Lanthanide luminescent mesomorphic complexes with macrocycles derived from diaza-18-crown-6

Article abstract of DOI:10.1039/b503591k

Four tetracatenar (L1-L4) and one hexacatenar (L5) ligands, derived from the diaza-18-crown-6 framework, are synthesized and characterized. In these ligands, the amine functions are fitted with benzoyloxybenzyl linker groups, attached either with a carbon

Full text of DOI:10.1039/b503591k

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P A P E R
Lanthanide luminescent mesomorphic complexes with macrocycles
derived from diaza-18-crown-6wz
a
a
a
b
´
´
Stephane Suarez, Olimpia Mamula, Rosario Scopelliti, Bertrand Donnio,
Daniel Guillon,b Emmanuel Terazzi,c Claude Piguetc and Jean-Claude G. Bu
¨
nzli*a
a
b
´
´ ´
Ecole Polytechnique Federale de Lausanne (EPFL), Laboratory of Lanthanide
Supramolecular Chemistry, BCH 1402, CH-1015 Lausanne, Switzerland.
E-mail: jean-claude.bunzli@epfl.ch
´
Institut de Physique et Chimie des Materiaux de Strasbourg, Groupe des Materiaux
Organiques, UMR 7504, CNRS-Universite Louis Pasteur, BP 43, 23, rue du Loess,
´
´
F-67034 Strasbourg Cedex 2, France
c Department of Inorganic, Analytical and Applied Chemistry, University of Geneva,
30 quai E. Ansermet, CH-1211 Geneva 4, Switzerland
Received (in Montpellier, France) 10th March 2005, Accepted 12th July 2005
First published as an Advance Article on the web 29th July 2005
Four tetracatenar (L1–L4) and one hexacatenar (L5) ligands, derived from the diaza-18-crown-6 framework,
are synthesized and characterized. In these ligands, the amine functions are fitted with benzoyloxybenzyl
linker groups, attached either with a carbonyl function (L1) or a methylene bridge (L2–L5) and bearing
alkoxy chains, R, of various lengths: R ¼ OCH3 for L2, OC10H21 for L3 and L5, OC12H25 for L1, and
OC16H33 for L4. The non-mesomorphic ligands L1 and L3–L5 react with various lanthanide salts to give
complexes forming thermotropic hexagonal columnar phases, as ascertained by thermal, optical and small-
angle X-ray diffraction methods. The length of the alkoxy chains (L3 and L4) does not much influence the
mesogenic behaviour, irrespective of the linker function, the number of alkoxy chains, the counterion or the
lanthanide ion. The best systems proved to be the nitrato lanthanide complexes with L3, which present a
Colh phase over 100 1C (up to 147 1C for La) with melting transition temperatures between 58 (La) and 86
(Tb) 1C. In the case of [Eu(NO3)3L3], chosen as a representative example of all the complexes in this
analysis, the inter-column separation of 29.2 A agrees well with the packing of cylindrical columns resulting
from an alternated stacking of the molecules, in which the two mesogenic arms extend on the same side, i.e.
stacking the molecules in a bent conformation. The liquid crystalline phases containing Eu and Tb display
metal-centred emission, meaning that these complexes are interesting building blocks for the design of
luminescent liquid crystalline materials.
crystalline properties started to develop.8–12 Basically, such
Introduction
materials can be obtained either by mixing lanthanide salts13
and complexes14 with mesogenic materials, or by synthesizing
lanthanide complexes with mesomorphic properties.
The present upsurge in the design and study of lanthanide-
containing mesophases1 is justified by several potential appli-
cations pertaining both to bio-analysis and materials science.
For instance, liquid crystal systems are routinely used in
protein structure determination by NMR spectroscopy.2 Since
lanthanide-induced shifts are of great help in this respect,
combining both the orientation effect of a liquid crystalline
Currently known lanthanide-containing molecular com-
pounds that exhibit liquid crystalline phases belong to four
different classes. (i) Lanthanide alkanoates, which form ther-
motropic smectic A-phases for alkoxy chains bearing between
five and fifteen carbon atoms;15 mesophases can also be
induced by doping a non-mesogenic lanthanide dodecanoate
with a few percent of the corresponding mesomorphic lantha-
nide salt.16 (ii) Schiff base derivatives, which form metallome-
sogens and several series of mesomorphic lanthanide-
containing complexes have been reported since 1991.8 In
particular, reaction of a hydroxybenzaldimine derivative with
lanthanide nitrates yields smectic liquid crystals of unusually
high magnetic anisotropy.9,17,18 Recently, mixed 4f–3d colum-
nar metallomesogens have been obtained by adduct formation
between a mesomorphic M(salen) complex (salen ¼ 2,20,N,N0-
bis(salicylidene)ethylenediamine) and a lanthanide nitrate.19,20
(iii) A third class of compounds takes advantage of tridentate
aromatic receptors derived from substituted 2,6-bis(benzimi-
dazolpyridine).17 A rich variety of mesophases have been
reported, for which the type of mesomorphism (calamitic,
columnar or cubic) can be tuned by the size of the lanthanide
phase and the large magnetic anisotropy of, for instance, YbIII
,
yields an efficient structural method.3 In addition, lanthanide-
containing trichromatic materials emit narrow bands at pri-
mary colour wavelengths, and so are employed in lighting
devices and displays.4 Finally, the large magnetic anisotropy
of some LnIII ions could also be used to perform magnetic
rather than electric switching in liquid crystalline materials.1,5
Lanthanide-containing mesophases have largely remained
scientific curiosities until the mid 1980s,6,7 when systematic
efforts aimed at isolating lanthanide complexes with liquid
w Electronic supplementary information (ESI) available: Selected
NMR and electronic absorption data, SAXS patterns, luminescence
spectra of La and Eu complexes and thermogravimetric analysis of
EuL3, see http://dx.doi.org/10.1039/b503591k.
z Dedicated to Professor Erno Brucher on the occasion of his 70th
¨
¨
birthday.
T h i s j o u r n a l i s & T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 5
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 3 2 3 – 1 3 3 4
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underlying synthetic principle is a multi-step synthesis of the
entire substituent, spacer and alkoxy chain, in the form of a
bromide or carboxyl, before coupling them with the (2,2)
macrocycle. We have tested two types of spacers, 4-carboxy-
phenyl benzoate (L1) and 4-methylenephenyl benzoate (L2–
L5). The linking of carboxyl groups confer some rigidity to the
ligand, which could be favourable for intermolecular interac-
tions. On the other hand, they also reduce the electron density
on the nitrogen atoms, which is detrimental to the complexa-
tion of the lanthanide ion, and hence in L2–L5 have been
replaced by methylene bridges. The dicatenar pendant arms of
ligands L1–L4 were synthesized from 3,4-dihydroxybenzoic
acid (1, Scheme 2) according to the procedure described by
Goodby et al.36 A similar strategy was adopted for the synth-
esis of the tricatenar pendant arm, which was isolated with an
overall yield of 38% (Scheme 3). The target ligands were
obtained by nucleophilic substitution of the (2,2) macrocycle
in a basic medium, with yields of 41, 86, 89 and 42% for L2,
L3, L4 and L5 respectively. In the case of L1, the correspond-
ing chloride of acid 18 was used as an intermediate in the
macrocycle functionalisation (yield 70%).
Scheme 1
ion.21 (iv) Macrocyclic complexes were among the first re-
ported lanthanide-containing mesogens.7,22,23 They often dis-
play discotic phases and most of the receptors used are either
phthalocyanines,7,24,25 benzoporphyrins26,27 or porphyr-
ins.28,29 In the former compounds, the lanthanide ion is
sandwiched between two macrocycles, and it has been foreseen
that these complexes could act as one-dimensional molecular
semiconductors.22 They indeed form hexagonal columnar
phases, some of which have been shown to be p-type semi-
conductors.27
Single crystals of L2 suitable for X-ray analysisy were grown
from a mixture of acetonitrile and dichloromethane. They
ꢀ
crystallize in the triclinic space group P1 and their molecular
structure, along with the atom numbering scheme, is shown in
Fig. 1. The core macrocycle adopts a flat conformation, with
an inversion centre located in the middle of the ring. The
benzene rings connected to the amine functions are perpendi-
cular to the mean plane of the macrocycle and to the other
benzene rings of the arms. The latter extend along the mole-
cular axis, the distance between the furthermost carbon atoms
C21 and C21A amounting to 34.15 A. Overall, the molecule
adopts an extended chair conformation. There are two weak
intramolecular hydrogen bonds between H1 and O2A (and
between H1A and O2), the contact Cꢀ ꢀ ꢀO distance being 3.05 A
and the CHꢀ ꢀ ꢀO angle 134.51. In the crystal packing (Fig. 1),
one ligand molecule inserts itself between pairs of molecules
lying exactly parallel to each other. The first molecule is linked
to the others by a weak intermolecular hydrogen bond between
the benzyl H7 atom and the aromatic ring (C8 to C13) of a
neighbouring molecule; the contact distance amounts to 2.70 A
and the CHꢀ ꢀ ꢀO angle to 1501.
To our knowledge, only one paper has reported on the
thermal behaviour of lanthanide complexes with a coronand,
namely a benzo-15-crown-5 ether derivatised with a 40-(chol-
esteryloxy)carbonyl pendant arm. The ligand itself is liquid
crystalline, displaying a monotropic chiral nematic mesophase,
and its complexes with lanthanide nitrates form highly viscous
mesophases.30 Several substituted diaza crown ethers and their
complexes with alkali metal ions are known to be meso-
morphic.31,32 Since diaza crowns form stable complexes with
trivalent lanthanide ions,33 we have investigated whether or not
suitably derivatised macrocycles of this type (Scheme 1) are
adequate receptors for generating lanthanide complexes that
exhibit thermotropic columnar mesomorphism. In a prelimin-
ary communication, we have shown that the non-mesomorphic
ligand L3 (Scheme 1) indeed reacts with Eu and Tb nitrates to
form luminescent 1 : 1 complexes that display thermotropic
columnar hexagonal mesophases over a wide temperature
range.34 Moreover, we have demonstrated that the intensity
and lifetime of the Eu- and Tb-centred luminescence can be
used to monitor the crystal (Cr) to hexagonal columnar (Colh)
phase transition and vice versa.34,35 In this paper we present the
synthesis and characterization of ligands L1–L5 and their
complexes with lanthanide nitrates, triflates and chlorides.
The photophysical properties of the complexes are reported
and the mesophases obtained are identified from a combina-
tion of experimental techniques (thermal analysis, polarized
light microscopy and small angle X-ray scattering). We also
investigate the parameters influencing the transition tempera-
ture, namely the nature of the counterion and the number and
length of the alkoxy chains grafted onto the terminal benzyl
rings.
Interaction of the ligands with lanthanide ions
We have probed the interaction between L3 or L4 and lantha-
num nitrate by 1H NMR spectroscopy. The ligands in 10ꢁ2 M
deuterated THF have been titrated at room temperature with
partially dehydrated La(NO3)3 ꢀ xH2O (x ¼ 3) and a total of 16
spectra recorded, with ratios R ¼ [La]tot/[L]tot ranging between
0 and 4. The benzyl N-CH2-Ph and methylene protons from
the (2,2) core appear in the range 2.5–4.5 ppm. There is a
considerable overlap between the signals of the free and
complexed ligand, meaning that only the aromatic region of
the spectra yield useful information. Typical spectra for L3 are
shown in Fig. 2. As expected, protons H1,10 and H2,20 are the
most sensitive to complexation, with chemical shift differences
between free and bound ligand of about 0.1 ppm (the exact
structural assignment of the resonances H1,10 and H2,20 has not
been completed). Two conclusions may be drawn from these
spectra. Firstly, only one complexed species is formed, and
secondly, the free and complexed ligand are in slow exchange
with each other, as observed previously for the corresponding
Results and discussion
Ligand synthesis
The macrocyclic receptors are built from three different syn-
thons: (i) a 1,10-diaza-4,7,13,16-tetraoxacyclooctadecane core
for LnIII complexation—the so-called (2,2) macrocycle, (ii) two
anisometric spacers connected to the amine functionalities
which also play the role of antennae for sensitizing the LnIII
luminescence, and (iii) long terminal alkoxy chains of 10, 12 or
16 carbon atoms connected to the mesogenic spacers. The
y C44H54N2O12, M ¼ 802.89, triclinic, a ¼ 8.7954(11), b ¼ 9.5631(13), c
¼ 13.9798(18) A, a ¼ 95.811(11), b ¼ 91.078(11), g ¼ 115.790(13)1, U ¼
0.092 mmꢁ1, 6249 reflections measured, 3242 unique (Rint ¼ 0.0340)
which were used in all calculations. The final wR2 was 0.1194 (all data).
CCDC 276955. See http://dx.doi.org/10.1039/b503591k for crystallo-
graphic data in CIF or other electronic format.
3
ꢀ
1050.7(2) A , T ¼ 140 K, space group P1 (no. 2), Z ¼ 1, m(Mo-Ka) ¼
1324
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Scheme 2 (i) H2SO4, MeOH; (ii) CnH2n11Br, Cs2CO3, butanone; (iii) KOH, EtOH/H2O; (iv) DCC, DMAP, CH2Cl2; (v) Pd/C, THF
(for R ¼ benzyl); anisole, CF3COOH, CH2Cl2 (for R ¼ tert-butyl); (vi) B2H6, THF; (vii) PBr3, CH2Cl2.
complexes of 18-crown-6 ether (18C6).37 Analysis of the inte-
grated intensity of H1,10 and H2,20 (Figure S1 and Table S1,
ESIw) clearly shows only the formation of 1 : 1 complexes, in
line with former studies of lanthanide complexes with 18-
membered macrocycles.33,38 This demonstrates that sandwich
complexes of 18C6 ethers form solely in the presence of weakly
coordinating anions.39 From these data, the following stability
constants could be extracted: log K ¼ 2.8 ꢂ 0.2 and 2.7 ꢂ 0.2
for ligands L3 and L4 respectively.
EuCl3 and L3, Ln(NO3)3 and L2 (Ln ¼ La, Eu), and Eu
(CF3SO3)3 and L5 were also isolated. Elemental analyses are
reported in Table 1. No single crystal amenable to X-ray
analysis could be obtained, but a high resolution luminescence
La(NO3)3 ꢀ 3H2O (solv) þ L(solv) " [La(NO3)3L] þ 3H2O þ solv
K ¼ [La(NO3)3L]/[La31][L]
These values are surprisingly low compared to literature data
on similar macrocyclic complexes. For instance, a value of log
K ¼ 4.3 has been determined by NMR spectroscopy for
[La(NO3)3(18C6)] in acetonitrile, and it is known that replace-
ment of two ether functions by two amine moieties to yield
macrocycle (2,2) results in an enhancement of K by 5–6 orders
of magnitude in propylene carbonate and in the absence of a
coordinating anion.33 The weak interaction between lantha-
num nitrate and the macrocyclic receptors L3 and L4 can be
traced back to the bulky substituents on the nitrogen atoms,
which hinder the necessary flexibility of the ligand to adjust
itself to the size of the lanthanide ion, and also which impose
unfavourable orientations on the nitrogen lone pairs. Never-
theless, these data unambiguously demonstrate the formation
of 1 : 1 nitrato complexes, and that the length of the alkoxy
chain has only a marginal effect on the complexation process.
Complexes with the formulae Ln(NO3)3L3 ꢀ solv could be
isolated for La (solv ¼ 2H2O), Nd (solv ¼ 3 THF), Eu (solv ¼
0.25H2O) and Tb (solv ¼ H2O), while similar compounds were
obtained with L4 for La (solv ¼ 2H2O), Nd (solv ¼ 0.5H2O)
and Eu (solv ¼ 1.5H2O). In addition, 1 : 1 complexes between
Ln(CF3SO3)3 and L1 (Ln ¼ La, Eu), Eu(CF3SO3)3 and L3,
Fig. 1 Molecular structure of L2 with ellipsoids drawn to 50%
probability (top), the unit cell with the Hꢀ ꢀ ꢀaryl hydrogen bond evident
(middle) and crystal packing (bottom).
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 3 2 3 – 1 3 3 4
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Scheme 3 (i) C10H21Br, Cs2CO3, butanone; (ii) KOH, EtOH, H2O; (iii) DCC, DMAP, CH2Cl2; (iv) H2, Pd/C, THF; (v) B2H6, THF; (vi) PBr3
CH2Cl2.
study has shown that Eu(NO3)3L3 ꢀ 0.25H2O is comprised of
two different species in a 3 : 1 proportion; the more abundant
being anhydrous and the other featuring one water molecule in
the inner coordination sphere of the metal ion.35,40
Photophysical properties
Absorption spectra of the ligands (Table 2; Figure S2, ESIw)
feature three p - p* bands around 45 000, 37 000 and 34 000
(with an additional shoulder around 32 500) cmꢁ1. When the
length of the alkoxy chain is increased, in going from L1 to L3
and L4, all the bands sustain a small bathochromic shift, while
the addition of two extra alkoxy chains in L5 results in a larger
modification of the spectrum, with the low energy band
decreasing in energy and only seen as a shoulder on the broader
and substantially red-shifted middle band. It is noteworthy
that the presence of carbonyl functions in L1 does not influence
the energy of the electronic absorption bands compared to L3.
Low temperature luminescence spectra of solid samples under
UV excitation allowed us to identify both an emitting singlet
state in the spectral range 29 340–30 670 cmꢁ1 (26 000 cmꢁ1 for
L5), except for L2, and an emitting triplet state in the range
1
19 590–20 880 cmꢁ1. Emission from the pp* state disappears
as soon as a time delay (0.05 ms) is enforced, confirming the
assignment of the two emission bands. The carbonyl groups in
L1 induce a 1pp* state 1300 cmꢁ1 lower in energy compared to
3
L3 and L4, while the energy of the pp* state is lowered by
about 1000–1290 cmꢁ1 with respect to L2–L5. The energy
difference between the singlet and triplet states, which is of
3
importance in populating the pp* state through intersystem
crossing (ISC), is around 10 000 cmꢁ1 for L1–L4 and 6000
cmꢁ1 for L5, way above the ‘‘ideal’’ value of 5000 cmꢁ1 41
Therefore, we do not expect a particularly large sensitization of
the metal-centred luminescence.42
.
Fig. 2 Aromatic region of the NMR spectrum of 10ꢁ2 M L3 in deu-
terated THF at 298 K, vs. the amount of added La(NO3)3 ꢀ 3H2O; R ¼
[L3]t/[La]t; arrows point to resonances specific to the 1 : 1 complex.
1326
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Table 1 Elemental analyses of the isolated complexes. Calculated values are given within parentheses
Complex
Formula
fw
%C
%H
%N
La(CF3SO3)3L1 ꢀ 7H2O
Eu(CF3SO3)3L1 ꢀ 3.5H2O
La(NO3)3L2 ꢀ H2O
C91H138LaF9N2O23S3 ꢀ 7H2O
C91H138LaF9N2O23S3 ꢀ 3.5H2O
C44H54LaN5O21 ꢀ H2O
2160.27
2110.27
1145.85
1153.86
1668.84
1854.46
1650.37
1943.12
1710.41
1670.84
2005.48
1983.8
50.5 (50.6)
51.8 (51.6)
46.1 (46.1)
45.4 (44.8)
57.6 (57.6)
60.1 (59.6)
58.0 (58.2)
52.4 (52.5)
62.2 (61.8)
57.4 (57.5)
62.2 (62.3)
63.1 (63.0)
62.1 (62.4)
60.2 (60.2)
7.1 (7.2)
6.9 (7.0)
4.9 (4.9)
5.0 (5.0)
7.5 (7.9)
8.0 (8.2)
7.6 (7.7)
6.9 (6.7)
8.6 (8.4)
7.7 (7.7)
8.8 (8.9)
9.0 (8.9)
8.9 (8.9)
8.7 (8.6)
1.3 (1.2)
1.3 (1.2)
6.0 (6.1)
5.8 (6.1)
4.3 (4.2)
3.9 (3.8)
4.2 (4.2)
1.4 (1.4)
1.8 (1.6)
4.1 (4.2)
3.6 (3.5)
3.4 (3.5)
3.5 (3.5)
3.4 (3.5)
Eu(NO3)3L2 ꢀ 1.5H2O
La(NO3)3L3 ꢀ 2H2O
Nd(NO3)3L3 ꢀ 3THF
Eu(NO3)3L3 ꢀ 0.25H2O
Eu(CF3SO3)3L3 ꢀ 0.5THF
EuCl3L3 ꢀ 2THF
C44H54EuN5O21 ꢀ 1.5H2O
C80H126LaN5O21 ꢀ 2H2O
C80H126NdN5O21 ꢀ 3THF
C80H126EuN5O21 ꢀ 0.25H2O
C83H126EuF9N2O21S3 ꢀ 0.5 THF
C80H126Cl3EuN2O12 ꢀ 2 THF
C80H126TbN5O21 ꢀ H2O
Tb(NO3)3L3 ꢀ H2O
La(NO3)3L3 ꢀ 2H2O
Nd(NO3)3L4 ꢀ 0.5H2O
Eu(NO3)3L4 ꢀ 1.5H2O
Eu(NO3)3L5 ꢀ 2H2O
C104H174LaN5O21 ꢀ 2H2O
C104H174NdN5O21 ꢀ 0.5H2O
C104H174EuN5O21 ꢀ 1.5H2O
C100H166EuN5O23 ꢀ 2H2O
2000.53
1994.42
Luminescence spectra of the complexes have been measured
on solid state samples at 77 K upon excitation between 40 000
and 30 000 cmꢁ1. The La and Nd complexes displayed emission
from both the 1pp* (except Nd(NO3)3L4) and 3pp* states (Fig.
3; Figure S2 ESIw), from which the energy of the 1pp* and 3pp*
states of the complexed ligands could be deduced (Table S3,
ESIw). Most of the complexes with the luminescent lanthanide
ions Eu and Tb also display singlet state emission, except
Eu(NO3)3L (L ¼ L2 and L4) and Eu(CF3SO3)3L3, reflecting
the relatively poor efficiency of the ISC process. On the other
hand, triplet state emission is completely quenched by ligand-
to-metal energy transfer for all the Eu and Tb complexes, with
the exception of Eu(NO3)3L5. Lifetimes of the 5D0(Eu) excited
states have been determined. Luminescence decays are bi-
exponential and the corresponding lifetimes are reported in
Table 3. As for Eu(NO3)3L3,35 its bi-exponential behaviour
can be explained by solvation, which generates metal ion sites
both with and without coordinated solvent molecules. In the
case of Eu(NO3)3L3, the relative contribution to the lumines-
cence decay is 71 ꢂ 3% for the coordination environment
without water; for the other complexes, this proportion
varies between 60 and 75%. We note that the lifetimes
recorded for the three nitrato complexes with L2–L4 are very
similar, pointing to them having a similar inner-sphere ar-
rangement, and particularly to the coordination of the nitrate
ions.35 When the anion is less coordinating (Cl or CF3SO3) the
lifetime tends to be longer (except for Eu(CF3SO3)3L4), in-
dicating a less efficient deactivation process compared to the
quenching efficiency of nitrate, while the second lifetime be-
comes shorter.
Mesomorphic properties of the complexes
Transition temperatures of the complexes (Table 5) were
determined by differential scanning calorimetry (DSC), upon
heating during the second heating/cooling cycle (see Experi-
mental section). Indeed, most of the complexes are solvated
(see elemental analyses, Table 1) and the solvent molecules are
liberated during the first heating, which subsequently slightly
modifies the mesomorphic properties. We have checked that
subsequent heating/cooling cycles generate the same thermo-
grams. Most of the isolated complexes, except those of L2,
exhibit a liquid crystalline behaviour, most likely resulting
from the rigidifying of the systems upon complexation.5
Eu(NO3)3L3. Since the feasibility of using luminescence
parameters to detect the crystalline to liquid crystalline phase
transition was demonstrated with this complex,35 its thermal
behaviour was also thoroughly investigated. Two differently-
hydrated complexes were obtained, dependant on the drying
conditions, with 0.25 or 0.5 H2O per formula weight. Thermo-
gravimetric analysis (Figure S4, ESIw) shows the loss of water
of hydration for the latter (loss of 0.54 weight %) between
room temperature and 150 1C and that decomposition takes
Thermal properties of the ligands
Transition temperatures and thermodynamic parameters for
the investigated ligands are reported in Table 4. Ligand L1, in
which the pendant arms are attached to the core macrocycle via
a carbonyl group, melts at 101 1C into its isotropic liquid, after
an initial crystalline-to-crystalline transition at low tempera-
ture. Its thermal behaviour parallels that of its analogue with
C
10 alkoxy chains, L1C10, which melts at 104 1C.32 None of the
other ligands (L3, L4 or L5), in which the pendant groups are
linked to the macrocyclic unit by methylene bridges, display
mesomorphic behaviour. The addition of a third alkoxy chain
in L5 leads to a dramatic lowering of the melting point, by 48 1C
compared to L3. The origin of this effect is mainly entropic, the
entropic term in L5 being significantly higher compared to L3
(see Table 4). The presence of two supplementary alkyl chains in
the case of L5 demands a better organisation of the solid phase
in order to accommodate them, and as a consequence, results in
an increase in the entropy of the melting process.43
Fig. 3 Emission spectra of the complexes with L3 at 77 K from solid
state samples and under ligand excitation: (a) La(NO3)3L3, (b) Eu
(NO3)3L3, (c) Eu(CF3SO3)3L3, (d) EuCl3L3, (e) Tb(NO3)3L3.
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Table 2 Photophysical properties of the ligands
Table 3 Lifetimes of the 5D0 excited state (/ms, ꢂ5%) in the Eu
complexes upon laser excitation of the 5D2 level
Ligand
E/cmꢁ1 a (log e)
E/cmꢁ1 b 1pp*
E/cmꢁ1 b 3pp*
295 K
77 K
L1
44 840 (4.80)
37 450 (4.54)
33 900 (4.26)
29 340c
19 590
t1
t2
t1
t2
Complex
Eu(CF3SO3)3L1a
Eu(NO3)3L2
Eu(NO3)3L3cd
Eu(NO3)3L4
EuCl3L3
1.39
1.06
1.08
1.06
1.63
0.95
0.38
0.38
0.58
0.40
0.43
0.37
b
b
0.78
0.76
0.78
1.28
0.64
0.26
b
d
L2
L3
L4
45 040 (4.62 sh)
37 590 (4.31)
34 010 (4.05)
20 620
20 760
20 660
20 880
0.23
0.33
0.22
Eu(CF3SO3)3L3
a
45 040 (4.71)
37 450 (4.42)
33 900 (4.15)
30 670
29 970 sh
Excitation of the D0 level (17 259 cmꢁ1). Not determined. From
d
ref. 35. At 10 K; relative population of the site with the longer
5
b
c
lifetime 71 ꢂ 3%.
45 040 (4.76)
37 450 (4.47)
33 900 (4.20)
30 550
29 700 sh
unchanged up to 200 1C. Fig. 5 presents the diffraction pattern
of the latter, which is also evident during subsequent heating/
cooling cycles. It features a broad diffuse halo at 4.6 A and
three small angle diffraction peaks (Table S3, ESIw) corre-
sponding to distances of 25.3, 14.5 and 12.5 A, which are in the
relationship 1 : 1/O3 : 1/O4, characteristic of a hexagonal
columnar phase, Colh, with an inter-column separation of 29.2
A and a cross-section area of S ¼ 740 A2 (Fig. 6(c)).45 The
diffuse band around 4.6 A is assigned to the liquid-like order of
the molten alkoxy substituents. The absence of additional
features in the wide angle part of the diffractogram, apart
from this diffuse band, suggests a short range correlation of the
molecular stacking within the column. During the cooling
process (of the mesophase to ensure the absence of decom-
position) the pattern of the Colh phase persists down to 40 1C
without any change in phase structure or spacing distances.
Therefore, the thermal event observed during the first heating
around 150 1C probably corresponds to the transition of a
transient metastable mesophase (lamellar type) into a hexago-
nal arrangement of the molecules, a likely consequence of a
change of macrocyclic conformation, induced perhaps by
water loss. By taking a typical stacking period to be approxi-
mately h E 4.5 A between two stacked complexes within the
column (i.e. the associated broad peak could be masked by one
of the molten chains)17 and a density of d ¼ 1 for the Colh
mesophase, we calculate Z ¼ (d ꢃ NAv ꢃ V ꢃ 10ꢁ24)/FW ¼
1.1(1), i.e. E 1 molecule per unit cell (NA is Avogadro’s
number, FW is the formula weight of the molecule in g molꢁ1
and V is the volume of the unit cell in A3).46 This is consistent
with either a single hemi-disk-like complex [Eu(NO3)3L3]
occupying the cross-section of one column, or two complex
molecules occupying a cell 9 A thick (Fig. 6). The length of the
coordinated ligand strand in its bent form in [Eu(NO3)3L3] can
be reasonably estimated from the crystal structures of L2 (Fig.
1) and [Eu(2,2)(NO3)3]47 as amounting to L E 29 A, in very
good agreement with the inter-column separation found in the
Colh mesophase (Fig. 6(a)).18 Since coordination of the bulky
Ln(NO3)3 metallic unit restricts intermolecular p-stacking
between adjacent packed complexes, we propose that the
complexes in one column adopt head-to-tail orientations to
ensure (i) weak intra-columnar packing via the aromatic
groups and (ii) pseudo-circular spreading of the flexible chains
(Fig. 6(b)).
L5
45 450 (4.82)
36 500 (4.33)
33 780 (4.02 sh)
26 140
a
Maximum of the band envelope from absorption spectra in THF,
b
sh ¼ shoulder. From emission spectra of solid state samples at
c
77 K. At 295 K. Not observed.
d
place slightly above 200 1C. Elemental analysis of the former
compound (0.25 H2O) is reported in Table 1, since this
compound was used for all the other physicochemical char-
acterizations. During the first heating, the DSC trace (Fig. 4)
shows (i) an endothermic feature at 86 1C (DH ¼ 20 kJ molꢁ1
,
DS ¼ 56 J molꢁ1 Kꢁ1), corresponding to a transition to a liquid
crystalline phase, (ii) an intricate series of exothermic events in
the range 125–140 1C, and (iii) endothermic isotropisation,
followed by decomposition at around 200–205 1C. The
exothermic events occurring at lower temperatures are puzzling
since the product is pure. If care is exercised not to heat the
compound above 180 1C to avoid any decomposition, they
disappear in the subsequent heating/cooling cycles, which can
be performed more than ten times without altering the sample.
Polarized light optical microscopy (POM) observations re-
vealed birefringent and fluid domains which merged on further
heating into large homogeneous textures. The birefringent
textures observed show cylindrical and well developed do-
mains, typical of either orthogonal smectic phases (SmA and
SmB) or a hexagonal columnar phase (Colh).34 It is noteworthy
that no transition was detected between 86 and 200 1C by this
technique, except isotropisation. Similar situations have been
reported—for instance, in the case of Pd(II) complexes with
macrocyclic polycatenar receptors.44 Finally, we have resorted
to small angle X-ray scattering (SAXS) to fully identify the
nature of the mesophase. As expected from the DSC traces, a
change in the X-ray pattern corresponding to a modification of
the molecular packing was detected between 80 and 90 1C. This
change was characterized by the disappearance of the intense
and sharp peaks of the crystalline phase and the appearance of
a small angle reflection with a periodicity of about 45 A, along
with a broad scattering at 4.6 A, corresponding to the liquid-
like ordering of the chains (Fig. 5). The large periodicity is in
agreement with the packing of the complex into smectic layers
and in agreement with the length of the molecule estimated
from molecular models. From the molecular volume, V, esti-
mated to 2800 A3, the molecular area is found to be 60 A2 for
two chains (see Fig. 6(a)), consistent with a smectic phase. This
value also suggests that the chains are in a disordered coil
conformation so as to compensate for the large molecular area
of the central macrocycle, or that they are interdigitated with
the chains of the neighbouring layers. On further heating, the
X-ray pattern is transformed once more at 150 1C, and remains
Other complexes. The results of the thermal and optical
analyses performed on the other complexes are summarized
in Table 5. The transition temperatures for complexes Eu
(CF3SO3)3L1 and Eu(NO3)3L5 have been determined by
POM only, since no first order transition was observed by
DSC. The two compounds are, however, mesomorphic in
the range 145–163 1C and 110–135 1C respectively. For Eu
(NO3)3L5, the mesophase is not seen during the first heating
1328
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 3 2 3 – 1 3 3 4

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Table 4 Thermal properties of the ligandsa
Compound Transition T/1C DH/kJ molꢁ1 DS/J molꢁ1 Kꢁ1
L1
Cr–Cr0
Cr–I
Cr–I
Cr–I
Cr–I
Cr–I
42
101
166
85
4
95
13
254
226
279
328
303
L2
L3
L4
L5
a
99
100
120
94
93
37
Cr ¼ crystal, I ¼ isotropic liquid.
but is obtained in the first cooling and is present in subsequent
heating/cooling cycles. The other complexes display the same
behaviour as Eu(NO3)3L3. During the first heating, they
sustain a phase transition from either a crystalline or a lamellar
mesophase into an isotropic liquid phase, which, upon heating,
transforms into a mesophase. The latter remains unchanged
during the cooling process and also reappears during the
subsequent heating/cooling cycles, provided that the decom-
position temperature is not reached. According to SAXS
measurements, the luminescent EuX3L3 (X ¼ NO3 and Cl),
Tb(NO3)3L3 and Eu(NO3)3L4 complexes present, in addition
to the broad and weak reflection associated with the melting of
the aliphatic chains (at E 4.6 A), three low-angle reflections—
their associated distances pointing unambiguously to the pre-
sence of a Colh mesophase, similar to the one characterized by
the diffractogram shown in Fig. 5.
Fig. 4 DSC traces of the [Eu(NO3)3L3] complex during the first (top)
and second (bottom) heating cycle, after the first heating cycle did not
reach sample decomposition temperature (5 1C minꢁ1, under N2
atmosphere).
Parameters influencing the formation of the liquid crystalline
phases in the studied complexes. The structure of the ligand
influences considerably the formation of the mesophases, as
exemplified by the complexes Eu(CF3SO3)3L with L ¼ L1 and
L3. The temperature range in which the latter is liquid crystal-
line (90–195 1C) is four times larger than is the case for the
former, while its mesophase forms at a much lower tempera-
ture (145 1C for the complex with L1). Replacing the carbonyl
bridge in L1 with a methylene linkage in L3 results in a
lowering of the ligand polarity and an increased flexibility.
However, metal coordination rigidifies the systems and so
could diminish the differences between them. It is known that
the introduction of nitrogen atoms into crown ethers is favour-
able for the coordination by lanthanide ions.42 Here however,
the nucleophilicity of the amine functionality is considerably
reduced by the presence of the carbonyl groups in L1, which
may result in some dissociation of the complex and thus in a
shrinkage of the mesophase domain by the presence of solid
free lanthanide salt and/or liquid ligand (fusion at 101 1C).
As far as the counterion is concerned, the nitrato complexes
possess the best mesomorphic properties, as demonstrated by
the series of complexes EuX3L3 (X ¼ NO3, Cl and CF3SO3).
The influence of the metal ion on the temperature range of the
Colh mesophase in nitrato complexes is illustrated in Fig. 7, as
determined by calorimetry and polarized light microscopy.
While all the complexes studied present the same Colh meso-
phase, its temperature range depends heavily on the nature of
the metal ion. La leads to the largest range (147 1C) and lowest
transition temperature (58 1C), while the luminescent comple-
xes of Eu and Tb have higher transition temperatures (E85 1C)
but remain liquid crystalline up to almost 200 1C. The length of
the alkoxy chain does not seem to play an essential role, since
data for complexes with L3 (C10) and L4 (C16) are almost
identical. The exception here is La, the temperature range of
the mesophase here being reduced by about 20 1C in its L4
complex. Finally, we have investigated the influence of the
number of alkoxy chains by designing the hexacatenar ligand,
L5. The addition of two more flexible alkoxy chains to L3 to
Table 5 Transition temperatures in some of the studied complexes
with associated thermodynamic parameters (ꢂ1 1C), as determined by
DSC (second heating)
Complex
Transitiona T/1C DH/kJ molꢁ1 DS/J molꢁ1 Kꢁ1
La(NO3)3L3
Cr–Colh
Colh–Ib
58
205
85
13
81
25
20
11
32
23
48
36
13
40
171
71
Nd(NO3)3L3b Cr–Colh
Eu(NO3)3L3b Cr–Colh
Tb(NO3)3L3b Cr–Colh
86
81
56
32
EuCl3L3b
Cr–Colh
Cr–Colh
Colh–I
75
71
92
67
La(NO3)3L4
199
88
101
100
35
Nd(NO3)3L4b Cr–Colh
Eu(NO3)3L4
Cr-Colh
84
a
Cr ¼ crystal, semi-crystal or amorphous, I ¼ isotropic liquid, Colh ¼
b
hexagonal columnar. Decomposition occurs shortly after isotropisa-
tion meaning that the transition temperature (and whenever relevant,
the associated thermodynamic parameters) could only be determined
reliably during the first heating cycle (see Fig. 7).
Fig. 5 SAXS diffractogram of [Eu(NO3)3L3] during the first heating
at 200 1C, displaying the characteristic pattern of a columnar hexa-
gonal phase.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 3 2 3 – 1 3 3 4
1329

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Fig. 7 Phase diagram for the complexes Ln(NO3)3L (’: L ¼ L3,
Ln ¼ La, Nd, Eu and Tb; J: L ¼ L4, Ln ¼ La, Nd and Eu).
complexes. This in turn leads to intermolecular interactions
strong enough to form hexagonal columnar mesophases, while
the ligands themselves, with the exception of L1, are non-
mesomorphic. The more stable mesophases occur with lantha-
nide nitrates and the tetracatenar ligands L3 and L4, which
feature a methylene moiety in the spacer between the macro-
cyclic core and the pendant mesogenic groups. Indeed the
presence of a carbonyl function in the linking unit of L1
reduces the complexation ability of the ligand and yields less
thermally-stable complexes and mesophases. Of those ligands
examined, the best proved to be L3, which bears four decyloxy
chains, since the corresponding complexes exhibit a Colh meso-
phase. The latter starts to form between 58 and 86 1C and often
extends over a 100 1C temperature range, up to 147 1C
for La. The liquid crystalline phases containing luminescent
Ln ions (Eu and Tb) retain their emission properties almost up
to isotropization.35 Therefore, these systems could represent
interesting building blocks for the design of liquid crystalline
luminescent materials, providing the transition temperature is
lowered and the antenna effect is optimized. Work toward this
goal is currently in progress in our laboratory.
Experimental
Sample handling
The mesomorphic complexes display a decomposition tem-
perature close to the isotropisation temperature. As a result,
initial physicochemical experiments led to decomposition of
the samples. To cope with this problem, samples for DSC,
POM, luminescence and SAXS measurements were handled
under an inert atmosphere of nitrogen. Moreover, in the case
of the DSC and luminescence experiments reported in ref. 35,
the samples were not heated too high (to around 180 1C) in
order to avoid such problems. As a consequence, transition
temperatures were easily reproduced. For instance, the follow-
ing temperature transitions were obtained for the europium–
nitrato complex with L3 during six heating/cooling cycles: T ¼
85.5, 86.3, 86.7, 86.6, 85.1 and 85.4 1C. For this particular
sample, this transition temperature has also been confirmed by
four other independent measurements (polarized light micro-
scopy and small angle X-ray diffraction measured on three
different instruments) with temperatures ranging from 83 to
86 1C, depending on the experimental technique. For POM
experiments, the samples were only kept for a few seconds at
the isotropisation temperature. For SAXS measurements, both
techniques were used (heating/cooling cycles with maximum
temperatures lower than the isotropisation temperature and
leaving the samples for only a few seconds at the latter
temperature). In any given case, when quantitative thermo-
Fig. 6 Molecular modelling of [Eu(NO3)3L3] in the Colh mesophase
(see text). Schematic representations of (a) the unit cell, (b) the head-to-
tail packing of two adjacent cells within a column and (c) the arrange-
ment of the columns within the hexagonal lattice.
yield L5 leads both to an increase (24 1C) in the temperature at
which the mesophase appears (110 1C for Eu(NO3)3L5) and a
large decrease (70 1C) in the isotropisation temperature, result-
ing in a very narrow mesomorphic range (25 1C as compared to
114 1C for the complex with tetracatenar L3).
Conclusion
Complexation of lanthanide salts to the derivatised (2,2)
macrocyclic ligands L1 and L3–L5 rigidifies the receptor
framework and confers an increased polarity on the resulting
1330
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dynamic parameters are quoted (e.g. Table 5), they are the
average of at least three determinations.
was washed with water until a neutral pH was obtained, dried
over MgSO4, and after the evaporation of the solvent, 28
recovered as a white powder.
Physicochemical measurements
4-[3,4-Di(methoxy)benzoyloxy] benzoate (12). Benzyl 4-
hydroxybenzoate 10 (2.51 g, 11 mmol), 4-(N,N-dimethylami-
no)pyridine (DMAP; 1.34 g, 11 mmol), N,N0-dicyclohexyl-
carbodiimide (DCC; 2.27 g, 11 mmol) and veratric acid (2 g,
11 mmol) were heated under reflux for 48 h in dichloromethane
(60 cm3). The solvent was removed under reduced pressure and
the residue purified by flash column chromatography (silica
gel, 40–60 mm) using a mixture of CHCl3/methanol (98 : 2) as
eluent to give 4.09 g (95%) of 12 as white powder. dH (400
MHz, CDCl3, 25 1C, TMS): 8.15 (2 H, d, 3J ¼ 9 Hz), 7.85 (1 H,
IR spectra were obtained either from KBr pellets on a Mattson
a-Centauri FT-IR spectrometer or from powders on a Spec-
trum One FT-IR Perkin-Elmer instrument fitted with an ATR
attachment. Electronic spectra in the UV-vis range were re-
corded with a Perkin-Elmer Lambda-900 spectrometer in 1.0
and 0.1 cm quartz cells. Semi-empirical calculations were
performed with the CAChe Pro 6.1 program package for
Windowss (Fujitsu Ltd., 2000–2003). 1H and 13C NMR
spectra were recorded at 25 1C on either a Bruker AM-360
(360 MHz) or AVANCE 400-DRX (400 MHz) spectrometer.
Mass spectra were obtained at EPFL using a Finnigan SSQ-
710C or LCQ deca XP plus spectrometer, or at the University
of Fribourg (Switzerland) on a Bruker FTMS 4.7T BioPEX II
spectrometer. Low-resolution luminescence spectra were mea-
sured on a Perkin-Elmer LS-50B spectrometer. Experimental
procedures for lifetime measurements under high resolution
selective excitation have been published previously.48 Bi-expo-
nential luminescence decays were fitted to the equation:
3
dd, J ¼ 9, 4J ¼ 2 Hz), 7.66 (1 H, d, 4J ¼ 2 Hz), 7.3–7.5 (5 H,
m), 7.28 (2 H, d, 3J ¼ 9 Hz), 6.95 (1 H, d, 3J ¼ 9 Hz), 5.38 (2 H,
s), 3.97 (3 H, s) and 3.96 (3 H, s).
4-[3,4-Di(dodecyloxy)benzoyloxy] tert-butanoate (15). Fol-
lowing a modified procedure,54 8 (8 mmol, 3.92 g), 11 (8 mmol,
1.55 g), DCC (8 mmol, 1.64 g) and DMAP (8 mmol, 0.97 g)
were refluxed under an inert atmosphere in dichloromethane
(200 cm3) for 60 h. The warm mixture was filtered and the
filtrate obtained absorbed onto a small amount of silica gel,
which, after the elimination of the solvent, was placed on the
top of a silica gel column (hexane : ethyl acetate, 95 : 5) and
purified by chromatography. Yield: 68%. dH (400 MHz,
I(t) ¼ A1eꢁk t þ A2eꢁk t þ B, where l/k ¼ t
l
2
where I(t) is the luminescence intensity versus time, A1 and A2
are pre-exponential parameters, k1 and k2 are the de-activation
rate constants, and t is the lifetime of the excited state. DSC
thermograms were collected on Setaram DSC-131 S and Seiko
DSC-220C instruments at 5–10 1C minꢁ1 under a nitrogen
atmosphere. Thermogravimetric analyses were performed with
a Seiko TG/DTA 320 balance under a nitrogen atmosphere.
POM was performed on a Leitz Orthoplan-Pol microscope
equipped with a Leitz LL 20 ꢃ 0.40 polarization lens, a
Linkam THMS 600 variable temperature oven and a Leica
D300 F camera.
3
3
CDCl3): 8.07 (2 H, d, J ¼ 8.6 Hz), 7.81 (1 H, dd, J ¼ 8.6,
4J ¼ 2.0 Hz), 7.66 (1 H, d, 4J ¼ 2.0 Hz), 7.25 (2 H, d, 3J ¼ 8.5
Hz), 6.94 (1 H, d, 3J ¼ 8.6), 4.07 (4 H, m), 1.87 (4 H, m), 1.58 (9
H, s), 1.52–1.43 (6 H, m), 1.40–1.23 (32 H, m) and 0.87 (4 H,
m). MS (CI): m/z ¼ 667 (M1, 8%), 473 (M1 ꢁ C6H4COOtBu,
100%) and 137 (M1 ꢁ 2OC12H25-C6H4COOtBu, 33%).
4-[3,4-Di(methoxy)benzoyloxy] benzoic acid (16).55 Com-
pound 12 (4.08 g, 10.39 mmol) was dissolved in THF (100
cm3) and 10% of Palladium on charcoal catalyst added (0.43
g). The reaction was stirred under a hydrogen atmosphere for 3
h. The catalyst was removed by filtration through Celite and
the solvent removed under reduced pressure to give 2.60 g
(81%) of 16. dH (400 MHz, CDCl3, 25 1C, TMS): 7.87 (2 H, d,
3J ¼ 9 Hz), 7.61 (1 H, dd, 3J ¼ 9, 4J ¼ 2 Hz), 7.42 (1 H, d, 4J ¼
2 Hz), 7.04 (2 H, d, 3J ¼ 9 Hz), 6.76 (1 H, d, 3J ¼ 9 Hz), 3.72
(3 H, s) and 3.71 (3 H, s).
Synthesis and characterisations
Solvents and starting materials were purchased from Fluka
AG (Buchs, Switzerland) and Acros. Acetonitrile and dichloro-
methane were distilled from CaH2, THF was distilled over
sodium and benzophenone, and triethylamine was distilled
from KOH. The following intermediates were commercial
compounds: 6 (Aldrich), 10 (Lancaster) and 26 (Acros).
Lanthanide trifluoromethanesulfonates (triflates)49 and ni-
trates50 were prepared from the oxides (Rhone-Poulenc,
99.99%) and the corresponding trifluoroacetic or nitric acid.
Their metal content was determined by titration with Na2ED-
TA-H2 in the presence of urotropine and xylene orange.51
Elemental analyses were performed by Dr. H. Eder (Micro-
chemical Laboratory), University of Geneva, Switzerland.
Methyl 3,4-di(hydroxyl)benzoate (2)52 and 4-hydroxyben-
zoic acid tert-butylester (11) were prepared as reported in the
literature.53 Methyl 3,4-di(decyloxy)benzoate (3, yield 91%),
methyl 3,4-di(dodecyloxy)benzoate (4, 89%), methyl 3,4-di
(hexadecyloxy)benzoate (5, 74%), 3,4-di(decyloxy)benzoic acid
(7, 96%), 3,4-di(dodecyloxy)benzoic acid (8, 85%), 3,4-di(hex-
adecyloxy)benzoic acid (9, 100%), 4-[3,4-di(decyloxy)benzoy-
loxy] benzoate (13, 67%), 4-[3,4-di(hexadecyloxy)benzoyloxy]
benzoate (14, 68%), 4-[3,4-di(decyloxy)benzoyloxy] benzoic
acid (17, 100%), and 4-[3,4-di(hexadecyloxy)benzoyloxy] ben-
zoic acid (19, 100%) were synthesised according to Goodby
et al.36 and characterized by NMR spectroscopy. The similar
tricatenar derivatives (see Scheme 3) 27 (71%), 28 (90%), 29
(71%) and 30 (99%) were obtained by following the same
protocols. 36 In the synthesis of 28, due to the formation of an
emulsion after the acidification of the reaction, the solvent
(ethanol) was evaporated and the residue extracted from a
mixture of dichloromethane and dilute HCl. The organic phase
4-[3,4-Di(dodecyloxy)benzoyloxy] benzoic acid (18). Follow-
ing a modified procedure,53 a solution of ester 15 (167 mg, 0.25
mmol) in dichloromethane (10 cm3) was cooled to 0 1C.
Anisole (1 cm3) followed by trifluoroacetic acid (2.5 cm3) were
added and the mixture stirred at 0 1C for 3 h and then 1 h at
room temperature. The evaporation of the solvent lead to a
neat white precipitate of 18 which was washed with diethyl
ether (20 cm3) and dried. Yield: 82%. dH (400 MHz, CDCl3):
8.21 (2 H, d, 3J ¼ 8.8 Hz), 7.83 (1 H, dd, 3J ¼ 8.4, 4J ¼ 2.0 Hz),
7.67 (1 H, d, 4J ¼ 2.0 Hz), 7.34 (2 H, d, 3J ¼ 8.8 Hz), 6.95 (1 H,
d, 3J ¼ 8.4 Hz), 4.09 (4 H, m), 1.87 (4 H, m), 1.49 (4 H, m), 1.4–
1.2 (32 H, m) and 0.89 (6 H, m). MS (CI): m/z ¼ 611 (M1,
23%), 628 (M1 þ NH3, 74%), 667 (M1 þ NH3 þ K1, 21%),
684 (M1 þ 2NH3 þ K1, 100%), 473 (M1 ꢁ OC6H4COOH,
60%), 305 (M1 ꢁ OC6H4COOH – C12H25, 10%) and 137
(M1 ꢁ OC6H4COOH ꢁ 2C12H25, 12%).
4-[3,4-Di(methoxy)benzoyloxy] benzyl alcohol (20). Com-
pound 16 (2.49 g, 8.22 mmol) was dissolved in THF (50 cm3)
and 1 M diborane in THF (12.5 cm3) was added under an inert
atmosphere. The mixture was stirred for 24 h and water (50
cm3) then added carefully. After removal of THF, the pre-
cipitate was washed with further water to give 2.25 g (95%) of
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 3 2 3 – 1 3 3 4
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20. dH (400 MHz, CDCl3, 25 1C, TMS): 3.46 (3 H, s), 3.49 (3 H,
m), 1.88–1.73 (6 H, m), 1.49 (6 H, m), 1.28 (36 H, br) and 0.89
(9 H, m). MS (CI): m/z ¼ 760 (M1, 5%) and 574 (M1
ꢁ
3
3
s), 4.20 (2 H, s), 6.64 (1 H, d, J ¼ 8 Hz), 6.78 (2 H, d, J ¼ 8
Hz), 7.00 (2 H, d, 3J ¼ 8 Hz), 7.23 (1 H, d, 4J ¼ 2 Hz) and 7.39
OC6H4CH2Br, 100%).
3
4
(1 H, dd, J ¼ 8, J ¼ 2 Hz).
N,N0 -bis{4-[3,4-di(decyloxy)benzoyloxy]benzoyl}-1,10-diaza-
4,7,13,16-tetraoxacyclooctadecane (L1). Under an inert atmo-
sphere, a solution of acid 18 (183 mg, 0.3 mmol) in freshly
distilled dichloromethane (3 cm3) was cooled to 0 1C using an
ice bath and oxalyl chloride (39 ml, 0.45 mmol) added with a
microsyringe. A few drops of DMF were then added with a
normal syringe. The mixture was allowed to warm to room
temperature and stirring maintained for 5 h. The solvent was
evaporated and the white compound that resulted dried under
high vacuum for 1 h and used for the next step without any
other purification. Diaza-18-crown-6-ether (39 mg, 0.15
mmol), freshly distilled THF (2 cm3) and triethylamine (42
mL, 0.3 mmol) were placed in a two-necked flask under argon.
The suspension was cooled to 0 1C by an ice bath and the acid
chloride (0.3 mmol) in THF (2 cm3) added slowly over 30 min.
The mixture was allowed to warm to room temperature and
stirring maintained overnight. The solution was filtered and the
filtrate evaporated. The white solid obtained was purified by
4-[3,4-Di(decyloxy)benzoyloxy] benzyl alcohol (21). Prepared
by a method similar to that described for 20. Yield: 1.59 g
(100%). dH (400 MHz, CDCl3, 25 1C, TMS): 0.88 (6 H, m),
1.21–1.53 (28 H, m), 1.84 (4 H, m), 4.06 (4 H, m), 4.72 (2 H, s),
6.92 (1 H, d, 3J ¼ 9 Hz), 7.18 (2 H, d, 3J ¼ 8 Hz), 7.41 (2 H, d,
3J ¼ 8 Hz), 7.66 (1 H, d, 4J ¼ 2 Hz) and 7.80 (1 H, dd, 3J ¼ 9,
4J ¼ 2 Hz).
4-[3,4-Di(hexadecyloxy)benzoyloxy] benzyl alcohol (22). Pre-
pared by a method similar to that described for 15. Yield: 5.15
g (96%). dH (400 MHz, CDCl3, 25 1C, TMS): 7.80 (1 H, dd,
3J ¼ 9, 4J ¼ 2 Hz), 7.66 (1 H, d, 4J ¼ 2 Hz), 7.42 (2 H, d, 3J ¼ 9
3
3
Hz), 7.19 (2 H, d, J ¼ 9 Hz), 6.92 (1 H, d, J ¼ 9 Hz), 4.72
3
(2 H, d, J ¼ 5 Hz), 4.07 (4 H, m), 1.84 (4 H, m), 1.53–1.21
(52 H, m) and 0.88 (6 H, m).
4-[3,4-Di(methoxy)benzoyloxy] benzyl bromide (23). Phos-
phorus tribromide (1.4 cm3, 14.9 mmol) was added under an
inert atmosphere to a solution of 20 (2.15 g, 7.46 mmol) in dry
dichloromethane (20 cm3). The mixture was heated under
reflux for 48 h and water (20 cm3) added carefully. The
compound was extracted with dichloromethane (3 ꢃ 20 cm3)
and dried over Na2SO4. After removal of the solvent, 2.51 g
(96%) of 23 were obtained as a white powder. dH (400 MHz,
CDCl3, 25 1C, TMS): 7.84 (1 H, dd, 3J ¼ 9, 4J ¼ 2 Hz), 7.66 (1
H, d, 4J ¼ 2 Hz), 7.44 (2 H, d, 3J ¼ 9 Hz), 7.18 (2 H, d, 3J ¼ 9
column chromatography (silica gel; CH3OH
: dichloro-
methane, 5 : 95). Yield: 70%. dH (400 MHz, CDCl3, 25 1C,
TMS): 7.79 (2 H, dd, 3J ¼ 8.6, 4J ¼ 2 Hz), 7.64 (2 H, d, 4J ¼ 2
Hz), 7.46 (4 H, d, 3J ¼ 8.5 Hz), 7.23 (4 H, d, 3J ¼ 8.5 Hz), 6.92
(2 H, 3J ¼ 8.6 Hz), 4.07 (8 H, m), 3.8 (8 H, m, large), 3.81–3.54
(24 H, m, large), 1.8 (8 H, m), 1.5 (8 H, m), 1.3 (20 H, large)
and 0.87 (6 H, t). dC (100 MHz, CDCl3, 25 1C, TMS): 171.8,
165.0, 154.3, 152.1, 149.0, 134.3, 121.5 (quat.), 128.4, 124.7,
122.2, 114.9, 112.2 (tert.), 71.1–70.8, 69.7, 69.4, 32.2, 30.1–29.9,
29.75–29.69, 29.5, 29.3, 26.35, 26.30, 23.0 (sec.) and 14.4
(prim.). IR: nmax = 2918, 2850, 1724, 1628, 1596, 1466, 1427,
1272, 1193, 1132, 1074, 1019 and 753 cmꢁ1. UV-vis (25 1C,
THF): lmax(e) ¼ 305 nm (sh, 16 ꢃ 103 Mꢁ1 cmꢁ1), 296 (19 ꢃ
103), 267 (37 ꢃ 103), 225 (58 ꢃ 103) and 207 (67 ꢃ 103). ES-MS
(CHCl3): m/z ¼ 1448 (M1, 90%) and 1225 (100%). Found: C,
72.81; H, 9.58; N, 1.92. L1 ꢀ 0.2H2O requires: C, 72.81; H, 9.61;
N, 1.93%. M.p. ¼ 101 1C.
3
Hz), 6.95 (1 H, d, J ¼ 9 Hz), 4.52 (2 H, s), 3.98 (3 H, s) and
3.97 (3 H, s).
4-[3,4-Di(decyloxy)benzoyloxy] benzyl bromide (24). Phos-
phorus tribromide (2.4 cm3, 25.5 mmol) was added under an
inert atmosphere to a solution of 21 (4.12 g, 7.62 mmol) in dry
dichloromethane (60 cm3). The mixture was heated under
reflux for 96 h and water (50 cm3) added carefully. The
compound was extracted with CHCl3 (3 ꢃ 70 cm3) and purified
by flash column chromatography (silica gel, 40–60 mm) using
dichloromethane as eluent to give 3.61 g (78%) of 24. dH (400
MHz, CDCl3, 25 1C, TMS): 7.78 (1 H, dd, 3J ¼ 8, 4J ¼ 2 Hz),
7.64 (1 H, d, 4J ¼ 2 Hz), 7.43 (2 H, d, 3J ¼ 9 Hz), 0.88 (6 H, m),
7.16 (2 H, d, 3J ¼ 9 Hz), 6.91 (1 H, d, 3J ¼ 8 Hz), 4.52 (2 H, s),
4.06 (4 H, m), 1.85 (4 H, m) and 1.53–1.21 (28 H, m).
N,N0 -bis{4-[3,4-di(methoxy)benzoyloxy]benzyl}-1,10-diaza-
4,7,13,16-tetraoxacyclooctadecane (L2). Sodium carbonate
(0.83 g, 7.83 mmol) and 1,10-diaza-4,7,13,16-tetraoxacyclooc-
tadecane (0.934 g, 3.56 mmol) were stirred in acetonitrile
(40 cm3) for 1 h at 60 1C. A solution of 23 (2.5 g, 7.12 mmol)
in acetonitrile (50 cm3) was added and the mixture heated at
60 1C for 48 h. After removal of the solvent, the compound was
extracted with dichloromethane (100 cm3) and washed with
water (3 ꢃ 100 cm3). Ligand L2 was precipitated from a
mixture of acetonitrile/dichloromethane (3 : 7). Yield: 1.172
g (41%). dH (400 MHz, CDCl3, 25 1C, TMS): 7.83 (2 H, dd,
3J ¼ 8, 4J ¼ 2 Hz), 7.66 (2 H, d, 4J ¼ 2 Hz), 7.39 (4 H, d, 4J ¼ 9
4-[3,4-Di(hexadecyloxy)benzoyloxy] benzyl bromide (25). Pre-
pared by a method similar to the one described for 24. Yield:
3.81 g (70%). dH (400 MHz, CDCl3, 25 1C, TMS): 7.79 (1 H,
dd, 3J ¼ 9, 4J ¼ 2 Hz), 7.65 (1 H, d, 4J ¼ 2 Hz), 7.44 (2 H, d,
3J ¼ 9 Hz), 7.17 (2 H, d, 3J ¼ 9 Hz), 6.92 (1 H, d, 3J ¼ 9 Hz),
4.52 (2 H, s), 4.06 (4 H, m), 1.85 (4 H, m), 1.53–1.21 (52 H, m)
and 0.88 (6 H, m).
3
3
Hz), 7.12 (4 H, d, J ¼ 9 Hz), 6.93 (2 H, d, J ¼ 8 Hz), 3.96
(6 H, s), 3.95 (6 H, s), 3.71–3.60 (20 H, m) and 2.84 (8 H, t, 3J ¼
6 Hz). dC (100 MHz, CDCl3, 25 1C, TMS): 165.0–137.3 (quat.),
129.7 (tert.), 124.3, 121.9, 121.4, 112.3, 110.3, 70.7 (sec.), 70.0,
59.4, 56.0 (prim.) and 53.8. IR: nmax = 2879, 2800, 1720, 1598,
1588, 1512, 1418, 1189, 1086, 1013, 755 and 639 cmꢁ1. ESI-MS
(CHCl3): m/z ¼ 803 (M1) and 826 ([M þ Na]1). Found: C,
63.4; H, 6.6; N, 3.2. C44H54N2O12 ꢀ 1.5H2O requires: C, 63.7;
H, 6.9; N, 3.4%. M.p. ¼ 166 1C.
4-[3,4,5-Tri(decyloxy)benzoyloxy] benzyl alcohol (31). This
compound was prepared by a method similar to that described
for 21. Yield: 93%. dH (400 MHz, CDCl3, 25 1C, TMS): 7.43 (2
H, d, 3J ¼ 8.4 Hz), 7.41 (2 H, s), 7.19 (2 H, d, 3J ¼ 8.4 Hz), 4.74
(2 H, s), 4.05 (6 H, m), 1.87–1.73 (6 H, m), 1.49 (6 H, m), 1.30
(36 H, br) and 0.89 (9 H, m). MS (CI): m/z ¼ 697 (M1, 92%),
714 (M1 þ NH3, 98%) and 574 (M1 ꢁ OC6H4CH2OH,
100%).
N,N0 -bis{4-[3,4-di(decyloxy)benzoyloxy]benzyl}-1,10-diaza-
4,7,13,16-tetraoxacyclo-octadecane (L3). A solution of 24 (6.16
g, 10.2 mmol) in DMF (90 cm3) was added to a solution of
sodium carbonate (1.19 g, 11.22 mmol) and 1,10-diaza-
4,7,13,16-tetraoxacyclooctadecane (1.34 g, 5.1 mmol) in
DMF (40 cm3). The mixture was heated at 100 1C for 24 h
and the reaction allowed to cool to room temperature. After
4-[3,4,5-Tri(decyloxy)benzoyloxy] benzyl bromide (32). This
compound was prepared in the same way as 24. Yield: 92%. dH
3
(400 MHz, CDCl3, 25 1C, TMS): 7.46 (2 H, d, J ¼ 8.3 Hz),
7.40 (2 H, s), 7.18 (2 H, d, 3J ¼ 8.3 Hz), 4.53 (2 H, s), 4.05 (6 H,
1332
N e w J . C h e m . , 2 0 0 5 , 2 9 , 1 3 2 3 – 1 3 3 4

View Article Online
addition of water (100 cm3) the precipitate was filtered and
washed with water and acetone to yield 5.74 g (86%) of L3. dH
(400 MHz, CDCl3, 25 1C, TMS): 7.80 (2 H, dd, 3J ¼ 8, 4J ¼ 2
Hz), 7.71 (2 H, d, 4J ¼ 2 Hz), 7.45 (2 H, d, 4J ¼ 2 Hz), 7.16 (4
H, d, 3J ¼ 8 Hz), 7.05 (4 H, d, 3J ¼ 8 Hz), 6.91 (2 H, d, 3J ¼ 8
Small angle diffraction X-ray scattering
The SAXS patterns were obtained using two different experi-
mental setups. In all cases, a linear monochromatic Cu-Ka1
beam (l ¼ 1.5405 A) was obtained using a sealed-tube gen-
erator (900 W) equipped with a bent quartz monochromator.
In the first setup, the transmission Guinier geometry was used,
whereas a Debye–Scherrer-like geometry was used in the
second experimental setup. In all cases, the crude powder
was filled into Lindemann capillaries of 1 mm diameter. An
initial set of diffraction patterns was recorded on an image
plate. Periodicities up to 80 A could be measured and the
sample temperature controlled to within ꢂ0.3 1C. The second
set of diffraction patterns were recorded with a curved Inel CPS
120 counter gas-filled detector linked to a data acquisition
computer. Here periodicities up to 60 A could be measured and
the sample temperature controlled to within ꢂ0.05 1C. The
feature occurring close to the beam stopper in Fig. 5 is not a
reflection. It arises from interference with the edges of the beam
stopper and is typically observed with lanthanide compounds
which have a large absorption coefficient, resulting in a less
intense fundamental reflection and therefore a poorer signal-
to-noise ratio.
3
Hz), 4.06 (8 H, m), 3.70–3.60 (20 H, m), 2.84 (8 H, t, J ¼ 6
Hz), 1.84 (4 H, m), 1.53–1.21 (56 H, m) and 0.88 (12 H, m). dC
(100 MHz, CDCl3, 25 1C, TMS): 165.1–137.2 (quat.), 129.7
(tert.), 124.3, 121.7, 121.4, 114.6, 112.0, 70.7–22.7 (sec.) and
14.1 (prim.). IR: nmax = 2918, 2850, 1722, 1516, 1189, 1086
and 755. ESI-MS (CH3OH): m/z ¼ 1307.86 ([M þ H]1) and
654.87 ([M þ 2H]21). Found: C, 73.3; H, 9.7; N, 2.1.
C80H126N2O12 requires: C, 73.5; H, 9.7; N, 2.1%. M.p. ¼
85 1C.
N,N0 -bis{4-[3,4-di(hexadecyloxy)benzoyloxy]benzyl}-1,10-
diaza-4,7,13,16-tetraoxacyclo-octadecane (L4). Prepared by a
method similar to the one described for L3. Yield: 3.45 g
(89%). dH (400 MHz, CDCl3, 25 1C, TMS): 7.79 (2 H, dd,
3J ¼ 9, 4J ¼ 2 Hz), 7.65 (2 H, d, 4J ¼ 2 Hz), 7.38 (4 H, d, 3J ¼ 8
Hz), 7.11 (4 H, d, 3J ¼ 8 Hz), 6.91 (2 H, d, 3J ¼ 9 Hz), 4.06 (8
H, m), 3.70–3.60 (20 H, m), 2.84 (8 H, t, 3J ¼ 6 Hz), 1.84
(4 H, m), 1.53–1.21 (104 H, m) and 0.88 (12 H, m). dC (100
MHz, CDCl3, 25 1C, TMS): 165.1–137.2 (quat.), 129.7 (tert.),
124.3, 122.4, 121.7, 114.6, 111.9, 70.7–22.7 (sec.) and 14.1
(prim.). nmax = 2918, 2850, 1722, 1516, 1189, 1086 and 755.
ESI-MS (CDCl3): m/z ¼ 1667.3 ([M þ Na]1) and 1645.2 ([M þ
H]1). Found: C, 75.7; H, 10.8; N, 1.7. C104H174N2O12 requires:
C, 76.0; H, 10.7; N, 1.7%. M.p. ¼ 93 1C.
Acknowledgements
Financial support from the Swiss National Science Founda-
tion, National Research Program 47 ‘‘Supramolecular Func-
tional Materials’’ is gratefully acknowledged. We thank B.
Hernach for the synthesis of L3, H. Lartigue for the TG/
DTA measurements, J.-P. Rivera for his help with the POM
experiments, F. Sepulveda and A. Dorcier for recording the
MS spectra and F. Gumy for gathering some of the lumines-
cence data.
N,N0-bis{4-[3,4,5-tri(decyloxy)benzoyloxy]benzyl}-1,10-diaza
-4,7,13,16-tetraoxacyclo-octadecane (L5). Prepared by a meth-
od similar to the one described for L3. Yield: 41%. dH (400
MHz, CDCl3, 25 1C, TMS): 7.41 (4 H, s), 7.40 (4 H, d, J3 ¼ 8.4
Hz), 7.13 (4 H, d, J3 ¼ 8.4 Hz), 4.05 (6 H, m), 3.72 (2 H, s), 3.64
(6 H, m), 2.85 (4 H, dd, J3 ¼ 5.7 Hz), 1.80 (6 H, m), 1.49 (6 H,
m), 1.29 (38 H, large) and 0.88 (9 H, m). dC (100 MHz, CDCl3,
25 1C, TMS): 165.2, 153.0, 150.0, 143.1, 137.4, 129.8, 124.1,
121.5, 108.7, 73.7, 70.8, 70.2, 69.4, 59.5, 53.9, 32.06, 32.03, 30.4,
29.85, 29.81, 29.80, 29.75, 29.72, 29.70, 29.54, 29.51, 29.47,
29.44, 26.21, 26.19, 22.82, 22.80 and 14.2. IR: nmax = 2919,
2851, 1731, 1429, 1336, 1205, 1191, 1118, 961 and 749. UV-vis
(25 1C, THF): lmax(e) ¼ 310 (sh, 4200), 274 (21 000) and 219
(66 000). ES-MS: m/z ¼ 1621 (M1, 85%) and 811 (M21, 93%).
Found: C, 73.91; H, 10.35. L5 ꢀ 0.25H2O requires: C, 73.92; H,
10.33. M.p. ¼ 37 1C.
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