Preparation, spectroscopy, EXAFS, electrochemistry and pharmacology of new ruthenium(II) carbonyl complexes containing ferrocenylthiosemicarbazone and triphenylphosphine/arsine

Article abstract of DOI:10.1016/j.saa.2010.12.046

A new series of new hetero-bimetallic complexes containing iron and ruthenium of the general formula [RuCl(CO)(B)(EPh₃)(L)] (where E = P or As; B = PPh₃, AsPh₃, py or pip; L = ferrocene derived monobasic bidentate thiosemi

Full text of DOI:10.1016/j.saa.2010.12.046

Spectrochimica Acta Part A 78 (2011) 844–853
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Preparation, spectroscopy, EXAFS, electrochemistry and pharmacology of new
ruthenium(II) carbonyl complexes containing ferrocenylthiosemicarbazone and
triphenylphosphine/arsine
R. Prabhakarana,b, S. Anantharamanc, M. Thilagavathia, M.V. Kaveria, P. Kalaivania,
R. Karvembud, N. Dharmaraja, H. Bertagnollic,∗, F. Dallemerb, K. Natarajana,∗∗
a Department of Chemistry, Bharathiar University, Coimbatore 641 046, India
b Laboratorie Chimie Provence-CNRS UMR6264, University of Aix-Marseille I, II et III – CNRS, Campus Scientifique de Saint-Jérôme,
Avenue Escadrille Normandie-Niemen, F-13397 Marseille Cedex 20, France
c Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
d Department of Chemistry, National Institute of Technology, Tiruchirappalli 620 015, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of new hetero-bimetallic complexes containing iron and ruthenium of the general formula
[RuCl(CO)(B)(EPh3)(L)] (where E = P or As; B = PPh3, AsPh3, py or pip; L = ferrocene derived monobasic
bidentate thiosemicarbazone ligand) have been synthesized by the reaction between ferrocene-derived
thiosemicarbazones and ruthenium(II) complexes of the type [RuHCl(CO)(B)(EPh3)2] (where E = P or
As; B = PPh3, AsPh3, py or pip). The new complexes have been characterized by elemental analyses, IR,
electronic, NMR (1H, 13C and 31P), EXAFS (extended X-ray absorption fine structure spectroscopy) and
cyclic voltammetric techniques. Antibacterial activity of the new complexes has been screened against
Escherichia coli, Vibrio cholerae, and Pseudomonas aeruginosa species.
Received 26 February 2010
Received in revised form
10 December 2010
Accepted 14 December 2010
Keywords:
Ruthenium(II) complexes
Ferrocenylthiosemicarbazone
Spectroscopy
© 2010 Elsevier B.V. All rights reserved.
EXAFS
Electrochemistry
Pharmacological studies
1. Introduction
cides and fungicides [15]. Complexes of thiosemicarbazones have
also been screened for medicinal properties [16], shown to pos-
Hetero-bimetallic compounds have become increasingly impor-
tant in recent years in view of their potential applications in the
fields of catalysis, drug design [1–3]. Many transition metal com-
plexes of ferrocene derived thiosemicarbazones, semicarbazones
are reported [4,5]. Ferrocene and its derivatives have been inves-
tigated [6,7] due to their use as colour pigments [8] and as high
burning rate catalysts [9]. Even today, cisplatin is one of the most
widely used metal containing chemotherapeutic drugs in USA,
Europe and Japan [10]. However, it has been shown that certain
sess some degree of cytotoxic activity [17]. In continuation of our
interest on bimetallic complexes [18,19], we report in this article,
the synthesis, analytical, spectral, characterization, EXAFS studies,
antibacterial activities of ferrocenylthiosemicarbazone complexes
of ruthenium(II). The general structure of the ligands is given in
Fig. 1.
2. Experimental
ferrocenium salts have more favourable 50% lethal dosage (LD50
)
2.1. Reagents and materials
values compared to cisplatin [11,12]. Moreover, ferrocenylth-
iosemicarbazone containing transition metal complexes have been
found to be active against protozoa [13], tumours [14], pesti-
RuCl3·3H2O was purchased from Himedia, used without fur-
ther purification. All the reagents used were chemically pure grade.
Solvents were purified, dried according to the standard procedure
[20]. Ferrocenylthiosemicarbazone ligands, the starting complexes
[RuHCl(CO)(B)(EPh3)2] (where E = P or As; B = PPh3, AsPh3, pyridine
(py) or pipyridine (pip)) were prepared by the reported procedures
[21–25].
∗
Corresponding author. Tel.: +49 711 685 64450; fax: +49 711 685 64443.
Corresponding author. Tel.: +91 422 2422222; fax: +91 422 2422387.
E-mail addresses: h.bertagnolli@ipc.uni-stuttgart.de (H. Bertagnolli),
∗∗
k natraj6@yahoo.com (K. Natarajan).
1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.12.046

R. Prabhakaran et al. / Spectrochimica Acta Part A 78 (2011) 844–853
845
The positron energy was 4.45 GeV, the beam current was between
90 mA and 130 mA. Energy calibration was monitored by measur-
ing the absorption through a reference simultaneously with the
absorption through the complexes, by means of a third ion cham-
ber. For Ru K-edge measurements ruthenium metal foil was used
as the reference. A 20-␮m thick gold metal foil having LIII-edge at
11,919 eV was used as reference for As K-edge measurements. The
complexes in solid state were embedded in a polyethylene matrix,
pressed into pellet and the concentration was adjusted to yield an
extinction of 1.5. Data evaluation started with the removal of back-
ground absorption from the experimental absorption spectrum by
subtraction of a Victoreen-type polynomial. Then, the spectrum
was convoluted with a series of increasingly broader Gaussian func-
tions, the common intersection point of the convoluted spectra was
taken as energy E0 [26,27]. To determine the smooth part of the
spectrum, corrected for pre-edge absorption and a piecewise poly-
nomial was used. It was adjusted in such a manner that the low-R
components of the resulting Fourier transform were minimal. After
division of the background-subtracted spectrum by its smooth part,
the photon energy was converted into a photoelectron wave vec-
tor scale, the resulting EXAFS function was weighted with k3. Data
analysis in k space was performed according to the curved-wave
formalism of the program EXCURVE98 with the XALPHA phase,
amplitude functions [28]. The amplitude factor (AFAC) was fixed
at 0.8, an overall energy shift (ꢀE0) was introduced to give a best
fit to the data. The mean free path of the scattered electrons was
calculated from the imaginary part of the potential (VPI was set to
−4.00).
R
HN
HN
S
N
Fe
R
Abbreviation
HFctsc
H
C6H5
CH3
HFcptsc
HFcmtsc
Fig. 1. General structure of the ligand.
2.2. Physical measurements
The elemental analyses of the complexes were performed with
Vario EL III CHNS analyzer. IR spectra of the ligands and the com-
plexes (KBr pellets) have been recorded with Shimadzu/Nicolet
instruments in 4000–400 cm−1 range. Electronic spectra of the
complexes have been recorded in methanol using a Systronics
119 spectrophotometer in the 800–200 nm range. 1H NMR, 13C
NMR and 31P NMR spectra were recorded in CDCl3 with Varian
AMX 400 instrument using tetramethylsilane and orthophospho-
ric acid as references, respectively. Cyclic voltammetric studies
of the complexes have been carried out with EG & G-Princeton
Applied Research Electrochemical Analyzer in dichloromethane
using a glassy carbon working electrode and all the potentials were
referenced to standard silver/silver chloride electrode. Ferrocene
was used as external standard. Melting points were recorded on
a Raaga melting point apparatus. In spite of several attempts to
prepare single crystals, suitable for X-ray structure determination
were not succeeded. Hence, the local structure and the coordi-
nation geometry of the complexes were determined by extended
X-ray absorption fine structure (EXAFS) spectroscopy. The trans-
mission mode EXAFS measurements were performed at Ru K-edge
at 22,117 eV, As K-edge at 11,867 eV and Fe K-edge at 7112 eV
at the beamline X1.1 of the Hamburger Synchrotron Radiation
Laboratory (HASYLAB) at DESY, Hamburg. The complexes were
measured with Si(3 1 1) double crystal monochromator at the Ru
K-edge, with Si(1 1 1) double crystal monochromator at the As, Fe
K-edges. The measurements were carried out at ambient condi-
tions and ion chambers filled with inert gases (nitrogen, argon)
were used to measure the incident and transmitted intensities.
2.3. Recommended procedures
2.3.1. Synthesis of new hetero binuclear complexes
To a benzene (25 cm3) solution of [RuHCl(CO)(PPh3)3] (0.030 g;
0.1 mmol) and the ferrocenylthiosemicarbazone ligand (HFctsc)
(0.095 g; 0.1 mmol) was added. The mixture was refluxed for 6 h
and the resulting brown solution was concentrated to about 3 cm3.
The new complex was separated by adding a small quantity (6 cm3)
of petroleum ether (60–80 ◦C). They were recrystallised from
CH2Cl2/petroleum ether (60–80 ◦C) mixture and dried in vacuo.
[RuCl(CO)(PPh3)2(Fctsc)] (1) yield: 70% (66.7 mg). M.p. > 300 ◦C. FT-
IR (KBr): 1625 cm−1 (ꢁC N), 1957 cm−1 (ꢁC O), 748 cm−1 (ꢁC–S),
1433, 1093, and 693 cm−1 (for PPh3). UV–vis (methanol), ꢂmax (234,
260, 281, 302, and 466 nm). Anal. Calc. for C50H44N3OP2SClFeRu:
C, 60.7; H, 4.48; N, 4.25; S, 3.24; Found: C, 59.98; H, 5.18; N,
4.97; S, 4.02. 1H NMR (CDCl3 ı ppm); 7.0–7.9 (m, aromatic), 2.2
(s, CH3), 4.2 (s, Cp ring), 5.4 (s, –NH2); 31P NMR (CDCl3 ı ppm);
28.6.
The similar procedure has been followed to prepare the other
complexes also.
[RuCl(CO)(PPh3)(py)(Fctsc)] (2) yield: 65% (50.09 mg).
M.p. > 300 ◦C. FT-IR (KBr): 1620 cm−1 (ꢁC N), 1948 cm−1 (ꢁC O),
755 cm−1 (ꢁC–S), 1436, 1070, and 694 cm−1 (for PPh3). UV–vis
(methanol), ꢂmax (232, 255, 290, and 476 nm). Anal. Calc. for
C37H34N4OPSClFeRu: C, 55.13; H, 4.25; N, 6.95; S, 3.98; Found: C,
55.89; H, 4.72; N, 6.44; S, 4.04. 1H NMR (CDCl3 ı ppm); 6.9–7.7 (m,
aromatic), 2.25 (s, CH3), 4.1 (s, Cp ring), 5.4 (s, –NH2).
[RuCl(CO)(PPh3)(pip)(Fctsc)] (3) yield: 55% (42.72 mg).
M.p. > 300 ◦C. FT-IR (KBr): 1618 cm−1 (ꢁC N), 1944 cm−1 (ꢁC O),
746 cm−1 (ꢁC–S), 1434, 1093, and 696 cm−1 (for PPh3). UV–vis
(methanol), ꢂmax (221, 260, 294, 442, and 468 nm). Anal. Calc. for
C37H39N4OPSClFeRu: C, 54.78; H, 4.85; N, 6.9; S, 3.95; Found: C,
55.08; H, 4.48; N, 3.90; S, 3.08.
[RuCl(CO)(AsPh3)2(Fctsc)] (4) yield: 65% (67.71 mg). M.p.
258 ◦C. FT-IR (KBr): 1618 cm−1 (ꢁC N), 1956 cm−1 (ꢁC O),
736 cm−1 (ꢁC–S), 1438, 1088, and 704 cm−1 (for AsPh3). UV–vis
(methanol), ꢂmax (267, 293, 327, 368, and 464 nm). Anal. Calc. for
Fig. 2. 1H NMR spectrum of [RuCl(CO)(pip)(PPh3)(Fcmtsc)] (11).

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R. Prabhakaran et al. / Spectrochimica Acta Part A 78 (2011) 844–853
Fig. 3. 13C NMR spectrum of [RuCl(CO)(PPh3)2(Fcptsc)] (5).
C50H44N3OAs2SClFeRu: C, 55.75; H, 4.10; N, 3.90; S, 2.97; Found:
C, 56.08; H, 4.48; N, 4.28; S, 3.08.
C43H38N4OPSClFeRu: C, 60.99; H, 4.52; N, 6.61; S, 3.78; Found: C,
60.16; H, 4.48; N, 6.88; S, 4.08. 1H NMR (CDCl3 ı ppm); 6.2–7.4 (m,
aromatic), 1.7 (s, CH3), 4.1 (s, Cp ring), 11.6 (s, terminal –NH).
[RuCl(CO)(PPh3)(pip)(Fcptsc)] (7) yield: 60% (51.17 mg).
M.p. > 300 ◦C. FT-IR (KBr): 1600 cm−1 (ꢁC N), 1930 cm−1 (ꢁC O),
746 cm−1 (ꢁC–S), 1431, 1086, and 704 cm−1 (for PPh3). UV–vis
(methanol), ꢂmax (228, 296, 326, 370, and 471 nm). Anal. Calc. for
[RuCl(CO)(PPh3)2(Fcptsc)]
(5)
yield:
65%
(66.95 mg).
M.p. > 300 ◦C. FT-IR (KBr): 1600 cm−1 (ꢁC N), 1935 cm−1 (ꢁC O),
744 cm−1 (ꢁC–S), 1435, 1095, and 698 cm−1 (for PPh3). UV–vis
(methanol), ꢂmax (264, 298, 324, 370, and 468 nm). Anal. Calc. for
C56H48N3OP2SClFeRu: C, 65.30; H, 4.69; N, 4.07; S, 3.11; Found: C,
64.93; H, 4.88; N, 3.98; S, 3.25. 1H NMR (CDCl3 ı ppm); 6.5–8.1 (m,
C
43H43N4OPSClFeRu: C, 60.56; H, 5.20; N, 6.56; S, 3.76; Found: C,
aromatic), 1.98 (s, CH3), 4.2 (s, Cp ring), 11.8 (s, terminal –NH), 13
C
61.48; H, 5.36; N, 7.08; S, 3.96. 1H NMR (CDCl3 ı ppm); 6.0–7.8 (m,
aromatic), 2.1 (s, CH3), 4.15 (s, Cp ring), 3.1–3.5 (m, pip), 11.6 (s,
terminal –NH).
NMR (CDCl3 ı ppm); 207 (CO), 134.4, 129.7, 128.4, 127.6 (phenyl
protons), 96 (cyclo pentadienyl), 30.9 (CH3); 31P NMR (CDCl3
ppm); 36.25.
ı
[RuCl(CO)(AsPh3)2(Fcptsc)]
(8)
yield:
75%
(83.84 mg).
[RuCl(CO)(PPh3)(py)(Fcptsc)] (6) yield: 65% (55.04 mg).
M.p. > 300 ◦C. FT-IR (KBr): 1602 cm−1 (ꢁC N), 1965 cm−1 (ꢁC O),
742 cm−1 (ꢁC–S), 1434, 1092, and 698 cm−1 (for PPh3). UV–vis
(methanol), ꢂmax (242, 292, 360, and 465 nm). Anal. Calc. for
M.p. > 300 ◦C. FT-IR (KBr): 1602 cm−1 (ꢁC N), 1957 cm−1 (ꢁC O),
748 cm−1 (ꢁC–S), 1436, 1092, and 696 cm−1 (for AsPh3). UV–vis
(methanol), ꢂmax (223, 260, 277, 320, and 460 nm). Anal. Calc. for
C56H48N3OAs2SClFeRu: C, 60.17; H, 4.32 N, 3.75; S, 2.87; Found: C,
Fig. 4. 31P NMR spectrum of [RuCl(CO)(PPh3)2(Fcptsc)] (5).

R. Prabhakaran et al. / Spectrochimica Acta Part A 78 (2011) 844–853
847
59.86; H, 4.62; N, 4.16; S, 3.02. 1H NMR (CDCl3 ı ppm); 6.5–7.8 (m,
aromatic), 1.63 (s, CH3), 4.2 (s, Cp ring), 11.6 (s, terminal –NH).
1600–1647 cm−1 indicating the coordination of azomethine nitro-
gen to ruthenium [30]. In the IR spectra of all the new complexes,
a strong band in the region 1930–1965 cm−1 has been observed
due to the presence of terminally coordinated carbonyl group [28].
A medium intensity band observed in the region 821–823 cm−1
in the spectra of the ligands has been assigned as due to >C S,
which was completely disappeared in the complexes and a new
band appeared in the region 736–755 cm−1 indicating coordina-
tion of thiolate sulphur after the enolisation of –NH–C S– group
and subsequent deprotonation [31,32]. Characteristic bands due
to triphenylphosphine / triphenylarsine were also present in the
expected region. The complexes containing coordinated nitrogen
bases exhibited a medium intensity band around 1020–1040 cm−1
region, which is characteristic of coordinated pyridine or piperidine
[30].
[RuCl(CO)(PPh3)2(Fcmtsc)]
(9)
yield:
65%
(62.91 mg).
M.p. > 300 ◦C. FT-IR (KBr): 1640 cm−1 (ꢁC N), 1951 cm−1 (ꢁC O),
748 cm−1 (ꢁC–S), 1434, 1094, and 695 cm−1 (for PPh3). UV–vis
(methanol), ꢂmax (234, 260, 281, 302, and 466 nm). Anal. Calc. for
C51H46N3OP2SClFeRu: C, 61.05; H, 4.60; N, 4.19; S, 3.20; Found: C,
60.21; H, 4.74; N, 4.19; S, 3.24.
[RuCl(CO)(PPh3)(py)(Fcmtsc)] (10) yield: 65% (51 mg).
M.p. > 300 ◦C. FT-IR (KBr): 1647 cm−1 (ꢁC N), 1953 cm−1 (ꢁC O),
748 cm−1 (ꢁC–S), 1431, 1095, and 696 cm−1 (for PPh3). UV–vis
(methanol), ꢂmax (230, 260, 298, and 466 nm). Anal. Calc. for
C38H36N4OPSClFeRu: C, 55.65; H, 4.42; N, 6.83; S, 3.91; Found: C,
56.04; H, 4.68; N, 7.04; S, 4.16.
[RuCl(CO)(PPh3)(pip)(Fcmtsc)] (11) yield: 60% (47.44 mg).
M.p. > 300 ◦C. FT-IR (KBr): 1647 cm−1 (ꢁC N), 1951 cm−1 (ꢁC O),
748 cm−1 (ꢁC–S), 1434, 1093, and 692 cm−1 (for PPh3). UV–vis
(methanol), ꢂmax (238, 272, 296, 346, and 462 nm). Anal. Calc. for
3.2. Electronic spectra
C
38H41N4OPSClFeRu: C, 55.31; H, 5.00; N, 6.79; S, 3.89; Found: C,
All the new ruthenium(II) complexes have been found to be
diamagnetic indicating the presence of ruthenium in +2 oxida-
tion state. The ground state of ruthenium(II) (t62g configuration)
54.98; H, 4.98; N, 7.03; S, 4.01. 1H NMR (CDCl3 ı ppm); 6.7–7.8 (m,
aromatic), 2.2 (s, CH3), 4.4 (m, Cp ring), 3.2–3.5 (m, pip), 2.4 (m,
NH–CH3), 11.8 (s, terminal –NH).
is A1g. The excited states corresponding to t5 eg1 configuration
1
2g
[RuCl(CO)(AsPh3)2(Fcmtsc)] (12) yield: 75% (79.18 mg).
M.p. > 300 ◦C. FT-IR (KBr): 1631 cm−1 (ꢁC N), 1955 cm−1 (ꢁC O),
740 cm−1 (ꢁC–S), 1438, 1094, and 702 cm−1 (for AsPh3). UV–vis
(methanol), ꢂmax (242, 302, 350, 385, and 474 nm). Anal. Calc. for
3
1
are T1g
,
3T2g
,
1T1g and T2g in the order of increasing energy.
Hence, four bands are possible corresponding to the transitions
1A1g → T1g
,
1A1g → T2g
,
1A1g → T1g and 1A1g → T2g, in the order
3
3
1
1
of increasing energy. The electronic spectra of all the complexes
were recorded in methanol. The spectra of the complexes showed
four to five bands in the region 221–476 nm. The bands appearing
in the region 330–385 nm have been assigned to charge transfer
transitions arising from excitation of an electron from the metal t2g
level to an unfilled molecular orbital derived form the ␲* level of
the ligands [33]. This assignment is in conformity with the assign-
ments made for similar other ruthenium(II) octahedral complexes
[34]. The broad band observed around 442–476 nm in the com-
plexes may be assigned to charge transfer from the iron to either
the non-bonding or anti-bonding orbitals of the cyclopentadienyl
ring [35].
C
51H46N3OAs2SClFeRu: C, 56.14; H, 4.25; N, 3.85; S, 2.94; Found:
C, 56.28; H, 4.37; N, 3.98; S, 3.18.
2.3.2. Procedure for antibacterial activity studies
Antibacterial activity of the ligands and ruthenium(II) com-
plexes have been carried out against the pathogenic bacteria
Escherichia coli, Vibrio cholerae and Pseudomonas aeruginosa species
[29]. The test organisms were grown on nutrient agar medium in
Petri plates. The complexes to be tested were dissolved in CHCl3
and soaked in filter paper disc of 5 mm diameter and 1 mm thick-
ness. The concentrations used in this study were 0.25–2%. The discs
were placed on the previously seeded plates and incubated at 37 ◦C
for 24 h. The diameter (mm) of the inhibition zone around each disc
was measured after 24 h. Streptomycin was used as standard.
3.3. NMR spectra
1H NMR spectra of some of the complexes have been recorded
to confirm the presence of the coordinated ferrocenylthiosemicar-
bazone ligands. In all the complexes, a broad multiplet observed in
the region 6.5–8.1 ppm is due to the aromatic protons of the phenyl
groups in triphenylphosphine / triphenylarsine and thiosemicar-
bazone ligand [29]. The sharp singlets/multiplets observed around
4.1–4.4 ppm and 1.58–2.2 ppm was assigned to the protons of fer-
rocenyl cyclopentadienyl ring and methyl groups, respectively [36]
(Fig. 2). A broad multiplet appeared around 3.1–3.5 ppm for the
complexes 7 and 11 is due to the protons of piperidine. In the
spectra of the complexes 5, 6, 7, 8 and 11, a singlet is observed
at 11.6–11.8 ppm due to the –NH– proton of ligand [37]. There is
an another multiplet at 2.4 ppm was observed for terminal CH3
group of the coordinated ligand [31]. The complexes 1 and 2 showed
a sharp singlet at 5.4 ppm due to –NH2– protons [21]. A repre-
sentative 13C NMR spectrum of the complex 5 was recorded and
it contains four signals corresponding to the aromatic protons
at 134.4, 129.7, 128.4, and 127.6 ppm of triphenylphosphine and
phenyl group of the ligand (Fig. 3). A carbonyl carbon signal appears
at 207 ppm and the signals corresponding to cyclo pentadienyl car-
bons also found at 96 ppm. In addition, a signal corresponding to
methyl group of the ligand was found at 30.9 ppm. In order to
confirm the presence of triphenylphosphine group and determine
the geometry of the ruthenium(II) complexes, a representative
31P NMR spectra were recorded for complexes 1 and 5. A singlet
3. Results and discussion
The new ruthenium(II) complexes are stable to air, light stable
and soluble in organic solvents such as benzene, CHCl3, CH2Cl2,
DMF and DMSO. The elemental analyses obtained for the com-
plexes are in good agreement with the proposed molecular formula.
In all the reactions, it has been observed that the ferrocenylth-
iosemicarbazones behaved as monofunctional bidentate ligand by
substituting one of the triphenylphosphines / triphenylarsines and
a hydride ion from the starting complexes (Scheme 1). One inter-
esting aspect is that the heterocyclic nitrogen base (pyridine or
piperidine) remains intact without being eliminated in the com-
plexes. The reason for the non-replacement of coordinated bases
is due to the fact that the Ru–P or Ru–As bond is more labile than
Ru–N bond due to the better ␴-donating ability of nitrogen atom
[30].
3.1. IR spectra
The IR spectra of the complexes have been compared with that of
the ligands in order to fix the mode of coordination. The free ligands
showed a very strong absorption around 1651–1654 cm−1 charac-
teristic of the azomethine (>C N) group. In all the complexes, the
band due to azomethine was observed at a lower region around

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R. Prabhakaran et al. / Spectrochimica Acta Part A 78 (2011) 844–853
HN
R
S
B
R
HN
CO
Cl
S
HN
Ru
N
N
N
EPh3
Benzene, 6h
[RuHCl(CO)(B)(EPh3)2]
+
Fe
Fe
E = P or As
B= PPh3 (or) AsPh3 (or) py (or) pip
R = H (or) C6H5 (or) CH3
Scheme 1. Preparation of new hetero-bimetallic binuclear complexes.
observed at 28.6 ppm and 36.25 ppm suggested the presence of two
magnetically equivalent triphenylphosphine groups trans to each
other (Fig. 4) [38].
Oxidation
−
−
−e
−e
Fe(II)–Ru(II)
ꢀ
Fe(III)–Ru(II)
Fe(I)–Ru(II)
ꢀ
(Oxd 2)
1/2
Fe(III)–Ru(III)
E
(Oxd 1)
E
1/2
Reduction
3.4. Electrochemistry
−
−
ꢀ
e
e
Fe(II)–Ru(II)
ꢀ
Fe(I)–Ru(I)
Typical cyclic voltammogram of new hetero-bimetallic
E
(Red 1)
E
(Red 2)
1/2
1/2
mixed valance complexes in dichloromethane showed
a
pair of peaks on both positive and negative potential sides,
corresponding to two successive one electron oxidation
FeII–RuII → FeIII–RuII → FeIII–RuIII and similar one electron reduc-
tion FeII–RuII → FeI–RuII → FeI–RuI processes. The observed
oxidation potential values of FeII–RuII → FeIII–RuIII were found to
be in good agreement with the reported values for Fe(II)–Fe(III) and
Ru(II)–Ru(III) process. The comproportionation constant values for
these complexes indicate a strong electronic coupling between
iron and ruthenium ions (Table 1) and confirm the strong coupling
is through –Cp–C N–N C–S– spacer. We strongly feel that this is
one of the better examples of class-III type of hetero binuclear com-
plex with long range coupling [39]. The comproportionation values
for the reduction processes were higher than that of the oxidation
process in the complexes 4, 5, 8, 10, 11 and 12 which is a strong
evidence for the existence of Fe(I)–Ru(I) oxidation states (Fig. 5).
It reveals that the electronic coupling between Fe(I) and Ru(I) is
as strong as Fe(III)–Ru(III) coupling. The equilibrium constant Kc
for comproportionation reaction in these hetero-bimetallic mixed
valence complexes is defined as:
[Fe(III)–Ru(II)]2
[Fe(II)–Ru(II)][Fe(III)–Ru(III)]
Kc(II–III) =
[Fe(I)–Ru(II)]2
[Fe(II)–Ru(II)][Fe(I)–Ru(I)]
Kc(II–I) =
Kc = exp(F/RT)[E
(1)–E
(2)]
1/2
1/2
3.5. EXAFS studies
EXAFS spectroscopy provides information on the coordination
number, the nature of the scattering atoms surrounding the absorb-
ing atom, the interatomic distance between the absorbing atom
and the backscattering atoms and the Debye–Waller factor which
accounts for the disorders due to the static displacements and
thermal vibrations. In the fitting procedure, for all the cases the
coordination numbers were fixed to known values for different
backscatterers surrounding the excited atom, and the other param-
eters including interatomic distances, Debye–Waller factor and
Fermi energy value were varied by interactions.
3.5.1. Fe K-edge investigation
The experimentally determined and theoretically calculated
EXAFS functions in k space and their Fourier transforms in real
space for the different ruthenium(II) ferrocenylthiosemicarbazone
complexes containing triphenylphosphine/arsine were measured.
In order to study the presence of ferrocenyl unit, the measurement
was done at Fe K-edge are shown in Fig. 6a–c and the corresponding
structural parameters are summarized in Table 2. In the analysis
of the complexes 1, 4 and 5 the shell was determined at about
˚
1.99–2.07 A corresponding to Fe–C backscatterers arising from the
ferrocenyl unit. This value is in good agreement with the reported
value [40]. The EXAFS results indicate the attachment of ten carbon
atoms of both the cyclopentadienyl ligand to Fe centre.
3.5.2. Ru K-edge investigation
EXAFS evaluations were performed at k space were measured
at the Ru K-edge are shown in Fig. 7a–c and the corresponding
structural parameters are summarized in Table 3. In the analysis of
the complexes 1, 4 and 5, the first shell was determined at about
Fig. 5. Cyclic voltammogram of [RuCl(CO)(AsPh3)2(Fcmtsc)] (12).

R. Prabhakaran et al. / Spectrochimica Acta Part A 78 (2011) 844–853
849
Table 1
Electrochemical data of Fe(II)–Ru(II) complexes.
Complex
Reduction (V)
Oxidation (V)
E1/2(1)
E1/2(2)
log Kc
Kc
E1/2(1)
E1/2(2)
Log Kc
Kc
(2)
(4)
(5)
(6)
(8)
(9)
(10)
(11)
(12)
0.347
0.778
0.576
0.984
0.70
0.363
0.337
0.338
0.364
–
–
–
1.092
1.462
1.066
1.460
1.246
.939
1.056
1.241
1.254
0.577
0.568
0.378
0.837
0.462
0.081
0.316
0.585
0.808
8.71
15.12
11.63
10.54
13.26
14.51
12.515
11.09
7.54
5.13 × 108
1.32 × 1015
4.23 × 1011
3.44 × 1010
1.82 × 1013
3.24 × 104
3.3 × 1012
1.25 × 1011
3.49 × 107
−0.449
−0.589
–
−0.212
−0.274
−0.724
−0.772
0.562
20.75
19.7035
–
15.425
10.77
17.95
18.733
15.66
5.6 × 1020
5.1 × 1019
–
2.6 × 1015
6.0 × 1010
2.8 × 1017
5.9 × 1018
4.5 × 1015
Fig. 6. Experimental (solid line) and calculated (dotted line) EXAFS function and Fourier Transform plots for (a) [RuCl(CO)(PPh3)2(Fctsc)] (1), (b) [RuCl(CO)(AsPh3)2(Fctsc)]
(4), and (c) [RuCl(CO)(PPh3)2(Fcptsc)] (5), measured at the Fe K-edge (7112 eV).

850
R. Prabhakaran et al. / Spectrochimica Acta Part A 78 (2011) 844–853
Table 2
EXAFS determined structural parameters at Fe K-edge.
e
Complex
A–Bsa
Nb
rc[Å]
ꢃ
d[Å]
EF [eV]
k-range [Å−1
]
R-factor
1
4
5
Fe–C
Fe–C
Fe–C
10
10
10
2.04 0.02
2.01 0.02
2.07 0.02
0.095 0.009
0.084 0.008
0.092 0.009
7.522
8.943
5.841
3.13–3.04
3.13–3.01
3.06–3.03
31.94
30.76
36.37
a
Absorber (A) – backscatterers (Bs).
Coordination number N.
Interatomic distance r.
Debye–Waller factor ꢃ with its calculated deviation.
Fermi energy EF.
b
c
d
e
Fig. 7. Experimental (solid line) and calculated (dotted line) EXAFS function and Fourier Transform plots for (a) [RuCl(CO)(PPh3)2(Fctsc)] (1), (b) [RuCl(CO)(AsPh3)2(Fctsc)]
(4), and (c) [RuCl(CO)(PPh3)2(Fcptsc)] (5), measured at the Ru K-edge (22117 eV).

R. Prabhakaran et al. / Spectrochimica Acta Part A 78 (2011) 844–853
851
Fig. 8. Experimental (solid line) and calculated (dotted line) EXAFS function and Fourier Transform plots for [RuCl(CO)(AsPh3)2(Fctsc)](4) measured at the As K-edge
(11867 eV).
˚
3.5.3. As K-edge investigation
1.85 A with one carbon backscatterer arising from the coordinated
The EXAFS evaluation at the As K-edge was performed using
the multiple scattering formalism, as there could be consider-
able interference effects due to the neighbouring backscatterers.
The multiple scattering calculations were done considering all
the different pathways surroundings the central arsenic atom.
The maximum order of scattering and the maximum atoms in
one path were set to three and the maximum path length was
set to ten during the calculations. The experimentally deter-
mined and theoretically calculated EXAFS functions in k space
and their Fourier transforms in real space for the different
ruthenium(II)ferrocenylthiosemicarbazone complexes with triph-
enylarsine measured at the As K-edge evaluated using the multiple
scattering formalism are shown in Fig. 8. The EXAFS deter-
mined structural parameters are given in Table 4. In the complex
(4), the k3-weighted EXAFS function was best described by a
CO ligand.
˚
This value is in very good agreement with the value of 1.86 A
reported for ruthenium carbonyl clusters [41]. The second shell
was determined at about 2.25 A, it was fitted with a coordi-
˚
nation number of one consisting of a nitrogen backscatterer in
[RuCl(CO)(PPh3)2(Fctsc)](1) and in the complexes 1, 4 and 5 were
fitted with a coordination number of one consisting of a nitro-
gen backscatterer from the corresponding ligand, in the case of
the [RuCl(CO)(PPh3)2(Fctsc)](1) and [RuCl(CO)(AsPh3)2 (Fctsc)](4).
For the complex [RuCl(CO)(PPh3)2(Fcptsc)](5), it was fitted at about
˚
2.20 A, similar to backscattering behaviour of the near neighbours
(chlorine, sulphur and two phosphorous backscatterers) occurring
at nearly the same distance. Hence, they could not be fitted sepa-
rately in the complexes 1 and 5 and thus were fitted into the single
shell with combined coordination number with sulphur amplitude
and phase functions. Whereas in the complex 4, the second shell
˚
three-shell model. The first shell at about 1.95 A was fitted
with the carbon backscatterers originating from the proximal
carbon atoms of the coordinating triphenylarsine group. The
˚
was determined at about 2.44 A consisting of one sulphur and one
chlorine backscatterers. This is because of the similar backscat-
tering behaviour of the near neighbour (sulphur and chlorine)
occurring at nearly the same distance and hence they could not be
fitted separately, thus were fitted as one shell with sulphur ampli-
tude and phase functions. In addition, two arsenic backscatterers
˚
˚
reported arsenic–carbon distances ranges from 1.90 A to 1.97 A.
The second shell consisting of a single ruthenium backscatterer
˚
was determined at about 2.45 A and the third shell comprising
of six carbon backscatterers stemming from the second near-
neighbour carbon atoms of the phenyl ring was determined
[45].
On the basis of IR, electronic, NMR spectral data and EXAFS,
an octahedral geometry has been confirmed for the new hetero-
bimetallic complexes (Fig. 9).
˚
were determined at about 2.45 A distance. The determined Ru–As
distance was in good agreement with those reported for similar
ruthenium complexes [42–44]. The determined Ru–N, Ru–C and
Ru–P/Cl/S distances are in good agreement with the reported com-
plexes.
Table 3
EXAFS determined structural parameters at the Ru K-edge.
A–Bsa
Nb
rc [Å]
ꢃd [Å]
EF [eV]
k-range [Å−1
]
R-factor
e
Complex
Ru–C
Ru–N
Ru–S/P/Cl
Ru–C
Ru–N
Ru–S/Cl
Ru – As
Ru – C
Ru – N
Ru – S/P/Cl
1
1
4
1
1
2
2
1
1
4
1.85 0.02
2.25 0.02
2.41 0.02
1.84 0.02
2.24 0.02
2.39 0.02
2.75 0.02
1.85 0.02
2.20 0.02
2.42 0.02
0.055 0.006
0.063 0.009
0.102 0.015
0.050 0.005
0.105 0.015
0.055 0.008
0.100 0.015
0.050 0.005
0.112 0.017
0.095 0.014
1
4
2.692
2.94–13.07
34.73
2.966
1.755
3.11–13.04
2.96–13.02
21.75
33.61
5
a
Absorber (A) – backscatterers (Bs).
Coordination number N.
Interatomic distance r.
Debye–Waller factor ꢃ with its calculated deviation.
Fermi energy EF.
b
c
d
e

852
R. Prabhakaran et al. / Spectrochimica Acta Part A 78 (2011) 844–853
Table 4
EXAFS determined structural parameters at the As K-edge.
e
Complex
A–Bsa
Nb
rc [Å]
ꢃd [Å]
EF [eV]
k-range [Å−1
]
R-factor
4
As–C
As–Ru
As–C
3
1
6
1.95 0.02
2.45 0.02
2.92 0.03
0.050 0.005
0.071 0.010
0.084 0.012
−3.637
2.92–15.04
41.58
a
Absorber (A) – backscatterers (Bs).
Coordination number N.
Interatomic distance r.
Debye–Waller factor ꢃ with its calculated deviation.
Fermi energy EF.
b
c
d
e
Table 5
Antibacterial activity of ruthenium(II) Schiff base complexes.
Compound
Diameters inhibition zone (mm)
E. coli
Vibrio cholerae
P. aeruginosa
0.25
0.5
1
2
0.25
0.5
1
2
0.25
0.5
1
2
HFctsc
HFcptsc
HFcmtsc
(2)
(3)
(4)
(5)
(6)
(7)
(8)
5
4
5
–
10
–
12
–
12
11
–
10
11
7
6
5
–
12
–
14
15
14
13
–
8
8
7
–
12
–
15
16
15
15
–
–
9
8
–
14
–
17
18
17
16
–
4
5
–
6
6
–
8
7
6
13
15
12
16
–
13
14
–
–
13
9
9
8
–
6
7
11
12
–
10
–
5
8
7
7
–
8
9
9
9
13
–
13
16
–
17
–
15
14
14
12
11
11
13
11
–
11
10
–
13
12
12
15
13
12
13
11
–
14
16
13
–
18
15
16
–
11
13
10
12
13
–
12
11
12
11
12
14
12
13
14
15
14
12
13
–
–
11
11
11
10
(9)
(10)
(12)
11
11
–
12
–
13
–
14
10
12
Streptomycin
18
20
22
25
14
17
20
22
18
21
23
24
3.6. Antibacterial activity
activity than the free ligands, they could not reach the effectiveness
of standard drug Streptomycin.
Antibacterial activity of the ligands and the complexes has been
carried out against E. coli, V. cholerae and P. aeruginosa, the results
were given in Table 5. From the data we observed that the metal
chelates exhibited higher activity than the respective free ligands.
Such increased activity of the metal chelates can be explained on
the basisof Overtone’s concept and chelationtheory [46]. According
to Overtone’s concept of cell permeability, the lipid membrane that
surrounds the cell favours the passage of only lipid soluble materi-
als due to which liposolubility is an important factor that controls
antimicrobial activity. On chelation, the polarity of the metal ion is
reduced to a greater extent due to the overlap of the ligand, orbital
and partial sharing of the positive charge of the metal ion with
donor groups. Further, it increases the delocalisation of ␲-electrons
over the whole chelate ring and enhances the lipophilicity of the
complex. This increased lipophilicity enhances the penetration of
the complexes into lipid membranes and blocking of metal bind-
ing sites on the enzymes of the microorganism. Among the various
compounds tested, only the complex 5 is very active against all the
bacteria. Complexes 6 and 7 show higher potential against the bac-
teria E. coli while the complexes 3, 6 and 8 exhibited better activity
against of V. cholerae. Eventhough the complexes possess higher
4. Conclusion
New hetero-binuclear complexes have been synthesized and
characterized by the analytical and spectral methods. Though num-
ber of attempt made to get single crystals for X-ray diffraction
studies were unsuccessful and the structure of the complexes has
been confirmed by EXAFS. The electrochemical properties of the
complexes have been examined and the higher comproportiona-
tion constant values suggesting that the current system can be a
good molecular wire with very strong coupling between the metal
centers and may be the first hetero metallic system exhibiting
such a behaviour. The complexes also exhibited significant activ-
ity against the pathogenic bacteria such as E. coli, V. cholerae and P.
aeruginosa. The complex 5 exhibited higher activity over all the bac-
teria which were taken. All the complexes exhibited higher activity
than the free ligands.
Acknowledgement
Financial support received from Department of Science and
Technology by SERC, New Delhi, India is gratefully acknowledged.
B
R
HN
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