Syntheses, structures and luminescence behaviors of zinc(II) complexes containing a tetradentate Schiff base: Variation in nuclearity and geometry with the change of halide/pseudohalide/carboxylate and counter anion

Article abstract of DOI:10.1016/j.molstruc.2012.12.018

A series of pentacoordinated mono-/dinuclear compounds, [Zn(L)(Br)]PF ₆ (1), [Zn(L)(NCS)]ClO₄ (2) and [Zn₂(L) ₂(μ-tp)](ClO₄/PF₆)₂ (3/4) [L = N,N′-(bis(pyridin-2-yl)benzylidene)-1,3-propanediamine, tp = terephthalate dianion], have been synthesized using one-pot reactions of the building components. All the complexes are characterized using microanalytical, spectroscopic and other physicochemical results. Structures of 1-4 are solved by single crystal X-ray diffraction measurements. Structural analyses reveal that each zinc(II) center in 1 and 3 adopts a distorted trigonal bipyramidal geometry with ZnN₄Br and ZnN₄O chromophores, respectively, whereas zinc(II) centers in 2 and 4 have a distorted square pyramidal geometry with ZnN₅ and ZnN₄O chromophores, respectively. Intermolecular CH?Br, CH?F and CH?O hydrogen bondings along with CH?π and π?π interactions as the case in 1-4 lead to different crystalline aggregates. The compounds show intraligand π-π^- fluorescence in solid states and in DMF solutions at room temperature.

Full text of DOI:10.1016/j.molstruc.2012.12.018

Journal of Molecular Structure 1037 (2013) 160–169
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Syntheses, structures and luminescence behaviors of zinc(II) complexes containing
a tetradentate Schiff base: Variation in nuclearity and geometry with the change
of halide/pseudohalide/carboxylate and counter anion
Subhasis Roy a, Bhola Nath Sarkar a, Kishalay Bhar a, Smita Satapathi 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
h i g h l i g h t s
"
"
"
"
Mono- and dinuclear zinc(II) halide/pseudohalide/carboxylate compounds with a Schiff base are isolated and characterized.
X-ray structures show interesting variations in geometries and superstructures.
Thermogravimetric analyses reveal their thermal stability and decomposition pattern.
Fluorescence studies illustrate ligand based p–
pꢀ emission behaviors.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 August 2012
Received in revised form 11 December 2012
Accepted 11 December 2012
Available online 7 January 2013
A series of pentacoordinated mono-/dinuclear compounds, [Zn(L)(Br)]PF6 (1), [Zn(L)(NCS)]ClO4 (2) and
[Zn2(L)2(l
-tp)](ClO4/PF6)2 (3/4) [L = N,N0-(bis(pyridin-2-yl)benzylidene)-1,3-propanediamine, tp = tere-
phthalate dianion], have been synthesized using one-pot reactions of the building components. All the
complexes are characterized using microanalytical, spectroscopic and other physicochemical results.
Structures of 1–4 are solved by single crystal X-ray diffraction measurements. Structural analyses reveal
that each zinc(II) center in 1 and 3 adopts a distorted trigonal bipyramidal geometry with ZnN4Br and
ZnN4O chromophores, respectively, whereas zinc(II) centers in 2 and 4 have a distorted square pyramidal
geometry with ZnN5 and ZnN4O chromophores, respectively. Intermolecular CAHꢁ ꢁ ꢁBr, CAHꢁ ꢁ ꢁF and
Keywords:
Mono-/dinuclear zinc(II)
Halide/pseudohalide/carboxylate
Schiff base
CAHꢁ ꢁ ꢁO hydrogen bondings along with CAHꢁ ꢁ ꢁ
p
and
p p interactions as the case in 1–4 lead to differ-
ꢁ ꢁ ꢁ
ent crystalline aggregates. The compounds show intraligand
p
–
pꢀ fluorescence in solid states and in DMF
X-ray structure
solutions at room temperature.
Luminescence
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
[14,15] are suitable terminal and/or bridging units which in com-
bination with organic blockers may control nuclearities and struc-
tural diversities resulting in different mono-, di- and polynuclear
coordination molecules and supramolecular entities. Zinc(II) [16–
18] with its d10 configuration permits a wide range of symmetries
and coordination numbers and it has significant use in bioinor-
ganic chemistry [19]. Recently, we are active [20–22] to isolate dif-
ferent zinc(II) compounds in combination with multidentate N-
donor Schiff bases with interesting tunable molecular properties.
In the present endeavor, we have chosen a tetradentate Schiff base,
Construction of self-assembled coordination molecules and
supramolecular entities [1] of varied nuclearities formed through
control and manipulation of strong metal–ligand covalent bonds
[2] and multiple weak non-covalent forces [1,3–5] is the center
of attraction to the coordination chemists for preparation of differ-
ent varieties of functional materials [6–8]. One-pot synthesis [9]
using metal ions, organic spacers and suitable terminal/bridging
units in pre-assigned ratios is an efficient approach to isolate such
target molecules. Schiff bases [10] are important organic ligands
because of their ease of preparation, structural varieties and varied
denticities. Halides [11], pseudohalides [12,13] and carboxylates
N,N0-(bis(pyridin-2-yl)benzylidene)-1,3-propanediamine
(L,
Scheme 1) to isolate zinc(II) halide, pseudohalide and carboxylate
compounds. Successfully, we have isolated two mononuclear
compounds [Zn(L)(Br)]PF6 (1) and [Zn(L)(NCS)]ClO4 (2) and two
dinuclear compounds [Zn2(L)2(
crystallographically characterized. The details of syntheses,
l-tp)](ClO4/PF6)2 (3/4) and X-ray
⇑
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.2012.12.018

S. Roy et al. / Journal of Molecular Structure 1037 (2013) 160–169
161
[24]. All other chemicals and solvents used were AR grade. The syn-
thetic reactions and work-up were done in open air.
i
i
N
p
N
C
C
p
N
N
2.1.2. Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen) were per-
formed on a Perkin-Elmer 2400 CHNS/O elemental analyzer. IR
spectra (KBr disks, 4000–400 cmꢂ1) were recorded using a Per-
kin-Elmer FTIR model RX1 spectrometer. Molar conductances were
measured using a Systronics conductivity meter where the cell
constant was calibrated with 0.01 M KCl solution and MeCN was
used as solvent. Thermal studies were made with a Perkin-Elmer
Diamond TG/DT analyzer heated from 30–700 °C (for 1 and 2)
and 30–850 °C (for 3 and 4) under nitrogen. Ground state absorp-
tions were measured with a Jasco model V-530 UV–Vis spectro-
photometer. Fluorescence measurements in DMF solutions were
done using Perkin Elmer LS55 Fluorescence Spectrometer. Solid
state fluorescence measurements were done using a Hitachi Fluo-
rescence Spectroflurimeter F-4500.
Scheme 1. (Np,Ni,Ni,Np) set in L.
structures and spectroscopic, thermal and luminescence behaviors
of these compounds are described below.
2. Experimental
2.1. General remarks and physical measurements
2.1.1. Materials
High purity 1,3-propanediamine (SRL, India), 2-benzoylpyridine
(Lancaster, UK), terephthalic acid (Loba Chemie, India), pipyridine
(Loba Chemie, India), zinc(II) bromide (SRL, India), zinc(II) acetate
(E. Merck, India), ammonium thiocyanate (E. Merck, India), sodium
perchlorate (Fluka, Germany) and ammonium hexafluorophos-
phate (Fluka, Germany) were purchased from respective concerns
and used as received. Zinc(II) perchlorate hexahydrate was pre-
pared [20] by treatment of the corresponding zinc(II) carbonate
(E. Merck, India) with perchloric acid (E. Merck, India) followed
by slow evaporation on a steam-bath, filtration through a fine
glass-frit and preserved in a desiccator containing concentrated
sulfuric acid (E. Merck, India) for subsequent uses. The Schiff base,
N,N0-(bis(pyridin-2-yl)benzylidene)-1,3-propanediamine (L) was
prepared by condensation of a 1:2 M ratio of 1,3-propanediamine
and 2-benzoylpyridine following the reported procedure [23] and
was isolated as a faint yellow gummy mass. Piperidinium tere-
phthalate (ptp) was isolated using a method described elsewhere
2.2. General synthesis of the complexes
2.2.1. [Zn(L)(Br)]PF6 (1)
L (0.405 g, 1 mmol) in acetonitrile (20 ml) was added dropwise
to a solution containing ZnBr2 (0.225 g, 1 mmol) followed by NH4-
PF6 (0.163 g, 1 mmol) in methanol (20 ml). The final light yellow
solution was filtered and left for slow evaporation in air. After a
few days colorless crystals of 1 that separated, were washed with
hexane and dried in vacuo over silica gel indicator. The yield was
0.556 g (80%) for 1. Anal. calcd. for C27H24N4F6PBrZn (1): C, 46.7;
H, 3.5; N, 8.1. Found: C, 46.9; H, 3.6; N, 8.2%. IR (KBr, cmꢂ1):
m
(C@N) +
m(C@C) 1629, 1597; m(PF6) 839, 557. UV–Vis [DMF, kmax/
nm (
e
, Mꢂ1 cmꢂ1)]: 274 (0.67 ꢃ 104). KM (MeCN, ohmꢂ1 cm2 -
molꢂ1): 120.
Table 1
Crystallographic data and structure refinement parameters for 1–4.
Complex
1
C
2
3
4
Formula
27H24N4F6PBrZn
C28H24N5O4SClZn
627.40
Monoclinic
P2(1)/c
14.935(2)
10.3925(16)
18.450(3)
C62H52N8O12Cl2Zn2
1302.76
Monoclinic
C2/c
15.027(10)
27.34(2)
15.283(10)
90.00
C62H52N8O4F12P2Zn2
1393.80
Monoclinic
P21/c
10.130(4)
14.838(6)
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
694.75
Monoclinic
Cc
20.548(6)
12.349(6)
11.232(3)
90.00
20.044(8)
90.00
a
(°)
90.00
b (°)
102.590(9)
90.00
2781.6(17)
0.71073
94.378(2)
90.00
2855.3(8)
0.71073
98.301(18)
90.00
6214(8)
0.71073
1.392
90.734(12)
90.00
3012(2)
0.71073
1.537
c
(°)
V (Å3)
k (Å)
qcalcd (g cmꢂ3
)
1.659
1.459
Z
4
4
4
2
T (K)
l
150(2)
2.442
150(2)
1.070
293(2)
0.925
293(2)
0.942
(mmꢂ1
)
F (000)
1392
1288
2680
1420
Crystal size (mm3)
h ranges (°)
0.19 ꢃ 0.15 ꢃ 0.07
1.94–25.00
ꢂ24, 24/ꢂ14, 14/ꢂ13, 13
12976
0.24 ꢃ 0.22 ꢃ 0.18
1.37–22.65
ꢂ16, 16/ꢂ11, 11/ꢂ19, 19
21548
0.09 ꢃ 16.0 ꢃ 21.0
1.56–19.07
ꢂ13, 13/ꢂ24, 25/ꢂ13, 13
19023
0.18 ꢃ 0.16 ꢃ 0.12
1.71–28.04
ꢂ13, 12/ꢂ19, 19/ꢂ25, 25
25215
h/k/l
Reflections collected
Independent reflections (Rint
Tmax and Tmin
)
4860
3800
2504
6889
0.84 and 0.65
4860/2/361
0.914
0.82 and 0.77
3800/0/361
1.029
0.92 and 0.00
2504/0/399
1.183
0.94 and 0.92
6889/0/406
0.949
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R = 0.0356 and wR = 0.0710
R = 0.0451 and wR = 0.0752
ꢂ0.301 and 0.300
R = 0.0387 and wR = 0.0900
R = 0.0587 and wR = 0.1005
ꢂ0.398 and 0.782
R = 0.0688 and wR = 0.1915
R = 0.1088 and wR = 0.2197
ꢂ0.248 and 1.254
R = 0.0566 and wR = 0.1170
R = 0.1378 and wR = 0.1586
ꢂ0.426 and 0.484
Largest peak and hole (eÅꢂ3
)
Weighting scheme: R =
y = 0.0000 (for 1), 2.3189 (for 2), 0.0000 (for 3), 0.0000 (for 4); where P = (F2o + 2Fc2)/3.
R||Fo| – |Fc||/R|Fo|, wR = [R R r
w(F2o - Fc2)2/ w(F2o )2]1/2, calcd w = 1/[ 2(F2o ) + (xP)2 + yP]; x = 0.0000 (for 1), 0.0449 (for 2), 0.1257 (for 3), 0.0664 (for 4) and

162
S. Roy et al. / Journal of Molecular Structure 1037 (2013) 160–169
2.2.2. [Zn(L)(NCS)]ClO4 (2)
All calculations were carried out using SHELXL-97, SHELXTL [27],
Mercury 2.3 [28] and ORTEP-3 [29] programs. A summary of the
crystallographic data and structure determination parameters for
1–4 is given in Table 1.
Zn(ClO4)2ꢁ2H2O (0.372 g, 1 mmol) was dissolved in methanol
(10 ml) and to this solution L (0.405 g, 1 mmol) in acetonitrile
(20 ml) was added dropwise followed by NH4SCN (0.076 mg,
1 mmol) in methanol (10 ml). The resulting light yellow solution
was filtered and left for slow evaporation in air to yield colorless
block shaped crystals of 2. The yield was 0.470 g (75%). Anal. calcd.
for C28H24N5O4SClZn (2): C, 53.6; H, 3.9; N, 11.2. Found: C, 53.8; H,
3. Results and discussion
3.9; N, 11.0%. IR (KBr, cmꢂ1):
m(NCS) 2092;
m
(C@N) +
m(C@C) 1629,
3.1. Synthesis and formulation
1595; m(ClO4) 1093, 623. UV–Vis [DMF, kmax/nm (e
, Mꢂ1 cmꢂ1)]:
281 (1.1 ꢃ 104). KM (MeCN, ohmꢂ1 cm2 molꢂ1): 110.
The pentacoordinated mononuclear compound [Zn(L)(Br)]PF6
(1) was isolated as colorless crystals through one-pot synthesis
of a 1:1:1 M ratio of ZnBr2, L and NH4PF6 from methanol–acetoni-
trile (1:1) solution mixture at room temperature. Use of 1:1:1 M
ratio of Zn(ClO4)2ꢁ6H2O, L and NH4SCN in the same solvent mixture
resulted in 2. Compounds 3 and 4 were obtained using a 2:2:1:2 M
ratio of Zn(OAc)2ꢁ2H2O, L, ptp and NaClO4/NH4PF6. 4 was also iso-
lated by metathesis of 3 and NH4PF6 in 1:2 ratio from a methanolic
solution. Compounds 1 and 2 were also isolated from Zn(OAc)2-
ꢁ2H2O and L by adding respective halide/pseudohalide i.e. NaBr in
1 and NH4SCN in 2 followed by the addition of NH4PF6 in 1 and
2.2.3. [Zn2(L)2(l-tp)](ClO4)2 (3) and [Zn2(L)2(l-tp)](PF6)2 (4)
To a methanolic solution (10 ml) of Zn(OAc)2ꢁ2H2O (0.044 g,
0.2 mmol), L (0.081 g, 0.2 mmol) in methanol (10 ml) and piperid-
inium terephthalate (ptp) (0.034 g, 0.1 mmol) in the same solvent
(5 ml) were added in succession. To this resulting solution mixture,
a methanolic solution (5 ml) of NaClO4 (0.028 g, 0.2 mmol) was
added as counter anion. The colorless reaction mixture was kept
in an open air for slow evaporation. After a few days colorless
microcrystals of 3 were collected and dried in vacuo over silica
gel indicator. Yield: 0.977 g (75%). Complex 4 was prepared simi-
larly using the same reaction stoichiometry and reaction condition
as in 3 except that methanolic solution (10 ml) of NH4PF6 (0.037 g,
0.2 mmol) instead of NaClO4 was added to the reaction mixture.
Yield: 0.975 g (70%). 4 was also isolated by metathesis of 3 and
NH4PF6 in 1:2 ratio from a methanolic solution with constant stir-
ring for 45 min at room temperature. The microanalytical and
spectroscopic results for 4 obtained from both methods were very
similar. Anal. Calc. for C62H52N8O12Cl2Zn2 (3): C, 57.1; H, 4.0; N, 8.6.
Found: C, 57.3; H, 3.8; N, 8.5%. IR (KBr, cmꢂ1): as(COOꢂ) 1595;
m ms(-
COOꢂ) 1369; (ClOꢂ4 ) 1091, 624; UV–
m(C@N) + m(C@C) 1630, 1590; m
Vis [DMF, kmax/nm (
e
, Mꢂ1 cmꢂ1)] 282 (2.85 ꢃ 104). KM (MeCN,
ohmꢂ1 cm2 molꢂ1): 230. Anal. Calc. for C62H52N8O4F12P2Zn2 (4):
C, 53.4; H, 3.8; N, 8.0. Found: C, 53.6; H, 3.7; N, 7.9%. IR (KBr,
cmꢂ1):
1597;
m
m
as(COOꢂ) 1586;
m
s(COOꢂ) 1373;
m
(C@N) +
m
(C@C) 1630,
(PFꢂ) 842, 558; UV–Vis [DMF, kmax/nm (
e
, Mꢂ1 cmꢂ1)]
6
280 (2.26 ꢃ 104). KM (MeCN, ohmꢂ1 cm2 molꢂ1): 225.
2.3. X-ray crystallographic analyses
Diffraction data of the single crystals of 1 and 2 were collected
at 150(2) K, and for 3 and 4 at 293(2) K on a Bruker AXS SMART
APEX-II CCD area-detector diffractometer using graphite mono-
chromated Mo Ka radiation. The unit cell parameters were ob-
tained from SAINT [25] and absorption corrections were
performed with SADABS [26]. The structures were solved by direct
methods and refined by full-matrix least-squares method based on
|F|2 using SHELXL-97 [27]. All non-hydrogen atoms were refined
with anisotropic displacement parameters. The H atoms were
placed in calculated positions (dCH = 0.97 Å for methylene and
0.93 Å for phenyl) after checking their positions in the difference
map. The Uiso values were constrained to be 1.2Ueq of the carrier
atoms for all H atoms. Several attempts to crystallize 2 and 3 gave
crystals that were brittle needles and were difficult to cut. The best
possible crystal that was finally selected for data collection gave
diffuse diffraction spots, indicating the crystal to have a large mo-
saic spread. As a result of this, a few of the diffraction spots were
overlapping and the integration of these spots could not be carried
out properly by the processing software. A small portion of the col-
lected reflections was therefore rejected assuming that they were
incorrectly measured. Despite this, structures of 2 and 3 were re-
fined using the available data (1.37° 6 h 6 22.65° for
2 and
1.56° 6 h 6 19.07° for 3), which was adequate to give a precise
structure. Two O atoms (O5 and O7) of one perchlorate moiety in
3 are disordered with fractional occupancy of 50% for each atom.
Fig. 1. The asymmetric units for the complexes: (a) 1 and (b) 2. Displacement
ellipsoids are drawn at 30% probability for all non-hydrogen atoms.

S. Roy et al. / Journal of Molecular Structure 1037 (2013) 160–169
163
NaClO4 in 2. To get X-ray quality single crystals we used ZnBr2 in 1,
Zn(ClO4)2ꢁ6H2O in 2 and Zn(OAc)2ꢁ2H2O in 3 and 4. The reactions
are summarized in the following equations:
MeOHꢂMeCN
the other hand 3 and 4 show 2:1 electrolytic behavior [30] with
a bi-positive molecular cation and two uni-negative anions present
outside the coordination sphere, as reflected in their respective
conductivity values (vide Experimental). Thus the formulations of
the compounds can be made from their conductance values. In IR
ZnBr2 þ L þ NH4PF6
!
½ZnðLÞðBrÞꢄPF6
ð1Þ
ð1Þ
spectra,
m(C@N) plus m(C@C) stretching vibrations of the metal-
bound Schiff base are observed within 1630–1590 cmꢂ1 range.
ZnðClO4Þ ꢁ 6H2O þ L þ NH4SCN MeOHꢂMeCN
!
½ZnðLÞðNCSÞꢄClO4
ð2Þ
2
Compound
2
shows characteristic asymmetric thiocyanate
ð2Þ
stretching vibration at 2092 cmꢂ1. The position of the band
strongly suggests N-coordination rather than S-bonding [31]. The
stretching vibrations of terephthalate (tp) in 3 and 4 are seen as
NaClO4
NH4PF6
[Zn2(L)2(µ-tp)](ClO4)2
(3)
MeOH
strong m m
as(COOꢂ) and s(COOꢂ) in the range 1585–1595 cmꢂ1 and
Zn(OAc)2 .2H2O + L + ptp
NH4PF6
[Zn2(L)2(µ-tp)](PF6)2
1365–1375 cmꢂ1, respectively indicating bis(monodentate) behav-
ior of terephthalate dianion [32]. Additionally, presence of hexa-
fluorophosphate stretches in 1, and 4 at ꢅ840 and 555 cmꢂ1 and
perchlorate bands at ꢅ1090 and 625 cmꢂ1 in 2 and 3 (vide Exper-
imental) are indicative of non-coordination [31] to the metal cen-
ter. X-ray study corroborates this hypothesis. In DMF solutions, L
shows absorption maxima at 274 nm and the corresponding zin-
c(II) compounds 1–4 exhibit bands at ꢅ280 nm (Fig. S7) assignable
to ligand-based charge transfer [33].
(4)
ð3Þ
The new complexes were characterized by microanalytical (C, H
and N), spectroscopic, thermal and other physicochemical results.
The microanalytical results are in good conformity with the formu-
lations of 1–4. The moisture-insensitive complexes are stable over
long periods of time in powdery and crystalline states. Compounds
1 and 2 are soluble in methanol, ethanol, acetonitrile, dimethyl-
formamide and dimethylsulfoxide whereas 3 and 4 are moderately
soluble in these solvents at room temperature but upon warming
they are completely soluble. In MeCN solutions, 1 and 2 behave
as 1:1 electrolytes with a uni-positive molecular cation and a
uni-negative anion present outside the coordination sphere; on
3.2. Description of crystal structures
ORTEP diagrams with atom numbering schemes and perspec-
tive views of the crystalline architectures in 1–4 are shown in
Fig. 2. (a) A perspective view of 2D sheet structure in 1 formed through cooperative CAHꢁ ꢁ ꢁBr hydrogen bonds and CAHꢁ ꢁ ꢁ
p interactions in ac-plane. (b) 2D sheet structure in
2 formed through CAHꢁ ꢁ ꢁ interactions and multiple CAHꢁ ꢁ ꢁO hydrogen bonds in an interwoven fashion parallel to crystallographic ab-plane.
p

164
S. Roy et al. / Journal of Molecular Structure 1037 (2013) 160–169
Figs. 1–4 and Figs. S1 and S2. Selected bond distances and bond
angles relevant to the metal coordination spheres and the
non-covalent bonding parameters are set in Tables 2–4. Single
crystal X-ray structure analyses show that compounds 1–4 consist
of mono-/dinuclear units which are further engaged in different
kinds of cooperative hydrogen bondings like CAHꢁ ꢁ ꢁBr, CAHꢁ ꢁ ꢁF
a distorted square pyramidal geometry. Thus different molecular
geometries may arise due to the difference in length of the chains
in the Schiff bases. One Np (N9) and one Ni (N8) atom [Np = N(pyr-
idine) and Ni = N(imine)] of L along with the terminal halide define
the equatorial plane in 1 and the remaining Np (N7) and Ni (N3)
atoms of the Schiff base occupy the axial sites. The basal plane of
2 consists of two Np (N1 and N4) and two Ni (N2 and N3) atoms
of L while the apical position is occupied by N5 atom of the termi-
nal pseudohalide. The larger ionic radius of bromide in 1 results in
longer ZnABr distance [2.3890(8) Å] over ZnAN bond lengths (Ta-
ble 2). Compound 2 has ZnAN(Schiff base) bond distances within a
range of 2.084(3)–2.150(3) Å (Table 2) which are somewhat short-
er than the reported [16] one. The smaller ZnAN(thiocyanate) bond
distance over the other ZnAN(Schiff base) distances indicates
stronger coordination of the anionic thiocyanate over the other
neutral N-donor centers. The ZnAN(thiocyanate) bond distance is
almost comparable to the reported complex [16]. The quasi-linear
N-donor thiocyanate is ligated to zinc(II) center in an almost linear
fashion (Table 2). L forms two five-membered and one six-mem-
bered chelate loop around zinc(II) center in both 1 and 2. The pro-
pylenic arm of the Schiff base in 1 and 2 is to some extent
puckered. The zinc(II) center in 1 and 2 departs 0.084 Å and
0.598 Å, respectively from the corresponding mean plane (N8,
N9, Br1 for 1 and N1, N2, N3, N4 for 2) towards the axial N3 atom
in 1 and N5 atom in 2.
and CAHꢁ ꢁ ꢁO along with CAHꢁ ꢁ ꢁ
p
and
pꢁ ꢁ ꢁp interactions as the
case among themselves resulting in different crystalline
architectures.
3.2.1. [Zn(L)(Br)]PF6 (1) and [Zn(L)(NCS)]ClO4 (2)
The structures of 1 (Fig. 1a) and 2 (Fig. 1b) consist of [Znꢂ(L)(Br)]+
and [Zn(L)(NCS)]+ cation, respectively and PF6ꢂ in 1 and ClO4 in 2 as
counter anion. The zinc(II) center in 1 has a distorted trigonal bipy-
ramidal (tbp) [34] [
ligated by four N atoms (N7, N8, N3 and N9 of L1) and one terminal
bromide. A distorted square pyramidal (sp) ( = 0.43) [34] environ-
s = 0.53] geometry with ZnN4Br chromophore
p
ment around zinc(II) center in 2 is observed with a ZnN5 chromo-
phore ligated by four N atoms (N1, N2, N3 and N4) of the chelated
Schiff base (L) and one N atom (N5) of terminal thiocyanate. In con-
trast, a reported pentacoordinated mononuclear zinc(II) thiocya-
nate complex [16] with
a tetradentate macrocyclic N-donor
ligand results in trigonal bipyramidal environment around the me-
tal center. Earlier, we have reported a zinc(II) thiocyanate complex
[22] using a tetradentate Schiff base with butylenic arm that
adopts a distorted trigonal bipyramidal geometry, whereas com-
plex 2 with tetradentate Schiff base having propylenic arm affords
In the crystalline state, mononuclear units of 1 are associated by
weak CAHꢁ ꢁ ꢁBr hydrogen bonds (Table 3) affording a 1D zigzag
Fig. 3. (a) Molecular structure of [Zn2(L)2(
in 3 formed through interactions along crystallographic b-axis.
ꢁ ꢁ ꢁ
l
-tp)]2+ in 3 with atom numbering scheme and 10% thermal ellipsoid probability for all non-hydrogen atoms. (b) A view of 1D chain
p
p

S. Roy et al. / Journal of Molecular Structure 1037 (2013) 160–169
165
Fig. 4. (a) ORTEP representation of [Zn2(L)2(l
-tp)]2+ in 4 with atom numbering scheme and 30% thermal ellipsoid probability for all non-hydrogen atoms. (b) Extended 3D
network structure in 4 formed through CAHꢁ ꢁ ꢁO and CAHꢁ ꢁ ꢁF hydrogen bonds.
chain (Fig. S1a) along crystallographic c-axis. The chains further
center in 3 and 4 is best described with a ZnN4O chromophore li-
gated with four N atoms of the Schiff base and one O atom of bridg-
ing tp unit. One Np (N2) and one Ni (N3) atom of L along with the
O4 atom of tp unit define the equatorial plane in 3, whereas
remaining Np (N1) and Ni (N4) atoms of the Schiff base occupy
the axial sites. The basal plane of 4 consists of two Ni (N2, N3),
one Np (N1) of the chelated Schiff base (L) and O1 atom of the tp
bridge, while the apical position is occupied by rest Np (N4) atom
of L. The smaller ZnAO(tp) bond distances [Zn1AO4 1.990(7) Å in
3 and Zn1AO1 2.021(3) Å in 4] over the other ZnAN(Schiff base)
distances [2.087(8)–2.129(8) Å in 3 and 2.105(4)–2.148(4) Å in 4]
[14] is indicative of the stronger coordination of the anionic O atom
of tp over the neutral N-donors of the Schiff base. Each zinc (II) cen-
ter in 3 and 4 deviates 0.146 Å and 0.267 Å, respectively from mean
basal plane (N2, N3 and O4 in 3 and N1, N2, N3 and O1 in 4)
towards apical N1 atom in 3 and apical N4 atom in 4. The three
equatorial bond angles in 3, N2AZn1AO4 [125.0(3)°], N3AZn1AO4
[107.5(3)°] and N2AZn1AN3 [126.1(3)°] show slight deviation
from 120° (avg. 119.53°), whereas the axial N1AZn1AN4
pack through weak intermolecular CAHꢁ ꢁ ꢁ
p interactions (Table 3)
along crystallographic ac plane leading to a 2D sheet structure
(Fig. 2a). Each mononuclear unit is coordinated with a hexafluoro-
phosphate moiety by CAHꢁ ꢁ ꢁF hydrogen bondings (Table 3). Inter-
molecular edge-to-face CAHꢁ ꢁ ꢁ
p interactions (Table 3) join two
adjacent molecules of 2 to construct a supramolecular 1D chain
(Fig. S1b) along crystallographic a-axis. The 1D chains pack along-
side each other to give a 2D sheet structure in ab plane (Fig. 2b)
through multiple interwoven CAHꢁ ꢁ ꢁO hydrogen bondings with
the perchlorate ions embedded among the chains.
3.2.2. [Zn2(L)2(l-tp)](ClO4)2 (3) and [Zn2(L)2(l-tp)](PF6)2 (4)
The centrosymmetric dinuclear units of 3 and 4 (Figs. 3a and 4a)
have an inversion center located at the middle of the benzene ring
of the tp bridge. Each pentacoordinated zinc(II) center in 3 has a
trigonal bipyramidal geometry (
of compound 4 adopt a distorted square pyramidal geometry
= 0.367) [34]. The coordination polyhedron around each zinc(II)
s = 0.52) whereas zinc (II) centers
(s

166
S. Roy et al. / Journal of Molecular Structure 1037 (2013) 160–169
Table 2
0
Selected bond distances (ÅA) and bond angles (°) for 1–4.
Bond distances for 1
Bond distances for 2
Bond distances for 3
Zn1AO4
Zn1AN1
Zn1AN2
Zn1AN3
Zn1AN4
O4AC9
O1AC9
Br1AZn2
Zn2AN8
Zn2AN7
Zn2AN3
Zn2AN9
2.3890(8)
2.082(3)
2.149(4)
2.128(4)
2.071(3)
Zn1AN5
Zn1AN1
Zn1AN4
Zn1AN3
Zn1AN2
N5AC28
S3AC28
1.961(4)
2.103(3)
2.150(3)
2.084(3)
2.130(3)
1.161(5)
1.629(5)
1.990(7)
2.129(8)
2.125(8)
2.087(8)
2.107(8)
1.250(13)
1.241(14)
Bond distances for 4
Zn1AO1
Zn1AN1
Zn1AN2
Zn1AN3
Zn1AN4
O1AC28
O2AC28
2.021(3)
2.148(4)
2.105(4)
2.117(4)
2.121(4)
1.282(5)
1.250(5)
Bond angles for 1
N9AZn2AN8
N8AZn2AN3
N8AZn2AN7
N9AZn2ABr1
N3AZn2ABr1
N9AZn2AN3
N9AZn2AN7
N3AZn2AN7
N8AZn2ABr1
N7AZn2ABr1
Bond angles for 2
N5AZn1AN3
N3AZn1AN1
N3AZn1AN2
N5AZn1AN4
N1AZn1AN4
C28AN5AZn1
N5AZn1AN1
N5AZn1AN2
N1AZn1AN2
N3AZn1AN4
N2AZn1AN4
N5AC28AS3
Bond angles for 3
O4AZn1AN3
O4AZn1AN4
N3AZn1AN4
O4AZn1AN2
N3AZn1AN2
N4AZn1AN2
O4AZn1AN1
N3AZn1AN1
N4AZn1AN1
N2AZn1AN1
O4AC9AO1
126.02(14)
87.88(14)
77.09(14)
104.19(10)
97.01(10)
78.13(13)
101.26(13)
161.01(14)
129.34(10)
101.48(10)
118.21(14)
132.87(12)
88.22(13)
97.67(13)
101.32(12)
177.2(4)
108.76(14)
102.64(13)
77.76(12)
76.91(12)
158.84(12)
178.1(4)
107.5(3)
95.2(3)
87.9(3)
125.0(3)
126.1(3)
76.6(3)
105.1(3)
76.7(3)
157.3(3)
99.1(3)
123.3(12)
Bond angles for 4
O1AZn1AN1
O1AZn1AN2
O1AZn1AN3
O1AZn1AN4
N1AZn1AN2
N1AZn1AN3
N1AZn1AN4
N2AZn1AN3
N2AZn1AN4
N3AZn1AN4
O1AC28AO2
90.49(13)
139.16(13)
108.26(13)
93.88(13)
76.38(14)
161.22(14)
100.03(13)
89.46(14)
126.19(13)
78.25(14)
122.0(4)
Table 3
[76.38(14)–126.19(13)°] and transoid [139.16(13)–161.22(14)°]
bond angles in 4. Zinc(II) centers in 3 and 4 are linked through a
bis(monodentate) tp bridge with Znꢁ ꢁ ꢁZn separations of 10.994 Å
and 10.809 Å, respectively.
Hydrogen bond distances (Å) and angles (°) for 1–4 and CAHꢁ ꢁ ꢁ
p
interactions (Å, °) for
1 and 2.
Compounds DAHꢁ ꢁ ꢁA
1
DAH Hꢁ ꢁ ꢁA Dꢁ ꢁ ꢁA
DAHꢁ ꢁ ꢁA
C2AH2ꢁ ꢁ ꢁF8a
0.93
0.97
0.93
0.97
0.93
0.93
0.93
0.93
0.93
0.97
0.97
0.93
0.93
0.93
0.97
0.97
2.50
2.91
2.56
2.51
2.41
2.49
2.54
2.51
2.59
2.42
2.54
2.51
2.30
2.37
2.57
2.36
3.119(5)
3.548(5)
3.274(5)
3.474(5)
3.264(5)
3.170(5)
2.843(16) 100
3.14(2)
3.40(3)
3.203(13) 137
3.466(14) 160
3.413(15) 164
3.213(7)
3.175(6)
3.371(5)
3.213(6)
124
124
134
170
152
130
The tetradentate Schiff base (L) is twisted around the metal(II)
center such that the two planes containing the unsaturated chelate
rings [(Zn1, N1, C29, C13, N3) and (Zn1, N2, C1, C2, N4) in 3 and
(Zn1, N1, C5, C6, N2) and (Zn1, N3, C16, C17, N4) in 4 are inclined
to each other at 56.42° and 52.01°, respectively. The propylenic
arm of L is to some extent puckered in both the compounds. The
values of dihedral angles 23.65° in 3 and 19.84° in 4 between the
carboxylate group (C9, O1, O4 for 3 and C28, O1, O2 for 4) and ben-
zene ring (C10, C11, C12 for 3, C29, C30, C31 for 4) are in line with
the twisting of the tp bridge upon coordination to metal atoms. The
carboxylate group shows the expected trigonal geometry. For
monodentate carboxylate coordination, significant differences are
observed in the values of the carbon–oxygen bond distances: the
values are 1.241(14)/1.250(13) Å for 3 and 1.250(5)/1.282(5) Å
for 4.
C17AH17Aꢁ ꢁ ꢁBr1b
C8AH8ꢁ ꢁ ꢁO3c
2
C15AH15Aꢁ ꢁ ꢁO1
C22AH22ꢁ ꢁ ꢁO4d
C27AH27ꢁ ꢁ ꢁO4e
C12AH12ꢁ ꢁ ꢁO1
C15AH15ꢁ ꢁ ꢁO6f
C16AH16ꢁ ꢁ ꢁO5f
C22AH22Bꢁ ꢁ ꢁO3g
C23AH23Aꢁ ꢁ ꢁO3
C28AH28ꢁ ꢁ ꢁO2
C19AH8ꢁ ꢁ ꢁO2e
C27AH13ꢁ ꢁ ꢁF6h
C14AH18ꢁ ꢁ ꢁO2
C1AH24ꢁ ꢁ ꢁF4i
3
4
125
145
169
144
147
152
1
2
C(18)AH(18)ꢁ ꢁ ꢁCg(6)j
0.93
2.93
2.79
3.708(5)
3.678(5)
142
153
C(13)AH(13A)ꢁ ꢁ ꢁCg(6)k 0.97
In the crystalline state both 3 and 4 pack through intermolecu-
lar face-to-face
p p interactions through two closest pyridine
ꢁ ꢁ ꢁ
rings (Table 4) and join two adjacent molecules to afford a supra-
molecular 1D chain along crystallographic b-axis and a-axis,
respectively (Fig. 3b and S2b). Different intermolecular CAHꢁ ꢁ ꢁO
hydrogen bonds (Table 3) form a 2D sheet structure (Fig. S2a)
parallel to ac-plane in 3. On the other hand, CAHꢁ ꢁ ꢁF and CAHꢁ ꢁ ꢁO
[157.93(3)°] angle deviates slightly larger than 180°, reflecting that
the coordination geometry around each zinc(II) in the compound is
a slightly distorted trigonal bipyramid. The degree of distor-
tion from ideal square pyramidal geometry is seen in cisoid

S. Roy et al. / Journal of Molecular Structure 1037 (2013) 160–169
167
Table 4
ꢁ ꢁ ꢁ interactions (Å, °) for 3 and 4.
p
p
Compounds
Cg–Cg
Cg–Cg distance
Dihedral angle (i, j)
Perpendicular distances between baricentres (i, j)
3
4
Cg5–Cg5l
3.713(6)
3.789(3)
0.00
0.00
3.655(4)
3.506(17)
Cg5–Cg5m
Symmetry codes: a = 1/2 + x, ꢂ1/2 + y, z; b = x, ꢂy, ꢂ1/2 + z; c = 2ꢂx, ꢂ1/2 + y, 1/2ꢂz; d = 1ꢂx, ꢂ1/2 + y, 1/2ꢂz; e = x, 1/2ꢂy, 1/2 + z; f = ꢂ1 + x, y, z; g = 1ꢂx, 1ꢂy, 1ꢂz;
h = ꢂ1 + x, y, z; i = 1ꢂx, ꢂ1/2 + y, 1/2ꢂz; j = ꢂ1/2 + x, 1/2ꢂy, ꢂ1/2 + z; k = 1/2ꢂx, 3/2ꢂy, 1ꢂz; l = 1/2ꢂx, 3/2ꢂy, 1ꢂz; m = ꢂx, ꢂy, ꢂz.
[For
1,
Cg(6):
C(1) ? C(2) ? C(9) ? C(15) ? C(16) ? C(10);
for
2,
Cg(6):
C(7) ? C(8) ? C(9) ? C(10) ? C(11) ? C(12)
for
3,
Cg(5):
N(1) ? C(15) ? C(16) ? C(31) ? C(30) ? C(29); for 4, Cg(5): (N(1) ? C(1) ? C(2) ? C(3) ? C(4) ? C(5)].
(Table 3) hydrogen bondings among the dinuclear units in 4 result
in an extended 3D network structure (Fig. 4b).
166–175 °C is in line with the release of the terminal thiocyanate.
The next step in the range of 260–680 °C with an exothermic effect
at 312 °C corresponds to a large weight loss (obs.: 54.9%, calcd.:
64.5%) due to the removal of the L moiety. Compound 3 is stable
up to 311 °C (Fig. S5). It loses two L in two different steps (obs.:
28.3%, calcd.: 31.0% and obs.: 35.1%, calcd.: 31.0%) within the tem-
perature ranges 311–349 °C and 439–790 °C, respectively. Com-
3.3. Thermogravimetric studies
TG–DTA curve shows that pyrolysis of 1 starts around 280 °C
(Fig. S3). The weight loss (obs.: 66.4%, calcd.: 69.7%) within the
temperature range 280–650 °C is associated with the simultaneous
decomposition of the Schiff base and the terminal halide in a con-
tinuous fashion with an endothermic effect at 322 °C. TG–DTA
curve (Fig. S4) shows that compound 2 is stable up to 166 °C.
The weight loss (obs.: 05.1%, calcd.: 09.3%) in the first step between
pound
3 shows an exothermic effect at 111 °C and an
endothermic effect at 280 °C during its decomposition. Terephthal-
ate dianion dissociates (obs.: 14.0%, calcd.: 12.7%) in a single step
between the temperature range 349–439 °C. TG–DTA curve of 4
(Fig. S6) shows a simultaneous weight loss due to the removal of
Fig. 5. (a) (i) Solid state fluorescence behaviors of compounds 1 and 2, and (ii) fluorescence behaviors of L, 1 and 2 in DMF solutions. (b) (i) Solid state fluorescence behaviors
of ptp, 3 and 4 and (ii) fluorescence behaviors of L, ptp, 3 and 4 in DMF solutions.

168
S. Roy et al. / Journal of Molecular Structure 1037 (2013) 160–169
two L and terephthalate dianion (obs.: 61.6.8%, calcd.: 69.9%) in a
single step between the temperature range 280–846 °C with an
endothermic effect at 323 °C. Moreover, the thermogravimetric
analyses reveal that 1 is more stable than 2 and again 3 is more sta-
ble than 4.
SR 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 crystallographic study.
Appendix A. Supplementary material
3.4. Luminescence behaviors
Crystalline architectures (Figs. S1 and S2) of 1–4 formed
through different non-covalent interactions, thermal decomposi-
tion patterns (Figs. S3–S6) of 1-4, UV–Vis spectra in DMF solutions
(Fig. S7) and in solid-states (Fig. S8) of L, ptp and 1–4 are available
in the supporting information. Full cif depositions, excluding struc-
ture factor amplitudes, reside with the Cambridge Crystallography
Data center, CCDC-826782 for 1, CCDC-826784 for 2, CCDC-893270
for 3 and CCDC-893271 for 4. Copies of the data can be obtained,
free of charge, on application from CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK (fax: +44 1223 336033 or e-mail: depos-
it@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.2012.12.018.
The photoluminescence behaviors of the dicarboxylate (ptp)
and the compounds (1–4) were examined in DMF solutions and
in the solid state at room temperature (298 K). As the Schiff base
(L) was isolated in the form of a gummy mass, its fluorescence
behavior could not be measured in solid state. The spectral pat-
terns are shown in Fig. 5. In DMF solution free L exhibits a broad
fluorescent emission centered at 365 nm along with a weak emis-
sion at 330 nm upon photoexcitation at the corresponding absorp-
tion band (274 nm; Fig. S7). The corresponding compounds 1 and 2
show emission bands at the same wavelength with higher inten-
sity when excited at 274 and 281 nm (Fig. S7), respectively. Ptp,
upon excitation at 281 nm (Fig. S7) gives a broad emission band
ca. 362 nm along with a weak band ca. 333 nm. Compounds 3
and 4 also exhibit more intense emission bands at the same wave-
length as shown by L and ptp upon excitation to their correspond-
ing absorption bands (282 nm for 3 and 280 nm for 4; Fig. S7).
Therefore the emission bands in 1–4 may be assigned to the ligand
References
[1] J.W. Steed, J.L. Atwood, Supramolecular Chemistry, 2nd ed., John Wiley & Sons,
New York, 2009.
[2] H.A. Habib, B. Gil-Hernández, K. Abu-Shandi, J. Sanchiz, C. Janiak, Polyhedron
29 (2010) 2537–2545.
[3] G.A. Jeffrey, An Introduction to Hydrogen Bonding, Oxford University Press,
Oxford, 1997.
[4] F. Awwadi, R.D. Willett, B. Twamley, Cryst. Growth Des. 11 (2011) 5316–5323.
(L and/or ptp) based p–
pꢀ transitions. In the solid state, upon exci-
tation at 292 nm (Fig. S8), ptp exhibits the main emission centered
at 423 nm with two weak bands at 370 nm and 486 nm. Com-
pounds 1 and 2 show photoluminescence characteristics with
main emission centered at 423 and 421 nm, respectively upon
excitation at their corresponding absorption bands (300 nm for 1
and 272 nm for 2; Fig. S8) which may presumably be due to ligand
[5] M. Nishio, M. Hirota, Y. Umezawa, The CH/
1998.
p Interaction, Wiley-VCH, New York,
[6] X.-L. Yang, M.-H. Xie, C. Zou, Y. He, B. Chen, M. O’Keeffe, C.-D. Wu, J. Am. Chem.
Soc. 134 (2012) 10638–10645.
[7] S. Horike, K. Kishida, Y. Watanabe, Y. Inubushi, D. Umeyama, M. Sugimoto, T.
Fukushima, M. Inukai, S. Kitagawa, J. Am. Chem. Soc. 134 (2012) 9852–9855.
[8] M. Petty, Molecular Electronics: From Principles to Practice, Wiley, Chichester,
2008.
[9] H.-B. Yang, K. Ghosh, Y. Zhao, B.H. Northrop, M.M. Lyndon, D.C. Muddiman, H.S.
White, P.J. Stang, J. Am. Chem. Soc. 130 (2008) 839–841.
[10] P.A. Vigato, S. Tamburini, L. Bertolo, Coord. Chem. Rev. 251 (2007) 1311–1995.
[11] U. Englert, Coord. Chem. Rev. 254 (2010) 537–554.
[12] A.M. Golub, H. Kohler, V.V. Skopenko (Eds.), Chemistry of Pseudohalides,
Elsevier, Amsterdam, 1986.
[13] D.A. Buckingham, Coord. Chem. Rev. 135–136 (1994) 587–621.
[14] H.A. Habib, A. Hoffmann, H.A. Höppe, C. Janiak, Dalton Trans. (2009) 1742–
1751.
based p–
pꢀ transition. 3 and 4 show emissions centered at 370, 430
and 485 nm when excited to their corresponding absorption bands
(326 nm for 3 and 315 nm for 4; Fig. S8). The intensity of the emis-
sion bands in 3 and 4 are also increased with respect to ligands as
seen in DMF solutions. These emissions are assignable to the ligand
(L and/or ptp) based
of luminescence in the complexes over the ligands may be attrib-
uted to the metal-perturbed intraligand
pꢀ transition becoming
p–
pꢀ transitions [35–38]. The greater intensity
p
–
more permissible upon coordination. The emission band for each
compound is red-shifted in the solid state as compared to that in
solution, which may be due to intermolecular interactions arising
from the close proximity of the molecules in the crystalline state,
leading to stable excimer formation.
[15] H.-Y. Liu, H. Wu, J.-F. Ma, Y.-Y. Liu, B. Liu, J. Yang, Cryst. Growth Des. 10 (2010)
4795–4805.
[16] P. Jiang, Z. Guo, Coord. Chem. Rev. 248 (2004) 205–229.
[17] W. Huang, H.-B. Zhu, S.-H. Gou, Coord. Chem. Rev. 250 (2006) 414–423.
[18] C. Nazikkol, R. Wegner, J. Bremer, B. Krebs, Z. Anorg. Allg. Chem. 622 (1996)
329–336.
[19] A.S. Prasad, Biochemistry of Zinc, Plenum, New York, 1993.
[20] D. Bose, S.H. Rahaman, G. Mostafa, R.D.B. Walsh, M.J. Zaworotko, B.K. Ghosh,
Polyhedron 23 (2004) 545–552.
4. Conclusion
[21] S. Satapathi, S. Das, K. Bhar, K. Ramachandran, T.K. Maji, B.K. Ghosh,
Polyhedron 30 (2011) 387–396.
[22] S. Das, K. Bhar, S. Chattopadhyay, P. Mitra, V.J. Smith, L.J. Barbour, B.K. Ghosh,
Polyhedron 38 (2012) 26–35.
[23] K. Bhar, S. Khan, S. Das, P. Mitra, G. Rosair, J. Ribas, B.K. Ghosh, Inorg. Chim.
Acta 363 (2010) 3308–3315.
[24] M. Verdaguer, J. Gouteron, S. Jeannin, Y. Jeannin, O. Kahn, Inorg. Chem. 23
(1984) 4291–4296.
Four luminous zinc(II) halide/pseudohalide/carboxylate com-
plexes in combination with a tetradentate N-donor Schiff base
have been synthesized and X-ray crystallographically character-
ized. Using different terminal/bridging units, variation in crystal-
line architectures is observed. Trans-bis(monodentate) bridging
behavior of tp in 3 and 4 is seen. A subtle change in coordination
geometry (tbp to sp) in 1 and 2 is observed with changing the ter-
minal units from Brꢂ to NCSꢂ whereas variation of counter anion
changes geometry (tbp to sp) in 3 and 4. Structures of 1–4 repre-
sent reliability of the combination of strong covalent bonds and
weak non-covalent interactions in crystal engineering for the ra-
tional design of functional materials at molecular level.
[25] G.M. Sheldrick, SAINT, V4: Software Reference Manual Siemens Analytical X-
ray Systems, Madison, WI, USA, 1996.
[26] G.M. Sheldrick, SADABS: Program for empirical absorption correction of area
detector data, University of GÖttingen, Germany, 1996.
[27] G.M. Sheldrick, Acta Crystallogr. A64 (2008) 112–122.
[28] C.F. Macrae, P.R. Edgington, P. McCabe, E. Pidcock, G.P. Shields, R. Taylor, M.
Towler, J. van de Streek, J. Appl. Cryst. 39 (2006) 453–457.
[29] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[30] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81–122.
[31] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, Part B, 6th ed., John Wiley & Sons, Hoboken, New Jersey, 2009.
[32] F.A. Mautner, R. Vicente, F.R.Y. Louka, S.S. Massoud, Inorg. Chim. Acta 361
(2008) 1339–1348.
[33] A.B.P. Lever, Inorganic Electronic Spectroscopy, 2nd ed., Elsevier, New York,
1984.
Acknowledgements
Financial support from the DST and CSIR, New Delhi, India is
gratefully acknowledged. SS and KB are grateful to the CSIR, and

S. Roy et al. / Journal of Molecular Structure 1037 (2013) 160–169
169
[34] A.W. Addision, T.N. Rao, J. Reedijik, J.V. Rijn, G.C. Verschoor, J. Chem. Soc.
Dalton Trans. (1984) 1349–1356.
[36] J.R. Lakowicz, Principles of Fluorescence Spectroscopy, 3rd ed., Springer, USA,
2006.
[35] S. Das, S. Satapathi, S. Roy, K. Bhar, P. Mitra, B.K. Ghosh, J. Mol. Struct. 982
(2010) 113–120.
[37] B. Dutta, P. Bag, U. Florke, K. Nag, Inorg. Chem. 44 (2005) 147–157.
[38] X.-J. Yang, X. Liu, Y. Liu, Y. Hao, B. Wu, Polyhedron 29 (2010) 934–940.