Supramolecular aggregates in fluid phases: Mesomorphic ortho-palladated complexes with substituted crown ethers and their potassium adducts

Article abstract of DOI:10.1002/ejic.200700786

New imines (HL) containing substituted dibenzo-18-crown-6-ethers and their dinuclear ortho-palladated complexes, [Pd(μ-X)L]₂ (X^- = CH₃COO^-, Cl^-), have been prepared. The free imine ligands are not liq

Full text of DOI:10.1002/ejic.200700786

FULL PAPER
DOI: 10.1002/ejic.200700786
Supramolecular Aggregates in Fluid Phases: Mesomorphic ortho-Palladated
Complexes with Substituted Crown Ethers and Their Potassium Adducts
Silverio Coco,*[a] Carlos Cordovilla,[a] Pablo Espinet,*[a] Jean-Louis Gallani,[b]
Daniel Guillon,[b] and Bertrand Donnio[b]
Keywords: Crown ethers / Palladium / Liquid crystals / Langmuir films
New imines (HL) containing substituted dibenzo-18-crown-
6-ethers and their dinuclear ortho-palladated complexes,
[Pd(µ-X)L]2 (X– = CH3COO–, Cl–), have been prepared. The
free imine ligands are not liquid crystals, but the palladium
complexes, including acetato-bridged derivatives, show li-
ens prepared, which show a smectic C mesophase. Complex-
ation with potassium produces a significant increase in the
mesophase range and stability. Moreover, both the free im-
ines and the corresponding liquid-crystalline ortho-pallad-
ated complexes form stable Langmuir films at the air–water
quid-crystal properties. The mesomorphic palladium com- interface.
plexes bear six or eight alkoxy chains. Although a columnar
arrangement of these chains might be expected, a smectic
arrangement is in fact preferred for half of the metallomesog-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
of molecular recognition and interaction phenomena at in-
terfaces.[4,13,14]
Introduction
Functional liquid crystals that combine specific proper-
ties with supramolecular organization and fluidity in the
mesophase have attracted considerable attention in materi-
als research because they are academically interesting and
because of their potential applications in a wide variety of
advanced technologies.[1,2] They can be used as functional
materials for information and mass transport,[3,4] sens-
ing,[5,6] catalysis, stimuli responsiveness and electrooptical
displays.[7,8] The range of systems that can be used in this
field has provided a rich diversity of functional liquid-crys-
talline assemblies. Among them, an interesting example
consists of liquid-crystalline phthalocyanines modified with
crown ether moieties that combine ion channels and elec-
tron wires in hexagonal columnar (Colh) phases.[9] In this
mesophase there is a central electron wire of stacked
phthalocyanine cores surrounded by four ion channels
formed from dialkoxy-substituted dibenzo-18-crown-6
groups.[4] Also well-known is the ability of crown ether
groups to coordinate cations and thus promote the solubil-
ity of inorganic salts in organic solutions; this has made
them attractive building blocks in supramolecular chemis-
try.[10–12] Moreover, the incorporation of crown ether
groups into thin ordered films is a rapidly growing field
because these systems can be used as models for the study
Some organic liquid crystals containing crown ethers are
also known;[2,15–25] the coordination of alkaline salts to the
crown ether group of mesogenic systems produces different
modifications of their mesogenic properties. These modifi-
cations include increases or decreases in the mesophase sta-
bility,[15,16,20,21,23] as well as changes in the mesophase
types.[2,16,19–21,25]
On the other hand, a large variety of metals and ligands
have been used to prepare metal-containing liquid crystals.
Among them, ortho-palladated complexes are one of the
most studied classes of metallomesogens.[26–29] It is surpris-
ing that only a few examples of metallomesogens containing
crown ethers have been reported: namely, a family of ortho-
palladated complexes[30] and some crown ether substituted
phthalocyanine complexes of copper, lutetium and lith-
ium.[31–33]
Our group has recently reported palladium(II) metallo-
mesogens of crown ether derivatized imines, which have al-
lowed us to propose and support a plausible model for ex-
traction and transport with these complexes.[34] As a contin-
uation of these studies, we report here the synthesis of li-
quid-crystalline ortho-palladated complexes with substi-
tuted dibenzo-18-crown-6-ethers. This family of complexes
has afforded examples of metallomesogens based on dinu-
clear imino palladium(II) complexes including complexes
with acetato bridges, which generally do not display meso-
morphic behaviour. Their complexation with potassium
produces a significant increase in mesophase range and sta-
bility. Moreover, both the free imines and the correspond-
[a] Química Inorgánica, Facultad de Ciencias, Universidad de Val-
ladolid,
47005 Valladolid, Spain
[b] Institut de Physique et Chimie des Matériaux de Strasbourg
(IPCMS), UMR 7504 (CNRS-ULP),
23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France
1210
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 1210–1218

Mesomorphic Palladium Complexes
ing liquid-crystalline ortho-palladated complexes form
stable Langmuir films at the air–water interface.
Results and Discussion
Synthesis and Characterization
The Schiff bases 1 were synthesized in ethanol by an ace-
tic acid catalyzed condensation between the corresponding
substituted benzaldehyde and the amines containing the di-
benzo-18-crown-6 group (Scheme 1), as described for re-
lated Schiff bases.[35]
Scheme 1.
Scheme 2.
The dibenzo-18-crown-6 aniline F used in this work was
prepared in five steps by starting from cathecol (Scheme 2).
The alkylation of catechol with tetrahydropyranyl-pro-
tected diethyleneglycol chloride gave, after in situ deprotec-
tion, dialcohol A, which was converted into B by subse-
quent nitration. The treatment of B with p-toluenesulfonyl
chloride yielded the p-toluenesulfonate dialcohol C. Coup-
ling this with 1,2-bis(decyloxy)-4,5-bis(acetoxy)benzene (D)
gave the nitro crown ether derivative E. Finally, the re-
duction of E with hydrazine monohydrate with a palla-
dium-on-carbon catalyst produced the desired amine F.
The cyclopalladated complexes were synthesized as de-
picted in Scheme 3. The ortho-metallation of the imine li-
gand to give acetato complexes was carried out as described
elsewhere.[36] The treatment of the acetato-bridged deriva-
tives 2 in dichloromethane with a solution of HCl in diethyl
ether afforded the chloro compounds 3 (Scheme 3), which
were isolated as yellowish solids.
1
The elemental analyses, yields, relevant IR data and H
NMR spectra for the complexes are given in the experimen-
tal section. The main structural features for complexes anal-
ogous to 1, 2 and 3 but without crown ether groups have
been reported in detail in previous papers,[37–40] and are as-
sumed to be similar here. The acetato-bridged complexes
are butterfly-shaped, while the chloro-bridged complexes
are planar. In both types of complexes only the anti isomer
is formed in the cases reported here.
Scheme 3.
The complexation of 2b,c and 3b,c with KClO4 was
achieved by dissolving the corresponding crown ether com-
Eur. J. Inorg. Chem. 2008, 1210–1218
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1211

S. Coco, C. Cordovilla et al.
FULL PAPER
pound with the potassium salt in dichloromethane/ethanol Table 1. Optical, thermal and thermodynamic data for complexes
1, 2 and 3.
(2:1) in a crown ether/potassium molar ratio of 1:1 at room
Transition[a]
T/°C
161.4
∆H/kJmol–1
temperature, and by subsequently removing the solvent in
vacuo. All potassium perchlorate complexes were isolated
as pale brown solids. Potassium was chosen according to
its cation size; it forms the most stable 1:1 complexes with
dibenzo-18-crown-6.[41] The perchlorate anion was chosen
because of its relatively weak coordination character
towards soft transition metals. The potassium-containing
complexes are soluble in dichloromethane and CDCl3,
while KClO4 is insoluble. The coordination of the perchlo-
rate group to the potassium cation is evident from the IR
spectra that show three bands at ca. 1122, 1111 and
1087 cm–1.[42] The number of bands in the IR spectrum has
been successfully used to derive information regarding the
bonding modes of the perchlorate group. Three bands in
the Cl–O stretching region indicate the presence of a per-
chlorate group coordinated in a bidentate fashion. Thus,
two oxygen atoms of the perchlorate ligand together with
the oxygen atoms of the crown ether would complete the
coordination of potassium (Figure 1), as described for sim-
ilar sodium and potassium perchlorate adducts.[34,43]
1a
1b
Cr Ǟ I
Cr Ǟ CrЈ
CrЈ Ǟ I
68.3
10.1
91.21
118.3
–
12.1
35.7
3.6
34.9
124.9
121.9
1c
2a
2b
Cr Ǟ I
Cr Ǟ dec
Cr Ǟ CrЈ
CrЈǞ SmC
SmC Ǟ I
I Ǟ SmC
SmC Ǟ G
G Ǟ SmC
SmC Ǟ I
Cr Ǟ CrЈ
CrЈǞ I
I Ǟ M
M Ǟ G
G Ǟ CrЈЈ
CrЈЈǞ I
Cr Ǟ dec
Cr + G Ǟ Cr + CrЈ
Cr + CrЈ Ǟ SmC
SmC Ǟ I
Cr Ǟ CrЈ
CrЈ Ǟ CrЈЈ
CrЈЈ Ǟ I
110[c]
81.0
107.6
121.9
117.7
49.2
55.8
119.7
47.5
96.4
77.1
43.8
66.6
–5.3
4.5
2c
13.3
73.6[b]
–9.3
–16.7[b]
63.7[b]
–
–19.3
235.7[b]
–
41.3
21.4
46.7
–3.0
18.3
93.1
3a
3b
215[c]
80.6
109.8
200[c]
3c
53.0
92.5
141.4[d]
139.0
90.1
I Ǟ M
M Ǟ CrЈЈЈ
[a] Data refer to the second heating DSC cycle (for monotropic
compounds 2c and 3c, first heating and cooling data were also
collected); Cr = crystal, SmC = smectic C, G = glass, M = unidenti-
fied mesophase, I = isotropic liquid, dec = decomposition. [b] Com-
bined enthalpies. [c] Optical microscopy data. [d] Peak data.
Figure 1. Chemical structure of the potassium perchlorate adducts.
The dimeric molecules of the acetato and chloro com-
plexes 2b and 3b bear six alkoxy chains altogether. Al-
though one might expect a columnar arrangement of these
chains, a smectic arrangement seems to be preferred, and
the compounds show a smectic C mesophase. This meso-
phase was identified with optical microscopy by its texture
(Figure 2) and by the fact that it was not possible to induce
either hometropic regions or brownian flashes under me-
chanical stress. However, greyish textures are observed by
mechanical displacement.[44,45]
1
The potassium adducts were characterized by H NMR
spectroscopy. In contrast to its ortho-palladated precursor,
the acetato-bridged complex [k2b] shows, in addition to
small shifts of the aromatic protons, two sets of resonances
in a molar ratio close to 1:2. The signals for the methyl
groups of the acetato bridges and those of the imine ligands
reveal that this splitting corresponds to the presence of syn
and anti isomers in the potassium perchlorate crown com-
plexes, which shows that complexation induces anti to syn
isomerization so that a slow equilibrium is reached.
Mesomorphic Behaviour
Although the free imine ligands used are not liquid crys-
tals, all the palladium complexes show a mesomorphic be-
haviour except complexes of series a. In fact, the series a
compounds lack flexible lateral groups and do not possess
the basic requirements to be mesogenic. They were synthe-
sized with the main purpose being to obtain suitable crys-
tals for X-ray determination; unfortunately, this was not
achieved. The optical, thermal and thermodynamic data of
all the prepared compounds are gathered in Table 1.
Figure 2. Polarized optical microscopic texture (ϫ200) observed for
2b at 110 °C on cooling from the isotropic liquid.
1212
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 1210–1218

Mesomorphic Palladium Complexes
In contrast, complexes 2c and 3c, having one more chain defined, flattened endothermic peaks. Yet, on subsequent
per Pd atomϪthat is eight alkoxy chains per dimerϪshow heat–cool cycles, the DSC traces clearly appear simpler. We
monotropic mesomorphic behaviour. The optical textures, suspect that during the first heating there are a number of
when viewed with a polarizing microscope on cooling from small conformational changes that occur upon going from
the isotropic melt, exhibit a fan-like texture frequently ob- the crystal to the mesophase, which remain in the glass ob-
served for columnar hexagonal mesogens. However, the tained upon cooling, and thus result in a simpler behaviour
small sizes of the domains formed did not allow us to con- during the second heating (except for [k2c], which displays
clusively identify the type of mesophase.
a melting point in the second heating). Compared to the
When derivative 2b is cooled from the mesophase, parent complexes, the potassium complexes demonstrate an
crystallization is not observed, and a glass transition ap- important increase in the clearing temperatures and the me-
pears [Figure 3, (b)]. The glass transition is reversible to sophase stability; as a consequence, all of the potassium
give a glass–SmC transition followed by a SmC–isotropic complexes studied show enantiotropic liquid-crystalline be-
liquid transition [Figure 3, (c)]. Similar behaviour is ob- haviour (Table 2).
served for compound 2c.
Table 2. Optical, thermal and thermodynamic data for potassium
crown complexes.
Compound
Transition[a]
T/°C
81.5
193.3
93.7
147.0
85.4
178.5
110.0[c]
207.1
∆H/kJmol–1
[k2b]
G Ǟ SmC
SmC Ǟ I[b]
Cr Ǟ M
M Ǟ I
G Ǟ SmC
SmC Ǟ I
G Ǟ M
1.8
5.8
3.2
[k2c]
[k3b]
[k3c]
0.5
M Ǟ I
3.3
[a] Data refer to the second heating DSC cycle; Cr = crystal, Sm
= smectic, G = glass, M = unidentified mesophase, I = isotropic
liquid. [b] Decomposition. [c] Optical microscopy data.
The changes in intermolecular forces upon potassium
complexation are manifold: the molecules become more po-
lar, and the inclusion of potassium ions into the cavities of
the macrocyclic units increases the rigidity of the crown
ether group, but probably also increases the width of the
Figure 3. DSC scans of 2b: (a) first heating, (b) first cooling and
(c) second heating.
In general, butterfly-shaped ortho-metallated acetato- molecule (Figure 1).[43] On the other hand, microsegrega-
bridged complexes are not mesomorphic because of their tion probably improves upon complexation, and this is
unfavourable molecular structure.[29,40] Thus it is somewhat known to stabilize the mesophases. For the acetato com-
unexpected that the compounds reported here are meso- plexes, an important change is the formation of a syn/anti
morphic; the positive change must be related to the pres- isomeric mixture. In such a complex system, a simple ratio-
ence of crown ether groups. The effect of incorporating cy- nal explanation of the effect of potassium complexation on
clic polyether moieties in ortho-palladated systems is not a the mesomorphic behaviour is impossible, but at least we
simple matter, but the importance of the distribution of po- see that the effect is systematic.
lar and nonpolar structural units within anisotropic mole-
Temperature-dependent X-ray diffraction experiments
cules for the formation of mesophases is well-known. In this were systematically carried out in order to unequivocally
respect, besides the effects in molecular geometry and the identify the nature of the mesophase.
possible conformational effects, microsegregation is proba-
The XRD patterns of 2b measured between 100 and
bly an important contribution to the induction of a liquid- 120 °C exhibit a broad scattering in the wide angle part of
crystalline behaviour. Microsegregation is favoured in mole- the diffractogram (at ca. 4.5–4.6 Å), which corresponds to
cules with a well-defined intramolecular contrast, i.e. in the molten chains in the liquid-like order, and only one fine,
complexes with distinct polar/rigid and less polar/flexible sharp signal in the small angle region (39.1 Å). Thus, the
segments.[46] Thus, the introduction of crown ether groups mesophase was assigned on the basis of its texture only,
in a system, which is expected to enhance microsegregation, obtained by polarized-light optical microscopy, as a smectic
will facilitate mesophase formation, as observed.
C phase (Figure 2). Another broad peak at 9.0–10.0 Å
The complexation of the crown ether derivatives with could be assigned to the average distance between com-
KClO4 to give the corresponding adducts produces an im- plexes in the smectic layers. The occurrence of this meso-
portant change in the mesomorphic properties. The optical phase is consistent with the presence of a transverse dipolar
textures observed from the first heating cycle are the same moment in the molecule.[47]
as those for the crown ether parent palladium complexes;
As expected from the DSC traces of 3b, a change in the
the DSC traces, however, are complex and show several ill- X-ray pattern, which corresponds to a modification of the
Eur. J. Inorg. Chem. 2008, 1210–1218
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1213

S. Coco, C. Cordovilla et al.
FULL PAPER
molecular packing, was detected between 115 and 125 °C. Table 3. Structural data from X-ray diffraction experiments for 2b
and 3b.
This change was characterized by the disappearance of the
strong, sharp peaks of the crystalline phase and the appear-
ance of a small-angle reflection with a periodicity of about
42 Å. At 145 °C, three sharp, intense small-angle diffraction
peaks, corresponding to distances of 39.7, 19.8 and 13.1 Å
in a 1:2:3 ratio, were indexed as (00l) = (001), (002), (003),
respectively. In addition, two diffuse peaks observed around
9.0–10.0 and 4.5 Å were assigned to the average distance
between molecules in the smectic layers and to the liquid-
like order of the molten alkoxy chains, respectively.
For both complexes (2b and 3b), although the molecular
areas are rather large because of the bulky crown ether moi-
eties, they are indeed compatible with a smectic-like meso-
morphism, with the core being slightly tilted in the layers
and the aliphatic chains being in a very disordered state
(Table 3). A possible molecular arrangement for 3b is
sketched in Scheme 4. Since the molecules are composed of
Transition
T/°C
Indexing[a]
Parameters[b]
dmes/Å
I
hkl dcalc/Å
2b
3b
Cr 107.6
SmC 121.9 I
39.1
VS (sh) 001
39.1
V = 3890 Å3
9.0–10.0
4.5
39.71
VS (br)
VS (br)
VS (sh) 001
AM = 99.5 Å2
Ach = 33.17 Å2
Cr 109.8
SmC 200 dec
39.57 V = 3880 Å3
19.81
13.13
9.0–10
4.6
S (sh)
S (sh)
VS (br)
VS (br)
002
003
19.78 AM = 98.0 Å2
13.19 Ach = 32.7 Å2
[a] [dcalc = 1/3·(d001 + 2·d002 + 3·d003)]. [b] V is the molecular vol-
ume, AM the molecular area (AM = V/d) and Ach the chain area
(Ach = AM/3).
three different chemically incompatible blocks, they are patterns registered on cooling, cannot confirm the phase
likely to segregate in the bulk in order to minimize their identity. Another broad peak at 5.0 Å, which can be as-
interactions, which would form three different zones. The signed to the molten chains, was also seen.
rigid central part forms a central sublayer, and since the
In the event of a smectic phase, the molecular area (AM
complexes are preferentially in a trans symmetry (due to = 100.75 Å2, i.e., 25.0 Å2 per chain for an estimated volume
the bulky crown ether part), the outer sublayers consist of of 3940 Å3) is indicative of a dense packing of the molecules
alternating aliphatic chains and crown ether parts on either into a nontilted phase. In the case of a Colh phase, the only
side of the central inner sublayer. Moreover, the distance of possible columnar arrangement, about two molecules or,
ca 9.0 Å would then correspond to the lateral interactions more precisely, two molecular equivalents, would match
between neighbouring crown ethers organized into a hexag- perfectly with the volume of a 4.5 Å thick columnar slice.
onal network. In such a case, the hexagonal surface area Thus, columnar and smectic arrangements cannot be dis-
(SH = 1/2.9.52.31/2 = 80 Å2) almost matches the molecular criminated nor excluded here.
area.
As for the complexes incorporating potassium perchlo-
As for 2c and 3c, their monotropic behaviour precludes rate, the phases were assigned mainly on the basis of their
any unequivocal phase assignment. The results of the polar- optical textures because of the limited thermal stability of
ized optical microscopy (POM) studies allow to tentatively the sample under the X-ray diffraction experimental condi-
predict the formation of a hexagonal columnar phase (the tions. In all cases, only one diffraction peak was observed
complexes have eight chains in total), although the presence {[2bk] 38.6; [2ck] 38.0; [3bk] 38.0, 9.4, 4.5; [3ck] 36.6 Å},
of only one peak at 39.1 Å (3c), observable on the X-ray and no unequivocal phase assignment can be made.
Scheme 4.
1214
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 1210–1218

Mesomorphic Palladium Complexes
Langmuir Films
be some aggregation remaining, in particular around the
Wilhelmy plate, as the surface pressure does not return to
zero.
The imines 1b,c and the complexes 2b,c and 3b,c can
form Langmuir films at the air–water interface. The iso-
therms obtained at 25 °C and the molecular areas extrapo-
lated to zero surface pressure are shown in Figure 4. These
values are in good agreement with the areas estimated by
molecular modeling, which means that the molecules
spread as monomolecular layers at the air–water interface.
In the case of the imines 1b,c, these areas are very similar
to the estimated value for the area of the molecular core
(palladium-coordinated core plus crown ether), which sug-
gests that these groups are arranged parallel to the water
surface (side-on disposition) and the alkoxy substituents
normal to the film surface. In contrast, the molecular areas
of the palladium complexes 2b,c and 3b,c are slightly
smaller than expected for a side-on disposition of the mo-
lecular core, but larger than expected for an edge-on orien-
tation, which indicates that the molecules will take a tilted
edge-on disposition.
Conclusions
In summary, mesomorphic ortho-palladated [Pd(µ-X)L]2
(X– = CH3COO–, Cl–) complexes with unusual imines con-
taining substituted dibenzo-18-crown-6-ethers have been
prepared. Although the free imine ligands obtained are not
liquid crystals, the palladium complexes, including the usu-
ally unfavorable acetato-bridged derivatives, show liquid-
crystal properties. In spite of having six or eight alkoxy
chains that might induce discotic phases, at least half of
the prepared palladium complexes self-organize in what is
clearly a smectic order. Complexation with potassium pro-
duces a significant increase in the mesophase range and sta-
bility. Moreover, both the free imines and the correspond-
ing liquid-crystalline ortho-palladated complexes form
stable Langmuir films at the air–water interface.
Experimental Section
1H NMR spectra were recorded at 300 MHz with a Bruker AC 300
instrument in CDCl3 and CD2Cl2. Chemical shifts, in ppm, are
reported relative to internal TMS for 1H. Combustion analyses
were performed with a Perkin–Elmer 2400 microanalyzer. IR spec-
tra were recorded on a FT 1720X Perkin–Elmer instrument (400–
4000 cm–1), with samples being prepared as KBr pellets, or a Per-
kin–Elmer 883 spectrophotometer (400–200 cm–1), with samples
being prepared as a Nujol emulsion supported between two poly-
ethylene films. Microscopy studies were carried out by using a Leitz
polarizing microscope equipped with a Mettler FP-82HT hot stage
and a Mettler FP-90 temperature controller at a heating rate of ca.
10 °Cmin–1. For DSC, a Perkin–Elmer DSC7 instrument was used,
which was calibrated with water and indium; the scanning rate was
10 °C min–1, the samples were sealed in aluminum capsules in the
air and the holder atmosphere was dry nitrogen.
Figure 4. Surface pressure–molecular area isotherms at 25 °C. Ex-
trapolated molecular areas are given in brackets.
Brewster angle microscopy (BAM) was used in successive
compression/decompression cycles in the case of 1b and 2b
to study the reversibility of the process and the homo-
geneity of the films. Compound 2b spontaneously forms a
liquid film at large molecular areas. Upon compression, the
film becomes continuous and defectless. The collapse takes
the appearance of linear/ramified structures. The decom-
pression is reversible: expanding holes form in the liquid
film during decompression. Compound 1b also has an ini-
tial state in which the molecules spontaneously form liquid-
like assemblies. The completed film looks homogeneous
and defectless. Collapse appears at a lower surface pressure
than for 2b and seems to be cooperative in the sense that
the collapse of the film keeps progressing even if the com-
pression is stopped. This is seen with the BAM and also
because the surface pressure keeps decreasing even without
motion of the barriers. The molecules form aggregates of
irregular shape, and hence the films are probably solid.
Upon decompression there is some degree of reversibility.
The solid/collapsed structures seem to melt into a liquid
again. After 15 minutes the film has evolved into a 2D foam
The XRD patterns were obtained with two different experimental
setups (I, II). In all cases, a linear monochromatic Cu-Kα1 beam (λ
= 1.5405 Å) was obtained using a sealed-tube generator (900 W)
equipped with a bent quartz monochromator. In the first set, the
transmission Guinier geometry (I) was used, whereas Debye–
Scherrer-like (II) was used in the second experimental setup. In all
cases, the crude powder was used to fill Lindemann capillaries of
1 mm diameter and 10 µm wall thickness. The initial set of diffrac-
tion patterns was recorded on an image plate; periodicities up to
80 Å could be measured, and the sample temperature controlled to
within Ϯ0.3 °C in the 20 to 350 °C temperature range. The second
set of diffraction patterns (II) was recorded with a curved Inel
CPS120 counter gas-filled detector linked to a data acquisition
computer (for periodicities up to 60 Å) or these could be measured
on image plates (for periodicities up to 100 Å); the sample tempera-
ture was controlled to within Ϯ0.05 °C in the 20 to 200 °C tempera-
ture range. In each case, exposure times were varied from 1 to 24 h.
Langmuir films have been prepared on a standard TEFLON®
trough filled with ultrapure water at room temperature. The com-
pounds were dissolved in dichloromethane in 1 mgmL–1 concentra-
where only very few solid parts remain. Still, there must tions to prepare the spreading solution.
Eur. J. Inorg. Chem. 2008, 1210–1218
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1215

S. Coco, C. Cordovilla et al.
FULL PAPER
Brewster angle microscopy observations were performed with an
apparatus from NFT (Göttingen, Germany, www.nanofilm.de).
δ = 0.88 (t, 6 H, CH3), 1.27–1.80 (m, 32 H, CH2), 3.90–4.12 (m,
32 H, CH2O), 6.22 (dd, 1 H, ArH), 6.28 (d, 1 H, ArH), 6.58 (s, 2
H, ArH), 6.71 (d, 1 H, ArH) ppm.
All solvents were dried and distilled before use. All reactions were
carried out under nitrogen atmosphere. p-Toluenesulfonyl chloride
was recrystallized[48] and K2CO3 was dried in an oven prior to use.
Literature methods were used to prepare [Pd(AcO)2]3,[49] 2-(2Ј-
chloroethoxy)ethyl 2ЈЈ-tetrahydropyranyl ether[50] and 1,2-bis(decy-
loxy)-4,5-bis(acetoxy)benzene.[51]
Preparation of the Imines 1a–c: All of the imines were synthesized
by condensation of their respective aldehydes and anilines in abso-
lute ethanol with acetic acid as catalyst.[35]
1a: Yield 0.11 g (81%). IR (KBr): ν = 1604 [ν(C=N)] cm–1. 1H
˜
NMR (CDCl3): δ = 1.45 (t, 3 H, CH3), 4.11 (c, 2 H, ArOCH2),
4.05–4.20 (m, 16 H, CH2O), 6.77 (dd, 1 H, ArH), 6.83 (d, 1 H,
ArH), 6.86 (m, 4 H, ArH), 6.87 (d, 1 H, ArH), 6.98 (d, 2 H, ArH),
7.81 (d, 2 H, ArH), 8.39 (s, 1 H, CH=N) ppm. C29H33NO7 (507.6):
calcd. C 68.6, H 6.6, N 2.8; found C 68.3, H 6.8, N 3.0.
Preparation of 1,2-Bis[2Ј-(2ЈЈ-hydroxyethoxy)ethoxy]benzene (A): 2-
(2Ј-Chloroethoxy)ethyl 2Љ-tetrahydropyranyl ether (90.08 g, 0.43
mol) was added dropwise to a refluxing suspension of catechol
(23.63 g, 0.21 mol) and NaOH (17.2 g, 0.43 mol) in 1-butanol
(0.5 L). The suspension was heated at reflux for 20 h and, once the
mixture was cooled, concentrated HCl (12 mL) was added, and the
mixture was stirred for 1 h. NaHCO3 (58 g, 0.82 mol) was then
added, and the filtered solution was washed with 1  NaOH and
with water. Volatiles were pumped off in vacuo (130 °C, 5 Torr).
1b: Yield 1.38 g (95%). IR (KBr): ν = 1605 [ν(C=N)] cm–1. 1H
˜
NMR (CDCl3): δ = 0.88 (t, 9 H, CH3), 1.28–1.86 (m, 48 H, CH2),
3.81–4.22 (m, 22 H, CH2O), 6.60 (s, 2 H, ArH), 6.78 (dd, 1 H,
ArH), 6.84 (d, 1 H, ArH), 6.89 (d, 1 H, ArH), 6.97 (d, 2 H, ArH),
7.81 (d, 2 H, ArH), 8.39 (s, 1 H, CH=N) ppm. C57H89NO9 (932.2):
calcd. C 73.4, H 9.6, N 1.5; found C 73.2, H 9.4, N 1.8.
1
Yield 33.48 g (56%) of a dark viscous oil. H NMR (CDCl3): δ =
3.63–4.13 (m, 16 H, CH2O), 6.86–6.91 (m, 4 H, ArH) ppm.
1c: Yield 1.39 g (80%). IR (KBr): ν = 1598 [ν(C=N)] cm–1. 1H
˜
Preparation of 1,2-Bis[2Ј-(2ЈЈ-hydroxyethoxy)ethoxy]-3-nitrobenzene
(B): Compound A (33.84 g, 0.12 mol) and NaNO2 were dissolved
in CH2Cl2 (200 mL), and concentrated HNO3 (27 mL, 68%) was
added. The solution was stirred for 1 h and then washed with water
until a neutral pH was obtained. The organic layer was dried with
anhydrous MgSO4 and filtered, and the solvent was evaporated.
NMR (CDCl3): δ = 0.88 (t, 12 H, CH3), 1.28–1.84 (m, 64 H, CH2),
3,89–4.17 (m, 24 H, CH2O), 6.56 (s, 2 H, ArH), 6.77 (dd, 1 H,
ArH), 6.82 (d, 1 H, ArH), 6.88 (d, 1 H, ArH), 6.92 (d, 1 H, ArH),
7.28 (dd, 1 H, ArH), 7.53 (d, 1 H, ArH), 8.36 (s, 1 H, CH=N)
ppm. C67H109NO10 (1088.6): calcd. C 73.9, H 10.1, N 1.3; found C
73.8, H 10.1, N 1.5.
1
Yield 23.38 g (59%) of a white solid. H NMR (CDCl3): δ = 3.43
(s, 2 H, OH), 3.66–4.25 (m, 16 H, CH2O), 6.90 (d, 1 H, ArH), 7.74
(d, 1 H, ArH), 7.85 (dd, 1 H, ArH) ppm.
Preparation of the [Pd(µ-OAc)L]2 Acetate Complexes 2a–c: A mix-
ture of palladium acetate and a stoichiometric amount of the corre-
sponding imine in glacial acetic acid was stirred at 50 °C for 16 h.
The solvent was removed and the residue was dissolved in CH2Cl2
and filtered through silica before the solvent was again evaporated.
The resulting oil was treated with acetone and the yellow solid was
collected by filtration.
Preparation of 1,2-Bis{2Ј-[2ЈЈ-(p-tolylsufonyloxy)ethoxy]}-3-nitro-
benzene (C): Compound B (15.41 g, 46.4 mmol) was dissolved in
pyridine (75 mL), and the solution was cooled down to –10 °C.
A solution of p-toluenesufonyl chloride (21.09 g, 110.6 mmol) in
pyridine was added dropwise to this and stirred for 2 h at –5 °C
and overnight at 0 °C. The resulting solution was poured onto ice
(100 g), acidified with 6  HCl and extracted with CH2Cl2. The
organic layer was dried with anhydrous MgSO4 and filtered, and
the solvents were evaporated. Yield 24.02 g (80%) of a dark viscous
oil. 1H NMR (CDCl3): δ = 2.37 (s, 6 H, CH3), 3.72–4.14 (m, 16 H,
CH2O), 6.88 (d, 1 H, ArH), 7.27 (d, 4 H, ArH), 7.67 (d, 1 H, ArH),
7.73 (d, 4 H, ArH), 7.81 (dd, 1 H, ArH) ppm.
2a: Yield 0.09 g (76%). IR (KBr): ν = 1590 [ν(C=N)], 1570
˜
1
[ν(COO)as], 1413 [ν(COO)s] cm–1. H NMR (CDCl3): δ = 1.31 (t,
6 H, CH3), 1.91 (s, 6 H, CH3CO2), 3.59–3.61 (m, 4 H, ArOCH2),
3.78–4.17 (m, 32 H, CH2O), 5.90 (dd, 2 H, ArH), 6.00 (d, 2 H,
ArH), 6.56 (m, 4 H, ArH), 6.81 (d, 2 H, ArH), 6.88 (m, 8 H, ArH),
7.11 (d, 2 H, ArH), 7.46 (s, 2 H, CH=N) ppm. C62H70N2O18Pd2
(1344.1): calcd. C 55.4, H 5.2, N 2.1; found C 55.6, H 4.9, N 2.4.
Preparation of [4Ј,5Ј-Bis(decyloxy)-4ЈЈ-nitro]dibenzo[1Ј,2Ј-b:1ЈЈ,2ЈЈ-
k]-1,4,7,10,13,16-hexaoxacyclooctadeca-2,11-diene (E): Compound
D (2.62 g, 5.2 mmol) was heated at reflux with NaH (832.0 mg,
60% dispersion in mineral oil, 20.8 mmol) in THF (100 mL) for 1
h. A solution of C (3.31 g, 5.2 mmol) in THF (100 mL) was added
dropwise to this, and the mixture was refluxed for 48 h. The suspen-
sion was cooled, and water (50 mL) and diethyl ether (100 mL)
were added to it. After being stirred for 5 min, the solid that formed
was collected by filtration and redissolved in dichloromethane. The
solution was filtered through a hydrophilic polypropylene mem-
brane filter (0.2 mm), and the solvents were evaporated. Yield
1.55 g (42%) of a slightly brown solid. 1H NMR (CDCl3): δ = 0.88
(t, 6 H, CH3), 1.27–1.78 (m, 32 H, CH2), 3.90–4.25 (m, 32 H,
CH2O), 6.57 (s, 2 H, ArH), 6.88 (d, 1 H, ArH), 7.67 (d, 1 H, ArH),
7.72 (d, 1 H, ArH), 7.90 (dd, 1 H, ArH) ppm.
2b: Yield 0.92 g (82%). IR (KBr): ν = 1592 [ν(C=N)], 1570
˜
1
[ν(COO)as], 1414 [ν(COO)s] cm–1. H NMR (CD2Cl2): δ = 0.88 (t,
18 H, CH3), 1.27–1.77 (m, 96 H, CH2), 1.87 (s, 6 H, CH3CO2),
3.54–4.16 (m, 44 H, OCH2), 5.93 (dd, 2 H, ArH), 5.96 (d, 2 H,
ArH), 6.52 (m, 4 H, ArH), 6.55 (s, 4 H, ArH), 6.75 (d, 2 H, ArH),
7.13 (d, 2 H, ArH), 7.50 (s, 2 H, CH=N) ppm. C118H182N2O22Pd2
(2193.6): calcd. C 64.6, H 8.4, N 1.3; found C 64.3, H 8.2, N 1.5.
2c: Yield 0.98 g (85%). IR (KBr): ν = 1592 [ν(C=N)], 1570
˜
1
[ν(COO)as], 1417 [ν(COO)s] cm–1. H NMR (CD2Cl2): δ = 0.88 (t,
24 H, CH3), 1.28–1.86 (m, 128 H, CH2), 1.88 (s, 6 H, CH3CO2),
3.42–4.15 (m, 48 H, OCH2), 5.88 (d, 2 H, ArH), 5.95 (dd, 2 H,
ArH), 6.48 (d, 2 H, ArH), 6.55 (s, 4 H, ArH), 6.74 (s, 2 H, ArH),
6.81 (s, 2 H, ArH), 7.48 (s, 2 H, CH=N) ppm. C138H222N2O24Pd2
(2506.1): calcd. C 66.1, H 8.9, N 1.1; found C 66.0, H 8.8, N 1.3.
Preparation of [4Ј,5Ј-Bis(decyloxy)-4ЈЈ-amino]dibenzo[1Ј,2Ј-b:1ЈЈ,2ЈЈ- Preparation of the [Pd(µ-Cl)L]2 Chloro Complexes, 3a–c: To a
k]-1,4,7,10,13,16-hexaoxacyclooctadeca-2,11-diene (F): Compound
E (500 mg, 0.70 mmol), Pd/C (45 mg, 5%) and hydrazine monohy-
drate (4.63 g, 92 mmol) were suspended in ethoxyethanol (50 mL)
and heated at reflux for 1 h. The hot solution was filtered, and the
stirred solution of [Pd(µ-OAc)L]2 in CH2Cl2 was added dropwise a
stoichiometric amount of a HCl solution in diethyl ether. After the
solution was stirred for 1 h, the solvent was evaporated, and the
resulting oil was treated with acetone in order to obtain a yellow
solid, which was filtered off.
1
solvents were evaporated. Yield 0.43 g (90%). H NMR (CDCl3):
1216
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 1210–1218

Mesomorphic Palladium Complexes
3a: Yield 0.042 g (85%). IR (Nujol): ν = 1578 [ν(C=N)], 247 [ν(Pd–
˜
Cl)] cm–1. 1H NMR (CDCl3): δ = 1.35 (t, 6 H, CH3), 3.91–4.50 (m,
36 H, CH2O), 6.55 (dd, 2 H, ArH), 6.76–6.85 (m, 6 H, ArH), 6.90
(s, 8 H, ArH), 7.04 (d, 2 H, ArH), 7.20 (d, 2 H, ArH), 7.81 (s, 2
H, CH=N) ppm. C58H64N2Cl2O14Pd2 (1225.2): calcd. C 53.7, H
5.0, N 2.2; found C 54.0, H 5.3, N 2.0.
[1]
[2]
T. Kato, N. Mizoshita, K. Kishimoto, Angew. Chem. Int. Ed.
2006, 45, 38–68.
J. W. Goodby, G. H. Mehl, I. M. Saez, R. P. Tuffin, G. Macken-
zie, R. Auzély-Velty, T. Benvegnu, D. Plusquellec, Chem. Com-
mun. 1998, 2057–2058.
M. Yoshio, T. Mukai, H. Ohno, T. Kato, J. Am. Chem. Soc.
2004, 126, 994–995.
C. F. van Nostrum, S. J. Picken, A.-J. Schouten, R. J. M. Nolte,
J. Am. Chem. Soc. 1995, 117, 9957–9965.
K. Kimura, Y. Kawai, S. Yajima, Y. Sakurai, Chem. Commun.
2001, 1302–1303.
[3]
[4]
[5]
[6]
[7]
3b: Yield 0.42 g (83%). IR (Nujol): ν = 1578 [ν(C=N)], 248 [ν(Pd–
˜
1
Cl)] cm–1. H NMR (CD2Cl2): δ = 0.88 (t, 18 H, CH3), 1.27–1.78
(m, 96 H, CH2), 3.90–4.26 (m, 44 H, OCH2), 6.58 (s, 4 H, ArH),
6.60–6.80 (m, 8 H, ArH), 7.01 (d, 2 H, ArH), 7.25 (d, 2 H, ArH),
7.86 (s, 2 H, CH=N) ppm. C114H176N2Cl2O18Pd2 (2146.4): calcd.
C 63.8, H 8.3, N, 1.3; found C, 63.6, H 8.2, N 1.6.
M. Stepien, B. Donnio, J. L. Sessler, Angew. Chem. Int. Ed.
˛
2007, 46, 1431–1435.
M. J. O’Callagham, M. D. Wand, C. M. Walker, M. Nakata,
Appl. Phys. Lett. 2004, 85, 6344–6346.
H. J. Coles, M. N. Pivnenko, Nature 2005, 436, 997–1000.
C. F. van Nostrum, S. J. Picken, R. J. M. Nolte, Angew. Chem.
Int. Ed. Engl. 1994, 33, 2173–2175.
J.-M. Lehn, Angew. Chem. Int. Ed. Engl. 1988, 27, 89–112.
D. J. Cram, Angew. Chem. Int. Ed. Engl. 1988, 27, 1009–1020.
C. J. Pedersen, Angew. Chem. Int. Ed. Engl. 1988, 27, 1021–
1027.
I. K. Lednev, M. C. Petty, Adv. Mater. 1996, 8, 615–630.
T. I. Sergeeva, S. P. Gromov, A. I. Vedernikov, M. S. Kapichni-
kova, M. V. Alfimov, V.-T. Lieu, D. Möbius, M. S. Tsarkova,
S. Y. Zaitsev, Colloids Surf. 2005, 255, 201–209.
G.-X. He, F. Wada, K. Kikukawa, S. Shinkai, T. Matsuda, J.
Org. Chem. 1990, 55, 541–548.
G. Johansson, V. Percec, G. Ungar, D. Abramic, J. Chem. Soc.
Perkin Trans. 1 1994, 447–459.
R. P. Tuffin, K. J. Toyne, J. W. Goodby, J. Mater. Chem. 1996,
6, 1271–1282.
C. F. van Nostrum, Adv. Mater. 1996, 8, 1027–1030.
V. Percec, G. Johansson, G. Ungar, J. P. Zhou, J. Am. Chem.
Soc. 1996, 118, 9855–9866.
J. A. Schröter, C. Tschierske, M. Wittenberg, J. H. Wendorff,
Angew. Chem. Int. Ed. Engl. 1997, 36, 1119–1121.
K. Leblanc, P. Berdagué, J. Rault, P.-P. Bayle, P. Judeinstein,
Chem. Commun. 2000, 1291–1292.
3c: Yield 0.11 g (59%). IR (Nujol): ν = 1587 [ν(C=N)], 245 [ν(Pd–
˜
Cl)] cm–1. 1H NMR (CDCl3): δ = 0.88 (t, 24 H, CH3), 1.26–1.76
(m, 128 H, CH2), 3.89–4.12 (m, 48 H, OCH2), 6.58 (s, 4 H, ArH),
6.82–6.97 (m, 8 H, ArH), 6.97 (d 2 H, ArH), 7.75 (s, 2 H, CH=N)
ppm. C134H216N2Cl2O20Pd2 (2458.9): calcd. C 65.4, H 8.9, N 1.1;
found C 65.1, H 8.6, N 1.3.
[8]
[9]
[10]
[11]
[12]
General Procedure for Complexation: All potassium complexes were
prepared by following the same general procedure. KClO4 and the
corresponding crown ether compound, in a crown ether/potassium
molar ratio of 1:1, were dissolved in dichloromethane/ethanol (2:1).
The solvent was removed under vacuum, and all complexes were
isolated as pale brown solids.
[13]
[14]
[15]
[16]
[17]
2bk [(O ClO )KCrown2b]: IR (KBr): ν = 1591 [ν(C=N)], 1570
˜
2
2
[ν(COO)as], 1420 [ν(COO)s], 1122, 1111, 1087 [ν(Cl–O)] cm–1. 1H
NMR (CD2Cl2): syn isomer: δ = 0.86 (t, 18 H, CH3), 1.39–1.76 (m,
96 H, CH2), 2.12 (s, 3 H, CH3CO2), 2.26 (s, 3 H, CH3CO2), 3.56–
4.36 (m, 44 H, OCH2), 6.14 (d, 2 H, ArH), 6.31 (dd, 2 H, ArH),
6.45–6.70 (m, 10 H, ArH), 6.99 (d, 2 H, ArH), 7.78 (s, 2 H,
CH=N). anti isomer: δ = 0.86 (t, 18 H, CH3), 1.39–1.76 (m, 96 H,
CH2), 1.90 (s, 6 H, CH3CO2), 3.56–4.36 (m, 44 H, OCH2), 5.88 (d,
2 H, ArH), 6.15 (dd, 2 H, ArH), 6.45–6.70 (m, 8 H, ArH), 6.67 (d,
2 H, ArH), 7.18 (d, 2 H, ArH), 7.59 (s, 2 H, CH=N) ppm.
[18]
[19]
[20]
[21]
[22]
[23]
2ck [(O ClO )KCrown2c]: IR (KBr): ν = 1582 [(νC=N + νCOO )],
˜
2
2
as
1415 [ν(COO)s], 1123, 1111 (sh), 1095 [ν(Cl–O)] cm–1. 1H NMR
(CD2Cl2): δ = 0.88 (t, 24 H, CH3), 1.28–1.77 (m, 128 H, CH2), 2.05
(s, 6 H, CH3CO2), 3.67–4.24 (m, 48 H, OCH2), 5.70 (d, 2 H, ArH),
6.45 (br, 2 H, ArH), 6.61 (m, 6 H, ArH), 7.07 (m, 4 H, ArH), 7.94
(s, 2 H, CH=N) ppm.
A. Mourran, U. Beginn, G. Zipp, M. Möller, Langmuir 2004,
20, 673–679.
A. Schultz, S. Laschat, A. Saipa, F. Gießelmann, M. Nimtz,
J. L. Schulte, A. Baro, B. Miehlich, Adv. Funct. Mater. 2004,
14, 163–168.
[24]
[25]
[26]
T. Hegmann, B. Neumann, R. Wolf, C. Tschierske, J. Mater.
Chem. 2005, 15, 1025–1034.
N. Steinke, W. Frey, A. Baro, S. Laschat, C. Drees, M. Nimtz,
C. Hägele, F. Giesselmann, Chem. Eur. J. 2006, 12, 1026–1035.
P. Espinet, M. A. Esteruelas, L. A. Oro, J. L. Serrano, E. Sola,
Coord. Chem. Rev. 1992, 117, 215–274.
Metallomesogens (Ed,: J. L. Serrano), VCH, Weinheim, 1996.
a) D. W. Bruce, Inorganic Materials (Eds.: D. W. Bruce, D.
O’Hare), Wiley, Chichester, 2nd ed., 1996, ch. 8.
B. Donnio, D. Guillon, D. W. Bruce, R. Deschenaux, Metall-
omesogens, Comprehensive Organometallic Chemistry III: From
Fundamentals to Applications (Eds.: R. H. Crabtree, D. M. P.
Mingos), Elsevier, Oxford, UK, vol 12, 2006: Applications III:
Functional Materials, Environmental and Biological Applica-
tions, (Ed.: D. O’Hare), ch. 12.05, pp. 195–294.
T. Hegmann, B. Neumann, J. Kain, S. Diele, C. Tschierske, J.
Mater. Chem. 2000, 10, 2244–2248.
C. Sirlin, L. Bosio, J. Simon, V. Ahsen, E. Yilmazer, Ö. Bekâro-
glu, Chem. Phys. Lett. 1987, 139, 362–364.
Z. Belardi, C. Sirlin, J. Simon, J. J. Andre, J. Phys. Chem. 1989,
93, 8105–8110.
J. F. Van der Pol, E. Neeleman, J. W. Zwikker, R. J. M. Nolte,
W. Drenth, J. Aerts, R. Visser, S. J. Picken, Liq. Cryst. 1989, 6,
577–592.
3bk [(O ClO )KCrown3b]: IR (Nujol): ν = 1580 [ν(C=N)], 248
˜
2
2
[ν(Pd–Cl)], 1122, 1109, 1093 [ν(Cl–O)] cm–1. 1H NMR (CD2Cl2): δ
= 0.86 (t, 18 H, CH3), 1.39–1.76 (m, 96 H, CH2), 3.79–4.22 (m, 44
H, OCH2), 6.56 (s, 4 H, ArH), 6.65 (dd, 2 H, ArH), 6.82 (dd, 2 H,
ArH), 6.90 (m, 4 H, ArH), 7.11 (d, 2 H, ArH), 7.31 (d, 2 H, ArH),
7.92 (s, 2 H, CH=N) ppm.
[27]
[28]
3ck [(O ClO )KCrown3c]: IR (Nujol): ν = 1588 [ν(C=N)], 245
˜
2
2
[ν(Pd–Cl)], 1123, 1113, 1089 [ν(Cl–O)] cm–1. 1H NMR (CD2Cl2): δ
= 0.88 (t, 24 H, CH3), 1.28–1.75 (m, 128 H, CH2), 3.92–4.11 (m, [29]
48 H, OCH2), 6.56 (s, 4 H, ArH), 6.82 (dd, 2 H, ArH), 6.89 (d, 2
H, ArH), 6.90 (s, 2 H, ArH), 6.94 (s, 2 H, ArH), 7.10 (d, 2 H,
ArH), 7.88 (s, 2 H, CH=N) ppm.
CAUTION: Perchlorates are potentially explosive. Although we
have not experienced any problems, even under heating conditions,
they should be handled with care and small samples should be
used.
[30]
[31]
[32]
[33]
Acknowledgments
This work was sponsored by the Ministerio de Educación y Ciencia
(MEC) (Project CTQ2005-08729/BQU) and the Junta de Castilla y
León (Project VA099A05). C. C. thanks the MEC for a grant.
Eur. J. Inorg. Chem. 2008, 1210–1218
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1217

S. Coco, C. Cordovilla et al.
FULL PAPER
[34] J. Arias, M. Bardají, P. Espinet, J. Organomet. Chem. 2006, 691,
4990–4999.
[44]
[45]
G. W. Gray, J. W. Goodby, Smectic Liquid Crystals. Textures
and Structures, Hill, Glasgow, London, 1984.
I. Dierking, Textures of Liquid Crystals, Wiley-VCH,
Weinheim, 2003.
C. Tschierske, J. Mater. Chem. 1998, 8, 1485–1508.
N. L. Mc Millan, Phys. Rev. A 1973, 8, 1921–1929.
[35] M. B. Ros, N. Ruiz, J. L. Serrano, P. Espinet, Liq. Cryst. 1991,
9, 77–96.
[36] M. J. Baena, P. Espinet, M. B. Ros, J. L. Serrano, J. Mater.
Chem. 1996, 6, 1291–1296.
[37] H. Onoue, K. Minami, K. Nakagawa, Bull. Chem. Soc. Jpn.
1970, 43, 3480–3485.
[38] N. Nakamoto, IR and Raman Spectra of Inorganic and Coordi-
nation Compounds, Wiley Interscience, 3rd ed., 1978.
[39] M. J. Baena, J. Buey, P. Espinet, H.-S. Kitzerow, G. Heppke,
Angew. Chem. Int. Ed. 1993, 32, 1201–1203.
[40] M. J. Baena, J. Buey, P. Espinet, C. E. García-Prieto, J. Or-
ganomet. Chem. 2005, 690, 998–1010.
[41] C. J. Pedersen, J. Am. Chem. Soc. 1967, 89, 7017–7036.
[42] A. R. Davis, C. J. Murphy, R. A. Plane, Inorg. Chem. 1970, 9,
423–425.
[46]
[47]
[48] D. D. Perrin, W. L. F. Armarego, Purification of Laboratory
Chemicals, Pergamon Press, Oxford, 3rd ed., 1988, pp. 291.
[49] T. A. Stephenson, S. M. Morehouse, A. R. Powell, J. P. Heffer,
G. Wilkinson, J. Chem. Soc. 1965, 3632–3640.
[50] E. P. Kyba, R. C. Helgeson, K. Madan, G. W. Gokel, T. L. Tar-
nowski, S. S. Moore, D. J. Cram, J. Am. Chem. Soc. 1977, 99,
2564–2571.
[51] C. F. Van Nostrum, S. Picken, A. Schouten, J. M. Nolte, J. Am.
Chem. Soc. 1995, 117, 9957–9965.
Received: July 24, 2007
Published Online: January 15, 2008
[43] J. S. Kim, W. K. Lee, L.-H. Suh, J.-G. Kim, J. Yoon, J. H. Lee,
J. Org. Chem. 2000, 65, 7215–7217.
1218
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 1210–1218