Four novel isostructural coordination polymers {[M(H′L) 2(H2O)2]·2DMF} [M =Zn(II), Cd(II), Mn(II) and Co(II)] built using a nitrogen and oxygen donor azo ligand: Crystal structures and fluorescence studies

Article abstract of DOI:10.1016/j.poly.2013.02.044

When the ligand HH′L was treated with different transition metal salts at room temperature, four new isostructural coordination polymers, {[Zn(H′L)₂(H₂O)₂]·2DMF} _n (1), {[Cd(H′L)₂(H₂O) ₂]·2DMF}_n (2), {[Mn(H′L)₂(H ₂O)₂]·2DMF}_n (3), and {[Co(H′L)₂(H₂O)₂]·2DMF} _n (4) (HH′L = 2-hydroxy-5-(pyridin-4-ylazo)-benzoic acid) were formed. These polymers were characterized by IR spectroscopy, elemental analysis, powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA), in addition to X-ray crystallography. X-ray single crystal studies revealed that 1-4 are 1D coordination polymers that are further extended by weak interactions to afford 3D coordination polymers. All the complexes show high thermal stability after losing coordinated and lattice solvent molecules in the temperature range 80-200 °C. Upon excitation at 344 nm, complexes 1-4 exhibit solid-state luminescence at room temperature.

Full text of DOI:10.1016/j.poly.2013.02.044

Polyhedron 54 (2013) 189–195
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Four novel isostructural coordination polymers {[M(H0L)2(H2O)2]ꢀ2DMF}
[M = Zn(II), Cd(II), Mn(II) and Co(II)] built using a nitrogen and oxygen
donor azo ligand: Crystal structures and fluorescence studies
Rupali Mishra a, Musheer Ahmad b, Madhav Ram Tripathi a,
⇑
a Department of Chemistry, D.A.V. College, C.S.J.M. University, Kanpur 208001, India
b Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
a r t i c l e i n f o
a b s t r a c t
When the ligand HH0L was treated with different transition metal salts at room temperature, four new
isostructural coordination polymers, {[Zn(H0L)2(H2O)2]ꢀ2DMF}n (1), {[Cd(H0L)2(H2O)2]ꢀ2DMF}n (2),
{[Mn(H0L)2(H2O)2]ꢀ2DMF}n (3), and {[Co(H0L)2(H2O)2]ꢀ2DMF}n (4) (HH0L = 2-hydroxy-5-(pyridin-4-
ylazo)-benzoic acid) were formed. These polymers were characterized by IR spectroscopy, elemental
analysis, powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA), in addition to X-ray
crystallography. X-ray single crystal studies revealed that 1–4 are 1D coordination polymers that are fur-
ther extended by weak interactions to afford 3D coordination polymers. All the complexes show high
thermal stability after losing coordinated and lattice solvent molecules in the temperature range 80–
200 °C. Upon excitation at 344 nm, complexes 1–4 exhibit solid-state luminescence at room temperature.
Ó 2013 Elsevier Ltd. All rights reserved.
Article history:
Received 16 January 2013
Accepted 9 February 2013
Available online 27 February 2013
Keywords:
Coordination polymer
Transition metal ions
X-ray structural studies
Crystal structure
Thermogravimetric analyses (TGA)
Photoluminescence studies
1. Introduction
Most researchers pay attention to design and exploit symmetric
cylindrical or bridging organic ligands for the construction of coor-
Recent years have witnessed an immense growth in the field of
coordination polymers (CPs) for their potential applications in gas
adsorption [1–3], molecular storage [4,5], catalysis [6–8], proton
conductivity [9], magnetism [10–13], luminescence [14–16], drug
delivery [17,18] and so on. Specifically, controlled design to accom-
modate small molecules that can be further assembled into supra-
molecular entities is one of the promising areas of increasing
interest in recent years [19]. Usually the intriguing topologies of
coordination polymers can be controlled by proper design and
characteristic features of the ligands, like rigidity, flexibility, bulk-
iness and so on [20]. Since the incorporation of well-organized
structural motifs into a crystal lattice may generate novel materials
with engineered physical and chemical features, such work can
give an insight into the molecular assemblies and their functions.
Additionally, the tendency of metal ions to adopt certain geome-
tries and the prevailing experimental conditions, counter-anions,
temperature, solvents, pH and so on, have considerable influence
on the overall structure of the frameworks [21]. Besides the above
factors, the crystallization conditions play a crucial role in the self-
assembly processes.
dination polymers [22]. However, unsymmetrical ligands having
different denticities with different donors can assemble metal cen-
ters to give rise to a large number of coordination polymers. Li-
gands having both nitrogen [23] and carboxylate [24–27] donors
have been used extensively for this purpose. Motivated by this,
we have designed the ligand, 2-hydroxy-5-(pyridin-4-ylazo)-ben-
zoic acid, with an azo moiety in the middle as shown in the
Scheme 1. This design provides a certain degree of conformational
freedom around the azo moiety that may lead to CPs with different
overall architectures.
Herein, we report the synthesis and crystal structural studies of
four coordination polymers, {[Zn(H0L)2(H2O)2]ꢀ2DMF}n (1),
{[Cd(H0L)2(H2O)2]ꢀ2DMF}n (2), {[Mn(H0L)2(H2O)2]ꢀ2DMF}n (3), and
{[Co(H0L)2(H2O)2]ꢀ2DMF}n (4). These compounds have also been
subjected to different physico-chemical studies, including solid-
state photoluminescence.
2. Experimental
2.1. General methods and materials
4-Aminopyridine, salicylic acid, Zn(ClO4)2ꢀ6H2O, Cd(NO3)2ꢀ4H2-
O, MnSO4ꢀH2O and CoCl2ꢀ6H2O were purchased from Aldrich, USA
and were used as received. Hydrochloric acid, sodium hydroxide
⇑
Corresponding author. Tel.: +91 512 2306687; fax: +91 512 2304534.
E-mail address: madhavramtripathi@gmail.com (M.R. Tripathi).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.02.044

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R. Mishra et al. / Polyhedron 54 (2013) 189–195
2.2. Synthesis
2.2.1. Synthesis of 2-hydroxy-5-(pyridin-4-ylazo)-benzoic acid (HH0L)
The ligand was synthesized following an earlier reported [28]
procedure with a slight modification. 4-Aminopyridine (5.06 g,
53.8 mmol) was mixed with HCl (16 mL) and digested in a water
bath for 50 min. The hydrochloride was cooled to 5 °C and diazo-
tized with ice-cold aqueous NaNO2 (3.7 g, 20 mL). A cold solution
of salicylic acid (7.42 g, 53.8 mmol), previously dissolved in 10%
NaOH solution (50 mL), was then added to the cold solution of
the diazonium salt solution with vigorous stirring. An orange color
developed almost immediately and the stirring was continued for
1 h. The reaction mixture was kept overnight in a refrigerator, fol-
lowed by 5 h at room temperature and then poured into water,
whereupon an orange colored product precipitated out. The pre-
cipitate was filtered, washed several times with water and air-
dried. The crude product was recrystallized from methanol to yield
pure HH0L (4.72 g, 36%). 1H NMR (DMSO-d6), d (ppm): 8.77 (Ar, 2H),
8.3 (ArH, 1H), 8.05 (ArH, 2H), 7.47 (Ar, 1H), 7.08 (ArH, 1H), due to
moisture both the acid and hydroxyl protons mutually exchanged.
13C NMR (DMSO-d6), d (ppm): 114.2, 117.6, 119.7, 130.8, 136.2,
150.4, 161.6, 162.6, 172.5. Elemental analysis: Anal. Calc. for
C
12H9N3O3 (243.2211): C, 59.26; H, 3.73; N, 17.27. Found: C,
59.38; H, 3.62; N, 17.12%. ESI-MS m/z: 244.0727 [M+1]+.
Scheme 1. Synthetic reaction scheme of HH0L.
2.2.2. Synthesis of {[Zn(H0L)2(H2O)2 ]ꢀ2DMF}n (1)
pellets, NaNO2 and solvents were procured from S. D. Fine Chemi-
cals, India. All the solvents were purified prior to use following
standard methods.
A
hot DMF solution (3 mL) of the ligand HH0L (0.039 g,
0.16 mmol) was added to a MeOH/H2O solution (1:1, 2 mL) of
Zn(ClO4)2ꢀ6H2O (0.059 g, 0.16 mmol). On slow evaporation of the
filtrate at RT, orange crystals of 1 were obtained in ꢂ80% Yield.
Anal. Calc. for C30H34N8O10Zn: C, 49.22; H, 4.68; N, 15.31. Found:
C, 49.34; H, 4.78; N, 15.22%. IR (KBr, cmꢁ1): 3205(s), 2929(w),
1666(s), 1620(m), 1602(m), 1483(m), 1461(s), 1435(s), 1384(m),
1352(m), 1272(w), 1166(s), 1074(m), 840(s), 811(m), 784(m)
691(m).
Infrared spectra were recorded on a Perkin-Elmer Model 1320
spectrometer (KBr disk, 400–4000 cmꢁ1). 1H NMR and 13C NMR
spectra were recorded on a JEOL-ECX 500 FT (500 and 125 MHz,
respectively) instrument in DMSO-d6 with Me4Si as the internal
standard. ESI-mass spectra were recorded on a WATERS Q-TOF Pre-
mier mass spectrometer. Thermogravimetric analyses (TGA) were
recorded on a Mettler Toledo Star System (heating rate of 5 °C/
min). Microanalyses for the compounds were obtained using a
CE-440 elemental analyzer (Exeter Analytical Inc.). Solid-state
photo-excitation and emission spectra were recorded using a dou-
ble UV–Vis spectrophotometer (Shimadzu, UV-2450) and a Jobin
Yvon Horiba Fluorolog-3 spectrofluorimeter at room temperature.
2.2.3. Synthesis of {[Cd(H0L)2(H2O)2 ]ꢀ2DMF}n (2)
A mixture of Cd(NO3)2ꢀ4H2O (0.062 g, 0.2 mmol) and HH0L
(0.049 g, 0.2 mmol) was dissolved in DMF/EtOH/H2O solution
(6 mL, 1.5:1:1 v/v), and the mixture was stirred for 2 h at room
temperature, then filtered. On slow evaporation of the filtrate, or-
ange block shaped crystals of 2 were obtained in ꢂ48% yield. The
crystals were repeatedly washed with EtOH and dried in air. Anal.
Powder X-ray diffraction (Cu K
a radiation, scan rate 3°/min,
293 K) was performed on a Bruker D8 Advance Series 2 powder
X-ray diffractometer.
Table 1
Crystal and structure refinement data for 1–4.
Compound
1
2
3
4
Formula
Formula weight
T (K)
C
30H34N8O10Zn
C30H34N8O10Cd
779.05
100(2)
C30H30N8O10Mn
717.56
100(2)
C30H34N8O10Co
725.58
100(2)
732.02
100(2)
System
Space group
a Å
monoclinic
C2/c
18.151(5)
monoclinic
C2/c
18.423(5)
monoclinic
C2/c
18.319(5)
monoclinic
C2/c
18.170(5)
b Å
11.169(5)
11.190(7)
11.066(5)
11.067(5)
c Å
18.400(5)
18.324(5)
18.528(5)
18.487(5)
a
(°)
90.000
90.000
90.000
90.000
b (°)
118.825(5)
118.351(4)
118.619(5)
118.954(5)
c
(°)
90.000
3268.0(19)
90.000
3324(2)
90.000
3297(2)
90.000
3252.7(19)
V [Å3]
Z
4
4
4
4
qcalc [g/cm3]
1.488
0.821
1.557
0.725
1.446
0.469
1.482
0.597
l
[mmꢁ1
]
F(000)
1520
1592
1484
1508
Goodness-of-fit
1.035
1.131
1.091
1.036
Final R indices [I > 2
R indices (all data)
CCDC number
r(I)]
R1 = 0.0557, WR2 = 0.1461
R1 = 0.0713, WR2 = 0.1626
890674
R1 = 0.0417, WR2 = 0.1046
R1 = 0.0479, WR2 = 0.1196
890675
R1 = 0.0634, WR2 = 0.1732
R1 = 0.0856, WR2 = 0.2058
890676
R1 = 0.0616, WR2 = 0.1578
R1 = 0.0822, WR2 = 0.1732
890677

R. Mishra et al. / Polyhedron 54 (2013) 189–195
191
ature; red colored crystals of 3 were obtained in ꢂ52% yield. The
crystals were filtered, washed with acetone and dried in air. Anal.
Calc. for 3, C30H34N8O10Mn: C, 50.21; H, 4.21; N, 15.61. Found: C,
49.72; H, 4.93; N, 15.42%. IR (KBr, cmꢁ1): 3265(s), 2922(w),
1668(s), 1610(s), 1593(s), 1460(s), 1383(s), 1352(s), 1294(m),
1273(m), 1167(s), 1099(m), 1075(m), 934(w), 891(w), 839(s),
811(s), 666(m).
2.2.5. Synthesis of {[Co(H0L)2(H2O)2 ]ꢀ2DMF}n (4)
A
mixture of CoCl2ꢀ6H2O (0.059 g, 0.25 mmol) and HH0L
(0.073 g, 0.3 mmol) was dissolved in DMF/MeOH/H2O (3 mL,
1:1:1 v/v). The above solution was stirred for 10 h at room temper-
ature. After filtration, the filtrate was kept at room temperature for
slow evaporation. Dark orange colored crystals of 4 were obtained
in ꢂ62% yield. The crystals were filtered, washed with acetone and
dried in air. Anal. Calc. for 4, C30H34N8O10Co: C, 49.66; H, 4.72; N,
15.44. Found: C, 49.58; H, 4.60; N, 15.32%. IR (KBr, cmꢁ1):
3253(s), 2930(w), 1667(s), 1620(s), 1435(s), 1384(m), 1353(s),
1166(s), 1098(m), 1074(m), 967(w), 840(s), 811(m), 691(m),
580(s).
2.3. X-ray structural studies
Single crystal X-ray data of complexes 1–4 were collected at
100 K on a Bruker SMART APEX CCD diffractometer using graphite
monochromated Mo
Ka radiation (k = 0.71073 Å). The linear
absorption coefficients, scattering factors for the atoms and anom-
alous dispersion corrections were taken from the International Ta-
bles for X-ray Crystallography [29]. The data integration and
reduction were carried out with SAINT [30] software. An empirical
absorption correction was applied to the collected reflections with
SADABS [31] and the space group was determined using XPREP [32].
The structures were solved by direct methods using SHELXTL-97
[33] and refined on F2 by full-matrix least-squares using the SHEL-
XL-97 [34] program package. The H atoms were refined as follows;
the hydrogen atoms attached to carbon atoms were positioned
geometrically and treated as riding atoms using SHELXL default
parameters. The H atoms of the coordinated water molecule in
complex 3 could not be fixed using refinement with the DFIX com-
mand, while in the cases of 1, 2 and 4 the H atoms of coordinated
water molecules were located from difference Fourier maps. So,
the H-bonding parameters in complex 3 due to the coordinated
aqua hydrogen could not be located. The crystal and refinement
data are collected in Table 1.
3. Results and discussion
Complexes 1–4, once isolated, were found to be air-stable and
slightly soluble in DMF, but insoluble in other common organic sol-
vents or water. The IR spectra of 1–4 show strong absorption bands
between 1414 and 1620 cmꢁ1, attributable to coordinated carbox-
ylate groups.1 The broad peak centered in the region 3205–
3395 cmꢁ1 indicates the presence of coordinated water molecules
[35]. The sharp stretching frequency at ꢂ1667 cmꢁ1 is the signature
of the carbonyl group of lattice DMF molecules.
Fig. 1. Diaꢁg1ram showing (a) the asymmetric unit, (b) the coordination modes of the
ligand H0L and (c) the coordination modes of the M(II) ions.
Calc. C30H34N8O10Cd: C, 46.25; H, 4.39; N, 14.38. Found: C, 46.13;
H, 4.46; N, 14.27%. IR (KBr, cmꢁ1): 3395(s), 2928(w), 1667(m),
1599(s), 1464(s), 1416(s), 1385(s), 1296(w), 1165(s), 1098(m),
1073(m), 1012(m), 832(w), 810(s), 692(w).
3.1. Structural description
Single-crystal X-ray determination at 100 K reveals that com-
plexes 1–4 are isostructural. Interestingly, all the structures were
successfully solved and converged in the monoclinic space group
C2/c. Here we describe the structure 1 only. The asymmetric unit
of 1 contains one Zn(II) ion with half occupancy, one ligand unit
2.2.4. Synthesis of {[Mn(H0L)2(H2O)2 ]ꢀ2DMF}n (3)
A mixture of MnSO4ꢀH2O (0.084 g, 0.5 mmol) and HH0L (0.097 g,
0.4 mmol) was dissolved in DMF/H2O solution (6 mL, 2:1 v/v), and
the mixture was then stirred for 10 h at room temperature. The
resulting solution was filtered and allowed to cool to room temper-
1
See Supporting information.

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R. Mishra et al. / Polyhedron 54 (2013) 189–195
Fig. 2. 1D view of the coordination polymers (a) running along the crystallographic bc plane and (b) the chain propagating along the crystallographic b-axis.
H0Lꢁ1, one coordinated aqua molecule and one DMF molecule in
Table 2
Selected bond distances (Å) and bond angles (°) for 1–4.
the lattice Fig. 1(a).
The coordination mode of the ligand H0Lꢁ1 is given in Fig. 1(b).
The ligand binds the metal via the N atom of the pyridyl moiety
and a different metal through the carboxylate O atom in monoden-
tate fashion. The other carboxylate oxygen atom of the ligand re-
mains uncoordinated. In coordination polymers 1–4, each metal
ion shows a distorted octahedral MN2O4 coordination environ-
ment, Fig. 1(c), with ligation fromꢁt1wo monodentate carboxylate
oxygen atoms of independent H0L ligands, two oxygen atoms
from coordinated water molecules and two nitrogen atoms from
two independent pyridyl moieties.
Compound
Bond distances (Å)
Bond angles (°)
Complex 1
Zn1 O1 W = 2.089(3)
Zn1 N1 = 2.164(3)
Zn1 O1 = 2.127(3)
O1 W Zn1 N1 = 88.40(14)
O1 W Zn1 O1 = 87.71(12)
O1 Zn1 N1 = 85.45(11)
Complex 2
Complex 3
Complex 4
Cd1 OW1 = 2.278(3)
Cd1 N1 = 2.343(3)
Cd1 O1 = 2.291(3)
OW1 Cd1 N1 = 87.12(11)
OW1 Cd1 O1 = 85.36(9)
O1 Cd1 N1 = 91.90(10)
Mn1 OW1 = 2.175(3)
Mn1 N3 = 2.271(3)
Mn1 O1 = 2.180(3)
OW1 Mn1 N1 = 88.45(11)
OW1 Mn1 O1 = 85.86(9)
O1 Mn1 N1 = 91.89(10)
Co1 O5 = 2.088(3)
Co1 N1 = 2.148(3)
Co1 O1 = 2.114(3)
O5 Co1 N1 = 88.63(13)
O5 Co1 O1 = 87.71(12)
O1 Co1 N1 = 91.71(11)
Therefore, efficiently packed 1D ladder-like double chain coor-
dination polymers have been formed (Fig. 2a). The double-chain
frameworks consist of two one-dimensional linear chains which
extend in parallel pairs and are thus joined at the metal node in
a ladder fashion. Two ligands adopt a certain configuration to con-
nect two metal centers in such a way to form rectangular units
(Fig. 2b). In each rectangular units the Mꢀ ꢀ ꢀM distance is 11.70 Å.
It is worth noting that the alternating rectangular planes are al-
most perpendicular to each other. Moreover, both the phenyl rings
in each unit are no longer coplanar, but are twisted with a dihedral
angle of 37.22° with respect to each other. All the metal coordi-
nated N and O distances are within the normal ranges allowing
for statistical errors [36]. The salient parameters of complexes 1–
4 are summarized in Table 2.
The supramolecular frameworks are primarily stabilized by
Hꢀ ꢀ ꢀO interactions (2.529(5)–2.686(5) Å) originating from the H-
atoms of coordinated water molecules and the O atoms of the lat-
tice DMF molecules. Intramolecular H-bonding also exists between
hydroxyl-H atoms with one of the free carboxylate oxygen atoms.
Selected hydrogen bond distances (Å) and bond angles (°) in 1–4
are summarized in Table 3. Furthermore, there are CꢁHꢀ ꢀ ꢀO short
contacts between aromatic CꢁH groups of H0Lꢁ1 units with the O
Table 3
Selected hydrogen bond distances (Å) and bond angles (°) in 1–4.
Compound Donor–Hꢀ ꢀ ꢀacceptor D–H Hꢀ ꢀ ꢀA Dꢀ ꢀ ꢀA
D– Hꢀ ꢀ ꢀA
Complex 1 O1W–H1Wꢀ ꢀ ꢀO4
O1W–H2Wꢀ ꢀ ꢀO2
0.62 (5) 2.09 (5) 2.686(5) 161
0.88 (8) 1.85 (8) 2.676(5) 155
O3–H1W1ꢀ ꢀ ꢀO2
0.82
1.80 (3) 2.533(5) 148
Complex 2 O1W–H1W1ꢀ ꢀ ꢀO2
O1W–H2W1ꢀ ꢀ ꢀO3
0.93 (4) 1.88 (4) 2.686(5) 143
0.96 (4) 1.82 (5) 2.674(5) 147
O(4)–H(3) ꢀ ꢀ ꢀO
0.82
1.81 (2) 2.537 (3) 147
Complex 3 O(3)–H(3) ꢀ ꢀ ꢀO
0.82
1.80 (4) 2.529(5) 148
Complex 4 O(5)–H1W1ꢀ ꢀ ꢀO
O(5)–H2W1ꢀ ꢀ ꢀO
0.86 (8) 1.84 (8) 2.672(5) 162
0.6 6(6) 2.07 (6) 2.693(5) 157
O(3)–H(3) ꢀ ꢀ ꢀO
0.82
1.80 (3) 2.537(5) 148
Symmetry transformation used to generate equivalent atoms: (1) 1/2 ꢁ x, 1/2 + y, 1/
2ꢁz; 1 ꢁ x, y, 1/2ꢁz. (2) 1/2 + x, ꢁ1/2 + y, z. (3) x, 1 ꢁ y, ꢁ1/2 + z. (4) 1ꢁx, y, 1/2 ꢁ z;
1/2 ꢁ x, 1/2 + y, ꢁz.

R. Mishra et al. / Polyhedron 54 (2013) 189–195
193
Fig. 3. 3D architecture showing (a) C–Hꢀ ꢀ ꢀ
p
interactions between the H atom of the methyl group of lattice DMF and the aromatic ring of the ligand H0Lꢁ1 and (b) H-bonded
structure.
atoms of neighboring coordinated water molecules, as well as with
O atoms of the hydroxyl group of the ligand. The H atoms of the
with aromatic CꢁH groups (Fig. 3). Therefore the supramolecular
structures of 1–4 involve weak C–Hꢀ ꢀ ꢀ interactions between the
H atoms of the methyl group of lattice DMF and the aromatic ring
p
DMF molecules also show CꢁHꢀ ꢀ ꢀ
p interactions (2.860–2.870 Å)

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R. Mishra et al. / Polyhedron 54 (2013) 189–195
representative of the bulk phase. The observed differences in inten-
sity could be due to the preferred orientation of the powder sam-
ples (Supplementary information, Figs. S9–S12).
3.3. Thermogravimetric analysis (TGA)
In order to examine the thermal stabilities of complexes 1–4,
thermal analyses were carried out in a N2 atmosphere at the rate
1
of 5 °C per minute. Since all the coordination polymers are iso-
structural and have equal numbers of coordinated water and lat-
tice DMF molecules, they exhibit a similar type of weight loss
pattern in the thermograms. Complex 1 shows a weight loss of
24.65% (expected = 24.89%) within the temperature range 80–
260 °C that corresponds to the release of both coordinated water
and lattice DMF molecules. The framework is stable up to 400 °C.
Complex 2 exhibits a weight loss of 23.17% (expected = 23.39%)
within the temperature range 80–230 °C. The framework starts
to decompose beyond 350 °C. Similarly, complexes 3 and 4 shows
a weight loss of 25.11% (expected = 25.25%) within the tempera-
ture range 80–230 °C. Both frameworks are stable up to ꢂ380 °C
(see Figs. S13–S16, Supporting information).
3.4. Photoluminescence studies
Fluorescent compounds are an immense current research area
because of their diverse applications in chemical sensors, photo-
chemistry, as well as electroluminescent displays [36–38]. Metal
coordination compounds have been reported to exhibit the ability
to tune the emission wavelength as well as the intensity of the
free-organic compounds after coordination with metals. The pho-
toluminescent properties of compounds 1–4 and the metal-free li-
gand HH0L were investigated in the solid state at room
temperature. The emission spectra of complexes 1–4 and the HH0L
ligand are depicted in Fig. 5. Upon excitation at 344 nm (Support-
ing information, S17), 1–4 show an unsymmetrical emission as a
pair of bands at 438, 437, 431 and 435 nm and correspondingly
other bands at 420, 417, 414 and 419 nm, respectively. However,
the emission wavelengths at higher energy could be due to intra-
ligand interactions as the profile of the emission band is quite sim-
ilar to that of the free-ligand, while the low energy bands probably
originate from ligand-to-metal charge transfer [39]. Compared
with the ligand, complexes 1 and 2 exhibit enhanced luminescent
intensity, while 3 and 4 show the opposite behavior. Usually, upon
complexation with a metal center a degree of enhancement in pho-
toluminescent intensities are observed as the metal center effec-
tively increases the rigidity of the ligand and reduces the loss of
energy by radiation-less decay [40]. In the case of complexes 3
and 4, however, the quenching of the photoluminescent intensity
has been observed due to presence of paramagnetic metal ions
[41–44]. Therefore, the quenching of the luminescent emissions
Fig. 4. 3D architecture showing embedded DMF molecules in a space-filled model.
Fig. 5. Solid-state emission spectra at room temperature.
of the ligand H0Lꢁ1, which is further reinforced by strong non-cova-
lent H-bonding interactions involving solvent molecules, to form
an overall 3D structure (Fig. 4).
It is obvious from the descriptions that the behavior of the
ligand and the reaction conditions have not shown any significant
effects on the final architectures of the resulting complexes, hence
resulting in the formation of the isostructural polymers. In
addition, a non-symmetric ligand like HH0L does not favor high
dimensional supramolecular architectures, possibly due to its
stabilization.
in 3 and 4 could be attributed to the
r-donation coordination envi-
ronment of the Mn(II)/Co(II) ions, which result in the lowering of
the energy gaps between two energy states. The metalꢀ ꢀ ꢀmetal dis-
tances are long enough (more than 3.6 Å) to explain a cluster-cen-
tered transition caused by the metalꢀ ꢀ ꢀmetal interactions in all the
complexes.
4. Conclusion
In conclusion, we have described the construction of four new
isostructural coordination polymers at room temperature. We have
chosen an unsymmetrical azo-group containing organic ligand for
the construction of coordination polymers with different transition
metal ions. Solid-state luminescence of the complexes has been
achieved at room temperature. We are in the process of synthesizing
3.2. PXRD analysis
Powder X-ray diffraction (PXRD) patterns of complexes 1–4 are
in agreement with the simulated patterns obtained from the single
crystal X-ray data. It confirms that the crystal structures are truly

R. Mishra et al. / Polyhedron 54 (2013) 189–195
195
[16] M.D. Aleenfort, C.A. Bauer, R.K. Bhakta, R.J.T. Houk, Chem. Soc. Rev. 38 (2009)
1330.
similar type of ligands for constructing coordination polymers for
various applications.
[17] P. Harcajada, T. Chalati, C. Serre, B. Gillet, C. Sebrie, T. Baati, J.F. Eubank, D.
Heurtaux, P. Clayette, C. Kreuz, J.-S. Chang, Y.K. Hwang, V. Marsaod, P.-N.
Baries, L. Cynaber, S. Gil, G. Ferey, P. Couvereur, R. Gref, Nat. Mat. 9 (2010) 172.
[18] H. Chun, H. Jung, J. Seo, Inorg. Chem. 48 (2009) 2043.
[19] A.-W. Xu, C.-Y. Su, Z.-F. Zhang, Y.-P. Cai, C.-L. Chen, New. J. Chem. 25 (2001)
479.
Acknowledgements
We gratefully acknowledge Prof. P.K. Bharadwaj for providing
laboratory facilities. M.A thanks the CSIR for a SRF.
[20] H. Wang, L.-H. Huo, Z.-P. Deng, H. Zhao, S. Gao, Cryst. Eng. Comm. 14 (2012)
3501.
[21] M.-S. Liu, Q.-Y. Yu, Y.-P. Cai, C.-Y. Su, X.-M. Lin, X.-X. Zhou, J.-W. Cai, Cryst.
Growth Des. 8 (2008) 4083.
Appendix A. Supplementary data
[22] A. Aijaz, P. Lama, P.K. Bharadwaj, Inorg. Chem. 49 (2010) 5883.
[23] O. Ohmori, M. Fujita, Chem. Commun. 14 (2004) 1586.
[24] K. Koh, A.G.-F. Wong, A.J. Matzger, Angew. Chem., Int. Ed. 47 (2008) 677.
[25] P. Lama, A. Aijaz, E.C. Sañudo, P.K. Bharadwaj, Cryst. Growth Des. 10 (2010)
283.
[26] S.-S. Chen, Y. Zhao, J. Fan, T.-A. Okamura, Z.-S. Bai, Z.-H. Chen, W.-Y. Sun, Cryst.
Eng. Comm. 14 (2012) 3564.
[27] S.S. Nagarkar, A.K. Chaudhari, S.K. Ghosh, Inorg. Chem. 51 (2012) 572.
[28] T.S. Basu, S. Dhar, S.M. Pyke, E.R.T. Tiekink, E. Rivarala, R. Batcher, F.E. Smith, J.
Organomet. Chem. 633 (2001) 7.
[29] International Tables for X-Ray Crystallography, vol. III, Kynoch Press,
Birmingham, England, 1952.
[30] SAINT, version 6.02, Bruker AXS, Madison, WI, 1999.
[31] G.M. Sheldrick, SADABS, Empirical Absorption Correction Program, University of
Göttingen, Göttingen, Germany, 1997.
[32] XPREP, version 5.1, Siemens Industrial Automation Inc., Madison, WI, 1995.
[33] G.M. Sheldrick, SHELXTL Reference Manual, Version 5.1, Bruker AXS, Madison,
WI, 1997.
[34] G.M. Sheldrick, SHELXL-97: Program for Crystal Structure Refinement, University
of Göttingen, Göttingen, Germany, 1997.
[35] D. Dobrzynska, L.B. Jerzykiewicz, J. Jezierska, M. Duczmal, Cryst. Growth Des. 5
(2005) 1945.
[36] J.E. McGarrah, Y.J. Kim, M. Hissler, R. Eisenberg, Inorg. Chem. 40 (2001) 4510.
[37] Q. Wu, M. Esteghamatian, N.X. Hu, Z. Popovic, G. Enright, Y. Tao, M. D’Iorio, S.
Wang, Chem. Mater. 12 (2000) 79.
[38] M.D. Allendorf, C.A. Bauer, R.K. Bhakta, R.J.T. Houk, Chem. Soc. Rev. 38 (2009)
1330.
[39] Y. Zhou, W.X. Mingyan, A. Lan, L. Zhang, R. Feng, F. Jiang, M. Hong, Inorg. Chem.
Commun. 15 (2012) 140.
[40] S.L. Zheng, J.H. Yang, X.L. Yu, X.M. Chen, W.T. Wong, Inorg. Chem. 43 (2004)
830.
[41] H. Yersin, A. Vogler, Photochemistry and Photophysics of Coordination
Compounds, Springer, Berlin, 1987.
[42] B. Valeur, Molecular Fluorescence: Principles and Application, Wiley-VCH,
Weinheim, 2002.
[43] T.M. Muzioł, T. Lis, M. Barwiolek, E. Szlyk, Dalton Trans. 40 (2011) 11012.
[44] R. Singh, M. Ahmad, P.K. Bharadwaj, Cryst. Growth Des. 12 (2012) 5025.
CCDC 890674–890677 contains the supplementary crystallo-
graphic data for Compounds 1–4. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223 336 033; or e-mail: de-
posit@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.poly.2013.02.044.
References
[1] M.K. Sharma, I. Senkovska, S. Kaskel, P.K. Bharadwaj, Inorg. Chem. 50 (2011)
539.
[2] Z. Chang, D.-S. Zhang, T.-L. Hu, X.-H. Bu, Cryst. Growth Des. 11 (2011) 2050.
[3] H. Furukawa, N. Ko, Y.B. Go, N. Aratani, S.B. Choi, E. Choi, A.O. Yazaydin, R.Q.
Snurr, M. O’Keeffe, J. Kim, O.M. Yaghi, Science 329 (2010) 424.
[4] R. Matsuda, R. Kitaura, S. Kitagawa, Y. Kubota, R.V. Belosludov, T.C. Kobayashi,
H. Sakamoto, T. Chiba, M. Takata, Y. Kawazoe, Y. Mita, Nature 436 (2005) 238.
[5] H.-S. Choi, M.P. Suh, Angew. Chem., Int. Ed. 48 (2009) 6865.
[6] R.K. Das, A. Aijaz, M.K. Sharma, P. Lama, P.K. Bharadwaj, Chem. A – Eur. J. 18
(2012) 6866.
[7] A. Karmakar, H.M. Titi, I. Goldberg, Cryst. Growth Des. 11 (2011) 2621.
[8] L. Ma, C. Abney, W. Lin, Chem. Soc. Rev. 38 (2009) 1248.
[9] T. Kundu, S.C. Sahoo, R. Banerjee, Chem. Commun. 48 (2012) 4998.
[10] M. Ahmad, M.K. Sharma, R. Das, P. Poddar, P.K. Bharadwaj, Cryst. Growth Des.
12 (2012) 1571.
[11] H. Miyasak, M. Julve, M. Yamashita, R. Clerac, Inorg. Chem. 48 (2009) 3420.
[12] H.-L. Jiang, Q. Xu, Chem. Commun. 47 (2011) 3351.
[13] K. Yaneda, M. Ohba, T. Singa, H. Oshio, S. Kitagawa, Chem. Lett. 36 (2007) 1184.
[14] Y. Cui, Y. Yue, G. Qian, B. Chen, Chem. Rev. 112 (2012) 1126.
[15] K.E. Knope, D.T. de Lill, C.E. Rowland, P.M. Cantos, A. de Bettencourt-Dias, C.L.
Cahill, Inorg. Chem. 51 (2012) 201.