"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."

Electrochemical and Resonance Raman Spectroscopic Studies of
Water-Oxidizing Ruthenium-Terpyridyl-Bipyridyl Complexes
Anke Keidel,[a]§ Isidoro López,[b]§ Jana Staffa,[a] Uwe Kuhlmann,[a] Fernando Bozoglian,[b] Carolina
Gimbert-Suriñach,[b] Jordi Benet-Bucholz,[b] Peter Hildebrandt,*[a] and Antoni Llobet*[b][c]
§

Equal contribution to the work

Abstract: The irreversible conversion of single-site water oxidation
catalysts (WOC) into the more rugged catalysts structurally related
to [(trpy)(5,5’-X2-bpy)RuIV(µ-O)RuIV(trpy)(O)(H2O)]4+ (X = H, 1-dn4+; X
= F, 2-dn4+) represents a critical issue in developing active and
durable WOC. In this work, the electrochemical and acid-base
properties of 1-dn4+ and 2-dn4+ were evaluated. In-situ resonance
Raman spectroscopy was employed to characterize species formed
upon stoichiometric oxidation of single-site catalysts demonstrating
the formation of high oxidation states mononuclear Ru=O and RuOO complexes. Under turnover conditions, the dinuclear intermediates,
1-dn4+ and 2-dn4+, as well as the previously proposed
[RuVI(trpy)(O)2(H2O)]2+ complex (32+) are formed. 32+ is a pivotal
intermediate that provides access to the formation of dinuclear
species. Single crystal X-ray diffraction analysis of the isolated
complex [RuIV(O)(trpy)(5,5’-F2-bpy)]2+ reveals a clear elongation of
the Ru-N bond located in the trans position to the oxo group,
documenting the weakness of this bond which promotes the release
of the bpy ligand and the subsequent formation of 32+.

Introduction

[a]

[b]

[b]

A. Keidel, J. Staffa, Dr. U. Kuhlmann, Prof. Dr. P. Hildebrandt
Institut für Chemie Department
Technische Universität Berlin
Sekr. PC14, Straße des 17. Juni 135
D-10623 Berlin 1
E-mail: Hildebrandt@chem.tu-berlin.de
Dr. I. López, Dr. F. Bozoglian, Dr. C. Gimbert-Suriñach, Dr. J. BenetBuchholz, Prof. Dr. A. Llobet
Institute of Chemical Research of Catalonia (ICIQ)
Barcelona Institute of Science and Technology (BIST)
Av. Països Catalans, 16, 43007, Tarragona, Spain
E-mail: allobet@iciq.cat
Prof. A. Llobet
Departament de Química
Universitat Autònoma de Barcelona
Cerdanyola del Vallès, 08193 Barcelona, Spain
Supporting information for this article is given via a link at the end of
the document

The generation of molecular oxygen from water is one of the key
challenges in contemporary chemistry and it has been in the
focus of researchers for many decades. The research in this
field has strongly profited from the development of catalytically
competent well-defined transition metal complexes since they
allow for profound mechanistic studies. Single-site water
oxidizing catalysts (WOC) have gained strong interest, starting
with the synthesis and characterization of the first active
mononuclear ruthenium complex by Thummel et al.[1]
Subsequent mechanistic studies by Meyer et al.[2-4] have led to a
proposal of the catalytic pathway in which the key O-O bond
formation step results from a water nucleophilic attack on the
RuV=O unit (Figure 1). It is assumed that this mechanism holds
for a variety of mononuclear Ru catalysts from
[Ru(trpy)(bpy)(H2O)]2+ (12+) (where trpy is 2,2’:6’,2”-terpyridine
and bpy is 2,2’-bipyridine) analogues[5,6] to single site Ru
polyoxometalates,[7] and may also provide a description of
molecular catalysts involving iridium[8] and other first-row
transition metals.[9,10] Substantial efforts have been made to
identify the proposed metal peroxido and hydroperoxido
intermediates and possible side products via EPR, UV-vis and
vibrational
spectroscopy.
However,
a
comprehensive
characterization of all intermediates and an unambiguous
confirmation of the mechanism has not been achieved up to
now.[3,11] Additional information can be derived from kinetic
analyses, extended to compounds with modifications in the
ligand framework. For instance, Fujita et al.[12] and Yagi et al.[13]
have examined the effect of a pendant base on catalytic water
oxidation. They found a drastic decrease of the activity when the
base is placed next to the aquo ligand while the stereoisomeric
complex with a distant pendant base displays an improved
catalytic performance compared to 12+. We have also studied
the remarkable effect exerted by a proximal fluorine atom on the
Ru-aqua group of the complex.[6] The modified bipyridine ligand
forms a hydrogen bond with the active site which lowers the
activity. It is further worth mentioning that 2,2’-bipyridine N,Ndioxide has been observed as the main deactivation product
after catalysis with 12+ and using a large excess of
[(NH4)2Ce(NO3)6] (CeIV hereafter) as sacrificial oxidant,[14] which
points to the dissociation of the bpy ligand as an important
pathway of catalyst degradation. Finally Sakai et al. found kinetic

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."
evidence that the Ce(IV) might have a role in the O-O bond
formation pathway pointing out to a different reaction
mechanism.[15]
Recently, our group has demonstrated that 12+ and the
structurally related complex [Ru(trpy)(5,5’-F2-bpy)(H2O)]2+
(where 5,5’-F2-Bpy is 5,5'-difluoro-2,2'-bipyridine, 22+) are partly
converted into the new oxidatively rugged and active dinuclear
catalysts [(trpy)(5,5’-X2-bpy)RuIV(µ-O)RuIV(trpy)(O)(H2O)]4+ (X =
H, 1-dn4+; X = F, 2-dn4+) under catalytic conditions (Figure 1).[16]
This finding provided novel insight into the reactivity of so-called
single-site water oxidation catalysts and did not only question
the original mechanistic description of these catalysts but also
disclosed the true molecular nature of the species responsible

for the catalytic reaction. In this respect, two catalytic cycles run
concurrently, one involving mononuclear complexes and the
other one dinuclear complexes (Figure 1). The mononuclear
species are irreversibly converted into the dinuclear ones via
[RuVI(trpy)(O)2(H2O)]2+ (32+) that acts as a gate between the two
mechanistic cycles (Figure 1).
In this work, we have studied the spectroscopic and
electrochemical properties of 1-dn4+ and 2-dn4+. Using time
resolved resonance Raman (RR) spectroscopy, we analysed the
reactions of 12+ and 22+ with CeIV under stoichiometric and
turnover conditions to identify intermediates of the catalytic cycle.
The results are discussed on the background of the previously
proposed
two-cycle
mechanism.[16]

II

2+

2+

IV

IV

Figure 1. Left, Proposed reaction scheme for the water oxidation mechanisms by the monomeric Ru complexes 1 , 2 and dinuclear Ru Ru complexes 1dn4+ and 2-dn4+, the two cycles are connected through the intermediate 32+ according to previous results.[16] Polypyridyl ligands are omitted for clarity. Right,
Structural formulas of 12+, 22+, 32+, 1-dn4+ and 2-dn4+.

Results and Discussion
1—Synthesis and electrochemical properties of dinuclear
complexes

The synthesis of the dinuclear complexes 1-dn4+ and 2-dn4+ was
described previously.[16] Briefly, both compounds were prepared
by reacting equimolar amounts of trans-[RuVI(trpy)(O)2(H2O)]2+
(32+) and the corresponding mononuclear complex, 12+ and 22+,
in the presence of CeIV for two or three days. After filtration, the

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."
pure dinuclear compounds are isolated in moderate yields (40 –
50 %) (Eq. 1, polypyridyl ligands not shown).

In order to characterize the different oxidation states of the
dinuclear complexes, the electrochemical properties were
studied within a wide range of pHs.
The CVs of 1-dn4+ and 2-dn4+ in 0.1 M triflic acid (pH = 1) show
an electrochemically and chemically reversible wave (Ep,a – Ep,c
= 42 - 60 mV and ip,c/ip,a ≈ 1.0) followed by a chemically
irreversible wave (Figure 2). The first one is attributed to the 2electron reduction (as determined by coulometry) of the IV,IV to
the III,III oxidation state. This reduction is accompanied by a
double protonation of the terminal oxo groups as indicated in Eq.
2.

According to the relative peak height, the second wave is
consistent with another two-electron reduction process from the
III,III to the II,II oxidation state, which is associated with the
protonation on the oxo bridge in agreement with related
dinuclear III,III complexes (Eq. 3).[17-18]

The oxidation state II,II is unstable in acidic pH and is cleaved at
the oxo bridge, generating the corresponding mononuclear
complexes. This is reflected by new waves emerging after a
subsequent anodic scan and are thus attributed to the
mononuclear compounds 32+ and 12+ (or 22+). At pH > 4 the
reduction wave becomes chemically reversible suggesting that
the hydroxo-bridged complex is stable on the time scale of a CV
experiment (Figure S1).
Figure 2. CVs of 0.5 mM solutions in 0.1 M triflic acid (pH 1.0) for complexes
4+
4+
1-dn (top) and 2-dn (bottom). The insets show CVs where the potential
was switched before the irreversible reduction at E = 0.5 V. The asterisks mark
electrochemical features for the mononuclear complexes. A scan rate of 100
mV s‒1 was used.

The standard potentials for 1-dn4+, 2-dn4+ and several dinuclear
and mononuclear complexes are listed in Table 1. The potentials
for 1-dn4+and 2-dn4+ are quite similar (entry 1 vs. 2), despite the
electron-withdrawing fluorine atoms in the bpy ring of 2-dn4+
which only slightly affect the potentials (20 - 30 mV). A mixed
valence state III,IV, or III.5,III.5, which might be expected in view
of the strong electronic coupling through the oxo bridge,[17,20,21] is
not identified in the electrochemical experiments. This suggests

that E0(III,IV/III,III) ≥ E0(IV,IV/III,IV), i. e. the oxidation state III,IV
is unstable with respect to disproportion. In contrast, the
complex {[Ru(trpy)(bpy)]2(µ-O)}4+ where the terminal oxo and the
aquo ligands were replaced by the bidentate bpy ligand shows
only the III,IV/III,III couple in the anodic region and at higher
potential (entry 5 vs. 1 or 2). The wave corresponding to the
IV,IV/III,IV lies probably in a very high potential region where
also electrode oxidation occurs. These dramatically different
electrochemical properties reveal that the two aquo ligands in
the oxidation state III,III of 1-dn4+ or 2-dn4+ play a crucial role in
lowering the potentials since building-up a positive charge after
oxidation can be avoided by proton-coupled electron transfer
processes. Furthermore, the trans dioxo coordination in the
oxidation state IV,IV stabilizes this species, contributing to a
lowering of the potentials.[21,22]
The two-electron reduction wave assigned to the III,III/II,II couple
in 1-dn4+ and 2-dn4+ indicates that E0(II,III/II,II) ≥ E0(III,III/II,III)
such that the mixed valence state II,III is unstable with respect to
disproportion. Such a behavior in water has already been
observed for previously reported dinuclear oxo-bridged
complexes (entries 1 or 2 vs. 5).[17,18] The pH-dependence of the
potential for this couple shows that a proton is added upon
reduction (vide infra), probably by protonating the oxo bridge
group to form the corresponding hydroxo bridge in the oxidation
state II,II. Because the µ-oxo group is strongly basic in that
species, it is stabilized by protonation and consequently the
potential for the (undetectable) II,III/II,II couple is increased. The
standard potentials for this couple in 1-dn4+ and 2-dn4+ are
similar to that of {[Ru(trpy)(bpy)]2(µ-O)}4+, indicating that the
electrochemical process mainly refers to the Ru-O-Ru core. On
the other hand, the well-known oxo-bridged water oxidation
catalyst {[Ru(bpy)2(H2O)]2(µ-O)}4+, the blue dimer, differs from
the previously discussed structurally related complexes (entry 3
vs. 1, 2 or 5). It exhibits a one-electron irreversible reduction
from the oxidation state III,III to II,III where the latter is unstable
towards oxo bridge cleavage.
The dinuclear complex {[Ru(trpy)(H2O)]2(µ-bpp)}3+ (bpp = bis(2pyridyl)-3,5-pyrazolate) illustrates that the substitution of the oxo
bridge by a rigid aromatic ligand has drastic consequences on
the electrochemical properties. The standard potentials for the
IV,IV/III,III and III,III/II,II couples of {[Ru(trpy)(H2O)]2(µ-bpp)}3+
are higher than those for 1-dn4+and 2-dn4+ (entry 4 vs. 1 or 2).
This trend can be explained by simple electrostatic arguments,
since the bridging ligand µ-bpp is formally monoanionic while the
µ-oxo group is dianionic. It was found that the impact of this
difference is more pronounced for E0(III,III/II,II) than for

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."
E0(IV,IV/III,III). Thus, the low value of the potential for the
III,III/II,II couple explains why the oxo-bridged dinuclear
complexes are usually isolated in high oxidation states, typically
III,III.
The standard potentials for the IV,IV/III,III couple in 1-dn4+ and
2-dn4+ are slightly lower than the potentials for the IV/III or IV/II
couples of the related mononuclear complexes 12+ and 22+ (entry
1 vs. 6 and entry 2 vs. 7). However, the onset potential for the
electrocatalytic current is quite similar.
The formal potentials for the reduction of 1-dn4+ depend on the
pH due to the acid-base properties of the different oxidation
states (Eq. 2 and 3). This dependence was studied over a broad
pH range and is shown in the Pourbaix diagram depicted in

Figure 3. The figure contains the E1/2-pH values obtained from
CV experiments.
The straight line corresponding to the IV,IV/III,III couple displays
a constant slope of 59 mV/pH unit in the pH range studied here
(0 - 9). This value is consistent with a two-electron reduction with
the addition of two protons. Regarding the couple III,III/II,II, a
slope of approximately 30 mV/pH unit is observed in agreement
with a two-electron reduction accompanied by the addition of
one proton. Because both couples exhibit a constant slope in the
entire pH range, spectrophotometric determinations of the pKa
values for the oxidation states IV,IV and III,III were carried out
(Figure 4).

Table 1. Summary of reduction potentials (V vs. SSCE) for various dinuclear and mononuclear complexes at pH 1.
Dinuclear complexes
E

0

Complex[a]

III,IV/III,III

IV,IV/III,III

III,III/II,II

Eonset[b]

1

1-dn4+

---

0.78[d]

0.18[d,e]

1.45

Tw.[c]

2

2-dn

4+

---

0.80

[d,e]

1.47

Tw.

Entry

[d]

3

{[Ru(bpy)2(H2O)]2(µ-O)}4+

4

{[Ru(trpy)(H2O)]2(µ-bpp)}

0.88

0.98

5

{[Ru(trpy)(bpy)]2(µ-O)}

4+

1.08

0.21

> 1.17[f]

---

0.79

3+

Ref.

[c]

< 0.06[g]

19

0.62

[h]

--1.30

25, 26

---

27

[d,e]

0.21

Mononuclear complexes
E

0

Entry

Complex

III/II

IV/III

IV/II

V/IV

Eonset[b]

Ref.

6

12+

0.82

0.98

0.90

1.62

1.45

6, 24

7

22+

---

---

0.87[d]

1.68

1.48

6

8

3

0.47

0.87

0.67

> 1.03

---

22

2+

[i]

[a] Ligand abbreviation: bpp = bis(2-pyridyl)-3,5-pyrazolate. [b] Potential refers to the value where electrocatalysis starts. [c] Tw: this work. [d] Two electron
process. [e] Chemically irreversible process; the indicated potential corresponds to Ep,c -0.015 V. [f] The oxidation state IV,IV is unstable with respect to
0

0

0

disproportion. Thus, E is estimated considering that E (IV,IV/III,IV) > E (V,V/III,IV) where the latter is 1.22 V. [g] The oxidation state II,III undergoes oxo
0

0

bridge cleavage on the time scale of the CV; however, E (III,III/II,II) cannot be lower than E (III,III/II,III). [h] The wave associated with the IV,IV/III,IV couple is
electrochemically irreversible; thus, E1/2 was estimated taking Ep,a-0.03 V. [i] The oxidation state V is unstable with respect to disproportion; thus this E0 must
be larger than E0(VI/IV) = 1.03 V.

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."
evidenced by the standard potentials (Table 1) and the UV-vis
spectra (Figure S3 and Table S1).
The pKa value associated with the oxidation state II,II must be
similar to that of the III,III state to account for the constant slope
of this couple for the same reasons outlined above for IV,IV/III,III.
However, we could not determine this quantity due to the
previously discussed instability of this oxidation state with
respect to oxo bridge cleavage. The release of the proton is
ascribed to one of the aquo ligands rather than from the hydroxyl
group, in line with conclusions drawn from studies of structurally
related complexes.[17]

4+

Figure 3. Pourbaix diagram for 1-dn . The potential-pH regions where the
various oxidation states are the dominant forms are indicated. The vertical line
represents the pKa values obtained by spectrophotometric titrations. E1/2
values were obtained by CV using a scan rate of 100 mV cm‒1.

The acid-base titration of IV,IV showed distinct isosbestic points
at 363, 415, 481 and 707 nm and the pKa(IV,IV) was calculated
to be 4.4. The acid-base titration of the III,III derivative was
determined using a solution of the complex obtained by
coulometric reduction of the initial IV,IV form yielding a pKa(III,III)
of 4.3. In this case, the UV-Vis spectra show more subtle
changes as it has been previously observed in the oxidation
state III,III of the blue dimer.[18] The close similarity between both
pKa values explains why the slopes of the Pourbaix diagram for
the two redox couples remain unmodified in the entire pH range.
Deprotonation of IV,IV would result in a change of the slope for
the redox IV,IV/III,III couple from -59 mV/pH unit (2 e-/2 H+
exchanged) to -29 mV/pH unit (2 e-/1 H+ exchanged) but
deprotonation of III,III at near the same pH affords again an
exchange of 2 protons in the couple. Instability of 1-dn4+ above
pH 9.50, probably because of dimerization reactions, prevents
us from obtaining reliable measurements at basic pHs.
The pKa for the oxidation state IV,IV of 2-dn4+ was also
determined spectrophotometrically in order to gain insight into
the influence of the bpy ligand on the acid-base properties of the
dinuclear complexes (Figure S2). The calculated pKa (4.0) is
lower than that found for 1-dn4+ as expected from the electronwithdrawing effect of the fluorine substituents in the bpy ligand.
The same behavior has been reported for the mononuclear
parent complexes 12+ and 22+.[6] However, the effect is smaller in
the dinuclear complexes because the bpy ligand has a weaker
influence on the electronic structure of the complex as

Figure 4. Top, Acid-base spectrophotometric titration of the oxidation state
4+
IV,IV (left) and III,III (right) of 1-dn after consecutive additions of 1 - 5 µL of
6.16 M NaOH to a 25 µM solution of the complex in 0.1 M H3PO4 / NaH2PO4
buffer at pH 2.15. pH changes for the titration of IV,IV: 2.32, 2.52, 2.78, 3.29,
3.41, 3.70, 4.04, 4.26, 4.60, 4.79, 5.03, 5.21, 5.44, 5.73 and 5.95. pH changes
for the titration of III,III: 2.94, 3.33, 3.52, 3.78, 4.65 and 5.22. Bottom,
Calculation of the pKa value of the oxidation state IV,IV from the absorbance at
519 nm (left) and of the oxidation state III,III from the absorbance at 727 nm
(right).

The interpretation of the Pourbaix diagram (Figure 3) is
supported by the RR spectra of the oxidation states IV,IV and
III,III (Figure 5). The spectrum of IV,IV, obtained with 514 nm
laser excitation, is dominated by a strong band at 803 cm‒1. In
our previous work, this band was assigned to a mode including
the stretching of the terminal Ru=O bond, consistent with the ca.
40 cm‒1 18O/16O isotopic shift.[16] A closer inspection reveals an
additional weak band on the high-frequency side (833 cm‒1)
which also falls into the region expected for Ru=O stretching.
Upon 413 nm laser excitation, this latter band is preferentially

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."
enhanced compared to the 803 cm‒1 band. Thus, we conclude
that the Ru=O and Ru-O-Ru stretching coordinates are strongly
coupled, giving rise to two closely spaced modes at 803 and 833
cm‒1 with different excitation profiles. Conversely, no 18O/16Osensitive bands were observed in the region between 350 and
400 cm‒1. Thus, the RR spectroscopic signature of the Ru=O
and Ru-O-Ru containing modes is quite different in the IV,IV
state of 1-dn4+ as compared to the corresponding ruthenium
“blue dimer” species which displays “pure” (symmetric) Ru-O-Ru
and Ru=O stretching modes at ca. 369 and 818 cm‒1
respectively, in its formal V,IV oxidation state.[28,29]
Upon reduction of the IV,IV form of 1-dn4+ to the III,III state by
addition of 2 equivalents of Mohr’s salt, (NH4)2Fe(SO4)2, the RR
intensities of the bands at 803 and 833 cm‒1 are strongly
decreased (Figure 5C) consistent with the lack of a Ru=O
function as concluded from the Pourbaix diagram (Figure 3).

OH2 state, namely RuIV=O and RuV=O (Figure 1). Here we
succeeded to obtain single crystals suitable for X-Ray diffraction
analysis of the RuIV=O intermediate [RuIV(O)(trpy)(5,5’-F2-Bpy)]2+
that is obtained from the removal of two protons and two
electrons from 22+. The corresponding ORTEP plot is shown in
Figure 6. The structure consists of a RuIV with distorted
octahedral geometry with coordinated trpy, bpy and terminal oxo
ligands. The oxo ligand displays a Ru-O distance of 1.85 Å that
confirms its double bond character as it falls within the range of
previously reported related complexes.[27,30-36] The complex
crystallizes with a solvent water molecule that is hydrogen
bonded to the oxygen atom of the Ru=O group (Ooxo-Owater =
2.674 Å; Ooxo-H = 1.982 Å; Owater-H = 0.859 Å; Ooxo-H-Owater =
136.59º). A particularly interesting feature of the structure is the
remarkable elongation of the Ru-N bpy bond of 2.14 Å located
trans to the Ru=O group. The same bond for the reduced
complex [RuII(trpy)(5,5’-F2-bpy)(H2O)]2+ (22+) is only 2.02 Å.6
These striking differences reflect the weakness of this Ru-N
bond, favoring bpy decoordination and water substitution as we
and others have suggested earlier.[14,16] An even larger effect
would be expected for the one electron oxidized species RuV=O,
that is proposed to undergo this bpy loss to generate 32+ as
shown in Figure 1.

Figure 6. ORTEP plot (ellipsoid drawn at 50% probability) of the X-ray
IV
2+
diffraction structure of dication {[Ru (O)(trpy)(5,5’-F2-bpy)]—H2O} generally
IV
2+
indicated as [Ru =O] in Figure 1. Color codes: Ru, cyan; O, Red; N, Blue; C,
black; F, green. H atoms are not shown except for a crystallized water
molecule forming a H-bond with the oxo group.
4+

Figure 5. RR spectra of 1-dn in the oxidation state IV,IV obtained with (A)
413 nm (blue) and (B) 514 nm excitation (black), compared with the RR
spectrum of (C) the III,III form of the complex, generated after the addition of 2
4+
equivalents of (NH4)2Fe(SO4)2 to the 1-dn (red), 514 nm excitation. “S” refers
to a Raman band of triflic acid. Details of the RR experiments are given in the
text.

2—The RuIV=O reactive intermediate
Critical species of single-site Ru-pyridyl type of catalysts are the
corresponding high oxidation states derived from the initial RuII-

3—Time-dependent resonance Raman (RR) experiments
RR spectra of the mononuclear complexes 12+ and 22+ were
measured with 413 nm laser excitation which is in resonance
with a metal-ligand charge transfer transition[5] presumably
involving the bidentate ligand (Figure 7A). As a consequence,
the vibrational band patterns differ quite substantially for 12+ and
22+ in the entire spectral range. Here we focused on the region
below 1000 cm−1 to monitor the modes containing coordinates of

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."
the oxygen ligands. For the reduced parental species, these
modes are not detectable as verified by the lack of any 18O/16Oand 2H/1H-sensitive bands.
3—1—Stoichiometric oxidation of RuII complexes
We first studied the stoichiometric oxidation of 12+, using two
equivalents of CeIV (Figure 7, left). Immediately after addition of
the oxidant, the band intensities of the RuII complex (i.e., at 667,
676, and 729 cm−1) strongly decreased with respect to the
solvent band whereas new bands at 719, 798, and 919 cm−1
appeared (Figure 7B). The stoichiometric oxidation of 22+ (Figure
7, right) offers a similar picture as far as the intensity loss of the
RuII bands and the concomitant increase of the product bands at
657, 719, 800, 879, and 919 cm−1 are concerned (Figure 7B).
Like the 798 cm−1 band of the oxidation product of 12+, the band
at 800 cm−1 of 22+ has decayed after 24 h (Figure 7C). The
temporal evolution of these bands after addition of CeIV indicates
that the stoichiometric oxidation of the mononuclear complexes
involves two spectroscopically detectable states, characterized
by the bands with red and green colored labels in Figure 7 B,C.
Essentially the same results were obtained upon addition of
three instead of two oxidation equivalents, except for a faster
decay of the 800 (798) cm−1 bands (red label) and a somewhat
larger contribution of the “green” species compared to the parent
states.
This band at 800 cm−1 is of particular interest since it can be
assigned to the mononuclear RuIV=O or RuV=O species (see
scheme in Figure 7, red labels), in line with the assignment for
related dinuclear complexes 1-dn4+ and 2-dn4+ also containing a
Ru=O group (see Figure 5, vide supra).[16] Indeed, isotopic
labeling experiments using H218O show the expected 40 cm-1
shift of the Ru=O resonance from 800 cm-1 to 760 cm-1 (Figure
S4).

Figure 7. RR spectra of 12+ and 22+ measured upon stoichiometric oxidation
IV
II
with 2 equivalents of Ce . (A) parental reduced Ru state; (B) 30 seconds
IV
IV
after addition of Ce ; (C) 24 h after addition of Ce . The spectra were
obtained with 413 nm excitation at room temperature. “S” refers to a Raman
band of triflic acid. The color code of the RR band labels is related to the
reaction scheme indicated at the top of the figure.

The nature of the oxidized species with resonances at 879 cm−1
(only for 22+) and 919 cm−1 (for both 12+ and 22+) was assessed
through the stoichiometric oxidation of 22+ in pure H216O or
H218O, and a 1:1 mixture of H216O and H218O (Figure 8). In this
case, the 18O/16O shift was only 6 cm−1 and thus much smaller
than that expected for a Ru=O containing modes (ca. 40 cm−1
band).[16] For the 1:1 mixture of H216O and H218O, a broad peak
is observed that evidently involves more than one band. The 919
cm−1 band lies within the range of the O-O fragment stretching
modes for which quite different values of ∆ʋ have been observed
in the past.[11,28] Although typical isotopic shift values of ca. 50
cm−1 are expected for a 18O/16O substitution in the O-O fragment,
distinctly smaller shifts below 20 cm−1 have been reported for Ru
compounds that were assigned to peroxo or superoxo
derivatives.[11] Such small shifts suggest a distribution of the O-O
stretching coordinate and thus of the isotopic shift among
several modes. Accordingly, this 919 cm−1 band can be ascribed
to the O-O stretching of either the RuIII hydroperoxo [RuIII-O-O-

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."
H]2+ or the RuIII superoxo [RuIII-O-O•]2+ intermediates (indicated
as green labels in the catalytic cycle depicted in Figure 7),[16]
which is in line with a previous suggestions.[3,15a] Moreover, the
H/D sensitivity of this band favors the assignment to the
hydroperoxo complex although the H/D shift cannot be
determined precisely (Fig. S5). All other bands originating from
the same peroxido complex, are attributed to modes of the
polypyridyl ligands since they did not display any 18O/16O shift
and are found at similar position as their counterparts in the
parent (reduced) complexes.

Figure 8. Section of the RR spectrum associated with the “O-O” fragment. The
spectra were obtained from solutions of 22+ and measured 24 hours after the
IV
addition of 2 equivalents of Ce in H216O (top), in a 1:1 mixture of H218O/H216O
(middle) and in H218O (bottom). The green color of the band labels is related to
the reaction scheme in Figure 7.

3—2—Oxidation of RuII complexes under turnover conditions
We studied the oxidation of the mononuclear complexes 12+ and
22+ under turnover conditions, i.e. at a large (100-fold) excess of
CeIV. This process is accompanied by the clearly visible
evolution of O2. Spectra were measured consecutively each 30
minutes after addition of the oxidant. Both complexes display the
same time-dependent behavior as illustratively shown for the
oxidation of 12+ (Figure 9). Thirty minutes after CeIV addition, the
characteristic bands of 12+, such as that at 676 cm−1, have

disappeared and new bands at 835 and 717 cm−1 have grown in.
After one hour, an additional band emerges at 799 cm−1 and
after ca. two hours the process has evidently reached
equilibrium concentrations. Thus, under turnover conditions, two
different Ru species are detectable in the RR spectra, an “early”
intermediate and a final product with the color labels yellow and
blue, respectively (Figure 9). No signal at 919 cm-1 attributed to
the O-O vibration was observed in any of the spectra.
To identify these two species, the RR spectra of the reaction
mixture at early (30 min) and late times (120 min) were
compared with those of separately synthesized and purified Ru
reference complexes (Figure 10). Complex 32+, that is suggested
to be the intermediate connecting the monomeric and the
dimeric water oxidation reaction cycles, shows a simple RR
spectrum with only five bands in the range between 300 and 900
cm−1(Figure 10B, yellow label). Four rather weak bands that are
at positions very similar to those of 12+, i.e. at ca. 685, and 734
cm−1, most likely originate from vibrational modes of the trpy
ligand (compare Figure 10A and 10B). The most intense band is
observed at 835 cm−1 and is readily attributed to a mode
including the O=Ru=O stretching coordinate.[21] Only this mode
can be identified in the “early” RR spectrum of the catalytic
process, implying that soon after the addition of excess CeIV the
RuVI-dioxo complex 32+ is formed. With increasing time, the 835
cm−1 band broadens concomitant to the growing-in of the 799
cm−1 band. The unusually broad shape of the 835 cm−1 band
indicates the involvement of several components with similar
frequencies. The comparison with the RR spectrum of isolated
1-dn4+ suggests that it is this dimer and closely related species
(compare Figure 10D and 10E, blue labels) that dominate the
RR spectrum at “late” times. Note that the 833 cm−1 band of the
isolated and purified dimer 1-dn4+ is slightly lower in frequency
than the O=Ru=O stretching mode of 32+ (835 cm−1). Thus, it
may well be that residual contributions of 32+ species also
contribute to the broadening of 835 cm−1 band.
3—3—Implications for the reaction mechanism
Time-resolved RR spectroscopy of a chemical reaction probes
the actual composition of the sample solution at given delay
times with respect to the addition of the oxidant. However, the
RR spectra do not reflect the true relative concentrations of the
reaction mixture, since at a given excitation line the relative and
absolute Raman cross sections of the individual species may be
quite different. For this reason and due to unfavorable kinetics
not all intermediate states that are involved can be detected in
the time-dependent RR experiments. For instance, the primary
oxidation product of RuII-OH2, i.e. RuIII-OH (or RuII-OH2 at pH 1),
is not detected at any time, although it has to be transiently
formed as proven by EPR spectroscopy.[11b]

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."
We first consider the stoichiometric oxidation of RuII which
requires hours to reach the chemical equilibrium. In the
presence of 2 and 3 equivalents of CeIV the originally proposed
reaction scheme (Figure 1) implies that the reaction can only run
up to the RuIV=O and RuV=O complexes. While the latter is EPR
active, the first is EPR silent so the best way to detect it is by
using rR spectroscopy due to strong signature of the Ru=O
vibrations. In fact, in both cases (2 and 3 equivalents of CeIV) we
note the formation of a Ru=O species from 12+ and 22+ in the first
spectra measured immediately after addition of the oxidant
(Figure 7B). These reactions may be rather fast (minute time
scale). However, under these conditions the Ru=O species can
slowly decay to the [RuIII-O-O⋅+]2+ or, more likely, [RuIII-O-O-H]2+

complex (Figure 7C), via the proposed disproportionation
reaction indicated in Eq. 4-5.

A pathway that we have previously found and discussed for
related complexes.[37] However other potential pathways for the
generation of [RuIII-O-O-H]2+ involving CeIV may exist as
proposed by Sakai et al. [15]

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."
2+

IV

II

Figure 9. RR spectra of 1 measured upon oxidation with excess (100 equivalents) of Ce . (A) parental reduced Ru state; (B) 30 min after addition; (C) 60 min
after addition; (D) 90 min addition; (E) 120 min after addition. The spectra were obtained with 413 nm excitation at room temperature. “S” refers to a Raman band
of triflic acid. The color code of the band labels is related to the reaction scheme depicted in the right of the figure.

This finding also implies that the monomeric 12+ and 22+
complexes are catalytically competent insofar as they catalyse
O-O bond formation from water. The identification of the O2releasing state to a RuIII (superoxo) hydroperoxo complex
confirms previous suggestions in the literature.[3,15a]
This disproportionation reaction seems to play only a minor role
upon oxidation of RuII with large excess of CeIV as the signal
attributed to [Ru-O-O]n+ type of complexes is very weak under
these conditions (Fig. S6). The spectrally prevalent species at
early times is instead the trans-dioxo RuVI complex 32+ that
according to the proposed scheme links the monomeric and
dimeric reaction cycle (Figure 1 and 9). Using a 100-fold excess
of CeIV, the reaction runs repetitively through the dinuclear cycle
under evolution of O2. Here the RR spectra only reveal
contributions from 1-dn4+ and 32+ (Figure 9 and 10). The failure
to detect other intermediates of the reaction scheme may either
be due to their low resonance enhancement or their short
lifetime due to fast decay kinetics. Consequently, the species
contributing to the RR spectra measured during turnover and
after consumption of all oxidizing equivalents are nearly the
same. It is important to keep in mind that the RR analysis does
not provide a quantitate analysis related to the relative amount
of the species in the reaction sequence and thus only give a
qualitative picture.
Altogether, the results of the present study are fully consistent
with the previously proposed reaction scheme (Figure 1),
demonstrating that formation of dinuclear complex 1-dn4+ is
essential for an efficient catalytic process, especially if long
lasting performance is needed for potential technological
applications.

Figure 10. RR spectra of 12+ measured upon oxidation with excess (100
equivalents) of CeIV, compared with the RR spectra of reference complexes.
2+
2+
2+
IV
2+
(A) pure 1 ; (B) pure 3 ; (C) 1 , 30 min after Ce addition; (D) 1 , 120 min
IV
4+
after Ce addition; (E) pure 1-dn . The right panel shows the RR spectra
between 770 and 870 cm−1 on an expanded view. The spectra were obtained
with 413 nm excitation at ambient temperature. “S” refers to a Raman band of
triflic acid. The color code of the band labels is related to the reaction scheme
in Figure 9.

Conclusions
In a previous study we demonstrated that single-site WOCs
structurally related to 12+ evolved to oxo-bridge dinuclear
complexes which are rugged catalysts. The presented work
constitutes a mandatory continuation where the electrochemical
and acid-base properties of the dinuclear compounds 1-dn4+ and
2-dn4+ have been thoroughly examined. 1-dn4+ shows two pHdependent 2 electron waves in cyclic voltammetry. The wave
attributed to the IV,IV/III,III couple is associated with the double
protonation of the terminal oxo ligand of IV,IV according to the
Pourbaix diagram. The second wave proceeds from the III,III/II,II
couple and is associated with protonation of the oxo bridge
ligand according to its pH-dependency. The pKa values of the
aquo ligands in IV,IV and III,III were determined
spectrophotometrically. Both values are quite similar (pKa(IV,IV)
= 4.4 and pKa(III,III) = 4.3), accounting for the constant slope for

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."
the two couples in the Pourbaix diagram. Additionally, the pKa
for the IV,IV oxidation state of 2-dn4+ was found to be slightly
lower than that for 1-dn4+ (4.0 vs. 4.4), which is consistent with
the electron-withdrawing effect exerted by the fluorine atoms of
the bpy ligand.
The conversion of 12+ to 1-dn4+ was studied thoroughly by in situ
RR spectroscopy after the addition of stoichiometric amounts or
an excess, that is under catalytic conditions, of CeIV. In the first
case we have observed two different species which can be
assigned to [Ru=O]n+ and [Ru-O-O]n+ type of complexes. Under
turnover conditions, the intermediate appearing immediately
after the addition of the oxidant was unambiguously identified as
the trans-dioxo complex 32+. The second species that
accumulated later during catalytic turnover is the crucial
dinuclear complex 1-dn4+. These findings support our previously
proposed mechanism and complete the characterization of most
of the envisaged intermediates.
Finally, the X-Ray structure of the oxidation state IV from 22+
evidences the proposed trans effect exerted by the oxo group
and that eventually leads to the release of the bpy ligand and the
consecutive formation of 32+. This critical process constitutes the
origin of the formation of the highly rugged dinuclear WOCs 1dn4+ and 2-dn4+.

Experimental Section
Materials. RuCl3—3H2O was supplied by Alfa Aesar and was used as
received. Trifluoromethanesulfonic acid (HOTf) was purchased from
CYMIT. All other reagents used in the present work were obtained from
Aldrich Chemical Co. and were used without further purification.
Reagent-grade organic solvents were obtained from SDS and high-purity
deionized water was obtained by passing distilled water through a
nanopure Milli-Q water purification system.
Preparations. [RuII(trpy)(bpy)(H2O)](PF6)2 (12+),[23] [RuII(trpy)(5,5’-F2bpy)(H2O)](PF6)2 (22+),[6] trans-[RuVI(trpy)(O)2(H2O)](PF6)2 (32+),[21]
[(trpy)(bpy)RuIV(µ-O)RuIV(trpy)(O)(H2O)](ClO4)4
(1-dn4+),[16]
and
[(trpy)(5,5’-F2-bpy)RuIV(µ-O)RuIV(trpy)(O)(H2O)](ClO4)4 (2-dn4+)[16] were
prepared as described in the literature. Warning. Perchlorate salts are
hazardous because of the possibility of explosion. They should be
prepared in small amounts, stored appropriately and not warmed above
40°C.
Samples for RR spectroscopy using 514 nm excitation were prepared by
mixing a 1 mM solution of 1-dn4+ in 0.1 M triflic acid (pH 1.0) with two
equivalents of (NH4)2Fe(SO4)2 (FeII in text). 100 µL of the reaction
solution were transferred to an aluminium crucible and subsequently
frozen in liquid N2. Then, the crucible was placed into a Linkam THMS
600 temperature-controlled cryostage to keep the temperature at -12 °C.
For RR measurements using 413 nm excitation, the complexes were
dissolved in triflic acid at pH 1.0 with a concentration of 1 mM. Spectra
were measured at ambient temperature. For determining 18O/16O isotopic
shifts, the experiments were carried out in H216O, H218O, and 1:1

mixtures of H216O and H218O. Oxidation of the Ru(II) complexes was
achieved by addition of [(NH4)2Ce(NO3)6] (CeIV in text).
Methods. UV/Vis spectroscopy was carried out with a Cary 50 (Varian)
UV/Vis spectrophotometer. Cyclic voltammetry (CV) and differential pulse
voltammetry (DPV) experiments were performed using a IJ-Cambria CHI660 or a Bio-Logic SP-150 potentiostat controlling a three-electrode cell.
Typical CV experiments were carried out at a scan rate of 100 mV s-1.
For DPV experiments, we used a pulse height and width of 50 mV and
50 ms, respectively. The step height and step time was set to 4 mV and
200 ms, respectively. A glassy carbon electrode (3 mm diameter) was
used as working electrode, platinum wire as auxiliary electrode, and a
SSCE or Hg/Hg2SO4 (sat. K2SO4) as reference electrode. Working
electrodes were polished with 0.05 micron alumina paste and rinsed with
distilled water and acetone followed by blow-drying before each
measurement. For activation of glassy carbon electrodes, a procedure
described by Meyer et al. was used.[38] All CVs presented in this work
were recorded in the absence of light and inside a Faraday cage. The
electrochemical experiments were carried out in 1 M HOTf (pH 0.0) or
0.1 M HOTf (pH 1.0). For higher pH values, different buffers were used,
NaH2PO4/H3PO4 (pH range 2.0 – 4.0), Na2HPO4/NaH2PO4 (pH range =
4.0 – 8.0), sodium tetraborate (pH range 8.0 – 9.5). In each case, the
ionic strength was set to 0.1 M. E1/2 values reported in this work were
estimated from the oxidative and reductive peak potentials in CV
experiments, i.e. (Ep,a + Ep,c)/2, or as the potential at maximum current
E(Imax) in DPV measurements.
RR spectra at 514 nm excitation were measured using a Renishaw inVia
Reflex RAMAN confocal microscope (Gloucestershire, UK), equipped
with an Ar ion laser. The spectrometer was equipped with a Peltiercooled CCD detector (-70°C) coupled to a Leica DM-2500 microscope.
Calibration was carried out with respect to the Raman spectrum of an Si
standard. Spectra were recorded with an accumulation of 5 x 20 s. A 10x
working distance microscope objective was used to focus the laser beam
(25 mW) onto the sample.
RR spectra with 413 nm excitation (Kr ion laser) were measured using a
confocal Raman spectrometer (LabRAM HR800, Horiba), equipped with
a liquid-nitrogen cooled CCD detector. The laser beam (10 mW) was
focused onto the sample contained in a rotating quartz cell. The total
accumulation time of the spectra was ca. 10 minutes at room
temperature. The spectral resolution was ca. 2 cm−1. Details of the
experimental set-up were described elsewhere.[39]
Single-Crystal X-Ray Structure Determination. Single crystals of
[RuIV(O)(trpy)(5,5’-F2-bpy)](PF6)2 were grown for 4 days after the
dropwise addition of an aqueous saturated NH4PF6 solution to a reaction
mixture of 3 equivalents of CeIV and 22+ in 0.1 M HOTf that was
previously left reacting for one day. All crystals were prepared under inert
conditions immersed in perfluoropolyether as the protecting oil for
manipulation.
Data collection. Crystal structure determination was carried out using a
Apex DUO Kappa 4-axis goniometer equipped with an APPEX 2 4K CCD
area detector, a Microfocus Source E025 IuS using MoKα radiation,
Quazar MX multilayer Optics as monochromator, and an Oxford
Cryosystems low temperature device Cryostream 700 plus (T = -173 °C).
Full-sphere data collection was used with ω and φ scans. Data collection
and reduction were carried out with the programs APEX-2 and Bruker
Saint19 V/.60A, respectively.[40,41]

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."
Structure Solution and Refinement. Crystal structure solution was
achieved using direct methods as implemented in SHELXTL[42] and
visualized using the program XP. Missing atoms were subsequently
located from difference Fourier synthesis and added to the atom list.
Least-square refinement on F2 using all measured intensities was carried
out using the program SHELXTL. All non-hydrogen atoms were refined
including anisotropic displacement parameters.

Acknowledgements

[14]

[15]

[16]

[17]
[18]

The work was supported by the Cluster of Excellence UniCat
and the IRTG 1524, funded by the DFG. A.L. thanks MINECO
(CTQ-2013-49075-R, SEV-2013-0319, CTQ2014-52974-REDC),
Feder Funds and AGAUR (2014 SGR 915), for financial support.
The Fotofuel Network of Excellence 2014 and the EU COST
actions CM1202 and CM1205 are also gratefully acknowledged.
IL thanks FPU for a PhD grant.
Keywords: peroxido • resonance Raman • ruthenium •
superoxido • water oxidation
[1]
[2]
[3]
[4]
[5]

[6]
[7]
[8]

[9]
[10]
[11]

[12]
[13]

R. Zong and R. P. Thummel, J. Am. Chem. Soc. 2005, 127,
12802-12803.
J. J. Concepcion, J. W. Jurss, J. L. Templeton and T. J. Meyer, J.
Am. Chem. Soc. 2008, 130, 16462-16463.
J. J. Concepcion, M.-K. Tsai, J. T. Muckerman and T. J. Meyer, J.
Am. Chem. Soc. 2010, 132, 1545-1557.
J. J. Concepcion, J. W. Jurss, M. R. Norris, Z. Chen, J. L.
Templeton and T. J. Meyer, Inorg. Chem. 2010, 49, 1277-1279.
D. J. Wasylenko, C. Ganesamoorthy, M. A. Henderson, B. D.
Koivisto, H. D. Osthoff and C. P. Berlinguette, J. Am. Chem. Soc.
2010, 132, 16094-16106.
S. Maji, I. López, F. Bozoglian, J. Benet-Buchholz and A. Llobet,
Inorg. Chem. 2013, 52, 3591-3593.
M. Murakami, D. Hong, T. Suenobu, S. Yamaguchi, T. Ogura and
S. Fukuzumi, J. Am. Chem. Soc. 2011, 133, 11605-11613.
J. D. Blakemore, N. D. Schley, D. Balcells, J. F. Hull, G. W. Olack,
C. D. Incarvito, O. Eisenstein, G. W. Brudvig and R. H. Crabtree, J.
Am. Chem. Soc. 2010, 132, 16017-16029.
D. J. Wasylenko, R. D. Palmer, E. Schott and C. P. Berlinguette,
Chem. Commun. 2012, 48, 2107-2109.
M.-T. Zhang, Z. Chen, P. Kang and T. J. Meyer, J. Am. Chem.
Soc. 2013, 135, 2048-2051.
(a) D. E. Polyansky, J. T. Muckerman, J. Rochford, R. Zong, R. P.
Thummel and E. Fujita, J. Am. Chem. Soc. 2011, 133, 1464914665. (b) Y. Pushkar, D. Moonshiram, V. Purohit, L. Yan, I.
Alperovich, J. Am. Chem. Soc. 2014, 136, 11938-11945. (c) J.
Honta, S. Tajima, T. Sato, K. Saito, T. Yui, M. Yagi, J. Photochem.
Photob. A: Chem. 2015, 313, 126-130.
J. L. Boyer, D. E. Polyansky, D. J. Szalda, R. Zong, R. P. Thummel
and E. Fujita, Angew. Chem. Int. Ed. 2011, 50, 12600-12604.
H. Yamazaki, T. Hakamata, M. Komi and M. Yagi, J. Am. Chem.
Soc. 2011, 133, 8846-8849.

[19]

[20]
[21]

[22]
[23]
[24]
[25]

[26]
[27]
[28]

[29]

[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]

D. J. Wasylenko, C. Ganesamoorthy, B. D. Koivisto, M. A.
Henderson and C. P. Berlinguette, Inorg. Chem. 2010, 49, 22022209.
a) A. Kimoto, K. Yamauchi, M. Yoshida, S. Masaoka, K. Sakai,
Chem. Commun. 2012, 48, 239-241; b) S. Masaoka, K. Sakai,
Chem. Lett. 2009, 38, 182-183.
I. López, M. Z. Ertem, S. Maji, J. Benet-Buchholz, A. Keidel, U.
Kuhlmann, P. Hildebrandt, C. J. Cramer, V. S. Batista and A.
Llobet, Angew. Chem. Int. Ed. 2014, 53, 205-209.
A. Llobet, P. Doppelt and T. J. Meyer, Inorg. Chem. 1988, 27, 514520.
A. Llobet, M. E. Curry, H. T. Evans and T. J. Meyer, Inorg. Chem.
1989, 28, 3131-3137.
J. A. Gilbert, D. S. Eggleston, W. R. Murphy, D. A. Geselowitz, S.
W. Gersten, D. J. Hodgson and T. J. Meyer, J. Am. Chem. Soc.
1985, 107, 3855-3864.
R. Schneider, T. Weyhermueller, K. Wieghardt and B. Nuber,
Inorg. Chem. 1993, 32, 4925-4934.
J. W. Jurss, J. J. Concepcion, J. M. Butler, K. M. Omberg, L. M.
Baraldo, D. G. Thompson, E. L. Lebeau, B. Hornstein, J. R.
Schoonover, H. Jude, J. D. Thompson, D. M. Dattelbaum, R. C.
Rocha, J. L. Templeton and T. J. Meyer, Inorg. Chem. 2012, 51,
1345-1358.
S. A. Adeyemi, A. Dovletoglou, A. R. Guadalupe and T. J. Meyer,
Inorg. Chem. 1992, 31, 1375-1383.
J. M. Mayer, Comments Inorg. Chem. 1988, 8, 125-135.
K. J. Takeuchi, M. S. Thompson, D. W. Pipes and T. J. Meyer,
Inorg. Chem. 1984, 23, 1845-1851.
F. Bozoglian, S. Romain, M. Z. Ertem, T. K. Todorova, C. Sens, J.
Mola, M. RodriÌ guez, I. Romero, J. Benet-Buchholz, X.
Fontrodona, C. J. Cramer, L. Gagliardi and A. Llobet, J. Am.
Chem. Soc. 2009, 131, 15176-15187.
S. Roeser, PhD Thesis, Universitat Rovira i Virgili, 2011.
I. López, S. Maji, J. Benet-Buchholz and A. Llobet, Inorg. Chem.
2015, 54, 658-666.
D. Moonshiram, J. W. Jurss, J. J. Concepcion, T. Zakharova, I.
Alperovich, T. J. Meyer and Y. Pushkar, J. Am. Chem. Soc. 2012,
134, 4625-4636.
a) J. K. Hurst, J. Zhou, Y. Lei, Inorg. Chem. 1992, 31, 1010-1017;
b) H. Yamada, J. K. Hurst, J. Am. Chem. Soc. 2000, 122, 53035311.
T. W. Welch, S. A. Ciftan, P. S. White and H. H. Thorp, Inorg.
Chem. 1997, 36, 4812-4821.
C. M. Che, T. F. Lai and K. Y. Wong, Inorg. Chem. 1987, 26, 22892299.
W.-C. Cheng, W.-Y. Yu, K.-K. Cheung and C.-M. Che, J. Chem.
Soc., Dalton Trans. 1994, 57-62.
C. M. Che, W. T. Tang, W. T. Wong and T. F. Lai, J. Am. Chem.
Soc. 1989, 111, 9048-9056.
T. Kojima, K. Nakayama, K. Ikemura, T. Ogura and S. Fukuzumi,
J. Am. Chem. Soc. 2011, 133, 11692-11700.
W.-C. Cheng, W.-Y. Yu, J. Zhu, K.-K. Cheung, S.-M. Peng, C.-K.
Poon and C.-M. Che, Inorg. Chim. Acta 1996, 242, 105-113.
E. L. Lebeau, S. A. Adeyemi and T. J. Meyer, Inorg. Chem. 1998,
37, 6476-6484.
R. Roeser, P. Farras, F. Bozoglian, M. Martínez-Belmonte, J.
Benet-Buchholz, A. Llobet, ChemSusChem 2011, 4, 197-207.

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."
[38]
[39]

G. E. Cabaniss, A. A. Diamantis, W. R. Murphy, R. W. Linton and
T. J. Meyer, J. Am. Chem. Soc. 1985, 107, 1845-1853.
H. K. Ly, T. Utesch, I. Díaz-Moreno, J. M. García-Heredia, M. Á.
De La Rosa and P. Hildebrandt, J. Phys. Chem. B 2012, 116,
5694-5702.

[40]
[41]
[42]

Data collection with APEX II, v2009.1-0.2, Bruker AXS Inc.,
Madison, Wisconsin, USA, 2009.
Data reduction with Buker SAINT V7.60A, Bruker AXS Inc.,
Madison, Wisconsin, USA, 2007.
G. Sheldrick, Acta Crystallographica Section A 2008, 64, 112-122.

"This is the peer reviewed version of the following article:

Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes,which has been published in final form at
http://onlinelibrary.wiley.com/doi/10.1002/cssc.201601221/abstract
This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving."

The conversion of single-site water
oxidation catalysts of type 12+ into
the more rugged dinuclear
derivatives of type 1-dn4+ has been
studied with time resolved
resonance Raman spectroscopy.
Key intermediates of the
mononuclear and dinuclear water
oxidation catalytic cycles have been
identified. The electrochemistry of
1-dn4+ has been examined in detail
showing a strong pH dependent
redox events. The bridging and
terminal oxo ligands play a crucial
role in the redox properties of the
dinuclear catalysts.

Anke Keidel, Isidoro López,Jana
Staffa, Uwe Kuhlmann, Fernando
Bozoglian, Carolina GimbertSuriñach, Jordi Benet-Bucholz, Peter
Hildebrandt,* and Antoni Llobet*
Page No. – Page No.
Electrochemical and Resonance
Raman Spectroscopic Studies of
Water-Oxidizing RutheniumTerpyridyl-Bipyridyl Complexes