Acetylacetonato chelated ruthenium organometallics incorporating imine-phenol function: Spectroscopic, structural, electrochemical and cytotoxicity studies

Article abstract of DOI:10.1016/j.ica.2015.02.023

The heterogeneous phase reaction of Ru(η²-RL)(PPh₃)₂(CO)Cl, 1 with lithium acetylacetonate (Liacac) afforded the complexes of the type Ru(η¹-RL)(PPh₃)₂(CO)(acac), 2 in excellent yield where

Full text of DOI:10.1016/j.ica.2015.02.023

Inorganica Chimica Acta 430 (2015) 36–45
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Acetylacetonato chelated ruthenium organometallics incorporating
imine–phenol function: Spectroscopic, structural, electrochemical and
cytotoxicity studies
Suman Mallick a, Mrinal Kanti Ghosh a, Ananda Sarkar b, Samir Jana c, Arindam Bhattacharyya c,
Sudip Mohapatra d, Swarup Chattopadhyay a,
⇑
a Department of Chemistry, University of Kalyani, Kalyani, Nadia 741235, WB, India
b Department of Physics, Acharya Prafulla Chandra College, New Barrackpore, Kolkata 700131, India
c Immunology Laboratory, Department of Zoology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700019, India
d Department of Chemistry, Missouri University of S & T, Rolla, MO 65409, USA
a r t i c l e i n f o
a b s t r a c t
2-RL)(PPh3)2(CO)Cl, 1 with lithium acetylacetonate (Liacac)
1-RL)(PPh3)2(CO)(acac), 2 in excellent yield where 2-RL is
1-RL is C6H2OH-2-CHNC6H4R(p)-3-Me-5 and R is H, Me, Cl.
The chelation of acac is attended with the cleavage of Ru–O and Ru–Cl bonds and iminium–phenola-
to ? imine–phenol prototropic shift. sterically controlled change in rotational conformation is
Article history:
The heterogeneous phase reaction of Ru(
g
Received 14 October 2014
Received in revised form 8 January 2015
Accepted 18 February 2015
Available online 6 March 2015
afforded the complexes of the type Ru(
C6H2O-2-CHNHC6H4R(p)-3-Me-5 and
g
g
g
A
involved in the 1 ? 2 conversion. The conversion is irreversible and the type 2 species are thermody-
namically more stable than the carboxylate, nitrite and nitrate complexes of 1. The crystal structures
Keywords:
Ruthenium
Iminium–phenolato
Redox chemistry
Cytotoxicity
of Ru(g g
1-MeL)(PPh3)2(CO)(acac), 2(Me) and Ru( 1-ClL)(PPh3)2(CO)(acac), 2(Cl) are reported. Spectral
(UV–Vis, IR, 1H NMR) and electrochemical data of the complexes are also reported. The electronic
structure and the absorption spectra of the complexes are scrutinized by the density functional theory
(DFT) and time-dependent density functional theory (TD-DFT) analyses. The complexes were also
screened in vitro for their antiproliferative properties against the MCF-7 breast cancer cell lines by
using the MTT assay. Flow cytometric analysis showed that the complexes arrested the cell cycle
in the sub G0 phase.
Theoretical study
Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction
The reaction of the Schiff mono bases of 4-methyl-2,6-
diformylphenol with Ru(PPh3)3Cl2 in ethanol afforded the novel
ruthenium organometallics of type Ru(g
2-RL)(PPh3)2(CO)Cl 1 by
decarbonylative orthometallation [1]. The four membered metalla-
cycle incorporating the phenolato function is unprecedented and
the CO ligand lies cis to the orthometallated carbon where the alde-
hyde function was attached before decarbonylative metallation.
Also notable is the iminium–phenolato zwitterionic function in
the six-membered hydrogen bonded chelate ring.
The reactivity of these compounds has also been investigated.
Complex 1 undergoes facile regiospecific insertion of alkynes into
the Ru–C(aryl) bond [2,3] of the four membered metallacycle ring
making it six-membered. Isonitriles have also been found to insert
into the Ru–O bond of 1 promoting metallacycle expansion [4]. It
⇑
has also been observed that mono-anionic
as carboxylate [5], nitrate, nitrite [6], xanthate [7] and pyridine-2-
r-donor ligands such
Corresponding author. Tel.: +91 33 25828750; fax: +91 33 25828282.
E-mail address: icskc@klyuniv.ac.in (S. Chattopadhyay).
http://dx.doi.org/10.1016/j.ica.2015.02.023
0020-1693/Ó 2015 Elsevier B.V. All rights reserved.

S. Mallick et al. / Inorganica Chimica Acta 430 (2015) 36–45
37
g g
1-MeC6H4L)(PPh3)2(CO)(
2-acac), 2(Me)
thiolate [8] undergo four-membered chelation via displacement of
Ru–O and Ru–Cl bonds affording new organometallics. A facile reac-
tion has also been observed between 1 and 2,20-bipyridine or 1,10-
2.2.1. Ru(
To a vigorously stirred solution of Ru(
g
2-MeC6H4L)(PPh3)2
(CO)Cl (100 mg, 0.1094 mmol) in dichloromethane (20 ml) and
acetone (20 ml) was added dropwise an aqueous solution of
Liacac (58 mg, 0.5474 mmol). The mixture was then stirred for
3 h when the original violet color of the solution became clear
yellow. The organic solvents were then removed under reduced
pressure leaving an aqueous suspension of a yellow residue, which
was isolated by filtration followed by washing repeatedly with
water, and dried in vacuo; yield 97 mg (91%). Anal. Calc. for
phenanthroline [9] leading to five-membered a-diimine chelation.
All the ligands cited above either make four or five-membered
chelation with 1, but none has yet been reported in which six-mem-
bered chelation with 1 is present.
In the present work we are exploring the feasibility of introduc-
ing a six-membered chelate ring into the organometallic frame of 1
via displacement of Ru–O and Ru–Cl bonds using b-diketonate as
the incoming ligand. This ligand choice was based on the reported
affinity of b-diketonate for ruthenium [10–14]. A facile reaction has
indeed been observed between 1 and lithium acetylacetonate in
dichloromethane–acetone–water medium leading to six-mem-
C57H51NO4P2Ru: C, 70.07; H, 5.26; N, 1.43. Found: C, 70.16; H,
5.19; N, 1.45%.
g g
1-ClC6H4L)(PPh3)2(CO)( 2-acac), 2(Cl)
bered O,O-chelated organometallics of type Ru(
g
1-RL)(PPh3)2(CO)
2.2.2. Ru(
This complex was prepared following the same procedure as
above using Ru(
2-ClC6H4L)(PPh3)2(CO)Cl as the starting material;
(g
2-acac) 2, the structure and properties of which are described
g
in this work.
yield 95 mg (89%). Anal. Calc. for C56H48NO4P2ClRu: C, 67.43; H,
4.85; N, 1.40. Found: C, 67.56; H, 4.93; N, 1.44%.
Investigations into the development of new anticancer drugs
have highlighted ruthenium as a potential metal center [15–17]
because ruthenium possesses several favorable properties such as
cytotoxicity against cancer cells, similar exchange properties to
those of Pt(II) complexes and is easily absorbed and rapidly excret-
ed by the body. It also has reduced toxicity against healthy tissues
due to transferrin transport [18,19]. Several ruthenium complexes
have displayed promising anticancer activity [20,21]. Cytotoxicity
of the complexes of type 1 or its derivatives has not been reported
earlier. This has prompted us to examine the cytotoxicity of the
complexes of type 2 with the human breast cancer cell line MCF-
7 which was evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5
diphenyltetrazolium bromide) assay. The cell cycle arrest was also
analyzed by flow cytometry. We have also examined the effect of
2.2.3. Ru(
Ru(
2-C6H5L)(PPh3)2(CO)Cl was employed as the starting mate-
g g
1-C6H5L)(PPh3)2(CO)( 2-acac), 2(H)
g
rial; yield 96 mg (90%). Anal. Calc. for C56H49NO4P2Ru: C, 69.84; H,
5.13; N, 1.45. Found: C, 69.75; H, 5.26; N, 1.52%.
2.3. X-ray crystallography
Single crystals of compositions Ru(
g
1-MeC6H4L)(PPh3)2(CO)
2-acac) 2(Cl)
(g
2-acac) 2(Me) and Ru( 1-ClC6H4L)(PPh3)2(CO)(
g
g
were grown by slow diffusion of hexane into benzene solution of
the complexes. The crystals were mounted on a Bruker AXS
different para-substituent of the Schiff base ligand (
antiproliferative effect of the complexes of type 2.
g
1-RL) on the
0
SMART APEX CCD diffractometer (Mo Ka, k = 0.71073 ÅA). The data
were reduced in SAINTPLUS [22] and empirical absorption corrections
were applied using the SADABS [22] package. The metal atoms were
located by the Patterson method and the rest of the non-hydrogen
atoms emerged from successive Fourier synthesis. Hydrogen atoms
were placed in idealized positions. The structures were refined by a
full matrix least-squares procedure on F2. All non-hydrogen atoms
were refined anisotropically. All calculations were performed using
the SHELXTL V6.14 program package [23]. Molecular structure plots
were drawn using the Oak Ridge thermal ellipsoid plot ORTEP-32
[24]. The key crystallographic data for 2(Me) and 2(Cl) are given
in Table 1.
To get better insight into the electronic structure and optical
properties of these complexes, density functional theory (DFT)
and time-dependent density functional theory (TD-DFT) studies
have also been presented. These combined experimental and theo-
retical studies provide the first detailed investigation of the elec-
tronic structure of the complexes of type 2.
2. Experimental
2.1. Materials and methods
The compound Ru(g
2-RL)(PPh3)2(CO)Cl 1 was prepared by the
literature method [1]. Lithium acetylacetonate (Liacac) was pur-
chased from Sigma Aldrich, India. All other reagents were obtained
from commercial sources and were used as received. Infrared spec-
tra were recorded on a Perkin-Elmer L120-00A FT-IR spectrometer
as a KBr pellet. Electronic spectra were recorded on a Shimadzu
UV-1800 PC Spectrophotometer. 1H NMR spectra were collected
on a Bruker DPX-400 spectrometer in CDCl3. Microanalyses were
performed using a Perkin-Elmer 2400 series-II elemental analyser.
Fluorescence spectra were measured on a Perkin-Elmer LS50B
spectrofluorimeter. All electrochemical measurements were per-
formed under a nitrogen atmosphere using CHI 600D electrochem-
istry system. The supporting electrolyte was tetrabutylammonium
perchlorate and potentials are referenced to Ag/AgCl electrode.
Table 1
Summary of X-ray crystallography for 2(Me) and 2(Cl).
2(Me)
2(Cl)
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C57H51NO4P2Ru
977.00
orthorhombic
Pbca
18.2354(5)
17.5247(5)
29.8717(8)
90
90
90
9546.1(5)
8
0.444
C56H48ClNO4P2Ru
997.47
orthorhombic
Pbca
18.094(5)
17.500(5)
29.358(9)
90
90
90
9296(5)
8
0.513
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
2.2. Preparation of complexes
l
(Mo K
Total reflections
Independent reflections (Rint
R1, wR2 [I > 2 (I)]
Goodness-of-fit (GOF) on F2
Largest difference in peak and hole
(e Åꢀ3
a
) (mmꢀ1
)
153808
10946 (0.0777)
0.0391, 0.0841
1.033
92381
The acetylacetonato complexes Ru(
g
1-RL)(PPh3)2(CO)(
g
2-acac)
1 with
)
8824 (0.0366)
0.0289, 0.0751
1.063
were synthesized by reacting Ru(
g
2-RL)(PPh3)2(CO)Cl
r
lithium salt of acetylacetone (Liacac) in dichloromethane
–acetone–water medium. Details of a representative case are given
below. The other compounds were prepared analogously.
0.494 and ꢀ0.346 0.587 and ꢀ0.449
)

38
S. Mallick et al. / Inorganica Chimica Acta 430 (2015) 36–45
2.6. Cell culture
2(H)
24000
18000
12000
6000
0
2(Me)
Human breast cancer MCF-7 cells were obtained from the
National Centre for Cell Science, Pune, India and cultured in
DMEM supplemented with 10% FCS and antibiotics/antimycotic
and gentamycin (50 lg/ml) solution with Na-pyruvate (1 mM) in
a humidified incubator at 37 °C in 5% CO2.
2(Cl)
ε
2.7. Phase contrast micrography
Cells were seeded in 24 well culture plates at a density of
1 ꢂ 105 cells/well and incubated in DMEM medium containing
10% FCS for 24 h. After attachment of the cells to the plates, the
cells were incubated with the complexes 2(H), 2(Me) and 2(Cl)
300
350
400
450
500
550
600
Wavelength (nm)
(60–80 lM) for 48 h. After treatment, phase contrast micrographs
Fig. 1. Absorption spectra of 2(R) [R = H, Me, Cl] in dichloromethane solution.
were taken using
a phase contrast microscope (Victory-FL,
Dewinter, Italy).
2.8. Cell proliferation-MTT assay
2.4. Computer generation of motif 6
Standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetraazoli-
um bromide (MTT) assay procedure was used. Cells were placed
in 96-well microassay culture plates (1 ꢂ 104 cells per well) in
The relative positions of CO and the acac chelate were retained
as in the structure of 2(Me) or 2(Cl) but the phenolic oxygen (O1)
(the phenolic C–O length was set at 1.361 Å for 2(Cl) and 1.358 Å
for 2(Me)) was shifted so as to correspond to the relative position
in 1 (R = Me or Cl). The O1ꢁ ꢁ ꢁO2 distances are then found to be
2.161 Å in 2(Cl) and 2.174 Å in 2(Me).
100 ll DMEM medium and grown overnight for attachment at
37 °C in a 5% CO2 incubator. After attachment of the cells to the
plates, compounds tested [2(H), 2(Me), 2(Cl)] were then added to
the wells to achieve final concentrations ranging from 0 to
120
um (100
bator for 48 h. Upon completion of the incubation, stock MTT dye
solution (10 l, 5 mg/ml) was added to each well and the cells were
l
M. Control wells were prepared by addition of culture medi-
ll). The plates were incubated at 37 °C in a 5% CO2 incu-
2.5. Computational study
l
The molecular geometries of the singlet ground state (S0) of the
synthesized complexes 2(H) and 2(Me) have been calculated by
the DFT method [25] using the (R)B3LYP hybrid functional
approach [26] incorporated into the GAUSSIAN 03 program package
[27]. The geometry of the complexes were fully optimized in the
gas phase without imposing any symmetry constraints. The single
crystal X-ray coordinates of 2(Me) have been used as the initial
input in the calculation. The calculated S0 structure corresponds
nicely to the geometrical parameters obtained experimentally by
X-ray diffractometry. On the basis of the optimized ground state
geometry, the absorption spectral properties were calculated by
the time-dependent density functional theory (TD-DFT) approach
[28,29]. The ruthenium atom was described by a double-f basis
set with the effective core potential of Hay and Wadt (LANL2DZ),
and the 6-31+G(d) basis set was used for the other elements pre-
sent in the complexes to optimize the ground state geometry.
The vibrational frequency calculations were performed to ensure
that the optimized geometry represents the local minima and that
there are only positive eigenvalues. The calculated electronic den-
sity plots for frontier molecular orbitals were prepared by using
incubated for a further 4 h. The optical density of each well was
then measured with a microplate spectrophotometer at a wave-
length of 570 nm. The IC50 values were determined by plotting
the optical density versus concentration and reading off the con-
centration at which 50% of cells remain viable relative to the
control.
2.9. Cell cycle distribution-flow cytometry
MCF-7 cells were seeded in six-well culture plates at a density
of 5 ꢂ 105 cells/well and incubated in DMEM medium containing
10% FCS for 24 h. After attachment, the cells were further incubat-
ed with the complexes [2(H), 2(Me) and 2(Cl); 80 lM] for 48 h.
After incubation the cell layer was trypsinized and collected by
centrifugation at 1500 rpm for 10 min. The cell pellet was fixed
with 70% ethanol and then permeabilized with PBS (phosphate
buffered saline) solution containing 0.1% triton X-100 with
RNAse (40
lg/ml) for 45 min. The cells were then stained with pro-
pidium iodide (PI) solution (50
lg/ml) on ice for 30 min. The PI
fluorescence was measured through a FL-2 filter (585 nm) using
a FACS Verse (BD Biosciences) flow cytometer. Flow cytometry data
were analyzed using Cell Quest software.
the GaussView 5.0 software. GAUSSSUM 2.1 program was used to cal-
culate the molecular orbital contributions of groups or atoms.
Table 2
1H NMR data in CDCl3 and UV–Vis spectral data in CH2Cl2.
a,b
Compd
d, ppm
UV–Vis data
2-Hs
4-Hs
O–Hs
3-Mes
16-Mes
18-Mes
17-Hs
7-Hs
kmax, nm (e c Mꢀ1 cmꢀ1
, )
2(H)
2(Me)
2(Cl)
6.19
6.26
6.27
6.66
6.72
6.78
12.50
12.65
12.39
1.72
1.79
1.79
1.31
1.37
1.37
1.10
1.17
1.18
4.40
4.47
4.47
7.90
7.96
7.94
409(3761), 317(23055)
413(4047), 322(26137)
421(3674), 320(27082)
a
b
c
Atom numbering is as in Figs. 5 and 6.
Aryl protons, 7.00–7.38m; s = singlet; m = multiplet.
Extinction coefficient.

S. Mallick et al. / Inorganica Chimica Acta 430 (2015) 36–45
39
associative pathway in which the acetylacetonate cis attack occurs
on the chloride atom as in 3. Once anchored the acac displaces
the phenolic oxygen completing the six-membered RuOO chelation
(4,5). The displaced phenolato ion pulls the originally zwitterionic
proton close to it and to avoid steric crowding the monodentate
RL ligand rotates around the Ru–C bond (vide infra).
40
30
20
10
0
2(H)
2(Me)
2(Cl)
O
O
P
O
P
H
H
P
N
N
O
O
O
O
Cl
O
350
400
450
500
550
600
C
C
OC
OC
C
OC
P
4
P
Wavelength (nm)
P
O
N
H
Fig. 2. Emission spectra of 2(R) [R = H, Me, Cl] in dichloromethane solution.
5
3
In dichloromethane solution the complexes uniformly display two
allowed absorption bands in the region 409–421 nm and 317–
322 nm, the later being more intense. Electronic spectra of the com-
plexes are shown in Fig. 1 and spectral data are given in Table 2. The
solutions of 2 show emission activity, the peak being in the region
429–431 nm, Fig. 2. In IR spectra, the CO stretch appears as a sharp
band in the region 1924–1928 cmꢀ1. The C@N stretching frequency
0.000000
2(H)
-0.000005
2(Me)
2(Cl)
in
2
(ꢃ1580 cmꢀ1
) is significantly lower than that in 1
(ꢃ1630 cmꢀ1) [1] as expected which is consistent with the pro-
totropic shift within the salicylaldimine function.
-0.000010
In the 1H NMR spectra of 2 the 2-H and 4-H resonances of the
metallated ring occur as sharp singlets between 6 and 7 ppm.
The PPh3 and Schiff base aromatic protons form a complex multi-
plet in the region 7.0–7.5 ppm and the azomethine proton occurs
as a singlet near 7.9 ppm. The phenolic proton appears as a sharp
signal near 12.5 ppm and the signal ‘‘disappears’’ upon shaking
with D2O. This behavior is similar to that of the carboxylate species
[5]. Selected 1H NMR chemical shift data are listed in Table 2.
The present complexes are unreactive towards displacement of
acetylacetonate by halide. No reaction was observed upon treat-
ment of 2 with tetraethyl ammonium chloride in acetone-ethanol
mixture. This is in contrast to the acetate [5], nitrite and nitrate
[6] complexes which are converted to 1 upon treatment with
halide. This observation clearly indicates that the six-membered
Ru(O,O) ring in 2 is more stable than four-membered Ru(O,O) ring
in the acetate, nitrate or nitrite complexes.
1.5
1.2
0.9
0.6
0.3
0.0
-0.3
Potential/V
Fig. 3. Cyclic voltammogram of 2(R) [R = H, Me, Cl] in dichloromethane solution
recorded at a scan rate of 100 mV sꢀ1
.
3. Results and discussion
3.1. Synthesis and characterization
In dichloromethane–acetone solution Ru(g
2-RL)(PPh3)2(CO)Cl 1
reacts smoothly with fivefold excess of aqueous lithium acetylace-
tonate (Liacac) furnishing a yellow solution from which Ru(g1
RL)(PPh3)2(CO)(
2-acac) 2 was isolated as yellow crystalline solid
in excellent yield. The
1-RL ligand in 2 is a tautomeric form of g2
-
g
g
-
RL ligand [1] in 1. Three different R groups have been used in this
work: H, Me and Cl. Specific compounds will be identified by putting
R in parenthesis e.g. 2(H) stands for Ru(g g
1-HL)(PPh3)2(CO)( 2-acac).
3.2. Electrochemical study
The organometallics of type 2 are diamagnetic in agreement with
metal oxidation state +2 (idealized t62g). They behave as non elec-
trolytes in acetone, methanol and other common solvents.
All the organometallics of type 2 are electroactive in dichloro-
methane solution and display three successive cyclic voltammetric
responses. Typical voltammograms are shown in Fig. 3 and the
potentials versus Ag/AgCl are listed in Table 3. The first oxidation
Table 3
Cyclic voltammetric redox potentialsa and IR spectral data.b
Compd Ox1 V (
D
EP, mV) Ox2 V (
D
EP, mV) Ox3 V (
D
EP, mV) IR data:
m
max, cmꢀ1
C@N C„O
2(H)
2(Me) 0.59 (160)
2(Cl) 0.64 (190)
0.61 (210)
1.01 (240)
1.01 (160)
1.01 (260)
1.29 (200)
1.27 (150)
1.26 (170)
1583 1924
1585 1928
1581 1924
a
Conditions: solvent, dichloromethane; supporting electrolyte, TBAP (0.1 M);
working electrode, platinum; reference electrode, Ag/AgCl; solute concentra-
tion, ꢃ10ꢀ3 M; E1/2 = 0.5(Epa + Epc) at scan rate 100 mV sꢀ1, where Epa and Epc
The mechanism of the synthetic reaction has not been investigated
but a pathway is depicted below on the basis of analogy [5]. It is an
are the anodic and cathodic peak potentials, respectively;
In KBr disk.
D
EP = Epa ꢀ Epc
.
b

40
S. Mallick et al. / Inorganica Chimica Acta 430 (2015) 36–45
2(Cl)
The acetylacetonate chelate ring (Ru, C16 to C20, O2, O3) along
0.64
0.63
0.62
0.61
0.60
0.59
with the carbon monoxide ligand and the C1 atom defines a good
plane (Plane B) with mean deviation of 0.1233 Å in 2(Me) and
0.1333 Å in 2(Cl). The dihedral angle between plane A and B is
27.6° in 2(Me) and 29.7° in 2(Cl).
2(H)
The acac ligand is chelated and the Schiff base ligand is mon-
odentate, bonded at the C1 atom only. The PPh3 ligands lie in trans
positions (P1–Ru–P2, 178.95(3)° in 2(Me) and 178.263(17)° in
2(Cl)). The phenolic oxygen atom is too far away (Ruꢁ ꢁ ꢁO1,
3.376 Å in 2(Me) and 3.350 Å in 2(Cl)) for metal binding.
Acetylacetonate chelation has cleaved the Ru–O(phenolato) bond
of the precursor complex 1. As a result the Schiff base fragment
tautomerizes from iminium–phenolato in 1 to imine–phenol in 2.
The Nꢁ ꢁ ꢁO distances in 2(Me) and 2(Cl) are 2.618 Å and 2.608 Å
respectively. The relative orientation of the Schiff base ligand in
2 is different from that in 1. In 2 the carbonyl group is positioned
on the same side of the Schiff base ligand as the uncoordinated
phenolic function. While in 1 the carbonyl group lies trans to the
coordinated phenolic function. In effect the Schiff base ligand has
undergone a large rotation around the Ru–C(aryl) bond in going
from 1 ? 2. This rotation and the consequent distancing of the
phenolic function from coordinated acetylacetonate is consistent
with steric consideration. If the phenolic oxygen was placed at
the carbon site close to the acetylacetonate function (O2 in
particular) the situation depicted in 6 will arise.
2(Me)
-0.2 -0.1 0.0 0.1 0.2 0.3
Hammett Constant (σ)
Fig. 4. Plot of Ox1 vs rR for the electrochemical transformation of 2(R) ? 2(R)+.
potential (Ox1) values shift marginally to the higher potential as
the R-substituent becomes more electron withdrawing. As R is var-
ied, the Ox1 values increase in the Hammett order Me < H < Cl.
Indeed, the plot of Ox1 versus Hammett constants [30,31] of R
are found to be linear [Fig. 4]. According to DFT results the compo-
sitions of HOMO and HOMOꢀ1 are metal–ligand mixed centered
which indicates that the oxidations are mixed metal–ligand cen-
tered. The second (Ox2) and third (Ox3) oxidation potential values
do not vary linearly with the Hammett order of the substituents (H,
Me, Cl). The acetate [5], nitrato, nitrito [6] and thioxanthato [7]
complexes of 1 display only one quasi-reversible cyclic voltammet-
ric response. The presence of three successive cyclic voltammetric
responses in the electrochemical experiment of 2 seems to be
favored by the strong
lacetonato ligand.
r-donor property of the electron rich acety-
3.3. Crystal structure
The crystal structures of Ru(
and Ru(
1-ClL)(PPh3)2(CO)(acac) 2(Cl) have been determined
g
1-MeL)(PPh3)2(CO)(acac) 2(Me)
g
authenticating the binding mode shown in 2. Molecular views
are shown in Figs. 5 and 6 and selected bond parameters are listed
in Table 4. The RuC2P2O2 coordination sphere has distorted octahe-
dral geometry as can be seen from the angles at the metal center.
The Ru, C1, O2, O3 and C40 atoms define an equatorial plane with
mean deviation of 0.0647 Å in 2(Me) and 0.0742 Å in 2(Cl). The
metallated aldimine ring (Ru, C1 to C7, C14, N1, O1) constitutes a
good plane (plane A) with mean deviation of 0.0238 Å in 2(Me)
and 0.0366 Å in 2(Cl). The pendant tolyl plane (C8 to C13, C15) in
2(Me) makes a dihedral angle of 10.2° with plane A whereas for
the chlorophenyl ring (C8 to C13, Cl1) in 2(Cl) the angle is 7.5°.
Here the O1ꢁ ꢁ ꢁO2 distance would be 2.161 Å in 2(Cl) and 2.174 Å in
2(Me). The van der Waals radius of oxygen is 1.4 Å [32,33]. Clearly
strong O1ꢁ ꢁ ꢁO2 repulsion is present in 6 and this is believed to lead
to rotation of the phenolic function to the position in 2 where the
Fig. 5. ORTEP representation of the complex 2(Me). Thermal ellipsoids are drawn at
Fig. 6. ORTEP representation of the complex 2(Cl) with thermal ellipsoids drawn at
the 30% probability level. Hydrogen atoms have been omitted for clarity.
the 30% probability level. Hydrogen atoms have been omitted for clarity.

S. Mallick et al. / Inorganica Chimica Acta 430 (2015) 36–45
41
Table 4
Table 5
Selected bond distances (Å) and angles (°) and their estimated standard deviations for
2(Me) and 2(Cl).
Selected DFT optimized geometrical parameters (bond lengths (Å) and angles (°)) of
2(H) and 2(Me) in the ground state.
2(Me)
2(Cl)
2(H)
2(Me)
Distances
Ru1–P1
Ru1–P2
Ru1–O2
Ru1–O3
Ru1–C40
Ru1–C1
O3–C18
O2–C16
C17–C18
C17–C16
C7–N1
Distances (Å)
Ru1–P1
Ru1–P2
2.4138(8)
2.4160(8)
2.424
2.467
2.3992(8)
2.1287(18)
2.166(2)
1.822(3)
2.089(3)
1.268(4)
1.275(3)
1.386(4)
1.385(4)
1.269(4)
2.3955(8)
2.1309(13)
2.1604(14)
1.8248(19)
2.0908(19)
1.268(2)
1.279(2)
1.399(3)
1.392(3)
1.283(3)
2.452
2.167
2.197
1.838
2.111
1.279
1.290
1.423
1.412
1.309
2.491
2.186
2.229
1.849
2.117
1.266
1.278
1.415
1.402
1.297
Ru1–O2
Ru1–O3
Ru1–C40
Ru1–C1
O3–C18
O2–C16
C17–C18
C17–C16
C7–N1
Angles
Angles (°)
P1–Ru1–P2
C1–Ru1–O3
C40–Ru1–O2
O2–Ru1–O3
C1–Ru1–C40
C40–Ru1–O3
C1–Ru1–O2
Ru1–C40–O4
178.95(3)
178.263(17)
171.55(6)
175.64(7)
86.39(5)
94.16(8)
92.15(7)
P1–Ru1–P2
C1–Ru1–O3
C40–Ru1–O2
O2–Ru1–O3
C1–Ru1–C40
C40–Ru1–O3
C1–Ru1–O2
Ru1–C40–O4
177.72
171.99
175.74
85.57
96.59
90.87
176.91
172.81
173.66
83.94
96.39
90.23
171.97(9)
175.62(11)
85.69(7)
94.35(12)
92.11(11)
88.17(9)
87.72(6)
174.85(16)
87.09
172.53
89.55
171.67
174.6(3)
representative complex, 2(Me) was calculated by time dependent
density functional theory (TD-DFT) [28,29] approach on the basis
of the optimized ground state geometry. For many transition metal
complexes, the TD-DFT approach had been found to be reliable for
calculating spectral properties [34,35]. TD-DFT method provides
more accurate electronic excitation energies because of the pres-
ence of electronic correlation.
The geometry optimized structures of 2(H) and 2(Me) have been
depicted in Fig. 7 and the significant metrical parameters are listed
in Table 5. The optimized geometries of the complexes do not show
significant differences in the coordination sphere around the ruthe-
nium center which means that the ligands bind in a similar fashion
in the complexes. The optimized structural parameters of the com-
plexes are in general agreement with the experimental values
(Table 4) and the slight discrepancy (maximum deviation
0.0918 Å for Ru–P2 bond distance) arises due to the crystal lattice
distortion existing in the real molecule. The isodensity plots from
HOMOꢀ5 to LUMO+5 are shown in Fig. 8 and partial frontier mole-
cular orbital compositions and energy levels are listed in Table 6.
The compositions of HOMOs and LUMOs are important in under-
standing the nature of transition in the absorption spectra of the
O1ꢁ ꢁ ꢁO2 and O1ꢁ ꢁ ꢁO3 distances are 4.950 Å and 5.272 Å, respective-
ly in 2(Me) and 4.910 Å and 5.236 Å, respectively in 2(Cl). The trans
influence of the metallated carbanionic site C1 is expected to
lengthen the Ru–O3 distance compare to Ru–O2 distance. Indeed,
the Ru–O3 distance is slightly longer than the Ru–O2 distance in
both 2(Me) and 2(Cl). In chelated acetylacetonates the RuII–O bond
lengths usually lie in the range 1.99–2.08 Å [10–14]. The RuII–O
bond lengths in 2(Me) and 2(Cl) [Ru–O2: 2.129 Å in 2(Me) and
2.131 Å in 2(Cl); Ru–O3: 2.166 Å in 2(Me) and 2.160 Å in 2(Cl)]
are slightly longer than that observed in other structurally charac-
terized RuII–acetylacetonate species [10–14]. The similarities in
the two C–O and two C–C distances in the acetylacetonate frame
in both 2(Me) and 2(Cl) correspond to a delocalized situation.
3.4. DFT study and computational details
In spite of several attempts, we were unable to grow the X-ray
quality single crystals of the complex 2(H). The geometrical struc-
tures of the singlet ground state (t62g) of 2(H) along with 2(Me)
were optimized by the DFT [25] method with B3LYP exchange cor-
relation functional [26] approach. The geometry used for the
ground state optimization is based on the crystal structure para-
meters of complex 2(Me) without any ligand simplification and
symmetry constraints. Since the three complexes have very similar
spectroscopic and cyclic voltammetric properties (vide supra)
which implies a close similarity between their electronic and mole-
cular structures, the absorption spectral property of one
complexes. HOMO is mainly composed of RL ligand
p-orbital
(60.4%) and filled d-orbital of Ru (29.75%) while LUMO is mainly
composed of RL ligand p⁄ orbital (78.95%). The relative energy levels
of FMOs are depicted in Fig. 9.
The calculated charge on the ruthenium atom is considerably
lower than the formal charge of +2 (Table 7). This is due to the sig-
nificant charge donation from the Caryl, Ccarbonyl, Pphosphine and
Fig. 7. Optimized molecular structures of 2(Me) and 2(H). [C: Grey, N: Sky Blue, O: Red, P: Orange, Ru: Green]. All hydrogen atoms are omitted for clarity. (For interpretation
of the references to colour in this figure legend, the reader is referred to the web version of this article.)

42
S. Mallick et al. / Inorganica Chimica Acta 430 (2015) 36–45
Oacetylacetonato donors. The charge on the Caryl atom is significantly
lower than ꢀ1 indicating that there is higher electron density delo-
calization from the Caryl to ruthenium center.
f = 0.2146) and 340.55 nm (3.641 eV, f = 0.1628). The first
transition is mainly due to the Hꢀ3 ? L+1 (12%), Hꢀ1 ? L (45%)
and Hꢀ1 ? L+1 (17%) transitions and can be ascribed to
The computed vertical transitions were calculated at the equi-
librium geometry of the S0 state and described in term of one-elec-
tron excitations of the molecular orbitals of the corresponding S0
geometry. The calculated absorption energies associated with their
oscillator strengths, the main configurations and their assignments
as well as the experimental data for 2(Me) are given in Table 8.
For 2(Me) mainly two transitions have been observed going
from the lower to the higher energy region of the spectra. The
low energy transition is observed near 413 nm as broad band.
This feature is analyzed and it is in excellent agreement with the
absorptions at 402.58 nm (3.079 eV, f = 0.0605) which is due to
the H ? L (89%) transition and it is assigned to the
[d(Ru) + p(Oacac) + p
(CO)] ? [d(Ru) + p⁄(PPh3)], [d(Ru) + p(Oacac) +
p
(RL)] ? [p⁄(RL) + p⁄(PPh3)]
and
[d(Ru) + p(Oacac) + p(RL)] ?
[d(Ru) + p⁄(PPh3)] transitions. The second one appeared as a linear
combination of Hꢀ2 ? L+1 (19%), Hꢀ1 ? L (22%) and Hꢀ1 ? L+1
(30%) transitions and they are assigned primarily to the [p(Oacac
)
+
p
(RL) +
p
(PPh3)] ? [d(Ru) + p⁄(PPh3)], [d(Ru) + p(Oacac) +
p(RL)]
? [p⁄(RL) + p⁄(PPh3)] and [d(Ru) + p(Oacac) +
p(RL)] ? [d(Ru) +
p⁄(PPh3)] transitions. Those transitions are essentially MLCT,
LLCT and ILCT in nature.
3.5. Cytotoxicity
[d(Ru)
in nature.
The other experimentally observed absorption in the UV region
at 322 nm comprises the excitations at 345.50 nm (3.589 eV,
p
(RL)] ? [p⁄(RL) + p⁄(PPh3)] character and is mainly ILCT
The cytotoxicity of the complexes 2(H), 2(Me) and 2(Cl) to
human breast cancer cell line MCF-7 was assayed by cell survival
after 48 h of exposure to the desired concentration range
(0–120
lM) using the MTT assay which is depicted in Fig. 10. It
HOMO –4
HOMO –3
HOMO –5
HOMO –2
HOMO –1
HOMO
LUMO +2
LUMO +1
LUMO
LUMO +3
LUMO +4
LUMO +5
Fig. 8. Isodensity plot of frontier molecular orbitals of 2(Me) with isodensity value 0.04.

S. Mallick et al. / Inorganica Chimica Acta 430 (2015) 36–45
43
Table 6
Frontier molecular orbital composition (%) in the ground state for 2(Me).
Orbital
Energy (eV)
Contribution (%)
Ru
Main bond type
PPh3
Oacac
RL
0.26
1.38
0.41
0.38
2.32
78.95
60.40
69.69
30.15
3.75
CO
1.23
LUMO+5
LUMO+4
LUMO+3
LUMO+2
LUMO+1
LUMO
ꢀ0.416
ꢀ0.472
ꢀ0.554
ꢀ0.610
ꢀ0.887
ꢀ1.156
ꢀ4.770
ꢀ5.175
ꢀ5.411
ꢀ5.638
ꢀ6.030
ꢀ6.148
1.49
5.18
3.37
0.27
19.00
0.19
29.75
11.02
8.05
67.44
22.07
7.55
92.62
91.35
44.53
62.07
71.72
20.56
2.21
3.7
15.58
1.02
4.40
1.15
51.42
32.62
4.73
0.25
7.32
15.47
45.16
14.29
2.82
p⁄(PPh3)
0.94
0.27
4.66
2.23
0.05
0.32
0.12
1.06
p⁄(PPh3)
p⁄(PPh3) + p⁄(Oacac
p⁄(PPh3) + p⁄(Oacac
d(Ru) + p⁄(PPh3)
p⁄(RL) + p⁄(PPh3)
)
)
HOMO
d(Ru) +
d(Ru) + p(Oacac) +
p(Oacac) + (RL) +
d(Ru) + p(Oacac) +
d(Ru) + (RL)
p(Oacac) + (PPh3)
p(RL)
HOMOꢀ1
HOMOꢀ2
HOMOꢀ3
HOMOꢀ4
HOMOꢀ5
p(RL)
p
p(PPh3)
13.5
0.79
0.38
p(CO)
5.74
76.04
68.58
0.27
p
15.76
p
Table 7
Mulliken atomic charges for 2(Me).
Atom
Atomic charges
Ru
Caryl
ꢀ0.134606
ꢀ0.058835
0.243174
0.614004
0.635973
ꢀ0.518311
ꢀ0.481334
ꢀ0.302586
Ccarbonyl
Pphosphine
Pphosphine
Oacetylacetonato
Oacetylacetonato
Ocarbonyl
Table 8
Main calculated optical transitions for the complex 2(Me) with composition in terms
of molecular orbital contribution of the transition, computed vertical excitation
energies and oscillator strength (f).
Excitation Composition
E (eV)
f
ktheo (nm) Assign kexp (nm)
ILCT 413
2
5
H ? L (89%)
3.079 0.0605 402.58
Hꢀ3 ? L+1 (12%) 3.589 0.2146 345.50
Hꢀ1 ? L (45%)
MLCT 322
ILCT
LLCT
LLCT
ILCT
Hꢀ1 ? L+1 (17%)
7
Hꢀ2 ? L+1 (19%) 3.641 0.1628 340.55
Hꢀ1 ? L (22%)
Hꢀ1 ? L+1 (30%)
LLCT
Fig. 9. Partial molecular orbital diagram for complex 2(Me). The arrow is intended
to highlight the HOMO–LUMO energy gap. The DFT energy value is given in eV.
has been found that increasing complex concentrations decrease
the MCF-7 cell viability in a dose-dependent manner. The IC50 val-
ues obtained after 48 h of drug treatment with the MTT assay are
found to be around 80 lM.
To further observe and study the antitumor activity of these
ruthenium complexes, morphological study was performed. Cell
death was characterized by obvious morphological characteristics.
MCF-7 cells treated with the ruthenium complexes showed clear
morphological change and quantity decrease, as shown in Fig. 11.
The morphological change of the cells is positively correlated with
dosage. These phenomena suggest that the ruthenium complexes
block the growth of MCF-7 cells. The detachment of cells from
the substratum, change of cell morphology and cell shrinkage were
clearly observed which points to the cell death after 48 h exposure
of the compounds on MCF-7 cells.
Inhibition of cancer-cell proliferation by cytotoxic drugs could
be the result of cell cycle arrest [36,37]. According to the result
of the MTT assay, complexes of type 2 are active in inhibiting
MCF-7 cell growth. Thus, these complexes were used for further
investigation of the underlying mechanism. The effect of the com-
plexes [2(H), 2(Me), 2(Cl)] on the cell cycle of MCF-7 cells were
Fig. 10. Growth inhibitory effect of the complex 2(R) on MCF-7 cells.
studied by flow cytometry in propidium iodide (PI)-stained cells
after treatment with the complexes for 48 h to determine the pos-
sible mechanism of cell-growth inhibition. The representative DNA

44
S. Mallick et al. / Inorganica Chimica Acta 430 (2015) 36–45
Fig. 11. Phase contrast micrographs (20ꢂ magnifications) of MCF-7 cells after exposure of 2(R) for 48 h.
Fig. 12. Flow cytometry analysis of the cell cycle distribution of MCF-7 cells after exposure of 2(R) for 48 h.
distribution histograms of MCF-7 cells in the absence and presence
of the complexes are shown in Fig. 12. The cell cycle distribution
pattern shows an obvious enhancement (ꢃ12%) in the percentage
of cells at sub G0 phase accompanied by reduction in the percent-
age of cells in the G0/G1 phase and S phase. Increase in the per-
centage of cells at the sub G0 phase clearly indicates the
induction of sub G0 phase arrest by complexes of type 2.
that the para-substituents on the g
1-RL ligand do not induce any
change in the antiproliferative activity of the complexes of type 2.
4. Conclusions
The main finding of this work will now be summarized. It is
We were expecting that the cytotoxic properties of the com-
plexes of type 2 should correlate somewhat with the electronic
nature [38] of the three different para-substituents (H, Me, Cl) on
demonstrated that Ru(
stitution of chloride by acetylacetonate affording a new family of
aryl ruthenium species, Ru(
1-RL)(PPh3)2(CO)(acac) 2. The com-
g
2-RL)(PPh3)2(CO)Cl 1 undergoes facile sub-
g
the
g
1-RL ligand but the IC50 values obtained after 48 h of drug
plexes are characterized by different spectroscopic techniques, ele-
mental analysis and X-ray structure determination. Structure
determination has revealed that in going from 1 ? 2 the RL ligand
treatment are found to be around 80
l
M (Fig. 10) for all the three
complexes. Flow cytometry analysis also shows the similar cell
cycle distribution pattern for 2(H), 2(Me) and 2(Cl). So the MTT cell
proliferation assay and flow cytometry analysis experiments show
changes its hapticity from
tion tautomerizes to the imine–phenol function. In 2 the metallated
g g
2 to 1 as the iminium–phenolato func-

S. Mallick et al. / Inorganica Chimica Acta 430 (2015) 36–45
45
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Financial support from the Department of Science and
Technology, Government of India (No. SR/S1/IC-65/2010) is grate-
fully acknowledged. University of Kalyani for infrastructural facil-
ities. The support of DST under FIST program to the Department
of Chemistry and PURSE to the University of Kalyani is also
acknowledged. We are also thankful to Dr. Rajat Saha of Jadavpur
University for help with the crystallography. S.M. thanks UGC,
India and M. K. G. thanks University of Kalyani for the pre-doctoral
fellowships.
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Appendix A. Supplementary material
CCDC 991302 and 991303 contains the supplementary crystal-
lographic data for 2(Me) and 2(Cl), respectively. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at http://dx.doi.org/10.1016/j.ica.2015.02.023.
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