Synthesis and properties of trinuclear polypyridyl complexes Ru(II)-Co(II)-Ru(II) and Ru(II)-Co(III)-Ru(II): Their photoinduced interconversion

Article abstract of DOI:10.1016/j.ica.2009.08.020

The trinuclear Ru^II(bpy)₂(bpy-terpy)₂Co ^II6+ complex (1⁶⁺) in which a Co(II)-bis-terpyridine-like centre is covalently linked to two Ru(II)-tris-bipyridine-like moieties by a bridging bipyridine-terpyridine ligand has been synthesised and characterised. Its electrochemical, photophysical and photochemical properties have been investigated in CH₃CN. The cyclic voltammetry exhibits two successive reversible oxidation processes, corresponding to the Co^III/Co^II and Ru^III/Ru^II redox couples at E_1/2 = -0.06 and 0.91 V vs Ag/Ag⁺ 10 mM, respectively. The one-electron oxidized form of the complex, Ru^II(bpy)₂(bpy-terpy)₂Co ^III7+ (1⁷⁺) obtained after exhaustive electrolysis carried out at 0.2 V is fully stable. 1⁶⁺ and 1⁷⁺ are only poorly luminescent, indicating that the covalent linkage of the Ru(II)-tris-bipyridine centre to the cobalt subunit leads to a strong quenching of the Ru^II excited state by an intramolecular process. Luminescence lifetime experiments carried out at different temperatures indicate that the transfer is more efficient for 1⁷⁺ compare to 1⁶⁺ due to lower activation energy. Continuous irradiation of 1⁷⁺ performed at 405 nm in the presence of P(Ph)₃ acting as sacrificial electron donor leads to its quantitative reduction into 1⁶⁺, whereas similar experiment starting from 1⁶⁺ with a sulfonium salt as sacrificial electron acceptor converts 1⁶⁺ into 1⁷⁺ with a slower rate and a maximum yield of 80%. These photoinduced electron transfers were followed by UV-Visible spectroscopy and compared with those obtained with a simple mixture of both mononuclear parent complexes i.e. Ru^II(bpy)₃²⁺ and Co^II(tolyl-terpy)₂²⁺ or Co^III(tolyl-terpy)₂³⁺ (tolyl-terpy = 4′-(4-methylphenyl)-2,2′:6′,2′′-terpyridin e).

Full text of DOI:10.1016/j.ica.2009.08.020

Inorganica Chimica Acta 363 (2010) 234–242
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and properties of trinuclear polypyridyl complexes Ru(II)–Co(II)–Ru(II)
and Ru(II)–Co(III)–Ru(II): Their photoinduced interconversion
*
Jean Lombard, Rachid Boulaouche, D. Amilan Jose, Jérôme Chauvin ,
*
*
Marie-Noëlle Collomb , Alain Deronzier
Université Joseph Fourier Grenoble 1/CNRS, Département de Chimie Moléculaire, UMR-5250, Laboratoire de Chimie Inorganique Rédox,
Institut de Chimie Moléculaire de Grenoble FR-CNRS-2607, BP-53, 38041 Grenoble Cedex 9, France
a r t i c l e i n f o
a b s t r a c t
The trinuclear [{RuII(bpy)2(bpy-terpy)}2CoII]6+ complex (16+) in which a Co(II)-bis-terpyridine-like centre
is covalently linked to two Ru(II)-tris-bipyridine-like moieties by a bridging bipyridine–terpyridine
ligand has been synthesised and characterised. Its electrochemical, photophysical and photochemical
properties have been investigated in CH3CN. The cyclic voltammetry exhibits two successive reversible
oxidation processes, corresponding to the CoIII/CoII and RuIII/RuII redox couples at E1/2 = ꢀ0.06 and
Article history:
Received 14 April 2009
Received in revised form 7 August 2009
Accepted 12 August 2009
Available online 19 August 2009
0.91 V vs Ag/Ag+ 10 mM, respectively. The one-electron oxidized form of the complex, [{RuII(bpy)2-
Keywords:
Heterotopic bridging ligands
Cobalt
Ruthenium
Electrochemistry
Photophysics
7+
(bpy-terpy)}2CoIII
]
(17+) obtained after exhaustive electrolysis carried out at 0.2 V is fully stable. 16+
and 17+ are only poorly luminescent, indicating that the covalent linkage of the Ru(II)-tris-bipyridine
centre to the cobalt subunit leads to a strong quenching of the RuII excited state by an intramolecular pro-
cess. Luminescence lifetime experiments carried out at different temperatures indicate that the transfer
is more efficient for 17+ compare to 16+ due to lower activation energy. Continuous irradiation of 17+ per-
formed at 405 nm in the presence of P(Ph)3 acting as sacrificial electron donor leads to its quantitative
reduction into 16+, whereas similar experiment starting from 16+ with a sulfonium salt as sacrificial elec-
tron acceptor converts 16+ into 17+ with a slower rate and a maximum yield of 80%. These photoinduced
electron transfers were followed by UV–Visible spectroscopy and compared with those obtained with a
simple mixture of both mononuclear parent complexes i.e. [RuII(bpy)3]2+ and [CoII(tolyl-terpy)2]2+ or
[CoIII(tolyl-terpy)2]3+ (tolyl-terpy = 40-(4-methylphenyl)-2,20:60,200-terpyridine).
Photoinduced electron transfer
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
signs the different active sites are maintained in a close
proximity (with or without electronic connection between them)
to ensure efficient intramolecular electron transfer. In this area
some interesting efficient systems have been recently described
for the photoreduction of protons [3] or of CO2 [4]. In contrast
some attempts to photooxidize water into dioxygen using linked
ruthenium-manganese centres have failed, although an efficient
net oxidation of the manganese centres by the photooxidized
ruthenium one has been observed [5,6]. We have in particular
demonstrated that irradiation of such complexes made from the
linkage of Ru(II)-tris-bipyridine and Mn(II)-tris-bipyridine sub-
units by covalently bridging bis-bipyridine induces, in the presence
Construction of light driven catalytical molecular systems to
achieve high energy efficient chemical reactions has received con-
siderable interest since the end of the seventies [1]. They are based
on solutions of a mixture of a redox photosensitizer, usually the
[RuII(bpy)3]2+ complex, a catalyst associated or not with an elec-
tron relay and a sacrificial electron donor or acceptor depending
on the desired reaction to drive (reduction or oxidation). However
in this simple approach the final catalytic efficiency remains quite
low as a consequence of the need of the collision between the dif-
ferent species involved to ensure an intermolecular electron trans-
fer and the presence of various reaction intermediates. A recent
approach inspired by the natural photosynthetic system, in which
the light harvesting units and catalytic centres are well-organized
in assemblies, uses systems in which the photosensitizer is cova-
lently linked by a bridge to the catalytical centre [2]. In these de-
of an electron acceptor, the formation of a Mn2(III,IV)-di-l-oxo
core, the latter being further oxidized into a Mn2(IV,IV) one [6].
This core is however inactive toward catalytic oxidation of water
[7]. In our search of new bridged multitopic ligands to construct
more efficient catalytical systems we have previously reported
the synthesis of a disymmetrical polypyridyl ligand (bpy-terpy)
in which a bidentate bipyridine (bpy) site is connected to a
tridentate terpyridine (terpy) one [8]. The corresponding trinuclear
complex [{RuII(bpy)2(bpy-terpy)}2FeII]6+ has been recently synthe-
* Corresponding authors. Fax: +33 0 4 76 51 42 67.
E-mail addresses: jerome.chauvin@ujf-grenoble.fr (J. Chauvin), marie-noelle.
collomb@ujf-grenoble.fr (M.-N. Collomb), alain.deronzier@ujf-grenoble.fr (A. Deronzier).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.08.020

J. Lombard et al. / Inorganica Chimica Acta 363 (2010) 234–242
235
sized. This complex exhibits a strong intramolecular quenching of
and stored under argon in a dry-glovebox (Jaram). Triphenylphos-
phine P(Ph)3 was purchased from Acros and purified by recrystal-
lisation in ethanol prior to use. Phenacyldimethyl sulfonium salt
(PhCOCH2S(CH3)2(PF6), denoted R–S+(CH3)2, PF6ꢀ) has been synthe-
sis following a procedure already describe for the bromide salt
II
*
the Ru -tris-bipyridine excited state, Ru(II) , by energy transfer to
the FeII-bis-terpyridine centre. Nevertheless we have shown that
the energy transfer can be efficiently short-circuited in the pres-
ence of a sacrificial electron acceptor (diazonium salt) leading to
the fast and net photoinduced oxidation of the Fe(II) centre into
the Fe(III) species [9]. In the line of this work we report here the
synthesis and the main redox and photoredox properties of a sim-
ilar trinuclear complex in which Fe(II) ion is replaced by a Co(II)
(16+) or a Co(III) ion (17+) (Scheme 1).
ꢀ
[12]. The Brꢀ anion was exchanged by PF6 by precipitation of
the complex with a saturated aqueous KPF6 solution.
2.2. Synthesis
Bis-terpyridine like cobalt complexes are known to exhibit a
reversible CoIII/CoII redox system near 0 V vs Ag/Ag+ 10 mM allow-
ing electron transfer reactions with the Ru(II) excited state. Such
photoinduced electron transfer processes have been already re-
ported in dinuclear tris-diimine Ru(II)–Co(III) complexes, where
the two metal centres are linked via an innocent bridge [10]. In
these dinuclear systems, the kinetic rate constant of the process
occurs between 108 and 4 ꢁ 109 sꢀ1. Otherwise, to our knowledge,
the only previous example of a Ru–Co system with a heteroditopic
bipy-terpy ligand published [11] presents electronic connection
due to the direct linkage of the bpy and terpy ligands.
In that context, we have studied the photoinduced electron
transfer reactions occurring in 16+ and 17+. We have also investi-
gated the possibility to photoinduce the interconversion of these
two complexes under continuous irradiation using a sacrificial
electron donor or acceptor.
2.2.1. Synthesis of [Ru(bpy)2(bpy-terpy)](PF6)2
The heterodipotic bpy-terpy ligand and its ruthenium complex
were synthesized following procedure already published [8].
2.2.2. Synthesis of [Co(tolyl-terpy)2](PF6)2
A solution of CoCl2ꢂ6H2O (35 mg, 0.147 mmol) in methanol
(5 mL) was added to a tolyl-terpy (tolyl-terpy = 40-(4-methyl-
phenyl)-2,20:60,200-terpyridine) solution (100 mg, 0.309 mmol) in
methanol (15 mL). The resulting red solution was heated at reflux
for 1 h. After cooling to room temperature, addition of a methanol
Bu4NPF6 solution (120 mg in 100 mL of methanol) allowed the par-
tial precipitation of the complex. Methanol was then removed un-
der vacuum to give more precipitate which was filtered off, washed
with ethanol and diethylether, and dried under vacuum. Yield:
65 mg (49%). Anal. Calc. for C44H34N6CoP2F12 (995.64): C, 53.08;
H, 3.44; N, 8.44. Found: C, 52.90; H, 3.27; N, 8.53%. ESI-MS: m/z
(%) 850.07 (67) [M-PF6]+, 352.25 (100) [M-2PF6]2+. UV–Visible
characterisation: see Table 2.
2. Experimental
2.1. Materials and general
2.2.3. Synthesis of [{RuII(bpy)2(bpy-terpy)}2CoII](PF6)6 (1(PF6)6)
A solution of CoCl2ꢂ6H2O (5.1 mg, 0.021 mmol) in methanol
(5 mL) was added to a stirred solution of [Ru(bpy)2(bpy-ter-
py)](PF6)2 (50 mg, 0.041 mmol) in methanol (20 mL). The reaction
Acetonitrile (CH3CN, Rathburn, HPLC grade), tetra-n-butylam-
monium perchlorate (Bu4NClO4, Fluka) were used as received
6+
N
N
N
RuII
N
N
N
CoII
N
N
N
N
RuII
N
N
N
N
N
N
N
N
[{Ru(bpy)2(bpy-terpy)}2Co]6+ (16+
)
2+
2+
N
N
N
N
N
N
N
N
RuII
N
CoII
N
N
N
N
N
N
[Co(tolyl-terpy)2]2+
[Ru(bpy)2(bpy-terpy)]2+
Scheme 1. Chemical structure of the polypyridyl complexes of Ru(II) and Co(II).
Table 1
Redox potentials of [Co(tolyl-terpy)2]2+, [Ru(bpy)2(bpy-terpy)]2+ and (16+) in deoxygenated CH3CN + 0.1 M Bu4NClO4 at a scan rate of 100 mV sꢀ1. E1/2(V) (
D
Ep/mV) vs Ag/Ag+
(AgNO3 10 mM in CH3CN + 0.1 M Bu4NClO4).
Oxidation processes
CoII/CoIII
Reduction processes
CoII/CoI
Ligand centered processes
Complexes
RuII/RuIII
[Co(tolyl-terpy)2]2+,a
ꢀ0.06 (70)
ꢀ1.06 (70)
ꢀ1.90 (60)
ꢀ2.26 (50)
ꢀ2.13 (70)
ꢀ2.13 (120)b
[Ru(bpy)2(bpy-terpy)]2+ [14]
[{Ru(bpy)2(bpy-terpy)}2Co]6+ (16+
0.92 (60)
0.91 (60)
ꢀ1.67 (60)
ꢀ1.67 (60)
ꢀ1.87 (70)
)
ꢀ0.06 (50)
ꢀ1.07 (60)
ꢀ1.84 (60)
The electrochemical properties of this complex have been studied in CH3CN + 0.05 M Bu4NBF4 owing to the low solubility of [CoIII(tolyl-terpy)2]3+ in the presence of ClO4
This value cannot be accurately measured since the wave is strongly distorted by adsorption of the reduction product on the electrode surface.
.
a
ꢀ
b

236
J. Lombard et al. / Inorganica Chimica Acta 363 (2010) 234–242
mixture was heated at 75 °C for 90 min. The colour of the reaction
mixture becomes more intense compared to the initial solution.
After cooling to room temperature, addition of an aqueous KPF6
solution (1 g in 100 mL of water) allowed the precipitation of the
complex. The precipitate was filtered off and washed with water.
The bright orange product was reprecipitated in CH3CN/
diethylether, washed with diethylether and dried under vacuum.
Yield: 45 mg (77%). Anal. Calc. for C108H86N18Ru2CoP6F36ꢂ4H2O
(2838.88): C, 45.69; H, 3.34; N, 8.88. Found: C, 45.45; H, 3.43; N,
tube (Hamamatsu model R3809U-50) followed by a time-corre-
lated single photon counting system from Picoquant (Pico-
Harp300). The ultimate time resolution of the system is close to
30 ps. Luminescence decays were analyzed with Fluofit software
available from Picoquant. The fractional intensity of the bi-expo-
nential decay is defined as:
Aisi
xi ¼
RiAisi
8.55%. ESI-MS: m/z (%) 1238.5 (4) [M-2PF6]2+
, 777.5 (3)
where Ai and si are the parameter of the bi-exponential fit (pre-fac-
tor and luminescence lifetime).
[M-3PF6]3+, 408.4 (60) [M-5PF6]5+. UV–Visible characterisation:
see Table 2.
2.5. Continuous irradiations
2.2.4. [{RuII(bpy)2(bpy-terpy)}2CoIII]7+ (17+
)
All attempts to isolate 17+ as a pure compound has failed so,
CH3CN solutions of 17+ for photophysical and photochemical
experiments are obtained by exhaustive electrolyses of solutions
of 16+ in deoxygenated CH3CN + 0.1 M Bu4NClO4 carried out at
0.20 V vs Ag/Ag+ 10 mM. The quantitative formation of 17+ is
checked by electrochemistry and UV–Visible spectroscopy re-
corded after electrolysis. UV-Visible characterisation: see Table 2.
Photoinduced transformations were performed using a diode
laser (BFI optilas PMM608G) (k = 405 nm, P = 25 mW) as excitation
light. For these experiments, all the solutions were prepared in a
dry-glovebox under argon in a 1 cm path length quartz cuvette.
The solutions contained a mixture of the complexes 16+ or 17+
(around 0.02 mM) and R–S+(CH3)2 or P(Ph)3 (15 mM), or a mixture
of the mononuclear complexes [Ru(bpy)3]2+ and [CoII(tolyl-ter-
py)2]2+ or [CoIII(tolyl-terpy)2]3+), with R–S+(CH3)2 or P(Ph)3
(15 mM) in a CH3CN + 0.1 M Bu4NClO4 solution. Under these condi-
tions, the concentration of the sacrificial donor or acceptor can be
considered as constant during the irradiation experiments. Photo-
induced oxidation and reduction were followed by UV–Visible
spectroscopy.
2.3. Electrochemistry
All electrochemical measurements were run under an argon
atmosphere in a dry-glovebox at room temperature. Cyclic voltam-
metry (CV) (Epa, anodic peak potential; Epc, cathodic peak potential;
E1/2 = (Epa + Epc)/2;
D
Ep = EpaꢀEpc) and controlled potential electrol-
ysis experiments were performed using an EG&G PAR model 173
potentiostat/galvanostat equipped with a PAR model universal
programmer 175 and a PAR model 179 digital coulometer. A stan-
dard three-electrode electrochemical cell was used. Potentials
were referenced to an Ag/10 mM AgNO3 reference electrode in
CH3CN + 0.1 M Bu4NClO4. Potentials referred to that system can
be converted to the ferrocene/ferricinium couple by subtracting
87 mV, to the SCE by adding 298 mV or to the NHE reference elec-
trode by adding 548 mV. The working electrodes were platinum
3. Results and discussion
3.1. Electrochemistry
We have firstly reinvestigated the electrochemical and spectro-
scopic (UV–Visible) properties of the mononuclear [CoII(tolyl-ter-
py)2]2+ complex in CH3CN and the stability of its corresponding
oxidized form (i.e. [CoIII(tolyl-terpy)2]3+). Redox potentials and
UV–Visible data are reported in Tables 1 and 2, respectively.
The cyclic voltammetry (CV) of [CoII(tolyl-terpy)2]2+ exhibits the
reversible CoIII/CoII oxidation process at E1/2 = ꢀ0.06 V vs Ag/AgNO3
10 mM, as previously described [15], and in the more negative
potential region, three successive one-electron reversible waves
corresponding respectively to the CoII/CoI reduction process and
to the first and the second one-electron reduction of the two
terpyridine ligands. An exhaustive electrolysis of the solution at
E = 0.20 V leads to the quantitative formation of [CoIII(tolyl-ter-
py)2]3+, after one electron has been passed (coulometric measure-
ment), as evidenced by rotating disk electrode experiments (RDE).
This oxidation process is associated by significant changes in
UV–Visible spectroscopy. The spectrum of the initial solution
disks polished with 2 lm diamond paste (Mecaprex Presi). They
were 5 mm in diameter for CV and 2 mm for rotating disk electrode
(RDE) experiments. Exhaustive electrolyses were carried out on a
reticulated vitreous carbon electrode 45 PPI (the electrosynthesis
Co. Inc.) three-dimensional meshes (1.0 cm ꢁ 1.0 cm ꢁ 0.3 cm).
Initial and electrolyzed solutions were transferred to 1 mm or
1 cm path length quartz cuvette cells and the UV–Visible spectra
were recorded directly in the glovebox with a Cary 50 using optical
fibres.
2.4. Absorbance and emission
UV–Visible spectra were obtained using a Cary 1 absorption
spectrophotometer. For emission experiments, samples were pre-
pared under Ar in a dry-glovebox and contained in a 1 cm path
length quartz cuvette. Samples were maintained under anaerobic
conditions with a Teflon cap. Emission spectra were recorded at
room temperature on a Photon Technology International (PTI)
SE-900M spectrofluorimeter. The excitation wavelength was
450 nm. Spectra were recorded from 500 to 850 nm. Emission
quantum yield uL were determined at 25 °C in deoxygenated ace-
tonitrile solutions with [Ru(bpy)3](PF6)2 used as a standard (uL-
ref. = 0.062 [13]) and using methodology already presented [14].
Emission lifetime measurements were performed after irradiation
at k = 400 nm obtained by the second harmonic of Titanium: Sap-
phire laser (picosecond Tsunami laser spectra physics 3950-
M1BB + 3986-03 pulse picker doubler) at a 400 KHz repetition rate.
Fluotime 200 from AMS technologies was used for the decay acqui-
sition. It consists of a GaAs micro channel plate photomultiplier
Table 2
UV/Visible data in deoxygenated CH3CN solution at 298 K.
k
/nm (e )
Mꢀ1 cmꢀ1
abs
Complexes
max
[Co(tolyl-terpy)2]2+
315 (52000), 415a (3100),
444a (2700), 480a (2400),
513 (2700), 560a (600)
[Co(tolyl-terpy)2]3+
350 (51000), 365a (50500)
326a (21900), 354a (6400),
430a (12000), 455 (14300)
320a (77000), 358a (26600),
393a (16000), 423a (26000),
454 (31200), 513a (6300)
350 (65000), 365a (64000),
430a (27000), 455 (30000)
[Ru(bpy)2(bpy-terpy)]2+ [14]
[{Ru(bpy)2(bpy-terpy)}2Co]6+ (16+
)
)
[{Ru(bpy)2(bpy-terpy)}2Co]7+ (17+
a
Shoulder.

J. Lombard et al. / Inorganica Chimica Acta 363 (2010) 234–242
237
B
A
1.5
1.5
1.0
0.5
0
1.0
0.5
0
300
400
500
600
700
300
400
500
600
700
Wavelength (nm)
Wavelength (nm)
Fig. 1. Absorption spectra of a 0.27 mM solution of [CoII(toly-terpy)2]2+ in CH3CN + 0.05 M Bu4NBF4: initial solution (black line) after exhaustive electrolysis carring out at
0.20 V (doted line) (A: l = 1 mm and B: l = 1 cm optical pathway).
exhibits the typical visible band of [CoII(tolyl-terpy)2]2+ at 513 nm
6þ
½fRuIIðbpyÞ2ðbpy-terpyÞg2CoIIꢄ þeꢀ
(e
ꢃ 2700 Mꢀ1 cmꢀ1 transition d–d) associated with a succession of
5þ
¢½fRuIIðbpyÞ2ðbpy-terpyÞg2CoIꢄ
ð3Þ
ð4Þ
shoulders with similar molar absorption coefficient between 400
5þ
½fRuIIðbpyÞ2ðbpy-terpyÞg2CoIꢄ þ2eꢀ
and 500 nm (Fig. 1) [16]. The formation of [Co(tolyl-terpy)2]3+ is
Åꢀ
3þ
¢½fRuIIðbpyÞðbpy Þðbpy-terpyÞg2CoIꢄ
evidenced by the appearance of a new intense band at 350 nm
*
p–p ) [17]. The electrochemical
(e
ꢃ 51 000 Mꢀ1 cmꢀ1 transition
Åꢀ
3þ
½fRuIIðbpyÞðbpy Þðbpy-terpyÞg2CoIꢄ þ3eꢀ
behaviour of the [Ru(bpy)2(bpy-terpy)]2+ complex has already
been published [8]. The CV of 16+ is actually the superposition of
the electroactivity of both parents subunits (i.e. [Ru(bpy)2-
(bpy-terpy)]2+ and [Co(tolyl-terpy)2]2+) in their respective ratio
(2:1, RuII/CoII). Two well-separated reversible oxidation process
¢½fRuIIðbpyÅꢀÞ2ðbpy-terpyÅꢀÞgCoIfRuIIðbpyÅꢀÞ2ðbpy-terpyÞgꢄ ð5Þ
½fRuIIðbpyÅꢀÞ2ðbpy-terpyÅꢀÞgCoIfRuIIðbpyÅꢀÞ2ðbpy-terpyÞgꢄ
þ3eꢀ ¢½fRuIIðbpyÅꢀÞ2ðbpyÅꢀ-terpyÅꢀÞg2CoIꢄ
ð6Þ
2ꢀ
are observed at E1/2 = ꢀ0.06 and 0.91 V (DE = 970 mV) (Fig. 2A).
Two successive exhaustive electrolyses of the 16+ solution car-
ried out at 0.20 and 1.10 V consumed one and two electrons
respectively per initial complex, and allow the build up of [{RuII(b-
py)2(bpy-terpy)}2CoIII]7+ (17+) and [{RuIII(bpy)2(bpy-terpy)}2CoIII]9+
(19+). RDE experiments show that these oxidized forms are ob-
tained quantitatively (Fig. 2B). This is illustrated by the evolution
of the absorption spectrum of the solution after these sequential
electrolyses (Fig. 3). Absorption spectrum of 16+ closely results
from the absorption overlap of the two parent subunits (Table 2).
The potentials of these systems are similar to those of the mononu-
clear parents (Table 1), allowing to assign the first oxidative pro-
cess to the CoIII/CoII redox couple and the more positive one to
the RuIII/RuII system (Eqs. (1) and (2)). Moreover, RDE experiments
confirm that the trinuclear complex is obtained in pure form and
that no dissociation occurs in CH3CN, since the height of the RuII/
RuIII wave is two times higher than that of CoIII/CoII, in accordance
with the 2:1 Ru/Co stoechiometry (Fig. 2B).
The band at 454 nm (e
= 31200 Mꢀ1 cmꢀ1) is attributed to the
6þ
½fRuIIðbpyÞ2ðbpy-terpyÞg2CoIIꢄ
Ru(II) MLCT transition and the shoulder at 513 nm to the Co(II)
transition. After one electron per complex has been passed at
0.20 V, the shoulder at 513 nm disappears at the expense of the
7þ
¢ ½fRuIIðbpyÞ2ðbpy-terpyÞg2CoIIIꢄ þ eꢀ
ð1Þ
7þ
½fRuIIðbpyÞ2ðbpy-terpyÞg2CoIIIꢄ
appearance of the intense band at 350 nm (e )
= 65 000 Mꢀ1 cmꢀ1
9þ
¢ ½fRuIIIðbpyÞ2ðbpy-terpyÞg2CoIIIꢄ þ 2eꢀ
ð2Þ
typical of the Co(III)-bis-terpyridine unit (Fig. 3). After exchange
of two other electrons at 1.10 V, the band of the Ru(II)-tris-bipyri-
dine units at 454 nm disappears and is replaced by the lower inten-
The CV of 16+ exhibits also four successive reduction processes.
The first one, reversible, located at E1/2 = ꢀ1.07 V is attributed to
the CoII/CoI system (Eq. (3)) and the three following ones are cen-
tred on the ligands. The first ligand-centred reduction process
(E1/2 = ꢀ1.67 V) is reversible and corresponds to the simultaneous
reduction of one bpy ligand per Ru(II) centre (exchange of two
electrons) (Eq. (4)). The second system (E1/2 = ꢀ1.84 V) is associ-
ated to the simultaneous reduction of a second bpy per Ru(II) cen-
tres and of a terpy of the Co(II) centre (exchange of three electrons)
(Eq. (5)). Some adsorption phenomena are coupled to this reduc-
tion process (formation of the insoluble neutral species [{RuII(b-
py.-)2(bpy-terpy.-)}CoI{RuII(bpy.-)2(bpy-terpy)}]) that lead to
distortion of this wave on the reverse scan as well as of the third
ligand reduction wave due to redissolution phenomena. Finally,
this third system (Epc = ꢀ2.13 V) probably corresponds to the
simultaneous reduction of the bpy connected to the terpy and of
the second terpy (Eq. (6)). RDE experiments confirm, for the three
first reduction processes, the number of electron exchanged: 1/2/3
(Fig. 2B, Eqs. (3)–(5)).
sity Ru(III) ones at 434
(e ) and 670 nm
= 6400 Mꢀ1 cmꢀ1
(e
= 1200 Mꢀ1 cmꢀ1) [18].
3.2. Photophysics
The emission spectra of complexes 16+ and 17+ are typical of the
3MLCT excited state of [Ru(bpy)3]2+ like complexes, although the
intensities of the luminescence are drastically lowered (Table 3).
Indeed, emission of 16+ and 17+ represents only 10% and 14%,
respectively of the emission of [Ru(bpy)2(bpy-terpy)]2+ (based on
the ratio of their quantum yield). This result indicates a strong
*
quenching of a Ru(II) unit by the cobalt one. The quenching pro-
cess in 17+ can be reasonably attributed to an electron transfer
mechanism following Eq. (7) as it was reported for other kind of
binuclear polypyridyl complexes of Co(III) and Ru(II) [10]. This
reaction offers a largely negative free enthalpy
D
G = ꢀ1.06 V
(assuming E°(RuIII/II*) to ꢀ1.12 V by the Rehm-Weller relation,
and CoIII/CoII to ꢀ0.06 V). An energy transfer does not occur since

238
J. Lombard et al. / Inorganica Chimica Acta 363 (2010) 234–242
plexes. To calculate the quenching rate constant, the dependence
of the luminescence lifetime of [Ru(bpy)3]2+ with a variable con-
*
centration of the cobalt complexes following a Stern-Vollmer equa-
tion, has been used. Quenching rate constants of 3.9 ꢁ 109 Mꢀ1 sꢀ1
A
and 1.6 ꢁ 109 Mꢀ1 sꢀ1 have been respectively obtained for the
10
A
bimolecular interaction between [Ru(bpy)3]2+ /[Co(tolyl-terpy)2]
*
3+
and [Ru(bpy)3]2+ /[Co(tolyl-terpy)2]2+. These values are in accor-
*
dance with other quenching rate constant found for a mixture of
[Ru(bpy)3]2+ and [Co(bpy)3]3+, [Co(phen)3]3+ [19] or [Co(terpy)2]3+
[20] and indicate that the quenching process is essentially diffu-
sion controlled.
-1.0
0.0
1.0
E/V
-2.0
vs Ag/Ag+
The quenching process in 16+ and 17+ can be due to an intra and/
or an intermolecular process. When the two metal centres are
linked by a
p-conjugated bridge the intramolecular quenching is
(a)
(b)
believe to be more efficient and is largely dominated. In contrast,
with an innocent bridged system, the electron transfer may pro-
ceed efficiently by the both processes. The kinetics of the quench-
ing in 16+ and 17+ have been determined by luminescence lifetime
measurements. The luminescence lifetime values obtained are
essentially independent on the concentration of the samples, evi-
dencing that the intermolecular quenching is limited. Lumines-
cence lifetime of 16+ and 17+ are described by a bi-exponential fit
(Table 4), reflecting contribution from quenched and unquenched
2
A
B
2e-
1e-
(c)
1e-
E/V
1.0
-1.0
0.0
-2.0
3e-
2e-
ruthenium centres. The shorter component of the decays (s1) rep-
resents around 95% of the total intensity decay and is attributed to
an intramolecular quenching. The process occurs within 30 ns for
16+ and is shorter in case of 17+ (following Eq. (7)) where it occurs
within 19 ns at 293 K. The longer component (s2) which represents
around 5% of the total intensity decay is close to the luminescence
Fig. 2. (A) Cyclic voltammograms of a 0.15 mM solution of 16+ in CH3CN + 0.1 M Bu4
lifetime of [Ru(bpy)3]2+
(s0 = 898 ns in the same experimental
*
NClO4 at a platinium electrode (0.5 cm of diameter); scan rate: 100 mV sꢀ1, (B)
condition) and is then assigned to the unquenched Ru centre by
the intramolecular process. The reason for this incomplete quench-
ing phenomenon remains uncertain. A similar behaviour has been
observed for dinuclear polypyridyl complexes of Ru(II) and Co(III)
linked by an alkyl chain and was attributed to dissociation due
to the instability of the cobalt complexes under irradiation that re-
lease some free Ru units in solution [10b]. A bi-exponential decay
in a similar ratio was also obtained with the trinuclear [{Ru(b-
py)2(bpy-terpy)}2Fe]6+ complex [9]. In this case, the dissociation
of the complex cannot be responsible of the bi-exponential decay
since Fe(II) bis-terpyridinyl complexes are stable under irradiation.
Another possible explanation is that, since the trinuclear com-
plexes associate two photosensitizers, about 5% of the complexes
undergo a double excitation of the sensitizers. One excited ruthe-
nium is efficiency quenched by the cobalt core whereas the second
excited ruthenium has a luminescence lifetime only slightly short-
er compared to that of the free [Ru(bpy)2(bpy-terpy)]2+ complex
Voltammograms at
x
electrolysis at 0.20 V, (c) after exhaustive electrolysis at 1.10 V.
a platinium electrode (0.2 cm of diameter); rotation rate
= 600 rot minꢀ1; scan rate: 10 mV sꢀ1, (a) initial solution, (b) after exhaustive
there is no overlap between the emission spectrum of the Ru(II)
subunit and the absorption spectrum of the Co(III) core.
In 16+ the quenching mechanism is more complicated. The
reductive quenching process following Eq. (8) would be thermody-
G = ꢀ0.42 V (assuming E°(RuII /I) to
*
namically favoured with a
D
0.36 V, and CoIII/II to ꢀ0.06 V) and the oxidative quenching process
that leads to the formation of the transient RuIII/CoI mixed valent
complex (Eq. (9)) would also be favoured with
D
G = ꢀ0.05 V
(assuming E°(RuIII/II*) to ꢀ1.12 V and CoII/I to ꢀ1.07 V). These two
redox processes may contribute to the net quenching. In addition
to these electron transfer processes, an energy transfer path (Eq.
(10)) cannot be ruled out since the Ru(II) emission band (520–
780 nm) overlaps in part the absorption spectrum of the Co(II) core
(until 600 nm).
(s
= 999 ns at 298 K).
The intramolecular quenching rate constant of 16+ and 17+ was
calculated using Eq. (11) [5a].
7þ
½fRuIIꢅðbpyÞ2ðbpy-terpyÞgCoIIIfRuIIðbpyÞ2ðbpy-terpyÞgꢄ
7þ
! ½fRuIIIðbpyÞ2ðbpy-terpyÞgCoIIfRuIIðbpyÞ2ðbpy-terpyÞgꢄ
ð7Þ
1
1
kqðTÞ ¼
ꢀ
ð11Þ
6þ
½fRuIIꢅðbpyÞ2ðbpy-terpyÞgCoIIfRuIIðbpyÞ2ðbpy-terpyÞgꢄ
s1ðTÞ s0ðTÞ
Åꢀ
6þ
! ½fRuIIðbpy ÞðbpyÞðbpy-terpyÞgCoIIIfRuIIðbpyÞ2ðbpy-terpyÞgꢄ
where s1 represent the shorter lifetime of the decay and s0 the
luminescence lifetime of the [Ru(bpy)3]2+ complex. kq values deter-
mined at 293 K are listed in Table 4. The intramolecular quenching
are in the same order of magnitude. Nevertheless as in the case of a
simple mixture of the mononuclear complexes where the quench-
ð8Þ
6þ
½fRuII ꢅðbpyÞ2ðbpy-terpyÞgCoIIfRuIIðbpyÞ2ðbpy-terpyÞgꢄ
6þ
! ½fRuIIIðbpyÞ2ðbpy-terpyÞgCoIfRuIIðbpyÞ2ðbpy-terpyÞgꢄ
ð9Þ
6þ
½fRuIIꢅðbpyÞ2ðbpy-terpyÞgCoIIfRuIIðbpyÞ2ðbpy-terpyÞgꢄ
ing of [Ru(bpy)3]2+ by [Co(tolyl-terpy)2]3+ is slightly more efficient
*
2+
than the quenching between [Ru(bpy)3]2+ and [Co(tolyl-terpy)2]
,
*
6þ
! ½fRuIIðbpyÞ2ðbpy-terpyÞgCoIIꢅfRuIIðbpyÞ2ðbpy-terpyÞgꢄ
ð10Þ
the intramolecular quenching process into 17+ appears also more
efficient that the one occurring into 16+ (kq for 17+ is 1.6 time higher
than for 16+). To evaluate the activation energy of the photoinduced
intramolecular processes that occur in 17+ and 16+, kq have been cal-
culated between 278 and 313 K. Fig. 4 represents the Arrhenius plot
Kinetics of the quenching processes have been studied in deox-
ygenated CH3CN + 0.1 M Bu4NClO4. The bimolecular quenching has
been firstly investigated using a mixture of the mononuclear
[Ru(bpy)3]2+ and [Co(tolyl-terpy)2]3+ or [Co(tolyl-terpy)2]2+ com-

J. Lombard et al. / Inorganica Chimica Acta 363 (2010) 234–242
239
2.0
1.5
1.0
0.5
0
1.2
B
A
0.9
0.6
c
b
a
a
0.3
0
c
b
400
500
600
700
800
300
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Fig. 3. Absorption spectra of a 0.16 mM solution of 16+ in CH3CN + 0.1 M Bu4NClO4: initial solution (a-black line) after exhaustive electrolysis carring out at 0.20 V (b-doted
line), after electrolysis at 1.10 V (c-dashed line) (A: l = 1 mm and B: l = 1 cm optical pathway).
Table 3
18.2
18.0
17.8
17.6
17.4
17.2
17.0
16.8
Luminescence maxima (kmaxem) and emission quantum yield uem of the complexes.
exc
em
Complexes
kmax
/
kmax
/
uem
uem/
nm
nm
u0 (%)
[{Ru(bpy)2(bpy-terpy)}2Co]6+ (16+
[{Ru(bpy)2(bpy-terpy)}2Co]7+ (17+
[Ru(bpy)2(bpy-terpy)]2+
)
)
455
455
455
611
611
609
0.0054
0.0073
0.054
10
14
100
Table 4
Lifetime of the quenched (
s
1) and unquenched (s2) ruthenium centres determined in
3.30
3.35
3.40
3.45
3.50
3.55 3.60x10-3
deoxygenated CH3CN + 0.1 M Bu4NClO4 solution at 293 K. kq is the intramolecular
quenching constant determined from Eq. (11).
1/T (K-1
)
Complexes
s
1/ns (%)a
s
2/ns (%)a
kq/sꢀ1
Fig. 4. Arrhenius plot of the intramolecular quenching constant of 16+ (dotted line)
fit: 21.98–1378 ꢁ 1/T and 17+ (straight line) fit: 21.07–982 ꢁ 1/T.
[{Ru(bpy)2(bpy-terpy)}2Co]6+ (16+
[{Ru(bpy)2(bpy-terpy)}2Co]7+ (17+
)
)
30 (93)
19 (95)
855 (7)
889 (5)
3.2 107
5.1 107
a
These percentages correspond to the fractional intensities of the bi-exponen-
has a lifetime sufficiently long to react with an external electron
donor.
tional decay (see text and Section 2).
We found that the classical sacrificial reductive quenchers such
as triethanolamine (TEOA) or triethylamine (TEA) cannot be used
here, since a partial thermal reduction of the Co(III) core occurs
in that case. So triphenylphosphine P(Ph)3 (Epa = 0.93 V) has been
selected as a sacrificial electron donor. Trivalent phosphorus com-
pounds have already been used to irreversibly react by electron
transfer with [Fe(phen)3]3+, porphyrines or organic dyes [22]. The
oxidized form of the phosphine, PÅ+(Ph)3, reacts rapidly with resid-
ual water of CH3CN to form OP(Ph)3. Feasibility of a photo-catalytic
cycle has been firstly test to reduce [Co(tolyl-terpy)2]3+ into [Co(to-
lyl-terpy)2]2+ using [Ru(bpy)3]2+ as sensitizer in low concentration
of both quenching rate constant. An activation energy of 960 and
700 cmꢀ1 has been determined respectively for the quenching pro-
cess in 16+ and 17+. By a similar methodology, on a larger tempera-
ture range, Endicott et al. [10a] have estimated an activation energy
of 2200 cmꢀ1 for the quenching process in a binuclear complex
where a [Ru(bpy)3]2+ electron donor is linked via a bis-bipyridyl
ethane ligand to a [Co(bpy)3]3+ electron acceptor. The weaker
Arrhenius activation energy value obtained in our trinuclear 17+
complex compared to their result indicates that the heterotopic
bpy-terpy bridge promotes electron transfer process by decreasing
the energy barrier. This can be due to the more planar structure
of the [Co(tolyl-terpy)2]3+ core compared to the [Co(bpy)3]3+ one.
Ru(II)-1Co(III)-Ru(II*) + D
kq
Ru(II)-2Co(II)-Ru(III) + D
Ru(II)-4Co(II)-Ru(III) + D
kBET
3.3. Photoinduced reduction of 17+
To induce a net photoreduction of 17+ into 16+, an external irre-
versible electron donor is needed. The role of this external electron
donor is to short-circuit the back electron transfer process. As illus-
trated in Scheme 2, after excitation of a RuII-tris-bipyridine unit in
the MLCT band, a quick electron transfer occurs (within 19 ns at
293 K) followed by a spin relaxation at the Co(II) centre from the
photogenerate low spin Co(II) doublet to the high spin quadruplet
state [10a,21]. The back electron transfer (BET) process is then for-
bidden and therefore the transient Ru(II)–4Co(II)–Ru(III) species
Ru(II)-1Co(III)-Ru(II) + D
Ru(II)-4Co(II)-Ru(II) + D’
Scheme 2. Electron transfer pathway in 17+ for a net-photoinduced reduction.

240
J. Lombard et al. / Inorganica Chimica Acta 363 (2010) 234–242
and P(Ph)3 in large excess. No significant quenching of [Ru(bpy)3]2+
by P(Ph)3 has been detected, as well as no significant thermal
reduction of [Co(tolyl-terpy)2]3+ by P(Ph)3 in the dark. Moreover
no photoinduced reduction of the [Co(tolyl-terpy)2]3+ complex un-
der illumination at 405 nm without the [Ru(bpy)3]2+ is observed.
Evolution of the electronic absorption spectrum of a solution of
the three components during irradiation is presented in Fig. 5. Un-
der continuous irradiation at k = 405 nm, the absorption band
around 350 nm typical of the [Co(tolyl-terpy)2]3+ species decreases
and new ones appear in the visible part of the spectrum due to the
formation of the [Co(tolyl-terpy)2]2+ complex. The permanent
build-up of [Co(tolyl-terpy)2]2+ arises following the mechanism
showed in Scheme 3:
*
hν
RuII*
CoIII
CoII
RuII
H2O
O=P(Ph)3
P•+(Ph)3
RuIII
P(Ph)3
Scheme 3. Photoinduced reduction mechanism of 17+ into 16+ in the presence of
P(Ph)3.
With a large excess of P(Ph)3, the bimolecular reaction that
leads to the irreversible oxidation of the phosphine is sufficiently
efficient to short-circuit the back electron transfer between
[Ru(bpy)3]3+ and [Co(tolyl-terpy)2]2+. Evolution of the absorbance
of [Co(tolyl-terpy)2]2+ is followed at 513 nm during the irradiation
time (Fig. 5 inset). The transformation is almost finished after
100 min and the absorbance value reached indicates that the trans-
formation is quantitative. For 17+ the same behaviour is observed
and illustrated in Fig. 6. The absorption at 350 nm decreases and
a small increase at 513 nm at the foot of the [Ru(bpy)3]2+ MLCT
unit band is observed, with an isobestic point at 400 nm. The
absorption at 513 nm can be followed during irradiation time
and fitted as in Fig. 6 (inset) by an exponential function. It gives
a time constant of K = 4.3 ꢁ 10ꢀ2 minꢀ1
(s = 23 min) compared to
(s = 33 min) for the mixture of complexes. The
3.1 ꢁ 10ꢀ2 minꢀ1
photoinduced reduction of the Co(III) appears then more efficient
within the superstructured complex than in the simple mixture
of the parent complexes, where [Ru(bpy)3]2+ is at lower concentra-
tion. Prolonged irradiation does not lead to the reduction of the
Co(II) core to a Co(I) one since the absorbance band at 513 nm is
stable. Two reasons for this lack of reactivity can be listed: (i) the
Co(I) complexes are not stable in an octahedral environment, and
the back electron transfer between the transient Ru(III)–Co(I)–
Ru(II) species is too efficient to be short-circuited by an electron
transfer involving the external P(Ph)3; (ii) the oxidative quenching
process in 16+ that would lead to the transient Ru(III)–Co(I)–Ru(II)
species can be, for some kinetical consideration, neglected toward
the reductive one (following Eq. (8)) in the overall quenching pro-
Fig. 6. Visible absorption change of a mixture of 17+ (0.022 mM), and PPh3 (15 mM)
in CH3CN + 0.1 M Bu4NClO4 under visible irradiation; l = 1 cm.
complexes in aqueous acetonitrile solution where the photoin-
duced oxidation process is believed more efficient than the reduc-
tive one [1g].
*
cess of the Ru(II) centre. This behaviour is somehow different that
what was evidenced in a mixture of [Co(bpy)3]2+ and [Ru(bpy)3]2+
3.4. Photoinduced oxidation of 16+
To induce the oxidation of 16+ into 17+ under irradiation, an irre-
versible electron acceptor is required. We chose a phenacyldimeth-
yl sulfonium salt (R–S+(CH3)2, PF6ꢀ) which exhibits an irreversible
reduction peak at Epc = ꢀ1.0 V vs Ag/AgNO3 in CH3CN [23]. The
irreversibility of the sulfonium reduction is due to a one-electron
reductive cleavage reaction that leads to the phenacyl radical,
which is then converted into its hydrocarbon derivatives by reac-
tion with the solvent.
Since the quenching rate constant of [Ru(bpy)3]2+ by R–
*
S+(CH3)2 determined by a Stern-Vollmer plot (4 ꢁ 106 Mꢀ1 sꢀ1) is
considerably much lower than the quenching rate of the process
occurring between [Ru(bpy)3]2+ and [Co(tolyl-terpy)2]2+ (kq =
*
1.6 ꢁ 109 Mꢀ1 sꢀ1), photoinduced build-up of 17+ from 16+ is
mainly attributed to the process depicted in Scheme 4. The photo-
generated species noted Ru(I)–Co(III)–Ru(II) (where Ru(I) stands
for the formal [RuII(bpyÅꢀ)(bpy)(bpy-terpy)] subunit) is then able
to be oxidized by the sulfonium salt present in large excess in
agreement with its Epc values, preventing the back electron trans-
fer process.
Fig. 5. Visible absorption change of a mixture of [Co(tolyl-terpy)2]3+ (0.15 mM),
[Ru(bpy)3]2+ (0.02 mM) and PPh3 (15 mM) in CH3CN + 0.1 M Bu4NClO4 under visible
irradiation (k = 400 nm, P = 25 mW); l = 1 cm optical pathway.
A solution of 16+ with R–S+(CH3)2 has been irradiated and the
photoinduced transformation is followed by the evolution of the

J. Lombard et al. / Inorganica Chimica Acta 363 (2010) 234–242
241
be only an oxidative quenching, whereas in 16+ the quenching fol-
lows different process that may occur in parallel (energy transfer,
oxidative and reductive electron transfers). The efficiency of the
hν
RuII*
CoII
photoinduced formation of Ru(I)–Co(III)–Ru(II) from 16+ is there-
*
CoIII
RuII
fore lower. Moreover it has been suggested that the formation of
a polypyridyl Co(III) core from a Co(II) one is accompanying by a
negative entropy variation, that is thermodynamically less favour-
able [21]. Indeed the Co–N bond distances are shorter in the case of
a [Co(terpy)2]3+ compared to [Co(terpy)2]2+ [17,24]. This entropy
variation can also be a reason of the lower Arrhenius activation en-
ergy for the photoinduced process occurring into 17+ compared to
16+ and hence the difference of the relative time for the photo-
conversion.
solvent
RuI
RH + S(CH3)2
R• + S(CH3)2
R-S+(CH3)2
Scheme 4. Photoinduced oxidation mechanism of 16+ into 17+ in the presence of R–
S+(CH3)2. RuI stands for the formal [RuII(bpyꢆ-)(bpy)(bpy-terpy)] subunit.
4. Conclusion
electronic absorption spectrum (Fig. 7). During irradiation, the
absorption band at 513 nm disappears and a new one appears at
350 nm. This spectrum evolution occurs with an isobestic point
(at least of the beginning of the transformation) located at
400 nm and is in accordance with the oxidation of Co(II) into
Co(III). Comparison of the two photoinduced electron rates (as
shown in Figs. 6 and 7) indicates that the oxidation of the Co(II)
core is five times longer than the reduction of the Co(III) one for
the same experimental conditions. Furthermore a maximum of
only 80% of Co(II) is oxidized into Co(III) as estimated by the absor-
bance reaches at 350 nm. During the irradiation some degradation
of the trinuclear complex occurs as demonstrated by the slight de-
crease of the absorbance of the Ru(II)-tris-bipyridine subunit at
450 nm.
In this study we have evaluated the possibilities to achieve a net
photoinduced interconversion between the Co(II) and the Co(III)
cores in a trinuclear Ru(II)–Co(II/III)–Ru(II) complex (16+/7+) in
CH3CN. It appears that under continuous irradiation performed at
405 nm, in the presence of P(Ph)3 as sacrificial electron donor,
17+ is quantitatively converted into 16+ within 100 min, whereas
16+ is markedly slower and only partially converted into 17+ in
the presence of a sacrificial electron acceptor like a sulfonium salt.
This difference of behaviours can be attributed to the quenching
mechanisms of the excited state of a Ru(II) subunit in those com-
plexes. In 17+ the quenching is only an oxidative one whereas in
16+ several quenching processes are probably involved. Moreover
the electron transfer that occurs into 17+ under continuous irradi-
ation induces a spin relaxation from a low spin Co(III) to a high spin
Co(II) core. This relaxation leads to some rearrangements of the
complexes (bonds and angles) that are thermodynamically more
favourable in the case of the photoinduced reduction of 17+ com-
pared to the photoinduced oxidation of 16+. All these reasons
may explain the difference of the kinetics of both processes. Finally
prolonged irradiation of 16+ causes also some degradation of the
Ru(II) subunits. Nevertheless 17+ appears as good candidate to
store electron on the cobalt centre, under irradiation, that can be
used in a future reduction reaction. This work follows a previous
one where we evidenced the possibility to store under irradiation
an oxidative equivalent in a similar [{RuII(bpy)2(bpy-terpy)}2FeII]6+
complex in the presence of ArN2+ [9], both systems can be coupled
to construct a dual photoelectro-chemical cell.
A mixture of complexes [Ru(bpy)3]2+ and [Co(tolyl-terpy)2]2+
with R–S+(CH3)2 in the respective concentration 0.013, 0.15 and
15 mM has also been irradiated at 405 nm. The same conclusion
can been drawn: the formation of Co(III) is evidenced by its UV–
Visible absorption signature, the photo-oxidation takes much long-
er time (after 790 min only half of the initial [Co(tolyl-terpy)2]2+
concentration is converted into its Co(III) form) than the photoin-
duced reduction of the Co(II) to Co(III) core and a degradation of
the [Ru(bpy)3]2+ is also observed. The slower overall kinetical pro-
cess, which induces a longer irradiation time, is presumably
responsible of the degradation of the [Ru(bpy)3]2+ occurring in
parallel.
Some kinetically and thermodynamically reasons may explain
theses differences in the relative time of the overall interconver-
sion process. In 17+ the photoinduced interaction is supposed to
Acknowledgements
The authors thank the Agence Nationale pour la Recherche
(Grant No. ANR-05-JCJC-017-01) (Polycomsa) for financial support,
the technical support from the chemistry platform hhNanoBio cam-
pusii in Grenoble (France) for luminescence lifetime measure-
ments and Dr. D. Jouvenot and Prof. J.-C. Leprêtre for their kind
help in the synthesis of the complexes.
References
[1] (a) J.-M. Lehn, J.-P. Sauvage, Nouv. J. Chim. 1 (1977) 449;
(b) M. Kirch, J.-M. Lehn, J.-P. Sauvage, Helv. Chim. Acta (1979) 1345;
(c) J. Hawecker, J.-M. Lehn, R. Ziessel, Helv. Chim. Acta (1986) 1065;
(d) K. Kayanasundaram, J. Kiwi, M. Grätzel, Helv. Chim. Acta (1978) 2720;
(e) A. Moradpour, E. Amouyal, P. Keller, H.B. Kagan, Nouv. J. Chim. 2 (1978)
547;
(f) E. Amouyal, Sol. Energy Mater. Sol. Cells 38 (1995) 249;
(g) C.V. Krishnan, B.S. Brunschwig, C. Creutz, N. Sutin, J. Am. Chem. Soc. 107
(1985) 2005;
(h) N. Sutin, C. Creutz, E. Fujita, Comments Inorg. Chem. 19 (1997) 67;
(i) W. Youngblood, S.-H. Lee, Y. Kobayashi, E. Hernandez-Pagan, P. Hoertz, T.
Moore, A. Moore, D. Gust, T. Mallouk, J. Am. Chem. Soc. 131 (2009) 926;
for a recent review (j) L Tinker, N. McDaniel, S. Bernhard, J. Mater. Chem. 19
(2009) 3328.
Fig. 7. Visible absorption change of
(15 mM) in CH3CN + 0.1 M Bu4NClO4 under visible irradiation; l = 1 cm.
a
mixture of 16+ (0.025 mM), and RS+R2

242
J. Lombard et al. / Inorganica Chimica Acta 363 (2010) 234–242
[2] (a) R. Sahai, D. Baucom, D.P. Rillema, Inorg. Chem. 25 (1986) 3843;
(b) M.-N.C. Dunand-Sauthier, A. Deronzier, X. Pradon, S. Ménage, C. Philouze, J.
Am. Chem. Soc. 119 (1997) 3173;
(c) M.-N.C. Dunand-Sauthier, A. Deronzier, A. Piron, X. Pradon, S. Ménage, J.
Am. Chem. Soc. 120 (1998) 5373;
(b) V. Balzani, A. Juris, M. Venturi, S. Campagna, S. Serroni, Chem. Rev. 96
(1996) 759;
(c) C.A. Bignozzi, J.R. Schoonover, F. Scandola, Prog. Inorg. Chem. 44 (1997) 1;
(d) L. Hammarström, Curr. Opin. Chem. Biol. 7 (2003) 666;
(e) S. Rau, D. Walter, J.G. Vos, Dalton Trans. (2007) 915.
[3] (a) S. Rau, B. Schäfer, D. Gleich, E. Anders, M. Rudolph, M. Friedrich, H. Görls, W.
Henry, J. Vos, Angew. Chem., Int. Ed. 45 (2006) 6215;
(b) H. Ozawa, M. Haga, K. Sakai, J. Am. Chem. Soc. 128 (2006) 4926;
(c) M. Elvington, J. Brown, S. Arachchige, K. Brewer, J. Am. Chem. Soc. 129
(2007) 10644;
(d) C. Baffert, S. Romain, A. Richardot, J.-C. Leprêtre, B. Lefebvre, A. Deronzier,
M.-N. Collomb, J. Am. Chem. Soc. 127 (2005) 13694.
[8] B. Galland, D. Limosin, H. Laguitton-Pasquier, A. Deronzier, Inorg. Chem.
Commun. 5 (2002) 5.
[9] J. Lombard, J.-C. Leprêtre, J. Chauvin, M.-N. Collomb, A. Deronzier, Dalton Trans.
(2008) 658.
[10] (a) X. Song, Y. Lei, S. Wallendal, M. Perkovic, D. Jackman, J. Endicott, D.P.
Rillema, J. Phys. Chem. 97 (1993) 3225;
(d) H. Ozawa, Y. Yokoyama, M.-A. Haga, K. Sakai, Dalton Trans. (2007) 1197;
(e) S.M. Arachchige, J. Brown, K. Brewer, J. Photochem. Photobiol. A 197 (2008)
13;
(b) A. Yoshimura, K. Nozaki, N. Ikeda, T. Ohno, J. Am. Chem. Soc. 115 (1993)
7521;
(f) S. Arachchige, J. Brown, E. Chang, A. Jain, D. Zigler, K. Rangan, K. Brewer,
Inorg. Chem. 48 (2009) 1989;
(c) N. Komatsuzaki, Y. Himeda, T. Hirose, H. Sugihara, K. Kasuga, Bull. Chem.
Soc. Jpn. 72 (1999) 725.
(g) P. Lei, M. Hedlund, R. Lomth, H. Rensmo, O. Johansson, L. Hammarström, J.
Am. Chem. Soc. 130 (2008) 26;
[11] E. Constable, E. Figgemeier, C. Housecroft, J. Olsson, Y. Zimmermann, Dalton
Trans. (2004) 1918.
(h) A. Fihri, V. Artero, M. Razavet, C. Baffert, W. Leibl, M. Fontecave, Angew.
Chem., Int. Ed. 47 (2008) 564;
(i) A. Fihri, V. Artero, A. Pereira, M. Fontecave, Dalton Trans. (2008) 5567.
[4] (a) B. Gholamkhass, H. Mametsuka, K. Koike, T. Tanabe, M. Furue, O. Ishitani,
Inorg. Chem. 44 (2005) 2326;
[12] E. Armani, A. Dossena, R. Marchelli, G. Casnati, Tetrahedron 40 (1984) 2035.
[13] J.V. Caspar, T.J. Meyer, J. Am. Chem. Soc. 105 (1983) 5583.
[14] F. Lafolet, J. Chauvin, M.-N. Collomb, A. Deronzier, H. Laguitton-Pasquier, J.-C.
Leprêtre, J.-C. Vial, B. Brasme, Phys. Chem. Chem. Phys. 5 (2003) 2520.
[15] J. Chambers, B. Eaves, D. Parker, R. Claxton, P. Ray, S. Slattery, Inorg. Chim. Acta
359 (2006) 2400.
[16] H. Torieda, A. Yoshimura, K. Nozaki, S. Sakai, T. Ohno, J. Phys. Chem. A 106
(2002) 11034.
[17] R. Indumathy, S. Radhika, M. Kanthimathi, T. Weyhermuller, B.U. Nair, J. Inorg.
Biochem. 101 (2007) 434.
(b) S. Sato, K. Koike, H. Inoue, O. Ishitani, Photochem. Photobiol. Sci. 6 (2007)
454;
(c) Z.-Y. Bian, K. Sumi, M. Furue, S. Sato, K. Koike, O. Ishitani, Inorg. Chem. 47
(2008) 10801.
[5] (a) D. Burdinski, E. Bothe, K. Wieghardt, Inorg. Chem. 39 (2000) 105;
(b) L. Sun, L. Hammarström, B. Akermark, S. Styring, Chem. Soc. Rev. 30 (2001)
36;
[18] M.K. Nazeeruddin, S.M. Zakeeruddin, K. Kalyanasundaram, J. Phys. Chem. 97
(1993) 9607.
(c) M. Abrahamsson, H. Baudin, A. Tran, C. Philouze, K. Berg, M. Raymond-
Johansson, L. Sun, B. Akermark, S. Styring, L. Hammarström, Inorg. Chem. 41
(2002) 1534;
[19] (a) R. Berkoff, K. Krist, H.D. Gafney, Inorg. Chem. 19 (1980) 1;
(b) D. Sandrini, M.T. Gandolfi, M. Maestri, F. Bolletta, V. Balzani, Inorg. Chem.
23 (1984) 3017.
(d) M. Borgström, N. Shaikh, O. Johansson, M. Anderlund, S. Styring, B.
Akermark, A. Magnuson, L. Hammarström, J. Am. Chem. Soc. 127 (2005) 17504.
[6] (a) C. Baffert, S. Dumas, J. Chauvin, J.-C. Leprêtre, M.-N. Collomb, A. Deronzier,
Phys. Chem. Chem. Phys. 7 (2005) 202;
[20] A. Yoshimura, Md.J. Uddin, N. Amasaki, T. Ohno, J. Phys. Chem. A 105 (2001)
10846.
[21] A. Yoshimura, K. Nozaki, N. Ikeda, T. Ohno, J. Phys. Chem. 100 (1996) 1630.
[22] (a) S. Takagi, T. Okamoto, T. Shiragami, H. Inoue, J. Org. Chem. 59 (1994) 7373;
(b) S. Yasui, M. Tsujimoto, K. Itoh, A. Ohno, J. Org. Chem. 65 (2000) 4715;
(c) S. Yasui, K. Itoh, M. Tsujimoto, A. Ohno, Bull. Chem. Soc. Jpn. 75 (2002)
1311.
[23] (a) F. Saeva, B. Morgan, J. Am. Chem. Soc. 106 (1984) 4121;
(b) C. Andrieux, M. Robert, F. Saeva, J.-M. Saveant, J. Am. Chem. Soc. 116 (1994)
7864 (and references therein).
(b) S. Romain, C. Baffert, S. Dumas, J. Chauvin, J.-C. Leprêtre, D. Daveloose, A.
Deronzier, M.-N. Collomb, Dalton Trans. 48 (2006) 5691;
(c) S. Romain, J.-C. Leprêtre, J. Chauvin, A. Deronzier, M.-N. Collomb, Inorg.
Chem. 7 (2007) 2735;
(d) M.-N. Collomb, A. Deronzier, Eur. J. Inorg. Chem. 14 (2009) 2045.
[7] (a) M.-N.C. Dunand-Sauthier, A. Deronzier, J.-C. Moutet, S. Tingry, J. Chem. Soc.,
Dalton Trans. (1996) 2503;
[24] J. Beattie, H. Elsbernd, Inorg. Chim. Acta 240 (1995) 641.