Influence of the protonic state of an imidazole-containing ligand on the electrochemical and photophysical properties of a ruthenium(II)-polypyridine- type complex

Article abstract of DOI:10.1002/chem.200700185

The synthesis and characterisation of [Ru(bpy)₂(PhenImHPh)] ^2:+ where PhenlmHPh represents the 2-(3,5-di-tert-butylphenyl) imidazo[4,5-f|-[1,10]phenanthroline ligand are described. The compounds issued from the three different protonic states of the imidazole ring [Ru(bpy) ₂-(PhenImPh)]⁺ (I), [Ru(bpy)₂(PhenImHPh)] ²⁺ (II) and [Ru(bpy)₂(PhenImH₂Ph)]³⁺ (III) were isolated and spectroscopically characterised. The X-ray structures of [Ru(bpy)₂(PhenImPh)](PF₆)·H₂O· 6MeOH, [Ru(bpy)₂-(PhenImHPh)](NO₃)₂· H₂O₃ MeOH and [Ru(bpy)₂(PhenImH ₂Ph)](PF₆)₃· 5H₂O are reported. Electrochemical data obtained on these complexes indicate almost no potential shift for the Ru^III/II redox couple. Therefore a Coulombic effect between the imidazole ring and the metal centre can be ruled out. The monooxidised forms of I and II have been characterised by EPR spectroscopy and are reminiscent of the presence of a radical species, The emission properties of the parent compound [Ru(bpy)₂(PhenImHPh)]²⁺ were studied as a function of pH and both the lifetimes and intensities decreased upon deprotonation. Photophysical properties, investigated in the absence and presence of an electron acceptor (methylviologen), were distinctly different for the three compounds. Transient absorption features indicate that unique excited states are involved. Theoretical data obtained from DFT calculations in water on the three protonic forms are presented and discussed in the light of the experimental results.

Full text of DOI:10.1002/chem.200700185

FULL PAPER
DOI: 10.1002/chem.200700185
Influence of the Protonic State of an Imidazole-ContainingLigand on the
Electrochemical and Photophysical Properties of a Ruthenium(II)–
Polypyridine-Type Complex
Annamaria Quaranta,[a] Fabien Lachaud,[b] Christian Herrero,[a] RØgis Guillot,[b]
Marie-France Charlot,*[b] Winfried Leibl,*[a] and Ally Aukauloo*[a, b]
Abstract: The synthesis and characteri-
sation of [Ru
(bpy)2(PhenImHPh)]2+
where PhenImHPh represents the 2-
(3,5-di-tert-butylphenyl)imidazo[4,5-f]-
ACHTREUNG[1,10]phenanthroline ligand are de-
5H2O are reported. Electrochemical
data obtained on these complexes indi-
cate almost no potential shift for the
RuIII/II redox couple. Therefore a Cou-
lombic effect between the imidazole
ring and the metal centre can be ruled
out. The monooxidised forms of I and
II have been characterised by EPR
spectroscopy and are reminiscent of
the presence of a radical species. The
emission properties of the parent com-
(bpy)2(PhenImHPh)]2+ were
pound [RuACHTREUNG
A
studied as a function of pH and both
the lifetimes and intensities decreased
upon deprotonation. Photophysical
properties, investigated in the absence
and presence of an electron acceptor
(methylviologen), were distinctly differ-
ent for the three compounds. Transient
absorption features indicate that
unique excited states are involved.
Theoretical data obtained from DFT
calculations in water on the three pro-
tonic forms are presented and dis-
cussed in the light of the experimental
results.
AHCTREUNG
scribed. The compounds issued from
the three different protonic states of
the
(PhenImPh)]+ (I), [Ru
ImHPh)]2+ (II) and [Ru
ImH2Ph)]3+ (III) were isolated and
spectroscopically characterised. The X-
ray structures of [Ru(bpy)2A(Phen-
ImPh)](PF6)·H2O·6MeOH, [Ru(bpy)2-
(PhenImHPh)](NO3)2·H2O·3MeOH
and [Ru(bpy)2(PhenImH2Ph)](PF6)3·
imidazole
ring
[Ru
(bpy)2(Phen-
ACHTRE(UGN bpy)2(Phen-
ACHTRE(UNG bpy)2-
G
ACHTREUNG
H
ACHTREUNG
A
CHTREUNG
Keywords: density functional calcu-
lations · imidazole · photophysical
studies · protonic states · ruthenium
ACHTREUNG
A
ACHTREUNG
A
ACHTREUNG
Introduction
the realms of this coordination metal complex core stem
from its high chemical stability and its exceptional photo-
physical properties.[1,2] Domains extending from electron-
and energy-transfer processes to molecular switches, are all
based on the well known metal-to-ligand charge transfer
Even after decades of intensive investigations, rutheni-
um(II)–polypyridine-type complexes (with [Ru
(bpy)3]2+ as
the prototype complex) are still opening new avenues in
modern coordination chemistry and photochemistry. Indeed,
G
ACHTREUNG
(MLCT) transitions within this family of complexes.[3–8]
most important electronic feature of [Ru
(bpy)3]2+ is that the
A
AHCTREUNG
lowest excited states are of metal-to-ligand charge transfer
character. Upon irradiation in this absorption band, a long-
lived excited state (ꢀ600 ns) is reached where the electronic
distribution is best described as the presence of a RuIII ion
and one electron on the bpy ligands.[9–11] The fact that this
state can be quenched through a bimolecular pathway,
either by an electron acceptor to generate the highly oxidis-
ing RuIII species or by an electron donor to give the formal
[a] Dr. A. Quaranta, C. Herrero, Dr. W. Leibl, Prof. Dr. A. Aukauloo
iBiTec-S, CEA Saclay, Bât. 532
91191 Gif-sur-Yvette Cedex (France)
E-mail: winfried.leibl@cea.fr
aukauloo@icmo.u-psud.fr
[b] F. Lachaud, Dr. R. Guillot, Dr. M.-F. Charlot, Prof. Dr. A. Aukauloo
Laboratoire de Chimie Inorganique
ACHTREUNG
reducing RuI form has prompted the use of [Ru(bpy)3]2+
Institut de Chimie MolØculaire et des MatØriaux
d’Orsay UMR CNRS 8182, Univ Paris-Sud
91405 Orsay Cedex (France)
complex as the promising candidate in the field of photoin-
duced electron transfer studies.[12–15] More sophisticated sys-
tems have been developed where this photoactive module
was covalently linked to an electron acceptor or donor.
E-mail: mcharlot@icmo.u-psud.fr
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2007, 13, 8201 – 8211
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
8201

These diads were elaborated to duplicate the early events in
the conversion of light into chemical energy in the reaction
centre of photosynthetic systems.[16] In doing so, chemists
have overcome the diffusion limits between the donor and
acceptor partners and have also gained a better control on
the directionality of electron transfer from the donor to the
acceptor side. Continuous research is devoted to fine tune
both the intramolecular distance between the integrated
modules and the nature of the organic spacer, which are cru-
cial parameters for the control of electron transfer rates and
understanding the pathways of the electron flow.
Experimental and Theoretical Results
Synthesis: The ligand PhenImHPh was prepared following a
well established imidazole synthetic procedure.[23] An equi-
molar mixture of phenanthrolinedione and 3,5-di-tert-butyl-
benzaldehyde were heated under reflux in glacial acetic acid
containing an excess of ammonium acetate. The compound
precipitated as a yellow powder upon cooling. Metathesis of
the chloride ions from the RuCATHRE(UNG bpy)2Cl2 source to nitrate
ions was realised prior to metallation of the phenanthroline
end of the ligand. A methanolic solution of the RuII salt was
heated to reflux in the presence of the ligand. The target
Our laboratory is involved in the development of molecu-
lar assemblies composed of a photoactive chromophore and
a metal complex, the latter being capable of storing oxida-
tive or reductive equivalents. En route towards these target
systems, we have prepared and characterised different heter-
oditopic ligands.[17,18] Recently, we have reported on the syn-
thesis of an imidazole–phenol containing ligand covalently
compound [RuACTHERNGU(bpy)2(PhenImHPh)]ACHTREU(NG PF6)2 was isolated upon
addition of an excess of NaPF6 in a concentrated solution of
the reacting mixture and was purified by column chromatog-
raphy on neutral alumina. The protonated form [Ru-
ACHRTE(UNG bpy)2(PhenImH2Ph)]AHCTRE(UGN PF6)3 could be isolated by addition of
a dilute solution of HNO3 followed by an excess of NaPF6
salt. The deprotonated form was isolated after treatment
with sodium methoxide.
linked to the [RuACHTREUNG
(bpy)3]2+ chromophore as a biomimetic
model of the His190/TyrZ pair of amino acid residues, which
are involved in the catalytic cycle of light-driven water oxi-
dation in photosystem II.[19] A photoinduced electron trans-
fer to an external acceptor (MV2+) was observed to gener-
ate the phenoxyl radical concomitantly to the reduction of
the photogenerated RuIII. Under identical experimental con-
ditions, a rapid intramolecular reduction of the photogener-
ated RuIII was evidenced for a related compound lacking the
phenol function. It was suspected that in this case the imida-
zole ring fused to the phenanthroline was the electron
donor site. As the imidazole ring is the connecting fragment
in this organised assembly of components, we have been in-
terested in elucidating the primary electrochemical and pho-
X-ray structures: The crystal structures of the three different
protonated forms of the ruthenium complex were obtained.
We summarise here the main crystallographic parameters.
X-ray data revealed that the parent compound II is de-
scribed
(bpy)2(PhenImHPh)]
of the monomeric [Ru
in Figure 1. ORTEP views of the cationic complexes [Ru-
(bpy)2A
(PhenImPh)]+ and [Ru(bpy)2(PhenImH2Ph)]2+ are re-
with
a
chemical
(NO3)2·H2O·3MeOH. An ORTEP view
(bpy)2(PhenImHPh)]2+ unit is shown
formula
of
[Ru-
N
ACHTREUNG
AHCTREUNG
G
U
ACHTREUNG
ported in the Supporting Information.
A selection of the bond lengths and angles for the units
tophysical behaviour of the [Ru
complex which contains only the lumophore and the spacer
2-[(3’,5’-di-tert-butylbenzene)]imidazo[4,5-f][1,10]-phenanthro-
line (PhenImHPh). Such a family of ligands has been used
A
[Ru
[Ru
R
(PhenImPh)]+, [Ru(bpy)2(PhenImHPh)]2+ and
2ACHRTEUNG ACHTREUGN
AHCTREUNG
A
N
In all cases, the coordination sphere around the metal ion
can be best described as a trigonally distorted octahedral ge-
ometry. The angles around the ruthenium centre deviate sig-
nificantly from ideal octahedral geometry as a result of the
constraints imposed by the five-membered chelate rings.
ACHTREUNG
in the studies on the interaction between transition-metal
complexes and DNA.[20–22]
In order to shed light on the influence of the protonic
states of the imidazole ring on both the ground and excited
states properties of the chromophore/spacer system, we
ꢁ
The average Ru N bond length is 2.058, 2.055 and 2.063Š
for I, II and III, respectively. These values fall within the
have also isolated and characterised [Ru
A
(bpy)3]2+ (2.056 Š) and
same range as those found for [RuACHTREUNG
A
N
related compounds[24] supporting the fact that the protonic
states of the ligand do not influence the coordinating prop-
erties of the latter to the ruthenium(II) centre. The torsional
angle between the imidazole and the phenyl ring is found to
be around 17 and 148 for I and II, respectively while it is
38.58 for III. The larger value, when compared with I and II,
can be attributed to the steric hindrance between the pro-
tons on the nitrogen atoms of the imidazole and those on
the phenyl rings. In the X-ray analysis of III, two types of
water molecules of crystallisation are identified. Four mole-
cules of water are not involved in the close interaction with
either the cation or the anion. While three molecules of
water are intercalated between the NH group of the imida-
zolium ring of two contiguous monomeric units leading to
the existence of a hydrogen-bonding network between the
the first compound, the secondary amino group is in the de-
protonated state, while in the second the imino nitrogen of
the imidazole ring is protonated (see below).
and the corresponding deprotonated derivative, I and pro-
tonated form III, have been also characterised by X-ray dif-
fraction technique. The photophysical properties for the
three different protonic states were investigated in aqueous
solutions at different pH and revealed distinct effects on
functional properties of the ensemble. To rationalise the ex-
perimental results we will compare them with the theoreti-
cal data from DFT calculations obtained on the three water
(bpy)2(PhenImHPh)]2+
solvated protonic forms of [RuCAHTREUNG .
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Ruthenium–Polypyridine Complexes
FULL PAPER
Figure 2. Hydrogen network bonding running between contiguous [Ru-
AHCTRE(UNG bpy)2(PhenImH2Ph)] entities and water molecules.
121.2(5) and 112.6(2)8, respectively) confers a zig–zag con-
figuration to the one dimensional hydrogen-bonding net-
work.
1H NMR and UV-visible spectra: The protonation and de-
protonation steps of the parent complex II were monitored
1
by H NMR spectroscopy (see Supporting Information). Not
surprisingly, upon protonation, a deshielding of the signals
for the imidazole containing ligand was observed while an
upfield shift of these signals was perceptible upon deproto-
nation. A small effect was also depicted for the protons in
ortho-position of the bpy ligands. The major shift (0.2 ppm)
was observed for the aromatic proton in para-position to the
imidazole ring from the deprotonated to the protonated
state. This experimental fact suggests that there is no drastic
electronic reshuffling upon these chemical processes.
Figure 1. ORTEP drawing of [Ru
3MeOH with partial atom numbering.
ACHRTNUEG(bpy)2(PhenImHPh)]AHCRTE(UGN NO3)2·H2O·
Table 1. Selected bond lengths [Š] and angles [8] for complexes [Ru-
(bpy)2A(PhenImPh)](PF6)·H2O·6MeOH (I), [Ru(bpy)2(PhenImHPh)]-
(NO3)2·H2O·3MeOH (II) and [Ru(bpy)2(PhenImH2Ph)](PF6)3·5H2O
A
G
A
ACHTREUNG
A
N
ACHTREUNG
(III).
The electronic absorption spectrum of II in an organic sol-
vent such as acetonitrile is composed of three sets of bands,
one intense band at high energy corresponding to the p–p*
transitions of the bpy ligands and a double-humped band in
the visible region corresponding to the MLCT transitions in
I
II
III
ꢁ
Ru N1
2.0632.059
2.0632.068
2.047
2.055
2.055
2.061
1.352
1.352
2.058
2.068
ꢁ
Ru N2
ꢁ
Ru N32.061
2.053
ꢁ
Ru N4
2.054
2.052
2.054
1.355
1.364
79.6(5)
78.5(5)
78.9(8)
2.070
2.065
2.064
1.351
(bpy)3]2+ (Figure 3).
analogy to the spectrum of the [RuACHTREUNG
ꢁ
Ru N5
ꢁ
Ru N6
However, the spectrum presents unique features like the
band at around 340 nm and the shoulder to the MLCT band
tailing up to 550 nm which may be attributed to transitions
involving the PhenImHPh ligand.
ꢁ
C4 N7
ꢁ
C4 N8
1.338
N1-Ru-N2
N3-Ru-N4
N5-Ru-N6
80.0(8)
78.9(7)
78.9(7)
79.5(2)
78.9(9)
78.1(0)
The spectral features for the deprotonated form are simi-
lar to those of the parent compound. Nevertheless, we no-
ticed a decrease of intensity of the p–p* transitions at high
energy together with an increase in the intensity of the ab-
sorption band at 340 nm. It is worthwhile to note that the
shoulder to the MLCT band still persists for the deprotonat-
ed state. In the case of the protonated state, two main
changes are observed on the electronic absorption spectrum
in that both bands at 340 nm and the shoulder at 500 nm de-
crease in intensity. From this experimental data, we can ten-
tatively propose that those bands which fade upon protona-
tion are assigned to the PhenImHPh ligand in the coordina-
tion sphere of the ruthenium centre.[27] Notably the absorp-
tion spectra are modified in protic solvents like water and
monomeric cationic species. The availability of hydrogen-
bonding sites on each edge of the imidazolium ring (NH
group) leads to saturation of hydrogen bonds in one dimen-
sion as shown in Figure 2.
The hydrogen bond length
dACHTRE(UNG N-H-Ow1) is equal to
2.74(1) Š and is thus in the range of very strong hydrogen
bonds.[25] The Ow1 Ow3 and Ow2 are also involved in hydro-
ꢁ
gen-bonding interaction with an average separation of
2.77 Š.[26] The N-H-O motifs are almost linear with N-H-Ow1
and N-H-Ow2 bond angles between 173and 178 8. However,
the kink at the N-O-O angles (N-Ow1-Ow3 and N-Ow2-Ow3
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W. Leibl, M.-F. Charlot, A. Aukauloo et al.
the ligand when compared with the redox behaviour of the
ligand only (see Table 2). A shift of about 150 mV to less
positive potential is observed for the first anodic wave when
going from II to I, which was logically attributed to the
more easy oxidation of the deprotonated imidazole ring.
Under our experimental conditions, this wave gains in rever-
sibility in the case of I. This observation is most likely due
to the loss of the chemical step (proton release) following
the one electron-abstraction process in case of compound II.
An exhaustive one electron electrolysis was performed on I
and II at around 1.0 and 1.2 V versus SCE, respectively. The
reversibility of the redox process for compound I was justi-
fied by the observation of the same cyclic voltammogram
trace before and after electrolysis. The X-band EPR spec-
trum of the frozen sample of the oxidised form of I and II
indicates an isotropic signal centred at g=2.0024 in both
cases (see Supporting Information) with a peak-to-peak
through width of 0.78 mT. No hyperfine coupling is observed
not even with the nitrogen atoms of the imidazolate ring.[28]
This indicates that the spin density is not centred on the ni-
trogen atoms and is delocalised on a more extended p-skele-
ton. On the cathodic side of the cyclic voltammograms of
the three complexes no noticeable change is observed at
least for the first two reduction waves.
Figure 3. Absorption spectra in CH3CN for complexes I (g), II (c)
and III (a).
methanol (see Supporting Information). The experimental
observation is a decrease in intensity of both bands at 340
and 500 nm. This is also the case when methanol is added to
a solution of II in acetonitrile. Thus it is more likely that the
imidazole containing ligand is sensitive to protic solvents,
probably due to the formation of hydrogen bonds between
the imidazole and the molecules of solvent. Analogous
modifications of the ground state absorption spectrum are
observed in aqueous solution upon decrease of pH. The pK
values of the imidazole ring (pK1 3.1ꢂ0.3, corresponding to
deprotonation of the iminium fragment, and pK2 8.7ꢂ0.3,
corresponding to deprotonation of the secondary amine)
were obtained from titration experiments following the elec-
tronic spectral changes (see Supporting Information).
Photochemistry
Emission: The emission spectrum of II (between pH ꢀ3
and ꢀ9) exhibits a broad band with a maximum at 608 nm
and a shoulder at 695 nm (Figure 4). The observed emission
Electrochemistry: Electrochemical studies were performed
on the chemically isolated forms of I, II and III in dichloro-
methane and the data are collected in Table 2.
Table 2. Half-wave potentials for the reduction (NE) and oxidation (niE)
of ligand PhenImHPh and complexes I, II and III in CH2Cl2.
Compound
IIE[a]
IE[a]
iE[a]
iiE[a]
iiiE[a]
PhenImHPh
I
II
III
1.15[b]
0.85
1.64[b]
1.35[b]
1.36[b]
ꢁ1.65[b]
ꢁ1.65[b]
ꢁ1.65[b]
ꢁ1.35
ꢁ1.35
ꢁ1.35
1.43
1.46
1.46
1.00[b]
[a] Determined by CV at 100 mVsꢁ1; E=1/2 (Epa +Epc) in V versus SCE
in the presence of tetra-n-butylammonium perchlorate. [b] Irreversible.
Figure 4. Emission spectra in aqueous solution at pH 2.0 (III, a), 7.6
(II, c) and 10.5 (I, g) in mixed buffer solutions. Excitation wave-
length: 440 nm. Samples optically matched at 440 nm (A440 =0.1).
The most surprising observation on the anodic side of the
cyclic voltammograms of the three compounds (see Support-
ing Information) is that the redox potential of the RuIII/II
couple is almost unaltered upon remote protonation or de-
protonation of the imidazole unit. This result supports the
fact that no significant Coulombic effect is exerted on the
ruthenium ion by the charge carried on the imidazole ring.
Two oxidative processes are observed at lower potentials
than that of the RuIII/II redox couple for I and II. They are
assigned to the oxidation of the imidazole–phenyl part of
lifetime (tem), ꢀ800 ns, (see below for more detailed de-
scription of each component) is slightly longer than that of
[Ru
longer lifetime, the emission quantum yield (Fem =0.054) is
higher than that of [Ru
(bpy)3]2+ (Fem =0.042).[29]
(bpy)3]2+, for which tem =620 ns. Consistent with the
ACHTREUNG
AHCTREUNG
The protonation of the imidazole moiety to the protonic
state III does not alter the emission quantum yield and life-
time, although a red-shift in the emission maximum (lmax
=
622 nm at pH ꢀ2) is observed. From the inflection point in
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Ruthenium–Polypyridine Complexes
FULL PAPER
an emission maximum wavelength versus pH plot (see Sup-
porting Information) an apparent pK1* value of 2.4ꢂ0.3
was extracted. However, since a true thermodynamic acid–
base equilibrium is not necessarily established within the
lifetime of the excited state (< 1 ms), the correct pK1* value
for the imidazole protonation in the excited state is calculat-
ed using Equation (1)[30] based on the Fçrster thermodynam-
ic cycle:[31] and references therein
0:625
T
ð1Þ
*
pK1 ¼ pK1 þ
ðnBꢁnAÞ
In Equation (1) nB and nA, the wavenumbers of the 0–0 tran-
sition in the base and acid forms, were evaluated as the in-
tersection between the normalised absorption and emission
spectra. A pK1* value of 3.6 was obtained thus indicating
that the excited state is a slightly weaker acid than the
ground state (pK1 3.1). Deprotonation of the imidazole to
reach the protonic state I results in a red shift of the emis-
sion accompanied by a decrease in the emission quantum
yield (Fem =0.032) and lifetime (500 ns). The inflection
point in the emission maximum wavelength versus pH plot
gave an apparent pK2* 8.9ꢂ0.3, while the calculated Fçrster
value is pK2* 8.3, indicating that the excited state is a slight-
ly weaker base than the ground state (pK2 8.7).
A closer inspection of the emission kinetic traces obtained
upon excitation at 440 nm with ns laser pulses shows a gen-
erally biphasic decay containing a minor fast phase whose
amplitude relative to the slow phase is virtually independent
of pH (ꢀ25%, not shown). The lifetime of this fast phase is
ꢀ10 ns (close to time resolution) increasing to 30 ns for III.
The lifetime of the slow phase decreases from 900 to 500 ns
for increasing pH between pH 2 and 11, following a classical
titration curve with an apparent pK2* value of 8.2. The rela-
tive yield of the time resolved emission of the protonic state
I (calculated as the sum of the product of the relative ampli-
tudes and time constants for the different kinetic phases)
falls to about 40% of the neutral state. The decrease in the
emission yield indicates an apparent pK2* of 9.0.
Figure 5. Transient absorption spectra in Argon purged aqueous solutions
at pH 2 (10 mm citrate buffer), pH 7 (10 mm HEPES buffer) and pH 11
(10 mm CAPS buffer). Absorption changes taken 230 ns after laser pulse.
Excitation wavelength: 440 nm. Samples optically matched at 440 nm
~
*
(A440 =0.3); inset: kinetics at 460 nm at pH 2 (III, ), 7 (II, ) and 11
&
A
ed to some degree due to changes in sample concentration
related to the degassing procedure.[32]
Photoinduced electron transfer in the presence of an exter-
nal acceptor: In Figure 6, the kinetic traces of absorption
changes at two different wavelengths, 460 and 605 nm are
presented. These wavelengths are probes for the recovery of
+
the photogenerated RuIII to RuII and the presence of MV
respectively.
C
At pH 7, the depletion signal at 460 nm exhibits a much
shorter lifetime than MV +, indicating that the reduction of
C
RuIII to RuII is faster than re-oxidation of methyl viologen
+
MV to MV2+. This gives evidence that the recovery of
C
RuII involves a fast intramolecular electron transfer. The
low intensity and very fast reappearance of the MLCT band
at 460 nm at pH 11, indicates that RuIII is almost not evi-
denced on this time scale in the deprotonated form of the
Transient absorption: The excited state transient kinetics ob-
tained for the complex in its neutral and protonated forms
at pH 7 (II) and 2 (III), respectively, exhibit a monoexpo-
nential decay in the investigated range (400–900 nm) with a
lifetime t=(900ꢂ50) ns. At pH 11.0 (I), the excited state of
the complex in its deprotonated form has a lifetime of
(600ꢂ50) ns (see inset Figure 5). Those values are in good
agreement with the emission lifetimes.
The transient difference absorption spectra taken at
230 ns after excitation for I, II and III (Figure 5) exhibit typ-
(bpy)3]2+, that is, a
ical features related to the parent [RuACHTREUNG
negative band centred at 460 nm due to depletion of the
ground state MLCT absorption band, and a very weak tran-
sient absorption increase in the region 600–900 nm. For the
protonic state I, the bleaching in the 400–500 nm region ap-
pears to be strongly reduced. However, this decrease in am-
plitude of the absorption changes at high pH is overestimat-
Figure 6. Absorption change kinetics for complexes I, II and III at 460
and 605 nm in Argon purged aqueous solutions in the presence of 10 mm
MV2+. Excitation wavelength: 532 nm. Samples optically matched at
532 nm; A532 =0.3.
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W. Leibl, M.-F. Charlot, A. Aukauloo et al.
imidazole containing ligand. The absorption at 605 nm indi-
cates that methylviologen can still be efficiently reduced.
However, the nature of the excited state(s) responsible for
the reduction of MV2+ remains unclear. To characterise the
species after electronic excitation of the RuII centre, MV2+
served for compounds I, II and III, we will focus in this
paper on some of our theoretical results obtained for the
named compounds in a water surrounding such as i) the rel-
ative energies of the different type of molecular orbitals in
the ground state, ii) the nature of the low-lying excited sin-
glet states and iii) the nature of the lowest triplet state and
the singly oxidised forms. A more in detail analysis of the
impact of the surrounding medium will be reported in a
forthcoming paper.
(NH3)6]3+, a reversible electron accept-
was replaced by [RuACHTREUNG
or which is optically transparent in the visible region in both
forms. Immediately after irradiation, the transient absorp-
tion spectrum collected (see Supporting Information) indi-
cates an absorption band extending from 500 to above
600 nm which can be attributed to the formation of a neutral
imidazolyl radical.[33] For III, the decay of the kinetic traces
at 460 nm and 605 nm is very similar, supporting the fact
Energy levels and molecular orbitals in the ground state:
Some typical MOs of II, the parent compound for this study,
are given in the Supporting Information. A comparison of
the ground state MOs of the protonated (III) and deproton-
ated (I) complexes with compound II allows to establish a
correlation between the orbitals of the three complexes (see
Supporting Information). The striking evidence is the down-
shift in energy for all the orbitals located on the ligand upon
protonation, that is, a decrease of the electronic density on
this part of the molecule. In I the negative charge on the
imidazole–phenyl fragment is responsible for a HOMO de-
localised on L, while the HOMOs of II and III are dp orbi-
tals as mostly encountered in such complexes. For the same
reason, the LUMO is a combination of the p1* orbitals of
the two bipyridines in I and II but is the y orbital of local b
symmetry on phenanthroline in III.
that the recovery of the photogenerated RuIII to RuII in-
+
C
volves the re-oxidation of MV through a bimolecular reac-
tion, thus excluding any intramolecular electron transfer.
These experimental observations will be analysed in more
details below in the light of theoretical data.
Theoretical results: We have performed DFT calculations
for both the ground and selected excited states (see Charlot
et al.[9] and more experimental details in the Experimental
Section). As a prerequisite to these calculations the opti-
mised geometric parameters for the ground singlet state S0,
the lowest triplet state T1 and the lowest D0 doublet state of
the oxidised form were calculated at the (U)B3LYP/
LanL2DZ level for the three complexes. They are given in
the Supporting Information for states S0 and T1 of the three
complexes.
The mean difference in energy between the set of dp orbi-
tals and the LUMO is nearly the same that is, 3.41, 3.45 and
3.38 eV for I, II and III, respectively, in comparison to
3.39 eV that we have calculated in the same manner in
DFT calculations realised on isolated molecules (see
below) have allowed in many cases to bring conclusive infor-
mation in rationalising the physical behaviour of coordina-
tion metal complexes.[9] However, the extension of these
theoretical data from the gas phase to the experimental re-
sults in solution is often misleading. For instance, it has been
shown that the medium tends to spread the accumulation of
charges,[34] so that solvent effects may alter the electronic
state of molecules bearing different charges in a dissimilar
way. Indeed, electrostatic effects are often much less impor-
tant for species placed in a solvent with a high dielectric
constant than they are in the gas phase.[35] Recent theoreti-
cal work on ruthenium–polypyridine complexes have also
pointed out the importance of solvent effects to improve the
description of electronic spectra.[36–39] Henceforth, owing to
the dissymmetry of charges in our molecular systems studied
herein, we have analysed our chemical models in solution in
the framework of a self-consistent reaction field method
(SCRF). The polarizable continuum model (PCM)[40] was
used. This approach places the solute in a cavity defined by
the union of a series of interlocking atomic spheres within
the solvent represented as a polarisable dielectric. All calcu-
lations were hence repeated in water. This choice was
guided by the fact that all the photophysical experiments
were realised in an aqueous solution. Notably the time-con-
suming geometry optimisations in a water medium was
omitted for which convergence problems have been report-
ed.[41] In the aim to clarify the photophysical properties ob-
(bpy)3]2+. The HOMO–LUMO energy gap is
water for [RuACHTREUNG
2.84 eV in I, 3.36 eV in II and 3.28 eV in III, the small gap
for I resulting from the destabilisation of the HOMO on L.
Excited singlet states and electronic absorption spectra:
The low-lying singlet excited states of the three complexes
in their ground-state geometry were studied using time-de-
pendent DFT (TDDFT) calculations, a method which de-
scribes these states in terms of monoexcitations from occu-
pied to vacant MOs of the ground state. Our calculations in-
dicate that for I, the lowest excited singlet state S1 results es-
sentially from a HOMO to LUMO monoexcitation and is
hence a ligand-to-bipyridine charge transfer, abbreviated as
LBCT. In contrast, S2 to S6 states involve either LBCT or
charge shifts from the HOMO developed on the imidazole–
phenyl part of the ligand to the vacant p orbitals of the phe-
nanthroline moiety of the same ligand, that is, intraligand
charge transfers (ILCT). In the case of I, MLCT states are
encountered at higher energies. For II, S1 results essentially
from a charge transfer from dp to p1*
MBCT) while for III S1 is obtained by an excitation from
the highest dp MO toward y(phen) (MPCT).
ACHTRE(UNG bpy) (referred to as
AHCTREUNG
Lowest triplet state and oxidised complexes: The lowest
triplet state T1 of each compound was investigated using
spin-unrestricted UB3LYP/LanL2DZ calculations followed
by geometry optimisation in vacuo. Single point calculations
8206
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Ruthenium–Polypyridine Complexes
FULL PAPER
using this geometry were then performed with the PCM
model and water as medium. The same procedure was fol-
lowed for the ground doublet state D0 of the oxidised com-
plexes. The theoretical outcomes are reflected by the spin
density distributions and are reported in Figure 7 for the T1
and D0 states of the three complexes.
in all cases an emission band centred at around 610 nm. Our
calculated lowest triplet states for all three compounds
indeed show that they can be described as the charge sepa-
rated state found for the prototype ruthenium tris(bipyri-
dine) complex. The ruthenium ion is formally in a +III oxi-
dation state characterised by the absence of MLCT transi-
tions and absorption in the 400–460 nm region which is
much weaker than the absorption of the ground state. Con-
sequently, a bleaching is observed around 460 nm in the
transient spectra (see Figure 5). As RuIII possesses a local
unpaired spin, spin-orbit coupling may produce a radiative
3
luminescent decay from the lowest MLCT state as observed
in Figure 4 for the three complexes. However, other deacti-
vation paths may be efficient or changes of protonation may
occur.
On the basis of both experimental and theoretical results,
we now propose different schematic pathways for the inter-
pretation of the photoinduced electron transfer studies for
compounds I, II and III in the presence of an external elec-
tron acceptor. The map for the different electronic and pro-
tonic states for compound I is shown in Scheme 1.
Figure 7. Spin density distribution for the lowest triplet state and the oxi-
dised form of the three complexes calculated in water.
As depicted in Figure 7, all the T1 states can be viewed as
the distribution of one spin on the ruthenium while the
other is spread over the two coordinated bipyridines in
cases I and II or over the phenanthroline part of the ligand
for III. These calculated triplet states resemble that of
ruthenium–tris(bipyridine),[9] and can be qualified as the
“charge-separated states” in which ruthenium is oxidised in
RuIII with partial reduction of the corresponding ligand(s).
It is noteworthy that the protonic states of the ligand confer
a directionality to the charge separated state: in I and II the
T1 state is directed from the metal to the bipy motifs
(3MBCT), while in III it is directed from the metal to the
phenanthroline part of the protonated ligand (3MPCT).
Our computed data for the monooxidised form of com-
plex I show that almost one spin is localised essentially on
the imidazole–phenyl moiety of the ligand and that rutheni-
um bears no spin (Figure 7). This supports the fact that the
first electron abstraction has occurred on the deprotonated
imidazole–phenyl part of the ligand (2LC state) and not on
the metallic ion which remains formally RuII. In contrast,
for the singly oxidised complexes II and III, ruthenium
bears one spin and oxidation is metal-centred (2MC) as
shown in Figure 7.
Scheme 1. hn: Laser excitation at l = 440 nm; ISC: intersystem crossing
3
(1MLCT! MLCT); EET: external (bimolecular) electron transfer
(redox reaction); IET: internal electron transfer.
After irradiation in absence of an external electron ac-
3
ceptor (hn step), the emitting MBCT is reached. However,
in the case of I, both the emission intensity at 610 nm
(Figure 4) and the bleaching of the MLCT band at 450 nm
are less pronounced (Figure 5) as compared to II and III.
These experimental facts suggest the rapid recovery of a
RuII centre. In effect, the oxidising power of the photogener-
ated RuIII is sufficient to abstract one electron from the de-
3
protonated imidazole part leading to a LBCT state through
a ligand-to-metal electron transfer. This redox reaction is
thermodynamically favourable as confirmed by electrochem-
ical studies. An equilibrium between 3MBCT and 3LBCT
may be present in the medium.[42]
Discussion
The photophysical behaviour of compounds I, II and III
after a flash excitation at 450 nm in the MLCT band show
In the presence of MV2+, electron density is removed
3
from the high-lying p*
A
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8207

W. Leibl, M.-F. Charlot, A. Aukauloo et al.
2
state (EET) generating a MC state of the oxidised complex
copy of II in the presence of a non-absorbing electron ac-
(Iox). Simultaneously equilibrium between the low lying trip-
lets is shifted toward LBCT. Therefore, these processes can
(NH3)6]3+ (see Supporting Information).
ceptor, [RuACHTREUNG
3
A stepwise proposal for the photodriven charge shifts of
account for the weak absorption changes (Figure 6) in con-
trast with the formation of a genuine RuIII intermediate.
After bimolecular charge shifts reaction between [(bpy)-
compound III (pHꢀ1) is given in Scheme 3.
II
+
2
C C
ACHTREUNG(bpy )–Ru (PhenImPh )] and methylviologen, a LC state
in which the unpaired electron is localised on the deproton-
ated imidazole–phenyl is reached. An alternate pathway to
this state is obtained following an intramolecular electron-
transfer process from the deprotonated anionic form of the
(III) centre, the 2MC
ligand to photogenerated rutheniumACHTREUNG
state. The X-band EPR data for the monooxidised species
of I (see Supporting Information) confirm the nature of this
oxidised state which is furthermore supported by DFT cal-
culations.
The photoinduced electron pathways for compound II
(i.e., at pHꢀ7) is given in Scheme 2.
Scheme 3.
The computed lowest triplet state of the protonated com-
3
plex is a MPCT state and the emission properties of III are
(bpy)3]2+. Upon irradiation in
comparable to those of [RuACHTREUNG
the presence of an electron acceptor, the charge accumulat-
ed on the phenanthroline moiety is transferred to the exoge-
+
nous MV2+. Both the formation of the MV and the
C
bleaching of the MLCT band account for this reaction
(Figure 6). The concomitant regeneration of the RuII and
MV2+ in this case (Figure 6) indicates that the RuIII is not
quenched through an intramolecular electron transfer. This
is supported from the electrochemical data where no redox
process is depicted before the RuIII/II couple in acidic
2
medium. As can be noticed, the MC state is described with
a RuIII containing centre and we propose here that a mono
deprotonation of the imidazolium may occur under our ex-
perimental conditions. However, both oxidised 2MC states
Scheme 2.
3
The lowest triplet MBCT state is reached after light exci-
(of IIIox or IIox) will experience a similar back electron trans-
+
C
tation. This state is responsible for the excited state lumines-
cence (Figure 4) and the bleaching at 450 nm observed on
the transient spectrum (Figure 5) at neutral pH in absence
of an electron acceptor. In the presence of an electron ac-
ceptor (MV2+), an electron is transferred from the bipyri-
dines and the bleaching at 460 nm (Figure 6) evidences the
formation of RuIII intermediate in agreement with the calcu-
fer with MV to return to the ground state, as demonstrat-
ed by the similar absorption change kinetics at 460 and
605 nm.
Conclusion
2
lated ground MC state of the oxidised complex (IIox). This
In this work, we have described the physical properties of a
ruthenium–polypyridine-type complex holding a modified
phenanthroline ligand fused with an imidazole ring. The
combined electrochemical and photophysical studies sup-
ported by DFT calculations have allowed us to understand
the electronic perturbations undergoing upon (de)protona-
tion of the imidazole ring. We have shown how the protonic
states of the imidazole ring modified drastically the photo-
physical properties and therefrom the pathways involved in
the photoinduced electron transfer process. These results set
the basis for future work on more elaborate systems using
this chromophore/spacer as the molecular lynchpin to hold a
putative metal complex catalyst.
high valent metal RuIII species ([(bpy)2Ru(PhenImHPh)]3+
on Scheme 2) must be highly polarising therefore enhancing
the acidity of the imidazole ring. A subsequent deprotona-
tion step in experimental pH conditions (pHꢀ7) leads to
(PhenImPh)]2+. As dis-
the oxidised Iox complex [(bpy)2RuACHTREUNG
2
cussed above, the ground state of Iox is a LC state resulting
from an internal electron transfer from the deprotonated
imidazole fragment of the ligand to RuIII. This proton cou-
pled electron transfer process is most likely at the origin for
the rapid recovery of the RuII MLCT absorption band
(Figure 6). An imidazolyl-type radical was evidenced both
by EPR spectroscopy and by transient absorption spectros-
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Chem. Eur. J. 2007, 13, 8201 – 8211

Ruthenium–Polypyridine Complexes
FULL PAPER
ꢀ5 mJcmꢁ2). Absorbance changes were detected with a silicon photo-
diode and signals were amplified by a wideband preamplifier (model
5185, EG&G) before recording by a digital oscilloscope (TDS 3034B,
Tektronix). Solutions were purged with Argon for ꢀ20 minutes prior to
measurements. A flow-through system was employed to avoid sample
degradation due to prolonged exposure to light. For emission transients
excitation was done by a flash from a frequency-doubled picosecond Nd/
YAG laser (532 nm, duration 25 ps, ꢀ300 mJcmꢁ2; continuum) or from a
frequency-doubled nanosecond Nd/YAG laser (532 nm, duration 7 ns,
2 mJ/cm2; Quantel). The detection wavelength was selected by interfer-
ence filters and signals detected with a microchannel plate photomultipli-
Experimental Section
X-ray crystallography: X-ray diffraction data for [Ru
(PF6)·H2O·6MeOH, [Ru(bpy)2(PhenImHPh)](NO3)2·H2O·3MeOH and
[Ru(bpy)2(PhenImH2Ph)](PF6)3·5H2O were collected by using a Kappa
ACHRTUNEG(bpy)2AHCTRE(UGN PhenImPh)]-
G
A
ACHTREUNG
E
ACHTREUNG
X8 APPEX II Bruker diffractometer with graphite-monochromated
MoKa radiation (l=0.71073Š). The temperature of the crystal was main-
tained at the selected value (100 K) by means of a 700 series Cryostream
cooling device to within an accuracy of ꢂ1 K. The data were corrected
for Lorentz, polarization, and absorption effects. The structures were
solved by direct methods using SHELXS-97[43] and refined against F2 by
full-matrix least-squares techniques using SHELXL-97[44] with anisotropic
displacement parameters for all non-hydrogen atoms. Hydrogen atoms
were located on a difference Fourier map and introduced into the calcu-
lations as a riding model with isotropic thermal parameters. All calcula-
tions were performed by using the Crystal Structure crystallographic soft-
er tube (R2566U, Hamamatsu) and
a 7 GHz digitising oscilloscope
(IN7000, Intertechnique) or by a digital oscilloscope (TDS 744 A, Tektro-
nix).
Computation methods: Density Functional Theory calculations were car-
ried out using Beckeꢁs three-parameter hybrid functional B3LYP.[46,47]
along with the valence double-z basis set LanL2DZ[48,49] including the
Los Alamos effective core potential for heavy atoms. All the calculations
were performed using the Gaussian 98[50] and Gaussian 03[51] software
packages. For consistency reasons we used calculated geometries which
were fully optimised in the ground state (closed-shell singlet S0) for the
three compounds. However, in order to decrease the computation time,
the two tBu groups on the phenyl ring, which present numerous degrees
of freedom without influence on our problem, were replaced by two
methyl groups. Starting from the closed-shell S0 state, time-dependent
density functional calculations (TDDFT)[52] were performed to determine
the energies and character of the lowest excited singlets and triplets
states in the ground-state geometry. As photophysical experiments, in ab-
sence as well as in the presence of an electron acceptor, may involve the
lowest triplet state T1 and the ground doublet state D0 of the oxidised
complex, these two states were completely studied using a different ap-
proach : spin-unrestricted calculations were performed and the corre-
sponding geometries of T1 and D0 were fully optimised at the UB3LYP/
LanL2DZ level, except for the oxidised form of III, a highly-charged
(+4) complex for which convergence of the geometry optimisation was
not achieved. We have checked that in the open-shell calculations the
spin contamination from states of higher spin multiplicity is low by look-
ing at the values of <S2 > (typically 2.006 to 2.009 for a triplet state).
The nature of these states was precised by analysis of the corresponding
spin-orbitals and spin density distributions, as done by other authors, for
instance ref. [53].
ware package WINGX.[45]
ꢁ
One
NO3
anion
of
structure
[RuACHRTE(UNG bpy)2(PhenImHPh)]-
ACHTREUNG(NO3)2·H2O·3MeOH appeared to be disordered. The occupancy factors
were fixed in the ratio 50:50 for the N atom and one O atom, the two
other O atoms being refined with an occupancy factor of 1.0. For this
structure also, the hydrogen atom carried by nitrogen is disordered on
the two sites with an occupancy rate of 0.5.
The crystal data collection and refinement parameters are given in Table
S1 of the Supporting Information.
CCDC-609989, -609990, and -652213contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
Electrochemical measurements: The experiments were performed with
an EGG PAR (model 273A) electrochemical workstation. The solvents
were distilled under nitrogen in the presence of dry calcium chloride and
the solution (1 mmolLꢁ1 for complexes and ligand and 0.1 molLꢁ1 of tet-
rabutylammonium perchlorate (TBAClO4) introduced within an argon
purged heart shaped cell. Cyclic voltammetry was performed using a
glassy carbon electrode (3mm in diameter) as working electrode, a plati-
num grid as the counter electrode and an Ag/AgClO4 (0.01m) electrode
in acetonitrile as the reference (Eref =0.3V/ECS). Electrolyses were car-
ried out at controlled potentials in a three-electrode cell, using a plati-
num gauze as working electrode, a platinum grid as counter electrode
and an Ag/AgClO4 (0.01m) in acetonitrile electrode as the reference.
Low temperature electrolyses were run with 0.2m of TBAClO4.
In a first step, all these calculations were performed on the isolated mole-
cule (gas phase) and, in a second step, solvent effects were modelled in
the framework of a self-consistent reaction field method (SCRF). Calcu-
lations on the gas-phase optimised geometries were performed with the
polarized dielectric model (PCM)[40,54] using the integral equation formal-
ism (IEF).[55,56] The selected solvent was water and all parameters were
kept to their implemented Gaussian 03values. No geometry optimisation
was attempted in the solvent.
UV-visible-NIR spectra: The spectra were recorded with a Varian Cary
5E spectrophotometer (200–1500 nm), with 1 cm quartz cells. Spectro-
ACHTREUNGelectrochemical data were obtained by combination of a three electrode
thin cell (0.5 mm) mounted in a UV-visible-NIR spectrophotometer. IR
spectra were performed with a Perkin–Elmer spectrum 1000 spectrome-
ter, using KBr matrix pellets. NMR spectra were obtained with a Bruker
spectrometer AV 360 (360 MHz). The solvents used were CDCl3 or
[D6]DMSO. The 1H NMR spectra are given in the Supporting informa-
tion. EPR spectra were recorded on a X-band spectrometer Elexsys
E500 (Bruker) at 100 K. Elemental analyses were performed at Services
de Microanalyse, ICSN-CNRS, Gif-sur-Yvette. Mass spectra were record-
ed on a Finnigan Mat, Mat95S in a BE configuration at low resolution.
Materials: Ruthenium trichloride was purchased from the Aldrich Chem-
ical Company. 2,2’-Bipyridine (bpy) and 1,10-phenanthroline (phen) were
obtained from Janssen Chemical Company. 1,10-Phenanthroline-5,6-
dione,[57] 3,5-di-tert-butylbenzaldehyde,[58] and [Ru(bpy)2Cl2][59] were syn-
ACHTREUNG
thesised as described in the literature.
PhenImHPh:
A 1:1 mixture of 5,6-phenanthrolinedione (420 mg,
2 mmol) and 3,5-di-tert-butyl-benzaldehyde (444 mg, 2 mmol) in AcOH
together with an excess of NH4OAc (3.1 g, 40 mmol) was heated to
reflux. A yellow solid precipitates out upon cooling, which was isolated
by filtration and washed with water and vacuum dried (610 mg, ꢀ75%).
1H NMR ([D6]DMSO, 360 MHz): d = 13.70 (s, NH), 9.05 (d, 2H), 8.90
(d, 2H), 8.20 (d, 2H) 7.86 (m, 2H), 7.60 (s, 1H), 1.50 ppm (s, 18H); IR:
n˜ = 3385 (NH), 2952, 2900, 2864 (CH), 1643 cmꢁ1 (C=N Phen); ESI MS:
m/z (%): 409.2 [M+H]+.
Photochemistry: In order to cover a large range of pH and to exclude ef-
fects of the buffer, several buffers were used (CAPS, TRIS, HEPES,
MES, citrate) as well as their mixture. Steady-state emission spectra were
recorded on a Varian Cary Eclipse Spectrofluorimeter upon excitation at
440 nm. All the solutions were optically matched with absorbances of 0.1
at excitation wavelength. Flash-absorption and emission transients were
measured with setups of local design. All measurements were done at
296 K. For absorption transients the measuring light was provided by a
450 W xenon lamp. The wavelength was selected with a monochromator
(Czerny-Turner) placed after the 10”10 mm, sealed cuvette containing
the sample. The sample was excited at 908 to the measuring beam by a
flash from a frequency-tripled Nd/YAG laser (Surelight, Continuum)
equipped with an OPO. Excitation was set at 440 nm (duration 5 ns,
Complex II: [RuACHTRE(UGN bpy)2Cl2] (242 mg, 0.5 mmol) was treated with AgNO3
(170 mg, 1.0 mmol) in MeOH (5 mL) for 1 h. The AgCl precipitate was
filtered off and the filtrate evaporated to dryness. Ligand PhenImHPh
(204 mg, 0.5 mmol) was added to the ruthenium salt in MeOH (10 mL)
and stirred under reflux for 3h. The solvent was removed by rotary evap-
Chem. Eur. J. 2007, 13, 8201 – 8211
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8209

W. Leibl, M.-F. Charlot, A. Aukauloo et al.
oration and the crude product was purified by column chromatography
on neutral alumina (CH2Cl2/MeOH 90:10) to afford II(NO3)2 (353 mg,
[9] M.-F. Charlot, Y. Pellegrin, A. Quaranta, W. Leibl, A. Aukauloo,
Chem. Eur. J. 2006, 12, 796–812.
AHCTREUNG
72%) as an orange solid. The corresponding hexaflurophosphate salt was
isolated upon addition of a saturated aqueous solution of NaPF6 to a con-
[10] C. Daul, E. J. Baerends, P. Vernooijs, Inorg. Chem. 1994, 33, 3 53 8–
3543.
[11] J. K. McCusker, Acc. Chem. Res. 2003, 36, 876–887.
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4824.
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93, 5750–5756.
(NO3)2 in methanol. 1H NMR ([D6]DMSO,
centrated solution of IIACHTREUNG
360 MHz): d = 9.05 (d, 2H), 8.90, 8.85 (d, 4H), 8.27 (d, 2H), 8.22 (t,
2H), 8.10 (t, 2H), 7.89 (d, 2H), 7.81 (d, 2H), 7.73(dd, 2H), 7.59 (m,
4H), 7.39 (m, 3H), 1.38 ppm (s, 18H); IR: n˜ = 2951, 2902, 2863(CH),
1623(C =N), 1360 cmꢁ1 (N=O, NO3ꢁ); UV lmax (e)=240 (26500), 250 (sh,
22000), 287 (61500), 335 (23400), 430 (9500), 460 (10000), 520 nm (sh,
3000); ESI MS: m/z (%): 411.3(100) [ M]2+; elemental analysis calcd (%)
for C47H44N10O6Ru·2H2O (982.02): C 57.48, H 4.93, N 14.26; found: C
57.90, H 5.09, N 14.20.
[15] H.-B. Kim, N. Kitamura, Y. Kawanishi, S. Tazuke, J. Phys. Chem.
1989, 93, 5757–5764.
Complex III: IIACHTREUNG(NO3)2 (67 mg, 0.07 mmol) was dissolved in methanol
[16] F. Scandola, C. Choiorboli, M. T. Indelli, M. A. Rampi, Vol.
(Ed.: V. Balzani), Wiley-VCH, Weinheim, 2001, pp. 337–408.
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Leibl, A. Aukauloo, Eur. J. Inorg. Chem. 2003, 1900–1910.
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3
(3mL). To this solution was added 1 m nitric acid (80 mL). This solution
was stirred for an hour, and then concentrated under reduced pressure.
The hexafluorophosphate salt was isolated upon addition of a saturated
aqueous solution of NaPF6 to give an orange powder (78 mg, 85%).
1H NMR ([D6]DMSO, 360 MHz): d = 9.13(d, 2H), 8.90, 8.86 (d, 4H),
8.23(t, 2H), 8.18 (d, 2H), 8.13(t, 2H), 8.03(d, 2H), 7.9 (m, 4H), 7.6 (m,
5H), 7.37 (t, 2H), 1.43 ppm (s, 18H); IR: n˜ = 3104 (NH), 2952, 2900,
2864 (CH), 1624 cmꢁ1 (C=N phen); UV: lmax (e)=286 (67000), 430
(10000), 460 nm (11500); ESI MS: m/z (%): 411.2 (100) [M]2+; elemental
analysis calcd (%) for C47H45F18N8P3Ru·3H2O (1311.92): C 43.03, H 3.92,
N 8.54; found C 43.17, H 4.09, N 8.62.
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Complex I: IIACHTREUNG(NO3)2 (67 mg, 0.07 mmol) was dissolved in acetonitrile
(3mL). An excess of sodium methoxide was added to this solution. The
mixture was stirred for 2 h then filtered to remove undissolved material.
The filtrate evaporated to dryness. The solid was dissolved in a small
amount of methanol and precipitated with an excess of NaPF6 salt
(62 mg, 87%). 1H NMR ([D6]DMSO, 250 MHz): d = 8.97 (d, 2H), 8.90,
8.86 (d, 4H), 8.27 (d, 2H), 8.22 (t, 2H), 8.16 (t, 2H), 7.89 (d, 2H), 7.71
(m, 4H), 7.60 (m, 4H), 7.36 (m, 3H), 1.40 ppm (s, 18H); IR: n˜ = 2954,
2900, 2866 (CH), 1629 cmꢁ1 (C=N phen); UV: lmax (e)=240 (23500), 250
(sh, 18000), 290 (55000), 337 (26000), 425 (9000), 460 (8000), 520 (sh,
3000); ESI MS: m/z (%): 411.3(100) [ M]2+, 821.3(21) [ M]+; elemental
analysis calcd (%) for C47H43F6N8PRu·H2O·CH3OH (1015.99): C 56.74, H
4.86, N 11.03; found C 56.80, H 4.92, N 11.20.
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Acknowledgements
This work was supported by the CNRS (ANR Blanc HYPHO) and the
European Commission (NEST STREP SOLAR-H contract No 516510).
We thank the Centre Informatique National de l’Enseignement SupØrieur
at Montpellier (France) and the Institut du DØveloppement et des Res-
ACHTREUNGsources en Informatique Scientifique at Orsay (France) for providing cal-
culation means. C.H. is grateful to the International Chair of Blaise
Pascal for a scholarship.
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Received: February 2, 2007
Published online: July 16, 2007
Chem. Eur. J. 2007, 13, 8201 – 8211
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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