Syntheses, structures, and properties of two luminous mercury(II) halide compounds containing a tetradentate N-donor Schiff base

Article abstract of DOI:10.1016/j.molstruc.2012.03.027

A 1D coordination polymer [Hg₂(L)Br₄]_n (1) and one dinuclear compound [Hg₂(L)I₄] (2) [L = N,N′-(bis(pyridin-2-yl)benzylidene)ethane-1,2-diamine] are isolated using a 2:1 M ratio of HgBr₂/HgI₂ and Schiff base (L) in methanol-acetonitrile solution mixture and X-ray crystallographically characterized. Structural analyses show that in 1 1D chain is formed through binucleating bis(bidentate) bridging behavior of L and asymmetric Hg-(μ-Br)₂-Hg bridges in an alternate fashion; one terminal bromide unit completes the distorted square pyramidal geometry around each mercury(II). In 2, two mercury(II) centers are connected by bis(bidentate) bridging behavior of L and two iodides bound to each metal(II) center remain as terminal resulting in a discrete dinuclear entity with distorted tetrahedral geometry. Weak intermolecular Hg?I and I?I interactions in 2 promote dimensionality. In DMF solutions, 1 and 2 display intraligand ¹(π-π) fluorescence.

Full text of DOI:10.1016/j.molstruc.2012.03.027

Journal of Molecular Structure 1030 (2012) 138–144
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Syntheses, structures, and properties of two luminous mercury(II) halide
compounds containing a tetradentate N-donor Schiff base
Smita Satapathi a, Soumi Chattopadhyay a, Subhasis Roy a, Kishalay Bhar a, Partha Mitra b,
Barindra Kumar Ghosh a,
⇑
a Department of Chemistry, The University of Burdwan, Burdwan 713 104, India
b Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, India
a r t i c l e i n f o
a b s t r a c t
A 1D coordination polymer [Hg2(L)Br4]n (1) and one dinuclear compound [Hg2(L)I4] (2) [L = N,N0-
(bis(pyridin-2-yl)benzylidene)ethane-1,2-diamine] are isolated using a 2:1 M ratio of HgBr2/HgI2 and
Schiff base (L) in methanol–acetonitrile solution mixture and X-ray crystallographically characterized.
Structural analyses show that in 1 1D chain is formed through binucleating bis(bidentate) bridging
Article history:
Received 10 February 2012
Received in revised form 10 March 2012
Accepted 12 March 2012
Available online 21 March 2012
behavior of L and asymmetric Hg-(l-Br)2-Hg bridges in an alternate fashion; one terminal bromide unit
completes the distorted square pyramidal geometry around each mercury(II). In 2, two mercury(II)
centers are connected by bis(bidentate) bridging behavior of L and two iodides bound to each metal(II)
center remain as terminal resulting in a discrete dinuclear entity with distorted tetrahedral geometry.
Keywords:
Mercury(II) halide
Schiff base
X-ray structure
Hgꢀ ꢀ ꢀI/Iꢀ ꢀ ꢀI interaction
Luminescence
Weak intermolecular Hgꢀ ꢀ ꢀI and Iꢀ ꢀ ꢀI interactions in 2 promote dimensionality. In DMF solutions, 1 and
1
2 display intraligand
(p–
p⁄) fluorescence.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
lides in combination with a tetradentate Schiff base, N,N0-(bis(pyri-
din-2-yl)benzylidene)ethane-1,2-diamine (L) (Scheme 1). Successfully,
two neutral mercury(II) halide compounds of the types [Hg2(L)Br4]n (1)
and [Hg2(L)I4] (2) have been isolated from reactions of appropriate
building components. The details of syntheses, crystal structures,
thermal and luminescence behaviors of these compounds are
described below.
Research on design and synthesis [1] of mono-, di- and polynu-
clear coordination compounds of mercury(II) [2–12] has been the
center of attraction in chemistry and materials science due to their
potential applications in paper industry and as paints, cosmetics,
preservatives, cleaning solutions, manometers, thermostat probes,
thermoelectric devices, fluorescent lamps, sensors and mercury
batteries [13–17]. Exploiting the diversity in coordination environ-
ments around this 5d10 ion, different metal-organic frameworks
[2,18,19] may be accessed using a variety of organic coligands
along with different inorganic/organic bridges. Schiff bases are
important chelating ligands [20,21] in this regard due to their ease
of preparation, structural varieties, varied denticities and subtle
steric and/or electronic effects. Halides [6,8,22–26] are suitable ter-
minal/bridging units which in combination with such organic li-
gands results in different molecular and crystalline architectures
through their versatile ligational modes and different non-covalent
interactions [23–26,27]. Self-assembly [28] of the molecular com-
ponents is an efficient synthetic approach towards preparation of
such materials. In our earlier endeavour, we have reported the syn-
theses, structures and properties of different mercury(II) pseudo-
halide compounds in combination with Schiff bases of varied
denticities [21]. We wished to extend such work to mercury(II) ha-
2. Experimental
2.1. General remarks and physical measurements
2.1.1. Materials
High purity 2-benzoylpyridine (Lancaster, UK), 1,2-ethanedia-
mine (Spectrochem, India), mercury(II) bromide (E. Merck, India)
and mercury(II) iodide (E. Merck, India) were purchased from
respective concerns and used as received. The Schiff base, N,N0-
(bis-(pyridin-2-yl)benzylidene)ethane-1,2-diamine (L) was pre-
pared following the reported methods described elsewhere [21].
All other chemicals and solvents used were AR grade. The synthetic
reactions and work-up were done in open air.
2.1.2. Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen) were
performed on a Perkin–Elmer 2400 CHNS/O elemental analyzer.
IR spectra (KBr discs, 4000–400 cmꢁ1) were recorded using a
Perkin–Elmer FTIR model RX1 spectrometer. Thermal behavior
⇑
Corresponding author. Tel.: +91 342 2533913; fax: +91 342 2530452.
E-mail address: barin_1@yahoo.co.uk (B.K. Ghosh).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.03.027

S. Satapathi et al. / Journal of Molecular Structure 1030 (2012) 138–144
139
HgBr2 was used. The light yellow solution was processed as in 1.
Yield: 0.487 g (75%). Anal. Calc. for C26H22N4Br4Hg2 (1) C, 28.1; H,
1.9; N, 5.0. Found: C, 28.3; H, 1.8; N, 5.3%. IR (KBr, cmꢁ1): 2926
(m), 2874 (w), 1655 (vw), 1626 (s), 1592 (m), 1466 (w), 1436 (s),
1322 (s), 1296 (w), 1258 (s), 1185 (vw), 1108 (w), 1076 (vw),
1056 (vw), 1038 (vw), 1010 (s), 953 (w), 906 (vw), 796 (s), 764
(s), 748 (s), 726 (m), 698 (s), 682 (w), 666 (m), 636 (w), 486 (m),
415 (m). UV–Vis (DMF, kmax/nm): 272. Anal. Calc. for
Ni
Ni
C26H22N4I4Hg2 (2) C, 24.0; H, 1.7; N, 4.3. Found: C, 24.1; H, 1.8;
N, 4.4%. IR (KBr, cmꢁ1): 2948 (w), 2927 (w), 2868 (w), 1624 (s),
1590 (m), 1459 (w), 1433 (s), 1320 (s), 1255 (s), 1180 (w), 1152
(w), 1106 (m), 1076 (vw), 1054 (vw), 1036 (vw), 1021 (m), 1008
(s), 912 (vw), 850 (vw), 798 (s), 763 (s), 746 (m), 724 (m), 703
(s), 678 (s), 666 (s), 633 (m), 518 (vw), 484 (m), 418 (vw). UV–
Vis (DMF, kmax/nm): 271.
Np
Np
Scheme 1. (Np,Ni,Ni,Np) donor sets of L.
2.3. X-ray crystallographic analyses
was examined with a Perkin–Elmer Diamond TG/DT analyzer
heated from 30 to 650 °C under nitrogen. Ground state absorption
and steady-state fluorescence measurements (in DMF) were made
with a Shimadzu model UV-2450 UV–VIS spectrophotometer and a
Hitachi model F-4010 Spectrofluorimeter, respectively.
Single crystals of 1 and 2 suitable for X-ray analyses were se-
lected from those obtained by slow evaporation of methanol–ace-
tonitrile solution mixtures at 298 K. Diffraction data were collected
on a Bruker SMART APEX-II CCD area-detector diffractometer (for 1
at 150 K with the Oxford Cryosystem Cobra low-temperature
attachment and for 2 at 293 K) using graphite monochromated
2.2. Syntheses of [Hg2(L)Br4]n (1) and [Hg2(L)I4] (2)
Mo Ka radiation (k = 0.71073 Å). The unit cell parameters were ob-
tained from SAINT [29] and absorption corrections were performed
with SADABS [30]. The structures were solved by direct methods,
using the SHELXTL [31] program. For compound 2, the highest peak
of 2.81 Å located in the difference Fourier map is nearest to the
heavy atom Hg which gives rise to maximum residual density alert
in checkcif. All non-hydrogen atoms were refined with anisotropic
displacement parameters. The hydrogen atoms were fixed geomet-
rically and refined using a riding model. Materials for publication
were prepared using SHELXTL, PLATON [32], Diamond [33] and
ORTEP-3 [34] programs. Further details are given in Table 1.
HgBr2 (0.360 g, 1 mmol) in methanol (20 mL) and light yellow
acetonitrile solution (20 mL) of L (0.195 g, 0.5 mmol) were mixed
together slowly. The resulting light yellow solution was filtered
and left undisturbed in an open air for slow evaporation. After a
week, crystals of 1 were isolated by filtration, washed with dehy-
drated alcohol and dried in vacuo over silica gel. Yield: 0.400 g
(72%). For preparation and isolation of 2 in pure crystalline state,
similar reaction condition and reaction stoichiometry as used in
1 were followed except that HgI2 (0.454 g, 1 mmol) instead of
Table 1
Crystallographic data for 1 and 2.
Complex
Formula
Formula weight
Crystal system
Space group
a (Å)
1
C
2
26H22N4Br4Hg2
C26H22N4I4Hg2
1299.26
Monoclinic
P21/n
11.3555(16)
8.9735(12)
16.461(2)
90.00
1111.3
Monoclinic
P21/c
10.9354(14)
10.2046(13)
14.285(2)
90.00
b (Å)
c (Å)
a
(°)
b (°)
110.908(3)
90.00
1489.2(3)
0.71073
106.641(4)
90.00
1607.1(4)
0.71073
c
(°)
V (Å3)
k (Å)
qcalcd (gm cmꢁ3
)
2.478
2.685
Z
4
2
T (K)
l
150(2)
15.686
293(2)
13.404
(mmꢁ1
)
F(000)
1012
1156
Crystal size (mm3)
h ranges (°)
0.08 ꢂ 0.21 ꢂ 0.29
1.99–28.07
ꢁ13,13/ꢁ12,12/ꢁ16,16
13,703
0.09 ꢂ 0.16 ꢂ 0.21
1.95–27.00
ꢁ14,14/ꢁ11,11/ꢁ20,21
21,041
h/k/l
Reflections collected
Independent reflections (Rint
Tmax and Tmin
)
2623
3504
0.285 and 0.027
2623/0/163
1.090
0.30 and 0.09
3504/0/163
1.070
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R = 0.0317, wR = 0.0621
R = 0.0494, wR = 0.0674
0.472 and ꢁ0.960
R = 0.0361, wR = 0.0757
R = 0.0562, wR = 0.0838
3.134 and ꢁ1.114
Largest peak and hole (eÅꢁ3
)
Weighting scheme: R =
R
||Fo| ꢁ |Fc||/
R
|Fo|, wR = [
R
w(F2o ꢁ F2c )2/
R
w(F2o )2]1/2, calcd. w = 1/[
r
2(F2o ) + (xP)2 + yP]; x = 0.0245 (for 1), 0.0342 (for 2)
and y = 0.0000 (for 1), 3.4102 (for 2); where P = (F2o þ 2Fc2)/3.

140
S. Satapathi et al. / Journal of Molecular Structure 1030 (2012) 138–144
X
2:1
Hg
X
Np
Ni
Ni
Ni
Ni
HgX2
Np
+
Hg
X = I
Np
Np
X
X
2:1
X = Br
Dinuclear
Np
Np
Np
X
X
X
Ni
X
Ni
Hg
X
Ni
Hg
Ni
Hg
Hg
Ni
Hg
Ni
Hg
Np
X
X
X
Np
X
X
Np
X
1D polymer
Scheme 2. Schematic representation of the reactions.
1 and 2 can be found in Table 2 and non-covalent interaction
parameters for 2 are given in Table 3.
3. Results and discussion
3.1. Synthesis and formulation
Structures of 1 and 2 consist of a neutral dinuclear core [X2-Hg-
(L)-Hg-X2] (X = Br for 1 and I for 2) formed by binucleating
bis(bidentate) bridging behavior of L (Figs. 1a and 2a) through
donation of two N atoms (N1 and N3 for 1; N1 and N2 for 2) to
Hg1 and the remaining two N atoms (N1b and N3b, b: 2 ꢁ x,
1 ꢁ y, ꢁz for 1; N1a and N2a, a = 1 ꢁ x, 1 ꢁ y, ꢁz for 2) to Hg1b
(for 1)/Hg1a (for 2). Two adjacent dinuclear units are further con-
nected through asymmetric Hg-(Br)2-Hg covalent bridges [7] in 1
and double intermolecular Hgꢀ ꢀ ꢀI interactions [5,8] in 2 involving
two halides (Br2 and Br2a for 1; I3 and I3b for 2) and two mer-
cury(II) centers (Hg1 and Hg1a for 1; Hg1 and Hg1b for 2). Such
alternating binucleating bis(bidentate) L bridge and double me-
tal-halide bridges in 1/intermolecular metal-halide interactions
in 2 propagate throughout the entire coordination frame in an infi-
nite fashion to form a 1D zig–zag chain along a-axis (Figs. 1a and
2b). Each mercury(II) center adopts a distorted square pyramidal
A 2:1 M ratio of HgX2 (X = Br and I) and the Schiff base (L) in
methanol–acetonitrile (1:1) solution mixtures at room tempera-
ture expected to yield either a pentacoordinated 1D coordination
polymer [Hg2(L)(X)4]n or a tetracoordinated dinuclear compound
[Hg2(L)(X)4] (see Scheme 2). Reaction of HgBr2 with L resulted in
the formation of the 1D polymer 1. Change of starting material
from HgBr2 to HgI2 afforded the dinuclear 2. The reactions were
reproducible as were evident from repetitive microanalytical re-
sults, spectral behaviors and other physicochemical properties.
The new complexes were characterized by microanalytical (C, H
and N), spectroscopic and other physicochemical results. The
microanalytical data are in good conformity with the formulations
1 and 2. The moisture-insensitive complexes are stable over long
periods of time in powdery and crystalline states, and are soluble
in methanol, ethanol, acetonitrile, dimethylformamide (DMF) and
dimethylsulphoxide (DMSO) but are insoluble in water. In the IR
spectra, the Schiff base, L in the metal bound states exhibit
geometry (s = 0.024) [37] in 1 and tetrahedral coordination envi-
ronment in 2. Hg-Br(bridging) distances [2.5436(8) and 3.2084(10) Å]
in 1 and Hgꢀ ꢀ ꢀI interactions [3.8995(9) Å] in 2 (Tables 2 and 3)
are comparable to those of the reported compounds [5–8]. In 1,
one bridging bromide (Br2a), one terminal bromide (Br3) and
two N atoms (N1 and N3) of L define the equatorial plane around
Hg1 whereas the apical position is occupied with remaining bridg-
ing bromide (Br2). Hg1 center deviates 0.7701(3) Å from the basal
plane towards Br2. Among four equatorial atoms, N3 and Br2a
deviate 0.457(5) Å and 0.0068(8) Å, respectively towards Br2
whereas N1 and Br3 show considerable deviation [N1 0.471(5) Å
and Br3 0.0058(8) Å] opposite to Br2 (Fig. 1b). The internuclear
Hgꢀ ꢀ ꢀHg separation [7.2732(9) Å)] through Schiff base bridge in 1
is larger than that [7.023(1) Å] in 2; whereas the Hgꢀ ꢀ ꢀHg separa-
tion [4.2216(6) Å] through asymmetric double bromide bridges
in 1 is much shorter than the Hgꢀ ꢀ ꢀHg distance [4.8126(8) Å]
through double intermolecular Hgꢀ ꢀ ꢀI interactions in 2.
(C@N) plus (C@C) stretching vibrations at ꢃ1625 and 1590 cmꢁ1
.
Weak bands in the range 2980–2850 cmꢁ1 are assignable to the
aliphatic CAH stretching frequency. All other characteristic organic
ligand vibrations (see Section 2) are seen in the range 1600–
400 cmꢁ1 [35]. Colorless DMF solutions of 1 and 2 exhibit absorp-
tion at ꢃ270 nm assignable to ligand based n–p⁄
/p–
p⁄ transition
[36]. The absorbance of the complexes 1 and 2 increases linearly
with the increase in concentration (Table S1). The quantitative
spectral patterns are given in Figs. S1 and S2.
3.2. Crystal structures of [Hg2(L)Br4]n (1) and [Hg2(L)I4] (2)
In order to define the coordination spheres conclusively, single-
crystal X-ray diffraction studies of 1 and 2 were made. ORTEP rep-
resentations of the individual units of 1 and 2, and perspective
view of the packing diagrams for 2 are shown in Figs. 1–3. Selected
bond distances and angles relevant to the coordination spheres for
In the long-range form, 1D chains in 2 are further connected by
short intermolecular Iꢀ ꢀ ꢀI contacts (Table 3) to form a 2D sheet
structure parallel to the ab-plane (Fig. 3). The Iꢀ ꢀ ꢀI distance

S. Satapathi et al. / Journal of Molecular Structure 1030 (2012) 138–144
141
Fig. 1. (a) An ORTEP plot (50% thermal ellipsoid probability) of a segment of the 1D chain in 1 formed through double bromide bridges and bis(bidentate) behavior of L in an
alternating fashion and (b) a view of square pyramidal coordination geometry around Hg1 in 1.
0
[4.2697(10) ÅA] is shor0ter than twice the Pauling’s van der Waals ra-
dius of I atom (4.30 ÅA) [38] and lies within the reported range of
4.1859(7)–4.279(2) Å [23,25,26].
It is worth mentioning that Mahmoudi et al. [2,6,10] have re-
ported some 1D and 2D coordination polymers of pentacoordinat-
up to 246 °C; the TG curve shows (Fig. 4) that it decomposes within
the temperature range 246–552 °C corresponding to the simulta-
neous departure (obs.: 66.7%, calcd.: 63.9%) of the Schiff base (L)
and four bromide units, ultimately giving a dirty brown colored
amorphous solid that appears to be HgO (obs.: 26.0%, calcd.:
19.5%). The thermal analysis of 2 reveals (Fig. 5) that the compound
remains intact until it is heated to 196 °C; the TG curve shows
simultaneous loss (obs.: 75.0%, calcd.: 69.1%) of the Schiff base
(L) and four iodide moieties in the temperature range 196–
495 °C. A dirty brown amorphous residue of HgO (obs.: 24.9%,
calcd.: 16.7%) remained. The organic ligand (L) and the halides
are found to be decomposed from two different metal complexes
at distinctly different temperatures. This demonstrates that differ-
ent covalent and/or non-covalent forces acting within the crystal
structures may be associated with the thermal stabilities of the
title compounds. In summary, the thermogravimetric analyses
show that the compounds have reasonable thermal stabilities.
ed mercury(II) formed through Hg-(l-Br/I)-Hg bridges in
combination with binucleating bis(bidentate) aromatic imines,
1,4-bis(2-pyridyl)-2,3-diaza-1,3-butadiene and 2,5-bis(2-pyridyl)-
3,4-diaza-2,4-hexadiene. In comparison to such reported compounds
[6,10], the Schiff base (L) in 1 and 2 shows similar binucleating
bis(bidentate) coordination motif [21]; however, the coordination
geometries around mercury(II) and thereby the molecular and
crystalline architectures are different due to the formation of dou-
ble bromide bridges in 1 and weak double Hgꢀ ꢀ ꢀI interactions/Iꢀ ꢀ ꢀI
contacts in 2. Furthermore, Wei et al. [5] have reported 1D coordi-
nation polymers of mercury(II) halides with weak Hgꢀ ꢀ ꢀX interac-
tions similar to that in 2; face-to-face
p p stacking interactions
ꢀ ꢀ ꢀ
in such complexes instead of Iꢀ ꢀ ꢀI contacts in 2 was found to pro-
mote dimensionality with different crystalline architectures.
3.4. Luminescence behaviors
3.3. Thermogravimetric studies
The photoluminescence behaviors of the free ligand (L) and its
compounds (1 and 2) are examined in DMF solutions. The nature
of the emission spectra of L and 1 and 2 are depicted in Fig. 6. Upon
photoexcitation at 270 nm, L exhibits a fluorescent emission cen-
tered at 378 nm. The compounds 1 and 2, upon photoexcitations
To examine thermal stabilities of the compounds 1 and 2, ther-
mogravimetric analyses (TGAs) were carried out between 30 and
650 °C in a static atmosphere of nitrogen. Compound 1 is stable

142
S. Satapathi et al. / Journal of Molecular Structure 1030 (2012) 138–144
Fig. 2. (a) An ORTEP diagram of 2 with atom labeling scheme and 50% thermal ellipsoid probability for all non-hydrogen atoms, and (b) a segment of the 1D chain in 2 formed
through weak double Hgꢀ ꢀ ꢀI interactions.
Fig. 3. A view of 2D sheet structure parallel to ab-plane in 2 formed through interwoven Hgꢀ ꢀ ꢀI and Iꢀ ꢀ ꢀI interactions.
at same wavelength (270 nm) show less intense photolumines-
4. Conclusion
cence with the main emission at ꢃ381 nm. The luminescence
behavior in 1 and 2 may be attributed to [39,40] the intraligand
Two luminous coordination compounds of mercury(II) have
been synthesized through single-pot reactions of the molecular
building components with preassigned molar ratio. X-ray struc-
tures demonstrate binucleating bis(bidentate) behavior of L, different
nuclearities of 1 and 2, and coordination numbers of mercury(II)
1
(p–
p⁄) emission. The decrease in luminous intensity values of
the complexes as compared to that of the free L may presumably
be due to the heavy atom effect [5,41,42] on ligand upon
coordination.

S. Satapathi et al. / Journal of Molecular Structure 1030 (2012) 138–144
143
Table 2
Selected bond distances (Å) and bond angles (°) for 1 and 2.
Bond distances
Bond angles
Compound 1
Compound 1
68.19(16)
128.52(13)
94.06(12)
104.42(13)
107.98(12)
Hg1-N1
Hg1-N3
Hg1-Br2
Hg1-Br3
Hg1-Br2a
2.379(5)
2.469(5)
2.5436(8)
2.4944(8)
3.2084(10)
N1-Hg1-N3
N1-Hg1-Br3
N3-Hg1-Br3
N1-Hg1-Br2
N3-Hg1-Br2
Br3-Hg1-Br2
Br2-Hg1-Br2a
Hg1-Br2a-Hg1a
127.05(3)
86.284(25)
93.716(26)
Compound 2
Hg1-N1
Hg1-N2
Hg1-I2
Compound 2
66.67(19)
103.14(15)
107.11(15)
112.56(15)
2.463(6)
2.446(6)
2.6396(7)
2.6377(7)
N2-Hg1-N1
N2-Hg1-I3
N1-Hg1-I3
N2-Hg1-I2
N1-Hg1-I2
I3-Hg1-I2
98.21(15)
142.23(2)
Hg1-I3
Symmetry code: a = 1 ꢁ x, 1 ꢁ y, ꢁz.
Table 3
Non-covalent interaction parameters for 2.
Hgꢀ ꢀ ꢀI interactions (Å)
Hgꢀ ꢀ ꢀI interaction
Hg1ꢀ ꢀ ꢀI3b
Distance
3.8995(9)
Iꢀ ꢀ ꢀI interactions (Å)
Iꢀ ꢀ ꢀI interaction
I2ꢀ ꢀ ꢀI3c
Distance
4.2697(10)
Symmetry code: b = 2 ꢁ x, 1 ꢁ y, ꢁz; c = x, 1 + y, z.
Fig. 6. Fluorescence excitation and emission spectra of: L, 1 and 2 in DMF solutions
at room temperature.
Acknowledgements
B.K.G thanks the DST and CSIR, New Delhi, India for financial
support. S.S, K.B are grateful to CSIR and S.C, S.R to UGC, New Delhi,
India for fellowships. The authors also acknowledge the use of DST-
funded National Single Crystal X-ray Diffraction Facility at the
Department of Inorganic Chemistry, IACS, Kolkata, India for crystal-
lographic studies.
Fig. 4. Thermal behavior of 1.
Appendix A. Supplementary material
Crystallographic data for the structural analyses have been
deposited with the Cambridge Crystallographic Data Centre Nos.
852677 for 1 and 852678 for 2. Copies of the data can be obtained
free of charge from the Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44 (0) 1223 336033; or e-mail: deposit@ccdc.-
cam.ac.uk or http://www.ccdc.cam.ac.uk). Supplementary data
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.molstruc.2012.03.027.
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