Ru(EDTA) mediated partial reduction of O2 by H2S

Article abstract of DOI:10.1039/c5dt00472a

An effective procedure for selective reduction of O₂ to H₂O₂ exploring the use of hydrogen sulfide, an obnoxious industrial pollutant as reductant is reported herein. The reduction of [Ru^III(EDTA)pz]^- (EDTA^4- = ethylenediaminetetraacetate; pz = pyrazine) by hydrogen sulfide resulting in the formation of a red [Ru^II(EDTA)pz]^2- complex (λ_max = 462 nm) has been studied spectrophotometrically and kinetically using both rapid scan and stopped-flow techniques. The time course of the reaction was followed as a function of [HS^-]_i, pH (5.5-8.5), and temperature. Alkali metal ions were found to have a positive influence (K⁺ > Na⁺ > Li⁺) on the reaction rate. Kinetic data and activation parameters are interpreted in terms of a mechanism (admittedly speculative) involving outer-sphere electron transfer between the reaction partners. Reaction of the red [Ru^II(EDTA)pz]^2- complex with molecular oxygen regenerates the [Ru^III(EDTA)pz]^- species in the reacting system along with the formation of H₂O₂, a partially reduced product of dioxygen (O₂) reduction. A detailed reaction mechanism in agreement with the spectral and kinetic data is presented.

Full text of DOI:10.1039/c5dt00472a

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Graphical Abstract
Ru(EDTA) mediated partial reduction of O2 by H2S
Debabrata Chatterjee* Namita Jaiswal and Papyia Sarkar
S + 2H+
H2S
[RuIII(EDTA)(pz)]- (EDTA4- = ethylenediaminetetraacetate),
pz = pyrazine) mediates two-electron reduction of O2 to
[RuIII(edta)(pz)]-
[RuII(edta)(pz)]2-
produce H2O2 using H2S as a reducing agent.
2H+
O2
H2O2

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DOI: 10.1039/C5DT00472A
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FULL PAPER
Ru(EDTA) mediated partial reduction of O2 by H2S†
Debabrata Chatterjee* Namita Jaiswal and Papyia Sarkar
Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X
First published on the web Xth XXXXXXXXX 200X
5
DOI: 10.1039/b000000x
An effective procedure for selective reduction of O2 to H2O2 exploring the use of hydrogen sulfide, an
obnoxious industrial pollutant as reductant is reported herein. The reduction of [RuIII(EDTA)pz]ꢀ
(EDTA4ꢀ = ethylenediaminetetraacetate; pz = pyrazine) by hydrogen sulfide resulting in the formation
of a red [RuII(EDTA)pz]2ꢀ complex (λmax = 462 nm) has been studied spectrophotometrically and
10 kinetically using both rapid scan and stoppedꢀflow techniques. The time course of the reaction was
followed as a function of [HSꢀ]i, pH (5.5 ꢀ 8.5), and temperature. Alkali metal ions were found to have
a positive influence (K+ > Na+ > Li+) on the reaction rate. Kinetic data and activation parameters are
interpreted in terms of a mechanism (admittedly speculative) involving outerꢀsphere electron transfer
between the reaction partners. Reaction of red [RuII(EDTA)pz]2ꢀ complex with molecular oxygen
15 regenerates the [RuIII(EDTA)pz]ꢀ species in the reacting system along with the formation of H2O2, a
partially reduced product of dioxygen (O2) reduction. A detailed reaction mechanism in agreement
with the spectral and kinetic data is presented.
Introduction
present studies we have explored the possibility of using the
hydrogen sulfide in the catalytic scheme on the selective reduction
Development of metal complexes as catalyst for the oxygen of O2 to H2O2. It is noteworthy, hydrogen sulfide, the smallest
20 reduction reaction (ORR) is of continued interest 1 in its own right thiol is now believed to be an important redoxꢀsignaling molecule,
and in the context of life processes such as biological respiration, 55 and various beneficial effects of H2S in our bodies have recently
and in energy converting systems such as fuel cells. In this regard been recognized.6
use of H2S, an obnoxious industrial pollutant as an effective
reducing agent was exemplified long back by the Claus process' in
25 which O2 is reduced directly to H2O by undergoing 4ꢀelectron
reduction.2
In the present work, we have undertaken a detailed kinetic
and mechanistic investigation of the reduction of [RuIII(EDTA)pz]ꢀ
to [RuII(EDTA)pz]2ꢀ with hydrogen sulfide, and reoxidation of
60 [RuII(EDTA)pz]2ꢀ by molecular oxygen, O2. The reason for
choosing [RuIII(EDTA)pz]ꢀ complex for the present investigation is
the substantial spectral difference between Ru(III)ꢀ and Ru(II)ꢀ
species affording an amenable way for the kinetic studies. The
results of these studies together allow rationalization of the
65 Ru(EDTA) mediated catalysis of dioxygen (O2) reduction to
hydrogen peroxide (H2O2) using hydrogen sulfide (H2S) as
reducing agent.
O
O
O
30
N
N
III
Ru
O
OH2
O
HO
O
O
35
Experimental
Materials
Fig. 1 Pictorial representation of the [RuIII(HEDTA)(H2O)] complex
70 K[RuIII(HEDTA)Cl].2H2O was synthesized according to the
40 In recent past we have shown that Ru(EDTA) complex could act published procedure.7 Anal. calculated for K[RuIII(HEDTA)Cl].
as an efficient electron transfer and Oꢀatom transfer agent for 2H2O: C 24.0, H 3.42, N 5.59; Found. C 23.8, H 3.45, N 5.63. IR,
effecting oxidation of biologically important thiols (cysteine, ν/cmꢀ1: 1720 (free ꢀCOOH), 1650 (coordinated ꢀCOOꢀ). UVꢀVis in
glutathione).3 The Ru(EDTA) complexes have been proposed as H2O: λmax/nm (εmax/Mꢀ1 cmꢀ1): 283 (2800 ± 50), 350 sh (680 ± 10).
alternatives to Pt(II) antiꢀtumour agents, as reported in several 75 The K[RuIII(HEDTA)Cl] complex rapidly converts into the
45 reviews.4 Electron transfer reaction leading to the reduction of [RuIII(HEDTA)(H2O)] complex when dissolved in water.8,9 The
Ru(III) to Ru(II) assumes immense importance as tumour cell sixth coordination site of the ruthenium complex is occupied either
metabolism favours the presence of Ru(II) relative to Ru(III), thus at low pH by a water molecule (Fig. 1) or at high pH by a
increasing the selective tumour toxicity.5a Furthermore, metabolic hydroxide ion. The pKa values related to the acidꢀdissociation
conditions such as hypoxia in tumour cells provide a more 80 equilibria of the pendant carboxylic acid arm and the coordinated
50 reductive environment than is found in normal tissue.5b In the water molecule are 2.4 and 7.6, respectively at 25 °C.8,9 The
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[RuIII(EDTA)pz]ꢀ complex can very easily be prepared by mixing on the kinetic profile (time versus absorbance traces at 462 nm) is
equimolar amounts of [RuIII(EDTA)(H2O)]ꢀ and pyrazine (pz) 55 typically displayed in Fig. 2b.
through a very rapid and straightforward water substitution
reaction (k = 2 x 104 Mꢀ1 sꢀ1 at 25 °C).8 Details of the spectral and
5
electrochemical properties of [RuIII/II(EDTA)(pz)])ꢀ/2ꢀ complexes
were reported in the earlier papers.8 The absorption spectrum of
60
the ruthenium(III) species is almost featureless above 390 nm,
whereas the ruthenium(II) complex exhibits a strong characteristic
5.00
(a)
4.00
metalꢀtoꢀligand charge transfer band in the visible region (λmax
=
10 462 nm, εmax = 11,000 Mꢀ1 cmꢀ1).8 All other chemicals used were
of A.R grade and of the highest purity available. Experimental
solutions of sodium bisulfide (Sigma Aldrich) were prepared by
using argon saturated doubly distilled water, and their
concentration was determined by iodometric titration.10
15 Concentration of bisulfide is expressed as initial concentration of
bisulfide ([HSꢀ]i). Considering pKa values (pKa1 = 7.02 and
pKa2 ∼17.1)11,12 of related to the proton dissociation equilibria of
H2S, it is presumed that at pH > 8.0 presence of H2S and S2ꢀ in the
solution is insignificant, whereas, at pH < 6.0 H2S is the most
20 predominant reacting species. Gasꢀtight Hamilton syringes were
used to transfer these solutions throughout our studies.
65
70
75
80
85
90
3.00
2.00
1.00
0.0
22.5
12.5
2.5
325
375
425
475
525
575
625
675
Wavelength (nm)
2.5
2.0
1.5
1.0
0.5
0.0
(b)
[HS-]i = 2 X 10-3M
[HS-]i = 2.5 X 10-3M
[HS-]i = 3 X 10-3M
[HS-]i = 4 X 10-3M
Instrumentation
UVꢀvis absorption spectra were recorded on a Varian Model Cary
100 spectrophotometer using 1 cm path standard quartz cells.
25 Stoppedꢀflow experiments were carried out with a HiꢀTech SFꢀ61
SX2 (TgK Scientific Ltd.) spectrophotometer using a 1 cm optical
path length. The reaction of [RuIII(EDTA)(pz)]ꢀ with hydrogen
sulfide was followed at 462 nm. Single wavelength kinetic profiles
were collected in the photomultiplier mode by following the
30 appearance of [RuII(EDTA)pz]2ꢀ at 462 nm, and data were
processed using HiꢀTech KinetAsyst 3 software. Timeꢀresolved
UVꢀvis spectra were recorded with a HiꢀTech SFꢀ61 SX2 (TgK
Scientific Ltd.) spectrophotometer equipped with a rapid scan
diode array spectral attachment (KinetaScan). The solution
35 temperature was regulated with a thermostat water bath (JEIO
TECH RWꢀ1025G) within ±0.1 °C. The pH of the solutions was
measured with a Mettler Delta 350 pH meter. Acetate, phosphate100
and borate buffers were used to control the pH of the experimental
solutions. NaCl was used to control the ionic strength. LiCl and
40 KCl were used to investigate the effect of varying the alkali metal
cations. Kinetic data are presented as an average of several kinetic
runs (at least 3–5) and were reproducible within ±4 %.
0
5
10
15
20
time,s
Fig. 2 (a) UVꢀVis spectral changes for the reaction of [RuIII(EDTA)(pz)]ꢀ
(0.2 mM) with HSꢀ (2.0 mM), (b) kinetic traces (recorded at 462 nm) at
various [HSꢀ]i at 25 °C, [RuIII] = 0.2 mM, pH 8.5 (phorphate buffer)
95
At a constant pH of 8.5 the rate of reduction estimated from
the maximum slope of the kinetic traces (Fig. 2b), increases
linearly (Fig. 3) with increasing initial concentration of bisulfide
([HSꢀ]i). Based on the above experimental observations, and
considering that HSꢀ is the dominant reacting species at pH 8.5 a
working mechanism is proposed in Scheme 1 for the reduction of
[RuIII(EDTA)(pz)]ꢀ with HSꢀ.
0.00007
0.00006
0.00005
0.00004
0.00003
0.00002
Results and discussion
Reaction of [RuIII(EDTA)pz]ꢀ with hydrogen sulfide was
45 carried out strictly under argon atmosphere. Addition of argon
purged solution of NaHS to the paleꢀyellow solution of
[RuIII(EDTA)pz]ꢀ (prepared by mixing the argon purged solutions
of [RuIII(EDTA)(H2O)]ꢀ and pyrazine in an equimolar ratio) at pH
8.5 (phosphate buffer) resulted in rapid changes of the spectral
50 features as shown typically in Fig. 2a. The observed spectral
changes are ascribed to the formation of [RuII(EDTA)pz]2ꢀ via
reduction of [RuIII(EDTA)pz]ꢀ by HSꢀ under the specified105
conditions. The effect of concentration of bisulfide concentration
0.0015
0.0020
0.0025
0.0030
0.0035
0.0040
[HS-]i, M
Fig. 3 Effect of [HSꢀ]i on the rate of formation of [RuII(EDTA)(pz)]2ꢀ at 25
οC, [RuIII(EDTA)(pz)]ꢀ = 0.2 mM, pH 8.5 (phosphate buffer).
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The rate determining step (1) proposed in the above
The temperature dependence of kred was investigated from 15
mechanism involves oneꢀelectron transfer from HSꢀ to to 30 °C at pH 8.5, and the values of kred so estimated are 29 ± 1,
ruthenium(III) complex in an outerꢀsphere manner to yield the 55 41 ± 2, 50 ± 2, and 70 ± 2 M−1 s−1 at 15, 20, 25 and 30 °C,
ruthenium(II) complex and the HS● radical. Reduction of another respectively. The values of ꢁH≠ and ꢁS≠ determined from the
molecule of ruthenium(III) complex by HS● radical occurred in a Eyring plot (Fig.4) are 39 ± 2 kJ mol−1 and −60 ± 6 J mol−1 deg−1,
subsequent rapid and kinetically inconsequential step as outlined in respectively are quite comparable with the ꢁH≠ and ꢁS≠ values
Eq 2. Formation of colloidal sulfur in the reacting system was reported for the reduction of [RuIII(EDTA)(pz)]ꢀ by negatively
5
visible at the end of the reaction.
60 charged reductants,13,14 and consistent with the proposed rate law.
kred
[RuIII(EDTA)pz]ꢀ + HSꢀ
[RuIII(EDTA)pz]ꢀ + HS
[RuII(EDTA)(pz)]2ꢀ + HS
[RuII(EDTA)(pz)]2ꢀ + S + H+
(1)
(2)
-1.4
-1.6
-1.8
-2.0
-2.2
-2.4
65
70
75
10 Scheme 1 Mechanism for the reduction of [RuIII(EDTA)(pz)]ꢀ by HSꢀ
Electron transfer reaction involving [RuIII(EDTA)(pz)]ꢀ complex
generally occurs in an outersphere manner.3a,13,14 In order to
substantiate the occurrence of outersphere electron transfer
15 reaction in the present case we have examined the role of alkali
cations on the rate of reduction of [RuIII(EDTA)pz]ꢀ by HSꢀ at pH
8.5. The positive effect of alkali metal cations on the electron
transfer rate for a reaction of two negatively charged reacting
species occurring through an outerꢀsphere manner is well
20 documented in the literature.15ꢀ18 It had been reported that the
cation acts as a bridge or as a means of allowing two negatively
charged reacting ions close enough to form a triple ion, and thus
facilitating the electron transfer process.15ꢀ18 In the present case,
the observed increase in the reaction rate on going from Li+ to Na+
25 to K+ (see Fig.S1 in ESI) essentially support the argument in
favour of the outersphere electron transfer reaction. Considering
the size of hydrated cations which is in the order: Li+ > Na+ > K+,
the K+ would be more effective than Na+ or Li+ in bringing the
reacting species close enough in forming the tripletꢀion species
30 ([RuIII(EDTA)(pz)]ꢀꢀꢀM+ꢀꢀHSꢀ), and thus facilitating the electron
transfer reaction as typically revealed by the increase in the
reaction rate in the present studies (see Fig.S1 in ESI).
0.00330
0.00335
0.00340
1/T
0.00345
0.00350
Fig. 4 Eyring plot for the reduction of [RuIII(EDTA)(pz)]ꢀ with HSꢀ at pH
8.5 (phosphate buffer).
80
The [RuII(EDTA)(pz)]2ꢀ complex was found to be unstable
when exposed to the oxygen atmosphere. Addition of oxygen
saturated solution of acetate buffer (1mM) to the red solution of
[RuII(EDTA)(pz)]2ꢀ (prepared by mixing the solutions of
[RuIII(EDTA)(pz)]ꢀ and NaHS in an equimolar ratio at pH 5.5)
85 resulted in a gradual drop of the spectral features (Fig. 5a)
characteristic of the [RuIII(EDTA)(pz)]2ꢀ complex.
0.5
0.4
90
(a)
0.3
0.2
0.1
Considering two molecules of [RuIII(EDTA)(pz)]2ꢀ is
produced by one HSꢀ as outlined in Scheme 1, the following rateꢀ
35 law can be derived on the basis of the rateꢀdetermining appearance
of the [RuIII(EDTA)(pz)]2ꢀ complex monitored at 462 nm.
95
0.0
300
350
400
450
500
550
600
650
700
Wavelength (nm)
rate =2 kred [RuIII(edta)(pz)ꢀ][HSꢀ]
(3)
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
40
[HS-]i = 5 x 10-5
[HS-]i = 2.5 x 10-4
M
100
M
The linear dependence of the rate on [HSꢀ] (Fig. 3) is in line
with the suggested mechanism. The value of the secondꢀorder rate
constant (kred) estimated using the slope of the plot of rate versus
45 [HSꢀ] (as shown in Fig. 3) is 50 ± 1 Mꢀ1 sꢀ1 at 25 °C and pH 8.5.
(b)
However, at lower pH (5.5) the rate of the reduction of 105
[RuIII(EDTA)(pz)]ꢀ by hydrogen sulfide was found to be
considerably slower as revealed by the time versus absorbance
trace (see Fig.S2). The observed decrease in reaction rate at lower
50 pH, is understandable by the fact that the reducing ability of H2S, 110
which is the major reacting species at pH 5.5 (pK1 of H2S is
7.02)11 appreciably lesser from that of its conjugate base HSꢀ.19
0
1000 2000 3000 4000 5000 6000 7000
time, sec
Fig. 5 (a) Spectral changes for the oxidation of [RuII(EDTA)(pz)]ꢀ (0.05
mM) with O2, (b) kinetic traces (recorded at 462 nm) at different [HSꢀ]i at
25 °C, pH 5.5 (acetate buffer).
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The observed spectral changes (Fig. 5a) are attributed to the based catalysts for the selective reduction of O2 via two oneꢀ
oxidation of the complex to electron outersphere reductions to produce H2O2, which is a
[RuII(EDTA)(pz)]2ꢀ
[RuIII(EDTA)(pz)]ꢀ by O2
under the specified conditions. promising candidate for a renewable energy source.
Absorbanceꢀtime traces shown in Fig. 5b exhibit an initial
5
induction period at higher hydrogen sulfide concentration which Acknowledgments
could be explicable in terms of the reformation of the
[RuII(EDTA)(pz)]2ꢀ complex in the presence of excess of HSꢀ 55 DC is thankful to Dr. P Pal Roy, Director of the Central
under the specified conditions. Appearance of the induction period Mechanical Engineering Research Institute, for his support of this
as a result of the continued reformation of [RuII(EDTA)(pz)]2ꢀ work. PS thanks to CSIR, New Delhi for junior research
10 indicating recycling of the catalyst complex at higher hydrogen fellowship (CSIRꢀJRF).
sulfide concentration. Above observations clearly indicate the
occurrence of a catalytic process (Scheme 2) in the reduction of Notes and references
dioxygen (O2) by H2S in presence of [RuIII(edta)(pz)]ꢀ as catalyst.
60 Chemistry and Biomimetics Group, CSIR-Central Mechanical Engineering
Research Institute, MG Avenue, Durgapur-713209, India, Fax: 91-343-
2546745; Tel: 91-343-2546828; E-mail: dchat57@hotmail.com
S + 2H+
H2S
15
†Electronic supplementary information (ESI) available: kinetic traces.
[RuIII(edta)(pz)]ꢀ
[RuII(edta)(pz)]2ꢀ
O2
65
70
75
80
85
1. (a) J. P. Collman, R. Boulatov, C.J. Sunderland and L.Fu, Chem. Rev.
2004, 104, 561.
2H+
(b) Stuart B. Adler, Chem. Rev. 2004, 104, 4791.
(c) E. Kim, E. E. Chufan, K. Kamaraj and K. D. Karlin, Chem. Rev.
2004, 104, 1077.
(d) J. Rosenthal, D. G. Nocera, Acc. Chem. Res. 2007, 40, 543.
(e) J. J Warren, T. A.Tronic, J. M. Mayer, Chem. Rev. 2010, 110,
6961.
(f) S. Fukuzumi and K. D. Karlin, Coord. Chem. Rev. 2013, 257,187.
(g) M. A.Thorseth, C. E. Tornow, E. C. M.Tse and A. A. Gewirth,
Coord. Chem. Rev. 2013, 257, 130
H2O2
Scheme 2 Mechanism for the reduction of O2 by H2S mediated by of
20 [RuIII(EDTA)(pz)]ꢀ.
While elemental sulfur, a twoꢀelectron oxidation product of
H2S visibly appeared in the reacting system at the end of the
reaction, formation of H2O2, a twoꢀelectron reduction product of
25 O2 was confirmed by permanganate titration.20 No H2O2 was
detected in absence of Ru(EDTA) complex in the reacting system.
However, formation of H2O2 with 88% yield (0.22 mM) was
evidenced when 0.25 mM of NaHS was used as reductant in
presence of Ru(EDTA) catalyst (0.05mM). Above results establish
30 the fact that the studied reaction is catalytic in nature. Considering
[RuII(EDTA)(pz)]2ꢀ complex is the catalytic active species
responsible for H2O2 production, the catalytic turnꢀover number
(TON) achieved is 4.2 under the employed conditions (as specified
under Fig.5b). Addition of Lꢀascorbic acid (a stronger reducing
35 agent) to the resultant solution immediately recovered the spectral
features of the [RuII(EDTA)(pz)]2ꢀ complex almost quantitatively
which supports the fact that the Ru(EDTA) catalyst is not degraded
under turnꢀover conditions.
2. (a) B. W. Gamson and R. H. Elkins, Chem. Eng. Prog. 1953, 49, 203.
(b) J.W. Palm, Hydrochem. Process. 1972, 51, 105
3. (a) D. Chatterjee, U. Pal, S. Ghosh and R. van Eldik, Dalton Trans.,
2011, 40, 1102.
(b) D. Chatterjee, U. Pal, S. Ghosh and R. van Eldik, Dalton Trans.,
2011, 40, 10997.
4
(a) J. Cummings, R. E. Aird, R. E. Morris, H. Chen, P. d. S. Murdoch,
P. J. Sadler, J. F. J. Smyth and D. I. Jodrell, Clin. Cancer Res., 2000, 6,
142.
(b) W. H. Ang and P. G. Dyson, Eur. J. Inorg. Chem., 2006, 4003.
5. (a) F. Wang, H. Chen, J. A. Parkinson, P. S. Murdoch and P. J. Sadler,
Chem. Rev., 1999, 99, 2511.
(b) D. Miklavcic, G. Sersa and S. Novakovic, J. Bioelect. 1990, 9, 133.
90 6. (a) L. Li, P Rose and P. K. Moore, Annu. Rev. Pharmacol. Toxicol.
2011, 51, 169.
.
(b) G.K. Kolluru, X. Shen, and C. G. Kevil, Redox Biology 2013, 1,
313.
7. A. A. Diamantis and J. V. Dubrwaski, Inorg. Chem., 1981, 20, 1142
95 8. T. Matsubara and C. Creutz, Inorg. Chem., 1979, 18, 1956.
9. H. C. Bajaj and R.van Eldik, Inorg. Chem., 1988, 27, 4052.
10. S. Carballal, M. Trujillo, E. Cuevasanta, S. Bartesaghi, M.N. Möller,
L. K. Folkes, M. A. GarcíaꢀBereguiaín, C. GutiérrezꢀMerino, P.
Wardman, A. Denicola, R.Radi and B. Alvarez, Free Radic Biol
Conclusions
100
Med. 2011, 50, 196.
11. D.D. Perrin, Ionisation Constants of Inorganic Acids and Bases in
Aqueous Solution, 2nd Ed., Pergamon Press: Oxford, 1982.
12. B. Meyer, K. Ward, K. Koshlap and L.Peter, Inorg. Chem. 1983, 22,
2345.
40 In the present study, we have conclusively demonstrated that the
[RuIII(EDTA)(pz)]ꢀ complex can effectively and readily be reduced
to the corresponding ruthenium(II) complex by hydrogen sulfide.
The proposed outersphere mechanism is admittedly speculative as
other mechanisms with the evidence presented herein cannot be
45 ruled out. Reoxidation of [RuII(EDTA)(pz)]2ꢀ complex
accompanied with the formation H O and ruthenium(III) analogue110
could be achieved by molecular oxygen (O2). In summary, the
present redox studies of Ru(EDTA) complexes containing the
aromatic Nꢀheterocyclic ligand pyrazine is definitely an instructive
50 beginning toward the development of more efficient ruthenium115
105 13. D. Chatterjee, J. Chem. Soc., Dalton Trans., 1996, 4389
14. D. Chatterjee, Trans.Met.Chem., 2000, 25, 227.
15. P. D. Metelski and T. W. Swaddle, Inorg. Chem., 1999, 38, 301.
16. W. H. Mulder, T. P. Dasgupta and G. Stedman, Inorg. React. Mech.,
2000, 1, 257.
17. A. Rodrigenz, S. Lopez, C. G. Carmona and F. Sanchez, J. Chem. Soc.
Dalton Trans., 1986, 1265.
18. S. K. Saha, M. C. Ghoshand and P. Banerjee, J. Chem. Soc., Dalton
Trans., 1986, 1301.
19. P. Nicholls and J.K Kim,. Can J. Biochem 1982, 60, 613.
20. A. I. Vogel, Textbook of Qualitative Inorganic Analysis, Wiley, New
York, 3rd edn, 1961, p. 325.
2
2
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