1D, 2D and 3D coordination polymers of 5,5′-methylenebis(oxy) dinicotinic acid with Co(ii), Mn(ii), Cu(ii) and Cd(ii) ions

Article abstract of DOI:10.1039/c3ce41169a

A series of new coordination polymers of the 5,5′-methylenebis(oxy) dinicotinic acid ligand with various metal ions, have been synthesized under hydro(solvo)thermal conditions and characterized by X-ray crystallography: [Co(L)(H₂O)₄]_n (1), [Cu(L)(H₂O) ₂]_n (2), two polymorphs of [Cd(L)(H₂O)] _n·(DMA)_n (3 and 4), [Co₄(L) ₄(H₂O)₃]_n·(acetonitrile) _n (5), [Mn₂(L)₂(H₂O)] _n·(acetonitrile)_n (6) and [Cd₂(L) ₂(H₂O)]_n·(DMA)_n·1/ 2;(H₂O)_n (7) (H₂L = 5,5′- methylenebis(oxy)dinicotinic acid; DMA = dimethyl acetamide) The hybrid metal-organic polymeric assemblies reveal diverse connectivity and topological features in one-, two- and three-dimensions, depending on the number of ligation sites available on the metal centers for binding the organic ligands and the nuclearity of connecting nodes. Compounds 1-4 involve mono-nuclear metal connectors and represent 1D and 2D coordination polymers. The three-dimensional single-framework polymers in compounds 5-7 are tessellated via dinuclear coordination nodes. Solid-state variable temperature magnetic susceptibility data of 5 and 6 involving the paramagnetic Co(ii) and Mn(ii) ions are reported as well. They reveal week anti-ferromagnetic coupling between the proxime metal centers observed in these two complexes.

Full text of DOI:10.1039/c3ce41169a

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1
5
D, 2D and 3D coordination polymers of
,59-methylenebis(oxy)dinicotinic acid with Co(II),
Cite this: CrystEngComm, 2013, 15,
7
257
Mn(II), Cu(II) and Cd(II) ions3
Ranjan Patra,{ Hatem M. Titi{ and Israel Goldberg*
A series of new coordination polymers of the 5,59-methylenebis(oxy)dinicotinic acid ligand with various
metal ions, have been synthesized under hydro(solvo)thermal conditions and characterized by X-ray
crystallography: [Co(L)(H
2
O)
4
]
n
(1), [Cu(L)(H
2
O)
2
]
n
(2), two polymorphs of [Cd(L)(H
?(acetonitrile) (6) and [Cd (L) (H
2
O)]
O)]
n
?(DMA)
?(DMA)
n
(3 and 4),
?1K(H O)
[
Co
4
(L)
4
(H
2
O)
3
]
n
?(acetonitrile)
n
(5), [Mn (L) (H
2
2
2
O)]
n
n
2
2
2
n
n
2
n
2
(7) (H L = 5,59-methylenebis(oxy)dinicotinic acid; DMA = dimethyl acetamide) The hybrid metal–organic
polymeric assemblies reveal diverse connectivity and topological features in one-, two- and three-
dimensions, depending on the number of ligation sites available on the metal centers for binding the
organic ligands and the nuclearity of connecting nodes. Compounds 1–4 involve mono-nuclear metal
connectors and represent 1D and 2D coordination polymers. The three-dimensional single-framework
polymers in compounds 5–7 are tessellated via dinuclear coordination nodes. Solid-state variable
temperature magnetic susceptibility data of 5 and 6 involving the paramagnetic Co(II) and Mn(II) ions are
reported as well. They reveal week anti-ferromagnetic coupling between the proxime metal centers
observed in these two complexes.
Received 18th June 2013,
Accepted 9th July 2013
DOI: 10.1039/c3ce41169a
www.rsc.org/crystengcomm
modes, and can adopt different conformations according to
the restrictions imposed by the coordination geometry and the
Introduction
During the past few decades, crystal engineering of hybrid
metal–organic coordination polymers and frameworks has
received increasing interest as a result of their fascinating
structures and topologies as well as their potential applica-
tions in various fields of gas storage, separation, catalysis, and
valency of the metal ion involved in the polymerization
7
reaction. Yet, the use of flexible ligands in the construction
of MOFs may have some advantages too, and in particular
generation of novel complexes with interesting topologies,
dynamic pores and attractive applications in sorption and
1
–4
ion exchange.
A large number of coordination polymers
8
materials storage. The flexible MOFs can change their
have already been obtained through the assembly of various
organic ligands and metal ions. However, the rational design
and controllable prediction of prospective networks and their
topology, is still a great challenge. With the development of
supramolecular chemistry and crystal engineering of metal–
organic frameworks (MOFs), it has been possible in selected
cases to design and construct novel MOFs with desired
topologies and rationally predict the final structures of the
architecture and adjust their topology to the shape and size
of the adsorbed guest.
8
Following our earlier efforts of MOF synthesis with the
relatively rigid porphyrin platform substituted with carboxy-
9
phenyl and pyridyl residues, we have also recently engaged in a
parallel avenue of crystal engineering investigations with more
flexible multi-dentate (e.g., tri- and tetra-carboxylate) scaf-
10
folds. In order to increase the odds for formulating coordina-
5
product. However, this predictive ability is mainly limited to
MOFs containing rigid organic ligands and polynuclear metal
ion connectors/nodes (termed also as secondary building units
tion polymers of higher dimensionality, these designs generally
involve organic moieties functionalized with multiple ligation
sites. The latter have high coordination affinity to metal ions,
and due to their pre-organized disposition on the organic
framework they are oriented in diverging directions. In this
report, we evaluate the self-assembly of various transition
metals with a newly synthesized flexible ligand 5,59-methylene-
–
SBUs). An a priori prediction of the products with
conformationally flexible ligands is considerably more com-
6
plex. Such organic linkers may have variable coordination
School of Chemistry, Sackler Faculty of Exact Sciences, Tel-Aviv University, Ramat-
Aviv, 69978 Tel-Aviv, Israel. E-mail: goldberg@post.tau.ac.il
2
bis(oxy)dinicotinic acid (H L, Scheme 1). It has a conforma-
tionally flexible central backbone, and four peripherally
positioned binding sites oriented laterally in different direc-
tions. The tetrahedral geometry around the central methylene
3
CCDC 943726–943732. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c3ce41169a
R. Patra and H. M. Titi contributed equally to this paper.
{
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solid product H
2
L was filtered and washed with water until
2
1
free from acid. Yield: 62%. FT-IR (KBr, cm ): 3286 (br, cO–H),
987 (mb, cC–H), 1602 (s, cCLO asymmetric), 1542 (s, cCLC), 1360
m, cCLO symmetric), 1269 (s, cC–O), 1034 (w), 1024 (s), 907 (w),
2
(
1
776 (s), 721 (w), 594 (m); H-NMR (DMSO-d6): 8.80 (2H, s), 8.76
(2H, s), 7.82 (2H, s), 5.88 (2H, s).
Synthesis of compound 1
3 2 2
A mixture of H L (5.8 mg, 0.02 mmol) and Co(NO ) ?6H O (5.8
2
mg, 0.02 mmol) in 6 mL of DMA : water (1 : 1) was heated in a
bath-reactor for 24 h at 100 uC. Pink crystals were obtained
after cooling to room temperature, separating by filtration,
washing with water and DMA, and then drying in air. The yield
was approximately 51% based on metal salt. FT-IR (KBr,
2
Scheme 1 (a) Molecular formula of 5,59-methylenebis(oxy)dinicotinic acid (H L).
(
b) Typical pseudo-V shape of the dicarboxylate ligand in the analyzed
21
cm ): 3193 (br, cO–H), 1608 (s, cCLO asymmetric), 1372 (s,
structures, which can be characterized by the dihedral angle d between the
cCLC), 1304 (m, cCLO symmetric), 1268 (s, cC–O), 1142, 1047, 792,
…
… …
O N torsion angle t.
two aromatic rings ‘a’ and ‘b’, as well as by the N
O
688, 600.
Synthesis of compound 2
A mixture of Cu(NO ?2KH
5.8 mg, 0.02 mmol) was dissolved in 8 ml of DMA : water
1 : 1). Then, 0.5 ml of 12(N) HNO was added. The mixture
C-atom imparts a pseudo V-shape of C symmetry to this ligand
2
3
)
2
2 2
O (4.6 mg, 0.02 mmol) and H L
(with opposing orientations of the functionalized aryl groups).
(
(
The two carboxylic acid groups can be readily de-protonated in
basic environments into the corresponding di-anionic form (L),
which favors 1 : 1 coordination stoichiometry with divalent
cations. Seven new coordination network materials have been
successfully synthesized and structurally characterized to this
3
was heated for 48 h in a bath-reactor at 80 uC, and after cooling
to room temperature green crystals were obtained, separated
by filtration, washed with water and DMA, and then dried in
2
1
air. The yield was 52% based on metal salt. FT-IR (KBr, cm ):
3193 (br, cO–H), 1568 (s, cCLO asymmetric), 1453 (s, cCLC), 1372
(m, cCLO symmetric), 1272 (s, cC–O), 1166, 1009, 788, 600, 498.
end: [Co(L)(H
2
O)
Cd(L)(H O)] ?(DMF) (3 and 4), [Co (L) (H O) ] ?(acetonitrile)
xn
4 n 2 2 n
] (1), [Cu(L)(H O) ] (2), two polymorphs of
[
(
(
2
n
n
4
4
2
3 n
2 2 2 n 2 2 2 n
5), [Mn (L) (H O)] ?(acetonitrile)xn (6) and [Cd (L) (H O)] ?
Synthesis of compound 3
DMF) ?1K(H O) (7). Crystals of 3–7 were obtained in solvated
n
2
n
2
Into a bath reactor, a mixture of H L (5.8 mg, 0.02 mmol) and
forms.
Cd(NO ?4H O (6.16 mg, 0.02 mmol) in 8 mL of DMA was
3
)
2
2
heated for 48 h at 100 uC. The resulted colorless crystals were
separated by filtration, washed with water and DMA, and then
dried in air (yield 55% based on metal salt). FT-IR (KBr, cm ):
Experimental
21
3
314 (br, cO–H), 1607 (s, cCLO asymmetric), 1557 (s, cCLC), 1387
All chemicals for the syntheses were commercially available
reagents of analytical grade and were used without further
purification. The FT-IR spectra were recorded from KBr pellets
(m, cCLO symmetric), 1269 (s, cC–O), 1164, 1001, 787, 691, 596.
Synthesis of compound 4
4 2 2
A mixture of H L (3 mg, 0.01 mmol) and Cd(ClO ) ?6H O (12
mg, 0.04 mmol) was dissolved in 4 mL of DMA : water and
heated for 48 h in a bath-reactor at temperature of 80 uC. The
resulted solution was left for slow evaporation after cooling to
room temperature. Colorless crystals were observed, separated
by filtration, washed with water, and then dried in air (yield
2
1
in the 4000–400 cm range on a Nicolet 5DX spectrometer.
The magnetic data were collected on a Quantum Design MPMS
SQUID-XL-5 magnetometer using crushed single-crystal sam-
ples. Magnetic data were corrected for the diamagnetic
2
1
1
contribution calculated from Pascal constants and a back-
ground of the sample holder.
2
1
4
1
1% based on metal salt). FT-IR (KBr, cm ): 3123 (br, cO–H),
598 (s, cCLO asymmetric), 1377 (s, cCLC), 1299 (m, cCLO
Synthesis of the H
Methyl 5-hydroxy-3-pyridinecarboxylate (306 mg, 2 mmol) was
dissolved in 20 ml acetonitrile, and then anhydrous K CO was
2
L ligand
symmetric), 1270 (s, cC–O), 1009, 792, 690, 598.
2
3
Synthesis of compound 5
added. The mixture was heated to reflux, after that dibromo-
methane (175 mg, 1.1 mmol) was added. The whole reaction
mixture was refluxed for 3 h. Then, the solvent was removed
and water was added to yield a white solid. (Yield 272 mg,
2
Pink crystals were obtained by heating a mixture of H L (5.8
mg, 0.02 mmol) and Co(NO ) ?6H O (5.8 mg, 0.02 mmol) in 8
3 2 2
mL of acetonitrile : water (1 : 1) for 24 h in a bath-reactor at
temperature of 100 uC. These crystals were separated by
filtration, washed with acetonitrile and water, and then dried
in air. The yield was approximately 51% based on metal salt.
FT-IR (KBr, cm ): 3153 (br, cO–H), 1598 (s, cCLO asymmetric),
1377 (s, cCLC), 1299 (m, cCLO symmetric), 1268 (s, cC–O), 1009,
792, 690, 598.
85%.) The second step was to dissolve the isolated ester (636
mg, 2 mmol) and NaOH (240 mg, 6 mmol) in 10 mL of
ethanol : water (4 : 1). The reaction mixture was refluxed for 4
h at 80 uC, after which the solvent was removed under reduced
pressure, 10 mL of water was added to it, and the solution was
acidified (pH = 2) with dilute HCl solution. The obtained white
2
1
7
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Synthesis of compound 6
The crystallographic and experimental data for 1–7 are given
in Table 1. The corresponding CCDC deposition numbers of
A mixture of H L (5.8 mg, 0.02 mmol) and MnClO ?4H O (5.2
2
4
2
the seven structures are: 943726–943732.
3
mg, 0.02 mmol) was dissolved in 8 mL of acetonitrile : water
1 : 1). Colorless crystals were obtained after heating the
(
mixture for 24 h in a bath-reactor at 120 uC. The mixture was
allowed to cool to room temperature and the resulted crystals
were separated by filtration, washed with water, and then
dried in air. The yield was approximately 49% based on metal
salt. FT-IR (KBr, cm ): 3103 (br, cO–H), 1619 (s, cCLO
asymmetric), 1573 (s, cCLC), 1385 (m, cCLO symmetric), 1267
Results and discussion
This work is part of a series of investigations aimed to explore
the coordination patterns of differently functionalized multi-
dentate new ligands (with a combination of pyridyl and
carboxylate-type substituents) towards transition metal ions,
and to identify the most promising compounds for possible
2
1
(s, cC–O), 1144, 1013, 899, 778, 682, 597.
1
0
Synthesis of compound 7
practical applications. In the present case, the title ligand
contains two pyridyl and two carboxylate sites (in the form of
two isonicotinic acid residues) for metal binding, and
correspondingly all the syntheses of the metal–organic
materials were carried out with divalent transition metal ions
which favor octahedral coordination environment, and 1 : 1
stoichiometry. The constitution and topology of the resulting
polymeric aggregates appear to be affected by three main
features: the adapted conformation of the flexible ligand, the
degree of exploitation of its coordination potential toward the
metal ions and the nuclearity of the metallic nodes. Thus, the
nature of the products is associated e.g., with the extent to
which the water molecules in the coordination shell of the
metal ion reagents are replaced by the carboxylate and pyridyl
sites of the organic species during the preparative procedures.
The geometry of the organic partner can be adjusted during
the polymerization reaction primarily by the little-restricted
A mixture of H L (5.8 mg, 0.02 mmol) and Cd(NO ) ?4H O
2
3 2
2
(6.16 mg, 0.02 mmol) was dissolved in 8 mL of DMA : H
2
O
mixture (1 : 1). The mixture was heated for 48 h in a bath-
reactor at temperature of 100 uC. Colorless crystals were
obtained after cooling to room temperature separated by
filtration, washed with water and DMA, and then dried in air
2
1
(
3
(
the yield was 55% based on metal salt). FT-IR (KBr, cm ):
057 (br, cO–H), 1608 (s, cCLO asymmetric), 1548 (s, cCLC), 1391
m, cCLO symmetric), 1271 (s, cC–O), 1161, 1126, 1050, 994, 815,
787, 691, 594.
The IR spectral data of compounds 1–7 show broad
2
1
absorption at 3100–3400 cm which indicates the presence
of coordinated water molecules. The strong band at 1360–1650
2
1
cm
of all compounds is characteristic of the carbonyl
21
groups. The absorption at 1269 cm is attributed to the C–O–C
stretching vibration of Cphenyl–O–C groups. In the 490–420 cm
21
range there are some medium and weak bands that could be
rotations about the saturated CH –O and Cphenyl–O bonds on
2
assigned to the c(M–O) stretching vibrations.
the central part of the molecule. The terminal carboxylate
functions are usually coplanar (or nearly coplanar) with
respect to the adjacent aryl residues they are bound to in
order to optimize p-electron delocalization. Compounds 1–4
which involve mono-nuclear nodes reveal either one-dimen-
sional or two-dimensional coordination polymers. The frame-
work solids 5–7 are characterized by di-nuclear metal-ion
connectors and represent three-dimensional single-framework
materials.
The crystal structure of 1 provides an exception to the
characteristics of the other compounds studied here. In this
product only two water molecules (out of six) were replaced in
the coordination sphere of the Co-ion by the organic linker,
while in the other compounds (2–7) at least four L ligands and
only one or two molecules of water occupy the coordination
sites around every metal center. As a result, only a one-
dimensional coordination polymer was formed in 1, where
every ligand (located on a twofold rotation axis) coordinates
through its two pyridyl sites to two different metal centers
Crystal structure determinations
The X-ray measurements [Bruker-ApexDuo diffractometer, Mo
Ka Im micro-focus X-ray source) were carried out at ca. 110(2) K
on crystals coated with a thin layer of amorphous oil to
minimize crystal deterioration, possible structural disorder
and related thermal motion effects, and to optimize the
precision of the structural results. These structures were
solved by direct methods and refined by full-matrix least-
1
2,13
squares (SIR-97, SHELXS and SHELXL-97).
All non-hydro-
gen atoms were refined anisotropically. The hydrogen atoms
were located in idealized/calculated positions and were refined
using a riding model; some of those involved in hydrogen
bonds were located directly in difference-Fourier maps but
were not refined. Compounds 3–7 were found to contain
crystallization solvent (DMA, acetonitrile and water) within the
intra-lattice voids. The solvent species could be clearly
recognized in difference electron-density maps, and modeled
reliably in 3, 4 and 7. The acetonitrile solvent could be partly
located in 5 but not in 6. The contribution of the disordered
solvent species in these two structures was subtracted from the
diffraction pattern by the SQUEEZE procedure and PLATON
2 4 2
(Fig. 1). The cobalt ion has an [Co(H O) (Npyridyl) ] octahedral
coordination environment with four water molecules bound to
it in the equatorial plane (at C–O = 2.090 and 2.101(1) Å) and to
two pyridyls of different ligands at the axial sites (at C–N =
2.150(1)) Å. The coordination chains extend along the c-axis of
the crystal. The carboxylate groups are not involved in metal-
1
4
software. The uniform identity of the formed crystal lattices
in a given reaction were confirmed in each case by uniform
morphology of crystals in the bulk and repeated measure-
ments of the unit-cell dimensions from different single
crystallites.
ion coordination. Instead, they are involved in a series of
…
H
2
O OOC hydrogen bonds that inter-connect between neigh-
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nodes connecting between the organic ligands are mono-
nuclear of octahedral geometry, wherein two pyridyl and two
mono-dentate carboxylate groups occupy the equatorial sites
in the coordination sphere of the copper ion, while only the
two axial sites are taken by the water molecules
2
[
2 2 2 2
Cu(Npyridyl) (COO ) (H O) ]. The corresponding coordination
bond lengths are Cu–N = 2.009 and 2.022(2) Å, Cu–Ocarboxylate
=
Fig. 1 Parallel crystal packing of the one-dimensional polymeric arrays in 1. The
…
1.937 and 1.995(2) Å and Cu–Owater = 2.293 and 2.652(2) Å (the
longer distances to the axially disposed water ligands reflect
on the well know Jahn–Teller distortions in Cu-complexes). In
the polymeric networks every copper ions binds to four
different ligands, and every ligand coordinates in turn to four
different metal centers (Fig. 2). The organic molecules in this
structure are located on axes of twofold rotation, and are
considerably bent as it is reflected by the t torsion angles of
inter-chain H
2
O
OOC hydrogen bonds are indicated by dashed black lines.
boring polymeric arrays in the crystal (Table 2). The nearly
linear coordination pattern is associated with an unusual
flattening of the ligand backbone in order to optimize the
trans-related Co–N coordinations. The two aryl rings of a given
ligand are nearly coplanar with a dihedral angle between them
of 12.4u. They are aligned in opposite directions with respect to
the aliphatic center with an N O O N torsion angle (see
Scheme 1b) of 160.7u (Table 3).
More effective coordination polymerization occurred in the
following examples 2–7. The product of the reaction between
112.2 and 114.9u and d dihedral angles between the aryl rings
…
… …
of 69.8 and 77.5u (Scheme 1 and Table 3). Due to this ligand-
bending the two-dimensional polymeric arrays, aligned paral-
lel to the ac-plane of the crystal, have a bi-layered nature
(Fig. 2). The copper-bound water ligands are oriented roughly
perpendicular to the layered assemblies that stack in an offset
H L with hydrated copper nitrate represents the coordination
2
polymer 2 with two-dimensional connectivity features. The
Table 2 Hydrogen-bonding parameters in compounds 1–7
…
…
…
OHwater (donor D)
O/N (acceptor A)
O–H (Å)
H
A (Å)
D
A (Å)
D–H A (u)
1
OH(1)
OH(1)
OH(2)
OH(2)
O4 (K 2 x, y, 1K 2 z)
O3 (K 2 x, 1 2 y, z 2 K)
O4 (1 + x, y, z)
0.84
0.86
0.83
0.85
2.00
1.85
1.85
1.91
2.786(2)
2.708(2)
2.677(2)
2.752(2)
157
177
171
177
O3 (1 2 x, 2 2 y, 2 2 z)
2
OH(7)
OH(7)
OH(8)
OH(8)
O2 (1K 2 x, y 2 K, z)
O4
O2
0.85
0.93
0.80
0.84
2.08
1.93
1.96
1.99
2.938(4)
2.778(4)
2.754(3)
2.824(3)
179
150
167
174
O1 (1K 2 x, K 2 y, z)
3
OH(7)
OH(7)
O6 (2 2 x, 2 2 y, 2 2 z)
O8 (2 2 x, 1 2 y, 2 2 z)
0.86
0.83
1.98
1.87
2.836(3)
2.670(3)
174
164
a
4
OH(22)
OH(22)
O6 (K 2 x, 1 2 y, z 2 K)
O20 (K 2 x, 2y, z 2 K)
0.91
0.90
2.06
1.84
2.967(4)
2.747(4)
179
178
5
b
OH(3)
OH(3)
OH(15)
OH(15)
OH(24)
OH(24)
O5
O26
O20
O12
0.81
0.81
0.82
0.81
0.82
0.82
1.74
1.73
1.74
1.81
2.21
1.87
2.544(2)
2.531(2)
2.547(2)
2.587(2)
2.997(4)
2.688(3)
171
170
170
b
b
b
161c
N1
166
170
c
N6 (K 2 x, y 2 K, K 2 z)
6
b
OH(10)
OH(10)
O7 (1 2 x, 2y, 1 2 z)
O11 (2 2 x, 1 2 y, 2 2 z)
0.89
0.89
1.73
1.65
2.538(5)
2.521(5)
148
163
b
7
b
OH(14)
OH(14)
O6 (x, y, 1 + z)
O12 (2x, 1 2 y, 2 2 z)
0.86
0.96
1.73
1.60
2.567(5)
2.555(5)
168
169
b
a
b
The O8 acceptor belongs to the carbonyl group of the DMA solvent. These H-bonds are from the bridging water to the adjacent carboxylate
c
groups bound to the same dinuclear synthon. The N1 and N6 acceptors in 5 belong to the acetonitrile solvent.
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…
… …
O N torsion angle t and the dihedral angle d between aryls a and b (Scheme 1) of the organic ligand is structures 1–7
Table 3 The N
O
1
2
3
4
5
6
7
d = 12.39(2)u
t = 160.7(1)u
d = 69.76(6), 77.49(6)u
d = 66.59(9)u
t = 112.19(8), 114.87(8)u
t = 82.89(10)u
d = 61.36(12)u
t = 85.67(14)u
d = 57.86(7), 66.19(7), 75.89(7), 77.64(7)u
d = 75.24(16), 80.15(16)u
d = 73.50(13), 75.85(15)u
t = 18.38(5), 75.17(6), 84.62(3), 53.71(7)u
t = 91.1(2), 96.5(2)u
t = 65.2(1), 160.0(2)u
manner along the b-axis, being involved in interlayer hydrogen
bonding (Table 2).
The topologies of the extended coordination polymers
obtained in this work have been analyzed with the TOPOS (v.
4
.0) software, reducing the complex structure to a simpler
1
5
node-and-linker net. In 2 the 2D coordination polymer with
monodentate binding of the carboxylates can be described as a
(1,4,6)-connected 3-nodal net having point symbol
{
0} {4 ?8 }{4 }. When the water ligands are excluded the
2
2
4
6
definition is simplified to a (4,4)-connected 2-nodal net with
Schlafli symbol {4 ?8 }{4 } (Fig. 4a). The bi-layered polymers
2
4
6
are tightly packed in an offset manner along the b-axis,
without leaving empty voids in the crystal lattice.
Compounds 3 and 4 with mono-nuclear Cd-ion connectors
represent two structural polymorphs with nearly isometric
unit-cell dimensions. They crystallize in different space
Fig. 3 A single ‘‘bi-layered’’ coordination network in 4 (the coordination pattern
in 3 is very similar). The seven-coordinate coordination synthon is shown in the
inlet. Ligand molecules in the ‘‘upper’’ layer have slightly darker C-atoms.
metal centers. The Cd–O and Cd–N coordination distances
1 1 1 1
groups, monoclinic P2 /n (3) and orthorhombic P2 2 2 (4),
2
2 2 2
characterizing the binding synthon [Cd(Npyridyl) (COO ) (H O)]
both consisting of two-dimensional hybrid metal organic
networks of the same connectivity pattern and spatial
topology. Moreover, the two structures incorporate in the
asymmetric unit one molecule of the DMA crystallization
solvent. The following discussion addresses, therefore, their
common structural features (Fig. 3).
The Cd-center in 3 and 4 is seven-coordinate, binding to each
of the two carboxylate groups of neighboring ligands in a
chelating bi-dentate mode, to the pyridyl sites of two other
organic linkers, as well as to an additional molecule of water.
Each of the organic spacer ligands links between four different
are within 2.302–2.582(2) Å in 3 and 2.303–2.532(3) Å in 4. The
V-conformation of the organic component has the following
parameters (Scheme 1 and Table 3): t = 97.1 (3) and 95.3u (4); d =
66.6 (3) and 61.4u (4). The bi-layered coordination polymers in
both structures are aligned parallel to the ab-plane of the
corresponding crystal with the metal-bound water ligands on
the upper and lower surface of the layered ensemble directed
outward. Crystal packing of the layers in a perpendicular
direction (along the c-axis in 3 as well as in 4) is associated with
hydrogen bonding from the water ligands of one layer to the
carboxylate fragments of neighboring layers above and below.
In 3 and 4 the void pockets in the ‘‘upper’’ as well as ‘‘lower’’
part of the bi-layered polymer are accommodated by molecules
Fig. 2 A single coordination ‘‘bi-layered’’ network in 2. The polymeric layers
stack efficiently in an offset manner along the b-axis, so that the filled zones of
one layer are positioned above the void zones of an adjacent layer. The
octahedral coordination synthon is shown in the inlet.
Fig. 4 Node-and-linker-type description of the 2D coordination bi-layered
networks in (a) 2 and (b) 3 and 4. The water ligands bound to the metal centers
are omitted for clarity. The organic linkers are in blue and the metal centers in
purple.
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Fig. 6 Partial view of structure 5, showing two inversion related asymmetric
units (excluding the solvent) along with some additional Npyridyl and Ocarboxylate
-
atoms connected to the Co-ions to show the complete coordination pattern
Fig. 5 The dinuclear coordination synthons in (a) 5 with two crystallographically
independent units, (b) 6 and (c) 7. Note that a bridging molecule of water is
present in all cases.
around them. The bridging and non-bridging water species around the metal
centers are marked by darkened spheres.
The four crystallographically unique ligands have slightly
different conformational features (Table 3) to optimize the
extended polymerization. All the Co–N and Co–O independent
coordination bonds are within the range 2.014–2.192(2) Å. The
polymeric framework thus formed has narrow channel voids
which propagate along the a-axis of the crystal and are
accommodated by the acetonitrile solvent. The latter is
hydrogen bonded to the non-bridging water ligand (Table 2).
The topology of this 3D coordination polymer represents a
rather complex (1,2,2,4,5,5,5,6,6,6,6)-connected 11-nodal net
having point symbol {0}{4 .6 }{4 .6 .8 }{4 .6 } {4 .6 .8 }
of the DMA solvent. The topology of the 2D network in 3 and 4
can be characterized as a (1,4,5) connected 3-nodal net with
Schlafli symbol {0}{4 .6 } . Exclusion of the water ligand from
2
4 2
the analysis simplifies the description to 4-connected uninodal
net having point symbol {4 .6 } (Fig. 4b).
2
4
Coordination polymers in 5–7 are tessellated by dinuclear
metal clusters and they represent three-dimensional frame-
works of a considerably more complex topology. The composi-
2
2 2 4 4
tion of these cluster is [M (H O)(COO ) (py) ] (M = Co/Mn/Cd),
involving a bridging water between the two nuclei, two pyridyl
functions on each metal center, two carboxylates bound in a
monodentate fashion and two carboxylates that bridge between
3
3
4
4
2
4
6 2
5
3
2
{
4
6
.6
it is reduced to a (2,2,4,5,5,5,5,6,6,6)-connected 10-nodal net
having point symbol {4 .6 }{4 .6 .8 }{4 .6 {4 .6 .8 }{4 .6 .8
.6 .8 }{4}
The coordination polymers in 6 and 7 are characterized by a
more uniform topology, containing only a single type of the
5 4 2 6 6 3 2
.8 } {4 .6 .8 }{4} . Without the non-bridging water ligand
2
1
1
the two nuclei in a m -g -g -bridging mode (Fig. 5). In structure
the asymmetric unit contains a second dinuclear connector,
in which one of the four pyridyl groups is replaced by a water
3
3
4
4
2
4
6
}
2
5
3
2
6
5
4 2
}
5
{
4
6
6
3
2
.
2
2 2 4 3 2
ligand [[Co (H O)bridging(COO ) (py) (H O)]; the asymmetric
unit in 5 thus consists of (excluding the acetonitrile solvent)
four metal ions, four ligand moieties and either one or two
molecules of water. All the Co, Mn and Cd centers in 5–7 are six-
coordinate to a pseudo-octahedral environment of the sur-
rounding ligating sites.
2
2 2 4 4
connecting SBU9s [M (H O)(COO ) (py) ] (Fig. 5b and c). They
represent a (2,4,6,6)-connected 4-nodal net having point
Presence of dinuclear instead of mononuclear metal
connectors (in particular in the case of small ions) increases
the odds of obtaining coordination frameworks of three-
dimensional connectivity. Evidently, this is associated with
higher coordination numbers and larger volume of the
dinuclear SBUs. Thus, while in compounds 1–4 only up to
four of the L-ligands could bind to the mononuclear centers,
in 5–7, the coordination sphere of the {M–(H O)–M} con-
2
nectors was found to accommodate either seven or eight (after
optimal replacement of the water shell around the hydrated
metal ions in the inorganic reagents) ligating sites of the
organic spacer units oriented in three dimensions. Fig. 6
shows a fragment of structure 5, depicting the connectivity
features around metal connectors.
Fig. 7 Node-and-linker-type description of the 3D coordination bi-layered
networks in 7 (the same connectivity scheme is observed in 6). The bent organic
linkers are in blue, the metal centers in purple, and the bridging water in red.
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Fig. 10 Plots of the temperature dependence of X
compound 6.
M M M
T and X and 1/X for
Fig. 8 Crystal structures of the 3D coordination frameworks in (a) 6 and (b) 7.
The metal ions are depicted by small spheres (Mn – violet, Cd – yellow). The
crystallization solvent in 6 and 7 has been omitted for clarity. Note the V-shape
of the organic ligand, as well as its tetradentate coordination to four different
metal ion connectors.
4
octahedral Co(II) ion with a
temperature.
T
1g ground state at high
T value
1
6,17
With decreasing temperature, the X
decreases smoothly to a value of 6.54 cm K mol at 50 K,
then reaches a minimum of 2.51 cm K mol at 4 K. The XM
M
3
21
3
21
21
vs. T plot gives a straight line, indicating a paramagnetic
behavior of the complex. Fitting of data obeys the Curie–Weiss
3
21
symbol {4 .6 }{4 .6 .8 } {4 .6 .8 }{4} (Fig. 7). The water-
law resulting in the Curie constant C = 2.12 cm K mol and
Weiss constant h = 236.5 K. The negative Weiss constant value
indicates the presence of anti-ferromagnetic coupling between
the Co(II) ions, although the spin–orbit coupling and
anisotropy can also contribute to this value. The anti-
ferromagnetic interactions between the Co(II) ions is via the
3
3
7
5
3 2
7
6
2
bridged dinuclear nodes connect to eight different ligand
spacers, each of which is bound in turn to four different SBUs.
Although the coordination polymers in 6 and 7 exhibit the
same networking and topology, they crystallize differently.
Structure 6 has triclinic space symmetry, while structure 7 is
characterized by a monoclinic symmetry; both contain crystal-
lization solvent trapped in the crystal lattice. This variation is
associated with slightly different conformational twist of the
V-shaped organic ligand in the two structures (Table 3),
reflecting on its ability to adjust the conformation and
optimize its metal-coordination in different reaction condi-
tions. The twelve coordination bonds within the SBUs are also
rather uniform. In 6 they are within Mn–O = 2.163–2.211(4) Å
and Mn–N = 2.230–2.325(4) Å, while in 7 they are slightly
longer within Cd–O = 2.274–2.317(4) Å and Cd–N = 2.324–
1
0,18
Co/O–C–O(carboxylate)/Co and Co–O(oxo)–Co pathways.
…
Although the Co Co distances in the SBUs are rather short
(3.558 and 3.612 Å) there is no ferromagnetic interactions
observed between these metal centers. Weak ferromagnetic
interactions have been reported in the literature for cases with
1
9
smaller Co–O–Co angle within 96–99u.
The magnetic susceptibility of compound 6 was measured
in the temperature range of 5–300 K under a 1000 Oe field. The
plots of X T and X as well as XM vs. T are shown in Fig. 10.
The experimental X T value at 300 K is about 7.62 cm
mol , slightly lower than the spin-only value of 8.76 cm K
mol for two magnetically isolated high-spin Mn(II) ions with
With decreasing
temperature, the X T value decreases smoothly to a value of
2
1
M
M
3
K
M
2
1
3
2.354(4) Å. The two crystal structures are illustrated in Fig. 8.
2
1
The proximity of the metal ions within the SBUs prompted
1
6,17
us to study the magnetic properties of 5 and 6. The plots of the
magnetic susceptibilities X , 1/X and X T vs. T in 5 are
shown in Fig. 9. The measured X T value at 300 K is 8.17 cm
spin value 5/2 and Land ´e g value of 2.
M
M
M
M
3
3
21
M
5.29 cm K mol at 50 K, then reaches a minimum of 2.52
2
1
3
3
21
K mol , which is higher than the spin-only value of 7.5 cm K
cm K mol
at 5 K. The inverse susceptibility plot as a
function of temperature (Fig. 10) is linear above 50 K,
following the Curie–Weiss law, resulting in the Curie constant
2
1
mol for four isolated Co(II) ions, with spin value 3/2 and
Land ´e g value of 2. This result is consistent with the well-
documented orbital angular momentum contribution of the
3
21
C = 2.64 cm K mol and Weiss constant, h = 248.5 K. The
high negative Weiss constant suggests that there exists
predominantly anti-ferromagnetic interaction between two
…
= 3.676 Å) via the Mn/O–C–
Mn center (at Mn Mn
O(carboxylate)/Mn and Mn–O(water)–Mn pathways as
1
0,18,20
observed previously in a similar context.
Concluding remarks
This study reveals the coordination patterns of the title
multidentate organic spacer ligand (in its dicarboxylate form)
with a series of transition metal ions. The newly synthesized
ligand has four diverging sites (two carboxylate and two pyridyl
21
Fig. 9 Plots of the temperature dependence of X
compound 5.
M
, X
M
M
and X T for
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functions) readily available for metal coordination, a bent
flexible conformation, and high affinity for coordination
polymerization with transition metals. The inorganic reagents
used in the polymerization reactions involved compounds
with hydrated metal ions of oxo- as well as aza-philic nature,
the water ligands competing with the carboxylate and pyridyl
groups for the coordination sited on the metal ions. Partial
substitution of the water by the organic ligands effects
coordination polymers of low dimensionality as in 1–4. The
nuclearity of the inorganic connecting nodes is another
feature with a major impact on the dimensionality of the
hybrid polymeric network that forms. Optimal exchange of the
water ligands and dinuclear clustering of the metal ions in a
given connecting node, provides a larger and multi-valent
coordination sphere around the metal clusters and promotes
the formation of three-dimensional coordination polymers in
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2
1
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Acknowledgements
This research was supported by The Israel Science Foundation
(Grant No. 108/12).
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