Synthesis and evaluation of neutral anion receptors based on acylhydrazide-appended calix[4]arenes

Article abstract of DOI:10.1080/10610278.2012.695788

A new class of neutral receptors based upon acylhydrazide-appended calix[4]arenes was synthesised and evaluated for recognition of anions. Detailed NMR and single-crystal X-ray analyses of one of the synthesised compounds reveal that anion recognition in

Full text of DOI:10.1080/10610278.2012.695788

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Supramolecular Chemistry
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Synthesis and evaluation of neutral anion receptors
based on acylhydrazide-appended calix[4]arenes
H. M. Chawla a , Rahul Srivastava a , Satya Narayan Sahu a , Satish Kumar a & Shailesh Upreti
a
a Department of Chemistry , Indian Institute of Technology , Hauz Khas, New Delhi , 110016 ,
India
Published online: 06 Aug 2012.
To cite this article: H. M. Chawla , Rahul Srivastava , Satya Narayan Sahu , Satish Kumar & Shailesh Upreti (2012) Synthesis
and evaluation of neutral anion receptors based on acylhydrazide-appended calix[4]arenes, Supramolecular Chemistry, 24:9,
672-683, DOI: 10.1080/10610278.2012.695788
To link to this article: http://dx.doi.org/10.1080/10610278.2012.695788
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Supramolecular Chemistry
Vol. 24, No. 9, September 2012, 672–683
Synthesis and evaluation of neutral anion receptors based on acylhydrazide-appended
calix[4]arenes
H.M. Chawla*, Rahul Srivastava, Satya Narayan Sahu, Satish Kumar and Shailesh Upreti
Department of Chemistry, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India
(Received 1 October 2011; final version received 10 May 2012)
A new class of neutral receptors based upon acylhydrazide-appended calix[4]arenes was synthesised and evaluated for
recognition of anions. Detailed NMR and single-crystal X-ray analyses of one of the synthesised compounds reveal that
anion recognition in such derivatives is achieved through cooperative hydrogen bond interactions. The presence of three
centred NHZO and two OHZO hydrogen bonds at the lower rim of the synthesised calixarene architecture apparently helps
the molecular scaffold to retain cone conformation to enable deployment of intermolecular hydrogen bonds for selective
recognition of HSO42 ion in preference to F2, Cl2, Br2, I2, ClO42, AcO2 and PF62 ions.
Keywords: calix[4]arenes; receptors; anions; recognition; hydrogen sulfate
1. Introduction
networks at the lower rim of the molecular annulus which
can be used for anion recognition. In a similar report, Zinic
et al. (9) have described intramolecular hydrogen bonded
systems within the peptide functionalities appended at the
lower rim of calixarene units. These observations are in
consonance with previous reports on amido-calix[4]arenes
which can form both inter- and intramolecular organis-
ations through hydrogen bonds to affect the plausible
selectivity and binding characteristics of designed molecu-
lar receptors (5, 10) as explained by the work of Tomisic
et al. (11) and Kim et al. (3) on amido-calix[4]arenes.
Molecular systems containing a diverse combination of
hydrogen bond donors such as urea, thiourea, pyrrole,
catechol and amide have also been investigated as neutral
receptors for anion recognition (12).
One of the possible approaches for determining systems for
recognition of anions involves the design and development
of suitable electron-deficient molecular scaffolds that can
fit the geometry of anions of interest selectively and
specifically. This anion-molecular scaffold fit can then be
evaluated for specific non-covalent interaction involved in
the recognition process. Most important non-covalent
interaction involved in such studies is cooperative
hydrogen bonding which allows minimal manoeuvrability
of changes occurring during the recognition event besides
operating as a useful tool to manage the diversity of shapes
of anions present in biological processes of varying
complexity (1–3). The directional nature of hydrogen bond
was used previously to obtain preorganised concave
molecular platforms with the required cavity and
capability of binding anionic species (4, 5). In this context,
calix[n]arenes seem to be appropriate molecular matrices in
which the molecular architecture, hydrogen bonding and
complexation ability are present in unison and structural
motifs can be varied relatively easily by changing either the
nature or the number of binding sites located at their upper
or the lower rim or through conformational controls (6, 7).
Electron-deficient calixarenes are, however, scarce and we
have to achieve the objectives by attaching suitable
functionalities at their upper or the lower rim. For instance,
Nomura et al. (8) have demonstrated that the amino acid
substituted p-tert-butyl-calix[4]arenes possess a circular
pattern of N–H· · ·OvC intramolecular hydrogen bond
Development of artificial neutral receptors for binding
specific anionic species seems to be more challenging than
that for cations of similar dimensions and electronic cores
due to higher charge polarisability, variable shape and
complex stereochemicalproperties of biologically important
anions (1, 7, 13). In continuation of our recent work on anion
sensing (14), it was envisaged that acylhydrazides posses-
sing acidic NH protons when embedded into a calix[4]arene-
scaffold would in principle offer suitable binding affinities
for anions through hydrogen bonds. Accordingly, we report
herein the synthesis of a series of novel calix[4]arene
based receptors bearing two acylhydrazide functionalities
at their distal 1,3-positions. The structures of the synthesised
compounds were established by NMR and FAB mass
spectrum analysis. Detailed solution-state NMR data and
*Corresponding author. Email: hmchawla@chemistry.iitd.ac.in
ISSN 1061-0278 print/ISSN 1029-0478 online
q 2012 Taylor & Francis
http://dx.doi.org/10.1080/10610278.2012.695788
http://www.tandfonline.com

Supramolecular Chemistry
analysis of the solid-state structure of one of the 2.1 Characterisation of compounds 4a–h
673
synthesised receptors by single-crystal X-ray have revealed
that the synthesised receptors exhibit significant binding
The synthesised compounds were characterised by
1
analysis of their H NMR, 13C NMR, FT-IR, FAB mass
2
characteristics for tetrahedral HSO4 ion in preference to
spectral and elemental analysis. For instance, the 1H NMR
spectrum of 4a showed a typical AB pattern represented by
a pair of doublets at d 3.48 and d 4.25 for the equatorial
and axial protons, respectively, for the methylene-bridged
carbons indicating that 4a existed in a symmetrical cone
conformation. This was further confirmed by the
appearance of a distinct signal at d 32.3 for the
methylene-bridged carbons in the 13C NMR spectrum
(17). The tert-butyl protons appeared as two singlets at d
1.09 and d 1.26 whereas a singlet at d 4.81 could be
ascribed to the OCH2 protons. The aromatic protons of
nitrophenyl moiety appeared as two doublets at d 8.02 and
d 8.25. This assignment was further confirmed by the
DQF-COSY experiments. The OH, NHa and NHb protons
appeared at d 8.26, 11.63 and 9.22, respectively, which
disappeared on deuteration with D2O. Individual assign-
ments of the OH, NHa and NHb protons were confirmed by
comparison of their spectra with those of precursor
compounds. Other synthesised compounds were similarly
characterised by various spectroscopic techniques (see
experimental section). The cone conformation of 4c was
further established from its single-crystal X-ray analysis
2
other anions which include Cl2, Br2, I2, ClO42 and PF6
ions.
2. Results and discussions
The required starting materials p-tert-butyl-calix[4]arene
1a and debutylated calix[4]arene 1b were obtained by
using the literature procedures (15). Compounds 1a and 1b
were esterified by reaction with bromoethylacetate in the
presence of K2CO3 in CH3CN for 15 h to give 5,11,17,23-
tetra-tert-butyl-25,27-bis[(ethoxy-carbonyl)methoxy]-
26,28-dihydroxy calix[4]arene 2a and 25,27-bis[(ethoxy-
carbonyl)methoxy]-26,28-dihydroxycalix[4]arene 2b in
88% and 90% yields, respectively (16). Compounds 2a
and 2b when reacted with excess of hydrazine hydrate in
toluene–methanol (1:1) at room temperature for 14 h gave
3a and 3b in 93% and 95% yields, respectively. Treatment
of 3a and 3b with benzoyl chloride derivatives at reflux
condition in the presence of K2CO3 in anhydrous CH3CN
under nitrogen atmosphere gave the target compounds 4a–
h in good yields as depicted in Scheme 1.
R
R
R
R
R
R
R
R
R
R
R
R
BrCH2CO2C2H5
NH2NH2
Methanol:
Toluene(1:1)
K2CO3, CH3CN
reflux,15h
O
O
OH
OH
O
O
OH
OH
HO
OH OH
OH
O
R.T.,14h
O
O
O
NH
HN
OC2H5
R=C(CH3)3
R=H
C2H5O
3a
3b
1a R=C(CH3)3
1b
R=C(CH3)3
R=H
2a
2b
NH2
H2N
R=H
K2CO3, CH3CN
reflux, 48h
Substituted
benzoyl
chloride
R
R
R
R
No.
4a
4b
4c
4d
4e
4f
R
R1
Yield (%)
91
C(CH3)3
C(CH3)3
C(CH3)3
C(CH3)3
H
NO2
CH3
OCH3
H
NO2
CH3
O
O
OH
OH
84
87
78
89
86
O
O
N–Ha
aH–N
bH–N
cH
N–Hb
Hc
H
H
H
C=O
O=C
4g
4h
OCH3
H
82
80
R1
R1
Scheme 1. Synthesis of compounds 4a–h.

674
H.M. Chawla et al.
and is represented by the ORTEP diagram shown in
Figure 1(a). The torsion angles w and x around ArCH2Ar
bonds about C8, C51, C52 and C26 are 83.88 (12), 295.68
(12), 89.58 (12), 273.78 (13), 79.78 (12), 289.38 (12),
84.58 (11) and 279.08 (13), respectively. This alternate ^
sequence is characteristic of the cone conformation of the
molecule (18). All the four aromatic rings seem to be
atom N1 points towards the oxygen atoms at the lower rim
of the calixarene cavity and seems to be involved in a
unique three-centred intramolecular hydrogen bond
interaction with lower rim oxygens O4 and O2 of the
˚
calixarene unit with a distance of 2.158 A (N1–H1· · ·O4)
˚
and 2.295 A (N1–H1· · ·O2), respectively. Likewise proton
at nitrogen atom N3 also seems to be involved in a three-
centred intramolecular hydrogen bond interaction with
˚
phenolic oxygen atom O3 with a bond distance of 2.055 A
˚
planar with a maximum deviation of 0.022 A from a least
square plane.
The interplanar angles between this plane (hypothe-
tical plane along methylene carbons C8, C26, C51 and
C52) and the rings A(C1–C6), B(C9–C14), C(C23–C29)
and D(C37–C42) were 52.628, 63.688, 58.858 and 68.438,
respectively. The interplanar angle between A and C was
determined to be 68.56(2)8 whereas that between rings B
and D was 47.92(2)8. The OZO separation between O(2)
˚
and with ether oxygen O1 with a bond distance of 2.182 A.
The phenolic hydroxyl groups corresponding to the planes
A and C seem to take part in intramolecular hydrogen
bonding with the phenolic hydroxyl group attached to the
plane B (O2–H2· · ·O1) and C (O3–H3· · ·O4) with a
˚
distance of 1.91 and 2.043 A, respectively, to complete a
circular hydrogen bond arrangement which is in the form
of a twisted hexagonal ring (Figure 1(b)). The protons of
the nitrogen atom N4 of one of acylhydrazide moiety are
involved in the strong hydrogen bond with the adjacent
distally positioned carbonyl oxygen atom (O6) with a
˚
and O(3), and between O(1) and O(4) is 3.652 and 4.434 A,
respectively. Likewise, the OZO distance between
adjacent phenolic oxygens O(1)–O(2), O(2)–O(4),
O(4)–O(3) and O(3)–O(1) was determined to be 2.705,
˚
2.983, 2.833 and 2.980 A, respectively. The main deciding
˚
distance of 2.019 A (N4–H4A· · ·O6), whereas two
factor for determining the conformation of this molecule
seems to be the presence of both intra- and intermolecular
hydrogen bond interactions. The crystal structure of 4c
revealed the presence of a circular intramolecular
hydrogen bond arrangement (Table 1).
carbonyl groups (C62–O8 and C64–O9) are directed
outward of the macrocyclic cavity with little opportunity
to take part in hydrogen bonding. The remaining two
carbonyl groups participate in intramolecular and inter-
molecular hydrogen bonding. The donor N2–H partici-
pates in an intermolecular hydrogen bonding with the
oxygen atom (O5) of carbonyl group of neighbouring
It was observed that two unsubstituted phenolic
hydroxyl groups could be available both as hydrogen
bond donors and acceptors. The proton of the nitrogen
Figure 1. (a) ORTEP diagram numbering scheme of 4c (hydrogen atoms and solvent molecule have been omitted for clarity);
(b) intramolecular hydrogen bonding in 4c; only hydrogen atoms involved in hydrogen bonds are shown.

Supramolecular Chemistry
Table 1. Intramolecular hydrogen bonding interaction of 4c.
675
Da–H· · ·Ab
/D–H· · ·A (8)
˚
D–H (A)
˚
H· · ·A (A)
˚
D· · ·A (A)
S.no.
1.
2.
3.
4.
5.
6.
7.
O2–H2· · ·O1
O3–H3· · ·O4
N1–H1· · ·O4
N1–H1· · ·O2
N3–H3A· · ·O1
N3–H3A· · ·O3
N4–H4A· · ·O6
0.821
0.821
0.859
0.859
0.861
0.861
0.861
1.91
2.705
2.833
2.584
3.057
2.606
2.873
2.822
162.8
161.4
110.2
147.8
110.0
158.4
154.9
2.043
2.158
2.295
2.182
2.055
2.019
a Donor.
b Acceptor.
˚
molecule with a distance of 1.930 A, which organises this
structure in an infinite chain (Figure 2).
intramolecular hydrogen bond interactions, than NHb
protons. Such an interaction seems to result in the
appearance of NHa protons at d 11.10 in comparison to
NHb proton appearing at d 9.08 in the 1H NMR spectrum
of 4c at 258C. This conclusion was also supported by
observing intense infrared absorptions at 1658 cm21 and
NH stretching vibrations at 3281 cm21 which are in
consonance with earlier observations which demonstrated
that free NH usually appears at frequencies higher than
3400 cm21 in the FT-IR spectrum.
2.2 NMR studies in solution phase
Intramolecular hydrogen bonding observed in the crystal
structure of 4c was also confirmed in the solution phase by
variable temperature NMR experiments. The variable
temperature studies revealed that an increase in the
temperature leads to a significant upfield shift of both the
NH protons though the extent of upfield shift was found to
be larger for NHa protons than for NHb protons. NMR
experiments at different concentrations revealed that on
lowering the concentration of receptor molecule from 16
to 0.2 mM in CDCl3, none of the NH protons exhibit any
change in chemical shifts. This indicated that NHa and
NHb protons are involved in intramolecular hydrogen bond
interactions within the receptor molecules.
2.3 Binding studies
The host–guest interaction properties of the synthesised
hosts 4a–h towards anionic guests were determined by 1H
NMR experiments using WinEQNMR software (19).
Addition of various anions (such as F2, Cl2, Br2, I2,
2
ClO42, PF62, HSO42, H2PO4 and AcO2 in the form of
their tetrabutylammonium salts) to the solution of
receptors in CDCl3 resulted in a significant change in
NH resonances in their 1H NMR spectrum which indicated
The NHa protons exhibit larger downfield shift, which
could be ascribed to its involvement in multiple or stronger
Figure 2. Intermolecular hydrogen bonding between three neighbouring molecules of 4c (hydrogen and solvent molecules have been
omitted for clarity and only hydrogen atoms involved in hydrogen bonds are shown).

676
H.M. Chawla et al.
the presence of strong hydrogen bonding interactions
between the anions and NH protons of receptor molecules.
The recognition characteristics of 4a when investigated in
detail by 1H NMR experiments revealed that the NHa
signal at d 11.63 exhibited an upfield shift whereas the
NHb signal at d 9.22 and Hc proton of nitrophenyl moiety
at d 8.02 exhibited downfield shifts upon addition of
Table 2. Chemical shift values (Dd, ppm) of NHb proton
resonance of receptors (4a–h) upon addition of 100 equivalents
2
of tetrabutylammonium anions (HSO42, Cl2, Br2, I2, ClO4
and PF62) in CDCl3 (300 MHz and 298 K).
Anion
HSO24
Cl2
4a
4b
4c
4d
4e
4g
4h
1.45
0.87
0.72
0.14
0.23
NS
0.78
0.34
0.07
0.01
NS
0.33
0.17
0.04
NS
NS
NS
0.73
0.29
0.04
0.02
NS
1.45
0.87
0.72
0.13
0.22
0.02
0.33
0.17
NS
NS
NS
0.73
0.28
0.03
NS
NS
NS
Br2
tetrabutylammonium salts of Cl2, Br2, I2, ClO42, PF6
2
I2
2
and HSO4 ions. The observed change in chemical shift
ClO24
PF26
values of NHa, NHb and Hc proton resonances was found
to be highest for hydrogen sulphate anion as compared to
NS
NS
NS
those of other anions (Cl2, Br2, I2, ClO4 and PF62) in
2
Note: NS indicates no change in chemical shifts.
deuterated chloroform (Table 2). No effect on the chemical
shift of phenolic OH signal at d 8.25 was observed upon
addition of anionic species to the receptor solutions.
Interestingly, addition of more basic anions such as
equivalents to solution of receptor 4a resulted in small
upfield chemical shifts in Hc and Hd aromatic proton
resonances of the nitrophenyl units which could be
ascribed to the presence of highly negative HF22 species
near the vicinity of the aromatic protons. On the other
hand, analogous addition of more than four equivalents of
F2, H2PO4 and AcO2 to solution of receptor 4a in
2
CDCl3 leads to broadening of NHa and NHb signals at d
11.63, d 9.22, respectively, which completely disappeared
on addition of excess of these anions (Figures 3 and S1).
Detailed analysis of the 1H NMR titration spectra revealed
that gradual addition of F-ions to 4a results in a broadening
of NHa and NHb signals which completely disappeared
after the addition of eight equivalents of fluoride ions.
However, addition of fluoride ions beyond three
H2PO4 and AcO2 ions resulted in complete disappear-
2
ance of NHa and NHb signals, while no significant effect
was observed on Hc and Hd protons of the nitrophenyl
units. These observations indicated that strong basic
anions such as F2, H2PO42 and AcO2 completely disrupt
the intramolecular hydrogen bonding network present
1
Figure 3. Partial H NMR (300 MHz and 298 K) spectra of host 4a (10 mM) upon addition of 10 equiv. TBAzF (40 mM) in CDCl3.
(a) Host 4a; (b) 4a þ 10.0 equiv. of F2 (’ ¼ NHa, P ¼ NHb, † ¼ Hc, † ¼ Hd).

Supramolecular Chemistry
within the receptor molecule and possibly interact with
677
acidic NH protons of the receptor molecule through a
typical Bronsted acid–base type reaction rather than a
cooperative binding phenomena.
Interestingly, addition of more basic anions such as
F2, H2PO4 and AcO2 to solution of receptor 4a in
2
CDCl3 leads to broadening of NHa and NHb signals at d
11.63 and d 9.22, respectively, with no change in chemical
shifts.
2
A detailed study on the binding of HSO4 with 4a
revealed maximum downfield shift of 1.45 ppm for the
NHb signal and 0.28 ppm for Hc proton of nitrophenyl
moiety, whereas an unexpected upfield shift of 0.48 ppm
for NHa signal was observed for 4a when 1.0 equiv. of
TBAzHSO4 was added to it (Figure 4). A plot of chemical
shift for the NHb proton versus concentration of
TBA z HSO4 showed an isotherm which was consistent
with a 1:1 host–guest binding stoichiometry (Figure 5).
Job’s continuous variation plot experiment further
confirmed the 1:1 binding stoichiometry when maximum
complexation was observed at 0.5 mol fraction of the anion
(Figure 6).
Similarly, the binding-stoichiometry of 4a with other
anions (such as Cl2, Br2, I2 and ClO42) was also
determined to be 1:1 by Job’s plot experiments.
Since a downfield shift in resonance signals was
observed for the NHb and Hc protons upon addition of
HSO42 ion to a CDCl3 solution of 4a and no effect for the
OH signals was notified, it indicated that both the NHb and
Hc protons participate in the formation of cooperative
hydrogen bonds with the anionic guest whereas the
phenolic protons do not. As a result, the chemical shift of
the OH signal remained unaffected during the titration.
The unexpected upfield shift for NHa proton resonance of
2
4a on interaction with HSO4 could possibly be ascribed
to the disruption of strong hydrogen bond interactions of
NHa protons with oxygen atoms of the phenoxy and
phenolic ring of calix[4]arene skeleton due to the
complexation-induced conformational changes in 4a. A
Figure 4. Partial 1H NMR (300MHz and 298K) spectra of host
4a (10 mM) upon addition of various aliquots of a TBAzHSO4
2
(40 mM) in CDCl3. (a) Host 4a; (b) 4a þ 0.25 equiv. of HSO42
;
;
2
higher affinity of synthesised receptors towards HSO4
ion could possibly be ascribed to the flexibility of receptor
(c) 4a þ 0.50 equiv. of HSO42; (d) 4a þ 0.75 equiv. of HSO4
2
(e) 4a þ 1.0 equiv. of HSO42; (f) 4a þ 2.5 equiv. of HSO4
(’ ¼ NHa, P ¼ NHb, X ¼ ArHc).
2
molecule for better entrapment of HSO4 ion such that
2
anionic oxygen atoms of tetrahedral HSO4 ion form
2.4 Association constants for anions and molecular
receptors
cooperative hydrogen bonds with the two NHb protons as
well as Hc protons of nitrophenyl moiety of 4a.
Similar experiments with 4b–h also gave a downfield
shift for NHb protons and upfield shift for NHa protons in
the 1H NMR spectrum at 258C. In a comparative study of
4a, 4b and 4c, it was observed that receptor 4a exhibited
larger downfield shift for NHb protons than 4b and
4c, possibly due to the presence of stronger hydrogen
bonding in 4a which could be ascribed to the presence of
electron-withdrawing nitro substituents than their absence
in 4b and 4c.
The association constants for 4a–d with different anions
could be determined by using WinEQNMR software (19)
(Table 3).
Receptor 4a showed higher affinity for HSO42 than for
other examined anions (Cl2, Br2, I2 and ClO42) with an
association constant of 5700 M21. The 4b and 4c showed
association constants of 3850 and 2870 M21, respectively,
2
for HSO4 ion. The higher association constant of 4a for
HSO42 could possibly be ascribed to the less basic nature

678
H.M. Chawla et al.
Table 3. Association constant (Ka)a for 1:1 complex of hosts
with anions in CDCl3 at 298 K.
Ka [M21
]
Anionb
4a
4b
4c
2
HSO4
5700
430
360
70
3850
280
140
–
2870
210
80
–
Cl2
Br2
I2
2
ClO4
120
60
–
a Estimated error ,10%.
b Anions were used as tetrabutylammonium salt.
sulphate moiety (Table S4, Supplementary file, available
online). While two other oxygen (SvO) were found to be
closer to the ortho hydrogens (Hc) of nitrophenyl moiety.
Though it is yet speculative, the negatively charged oxygen
atom of HSO42 seems to interact with the NHb proton while
OH of HSO42 interactions with carbonyl group in structure
b. The hydrogen sulphate found a position close to the ortho
hydrogens (Hc) of nitrophenyl moiety in the energy
minimised conformation.
Figure 5. 1H NMR titration curve of 4a with
tetrabutylammonium anions (CDCl3, 300 MHz, 298 K).
of NH protons due to the presence of electron-withdrawing
nitro substituent which enhances its anion binding ability
through hydrogen bond. The observed selectivity order
2
2
was determined to be HSO4 . Cl2 . Br2 . ClO4
. I2 for 4a–d.
2
Tentative association modes of HSO4 with 4a
when studied through Gaussian 09 software package
(20) by using STO-3G/631G* level of theory gave
some insight into the host–guest chemistry of hydrogen
sulphate and receptor 4a. Amongst several possible
conformers, it was determined that the two low energy
conformers (shown in Figure 7) had Emin for structure b
(22,686,307.8 kcal/mol) approximately 40 kcal/mol
lower than structure a (22,686,267.8 kcal/mol). In
structure a with hydrogen bonding network remaining
intact in both structures, the negatively charged oxygen
To investigate the role of preorganised structure of
calix[4]arene, model compounds (5, 6) akin to a single
binding pod of receptors 4a and 4b were also synthesised
(Figure 8).
Anion recognition experiments with these model
compounds at 100 mM concentration revealed no signifi-
1
cant change in their H NMR spectrum upon addition of
tetrabutylammonium salt of chloride, bromide and iodide,
whereas addition of excess of hydrogen sulphate led to
broadening of NHa and NHb protons. This clearly
indicated the presence of non-cooperative hydrogen
bond formation between the single pod receptors 5 and 6
with HSO42 ions. These observations reaffirm that though
4a, 5, 4b and 6 have the same type of binding sites, only an
appropriate size of the cavity of 4a and 4b can bind these
anions more effectively.
2
of HSO4 occupies a position between two NHb
protons that can induce a shift in NHb protons as
observed in solution 1H NMR. The Hb protons also
have a very high positive charge required for interaction
with negatively charged oxygen atom of hydrogen
0.2
0.18
0.16
0.14
0.12
0.1
3. Conclusion
In conclusion, we can state that new neutral calix[4]arene-
based diacylhydrazide receptors 4a–h promise high
selectivity for recognition of HSO4 ion in preference to
2
Cl2, Br2, I2, ClO4 and PF6 ions with a 1:1 binding
stoichiometry. Although studies with analogous phosphate
led to broadening of relevant signals, hydrogen sulphate
recognition is clear indicating the necessity of further work
towards identification of suitable molecular receptors for
complex anions. The recognition behaviour of synthesised
receptors indicates that strong hydrogen bonding inter-
action between NHb and ArHc protons and anions is
extremely useful. Further work on the design, synthesis
and evaluation of molecular receptors for recognition of
target critical anions recognition is in progress.
2
2
0.08
0.06
0.04
0.02
0
0
0.2
0.4
0.6
0.8
1
Mol fraction of hydrogen sulphate
Figure 6. Job’s continuous variation plot of the ligand 4a with
HSO4 ion.
2

Supramolecular Chemistry
679
2
Figure 7. Structure of conformers of complex of 4a with HSO4
.
4. Experimental section
discs, whereas CHN analysis was carried out on a Perkin-
1
Elmer 240C elemental analyser. H NMR spectra were
4.1 General
recorded on a 300 MHz Bruker DPX 300 instrument at
room temperature using tetramethylsilane as an internal
standard. FAB mass spectra were recorded on a JEOL SX
102/DA-6000 Mass spectrometer/Data System using
Argon/Xenon (6 kV, 10 mA) as the FAB gas. Compounds
1a and 1b and 2a and 2b were synthesised by the methods
reported earlier (15, 16).
All the reagents used in the study were purchased from
Sigma-Aldrich or Merck and were considered chemically
pure. Solvents used were pre-dried and purified by
distillation. Column chromatography was carried out on
silica gel (60–120 mesh) obtained from Merck. Melting
points were recorded on an electric melting point apparatus
(Toshniwal, India) and are uncorrected. FT-IR spectra were
´ ´
recorded on a Nicolet Protege 460 spectrometer using KBr
4.1.1 General procedure or synthesis of compounds
3a and 3b
A
solution of 5,11,17,23-tetra-tert-butyl-25,27-
bis[(ethoxy-carbonyl)methoxy]-26,28-dihydroxy calix[4]-
arene 2a (0.87 g, 1.3 mmol) and 25,27-bis[(ethoxy-
carbonyl)methoxy]-26,28-dihydroxy calix[4]arene 2b
(0.97 g, 1.3 mmol) in 50 ml of toluene and methanol
mixture (1:1, v/v) was treated with 3.0 ml of hydrazine
hydrate. After stirring for 14 h at room temperature, the
reaction mixture was evaporated under vacuum and the
residue was diluted with CHCl3. The organic layer was
washed with water, dried over anhydrous Na2SO4 and
evaporated to dryness. The white solid residue was purified
by crystallisation in chloroform and methanol at room
temperature to give 3a and 3b as white solids.
O
O
CH2
CH2
O
C
O
C
N H
N H
H N
H N
C
O
C
O
CH3
NO2
6
5
Figure 8. Structures of model compounds 5 and 6.

680
H.M. Chawla et al.
4.1.1.1 Compound 3a. Yield (88%). mp ¼ 1688C. IR
(KBr, cm21): 3250 (OH); 1689 (CvO). 1H NMR
(300 MHz, CDCl3): d 1.03 (s, 18H, t-butyl), d 1.27 (s,
18H, t-butyl), d 1.68 (bs, 4H, NH2), d 3.41 (d, 4H,
J ¼ 13.2 Hz, Ar–CH2–Ar), d 4.09 (d, 4H, J ¼ 13.2 Hz,
Ar–CH2–Ar), d 4.64 (s, 4H, OCH2), d 6.9 (s, 4H, Ar–
126.4, 126.7, 128.7, 132.3, 137.3, 143.4, 148.8, 149.0,
149.2, 149.3, 162.8, 166.3. Anal. Calcd for C62H70N6O12:
C, 68.24; H, 6.47; N, 7.70; Found: C, 68.39; H, 6.56; N,
7.50. FAB-MS m/z Calcd: 1091. Found 1092 (Mþ þ 1).
H
calix), d 7.08 (s, 4H, Ar–Hcalix), d 7.74 (s, 2H, OH), d 9.69
4.1.2.2 Compound 4b. Yield (84%). mp ¼ 2428C. IR
(s, 2H, NH). 13C NMR (CDCl3): 30.7, 31.2, 32.6, 33.8, 34.4,
72.5, 114.8, 119.7, 125.7, 127.8, 128.6, 129.6, 131.9, 133.1,
151.2, 152.9, 164.5, 165.1. Anal. Calcd for C48H64N4O6: C,
72.70; H, 8.13; N, 7.06; Found: C, 72.53; H, 8.16; N, 7.19.
FAB-MS m/z Calcd: 793. Found 794 (Mþ þ 1).
1
(KBr, cm21): 3281 (NH); 1711, 1658 (CvO). H NMR
(300 MHz, CDCl3): d 1.07 (s, 18H, t-butyl), d 1.26 (s, 18H,
t-butyl), d 2.34 (s, 6H, ZCH3), d 3.45 (d, 4H, J ¼ 13.0 Hz,
Ar–CH2–Ar), d 4.27 (d, 4H, J ¼ 13.0 Hz, Ar–CH2–Ar),
d 4.79 (s, 4H, OCH2), d 6.96 (s, 4H, Ar–Hcalix), d 7.08 (s,
4H, Ar–Hcalix), d 7.77 (d, 4H, J ¼ 6.9 Hz, Ar–H), d 7.94
(d, 4H, J ¼ 6.9 Hz, Ar–H), d 8.08 (s, 2H, OH), d 9.19 (s,
2H, NHb), d 11.23 (s, 2H, NHa). 13C NMR (CDCl3): 30.9,
31.6, 32.2, 33.9, 34.2, 55.3, 74.4, 113.8, 124.2, 125.6,
126.9, 129.4, 132.4, 143.0, 148.4, 149.1, 149.5, 162.6,
164.8, 166.3. Anal. Calcd for C64H76N4O8: C, 74.68; H,
7.44; N, 5.44; Found: C, 74.45; H, 7.32; N, 5.53. FAB-MS
m/z Calcd: 1029. Found 1030 (Mþ þ 1).
4.1.1.2 Compound 3b. Yield (91%). mp ¼ 1678C. IR
(KBr, cm21): 3245 (OH); 1681 (CvO). 1H NMR
(300 MHz, CDCl3): d 1.65 (bs, 4H, NH2), d 3.42 (d, 4H,
J ¼ 13.3 Hz, Ar–CH2–Ar), d 4.05 (d, 4H, J ¼ 13.3 Hz,
Ar–CH2–Ar), d 4.59 (s, 4H, OCH2), d 6.65 (t, 2H,
J ¼ 7.4 Hz, Ar–Hcalix), d 6.75 (t, 2H, J ¼ 7.8 Hz, Ar–
H
calix), d 6.89 (d, 4H, J ¼ 7.4 Hz, Ar–Hcalix), d 7.02 (d,
4H, J ¼ 7.8 Hz, Ar–Hcalix), d 7.90 (s, 2H, OH), d 9.50 (s,
2H, NH). 13C NMR (CDCl3): 29.3, 31.5, 63.9, 72.3, 115.2,
118.3, 125.2, 127.4, 128.69, 130.3, 143.2, 150.7, 152.4,
163.5, 164.3. Anal. Calcd for C32H32N4O6: C, 67.59; H,
5.67; N, 9.80;. Found: C, 67.43; H, 5.76; N, 9.69. FAB-MS
m/z Calcd: 568. Found 569 (Mþ þ 1).
4.1.2.3 Compound 4c. Yield (87%). mp ¼ 2328C. IR
1
(KBr, cm21): 3281 (NH); 1713, 1653 (CvO). H NMR
(300 MHz, CDCl3): d 1.07 (s, 18H, t-butyl), d 1.26 (s,
18H, t-butyl), d 3.45 (d, 4H, J ¼ 12.7 Hz, Ar–CH2–Ar),
d 3.82 (s, 6H, OCH3), d 4.26 (d, 4H, J ¼ 12.7 Hz, Ar–
CH2–Ar), d 4.78 (s, 4H, OCH2), d 6.88 (d, 4H,
J ¼ 8.4 Hz, Ar–H), d 6.96 (s, 4H, Ar–Hcalix), d 7.08 (s,
4H, Ar–Hcalix), d 7.86 (d, 4H, J ¼ 8.4 Hz, Ar–H), d 8.05
(s, 2H, OH), d 9.08 (s, 2H, NHb), d 11.10 (s, 2H, NHa).
13C NMR (CDCl3): 30.9, 31.4, 32.4, 33.8, 34.3, 73.4,
74.7, 113.3, 124.4, 125.9, 126.9, 130.3, 133.7, 144.3,
148.9, 149.8, 150.7, 163.2, 164.2, 166.9. Anal. Calcd for
C64H76N4O10: C, 72.43; H, 7.22; N, 5.28. Found: C,
72.37; H, 7.76; N, 5.53. FAB-MS m/z Calcd: 1061. Found
1062 (Mþ þ 1).
4.1.2 General procedure for the synthesis of compounds
4a–h
A mixture of compounds 3a (1.17 mmol) and 3b
(1.17 mmol), K2CO3 (7.19 mmol) and substituted benzoyl
chloride (4.5 mmol) was stirred under reflux in 20 ml of
anhydrous acetonitrile for 48 h. The reaction mixture was
cooled to room temperature and then carefully neutralised
with dilute hydrochloric acid (10%) and extracted with
chloroform. The organic layer was washed with water,
dried over Na2SO4 and evaporated to dryness. The white
solid residue was purified by column chromatography on
silica gel using hexane–ethyl acetate (gradient from
9.5:0.5 to 8:2) as eluent. Selected analytical data for
compounds 4a–h are given below.
4.1.2.4 Compound 4d. Yield (78%). mp ¼ 2288C. IR
1
(KBr, cm21): 3280 (NH); 1712, 1657 (CvO). H NMR
(300 MHz, CDCl3): d 1.07 (s, 18H, t-butyl), d 1.27 (s,
18H, t-butyl), d 3.44 (d, 4H, J ¼ 13.4 Hz, Ar–CH2–Ar),
d 4.29 (d, 4H, J ¼ 13.4 Hz, Ar–CH2–Ar), d 4.82 (s, 4H,
OCH2), d 6.98 (s, 4H, Ar–Hcalix), d 7.07 (s, 4H, Ar–
4.1.2.1 Compound 4a. Yield (91%). mp ¼ 2408C. IR
H
calix), d 7.36 (t, 4H, J ¼ 7.2 Hz, ArH), d 7.41 (d, 2H,
1
(KBr, cm21): 3283 (NH); 1711, 1656 (CvO). H NMR
J ¼ 7.2 Hz, Ar–H), d 7.80 (d, 4H, J ¼ 7.2 Hz, Ar–H), d
8.37 (s, 2H, OH), d 9.11 (s, 2H, NHb), d 11.19 (s, 2H,
NHa). 13C NMR (CDCl3): 30.8, 31.1, 32.5, 33.7, 34.5,
74.1, 113.7, 124.3, 126.1, 127.1, 130.3, 133.2, 145.8,
148.3, 149.8, 149.9, 162.7, 164.8, 166.1. Anal. Calcd for
C62H72N4O8: C, 74.37; H, 7.25; N, 5.60. Found: C, 74.25;
H, 6.98; N, 5.53. FAB-MS m/z Calcd: 1000. Found 1001
(Mþ þ 1).
(300 MHz, CDCl3): d 1.09 (s, 18H, t-butyl), d 1.26 (s, 18H,
t-butyl), d 3.48 (d, 4H, J ¼ 12.9 Hz, Ar–CH2–Ar), d 4.25
(d, 4H, J ¼ 12.9 Hz, Ar–CH2–Ar), d 4.83 (s, 4H, OCH2),
d 7.01 (s, 4H, Ar–Hcalix), d 7.12 (s, 4H, Ar–Hcalix), d 8.02
(d, 4H, J ¼ 7.2 Hz, Ar–H), d 8.25 (m, 6H, Ar–H þ OH),
d 9.22 (s, 2H, NHb), d 11.63 (s, 2H, NHa). 13C NMR
(CDCl3): 30.9, 31.5, 32.3, 33.9, 34.2, 74.4, 123.8, 125.7,

Supramolecular Chemistry
681
4.1.2.5 Compound 4e. Yield (89%). mp ¼ 2438C. IR
4H, OCH2), d 6.70 (t, 2H, J ¼ 7.5 Hz, Ar–Hcalix), d 6.82 (t,
2H, J ¼ 7.5 Hz, Ar–Hcalix), d 6.98 (d, 4H, J ¼ 9.3 Hz, Ar–
1
(KBr, cm21): 3281 (NH); 1710, 1657 (CvO). H NMR
(300 MHz, DMSO): d 3.49 (d, 4H, J ¼ 12.7 Hz, Ar–CH2–
Ar), d 4.33 (d, 4H, J ¼ 12.7 Hz, Ar–CH2–Ar), d 4.78 (s,
4H, OCH2), d 6.64 (t, 2H, J ¼ 6.7 Hz, Ar–Hcalix), d 6.84 (t,
2H, J ¼ 6.5 Hz, Ar–Hcalix), d 7.07 (d, 4H, J ¼ 6.7 Hz, Ar–
H
calix), d 7.09 (d, 4H, J ¼ 7.5 Hz, Ar–Hcalix), d 7.36 (t, 4H,
J ¼ 7.2 Hz, ArH), d 7.44 (d, 2H, J ¼ 7.2 Hz, Ar–H), d
7.82 (d, 4H, J ¼ 7.2 Hz, Ar–H), d 8.41 (s, 2H, OH), d 9.16
(s, 2H, NHb), d 11.50 (s, 2H, NHa). 13C NMR (CDCl3): d
30.6, 73.3, 119.4, 123.4, 125.7, 127.5, 128.7, 128.9, 129.2,
133.5, 137.9, 149.1, 152.1, 163.7, 167.4. Anal. Calcd for
C46H40N4O8: C, 71.12; H, 5.19; N, 7.21; Found: C, 71.31;
H, 5.38; N, 7.56. FAB-MS m/z Calcd: 776. Found 777
(Mþ þ 1).
H
calix), d 7.09 (d, 4H, J ¼ 6.5 Hz, Ar–Hcalix), d 8.04 (d,
4H, J ¼ 7.5 Hz, ArH), d 8.13 (d, 4H, J ¼ 7.5 Hz, ArH), d
8.38 (s, 2H, OH), d 10.55 (s, 2H, NHb), d 10.78 (s, 2H,
NHa). 13C NMR (DMSO): 32.1, 73.9, 124.1, 125.9, 127.2,
127.7, 129.3, 131.9, 137.5, 143.4, 148.7, 149.0, 149.3,
149.5, 162.9, 166.8. Anal. Calcd for C46H38N6O12: C,
63.74; H, 4.42; N, 9.70. Found: C, 64.79; H, 4.38; N,
10.12. FAB-MS m/z Calcd: 866. Found 867 (Mþ þ 1).
4.1.3 General procedure for the synthesis of compounds
5 and 6
A mixture of phenoxy acetyl hydrazide (1.1 mmol),
anhydrous K2CO3 (3.2 mmol) and 4-nitro (or 4-methyl)-
substituted benzoyl chloride (1.5 mmol) was stirred under
reflux in 25 ml of pre-dried acetonitrile for 48 h. The
reaction mixture was cooled to room temperature and then
carefully neutralised with aqueous hydrochloric acid
(10%) and extracted with chloroform. The organic layer
was washed with water, dried over Na2SO4 and evaporated
to dryness. The white solid residue was purified by column
chromatography on silica gel using hexane–ethyl acetate
(7:3) as eluent. Selected analytical data for compounds 5
and 6 are given below.
4.1.2.6 Compound 4f. Yield (86%). mp ¼ 2498C. IR
1
(KBr, cm21): 3280 (NH); 1711, 1659 (CvO). H NMR
(300 MHz, CDCl3): d 2.31 (s, 6H, –CH3), d 3.42 (d, 4H,
J ¼ 12.8 Hz, Ar–CH2–Ar), d 4.29 (d, 4H, J ¼ 12.8 Hz,
Ar–CH2–Ar), d 4.77 (s, 4H, OCH2), d 6.65 (t, 2H,
J ¼ 6.4 Hz, Ar–Hcalix), d 6.81 (t, 2H, J ¼ 6.7 Hz, Ar–
H
calix), d 7.06 (d, 4H, J ¼ 6.4 Hz, Ar–Hcalix), d 7.12 (d,
4H, J ¼ 6.7 Hz, Ar–Hcalix), d 7.73 (d, 4H, J ¼ 6.7 Hz, Ar–
H), d 7.99 (d, 4H, J ¼ 6.7 Hz, Ar–H), d 8.05 (s, 2H, OH),
d 9.13 (s, 2H, NHb), d 11.03 (s, 2H, NHa). 13C NMR
(CDCl3): 32.5, 55.1, 74.1, 113.6, 124.6, 125.4, 126.5,
128.9, 132.7, 143.2, 147.9, 149.2, 149.8, 163.2, 164.6,
166.6. Anal. Calcd for C48H44N4O8: C, 71.63; H, 5.51; N,
6.96; Found: C, 71.49; H, 5.22; N, 6.53. FAB-MS m/z
Calcd: 804. Found 805 (Mþ þ 1).
4.1.3.1 Compound 5. Pale white solid (85%).
mp ¼ 2028C. IR (KBr, cm21): 3269 (OH); 1693
(CvO). 1H NMR (300 MHz, CDCl3): d 9.53 (s, 1H,
NH), 8.21 (s, 1H, NH), 7.63 (d, 2H, J ¼ 8.1 Hz,
ArHNO2), 7.11 (brs, 4H, ArH þ ArHNO2), 6.73 (d, 2H,
J ¼ 7.7 Hz, ArH), 6.70 (s, 1H, ArH), 4.79 (s, 2H,
OCH2). 13C NMR (75 MHz, CDCl3): d 192.2, 188.3,
128.3, 126.3, 125.7, 124.7, 123.1, 121.4, 120.6, 118.9,
116.8, 112.6, 108.3, 72.8, 31.9. Anal. Calcd for
C15H13N3O5: C, 57.14; H, 4.16; N, 13.33. Found: C,
57.27; H, 4.34; N, 13.63. FAB-MS m/z Calcd: 315.
Found 316 (Mþ þ 1).
4.1.2.7 Compound 4g. Yield (82%). mp ¼ 2318C. IR
1
(KBr, cm21): 3282 (NH); 1712, 1657 (CvO). H NMR
(300 MHz, CDCl3): d 3.42 (d, 4H, J ¼ 12.7 Hz, Ar–CH2–
Ar), d 3.83 (s, 6H, OCH3), d 4.28 (d, 4H, J ¼ 12.7 Hz, Ar–
CH2–Ar), d 4.73 (s, 4H, OCH2), d 6.68 (t, 2H, J ¼ 6.2 Hz,
Ar–Hcalix), d 6.79 (t, 2H, J ¼ 6.6 Hz, Ar–Hcalix), d 6.89
(d, 4H, J ¼ 8.4 Hz, Ar–H), d 7.03 (d, 4H, J ¼ 6.2 Hz, Ar–
H
calix), d 7.12 (d, 4H, J ¼ 6.6 Hz, Ar–Hcalix), d 7.86 (d,
4H, J ¼ 8.4 Hz, Ar–H),), d 8.02 (s, 2H, OH), d 9.03 (s, 2H,
NHb), d 11.15 (s, 2H, NHa). 13C NMR (CDCl3): 32.1, 73.2,
74.4, 114.1, 125.1, 126.1, 126.7, 129.8, 132.9, 144.8,
148.3, 149.7, 150.1, 163.1, 164.3, 166.4. Anal. Calcd for
C48H44N4O10: C, 68.89; H, 5.30; N, 6.69; Found: C, 68.75;
H, 5.16; N, 6.52. FAB-MS m/z Calcd: 836. Found 837
(Mþ þ 1).
4.1.3.2 Compound 6. White solid (89%). mp ¼ 2058C.
IR (KBr, cm21): 3268 (OH); 1690 (CvO). 1H NMR
(300 MHz, CDCl3): d 9.52 (s, 1H, NH), 8.23 (s, 1H,
NH), 7.11 (brs, 4H, ArH þ ArHCH3), 6.73 (brs, 5H,
ArH þ ArHCH3), 4.79 (s, 2H, OCH2), 2.37 (s, 3H,
CH3). 13C NMR (75 MHz, CDCl3): d 197, 189, 128.3,
126.3, 125.7, 124.7, 123.1, 121.4, 120.6, 118.9, 116.8,
112.6, 108.3, 73.1, 32.1, 28.6. Anal. Calcd for
C16H16N2O3: C, 67.59; H, 5.67; N, 9.85. Found: C,
67.33; H, 5.36; N, 9.41. FAB-MS m/z Calcd: 284.
Found 285 (Mþ þ 1).
4.1.2.8 Compound 4h. Yield (80%). mp ¼ 2338C. IR
1
(KBr, cm21): 3279 (NH); 1714, 1653 (CvO). H NMR
(300 MHz, CDCl3): d 3.51 (d, 4H, J ¼ 13.4 Hz, Ar–CH2–
Ar), d 4.31 (d, 4H, J ¼ 13.4 Hz, Ar–CH2–Ar), d 4.84 (s,

682
H.M. Chawla et al.
Research (CSIR), India for Senior Research Fellowships to R.S.
and S.N.S.
4.1.4 H NMR titration experiments
A 10 mM solution of the host 4a–h was prepared in
CDCl3. To a 0.5 ml of 4a–h solution, 0–5 equiv. of
tetrabutylammonium hydrogen sulphate (40 mM) was
added to an NMR tube and the spectra were recorded. The
chemical shifts of the NHb and CH protons were followed
and plotted against the equivalents of TBA z HSO4 added.
References
(1) Chawla, H.M.; Pant, N.; Kumar, S.; Black, D.S.; Kumar, N.
In Chemical Sensors: Fundamentals of Sensing Materials;
Korotcenkov, G., Ed.; Polymers and Other Materials, vol. 3,
pp. 117–182, Momenturm Press: New York, 2010.
(2) Kirk, K.L. Biochemistry of the Elemental Halogens and
Inorganic Halides; Plenum Press: New York, 1991;
Ullman’s Encyclopedia of Industrial Chemistry, 6th ed.;
Wiley-VCH: New York, 1998; De Silva Frausto, J.J.R.;
Williams, R.J.P. Struct. Bond 1976, 29, 67; Yoon, D.-W.;
Gross Dustin, E.; Lynch Vincent, M.; Sessler Jonathan, L.;
Hay Benjamin, P.; Lee, C.-H. Angew. Chem. Int. Ed. Engl.
2008, 47, 5038–5042; Gentile, S.; Gulino, F.G.; Sciotto, D.;
Sgarlata, C. Lett. Org. Chem. 2006, 3, 48–53; Bianchi, A.;
4.1.5 Job’s plot experiments
Stock solutions of hosts 4a–h (10 mM) and tetrabutyl-
ammonium hydrogen sulphate (10 mM) were prepared in
CDCl3. A total volume of 500 ml of 4a–h and TBA z HSO4
was added to nine NMR tubes in the following volume
ratios: 50:450, 100:400, 150:350, 200:300, 250:250,
200:300, 150:350, 100:400 and 50:450.
´
Bowman-James, K.; Garcıa-Espana, E. Supramolecular
Chemistry of Anions; VCH Pub: New York, 1997; Gale,
P.A. Chem. Commun., 2005, 2005, 3761–3772; Kerckhoffs,
J.M.C.A.; Ishi-i, T.; Paraschiv, V.; Timmerman, P.;
Crego-Calama, M.; Shinkai, S.; Reinhoudt, D.N. Org.
Biomol. Chem. 2003, 1, 2596–2603.
4.1.6 X-ray structure determination of 4c
The crystals of 4c were obtained when the compound was
crystallised from CHCl3–C2H5OC2H5 (7:3). X-ray crystal
data for 4c-C64H76N4O10, M ¼ 4712.77, monoclinic,
(3) No, K.; Lee, J.H.; Yang, S.H.; Noh, K.H.; Lee, S.W.;
Kim, J.S. Tetrahedron 2003, 59, 2403–2407.
(4) Chen, X.; Jiang, D.; Shi, L. Huaxue Jiaoyu 2009, 30, 6–10,
Rudkevich, D.M. Chem. Eur. J. 2000, 6, 2679–2686;
Mogck, O.; Paulus, E.F.; Bohmer, V.; Thondorf, I.; Vogt, W.
Chem. Commun. 1996, 52, 2533–2534; Ajami, D.; Rebek,
J. J. Org. Chem. 2009, 74, 6584–6591; Cho, Y.L.;
Rudkevich, D.M.; Shivanyuk, A.; Rissanen, K.; Rebek, J.
Chem. Eur. J. 2000, 6, 3788–3796.
˚
˚
a ¼ 21.7362(17)A, b ¼ 14.6949(12) A, c ¼ 23.4308(18)
˚
A,
a ¼ 90.08,
b ¼ 114.1210(10)8,
g ¼ 90.08,
3
V ¼ 6830.6(9) A , Z ¼ 1, Dc ¼ 1.146 g cm23, m (Mo
Ka) ¼ 0.081 mm21, goodness of fit (GOF) ¼ 0.994, space
group ¼ P21/c. Intensity data were collected up to u ¼ 428
by using 2u scanning mode with graphite-filtered Mo Ka
radiation (l ¼ 0.71073) on a 0.291 £ 0.168 £ 0.098 mm3
crystal at 298 K. A total of 43,914 reflections were
measured, of which 7314 were independent. The structure
was solved by direct methods and refined by full matrix
least-square techniques on F2 using SHELXTL. All the
non-hydrogen atoms were refined anisotropically. C–H
hydrogen atoms were placed in geometrically calculated
positions by using a riding model. SADABS was applied
for absorption correction. Final R indices [I . 2ss(I)]
R1 ¼ 0.0662, wR2 ¼ 0.1844, and R indices (all data)
R1 ¼ 0.0789, wR2 ¼ 0.1952 were found for 7314
observed reflections, 0 restraints and 868 parameters.
In order to bring down the value of residual factor, we have
omitted the higher 2u values in this case. The apparently
high value for R factor probably originates from the
disorder due to the solvent. Torsion angles and H-bonding
were calculated by using PARST. Crystal data have been
deposited at the Cambridge Crystallographic Data Center,
under reference CCDC 717989.
˚
(5) Mogck, O.; Bohmer, V.; Vogt, W. Tetrahedron 1996, 52,
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Acknowledgements
The authors gratefully acknowledge the assistance received from
the Sophisticated Analytical Instrument Facility (SAIF), CDRI,
Lucknow, for recording the FAB-MS spectra reported in this
paper. DST, DBT, MOEF, MFPI and MRD, Govt. of India for
financial assistance and the Council of Scientific and Industrial

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