Oxidative cyclization of thiosemicarbazone: An optical and turn-on fluorescent chemodosimeter for Cu(ii)

Article abstract of DOI:10.1039/c0dt01549k

A weakly fluorescent thiosemicabazone (L₁H) was found to be a selective optical and "turn-on" fluorescent chemodosimeter for Cu ²⁺ ion in aqueous medium. A significant fluorescence enhancement along with change in color was only observed for Cu²⁺ ion; among the other tested metal ions (viz. Na⁺, K⁺, Mg²⁺, Ca²⁺, Cr³⁺, Zn²⁺, Cd²⁺, Hg ²⁺, Pb²⁺, Ag⁺, Ni²⁺, Co ²⁺, Fe³⁺ and Mn²⁺). The Cu²⁺ selectivity resulted from an oxidative cyclization of the weak fluorescent L₁H into highly fluorescent rigid 4,5-dihydro-5,5-dimethyl-4- (naphthalen-5-yl)-1,2,4-triazole-3-thione (L₂). The signaling mechanism has been confirmed by independent synthesis with detail characterization of L₂. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c0dt01549k

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PAPER
Oxidative cyclization of thiosemicarbazone: an optical and turn-on fluorescent
chemodosimeter for Cu(II)†
Arghya Basu and Gopal Das*
Received 7th November 2010, Accepted 12th January 2011
DOI: 10.1039/c0dt01549k
A weakly fluorescent thiosemicabazone (L
fluorescent chemodosimeter for Cu ion in aqueous medium. A significant fluorescence enhancement
1
H) was found to be a selective optical and “turn-on”
2
+
2
+
+
along with change in color was only observed for Cu ion; among the other tested metal ions (viz. Na ,
+
2+
2+
3+
2+
2+
2+
2+
+
2+
2+
3+
2+
2+
K , Mg , Ca , Cr , Zn , Cd , Hg , Pb , Ag , Ni , Co , Fe and Mn ). The Cu selectivity
resulted from an oxidative cyclization of the weak fluorescent L H into highly fluorescent rigid
,5-dihydro-5,5-dimethyl-4-(naphthalen-5-yl)-1,2,4-triazole-3-thione (L ). The signaling mechanism has
been confirmed by independent synthesis with detail characterization of L
1
4
2
2
.
Introduction
Recently, there has been immense interest in chemodosimeter-
based chemical sensing through a specific irreversible chemical
reaction between dosimetric molecules and the target species,
Thiosemicarbazones are a class of compounds very promising
in the treatment of many diseases, cancer in particular, and their
development is still in progress. In addition, they continue to draw
attention not only as multifunctional ligands, but also because
they can undergo ring closure processes by the action of bases,
acids or oxidants. Although these cyclizations are well described
in the literature, especially those involving Cu or Fe cations,
their mechanism is still not clearly resolved.
10
leading to a fluorescent/color change in the receptor. It should be
1
2+
pointed out that there have been several nice Cu chemodosime-
2
ters with enhanced fluorescence signal outputs, which however
11
12
follow hydrolysis or rearrangement reactions. Moreover, re-
ports on the single-crystal X-ray crystallographic characterization
3
2
+
3+
13
of chemodosimetric sensing are very rare.
4
Herein we report our successful development of a chemod-
The development of sensitive and selective fluorescent
chemosensors for biologically important metal ions is of intense
current interest because these metal ions play important roles
2+
osimetric fluorescent chemosensor selective for Cu . Detailed
experiments allowed us to ascertain that the enhanced fluorescence
2+
was due to an oxidative cyclization by Cu of the comparatively
5
in living and environmental systems. The third most abundant
less fluorescent thiosemicarbazone ligand (L
orescent rigid 4,5-dihydro-5,5-dimethyl-4-(napthalen-5-yl)-1,2,4-
triazole-3-thione (L ). The ligand L H therefore shown to be a
1
H) into highly flu-
2
+
2+
2+
(
after Fe and Zn ) transition metal ion Cu is an essential
trace element present in the human body and plays a vital role
in a variety of fundamental physiological processes in organisms
ranging from bacteria to mammals but can often be toxic to
certain biological systems when the levels of Cu exceed cellular
needs. It is also associated with neurodegenerative diseases such
as Alzheimer’s and Parkinson’s and is also suspected to cause
2
1
kind of redox based “turn-on” fluorescent chemodosimeter for
2+
Cu .
2
+
Results and discussion
6
amyloidal precipitation and toxicity. For most of the reported
fluorescent sensors of Cu , binding of the metal ion causes a
The synthesized thiosemicarbazone ligand L H (Scheme 1) shows
1
2
+
2
+
remarkable selectivity towards Cu by both UV-Vis and fluores-
cence spectroscopic methods. A beautiful yellowish orange color
is formed with dramatic enhancement of fluorescence intensity
7
quenching of the fluorescence emission due to its paramagnetic
8
2+
nature. Only a few sensors in which the binding of Cu ion causes
9
an increase in the fluorescence intensity have been reported.
2
+
when equivalent amount of Cu ions was added to the colorless
aqueous ethanolic solution of L H, whereas other tested metal
1
ions produce insignificant or minor changes.
Department of Chemistry, Indian Institute of Technology Guwahati, Guwa-
hati, 781039, Assam, India. E-mail: gdas@iitg.ernet.in; Fax: +91 0361
2
582349; Tel: +91 361 258231
Photophysical studies
†
Electronic supplementary information (ESI) available: Crystallographic
1
13
CIF, H and C NMR, UV-visible spectra, FT-IR, X-ray tables,
and figures. CCDC reference numbers 777755–777758. For ESI and
crystallographic data in CIF or other electronic format see DOI:
The photophysical properties of the ligand L H with several
1
+
+
2+
2+
2+
3+
2+
2+
2+
metal cations (Na , K , Mg , Ca , Cu , Cr , Zn , Cd , Hg ,
2
+
+
2+
2+
3+
2+
1
0.1039/c0dt01549k
Pb , Ag , Ni , Co , Fe and Mn ) using their perchlorate
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1 1
Scheme 1 Synthesis of ligand L H and molecular structure of L H with
thermal ellipsoids set to the 50% probability level.
or chloride salts in H O–EtOH (90 : 10, v/v) are investigated
2
by UV-Vis and fluorescence measurements and titration studies
that are conducted at pH 7.2 (buffered by 10 mM Tris-HCl).
2
+
However perchlorate salt of Cu has been used through out all
photophysical studies.
-6
Fig. 1 (a) UV-Vis spectra of 5 ¥ 10 M solutions of L
1
H with 30 equiv. of
UV-Vis absorption studies
various metal ions in water–ethanol (90 : 10). (b) UV-Vis titration spectra
2+
of L
1
H upon addition of Cu ion in water–ethanol (90 : 10). Inset shows
-
5
The absorption spectrum of the ligand L
in H O–EtOH (90 : 10, v/v) exhibits lmax at 267 nm with molar
absorption coefficient 1.93 ¥ 10 M cm indicative of the (p–p*)
1
H (c = 1.33 ¥ 10 M)
2+
quotient of absorbance at 328 and at 267 nm as a function of Cu
concentration. Aqueous solutions are buffered by 10 mM Tris-HCl at
pH 7.2.
2
4
-1
-1
14
2+
transition character. However during titration with Cu (c = 5 ¥
-
4
10
M) ions the absorption intensity decreases at 267 nm with
increasing intensity concomitantly at 328 nm and 242 nm. Two
isosbestic points were observed at 288 nm and 251 nm (Fig. 1b)
which indicates the formation of new species by the influence
2
+
2+
selectivity for Cu therefore could not be simply attributed to Cu
coordination to L H.
1
2
+
Cu ion over L
1
H. The red shift in absorption spectra could be
applied to detect the sensing process by the naked eye. A beautiful
Rationalization of photophysical studies
2
+
yellowish orange color is formed when equivalent amount of Cu
ions was added to the colorless aqueous ethanolic solution of
The fluorescence emission of a ligand can be not only affected
by metal ion coordination, but by a metal ion mediated reaction
+
+
L H (Fig. 3b). The addition of other metal ions such as Na , K ,
1
2
+
2+
3+
2+
2+
2+
2+
+
2+
2+
3+
Mg , Ca , Cr , Zn , Cd , Hg , Pb , Ag , Ni , Co , Fe
15
as well. It was well reported that thiosemicarbazone undergoes
2
+
and Mn produces insignificant or minor changes in absorption
spectra (Fig. 1a).
3
oxidative cyclization by several oxidants. Thus we assume that the
unexpected spectral change (both by UV-Vis and fluorescence)
2
+
and the high selectivity for Cu therefore could not be simply
2
+
attributed to Cu coordination to L
1
H; therefore it is probably
H. The most decisive
Fluorescence studies
due to the oxidative cyclization of L
1
Fluorescence emission spectra at RT of the receptor L
1
H (c = 1.33 ¥
O–EtOH (90 : 10, v/v) are recorded upon excitation
at 270 nm to understand the nature of interactions in the excited
evidence supporting this assumption was obtained from the in-
dependent synthesis of 4,5-dihydro-5,5-dimethyl-4-(napthalen-5-
-
5
10
M) in H
2
yl)-1,2,4-triazole-3-thione (L
2
; Fig. 3a). The oxidative cyclization
2
+
1
13
state. In the presence of Cu however, an instant response was
observed by a dramatic enhancement of up to 10-fold, despite
product L was fully characterized by ESIMS, H NMR,
2
C
NMR and single-crystal X-ray crystallographic characterization.
Fluorescence emission and UV-Vis spectra of the synthesized
2
+
the well known quenching character of Cu . A sharp increase
in the fluorescence intensity with a red-shifted emission maxima
at 363 nm to 390 nm is observed reaching its limit value after
oxidative cyclization product L
2
was found almost identical to L
1
H
2
+
in the presence of 1.0 equivalent of Cu . Interestingly, the UV-Vis
2
+
2+
adding ~15 mM Cu . This is probably due to instant formation
highly fluorescent rigid cyclic product L . Thus the ligand L H
titration of L
328 nm which is almost identical to absorption spectrum of pure
situated at the same wavelength under the same experimental
conditions (ESI, Fig. S18†). Hence, it is quite logical to believe
1
H with Cu results in a new band arises centered at
2
1
2
+
behaves as an “off -on” type of fluorescence probe towards Cu .
Whereas other metal ions did not induce any discernible spectral
changes (Fig. 2a). The unexpected spectral change and the high
L
2
2
+
that Cu induced formation of the new band at 328 nm in the
2
838 | Dalton Trans., 2011, 40, 2837–2843
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continuously decreases with increasing L
1
H concentration (Fig. 4).
It was therefore suggested that conversion of paramagnetic
2
+
+
Cu into diamagnetic Cu which is stabilized through CH
coordination.
3
CN
2+
1
Fig. 4 EPR spectrum Cu with increasing concentration of L H (taken
at RT, 298 K).
In addition to the EPR study we have also confirmed the
2
+
+
reduction process of Cu to Cu during cyclization by UV-
16
Fig. 2 (a) Fluorescence spectra (lex = 270 nm) of L
measured in water–ethanol (90 : 10) respective metal cations (30 equiv.).
1
H (13 mM)
Vis spectroscopic analysis in CH CN. Similar to EPR study
3
2+
here also Cu concentration maintained constant while the
-
5
(
1
b) Fluorescence spectra of L H (c = 1.33 ¥ 10 M) in the absence and
L H concentration varied. It was found that the absorbance of
1
2+
presence of Cu in water–ethanol (90 : 10). Aqueous solutions are buffered
by 10 mM Tris-HCl at pH 7.2.
2+
the d-d transition band of Cu situated at 760 nm decreases
with increasing concentration of L H thus it was suggested the
1
2
+
9
+
10
conversion of Cu (d ) to Cu (d ) where d-d transition is not
possible (ESI, Fig. S15†). Thus a plausible mechanism of the
2
+
oxidative cyclization by Cu was therefore suggested (Scheme 2).
Hence, both the experiments convincingly ascertain that the
2
+
selective Cu sensing is due to oxidative cyclization of L H.
1
Fig. 3 (a) Synthesis of cyclic product L
2
. (b) Digital photographs of L
1
H
-3
-3
2+
(
~10 M) and L
1
H (~10 M) in presence of equivalent amount of Cu
under normal light (left) and under UV irradiation (right).
2
+
UV-Vis spectra of L H is not due to Cu coordination; therefore
1
2
it is due to the formation of cyclized product L .
EPR study
2
+
To assure the role of Cu during cyclization reaction EPR
2+
1
Scheme 2 Proposed oxidative cyclization mechanism of L H by Cu .
2
+
experiment in CH
3
CN at RT was carried out in which the Cu
H concentration
2
+
2+
concentration was kept constant while the L
1
The formation of stable metal complexes with Zn and Ni
with no significant spectral changes also supports our assumption
16
2+
varied. It was found that the intensity of EPR signal of Cu was
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2
+
that the Cu selective spectral changes of L
1
H are not due to
simple metal ligand coordination therefore, due to the formation
of rigid cyclic product L .
2
Crystal structure
The structure of L
ray diffraction of single crystals. Crystals of L
slow-driven crystallization from dilute solution of ethanol. L
1
H has been established unambiguously by X-
1
H were obtained by
1
H
¯
crystallized in the space group P1. The structure determination of
H shows (Fig. 5) that in the solid state the thiosemicarbazone
exists in the thione form, supported by the presence of hydrazinic
L
1
˚
Fig. 6 Molecular structure of L with thermal ellipsoids set to the 50%
hydrogens and a C–S distance of 1.674(3) A, which is much
2
shorter than a single C–S bond. The sulfur atom S(1) and the
hydrazone nitrogen N(3) are in the E position with respect to
the C(11)–N(2) bond. This configuration is probably due to
the formation of centrosymmetric dimer through N(2)–H ◊ ◊ ◊ S(1)
probability level.
˚
hydrogen bond interaction. The N(2)–N(3) (1.386(4) A) and N(2)–
˚
C(11) (1.355(4) A) bond distances in L
1
H are intermediate between
˚
˚
ideal values of corresponding single [N–N, 1.45 A; C–N, 1.47 A]
˚
˚
and double bonds [N N, 1.25 A, C N, 1.28 A], giving evidence
for an extended p-delocalization along the semicarbazone chain.
The solid state packing of the ligand is mainly governed by the
different C–H ◊ ◊ ◊ p interactions.
1
Fig. 7 ORTEP plot of (a) nickel and (b) zinc complexes with L H.
Thermal ellipsoids set to the 50% probability level.
two deprotonated S,N-bidentate ligands chelate the nickel atom
in its iminothiolate form via the thiolate sulfur atom and the
azomethine nitrogen atom in a Z configuration around the C(1)–
N(2) bond. The negative charge of the deprotonated ligand is
fully delocalized along the thiosemicarbazone moiety. The solid
state packing of the complex is mainly governed by the different
C–H ◊ ◊ ◊ p and N–H ◊ ◊ ◊ p interactions.
Fig. 5 Inter molecular dimeric hydrogen bonding interaction between
two ligands (L H).
1
The single crystals of L
lization from dilute solution of acetonitrile. L
space group P2 with Z = 4. Molecular structure of L
with atom numbering is shown in Fig. 6. In the crystal structure
the two rings are perpendicular to each other. The significant
2
were obtained by slow-driven crystal-
crystallized in the
along
2
1
2
1
2
1
2
Single crystals of Zn(L
1
)
2
were grown by vapor diffusion of Et O
2
into a 2 : 1 CHCl –DMF solution. An ORTEP plot of the Zn(L )
3
1 2
L
2
is shown in Fig. 7b along with the atom numbering scheme. The
complex crystallized into a monoclinic space group C2/c. The
crystallographic data reveals that two deprotonated S,N-bidentate
ligands chelate the zinc atom in its iminothiolate form via the
thiolate sulfur atom, the azomethine nitrogen atom, giving rise to
a distorted tetrahedral coordination polyhedron with S(1)–Zn(1)–
˚
˚
change in bond lengths N2–N3 1.386 A to 1.235 A and N3–C12
˚
˚
1
.272 A to 1.476 A in L
bond was shifted between N3–C12 to N2–N3 in L
from crystallographic data it is apparent that removal two N–H
2
compared to L
1
H reveals that the double
2
. In addition,
protons of thiourea moiety in L H occurs during the cyclization
1
◦
procedure.
N(3) angle is 86.65 . While coordinating in their iminothiolate
Single crystals of Ni(L
O into a 2 : 1 CHCl –DMF solution. The complex crystallized
into a monoclinic space group C2/c. An ORTEP plot along with
the atom numbering scheme of Ni(L is shown in Fig. 7a. The
crystallographic data reveals that the complex species Ni(L is
1
)
2
were grown by vapor diffusion of
forms, the negative charges generated by deprotonation are well
delocalized in the C–N–N–C system as shown by the intermediate
Et
2
3
˚
˚
C(12)–N(3) [1.299 A], N(3)–N(2) [1.399 A] and N(2)–C(11)
˚
1
)
2
[1.297 A] bond distances. The N(3) atom is in Z configuration
1
)
2
around the C(11)–N(2) bond. Here also the three dimensional
solid state packing is mainly controled by the different C–H ◊ ◊ ◊ p
and N–H ◊ ◊ ◊ p interactions.
centrosymmetric where the nickel atom at the centre of symmetry.
The coordination results in a square-planar geometry involving
2
840 | Dalton Trans., 2011, 40, 2837–2843
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1
Conclusions
vacuum (yield 80%). H NMR (400 MHz, CDCl
3
) d (ppm): 9.45(s,
1
7
H–N1) 8.7(s, 1H–N2), 7.94(d, 1H), 7.88(m, 2H), 7.53(m, 3H),
.81(d, 1H), 2.107(s, 3H) and 1.997(s, 3H). C NMR (100 MHz,
) d (ppm): 17.05, 25.52, 122.07, 125.11, 125.50, 126.34,
26.71, 127.58, 128.68, 129.78, 133.91, 134.33, 150.21, and 178.13
In conclusion we have developed a simple thiosemicarbazone
13
ligand L
1
H for selective colorimetric and fluorometric detection
CDCl
3
2
+
of Cu by a chemodosimetric approach. Isolation of oxidative
1
2
+
+
cyclized product and detection Cu to Cu reduction process
during cyclization allowed us to establish that the enhanced fluo-
rescence was due to an oxidative cyclization by Cu of the com-
paratively less fluorescent thiosemicarbazone ligand (L H) into
highly fluorescent rigid 4,5-dihydro-5,5-dimethyl-4-(napthalen-5-
yl)-1,2,4-triazole-3-thione (L ). The cyclized compound L has
+
ESI mass spectrometry: calcd for 258.10. [M + H ]; found 258.10
+
[
M + H ].
2
+
Synthesis of L
2
.
A aqueous ethanolic solution of L
(1.1 g, 3 mmol, 15 ml).
1
H (0.257
1
gm 1 mmol) was mixed with Cu(ClO
)
4 2
The whole solution became yellowish orange after few minutes.
The mixture was stirred at room temperature for 6 h and then
evaporated in vacuo. Aqueous NaCl solution was added and the
solution was then extracted by ethyl acetate (3 ¥ 25 ml). The
2
2
been characterized by both structurally and spectroscopically. The
selective sensing process and the formation of cyclized product
L
2
also been observed in CH
3
CN as well. Formation of stable
2
+
2+
metal complexes with other metal ions such as Ni and Zn
organic layer was dried over anhydrous Na
2
SO , and concentrated
4
also convincingly supports that the sensing process is not simply
due to the metal ligand coordination; therefore it is due to
the oxidative cyclization of the thiosemicarbazone ligand. The
chemodosimetric reaction, in combination with selective metal
ion-induced catalysis, may be a promising approach to develop
selective detection methods toward various metal ions.
under vacuum, then purified by column chromatography on silica
gel with ethyl acetate hexane (1 : 4) as eluent. H NMR (400 MHz,
1
CDCl
1H), 1.803(s, 3H) and 1.59(s, 5H,(CH
(100 MHz, CDCl ) d (ppm): 22.80, 23.19, 111.22, 122.89, 125.75,
126.01, 127.24, 127.68, 128.94, 129.26, 130.76, 131.33, 135.02 and
3
) d (ppm): 7.81(m, 2H), 7.55(m, 3H), 7.41(d, 1H), 7.27(d,
13
3
+ H O)). C NMR
2
3
+
1
88.03. ESI mass spectrometry: calcd for 256.09. [M + H ]; found
+
256.09 [M + H ].
Experimental
Synthesis of [Ni(L
to the ethanolic solution of L
1
)
2
]. NiCl
2
(0.24 g; 1 mmol 10 ml) was added
Materials and methods
1
H (0.64 g; 2.5 mmol; 25 ml) under
All reagents were obtained from commercial sources and used
as received. Solvents were distilled freshly following standard
procedures.
refluxing condition. An aqueous solution of sodium hydroxide was
added drop wise to reach pH in the range of 6–7. The reflux was
maintained for 5 h. The complexes were removed by filtration,
washed with EtOH and finally dried in vacuum over silica gel.
1
Instrumentation
H NMR (400 MHz, CDCl
3
) d (ppm): 7.90(d, 2H), 7.83(d, 1H),
7
.46(m, 4H), 6.736(s, 1H–N1), 2.89(s, 3H) and 2.47(s, 3H). ESI
The IR spectra were recorded on a Perkin Elmer-Spectrum
One FT-IR spectrometer with KBr disks in the range 4000–
+
mass spectrometry: calcd for 571.12. [M + H ]; found 571.06 [M +
H ].
+
-
1
400 cm . UV-Vis and Fluorescence spectra were recorded with
Perkin–Elmer Lambda-25 UV-Visible spectrophotometer and
Carry eclipse spectrofluorometer respectively. NMR spectra were
recorded on a Varian FT-400 MHz instrument. The chemical
shifts were recorded in parts per million (ppm) on the scale
using tetramethylsilane (TMS) as a reference. ESIMS spectra were
recorded in WATERS LC-MS/MS system, Q-Tof Premier in the
Central Instrument Facility (CIF) of IIT Guwahati.
Synthesis of [Zn(L
added to the ethanolic solution of L
5 ml) under refluxing condition. An aqueous solution of sodium
hydroxide was added drop wise to reach pH in the range of 6–7.
The reflux was maintained for 5 h. The complexes were removed
1
)
2
]. ZnCl
2
(0.27 g; 2 mmol; 10 ml) was
1
H (1.156 g; 2.5 mmol;
2
by filtration, washed with EtOH and finally dried in vacuum over
1
silica gel. H NMR (400 MHz, CDCl
3
) d (ppm): 8.43(d, 1H),
8
.0(d, 1H), 7.84(d, 1H), 7.6(d, 1H), 7.495(m, 3H), 7.132(s, 1H–
Synthesis of compounds
N1), 2.193(s, 3H) and 2.164(s 3H). ESI mass spectrometry: calcd
for 577.12. [M + H ]; found 577.05 [M + H ].
+
+
Designing aspect of thiosemicarbazone ligand L H. For chemo-
1
dosimetric detection of particular metal ion the ligand should be
design such a way that the ligand undergoes some irreversible
change in presence of a particular metal ion. The designing
X-Ray crystallography
The intensity data were collected using a Bruker SMART APEX-
II CCD diffractometer, equipped with a fine focus 1.75 kW
sealed tube Mo-Ka radiation (l) 0.71073 A) at 298 K, with
increasing w (width of 0.3 per frame) at a scan speed of 5 s
per frame. The SMART software was used for data acquisition.
principles of L
1
H are as follows: (1) The ligand L H composed
1
with various multidented donor atoms in suitable position for
both metal complexation and self cyclization process. (2) The metal
induce oxidative cyclization of thiosemicarbazone ligand are well
˚
◦
3
established in the literature. (3) The naphthalene fluorophore unit
Data integration and reduction were undertaken with SAINT and
presence in L
1
H is responsible for signal transduction during
18
XPREP software Multiscan empirical absorption corrections
spectroscopic studies.
19
were applied to the data using the program SADABS. Structures
were solved by direct methods using SHELXS-97 and refined
with full-matrix least-squares on F using SHELXL-97. All
non-hydrogen atoms were refined anisotropically. The hydrogen
atoms were located from the difference Fourier maps and refined.
17
Synthesis of L H. The ligand L
refluxing 4-(1-naphthyl)-3-thiosemicarbazide 0.217 g (1 mmol) in
0 ml acetone, followed by removal of excess solvent under reduced
1
1
H was facilely synthesized by
2
20
5
pressure. White solid was obtained after drying the residue in
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Structural illustrations have been drawn with ORTEP-3 for
Soltani, M. Asgharian-Rezaee, S. Dabiri, A. Kharazmi and A. Shafiee,
Bioorg. Med. Chem. Lett., 2005, 15, 1983–1985; (e) A. Foroumadi, Z.
Kiani and F. Soltani, Farmaco, 2003, 58, 1073–1076; (f) J. P. Kilburn, J.
Lau and R. C. F. Jones, Tetrahedron Lett., 2003, 44, 7825–7828; (g) R.
Severinsen, J. P. Kilburn and J. F. Lau, Tetrahedron, 2005, 61, 5565–
21
Windows.
Crystal data for L
57.36, crystal system = triclinic, space group = P1, a/A =
1
H. Formula = C14
H
15
N S, formula weight =
3
¯
˚
2
8
5
575; (h) E. Lopez-Torres, A. R. Cowley and J. R. Dilworth, Dalton
◦
˚
˚
.8572(9), b/A = 8.9640(9), c/A = 9.6791(10), a ( ) = 98.898(7),
Trans., 2007, 1194–1196.
◦
◦
3
˚
b ( ) = 99.319(7), g ( ) = 113.365(5), Volume/A = 675.52(12),
Z = 2, T/K = 298(2), m/cm = 0.227, dcal/g cm = 1.270, crystal
5 (a) A. P. de Silva, H. Q. N. Gunaratne, T. A. Gunnlaugsson, J. M.
Huxley, C. P. McCoy, J. T. Rademacher and T. E. Rice, Chem. Rev.,
1997, 97, 1515–1566; (b) B. Valeur and I. Leray, Coord. Chem. Rev.,
-
1
-3
3
dimensions/mm = 0.34 ¥ 0.30 ¥ 0.25, no. of reflns collected =
2
1
000, 205, 3–40; (c) J. S. Kimand and D. T. Quang, Chem. Rev., 2007,
07, 3780–3799.
5
>
694, no. of unique reflns = 5284, no. of params = 174, R
2s(I)) = 0.0828, 0.1368, Rint = 0.0795, GOF(F ) = 1.062, CCDC
1
, wR
2
(I
2
6 (a) G. Muthaup, A. Schlicksupp, L. Hess, D. Beher, T. Ruppert, C. L.
Masters and K. Beyreuther, Science, 1996, 271, 1406–1409; (b) R. A.
Løvstad, BioMetals, 2004, 17, 111–113; (c) K. J. Barnham, C. L.
Masters and A. I. Bush, Nat. Rev. Drug Discovery, 2004, 3, 205–214;
No. = 777756.
Crystal data for L
2
.
Formula = C14
H
13
3
N S, formula weight =
(
(
d) D. R. Brown and H. Kozlowski, Dalton Trans., 2004, 1907–1917;
e) G. L. Millhauser, Acc. Chem. Res., 2004, 37, 79–85; (f) E. Gaggelli,
2
55.34, crystal system = orthorhombic, space group = P2
1
2
1
2 ,
1
◦
˚
˚
˚
a/A = 7.2254(3), b/A = 8.4194(4), c/A = 21.4719(10), a ( ) = 90, b
H. Kozlowski, D. Valensin and G. Valensin, Chem. Rev., 2006, 106,
1995–2044.
◦
◦
3
˚
(
) = 90, g ( ) = 90, Volume/A = 1306.21(10), Z = 4, T/K = 298(2),
1 3
-
-3
7 (a) Y. Zheng, J. Orbulescu, X. Ji, F. M. Andreopoulos, S. M. Pham
and R. M. Leblanc, J. Am. Chem. Soc., 2003, 125, 2680–2686; (b) Y.
Xiang and A. Tong, Luminescence, 2008, 23, 28–31; (c) H. J. Kim,
S. Y. Park, S. Yoon and J. S. Kim, Tetrahedron, 2008, 64, 1294–1230;
(d) H. J. Kim, J. Hong, A. Hong, S. Ham, J. H. Lee and J. S. Kim,
Org. Lett., 2008, 10, 1963–1966; (e) W. Lin, L. Yuan, W. Tan, J. Feng
and L. Long, Chem.–Eur. J., 2009, 15, 1030–1035; (f) D. Y. Sasaki,
D. R. Shnek, D. W. Pack and F. H. Arnold, Angew. Chem., Int. Ed.
Engl., 1995, 34, 905–907; (g) J. Yoon, N. E. Ohler, D. H. Vance, W. D.
Aumiller and W. Czarnik, Tetrahedron Lett., 1997, 38, 3845–3848; (h) B.
Bodenant, T. Weil, M. Businelli-Pourcel, F. Fages, B. Barbe, I. Pianet
and M. Laguerre, J. Org. Chem., 1999, 64, 7034–7039; (i) Y. Zheng,
K. M. Gatta’s-Asfura, V. Konka and R. M. Leblanc, Chem. Commun.,
m/cm = 0.235, dcal/g cm = 1.305, crystal dimensions/mm =
.31 ¥ 0.27 ¥ 0.21, no. of reflns collected = 1854, no. of unique
reflns = 1645, no. of params = 166, R , wR (I > 2s(I)) = 0.0368,
.0557, Rint = 0.0874, GOF(F ) = 1.035, CCDC No. = 777755.
0
1
2
2
0
Crystal data for Ni(L Formula = C28 Ni, formula
1
)
2
.
H
28
N
6
S
2
weight = 571.39, crystal system = monoclinic, space group = C2/c,
◦
˚
˚
˚
a/A = 25.9620(10), b/A = 7.7407(3), c/A = 13.1235(5), a ( ) =
◦
◦
3
˚
9
4
0, b ( ) = 96.079(4), g ( ) = 90, Volume/A = 2622.52(17), Z =
1
-
-3
, T/K = 298(2), m/cm = 0.929, dcal/g cm = 1.447, crystal
3
dimensions/mm = 0.34 ¥ 0.31 ¥ 0.28, no. of reflns collected =
2
002, 2350–2351.
3
>
275, no. of unique reflns = 2473, no. of params = 175, R
2s(I)) = 0.0348, 0.0493, Rint = 0.0993, GOF(F ) = 0.978, CCDC
1
; wR
2
(I
8
(a) A. V. Varnes, R. B. Dodson and E. L. Whery, J. Am. Chem. Soc.,
1972, 94, 946–950; (b) K. Rurack, U. Resch, M. Senoner and S. Daehne,
J. Fluoresc., 1993, 3, 141–143; (c) H. Mu, Rui. Gong, Q. Ma, Y. Sun
and E. Fu, Tetrahedron Lett., 2007, 48, 5525–5529; (d) S. Goswami and
R. Chakraborty, Tetrahedron Lett., 2009, 50, 2911–2914.
2
No. = 777757.
Crystal data for Zn(L
1
)
2
.
Formula = C28
H
28
N
6
2
S Zn, formula
9
(a) P. Ghosh and P. K. Bharadwaj, J. Am. Chem. Soc., 1996, 118, 1553–
weight = 578.09, crystal system = monoclinic, space group = C2/c,
1
1
554; (b) B. Ramachandram and A. Samanta, Chem. Commun., 1997,
037–1038; (c) K. Rurack, M. Kollmannsberger, U. Resch-Genger and
◦
˚
˚
˚
a/A = 26.8575(10), b/A = 7.4489(3), c/A = 13.6206(4), a ( ) =
◦
◦
3
˚
9
4
0, b ( ) = 98.572(4), g ( ) = 90, volume/A = 2694.48(17), Z =
, T/K = 298(2), m/cm = 1.096, dcal/g cm = 1.425, crystal
dimensions/mm = 0.34 ¥ 0.29 ¥ 0.25, no. of reflns collected =
J. Daub, J. Am. Chem. Soc., 2000, 122, 968–969; (d) J. S. Yang, C. S.
Lin and C. Y. Hwang, Org. Lett., 2001, 3, 889–892; (e) Z. C. Weng, R.
Yang, H. He and Y. B. Jiang, Chem. Commun., 2006, 106–108; (f) H.
Yang, Z. Q. Liu, Z. G. Zhou, E. X. Shi, F. Y. Li, Y.-K. Du, T. Yi and
C. H. Huang, Tetrahedron Lett., 2006, 47, 2911–2914.
-
1
-3
3
3
>
321, no. of unique reflns = 2079, no. of params = 175, R
2s(I)) = 0.0441, 0.0717, Rint = 0.0789, GOF(F ) = 0.890, CCDC
1
; wR
2
(I
2
10 (a) M. Suresh, S. K. Mishra, S. Mishra and A. Das, Chem. Commun.,
009, 2496–2498; (b) M. H. Lee, T. V. Giap, S. H. Kim, Y. H. Lee, C.
2
No. = 777758.
Kang and J. S. Kim, Chem. Commun., 2010, 46, 1407–1409; (c) A. F. Li,
H. He, Y. B. Ruan, Z. C. Wen, J. S. Zhao, Q. J. Jiang and Y. B. Jiang, Org.
Biomol. Chem., 2009, 7, 193–200; (d) B. N. Ahamed, M. Arunachalam
and P. Ghosh, Inorg. Chem., 2010, 49, 4447–4457; (e) J. Du, J. Fan, X.
Peng, P. Sun, J. Wang, H. Li and S. Sun, Org. Lett., 2010, 12, 476–
Acknowledgements
GD acknowledges DST (SR/S1/IC-01/2008) and CSIR (01-
235/08/EMR-II), New Delhi India for financial support, CIF
4
79; (f) F. Song, S. Watanabe, P. E. Floreancig and K. Koide, J. Am.
2
Chem. Soc., 2008, 130, 16460–16461; (g) J. V. Ros-Lis, M. D. Marcos, R.
Matinez-Manez, K. Rurack and J. Soto, Angew. Chem., Int. Ed., 2005,
44, 4405–4407; (h) X. Zhang, Y. Xiao and X. Qian, Angew. Chem., Int.
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Chem. Soc., 2005, 127, 16760–16761; (j) J.-S. Wu, I. C. Hwang, K. S.
Kim and J. S. Kim, Org. Lett., 2007, 9, 907–910; (k) M. Y. Chae and
A. W. Czarnik, J. Am. Chem. Soc., 1992, 114, 9704–9705; (l) J. Huang,
Y. Xu and X. Qian, J. Org. Chem., 2009, 74, 2167–2170; (m) M. Suresh,
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3013–3016; (n) Y.-K. Yang, K.-J. Yook and J. Tae, J. Am. Chem. Soc.,
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11 (a) V. Dujols, F. Ford and A. W. Czarnik, J. Am. Chem. Soc., 1997, 119,
7386–7387; (b) R. M. Kierat and R. Kramer, Bioorg. Med. Chem. Lett.,
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Mokhir, Angew. Chem., 2006, 118, 7979–7981; (e) X. Qi, E. J. Jun, L.
Xu, S.-J. Kim, J. S. J. Hong, Y. J. Yoon and J. Yoon, J. Org. Chem.,
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47, 1880–1882.
and IIT Guwahati for providing instrument facility and DST-
FIST for single crystal X-ray diffraction facility. A.B thanks IIT
Guwahati for fellowship.
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