4-Salicylideneamino-3-methyl-1,2,4-triazole-5-thione as a sensor for aniline recognition

Article abstract of DOI:10.1016/j.saa.2011.03.030

Tridentate triazole based Schiff base 4-salicylideneamino-3-methyl-1,2,4- triazole-5-thione has been found to selectively detect toxic aromatic amines such as aniline and benzene-1,4-diamine by simple titration techniques like UV-visible, fluorescence spe

Full text of DOI:10.1016/j.saa.2011.03.030

Spectrochimica Acta Part A 79 (2011) 370–375
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
4
-Salicylideneamino-3-methyl-1,2,4-triazole-5-thione as a sensor for aniline
recognition
∗
M. Saravana Kumar, R. Tamilarasan, A. Sreekanth
Department of Chemistry, National Institute of Technology – Tiruchirappalli, Tiruchirappalli 620015, Tamilnadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Tridentate triazole based Schiff base 4-salicylideneamino-3-methyl-1,2,4-triazole-5-thione has been
found to selectively detect toxic aromatic amines such as aniline and benzene-1,4-diamine by simple
titration techniques like UV–visible, fluorescence spectral studies (PL) and H NMR titrations. The Schiff
base receptor utilizes, thione sulfur, NH-thione and the phenolic hydroxyl group to form hydrogen bonded
adduct of aniline and benzene-1,4-diamine with high binding affinity, followed by a slow removal of the
corresponding hydrogens thus providing a promising candidate and an unique receptor for toxic aromatic
amines.
Received 2 December 2010
Received in revised form 2 March 2011
Accepted 11 March 2011
1
Keywords:
Schiff base
Sensor
Aniline
©
2011 Elsevier B.V. All rights reserved.
Benzene-1,4-diamine
UV–visible spectroscopy
1
H NMR titration
Photoluminescence
1
. Introduction
to be an efficient receptor for binding aniline with high affinity
6]. It is observed that the host–guest complex formed between
[
Most of the aromatic amines are found to be toxic in humans
the 2,6-Bis(2-benzimidazolyl)pyridine and aniline is very stable,
where 2,6-Bis(2-benzimidazolyl)pyridine utilizes not only its cav-
ity but also the imine nitrogen located on the outer core to form
a stable complex. Encouraged by this, we investigated the sensing
behavior of 4-salicylideneamino-3-methyl-1,2,4-triazole-5-thione
[7] against aniline and benzene-1,4-diamine. There are only few
reports on aniline sensors and Schiff base functioning as aniline
receptor has not been found anywhere in the literature.
leading to bladder cancer when inhaled [1]. Aniline is one of the
most toxic among the aromatic amine family, but has a wide spread
application as a precursor to more complex chemicals. The toxic-
ity of aniline and similar types of compounds on humans is well
documented [2,3], with an oral lethal dose being 50–500 mg/kg for
a grown man. The primary toxicity of aniline is characterized by
methemoglobinemia; the increased production of methemoglobin
can cause interference with the oxygen-carrying capacity of the
blood. Despite its structural simplicity, the metabolism of aniline
is complex and hence it is important to find out a good receptor to
sense the aniline.
2. Experimental
2.1. Materials and methods
Only few synthetic receptors have been developed in the recent
past due to the challenge in binding of the guest molecule (ani-
line) with the synthetic receptors developed. Such systems are
generally composed of anion binding sites and the chromogenic
moieties. When anions interact with the sensor via electrostatic,
hydrogen bonding, coordination to a metal center, hydrophobic
interaction, or a combination of any two or more of these inter-
actions, the sensor can output binding information either by its
altered behavior in fluorescence or in absorption spectra [4,5]. Li
et al., have used 2,6-Bis(2-benzimidazolyl)pyridine and showed it
Thiocarbohydrazide, glacial acetic acid, salicylaldehyde, ani-
line (G1) and benzene-1,4-diamine (G2) were purchased from
Aldrich Chemicals and were used without further purification. 4-
Salicylideneamino-3-methyl-1,2,4-triazole-5-thione and 4-amino-
-methyl-1,2,4-triazole-5-thione was synthesized according to
the literature methods [7,8]. Acetonitrile was purified using
the standard procedure. Titration of the receptor molecule
3
4
-salicylideneamino-3-methyl-1,2,4-triazole-5-thione (receptor)
with the guest molecules was performed cautiously by careful addi-
tions of G1 aliquots in to the acetonitrile solution of the receptor.
The ratios of receptor/G1 and receptor/G2 are given as follows, A:
−
5
−5
∗ Corresponding author. Tel.: +91 431 2503642; fax: +91 431 2500133.
E-mail addresses: sreekanth@nitt.edu, sreekanth a@yahoo.com (A. Sreekanth).
pure receptor (1 × 10
mol/L); B: 1:0.2 (1 × 10
mol/L:0.2 ×
−
5
−5
−5
10 mol/L); C: 1:0.4 (1 × 10 mol/L:0.4 × 10 mol/L); D: 1:0.6
1
386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.03.030

M.S. Kumar et al. / Spectrochimica Acta Part A 79 (2011) 370–375
−5
371
−
5
−5
(
1
1 × 10 mol/L:0.6 × 10 mol/L); E: 1:0.8 (1 × 10 mol/L:0.8 ×
−
5
−5
−5
0
mol/L); F: 1:1 (1 × 10 mol/L:1 × 10 mol/L); G: 1:1.2 (1
−
5
−5
−5
×
10 mol/L:1.2 × 10 mol/L); H: 1:1.4 (1 × 10 mol/L:1.4 ×
−
5
−5
−5
1
0
mol/L); I: 1:1.6 (1 × 10 mol/L:1.6 × 10 mol/L); J: 1:1.8 (1
−5
−5
−5
−5
×
10 mol/L:1.8 × 10 mol/L); K: 1:2 (1 × 10 mol/L:2 × 10
−5
−5
mol/L); L: 1:2.2 (1 × 10 mol/L:2.2 × 10 mol/L); M: 1:2.4 (1
−5
−5
−5
−5
×
10 mol/L:2.4 × 10 mol/L);N: 1:4 (1 × 10 mol/L:4 × 10
−5
−5
mol/L); O: 1:10 (1 × 10 mol/L:10 × 10 mol/L); P: 1:20 (1 ×
−
5
−5
−5
−5
1
0
mol/L:20 × 10 mol/L); Q: 1:30 (1 × 10 mol/L:30 × 10
−5
−5
mol/L); R: 1:40 (1 × 10 mol/L:40 × 10 mol/L); and S: 1:50 (1 ×
−
5
−5
1
0
mol/L:50 × 10 mol/L). A quartz cell (1 cm width) was used
to record their corresponding UV–visible and fluorescence spectra
at 298 K.
Fig. 1. Structural formulae of the receptor and guests (G1 and G2).
ference Fourier map and refined isotropically with displacement
coefficients U(H) = 1.2 U(C) or 1.5 U(Cmethyl). However the crystal
structure and related data is reported else were [7], the structural
refinement parameters were also found to be the same to that of
the reported data.
2
4
.2. Synthesis of
-salicylideneamino-3-methyl-1,2,4-triazole-5-thione (receptor)
4
-Amino-3-methyl-1,2,4-triazole-5-thione (1 g, 0.0072 mol)
and salicylaldehyde (0.88 g, 0.0072 mol) were dissolved in
methanol and the resulting solution was gently refluxed for 2 h
with constant stirring. The precipitate obtained was filtered out
and kept for crystallization dissolving in methanol and chloroform
mixture. Fine colorless single crystals obtained upon slow evapo-
ration at room temperature in 5 days were used for single X-ray
diffraction. Experimental results of elemental analysis. Calc. for
2.5. NMR titrations
1
All the H NMR titrations were carried out at room temperature
and the spectra were recorded on a Bruker Avance III, 400 MHz in
DMSO-d6 at 298 K with TMS as an internal standard. The recep-
−
4
tor prepared as 1 × 10 M solutions (DMSO-d ) and was titrated
6
C10H10N OS: C, 51.27; H, 4.30; N, 23.91; O, 6.83; S, 13.69. Found:
C, 51.05; H, 4.10; N, 23.75; O, 6.51; S, 13.53%. NMR data H NMR
4
1
against the guest molecules by increasing its equivalents by 0.25
each time.
(
ı, ppm DMSO-d , 400 MHz): 13.69 (br, s, –NH, 1H), 10.43 (s, –OH,
6
1
H), 10.14 (s, CH N, 1H), 6.97–7.89 (m, Ar, 4H), 2.35 (s, C–CH , 3H).
3
13
3. Results and discussion
C NMR (DMSO-d , 100 MHz): 165.7, 162.7, 159.7, 148.4, 134.7,
6
−
1
1
3
33.6, 120.2, 117.5, 116.08, 11.1. IR data (KBr disc, cm ): 3433,
105, 1603, 1590, 1298, 1264. UV–visible: [acetonitrile, ꢀmax cm
−
1
4 -Salicylideneamino-3-methyl-1,2,4-triazole - 5 - thione was
synthesized by the condensation of the salicylaldehyde with
triazole amine. Fig. 1 shows the chemical structure of the receptor
along with guest molecules G1 and G2. Experimental results of
elemental analysis are in good agreement with the calculated data.
−1 −1
(
ε M cm )]: 46,940 (97,800), 39,060 (34,000), 30,300 (12,000).
2.3. Physical measurements
−
1
IR spectrum of the receptor showed a weak band at 3433 cm
corresponding to ꢁ(NH) of the triazole ring system and a stretching
All experiments were carried out at room temperature, unless
otherwise mentioned. 1H NMR and
recorded on a Bruker Avance III 400 MHz in DMSO-d6 at 298 K
with TMS as an internal standard. D O exchange was performed
13
C NMR (100 MHz) were
−
1
band around 3105 cm
was assigned to ꢁ(OH), various bands
−
1
in the same region of 3067m, 2936s, 2759s cm
indicated that
2
extensive hydrogen bonding interactions, may be present. It is later
discussed that both these groups –NH and –OH plays a vital role
in binding to the incoming guest molecule. Very sharp stretching
by adding 1 drop of D O to the NMR tube containing the com-
2
pound in DMSO-d . UV–visible spectra were measured using an
6
ultraviolet spectrometer, PG-90+ (PG Instruments UK). Photolumi-
nescence data (PL hereafter) were recorded in a JASCO FP – 6200
spectrofluorometer. FT-IR spectra were recorded in PerkinElmer-
BX instrument. Both the UV–visible and fluorescence spectra are
recorded using a 1 cm path length quartz cell. High Performance
Liquid Chromatography (HPLC) of the receptor were recorded in
−
1
band at 1603 cm corresponding to ꢁ(C N), is observed which is
very typical for azomethine groups and indicates the formation of
−
1
the C N after the reaction. A second stretch at 1590 cm indicates
the ꢁ(C N) in the triazole ring, other characteristic frequencies
−
1
corresponding to 1505m, 1488m, 1412s, 1346m cm are assigned
TM
to be those arising from the triazole moiety. The ꢁ(C S) stretching
SHIMADZU CLASS VP -SPD-M20A with the mobile phase ace-
−
1
absorption appears at 1298 cm and ꢁ(C–N) thioamide appears
tonitrile:water mixture system (50:50), and the column used for
recording the chromatogram was Luna 5 ␮ C18(2) 100A. All mea-
surements were carried out in the air at room temperature without
being specified.
−
1
at 1264 cm . IR spectrum of the receptor gives an insight to the
molecular functionality in general.
3.1. NMR spectra
2.4. X-ray crystallography
1H NMR spectrum of the compound have two sharp singlets
A colorless monoclinic block crystal having approximate dimen-
in the region around ı ∼ 10.1–10.4 ppm both accounting for single
proton each, which accounts for the CH N, phenolic –OH group as
evident from a previous report [7] however they have not reported
the NH proton, appearing as relatively broad singlet at ı 13.69 ppm
as is evident that there are some quadrupole interaction from nitro-
gen. However, the proton is sufficiently labile and hence much
deshielded. This is to be understood on the basis of extensive
hydrogen bonding in the system. Both 10.43 and 13.69 peaks dis-
sions 0.35 mm × 0.30 mm × 0.25 mm was sealed in a glass capillary,
and intensity data were measured at room temperature (296 K)
on a Bruker Kappa APEXII diffractometer equipped with graphite-
monochromated Mo K␣ (ꢀ = 0.71073 A˚ ) radiation. All structures
were solved by direct methods and refined by fullmatrix least-
squares calculations with the SHELXTL-PLUS software package
9]. Absorption corrections were employed using SADABS (Tmax
.9319 and Tmin 0.9065). The non-hydrogen atoms were refined
anisotropically and all hydrogen atoms were found from the dif-
[
0
appear on addition of D O confirming the functional groups. The
2
assignment is also based on the hydrogen bonding interactions as

3
72
M.S. Kumar et al. / Spectrochimica Acta Part A 79 (2011) 370–375
Table 1
Hydrogen bonding interactions.
◦
D–H. . .A
H. . .A (Å)
D. . .A (Å)
∠D–H. . .A ( )
Intra O(1)–H(1O). . .N(1)
N(3)–H(3 N). . .S(1)a
1.98
2.46
2.49
2.83
2.6778
3.2650
3.1936
3.7899
149
175
135
173
Intra C(7)–H(7). . .S(1)
C(10)–H(10A). . .S(1)b
a
−
x, −y, −z.
b
1
/2 + x, 1/2 − y, 1/2 + z.
seen in the crystal data (Table 1) which clearly shows an intra-
molecular hydrogen bonding for OH group, whereas –NH proton
1
13
has an intermolecular hydrogen bonding. The H NMR and C NMR
assignments are shown in Fig. 2.
Fig. 3. PLATON plot showing intra and intermolecular hydrogen bonding in the
compound.
3.2. Molecular and crystal structure of the receptor
Single crystal X-ray crystallography was carried out to confirm
lar hydrogen bonding with N1. There are previous reports of crystal
structures of receptor and guest together [10,11] but our attempts
to grow similar crystals failed.
the structure of the molecule, since Schiff bases has a tendency
to get hydrolyzed easily in solvents like methanol as well as very
sensitive to pH. The molecular structure of the receptor has been
reported earlier [7] were it crystallizes in to a monoclinic lattice
3.3. High performance liquid chromatography of the receptor
with a space group of P2 /n. The bond lengths and angles are
1
unchangedhowever thecompound existsas amonomerinourcase.
The previous report suggesting the molecule as centrosymmetric
dimer structure of the molecule may be due to the extensive hydro-
gen bonding both inter as well as intra as seen in Fig. 3. The details
of which are appended in Table 1. Since this type of aniline sensors
is reportedly bind to the guest molecule via tridentate donor atoms
through inter molecular hydrogen bonding interactions [6,10,11],
we also suggest a similar type of mechanism operational in the
solution of the compounds. It is clear from the NMR data as well
as the titration data that the removal of NH proton is very easy,
while still phenolic OH is difficult to remove with the addition of
the guest to the receptor. Even though eventually phenolic OH dis-
appears, the time taken for this change is not the same as to that of
the NH removal which is instantaneous. The reason can be clearly
seen from Fig. 3 as, the phenolic OH is engaged in an intramolecu-
Synthesized receptor 4-salicylideneamino-3-methyl-1,2,4-
triazole-5-thione purity was confirmed using a HPLC, recorded
with a mobile phase of acetonitrile:water system mixture (50:50),
and the column used for recording the chromatogram was Luna 5 ␮
C18(2) 100A. Fig. 4 shows the HPLC chromatogram of the receptor
molecule, which shows a single peak with an area percentage of
1
00, at a retention time 6.912 min, thus determining the purity of
the receptor molecule used as a sensor. Purity of the receptor in
HPLC hence provides the evidence that there is no other impurity
in the system to interact with the incoming guest molecules.
3
.4. UV–visible titration
The UV–visible spectrum of the receptor was recorded in ace-
tonitirile showed significant absorptions at ca. 250 nm, 280 nm and
30 nm. In the case of thiosemicarbazone type systems these bands
3
*
*
are assigned due to the n → ␲ and ␲ → ␲ transitions arising from
thiocarbonyl group and azomethine group. However a clear dis-
tinction of them is often not possible. In the case of coordination
normally there will be a bathochromic shift, along with a hyper-
chromic shift due to charge transfer transitions [12,13]. The change
in optoelectronic properties with the addition of the guest was
studied using the UV–visible spectral titrations. Fig. 5(A) demon-
strates the absorption spectra upon the addition of G1 in to the
acetonitrile solutions of the receptor. It can be seen in Fig. 5(A) and
(B) that on increasing the concentration of G1 from 0 equivalents
to higher concentration, a decrease of absorption around 330 nm
occurs. Concurrently, a new absorption band around 275 nm with
a higher intensity shows up. This new absorption band is due to
the potential formation of a stable complex between the Schiff
base receptor and the G1 [6,10,11]. Also we observed a formation
of Isosbestic point at ∼290 nm, indicating the presence of at least
one species at equilibrium as indicated by Li and co-workers [6].
Upon higher G1 concentrations, the absorption spectra also exhibit
characters of G1’s absorption spectrum. The absorption at 330 nm
becomes constant with the increasing concentration of G1. The
absorption edge of G1 ends at 310 nm, the absorption peak around
3
30 nm is mainly dominated by the complex formed between the
receptor and the G1 and also by the absorption due to the receptor.
Throughout the spectral titration, the amount of free receptor tends
to decrease as the formation of the complex between the receptor
and G1 increases, until the complex achieves a balance state. Once
Fig. 2. 1H NMR (top) and 13C NMR (bottom) assignments for the receptor.

M.S. Kumar et al. / Spectrochimica Acta Part A 79 (2011) 370–375
373
Fig. 4. HPLC of the receptor.
after reaching the balance state the absorption at 330 nm becomes
3.5. Fluorescence spectral studies
constant invariably of any further increase in the concentration of
the G1.
Fig. 7(A) shows the PL spectra upon the addition of the G1 in
to the acetonitrile solution of the receptor. It can be seen from the
spectra that the increase in the concentration of G1, the emission
spectra of the receptor/G1 system increases without any quenching
of the luminescence. As for the receptor/G1 system a new emission
peak at 330 nm is perhaps due to the formation of receptor/G1 com-
plex. Interestingly we also observed a spectral bathochromic shift
from 315 nm to 330 nm confirming the stable receptor/G1 com-
plex formed. Emission intensity increases as the concentration of
G1 increases in the system.
In the case of benzene-1,4-diamine (G2), we were unable to
account the spectral evidence for the formation of stable complex
between the receptor NH-thione and phenolic –OH groups with
the G2 molecule unfortunately due to the strong absorption of G2
at ∼324 nm which is quite close to the absorption maximum of the
receptor, Fig. 6.
−
Even though Schiff bases are known to sense F anions, the
present receptor does not sense any of the halides, neither visible
change nor spectral changes. The experiments repeated in DMF and
DMSO did not show any significant change in the spectral features
indicating that even in competing solvents the receptor functioning
is much better.
Fig. 7(B) shows the PL spectra of receptor/G2 system. receptor
shows an emission peak at 310 nm. Increasing the concentration
of the G2, the emission spectra shows a clear bathochromic shift
Fig. 5. (A) UV–visible spectra of receptor/G1 system recorded in acetonitrile. (B) A
magnified view of absorption spectrum of receptor/G1 system recorded in acetoni-
trile.
Fig. 6. (A) UV–visible spectra of receptor/G2 system recorded in acetonitrile. (B) A
magnified view of absorption spectrum of receptor/G2 system.

3
74
M.S. Kumar et al. / Spectrochimica Acta Part A 79 (2011) 370–375
Scheme 1. Tentative coordination behavior of receptor towards G1.
3
.6. 1H NMR titration
UV–visible and PL spectra show that the titration of receptor
with both the G1 and G2 form a new species which is lead-
ing to a new absorption band in UV–visible spectra and a clear
bathochromic shift in PL spectral studies. To further look in to
the nature of the receptor and guest molecule interactions and
to understand the sensing behavior of the receptor towards the
guest molecules 1H NMR titration was conducted in DMSO-d . In
6
the benzene-1,4-diamine case (G2), the new species formation was
overshadowed by the strong absorption of G2 around 324 nm, thus
no conclusion could be arrived from its absorption spectral data,
but the formation of new species in the G2 with the receptor was
evident from its bathochromic shift in the PL spectra.
Fig. 7. (A) PL spectra of receptor and G1 system recorded in acetonitrile, excited at
wavelength 275 nm, (B) PL spectra of receptor and G2 system recorded in acetoni-
trile, excited at wavelength 330 nm.
1
H NMR titration of the receptor with aniline (G1) is shown in
Fig. 8. Upon addition of 0.25 equiv of G1, the peaks at ı 13.69 ppm
and ı 10.43 ppm, which were assigned to NH-thione of triazole moi-
ety and phenolic –OH, respectively, were shifted slightly downfield
and the intensity of both the peaks starts to decrease. This indicated
the formation of a hydrogen bonding between the receptor and G1.
With further addition of G1, the signal corresponding to –NH were
disappeared and the signal of –OH too disappeared, but in very slow
from 315 nm to 335 nm, it is thus confirmed that the PL spectral
bathochromic shift are caused by the stable adduct between the
receptor and the G2. Thus providing a strong evidence of the com-
plex formed, which is overshadowed in the UV–visible absorption
spectra for the same receptor/G2 system.
Fig. 8. 1H NMR (400 MHz) spectra of receptor (1 × 10−4 M solutions in DMSO-d6).
Bottom one receptor only; (A) receptor + 0.25 equiv. of G1; (B) receptor + 0.5 equiv.
of G1; (C) receptor + 0.75 equiv. of G1; (D) receptor + 1 equiv. of G1.
Fig. 9. 1H NMR (400 MHz) spectra of receptor (1 × 10 M solutions in DMSO-d6).
Bottom one receptor only; (A) receptor + 0.25 equiv. of G2; (B) receptor + 0.5 equiv.
of G2; (C) receptor + 1 equiv. of G2.
−4

M.S. Kumar et al. / Spectrochimica Acta Part A 79 (2011) 370–375
375
rate compared to the –NH signal. Binding mode of receptor and G1
is found to be in the ratio of 1:2 from the 1H NMR titration results.
Concluding from this the tentative binding mode of the receptor
could be visualized as seen in Scheme 1.
obtained free of charge from The Director, CCDC, 12 Union
Road, Cambridge, CB2 IEZ, UK (fax: +44 1223 336 033; e-mail:
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
1
H NMR titration of the receptor with benzene-1,4-diamine (G2)
Acknowledgements
is shown in Fig. 9. In the case of G2, we found quiet interesting
results with the addition of G2 to the NMR tube containing the
receptor. Addition of the initial 0.25 equiv. of the G2, we found that
the peak intensity of –NH and –OH disappeared drastically. Upon
further addition of 0.25 equiv. of G2 to the receptor, resulting into a
total of 0.5 equiv. the peaks corresponding to –NH and –OH disap-
peared completely, which clearly shows the new species formation
between the receptor and the G2. Further addition of G2 has no
change in the NMR spectrum. Binding mode of receptor and G2 is
found to be in the ratio of 2:1 from the 1H NMR titration results.
AS acknowledges CSIR for a research grant (CSIR Sanction No.
01(2304)/09/EMR-II Dated 17.03.2009). AS is thankful to Dr. S.
Abraham John, Associate Professor; Gandhigram Rural Univer-
sity, Tamilnadu, India for PL measurements and to Dr. Rohith
P. John, Associate Professor, Department of Applied Chemistry,
Indian School of Mines for XRD discussions. The authors are
also thankful to SAIF-STIC at Cochin University of Science and
Technology, Cochin 682 022, India for NMR as well as single
crystal X-ray data.
4
. Conclusion
References
[
1] E. Ward, A. Carpenter, S. Markowitz, D. Roberts, W. Halperin, J. Natl. Cancer Inst.
3 (1991) 501–506.
2] T.W. Schultz, T.C. Allison, Bull. Environ. Contam. Toxicol. 23 (1979) 814–819.
The tridentate triazole based Schiff base 4-salicylideneamino-
-methyl-1,2,4-triazole-5-thione has a highly optical sensitivity
8
3
[
towards aniline and benzene-1,4-diamine. Crystal structure of the
receptor as well as the NMR titrations also indicates that the bind-
ing to aniline and benzene-1,4-diamine might be due to extensive
hydrogen bonding interaction. The sensing is even possible in com-
petitive solvents like DMSO and DMF indicating that the present
Schiff base is a promising sensor for aniline.
[3] M.F. Khan, B.S. Kaphalia, P.J. Boor, G.A. Ansari, Arch. Environ. Contam. Toxicol.
4 (1993) 368–374.
4] W.T. Gong, S. Bao, F. Wang, J.W. Ye, G.L. Ning, K. Hiratani, Tetrahedron Lett. 52
2011) 630–634.
[5] Q. Zou, J. Jin, B. Xu, L. Ding, H. Tian, Tetrahedron 67 (2011) 915–921.
[6] L. Zhang, B. Li, Spectrochim. Acta. A 74 (2009) 1060–1063.
2
[
(
[
7] F. Heshmatpour, M. Ghassemzadeh, M. Semsarha, B. Neumuller, Z. Anorg, Allg.
Chem. 633 (2007) 465–469.
[
8] F. Kurzer, M. Wikinson, Chem. Rev. 70 (1990) 111–149.
Supplementary information
[9] G.M. Sheldrick, T.R. Schneider, Methods Enzymol. 277 (1997) 319–343.
10] B. Chetia, P.K. Iyer, Tetrahedron Lett. 47 (2008) 8115–8117.
11] B. Chetia, P.K. Iyer, Tetrahedron Lett. 48 (2007) 47–50.
12] A. Sreekanth, M.R.P. Kurup, Polyhedron 23 (2004) 969–978.
[13] P.B. Sreeja, A. Sreekanth, C.R. Nayar, M.R.P. Kurup, A. Usman, I.A. Razak, S.
Chantrapromma, H.K. Fun, J. Mol. Struct. 645 (2003) 221–226.
[
[
[
Crystallographic data for the structural analysis has been
deposited with the Cambridge Crystallographic Data Center, CCDC
8
02088 for the receptor. Copies of this information may be