Novel CdII coordination polymers (1-D, 2-D to 3-D) constructed from 1,2-cyclohexanedicarboxylate and various bipyridyl ligands

Article abstract of DOI:10.1016/j.molstruc.2011.03.046

Four Cd^II-(e,a-cis-1,2-chdc) complexes, [Cd(H ₂O)(1,2-chdc)(2,2′-bpy)] 1, [Cd(1,2-chdc)(bpe)]_n 2, [Cd₂(1,2-chdc)(4,4′-bpy)₂]_n 3A, and [Cd(H₂O)(1,2-chdc)(4,4′-bpy)₂]_n· 3n(H₂O) 3B (1,2-chdc = 1,2-cyclohexanedicarboxylate), with different assistant ligands (2,2′-bipyridine (2,2′-bpy), 1,2-bis(4-pyridyl) ethene (bpe), and 4,4′-bipyridine (4,4′-bpy)) have been synthesized and their structures were determined. Depending on the assistant ligands, the structures and dimensionalities of Cd^II-(e,a-cis-1,2-chdc) complexes have been varied. Two carboxylates in e,a-cis-1,2-chdc coordinate to Cd ^II ions in chelating (η¹:η¹), bridging (η¹:η¹:μ₂), and chelating/bridging (η²:η¹:μ₂) modes. Photoluminescence study of the compounds 1 and 2 showed that emission spectrum of compound 1 was observed at 348 nm, while relatively weak luminescence was displayed at 516 nm for 2. The thermal stabilities of these complexes were also examined.

Full text of DOI:10.1016/j.molstruc.2011.03.046

Journal of Molecular Structure 994 (2011) 335–342
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Novel CdII coordination polymers (1-D, 2-D to 3-D) constructed
from 1,2-cyclohexanedicarboxylate and various bipyridyl ligands
Eun Young Kim a, Hyun Min Park a, Ha-Yeong Kim b, Jin Hoon Kim a, Min Young Hyun a,
Ju Hoon Lee a, Cheal Kim a, , Sung-Jin Kim b, , Youngmee Kim b
⇑
⇑
a Department of Fine Chemistry, Seoul National University of Science and Technology, Seoul 139-743, Republic of Korea
b Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Four CdII-(e,a-cis-1,2-chdc) complexes, [Cd(H2O)(1,2-chdc)(2,20-bpy)] 1, [Cd(1,2-chdc)(bpe)]n 2, [Cd2(1,2-
chdc)(4,40-bpy)2]n 3A, and [Cd(H2O)(1,2-chdc)(4,40-bpy)2]nꢀ3n(H2O) 3B (1,2-chdc = 1,2-cyclohexanedi-
carboxylate), with different assistant ligands (2,20-bipyridine (2,20-bpy), 1,2-bis(4-pyridyl)ethene (bpe),
and 4,40-bipyridine (4,40-bpy)) have been synthesized and their structures were determined. Depending
on the assistant ligands, the structures and dimensionalities of CdII-(e,a-cis-1,2-chdc) complexes have
Article history:
Received 18 February 2011
Received in revised form 17 March 2011
Accepted 18 March 2011
Available online 25 March 2011
been varied. Two carboxylates in e,a-cis-1,2-chdc coordinate to CdII ions in chelating (g1
:g
1), bridging
Keywords:
(
g1
:
g1
:
l
2), and chelating/bridging (g2
: :l
g1
2) modes. Photoluminescence study of the compounds 1
CdII complexes
and 2 showed that emission spectrum of compound 1 was observed at 348 nm, while relatively weak
luminescence was displayed at 516 nm for 2. The thermal stabilities of these complexes were also
examined.
Bipyridyl ligands
Photoluminescence
1,2-Cyclohexanedicarboxylate
Coordination polymers
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
monodentate coordination modes while the chelating/bridging
mode was not observed in ZnII-(1,2-chdc) system with the assis-
Carboxylate-including ligands have provided a variety of metal–
organic frameworks (MOFs) with several metal ions [1–7]. Their
structures with various dimensionalities can control the coordina-
tion modes and the pore sizes. Recently, coordination polymers with
flexible multicarboxylates, such as 1,4-cyclohexanedicarboxylate
(1,4-chdc) [8–22], 1,3-cyclohexanedicarboxylate (1,3-chdc) [23],
1,2,3,4,5,6-cyclohexanehexacarboxylate (chhc) [24–27], and cyclo-
hexane-1,2,4,5-tetracarboxylate (cht) [28], which can control con-
formation and configuration conversion in coordination networks,
have been synthesized and intensively studied [29]. Compare to me-
tal-(1,4-chdc) complexes, few metal complexes with 1,2-cyclohex-
anedicarboxylate (1,2-chdc) have been reported in the literature
[30–35].
While there are a few reports that different assistant ligands can
have profound effects on coordination geometry [36,6,37–42],
however, such an effect was only once reported in the system of
zinc nitrate with 1,2-chdc that showed six novel ZnII coordination
polymers (0-D, 1-D, 2-D to 3-D) constructed from 1,2-chdc and
various bipyridyl ligands [43]. Significantly, the use of assistant
ligands influenced coordination modes of carboxylates: two
carboxylates coordinate to ZnII ions in chelating, bridging, and
tant ligands. These results suggested that further study is neces-
sary to see which factor (the assistant ligand vs the metal ion)
influences the whole structure including coordination modes of
carboxylates.
For a further systematic investigation of the relationship be-
tween the metal ions and the nature of the different assistant li-
gands in the system with M-(1,2-chdc) unit, therefore, we have
employed CdII-(1,2-chdc) unit with three different assistant li-
gands, 2,20-bipyridine (2,20-bpy), 4,40-bipyridine (4,40-bpy), 1,2-
bis(4-pyridyl)ethene (bpe). Depending on the assistant ligands,
the dimensionality of CdII-(1,2-chdc) complexes has also been var-
ied as shown in the ZnII-(1,2-chdc) system.
We report here the syntheses, structures, thermal stabilities,
and photoluminescence of four novel CdII coordination polymers
(1-D, 2-D to 3-D) constructed from 1,2-chdc and three different
bipyridyl ligands.
2. Experimental
2.1. Materials
2,20-Bipyridine, cis-1,2-cyclohexanedicarboxylic acid, 1,2-bis(4-
pyridyl)ethene, 4,40-bipyridine, acetonitrile, acetone, methanol,
para-substituted phenyl acetate, para-substituted phenyl
benzoate, methyl acetate, methyl benzoate, ammonium hydroxide,
⇑
Corresponding authors. Tel.: +82 2 970 6693; fax: +82 2 973 9149 (C. Kim), tel.:
+82 2 3277 3589; fax: +82 2 3277 3419 (S.-J. Kim).
E-mail addresses: chealkim@snut.ac.kr (C. Kim), sjkim@ewha.ac.kr (S.-J. Kim).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.03.046

336
E.Y. Kim et al. / Journal of Molecular Structure 994 (2011) 335–342
and Cd(NO3)2ꢀ6H2O were purchased from Aldrich and were used as
was solved and refined using SHEXTL V6.12 [44]. All hydrogen
atoms were placed in the calculated positions. The crystallographic
data for compounds 1–3 are listed in Table 1. Structural informa-
tion was deposited at the Cambridge Crystallographic Data Center
(CCDC Reference Numbers 790089, 790090, 790091, and 812938
for 1, 2, 3A, and 3B respectively).
received.
2.2. Instrumentation
Elemental analysis for carbon, nitrogen, and hydrogen was car-
ried out by using a vario MACRO (Elemental Analysensysteme, Ger-
many) in the Laboratory Center of Seoul National University of
Science and Technology, Korea. IR spectra were measured on a
BIO RAD FTS 135 spectrometer as KBr pellets. Thermogravimetric
analyses (TGA) were carried out on a Shimadzu TA50 integration
thermal analyzer. The emission/excitation spectra were recorded
on a Perkin Elmer LS45 fluorescence spectrometer.
3. Results and discussion
3.1. Syntheses and general characterization
Complexes 1–3 were obtained as colorless crystalline materials
by the reaction of 1,2-H2chdc and cadmium(II) nitrate with various
bipyridyls in aqueous medium in a molar ratio of 1:1:2 except for 2
with the ratio of 2:1:2, respectively. In addition, they are air stable,
and can retain their crystalline integrity at ambient conditions for a
considerable length of time. It should be noted that 1,2-chdcH2
used in the experiments is cis-conformer, and the 1,2-chdc dianion
in all four compounds possesses only e,a-cis conformation. The
infrared spectra of 1–3 were fully consistent with their formula-
tions. Asymmetric and symmetric C@O stretching modes of the li-
gated benzoate moieties were evidenced by very strong, slightly
broadened bands at ꢃ1600 cmꢁ1 and ꢃ1400 cmꢁ1 [45–47]. The ab-
sence of any bands in the area of ꢃ1710 cmꢁ1 indicates full depro-
tonation of all carboxylate groups in 1–3 [45–47], which is
consistent with the results of the X-ray analysis. Scheme 1 shows
all four structures constructed by CdII-(e,a-cis-1,2-chdc) and differ-
ent assistant bipyridyl ligands.
2.3. 1-D chain of [Cd(H2O)(1,2-chdc)(2,20-bpy)]n (1)
14.06 mg (0.08 mmol) of 1,2-cyclohexanedicarboxylic acid,
10.74 lL (0.08 mmol) of NH4OH and 24.28 mg (0.08 mmol) of
Cd(NO3)2ꢀ6H2O were dissolved in 4 mL H2O and carefully layered
by 4 mL acetone solution of 2,20-bipyridine (25.24 mg, 0.16 mmol).
Suitable crystals of compound 1 for X-ray analysis were obtained
in 2 weeks. The yields were 10.98 mg (30.1%). Purity of bulk sample
of 1 was checked by powder XRD (see Fig. S1 in Supporting informa-
tion). Anal. Calcd. for C18H20CdN2O5 (456.76), 1: C, 47.33; H, 4.42; N,
6.13. Found: C, 47.57; H, 4.36; N, 5.81%. IR (KBr):
m
(cmꢁ1) =
3417(brs), 3066(m), 2973(m), 2900(m), 2850(m), 1680(w),
1580(s), 1536(s), 1477(m), 1440(m), 1407(s), 1291(m), 1157(m),
1018(m), 928(w), 843(w), 780(s), 737(w), 652(w), 581(w), 415(w).
2.4. 2-D sheet of [Cd(1,2-chdc)(bpe)]n (2)
3.2. Structure description of 1, 1-D
14.06 mg (0.08 mmol) of 1,2-cyclohexanedicarboxylic acid,
10.74 lL (0.08 mmol) of NH4OH and 24.28 mg (0.08 mmol) of
Asymmetric unit contains a CdII ion, an e,a-cis-1,2-chdc, a water
ligand, and a 2,20-bpy ligand, and symmetry operations (ꢁx + 3/2,
y + 1/2, ꢁz + 1/4) and (ꢁx + 3/2, y ꢁ 1/2, ꢁz + 1/4) produce a one-
dimensional chain 1 (Fig. 1). The CdII ion is seven-coordinated with
four O atoms from two chelating 1,2-chdc, two N atoms from a
bidentate 2,20-bpy, and an O atom from a water. CdII ions are
bridged by e,a-cis-1,2-chdc ligands to form a one-dimensional
chain (Fig. 1). The coordination mode for two carboxylates in 1,2-
Cd(NO3)2ꢀ6H2O were dissolved in 4 mL H2O and carefully layered
by 4 mL acetonitrile solution of 1,2-bis(4-pyridyl)ethylene
(30.06 mg, 0.16 mmol). Suitable crystals of compound 2 for X-ray
analysis were obtained in 3 weeks. The yields were 26.24 mg
(70.6%). Purity of bulk sample of 2 was checked by powder XRD
(see Fig. S2 in Supporting information). Anal. Calcd. for
C
20H20CdN2O4 (464.78) 2: C, 51.68; H, 4.35; N, 6.03. Found: C,
51.54; H, 4.12; N, 6.47%. IR (KBr):
m
(cmꢁ1) = 3058(m), 2927(m),
chdc is the asymmetric chelating (g1 1) [30–35,48]. The intra-
:g
1607(s), 1548(s), 1427(s), 1342(m), 1308(m), 1014(m), 967(m),
892(w), 840(s), 827(s), 764(m), 623(w), 551(s).
molecular hydrogen bond between water hydrogen atom and next
carboxylate oxygen atom in a chain makes the one-dimensional
chain structure stronger (green dotted lines in Fig. 1). The
CdAO1,2-chdc distances of asymmetric chelating carboxylates are
2.259(4), 2.283(4) Å and 2.537(5), 2.620(4) Å. The CdAOwater dis-
tance is 2.518(5) Å, and the CdAN bond distances are 2.322(4)
and 2.372(4) Å (Table S1). The Cdꢀ ꢀ ꢀCd distance is 6.197(1) Å.
2.5. 3-D of [Cd2(NO3)2(1,2-chdc)(4,40-bpy)2]n (3A) and 1-D of [[Cd(H2
O)(1,2-chdc)(4,40-bpy)2]ꢀ3(H2O)]n (3B)
14.06 mg (0.08 mmol) of 1,2-cyclohexanedicarboxylic acid,
10.74 lL (0.08 mmol) of NH4OH and 24.28 mg (0.08 mmol) of
Cd(NO3)2ꢀ6H2O were dissolved in 4 mL H2O and carefully layered
by 4 mL acetone solution of 4,40-dipyridine (25.24 mg, 0.16 mmol).
Two kinds of crystals 3A (small block, 0.08 ꢂ 0.08 ꢂ 0.05) and 3B
(big block, 0.20 ꢂ 0.20 ꢂ 0.08) for X-ray analysis were obtained in
3.3. Structure description of 2, 2-D
Asymmetric unit contains a CdII ion, an e,a-cis-1,2-chdc and a
bpe ligand, and symmetry operations (ꢁx + 1, ꢁy + 1, ꢁz), (ꢁx + 2,
ꢁy + 1, ꢁz), (x, y ꢁ 1, z + 1), and (x, y + 1, z ꢁ 1) produce a two-
dimensional sheet 2 (Fig. 2). Two carboxylates of e,a-cis-1,2-chdc
ligands bridge CdII ions to form one-dimensional chains, and bpe
ligands bridge those chains to form a two-dimensional sheet
(Fig. 2). Two carboxylates in 1,2-chdc show two different coordina-
2 weeks. IR (KBr) for the mixture of 3A and 3B:
m
(cmꢁ1) =
3453(brs), 3243(brs), 2970(w), 2923(s), 2839(m), 1664(s),
1599(w), 1558(s), 1446(w), 1400(s), 1310(w), 1258(w), 1218(s),
1040(m), 1010(m), 990(w), 930(w), 894(w), 812(s), 666(w),
610(s), 505(s).
2.6. X-ray crystallography
tion modes: the chelating (g1 1) and the bridging (g1 g1
:g : :l2). The
coordination geometry of CdII ion is distorted octahedral con-
structed by two O atoms from a chelating cis-1,2-chdc, two O
atoms from two bridging cis-1,2-chdc, and two N atoms from
two bpe ligands. The CdAO1,2-chdc bond distances range from
2.2394(18) to 2.4455(19) Å, and the CdAN bond distances are
2.342(2) and 2.363(2) Å (Table S1). The Cdꢀ ꢀ ꢀCd distances in a
The X-ray diffraction data for all four compounds were collected
on a Bruker SMART APX diffractometer equipped with a mono-
chromater in the Mo Ka (k = 0.71073 Å) incident beam. Each crys-
tal was mounted on a glass fiber. The CCD data were integrated and
scaled using the Bruker-SAINT software package, and the structure

E.Y. Kim et al. / Journal of Molecular Structure 994 (2011) 335–342
337
Table 1
Crystallographic data for compounds 1–3.
1
2
3A
3B
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Space group
a (Å)
C
18H20CdN2O5
C20H20CdN2O4
464.78
293(2)
C14H13CdN3O5
415.67
170(2)
0.71073
C2/c
20.835(4)
10.177(2)
16.014(3)
90.00
106.12(3)
90.00
C28H32CdN4O8
664.98
293(2)
0.71073
C2/c
26.740(4)
10.4638(15)
21.003(3)
90.00
97.270(2)
90.00
456.76
293(2)
0.71073
P41212
10.3296(5)
10.3296(5)
90.00
90.00
90.00
0.71073
P ꢁ 1
7.7115(6)
b (Å)
c (Å)
9.7515(7)
12.6997(10)
76.4650(10)
76.8020(10)
88.1130(10)
903.74(12)
2
a
(°)
b (°)
c
(°)
91.366(2)
3466.8(4)
8
Volume (Å3)
3262.1(11)
8
5829.4(15)
8
Z
Density (calc.) (Mg/m3)
Absorption coeff. (mmꢁ1
Crystal size (mm3)
Reflections collected
Independent reflections
1.750
1.293
1.708
1.237
1.693
1.366
1.515
0.804
)
0.25 ꢂ 0.10 ꢂ 0.10
0.30 ꢂ 0.10 ꢂ 0.10
0.08 ꢂ 0.08 ꢂ 0.05
0.20 ꢂ 0.20 ꢂ 0.08
19,284
5046
8972
15,785
4169 [R(int) = 0.0812]
4169/2/242
0.944
3469 [R(int) = 0.0307]
3469/0/244
1.015
3212 [R(int) = 0.0630]
3212/5/201
0.940
5705 [R(int) = 0.0827]
5705/6/388
0.877
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0444, wR2 = 0.1136
R1 = 0.0567, wR2 = 0.1217
0.721 and ꢁ0.821
R1 = 0.0267, wR2 = 0.0668
R1 = 0.0290, wR2 = 0.0674
0.430 and ꢁ0.891
R1 = 0.0379, wR2 = 0.0890
R1 = 0.0569, wR2 = 0.0919
1.808 and ꢁ0.833
R1 = 0.0318, wR2 = 0.0738
R1 = 0.0489, wR2 = 0.0770
0.478 and ꢁ0.588
Largest diff. peak and hole (e Åꢁ3
)
Scheme 1. Structures from CdII-(e,a-cis-1,2-chdc) with assistant bipyridyl ligands.
one-dimensional chain are 3.930(2) and 5.737(3), and the Cdꢀ ꢀ ꢀCd
y ꢁ 1/2, z), (ꢁx, ꢁy, ꢁz + 2), (x + 1/2, y + 1/2, z), and (ꢁx, y, ꢁz + 3/
2) produce a three-dimensional structure 3A (Fig. 3a). The cyclo-
hexyl group is disordered as shown in Fig. 3b. Two Cd(NO3)+ are
bridged by two e,a-cis-1,2-chdc to form dinuclear units, and these
dinuclear units are connected by 4,40-bpy ligands to form a three-
dimensional structure 3A (Fig. 3). Assuming the cadmium dimers
act as nodes, the complete Schläfli symbol of the 4-connected unin-
distance between chains is 14.086(9) Å.
3.4. Structure description of 3A, 3-D
Asymmetric unit contains a CdII ion, half of e,a-cis-1,2-chdc, a
4,40-bpy ligand, and a nitrate, and symmetry operations (x ꢁ 1/2,

338
E.Y. Kim et al. / Journal of Molecular Structure 994 (2011) 335–342
2.381(3) Å, and the CdAOnitrate distances are 2.420(4) and
2.455(4) Å. The CdAN bond distances are 2.268(4) and 2.280(4) Å
(Table S1). The Cdꢀ ꢀ ꢀCd distance in a dinuclear unit is 3.70(5) Å.
3.5. Structure description of 3B, 1-D
Asymmetric unit contains a CdII ion, an e,a-cis-1,2-chdc, two
4,40-bpy ligands, a water ligand, and three water solvent molecules,
and symmetry operations (ꢁx + 1/2, y + 1/2, ꢁz + 1/2) and (ꢁx + 1/
2, y ꢁ 1/2, ꢁz + 1/2) produce a one-dimensional structure 3B
(Fig. 4a). The e,a-cis-1,2-chdc ligands bridge CdII to form a one-
dimensional structure, and the coordination mode for carboxylates
Fig. 1. Structure of 1-D chain of [Cd(H2O)(1,2-chdc)(2,20-bpy)] 1. All hydrogen
atoms were omitted for clarity. Intra-molecular hydrogen bonds are shown in green
lines (OwaterAHꢀ ꢀ ꢀOcarboxylate 2.134 Å (141.54°)). (For interpretation of the references
to color in this figure legend, the reader is referred to the web version of this
article.)
in 1,2-chdc is the chelating (g1 g1). The 4,40-bpy ligands act as a
:
monodentate dangling ligand in 3B while they do as a bridging li-
gand in 3A. The CdII is seven-coordinated by four O atoms from two
chelating cis-1,2-chdc ligands, two N atoms from two 4,40-bpy li-
gands, and an O atom from a water ligand to form a distorted pen-
tagonal bipyramid. Inter- and intra-molecular OAHꢀ ꢀ ꢀO hydrogen
bonding interactions provide a two-dimensional sheet (Fig. 4b,
see Table S2). The CdAO1,2-chdc bond distances are 2.37585(18)
and 2.4626(17) Å, and the CdAOwater distance is 2.330(2) Å. The
CdAN bond distances are 2.361(2) and 2.389(2) Å (Table S1). The
Cdꢀ ꢀ ꢀCd distance is 6.756(3) Å.
odal net was calculated as 65ꢀ8 network topology based on the TO-
POS analysis. The coordination mode of carboxylates is the chelat-
ing/bridging (g2 g1 2). The CdII ion is seven-coordinated by two O
: :l
atoms from one e,a-cis-1,2-chdc, an O atom from the other e,a-cis-
1,2-chdc, two O atoms from a nitrate, and two N atoms from two
4,40-bpy to form a distorted pentagonal bipyramid in which five
O atoms are in the equatorial positions and two N atoms are in
axial positions. The CdAO1,2-chdc bond distances are 2.358(3) and
Fig. 2. Structure of 2-D sheet of [Cd(1,2-chdc)(bpe)]n 2. All hydrogen atoms were omitted for clarity.

E.Y. Kim et al. / Journal of Molecular Structure 994 (2011) 335–342
339
Fig. 3. (a) 3-D structure of [Cd2(NO3)2(1,2-chdc)(4,40-bpy)2]n 3A. (b) The dinuclear unit of 3A with disordered 1,2-chdc in green color. All hydrogen atoms were omitted for
clarity.
Like ZnII-(a,e-cis-1,2-chdc) system, we have also systematically
investigated CdII complexes containing particularly 1,2-chdc ligand
with different assistant bipyridyl ligands, 2,20-bpy, bpe, and 4,40-
bpy. According to the change of assistant bipyridyl ligands, CdII-
(e,a-cis-1,2-chdc) provides 1-D, 2-D and 3-D compounds as shown
in Scheme 1. Only one conformer (a,e-cis) has also been observed in
1,2-chdc ligands of all four CdII compounds as shown in ZnII com-
pounds. The observed coordination modes of two carboxylates in
CdII-(a,e-cis-1,2-chdc) complexes are shown in Scheme 2. For 1,
two carboxylates coordinate to CdII ions, and both carboxylates
and for 3B, they show the chelating (g1 1) modes. From the pre-
:g
vious work of ZnII-(a,e-cis-1,2-chdc), it was noted that carboxylates
of a,e-cis-1,2-chdc with chelating, bridging, and monodentate coor-
dination modes have been observed in all six compounds, but for
this CdII system, their chelating/bridging (g2
:
g1
:
:
l
)
2) mode has also
and bridging
2) mode of carboxyl-
been observed as well as chelating
(
g1 g1
(
g1
:
g1
:l
2). The chelating/bridging (g2
:
g1
:l
ates has been observed in recent literatures [25–31], and M-(1,2-
chdc) system without assistant ligands can provide favorably me-
tal–oxygen–metal networks [25–35]. In the previous work of
ZnII-(1,2-chdc) system, it was suggested that construction of me-
tal–oxygen–metal linkages might be prevented if assistant ligands
were employed to M-(1,2-chdc) system, and that they can provide
various structures according to the change of the assistant ligands
are in chelating (g1
dinate to CdII ions: one carboxylate is in the chelating (g1
mode and the other one is in the bridging (g1
2) mode. For
3A, carboxylates show the chelating/bridging (g2
2) modes,
:g
1) modes. For 2, two carboxylates also coor-
:
g1
)
:
g1
:l
:
g1
:l

340
E.Y. Kim et al. / Journal of Molecular Structure 994 (2011) 335–342
Fig. 4. (a) 1-D structure of [[Cd(H2O)(1,2-chdc)(4,40-bpy)2]ꢀ3(H2O)]n 3B. All hydrogen atoms were omitted for clarity. (b) Two-dimensional sheet through hydrogen bonds in
3B. All pyridyl and cyclohexyl hydrogen atoms were omitted for clarity. The hydrogen bonds are shown in the green dotted lines. (For interpretation of the references to color
in this figure legend, the reader is referred to the web version of this article.)
Scheme 2. Coordination modes in CdII-(a,e-cis-1,2-chdc) complexes.
[43]. Also, it was showed that the use of assistant ligands may influ-
ence coordination modes of carboxylates in the previous ZnII-(1,2-
3.6. Photoluminescence property
chdc) system. Carboxylates in chelating/bridging
(
g2
:
g1
:l2
)
We have examined the emission spectra of CdII complexes 1 and
2, since coordination polymers containing cadmium and zinc
exhibited excellent photoluminescent properties [49,50]. The
emission spectra of CdII complexes 1 and 2, together with those
of the ligands 2,20-bpy, bpe, and cis-1,2-chdcH2, were measured
in the solid state at room temperature (see Fig. 5). Emission of
modes provide dinuclear Cd2 units which could not be
observed in the ZnII-(1,2-chdc) system. From these results, it is
noted that the metal ion as well as the assistant ligand can
influence both the whole structure and coordination modes of
carboxylates.

E.Y. Kim et al. / Journal of Molecular Structure 994 (2011) 335–342
341
1000
800
600
400
200
0
280
330
380
430
480
530
580
630
Wavelength (nm)
Fig. 5. Emission spectra of complexes 1, 2, and ligands (2,20-bpy, bpe, and cis-1,2-chdc) at room temperature.
compound 1 was observed at 348 nm (kex = 267 nm), while rela-
and two carboxylates coordinate to CdII ions in chelating (g1
:g
1),
tively weak luminescence was observed at 516 nm (kex = 441 nm)
for 2 under the same experimental conditions. Such emission of
complex 2 can be tentatively assigned to the intraligand transition
of bpe ligand, since the similar emissions were observed for the li-
gand (511 nm for bpe (kex = 413 nm)) [51–53]. The emission band
of complex 1 is blue-shifted compared to the corresponding li-
gands (390 nm for 2,20-bpy (kex = 340 nm) or 403 nm for cis-1,2-
chdc (kex = 263 nm)). In addition, it is noteworthy that compound
1 showed an intense emission compared with that of compound
2 at room temperature, which may be attributed to effective in-
crease of the rigidity of the complex and reduces the loss of energy
by radiationless decay. This suggests that 1 may be a good candi-
date for a potential hybrid inorganic–organic photoactive material
[54].
bridging (g1 2), and chelating/bridging (g2
:
g1
:l
: :l
g1
2) modes.
This study indicates that the structures and dimensionalities of
CdII-(a,e-cis-1,2-chdc) compounds could be controlled by changing
of assistant bipyridyl ligands. Moreover, the present CdII and the
previous ZnII systems suggest that both assistant ligands and metal
ions could influence the whole structures and coordination modes
of carboxylates. Photoluminescence study suggested that the pho-
toluminescence property of the CdII complexes could be tuned by
the change of the assistant ligands, and that they may be good can-
didates for luminescent materials.
Acknowledgements
Financial support from the Korean Science & Engineering
Foundation (R01-2008-000-20704-0 and 2009-0074066), the
Converging Research Center Program through the National
Research Foundation of Korea (NRF) funded by the Ministry of
Education, Science and Technology (2009-0082832), and the SRC
program of the Korea Science and Engineering Foundation (KOSEF)
through the Center for Intelligent Nano-Bio Materials at Ewha
Womans University (Grant R11-2005-008-00000-0) is gratefully
acknowledged.
3.7. Thermogravimetric analysis
To study the thermal stabilities of these complexes, thermal
gravimetric analysis (TGA) of compounds 1 and 2 was performed
(see Supporting information: Figs. S3 and S4). Compound 1 first
lost its coordinated one OHꢁ between 131 and 237 °C; the ob-
served weight loss of 3.5% was consistent with that calculated
(3.9%). After this, the 1-D framework was stable up to 237 °C and
then began to decompose upon further heating. The second grad-
ual weight loss of 31.1% in the temperature range of 237–296 °C
corresponds to the loss of a coordinated 2,20-bpy ligand (calcd.
34.2%). The third weight loss of 40.8% from 336 to 434 °C may be
attributed to the loss of one coordinated cis-1,2-chdc ligand (calcd.
37.3%). The TGA curve of compound 2 showed that it underwent a
rapid and significant weight loss of 38.0% in the temperature range
of 225–378 °C, which corresponds to the loss of one bpe ligand
(calcd. 39.2%). The second gradual weight loss of 33.2% from 378
to 425 °C may be attributed to the loss of coordinated cis-1,2-chdc
ligand (calcd 33.2%). The residue started to decompose completely
to CdO upon further heating.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2011.03.046.
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