Four novel coordination polymers of transition metals built using a semi rigid oxygen donor ligand: Crystal structures, novel topology and emission studies

Article abstract of DOI:10.1016/j.poly.2012.10.045

Four new coordination polymers namely, [Cd₃(L₁) ₂(DMA)₄]_n (1), [Mn(HL₁)(H ₂O)₃]_n (2), [Mn(H₂L ₂)]_n (3) and {[Co₂(HL₂)(L ₂)]·(Et₄N)·(1.5H₂O)}_n (4) have been synthesized with semi-rigid ether bridged tricarboxylic acid ligands H₃L₁ and H₃L₂ [H ₃L₁ = 5-(4-carboxy-phenoxy)-isophthalic acid and H ₃L₂ = 5-(2-carboxy-phenoxy)-isophthalic acid] with various transition metal ions using hydro(solvo)thermal techniques. All the coordination polymers have been structurally characterized by IR spectroscopy, elemental analysis, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and X-ray single crystallography. Single crystal X-ray studies show that these coordination polymers contain homometallic clusters varying from dimeric to trimeric units except 2 which is a linear monomeric. On reacting para-isomer of the ligand H₃L₁ with metal ions, 2D and 3D supramolecular structures have been obtained while with the ortho-isomer H ₃L₂ dimeric 2D and 3D framework were obtained. Topological analysis reveals that 1 and 3 are binodal (3,6)-connected kgd net, 2 is also a binodal (3,3)-connected honey-comb type hcb net, while 4 shows unprecedented (3,3,6)-connected pkb5 topological trinodal-network. Interestingly, 3 and 4 exhibits unusual coordination modes involving one of carbonyl O atom of an acid functional group. Moreover, in 4 ethereal O atom is also coordinated to one of the metal center. All complexes show high thermal stability, thus losing coordinated and lattice solvent molecules in the range, ～100-200 °C. Upon excitation at 325 nm, compounds 1-4 exhibit solid-state luminescences at room temperature.

Full text of DOI:10.1016/j.poly.2012.10.045

Polyhedron 50 (2013) 169–178
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Four novel coordination polymers of transition metals built using a semi rigid
oxygen donor ligand: Crystal structures, novel topology and emission studies
c
Rupali Mishra a, Musheer Ahmad b, Madhav Ram Tripathi a, , Ray J. Butcher
⇑
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
c Department of Chemistry, Howard University, Washington, DC 20059, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Four new coordination polymers namely, [Cd3(L1)2(DMA)4]n (1), [Mn(HL1)(H2O)3]n (2), [Mn(H2L2)]n (3)
and {[Co2(HL2)(L2)]ꢀ(Et4N)ꢀ(1.5H2O)}n (4) have been synthesized with semi-rigid ether bridged tricarbox-
ylic acid ligands H3L1 and H3L2 [H3L1 = 5-(4-carboxy-phenoxy)-isophthalic acid and H3L2 = 5-(2-carboxy-
phenoxy)-isophthalic acid] with various transition metal ions using hydro(solvo)thermal techniques. All
the coordination polymers have been structurally characterized by IR spectroscopy, elemental analysis,
powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and X-ray single crystallography. Sin-
gle crystal X-ray studies show that these coordination polymers contain homometallic clusters varying
from dimeric to trimeric units except 2 which is a linear monomeric. On reacting para-isomer of the
ligand H3L1 with metal ions, 2D and 3D supramolecular structures have been obtained while with the
ortho-isomer H3L2 dimeric 2D and 3D framework were obtained. Topological analysis reveals that 1
and 3 are binodal (3,6)-connected kgd net, 2 is also a binodal (3,3)-connected honey-comb type hcb
net, while 4 shows unprecedented (3,3,6)-connected pkb5 topological trinodal-network. Interestingly,
3 and 4 exhibits unusual coordination modes involving one of carbonyl O atom of an acid functional
group. Moreover, in 4 ethereal O atom is also coordinated to one of the metal center. All complexes show
high thermal stability, thus losing coordinated and lattice solvent molecules in the range, ꢁ100–200 °C.
Upon excitation at 325 nm, compounds 1–4 exhibit solid-state luminescences at room temperature.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 17 September 2012
Accepted 19 October 2012
Available online 15 November 2012
Keywords:
Coordination polymer
Transition metal ions
Crystal structure
Homometallic clusters
Thermogravimetric analyses (TGA)
Photoluminescence studies
1. Introduction
donors, depending on the number of deprotonated carboxylic
groups to assemble supramolecular structures [18–21]. Carboxyl-
Coordination polymers (CPs) have been a subject of immense
current interest in research activities in many laboratories due to
their diverse properties and highly tunable construction. CPs are
potential candidates for investigating numerous uses including
gas adsorption [1–3], molecular sieves [4,5], ion exchange [6,7],
heterogeneous catalysis [8,9], host–guest induced separation
[10,11] magnetic materials [12–14], luminescence materials [15–
17] and so on. The design possibilities of CPs depends upon the or-
ganic connector and the coordination tendencies of metal ions
which gives rise to an innumerable number of coordination poly-
meric structures quite often endowed with novel structural fea-
tures as well as the intriguing nature of molecular connectivities
and topologies.
ate groups can take part in coordination as bridging ligands, and
they usually have the tendency to form metal–carboxylate clusters,
such as dinuclear, trinuclear, and even higher nuclear clusters.
Having various bridging modes between metal ions, the carboxyl-
ate group has been widely used in the synthesis of CPs [22–28].
The high thermal stability of polycaboxylate complexes enables re-
moval of solvent molecules from the lattice without destruction of
the original framework [29,30]. A vast majority of CPs with struc-
tural variations are known with both transition metal ions and car-
boxylate donor ligands connected to rigid aromatic groups.
Recently, non-rigid ligands are usually the typical building reac-
tants in the multidimensional networks. The conformational free-
dom nature of the flexible ligand may provide more possibility
for the construction of unusual topologies and structures [31].
Herein, we report the synthesis and crystal structural studies of
four coordination polymers, [Cd3(L1)2(DMA)4]n (1), [Mn(HL1)
(H2O)3]n (2), [Mn(H2L2)]n (3) and {[Co2(HL2)(L2)]ꢀ(Et4N)ꢀ(1.5H2O)}n
(4) with semi rigid ether bridged tricarboxylic acid, H3L1 and
H3L2 ligands (Scheme 1) that incorporates flexibility in the con-
struction of co-ordination polymers due to the rotation of single
A variety of multi-carboxylate ligands are often selected as mul-
tifunctional organic linkers because of their abundant coordination
modes to metal ions, allowing different type of structural topolo-
gies and because of their ability to act as H-bond acceptors and
⇑
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 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.10.045

170
R. Mishra et al. / Polyhedron 50 (2013) 169–178
(302.04): C, 59.61; H, 3.33. Found: C, 59.77; H, 3.39%. ESI-MS:
m/z (100%) 302.0429 [M]+.
2.2.2. Synthesis of 5-(2-carboxy-phenoxy)-isophthalic acid (H3L2)
The ligand was synthesized following an earlier reported [33]
procedure with slight modifications.5-Hydroxyisophthalic acid
diethyl ester (3.5 g, 14.7 mmol), dry K2CO3 (3.1 g, 22.1 mmol)
was mixed in a 50 mL round-bottomed flask under an inert atmo-
sphere and then 20 mL of dry DMF was added to it. The mixture
was stirred for 30 min at 80 °C and treated with 2-fluorobenzoni-
trile (1.8 mL, 16.6 mmol). The resulting mixture was then stirred
for 24 h in an oil-bath at 80 °C. It was then cooled to room temper-
ature and poured into ice-cold water (100 mL) whereupon a white
solid precipitated. The solid was collected by filtration and dried in
air which was further hydrolyzed by refluxing with 6(N) NaOH
solution (50 mL) for 24 h. Finally, the resultant solution was care-
fully acidified in cold condition, with drop wise addition of 6(N)
HCl to obtain a white precipitate. Keeping the flask over-night in
the freezer, the white solid was collected by filtration, washed
thoroughly with water and dried at 80 °C in vacuum. Yield: 2.9 g
(82%). This compound did not melt up to 300 °C.IR: sharp peak at
Scheme 1. Schematic representation of ligands H3L1 and H3L2.
C–O bond. Solid-state photoluminescence behaviors were achieved
at room temperature.
2. Experimental
2.1. General methods and materials
1700 cmꢂ1corresponding to mCO (str); 1H NMR (DMSO-d6),
d
The transition metal salts Cd(NO3)2ꢀ6H2O, Mn(OAc)2ꢀ4H2O,
MnCl2ꢀ4H2O, CoCl2ꢀ6H2O, 5-hydroxyisophthalic acid, 2-fluoroben-
zonitrile and 4-fluorobenzonitrile were purchased from Aldrich,
USA and used as received. All solvents, N,N0-dimethylacet-
amide(DMA), Tetra-ethyl ammonium hydroxide(TEAH), sodium
hydroxide and K2CO3 were procured from S.D. Fine Chemicals, In-
dia. All the solvents were purified prior to use following standard
methods. Infrared spectra were recorded on Perkin-Elmer Model
1320 spectrometer (KBr disk, 400–4000 cmꢂ1). 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 Premier mass spectrometer. Thermogravimetric analyses
(TGA) were recorded on 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
double UV–Vis spectrophotometer (shimadzu, UV-2450) and Jobin
Yvon Horiba Fluorolog-3 spectrofluorimeter at room temperature.
(ppm): 7.16 (d, J = 8.3 Hz, 1H); 7.33 (t, J = 7.6 Hz, 1H); 7.48 (s,
2H); 7.58–7.61 (m, 1H); 7.85 (d, J = 7.7 Hz, 1H); 8.12 (s, 1H); 13 C
NMR (DMSO-d6), d (ppm): 120.6, 122.7, 123.9, 125.4, 125.7,
131.8, 133.9, 153.6, 158.5, 166.4, 166.5. Elemental Anal. Calc. for
C15H10O7 (302.04): C, 59.61; H, 3.33. Found: C, 59.74; H, 3.21%.
ESI-MS: m/z (100%) 301.0427 [Mꢂ1].
2.2.3. Synthesis of [Cd3(L1)2(DMA)4]n (1)
A mixture containing H3L1 (0.04 g, 0.13 mmol), Cd(NO3)2ꢀ6H2O
(0.123 g, 0.4 mmol) in 3 mL N,N’-dimethylacetamide(DMA), was
sealed in a Teflon-lined autoclave and heated under autogenous
pressure to 180 °C for three days and then allowed to cool to room
temperature at the rate of 1 °C per minute. Block-shaped colorless
crystals of 1 were collected in ꢁ40% yield. The crystals were
washed with acetone and air-dried. Anal. Calc. for C46H50N4O18Cd3:
C, 43.03; H, 3.92; N, 4.36. Found: C, 42.85; H, 3.51; N, 4.08%. IR
(cmꢂ1): 3066(s), 2924(s), 1615(m), 1572(s), 1515(s), 1454(m),
1382(s), 1249(m), 1207(m),1159(m), 1017(m), 834(m), 712(s),
666 (m).
Powder X-ray diffraction (Cu K
a radiation, scan rate 3 °C/min,
293 K) was performed on a Bruker D8 Advance Series 2 powder
X-ray diffractometer.
2.2.4. Synthesis of [Mn(HL1)(H2O)3]n (2)
A mixture containing H3L1 (0.04 g, 0.13 mmol), Mn(OAc)2ꢀ4H2O
(0.13 g, 0.53 mmol) and 1 M NaOH (0.15 mL) in 3 mL water, was
sealed in a Teflon-lined autoclave and heated under autogenous
pressure to 180 °C for 3 days and then allowed to cool to room
temperature at the rate of 1 °C per minute. Block-shaped pink
crystals of 2 were collected in ꢁ65% yield. The crystals were
washed with water followed by acetone and air-dried. Anal. Calc.
for C15H14O10Mn: C, 44.03; H, 3.45. Found: C, 43.79; H, 3.11%. IR
(cmꢂ1): 3387(w, br), 3065(s), 2921(s),1616(m), 1594(m), 1536(m),
1462(m), 1392(m), 1246(m), 1211(m),1167(s), 1014(m), 976(m),
917(m), 863(m), 781(s), 718(s), 636(m).
2.2. Synthesis
2.2.1. Synthesis of 5-(4-carboxy-phenoxy)-isophthalic acid (H3L1)
The ligand was synthesized following an earlier reported [32]
procedure with slight modifications. 5-Hydroxy-isophthalic acid
diethyl ester (4 g, 16.8 mmol), dry K2CO3 (2.14 g, 24.12 mmol)
was mixed in a 50 mL round-bottom flask under an inert atmo-
sphere and then 10 mL of dry DMF was added to it. The mixture
was stirred for a while at 80 °C followed by addition of 4-fluoro-
benzonitrile (2.4 g, 18.4 mmol) and the resulting mixture was stir-
red for 24 h in an oil-bath at 80 °C. The resulting solution was
poured into ice-cold water (150 mL) whereupon a white solid pre-
cipitated that was collected by filtration and dried in air. This white
solid was hydrolysed by refluxing in aqueous ethanol containing
6(N) NaOH solution (100 mL). Finally, the resulting solution was
acidified with 6(N) HCl solution to obtain a white precipitate. After
keeping it overnight in the freezer, it was collected by filtration and
dried at 80 °C. Yield: 1.9 g (80%). This compound did not melt up to
300 °C. IR: broad peak (s) at 3555 and 3100 cmꢂ1 corresponding to
mO–H (str); sharp peak at 1722 cmꢂ1 corresponding to mCO (str);1H
NMR, d (ppm): 7.12 (d, J = 6.8 Hz, 2H); 7.70 (s, 2H); 7.95 (d,
J = 6.8 Hz, 2H); 8.24(s, 1H). Elemental Anal. Calc. for C15H10O7
2.2.5. Synthesis of [Mn(H2L2)]n (3)
A mixture containing H3L2 (0.04 g, 0.13 mmol) and MnCl2ꢀ4H2O
(0.079 g, 0.4 mmol) in 3 mL water and 0.15 mL of Et4NOH (tetra-
ethyl ammonium hydroxide) were sealed in a Teflon-lined auto-
clave and heated under autogenous pressure to 180 °C for three
days and then allowed to cool to room temperature at the rate of
1 °C min. Block-shaped crystals of 3 were collected in ꢁ51% yield.
The crystals were washed with water followed by acetone and
air-dried. Anal. Calc. for C30H18O14Mn: C, 54.98; H, 2.76. Found:
C, 54.65; H, 2.26%. IR (cmꢂ1): 3441(w, br), 3065(s), 1607(m),
1557(m), 1450(m), 1379(m), 1316(s), 1245(m), 1217(s), 1165(s),

R. Mishra et al. / Polyhedron 50 (2013) 169–178
171
1091(s), 1008(s), 973(m), 906(s), 845(s), 807(s),775(m), 752(s),
3. Results and discussion
723(m), 660(s).
The semi-rigid tripodal ligands, H3L1 and H3L2 have been de-
signed to provide rotational liberty for the aromatic carboxylate
that can facilitate bridging of transition metal ions. The coordina-
tion polymers, once isolated are found to be air-stable and also
insoluble in common organic solvents as well as in water. The IR
spectra of 1–4 show strong absorption bands between ꢁ1450
and 1627 cmꢂ1, attributable to coordinated carboxylate groups
(See Figs. S9–S12, Supporting information). The broad peak center-
ing in the region, 3205–3395 cmꢂ1 indicates [40,41] the presence
of coordinated water molecules in complex 2. A broad hump in 2
and 3 clearly, indicates the presence of free carboxylic acid groups.
2.2.6. Synthesis of {[Co2(HL2)(L2)]ꢀ(Et4N)ꢀ(1.5H2O)}n (4)
A mixture containing H3L2 (0.04 g, 0.13 mmol) and CoCl2ꢀ6H2O
(0.15 g, 0.63 mmol) in 3 mL water and 0.2 mL of Et4NOH were
sealed in a Teflon-lined autoclave and heated under autogenous
pressure to 180 °C for 3 days and then allowed to cool to room
temperature at the rate of 1 °C min. Block-shaped dark pink crys-
tals of 4 were collected in ꢁ60% yield. The crystals were washed
with water followed by acetone and air-dried. Anal. Calc. for
C
38H38Co2NO15.5: C, 52.25; H, 4.04; N, 1.60%. Found: C, 52.75; H,
4.16; N, 1.68%. IR (cmꢂ1): 3553(s), 2925(s), 1572(m), 1480(m),
1453(m), 1363(m), 1262(m), 1213(s), 1156(s), 1096(s), 1018(s),
980(m), 903(s), 850(s), 801(s), 787(m), 763(s), 728(m), 664(s).
3.1. Crystal structure of [Cd3(L1)2(DMA)4]n
1
ꢀ
Compound 1 crystallizes in the triclinic space group P1 with the
asymmetric unit consisting of two crystallographically indepen-
dent Cd(II) ions (one having full occupancy and second one with
2.3. X-ray structural studies
3ꢂ
half occupancy), one L1 ligand and two metal coordinated N,N0-
Single crystal X-ray data on complexes 1–4 were collected at
100 K on a Bruker SMART APEX CCD diffractometer using graphite
dimethylacetamide (DMA) molecules. Three carboxylate groups
of the L1
ligand bind the metal ions as l6- : : : : :
g1 g1 g1 g1 g2 g1
3ꢂ
monochromated Mo
K
a
radiation (k = 0.71073 Å). The linear
modes, both chelating and bridging fashion (Fig. 1a).
absorption coefficients, scattering factors for the atoms, and the
anomalous dispersion corrections were taken from the Interna-
tional Tables for X-ray Crystallography [34]. The data integration
and reduction were carried out with SAINT [35] software. Empirical
absorption correction was applied to the collected reflections with
SADABS [36] and the space group was determined using XPREP [37].
The structure was solved by the direct methods using SHELXTL-97
[38] and refined on F2 by full-matrix least-squares using the SHEL-
XL-97 [39], program package. The H atoms have been refined as fol-
lows; the hydrogen atoms attached to carbon atoms were
positioned geometrically and treated as riding atoms using SHELXL
default parameters. The H atoms of coordinated water molecule
in complex 2 were located from difference Fourier maps. For com-
pound 4, squeeze refinement has been performed using PLATON that
shows one and half water molecules per formula weight. The con-
tribution of both the hydrogen atoms and the oxygen atoms have
been incorporated in both the empirical formula and formula
weight in Table 1. The crystal and refinement data are collected
in Table 1.
Cd1 shows distorted octahedral CdO6 coordination from six dif-
ferent carboxylate of L1 in bridging fashion (Cd1–O = 2.224(6)–
3ꢂ
2.287(6) Å. The Cd2 has a penta-coordinated distorted trigonal
bipyramidal CdO5 coordination (Cd2–O = 2.213(6)–2.290(6) Å)
from three bridging carboxylate O and two oxygen atoms (Cd–
O = 2.262(7)–2.287(6) Å) from two N,N’-dimethylacetamide(DMA)
(Fig. 2a). One of the carboxylate O occupying the axial position
while two carboxylate O and two N,N0-dimethylacetamide oxygen
sitting on equatorial plane. The five coordinate geometry about the
Cd(II) ion is intermediate between a trigonal bipyramid (ideal
tau = 1) and a square pyramid (ideal tau = 0) with a tau factor of
0.90. Therefore, the geometry about Cd(II) center is closer to a tri-
gonal bipyramidal structure than a square based pyramid [42]. All
the Cd–O bond distances are within the range reported for octahe-
dral Cd(II) complexes [43,44].
Interestingly, complex 1 consists of linear trimetallic cluster in
which Cd1 sits on center of symmetry. The Cdꢀ ꢀ ꢀCd distance in
the trimeric unit is found to be 3.586 Å (Fig. 3b). These trimeric
units extend to 2D framework via bridging carboxylate groups of
Table 1
Crystal and Structure Refinement data for 1–4.
Compound
1
2
3
4
Formula
Formula weight
T (K)
C
46H50 Cd3N4O18
C15 H14MnO10
409.20
100(2)
C30H18MnO14
657.38
100(2)
C38H38Co2NO15.5
873.54
100(2)
1284.10
100(2)
System
Space group
a (Å)
b (Å)
c (Å)
triclinic
P1
orthorhombic
Pna21
30.823(5)
4.976(5)
10.190(5)
90.000
90.000
90.000
1562.9(18)
4
1.739
monoclinic
P21/n
16.091(3)
4.791(5)
17.296(7)
90.000
107.557(2)
90.000
1271.3(14)
2
monoclinic
P121/c
19.936(5)
10.251(4)
17.910(5)
90.00
94.734(2)
90.00
3648(2)
4
ꢀ
9.637(5)
12.038(4)
12.296(5)
110.078(7)
104.088(2)
101.488(5)
1235.3(10)
1
a
(°)
b (°)
c
(°)
V (Å3)
Z
qcalc (g cmꢂ3
)
1.726
1.357
1.717
0.603
1.543
0.982
l
(mmꢂ1
)
0.902
F (000)
642
1.180
836
1.031
670
1.080
1744
1.018
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
CCDC
r(I)]
R1 = 0.0606
wR2 = 0.1523
R1 = 0.0941
wR2 = 0.2402
896107
R1 = 0.0665
wR2 = 0.0302
R1 = 0.0695
wR2 = 0.0349
896108
R1 = 0.0404
wR2 = 0.1083
R1 = 0.0465
wR2 = 0.1128
896109
R1 = 0.0524
wR2 = 0.1312
R1 = 0.0720
wR2 = 0.1472
896110

172
R. Mishra et al. / Polyhedron 50 (2013) 169–178
Fig. 1. Diagram showing different coordination modes of ligands in 1–4.
Fig. 2. Diagram showing different coordination environment in 1–4. Symmetry Codes (a) (i) 1 ꢂ x, ꢂy, ꢂz, (ii) 1 + x, ꢂ1 + y, z; (b) (i) x, 1 + y, z (ii) ꢂx, ꢂ1 ꢂ y, ꢂ1/2 + z; (c) (i)
1 ꢂ x, 2 ꢂ y, 1 ꢂ z, (ii) 3/2 ꢂ x, 5/2 = y, 3/2 ꢂ z (d) (i) ꢂ1 + x, ꢂ1 + y, z, (ii) ꢂx, ꢂy, ꢂz,(iii) ꢂ1 + x, ꢂ0.5 ꢂ y, ꢂ0.5 + z, (iv) 1 ꢂ x, ꢂy, ꢂz, (v) 1 ꢂ x,1 ꢂ y, ꢂz.
L13ꢂ ligands (Fig. 3a). Furthermore, the intricate H-bonding leads to
an overall 3D architecture as given in Fig. 4.
shows distorted octahedral MnO6 coordination from three car-
boxylate O (Mn1–O = 2.083(2)–2.216(2) Å) from three indepen-
2ꢂ
Topology analysis of 1 using the TOPOS software [45–47] indi-
cates that it can be described as a binodal (3,6)-connected kgd
topology (Fig. 5), in which each Cd(II) ion is considered as a 6-con-
dent HL1
ligands, three O (Mn1–O = 2.185(2)–2.229(2) Å)
(Fig. 2b) from coordinated water molecules. All the Mn–O bond
distances are within the range reported for octahedral Mn(II)
complexes [48–50].
The zig-zag supramolecular framework (Fig. 6) is mainly stabi-
lized by Hꢀ ꢀ ꢀO interactions (2.529(5)–2.686(5) Å) originating from
the H-atoms of coordinated water molecules and O atom of free
carboxylic acid group. Furthermore, the weak and multipoint
3ꢂ
nected node while each L1 ligand as 3-connected linker. The
point symbol for this network is {43}2{46.66.83}.
3.1.1. Crystal structure of [Mn(HL1)(H2O)3]n
2
Compound 2 crystallizes in the orthorhombic space group
p p interactions and strong H-bonding leads to an overall 3D
ꢀ ꢀ ꢀ
Pna21 with the asymmetric unit consists of one Mn(II) ion, one
3-
architecture as given in Fig. 7. Selected hydrogen bond distances
(Å) and bond angles (°) in 2 are summarized Table S2 in Supporting
information.
L1 ligand and three coordinated water molecules. The carboxyl-
ate groups of the HL12ꢂ ligand bind the metal ions as l3 g1 g0 1:-
- : :g
g1 g0 g0 modes, in bridging fashion (Fig. 1b). Each Mn(II) ion
: :

R. Mishra et al. / Polyhedron 50 (2013) 169–178
173
Fig. 3. 3D view of the coordination polymers (a) running along crystallographic a axis, and (b) trimeric units propagating along crystallographic bc plane in 1. Symmetry
Codes (i) 2 + x, 2 + y, ꢂ1 + z, (ii) 2 ꢂ x, ꢂ1 ꢂ y, ꢂ1 ꢂ z, (iii) 1 + x, ꢂ2 + y, ꢂ1 + z, (iv) 1 ꢂ x, ꢂ1 ꢂ y, ꢂ1 ꢂ z, (v) x, ꢂ2 + y, ꢂ1 + z, (vi) ꢂx, ꢂ1 ꢂ y, ꢂ1 ꢂ z.
Fig. 4. Representation of H-bonding in 1.
ꢂ
Topologically, each Mn(II) ion is considered as a 3-connected
node while each HL1 ligand as 3-connected linker. On the basis
inversion center. The carboxylate groups of the H2L2 ligand bind
the metal ions as l3- : : : : :
g1 g0 g1 g1 g0 g0 modes, in bridging fashion
2ꢂ
of this simplification, 2 is having a 2-dimensional non-interpene-
trated (3,3)-connected hcb net (Fig. 8). The point symbol for this
network is {63}.
(Fig. 1c). Mn1 shows distorted octahedral MnO6 coordination from
ꢂ
six different carboxylate of H2L2 ligand in bridging fashion (Mn–
ꢂ
O = 2.148(2)–2.2466(16) Å (Fig. 2c). The H2L2 ligand shows unu-
sual kind of coordination mode involving one of carbonyl (–C@O)
O atom while one of the acid (–COOH) group remain free as shown
in Fig. 1c. Thꢂe linear dimeric Mn(II) unit, which is further extended
by the H2L2 ligand to give an overall 2D coordination polymer
(Fig. 9). The Mnꢀ ꢀ ꢀMn distance in the dimeric unit is found to be
3.1.2. Crystal structure of [Mn(H2L2)]n (3)
Complex 3 crystallizes in a monoclinic system with space group
P21/n. Asymmetric unit of 3 consist of one Mn(II) ion and one
ꢂ
H2L2 ligand. Mn(II) ion is situated at the crystallographic

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R. Mishra et al. / Polyhedron 50 (2013) 169–178
Fig. 7. Depiction of H-bonding interactions in 2.
the ligands. All the Mn–O bond distances are within the range re-
ported for octahedral Mn(II) complexes [48–50].
Topologically, each Mn(II) ion is considered as a 6-connected
ꢂ
node while each H2L2 ligand as 3-connected linker. On the basis
of this simplification, 3 is having a 3D non-interpenetrated (3,6)-
connected kgd net (Fig. 11). The point symbol for this network is
{43}2{46.66.83}.
Fig. 5. Topological view of (3,6)-connected kgd net in 1.
3.1.3. Crystal structure of {[Co2(HL2)(L2)]ꢀ(Et4N)ꢀ(1.5H2O)}n
4
4.791 Å. The 2D architecture further, give rise to an overall 3D
supramolecular framework (Fig. 10) involving very strong H-bond-
ing interactions between the free acidic group (Hꢀ ꢀ ꢀO = 1.844 Å) of
Complex 4 crystallizes in a monoclinic system with space group
P121/c with the asymmetric unit consists of two crystallographi-
3ꢂ
2ꢂ
cally independent Co(II) ions, one L2 ligand, one HL2 ligand,
Fig. 6. 3D view of the coordination polymers (a) running along crystallographic b axis, and (b) linear monomeric chain propagating along crystallographic a axis in 2.
Symmetry Codes (i) 1 + x, 3 + y, ꢂ1 + z; (ii) 1 + x, 4 + y, ꢂ1 + z; (iii) 1 ꢂ x, 2 ꢂ y, 3/2 + z; (iv) 1 ꢂ x, 1 ꢂ y, 3/5 + z; (v) 1 + x, 2 + y, ꢂ1 + z.

R. Mishra et al. / Polyhedron 50 (2013) 169–178
175
2ꢂ
3ꢂ
(Co1–O, 2.036(3)–2.307(3) Å from both HL2
and L2
ligands
(Fig. 2d). All the Co–O bond distances are within the range as re-
ported for cobalt based coordination polymers [51].
2ꢂ
Interestingly, in case of HL2 ligand one of carbonyl (–C@O) O
atom coordinated to the metal ions as shown in Fig. 1e. The Coꢀ ꢀ ꢀCo
distance in the dimeric unit is found to be 3.320 Å. The dimeric unit
3ꢂ
2ꢂ
in complex 4 is extended by both L2 and HL2 ligands to give a
3D supramolecular framework as depicted in Fig. 12.
Topologically, each Co(II) ion is considered as a 6-connected
2ꢂ
3ꢂ
node, while both H1L2 and L2 ligands as 3-connected linker.
On the basis of this simplification, 4 is having a 3D non-interpene-
trated unprecedented (3,3,6)-connected pkb5 net (Fig. 13). The
point symbol for this network is {4.6.8}{42.6}{43.64.88}.
3.2. Photoluminescence studies
Coordination polymers especially those with d10 transition me-
tal centers are immensely studied nowadays for photoluminescent
properties and also for its potential applications in chemical sen-
sors, photochemistry, as well as electroluminescent display [52–
54]. Metal coordination frameworks have been reported to exhibit
their high thermal stability and the ability to tune the emission
wavelength as well as intensity of the free-organic compounds
after coordination with metals. The photoluminescent behaviors
of compound 1–4 and organic ligands H3L1 and H3L2 were investi-
gated in the solid state at room temperature, and the results are
depicted in Fig. 14. Irradiation of crystalline compounds of 1–4
with ultraviolet light (kex = 325 nm) at room temperature resulted
in broad unsymmetrical emission as a pair of bands at 432, 423,
436 and 418 nm and also accompanied by other bands at 403,
391, 397 and 400 nm, respectively. The pronounced variations in
the luminescent spectra, particularly in the intensity of emission
maxima of 1–4 may be due to differences in their compositions,
crystal packing and nature of metal in clusters. However, the
Fig. 8. Topological view of (3,3)-connected hcb net in 2.
and one tetra-ethylammonium cation and one and half water mol-
ecules in lattice space. The carboxylate groups of the ligand shows
two type of coordination modes. The carboxylate groups of the
g1
:
g1
:
g1
:
3ꢂg0
:
g1
:
g0 modes,
2ꢂ
H1L2 ligand bind the metal ions as l4
-
in bridging fashion only (Fig. 1d and e) while L2 ligand, the car-
boxylate groups bind the metal ions as l6- : : : : :g
g1 g0 g1 g1 g1 2 modes,
in both bridging as well as chelating fashion. Crystallographically,
it is observed that the ethereal O atom of the ligand L23ꢂ also binds
with one of the metal ion. Co1 ion shows distorted octahedral CoO6
coordination from six carboxylate O (Co1–O, 2.007(3)–2.319(3) Å
2ꢂ
3ꢂ
from both HL2 and L2 ligands. Co2 ion also exhibits distorted
octahedral CoO6 coordination from six different carboxylate O
Fig. 9. 3D view of the coordination polymers (a) running along crystallographic b axis, and (b) dimeric cluster propagating along crystallographic a axis in 3. Symmetry Codes
(i) 3/2 ꢂ x, ꢂ1/2 + y, 3/2 – z; (ii) x, ꢂ1 + y, z; (iii) 1 ꢂ x, ꢂ2 ꢂ y, 1 ꢂ z, (iv) ꢂ1/2 + x, ꢂ3/2 ꢂ y, ꢂ1/2 + z; (v) 1 + x, ꢂ1 ꢂ y, 1 ꢂ z (vi)1 ꢂ x, ꢂy, 1 ꢂ z.

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R. Mishra et al. / Polyhedron 50 (2013) 169–178
Fig. 10. Diagram showing intricate H-bonding Interactions in 3.
presence of paramagnetic metal clusters. Moreover, in complex 2
the quenching of photolumniscent emission is very pronounced
due to presence of some coordinated aqua molecules [56].
3.3. Thermogravimetric analysis (TGA)
Thermal analyses of the complexes 1–4 were carried out in N2
atmosphere at the rate of 5 °C per minute. Complexes 1–4 exhibit
different type of weight loss pattern in thermograms (see Support-
ing information). TGA of compound 1 shows a weight loss of
ꢁ27.92% (expected = 27.8%) within the temperature range 120–
140 °C that corresponds to the loss of two coordinated DMA mole-
cules and the mass remained constant up to 420 °C beyond it starts
to decompose. On the other hand, TGA of complex 2 exhibits a
gradual weight loss of ꢁ13.20% (expected = 13.25%) within the
temperature range 100–130 °C due to loss of three coordinated
water molecules, the weight remained constant up to 400 °C. Com-
plex 3 shows no weight loss up to 410 °C and started to decompose
after this temperature. Complex 4 shows a loss of ꢁ18.00% (ex-
pected = 18.1%) due to removal of lattice molecules, and the mass
remained intact up to 410 °C. (See Figs. S13–S16, Supporting
information).
Fig. 11. Topological view of (3,6)-connected kgd net in 3.
3.4. PXRD analysis
emission at lower wavelength could be due to intra-ligand interac-
tions as the profile of the emission band is quite similar to that of
the free organic ligands, while the longer wavelength bands prob-
ably originate from ligand-to-metal charge transfer. In case of 1
and 4, possibility of cluster-centered transitions cannot be ruled
out because of the metalꢀ ꢀ ꢀmetal separation in the cluster is less
then ꢁ3.6 Å. Compared with the ligands, the complexes 1–4 exhi-
bit enhancement in luminescent intensity. Usually, upon complex-
ation with metal, enhancement in photolumniscent intensities
have been observed as the metal cluster effectively increases the
rigidity of the ligand and reduces the loss of energy by radiation-
less decay [55]. An obvious enhancement in the fluorescent inten-
sity is observed for 1, it could be attributed to the presence of d10
transition metal centers. But, in case of 2–4 the quenching of pho-
tolumniscent intensity have been observed; possibly be due to the
Powder X-ray diffraction patterns of 1–4 are in excellent agree-
ment with the simulated patterns. It exhibits that the crystal struc-
tures are truly representative of the bulk phase. The differences in
intensity could be attributed to different orientations of the pow-
der samples (Supporting information, S17–S20).
4. Conclusion
In summary, we have synthesized four different coordination
polymers of Cd(II), Mn(II) and Co(II) ions having different metal-
nuclearity using a semi-rigid bent ether-bridged tricarboxylate li-
gand under hydro(solvo)thermal conditions. The para-isomer of
the ligand give rise to two different coordination polymers with
Cd(II) and Mn(II) ions, former is a 2D linear trinuclear metal cluster

R. Mishra et al. / Polyhedron 50 (2013) 169–178
177
Fig. 12. 3D view of the coordination polymers (a) running along crystallographic b axis, (b) space fill model showing embedded TEA cation along crystallographic b axis and
(c) dimeric cluster running along crystallographic ac plane in 4. Symmetry Codes (i) x, 5/2 ꢂ y, 1/2 + z, (ii) 2 ꢂ x, 5/2 + y, 1/2 ꢂ z, (iii) x, 2 + y, z, (iv) 1 ꢂ x, 3/2 + y, 1/2 ꢂ z, (v)
2 ꢂ x, 3/2 + y, 1/2 ꢂ z, (vi) x, 3/2 ꢂ y, 1/2 + z.
Fig. 14. Solid-state emission spectra at room temperature.
Fig. 13. Topological view of (3,3,6)-connected pkb5 net in 4.
Acknowledgements
We gratefully acknowledge Prof. P.K. Bharadwaj for providing
while later is a 3D mononuclear structure. Similarly, the ortho-iso-
laboratory facilities. M.A. thanks the CSIR for SRF.
mer also give rise to two different Mn(II) and Co(II)-based supra-
molecular framework having binuclear metal clusters.
Interestingly, the complex 4 exhibits a novel trinodal pkb5 topo-
logical net while 1–3 give rise to binodal kgd and honey-comb
hcb type network. Solid-state emission studies of the complexes
1–4 have been achieved at room temperature. Such type of cluster
containing coordination polymers with transition metal and lan-
thanides ions are under investigation with this and other ditopic
pyridine-based coligands in our laboratory.
Appendix A. Supplementary material
CCDC 896107–896110 contain the supplementary crystallo-
graphic data for complexes 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:

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R. Mishra et al. / Polyhedron 50 (2013) 169–178
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