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Liquid-Crystalline Crown Ether Forming Columnar Mesophases by Molecular Recognition.

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[ l I ] Crystal structure analysis of 7 (C,,H,,B,Fe,O,,
M = 491.3): F(000) = 504;
red prism (0.35 x 0.20 x 0.17 mm3); triclinic; Pi; (1 = 8.476(2), b = 9.445(2).
~ = 1 5 . 1 8 0 ( 2 ) , &=. ~90.84(2),p= 98.33(2),;.=114.58(2)*; V=1089.7(4)A3;
2 = 2. hi =1.362 mm-'; pCalcd
=1 497 Mgm-3; data were collected with a
Siemens P4 diffractometer (Mo,,. graphite monochromator, 7. = 0.71073 A,
2.0 i
20 i
55 ): T = 296 K, of 6642 reflections 4977 were independent
(R,,, = 0.0136) and 41 50 observed [F> 2.0a(F)]; Lorentzian and polarization
correction. absorption correction (empirical by Y-scans), min./max. transmission factors arc 0.661410 8026; structure solution by direct methods followed
by Fourier synthesis with the SHELXTL-Plus program and refinement against
F (non-hydrogen atoms anisotropic, all hydrogen positions calculated and
refined using the "riding model" with fixed isotropic temperature factors). The
refincment (full-matrix least squares) with 272 parameters converged at
R = 0 03x8 and i1.R = 0.0268. The max !min. residual electron density was
0.44 - 0.38 e ,& - 3 . Crystallographic data (excluding structure factors) for
the structures rcported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no. CCDC100279. Copies of the data can he obtained free of charge on application to The
Director. CCDC. 12 Union Road, Cambridge CBZlEZ, UK (fax: int code
+ (1223)336-033, e-mail: deposit@chemcrys.cam.ac.uk).
[12] a ) A. Zallkin. D. H. Tempelton, T. E. Hopkins, J Am. Chem. Soc. 1965,87.
3988-3900; b) R. P. Micciche, J. J. Briguglio. L. G. Sneddon, Organomrtn//ics
1984, 3. 1396 1402; c) H. A Boyter, Jr.. R G . Swisher, E. Sinn. R. N.
Grimes, InorK Cliem. 1985, 24. 3810-3819.
[ 13) N. N. Greenwood in EferrronDcficirnr Boron and Curbon Clusters (Eds.: G. A.
Olah, K Wade. R. E. Williams) Wiley. New York, 1991, chap. 6.
[14] B Wrackmcyer. 14. Noth, Cliem. Ber. 1977, 110. 1086-1094.
[15] H . Schulz. G. Cabbcrt. H. Pritzkow, W. Siebert. Chem. Ber. 1993, 126. 1593159s
Liquid-Crystalline Crown Ether:
Forming Columnar Mesophases by
Molecular Recognition**
Jorg Andreas Schroter, Carsten Tschierske,*
Michael Wittenberg, and Joachim Heinz Wendorff/
Dedicated to Professor Waldemar Adam
on the occasion of his 60th birthday
Crown ethers are well-known for their ability to form
complexes with alkali metal cations,['] and the possiblity of
combining this property with the supramolecular arrangements
provided by liquid crystals has been demonstrated. Predominately nematic phases and also smectic layer structures were
obtained from calamitic compounds with a crown ether moiety
at one of the termini of an extended, rodlike, rigid core.''] The
isotropization temperatures of low molecular mass liquid crystals containing crown ethers decrease upon complexation with
alkali metal salts,[2.31 whereas smectic mesophases of polymeric
liquid crystals crown ethers can be stabilized by complexation.14. On the other hand, columnar mesophases were induced by the interaction of heavy metal cations with multiarmed
azacrowns16-81or by addition of alkali metal triflates to tapered-shaped crown ether derivatives.['. l o ]
We recently reported on a novel class of mesogenic compounds, in which hydrophilic functional groups such as diol or
carbohydrate[' ' I were laterally attached to a rigid p-terphenyl
[*] Prof. Dr C Tschierske. J. A. Schroter
[**I
Insitiut fur Organische Chemie der Universitat
Kurt-Mothes-Strasse 2, D-06120 Halle (Germany)
Fax: Int. code +(345)55-27030
c-mail - coqfxia mlucom.urz.uni-halle.de
Prof. Dr. J. H Wendorff, M. Wittenberg
Institut fur Physikalische Chemie und Zentrum fur Materialwissenschaften der
Universitat Marburg (Germany)
This work was supported by the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie.
Angew. Cliem. hi1 E d E n d . 1997, 36. No. 10
core. Their smectic layer structures are significantly more stable
than those of related nonamphiphilic mesogens, and columnar
mesophases were observed for compounds carrying long, lateral
polyether chains.["] Therefore these molecules provide the possibility of changing the phase structure from layerlike to columnar with minor adjustments of the chemical structure. Here we
report attempts to change the aggregation pattern of this kind
of molecule by using the ability of crown ethers to specifically
recognize cations.
We synthesized 1, which consists of a rodlike 4,4"-didecyloxyp-terphenyl rigid core with a laterally attached [18]crown-6
unit (Figure l).t131The thermotropic properties of pure 1 were
C 45 (Sn 13 N 15)I
42.1 0.1 0.4
Figure 1. Thermotropic transition temperatures 1'C] (upper line) and transition
enthalpies [kJrnol-'] (lower line) of pure 1; C = crystalline solid. S, = srnectic A
phase, N = nematic phase. I = isotropic liquid; values in parenthesis refer to
monotropic phase transitions.
studied with polarizing optical microscopy and differential
scanning calorimetry. On cooling pure 1 two monotropic liquidcrystalline phases were observed, a nematic phase (schlieren
texture) and at lower temperature a smectic A phase (fanlike
texture with homeotropically oriented regions). The low
mesophase stability results from the significant disturbance of
the rodlike molecular structure by the bulky crown ether units.
We then investigated the influence of water on the mesomorphic properties with the solvent-penetration technique.['41 The
nematic phase and the S, phase disappear in the contact region
of 1 with water. In the middle concentration range only an
isotropic liquid can be detected. However, another liquid-crystalline phase occurs in regions with a further increased water
content. It displays a spherulitic texture between crossed polarizers, which points to a columnar mesophase. In the water-saturated sample, this induced mesophase is stable up to 22 "C.
The influence of cations on the liquid-crystalline behavior
was also investigated. In principal the same behavior was observed in the contact region between 1 and 1 M aqueous KCl
solution as with water. However, the induced phase was significantly more stable (up to 64°C). Mixtures with water and with
1M KCI solution or solutions of other K + salts showed the same
spherulitic texture (Figure 2).
The mesophase structure that is formed by 1 in the presence
of excess 1 M aqueous KCI was investigated by small-angle Xray diffraction with a Kratky compact camera. The X-ray pattern shows several sharp reflections in the small-angle region,
whose positions exclude a smectic layer structure (Figure 3).
However, they can be indexed as a rectangular columnar structure (lattice parameter: a = 4.1, b = 2.9 nm, the scattering vector q is defined by q = 2n/d). The textures of systems formed
from 1 and I M aqueous solutions of other alkali metal salts
correspond to that for l/KCl. We therefore assume that columnar mesophases were also induced in these cases.
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relate very well with the stability constants of the cation/
[18]crown-6 complexes in water." Therefore we can conclude
that the mesophases of this special kind of facial amphiphiles
can be influenced by a molecular recognition process.
The anions also influence the mesomorphic behavior. The
clearing temperatures of the systems 1 and 1M KX increase in
the order X = C1 (T,, = 64"C), X = Br (Tc, =78"C), X = I
(Tc, = 93 "C), that is, with increasing ion radius.[161
A possible model of the columnar mesophase is shown in
Figure 5. In strong analogy to the columnar thermomesophases
Figure 2 Optical photomicrograph of the texture of 1 saturated with 1 M aqueous
KBr between crossed polarizers at 83'C as obtained by coohng from the isotropic
state.
4.106 nrn (100)
4.40
I
I
t
I 1 I"
3.60
2.05 nm (200)
2.37
("O)
3.40
3.201
1.449 nm (020)
3.00
2
.
0.00
8
0
1.00
'
~
'
.
2.00
'
3.00
.
'
.
4.00
'
.
5.00
'
*
6.00
1
q / nm-' --L
Figure 3 Small-angle region of the X-ray scattering diagram of 1 saturated wlth 1M
aqueous KCI at 50 C
The stability of the induced mesophases depends strongly on
the size of the cation. Potassium ions, which fit in the cavity of
the [18]crown-6 unit well, give rise to the highest clearing temperature, whereas the transition temperatures are only marginally influenced by Li' and N a + . The larger cations Rbt and
Cs+ give lower mesophase stabilities than K'. As seen in Figure 4, the clearing temperatures of the induced mesophases cor-
r 70
51
.'
0
HzO
Li'
10
Na'
K'
Rb'
Cs'
Figure 4. Dependence of the clearing temperatures T,, of the columnar mesophases
of the systems l / l M MCl/H,O on cation M + (m) and on the equilibrium constants
(IgK) of the [lB]crownd/M+ systems in water ( 0 ) [15]. The transition temperatures
were obtained by polarizing microscopy.
1120
V C H Verlagsgesellschaff mbH, 0-69451 Weinheim. 1997
Figure 5. a) Schematic sketch of a possible ribbon arrangement of the rectangular
columnar phase (Col,). The ribbons consist of parallel p-terphenyl cores separated
by the polar regions (crown units, water molecules, and ion pairs, black areas).
b) CPK model showing a possible arrangement for the ribbons. Water molecules
and ions are omitted for clarity.
of facial amphiphiles with lateral polyether chains,["] we propose a ribbon model for this columnar mesophase. The ribbons
should be made up of rigid p-terphenyI cores that are arranged
parallel to one another and separated by the hydrophilic domains of the lateral groups consisting of the crown ether moieties, the complexed ions, and the solvent molecules. The alkyl
chains are molten and fill up the space between the ribbons. The
observed values of the lattice parameters a and b of the CoI,
phase represent the lateral distances between the centers of the
ribbons'"] and the thickness of the ribbons. According to this
model the ribbon may be regarded as bandlike segments of a
collapsed smectic layer structure. The formation of the ribbons
is caused by the segregation of hydrophilic and lipophilic units
into separate regions. From the observed lattice parameters it
can be concluded that more than two (about four) terphenyl
units have to be arranged side-by-side in the cross-section of the
ribbons. This requires that the polar lateral groups of the molecules in the middle of these ribbons cross over the neighboring
calamitic terphenyl units in order to be incorporated into the
polar regions. This should be possible (see Figure 5b) because
the lateral crown units are decoupled from the terphenyl cores
by the COOCH, spacers and because they are rather large.['81
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Furthermore, this arrangement allows simultaneously the parallel organization of the rodlike molecules and the segregation of
polar and lipophilic units into different regions.
A novel case of mesophase induction by self assembly directed by molecular recognition has been described. It is the first
example of mesophase stabilization and induction by interaction of alkali metal cations with a low molecular weight
calamitic crown compounds. It is especially remarkable, that
this rod-shupedmolecule can organize as a columnar mesophase.
In all previously reported cases of mesophase induction by complex formation of crown ethers with alkali metal ions, columnar
mesophases were only obtained with tapered-shaped molecules,
that is, compounds that have a "pre-disc" shape.
Received: October 9, 1996 [Z9636IE]
German version: Angeir. Chem. 1997, 109, 1160-1163
-
Keywords: crown compounds liquid crystals * mesophases
molecular recognition supramolecular chemistry
-
[17] The molecular length is 4.1 nm (CPK models). The layer thickness of the S,
phase of related 4,4-didecyloxy-p-terphenyl derivatives IS 3.3 nm I111.
1181 The layered organization of the terphenyl cores can tolerate rather large polar
lateral substituents [ll]. Therefore the crossing of the lateral substituents over
the terphenyl units in the periphery should be possible Furthermore, we have
recently found columnar mesophases for facial amphiphiles in which lateral
diol groups are connected through polyether chains to thc rigid cores. However, columnar mesophases can only be found if the lateral hydrophilic group
exceeds a certain length [12]. This means that a certain polarity and also a
certain length of the lateral groups are important prerequisites for the formation of these ribbon phases.
K,Sb~109Se,.3H,0:The First Crystalline
Nanoporous Material with a Photo-Semiconducting Host Structure**
*
Ulrich Simon,* Ferdi Schiith, Stephan Schunk,
Xiqu Wang, and Friedrich Liebau
[l] C. J. Pedersen. J. A m . Chem. Soc. 1967, 89. 7017; C. J. Pedersen, H. K. Frensdorf, Angen. Chrm 1972,84, 16; Angew. Chem. Int. Ed. Engl 1972, l l >16; see
also C J. Pedersen, ibid 1988, 100, 1053 and 1988, 29, 1021.
[2] G. X. He. F. Wada. K. Kikukawa, T. Matsuda, J. Chem. Soc. Chenz. Commun.
1987. 1294: G X. He. F. Wada, K. Kikukawa. S. Shinkai, T. Matsuda, J. Org.
Chenl. 1990, 55, 541. 548.
[3] X. Minggui. Q. Jun. H. Feng, Mol. Crjst. Liq. Cryst. 1991, 209. 309.
(41 V Percec. V. Rodenhouse. Macromolecules 1989, 22. 2043.
[5J V. Percec. G. Johansson. R. Rodenhouse, Macromolecules 1992, 25, 2563.
[6] J. M Lehn. J. Malthete, A. Levelut, J. Chem. SOC.Chem. Commun. 1985,1794.
[7] A. Liebmann. C Mertesdorf. T Plesnivy, H Ringsdorf, J H. Wendorff,
Angen. c'him 1991. 103, 1358; Angeu. Chrm 1nf. Ed. Engl. 1991, 30.
1375.
[XI G. Lattermann. S Schmidt. R. Kleppinger, J. H. Wendorff, Adv. Mafer. 1992.
4, 30.
[9] V. Perccc. G. Johansson. J. Heck, G. Ungar, S . V. Batty, J Chem. Soc ferkin
Trans. I 1993. I41 1 ;V Percec, J. Heck, G. Johansson, D. Tomazos. G. Ungar,
Mucroniol. Sjnip 1994. 77, 237, and references therein.
[lo] Columnar mesophases were induced by complexation of rod -coil molecules
containing terminal poly(ethy1ene oxide) chains with LiOTf M. Lee, N.-K.
Oh, Mol. Ci-ysr. Liy. Crjsr 1996, 280, 283.
[ l l ] F. Hildebrandt. J. A. Schroter, C. Tschierske, R. Festag, R. Kleppinger. J. H.
Wendorff. Ang(,ir Chem. 1995, 107, 1780; Angeu. Chem I n f . Ed. Engl. 1995,
34. 1631.
[12] F. Hildcbrandt. J A Schroter. C. Tschierske. R. Festag. M. Wittenberg J. H.
Wendorff. A d i Muter. 1997, 9, 564-566.
1131 Obtained by esterification of 4,4-didecyloxy-p-terphenyl-2'-carboxylic
acid [ I 11 with hydroxymethyl[l8]crown-6 (Aldrich) in the presence of N-cyclohcxyl-N'-[2-(4-methyImorpholino)ethyl]carbodiimide
(Aldrich) and catalytic
amounts of 4-dimethylaminopyridine.All analytical data agree with the proposed structure for 1: 'H NMR (500 MHz, CDCI,. 25°C. TMS): 6 = 0.87 (t,
J = 6.7 Hz, 613, CH,), 1.21-1.51 (m, 28H, CH,), 1.74-1.83 (m, 4H.
ArOCHJH,). 3.30 (dd, J =14.8, 4.2 Hz, l H , OCHCH,H,O). 3.37 (dd,
J=16X. 6.05Hz. I H , OCHCH,H,O), 3.54-3.67 (m, 21H, OCH,CH,O,
CH), 3.95 (t. J = 6.3 Hz. 2H, ArOCH,), 3.99 (t, J = 6.5 Hz, 2H,ArOCH,),
During the nineties the preparation of nanostructured materials has evolved to an important and promising area for physicists and chemists. The topic of many developments is the designed formation of specific structures of matter, for example
the generation of quantum dots, quantum wires, or multiple
quantum wells, for integration into microelectronic circuits to
miniaturize functional elements." - 3 1
To generate nanostructures physicists usually adopt preparation methods like electron beam lithography, which create the
small from the large structure and are consequently termed
"top-down'' methods. However, these methods can only generate structures that have a certain size distribution. but not those
of uniform size. This is a disadvantage when quantum size properties are investigated, because these properties are very sensitive to structural changes.
In order to cope with this problem, chemistry has evolved an
approach that has so far attracted only little attention. Elaborately optimized synthesis and self-assembly techniques have
made available nanostructured materials of uniform shape and
size, which may be smaller than one nanometer. These approaches start from atomic or molecular precursors and create
large from small. Thus, they are termed "bottom-up'' methods.
Among these materials are many metal and semiconductor clust e r ~ [ "(which
~
in some cases are arranged in superstructures) as
well as a large number of meso- to nanoporous solids. The latter
consist of a host structure containing cage- or channel-type
pores, or both. Guests are occluded in these voids. By far the
best known solids of this kind are zeolites and zeolite-type metal
4.11(dd.J=151.5.5H~.lH,CO,CH,H,),4.20(dd,J=16.6,5.05H~,1H,
CO,CH,H,). 6.90 (dd, J = 8 . 7 , 2.0Hz. 2H. arom. H), 6.96 (dd, J = 8 . 7 ,
. which the host structure is a porous, three-dioxides,[2.5 71 in
2.0Hz. 2H. arom. H), 7.25 (dd, J = 8 . 7 , 2.0Hz, 2H. arom. H), 7.36 (d,
mensional, polyhedral framework. Among the metal oxide
J = 8.0 Hz. 1 H. arom. H). 7.54 (dd, J = 8.7. 2.0 Hz, 2H. arom. H), 7.66 (dd.
group are mainly compounds that fulfil the structural demands
J = 8.1,2.0 Hz. 1 H, arom H), 7 93 (d. J = 2.0 Hz, 1 H, arom. H); MS (70 eV):
of semiconductors but are electrical insulators due to their
m / z ( % )= X62(100, [M']), 586(13). 569(8), 442(5),429(13).
114) These penetration experiments cannot give precise data concerning the water
chemical composition.
concentration. Related open-chain compounds can take up to 10 molequiv of
water. J A. Schrbrer, C Tschierske. M. Wittenberg, J. H. Wendorff, unpublished results
[15] R. M Izatt. J. S . Brandshaw. S . A. Nielsen, J. D Lamb, J. J. Christensen, D.
Sen. Chmi Rev. 1985.85.271, R. M. Izatt. R. E. Terry, B. L. Maymore, L D.
Hansen. N. K. Dalley. A G. Avondet. J. J. Christensen, J Am. Chem. Soc
1976. 98, 7620.
1161 The dependence of the clearing temperature on the anions can be caused by
several influences The equil~briumconstants of the crown/M+/X-/water systems should depend on X - . However. the differences are small (IgK(KC1) =
1.97;lgK(KBr) = 1 98;lgK(KI) =1.94;Y Liu, J. Hu, WuliHuaxueXuebaro.
1987, 3. I 1 ; R. M. Izatt, K. Pawlak, J. S. Brandshaw. R. L Bruening, Chem.
R e ' . 1991. Y I . 1721) and cannot explain this effect. In addition, the ability to
coordinate water decreases. and the lipophilic character of the anions increases
in the order Cl - . Br . I - .
Ang6m Chcni. h i . Ed. Engl. 1997, 36. No. 10
[*I Dr. U Simon
Institut fur Anorganische Chemie der Universitit Gesamthochschule Essen
Schutzenbahn 70, D-45127 Essen (Germany)
Fax: 1nt.code +(201)183-2417
e-mail: u.simon@uni-essen.de
Prof. Dr. F. Schuth. Dipl. Chem. S. Schunk
Institut fur Anorganische Chemie der Universitat Frankfurt (Germany)
Dr. X. Wang, Prof. Dr. F. Liebau
Mineralogisch-petrographisches Institut der Universitit Kiel (Germany)
[**I We thank Prof Dr. M. Czank (Kiel) for the preparation of the electron micrographs. Dr. D. Ackermand (Kiel) for the microprobe analyses as well as Dr. H.
Wiggers and J. Jockel (Essen) for their assistance with the impedance measurements. Financial support from the DFG IS acknowledged (Li 158;29).
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