K[RuSalphenCl2], K[RuSalenCl2], and Electroconducting Polymers: Synthesis and Electrochemical Properties

Article abstract of DOI:10.1023/A:1024094413322

K[RuSalphenCl₂], K[RuSalenCl₂], and electroconducting polymers on their basis are synthesized and their electrochemical properties are studied in solutions of two supporting electrolytes tetrabutylammonium perchlorate (TBAP) and NaClO₄. A comparative analysis of electroreduction and electropolymerization processes in these two electrolytes is performed. The cyclic voltammograms (CV) obtained for K[RuSalphenCl₂] are similar to those previously measured for K[RuSalenCl₂]. The polymers are synthesized for the first time that exhibit the reversible charge transport and the conditions of their formation are considered. The kinetics of formation of the redox-polymers is studied. The dependence of the polymer film thickness on the reduction potential and concentration of the starting Ru(III) complex is established.

Full text of DOI:10.1023/A:1024094413322

Russian Journal of Coordination Chemistry, Vol. 29, No. 6, 2003, pp. 435–440. Translated from Koordinatsionnaya Khimiya, Vol. 29, No. 6, 2003, pp. 465–470.
Original Russian Text Copyright © 2003 by Popova, Shagisultanova.
K[RuSalphenCl2], K[RuSalenCl2], and Electroconducting
Polymers: Synthesis and Electrochemical Properties
E. O. Popova and G. A. Shagisultanova
Gertsen Russian State Pedagogical University, St. Petersburg, Russia
Received June 21, 2001; in final form, March 12, 2002
Abstract—K[RuSalphenCl2], K[RuSalenCl2], and electroconducting polymers on their basis are synthesized
and their electrochemical properties are studied in solutions of two supporting electrolytes tetrabutylammonium
perchlorate (TBAP) and NaClO4. A comparative analysis of electroreduction and electropolymerization pro-
cesses in these two electrolytes is performed. The cyclic voltammograms (CV) obtained for K[RuSalphenCl2]
are similar to those previously measured for K[RuSalenCl2]. The polymers are synthesized for the first time that
exhibit the reversible charge transport and the conditions of their formation are considered. The kinetics of for-
mation of the redox-polymers is studied. The dependence of the polymer film thickness on the reduction poten-
tial and concentration of the starting Ru(III) complex is established.
The Pd, Pt, Cu, and Ni complexes with the Schiff the acetonitrile solutions made it possible to conclude
bases, such as bis(salicylidene)ethylenediamine that the Cl– ions in these complexes are also replaced by
(H2Salen) and bis(salicylidene)-Ó-phenylenediamine the solvent molecules to give [RuSalenCl(ëH3CN)] and
(H2Salphen), used as ligands, are well studied [1–3]. It [RuSalphenCl(ëH3CN)], respectively. The replacement
was shown that in the course of electropolymerization of the ligand by the solvent molecule was monitored by
carried out in the potential range (E) from 0 to +1.3 V, the electronic absorption spectra.
monomers form optically transparent electroconduct-
ing polymers. The octahedral Ru(II) complexes with 5-
chloro-1,10-phenanthroline (Ru(5-Cl-Phen)3)2+ were
shown [4, 5] to undergo polymerization in the potential
interval from –1.6 to 0 V. Previously, we reported the
electrochemical polymerization during electroreduc-
tion of the K[RuSalenCl2] complex [6]. In the continua-
tion of our studies, in this article, we report some new
data on the K[RuSalphenCl2] and K[RuSalenCl2] com-
plexes and electroconducting polymers on their basis.
The [RuSalenCl(ëH3CN)] and [RuSalphenCl(ëH3CN)]
crystals were obtained by repeated recrystallization
from the K[RuSalenCl2] and K[RuSalphenCl2] solu-
tions in acetonitrile. A specimen of the starting dichlo-
ride was dissolved in a minimum volume of acetoni-
trile, and the solution obtained was evaporated on slow
heating (below 40°ë) to 2–3 ml and cooled for a day.
The precipitated crystals were filtered off and washed
with ether many times. The recrystallization process
was repeated. The yield of [RuSalenCl(ëH3CN)] and
[RuSalphenCl(ëH3CN)] was 70% and 65%, respec-
tively.
EXPERIMENTAL
For [RuSalenCl(CH3CN)]
H2Salphen was produced by condensation according
to the known procedure [7]. The K2[Ru(H2O)Cl5] com-
plex was synthesized from ruthenium(III) chloride
RuCl3 · 3H2O as described in [8]. The K[RuSalenCl2]
and K[RuSalphenCl2] compounds were obtained
according to the procedures used in [8] and [9], respec-
tively.
anal. calcd. (%):
Found (%):
C, 43.48;
C, 43.45;
H, 3.40;
H, 3.44;
N, 9.51.
N, 9.55.
For [RuSalphenCl(CH3CN)]
anal. calcd. (%):
Found (%):
C, 53.70;
C, 53.79;
H, 3.46;
H, 3.49;
N, 8.54.
N, 8.57.
In the Ru(III) and Ru(II) complexes, such as
[Ru(Bipy)2(H2O)2]2+, Ru(Hfac)3 (Hfac is 1,1,1,5,5,5-
hexafluoroacetylacetonate) [10], [Ru(H2O)6]2+ [11], and
cis-[Ru(Phen)2(Py)2]2+ [12], ligands H2O, Hfac, and Py
can be replaced by the acetonitrile CH3CN molecule.
The replacement of the ël– ions by the CH3CN mole-
cule has been reported in the literature. For example,
[Ru(Bipy)2Cl2] in the CH3CN solution reacts with the
The starting reagents used in the electrochemical
experiments were the 1 × 10–3 M solutions of
K[RuSalenCl2], [RuSalenCl(ëH3CN)], K[RuSalphenCl2],
and [RuSalphenCl(ëH3CN)] in acetonitrile. Further in
the text, we shall indicate the forms in which the com-
plexes occur in the test solutions.
The electrochemical studies were carried out in a
latter to give [Ru(Bipy)2(CH3CN)Cl]+ [12]. The studies three-electrode cell with partitioned compartments of
of the K[RuSalenCl2] and K[RuSalphenCl2] behavior in the working, auxiliary, and reference electrodes. Plati-
1070-3284/03/2906-0435$25.00 © 2003 åÄIä “Nauka /Interperiodica”

436
D, arb. units
POPOVA, SHAGISULTANOVA
The voltammogram obtained under the potentiody-
D, arb. units
2.0
1.6
1.2
0.8
namic conditions during the electrode polarization in
the 1 × 10–3 M solution of [RuSalphenCl(ëH3CN)] in
acetonitrile at E from –1.6 to +1.2 V is similar the CV
obtained for [RuSalenCl(ëH3CN)] under similar condi-
tions [6]. The [RuSalphenCl(ëH3CN)] voltammogram
contains the cathode and anode peaks at –1.2 and
+1.2 V. The cathode peak is due to the Ru(III)/Ru(II)
transition, while the anode peak is produced by the
Ru(III)/Ru(IV) transition [4, 6].
0.14
(a)
(b)
3
0.12
4
0.10
300
400
500
It was of interest to study the possibility of obtaining
the Ru(II) complex during the electroreduction of the
[RuSalphenCl(ëH3CN)] complex. The electroreduc-
tion was carried out under potentiostatic conditions in
the 1 × 10–3 M solutions in the atmosphere of dry argon
at the –1.4 V potential. In the case of the starting
K[RuSalphenCl2] solution, the reduction time was 10 h.
When [RuSalphenCl(ëH3CN)] was the starting solu-
tion, the reduction and polymerization, which occurred
under potentiostatic conditions and resulted in the for-
mation of a significant amount of transparent dark
brown polymer film on the electrode surface, termi-
nated in 6 h.
λ, nm
2
1
0.4
0
250 300 350 400 450 500 550 600
λ, nm
Fig. 1. Electronic absorption spectra recorded in (a) CH CN
3
–6
for (1) a 1 × 10 M solution of a free ligand H Salphen, (2)
2
–4
a 1 × 10 M K[RuSalphenCl ] solution, (3) for the latter
2
In the course of the electrolysis, the test solutions of
the Ru(III) complex with the (Salphen)2– ligand
changed their colors from brown to dark brown. The
electronic absorption spectra of the K[RuSalphenCl2]
solution recorded before and after the reduction are
shown in Fig. 1a. As compared to the spectrum of the
starting complex solution, the spectrum of the reduced
solution exhibits an increase in the absorption intensity
in the range of 320–600 nm, which is typical of the
polymer structures. This fact suggests the formation of
the dimers and polymers responsible for the formation
of the polymer film.
solution after its electroreduction for 6 h at E = –1.4 V, (4) a
–4
1 × 10 M [RuSalphenCl(CH CN)] solution; (b) for poly-
3
mer film obtained during the electroreduction and elec-
tropolymerization of [RuSalphenCl(CH CN)] at E = –1.6 V
3
for 6 h. The supporting electrolyte is TBAP; V = 100 mV/s.
p
num wire with a surface area of 0.39 cm2 and quartz
glasses covered with platinum (optically transparent
electrodes) were used as working electrodes. Platium
gauze served as the auxiliary electrode. All potentials
were reduced to the silver chloride reference electrode
filled with the saturated KCl solution. The 0.1 M solu-
tions of tetrabutylammonium perchlorate (TBAP) and
NaClO4 in acetonitrile were used as the supporting
electrolytes. Measurements were carried out using a
PI50-1 potentiostat with a PR-8 programmer. All elec-
trochemical tests were performed under the atmosphere
of argon.
The studies performed showed that no polymer is
formed in the potentiodynamic conditions. Therefore,
in the further experiments, the polymer film was
obtained by reducing the complexes in the potentio-
static conditions. The electroconducting optically
transparent polymer is assumed to be formed by the
structural units of the coordinatively unsaturated
[RuIISalphen] molecules, which are produced in the
course of one-electron reduction of the Ru(III) com-
plex. The Ru(II) complex is unstable, but it is stabilized
through the formation of the dimers in the bulk of a
solution and of a polymer on the electrode surface. The
polymer contains the Ru(II) molecules, which is con-
firmed by X-ray photoelectron spectroscopy. It is note-
worthy that the [RuIISalphen] fragments contained in a
solid polymer film are liable to oxidation and give the
redox-polymer poly-Ru(II)/Ru(III).
The electronic absorption spectra of the solutions
and polymers were recorded on a SF-26 spectropho-
tometer.
ELECTROCHEMICAL STUDIES
OF K[RuSalphenCl2] IN TBAP ELECTROLYTE
In the previous study of the electrochemical proper-
ties of K[RuSalenCl2] in a solution of the TBAP sup-
porting electrolyte in acetonitrile [6], we obtained a
cyclic voltammogram (CV), which characterizes the
In order to study the electrochemical properties of
[RuSalenCl(ëH3CN)] properties in the potential range poly-[RuIISalphen], the product deposited on the elec-
from –1.6 to +1.2 V; the cathode peak at –1.2 V was trode in the course of a 30-min reduction at E = –1.4 V
assigned to the Ru(II)/Ru(III) electron transition, while was transferred into pure solution of the supporting
the anode peak at +1.1 V, to the Ru(III)/Ru(IV) electron electrolyte and the cyclic voltammograms were
transition.
recorded in the interval from 0 to –1.6 V and from 0 to
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 6 2003

K[RuSalphenCl2], K[RuSalphenCl2], AND ELECTROCONDUCTING POLYMERS
437
+1.3 V. Given in Fig. 2 is the cyclic voltammogram,
I, µA
8
which characterizes the redox properties of a polymer
obtained from [RuSalphenCl(ëH3CN)]. The current
peaks corresponding to the potentials –1.4 and –0.6 V
are due to the Ru(III)/Ru(II) and Ru(II)/Ru(III) transi-
tions, respectively, while the current peak correspond-
ing to the potential +1.3 V can be assigned to the
Ru(III)/Ru(IV) transition [6]. One should note for com-
parison that the current peaks corresponding to the
Ru(III)/Ru(II) and Ru(III)/Ru(IV) transitions for a
solution of the starting K[RuSalphenCl2] complex used
for the polymer synthesis are observed at E = –1.2 and
+1.2 V.
4
0
1 – 4
2
–4
1
–8
–12
–16
In the further studies, the potential of electropoly-
merization was chosen with account of the voltammo-
gram (1) in Fig 2 and of the dependence of the polymer
film thickness on the accumulation potential. The poly-
merization process is most effective at the potentials
close to that of the Ru(III)/Ru(II) transition, i.e., at the
potentials from –1.0 to –1.6 V.
We studied also the growth in the film thickness as a
function of the electroreduction and electropolymeriza-
tion time. The film thickness (calculated as described in
[13]) increases in the course of electropolymerization
to the ultimate value and then decreases with time. The
ultimate film thickness increases with the concentration
of the initial solution. Thus, at the complex concentra-
tion 0.5 × 10–3 mol/l, the film thickness is 0.05 µm,
while at 5 × 10–3 mol/l, the film is 0.17 µm thick.
3
4
–2
–1
0
1
2
E, V
–3
Fig. 2. The cyclic voltammograms of (1) a 1 × 10
[RuSalphenCl(CH CN)] solution and (2) a polymer prod-
uct obtained on the electrode in the course of the electrore-
duction and electropolymerization at E = –1.4 V for 15 min,
(3) for 30 min, and (4) for 1 h. The supporting electrolyte is
TBAP.
M
3
potential range from 0 to –1.6 V and from 0 to +1.3 V
(Fig. 3). As follows from the results obtained, the poly-
mer fully retains the voltammogram shape in the nega-
tive potential region and the values of the current peaks
within a long cycling time in the supporting electrolyte.
Thus, one can state that the polymer is stable and
retains its redox and electroconducting properties when
it is cycled in the potential interval from 0 to –1.6 V.
When the cycling is performed in the positive range
from 0 to +1.3 V, the intensity of the current peaks sig-
nificantly decreases due to the change in the polymer
structure, probably as a result of the rapid oxidation of
Ru(II) to Ru(III) and diffusion of the supporting elec-
trolyte ions and of the solvent molecules into the poly-
mer bulk.
The equilibrium potential for the redox-polymer
was determined. The electrochemical synthesis was
performed at –1.4 V and resulted in the reduced form of
the polymer film with composition poly-[RuIISalphen].
When the potential applied to the electrode with the
polymer on its surface was switched off, we observed
the rapid spontaneous growth of the film potential to the
equilibrium value of –0.5V. Such a growth in the poten-
The results obtained were used to calculate the dif-
fusion coefficient (Dst) determining the rate of the elec-
tron transport in the polymer chain [13]. The value of
Dst was found to increase with the polymer thickness.
For instance, for the polymer 0.015 µm thick, Dst = 1 ×
10–13 cm2/s, while this value increases by an order of
magnitude and amounts to 1 × 10–12 cm2/s when the
polymer thickness is twice as much.
To study the spectral properties of the polymer
under consideration, we carried out the electrochemical
synthesis on the flat optically transparent electrodes, pro-
duced by platinum deposition onto the surface of quartz
glass. The electronic absorption spectra of the polymer
product obtained during the cathode polarization of the
electrode in the 1 × 10–3 M [RuSalphenCl(ëH3CN)]
solution in acetonitrile for 6 h are shown in Fig. 1b. The
bands observed in the monomer spectrum disappear
from these spectra in the region of 290 and 330 nm and
a new band appears in the region of 300–400 nm. The
broadening and shift of the absorption band toward red
region as compared with the spectrum of the starting
complex is typical of the polymer structures and of the
Ru(II) complexes with the Schiff bases [14].
With the aim to investigate the stability of the poly- tial is explained by the oxidation of Ru(II) to Ru(III)
mer product, the electrode with the polymer, obtained until the concentration equilibrium is attained between
in the 1 × 10–3 M [RuSalphenCl(CH3CN)] solution at the reduced and oxidized forms Ru(II)
Ru(III) in
−1.2 V for 1 h of the electrochemical reduction, was the polymer composition. The further potential increase
transferred into the supporting electrolyte solution and to 0V is likely to be accompanied by the structural rear-
multiple cycling was performed for 15 min in the rangements and physical destruction of the polymer
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 6 2003

438
POPOVA, SHAGISULTANOVA
I, µA
8
I, µA
15
10
5
4
0
0
–5
–4
–10
–2
–1
0
1
2
E, V
–8
–3
Fig. 4. The cyclic voltammograms of a 1 × 10
M
K[RuSalphenCl ] solution in the NaClO electrolyte
obtained with continuous scanning of the potential from 0
2
4
–12
–1.6
–1.2
–0.8
–0.4
0
E, V
to –1.4 V for 30 min; V = 100 mV/s.
p
Fig. 3. The cyclic voltrammograms of the polymer film (syn-
thesized by electropolymerization of [RuSalphenCl(CH CN)]
(Fig. 4). With continuous cycling in the range from 0 to –
1.4 V for 30 min, the current peak at –0.35 V decreases
and that at –0.6 V shifts by 0.3 V toward the negative
region of potentials. As was indicated above, the cyclic
voltammogram of K[RuSalphenCl2] in the TBAP sup-
porting electrolyte contains only one current peak in the
negative region of potentials at –1.0 V, this peak disap-
pears with further cycling.
3
at E = –1.4 V for 1 h) recorded with continuous potential
scanning for 15 min. The supporting electrolyte is TBAP;
V = 100 mV/s.
p
film. One can assume that when the potential is
increased to 0 V, the processes of oxidation of Ru(II) to
Ru(III) and coordination of the solvent molecules
CH3CN due to the conversion of Ru(II) into the octahe-
dral Ru(III) form cause the polymer destruction.
In the case of the starting K[RuSalphenCl2] com-
plex, the processes of electroreduction and polymeriza-
tion occur at the lower rates. That is why we used the
starting [RuSalphenCl(CH3CN)] solutions in a number
of experiments.
In the case of TBAP, the positive region of potentials
contains only one current peak at +1.1 V (due to the
Ru(III)/Ru(IV) transition), while in the case with the
NaClO4 supporting electrolyte, two current peaks are
observed at +1.0 and +0.5 V (due to the Ru(III)/Ru(IV)
and Ru(IV)/Ru(III) transitions, respectively). In the
long-term cycling from 0 to +1.3 V, both the voltammo-
gram shape and the values of the current peaks remain
unchanged, which confirms the reversible nature of the
redox processes in the test solution.
ELECTROCHEMICAL STUDIES
OF K[RuSalphenCl2] IN NaClO4 ELECTROLYTE
Under the potentiodynamic conditions and in the
case with the NaClO4 supporting electrolyte, as with
TBAP, no polymer formation was observed on the elec-
trode surface. The polymer film was obtained under the
potentiostatic conditions. The electroreduction of the 1 ×
10–3 M solutions of the starting complex under the poten-
tiostatic conditions at –1.4 V in the atmosphere of dry
argon resulted in the electroconducting optically trans-
parent and dark brown polymer films, which looked
We have previously established how the nature of
electrolyte influences the electrochemical properties of
the complexes and the efficiency of formation of their
polymers [5]. In this work, we studied the electrochem-
ical properties of K[RuSalphenCl2] in the NaClO4 sup-
porting electrolyte.
Figure 4 shows the cyclic voltammogram of
K[RuSalphenCl2] in a 0.1 M NaClO4 supporting elec-
trolyte. The shape of a curve and its pathway in the like the films obtained in the case of TBAP. The com-
course of a long-term potential scanning coincide with position of the polymer product obtained in the elec-
the cyclic voltrammogram previously obtained in a 2 × tropolymerization is supposed to be poly-[RuIISalphen].
10–3 M solution of Ru(5-Cl-Phen) 32+ in the solution of
tetraethylammonium perchlorate in acetonitrile [4, 5].
One should note that the electroreduction and elec-
tropolymerization process occur in the NaClO4 solu-
The voltammogram contains two distinct current peaks tions at the rates higher than in the TBAP solutions.
at –0.35 and –0.6 V corresponding to the electron tran- Moreover, the reduced polymer form (obtained at –1.4V)
sitions Ru(II)/Ru(III) and Ru(III)/Ru(II), respectively is unstable and is easily oxidized in the solutions and in
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 6 2003

K[RuSalphenCl2], K[RuSalphenCl2], AND ELECTROCONDUCTING POLYMERS
439
I, µA
20
I, µA
20
2
10
0
10
1
0
–10
–10
–20
–1.6
–1.2
–0.8
–0.4
0
E, V
–20
–2
–1
0
1
2
Fig. 5. The cyclic voltammogram of the polymer synthe-
E, V
–3
sized by electropolymerization of
a
1
× 10
M
[RuSalphenCl(CH CN)] solution in acetonitrile at E = –1.4V
3
Fig. 6. The cyclic voltammograms of the polymer (synthe-
sized by the electropolymerization of a 1 × 10
[RuSalphenCl(CH CN)] solution at –1.4 V for 30 min)
for (1) 30 min (2) after cycling in the NaClO supporting
–3
4
M
electrolyte from 0 to –1.4 V for 30 min; V = 100 mV/s.
p
3
recorded with continuous potential scanning from 0 to –1.4V
for 30 min and 5 min, respectively, in the NaClO support-
4
air. The partial oxidation gives the [RuIIISalphen]+ cat-
ions, which favors the diffusion of the ClO–4 counteri-
ing electrolyte; V = 100 mV/s.
p
ons into the polymer bulk. The presence of the Na+ and
–0.3 V (the anode peak), at –0.65 and –1.0 V (the cath-
ode peaks) which grow in the course of a continuous
potential scanning for 30 min.
TBA+ cations and the ClO–4 anions in the bulk of the
polymer was confirmed by X-ray photoelectronic spec-
troscopy.
Thus, one can assume that the potential cycling in
the negative region of the potentials yields a stable
polymer product with the reversible redox properties as
distinct from the polymer initially obtained during the
reduction of the [RuSalphenCl(CH3CN)]] solution. The
cyclic voltammogram describing the properties of the
polymer obtained during cycling is given in Fig 5, 2.
The cathodic and anodic waves on the recorded cyclic
voltammograms confirm the solid-phase reversible
redox reactions that occur in the polymer film.
When the electrosynthesis was carried out under the
potentiostatic conditions at –1.4V, the reduced polymer
form (poly-[RuIISalphen]) was produced. However, as
was already mentioned above, the state of Ru(II) in a
solid polymer film is unstable at less negative potentials
and it is oxidized to Ru(III). That is why the potential
cycling from –1.4 to 0 V gives the partially oxidized
form of the polymer. The equilibrium polymer form
(redox-polymer) is produced when the polymer poten-
tial spontaneously increases to –0.6 V in the case the
current is switched off. A stable equilibrium Ru(II)
Ru(III) is supposed to be established in such a polymer
form.
The polymers produced in TBAP did not show the
indicated changes in their electroconducting properties.
The cyclic voltammogram of the polymer obtained with
TBAP contains two current peaks at –1.4 and –0.6 V,
their shapes and intensities remain unchanged during
the long-term cycling from 0 to –1.4 V. These data con-
firm the influence of the nature of the supporting elec-
trolyte on the structure and properties of the polymer
films.
The cyclic voltammogram of the reduced form of
the polymer product obtained by the electropolymer-
ization of the 1 × 10–3 M [RuSalphenCl(CH3CN)] solu-
tion on the electrode surface under the potentiostatic
conditions at –1.4 V for 30 min was recorded in the
NaClO4 supporting electrolyte (Fig. 5, 1). The voltam-
In the positive potential region, the electrochemical
mograms contain neither the cathode nor the anode properties of the polymer obtained with NaClO4 also
peaks, which suggests that the structure of the polymer differ from those of the polymer synthesized in TBAP.
produced does not favor the reversible redox reactions. With the aim to study the electrochemical properties of
Further continuous scanning of the potential from 0 to a polymer in the positive potential region, an electrode
–1.4 V for 30 min gave the cyclic voltammograms pre- with the polymer film of poly-[RuSalphen] obtained at
sented in Fig. 6. The cycling produced current peaks at –1.4 V for 30 min in the NaClO4 electrolyte solution
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 6 2003

440
POPOVA, SHAGISULTANOVA
was transferred into the supporting electrolyte solution sonal grant for students, post-graduate students, and
and cycled in the range from 0 to +1.3V. The cyclic vol- young scientists established by St. Petersburg authori-
tammograms obtained with continuous cyclic for 5 min ties (2001).
are presented in Fig. 6. The potentiodynamic curve con-
tains two current peaks at +0.9 V (the anode peak) and
at +0.5 V (the cathode peak). We assigned them to the
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Ru(III) state already in the negative potential region,
Ru(III) is supposed to be further oxidized to Ru(IV) in
the positive potential region, which corresponds to the
current peak at +0.9 V.
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ACKNOWLEDGMENTS
This work was supported by Russian Foundation for
Basic Research (project no. 01-03-33155), RF Ministry
of Education (project no. EOO-5.0-210), and by per-
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RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 6 2003