Coordination polymers constructed by diverse metal centers and the rigid ligand 3,5-di(1H-imidazol-1-yl)pyridine: Synthesis, structure and properties

Article abstract of DOI:10.1016/j.poly.2012.02.027

Six new coordination polymers, [Cu(L)₂(H₂O) ₂](NO₃)₂ (1), [Cu(L)₂](ClO ₄)₂ (2), [Cd(L)₂(H₂O) ₂](ClO₄)₂ (3), [Cd(L)(OAc)₂(H ₂O)] (4), [Cu₃(L)₄(H₂O) ₂(SO₄)](SO₄)₂·30H ₂O (5), and [Ni(L)(H₂O)₃(SO₄)] (6) [L = 3,5-di(1H-imidazol-1-yl)pyridine, OAc^- = CH₃COO ^-], have been prepared and characterized by X-ray diffraction, IR, elemental and thermogravimetric analyses. Complexes 1, 4 and 6 have different one-dimensional (1D) chain structures, while 2 and 4 are two-dimensional (2D) networks. The chains and layers are further linked together by hydrogen bonds to generate three-dimensional (3D) frameworks. Complex 5 is a (3,4,4)-connected 3D framework with a Point (Schlaefli) symbol of (4.8²) ₄(4.8³.10²)₂(4².8 ².10²). The influences of the coordination modes of the ligand L, metal center as well as the counteranion on the structures of the complexes are discussed. Furthermore, the reversible anion exchange property of 3 and the photoluminescence properties of 3 and 4 have been investigated.

Full text of DOI:10.1016/j.poly.2012.02.027

Polyhedron 38 (2012) 88–96
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Polyhedron
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Coordination polymers constructed by diverse metal centers and the rigid ligand
3,5-di(1H-imidazol-1-yl)pyridine: Synthesis, structure and properties
Li Luo a, Yue Zhao a, Yi Lu a, Taka-aki Okamura b, Wei-Yin Sun a,
⇑
a Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering,
Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093, China
b Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Six new coordination polymers, [Cu(L)2(H2O)2](NO3)2 (1), [Cu(L)2](ClO4)2 (2), [Cd(L)2(H2O)2](ClO4)2 (3),
[Cd(L)(OAc)2(H2O)] (4), [Cu3(L)4(H2O)2(SO4)](SO4)2Á30H2O (5), and [Ni(L)(H2O)3(SO4)] (6) [L = 3,5-di(1H-
imidazol-1-yl)pyridine, OAcÀ = CH3COOÀ], have been prepared and characterized by X-ray diffraction,
IR, elemental and thermogravimetric analyses. Complexes 1, 4 and 6 have different one-dimensional
(1D) chain structures, while 2 and 4 are two-dimensional (2D) networks. The chains and layers are fur-
ther linked together by hydrogen bonds to generate three-dimensional (3D) frameworks. Complex 5 is a
(3,4,4)-connected 3D framework with a Point (Schläfli) symbol of (4.82)4(4.83.102)2(42.82.102). The influ-
ences of the coordination modes of the ligand L, metal center as well as the counteranion on the struc-
tures of the complexes are discussed. Furthermore, the reversible anion exchange property of 3 and
the photoluminescence properties of 3 and 4 have been investigated.
Received 22 November 2011
Accepted 13 February 2012
Available online 3 March 2012
Keywords:
Coordination polymers
3,5-Di(1H-imidazol-1-yl)pyridine
Anion exchange
Photoluminescence property
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
We focused our attention on the constructions, structures and
properties of MOFs with imidazole-containing organic ligands
In recent years, metal–organic frameworks (MOFs) have at-
tracted great attention from chemists, not only due to their intrigu-
ing structures [1] but also because of their potential applications in
gas storage, optics, ion exchange, separation, catalysis and so on
[2–7]. However, it is still a challenge to predict and exactly control
the compositions and structures of the complexes [8]. Employing
multidentate organic ligands and metal ions to construct inor-
ganic–organic hybrid materials through metal–ligand coordination
and hydrogen bonding interactions has become a major strategy.
In previously reported works, rigid or flexible tripodal ligands such
as 2,4,6-tris(4-pyridyl)-1,3,5-triazine, 1,3,5-tris(1-imidazolyl)ben-
zene and 1,3,5-tris(imdazol-1-ylmethyl)benzene have been well
used to prepare complexes with varied metal salts [9–11]. For
example, metal complexes with different structures and properties
have been obtained by the reactions of the 1,3,5-tris(imdazol-1-
ylmethyl)benzene ligand with a variety of metal salts, such as Cu-
SO4Á5H2O, MnSO4ÁH2O, CdSO4Á8/3H2O and Cu(ClO4)2Á6H2O [10,11].
The results show that many factors, such as the coordination
geometry of metal center, the counteranion, the coordination
mode of the ligand, the ratio of metal salt to ligand, the reaction
medium and temperature can influence the structure of the
complexes. This attracted us to carry out further studies to under-
stand the impact of the assembly process.
[12]. Given that the coordination abilities of the N atom of pyridine
and imidazole groups have subtle differences, in this work we de-
signed a new ligand, 3,5-di(1H-imidazol-1-yl)pyridine (L), which
includes both pyridine and imidazole groups. Herein, we report
the preparations and crystal structures of six new complexes,
[Cu(L)2(H2O)2](NO3)2 (1), [Cu(L)2](ClO4)2 (2), [Cd(L)2(H2O)2](ClO4)2
(3), [Cd(L)(OAc)2(H2O)] (4), [Cu3(L)4(H2O)2(SO4)](SO4)2Á30H2O (5)
and [Ni(L)(H2O)3(SO4)] (6). The thermal stability, photolumines-
cence and anion exchange properties of the complexes have been
investigated.
2. Experimental
2.1. Materials and measurements
All commercially available chemicals and solvents are of reagent
grade and were used as received without further purification.
Elemental analyses for C, H and N were performed on a Perkin-
Elmer 240C Elemental Analyzer at the analysis center of Nanjing
University. Thermogravimetric analyses (TGA) were performed on
a simultaneous SDT 2960 thermal analyzer under nitrogen, with a
heating rate of 10 °C minÀ1. FT-IR spectra were recorded in the
range 400–4000 cmÀ1 on a Bruker Vector22 FT-IR spectrophotome-
ter using KBr pellets. X-ray powder diffraction (XRPD) patterns
were obtained on a Shimadzu XRD-6000 X-ray diffractometer
⇑
Corresponding author. Tel.: +86 25 83593485; fax: +86 25 83314502.
E-mail address: sunwy@nju.edu.cn (W.-Y. Sun).
with Cu Ka (k = 1.5418 Å) radiation at room temperature. The
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2012.02.027

L. Luo et al. / Polyhedron 38 (2012) 88–96
89
luminescence spectra for the powdered solid samples were mea-
sured on an Aminco Bowman Series 2 spectrofluorometer with a
xenon arc lamp as the light source. In the measurements of emis-
sion and excitation spectra, the pass width was 5 nm, and all the
measurements were carried out under the same experimental
conditions.
(s), 1313 (s), 1256 (m), 1120 (w), 1070 (m), 1006 (w), 921 (w),
757 (m), 671 (m), 643 (m).
2.7. Synthesis of [Cu3(L)4(H2O)2(SO4)](SO4)2Á30H2O (5)
The complex was obtained by the same procedure used for the
preparation of 1, except that CuSO4Á5H2O (12.5 mg, 0.05 mmol) in-
stead of Cu(NO3)2Á3H2O was used as the starting material. Blue
block crystals were obtained in 90% yield after 2 weeks. Anal. Calc.
for C44H102N20O45S3Cu3: C, 27.55; H, 5.36; N, 14.60. Found: C,
27.50; H, 5.37; N, 14.57%. IR (KBr pellet, cmÀ1): 3390 (m), 3120
(m), 1609 (m), 1514 (s), 1272 (m), 1126 (s), 964 (w), 854 (w),
774 (w), 685 (w), 613 (m).
2.2. Synthesis of the ligand L
The title compound was prepared by a similar procedure re-
ported for the preparation of 1,3,5-tris(1-imidazolyl)benzene using
3,5-dibromopyridine instead of 1,3,5-tribromobenzene [13]. 3,5-
Dibromopyridine (2.84 g, 12.0 mmol), imidazole (3.26 g, 48.0
mmol), K2CO3 (4.42 g, 32.0 mmol) and anhydrous CuSO4 (0.05 g,
0.31 mmol) were mixed well and heated at 180 °C for 12 h under
a nitrogen atmosphere. The mixture was cooled to room tempera-
ture and washed with water. The residue was dissolved in boiling
water, filtered while hot and left to crystallize, to give the ligand L
in 86% yield. 1H NMR [(CD3)2SO] d (ppm): 8.97 (s, 2H), 8.50 (s, 2H),
8.48 (s, 1H), 7.98 (s, 2H), 7.21 (s, 2H); Anal. Calc. for C11H9N5: C,
62.55; H, 4.29; N, 33.16. Found: C, 62.74; H, 4.18; N, 33.04%.
2.8. Synthesis of [Ni(L)(H2O)3(SO4)] (6)
This complex was obtained by the same procedure used for the
preparation of 5, except that NiSO4Á6H2O (13.1 mg, 0.05 mmol) in-
stead of CuSO4Á5H2O was used as the starting material. Blue-green
block crystals were obtained in 87% yield after 2 weeks. Anal. Calc.
for C11H15N5O7SNi: C, 31.45; H, 3.60; N, 16.67. Found: C, 31.39; H,
3.61; N, 16.64%. IR (KBr pellet, cmÀ1): 3252 (m), 1683 (w), 1602
(m), 1522 (s), 1272 (s), 1170 (s), 1096 (s), 1052 (s), 958 (m), 884
(w), 825 (w), 723 (m), 649 (m), 576 (m).
2.3. Synthesis of [Cu(L)2(H2O)2](NO3)2 (1)
The title complex was prepared by the layering method. A buf-
fer layer of a CH3OH/H2O (1:1) solution (8 mL) was carefully lay-
ered over a solution of L (10.5 mg, 0.05 mmol) in H2O (3 mL).
Then a solution of Cu(NO3)2Á3H2O (12.5 mg, 0.05 mmol) in CH3OH
(3 mL) was layered over the buffer layer. Block blue crystals were
obtained after 2 weeks in 82% yield. Anal. Calc. for C22H22N12O8Cu:
C, 40.90; H, 3.43; N, 26.02. Found: C, 40.95; H, 3.44; N, 25.97%. IR
(KBr pellet, cmÀ1): 3393 (m), 1604 (m), 1512 (s), 1455 (w), 1398
(s), 1355 (s), 1326 (s), 1255 (m), 1127 (w), 1077 (m), 999 (w),
863 (w), 770 (w), 740 (m), 685 (m), 664 (m).
2.9. Procedure for reversible anion exchange of complex 3
A well-ground powder of the complex [Cd(L)2(H2O)2](ClO4)2 (3)
(60 mg) was suspended in a water (5 mL) solution of NaNO3 (1.0 g),
and the mixture was well stirred for 1 day at room temperature,
then the solid was collected by centrifuging, washed with water
several times, and eventually dried in a vacuum to give the anion
exchanged product [Cd(L)2(H2O)2](NO3)2 (3A). Anal. Calc. for 3A
(C22H22N12O8Cd): C, 38.03; H, 3.19; N, 24.19. Found: C, 37.97; H,
3.18; N, 24.23%. To investigate the reversibility of such an anion ex-
change, the anion exchanged solid 3A was suspended in an aqueous
solution (5 mL) of NaClO4 (1.0 g). The mixture was stirred for 1 day
at room temperature, and then handled by the same procedure de-
scribed above, and the anion exchanged sample [Cd(L)2(H2O)2]
(ClO4)2 (3B) was obtained. Anal. Calc. for 3B (C22H22Cl2N10O10Cd):
C, 34.33; H, 2.88; N, 18.20. Found: C, 34.28; H, 2.87; N, 18.21%.
2.4. Synthesis of [Cu(L)2](ClO4)2 (2)
This complex was obtained by the same procedure used for the
preparation of 1, except that Cu(ClO4)2Á6H2O (18.6 mg, 0.05 mmol)
instead of Cu(NO3)2Á3H2O was used as the starting material. Purple
platelet crystals were obtained in 75% yield after 1 month. Anal.
Calc. for C22H18Cl2N10O8Cu: C, 38.58; H, 2.65; N, 20.45. Found: C,
38.50; H, 2.64; N, 20.49%. IR (KBr pellet, cmÀ1): 3405 (w), 1602
(m), 1522 (s), 1463 (w), 1323 (w), 1272 (m), 1081 (s), 950 (m),
899 (m), 825 (m), 736 (m), 693 (m), 642 (m), 619 (s).
2.10. X-ray crystallography
The X-ray diffraction measurements for complexes 2, 5 and 6
were made on a Rigaku Rapid II imaging plate area detector with
2.5. Synthesis of [Cd(L)2(H2O)2](ClO4)2 (3)
Mo Ka radiation (k = 0.71075 Å) using a MicroMax-007HF micro-
focus rotating anode X-ray generator and a VariMax-Mo optics at
This complex was obtained by the same procedure used for the
preparation of 2, except that Cd(ClO4)2Á6H2O (20.1 mg, 0.05 mmol)
instead of Cu(ClO4)2Á6H2O was used as the starting material. Color-
less block crystals were obtained in 85% yield after 2 weeks. Anal.
Calc. for C22H22Cl2N10O10Cd: C, 34.33; H, 2.88; N, 18.20. Found: C,
34.26; H, 2.87; N, 18.23%. IR (KBr pellet, cmÀ1): 3464 (m), 2923
(w), 1604 (m), 1497 (s), 1326 (w), 1291 (w), 1248 (s), 1085 (s),
928 (w), 891 (w), 827 (m), 777 (w), 693 (w), 621 (m).
200 K. The structures of 2, 5 and 6 were solved by direct methods
with SIR92 [14] and expanded using Fourier techniques with DIRFID
-
99 [15]. The non-hydrogen atoms were refined anisotropically by
the full matrix least-squares method on F2. The hydrogen atoms
of coordinated water molecules in 6 were located from the Fourier
map, while the ones of the uncoordinated water molecules in 5
were not found. The hydrogen atoms of the ligand L were generated
geometrically and refined isotropically using the riding model. All
calculations of 2, 5 and 6 were performed using the CrystalStructure
[16] crystallographic software package, except for refinement
which was performed using SHELXL-97 [17]. The crystallographic
data collections for 1, 3 and 4 were carried out on a Bruker Smart
2.6. Synthesis of [Cd(L)(OAc)2(H2O)] (4)
This complex was obtained by the same procedure used for the
preparation of 3, except that Cd(OAc)2Á2H2O (13.3 mg, 0.05 mmol)
instead of Cd(ClO4)2Á6H2O was used as the starting material. Color-
less platelet crystals were obtained in 80% yield after 2 weeks. The
crystals were collected by filtration. Anal. Calc. for C15H17N5O5Cd:
C, 39.19; H, 3.73; N, 15.23. Found: C, 39.24; H, 3.72; N, 15.20%. IR
(KBr pellet, cmÀ1): 3243 (w), 3122 (m), 1576 (s), 1497 (s), 1405
Apex CCD with graphite-monochromated Mo
Ka radiation
(k = 0.71073 Å) at 293(2) K using the -scan technique. The data
x
were integrated using the SAINT program [18], which was also used
for the intensity corrections for Lorentz and polarization effects. A
semi-empirical absorption correction was applied using the SADABS
program [19]. The structures were solved by direct methods and

90
L. Luo et al. / Polyhedron 38 (2012) 88–96
Table 1
Crystal data and structure refinements for complexes 1–6.
Compound
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
22H22N12O8Cu
C22H18Cl2N10O8Cu
684.90
monoclinic
P21/c
10.429(4)
9.147(2)
16.235(5)
90.00
127.659(15)
90.00
200
1226.1(7)
2
1.855
1.184
C22H22Cl2N10O10Cd
769.80
monoclinic
P21/n
8.9190(16)
10.5618(19)
15.241(3)
90.00
98.550(3)
90.00
293
1419.8(4)
2
1.801
1.032
646.07
triclinic
P1
ꢀ
8.119(2)
9.100(3)
10.427(3)
114.069(4)
108.807(5)
92.394(5)
293
652.3(3)
1
1.645
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
T (K)
V (Å3)
Z
Dcalc (g cmÀ3
)
l
(mmÀ1
)
0.911
F(000)
331.00
694.00
772
h for data collection (°)
Reflections collected
Unique reflections
2.5–25.10
3278
2264
3.17–27.48
11279
2807
2.35–25.10
6890
2529
Goodness-of-fit
1.228
0.0689, 0.1418
0.0753, 0.1447
1.136
0.0332, 0.0890
0.0366, 0.0907
1.056
0.0686, 0.1450
0.0721, 0.1469
b
R1a, wR2 [I > 2
r
(I)]
R1, wR2 (all data)
Compound
4
5
6
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
15H17N5O5Cd
C44H102N20O45S3Cu3
1918.26
monoclinic
P21/c
12.6148(18)
10.9249(19)
32.348(5)
90.00
C11H15N5O7SNi
420.05
monoclinic
P21/c
7.5823(17)
11.145(3)
17.811(6)
90.00
102.875(14)
90.00
459.75
monoclinic
C2/c
11.8243(8)
17.7204(12)
8.4141(6)
90.00
96.2970(10)
90.00
b (Å)
c (Å)
a
(°)
b (°)
(°)
112.180(7)
90.00
c
T (K)
293(2)
1752.4(2)
4
1.743
1.282
200
4128.2(11)
2
1.543
0.948
200
1467.2(7)
4
1.902
1.517
V (Å3)
Z
Dcalc (g cmÀ3
)
l
(mmÀ1
)
F(000)
920
2.08–25.09
4404
2002.00
3.19–25.00
27375
864.00
3.20–27.49
13061
h for data collection (°)
Reflections collected
Unique reflections
1566
7186
3332
Goodness-of-fit
1.026
0.0212, 0.0494
0.0226, 0.0501
1.052
0.0662, 0.1844
0.0756,0.1923
1.127
0.0335, 0.0842
0.0355, 0.0850
b
R1a, wR2 [I > 2
r
(I)]
R1, wR2 (all data)
a
R1
wR2 = |
=
R
||Fo| À |Fc||/
R|Fo|.
b
R
w(|Fo|2 À |Fc|2)|/
R
|w(Fo)2|1/2, where w = 1/[
r
2(Fo2) + (aP)2 + bP]. P = (Fo2 + 2Fc2)/3.
all non-hydrogen atoms were refined anisotropically on F2 by the
full-matrix least-squares technique using the SHELXL crystallo-
graphic software package [20]. The hydrogen atoms of coordinated
water molecules in 1, 3 and 4 were located from the Fourier map
and all the other hydrogen atoms were generated geometrically
and refined isotropically using the riding model. Details of the crys-
tal parameters, data collection and refinements for the complexes
are summarized in Table 1, and selected bond lengths and angles
are listed in Table 2.
of 2.446 Å [21], and the bond angles around Cu1 are in the range
86.6(1)–180°. Each L ligand links two Cu(II) atoms using its two
imidazole groups, while the pyridine group of the ligand L does
not participate in the coordination (Scheme 1a). Such a coordina-
tion mode makes 1 an infinite one-dimensional (1D) hinged chain
structure (Fig. 1b). The adjacent chains are further held together
through O–HÁÁÁN and O–HÁÁÁO hydrogen bonding interactions, gen-
erating a two-dimensional (2D) network (Fig. S1a). The layers are
then linked by C–HÁÁÁO hydrogen bonds to give rise to the final
three-dimensional (3D) framework structure (Fig. S1b). The hydro-
gen bonding data of 1–6 are provided in the Supporting information
(Table S1).
3. Results and discussion
3.1. Crystal structural description of [Cu(L)2(H2O)2](NO3)2 (1)
3.2. Crystal structural description of [Cu(L)2](ClO4)2 (2)
The coordination environment around the Cu(II) atom is shown
in Fig. 1a, along with the atom numbering scheme. Cu1 is six-coor-
dinated with a distorted octahedral coordination geometry by four
N atoms (N52, N52D, N32B, N32C) from four distinct L ligands, with
Cu1–N bond distances of 2.011(4) and 2.026(4) Å, and two O atoms
from two coordinated water molecules with a Cu1–O bond length
In order to investigate the effect of the counteranion on the
structure of the complexes, the reaction using Cu(ClO4)2Á6H2O
was carried out under the same reaction conditions as for the syn-
thesis of 1, and fortunately complex 2, with a different structure,
was obtained. The crystal structure of 2 is shown in Fig. 2a, each

L. Luo et al. / Polyhedron 38 (2012) 88–96
91
Table 2
Selected bond lengths (Å) and angles (o) for complexes 1–6.a
Compound 1
Cu(1)–N(52)
N(52)–Cu(1)–N(32)
N(52)#2–Cu(1)–O(1)
2.011(4)
87.6(2)
91.6(2)
Cu(1)–N(32)#1
N(52)#2–Cu(1)–N(32)#3
N(32)#3–Cu(1)–O(1)
2.026(4)
92.4(2)
86.6(1)
Cu(1)–O(1)
N(52)–Cu(1)–O(1)
N(32)#1–Cu(1)–O(1)
2.446(4)
88.4(2)
93.4(1)
Compound 2
Cu(1)–N(32)
N(32)#2–Cu(1)–N(52)#1
1.995(2)
91.31(6)
Cu(1)–N(52)#1
N(32)–Cu(1)–N(52)#1
2.011(2)
88.69(6)
Compound 3
Cd(1)–N(52)
N(52)#2–Cd(1)–O(5)#2
O(5)–Cd(1)–N(32)#1
2.307(5)
92.8(2)
85.4(2)
Cd(1)–O(5)
N(52)–Cd(1)–O(5)#2
N(52)#2–Cd(1)–N(32)#1
2.311(5)
87.2(2)
92.0(2)
Cd(1)–N(32)#1
O(5)#2–Cd(1)–N(32)#1
N(52)–Cd(1)–N(32)#1
2.342(5)
94.6(2)
88.0(2)
Compound 4
Cd(1)–N(3)
Cd(1)–O(2)
O(1)–Cd(1)–O(2)
N(3)#1–Cd(1)–O(1)
N(3)–Cd(1)–O(1)
O(2)–Cd(1)–O(5)
2.307(2)
2.476(2)
53.09(6)
90.99(7)
88.87(7)
140.87(4)
Cd(1)–O(1)
2.405(2)
Cd(1)–O(5)
2.291(3)
N3#1–Cd(1)–N(3)
N(3)–Cd(1)–O(5)
O(1)–Cd(1)–O(5)
O(1)–Cd(1)–O(2)#1
176.52(9)
88.26(4)
87.78(4)
131.34(6)
N(3)–Cd(1)–O(2)#1
N(3)#1–Cd(1)–O(2)#1
O(1)#1–Cd(1)–O(1)
O(2)–Cd(1)–O(2)#1
91.42(6)
91.29(6)
175.56(8)
78.26(8)
Compound 5
Cu(1)–N(32)#1
Cu(2)–O(1)
Cu(2)–N(101)#2
N(32)#1–Cu(1)–N(152)
O(1)–Cu(2)–N(52)#1
N(52)#1–Cu(2)–N(101)#2
N(1)–Cu(2)–N(132)
2.023(4)
2.179(3)
2.030(3)
92.2(2)
97.0(2)
166.6(1)
166.2(1)
Cu(1)–O(9)
Cu(2)–N(1)
Cu(2)–N(132)
N(32)#3–Cu(1)–N(152)
O(1)–Cu(2)–N(101)#2
O(1)–Cu(2)–N(132)
N(132)–Cu(2)–N(101)#2
2.447(4)
2.045(3)
2.003(3)
87.8(2)
96.4(2)
96.6(2)
86.4(2)
Cu(1)–N(152)
Cu(2)–N(52)#1
2.019(4)
1.985(4)
O(1)–Cu(2)–N(1)
97.1(1)
91.8(2)
87.8(2)
90.9(1)
N(52)#1–Cu(2)–N(132)
N(1)–Cu(2)–N(52)#1
N(1)–Cu(2)–N(101)#2
Compound 6
Ni(1)–O(1)
Ni(1)–O(11)
2.084(1)
2.082(1)
177.66(6)
90.29(6)
90.48(6)
86.71(6)
89.37(6)
Ni(1)–O(2)
Ni(1)–N(1)#1
2.107(1)
2.135(2)
94.19(6)
91.29(6)
91.67(6)
88.10(6)
176.87(6)
Ni(1)–O(3)
Ni(1)–N(32)
2.054(1)
2.051(2)
87.05(6)
89.16(6)
91.11(6)
90.63(6)
177.49(6)
O(1)–Ni(1)–O(2)
O(1)–Ni(1)–N(1)#1
O(3)–Ni(1)–N(32)
O(3)–Ni(1)–N(1)#1
O(2)–Ni(1)–N(1)#1
O(1)–Ni(1)–O(3)
O(1)–Ni(1)–N(32)
O(11)–Ni(1)–N(32)
O(2)–Ni(1)–O(3)
N(1)#1–Ni(1)–N(32)
O(1)–Ni(1)–O(11)
O(2)–Ni(1)–N(32)
O(11)–Ni(1)–N(1)#1
O(2)–Ni(1)–O(11)
O(3)–Ni(1)–O(11)
a
Symmetry operators: #1: 1 + x, y, 1 + z; #2: 2 À x, Ày, 2 À z; #3: 1 À x, Ày, 1 À z for 1; #1: ÀX + 2, Y À 1/2, ÀZ + 3/2; #2: ÀX + 2, ÀY + 1, ÀZ + 1 for 2; 1#: 1/2 À x, 1/2 + y, 1/
2 À z; 2#: 1 À x, 2 À y, Àz for 3; #1: Àx, y, À1/2 À z for 4; #1: ÀX + 1, Y + 1/2, ÀZ + 1/2; #2: ÀX + 2, Y À 1/2, ÀZ + 1/2; #3: X + 1, ÀY + 1/2, Z + 1/2; #4: ÀX + 1, Y À 1/2, ÀZ + 1/2;
#5: ÀX + 2, ÀY + 1, ÀZ + 1 for 5; #1: X, ÀY + 3/2, Z À 1/2 for 6.
asymmetric unit of 2 contains one Cu(II) atom sitting on an inver-
sion center, one L ligand and one perchlorate anion. The Cu1 atom
is four coordinated with a nearly ideal square planar coordination
geometry by four N atoms (N32, N32F, N52C, N52G) from four dif-
ferent L ligands, with N–Cu1–N bond angles in the range 88.69(6)–
180° and Cu1–N bond lengths of 1.995(2) and 2.011(2) Å (Table 2).
The coordination mode of L in 2 is similar to that in 1 (Scheme 1a),
however, a layer structure, rather than the chain structure of 1, is
observed in 2 (Fig. 2b). Four L ligands and four Cu(II) atoms form
a 40-membered macrocycle, which is further linked by Cu–N coor-
dinated bonds to generate a 2D net with (4, 4) topology. The layers
of 2 are packing along the c axis and the perchlorate anions are lo-
cated in the voids (Fig. 2c). The layers are then linked by C–HÁÁÁO
hydrogen bonds to form the final 3D framework structure (Fig. S2).
3.3. Crystal structural description of [Cd(L)2(H2O)2](ClO4)2 (3)
When Cd(ClO4)2Á6H2O was reacted with the ligand L to see the
effect of the metal center on the structure, complex 3 was ob-
tained. As illustrated in Fig. 3a, Cd1 in 3 has a distorted octahedral
coordination geometry, six-coordinated with an N4O2 donor set.
Fig. 1. (a) Coordination environment of the Cu(II) atom in complex 1 with the
ellipsoids drawn at the 30% probability level. The hydrogen atoms and nitrate anion
are omitted for clarity. (b) The infinite hinged chain structure of complex 1.
Scheme 1. Coordination modes of the ligand L in complexes 1–6.

92
L. Luo et al. / Polyhedron 38 (2012) 88–96
Fig. 3. (a) Coordination environment of the Cd(II) atom in complex 3 with the
ellipsoids drawn at the 30% probability level. The hydrogen atoms and perchlorate
anion are omitted for clarity. (b) The 2D network of complex 3.
effect of counteranions with different coordination abilities on the
structures of the complexes, the reaction of L with Cd(OAc)2Á2H2O
was carried out, and complex 4 was isolated. Each asymmetric unit
of 4 contains one Cd(II) atom sitting on a special position, half L
ligand and one acetate anion. As shown in Fig. 4a, the Cd1 atom is
seven coordinated with a distorted pentagonal bipyramid coordina-
tion geometry, by two N atoms (N3, N3A) from the imidazole groups
of two distinct L ligands with a Cd1–N bond distance of 2.307(2) Å,
one O atom from water molecule with a Cd1–O5 bond distance of
2.291(3) Å and four O atoms from two acetate anions with Cd1–O
bond lengths of 2.405(2) and 2.476(2) Å. The coordination angles
around the Cd(II) center are in the range 53.09(6)–176.52(9)° (Table
2). On the other hand, each L ligand connects two Cd(II) atoms using
its two imidazole groups to generate an infinite chain (Fig. 4b). The
adjacent chains are further held together through O(5)–H(4)ÁÁÁO(1)
and C(3)–H(3)ÁÁÁO(1) hydrogen bonding interactions, generating a
2D network (Fig. S4a). The layers are then linked together by
C(1)–H(1)ÁÁÁO(2) hydrogen bonds to give rise to the final 3D frame-
work structure (Fig. S4b).
Fig. 2. (a) Coordination environment of the Cu(II) atom in complex 2 with the
ellipsoids drawn at the 30% probability level. The hydrogen atoms and perchlorate
anion are omitted for clarity. (b) The 2D network in complex 2 with (4, 4) topology.
(c) Crystal packing diagram of complex 2 with perchlorate anions shown in the Ball
and Stick mode and different colors for different layers. (Color online.)
The Cd–N bond distances are 2.307(5) and 2.342(5) Å and that of
Cd–O is 2.311(5) Å. The range of bond angles is 85.4(2)–180.0°
(Table 2). Due to the absence of the coordination of the pyridine
group, the L ligand is a two-connector and links the Cd(II) centers
to generate a 2D network structure (Fig. 3b), which is similar to
that in 2.
3.5. Crystal structural description of
[Cu3(L)4(H2O)2(SO4)](SO4)2Á30H2O (5)
To compare with 1 and 2, as well as to study the effect of a
counteranion with a different charge and coordination ability on
the structure of the complexes, the reaction of L with CuSO4Á5H2O
was carried out. As illustrated in Fig. 5a, there are two different
Cu(II) atoms in the asymmetric unit of 5. Each Cu1, sitting on an
inversion center, is six-coordinated with a distorted octahedral
coordination geometry by four N atoms (N32H, N152E, N32G,
N152) from the imidazole groups of four distinct L ligands and
two O atoms (O9, O9E) from water molecules. The Cu1–N bond
lengths are 2.019(4) and 2.023(4) Å and the Cu1–O bond length
is 2.447(4) Å (Table 2). While Cu2, with a distorted tetragonal pyra-
The layers of 3 are packed in an –ABAB– sequence along the c
axis, and the perchlorate anions are located at the edge of the lay-
ers. There are O–HÁÁÁN, O–HÁÁÁO and C–HÁÁÁO hydrogen bonds (Table
S1) which link the layers and perchlorate anions to give rise to a 3D
framework (Fig. S3).
3.4. Crystal structural description of [Cd(L)(OAc)2(H2O)] (4)
Considering that the nitrate and perchlorate anions in 1–3 do not
take part in coordination with the metal centers, to investigate the

L. Luo et al. / Polyhedron 38 (2012) 88–96
93
other N from the imidazole group of another L ligand. On the other
hand, the L ligand links two Ni(II) atoms to generate an infinite zig-
zag chain (Fig. 6b). The adjacent chains are joined together by O–
HÁÁÁO and O–HÁÁÁN hydrogen bonds to give rise to
a layer
(Fig. S5a), which is further linked by O(1)–H(10)ÁÁÁO(14) and
O(3)–H(15)ÁÁÁO(14) hydrogen bonds to generate the final 3D frame-
work of 6 (Fig. S5b).
3.7. Comparison of the structures
Six coordination complexes of Cu(II), Cd(II) and Ni(II) were suc-
cessfully obtained by the reactions of the rigid ligand L with the
À
corresponding metal salts with different counteranions of NO3
,
À
2À
ClO4 and SO4 under the same reaction conditions. The results
show that the L ligand adopts three different coordination modes
in 1–6 (Scheme 1). In the complexes 1–4, each L ligand acts as a
bidentate ligand using its two imidazole groups, with the pyridine
group of L free of coordination (Scheme 1a). In 5, the L ligand
adopts a tridentate mode using its pyridine and two imidazole
groups (Scheme 1b), while in 6, the L ligand still adopts a bidentate
mode, but using the pyridine and one of the imidazole groups
(Scheme 1c). While compounds 1 and 2 have the same Cu(II) cen-
ters, they display different structures, namely 1 is an infinite chain,
2 is a 2D network. It can be seen that the distinct coordination
number of the Cu(II) center results in the different structure, since
the Cu(II) center is 6-coordinated in 1 and 4-coordinated in 2. This
phenomenon is also observed in complexes 3 and 4. Comparing the
structures of 3 and 4, one more remarkable difference can be
founÀd, i.e. the OAcÀ anion participates in coordination while the
ClO4 anion does not take part in the coordination, which can be
ascribed to the different coordination ability of the counteranions.
Comparing complexes 5 and 6 with the same counteranion, the
distinct structures can be brought about by the different coordina-
tion geometries of the metal centers as well as the different coor-
dination mode of the L ligand (vide supra). The results further
confirm that metal centers with different coordination numbers
and geometries, counteranions with different coordination abilities
and ligands with varied coordination modes play important roles
in determining the structures of the complexes. At the same time,
the present study implies that it is still a great challenge to control
or foresee the overall structures of complexes at present since they
can be influenced by subtle changes of factors such as metal center,
counteranion and so on.
Fig. 4. (a) Coordination environment of the Cd(II) atom in complex 4 with the
ellipsoids drawn at the 30% probability level. The hydrogen atoms are omitted for
clarity. (b) The infinite chain structure of complex 4.
midal coordination geometry, is five-coordinated by four N atoms
(N1, N132, N101C, N52B) and one O atom from a sulfate anion.
One of the N atoms is from the pyridine of one L ligand, and the
others are from the imidazole groups of three other distinct L li-
gands. Thus, each Cu(II) atom in 5 links four L ligands. On the other
hand, each L ligand connects three Cu(II) atoms using its pyridine
and imidazole groups (Scheme 1b). If the coordination between
Cu2 and N101 is neglected, the Cu(II) centers are bridged by L li-
gands to give rise to a 2D network in the ab plane, as illustrated
in Fig. 5b. The layers are further linked together by Cu2–N101
bonds to generate a 3D framework with two different channels,
A and B (Fig. 5c). The free sulfate anions occupy channel A along
the b-axis, while the coordinated sulfate anions occupy channel
B. The uncoordinated water molecules fill the vacancy of the 3D
framework and are linked together via O–HÁÁÁO hydrogen bonding
interactions, though the hydrogen atoms of the uncoordinated
water molecules in 5 could not be found.
To further understand the structure of 5, a topological analysis
by reducing the multi-dimensional structure to a simple node and
linker net was carried out. The coordinated water molecules and
sulfate anions are ignored in the topological analysis and each L li-
gand is a 3-connector, since one L ligand links three Cu(II) atoms.
Each Cu(II) atom is attached to four L ligands, and thus can be re-
garded as a 4-connected node. The nodes corresponding to the L li-
gands are topologically equivalent while the Cu(II) nodes are
different, therefore the overall structure of 5 is a (3,4,4)-connected
trinodal 3D net, as shown in Fig. 5d, which is similar to the previ-
ously reported complex [Cu3(trz)4(H2O)3]F2 (trzÀ = 1,2,4-triazolate)
with 3- and 4-connected nodes of trz and Cu(II), respectively [22].
The Point (Schläfli) symbol for the net is (4.82)4(4.83.102)2
(42.82.102), calculated by the TOPOS program [23], and the name
for the net is 3,4,4T24 [24].
3.8. Thermal stabilities and XRPD of the complexes
Thermogravimetric analyses (TGA) were carried out for the com-
plexes, except for 2 and 3 with perchlorate anions, and the results of
the TGA are shown in Fig. S6. Complex 1 shows a weight loss of
5.08% before 165 °C, corresponding to the release of the coordinated
water molecules (Calc. 5.18%), and further decomposition occurred
at 320 °C. For 4, the weight loss was found before 100 °C due to the
release of the coordinated water molecules with a weight loss of
4.03% (Calc. 3.92%), and the decomposition temperature is 240 °C.
For complex 5, a weight loss of 26.1% was observed in the temper-
ature range 30–170 °C, which corresponds to the release of water
molecules, but it does not agree with the calculated value of
30.97%. The reason is that the solvent water molecules in 5 can be
easily lost at room temperature. Complex 6 loses 12.70% of its
weight in the temperature range 200–280 °C, which is attributed
to the departure of the coordinated water molecules (Calc.
12.86%), and the residue is stable up to ca. 400 °C.
3.6. Crystal structural description of [Ni(L)(H2O)3(SO4)] (6)
To further investigate the impact of the metal center on the
structure of the complexes, NiSO4Á6H2O was used in the reaction
instead of CuSO4Á5H2O to give complex 6. It is interesting to find
that one of the two imidazole groups, rather than the pyridine
one as observed in 1–4, does not participate in the coordination
(Scheme 1c). As shown in Fig. 6a, in 6 each Ni(II) atom, with a dis-
torted octahedral coordination geometry, is six-coordinated by
three O atoms from three water molecules, one O from a sulfate an-
ion, one N atom from the pyridine group of an L ligand and the
The purities of 1–6 were certified by X-ray powder diffraction
(XRPD) measurements, and the results are given in Fig. S7. In addi-
tion, the diffraction patterns of 3A and 3B are shown in Fig. S8,
which are in good agreement with that of 3.

94
L. Luo et al. / Polyhedron 38 (2012) 88–96
Fig. 5. (a) Coordination environment of the Cu(II) atoms in 5 with the ellipsoids drawn at the 30% probability level. The hydrogen atoms and uncoordinated sulfate anions are
omitted for clarity. (b) The 2D network in 5. (c) The 3D framework of 5 with different colors for different layers (yellow: Cu2–N101 bond). (d) The topological representation
of the (3,4,4)-connected trinodal 3D structure of 5 with the (4.82)4(4.83.102)2(42.82.102) new topology (blue: Cu1 and Cu2; turquoise: L ligand). (Colour online.)
3.9. Reversible anion exchange property of complex 3
stirring for 1 day to allow the reverse anion exchange, and the
product 3B was obtained. The band of ClO4À appeared in the spec-
trum of 3B, and the bands of NO3À disappeared (Fig. 7). The results
indicate that 3 shows a reversible anion exchange property.
The complex [Cd(L)2(H2O)2](ClO4)2 (3) has a 2D network struc-
ture, and the perchlorate anions are located in the voids of the lay-
ers. Furthermore, 3 is insoluble in water and common organic
solvents, thus anion exchange experiments were performed. The
results show that 3 shows a reversible anion exchange property.
A well-ground powder of 3 was suspended in an aqueous solution
of NaNO3 and stirred for 1 day, and then the exchanged product
[Cd(L)2(H2O)2](NO3)2 was obtained (see Section 2). The FT-IR spec-
tra of 3 and the exchanged product are shown in Fig. 7. It can be
seen that theÀintense bands at 1383 and 1312 cmÀ1, originating
from the NO3 anion, appear in the spectrum of 3A, while the in-
tense bands around 1132 and 1099 cmÀ1 of the ClO4À anion disap-
pear. Furthermore, the results of the elemental analyses also
confirm the complete anion exchange. Through the anion exchange
of 3, the framework structure is retained, which can be confirmed
by the XRPD spectra of 3 and 3A (Fig. S8). A powder sample of 3A
was suspended in an aqueous solution of NaClO4 with constant
3.10. Photoluminescence of the complexes
The photoluminescence properties of the Cd(II) complexes have
been well studied because of their potential application as fluores-
cence-emitting materials. The emission spectra of the Cd(II) com-
plexes 3 and 4, together with the free ligand L, were measured in
the solid state at room temperature. Intense emission bands were
observed at 398 nm for the free ligand L, with the excitation at
363 nm. As shown in Fig. S9, intense bands were observed at
397 nm (kex = 362 nm) for 3 and 406 nm (kex = 353 nm) for 4. The
emissions of 3 and 4 may tentatively be assigned to the intraligand
transition of L as a result of their close similarity [25]. The small red
shift of the emission maximum between the complex and the li-

L. Luo et al. / Polyhedron 38 (2012) 88–96
95
21021062) and the National Basic Research Program of China
(Grant Nos. 2007CB925103 and 2010CB923303).
Appendix A. Supplementary data
CCDC 851230, 851231, 851232, 851233, 851234 and 851235
contain the supplementary crystallographic data for 1, 2, 3, 4, 5
and 6. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2012.02.027.
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