Bent tridentate receptors in calamitic mesophases with predetermined photophysical properties: New luminescent lanthanide-containing materials

Article abstract of DOI:10.1021/ja982545n

A new synthetic strategy has been developed to introduce bent and rigid tridentate 2,6-bis(benzimidazol-2'-yl)pyridine cores into rodlike ligands L(11-17). The crystal structure of the nonmesogenic ligand L¹³ (C₃₉H₃₇N₅O₄, triclinic, P1, Z = 2) shows the expected trans-trans conformation of the tridentate binding unit, which provides a linear arrangement of the semirigid aromatic sidearms. The crystal structure of the related mesogenic ligand L¹⁶ (C⁶¹H₈₁N₅O₄, triclinic, P1, Z = 2) demonstrates the fully extended conformation adopted by the lipophilic side chains, leading to a slightly helically twisted I-shaped molecule. A rich and varied mesomorphism results which can be combined with the simultaneous tuning of electronic and photophysical properties via a judicious choice of the spacers between the rigid central core and the semirigid lipophilic sidearms. Ligands L^13,14 react with Ln(NO₃)₃·χH₂O to give quantitatively and selectively the neutral 1:1 complexes [Ln(L')(NO₃)₃] (Ln = La to Lu), which are stable in the solid state at room temperature but partially dissociate in acetonitrile to give the cationic species [Ln(L')(NO₃)₂]⁺. The crystal structure of [Lu-(L¹³)(NO₃)₃]·3CH₃CN (30, LUC₄₅H₄₆N₁₁O₁₃, monoclinic, C2/c, Z = 8) reveals a U-shaped arrangement of the ligand strand arising from the cis-cis conformation of the coordinated tridentate binding unit. This drastic geometric change strongly affects the thermal behavior and the photophysical and electronic properties of the lipophilic complexes [Ln(L¹⁴)(NO₃)₃]. Particular attention has been focused on structure-properties relationships, which can be modulated by the size of the lanthanide metal ions.

Full text of DOI:10.1021/ja982545n

12274
J. Am. Chem. Soc. 1998, 120, 12274-12288
Bent Tridentate Receptors in Calamitic Mesophases with
Predetermined Photophysical Properties: New Luminescent
Lanthanide-Containing Materials
Homayoun Nozary,† Claude Piguet,*,† Paul Tissot,† Ge´rald Bernardinelli,§
Jean-Claude G. Bu1nzli,‡ Robert Deschenaux, and Daniel Guillon|
Contribution from the Department of Inorganic, Analytical and Applied Chemistry, UniVersite´ de Gene`Ve,
30 quai E. Ansermet, CH-1211 GeneVa 4, Switzerland, Laboratory of X-ray Crystallography, UniVersite´ de
Gene`Ve, 24 quai E. Ansermet, CH-1211 GeneVa 4, Switzerland, Institute of Inorganic and Analytical
Chemistry, UniVersite´ de Lausanne, BCH 1402, CH-1015 Lausanne, Switzerland, Institut de Chimie,
UniVersite´ de Neuchaˆtel, 51 AVenue de BelleVaux, CH-2000 Neuchaˆtel, Switzerland, and Groupe des
Mate´riaux Organiques, Institut de Physique et de Chimie des Mate´riaux de Strasbourg, 23 rue du Loess,
F-67037 Strasbourg Cedex, France
ReceiVed July 20, 1998
Abstract: A new synthetic strategy has been developed to introduce bent and rigid tridentate 2,6-bis-
(benzimidazol-2′-yl)pyridine cores into rodlike ligands L11-17. The crystal structure of the nonmesogenic ligand
L13 (C39H37N5O4, triclinic, P1h, Z ) 2) shows the expected trans-trans conformation of the tridentate binding
unit, which provides a linear arrangement of the semirigid aromatic sidearms. The crystal structure of the
related mesogenic ligand L16 (C61H81N5O4, triclinic, P1h, Z ) 2) demonstrates the fully extended conformation
adopted by the lipophilic side chains, leading to a slightly helically twisted I-shaped molecule. A rich and
varied mesomorphism results which can be combined with the simultaneous tuning of electronic and
photophysical properties via a judicious choice of the spacers between the rigid central core and the semirigid
lipophilic sidearms. Ligands L13,14 react with Ln(NO3)3‚xH2O to give quantitatively and selectively the neutral
1:1 complexes [Ln(Li)(NO3)3] (Ln ) La to Lu), which are stable in the solid state at room temperature but
partially dissociate in acetonitrile to give the cationic species [Ln(Li)(NO3)2]+. The crystal structure of [Lu-
(L13)(NO3)3]‚3CH3CN (30, LuC45H46N11O13, monoclinic, C2/c, Z ) 8) reveals a U-shaped arrangement of the
ligand strand arising from the cis-cis conformation of the coordinated tridentate binding unit. This drastic
geometric change strongly affects the thermal behavior and the photophysical and electronic properties of the
lipophilic complexes [Ln(L14)(NO3)3]. Particular attention has been focused on structure-properties relation-
ships, which can be modulated by the size of the lanthanide metal ions.
Introduction
successfully used for the design of metallomesogens,3 but it has
been shown that metal complexes with thermotropic calamitic5
and discotic6 mesogenic ligands containing linear bidentate 2,2′-
bipyridine units4 display only poor7 or no8 mesogenic behavior.
The origin of these failures has been tentatively attributed (i)
to the large increase of the electric dipole moment which occurs
upon complexation8 and (ii) to the limited anisometry of the
rigid core, although this has been recently overcome in extended
systems.9 The closely related tridentate receptor 2,2′:6′,2′′-
terpyridine is essentially ignored in this field,3 as are other
tridentate binding units.10 To the best of our knowledge, a single
The recent recognition of the importance of metallomesogens
(i.e., liquid crystals containing metal ions) for the development
of advanced materials1 with new electronic, optical, and
magnetic properties2 has encouraged coordination chemists to
design new lipophilic rodlike or disklike complexes exhibiting
mesomorphic behavior.3 Liquid crystalline (or mesomorphic)
properties result from phases in which the molecular order is
intermediate between that of an ordered solid crystal and a
disordered liquid. A thermotropic mesophase is formed by the
influence of temperature, and the resulting thermotropic liquid
crystals are divided in two main categories depending on their
molecular axial anisotropies: calamitic (rodlike) and discotic
(disklike).3 A large variety of bidentate chelating units has been
(4) Summers, L. A. AdV. Heterocycl. Chem. 1984, 281. Constable, E.
C. AdV. Inorg. Chem. Radiochem. 1989, 34, 1.
(5) El-Ghayoury, A.; Douce, L.; Ziessel, R.; Seghrouchni, R.; Skoulios,
A. Liq. Cryst. 1996, 21, 143. Douce, L.; Ziessel, R.; Seghrouchni, R.;
Skoulios, A.; Campillos, E.; Deschenaux, R. Liq. Cryst. 1996, 20, 235.
Bruce, D. W.; Rowe, K. E. Liq. Cryst. 1995, 18, 161.
(6) Palmans, A. R. A.; Vekemans, J. A. J. M.; Fischer, H.; Hickmet, R.
A.; Meijer, E.-W. Chem. Eur. J. 1997, 3, 300.
(7) Kuboki, T.; Araki, K.; Yamada, M.; Shiraishi, S. Bull. Chem. Soc.
Jpn. 1994, 67, 948.
(8) Rowe, K. E.; Bruce, D. W. Liq. Cryst. 1996, 20, 183.
(9) Rowe, K. E.; Bruce, D. W. J. Chem. Soc., Dalton Trans. 1996, 3913.
Morrone, S.; Guillon, D.; Bruce, D. W. Inorg. Chem. 1996, 35, 7041.
(10) Serrete, A. G.; Swager, T. M. Angew. Chem., Int. Ed. Engl. 1994,
33, 2342. Lai, C. K.; Serrette, A. G.; Swager, T. M. J. Am. Chem. Soc.
1992, 114, 7949. Serrette, A. G.; Lai, C. K.; Swager, T. M. Chem. Mater.
1994, 6, 2252.
* To whom correspondence should be addressed. E-mail: Claude.Piguet@
chiam.unige.ch.
† Department of Inorganic, Analytical and Applied Chemistry, Universite´
de Gene`ve.
§ Laboratory of X-ray Crystallography, Universite´ de Gene`ve.
‡ Institute of Inorganic and Analytical Chemistry, Universite´ de Lausanne.
Institut de Chimie, Universite´ de Neuchaˆtel.
| Institut de Physique et de Chimie des Mate´riaux de Strasbourg.
(1) Giroud-Godquin, A. M.; Maitlis, P. M. Angew. Chem., Int. Ed. Engl.
1991, 30, 375. Hudson, S. A.; Maitlis, P. M. Chem. ReV. 1993, 93, 861.
(2) Bruce, D. W. J. Chem. Soc., Dalton Trans. 1993, 2983.
(3) Metallomesogens, Synthesis, Properties and Applications; Serrano,
J. L., Ed.; VCH: Weinheim, 1996.
10.1021/ja982545n CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/12/1998

Bent Tridentate Receptors in Calamitic Mesophases
J. Am. Chem. Soc., Vol. 120, No. 47, 1998 12275
Chart 1
example of lyotropic mesophases with Ru(II)11 coordinated to
terminal 4′-substituted terpyridine derivatives has been reported,
and the analogous 4′-substituted tridentate C,N,N chelating
ligand 6-phenyl-2,2′-bipyridine cyclometalated to Pd(II) displays
a monotropic nematic phase at high temperature.12 We have
shown13 that related tridentate ligands L1-10 (Chart 1) are
particularly well-suited to produce lanthanide building blocks
[Ln(Li)(NO3)3] (i ) 3-10)14 and [Ln(Li)3](ClO4)3 (i ) 1-10),15
exhibiting predetermined structural, thermodynamic, magnetic,
and spectroscopic characteristics which might induce fascinating
new properties in advanced materials. The recent incorporation
of related lanthanide complexes into Langmuir-Blodgett films
to produce luminescent materials16 and into magnetically
adjustable liquid crystals17 demonstrates the potential of this
approach. However, the inherent bent conformations associated
with either free (trans-trans) or complexed (cis-cis) chelating
tridentate aromatic binding units severely limits the design of
rodlike or disklike molecules required for the formation of
calamitic or discotic mesophases, respectively.1-3,10 The relative
weakness of the Ln-N(heterocyclic) bond15,18 together with the
ionic size8,9 and high coordination number of Ln(III) are also
crucial factors which must be considered if these building blocks
are to be introduced into thermotropic mesophases.19
Figure 1. Conformational changes occurring upon complexation of
L3 to Ln(III).
large molecular anisometry combined with suitable intermo-
lecular interactions to produce calamitic mesophases (five
aromatic rings are required for metallomesogens based on 2,2′-
bipyridine units)9 has led us to connect lipophilic tails with
additional rigid aromatic groups to the 5-positions of the
benzimidazole rings. Structural and electronic changes resulting
from the complexation process are crucial points which have
been carefully investigated in order to establish structure-
function relationships. A partial report of this work appeared
as a preliminary communication.21
Results and Discussion
Synthesis of the Ligands L11-17. We have developed a
convergent synthetic approach leading to the preparation of two
different tridentate binding units substituted at the 5-positions
of the benzimidazole rings with carbon (8) or oxygen linkers
(9, Scheme 1). Tunable semirigid para-disubstituted phenyl
rings bearing long terminal lipophilic alkyloxy chains (14, 16-
21, Scheme 2) can be then easily attached to the central core
using modulable three- (L11,12) or two-atom (L13-17) spacers
(Scheme 3). The synthons 8 and 9 are synthesized by using a
recently developed strategy based on a modified Phillips
reaction,22 in which the two benzimidazole rings are formed in
one step from the symmetrical bis-o-nitroarenecarboxamides 6
and 7. Surprisingly, the treatment of 8 with boron tribromide
followed by hydrolysis produces quantitatively the bis-bromo-
methyl derivative 10 instead of the expected bis-hydroxymethyl
compound as a result of the high sensitivity of the benzylic
positions toward nucleophilic displacements. Subsequent nu-
cleophilic attacks with carboxylate (14, 19) or phenolate (16-
18) groups provide the ligands L11-15 in good yields. A similar
deprotection procedure for 9 gives the expected and poorly
soluble bis-hydroxy compound 11, which is transformed into
ligands L16,17 by electrophilic attack of its deprotonated salt
(NBu4)2[11-2H] with 21 or the acyl chloride derivative of 19,
In this paper, we present a new approach aimed at introducing
bent rigid tridentate aromatic receptors related to L3-10 into
extended rodlike molecules suitable for the preparation of
calamitic mesophases. Substitution of the lateral benzimidazole
rings at the 4- or 5-positions is promising because the confor-
mational change occurring upon complexation to Ln(III) (trans-
trans f cis-cis, Figure 1) interconverts the topological
orientation of these substituents.14,20 However, the need for
(11) Holbrey, J. D.; Tiddy, G. J. T.; Bruce, D. W. J. Chem. Soc., Dalton
Trans. 1995, 1769.
(12) Neve, F.; Ghedini, M.; Crispini, A. Chem. Commun. 1996, 2463.
Neve, F.; Ghedini, M.; Francescangeli, O.; Campagna, S. Liq. Cryst. 1998,
24, 673.
(13) For reviews, see: Piguet, C. Chimia 1996, 50, 144. Piguet, C.;
Bu¨nzli, J.-C. G. Eur. J. Solid State Inorg. Chem. 1996, 33, 165. Piguet, C.;
Bu¨nzli, J.-C. G. Chimia 1998, 52, 579.
(14) Piguet, C.; Williams, A. F.; Bernardinelli, G.; Moret, E.; Bu¨nzli,
J.-C. G. HelV. Chim. Acta 1992, 75, 1697. Petoud, S.; Bu¨nzli, J.-C. G.;
Schenk, K. J.; Piguet, C. Inorg. Chem. 1997, 36, 1345.
(15) Piguet, C.; Williams, A. F.; Bernardinelli, G.; Bu¨nzli, J.-C. G. Inorg.
Chem. 1993, 32, 4139. Piguet, C.; Bu¨nzli, J.-C. G.; Bernardinelli, G.; Bochet,
C. G.; Froidevaux, P. J. Chem. Soc., Dalton Trans. 1995, 83. Petoud, S.;
Bu¨nzli, J.-C. G.; Renaud, F.; Piguet, C.; Schenk, K. J.; Hopfgartner, G.
Inorg. Chem. 1997, 36, 5750.
1
respectively. The H and 13C NMR spectra of L11-17 confirm
the proposed structures, and the systematic absence of observ-
able NOE effects between the protons of the ethyl substituents
of the benzimidazole ring (H8,9) and the pyridine proton H2
strongly suggests a trans-trans conformation (i.e., the nitrogen
of the pyridine ring is trans to the unsubstituted nitrogen atoms
of the benzimidazole rings)14 of the tridentate binding unit in
(16) Qian, D.-J.; Yang, K.-Z.; Nakahara, H.; Fukuda, K. Langmuir 1997,
13, 5925.
(17) Wang, Z. K.; Huang, C. H.; Zhou, F. Q. Solid State Commun. 1995,
95, 223. Galymetdinov, Y.; Athanassopoulou, A. M.; Kharitonova, O.; Soto-
Bustamante, E. A.; Ovchinnikov I. K.; Hasse, W. Chem. Mater. 1996, 8,
922. Bikhantaev, I.; Galymetdinov, Y.; Kharitonova, O.; Ovchinnikov, I.
K.; Bruce, D. W.; Dunmur, D. A.; Guillon, D.; Heinrich, B. Liq. Cryst.
1996, 20, 489.
(20) Piguet, C.; Rivara-Minten, E.; Hopfgartner, G.; Bu¨nzli, J.-C. G. HelV.
Chim. Acta 1995, 78, 1541.
(18) Forsberg, J. H. Coord. Chem. ReV. 1973, 10, 195.
(19) Pegenau, A.; Go¨ring, P.; Tschierske, C. Chem. Commun. 1996, 2563.
Deschenaux, R.; Goodby, J. W. In Ferrocenes; Togni, A., Hayashi, T.,
Eds.; VCH: Weinheim, 1995; p 471ff.
(21) Nozary, H.; Piguet, C.; Tissot, P.; Bernardinelli, G.; Deschenaux,
R.; Vilches, M.-T. Chem. Commun. 1997, 2101.
(22) Piguet, C.; Bocquet, B.; Hopfgartner, G. HelV. Chim. Acta 1994,
77, 931.

12276 J. Am. Chem. Soc., Vol. 120, No. 47, 1998
Nozary et al.
Scheme 1a
Scheme 3a
a Reagents: (i) KOH, DMSO, MeI; (ii) EtNH2, EtOH; (iii) SOCl2,
CH2Cl2, DMFcat.; (iv) NEt3, CH2Cl2; (v) Fe, HCl, EtOH, H2O; (vi) BBr3,
CH2Cl2.
Scheme 2a
a Reagents: (i) 14 or 19, NBu4OH, CH2Cl2; (ii) 16-18, NBu4OH,
CH2Cl2; (iii) 19, SOCl2, CH2Cl2, DMFcat.; (iv) 21, NBu4OH, CH2Cl2.
a Reagents: (i) C12H25Br, KOH, DMSO; (ii) KOH, EtOH, H2O; (iii)
RBr, KHCO3, dioxane-water; (iv) LiAlH4, THF; (v) PBr3, CH2Cl2.
Figure 2. Atomic numbering scheme for (a) L13 and (b) L.16 Ellipsoids
are represented at 50% probability level.
solution, as previously proposed for terpyridine derivatives.23
A related trans-trans arrangement is observed in the crystal
structure of the protonated ligand [L3 + H](ClO4),14 but a
complete structural and geometrical characterization of the free
unprotonated ligands is required since this point is crucial for
the development of rodlike molecules incorporating bent tri-
dentate units.
The central aromatic cores of L13 and L16 are very similar,
except for the inversion of the carbon and oxygen atoms of the
spacer between the benzimidazole rings and the para-disubsti-
tuted phenyl sidearms. C-C, C-O, and C-N bond distances
and bond angles are within standard values26 for both ligands.
The dihedral angles involving the carbon and oxygen atoms of
the spacers as the central atoms (C8-O1 and C28-O3 for L13,
C15-O1 and C43-O3 for L16) are close to 180° (174.5-
179.7°), leading to an elongated antiperiplanar arrangement of
the benzimidazole and phenyl rings. The tridentate 2,6-bis-
(benzimidazol-2-yl)pyridine units adopt the expected trans-
trans conformation, which minimizes the dipolar moment and
the repulsion between nitrogen lone pairs26 and maximizes
Crystal Structures of L13 and L16. Figure 2 shows the
atomic numbering scheme for L13 and L16, and Figures 3 and 4
display ORTEP24 stereoviews of the ligands. Atomic coordi-
nates, displacement parameters, bond distances, bond angles,
and least-squares plane data are given as Supporting Information
(Tables S1-S8).
(23) Bessel, C. A.; See, R. F.; Jameson, D. L.; Churchill, M. R.; Takeuchi,
K. J. J. Chem. Soc., Dalton Trans. 1992, 3223 and references therein.
Constable, E. C.; Lewis, J.; Liptrot, C. M. Inorg. Chim. Acta 1990, 178,
47.
(24) Johnson, C. K. Ortep II; Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.
(25) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A.
G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1.
(26) Case, F. H.; Kasper, T. J. J. Am. Chem. Soc. 1956, 78, 5842.

Bent Tridentate Receptors in Calamitic Mesophases
J. Am. Chem. Soc., Vol. 120, No. 47, 1998 12277
58.0 Å (C33‚‚‚C61), a width of ca. 5.8 Å (C3‚‚‚C42), and a
length/width ratio of 10. In L13, the almost coplanar pyridine-
benzimidazole unit (interplanar angle 3.2°) of one ligand
strongly interacts with the related unit of a second molecule
related by an inversion center, producing head-to-tail π-stacked
pairs in the unit cell aligned with their long molecular axis,
making an angle of 13° with the [1 1h 1] direction (Figure 3).
The slight helical twist observed for L16 (the total helical torsion
angle of the rigid core amounts to ≈136° for a total length of
≈28.6 Å, thus leading to an approximate pitch of 76 Å) prevents
strong interstrand stacking interactions, and the elongated ligands
are packed in the unit cell with their long molecular axis aligned
in a common direction, making angles of 51°, 70°, and 62° with
a, b, and c, respectively (Figure 4).
Mesogenic Properties of Ligands L11-17. The mesomorphic
properties of the ligands have been investigated by a combina-
tion of differential scanning calorimetry (DSC), polarized optical
microscopy, and X-ray diffraction. L11,12 possess three-atom
spacers (CH2-O-CO) between the benzimidazole rings and
the para-disubstituted phenyl rings and do not exhibit mesogenic
behavior. The crystals melt to give the isotropic fluids (Table
1). Attachment of a second dodecyloxy chain in L12 does not
induce mesomorphism but decreases the melting point by 18
°C. The use of two-atom spacers in L13-17 severely decreases
the degrees of freedom of the aromatic core, as demonstrated
by the rodlike shape adopted by L13 in the solid state. The
crystal phase in L13 is stable, and the melting process leads only
to isotropization at high temperature. The connection of two
peripheral lipophilic chains in L14,15 induces the formation of
an enantiotropic smectic A (SA) phase and a monotropic smectic
C (SC) one. X-ray diffraction studies at small angles for L14 in
the SA phase at 150 °C gives a d-layer spacing of 51 Å (Figure
F2, Supporting Information). Compared to the total length
found for the closely related ligand L16 in its fully extended
conformation in the solid state (l ) 58.0 Å), we calculate a d/l
ratio of 0.88, which is compatible with monomolecular orga-
nization with a pronounced disorganization of the chains.
Figure 3. ORTEP24 stereoview of a stacked pair of ligands L13.
L16 is similar to L14 except for the inversion of the carbon
and oxygen atoms of the spacers, but this has only little effect
on the mesomorphic behavior. On the other hand, the replace-
ment of the CH2 unit of the spacer with a carbonyl group in
L17 produces different mesogenic properties with the formation
of enantiotropic SC, SA, and nematic phases. According to the
unpredictable effects of carbonyl groups on mesomorphic and
ferroelectric properties of liquid crystals containing extended
heterocyclic cores,3,8,27 this peculiar behavior is not completely
unexpected, but the poor resistance of aromatic esters toward
hydrolysis strongly limits their use as ligands for lanthanide
metal ions.
Photophysical Properties of Ligands L13-17. Except for
better resolution in solution, the absorption spectra of the ligands
L13-17 are similar for solid-state (reflectance spectra) and
solution (transmission spectra) samples, which suggests that the
trans-trans conformation of the tridentate binding unit exem-
plified in the crystal structures of L13 and L16 is maintained in
solution, in agreement with NMR data. A previous spectro-
scopic study showed the electronic absorption spectrum of L7
in solution to be dominated by an intense transition with a
maximum at 30 860 cm-1, assigned to the π1(A2)fπ*(B1)
transition centered on the tridentate binding unit (trans-trans
conformation, C2V symmetry), and shoulders at higher energies
involving low-lying π orbitals.15 It was suggested that π-donor
Figure 4. ORTEP24 stereoview of L16, showing the helical twist of
the aromatic core.
π-overlap as established for terpyridine derivatives.12 However,
deviation from planarity is significant for both ligands, with
dihedral interplanar angles between the central pyridine and the
connected benzimidazole rings in the range 3-36° (Tables S4
and S8). The lateral para-disubstituted phenyl rings also display
sizable interplanar angles with the benzimidazole rings to which
they are connected via the two-atom spacer (22-61°), leading
to a wavy arrangement of the five aromatic rings in L13 (Figure
3) and a helical twist in L16 resulting from a sequence of
interannular rotations between the aromatic rings with the same
screw direction (Figure 4). The total length between the
terminal oxygen atoms of the semirigid cores (O2‚‚‚O4) is
similar for both ligands (29.07 Å for L13 and 28.63 Å for L16),
thus producing elongated (I-shape) basic units. As a result of
the trans-trans conformation of the tridentate binding units,
the all-trans terminal lipophilic dodecyloxy chains in L16 are
approximately collinear and run in opposite directions, giving
a highly anisotropic rodlike ligand with a total length of ca.
(27) Hoschino, N.; Takahashi, K.; Sekiuchi, T.; Tanaka, H.; Matsunaga,
Y. Inorg. Chem. 1998, 37, 882.

12278 J. Am. Chem. Soc., Vol. 120, No. 47, 1998
Nozary et al.
Table 1. Phase-Transition Temperatures and Enthalpy and Entropy Changes for Ligands L11-17 and Thermal Behavior of the Complexes
[Ln(L14)(NO3)3]‚xH2O (22-29)
compound
transitiona
T/°C
∆H/kJ‚mol-1
∆S/J‚mol-1‚K-1
L11
L12
L13
L14
K-I
107
80
112
46
50
c
17
57
c
19
28
c
18
35
c
211
309
99
K-I
89
195
132
98f
K-I
K-SA
122
(SC-SA)b
SA-I
188
130
105
184
144
107f
193
131
217
223
226
37
141
L15
L16
L17
K-SA
(SC-SA)b
SA-I
40
66
K-SA
(SC-SA)b
SA-I
39
86
K-SC
SC-SA
SA-N
d
N-I
7e
14e
[La(L14)(NO3)3]‚3H2O (22)
loss: 2 H2O
loss: 1 H2O
decg
25-80
100-125
130
[Sm(L14)(NO3)3]‚H2O (23)
[Eu(L14)(NO3)3]‚H2O (24)
[Gd(L14)(NO3)3]‚H2O (25)
[Tb(L14)(NO3)3]‚H2O (26)
[Y(L14)(NO3)3]‚H2O (29)
[Yb(L14)(NO3)3]‚H2O (27)
[Lu(L14)(NO3)3]‚H2O (28)
loss: 1 H2O
25-110
132
25-100
132
90-140
193
90-110
190
25-80
189
25-70
191
25-70
194
decg
loss: 1 H2O
decg
loss: 1 H2O
K-I
22
30
39
39
17
47
65
84
83
36
loss: 1 H2O
K-I
loss: 1 H2O
K-I
loss: 1 H2O
K-I
loss: 1 H2O
K-I
a K ) crystal, SC ) smectic C phase, SA ) smectic A phase, N ) nematic phase, I ) isotropic fluid. Temperatures are given as the onset of the
peak (Seiko DSC 220C differential scanning calorimeter, 5 °C‚min-1, under N2). The liquid-crystalline phases were identified from their optical
textures: SC ) broken focal-conic fan and schlieren textures; SA ) focal-conic fan texture and homeotropic zones; N ) schlieren and marbled
textures. b Monotropic transition. c Second-order transition determined by polarized optical microscopy. d Masked by isotropization. e Cumulated
enthalpies and entropies. f Approximate value: the SC phase formed during the crystallization process. g Decomposition, see text.
The direct attachment of strong π-donor oxygen atoms to
the 5-positions of the benzimidazole rings in L16 produces the
expected large shift of the πfπ* transition toward lower
energies (∆E ) 2480 cm-1 with respect to L14). A weaker
broad band centered at 36 230 cm-1 is attributed to internal
transitions centered on the 4-alkoxybenzyl moiety (anisole
displays a similar but structured transition at 36 900 cm-1).28
The reduced π-donor character of ester groups in L17 restores
the usual πfπ* transition at 30 770 cm-1, together with (i) a
new maximum at high energy (39 370 cm-1) assigned to a
transition centered on the 4-alkoxybenzoic acid sidearms (p-
anisic acid displays a broad transition at 40 160 cm-1 29
and
)
(ii) a weakly absorbing tail covering the low-energy domain
(Figure 5).
The emission spectra of 10-5 M solutions of L13-17 display
broad and Stokes-shifted bands originating from the 1ππ*
state14,15 whose relative energies closely parallel the trends found
for the absorption spectra (Table 3, Figure 6). However, 8, L7,
and L16 display comparable emission intensities, while L13,14,17
are ca. 50-fold less fluorescent. The excitation spectra recorded
under analysis of the 1ππ* emission closely match the absorption
spectra, indicating similar UV light-harvesting properties for
all studied ligands, and we conclude that nonradiative internal
conversion processes are more efficient for L13,14,17. The poor
Figure 5. Absorption spectra of L7, L14, L16, and L17 (10-5 M) in CH3-
CN/CH2Cl2 (7:3) at 298 K.
substituents bound to the 5-position of the benzimidazole rings
(i.e., methyl groups in L7) destabilize the π1(A2) level, leading
to a shift of the πfπ* transition toward lower energy. The
substitution of one hydrogen atom of these methyl groups of
L7 by a methoxy group in 8 or a 4-alkoxyphenol group in L13,14
has only minor electronic effects, leading to very similar πfπ*
transitions (Figure 5, Tables 2 and 3). However, new shoulders
appear around 33 900 cm-1 in L13,14 which are assigned to
πfπ* transitions centered on the p-dihydroxyphenyl moiety
by comparison with the single broad transition observed at
34 010 cm-1 for 1,4-dihexadecyloxybenzene.
(28) Perkampus, H. H. UV-Vis Atlas of Organic Compounds, 2nd ed.;
VCH: Weinheim, 1992.
(29) Baker, J. W.; Barret, G. F. C.; Tweed, W. T. J. Chem. Soc. 1952,
2831.

Bent Tridentate Receptors in Calamitic Mesophases
J. Am. Chem. Soc., Vol. 120, No. 47, 1998 12279
Table 2. Ligand-Centered Absorption and Emission Properties of Ligands 8, L7, L13-17, and Complexes [Ln(L14)(NO3)3] (24-26, 28) in the
Solid Statea
emission/cm-1
absorption/cm-1
πfπ* + nfπ*
,
lifetime/ms,
compound
1ππ*
3ππ*
τ (3ππ*)
L7
28 410
26 250
20 120
671(28)
25 770 sh
21 505 sh
20 405
8
38 670
33 820 sh
28 170
38 700 sh
28 330
38 460 sh
32 470
20 580
18 450 sh
17 270 sh
b
572(18)
L13
L14
b
b
27 320 sh
26 455
25 060 sh
26 180 sh
25 380
24 880
24 100
26 810 sh
25 970
24 450
23 200
27 760
26 315
25 510
25 000 sh
24 510
23 530 sh
20 410
18 350
17 120
20 700
415(5)
28 330
L16
39 000 sh
32 260 sh
26 920
592(10)
614(34)
12.0(2)
76.5(6)
L17
28 410 (br)
19 380
18 450
[Gd(L14)(NO3)3] (25)
[Lu(L14)(NO3)3] (28)
39 220 sh
26 670
21 800
20 120
18 870
17 540 sh
20 920
19 270
17 860
16 400 sh
c
39 300 sh
26 670
[Eu(L14)(NO3)3] (24)
[Tb(L14)(NO3)3] (26)
40 000 sh
35 710 sh
26 670
39 200 sh
33 900 sh
26 700
26 385
25 000 sh
c
c
26 455
25 000 sh
c
a Reflectance spectra recorded at 295 K, luminescence data at 77 K, and lifetime measurements at 10 K (λexc ) 308 nm); sh ) shoulder. b Too
c
weak to be measured. 3ππ* luminescence quenched by transfer to Ln ion.
emissive properties of L14 compared to those of L16 strikingly
demonstrate the sensitivity of electronic properties to minor
structural changes, while molecular structures and thermal
behavior are only marginally affected. The significantly lower
oxidation potential30 of 1,4-dialkoxybenzene (corresponding to
the sidearms in L14) compared to that of 4-alkoyltoluene
(corresponding to the sidearms in L16) might induce PET
(photoinduced electron transfer) processes for L13,14 which
partially quench the luminescence.31 Other quenching mech-
anisms based on some specific phonon-assisted deactivation
pathways associated with the structures of L13, L14, and L17
cannot be excluded.
Synthesis and Characterization of the Complexes [La(L14)-
(NO3)3]‚3H2O (22) and [Ln(L14)(NO3)3]‚H2O (Ln ) Sm, 23;
Eu, 24; Gd, 25; Tb, 26; Yb, 27; Lu, 28; Y, 29). L14 has been
selected for the investigation of 1:1 complexes with Ln(III)
because of (i) its resistance toward hydrolysis, (ii) its 1ππ* and
3ππ* excited states located at high energy, similarly to L7,15
and (iii) its synthetic accessibility. The mixing of stoichiometric
quantities of L14 and Ln(NO3)3‚xH2O (x ) 2-6) in acetonitrile/
dichloromethane gives the complexes [La(L14)(NO3)3]‚3H2O
(22) and [Ln(L14)(NO3)3]‚H2O (Ln ) Sm, 23; Eu, 24; Gd, 25;
Tb, 26; Yb, 27; Lu, 28; Y, 29) in good yields (61-84%). The
IR spectra show the characteristic ligand vibrations between
1500 and 1600 cm-1 (CdC, CdN stretchings) which are slightly
shifted (5-10 cm-1) upon complexation, together with four
transitions in the range 1600-800 cm-1 characteristic of
bidentate coordinated nitrate groups.14 Unfortunately, we were
unable to obtain X-ray quality crystals for the lipophilic
complexes 22-29, but yellow prisms of the model compound
[Lu(L13)(NO3)3]‚2CH3CN (30) have been grown for diffraction
studies.
Crystal Structure of [Lu(L13)(NO3)3]‚3CH3CN (30). The
crystal structure of 30 shows it to be comprised of a neutral
complex [Lu(L13)(NO3)3] and three solvent molecules, of which
two are slightly disordered. L13 adopts the expected almost
planar cis-cis conformation (interplanar angles between pyri-
dine and benzimidazole rings, 6.2° and 12.1°, Table S12)
resulting from its meridional tricoordination to Lu(III) with Lu,
N1, N3, and N4 distributed in a plane (maximum deviation,
0.07 Å for N4). In agreement with IR results, three bidentate
nitrate groups of pseudo-C2V symmetry occupy the vacant
Emission spectra in the solid state (77 K) display structured
1ππ* emission bands at energies similar to those found in
solution, except for 8, where a significant shift of the maximum
toward lower energy (∆E ) 6150 cm-1) is attributed to the
formation of excimers in the crystal.32 Time-resolved emission
spectra (delay, 0.2-0.8 ms) exhibit faint but structured and long-
lived (400-600 ms, Table 2) phosphorescence of the 3ππ* states
around 19 380-20 700 cm-1 (given for the 0-0 phonon
transitions) for 8 and L13-17, as previously reported for L3-7 14,15
.
We do not observe any significant correlation between the
energy of 3ππ* level and the structural variation in L13-17, which
indicate a common triplet state centered on the tridentate bis-
(benzimidazole)pyridine units for all ligands.
(30) Effenberger, F.; Kottmann, H. Tetrahedron 1985, 41, 4171. Mattes,
S. L.; Farid, S. J. Am. Chem. Soc. 1982, 104, 1454.
(31) Ghosh, P.; Bharadway, P. K.; Roy, J.; Ghosh, S. J. Am. Chem. Soc.
1997, 119, 11903 and references therein.
(32) Turro, N. J. Modern Molecular Photochemistry; Benjamin/Cum-
mings Publishing Co, Inc.: Menlo Park, CA, 1978.

12280 J. Am. Chem. Soc., Vol. 120, No. 47, 1998
Nozary et al.
Table 3. Ligand-Centered Absorptions and Emission Properties of
Ligands 8, L7, L13-17, 10-5 M in CH3CN/CH2Cl2 (7:3), and
Complexes [Ln(L14)(NO3)3] (22-29), 10-4 M in CH3CN, at 298 K
absorption/cm-1
πfπ* + nfπ*
,
emission/cm-1
,
compound
1ππ*
λ
exc/nm
331
L7
35 715 (21 000 sh)a
30 860 (43 700)
35 700 (24 100 sh)
31 250 (44 030)
33 900 (29 000 sh)
30 960 (38 200)
33 900 (30 900 sh)
31 050 (40 100)
38 460 (7 230 sh)
36 230 (11 470)
28 570 (30 830)
39 370 (16 150)
30 769 (32 340)
25 970 (7 600 sh)
26 315
26 560
26 280
26 740
23 980
8
328
328
328
345
L13
L14
L16
L17
23 640
334
[La(L14)(NO3)3] (22) 33 445 (25 100 sh)
31 450 (24 000 sh)
b
b
b
c
c
Figure 7. Atomic numbering scheme for [Lu(L13)(NO3)3]. Ellipsoids
are represented at the 50% probability level.
28 570 (28 500)
[Y(L14)(NO3)3] (29) 33 500 (25 200 sh)
31 450 (24 100 sh)
27 950 (28 400)
[Lu(L14)(NO3)3] (28) 33 430 (26 200)
31 430 (28 500 sh)
27 980 (28 900)
[Eu(L14)(NO3)3] (24) 33 300 (24 400)
31 420 (24 100 sh)
28 800 (23 200)
[Tb(L14)(NO3)3] (25) 33 300 (28 700)
31 250 (26 200 sh)
28 900 (25 600)
a Energies are given for the maximum of the band envelope in cm-1
,
and the molar absorption coefficient (ꢀ) is given in parentheses in
M-1‚cm-1; sh ) shoulder. b Not measured. c Not detected due to
L14fLn(III) energy transfer.
Figure 6. Emission spectra of L7, L14, L16, and L17 (10-5 M) in CH3-
CN/CH2Cl2 (7:3) at 298 K. The intensities for L7 and L16 are divided
by a factor of 5 (λexc are given in Table 3).
Figure 8. ORTEP24 view of three stacked complexes in the unit cell.
1.46 Å and r(O) ) 1.31 Å amounts to 1.027 Å, in agreement
with the expected value of 1.032 Å for nine-coordinate Lu-
(III).33 The CH2-O spacers between the benzimidazole rings
and the 4-methoxyphenyl sidearms adopt a slightly staggered
antiperiplanar conformation (dihedral angles Cbzim-C-O-
Cphenyl ) 167.8(5)° and 160.5(5)°), which results in a quasi-
linear arrangement of the two connected aromatic moieties, as
similarly found in the crystal structure of L13. However, the
cis-cis conformation of the coordinated bis(benzimidazole)-
pyridine unit induces a U-shaped arrangement of the ligand
strand associated with a reduced separation between the terminal
oxygen atoms (O2‚‚‚O4 ) 14.90 Å) compared to that found in
the free ligand L13 (O2‚‚‚O4 ) 29.07 Å). The coordinated
bidentate nitrate groups fill the free space between the branches
positions around the metal, leading to a low-symmetry nine-
coordinate Lu atom, as similarly reported for the closely related
complex [Eu(L5)(NO3)3].14 Selected bond distances and bond
angles are given in Table 4. Figure 7 shows the atomic
numbering scheme, and Figure 8 shows an ORTEP24 view
illustrating the intermolecular stacking interactions observed in
the unit cell.
The Lu-N(bzim) bond distances are ca. 0.1 Å shorter than
the Lu-N(py) as a result of the larger ionic radius of Lu(III)
(compared to 3d-block metal ions), as reported for the related
1:2 complex [Lu(L3)2(CH3OH)(OH2)]3+ 15
The Lu-O distances
.
are within standard values (2.328-2.50 Å, average 2.377 Å),
except for Lu-O101, which is slightly longer. The calculated
ionic radius of Lu(III) using Shannon’s definition33 and r(N) )
(33) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.

Bent Tridentate Receptors in Calamitic Mesophases
J. Am. Chem. Soc., Vol. 120, No. 47, 1998 12281
Table 4. Selected Bond Distances (Å) and Bond Angles (Deg) for [Lu(L13)(NO3)3]‚3CH3CN (30)
Bond Distances
Lu-N1
2.382(5)
2.476(5)
2.362(5)
1.372(8)
1.436(8)
1.272(9)
1.234(9)
1.216(8)
Lu-O101
Lu-O102
Lu-O201
C4-C8
2.500(4)
2.328(4)
2.368(5)
1.505(9)
1.373(8)
1.265(8)
1.28(1)
Lu-O202
Lu-O301
Lu-O302
C28-O3
C24-C28
N300-O301
N300-O302
N300-O303
2.357(5)
2.341(4)
2.423(5)
1.437(7)
1.505(9)
1.253(8)
1.292(8)
1.205(9)
Lu-N3
Lu-N4
C9-O1
C8-O1
C29-O3
N100-O101
N100-O102
N100-O103
N200-O201
N200-O202
N200-O203
1.21(1)
Bite Angles
N1-Lu-N3
O101-Lu-O102
66.2(2)
52.5(2)
N3-Lu-N4
66.4(2)
54.2(2)
N1-Lu-N4
O301-Lu-O302
132.4(2)
53.5(2)
O201-Lu-O202
N-Lu-O Angles
N1-Lu-O101
N1-Lu-O102
N3-Lu-O101
N3-Lu-O102
N4-Lu-O101
N4-Lu-O102
122.3(2)
74.3(2)
113.1(2)
75.7(2)
73.6(2)
89.9(2)
N1-Lu-O201
N1-Lu-O202
N3-Lu-O201
N3-Lu-O202
N4-Lu-O201
N4-Lu-O202
134.1(2)
86.2(2)
155.7(2)
150.0(2)
93.0(2)
N1-Lu-O301
N1-Lu-O302
N3-Lu-O301
N3-Lu-O302
N4-Lu-O301
N4-Lu-O302
104.9(2)
73.8(2)
81.4(2)
106.9(2)
72.2(2)
125.4(2)
138.1(2)
O-Lu-O Angles
O101-Lu-O201
O101-Lu-O302
O102-Lu-O301
O201-Lu-O302
70.1(2)
139.9(2)
155.3(2)
73.7(2)
O101-Lu-O202
O102-Lu-O201
O102-Lu-O302
O202-Lu-O302
70.9(2)
118.9(2)
143.3(2)
74.3(2)
O101-Lu-O301
O102-Lu-O202
O201-Lu-O301
O202-Lu-O301
132.7(2)
85.9(2)
80.0(2)
118.8(2)
Table 5. Corrected Integrated Intensities (Irel) and Main Identified
of the U-shaped ligand strand, and two weak CH‚‚‚O hydrogen
bonds (C3‚‚‚O202 ) 3.050(8) Å, C3-H3‚‚‚O202 ) 139.2(3)°
and C23‚‚‚O201 ) 3.310(8) Å, C23-H23‚‚‚O201 ) 134.7-
(3)°) may be proposed according to recently published criteria.34
The packing in the unit cell is controlled by two almost
perpendicular π-stacking interactions. Head-to-tail dimers result
from the stacking of the almost coplanar pyridine-benzimidazole-
(N4,N5) unit of one complex (dihedral interplanar angle 12.1°)
with the almost coplanar benzimidazole(N1,N2)-phenyl(C9-
C14) unit (dihedral interplanar angle 13.3°) of the symmetry-
related complex 3/2-x, 1/2+y, 1/2-z (average distance between
stacked plane, 3.75 Å, Figure 8). Pairs of head-to-tail dimers
are then formed in a perpendicular direction via a second
intermolecular π-stacking interaction involving the phenyl rings
(C29-C34) of two complexes related by an inversion center
(1-x, 1-y, 1-z; interplane distance, 3.75 Å). This latter
interaction is likely responsible for (i) the almost orthogonal
arrangement (dihedral interplanar angle, 85.2°, Table S12) of
the phenyl (C29-C34) and benzimidazole (N4, N5) rings within
one ligand strand and (ii) the production of double layers of
complexes running perpendicular to the [101] direction in the
unit cell.
7
Eu(7Fj) Energy Levels (cm-1, j ) 1-4, origin F0) in
[Eu(L14)(NO3)3H2O] (24) As Calculated from Luminescence Spectra
in the Solid State at 10 and 295 K and in Acetonitrile Solution
(295 K)
level
10 K
Irel
295 K
Irel
295 Ka
Irel
b
7F0 (λexc
)
17 229
336
17 244
341
17 238c
312
7F1
1.00
1.00
1.00
363
366
380
414
978
418
982
460
966
7F2
7.17
8.20
5.95
1015
1032
1063
1305
1838
1884
2588
2627
2668
2704
2862
2963
1032
1069
1070
1113
1302
7F3
7F4
0.09
0.96
1852
1890
2595
2681
2870
2964
0.05
1.07
1839
1918
2612
2704
2857
2968
0.09
1.00
5
a 10-4 M in acetonitrile. b Energy of the D0r7F0 transition (given
in cm-1) used as λexc for the laser-excited emission spectra. c Excitation
via the ligand states (25 316 cm-1).
Photophysical Properties of Complexes [Ln(L14)(NO3)3]‚
H2O (Ln ) Eu, 24; Gd, 25; Tb, 26; Lu, 28). Upon
complexation of L14 to Ln(III), the intense πfπ* transition
centered at 31 050 cm-1 is split into two main components at
28 000 and 33 000 cm-1, as previously reported for L3 and
L7.14,15 This observation reflects the electronic transformations
associated with the trans-trans f cis-cis conformational
change and the complexation of the lanthanide metal ions to
the tridentate binding unit. Simple theoretical calculations15
using EHMO have associated the observed variations in the
electronic spectra with a reorganization of the aromatic π
orbitals. The solid-state emission spectra of [Gd(L14)(NO3)3]
(25) and [Lu(L14)(NO3)3] (28) recorded upon excitation of the
ligand-centered transitions are similar to that observed for the
going from Gd to Lu (∆E ) 2960 cm-1) is reminiscent of a
similar but reduced difference in the emission of the triplet states
3ππ* arising at 21 800 cm-1 for Gd and 20 900 cm-1 for Lu
(Table 2, values are given for the 0-0 phonon transition). These
features closely match those previously discussed for [Ln(L3)-
1
(NO3)3] (Ln ) Gd, Lu),14 except for a blue shift of the ππ*
state in [Ln(L14)(NO3)3] (∆E ) 3800 cm-1 for Ln ) Gd and
980 cm-1 for Ln ) Lu). In the Eu complex 24 and Tb complex
26, the ligand-centered 3ππ* phosphorescence vanishes, leading
to typical metal-centered emission.13-15 However, a residual
1
faint emission of the ππ* emission is observed at 77 K for
both complexes (Table 2), which implies an incomplete
L14fLn(III) energy transfer in these complexes. Eu(III) in 24
has been used as a luminescent structural probe to investigate
the nature and geometry of the coordination site.35 Excitation
via the ligand-centered 1ππ* state and direct laser excitation of
1
free ligand L14 with ππ* excited states located at 27 470 (Ln
) Gd) and 24 510 cm-1 (Ln ) Lu). The energy difference on
(34) Steiner, T. Chem. Commun. 1997, 727. Desiraju, G. R. Acc. Chem.
Res. 1996, 29, 441.

12282 J. Am. Chem. Soc., Vol. 120, No. 47, 1998
Nozary et al.
Table 6. Selected Observed Lifetimes (τ, ms) of the Eu(5D0) and Tb(5D4) Levels in [Ln(L14)(NO3)3H2O] (Ln ) Eu, 24; Tb, 26) at Various
Temperatures in the Solid State and in Degassed Acetonitrile Solution
compd
λ
exc/cm-1
10 K
77 K
200 K
250 K
295 K
295 K (solution)
0.728(2)
24
24
24
26
26
26
32 468
27 027
17 256
32 468
27 170
20 492
0.598(2)
0.605(2)
0.597(2)
1.20(1)
1.13(1)
1.16(1)
0.587(2)
0.610(7)
0.585(1)
1.19(1)
1.09(3)
1.11(1)
0.581(2)
0.606(2)
0.579(1)
0.58(1)
0.54(1)
0.55(1)
1.05(1)
0.77(1)
0.97(1)
0.92(1)
0.78(1)
0.84(1)
a
a Too weak to be measured.
energy of the 5D0r7F0 transition ν˜ depends on the ability of ni
coordinating atoms to produce a nephelauxetic effect δi:39 ν˜ -
ν˜0 ) CCn∑iniδi, where CCN is a function of the total coordination
number of the Eu(III) ion (0.95 for CN ) 10) and ν˜0 ) 17 374
cm-1 at 295 K. Taking δN(N-heterocyclic) ) -15.3,20,40
δO(NO3-) ) -13.3,14 and δO(H2O) ) -9.9,39 we calculate ν˜0
) 17 245 cm-1 for 10-coordinate Eu(III) in [Eu(L14)(NO3)3-
(H2O)] at 295 K, a value which almost exactly fits the
experiment (17 244 cm-1) and supports the latter formulation
of the complex.
Excitation of the ligand-centered 1ππ* excited state in 26 at
room temperature produces only weak Tb-centered emission
bands assigned to 5D4f7Fj (j ) 1-6) transitions whose
intensities significantly increase upon cooling the sample (Figure
F1). The lifetime of the Tb(5D4) level measured under direct
laser excitation of the 5D4r7F6 transition is temperature
dependent, decreasing from 1.16 ms at 10 K to 0.55 ms at 295
K (Table 6), pointing to a particular quenching process operating
in this complex. Analysis of τ(5D4) in the range 40-295 K
according to an Arrhenius plot of the type ln(τ-1 - τ0-1) ) A -
(Ea/RT) (τ0 is the lifetime in the absence of quenching process,
taken here as τ at 10 K)41 gives a straight line corresponding to
an activation energy, Ea ) 200 ( 50 cm-1, very similar to that
found for Tb(5D4)f3ππ* energy back transfer in a Tb complex
with a calixarene (Ea ) 180 cm-1).41 We conclude that a related
back transfer occurs in 26 as previously proposed for the
analogous complex [Tb(L3)(NO3)3(CH3OH)].14 Following the
same reasoning as above with AH2O ) 4.2,37 τH O ) 1.16 ms (at
Figure 9. Emission spectra of [Eu(L14)(NO3)3(H2O)] (24) measured
under excitation through the ligand levels at various temperatures.
7
the F0f5D0 transition between 10 and 295 K produce very
similar emission spectra, except for the expected better resolu-
tion at low temperature. The maximum multiplicity (2J + 1)
5
observed for the D0f7Fj (j ) 1, 2; Table 5) and the sizable
5
relative intensity of the D0f5F2 point to an Eu(III) ion in a
low-symmetry site, which is compatible with the C1 symmetry
observed in the crystal structure of the model complex [Lu-
(L13)(NO3)3]‚3CH3CN (30). The lifetime of the Eu(5D0) level
in 24 does not display significant temperature dependence, in
agreement with negligible energy back transfer to the 3ππ* level
2
Tb
5
located 3750 cm-1 above the emitting D0 level.36 Its short
10 K where no back transfer remains), and τD O ≈ 1.87 ms
2
value (0.579 ms) can be compared with that found for [Eu(L3)-
(NO3)3(CH3OH)], 0.840 ms,14 where one methanol molecule is
bound to Eu(III), and points to water interaction in the first
coordination sphere. The empirical equation of Horrocks and
([Tb(NO3)3(MeCN)3]35,38), we find q ) 1.4. As for the Eu
complex, the water molecule in [Tb(L14)(NO3)3]‚H2O (26) is
therefore bound in the first coordination sphere, leading to the
correct formulation [Tb(L14)(NO3)3(H2O)].
Sudnick37 allows one to determine the number of coordinated
Thermal Behavior of Complexes [La(L14)(NO3)3]‚3H2O
(22) and [Ln(L14)(NO3)3]‚H2O (Ln ) Sm, 23; Eu, 24; Gd,
25; Tb, 26; Yb, 27; Lu, 28; Y, 29). According to (i) the
elemental analyses of complexes 22-29 (Table S13), (ii) the
metal-centered luminescence lifetimes for 24 and 26, and (iii)
the crystal structure of 30, we deduce that one water molecule
completes the first coordination sphere, leading to 10-coordinate
metal sites for larger Ln(III) ions (Ln ) La-Tb), while smaller
ions (Ln ) Yb, Lu, Y) are nine-coordinate, with one interstitial
water molecule. The IR spectra of complexes 22-29 cor-
roborate this statement and show a broad absorption in the range
3300-3500 cm-1 for Ln ) La-Tb assigned to a coordinated
water molecule, while the observation of only one narrow
transition at 3640 cm-1 for complexes 27-29 is characteristic
of lattice hydrogen-bonded water molecules.42 Thermal analyses
based on DSC and thermogravimetry show the latter complexes
-1
H2O
water molecules: q ) AHEuO(τ
- τ-H1O), with AEHuO ) 1.05. In
2
2
2
our case, the lifetime in the absence of OH oscillators bound to
Eu(III) may be estimated to lie in the range 1.11 < τD O
<
2
1.35 ms, the lower and upper values corresponding respectively
to τ measured for [Eu(L5)(NO3)3]14 and [Eu(NO3)3(CH3-
CN)3]35,38 at 295 K. We find 0.87 < q < 1.04 and conclude
that [Eu(L14)(NO3)3]‚H2O is better formulated as [Eu(L14)-
(NO3)3(H2O)], with one water molecule bound to Eu(III),
leading to a low-symmetry 10-coordinate metal ion. Moreover,
the 5D0r7F0 excitation spectrum consists of a single band
(17 244 cm-1, full width at half-height (fwhh) ) 7.7 cm-1 at
295 K), implying a unique coordination site for Eu(III). The
(35) Bu¨nzli, J.-C. G. In Lanthanide Probes in Life, Chemical and Earth
Sciences; Bu¨nzli, J.-C. G., Choppin, G. R., Eds.; Elsevier Publishing Co.:
Amsterdam, 1989; Chapter 7.
(36) Latva, M.; Takalo, H.; Mukkala, V.-M.; Matachescu, C.; Rodriguez-
Ubis, J. C.; Kankare, J. J. Luminesc. 1997, 75, 149.
(37) Horrocks, W. deW., Jr.; Sudnick, D. R. J. Am. Chem. Soc. 1979,
101, 334. Horrocks, W. deW., Jr.; Sudnick, D. R. Science 1979, 206, 1194.
(38) Bu¨nzli, J.-C.G.; Milicic-Tang, A.; Mabillard, C. HelV. Chim. Acta
1993, 76, 1292. Bu¨nzli, J.-C.G; Yersin, J.-R. Inorg. Chim. Acta 1984, 94,
301.
(39) Frey, S. T.; Horrocks, W. deW., Jr. Inorg. Chim. Acta 1995, 229,
383.
(40) Piguet, C.; Bu¨nzli, J.-C. G.; Bernardinelli, G.; Hopfgartner, G.;
Petoud, S.; Schaad, O. J. Am. Chem. Soc. 1996, 118, 6681.
(41) Charbonnie`re, L. J.; Balsiger, C.; Schenk, K. J.; Bu¨nzli, J.-C. G. J.
Chem. Soc., Dalton Trans. 1998, 505.

Bent Tridentate Receptors in Calamitic Mesophases
J. Am. Chem. Soc., Vol. 120, No. 47, 1998 12283
Figure 11. Spectrophotometric titration of L14 (10-4 M in CH3CN/
CH2Cl2 ) 1:1) by Lu(NO3)3‚2.7H2O for Lu:L14 ratio in the range 0.1-
1.8.
the melting KfSA process of the free ligand) are systematically
detected for 22-26 prior to decomposition.
Structure of Complexes [La(L14)(NO3)3]‚3H2O (22) and
[Ln(L14)(NO3)3]‚H2O (Ln ) Sm, 23; Eu, 24; Gd, 25; Tb, 26;
Yb, 27; Lu, 28; Y, 29) in Solution. The splitting of the ligand-
centered πfπ* transition of L14 upon complexation to Ln(III)
(Ln ) La-Lu) previously discussed in the solid state can be
easily monitored by spectrophotometry in solution (Figure 11).
Titrations of L14 (10-4 M in 1:1 CH3CN/CH2Cl2) with Ln-
(NO3)3‚3H2O (Ln ) La, Sm, Lu) show (i) an end point for Ln:
L14 ) 1.0 and (ii) an isobestic point at 345 nm. These
observations imply the existence of only two absorbing species
in solution according to equilibrium 1, and the data can be
Figure 10. Differential scanning thermogramms of [Lu(L14)(NO3)3]‚
H2O (28): (a) first heating process and (b) second heating process after
a prior 25 °Cf150 °Cf25 °C cycle.
Ln(NO3)3‚3H2O + L14 h [Ln(L14)(NO3)3(H2O)x] +
(3 - x)H2O log(â) (1)
27-29 to lose their lattice water molecule in the range 25-80
°C (Table 1). Subsequent crystal rearrangements produce
complicated DSC traces during the first heating process, but
meltings in the range 190-194 °C are found for the three
complexes (Table 1, Figure 10a). Fast decomposition occurs
in the isotropic liquid which strongly limits reversibility, but a
preliminary cycle 25 °Cf150 °Cf25 °C leads to the exclusive
observation of the endothermic isotropisation process during
the second heating without complications associated with water
loss and crystal rearrangements (Figure 10b). No mesophases
have been detected by polarizing microscopy. For complexes
23-26, the bound water molecule requires higher temperatures
to be removed (90-140 °C), which supports its coordination
to the metal ion, but this process is followed by a fast
decomposition of the complexes on the heated plate. A related
behavior is observed for [La(L14)(NO3)3]‚3H2O (22): two
interstitial water molecules are lost between 25 and 80 °C, while
the coordinated water molecule is removed at 100-125 °C prior
to decomposition. We conclude that no thermotropic meso-
phases are formed during the heating processes for 22-29, but
the thermal properties strongly depend on the size of Ln(III),
as previously noticed in other complexes.17 It is well established
that the stability of nitrate salts varies markedly with the basicity
of the metal, decomposition being significantly delayed for small
cations with high positive charge.43 This may partially explain
the higher thermal stability of 27-29 compared to that of 22-
26, but we cannot exclude (i) some specific destabilization
associated with the removal of the water molecule from the first
coordination sphere in 22-26 and (ii) a partial decomplexation
of the tridentate binding unit with large Ln(III) ions since weak
but observable thin endotherms at 132 °C (corresponding to
satisfactorily fitted with log(âLa) ) 5.7(2), log(âSm) ) 6.0(3),
and log(âLu) ) 6.5(1). The stability constants are comparable
within experimental errors, and despite systematic better fits
with Ln ) Lu, no clear thermodynamic size-discriminating
effect14 is evidenced in solution (the water content of each
titrated solution was similar, with H2O:Ln g 20).
1H NMR titrations in CDCl3 and CD3CN confirm the
formation of 1:1 complexes [Ln(L14)(NO3)3(H2O)x] (Ln ) La,
Sm, Eu, Lu) in solution. However, except in one case (Ln )
Lu, CDCl3), two sets of signals for the same proton and
corresponding to two different complexes are systematically
observed. Two-dimensional {1H-1H}-COSY and NOEDIF
spectra allow the complete attribution of the signals to two
closely related C2V-symmetrical complexes which do not inter-
convert on the NMR time scale at room temperature (seven
signals observed for the aromatic protons of each complex H1-7
,
H8,9, and H10,11 appear as pairs of enantiotopic protons), as
mentioned previously for [Eu(L3)(NO3)3(CH3OH)].14 The com-
plexation of the tridentate binding unit to Ln(III) is demonstrated
by (i) the systematic downfield shift14,15 of the triplet attributed
of H1 upon complexation to La, Y, and Lu and (ii) the strong
NOE effects detected between H8,9 and H2 only compatible with
a cis-cis conformation of the receptor. Table 7 reports the
chemical shifts of the protons of the main complex observed in
solution. The ratios of each complex within the mixture depend
on the solvent used, the temperature, and the metal ion. A
detailed investigation of the NMR spectra of [Y(L14)(NO3)3] in
CD3CN between 253 and 323 K (Table S14) shows these ratios
varying from 70:30 at 243 K to 100:0 at 323 K, pointing to
complexes under thermodynamic equilibrium. Conductivity
measurements for 10-3 M acetonitrile solution of complexes
22-29 at 293 K give molar conductivity ΛM ) 65(5), 77(6),
(42) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 3rd ed.; J. Wiley: New York, 1972; p 226.
(43) Field, B. O.; Hardy, C. J. Q. ReV., Chem. Soc. 1964, 18, 361.

12284 J. Am. Chem. Soc., Vol. 120, No. 47, 1998
Nozary et al.
Table 7. Proton NMR Shifts (with Respect to TMS) for Ligand L14 in CDCl3 and Its Main Complexes [Ln(L14)(NO3)3] (Ln ) La, Sm;
Y, Lu) in CD3CN at 298 Ka
compd
H1
H2
H3
H4
H5
H6,6′
H7,7′
H8,9
H10,11
L14 b
8.06
8.40
8.35
8.51
8.56
8.73
8.35
8.10
7.80
8.33
8.26
8.39
7.50
7.67
7.61
7.77
7.47
7.06
7.46
7.50
7.45
7.61
7.22
7.89
7.91
8.38
7.81
8.18
7.21
5.08
6.95
6.97
6.95
6.98
6.67
6.42
6.84
6.85
6.83
6.84
6.56
6.66
4.80
4.67
4.80
4.73
4.60
4.63
5.18
5.22
5.20
5.22
4.75
4.44
[Lu(L14)(NO3)3]b
[Lu(L14)(NO3)3]
[Y(L14)(NO3)3]
[La(L14)(NO3)3]
[Sm(L14)(NO3)3]
a See Scheme 3 for numbering scheme. b In CDCl3.
85(7), 70(4), 46(6), 30(6), and 28(7) Ω-1 mol-1 cm2 for Ln )
La, Sm, Eu, Gd, Y, Yb, and Lu, respectively, which are
intermediate between nonelectrolyte and 1:1 electrolyte (120-
160 Ω-1 mol-1 cm2) in this solvent.44 These results strongly
suggest a partial decomplexation of the nitrate anion according
to eq 2, which is corroborated by the ES-MS spectra recorded
under the same conditions and showing [Ln(L14)(NO3)2]+ as
being the only charged complex in significant concentration.
quantum yields for Tb in 26 failed as a result of the efficient
back transfer occurring at 295 K.
Conclusions
The mesomorphism observed for L14-17 fully justifies our
initial assumption that semilipophilic sidearms connected to the
5-position of the benzimidazole ring in L3 may compensate the
bent arrangement of the tridentate binding unit. These elongated
receptors behave as rodlike molecules (I-shape) in the solid state
and in the mesophase and melt at reasonable temperatures to
consider them as promising receptors for metallomesogens. Two
points appear to be crucial for the formation of calamitic
mesophases incorporating bent tridentate bis(benzimidazole)-
pyridine receptors: (i) the length and nature of the spacers
between the benzimidazole rings and the phenyl sidearms, which
control the degrees of freedom of the central aromatic moiety,
and (ii) the conformation of the bis(benzimidazole)pyridine core,
which must provide a linear arrangement of the semirigid
lipophilic side chains. Our detailed photophysical investigation
shows that electronic properties are also strongly affected by
the choice of the spacer, which offers fascinating possibilities
for the design of liquid crystals with predetermined photophysi-
cal properties. The drastic structural changes associated with
the trans-trans f cis-cis conformational interconversion
occurring upon complexation of the tridentate binding unit
produces a U-shaped organization of the ligand strand in [LnL14-
(NO3)3(H2O)x] (Ln ) La-Tb, x ) 1; Ln ) Yb, Lu, Y, x ) 0),
being located in the resulting internal cavity. For larger Ln-
(III) ions (La-Tb), decomposition of the complexes occurs at
rather low temperature (∼120-130 °C), thus preventing a
detailed investigation of the thermal behavior. For smaller ions
(Ln ) Gd-Lu, Y), the increased stability resulting from a
combination of improved electrostatic effects with a reduced
coordination number (no water molecule bound to Ln(III))
delays the decomposition processes and allows the observation
of a simple isotropization processes around 190 °C. No
mesogenic behavior is observed for the complexes, and we
tentatively assign this failure essentially to the reduced length/
width ratio associated with the U-shaped arrangement of the
ligand strand in the complex. These results refute the simplistic
idea that mesogenic ligands lead to metallomesogens upon
complexation,1-3 although this approach remains justified when
no major geometrical or structural changes occur upon com-
plexation, as found for pseudo-linear binding units.8,9
[Ln(L14)(NO3)3(H2O)x] + nCH3CN h
[Ln(L14)(NO3)2(H2O)x(CH3CN)n]+ + NO3 (2)
-
We also notice that molar conductivity decreases for small
Ln(III), in agreement with the expected larger electrostatic
interaction. We conclude that complexes 22-29 exist in
solution as thermodynamic mixtures of solvated and averaged
C2V symmetrical complexes [Ln(L14)(NO3)3(H2O)x] and [Ln-
(L14)(NO3)2(H2O)x(CH3CN)n]+, which do not interconvert on
the NMR time scale.
Finally, emission spectra of a 10-4 M solution of [Eu(L14)-
(NO3)3(H2O)] (24) in acetonitrile, for which the 1:1 complex
represents 91% of the ligand speciation (calculated by using
5
log(âEu) ≈ log(âSm) ) 6.0), display D0f7Fj transitions (j )
1-4) whose relative intensities point to low symmetry in
solution compatible with C2V point group.35 Despite the lower
resolution in solution, the crystal field splittings of the 7Fj levels
are different from those reported in the solid state, as revealed
by the total separation of the three components of the 7F1 level
(148 cm-1 in solution compared to 77 cm-1 in the solid) and
7
7
the variable multiplicity of F2 and F4 levels (Table 5, Figure
9), which are attributed to a mixture of at least two complexes
with different coordination spheres around Eu(III) (eq 2).
Excitation profiles of the 7F0f5D0 transition reveal a broad band
(fwhh ) 28.6 cm-1) centered at 17 255 cm-1, compatible with
a mixture of closely related complexes; for instance, we
calculate39 ν˜calc ) 17 245 and 17 250 cm-1 for [Eu(L14)(NO3)3-
(H2O)]) and [Eu(L14)(NO3)2(H2O)(CH3CN)2]+, respectively. The
Eu(5D0) lifetime amounts to 0.728(2) ms, a value only somewhat
longer than that measured in the solid state, indicating that the
coordinated water molecule is maintained in solution and which
is compatible with nitrate decomplexation.38 The emission
quantum yield relative to [Eu(terpy)3]3+ obtained upon irradia-
tion of the ligand (λexc ) 26 667 cm-1) amounts to Φrel ) 0.29,
an order of magnitude lower than that reported for [Eu(L3)-
(NO3)3(CH3OH)] in the same conditions (Φrel ) 2.74).14 This
10-fold decrease cannot be explained by the small difference
in Eu(5D0) lifetimes of the two complexes, but it parallels the
50-fold quenching of the fluorescence intensity (1ππ* state)
observed between L7 and L14, which strongly suggests that the
ligand-centered nonradiative processes associated with the
elongated ligand strand L14 limit the uvfvisible light-converting
process in the Eu complex. Attempts to determine solution
Experimental Section
Solvents and starting materials were purchased from Fluka AG
(Buchs, Switzerland) and used without further purification, unless
otherwise stated. Acetonitrile, dichloromethane, N,N-dimethylform-
amide (DMF), dimethyl sulfoxide (DMSO), and triethylamine were
distilled from CaH2, thionyl chloride from elemental sulfur. The nitrate
salts Ln(NO3)3‚nH2O (Ln ) La to Lu) were prepared from the
corresponding oxides (Glucydur, 99.99%) according to literature
(44) Geary, W. J. Coord. Chem. ReV. 1971, 7, 81.

Bent Tridentate Receptors in Calamitic Mesophases
J. Am. Chem. Soc., Vol. 120, No. 47, 1998 12285
procedures.14 Silica gel (Merck 60, 0.040-0.060 mm) was used for
preparative column chromatography.
was purified by column chromatography (silica gel; CH2Cl2/MeOH 99:
1f97:3) and crystallized from CH2Cl2/hexane to give 2.05 g (4.5 mmol,
yield 80%) of 8 as white microcrystals. 1H NMR in CDCl3: δ 1.37
(6H, t, J3 ) 7 Hz), 3.42 (6H, s), 4.63 (4H, s), 4.80 (4H, q, J3 ) 7 Hz),
7.39 (2H, dd, J3 ) 8 Hz, J4 ) 1 Hz), 7.47 (2H, d, J3 ) 8 Hz), 7.82
(2H, d, J4 ) 1 Hz), 8.06 (1H, t, J3 ) 8 Hz), 8.35 (2H, d, J3 ) 8 Hz).
ES-MS (CH2Cl2): m/z 478.3 ([M + Na]+). The same procedure was
used for the preparation of 2,6-bis(1-ethyl-5-methoxybenzimidazol-2-
yl)pyridine (9) as white microcrystals from 7 (CC, silica gel; CH2Cl2/
MeOH 98:2, yield 60%). 1H NMR in CDCl3: δ 1.36 (6H, t, J3 ) 7
Hz), 3.91 (6H, s), 4.79 (4H, q, J3 ) 7 Hz), 7.03 (2H, dd, J3 ) 9 Hz,
J4 ) 2 Hz), 7.34 (2H, d, J4 ) 2 Hz), 7.36 (2H, d, J3 ) 9 Hz), 8.03
(1H, t, J3 ) 8 Hz), 8.32 (2H, d, J3 ) 8 Hz). ES-MS (CH2Cl2): m/z
428.3 ([M + H]+).
Preparation of 1-Chloro-4-methoxymethyl-2-nitrobenzene (2).
KOH (85%, 7.0 g, 107 mmol) was dissolved in freshly distilled DMSO,
and 1 (5.0 g, 27 mmol) and methyl iodide (9.12 g, 64.2 mmol) were
added in this order. After 1 h of stirring at room temperature, water
(60 mL) was added, and the resulting mixture was extracted with
dichloromethane (3 × 40 mL). The combined organic fractions were
washed with water (5 × 30 mL), dried (Na2SO4), and evaporated, and
the residual oil was distilled (90 °C, 10-2 Torr) to give 4.48 g (22.2
mmol, yield 83%) of 2 as a colorless liquid. 1H NMR in CDCl3: δ
3.44 (3H, s), 4.49 (2H, s), 7.48 (1H, dd, J3 ) 8 Hz, J4 ) 2 Hz), 7.53
(1H, d, J3 ) 8 Hz), 7.85 (1H, d, J4 ) 2 Hz). EI-MS: m/z 201/203
(M+).
Preparation of 2,6-Bis(1-ethyl-5-bromomethylbenzimidazol-2-yl)-
pyridine (10). 2,6-Bis(1-ethyl-5-methoxymethylbenzimidazol-2-yl)-
pyridine (8, 200 mg, 0.439 mmol) was dissolved in dichloromethane
(25 mL), and boron tribromide (1 M in CH2Cl2, 8.78 mL, 0.878 mmol)
was added via a syringe under an inert atmosphere. After 3 h of stirring
at room temperature, water (30 mL) was added, and the aqueous phase
was neutralized until pH ) 7-8 with saturated aqueous NaHCO3. The
organic layer was separated and the aqueous phase extracted with CH2-
Cl2 (3 × 30 mL). The combined organic phases were dried (Na2SO4),
concentrated to 5 mL, filtered on silica gel (CH2Cl2/MeOH 97:3), and
evaporated to dryness. The crude residue was crystallized from CH2-
Cl2/hexane (1:1) to give 223 mg (0.404 mmol, yield 92%) of 10 as
white microcrystals. 1H NMR in CDCl3: δ 1.37 (6H, t, J3 ) 7 Hz),
4.74 (4H, s), 4.77 (4H, q, J3 ) 7 Hz), 7.43 (2H, dd, J3 ) 8 Hz, J4 )
1 Hz), 7.47 (2H, d, J3 ) 8 Hz), 7.88 (2H, s br), 8.07 (1H, t, J3 ) 8
Hz), 8.34 (2H, d, J3 ) 8 Hz). ES-MS (CH2Cl2): m/z 552/554 ([M +
H]+). The same procedure was used for the preparation of 2,6-bis(1-
ethyl-5-hydroxybenzimidazol-2-yl)pyridine (11) from 9, except for the
workup procedure. After neutralization with saturated aqueous NaH-
CO3, the crude solution was evaporated to dryness. The solid residue
was dissolved in a minimum of CH2Cl2/CH3OH (1:1), silica gel (10 g)
was added, and the solvent was evaporated. The resulting powder was
deposited on top of the column and chromatographed (silica gel; CH2-
Cl2/MeOH 99:1f95:5) and then crystallized from CH2Cl2/CH3OH (1:
Preparation of N-Ethyl-(4-methoxymethyl-2-nitrophenyl)amine
(3). 1-Chloro-4-methoxymethyl-2-nitrobenzene (2, 4.48 g, 22.2 mmol)
and ethylamine (70% in water, 50 mL) were heated in an autoclave at
100 °C for 12 h. The dark mixture was evaporated to dryness, extracted
with dichloromethane (100 mL), filtered over Celite, and washed with
half-saturated aqueous NH4Cl solution (30 mL). The organic phase
was dried (Na2SO4), the solvent evaporated, and the resulting oil
distilled (140 °C, 10-2 Torr) to give 3.9 g (18.6 mmol, yield 84%) of
3 as a red oil. 1H NMR in CDCl3: δ 1.37 (3H, t, J3 ) 7 Hz), 3.36
(3H, s), 3.37 (2H, q, J3 ) 7 Hz), 4.34 (2H, s), 6.85 (1H, d, J3 ) 8 Hz),
7.45 (1H, dd, J3 ) 8 Hz, J4 ) 2 Hz), 8.01 (1H, s br), 8.14 (1H, d, J4
) 2 Hz). EI-MS: m/z 210 (M+). The same procedure was used for
the preparation of N-ethyl-(4-methoxy-2-nitrophenyl)amine (5) from
4-chloro-3-nitroanisole (4) yielding red microcrystals (from CH2Cl2/
hexane, yield 90%). 1H NMR in CDCl3: δ 1.36 (3H, t, J3 ) 7 Hz),
3.35 (2H, q, J3 ) 7 Hz), 3.80 (3H, s), 6.83 (1H, d, J3 ) 9 Hz), 7.16
(1H, dd, J3 ) 9 Hz, J4 ) 3 Hz), 7.62 (1H, d, J4 ) 3 Hz), 7.94 (1H, s
br). EI-MS: m/z 196.2 (M+).
Preparation of Bis[N-ethyl-N-(4-methoxymethyl-2-nitrophenyl)]-
pyridine-2,6-dicarboxamide (6). Pyridine-2,6-dicarboxylic acid (4.38
g, 26 mmol) and DMF (50 µL) were refluxed in freshly distilled thionyl
chloride (35 mL) for 45 min. Excess thionyl chloride was distilled
from the reaction mixture, which was then coevaporated with dry
dichloromethane (2 × 20 mL) and dried under vacuum. N-Ethyl-(4-
methoxymethyl-2-nitrophenyl)amine (3) (5.51 g, 26.2 mmol) and
triethylamine (39.4 mL, 0.26 mol) were refluxed in dry dichloromethane
(15 mL), and the solid 2,6-dichlorocarboxypyridine previously prepared
was added. The resulting mixture was refluxed for 8 h, evaporated to
dryness, and partitioned between dichloromethane (3 × 30 mL) and
half-saturated aqueous NH4Cl (30 mL). The combined organic fractions
were evaporated to dryness, and the crude product was purified by
column chromatography (silica gel; CH2Cl2/MeOH 100:0f99.5:0.5)
to give 4.53 g (8.2 mmol, yield 62%) of 6 as a pale yellow powder. 1H
NMR in CDCl3: δ 1.00-1.28 (6H, m), 3.32-3.45 (6H, m), 3.48-
4.26 (4H, m), 4.40-4.56 (4H, m), 7.09 (2H, m), 7.40 (2H, m), 7.38
(2H, m), 7.53 (1H, m), 7.88 (2H, m). ES-MS (CH2Cl2): m/z 552.3
([M + H]+). The same procedure was used for the preparation of bis-
[N-ethyl-N-(4-methoxy-2-nitrophenyl)]pyridine-2,6-dicarboxamide (7)
as a pale yellow powder from 5 (CC, silica gel; CH2Cl2/MeOH 99.8:
0.2f99:1, yield 75%). 1H NMR in CDCl3: δ 1.01-1.24 (6H, m),
3.46-4.27 (4H, m), 3.75-3.91 (6H, m), 6.95 (2H, m), 7.04 (2H, m),
7.39 (2H, m), 7.52 (1H, m), 7.82 (2H, m). ES-MS (CH2Cl2): m/z 524.2
([M + H]+).
1
1) to give 8 as a pale yellow powder (yield 70%). Mp > 250 °C. H
NMR in DMSO-d6: δ 1.27 (6H, t, J3 ) 7 Hz), 4.79 (4H, q, J3 ) 7
Hz), 6.85 (2H, dd, J3 ) 9 Hz, J4 ) 2 Hz), 7.00 (2H, d, J4 ) 2 Hz),
7.50 (2H, d, J3 ) 9 Hz), 8.16 (1H, t, J3 ) 8 Hz), 8.29 (2H, d, J3 ) 8
Hz), 9.20 (2H, s). ES-MS (CH2Cl2): m/z 400.2 ([M + H]+).
Preparation of 3,4-Bis(dodecyloxy)benzoic Acid Dodecyl Ester
(13). 3,4-Dihydroxybenzoic acid (12, 1.0 g, 6.48 mmol) and 1-bro-
mododecane (5.16 g, 20.7 mmol) were dissolved in DMSO (15 mL),
and powdered potassium hydroxide (85%, 1.28 g, 19.4 mmol) was
added in one portion. After 12 h of stirring at 80 °C under an inert
atmosphere, half-saturated aqueous NH4Cl (30 mL) was added, and
the resulting mixture was extracted with dichloromethane (3 × 30 mL).
The combined organic layer was washed with water (5 × 30 mL), dried
(Na2SO4), and evaporated. The crude residue was purified by column
chromatography (silica gel; hexane/CH2Cl2 90:10) to give 3.43 g (5.2
mmol, yield 80%) of 13 as a white powder. Mp 64-65 °C. 1H NMR
in CDCl3: δ 0.90 (9H, t, J3 ) 7 Hz), 1.2-2.0 (60H, m), 4.04 (2H, t,
J3 ) 7 Hz), 4.05 (2H, t, J3 ) 7 Hz), 4.28 (2H, t, J3 ) 7 Hz), 6.86 (1H,
d, J3 ) 8 Hz), 7.54 (1H, d, J4 ) 2 Hz), 7.64 (1H, dd, J3 ) 8 Hz, J4 )
2 Hz). EI-MS: m/z 658.7 (M+).
Preparation of 2,6-Bis-(1-ethyl-5-methoxymethyl-benzimidazol-
2-yl)pyridine (8). Bis[N-ethyl-N-(4-methoxymethyl-2-nitrophenyl)]-
pyridine-2,6-dicarboxamide (6, 3.09 g, 5.6 mmol) was dissolved in
ethanol/water (480 mL:120 mL). Activated iron powder (6.26 g, 0.11
mol) and concentrated hydrochloric acid (37%, 15 mL, 0.18 mol) were
added, and the mixture was refluxed for 12 h. The excess of iron was
filtered and ethanol distilled under vacuum. The resulting mixture was
poured into CH2Cl2 (200 mL), Na2H2EDTA‚2H2O (30 g) dissolved in
water (150 mL) was added, and the resulting stirred mixture was
neutralized (pH ) 8.5) with 24% aqueous NH4OH. Concentrated
hydrogen peroxide (30%, 5 mL) was added under vigorous stirring.
After 15 min, the organic layer was separated and the aqueous phase
extracted with CH2Cl2 (3 × 40 mL). The combined organic phases
were dried (Na2SO4) and evaporated to dryness, and the crude residue
Preparation of 3,4-Bis(dodecyloxy)benzoic Acid (14). 3,4-bis-
(dodecyloxy)benzoic acid dodecyl ester (13, 3.43 g, 5.21 mmol) and
powdered potassium hydroxide (85%, 7.92 g, 0.2 mol) were refluxed
in ethanol/water (1:1, 60 mL) for 12 h. Ethanol was distilled and the
pH adjusted to 3.0 with concentrated hydrochloric acid (37%). The
resulting aqueous phase was extracted with dichloromethane (3 × 30
mL), and the combined organic phases were dried (Na2SO4) and
evaporated to dryness. The crude product was crystallized from hot
ethanol to give 2.02 g (4.11 mmol, yield 79%) of 14 as a white powder.
Mp 58-59 °C. 1H NMR in CDCl3: δ 0.88 (6H, t, J3 ) 7 Hz), 1.2-
1.9 (40H, m), 4.05 (2H, t, J3 ) 7 Hz), 4.07 (2H, t, J3 ) 7 Hz), 6.89
(1H, d, J3 ) 8 Hz), 7.58 (1H, d, J4 ) 2 Hz), 7.72 (1H, dd, J3 ) 8 Hz,
J4 ) 2 Hz). EI-MS: m/z 490.4 (M+).

12286 J. Am. Chem. Soc., Vol. 120, No. 47, 1998
Nozary et al.
Preparation of 4-Dodecyloxyphenol (17). p-Hydroquinone (5.5
g, 50 mmol), 1-bromododecane (12.46 g, 50 mmol), and potassium
hydrogen carbonate (5.0 g, 50 mmol) were refluxed in dioxane/water
(1:1, 200 mL) for 12 h. Dioxane was distilled and the pH adjusted to
3.0 with concentrated hydrochloric acid (37%). The resulting aqueous
phase was extracted with dichloromethane (3 × 30 mL), and the
combined organic phases were dried (Na2SO4) and evaporated to
dryness. The crude product was purified by column chromatography
(silica gel; CH2Cl2) to give 4.2 g (14.6 mmol, yield 29%) of 13 as a
white powder. Mp 74-75 °C. 1H NMR in CDCl3: δ 0.88 (3H, t, J3
) 7 Hz), 1.25-1.75 (20H, m), 3.89 (2H, t, J3 ) 7 Hz), 4.42 (1H, s),
6.75 (2H, dd, J3 ) 9 Hz, J4 ) 2 Hz), 6.78 (2H, dd, J3 ) 9 Hz, J4 ) 2
Hz). EI-MS: m/z 278.3 (M+). The same procedure was used to prepare
18 from p-hydroquinone and 1-bromohexadecane (yield ) 20%). Mp
85 °C. 1H NMR in CDCl3: δ 0.88 (3H, t, J3 ) 7 Hz), 1.25-1.75
(29H, m), 3.89 (2H, t, J3 ) 7 Hz), 6.75 (2H, dd, J3 ) 9 Hz, J4 ) 2
Hz), 6.78 (2H, dd, J3 ) 9 Hz, J4 ) 2 Hz). EI-MS: m/z 334 (M+).
Preparation of 4-Dodecyloxybenzyl Alcohol (20). LiAlH4 (247
mg, 6.53 mmol) was dissolved in dry tetrahydrofuran (90 mL), and
4-dodecyloxybenzoic acid (19, 2.0 g, 6.53 mmol) dissolved in tetrahy-
drofuran (10 mL) was slowly added under an inert atmosphere. The
resulting mixture was refluxed for 10 h. The remaining LiAlH4 was
destroyed with an excess of water, and the resulting heterogeneous
mixture was evaporated to dryness and partitioned between CH2Cl2
and water. The organic phase was carefully separated and the aqueous
phase extracted with dichloromethane (3 × 30 mL), and the combined
organic phases were filtered, dried (Na2SO4), and evaporated to dryness.
The crude product was crystallized from CH2Cl2/hexane to give 1.6 g
(5.48 mmol, yield 84%) of 20 as a white powder. Mp 67 °C. 1H
NMR in CDCl3: δ 0.88 (3H, t, J3 ) 7 Hz), 1.3-1.8 (20H, m), 3.95
(2H, t, J3 ) 7 Hz), 4.62 (2H, s), 6.88 (2H, d, J3 ) 9 Hz), 7.28 (2H, dd,
J3 ) 9 Hz). EI-MS: m/z 292 (M+).
and 2,6-bis{1-ethyl-5-[4-(R-oxy)phenoxymethyl]benzimidazol-2-yl}-
pyridine (R ) methyl, L13, yield 84%; R ) dodecyl, L14, yield 82%;
and R ) hexadecyl, L15, yield 79%) with respectively 14, 16-18 as
sidearms.
L12. Mp 89 °C. 1H NMR in CDCl3: δ 0.87 (12H, t, J3 ) 7 Hz),
1.42 (6H, t, J3 ) 7 Hz), 1.2-1.8 (80H, m), 4.03 (4H, t, J3 ) 7 Hz),
4.04 (4H, t, J3 ) 7 Hz), 4.80 (4H, q, J3 ) 7 Hz), 5.51 (4H, s), 6.85
(2H, d, J3 ) 9 Hz), 7.49 (4H, m), 7.58 (2H, d, J4 ) 2 Hz), 7.70 (2H,
dd, J3 ) 9 Hz, J4 ) 2 Hz), 8.00 (2H, s), 8.10 (1H, t, J3 ) 8 Hz), 8.35
(2H, d, J3 ) 8 Hz). 13C NMR in CDCl3: δ 14.15, 15.47 (primary C);
22.73, 26.01, 29.10, 29.24, 29.41, 29.43, 29.66, 29.80, 31.96, 40.07,
66.86, 69.05, 69.38 (secondary C); 110.45, 111.93, 114.48, 120.12,
122.43, 123.78, 124.48, 126.18, 138.42 (tertiary C); 131.62, 135.65,
148.58, 149.59, 150.12, 153.37, 166.46, 180.97 (quaternary C). ES-
MS (CH2Cl2): m/z 1372.9 ([M + H]+).
L13. Mp 195 °C. 1H NMR in CDCl3: δ 1.37 (6H, t, J3 ) 7 Hz),
3.77 (6H, s), 4.80 (4H, q, J3 ) 7 Hz), 5.19 (4H, s), 6.84 (4H, d, J3 )
9 Hz), 6.96 (4H, d, J3 ) 8 Hz), 7.46 (2H, d, J3 ) 8 Hz), 7.50 (2H, d,
J3 ) 8 Hz), 7.92 (2H, s), 8.06 (1H, t, J3 ) 8 Hz), 8.35 (2H, d, J3 ) 8
Hz). 13C NMR in CDCl3: δ 15.49, 55.77 (primary C); 22.75, 39.97,
71.15 (secondary C); 110.46, 114.69, 115.99, 119.69, 123.58, 125.79,
135.77 (tertiary C); 132.13, 138.18, 142.90, 149.90, 150.37, 153.00,
153.90 (quaternary C). ES-MS (CH2Cl2): m/z 640.1 ([M + H]+).
L14. Mp 188 °C. 1H NMR in CDCl3: δ 0.88 (6H, t, J3 ) 7 Hz),
1.42 (6H, t, J3 ) 7 Hz), 1.2-1.8 (40H, m), 3.90 (4H, t, J3 ) 7 Hz),
4.80 (4H, q, J3 ) 7 Hz), 5.18 (4H, s), 6.84 (4H, d, J3 ) 9 Hz), 6.95
(4H, d, J3 ) 8 Hz), 7.46 (2H, d, J3 ) 8 Hz), 7.50 (2H, d, J3 ) 8 Hz),
7.97 (2H, s), 8.06 (1H, t, J3 ) 8 Hz), 8.35 (2H, d, J3 ) 8 Hz). 13C
NMR in CDCl3: δ 14.17, 15.49 (primary C); 22.73, 26.10, 29.45, 29.65,
31.96, 39.97, 66.68, 71.13 (secondary C); 110.44, 115.44,115.94,
119.68, 123.60, 125.80, 138.18 (tertiary C); 132.20, 135.75, 142.05,
149.93, 150.33, 152.88, 153.53 (quaternary C). ES-MS (CH2Cl2): m/z
948.5 ([M + H]+).
Preparation of 4-Dodecyloxybenzyl Bromide (21). 4-Dodecyl-
oxybenzyl alcohol (20, 1.2 g, 4.2 mmol) and phosphorus tribromide
(550 mg, 2.04 mmol) were refluxed for 15 h in dichloromethane (75
mL). Excess PBr3 was hydrolyzed with water (20 mL) and brine (80
mL). The organic phase was separated and the aqueous phase extracted
with dichloromethane (3 × 30 mL), and the combined organic phases
were dried (Na2SO4) and evaporated to dryness. The crude product
was crystallized from CH2Cl2 to give 1.46 g (4.10 mmol, yield 99%)
of 21 as white microcrystals. Mp 42-43 °C. 1H NMR in CDCl3: δ
0.88 (3H, t, J3 ) 7 Hz), 1.3-1.8 (20H, m), 3.95 (2H, t, J3 ) 7 Hz),
4.51 (2H, s), 6.85 (2H, d, J3 ) 9 Hz), 7.30 (2H, dd, J3 ) 9 Hz). EI-
MS: m/z 354/356 (M+).
L15. Mp 184 °C. 1H NMR in CDCl3: δ 0.88 (6H, t, J3 ) 7 Hz),
1.42 (6H, t, J3 ) 7 Hz), 1.2-1.8 (56H, m), 3.90 (4H, t, J3 ) 7 Hz),
4.80 (4H, q, J3 ) 7 Hz), 5.18 (4H, s), 6.84 (4H, d, J3 ) 9 Hz), 6.95
(4H, d, J3 ) 8 Hz), 7.46 (2H, d, J3 ) 8 Hz), 7.50 (2H, d, J3 ) 8 Hz),
7.97 (2H, s), 8.06 (1H, t, J3 ) 8 Hz), 8.35 (2H, d, J3 ) 8 Hz). 13C
NMR in CDCl3: δ 14.17, 15.49 (primary C); 22.73, 26.10, 29.45, 29.65,
31.96, 39.97, 66.68, 71.13 (secondary C); 110.44, 115.44, 115.94,
199.68, 123.60, 125.80, 138.18 (tertiary C); 132.20, 135.75, 142.95,
149.93, 150.33, 152.88, 153.53 (quaternary C). ES-MS (CH2Cl2): m/z
1060.5 ([M + H]+).
Preparation of 2,6-Bis[1-ethyl-5-(4-dodecyloxy)benzyloxybenz-
imidazol-2-yl]pyridine (L16). A suspension of 2,6-bis(1-ethyl-5-
hydroxy-benzimidazol-2-yl)pyridine (11, 300 mg, 0.751 mmol) in
dichloromethane (10 mL) was reacted with tetra-n-butylammonium
hydroxide (0.38 M in methanol, 4.34 mL, 1.65 mmol). After complete
solubilization, the solvent was evaporated and the resulting salt dried
under vacuum and redissolved in dry dichloromethane (20 mL).
4-Dodecyloxybenzyl bromide (21, 586 mg, 1.65 mmol) in dry dichlo-
romethane (10 mL) was added and the solution refluxed for 10 h under
an inert atmosphere. The standard workup described for L11 gave 410
mg (0.43 mmol, yield 57%) of L16, which was crystallized from CH2-
Cl2/hexane. Mp 193 °C. 1H NMR in CDCl3: δ 0.88 (6H, t, J3 ) 7
Hz), 1.40 (6H, t, J3 ) 7 Hz), 1.3-1.8 (40H, m), 3.96 (4H, t, J3 ) 7
Hz), 4.77 (4H, q, J3 ) 7 Hz), 5.08 (4H, s), 6.91 (4H, d, J3 ) 9 Hz),
7.10 (2H, dd, J3 ) 8 Hz, J4 ) 2 Hz), 7.36 (2H, d, J3 ) 8 Hz), 7.40
(4H, d, J3 ) 8 Hz), 7.42 (2H, s), 8.04 (1H, t, J3 ) 8 Hz), 8.32 (2H, d,
J3 ) 8 Hz). 13C NMR in CDCl3: δ 14.17, 15.56 (primary C); 22.74,
26.00, 29.41, 31.96, 39.92, 68.10, 70.59 (secondary C); 103.61, 110.72,
114.63, 114.95, 125.47, 129.34, 138.00 (tertiary C); 128.90, 155.81,
159.07 (quaternary C). ES-MS (CH2Cl2): m/z 948.3 ([M + H]+). The
same procedure was used for the syntheses of 2,6-bis[1-ethyl-5-(4-
dodecyloxybenzoic ester) benzimidazol-2-yl]pyridine (L17) from the acyl
chloride of 19 (yield 60%).
Preparation of 2,6-Bis[1-ethyl-5-(4-dodecyloxybenzoic acid) meth-
yl ester benzimidazol-2-yl]pyridine (L11). 4-Dodecyloxybenzoic acid
(19, 336 mg, 1.09 mmol) and tetra-n-butylammonium hydroxide (0.1
M in 2-propanol/methanol, 10.9 mL, 1.09 mmol) were dissolved in
dichloromethane (10 mL). The solvent was evaporated to dryness and
the resulting salt dried under vacuum. 2,6-Bis(1-ethyl-5-bromometh-
ylbenzimidazol-2-yl)pyridine (10, 200 mg, 0.361 mmol) in dry dichlo-
romethane (20 mL) was poured onto the salt under an inert atmosphere
and stirred for 48 h. Half-saturated aqueous NH4Cl (50 mL) was added,
the organic layer separated, and the aqueous phase extracted with CH2-
Cl2 (3 × 30 mL). The combined organic phases were dried (Na2SO4)
and evaporated to dryness, and the crude residue was purified by column
chromatography (silica gel; CH2Cl2/MeOH 100:0f99:1) to give 370
mg (0.369 mmol, yield 84%) of L11 as a white precipitate. Mp 103-
104 °C. 1H NMR in CDCl3: δ 0.88 (6H, t, J3 ) 7 Hz), 1.37 (6H, t,
J3 ) 7 Hz), 1.1-1.8 (40H, m), 4.00 (4H, t, J3 ) 7 Hz), 4.80 (4H, q,
J3 ) 7 Hz), 5.50 (4H, s), 6.90 (4H, d, J3 ) 9 Hz), 7.46 (2H, d, J3 )
8 Hz), 7.50 (2H, d, J3 ) 8 Hz), 7.97 (2H, s), 8.02 (4H, d, J3 ) 9 Hz),
8.07 (1H, t, J3 ) 8 Hz), 8.36 (2H, d, J3 ) 8 Hz). 13C NMR in CDCl3:
δ 14.18, 15.51 (primary C); 22.74, 26.03, 29.16, 29.41, 29.63, 29.69,
31.96, 39.99, 66.87, 68.26 (secondary C); 110.37, 114.09, 120.25,
122.38, 124.15, 125.82, 131.77, 138.00 (tertiary C); 131.21, 143.01,
145.69, 149.92, 150.48, 163.07, 166.40, 180.97 (quaternary C). ES-
MS (CH2Cl2): m/z 1004.6 ([M + H]+).
L17. Mp 226 °C. 1H NMR in CDCl3: δ 0.88 (6H, t, J3 ) 7 Hz),
1.40 (6H, t, J3 ) 7 Hz), 1.3-1.8 (40H, m), 4.60 (4H, t, J3 ) 7 Hz),
4.81 (4H, q, J3 ) 7 Hz), 7.00 (4H, d, J3 ) 9 Hz), 7.23 (2H, dd, J3 )
8 Hz, J4 ) 2 Hz), 7.51 (2H, d, J3 ) 8 Hz), 7.68 (4H, d, J4 ) 2 Hz),
8.08 (1H, t, J3 ) 8 Hz), 8.10 (4H, d, J3 ) 9 Hz), 8.36 (2H, d, J3 ) 8
Preparation of Ligands L12-L15. The same procedure as above
was used for the syntheses of 2,6-bis{1-ethyl-5-[3,4-bis(dodecyloxy)-
benzoic acid] methyl ester benzimidazol-2-yl}pyridine (L12, yield 80%)

Bent Tridentate Receptors in Calamitic Mesophases
Table 8. Summary of Crystal Data, Intensity Measurements, and Structure Refinement for L,13 L16, and [Lu(L13)(NO3)3]‚3CH3CN (30)
L13 L16 [Lu(L13)(NO3)3]
C39H37N5O4 C61H81N5O4 LuC45H46N11O13
J. Am. Chem. Soc., Vol. 120, No. 47, 1998 12287
formula
mol wt
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
639.8
triclinic
P1h
948.3
triclinic
P1h
1123.9
monoclinic
C2/c
21.273(1)
19.9614(6)
23.0538(7)
90
102.322(3)
90
9564.0(6)
8
10.315(1)
11.8767(7)
14.170(2)
105.076(5)
108.972(6)
95.109(5)
1556.2(2)
2
1.37
676
0.721
1.102/1.186
8.7732(8)
10.686(1)
29.997(5)
90.134(8)
94.383(8)
108.593(8)
2656.6(6)
2
1.19
1028
0.574
1.042/1.209
Z
D
F(000)
calc, g‚cm-3
1.56
4544
4.595
2.698/3.976
µ
Cu KR, mm-1
abs, A*min/A*max
cryst size, mm
temp, K
0.15 × 0.20 × 0.37
0.076 × 0.22 × 0.60
0.15 × 0.17 × 0.17
200
170
200
reflns measured
θ range
3741
6658
5622
3° < 2θ < 105°
-10 < h < 10
-12 < k < 11
0 < l < 14
3561
3° < 2θ < 110°
-9 < h < 9
-11 < k < 11
0 < l < 31
6502
3° < 2θ < 105°
-21 < h < 21
0 < k < 20
0 < l < 23
5450
h,k,l range
reflns unique
reflns obsd (|Fo| > 4σ(Fo))
3091
434
5277
632
4783
603
variables
R
ω
Rω
0.044
0.048
0.040
1/(σ2(Fo) + 0.0001(Fo)2)
0.049
1/(σ2(Fo) + 0.0001(Fo)2)
0.047
1/(σ2(Fo) + 0.0002(Fo)2)
0.045
max Fourier diff, e Å-3
-0.28, 0.20
-0.30, 0.24
-1.18, 0.74
Hz). 13C NMR in CDCl3: δ 14.19, 15.54 (primary C); 22.27, 26.00,
29.15, 29.42, 29.60, 29.70, 31.90, 40.15, 66.30 (secondary C); 110.50,
112.90, 114.33, 132.20, 126.00, 138.00 (tertiary C); 118.70, 121.62,
128.22, 138.42, 147.20, 163.50, 165.70 (quaternary C). ES-MS (CH2-
Cl2): m/z 976.3 ([M + H]+).
program.45 IR spectra were obtained from KBr pellets with a Perkin-
Elmer 883 spectrometer. 1H and 13C NMR spectra were recorded at
25 °C on a Broadband Varian Gemini 300 spectrometer. Chemical
shifts are given in ppm with respect to TMS. EI-MS (70 eV) were
recorded with VG-7000E and Finnigan-4000 instruments. Pneumati-
cally assisted electrospray (ES-MS) mass spectra were recorded from
dichloromethane solutions for the ligands on a Finnigan MAT SSQ
7000 and from 10-4 M acetonitrile solution for the complexes on an
API III tandem mass spectrometer (PE Sciex). The spectra were
recorded under low up-front declustering or collision-induced dissocia-
tion (CID) conditions, typically ∆V ) 0-30 V between the orifice
and the first quadrupole of the spectrometer.46 The experimental
procedures for high-resolution, laser-excited luminescence measure-
ments have been published previously.14,15 Solid-state samples were
finely powdered, and low temperature (77 or 10 K) was achieved by
means of a Cryodyne model 22 closed-cycle refrigerator from CTI
Cryogenics. Luminescence spectra were corrected for the instrumental
function, but not excitation spectra. Lifetimes are averages of at least
3-5 independent determinations. Ligand excitation and emission
spectra were recorded on a Perkin-Elmer LS-50B spectrometer equipped
for low-temperature measurements. The relative quantum yields were
calculated using the following formula:15 Qx/Qr ) Ar(λr)/Ax(λx) I(λr)/
I(λx) n2 /n2 Dx/Dr , where subscript r stands for the reference and x
for the samples; A is the absorbance at the excitation wavelength, I is
the intensity of the excitation light at the same wavelength, n is the
refractive index (1.341 for all solutions in acetonitrile), and D is the
measured integrated luminescence intensity. DSC traces were obtained
with a Seiko DSC 220C differential scanning calorimeter from 3-5
mg samples (5-10 °C‚min-1, under N2). Thermogravimetric analyses
were performed with a thermogravimetric balance Seiko TG/DTA 320
(under N2). The characterization of the mesophases was performed
with a polarizing microscope, Zeiss Axioskop, equipped with a Linkam
THMS 600 variable-temperature stage. Powder X-ray diffraction
patterns were recorded as a function of temperature using a Debye-
Scherrer type camera with bent quartz monochromator (Cu KR
Preparation of the Complexes [La(L14)(NO3)3]‚3H2O (22), [Ln-
(L14)(NO3)3]‚H2O (Ln ) Sm, 23; Eu, 24; Gd, 25; Tb, 26; Yb, 27;
Lu, 28; Y, 29) and [Lu(L13)(NO3)3]‚3CH3CN (30). L14 (50 mg, 0.053
mmol) in dichloromethane (5 mL) was added to Ln(NO3)3‚xH2O (Ln
) La, Sm, Eu, Gd, Yb, Lu, Y; x ) 2-6, 0.053 mmol) in acetonitrile
(5 mL). After 1 h of stirring at room temperature, the solvents were
evaporated to dryness, and the residual solid was solubilized in a
minimum of hot acetonitrile. Cooling the solution produced white
powders, which were again recrystallized from acetonitrile (propionitrile
or isobutyronitrile) to give 61-84% of complexes [Ln(L14)(NO3)3]‚
H2O (Ln ) Sm, 23; Eu, 24; Gd, 25; Tb, 26; Yb, 27; Lu, 28; Y, 29).
X-ray quality crystals of [Lu(L13)(NO3)3]‚3CH3CN (30) were obtained
with the same procedure using L13. Complexes 22-29 were character-
ized by their IR spectra and gave satisfactory elemental analyses (Table
S13 in the Supporting Information).
Physicochemical Measurements. Reflectance spectra were re-
corded as finely ground powders dispersed in MgO (5%) with MgO
as reference on a Perkin-Elmer Lambda 900 spectrophotometer
equipped with a PELA-1000 integration sphere from Labsphere.
Electronic spectra in the UV-visible range were recorded at 20 °C
from 10-3-10-4 M dichloromethane/acetonitrile solutions with a
Perkin-Elmer Lambda 5 spectrometer using quartz cells of 0.1- and
1-cm path length. Spectrophotometric titrations were performed with
a Perkin-Elmer Lambda 5 spectrophotometer connected to an external
computer. In a typical experiment, 25 mL of ligand L14 (10-4 M) in
dichloromethane/acetonitrile (1:1) was titrated at 20 °C with a solution
of Ln(NO3)3‚3H2O, 1 mM in acetonitrile. After each addition of 0.1
mL, the absorption spectra were recorded using a 0.1-cm quartz cell
and transferred to the computer. Plots of extinction as a function of
the metal/ligand ratio gave a first indication of the number and
stoichiometry of the complexes formed; factor analysis was then applied
to the data to confirm the number of different absorbing species, and
finally, a model for the distribution of species was fitted with a nonlinear
least-squares algorithm to give stability constants using the SPECFIT
x
r
(45) Gampp, H.; Maeder, M.; Meyer, C. J.; Zuberbu¨hler, A. D. Talanta
1985, 32, 257.
(46) Hopfgartner, G.; Piguet, C.; Henion, J. D. J. Am. Soc. Mass
Spectrom. 1994, 5, 748.

12288 J. Am. Chem. Soc., Vol. 120, No. 47, 1998
Nozary et al.
radiation, λ ) 1.5418 Å), an INSTEC hotstage ((0.01 °C), and an
INEL curved position-sensitive gas detector associated with a data
acquisition computer system. It was possible to measure periodic
distances up to 60 Å, with experimental resolution of 2θ ) 0.07°. Some
of the patterns were also registered photographically using Guinier
cameras. Elemental analyses were performed by Dr. H. Eder from the
Microchemical Laboratory of the University of Geneva. Metal contents
were determined by ICP (Perkin-Elmer Plasma 1000) using internal
standard techniques after mineralization of the complexes.
X-ray Crystal Structure Determination of L13, L16, and [Lu(L13)-
(NO3)3]‚3CH3CN (30). A summary of the crystal data, intensity
measurements, and structure refinements is reported in Table 8.
(i) Data Collection and Processing. Stoe STADI4 diffractometer,
ω-2θ scan, scan width ) 1.05 + 0.35 tan θ, scan speed 0.06°‚s-1, Cu
KR radiation (λ ) 1.5418 Å). Two reference reflections were measured
every 45 min and showed no significant variations.
the disordered solvent molecules in 30. H atoms were placed in
calculated positions and contributed to Fc calculations.
Acknowledgment. We gratefully acknowledge Ms. H.
Lartigue and V. Foiret for their technical assistance, Ms. M.-T.
Vilches for observation of textures by polarizing microscopy,
and Dr. G. Hopfgartner (Hofmann-La Roche) for recording ES-
MS spectra of the complexes. C.P. thanks the Werner Founda-
tion for a fellowship, and J.-C.G.B. thanks the Fondation
Herbette (Lausanne) for the gift of spectroscopic equipment.
This work is supported through grants from the Swiss National
Science Foundation.
Supporting Information Available: Tables of atomic
coordinates, bond distances and bond angles, anisotropic
displacements parameters and selected least-squares planes data
for L13 (Tables S1-S4), L16 (Tables S5-S8), and [Lu(L13)-
(NO3)3](CH3CN)3 (30) (Tables S9-S12); Table S13 of elemen-
tal analyses for complexes 22-29 and Table S14 listing the
variable-temperature 1H NMR chemical shifts in [Y(L14)(NO3)3];
Figure F1 showing the emission spectra of [Tb(L14)(NO3)3-
(OH2)] (26) measured under excitation through the ligand levels
at various temperatures and Figure F2 showing the d-layered
spacing for L14 at different temperatures (29 pages, print/PDF).
See any current masthead page for ordering information and
Web access instructions.
(ii) Structure Analysis and Refinement. Data were corrected for
Lorentz, polarization, and absorption effects.47 The structures were
solved by direct methods using MULTAN 87;48 all other calculations
used XTAL49 system and ORTEP II24 programs. Full-matrix least-
squares refinements (on F). The non-H atoms were refined with
anisotropic displacement parameters, except for the non-H atoms of
(47) Blanc, E.; Schwarzenbach, D.; Flack, H. D. J. Appl. Crystallogr.
1991, 24, 1035.
(48) Main, P.; Fiske, S. J.; Hull, S. E.; Lessinger, L.; Germain, D.;
Declercq, J. P.; Woolfson, M. M. MULTAN 87; Universities of York,
England, and Louvain-La-Neuve, Belgium, 1987.
(49) Hall, S. R., Stewart, J. M., Eds. XTAL 3.2 User’s Manual;
Universities of Western Australia and Maryland, 1992.
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