Multiple regulated assembly, crystal structures and magnetic properties of porous coordination polymers with flexible ligands

Article abstract of DOI:10.1002/ejic.200500217

Four novel coordination polymers of Ni^II and Co^II with flexible ligands, namely [Ni(oba)(bpe)] _n·_nH₂O (1), [Co(oba)-(bpe)]_n (2), [Ni₂(oba)₂(bpy)₂(H₂O) ₂]_n·nbpy (3), and [Co(oba)-(bpy) _1/2]_n (4) [H₂oba = 4,4′-oxybis(benzoic acid), bpe = 1,2-bis(4-pyridyl)ethane, bpy = 4,4′-bipyridine] were synthesised by hydrothermal reactions and characterised by single-crystal X-ray diffraction, elemental analysis and IR spectroscopy. The Ni^II ions in complex 1 are linked by flexible oba and bpe ligands to form square-grid-like corrugated sheets. These sheets are interpenetrated with each other, resulting in the formation of a 3D porous network with lattice water molecules in the channels. The variable temperature X-ray diffraction analysis shows that the framework is stable up to 300°C despite the complete removal of the lattice water molecules during the heat treatment. Complex 2 can be regarded as possessing a α-polonium-related topology. Triple interpenetration occurs to form a nonporous structure. In complex 3, the oba and bpy ligands link Ni^II ions into 1D train-like boxes. These boxes are entangled, with the aid of hydrogen bonds, leading to the formation of a 3D porous supramolecular architecture. Free bpy ligands reside in the channels. The Co^II ions in complex 4 are linked by oba and bpy ligands to form a complicated 3D coordination polymer. The lattice water molecules in complex 1 and free bpy ligands in complex 3 can be regarded as templates that play an important role in the formation of the porous structures of complexes 1 and 3. The magnetic properties of complexes 1, 2, and 4 have also been investigated. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejic.200500217

FULL PAPER
Multiple Regulated Assembly, Crystal Structures and Magnetic Properties of
Porous Coordination Polymers with Flexible Ligands
Chang-Yan Sun,[a] Xiang-Jun Zheng,[a] Song Gao,[b] Li-Cun Li,[c] and Lin-Pei Jin*[a]
Keywords: Cobalt / Coordination polymers / Magnetic properties / Nickel / Porous materials
Four novel coordination polymers of NiII and CoII with flexi-
ble ligands, namely [Ni(oba)(bpe)]n·nH2O (1), [Co(oba)-
(bpe)]n (2), [Ni2(oba)2(bpy)2(H2O)2]n·nbpy (3), and [Co(oba)-
garded as possessing a α-polonium-related topology. Triple
interpenetration occurs to form a nonporous structure. In
complex 3, the oba and bpy ligands link NiII ions into 1D
train-like boxes. These boxes are entangled, with the aid of
hydrogen bonds, leading to the formation of a 3D porous
supramolecular architecture. Free bpy ligands reside in the
channels. The CoII ions in complex 4 are linked by oba and
bpy ligands to form a complicated 3D coordination polymer.
The lattice water molecules in complex 1 and free bpy li-
gands in complex 3 can be regarded as templates that play
an important role in the formation of the porous structures of
complexes 1 and 3. The magnetic properties of complexes 1,
2, and 4 have also been investigated.
(bpy)1/2]n (4) [H2oba = 4,4Ј-oxybis(benzoic acid), bpe = 1,2-
bis(4-pyridyl)ethane, bpy = 4,4Ј-bipyridine] were synthesised
by hydrothermal reactions and characterised by single-crys-
tal X-ray diffraction, elemental analysis and IR spectroscopy.
The NiII ions in complex 1 are linked by flexible oba and bpe
ligands to form square-grid-like corrugated sheets. These
sheets are interpenetrated with each other, resulting in the
formation of a 3D porous network with lattice water mole-
cules in the channels. The variable temperature X-ray dif-
fraction analysis shows that the framework is stable up to
300 °C despite the complete removal of the lattice water
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
molecules during the heat treatment. Complex 2 can be re- Germany, 2005)
easily linked to form grid,[8] honeycomb,[9] brick-wall[10]
Introduction
and other geometries.[11] Long flexible ligands, because of
their easy interpenetration, are seldom used in the construc-
tion of porous coordination polymers, although with inge-
nious design, interpenetrated networks can give novel top-
ologies and useful properties.[12] More and more interest
has focused on long flexible ligands recently, and how to
avoid, or make use of, their interpenetration to construct
porous coordination polymers is an interesting challenge.
4,4Ј-Oxybis(benzoic acid) (H2oba) is the typical example of
a long, V-shaped, flexible ligand. As far as we know, its
coordination chemistry has been studied and several coor-
dination polymers have been obtained.[13] Of these coordi-
nation polymers, only one complex, [Zn2(oba)2(DMF)2]
·2DMF, possesses a porous structure.[13f] In this complex,
the DMF molecules act as guests, thus preventing interpen-
etrating. It is supposed that appropriate molecules may
function as guests occupying the pores and consequently
promote the formation of large pores,[14] and the introduc-
tion of ancillary ligands, such as the N-containing ligands
1,2-bis(4-pyridyl)ethane (bpe) and 4,4Ј-bipyridine (bpy),
often has a significant effect on the formation and dimen-
sion of the resulting structures. With this idea in mind, we
chose H2oba as a bridging ligand to react with the d-block
metal ions NiII and CoII. The neutral ligands bpe and bpy
were introduced into the MII/oba system, and four novel
coordination polymers, namely [Ni(oba)(bpe)]n·nH2O (1),
Porous coordination polymers are of current interest in
the fields of supramolecular chemistry and crystal engineer-
ing not only because of the intriguing variety of architec-
tures and topologies but also because of their potential ap-
plications in gas storage,[1] separation,[2] sensors[3] and catal-
ysis.[4] The most commonly used synthetic strategy is to se-
lect appropriate ligands to bridge metal ions, with the aid
of hydrogen bonds, metal–metal bonds, π-π stacking, van
der Waals and electrostatic interactions, to form the desired
extended network under mild conditions.[5] It is well-known
that the topology of porous coordination polymers depends
both on the coordination behaviour of the organic ligands
and on the selection of the coordination geometry of the
metal centres. Thus far, porous coordination polymers have
centred on the assembly of linear rigid polycarboxylates,
especially dicarboxylates,[6,7] and d-block metal ions, as
these metal ions have low coordination numbers and are
[a] Department of Chemistry, Beijing Normal University,
Beijing 100875, China
Fax: +86-10-5880-2075
E-mail: lpjin@bnu.edu.cn
[b] State Key Laboratory of Rare Earth Materials Chemistry and
Applications, College of Chemistry and Molecular Engineering,
Peking University,
Beijing, 100871, China
[c] Department of Chemistry, Nankai University,
Tianjin 300071, China
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DOI: 10.1002/ejic.200500217
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Porous Coordination Polymers with Flexible Ligands
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Scheme 1. The coordination modes of the oba ligands in complexes 1–4.
[Co(oba)(bpe)]n (2), [Ni2(oba)2(bpy)2(H2O)2]n·nbpy (3) and of two oba ligands and two nitrogen atoms of two bpe li-
[Co(oba)(bpy)1/2 n (4) were obtained. The details of their gands, as shown in Figure 1. The average Ni–N bond length
synthesis, structure and magnetic properties are reported is 2.051 Å and the Ni–O bond lengths are in the range
]
below.
2.010(2)–2.312(3) Å. The details are depicted in Table 1.
Each oba ligand adopts a bis(chelating bidentate) mode,
linking two NiII ions [see Scheme 1 (a)].
The NiII ions are linked by oba and bpe ligands into
square-grid-like corrugated sheets with grid dimensions of
about 13×13 Å2 in the bc plane, as shown in Figure 2 (a)
(based on the separation of the metal ions). It is noteworthy
that all the metal ions in the layer of complex 1 are not
coplanar, but are present in a stair-like fashion. These stair-
like layers are interpenetrated with each other, resulting in
the formation of the 3D network. Although interpen-
etration occurs in complex 1, there are still channels in the
3D network [see Figure 2 (b)], and lattice water molecules
are accommodated in the channels. Hydrogen bonds are
formed between the lattice water molecules and the carbox-
ylate groups {d[O(6)···O(2)i] = 3.005 Å (symmetry code i: x
+ 1, y, z), d[O(2)i···H(6B)] = 2.562 Å and θ[O(6)–H(6B)
Results and Discussion
Description of the Structures
The oba ligands in complexes 1–4 are completely depro-
tonated and are significantly bent at the ether-oxygen sites
[C–O–C = 115.9(3)–119.2(7)°]. They afford four kinds of
coordination modes (see Scheme 1). All bpe ligands are in
an anti conformation.
[Ni(oba)(bpe)]n·nH2O (1)
In the asymmetrical unit of complex 1, there is one NiII
ion, one oba ligand, one bpe ligand and one lattice water
molecule. The NiII ion is located in a slightly distorted octa-
hedral geometry and is coordinated to four oxygen atoms
Figure 1. The coordination environment of the NiII ion in complex 1 with 30% thermal ellipsoids. All hydrogen atoms and lattice water
molecules have been omitted for clarity.
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Table 1. Selected bond lengths [Å] and angles [°] for 1 and 2.
1[a]
Ni(1)–O(1)
Ni(1)–O(2)
Ni(1)–O(4)#1
2.169(3) Ni(1)–O(5)#1
2.073(2) Ni(1)–N(1)
2.010(2) Ni(1)–N(2)
86.89(9) N(1)–Ni(1)–O(1)
61.79(9) N(1)–Ni(1)–O(2)
107.86(9) N(1)–Ni(1)–O(5)#1
97.82(1) N(1)–Ni(1)–N(2)
158.11(1) N(2)–Ni(1)–O(1)
2.312(3)
2.050(3)
2.053(3)
96.67(1)
96.14(1)
154.26(1)
98.24(1)
150.66(1)
91.53(1)
90.47(1)
O(1)–Ni(1)–O(5)#1
O(2)–Ni(1)–O(1)
O(2)–Ni(1)–O(5)#1
O(4)#1–Ni(1)–O(1)
O(4)#1–Ni(1)–O(2)
O(4)#1–Ni(1)–O(5)#1 60.22(9) N(2)–Ni(1)–O(2)
O(4)#1–Ni(1)–N(1)
O(4)#1–Ni(1)–N(2)
94.05(1) N(2)–Ni(1)–O(5)#1
106.13(1)
2[b]
Co(1)–O(1)
Co(1)–O(2)#1
Co(1)–O(4)#3
O(1)–Co(1)–O(2)#1
O(1)–Co(1)–O(4)#3
O(1)–Co(1)–O(5)#3
O(1)–Co(1)–N(1)
O(1)–Co(1)–N(2)#2
2.020(2) Co(1)–O(5)#3
2.026(2) Co(1)–N(1)
2.170(2) Co(1)–N(2)#2
112.46(8) O(2)#1–Co(1)–N(1)
151.03(8) O(2)#1–Co(1)–N(2)#2 89.76(8)
91.35(9) N(1)–Co(1)–O(4)#3 87.64(9)
87.89(9) N(2)#2–Co(1)–O(4)#3 88.73(9)
95.52(9) N(2)#2–Co(1)–N(1) 176.34(8)
2.232(2)
2.164(3)
2.147(3)
90.17(8)
O(2)#1–Co(1)–O(4)#3 96.17(8)
[a] Symmetry transformations used to generate equivalent atoms:
#1 x, y – 1, z + 1. [b] Symmetry transformations used to generate
equivalent atoms: #1 –x + 1, –y, –z + 1; #2 x + 1, y, z + 1; #3 x
+ 1, –y + 1/2, z – 1/2.
···O(2)i] = 111.69°}, which enhances the stability of the
open framework.
[Co(oba)(bpe)]n (2)
In complex 2, one carboxylate group of an oba ligand
adopts a chelating bidentate mode while the other adopts a
bridging bidentate mode, which means that every oba li-
gand links three CoII ions [see Scheme 1 (b)]. There is only
one crystallographically unique CoII centre, which is coor-
dinated to four carboxylate oxygen atoms of three oba li-
gands and two nitrogen atoms of two bpe ligands (see Fig-
ure 3). The average Co–N bond length is 2.155 Å and the
Co–O bond lengths are in the range 2.020(2)–2.232(2) Å.
Thus, the CoII centre displays a distorted octahedral geome-
Figure 2. (a) Square-grid-like sheet of complex 1 in the bc plane.
(b) The 3D porous network of complex 1, with lattice water mole-
cules in the channels, viewed along the a axis.
a rod from each of the adjacent two nets passing through
it, giving a complicated nonporous structure.
[Ni2(oba)2(bpy)2(H2O)2]n·nbpy (3)
There are two kinds of metal coordination environments
try with one [CoO4N2] unit. Two such [CoO4N2] units are in complex 3, as shown in Figure 5. Ni(1) and Ni(2) are
connected together by two carboxylate groups, leading to both six-coordinate and their coordination geometries can
the formation of a binuclear secondary building unit (SBU) be described as distorted octahedral. Both NiII ions are co-
in which the Co···Co distance is 4.298 Å. The oba ligands ordinated to three oxygen atoms of two oba ligands, two
link the SBUs into 2D layers with rhombus-shaped cavities nitrogen atoms of two bpy ligands and one oxygen atom
of about 13×15 Å2. Although this framework motif is com- of one water molecule. However, the corresponding bond
mon, the bent oba structure provides a new aspect in the lengths and bond angles are different. The Ni(1)–O bond
cavity shape, and it has seldom been reported that this motif lengths are in the range 1.992(4)–2.143(5) Å and the average
contains concertinaed corners.[15] These layers are pillared value is 2.095 Å, while for Ni(2) the bond lengths range
by bpe ligands with a Co–N coordination bond, resulting from 2.026(4) Å to 2.195(4) Å and the average value is
in the formation of a 3D net that can be regarded as pos- 2.091 Å. The details are depicted in Table 2. In complex 3,
sessing an α-polonium-related topology [see Figure 4 (a)]. one carboxylate group of an oba ligand coordinates to a
There are large channels (13×15 Å2) in the open sub-frame- NiII ion in a monodentate mode while the other adopts a
work (named net), but triple interpenetration occurs, as chelating-bidentate mode. Thus, every oba ligand links two
shown in Figure 4 (b). The nodes of the second and third NiII ions [see Scheme 1 (c)]. Ni(1) and Ni(2) are bridged by
nets are located, equally spaced, along the rhombohedral a bpy ligand with a distance of 11.129 Å, which can be re-
diagonal of the first net, and each rhombic “window” has garded as a binuclear SBU. Such SBUs are linked together
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Porous Coordination Polymers with Flexible Ligands
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Figure 3. The coordination environment of the CoII ion in complex 2 with 30% thermal ellipsoids. All hydrogen atoms have been omitted
for clarity.
Figure 4. (a) The 3D framework of complex 2 with channels viewed along the [101] direction. (b) A simplified representation of the
interpenetrating framework of complex 2, the alternating frameworks are shown in black, red and blue.
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Figure 5. The coordination environments of the NiII ions in complex 3 with 30% thermal ellipsoids. All hydrogen atoms and free bpy
ligands have been omitted for clarity.
by the oba ligands, resulting in 1D train-like boxes that con-
tain free bpy ligands (see Figure 6). Each box is entangled
with another two adjacent boxes. There are hydrogen bonds
between the water molecules and the carboxylate groups
{d[O(6)···O(2)] = 2.669 Å, d[O(2)···H(6A)] = 2.128 Å and
θ[O(6)–H(6A)···O(2)] = 113.19°; d[O(12)···O(11)i] = 2.553 Å
(symmetry code i: x, y – 1, z), d[O(11)i···H(12B)] = 2.027 Å
and θ[O(12)–H(12B)···O(11)i] = 119.37°}, which leads to
the formation of a 3D porous supramolecular architecture.
Table 2. Selected bond lengths [Å] and angles [°] for 3 and 4.
3[a]
Ni(1)–O(1)
1.992(4)
2.054(4)
2.143(5)
2.081(5)
2.053(6)
2.137(5)
165.4(2)
Ni(2)–O(7)
Ni(2)–O(8)
2.195(4)
2.112(4)
2.026(4)
2.030(4)
2.060(5)
2.059(5)
60.77(2)
103.92(2)
164.60(2)
88.67(2)
90.83(2)
Ni(1)–O(4)#1
Ni(1)–O(5)#1
Ni(1)–O(6)
Ni(1)–N(1)
Ni(1)–N(3)
O(1)–Ni(1)–O(4)#1
O(1)–Ni(1)–O(5)#1
O(1)–Ni(1)–O(6)
O(1)–Ni(1)–N(3)
Ni(2)–O(10)#2
Ni(2)–O(12)
Ni(2)–N(2)
Ni(2)–N(4)#3
O(8)–Ni(2)–O(7)
103.88(2) O(10)#2–Ni(2)–O(7)
90.76(2)
85.10(2)
The Structure of [Co(oba)(bpy)1/2]n (4)
O(10)#2–Ni(2)–O(8)
O(10)#2–Ni(2)–O(12)
O(10)#2–Ni(2)–N(2)
The coordination environment of the CoII ions in com-
plex 4 is shown in Figure 7. The CoII ion is five-coordinate,
with four oxygen atoms from four oba ligands and one ni-
trogen atom from one bpy ligand. The coordination geome-
try of the CoII ion can best be described as a distorted tri-
angular bipyramid. The Co–N bond length is 2.084(3) Å
and the Co–O bond lengths are in the range 1.976(3)–
2.077(3) Å. Every oba ligand in complex 4 adopts a
bis(bridging-bidentate) mode and links four CoII ions [see
Scheme 1 (d)]. The CoII ions are bridged by the carboxylate
groups of oba ligands into 1D chains along the c axis, in
which the adjacent Co···Co distances are alternately
3.288 Å and 4.238 Å. These chains are further bridged by
the bent oba ligands to produce 2D regular metal-organic
layers. When viewed along the c axis, these 2D layers can
be regarded as sine- and cosine-type curves intersecting at
the zero points. The bpy ligands connect the CoII ions in
these 2D layers into a 3D structure.
O(4)#1–Ni(1)–O(5)#1 61.81(2)
O(4)#1–Ni(1)–O(6)
O(4)#1–Ni(1)–N(3)
O(6)–Ni(1)–O(5)#1
O(6)–Ni(1)–N(3)
N(1)–Ni(1)–O(4)#1
N(1)–Ni(1)–O(5)#1
N(1)–Ni(1)–O(6)
92.89(2)
92.18(2)
93.5(2)
O(10)#2–Ni(2)–N(4)#3 96.43(2)
O(12)–Ni(2)–O(7)
O(12)–Ni(2)–O(8)
88.91(2)
89.29(2)
172.71(2)
93.75(2)
84.15(2)
89.27(2)
159.54(2)
98.94(2)
93.5(2)
174.03(2) O(12)–Ni(2)–N(2)
94.8(2)
156.5(2)
89.1(2)
87.3(2)
O(12)–Ni(2)–N(4)#3
N(2)–Ni(2)–O(7)
N(2)–Ni(2)–O(8)
N(1)–Ni(1)–N(3)
N(4)#3–Ni(2)–O(7)
N(4)#3–Ni(2)–O(8)
N(4)#3–Ni(2)–N(2)
4[b]
Co(1)–O(1)
2.077(3)
2.000(3)
2.020(3)
Co(1)–O(5)#1
Co(1)–N(1)
1.976(3)
2.084(3)
Co(1)–O(2)#2
Co(1)–O(4)#3
O(1)–Co(1)–N(1)
O(2)#2–Co(1)–O(1)
O(2)#2–Co(1)–O(4)#3 141.82(2) O(5)#1–Co(1)–O(2)#2
O(2)#2–Co(1)–N(1)
O(4)#3–Co(1)–O(1)
170.89(2) O(4)#3–Co(1)–N(1)
85.31(1) O(5)#1–Co(1)–O(1)
88.85(2)
88.94(1)
112.92(2)
104.97(1)
88.15(1)
87.87(1)
O(5)#1–Co(1)–O(4)#3
100.25(1) O(5)#1–Co(1)–N(1)
[a] Symmetry transformations used to generate equivalent atoms:
#1 x, y + 1, z; #2 x, y – 1, z; #3 –x + 1, –y + 1, –z + 2. [b]
Symmetry transformations used to generate equivalent atoms: #1
–x + 2, –y + 1, –z + 2; #2 –x + 2, y, –z + 3/2; #3 x, y – 1, z.
Effect of the Metal Ions on the Molecular Structure
It is interesting that, although they are bound to the
same ligands, NiII and CoII give completely different pro-
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Porous Coordination Polymers with Flexible Ligands
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different. The oba ligands adopt a bis(chelating-bidentate)
mode in complex 1 and a chelating-bridging mode in com-
plex 2 (see parts a and b in Scheme 1), which results in the
different structures of the corresponding complexes. Similar
results are found for complexes 3 and 4. This may also be
attributed to the different size of the metal ions. Lower-
dimensional nets are usually less likely to interpenetrate be-
cause there are more possible ways to maximize the packing
efficiency.[16] So, after the stacking of 2D layers, complex 1
possesses 3D porous structure, while triple interpenetration
occurs in complex 2, as shown in Figure 6, to give a non-
porous structure. A rational assembly of metal ions and
flexible ligands is critical for the formation of a porous
structure.
Effect of the Ligand on the Molecular Structure
Although the bpe and bpy ligands are both N-containing
spacers, they are quite different. For example, bpe has anti
and gauche conformations and is more flexible than bpy.
When the bpe ligand is in the anti conformation, the dis-
tance between the two nitrogen atoms is larger than that of
the bpy ligand, therefore anti-bpe is a longer spacer than
bpy. When the bpe ligand is introduced into the MII/H2oba
system, we obtain 2D square-grid-like sheets for NiII and a
3D α-polonium-related framework for CoII, while with bpy
we obtain 1D train-like boxes for the NiII complex and a
complicated 3D framework for the CoII complex. The oba
ligands in the four complexes adopt four different coordina-
tion modes, as shown in Scheme 1, so for a special MII/
H2oba system, the ancillary ligand has a significant effect
on the formation and structure of the coordination poly-
mers. In order to construct porous coordination polymers,
it is a feasible method to introduce ancillary ligands.
Figure 6. (a) The 1D train-like box in complex 3 (space-filling dia-
grams represent free bpy ligands). (b) A simplified representation
of the 1D train-like box in complex 3 (nodes represent NiII ions
and the balls represent free bpy ligands).
ducts, as shown in Scheme 2. We found from the structural
analysis of complexes 1–4 that the two NiII complexes 1
and 3 possess a 3D open supramolecular architecture while
the two CoII complexes 2 and 4 have a 3D non-porous
structure. Taking 1 and 2 as examples, the NiII and CoII
ions are both six-coordinate and in distorted octahedral ge-
ometries, but their coordination environments are different.
In complex 1, there are two oba ligands and two bpe li-
gands around each NiII ion, while in complex 2, there are
three oba ligands and two bpe ligands around each CoII
ion. More ligands are around each CoII ion than each NiII
ion. This is consistent with the fact that the radius of CoII
ion is larger than that of NiII ion. Furthermore, the coordi-
Effect of Guest Molecules on the Molecular Structure
From the structural descriptions above, we know that lat-
nation modes of the oba ligands in the two complexes are tice water molecules are accommodated in the channels of
Figure 7. The coordination environment of the CoII ion in complex 4 with 30% thermal ellipsoids. All hydrogen atoms have been omitted
for clarity.
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Scheme 2. Self-assembly of the coordination polymers.
complex 1 and free bpy ligands reside in the channels of
complex 3. The presence of lattice water molecules and free
bpy ligands may be one of the more important factors for
constructing the porous structures of complexes 1 and 3
as they occupy the pores and function as templates, thus
preventing further interpenetration. This provides a valu-
able approach for constructing porous coordination poly-
mers. If the potential pore walls are formed by the hydro-
phobic parts of ligand molecules, we can introduce hydro-
phobic molecules to function as guest molecules and oc-
cupy the pores through hydrophobic interactions with the
ligands;[2b,14] on the other hand, if the potential pore walls
are formed by the hydrophilic parts of ligand molecules, we
can introduce hydrophilic molecules.[17] It can be expected Figure 8. The powder X-ray diffraction patterns of complex 1 at
different temperatures.
that the presence of these guest molecules promotes the for-
mation of large pores.
Magnetic Properties
Because the bridging ligands oba, bpe and bpy are quite
long in complexes 1 and 3, and thus the Ni···Ni distances
Thermal Stability Analysis of Complex 1
are very long too, the magnetic interactions transferred by
The thermal analysis of complex 1 is consistent with the
these ligands should be very weak. The magnetic properties
crystallographic observations. The TG curve shows that the
of complexes 1 and 3 can be regarded as those of a single
first weight loss of 3.7% from 75 °C to 290 °C corresponds
metal ion anisotropy. Here, we only give the magnetic prop-
to the loss of the lattice water molecules (calcd. 3.5%), leav-
erty of complex 1 as an example.
ing a framework of [Ni(oba)(bpe)]. This framework remains
stable beyond 300 °C and it begins to decompose at 390 °C.
This further decomposition finishes at 550 °C, leaving a
powder of NiO. It is the interpenetrated nature of the struc-
ture that causes the higher thermal stability of complex 1.
To further test the thermal stability of complex 1, powder
samples were examined by powder X-ray diffraction analy-
sis. Corresponding to the TG analysis, powder XRD pat-
terns were recorded at 20, 100, 300 and 450 °C (see Fig-
ure 8). It can be seen from Figure 8 that the XRD patterns
at 100 °C and 300 °C are similar to that at room tempera-
ture, but not the same, indicating that the framework is able
to survive. However, there are changes in the XRD patterns
at 20, 100, and 300 °C, which are probably due to the con-
traction of the structure upon removal of the water mole-
cules and the presence of the flexible ligands. At 450 °C, the
XRD pattern changes completely, revealing the collapse of
the framework, which is in accordance with the result of
the thermogravimetric analysis.
Complex 1
The magnetic properties of complex 1 in the form of χM
and µeff vs. T plots (χM is the molar magnetic susceptibility
and µeff is the effective magnetic moment) are shown in Fig-
ure 9. Data were collected in the range 2–300 K in a mag-
netic field of 5 kOe. The µeff value for complex 1 is 3.15 µB
at 300 K and it is practically constant in the temperature
range analysed. It only starts to decrease at around 10 K,
reaching a minimum value of 2.83 µB at 2 K, which should
be mainly attributed to the zero-field splitting of NiII ions.
The experimental susceptibility data were fitted to the
equation that considers only non-interacting S = 1 ions in
the presence of a single ion anisotropy. The magnetic
susceptibility is given in Equation (1).[18]
2Ng2β2 2x–1 – 2exp(–x)x–1 + exp(–x)
χM
=
×
(1)
3kT
1 + 2exp(–x)
4156
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Eur. J. Inorg. Chem. 2005, 4150–4159

Porous Coordination Polymers with Flexible Ligands
FULL PAPER
Figure 9. Plots of χM (᭺) and µeff (ᮀ) vs. T for complex 1; the solid lines are theoretical fits based on Equation (1).
where x = D/kT. The best fit is given by the parameters g Complex 4
= 2.23, D = 2.62 cm–1, with an agreement factor, R, of
Figure 11 shows the magnetic properties of complex 4 in
2.03×10–4 {R = ∑[(χM)obs – (χM)calc]2/∑[(χM)calc]2}.
the form of 1/χM and µeff vs. T plots in the range 2–300 K
measured at 1 kOe. It can be seen that the µeff value de-
creases very gradually upon cooling and the µeff value at
300 K is 4.71 µB, which is obviously larger than the ex-
pected spin-only value of 3.87 µB for a CoII ion with S =
3/2, thus showing an unquenched orbital contribution. The
magnetic data above 50 K can be fitted to the Curie–Weiss
law with C = 2.836(6) cm3 mol–1 K and θ = –7.3(1) K. The
C value corresponds to g = 2.46 with S = 3/2. These results
suggest a weak antiferromagnetic interaction.
Complex 2
The magnetic susceptibility data of complex 2 in the
form of 1/χM and µeff vs. T plots are given in Figure 10.
They were measured in the range 2–300 K in a magnetic
field of 1 kOe. It can be seen that the µeff value decreases
very gradually upon cooling and the µeff value at 300 K is
4.25 µB, which is larger than that expected for the spin-only
case of CoII (µeff = 3.87 µB), indicating an unquenched or-
bital contribution. The magnetic data above 30 K can be
fitted to the Curie–Weiss law with C = 2.268(5) cm3 mol–1
K
and θ = –1.8 K. The C value corresponds to g = 2.20 with
S = 3/2. These results suggest a possible very weak antifer-
romagnetic coupling.
Figure 11. Plots of 1/χm (ᮀ) and µeff (᭺) vs. T for complex 4; the
solid line is the best fit based on the Curie–Weiss law.
Conclusions
We have successfully obtained four novel coordination
Figure 10. Plots of 1/χM (ᮀ) and µeff (᭺) vs. T for complex 2; the
solid line is the theoretical fit based on the Curie–Weiss law.
polymers of NiII and CoII, namely [Ni(oba)(bpe)]n·nH2O
Eur. J. Inorg. Chem. 2005, 4150–4159
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4157

C.-Y. Sun, X.-J. Zheng, S. Gao, L.-C. Li, L.-P. Jin
FULL PAPER
Synthesis of [Co(oba)(bpe)]n (2): The synthesis of complex 2 fol-
lowed the same procedure as complex 1 except that the volume of
aqueous NaOH solution added was 0.3 mL. Yield: 0.04 g (80.1%)
C26H20CoN2O5 (499.37): calcd. C 62.48, H 4.00, N 5.61; found C
(1), [Co(oba)(bpe)]n (2), [Ni2(oba)2(bpy)2(H2O)2]n·nbpy (3)
and [Co(oba)(bpy)1/2]n (4), with different dimensionalities.
Comparing the structures of complexes 1 and 2, and com-
plexes 3 and 4, it has been found that the different size of
the metal ions has a significant effect on the formation and
dimensions of the resulting structures. Furthermore, com-
paring the structures of complexes 1 and 3, and complexes
2 and 4, we can see that the neutral ancillary ligand is very
important for the formation of coordination polymers. The
presence of guest molecules can promote the formation of
larger pores.
62.70, H 4.13, N. 5.50. IR data (KBr pellet): ν = 3445 cm–1 (m),
˜
3058 (w), 2971 (w), 2928 (w), 1616 (m), 1596 (s), 1538 (m), 1503
(m), 1417 (s), 1227 (s), 1163 (m), 1094 (w), 1049 (w), 1025 (w), 875
(m), 836 (w), 781 (m), 662 (w), 546 (w).
Synthesis of [Ni2(oba)2(bpy)2(H2O)2]n·nbpy (3): A mixture of H2oba
(0.1 mmol), NiCl2·6H2O (0.1 mmol), bpy (0.1 mmol) and 5 mL of
deionised water was placed in a Teflon-lined stainless vessel (25 ml)
and 0.2 mL of a 0.65  aqueous NaOH solution was added whilst
stirring. The vessel was then sealed and heated to 180 °C for 72 h
under autogenous pressure, and then cooled slowly to room tem-
perature. Single crystals were obtained by filtration, washed with
deionized water and ethanol, and dried in air. Yield: 0.024 g
(42.3%). C58H44N6Ni2O12 (1134.4): calcd. C 61.35, H 3.88, N 7.40;
Experimental Section
General Remarks: All reagents were used as received without fur-
ther purification. The C, H and N microanalyses were carried out
with a Vario EL elemental analyzer. The IR spectra were recorded
with a Nicolet Avatar 360 FT-IR spectrometer using the KBr pellet
technique. Thermogravimetric curves were measured on a Perkin–
Elmer TGA-7 (USA) at a heating rate of 5 °Cmin–1 from room
temperature to 600 °C under nitrogen. The magnetic susceptibilities
were obtained on crystalline samples using a Quantum Design
MPMS SQUID magnetometer. The experimental susceptibilities
were corrected for the sample holder and the diamagnetism contri-
butions estimated from Pascal’s constants. The powder X-ray dif-
fraction patterns were recorded on a Bruker AXS D8 ADVANCE
diffractometer.
found C 61.20, H 3.74, N 7.04. IR data (KBr pellet): ν = 3444 cm–1
˜
(m), 1595 (s), 1540 (m), 1496 (w), 1420 (s), 1381 (s), 1300 (w), 1248
(m), 1232 (m), 1158 (w), 875 (w), 808 (w), 784 (w), 659 (w), 635
(w).
Synthesis of [Co(oba)(bpy)1/2]n (4): The synthesis of complex 4 was
similar to that of complex 3. Yield: 0.027 g (68.7%) C19H12CoNO5
(393.23): calcd. C 57.98, H 3.05, N 3.56; found C 57.95, H 3.03, N
4.01. IR data (KBr pellet): ν = 3436 cm–1 (w), 3063 (w), 2924 (w),
˜
1594 (s), 1551 (m), 1499 (m), 1393( s), 1299 (w), 1240 (s), 1221 (m),
1159 (m), 1013 (w), 877 (m), 779 (m), 675 (w), 565 (w), 514 (w).
Synthesis of [Ni(oba)(bpe)]n·nH2O (1):
A
mixture of H2oba
X-ray Crystallographic Study: Diffraction intensities for the four
(0.1 mmol), NiCl2·6H2O (0.1 mmol), bpe (0.1 mmol) and 5 mL of complexes were collected at 293 K on a Bruker SMART 1000 CCD
deionised water was placed in a Teflon-lined stainless vessel
(25 mL) and 0.2 mL of a 0.65  aqueous NaOH solution was
added whilst stirring. The vessel was then sealed and heated to
180 °C for 72 h under autogenous pressure, and then cooled slowly
to room temperature. Single crystals were obtained by filtration,
washed with deionized water and ethanol, and dried in air. Yield:
0.042 g (81.2%) C26H22NiN2O6 (517.17): calcd. C 60.33, H 4.25, N
diffractometer employing graphite-monochromated Mo-Kα radia-
tion (λ = 0.71073 Å). A semi-empirical absorption correction was
applied using the SADABS program.[19] The structures were solved
by direct methods and refined by full-matrix least-squares on F2
using the SHELXS 97 and SHELXL 97 programs, respec-
tively.[20,21] Non-hydrogen atoms were refined anisotropically and
hydrogen atoms were placed in geometrically calculated positions.
The crystallographic data for complexes 1–4 are listed in Table 3,
and selected bond lengths and angles are listed in Tables 1 and 2.
CCDC-265220–265223 (for 1–4, respectively) contain the supple-
mentary crystallographic data for this paper. These data can be
5.41; found C 60.44, H 3.91, N 5.53. IR data (KBr pellet): ν =
˜
3449 cm–1 (m), 3063 (w), 2929 (w), 1616 (m), 1596 (s), 1534 (m),
1504 (m), 1417 (s), 1226 (m), 1165 (m), 1098 (w), 1071 (w), 1025
(w), 876 (m), 835 (w), 781 (m), 662 (w), 548 (w).
Table 3. Crystal data and structure refinement parameters for 1–4.
1
2
3
4
Chemical formula
Crystal system
Space group
Formula mass
a [Å]
b [Å]
c [Å]
C26H22N2NiO6
triclinic
P1
C26H20CoN2O5
monoclinic
P21/c
C58H44N6Ni2O12
triclinic
P1
C19H12CoNO5
monoclinic
C2/c
¯
¯
517.17
499.37
1134.41
12.375(5)
14.886(6)
15.858(7)
88.144(7)
73.229(7)
69.927(7)
2620.0(19)
2
393.23
9.254(3)
11.512(4)
12.298(4)
69.890(6)
80.995(6)
86.981(6)
1215.1(7)
2
10.466(6)
18.575(13)
12.637(7)
90
108.47(6)
90
22.376(7)
13.685(5)
12.770(4)
90
116.207(6)
90
α [°]
β [°]
γ [°]
V [Å3]
2330(2)
4
3508(2)
8
Z
F(000)
536
1.413
293(2)
1028
1.423
293(2)
1172
1.438
293(2)
1600
1.489
293(2)
Dc [mgm–3]
T [K]
θ range [°]
Goodness-of-fit on F2
Rint [I Ͼ 2σ(I)]
1.88–26.45
1.019
R1 = 0.0494
wR2 = 0.1069
2.02–26.50
1.084
R1 = 0.0415
wR2 = 0.1003
2.57–25.01
1.015
R1 = 0.0799
wR2 = 0.1812
2.03–25.01
1.000
R1 = 0.0613
wR2 = 0.1071
4158
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Eur. J. Inorg. Chem. 2005, 4150–4159

Porous Coordination Polymers with Flexible Ligands
FULL PAPER
Tong, M. L. Gong, X. M. Chen, Eur. J. Inorg. Chem. 2003,
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Published Online: September 5, 2005
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4159