A study of anion binding behaviour of 1,3-alternate thiacalix[4]arene-based receptors bearing urea moieties

Article abstract of DOI:10.1039/c6nj00923a

Three novel thiacalix[4]arene receptors 4_a-c each with a 1,3-alternate conformation and possessing two urea moieties linking various phenyl groups substituted with either para electron-donating or -withdrawing groups have been synthesized. The

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A study of anion binding behaviour of
1,3-alternate thiacalix[4]arene-based receptors
bearing urea moieties†
Cite this:DOI: 10.1039/c6nj00923a
Shofiur Rahman,ab Hirotsugu Tomiyasu,a Hiroto Kawazoe,a Jiang-Lin Zhao,a
Hang Cong,c Xin-Long Ni,c Xi Zeng,c Mark R. J. Elsegood,d Thomas G. Warwick,d
Simon J. Teat,e Carl Redshaw,f Paris E. Georghioub and Takehiko Yamato*a
Three novel thiacalix[4]arene receptors 4a–c each with a 1,3-alternate conformation and possessing two
urea moieties linking various phenyl groups substituted with either para electron-donating or -withdrawing
groups have been synthesized. The binding properties of these receptors were investigated by means of
1H NMR spectroscopy and UV-vis absorption titration experiments using various anions. The structures and
complexation energies were also studied by density functional theory (DFT) methods. The results suggested
that receptor 4c, which possesses two p-(trifluoromethyl)phenyl ureido moieties, can complex most
efficiently in the urea cavity and exhibits high selectivity towards Fꢀ and AcOꢀ ions.
Received (in Montpellier, France)
23rd March 2016,
Accepted 7th September 2016
DOI: 10.1039/c6nj00923a
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tetrahedral (H2PO4ꢀ), etc. Anion recognition using artificially
designed receptors6 based on calix[n]arenes is an important
Introduction
Calix[n]arenes1 have three-dimensional tuneable shapes and research topic in the area of supramolecular chemistry. Calix[n]-
are used as molecular building blocks with potentially many arene urea derivatives are capable of effectively recognizing and
applications in supramolecular chemistry. Thiacalix[4]arenes2,3 sensing important anions via hydrogen-bonding interactions
are calix[n]arenes in which the phenolic groups are bridged by between the anions and the urea NH protons.7,8
9
´
sulfur atoms instead of methylene groups, and have received
Lhotak and co-workers have reported anion receptors based
much recent attention for potential applications in various on either upper-rim substituted calix[4]arenes or thiacalix[4]arenes
fields across chemistry, biology and environmental science. which contain two p-nitrophenyl or p-tolyl urea moieties.9a–c,h
Various anions such as Fꢀ also play fundamental roles in These anion receptors exhibited effective recognition abilities
biological, medicinal, catalysis, and environmental chemistry.4 towards selected anions in common organic solvents. Recently,
The design and synthesis of anion-selective receptors5 are more Kumar and co-workers reported an anion receptor based on a
difficult than those of cation-selective receptors. This is due to calix[4]arene in a 1,3-alternate conformation and bearing two
some unique features of anions such as their much larger sizes p-nitrophenyl-ureido moieties.10 This compound exhibited
in comparison with those of cations, and also due to the large strong binding and good selectivity towards the Clꢀ ion due
variety of geometries available,6 with some being spherical (Fꢀ, to strong hydrogen bonding between the Clꢀ ion and the NH
Clꢀ, Brꢀ, Iꢀ), others trigonal or Y-shaped (AcOꢀ) and yet others protons, both in THF and chloroform solutions. However,
investigations concerning the influence on the acidity of the
a Department of Applied Chemistry, Faculty of Science and Engineering, Saga University,
Honjo-machi 1, Saga 840-8502, Japan. E-mail: yamatot@cc.saga-u.ac.jp
b Department of Chemistry, Memorial University of Newfoundland,
St. John’s, Newfoundland and Labrador A1B 3X7, Canada
c Department Key Laboratory of Macrocyclic and Supramolecular Chemistry of
Guizhou Province, Guizhou University, Guiyang, Guizhou, 550025, China
d Chemistry Department, Loughborough University, Loughborough LE11 3TU, UK
e ALS, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley,
CA 94720, USA
urea protons by either electron-donating or electron-withdrawing
groups located on the p-position of phenyl groups of urea moieties
in analogous thiacalix[4]arenes, and the binding of various anions,11
have received scant attention.11j
In this article, we report the synthesis of three novel thiacalix-
[4]arene receptors 4a–c all having 1,3-alternate conformations
and possessing two urea moieties linking various phenyl groups
bearing either para electron-donating or electron-withdrawing
groups, together with two benzyl groups at the opposite sides of
the thiacalix[4]arene cavity.11 In our studies, the complexation
f Department of Chemistry, The University of Hull, HU6 7RX, UK
† Electronic supplementary information (ESI) available: 1H, 13C NMR & IR spectra of
compounds 2, 3 and 4a–c,
1H NMR spectroscopic and UV-vis titration experimental
properties of 4a–c towards Fꢀ, Clꢀ, Brꢀ, Iꢀ, AcOꢀ and H2PO4
ꢀ
data and computational studies. CCDC 1062186. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c6nj00923a
1
ions were investigated by H-NMR spectroscopy (with 4a–c) and
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UV-vis absorption (with 4c) titration experiments. Furthermore,
the structures and complexation energies for all complexes of
receptors 4a–c with various anions were also determined by
theoretical studies using DFT methods, and experimentally by
single crystal X-ray diffraction using synchrotron radiation for 4a.
Results and discussions
Synthesis
o-Alkylation of 1,3-alternate-1 was conducted using 2 equiva-
lents of bromoacetamide in the presence of 2 equivalents of
Cs2CO3 according to the reported procedure, and afforded the
desired 1,3-alternate-2 in 60% yield.12 The amide reduction of
1,3-alternate-2 was carried out with a large excess of BH3/THF
solution, and afforded the desired 1,3-alternate-3 in 65% yield.
The condensation of 1,3-alternate-3 with 2.2 equivalents of the
appropriate isocyanate in CH2Cl2 furnished the receptors 4a–c
in good yields (Scheme 1). The 1H NMR spectra of receptors 4a–c
in CDCl3 exhibit the characteristics of a 1,3-alternate conforma-
tion such as two singlets (18H each) for the tert-butyl protons,
two triplets (4H each) for the –OCH2CH2– protons, two singlets
(4H each) for the aromatic protons and two singlets (2H each)
for the four urea NH protons. Moreover, concentration dependence
of the 1H NMR chemical shifts of the urea protons in receptor 4c
was not observed (Fig. S11, ESI†). This (lack of) observation
indicates that receptor 4c has strong intramolecular hydrogen
bonds between the two urea groups linking the p-(trifluoro-
methyl)phenyl moieties. The molecular structure of receptor 4a
was also verified by X-ray crystallographic analysis (Fig. 1 and
Fig. S12, ESI†). Receptor 4a was recrystallized from a CHCl3–
CH3CN (3 : 2, v/v) mixture by slow evaporation. These results
indicate that receptor 4a adopts the 1,3-alternate conformation
in the solid state. In the case of receptor 4a, there are four
thiacalixarenes, two Clꢀ ions, two tetra-n-butylammonium ions,
one chloroform and two acetonitrile molecules in the asym-
metric unit. Interestingly, it was found that the two urea groups
approach each other and are oriented in parallel due to the
Fig. 1 X-ray crystal structure of receptor 4aꢁClꢀ. H-Bonds shown as
dashed lines. This figure shows one of four similar calixarene molecules
in the asymmetric unit and one of two chloride ions. H atoms not involved
in H-bonding, (nBu)4N+ cations, minor disorder components, and solvent
of crystallization are omitted for clarity. Guest used: tetra-n-butylammonium
(TBA) chloride.
existence of dual intramolecular hydrogen bonding (in the case
of receptor 4a, for the molecule shown: N(3)–H(3)ꢁ ꢁ ꢁO(5) 2.13(3);
N(4)–H(4)ꢁ ꢁ ꢁO(5) 2.17(3) Å; for the second molecule: N(1A)–
H(1A)ꢁ ꢁ ꢁO(6A) 2.15(3), N(2A)–H(2A)ꢁ ꢁ ꢁO(6A) 2.20(3) Å; for the
third molecule: N(3B)–H(3B)ꢁꢁꢁO(5B) 2.30(3), N(4B)–H(4B)ꢁꢁꢁO(5B)
2.17(2) Å; for the fourth molecule: N(1C)–H(1C)ꢁꢁꢁO(6C) 2.31(3),
N(2C)–H(2C)ꢁ ꢁ ꢁO(6C) 2.27(3) Å) (Fig. 1 and Fig. S12, ESI†).
Moreover, in the case of receptor 4a, pairs of calixarene molecules
are linked via four H-bonds between two urea NH moieties on each
calixarene and a Clꢀ ion.
Binding studies
The binding properties of receptors 4a–c in the presence of
various anions as their tetra-n-butylammonium (TBA) salts, in
CDCl3–CD3CN (10 : 1) solution, were investigated by means of
1H-NMR titration spectroscopic experiments. As shown in
Fig. 2, for the complexation of the Fꢀ ion with receptor 4c,
the signals for the NHa protons (red) progressively shifted
downfield by 4.64 ppm (d = 7.35 to 11.99 ppm) until five
equivalents of the Fꢀ ion were added. The signals for the NHb
protons (blue) progressively shifted downfield by 3.88 ppm
(d = 5.72 to 9.60 ppm) until five equivalents of the Fꢀ ion
Scheme 1 Synthesis of receptors 1,3-alternate-4a–c
.
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were added. On the other hand, the methylene protons adja-
cent to the NHb moiety (green) are shifted slightly upfield.
These results are strongly suggestive of Fꢀ ion recognition by
receptor 4c via hydrogen-bonding interactions between the Fꢀ
ion and the NH protons. The titration curves shown in Fig. 2
and 3 (for 4c) and Fig. S13–S49 (ESI†) show that further addition
of various anions to the solution of each receptor 4a–c in CDCl3
solution resulted in clear downfield shifts of the 1H NMR
signals of the NHa protons. All of the results obtained clearly
suggest that anion recognition by the receptors is via hydrogen-
bonding interactions between the anion and the NH protons. In
particular, as shown in Fig. 3, receptor 4c exhibited the highest
selectivity amongst all of the anions tested, toward Fꢀ and AcOꢀ
ions. Ka values for receptors 4a–c and the anions tested were
determined by 1H NMR spectroscopic titration experiments
using a 1 : 1 global fit analysis of the NHa proton13 (see Fig. 2
and 3; Table 1). These results suggest that the Ka values are
influenced by the electron-donating or electron-withdrawing
groups located at the p-position of the phenyl ureido moieties.
The Ka values for 4c having the electron-withdrawing CF3
groups on the phenyl ureido moieties were greater than those
for the other two receptors. The Ka values for 4b which had the
electron-donating CH3 groups on the ureido phenyl moieties
were lower than those for 4a and 4c. Therefore, the introduction
of electron-withdrawing groups at the p-position of the phenyl
ureido groups appears to increase the acidity of the urea
protons, and hence enhance the anion-binding ability through
hydrogen-bonding interactions. Furthermore, receptor 4c had
the highest Ka values of all three receptors with each of the
anions tested and also had the most effective recognition ability
toward Fꢀ and AcOꢀ ions. Further complexation studies of 4c
Fig. 2 Binding mode of receptor 4c upon addition of Fꢀ ion at 298 K as its
TBA (not shown) salt, and partial 1H NMR spectra of 4c (4.0 ꢂ 10ꢀ3 M) in
CDCl3–CD3CN (10 : 1, v/v) upon addition of TBAF at 298 K.
with Fꢀ, Clꢀ, AcOꢀ and H2PO4 ions were carried out using
ꢀ
UV-vis spectroscopic titration experiments. Receptor 4c (2.5 mM)
exhibits a broad absorption band at 295 nm in its UV-vis
absorption spectrum. Upon addition of the Fꢀ ion (0–50 mM)
to the solution of 4c, Fig. 4 reveals a gradual decrease in the
absorption of the band at 288 nm with a simultaneous increase
in the absorption at 320 nm and a clear isosbestic point at
295 nm. From above, it is clear that receptor 4c bearing the CF3
groups has the most effective recognition ability toward Fꢀ
ions. A Job’s plot13c for the binding between the receptor 4c and
Fꢀ ion reveals a 1 : 1 stoichiometry (Fig. S52, ESI†), and the Ka
value for the complexation13b of receptor 4c with the Fꢀ ion was
determined to be 13 000 Mꢀ1 by UV-vis titrations in CH2Cl2
solution (Fig. S51, ESI†).
Fig. 3 Titration curves of receptor 4c with various anions as their TBA salts
in CDCl3–CD3CN (10 : 1, v/v) at 298 K.
Table 1 Association constantsa of receptors 4a–c with anionsb
Fꢀ
Clꢀ
Brꢀ
Iꢀ
AcOꢀ
H2PO4
ꢀ
Host
Ar
spherical
spherical
spherical
spherical
Y-shape
tetrahedral
Association constants Ka [Mꢀ1] (ꢃ% Kerror
)
c
4a
4b
4c
C6H5–
1000 (ꢃ17)
800 (ꢃ12)
1500 (ꢃ12)
840 (ꢃ10)
740 (ꢃ11)
890 (ꢃ10)
760 (ꢃ16)
720 (ꢃ11)
840 (ꢃ18)
690 (ꢃ16)
660 (ꢃ8)
740 (ꢃ13)
620 (ꢃ 6)
570 (ꢃ11)
630 (ꢃ12)
200 (ꢃ 9)
190 (ꢃ13)
284 (ꢃ13)
p-CH3–C6H4–
p-CF3–C6H4–
a
1
Association constants (Kassoc) based on the H NMR data (chemical shift changes of NHa proton, Fig. S13–S49, ESI) obtained in CDCl3ꢀCD3CN
(10 : 1, v/v) at 298 K were calculated using Thordarson’s global-fit (1 : 1) method13 (Fig. S13–S49, ESI); host concentration was 4.0 ꢂ 10ꢀ3 M. Guests
b
c
used: TBA salts. The %error here is not a measure of precision of replicates but represents the %error resulting from the global-fit calculations
since only single titration experiments in each case were conducted.
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Fig. 4 UV-vis absorption spectra of receptor 4c (2.5 mM) upon the
addition of Fꢀ (0–50 mM) at 298 K as its TBA salt in CH2Cl2.
Fig. 5 Geometry-optimized (ball-and-stick) structures of (left) 4c and
(right) 1:1 complex of 4c*Fꢀ. Colour code: Fꢀ = magenta; nitrogen =
blue; NHa = light blue; NHb = light green; sulphur = yellow; CF3 (fluoride) =
orange; and oxygen atom = red.
These results strongly suggested that Fꢀ ion recognition by
receptor 4c was via a hydrogen-bonding interaction between the
Fꢀ ion and NH protons. The Ka values obtained by similar
UV-vis titration experiments of 4c with the other anions are
summarized in Table 2. To further investigate the binding
properties of receptors 4a–c with the anions tested, a density
functional theory (DFT) computational study was carried out.
The individual structures for all studies in the gas phase were
fully geometry-optimized using Gaussian 0914 with the B3LYP
level of DFT and the 3-21G basis set. Significant changes were
observed for the distances between two urea NH moieties
on each of the receptors 4a–c in their anion complexes. The
conformation changes for 4c upon 1 : 1 complexation with
the Fꢀ ion can be seen in Fig. 5 (more precise details for
the computation studies for receptors 4a–c with different anions
are shown in Fig. S59–S94, ESI†). Fig. 5 shows the computed
structure (right) of the 1 : 1 complex of 4c with the Fꢀ ion.
Because of the hydrogen-bonding between the Fꢀ ion and two
urea NH protons, distances between two urea NH moieties
Table 3 Calculated binding energies for the receptors 4a–c with anions
Binding energies DE (kJ moleꢀ1
Clꢀ Brꢀ Iꢀ AcOꢀ H2PO4
)
ꢀ
Host Ar
Fꢀ
4a
C6H5–
ꢀ786.6 ꢀ234.0 ꢀ232.1 ꢀ150.9 ꢀ380.1 ꢀ367.1
4b
4c
p-CH3–C6H4– ꢀ783.2 ꢀ236.8 ꢀ233.8 ꢀ146.3 ꢀ378.4 ꢀ364.4
p-CF3–C6H4– ꢀ820.5 ꢀ271.8 ꢀ268.6 ꢀ178.1 ꢀ433.4 ꢀ395.5
observed for the observed complexation data obtained by means of
1H NMR spectroscopy and UV-vis absorption titration experiments.
Conclusion
In summary, three new receptors 4a–c each bearing a thiacalix[4]-
arene in a 1,3-alternate conformation have been synthesized.
These receptors possess two urea moieties linking various aryl
groups bearing electron-donating or -withdrawing groups at
their p-positions, which act as anion-binding sites and two
benzyl groups at the opposite side of the thiacalix[4]arene cavity.
The binding of various anions at the two urea moieties was
0
0
(NHaꢁ ꢁ ꢁNHa and NHbꢁ ꢁ ꢁNHb ) on two p-(trifluoromethyl)phenyl
ureido moieties decrease from 8.783 to 2.530 (Å) and from 8.379 to
3.251 (Å), respectively. This also strongly supports the experimental
evidence obtained for the formation of a 1 : 1 (4c*Fꢀ) complex.
The calculated binding energies (DE kJ molꢀ1) for receptors 4a–c
with the anion complexes are shown in Table 3. The trend for
1
investigated by using H NMR and UV-vis absorption titration
the complexation energies for 4a–c is in the order: Fꢀ > AcOꢀ
>
experiments. It was found that receptor 4c exhibits a much
higher affinity towards all of the selected anions and especially
for Fꢀ and AcOꢀ ions.
H2PO4ꢀ > Clꢀ > Brꢀ > Iꢀ, which is in agreement with the trend
Table 2 Association constantsa of receptors 4c with anionsb
Experimental section
General
Fꢀ
Clꢀ
AcOꢀ
H2PO4
ꢀ
Anion
Association constants Ka [Mꢀ1] (ꢃ% Kerror
)
c
Ka [Mꢀ1
]
16 000 (ꢃ0.3) 14 000 (ꢃ0.6) 13 000 (ꢃ0.3) 8800 (ꢃ0.2)
All melting points were determined using a Yanagimoto MP-S1
melting point apparatus. 1H-NMR spectra were recorded at
300 MHz using a Nippon Denshi JEOL FT-300 NMR spectrometer
a
Measured in CH2Cl2 at 298 K by UV-vis titration. Ka values were
calculated using 1 : 1 global fit analysis13 of the entire UV-vis spectra
(Fig. S50–S58, ESI); host concentration in each case was 2.5 mM. with TMS as an internal reference; J-values are given in Hz.
b
c
Guests used: TBA salts. The %error here is not a measure of
UV-vis spectra were recorded using a Shimadzu 240 spectro-
photometer. Mass spectra were recorded on a Nippon Denshi
JMS-01SG-2 mass spectrometer at an ionization energy of 70 eV
precision of replicates but represents the %error resulting from the
global-fit calculations since only single titration experiments in each
case were conducted.
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using a direct inlet system through GLC. Elemental analyses temperature for 24 h under argon. The resulting precipitate
were performed using a Yanaco MT-5 system.
was collected by filtration, washed with CH3OH to give receptor
4c as a white solid. Recrystallization from CHCl3–CH3OH (3 : 2)
gave receptor 4c (147 mg, 65%) as a white solid. M.p.: 210–
Materials
Unless otherwise stated, all other reagents used were purchased 211 1C. IR: nmax (KBr)/cmꢀ1: 3279, 2923, 1602, 1572, 1538, 1225,
1
from commercial sources and were used without further 1170, 1091, 1068, 905 and 794. H NMR (300 MHz, CDCl3): d =
purification. Compounds 1,11d,12 212 and 312 were prepared 0.82 (18H, s, tBu ꢂ 2), 1.19 (18H, s, tBu ꢂ 2), 3.12 (4H, br,
following the reported procedures.
CH2NH ꢂ 2), 4.03 (4H, br, OCH2 ꢂ 2), 5.08 (4H, s, OCH2 ꢂ 2),
5.75 (2H, s, NH ꢂ 2), 6.92–7.30 (18H, m, phenyl-H ꢂ 18), 7.13
(4H, s, Ar-H ꢂ 4), 7.33 (2H, s, NH ꢂ 2) and 7.41 (4H, s, Ar-H ꢂ 4)
Synthesis of receptors 4a–c
4a. To a solution of compound 3 (150 mg, 0.166 mmol) in ppm. 13C NMR (100 MHz, CDCl3): d = 32.1 (CH3), 35.6 (C(CH3)3),
CH2Cl2 (10 mL) was added phenyl isocyanate (44 mg, 0.37 mmol), 40.0 (CH2), 70.1 (OCH2), 70.9 (OCH2), 118.1 (ArC), 118.8 (ArC),
and the mixture was stirred at room temperature for 24 h under 122.2 (ArC), 122.4 (ArC), 122.7 (ArC), 122.9 (ArC), 123.0 (ArC),
argon. The resulting precipitate was collected by filtration, 123.3 (ArC), 123.6 (ArC), 124.0 (ArC), 124.4 (ArC), 124.8
washed with CH3OH to give receptor 4a as a white solid. (ArC), 126.1 (ArC), 126.5 (ArC), 126.8 (ArC), 127.3 (ArC), 127.8 (ArC),
Recrystallization from CHCl3–CH3OH (2 : 1) gave receptor 4a 128.0 (ArC), 128.7 (ArC), 129.3 (ArC), 129.5 (ArC), 138.2 (ArC),
(146 mg, 72%) as a white solid. M.p.: 200–202 1C. IR: nmax 138.9 (ArC), 149.2 (ArC), 155.2 (ArC) and 160.7 (CO) ppm.
(KBr)/cmꢀ1: 3220, 2958, 1683, 1542, 1439, 1214, 1206, 1137, 994, FABMS: m/z: 1361.4861 [M + H]+. C74H79F6N4O6S4 (1361.4787):
812 and 760. 1H NMR (300 MHz, CDCl3): d = 0.85 (18H, s, calcd C 65.27, H 5.77, N 4.11. Found: C 65.32, H 5.75, N 4.08.
tBu ꢂ 2), 1.22 (18H, s, tBu ꢂ 2), 3.05 (4H, br, CH2NH ꢂ 2), 4.01
Determination of the association constants
(4H, br, OCH2 ꢂ 2), 5.08 (4H, s, OCH2 ꢂ 2), 5.56 (2H, s, NH ꢂ 2),
6.90–7.22 (20H, m, phenyl-H ꢂ 20), 7.09 (4H, s, Ar-H ꢂ 4), 7.18 The association constants (Ka) were determined by using
(2H, s, NH ꢂ 2) and 7.41 (4H, s, Ar-H ꢂ 4) ppm. 13C NMR (100 1H NMR spectroscopic titration experiments with a constant
MHz, CDCl3): d = 30.9 (CH3), 31.0 (CH3), 33.9 (C(CH3)3), concentration of host receptor (4.0 ꢂ 10ꢀ3 M) and varying the
34.1 (C(CH3)3), 40.9 (CH2), 70.8 (OCH2), 72.0 (OCH2), 124.6 (ArC), guest concentrations (0–8.0 ꢂ 10ꢀ3 M). The H NMR chemical
1
125.9 (ArC), 126.2 (ArC), 126.3 (ArC), 126.5 (ArC), 126.7 (ArC), 128.0 shifts of the signal of urea protons (NH) were used as a probe.
(ArC), 128.3 (ArC), 128.5 (ArC), 128.6 (ArC), 128.8 (ArC), 129.0 (ArC), The Ka values for the complexes of receptor 4a–c were calculated
129.1 (ArC), 129.3 (ArC), 130.0 (ArC), 132.0 (ArC), 135.2 (ArC), 142.8 by nonlinear curve-fitting analysis of the observed chemical
(ArC), 146.1 (ArC) and 155.4 (CO) ppm. FABMS: m/z: 1224.50 (M+). shifts of the NH protons according to the literature procedure.13a
C72H80N4O6S4 (1224.50): calcd C 70.55, H 6.58, N 4.57. Found:
1H NMR titration experiments
C 70.52, H 6.57, N 4.58.
4b. To a solution of compound 3 (150 mg, 0.166 mmol) in A solution of nBu4NX (X = F, Cl, Br, I, AcO, H2PO4) in CD3CN
CH2Cl2 (10 mL) was added p-tolyl isocyanate (48 mg, 0.37 mmol), (4.0 ꢂ 10ꢀ3 M) was added to a CDCl3 solution of receptor 4a–c in
and the mixture was stirred at room temperature for 24 h under an NMR tube. The 1H NMR spectra were recorded after the
argon. The resulting precipitate was collected by filtration, addition of the reactants and the temperature of the NMR
washed with CH3OH to give receptor 4b as a white solid. probe was kept constant at 27 1C.
Recrystallization from CHCl3–CH3OH (3 : 1) gave receptor 4b
(146 mg, 70%) as a white solid. M.p.: 203–204 1C. IR: nmax
Crystallographic analyses of 4a
(KBr)/cmꢀ1: 3301, 2946, 1605, 1583, 1426, 1211, 1196, 1123, Diffraction data were collected on a Bruker D8 diffractometer
1016, 889 and 802. 1H NMR (300 MHz, CDCl3): d = 0.82 (18H, s, with a PHOTON 100 detector at 100 K. The radiation source was
tBu ꢂ 2), 1.22 (18H, s, tBu ꢂ 2), 2.29 (6H, s, CH3 ꢂ 2), 3.06 (4H, the Advance Light Source, Station 11.3.1, with silicon 111-
br, CH2NH ꢂ 2), 4.03 (4H, br, OCH2 ꢂ 2), 5.05 (4H, s, OCH2 ꢂ 2), monochormated radiation.15 Data were corrected for Lorentz
5.50 (2H, br, NH ꢂ 2), 6.86 (2H, s, NH ꢂ 2), 6.96–7.18. (18H, m, and polarisation effects and for absorption.15 The structure was
phenyl-H ꢂ 18), 7.10 (4H, s, Ar-H ꢂ 4) and 7.41 (4H, s, Ar-H ꢂ 4) solved using direct methods and refined using full-matrix least-
ppm. 13C NMR (100 MHz, CDCl3): d = 20.0 (CH3), 31.3 (CH3), squares methods, on F2.16,17 The asymmetric unit contains four
34.3 (C(CH3)3), 39.4 (CH2), 70.1 (OCH2), 71.3 (OCH2), 119.8 calixarenes, two chloride anions, two tetra-n-butylammonium
(ArC), 121.9 (ArC), 125.1 (ArC), 125.2 (ArC), 125.4 (ArC), 125.9 cations, one chloroform and two acetonitrile molecules of
(ArC), 126.2 (ArC), 126.5 (ArC), 127.1 (ArC), 127.5 (ArC), 127.8 crystallisation. Within each of the four calixarenes there are
(ArC), 128.0 (ArC), 128.3 (ArC), 128.5 (ArC), 128.6 (ArC), 128.8 pairs of N–HꢁꢁꢁO hydrogen bonds between urea moieties to a single
(ArC), 129.0 (ArC), 129.1 (ArC), 129.3 (ArC), 130.0 (ArC), 135.1 carbonyl O atom. Looking down on the S4 square-shaped planes of
(ArC), 136.2 (ArC), 147.8 (ArC), 148.0 (ArC), 149.5 (ArC), 151.9 the four unique calixarenes, three are approximately geometrically
(ArC), 154.0 (ArC) and 158.4 (CO) ppm. FABMS: m/z: [M + H]+ aligned in parallel, while one, containing S(1A), is slightly twisted.
calcd for C74H85N4O6S4 (1253.5352); found 1253.4812.
Two tBu groups on calixarenes were modelled as disordered
4c. To a solution of compound 3 (150 mg, 0.166 mmol) in over two sets of positions for the Me groups. Two n-butyl chains
CH2Cl2 (10 mL) was added p-(trifluoromethyl)phenyl isocyanate in the cations exhibit some signs of disorder, but this was not
(68 mg, 0.37 mmol), and the mixture was stirred at room modelled. The chloroform molecule was modelled as fully
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NJC
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disordered over two sets of positions. There are two molecules
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Pairs of calixarene molecules are linked via four H-bonds
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between them. TBA cations reside close to the chloride anions,
due to electrostatic attraction. So, each pair of calixarenes is
able to capture one chloride ion. The overall packing type is
in layers.
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Crystal data for 4a. C144H160N8O12S8ꢁC16H36N+ꢁClꢀ ꢁ0.5(CHCl3)ꢁ
%
C2H3N, M = 2829.91. Triclinic, space group P1 a = 15.1315(5) Å,
b = 28.8618(11) Å, c = 35.9491(13) Å, V = 15113.8(9) Å3. Z = 4,
Dc = 1.244 g cmꢀ3, F(000) = 6044, T = 100(2) K, m = 0.226 cmꢀ1
,
l = 0.7749 Å, colourless crystal of size 0.16 ꢂ 0.13 ꢂ 0.04 mm3.
The total number of reflections measured, to ymax = 25.31, was
116 001, of which 42 128 were unique (Rint = 0.062); 27 707 were
‘observed’ with I 4 2s(I). For the ‘observed’ data only, R1 = 0.068
and wR2 = 0.185 for all 42 128 reflections and 3705 parameters.
Residual electron density is within ꢃ1.78 e Åꢀ3
CCDC 1062186 for 4a.
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Acknowledgements
This work was performed under the Cooperative Research
Program of ‘‘Network Joint Research Center for Materials and
Devices (Institute for Materials Chemistry and Engineering,
Kyushu University)’’. We would like to thank the OTEC at Saga
University and the International Cooperation Projects of Guizhou
Province (No. 20137005) for financial support. CR thanks the
EPSRC for a travel grant. The Advanced Light Source is supported
by the Director, Office of Science, Office of Basic Energy
Sciences, U.S. Department of Energy, under contract No.
DE-AC02-05CH11231. The computational work has been assisted
by the use of computing resources provided by WestGrid and
Compute/Calcul, Canada. We thank Dr Grigory Shamov,
Westgrid/U., Manitoba, for support.
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