Synthesis and properties of azobenzocrown ethers with π-electron donor, or π-electron donor and π-electron acceptor group(s) on benzene ring(s)

Article abstract of DOI:10.1016/j.tet.2005.08.071

New azobenzocrown ethers of differentiated size and with substituted benzene residues have been synthesized. These crown ethers possess π-electron donor, or π-electron donor-π-electron acceptor pair of functional group(s) in benzene ring(s) in the para position to azo-grouping. Their metal ion complexation abilities in solution were studied using UV-vis spectrophotometry. The X-ray structure of a 19-membered crown ether with 4-dimethylamino-4′-nitroazobenzene fragment has been solved.

Full text of DOI:10.1016/j.tet.2005.08.071

Tetrahedron 61 (2005) 10738–10747
Synthesis and properties of azobenzocrown ethers with p-electron
donor, or p-electron donor and p-electron acceptor group(s) on
benzene ring(s)
a
a
Elz˙bieta Luboch,a, Ewa Wagner-Wysiecka, Zuzanna Poleska-Muchlado
*
and Victor Ch. Kravtsovb
a
´
Department of Chemical Technology, Chemical Faculty, Gdansk University of Technology, Narutowicza 11/12, 80-952 Gdansk, Poland
bInstitute of Applied Physics, Academy of Science of Moldova, Kishinev, Academy 5, MD 2028, Moldova
Received 19 May 2005; revised 29 July 2005; accepted 18 August 2005
Available online 21 September 2005
Abstract—New azobenzocrown ethers of differentiated size and with substituted benzene residues have been synthesized. These crown
ethers possess p-electron donor, or p-electron donor–p-electron acceptor pair of functional group(s) in benzene ring(s) in the para position
to azo-grouping. Their metal ion complexation abilities in solution were studied using UV–vis spectrophotometry. The X-ray structure of a
19-membered crown ether with 4-dimethylamino-40-nitroazobenzene fragment has been solved.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
(ISME’s)6,7 and chemically sensitive field effect transistors
(ChemFET’s)8 was studied. As found for non-cyclic
azobenzene derivatives, amphiphilic azobenzocrown ethers
form stable Langmuir monolayers6,9 capable of E%Z
isomerization.
Crown ethers possessing an azo group as a part of the
macrocycle are interesting metal complexing reagents
preserving properties typical for azo metallochromic
reagents.1 The arrangement of lone electron pairs and the
diameter of the macrocyclic cavity additionally discrimi-
nates between complexed species according to their size.
Moreover, the presence of benzene rings allows almost
unlimited modifications of these compounds to obtain new
chromo- or fluoroionophores. Azobenzocrown ethers bear-
ing 2,20-linked azobenzene were prepared by Williamson
ether synthesis using 2,20-dihydroxyazobenzene.2,3 Another
route leading to the discussed crown ethers consists in using
2,20-difluoroazobenzene; this method also enables the
preparation of aza and thia analogs.4 Alternatively, azobenzo-
crown ethers were obtained by stannite reduction followed by
macrocyclization of the respective bis(2-nitrophenoxy)-
oxaalkanes.5 The last procedure was used in the synthesis of
numerous azobenzocrown ethers, and derivatives substituted
mainly with alkyl groups in aromatic rings.6,7
The complexation properties of azobenzocrown ethers with
alkali and alkaline earth metal salts were investigated
spectrophotometrically in acetonitrile solution.3,10,11 13-
and 16-membered chromoionophoric azobenzocrown ethers
with a hydroxyl or dimethylamino group in aromatic ring,
in the para position to the azo group, were investigated
among others.11
For para or ortho hydroxyazobenzenes the tautomerization
to quinone–hydrazone form is known to occur.12 The
physical properties of azo dyes (e.g., colour) are closely
related to this tautomerism. The phenylazophenol%qui-
none–phenylhydrazone tautomerization also proceeds in the
case of macrocyclic azophenol chromoionophores, cf.13
It was stated that compound 1 (Fig. 1) dissolved in, for
example, chloroform, acetonitrile or methanol exists in the
quinone–hydrazone form; in dimethyl sulfoxide this form
predominates.11 The structure of the quinone–hydrazone
form of crown ether 1 (1-QH) was solved by X-ray
crystallographic analysis.14 Compound 2 (Fig. 1) in chloro-
form and in acetonitrile exists, like 1, in the quinone–
hydrazone form but in dimethyl sulfoxide only the
The behaviour of lipophilic azobenzocrown ethers as
ionophores in ion selective membrane electrodes
Keywords: Azo compounds; Chromoionophores; Macrocyclic ligands;
Synthetic methods; UV–vis spectroscopy.
*
Corresponding author. Tel.: C48 58 3471759; fax: C48 58 3471949;
e-mail: elub@chem.pg.gda.pl
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.08.071

E. Luboch et al. / Tetrahedron 61 (2005) 10738–10747
10739
Figure 1. Structures of investigated azobenzocrown ethers.
azophenol form was observed. Cation complexation by
compounds 1 and 2 affects the tautomeric equilibrium.11
properties and metal ion complexation studies were carried
out. Their complexation properties were compared to
properties of unsubstituted azobenzocrown ethers 10–12.3,10
The presence of the dimethylamino substituent (para to the
azo group) in azobenzocrowns 4 and 5 (Fig. 1) made the
absorption maxima well pronounced compared to the
spectra of parent compounds 10 and 11.11 In the case of
compounds 4 and 5 complexation of lithium ions in
acetonitrile is clearly evident from spectrophotometric
studies due to adequate spectral band separation (60 nm)
of crown ether and its complex.
2. Results and discussion
2.1. Synthesis
The synthesis of compounds 3, 4–6 and 7–9 is presented in
Schemes 1–3. The 19-membered hydroxyazobenzocrown
ether 3 was obtained by stannite reduction of dinitropodand
13 (Scheme 1) in a way similar to the method described
earlier for azobenzocrown ethers of smaller size.11 It is
worth noting that Williamson synthesis of this compound
starting from 4-protected 2,20,4 -trihydroxyazobenzene
resulted in lower yield (around 1%) of 3.
This paper describes the synthesis and properties of new 19-
membered azobenzocrown ethers containing hydroxyl or
dimethylamino group in para position to azo group.
The synthesis of new 13-, 16- and 19-membered crowns
bearing two different electron donating/accepting groups
(dimethylamino and nitro) in the azobenzene fragment was
also elaborated. For the synthesized compounds, spectral
Tautomeric equilibria for 19-membered azobenzocrown
ether with a hydroxyl group were successfully investigated
Scheme 1. Synthesis of 19-membered azobenzocrown ether 3.

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E. Luboch et al. / Tetrahedron 61 (2005) 10738–10747
Scheme 2. Synthesis of azobenzocrown ethers 4–6.
1
using H NMR spectroscopy and compared with data for
smaller analogs. It was found that the equilibrium depends
on the size of the macrocycle. 13-Membered compound 1
exists in quinone–hydrazone form, which is stabilized by a
strong intramolecular hydrogen bond.14 19-Membered
compound 3 exclusively exists in the azophenol form in
DMSO and chloroform, whereas in acetonitrile this form is
present in no less than 75%.
only exist in E form. Single crystal X-ray diffraction study
of 9$2H2O confirmed the E geometry of the azo unit with
aromatic moieties in the trans-positions and proved the
existence of a molecular diaqua-complex (Fig. 2).
Compound 6 was obtained by two routes. The first synthesis
was performed analogously to the previously described
method,11 which consists of reductive macrocyclization of the
appropriate dinitropodand 14(yield4%, Scheme 2, method1).
The second synthetic procedure involved diazocoupling of
2-hydroxybenzenediazonium salt with 3-dimethylamino-
phenol. The obtained 4-dimethylamino-2,20-dihydroxyazo-
benzene, upon reaction with 1,13-ditosyl-1,4,7,10,13-pen-
taoxatridecane produced macrocyclic azo compound 6
(Scheme 2, method 2) with much better yield (55%). This
method was also used for the efficient synthesis of
compounds 4 and 5 with yields of 42 and 38%, respectively.
Figure 2. Molecular structure of 9$2H2O with the atom labeling scheme;
ellipsoids are drawn at 50% probability level.
Azobenzocrowns 7–9 were obtained by reacting 4-dimethy-
lamino-40-nitro-2,20-dihydroxyazobenzene with the appro-
priate ditosylates (Scheme 3, nZ1–3).
The heteroatoms of macrocyclic unit deviate from their
˚
mean plane in the range of K0.255(2)–0.217(2) A. The flat
nitrobenzene and dimethylaminobenzene moieties are
located at opposite sides of the plane. The dihedral angle
between these two aromatic systems equals 79.4(2)8. The
torsion angles around C15–N16 and N17–C18 bonds equal
It was found that compounds 7–9, contrary to the parent
azobenzocrown ethers, in solution and in the solid state,
Scheme 3. Synthesis of azobenzocrown ethers 7–9.

E. Luboch et al. / Tetrahedron 61 (2005) 10738–10747
Table 1. Hydrogen bonds in the structure of 9$2H2O (A and 8)
10741
a
˚
D–H/A
d (D–H)
d (H/A) d (D/A) Angle
(D–H/A)
O1w–H1w1/O7
O1w–H2w1/N16
O2w–H1w2/
O1w#1
1.01(2)
1.00(2)
1.05(2)
2.10(6)
2.31(7)
1.87(3)
2.923(6)
3.157(6)
2.904(7)
137(7)
142(8)
166(6)
O2w–H2w2/O1w 1.08(2)
1.97(4)
2.967(7)
153(6)
a Symmetry transformations used to generate equivalent atoms: #1 Kx,
KyC2, KzC1.
In turn, the dimers associate to form chains along the [0 K1 1]
direction of crystal due to p-stacked assembly of
centrosymmetrically related dimethylaminobenzene moi-
eties. The centroid–centroid distance and the interplanar
separations between the corresponding aromatic rings in the
stack are 3.908 and 3.530 A, respectively. No distinct p–p
stacking interactions were found for the nitrobenzene
aromatic moiety (Fig. 4).
Figure 3. Hydrogen bonded centrosymmetric dimer in the structure of
9$2H2O. Hydrogen atoms of crown ethers are omitted for clarity.
˚
164.0(4) and 125.7(4)8, respectively. These differences
indicate various degree of p-conjugation of the azo-group
with the adjacent aromatic rings and agree well with the
˚
corresponding bond lengths of C15–N16 [1.417(6) A] and
˚
N17–C18 [1.431(6) A]. In the polyether chain the torsion
2.2. Spectroscopy and complexation behaviour
angles around C–C bonds are gauche and equal 62.4(5),
K73.7(5), 67.8(5) and K72.18 clockwise starting from the
C2–C3 bond. The majority of C–O bonds adopt an anti
conformation and their deviations from 1808 are less than
208 except for the torsion angle C19–O1–C2–C3, which is
gauche and equals 71.48. The sequence of two gauche
torsion angles at C2 atom forms the corner fragment.15
The UV–vis spectroscopic properties of investigated and
parent compounds (Fig. 1) are collected in Table 2.
The general solvatochromic effect for the above dimethyl-
aminocrown ethers was studied for 19-membered crown
ether 6 as an example. UV–vis spectra of 6 in methylene
chloride, acetonitrile, acetone, methanol and DMSO were
recorded. Characteristic absorption bands and molar
absorptivity coefficients in different solvents are collected
in Table 3. In all cases noticeable bathochromic shifts of
absorption bands at about 390 nm were observed comparing
to spectra in acetonitrile. The most significant intensity
changes were found for methylene chloride and DMSO;
hyper- or hypochromic effects were observed for these
solvents, respectively, (Fig. 5).
To the best of our knowledge, this is the first structurally
characterized example of water molecule coordination by
crown ethers with azobenzene subunit in the macrocycle,
although water complexation by Pedersen type macro-
cycles16 is an ordinary and well established phenomenon.17
˚
One water molecule is located 1.723(5) A above
the macrocycle mean plane, and donates protons to form
O1w–H/O7 and O1w–H/N16 hydrogen bonds. Two
other water molecules bridge neighbouring aqua complexes
via O2w–H/O1w hydrogen bonds and result in formation
of a centrosymmetric H-bonded dimer. In this dimer, two
crown ether molecules encapsulate a tetrameric water
cluster (Fig. 3, Table 1).
As expected, the presence of p-electron donor, or
p-electron donor and p-electron acceptor groups attached
to benzene ring(s) of azobenzocrown ether causes a red shift
of the absorption maximum.
Figure. 4. Hydrogen bonds and p–p stacking interactions linking crown ether and water molecules into chain laying in the [0 K1 1] direction of crystal. Only
hydrogen atoms involved in H-bonds are shown.
Table 2. Characteristic absorption bands and molar absorptivity coefficients for azobenzocrown ethers in acetonitrile
Crown ether
lmax (nm)
3max
Crown ether
lmax (nm)
3max
111
211
3
434
431
342, 434
403
400
2.31!104
7
8
9
459
463
287, 485
347, 456
351, 461
337, 439
1.90!104
2.05!104
1.90!104
1.70!104, 1.60!104
7.70!103
8.30!103, 1.70!104
1.10!104, 5.04!102
9.40!103, 9.80!102
7.88!103, 2.83!103
411
511
6
10(trans)
11(trans)10
12(trans)10
1.78!104
380, 455
1.30!104, 8.10!103

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E. Luboch et al. / Tetrahedron 61 (2005) 10738–10747
Table 3. Characteristic absorption bands and molar absorptivity coefficients for azobenzocrown ether 6 in different solvents
Solvent
lmax (nm)
3max
Solvent
lmax (nm)
3max
Methylene chloride
Methanol
394, w460
389, w460
2.40!104, 1.20!104
1.70!104, 1.20!104
Acetone
Dimethyl sulfoxide
393, w460
392, w460
1.40!104, 6.50!103
7.00!103, 4.60!103
signals for only the azophenol form are observed in the
presence of barium, strontium and calcium salts. UV–vis
absorption spectra registered in acetonitrile show a decrease
of band intensity at 430 nm followed by an increase of the
band at 350 nm (typical for the azo form) upon titration with
the above metal perchlorates. The respective changes for
interaction with strontium perchlorate are exemplified in
Figure 7.
The results of spectrophotometric titration did not allow full
characterization of the equilibria that occur in the system
with compound 3. It was only stated that beside complex
formation tautomeric equilibrium takes place.
For 19-membered azobenzocrown ether with dimethyla-
mino group (compound 6) selective complex formation was
found with the magnesium cation among alkali and alkaline
earth metal cations in acetonitrile solution. The complexa-
tion was manifested by characteristic colour change from
orange to pink. The spectral changes accompanying
complex formation are presented in Figure 8.
Figure 5. Absorption spectra of compound 6 (cZ4.1!10K5 mol dmK3) in
different solvents.
Furthermore, the absorption maxima for substituted crown
ethers are well pronounced compared with the spectra of the
parent unsubstituted crown ethers. A significant effect of
the presence of dimethylamino-, or dimethylamino- and
nitro-group(s) in benzene rings for compounds 4–6 and 7–9
is that the E/Z isomerization in different solvents under
usual conditions is not observed. Absorption spectra of 13-
membered crown ethers 10, 4 and 7 in acetonitrile are
presented in Figure 6.
Other studied cations do not cause such distinct colour
changes. Comparison of spectral changes of compound 6 in
the presence of potassium, strontium and magnesium
perchlorate with evident selectivity for magnesium is
shown in Figure 9.
Complexation studies for compound 6 were also carried out
in methanol. In this case, no significant spectral changes
enabling determination of binding constants were found in
the presence of lithium, sodium, potassium and magnesium
salts. As could be expected the values of stability constants
in methanol are smaller than in acetonitrile. However, in
both solvents the largest value of stability constant was
found for barium complex (Table 4).
Complexation of alkali and alkaline earth metal ions by
macrocycles was investigated by UV–vis spectroscopy in
organic solvents. Studies of metal cation complexation
performed for 19-membered hydroxyazobenzocrown ether
3 were combined with studies of azophenol%quinone–
hydrazone equilibration. It was found that the azophenol
1
form is stabilized by complexation of metal cations. In H
NMR spectra recorded in acetonitrile well pronounced
Figure 7. Changes of absorption spectra upon titration of compound 3 (cZ
Figure 6. Absorption spectra of azobenzocrown ethers: 10, 4 and 7 (cZ
7.0!10K5 mol dmK3) in acetonitrile.
3.0!10K5 mol dmK3) with strontium perchlorate (0–4.4!10K5 mol dmK3
)
in acetonitrile.

E. Luboch et al. / Tetrahedron 61 (2005) 10738–10747
10743
for unsubstituted compound 10, changes in the absorption
spectra made determination of stability constant impossible.
Generally, the values of the stability constants are higher
for alkaline earth metal cation complexes than for lithium
and sodium. Changes in the absorption spectra of
compound 7 in the presence of alkaline earth metal cations
perchlorates are presented in Figure 10. Changes upon
titration of above crown ether with lithium perchlorate are
shown in Figure 11. The respective values of stability
constants for compounds 7–9 and shifts of absorption bands
are collected in Table 5.
Figure 8. Spectral changes of compound 6 (cZ5.7!10K5 mol dmK3
)
upon titration with magnesium perchlorate (0–1.9!10K3 mol dmK3) in
acetonitrile.
Figure 10. Absorption spectra of compound 7 and its complexes. ‘Free’
ligand (cZ3.5!10K5 mol dmK3); and limiting spectra in the presence of:
magnesium (cZ2.2!10K4 mol dmK3); calcium (cZ4.5!10K4 mol dmK3);
strontium (cZ4.1!10K4 mol dmK3); and barium (cZ3.9!10K4 mol dmK3
)
perchlorates in acetonitrile.
Figure 9. Absorption spectra of compound 6 and its complexes. ‘Free’
ligand (cZ5.7!10K5 mol dmK3) and limiting spectra in the presence of:
potassium (cZ2.6!10K3 mol dmK3); strontium (cZ4.4!10K5 mol dmK3);
and magnesium (cZ1.9!10K3 mol dmK3) perchlorates in acetonitrile.
Investigations of metal ion complexation were performed
also for new type of synthesized compounds containing two
different functional groups on the benzene rings (com-
pounds 7–9). It was found that the crown ethers complex
alkali and alkaline earth metal cations and that the
selectivity depends on the cavity size. 13-Membered
azobenzocrown 7 forms complexes with most of the
investigated metal cations. Only the presence of potassium
salt causes small changes in the absorption spectra preclude
determination of stability constant, similarly to other 13-
membered azobenzocrowns. For the sodium complex of
compound 7 the calculated stability constant is a little
smaller than for sodium complex of compound 4, whereas
Figure 11. Changes of absorption spectra upon titration of compound 7
(cZ3.5!10K5 mol dmK3
)
with lithium perchlorate (0–4.1!10K3
mol dmK3) in acetonitrile.
Table 4. Stability constants of 1:1 complexes of compound 6 with metal perchlorates in acetonitrile and methanol
Solvent
Log KMe (Dl (nm))
Li
Na
K
Mg
Ca
Sr
Ba
Acetonitrile
Methanol
2.7a
—
3.4a
—
4.3b
—
4.2 (46)
—
5.1a
2.7a
5.4a
3.5a
6.7a
4.3a
a Increase of intensity for band at 442 nm.
b Increase of intensity for bands at 380 and 442 nm.

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E. Luboch et al. / Tetrahedron 61 (2005) 10738–10747
Table 5. Stability constants of 1:1 complexes of compounds 7–9 with metal perchlorates in acetonitrile
Compound
Log KMe (Dl (nm))
Li
Na
K
Mg
Ca
Sr
Ba
7
8
9
3.1 (51)
4.3 (37)
2.1a
1.8 (28)
3.7 (37)
2.9a
—
3.2 (27)
2.8a
4.3 (37)
5.0 (35)
2.5a
4.5 (56)
5.3 (55)
6.2a
3.6 (45)
5.4 (55)
5.7a
3.8 (39)
5.1 (37)
5.6a
a Increase of intensity for band at w480 nm.
3. Conclusions
JZ8.8 Hz, 1H), 7.50–7.54 (m, 1H), 7.83 (dd, J1Z8.3 Hz,
J2Z1.6 Hz, 1H).
New approaches to the synthesis of functionalized
azobenzocrown ethers were presented. In most cases these
unsymmetrical compounds were obtained with more than
satisfactory yield (even over 55%). For the synthesized
compounds, in particular for compounds 7–9, no detectable
E%Z isomerization under ordinary conditions was found.
This presents an advantage of the synthesized macrocycles
because it simplifies UV–vis and NMR spectra and limits
the number of species during complexation. Selective
magnesium cation complexation was found for 19-
membered dimethylaminoazobenzocrown ether 6.
Compared with the parent, non-functionalized azobenzo-
crown ethers, for the studied compounds beneficial
influence of the presence of functional groups on changes
in absorption spectra upon metal cation complexation was
observed.
4.2.1.2. Podand 13. A mixture of 2-nitro-5-tetrahydro-
pyranyloxyphenol11 (3 g, 12.5 mmol), anhydrous potassium
carbonate (4 g), 1-chloro-11-(2-nitrophenoxy)-3,6,9-triox-
aundecane (3.9 g, 11.7 mmol) and dimethylformamide
(12 mL) was heated for 14 h at 90 8C. The cooled reaction
mixture was diluted with water and extracted with chloro-
form. The desired product was isolated by column
chromatography using methylene chloride as an eluent. A
crude product 13 was obtained of insufficient purity.
Therefore, the product was fully characterized after
removing tetrahydropyranyl protecting group. To the
crude product in ethanol (20 mL), catalytic amount of
p-toluenesulfonic acid was added and the mixture was
refluxed for 2 h. After solvent evaporation, the residue was
chromatographed using methylene chloride at the beginning
and methylene chloride/acetone 10:1 v/v mixture at the end.
1
Yield 2.63 g (42%) of product 13a as a pale yellow oil. H
4. Experimental
4.1. General
NMR (CDCl3): d 3.66–3.72 (m, 4H), 3.72–3.76 (m, 2H),
3.81–3.85 (m, 4H), 3.93 (t, JZ4.4 Hz, 2H), 4.19–4.24 (m,
4H), 6.40 (dd, J1Z8.8 Hz, J2Z2.4 Hz, 1H), 6.68 (d, JZ
2.4 Hz, 1H), 7.01–7.05 (m, 2H), 7.50 (dt, J1Z7.8 Hz, J2Z
1.7 Hz, 1H), 7.80–7.84 (m, 2H). IR (film): nmax 3167, 3113,
2925, 2878, 1607, 1584, 1518, 1487, 1453, 1352, 1304,
1275, 1197, 1126, 1093, 1046, 949, 851, 747 cmK1. HRMS
m/z: calcd for C20H24O10N2: 452.1431; found: 452.1436.
All solvents were of analytical reagent grade. Tetrahydro-
furan was distilled from LiAlH4 and stored over molecular
sieves. For spectrophotometric measurements HPLC grade
solvents were used. The reagents from Aldrich were used
without further purification. Silica gel 60 (63–200 mm) was
used for column chromatography (Merck). 1H NMR and 13
C
4.2.1.3. Azobenzocrown ether 3. To a vigorously stirred
suspension of podand 13 (0.72 g, 1.3 mmol) stannous
chloride dihydrate (1.47 g, 6.43 mmol), potassium hydrox-
ide (2.5 g), and acetone (9 mL) water (8 mL) was added
dropwise. When the exothermic reaction ceased, the
mixture was heated to 55 8C for 1.5 h. After this time
chloroform was added, the organic layer was separated,
washed with water and evaporated to dryness. The residue
was chromatographed on a column. The orange fraction
containing azocrown was hydrolyzed in ethanol in the
presence of catalytic amount of p-toluenesulfonic acid for
15 min. The solvent was removed and the residue was
rechromatographed. Azobenzocrown ether 3 was eluted
with methylene chloride/acetone 4:1 mixture. An oily
NMR spectra were recorded on Varian instrument at 500
and 125 MHz, respectively. Chemical shifts are reported as
d values in ppm in relation to TMS. IR spectra were
recorded on Mattson Genesis II instrument. UV–vis spectra
were recorded on a UNICAM UV 300 apparatus. Mass
spectrometry was conducted on an AMD-604 apparatus
(70 eV, EI method). Melting points (mp) are uncorrected.
4.2. Synthesis
4.2.1. Synthesis of azobenzocrown ether with peripheral
hydroxyl group (compound 3).
4.2.1.1. 1-Chloro-11-(2-nitrophenoxy)-3,6,9-trioxaun-
decane. A mixture of 2-nitro-phenol (3.8 g, 25 mmol),
anhydrous potassium carbonate (5 g), 1,11-dichloro-3,6,9-
trioxaundecane (17.33 g, 75 mmol) and dimethylformamide
(10 mL) was heated for 20 h at 95 8C. The cooled reaction
mixture was diluted with water and extracted with chloro-
form. The desired product was isolated by column
chromatography using hexane/methylene chloride 5:1
mixture as an eluent. Yield 3.2 g (38%) of oily product.
1H NMR (CDCl3): d 3.63 (t, JZ6.1 Hz, 2H), 3.65–3.69 (m,
6H), 3.73–3.77 (m, 4H), 3.91 (t, JZ4.9 Hz, 2H), 4.27 (t, JZ
4.9 Hz, 2H), 7.04 (dt, J1Z7.6 Hz, J2Z1.5 Hz, 1H), 7.11 (d,
1
orange-red crown ether (0.062 g, 12%) was obtained. H
NMR (d-acetonitrile), signals characteristic for azo form,
selected from spectrum of mixture of tautomeric forms: d
3.42–3.54 (m, 8H), 3.70–3.77 (m, 4H), 4.23–4.34 (m, 4H),
6.50 (d, JZ8.3 Hz, 1H), 6.64 (s, 1H), 6.93–7.15 (m, 4H),
7.35–7.42 (m, 1H). Some selected signals of quinone–
hydrazone form: 5.91 (s); 6.22 (d, JZ7.8 Hz); 11.78 (s); ratio
1
3:1 azophenol:quinone–hydrazone. H NMR (d-acetonitri-
leCstrontium perchlorate): d 3.78–3.81 (m, 4H), 3.85–3.90
(m, 4H), 3.97 (d, JZ4 Hz, 2H), 4.03 (d, JZ4.4 Hz, 2H), 4.42–
4.47 (m, 4H), 6.77 (dd, J1Z8.8 Hz, J2Z2.4 Hz, 1H), 6.82

E. Luboch et al. / Tetrahedron 61 (2005) 10738–10747
10745
(d, JZ2 Hz, 1H), 7.24 (t, JZ7.6 Hz, 1H), 7.32 (d, JZ
8.3 Hz, 1H), 7.50–7.55 (2H, m), 7.70 (d, JZ8.8 Hz, 1H),
8.34 (br s, 1H). 13C NMR (d-acetonitrileCstrontium
perchlorate): d 69.43, 69.56, 69.74, 70.22, 70.47, 70.49,
70.89, 70.92, 103.01, 111.33, 114.94, 124.02, 124.79,
131.56, 133.00, 137.61, 163.92, 151.08, 151.49, 162.73.
IR (film): nmax 3303, 2924, 1622, 1601, 1518, 1488, 1447,
.
HRMS m/z: calcd for C20H24O6N2: 388.1634; found:
388.1639.
(0.28 g in 2 mL cold water). Then the reaction mixture was
kept at 5 8C for 15 min.
The obtained diazonium salt was added dropwise to an ice-
cold solution of 3-dimethylamino-phenol (0.55 g, 4 mmol)
and NaOH (0.4 g) in water (10 mL). The reaction mixture
was stirred at 10 8C for 1 h. The mixture was then cooled
and made slightly acidic with 0.1 M hydrochloric acid. The
precipitated solid was separated and washed with water. The
solid was in turn suspended in a small amount of acetone,
cooled and filtered. The crude, solid 4-dimethylamino-2,20-
dihydroxyazobenzene (0.8 g, 78%) was used for macrocycle
synthesis. Analytical sample was obtained by purifying
crude product on column chromatography using methylene
chloride/acetone 30:1 mixture as an eluent. Crystallization
from propan-2-ol gave the title compound as a red-brown
solid. Mp 235–237 8C. 1H NMR (d-DMSO): d 3.06 (s, 6H),
6.05 (d, JZ2.9 Hz, 1H); 6.50 (dd, J1Z9.2 Hz, J2Z2.4 Hz,
1H); 6.92 (dt, J1Z7.6 Hz, J2Z1 Hz, 1H); 6.98 (dd, J1Z
8.3 Hz, J2Z1.2 Hz, 1H); 7.19 (dt, J1Z7.6 Hz, J2Z1.5 Hz,
1H); 7.52 (d, JZ9.2 Hz, 1H); 7.67 (dd, JZ8.3, 1.5 Hz, 1H);
10.95 (s, 1H); 13.88 (s, 1H). The NOESY spectrum confirms
the position of the dimethylamino group in benzene ring. IR
(nujol): nmax 1631, 1535, 1328, 1255, 1238, 1213, 1147,
795, 750 cmK1. UV–vis (acetonitrile): l1Z264 nm, 31Z
2.56!103; l2Z287 nm, 32Z2.161!103; l3Z470 nm, 33Z
1.50!104. MS m/z: calcd for C14H15O2N3: 257; found: 257.
HRMS m/z: calcd for C14H15O2N3: 257.1164; found:
257.1169.
1308, 1263, 1240, 1182, 1108, 1047, 946, 854, 753 cmK1
4.2.2. Synthesis of azobenzocrown ethers with peripheral
dimethylamino group (compounds 4–6). Method A.
According to this method, compound 6 was obtained, as
described above for compounds 4 and 5,11 using 1-chloro-
11-(2-nitrophenoxy)-3,6,9-trioxaundecane.
4.2.2.1. Podand 14. A mixture of 5-dimethylamino-2-
nitro-phenol11 (1.46 g, 8 mmol), 1-chloro-11-(2-nitrophe-
noxy)-3,6,9-trioxaundecane (2.7 g, 8.2 mmol), potassium
carbonate (2.2 g) and dimethylformamide (10 mL) was
stirred and heated at 110 8C for 8 h. Then water was added
and the product was extracted with methylene chloride. The
evaporated extract was chromatographed using methylene
chloride as an eluent. Compound 14 (2.5 g, 65%) was
1
obtained as a yellow oil. H NMR (CDCl3): d 3.1 (s, 6H),
3.67–3.72 (m, 4H), 3.74–3.83 (m, 4H), 3.90–3.98 (m, 4H),
4.24–4.29 (m, 4H), 6.21 (s, 1H), 6.29 (dd, J1Z9.3 Hz, J2Z
2.4 Hz, 1H), 7.03 (t, JZ7.8 Hz, 1H), 7.12 (d, JZ8.3 Hz,
1H), 7.52 (t, JZ7.8 Hz, 1H), 7.83 (dd, J1Z8.3 Hz, J2Z
1.5 Hz, 1H), 8.01 (d, JZ9.3 Hz, 1H). IR (film): nmax 2875,
1607, 1572, 1524, 1491, 1349, 1300, 1252, 1130, 1096,
1046, 947, 928, 852, 810, 747 cmK1. HRMS m/z: calcd for
C22H29O9N3: 479.1904; found: 479.1913.
4.2.2.4. 0 Azobenzocrown ethers 4–6. To 4-dimethy-
lamino-2,2 -dihydroxyazobenzene (0.52 g, 2 mmol) potass-
ium tert-butoxide (0.78 g, 7 mmol) in dry THF (50 mL) was
added. The mixture was stirred for 0.5 h at room
temperature and then (in case of compounds 4 and 5) 18-
crown-6 (10 mg) was added. After that, the appropriate
ditosyl derivative18 (2.2 mmol) in THF (50 mL) was added
dropwise over 1 h. The reaction mixture was heated at 70 8C
for 24 h. The solid was removed by filtration and washed
with THF until colorless filtrate was obtained. The filtrate
was evaporated under reduced pressure, the residue was
dissolved in methylene chloride and chromatographed on
column using methylene chloride, acetone/methanol mix-
tures and finally pure methanol as eluents. The fractions
containing the azobenzocrown ether were evaporated, the
red residue was dissolved in methylene chloride, filtered and
the filtrate was evaporated to dryness. Crystallization from
acetone/hexane mixture or propan-2-ol gave desired
compounds identical with those obtained by method A or
described earlier.11
4.2.2.2. Azobenzocrown ether 6. To vigorously stirred
mixture of podand 14 (1.29 g, 2.7 mmol) in acetone
(10 mL), stannous chloride dihydrate (2.5 g, 11 mmol) and
potassium hydroxide (4.76 g) water (9 mL) was added and
the mixture was gently boiled for 1.5 h. Isolation was
carried out as described.11 The desired product was eluted
from chromatographic column as the last using methanol as
an eluent. Compound 6, crystallized from acetone/hexane
mixture, was obtained (44 mg, 4%) as a fire-brick solid. Mp
105–107 8C. 1H NMR (d-acetone): d 3.10 (s, 6H), 3.38–3.44
(m, 4H), 3.48–3.52 (t, JZ4.6 Hz, 2H), 3.54–3.58 (t, JZ
4.40 Hz, 2H), 3.78–3.82 (t, JZ4.6 Hz, 2H), 3.83–3.86 (t,
JZ4.6 Hz, 2H), 4.28–4.32 (t, JZ4.8 Hz, 2H), 4.34–4.38
(m, 2H), 6.41–6.46 (m, 2H), 7.02 (t, JZ7.6 Hz, 1H), 7.15 (d,
JZ7.8 Hz, 1H), 7.30 (t, JZ7.8 Hz, 2H), 7.55 (d, JZ8.3 Hz,
1H). 13C NMR (d-acetone): d 39.76, 69.55, 69.58, 69.87,
70.12, 70.69, 70.71, 70.74, 70.78, 98.29, 105.06, 116.03,
119.97, 121.24, 129.31, 135.63, 146.08, 153.86, 154.00,
157.52. IR (film): nmax 2923, 2874, 1608, 1516, 1485, 1446,
1363, 1279, 1243, 1107, 1048, 950, 810, 753 cmK1. HRMS
m/z: calcd for C22H29O5N3: 415.2107; found: 415.2091.
By this method were obtained: compound 4 as a dark red
solid, yield 42%, mp 121–123 8C; compound 5 as a fire-
brick solid, yield 38%, mp 113–116 8C; compound 6 as a
dark red solid, yield 55%, mp 105–107 8C.
4.2.3. Synthesis of azobenzocrown ethers 7–9.
4.2.3.1. 4-Dimethylamino-40-nitro-2,20-dihydroxyazo-
benzene. Method A. To a suspension of 2-amino-5-nitro-
phenol (1.23 g, 8 mmol) in water (10 mL) concd HCl
(2 mL) was added. The mixture was diazotized with NaNO2
(0.56 g) dissolved in water (4 mL). The precipitated, wet
solid was collected (caution!), suspended in a mixture of
Method B
4.2.2.3. 4-Dimethylamino-2,20-dihydroxyazobenzene.
A suspension of 2-amino-phenol (0.44 g, 4 mmol) in water
(10 mL) was cooled and acidified with concd hydrochloric
acid (1 mL). The solution was diazotized with sodium nitrite

10746
E. Luboch et al. / Tetrahedron 61 (2005) 10738–10747
DMF (10 mL) and pyridine (4 mL), stirred and cooled in an
ice-water bath. To this mixture solution of 3-dimethyl-
amino-phenol (1.1 g, 8 mmol) in DMF (10 mL) was added.
The reaction mixture was stirred for 3 h at 5 8C, 3 h at room
temperature and diluted with cold water (30 mL). The solid
was collected and dried (2 g). Afterwards the solid was
triturated with acetone (10 mL), filtered and the solid
washed with cold acetone. The crude solid product (1.32 g,
54%) was used in the synthesis of azobenzocrown ethers.
An analytical sample was obtained by column chromato-
graphy using THF as an eluent. The eluate was evaporated
and the product was precipitated with propan-2-ol.
potassium tert-butoxide (0.39 g, 3.5 mmol) in dry THF
(30 mL) was added. The mixture was stirred at room
temperature for 0.5 h, then heated to 40 8C. 5 mg 18-crown-
6 was added and next the appropriate ditosyl derivative
(1 mmol) in THF (30 mL) was added dropwise over 3 h.
The synthesis was continued at gentle boiling for 48 h. The
solid was separated and washed with THF until a colorless
filtrate was obtained. The filtrate was evaporated and the
residue was extracted with methylene chloride. The
concentrated extract was chromatographed on a column.
Mixtures of methylene chloride with acetone and finally
acetone were used as eluents. The crude product was
rechromatographed using the same eluents. Azobenzocrown
ethers were crystallized from propan-2-ol. By this method
were obtained compounds 7, 8, 9 as black-brown solids with
23, 24 and 33% yield, respectively.
The residual acetone filtrate contains0 mainly isomeric
compound—2-dimetylamino-40-nitro-2 ,4-dihydroxyazo-
benzene (about 30% in the main reaction product), which
was also isolated (purification: column chromatography
with a methylene chloride/acetone 30:1 mixture) and
characterized by spectroscopic methods.
Compound 7. Mp 165–168 8C. 1H NMR (d-acetone): d 3.16
(s, 6H), 3.89 (t, JZ4.5 Hz, 2H), 3.93 (t, JZ4.3 Hz, 2H),
4.33 (t, JZ4.5 Hz, 2H), 4.42 (t, JZ4.3 Hz, 2H), 6.45 (d, JZ
2.6 Hz, 1H), 6.60 (dd, J1Z9.2 Hz, J2Z2.7 Hz, 1H), 7.78 (d,
JZ9.3 Hz, 1H), 7.81 (d, JZ8.8 Hz, 1H), 7.97 (d, JZ
2.3 Hz, 1H), 8.02 (dd, J1Z8.8 Hz, J2Z2.3 Hz, 1H). 13C
NMR (CDCl3 and one drop of CD3OD): d 40.49, 69.57,
70.02, 70.99, 71.36, 100.34, 106.89, 113.22, 117.97, 123.86,
125.54, 135.92, 147.10, 149.50, 152.38, 154.59, 157.44. IR
(nujol): nmax 1610, 1542, 1509, 1327, 1256, 1211, 1172,
4-Dimethylamino-40-nitro-2,20-dihydroxyazobenzene.
Black solid, mp 275 8C (dec). H NMR (d-DMSO): d 3.14
1
(s, 6H), 5.82 (d, JZ2.4 Hz, 1H), 6.71 (dd, J1Z9.6 Hz, J2Z
2.5 Hz, 1H), 7.30 (d, JZ9.6 Hz, 1H), 7.75 (s, 1H), 7.80 (s,
2H), 11.28 (s, 1H), 14.6 (br s, 1H). IR (nujol): nmax 1633,
1602, 1535, 1504, 1320, 1259, 1240, 1271, 1150, 1074, 929,
870, 816, 791, 745 cmK1. (UV–vis (acetonitrile): l1Z
292 nm, 31Z2.89!102; l2Z518 nm, 32Z2.21!103.
HRMS m/z: calcd for C14H14O4N4: 302.1015; found:
302.1013.
1136, 1108, 1080, 1046, 955, 922, 892, 828, 807, 723 cmK1
.
HRMS m/z: calcd for C18H20N4O5: 372.1434; found:
372.1431.
2-Dimethylamino-40-nitro-20,4-dihydroxyazobenzene.
Black solid, mp 164–165 8C. 1H NMR (d-DMSO): d 3.08 (s,
6H), 6.34 (dd, J1Z9.2 Hz, J2Z2.1 Hz, 1H), 6.39 (d, JZ
2.1 Hz, 1H), 7.67 (d, JZ8.6 Hz, 1H), 7.75–7.80 (m, 2H),
7.87 (d, JZ8.8 Hz, 1H), 10.36 (s, 1H), 11.18 (s, 1H). The
NOE spectrum confirms position of dimethylamino group in
benzene ring. IR (nujol): nmax 3301, 1607, 1566, 1511, 1339,
1304, 1257, 1178, 1123, 1074, 985, 856, 740 cmK1. UV–vis
(acetonitrile): l1w280 nm, 31Z9.88!102; l2Z385 nm,
32Z1.20!103; l3Z499 nm, 33Z1.43!103. MS m/z:
calcd for C14H14O4N4: 302; found: 302.
Compound 8. Mp 168–170 8C. 1H NMR (d-acetone): d 3.17
(s, 6H), 3.69–3.73 (m, 4H), 3.93–3.67 (m, 4H), 4.29 (t, JZ
4.5 Hz, 2H), 4.38 (t, JZ4.5 Hz, 2H), 6.40 (d, JZ2.4 Hz,
1H), 6.54 (dd, J1Z9.2 Hz, J2Z2.5 Hz, 1H), 7.64 (d, JZ
8.6 Hz, 1H), 7.79 (d, JZ9.3 Hz, 1H), 7.94 (dd, J1Z8.6 Hz,
J2Z2.5 Hz, 1H), 7.96 (d, JZ2 Hz, 1H). 13C NMR (CDCl3):
d 40.56, 68.98, 69.17, 69.46, 70.22, 70.48, 96.39, 105.28,
108.90, 116.75, 121.22, 131.07, 147.37, 148.60, 153.12,
154.28, 155.15. IR (nujol): nmax 1614, 1511, 1321, 1254,
1218, 1162, 1136, 1084, 964, 861, 809, 730 cmK1. HRMS
m/z: calcd for C20H24N4O6: 416.1696; found: 416.1688.
Method B. Solution A: to a suspension of 5-nitro-2-amino-
phenol (1.23 g, 8 mmol) in water (20 mL) concd HCl
(2 mL) was added. The mixture was diazotized with NaNO2
(0.56 g) dissolved in water (4 mL) for 15 min at w3 8C.
Compound 9. Mp 133–135 8C. 1H NMR (d-acetone): d 3.15
(s, 6H),3.37–3.43(m, 4H),3.49(t, JZ4.6 Hz, 2H),3.58(t, JZ
4.6 Hz, 2H), 3.82–3.87 (m, 4H), 4.37 (t, JZ4.6 Hz, 2H), 4.45
(t, JZ4.6 Hz, 2H), 6.42 (d, JZ2.4 Hz, 1H), 6.49 (dd, J1Z
8.7 Hz, J2Z2.4 Hz, 1H), 7.40 (d, JZ8.3 Hz, 1H), 7.64 (d, JZ
9.3 Hz, 1H), 7.92 (dd, J1Z8.7 Hz, J2Z2.4 Hz, 1H), 7.96 (d,
JZ2 Hz, 1H). NOE spectrum confirmed the position of
substitution of the benzene rings. 13C NMR (d-acetone): d
39.75, 69.44, 69.48, 69.81, 70.60, 70.61, 70.67, 70.74, 70.85,
97.43, 105.28, 110.93, 116.82, 119.84, 122.21, 135.61,
147.51, 150.62, 153.88, 155.05, 158.44. IR (nujol): nmax
1609, 1544, 1512, 1328, 1245, 1226, 1138, 1083, 1028, 979,
876, 866, 807, 728 cmK1. HRMS m/z: calcd for
C22H28N4O7 460.1958; found: 460.1950.
Solution B: 3-dimethylamino-phenol (1.1 g, 8 mmol) and
NaOH (0.8 g) were dissolved in cold water (20 mL).
Both solutions were added dropwise to ice-cold water (60 mL)
over 15 min with the same molar rate. The mixture was kept at
5 8C at the beginning and at 15 8C at the end for 3 h. The reaction
mixture was cooled and 0.1 M HCl (50 mL) was added. The
precipitate (2.2 g, 91%), containing 4-dimethylamino-40-nitro-2,
20-dihydroxyazobenzene and 2-dimethylamino-40-nitro-20,4-
dihydroxyazobenzene in 4:1 ratio, was separated, washed
with water and dried at room temperature. The mixture of
isomers was separated as described above in method A.
4.3. X-ray structure determination
Crystallographic data for 9$2H2O were collected at 100 K
on a Bruker SMART-APEX diffractometer using Mo Ka
radiation (lZ0.7107 A) equipped with CCD-type area
4.2.3.02. Azobenzocrown ethers 7–9. To 4-dimethyl-
amino-4 -nitro-2,20-dihydroxyazobenzene 0.3 g (1 mmol)
˚

E. Luboch et al. / Tetrahedron 61 (2005) 10738–10747
10747
detector and an Oxford Cryosystems open flow Nitrogen gas
References and notes
cooling device. The data were corrected for Lorentz and
polarization effects and for absorption using the SADABS
program. The structure was solved using direct methods and
refined by full-matrix least squares on F2.19 All non-
hydrogen atoms were refined anisotropically. Hydrogen
atoms of water molecules were located on a difference
Fourier map and refined isotropically. Other hydrogen
atoms were placed in geometrically calculated positions and
refined with temperature factors 1.2 and 1.5 times of those
of their bonded atoms for CH2 and CH3 groups,
respectively. Crystal data for 9$2H2O: triclinic, space
1. For example see review: Luboch, E.; Bilewicz, R.; Kowalczyk,
M.; Wagner-Wysiecka, E.; Biernat, J. F. Azo Macrocyclic
Compounds. In Gokel, G. W., Ed.; Advances in Supra-
molecular Chemistry; Cerberus: South Miami, USA, 2003;
Vol. 9, p 71.
2. Shiga, M.; Takagi, M.; Ueno, K. Chem. Lett. 1980, 1021.
3. Shiga, M.; Nakamura, H.; Tagaki, M.; Ueno, K. Bull. Chem.
Soc. Jpn. 1984, 57, 412.
4. Luboch, E.; Biedrzycka, A. Pol. J. Chem. 2003, 77, 47.
5. Biernat, J. F.; Luboch, E.; Cygan, A.; Simonov, Yu. A.;
Dvorkin, A. A.; Muszalska, E.; Bilewicz, R. Tetrahedron
1992, 48, 4399.
˚
group P-1, aZ8.647(3), bZ12.109(4), cZ12.505(5) A,
3
˚
aZ85.538(7), bZ75.995(6), gZ76.519(6)8, VZ1235.1(8) A ,
ZZ2, DcZ1.335 g/m3, mZ1.04 cmK1, F(000)Z528, qmax
Z
6. Luboch, E.; Biernat, J. F.; Muszalska, E.; Bilewicz, R.
Supramol. Chem. 1995, 5, 201.
25.258 (K10%h%10, K14%k%8, K14%l%14), reflec-
tions collected 5167, independent reflections 4068 (RintZ
0.0405), GOF on F2 1.016. Final residuals (for 334
parameters) R1Z0.0822, wR2Z0.1930 for 2270 reflections
with IO2s(I), and R1Z0.1424, wR2Z0.2139 for all data.
7. Luboch, E.; Biernat, J. F.; Simonov, Yu. A.; Dvorkin, A. A.
Tetrahedron 1998, 54, 4977.
8. Pijanowska, D. G.; Luboch, E.; Biernat, J. F.; Dawgul, M.;
Torbicz, W. Sens. Actuators, B 1999, 58, 384.
¨
9. For example see: (a) Huesmann, H.; Maack, J.; Mobius, D.;
K3
˚
Residual electron density: 0.767 and K0.493 e A
.
Biernat, J. B. Sens. Actuators, B 1995, 29, 148. (b) Muszalska,
E.; Bilewicz, R. Analyst 1994, 119, 1235. (c) Muszalska, E.;
Bilewicz, R.; Luboch, E.; Skwierawska, A.; Biernat, J. F.
J. Inclusion Phenom. 1996, 26, 47. (d) Zawisza, I.; Bilewicz,
R.; Luboch, E.; Biernat, J. F. J. Chem. Soc., Dalton Trans.
2000, 499.
Crystallographic data (excluding structure factors) for the
structure in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication numbers CCDC 287144. Copies of the data can
be obtained, free of charge, on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK [fax: C44 1223
336033; or e-mail: deposit@ccdc.cam.ac.uk].
10. Tahara, R.; Morozumi, T.; Nakamura, H.; Shimomura, M.
J. Phys. Chem. B 1997, 101, 7736.
11. Luboch, E.; Wagner-Wysiecka, E.; Biernat, J. F. J. Supramol.
Chem. 2002, 2, 279.
4.4. Determination of stability constants
12. Hofer, E.; Uffman, H. Tetrahedron Lett. 1971, 3241.
13. Chapoteau, E.; Czech, B. P.; Gebauer, C. R.; Kumar, A.;
Leong, K.; Mytych, D.; Zazulak, W.; Desai, D. H.; Luboch, E.;
Krzykawski, J.; Bartsch, R. A. J. Org. Chem. 1991, 56, 2575.
14. Luboch, E.; Kravtsov, V. Ch. J. Mol. Struct. 2004, 699, 9.
15. Dale, J. Acta Chem. Scand. 1973, 27, 1115.
Stability constants for complexes were determined by
spectrophotometric titration of ligand solution with the
appropriate metal perchlorate solution. The stability
constants were calculated with a program DynaFit.20
16. Pedersen, C. J. J. Am. Chem. Soc. 1967, 89, 2945.
¨
17. (a) Mootz, D.; Albert, A.; Schaefgen, S.; Staben, D. J. Am.
Acknowledgements
Chem. Soc. 1994, 116, 12045. (b) Krongsuk, S.; Kerdcharoen,
T.; Hannongbua, S. J. Phys. Chem. B 2003, 107, 4175.
18. Ouchi, M.; Inoue, Y.; Liu, Y.; Nagamune, S.; Nakamura, S.;
Wada, K.; Hakushi, T. Bull. Chem. Soc. Jpn. 1990, 63, 1260.
19. Sheldrik, G. M. SHELX-97: Programs for the solution and
refinement of crystal structures; University of Gottingen:
Gottingen, Germany, 1997.
Financial support of this work from the Gdansk University
of Technology (DS Grant no. 014668/003) and Grant 3
T09A 151 27 from Polish State Committee for Scientific
Research are kindly acknowledged. The authors are
indebted to Professor J. F. Biernat for his assistance in
preparation of this manuscript. The authors thank Jolanta
ˇ
20. Kuzmic, P. Anal. Biochem. 1996, 237, 260; http://wwwbiokin.
com.
˙
Zochowska for remarkable experimental help.