Coumarin derived chromophores in the donor-acceptor-donor format that gives fluorescence enhancement and large two-photon activity in presence of specific metal ions

Article abstract of DOI:10.1016/j.ica.2010.03.058

Two coumarin derived dyes (compounds L_a and L) have been synthesized in high yields by Schiff base condensation. On probing with a femtosecond laser, none of these compounds show any two-photon activity in the wavelength range, 760-860 nm. Howe

Full text of DOI:10.1016/j.ica.2010.03.058

Inorganica Chimica Acta 363 (2010) 2824–2832
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Coumarin derived chromophores in the donor–acceptor–donor format that
gives fluorescence enhancement and large two-photon activity in presence
of specific metal ions
*
Debdas Ray, Amit Nag, Atanu Jana, Debabrata Goswami, Parimal K. Bharadwaj
Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Two coumarin derived dyes (compounds La and L) have been synthesized in high yields by Schiff base
condensation. On probing with a femtosecond laser, none of these compounds show any two-photon
activity in the wavelength range, 760–860 nm. However, La in presence of Zn(II) and L in presence of
Mg(II), exhibit large two-photon absorption as well as emission in the same wavelength range. Theoret-
ical calculations at the B3LYP functional with 6-31G* and LanL2DZ mixed basis set under DFT formalism
support experimental results.
Received 19 January 2010
Received in revised form 18 March 2010
Accepted 24 March 2010
Available online 27 March 2010
Dedicated to Animesh Chakravorty
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Fluorescence
Optical nonlinearity
Sensor
Coumarin
DFT
1. Introduction
upon excitation [3]. These studies also reveal that the effect of
molecular charge transfer symmetry, donor/acceptor group
Search for new molecular two-photon absorbing materials is
currently of great interest because of their potential applications
in several areas of opto-electronics [1]. Two-photon absorption
(TPA) sensing materials with two-photon fluorescence have many
advantages over the commonly used one-photon fluorescence
materials. These include exclusive confinement of the excitation
to the focal volume with high 3D resolution and reduced photoble-
aching by virtue of the low-energy NIR excitation with greater
depths of penetration for biological applications. However, most
of the fluorescent probes presently used for two-photon laser
scanning microscopy are Mag-fura-2, Magnesium Green (MgG),
and Oregon green 488 BAPTA-1 (OG) based on fluorescein or
benzofuran as the fluorophore having small two-photon cross-sec-
tions (d < 50 GM, 1 GM = 1 ꢀ 10ꢁ50 cm4 s photonꢁ1 moleculeꢁ1) [2].
Therefore, more efficient two-photon probes with large TPA cross-
section are required for biological application. The selectivity and
sensitivity demonstrated in these sensing materials is still need to
be improved. Both theoretical considerations and experimental re-
sults led to the molecules with high TPA activity as the ones where
donor and acceptor groups are symmetrically disposed resulting in
a substantial symmetric intramolecular charge re-distribution
strength, chromophore number density and length of the conju-
gated backbone are the most important factors affecting the
molecular TPA activity [4]. These findings have led to molecules
with D- -D, A- -D- -A and D- -A- -D (D = donor, A = acceptor,
-bridge) conjugated structural motifs. Metal ions can assemble
organic ligands around to build a variety of multi-polar arrange-
ments to tune the molecular NLO property [5] by virtue of inducing
a strong intra-ligand charge transfer (ILCT) as well as low-energy
metal-ligand charge transfer (MLCT) transitions. If large increment
of TPA cross-section of organic molecules upon metal binding can
be achieved, its scope in various opto-electronic applications can
be increased. This can also be useful in reporting on the static con-
centration of a metal ion in vivo for understanding biological pro-
cesses. Recently, a few fluorescence materials sensitive to metal
ions working on the two-photon excited fluorescence principle, ap-
peared in the literature [6]. The use of Mg(II) and Ca(II) for this pur-
pose are fewer in number [7].
The development of fluorescence chemosensors with high
selectivity and sensitivity for biologically important analytes has
emerged as an important area of contemporary research [8]. In this
respect, detection of Mg(II) in presence of Ca(II), Na(I), and K(I) as
well as biologically relevant transition–metal ions is of particular
significance. Mg(II) is one of the most abundant divalent ions in
the cell and plays a crucial role in cell proliferation and cell death.
p
p
p
p
p
p
p = p
* Corresponding author. Tel.: +91 512 259 7034, fax: +91 512 259 7436.
E-mail address: pkb@iitk.ac.in (P.K. Bharadwaj).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.03.058

D. Ray et al. / Inorganica Chimica Acta 363 (2010) 2824–2832
2825
NO2
NO2
NH2
O
CHO
OH
SnCl 2 , HCl
H2O , RT
CO2Et
N
O
O
N
O
n-BuOH
Reflux
N
L1
LO
NH2
CHO
OH
EtOH
N
+
N
HO
N
O
O
RT
O
O
La
L1
NH2
N
CHO
EtOH
RT
N
+
N
L
N
O
O
O
N
O
O
O
O
O
L1
L2
Scheme 1. Synthetic route for L and La.
It also participates in the modulation of signal transduction, vari-
ous transporters, and ion channels [9–11]. On the other hand, Zn(II)
is an essential nutrient required for normal growth and develop-
ment [12] and for cellular processes such as DNA repair [13] and
apoptosis [14]. This metal plays a key role in the synthesis of insu-
lin and the pathological state of diabetes [15].
Herein, our discussion is focused on two coumarin-derived li-
gands L and La (Scheme 1). Our interest in coumarin derivatives
as fluorescence signaling systems stems from the fact that they
have large Stokes shift upon metal binding as well as visible exci-
tation and emission wavelengths [16]. Previously, we reported the
bis-coumarin [17] derivative L acts as a fluorescence signaling sys-
tem selectively for Mg(II). It is shown here that the free ligand La
exhibits low fluorescence due to excited-state intramolecular pro-
ton transfer (ESIPT) [18] but specifically in presence of Zn(II) ion
high fluorescence is observed due to blockage ESIPT. We also re-
port the TPA activity of the ligands in the metal-free state as well
as in presence of metal ions. To support the experimental findings,
DFT calculations are also carried out.
in presence of the metal ions are described in our earlier report
[17]. Metal free ligand La shows an absorption maximum at
445 nm with a shoulder at lower wavelength due to intramolecular
charge transfer (ICT) transitions [17]. On addition of Zn(II), these
bands are appreciably red-shifted (Fig. 1a). An isosbestic point is
observed at 460 nm (Fig. 1b) on recording the spectra with varying
concentrations of Zn(II) ion, indicating 1:1 complex formation.
Metal-free La shows weak emission in MeCN when excited at
445 nm and no emission enhancement is observed upon addition
of metal ions like Na(I), K(I), Ca(II) or Mg(II). Also, no enhancement
in emission is observed in presence of first-row transition metal
ions except for Zn(II) which leads to a large emission enhancement
with a slight red-shift of the emission band (Fig. 2a). The fluores-
cence quantum yield steadily increases (Fig. 2b) upon addition of
Zn(II). The maximum is reached upon addition of 1.2 equiv. of
the metal ion. Association constant of the complex between ligand,
La and Zn(II) is determined [17,19] from absorption and fluores-
cence titration data afford a value of 8.2 ꢀ 104 Mꢁ1
.
Binding of Zn(II) to La prevents excited-state intramolecular
proton transfer (ESIPT) [18] between the enol-imine and the
keto-enamine forms (Scheme 2) leading to enhancement. Chang-
ing the solvent to EtOH or MeCN afford similar results. Emission re-
sponses of the ligand in presence of different metal ions are shown
in Fig. 3 in the form of a bar diagram.
2. Results and discussion
The ligand L is synthesized by Schiff base condensation of two
coumarin derivatives. The coumarin derivatives, L1 and L2, are syn-
thesized in several steps [17]. Synthesis of La can be achieved very
easily in 80% yield by Schiff base condensation of 2-hydroxybenz-
aldehyde with L1. All synthesized compounds are characterized by
NMR, electrospray ionization mass spectrometry (ESI-MS), and ele-
mental analysis. The zinc complex, Zn(La)(ClO4) (1) is characterized
by ESI-MS1 and elemental analysis. The magnesium complex,
Mg(L)(ClO4)2 (2), has also been synthesized and characterized by
ESI-MS [17].
The nonlinear optical measurements were performed in the
near-infrared region since it was clear from the UV–Vis spectra
that the Schiff base (L and La) and their metal complexes are trans-
parent in this region. Two-photon absorption properties of Zn(II),
Ca(II) and Mg(II) complexes are measured by two-photon induced
fluorescence technique [20]. The solvent itself does not show any
TPA activity under experimental conditions. The linear and nonlin-
ear spectroscopic data of L and La are summarized in Table 1.
The ligand does not show any measurable TPA activity even at
10ꢁ1 M solution in the 740–860 nm wavelength region. The ligands
2.1. Electronic spectroscopy
(L and La) belong to the D-p p-D (L) and D-p
-A0- -A0 (La) analogue
since the NO2 site possesses very weak electron-withdrawing char-
acter. Addition of a metal ion like Ca(II), Mg(II) or Zn(II) results in
significant two-photon action cross-section (Table 1). Complexa-
tion with Ca(II), Mg(II) or Zn(II), enhances the electron-acceptor
character of the NO2 moiety converting L and La to a more strongly
All UV–Vis and fluorescence measurements are carried out in
acetonitrile at room temperature while metal perchlorates are
used as source of metal ions. The single photon absorption as well
as fluorescence behavior of bis-coumarin derivative (L) alone and
polarized D-
high TPA activity.
p-A-p-D (L) and D-p-A (La) units (Scheme 3) affording
1
Supporting Information.

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D. Ray et al. / Inorganica Chimica Acta 363 (2010) 2824–2832
Fig. 1. (a) Absorption spectra of La (0.012 mM) alone and in presence of Zn(II) (0.12 mM) in ethanol. (b) Absorption spectra of La (0.01 mM) in ethanol at room temperature
upon addition of increasing concentrations of Zn(II) ions (0–0.01 mM).
Fig. 2. (a) Fluorescence intensity change of La (0.25
lM) upon addition of various metal cations: 2.5
lM for Zn(II) and 25 lM for other metal ions in MeCN. (b) Fluorescence
spectra (kex = 460 nm) of La (1.2
increasing [Zn(II)].
lM) at room temperature upon addition of increasing amounts of Zn(II) ions (0ꢁ1.2
lM). Inset: Change of quantum yield upon addition of
Scheme 2. Schematic representation of Zn(II)-induced fluorescence.
We also recorded the change in TPA cross-section values as a
function of wavelengths for all the complexes of L and La. The
TPA cross-section varies appreciably in the region, 760–860 nm
for L in presence of Ca(II) or Mg(II) (Fig. 4a). Zinc complex of La also
exhibit variation with wavelength (Fig. 4b).
Unfortunately, our experimental setup did not allow us to ex-
tend the measurements to higher wavelength beyond 900 nm.
We have scanned the range, 740ꢁ900 nm and the maximum TPA
cross-section values and their corresponding kmax are shown in Ta-
ble 1 separately. The results are graphically given in Fig. 4.
TPA titration experiment was carried out in 10ꢁ5 (M) acetoni-
trile solution at 860 nm. From the titration curve (Fig. 5) of ligand
L, it is clear that upon addition of Mg(II) ion the TPA value gradu-
ally increases to a certain limit, and then further addition of the
metal ion cannot change any significant TPA value, which indicates
formation of 1:1 complex and saturation thereafter.
The increased fluorescence quantum yield [17] in [LꢂMg(II)]
complex is possibly the factor responsible for large two-photon ac-
tion cross-section compared to the [LꢂCa(II)] complex. The associa-
tion constants of the complexes between ligands and metal cations

D. Ray et al. / Inorganica Chimica Acta 363 (2010) 2824–2832
2827
and 1.1 ꢀ 106 Mꢁ1, respectively. Thus, complex stability constant
data are consistent with the TPA values. When we take a different
magnesium or zinc salt, the TPA values do not change.
2.2. Theoretical studies
We employed a blend of quantum-chemical approaches to
rationalize linear and nonlinear spectra of the compounds of inter-
est. Geometry optimization has been carried out for the metal free
ligands L and La and their corresponding metal complexes. All cal-
culations were performed by the GAUSSIAN-03 program [21] using
the B3LYP functional with a 6-31G* basis set. The observed opti-
mized geometry of these molecules predicts that the free rotation
around C@N bond is restricted by metal ion as input which leads to
a planar configuration to the whole moiety. In case of cis-isomer
there is less electronic delocalization due to tilted structure. While
on addition of metal ion free rotation around C@N bond is stopped
which leads a higher symmetry of charge delocalization in the me-
tal complexes. This demonstrates an interesting point that the pla-
nar arrangement of this kind of compound has a marked influence
upon their electronic properties.
Fig. 3. The emission response of compound La (1 lM) to metal solutions (20 lM) in
ethanol. Excitation was at 445 nm.
determined [17,19] from absorption and fluorometric titration
data give Ks for Ca(II) and Mg(II) complexes of L as 6.0 ꢀ 104 Mꢁ1
Table 1
Linear and nonlinear spectroscopic data for L, La and their metal complexes.
Compound
kmax (nm)
kem (nm)
g
agdmax (GM)
bdmax (GM)
Ks (Mꢁ1
)
L
La
488
445
555
510
505
0.0003
0.08
0.176
0.010
0.45
535
602
596
550
L + Mg(II)
L + Ca(II)
La + Zn(II)
453
5.5
11.5
2574
550
1.1 ꢀ 106
6.0 ꢀ 104
8.2 ꢀ 104
25.7c
Excitation wavelength for single photon fluorescence were 505 nm for [LꢂMg(II)], 488 nm for [LꢂCa(II)] and 460 nm for [LaꢂZn(II)]. Fluorescence maxima was obtained by
taking [L] = 0.8 M, [La] = 1 M. The quantum yield ( ) is calculated by taking standard fluorescein in 0.1 N NaOH ( = 0.85).
l
l
M; [Mn+] = 10
l
g
g
a
Two-photon action cross-section values at 800 nm for [La.Zn(II)], 830 nm for Mg(II) and 840 nm for Ca(II) complex of L.
Two-photon cross-section at 800 nm for [La.Zn(II)], 830 nm for Mg(II) and 840 nm for Ca(II)complex of L. 1 GM = 1 ꢀ 10ꢁ50 cm4 s photonꢁ1 molecule.
b
c
Two-photon absorption cross-section at 10ꢁ3 M solution.
Strong ICT
N
Weak ICT
N
D
D
π
π
O
O
O
O
Mn+
O
O
Receptor for
metal ions
Mn+
R
A
R
N
A
π
D
N
X
O
π
O
D
N
N
X = Solvent or ClO4
Highly TPA active
L, TPA Inactive
H
O
O
O
O
X
Zn(II)
Zn
N
N
O
O
N
N
TPA Inactive
TPA active
D-π-A
La, D-π-A
Scheme 3. Plan for cation-induced TPA response. D, donor; p
, conjugated bridge; D0, weak donor; A, acceptor.

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D. Ray et al. / Inorganica Chimica Acta 363 (2010) 2824–2832
Fig. 4. Two-photon action spectra of (a) [LꢂMg(II)] and [LꢂCa(II)] complexes in MeCN (
g
d values for [LꢂCa(II)] complex is showing 10 times increment for clarity) (b) [LaꢂZn(II)]
complex in MeCN obtained using Rhodamin 6G as a reference.
method on the basis of optimized geometry in acetonitrile solvent.
Our theoretically calculated OPA parameters are quite similar to
the experimental results. The experimentally determined kmax
and the calculated values, the nature of the electronic transitions,
corresponding oscillator strengths, major orbitals participate in
transitions in case of free ligands and their corresponding metal
complexes are given in Table 2.
3. Conclusion
In conclusion, we have reported the synthesis of a new magne-
sium responsive molecule in the format donor–acceptor–donor
that exhibits large two-photon action cross-section measured by
two-photon induced fluorescence technique in a femtosecond la-
ser. Its TPA activity increases in presence of selective metal ions
to different extents in consistent with their stability constant val-
ues. Interestingly, each of the ligand shows very high fluorescence
increment upon metal binding. Fluorophores with large two-pho-
ton absorption cross-section are potentially important in TPLSM
applications. Theoretical calculations carried out at the B3LYP/6-
31G* formalism show that upon metal binding, charge delocaliza-
tion increases significantly leading to higher TPA activity in the
metal complexes. Further studies on similar systems are in pro-
gress in our laboratory.
Fig. 5. Titration curve for the Mg(II) complex of L2 (10ꢁ5 M) in different metal ion
concentrations (0–1.2) at 840 nm in MeCN solution.
Experimentally, we found that when free chromophores (L and
La) coordinate with metal ions, the magnitude of the TPA cross-sec-
tion is increased. Compared to La, the change is much more exten-
sive in case of L (Table 1). The TPA cross-section is directly
correlated with the extent of intramolecular charge transfer transi-
tion through
p-conjugated bridge. Planar geometry of the com-
4. Experimental
plexes may also have significant contribution towards the
nonlinear effects. For more intuitional analysis of the influence of
the metal ion upon electronic property, we should consider the con-
tours of some occupied and unoccupied frontier orbitals (Fig. 6).
From contour surface diagrams of L and its metal complex it is
clear that in case of the free ligand, both the HOMO’s and LUMO’s
are nearly completely localized upon the conjugated side arm of
the ligand, indicating only a
tra-ligand charge transfer, ILCT). Metal ion only lowers the energy
levels leading to the red shifting of absorption band and facilitate
4.1. Materials
All reagent-grade chemicals were used without purification un-
less otherwise specified. Perchlorate salts of metal ions, 4-(diethyl-
amino)salisaldehyde, diethylmalonate and nitroethylacetate were
purchased from Aldrich (USA). Anhydrous stannous chloride, sali-
cyldehyde and solvents were obtained from S.D. Fine Chemicals
(India). All the solvents were purified prior to use. The syntheses
of the compounds were achieved in several steps as illustrated in
Scheme 1.
p ? p* electronic transition (i.e., in-
p
?
p* electronic transition.
Again from the energy level diagrams of each of the compounds
and their metal complex, it is also clear that the energy gap be-
tween HOMO and LUMO orbitals decreases significantly suggesting
extensive electronic charge delocalization after complexation
(Fig. 7) leading to more facile charge transfer transition and higher
TPA values.
We also performed theoretical calculations to explain the origin
of the peaks appear in UV–Vis spectra for L, La and their corre-
sponding metal complexes using time-dependent DFT (TDDFT)
4.1.1. Physical measurements
1H NMR and 13C NMR spectra were recorded on a JEOL JNM-
LA400 FT (400 MHz and 100 MHz, respectively) and JEOL ECX-
500 instrument in CDCl3. ESI mass spectra were recorded on a Q-
TOF Premier micromass spectrometer. The ESI capillary was set
at 3.5 kV and the cone voltage was 40 V. Melting points were
determined with an electrical melting point apparatus by PERFIT,

D. Ray et al. / Inorganica Chimica Acta 363 (2010) 2824–2832
2829
Fig. 6. Contour surfaces of HOMO and LUMO of L and La and their corresponding Mg(II), Ca(II) and Zn(II) complexes.
India and were uncorrected. UV–Vis spectra were recorded on a
JASCO V-570 spectrophotometer at 293 K and the average of three
measurements was taken. The deviations in molar absorption coef-
ficients were in the last digit only. Steady-state fluorescence spec-
tra were obtained using a Perkin–Elmer LS 50B Luminescence
Spectrometer at 293 K with excitation and emission band-pass
5 nm. Fluorescence quantum yields in each case were determined
by comparing the corrected spectrum with that standard Fluores-
cin [22] (g 0.85 in 0.1(N) NaOH) taking the area under the total
emission. The fluorescence measurements in solutions were car-
ried out at ꢃ10ꢁ6 M concentration unless otherwise specified.
The complex association constant Ka was determined [17,19] from

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D. Ray et al. / Inorganica Chimica Acta 363 (2010) 2824–2832
6
3
of the limited sensitivity of our experimental setup, we have been
able to work only with relatively concentrated solutions, typically
in the range of 1 ꢀ 10ꢁ3–1 ꢀ 10ꢁ5 M for both the reference and the
investigated chromophore. No aggregate formation was observed
in solution, even at such a high concentration. Our femtosecond
experimental scheme involves mode-locked coherent Mira tita-
nium: sapphire laser (Model 900) which is pumped by coherent
Verdi frequency doubled Nd: vanadate laser. We employ blanking
in our measurements by using a mechanical chopper MC1000A,
Thorlabs Inc. at 50% duty cycle. Our z-scan setup is already de-
scribed in detail elsewhere [23].
0
L
L
-3
H
L
H
L
L
-6
L
H
L
L
H
H
-9
4.3. Synthesis
H
H
H
4.3.1. 7-Diethylamino-3-nitro-chromene-2-one L0
-12
-15
1.4 g (7.24 mmol) of 4-diethylamino-salicylaldehyde, 0.80 ml
(7.96 mmol) of ethylnitroacetate, 0.1 ml piperidine and 0.2 ml gla-
cial acetic acid were taken in 20 ml of n-BuOH and the reaction
mixture was refluxed for 12 h. Orange solids were formed while
cooling. The solids were filtered and washed with n-BuOH
(2 ꢀ 10 ml) and finally dried in vacuum, which affords an orange
L
L
La+Mg(II)
L +Ca(II)
L +Zn(II)
L+Mg(II) L+Ca(II) L+Zn(II)
a
a
a
Fig. 7. B3LYP/6-31G* predicted molecular orbital energy levels for metal free
ligands and their corresponding Mg(II), Ca(II) and Zn(II) complexes.
solid (1.7 g, 90% Y). m.p. 170 °C.
m
max/cmꢁ1 1745 (C@O); dH
(400 MHZ, CDCl3) 1.25 (t, 6H, J = 7.2 Hz, CH3), 3.47 (q, 4H,
J = 7.1 Hz, CH2), 6.46 (s, 1Har), 6.68 (dd, 1H, J = 9.2, 2.6 Hz, Har),
7.42 (d, 1H, J = 9.0 Hz, Har), 8.70 (s, 1Har). 13C NMR (100 MHz,
CDCl3,) 12.4, 45.5, 96.9, 106.2, 111.1, 132.5, 138.1, 143.2, 154.5,
156.5, 158.8. Anal. Calc. for C13H14N2O4: C, 59.54; H, 5.38; N,
10.68. Found: C, 59.29; H, 5.44; N, 10.93%.
the change in absorbance or fluorescence intensity resulting from
the titration of dilute solutions (ꢃ10ꢁ5–10ꢁ6 M) of L and La against
metal ion concentration. The reported values gave good correlation
coefficients (P0.99).
4.2. Two-photon fluorescence studies
Two-photon absorption cross-section values of these samples
are measured by two-photon induced fluorescence technique. All
measurement is done in freshly purified MeCN solvent. Because
4.3.2. 3-Amino-7-diethylamino-chromene-2-one L1
In a 100 ml round-bottomed flask SnCl2.2H2O (10 mmol) and
20 ml 15% HCl were taken. To it compound Lo (1 g, 4.3 mmol)
Table 2
The OPA data for compounds L, La and their corresponding metal complexes.
Molecules
Experimental kmax (nm)
Theoretical kmax (nm)
Transitions
fos
Major contributions
488
470
388
377
S
S
S
0 ? S1
0 ? S2
0 ? S3
1.959
0.078
0.003
H ? L (66%)
L
360ꢁ400
H-1 ? L (54%)
H-1 ? L (37%)
H ? L+1 (49%)
H ? L (63%)
H ? L+1 (60%)
H-1 ? L (31%)
H ? L (80%)
H ? L+1 (99%)
H-1 ? L (20%)
H ? L+2 (69%)
H ? L (63%)
H ? L+1 (12%)
H ? L+1 (60%)
H-1 ? L (48%)
H ? L+1 (21%)
H ? L (64%)
Band
555
450
546
468
S
S
0 ? S1
0 ? S2
1.410
0.403
L + Mg2+
L + Ca2+
510
546
536
478
S0 ? S1
S0 ? S2
S0 ? S3
1.334
0.0013
0.3999
L + Zn2+
560
440
543
S0 ? S1
1.391
468
433
S
S
0 ? S2
0 ? S3
0.409
0.004
La
440
335
425
344
334
489
434
S0 ? S1
S0 ? S2
S0 ? S3
S0 ? S1
S0 ? S2
1.259
0.019
0.039
0.574
0.453
H-1 ? L (67%)
H ? L+1 (66%)
H ? L (59%)
H-1 ? L (61%)
H ? L (21%)
La + Mg2+
490
370ꢁ400
380
377
S
S
0 ? S3
0 ? S4
0.007
0.081
H ? L+2 (67%)
H-2 ? L (14%)
H ? L+1 (64%)
H-1 ? L+1 (3%)
H1 ? L+1 (96%)
H-1 ? L (9%)
H ? L (77%)
H-1 ? L+1 (96%)
H ? L+1 (3%)
H-1 ? L (79%)
H ? L (5%)
Band
La + Ca2+
449
530
531
432
431
480
S0 ? S1
S0 ? S2
S0 ? S3
S0 ? S4
S0 ? S1
0.0038
0.536
0.0009
0.454
0.627
La + Zn2+
505
H ? L (58%)

D. Ray et al. / Inorganica Chimica Acta 363 (2010) 2824–2832
2831
(g) B.R. Cho, K.H. Sou, S.H. Lee, Y.-S. Song, Y.-K. Lee, S.-J. Jeon, J.H. Choi, H. Lee,
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[5] (a) S.D. Bella, Chem. Soc. Rev. 30 (2001) 355;
was added portion wise and the solution was stirred at RT for 6 h.
Then 5 M NaOH solutions were added to neutralize the excess acid.
The aqueous phase was extracted with ethyl acetate (3 ꢀ 30 ml).
The organic layer was dried with anhy. Na2SO4 and evaporated
to dryness. A yellow semi solid came, which was directly used
for the next step without any characterization.
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A mixture of 3-amino-7-diethylamino-chromene-2-one (0.5 g,
1.48 mmol), salicylaldehyde (0.22 ml, 2.15 mmol), in dry ethanol
(20 ml) was stirred overnight at room temperature under N2 atmo-
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ford a yellow crystalline solid (0.51 g, 70.8% Y). mp 180 °C. mmax
/
cmꢁ1 1703 (C@O) and 1616 (C@N). dH (500 MHz, CDCl3) 1.22 (t,
6H, J = 6.5 Hz, CH3), 3.43 (q, 4H, J = 6.7 Hz, CH2), 6.56 (s, 1Har),
6.67 (s, 1Har), 6.9 (t, 1H. J = 7 Hz, Har), 6.97 (t, 1H, J = 7 Hz, Har),
7.34 (d, 1H, J = 8.5 Hz, Har,), 7.40 (d, 1H, J = 7.5 Hz, Har), 7.26 (s,
1Har), 7.65 (s, 1Har), 9.57 (s, 1H, C@NH), 13.34 (s, 1H, OH). m/z
337.13 (La, 100%) (ESI). Anal. Calc. for C20H20N2O3: C, 71.41; H,
5.99; N,8.33. Found: C, 71.69; H, 6.01; N, 8.34%.
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which precipitated the desired complex as a red solid. It was col-
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Acknowledgments
Financial support received from DRDO & DST, New Delhi, India
(to P.K.B.), is gratefully acknowledged. D.G. thanks DST, MCIT (In-
dia) and international SRF program of Welcome Trust (UK) for
the financial grant. D.R. thanks CSIR for SRF and A.N. thanks UGC
for SRF and A.J. thanks CSIR for SRF.
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