Crown ethers with lateral ortho-terphenyl units: Effect of ester groups and sodium salts on the mesomorphic properties

Article abstract of DOI:10.1039/b814536a

Unsymmetrical crown ether derivatives 7 and 12 with one lateral o-terphenyl unit bearing different ester substituents were synthesized starting from methoxymethyl (MOM) protected bromobenzenes 3 and 8 by conversion into the respective borolanes 4 and 9, t

Full text of DOI:10.1039/b814536a

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Crown ethers with lateral ortho-terphenyl units: effect of ester groups and
sodium salts on the mesomorphic properties
a
b
b
Nelli Steinke, Michael Jahr, Matthias Lehmann, Angelika Baro,a Wolfgang Frey,a
*
a
Stefan Tussetschlager, Sven Sauer and Sabine Laschat
a
a
*
¨
Received 21st August 2008, Accepted 12th November 2008
First published as an Advance Article on the web 16th December 2008
DOI: 10.1039/b814536a
Unsymmetrical crown ether derivatives 7 and 12 with one lateral o-terphenyl unit bearing different ester
substituents were synthesized starting from methoxymethyl (MOM) protected bromobenzenes 3 and 8
by conversion into the respective borolanes 4 and 9, twofold Suzuki coupling with
dibromobenzo[15]crown-5, acidic deprotection and finally esterification either with various alkanoic
chlorides or gallic acids. Reaction with NaI provided the complexes [NaI$(7a–g)] and [NaI$(12a–d)],
respectively. Uncomplexed crown ethers as well as their complexes [NaI$7a–c] and [NaI$12a–d] are
non-mesogenic. In the case of [NaI$(7d–g)], however, the complexation induced a mesophase
formation. As exemplarily shown for [NaI$7d], different textures were observed upon cooling,
a fan-shaped texture, which is typical for a columnar hexagonal mesophase, and a striped fan-shaped
texture, indicating a second mesophase Colx at low-temperature. From the SAXS diffraction pattern
this mesophase was assigned to be columnar rectangular. For [NaI$7g] a different diffraction pattern
was found, from which the low-temperature mesophase might be attributed to a soft crystal or a highly
ordered columnar mesophase with orthorhombic symmetry.
1.0 Introduction
The combination of crown ethers or azacrowns with mesogenic
groups in one molecular entity leads to unprecedented properties
of these novel materials. Prominent examples with respect to
discotic liquid crystals are induction or stabilization of meso-
phases by selective cation complexation1,2 as described first by
Percec,2k elastic anisotropy,3 membranes containing ion-selective
transport channels,4 amphiphilic metallomesogens with high
charge carrier mobilities, which can be used as high performance
organic field effect transistors5 and conducting wires,6 induction
of tubular mesophases,7 organic gelators6b,e,8 and helical fibers
for self-assembly at gel-graphite interfaces.9–11 Recently we
reported on the mesomorphic properties of unsymmetrical
benzo[15]crown-5 ethers 1 with only one o-terphenyl unit bearing
alkoxy side chains, which stabilize the mesophases (Scheme 1).12
Uncomplexed derivatives 1 with chain lengths of at least C12
formed smectic mesophases, while complexation with alkali metal
Scheme 1
decrease the electron density to some extent in the aromatic ring,
which is directly attached to the crown ether moiety. Furthermore,
the influence of sodium iodide on the self-organisation is investi-
˚
gated. NaI fits perfectly into the [15]-crown-5 ether (Ø1.7–2.2 A) due
˚
to its cationic radius of 0.9 A. Comparison of the mesomorphic
salts induced
a
transformation to columnar mesophases.12
properties of mesogens with different side chains but the same core
and the same alkali salt allows a more detailed understanding of the
structure-property relationships in columnar liquid crystals.
Regarding wedge-shaped benzo[15]crown-5 ether derivatives 1, we
were particularly interested in whether the change of polarity
together with geometric restraints by replacement of the four
peripheral alkoxy chains with four various ester moieties would exert
any influence on the mesomorphic properties such as the structure
and stability of the mesophase. Ester groups not only change the
polarity of the side chains as compared to ether side chains, but also
2.0 Experimental
Melting points were measured on a Mettler Toledo DSC822 and
are uncorrected. NMR spectra were recorded on an Avance 300
and Avance 500 spectrometer, Bruker. FTIR spectra were
recorded on a Vektor22 spectrometer, Bruker, with MKII
Golden Gate Single Reflection Diamant ATR system. Mass
spectra were recorded on a Finnigan MAT 95 and a Varian MAT
711 apparatus. Elemental analysis were performed on a Carlo
Erba Strumentazione Elemental Analyzer Model 1106. X-Ray
powder experiments were performed on a Nanostar, Bruker;
aInstitut fu¨r Organische Chemie, Universita¨t Stuttgart, Pfaffenwaldring 55,
70569 Stuttgart, Germany. E-mail: sabine.laschat@oc.uni-stuttgart.de;
Fax: +49 711 68564285; Tel: +49 711 68564565
bInstitut fu¨r Chemie, Technische Universita¨t Chemnitz, Straße der
Nationen 62, 09111 Chemnitz, Germany. E-mail: Matthias.Lehmann@
Chemie.tu-chemnitz.de; Fax: +49 371 53121229; Tel: +49 371 53131205
This journal is ª The Royal Society of Chemistry 2009
J. Mater. Chem., 2009, 19, 645–654 | 645

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software: SAXS 4.1.26. The samples were kept in Hilgenberg-
glass capillaries of 0.7 mm outside diameter in a temperature-
controlled heating stage (ꢀ1 ꢁC). A monochromatic Cu–Ka1
OC(CH3)2C(CH3)2O], 3.47 (s, 3 H, CH3), 5.20 (s, 2 H,
OCH2OCH3), 7.01–7.04 (m, 2 H, 3-H, 5-H), 7.74–7.77 (m, 2 H,
2-H, 6-H). 13C NMR (CDCl3, 125 MHz): d 24.9 [OC(CH3)2C
(CH3)2O], 56.0 (CH3), 83.6 [OC(CH3)2C(CH3)2O], 94.1
(OCH2OCH3), 115.4, 136.5 (C-2, C-3, C-5, C-6), 159.8 (C-4).
FT-IR (ATR): n ¼ 2976 (s), 1604 (w), 1357, 1316, 1272, 1233,
1139, 1077, 993, 920, 859, 835 (s) cmꢃ1. Anal. calcd for
C14H21BO4: C, 63.66; H, 8.01. Found: C, 63.45; H, 8.00%.
˚
beam (l ¼ 1.5405 A) was obtained using a ceramic tube gener-
ator (1500 W) with cross-coupled Go¨bel-mirrors as the mono-
chromator. The diffraction patterns were recorded on a real-time
2D-detector (HI-STAR, Bruker). The calibration of the patterns
occurred with the powder pattern of Ag-Behenate.
Differential scanning calorimetry (DSC) was performed using
a Mettler Toledo DSC822, and polarizing optical microscopy
(POM) using an Olympus BX50 polarizing microscope combined
with a Linkam LTS350 hot stage and a Linkam TP93 central
processor.
Suzuki coupling of borolanes with 4,5-dibromobenzo[15]crown-5
to crown ethers 6a and 10a. To a solution of 5 (0.04 g, 0.10 mmol)
in degassed dimethoxyethane–water (10 mL:1 mL) the respective
4 or 9 (0.23 mmol), K2CO3 (0.16 g, 1.15 mmol), KF (0.07 g,
1.15 mmol) and Pd(PPh3)4 (0.02 g, 0.02 mmol) ꢁwere successively
added, and the reaction mixture stirred at 95 C for 48 h. The
reaction mixture was cooled to r.t. and concentrated. The residue
was taken up in CH2Cl2 (100 mL), washed with water (3 ꢂ 40
mL), dried (MgSO4), concentrated and purified by chromatog-
raphy on SiO2 with hexanes–EtOAc (1:5, Rf ¼ 0.14) (for 6a) or
CH2Cl2–EtOAc (4:1, Rf ¼ 0.20) (for 10a). Product 6a was
2.1 Materials synthesis
Synthesis of 4-bromo-1,2-bis(methoxymethoxy)benzene (3). To
a solution of 2 (4.50 g, 23.8 mmol) and dimethoxymethane
(90 mL, 77.4 g, 1.0 mol) in CHCl3 (150 mL) at 0 ꢁC P4O10 (67 g,
0.47 mol) was added portionwise and the reaction mixture stirred
for 30 min (tlc control). The reaction mixture was filtered and the
filtrate washed successively with an aqueous Na2CO3 solution
(3 ꢂ 100 mL) and HCl (1 N, 2 ꢂ 100 mL), dried (MgSO4) and
concentrated. The residue was chromatographed on SiO2 with
hexanes–EtOAc (9:1, Rf ¼ 0.26) to give 3 as a colorless oil, 4.66 g;
ꢁ
precipitated from CH2Cl2–ethanol at +4 C as a colorless solid,
1
1.33 g; yield, 40%. Mp 95.4 ꢁC. H NMR (CDCl3, 500 MHz):
d 3.35, 3.50 (2 s, 12 H, CH3), 3.78 [s, 8 H, CH2O(CH2-
CH2O)2CH2], 3.93 (s, 4 H, ArOCH2CH2O), 4.19–4.20 (m, 4 H,
ArOCH2CH2O), 4.95, 5.20 (2s, 8 H, OCH2OCH3), 6.83–6.86 (m,
4 H, 20-H, 50-H), 6.91 (s, 2 H, 3-H, 6-H), 7.05–7.06 (m, 2H, 60-H).
13C NMR (CDCl3, 125 MHz): d 55.9, 56.2 (CH3), 69.5, 69.7
[CH2O(CH2CH2O)2CH2], 70.7, 71.2 (ArOCH2CH2O), 95.4, 95.5
(OCH2OCH3), 116.3, 116.4 (20-C, C-3, C-6), 119.1 (C-50), 123.5
(C-60), 133.1 (C-5, C-4), 136.0 (C-10), 145.8, 146.8 (C-30, C-40),
148.3 (C-1, C-2). FT-IR (ATR): n ¼ 2869 (ms), 1604 (w), 1495,
1453, 1354, 1244, 1196, 1153, 1132, 1070 (m) cmꢃ1. MS (EI): m/z
(%) ¼ 663 (1), 662 (6), 661 (23), 660 (65) [M+], 584 (4), 508 (3), 376
(8), 45 (100) [CH2OCH3]. HRMS (EI): m/z (%) calcd for
C34H44O13: 660.2782. Found: 660.278ꢁ2. Product 10a was
precipitated from CH2Cl2–ethanol at +4 C as a colorless solid,
1
yield 71%. H NMR (CDCl3, 500 MHz): d 3.51, 3.52 (2s, 6 H,
CH3), 5.20, 5.22 (2s, 4 H, ArOCH2OCH3), 7.03 (d, J5,6 ¼ 8.7 Hz,
1 H, 5-H), 7.08 (dd, J6,5 ¼ 8.7, J6,2 ¼ 2.2 Hz, 1 H, 6-H), 7.31 (d,
J2,6 ¼ 2.2Hz, 1H, 2-H).13CNMR(CDCl3, 125MHz):d53.1(CH3),
95.4 (OCH2OCH3), 114.3 (C-1), 118.0, 119.9, 125.1 (C-2, C-6, C-5),
146.4, 148.0 (C-4, C-3). FT-IR (ATR): n ¼ 2955, 2901, 2827 (w),
1587 (w), 1490, 1386, 1246, 1150, 1072 (m) cmꢃ1. Anal. calcd for
C10H13BrO4: C, 43.34; H, 4.73. Found: C, 43.06; H, 4.71%.
Synthesis of borolanes 4 and 9. Under an inert gas atmosphere
n-BuLi (2.00 mL, 3.20 mmol, 1.6 M in hexane) was added drop-
wise to a solution of 3 or 8 (2.00 mmol) in abs. THF (100 mL) and
the reaction mixture stirred at ꢃ78 ꢁC for 10 min. After addition
of B(OMe)3 (0.39 mL, 0.36 g, 3.50 mmol) and stirring for 30 min,
the reaction mixture was warmed to r.t. within 2 h. Then pinacol
(0.40 g, 3.40 mmol) in THF (ca. 2 mL) was added and the reaction
mixture stirred for 1 h. After dropwise addition of conc. HOAc
(0.20 mL, 0.21 g, 3.50 mmol), the reaction mixture was stirred for
a further 18 h. The solvent was removed under vacuum, the
residue taken up in CH2Cl2, washed with water, dried (MgSO4)
and concentrated. Chromatography on SiO2 with hexanes–
EtOAc (8:1, Rf ¼ 0.18) gave 4 as a colorless solid, 0.47 g; yield,
1
1.91 g; yield, 46%. Mp 91.6 ꢁC. H NMR (CDCl3, 500 MHz):
d 3.47 (s, 6 H, CH3), 3.78 [s, 8 H, CH2O(CH2CH2O)2CH2], 3.92–
3.94 (m, 4 H, ArOCH2CH2O), 4.18–4.20 (m, 4 H, ArOCH2CH2O),
5.15 (s, 4 H, OCH2OCH3), 6.87–6.88 (m, 6 H, 6-H, 3-H, 20-H,
60-H), 7.02–7.04 (m, 4 H, 30-H, 50-H). 13C NMR (CDCl3, 125
MHz): d 56.0 (CH3), 69.4, 69.7 [CH2O(CH2CH2O)2CH2], 70.7,
71.2 (ArOCH2CH2O), 94.6 (OCH2OCH3), 115.7 (C-60, C-20),
116.6 (C-6, C-3), 130.9 (C-50, C-30), 133.1, 135.2 (C-5, C-10), 148.2
(C-1, C-2), 155.8 (C-40). FT-IR (ATR): n ¼ 2931, 2864 (m), 1603,
1494, 1442, 1355 (s), 1230, 1195, 1149, 1074, 1056 (s), 986, 919,
831 (s) cmꢃ1. Anal. calcd for C30H36O9: C, 66.65; H, 6.71. Found:
C, 66.69; H, 6.75%. Single crystals of the sodium complex
[NaI$10] were crystallized from CH2Cl2–MeOH/THF.
ꢁ
1
68%. Mp 50 C. H NMR (CDCl3, 500 MHz): d 1.32 [s, 12 H,
OC(CH3)2C(CH3)2O], 3.50, 3.54 (2s, 6 H, CH3), 5.26, 5.28 (2s, 4
H, OCH2OCH3), 7.15 (d, J5,6 ¼ 8.0 Hz, 1 H, 5-H), 7.44 (dd, J6,5
¼
8.0, J6,2 ¼ 1.1 Hz, 1 H, 6-H), 7.54 (d, J2,6 ¼ 1.1 Hz, 1 H, 2-H). 13
C
Crystal structure determination of complex [NaI$10a]. Crystal
NMR (CDCl3, 125 MHz): d 24.9 [OC(CH3)2C(CH3)2O], 56.2,
56.3 (CH3), 83.7 [OC(CH3)2C(CH3)2O], 95.1, 95.5 (OCH2OCH3),
115.7, 122.8 (C-5, C-6), 129.9 (C-2), 146.5, 150.2 (C-3, C-4).
FT-IR (ATR): n ¼ 2973 (w), 1601 (w), 1424, 1382, 1351, 1249,
1143, 1126, 1070 (m) cmꢃ1. Anal. calcd for C16H25BO6: C, 59.28;
H, 7.77. Found: C, 59.24; H, 7.74%. Chromatography on SiO2
with hexanes–Et2O (20:1) gave 9 as a colorless oil, 5.77 g; yield:
data. C30H36INaO9, M ¼ 690.50, monoclinic, a ¼ 20.0711(14), b ¼
3
˚
˚
8.4281(6), c ¼ 21.3869(14) A, V ¼ 3551.2(4) A , T ¼ 293 K, space
group P2(1)/n, Z ¼ 4, 7318 reflections measured, 3093 unique, which
were used in all calculations. The final wR(F2) was 0.1769 (all data).
Deprotection and alkylation with alkanoic chlorides to crown
ethers 7. To a solution of 6a (0.97 g, 1.46 mmol) in methanol–
CH2Cl2 (10 mL:10 mL) conc. HCl (3 mL) was added and the
1
61%. Rf ¼ 0.20. H NMR (CDCl3, 300 MHz): d 1.33 [s, 12 H,
646 | J. Mater. Chem., 2009, 19, 645–654
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reaction mixture stirred at r.t. for 4 h. The solvent was removed
under vacuum and 4,5-bis(3’,4’-dihydroxyphenyl)benzo[15]-
crown-5 (6b) precipitated from CH2Cl2–acetone at +4 ꢁC as
a colorless solid, 0.71 g; yield, quant. The product was used in the
next step without further purification. Mp 217 ꢁC. 1H NMR (d6-
DMSO, 500 MHz): d 3.63–3.66 [m, 8 H, CH2O(CH2CH2O)2-
CH2], 3.78–3.80 (m, 4 H, ArOCH2CH2O), 4.10–4.11 (m, 4 H,
concentrated and the remaining solid freeze-dried under high
vacuum. Even upon prolonged standing at r.t. complexes showed
no sign of hygroscopic properties and NMR and DSC data were
reproducible. The complexes were obtained as light yellow solids.
[NaI$7d]: 29.7 mg. DSC, Cr 94.9 ꢁC [53.0 kJ molꢃ1] Colr 121.8 ꢁC
[1.3 kJ molꢃ1] I (1. heating curve). 1H NMR (CDCl3, 500 MHz):
d 0.87–0.90 (m, 12 H, CH3), 1.27–1.39 [m, 56 H, OCOCH2CH2-
(CH2)7CH3], 1.67–1.77 [m, 8 H, OCOCH2CH2(CH2)7CH3],
2.49–2.52 [m, 8 H, OCOCH2(CH2)8CH3], 3.77–3.79 [m, 4 H,
CH2O(CH2CH2O)2CH2], 3.90–3.91 [m, 4 H, CH2O(CH2CH2O)2-
CH2], 4.08–4.10 (m, 4 H, ArOCH2CH2O), 4.29–4.31 (m, 4 H,
ArOCH2CH2O), 6.35 (dd, J6 ,5 ¼ 8.2, J6 ,2 ¼ 2.1 Hz, 2 H, 60-H),
0
0
0
0
0
0
0
0
0
0
6.52 (d, J2 ,6 ¼ 2.1 Hz, 2 H, 2 -H), 6.57 (d, J5 ,6 ¼ 8.2 Hz, 2 H, 5 -H),
6.80 (s, 2 H, 3-H, 6-H), 8.74 (br s, 4 H, OH). 13C NMR (d6-
DMSO, 125 MHz): d 68.7, 68.9, 69.9, 70.4 [CH2O(CH2CH2O)2-
CH2, ArOCH2CH2O], 115.1, 115.9, 117.0, 120.5 (C-20, C-50, C-60,
C-3, C-6), 132.6, 132.7 (C-4, C-5, C-10), 143.7, 144.5, 147.2 (C-1,
C-2, C-30, C-40). MS (EI): m/z (%) ¼ 486 (5), 485 (28), 484 (100)
[M+], 352 (23), 326 (5), 45 (4). HRMS (EI): m/z (%) calcd for
C26H28O9: 484.1733. Found: 484.1738.
ArOCH2CH2O), 6.87 (dd, J6 ,5 ¼ 8.3, J6 ,2 ¼ 2.2 Hz, 2 H, 60-H),
0
0
0
0
6.93 (s, 2 H, 3-H, 6-H), 6.98 (d, J2 ,6 ¼ 2.2 Hz, 2 H, 20-H), 7.01 (d,
0
0
J5 ,6 ¼ 8.3 Hz, 2 H, 50-H). 13C NMR (CDCl3, 125 MHz): d 14.1
(CH3), 22.7, 24.90, 24.94, 29.17, 29.19, 29.3, 29.4, 29.50, 29.53,
29.60, 29.63, 31.9 [OCOCH2(CH2)7CH3], 34.05, 34.11
[OCOCH2(CH2)7CH3], 67.4, 67.8 (ArOCH2CH2O), 69.19, 69.22
[CH2O(CH2CH2O)2], 114.7 (C-3, C-6), 123.1 (C-50), 124.6 (C-20),
128.0 (C-60), 132.7 (C-4, C-5), 138.7 (C-10), 141.1, 141.9 (C-30, C-40),
146.2 (C-4, C-5), 170.9, 171.0 (C]O). FT-IR (ATR): n ¼ 2921,
2852 (s), 1765 (s), 1493, 1458 (s), 1245, 1102, 1053 (s) cmꢃ1. MS
0
0
To a solution of 6b (0.07 g, 0.15 mmol) in THF (3 mL) at 0 ꢁC
DMAP (8.55 mg, 0.07 mmol), Et3N (0.30 mL, 0.22 g, 2.13 mmol)
and the appropriate alkanoic chloride (0.88 mmol) in THF
(2 mL) were successively added. The reaction mixture was
allowed to warm to r.t. and stirred for a further 18 h. The yellow
suspension was then concentrated, the residue taken up in
CH2Cl2 (20 mL), washed with water (3 ꢂ 10 mL), dried (MgSO4)
and concentrated. The crude products 7 were purified by chro-
matography on SiO2 with hexanes–EtOAc and obtained as
colorless oil (7a,b) or colorless solid (7c–g).
+
(MALDI-TOF):m/z ¼ 1179.8 [M+ +Na], calcdfor C70H108NaO13
1179.8. [NaI$7e]: 10.1 mg. DSC, Cr1 40.9 ꢁC [1.9 kJ molꢃ1] Cr2 97.3
ꢁC [49.9 kJ molꢃ1] Col 131.8 ꢁC [0.8 kJ molꢃ1] I. 1H NMR (CDCl3,
500 MHz): d 0.87–0.90 (m, 12 H, CH3), 1.27–1.39 [m, 64 H,
OCOCH2CH2(CH2)8CH3], 1.69–1.73 [m, 8 H, OCOCH2CH2-
(CH2)8CH3], 2.48–2.51 [m, 8 H, OCOCH2(CH2)9CH3], 3.78–3.79
Deprotection and alkylation with gallic acids 11 to crown ethers
12. A solution of 10a (1.06 g, 1.95 mmol) in methanol–CH2Cl2 (20
mL:10 mL) and conc. HCl (4 mL) was stirred at r.t. for 1 h. After
removal of the solvent under vacuum, 4,5-bis(4’-hydroxy-phe-
nyl)benzo[15]crown-5 (10b) was obtained as a colorless precipitate,
0.82 g; yield, quant. The product was used in the next step without
further purification. Mp 213.9 ꢁC. 1H NMR (d6-DMSO,
500 MHz): d 3.62–3.66 [s, 8 H, CH2O(CH2CH2O)2CH2], 3.78–3.80
(m, 4 H, ArOCH2CH2O), 4.11–4.13 (m, 4 H, ArOCH2CH2O),
6.60–6.62 (m, 4 H, 30-H, 50-H), 6.86–6.90 (m, 6 H, 6-H, 3-H, 20-H,
60-H), 9.30 (bs, 2 H, OH). 13C NMR (d6-DMSO, 125 MHz): d 68.7,
68.9, 70.0, 70.4 [CH2O(CH2CH2O)2CH2, ArOCH2CH2O], 114.7
(C-30, C-50), 115.9 (C-3, C-6), 130.6 (C-20, C-60), 131.9, 132.5 (C-4,
C-5, C-10), 147.4 (C-1, C-2), 155.7 (C-40). Anal. calcd for C26H28O7:
C, 69.01; H, 6.24. Found: C, 68.84; H, 6.21%.
[m,
4 H, CH2O(CH2CH2O)2CH2], 3.89–3.91 [m, 4 H,
CH2O(CH2CH2O)2CH2], 4.07–4.09 (m, 4 H, ArOCH2CH2O),
0
0
0
0
4.28–4.30 (m, 4 H, ArOCH2CH2O), 6.86 (dd, J6 ,5 ¼ 8.3, J6 ,2 ¼ 2.0
Hz, 2 H, 60-H), 6.92 (s, 2 H, 3-H, 6-H), 6.98 (d, J2 ,6 ¼ 2.0 Hz, 2 H,
0
0
20-H), 7.00 (d, J5 ,6 ¼ 8.3 Hz, 2 H, 50-H). 13C NMR (CDCl3, 125
MHz): d 14.1 (CH3), 22.7, 24.9, 25.0, 29.17, 29.19, 29.21, 29.3, 29.4,
29.51, 29.53, 29.6, 29.65, 29.69, 31.9 [OCOCH2(CH2)9CH3], 34.0,
34.1 [OCOCH2(CH2)9CH3], 67.5, 68.0 (ArOCH2CH2O), 69.3
[CH2O(CH2CH2O)2], 114.8 (C-3, C-6), 123.1 (C-50), 124.7
(C-20), 128.0 (C-60), 132.7 (C-4, C-5), 138.7 (C-10), 141.1, 141.9 (C-
30, C-40), 146.4 (C-4, C-5), 170.9, 171.0 (C]O). FT-IR (ATR):
n ¼ 2917, 2849 (m), 2360, 2341 (s), 1770 (s), 1558, 1541, 1506,
1496 (m), 1245, 1100 (s), 719 (s) cmꢃ1. MS (MALDI-TOF):
0
0
m/z (%) ¼ 1235.7 [M+ + Na], calcd for C74H116NaO13 1235.8.
+
[NaI$7f]: 23.8 mg. DSC, Cr 58.6 C [6.7 kJ molꢃ1] LC2 103.0 C
[10.7 kJ molꢃ1] LC1 136.7 ꢁC [0.9 kJ molꢃ1] I. 1H NMR (CDCl3, 500
MHz): d 0.87–0.90 (m, 12 H, CH3), 1.27–1.39 [m, 72 H,
OCOCH2CH2(CH2)9CH3], 1.64–1.73 [m, 8 H, OCOCH2CH2-
(CH2)9CH3], 2.49–2.52 [m, 8 H, OCOCH2(CH2)10CH3], 3.78–3.79
ꢁ
ꢁ
A solution of 10b (0.11 g, 0.25 mmol) in THF–DMSO (15 mL:1
mL) was added dropwise to a solution of the respective 11a–d (0.80
mmol), DCC (0.22 g, 1.05 mmol)and DMAP(0.02 g, 0.15 mmol)in
CH2Cl2 (10 mL) at 0 ꢁC. The reaction mixture was warmed to r.t.
and stirred for 18 h. The precipitate was filtered off. The filtrate was
concentrated and the residue taken up in CH2Cl2 (30 mL), washed
with HCl (1 N, 2 ꢂ 10 mL) and water (1 ꢂ 10 mL), dried (MgSO4)
and concentrated. The residue was chromatographed on SiO2 with
hexanes–EtOAc and the products 12 precipitated from CH2Cl2–
ethanol at +4 ꢁC and obtained as colorless solids.
[m,
4 H, CH2O(CH2CH2O)2CH2], 3.91–3.92 [m, 4 H,
CH2O(CH2CH2O)2CH2], 4.09–4.11 (m, 4 H, ArOCH2CH2O),
0
0
0
0
4.29–4.31 (m, 4 H, ArOCH2CH2O), 6.86 (dd, J6 ,5 ¼ 8.3, J6 ,2 ¼ 2.0
Hz, 2 H, 60-H), 6.92 (s, 2 H, 3-H, 6-H), 6.98 (d, J2 ,6 ¼ 2.0 Hz, 2 H,
0
0
20-H), 7.00 (d, J5 ,6 ¼ 8.3 Hz, 2 H, 50-H). 13C NMR (CDCl3, 125
MHz): d 14.1 (CH3), 22.7, 24.91, 24.94, 29.18, 29.20, 29.34, 29.4,
29.52, 29.54, 29.6, 29.66, 29.69, 29.71, 31.9[OCOCH2(CH2)10CH3],
34.0, 34.1 [OCOCH2(CH2)10CH3], 67.3, 67.8 (ArOCH2CH2O),
69.17, 69.20 [CH2O(CH2CH2O)2], 114.6 (C-3, C-6), 123.1 (C-50),
124.6(C-20),128.0(C-60),132.7(C-4, C-5),138.6(C-10),141.1, 141.9
(C-30, C-40), 146.2 (C-4, C-5), 170.9, 171.0 (C]O). FT-IR (ATR): n
¼ 2918, 2850 (m), 1765 (s), 1492, 1465, 1363 (m), 1246, 1111 (s)
cmꢃ1. MS (MALDI-TOF): m/z (%) ¼ 1291.9 [M+ + Na], calcd for
0
0
Complexation of 7 and 12 with NaI. A solution of NaI (0.02
mmol)in acetone (1 mL) was added to a solution of the appropriate
7 or12 (0.02 mmol) inCH2Cl2 (1mL), andthe reaction mixturewas
allowed to stay at r.t. for 16 h. The solvent was then evaporated
under a weak nitrogen flow, the residue taken up in CH2Cl2 (2 mL)
and unsolved NaI filtered off through cellulose. The filtrate was
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C78H124NaO13+ 1291.9. [NaI$7g]: 21 mg. DSC, Cr1 41.1 ꢁC [22.5 kJ
Following a procedure by Fujita and coworkers13 4-bromoca-
techol 2 was treated with dimethoxymethane in CH2Cl2 in the
presenceofP4O10 togivethe bis-MOM-protectedbromide3in71%
yield. In a one-pot procedure12,14 compound 3 was converted into
the borolane 4, which was isolated in 68% yield. Twofold Suzuki
cross-coupling of 4 with dibromide 56e,12,15 in the presence of
Pd(PPh3)4, K2CO3 and KF12,14a followed by deprotection of 6a
under acidic conditions according to the method by Fletcher and
Yardley16 and final esterification with acid chlorides in the presence
1
molꢃ1] Cr2 90.6 ꢁC [32.7 kJ molꢃ1] Col 117.1 ꢁC (POM) I. H
NMR (CDCl3, 500 MHz): d 0.87–0.90 (m, 12 H, CH3), 1.30–
1.39 [m, 80 H, OCOCH2CH2(CH2)10CH3], 1.66–1.73 [m, 8 H,
OCOCH2CH2(CH2)10CH3], 2.48–2.51 [m,
8 H, OCOCH2-
(CH2)11CH3], 3.77–3.79 [m, 4 H, CH2O(CH2CH2O)2CH2],
3.88–3.90 [m, 4 H, CH2O(CH2CH2O)2CH2], 4.06–4.08 (m, 4 H,
ArOCH2CH2O), 4.27–4.29 (m, 4 H, ArOCH2CH2O), 6.87 (dd,
0
0
0
0
0
J6 ,5 ¼ 8.3, J6 ,2 ¼ 2.0Hz, 2H, 6 -H),6.92(s, 2 H, 3-H, 6-H),6.98(d,
J2 ,6 ¼ 2.0 Hz, 2 H, 20-H), 7.00 (d, J5 ,6 ¼ 8.3 Hz, 2 H, 50-H). 13
C
0
0
0
0
NMR (CDCl3, 125 MHz): d 14.1 (CH3), 22.7, 24.9, 25.0, 29.20,
29.21, 29.35, 29.38, 29.5, 29.6, 29.69, 29.71, 29.74, 31.9
[OCOCH2(CH2)11CH3], 34.07, 34.13 [OCOCH2(CH2)11CH3],
67.7, 68.1 (ArOCH2CH2O), 69.4, 69.5 [CH2O(CH2CH2O)2], 114.9
(C-3, C-6), 123.1 (C-50), 124.7 (C-20), 128.0 (C-60), 132.7 (C-4, C-5),
138.8 (C-10), 141.1, 141.9 (C-30, C-40), 146.6 (C-4, C-5), 170.9, 171.0
(C]O). FT-IR (ATR): n ¼ 2918, 2850 (m), 2360 (s), 1764 (s), 1495,
1457, 1362 (m), 1246, 1185, 1108, 1056 (s), 943 (m) cmꢃ1. MS
(MALDI-TOF): m/z (%) ¼ 1347.9 [M+ + Na], calcd for
C82H132NaO13+ 1347.9.
3.0 Results and discussion
3.1 Synthesis of benzo[15]crown-5 ether derivatives 7 and 12
and their NaI complexes
The synthetic strategy to crown ethers 7 with alkyl ester groups is
shown in Scheme 2. In order to avoid tedious chromatographic
purification steps of intermediates with long side chains, we
envisaged introducing first protecting groups which can be
carried throughout the synthesis and can be replaced by alkyl
carboxylates in the last step. For our purposes we chose the
methoxymethyl (MOM) group because the final deprotection
should not interfere with the crown ether moiety.
Scheme 3
Scheme 2
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of DMAP and NEt3 in THF at 0 ꢁC17 yielded the desired tetraesters
7 in 42–65%. Treatment of 7 with NaI in CH2Cl2/acetone gave
quantitatively the corresponding complexes [NaI$(7a–g)].
for nanosegregation for compounds 12 and their sodium salts is
dramatically reduced compared with the ether derivatives 1 (c.p.
Scheme 1), resulting in a complete destabilization of mesophases.
A similar strategy was used for the synthesis of gallic ester
derivatives 12 (Scheme 3). Under the conditions described above,
1-bromo-4-methoxymethoxybenzene 818 was converted into the
borolane 9 in 61% yield. Suzuki coupling with dibromide 5 gave
the MOM-protected crown ether 10a in 46% yield. Subsequent
acidic deprotection and esterification with gallic acid derivatives
11 in the presence of DCC and DMAP employing the conditions
by Hess and Sheehan19 yielded the diesters 12 in 63–73%. Their
complexation to [NaI$(12a–d)] proceeded smoothly. It should be
noted that complexation of 7 and 12 could be monitored by NMR
spectroscopy. For example, the 1H NMR spectrum of 7d revealed
downfield shifts upon complexation from d ¼ 4.18–4.20 to 4.29–
4.31 ppm for ArOCH2CH2O, from d ¼ 3.93–3.94 to 4.08–4.10
ppm for ArOCH2CH2O, and from d ¼ 6.90 to 6.93 ppm for 3-H
and 6-H, whereas the 13C NMR spectrum revealed upfield shifts
for C3, C6 from d ¼ 116.1 to 114.7 and for C1, C2 from d ¼ 148.6
to 146.2 ppm. In the case of series 12, similar shifts were found.
Most characteristic is the upfield shift for C3, C6 from d ¼ 116.5 to
115.4 ppm upon complexation (e.g. 12b).
3.2.2 Mesomorphic behavior of alkyl ester derivatives 7a–g
and their NaI complexes. None of the uncomplexed alkyl esters
7a–g was found to be mesomorphic, and complexes [NaI$(7a–c)]
with shorter alkyl chains (n ¼ 6–8) melted directly into an
isotropic liquid. In contrast, the corresponding complexes
[NaI$(7d–g)] with longer alkyl chain lengths (n ¼ 9–12) displayed
mesomorphism. These findings for 7 and 12 indicate that
It should be noted that upscaling is easily possible and purifica-
tion of the crude tetra- and diesters 7 and 12 can be conveniently
achieved by simple recrystallization from CH2Cl2–ethanol. Struc-
ture and purity of all compounds were determined by conventional
spectroscopic methods, mass spectrometry and elemental analysis.
Fig. 1 DSC curves of [NaI$7d]. Heating/cooling rate 10 K minꢃ1
.
3.2 Thermotropic properties
The thermotropic properties of molecules 7 and 12 and their
sodium salts were investigated by differential scanning calorim-
etry (DSC) and polarizing optical microscopy (POM).
3.2.1 Mesomorphic behavior of gallic ester derivatives 12a–
d and their NaI complexes. Neither the uncomplexed derivatives
12a–d nor the corresponding complexes with sodium iodide
[NaI$(12a–d)] revealed any liquid crystalline properties. Taking
similar observations by Donnio and coworkers20 into account,
the absence of mesomorphism is not completely unexpected. Two
trisalkyloxygallic acid building blocks assemble a large number of
non-polar aliphatic chains to the o-terphenyl unit and thus, the
polar crown ether unit seems to play a minor role as compared to
the volume of the aliphatic chains. Consequently, the tendency
Table 1 Phase transition temperatures and enthalpies (in parentheses) of
sodium complexes [NaI$(7d–g)] in the second heating cycle
Phase transition temperature/ꢁC, enthalpies/kJ molꢃ1
Compd
Colr
Colh
I
NaI$7d
NaI$7e
NaI$7f
NaI$7g
ꢄ
ꢄ
ꢄ
90a
ꢄ
ꢄ
ꢄ
ꢄ
116.4 (1.0)
129.4 (0.9)
120.2 (0.8)
135.5 (0.9)
ꢄ
ꢄ
ꢄ
ꢄ
100a
—
b
c
b
—
ꢄ
a
The transition Colr / Colh was determined by X-ray measurement.
The transition Colr / Colh could not be determined neither by POM
Fig. 2 Textures of complex [NaI$7d] as seen between crossed polarizers
upon cooling from the isotropic state (cooling rate 1 K minꢃ1). (a) Fan-
shaped texture of the Colh phase at 113 ꢁC and (b) striped fan-shaped
texture of the second ColX phase at 78 ꢁC (magnification 200ꢂ).
b
c
nor DSC. Columnar soft crystal. Heating rate 10 K minꢃ1. Colr
¼
rectangular columnar, Colh ¼ hexagonal columnar, I ¼ isotropic.
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mesomorphism in the series of ester derivatives depends on
a sensitive balance of core size and volume fraction of aliphatic
chains. Upon heating the DSC curves of complexes [NaI$(7d,e)]
with decyl and undecyl chains showed a large endothermal
melting transition from a crystalline to a liquid crystalline state at
87 ꢁC and 89 ꢁC and a small clearing transition at 122 ꢁC and 131
ꢁC, respectively. All other consecutive heating (Table 1) and
cooling cycles exhibited only the clearing transition.
was still possible. These slight texture alterations indicate the
existence of a second mesophase ColX at low-temperatures. The
increase in birefringence, viscosity and the additional fine structure
in the texture points to the formation of a mesophase of higher
order. Typically mesogens aggregating in columnar phases exhibit
phase sequences from Colh to Colr upon cooling.
3.2.3 Comparison of ester derivatives 7, 12 with ethers 1 and
the corresponding NaI complexes. For classical disc-shaped hex-
akisalkyloxytriphenylenes or cone-shaped hexakisalkyloxy-
tribenzocyclononatrienes the replacement of the ether side chains
with ester groups resulted in a significant increase of the clearing
points, while the melting points remained constant. As a conse-
quence, the mesophase stability was dramatically improved.22 In
contrast, wedge-shaped crown ether derivatives 1, 7, and 12
behaved differently. They showed similar melting points in the
range 27–64 ꢁC with the alkyl chain length having a stronger
influence than the connecting ether or ester moiety. As
mentioned above, ethers 1 are mesomorphic (SmA) with
a minimum chain length of C12, whereas both esters 7 and 12 do
not show any mesophase. Regarding the NaI complexes, mixed
results were obtained. Complexes [NaI$1] with a minimum chain
length of C12 displayed columnar phases with melting points
around 28–55 ꢁC and clearing temperatures at 157–185 ꢁC, thus,
complexation considerably increased the mesophase stability.
Complexation of 7 to [NaI$7] shifted the melting points from
Complexes [NaI$(7f,g)] with longer dodecyl and tridecyl chains
revealed a more complex thermotropic behaviour upon first heat-
ing with several melting and recrystallization transitions before
they cleared from the high temperature mesophase to the isotropic
liquid. However, all further heating and cooling curves showed
again only a transition from the mesophase to the isotropic liquid
(Table 1). No recrystallization could be observed even after pro-
longed annealing below the initial melting temperature. Typical
DSC heating and cooling cycles of [NaI$7d] are shown in Fig. 1.
Decomposition of the salts did not occur upon heating up to
250 ꢁC as proved by TGA measurements for [NaI$7g], thus
indicating the thermal stability in this temperature range.
In contrast to DSC studies, POM studies of complexes
[NaI$(7d–g)] confirmed the presence of two different meso-
phases. This is exemplarily shown for [NaI$7d] (Fig. 2).
Upon slow cooling from the isotropic liquid fan-shaped textures
were observed at 113 ꢁC (Fig. 2a) which are frequently found for
columnar hexagonal (Colh) mesophases.21 Upon further cooling to
ꢁ
ꢁ
ꢁ
78 C striped fan-shaped textures appeared (Fig. 2b). Although
34–63 C to 72–118 C for non-mesomorphic esters 7a–c (chain
lengths #C9) and to 95–103 ꢁC for mesogens 7d–g (chain lengths
complex [NaI$7d] was highly viscous at this temperature, shearing
Fig. 3 X-Ray diffraction pattern and the corresponding small-angle X-ray scattering (SAXS) profiles of an oriented sample of [NaI$7d] (obtained by
prolonged annealing) in the Colh phase at 95 ꢁC (a), (b) and in the Colr phase at 75 ꢁC (c), (d). Columns are oriented parallel to the X-ray beam.
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>C9), respectively. Clearing temperatures of [NaI$7d–g] are in
the range 117–136 ꢁC. Overall, mesophase stabilities were much
lower for ester complexes [NaI$7] than for ether complexes
[NaI$1]. In the case of gallic esters 12, the complexation shifted
the melting points from 27–45 ꢁC to much higher temperatures of
Oriented samples were obtained by extrusion from the
columnar mesophase or prolonged annealing. A diffraction
pattern at small angles of a homeotropic oriented sample of
[NaI$7d] in the Colh phase is shown in Fig. 3a and the corre-
sponding small-angle X-ray scattering (SAXS) profile in Fig. 3b.
Since the columns are parallel aligned with the X-ray beam the
diffraction pattern reflects the hexagonal symmetry of the 2D
organisation of columns, which is confirmed by the ratio 1 : O3 : 2
for the reciprocal Bragg distances of the three reflections in
Fig. 3b. The reflections are consequently indexed with hk ¼ 10,
11 and 20 and the mesophase symmetry can be assigned to the
p6mm plane group. Upon cooling the 10 reflection splits into two
reflections (Fig. 3c) as recently observed also for hexacetenar
metallomesogens.23 The indexation of the large number of new
small angle reflections clearly verify the rectangular symmetry
(p2gg) of the columnar phase (Fig. 3d). Temperature-dependent
X-ray measurements during heating and cooling cycles
confirmed the enantiotropic nature of the mesophases.
ꢁ
131–206 C and no mesophase could be observed.
3.3 X-Ray diffraction
In order to confirm the preliminary assignment of the meso-
phases based on POM studies, X-ray diffraction experiments
were carried out.
The wide-angle X-ray scattering (WAXS) profile of the Colh
˚
phase of [NaI$7d] (Fig. 4) reveals only a broad halo at 4.6 A due
to the average separation of the liquid alkyl chains and the
mesogens along the column.
The higher homologues [NaI$(7e–g)] gave similar results as
depicted in Fig. 5a and b for the columnar rectangular mesophases.
In the columnar rectangular phase of [NaI$7e] two reflections
˚
at (i) ca. 4.2 A, and (ii) 4.5 A appear at the meridian of the
˚
Fig. 4 Wide-angle X-ray scattering (WAXS) profile of [NaI$7d] in the
columnar hexagonal mesophase.
Fig. 5 Small-angle (a) and wide-angle X-ray scattering profiles (b) of complexes [NaI$(7d–g)] in the Colr mesophase at 70 ꢁC (7g), 75 ꢁC (7d), 80 ꢁC (7f),
and 95 ꢁC (7e), and X-ray diffraction pattern of an oriented sample [NaI$7e] in its columnar rectangular mesophase (c).
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diffraction pattern of an oriented sample (Fig. 5c), pointing to
additional intracolumnar periodicity.
The data of X-ray diffraction experiments,24 summarized in
Table 2, reveal that for both columnar rectangular and columnar
hexagonal phases increasing chain lengths led to increasing
lattice parameters. With the exception of [NaI$7g], the lattice
parameter b of the Colr phase corresponds to the lattice
parameter a of the Colh phase. That means the relative positions
of columns are changing with decreasing temperature.
Fig. 6 Schematic illustration of the change of column orientation from
Colh to Colr with decreasing temperature; a(hex) ¼ b(rec).
This can be attributed to the tilt of mesogens versus the
columnar axes and thus the formation of an elliptical cross
section of the columnar cores as exemplified in Fig. 6.
by Hendrikx and Levelut for truxene derivatives.25 Alternatively,
the Colr to Colh transition with increasing temperature might also
be explained by conformational changes, i.e., with increasing
temperature the alkyl chains are more flexible and thus require
more space, which can be accommodated better in a columnar
hexagonal unit cell than in a columnar rectangular unit cell.26
Upon cooling from the Colh mesophase complexes [NaI$(7d–f)]
formed a disordered Colr mesophase. In the case of [NaI$7g],
a different diffraction pattern was observed (Fig. 7). Along the
meridian two layer lines of reflections with two relatively sharp
Another feature of the columnar rectangular mesophase is the
change of symmetry of the unit cell with increasing chain length
from p2gg for complexes [NaI$(7d–f)] to an orthorhombic struc-
ture for derivative [NaI$7g]. A change of symmetry was reported
Table 2 d Spacings and lattice parameters for both low and high
temperature mesophases of sodium complexes [NaI$(7d–g)]
˚
d spacing/A Miller
Lattice
spacing/A obsd (calcd) indices
˚
Compd Mesophase
˚
reflections at the meridian at 4.55 and 8.99 A are visible. The latter
NaI$7d Colr (p2gg) at 75 ꢁ
C
a ¼ 68.2
b ¼ 50.8
40.7 (40.7)
34.1 (34.1)
28.4 (28.3)
23.7 (23.8)
20.3 (20.4)
17.0 (17.0)
40.6 (40.6)
23.6 (23.5)
20.3 (20.3)
40.9 (40.9)
35.1 (35.1)
24.1 (23.7)
21.1 (21.2)
20.4 (20.5)
17.7 (17.6)
41.0 (41.0)
23.8 (23.7)
20.7 (20.5)
42.9 (42.9)
36.2 (36.2)
25.2 (25.0)
22.0 (22.0)
21.0 (21.4)
18.1 (18.1)
42.6 (42.6)
24.6 (24.6)
21.4 (21.3)
47.2 (47.2)
37.2 (37.2)
23.5 (23.6)
18.6 (18.6)
9.0 (9.0)
11
20
21
12
22
40
10
11
20
11
20
12
31
22
40
10
11
20
11
20
12
31
22
40
two signals can be indexed as 001 and as 002 reflections. The other
Colh (p6mm) at 95 ꢁ
C
a ¼ 46.9
NaI$7e Colr (p2gg) at 95 ꢁ
C
a ¼ 70.3
b ¼ 50.3
Colh at 90 ꢁ
C
a ¼ 47.3
NaI$7f
Colr (p2gg) at 80 ꢁ
C
a ¼ 72.4
b ¼ 53.2
Colh (p6mm) at 100 ꢁ
C
a ¼ 49.2
10
11
20
NaI$7g Crcol at 70 ꢁ
C
a ¼ 74.5
b ¼ 61.1
110b
200
220
400
001
351
880
671
861
002
442
352
532
10
a
7.0 (6.9)
5.8 (5.9)
5.5 (5.6)
5.5 (5.5)
4.6 (4.5)
4.2 (4.2)
4.2 (4.2)
4.2 (4.2)
Colh (p6mm) at 120 ꢁ
C
a ¼ 49.6
42.9 (42.9)
24.6 (24.8)
21.4 (21.5)
11
20
Fig. 7 2D X-ray diffraction pattern of an oriented sample of [NaI$7g] at
70 ꢁC (a) and a schematic illustration (b). Empty ellipsoids symbolize
weak reflections, grey ellipsoids strong reflections.
a
Columnar soft crystal. b hkl values in the case of soft crystal phase.
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reflections which are not located at the meridian result from layers
with mixed indices hkl, indicating a 3-dimensional order in this
columnar mesophase, which was recently also observed in different
non-conventional mesogenic materials.27 Thus, the low-tempera-
ture mesophase of [NaI$7g] possess a base-centred orthorhombic
structure and may be attributed to a soft crystal or a highly ordered
columnarliquid crystal. Fromthe comparison ofWAXSprofiles of
[NaI$7g] (Fig. 5b) with the corresponding shorter homologues
˚
[NaI$(7d–f)] it is obvious that the reflections at 4.55 and 8.99 A are
much more pronounced for 7g than for the other complexes
[NaI$(7d–f)]. In this case, a soft crystal might also be proposed.28
3.4 Arrangement of the molecules in the column: packing study
In order to explain the self-assembly of o-terphenyl crown ethers
such as 1 into columnar mesophases, we recently used X-ray
crystal structure analyses of non-mesogenic short-chain
analogues as a tool.12 The obtained data allowed us to calculate
the molecular dimensions. Unfortunately, it was impossible to
grow suitable single crystals from complexed [NaI$1]. However,
MOM ether complex [NaI$10a] gave single crystals which were
analyzed by X-ray crystallography (Fig. 8). In the solid state
structure of [NaI$10a] the Na+ cation is positioned in the middle
of the crown with the iodide anion residing close to the Na+
Fig. 9 Simple molecular modeling (Chem3D) of a columnar unit con-
sisting of four [NaI$7g] molecules.
were caused by core–core and alkyl–alkyl interactions, over-
˚
lapped resulting in a broad halo at 4.6 A. Thus the height of the
˚
a columnar slice in the Colh phase was estimated to be h ¼ 4.6 A.
˚
(Na–I distance 2.98 A), thus allowing sixfold coordination of
Eqn (1), applied to complex [NaI$7g] with the lattice parameter
˚
Na+. Although complex [NaI$10a] is not mesogenic, its struc-
tural data of the core unit were taken as input parameters for
simple molecular modeling of complexes [NaI$(7d–g)].
a ¼ 49.6 A yielded Z ¼ 3.9. For the other mesogens [NaI$7d,e,f]
in the hexagonal columnar phases Z values of 4.0, 3.9, and 4.1,
respectively, were obtained. These results point to a tetramer
forming a slice of column. From these results the volume fraction
of the core of a columnar slice can be calculated by Vcore ¼ Vunit
Based on the studies of Percec1c we propose that nano-
segregation and steric constraints should lead to the formation of
supramolecular assemblies, in which the polar crown ether
moieties are located in the centre of the column, whereas the
hydrophobic aliphatic chains point outwards. Due to the
twisting of the o-terphenyl unit p–p interactions contribute only
to a minor extent to the overall intracolumnar stability. The
number of molecules per unit cell Z for the columnar hexagonal
mesophases of [NaI$(7d–g)] was obtained by eqn (1).29
cell ꢃ Z$Vchains
.
23 Assuming a circular cross section of the column
core in the uniaxial hexagonal mesophase, the radius of the core
from an ester oxygen to the centre can be estimated by
rcore ¼ O(Vcore/(ph)). The values obtained for the hexagonal
˚
phases range from 15.9–16.8 A and are in excellent agreement
with the measured radius of a molecular model (Fig. 9) which
˚
amounts to approximately 17 A.
NAAhr
Z ¼
(1)
Mw
4.0 Conclusion
where Mw ¼ molecular weight, NA ¼ Avogadro’s constant,
A ¼ a2$sin 60ꢁ ¼ cross section of the hexagonal unit cell,
h ¼ height of the columnar unit, r ¼ density (with r ¼ 1 g cmꢃ3 as
a typical value for organic material); A and h were obtained by
SAXS and WAXS experiments.
Novel ester-substituted [15]crown-5 ethers 7 and 12 with an
o-terphenyl unit have been prepared and their mesomorphic
behavior studied. Neither the alkanoic esters 7 nor the gallic
esters 12 and their sodium complexes [NaI$12] displayed any
liquid crystalline properties. In contrast, complexation of alka-
noic esters 7d–g with NaI resulted in the formation of meso-
phases. The complexes [NaI$(7d–g)] with a minimum alkyl chain
length of C10 formed columnar rectangular mesophases at lower
temperatures and columnar hexagonal mesophases at higher
temperatures. Due to the increased rotational freedom of the
molecules around the columnar axis at higher temperature the
hexagonal symmetry is preferred for optimum space filling.30 For
[NaI$7g] a low-temperature mesophase was observed, which
might be attributed to a soft crystal or highly orderd columnar
mesophase with orthorhombic symmetry. The striking difference
between the two series of NaI complexes has still not been fully
understood and future work is necessary to study the influence of
alkali salts on mesomorphic properties.
As discussed above, no sharp WAXS reflections were obtained
for the Colh mesophase due to its disorder. The reflections, which
Fig. 8 Structure of complex [NaI$10a] in the solid state.
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ˆ
7 (a) J. Malthete, A.-M. Levelut and J.-M. Lehn, Chem. Commun.,
1992, 1434–1436; (b) S. H. J. Idziak, N. C. Maliszewskyj,
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Acknowledgements
Generous financial support by the Deutsche For-
schungsgemeinschaft, the Fonds der Chemischen Industrie, the
ˆ
J. Malthete and A. M. Levelut, Chem. Commun., 1985, 1794–1796;
Bundesministerium fur Bildung und Forschung (BMBF-grant
¨
01RI05177) and the Ministerium fur Wissenschaft, Forschung
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