Bru-
ker Smart Apex CCD diffractometer using graphite monochromated
2.2. Physical measurements
Mo K
a radiation (k = 0.71073 Å), employing the x–2h scan tech-
nique. The intensity data were corrected for Lorentz, polarization
and absorption effects. The structures were solved with SHELXS97
[53] and refined with SHELXL97 [53]. The H-atoms were included
in calculated positions and treated as riding atoms using SHELXL
default parameters. The non-H atoms were refined anisotropically,
using weighted full-matrix least-squares on F2. Further crystallo-
graphic data and refinement details are given in Table 1. The
molecular structures and crystal packing of the two complexes
are illustrated in the Figs. 2–5 drawn with Mercury [54].
Elemental analyses were performed on a Vario ELcube CHNS
Elemental analyzer. IR spectra were recorded on a Perkin-Elmer
Spectrum RXI spectrometer. 1H NMR spectra were recorded with
a Bruker Ultrashield 400 MHz spectrometer using SiMe4 as an
internal standard. Electronic spectra were recorded on a Lamda25,
PerkinElmer spectrophotometer. Magnetic susceptibility was mea-
sured with a Sherwood Scientific AUTOMSB sample magnetometer.
Electrochemical data were collected using a PAR electrochemical
analyzer and
a PC-controlled Potentiostat/Galvanostat (PAR
273A) at 298 K in a dry nitrogen atmosphere. Cyclic voltammetry
experiments were carried out with a platinum working electrode,
platinum auxiliary electrode, Ag/AgCl as reference electrode and
TBAP as supporting electrolyte.
2.7. Cytotoxic assay
HeLa (human cervical carcinoma cells) were obtained from
National Centre of Cell Science (NCCS), Pune, India and were main-
tained in minimal essential medium supplemented with 10% fetal
bovine serum, penicillin streptomycin solution and incubated at
37 °C in 5% CO2 and 95% humidified incubator. HeLa cells were
harvested from maintenance cultures in logarithmic phase, after
counting in a hemocytometer using trypan blue solution. The cell
concentration was adjusted to 5x104 cells/ml and the cells were
plated in a 96 well flat bottom culture plate and incubated for
72 h with various concentrations of the test compounds which
were dissolved in a 90% (v/v) DMF solution. The effect of the drugs
on the cancer cell viability was studied using MTT dye reduction
assay by measuring the optical density at 595 nm using micro-
plate reader spectrophotometer (Perkin–Elmer 2030) [55]. DMF
solution that was used to dissolve the drugs was used in control
group treatment. MTT (yellow colored) enters the living cells’
mitochondria where mitochondrial succinate dehydrogenase
2.3. Synthesis of 2-hydroxybenzoylhydrazone of acetophenone
The ligand 2-hydroxybenzoylhydrazone of acetophenone was
prepared by the condensation of equimolar ratio of salicyloylhyd-
razide 2.72 g (20.00 mmol) and acetophenone 2.38 g (20.00 mmol)
in stirring ethanol (25 ml) for 2 h following a standard procedure
[51]. The resulting yellowish-white compound was filtered,
washed with ethanol and dried over fused CaCl2. Yield: 0.18 g
(75%). Anal. Calc. for C15H14N2O2: C, 70.88; H, 5.55; N, 11.08. Found:
C, 70.90; H, 5.54; N, 11.06%. 1H NMR (400 MHz, DMSO-d6):
d = 11.83 (s, 1H, OH), 11.35 (s, 1H, NH), 8.03–6.97 (m, 9H, Aro-
matic), 2.33 (s, 3H, CH3),.13
C NMR (DMSO-d6, 100 MHz):
d = 164.99, 159.50, 157.99, 149.49, 134.44, 132.08, 129.04,
128.83, 126.89, 119.85, 119.08, 117.77, 116.92, 116.06, 14.34.
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S. Pasayat et al. / Polyhedron xxx (2014) xxx–xxx
3
Table 1
glass slide, cells were fixed with 3.7% formaldehyde for 15 min.,
permeabilized with 0.1% Triton X-100 and stained with 1 g/ml
Crystal and refinement data of complexes 1 and 2.
l
DAPI for 5 min at 37 °C. The cells were then washed with PBS
(phosphate buffer saline) and examined by fluorescence micros-
copy (Olympus IX 71) to determine condensation or fragmentation
of the nuclei indicating cells undergoing apoptosis. Normal cells
display a round uniform margin whereas drug induced apoptosis
initiates chromatin condensation and membrane blebbing. Hence
drug treated cells with condensed chromatin display a broken mar-
Compound
1
2
Formula
M
Crystal symmetry
Space group
a (Å)
C
14H8Mo2N2O8
C36H40Mo4N4O20
1232.50
triclinic
524.10
triclinic
P1
ꢀ
ꢀ
P1
3.96540(10)
9.5080(2)
10.1683(2)
76.167(10)
87.856(10)
82.230(10)
368.834(14)
1
2.360
254
1.753
26.37
9.5892(3)
10.7151(4)
11.4986(4)
68.042(10)
73.353(10)
81.152(2)
1048.39(6)
1
1.952
612
1.256
25.50
b (Å)
c (Å)
gin which is
apoptosis.
a characteristic phenotype of cells undergoing
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
F(000)
)
3. Results and discussion
l(Mo K
a
) (mmꢁ1
)
3.1. Synthesis
2h (max) (°)
Reflections collected/
unique
11936/1498
9430/3870
Scheme 1 summarizes the synthesis of two new dimeric and
tetrameric oxidomolybdenum(VI) complexes 1 and 2 from the
common ligand, N,N0-disalicyloylhydrazine (H2L) employed in the
present study. According to the demand, to provide the exact ste-
reo and electronic environment for the stability of well known
penta- and hexacoordinated dioxidomolybdenum(VI) complexes,
the N,N0-disalicyloylhydrazine ligand (H2L) was synthesized by
the self-combination of salicyloylhydrazide or its corresponding
hydrazone of acetophenone and subsequently transformed to the
corresponding oxidomolybdenum(VI) species through in situ reac-
tion with metal precursor MoO2(acac)2. The in situ formation of
this type of intermediate ligand (H2L) is a general phenomenon
and can be prepared in absence of any basic or acidic condition
[57]. There is also report where the reaction is accelerated in
presence of acidic [37] and basic [58] medium. In the present
report the metal precursor in ethanol may provide the acidic
medium (pH 3.5) required for this self-combination.
R1a[I > 2
r(I)]
R1 = 0.0224,
wR2 = 0.0782
R1 = 0.0214,
R2 = 0.0815
0.793
R1 = 0.0413,
wR2 = 0.0790
R1 = 0.0285,
wR2 = 0.0736
1.062
wR2b(all data)
S (goodness of fit)
Min./max. res. (e Åꢁ3
)
0.843/ꢁ0.649
0.920/ꢁ0.873
P
P
a
R1
=
|FO| ꢁ |FC|/ |FO|.
P
P
wR2 = { [w(FO ꢁ FC2)2]/ [w(FO2)2]}
.
b
2
½
-1.2
-0.82
Methods used for synthesis of the precursor hydrazide, hydra-
zone and oxidomolybdenum complexes (1 and 2) are given in
experimental section. Proposed structures of these complexes
(Scheme 1) are based on their spectroscopic characterization (IR,
electronic and 1H NMR spectroscopy), elemental analyses and sin-
gle crystal X-ray diffraction studies. The binucleating ligand coor-
dinates through its dianionic (ONO)2– enolate tautomeric forms.
The compounds are highly soluble in aprotic solvents, viz. DMF
or DMSO and are sparingly soluble in alcohol, CH3CN and CHCl3.
The complexes are diamagnetic, indicating the presence of molyb-
denum in the +6 oxidation state.
+1.27
3.2. Spectral properties
-2.0
-1.5
-1.0
-0.5
Potential (V)
0.0
0.5
1.0
1.5
2.0
Spectral characteristics of precursor 2-hydroxybenzoylhydraz-
one of acetophenone and complexes 1 and 2 are listed in Table 2.
The IR spectra of complexes exhibit two peaks in the range
Fig. 1. Cyclic voltammogram of [(MoVIO2)2L] (1) in DMSO showing (a) reduction of
(Mo(VI)?Mo(V)), (b) reduction of (Mo(V) ? Mo(IV)) and (c) oxidation of ligand.
1602–1601 cmꢁ1 and 1579–1549 cmꢁ1 due to
m
(C@C/aromatic)
(C@N) stretching modes [51] respectively. New bands at
662–644 cmꢁ1 are assigned to
(Mo–N) [59]. In addition, 1 and 2
display strong and moderately strong band in the range
and
m
m
reduces MTT to produce the insoluble purple colored formazan.
Only living cells are able to reduce MTT. This formazan is solubi-
lised by DMSO in order to quantify (spectrophotometrically) the
viable number of cellular population that could survive the drug
insult.
a
944–943 cmꢁ1 and 921–918 cmꢁ1 due to terminal
m(M@Ot) stretch
[30,33,51]. A strong band at 752 cmꢁ1 for complex 2 may be
assigned to (Mo–O–Mo) stretch [60].
The DMSO solution of 1 and 2 displays a shoulder in the 426–
423 nm region and two strong absorptions are located in the
314–312 nm and 274–260 nm range, which are assignable to
2.8. Nuclear staining
L ? Mo (dp) LMCT and intraligand transitions respectively
Nuclear staining using DAPI stain was performed according to
the method previously described [56]. Briefly, HeLa cells either
treated or untreated with test compounds were smeared on a clean
[30,33,51].The above results and absence of low energy transition
peaks in UV–Vis spectrum clearly suggest the presence of corre-
sponding Mo(VI) species in solution.
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4
S. Pasayat et al. / Polyhedron xxx (2014) xxx–xxx
Fig. 2. The molecular structure of [(MoVIO2)2L] (1), with atom labeling. Displacement ellipsoids are drawn at the 50% probability level. The molecule possesses inversion
symmetry. [symmetry codes: (A) = ꢁx, ꢁy, ꢁz + 1; (B) x ꢁ 1, y, z].
Fig. 4. The molecular structure of [{(C2H5OH)LO3MoV2I}2(
atom labeling. Displacement ellipsoids are drawn at the 50% probability level. The
molecule possesses inversion symmetry. The ethanol solvent molecule of crystal-
lization has been omitted for clarity.
l-O)2]ꢀC2H5OH (2), with
Fig. 3. A view along the c axis of the crystal packing of [(MoVIO2)2L] (1).
The 1H and 13C NMR data of the 2-hydroxybenzoylhydrazone of
acetophenone and complexes are given in the experimental sec-
tion. The spectrum of the hydrazone exhibits an –OH (phenolic)
resonance at d = 11.83 ppm and one –NH proton resonance at
d = 11.35 ppm. All the aromatic proton signals are clearly observed
at d = 8.03–6.97 ppm and the CH3 proton resonance is observed at
d = 2.33 ppm. In the NMR spectra of complexes (1 and 2), the
absence of signal due to aromatic –OH indicates that the phenolic
group is coordinated to the metal centre after proton replacement.
The aromatic protons are observed at d = 8.14–7.02 ppm
[30,33,51]. The chemical shift of the coordinated C2H5OH of com-
plex (2) exhibits an –OH resonance at d = 4.36 ppm, –CH2 reso-
nance at d = 3.42 ppm and –CH3 resonance at d = 1.05 ppm.
wave at positive potentials in the range of +1.27 to +1.48 V is
assigned to the oxidation of the coordinated ligand [61]. As the
Mo(VI) complex cannot undergo a metal-centered oxidation, this
is attributed to a ligand-centered process [51].
3.4. Description of the X-ray structure of complex [(MoVIO2)2L] (1) and
[{(C2H5OH)LO3MoV2I}2(
l-O)2]ꢀC2H5OH (2)
The reaction of salicyloylhydrazide and its corresponding
hydrazone of acetophenone with the metal precursor does not pro-
duce the expected complexes I and II (Chart 1). However, during
in situ reaction the hydrazide and its hydrazone were transformed
into N,N0-disalicyloylhydrazine (H2L), which subsequently reacts
with MoO2(acac)2 and produced two novel bi- and tetranuclear
oxidomolybdenum(VI) complexes [(MoO2)2L] (1) and [{(C2H5-
3.3. Electrochemical properties
Electrochemical properties of the complexes were studied by
cyclic voltammetry in DMSO solution (0.1 M TBAP). The potential
data are listed in Table 3 and Fig. 1 depicts a representative voltam-
mogram of complex 1. The CV traces of complexes (1 and 2) exhibit
two irreversible reductive responses within the potential window
ꢁ0.15 to ꢁ0.82 V and ꢁ1.06 to ꢁ1.2 V, which are assigned to MoVI/
MoV and MoV/MoIV processes respectively [30,33,51]. An oxidation
OH)LO3MoV2I}2(
l
-O)2]ꢀC2H5OH (2), respectively (Scheme 1).
The molecular structure and atom numbering scheme for com-
plex 1 is shown in Fig. 2, with the relevant bond distances and
angles collected in Table 4. The molecule possesses inversion sym-
metry. Each molybdenum atom coordinates with an ‘NO4’ chromo-
phore and adopts a distorted tetragonal pyramidal geometry. Both
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S. Pasayat et al. / Polyhedron xxx (2014) xxx–xxx
5
Fig. 5. A view along the b axis of the crystal packing of [{(C2H5OH)LO3MoV2I}2(
l-O)2]ꢀC2H5OH (2). The O–Hꢀ ꢀ ꢀO hydrogen bonds are shown as dashed lines.
O
CH3
C
N
N
H
OH
MoO2(acac)2,
EtOH
Reflux
Mo
O
O
O
Mo
HO
NH
O
O
O
O
NH2
NH
Reflux
N
NH
OH
N
O
O
OH
MoO2(acac)2,
EtOH
O
Mo
O
(H2L)
O
O
Mo
[(MoVIO2)2L] (1)
C2H5
O
OH
O
Mo
O
O
O
Mo
O
N
O
O
N
N
O
O
N
Mo
O
O
O
O
Mo
O
O
HO
C2H5
[{(C2H5OH)LO3Mo2VI}2(µ -O)2].C2H5OH (2)
Scheme 1. Schematic representation of synthesis of 1 and 2.
Table 2
Characteristic IRa bands and electronic spectral datab for the studied ligand and complexes (1 and 2).
Compounds
m(C@C)
m
(C@N)
m
(Mo@O)
m
(Mo–N)/cmꢁ1
kmax/nm (
e )
/dm3 molꢁ1 cmꢁ1
Precursor Ligand
Complex 1
Complex 2
1611
1602
1601
1581
1579
1549
–
–
662
644
331 (23524), 292 (15624)
426 (9439), 314 (25123), 274 (16352)
423 (9569), 312 (26126), 260 (15711)
944, 918
943, 921
a
In KBr pellet.
In DMSO.
b
sides of the ligand behave as a tridentate (ONO) binegative unit,
where one side of the ligand offers two oxygens as donors to the
Mo(1) center, one from the enolate oxygen O(1) and the other from
the phenolate oxygen O(2), and the last two are oxo O(3) and O(4)
atoms with bite angles of 71.90(7) [O(1)–Mo(1)–N(1A)] and
80.50(8) [O(2A)–Mo(1)–N(1A)], forming one five- and one six-
membered chelate ring. The planar structure of the chelating
groups of ligand H2L in compound 1 favors the delocalization of
the double bonds. Hence, bond N(1)–N(1A) = 1.380(3) Å [symme-
try code: (A) = x, ꢁy, ꢁz + 1] is shorter than a standard N–N bond
Please cite this article in press as: S. Pasayat et al., Polyhedron (2014), http://dx.doi.org/10.1016/j.poly.2014.04.007

6
S. Pasayat et al. / Polyhedron xxx (2014) xxx–xxx
Table 3
Table 5
Cyclic voltammetric results for oxidomolybdenum(VI) complexes (1 and 2) at 298 K.
Selected bond distances (Å) and bond angles (°) for complex 2.
Complexes
Epc [V]a
Distances
Mo(1)–O(1)
Mo(1)–O(4)
Mo(1)–O(5)
Mo(1)–O(6)
Mo(1)–O(9)
Mo(1)–N(2)
2.029(2)
1.919(3)
1.692(3)
1.715(2)
2.272(3)
2.204(3)
Mo(2)–O(2)
Mo(2)–O(3)
Mo(2)–O(7)
Mo(2)–O(8)
Mo(2)–O(6)
Mo(2)–N(1)
1.920(3)
2.043(3)
1.704(3)
1.694(3)
2.409(2)
2.199(3)
Complex 1
Complex 2
ꢁ0.82, ꢁ1.2
ꢁ0.15, ꢁ1.06
a
Solvent: DMSO; working electrode: platinum; auxiliary electrode: platinum;
reference electrode: Ag/AgCl; supporting electrolyte: 0.1 M TBAP; scan rate: 50 mV/
s. Epc is the cathodic peak potential.
Angles
O(1)–Mo(1)–O(4)
O(1)–Mo(1)–O(5)
O(1)–Mo(1)–O(6)
O(1)–Mo(1)–O(9)
O(1)–Mo(1)–N(2)
O(4)–Mo(1)–O(5)
O(4)–Mo(1)–O(6)
O(4)–Mo(1)–O(9)
O(4)–Mo(1)–N(2)
O(5)–Mo(1)–O(6)
O(5)–Mo(1)–O(9)
O(5)–Mo(1)–N(2)
O(6)–Mo(1)–O(9)
O(6)–Mo(1)–N(2)
O(9)–Mo(1)–N(2)
150.1(1)
97.2(1)
96.1(1)
82.2(1)
72.3(1)
104.3(1)
98.0(1)
80.5(1)
80.2(1)
105.2(1)
82.1(1)
157.5(1)
172.6(1)
95.8(1)
76.8(1)
O(2)–Mo(2)–O(3)
O(2)–Mo(2)–O(8)
O(2)–Mo(2)–O(7)
O(2)–Mo(2)–N(1)
O(2)–Mo(2)–O(6)
O(3)–Mo(2)–O(7)
O(3)–Mo(2)–O(8)
O(3)–Mo(2)–N(1)
O(3)–Mo(2)–O(6)
O(7)–Mo(2)–O(8)
O(7)–Mo(2)–N(1)
O(7)–Mo(2)–O(6)
O(8)–Mo(2)–N(1)
O(7)–Mo(2)–O(6)
N(1)–Mo(2)–O(6)
147.9(1)
101.4(1)
102.0(1)
80.3(1)
81.1(1)
96.8(1)
98.2(1)
71.8(1)
75.92(9)
105.6(1)
154.4(1)
82.1(1)
98.8(1)
171.0(1)
73.0(1)
CH3
C
OH
H3C
N
C
N
N
HO
CH
C
O
O
O
C
N
Mo
O
O
N
O
CH3
N
C
Mo
O
OH
O
II
H3C
C2H5OH
I
Chart 1. Expected oxidomolybdenum complexes from precursor hydrazide and
hydrazone.
Symmetry code: (C) = ꢁx, ꢁy, ꢁz + 2.
Table 4
coordinates to the molybdenum in the same manner as in complex
1. As expected from its structure, the tridentate ligand is bonded to
the Mo(1) centre in a planar fashion involving the xy-plane, coordi-
nating through the phenolate oxygen O(4), the enolate oxygen
O(1), the imine nitrogen atom N(2), and an oxo group O(5) lying
trans to N(2). The fifth and sixth positions of the distorted octahe-
dron are occupied by the bridging oxygen O(6) and the O atoms of
the free ethanol molecule, respectively. The coordination around
the Mo(2) centre is the same except that the sixth position is occu-
pied by an oxo group O(8). The Mo(1)–O(9) (alcohol) bond
[2.272(3) Å] is significantly longer than the other Mo(1)–O bonds
[1.692(3)–2.029(2) Å] indicating that the alcohol molecule is
weakly bonded to the MoO22+ core. The other bond lengths and
bond angles in the organic ligands are close to standard values
[62]. In the crystal of complex 2, molecules are bridged by
O–Hꢀ ꢀ ꢀO hydrogen bonds (dashed lines, Fig. 5) involving the
coordinated and solvent molecules of ethanol, forming chains
propagating along the c axis direction. Details of the classical
hydrogen bonding in complex 2 are given in Table 6.
Selected bond distances (Å) and bond angles (°) for complex 1.
Distances
Mo(1)–O(1)
Mo(1)–O(3)
Mo(1)–N(1A)
N(1)–N(1A)
2.037(2)
1.728(2)
2.211(2)
1.380(3)
Mo(1)–O(2A)
Mo(1)–O(4)
Mo(1)–O(3B)
N(1)–C(1)
1.900(2)
1.693(2)
2.252(2)
1.309(3)
Angles
O(1)–Mo(1)–O(2A)
O(1)–Mo(1)–O(4)
O(2A)–Mo(1)–O(3)
O(2A)–Mo(1)–N(1A)
O(3)–Mo(1)–N(1A)
150.01(8)
98.08(11)
98.85(9)
80.50(8)
96.15(9)
O(1)–Mo(1)–O(3)
O(1)–Mo(1)–N(1A)
O(2A)–Mo(1)–O(4)
O(3B)–Mo(1)–O(4)
O(4)–Mo(1)–N(1A)
95.59(9)
71.90(7)
103.20(9)
83.49(9)
157.24(9)
Symmetry codes: A = ꢁx, ꢁy, ꢁz + 1; B = xꢁ1, y, z.
distance (1.45 Å) [33]. At the same time, the N(1)–C(1)
bond = 1.309(3) Å is shorter than the length of a standard C@N
bond (1.34 Å) [45]. The other bond lengths and bond angles in
the organic ligands are close to standard values [62].
In the crystal of complex 1, the binuclear units are linked via
bridging Moꢀ ꢀ ꢀO bonds to form columns propagating along the a
axis direction (Fig. 3). Actually the sixth coordination site, trans
to the oxo-oxygen O(3), is occupied by an oxo-oxygen O(3B) of
the next neighboring complex molecule and this pattern is
repeated leading to a chain of [(MoO2)2L] molecules. This may be
visualized as an effect of stacking of the complex molecules along
the a-axis [30]. The length of the Mo–O(3B) bond (2.252 (2) Å) is
considerably longer than the other Mo–O bonds, the longest of
which [Mo–O(1)] is 2.037 (2) Å which suggests that this should
be explained as oligomeric structure where one of the oxygen of
one molybdenum weakly interacts with other.
3.5. Inhibition of cancer cell viability
In the present study antiproliferative efficacy of complexes 1
and 2 was assayed by determining the viability of HeLa cells using
the MTT assay method. The salicyloylhydrazide and MoO2(acac)2
gave high IC50 values of >200
lM, whereas 1 and 2 gave values
in the range 33–28 M. In contrast, cisplatin, gefitinib, gemcita-
l
bine, 5-fluorouracil and vinorelbine, the most commonly used che-
motherapeutic drugs, are comparably effective in HeLa cells with
an IC50 value of 13, 20, 35, 40 and 48 lM, respectively under sim-
ilar experimental conditions [63]. The significant decrease in the
Reaction of MoO2(acac)2 with 2-hydroxybenzoylhydrazone
of acetophenone lead to the formation of [{(C2H5OH)LO3MoV2I}2
inhibitory concentration for the ligand compared to the metal
(l-O)2]ꢀC2H5OH (2),
a novel di-l-oxido tetrameric structure,
illustrated in Fig. 4. The relevant bond distances and angles are
collected in Table 5. The molecular structure of 2 is similar to that
of complex 1; again the molecule possesses inversion symmetry.
The two crystallographically equivalent halves are bridged by
two oxygen atoms (only the geometry of one half of the complex
will be described in detail). Both the Mo centers [Mo(1) and
Mo(2)] are six coordinate having an ‘NO5’ chromophore, with a dis-
torted octahedral structure. The ligand N,N’–disalicyloylhydrazine
Table 6
Hydrogen bond distances (A) and angles (°) for complex 2.
D–Hꢀ ꢀ ꢀA
O9–H90. . .O10
O10–H100. . .O4
O10–H100. . .O9
D–H (Å)
Hꢀ ꢀ ꢀA (Å)
1.81(2)
2.27
Dꢀ ꢀ ꢀA (Å)
2.601(4)
2.988(4)
3.189(4)
\D–Hꢀ ꢀ ꢀA (°)
163(5)
147
0.811(19)
0.82
0.82
2.49
143
Symmetry transformations used to generate equivalent atoms: (a) ꢁx, ꢁy, ꢁz + 2.
Please cite this article in press as: S. Pasayat et al., Polyhedron (2014), http://dx.doi.org/10.1016/j.poly.2014.04.007

S. Pasayat et al. / Polyhedron xxx (2014) xxx–xxx
7
due to the presence of coordinated ethanol [66] and two bridging
oxygen. Very recently the antiproliferative activity of some di
and tri- oxomolybdenum(VI) compounds has been reported by
Feng et al. using the similar technique against six different human
cancer cell lines, i.e. A-549 (lung cancer), Bel-7402 (liver cancer),
HCT-8 (colon cancer), BCG-832 (gastric cancer), HL (leukemia),
and KB (nasopharyngeal), and the present results are in accordance
with the reported values [67].
Compounds
IC50 (µM)
1
2
32.66 2.34
28.33 1.29
3.6. Nuclear staining assay
To examine the apoptotic potential of test compounds in HeLa
cells, DAPI staining was done. Chromatin condensation that occurs
during apoptosis (type I programmed cell death) is a characterizing
marker of nuclear alteration. HeLa cells were treated with 30 and
Fig. 6. Effect of complexes 1 and 2 on cell viability and growth. HeLa cells were
treated with different concentrations of the test compounds for 72 h and then cell
viability was measured by MTT assay. Data reported as the mean S.D. for n = 6 and
compared against control by using a Student’s t-test. (⁄Significant compared to
control).
25 lM of 1 and 2 respectively. All the doses were given below
the calculated IC50 and the cells were incubated for 24 h before
DAPI nuclear staining assay. Control cells (treated with 90% DMF)
hardly showed any sort of condensation in comparison to the test
compound’s treated groups (as shown in Fig. 7), when the cells
were examined under fluorescent microscope, DAPI filter. All
images taken in grayscale demonstrate the brightly condensed
chromatin bodies and the nuclear blebbings as marked by arrows
in the figure. The drug treated groups besides showing nuclear
changes also revealed a shrinking morphology – another important
hallmark of apoptosis.
complex clearly indicates that incorporation of molybdenum in the
ligand environment has a marked effect on cytotoxicity. A possible
explanation is that by coordination the polarity of the ligand and
the central metal ion are reduced through the charge equilibration,
which favors permeation of the complexes through the lipid layer
of the cell membrane [64,65]. The present results are consistent
with the observation that metal complexes can exhibit greater bio-
logical activities than the free ligand [8].
4. Conclusions
Comparing the antiproliferative activity of two complexes, the
cytotoxicity follows the order 2 > 1, which is reflected from their
IC50 values with dose dependency illustrated in Fig. 6. The inhibi-
tory rate of 2 against HeLa cells is higher than 1, which may be
Two novel and unusual dimeric [(MoVIO2)2L] (1) and tetrameric
[{(C2H5OH)LO3MoV2I}2(
l-O)2]ꢀC2H5OH (2) oxidomolybdenum(VI)
complexes with N,N0-disalicyloylhydrazine have been synthesized
Fig. 7. Study of apoptosis by morphological changes in nuclei of HeLa cells. After treatment HeLa cells from control and treated group were fixed with 3.7% para formaldehyde
for 15 min, permeabilized with 0.1% Triton X-100 and stained with 1 lg/ml DAPI for 5 min at 37 °C. The cellswere then washed with PBS and examined by fluorescence
microscopy (Olympus IX 71) (200ꢂ).
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8
S. Pasayat et al. / Polyhedron xxx (2014) xxx–xxx
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The authors thank the reviewers for their comments and sug-
gestions, which were helpful in preparing the revised version of
the manuscript. Funding for this research was provided by CSIR,
Government of India (Grant No. 01(2735)/13/EMR-II). We
acknowledge the use of UV–Vis spectrophotometer purchased
from a DST (India) Grant No. SR/FT/CS-016/2008. Employing of
the instrument Bruker SMART APEX II CCD diffractometer, from
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Appendix A. Supplementary data
CCDC 972688 and 972689 contain the supplementary crystallo-
graphic data for complex 1 and complex 2 respectively. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/
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