Four new cadmium(II) homophthalate diimine complexes: Syntheses, structures and fluorescence

Article abstract of DOI:10.1016/j.poly.2005.08.042

Four new complexes of homophthalate (hpht), [Cd(hpht)(phen)]_n (1), [Cd(hpht)(2,2′-bpy)]_n (2), [Cd(hpht)(2,2′-bpy) (H₂O)]_n ? 2nH₂O (3), [Cd(hpht)(4,4′- bpy)]_n ? nH₂O (4), have been solvothermally synthesized and characterized. Both 1 and 2 are 1-D double-chains which are further extended to 2-D layer structure by the π-π interaction of phen (for 1) and 2,2′-bpy (for 2). Complex 3 is linear chain which is stacked to 3-D supramolecular network though the π-π interaction and hydrogen bonding. Complex 4 features a 2-D network formed by the linkages of bench-like chains though 4,4′-bpy. Both 1 and 2 exhibit intense blue fluorescence emission and 3 produces a green fluorescence, while 4 features a unique and very strong red fluorescence. Complexes 1-4 may be potential candidates for photoactive materials.

Full text of DOI:10.1016/j.poly.2005.08.042

Polyhedron 25 (2006) 1239–1246
www.elsevier.com/locate/poly
Four new cadmium(II) homophthalate diimine complexes:
Syntheses, structures and fluorescence
*
Jin-Run He, Yu-Ling Wang, Wen-Hua Bi, Yan-Qin Wang, Rong Cao
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Science,
Fujian, Fuzhou 350002, China
Received 15 August 2005; accepted 30 August 2005
Available online 7 October 2005
Abstract
Four new complexes of homophthalate (hpht), [Cd(hpht)(phen)]n (1), [Cd(hpht)(2,20-bpy)]n (2), [Cd(hpht)(2,20-bpy)(H2O)]n Æ 2nH2O
(3), [Cd(hpht)(4,40-bpy)]n Æ nH2O (4), have been solvothermally synthesized and characterized. Both 1 and 2 are 1-D double-chains which
are further extended to 2-D layer structure by the p–p interaction of phen (for 1) and 2,20-bpy (for 2). Complex 3 is linear chain which is
stacked to 3-D supramolecular network though the p–p interaction and hydrogen bonding. Complex 4 features a 2-D network formed by
the linkages of bench-like chains though 4,40-bpy. Both 1 and 2 exhibit intense blue fluorescence emission and 3 produces a green fluo-
rescence, while 4 features a unique and very strong red fluorescence. Complexes 1–4 may be potential candidates for photoactive
materials.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Homophthalate; Solvothermal synthesis; Crystal structure; Fluorescence
1. Introduction
cation, and to investigate the factors influencing the coor-
dination mode of the ligands and control the final
structure of the complexes. We hope to find out useful
strategy to manipulate the design and syntheses of com-
plexes of the unsymmetrical and flexible ligands.
Recently, the design and synthesis of inorganic–organic
hybrid coordination polymeric frameworks has been a field
of rapid growth due to their potential applications in many
areas [1]. In this field, benzene carboxylic acids have been
widely used, because their versatile coordination modes
can construct a great deal of interesting frameworks with
various topology and potential applications [2]. However,
many unsymmetrical and flexible benzene carboxylic acids
such as homophthalic acid have rarely been used, and the
study on the structures constructed from these ligands re-
mains undeveloped [3]. This is probably because that the
low symmetry and the flexibility of these ligands make it
difficult to forecast the final structure [4]. Our aim is to
use such ligands to construct metal–organic complexes
with interesting topology or properties for potential appli-
Compared with phthalic acid, unsymmetrical homoph-
thalic acid (H2hpht) has a relative flexible ethylic carboxyl-
ate, which may be not co-planar with benzene. The
flexibility makes H2hpht has various conformations as well
as coordination modes. On the other hand, the flexibility
makes it more difficult to forecast and control the final
structure. To our knowledge, there are only three com-
plexes constructed from H2hpht reported [5]. The three
complexes have been synthesized by conventional solution
method, and all of them are 0-D discrete dimers, in which
phth2ꢀ anions bridge two metal ions. Our study is to ex-
plore the solvothermal synthesis, and to construct some
complexes with new 1-D, 2-D and 3-D topology. We adopt
1,10-phenanthroline(phen), 2,20-bipyridine(2,20-bpy), and
4,40-bipyridine(4,40-bpy) as auxiliary ligands, hoping that
these diimine auxiliary ligands can not only adjust the final
*
Corresponding author. Tel.: +86 591 83796710; fax: +86 591
83714946.
E-mail address: rcao@ms.fjirsm.ac.cn (R. Cao).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.08.042

1240
J.-R. He et al. / Polyhedron 25 (2006) 1239–1246
structures but also make the complexes have particular
characters [6]. Herein, we report the syntheses and charac-
terizations of four new complexes, [Cd(hpht)(phen)]n (1),
[Cd(hpht)(2,20-bpy)]n (2), [Cd(hpht)(2,20-bpy)(H2O)]n Æ
2nH2O (3), and [Cd(hpht)(4,40-bpy)]n Æ nH2O (4).
25 mL Teflon-lined reactor and heated to 160 ꢁC for 3
days, and then slowly cooled to room temperature. Color-
less prism crystals of 1 were collected and washed with dis-
tilled water (yield: 67%). Complex 1 was also obtained by
using Cd(NO3)2 Æ 4H2O (pH 4.7, 58% yield), CdCl2 (pH
5.6, 43% yield), or CdSO4 (pH 5.4, 47% yield). Anal. Calc.
for 1: H, 3.00; C, 53.58; N, 5.95. Found: H, 3.08; C, 53.47;
N, 5.98%. IR(KBr) 3067m, 3011m, 2992m, 1575vs, 1548vs,
1509vs, 1389vs, 1295s, 1146m, 1097m, 844vs, 828m, 774m,
731vs, 677vs.
2. Experimental
2.1. Materials and analyses
All chemicals are used as purchased without further
purification. Thermogravimetric analyses were carried out
with a NETZSCH STA 449C unit at a heating rate of
15 ꢁC minꢀ1 under nitrogen. IR spectra were recorded on
a Magna 750 FT-IR spectrophotometer as KBr pallets.
Elemental analyses were carried out on an Elementar Vario
EL III analyzer. Fluorescence spectroscopy was performed
on an Edinburgh Analytical instrument FLS920.
2.2.2. [Cd(hpht)(2,20-bpy)]n (2)
The synthetic procedure of 2 is essentially the same as
that for 1, while Cd(NO3)2 Æ 4H2O and 2,20-bpy were used,
and the pH was adjusted to about 5.3 by diluent NaOH
aqueous solution. Colorless prism crystals of 2 were col-
lected and washed with distilled water (yield: 76%). Anal.
Calc. for 2: H, 3.16; C, 51.08; N, 6.27. Found: H, 3.50;
C, 50.89; N, 6.32%. IR(KBr) 3112m, 3077m, 3062m,
3027m, 2956m, 1590vs, 1544vs, 1485s, 1443vs, 1415vs,
1380vs, 1287s, 1061m, 1018s, 855m, 832m, 758vs, 723vs,
688s, 645m.
2.2. Syntheses
2.2.1. [Cd(phen)(hpht)]n (1)
H2hpht (0.055 g, 0.3 mmol), phen (0.060 g, 0.3 mmol),
and Cd(CH3COO)2 Æ 2H2O (0.12 g, 0.45 mmol) were put
in a mixed solution of 8 mL distilled H2O and 2 mL etha-
nol, and the pH was adjusted to about 5.6 by diluent
HCl aqueous solution. Then, the mixture was sealed in
2.2.3. [Cd(hpht)(2,20-bpy)(H2O)]n Æ 2nH2O (3)
The synthetic procedure is the same as that for 2, and
the pH was adjusted to about 5.5 by diluent NaOH aque-
ous solution. Colorless prism crystals of 3 were collected
Table 1
Crystallographic data for complexes 1–4
1
2
3
4
Empirical formula
Formula weight
T (K)
C
470.74
173(2)
21H14CdN2O4
C19H14CdN2O4
446.72
173(2)
C19H18CdN2O7
498.75
173(2)
C19H16N2CdO5
464.74
173(2)
˚
Wavelength (A)
0.71073
monoclinic
P21/n
7.5827(9)
21.9042(19)
11.2062(17)
90
108.499(5)
90
1765.1(4)
4
0.71073
monoclinic
P21/c
7.5458(2)
22.3825(4)
10.2930(3)
90
103.088(1)
90
1693.27(7)
4
0.71073
triclinic
0.71073
monoclinic
P21/n
8.7140(9)
9.2743(9)
22.003(2)
90
92.443(6)
90
1776.6(3)
4
Crystal system
Space group
ꢀ
P1
˚
a (A)
8.7507(18)
10.051(2)
11.637(3)
102.865(2)
102.865(2)
91.519(8)
943.6(4)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalc (Mg/mꢀ3
Absorption coefficient (mmꢀ1
F(000)
)
1.771
1.269
936
1.752
1.317
888
1.755
1.203
500
1.738
1.263
928
)
Crystal size (mm)
h Range for data collection (ꢁ)
0.40 · 0.20 · 0.04
3.02–27.48
0.52 · 0.46 · 0.12
1.82–25.00
0.40 · 0.20 · 0.10
3.06–27.48
0.80 · 0.40 · 0.30
3.21–27.47
Index ranges
ꢀ9 6 h 6 9,
ꢀ26 6 k 6 28,
ꢀ10 6 l 6 14
ꢀ8 6 h 6 8,
ꢀ26 6 k 6 23,
ꢀ12 6 l 6 4
ꢀ11 6 h 6 11,
ꢀ13 6 k 6 12,
ꢀ15 6 l 6 13
ꢀ11 6 h 6 9,
ꢀ12 6 k 6 12,
ꢀ28 6 l 6 28
Reflections collected
Refinement method
13489
4902
7729
12888
full-matrix
least-squares on F2
4024/253
1.006
0.0365
0.0942
0.876 and ꢀ0.609
full-matrix
least-squares on F2
2920/235
1.004
0.0449
0.2080
0.659 and ꢀ0.685
full-matrix
least-squares on F2
4245/274
1.001
0.0350
0.0946
1.033 and ꢀ0.835
full-matrix
least-squares on F2
4011/252
1.082
0.0339
0.0840
1.078 and ꢀ0.452
Data [I > 2r(I)]/parameters
Goodness-of-fit on F2
R1 indices (I > 2r(I))
wR2 indices (all data)
ꢀ3
˚
Largest difference peak and hole (e A
)

J.-R. He et al. / Polyhedron 25 (2006) 1239–1246
1241
and washed with distilled water (yield: 28%). Anal. Calc.
for 3: H, 3.64; C, 45.75; N, 5.62. Found: H, 3.76; C,
45.73; N, 5.60%. IR(KBr) 3433mb, 3106w, 3079w, 3057w,
3030w, 1587vs, 15g60vs, 1543vs, 1478m, 1440s, 1391vs,
1162w, 1020m, 841w, 754s, 737s.
cult to know what controls the coordination modes of
hpht2ꢀ ligand and the formation of the complexes. In this
work, we primarily studied the influence from auxiliary li-
gand, pH value, counter ion, and ratio of the starting
materials.
The employment of terminal ligands 2,20-bpy and 1,10-
phen prevents complexes 1–3 from being extended to 2D or
3D architectures, but yields infinite 1-D chain structures of
the three complexes. When bridging ligand 4,40-bpy was
used, 2D network 4 was obtained. Unfortunately, when
1,3-di(4-bpy)propane and piperazine were used as bridging
ligands, the experiments were failed. The pH value plays a
crucial role for the formation of the complexes. It is only
within the specific pH range that complexes 1–4 can be ob-
tained and different pH values lead to different yields of the
products. More interestingly, although the starting materi-
als and reaction conditions are quite similar, the structures
of 2 and 3 are significantly different, the slightly different of
the pH values of the reaction medium might play impor-
tant role, although detailed reaction mechanism still re-
mains unclear. We also studied the influence from
counter ions and the mole ratio of starting materials. The
results illustrate that the two factors only induce different
yields of the products and may be not the key factors for
the synthetic reactions.
2.2.4. [Cd(hpht)(4,40-bpy)]n Æ nH2O (4)
The synthetic procedure is the same as that for 2, while
4,40-bpy was used to replace 2,20-bpy, and the pH was ad-
justed to about 4.7 by diluent NaOH aqueous solution.
Colorless prism crystals of 4 were collected and washed
with distilled water (yield: 63%). Anal. Calc. for 4: H,
3.47; C, 49.10; N, 6.03. Found: H, 3.64; C, 48.84; N,
5.99%. IR(KBr) 3416s, 3093m, 3077m, 3042m, 3019m,
1684m, 1605vs, 1548vs, 1489s, 1419s, 1380vs, 1314m,
1217s, 1151m, 1037s, 816s, 738s, 676s, 641s.
2.3. X-ray data collection and structure determination
The intensity data of 1, 3, 4 were collected on a Rigaku
CCD diffractometer with graphite-monochromatized Mo
˚
Ka (k = 0.71073 A) radiation at 173 K, and the empirical
absorption corrections were performed using the CRYSTAL-
CLEAR program [7]. The intensity data of 2 were collected
on a SIEMENS SMART CCD diffractometer with graph-
˚
ite-monochromatized Mo Ka (k = 0.71073 A) radiation at
room temperature. The absorption correction was per-
formed using the SADABS program [8]. The structures were
solved by direct methods and refined on F2 by full-matrix
least-squares using the SHELXTL-97 program package [9].
All non-hydrogen atoms were refined anisotropically. The
organic hydrogen atoms were generated geometrically
3.2. Crystal structures
3.2.1. Crystal structures of complexes 1 and 2
The selected bond lengths and angles of complex 1 are
listed in Table 2. The asymmetric unit of 1 consists one
Cd(II) ion, a phen ligand and a hpht2ꢀ ligand. The Cd(II)
ion is six-coordinated by two nitrogen atoms from phen
and four oxygen atoms from three hpht2ꢀ ligands in a dis-
torted octahedron coordination geometry, as shown in
Fig. 1. The Cd–O(N) bond distances are in the range
˚
(C–H = 0.95 A). The H atoms of water were located from
E-map, but those of the lattice water (O7) in 3 could not be
located and were not taken into consideration, and the
hydrogen atoms of the water in complex 4 were refined
with AFIX 3 constraints on the O–H bonds. The crystallo-
graphic data for four complexes are listed in Table 1.
˚
˚
2.275–2.418 A, with an average value of 2.350 A. The
hpht2ꢀ ligand links three Cd(II) ions, in which the carbox-
ylate group chelates a Cd(II) ion and the ethylic carboxyl-
ate group bridges two Cd(II) ions (Scheme 1(a)). The two
Cd(II) ions connected by two bridging ethylic carboxylate
3. Results and discussion
˚
3.1. Syntheses
groups with interatomic distance of 4.023 A form the basic
building unit, Cd2(hpht)2(phen)2, of the whole structure.
Each two of such units are connected together through
sharing the hpht2ꢀ ligands to form the final double chain
structure. Two kinds of macrocyclic rings, one is 16-mem-
ber ring (A) and the other is 8-member ring (B), are ob-
served in the double chain (Fig. 2). Phen ligands are
As shown in Scheme 1, the coordination modes of
hpht2ꢀ ligand are different in the four complexes. Andrew
and co-workers have reported the second coordination
mode, while the other two modes are new. As known,
solvothermal reaction is complicated, and it is quite diffi-
a
c
O
Cd
b
O
Cd
Cd
Cd
O
Cd
Cd
C
C
C
C
C
C
O
O
O
Cd
Cd
O
O
O
O
O
O
Scheme 1. The coordination modes of hpht2ꢀ ligands in complexes 1–4.

1242
J.-R. He et al. / Polyhedron 25 (2006) 1239–1246
a
Table 2
Selected bond lengths and angles of complex 1
Cd(1)–O(4)#1
Cd(1)–O(3)#2
Cd(1)–O(2)
Cd(1)–N(2)
Cd(1)–N(1)
Cd(1)–O(1)
2.275(2)
2.282(2)
2.352(3)
2.382(3)
2.392(3)
2.418(3)
A
B
O(4)#1–Cd(1)–O(3)#2
O(4)#1–Cd(1)–O(2)
O(3)#2–Cd(1)–O(2)
O(4)#1–Cd(1)–N(2)
O(3)#2–Cd(1)–N(2)
O(2)–Cd(1)–N(2)
O(4)#1–Cd(1)–N(1)
N(1)–Cd(1)–O(1)
O(3)#2–Cd(1)–N(1)
O(2)–Cd(1)–N(1)
111.5(3)
90.0(3)
135.8(3)
b
78.1(3)
82.2(3)
141.4(3)
123.0(3)
94.0(4)
109.1(3)
87.6(3)
69.6(3)
128.2(3)
83.8(3)
N(2)–Cd(1)–N(1)
O(4)#1–Cd(1)–O(1)
O(3)#2–Cd(1)–O(1)
O(2)–Cd(1)–O(1)
Fig. 2. View of the chains in complexes 1 (a) and 2 (b). All the H atoms
53.6(3)
are omitted for clarity.
N(2)–Cd(1)–O(1)
153.5(3)
Symmetry transformations used to generate equivalent atoms: #1
ꢀx + 1,ꢀy,ꢀz; #2 x ꢀ 1, y, z.
alternately attached to the two sides of the double-chain,
and the vertical distance of the two adjacent phen planes
˚
at the same side is 6.897 A. The double-chains are further
˚
stacked by p–p interaction of phen (about 3.43 A) to form
the final layer structure, and the benzene planes of hpht2ꢀ
anions from two layers are meshed (Fig. 3). Since the pre-
viously reported homophthalate complexes are all 0-D
dimmers [5], to our knowledge, 1 is the first example of
homophthalate complexes with 1-D chain structure. The
selected bond lengths and angles of complex 2 are listed
in Table 3. The structure of 2 is quite similar to that of
1, only 2,20-bpy ligands replace the phen ligands. Detailed
discussion of the structure will not be made here.
3.2.2. Crystal structure of complex 3
The selected bond lengths and angles of complex 3 are
listed in Table 4. The asymmetric unit of 3 consists one
Fig. 3. View of the layer structure of complex 1 along a-axis. All the H
atoms are omitted for clarity.
a
b
Fig. 1. Coordination environments of Cd(II) ions in complexes 1 (a) and 2 (b). All the H atoms are omitted for clarity.

J.-R. He et al. / Polyhedron 25 (2006) 1239–1246
1243
two hpht2ꢀ ligands and one from coordinated water in a
highly distorted pentagonal bipyramid coordination geom-
etry, with O3A and N2 in the axial positions (Fig. 4). The
Table 3
Selected bond lengths and angles of complex 2
Cd(1)–O(4)#1
Cd(1)–N(1)
Cd(1)–N(2)
Cd(1)–O(3)#2
Cd(1)–O(1)
Cd(1)–O(2)
2.220(4)
2.362(4)
2.404(5)
2.261(4)
2.394(5)
2.411(4)
˚
Cd–O(N) bond distances are in the range 2.287–2.5l0 A
˚
with an average value of 2.373 A, slightly longer than those
in complex 2. Both carboxylate groups in hpht2ꢀ ligand
adopt chelating coordination mode (Scheme 1(b)). The
connections of Cd(II) ions and hpht2ꢀ ligands alternately
along the a-axis lead to the formation of 1-D linear chain,
as shown in Fig. 4. All the 2,20-bpy ligands arrange in the
same side of the chain and all the hpht2ꢀ ligands in the
other side, which is significantly different from 1 and 2.
There are four types of hydrogen bondings in 3. Two types
of them (O5–H20ꢁ ꢁ ꢁO1 and O5–H21ꢁ ꢁ ꢁO4) link linear
chains to form the double-chains, and the other two types
(O6–H22ꢁ ꢁ ꢁO2 and O6–H23ꢁ ꢁ ꢁO3) link the double-chains
to form the final 2-D network structure, as shown in
Fig. 5. The 2-D network is corrugated because different
double-chains are parallel but not in a plane. Different lay-
ers are stacked to produce the 3-D structure by the p–p
weak interaction of 2,20-bpy ligands along the a-axis, and
the vertical distance between two 2,2-bpy ligands is about
(4)#1–Cd(1)–O(3)#2
O(3)#2–Cd(1)–N(1)
O(3)#2–Cd(1)–O(1)
O(4)#1–Cd(1)–N(2)
N(1)–Cd(1)–N(2)
O(4)#1–Cd(1)–O(2)
N(1)–Cd(1)–O(2)
N(2)–Cd(1)–O(2)
O(4)#1–Cd(1)–N(1)
O(4)#1–Cd(1)–O(1)
N(1)–Cd(1)–O(1)
O(3)#2–Cd(1)–N(2)
O(1)–Cd(1)–N(2)
O(3)#2–Cd(1)–O(2)
O(1)–Cd(1)–O(2)
N(1)–Cd(1)–O(1)
108.0 (2)
107.2(2)
84.5(2)
80.4(2)
68.6(2)
91.1(2)
85.8(2)
136.5(2)
129.5(2)
120.5(2)
97.7(2)
84.2(2)
158.5(2)
138.2(2)
54.2(2)
94.0(4)
Symmetry transformations used to generate equivalent atoms: #1
ꢀ x + 1,ꢀy + 1,ꢀz; #2 x ꢀ 1, y, z.
˚
3.467 A. The free guest H2O molecules are hold in the
channels that formed by p–p interaction and hydrogen
bonding, as shown in Fig. 6.
Cd(II) ion, a 2,20-bpy ligand, a hpht2ꢀ ligand, a coordi-
nated water molecule and two guest water molecules.
Cd(II) ion is seven-coordinated by two nitrogen atoms
from 2,20-bpy and five oxygen atoms, four of which from
3.2.3. Crystal structure of complex 4
The selected bond lengths and angles of complex 4 are
listed in Table 5. The asymmetric unit of 4 consists a Cd(II)
ion, a hpht2ꢀ ligand, a 4,40-bpy ligand, and a guest water
molecule. Cd(II) ion is seven-coordinated by two nitrogen
atoms from two 4,40-bpy ligands and five oxygen atoms
from three hpht2ꢀ anions in a slightly distorted pentagonal
bipyramid coordination geometry (Fig. 7). Each hpht2ꢀ li-
gand links three Cd(II) ions, in which the methyl carboxyl-
ate group adopts bridging mode and the ethyl carboxylate
adopts bridging-chelating mode (Scheme 1(c)). Two Cd(II)
ions connected by two ethyl carboxylate groups with inter-
Table 4
Selected bond lengths and angles of complex 3
Cd(1)–O(5)
Cd(1)–O(3)#1
Cd(1)–N(1)
Cd(1)–O(2)
Cd(1)–N(2)
Cd(1)–O(1)
Cd(1)–O(4)#1
2.287(3)
2.305(3)
2.346(3)
2.437(2)
2.353(3)
2.376(2)
2.510(2)
O(5)–Cd(1)–O(3)#1
O(3)#1–Cd(1)–N(1)
O(3)#1–Cd(1)–N(2)
O(5)–Cd(1)–O(1)
N(1)–Cd(1)–O(1)
O(5)–Cd(1)–O(2)
89.6(2)
107.3(2)
173.8(9)
85.6(2)
121.9(9)
134.9(2)
81.6(9)
53.2(8)
53.78(8)
120.1(9)
127.0(8)
142.3(2)
90.5(2)
69.2(2)
101.5(9)
84.8(2)
82.7(9)
101.6(9)
79.1(2)
84.2(9)
150.5(9)
˚
atomic distance of 4.318 A, Cd2(hpht)2, form the basic
building unit of the whole structure. Each two of such units
are connected together through the bridging carboxylate
groups to form the 1-D chains, with benzene planes ar-
range on two sides of the chains reversely, which make
the chain like long bench, as shown in Fig. 8. The 4,40-
bpy ligands link 1-D chains to form the final 2-D layer
structure and to complete the coordination sphere of
N(1)–Cd(1)–O(2)
O(1)–Cd(1)–O(2)
O(3)#1–Cd(1)–O(4)#1
N(2)–Cd(1)–O(4)#1
O(2)–Cd(1)–O(4)#1
O(5)–Cd(1)–N(1)
O(5)–Cd(1)–N(2)
N(1)–Cd(1)–N(2)
O(3)#1–Cd(1)–O(1)
N(2)–Cd(1)–O(1)
O(3)#1–Cd(1)–O(2)
N(2)–Cd(1)–O(2)
O(5)–Cd(1)–O(4)# 1
N(1)–Cd(1)–O(4)# 1
O(1)–Cd(1)–O(4)# 1
Symmetry transformations used to generate equivalent atoms:
Fig. 4. View of the chain structure in complex 3. All the H atoms are
#1 x ꢀ 1,y, z.
omitted for clarity.

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J.-R. He et al. / Polyhedron 25 (2006) 1239–1246
Fig. 5. View of the corrugated 2-D network in complex 3. All the 2,20-bpy and free guest water molecules are omitted for clarity, as well as the H atoms
bonded to C atoms.
Table 5
Selected bond lengths and angles of complex 4
Cd(1)–N(2)# 1
Cd(1)–N(1)
Cd(1)–O(3)
Cd(1)–O(3)#3
Cd(1)–O(1)
Cd(1)–O(2)#2
Cd(1)–O(4)#3
2.289(2)
2.328(2)
2.428(3)
2.606(3)
2.328(2)
2.347(2)
2.462(3)
N(2)#1–Cd(1)–O(1)
O(1)–Cd(1)–N(1)
O(1)–Cd(1)–O(2)#2
N(2)#1–Cd(1)–O(3)
N(1)–Cd(1)–O(3)
93.7(8)
87.6(8)
85.8(8)
99.4(2)
86.6(2)
89.8(9)
87.7(9)
109.1 (2)
142.6(8)
131.3(8)
49.8(9)
173.9(9)
91.3(9)
82.9(8)
82.2(9)
164.3(2)
167.5(9)
82.1(9)
83.0(2)
99.5 (2)
61.9(2)
Fig. 6. View of the 3-D structure of complex 3 along a-axis. All the H
atoms bonded to C atoms are omitted for clarity.
N(2)#1–Cd(1)–O(4)#3
N(1)–Cd(1)–O(4)#3
O(3)–Cd(1)–O(4)#3
O(1)–Cd(1)–O(3)#3
O(2)#2–Cd(1)–O(3)#3
O(4)#3–Cd(1)–O(3)#3
N(2)#1–Cd(1)–N(1)
N(2)#1–Cd(1)–O(2)#2
N(1)–Cd(1)–O(2)#2
O(1)–Cd(1)–O(3)
O(2)#2–Cd(1)–O(3)
O(1)–Cd(1)–O(4)#3
O(2)#2–Cd(1)–O(4)#3
N(2)#1–Cd(1)–O(3)#3
N(1)–Cd(1)–O(3)#3
O(3)–Cd(1)–O(3)#3
Cd(II) ions, and the free water molecules are hold between
layers, as shown in Fig. 9.
3.3. Thermal gravimetric analysis
Thermal gravimetric analysis (TGA) diagram revealed
that 1 was stable up to 317 ꢁC, and then decomposed rap-
idly by the oxidation of the organic component. Complex 2
was stable up to 243 ꢁC, and then the structure collapsed
rapidly. For 3, the first weight loss of 11.07% from 81 to
294 ꢁC is attributed to the release of all water molecules
(Calc. 10.78%). We note that the crystallization guest water
is released at the same time as the coordinated water, sup-
porting the structural evidence of hydrogen bonding in 3.
Complex 4 loses 3.78% of total weight in a range of 120–
170 ꢁC, corresponding to the loss of the free guest water
(Calc. 3.87%), the framework is stable till 234 ꢁC and then
decomposed.
Symmetry transformations used to generate equivalent atoms: #1 x ꢀ 1/
2,ꢀy + 1/2, z ꢀ 1/2; #2 ꢀx + 1,ꢀy + 1,ꢀz; #3 ꢀx + 1,ꢀy,ꢀz.
that 1 exhibits an intense blue photoluminescence emission
at kmax = 406 nm and a very weak band at kmax = 524 nm
(kex = 350 nm). The emission of 1 probably can be assigned
to the intraligand fluorescent emission since very similar
emissions are also observed for free H2hpht (Fig. 10,
3.4. Fluorescence
k
ex = 274 nm) and phen ligands [10].
Complex 2 exhibits an intense blue emission band
The emission spectra of complexes 1–4 in the solid state
(kmax = 422, 498 nm, with a shoulder at 530 nm) from
at room temperature are shown in Fig. 11. It can be seen

J.-R. He et al. / Polyhedron 25 (2006) 1239–1246
1245
ex:370nm
ex:274nm
300
350
400
450
500
550
600
Wavelength(nm)
Fig. 10. Emission spectrum of homophthalic acid in the solid state.
Fig. 7. Coordination environment of Cd(II) ions in complex 4. All the H
4
atoms are omitted for clarity.
2
3
1
350
400
450
500
550
600
650
700
750
800
Fig. 8. View of the chain formed by Cd(II) ions and hpht2ꢀ ligands in
complex 4. All the H atoms are omitted for clarity.
Wavelength(nm)
Fig. 11. Emission spectrum of complexes 1–4 in the solid state.
375 to 650 nm on excitation at 310 nm (Fig. 11). The peak
at 422 nm can be assigned to the intraligand emission of
H2pht, since the free H2pht ligand exhibits intense emission
at kmax = 455 nm upon excitation at 370 nm (Fig. 10), and
the coordination of the ligand may lead to the blue-shift.
The peak at 498 nm may be attributed to the intraligand
emission from the 2,20-bpy ligand [11]. It is known that
the free 2,20-bpy molecule displays a weak luminescence
at ca. 535 nm. The enhancement and significant blue-shift
of the photoluminescence of the coordinated 2,20-bpy li-
gand compared to that of the free 2,20-bpy molecule may,
therefore, be attributed to the chelating of the 2,20-bpy li-
gand to the metal ion, which effectively increases the rigid-
ity of the ligand and reduces the loss of energy by
radiationless decay of the intraligand emission excited state
[12]. The shoulder emission at 530 nm may be assigned as
ligand-to-metal-charge-transfer (LMCT) [13].
Fig. 9. View of the layer structure of complex 4 along b-axis. All the H atoms are omitted for clarity.

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J.-R. He et al. / Polyhedron 25 (2006) 1239–1246
Complex 3 exhibits a broad green emission band
Province (E0520003), and the ‘‘one-hundred Talent’’ Pro-
ject from CAS.
(kmax = 459, 481 nm, with a shoulder at 603 nm) from
385 to 700 nm on excitation at 372 nm (Fig. 11). We noted
that the photoluminescence of 3 is similar to that of 2, and
the peaks can be assigned similarly. Compared with their
analogs, both the peak at 459 nm and the shoulder red-shift
and have lower intensity, which may be attributed to the
different coordination mode of the ligand and different
coordination environment of metal ions.
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5. Supplementary material
For the four complexes, full list of atomic coordinates,
isotropic thermal parameters, bond lengths and angles
are available from the authors on request. Crystallographic
data for the structural analyses have been deposited with
the Cambridge Crystallographic Data Center, CCDC
Nos. 278028–278031 for complexes 1–4, respectively. Cop-
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tallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; Fax: (internet.) +44 1223 336 033; e-mail:
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We thank the financial support from the National Nat-
ural Science Foundation of China (90206040, 20325106,
and 20333070), the Natural Science Foundation of Fujian