The structure and magnetic properties of a 3D pillared-layer polymer and two helical chains constructed from flexible ligands

Article abstract of DOI:10.1016/j.molstruc.2007.12.032

Three novel coordination polymers of Co^II and Cu^II with flexible ligands, namely [Co(oba)(dpa)]_n (1), [Cu(oba)(dpa)]_n (2) and [Cu(oba)(bpy)_1/2]_n (3) [H₂oba = 4,4′-oxybis(benzoic acid), dpa = 2,2′-dipyridylamine, bpy = 4,4′-bipyridine] were synthesized by hydrothermal reactions and characterized by single-crystal X-ray diffraction, thermogravimetric analyses, elemental analysis and IR spectroscopy. X-ray diffraction analysis reveals that complexes 1 and 2 are isostructural. In complexes 1 and 2, the Co^II and Cu^II ions are linked by flexible oba ligands to form 1D helical chain. These chains are further assembled into 3D supramolecular edifice via aromatic π-π stacking interactions and intermolecular hydrogen bonding. The Cu^II ions in complex 3 are linked by the carboxylate groups oba to form an eight-membered ring chains, the connectivity between the corner-shared eight-membered ring chains are further bridged by the bent oba ligands to produce 2D helical layer containing the right-handed helical chains. Furthermore, the adjacent helical layers are connected by bpy pillars to form a novel 3D framework with an unprecedented topology of (3¹⁵·4²⁰·5⁸·6²). The magnetic properties of complexes 1-3 have also been investigated.

Full text of DOI:10.1016/j.molstruc.2007.12.032

Available online at www.sciencedirect.com
Journal of Molecular Structure 888 (2008) 344–353
www.elsevier.com/locate/molstruc
The structure and magnetic properties of a 3D pillared-layer
polymer and two helical chains constructed from flexible ligands
a
a,
a
a
b,
*
*
Long Tang , Dongsheng Li , Feng Fu , Yapan Wu , Yaoyu Wang
Huaiming Hu b, Enbo Wang c
,
a Department of Chemistry and Chemical Engineering, Shaanxi Key Laboratory of Chemical Reaction Engineering,
Yan0an University, Yan0 an, Shaanxi 716000, China
b Department of Chemistry, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, Northwest University, Xi0an, Shaanxi 710069, China
c Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun 130024, China
Received 7 November 2007; received in revised form 20 December 2007; accepted 21 December 2007
Available online 10 January 2008
Abstract
Three novel coordination polymers of CoII and CuII with flexible ligands, namely [Co(oba)(dpa)]n (1), [Cu(oba)(dpa)]n (2) and [Cu(o-
ba)(bpy)1/2]n (3) [H2oba = 4,40-oxybis(benzoic acid), dpa = 2,20-dipyridylamine, bpy = 4,40-bipyridine] were synthesized by hydrothermal
reactions and characterized by single-crystal X-ray diffraction, thermogravimetric analyses, elemental analysis and IR spectroscopy.
X-ray diffraction analysis reveals that complexes 1 and 2 are isostructural. In complexes 1 and 2, the CoII and CuII ions are linked
by flexible oba ligands to form 1D helical chain. These chains are further assembled into 3D supramolecular edifice via aromatic p–p
stacking interactions and intermolecular hydrogen bonding. The CuII ions in complex 3 are linked by the carboxylate groups oba to form
an eight-membered ring chains, the connectivity between the corner-shared eight-membered ring chains are further bridged by the bent
oba ligands to produce 2D helical layer containing the right-handed helical chains. Furthermore, the adjacent helical layers are connected
by bpy pillars to form a novel 3D framework with an unprecedented topology of (315ꢀ420ꢀ58ꢀ62). The magnetic properties of complexes
1–3 have also been investigated.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Coordination polymer; Pillared-layer; Helical chains; Magnetic properties; Cobalt; Copper
1. Introduction
taking certain factors into account, such as the coordina-
tion nature of the metal ion and the shape, functionality,
flexibility and symmetry of organic ligand [3], of which
many are derived from dicarboxylate ligands because of
their interesting structural characteristics [4]. Thus, the
prospect of tuning the properties of metal–organic frame-
works through a systematic change of the organic ligands
provides an impetus to further research of metal–organic
supramolecular architectures. Lately, a series of open
metal–organic frameworks with various structural motifs,
including honeycomb, brick wall, bilayer, ladder, herring-
bone, diamondoid and rectangular grid, have been deliber-
ately designed, and discussed in comprehensive reviews by
Yaghi, Kitagawa, Rao and their co-workers [5]. Typically,
the as-synthesized porous frameworks can be divided into
The current interest in the crystal engineering of coordi-
nation polymer frameworks not only stems from their
potential applications in chemical separations, ion
exchange, microelectronics, nonlinear optics, porous mate-
rials and catalysis, but also from their intriguing variety of
architectures and topologies [1,2]. Therefore, a variety of
coordination polymers with interesting compositions,
architectures and topologies have been prepared through
*
Corresponding authors. Fax: +86 911 2332317 (D. Li); +86 29
88373398 (Y. Wang).
E-mail addresses: lidongsheng1@126.com (D. Li), wyaoyu@nwu.
edu.cn (Y. Wang).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.12.032

L. Tang et al. / Journal of Molecular Structure 888 (2008) 344–353
345
three groups, namely, metal–organic frameworks having
multidimensional channels, pillared-layer architectures,
and 3D nanotubular structures. Among them, pillared-
layer architectures, which have been proven to be an effec-
tive and controllable route to design 3D frameworks with
large channels [6–9]. Employing this approach, a variety
of pillared-layer structures including positively and nega-
tively charged or neutral layers have been synthesized [8].
This research area soon became very attractive because of
the merits of pillared-layer structures, such as control over
the porous structures and the chemical functionality by
simple modification of the pillar module [10].
rigid and flexible exo-bidentate pyridyl-containing ligands
on conformations of H2oba as well as the assembly process
of H2oba and metal ions, the hydrothermal reactions of
H2oba with M(II) and multidentate N-donor ligands were
carried out, and a series of coordination polymers were
obtained. Herein, we report the syntheses and characteriza-
tions of three novel M(II) compounds exhibiting different
topologies: [Co(oba)(dpa)]n (1), [Cu(oba)(dpa)]n (2) and
[Cu(oba)(bpy)1/2]n (3). The magnetic properties of com-
plexes 1–3have also been investigated.
2. Experimental
Helical structures have received much attention in coor-
dination chemistry and materials chemistry, that mainly
because helicity is an essence of life and is also important
in advanced materials, such as optical devices, enantiomer
separation, chiral synthesis, ligand exchange, biological
systems and, selective catalysis [11–15]. Many chemists
have made great contributions to this field, and the design
of helical coordination polymers through the self-assembly
of ligands and metal cations has shown significant progress
recently [13,14]. However, the occurrence of pillared-layer
complexes with helical character is particularly rare. Fur-
thermore, multidentate N- or O-donor ligands have been
extensively employed in the construction of pillared-layer
structures. For example, as an excellent candidate for rigid
rodlike organic building units, exo-bidentate 4,40-bipyri-
dine (bpy) has been relatively well-known and shows many
interesting supramolecular architectures [16]. Dicarboxyl-
ate ligands can bridge two or more different metal centers
and produce neutral architectures [17–19]. Hence, metal–
organic coordination polymers constructed by mixed
ligands of pyridyl groups and carboxylate groups, which
not only incorporate interesting properties of different
functional group [17], but also are more adjustive through
changing one of the above two organic ligands [18,19]. For
instance, using dipyridyl ligands as pillars between the neu-
tral layers of dicarboxylate and metal ions, a few three-
dimensional layer-pillar complexes have been constructed
[19]. And yet, because of the difficult prediction of either
the composition or the structure of the reaction product
[20], the architectures of coordination polymers from
mixed ligands and metal ions are still a long-term challenge
to chemists, especially those from flexible bridging ligands
because of their flexibility and conformational freedom in
assembly process [21]. Consequently, a great deal of work
is required to extend the knowledge of relevant structural
types and establish proper synthetic strategies leading to
desirable architectures and useful properties.
2.1. Materials and chemical analysis
The H2oba, bpy and dpa ligands were purchased in the
Alfa Aesar company; all other reagents and solvents
employed were commercially available and used without
further 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. Thermogravi-
metric curves were measured on a Perkin-Elmer TGA-7
(USA) at a heating rate of 10 °C minꢁ1 from room temper-
ature to 700 °C under nitrogen. The powder X-ray diffrac-
tion patterns were recorded on a Shimadzu XRD-7000
diffractometer. 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
contributions estimated from Pascal0s constants.
2.2. Synthesis of [Co(oba)(dpa)]n (1)
A
mixture of Co(NO3)ꢀ6H2O (0.1 mmol), H2oba
(0.1 mmol), dpa (0.1 mmol) and triethylamine (1.2 mmol)
and water (10 ml) was stirred for 20 min in air. The mixture
was then transferred to a 23 ml Teflon reactor and kept at
140 °C for 5 days under autogenous pressure, and then
cooled to room temperature at a rate of 5 °C hꢁ1. Red crys-
tals of 1 were obtained(yield: 69% based on Co). Elemental
analysis. Calcd for C24H17N3O5Co: C, 59.27; H, 3.52; N,
8.64%. Found: C, 59.45; H,3.16; N, 8.77%. IR data (KBr
cmꢁ1): 3320(m), 1649(vs), 1458(s), 1510(s), 1486(s),
1402(w), 1335(s), 1254(w), 1148(m), 1079(m), 1017(w),
870(m), 769(m), 721(w), 678(m).
2.3. Synthesis of [Cu(oba)(dpa)]n (2)
In our strategy, 4,40-oxybis(benzoic acid) (H2oba) is a
typical example of long V-shaped ligands, it has proven
to be able to establish bridges between metal centers. Its
coordination chemistry has been studied and some coordi-
nation polymers have been obtained [22]. Because of its
two oxo carboxylate groups, H2oba can coordinate to
metal ions in didentate, tridentate, tetradentate, pentaden-
tate and hexadentate modes. To investigate the effects of
Complex
2
was prepared as for
1
by using
Cu(NO3)ꢀ3H2O instead of Co(NO3)ꢀ6H2O. Blue crystals
of 2 were obtained (yield: 64% based on Cu). Elemental
analysis. Calcd for C24H17N3O5Cu: C, 58.71; H, 3.49; N,
8.56%. Found: C, 59.15; H,3.27; N, 8.76%. IR data (KBr
cmꢁ1): 3323(m), 1641(vs), 1462(s), 1514(s), 1482(s),
1406(w), 1335(s), 1252(w), 1153(m), 1087(m), 1018(w),
870(m), 775(m), 721(w), 687(m).

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L. Tang et al. / Journal of Molecular Structure 888 (2008) 344–353
2.4. Synthesis of [Cu(oba)(bpy)1/2]n (3)
mixture of Cu(NO3)ꢀ3H2O (0.1 mmol), H2oba
3. Results and discussion
A
3.1. Description of the structures
(0.1 mmol), bpy (0.1 mmol), and water (10 mL) was
placed in a Teflon reactor (23 mL). The pH was adjusted
to 7.0 by addition of triethylamine, the mixture was
heated at 160 °C for three days, and then it was cooled
to room temperature at 5 °C hꢁ1. Blue crystals of 3 were
obtained in 52% yield based on Cu. Elemental analysis
(%). Calcd for C19H12CuNO5: C 57.36, H 3.04, N 3.52.
Found: C 57.95; H 3.21; N 4.01; IR data IR (KBr
cmꢁ1) (KBr cmꢁ1): 3436(w), 3063(w), 2924(w), 1594(vs),
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).
The oba ligands in complexes 1–3 are completely depro-
tonated and are significantly bent at the ether–oxygen sites
[C–O–C = 116.6(7)–119.1(3)°]. They afford several kinds of
coordination modes: bis(chelating bidentate) and bis(bridg-
ing-bidentate) (see Scheme 1).
3.1.1. Structure of [Co(oba)(dpa)]n (1) and
[Cu(oba)(dpa)]n (2)
X-ray diffraction analysis reveals that compounds 1 and
2 are isostructural, and the structure of 1 will be discussed
in detail as a representative example, the structure of 2 can
be found in the Supporting Information (Figs. S1–S3). The
asymmetric unit of 1consists of one crystallographic inde-
pendent Co(II) atom, one oba ligand and one dpa ligand.
The Co(II) ion is located in a slightly distorted octahedral
geometry and is coordinated to four oxygen atoms of two
oba ligands and two nitrogen atoms of one dpa ligand, as
shown in Fig. 1. The average Co–N bond length is
2.5. X-ray crystallographic studies
Diffraction intensities for the three complexes were col-
lected at 293 K on a Bruker SMART 1000 CCD diffrac-
tometer employing graphite-monochromated Mo-Ka
˚
radiation (k = 0.71073 A). A semi-empirical absorption
˚
correction was applied using the SADABS program [23].
The structures were solved by direct methods and refined
by full-matrix least-squares on F2 using the SHELXS 97
and SHELXL 97 programs, respectively [24,25]. Non-
hydrogen atoms were refined anisotropically and hydrogen
atoms were placed in geometrically calculated positions.
The crystallographic data for complexes 1–3 are listed in
Table 1, and selected bond lengths and angles are listed
in Table 2.
2.056(4) A and the Co–O bond lengths are in the range
˚
2.112(3)–2.182(3) A. The details are depicted in Table 2.
Each oba ligand adopts a bis(chelating bidentate) mode
(see Scheme 1 (I)), linking two Co(II) ions.
The adjacent Co(II) ions are bridged by V-shaped oba
ligands to form a helical chain running along a-axis
(Fig. 2). The helix is generated around the crystallographic
˚
21 axis with a pitch of 12.125(2) A. Notably, the two ben-
zene rings of oba ligand are severely bent (the dihedral
Table 1
Crystal data and structure refinements for complexes 1–3
Complex
1
2
3
Formula
Mr [g]
C
486.34
24H17CoN3O5
C24H17CuN3O5
490.95
C19H12CuNO5
397.84
Crystal system
Monoclinic
P2(1)/c
12.125(2)
15.700(3)
11.271(2)
90
95.534(2)
90
2135.6(5)
4
Monoclinic
P2(1)/c
12.391(2)
15.590(3)
11.297(2)
90
96.219(3)
90
2169.6(7)
4
Monoclinic
C2/c
22.1792(17)
13.6526(11)
13.0343(10)
90
119.2810(10)
90
3442.6(5)
8
Space group
˚
a [A]
˚
b [A]
˚
c [A]
a [°]
b [°]
c [°]
3
˚
V [A ]
Z
qcalcd [g cmꢁ3
]
1.513
0.846
1.503
1.049
1.535
1.299
l [mmꢁ1
]
Collected reflections
9632
10742
8575
Unique reflections (Rint
Observed reflections [I > 2r(I)]
Refined parameters
)
3773(0.0597)
2089
298
3822(0.1866)
1160
298
3069(0.0385)
2277
236
Goodness of fit
1.006
0.810
1.042
b
R1a/wR2 [I > 2r(I)]
0.0496/0.0926
0.1096/0.1196
0.308/ꢁ0.535
0.0639/0.0747
0.0583/0.0898
0.412/ꢁ0.457
0.0381/0.0792
0.0583/0.0898
0.323/ꢁ0.335
b
R1a/wR2 (all data)
ꢁ3
˚
Largest residuals [eA
]
P
P
a
R1 ¼ kF oj ꢁ jF cjÞ= jF oj.
P
P
2
2 1=2
b
wR2 ¼ ½ wðF 2o ꢁ F c2Þ = wðF 2oÞ ꢂ
.

L. Tang et al. / Journal of Molecular Structure 888 (2008) 344–353
347
Table 2
Selected bond lengths (A) and angles (°) for complexes 1–3
a
˚
Complex 1
Complex 2
Complex 3
Co(1)–N(2)
Co(1)–N(1)
Co(1)–O(1)
Co(1)–O(4)
Co(1)–O(2)
Co(1)–O(3)
2.051(4)
2.061(4)
2.112(3)
2.168(3)
2.181(3)
Cu(1)–N(1)
Cu(1)–O(1)
Cu(1)–O(3)
Cu(1)–N(2)
Cu(1)–O(2)
Cu(1)–O(4)
1.989(6)
2.435(5)
2.452(5)
1.970(6)
2.016(5)
2.014(5)
93.2(3)
Cu(1)–O(1)
Cu(1)–O(4B)
Cu(1)–O(2C)
O(4)–Cu(1D)
Cu(1)–O(5A)
Cu(1)–N(1)
O(2)–Cu(1C)
O(5)–Cu(1E)
O(1)–Cu(1)–O(5A)
O(5A)–Cu(1)–O(4B)
O(5A)–Cu(1)–N(1)
O(1)–Cu(1)–O(2C)
O(4B)–Cu(1)–O(2C)
O(1)–Cu(1)–O(4B)
O(1)–Cu(1)–N(1)
O(4B)–Cu(1)–N(1)
O(5A)–Cu(1)–O(2C)
N(1)–Cu(1)–O(2C)
O(1)–Cu(1)–Cu(1D)
O(5A)–Cu(1)–Cu(1D)
N(1)–Cu(1)–Cu(1D)
C(8)–O(3)–C(5)
1.952(2)
1.985(2)
2.172(2)
1.985(2)
1.968(2)
1.999(2)
2.172(2)
1.968(2)
99.58(9)
85.86(9)
172.03(10)
100.50(9)
103.60(9)
155.34(10)
87.86(10)
88.54(10)
89.51(9)
86.31(9)
76.69(7)
75.38(7)
109.39(7)
119.1(3)
2.182(3)
N(2)–Co(1)–N(1)
N(2)–Co(1)–O(1)
N(1)–Co(1)–O(1)
N(2)–Co(1)–O(4)
N(1)–Co(1)–O(4)
O(1)–Co(1)–O(4)
N(2)–Co(1)–O(2)
N(1)–Co(1)–O(2)
O(1)–Co(1)–O(2)
O(4)–Co(1)–O(2)
N(2)–Co(1)–O(3)
N(1)–Co(1)–O(3)
O(1)–Co(1)–O(3)
O(4)–Co(1)–O(3)
O(2)–Co(1)–O(3)
C(5)–O(5)–C(12A)
a
91.10(14)
102.70(13)
105.74(13)
94.49(13)
95.39(12)
152.27(12)
163.88(13)
94.11(14)
61.19(12)
100.18(12)
92.61(13)
155.95(13)
96.60(12)
60.63(11)
88.82(12)
117.3(4)
N(2)–Cu(1)–N(1)
N(1)–Cu(1)–O(4)
N(1)–Cu(1)–O(2)
N(2)–Cu(1)–O(1)
O(4)–Cu(1)–O(1)
N(2)–Cu(1)–O(3)
O(4)–Cu(1)–O(3)
O(1)–Cu(1)–O(3)
N(2)–Cu(1)–O(4)
N(2)–Cu(1)–O(2)
O(4)–Cu(1)–O(2)
N(1)–Cu(1)–O(1)
O(2)–Cu(1)–O(1)
N(1)–Cu(1)–O(3)
O(2)–Cu(1)–O(3)
90.8(2)
158.7(3)
102.8(2)
102.5(2)
94.7(2)
58.55(18)
156.3(2)
153.2(2)
94.6(3)
91.1(2)
100.6(2)
58.33(18)
94.1(2)
104.9(2)
116.6(7)
C(12A)–O(5)–C(5)
´
Symmetry operations: for 1: (A) x ꢁ 1, ꢁy + 1/2, zꢁ 1/2; for 2: (A) x + 1, ꢁy + 1/2, z + 1/2; for 3: (A) x, y + 1, z; (B) ꢁx + 1, y + 1, ꢁz + 3/2; (C)
ꢁx + 1, ꢁy + 1, ꢁz + 2; (D) ꢁx + 1, y ꢁ 1, ꢁz + 3/2; (E) x, y ꢁ 1, z.
into a higher network through p–p stacking interactions
between the dpa pairs.
Interestingly, through strong aromatic p–p stacking
interactions between the dpa ligands (face-to-face
˚
3.685 A) and N–Hꢀ ꢀ ꢀO hydrogen bonds between the dpa
nitrogen atom (N(3)) and carboxyl oxygen atoms (O(4))
˚
(N(3)ꢀ ꢀ ꢀO(4) 2.886 A and N(1)–Hꢀ ꢀ ꢀO(2) 165.34°), the
adjacent helical chains generate a 2D wavelike network
with unusual parallelogram grids, and presents a (4,4) net
in topology, as shown in Fig. 3. As a result, the cavity
Scheme 1. The coordination modes of oba2ꢁ anions.
shape deviates from a regular square to a rhombus with
˚
size of about 21.377 ꢃ 15.729 A along the two diagonal
directions. The bent structure of oba contributes about
˚
10 A of the thickness of the layer, in which ether–oxygen
sites of oba remarkably stick out from the plane. The net-
work motif is similar to [Cu(oba)(2,20-bpy)]n [26], despite
the large cavities, these layers stack along the c-axis with-
out interpenetration. The thickness of the layer could inhi-
bit the possibility of interpenetration. Otherwise the
available void space of the grid is vacancy and the back-
bone is stabilized by N–Hꢀ ꢀ ꢀOcooꢁ hydrogen bonds. Fur-
thermore, those grids are enlarged to form the final 3D
framework when viewed along the crystallographic c-axis
(Fig. 4).
Fig. 1. The coordination environments of metal atoms in complex 1 with
30% thermal ellipsoids. All hydrogen atoms are omitted for clarity.
angle of the two benzene rings is ca. 80.9°). Obviously, this
twist is an important factor in forming the helical structure.
All dpa groups bristle out from the two sides of the helix,
and the oba phenyl rings at each side of the helix are
arranged in a parallel fashion with an interring distance
3.1.2. Structure of [Cu(oba)(bpy)1/2]n (3)
The coordination environment of the Cu(II) ions in
complex 3 is shown in Fig. 5. The asymmetric unit of 3 con-
sists of 26 non-hydrogen atoms, of which one Cu atom is
crystallographically independent. The Cu(II) ions have a
trigonal bipyramid geometry formed by four carboxylate
˚
of 25.737 A. This orientation plays a critical role in packing

348
L. Tang et al. / Journal of Molecular Structure 888 (2008) 344–353
Fig. 2. The helical chain of complex1 along the a-axis.
connectivity with the Cu(II) cations forming an eight-mem-
bered ring chains, as shown in Fig. 6; in which the adjacent
˚
˚
Cuꢀ ꢀ ꢀCu distances are alternately 3.0195 A and 4.414 A.
The bond distances and angles associated with the oba
anions are in the ranges expected for this type of bonding
[26,28]. The corresponding bond distances 3 are listed in
Table 2.
The connectivity between the corner-shared eight-mem-
bered ring chains are further bridged by the bent oba
ligands to produce 2D helical layers lying the ac plane
(Fig. 7). When viewed along the c-axis, these 2D layers
can be regarded as sine- and cosine-type curves intersecting
at the zero points (see Fig. S4 in the Supporting Informa-
tion). Of particular interest is that adjacent helical layers
are connected by bpy as molecular pillars to form a novel
3D framework featuring with channels along b-axis
(Fig. 8a). But the channels are too small to residue any
guests. From a topological perspective, the structure of 3
reveals that it is a complicated 3D framework containing
multiform adamantanoid cages. Considering the Cu atoms
and the C atoms of the l-carboxylate groups as nodes, we
can see that the neutral (3,5)-connected layer of composi-
tion [Cu(oba)], these 2D sheets are further connected
together in the third dimension by axially coordinating
bpy ligands to give a unique (3,5)-connected 3D net with
an unprecedented topology of (315ꢀ420ꢀ58ꢀ62) (Fig. 8b).
The potential free volume determined by PLATON [29]
Fig. 3. View of 2D grid layer along the ab plane and the (4,4) net in
complex 1.
´
´
3
˚
3
˚
calculation is 281 A per unit cell volume (3443 A ) which
represents 8.1% of void per unit volume for 3(taking into
account the van der Waals volume of the atoms).
The most fascinating structural feature of 3 is that the
two distinct helical chains running along the different crys-
tallographic axis coexist in the 3D network. One type of
helices are right-handed helical chains, and built from
bpy bridges between the Cu centers with a pitch of
Fig. 4. The 3D supramolecular framework of complexes 1 viewed along
the c-axis.
˚
13.034 A running along the c-axis (Fig. S5(a and b) in
the Supporting Information). These right-handed helical
chains, the one-end coordinated bpy groups, are further
grafted on the 3D network with helical channels (All oba2ꢁ
anions are omitted for clarity), as shown in Fig. 9a. The
other type of helices are the double-stranded helices chains
in the 2D helical layer and formed by the V-shaped oba
ligands bridging Cu atoms, which is generated around the
crystallographic 21 axis in the b direction with a pitch of
oxygen atoms and a nitrogen atom of the bpy. The Cu–O
˚
bond lengths are in the range 1.952(2)–2.172(2) A, and
˚
the Cu–N bond distance has a value of 1.999(2) A. So,
the coordination geometry around the copper(II) atom
can be regarded as a Jahn–Teller-distorted [27] trigonal
bipyramid. The O/N–Cu–O/N bond angles are in the range
85.86(9)–172.03(10)°. There is only one oba anion present
in the structure, and each oba ligand adopts a bis(bridg-
ing-bidentate) mode (see Scheme 1 (II)) and links four
Cu(II) ions. The carboxylate groups of oba ligands have
˚
13.653 A (Fig. 9b), displaying a same helical orientation
to the former helix. A striking feature of 3 is the alternating
interweaving of two types of helices along the b- and c-axis
to construct a 3D framework (Fig. 9c). Herein, the bpy

L. Tang et al. / Journal of Molecular Structure 888 (2008) 344–353
349
Fig. 5. The coordination environments of Cu atoms in complex 3. All hydrogen atoms are omitted for clarity.
Fig. 6. The eight-membered ring chains of complex 3.
Fig. 7. The 2D helical layers of complex 3 viewed lying the ac plane.
molecules have both in-plane and out of plane connectiv-
ity. Viewing down the c-axis, the linkages between the
Cu(II) ions and the oba anions are cross-linked by the
bpy molecules.
ligands up to 210 °C; after this, significant weight losses
occurred and ended at ca. 525 °C, indicating the complete
decomposition of the complex to form CoO, which was
confirmed by X-ray powder diffraction analysis. This con-
clusion has been also supported by the percentage of the
residues (15.67%), which is in accordance with the expected
value (15.41%). The TG traces of 2 and 1 are analogous.
Compared with 1 and 2, complex 3 exhibits relatively ther-
mal stability. TGA analyses show that it has an onset tem-
perature for decomposition above 300 °C. The stability of
the complex makes it potential candidates for practical
applications.
3.2. Thermogravimetric analysis
To study the thermal stability of 1–3, thermogravimetric
(TG) analyses were performed on polycrystalline samples
under a nitrogen atmosphere (Figs. S6 and S7 in the Sup-
porting information). TG curve of complex 1 illustrates
that no weight losses were observed for either of the two

350
L. Tang et al. / Journal of Molecular Structure 888 (2008) 344–353
perature range 5–300 K in here. The magnetic susceptibili-
ties vM and vMT versus T plots are shown in Fig. 10. For
complex 1, the experimental vMT value at 300 K is
1.95 cm3 K molꢁ1, somewhat larger than the spin-only
value (1.88 cm3 K molꢁ1) expected for two isolated spin-
only Co(II) ion (S = 3/2, Fig. 10a). The vMT value of 1
remains almost constant from 300 to 110 K, and then
decreases on further cooling, reaching
a value of
1.48 cm3 K molꢁ1 at 5 K. This behavior indicates a weak
antiferromagnetic interaction between the Co(II) ions in
the structures. In 1, the Coꢀ ꢀ ꢀCo distance through the oba
˚
bridge is 14.379 A. The temperature dependence of the reci-
procal susceptibilities (1/vM) obeys the Curie–Weiss law
above 5 K with h =ꢁ 1.68 K, C = 1.96 and R = 1.082 ꢃ
P
P
10ꢁ4 (R = [(vM)obs ꢁ (vM)calc]2/ [(vM)obs]2). The values
of h for the complex 1 indicate weak antiferromagnetic
interactions between the adjacent Co(II) (S = 3/2) ions.
For complex 2, the experimental vMT value at 300 K is
0.87 cm3 K molꢁ1, somewhat larger than the spin-only
value (0.75 cm3 K molꢁ1) expected for two isolated spin-
only Cu(II) ion (S = 1, Fig. 10b). As the temperature is
lowered, the vMT value increases gradually, which indicat-
ing the presence of antiferromagnetic interactions in 2. The
temperature dependence of the reciprocal susceptibilities
(1/vM) obeys the Curie–Weiss law above 5 K with
h =ꢁ2.06 K, C = 0.89 and R = 3.148 ꢃ 10ꢁ4. The values
of h for the complex 2 indicate weak antiferromagnetic
interactions between the adjacent Cu(II) ions.
For complex 3, the vMT value at 300 K is
0.229 cm3 K molꢁ1, which is much less than the expected
value (0.375 cm3 K molꢁ1) of two isolated spin-only Cu(II)
ions (S = 1/2, Fig. 10c). As T is lowered, vMT decreases
continuously to a value of 0.045 cm3 K molꢁ1 at 5 K. This
behavior indicates a dominant antiferromagnetic interac-
tion between the Cu(II) ions in the structures. As the short-
est Cuꢀ ꢀ ꢀCu distance across the carboxylate groups of oba
Fig. 8. (a) The 3D pillared-layer structure of complex 3 viewed along the
b-axis; (b) schematic views of the (3,5)-connected net of (315ꢀ420ꢀ58ꢀ62)
topology of 3.
˚
ligands are alternately 3.0195 and 4.414A in 3, the mag-
3.3. Magnetic properties
netic exchange coupling through the oba ligands are
expected to be very strong [30]. The observed antiferromag-
netic interaction, therefore, should mainly arise from the
magnetic superexchange through the –CO2 bridge. The
Complexes 1 and 2 are isostructural, and the magnetic
properties of complexes 1–3 were investigated over the tem-
Fig. 9. (a) The 3D network with helical channels by bpy bridges in complex 3 viewed along the c-axis, all oba2ꢁ anions are omitted for clarity. (b)
Spacefilling diagram of the helical chains in the 2D helical layer. (c) The 3D network of complex 3 viewed along the c-axis.

L. Tang et al. / Journal of Molecular Structure 888 (2008) 344–353
351
Ng2b2SðS þ 1Þ 1 þ u
0.30
0.25
0.20
0.15
0.10
0.05
0.00
2.0
vM
¼
ð1Þ
3KT
1 ꢁ u
1.9
1.8
1.7
1.6
1.5
1.4
where
ꢀ
ꢁ
ꢀ
ꢁ
JSðS þ 1Þ
kT
JSðS þ 1Þ
u ¼ coth
ꢁ
kT
Finally, this expression fits very well with the experimen-
tal susceptibilities of 1–3, giving J = ꢁ1.37 cmꢁ1, g = 2.04,
R = 8.30 ꢃ 10ꢁ5 for 1, J = ꢁ1.90 cmꢁ1, g = 2.18 and R =
3.406 ꢃ 10ꢁ5 for 2 and J = ꢁ23.0 cmꢁ1, g = 1.90 and
R = 1.018 ꢃ 10ꢁ3 for 3, the agreement factor defined as
0
0
0
50
50
50
100
100
100
150
T / K
200
200
200
250
250
250
300
300
300
P
P
R = [(vM)obs ꢁ (vM)calc]2/ [(vM)obs]2, where the J value
is in agreement with the value of h deduced above. It is
obviously due to a long-range superexchange pathway
between adjacent magnetic centers [32].
0.15
0.10
0.05
0.00
0.90
0.85
0.80
0.75
0.70
0.65
4. Conclusions
This work demonstrates that flexible exo-bidentate
ligands can be employed in transitional metal M(II) ions
(M = Co, Cu)/aromatic chelate ligand/linear ligand sys-
tems to generate both 1D helical and 3D pillared helical
layer polymers. In contrast to previously reported coordi-
nation polymers based on 4,40-oxy(bisbenzoate) ligand,
when employing the chelate ligand 2,20-dipyridylamine,
we obtained three isomorphous coordination polymers
with a 1D helical chain through hydrothermal method,
namely [Co(oba)(dpa)]n (1), [Cu(oba)(dpa)]n (2) and [Zn(o-
ba)(dpa)]n [33]. Herein, the presence of chelate ligands in
transition metal dicarboxylate systems usually results in
the formation of low-dimensional coordination polymers,
especially 1D chains, and the employment of a flexible
oba ligand may generate helical chains. While the rigid
ligand 4,40-bipyridine is used instead of chelate ligand,
the bpy molecule, a linear ancillary ligand, acting as molec-
ular pillar, a novel pillared helical layer coordination poly-
mer ([Cu(oba)(bpy)1/2]n (3)) is produced. The structure of 3
consists of the 2D helical layers, which are connected by
bpy pillars to generate a novel 3D framework with an
unprecedented topology of (315ꢀ420ꢀ58ꢀ62), in which two dis-
tinct helical chains coexist running along the different crys-
tallographic axis in the 3D network. In addition, the
magnetic behavior of complexes 1–3 were investigated
and exhibited antiferromagnetic interactions.
150
T / K
0.010
0.008
0.006
0.004
0.002
0.000
0.25
0.20
0.15
0.10
0.05
0.00
150
T / K
Fig. 10. a) Thermal variation of vM and vMT for compound 1. (b)
Thermal variation of vM and vMT for compound 2. (c) Thermal variation
of vM and vMT for compound 3.
temperature dependence of the reciprocal susceptibilities
(1/vM) obeys the Curie–Weiss law above 5 K with
h = ꢁ23.9 K, C = 0.25 and R = 1.774 ꢃ 10ꢁ4. The values
of h for the complex 3 exhibit very strong antiferromag-
netic interactions between the adjacent Cu(II) (S = 1/2)
ions.
To simulate the experimental magnetic behavior, we use
the analytical expression for a one-dimensional Heisenberg
chain of classical spins [S = 1] that similar to 1–3 [31].
Acknowledgments
This work was supported by the National Natural Sci-
ence Foundation of China (No. 20773104), the Program
for New Century Excellent Talents in University (NCET-
06-0891), the Nature Scientific Research Foundation of
Shaanxi Provincial Education Office of China (No.
06JK155) and the Natural Science Foundation of Shaanxi
Provinces of China (No. 2006B08).

352
L. Tang et al. / Journal of Molecular Structure 888 (2008) 344–353
Kobayashi, S. Horike, M. Takata, J. Am. Chem. Soc. 126 (2004)
Appendix A. Supplementary data
14063;
(c) C.N.R. Rao, S. Natarajan, R. Vaidhyanathan, Angew. Chem. Int.
Ed. 116 (2004) 1466.
[6] S. Kitagawa, R. Kitaura, Comments Inorg. Chem. 23 (2002) 101.
[7] (a) K.T. Holman, A.M. Pivowar, J.V. Swift, M.D. Ward, Acc. Chem.
Res. 34 (2001) 107;
(b) M.J. Zaworotko, Chem. Commun. (2001) 1.
[8] G.K.H. Shimizu, G.D. Enright, C.I. Ratcliffe, J.A. Ripmeester,
Chem. Commun. (1999) 461.
[9] (a) A. Clearfield, Prog. Inorg. Chem. 47 (1998) 371;
(b) D. Medoukali, P.H. Mutin, A. Vioux, J. Mater. Chem. 9 (1999)
2553.
Additional crystallographic data sets for the structures
are available through the Cambridge Structural Data Base,
as supplementary publication reference number CCDC-
661779 for complex (1); CCDC-661778 for complex (2)
and CCDC-661780 for complex (3). Copies of this informa-
tion may be obtained from the Director, CCDC, 12 Union
Road, Cambridge, CB21EZ, UK (fax: +44 1223 336033;
email: deposit@ccdc.cam.ac.uk or http:www.ccdc.cam.
ac.uk). Supporting information associated with this article
can be found, in the online version. The structure of 2,
the sine- and cosine-type curves of the 2D layer in complex
3 viewed along the c-axis, the right-handed helical chain is
built from bpy bridges between the Cu centers in complex
3 running along the c-axis, and TG curve of 1 and 3.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.molstruc.2007.12.032.
[10] (a) Y.D. Posner, S. Dahal, I. Goldberg, Angew. Chem. Int. Ed. 39
(2000) 1288;
(b) H.L. Ngo, W. Lin, J. Am. Chem. Soc. 124 (2002) 4298;
(c) J.L. Song, H.H. Zhao, J.G. Mao, K.R. Dunbar, Chem. Mater. 16
(2004) 1884;
(d) D.R. Xiao, E.B. Wang, H.Y. An, Y.G. Li, Z.M. Su, C.Y. Sun,
Chem. Eur. J. 12 (2006) 6528.
[11] (a) B. Moulton, M.J. Zaworotko, Chem. Rev. 101 (2001) 1629;
(b) M. Albrecht, Chem. Rev. 101 (2001) 3457;
(c) T. Nakano, Y. Okamoto, Chem. Rev. 101 (2001) 4013;
(d) Z. Shi, S.H. Feng, S. Gao, L. Zhang, G. Yang, J. Hua, Angew.
Chem. Int. Ed. 39 (2000) 2325;
References
(e) G. Tian, G.S. Zhu, X.Y. Yang, Q.R. Fang, M. Xue, J.Y. Sun, Y.
Wei, S.L. Qiu, Chem. Commun. (2005) 1396.
[1] (a) O.M. Yaghi, M. OOKeeffe, N.W. Ockwig, H.K. Chae, M.
Eddaoudi, J. Kim, Nature 423 (2003) 705;
[12] (a) T.E. Gier, X. Bu, P. Feng, G.D. Stucky, Nature 395 (1998) 154;
(b) D.R. Xiao, Y. Xu, Y. Hou, E.B. Wang, S.T. Wang, Y.G. Li, L.
Xu, C.W. Hu, Eur. J. Inorg. Chem. (2004) 1385;
(c) X.L. Wang, C. Qin, E.B. Wang, Y.G. Li, C.W. Hu, L. Xu, Chem.
Commun. (2004) 378.
[13] (a) Y. Cui, S.J. Lee, W. Lin, J. Am. Chem. Soc. 125 (2003) 6014;
(b) J.P. Zhang, Y.Y. Lin, X.C. Huang, X.M. Chen, Chem. Commun.
(2005) 1258;
(b) R. Kitaura, K. Fujimoto, S. Noro, M. Kondo, S. Kitagawa,
Angew. Chem. Int. Ed. 41 (2002) 133;
(c) S. Kitagawa, R. Kitaura, S.I. Noro, Angew. Chem. Int. Ed. 43
(2004) 2334;
(d) X.L. Wang, C. Qin, E.B. Wang, Y.G. Li, Z.M. Su, L. Xu, L.
Carlucci, Angew. Chem. Int. Ed. 44 (2005) 5824;
(e) C.N.R. Rao, S. Natarajan, A. Choudhury, S. Neeraaj, A.A. Ayi,
Acc. Chem. Res. 34 (2001) 80;
(f) B. Moulton, M.J. Zaworotko, Chem. Rev. 101 (2001) 1629;
(g) X.L. Wang, C. Qin, E.B. Wang, Z.M. Su, Chem. Eur. J. 12 (2006)
2680;
(c) X.L. Wang, C. Qin, E.B. Wang, L. Xu, Z.M. Su, C.W. Hu,
Angew. Chem. Int. Ed. 43 (2004) 5036;
(d) C.D. Wu, C.Z. Lu, X. Lin, D.M. Wu, S.F. Lu, H.H. Zhuang, J.S.
Huang, Chem. Commun. (2003) 1284;
(e) O. Mamula, A.V. Zelewsky, T. Bark, G. Bernardinelli, Angew.
Chem. Int. Ed. 38 (1999) 2945.
(h) S.N. Wang, H. Xing, Y.Z. Li, J.F. Bai, M. Scheer, Y. Pan, X.Z.
You, Chem. Commun. (2007) 2293.
[14] (a) M. Kondo, M. Miyazawa, Y. Irie, R. Shinagawa, T. Horiba, A.
Nakamura, T. Naito, K. Maeda, S. Utsuno, F. Uchida, Chem.
Commun. (2002) 2156;
(b) D.F. Sun, R. Cao, Y.Q. Sun, W.H. Bi, X. Li, M.C. Hong, Y.J.
Zhao, Eur. J. Inorg. Chem. (2003) 38.
[15] (a) L. Han, M.C. Hong, R.H. Wang, J.H. Luo, Z.Z. Lin, D.Q. Yuan,
Chem. Commun. (2003) 2580;
(b) J. Liang, Y. Wang, J.H. Yu, Y. Li, R.R. Xu, Chem. Commun.
(2003) 882.
[16] (a) S. Noro, S. Kitagawa, M. Kondo, K. Seki, Angew. Chem. Int. Ed.
39 (2000) 2081;
(b) M.L. Tong, H.J. Chen, X.M. Chen, Inorg. Chem. 39 (2000) 2235.
[17] (a) L. Pan, H.M. Liu, S.P. Kelly, X.Y. Huang, D.H. Olson, J. Li,
Chem. Commun. (2003) 854;
[2] (a) G.J. Halder, C.J. Kepert, B. Moubaraki, K.S. Murry, J.D.
Cashion, Science 298 (2002) 1762;
(b) T.J. Prior, D. Bradshaw, S.J. Teat, M.J. Rosseinsky, Chem.
Commun. (2003) 500;
(c) A. Galet, M.C. Munoz, J.A. Real, J. Am. Chem. Soc. 125 (2003)
14224;
(d) B.Q. Ma, H.L. Sun, S. Gao, Chem. Commun. (2003) 2164;
(e) L. Pan, H. Liu, X. Lei, X. Huang, D.H. Olson, N.J. Turro, J. Li,
Angew. Chem. Int. Ed. 42 (2003) 542;
(f) X.H. Bu, M.L. Tong, H.C. Chang, S. Kitagawa, S.R. Batten,
Angew. Chem. Int. Ed. 43 (2004) 192.
[3] (a) D.L. Reger, T.D. Wright, R.F. Semeniuc, T.C. Grattan, M.D.
Smith, Inorg. Chem. 40 (2001) 6212;
(b) M.B. Zaman, M.D. Smith, H.C. zur Loye, Chem. Commun.
(2001) 2256;
(c) R. Kitaura, K. Seki, G. Akiyama, S. Kitagawa, Angew. Chem. Int.
Ed. 42 (2003) 428.
(b) C.S.C. Fernandez, L.M. Thomson, J.R.G. Mascaros, O.Y. Xiang,
K.R. Dunbar, Inorg. Chem. 41 (2002) 1523;
(c) S.A. Bourne, J.J. Lu, B. Moulton, M.J. Zaworotko, Chem.
Commun. (2001) 861.
[4] (a) D.F. Sun, R. Cao, Y.Q. Sun, W.H. Bi, D.Q. Yuan, Q. Shi, X. Li,
Chem. Commun. (2003) 1528;
[18] (a) F.A. Cotton, C. Lin, C.A. Murillo, Inorg. Chem. 40 (2001) 478;
(b) G.F. Liu, B.H. Ye, Y.H. Ling, X.M. Chen, Chem. Commun.
(2002) 1442;
(c) X.J. Li, R. Cao, D.F. Sun, W.H. Bi, Y.Q. Wang, X. Li, M.C.
Hong, Cryst. Growth Des. 4 (2004) 775.
[19] (a) F.A.A. Paz, Y.Z. Khimyak, A.D. Bond, J. Rocha, J. Klinowski,
Eur. J. Inorg. Chem. (2002) 2823;
(b) S.A. Bourne, J.J. Lu, A. Mondal, B. Moulton, M.J. Zaworotko,
Angew. Chem. Int. Ed. 40 (2001) 2111;
(c) X.M. Zhang, X.M. Chen, Eur. J. Inorg. Chem. (2003) 413;
(d) S.T. Wang, Y. Hou, E.B. Wang, Y.G. Li, L. Xu, J. Peng, S.X. Liu,
C.W. Hu, New J. Chem. (2003) 1144.
[5] (a) N.W. Ockwig, O. Delgado-Friederichs, M. OZKeeffee, O.M.
Yaghi, Acc. Chem. Res. 38 (2005) 176;
(b) J. Tao, M.L. Tong, X.M. Chen, J. Chem. Soc. Dalton Trans.
(2000) 3669;
(b) R. Matsuda, R. Kitaura, S. Kitagawa, Y. Kubota, T.C.

L. Tang et al. / Journal of Molecular Structure 888 (2008) 344–353
353
(c) P.M. David, M.S. Ronald, L.L. Robert, Inorg. Chem. 46 (2007)
7917.
[23] G.M. Sheldrick, SADABS, A Program for Empirical Absorption
Correction of Area detector Data, University of Go¨ttingen, Germany,
1997.
[24] G.M. Sheldrick, SHELXS 97, Program for Crystal Structure Solu-
tion, University of Go¨ttingen, Germany, 1997.
[25] G.M. Sheldrick, SHELXL 97, Program for Crystal Structure Refine-
ment, University of Go¨ttingen, Germany, 1997.
[26] X.M. Chen, G.F. Liu, Chem. Eur. J. 8 (2002) 4811.
[27] X.J. Luan, Y.Y. Wang, L.J. Zhou, X.H. Cai, C.H. Zhou, Q.Z. Shi, J.
Mol. Struct. 750 (2005) 58.
[20] (a) Z. Shi, S.H. Feng, Y. Sun, J. Hua, Inorg. Chem. 40 (2001) 5312;
(b) P. Lightfoot, A. Snedden, J. Chem. Soc. Dalton Trans. (1999) 3549.
[21] (a) X.H. Bu, W. Chen, S.L. Lu, R.H. Zhang, D.Z. Liao, W.M. Bu, M.
Shionoya, F. Brisse, J. Ribas, Angew. Chem. Int. Ed. 40 (2001) 3201;
(b) D.M.L. Goodgame, D.A. Grachvogel, I. Hussain, A.J.P. White,
D.J. Williams, Inorg. Chem. 38 (1999) 2057.
[22] (a) Z.B. Han, X.N. Cheng, X.M. Chen, Cryst. Growth Des. 5 (2005)
695;
(b) Y.Z. Zheng, G.F. Liu, B.H. Ye, X.M. Chen, Z. Anorg. Allg.
Chem. 630 (2004) 296;
(c) Y.B. Wang, Z.M. Wang, C.H. Yan, L.P. Jin, J. Mol. Struct. 692
(2004) 77;
(d) M. Kondo, Y. Irie, Y. Shimizu, M. Miyazawa, H. KawaguchiA.
Nakamura, T. Naito, K. Maeda, F. Uchida, Inorg. Chem. 43 (2004) 6139;
(e) G.F. Liu, Z.P. Qiao, H.Z. Wang, X.M. Chen, G. Yang, New J. Chem.
26 (2002) 791;
[28] C.Y. Sun, L.P. Jin, J. Mol. Struct. 782 (2006) 171.
[29] A.L. Spek, PLATON, A Multipurpose Crystallographic Tool, Utr-
echt, The Netherlands, 2001.
[30] L.M. Zheng, X.Q. Wang, Y.S. Wang, A.J. Jacobson, J. Mater. Chem.
11 (2001) 1100.
[31] O. Kahn, Molecular Magnetism, VCH, New York, 1993.
[32] (a) P.S. Mukherjee, D. Ghoshal, E. Zangrando, T. Mallah, N.R.
Chaudhuri, Eur. J. Inorg. Chem. (2004) 4675;
(f) J. Tao, J.X. Shi, M.L. Tong, X.X. Zhang, X.M. Chen, Inorg. Chem. 40
(2001) 6328;
(g) C.Y. Sun, X.J. Zheng, S. Gao, L.C. Li, L.P. Jin, Eur. J. Inorg. Chem.
(2005) 4150.
(b) S. Dalai, P.S. Mukherjee, G. Rogez, T. Mallah, M.G.B. Drew,
N.R. Chaudhuri, Eur. J. Inorg. Chem. (2002) 3292.
[33] L. Tang, D.S. Li, F. Fu, J.J. Wang, H.M. Hu, Y.Y. Wang, Chin. J.
Chem. 25 (2007) 1641.