A new [2]pseudorotaxane from 1,2-bis(isoquinolinium)ethane salt/dibenzo-24-crown-8 ether

Article abstract of DOI:10.1080/15421400903290733

A new [2]pseudorotaxane from the 1,2-bis(isoquinolinium)ethane axle and the dibenzo-24-crown-8 ether wheel and its self-assembly were investigated by ¹H NMR spectroscopy and single crystal X-ray diffraction technique. The results demonstrated that the supramolecular adduct was held together by three noncovalent interaction such as N⁺ ... O ion-dipole interactions, C-H ... O hydrogen bonding, and π-stacking between electron-poor isoquinolinium rings of the axle and electron-rich catechol rings of the wheel. They, furthermore, showed that the phenyl ring as a substituent or a fused ring on pyridinium has a similar effect on the association ability. Copyright Taylor & Francis Group, LLC.

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A New [2]Pseudorotaxane from
1,2-Bis(isoquinolinium)ethane Salt/
Dibenzo-24-crown-8 Ether
Jiang-Sheng Li a , Mei-Lian Fan b , Li-Gong Chen c , Tuncer Hökelek d
& Peng-Mian Huang a
a School of Chemistry and Biological Engineering, Changsha
University of Science and Technology , Changsha, China
b College of Chemistry and Chemical Engineering, Hunan University ,
Changsha, China
c School of Chemical Engineering and Technology, Tianjin University ,
Tianjin, China
d Department of Physics , Hacettepe University , Beytepe, Ankara,
Turkey
Published online: 01 Mar 2010.
To cite this article: Jiang-Sheng Li , Mei-Lian Fan , Li-Gong Chen , Tuncer Hökelek & Peng-Mian Huang
(2010) A New [2]Pseudorotaxane from 1,2-Bis(isoquinolinium)ethane Salt/Dibenzo-24-crown-8 Ether,
Molecular Crystals and Liquid Crystals, 517:1, 3-9, DOI: 10.1080/15421400903290733
To link to this article: http://dx.doi.org/10.1080/15421400903290733
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Mol. Cryst. Liq. Cryst., Vol. 517: pp. 3–9, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400903290733
A New [2]Pseudorotaxane from
1,2-Bis(isoquinolinium)ethane Salt/
Dibenzo-24-crown-8 Ether
JIANG-SHENG LI,1 MEI-LIAN FAN,2
3
4
¨
LI-GONG CHEN, TUNCER HOKELEK, AND
PENG-MIAN HUANG1
1School of Chemistry and Biological Engineering, Changsha
University of Science and Technology, Changsha, China
2College of Chemistry and Chemical Engineering, Hunan University,
Changsha, China
3School of Chemical Engineering and Technology, Tianjin University,
Tianjin, China
4Department of Physics, Hacettepe University, Beytepe,
Ankara, Turkey
A new [2]pseudorotaxane from the 1,2-bis(isoquinolinium)ethane axle and the
dibenzo-24-crown-8 ether wheel and its self-assembly were investigated by 1H
NMR spectroscopy and single crystal X-ray diffraction technique. The results
demonstrated that the supramolecular adduct was held together by three noncovalent
interaction such as Nþ ꢀ ꢀ ꢀ O ion–dipole interactions, C-H ꢀ ꢀ ꢀ O hydrogen bonding,
and p-stacking between electron-poor isoquinolinium rings of the axle and
electron-rich catechol rings of the wheel. They, furthermore, showed that the phenyl
ring as a substituent or a fused ring on pyridinium has a similar effect on the associ-
ation ability.
Keywords DB24C8; hydrogen-bonding; ion–dipole interaction; pseudorotaxane;
p-stacking interaction
Introduction
The interpenetrated molecules have attracted an ever-increasing interest from
supramolecular scientists. They have widely been applied for the construction of supra-
molecular architectures with charming topological geometry. The motif of 1,2-
bis(pyridinium)ethane=crown ether has originally been demonstrated by Loeb and
Wisner [1–5] and further employed to construct many metal-organic rotaxane frame-
works (MORFs) [6–8]. Herein, an analog 1,2-bis(isoquinolinium)ethane is shown as
an axle to thread through the cavity of the dibenzo-24-crown-8 (DB24C8) ether, form-
ing a [2]pseudorotaxane, and it further packs to form supramolecular bricklaying [9].
Address correspondence to Jiang-Sheng Li, School of Chemistry and Biological Engineer-
ing, Changsha University of Science and Technology, Changsha 410076, China. E-mail:
js_li@yahoo.com.cn
3

4
J.-S. Li et al.
Experimental
General
Isoquinoline, 1,2-dibromoethane, and ammonium hexafluorophosphate were of
reagent grade. Dibenzo-24-crown-8 (DB24C8) was purchased from Sigma-Aldrich
Co. Ltd. Deuterated solvents were available from Cambridge Isotope Laboratories
and used as received. All other solvents were of analytical grade and used as received.
All NMR spectra were recorded at 25ꢁC on a Varian INOVA500 spectrometer using
the deuterated solvent as the lock and the residual solvent as the internal reference.
Determination of the unit cell and data collection were performed on a Bruker Smart
1000 diffractometer using graphite monochromated Mo Ka radiation.
Preparation of 1,2-Bis(isoquinolinium)ethane Hexafluorophosphate
The axle 1,2-bis(isoquinolinium)ethane salt was prepared by a modified literature
method [1]. A solution of isoquinoline (3.87 g, 30 mmol) in DMF (5 mL) was pre-
heated to 80ꢁC, followed by dropwise addition of a dilute DMF (10 mL) solution
of 1,2-dibromoethane (1.88 g, 10 mmol) over 4 h. After addition, the reaction contin-
ued over a 3-d period and gradually cooled to room temperature. The resulting pre-
cipitate was filtered, washed with anhydrous diethyl ether (3 ꢂ 20 mL), and dried
under vacuum. Recrystallization from distilled water provided brick-like red crystals
1
1
(0.47 g, 1.1 mmol) in a 11% yield. H NMR (500 MHz, D2O) d 9.55 (s, 2 H, CH),
8.35–8.32 (m, 4 H, Harom), 8.18–8.13 (m, 6 H, Harom), 7.93–7.90 (m, 2 H, Harom),
5.43 (s, 4 H, CH2-Nþ); 13C NMR (125 MHz, D2O) d 150.09 (2C), 138.54 (2C),
138.22 (2C), 133.86 (2C), 132.31 (2C), 130.48 (2C), 127.95 (2C), 127.70 (2C),
127.68 (2C), 60.38 (2C). The obtained Br salt (0.81 g, 5.0 mmol) was dissolved in
hot water (1 mL), and saturated aqueous NH4PF6 (1 mL) was added, resulting in
a white precipitate. The mixture was allowed to cool slowly to room temperature
and the white powder produced isolated by filtration. The yield of PF6 salt was
0.20 g (74%). 1H NMR (500 MHz, CD3CN) d 9.51 (s, 2 H, 1CH), 8.44 (d, J ¼ 6.8 Hz,
Hz, 2 H, Harom), 8.38 (dd, J1 ¼ 8.5 Hz, J2 ¼ 1.0 Hz, 2 H, Harom), 8.32–8.27 (m, 6 H,
H
arom), 8.10–8.06 (m, 2 H, Harom), 5.30 (s, 4 H, CH2-Nþ).
Preparation of [2]Pseudorotaxane Crystals
The PF6 salt and DB24C8 were dissolved in acetonitrile (0.5 mL), respectively. Both
the solutions were combined to form a light-yellow solution. It was allowed to stand

A New [2]Pseudorotaxane
5
at room temperature over about one week, and [2]pseudorotaxane was obtained as
1
light-yellow crystals, confirmed by X-ray single crystal diffraction and H NMR
spectrum.
Results and Discussion
Crystal Study
The DB24C8 complex of the 1,2-bis(isoquinolinium)ethane crystallized with two
[2]pseudorotaxane and four acetonitrile molecules per unit cell in the monoclinic
space group P21=c, requiring the solution of only half of one centrosymmetric pseu-
dorotaxane, the rest of the cell being related by symmetry (ꢃx, ꢃy þ 1, ꢃz þ 1) [10].
The PF6 counterions were found to be disordered, responsible for the high R1 value.
In the pseudorotaxane, the 1,2-bis(isoquinolinium)ethane axle has an anti-
conformation around the C22-C220 center, likely due to the intramolecular repulsion
˚
of the positively charged nitrogen atoms (dNꢃN ¼ 3.712 A), and the crown ether
extends both its ꢁcatechol rings with the S-shape configuration (Fig. 1). The catechol
˚
ring lies at a 5.3 interplanar angle and a ca. 3.63 A interplanar spacing to the iso-
quinolinium ring, indicative of p-p stacking interaction in this structure. The long
axis of the crown is inclined to that of the thread by 29.2ꢁ, and the aryl oxygen atom
(O1) is positioned over the isoquinolinium Nþ center. This results in the maximum
ion–dipole interaction and hydrogen bonding, as was reported in the pseudorotax-
ane from 1,2-bis-(4-phenyl- pyridinium)ethane and DB24C8 [11].
Nþ ꢀ ꢀ ꢀ O ion–dipole stabilization is evident from several short to medium contacts
between the quaternized nitrogen centers and the ether oxygen atoms (N1ꢀ ꢀ ꢀ O1 ¼
0
˚
˚
˚
˚
3.446 A, N1 ꢀ ꢀ ꢀ O2 ¼ 3.698 A, N1 ꢀ ꢀ ꢀ O3 ¼ 3.902 A, N1 ꢀ ꢀ ꢀ O4¼ 3.800 A, N1 ꢀ ꢀ ꢀ O3 ¼
˚
3.913 A). These contributions are augmented by the presence of eight hydrogen bonds
involving the central methylene and a-isoquinolinium hydrogen atoms of the axle and
Figure 1. Two views of the crystal structure of the pseudorotaxane formed from the axle and
DB24C8. Most of hydrogens, two acetonitrile molecules, and hexafluorophosphate counter-
ions are omitted for clarity.

6
J.-S. Li et al.
Table 1. Hydrogen bonding parameters in the crystal structure of
pseudorotaxane
C-H ꢀ ꢀ ꢀ O (ꢁ)
˚
˚
C-H ꢀ ꢀ ꢀ O
H ꢀ ꢀ ꢀ O (A)
C ꢀ ꢀ ꢀ O (A)
C13-H13 ꢀ ꢀ ꢀ O3
C21-H21 ꢀ ꢀ ꢀ O3
C22-H22A ꢀ ꢀ ꢀ O4
C22-H22B ꢀ ꢀ ꢀ O2
2.53
2.51
2.39
2.55
3.395
3.335
3.311
3.476
155
148
159
159
the six oxygen atoms of the DB24C8 ether (Table 1). It is worthwhile to note that
the aryl oxygen atoms display shorter H ꢀ ꢀ ꢀ O distances than their alkyl counterparts.
This is contrary to the fact that alkyl oxygen atoms with greater basicity generally
display shorter intramolecular contacts, and also is different from those reported by
Wisner [12].
From the analysis above, the relative orientation of the axle and the wheel
mainly results from the Nþ ꢀ ꢀ ꢀ O ion–dipole interactions, reinforced by C ꢀ ꢀ ꢀ O
hydrogen bonding and p-stacking.
Expectedly, no complex hydrogen-bonding network or linear tape occurs in the
spatial packing of this [2]pseudorotaxane, most probably due to the absence of good
hydrogen-bonding acceptors or donors in itself. However, pseudorotaxane sheets are
constructed by the aid of acetonitrile molecules and counterions. p-p interactions
ꢁ
˚
(with interplanar angle of 5.42 and interplanar spacing of 3.323 A) between adjacent
sheets facilitate to form supramolecular walls (Fig. 2) using the pseudorotaxane as
brick, just like the real wall in our life.
Evidently, the introduction of isoquinolinium ring apt to p-stacking is respon-
sible for this supramolecular bricklaying.
Figure 2. The supramolecular wall constructed by the axle ꢄDB24C8 via p-stacking between
catechol and pyridyl ring of isoquinolinium salt. The acetonitriles and counterions are omitted.

A New [2]Pseudorotaxane
7
Figure 3. 1H NMR spectra of (a) free DB24C8, (b) free axle, and (c) their equimolar mixture.
1H NMR Spectroscopy
Analysis of the 1H NMR spectrum of the pseudorotaxane complex was performed in
MeCN-d3 due to the good solubility of both the hexafluorophosphate and DB24C8
in this solvent. An integrated spectrum of a 1:1 mixture of the dication and DB24C8,
and the individuals are shown in Fig. 3.
As can be seen in Fig. 3, there are three sets of independent resonance signals at
equilibrium, corresponding to the free axle, free crown ether, and the complex,
respectively. This suggests that the rate of association and dissociation is slow with
respect to the NMR scale. After association, the chemical shifts of central methylene
protons (Hj, Dd ¼ 0.378 ppm) and a-isoquinolinium protons (Hf, Dd ¼ 0.427, and Hg,
Dd ¼ 0.339 ppm) on the axle moved downfield. This downshift is characteristic of the
existence of C-H ꢀ ꢀ ꢀ O hydrogen bonding between the axle and DB24C8. The reso-
nances of the other protons on isoquinolinium rings and all protons (Hd and He)
on catechol rings moved upfield. This results from the p-stacking between the host
and guest moieties. Besides, a-ethyleneoxyl protons Ha shifted upfield, while
b-ethyleneoxyl protons Hb and c-ethyleneoxyl protons Hc shifted downfield. The
typical chemical shifts of protons on the axle and DB24C8, and the corresponding
changes are shown in Table 2.
Determination of Associate Constant
As mentioned above, signals for the complexed and uncomplexed species are
observed (Fig. 3c). Since absolute concentrations can be deduced readily from the
relative abundances of the three species at equilibrium when the initial concentra-
tions of both the axle and DB24C8 are known, single point determination of the
association constant (Ka) is possible. As for this pseudorotaxane, if the integrals
for the central methylene protons of the complexed (d ¼ 5.668 ppm) and
uncomplexed (d ¼ 5.291 ppm) thread are 1 and 1.2, respectively, and the initial

8
J.-S. Li et al.
Table 2. The typical chemical shifts (d) of the axle, DB24C8 and their equimolar
mixture, and the corresponding changes
axle
DB24C8
axle ꢄDB24C8
d
d
d
Dd
Hf
Hg
Hh
Hi
9.506 (s)
8.428 (d)
8.376 (d)
9.933 (s)
8.767 (s)
8.302–8.272 (m)
8.103–8.063 (m)
7.999 (d)
7.956 (t)
0.427
0.339
8.318–8.271 (m)
8.097–8.063 (m)
5.291 (s)
7.903 (d)
6.543 (dd)
6.402 (dd)
5.669 (s)
Hd
He
Hj
6.916 (m)
6.899 (m)
0.378
Ha
Hb
Hc
4.097 (m)
3.801 (m)
3.691 (s)
3.960 (s)
3.941 (s)
concentrations of thread and crown are 5 ꢂ 10ꢃ3 M, then:
1
2:2 ꢂ 5 ꢂ 10ꢃ3M
½Thread ꢄ Crownꢅ
½Threadꢅ½Crownꢅ
Ka ¼
¼
¼ 306Mꢃ1
:
À
Á
2
1:2
2:2 ꢂ 5 ꢂ 10ꢃ3M
The association constant of this pseudorotaxane comes closely to that (320 Mꢃ1
)
for the [2]pseudorotaxane reported previously [11], in which the thread is
1,2-bis(4-phenylpyridinium)ethane. This indicates that whether the phenyl group
acts as a substituent or a fused ring at pyridinium has a similar effect on the
DB24C8 complexation ability.
Conclusions
We have presented the formation of [2]pseudorotaxane from the 1,2-bis(isoquinoli-
nium)ethane axle and the dibenzo-24-crown ether wheel. Both solution and solid
state evidence unambiquously demonstrate that this interlocked complex is held
together by Nþ ꢀ ꢀ ꢀ O ion-dipole interactions, C-H ꢀ ꢀ ꢀ O hydrogen bonding, and
p-stacking between electron-deficient isoquinolinium rings of the axle and
electron-rich catechol rings of the wheel. Preliminary results showed that the phenyl
ring as a substituent or a fused ring on pyridinium has a similar effect on the associ-
ation ability. Furthermore, the supramolecular adduct has been demonstrated to
construct a supramolecular wall in the solid state.
Supplementary Data
CCDC 682513 contains the supplementary crystallographic data for this article.
Copies of the data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving.html [or from the Cambridge Crystallographic Data Centre (CCDC),

A New [2]Pseudorotaxane
9
12 Union Road, Cambridge CB2 1EZ, UK; fax: þ44(0)1223-336033; e-mail:
deposit@ccdc.cam.ac.uk].
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