A novel helical chainlike nickel(II) coordination polymer containing 1D trigonal channels with water molecule guests

Article abstract of DOI:10.1016/j.inoche.2010.08.021

A novel 1D helical nickel coordination polymer, [Ni(TAU) ₂(4,4′-bipy)]_n?2nH₂O (TAU = taurine, 4,4′-bipy = 4,4′-bipyridine), was synthesized and its crystal structure has been determined by X-ray diffraction. Each helix interlinks with six adjacent helices through extensive hydrogen bonds to form 3D supramolecular structure, in which 1D trigonal microporous channels filled with water guest molecules exist within the polymer coils. The framework remains intact on removal of guest water molecules which is proved by XPRD and TGA. Variable temperature magnetic susceptibility indicates weak anti-ferromagnetic interactions between the Ni(II) ions.

Full text of DOI:10.1016/j.inoche.2010.08.021

Inorganic Chemistry Communications 13 (2010) 1476–1479
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
A novel helical chainlike nickel(II) coordination polymer containing 1D trigonal
channels with water molecule guests
b,
Chengzhi Xie a,b, Qiaojuan Su a, Shaohua Li a, Jingyuan Xu a, , Liya Wang
⁎
⁎
a
School of Pharmaceutical Sciences, Tianjin Medical University, Tianjin 300070, PR China
b
College of Chemistry & Chemical Engineering, Luoyang Normal University, Luoyang, 471022, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel 1D helical nickel coordination polymer, [Ni(TAU)2(4,4′-bipy)]n·2nH2O (TAU = taurine, 4,4′-bipy =
4,4′-bipyridine), was synthesized and its crystal structure has been determined by X-ray diffraction. Each
helix interlinks with six adjacent helices through extensive hydrogen bonds to form 3D supramolecular
structure, in which 1D trigonal microporous channels filled with water guest molecules exist within the
polymer coils. The framework remains intact on removal of guest water molecules which is proved by XPRD
and TGA. Variable temperature magnetic susceptibility indicates weak anti-ferromagnetic interactions
between the Ni(II) ions.
Received 29 June 2010
Accepted 17 August 2010
Available online 24 August 2010
Keywords:
Helical chain
1D channel
Solvothermal synthesis
Taurine
© 2010 Elsevier B.V. All rights reserved.
4,4′-Bipyridine
Magnetic property
Recently, the assembly of metal-organic open frameworks (MOFs)
has attracted great attention; MOFs with various network topologies
have been prepared by using metal ions and organic building blocks
[1]. MOFs with the flexible or rigid microporous channels have
potential applications in selective molecular recognition and separa-
tion [2], physical gas storage [3], sensors [4], ion-exchange [5] and
heterogeneous catalysis [6]. Chirality is also central in the assembly
and construction of biological and chemical materials, both in their
natural and synthetic forms. Among the chiral materials, there is
strong interest in the design of chiral coordination polymers [7]. In
many cases chiral coordination polymers are prepared with chiral
ligands, which is a reliable method to introduce chirality to the
structure but the preparation of chiral ligands is a laborious task [6,8].
Another approach is to form a chiral structure using chiral
arrangement of achiral components [9].
Although it is not yet possible to prepare fully predictable metal-
organic frameworks, the selective combination of metal centers,
bridging ligands and co-ligands is an effective strategy for rational
design and creative synthesis of desired frameworks. Thus, in
designing extended porous coordination polymers and helical
coordination polymers, the judicious selection of the properties of
the ligands, such as shape, functionality, flexibility, symmetry, length,
and substituent group is crucial to the construction of target polymers
[10]. Despite the simple and common formula, the rigid rod-like
ligand 4,4′-bipy has been used extensively to ligate metal ions into an
open framework with channels [5,11]. And 4,4′-bipy ligands can also
lead to the helical structures when linked by appropriate connectors
in assembly process. For example, [Ni(4,4′-bipy)(ArCOO)2(MeOH)2]n
self-assembles as a helical architecture, in which octahedral metals
are connected by linear 4,4′-bipy [9]. However, very few helical
structures constructed from sulfonic ligands have been reported,
partly due to the weak coordinating ability of sulfonate ligands [12].
Recently, we began to study the reactions of the flexible amino acid
ligand taurine (TAU), also named as 2-aminoethanesulfonic acid, and
co-ligand 4,4′-bipy with metal ions, with the aim of obtaining
information on the coordination ability of sulfonic ligands and for
constructing novel coordination architectures. Hydrothermal and
solvothermal syntheses have been demonstrated to be an effective
and powerful technique for forming extended porous coordination
polymer structures [13]. In this work, the solvothermal reaction of Ni
(CH3COOH)2 with 4,4-bipy, TAU and NaOH leads to the formation of a
crystalline complex [14], which was analyzed via X-ray crystallogra-
phy analysis [15].
Molecular structure of [Ni(TAU)2(4,4′-bipy)]n·2nH2O (1) is shown
in Fig. 1. Complex 1 crystallizes in the chiral space group P-3121 with
one-half Ni(II) ion, one TAU anion, one-half 4,4′-bipy ligand, and one
water guest molecule in the crystallographically asymmetric unit.
Each Ni(II) ion is six-coordinate in a distorted octahedral environment
defined by two oxygen atoms (O1 and O1A) and two nitrogen atoms
(N1 and N1A) from two chelate TAU ligands, as well as two nitrogen
atoms from two 4,4′-bpy ligands in cis fashion with the N2–Ni1–N2A
angle of 88.80(18)°. The Ni–N bond distances are 2.114(3) and 2.109
(3) Å, and the Ni–O bond distance is 2.101(2) Å, close to that of the
⁎
Corresponding authors. Xu is to be contacted at School of Pharmaceutical Sciences,
Tianjin Medical University, Tianjin 300070, PR China. Wang, College of Chemistry &
Chemical Engineering, Luoyang Normal University, Luoyang, 471022, PR China.
E-mail addresses: jyxem@yahoo.com.cn (J. Xu), wlya@lynu.edu.cn (L. Wang).
1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2010.08.021

C. Xie et al. / Inorganic Chemistry Communications 13 (2010) 1476–1479
1477
Fig. 1. Molecular structure of [Ni(TAU)2(4,4′-bipy)]n·2nH2O (1), all hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles (°): Ni1–O1 2.101(2); Ni1–N1
2.114(3); Ni1–N2 2.109(3); O1A–Ni1–O1 178.14(15); O1–Ni1–N2A 91.34(11); O1–
Ni1–N2 87.33(11); N2A–Ni1–N2 88.80(18); O1–Ni1–N1 89.56(12); N2–Ni1–N1 175.06
(14); O1–Ni1–NA1 91.68(12); N2–Ni1–N1A 87.43(12); N1–Ni1–N1A 96.50(18).
Symmetry code: A=−x, −x+y, −z+1/3.
literature [16]. The Ni(II) ions are bridged by bidentate 4,4′-bipy
ligand with the Ni–Ni distance of 11.288(1) Å (in which two pyridyl
rings are twisted from each other with the dihedral of 10.8°) to form
an infinite helical chain running along the c-axis (Fig. 2). The right-
handed helix is generated around the crystallographic 31 axis. Each set
of three crystallographically equivalent nickel centers constitutes a
single revolution of the helix with a distance of 21.53 Å. The helical
chains align in a parallel fashion. Therefore, the bulk crystal is chiral as
every helix in an individual crystal is of the homochirality. There is
one previous example of 1D Ni(II) zigzag chain polymer [4,4′-bipy-Ni
(Et-XA)2·0.5EtOH·CHCl3]n (Et-XA = ethylcarbonadithiolate), with
4,4′-bipy bridges having a similar cis-conformation, in which solvate
molecules sit in open channels which are formed by the packing of the
linear polymeric chains of the complex [17]. The similar local
coordination geometry of Ni(II) units of two complexes leads to two
different 1D structures because of the chiral arrangement of the Ni(II)
units in complex 1 comparing with the reported 1D zigzag complex.
Interestingly, the view along the polymer axis (Fig. 3) shows that a
trigonal channel with side length approximately 8.4 Å exists within
the polymer coil, which is filled with water guest molecules. The
PLATON [18] program reveals that the voids in complex 1 occupy
13.4% of the crystal volume (after the removal of the guest water
molecules). Each helix further interlinks with six adjacent helices to
give a periodically ordered 3D chiral framework, where the interchain
C–H⋯O hydrogen bond contacts between neighboring aromatic C–H
groups of 4,4′-bipy and the oxygen atoms of sulfonate groups of TAU
are found, and the C–H⋯O distances and the C–H⋯O angles are 3.222
(6) Å and 151.5(3)°, respectively (Fig. S1). In trigonal channels, the
guest water molecules are interconnected by single hydrogen bonds
(Fig. S2a) between two neighboring ones into helical chains (Fig. S2b).
The O–H⋯O distances and the O–H⋯O angles are 2.810(13) Å and
117.2(5)°, respectively. In addition, all water molecules are hydrogen
bonded to the sulfonate oxygen atoms (O2) of TAU in the
circumambient helical chain (the O–H⋯O distances and the O–H⋯O
angles are 2.810(13) Å and 117.2(5)°, respectively). Similar 1D helical
water chains have been reported in the cocrystal structure of
melamine and trimesic acid, in which a pair of 1:1 left- and right-
handed helices exists in the channels [19].
Fig. 2. Right-handed 31 helical chain built from alternating Ni(TAU)2 and 4,4-bipy.
condition from room temperature to 800 °C for examining the
properties of dehydration and stability of 1 (Fig. S3). The first stage
of weight loss is 7.05% in the temperature range 50–195 °C,
corresponding to the loss of two uncoordinated water molecules per
empirical formula (calculated 7.21%). The second weight loss occurs
from 265 to 550 °C corresponding to the loss of organic ligands. After
decomposition of complex 1 at high temperature, the weight of the
residue (15.65%) is responded to NiO (calcd: 14.96%). We explored
whether the framework would break down on removal of guest water
molecules. Water molecules were removed by heating 1 directly to
200 °C and keeping for 1 h in an oven. And the sample was re-
hydrated by standing the heated sample of 1 in air for 24 h. X-ray
powder diffraction (XPRD) patterns of hydrated, dehydrated and re-
hydrated samples of 1 are nearly identical (Fig. 4), which supports the
notion that the crystal lattice remains intact after the guest water
molecules have been removed and reintroduced.
Complex 1 is stable in air at ambient temperature and is almost
insoluble in common solvents such as water, alcohol, acetonitrile,
chloroform, acetone, and toluene, being consistent with its polymeric
nature. Thermal gravimetric analysis (TGA) was carried out in N2

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C. Xie et al. / Inorganic Chemistry Communications 13 (2010) 1476–1479
0 50 100
150
200
250
300
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.5
0.4
0.3
0.2
0.1
0.0
0.0
0
50
100
150
T/K
200
250
300
Fig. 5. μeff (Δ)versus Tandχm (ο)versus Tplot for 1, the solid lines represent the best fit curve.
fitted values are in good agreement with the experimental data and
the parameters J = −0.38 cm−1, g = 2.21 and R = 1.57×10−4
(R=∑(χobsd −χ′cacld)2/∑(χobsd)2), which further confirms weak
anti-ferromagnetic exchange coupling within the chain. The results
are according with those of other reported complexes bridged by
4,4′-bipy ligand [22].
Fig. 3. A schematic view showing the interlinking of adjacent helical chains and the 1D
channels existed within the polymer coils.
The magnetic susceptibility was measured in the temperature
range 2–300 K on a MPMS-7 SQUID magnetometer, and Fig. 5 shows
the plots of χm and μeff versus T. At room temperature the effective
magnetic moment equals 3.14 B.M. which is characteristic for a
pseudo-octahedral high spin Ni(II) complex (2.9–3.4 B.M.) [20]. Upon
cooling, the magnetic moment decreases slightly to a value of 2.63 B.
M. at 2.0 K, indicating a very weak magnetic interaction between the
Ni(II) ions. Considering the 1D infinite chain structure of complex 1,
assuming an isotropic exchange between Ni(II) ions, the magnetic
susceptibility per Ni(II) ion can be expressed as [21]:
In summary, we have demonstrated the self-assembly of homo-
chiral tubes based on helical chains that are built from 4,4′-bipy
ligands and linear metal-connecting points. The resulting framework
of 1 is robust and can remain intact after guest removal. The structure
of 1 effectively combines the presence of polarity and porosity, both of
which are of significant relevance to applications in chemistry and
materials science.
Acknowledgements
This work was supported by the National Natural Scientific
Foundation of China (20771054 and 20971099) and the Natural
Science Research Foundation of Education Minister, Henan Province
(2008A150017).
Ng2β2
kT
2 + 0:0194x + 0:777x2
χ =
3 + 4:34x + 3:232x2 + 5:834x3
with x = jJj = kT
Appendix A. Supplementary data
where J is the exchange integral between Ni(II) ions bridged by
4,4′-bipy, and the other parameters have their usual meanings. The
Crystallographic data for the structure reported in this article has
been deposited with the Cambridge Crystallographic Data Centre,
CCDC No. 674734. Copies of this information may be obtained free of
charge from the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ,
UK (fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or
http://www.ccdc.cam.ac.uk). Supplementary data associated with
this article can be found, in the online version doi:10.1016/j.
inoche.2010.08.021.
d
c
b
a
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