Benzthiazole-based multifunctional chemosensor: Fluorescent recognition of Fe3+ and chromogenic recognition of HSO4

Article abstract of DOI:10.1016/j.tet.2012.11.090

A benzthiazole-based multifunctional chemosensor was designed with siderophores like binding sites for recognition of Fe³⁺ and both hydrogen bond donor and acceptor binding sites for oxyanion HSO₄. The sensor recognizes Fe³⁺ selectively through enhancement of fluorescence emission intensity at 440 nm and recognizes HSO₄- through a bathochromic shift in UV-vis spectra from 315 nm to 365 nm with clear isosbestic points at 345 nm and 395 nm. The recognition of both Fe³⁺ and HSO₄ is free from the interference from the other cations and anions, respectively.

Full text of DOI:10.1016/j.tet.2012.11.090

Tetrahedron 69 (2013) 1606e1610
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Benzthiazole-based multifunctional chemosensor: fluorescent
ꢀ
recognition of Fe3þ and chromogenic recognition of HSO4
,
c,
*
Vimal K. Bhardwaj a, Preeti Saluja a, Geeta Hundal b, M.S. Hundal b, Narinder Singh a , Doo Ok Jang
*
a Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar 140001, Punjab, India
b Department of Chemistry, Guru Nanak Dev University, Amritsar 143005, Punjab, India
c Department of Chemistry, Yonsei University, Wonju 220-710, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
A benzthiazole-based multifunctional chemosensor was designed with siderophores like binding sites
ꢀ
for recognition of Fe3þ and both hydrogen bond donor and acceptor binding sites for oxyanion HSO4
.
Received 28 September 2012
Received in revised form 26 November 2012
Accepted 27 November 2012
Available online 3 December 2012
The sensor recognizes Fe3þ selectively through enhancement of fluorescence emission intensity at
ꢀ
440 nm and recognizes HSO4 through a bathochromic shift in UVevis spectra from 315 nm to 365 nm
ꢀ
with clear isosbestic points at 345 nm and 395 nm. The recognition of both Fe3þ and HSO4 is free from
the interference from the other cations and anions, respectively.
Keywords:
Chemosensor
Fe (IIIꢀ)
Ó 2012 Elsevier Ltd. All rights reserved.
HSO4
Fluorescent
Chromogenic
1. Introduction
sulfate. However, iron supplementation leads to accumulation of
externally administered iron in the body, which has deleterious
Recently, there has been significant interest in the design and
development of artificial optical chemosensors that recognize bi-
ologically and environmentally important analytes.1 Considerable
efforts have been made to develop multifunctional sensors that
simultaneously recognize multiple analytes.2 Due to their high
sensitivity and prompt analyte detection, UVevis absorption
spectroscopy and fluorescent spectroscopy-based analytical tech-
niques are immensely preferred. A large number of chemosensors
have been proposed to selectively detect cations and anions by
a simple turn-on or turn-off response.3 Most of these chemosensors
are selective for only one particular analyte.4 In various complex
molecular events, the simultaneous recognition of different ana-
lytes is required to screen for many target molecules at the same
time.
effects. For instance, a high level of iron in serum increases the risk
of several types of tumors.8 Iron excess also leads to Alzheimer’s
disease, which is responsible for some neural disorders.9 With
excess iron content, counter anion content (sulfate/hydrogen sul-
fate) also increases, which can also have harmful effects on the
body. High doses of sulfate may cause laxative effects that lead to
diarrhea.10 Iron and sulfate/hydrogen sulfate content should be si-
multaneously monitored. Although there are number of sensors
that separately detect iron11 and sulfate/hydrogen sulfate ions,12 to
best of our knowledge, there is no sensor for simultaneous esti-
mation of Fe3þ and HSO4ꢀ. Therefore, developing multiple analyte
sensors can be quite challenging.
ꢀ
The current work focuses on recognizing Fe3þ and HSO4
simultaneously. A coordination sphere that consists of an array of
hydrogen bond donors and acceptors is required. For this purpose,
we designed and synthesized sensors 1 and 2 as shown in Scheme 1.
The design of the sensors is based upon the reports available in
literature on iron chelating agents, such as siderophores and other
synthetic designs.13 The coordination sphere of these agents makes
use of the binding units containing phenol substituent along with
sp2-nitrogen donor. Thus, the insertions of these binding sites in
our designs might be beneficial for iron recognition. On the other
hand, these binding sites show both a hydrogen bond donor and
Iron plays an important role in several biological activities.5 Iron
deficiency is toxic and can lead to a number of severe neurological
disorders, developmental defects, and malfunctions.6 A lack of
adequate iron levels in the blood leads to anemia.7 To supplement
iron levels in the body, pharmacological forms that use the oral
route are recommended, such as iron sulfate and ferroglycine
acceptor, making an interesting combination for the coordination
* Corresponding authors. E-mail addresses: nsingh@iitrpr.ac.in (N. Singh),
dojang@yonsei.ac.kr (D.O. Jang).
ꢀ
of oxy-anions, such as HSO4
.
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.11.090

V.K. Bhardwaj et al. / Tetrahedron 69 (2013) 1606e1610
1607
1000
A
Fe(III)
800
600
400
Na(I), K(I), Mn(II),
Ca(II), Sr(II), Mg(II),
Cd(II), Ba(II), Co(II),
Ag(I) , Ni(II), Pb(II),
Zn(II),Cr(III), Hg(II),
Cu(II), Fe(II)
Scheme 1. Structure of sensors 1 and 2.
2. Results and discussion
Benzthiazole-based sensors 1 and 2 were synthesized by con-
densation of 2-(2-aminophenyl)-benzthiazole with 2-hydroxy-
naphthaldehyde or salicylaldehyde, respectively. The compounds
were characterized by spectroscopic methods. The presence of
imine linkages was confirmed by observing signals at 9.58 and
8.98 ppm in 1H NMR spectra and bands at 1610 and 1635 cmꢀ1 in IR
spectra. The structure of sensor 1 was also confirmed with a single
crystal X-ray crystallography image, as shown in Fig. 1. The crystal
structure of sensor 1 shows that all bond parameters are normal.
The benzthiazole ring and naphthyl ring were rotated by 15.10(5)ꢁ
and 47.29(4)ꢁ with respect to the central phenyl rings. The eOH
group formed intramolecular H-bondsꢁwith imine N and S, with
1
200
0
325
375
425
475
525
575
Wavelength (nm)
1000
800
600
400
200
0
B
ꢀ
ꢀ
O1eH1A/N2 (2.567(2) A, 1.84 A, 147 ), and with O1eH1A/S1
ꢁ
ꢀ
ꢀ
(3.441(2) A, 2.94 A, 121 ). Downfield chemical shift of hydroxyl
proton in sensor 1 and 2 is verifying intramolecular hydrogen
bonding in both. The chemical shift value for hydroxyl proton in the
case of sensor 1 is 14.67 ppm and in the case of sensor 2 is
11.59 ppm, indicating extensive hydrogen bonding in sensor 1.
375
425
475
525
575
Wavelength (nm)
Fig. 2. (A) Fluorescence spectra of sensor 1 (1.3
metal ions (20
M) in TRIS buffered CH3CN/H2O (8/2, v/v, pH¼7.6) when excited at
310 nm. (B) Fluorescence spectra of sensor 1 upon adding Fe3þ (0e20
M).
mM) upon adding nitrate salt of various
m
m
molecular rigidification and restricted PET binding with Fe3þ. In
addition, sensor 2 showed fluorescence intensity quenching at
440 nm with Fe3þ when excited at 370 nm (Fig. S2). Even the sensor
is selective for Fe3þ over Fe2þ, showing the incompatible co-
ordination sphere of sensor for Fe2þ in terms of size, shape and
steric factors. The selectivity of coordination sphere for one oxi-
dation state of iron over the other is the basis of redox-driven
translocations in molecular machines. The concept is well docu-
mented in literature, where the transition metal ions can be moved
reversibly between the two different co-ordination spheres using
some inputs.14 In addition, sensor 2 showed fluorescence intensity
quenching at 440 nm with Fe3þ when excited at 370 nm (Fig. S2).
Fig. 1. ORTEP diagram of sensor 1 labeling scheme.
UVevis absorption and fluorescence spectroscopy were used to
examine the binding behaviors of sensors 1 and 2 with different
cations and anions. UVevis absorption spectra of sensors 1 and 2
showed absorption bands at 310 and 370 nm, respectively, due to
imine linkages (Fig. S1). By recording UVevis absorption and
fluorescence spectra of sensors 1 and 2 in the presence of various
metal ions in TRIS buffered CH3CN/H2O (8/2, v/v, pH¼7.6), the
ability of sensors 1 and 2 to detect cations was investigated. There
was no unique and selective change in UVevis absorption spectra
of sensors 1 and 2 in the presence of any cation as shown in Fig. S1.
The fluorescence spectra of sensor 1 showed enhanced fluores-
cence intensity at 440 nm with Fe3þ when excited at 310 nm
(Fig. 2A), while there were no changes with any other tested
metal ions. The enhanced fluorescence intensity is attributed to
To further confirm the sensing properties of sensor 1 with Fe3þ
fluorescence titration was performed. As the concentration of Fe3þ
increased from 0 to 20 M, fluorescence intensity at 440 nm in-
,
m
creased (Fig. 2B). The effect of pH on sensor 1 was visualized by
recording UVevis absorption and fluorescence spectra of sensor 1
in CH3CN/H2O (8/2, v/v) at variable pH (Fig. S3). Variation in pH
caused drastic changes in the spectra of sensor 1. Thus, recognition
studies were carried out in TRIS buffered solution to exclude the

1608
V.K. Bhardwaj et al. / Tetrahedron 69 (2013) 1606e1610
effect of pH. The application of sensor 1 as a selective sensor for
Fe3þ was established by recording the spectra of sensor 1 with Fe3þ
in TRIS buffered CH3CN/H2O (8/2, v/v, pH¼7.6) in the presence of
the same equivalents of other tested metal ions. There was no
significant effect on the fluorescence emission profile of 1.Fe3þ in
the presence of any tested metal ion, as shown in Fig. S4. This result
clearly indicates that sensor 1 recognized Fe3þ selectively over
other metal ions. Mass spectrum of 1.Fe3þ showing a peak at
m/z¼560, which corresponds to 1þFe3þþ2NO3ꢀ, shows 1:1 bind-
ing of sensor 1 with Fe3þ (Fig. S5). The association constant for
1.Fe3þ was calculated as (2.9ꢂ0.13)ꢃ105 Mꢀ1 using Bene-
sieHildebrand plot (Fig. S6).15 The detection limit was calculated
Although there are no substantial differences between the
structures of sensors 1 and 2, the binding affinity for anions are quite
different. The structural features of the sensors might explain this
difference. All of our attempts failed to grow a single crystal on
sensor 2. We compared the optimized structure of sensors 1 and 2
using DFT calculations (Figs. 4 and 5). A comparison between the
crystal structures of sensor 1 with the optimized structure of sensor
2 may give some misleading information. The optimized structures
of sensors 1 and 2 lead to the conclusion that both the structures
have the same donor atoms in the pseudocavity of the sensors.
However, the difference lies in the relative distances and dihedral
angles of both the sensors. The donor sites of sensor 1 are planar
compared to sensor 2. The dihedral angle corresponding to an
angle between the planes of naphthalene rings or benzene rings
and the plane of the amine group plays an important role
in defining pseudocavities of both sensors. The dihedral angle
(C39eC25eC26eO44) in sensor 1 is 3.114, which leads to a regular size
and shape of cavity for metal ion coordination. On the other hand,
the same type of angle (C33eC25eC26eO36) in sensor 2 is in the re-
verse direction, (i.e., ꢀ1.697), which may influence the binding ca-
pacity of sensor 2. The other dihedral angles and bond angles also
support the poor binding cavity of sensor 2 (Table S6). Furthermore,
it was noticed that sensor 1 has smaller HOMOeLUMO energy gap
compared to sensor 2, resulting in effective overlapping (Table S7).
The smaller HOMOeLUMO energy gap has been reported to be
beneficial for metal binding.17
from titration data as 8.5 m
M (Fig. S7).16
Sensors 1 and 2 were checked for anion sensing by monitoring
UVevis absorption and fluorescent spectra in the presence of dif-
ferent anions. The absorption maxima of the UVevis absorption
spectra of sensor 1 in TRIS buffered CH3CN/H2O (8/2, v/v, pH¼7.6)
shifted to 365 nm with clear isosbestic points at 345 and 395 nm
ꢀ
upon treatment with HSO4 (Fig. 3A). However, there were no
changes in the UVevis absorption spectra of sensor 1 with any
other anions. There were no changes in the UVevis absorption
spectra of sensor 2 in the presence of any anions (Fig. S8). The
ꢀ
binding of sensor 1 with HSO4 was further verified by titration
ꢀ
with UVevis spectroscopy. Stepwise addition of HSO4 (0e20
mM)
to sensor 1 (1.3
m
M) in TRIS buffered CH3CN/H2O (8/2, v/v, pH¼7.6)
caused a decrease in absorbance at 310 and 450 nm and an increase
in absorbance at 365 nm. It also gave rise to a new absorptioꢀn
maximum at 365 nm (Fig. 3B). The association constant of 1.HSO4
was calculated from UVevis absorption titration data as
(1.8ꢂ0.05)ꢃ102 Mꢀ1 (Fig. S9).15 From UVevis absorption titration
ꢀ
data, the detection limit of HSO4 was calculated to be 5.4
mM
ꢀ
(Fig. S10).16 Selective binding of sensor 1 with HSO4 was de-
termined by executing competitive experiments in the presence of
ꢀ
other tested anions. The UVevis absorption profile of 1.HSO4
remained undisturbed (Fig. S11) in the presence of the same
equivalents of all other anions in TRIS buffered CH3CN/H2O (8/2,
v/v, pH¼7.6), verifying its selective binding. In 1H NMR titration,
ꢀ
upon interaction of HSO4 with sensor 1, major shifts were ob-
served for the signal eOH and eN]CH, both the signals shifted
downfield by Dd 0.05 ppm (Fig. S12). The shift in eOH signal shows
that the complex has intense hydrogen-bonding than one prevailed
in the pure receptor. The shifts of aromatic protons ꢀwere also ob-
served by Dd 0.02e0.07 ppm. These show that HSO4 binds in the
receptor pseudocavity by using both hydrogen bond donor and
hydrogen bond acceptor sites. The overall picture of 1H NMꢀR
spectra of pure host and spectra recorded upon addition of ꢀHSO4
Fig. 4. Optimized structure of sensor 1 (6,31G*d,p).
With fluorescence spectroscopy, sensor 1 selectively recognizes
ꢀ
Fe3þ over all tested cations while it recognizes HSO4 over all
tested anions using UVevis absorption spꢀectroscopy. We evaluated
the interference between Fe3þ and HSO4 by recording spectra of
ꢀ
sensor 1 with Fe3þ in the presence of HSO4 and vice versa. Fig. 6A
prevails the authentic bonding between sensor 1 and HSO4
.
A
0.5
0.4
0.3
0.2
0.1
0
B
0.5
-
-
- -
1, F , Cl , Br , I ,
3
-
-
-
0.4
0.3
0.2
0.1
0
NO3 , CN , PO4
ClO4 , AcO
,
-
-
-
HSO4
250
325
400
475
550
250
325
400
475
550
Wavelength (nm)
Wavelength (nm)
Fig. 3. (A) Changes in UVevis absorption spectra of sensor 1 (1.3
CH3CN/H2O, pH¼7.6). (B) Changes in UVevis absorption spectra of sensor 1 (1.3
m
M) upon adding tetrabutyl ammonium salt of various anions (20
m
M) in TRIS buffered CH3CN/H2O (8/2, v/v,
ꢀ
mM) upon successive addition of HSO4 (0e20
mM) in TRIS buffered CH3CN/H2O (8/2, v/v, pH¼7.6).

V.K. Bhardwaj et al. / Tetrahedron 69 (2013) 1606e1610
1609
3. Conclusion
In summary, we have synthesized a sensor that simultaneously
recognizes multiple analytes using two different spectroscopic
techniques. Sensor 1 selectively showed enhanced fluorescence
intensity at 440 nm with Fe3þ. It also demonstrated selectively for
ꢀ
HSO4 by a shift in absorption maxima to 365 nm with clear iso-
sbestic points at 345 and 395 nm.
4. Experimental section
4.1. Materials and methods
Chemicals were purchased from Sigma Aldrich and used with-
out further purification. The NMR spectra were recorded on an
Avance-II (Bruker) instrument, which operated at 400 MHz for 1H
NMR and 100 MHz for 13C NMR. IR spectra were recorded on
a Perkin Elmer Spectrum One for compounds in the solid state
prepared as KBr discs. Absorption spectra were recorded on a Per-
kin Elmer Lambda 25. Fluorescence measurements were performed
on a Perkin Elmer LS55 fluorescence spectrophotometer.
Fig. 5. Optimized structure of sensor 2 (6,31G*d,p).
A
1000
900
800
700
600
500
400
300
200
100
0
4.1.1. Synthesis of compound 1. A solution of 2-(2-aminophenyl)-
benzthiazole (226 mg, 1 mmol) and 2-hydroxy-1-naphthaldehyde
(258 mg, 1.5 mmol) in dry methanol (50 mL) was heated at reflux
for 14 h. After the reaction was completed, the solvent was evap-
orated to 25 mL and kept at 5 ꢁC for slow evaporation. A brown
crystalline material was separated out. The solid was filtered and
washed with cold methanol three times and compound 1 was
obtained in 85% yield (323 mg). Mp 214e215 ꢁC; 1H NMR (400 MHz,
Fe(III) only
Fe(III) + Hydrogen sulfate
DMSO-d6)
d 14.67 (br s, 1H, OH), 9.58 (s, 1H, CH]N), 8.59
(d, J¼8.4 Hz, 1H, Ar), 8.30e8.10 (m, 3H), 7.97 (d, J¼7.2 Hz, 1H, Ar),
7.83 (t, J¼6.8 Hz, 1H, Ar), 7.70 (t, J¼8.4 Hz, 1H, Ar), 7.61e7.45 (m, 5H,
Ar), 7.38 (t, J¼7.2 Hz, 1H, Ar), 7.06 (d, J¼9.2 Hz, 1H, Ar); 13C NMR
0
5
10
15
20
25
Concentration of HSO4- and Fe(III) (µM)
(100 MHz, DMSO-d6)
d 109.7, 116.8, 118.6, 119.8, 121.4, 121.7, 122.4,
B
0.5
0.4
0.3
0.2
0.1
0
123.7, 123.9, 124.5, 124.9, 125.3, 126.0, 128.4, 129.1, 130.3, 131.6,
139.2, 146.7, 153.1, 153.7, 156.1, 164.5, 169.2; IR (KBr) 1610 cmꢀ1
;
Hydrogen sulfate only
Anal. Calcd for C24H16N2OS: C, 75.77; H, 4.24; N, 7.36. Found: C,
75.91; H, 4.31; N, 7.26.
Hydrogen sulfate + Fe(III)
4.1.2. Synthesis of compound 2. A solution of 2-(2-aminophenyl)-
benzthiazole (226 mg, 1 mmol) and salicylaldehyde (183 mg,
1.5 mmol) in dry methanol (50 mL) was heated to reflux for 16 h.
After the reaction was completed, the solvent was evaporated to
25 mL and kept at 5 ꢁC for slow evaporation. An off-white solid
material was separated out. The solid was filtered and washed
with cold methanol three times. White solid compound 2 was
obtained in 82% yield (271 mg). Mp 139e140 ꢁC; 1H NMR
0
5
10
15
20
25
Concentration of HSO4- and Fe(III) (µM)
(400 MHz, DMSO-d6)
d 11.59 (br s, 1H, OH), 8.98 (s, 1H, CH]N),
Fig. 6. (A) Fluorescence intensity of sensor 1 at 440 nm in the presence of (a) Fe3þ
8.40e8.45 (m, 1H, Ar), 8.12 (d, J¼7.6 Hz, 1H, Ar), 8.08 (d, J¼6.8 Hz,
1H, Ar), 7.99e7.97 (m, 1H, Ar), 7.62e7.65 (m, 1H, Ar), 7.60e7.35
(m, 5H, Ar), 7.05 (d, J¼7.2 Hz, 1H, Ar), 7.02 (d, J¼8.0 Hz, 1H, Ar);
ꢀ
(blue diamonds) or (b) Fe3þ with equimolar HSꢀO4 (red squares). (B) Absorbance of
ꢀ
sensor 1 at 365 nm in the presence of (a) HSO4 (blue diamonds) or (b) HSO4 with
equimolar Fe3þ (red squares).
13C NMR (100 MHz, DMSO-d6)
d 116.8, 119.5, 120.1, 120.8, 121.9,
shows the overlay plots of fluorescence intensity at 440 nm for
solutions containing sensor 1 and Fe3þ with solutions containing
sensor 1, Fe3þ, and equimolar HSO4ꢀ. Likewise, Fig. 6B shows
overlay plots of absorbance at 365 nm for solutions containing
sensor 1 and HSO4ꢀ with solutions containing sensor 1, HSO4ꢀ, and
equimolar Fe3þ. Fluorescence emission intensity at 440 nm of
sensor 1 with Fe3þ only remains approximately the same even on
122.8, 125.2, 126.4, 126.6, 128.8, 130.9, 132.2, 134.0, 136.3, 148.9,
152.0, 159.7, 162.1, 163.6; IR (KBr) 1635 cmꢀ1. Anal. Calcd for
C20H14N2OS: C, 72.70; H, 4.27; N, 8.48. Found: C, 72.46; H, 4.61;
N, 8.53.
4.1.3. Metal recognition studies of sensors 1 and 2. All recognition
studies were performed at 25ꢂ1 ꢁC. Before recording any spectrum,
the sample was shaken to ensure solution uniformity. The effect of
pH on the UVevis absorption and fluorescence spectra of sensor 1
was investigated with a solution of sensor 1 prepared in a CH3CN/
H2O (8:2, v/v, pH¼7.6) solvent system. The cation binding ability of
sensors 1 and 2 in a TRIS buffered CH3CN/H2O (8:2, v/v, pH¼7.6)
solvent system was determined by preparing standard solutions of
ꢀ
addition of equimolar amountꢀof HSO4 (Fig. 6A). Absorbance of
sensor 1 at 365 nm with HSO4 remains approximately the same
on addition of equimolar amount of Fe3þ as well (Fig. 6B). These
facts remain true over a wide range of concentration of Fe3þ and
ꢀ
HSO4ꢀ. Thus, these plots signify that Fe3þ and HSO4 do not cause
any interference in recognition of each other.

1610
V.K. Bhardwaj et al. / Tetrahedron 69 (2013) 1606e1610
sensor 1 along with fixed amounts of a particular metal nitrate salt
in TRIS buffered CH3CN/H2O (8:2, v/v, pH¼7.6). The cation recog-
nition behavior of sensors 1 and 2 was evaluated by changes in the
photophysical properties of sensors upon adding metal salt. The
fluorescence spectra of sensors 1 and 2 were recorded with exci-
tation wavelengths as shown in the respective figures. Titrations
used volumetric flasks containing standard solutions of sensors 1
and 2 along with varied amounts of a particular metal nitrate salt in
TRIS buffered CH3CN/H2O (8:2, v/v, pH¼7.6). To evaluate possible
interference due to other metal ions, the solutions were prepared to
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contain sensor 1 (1.3 m ,
M) along with a fixed concentration of Fe3þ
both with and without other background cations in TRIS buffered
CH3CN/H2O (8:2, v/v, pH¼7.6). The fluorescence intensity of each
solution was recorded.
4.1.4. Anion recognition studies of sensors 1 and 2. These studies
were performed in a manner similar to those investigating the
cation recognition properties of sensor 1. Tetrabutylammonium
salts of anions were used and detailed concentrations are men-
tioned in the manuscript text.
4.1.5. X-ray structure data. Crystals of compound 1 were grown by
slow solvent evaporation from methanol solution. X-ray data were
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(
l
¼0.71069 A). The data were corrected for Lorentz and polariza-
tion effects, and empirical absorption corrections were applied
using SADABS from Bruker. A total of 32,150 reflections were
measured. Of these, 5973 were independent and 4288 were ob-
served [I>2s(I)] for q
32ꢁ. The structure was deduced by direct
methods using SIR-9218 and refined by full-matrix least squares
refinement methods based on F2 and using SHELX-97.19 All non-
hydrogen atoms were refined anisotropically. All hydrogen atoms
were fixed geometrically with their Uiso values at 1.2 times the
values of the phenylene carbons. All calculations were performed
using the Wingx package.20 Important crystal and refinement
parameters are given in Table S1.
Acknowledgements
This work was supported by the IndiaeKorea Joint Program of
Cooperation in Science &Technology (2011-0027710) and by a CSIR
project grant (01(2417)/10 EMR-II). P.S. is thankful to UGC India for
a research fellowship.
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Supplementary data
Electroanal. Chem. 2011, 655, 164.
Additional spectroscopic data, graphs, and crystallographic
data are available as supplementary data. Crystallographic data
have been deposited with the Cambridge Crystallographic Data
Centre, deposition number CCDC 892804. Supplementary data
related to this article can be found at http://dx.doi.org/10.1016/
j.tet.2012.11.090.
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