Ruthenium(II) as a novel labile partner in thermodynamic self-assembly of heterobimetallic d-f triple-stranded helicates

Article abstract of DOI:10.1002/chem.200400092

Unsymmetrical substituted bidentate benzimidazol-2-ylpyridine ligands L2 and L3 react with [Ru(dm-so)₄Cl₂] in ethanol to give statistical 1:3 mixtures of fac-[Ru(Li)₃]²⁺ mer-[Ru(Li)₃]²⁺ (i=2, 3; ΔGθ _{isomerisation}= -2.7 kJ mol^-1). In more polar solvents (acetonitrile, methanol), the free energy of the facial?meridional isomerisation process favours mer-[Ru(Li)₃]²⁺, which is the only isomer observed in solution at the equilibrium (ΔGθ _{isomerisation}≤-11.4 kJ mol^-1). Since the latter process takes several days for [Ru(L2)₃]²⁺, fac-[Ru(L2) ₃]²⁺ and mer-[Ru(L2)₃]²⁺ have been separated by chromatography, but the 28-fold increase in velocity observed for [Ru (L3)₃]²⁺ provides only mer-[Ru(L3)₃] (ClO₄)₂ after chromatography (RuC₆₀H ₅₁N₉O₈Cl₂, monoclinic, P2 ₁/n, Z=4). The facial isomer can be stabilised when an appended tridentate binding unit, connected at the 5-position of the benzimidazol-2- ylpyridine unit in ligand L1, interacts with nine-coordinate lanthanides (III). The free energy of the facial?meridional isomerisation is reversed (ΔGθ_{isomerisation}≥ 11.4 kJ mol^-1), and the Ru-N bonds are labile enough to allow the quantitative thermodynamic self-assembly of HHH-[RuLu(L1)₃]⁵⁺ within hours ([RuLu(L1)₃](CF₃SO₃)_4.5Cl _0.5(CH₃OH)_2.5: RuLuC₁₀₆H ₁₀₉Cl_0.5N₂₁O₁₉S_4.5F _13.5, triclinic, P1, Z=2). Electrochemical and photophysical studies show that the benzimidazol-2-ylpyridine units in L1-L3 display similar π-acceptor properties to, but stronger π-donor properties than, those found in 2,2′-bipyridine. This shifts the intraligand π→π * and the MLCT transitions toward lower energies in the pseudo-octahedral [Ru(Li)₃]²⁺ (i=2, 3) chromophores. The concomitant short lifetime of the ³MLCT excited state points to efficient, thermally activated quenching via low-energy Ru-centred d-d states, a limitation which is partially overcome by mechanical coupling in HHH-[RuLu(L1)₃] ⁵⁺.

Full text of DOI:10.1002/chem.200400092

FULL PAPER
Ruthenium(ii) as a Novel Labile Partner in Thermodynamic Self-Assembly of
Heterobimetallic d f Triple-Stranded Helicates
Stÿphane Torelli,[a] Sandra Delahaye,[b] Andreas Hauser,[b] Gÿrald Bernardinelli,[c] and
Claude Piguet*[a]
Abstract: Unsymmetrical substituted
bidentate benzimidazol-2-ylpyridine li-
gands L2 and L3 react with [Ru(dm-
so)4Cl2] in ethanol to give statistical 1:3
mixtures of fac-[Ru(Li)3]2+ and mer-
[Ru(L3)3](ClO4)2 after chromatography
(RuC60H51N9O8Cl2, monoclinic, P21/n,
Z=4). The facial isomer can be stabi-
lised when an appended tridentate
binding unit, connected at the 5-posi-
tion of the benzimidazol-2-ylpyridine
unit in ligand L1, interacts with nine-
coordinate lanthanides(iii). The free
energy of the facialÐmeridional iso-
([RuLu(L1)3](CF3SO3)4.5Cl0.5(CH3OH)2.5:
RuLuC106H109Cl0.5N21O19S4.5F13.5, triclin-
≈
ic, P1, Z=2). Electrochemical and
photophysical studies show that the
benzimidazol-2-ylpyridine units in L1
L3 display similar p-acceptor proper-
ties to, but stronger p-donor properties
than, those found in 2,2’-bipyridine.
This shifts the intraligand p!p* and
the MLCT transitions toward lower
energies in the pseudo-octahedral
[Ru(Li)3]2+ (i=2, 3) chromophores.
The concomitant short lifetime of the
3MLCT excited state points to efficient,
thermally activated quenching via low-
energy Ru-centred d d states, a limita-
tion which is partially overcome by
[Ru(Li)3]2+ (i=2, 3; DGAisomerisation
=
À2.7 kJmolÀ1). In more polar solvents
(acetonitrile, methanol), the free
energy of the facialÐmeridional iso-
merisation process favours mer-
[Ru(Li)3]2+, which is the only isomer
observed in solution at the equilibrium
(DGAisomerisation ꢀÀ11.4 kJmolÀ1). Since
the latter process takes several days for
[Ru(L2)3]2+, fac-[Ru(L2)3]2+ and mer-
[Ru(L2)3]2+ have been separated by
chromatography, but the 28-fold in-
crease in velocity observed for
merisation is reversed (DGAisomerisation
ꢁ
À1
À
11.4 kJmol ), and the Ru N bonds
are labile enough to allow the quantita-
tive thermodynamic self-assembly of
HHH-[RuLu(L1)3]5+
within hours
Keywords: helical structures ¥ iso-
merization ¥ lanthanides ¥ rutheni-
um ¥ self-assembly
mechanical
coupling
in
HHH-
[Ru(L3)3]2+
provides
only
mer-
[RuLu(L1)3]5+
.
[a] Dr. S. Torelli, Prof. Dr. C. Piguet
Introduction
Department of Inorganic, Analytical and Applied Chemistry
University of Geneva, 30 quai E. Ansermet
1211 Geneva 4 (Switzerland)
Kinetically inert, pseudo-octahedral [Ru(a,a’-diimine)3]2+
building blocks such as [Ru(2,2’-bipyridine)3]2+ and its de-
rivatives are used universally for inducing specific photo-
physical and electrochemical properties in coordination
complexes.[1] Of particular interest is their introduction into
metallosupramolecular polymetallic functional artificial pho-
tosynthetic systems in which electrons are directed towards
specific sites in order to perform light-activated secondary
reactions.[2] In a closely related context, Klink et al. demon-
strated that [Ru(2,2’-bipyridine)3]2+ can be used as an effi-
cient photosensitiser for lanthanide-centred near-infrared
emission (Ln=Nd, Yb) occurring after intramolecular inter-
metallic 4d!4f energy transfer.[3] When C2-symmetrical bi-
dentate a,a’-diimine ligands are used, a single pair of inert
helical enantiomers results (P-[Ru(a,a’-diimine)3]2+ and M-
[Ru(a,a’-diimine)3]2+), which can be separated after interac-
tion with enantiomerically pure counter-anions.[4] However,
for bidentate ligands L with two different donor sites, the
tris-chelates may exist as two pairs of helical enantiomers:
Fax: ( +41)22-379-6830
E-mail: Claude.Piguet@chiam.unige.ch
[b] S. Delahaye, Prof. Dr. A. Hauser
Department of Physical Chemistry
University of Geneva, 30 quai E. Ansermet
1211 Geneva 4 (Switzerland)
[c] Dr G. Bernardinelli
Laboratory of X-ray Crystallography
University of Geneva, 24 quai E. Ansermet
1211 Geneva 4 (Switzerland)
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author. 1H NMR data for
complexes 1 3 are collected in Table S1, while Tables S2 S4 list se-
lected structural parameters for the metallic coordination spheres in 4
and 6. Figure S1 shows plots of ln(jfac(t)j) versus t for [Ru(L2)3]2+
and [Ru(L3)3]2+; Figures S2 and S5 display the packing of the cations
in the crystal structures of 4 and 6. Figure S3 shows photophysical
data for [RuLu(L1)3]5+ in solution, Figure S4 exhibits an optimised
superimposition of the molecular structures of [RuLu(L1)3]5+ and
[CoLu(L1)3]6+, and Figure S6 displays variable-temperature H NMR
1
spectra for [Zn(L2)3]2+ and [Zn(L3)3]2+
.
Chem. Eur. J. 2004, 10, 3503 3516
DOI: 10.1002/chem.200400092
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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FULL PAPER
P-fac-[Ru(L)3]2+/M-fac-[Ru(L)3]2+ and P-mer-[Ru(L)3]2+/M-
mer-[Ru(L)3]2+, in which fac stands for the C3-symmetrical
facial isomer (three ligands with parallel orientations) and
mer characterises the C1-symmetrical meridional isomer
(one ligand adopts the opposite orientation).[5] Although the
separation of fac/mer isomers on the laboratory scale has
been reported together with different spectroscopic proper-
ties for each isomer,[6] it is only recently that pure facial iso-
mers have been designed for further functionalisation and
incorporation into stereocontrolled molecular architec-
tures.[7] Following our interest in the design of the triple-
stranded d f helicates [MLn(L1)3]6+ (Figure 1) in which the
stability of the inert helicates [CrLn(L1)3]6+ in solution. fac-
[Ru(benzimidazol-2-ylpyridine)3]2+ thus corresponds to an
attractive compromise displaying 1) photophysical proper-
ties compatible with intramolecular intermetallic 4d 4f
energy transfer processes in [RuLn(L1)3]5+, 2) a diamagnetic
1A1 (low-spin 4d6) ground state compatible with efficient
structural characterisation in solution by NMR techniques
and c) a small 2+ charge which reduces intermetallic elec-
trostatic repulsion in the final helicates. However, the relat-
ed [RuIII(a,a’-diimine)3]3+ is too oxidizing and kinetically
inert[13] to be used as a precursor in strict self-assembly pro-
cesses with lanthanides and L1, and the introduction of inert
RuII cannot take advantage of
reductive post-modification of
an RuIII analogue. Encouraged
by the 57% yield reported for
the formation of [(CuI)3{fac-
RuII(pyridine-pyrazolate)3}2]À,
which implies quite a fast (that
is, on the time scale of an
hour) fac-[RuII(pyridine-pyrazol-
ate)3]ÀÐmer-[RuII(pyridine-pyr-
azolate)3]À process,[14] we have
explored the factors that could
be responsible for the tuning of
the lability in pseudo-octahe-
dral [Ru(benzimidazol-2-ylpyri-
dine)3]2+ in order to induce
strict self-assembly between L1,
LnIII, and RuII. We report in
this paper the kinetic and ther-
modynamic properties of the
facialÐmeridional
isomerisa-
tion process occurring in
[Ru(Li)3]2+ (i=2, 3), together
with the first introduction of
the 4d-block RuII cation into
Figure 1. Structures of the ligands L1 L6, and of the heterobimetallic d f triple-stranded helicates HHH-
[LnM(L1)3]n+ (the crystal structure of HHH-[LuCr(L1)3]6+ is represented here).[9]
the d f helicate [RuLu(L1)3]5+
.
d-block ion (M=CrIII, CoIII) is inert enough to provide the
chiral facial receptors fac-[M(L1)3]3+ upon decomplexation
of LnIII,[8,9] we plan to investigate the introduction of inert
4d-block RuII ions as partners in strict self-assembly process-
es. Such a challenging approach has been developed success-
fully for CoIII[8] and CrIII,[9] because they possess reduced
forms (CoII and CrII) which exhibit similar stereochemical
preferences but which are labile enough to allow the explo-
ration of the energy hypersurface of the assembly process,
before undergoing oxidative post-modification leading to
the final inert architectures.[10] Interestingly, fac-[Cr(L1)3]3+
can be separated into its helical P and M enantiomers to
give dual CrIII and EuIII-centred circularly polarised emission
after recombination in the chiral PP-[CrEu(L1)3]6+ and
MM-[CrEu(L1)3]6+ helicates.[11] Moreover, the specific pho-
tophysical properties of fac-[Cr(benzimidazol-2-ylpyri-
dine)3]3+ have been exploited for sensitizing long-lived near-
infrared emission in rac-[CrLn(L1)3]6+ (Ln=Nd, Yb).[12]
However, the long electronic relaxation of paramagnetic
CrIII combined with its high positive charge strongly limits
the structural characterisation (NMR spectroscopy) and the
Particular attention is also focused on the photophysical
properties of the RuII centrs in these complexes for the
future induction of directional light-conversion processes in
luminescent heterobimetallic helicates.
Results and Discussion
Preparation and characterisation of mer-[Ru(L2)3](ClO4)2¥
2H2O (1), fac-[Ru(L2)3](ClO4)2¥2H2O (2) and mer-
[Ru(L3)3](ClO4)2¥CH3CN¥H2O (3): The bidentate ligand L2
was obtained according to a literature procedure[15] in which
the reductive cyclisation of an ortho-nitroarene carbox-
amide precursor provides the substituted benzimidazole ring
as the key step.[16] The same strategy was used for the syn-
thesis of L3, which was obtained in good yield (90%)
(Scheme 1). Refluxing Li (i=2, 3; 3 equiv) with [Ru(dm-
so)4Cl2] (1 equiv) in ethanol for 24 h followed by metathesis
with NaClO4 and precipitation from acetonitrile/diethyl
ether provided [Ru(L2)3](ClO4)2¥2H2O and [Ru(L3)3]-
(ClO4)2¥CH3CN¥H2O in 56% and 72% yield, respectively.
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Triple-Stranded Helicates
3503 3516
0.33 ratio reported for the analogous complex
[Ru(L6)3](PF6)2,[5b] although deviations favoring the meri-
dional isomer are often observed because of steric con-
straints in the facial one.[5,17]
[Ru(L2)3](ClO4)2¥2H2O was dissolved in dichloromethane,
extracted with an aqueous 0.1 molLÀ1 solution of
Na2Sb2[(+)-C4O6H2]2¥5H2O,[4a] and sorbed onto a Sephadex
SP-C25 ion exchange resin. Further elution with
Na2Sb2[(+)-C4O6H2]2¥5H2O (0.1 molLÀ1 in water) provided
two successive red bands which were collected separately.
Red solids were finally isolated by precipitation with
NaClO4. Their elemental analyses match the original empiri-
1
cal formula [Ru(L2)3](ClO4)2¥2H2O, but the H NMR spec-
trum of fraction I (with the shortest retention time: 1,
yield=69%) shows only the three nonequivalent bidentate
ligands of the C1-symmetrical mer-[Ru(L2)3]2+ (Fig-
ure 3a).[5,17] Clearly, fraction II (with the longest retention
time: 2, yield=20%) exhibits a much simpler 1H NMR
spectrum corresponding to the C3-symmetrical fac-
[Ru(L2)3]2+ (Figure 3b). The satisfying 89% recovery of the
original compound and the approximate invariance of the
fac/mer ratio (0.29:1 after chromatography) demonstrate
that [Ru(L2)3]2+ is inert enough in a polar solvent to be sep-
arated by chromatogaphy (3 4 h time scale). However,
when [Ru(L3)3](ClO4)2¥CH3CN¥H2O was subjected to chro-
Scheme 1. Synthesis of L3.
The 1H NMR spectra of
these complexes in CD3CN, re-
corded immediately after solu-
bilisation of the solid samples,
were characteristic of statistical
1:3 mixtures of fac-[Ru(Li)3]2+
and mer-[Ru(Li)3]2+ (i=2, 3)[5]
with four singlets of equal in-
tensities for the methyl groups
Me1. For the C3-symmetrical
fac-[Ru(Li)3]2+ (i=2, 3), the
three ligands are equivalent
and Me1 appears as a singlet at
d=2.25 ppm (fac-[Ru(L2)3]2+
Figure 2a) or at d=2.23 ppm
(fac-[Ru(L3)3]2+
(Figure 2b).
The three other signals of
equal intensities are assigned
to Me1 in the C1-symmetrical
mer-[Ru(Li)3]2+ (i=2, 3), in
which each ligand is nonequi-
valent (Figure 1). A complete
and
reliable
assignment
(Table S1, Supporting Informa-
tion) has been performed:
1) by using two-dimensional
1H 1H COSY and 1H 1H
NOESY spectra and 2) by
comparison with the 1H NMR
Figure 2. 1H NMR spectra of a) [Ru(L2)3](ClO4)2¥2H2O and b) [Ru(L3)3](ClO4)2¥CH3CN¥H2O, highlighting the
1:3 mixture of fac/mer isomers (CD3CN, 298 K; numbering as in Figure 1).
spectra of the pure isomers 1 3 (Figure 3a c, respectively).
The statistical 1:3 fac/mer mixtures found for [Ru(L2)3]-
(ClO4)2¥2H2O and [Ru(L3)3](ClO4)2¥CH3CN¥H2O match the
matography under the same conditions, a single large red
band was collected. Precipitation with NaClO4 gave a red
microcrystalline precipitate displaying the same constitution
Chem. Eur. J. 2004, 10, 3503 3516
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C. Piguet et al.
FULL PAPER
Figure 3. 1H NMR spectra of a) mer-[Ru(L2)3](ClO4)2¥2H2O (1), b) fac-[Ru(L2)3](ClO4)2¥2H2O (2) and c) mer-[Ru(L3)3](ClO4)2¥CH3CN¥H2O (3)
(CD3CN, 298 K; * denotes residual peak of solvent; numbering as in Figure 1 and Scheme 1).
as the original complex( 3, yield=90%). However, its
1H NMR spectrum corresponds to the exclusive existence of
mer-[Ru(L3)3]2+ in solution (Figure 3c), which suggests that
1) a relatively fast fac-[Ru(L3)3]2+Ðmer-[Ru(L3)3]2+ iso-
merisation process occurs during the chromatographic sepa-
ration and 2) mer-[Ru(L3)3]2+ is stabilised beyond the ex-
(erel =8.9), the original 1:3 mixture of fac-[Ru(L2)3]2+ and
mer-[Ru(L2)3]2+ remains invariant for months. In ethanol
(erel =24.5), small changes occur after one week, and in
more polar solvents (CD3CN, erel =37.5; CD3OD, erel =32.7)
the signals corresponding to the facial isomer disappear
slowly within five days to give mer-[Ru(L2)3]2+ exclusively
according to Equation (1) (Figure 4).
pected statistical entropic contribution: DGs1tat =ÀTDS1stat
=
À2.7 kJmolÀ1 at 298 K and Ks1tat =3.[5a,18] According to the
1
limit of detection of fac-[Ru(L3)3]2+ by H NMR spectros-
kfac
kfac
2þ
2þG
H
ð1Þ
fac-½RuðLiÞ3Š
mer-½RuðLiÞ Š
K1 ¼
kmer
3
copy (ꢁ1%), we calculate from the above equilibrium that
kmer
K1([Ru(L3)3]2+)ꢁ99,
À11.4 kJmolÀ1.
and
DGAisomerization([Ru(L3)3]2+)ꢀ
The complete mathematical treatment of the time-de-
pendent concentrations of fac-[Ru(L2)3]2+ (jfac(t)j)and of
mer-[Ru(L2)3]2+ (jmer(t)j) according to Equation (1) with
Kinetics of the fac-[Ru(Li)3]2+Ðmer-[Ru(Li)3]2+ (i=2, 3)
iomerisation process in solution: In weakly polar CD2Cl2
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Triple-Stranded Helicates
3503 3516
The plot of (jfac(t)j) versus t for fac-[Ru(L2)3]2+ in
CD3CN (298 K) is indeed linear and its slope corresponds to
Àkfac (Figure S1a, Supporting Information), from which we
298
calculate k ([Ru(L2)3]2+)=4.7(6)î10À6 sÀ1 with a half-life
fac
of t21 98([Ru(L2)3]2+)=41.03 h, in agreement with the limited
=
isom2erisation observed during the chromatographic separa-
tion of [Ru(L2)3]2+. However, the slow formation of mono-
crystals of [Ru(L2)3](ClO4)2 resulting from diffusion of
heavy ethers (tert-butyl methyl ether or diisopropyl ether)
into a solution of the complexin acetonitrile is limited to
the isolation of mer-[Ru(L2)3](ClO4)2. Interestingly, the in-
troduction of the bulky benzyl substituents in [Ru(L3)3]2+
significantly increases the lability of the fac!mer isomerisa-
tion process, and the analysis of the linear plot ln(jfac(t)j)
versus
t
(Figure S1b, Supporting Information) gives
([Ru(L3)3]2+)=1.3(1)î10À4 sÀ1 with
half-life of
t21 98([Ru(L3)3]2+)=1.45 h. This 28-fold increase in velocity
298
k
a
fac
=
2
explains the exclusive isolation of mer-[Ru(L3)3](ClO4)2
after column chromatography. We obtained monocrystals of
both mer-[Ru(Li)3](ClO4)2 (i=2, 3), but the X-ray diffrac-
tion data show that the benzimidazole and the pyridine
rings in mer-[Ru(L2)3](ClO4)2 are so similar that they crys-
tallise randomly over two positions. This limitation is re-
moved for mer-[Ru(L3)3](ClO4)2 (4) because the benzyl
groups connected to the benzimidazole rings induce greater
structural differences between the two aromatic rings, and a
regular packing results in the crystals of 4. In the absence of
detailed variable-temperature thermodynamic and kinetic
studies [that is, separation of the enthalpic and entropic con-
tributions to the thermodynamic (van×t Hoff equation) and
to the kinetic (Eyring equation) properties], the origins of
the increased lability of fac-[Ru(Li)3]2+ observed 1) on
going from [Ru(L2)3]2+ to [Ru(L3)3]2+ and 2) on increasing
the polarity of the solvent remain difficult to rationalise.
However, this observation has important synthetic conse-
quences for the use of RuII as a ™labile∫ partner in strict
self-assembly processes with L1, because the required ™error
checking∫ processes become available on the timescale of
an hour under judiciously chosen conditions.[10]
1
Figure 4. Selected parts of the time-dependent H NMR spectra recorded
for [Ru(L2)3](ClO4)2¥2H2O, showing the slow isomerisation of fac-
[Ru(L2)3]2+ (marked *) into mer-[Ru(L2)3]2+ according to Equation (1)
(CD3CN, 298 K; numbering as in Figure 1).
the first-order kinetic constants kfac and kmer leads to Equa-
tions (2) and (3).[19]
kmer
kfac þ kmer
kfacjfacð0ÞjÀkmerjmerð0Þj
kfac þ kmer
jfacðtÞj ¼
ðjfacð0Þj þ jmerð0ÞjÞþ
ꢀ
ꢁ
ð2Þ
ð3Þ
expðÀðkfac þ kmerÞtÞ
kfac
kfac þ kmer
kfacjfacð0ÞjÀkmerjmerð0Þj
kfac þ kmer
jmerðtÞj ¼
ðjfacð0Þj þ jmerð0ÞjÞÀ
ꢀ
ꢁ
expðÀðkfac þ kmerÞtÞ
As previously noticed for [Ru(L3)3]2+, mer-[Ru(L2)3]2+ is
the only isomer detected at the thermodynamic equilibrium
in CD3CN or CD3OD, which implies that the latter complex
is stabilised beyond the statistical entropic contribution for
which we expect a final 1:3 mixture of fac and mer isomers
Crystal and molecular structure of mer-[Ru(L3)3](ClO4)2
(4): The crystal structure of 4 shows RuII in a six-coordinate
environment, coordinated by the nitrogen donor atoms of
the three bidentate benzimidazol-2-ylpyridine ligands. Li-
gands a and b adopt the same orientation, while ligand c is
reversed; this confirms the formation of the cation mer-
[Ru(L3)3]2+ (Figure 5). One ionic perchlorate is disordered
(see Experimental Section), but shows no other interesting
feature. The coordination sphere of RuII can best be de-
scribed as an octahedron flattened along a pseudo-C3 axis
defined by the least-squares line passing through the ruthe-
nium and the barycentres of the triangular faces
F1 (N1a,N1b,N3c) and F2 (N1c,N3a,N3b; Figure 5).
(DS1stat =9.1 JmolÀ1 KÀ1,DH1stat =0 kJmolÀ1, DGs1tat =TDS1stat
=
À2.7 kJmolÀ1 at 298 K and Ks1tat =3).[5a,18] Again, if we fixthe
limit of detection of fac-[Ru(L2)3]2+ by 1H NMR spectrosco-
py at around 1%, we calculate from Equation (1) that
K1([Ru(L2)3]2+)ꢁ99
and
DGAisomerisation([Ru(L2)3]2+)ꢀ
À11.4 kJmolÀ1. This translates into kfac ꢁ99kmer for
[Ru(L2)3]2+ in CD3CN at 298 K, which allows us to neglect
the latter constant and Equations (2) and (3) reduce to the
classical Equations (4) and (5).
The classical geometrical analysis that measures the bend-
ing (f), flattening (qi) and twist (wij) of the octahedron[8,9,20]
displays a negligible bending (f=177.48 compared with f=
1808 for a perfect octahedron; Table S2, Supporting Infor-
mation), but a significant flattening along the pseudo-C3 axis
jfacðtÞj ¼ jfacð0Þj expðÀkfactÞ
ð4Þ
ð5Þ
jmerðtÞj ¼ jmerð0ÞjÀjfacð0Þj expðÀkfactÞ
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C. Piguet et al.
FULL PAPER
hedron (wij intraligand=608) towards a trigonal prism (wij
intraligand=08) as previously noticed in the crystal struc-
[21]
ture of [FeLa(L1)3]5+
.
The same geometrical analysis has
been applied to the reference complex[Ru(2,2 ’-bipyridi-
[22]
ne)3](ClO4)2 and shows very similar distortions (average
angles: f=177.48, qi =59.1(1.4)8, wij intraligand=51.0(7)8;
À
Table S2, Supporting Information). Similarly, the Ru
N1(benzimidazole) bonds (average: 2.06(1) ä; Table 1) and
À
Ru N3(pyridine) bonds (average: 2.078(2) ä; Table 1) in
mer-[Ru(L3)3]2+ closely match Ru N(pyridine)=2.058(2) ä
À
reported for [Ru(2,2’-bipyridine)3](ClO4)2.[22]
We thus conclude that the replacement of a six-membered
pyridine ring in 2,2’-bipyridine with a five-membered imida-
zole ring in L3 has a negligible effect on the arrangement of
the three bidentate ligands around RuII, and that the signifi-
cantly increased lability of the fac-[Ru(L3)3]2+Ðmer-
[Ru(L3)3]2+ isomerisation cannot be ascribed to a specific
electronic and/or steric effect induced by the benzyl sub-
À
stituents that affects the Ru N bonds. Although they are
not relevant to the solution behaviour, it is worth noting
that intermolecular p-stacking interactions occur between
the pyridine ring of ligand c and the peripheral phenyl ring
of the benzyl substituent of ligand a (interplanar angle
5.86(3)8, average interplanar distance 3.49 ä; Figure S2,
Supporting Information).
Figure 5. Perspective view of mer-[Ru(L3)3]2+ in the crystal structure of 4
showing the atomic numbering scheme.
(qi =57.6 62.88, average 60.3(1.8)8 compared with qi =54.78
for a perfect octahedron; Table S2, Supporting Information).
This distortion is typical for the [M(benzimidazol-2-ylpyri-
dine)3] units in the heterobimetallic d f helicates
[MLn(L1)3]n+ (M=FeII,[21] CrIII,[9] CoIII[8]), and it results
from the constrained intraligand bite angles, which are
smaller (77.1 77.78, average 77.4(3)8 Table 1), than the 908
required for a perfect octahedron. The twist of the two tri-
angular faces F1 and F2 in mer-[Ru(L3)3]2+ (wij intraligand=
50.6 53.6, average 51.9(1.5)8; Table S2, Supporting Informa-
tion) corresponds to a slight distortion from a perfect octa-
Electrochemical and photophysical properties of 1 3: The
cyclic voltammograms of mer-[Ru(L2)3]2+ and fac-
[Ru(L2)3]2+ in acetonitrile (0.1 molLÀ1 [N(nBu)4]ClO4) are
identical within experimental error and show the expected
reversible oxidation wave assigned to the metal-centred
RuII/RuIII process (E1/2([Ru(L2)3]3+/[Ru(L2)3]2+)=0.94 V
versus SCE; Table 2), together with the three ligand-centred
reductions in the range À1.37 to À1.82 V versus SCE
(Table 2; Figure 6).
This behaviour parallels that reported for [Ru(2,2’-bipyri-
dine)3]2+[13,23] except that the
RuII/RuIII
process
is cathodically
in
[Ru(L2)3]2+
Table 1. Selected bond lengths [ä] and bond angles [8] in mer-[Ru(L3)3](ClO4)2 (4) and [Ru(2,2’-bipyridi-
ne)3](ClO4)2.
shifted by 330 mV, and the first
ligand reduction is almost invar-
iant (cathodic shift 60 mV;
Table 2). Since the latter pro-
cess reflects the energy of the
p*-accepting orbitals in the
complex,[24] we deduce that L2
and 2,2’-bipyridine display com-
parable p-accepting properties.
The destabilisation of the elec-
tron-rich RuII in [Ru(L2)3]2+
thus results from L2 being a
stronger p-donor than 2,2’-bi-
pyridine in the tris-chelate
ruthenium complexes, and this
is strongly supported by the
4130 4790 cmÀ1 red shift of the
ligand-centred p!p* transitions
measured for [Ru(Li)3]2+ in so-
[a]
mer-[Ru(L3)3](ClO4)2 (4)
[Ru(2,2’-bipyridine)3](ClO4)2
ligand a
ligand b
ligand c
ligands a,b
ligand c
À
À
Ru N1
2.073(3)
2.079(3)
2.054(3)
2.076(3)
2.068(3)
2.069(3)
Ru N1
2.059(3)
2.060(3)
2.056(3)
2.056(3)
À
À
Ru N3
Ru N11
N1-Ru-N3
77.3(1)
101.7(1)
85.0(1)
95.5(1)
88.6(1)
96.8(1)
98.1(1)
96.1(1)
97.0(1)
90.3(1)
171.4(1)
174.3(1)
171.7(1)
77.7(1)
77.1(1)
N1-Ru-N11
N1-Ru-N11
N1-Ru-N11’
N1A-Ru-N11’
N11-Ru-N11’A
78.6(1)
97.9(1)
92.0(1)
94.9(1)
94.8(1)
78.5(1)
N1a-Ru-N1b
N1a-Ru-N1c
N1a-Ru-N3c
N1b-Ru-N3a
N1b-Ru-N3c
N1c-Ru-N3a
N1c-Ru-N3b
N3a-Ru-N3b
N3b-Ru-N3c
N1b-Ru-N1c
N1a-Ru-N3b
N3a-Ru-N3c
N1-Ru-N11A
172.6(1)
171.0(1)
N11’-Ru-N¥N11’A
[a] Taken from ref. [22]. [Ru(2,2’-bipyridine)3](ClO4)2 possesses a crystallographic twofold axis, and ligands a
and b are thus equivalent and related by the symmetry operation A=Àx,y,0.5Àz.
3508
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Chem. Eur. J. 2004, 10, 3503 3516

Triple-Stranded Helicates
3503 3516
Table 2. Electrochemical properties of mer-[Ru(L2)3](ClO4)2 (1), fac-
[Ru(L2)3](ClO4)2 (2) and mer-[Ru(L3)3](ClO4)2 (3) in CH3CN+
0.1 molLÀ1 [N(nBu)4]ClO4 (298 K).[a]
E1/2
E1/2
E1/2
E1/2
/
Ref.
(RuIII
RuII)
/
([RuL3]2+
[RuL3]+)
/
([RuL3]+/
[RuL3])
([RuL3]/
[RuL3]À)
1
2
3
0.94
0.94
1.08
1.27
À1.37
À1.37
À0.96[b]
À1.31
À1.56
À1.56
À1.26[b]
À1.50
À1.82
À1.82
À1.41[b]
this
work
this
work
this
work
[13]
[Ru(2,2’-
À1.77
bipy)3]2+
[Ru(L5)3]2+ 0.61
[Ru(L6)3]2+ 0.59
[25]
[25]
[c]
[c]
[c]
À2.00
À2.20
[a] Half-wave potentials E1/2 [V], versus SCE. [b] Irreversible redoxpro-
cesses; E1/2 for the cathodic process is reported. [c] No observed reduc-
tion wave (ref. [25]).
lution (i=2, 3; 10À4 molLÀ1 in ethanol/methanol (4:1);
Table 3). This trend parallels that reported for the analogous
homoleptic complexes [Ru(L5)3]2+ (E1/2([Ru(L5)3]3+
[Ru(L5)3]2+)=0.61 V versus SCE),[25] [Ru(L6)3]2+ (E1/2
/
-
([Ru(L6)3]3+/[Ru(L6)3]2+)=0.59 V versus SCE),[25] and for
the heteroleptic complex[Ru(2,2 ’-bipyridine)2(L4)]2+ (E1/2-
([Ru(bipy)2(L4)]3+/[Ru(bipy)2(L4)]2+ =1.18 V
versus
SCE).[26] The introduction of benzyl substituents in mer-
[Ru(L3)3]2+ induces a global anodic shift of 140 410 mV af-
fecting all redoxprocesses (Table 2), but the main difference
concerns the irreversibility of the ligand-centred reduction
processes (Figure 6). However, the difference DE1/2 between
the oxidation and the first reduction process for [Ru(L2)3]2+
Figure 6. Cyclic voltammograms of [Ru(L2)3]2+ and mer-[Ru(L3)3]2+ for
a) oxidation and b) reduction processes (CH3CN+0.1 molLÀ1
[N(nBu)4]ClO4, 100 mVsÀ1, 298 K).
(DE1/2 =E1/2([Ru(L2)3]3+/[Ru(L2)3]2+)ÀE1/2([Ru(L2)3]2+
/
[Ru(L2)3]+)=2.31 V) and mer-[Ru(L3)3]2+ (DE1/2 =2.04 V)
remain significantly smaller
Table 3. Photophysical properties of mer-[Ru(L2)3](ClO4)2 (1), fac-[Ru(L2)3](ClO4)2 (2), mer-[Ru(L3)3](ClO4)2
(3) and HHH-[RuLu(L1)3](CF3SO3)5 (5) in ethanol/methanol (4:1; 10À4 molLÀ1).
than DE1/2 =2.58 V calculated
for [Ru(2,2’-bipyridine)3]2+ in
the same conditions.[13] We
therefore expect that the
1MLCT and 3MLCT excited
states are located at lower ener-
gies in [Ru(Li)3]2+ (i=2, 3)
T [K]
p!p*(abs)
1MLCT(abs)
3MLCT(em)
t(em)
[msÀ1
F(em)
[a]
[a]
[b]
[cmÀ1
]
[cmÀ1
]
[cmÀ1
]
]
1
2
296
77
30770 (41250)
21370 (10730)
14325
15150
0.074(8)
1.62(3)
0.0010(1)
0.041(4)
than in [Ru(2,2’-bipyridine)3]2+
,
296
77
30960 (39850)
21185 (8440)
14345
15950
0.050(5)
3.2(1)
0.0010(1)
0.052(5)
assuming that the net reorgani-
sational free energy contribu-
tion cr is similar in these com-
plexes.[1d,27] The absorption
spectra recorded in solution
(10À4 molLÀ1 in ethanol/metha-
nol (4:1)) indeed confirms a
800 1000 cmÀ1 red shift of the
1MLCT transition on going
3
296
77
296
30300 (41300)
35090 (70000)
21320 (11570)
22170 (14730)
14450
15220
16285
0.112(4)
1.70(6)
0.643(4)
0.0030(3)
0.039(4)
0.055(6)
[Ru(2,2’-bipy)3]2+
[Ru(2,2’-bipy)3]2+
77
17210
5.2(2)
0.36(4)
[Ru(2,2’-bipyridine)3]2+
5
296
296
77
39840 (22120)
29850 (55000)
39525 (22050)
29940 (55000)
21100 (11350)
21100 (11100)
14730
14730
15470
0.242(5)
0.384(6)
2.0(1)
0.0056(6)
0.010(1)
0.028(3)
from
(n=22170 cmÀ1) to [Ru(Li)3]2+
(i=2, 3;
21185ꢀnꢀ
21370 cmÀ1; Table 3, Figure 7a).
[c]
mer-[Ru(L2)3]2+
and
fac-
[a] Molar extinction coefficients are given between parentheses. [b] nexc =20492 cmÀ1 and the values reported
at 77 K corrrespond to the 0 0 phonon transitions. [c] In acetonitrile.
[Ru(L2)3]2+ display slightly dif-
Chem. Eur. J. 2004, 10, 3503 3516
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3509

C. Piguet et al.
FULL PAPER
[Ru(L2)3]2+)=2740 cmÀ1 <cr(mer-[Ru(L3)3]2+)=4870 cmÀ1.
The last value is not very reliable because of the irreversibil-
ity of the corresponding reduction wave. The higher reor-
ganisational free energies exhibited by [Ru(Li)3]2+ (i=2, 3)
partially overcome the considerably higher value of DE1/2
characterizing [Ru(2,2’-bipyridine)3]2+, and this may explain
1
the only minor global red shift of the MLCT transition ob-
served on going from [Ru(2,2’-bipyridine)3]2+ to [Ru(Li)3]2+
(i=2, 3; Figure 7a). The emission spectra of [Ru(2,2’-bipyri-
dine)3]2+ and [Ru(Li)3]2+ (i=2, 3) obtained upon excitation
1
3
of the MLCT state originate from the MLCT state[1] and
confirm the red shift induced in these last complexes (Fig-
ure 7b,c). The lifetimes t(3MLCT) and the associated quan-
tum yields F measured at low temperature in frozen glasses
(77 K) are significantly reduced on going from [Ru(2,2’-bi-
pyridine)3]2+ to [Ru(Li)3]2+ (i=2, 3; Table 3). That this re-
duction is even greater at room temperature is diagnostic
for the existence of thermally activated de-excitation path-
ways involving d d excited states close in energy.[1,2] For
[Ru(2,2’-bipyridine)3]2+, the zero-point energy difference be-
tween the d d and the 3MLCT state, DEA=EA(d
d)ÀEA(3MLCT), has been estimated to be around
4040 cmÀ1.[29] From the maximum of the emission band,
3
nmax(em), the zero-point energy of the MLCT state can be
calculated according to EA(3MLCT)=hnmax(em)+cr. There-
fore the actual zero-point energy of the d d state is given by
EA(d d)=hnmax(em)+cr +DEA. From the room temperature
emission spectrum shown in Figure 7b, and assuming the re-
organisational energy of the ground state to be the same as
that in the MLCT states, EA(d d)ꢂ22500 cmÀ1 for [Ru(2,2’-
bipyridine)3]2+. Since the ratio of J˘rgensen×s ligand-field
parameters[30] between the bipyridine and benzimidazole-2-
ylpyridine units amounts to fbenzimidazol-2-ylpyridine/fbipyridine
=
0.87,[31] we deduce that the ratio of the ligand-field splittings
is 10Dq([Ru(Li)3]2+)/10Dq([Ru(2,2’-bipyridine)3]2+)=0.87.
Even though 10Dq for a given ligand depends upon the
metal ligand distance, this ratio is not only valid at the equi-
librium geometry of the ground state, but also for other ge-
ometries, and therefore EA(d d)ꢂ19500 cmÀ1 for [Ru(Li)3]2+
(i=2, 3). This, in turn, translates into DEA=EA(d
d)Àhnmax(em)Àcr ꢂ19500À14370À2650ꢂ2500 cmÀ1 for mer/
fac-[Ru(L2)3]2+, which is indeed lower than that found in
[Ru(2,2’-bipyridine)3]2+ (4040 cmÀ1),[29] in line with the
shorter lifetimes and the quantum yields, which are found to
be one order of magnitude smaller for [Ru(L2)3]2+ at 296 K
(Table 3). The rather uncertain value of cr for [Ru(L3)3]2+
due to the irreversibility of the reduction wave in the cyclic
voltammogram excludes the possibility of a reliable estimate
of DEA for this complex, but from the quantum yields and
luminescence lifetimes at both 77 and 298 K we conclude
that it must be of the same magnitude as that for
Figure 7. a) Absorption spectra of [Ru(Li)3]2+ (i=2, 3) and [Ru(2,2’-bi-
pyridine)3]2+ in ethanol/methanol (4:1, 296 K) showing the 1MLCT tran-
sition. b) Emission spectra of [Ru(Li)3]2+ (i=2, 3; 10À4 molLÀ1) and
[Ru(2,2’-bipyridine)3]2+ (10À5 molLÀ1) in ethanol/methanol (4:1) at 296 K
and c) in frozen glasses at 77 K.
ferent absorption spectra and spectroscopic properties, as
previously reported for analogous [Ru(pyridine-azole)3]2+
complexes.[6a]
On the basis of the pioneering work of Lever and co-
workers,[28] Endicott and co-workers[27] proposed a useful
and simple approximate correlation between DE1/2 and the
[Ru(L2)3]2+
.
1
spectroscopic energy of the MLCT transition in RuII com-
plexes: hnmax(abs)=FDE1/2 +cr in which F stands for the
Faraday constant and cr corresponds to the reorganisational
free energy. Taking nmax(abs) at room temperature from
Table 3 and DE1/2 reported above, we calculate that cr in-
Use of the ™labile∫ fac-[Ru(benzimidazol-2-ylpyridine)3]2+
Ðmer-[Ru(benzimidazol-2-ylpyridine)3]2+
isomerisation
process in solution for the strict self-assembly of
[RuLu(L1)3]5+: Preliminary attempts to make L1 react with
[Ru(dmso)4Cl2] or [Ru(dmso)5(H2O)](CF3SO3)2¥H2O in eth-
creases
in
the
order
cr([Ru(2,2’-bipyridine)3]2+)=
1360 cmÀ1 !cr(fac-[Ru(L2)3]2+)=2550 cmÀ1 ꢂcr(mer-
3510
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Chem. Eur. J. 2004, 10, 3503 3516

Triple-Stranded Helicates
3503 3516
anol produced intricate mixtures of mer-[Ru(L1)3]2+and fac-
[Ru(L1)3]2+, in which RuII was coordinated by the three bi-
dentate segments, together with considerable quantities of
noncharacterised species involving the complexation of the
tridentate segments. Taking advantage of the relative lability
of [Ru(benzimidazol-2-ylpyridine)3]2+ in polar solvents, we
performed the same reaction by using L1 (3 equiv) with an
equimolar mixture of [Ru(dmso)5(H2O)](CF3SO3)2¥H2O
(1 equiv) and Lu(CF3SO3)3¥1.4H2O in hot ethanol. Since
only fac-[Ru(L1)3]2+ can coordinate LuIII efficiently by
wrapping the three tridentate benzimidazole pyridine car-
boxamide units to give the triple-stranded helicate HHH-
[RuLu(L1)3]5+ (where HHH stands for head-to-head-to-
head),[10c] the facial conformation is strongly stabilised by
Figure 8. 1H NMR spectrum of HHH-[RuLu(L1)3]5+ (CD3CN, 298 K;
numbering as in Figure 1).
10]
enthalpic and entropic contributions,[8
and we have
indeed isolated HHH-[RuLu(L1)3](CF3SO3)5¥2CH3OH¥H2O
1
(5) in 70% yield after recrystallisation. The H NMR spec-
trum confirms the exclusive formation of the C3-symmetrical
HHH-[RuLu(L1)3]5+ in solution, resulting from three li-
gands adopting a parallel arrangement (Figure 8). The
fivefold longer than that measured for fac-[Ru(L2)3]3+ at
296 K, while these lifetimes remain comparable at low tem-
perature (t(3MLCT)=2.0(1) ms for HHH-[RuLu(L1)3]5+
and t(3MLCT)=3.2(1) ms for fac-[Ru(L2)3]2+ at 77 K;
Table 3). The quantum yields follow the same trend and we
tentatively assign this beneficial effect in the bimetallic heli-
cate to a slightly larger separation DE=E(d d)ÀE(3MLCT)
induced by a small distortion of the RuII coordination
sphere resulting from the complexation of LuIII in the neigh-
1
23 observed H NMR signals correspond to protons connect-
ed to 20 carbon atoms for which H7 H8, H15 H16 and H17
H18 are diastereotopic as a result of the blocked PÐM heli-
cal interconversion occurring in HHH-[RuLu(L1)3]5+ on the
NMR timescale (see Figure 1 for numbering). The unusual
shielding of the aromatic protons H6 and H9 is diagnostic for
the helical wrapping of the strands, which puts these protons
in the shielding region of the
neighbouring connected benzi-
midazole rings, as previously es-
tablished for the analogous dia-
magnetic d f helicates HHH-
[32]
[ZnLu(L1)3]5+
,
HHH-
[FeLu(L1)3]5+[21] and HHH-
[8]
[CoLu(L1)3]6+
.
The electronic absorption
spectrum of HHH-
[RuLu(L1)3]5+ in ethanol/meth-
anol (4:1) (Figure S3a, Support-
ing Information) shows the
1MLCT transition centred at
21100 cmÀ1 as similarly ob-
served
for
fac-[Ru(L2)3]3+
(Table 3), while the emission of
the 3MLCT excited state, ob-
served upon excitation of the
1MLCT transition, is slightly
blue-shifted
by
385 cmÀ1
(Table 3; Figure S3b,c, Support-
ing Information). This suggests
that the complexation of LuIII
in the distal nine-coordination
site affects the stereoelectronic
properties of the pseudo-octa-
hedral RuII site in HHH-
[RuLu(L1)3]5+ only very slight-
ly. However, the lifetime of the
triplet charge-transfer state
Figure 9. a) Perspective view of HHH-[RuLu(L1)3]5+ perpendicular to the pseudo-C3 axis in the crystal struc-
ture of 6, and b) atomic numbering scheme of strand a (ellipsoids are represented at the 40% probability
(t(3MLCT)=0.242(5) ms)
is level).
Chem. Eur. J. 2004, 10, 3503 3516
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¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3511

C. Piguet et al.
FULL PAPER
À
À
bouring site. Finally, fragile monocrystals suitable for X-ray
diffraction analysis are obtained when half a triflate anion is
replaced with ClÀ to give HHH-[RuLu(L1)3](CF3-
SO3)4.5Cl0.5¥2.5CH3OH (6).
The similarity of the Lu N and Lu O bond lengths in
HHH-[RuLu(L1)3]5+ and HHH-[CoLu(L1)3]6+[8] indicates
that the complexation of the large low-spin d6 RuII ion (we
CN¼6
calculate R
=0.595 ä in 6 according to Shannon×s defini-
Ru
tion and r(N)=1.46 ä)[33] does not induce significant me-
chanical constraints around LuIII compared with the alterna-
CN¼6
Crystal and molecular structure of HHH-[RuLu(L1)3](CF3-
SO3)4.5Cl0.5¥2.5CH3OH (6): The crystal structure of 6 consists
of triple-stranded cations HHH-[RuLu(L1)3]5+ together
with disordered ionic triflate and chloride anions, and non-
coordinated methanol molecules (see Experimental Sec-
tion). The wrapping of the ligands results from successive
tive complexation of the smaller CoIII ion (R
=
Co
0.545 ä).[33] The detailed geometrical analysis using the
angles f, qi and wij for the pseudo-tricapped trigonal pris-
matic LuIII site[8] shows only minor differences between
HHH-[RuLu(L1)3]5+ and HHH-[CoLu(L1)3]6+ (Table S3,
Supporting Information). However, the related analysis per-
formed on the pseudo-octahedral RuII and CoIII sites high-
lights a slightly smaller twist of the the bidentate binding
units around RuII (wij(intraligand)=52.9 54.58 compared
with 56 578 around CoIII in HHH-[CoLu(L1)3]6+; Table S4,
Supporting Information). This translates into a larger helical
pitch P12 =d(F1 F2)/(a/360)=13.35 ä for the helical portion
defined by the two facial planes F1 (N1a,N1b,N1c) and F2
À
torsions around the interaromatic C C bonds, and around
the central methylene unit as previously described for the
[32]
analogous d f bimetallic helicates HHH-[ZnEu(L1)3]5+
,
[21]
HHH-[FeLa(L1)3]5+
,
HHH-[CrLu(L1)3]6+[9] and HHH-
[8]
[CoLu(L1)3]6+
.
Selected bond lengths and bond angles for
HHH-[RuLu(L1)3]5+ are collected in Table 4, while Figure 9
displays its molecular structure together with the atomic
numbering scheme.
(N2a,N2b,N2c) (P12 =13.11 ä in HHH-[CoLu(L1)3]6+
,
Table 4. Selected bond lengths [ä] and bond angles [8] in [RuLu(L1)3](CF3SO3)4.5Cl0.5¥2.5CH3OH (6) and [CoLu(L1)3](CF3SO3)6(CH3CN)2(H2O).
[RuLu(L1)3](CF3SO3)4.5Cl0.5¥2.5CH3OH (6)
[CoLu(L1)3](CF3SO3)6(CH3CN)2(H2O)[a]
ligand a
ligand b
ligand c
ligand a
ligand b
ligand c
Lu¥¥¥Ru
9.0794(9)
2.345(5)
2.534(6)
2.518(4)
2.064(6)
2.051(5)
Lu¥¥¥Co
9.234(2)
2.316(5)
2.474(5)
2.526(6)
1.955(6)
1.929(6)
À
À
Lu O1
2.284(5)
2.469(6)
2.531(5)
2.060(5)
2.044(5)
2.326(4)
2.514(5)
2.515(4)
2.055(5)
2.057(5)
Lu O1
2.340(5)
2.516(6)
2.508(6)
1.956(6)
1.925(6)
2.339(5)
2.495(6)
2.518(6)
1.962(6)
1.914(6)
À
À
Lu N4
Lu N4
À
À
Lu N6
Lu N6
À
À
Ru N1
Co N1
À
À
Ru N2
Co N2
Bite angles
O1-Lu-N4
O1-Lu-N6
N4-Lu-N6
N1-Ru-N2
128.2(1)
63.8(2)
64.5(2)
77.8(2)
128.7(2)
64.2(2)
64.5(2)
77.5(2)
129.6(2)
65.2(1)
64.7(2)
77.9(2)
O1-Lu-N4
O1-Lu-N6
N4-Lu-N6
N1-Co-N2
N-Co-N
128.3(2)
63.3(3)
65.1(2)
83.2(2)
130.2(2)
65.9(2)
64.6(2)
83.1(2)
128.0(2)
64.1(2)
64.0(2)
82.1(2)
N-Ru-N
N1a-Ru-N1b
N1a-Ru-N2b
N1a-Ru-N2c
N1a-Ru-N1c
N2a-Ru-N1b
N2a-Ru-N1c
98.7(2)
175.7(2)
85.0(2)
95.0(2)
85.5(2)
172.5(2)
N2a-Ru-N2b
N2a-Ru-N2c
N1b-Ru-N1c
N1b-Ru-N2c
N2b-Ru-N1c
N2b-Ru-N2c
99.8(2)
99.3(2)
97.7(2)
174.5(2)
87.5(2)
99.0(2)
N1a-Co-N1b
N1a-Co-N2b
N1a-Co-N2c
N1a-Co-N1c
N2a-Co-N1b
N2a-Co-N1c
N-Lu-N
94.8(2)
176.2(2)
88.2(2)
95.4(2)
86.5(2)
178.6(2)
N2a-Ru-N2b
N2a-Ru-N2c
N1b-Ru-N1c
N1b-Ru-N2c
N2b-Ru-N1c
N2b-Ru-N2c
93.6(2)
97.6(2)
93.9(2)
175.2(2)
87.8(2)
94.1(2)
N-Lu-N
N4a-Lu-N4b
N4b-Lu-N4c
N4a-Lu-N4c
N4a-Lu-N6c
N6a-Lu-N4b
N6b-Lu-N4c
88.3(2)
82.7(2)
83.9(2)
74.7(2)
75.6(2)
76.5(2)
N6a-Lu-N6b
N6b-Lu-N6c
N6a-Lu-N6c
N4a-Lu-N6b
N4b-Lu-N6c
N6a-Lu-N4c
119.5(2)
117.4(2)
121.5(2)
148.0(2)
144.3(2)
141.6(2)
N4a-Lu-N4b
N4b-Lu-N4c
N4a-Lu-N4c
N4a-Lu-N6c
N6a-Lu-N4b
N6b-Lu-N4c
O-Lu-N
80.5(2)
86.2(2)
86.9(2)
76.1(2)
74.0(2)
77.2(2)
N6a-Lu-N6b
N6b-Lu-N6c
N6a-Lu-N6c
N4a-Lu-N6b
N4b-Lu-N6c
N6a-Lu-N4c
114.8(2)
124.0(2)
119.7(2)
142.2(2)
142.6(2)
147.6(2)
O-Lu-N
N4a-Lu-O1b
N6a-Lu-O1b
N6b-Lu-O1c
O1a-Lu-N6b
O1a-Lu-N4c
O1b-Lu-N4c
139.9(2)
132.1(2)
132.7(2)
67.5(2)
144.1(2)
86.1(2)
N4a-Lu-O1c
N6a-Lu-O1c
N4b-Lu-O1c
O1a-Lu-N4b
O1a-Lu-N6c
O1b-Lu-N6c
79.1(2)
67.4(2)
142.8(1)
82.7(2)
132.4(2)
65.9(2)
N4a-Lu-O1b
N6a-Lu-O1b
N6b-Lu-O1c
O1a-Lu-N6b
O1a-Lu-N4c
O1b-Lu-N4c
O-Lu-O
143.8(2)
134.1(2)
133.7(2)
65.4(2)
141.6(2)
78.1(2)
N4a-Lu-O1c
N6a-Lu-O1c
N4b-Lu-O1c
O1a-Lu-N4b
O1a-Lu-N6c
O1b-Lu-N6c
82.8(2)
66.7(2)
140.7(2)
85.5(2)
131.8(2)
67.7(2)
O-Lu-O
O1a-Lu-O1b
O1a-Lu-O1c
77.9(2)
78.3(2)
O1b-Lu-O1c
77.9(2)
O1a-Lu-O1b
O1a-Lu-O1c
78.9(2)
77.5(2)
O1b-Lu-O1c
81.1(2)
[a] Taken from ref. [8b].
3512
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 3503 3516

Triple-Stranded Helicates
3503 3516
Table 5).[8] The latter effect contrasts with the nonbonded
Ru¥¥¥Lu distance in HHH-[RuLu(L1)3]5+ (9.0794(9) ä),
which is indeed shorter than the analogous Co¥¥¥Lu distance
reported for HHH-[CoLu(L1)3]6+ (9.234(2) ä),[8] and which
the [111] direction, thus providing a pseudo-hexagonal ar-
rangement in the crystal of 6 (Figure S5, Supporting Infor-
mation). In each column, two successive helices are related
by an inversion centre leading to intermolecular Lu¥¥¥Lu and
Ru¥¥¥Ru distances of 12.9536(9)
and 9.1632(11) ä respectively.
Table 5. Helical pitches Pij, linear distances d(Fi Fj) and average twist angles aij along the pseudo-C3 axis[a] in
the crystal structures of [RuLu(L1)3](CF3SO3)4.5Cl0.5¥2.5CH3OH (6) and [CoLu(L1)3](CF3SO3)6(CH3CN)2-
(H2O).
HHH-[RuLu(L1)3]5+
d(Fi Fj) [ä]
HHH-[CoLu(L1)3]6+[b]
Conclusion
aij [8][c]
Pij [ä]
d(Fi Fj) [ä]
aij [8]
Pij [ä]
[d]
To the best of our knowledge,
the thermodynamic self-assem-
bly of the single-stranded bi-
metallic helicate [(terpy)Ru-
(quinquepyridine)Ru(terpy)-
Cl]3+ is the only previously re-
ported event in which RuII has
F1 F2
F2 F3
F3 F4
F4 F5
F1 F5
2.00
6.46
1.75
1.41
11.62
9.0794(9)
54
117
52
58
281
13.35
19.86
12.06
8.72
2.04
6.66
1.75
1.40
11.85
9.234(2)
56
117
52
58
284
13.11
20.49
12.11
8.68
14.88
15.02
Lu¥¥¥M
[a] Each helical portion F1 F2, F2 F3, F3 F4 and F4 F5 is characterised by 1) a linear extension d(Fi Fj) defined
by the separation between the facial planes, 2) an average twist angle aij defined by the angular rotation be-
tween the projections of Ni and Nj (or Oj) belonging to the same ligand strand onto an intermediate plane been tentatively used as
a
™labile∫ partner in the forma-
tion of helicates.[34] However,
no yield was reported and the
final complexwas obtained
upon reduction of a nonisolated
RuIII precursor, which prevents
passing through the metal (or the midpoint X in Scheme 2) and 3) its pitch Pij defined as the ratio of axial
over angular progressions along the helical axis Pij =d(Fi Fj)/(aij/360) (Pij corresponds to the length of a cylin-
der containing a single turn of the helixdefined by geometrical characteristics d(Fi Fj) and aij).[9] [b] Taken
from refs. [8b] and [9]. [c] aij are given as C3 average values. [d] F1: N1a, N1b, N1c; F2: N2a, N2b, N2c; F3:
N4a, N4b, N4c; F4: N6a, N6b, N6c; F5: O1a, O1b, O1c (see Scheme 2).
rationalisation of the chemical mechanism. Another attempt
provided a hexameric RuII wheel from the RuIII precursor,
but again it is not clear which oxidation state is involved in
the thermodynamic equilibria.[13b] In this contribution, we
have demonstrated that the kinetics of the fac-[Ru(benzimi-
dazol-2-ylpyridine)3]2+Ðmer-[Ru(benzimidazol-2-ylpyri-
dine)3]2+ isomerisation process depends on solvent polarity
and on the substitution of the benzimidazole ring. Although
the chemical origins of these effects await complete varia-
ble-temperature thermodynamic and kinetic studies, their
exploitation in the self-assembly of heterobimetallic d f hel-
icates has led to the first isolation of a triple-stranded Ru-
containing helicate, [RuLu(L1)3]5+. This opens interesting
perspectives for using [Ru(a,a’-diimine)3]2+ as sensitisers for
ultimate near-infrared emissions of distal 4f-block ions
(Ln=Nd, Er, Yb),[3] but the specific photophysical proper-
ties of the [Ru(benzimidazol-2-ylpyridine)3]2+ chromophore
is not ideal (short t(3MLCT) lifetimes and low quantum
yields), because interactions with low-energy excited d d
states provide efficient thermally activated pathways for
nonradiative deactivation. This situation is not desperate,
however, since such deleterous effects can be removed
either by the connection of p-attracting[35a] or s-donating[35b]
groups to the aromatic rings, which increases the ligand-
field strength without significantly affecting the energy of
the MLCT states. Finally, the comparison of the velocities of
Scheme 2. Helical portions Fi Fj (see Table 5).
may be ascribed to the increased wrapping (that is, a smaller
helical pitch) characterizing the large intermetallic helical
portion F2 F3 in HHH-[RuLu(L1)3]5+ (Table 5). Conse-
quently, the two triple-helical complexes HHH-
[RuLu(L1)3]5+ and HHH-[CoLu(L1)3]6+ cannot be strictly
superimposed (Figure S4, Supporting Information).
The pseudo-octahedral RuII coordination sphere in HHH-
[RuLu(L1)3]5+ shows that the three bidentate benzimidazol-
2-ylpyridine units adopt a facial arrangement at odds with
the molecular structure of mer-[Ru(L3)3]2+ (Figure 9). Inter-
estingly, both the Ru N1(pyridine) bond lengths (average:
the
fac-[M(benzimidazol-2-ylpyridine)3]2+Ðmer-[M(benz-
À
À
2.060(5) ä; Table 4) and the Ru N2(benzimidazole) bonds
imidazol-2-ylpyridine)3]2+ isomerisation processes for M=
RuII (a typical inert d-block cation) with M=ZnII (a typical
labile d-block cation) is very informative. Variable-tempera-
ture NMR data recorded for [Zn(L2)3]2+ and [Zn(L3)3]2+ in
CD3CN show an average D3h symmetry at room tempera-
ture compatible with fast facÐmer isomerisation on the
NMR timescale (that is, in the millisecond range; Figure S6,
Supporting Information). Separated signals are only ob-
(average: 2.051(7) ä; Table 4) are shorter than those mea-
sured in mer-[Ru(L3)3]2+, which implies that the complexa-
tion of LuIII constrains the bidentate binding to be closer to
the RuII ion. This is in line with the increased ligand field in
HHH-[RuLu(L1)3]5+ suggested by our photophysical data
(lifetimes and quantum yields). Finally, the triple-stranded
HHH-[RuLu(L1)3]5+ ions are packed into columns along
Chem. Eur. J. 2004, 10, 3503 3516
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3513

C. Piguet et al.
FULL PAPER
100 mL). The combined organic phases were dried over MgSO4 and the
solvent was evaporated. The resulting solid was recrystallised from di-
chloromethane/hexane (50:50) to give L3 (460 mg, 1.54 mmol; yield
served at the lowest accessible temperature (233 K), and we
can conclude that the assembly of the d f helicates
[MLn(L1)3]5+ can be performed successfully for noncovalent
tripods whose lability changes by more than sixorders of
magnitude (that is, from the millisecond (M=Zn) to the
hour (M=Ru) range).
90%) as
a
white microcrystalline powder. M.p.=1208C; 1H NMR
(CDCl3): d=8.41 (dd, J3 =8 Hz, J4 =1 Hz, 1H), 8.30 (d, J3 =9 Hz, 1H),
7.81 (dd, J3 =8 Hz, J4 =1 Hz, 1H), 7.60 (dd, J3 =8 Hz, J4 =1 Hz, 1H),
7.10 7.32 (m, 7H), 6.15 (s, 2H), 2.34 ppm (s, 3H); 13C NMR (CDCl3): d=
150.3, 149.1, 148.8, 148.0, 142.9, 137.9, 137.7, 137.5, 136.9, 133.8, 128.6,
127.3, 126.9, 124.3, 123.4, 122.8, 120.0, 110.8, 49.0, 18.5 ppm; EI-MS: m/z:
299 [M+]; elemental analysis calcd (%) for C20H17N3: C 80.24, H 5.72, N
14.04; found: C 80.30, H 5.65, N 14.17.
Experimental Section
Preparation of [Ru(dmso)5(H2O)](CF3SO3)2¥H2O: [Ru(dmso)4(Cl)2]
(300 mg, 0.62 mmol) and Ag(CF3SO3) (319 mg, 1.24 mmol, 2.1 equiv)
were dissolved in DMSO/acetone (2:1, 6.5 mL). After 1 h of stirring at
RT, the solution was filtered to remove AgCl and acetone (50 mL) was
added to induce precipitation. After 6 h at 48C, [Ru(dmso)5(H2O)](CF3-
SO3)2¥H2O (310 mg, 0.47 mmol; yield 70%) was isolated by filtration as a
pale yellow powder. ESI-MS: m/z: 257 [Ru(dmso)5(H2O)]2+; elemental
analysis calcd (%) for [Ru(dmso)5(H2O)](CF3SO3)2¥H2O: C, 17.50; H,
4.12. found: C, 17.51; H, 4.11.
Solvents and starting materials: These were purchased from Fluka AG
(Buchs, Switzerland) and used without further purification unless other-
wise stated. Acetonitrile, dichloromethane and N,N-dimethylformamide
were distilled from CaH2. The ligands 2-{6-[N,N-diethylcarboxamido]pyri-
din-2-yl}-1,1’-dimethyl-5,5’-methylene-2’-(5-methylpyridin-2-yl)bis[1H-
benzimidazole] (L1),[32] 5-methyl-(1-methylbenzimidazol-2-yl)pyridine
(L2),[15] 6-methylpyridine-2-carboxylic acid,[32] [Ru(dmso)4Cl2][36] and
Na2Sb2[(+)-C4O6H2]2¥5H2O[4a] were prepared according to literature pro-
cedures. The triflate salt Lu(CF3SO3)3¥1.4H2O was prepared from the cor-
responding oxide (Rhodia, 99.99%).[37] The Lu content of solid salts was
determined by complexometric titrations with Titriplex III (Merck) in
the presence of urotropine and xylene orange.[38]
Preparation of [Ru(L2)3](ClO4)2¥2H2O:
A mixture of L2 (100 mg,
0.45 mmol) and [Ru(dmso)4Cl2] (72.5 mg, 0.15 mmol) was refluxed in eth-
anol (20 mL) for 24 h. The solution turned deep red and was concentrat-
ed to a final volume of about 10 mL. Diethyl ether was added to induce
precipitation, and a red solid (90 mg) was collected by filtration and re-
dissolved in water (18 mL). A saturated aqueous solution of sodium per-
chlorate was added until precipitation occurred. The crude product was
extracted with dichloromethane (2î10 mL), and the red solid was sepa-
rated by filtration and precipitated from acetonitrile/diethyl ether to give
[Ru(L2)3](ClO4)2¥2H2O (81 mg, 0.084 mmol; yield 56%) as a 3:1 mixture
of mer-[Ru(L2)3](ClO4)2¥2H2O and fac-[Ru(L2)3](ClO4)2¥2H2O; ESI-MS:
m/z: 385 [Ru(L2)3]2+; elemental analysis calcd (%) for C42H39N9O8Cl2-
Ru¥2H2O: C 50.20, H 4.25, N 12.54; found: C 50.14, H 4.12, N 12.68.
Preparation of benzyl(2-nitrophenyl)amine: A mixture of 1-chloro-2-ni-
trobenzene (10 g, 0.0634 mol) and benzylamine (134 g, 1.25 mol) was stir-
red at 1008C for 24 h in an autoclave. The orange solution was poured
into water (80 mL) and extracted with dichloromethane (3î200 mL).
The combined organic layers were dried over MgSO4 and evaporated.
The excess of benzylamine was removed by vacuum distillation (5î
10À2 bar, 308C), and the resulting orange solid purified by column chro-
matography (silica gel, CH2Cl2) to give 10.5 g (46.1 mmol, yield 73%) of
benzyl(2-nitrophenyl)amine as an orange solid. M.p.=728C. 1H NMR
(CDCl3): d=8.40 (brs, 1H, NH), 8.15 (dd, J3 =8 Hz, J4 =1 Hz, 1H), 7.25
7.35 (m, 6H), 6.75 (d, J3 =8 Hz, 1H), 6.60 (dt, J3 =8 Hz, J4 =1 Hz, 1H),
4.58 ppm (d, J3 =6 Hz, 2H); 13C NMR (CDCl3): d=145.1, 137.2, 136.1,
132.0, 128.8, 127.6, 127.0, 126.7, 115.6, 114.1, 47.0 ppm; EI-MS: m/z: 228
[M+]; elemental analysis calcd (%) for C13H12N2O2: C 68.41, H 5.30, N
12.27; found: C 68.50, H 5.27, N 12.35.
Separation of mer-[Ru(L2)3](ClO4)2¥2H2O (1) and fac-[Ru(L2)3]-
(ClO4)2¥2H2O (2): In a typical experiment, a portion (50 mg) of the 3:1
mixture was dissolved in dichloromethane (1 mL) and extracted with an
aqueous solution of Na2Sb2[(+)-C4O6H2]2¥5H2O (1 mL, 0.1 molLÀ1). The
aqueous phase was separated and sorbed onto a column (1.5 cm diameter
and 1 m length) containing SephadexC-25 (10 g) suspended in water.
The elution was performed using an aqueous solution of Na2Sb2[(+)-
C4O6H2]¥5H2O (0.1 molLÀ1). Two successive bands were collected sepa-
rately. Precipitation with saturated aqueous NaClO4 (1 mL) gave mer-
[Ru(L2)3](ClO4)2¥2H2O (1, 34.5 mg; yield 69%) and fac-[Ru(L2)3]-
(ClO4)2¥2H2O (2, 10 mg; yield 20%).
mer-[Ru(L2)3](ClO4)2¥2H2O (1): ESI-MS: m/z: 385 [Ru(L2)3]2+; elemen-
tal analysis calcd (%) for C42H39N9O8Cl2Ru¥2H2O (mer): C 50.20, H 4.25,
N 12.54; found: C 50.14, H 4.18, N 12.69.
fac-[Ru(L2)3](ClO4)2¥2H2O (2): ESI-MS: m/z: 385 [Ru(L2)3]2+; elemen-
tal analysis calcd (%) for C42H39N9O8Cl2Ru¥2H2O (fac): C 50.20, H 4.25,
N 12.54; found: C 50.17,H 4.14, N 12.62.
Preparation of the [benzyl(2-nitrophenyl)]amide of 5-methylpyridine-2-
carboxylic acid: A mixture of 6-methylpyridine-2-carboxylic acid (1 g,
7.29 mmol), thionyl chloride (5.2 mL, 72.9 mmol) and DMF (300 mL) was
refluxed for 90 min in dry dichloromethane (100 mL). The mixture was
evaporated and dried under vacuum for 1 h. The resulting dark green
solid was dissolved in dichloromethane (50 mL) and added dropwise to a
solution of benzyl(2-nitrophenyl)amine (1.80 g, 7.9 mmol) and triethyl-
amine (11 mL, 79 mmol). The solution was refluxed for 12 h under an
inert atmosphere. After evaporation, the green residue was partitioned
between dichloromethane (200 mL) and half-saturated aqueous NH4Cl
solution (200 mL). The aqueous phase was extracted with dichlorome-
thane (3î150 mL), then the combined organic layers were dried
(MgSO4) and evaporated. The crude brown oil was purified by column
chromatography (silica gel, CH2Cl2/MeOH (100:0!98:2)) to give (1.7 g,
4.9 mmol; yield 67%) of 5-methylpyridine-2-carboxylic acid [benzyl(2-ni-
trophenyl)]amide as a pale orange solid. M.p.=808C; 1H NMR (CDCl3):
d=7.87 (s, 1H), 7.82 (dd, J3 =8 Hz, J4 =1 Hz, 1H), 7.68 (dd, J3 =8 Hz,
1H), 7.39 (dd, J3 =8 Hz, J4 =1 Hz, 1H), 7.31 7.22 (m, 7H), 6.90 (dd, J3 =
8 Hz, J4 =1 Hz, 1H), 5.71 (d, J2 =15 Hz, 1H), 4.45 (d, J2 =15 Hz, 1H),
2.16 ppm (s, 3H); 13C NMR (CDCl3): d=167.7, 150.0, 148.0, 146.8, 137.4,
137.2, 136.7, 134.8, 133.1, 132.3, 129.6, 129.0, 128.7, 128.0, 125.2, 124.3,
54.1, 18.3 ppm; EI-MS: m/z: 347 [M+]; elemental analysis calcd (%) for
C20H17N3O3: C 69.15, H 4.93, N 12.10; found: C 69.30, H 5.10, N 12.15.
Preparation of [Ru(L3)3](ClO4)2¥CH3CN¥H2O: A solution of L3 (100 mg,
0.34 mmol) and [Ru(dmso)4Cl2] (56.6 mg, 0.11 mmol) in ethanol was re-
fluxed for 24 h. Half of the solvent was removed by distillation and pre-
cipitation was induced by adding diethyl ether. After filtration, the resid-
ual red solid was dissolved in water (10 mL) and saturated aqueous
NaClO4 was added until a red solid was precipitated; it was collected by
filtration. Precipitation from acetonitrile/diethyl ether gave [Ru(L3)3]-
(ClO4)2¥CH3CN¥H2O (95 mg, 0.079 mmol; yield 72%) as a 3:1 mixture of
mer-[Ru(L3)3](ClO4)2¥CH3CN¥H2O and fac-[Ru(L3)3](ClO4)2¥CH3CN¥
H2O. ESI-MS: m/z: 499.8 [Ru(L3)3]2+; elemental analysis calcd (%) for
C60H51N9O8Cl2Ru¥CH3CN¥H2O: C 59.23, H 4.49, N 11.14; found: C 59.30,
H 4.55, N 11.21.
Preparation of 5-methyl(1-benzylbenzimidazol-2-yl)pyridine (L3): The
[benzyl(2-nitrophenyl)]amide of 5-methylpyridine-2-carboxylic acid
(600 mg, 1.7 mmol) was dissolved in ethanol (120 mL) containing distilled
water (40 mL), concentrated HCl (4 mL, 37%) and activated iron (2 g,
36 mmol). The solution was refluxed for 12 h under a nitrogen atmos-
phere. The excess of metallic iron was removed by filtration, the ethanol
was evaporated and a solution of Na2H2EDTA (20 g, 55 mmol, in 100 mL
of water) was added. The pH was adjusted to 9 with ammonium hydrox-
ide, and the aqueous phase was extracted with dichloromethane (3î
Separation of mer-[Ru(L3)3](ClO4)2¥CH3CN¥H2O (3): In a typical experi-
ment, a portion (50 mg) of the 3:1 mixture was dissolved in dichloro-
methane (1 mL) and extracted with an aqueous solution of Na2Sb2[(+)-
C4O6H2]2¥5H2O (1 mL, 0.1 molLÀ1). The aqueous phase was separated
and sorbed onto a column (diameter 1.5 cm, length 1 m) containing Se-
phadexC-25 (10 g) suspended in water. The elution was performed using
an aqueous solution of Na2Sb2[(+)-C4O6H2]¥5H2O (0.1 molLÀ1). A single
band was collected and precipitated with saturated aqueous NaClO4
3514
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 3503 3516

Triple-Stranded Helicates
3503 3516
(1 mL) to give mer-[Ru(L3)3](ClO4)2¥CH3CN¥H2O (3, 45 mg; yield 90%).
Table 6. Summary of crystal data, intensity measurements and structure
refinement for mer-[Ru(L3)3](ClO4)2 (4) and [RuLu(L1)3](CF3-
SO3)4.5Cl0.5¥2.5CH3OH (6).
ESI-MS: m/z: 499.6 [Ru(L3)3]2+
; elemental analysis calcd (%) for
C60H51N9O8Cl2Ru¥CH3CN¥H2O: C 59.23, H 4.49, N 11.14; found: C 59.32,
H 4.59, N 11.19. X-ray quality prisms of mer-[Ru(L3)3](ClO4)2 (4) were
obtained by slow diffusion of tert-butyl methyl ether into a concentrated
solution of 3 in acetonitrile.
4
6
formula
RuC60H51N9O8Cl2
RuLuC106H109N21
O19S4.5F13.5Cl0.5
2916.6
Preparation of HHH-[RuLu(L1)3](CF3SO3)5¥2CH3OH¥H2O (5): Ligand
L1 (100 mg, 0.183 mmol, 3 equiv) was suspended in ethanol (8 mL) under
an inert atmosphere and Lu(CF3SO3)3¥1.4H2O (39.7 mg, 0.0612 mmol,
1 equiv) dissolved in ethanol (0.5 mL) was added. This mixture was stir-
red for 30 min, then solid [Ru(dmso)5(H2O)](CF3SO3)2¥H2O (50.5 mg,
0.0612 mmol, 1 equiv) was added. The resulting mixture was refluxed for
6 h and then filtered to remove solid impurities. The solvent was distilled
under vacuum, and a red solid was obtained. Recrystallisation from
methanol/diethyl ether led to the formation of 5 (115 mg, 0.043 mmol;
yield 70%). ESI-MS: m/z: 514.4 (RuLu(L1)3(CF3SO3)]4+; elemental anal-
ysis calcd (%) for [LuRu(L1)3](CF3SO3)5¥2CH3OH¥H2O: C, 46.56; H,
4.02; N, 10.76; found: C, 46.71; H, 4.11; N, 10.87.
Mr
1198.2
colour
crystal system
space group
a [ä]
b [ä]
c [ä]
red
monoclinic
P21/n
12.2158(5)
19.2808(10)
23.3228(8)
90
96.145(4)
90
red
triclinic
17.7294(13)
19.2839(16)
19.2890(13)
74.791(8)
79.703(8)
69.673(9)
5939.4(9)
2
a [8]
b [8]
g [8]
V [ä3]
Z
5461.7(4)
4
1.457
1calcd [gcmÀ3
]
1.496
1.137
Preparation of HHH-[RuLu(L1)3](CF3SO3)4.5Cl0.5¥2.5CH3OH (6): The
procedure described for 5 was followed, except for the use of [Ru(dm-
so)4(Cl)2] (29.6 mg, 0.0612 mmol, 1 equiv). The resulting mixture was re-
fluxed for 16 h and then filtered to remove solid impurities. The solvent
was distilled under vacuum and a red solid was obtained. Diffusion of di-
ethyl ether into a concentrated methanol solution of the complexled to
HHH-[RuLu(L1)3]Cl2(CF3SO3)3¥3CH3OH¥2H2O (63 mg, 0.025 mmol;
yield 40%). ESI-MS: m/z: 514.4 [RuLu(L1)3(CF3SO3)]4+ elemental analy-
sis calcd (%) for [LuRu(L1)3]Cl2(CF3SO3)3¥3CH3OH¥2H2O: C, 46.90; H,
4.25; N, 10.77; found: C, 46.91; H, 4.23; N, 10.75%. Crystals of HHH-
[RuLu(L1)3](CF3SO3)4.5Cl0.5¥2.5CH3OH (6) suitable for X-ray diffraction
m(MoKa) [mmÀ1
]
0.451
min/maxtransmission
crystal size [mm3]
reflns measured
2q range
unique reflns
reflns observed
[jFo j>4s(F0)]
parameters
0.9117/0.9644
0.084î0.19î0.32
76213
4.68<2q<53.88
11325
0.7695/0.8779
0.13î0.21î0.29
70437
4.68<2q<53.88
23904
5994
13355
737
1.31(1)
1/
1500
1.59(1)
1/
GOF
w
were obtained by layering pentane onto
a solution of HHH-[Ru-
(s2(Fo)+0.00015(Fo)2) (s2(Fo)+0.0001(Fo)2)
Lu(L1)3]Cl2(CF3SO3)3¥3CH3OH¥2H2O in methanol.
R
Rw
0.036
0.037
À0.64/1.12
0.044
0.043
À2.64/1.77
Crystal structure determinations of mer-[Ru(L3)3](ClO4)2 (4) and HHH-
[RuLu(L1)3](CF3SO3)4.5Cl0.5¥2.5CH3OH (6): The crystal data, intensity
measurements and structure refinements are collected in Table 6. The
crystals were mounted on quartz fibre with protection oil. Cell dimen-
sions and intensities were measured at 200 K on a Stoe IPDS diffractom-
eter with graphite-monochromated MoKa radiation (l=0.71073 ä). Data
were corrected for Lorentz and polarisation effects and for absorption.
The structures were solved by direct methods (SIR97);[39] all other calcu-
lations were performed with the XTAL[40] system and ORTEP[41] pro-
grams.
min/max D1 [eäÀ3
]
Emission spectra were recorded on a home-built set-up consisting of a
single monochromator (Spex270M) equipped with a nitrogen-cooled
CCD camera (SpectrumOne Jobin Yvon-Spex) and appropriate collec-
tion optics. An Ar/Kr mixed-gas continuous-wave laser (Spectra Physics
Stabilite 2108) tuned to the 457.5 nm line was used as excitation source.
The emission quantum yields F were calculated using Equation (6),
where xrefers to the sample and r to the reference; A is the absorbance
at the excitation wavenumber used in the experiment, I the intensity of
the light, n the refractive indexand D the integrated emitted intensity.
mer-[Ru(L3)3](ClO4)2 (4): The hydrogen atoms of the methyl groups
were refined with restraints on bond lengths and bond angles, and
blocked during the last cycle. The positions of the other hydrogen atoms
were calculated. The perchlorate anion e was disordered and refined on
two positions with population parameters of 0.8 and 0.2, and possessing a
common position for the chlorine atom. The latter perchlorate (PP=0.2)
was refined with restraints on bond lengths and bond angles.
Fx ð1ÀexpðÀArðnÞÞ IrðnÞ n2x Dx
HHH-[RuLu(L1)3](CF3SO3)4.5Cl0.5¥2.5CH3OH (6): All the non-hydrogen
atoms of the cation HHH-[RuLu(L1)3]5+ and the triflate anions d and e
were refined with anisotropic displacement parameters. The triflates f
and g were disordered and each was refined on two positions with popu-
lation parameters of 0.7/0.3 (triflate f) and 0.5/0.5 (triflate g). The trif-
late h and two disordered chlorine atoms were located at about the same
site and were refined with population parameters of 0.5, 0.35 and 0.15 re-
spectively. Finally, 2.5 disordered methanol molecules were refined on
four sites with population parameters of 1.0, 0.5, 0.5 and 0.5.
ð6Þ
¼
ð1ÀexpðÀAxðnÞÞ IxðnÞ n2r Dr
Fr
[Ru(2,2’bipyridine)3](ClO4)2 (F=4.5% in water) was used as reference
for the determination of the quantum yields of complexes 1 5 in ethanol/
methanol (4:1).[1a] For excited-state lifetime measurements, samples were
excited at 532 nm with the second harmonic of a pulsed Nd:YAG laser
(Quantel Brillant B, 20 Hz). Emission decay curves were recorded on a
digital oscilloscope (TektronixTDS 540B) using a fast photomultiplier
tube (Hamamatsu TypH957-08). The time resolution of the set-up was
20 ns. Low-temperature glasses were produced in a custom-built sample
cell inserted into a closed-cycle helium refrigeration system (Oxford In-
struments CCC1100T). Cyclic voltammograms were recorded by using a
BAS CV-50W potentiostat connected to a personal computer. A three-
electrode system consisting of a stationary Pt disc working electrode, a Pt
counter-electrode and a nonaqueous Ag/AgCl reference electrode was
used. [N(nBu)4]ClO4 (0.1 molLÀ1 in MeCN) served as an inert electro-
lyte. The reference potential (EA=À0.16 V versus SCE) was standardised
against [Ru(bipy)3](ClO4)2 (bipy=2,2’-bipyridyl).[23] The scan speed was
100 mVsÀ1 and voltammograms were analysed according to established
procedures.[23] Elemental analyses were performed by Dr. H. Eder from
the Microchemical Laboratory of the University of Geneva.
CCDC-229557 (4) and CCDC-229558 (6) contain the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB21EZ, UK; fax: (+44)1223-336-033; or deposit@ccdc.cam.uk).
1
Spectroscopic and analytical measurements: H nmr spectra were record-
ed on a Broadband Varian Gemini 300 and on a Brucker DRX-500 spec-
trometer at 298 K. Chemical shifts are given in ppm versus TMS. Pneu-
matically assisted electrospray (ESI-MS) mass spectra were recorded
from 10À4 molLÀ1 acetonitrile solutions on a Finnigan SSQ7000 instru-
ment. Electronic spectra in the UV/Vis were recorded at 208C from
10À4 molLÀ1 solutions in ethanol/methanol (4:1) with a Perkin Elmer
Lambda 900 spectrometer using quartz cells of 0.1 and 1 cm path length.
Chem. Eur. J. 2004, 10, 3503 3516
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3515

C. Piguet et al.
FULL PAPER
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Received: January 29, 2004
Published online: May 26, 2004
3516
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 3503 3516