Synthesis, structure and properties of a 3D plywood-like nickel(II) hexaazamacrocyclic coordination polymer constructed from weak Ni?O interactions and hydrogen bonding

Article abstract of DOI:10.1016/j.molstruc.2011.12.011

A 3D plywood-like nickel(II) hexaazamacrocyclic coordination polymer {[Ni(hto)(H₂btec]}_n (2) (hto = 1,3,6,9,11,14- hexaazatricyclo[12.2.1.1^6,9]octadecane, H₄btec = 1,2,4,5-benzenetetracarboxylic acid) was synthesized by a slow diffusion method and characterized by X-ray crystallography and spectroscopic methods. The structure of 2 is made up of [Ni(hto)]²⁺ cation and H ₂btec^2- anion in a molecular ratio of 1:1. The nickel(II) ions in the complex are bridged by the H₂btec^2- ligand based on weak Ni?O coordination interactions to form a 1D chain. The alternate cross-like 1D chains are packed in a plywood-like structure and interconnected with each other by hydrogen bonding to form a 3D network. Complex 2 exhibits fluorescent emission in the solid state at room temperature.

Full text of DOI:10.1016/j.molstruc.2011.12.011

Journal of Molecular Structure 1011 (2012) 15–18
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structure and properties of a 3D plywood-like nickel(II)
hexaazamacrocyclic coordination polymer constructed from weak
NiÁ Á ÁO interactions and hydrogen bonding
a
Bo Tao a, Xiang Jiang b, Hua Xia b, , Hefa Cheng
⇑
a State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, PR China
b Faculty of Material Science and Chemistry Engineering, China University of Geosciences, Wuhan 430074, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A
3D plywood-like nickel(II) hexaazamacrocyclic coordination polymer {[Ni(hto)(H2btec]}n (2)
(hto = 1,3,6,9,11,14-hexaazatricyclo[12.2.1.16,9]octadecane, H4btec = 1,2,4,5-benzenetetracarboxylic acid)
was synthesized by a slow diffusion method and characterized by X-ray crystallography and spectroscopic
methods. The structure of 2 is made up of [Ni(hto)]2+ cation and H2btec2À anion in a molecular ratio of 1:1.
The nickel(II) ions in the complex are bridged by the H2btec2À ligand based on weak NiÁ Á ÁO coordination
interactions to form a 1D chain. The alternate cross-like 1D chains are packed in a plywood-like structure
and interconnected with each other by hydrogen bonding to form a 3D network. Complex 2 exhibits fluo-
rescent emission in the solid state at room temperature.
Received 8 November 2011
Received in revised form 8 December 2011
Accepted 8 December 2011
Available online 22 December 2011
Keywords:
Coordination polymer
Nickel(II) hexaazamacrocyclic complex
Weak coordination
Ó 2011 Elsevier B.V. All rights reserved.
3D plywood-like crystal structure
Fluorescence
1. Introduction
2. Experiment
The design and synthesis of coordination polymers have received
extensive attention owing to their potential as functional materials
and intriguingtopologies [1–13]. It is widely accepted thatcoordina-
tive bonding is the primary interaction to sustain the network, while
2.1. Materials and physical measurements
All the starting reagents were of analytical grade, obtained from
commercial sources and used without further purification. Elemen-
tal analyses (C, H and N) were performed using a vario EL cube CHNS/
O elemental analyzer. Solid state UV–Visible (UV–Vis) diffuse reflec-
tance spectra using samples diluted with BaSO4 were recorded with
a Shimadzu 2550 PC UV–Vis recording spectrophotometer. FT/IR
spectra were obtained on a Nicolet-Avatar 370 infrared spectros-
copy in the 4000–400 cmÀ1 regions, using KBr pellets. X-ray powder
diffraction (XRPD) pattern was recorded on a Shimadzu D/MAX-3BX
supramolecular interactions, such as hydrogen bonding,
pÁ Á Áp
stacking interactions and Van der Waals forces are also believed to
play important roles [14–22]. Recently, transition metal macrocyclic
complexes with bridging aromatic polycarboxylate ligands have
been shownto be good building blocks for constructing coordination
polymers [23–26]. Consequently, a wide range of coordination poly-
mers with complex architectures and topologies have been synthe-
sized successfully[27–37]. However, little attentionhas been paid to
incorporate weak coordination bonds into this type of coordination
polymers [38–43].
diffractometer with CuK
a radiation. Simulation of the XRPD pat-
terns was carried out with the Mercury software. Fluorescence spec-
tra were recorded with a Horiba FluoroMax-4 spectrofluorometer at
room temperature. The precursor complex [Ni(hto)]Cl2Á2H2O (1)
was prepared according to the procedures reported previously [44].
Here, we report a 3D plywood-like coordination polymer
{[Ni(hto)(H2btec]}n (2), which is self-assembled from a nickel(II)
hexaazamacrocyclic complex [Ni(hto)]Cl2Á2H2O (1) and a H2btec2À
ligand. In the structure of 2, 1D chains are formed by [Ni(hto)]2+
cations and H2btec2À anions based on weak NiÁ Á ÁO coordination
interactions and they are packed in a plywood-like structure and
linked together by hydrogen bonding to form a 3D network.
2.2. Preparation of {[Ni(hto)(H2btec]}n (2)
Single crystals of complex 2 were obtained by a slow diffusion
method using an H-shape tube. A solution of H4btec (0.044 g,
0.2 mmol) in CH3OH (7 ml) was added to one arm of the H-shape
tube, and [Ni(hto)]Cl2Á2H2O (0.084 g, 0.2 mmol) was dissolved in
CH3OH (7 ml) and added to another arm. The middle of the H-shape
⇑
Corresponding author. Tel.: +86 13377899148.
E-mail address: caihua223@gmail.com (H. Xia).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.12.011

16
B. Tao et al. / Journal of Molecular Structure 1011 (2012) 15–18
Table 1
Table 2
Crystallographic data and structure refinement for {[Ni(hto)(H2btec]}n.
Selected bond lengths (Å) and angles (°) for {[Ni(hto)(H2btec]}n
(symmetry transformations used to generate equivalent atoms:
#1 Àx + 1, Ày + 1, Àz).
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
C22H30N6O8Ni
565.22
298(2)
0.71073
Monoclinic
P2(1)/c
Bond lengths
Ni(1)–N(1)
Ni(1)–N(1)#1
Ni(1)–N(2)
1.9204(14)
1.9204(14)
1.9565(12)
1.9566(12)
Space group
Unit cell dimensions
a = 8.3541(5) Å
b = 10.0252(7) Å
c = 13.7490(9) Å
1129.20(13)
4, 1.662
a
= 90°
b = 101.2930(10)°
= 90°
Ni(1)–N(2)#1
Bond angles
c
N(1)–Ni(1)–N(1)#1
N(1)–Ni(1)–N(2)
N(1)#1–Ni(1)–N(2)
N(1)–Ni(1)–N(2)#1
N(1)#1–Ni(1)–N(2)#1
N(2)–Ni(1)–N(2)#1
180.0
Volume (Å3)
87.07(5)
92.93(5)
92.93(5)
87.06(5)
180.0
Z, calculated density
(Mg/m3)
Absorption coefficient
0.924
(mmÀ1
)
F (000)
592
h range for data
collection (°)
Index ranges
2.49–28.31
À11 6 h 6 11, À13 6 k 6 13,
À18 6 l 6 18
ligands, using two oxygen atoms (O2, O2#) to connect two Ni(II)
ions with weak NiÁ Á ÁO coordination interactions, and forms a 1D
chain structure (\O2Á Á ÁNi1Á Á ÁO2# = 180°) (Fig. 2). The Ni1Á Á ÁO2
(O2#) distance of 2.889 Å is longer than those of other regular
Ni–O bonds (1.92 Å), while shorter than the sum of the Van der
Waals radii of the oxygen and nickel atoms (3.15 Å) [46]. Based
on the lengths of Ni–O bonds in complex 2, each Ni(II) ion is coor-
dinated in a significantly distorted octahedral geometry. Some
nickel(II) macrocyclic coordination polymers have been reported
to possess similar weak NiÁ Á ÁO interactions with Ni–O bond dis-
tances ca. 2.8311–3.092 Å [40–43].
The packing of 1D chain polymers usually occurs with a parallel
orientation of all chains into a high-dimensional motif; they can
rarely extend along two different directions on the alternate neigh-
boring layers [1,5,8,13,21,27,47,48]. Herein, another prominent
structural feature of 2 is that two different series of 1D chains ex-
tend in different directions and pack alternately in nonparallel
fashion with cross-like arrangement, forming a 3D plywood-like
array with ABAB sequence (Fig. 3).
It is noteworthy that such ABAB stacking is caused by alternate
cross-like arrangement of 1D chains on every two neighboring lay-
ers. Therefore, the crystal packing exhibits a plywood-like structure
of AB type. Furthermore, the alternate cross-like 1D chains are inter-
connected with each other through hydrogen bonding [O(4)Á Á ÁO(1)
#1 = 2.637(16) Å, 170.5(19)°; C(6)Á Á ÁO(1) = 3.407 Å, 133°; C(6)Á Á Á
O(3) = 3.261(2) Å, 145°; symmetry codes: #1 x, Ày + 3/2, z À 1/2],
resulting a 3D network. To the best of our knowledge, similar 3D ply-
wood-like coordination polymer has not been reported in com-
plexes of H4btec with macrocyclic metal compounds.
Reflections collected/
unique
13,495/2804 [R(int) = 0.0380]
Completeness to
theta = 28.26%
Max. and min.
transmission
99.6
0.9132 and 0.8662
Refinement method
Full-matrix least-squares on
F2
Data/restraints/
parameters
2804/2/175
Goodness-of-fit on F2
1.087
Final R indices [I > 2
R indices (all data)
r
(I)] R1 = 0.0306, wR2 = 0.0877
R1 = 0.0340, wR2 = 0.0894
0.456 and À0.221
Largest diff. peak and
hole (e ÅÀ3
)
tube was filled with N,N-dimethylformamide. Red lump crystals of
2 were obtained after a week (yield 55.8% based on Ni). Anal. Calcd.
for C22H30N6O8Ni (%): C, 45.94; H, 5.384; N, 14.80. Found (%): C,
46.75; H, 5.35; N, 14.87. IR (KBr, cmÀ1): 3490(s), 3434(m),
3104(m), 3046(s), 2852(s), 2030(m), 1703(m), 1565(s), 1369(s),
1233(s), 1192(w), 1142(m), 1094(s), 1012(s), 936(m), 831(s),
755(m), 703(s), 642(m), 525(s).
2.3. X-ray crystallography
The red lump crystals of 2 (dimensions: 0.16 Â 0.12 Â 0.10 mm3)
were chosen for room temperature 298(2) K data collection on a
Bruker Smart Apex CCD diffractometer with a graphite monochro-
mated MoK
a radiation (k = 0.71073 Å). The structure was solved
by direct method and refined by full-matrix least-squares procedure
on F2 by the SHELXL-97 program [45]. All non-hydrogen atoms were
refined anisotropically, while the hydrogen atoms were located geo-
metrically and refined isotropically. Complete crystallographic data
and collection parameters are listed in Table 1. Selected bond
lengths and bond angles are listed in Table 2.
3.2. XRPD, IR spectra, UV–Vis spectra and fluorescent properties
The simulated and experimental XRPD patterns of 2 obtained at
room temperature are shown in Fig. S1. Their peak positions are in
good consistency with each other, indicating the phase purity of
the synthesized sample. The strong absorptions at 1565 and
1369 cmÀ1 in the IR spectrum suggest the presence of carboxylate
groups in 2 (Fig. S2). A characteristic absorption peak at 1703 cmÀ1
in 2, which is attributed to the protonated carboxylic groups, indi-
cates that deprotonation of the H4btec ligand is incomplete [49].
The solid state UV–Vis diffuse reflectance spectra of com-
plexes 1 and 2 exhibit strong broad peaks at 444 nm and 470 nm
in visible region, respectively, as shown in Fig. S3. The absorption
peak of 2 is clearly red-shifted compared to that of 1, which cor-
roborates the coordination of the oxygen atom in the H2btec2À
moiety to the Ni(II) ion in the solid state .
3. Results and discussion
3.1. Crystal structure of compound 2
The X-ray crystal structure of the fundamental building unit of
compound 2 is shown in Fig. 1. The coordination environment
around the nickel(II) ion shows a slightly distorted square-plane
with four equatorial N atoms of the macrocyclic ligand. The four
Ni–N distances are in the range of 1.9204(14)–1.9565(12) Å. The
average Ni–N distance (1.9385 Å) is consistent with that found in
the square-plane geometry of 1 (1.920 Å) [44]. The main structural
The luminescent spectrum of complex 2 was investigated in the
solid state together with complex 1 for comparison. As shown in
Fig. 4, complex 1 exhibits an intense emission peak at 540 nm,
feature of 2 is that the H2btec2À anions unit acts as
l2-bridging

B. Tao et al. / Journal of Molecular Structure 1011 (2012) 15–18
17
Fig. 1. The molecular structure diagram of complex 2 with the atom-labeling scheme.
Fig. 2. The 1D chain structure of complex 2 based on NiÁ Á ÁO weak interactions.
Fig. 3. Representation of cross-like arrangement of 1D chains in ABAB fashion to
generate 3D plywood-like array in 2.
Fig. 4. Luminescence emission spectra of
(kex = 350 nm).
1
and
2
at room temperature
effective synthetic strategy by employing hydrogen bonding and
weak metal–oxygen interactions to construct polymeric networks.
while that of complex 2 occurs at 400 nm. According to a previous
report, the free H4btec ligand exhibits a main emission peak at
342 nm upon excitation at 308 nm [50]. The emission peak of 2
is obviously blue-shifted compared to the emission peak of 1,
which may be attributed to the ligand-to-metal charge transfer
(LMCT). Compound 2 could be potentially used in blue-light emit-
ting diode devices because of its blue fluorescence emission.
Supplementary data
CCDC-780241 for C22H30N6O8Ni contains the supplementary
crystallographic data for this paper. These date can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
4. Conclusions
Acknowledgements
In summary, we have obtained a new 3D plywood-like nickel(II)
hexaazamacrocyclic coordination polymer based on self-assembly
of a nickel(II) hexaazamacrocyclic complex [Ni(hto)]Cl2Á2H2O. The
successful synthesis and isolation of 2 provide a feasible and
We thank Dr. Xiang-Gao Meng of Central China Normal Univer-
sity for providing the crystallographic data obtained with a Bruker
Smart Apex CCD diffractometer.

18
B. Tao et al. / Journal of Molecular Structure 1011 (2012) 15–18
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