Syntheses, structures and luminescent properties of three cadmium coordination polymers derived from (4-carboxymethoxy-phenyl)-acetate

Article abstract of DOI:10.1016/j.molstruc.2011.05.038

Three new cadmium(II) coordination polymers {[Cd(bipy)(cpa)(H ₂O)]·2H₂O}_n (1), {[Cd(phen)(cpa)] ·3H₂O}_n (2) and [Cd(cpa)]_n (3) (bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline, H₂

Full text of DOI:10.1016/j.molstruc.2011.05.038

Journal of Molecular Structure 998 (2011) 233–239
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Syntheses, structures and luminescent properties of three cadmium
coordination polymers derived from (4-carboxymethoxy-phenyl)-acetate
⇑
De-Yun Yuan, Ju Wang, Xin Qian, Bao-Long Li , Hai-Yan Li
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Material Science, Soochow University, Suzhou 215123, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new cadmium(II) coordination polymers {[Cd(bipy)(cpa)(H2O)]ꢀ2H2O}n (1), {[Cd(phen)(cpa)]ꢀ
3H2O}n (2) and [Cd(cpa)]n (3) (bipy = 2,20-bipyridine, phen = 1,10-phenanthroline, H2cpa = (4-carboxy-
methoxy-phenyl)-acetic acid) were synthesized and characterized. The cpa ligands exhibit the versatile
coordination modes and play an important role in the construction of their structures. The structures
of 1, 2 and 3 are comprised of one-dimensional chains, infinite molecular ladders and a (4,4)-connected
(each Cd(II) links four cpa and each cpa connects four Cd(II)) three-dimensional network, respectively. 1,
2 and 3 reveal the blue emission maximum at 414, 420 and 458 nm, respectively, in the solid state at
room temperature.
Received 31 October 2010
Received in revised form 21 May 2011
Accepted 21 May 2011
Available online 27 May 2011
Keywords:
Cadmium complex
Coordination polymer
(4-Carboxymethoxy-phenyl)-acetic acid
Ladder
Ó 2011 Elsevier B.V. All rights reserved.
Three-dimensional network
Luminescence
1. Introduction
cadmium(II) coordination polymers {[Cd(bipy)(cpa)(H2O)]ꢀ2H2O}n
(1), {[Cd(phen)(cpa)]ꢀ3H2O}n (2) and [Cd(cpa)]n (3) (bipy = 2,20-
The design and synthesis of metal–organic frameworks have
been intensely studied for their potential applications as functional
materials for gas storage, separation, microelectronics, nonlinear
optics and catalysis, as well as their intriguing variety of topologies
[1–7]. Design effective ligands and proper choice of metal centers
are the keys to design and construction of novel metal–organic
frameworks.
bipyridine, phen = 1,10-phenanthroline, H2cpa = (4-carboxymeth-
oxy-phenyl)-acetic acid). Herein we report their syntheses, crystal
structures and luminescent properties.
2. Experimental section
2.1. Materials and general methods
Symmetric organic aromatic polycarboxylate ligands, such as
1,2-benzenedicarboxylate
[10–12], 1,4-benzenedicarboxylate [10–14], 1,3,5-benzenetricarb-
oxylate [14–16], and 1,2,4,5-benzenetetracarboxylate
[8–10],
1,3-benzenedicarboxylate
All reagents were of analytical grade and used without further
purification. (4-Carboxymethoxy-phenyl)-acetic acid (H2cpa) was
synthesized according to literature method [25]. Elemental analy-
ses for C, H and N were performed on a Perkin–Elmer 240C ana-
lyser. IR spectra were obtained for KBr pellets on a Nicolet 170SX
FT-IR spectrophotometer in the 4000–400 cmꢁ1 region. The lumi-
nescence measurements were carried out in the solid state at room
temperature and the spectra were collected with a PerkinElmer
LS50B spectro-fluorimeter.
[9,14,17,18], are good building blocks for the construction of coor-
dination polymers and multidimensional supramolecular net-
works. However the coordination polymers assembled from
asymmetric carboxylate ligands have been less exploited. (4-Carb-
oxymethoxy-phenyl)-acetic acid (H2cpa) possesses two flexible
asymmetric carboxylate groups, one acetate and one oxyacetate,
which makes it flexible and can construct versatile coordination
polymers with novel structures (Scheme 1). On the other hand,
the d10 metal coordination polymers have been found to exhibit
interesting photoluminescent properties [19–24]. In order to syn-
thesis novel topological frameworks and potential luminescent
materials, in the present work, we have synthesized three new
2.2. Preparation of the complexes
2.2.1. Synthesis of {[Cd(bipy)(cpa)(H2O)]ꢀ2H2O}n (1)
A solution of H2cpa (0.042 g, 0.20 mmol) in 20 mL of H2O was
adjusted to pH 6 with NEt3. Then, the solution of bipy (0.031 g,
0.20 mmol) and Cd(NO3)2ꢀ4H2O (0.062 g, 0.20 mmol) in 5 mL of
EtOH was added. The mixture was stirred for 10 min and filtered.
The filtrate was stood on the desk at room temperature. The
⇑
Corresponding author.
E-mail address: libaolong@suda.edu.cn (B.-L. Li).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.05.038

234
D.-Y. Yuan et al. / Journal of Molecular Structure 998 (2011) 233–239
C5
C6
C1
O1
O3
O
O4
O
CH2
C7
C
Cd
Cd
Cd
O
C4
C3
C8
CH2
O
C
C2
O2
C9
O
C10
O5
(a)
(b)
C5
C4
C6
O1
O
Cd
Cd
O3
O
O4
CH2
C
O
C8
C7
C1
C2
O
CH2
C
O2
C3
C9
O
C10
O5
C5
C6
O1
O
Cd
O3
O
O5
CH2
C7
O
C
Cd
Cd
C1
C2
C4
C3
C8
CH2
C
O
C9
C10
O
Cd
O2
O4
(c)
Scheme 1. Three coordination modes of H2cpa ligand.
colorless single crystals of 1 were obtained after 1 week in 72%
yield (0.076 g). Anal. Calc. for C20H22CdN2O8 (1): C, 45.26; H,
4.18; N, 5.28. Found: C, 45.18; H, 4.13; N, 5.21%. IR data (cmꢁ1):
3445s, 1609vs, 1566vs, 1474w, 1439m, 1393s, 1335w, 1246m,
1169w, 1157w, 1061m, 1015w, 806w, 772m, 737w.
2.2.3. [Cd(cpa)]n (3)
A solution of H2cpa (0.042 g, 0.20 mmol) in 10 mL of H2O was
adjusted to pH
with NEt3. Then Cd(NO3)2ꢀ4H2O (0.062 g,
7
0.20 mmol) was added with stirring. The mixture was added to a
20 mL Teflon-lined stainless autoclave, and was sealed and heated
to 110 °C for 48 h and then cooled to room temperature. Colorless
block-shaped crystals 3 were collected in 67% yield (0.043 g). Anal.
Calc. for C10H8CdO5 (3): C, 37.47; H, 2.52. Found: C, 37.42; H, 2.47%.
IR data (cmꢁ1): 3441w, 1588s, 1509m, 1454m, 1401s, 1338w,
1298m, 1220m, 1184w, 1156w, 1115w, 1053m, 958w, 853w,
820m, 766w, 718w, 651m, 606w, 544m.
2.2.2. {[Cd(phen)(cpa)]ꢀ3H2O}n (2)
A solution of H2cpa (0.021 g, 0.10 mmol) in 15 mL of H2O was
adjusted to pH 6 with NEt3. Then, the solution of phen (0.018 g,
0.10 mmol) and Cd(NO3)2ꢀ4H2O (0.031 g, 0.10 mmol) in 5 mL of
EtOH was added with stirring. The mixture was added to a 30 mL
Teflon-lined stainless autoclave, and was sealed and heated to
110 °C for 24 h and then cooled to room temperature. Yellow
block-shaped crystals 2 were collected in 78% yield (0.043 g). Anal.
Calc. for C22H22CdN2O8 (2): C, 47.63; H, 4.00; N, 5.05. Found: C,
47.51; H, 3.93; N, 4.99%. IR data (cmꢁ1): 3429s, 1609vs, 1566vs,
1512s, 1423s, 1393m, 1335w, 1242m, 1146w, 1103w, 1061m,
860m, 806w, 783w, 725m.
2.3. Single-crystal x-ray crystallography
Suitable single crystals of compounds 1, 2 and 3 were carefully
selected under an optical microscope and glued to thin glass fibers.
The diffraction data were collected on a Rigaku Mercury CCD dif-
fractometer with graphite monochromated Mo
Ka radiation
Table 1
Crystallographic data for 1, 2 and 3.
1
2
3
Formula
Fw
C
20H22CdN2O8
C22H22CdN2O8
554.82
C10H8CdO5
320.56
530.80
Crystal system
Space group
Monoclinic
P21/n
Triclinic
Monoclinic
P21/n
P1
Temp (K)
a (Å)
b (Å)
293(2)
6.9411(10)
13.536(2)
22.360(4)
90
96.869(3)
90
2085.7(5)
4
293(2)
293(2)
10.3920(13)
7.1079(8)
12.9953(15)
90
102.764(3)
90
936.18(19)
4
8.941(3)
11.371(4)
12.541(5)
109.884(7)
110.124(7)
95.224(4)
1094.1(7)
2
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
qcalc (g/cm3)
1.690
1.098
1.684
1.050
2.274
2.334
l
(mmꢁ1
)
F(0 0 0)
1072
560
624
Reflections collected
Unique reflections
Parameters
16,876
3741 [R(int) = 0.0259]
293
10,823
3996 [R(int) = 0.0803]
299
8378
1713 [R(int) = 0.0472]
146
Goodness of fit
1.077
0.0309
0.0803
1.088
0.0835
0.2121
1.015
0.0222
0.0558
R1 [I > 2
r(I)]
wR2 (all data)

D.-Y. Yuan et al. / Journal of Molecular Structure 998 (2011) 233–239
235
Table 2
atoms from a bipy and four oxygen atoms from a water molecule
and two cpa ligands in a distorted octahedral coordination envi-
ronment (Fig. 1). The cpa ligand possesses two flexible asymmetric
carboxylate groups: one acetate and one oxyacetate. The acetate
group shows bidentate mode and the oxyacetate group exhibits
monodentate mode (Scheme 1a). Each cpa connects two Cd(II) ions
to form a one-dimensional chain with the Cdꢀ ꢀ ꢀCd distance of
11.308(2) Å.
The bipy rings in one chain are absolutely parallel with two bipy
rings (ꢁx, ꢁy, ꢁz; 1 ꢁ x, ꢁy, ꢁz) of two adjacent chains. The corre-
sponding perpendicular distances of bipy rings are 3.489 and
3.317 Å, and the centroid-to-centroid distances are 3.931 and
Selected bond lengths (Å) and angles (°) for 1, 2 and 3.
1
Cd(1)–O(1)
Cd(1)–O(4A)
Cd(1)–N(1)
2.426(2)
2.211(2)
2.344(2)
54.38(7)
136.43(8)
83.84(8)
87.24(8)
172.03(8)
70.39(8)
158.51(8)
103.38(9)
Cd(1)-O(2)
Cd(1)-O(6)
Cd(1)–N(2)
O(4A)–Cd(1)–O(1)
O(4A)–Cd(1)–O(2)
O(4A)–Cd(1)–O(6)
N(1)–Cd(1)–O(2)
O(6)–Cd(1)–N(1)
N(2)–Cd(1)–O(1)
O(4A)–Cd(1)–N(2)
2.369(2)
2.338(2)
2.330(2)
94.74(8)
99.20(8)
78.84(9)
88.24(8)
104.98(9)
120.03(8)
102.04(9)
O(1)–Cd(1)–O(2)
O(6)–Cd(1)–O(1)
O(6)–Cd(1)–O(2)
N(1)–Cd(1)–O(1)
O(4A)–Cd(1)–N(1)
N(2)–Cd(1)–N(1)
N(2)–Cd(1)–O(2)
N(2)–Cd(1)–O(6)
3.714 Å, respectively, exhibiting obvious p–p stacking interactions
2
[27–29]. There are O–Hꢀ ꢀ ꢀO hydrogen bonding interaction between
Cd(1)–O(1)
Cd(1)–O(4A)
Cd(1)–N(1)
2.388(8)
2.260(6)
2.383(8)
55.8(3)
86.3(3)
140.3(3)
86.5(3)
86.9(3)
168.6(3)
98.6(3)
71.1(3)
Cd(1)–O(2)
Cd(1)–O(4B)
Cd(1)–N(2)
O(4A)–Cd(1)–O(1)
O(4A)–Cd(1)–O(2)
O(4A)–Cd(1)–O(4B)
N(2)–Cd(1)–O(1)
O(2)–Cd(1)–N(2)
O(4B)–Cd(1)–N(1)
N(2)–Cd(1)–O(4B)
2.308(8)
2.330(7)
2.312(9)
103.3(2)
103.3(2)
71.7(3)
157.2(3)
124.5(3)
103.7(2)
94.9(3)
the coordination water, lattice water and carboxylate groups of cpa
ligands (Table 3). Through these
p–p stacking interactions and
O(2)–Cd(1)–O(1)
O(4B)–Cd(1)–O(1)
O(2)–Cd(1)–O(4B)
N(1)–Cd(1)–O(1)
O(2)–Cd(1)–N(1)
O(4A)–Cd(1)–N(1)
O(4A)–Cd(1)–N(2)
N(2)–Cd(1)–N(1)
hydrogen bond interaction complex 1 forms a three dimensional
network (Fig. 2).
The structure of 2 is comprised of infinite molecular ladders.
Each Cd(II) ion is six-coordinated by two nitrogen atoms from a
phen and four oxygen atoms from three cpa ligands in a distorted
octahedral geometry (Fig. 3). The acetate group of cpa ligand is
bidentate chelating and the oxyacetate group is bidentate bridging
(Scheme 1b). The Cd(1)ꢀ ꢀ ꢀCd(1D), Cd(1)ꢀ ꢀ ꢀCd(1B) and Cd(1)ꢀ ꢀ ꢀ
Cd(1C) distances are 3.721(2), 10.651(4) and 12.652(4) Å, respec-
tively (Fig. 3).
The cpa ligand exhibits a tetradentate coordination mode bridg-
ing three Cd(II) ions to form a one-dimensional molecular ladder
[30–33]. The most interesting feature in such infinite molecular
ladder is that the double bridging O(4) atoms are in rails and two
cpa are in rungs (Fig. 4). The phen rings of a ladder are absolutely
parallel with the phen rings (ꢁx, ꢁy, 1 ꢁ z) of the adjacent ladder
with the perpendicular distance 3.484 Å, and the centroid-to-
3
Cd(1)–O(1)
Cd(1)–O(2C)
Cd(1)–O(3A)
2.3350(19)
2.2986(18)
2.5081(16)
54.68(6)
135.49(7)
166.94(7)
87.83(6)
95.84(7)
86.32(7)
97.94(7)
154.22(6)
Cd(1)–O(2)
Cd(1)–O(5A)
Cd(1)–O(4B)
O(2C)–Cd(1)–O(1)
O(2C)–Cd(1)–O(2)
O(5A)–Cd(1)–O(2C)
O(2)–Cd(1)–O(3A)
O(5A)–Cd(1)–O(3A)
O(4B)–Cd(1)–O(1)
O(4B)–Cd(1)–O(2C)
2.3800(18)
2.2025(18)
2.2144(17)
124.96(7)
72.29(7)
95.41(7)
107.81(6)
68.27(6)
O(1)–Cd(1)–O(2)
O(5A)–Cd(1)–O(1)
O(5A)–Cd(1)–O(2)
O(1)–Cd(1)–O(3A)
O(2C)–Cd(1)–O(3A)
O(5A)–Cd(1)–O(4B)
O(4B)–Cd(1)–O(2)
O(4B)–Cd(1)–O(3A)
108.70(7)
90.67(7)
Symmetry transformations used to generate equivalent atoms: 1 A x ꢁ 1/2, ꢁy + 1/
2, z ꢁ 1/2; 2 A x ꢁ 1, y, z ꢁ 1; B ꢁx + 1, ꢁy + 1, ꢁz + 2; 3 A ꢁx + 1/2, y ꢁ 1/2, ꢁz + 1/2;
B x, y, z + 1; C ꢁx, ꢁy, ꢁz + 1.
Table 3
(k = 0.71073 Å). Intensities were collected by the
x scan technique.
Hydrogen bonds for 1 (Å and °).
The structures were solved by direct methods and refined with
full-matrix least-squares technique (SHELXTL-97) [26]. The param-
eters of the crystal data collection and refinement of 1, 2 and 3 are
given in Table 1. Selected bond lengths and bond angles are listed
in Table 2.
1
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA)
1.918(19)
2.04(2)
2.02(2)
2.11(2)
2.36(3)
2.59(3)
2.62(3)
d(Dꢀ ꢀ ꢀA)
2.751(3)
2.828(4)
2.819(4)
2.837(3)
2.818(4)
3.004(4)
3.247(4)
<(DHA)
172(3)
158(4)
159(4)
146(3)
118(3)
114(3)
136(3)
O(6)–H(1W)ꢀ ꢀ ꢀO(1)a
O(6)–H(2W)ꢀ ꢀ ꢀO(7)
O(7)–H(3W)ꢀ ꢀ ꢀO(8)
O(7)–H(4W)ꢀ ꢀ ꢀO(2)
O(8)–H(5W)ꢀ ꢀ ꢀO(5)b
O(8)–H(6W)ꢀ ꢀ ꢀO(4)c
O(8)–H(6W)ꢀ ꢀ ꢀO(6)d
0.838(18)
0.832(17)
0.832(17)
0.828(17)
0.787(17)
0.808(17)
0.808(17)
3. Results and discussion
Symmetry transformations used to generate equivalent atoms:
3.1. Description of the crystal structures
a
x ꢁ 1, y, z.
b
ꢁx + 3/2, y + 1/2, ꢁz + 1/2.
c
The structure of compound 1 consists of one-dimensional neu-
tral chains. Each Cd(II) ion is six-coordinated by two nitrogen
ꢁx + 1/2, y + 1/2, ꢁz + 1/2.
d
ꢁx, ꢁy + 1, ꢁz.
Fig. 1. The coordination environment of the Cd(II) atom in compound 1.

236
D.-Y. Yuan et al. / Journal of Molecular Structure 998 (2011) 233–239
Fig. 2. The packing plot in compound 1.
exhibits a novel hexadentate coordination mode bridging four Cd(II)
ions (The cpa ligand is also 4-connected). The separations of
Cd(1)ꢀ ꢀ ꢀCd(1C), Cd(1)ꢀ ꢀ ꢀCd(1D), Cd(1)ꢀ ꢀ ꢀCd(1E), Cd(1C)ꢀ ꢀ ꢀCd(1D),
Cd(1C)ꢀ ꢀ ꢀCd(1E) and Cd(1D)ꢀ ꢀ ꢀCd(1E) are 3.779(4), 10.372(1),
12.995(2), 9.902(1), 11.537(2) and 5.260(1) Å, respectively.
Each Cd(II) ion links four cpa ligands and joins ten Cd(II) ions via
four cpa ligands (Fig. 7) and further extends to form a novel (4,4)-
connected three-dimensional network (Fig. 8).
The structures of 1, 2 and 3 are comprised of one-dimensional
chains, infinite molecular ladders and a (4,4)-connected (Each Cd(II)
links four cpa and each cpa connects four Cd(II)) three-dimensional
network, respectively. For comparison, some Cd-bipy/phen-poly-
carboxylate complexes (1,2-bdc = 1,2-benzenedicarboxylate, 1,
3-bdc = 1,3-benzenedicarboxylate, 1,4-bdc = 1,4-benzenedicarbox-
ylate, btc = 1,3,5-benzenetricarboxylate and btec = 1,2,4,5-ben-
zenetetracarboxylate) are summarized in Table 4. The different
structures are mainly due to the different coordination modes of
carboxylate groups of polycarboxylate. Bis-monodentate coordina-
tion mode for the biscarboxylate ligand results the dimer
[Cd2(phen)4(1,2-bdc)2]ꢀ4H2O [34], 1D chain 1 and 1D helical chain
[Cd(H2O)(1,2-bdc)(bipy)] [35]. Monodentate and chelating or bis-
chelating mode forms 1D chain in [Cd(H2O)(1,4-bdc)(bipy] [38]
and [Cd(1,4-bdc)(phen)(H2O)]n [39]. Chelating and bidentate
Fig. 3. The coordination environment of the Cd(II) atom in compound 2.
centroid distance 3.593 Å, exhibiting obvious
tions (Fig. 5) [27–29].
p–p stacking interac-
Compound 3 has a novel (4,4)-connected three-dimensional net-
work. There are one independent Cd(II) ion and one independent cpa
ligand. Each Cd(II) ion is six-coordinated by six oxygen atoms from
four cpa ligands (Cd(II) is 4-connected) in a distorted octahedral
coordination environment (Fig. 6). The acetate group is tridentate
bridgingtwoCd(II)ionsandtheoxyacetategroupis tridentate bridg-
ing two Cd(II) ions in different mode (Scheme 1c). The cpa ligand
Fig. 4. The one-dimensional molecular ladder in 2.

D.-Y. Yuan et al. / Journal of Molecular Structure 998 (2011) 233–239
237
dentate bridging for two carboxylate groups and ether oxygen
monodentate and constructs a novel 3D network for 3.
3.2. Luminescent properties
The d10 metal compounds have exhibited some interesting pho-
toluminescent properties [19–24]. The solid-state luminescent
properties of coordination polymers 1, 2, 3 and free H2cpa were
investigated at room temperature and their emission spectra are
given in Fig. 9. For comparison, the luminescence data of 1–3 and
some Cd-bipy/phen polycarboxylate complexes are summarized
in Table 4. Because we cannot find one excitation wavelength suit-
able for the all compounds, we selected maximum excitation
wavelengths 350, 330, 380 and 303 nm for 1, 2, 3 and H2cpa,
respectively. 1, 2 and 3 reveal the blue emission maximum at
approximately 414, 420 and 458 nm, respectively. Free bipy exhib-
its the emission at 535 nm. Free phenꢀH2O shows the emissions at
365 and 388 nm. The similar luminescence emissions of 1 and 2 are
not from bipy and phen. The obvious difference emissions between
3 (458 nm) and 1 (414 nm) or 2 (420 nm) shows that the emissions
are not intraligand emission of cpa. Comparably, H2cpa in the solid
state displays a emission band centered at about 336 nm. 1, 2 and 3
exhibit the obvious red shifts of emission length 78, 84 and
122 nm, respectively. The emissions of 1–3 can be tentatively as-
signed to the ligand-to-metal charge transfer (LMCT) of cpa [36–
42]. [Cd(bipy)(1,3-bdc)] and [Cd(phen)(1,3-bdc)] with different
bipy and phen both exhibit intense blue luminescence at 422
and 423 nm, respectively, assigned to the emission of LMCT of
1,3-bdc [36]. The significant blue-shift emission at 405 nm of
[Cd(bipy)(1,3-bdc)] can be attributed to the intraligand emission
of bipy [36]. The intense luminescence at 435 nm of Cd2(bi-
py)2(1,3-bdc)2]n should be assigned to 1,3-bdc LMCT (not intrali-
Fig. 5. The packing in compound 2.
bridging mode for the biscarboxylate ligand constructs 1D molecu-
lar ladders in 2, [Cd (bipy)(1,3-bdc)] and [Cd(phen)(1,3-bdc)] [36].
[Cd(H2O)(1,3-bdc)] with bis-tridentate bridging mode has a new
two-dimensional network [35]. [Cd2(bipy)2(1,3-bdc)2]n contains a
three-dimensional polymeric channel with tetra –Cd-ip- as building
units with versatile monodentate, chelating and tridentate bridging
modes [37]. [Cd4(btec)2(phen)4(H2O)4]n possesses an infinite dou-
ble-chain structure with bis-chelating and bis-monodentate for four
carboxylate groups of btec ligand [40]. Cpa shows bidentate and tri-
gand
p–
pꢂ transition stated in [37]). The strong emission at
Fig. 6. The coordination environment of the Cd(II) atom in compound 3.
Fig. 7. The linking mode of a Cd(II) atom through four cpa in compound 3.

238
D.-Y. Yuan et al. / Journal of Molecular Structure 998 (2011) 233–239
Fig. 8. Three-dimensional network in compound 3.
Table 4
Summary of Cd-bipy/phen polycarboxylate compounds.
Compound
Structure
Coordination modes of carboxylate groups
Luminescence kem (nm)
Reference
Bipy
535 nm
[37]
Phen.H2O
H2cpa
365 and 388 nm
336 nm
414 nm (cpa LMCT)
420 nm (cpa LMCT)
[39]
This work
This work
This work
{[Cd(bipy)(cpa)(H2O)]ꢀ2H2O}n (1)
1D chain
1D
molecular
ladder
3D
network
Dimer
macrocycle
1D helical
chain
Bis-monodentate
Chelating, bidentate bridging
{[Cd(phen)(cpa)]ꢀ3H2O}n (2)
[Cd(cpa)]n (3)
Bidentate bridging, tridentate bridging, ether
oxygen monodentate
Bis-monodentate
458 nm (cpa LMCT)
This work
[34]
[Cd2(phen)4(1,2-bdc)2]ꢀ4H2O
[Cd(H2O)(1,2-bdc)(bipy)]
[Cd(H2O)(1,2-bdc)(phen)]
Bis-monodentate
[35]
1D helical
ribbon
chain
Monodentate, tridentate bridging, bidentate
chelating
[35]
[Cd(H2O)(1,3-bdc)]
[Cd (bipy)(1,3-bdc)]
2D
network
1D
molecular
ladder
1D
molecular
ladder
3D
Bis-tridentate bridging
[35]
[36]
Chelating, bidentate bridging
405 nm (intraligand emission of bipy),
422 nm (1,3-bdc LMCT)
[Cd(phen)(1,3-bdc)]
Chelating, bidentate bridging
423 nm (1,3-bdc LMCT)
[36]
[37]
[Cd2(bipy)2(1,3-bdc)2]n
Monodentate, chelating, tridentate bridging
435 nm (1,3-bdc LMCT)
polymeric
channel
1D zigzag
chain
2D
network
1D chain
[Cd(H2O)(1,4-bdc)(bipy)]
[Cd(1,4-bdc)(phen)].H2O
[Cd(1,4-bdc)(phen)(H2O)]n
Monodentate, chelating
Chelating, tridentate brdging
Chelating
379 nm (intraligand emission of 1,4-bdc)
[38]
[35]
367, 385 nm (intraligand charge transfer of [39]
phen), 404 nm (intraligand fluorescent of
phen)
[Cd2(Hbtc)2(phen)2]2nꢀnCd(Hbtc)(phen)2 1D chain
Chelating, bidentate bridging and uncoordination
for chain, bis-monodentate and uncoordination for phen)
dimer
380 nm (intraligand charge transfer of
[39]
and a
dimer
[Cd4(btec)2(phen)4(H2O)4]n
1D double
chain
Bis-chelating, bis-monodentate
[40]
379 nm of [Cd(H2O)(1,4-bdc)(bipy] is attributed to the intraligand
emission of 1,4-bdc [38] because the maximum blue-shift of bipy is
from 535 nm up to 400 nm [36]. Three emissions maxima at 367,
385 and 404 nm of [Cd(1,4-bdc)(phen)(H2O)]n are assigned to
intraligand charge transfer or fluorescence of phen [39] (Table 4).
There is no defined rule for the luminescent emissions.
(3) were synthesized and characterized. The cpa ligands exhibit
versatile coordination modes (Scheme 1): (1) a tridentate bridging
two Cd(II) ions in 1 (Scheme 1a); (2) a tetradentate bridging three
Cd(II) ions in 2 (Scheme 1b); (3) a novel hexadentate bridging four
Cd(II) ions in 3. The versatile coordination modes of cpa play an
important role in the construction of their structures. The struc-
tures of 1, 2 and 3 are comprised of one-dimensional chains, infi-
nite molecular ladders and a (4,4)-connected (Each Cd(II) links
four cpa and each cpa connects four Cd(II)) three-dimensional net-
work, respectively. 1, 2 and 3 reveal the blue emission maximum at
414, 420 and 458 nm, respectively, in the solid state at room
4. Conclusion
Three new cadmium(II) coordination polymers {[Cd(bipy)
(cpa)(H2O)]ꢀ2H2O}n (1), {[Cd(phen)(cpa)]ꢀ3H2O}n (2) and [Cd(cpa)]n

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Acknowledgments
This work was supported by the Natural Science Foundation of
China (No. 20671066), the Jiangsu Province (No. BK2006049), and
the Funds of Key Laboratory of Organic Synthesis of Jiangsu
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Appendix A. Supplementary material
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre with
CCDC numbers 796453–796455. Supplementary data associated
with this article can be found, in the online version, at
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