Synthesis, structures, and photoluminescence properties of three metal(II) coordination polymers derived from a flexible tripodal ligand and 2,6-pyridinedicarboxylic acid

Article abstract of DOI:10.1007/s11243-012-9673-5

Using a flexible tripodal ligand N,N′,N″-tris(3-pyridyl)-1,3,5- benzenetricarboxamide and 2,6-pyridinedicarboxylic acid, three metal(II) complexes formulated as [Co(pydc)(L)] _n (1), [Zn(pydc)(L)] _n (2), {[Ni(pydc)(L)]·2H₂O} _n (3) (L = N,N′,N″-tris(3-pyridyl)-1,3,5-benzenetricarboxamide, H ₂pydc = 2,6-pyridinedicarboxylic acid) have been hydrothermally synthesized and structurally characterized by physico-chemical and spectroscopic methods and single-crystal diffraction. In compounds 1 and 2, the L ligands acts as bridges to link the metal atoms into zigzag chain structures, which are further extended into three-dimensional (3D) metal-organic supramolecular frameworks by hydrogen bond interactions. In compound 3, the L ligands link three Ni(II) centers to form a two-dimensional (2D) hcb layered structure, and then, the adjacent nets interweave in parallel to generate a 3D structure by 2D → 3D interpenetration. The thermal stabilities of 1-3 and the luminescent properties of 2 in the solid state are also discussed. Graphical Abstract: Three metal(II) coordination polymers, based on a flexible ligand N,N′,N″-tris(3-pyridyl)-1,3,5-benzenetricarboxamide and 2,6-pyridinedicarboxylic acid, have been successfully synthesized under hydrothermal conditions, where thermal and photoluminescent properties were also investigated. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s11243-012-9673-5

Transition Met Chem (2013) 38:157–163
DOI 10.1007/s11243-012-9673-5
Synthesis, structures, and photoluminescence properties of three
metal(II) coordination polymers derived from a flexible tripodal
ligand and 2,6-pyridinedicarboxylic acid
•
Shi-Meng Wang Ling Qian Hong-Ye Bai
•
•
•
Wei-Qiang Fan Chun-Bo Liu Guang-Bo Che
•
Received: 10 October 2012 / Accepted: 6 November 2012 / Published online: 22 November 2012
Ó Springer Science+Business Media Dordrecht 2012
Abstract Using a flexible tripodal ligand N,N0,N00-tris(3-
pyridyl)-1,3,5-benzenetricarboxamide and 2,6-pyridinedi-
carboxylic acid, three metal(II) complexes formulated as
[Co(pydc)(L)]n (1), [Zn(pydc)(L)]n (2), {[Ni(pydc)(L)]ꢀ2H2O}n
(3) (L = N,N0,N00-tris(3-pyridyl)-1,3,5-benzenetricarbox-
amide, H2pydc = 2,6-pyridinedicarboxylic acid) have been
hydrothermally synthesized and structurally characterized
by physico-chemical and spectroscopic methods and sin-
gle-crystal diffraction. In compounds 1 and 2, the L ligands
acts as bridges to link the metal atoms into zigzag chain
structures, which are further extended into three-dimen-
sional (3D) metal–organic supramolecular frameworks by
hydrogen bond interactions. In compound 3, the L ligands
link three Ni(II) centers to form a two-dimensional (2D)
hcb layered structure, and then, the adjacent nets inter-
weave in parallel to generate a 3D structure by 2D ? 3D
interpenetration. The thermal stabilities of 1–3 and the
luminescent properties of 2 in the solid state are also
discussed.
Introduction
Coordination frameworks with transition metal atoms and
organic bridging ligands have been rapidly developed in
recent years and attracted great interest from chemists, not
only due to their intriguing topologies, such as molecular
cage, honeycomb, grid, ladder, rotaxane, catenane, but also
due to their interesting properties and potential applica-
tions, such as ion exchange, gas storage, recognition,
magnetism [1–6]. However, it is still a big challenge to
predict the exact structures of coordination polymers with
desired properties because many factors affect the result,
such as the coordination geometry of the central metal
atoms, connection modes of organic ligands, reaction
temperature, the ratio of solvents, pH value, and so on [7–
10]. The most effective approach to overcome this problem
is the appropriate choice of well-designed organic bridging
ligands, together with the metal centers with various
coordination preferences [11–13].
Up to now, flexible tripodal ligands provide one such
option and have drawn much attention. The flexible aryl-
heterocyclic tripodal ligands, such as 1,3,5-tris(imida
zol-1-ylmethyl)benzene, 1,3,5-tris(imidazol-1-ylmethyl)-2,
4,6-trimethylbenzene, 1,3,5-tris(4-pyridylmethyl)benzene,
1,3,5-tris(pyrazol-1-ylmethyl)-2,4,6-triethylbenzene, and 1,
3,5-tris[(ben-zimidazol-1-yl)methyl]-2,4,6-trimethylbenzene
[14–17], have proved to be useful building blocks to gen-
erate interesting metal complexes. In contrast to the rigid
tripodal ligands with little or no conformational changes
when they interact with metal salts, the flexible tripodal
ligands have much more abundant possible conformations
and coordination modes than the rigid ones due to their
flexibility; thus, they can adopt different conformations
according to the different geometric requirements of the
metal atoms and may offer various possibilities for syntheses
Keywords Coordination polymers ꢀ Flexible ligands ꢀ
Luminescence
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-012-9673-5) contains supplementary
material, which is available to authorized users.
S.-M. Wang ꢀ L. Qian ꢀ H.-Y. Bai ꢀ W.-Q. Fan ꢀ C.-B. Liu ꢀ
G.-B. Che (&)
School of Chemistry and Chemical Engineering, Jiangsu
University, Zhenjiang 212013, People’s Republic of China
e-mail: bhy19841009@yahoo.com.cn;
guangbocheujs@yahoo.com.cn
123

158
Transition Met Chem (2013) 38:157–163
Synthesis of [Co(pydc)(L)]n (1)
A mixture of CoCO3 (0.0090 g, 0.075 mmol), H2pydc
(0.0125 g, 0.075 mmol), L (0.0219 g, 0.05 mmol), and
water (10 mL) was stirred and then heated at 120 °C in a
Teflon-lined autoclave for 3 days, followed by slow cool-
ing to room temperature. The resulting purple prismatic
crystals were collected, washed with water, and dried in air
(yield, ca. 37 % based on Co). Elemental anal. found: C,
57.25; H, 3.24; N, 13.81 %. Calcd for C31H21CoN7O7
(Mr = 662.48): C, 56.20; H, 3.19; N, 14.80 %. IR (cm-1):
3242 (w), 3072 (w), 1671 (s), 1635 (s), 1550 (s), 1478 (s),
1417 (w), 1357 (m), 1309 (m), 1236 (m), 1067 (m), 1062
(s), 910 (w), 813 (s), 717 (s), 656 (m), 584 (w), 427 (w).
Scheme 1 Ligands used in this work
of intriguing MOFs with diverse structures and useful
properties [18–20]. In addition, polycarboxylate organic
groups have been found to be excellent structural contrib-
utors for their various coordination modes. Carboxylate
groups can act not only as hydrogen bond acceptors but
also as hydrogen bond donors, which would enrich the
versatility of coordination complexes [20–22]. On the basis
of the above considerations, we chose N,N0,N00-tris(3-pyri-
dyl)-1,3,5-benzenetricarboxamide (L) and 2,6-pyridinedi-
carboxylic acid (H2pydc) as functional ligands. In this
work, a series of coordination compounds [Co(pydc)(L)]n
(1), [Zn(pydc)(L)]n (2), {[Ni(pydc)(L)]ꢀ2H2O}n (3)
(L = N,N0,N00-tris(3-pyridyl)-1,3,5-benzenetricarboxamide,
H2pydc = 2,6-pyridinedicarboxylic acid) were prepared by
the hydrothermal method (Scheme 1). The thermal stabil-
ities of complexes 1–3 and fluorescent properties of com-
plex 2 have been investigated in the solid state at room
temperature.
Synthesis of [Zn(pydc)(L)]n (2)
A mixture of ZnCO3 (0.0125 g, 0.1 mmol), H2pydc
(0.0167 g, 0.1 mmol), L (0.0219 g, 0.05 mmol), and water
(10 mL) was stirred and then heated at 150 °C in a Teflon-
lined autoclave for 3 days, followed by slow cooling to
room temperature. The resulting colorless prismatic crys-
tals were collected. The yield of the colorless prismatic
crystals is ca. 45 % based on Zn. Elemental anal. found: C,
56.37; H, 3.82; N, 14.81 %. Calcd for C31H21ZnN7O7
(Mr = 668.92): C, 55.69; H, 3.16; N, 14.66 %. IR (cm-1):
3258 (m), 3070 (w), 1681 (s), 1639 (s), 1544 (s), 1474 (s),
1424 (w), 1373 (m), 1301 (m), 1257 (m), 1064 (m), 1047
(s), 927 (w), 807 (s), 739 (s), 653 (m), 585 (w), 396 (w).
Synthesis of {[Ni(pydc)(L)]ꢀ2H2O}n (3)
The synthesis of complex 3 was carried out as described
above for complex 1 except that NiCO3 was used instead of
CoCO3. The resulting green prismatic crystals were col-
lected. The yield of the green prismatic crystals is ca. 48 %
based on Ni. Elemental anal. found: C, 54.25; H, 4.10; N,
15.21 %. Calcd for C31H23NiN7O9 (Mr = 696.27): C,
53.48; H, 3.33; N, 14.08 %. IR (cm-1): 3233 (w), 3065
(w), 1660 (s), 1629 (s), 1538 (s), 1492 (s), 1415 (w), 1355
(m), 1294 (m), 1248 (m),1086 (m), 1080 (s), 912 (w), 805
(s), 698 (s), 658 (m), 591 (w), 438 (w).
Experimental section
Materials and physical measurements
The L ligand was prepared according to the literature [23].
All other chemicals were of reagent grade and purchased
from Alfa Aesar without further purification. Elemental
analyses were performed with a Perkin-Elmer 240C ele-
ment analyzer. IR spectra were recorded as KBr pellets in
the range 4,000–400 cm-1 on Perkin-Elmer spectrometer.
Powder X-ray diffraction patterns (PXRD) were recorded
on a Bruker D8 Advance diffractometer with Cu-Ka
Crystal structure determination
Single-crystal X-ray diffraction data of the three complexes
were recorded on an Oxford Diffraction Gemini R Ultra
diffractometer with graphite-monochromated Mo-Ka
˚
radiation (k = 1.54178 A) ranging from 5° to 35°. Ther-
˚
mogravimetric analysis (TGA) was performed on a NET-
ZCH STA 449C with a heating rate of 10 °C min-1 under
air atmosphere. The photoluminescent properties of the
ligands and compounds were measured on a Perkin-Elmer
LS 55 luminescence spectrometer.
radiation (k = 0.71073 A) at 293 K. All non-hydrogen
atoms were refined anisotropically, and the hydrogen atoms
of carbon atoms were generated geometrically. The
hydrogen atoms of water molecules were located from
difference Fourier map except OW2 in compound 3. The
123

Transition Met Chem (2013) 38:157–163
159
one pydc ligand, showing a tetragonal pyramidal coordi-
nation geometry. The Co–O bond distances are 2.075(2)
˚
and 2.149(2) A, respectively, and the Co–N bond lengths in
Table 1 Crystal data and structure refinement for complexes 1–3
Compounds
1
2
3
˚
the range of 2.002(2)–2.129(2) A. Each ligand L acts as a
Formula
fw
C31H21CoN7O7 C31H21ZnN7O7 C31H25NiN7O9
662.48
668.92
Monoclinic
P21/n
698.29
Hexagonal
R3c
bidentate ligand binding with two Co atoms in Mode I
(Scheme 2), forming a 1D infinite zigzag chain (Fig. 1b).
The adjacent 1D infinite chains are connected by one kind
of hydrogen bonding interactions between the oxygen atom
of pydc ligands and nitrogen atom of L ligand [N5ꢀꢀꢀO4
Crystal system Monoclinic
Spacegroup
P21/n
˚
a (A)
13.875(2)
9.366(1)
21.546(3)
90
14.192(6)
9.030(4)
22.118(9)
90
27.864(5)
27.864(5)
20.187(5)
90
˚
b (A)
˚
˚
c (A)
3.145(3) A] to form a 2D supramolecular network parallel
to the ab plane (Fig. 1c). The adjacent 2D supramolecular
layers are further connected by two other kinds of hydro-
a (°)
b (°)
c (°)
98.227(2)
90
100.322(5)
90
90
˚
˚
gen bonding interactions [N3ꢀꢀꢀO2 2.840(3) A, 162(3) and
120
3
˚
˚
˚
N6ꢀꢀꢀO(5) 2.943(3) A, 168(3), respectively] to form a three-
dimensional (3D) supramolecular network (Fig. 1d, Table
S1b). Additionally, the supramolecular network is further
stabilized by two types of p–p stacking interactions. One
exists between the phenyl rings of L ligands with the
V (A )
2771.1(6)
4
2788.5(19)
4
13573(5)
18
Z
Dcalcd (g cm-3
F(000)
h (°)
)
1.588
1.593
1.538
1356
1368
6480
1.64–27.56
0.685
1.59–27.98
0.946
1.46–27.51
0.712
˚
centroid-to-centroid separation of 3.565 A, and the other
l (mm-1
)
GOF on F2
Ra1[I[2r(I)]
wRb2[I[2r(I)]
1.061
1.022
1.020
appears between the phenyl ring of L ligand and pyridine
ring of pydc ligand with a centroid-to-centroid distance of
˚
3.8991 A.
0.0426
0.1150
0.0424
0.0891
0.0409
0.0900
Crystal structure of [Zn(pydc)(L)]n (2)
hydrogen atoms bonded to nitrogen atoms were also
located in a difference map and refined freely. All the
structures were solved by Direct Methods of SHELXS-97
and refined by full-matrix least-squares techniques using
the SHELXL-97 program [24]. The hydrogen atoms were
assigned with common isotropic displacement factors.
Crystallographic data and structure processing parameters
for complexes 1–3 are summarized in Table 1. Selected
bond distances and angles and hydrogen bonds for them are
listed in Table S1a–S3b (Supporting Information).
The experimental PXRD patterns of the polymers are
similar to those calculated from their single-crystal X-ray
data, which are a good indication of phase purity of the
products (Fig. S1). The differences in intensity between the
experimental and simulated XRPD patterns may be due to
the preferred orientation of the powder samples during the
experiment.
When CoCO3 was replaced by ZnCO3, a 3D supramolec-
ular network 2 was obtained. Complex 2 is isomorphous
with 1. The X-ray crystallographic study shows that there
are one Zn(II) atom, one pydc ligand, and one L ligand in
the asymmetric unit of complex 2 (Fig. 2a). Similar to
compound 1, the structural stability of compound 2 is also
provided by hydrogen bonding interactions between the N
atom of the L and O atoms of the pydc (N4ꢀꢀꢀO4 = 3.238(3)
˚
˚
A and N5ꢀꢀꢀO2 = 2.859(3) A, respectively) and between the
N atom of the one kind of L and another kind of L
˚
(N3ꢀꢀꢀO7 = 2.980(3) A). In addition, the crystal structure of
complex 2 is further strengthened through the p–p stacking
interactions between the phenyl rings of ligand L, with the
˚
centroid-to-centroid separation of 3.579 A.
Crystal structure of {[Ni(pydc)(L)]ꢀ2H2O}n (3)
When NiCO3 was selected to react with pydc and L under
similar synthetic conditions, a structurally different com-
plex 3 was obtained. As shown in Fig. 3a, the structure of 3
consists of one crystallographically independent Ni(II)
atom, one pydc ligand, one L ligand, and two lattice water
molecules. The Ni(II) atom is in an distorted octahedral
NiN4O2 coordination geometry, coordinated by three
nitrogen atoms from three L ligands (Ni–N 2.094(3)–
Results and discussion
Crystal structure of [Co(pydc)(L)]n (1)
Complex 1 crystallizes in monoclinic space group P21/n.
The X-ray crystallographic study shows that the asym-
metric unit of complex 1 consists of one Co(II) atom, one
pydc ligand, and one L ligand (Fig. 1a). The Co(II) center
is five-coordinated by three nitrogen atoms from two L
ligands and one pydc ligand, and two oxygen atoms from
˚
2.143(3) A) and one nitrogen atom from one pydc ligand
˚
(Ni–N 2.005(4) A) in the equatorial positions and two
carboxylate oxygen atoms from one pydc ligand (Ni–O
123

160
Transition Met Chem (2013) 38:157–163
Fig. 1 a Coordination environment around the Co(II) centers in 1.
Hydrogen atoms are omitted for clarity. Symmetry code: #1 = x - 1,
y, z; #2 = x ? 1, y, z; b the 1D structure of complex 1; c the 2D layer
of 1 formed between 1D chains by hydrogen bonding interactions;
d the 3D supramolecular structure of 1 formed through hydrogen
bonding interactions
Scheme 2 The coordination
modes of the L ligand
˚
2.078(3) and 2.231(2) A, respectively) in the apical posi-
structure (2D ? 3D parallel) (Fig. 3d). The crystal struc-
ture of complex 3 is further strengthened through hydrogen
bonding interactions and p–p stacking interactions.
tions. Each L ligand coordinates to three Ni(II) atoms
(Mode II) to form a two-dimensional (2D) layer structure
parallel to the ab plane (Fig. 3b). Topological analysis of
this compound reveals that it is a 3-connected net with hcb
topology, if the Ni(II) atoms are regarded as linkers, and
ligands L are considered as 3-connected nodes (Fig. 3c).
Adjacent nets interweave in parallel to generate a 3D
Coordination modes of ligand L
The L ligand can bend and rotate freely when coordinating
to the central metals due to the flexible nature of the three
123

Transition Met Chem (2013) 38:157–163
161
amide groups between the three pyridine rings [25–27]. It
can take on rich coordination modes, which may greatly
extend and enrich the MOFs’ structures. Scheme 2 shows
two different coordination modes of L ligands observed in
complexes 1–3, that is, tridentate mode and bidentate
mode, respectively. L molecules adopting the Mode I
coordination link two M (M = Co (1), Zn (2) atoms to
construct one-dimensional (1D) structures in 1 and 2.
Moreover, the adjacent 1D infinite chains are connected by
hydrogen bonding interactions to form a 3D supramolec-
ular network. For complex 3, the L ligands act as tridentate
ligands (Mode II) to link three metal atoms through pyridyl
nitrogen atoms and carbonyl oxygen atom. In fact, ligand L
has six potential coordination nodes (three pyridyl nitrogen
atoms and three carbonyl oxygen atoms), which can
coordinate to metal atoms entirely or partly and result in
many possible coordination modes. The L ligand may act
as several kinds of polydentate ligand (from monodentate
to hexadentate). Thus, it is a very useful ligand to construct
interesting MOF structures in the future work.
Thermal analyses
In order to characterize the compounds more fully in terms
of thermal stability, their thermal behaviors were studied
by TGA. For compound 1, the decomposition of the
compound occurs at 416 °C, indicating high thermal sta-
bility of the frameworks. For compound 2, only one step
occurs from 412 to 491 °C corresponding to the decom-
position of the coordination framework with ZnO as the
Fig. 2 ORTEP view of 2 showing the local coordination environment
of Zn(II) atom with hydrogen atoms for clarity. Symmetry code:
#1 = x - 1, y, z; #2 = x ? 1, y, z
Fig. 3 a Coordination environment around the Ni(II) centers in 3. Hydrogen atoms and solvent molecules are omitted for clarity; b the 2D
bilayer structure; c schematic diagram of the 2D net in 3; d schematic view of the 2D ? 3D interpenetrated framework of complex 3
123

162
Transition Met Chem (2013) 38:157–163
emission band in the spectra of the compounds are similar
to those observed in the free ligand, they can be assigned
mainly to intraligand transitions.
Conclusions
In this work, three metal(II) coordination polymers based on
N,N0,N00-tris(3-pyridyl)-1,3,5-benzenetricarboxamide and
2,6-pyridinedicarboxylic acid have been successfully pre-
pared under hydrothermal conditions. Compounds 1 and 2
are infinite 1D zigzag chain structures, whereas compound 3
possesses a 2D ? 3D interpenetration structure based on
the hcb net. It is anticipated that more metal complexes
containing polydentate neutral ligands with interesting
structures as well as physical properties will be synthesized.
Fig. 4 TGA curves of compounds 1–3
Supporting information
Selected bond distances and angles, and hydrogen bonding
geometry for compounds 1–3. CCDC 898448–898450
contain the supplementary crystallographic data for 1–3.
These data can be obtained free of charge via http://www.
ccdc.cam.ac.uk/conts/retrieving.html or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (?44) 1223-336-033; or
e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgments The authors are grateful for the National Nat-
ural Science Foundation of China (Grant No. 21201085), Natural
Science Foundation of Jiangsu Province (SBK2011460), Start-Up
Foundation of Jiangsu University (11JDG105, 11JDG153, 11JDG104
and 09JDG001), Jiangsu University College Student Scientific
Research Project (Y11A015), Postdoctoral Science Foundation of
China (2012M511202), and Postdoctoral research Funding Schemes
of Jiangsu Province (1102124C) for support.
Fig. 5 Solid-state photoluminescent spectra of L and compound 2 at
room temperature
residue (obsd 12.59 %, calcd 12.23 %). For compound 3,
the weight loss in the range from room temperature to
239 °C corresponds to the departure of water molecules
(obsd 5.32 %, calcd 5.17 %). The anhydrous compound
begins to decompose at 417 °C (Fig. 4).
References
1. Xiao J, Liu BY, Wei G, Huang XC (2011) Inorg Chem
50:11032–11038
2. Wang CY, Wilseck ZM, LaDuca RL (2011) Inorg Chem
50:8997–9003
3. Du M, Wang XG, Zhang ZH, Tang LF, Zhao XJ (2006) Cryst
Eng Comm 8:788–793
Luminescent properties
Coordination polymers, especially those with d10 metal
centers, have been investigated for their luminescent
properties and potential applications. Hence, the lumines-
cent properties of compound 2 and free ligand L were
measured in the solid state, as shown in Fig. 5. The max-
imum of the emission band is observed at 441 nm
(kex = 335 nm) for free L, which is ascribed to the
p* ? n nor p* ? p electronic transition of the free ligand
[28, 29]. For compound 2, its peak is at 453 nm
(kex = 345 nm). Since the profiles and locations of the
4. Du M, Jiang XJ, Zhao XJ (2007) Inorg Chem 46:3984–3995
5. Lu LH, Eychmuller A (2008) Acc Chem Res 41:244–253
6. Kanegawa S, Karasawa S, Maeyama M, Nakano M, Koga N
(2008) J Am Chem Soc 130:3079–3094
7. Dybtsev DN, Chun H, Kim K (2004) Angew Chem Int Ed
43:5033–5036
8. Liu PP, Cheng AL, Yue Q, Liu N, Sun WW, Gao EQ (2008)
Cryst Growth Des 8:1668–1674
9. Hu TL, Zou RQ, Li JR, Bu XH (2008) Dalton Trans 1302–1311
10. Hartshorn CM, Steel PJ (1997) Chem Commun 541–542
11. Sun WY, Fan J, Okamura T, Xie J, Yu KB, Ueyama N (2001)
Chem Eur J 7:2557–2562
123

Transition Met Chem (2013) 38:157–163
163
12. Shuichi H, Tao Y, Motoo S, Mitsuhiko S (2002) J Am Chem Soc
124:14510–14511
21. Lv DY, Gao ZQ, Gu JZ, Ren R, Dou W (2011) Trans Met Chem
36:313–318
13. Shuichi H, Kaori H, Mitsuhiko S (2004) Angew Chem Int Ed
43:3814–3818
22. Niu CY, Zheng XF, Wan XS, Kou CH (2011) Cryst Growth Des
11:2874–2888
14. Liu HK, Sun WY, Ma DJ, Yu KB, Tang WX (2000) Chem
Commun 591–592
15. Yin XJ, Zhou XH, Gu ZG, Zuo JL, You XZ (2009) Inorg Chem
Comm 12:548–551
23. Palmans ARA, Vekemans JAJM, Meijer EW, Palmans ARA,
Kooijman H, Spek AL (1997) Chem Commun 2247–2248
24. Sheldrick GM (2008) Acta Crystallogr Sect A: Found Crystallogr
64:112–122
16. Gong Y, Li J, Qin JB, Wu T, Cao R, Li JH (2011) Cryst Growth
Des 11:1662–1674
25. Ma LF, Wang LY, Hu JL, Wang YY, Yang GP (2009) Cryst
Growth Des 9:5334–5342
17. Lin JD, Long XF, Lin P, Du SW (2010) Cryst Growth Des
10:146–157
18. Wen LL, Lu ZD, Lin JG, Tian ZF, Zhu HZ, Meng QJ (2007)
Cryst Growth Des 7:93–99
19. Zhu QL, Sheng TL, Fu RB, Hu SM, Chen JS, Xiang SC, Shen CJ,
Wu XT (2009) Cryst Growth Des 9:5128–5134
20. Wang XJ, Liu YH, Xu CY, Guo QQ, Hou HW, Fan YT (2012)
Cryst Growth Des 12:2435–2444
26. Gu JZ, Gao ZQ, Tang Y (2012) Cryst Growth Des 12:3312–3323
27. Mu YJ, Han G, Li Z, Liu XT, Hou HW, Fan YT (2012) Cryst
Growth Des 12:1193–1200
28. Ohkoshi S, Tokoro H, Hozumi T, Zhang Y, Hashimoto K, Bord I,
Rombaut G, Verelst M, Moulin CC, Villain F (2006) J Am Chem
Soc 128:270–277
29. Zheng XJ, Jin LP, Gao S, Lu SZ (2005) New J Chem 29:798–804
123