Self-assembly of a series of cobalt(II) coordination polymers constructed from H2tbip and dipyridyl-based ligands

Article abstract of DOI:10.1021/ic801278j

A series of interesting Co(II)-H₂tbip coordination polymers incorporating different auxiliary ligands, {[Co(tbip)(bipy)-(H ₂O)₃] · 0.5(bipy) · H₂O) _n (1), [Co(tbip)(bipy)]_n (2), {[Co_3<

Full text of DOI:10.1021/ic801278j

Inorg. Chem. 2009, 48, 915-924
Self-Assembly of a Series of Cobalt(II) Coordination Polymers
Constructed from H2tbip and Dipyridyl-Based Ligands
Lu-Fang Ma,† Li-Ya Wang,*,† Yao-Yu Wang,‡ Stuart R. Batten,*,§ and Jian-Ge Wang†
College of Chemistry and Chemical Engineering, Luoyang Normal UniVersity,
Luoyang 471022, P. R. China, Key Laboratory of Synthetic and Natural Functional Molecule
Chemistry of Ministry of Education, Department of Chemistry, Northwest UniVersity,
Xi’an 710069, P. R. China, and School of Chemistry, Monash UniVersity, Victoria 3800, Australia
Received July 10, 2008
A series of interesting Co(II)-H2tbip coordination polymers incorporating different auxiliary ligands, {[Co(tbip)(bipy)-
(H2O)3] · 0.5(bipy) · H2O}n (1), [Co(tbip)(bipy)]n (2), {[Co3(tbip)3(dpe)3] · 0.5(dpe) · 3H2O}n (3), [Co2(tbip)2(dpe)(H2O)]n
(4), [Co2(tbip)2(bpa)(H2O)]n (5), and {[Co2(tbip)2(bpa)2] · 2.5H2O}n (6) (H2tbip ) 5-tert-butyl isophthalic acid; bipy )
4,4′-bipyridine; dpe ) 1,2-di (4-pyridyl)ethylene; bpa ) 1,2-bi(4-pyridyl)ethane) were synthesized. X-ray structural
analyses of 1-6 reveal a diverse range of structures, ranging from 1D (1) to 2D (2, 6) to 3D (3, 4, 5). Complex
1 shows 1D zigzag bipy-bridged polymeric chains with the terminal tbip ligands as pendants, which are extended
to a 3D hydrogen-bonded supramolecular framework involving 1D open channels which encapsulate guest bipy
molecules. Polymers 2 and 6 feature similar 2D infinite layer frameworks consisting of cobalt dimers. The structure
of 3 is constructed from [Co2(tbip)2]n layers, which consists of alternating left- and right-handed helical chains, and
further pillared by dpe ligands into a 3D six-connected self-penetrating 48.66.8 network. The prominent cavities in
3 are parallel to the (101) plane and encapsulate free dpe as guest molecules. Polymers 4 and 5 are isostructural,
showing 2-fold interpenetrating 3D R-Po networks constructed from binuclear cobalt nodes. The thermal stabilities
and X-ray powder diffraction studies indicate that the framework of 3 can keep stable after the loss of guest
molecules. Studies of the magnetic susceptibilities of 2-6 reveal weak antiferromagnetic exchange interactions
between adjacent Co(II) centers.
Introduction
cially interesting because they can adopt a variety of
coordination modes and result in diverse multidimensional
architectures.7-10 However, most of the reported work has
The design and synthesis of metal-organic frameworks
based on the selection of ligands and metal ions has become
a very attractive research field. The motive comes not only
from the intriguing structural diversity but also from the
demand for applications of functional materials in the fields
of catalysis, porosity, magnetism, luminescence, conductivity,
sensing, nonlinear optics, and chirality.1-6 One of the
obvious challenges is the rational and controllable preparation
of metal-organic frameworks, the formation of which is
greatly affected by the organic ligands, the nature of the metal
ions, the counterions, and other factors. Among the reported
studies, organic ligands with carboxylate groups are espe-
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* To whom correspondence should be addressed. E-mail: wlya@
lynu.edu.cn (L.-Y.W.).
†
Luoyang Normal University.
Northwest University.
Monash University.
‡
§
10.1021/ic801278j CCC: $40.75  2009 American Chemical Society
Inorganic Chemistry, Vol. 48, No. 3, 2009 915
Published on Web 12/31/2008

Ma et al.
Scheme 1. Coordination Modes of H2tbip Observed in 1-6
been devoted to the use of 1,3-benzenedicarboxylic acid,
1,3,5-benzenetricarboxylic acid, 1,2,4,5-benzenetetracarboxy-
lic acid, and so on, while the use of the large steric hindrance
of the H2tbip ligand remains largely unexplored. To the best
of our knowledge, there has been only one reported polymer
based on the H2tbip ligand hitherto.11 The presence of the
electron-donating (-C(CH3)3) noncoordinating groups in
dicarboxylate ligands changes their electronic and steric
properties, which can generate complexes different from
those of the common dicarboxylate ligands.
On the other hand, rodlike N,N′-donor building blocks,
such as the conventionally employed 4,4′-bipyridine, have
been extensively studied in coordination chemistry, and
modification by introducing spacers between the two 4-py-
ridyl groups can result in distinct spatial effects to produce
unexpected architectures with metal complexes. The use of
these auxiliary ligands may contribute to an understanding
of the assembly and recognition processes in coordination
chemistry.12,13 Therefore, systematic studies have been
carried out in our laboratory by the reaction of Co(II) salts,
the H2tbip ligand, and a series of N-donor ligands to
investigate the influence of multicarboxylate and N-donor
ligands on the properties and construction of coordination
frameworks, and six novel Co(II) coordination polymers,
{[Co(tbip)(bipy)(H2O)3]·0.5(bipy) ·H2O}n (1), [Co(tbip)(bi-
py)]n(2),{[Co3(tbip)3(dpe)3]·0.5(dpe)·3H2O}n(3),[Co2(tbip)2-
(dpe)(H2O)]n (4), [Co2(tbip)2(bpa)(H2O)]n (5), and {[Co2(tbip)2-
(bpa)2]·2.5 H2O}n (6), were successfully obtained by tuning
the reaction conditions including the pH value, reaction
temperature, and auxiliary ligand. They exhibit diverse
structures with dimensionalities from 1D to 3D, of which 1
shows a 1D zigzag chain, 2 and 6 exhibit a 2D layer motif,
3 displays a 3D self-penetrating framework, and interestingly
4 and 5 possess 2-fold interpenetrating 3D R-Po networks.
The details of their syntheses, structures, and magnetic
properties are reported below (see also Scheme 1).
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Experimental Section
Materials and Physical Measurements. All reagents used in
the syntheses were of analytical grade. Elemental analyses for
carbon, hydrogen, and nitrogen atoms were performed on a Vario
EL III elemental analyzer. The infrared spectra (4000∼400 cm-1
)
were recorded by using KBr pellets on an Avatar 360 E.S.P. IR
spectrometer. Thermogravimetric analyses (TG) were carried out
on a STA449C integration thermal analyzer. The powder X-ray
diffraction (PXRD) patterns were recorded with a Rigaku D/Max
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916 Inorganic Chemistry, Vol. 48, No. 3, 2009

Series of Cobalt(II) Coordination Polymers
Table 1. Crystallographic Data for Complexes 1-6
1
2
3
4
5
6
formula
fw
C27H32CoN3O8
585.49
C22H20CoN2O4
435.33
C78H77Co3N7O15
1529.3
C36H36Co2N2O9
758.53
C36H38 Co2N2O9
760.54
C48H53Co2N4O10.5
971.80
temperature
cryst syst
space group
291(2)
296(2)
monoclinic
C2/m
291(2)
monoclinic
C2/c
291(2)
monoclinic
P21/n
291(2)
monoclinic
P21/n
293(2)
triclinic
triclinic
j
j
P1
P1
unit cell dimensions (Å, deg) a ) 8.1028(2)
a ) 21.690(3)
b ) 11.399(14)
c ) 9.9980(12)
a ) 23.8309(11) a ) 9.5735(13)) a ) 9.5846(9)
a ) 10.1485(11)
b ) 11.6152(13)
c ) 23.006(3)
b ) 11.037(2)
b ) 13.3997(6)
c ) 46.339(2)
b ) 17.493(2)
c ) 21.188(3)
b ) 17.5051(17)
c ) 21.321(2)
c ) 16.541(4)
R ) 107.126(2)
R )76.6490(10)
ꢀ ) 103.022(2)
ꢀ ) 102.578(10) ꢀ ) 98.8(10)
ꢀ ) 102.191(2)
ꢀ ) 101.7560(10) ꢀ ) 77.8030(10)
γ ) 74.0840(10)
γ ) 91.105(3)
1371.5(5)
2
1.418
612
V(Å3)
Z
2412.6(5)
4
1.198
900
1.089
14623.0(12)
8
3468.2(8)
4
3502.2(6)
4
2505.5(5)
2
1.288
1014
1.046
F (g cm-3
F(000)
GOF
)
1.389
1.453
1.442
6360
1568
1576
1.049
1.080
1.026
1.025
R1,wR2 [I > 2σ (I)]
0.0452,0.1082
0.0666, 0.1194
0.460, -0.326
0.0813, 0.2611
0.0878, 0.2704
1.196, -0.928
0.0527, 0.1362
0.0728, 0.1476
0.533, -0.665
0.0275, 0.0665
0.0350, 0.0705
0.265, -0.375
0.0251, 0.0649
0.0282, 0.0669
0.338, -0.309
0.0663, 0.1997
0.1063, 0.2318
1.122, -0.750
R1,wR2 (all data)
residuals (e Å-3
)
3III diffractometer. Variable-temperature magnetic susceptibilities
were measured using a MPMS-7 SQUID magnetometer. Diamag-
netic corrections were made with Pascal’s constants for all
constituent atoms.
6 were obtained. Elem anal. (%) calcd for C48H53Co2N4O10.5: C,
59.32; H, 5.50; N, 5.77. Found: C, 59.21; H, 5.54; N, 5.69. IR
(cm-1): 3452 m, 2981 m, 1656 s, 1470 w, 1446 m, 1381s, 821 m,
732 m.
Synthesis of {[Co(tbip)(bipy)(H2O)3]·0.5(bipy) ·H2O}n (1). A
mixture of 5-tert-butyl isophthalic acid (0.1 mmol, 23.1 mg), bipy
(0.1 mmol, 15.9 mg), Co(OAc)2 ·4H2O (0.05 mmol, 12.0 mg),
NaOH (0.1 mmol, 4.0 mg), and H2O (15 mL) was placed in a
Teflon-lined stainless steel vessel, heated to 120 °C for 3 days,
and then cooled to room temperature over 24 h. Red block crystals
of 1 were obtained. Elem anal. (%) calcd for C27H32CoN3O8: C,
55.39; H, 5.51; N, 7.18. Found: C, 55.48; H, 5.39; N, 7.12. IR
(cm-1): 3437 m, 2926 m, 1609 s, 1558 m, 1371 s, 823 w, 545 m.
Synthesis of [Co(tbip)(bipy)]n (2). The synthesis was similar
to that described for 1, except that 0.2 mmol of NaOH was used
instead of 0.1 mmol of NaOH. Pink crystals of 2 were obtained.
Elem anal. (%) calcd for C22H20CoN2O4: C, 60.70; H, 4.63; N, 6.43.
Found: C, 60.78; H, 4.56; N, 6.32. IR (cm-1): 3400 m, 2964 m,
1685 s, 1606 m, 1550 m, 1367 m, 759 m, 631 m.
X-Ray Crystallography. Single-crystal X-ray diffraction analy-
ses of 1-6 were carried out on a Bruker SMART APEX II CCD
diffractometer equipped with graphite monochromated Mo KR
radiation (λ ) 0.71073 Å) by using the φ/ω scan technique at room
temperature. The structures were solved by direct methods with
SHELXS-97. The hydrogen atoms were assigned with common
isotropic displacement factors and were included in the final
refinement by use of geometrical constraints. A full-matrix least-
squares refinement on F2 was carried out using SHELXL-97. The
crystallographic data and selected bond lengths and angles for 1-6
are listed in Table 1 and Tables S1-S6, Supporting Information.
Crystallographic data for the structural analysis have been deposited
with the Cambridge Crystallographic Data Center. CCDC reference
numbers: 694013-694018.
Synthesis of {[Co3(tbip)3(dpe)3]·0.5(dpe) ·3H2O}n (3). A mix-
ture of 5-tert-butyl isophthalic acid (0.1 mmol, 23.1 mg), 1,2-di(4-
pyridyl)ethylene (0.1 mmol, 18.1 mg), Co(OAc)2 ·4H2O (0.05
mmol, 12.0 mg), NaOH (0.2 mmol, 8.0 mg), and H2O (15 mL)
was placed in a Teflon-lined stainless steel vessel, heated to 120
°C for 3 days, and then cooled to room temperature over 24 h.
Dark red block crystals of 3 were obtained. Elem anal. (%) calcd
for C78H77Co3N7O15: C, 61.26; H, 5.07; N, 6.41. Found: C, 61.39;
H, 5.09; N, 6.31. IR (cm-1): 3455 m, 2959 m, 1608 s, 1569 m,
1433 m, 1368 m, 779 m, 723 m.
Synthesis of [Co2(tbip)2(dpe)(H2O)]n (4). The synthesis was
similar to that described for 3 except that the reaction mixture was
heated at 160 °C. Red crystals of 4 were obtained. Elem anal. (%)
calcd for C36H36Co2N2O9: C, 57.00; H, 4.78; N, 3.69. Found: C,
57.08; H, 4.71; N, 3.62. IR (cm-1): 3443 m, 2965 m, 1624 s, 1609 s,
1561 m, 1437 m, 1385 m, 827 m, 714 m, 552 m.
Results and Discussion
Hydrothermal Synthesis. Because the mixing of metal
salts and carboxylate solutions usually results in precipitation
in traditional aqueous reactions, making it difficult to grow
crystals of complexes, hydrothermal methods were adopted
in our studies, and these methods were proven to be a
powerful approach for the preparation of sparingly soluble
organic-inorganic hybrid materials.14 As is known, there
are a variety of hydrothermal parameters such as reaction
time, temperature, pH value, template, and molar ratio of
the reactants, and small changes in one or more of the
parameters can have a profound influence on the final
reaction outcome.15,16 Our synthetic strategy for the
Co(II)-H2tbip coordination polymers is schematically de-
Synthesis of [Co2(tbip)2(bpa)(H2O)]n (5). The synthesis was
similar to that described for 4 except that 1,2-di(4-pyridyl)ethylene
was replaced by 1,2-bis(4-pyridyl)ethane. Red crystals of 5 were
obtained. Elem anal. (%) calcd for C36H38Co2N2O9: C, 56.85; H,
5.04; N, 3.68. Found: C, 56.79; H, 5.01; N, 3.74. IR (cm-1): 3381 m,
2963 m, 1613 s, 1571 s, 1432 m, 1368 m, 830 m, 721 m, 551 m.
Synthesis of {[Co2(tbip)2(bpa)2]·2.5H2O}n (6). The synthesis
was similar to that described for 3 except that 1,2-di(4-pyridyl)-
ethylene was replaced by 1,2-bis(4-pyridyl)ethane. Red crystals of
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Chem.Commun. 2000, 2043. (b) Feng, S.; Xu, R. Acc. Chem. Res.
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M. C. Eur. J. Inorg. Chem. 2005, 77. (b) Fang, R. Q.; Zhang, X. M.
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Inorganic Chemistry, Vol. 48, No. 3, 2009 917

Ma et al.
Scheme 2. Synthesis of Complexes 1-6
picted in Scheme 2. After many parallel experiments, it was
found that complexes 1 and 2 were obtained under different
pH values that were adjusted by the addition of NaOH.
Compound 1 was the favored product with a relatively lower
pH value (pH < 4), whereas compound 2 was the dominant
product with a relatively higher pH value (pH > 5). Both
novel 3D MOFs 3 and 4 were synthesized using the same
reaction mixture but at different hydrothermal temperatures.
The noninterpenetrating 3 was obtained at 120 °C, whereas
the 2-fold interpenetrating 4 was formed at 160 °C, sug-
gesting that the hydrothermal temperatures have a critical
impact on the construction of 3D MOFs. It is noted that the
change of hydrothermal temperatures to obtain interpenetrat-
ing and noninterpenetrating 3D MOFs has been reported
rarely,17 although several MOFs controlled by hydrothermal
temperatures had been documented.18 The successful isola-
tion of 1-4 prompted us to extend our study to use flexible
bpa instead of rigid bipy and dpe in 5 and 6. A 2-fold
interpenetrating 5 similar to 4 can be obtained, and a 2D
layer framework was formed in 6. Although detailed studies
are still required to better understand the reason for the
formation of the different types of structures, some similiar
works have been documented previously.7g
two pyridyl rings in a bipy ligand are almost coplanar.
Multiple hydrogen bonds are known to cooperatively exert
a dramatic influence on the control of molecular self-
assembly in chemical and biological systems.19 Here, in 1,
there exist extensive hydrogen-bonding interactions involving
the tbip ligand as well as coordinated and free water
molecules (Table S7, Supporting Information). Thus, a 3D
Description of Crystal Structures. {[Co(tbip)(bipy)-
(H2O)3] · 0.5(bipy)· H2O}n (1). X-ray analysis reveals that
the asymmetric unit of 1 consists of one cobalt(II) cation,
one monocoordinated tbip (Scheme 1a), one bridged bipy,
three coordinated water molecules, and half an uncoordinated
bipy as well as one free lattice water molecule. The
coordination environment around the Co(II) ion can be
described as a slightly distorted octahedron (as shown in
Figure 1a). Each Co(II) ion is six-coordinated by two bipy
nitrogen atoms, one carboxylic oxygen atom of tbip, and
three lattice water O atoms. The Co-O bond lengths are in
the range of 2.105(2)-2.155(2) Å, and the Co-N bond
distances are 2.162(3) and 2.169(3) Å, respectively. As
shown in Figure 1b, the bipy ligand acts as a µ2-bridge and
joins the Co atoms into an infinite 1D zigzag chain. The
(16) (a) Li, J. R.; Bu, X. H.; Zhang, R. H.; Ribas, J. Cryst.Growth Des.
2005, 5, 1919. (b) Zhang, X. J.; Zhou, X. P.; Li, D. Cryst. Growth
Des. 2006, 6, 1440. (c) Wang, R. H.; Yuan, D. Q.; Jiang, F. L.; Han,
L.; Gong, Y. Q.; Hong, M. C. Cryst. Growth Des. 2006, 6, 1351. (d)
Ghosh, S. K.; Savitha, G.; Bharadwaj, P. K. Inorg. Chem. 2004, 43,
5497. (e) Fan, S. R.; Zhu, L. G. Inorg. Chem. 2006, 45, 7935.
(17) Liu, C. M.; Gao, S.; Zhang, D. Q.; Zhu, D. B. Cryst. Growth Des.
2007, 7, 1312.
Figure 1. (a) Coordination environment of Co (II) ion in 1. The hydrogen
atoms, free bipy, and water are omitted for clarity. (b) View of the 1D
zigzag chain bridged by bipy ligands. (c) A perspective view of the 3D
network of compound 1 containing 1D open channels encapsulating bipy
molecules. The hydrogen-bonding interactions are indicated by dashed
lines.
(18) (a) Xue, X.; Wang, X. S.; Xiong, R. G.; You, X. Z.; Abrahams, B. F.;
Che, C. M.; Ju, H. X. Angew. Chem., Int. Ed. 2002, 41, 2944. (b)
Lee, L. S.; Shin, D. M.; Chung, Y. K. Chem.sEur. J. 2004, 10, 3158.
918 Inorganic Chemistry, Vol. 48, No. 3, 2009

Series of Cobalt(II) Coordination Polymers
tetradentate ligand in compound 2, connecting three Co ions
(Scheme 1b). Two carboxylic groups of the tbip ligand have
two coordination modes, one bidentately bridging two Co atoms
in a syn-syn fashion and the other chelating one Co atom.
Along the (110) direction, the Co atoms are bridged by the tbip
anions to generate 1D ribbonlike chains containing an alternative
arrangement of 8- and 16-membered rings (Figure 2b). Two
carboxylic groups bridge two Co(II) ions to form an eight-
membered ring, and two tbip ligands bridge two Co(II) ions to
form a 16-membered ring. Within the eight-membered ring and
16-membered ring, the Co · · ·Co separations are 4.11 and 7.37
Å, respectively. The resulting chains are interlinked by the rigid
bipy ligands to form a 2D layer (Figure 2c). Different from the
coplanar bipy molecule in 1, the bipy ligand is twisted with a
dihedral angle of 26.7° between the two pyridyl components.
Interestingly, comparison of the structures of 1 and 2 with
those of reported Co complexes constructed from 5-hydroxyl-
1,3-benzenedicarboxylic acid (OH-BDC) and bipy,20 {[Co-
(bipy)(H2O)4](OH-BDC)(H2O)}n (7) and {[Co(bipy)(OH-
BDC)(H2O)2](bipy)(DMF)}n (8), indicates some differences.
First, the coordination modes of the carboxylate groups in
polymers 1 and 2 are different from those of 7 and 8: mono
and tetradentate modes in 1 and 2 and noncoordinate and
bis-monodentate modes in 7 and 8. Second, compound 7
possesses hydrogen-bonded 3D networks encapsulating 1D
linear covalently bonded infinite [Co(bipy)(H2O)4]n chains,
and compound 8 shows a 2D architecture containing 1D
strand chains bridged by OH-BDC. Both of the structures
are different from those of 1 and 2. Thus, although the
carboxylic coordination sites of H2tbip and OH-BDC are
very similar, their coordination chemistries are obviously
different, presumably due to the steric hindrance of the bulky
tert-butyl skeleton.
{[Co3(tbip)3(dpe)3] · 0.5(dpe)· 3H2O}n (3). The crystal
structure of 3 exhibits a 3D network composed of binuclear
Co cluster nodes, dpe and tbip bridging ligands, free dpe,
and water molecules. There are three crystallographic
independent Co(II) ions in 3. Each Co(II) ion adopts a
distorted octahedral [O4N2] coordination geometry with four
carboxylic oxygen atoms from three tbip ligands and two
nitrogen atoms of two dpe ligands (Figure 3a). The Co-O
and Co-N bond distances are in the ranges of 1.996(2)-
2.246(3) and 2.133(3)-2.177(3) Å, respectively. The coor-
dination mode of tbip in 3 is similar to that of 2 (Scheme
1b). As shown in Figure 3c and d, two Co centers are bridged
by a pair of carboxylate groups into a dimer unit. Neighbor-
ing dimer units are further linked by tbip ligands to form a
2D helical layer in which the left and right helical chains
appear alternatively by sharing the [Co2(tbip)2] binuclear
nodes. One helix is formed by carboxylic oxygen atoms
bridging Co1 and Co3 atoms, which is generated around the
crystallographic 21 axis with a pitch of 13.4 Å. The other
type of helix is built from carboxylic oxygen atom bridges
between the Co2 centers, also with a pitch of 13.4 Å, but
displaying the opposite helical orientation to the former helix
(Figure 3b). Adjacent helical layers are connected by dpe
pillars to generate a novel 3D open framework encapsulating
Figure 2. (a) Coordination environment of the Co(II) ion in 2. The hydrogen
atoms are omitted for clarity. (b) View of a 1D ribbonlike chain of Co
atoms bridged by tbip ligands (c) Ribbonlike chains pillared by rigid bipy
ligands into a 2D layer. The tert-butyl groups are ommitted for clarity.
supramolecular framework encapsulating guest bipy mol-
ecules is formed through these hydrogen bonds among the
adjacent 1D chains. It is apparent that the formed 3D
supramolecular structure is stabilized by free bipy molecules,
which reside at the crossing positions of the tunnels (Figure
1c).
[Co(tbip)(bipy)]n (2). The asymmetric unit of 2 contains
one Co2+ cation, one bipy ligand, and one tbip anion. As shown
in Figure 2a, each Co atom is octahedrally coordinated by two
nitrogen atoms of two bipy ligands and four oxygen atoms from
three tbip ligands. The Co-O(carboxylate) and Co-N(bipy) bond
lengths are in agreement with those in carboxylate- and bipy-
containing cobalt(II) complexes. Each tbip anion acts as a
(19) (a) Fredericks, J. R.; Hamilton, A. D. Hydrogen Bonding Control of
Molecular Self-Assembly: Recent Advances in Design, Synthesis and
Analysis. In ComprehensiVe Supramolecular Chemistry; Sauvage, J. P.,
Hosseini, M. W., Eds.; Pergamon: Oxford, 1996; Vol. 9, chapter 16.
(b) Lehn, J. M. Science 2002, 295, 2400. (c) Zhang, J.; Li, Z. J.; Kang,
Y.; Cheng, J. K.; Yao, Y. G. Inorg. Chem. 2004, 43, 8085. (d) Ghosh,
S. K.; Bharadwaj, P. K. Eur. J. Inorg. Chem. 2005, 4886.
Inorganic Chemistry, Vol. 48, No. 3, 2009 919

Ma et al.
Figure 3. (a) Coordination environment of the trinuclear cobalt unit in 3. (b) View of left- and right-handed helical chains. The tert-butyl groups are omitted
for clarity. (c) View of a 2D layer constructed via the left-handed and right-handed helical chains. (d) Projection along the b axis of 3D framework in 3. (e)
The self-penetrating 48.66.8 six-connected topology. Purple spheres represent the Co2 dimer nodes (the lighter-shaded ones are the (Co3)2 dimers). Blue
bonds represent the tbip bridges, and black bonds represent the bridging dpe pairs. The passing of a rod through one of the six-membered shortest circuits
is highlighted.
free dpe guest molecules (Figure 3d and Figure S1, Sup-
porting Information). The effective free volume of 3 was
calculated by PLATON analysis as 14.6% of the crystal
volume (2135.1 out of the 14623.1 Å3 unit cell volume).
Topologically, the Co dimers can be regarded as the
network nodes. These are linked in two dimensions by the
tbip ligands, to give (4,4) sheets, and in the third dimension
by pairs of dpe ligands acting as single bridges. For each
cluster, one pair of dpe ligands bridges to the sheet above,
and another bridges to the sheet below, making the Co dimers
(20) He, H. Y.; Zhou, Y. L.; Hong, Y.; Zhu, L. G. J. Mol. Struct. 2005,
737, 97.
920 Inorganic Chemistry, Vol. 48, No. 3, 2009

Series of Cobalt(II) Coordination Polymers
Figure 4. (a) Coordination environment of the dinuclear cobalt unit in 4. The tert-butyl groups are ommitted for clarity. (b) The dinuclear cobalt clusters
connected by H2tbip ligands to form a 2D layer along c axis. (c) A polyhedral view of the 3D structure of 4 viewed along the c axis. (d) Schematic
representation of the interpenetration; spheres represent the cobalt dimer nodes.
six-connecting nodes. The dpe bridges, however, are slanted
rather than perpendicular to the sheets and crisscross in two
different directions (Figure 3e). Thus, the usual R-Po net is
not formed, but rather a more unusual uninodal six-connected
net with 48.66.8 topology is formed. This net is self-
penetratingsthat is, there are six-membered shortest circuits
that are penetrated by rods of the same net. Self-penetration
is an unusual form of topological entanglement,21 although
a number of related structures with self-penetrating networks
constructed from (4,4) sheets connected by slanted bridges
have been reported,22 including some examples with the same
topology as 3.22b,23
[Co2(tbip)2(dpe)(H2O)]n (4) and [Co2(tbip)2(bpa)(H2O)]n
(5). As listed in Table 1, compounds 4 and 5 crystallize in
the same monoclinic form with space group P21/n and have
Inorganic Chemistry, Vol. 48, No. 3, 2009 921

Ma et al.
pentadentate ligands to bridge four Co atoms together. On
the basis of these connection modes, each binuclear Co
cluster is linked to four neighboring clusters by four bridging
tbip ligands, to form a 2D (4,4) layer parallel to the [110]
direction, as shown in Figure 4b and Figure S2, Supporting
Information. The 2D sheets are further connected by dpe
ligands coordinating to the binuclear SBUs to form a 3D
framework with six-connected R-Po topology, and two of
these networks interpenetrate to generate the overall structure,
as depicted in Figure S2 and Figure 4e.
Hydrothermal reactions of cobalt(II) salt with dpe and
NO2-BDC (NO2-BDC ) 5-nitro-1,3-benzenedicarboxylic
acid) led to the formation of {Co(dpe)(NO2-BDC)} ·
0.5(dpe)]n · nH2O (9) in the literature.24 Compound 9 is a
noninterpenetrated 2D bilayer with nanoscale rectangular
channels that clathrate large organic molecules. This structure
was obviously different from those of 3 and 4, which further
confirms the effect of the steric bulk of the bulky tert-butyl
skeleton on the final structure.
{[Co2(tbip)2(bpa)2]·2.5H2O}n (6). As shown in Figure 5a,
there are two crystallographic independent cobalt ions in 6.
Each Co(II) ion is coordinated by four oxygen atoms of three
tbip anions and two nitrogen atoms of two bpa molecules.
The coordination geometry can be described as a distorted
octahedron. Two Co(II) ions are bridged by a pair of
carboxylic groups from two different tbip anions into a
binuclear Co unit with a Co · · ·Co distance of 4.40 Å, which
is larger than that in 2 (4.11 Å), revealing that the second
ligand has a great influence on the 2D framework. The
dimeric Co2 units are linked by two exotetradentate tbip
anions to two adjacent dinuclear cobalt units, thus generating
a 1D [Co2(tbip)2]n double chain (Figure S3, Supporting
Information), in which the coordination modes of tbip anions
are similar to those of 2. All of the bpa ligands adopt an
anti conformation and further link adjacent double chains
into a 2D layer (Figure 5b). There are hydrogen bonds
between the free water molecules and the coordinated
carboxylic oxygen atoms (O9-H(1W) · · · O4, O · · ·O )
2.991(12) Å, ∠OHO ) 174.8°), which brings further stability
for the structure. It is noteworthy that the 2D structure of 6
is similar to that of 2 except for the free water molecules.
This comparison indicates that the 2D structure of 6 can be
converted into the 2D layer of 2 through the replacement of
the rigid bipy ligands by flexible bpa ligands.
Figure 5. (a) Coordination environment of the dinuclear cobalt unit in 6.
(b) 1D chains pillared by flexible bpa ligands into a 2D layer.
similar cell parameters. The results of crystal structure
analysis reveal that they are isostructural, and thus only the
structure of 4 is described here as an example. The crystal
structure of 4 exhibits a 3D network composed of the
binuclear cobalt cluster nodes, dpe and tbip bridging ligands.
There are two crystallographic independent cobalt atoms in
compound 4 (Figure 4a). Co1 is six-coordinated and resides
in a distorted octahedral [O4N2] coordination geometry. The
six atoms coordinated to the Co1 ion come from two nitrogen
atoms of two dpe ligands and three oxygen atoms from two
tbip ligands, as well as one oxygen atom of a water molecule.
The Co1-N distances are 2.1044(16) and 2.1457(16) Å, and
theCo1-Odistancesareintherangeof2.0876(13)-2.3761(14)
Å. Co2 adopts a distorted tetrahedral [O4] coordination
environment and is coordinated by four carboxylic oxygen
atoms from four tbip ligands. The Co2-O bond distances
are in the range of 1.9585(14)-1.9976(13) Å, which is
shorter than those of the Co1-O bond lengths. In addition,
tbip ligands exhibit two kinds of coordination modes, as
shown in Scheme 1c and d. In the first mode, two carboxylate
groups act as bis-monodentate ligands to bridge two Co
atoms. In the second mode, two carboxylate groups act as
PXRD and Thermal Analysis. In order to check the phase
purity of these compounds, the PXRD patterns of compounds
1-6 were checked at room temperature. As shown in Figure
S4, Supporting Information, the peak positions of the
simulated and experimental PXRD patterns are in agreement
with each other, demonstrating the good phase purity of the
(22) (a) Sun, H.-L.; Gao, S.; Ma, B.-Q.; Batten, S. R. CrystEngComm 2004,
6, 579. (b) Abrahams, B. F.; Hardie, M. J.; Hoskins, B. F.; Robson,
R.; Sutherland, E. E. J. Chem. Soc., Chem. Commun. 1994, 1049.
(23) (a) Zhao, X. J.; Batten, S. R.; Du, M. Acta Crystallogr., Sect. E 2004,
60, m1237. (b) Long, D.-L.; Hill, R. J.; Blake, A. J.; Champness, N. R.;
Hubberstey, P.; Wilson, C.; Schro¨der, M. Chem.sEur. J. 2005, 11,
1384.
(21) (a) Batten, S. R. CrystEngComm 2001, 3, 67. (b) Carlucci, L.; Ciani,
G.; Proserpio, D. M. Coord. Chem. ReV. 2003, 246, 247. (c) Abrahams,
B. F.; Batten, S. R.; Grannas, M. J.; Hamit, H.; Hoskins, B. F.; Robson,
R. Angew. Chem., Int. Ed. 1999, 38, 1475. (d) Jensen, P.; Price, D. J.;
Batten, S. R.; Moubaraki, B.; Murray, K. S. Chem.sEur. J. 2000, 6,
3186. (e) Wang, X.-L.; Qin, C.; Wang, E.-B.; Su, Z.-M.; Xu, L.; Batten,
S. R. Chem. Commun. 2005, 4789. (f) Tong, M.-L.; Chen, X.-M.;
Batten, S. R. J. Am. Chem. Soc. 2003, 125, 16170.
(24) Luo, J. H.; Hong, M. C.; Wang, R. H.; Cao, R.; Han, L.; Yuan, D. Q.;
Lin, Z. Z.; Zhou, Y. F. Inorg. Chem. 2003, 42, 4486.
922 Inorganic Chemistry, Vol. 48, No. 3, 2009

Series of Cobalt(II) Coordination Polymers
Figure 6. Temperature dependence of ꢁMT and ꢁM for 2 (a), 3 (b) 4 (c), 5 (d), and 6 (e). Open points are the experimental data, and the solid line represents
the best fit obtained from the Hamiltonian given in the text.
compounds. The differences in intensity may be due to the
preferred orientation of the crystalline powder samples.
Due to the presence of large amounts of solvent and guest
molecules, thermogravimetric analysis (TGA) was performed
on samples of complexes 1, 3, and 6 to confirm their stability,
as shown in Figure S5, Supporting Information. The TG
curve of complex 1 reveals a steady weight loss between 25
and 300 °C, which is attributed to the loss of lattice water
molecules, coordinated water molecules, and free bipy
molecules (observed, 23.74%, calculated, 25.58%). In 3, the
first event occurs between 25 and 285 °C, which corresponds
to the loss of guest dpe and lattice water molecules (observed,
11.06%, calculated, 9.56%). And further weight loss was
observed at a temperature of 650 °C. The TG curve for 6
shows an initial weight loss in the temperature range 25-120
°C, which was due to the loss of the lattice water molecules
(observed, 3.8%, calculated, 4.6%). The further weight loss
represents the decomposition of the material.
solvent and guest dpe molecules. However, the crystalline
nature of 1 largely decreased after heating at 300 °C.
Magnetic Properties. The magnetic susceptibilities, ꢁM,
of 2-6 were measured in the 2-300 K temperature range,
and shown as ꢁMT and ꢁM versus T plots in Figure 6. As the
temperature was lowered to 2 K, the ꢁMT value continuously
decreased, which suggests that antiferromagnetic interactions
are operative in 2-6. The experimental ꢁMT values of 2-6
at room temperature are 5.40, 5.04, 5.81, 5.75, and 5.61 cm3
K mol-1, respectively, which are larger than two isolated
spin-only Co2+ cations (3.75 cm3 K mol-1). This larger value
is the result of contributions to the susceptibility from orbital
angular momentum at high temperatures.25a The temperature
dependence of the reciprocal susceptibilities (1/ꢁM) of 2-6
all obey the Curie-Weiss law above 50 K with θ ) -19.34
K, C ) 5.32 cm3 · K/mol, and R ) 2.13 × 10-3 for 2; θ )
-19.48 K, C ) 5.52 cm3 · K/mol, and R ) 1.47 × 10-3 for
3; θ ) -28.87 K, C ) 5.73 cm3 · K/mol, and R ) 4.8 ×
10-4 for 4; θ ) -24.48 K, C ) 5.86 cm3 · K/mol, and R )
4.22 × 10-4 for 5; and θ ) -18.92 K, C ) 5.37 cm3 · K/
mol, and R ) 3.14 × 10-4 for 6. The moderate negative θ
values indicate the presence of antiferromagnetic interactions
PXRD measurements at different temperatures show that,
for complexes 3 and 6 after heating at 285 and 120 °C, the
spectra are similar to the original ones, suggesting that their
crystalline nature is still maintained after removing the
Inorganic Chemistry, Vol. 48, No. 3, 2009 923

Ma et al.
among adjacent Co(II) ions even if a contribution from the
spin-orbit coupling of Co(II) is also present.25b,c Comparable
antiferromagnetic interactions between the Co(II) ions were
reported in other cobalt compounds.25
B ) 1 + 3 exp[-2J ⁄ KT] + 5 exp[-6J ⁄ KT] +
7 exp[-12J ⁄ KT]
The least-squares analysis of magnetic susceptibilities data
led to J ) -0.83 cm-1, g ) 2.32, zJ′ ) -0.09 cm-1, and R
) 9.25 × 10-5 for 2; J ) -1.8 cm-1, g ) 2.41, zJ′ ) -0.47
cm-1, and R ) 3.96 × 10-3 for 3; J ) -1.5 cm-1, g )
2.41, zJ′ ) -0.39 cm-1, and R ) 4.4 × 10-3 for 4; J )
-1.05 cm-1, g ) 2.45, zJ′ ) -0.21 cm-1, and R ) 2.5 ×
10-3 for 5; and J ) -0.68 cm-1, g ) 2.38, zJ′ ) -0.08
cm-1, and R ) 3.16 × 10-3 for 6.
According to the structural analyses of 2-6 discussed
above, at least one Co(II) ion in each structure has octahedral
geometry. It is well-known that the Co(II) ion in an
octahedron possesses a 4T1g ground state, and thus the orbit
angular momentum of the Co(II) ion will have a large
contribution to the magnetic susceptibilities of these com-
pounds. This implies that the magnetic analyses for Co-
containing compounds will become rather complicated,26 and
some approximate methods are often applied to analyze
magnetic interaction between Co ions. In this work, the main
magnetic interactions may be considered to occur between
adjacent Co(II) ions bridged by carboxylic groups and
oxygen atoms, whereas the exchange interactions between
Co(II) ions bridged through the tbip ligand and dpe or bpa
can be ignored because of the long Co · · · Co separations.
An attempt was made to fit the magnetic susceptibility data
assuming that the carboxylic group bridges between Co(II)
ions to form a binuclear unit with coupling constant J and
then tbip and dpe or bpa connect the binuclear units to form
a 3D network with an exchange constant zJ′. The susceptibil-
ity data were thus approximately analyzed by an isotropic
dimer mode of spin S ) 3/2.27
Conclusion
In summary, six novel Co(II) complexes have been
synthesized by the self-assembly of Co(II) salts with H2tbip
and dipyridyl-based ligands. Assemblies of these complexes
generate four types of diverse frameworks: a 1D chain, two
2D layers, one 3D self-penetrating 48.66.8 framework, and
two 2-fold interpenetrating 3D R-Po networks. We have
found that the presence of bulky electron-donating
(-C(CH3)3) noncoordinating groups in dicarboxylate ligands
is very helpful for the construction of metal-organic frame-
works. Compound 3 has a stable metal-organic framework
subject to the loss of guest molecules. In addition, the
magnetic properties for 2-6 have been investigated, along
with the corresponding J parameter related to their structural
characteristics. Subsequent works will be focused on the
construction of novel coordination polymers by reacting these
and other related ligands with more metal ions.
Ng2ꢀ2 A
KT B
ꢁM )
(1)
A ) 2 exp[-2J ⁄ KT] + 10 exp[-6J ⁄ KT] +
Acknowledgment. This work was supported by the
Natural Science Foundation of China (nos. 20471026 and
20771054), the Henan tackle key problem of science and
technology (nos. 072102270030 and 072102270034), and the
Foundation of Education Committee of Henan province (nos.
2006150017 and 2008A150018).
28 exp[-12J ⁄ KT]
(25) (a) Xu, Y. Q.; Yuan, D. Q.; Wu, B. L.; Han, L.; Wu, M. Y.; Jiang,
F. L.; Hong, M. C. Cryst. Growth Des. 2006, 6, 1168. (b) Bourne,
S. A.; Lu, J. J.; Mondal, A.; Moulton, B.; Zaworotko, M. J. Angew.
Chem., Int. Ed. 2001, 40, 2111. (c) Luo, J. H.; Zhao, Y. S.; Xu, H. W.;
Kinnibrugh, T. L.; Yang, D.; Timofeeva, T. V.; Daemen, L. L.; Zhang,
J. Z.; Bao, W.; Thompson, J. D.; Currier, R. P. Inorg. Chem. 2007,
46, 9021. (d) Sakiyama, H.; Tto, R.; Kumagai, H.; Inoue, K.;
Sakamoto, M.; Nishida, Y.; Yamasaki, M. Eur. J. Inorg. Chem. 2001,
2027. (e) Wang, Y. L.; Yuan, D. Q.; Bi, W. H.; Li, X.; Li, X. J.; Li,
F.; Cao, R. Cryst. Growth. Des. 2005, 5, 1849. (f) Blake, A. B.
J. Chem. Soc., Chem. Commun. 1966, 569.
Supporting Information Available: Crystallographic data in
CIF format and additional figures, selected bond distances and
angles, and patterns of TGA and PXRD in PDF format. This
information is available free of charge via the Internet at
http://pubs.acs.org.
(26) Fabelo, O.; Pasa´n, J.; Can˜adillas-Delgado, L.; Delgado, F. S.; Lloret,
F.; Julve, M.; Ruiz-Pe´rez, C. Inorg. Chem. 2008, [Online] DOI:
10.1021/ic800704y.
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IC801278J
924 Inorganic Chemistry, Vol. 48, No. 3, 2009