Synthesis, EPR, electrochemistry and EXAFS studies of ruthenium(III) complexes with a symmetrical tetradentate N2O2 Schiff base

Article abstract of DOI:10.1016/j.ica.2005.11.028

A series of new hexa-coordinated ruthenium(III) complexes of the type [RuX(Nap-o-phd)(EPh₃)] (where, H₂-Nap-o-phd = N,N′-bis(2-hydroxy-1-naphthaldehyde) o-phenylene diamine; X = Cl or Br; E = P or As) have been prepared by reacting [RuX₃(EPh₃) ₃] and [RuBr₃(PPh₃)₂(MeOH)] (where X = Cl or Br; E = P or As) with tetradentate Schiff base ligand (H ₂-Nap-o-phd) in 1:1 molar ratio. The complexes have been characterized by elemental analyses, infra red, electronic, electron paramagnetic resonance spectroscopy and cyclic voltammetry. The coordination geometry and structure of the complexes have been investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy and an octahedral structure has been proposed.

Full text of DOI:10.1016/j.ica.2005.11.028

Inorganica Chimica Acta 359 (2006) 1114–1120
www.elsevier.com/locate/ica
Synthesis, EPR, electrochemistry and EXAFS studies of
ruthenium(III) complexes with a symmetrical tetradentate
N2O2 Schiff base
a
b
a
Rathinasabapathi Prabhakaran , Venkata Krishnan , Arumugam Geetha ,
b
a,
*
Helmut Bertagnolli , Karuppannan Natarajan
a
Department of Chemistry, Bharathiar University, Coimbatore 641 046, Tamil Nadu, India
Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
b
Received 7 July 2005; received in revised form 3 November 2005; accepted 23 November 2005
Available online 4 January 2006
Abstract
A series of new hexa-coordinated ruthenium(III) complexes of the type [RuX(Nap-o-phd)(EPh3)] (where, H2-Nap-o-phd = N,N0-
bis(2-hydroxy-1-naphthaldehyde) o-phenylene diamine; X = Cl or Br; E = P or As) have been prepared by reacting [RuX3(EPh3)3]
and [RuBr3(PPh3)2(MeOH)] (where X = Cl or Br; E = P or As) with tetradentate Schiff base ligand (H2-Nap-o-phd) in 1:1 molar ratio.
The complexes have been characterized by elemental analyses, infra red, electronic, electron paramagnetic resonance spectroscopy and
cyclic voltammetry. The coordination geometry and structure of the complexes have been investigated by extended X-ray absorption fine
structure (EXAFS) spectroscopy and an octahedral structure has been proposed.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Ruthenium(III) complexes; EPR; EXAFS; Cyclic voltammetry
1. Introduction
agents [16–21]. The planarity of the Schiff base ligand pro-
vides a means of creating a large vacant site, where coordi-
nation of a transition metal could be carried out [22–24].
Transition metal complexes of ruthenium have proved
to be useful catalysts in many reactions, such as oxidation,
hydrogenation, carbonylation and hydroformylation, by
virtue of the accessibility of ruthenium in different oxida-
tion states and ease of coordination with different ligands
[25–27]. In connection with our ongoing interest in this
field of research we have already investigated several ruthe-
nium(II) and ruthenium(III) complexes [28–32].
In view of the diverse chemistry possessed by the Schiff
base ligands and transition metal like ruthenium, we under-
took the synthesis of a series of novel N2O2 chromophore
containing ruthenium(III) complexes. These complexes
are structurally characterized by extended X-ray absorp-
tion fine structure (EXAFS), spectral techniques and elec-
trochemistry. The structure of the Schiff base ligand used
in the present work is shown in Fig. 1.
Organometallic complexes containing Schiff bases have
played an important role in coordination chemistry of tran-
sition metals, mainly due to their stability, ease of prepara-
tion, structural variability and variety of applications [1].
Ligands containing two bidentate components separated
by a spacer group have been extensively used in self assem-
bly recently [2–5]. Schiff base ligands have been extensively
investigated with regard to their numerous applications in
organic synthesis as well as in pharmacology. Indeed, such
ligands are of interest not only in the field of optical sensors
[6] and liquid crystals [7] but also as transition metal chelat-
ing agents for applications in nuclear medicine [8–13] and
asymmetric catalysis [14,15]. Several N2S2 and N2O2
ligands have already been synthesized and used as chelating
*
Corresponding author. Tel.: +91 422 242 4655; fax: +91 422 242 2387.
E-mail address: k_natraj6@yahoo.com (K. Natarajan).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.11.028

R. Prabhakaran et al. / Inorganica Chimica Acta 359 (2006) 1114–1120
1115
Found: C, 64.84; H, 4.18; N, 3.76%. IR: m (C@N) 1602 s
cmꢀ1, m (C–O) m 1357 cmꢀ1. kmax 260, 320, 371, 465 nm.
M.p. 212 ꢁC.
OH
HO
HC
N
N CH
2.3. Measurements
Elemental analyses of the complexes were performed
with Vario EL III CHNS at Department of Chemistry,
Bharathiar University, Coimbatore, India. IR spectra of
the ligand and complexes have been recorded in KBr pel-
lets with a Shimadzu/Nicolet instrument in the 400–
4000 cmꢀ1 range. The electronic spectra of the complexes
have been recorded in methanol using a Systronics 119
spectrophotometer in the 800–200 nm range. Electron
paramagnetic resonance (EPR) spectra of the powder sam-
ples were recorded with a Jeol Tel-100 instrument at X-
band frequencies at room and liquid nitrogen temperatures
(77 K) using 2,20-diphenyl-1-picrylhydrazine hydrate
(DPPH) as internal standard. The cyclic voltammetric
studies were carried out on EG&G Princeton Applied
Research Electrochemical Analyzer in dichloromethane
using a glassy-carbon electrode and all potentials were ref-
erenced to standard Ag/AgCl electrode.
The transmission mode EXAFS measurements were
performed (Ru K-edge at 22117 eV, As K-edge at
11867 eV and Br K-edge at 13474 eV) at the beamline
X1.1 of the Hamburger Synchrotron Radiation Labora-
tory (HASYLAB) at DESY, Hamburg, and at the XAS
beamline at the Angstroemquelle Karlsruhe (ANKA) at
FZK, Karlsruhe, Germany. The complexes were measured
with Si(311) double crystal monochromator at the Ru
Fig. 1. Structure of the Schiff base ligand.
2. Experimental
2.1. Materials
All the reagents used were of Analar grade. Solvents
were purified and dried according to the standard
procedure [33]. The starting complexes [RuCl3(PPh3)3]
[34], [RuCl3(Ash3)3] [35], [RuBr3(AsPh3)3] [36] and
[RuBr3(PPh3)3(MeOH)] [37] and ligand [38–40] were pre-
pared and characterized according to the literature
procedures.
2.2. Preparation of ruthenium(III) complexes
All the ruthenium(III) complexes were prepared by the
following general procedure. To a benzene solution
(20 cm3) of [RuX3(EPh3)3] (E = P or As; X = Cl or Br)
or [RuBr3(PPh3)2(MeOH)] (0.1 mmol, 0.89–1.259 g) the
appropriate Schiff base (0.1 mmol, 0.0416 g) was added in
1:1 molar ratio. The mixture was refluxed for 5 h and the
solution was concentrated to ca. 3 cm3. The product was
separated by the addition of small quantity of petroleum
ether (60–80 ꢁC) and recrystallised from CH2Cl2/petroleum
ether (60–80 ꢁC). The individual synthesis is given below.
[RuCl(PPh3)(Nap-o-phd)] (1) was prepared from
[RuCl3(PPh3)3] (0.0994 g; 0.1 mmol) and H2-Nap-o-phd
(0.0416 g; 0.1 mmol). Yield (80%). Anal. Calc. for
[RuCl(PPh3)(Nap-o-phd)]: C, 67.94; H, 4.09; N, 3.44.
Found: C, 68.12; H, 4.87; N, 3.08%. IR: m (C@N)
1604 s cmꢀ1, m (C–O) m 1357 cmꢀ1. kmax 260, 320, 371,
465 nm. M.p. 283 ꢁC.
[RuCl(AsPh3)(Nap-o-phd)] (2) was prepared from
[RuCl3(AsPh3)3] (0.1126 g; 0.1 mmol) and H2-Nap-o-phd
(0.0416 g; 0.1 mmol). Yield (85%). Anal. Calc. for
[RuCl(AsPh3)(Nap-o-phd)]: C, 64.45; H, 3.88; N, 3.73.
Found: C, 64.62; H, 4.48; N, 3.84%. IR: m (C@N) 1604 s
cmꢀ1, m (C–O) m 1355 cmꢀ1. kmax 225, 272, 302, 478 nm.
M.p. 224 ꢁC.
Table 1
EPR spectral data of Ru(III) Schiff base complexes
Complex
Temperature (K)
gx
gy
gz
Ægæ*
1
1
2
3
4
77
298
298
298
298
2.28
2.87
2.46
2.56
2.37
2.04
2.38
2.18
2.28
2.18
1.88
2.10
2.11
2.14
2.08
2.073
2.47
2.28
2.33
2.21
1=2
hgiꢁ ¼ ½1=3gx2 þ 1=3gy2 þ 1=3g2z ꢂ
.
[RuBr(AsPh3)(Nap-o-phd)] (3) was prepared from
[RuBr3(AsPh3)3] (0.1259 g; 0.1 mmol) and H2-Nap-o-phd
(0.0416 g; 0.1 mmol). Yield (73%). Anal. Calc. for
[RuBr(AsPh3)(Nap-o-phd)]: C, 61.28; H, 3.69; N, 3.10.
Found: C, 60.94; H, 3.42; N, 3.04%. IR: m (C@N) 1604 s
cmꢀ1, m (C–O) m 1353 cmꢀ1. kmax 281, 337, 478 nm. M.p.
197 ꢁC.
[RuBr(PPh3)(Nap-o-phd)] (4) was prepared from
[RuBr3(PPh3)2(MeOH)] (0.0897 g; 0.1 mmol) and H2-
Nap-o-phd (0.0416 g; 0.1 mmol). Yield (75%). Anal. Calc.
for [RuBr(PPh3)(Nap-o-phd)]: C, 64.41; H, 3.87; N, 3.26.
Fig. 2. EPR spectrum of 1.

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R. Prabhakaran et al. / Inorganica Chimica Acta 359 (2006) 1114–1120
dent and transmitted intensities. Energy calibration was
monitored by measuring the absorption through a refer-
ence simultaneously with the absorption through the com-
plexes, by means of a third ion chamber. For Ru K-edge
measurements, ruthenium metal foil was used as the refer-
ence. A 20-lm thick gold metal foil having LIII-edge at
11919 eV was used as reference for As K-edge measure-
ments and the same foil having LII-edge at 13734 eV was
used as reference for Br K-edge measurements. The com-
plexes in solid state were embedded in a polyethylene
matrix and pressed into pellet. The concentration was
adjusted to yield an extinction of 1.5. The data were ana-
lysed with a program package especially developed for
the requirements of amorphous samples [41]. The program
AUTOBK [42] was used for the removal of background
and the program EXCURV98 [43] was used for the evalu-
ation of EXAFS function. Curved wave theory using XAL-
PHA phase and amplitude functions was used for the data
analysis in k space and the resulting EXAFS function was
weighted with k3. The mean free path of the scattered elec-
trons was calculated from the imaginary part of the poten-
tial (VPI set to ꢀ4.00), the amplitude reduction factor
AFAC was fixed at 0.8 and Fermi energy shift EF was
introduced to give a best fit to the data.
Fig. 3. Cyclic voltammogram of 2.
Table 2
Cyclic voltammetric dataa of Ru(III) Schiff base complexes
Complex
Epc (V)
Epa (V)
Ef (V)
DEp (mV)
1
2
3
4
a
ꢀ0.80
ꢀ0.82
ꢀ0.80
ꢀ0.86
ꢀ1.05
ꢀ1.08
ꢀ1.00
ꢀ1.08
0.925
0.95
0.90
0.97
250
260
200
220
Supporting electrolyte: [NBu4]BF4 (0.1 M); concentration of the
complex: 0.001 M; scan rate: 100 mV sꢀ1. All the potentials are referenced
to Ag/AgCl; Ef = 0.5 (Epa + Epc), where Epa and Epc are anodic and
cathodic potentials, respectively.
3. Results and discussion
K-edge and with Si(111) double crystal monochromator at
the As and Br K-edges. The measurements were carried out
at ambient conditions and, ion chambers filled with inert
gases (nitrogen and argon) were used to measure the inci-
3.1. EPR studies
The solid state EPR spectra of powdered samples were
recorded at room temperature and the ÔgÕ values are listed
Fig. 4. Experimental (solid line) and calculated (dotted line) EXAFS functions (a) and their corresponding Fourier transform plots (b) for the different
ruthenium(III) Schiff base complexes with triphenylphosphine/arsine measured at the Ru K-edge.

R. Prabhakaran et al. / Inorganica Chimica Acta 359 (2006) 1114–1120
1117
in Table 1. All the complexes showed three lines with three
different ÔgÕ values indicating magnetic anisotropy in these
systems. The average ÔgÕ value is in the range 2.21–2.47
and these values agree very well with the values obtained
for other similar ruthenium(III) complexes [44,45]. The
EPR spectrum recorded for [RuCl(PPh3)(Nap-o-phd)] at
liquid nitrogen temperature (77 K) showed very little vari-
ation from that observed at room temperature (Fig. 2) indi-
cating rhombic distortion in these complexes.
in the ꢀ0.8 to ꢀ1.08 V range (Fig. 3). The voltammetric
data are given in Table 2. As the ligand used in this work
is not reversibly reduced within the potential limit (0.00
to ꢀ2.00 V), we believe that the reduction processes
observed for these complexes are metal-centered only.
The peak-to-peak separation (DEp value) ranging from
200 to 260 mV reveals that the reduction process is quasi-
reversible [46]. It has been observed that there is no varia-
tion in the redox potential of the complexes due to the
replacement of triphenylphosphine by triphenylarsine.
Similar behaviour has been reported for b-diketonato
ruthenium(III) complexes [30] and complexes with N2S2
chromophore [28].
3.2. Electrochemical studies
Cyclic voltammetric studies were performed for all the
complexes at a glassy-carbon working electrode at a scan
rate of 100 mV sꢀ1. The supporting electrolyte used was
0.1 M [NBu4]BF4 in dichloromethane solution. The con-
centration of the complex was 0.001 M. The solution was
degassed with a continuous flow of N2 gas before scanning.
All the complexes showed only a reversible reduction wave
3.3. EXAFS studies
In spite of several attempts, single crystals suitable for
X-ray structure determination were not obtained. Hence,
the local structure and the coordination geometry of the
Table 3
EXAFS determined structural parameters at Ru, As and Br K-edges
c
e
ꢀ1
A–Bsa
Nb
r (A)
rd (A)
EF (eV)
k-range (A
)
R-factor
˚
˚
˚
Complex
1
Ru–N/O
Ru–Cl/P
Ru–C
4
2
2
2.01 0.02
2.36 0.03
2.92 0.03
0.050 0.005
0.077 0.009
0.050 0.006
6.514
3.59–16.08
25.00
2
Ru–N/O
Ru–Cl
Ru–As
Ru–C
4
1
1
2
2.01 0.02
2.35 0.03
2.48 0.03
2.82 0.03
0.077 0.008
0.050 0.006
0.063 0.008
0.081 0.010
8.064
3.46–16.05
26.57
3
4
Ru–N/O
Ru–As/Br
Ru–C
4
2
2
2.01 0.02
2.50 0.03
2.90 0.03
0.074 0.007
0.063 0.007
0.050 0.007
8.619
5.586
3.59–16.00
3.44–16.03
24.67
28.85
Ru–N/O
Ru–P
Ru–Br
Ru–C
4
1
1
2
2.00 0.02
2.34 0.03
2.52 0.03
2.91 0.03
0.059 0.006
0.067 0.008
0.071 0.008
0.050 0.008
2f
3f
2g
3g
3
As–C
As–Ru
As–C
3
1
6
1.93 0.02
2.49 0.03
2.90 0.03
0.055 0.006
0.071 0.008
0.077 0.009
ꢀ4.516
ꢀ7.526
ꢀ1.668
ꢀ5.238
3.05–16.03
2.82–16.00
3.15–16.05
3.00–16.00
47.62
40.80
34.05
29.52
As–C
As–Ru
As–C
3
1
6
1.94 0.02
2.49 0.03
2.91 0.03
0.055 0.006
0.077 0.008
0.077 0.009
As–C
As–Ru
As–C
3
1
6
1.92 0.02
2.48 0.03
2.91 0.03
0.055 0.006
0.071 0.008
0.077 0.009
As–C
As–Ru
As–C
3
1
6
1.93 0.02
2.48 0.03
2.91 0.03
0.055 0.006
0.077 0.008
0.077 0.009
Br–Ru
1
1
2.52 0.03
2.54 0.03
0.074 0.008
0.087 0.009
ꢀ0.665
ꢀ2.375
2.93–14.04
2.93–13.53
29.75
28.23
4
Br–Ru
a
Absorber (A)–backscatterers (Bs).
Coordination number N.
Interatomic distance r.
Debye-Waller factor r with its calculated deviation.
Fermi energy EF.
b
c
d
e
f
Evaluated using multiple scattering formalism.
Evaluated using Fourier filter analysis (1.0–3.0 A range).
g
˚

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R. Prabhakaran et al. / Inorganica Chimica Acta 359 (2006) 1114–1120
complexes were determined by EXAFS spectroscopy,
which 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 [47]. For all the com-
plexes in the fitting procedure, the coordination numbers
were fixed to known values for different backscatterers sur-
rounding the excited atom, and the other parameters
including interatomic distances, Debye–Waller factor and
Fermi energy value were varied by iterations.
number of two with chlorine amplitude- and phase-func-
tions. The Ru–P and Ru–Cl distances found for the new
complexes match very well with those found in cis-
[Ru(dppm)2(MeCN)2]-(BF4)2 (Ru–P distance ranges from
˚
˚
2.34 A to 2.37 A) [49] and mer-[RuCl3(AsMe2Ph)3] (Ru–
˚
˚
Cl distance ranges from 2.35 A to 2.39 A) [50]. In the case
of complexes 2 and 4, a well-defined second shell with
either chlorine or phosphorus backscatterer with a coordi-
˚
nation number of one could be fitted at about 2.35 A dis-
tance. Further, in complex 2,
a
single arsenic
˚
backscatterer was determined at about 2.48 A distance.
Due to the similar backscattering behaviour of arsenic
and bromine backscatterers, they were fitted together with
a combined coordination number of two, with arsenic
amplitude- and phase-functions at a distance of about
3.3.1. Ru K-edge
The experimentally determined and theoretically calcu-
lated EXAFS functions in k space and their Fourier trans-
forms in real space for the different ruthenium(III) Schiff
base complexes with triphenylphosphine/arsine measured
at the Ru K-edge are shown in Fig. 4 and the correspond-
ing structural parameters are summarized in Table 3. In the
analysis of the complexes 1–4, the first shell was found at
˚
2.50 A in complex 3, whereas in the case of complex 4,
the single bromine backscatterer was determined at about
˚
2.52 A distance. The determined ruthenium–arsenic and
ruthenium–bromine distances were in good agreement with
those reported for mer-[RuBr3(AsMe2Ph)3] [50]. Further,
in all the complexes an additional shell consisting of two
carbon backscatterers, possibly originating from the prox-
imal carbon atoms of the ligand, could be determined at
˚
about 2.01 A consisting of two nitrogen and two oxygen
backscatterers from the coordinating ligand. Due to the
similar backscattering behaviour of the near neighbours,
i.e., nitrogen and oxygen, occurring nearly at the same dis-
tance, they could not be fitted separately and thus were fit-
ted as one shell with a coordination number four, with
nitrogen amplitude- and phase-functions. The determined
ruthenium–nitrogen and ruthenium–oxygen distances are
in agreement with those found for similar organo-ruthe-
nium complexes [48]. In complex 1, the second shell was
˚
about 2.90 A distance (slightly shortened in the case of
complex 2). The obtained EXAFS results indicate sixfold
coordination geometry around the ruthenium atom.
3.3.2. As K-edge
The EXAFS evaluation at the As K-edge was performed
using the multiple scattering formalism, as there could be
considerable interference effects due to the neighbouring
backscatterers. The multiple scattering calculations were
done considering all the different pathways surrounding
the central arsenic atom. The maximum order of scattering
˚
determined at about 2.36 A having one phosphorus and
one chlorine backscatterer. For the same reason stated ear-
lier, a single shell was fitted with a combined coordination
Fig. 5. Experimental (solid line) and calculated (dotted line) EXAFS functions (a) and their corresponding Fourier transform plots (b) for the different
ruthenium(III) Schiff base complexes with triphenylarsine measured at the As K-edge evaluated using multiple scattering formalism.

R. Prabhakaran et al. / Inorganica Chimica Acta 359 (2006) 1114–1120
1119
Fig. 6. Experimental (solid line) and calculated (dotted line) EXAFS functions (a) and their corresponding Fourier transform plots (b) for the different
ruthenium(III) Schiff base complexes with triphenylphosphine/arsine measured at the Br K-edge.
and the maximum atoms in one path were set to three and
the maximum path length was set to ten during the calcu-
lations. The experimentally determined and theoretically
calculated EXAFS functions in k space and their Fourier
transforms in real space for the different ruthenium(III)
Schiff base complexes with triphenylarsine measured at
the As K-edge evaluated using the multiple scattering for-
malism are shown in Fig. 5. The EXAFS determined struc-
tural parameters are given in Table 3. In both the
complexes 2 and 3, the k3-weighted EXAFS function could
be best described by a three-shell model. The first shell at
about 29% in the case of complex 2 and about 28% in
the case of complex 3.
3.3.3. Br K-edge
The experimentally determined and theoretically calcu-
lated EXAFS functions in k space and their Fourier trans-
forms in real space for the different ruthenium(III) Schiff
base complexes with triphenylphosphine/arsine measured
at the Br K-edge are shown in Fig. 6 and the EXAFS deter-
mined structural parameters are summarized in Table 3.
The Br K-edge EXAFS spectra of the complexes 3 and 4
were almost similar to each other. Both of them show a sin-
˚
about 1.93 A was fitted with three carbon backscatterers
˚
originating from the three proximal carbon atoms of the
coordinating triphenyl group. The reported arsenic–carbon
gle huge peak in Fourier transform plot at about 2.52 A
˚
(for 3) or 2.54 A (for 4), which could be unequivocally fit-
˚
˚
distances range from 1.90 A to 1.97 A in mer-[RuCl3(As-
Me2Ph)3] and mer-[RuBr3(AsMe2Ph)3] [50]. The second
shell consisting of a single ruthenium backscatterer was
ted with a single ruthenium backscatterer. The obtained
bromine–ruthenium distances were in agreement with those
in similar bromo-ruthenium complexes [50]. Further, the
values were also in accordance with distances determined
from the Ru K-edge measurements.
˚
determined at about 2.49 A and the third shell comprising
of six carbon backscatterers stemming from the second
near-neighbour carbon atoms of the phenyl ring was deter-
˚
mined at about 2.91 A distance. In both the complexes 2
EPh
3 O
O
and 3, the arsenic–ruthenium distances determined at the
As K-edge were in good agreement with those determined
at the Ru K-edge. In both the cases, the fitting of the
EXAFS function to the experimental spectra resulted in
very high R-factor values. This could be attributed to the
ambiguous coordination geometry around the arsenic
atom and apart from the first three shells, the other shells
could not be fitted unequivocally. Further, to confirm this
supposition, Fourier filter analysis was performed in the
Ru
X
HC N
N
CH
E = P or As; X = Cl, Br
(1) =X = Cl, E = P
(2) =X = Cl, E = As
(3) =X = Br, E = As
(4) =X = Br, E = P
˚
range 1.0–3.0 A, in order that the contributions from only
the first three shells are considered. The results of the Fou-
rier filter analysis are summarised in Table 3 and it could be
noted that the R-factor value improved considerably by
Fig. 7. General structure of ruthenium(III) complexes.

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R. Prabhakaran et al. / Inorganica Chimica Acta 359 (2006) 1114–1120
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The EXAFS investigations allowed us to determine only
Dalton Trans. (1990) 2497.
the local structure, however the exact geometry of the coor-
dinated ligands could not be determined. Based on the ana-
lytical, spectral, cyclic voltammetry and EXAFS studies,
the following octahedral structure has been proposed for
the new ruthenium(III) complexes (Fig. 7).
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