Construction of several d10 metal coordination polymers based on aromatic polycarboxylate and flexible triazole-based ligand

Article abstract of DOI:10.1016/j.ica.2009.08.009

To investigate the effect of organic anions on the coordination frameworks, we synthesized five new complexes, namely, {[Zn₃(μ-OH₂)₂(btc)₂(btx)₃]·4H₂O}_n (1), [Zn(bdc)(btx)]_n

Full text of DOI:10.1016/j.ica.2009.08.009

Inorganica Chimica Acta 362 (2009) 5023–5030
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Construction of several d10 metal coordination polymers based on aromatic
polycarboxylate and flexible triazole-based ligand
*
Jiyong Hu, Jinpeng Li, Jin’an Zhao, Hongwei Hou , Yaoting Fan
Department of Chemistry, Zhengzhou University, Henan 450052, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 June 2009
Received in revised form 3 August 2009
Accepted 6 August 2009
Available online 12 August 2009
To investigate the effect of organic anions on the coordination frameworks, we synthesized five new com-
plexes, namely, {[Zn3(
(3), [Ag(2,6-Hpydc)(btx)]n (4) and [Cd2(
l
-OH2)2(btc)2(btx)3]ꢀ4H2O}n (1), [Zn(bdc)(btx)]n (2), {[Ag8(3,5-pydc)4(btx)4]ꢀ8H2O}n
l
2-OH2)(2,6-pydc)2(btx)]n (5) (H2bdc = 1,4-benzenedicarboxylic
acid; H3btc = 1,3,5-benzenetricarboxylate; 3,5-H2pydc = pyridine-3,5-dicarboxylic acid; 2,6-H2pydc =
pyridine-2,6-dicarboxylic acid), which were obtained by the reactions of 1,4-bis(1,2,4-triazol-1-
ylmethyl)benzene (btx) as main ligand, and several aromatic polycarboxylate as organic anions with
different d10 metal salts. Single crystal structure analysis shows that complexes 1, 3 and 5 possess 3D
structures, 2 takes a 2D layer motif, and 4 displays a 1D chain structure. The distinct structures
indicate that polycarboxylate anions with the diverse coordination modes and coordination groups can
affect the topologies of metal–organic frameworks. In addition, the luminescence measurements
reveal that the complexes 1, 2 and 5 exhibit strong fluorescent emissions in the solid state at room
temperature.
Keywords:
Aromatic polycarboxylate
Triazole-based ligand
Crystal structure
Luminescence
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
possess multiform coordination fashions and structural features,
may more effectively tune framework architectures [15–17]. Upon
Multifunctional metal–organic coordination frameworks con-
tinue to be of current interest due to the combination of the indi-
vidual properties associated with inorganic and organic
components [1–5]. Accordingly, the design and construction of
well-regulated network structures with new functions are impera-
tive, in which the key steps are to employ appropriate bridging li-
gands and to choose suitable metal ions. The ligands bearing
bis(triazole) groups are good candidates for the formation of novel
architectures. The ligands can adopt multiple coordination modes,
such as bidentate, tridentate or tetradentate, to meet the different
coordination requirements of metal centers [6,7]. As an excellent
derivative of triazole, the flexible 1,4-bis(1,2,4-triazol-1-ylmethyl)-
benzene (btx) not only possesses the merits of triazole, but also can
freely bend and rotate to interact with metal ions. Thus, a series of
metal–organic frameworks with novel topology were obtained by
assembling metal salts and btx ligand. Although the ligand plays
crucial role in determining these resulted polymeric structures,
the effect of anions cannot be ignored as well [8–10]. In fact, the
influence of inorganic anions (such as Clꢁ, SO42ꢁ, NO3ꢁ) on the
structures of complexes has been extensively studied [11–14]. By
contrast, the organic anions such as polycarboxylate, which usually
careful inspection of previous cases, we intend to probe into the
influence of aromatic polycarboxylates as anionic co-ligands on
the resulting complex architectures by using the btx as the main
ligand. Therefore, especially rich possibilities for the construction
of unique motifs with beautiful aesthetics and useful functional
properties may be anticipated, because triazole of btx and aromatic
polycarboxylates are complementary in their coordination prefer-
ences and may act synergetically [18–20].
Taking these into consideration, our synthetic strategy is to se-
lect neutral btx as the main ligand, in the presence of 1,3,5-benzen-
etricarboxylate (btc3ꢁ), pyridine-3,5-dicarboxylate (3,5-pydc2ꢁ),
pyridine-2,6-dicarboxylate (2,6-pydc2ꢁ) or 1,4-benzenedicarboxyl-
ate (bdc2ꢁ) anions as co-ligands and different d10 metal salts to
construct complexes. The four polycarboxylate anionic co-ligands
have rigid conformation and distinct structural features. The btc3ꢁ
has three equally spaced carboxylate groups oriented in three
directions, while bdc2ꢁ bears two carboxylate groups with linear
conformation. The 3,5-pydc2ꢁ and 2,6-pydc2ꢁ are isomers with dif-
ferent orientations of the functional groups. The structural differ-
ence of anions may have different impact on the construction of
frameworks in conjunction with the btx. As a result, a series of
mixed-ligand coordination complexes with different structure
types have been synthesized under hydrothermal conditions and
structurally characterized. Their thermal and fluorescence proper-
ties were also investigated.
* Corresponding author. Tel./fax: +86 371 67761744.
E-mail address: houhongw@zzu.edu.cn (H. Hou).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.08.009

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J. Hu et al. / Inorganica Chimica Acta 362 (2009) 5023–5030
44.38; H, 3.14; N, 19.07. Found: C, 44.31; H, 3.05; N, 19.22%.
2. Experimental
IR(KBr/pellet, cmꢁ1): 3410w, 3099w, 1703w, 1621s, 1380s,
1017s, 884m, 757m, 696m.
2.1. Materials and general methods
All chemicals were commercially available and used as pur-
chased. 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene (btx) was syn-
thesized according a literature method [21]. Thermogravimetric
experiments were performed using a TGA/SDTA instrument. IR
data were recorded on a BRUKER TENSOR 27 spectrophotometer
with KBr pellets in the region of 400–4000 cmꢁ1. Elemental analy-
ses (C, H and N) were carried out on a Flash EA 1112 elemental ana-
lyzer. Steady state fluorescence measurements were performed
using spectrofluorimeter Hitachi F–4500 at ambient temperature
in solid state. The excitation and emission slit width are both
1 nm, and response time is 0.1 s.
2.6. Synthesis of [Cd2(l2-OH2)(2,6-pydc)2(btx)]n (5)
A reaction mixture of Cd(NO3)2ꢀ4H2O (0.1 mmol, 0.0308 g), btx
(0.1 mmol, 0.012 g), 2,6-H2pydc (0.1 mmol, 0.0167 g), and water
10 mL was placed in a Teflon-lined stainless steel vessel, and then
the pH was adjusted to 7 by addition of methanolic NaOCH3 solu-
tion. The mixture was sealed and heated at 150 °C for three days,
and then the reaction system was cooled to room temperature.
Colorless crystals of 5 were obtained in yield (based on Cd): 55%.
Elemental Anal. Calc. for (C26H18Cd2N8O9): C, 38.49; H, 2.24; N,
13.82. Found: C, 38.72; H, 2.44; N, 13.97%. IR(KBr/pellet, cmꢁ1):
3088w, 1649s, 1523m, 1426m, 1377s, 1346m, 1274m, 775m, 721s.
2.2. Synthesis of {[Zn3(l-OH2)2(btc)2(btx)3]ꢀ4H2O}n (1)
A reaction mixture of Zn(NO3)2ꢀ6H2O (0.1 mmol, 0.0297 g), btx
(0.1 mmol, 0.012 g), H3BTC (0.1 mmol, 0.021 g), and water 10 mL
was placed in a Teflon-lined stainless steel vessel, and then the
pH was adjusted to 7 by addition of methanolic NaOCH3 solution.
The mixture was sealed and heated at 130 °C for three days, and
then the reaction system was cooled to room temperature. Color-
less crystals of 1 were obtained in yield (based on Zn): 60%. Ele-
mental Anal. Calc. for (C54H54N18O18Zn3): C, 45.06; H, 3.78; N,
17.52. Found: C, 44.93; H, 3.70; N, 17.63%. IR(KBr/pellet, cmꢁ1):
3415w, 3122w, 1626s, 1573m, 1528m, 1352s, 1281m, 1132m,
1000m, 771s, 734s, 733s.
2.7. Crystal structure determination
A crystal suitable for X-ray determination was mounted on a
glass fiber. The data of 1–5 were collected at room temperature
on a Rigaku Saturn 724 CCD with graphite monochromated Mo
Ka radiation (k = 0.71073 Å). The structures were solved by direct
methods and expanded with Fourier techniques. The non-hydro-
gen atoms were refined anisotropically. Hydrogen atoms were in-
cluded but not refined. The final cycle of full-matrix least-squares
refinement was based on observed reflections and variable param-
eters. All calculations were performed with the SHELXL-97 crystallo-
graphic software package [22–24]. Table 1 showed crystallographic
crystal data and processing parameters for all complexes, and Ta-
ble 2 listed their selected bond lengths and bond angles.
2.3. Synthesis of [Zn(bdc)(btx)]n (2)
A reaction mixture of Zn(NO3)2ꢀ6H2O (0.1 mmol, 0.0297 g), btx
(0.1 mmol, 0.012 g), H2bdc (0.1 mmol, 0.0166 g), and water 10 mL
was placed in a Teflon-lined stainless steel vessel and then the
pH was adjusted to 6 by addition of methanolic NaOCH3 solution.
The mixture was sealed and heated at 130 °C for three days, and
then the reaction system was cooled to room temperature. Color-
less crystals of 2 were obtained in yield (based on Zn): 55%. Ele-
mental Anal. Calc. for (C20H16N6O4Zn): C, 51.13; H, 3.43; N, 17.89.
Found: C, 51.48; H, 3.44; N, 17.63%. IR(KBr/pellet, cmꢁ1): 3117w,
1688s, 1613w, 1573w, 1352m, 1288s, 1132s, 999w, 783m, 744s,
673w.
3. Results and discussion
3.1. Syntheses
Although some complexes based on btx ligand have been re-
ported, the selection of counterions is mostly concentrated on inor-
ganic anions. In this paper, we expect to investigate the influence
of organic anions on the structures of complexes. As a widely used
polycarboxylic acid, the H3btc has three equally spaced carboxyl
groups, which can be completely or partially deprotonated. This
makes it very appealing for the design of MOFs with interesting
structures. Using btx in combination with H3btc under hydrother-
mal conditions, a 3D zinc complex 1 was obtained. When the star-
like H3btc was changed to linear H2bdc containing two carboxyl
groups, a 2D layer zinc complex 2 was achieved. Both complexes
1 and 2 are greatly different from previously reported 2D square
grid units [Zn(btx)2(NO3)2]n with inorganic anion [25]. In contrast
to the benzenecarboxylates, the heterocyclic carboxylates, such
as pyridine- and imidazole-carboxylates exhibit unique features.
These ligands can contribute their carboxylate oxygen as well as
pyridyl nitrogen atoms to metal coordination, to construct inter-
esting coordination networks [26,27]. The 3,5-H2pydc was em-
ployed to react with AgNO3 and btx, to form a 3D complex 3.
When 3,5-H2pydc was substituted by 2,6-H2pydc, a completely dif-
ferent 1D silver complex 4 was obtained under the similar condi-
tions. To further investigate various coordination modes of 2,6-
H2pydc, the reaction of 2,6-H2pydc with btx and Cd(NO3)2 was car-
ried out, to give rise to a 3D complex 5, which is greatly different
from previously reported complexes [Cd(btx)2(H2O)2](ClO4)2ꢀH2O
and [Cd(btx)2(H2O)2](BF4)2ꢀ3DMF as well [13].
2.4. Synthesis of {[Ag8(3,5-pydc)4(btx)4]ꢀ8H2O}n (3)
A
reaction mixture of AgNO3 (0.1 mmol, 0.0169 g), btx
(0.1 mmol, 0.012 g), 3,5-H2pydc (0.1 mmol, 0.0167 g), and water
10 mL was placed in a Teflon-lined stainless steel vessel, and then
the pH was adjusted to 6.5 by addition of methanolic NaOCH3 solu-
tion. The mixture was sealed and heated at 120 °C for two days,
and then the reaction system was cooled to room temperature.
Colorless crystals of 3 were obtained in yield (based on Ag): 55%.
Elemental Anal. Calc. for (C76H68Ag8N28O24): C, 34.83; H, 2.62; N,
14.97. Found: C, 34.58; H, 2.52; N, 14.96%. IR(KBr/pellet, cmꢁ1):
3418w, 3107w, 1742w, 1617w, 1516s, 1384s, 1271s, 1212m,
1142s, 1014m, 827m, 729s, 676s.
2.5. Synthesis of [Ag(2,6-Hpydc)(btx)]n (4)
The synthesis was similar to that described for 3 except using
2,6-H2pydc (0.1 mmol, 0.0167 g) instead of 3,5-H2pydc and heated
at 120 °C for three days. Then the reaction system was cooled to
room temperature. Colorless crystals of 4 were obtained in yield
(based on Ag): 55%. Elemental Anal. Calc. for (C19H16AgN7O4): C,

J. Hu et al. / Inorganica Chimica Acta 362 (2009) 5023–5030
5025
Table 1
Crystal data and structure refinement for complexes 1–5.
Complex
1
2
3
4
5
Formula
Formula weight
T (K)
C54H54N18O18Zn3
1439.26
293(2)
C20H16N6O4Zn
469.78
293(2)
C76H68Ag8N28O24
2620.54
293(2)
C19H16AgN7O4
513.25
293(2)
C26H18Cd2N8O9
811.28
293(2)
k (Mo K
a
) (Å)
0.71073
monoclinic
P2(1)/c
14.840(3)
10.125(2)
20.333(4)
90.00
0.71073
monoclinic
C2/c
18.735(4)
18.507(4)
11.587(2)
90.00
0.71073
monoclinic
C2/c
42.914(9)
8.7726(18)
12.182(2)
90.00
0.71073
monoclinic
C2/c
7.6733(15)
26.592(5)
9.957(2)
90.00
0.71073
monoclinic
P2/c
10.331(2)
9.827(2)
13.867(3)
90.00
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a
(°)
b (°)
99.35(3)
90.00
3014.3(10)
2
107.19(3)
90.00
3838.1(13)
8
92.22(3)
90.00
4582.6(16)
2
90.00(3)
90.00
2031.7(7)
4
90.69(3)
90.00
1407.8(5)
2
c
(°)
V (Å3)
Z
2hmax (°)
F(0 0 0)
Final R1a, wR2
54.00
1472
0.070, 0.163
1.144
50.00
1919
0.076, 0.137
1.201
50.00
2568
0.064, 0.159
1.145
58.00
1032
0.045, 0.103
1.107
54.98
796
0.023, 0.050
1.108
b
Goodness-of-fit (GOF) on F2
P
P
a
R1
=
||Fo|ꢁ|Fc||/ |Fo|.
P
P
wR2 = [ w(|F2o|ꢁ|F2c |)2/ w|Fo2|2]1/2. w = 1/[
r
2(Fo)2 + 0.0297P2 + 27.5680P], where P = (Fo2 + 2F2c )/3.
b
Table 2
equatorial positions are furnished by two carboxylate oxygen
atoms from two different btc3ꢁ, and two nitrogen atoms from
two different btx. The axial sites are occupied by two water mole-
Selected bond lengths and angles for complexes 1–5.
Complex 1
Zn(1)–O(6)#1
Zn(1)–N(4)#2
Zn(2)–O(3)
N(4)#2–Zn(1)–N(7)
O(6)#1–Zn(1)–O(2)
cules. The btc3ꢁ in 1 acts as
l3-bridge, in which all the carboxylate
1.989(3)
2.010(4)
2.086(3)
116.58(17)
96.95(12)
Zn(1)–O(2)
Zn(1)–N(7)
Zn(2)–O(7)
O(7)#3–Zn(2)–O(7)
O(6)#1–Zn(1)–N(4)#2
1.990(3)
2.016(4)
2.113(3)
180.0
groups adopt monodentate mode to connect two Zn1 and one Zn2
centers. The separations of the ZnꢀꢀꢀZn bridged by btc3ꢁ anion are
10.125 Å for Zn1ꢀꢀꢀZn1a, and 10.114 or 8.302 Å for Zn1ꢀꢀꢀZn2.
The btc3- anion, acting as a triconnector links the Zn2+ centers to
form a 1D chain running along the b-axis. It is noticeable that the
Zn2+ centers are arranged in coplanar parallel lines. All btx spacers
assume trans conformation. For the btx to which N1 belongs, the
dihedral angles between the two triazole ring planes and the
least-squares plane of phenyl group are 88.6° and 68.6°, respec-
tively, with the two triazole groups twisted by 47.2°. The bidentate
btx establishes a physical bridge between two chains generating an
infinite corrugated 2D layer motif (Fig. 1b). The btx containing N7,
possessing Ci symmetry, have the planes steeply tilted 77° with re-
spect to the average plane of phenyl ring. The 2D layers are further
pillared by btx, leading to the formation of 3D framework with the
void space occupied by uncoordinated water molecules. From the
topology viewpoint, if the bidentate btx is simplified to be linear
connector, the 3D framework can be reduced to a (3,4)-connected
(63)(64 ꢀ 7 ꢀ 8)(6 ꢀ 73 ꢀ 82) net, where the btc3ꢁ, Zn1, and Zn2 are as-
signed as three-, four- and four-connected nodes, respectively
(Fig. 1c).
The replacement of the H3btc molecule in 1 by H2bdc results in
a 2D complex 2. The asymmetric unit of complex 2 consists of one
Zn2+ center, two halves of bdc2ꢁ anions and two halves btx ligands.
Complex 2 crystallizes in the monoclinic with space group C2/c,
rather than in monoclinic with space group P2(1)/c as observed
in 1. Each Zn2+ center in 2 is coordinated to two carboxylate oxygen
atoms [Zn–O = 1.948–1.975 Å] and two btx nitrogen atoms (Zn–
N = 1.996–2.060 Å), completing a distorted tetrahedral coordina-
tion geometry (Fig. 2a). The Zn–O/N distances fall in the normal
range found in other Zn complexes [28]. It is interesting that two
different types of cis and trans conformations of btx simultaneously
coexist in 2.
103.37(16)
Complex 2
O(1)–Zn(1)
N(1)–Zn(1)
C(1)–O(1)–Zn(1)
C(15)–N(4)–Zn(1)
O(1)–Zn(1)–O(3)
1.948(4)
1.996(5)
109.3(4)
130.1(4)
105.82(16)
O(3)–Zn(1)
N(4)–Zn(1)
C(5)–O(3)–Zn(1)
C(16)–N(4)–Zn(1)
O(1)–Zn(1)–N(1)
1.975(4)
2.060(5)
110.4(3)
122.4(4)
120.63(17)
Complex 3
Ag(1)–N(1)
Ag(1)–O(2)
Ag(2)–O(4)
N(1)–Ag(1)–O(2)
N(5)–Ag(2)–O(3)
2.255(6)
2.424(6)
2.517(8)
99.7(2)
Ag(1)–N(4)#1
Ag(2)–N(5)
Ag(2)–O(3)
N(5)–Ag(2)–O(4)
O(4)–Ag(2)–O(3)
2.256(6)
2.348(6)
2.592(8)
82.4(3)
131.3(2)
48.9(3)
Complex 4
Ag(1)–N(2)
Ag(1)–N(2)#1
C(2)#1–N(1)–Ag(1)
N(2)–Ag(1)–N(2)#1
2.259(3)
2.259(3)
120.84(17)
118.14(13)
Ag(1)–N(1)
2.336(3)
120.93(7)
133.1(2)
120.93(7)
N(2)#1–Ag(1)–N(1)
C(9)–N(2)–Ag(1)
N(2)–Ag(1)–N(1)
Complex 5
Cd(1)–N(2)
Cd(1)–O(5)
Cd(1)–O(1)
N(2)–Cd(1)–O(1)
O(3)–Cd(1)–O(1)
2.279(2)
Cd(1)–N(1)
Cd(1)–O(3)
N(1)–Cd(1)–O(3)
N(2)–Cd(1)–N(1)
O(5)–Cd(1)–O(3)
2.331(2)
2.4036(18)
68.95(5)
93.69(8)
152.44(5)
2.3980(18)
2.5107(18)
86.89(6)
136.08(5)
Symmetry transformation used to generate equivalent atoms: #1 x,yꢁ1,z; #2
ꢁx,yꢁ1/2,ꢁz + 1/2; #3 ꢁx + 1,ꢁy + 1,ꢁz; #4 ꢁx,y + 1/2,ꢁz + 1/2; #5 ꢁx,ꢁy,ꢁz + 1; #6
x,y + 1,z for 1; #1 ꢁx + 2,y,ꢁz + 1/2; #2 ꢁx + 1,ꢁy + 1,ꢁz + 1; #3 ꢁx + 2,ꢁy + 1,ꢁz + 1;
#4 ꢁx + 1,y,ꢁzꢁ1/2 for 2; #1 x,ꢁy + 1,zꢁ1/2; #2 x,ꢁy + 3,zꢁ1/2; #3 ꢁx + 1/2,ꢁyꢁ1/
2,ꢁz + 1; #4 ꢁx,ꢁy + 3,ꢁz; #5 x,ꢁy + 1,z + 1/2; #6 x,ꢁy + 3,z + 1/2 for 3; #1
ꢁx + 1,y,ꢁz + 1/2; #2 ꢁxꢁ1/2,ꢁy + 1/2,ꢁz + 1 for 4; #1 ꢁx + 1,ꢁy + 3,ꢁz + 2; #2
ꢁx,y,ꢁz + 3/2; #3 ꢁx,ꢁy + 2,ꢁz + 2 for 5.
3.2. Crystal structures of 1 and 2
Both bdc2ꢁ and btx act as bidentate ligands bridging Zn2+ cen-
ters, resulting in two kinds of chains, namely single chain 1
(Fig. 2b) and composite chain 2 (Fig. 2c), respectively. In single
chain 1, the Zn2+ centers are in turn connected by bdc2ꢁ and btx
to form a single chain running along the c-axis, in which the flex-
ible btx ligands adopt trans conformation. The triple-stranded
The X-ray crystallographic analysis reveals that 1 is a 3D archi-
tecture. As depicted in Fig. 1a, the Zn1 center lies in tetrahedral
coordination geometry defined by two oxygen atoms from two dif-
ferent btc3ꢁ and two nitrogen atoms from two different btx. The
Zn2 center is in an octahedral coordination sphere, in which the

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J. Hu et al. / Inorganica Chimica Acta 362 (2009) 5023–5030
Fig. 1. (a) Two types of zinc coordination environments in the structure of polymer 1, one of which involves two terminal aqua molecules, all the hydrogen atoms, solvent
molecules and part atom labels are omitted for clarity. (b) The 1D chains bridged by bidentate btx containing N1 to form 2D layer motif. (c) Schematic drawing of the topology
for the 3D porous framework in 1.
composite chain 2 contains three ‘‘S” like interpenetrated single
chains running along the c-axis, in which the bdc2ꢁ and btx alter-
nately bond to different Zn2+ centers. In the composite chain, all
btx adopt cis conformation. Both sets of btx ligands possess Ci sym-
metry. For the btx adopting cis conformation, the triazole ring and
phenyl group are twisted by 120°, while the corresponding angle is
decreased to 80° for the btx in trans form. The single chain 1 resem-
bles a flexible ribbon, connecting three chains of composite chain 2
to extend into layers (Fig. 2d). The chain 1 and composite chain 2
are edge-sharing and both chains are arranged in the –ABAB–
arranging order. The 2D sheets are connected by H-bonded interac-
tions to form a 3D supramolecular framework. It is noteworthy
that btx ligands have different conformations in 1 and 2, although
they bind with the same Zn2+ center. All carboxyl groups of btc3-
and bdc2ꢁ adopt monodentate mode in 1 and 2, although they have
diverse binding modes. The primary difference between 1 and 2 is
the shape of organic anions. In 1, the tri(monodentate) btc3ꢁ anion
serves as a trigonal connector and possesses a rigid disk-like con-
formation, which connects Zn2+ centers oriented in three different
directions, thus contributing to forming structures of higher
dimensions. While bis(monodentate) bdc2ꢁ functions as a linear
linker in 2, each bdc2ꢁ can only bind two Zn2+ centers concurrently.
In the presence of bdc2ꢁ, the main ligand btx shows two distinct
types of conformation, which is different from complex 1. These re-

J. Hu et al. / Inorganica Chimica Acta 362 (2009) 5023–5030
5027
Fig. 2. (a) The crystal structure of polymer 2, the hydrogen atoms and part labels are omitted for clarity. (b) The zigzag-like chain 1 running along c-axis. (c) Composite chain 2
constructed from three interpenetrating chains running along c-axis. (d) The 2D layer motif of complex 2 parallel to a,c-plane.
sults indicated that the structurally different polycarboxylates
have profound impact on the conformation of btx and on the struc-
ture of resulted complexes [29,30].
trans conformations. For the bidentate btx, the dihedral angle be-
tween the triazole ring and the phenyl plane is 72.8°, which is lar-
ger than that in the tetradentate btx (66.6°). It is noticeable that
each tetradentate btx binds four Ag2 centers to form 1D ladder-like
motif propagating along c-axis (Fig. 3b). The 1D chains are further
cross-linked by 3,5-pydc2ꢁ bridges and Ag1 centers, resulting in an
infinite 2D bilayer motif extending parallel to the b,c-plane, in
which each Ag1 center ligates two 3,5-pydc2ꢁ molecules via coor-
dinating to one carboxylate and one pyridyl nitrogen atom
(Fig. 3c). Each bilayer contains many parallel 1D channels running
along c-axis. As shown in Fig. 3d, these bilayers are strongly puck-
ered allowing for an interpenetration of two such parallel bilayers
to form a composite layer. Such composite layers are further pil-
lared via the bidentate trans btx running along the a-axis in AA se-
quence. The crystalline water molecules are located in the voids of
the 3D framework. The single network 3 is a rare example with
parallel interpenetrated bilayers as building block. If the bidentate
btx is simplified as a line connecting the metal centers, the frame-
work of 3 can be symbolized as four-nodal (3,4)-connected net. The
network can best be described as a (4 ꢀ 102)(103)(103)(42 ꢀ 104)
3.3. Crystal structures of complexes 3 and 4
Complex 3 also crystallizes in the space group C2/c. The Ag1
adopts trigonal coordination geometry, which is defined by one
btx nitrogen atom, one nitrogen atom from 3,5-pydc2ꢁ anion and
one carboxylate oxygen atom from another 3,5-pydc2ꢁ (Fig. 3a).
Whereas the Ag2 is in a planar quadrilateral coordination sphere
surrounded by two nitrogen atoms from two different btx and
two oxygen atoms from one chelating carboxylate group. The val-
ues of Ag–N are 2.235–2.346 Å, and the slightly long Ag–O bond
lengths range from 2.432 to 2.581 Å, and the similar bond lengths
are observed in the reported complexes [31,32].
In the complex 3, each 3,5-pydc2ꢁ acts as a triconnector by one
monodentate carboxylate, one chelating carboxylate, and pyridyl N
moiety linking three silver centers. Both types of btx with bi- and
tetradentate coordination modes have Ci symmetry and adopt

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J. Hu et al. / Inorganica Chimica Acta 362 (2009) 5023–5030
When 2,6-H2pydc was incorporated into the reaction system in-
stead of 3,5-H2pydc in complex 3, an infinite 1D zigzag chain com-
plex was obtained. Crystallographic analysis reveals that
4
complex 4 crystallized in the monoclinic with space group C2/c
as well. The fundamental building unit of 4 is composed of one
Ag(I) center, half 2,6-Hpydc1ꢁ anion and half btx. As shown in
Fig. 4, each Ag center is coordinated by two nitrogen atoms from
two different btx and one nitrogen atom from 2,6-Hpydc1ꢁ to fur-
nish the triangular coordination geometry. The btx serves as
bismonodentate linker and bridges the adjacent Ag(I) centers.
The btx has Ci symmetry and adopts trans conformation, in which
triazole ring and phenyl group are twist by 86.8°. The 2,6-pydc1ꢁ
possesses a twofold axis through N1 as well as Ag1 atoms, and
serves as monodentate ligand using the pyridyl N group. The Ag–
N bond lengths range from 2.259 to 2.336 Å, within the normal
range. In addition, the strong AgꢀꢀꢀO contact (AgꢀꢀꢀO 2.649 Å) exists,
little beyond the values reported for other silver(I) complexes (Ag–
O 2.33–2.62 Å) [33,34]. The 1D chain structure is further stacked
into 3D supramolecular architecture via strong intermolecular
interaction with O1ꢀꢀꢀO10 2.445 Å and hydrogen bonds (CꢀꢀꢀO
3.129 Å for C8–HꢀꢀꢀO1 and CꢀꢀꢀO 3.34 Å for C10–HꢀꢀꢀO2). A compar-
ison between 3 and 4 indicates that the structural features and
coordination modes of the organic anions can clearly affect the
coordination sphere of metal center and hence framework connec-
tivity. The 3,5-pydc2ꢁ and 2,6-pydc1ꢁ are isomers with different
positions of carboxylate moieties on the pyridyl ring. In complexes
3, the tetradentate 3,5-pydc2ꢁ acting as a three-connected nodes of
trigonal geometry connects silver centers, which is conducive to
the formation of multidimensional coordination architecture.
Whereas the 2,6-pydc1ꢁ has a rigid 120° angle between the central
pyridyl ring and two carboxylate groups and therefore prefer to
form stable chelate. In 4, the pyridyl nitrogen atom and two car-
boxylate groups of chelate 2,6-pydc1ꢁ are on the same side of the
coordination sphere Ag(I) center and two btx reside on the oppo-
site side, thus the space hindrance prevents other carboxylate
groups further linking to other Ag(I) centers. Herein, the 2,6-
pydc1ꢁ only coordinated to one silver center, thus a 1D structure
was attained through bidentate btx bridging silver centers.
3.4. Crystal structure of complex 5
The X-ray crystallographic analysis shows that the asymmetric
unit of complex 5 contains one Cd2+ center, one 2,6-pydc2ꢁ anion,
half btx and one water molecule. The Cd2+ center is in a distorted
pentagonal bipyramidal coordination sphere, which is defined by
one nitrogen atom from btx and one carboxylate oxygen atom
occupying the apical positions, while the basal plane is completed
by three oxygen atoms (Cd–O = 2.303–2.511 Å) and one nitrogen
atom (Cd–N = 2.280–2.331 Å) from two different 2,6-pydc2ꢁ, as
well as one aqua molecule (Fig. 5a).
The 2,6-H2pydc can potentially provide various coordination
modes to form both discrete and consecutive metal complexes un-
der appropriate conditions [35,36]. In structure 5, the 2,6-pydc2ꢁ
acts as a triconnector through the bismonodentate carboxylate
and pyridyl N group linking three cadmium centers. Two Cd1 cen-
Fig. 3. (a) Perspective view of the coordination environment of the metal centers,
all the hydrogen atoms and solvent molecules are omitted for clarity. (b) The 1D
ladder-like chain running along c-axis based on btx and Ag ions. (c) The 2D bilayer
viewed along the a-axis. (d) The composite layer is constructed from two parallel
interpenetrated 2D bilayers viewed along the c-axis. (e) The schematic represen-
tation of 3D framework.
ters are bridged by three l2-O bridges from two separate carboxyl-
ate moieties and one aqua molecule to form dimer units, in which
the CdꢀꢀꢀCd separations is 3.453 Å. The dimer units are further
interconnected by another two carboxylate oxygen bridges to lead
to a 1D chain running along the c-axis (Fig. 5b). It should be noted
that the two 2,6-pydc2ꢁ of one dimer unit locate at the same side of
the chain with the dihedral angle of 21.553°, whereas the 2,6-
pydc2ꢁ of the adjacent dimer moieties lie on the opposite sides.
All btx possess Ci symmetry and hold trans conformation. The dihe-
dral angle between triazole ring and the phenyl group is 102.5°.
topology if we define the Ag2, 3,5-pydc2ꢁ anion, Ag1 and tetraden-
tate btx as three-, three-, three- and four-connected nodes, respec-
tively (Fig. 3e).

J. Hu et al. / Inorganica Chimica Acta 362 (2009) 5023–5030
5029
Fig. 4. The zigzag chain fragment of complex 4, all hydrogen atoms and part labels are omitted for clarity.
Fig. 6. The figure of TGA curves.
The 1D chain is further pillared along the a- and b-axes with biden-
tate btx resulting in the formation of a 3D framework (Fig. 5c).
3.5. Thermal properties
Complexes 1–5 are air-stable and can retain their crystalline
integrity at ambient temperature. The TGA curve (Fig. 6) shows
that the weight loss of 7.84% for 1 from 52 to 185 °C (calc. 7.52%)
corresponds to the loss of three water molecules per formula.
The dehydrated complex is stable up to 285 °C. For complex 3,
the weight loss takes place between 60 and 140 °C, and the total
weight loss in this temperature range is 4.93%, which is attributed
to the uncoordinated water molecules (calc. 5.51%), and then it is
stable up to 240 °C. For complex 5, it is stable up to 220 °C, which
shows that the H2O molecules are tightly held in the 3D frame-
work. The first weight loss of 4.43% is assigned to the liberation
of one water molecule (calc. 4.44%). The burning of the organic
groups starts from 330 °C. The anhydrous complexes 2 and 4 are
stable up to 300 and 225 °C, respectively.
3.6. Luminescence properties
The photoluminescence properties of complexes 1–5 were
investigated and the results were provided in Fig. 7. In the solid
state, strong emissions were found at 429 nm (kex = 371 nm),
438 nm (kex = 381 nm), and 437 nm (kex = 379 nm) for complexes
1, 2 and 5, respectively. For excitation wavelength between 298
Fig. 5. (a) View of the coordination environment of Cd2+ ions in complex 5 with part
atom label schemes. (b) The 1D chain running along the c-axis based on 2,6-pydc2ꢁ
anions and Cd2+ ions. (c) The 3D framework of complex 5.

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J. Hu et al. / Inorganica Chimica Acta 362 (2009) 5023–5030
Appendix A. Supplementary material
CCDC 723809, 723810, 723811, 723812 and 723813 contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-
tary data associated with this article can be found, in the online
version, at doi:10.1016/j.ica.2009.08.009.
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In summary, five new d10 metal coordination complexes were
synthesized and structurally characterized. Single crystal structure
analysis shows that 1, 3 and 5 possess 3D structures, 2 takes a 2D
layer motif, and 4 exhibits a 1D chain structure. These results dem-
onstrate the difference in coordination modes of the aromatic poly-
carboxylic acids has a significant influence on the formation and
structures of the resultant complexes. The flexible btx has the abil-
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coordination requirements of metal centers. The joint contribution
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of fascinating coordination polymers.
Acknowledgment
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We gratefully acknowledge the financial support by the Na-
tional Natural Science Foundation of China (No. 20671082), NCET
and the Outstanding Talents Foundation by the He’nan province.