A novel extended covalent tripod for assembling nine-coordinate lanthanide(III) podates: A delicate balance between flexibility and rigidity

Article abstract of DOI:10.1002/chem.200390099

The introduction of long semirigid spacers between the capping carbon atom of the tripod and the unsymmetrical tridentate binding units provides the novel, extended covalent podand tris-{2-[2-(6-diethylcarbamoylpyridin-2-yl)-1-ethyl-1H-benzoimidazol- 5-yl

Full text of DOI:10.1002/chem.200390099

FULL PAPER
A Novel Extended Covalent Tripod for Assembling Nine-Coordinate
Lanthanide(iii) Podates: A Delicate Balance between Flexibility and Rigidity
Sylvain Koeller,[a] Ge¬rald Bernardinelli,[b] Bernard Bocquet,[a] and Claude Piguet*[a]
Abstract: The introduction of long semi-
rigid spacers between the capping car-
bon atom of the tripod and the unsym-
metrical tridentate binding units pro-
vides the novel, extended covalent
podand tris-{2-[2-(6-diethylcarbamoyl-
pyridin-2-yl)-1-ethyl-1H-benzoimidazol-
5-yl-methoxy]ethyl}methane (L15). Re-
action of L15 with lanthanide(iii) in
acetonitrile produces stable podates
[Ln(L15)]3‡ (Ln ˆ La Lu) in which
three tridentate binding units are facial-
ly organized. These wrap around the
nine-coordinate pseudo-tricapped trigo-
nal-prismatic metal ions. The crystal
structure of [La(L15)](ClO4)3 (18,
Z ˆ 6) reveals the formation of a C3-
symmetrical triple-helical podate. Two
slightly different arrangements of the
flexible ethylenoxy parts of the spacer
are observed in the solid state in agree-
ment with the formation of two confor-
mational isomers (M:m) in a 4:1ratio. A
qualitative analysis of the aromatic dia-
magnetic anisotropies affecting the
NMR signals of [Ln(L15)]3‡ (Ln ˆ La,
Y, Lu) in solution, combined with the
quantitative determination of electron-
induced relaxation in the paramagnetic
complex [Nd(L15)]3‡, demonstrate that
the solid state structure is maintained in
solution. This leads to a mixture of two
triple-helical conformers of similar sta-
bilities and that do not interconvert on
the NMR timescale between 243 and
343 K. Particular attention has been
given to the structural programming of
extended covalent tripods for facially
organizing unsymmetrical tridentate
binding units around LnIII. Photophysi-
cal measurements show that L15 effi-
ciently protects the metallic coordina-
tion spheres and sensitizes EuIII and TbIII
upon UV irradiation.
Keywords: chelates ¥ helical struc-
tures ¥ lanthanides ¥ N ligands
LaC67H82N12O18Cl3,
trigonal,
R3c,
properties.[3] Interestingly, the number, nature, and arrange-
ment of the donor atoms in the first coordination sphere
produce weak crystal-field effects (10 400 cmÀ1),[4] which
allow an ultrafine tuning of the electronic properties as
demonstrated by the recent rational design of energy transfer
processes,[5] emission quantum yields,[6] and magnetic aniso-
tropies[7] in lanthanide complexes. However, the ultimate
programming of crystal-field parameters relies on a precise
structural control of the metallic site, which is difficult to
achieve owing to the poor stereochemical preferences of LnIII,
and to their tendency to adopt large and variable coordination
numbers.[2, 3, 8] In this context, the semirigid tridentate aro-
matic chelating units L1 L5 have attracted considerable
interest during the last decade. Wrapping of the strands in
the D3-symmetrical complexes [Ln(L1-2H)3]3À and [Ln(Li)3]3‡
(i ˆ 2 5) provides stable and well-defined nine-coordinate
tricapped trigonal prismatic lanthanide sites.[9] However, the
expected formation of a 1:3 statistical mixture of facial and
meridional isomers in [Ln(L6)3]3‡ prevents further molecular
and crystal-field programming with unsymmetrical tridentate
ligands.[10] A straightforward solution considers the connec-
tion of the unsymmetrical binding units to a tripod. Three
bidentate chelating units have been indeed facially organized
for the preparation of unsaturated C3-symmetrical hexaden-
tate[11] and heptadentate[12] lanthanide complexes working as
contrast agents for magnetic resonance imaging (the vacant
Introduction
Since the valence 4f orbitals of the lanthanide metal ions
(LnIII, electronic configurations [Xe]4fn) are shielded from
external perturbations by the outer filled 5s2 and 5p6 shells,[1]
the Ln ligand dative bonds are mainly electrostatic with only
minor covalent contributions resulting from the minute
mixing of 4f and ligand-centered wavefunctions.[2] The
electronic, spectroscopic, and magnetic properties of the free
trivalent ions are thus essentially maintained in their com-
plexes, and lead to functional devices with predetermined
[a] Prof. Dr. C. Piguet, Dr. S. Koeller, B. Bocquet
Department of Inorganic, Analytical and Applied Chemistry
University of Geneva, 30 quai E. Ansermet
1211 Geneva 4 (Switzerland)
Fax : (‡41)22-702-6830
E-mail: claude.piguet@chiam.unige.ch
[b] 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. Table S1lists the ES-MS
peaks observed during titrations, Table S2 lists elemental analyses for
complexes 11 17, and Table S3 collects structural data for the
lanthanum coordination sphere in [La(L15)](ClO4)3 (18). Figure S1
displays a view of the unit cell in 18 and Figure S2 shows a stereoview of
the major isomer of 18 with thermal ellipsoids.
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1062 1074
tion of a central pyridine ring in L10[17]
and L11[18] provides fused five-mem-
bered chelate rings that stabilize the
final podates [Ln(Li)]3‡. Attempts to
favor helical wrapping with a longer
tripod in L12 failed, thus leading to
flexible podates in solution.[19] Recently,
two water-stable nine-coordinate lan-
thanide podates [Ln(L13-3H)][20] and
[Ln(L14-3H)][21] were reported; these
compounds take advantage of rigid
positions being occupied by exchangeable solvent molecules).
The application of this concept to tridentate binding units is
more difficult, because the helical wrapping of the strands
resulting from their complexation to nine-coordinate LnIII
induces specific steric constraints within the tripod. This
prevents efficient complexation. Adaptable triple-helical
pseudo-octahedral [MII(a,a'-diimine)] moieties have been
designed as noncovalent tripods for facially organizing three
unsymmetrical tridentate binding units analogous to L6
around nine-coordinate LnIII in the self-assembled triple-
stranded helicates [LnM(L7)3]5‡ (MII ˆ Fe, Co, Zn).[13] How-
ever, these systems exist as dynamic libraries in solution, and
their extreme sensitivity to external conditions limits their use
as functional devices.[14] The replacement of the noncovalent
macrocyclic triazacyclononane platforms grafted with carbox-
ylate-containing side arms. However, the design of a helical
tripod possessing a single capping atom for organizing three
unsymmetrical tridentate binding units around LnIII remains a
challenge for the preparation of directional polymetallic d
f[22] and f f[23] light-converting devices. In this paper, we
consider an alternative strategy in which the spacers contain a
sequence of aromatic and aliphatic carbon atoms controlling
the balance between rigidity and flexibility in the tripod.
Particular attention is focused on the consequences of the
mechanical coupling occurring between the covalent tripod
and the tridentate binding units for programming the helical
wrapping of the strands in the podates [Ln(L15)]3‡.
tripod with
a covalent tris(2-aminoethyl)amine tripod
(TREN) has been first explored for L8[15] and L9;[16] these
give the podates [Ln(Li-3H)] in the solid state. The introduc-
Results and Discussion
Synthesis of the ligand L15 ¥ H2O: A
methine group has been introduced as
the capping atom in the tripod and
ether connectors ensure the fixation
of the side arms. Firstly, this prevents
the complications associated with the
protonation of the capping nitrogen
atom previously encountered with
[Ln(L10 ‡ H)]4‡,[17] and secondly it
limits de-activation of metal-centered
excited states by high-energy NH
vibrations in the final complexes.[24]
The podand tris-{2-[2-(6-diethylcarba-
moylpyridin-2-yl)-1-ethyl-1H-benzo-
imidazol-5-yl-methoxy]ethyl}methane
monohydrate (L15 ¥ H2O) is obtained
in fourteen steps according to a convergent strategy in which
three unsymmetrical side arms 7 are connected to the covalent
tripod 10 during the last step, as shown in Scheme 1. The
tridentate unit 7 is prepared from the unsymmetrical synthon
3[25] and o-nitro-N-ethylaminoarene 2[26] according to a
modified Philips reaction.[27] The tripod 10 is obtained is
three steps from the commercially available compounds 8
and 9.[28] All methylene protons in L15 are enantiotopic
on the NMR timescale, thus pointing to a flexible be-
havior in solution compatible with an average C3v sym-
metry.
Formation and isolation of the complexes [Ln(L15)](ClO4)3 ¥
nH2O (Ln ˆ La, n ˆ 1: 11; Ln ˆ Nd, n ˆ 1: 12; Ln ˆ Eu, n ˆ 1:
13; Ln ˆ Gd, n ˆ 1: 14; Ln ˆ Tb, n ˆ 1: 15; Ln ˆ Lu, n ˆ 4: 16;
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C. Piguet et al.
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evolution of the absorption spectra for
Ln:L15 in the range 0.1 1.0 with a single
sharp end point for Ln:L15 ˆ 1.0 (Fig-
ure 1b). The observation of three isosbestic
points at 245, 274, and 327 nm (Figure 1a)
indicates the existence of the free ligand
together with a single absorbing complex in
solution; this complex can be safely as-
signed to [Ln(L15)]3‡ in agreement with
ESI-MS results. The spectrophotometric
data can be fitted with non-linear least-
squares techniques to the equilibrium
shown in Equation (1).[29]
Ln
Ln3‡ ‡ L15 > [Ln(L15)]3‡
log(b
†
(1)
11
Ln
The formation constants log(b † ˆ 6.5
11
7.6 do not vary significantly along the
lanthanide series within experimental er-
rors and point to negligible size-discrimi-
nating effects (Table 1). They can be com-
Ln
pared with log(b † ˆ 6.5 6.6 obtained in
11
pure acetonitrile for [Ln(L11)]3‡ (Ln ˆ Ce
Eu),[18] in which LnIII is also in a nine-
coordinate environment surrounded by six
heterocyclic nitrogen atoms and three oxy-
gen atoms of carboxamide groups, and with
Scheme 1. Multi-step synthesis of L15 with numbering scheme for NMR
measurements.
Ln ˆ Y, n ˆ 1: 17): ESI-MS titrations of L15 ¥ H2O
(10À4 moldmÀ3, acetonitrile) with Ln(CF3SO3)3 ¥ xH2O (Ln ˆ
La, Eu, Lu; x ˆ 1 4) for Ln:L 15 ratios in the range 0.5 2.0
show the exclusive formation of the complex [Ln(L15)]3‡
together with its adduct ions [Ln(L15)(CF3SO3)n](3Àn)‡ (n ˆ
1 2). The replacement of triflate counterions with poorly
coordinating perchlorate anions has no significant effect on
the complexation process, and the ESI-MS spectra display the
peaks corresponding to [Ln(L15)(ClO4)n](3Àn)‡ (n ˆ 0 2) (See
Table S1, Supporting Information). Spectrophotometric titra-
Figure 1. a) Variation of absorption spectra observed for the spectropho-
À4
tometric titration of L15 ¥ H2O (1 0moldmÀ3 in acetonitrile
‡
À4
tions of L15 ¥ H2O (1 0moldmÀ3 in acetonitrile and
0.01moldm À3 [N(nBu)4]ClO4) with Gd(ClO4)3 ¥ 6.6H2O at 298 K
(Gd:L15 ˆ 0.1 1.5). b) Corresponding variation of observed molar extinc-
tions at four different wavelengths.
0.01moldm À3 [N(nBu)4]ClO4) with Ln(ClO4)3 ¥ xH2O (Ln ˆ
La, Pr, Nd, Sm, Gd, Dy, Er, Lu; x ˆ 6 8) show a smooth
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Lanthanide(iii) Podates
1062 1074
Ln
Table 1. Formation constants log(b † for the complexes [Ln(L15)]3‡ in
18; Ln ˆ Eu, 19) are isostructural, but the monocrystals
obtained for Ln ˆ La (18) were of higher quality and
the X-ray diffraction study has been focused on this com-
plex. The crystal structure of 18 confirms the formation
of the cationic 1:1 complex [La(L15)]3‡ together with
disordered ionic perchlorate anions (see Experimental
Section). The [La(L15)]3‡ cation is located on a crys-
tallographic threefold axis passing through C1and La
(special positions 6a). Figure 2 shows views of the
cations perpendicular to the threefold axis and
Table 2 collects together selected bond lengths and
bond angles.
11
acetonitrile (0.01moldm À3 [N(nBu)4]ClO4, 293 K).
LnIII
log(b11)
LnIII
log(b11)
LaIII
PrIII
NdIII
SmIII
7.0 Æ 0.2
7.3 Æ 0.4
6.5 Æ 0.3
6.8 Æ 0.3
GdIII
DyIII
ErIII
LuIII
7.6 Æ 0.3
7.2 Æ 0.2
7.5 Æ 0.4
6.8 Æ 0.3
log(b † ˆ 6.7 8.5[17] and log(b † ˆ 6.4 7.1[19] obtained for
Ln
Ln
11
11
[Ln(L10)]3‡ and [Ln(L12)]3‡ (Ln ˆ La Lu), respectively. In
this case, six oxygen atoms and three heterocyclic nitrogen
atoms are complexed to LnIII. Although strict comparisons are
limited by the different ionic
strengths used for recording the
spectroscopic data, the similar
formation constants found for
these podates indicate that the
length of the spacer (l) within
the tripod has only minor effects
on the stability of the final
complexes (l is defined as the
number of atoms separating the
apical atom and the first coor-
dinated atom, for example l ˆ 4
for [Ln(L10)]3‡ and [Ln(L11)]3‡,
l ˆ 5 for [Ln(L12)]3‡ and l ˆ 7 for
[Ln(L15)]3‡). Moreover, the rig-
id aromatic phenyl rings incor-
porated in the tripod of
[Ln(L15)]3‡ do not induce dra-
matic steric constraints preclud-
ing an efficient wrapping of the
strands around LnIII.
Diffusion of diethyl ether into
concentrated solutions of the
complexes in acetonitrile pro-
vides microcrystalline powders
of
[Ln(L15)](ClO4)3 ¥ nH2O
(Ln ˆ La, n ˆ 1: 11; Ln ˆ Nd,
n ˆ 1: 12; Ln ˆ Eu, n ˆ 1: 13;
Ln ˆ Gd, n ˆ 1: 14; Ln ˆ Tb,
n ˆ 1: 15; Ln ˆ Lu, n ˆ 4: 16;
Ln ˆ Y, n ˆ 1: 17) in 72 93%
yield. Elemental analyses sup-
port the proposed formulations
(see Table S2, Supporting Infor-
mation). IR spectra display the
vibrations typical of the coordi-
Figure 2. a) Perspective view of the [La(L15)]3‡ ion perpendicular to the threefold axis showing the atomic
numbering scheme (the indexes ' and '' denote the symmetry related strands). b) Stereoview of the major
conformer (M) perpendicular to the threefold axis.
Table 2. Selected bond lengths [ä] and bond angles [8] in [La(L15)](ClO4)3
(18).[a]
nated tridentate benzimidazole pyridine carboxamide
À1
ˆ
ˆ
binding unit (n(C O) ˆ 1585 1590 cm , n(C N) ˆ 1570
1574 cmÀ1)[13] together with bands at 1090 and 625 cmÀ1
typical of ionic perchlorates.[30] Fragile anhydrous monocrys-
tals suitable for X-ray diffraction studies were obtained for
[Ln(L15)](ClO4)3 (Ln ˆ La, 18; Ln ˆ Eu, 19) upon ultra-slow
diffusion of diethyl ether into concentrated acetonitrile
solutions under a dry atmosphere.
À
La N12.665(6)
O2-La-N3
2.695(8)
2.486(7)
61.3(2)
''
O2-La-N1'
70.2(3)
145.0(3)
79.5(3)
87.3(2)
75.0(2)
144.1(2)
119.9(2)
7.03(4)
À
La N3
À
La O2
O2-La-N1''
N1-La-N1'
N1-La-N3'
N1-La-N3''
N3-La-N3'
La ¥¥¥ C1[b]
N1-La-N3
N3-La-O2
N1-La-O2
O2-La-O2'
O2-La-N3'
62.5(2)
123.8(2)
81.3(3)
136.3(2)
Crystal and molecular structure of [Ln(L15)](ClO4)3 (Ln ˆ La,
18; Ln ˆ Eu, 19): The complexes [Ln(L15)](ClO4)3 (Ln ˆ La,
[a] The indexes ' and '' denote the symmetry related strands (see Figure 2).
[b] Nonbonded distance.
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C. Piguet et al.
FULL PAPER
and wij. The helical twist of the
tridentate binding units defined
by F1 F2 and F2 F3 is regu-
lar, but the associated pitches
P12 ˆ 10.11 ä and P23 ˆ 12.14 ä
are slightly shorter than those
reported for [Eu(L10 ‡ H)]4‡
(11.84 ä and 13.30 ä).[17] This
points to a tighter wrapping
process in [La(L15)]3‡ induced
by the longer tripod. In the rigid
aromatic F3 F4 portion, the
helical twist is significantly re-
Figure 3. Partial stereoview of the complex [La(L15)]3‡ along the threefold axis showing the two conformers M
(full line) and m (empty line).
Table 3. Helical pitches Pij, linear distances dij, and average twist angle wij
along the C3 axis for the major (M) and minor (m) conformers in the crystal
The C2, C3, and O1atoms display a significant disorder,
which can be solved with the refinement of two distinct atomic
sites for each atom (occupancy factors 0.8/0.2, see Exper-
imental Section) corresponding to two different conforma-
tions of the tripod. These will be refered to as a major (M,
80%) and a minor (m, 20%) conformer (see Figure 3). No
significant residual peak in the Fourier difference analysis is
located close to C1, and the displacement parameters of C1
are almost isotropic (the r.m.s.d. for C1parallel and perpen-
dicular to the C3 axis amount to 0.33 and 0.37 ä, respectively).
structure of [La(L15)]3‡ [a]
.
Helical portion[b] Conformer dij [ä]
wij [8]
Pij [ä]
F1 F2
F2 F3
F3 F4
F4 F5
F5 F6
F6 F7
M ˆ m
M ˆ m
M ˆ m
M (m)
M (m)
M (m)
1.53
1.71
3.72
1.27 (0.46)
0.11 (1.38) 23.1 (2.4)
1.00 (0.01) 15.2 (31.9)
54.6
50.8
60.6
10.11
12.14
22.10
2.8 (19.0) 162.51 (8.64)
1.75 (206.47)
23.69 (0.14)
[a] Each helical portion Fi Fj is characterised by i) a linear extension dij
defined by the separation between the facial planes, ii) an average twist
angle wij defined by the angular rotation between the projections of Ni and
Nj (or Oj) belonging to the same ligand strand, and iii) its pitch Pij defined
as the ratio of axial over angular progressions along the helical axis (see
text). [b] F1:{O2, O2', O2''}; F2:{N3, N3', N3''}; F3:{N1, N1', N1''}; F4:{C4,
C4', C4''}; F5:{O1, O1', O1''}; F6:{C3, C3', C3''}; F7:{C2, C2', C2''}.
À
We can therefore exclude an exo arrangement of the C1 H
bond and both conformers adopt the endo conformation of
the apical methine group with its hydrogen atom pointing
toward LaIII, as previously reported for the protonated
capping nitrogen atom in [Eu(L10 ‡ H)]4‡.[17]
A careful examination of Figure 3 reveals that the two
conformers display different wrapping of the ethyleneoxy
spacers connecting the apical methine group and the rigid
aromatic benzimidazole side arms. The helical threads in the
major conformer M adopt a single screw direction (except
within the small O1 C4 portion in which no significant
helical twist occurs), thus leading to an overall regular triple-
helical arrangement of the tripod. Conversely, the ligand
threads of the minor conformer m invert their screw direction
between the C2 C3 and C3 O1portions and provide two
successive domains with opposite helicities within the tripod
(an amphiverse triple-helical arrangement).[31] A detailed
quantitative structural analysis of the helical revolution of the
threads about the threefold axis in [La(L15)]3‡ requires the use
of seven parallel facial planes F1 F7 defined by the
symmetry related atoms of the three strands. The coordina-
tion sphere around LaIII is sliced into two helical portions
delimited by the three facial planes F1{O2,O2 ',O2''}, F2
{N3,N3',N3''}, and F3 {N1,N1',N1''}, while the covalent tripod
is further delimited by F4 {C4,C4',C4''}, F5 {O1,O1',O1''}, F6
{C3,C3',C3''}, and F7 {C2,C2',C2''}. The interplanar distance dij
corresponds to the linear progression of the strand along the
helical axis within each part limited by Fi and Fj. The wij angles
between the projections of the Xi and Yj atoms of the same
strand belonging to the different planes Fi and Fj measure the
angular rotation.[17] The pitch of each helical portion can be
then calculated according to Pij ˆ (dij/wij)  360 (see Table 3).
Pij corresponds to the length of a cylinder containing a single
turn of the helix defined by the geometrical characteristics dij
duced (P34 ˆ 22.1ä) and it even stops in the next F4 F5
domain for the major M conformer before its restoration in
the final portions F5 F6 and F6 F7 of the tripod. For the
minor m conformer, a tight helical twist is maintained in the
F4 F5 portion, but inversion of the screw sense occurs within
the F5 F6 domain and opposite helicity characterizes the
terminal F6 F7 portion (as shown in Figure 3). A rough CPK
molecular modeling of the podate [La(L15)]3‡ suggests that
the interconversion of the two isomers requires a considerable
distortion of bond lengths and bond angles within the tripod.
In the solid state, the two conformers display the same
metallic environment in which the La atom is nine-coordinate
in a distorted tricapped trigonal prismatic site with the three
oxygen atoms of the carboxamide groups and the three
nitrogen atoms of the benzimidazole rings occupying the
vertices of the prism, and the three nitrogen atoms of the
À
pyridine rings capping the rectangular faces. The La N(py),
À
À
La N(bzim), and La O(amide) bond lengths are standard
and closely match those found in the related noncovalent
podate [LaCo(L7)3]6‡ in which the tripod is constituted by an
inert triple-helical pseudooctahedral [CoIII(a,a'?diimine)3]
moiety (Figures 4a and b).[32] The detailed structural analysis
of the tricapped trigonal prismatic lanthanide site based on
the classical determination of the f, qi, and wi angles[9a, 13, 33]
shows only faint differences between [LaCo(L7)3]6‡ and
[La(L15)]3‡. This is in agreement with comparable helical
wrappings of the tridentate binding units (see Table S3,
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Lanthanide(iii) Podates
1062 1074
threefold axis as exemplified in Figure 4c. As a result of the
helical wrapping of the strands, the pyridine ring of each
strand is not coplanar with the adjacent benzimidazole ring
(interplanar angle: 258) and carboxamide group (interplanar
angle: 458). This helical twist prevents an adequate alignment
of the lone pair of the pyridine nitrogen atom with the
III
À
La N(py) bond (La lies 1.33 ä outside the plane of the
pyridine ring) as similarly observed for [LaCo(L7)3]6‡.[32]
However, the La atom almost lies in the intermediate F2
plane defined by the three pyridine nitrogen atoms (deviation
0.105(3) ä toward F3) in [La(L15)]3‡ as is observed similarly
for LaIII in [LaCo(L7)3]6‡ (0.104 ä toward F3).[32] We conclude
that the length of the spacers in the covalent tripod of L15
(l ˆ 7 atoms) is compatible with the regular wrapping of the
three strands around the nine-coordinate LaIII as observed in
the self-assembled helicate [LaCo(L7)3]6‡, which possesses
even longer spacers (l ˆ 8). This contrasts with the consid-
erable sterical constraints induced by the short TREN tripod
(l ˆ 4) and the resulting conical triple-helical arrangement of
the strands found in [Eu(L10 ‡ H)]4‡.[17] However, the two
different conformations observed in the solid state for the
ethyleneoxy groups in the two conformers of [La(L15)]3‡
suggest some residual strains within the tripod. In the unit
cell, [La(L15)]3‡ ions with opposite helicities are alternatively
packed into columns running along the c direction (see
Figure S1, Supporting Information).
Solution structure of the complexes [Ln(L15)](ClO4)3 ¥ nH2O
(Ln ˆ La, n ˆ 1: 11; Ln ˆ Nd, n ˆ 1: 12; Ln ˆ Eu, n ˆ 1: 13;
Ln ˆ Lu, n ˆ 4: 16; Ln ˆ Y, n ˆ 1: 17): We have previously
shown by ESI-MS and spectrophotometry that the complex-
ation of L15 to the diamagnetic LnIII (Ln ˆ La, Lu, Y) gives
exclusively [Ln(L15)]3‡ in acetonitrile, but their 1H NMR
spectra systematically display two different sets of sixteen
signals corresponding to two different C3-symmetrical species
in approximately 70:30% ratios (see Table 4). The 13C NMR
spectra confirm the existence of two C3-symmetrical species,
each displaying 23 signals. The minor variation of the
chemical shifts of the same nucleus in the two isomers points
to similar chemical environments and closely related arrange-
ments of the strands (as shown in Table 4 and Figure 5). From
Figure 4. Perspective views of the crystal structures of a) [La(L15)]3‡ (M
conformer), and b) [LaCo(L7)3]6‡[32] perpendicular to the C3 axis. c) Opti-
mized superposition of the two binding domains of [LaCo(L7)3]6‡ (in blue)
and [La(L15)]3‡ (in red) highlighting the minor contraction of the upper
triangular face of the trigonal prism in [La(L15)]3‡
.
Supporting Information). The main discrepancy concerns a
slightly tighter arrangement of the benzimidazole rings
induced by the shorter covalent tripod in [La(L15)]3‡. This
forces the six-membered phenyl rings to come closer to the
Table 4. 1H NMR shifts (with respect to SiMe4) of L15 and its complexes [Ln(L15)](ClO4)3 ¥ nH2O (Ln ˆ La, n ˆ 1: 11; Ln ˆ Nd, n ˆ 1: 12; Ln ˆ Eu, n ˆ 1: 13;
Ln ˆ Lu, n ˆ 4: 16; Ln ˆ Y, n ˆ 1: 17) in CD3CN at 298 K.[a]
[b]
%
H1
H2
H3
H4
H5
H6
H7
H8
H9
H10
H11
H12
H13
H14
H15
H16
L15
11
11
12
100
71( M)
29 (m)
66 (M)
1.79
0.02
0.48
À 0.63
1.57
0.74
0.74
À 0.09
3.51
2.45
2.70
1.87
4.51
7.62
7.25
7.35
7.43
6.90
7.42
7.74
7.81
8.27
7.46
7.93
7.95
8.97
7.95
8.40
8.42
9.49
8.30
8.29
8.34
4.69
4.77
4.77
3.06
3.35
3.06
3.35
4.19
4.33
4.19
4.33
4.83
4.83
1.33
1.70
1.70
3.51
3.49
3.49
3.91
1.20
1.06
1.06
1.49
3.28
2.88
2.88
5.22
0.99
0.80
0.80
2.18
3.62, 4.13
3.20, 4.37
2.88, 3.58
6.28
6.02
2.11
10.50
À 0.09
4.23
12
13
13
34 (m)
67 (M)
33 (m)
À 2.09
1.70
À 0.09
1.63
1.87
3.82
3.82
2.34, 3.81
4.59, 4.78
4.40, 5.08
2.11
10.04
10.04
6.93
6.60
6.67
8.33
7.91
8.00
9.04
4.79
4.66
9.62
6.79
6.72
10.71
6.04
6.00
À 0.09
3.91
4.23
2.62
3.04
2.62
3.04
3.55
3.55
1.49
0.47
0.47
5.22
2.18
2.03
2.03
1.10
1.10
2.48
2.78
2.48
2.78
2.68
2.68
3.05
1.63
16
16
17
17
68 (M)
32 (m)
64 (M)
36 (m)
0.40
À 0.29
0.43
À 0.28
0.60
0.60
2.37
2.54
3.70, 4.08
3.37, 4.34
5.75
5.60
5.817.317.72
7.31
7.38
7.94
7.79
7.73
7.80
8.36
7.94
7.98
7.98
8.36
8.36
8.40
8.40
8.40
8.40
1.74
1.74
1.11
1.11
0.76
0.76
0.612.713.66, 4.08
0.612.713.32, 4.34
4.81.731 3.52 .081 2.75
8.36 4.81.731 3.52 .081 2.75
0.76
5.67
7.38
0.76
[a] See Scheme 1for the numbering scheme. [b] Ratio of the two isomers according to the integration of 1H NMR signals (error Æ3%).
Chem. Eur. J. 2003, 9, No. 5
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C. Piguet et al.
FULL PAPER
2) The enantiotopic methylene
protons of the free ligands
(H2, H3, H4, H11, H13 and
H15) become diastereotopic
in the two isomeric forms of
the complexes [Ln(L15)]3‡,
leading to i) interpenetrated
ABX3 spin systems for the
ethyl residues (H11-H12,
H13-H14 and H15-H16);
ii) intractable ABCDX spin
systems for the protons of
the tripods (H1-H2-H3) and
iii) much simpler AB spin
systems for the isolated
methylene H4 (Figure 5).
These observations show
Figure 5. 1H NMR spectra of a) L15 and b) [La(L15)]3‡ in CD3CN (298 K).
that the three strands wrap
around LnIII to give C3-sym-
metrical [Ln(L15)]3‡ com-
the average 7:3 equilibrium distribution observed between the
two isomers in [Ln(L15)]3‡ (Ln ˆ La, Lu, Y, Table 4), a
difference in free energy of DG ˆ 2.1kJmol À1 can be calcu-
lated. Surprisingly, variable temperature NMR spectroscopy
(243 343 K) does not show significant variations of the
spectra in agreement with a considerable free energy of
activation (DG=) for the interconversion process. Taking into
account the difference in chemical shift between the NMR
signals of H5 (singlets) in the two isomers of [La(L15)]3‡
(dn(La) ˆ 78 Hz, Table 4) and the difference in population
between the two exchangeable sites Dp ˆ 0.4, the polynomial
expression of Equation (2) gives X ˆ 2.18. The classical
Equations (3) and (4) allow an estimation of the maximum
value for the rate constant k ꢀ 112 sÀ1 associated with a
minimum free energy of activation DG=(La) ꢁ 71kJmol À1
for the interconversion process at the highest accessible
temperature in acetonitrile (Tˆ 343 K and kB and h are
respectively the Boltzmann and the Planck constants).[34]
plexes that do not exhibit fast P > M intramolecular
helical interconversion on the NMR timescale at 298 K.
Variable temperature spectra (233 343 K) do not affect
the signals of the diastereotopic protons and a calculation
using Equations (2 4) for this dynamic process with
p
dn(H4) ˆ 153 Hz (Table 4), Dp ˆ 0 (X ˆ 2)[34] and Tˆ
343 K gives a maximum rate constant k ꢀ 340 sÀ1 associ-
ated with a minimum free energy of activation DG=(La) ꢁ
68 kJmolÀ1. This strongly contrasts with the fast helical
interconversion occurring in the triple-helical complex
[La(L2)3]3‡ at room temperature(DG=< 55 kJmolÀ1)[9a]
and the coalescence of the methylene protons observed
at 323 K for the podate [La(L10)]3‡ (DG=
ˆ
323 K
66 kJmolÀ1).[35] However, no helical interconversion can
be detected for the rigid noncovalent podates
[LnCo(L7)3]6‡ on the NMR timescale[13c] as found for
[Ln(L15)]3‡. This strongly suggests that the covalent tripod
in the last complexes is rigid enough to prevent fast helical
interconversion, but flexible enough to allow an efficient
wrapping of the strands.
X6 À 6X4 ‡ [12 À 27(Dp)2]X2 À 8 ˆ 0
pdn
(2)
(3)
(4)
3) The isolated aromatic proton H5 is shielded by Dd ˆ 1.48
1.74 ppm (Lnˆ La), Dd ˆ 2.01 2.16 ppm (Ln ˆ Lu) and
Dd ˆ 1.95 2.09 ppm (Lnˆ Y, Table 4) upon complexation
k ˆ
X
ꢀ
ꢁ
kBT
kh
DG=ˆ RTln
as previously reported for the related proton in
[13c]
[LnCo(L7)3]6‡ (Dd ˆ 1.91 ppm).
This behavior is diag-
nostic of the wrapping process of the strands which puts H5
in the shielding region of the aromatic imidazole ring of
the adjacent strand,[13a] as observed in the crystal structure
of [La(L15)]3‡ (Figure 2).
These results suggest that the two isomers observed in
solution for [Ln(L15)]3‡ (Ln ˆ La, Y, Lu) display comparable
ground-state energies, but that low-energy dynamic processes
are not accessible for their interconversion on the NMR
timescale.
4) The 1H NMR signal of the apical proton H1is shielded by
Dd ˆ 1.77 ppm for the major isomer and Dd ˆ 1.31 ppm for
the minor isomer in [La(L15)]3‡ as a result of the conforma-
tional change of the tripod occurring upon complexation.
In the crystal structure of [La(L15)]3‡ (Figure 2), the
capping methine group adopts an endo conformation with
H1pointing inside the cavity defined by the three wrapped
phenyl rings of the benzimidazole rings. Therefore, H1lies
in the shielding region of the diamagnetic anisotropic
tensor associated with aromatic rings, and the observed
Further structural information can be gained from the
detailed analysis of the complexation shifts and the diaste-
reotopic probes in the diamagnetic complexes [Ln(L15)]3‡
1
(Ln ˆ La, Lu, Y). Compared to the H NMR spectrum of
the free ligand L15, the complexation of LnIII (Ln ˆ La, Lu, Y)
induces four remarkable changes.
1) The complexation process provides two noninterconvert-
ing isomers (on the NMR timescale) in a 7:3 ratio as
previously discussed.
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Lanthanide(iii) Podates
1062 1074
downfield complexation shifts confirm that both isomers
adopt related endo conformations in solution. The exact
location of H1slightly changes between the two isomers. It
is worth noting that the 7:3 ratio observed for [La(L15)]3‡ in
solution is close to the 8:2 ratio observed for the two
different conformations of the tripod (M and m) in the
solid-state. We can thus tentatively assign the major isomer
observed in solution to the complex displaying a regular
triple-helical conformation within its tripod (related to the
solid-state M conformer). The minor isomer in solution
may therefore be assigned to the complex displaying an
amphiverse arrangement of the spacers within the tripod
(related to the solid-state m conformer). Closely related
complexation shifts are observed for [Lu(L15)]3‡ and
[Y(L15)]3‡ except for minor deviations resulting from the
tighter wrapping of the strands around the smaller
leading to Equation (7) for comparing Ln nucleus distances
para
when T1
are accessible for the same nucleus in both
i
conformers M and m. Finally, the paramagnetic contributions
para
i
to the longitudinal relaxation rates (1/T1 † in the para-
magnetic [Nd(L15)]3‡ complex can be extracted from the
exp
experimental relaxation rates (1/T1 † with Equation (8), in
i
dia
which the diamagnetic contributions (1/T1i † correspond to
the relaxation rates of the same nuclei in the analogous
diamagnetic complex [La(L15)]3‡ (Table 5).[9a]
!
6
para
T
T
ꢂM†
ꢂm†
riꢂM†
riꢂm†
1i
ˆ
(7)
(8)
para
1i
1
para
1i
1
1
ˆ
À
exp
dia
T
T
T
1i
1i
Table 5. Longitudinal 1H NMR relaxation rates (T1eixp [s]) for the com-
plexes [Ln(L15)](ClO4)3 ¥ H2O (Ln ˆ La: 11; Ln ˆ Nd: 12) in CD3CN at
298 K and calculated Ln H distances (ri [ä]) for H1and for the aromatic
protons H5 H10 in the two isomers of [Nd(L15)](ClO4)3 ¥ H2O.[a]
lanthanide
ions
as
previously
reported
for
[LnCo(L7)3]6‡.[13c] However, contrary to [La(L15)]3‡, the
major isomer for [Lu(L15)]3‡ and [Y(L15)]3‡ in solution
corresponds to that with the smaller complexation shift for
H1(Table 4). This strongly suggests that the relative ratio
of the two isomers in solution depends on the size of the
complexed metal (in other words, the free energy between
the ground states of the two conformers varies with the size
of LnIII).
[b]
%
H1H5
H6
H7
H8
H9 0 H1
11
71( M) 0.216 0.707 0.928 0.797
0.643 1.005 0.560
11
12
12
ri(M)[d]
ri(m)[e]
29 (m) 0.304 0.715 0.904 0.7604 0.619 1.051 0.629
[c]
66 (M) 0.185
34 (m) 0.240
6.00
0.534 0.400
0.572 0.397
7.01 5.54
0.140 0.296 0.135
0.139 0.293 0.129
[c]
3.917.43
6.24
5.54
5.43
6.20
[c]
5.88
7.70
7.05
5.35
A strict analogy between solid-state and solution structures
for [La(L15)]3‡ is precluded by the systematic splitting
observed for all signals in the NMR spectra of the two
isomers. While the solid-state structure implies that only the
conformation of the aliphatic part of the tripod significantly
changes, the tridentate binding units remaining invariable.
However, we suspect that the structure of the podate is
relaxed in solution and minor variations in the wrapping of the
strands in solution occur because solid-state intermolecular
packing forces have been removed. We have thus resorted to
electron-induced nuclear relaxation measurements to address
reliable Ln nucleus distances in solution for both iso-
mers.[13a, 36] For fast-relaxing lanthanide complexes (Ln ˆ
Ce Yb, except Gd), the contact relaxation can be neglected
and only transcient and static dipolar mechanisms contribute
to the induced paramagnetic nuclear relaxation process-
es.[36, 37] In the fast motion limit and in the absence of chemical
exchange processes (two conditions met for [Ln(L15)]3‡),[37]
[a] See Scheme 1for the numbering scheme. Typical relative errors for T1
are within 2%. [b] Ratio of the two isomers according to the integration of
1H NMR signals, M and m, respectively, are assigned to the major and
minor isomers. [c] Masked by aliphatic signals. [d] Taken from the crystal
structure of [La(L15)](ClO4)3 (18). [e] Calculated with Equations (7) and
(8) for the minor isomer.
À
Taking the Ln H distances measured in the crystal
structure of [La(L15)](ClO4)3 (18) as a model for the major
isomer (ri(M)) observed for [Nd(L15)]3‡ in solution, the
related distances in the minor isomer (ri(m)) have been
calculated with Equation (7) and collected in Table 5. Al-
though complicated interpenetrated signals prevent relaxa-
tion measurements for H2 and H3, the ri(m) distance obtained
for the apical proton H1shows only a small contraction in the
minor isomer (ri(M) À ri(m) ˆ 0.12 ä); this confirms both the
exclusive formation of endo isomers in solution and the slight
structural change affecting the tripod in the two isomers. This
is further exemplified by the 0.27 ä extension observed for
H6 when going from M to m.[39] However, the similar ri(m)
and ri(M) values found for the aromatic protons of the
tridentate binding units (H7 H10) strongly support the
existence of two conformers in solution with comparable
coordination spheres and slightly different arrangement of the
ethyleneoxy spacers as found in the solid state. The small DG
values measured in solution implies two well-defined minima
in the energy hypersurface explored by the conformations of
the tripod. The high activation energy DG= estimated for the
M > m process in solution suggests, however, that the
conformational interconversion requires the partial decom-
plexation of the metal.
the paramagnetic contribution to the longitudinal relaxation
para
i
rate of the nucleus i (1/T1 † is given by Equation (5). Here, ri
is the lanthanide nucleus distance, te and tr are the electronic
and rotational correlation times, respectively, meff is the effective
magnetic moment of the complex, and the other terms have
their usual meaning.[36, 37] Since both transcient and static
dipolar contributions depend on riÀ6, Equation (5) reduces to
Equation (6) for a given paramagnetic complex at fixed
ꢀ
ꢁ
ꢀ
ꢁ
ꢀ
ꢁ
1
para
1i
4
3
m0 gIm2effb2
6
5
m0 g2I m4effb4H20
4p r6i ꢂ3kT†
tr
2
2
ˆ
te ‡
(5)
(6)
2
T
4 p
ri6
1 ‡ w2I t2r
1
para
1i
Cj
ri6
ˆ
T
magnetic field and temperature.[38] For the two conformers of
[Ln(L15)]3‡ in acetonitrile, no significant change in te, tr, and
meff is expected. Identical Cj constants can be used, thus
Photophysical properties of [Ln(L15)](ClO4)3 ¥ H2O (Ln ˆ La:
11; Ln ˆ Eu: 13; Ln ˆ Gd: 14; Ln ˆ Tb: 15): The ligand L15
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1069

C. Piguet et al.
FULL PAPER
displays a broad and assymmetric absorption band envelope
centered at 31650 cmÀ1 in acetonitrile and assigned to the p !
p* transitions , as previously established for L7.[13a] Upon
complexation to LnIII in [Ln(L15)]3‡ (Ln ˆ La, Eu, Gd, Tb),
this band is red-shifted by approximately 1350 cmÀ1; this
allows the monitoring of the complexation process by
spectrophotometry (Figure 1). A parallel behavior is ob-
served in the solid state (Table 6) and excitation of the ligand-
centered transition in L15 (solid-state, 77 K, lexc ˆ 27620 cmÀ1)
provides a poorly resolved fluorescence spectrum originating
from the 1pp* level (0 0 phonon at 24330 cmÀ1). Time-
resolved spectra do not exhibit detectable phosphorescence
(delay times: 0.01 100 ms), which points to inefficient
intersystem crossing and/or efficient non-radiative quenching
3
of the pp* state. The complexed ligand in the diamagnetic
complex [La(L15)](ClO4)3 ¥ H2O (11) shows very similar emis-
sion spectra (Table 6). For the paramagnetic complex
[Gd(L15)](ClO4)3 ¥ H2O (14), the metal-centered excited levels
are too high to be accessible for intramolecular energy
Figure 6. Time-resolved phosphorescence spectra (delay 0.1ms) of
a) [Gd(L15)](ClO4)3 ¥ H2O (14, lexc ˆ 27030 cmÀ1
,
77 K), b) [Eu(L15)]-
(ClO4)3 ¥ H2O (13, lexc ˆ 27170 cmÀ1, 77 K), c) [Tb(L15)](ClO4)3 ¥ H2O (15,
lexc ˆ 27397 cmÀ1, 77 K), and d) [Eu(L15)]3‡ in acetonitrile (10À3 moldmÀ3
lexc ˆ 26385 cmÀ1, 298 K).
,
1
3
transfers from the pp* or pp* levels,[40] but the Coulomb
interactions between the electrons of the ligands and the
metal ion mix the ligand-centered triplet and singlet wave-
3
functions.[41] Consequently, both the 1pp* ! pp* intersystem
crossing (isc) and the radiative emission of the spin-forbidden
emission for the coordinated ligand in [Eu(L15)](ClO4)3 ¥ H2O
(13) and [Tb(L15)](ClO4)3 ¥ H2O (15) points to inefficient
L15 ! LnIII (Ln ˆ Eu, Tb) energy-transfer processes. This
behavior is confirmed by the concomittant observation of
faint emission of the ligand-centered triplet state in 13.
The emission spectra of the podates [Eu(L15)]3‡ and
[Tb(L15)]3‡ in acetonitrile (10À3 moldmÀ3, 293 K) closely
match those obtained in the solid state, in agreement with
the preservation of the C3-symmetrical structure in solution
previously demonstrated by NMR spectroscopy. The Eu(5D0)
and Tb(5D4) lifetimes measured upon irradiation of the
3pp* level become more efficient.[41] The emission spectrum of
1
14 at 77 K thus displays the expected pp* fluorescence at
24390 cmÀ1 together with a weak, but significant 3pp*
emission at 20370 cmÀ1 (0 0 phonon, vibronic progression
ꢃ1000 cmÀ1, Figure 6a). These values slightly differ from
those reported for [GdZn(L7)3]5‡ in which GdIII is nine-
coordinate in a similar N6O3 site (E(1pp*) ˆ 26600 cmÀ1 and
E(3pp*) ˆ 19960 cmÀ1). The adjacent bidentate binding unit
in the segmental ligand L7 complicates the interpretation of
the photophysical properties and prevents closer compari-
sons.[13a] The ligand-centered luminescence in [Eu(L15)]-
(ClO4)3 ¥ H2O (13) and [Tb(L15)](ClO4)3 ¥ H2O (15) is partially
quenched by L15 ! LnIII energy-transfer processes. Excitation
by means of the ligand-centered p ! p* transitions produces
ligand-centered levels amount to 2.58(3) ms (lexc
ˆ
26385 cmÀ1) and 0.019(1) ms (lexc ˆ 26455 cmÀ1), respectively.
The long lifetime obtained for [Eu(L15)]3‡ is diagnostic for the
absence of high-frequency oscillators in the first coordination
sphere,[24] implying that no solvent molecule is bound to the
metal in solution. Moreover, the spectral characteristics in
solution are very similar to those previously reported for
[EuZn(L7)3]5‡ (tEu(5D0) ˆ 2.56(2) ms),[13a] thus pointing to
similar pseudo-tricapped trigonal prismatic N6O3 coordina-
tion spheres in solution. The absolute quantum yield is modest
(FEu ˆ 4.3  10À3) and reflects the poor efficiency of intersys-
tem crossing and energy-transfer processes. It is, however,
more than twice that reported for [EuZn(L7)3]5‡.[13a] For
1
3
faint residual emission of the pp* (Ln ˆ Eu, Tb) and pp*
(Ln ˆ Eu) levels. Also seen is a strong metal-centered
luminescence characterized by sharp bands associated with
7
7
5D0 ! Fj (j ˆ 0 6) for 13 and 5D4 ! Fj (j ˆ 6 0) for 15
(Figure 6b and c). Detailed high-resolution emission studies
in the solid state are in progress and the discussion of
symmetry site, crystal-field and nephelauxetic parameters,
and excited-state lifetimes in the solid-state will be published
elsewhere.[10] However, the observation of residual 1pp*
Table 6. Ligand-centered absorption and emission properties for the ligand L15 and its complexes [Ln(L15)3](ClO4)3 ¥ H2O (Ln ˆ La: 11; Ln ˆ Eu: 13; Ln ˆ
Gd: 14; Ln ˆ Tb: 15).[a]
[b]
E(p ! p*) [cmÀ1
]
E(p ! p*) [cmÀ1
]
E(1pp*) [cmÀ1
Emission
]
E(3pp*) [cmÀ1
]
Emission
Absorption
Absorption
[c]
[c]
L15
31650 (59540)
30300 (49390)
30300 (47870)
30300 (47420)
30210 (50660)
31050
30390
29670
30870
31450
24330sh, 22220, 20535sh
24155
24390, 22420, 20370
24000 sh, 22700
23800 sh, 22400
[La(L15)3]3‡
[Gd(L15)3]3‡
[Eu(L15)3]3‡
[Tb(L15)3]3‡
20370, 19305, 18315
20280
[d]
[a] Solid-state reflectance spectra and transmission solution spectra recorded at 295 K, luminescence data on solid-state sample at 77 K; sh ˆ shoulder.
[b] 10À4 moldmÀ3 in acetonitrile. [c] Not detected. [d] 3pp* luminescence quenched by transfer to LnIII ion.
1070
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Chem. Eur. J. 2003, 9, No. 5

Lanthanide(iii) Podates
1062 1074
[Tb(L15)]3‡, the lifetime is dramatically short as a result of the
ture procedures. The triflate salts Ln(CF3SO3)3 ¥ nH2O (Ln ˆ La Lu) and
the perchlorate salts Ln(ClO4)3 ¥ nH2O (Ln ˆ La Lu) were prepared from
the corresponding oxides (Rhodia, 99.99%) and dried according to
published procedures.[43] The Ln content of solid salts was determined by
complexometric titrations with Titriplex III (Merck) in the presence of
urotropine and xylene orange.[44]
3
resonant positions of the ligand-centered pp* (20370 cmÀ1,
Table 6) and Tb(5D4) (20325 cmÀ1, Figure 6c) levels; this
induces efficient Tb ! ligand energy back-transfer.[42] The
associated quantum yield is consequently very low (FTb
ˆ
1.4Â 10À3), but again slightly better than that reported for
[TbZn(L7)3]5‡, for which the emission intensity was too weak
to be measured.[13a] We conclude that the replacement of the
noncovalent [Zn(a,a'-diimime)3] tripod in [LnZn(L7)3]5‡ with
a semirigid covalent tripod in [Ln(L15)]3‡ has negligible effects
on the photophysical properties of the ligand-centered excited
states associated with the tridentate binding units. The
luminescent behaviors of EuIII and TbIII coordinated in the
nine-coordinate metallic sites is also scarcely effected.
Caution: Dry perchlorates may explode and should be handled in small
quantities and with the necessary precautions.[45]
Preparation of compound 4: A mixture of 3 (9.33 g, 42 mmol), CH2Cl2
(120 mL), thionyl chloride (30.6 mL, 420 mmol), and DMF (0.1 mL) was
refluxed for 1.5 h under a nitrogen atmosphere and evaporated to dryness.
The white residue was dried under vacuum for 30 min, dissolved in CH2Cl2
(60 mL), and cooled to 08C. A mixture of 2 (7.36 g, 35 mmol), triethylamine
(25 mL), and CH2Cl2 (50 mL) was added dropwise. The resulting solution
was stirred for 10 min at 08C, refluxed for 2 h, and evaporated to dryness.
The residual brown oil was dissolved in CH2Cl2/aqueous half-saturated
NH4Cl (200 mL/300 mL), the organic layer was separated, and the aqueous
layer was extracted with CH2Cl2 (4 Â 25 mL). The combined organic phases
were washed with deionized water (50 mL), dried over MgSO4, filtered,
and evaporated to dryness. The resulting crude compound was purified by
column chromatography (silicagel, CH2Cl2/MeOH 99:1 ! 96:4) to afford 4
as a brown oil (12.28 g, 29.6 mmol, 85%). 1H NMR (CDCl3): d ˆ 0.91(t,
3J ˆ 7.2 Hz, 3H; CH3(amide)), 1.20 (t, 3J ˆ 7.2 Hz, 3H; CH3(amide)), 1.25 (t,
3J ˆ 7.2 Hz, 3H; CH3(amide)), 2.96 (sext, 2J ˆ 14.4, 3J ˆ 7.2 Hz, 1H;
CH2(amide)), 3.32 (sext, 2J ˆ 14.4, 3J ˆ 7.2 Hz, 1H; CH2(amide)), 3.40 (s,
3H; CH3), 3.51(sext, 2J ˆ 14.4, 3J ˆ 7.2 Hz, 1H; CH2(amide)), 3.60 (sext,
2J ˆ 14.4, 3J ˆ 7.2 Hz, 1H; CH2(amide)), 4.32 (sext, 2J ˆ 14.4, 3J ˆ 7.2 Hz,
1H; CH2(amide)), 4.45 (s, 2H; CH2), 7.17 (d, 3J ˆ 7.8 Hz, 1H; CH), 7.33 (dd,
Conclusion
The seven-atom mixed aliphatic-aromatic spacers separating
the tridentate binding units from the capping atom in the
tripod of [Ln(L15)]3‡ represent a compromise between the
regular helical wrapping of the strands, ensured by the rigid
aromatic eight-atom spacers in the noncovalent tripods of
[LnM(L7)3]5/6‡ (M ˆ ZnII,[13a] M ˆ CoIII[13c]), and the flexible
aliphatic four-atom TREN tripods in [Ln(L10)]3‡[17] and five-
atom TRPN tripods in [Ln(L12)]3‡.[19] The irregular wrapping
and fast dynamic behavior of the three strands in the two last
complexes is removed by the introduction of aromatic seg-
ments within the spacers of the tripod, and the selective
formation of stable podates [Ln(L15)]3‡ in solution results
from a delicate balance between rigidity and flexibility. This
allows the regular wrapping of the strands required for the
complexation of large metal ions in pseudo-tricapped trigonal
prismatic sites. However, the formation of two different
conformers, depending on the precise arrangement of the
aliphatic part of the tripod, indicates that structural program-
ming is not perfect in [Ln(L15)]3‡. It also suggests that a larger
free-energy gap between the possible conformers of the tripod
is required to design an universal tripod for lanthanide-
containing, trigonal, nine-coordinate podates. Our detailed
investigations in the solid-state and in solution demonstrate
that the two conformers of [Ln(L15)]3‡ display only minor
structural variations and possess similar ground-state ener-
gies. The kinetic barrier for their interconversion is, however,
considerable because it requires the partial decomplexation of
the metal. Further work aiming at the rational increases of DG
between the possible conformers for producing a single
isomer is currently under investigation.
4
3J ˆ 7.5, 4J ˆ 1.2 Hz, 1 H; CH), 7.43 (dd, 3J ˆ 8.4, J ˆ 1.2 Hz, 1 H; CH), 7.77
3
(d, J ˆ 7.8 Hz, 1H; CH), 7.82 (dd, 3J ˆ 8.1, 4J ˆ 1.5 Hz, 1 H; CH), 7.93 ppm
(d, 4J ˆ 1.8 Hz, 1 H; CH); 13C NMR (CDCl3): d ˆ 12.4, 12.6, 14.0, 39.8, 42.6,
45.9, 58.5, 72.6, 123.5, 123.9, 124.5, 131.8, 132.0, 135.7, 137.2, 139.8, 146.1,
151.3, 152.9, 166.3, 167.3 ppm; IR (KBr): nÄ ˆ 3070, 2980, 2940, 2880, 1640,
‡
‡
1570, 1530, 1485 cmÀ1; EI-MS: m/z (%): 415 (5) [M ], 368 (17) [M À
‡
‡
HNO2], 343 (27) [M À NEt2], 316 (13) [M À CONEt2‡H], 72 (100)
[NEt2].
Preparation of compound 5: A mixture of 4 (4.86 g, 11.7 mmol), ethanol
(420 mL), water (120 mL), powdered iron (5.24 g, 93.6 mmol), and
concentrated hydrochloric acid (37%, 14 mL, 168.5 mmol) was refluxed
for 18 h under a nitrogen atmosphere, filtered, and concentrated under
vacuum. The residual aqueous layer was poured into a mixture of CH2Cl2
(200 mL), water (370 mL) and Na2H2EDTA ¥ 2H2O (63.2 g, 169.6 mmol).
The pH was adjusted to 7 with a 25% aqueous ammonia solution, 30%
hydrogen peroxide solution (3.5 mL, 34.4 mmol) was slowly added, and the
mixture was stirred for 15 min. The pH was adjusted to 8.5 with a 25%
aqueous ammonia solution, the aqueous layer was extracted with CH2Cl2
(3 Â 50 mL), and the combined organic layers were washed with deionized
water until neutral, dried over MgSO4, filtered, and evaporated to dryness.
The resulting crude compound was purified by column chromatography
(silicagel, CH2Cl2/MeOH 98:2) to afford 5 as a pale yellow solid (4.01g,
10.96 mmol, 93%). 1H NMR (CDCl3): d ˆ 1.07 (t, 3J ˆ 7.2 Hz, 3H;
CH3(amide)), 1.29 (t, 3J ˆ 7.2 Hz, 3H; CH3(amide)), 1.48 (t, 3J ˆ 7.2 Hz,
3H; CH3(Et)), 3.35 (q, 3J ˆ 7.2 Hz, 2H; CH2(amide)), 3.40 (s, 3H; CH3),
3.62 (q, 3J ˆ 7.2 Hz, 2H; CH2(amide)), 4.61(s, 2H; CH 2), 4.78 (q, 3J ˆ
7.2 Hz, 2H; CH2(Et)), 7.39 (dd, J ˆ 8.4, 3J ˆ 1.2 Hz, 1 H; CH), 7.46 (d,
4
3J ˆ 8.4 Hz, 1H; CH), 7.57 (dd, 3J ˆ 7.6, J ˆ 1.2 Hz, 1 H; CH), 7.81 (s, 1 H;
CH), 7.97 (t, 3J ˆ 7.9 Hz, 1H; CH), 8.45 ppm (d, 3J ˆ 7.5 Hz, 1H; CH);
13C NMR (CDCl3): d ˆ 12.8, 14.3, 15.4, 39.5, 40.6, 42.8, 57.8, 75.1, 110.1,
119.7, 122.5, 123.9, 125.0, 132.9, 135.9, 138.0, 142.7, 149.4, 149.6, 154.5,
168.4 ppm; IR (KBr): nÄ ˆ 3050, 2980, 2940, 2880, 2820, 1715, 1635, 1570,
‡
‡
1485 cmÀ1; EI-MS: m/z (%): 366 (23) [M ], 335 (3) [M À OCH3], 267 (100)
‡
[M À CONEt2‡H].
Experimental Section
Preparation of compound 6: A mixture of 5 (990 mg, 2.70 mmol), acetic
anhydride (20 mL), and BF3 ¥ Et2O (3.8 mL, 30.0 mmol) was stirred at room
temperature (258C) for 1h and poured into an ice-cooled aqueous 2 m
KOH (500 mL). The aqueous layer was extracted with CH2Cl2 (4 Â 50 mL).
The combined organic layers were washed with deionized water until
neutral, dried over MgSO4, filtered, and evaporated to dryness to afford the
crude acetate as a pale yellow solid (1065 mg, 100%), which was dissolved
in methanol (50 mL) and 1m KOH aqueous solution (50 mL), stirred for
15 h at room temperature, concentrated under vacuum, poured into brine
Solvents and starting materials: These were purchased from Fluka AG
(Buchs, Switzerland) and used without further purification unless otherwise
stated. Thionyl chloride was distilled with elemental sulfur. Acetonitrile,
dichloromethane, N,N-dimethyformamide, and triethylamine were distil-
led with CaH2. Silicagel (Acros, 0.035 0.07 mm) was used for preparative
column chromatography. N-ethyl-(4-methoxymethyl-2-nitrophenyl)amine
(2),[26] 6-(N,N-diethylcarbamoyl)pyridine-2-carboxylic acid (3),[25] and 3-(2-
hydroxyethyl)pentane-1,5-diol (10)[28] were prepared according to litera-
Chem. Eur. J. 2003, 9, No. 5
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1071

C. Piguet et al.
FULL PAPER
(500 mL), and extracted with CH2Cl2 (7 Â 50 mL). The combined organic
layers were washed with deionized water until neutral, dried over MgSO4,
filtered, and evaporated to dryness. The resulting crude compound was
purified by column chromatography (silicagel, CH2Cl2/MeOH 95:5) to
afford 6 as a white solide (896 mg, 2.55 mmol, 94%). 1H NMR (CDCl3):
d ˆ 1.07 (t, 3J ˆ 7.2 Hz, 3H; CH3(amide)), 1.29 (t, 3J ˆ 7.2 Hz, 3H; CH3
(amide)), 1.46 (t, 3J ˆ 7.2 Hz, 3H; (CH3(Et)), 2.21(brs, 1H; OH), 3.35 (q,
3J ˆ 7.2 Hz, 2H; CH2(amide)), 3.61(q, 3J ˆ 7.2 Hz, 2H; CH2(amide)), 4.75
(3J, J ˆ 7.2 Hz, 2H; CH2(Et)), 4.81(s, 2H; CH 2), 7.37 (dd, 3J ˆ 9.3, 4J ˆ
1.5 Hz, 1 H; CH), 7.43 (d, 3J ˆ 8.4 Hz, 1H; CH), 7.55 (dd, 3J ˆ 7.8, 4J ˆ
1.1Hz, 1H; CH), 7.79 (s, 1H; CH), 7.94 (t, 3J ˆ 8.1Hz, 1H; CH),
Crystal structure determination of [Ln(L15)](ClO4)3 (Ln ˆ La, 18; Ln ˆ Eu,
19): Crystal structure determination of [La(L15)](ClO4)3 (18) and unit cell
parameters (between brackets) for the isostructural [Eu(L15)](ClO4)3 (19)
complex: LaCH(C22H27N4O3)3(ClO4)3: Mr ˆ 1588.9; m ˆ 0.79 mmÀ1, 1calcd
ˆ
1.478 gcmÀ3
,
trigonal, R3c, Z ˆ 6, a ˆ 22.1077(10) [21.9972(11)], c ˆ
25.2974(11) ä [25.4375(4)], Vˆ 10708(1) ä3 [10660(1)]; colorless prism
0.13 Â 0.14 Â 0.32 mm mounted on a quartz fiber with protection oil. Cell
dimensions and intensities were measured at 200 K on a Stoe IPDS
diffractometer with graphite-monochromated MoKa radiation (l ˆ
1.5418 ä); 45188 measured reflections, 2qmax ˆ 528, 4632 unique reflections
of wich 3241were observables jFo j> 4s(Fo)); Rint for 38948 equivalent
reflections 0.054. Data were corrected for Lorentz and polarization effects
and for absorption (min/max transmission ˆ 0.8590, 0.9261). The structure
was solved by direct methods (SIR97),[46] and all other calculation were
performed with XTAL[47] system and ORTEP[48] programs. Full-matrix
least-squares refinement based on F by using a weight of 1/(s2(Fo) ‡
0.00055(Fo2†) gave final values R ˆ 0.032, wR ˆ 0.039 and S ˆ 1.89(4) for
340 variables and 3241contributing reflections. Flack parameter x ˆ
À0.02(3). The final difference electron density map showed a maximum
of ‡0.43 and a minimum of À0.47 eäÀ3. The hydrogen atoms were placed
in calculated positions and contributed to Fc calculations. The C2, C3, and
O1atoms were disordered and refined with two distinct atomic sites for
each atom and population parameters of 0.8/0.2, thus leading to two
different conformations of the ethyleneoxy spacers of the tripods. The
minor conformation was refined with isotropic displacement parameters and
restraints on bond distances and bond angles. The major conformation was
refined with anisotropic displacement parameters (Figure S2, Supporting
Information). The perchlorate anion was fully disordered and refined with
two atomic sites for the chlorine atom and nine sites for the oxygen atoms.
3
8.39 ppm (dd, J ˆ 8.1, 4J ˆ 1.1 Hz, 1 H; CH); 13C NMR (CDCl3): d ˆ 12.9,
14.4, 15.5, 39.7, 40.8, 42.9, 65.8, 110.3, 118.8, 122.7, 123.5, 125.2, 135.8, 136.2,
‡
138.2, 142.7, 149.3, 149.7, 154.6, 168.6 ppm; EI-MS: m/z (%): 352 (29) [M ],
‡
‡
281(6) [ M À NEt2‡H], 253 (100) [M À CONEt2‡H].
Preparation of compound 7: A mixture of 6 (705 mg, 2.0 mmol), CH2Cl2
(20 mL), and thionyl chloride (1.46 mL, 20.0 mmol) was stirred at 08C for
30 min and at room temperature (258C) for 4 h; it was then poured into a
NaHCO3-saturated aqueous solution (250 mL). The aqueous layer was
extracted with CH2Cl2 (2 Â 10 mL). The combined organic layers were
washed with deionized water until neutral, dried over MgSO4, filtered, and
evaporated to dryness. The resulting crude compound was purified by
column chromatography (silicagel, CH2Cl2/MeOH 96:4) to afford 7 as a
white solid (725 mg, 1.96 mmol, 98%). 1H NMR (CDCl3): 1.05 (t, 3J ˆ
7.0 Hz, 3H; CH3(amide)), 1.26 (t, 3J ˆ 7.2 Hz, 3H; CH3(amide)), 1.46 (t,
3
3J ˆ 7.2 Hz, 3H; CH3(Et)), 3.32 (q, J ˆ 7.0 Hz, 2H; CH2(amide)), 3.59 (q,
3J ˆ 7.2 Hz, 2H; CH2(amide)), 4.75 (s, 2H; CH2Cl), 4.76 (q, 3J ˆ 7.1Hz, 2H;
CH2(amide)), 7.41(d, 3J ˆ 9.0 Hz, 1H; CH), 7.46 (d, 3J ˆ 8.4 Hz, 1H; CH),
7.56 (d, 3J ˆ 7.5 Hz, 1H; CH), 7.87 (s, 1H; CH), 7.96 (t, 3J ˆ 8.0 Hz, 1H;
CH), 8.45 ppm (d, 3J ˆ 8.1Hz, 1H; CH); 13C NMR (CDCl3): 13.2, 14.6, 15.7,
39.9, 41.1, 43.1, 47.5, 110.9, 120.6, 123.1, 125.0, 125.5, 132.8, 136.4, 138.5,
CCDC-192 826 contains the supplementary crystallographic data for
La(L15)(ClO4)3 (18). These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax:(‡44) 1223 336 033; or deposit@ccdc.cam.ac.uk).
‡
142.5, 149.2, 150.3, 154.9, 168.7 ppm; EI-MS: m/z (%): 370 (21) [M ], 335
‡
‡
(8) [M À Cl], 271(100) [ M À CONEt2‡H].
Preparation of ligand L15: A solution of 10 (30 mg, 0.20 mmol) in DMF
(2 mL) was added to a suspension of NaH (60% dispersion in mineral oil,
32 mg, 0.80 mmol) in dry DMF (2 mL). After 30 min of stirring at room
temperature (258C), a solution of 7 (260 mg, 0.70 mmol) in DMF (3 mL)
was added. The mixture was stirred at room temperature for 15 h and
poured into brine (200 mL). The solution was extracted with CH2Cl2 (4 Â
20 mL). The combined organic layers were washed with deionized water
until neutral, dried over MgSO4, filtered, and evaporated to dryness. The
resulting crude compound was purified by column chromatography
(silicagel, CH2Cl2/MeOH 95:5) to afford pure L15 ¥ H2O as a white solid
(171 mg, 0.146 mmol, 73%). 1H NMR (CDCl3): d ˆ 1.05 (t, 3J ˆ 7.2 Hz, 9H;
CH3(amide)), 1.27 (t, 3J ˆ 7.2 Hz, 9H; CH3(amide)), 1.43 (t, 3J ˆ 7.2 Hz, 9H;
Spectroscopic and analytical measurements: Reflectance spectra were
recorded as finely ground powders dispersed in MgO (5%) with MgO as
reference on a Perkin Elmer Lambda900 spectrophotometer equipped
with a PELA-1020 integrating sphere from Labsphere. Electronic spectra
in the UV-visible region were recorded at 208C from 10À4 moldmÀ3
solutions in MeCN with a Perkin Elmer Lambda900 spectrometer by
using quartz cells of 0.1and 1cm path length. Spectrophotometric titrations
were performed with a J&M diode array spectrometer (Tidas series)
connected to an external computer. In a typical experiment, 50 mL of L15
¥
H2O in acetonitrile (10À4 moldmÀ3 ‡ 0.01moldm À3 [N(nBu)4]ClO4) were
titrated at 208C with an equimolar solution of Ln(ClO4)3 ¥ nH2O
(10À3 moldmÀ3
) in acetonitrile under an N2 atmosphere. After each
3
3
À
À
CH3(Et)), 1.64 (q, J ˆ 6.7 Hz, 6H; HC CH2 CH2,), 1.80 (hept, J ˆ 6.2 Hz,
addition of 0.10 mL, the absorbances were recorded using Hellma optrodes
(optical path length 0.1and 0.5 cm) immersed in the thermostated titration
vessel and connected to the spectrometer. Mathematical treatment of the
spectrophotometric titrations was performed with factor analysis[49] and
with the SPECFIT program.[29] IR spectra were obtained from KBr pellets
with a Perkin Elmer883 spectrometer. 1H and 13C NMR spectra were
recorded at 258C on a Broadband Varian Gemini300 spectrometer.
Chemical shifts are given in ppm with respect to TMS. The determination
of longitudinal relaxation times (T1) used the inversion-recovery technique.
EI-MS (70 eV) were recorded with a VG-7000E instrument. Pneumati-
cally-assisted electrospray (ESI-MS) mass spectra were recorded from
10À4 moldmÀ3 acetonitrile solutions on a Finnigan SSQ7000 instrument.
Excitation and emission spectra as well as lifetime measurements were
recorded on a Perkin Elmer LS-50B spectrometer equipped for low-
temperature measurements.
1H; H1), 3.34 (q, 3J ˆ 7.1Hz, 6H; CH 2(amide)), 3.52 (t, 3J ˆ 6.9 Hz, 6H;
3
À
À
HC CH2 CH2), 3.60 (q, J ˆ 7.1Hz, 6H; CH 2(amide)), 4.60 (s, 6H; CH2),
4.74 (q, 3J ˆ 7.2 Hz, 6 H ; CH2(Et)), 7.33 (dd, 3J ˆ 8.4, 4J ˆ 1.2 Hz, 3H; CH),
3
3
4
7.40 (d, J ˆ 8.7 Hz, 3H; CH), 7.54 (dd, J ˆ 8.4, J ˆ 0.8 Hz, 3H; CH), 7.76
(s, 3H; CH), 7.92 (t, 3J ˆ 7.8 Hz, 3H; CH), 8.37 ppm (dd, 3J ˆ 7.8, 4J ˆ
0.8 Hz, 3H; CH); 13C NMR (CDCl3): d ˆ 13.1, 14.6, 15.7, 29.8, 34.2, 39.8,
40.9, 43.1, 68.5, 73.7, 110.4, 119.8, 122.8, 124.1, 125.3, 133.6, 136.1, 138.3,
‡
143.0, 149.7, 149.9, 154.7, 168.8 ppm; ESI-MS (CH2Cl2): 1152 [M ‡H];
elemental analysis calcd (%) for C67H84N12O7: C 68.81, N 14.37, H 7.24;
found: C 68.73, N 14.01, H 7.29.
Preparation of the complexes [Ln(L15)](ClO4)3 ¥ nH2O (Ln ˆ La, n ˆ 1: 11;
Ln ˆ Nd, n ˆ 1: 12; Ln ˆ Eu, n ˆ 1: 13; Ln ˆ Gd, n ˆ 1: 14; Ln ˆ Tb, n ˆ 1:
15; Ln ˆ Lu, n ˆ 4: 16; Ln ˆ Y, n ˆ 1: 17): A solution of Ln(ClO4)3 ¥ nH2O
(Ln ˆ La, Nd, Eu, Gd, Tb, Lu, Y; 0.017 mmol) in acetonitrile (3 mL) was
added to a solution of L15 ¥ H2O (20.0 mg, 0.017 mmol) in acetonitrile
(3 mL). Diethyl ether was diffused into the solution for 1day. The resulting
white microcrystalline powders were collected by filtration and dried to
give 72 93% of [Ln(L15)](ClO4)3 ¥ nH2O (Ln ˆ La, n ˆ 1: 11; Ln ˆ Nd, n ˆ
1: 12; Ln ˆ Eu, n ˆ 1: 13; Ln ˆ Gd, n ˆ 1: 14; Ln ˆ Tb, n ˆ 1: 15; Ln ˆ Lu,
n ˆ 4: 16; Ln ˆ Y, n ˆ 1: 17). All of these complexes were characterized by
their IR spectra and gave satisfying analyses (Table S2, Supporting
Information). Fragile monocrystals suitable for X-ray diffraction studies
were obtained for [Ln(L15)](ClO4)3 (Ln ˆ La, Eu) upon ultra-slow diffusion
of diethyl ether into concentrated acetonitrile solutions.
The quantum yields F were calculated by using Equation (9), in which x
refers to the sample and r to the reference; A is the absorbance, n the
Fx Arꢂn† Irꢂn† n2x Dx
~
~
ˆ
(9)
2
~
~
Fr Axꢂn† Ixꢂn† nr Dr
excitation wavenumber used, I the intensity of the excitation light at this
energy, n the refractive index, and D the integrated emitted intensity.
[Eu(terpy)3](ClO4)3 (F ˆ 1.3%, acetonitrile, 10À3 moldmÀ3
) and [Tb-
(terpy)3](ClO4)3 (F ˆ 4.7%, acetonitrile, 10À3 moldmÀ3) were used as
1072
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/03/0905-1072 $ 20.00+.50/0
Chem. Eur. J. 2003, 9, No. 5

Lanthanide(iii) Podates
1062 1074
references for the determination of quantum yields of respectively Eu- and
Tb-containing samples.[5b, 33] Elemental analyses were performed by Dr. H.
Eder from the Microchemical Laboratory of the University of Geneva.
Chem. Soc. Dalton Trans. 1997, 421; c) S. Rigault, C. Piguet, G.
Bernardinelli, G. Hopfgartner, J. Chem. Soc. Dalton Trans. 2000, 4587.
[14] J.-M. Lehn, Chem. Eur. J. 1999, 5, 2455.
[15] S. J. Archibald, A. J. Blake, S. Parsons, M. Schrˆder, R. E. P. Win-
penny, J. Chem. Soc. Dalton Trans. 1997, 173.
[16] J.-P. Costes, A. Dupuis, G. Commenges, S. Lagrave, J.-P. Laurent,
Inorg. Chim. Acta 1999, 285, 49.
Acknowledgement
[17] F. Renaud, C. Piguet, G. Bernardinelli, J.-C. G. B¸nzli, G. Hopfgart-
ner, J. Am. Chem. Soc. 1999, 121, 9326.
This work is supported through grants from the Swiss National Science
Foundation.
¡
¬
[18] Y. Bretonniere, R. Wietzke, C. Lebrun, M. Mazzanti, J. Pecaut, Inorg.
Chem. 2000, 39, 3499.
[19] F. Renaud, C. Decurnex, C. Piguet, G. Hopfgartner, J. Chem. Soc.
Dalton Trans. 2001, 1863.
[20] L. Tei, G. Baum, A. J. Blake, D. Fenske, M. Schrˆder, J. Chem. Soc.
Dalton Trans. 2000, 2793.
[1] A. J. Freeman, R. E. Watson, Phys. Rev. B. 1962, 127, 2058.
[2] J.-C. G. B¸nzli, in Rare Earths (Eds.: R. Saez Puche, P. Caro), Editorial
Complutense S. A., Madrid, 1998, pp. 223 259.
¡
[21] L. J. Charbonniere, R. Ziessel, M. Guardigli, A. Roda, N. Sabbatini,
[3] J.-C. G. B¸nzli, C. Piguet, Chem. Rev. 2002, 102, 1897.
M. Cesario, J. Am. Chem. Soc. 2001, 123, 2436.
[22] M. Cantuel, G. Bernardinelli, D. Imbert, J.-C. G. B¸nzli, G. Hopf-
gartner, C. Piguet, J. Chem. Soc. Dalton Trans. 2002, 1929.
[4] a) A. Abragam, B. Bleaney, Electron Paramagnetic Resonance of
Transitions Ions, Clarendon, Oxford, 1970; b) W. T. Carnall, in
Handbook on the Physics and Chemistry of Rare Earths (Eds.: K. A.
Gschneidner, L. Eyring), North-Holland, Amsterdam, 1979, pp. 171
208; c) C. Gˆrrler-Walrand, K. Binnemans, in Handbook on the
Physics and Chemistry of Rare Earths, Vol. 23 (Eds.: K. A. Gschneid-
ner, L. Eyring), North-Holland, Amsterdam, 1996, pp. 121 283; d) P.
Porcher, in Rare Earths (Eds.: R. Saez Puche, P. Caro), Editorial
Complutense S. A., Madrid, 1998, pp. 43 66.
[5] a) R. T. Wegh, H. Donker, K. D. Oskam, A. Meijerink, J. Lumin. 1999,
82, 93; b) S. Petoud, J.-C. G. B¸nzli, C. Piguet, Q. Xiang, R. Thummel,
J. Lumin. 1999, 82, 69; c) S. Heer, M. Wermuth, K. Kr‰mer, D.
Ehrentraut, H. U. G¸del, J. Lumin. 2001, 94 95, 337; d) C. Reinhard,
H. U. G¸del, Inorg. Chem. 2002, 41, 1048.
[6] a) M. H. V. Werts, J. W. Verhoeven, J. W. Hofstraat, J. Chem. Soc.
Perkin Trans. 2 2000, 433; b) G. F. de Sa, O. L. Malta, C. de Mello
Donega, A. M. Simas, R. L. Longo, P. A. Santa-Cruz, E. F. da Silva, Jr,
Coord. Chem. Rev. 2000, 196, 165; c) A. Beeby, L. M. Bushby, D.
Maffeo, J. A. G. Williams, J. Chem. Soc. Dalton Trans. 2002, 48.
[7] a) V. S. Mironov, Y. G. Galyametdinov, A. Ceulemans, K. Binnemans,
J. Chem. Phys. 2000, 113, 10293; b) I. Bertini, M. B. L. Janik, Y.-M.
Lee, C. Luchinat, A. Rosato, J. Am. Chem. Soc. 2001, 123, 4181;
c) V. S. Mironov, Y. G. Galyametdinov, A. Ceulemans, C. Gˆrller-
Walrand, K. Binnemans, J. Chem. Phys. 2002, 116, 4673; d) P.
Bernardo, R. Barbieri, E. Padros, C. Luchinat, M. Pons, J. Am. Chem.
Soc. 2002, 124, 374.
¬
[23] N. Andre, R. Scopelliti, G. Hopfgartner, C. Piguet, J.-C. G. B¸nzli,
Chem. Commun. 2002, 214.
[24] a) A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L.
Royle, A. S. de Sousa, J. A. G. Williams, M. Woods, J. Chem. Soc.
Perkin Trans. 2 1999, 493; b) S. Aime, M. Botta, R. S. Dickins, C. L.
Maupin, D. A. Parker, J. P. Riehl, J. A. G. Williams, J. Chem. Soc.
Dalton Trans. 1998, 881.
[25] M. Elhabiri, R. Scopelliti, J.-C. G. B¸nzli, C. Piguet, J. Am. Chem. Soc.
1999, 121, 10747.
[26] H. Nozary, C. Piguet, P. Tissot, G. Bernardinelli, J.-C. G. B¸nzli, R.
Deschenaux, D. Guillon, J. Am. Chem. Soc. 1998, 120, 12274.
[27] C. Piguet, B. Bocquet, G. Hopfgartner, Helv. Chim. Acta 1994, 77, 931.
[28] Y. Yamagiwa, Y. Koreishi, S. Kiyozumi, M. Kobayashi, T. Tamikawa,
M. Tsukino, H. Goi, M. Yamamoto, M. Munakata, Bull. Chem. Soc.
Jpn 1996, 69, 3317.
[29] a) H. Gampp, M. Maeder, C. J. Meyer, A. D. Zuberb¸hler, Talanta
1986, 33, 943; b) H. Gampp, M. Maeder, C. J. Meyer, A. D. Zuber-
b¸hler, Talanta 1985, 23, 1133.
[30] K. Nakamoto, Infrared and Raman Spectra in Inorganic and Coordi-
nation Compounds, 5th ed., Wiley, New York, 1997, Part A, p. 199.
[31] J. H. Brewster, Top. Curr. Chem. 1974, 47, 29.
[32] S. Rigault, C. Piguet, G. Bernardinelli, G. Hopfgartner, Angew. Chem.
1998, 110, 178; Angew. Chem. Int. Ed. 1998, 37, 169.
[33] C. Piguet, J.-C. G. B¸nzli, G. Bernardinelli, C. G. Bochet, P. Froide-
vaux, J. Chem. Soc. Dalton Trans. 1995, 83.
[34] M. Pons, O. Millet, Prog. Nucl. Magn. Reson. Spectrosc. 2001, 38, 267.
[35] Calculated with Equations (2) (4) and experimental data reported in
ref. [17].
[36] a) S. Aime, L. Barbero, M. Botta, G. Ermondi, J. Chem. Soc. Dalton
Trans. 1992, 225; b) M. D. Kemple, B. D. Ray, K. B. Lipkowitz, F. G.
Prendergast, B. D. N. Rao, J. Am. Chem. Soc. 1988, 110, 8275; c) M.
Allegrozzi, I. Bertini, M. B. L. Janik, Y.-M. Lee, G. Liu, C. Luchinat, J.
Am. Chem. Soc. 2000, 122, 4154.
[37] a) I. Bertini, C. Luchinat, Coord. Chem. Rev. 1996, 150, 1 ; b) J. A.
Peters, J. Huskens, D. J. Raber, Prog. Nucl. Magn. Reson. Spectrosc.
1996, 28, 283.
[8] J.-C. G. B¸nzli, A. Milicic-Tang, in Handbook on the Physics and
Chemistry of Rare Earths, Vol. 21 (Eds.: K. A. Gschneidner, L.
Eyring), Elsevier, Amsterdam, 1995, p. 305.
[9] a) F. Renaud, C. Piguet, G. Bernardinelli, J.-C. G. B¸nzli, G. Hopf-
gartner, Chem. Eur. J. 1997, 3, 1646; b) D. A. Bardwell, J. C. Jeffery,
P. L. Jones, J. A. McCleverty, E. Psillakis, Z. Reeves, M. D. Ward, J.
Chem. Soc. Dalton Trans. 1997, 2079; c) S. Petoud, J.-C. G. B¸nzli, F.
Renaud, C. Piguet, K. J. Schenk, G. Hopfgartner, Inorg. Chem. 1997,
36, 5750; d) H.-R. M¸rner, E. Chassat, R. P. Thummel, J.-C. G. B¸nzli,
J. Chem. Soc. Dalton Trans. 2000, 2809; e) L. I. Semenova, A. N.
Sobolev, B. W. Skelton, A. H. White, Aust. J. Chem. 1999, 52, 519; f) N.
Ouali, B. Bocquet, S. Rigault, P.-Y. Morgantini, J. Weber, C. Piguet,
Inorg. Chem. 2002, 41, 1436.
¬
[38] a) C. D. Barry, A. C. T. North, J. A. Glasel, R. J. P. Williams, A. V.
Xavier, Nature 1971, 232, 236; b) J. H. Forsberg, in Handbook on the
Physics and Chemistry of Rare Earths, Vol. 23 (Eds.: K. A. Gschneid-
ner, L. Eyring), North-Holland, Amsterdam, 1996, p. 1; c) J. M. Brink,
R. A. Rose, R. C. Holz, Inorg. Chem. 1996, 35, 2878.
[10] T. LeBorgne, N. Andre, J.-C. G. B¸nzli, G. Bernardinelli, C. Piguet
unpublished results.
[11] a) J. Xu, S. J. Franklin, D. W. Whisenhunt, K. N. Raymond, J. Am.
Chem. Soc. 1995, 117, 7245; b) A. R. Johnson, B. O×Sullivan, K. N.
Raymond, Inorg. Chem. 2000, 39, 2652; c) C. J. Sunderland, M. Botta,
S. Aime, K. N. Raymond, Inorg. Chem. 2001, 40, 6746; d) A.
Bismondo, P. Di Bernardo, R. Portanova, M. Tolazzi, P. L. Zanonato,
Polyhedron 2002, 21, 1393.
[39] Paramagnetic 13C NMR relaxation measurements failed because of
the limited solubility of [Ln(L15)]3‡ in acetonitrile.
[40] W. T. Carnall, P. R. Fields, K. Rajnak, J. Chem. Phys. 1968, 49, 4443.
[41] a) S. Tobita, M. Arakawa, I. Tanaka, J. Phys. Chem. 1984, 88, 2697;
b) S. Tobita, M. Arakawa, I. Tanaka, J. Phys. Chem. 1985, 89, 5649.
[42] N. Sabbatini, M. Guardigli, J.-M. Lehn, Coord. Chem. Rev. 1993, 123,
201.
[12] a) A. J. Blake, D. M. J. Doble, W.-S. Li, M. Schrˆder, J. Chem. Soc.
Dalton Trans. 1997, 3655; b) R. Wietzke, M. Mazzanti, J.-M. Latour, J.
¬
Pecaut, J. Chem. Soc. Dalton Trans. 1998, 4087; c) B. M. Flanagan,
P. V. Bernhardt, E. R. Krausz, S. R. L¸thi, M. J. Riley, Inorg. Chem.
¡
¬
[43] J. F. Desreux in Lanthanide Probes in Life, Chemical and Earth
Sciences (Eds.: J.-C. G. B¸nzli, G. R. Choppin), Elsevier, Amsterdam,
1989, Chapter 2, p. 43.
[44] G. Schwarzenbach, Complexometric Titrations, Chapman & Hall,
London, 1957, p. 8.
2001, 40, 5401; d) Y. Bretonniere, M. Mazzanti, J. Pecaut, F. A.
Dunand, A. E. Merbach, Inorg. Chem. 2001, 40, 6737.
[13] a) C. Piguet, J.-C. G. B¸nzli, G. Bernardinelli, G. Hopfgartner, S.
Petoud, O. Schaad, J. Am. Chem. Soc. 1996, 118, 6681; b) C. Piguet, E.
Rivara-Minten, G. Bernardinelli, J.-C. G. B¸nzli, G. Hopfgartner, J.
Chem. Eur. J. 2003, 9, No. 5
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/03/0905-1073 $ 20.00+.50/0
1073

C. Piguet et al.
FULL PAPER
[45] W. C. Wolsey, J. Chem. Educ. 1978, 50, A335.
[48] C. K. Johnson, ORTEP II; Report ORNL-5138, Oak Ridge National
Laboratory: Oak Ridge, Tennessee, 1976.
[49] E. R. Malinowski, D. G. Howery, Factor Analysis in Chemistry, Wiley,
New York, Chichester, 1980.
[46] A. Altomare, M. C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo,
A. Guagliardi, A. G. G. Moliterni, G. Polidori, R. Spagna, J. Appl.
Crystallogr. 1999, 32, 115.
[47] XTAL 3.2 User×s Manual (Eds.: S. R. Hall, H. D. Flack, J. M. Stewart),
Universities of Western Australia and Maryland, 1989.
Received: September 25, 2002 [F4451]
1074
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0947-6539/03/0905-1074 $ 20.00+.50/0
Chem. Eur. J. 2003, 9, No. 5