The structural diversity and luminescent properties of Zn(II) coordination assemblies with cyclohexane (or cyclohexene) dicarboxylate anions and two positional isomeric ligands

Article abstract of DOI:10.1016/j.poly.2011.12.030

Four Zn(II) coordination polymers, namely {[Zn(chedc)(4,4′-Hbpt)]} _n (1), {[Zn₃(chadc)₂(4,4′-Hbpt) ₂(4,4′-bpt)₂]·3H₂O}_n (2), {[Zn₂(chadc)₂(3,3′-Hbpt)]}_n (3) and {[Zn₂(chedc)₂(3,3′-Hbpt)]·H ₂O}_n (4) (chadc = cis-1,2-cyclohexanedicarboxylate anion, chedc = cis-4-cyclohexene-1,2-dicarboxylate anion, 4,4′-Hbpt = 1H-3,5-bis(4-pyridyl)-1,2,4-triazole, 3,3′-Hbpt = 1H-3,5-bis(3-pyridyl)-1, 2,4-triazole) have been produced by the reaction of two positional isomeric dipyridyl bridging ligands and two dicarboxylate anions with Zn(II) salts under hydrothermal conditions. Structural analysis reveals that 1 exhibits a double-chain and 2 exhibits a 3D network with a (6².10) ₂(6⁴.10²) topology, whilst 3 and 4 show similar layer structures. The luminescent properties of these complexes have been briefly investigated.

Full text of DOI:10.1016/j.poly.2011.12.030

Polyhedron 34 (2012) 129–135
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Polyhedron
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The structural diversity and luminescent properties of Zn(II) coordination
assemblies with cyclohexane (or cyclohexene) dicarboxylate anions and two
positional isomeric ligands
b,
Fu-Ping Huang a,b, Jing-Bin Lei a, Qing Yu a, He-Dong Bian a, , Shi-Ping Yan
⇑
⇑
a Key Laboratory for the Chemistry and Molecular Engineering of Medicinal Resources, Department Chemistry and Chemical Engineering, Guangxi Normal University,
Ministry of Education of China, Guilin 541004, PR China
b Department of Chemistry, Nankai University, Tianjin 300071, PR China
a r t i c l e i n f o
a b s t r a c t
Four Zn(II) coordination polymers, namely {[Zn(chedc)(4,40-Hbpt)]}n (1), {[Zn3(chadc)2(4,40-Hbpt)2
(4,40-bpt)2]ꢀ3H2O}n (2), {[Zn2(chadc)2(3,30-Hbpt)]}n (3) and {[Zn2(chedc)2(3,30-Hbpt)]ꢀH2O}n (4) (chadc =
cis-1,2-cyclohexanedicarboxylate anion, chedc = cis-4-cyclohexene-1,2-dicarboxylate anion, 4,40-Hbpt =
1H-3,5-bis(4-pyridyl)-1,2,4-triazole, 3,30-Hbpt = 1H-3,5-bis(3-pyridyl)-1,2,4-triazole) have been produced
by the reaction of two positional isomeric dipyridyl bridging ligands and two dicarboxylate anions with Zn(II)
salts under hydrothermal conditions. Structural analysis reveals that 1 exhibits a double-chain and 2 exhibits a
3D network with a (62.10)2(64.102) topology, whilst 3 and 4 show similar layer structures. The luminescent
properties of these complexes have been briefly investigated.
Article history:
Received 4 November 2011
Accepted 17 December 2011
Available online 8 January 2012
Keywords:
Zn(II) coordination polymers
Positional isomeric ligands
Luminescence properties
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
(4-pyridyl)-1,2,4-triazole (3,40-Hbpt) and 1H-3,5-bis(3-pyridyl)-
1,2,4-triazole (3,30-Hbpt) (Chart 1), and a series of interesting
The design and construction of coordination polymers is of cur-
rent interest in the field of crystal engineering not only for their
intriguing variety of architectures and topologies but also for their
tremendous potential application in luminescence, catalysis, non-
linear optics, gas adsorption, magnetism, and medicine [1,2]. How-
ever, it is still a great challenge to rationally prepare and predict
their exact structures. Generally, many factors can affect the struc-
tures of the final products, such as counter anions [3], the pH
values of the reaction solutions [4], temperature [5], molar ratio
between reactants [6] and solvent system [7]. One of the most use-
ful and important way of studying the controllable synthesis of the
molecular architecture is still the reasonable choice of well-de-
signed organic ligands as bridges or terminal groups (building
blocks) with metal ions or clusters as nodes, and many strategies
have already been developed based on previous works [8,9]. The
selection of the ligands plays a key role because deliberate modifi-
cations on the organic ligands can dramatically influence the ulti-
mate structural topologies of the coordination solids [10,11].
In the last few years, through introducing the 1H-1,2,4-triazole
moiety between a couple of 4-pyridyl (or 3-pyridyl) groups, we
have designed three positional isomeric N,N0-donor ligands: 1H-
3,5-bis(4-pyridyl)-1,2,4-triazole (4,40-Hbpt), 1H-3-(3-pyridyl)-5-
coordination polymers have been synthesized and structurally
characterized [12,13]. The different positions of the pyridyl N
atoms in the positional isomeric ligands may benefit the formation
of different topological structures, which are very useful in supra-
molecular chemistry, crystal engineering and design [14]. As a part
of this ongoing work, we present here the structural diversity and
luminescent properties of four Zn(II) complexes: {[Zn(chedc)(4,40-
Hbpt)]}n (1), {[Zn3(chadc)2(4,40-Hbpt)2(4,40-bpt)2]ꢀ3H2O}n (2),
{[Zn2(chadc)2(3,30-Hbpt)]}n (3) and {[Zn2(chedc)2(3,30-Hbpt)]ꢀ
H2O}n (4) (where chadc = cis-1,2-cyclohexanedicarboxylate anion,
chedc = cis-4-cyclohexene-1,2-dicarboxylate anion). In addition,
the luminescent properties of these compounds have been
investigated.
2. Experimental
2.1. Materials and physical measurements
With the exception of the ligands 4,40-Hbpt and 3,30-Hbpt,
which were prepared according to the literature procedure [15],
all reagents and solvents for the syntheses and analyses were com-
mercially available and used as received. IR spectra were taken on
a Perkin-Elmer spectrum One FT-IR spectrometer in the 4000–
400 cmꢁ1 region with KBr pellets. Elemental analyses for C, H
and N were carried out on a Model 2400 II, Perkin-Elmer elemental
⇑
Corresponding authors.
E-mail address: gxnuchem312@yahoo.com.cn (H.-D. Bian).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.12.030

130
F.-P. Huang et al. / Polyhedron 34 (2012) 129–135
N
N
N
N
N
N
N
HN
N
HN
4,4'-Hbpt
3,3'-Hbpt
H
H
COOH
COOH
H
H
COOH
cCheOdOcH
chadc
Chart 1. The ligands used in this work.
analyzer. Steady state fluorescence measurements were performed
using an FL3-P-TCSPC fluorescence spectrofluorometer at ambient
temperature in the solid-state.
2.6. X-ray crystallography
X-ray single-crystal diffraction data for 1–4 were collected with
a Bruker SMART CCD instrument using graphite monochromatic
MoKa radiation (k = 0.71073 Å). The data were collected at
2.2. Synthesis of {[Zn(chedc)(4,40-Hbpt)]}n (1)
293(2) K and there was no evidence of crystal decay during data
collection. A semi-empirical absorption correction was applied
using SADABS and the program SAINT was used for integration of the
diffraction profiles [16]. The structures were solved by direct meth-
ods with the program SHELXS-97 and refined by full-matrix least-
squares methods on all F2 data with SHELXL-97 [17]. The non-hydro-
gen atoms were refined anisotropically. Hydrogen atoms of water
molecules were located in a difference Fourier map and refined iso-
tropically in the final refinement cycles. Other hydrogen atoms
were placed in calculated positions and refined using a riding mod-
el. The final cycle of full-matrix least-squares refinement was
based on observed reflections and variable parameters. Further
crystallographic data and structural refinement details are summa-
rized in Table 1. Selected bond lengths and bond angles are given in
Table 2.
A mixture containing Zn(CH3COO)2ꢀ2H2O (110 mg, 0.5 mmol),
4,40-Hbpt (112 mg, 0.5 mmol), chedc (85 mg, 0.5 mmol), NaOH
(40 mg, 1 mmol), water (10 mL) and ethanol (3 mL) was sealed in
a Teflon-lined stainless steel vessel (23 mL), which was heated at
120 °C for 3 days and then cooled to room temperature at a rate
of 5 °C/h. Colorless block crystals of 1 were obtained and picked
out, washed with distilled water and dried in air. Anal. Calc. for
C
20H17ZnN5O4: C, 52.54; H, 3.72; N, 15.32. Found: C, 52.78; H,
3.54; N, 15.74%. IR (KBr, cmꢁ1): 3423.07w, 3027w, 2829.67m,
1621.41s, 1562.79s, 1436.63m, 1330.61w, 1028.84w, 993.18w,
847.78w, 604.15w.
2.3. Synthesis of {[Zn3(chadc)2(4,40-Hbpt)2(4,40-bpt)2]ꢀ3H2O}n (2)
The same synthetic procedure as that for 1 was used except that
chedc was replaced by chadc, giving colorless block X-ray-quality
crystals of 2. Anal. Calc. for C64H60Zn3N20O11: C, 51.83; H, 4.05; N,
18.90. Found: C, 51.27; H, 3.98; N, 18.68%. IR (KBr, cmꢁ1):
3441.29m, 3032.96m, 2934.06m, 1616.61s, 1566.54s, 1449.93s,
1220.88m, 1028.84w, 998.67w, 842.30m, 737.14m.
3. Results and discussion
3.1. Structural description of 1–4
3.1.1. {[Zn(chedc)(4,40-Hbpt)]}n (1)
Complex 1 is an infinite 1-D polymer with a double-chain struc-
ture. The asymmetric unit of 1 consists of one Zn(II) cation, one
4,40-Hbpt molecule and one chedc anion (Fig. 1(a)). The Zn(II) ions
exhibit a distorted tetrahedral environment with two carboxylic O
atoms from two chedc anions [Zn1–O1 = 1.967(2) Å; Zn1–
O3A = 1.955(19) Å] and two N atoms from two 4,40-Hbpt ligands
[Zn1–N1 = 2.044(2) Å; Zn1–N5B = 2.049(2) Å]. As illustrated in
Fig. 1(b), the 4,40-Hbpt ligands bridge adjacent Zn(II) ions to form
a 1-D chain running along the a-axis. Two single [Zn(4,40-Hbpt)]
chains are further combined by two carboxylic groups of chedc
to form a double-chain. The Znꢀ ꢀ ꢀZn distance separated by the
4,40-Hbpt linker is 13.763(3) Å, and it is 5.146(1) Å in the dimeric
unit bridged by a pair of carboxylate groups.
2.4. Synthesis of {[Zn2(chadc)2(3,30-Hbpt)]}n (3)
The same synthetic procedure as that for 2 was used except that
4,40-Hbpt was replaced by 3,30-Hbpt, giving colorless block X-ray-
quality crystals of 3. Anal. Calc. for C28H29Zn2N5O8: C, 48.39; H,
4.18; N, 10.08. Found: C, 48.56; H, 4.43; N, 10.14%. IR (KBr,
cmꢁ1): 3434.06m, 3082m, 2941.01s, 1604.62s, 1446.05s,
1426.63s, 1198.93w, 1053.53w, 979.46w, 842.30w, 697.13m.
2.5. Synthesis of {[Zn2(chedc)2(3,30-Hbpt)]ꢀH2O}n (4)
The same synthetic procedure as that for 1 was used except that
4,40-Hbpt was replaced by 3,30-Hbpt, giving colorless block X-ray-
quality crystals of 4. Anal. Calc. for C28H27Zn2N5O9: C, 47.44; H,
3.81; N, 9.88. Found: C, 47.05; H, 3.76; N, 9.96%. IR (KBr, cmꢁ1):
3434.06m, 3065.93m, 2921.95m, 1605.84s, 1421.08s, 1358.05w,
1220.88m, 1056.28w, 993.18w, 812.12m, 697.28m.
A 3D supramolecular structure (Fig. 1(d)) is constructed by
hydrogen bonding interactions between the triazole N atoms from
4,40-Hbpt and the carboxylate oxygen atoms from (chedc)2ꢁ anions
[N2–H2Aꢀ ꢀ ꢀO2#1, symmetry codes: (#1) x + 3/2, y + 1/2, z + 1].
Therefore, hydrogen bonding interactions play an important role
in stabilizing the supramolecular structures.

F.-P. Huang et al. / Polyhedron 34 (2012) 129–135
131
Table 1
Crystal data and structure refinement for 1–4.
Complex
1
2
3
4
Empirical formula
Formula weight (M)
C
20H17N5O4 Zn
C64H60N20O11Zn3
1481.49
C28H29N5O8Zn2
694.34
C28H27N5O9Zn2
708.33
456.78
Crystal system
Space group
monoclinic
C2/c
monoclinic
C2/c
monoclinic
P21/c
monoclinic
P21/c
a (Å)
b (Å)
c (Å)
22.388(5)
13.763(3)
15.079(3)
124.35(3)
3835.9(2)
8
35.823(7)
9.810(2)
25.171(5)
129.14(3)
6861(2)
7.0490(1)
18.214(4)
21.185(4)
91.28(3)
2719.3(9)
4
7.1260(1)
18.309(4)
21.127(4)
93.32(3)
2751.8(9)
4
b (°)
V (Å3)
Z
4
Dcalc (g/cm3)
1.582
1.434
1.696
1.710
F(000)
2496
3048
1768
1768
h Range for data collection (°)
Reflections collected/unique
Goodness-of-fit (GOF) on F2
3.11–27.48
18754/4367 [Rint = 0.0429]
1.175
3.02–25.00
17962/5985 [Rint = 0.1174]
1.090
3.09–25.50
23012/5051 [Rint = 0.0559]
1.028
3.07–25.25
13764/4804 [Rint = 0.0779]
1.042
Final R indices [I > 2
R indices (all data)
r(I)]
R1 = 0.0471
R1 = 0.0644
x
x
R2 = 0.0837
R2 = 0.0885
R1 = 0.1014
R1 = 0.1584
x
x
R2 = 0.2194
R2 = 0.2517
R1 = 0.0523
R1 = 0.0777
x
x
R2 = 0.1260
R2 = 0.1372
R1 = 0.0897
R1 = 0.1219
x
x
R2 = 0.1825
R2 = 0.1999
Table 2
Selected bond lengths (Å) and bond angles (°) for 1–4.
1 (Symmetry codes: for 1, A ꢁx + 1/2, ꢁy + 1/2, ꢁz + 1; B x, y + 1, z.)
Zn1–O1
1.967(2)
1.955(2)
105.29(9)
110.63(9)
114.22(8)
Zn1–N1
Zn1–N5B
O3A–Zn1–N1
O3A–Zn1–N5B
N1–Zn1–N5B
2.044(2)
2.049(2)
95.49(9)
106.47(9)
124.19(9)
Zn1–O3A
O1–Zn1–N1
O1–Zn1–N5B
O3A–Zn1–O1
2 (Symmetry codes: for 2, A ꢁx + 1/2, y ꢁ 1/2, ꢁz + 1/2; B ꢁx + 1/2, ꢁy + 1/2, ꢁz; C x ꢁ 1/2, ꢁy + 1/2, z ꢁ 1/2; D ꢁx, y, ꢁz ꢁ 1/2.)
Zn1–O1
1.910(6)
2.012(7)
2.046(6)
105.7(3)
122.9(3)
104.4(3)
110.6(3)
114.0(3)
99.5(3)
Zn1–N1
2.068(7)
1.947(6)
2.039(7)
115.2(4)
96.9(3)
Zn1–N9
Zn1–N10A
Zn2–O3B
Zn2–N6
O3B–Zn2–O3C
O3B–Zn2–N6
O3C–Zn2–N6
N6–Zn2–N6D
O1–Zn1–N9
O1–Zn1–N10A
N9–Zn1–N10A
O1–Zn1–N1
N9–Zn1–N1
N10A–Zn1–N1
121.2(3)
106.8(4)
3 (Symmetry codes: for 3, A x ꢁ 1, y, z; B x ꢁ 1, ꢁy + 1/2, z ꢁ 1/2; C x + 1, y, z.)
Zn1–O5A
1.920(3)
1.944(3)
1.955(3)
2.072(4)
2.461(4)
124.41(2)
117.73(2)
114.14(2)
93.82(1)
98.43(1)
97.13(2)
92.20(1)
99.76(1)
57.09(1)
153.00(1)
Zn2–O1C
Zn2–O6
Zn2–O3
Zn2–N1
1.925(3)
1.928(3)
2.029(3)
2.075(4)
2.325(4)
127.46(2)
114.36(2)
115.48(2)
93.08(1)
98.04(1)
95.11(1)
93.19(1)
98.48(13)
58.93(12)
153.46(13)
Zn1–O2
Zn1–O7
Zn1–N5B
Zn1–O8
Zn2–O4
O5A–Zn1–O2
O5A–Zn1–O7
O2–Zn1–O7
O5A–Zn1–N5B
O2–Zn1–N5B
O7–Zn1–N5B
O5A–Zn1–O8
O2–Zn1–O8
O7–Zn1–O8
N5B–Zn1–O8
O1C–Zn2–O6
O1C–Zn2–O3
O6–Zn2–O3
O1C–Zn2–N1
O6–Zn2–N1
O3–Zn2–N1
O1C–Zn2–O4
O6–Zn2–O4
O3–Zn2–O4
N1–Zn2–O4
4 (Symmetry codes: for 4, A x ꢁ 1, y, z; B x, ꢁy + 3/2, z + 1/2.)
Zn1–O1
1.945(6)
1.956(6)
2.052(7)
2.171(7)
2.181(7)
130.3(3)
93.8(3)
Zn2–O2
Zn2–O8A
Zn2–O6
Zn2–N1
1.929(6)
1.930(6)
1.976(7)
2.071(7)
2.383(9)
124.0(3)
115.8(3)
117.4(3)
97.8(3)
93.6(3)
95.2(3)
102.2(3)
92.2(3)
57.4(3)
Zn1–O7A
Zn1–N5B
Zn1–O4A
Zn1–O3A
Zn2–O5
O1–Zn1–O7A
O1–Zn1–N5B
O7A–Zn1–N5B
O1–Zn1–O4A
O7A–Zn1–O4A
N5B–Zn1–O4A
O1–Zn1–O3A
O7A–Zn1–O3A
N5B–Zn1–O3A
O4A–Zn1–O3A
O2–Zn2–O8A
O2–Zn2–O6
O8A–Zn2–O6
O2–Zn2–N1
O8A–Zn2–N1
O6–Zn2–N1
O2–Zn2–O5
O8A–Zn2–O5
O6–Zn2–O5
N1–Zn2–O5
95.2(3)
94.1(3)
100.6(3)
151.2(3)
112.1(3)
116.3(3)
92.0(3)
59.5(2)
151.1(3)

132
F.-P. Huang et al. / Polyhedron 34 (2012) 129–135
Fig. 1. (a) Structure of 1 showing the local coordination environments of the Zn(II) atoms; (b) the 1-D {[Zn(chedc)(4,40-Hbpt)]}n chain; (c) the simple form of 1-D
{[Zn(chedc)(4,40-Hbpt)]}n chain; (d) a view of the crystal packing of 1 along the a axis.
3.1.2. {[Zn3(chadc)2(4,40-Hbpt)2(4,40-bpt)2]ꢀ3H2O}n (2)
as depicted in Fig. 2(e). To the best of our knowledge, binodal
(3,4)-connected metal–organic networks constructed by mixed li-
gands have rarely been reported [19]. It should be noted that the
(3,4)-connected network in 2 is a new type, which is different from
other (3,4)-connected nets, for example, the coordination net with
a (4.82) (4.82.103) topology [20]. This result may offer new insights
into the controlled assembly of coordination solids.
The asymmetric unit of 2 consists of one and a half Zn(II) ions,
one 4,40-Hbpt molecule, one 4,40-bpt anion, one independent chadc
anion, and one and a half lattice water molecules. As shown in
Fig. 2(a), Zn1 takes a distorted tetrahedral geometry via coordinat-
ing to one carboxylic O atom of chadc [Zn1–O1 = 1.910(6) Å], two N
atoms of two 4,40-Hbpt ligands and one N atom of the 4,40-bpt li-
gand [Zn1–N10A = 2.046(6) Å, Zn1–N1 = 2.068(7) Å, Zn1–N9 =
2.012(7) Å], whereas the Zn2 ion is located on a crystallographic
2-fold axis and displays a similar distorted tetrahedral environ-
ment, which is provided by two carboxylic O atoms from two
chedc anions [Zn2–O3B = 1.947(6) Å] and two N atoms from two
4,40-bpt ligands [Zn2–N6 = 2.039(7) Å].
3.1.3. {[Zn2(chadc)2(3,30-Hbpt)]}n (3) and {[Zn2(chedc)2(3,30-
Hbpt)]ꢀH2O}n (4)
Single crystal X-ray diffraction analysis reveals that the crystal
structures of complexes 3 and 4 are very similar, except that one
chadc in 3 is replaced by chedc in 4. As a result, only the structure
of 3 is discussed in detail herein. Complex 3 presents a layered net-
work in which the Zn(II) centers are bridged by 3,30-Hbpt and
chadc ligands. The asymmetric unit of 3 consists of two Zn(II) cat-
ions (Fig. 3(a)), one independent 3,30-Hbpt molecule and two chadc
anions. Both crystallographically independent Zn(II) atoms are sur-
It is interesting that 4,40-Hbpt and 4,40-bpt coexist in 2, and they
adopt two types of coordination modes (Scheme 1). As is shown in
Fig. 2(a), one 4,40-Hbpt ligand coordinates to Zn1 in a monodentate
mode, with one uncoordinated pyridyl end (N5) dangling in the
free space. The other 4,40-bpt ligand acts as a
l3-bridge, which con-
nects the adjacent Zn1 through N9 and N10 resulting in a 1-D ar-
ray, and further connects the Zn2 ions through N6 thus forming
a 2-D polymeric layer, in which the Zn1ꢀ ꢀ ꢀZn2 distance separated
by 4,40-bpt is 9.773(2) Å. (Fig. 2(b)). Additionally, the two carbox-
ylic groups of chadc, that all adopt a monodentate mode, connect
with these zinc atoms to give a very complicated 3D network
architecture (Fig. 2(c)). The packing shows guest water molecules
O6 and O7 located inside tubular channels running down the c axis.
A better insight into the nature of this intricate architecture can
be achieved by topological analysis. In 2, on the basis of the con-
nectivity of the Zn1 and Zn2 atoms, both of them are viewed to
be 3-connected and 4-connected nodes, respectively. Moreover,
according to Wells’ topology definition [18], this 3D network can
be further simplified by considering each 4,40-bpt ligand as a 3-
connected node. Therefore, the overall structure of 2 is a binodal
(3,4)-connected net with Schläfli symbol of (62.10)2(64.102) [19],
rounded by one N atom from a
3,30-Hbpt ligand [Zn1–
N5B = 2.072(4) Å; Zn2–N1 = 2.075(4) Å] and four O atoms from
three chadc ligands [Zn1–O distances from 1.920(3) to
2.461(4) Å, Zn2–O distances from 1.925(3) to 2.325(4) Å], display-
ing a distorted five-coordinated tetragonal pyramid geometry. As
shown in Fig. 3(b) and (c), one carboxylate is in the chelate coordi-
nating mode whereas the other adopts a syn–anti bridging mode.
As a consequence, the adjacent Zn(II) atoms are bridged by three
chadc ligands to result in 1-D double chains along the a axis, which
are further linked by 3,30-Hbpt ligands to generated a 2D polymeric
coordination layer structure. The Znꢀ ꢀ ꢀZn distance separated by the
3,30-Hbpt linker is 8.791(1) Å, and it is 5.533(1) Å in the dimeric
unit bridged by a pair of carboxylate groups.
The structure of 3 is extended into a 3D supramolecular frame-
work by hydrogen-bonding interactions (N4–H4ꢀ ꢀ ꢀO3#1, symme-
try codes: #1 ꢁx + 2, y + 1/2, ꢁz + 3/2) and
pꢀ ꢀ ꢀp stacking

F.-P. Huang et al. / Polyhedron 34 (2012) 129–135
133
Fig. 2. (a) Structure of 2 showing the local coordination environments of the Zn(II) atoms; (b) view of the 2D network formed by 4,40-Hbpt and 4,40-bpt; (c) the simple form of
the 2D network; (d) the overall 3D network; (e) schematic representation of the (62.10)2(64.102) topology of 2.
M
M
M
M
M
N
N
N
N
N
N
N
N
N
N
N
HN
N
HN
N
N
I
II
M
N
III
M
M
M
N
N
N
N
N
N
N
N
HN
HN N
N
HN
M
M
M
IV (syn-syn)
V (anti-anti)
VI (syn-anti)
Scheme 1. Primary coordination modes of the 4,40-Hbpt and 3,30-Hbpt ligands used in the construction of coordination polymers.
interactions with centroid-to-centroid distances in the range
3.531–3.800 Å. Therefore, hydrogen-bonding interactions and
3.2. Photoluminescence properties
p
ꢀ ꢀ ꢀ
p
stacking interactions play important roles in stabilizing the
Compounds constructed by Zn(II) centers and conjugated or-
ganic linkers are promising candidates for photoactive materials
with potential applications such as chemical sensors and photo-
chemistry [21,22]. The synthesis of Zn(II) coordination polymers
with carefully chosen ligands can be an efficient method for the
construction of novel luminescence materials [23–25]. Therefore,
structure. Similar to 3, the overall 3D supramolecular framework
of 4 is generated incorporating N3–H3ꢀ ꢀ ꢀO3#1, O9–H9Aꢀ ꢀ ꢀN2 and
O9–H9Bꢀ ꢀ ꢀO6 hydrogen bonding (symmetry codes: #1 ꢁx + 1,
ꢁy ꢁ 1, ꢁz) and
pꢀ ꢀ ꢀp stacking interactions with centroid-to-cen-
troid distances in the range 3.591–3.745ꢀ ꢀ ꢀÅ (see Fig. 4).

134
F.-P. Huang et al. / Polyhedron 34 (2012) 129–135
Fig. 3. (a) Structure of 3 showing the local coordination environments of the Zn(II) atoms; (b) the 1-D [Zn(chadc)]n chain; (c) the 2-D layer of 3 formed by the [Zn(chadc)]n
chain and 3,30-Hbpt connector.
5000000
complex1
complex2
complex3
complex4
4000000
1
3000000
2000000
2
1000000
3
4
0
Fig. 4. Structure of 4 showing the local coordination environments of the Zn(II)
atoms.
350
400
450
500
550
600
650
700
wavelength/nm
Fig. 5. The solid-state emission spectra of 1–4 at room temperature.
the solid-state emission spectra of 1–4 have been investigated on
crushed single crystals at room temperature, as depicted in
Fig. 5. The bpt isomer ligands show very similar emission bands
at kmax values of 364 and 368 nm upon excitation at 327 nm, which
agree well with our previously reported studies [14]. On complex-
ation of these ligands with Zn(II) atoms, strong luminescence was
observable in the solid state at ambient temperature. For com-
plexes 1–4, the maximum emission bands are at 411
(kex = 347 nm), 379 (kex = 342 nm), 401 (kex = 335 nm) and
391 nm (kex = 322 nm), respectively, which should come from
fluorescence peaks, compared to that of free bpt isomers, is the re-
sult of the incorporation of metal–ligand coordination interactions
[14,27]. Furthermore, the enhancements of luminescence may be
attributed to the chelating and/or bridging effects of the ligands
to the metal centers, which effectively increases the rigidity of
the ligands and reduces the loss of energy via radiation less path-
ways [28].
intraligand
p
?
p⁄
transitions [26]. The blue-shift for such

F.-P. Huang et al. / Polyhedron 34 (2012) 129–135
135
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dicarboxylate ligands. It is evident that the bpt isomers and dicar-
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Acknowledgments
We gratefully acknowledge the National Nature Science Foun-
dation of China (Nos. 21061002, 21101035), Guangxi Natural Sci-
ence
Foundation
of
China
(2010GXNSFF013001,
2011GXNSFC018009, 0832098).
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