Syntheses and characterizations of five coordination polymers constructed by 3,5-bis(pyridin-3-ylmethoxy)benzoic acid ligand

Article abstract of DOI:10.1016/j.poly.2009.07.011

Five coordination polymers, namely [Cd(L3)₂]·H₂O (1), [Zn(L3)₂] (2), [Co(L3)₂] (3), [Ni(L3)₂] (4) and [Cu₂(L3)₂]·3H₂O (5), where L3 = 3,5-bis(pyridin-3-ylmethoxy)benzo

Full text of DOI:10.1016/j.poly.2009.07.011

Polyhedron 28 (2009) 3155–3161
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Syntheses and characterizations of five coordination polymers constructed
by 3,5-bis(pyridin-3-ylmethoxy)benzoic acid ligand
*
*
Guang-Juan Xu, Ya-Hui Zhao, Kui-Zhan Shao, Guang-Sheng Yang, Ya-Qian Lan, Zhong-Min Su , Li-Kai Yan
Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun 130024, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Five coordination polymers, namely [Cd(L3)2]ÁH2O (1), [Zn(L3)2] (2), [Co(L3)2] (3), [Ni(L3)2] (4) and
[Cu2(L3)2]Á3H2O (5), where L3 = 3,5-bis(pyridin-3-ylmethoxy)benzoic acid, have been synthesized under
hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction anal-
yses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses.
Compound 1 is a binodal (3,4)-connected net with (63)(66) topology. Compounds 2–4 are isostructural
and described by the uninodal (4,4)-connected net with (44 Á 62) Schläfli symbol. The structure of 5 is a
2D binodal (6,3) net. In addition, the luminescent properties of compounds 1 and 2 have been studied
in the solid state at room temperature.
Received 24 April 2009
Accepted 6 July 2009
Available online 5 August 2009
Keywords:
Coordination polymer
3,5-Bis(pyridin-3-ylmethoxy)benzoic acid
Crystal structure
Ó 2009 Elsevier Ltd. All rights reserved.
Luminescent property
1. Introduction
plane of the central phenyl ring and therefore it is a good candidate
to produce unique structural motifs with beautiful esthetics.
Recently, the construction of new coordination polymers has at-
tracted intense attention in the field of supramolecular chemistry
and crystal engineering because of their intriguing esthetic struc-
tures and topological features as well as their potential applica-
tions as functional materials [1–13]. Therefore, rational design
and synthesis of coordination polymers with intriguing diversity
of architectures has become a very important subject. It is well
known that the multiple coordination sites of ligands can form
the structures of higher dimensions and the high symmetry of li-
gands may result in new structures [14,15]. Pyridyl carboxylic
acids containing N- and O-donors are particularly attractive as
excellent building blocks with charge and multi-connecting ability
[16–19]. Such as pyridine-2,4-dicarboxylic acid, pyridine-2,5-
dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-3,4-
dicarboxylic acid and pyridine-3,5-dicarboxylic acid have been
widely used by Kitagawa, Wang, Cao, Zhu and their co-workers
in the construction of high-dimensional structures with large pores
or undulated layers [16–36]. However, compared with the rigid li-
gands, flexible ones have more advantages in that their flexibility
and conformational freedom allow them to conform to the coordi-
nation environment of the transition-metal ions; based on this, we
designed a new pyridyl carboxylic acid ligand, 3,5-bis(pyridin-3-
ylmethoxy)benzoic acid (L3), which contains a rigid spacer of phe-
nyl ring and two freely rotating pyridyl arms. This new ligand may
cause the planes of the pyridyl rings to rotate with respect to the
On the other hand, d10 metal (CdII, ZnII, CuI, AgI and AuI) com-
pounds have attracted extensive interest in recent years in that
they not only exhibit appealing structures but also possess photo-
luminescent properties [37–42]. However, to our best knowledge,
there have been no related reports of the polymers constructed
by d10 metal and L3 ligand so far. With this aim of understanding
the coordination chemistry of L3 and preparing new materials with
interesting structural topologies and excellent physical properties,
we have recently engaged in the research of these kinds of polymer
compounds with such ligands.
In this paper, we report five new coordination polymers, namely
[Cd(L3)2]ÁH2O (1), [Zn(L3)2] (2), [Co(L3)2] (3), [Ni(L3)2] (4) and
[Cu2(L3)2]Á3H2O (5). These five compounds are all based on the
assembly of 3,5-bis(pyridin-3-ylmethoxy)benzoic acid with Cd(II),
Zn(II), Co(II), Ni(II) and Cu(I) under hydrothermal conditions.
2. Experimental
2.1. Materials and analyses
All reagents and solvents employed were commercially avail-
able and used as received without further purification. The ligand
of L3 was synthesized readily by the procedure reported in the lit-
erature [43]. Elemental analyses (C, H and N) were performed on a
Perkin–Elmer 240 °C elemental analyzer. The Fourier transform
infrared (FT-IR) spectra were recorded from KBr pellets in the
range 4000–400 cmÀ1 on a Mattson Alpha-Centauri spectrometer.
Solid-state luminescent spectra were measured on a Cary Eclipse
* Corresponding authors.
E-mail address: zmsu@nenu.edu.cn (Z.-M. Su).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.07.011

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G.-J. Xu et al. / Polyhedron 28 (2009) 3155–3161
Table 1
Crystal data and structure refinements for compounds 1–5.
Compound
1
2
3
4
5
Formula
C38H32N4O9Cd
801.08
C38H30N4O8Zn
736.03
monoclinic
C2/c
20.535(4)
9.951(3)
16.532(4)
90
107.336(3)
90
3224.8(2)
4
C38H30N4O8Co
729.59
monoclinic
C2/c
20.504(3)
9.936(2)
16.493(2)
90
106.931(4)
90
3214.4(9)
4
C38H30N4O8Ni
729.37
monoclinic
C2/c
20.380(2)
9.925(3)
16.389(3)
90
106.454(2)
90
3179.3(1)
4
C38H36N4O11Cu2
851.79
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
triclinic
triclinic
ꢀ
ꢀ
P1
P1
11.047(2)
11.936(2)
14.397(3)
100.306(2)
108.342(2)
96.557(3)
1743.0(6)
2
8.484(3)
9.914(2)
11.446(2)
110.651(3)
93.259(2)
90.615(3)
898.9(8)
1
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc.(g cmÀ3
)
1.526
0.689
1.516
0.825
1.508
0.598
1.524
0.675
1.570
1.252
l
(mmÀ1
)
F (0 0 0)
816
1520
1508
1512
436
Reflections collected
8848
9625
7935
7883
4616
Independent reflections (Rint
)
6063 (0.0097)
6063/0/477
1.049
0.0272
0.0688
3797 (0.0227)
3797/0/231
1.051
0.0402
0.1124
2837 (0.0268]
2837/0/231
1.036
0.0392
0.1079
2808 (0.0294)
2808/0/231
1.047
0.0461
0.1282
3148 (0.0141)
3148/0/261
1.053
0.0369
0.0897
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
a
R1 [I > 2
r
(I)]
b
wR2 (all data)
P
P
a
R1
=
||Fo| À |Fc||/ |Fo|.
P
P
b
wR2 = | w(|Fo|2 À |Fc|2)|/ |w(Fo2)2|1/2
.
Table 2
Selected bond lengths (Å) and angles (°) for compounds 1–5.a
Compound 1
Cd(1)–O(1)#1
Cd(1)–O(5)
Cd(1)–N(1)
Cd(1)–N(3)#3
2.334(2)
Cd(1)–O(2)#1
Cd(1)–O(6)
Cd(1)–N(2)#2
2.4967(2)
2.3846(2)
2.354(2)
2.514(2)
2.378(2)
2.389(2)
92.10(8)
90.51(8)
166.17(7)
143.78(6)
84.16(7)
85.72(7)
82.32(7)
97.78(7)
96.03(8)
133.90(6)
53.98(6)
O(1)#1–Cd(1)–N(2)#2
O(1)#1–Cd(1)–N(1)
N(2)#2–Cd(1)–N(1)
O(1)#1–Cd(1)–O(6)
N(2)#2–Cd(1)–O(6)
N(1)–Cd(1)–O(6)
O(1)#1–Cd(1)–N(3)#3
N(2)#2–Cd(1)–N(3)#3
N(1)–Cd(1)–N(3)#3
O(6)–Cd(1)–N(3)#3
O(1)#1–Cd(1)–O(2)#1
N(2)#2–Cd(1)–O(2)#1
N(1)–Cd(1)–O(2)#1
O(6)–Cd(1)–O(2)#1
N(3)#3–Cd(1)–O(2)#1
O(1)#1–Cd(1)–O(5)
N(2)#2–Cd(1)–O(5)
N(1)–Cd(1)–O(5)
O(6)-Cd(1)–O(5)
N(3)#3–Cd(1)–O(5)
O(2)#1–Cd(1)–O(5)
89.04(7)
81.53(8)
89.88(6)
136.06(6)
162.75(6)
86.15(7)
95.28(8)
53.14(6)
80.93(6)
142.99(6)
Compound 2
Zn(1)–O(1)
Zn(1)–N(1)#2
2.333(2)
2.090(7)
59.69(6)
89.34(7)
93.85(1)
94.94(1)
98.00(7)
Zn(1)–O(2)
2.053(6)
O(2)–Zn(1)–O(1)
N(1)#3–Zn(1)–O(1)
N(1)#2–Zn(1)–N(1)#3
O(1)–Zn(1)–O(1)#1
O(2)#1–Zn(1)–O(1)
O(2)–Zn(1)–N(1)#2
O(2)–Zn(1)–N(1)#3
O(2)–Zn(1)–O(2)#1
N(1)#2–Zn(1)–O(1)
99.56(7)
101.73(7)
148.63(1)
159.19(6)
Compound 3
Co(1)–O(1)
Co(1)–N(1)#2
2.239(2)
2.094(2)
60.82(6)
89.72(7)
93.42(1)
94.46(1)
99.78(7)
Co(1)–O(2)
2.0785(2)
O(2)–Co(1)–O(1)
N(1)#3–Co(1)–O(1)
N(1)#2–Co(1)–N(1)#3
O(1)–Co(1)–O(1)#1
O(2)#1–Co(1)–O(1)
O(2)–Co(1)–N(1)#2
O(2)–Co(1)–N(1)#3
O(2)–Co(1)–O(2)#1
N(1)#2–Co(1)–O(1)
98.60(7)
99.86(7)
152.95(1)
159.40(6)
Compound 4
Ni(1)–O(1)
Ni(1)–N(1)#2
2.160(2)
2.052(2)
62.17(8)
90.80(9)
91.84(1)
93.00(1)
101.01(8)
Ni(1)–O(2)
2.072(2)
O(2)–Ni(1)–O(1)
N(1)#3–Ni(1)–O(1)
N(1)#2–Ni(1)–N(1)#3
O(1)–Ni(1)–O(1)#1
O(2)#1–Ni(1)–O(1)
O(2)–Ni(1)–N(1)#2
O(2)–Ni(1)–N(1)#3
O(2)–Ni(1)–O(2) #1
N(1)#2–Ni(1)–O(1)
97.50(9)
98.53(8)
156.88(1)
160.69(8)
Compound 5
Cu(1)–O(2)#2
Cu(1)–N(2)#1
N(2)#1–Cu(1)–O(2)#2
N(1)–Cu(1)–O(2)#2
2.097(2)
1.946(2)
109.69(1)
104.14(9)
Cu(1)–N(1)
1.954(3)
N(2)#1–Cu(1)–N(1)
145.81(1)
a
Symmetry transformations used to generate equivalent atoms: for 1: #1 x + 1, y, z; #2 x + 1, y + 1, z; #3 Àx + 1, Ày + 1, Àz + 1; for 2: #1 Àx, y, Àz + 1/2; #2 Àx + 1/2, yÀ1/2,
Àz + 1/2; #3 x À 1/2, y À 1/2, z; for 3: #1 Àx + 1, y,À z À 1/2; #2 Àx + 3/2, y À 1/2, Àz À 1/2; #3 x À 1/2, y À 1/2, z; for 4: #1 Àx, y, Àz + 1/2; #2 Àx + 1/2, y À 1/2, #3 x À 1/2,
y À 1/2, z; Àz + 1/2; for 5: #1 x À 1, y À 1, z À 1; #2 x À 1, y À 1, z.

G.-J. Xu et al. / Polyhedron 28 (2009) 3155–3161
3157
spectrofluorometer (Varian) equipped with a xenon lamp and
quartz carrier at room temperature. Thermogravimetric (TG) anal-
ysis was performed on a Perkin–Elmer TG-7 analyzer heated from
40 to 700 °C under nitrogen.
2.2.2. Synthesis of [Zn(L3)2] (2)
Similar procedures were performed to obtain colorless crystals
of compound 2, except that Zn(OOCCH3)2Á2H2O (0.30 mmol,
0.066 g) was used instead of Cd(OOCCH3)2Á2H2O. Yield, 25 mg
(38% based on Zn(II) salts). Elemental Anal. Calc. for C38H30N4O8Zn
(736.03): C, 62.01; H, 4.11; N, 7.61. Found C, 62.04; H, 4.12; N,
7.64%. IR (KBr pellet, cmÀ1): 3432 (w), 3041 (w), 1605 (m), 1553
(s), 1474 (m), 1440 (m), 1410 (s), 1374 (s), 1319 (m), 1143 (s),
1053 (m), 782 (m), 706 (m), 649 (w).
2.2. Syntheses of the compounds
2.2.1. Synthesis of [Cd(L3)2]ÁH2O (1)
A
mixture of Cd(OOCCH3)2Á2H2O (0.30 mmol, 0.080 g), L3
(0.20 mmol, 0.036 g) and NaOH (0.60 mmol, 0.024 g) in H2O
(14 ml) was sealed in a 25 ml Teflon-lined stainless steel container,
which was heated at 150 °C for 72 h and then cooled down to room
temperature at a rate of 5 °C hÀ1. Colorless crystals of 1 were col-
lected and washed with distilled water and dried in air to give the
product; yield, 35 mg (44% based on Cd(II) salts). Elemental Anal.
Calc. for C38H32N4O9Cd (801.08): C, 56.98; H, 4.03; N, 6.99. Found
C, 56.96; H, 4.01; N, 6.97%. IR (KBr pellet, cmÀ1): 3493 (w), 3072
(w), 1607 (m), 1557 (s), 1474 (w), 1435 (m), 1403 (m), 1371 (s),
1327 (m), 1154 (s), 1043 (m), 851 (w), 783 (s), 704 (m), 642 (w).
2.2.3. Synthesis of [Co(L3)2] (3)
Similar procedures were performed to obtain purple crystals of
compound 3, except that Co(OOCCH3)2Á4H2O (0.30 mmol, 0.075 g)
was used instead of Cd(OOCCH3)2Á2H2O. Yield, 31 mg (41% based
on Co(II) salts). Elemental Anal. Calc. for C38H30N4O8Co (729.59):
C, 62.56; H, 4.14; N, 7.68. Found C, 62.53; H, 4.14; N, 7.65%. IR
(KBr pellet, cmÀ1): 3432 (m), 3042 (w), 1609 (m), 1542 (s), 1474
(m), 1415 (s), 1376 (s), 1319 (m), 1293 (w), 1143 (s), 1052 (s),
781 (m), 706 (w).
Fig. 1. (a) The coordination environment of CdII atom in compound 1. All of the hydrogen atoms and lattice-water molecule were omitted for clarity. (b) View showing the
bilayer structure formed by connecting the CdII atom with tri-connected L3 and bridged L3 from b-axis. (c) Schematic view of the 2D binodal (3,4)-connected network of 1
with (63)(66) topology. (Symmetry transformations used to generate equivalent atoms: A, 1 + x, y, z; B, 1 + x, 1 + y, z; C, 1 À x, 1 À y, 1 À z.)
Scheme 1. Coordination modes of the L3 ligand in compounds 1–5.

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G.-J. Xu et al. / Polyhedron 28 (2009) 3155–3161
2.2.4. Synthesis of [Ni(L3)2] (4)
gram. The crystal structure was solved by direct methods and re-
fined with full-matrix least-squares SHELXTL-97) with atomic
Similar procedures were performed to obtain green crystals of
compound 4, except that NiCl2Á6H2O (0.30 mmol, 0.072 g) was
used instead of Cd(OOCCH3)2Á2H2O. Yield, 25 mg (35% based on
Ni(II) salts). Elemental Anal. Calc. for C38H30N4O8Ni (729.37): C,
62.58; H, 4.15; N, 7.68. Found C, 62.56; H, 4.16; N, 7.66%. IR (KBr
pellet, cmÀ1): 3432 (m), 3041 (w), 1610 (m), 1535 (s), 1475 (m),
1419 (s), 1376 (s), 1319 (m), 1292 (w), 1143 (s), 1051 (m), 783
(s), 705 (w).
(
coordinates and anisotropic thermal parameters for all nonhydro-
gen atoms. The hydrogen atoms of aromatic rings were included
in the structure factor calculation at idealized positions by using
a riding model. The hydrogen atoms from water molecules were
directly located from successive Fourier differences syntheses. In
compound 5, the hydrogen atoms of one lattice-water molecules
have not been found from Fourier maps due to the high disorder
of water molecules. The detailed crystallographic data and
structure refinement parameters for compounds 1–5 are summa-
rized in Table 1. Selected bond lengths and angles are given in
Table 2.
2.2.5. Synthesis of [Cu2(L3)2]Á3H2O (5)
Similar procedures were performed to obtain brown crystals of
compound 5, except that CuI (0.30 mmol, 0.057 g) was used in-
stead of Cd(OOCCH3)2Á2H2O. Yield, 16 mg (28% based on Cu(I)
salts). Elemental Anal. Calc. (%) for C38H36N4O11Cu2 (851.79): C,
53.58; H, 4.26; N, 6.58. Found C, 53.55; H, 4.29; N, 6.57%. IR (KBr
pellet, cmÀ1): 3394 (s), 1603 (m), 1540 (s), 1371 (m), 1276 (s),
1115 (w), 1023 (m), 782 (m), 705 (w).
3. Results and discussion
3.1. Description of the structures
3.1.1. [Cd(L3)2]ÁH2O (1)
2.3. X-ray crystallography analysis
The single-crystal X-ray diffraction analysis reveals that the
structure of 1 contains one kind of CdII atom, two kinds of L3 li-
gands and one lattice-water molecule in an asymmetric unit. Each
CdII atom is coordinated by four carboxylate oxygen atoms (Cd–O
2.334(2)–2.514(2) Å) of two L3 ligands and three nitrogen atoms
(Cd–N 2.354(2)–2.389(2) Å) of three L3 ligands to furnish a pentag-
Data collection of compounds 1–5 were performed on a Bru-
ker SMART APEX II CCD diffractometer with graphite-monochromat-
ed Mo Ka radiation (k = 0.71073 Å) at room temperature. All
absorption corrections were performed by using the SADABS pro-
Fig. 2. (a) The coordination environment of ZnII atom in compound 2. All of the hydrogen atoms were omitted for clarity. (b) Left-handed layer formed by L3 ligands and ZnII
atoms in 2 along the b-axis. (c) The packing diagram of the 2D polymeric layers in 2. (d) Schematic view of the uninodal (4,4)-connected net with (44 Á 62) Schläfli symbol.
(Symmetry transformations used to generate equivalent atoms: A, Àx, y, 0.5 À z; B, À0.5 + x, À0.5 + y, z; C, 0.5 À x, À0.5 + y, 0.5 À z.)

G.-J. Xu et al. / Polyhedron 28 (2009) 3155–3161
3159
onal bipyramidal coordination geometry (Fig. 1a). The Cd–O and
Cd–N bond distances are all in the normal ranges [44–49].
The coordination modes of L3 ligand in this work are summa-
rized in Scheme 1. In compound 1, L3 ligands adopt two coordina-
tion modes: one bridges two CdII atoms through one carboxylate
group and one pyridyl-N atom, containing an uncoordinated pyri-
dyl-N atom; and the other connects three CdII atoms through one
carboxylate group and two pyridyl-N atoms (Schemes 1a and
1b). As depicted in Fig. 1b, each tri-connected L3 ligand connects
with three metal centers to form (6,3)-connected net, which is fur-
ther linked by bridged L3 ligands to form the final 2D bilayer struc-
ture. If the two bridged L3 ligands between two CdII atoms can be
considered as one linker, each CdII atom can be treated a 4-con-
neccted node, the structure of 1 is a binodal (3,4)-connected net-
work with (63)(66) topology (Fig. 1c). Moreover, the lattice-water
molecules form hydrogen-bonding interactions with carboxylate
group and uncoordinated pyridyl-N atom of L3 ligands in the adja-
cent layers (dOwÁ Á ÁO5i = 2.951 Å, i: 1 À x, 1 À y, 1 À z; dOw-
N4ii = 2.884 Å, ii: x, y, À1 + z) to extend the 2D layer into a 3D
supramolecular net.
pyridyl-N atom and carboxylate group of L3 ligands (Scheme 1a)
to form helical chains running along b-axis (Fig. 2b). The adjacent
helical chains are also linked by L3 ligands to generate a 2D rhom-
bic structure (9.95 Â 20.54 Å2) involving 44-membered rings. With
in the layer, all Zn–L3 helical chains display the same chirality,
while those in adjacent layers display opposite chirality (Fig. 2c).
So the overall structure of 2 is a racemic structure. If L3 ligands
are considered as linear linkers, ZnII atoms are considered as 4-con-
nected nodes, the structure of 2 can be symbolized as a uninodal
(4,4)-connected net with (44 Á 62) Schläfli symbol (Fig. 2d).
3.1.3. [Cu2(L3)2]Á3H2O (5)
Single-crystal X-ray diffraction analysis reveals that compound
ꢀ
5 crystallizes in the triclinic space group P1 and there are one crys-
tallographic independent CuI atom, one L3 ligand and one and a
half lattice-water molecules in an asymmetrical unit. As shown
in Fig. 3a, the CuI atom is in a trigonal coordination geometry with
one carboxylate oxygen atom (Cu–O 2.097(2) Å) of one L3 ligand
and two nitrogen atoms (Cu–N 1.946(2)–1.954(3) Å) of two L3 li-
gands. The Cu–O and Cu–N bond distances are all in the normal
ranges [54–57].
3.1.2. [M(L3)2] (M = Zn, 2; Co, 3; Ni, 4)
Different from that of compounds 1 and 2, each L3 ligand acts as
a tri-connector linking three CuI atoms in compound 5 (Scheme
1c), the carboxylate group connects one CuI atom through a
mono-dentate oxygen atom, two pyridyl-N atoms bind to two
CuI atoms, consequently resulting in the formation of a 2D layer.
By treating the CuI atom as a single node and connecting the nodes
according to the connectivity defined by the geometrical centers of
the L3 ligand, a distorted 2D bimodal (6,3) network sustained by 3-
connected nodes is then yielded, as illustrated in Fig. 3b. Two types
Single-crystal X-ray diffraction analyses reveal that compounds
2–4 are isostructural, and crystallize in the monoclinic space group
C2/c; thus, only the structure of 2 is representatively described in
detail here. The crystal structure of 2 contains one kind of ZnII atom
and one kind of L3 ligand in an asymmetric unit. As shown in
Fig. 2a, each ZnII atom is coordinated by four carboxylate oxygen
atoms (Zn–O 2.053(6)–2.333(2) Å) of two L3 ligands and two nitro-
gen atoms (Zn–N 2.090(7) Å) of two L3 ligands, showing a distorted
octahedral coordination geometry. The Zn–O and Zn–N bond dis-
tances are all in the normal ranges [50–53]. It should be notewor-
thy that the adjacent ZnII atoms are linked to each other through
of supramolecular interactions,
tween phenyl rings of adjacent layer (3.490 Å) and hydrogen-
p p stacking interactions be-
Á Á Á
bonding interactions between lattice-water molecules and uncoor-
Fig. 3. (a) The coordination environment of CuI atom in compound 5. All of the hydrogen atoms and lattice-water molecules were omitted for clarity. (b) 2D layer structure of
5. (c) Topology of 5 showing the binodal (6,3)-net based on the CuI atoms and L3 ligands. (Symmetry transformations used to generate equivalent atoms: A, 1+x, 1+y, z; B, x, y,
-1+z.)

3160
G.-J. Xu et al. / Polyhedron 28 (2009) 3155–3161
dinated carboxylate oxygen atoms, contribute to the formation of
the 3D supramolecular architecture.
As to the syntheses of compounds 1–5, all the reaction condi-
tions are the same except for the difference of metal ions. From
the structural analyses of 1–5, we can see that the increase in coor-
dination number (from 3 to 7) of metal ions induces the progres-
sive increase in complexity of the ultimate net (from (6,3)-net to
bilayer (3,4)-net); in other words, the coordination number of me-
tal ions plays a significant role in tuning the connectivity of a spe-
cific network [58,59]. On the other hand, flexible L3 ligand has the
advantages in that its flexibility and conformational freedom allow
it to conform to the coordination environment of transition-metal
ions. This is further evidence that the selection of suitable metal
ions and organic ligands is a major strategy to synthesize func-
tional materials with useful properties.
3.2. Properties
Fig. 5. TG curves of 1–5.
3.2.1. Luminescent properties
Taking into account of the excellent luminescent properties of
Cd(II) and Zn(II), the solid-state luminescent spectra of 1 and 2
have been studied at room temperature. As shown in Fig. 4, com-
pound 1 shows the emission maxima at 453 nm (kex = 340 nm),
product. The TG curves of 2–4 all show one main weight loss. No
weight losses were observed for the compounds up to 280 °C;
above 280 °C, significant weight losses occurred and ended at
610 °C, 660 °C, 560 °C, respectively, indicating the removal of the
corresponding organic components. The remaining weight may
correspond to the final products of ZnO in 2 (obsd. 11.23%, calcd.
11.06%), CoO in 3 (obsd. 11.46%, calcd. 10.27%) and NiO in 4 (obsd.
10.42%, calcd. 10.24%). The TG curve of 5 shows that the first
weight loss of 6.08% between 70 °C and 130 °C, corresponding to
the loss of the lattice-water molecules (calcd. 6.35%). The frame-
work collapsed in the temperature range of 220–450 °C before
the final formation of a metal oxide.
compound
2
shows the emission maxima at 464 nm
(kex = 349 nm). In order to understand the nature of the emission,
we analyzed the photoluminescent property of L3 ligand and found
that the strongest emission peak at 392 nm (kex = 246 nm). The
*
*
?
emission of the ligand may be assigned to
p
? n and
p
p tran-
sitions of the intraligands. In comparison with the free ligand, the
emission of compounds 1 and 2 may be attributed to ligand to me-
tal charge transfer (LMCT) [60–63]. These observations indicate
that these condensed polymeric compounds could be potentially
used as photoactive materials, since they are thermally stable
and insoluble in common polar and nonpolar solvents.
4. Conclusion
In summary, we have synthesized five new coordination poly-
mers based on 3,5-bis(pyridin-3-ylmethoxy)benzoic acid ligand
under hydrothermal conditions. The successful syntheses of the
five compounds indicate that it is promising to build up unusual
architectures via combining transition metals and L3 ligands. Fur-
ther work on the properties of this new flexible organic ligand and
its metal compounds are still explored in our laboratory.
3.2.2. Thermal properties
To study the thermal stability of compounds 1–5, thermogravi-
metric (TG) analyses were performed on polycrystalline samples
under a nitrogen atmosphere with a heating rate of 10 °C minÀ1
(Fig. 5). The TG curve of 1 shows that the first weight loss of
2.46% between 46 and 120 °C corresponding to the loss of the lat-
tice-water molecules (calcd. 2.25%). A total weight loss of 81.39%
occurred in the temperature range of 240–560 °C, mainly corre-
sponding to the removal of the L3 ligands (calcd. 81.72%), no
weight loss were observed up to 700 °C indicating the complete
deposition of the compound with the formation of CdO as the final
Supplementary data
CCDC 722283, 722284, 722285, 722286, and 722287 contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/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.
Acknowledgements
The authors gratefully acknowledge the financial support from
the National Natural Science Foundation of China (Project No.
20703008), Chang Jiang Scholars Program (2006), Program for
Changjiang Scholars and Innovative Research Team in University
(IRT0714), the Training Fund of NENU’s Scientific Innovation Pro-
ject (NENU-STC07017) and Science Foundation for Young Teachers
of Northeast Normal University (20080502).
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