Structure modulation of metal-organic frameworks via reaction pH: Self-assembly of a new carboxylate containing ligand N-(3-carboxyphenyl)iminodiacetic acid with cadmium(II) and cobalt(II) salts

Article abstract of DOI:10.1016/j.poly.2007.11.029

Self-assembly of a new carboxylate containing ligand, N-(3-carboxyphenyl)iminodiacetic acid (H₃L), with Cd(II) and Co(II) salts under different reaction pH results in the formation of four new coordination polymers, namely [Cd(HL)(H₂O)] (1), [Co(HL)(H₂O)] (2), [Cd(HL)(H₂O)₄] (3) and [Cd₃(L)₂(H₂O)₉] · 7H₂O (4). Single crystal X-ray diffraction analysis indicates that 1 and 2 are isomorphous and isostructural with a 2D wave-like network structure, while 3 has a 1D zigzag chain structure. The complexes 1-3 were obtained at low pH (<7) which makes the ligands only partly deprotonated. However, complex 4, obtained at pH 7 with all the carboxylate groups deprotonated, exhibits a 2D network structure. The results suggest that the reaction pH is one of the key factors in the formation of the coordination architectures. In addition, the photoluminescence properties of the free ligand (H₃L) and complexes 1, 3 and 4 were studied in the solid state at room temperature. Moreover, the magnetic property of complex 2 was investigated.

Full text of DOI:10.1016/j.poly.2007.11.029

Available online at www.sciencedirect.com
Polyhedron 27 (2008) 812–820
www.elsevier.com/locate/poly
Structure modulation of metal–organic frameworks via
reaction pH: Self-assembly of a new carboxylate containing
ligand N-(3-carboxyphenyl)iminodiacetic acid with cadmium(II)
and cobalt(II) salts
Qian Chu a, Guang-Xiang Liu a, Taka-aki Okamura b, Yong-Qing Huang a,
a,
b
*
Wei-Yin Sun , Norikazu Ueyama
a State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, School of Chemistry and Chemical Engineering,
Nanjing University, Nanjing 210093, China
b Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
Received 19 July 2007; accepted 12 November 2007
Available online 2 January 2008
Abstract
Self-assembly of a new carboxylate containing ligand, N-(3-carboxyphenyl)iminodiacetic acid (H3L), with Cd(II) and Co(II) salts
under different reaction pH results in the formation of four new coordination polymers, namely [Cd(HL)(H2O)] (1), [Co(HL)(H2O)]
(2), [Cd(HL)(H2O)4] (3) and [Cd3(L)2(H2O)9] ꢀ 7H2O (4). Single crystal X-ray diffraction analysis indicates that 1 and 2 are isomorphous
and isostructural with a 2D wave-like network structure, while 3 has a 1D zigzag chain structure. The complexes 1–3 were obtained at
low pH (<7) which makes the ligands only partly deprotonated. However, complex 4, obtained at pH 7 with all the carboxylate groups
deprotonated, exhibits a 2D network structure. The results suggest that the reaction pH is one of the key factors in the formation of the
coordination architectures. In addition, the photoluminescence properties of the free ligand (H3L) and complexes 1, 3 and 4 were studied
in the solid state at room temperature. Moreover, the magnetic property of complex 2 was investigated.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Coordination polymer; Carboxylate ligand; Cadmium(II); Cobalt(II); Photoluminescence property
1. Introduction
such as monodentate, bis-monodentate, chelating, and as
a result diverse structures can be obtained [3]. However,
it is still a labyrinth because not all of the structures could
be generated as predicted, which might be attributed to the
factors that influence the formation of the architectures [4].
Particularly, the pH value of the reaction solution and crys-
tallization conditions are crucial parameters, for example,
Stock and co-workers have demonstrated the role of the
acid/base ratio, temperature, etc., in determining the struc-
ture of the complexes [5].
Taking in account of the factors mentioned above, we
have focused our attention on the reactions of various
metal salts with multi-carboxylate ligands and the influence
of reaction pH on the structure of the resultant complexes
was investigated. Recently, a new carboxylate containing
In recent years, much attention has been focused on
metal–organic frameworks (MOFs) due to their fascinating
structures such as zero-dimensional (0D) cages, one-dimen-
sional (1D) helical chains, two-dimensional (2D) grids and
three-dimensional (3D) frameworks [1], as well as their
attractive properties which can be further utilized in the
fields of magnetism, catalysis, absorption, optics, etc. [2].
Among them, MOFs with carboxylate containing ligands
are especially of great interest in recent years because the
carboxylate groups can adopt varied coordination modes
*
Corresponding author. Fax: +86 25 83314502.
E-mail address: sunwy@nju.edu.cn (W.-Y. Sun).
0277-5387/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.11.029

Q. Chu et al. / Polyhedron 27 (2008) 812–820
813
2.2. Synthesis of the ligand N-(3-carboxyphenyl)imino-
diacetic acid (H3L)
COOH
A solution of KOH (33.6 g, 0.6 mol) in water (100 ml)
was added dropwise to a solution of monochloroacetic acid
(28.4 g, 0.3 mol) in water (100 ml). To the resulting alkaline
solution, 3-aminobenzoic acid (13.7 g, 0.1 mol) was added
and the mixture was refluxed for 30 h. Then the reaction
mixture was cooled to room temperature and a pale brown
precipitate appeared, which was collected by filtration,
washed by water and recrystallized from water (yield:
52% based on 3-aminobenzoic acid). 1H NMR
(500 MHz, in K2CO3, D2O): d 7.18 (t, 1H), 7.03 (d, 1H),
6.89 (s, 1H), 6.55 (d, 1H), 3.83 (s, 4H). IR (KBr pellet,
cmꢁ1): 3446 (w), 2926 (w), 2552 (w), 1723 (m), 1682 (s),
1603 (m), 1580 (m), 1494 (w), 1465 (m), 1423 (w), 1376
(m), 1361 (m), 1299 (m), 1230 (w), 1183 (w), 1130 (w),
992 (w), 975 (w), 864 (w), 757 (m), 679 (w), 661 (w), 608
(w).
HOOC
N
COOH
Scheme 1. Schematic drawing structure of the H3L ligand.
ligand, N-(3-carboxyphenyl)iminodiacetic acid (H3L)
(Scheme 1), was obtained, which has remarkable features
as follows: (a) it contains three carboxylate groups, there-
fore quite a lot of bridging modes could be adopted in
the formation of MOFs; (b) the three carboxylate groups
would be partially or completely deprotonated by tuning
the reaction pH; (c) it is a semi-rigid ligand with a carboxy-
phenyl group fixed and an iminodiacetic moiety which is
somewhat flexible, whereby different conformations of the
ligand could be achieved which would further generate var-
ious architectures; (d) the introduced aromatic and the car-
boxylate groups could offer additional p–p and hydrogen
bonding interactions, respectively, to further consolidate
the structure [6].
Herein, we report the synthesis, crystal structure and
properties of four new coordination polymers, namely
[Cd(HL)(H2O)] (1), [Co(HL)(H2O)] (2), [Cd(HL)(H2O)4]
(3) and [Cd3(L)2(H2O)9] ꢀ 7H2O (4), obtained by the reac-
tions of H3L with Cd(NO3)2 ꢀ 4H2O or CoCl2 ꢀ 4H2O
under different reaction pH.
2.3. Synthesis of the complexes
2.3.1. Synthesis of [Cd(HL)(H2O)] (1)
A
mixture containing Cd(NO3)2 ꢀ 4H2O (30.8 mg,
0.1 mmol), H3L (25.3 mg, 0.1 mmol), KOH (2.8 mg,
0.05 mmol), 6 ml H2O and 3 ml CH3OH was sealed in a
16 ml Teflon lined stainless steel container and heated at
140 °C for 3 days. After cooling to room temperature for
12 h, colorless block crystals of 1 suitable for X-ray diffrac-
tion analysis were obtained in 68% yield. Anal. Calc. for
C11H11CdNO7: C, 34.62; H, 2.90; N, 3.67. Found: C,
34.65; H, 2.90; N, 3.70%. IR (KBr pellet, cmꢁ1): 3493
(m), 2917 (w), 1699 (m), 1583 (s), 1439 (m), 1416 (m),
1341 (w), 1313 (m), 1294 (m), 1197 (w), 1135 (w), 992
(w), 971 (w), 931 (w), 878 (w), 809 (w), 774 (w), 756 (w),
720 (w), 690 (w), 664 (w), 620 (w).
2. Experimental
2.1. Materials and methods
All commercially available chemicals and solvents are of
reagent grade and were used as received without further
purification. Elemental analyses for C, H and N were per-
formed on a Perkin–Elmer 240C Elemental Analyzer at the
Analysis Center of Nanjing University. FT-IR spectra were
recorded in the range 400–4000cmꢁ1 on a Bruker Vector22
FT-IR spectrophotometer as KBr pellets. 1H NMR spectra
were measured on a Bruker DRX 500 MHz NMR spec-
trometer at room temperature. Magnetic measurements
for complex 2 in the range 1.8–300 K were performed on
a MPMS-SQUID magnetometer at a field of 2 kOe on
crystalline samples in the temperature settle mode. The dia-
magnetic contributions of the samples were corrected by
using Pascal’s constants. The luminescent spectra for the
powdered solid samples were recorded at room tempera-
ture on an Aminco Bowman Series 2 spectrofluorometer
with a Xenon arc lamp as the light source. In the measure-
ments of emission and excitation spectra the pass width
was 5.0 nm. All the measurements were carried out under
the same experimental conditions.
2.3.2. Synthesis of [Co(HL)(H2O)] (2)
The preparation of 2 is similar to that of 1 except that
CoCl2 ꢀ 4H2O (30.8 mg, 0.1 mmol) was used and that the
Teflon container was heated at 120 °C for 3 days. After
cooling to room temperature for 12 h, purple block crystals
of 2 were collected in 63% yield. Anal. Calc. for
C11H11CoNO7: C, 40.26; H, 3.38; N, 4.27. Found: C,
40.16; H, 3.27; N, 4.38%. IR (KBr pellet, cmꢁ1): 3474
(m), 2921 (w), 1698 (m), 1586 (s), 1492 (w), 1445 (m),
1419 (m), 1340 (w), 1315 (m), 1295 (m), 1248 (w), 1193
(w), 1175 (w), 1123 (w), 1048 (w), 990 (w), 968 (w), 936
(w), 925 (w), 907 (w), 879 (w), 808 (w), 777 (w), 756 (w),
729 (w), 690 (w), 666 (w), 632 (w).
2.3.3. Synthesis of [Cd(HL)(H2O)4] (3)
Complex 3 was prepared by a layering method. An
aqueous solution (5 ml) of H3L (25.3 mg, 0.1 mmol) was
carefully adjusted to pH 6 by tetrabutylammonium
hydroxide (10%) solution and placed at the bottom of a
test tube. Then a buffer layer of a solution (5 ml) of

814
Q. Chu et al. / Polyhedron 27 (2008) 812–820
methanol/H2O 1:1 was layered over it, and afterward, a
solution of Cd(NO3)2 ꢀ 4H2O (30.8 mg, 0.1 mmol) in meth-
anol (5 ml) was layered over the buffer layer. Colorless
block crystals of 3 were collected in 61% yield after several
days. Anal. Calc. for C11H17CdNO10: C, 30.32; H, 3.93; N,
3.22. Found: C, 30.21; H, 3.91; N, 3.29%. IR (KBr pellet,
cmꢁ1): 3408 (m), 2930 (w), 1720 (m), 1572 (s), 1535 (s),
1455 (m), 1434 (m), 1413 (m), 1374 (m), 1357 (m), 1317
(m), 1295 (m), 1268 (w), 1234 (w), 1183 (w), 994 (w), 979
(w), 800 (w), 762 (w), 679 (w).
for intensity corrections for Lorentz and polarization
effects. An empirical absorption correction was applied
using the SADABS program [8]. The structures were solved
by direct methods using the program SHELXS-97 [9] and
all non-hydrogen atoms were refined anisotropically on
F2 by the full-matrix least-squares technique using the
SHELXL-97 crystallographic software package [10]. The
hydrogen atoms H2, H3, H5, H6, H7, H7A and H7B in
1, H7A, H7B and H16 in 2 and all of the hydrogen atoms
in 3 were located from difference Fourier maps, and the
other hydrogen atoms were generated geometrically. All
calculations were performed on a personal computer with
the SHELXL-97crystallographic software package. The
X-ray diffraction measurement for 4 was carried out on a
Rigaku RAXIS-RAPID imaging plate diffractometer at
200 K using graphite-monochromated Mo Ka radiation
2.3.4. Synthesis of [Cd3(L)2(H2O)9] ꢀ 7H2O (4)
The preparation of 4 was similar to that described for 3
except that the pH of the bottom solution of H3L was
adjusted to 7 rather than 6. Yield: 53%. Anal. Calc. for
C22H48Cd3N2O28: C, 23.47; H, 4.30; N, 2.49. Found: C,
23.59; H, 4.12; N, 2.45%. IR (KBr pellet, cmꢁ1): 3474
(m), 2908 (w), 1597 (s), 1574 (s), 1452 (w), 1402 (s), 1379
(m), 1329 (w), 1297 (m), 1215 (w), 1180 (w), 1135 (w),
987 (w), 933 (w), 891 (w), 800 (w), 762 (w), 681 (w).
˚
(k = 0.7107 A). A symmetry-related absorption correction
using the program ABSCOR [11] was applied and the data
were corrected for Lorentz and polarization effects. The
structure was solved by direct methods [11] and expanded
using Fourier techniques [12]. The non-hydrogen atoms
were refined anisotropically. All calculations for 4 were
performed using the TEXSAN crystallographic software
package of the Molecular Structure Corporation [13].
Atoms Cd2 and Cd3 in complex 4 are disordered Cd(II)
with an occupancy of 0.5, and atoms O3, O4, O10, C13
and C14 in 4 have two positions with site occupancy
factors of 0.53(2) and 0.47(2). Atom O17 in 4 is also
2.4. X-ray crystallography
The crystallographic data collections for complexes 1–3
were carried out on a Bruker Smart Apex CCD with graph-
˚
ite-monochromated Mo Ka radiation (k = 0.7107 A) at
293(2) K using the x-scan technique. The data were inte-
grated by using the SAINT program [7], which also used
Table 1
Crystallographic data for complexes 1–4
Compound
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
C
11H11CdNO7
C11H11CoNO7
328.14
monoclinic
C2/c
30.299(7)
9.513(2)
8.3489(18)
95.395(4)
293(2)
2395.8(9)
8
C11H17CdNO10
435.66
monoclinic
P21/n
5.4335(6)
25.563(3)
10.4650(11)
91.133(2)
293(2)
1453.3(3)
4
1.991
1.558
872
C22H48Cd3N2O28
1125.82
monoclinic
C2/m
20.837(3)
23.271(4)
8.3863(13)
97.352(3)
200
4033.0(11)
4
1.854
1.663
2248
381.61
monoclinic
C2/c
30.192(4)
9.6582(13)
8.4591(11)
93.916(2)
293(2)
2460.9(6)
8
˚
a (A)
˚
b (A)
˚
c (A)
b (°)
T (K)
3
˚
V (A )
Z
Dc (g cmꢁ3
)
2.060
1.808
1504
1.820
1.466
1336
l (mmꢁ1
F(000)
)
2hmax (°)
52.00
6436
2421
0.0346
209
50.98
6099
2226
0.0528
193
52.00
7750
2852
0.0489
276
50.00
14335
3638
0.0892
316
Data collected
Independent data
Rint
Parameters refined
Goodness-of-fit
R1 [I > 2r(I)]
wR2 [I > 2r(I)]
R1 (all data)
1.011
0.936
1.001
1.075
0.0365
0.0884a
0.0424
0.0919
0.0426
0.0658b
0.0635
0.0708
0.0259
0.0542c
0.0318
0.0562
0.0787
0.2046d
0.1018
0.2294
wR2 (all data)
P
2
2
2
a
b
c
w ¼ 1=½ ðF oÞ þ ð0:0560PÞ þ 1:7000Pꢂ, where P ¼ ðF 2o þ 2F c2Þ=3.
P
2
2
2
w ¼ 1=½ ðF oÞ þ ð0:0156PÞ ꢂ, where P ¼ ðF 2o þ 2F c2Þ=3.
P
2
2
2
w ¼ 1=½ ðF oÞ þ ð0:0208PÞ þ 0:0651Pꢂ, where P ¼ ðF 2o þ 2F c2Þ=3.
P
2
2
2
d
w ¼ 1=½ ðF oÞ þ ð0:1006PÞ þ 51:4441Pꢂ, where P ¼ ðF 2o þ 2F c2Þ=3.

Q. Chu et al. / Polyhedron 27 (2008) 812–820
815
disordered into two positions with site occupancy factors
of 0.63(5) and 0.37(5). The hydrogen atoms of the uncoor-
dinated water molecules O14, O15 and O16 could not be
found from the difference Fourier maps. The details of
the crystal parameters, data collection and refinements
for the complexes are summarized in Table 1, and selected
bond lengths and angles with their estimated standard devi-
ations are listed in Table 2.
water molecule. Each Cd(II) atom is six-coordinated with a
distorted octahedral geometry, by one nitrogen atom (N1)
from the HL2ꢁ ligand and five oxygen atoms from one
coordinated H2O molecule (O7) and three different HL2ꢁ
ligands (O3 and O5, O4A and O6B), as shown in Fig. 1a.
The coordination bond lengths and angles around the
˚
Cd(II) centre are in the range 2.234(3)–2.556(3) A and
68.59(10)–159.67(11)°, respectively as listed in Table 2.
On the other hand, each HL2ꢁ ligand adopts a l3 bridging
mode to connect three Cd(II) atoms using its iminodiace-
tate moiety, in which each carboxylate group links two
Cd(II) atoms in a syn–anti fashion and the central Cd(II)
atom is coordinated by two oxygen atoms from two
carboxylate groups and the central nitrogen atom
(Scheme 2a). In addition, it is noteworthy that the carboxy-
phenyl group of the ligand, without deprotonation, is free
of coordination. The non-deprotonation of the H3L ligand
in 1 and 2 was further confirmed by IR spectral measure-
ments. The IR spectra of complexes 1 and 2 indicate the
incomplete deprotonation of the H3L ligand since vibration
bands at 1699 cmꢁ1 for 1 and 1698 cmꢁ1 for 2 were
3. Results and discussion
3.1. Crystal structure of complexes 1–4
3.1.1. [Cd(HL)(H2O)] (1) and [Co(HL)(H2O)] (2)
The result of X-ray crystallographic analysis revealed
that complexes 1 and 2 crystallize in the same monoclinic
C2/c space group with similar cell parameters (Table 1),
which indicate that they are isomorphous and isostructur-
al. Thus, as a typical example, only the structure of 1 is
described here in detail. The asymmetric unit of 1 consists
of one Cd(II) atom, one HL2ꢁ ligand and one coordinated
Fig. 1. (a) Coordination environment of the Cd(II) atom in complex 1 with the ellipsoids drawn at the 30% probability level, hydrogen atoms are omitted
for clarity. (b) 2D network structure of 1. (c) Views of the M4L4 (left) and M4L2 (right) units linked by four and two ligands with the carboxylphenyl
groups omitted for clarity. (d) 3D structure of 1 with hydrogen bonds indicated by dashed lines.

816
Q. Chu et al. / Polyhedron 27 (2008) 812–820
Table 2
It can be seen clearly from Fig. 1b that there are two dif-
ferent macrocyclic rings in the 2D sheet of 1, namely M4L4
and M4L2 (Fig. 1c), respectively. In the M4L4 ring, each
iminodiacetate group of the HL2ꢁ ligand coordinates with
two Cd(II) atoms using three of its four oxygen atoms and
this affords one oxygen atom to link to another Cd(II)
atom from a neighbouring ring. While in the case of the
M4L2 ring, four Cd(II) centers are linked by two HL2ꢁ
ligands and in turn each HL2ꢁ ligand connects three Cd(II)
atoms using its four oxygen atoms. These two kinds of
macrocyclic rings are arranged alternately to generate a
2D wave-like network. Furthermore, as shown in Fig. 1b,
the M4L4 and M4L2 rings adopt entirely different motifs,
i.e. the iminodiacetate moiety of the ligand occupies the
space of the M4L2 ring whilst there is relatively large cavity
in the M4L4 ring which is filled by the coordinated water
molecules (Fig. S1).
˚
Selected bond lengths (A) and angles (°) for complexes 1–4
[Cd(HL)(H2O)] (1)
Cd(1)–N(1)
Cd(1)–O(4)#1
Cd(1)–O(6)#2
2.556(3)
2.250(3)
2.234(3)
Cd(1)–O(3)
Cd(1)–O(5)
Cd(1)–O(7)
2.283(3)
2.263(3)
2.306(3)
[Co(HL)(H2O)] (2)
Co(1)–N(1)
Co(1)–O(4)#3
Co(1)–O(6)#4
2.346(3)
2.086(2)
2.093(2)
Co(1)–O(3)
Co(1)–O(5)
Co(1)–O(7)
2.053(2)
2.067(2)
2.097(3)
[Cd(HL)(H2O)4] (3)
Cd(1)–O(1)
Cd(1)–O(3)#5
Cd(1)–O(8)
2.435(2)
2.282(2)
2.383(2)
2.339(2)
Cd(1)–O(2)
Cd(1)–O(7)
Cd(1)–O(9)
2.417(2)
2.237(2)
2.301(2)
Cd(1)–O(10)
[Cd3(L)2(H2O)9] ꢀ 7H2O (4)
Cd(1)–O(6)#6
Cd(1)–O(3)
Cd(1)–O(8)
Cd(2)–O(9)
Cd(2)–O(4)
Cd(3)–O(10B)
Cd(3)–O(13)
2.261(7)
Cd(1)–O(2)
Cd(1)–O(7)
Cd(1)–O(2)#7
Cd(2)–O(10)
Cd(2)–O(3)
2.333(7)
2.344(8)
2.446(6)
2.25(2)
2.517(15)
2.302(16)
2.36(2)
2.339(17)
2.380(7)
2.15(2)
2.339(14)
2.30(3)
The non-deprotonated carboxyphenyl groups point out
of the 2D sheet, up and down alternately, and further con-
nect the 2D network to give a 3D framework through the
formation of O–Hꢀ ꢀ ꢀO hydrogen bonds between the unco-
ordinated O atoms of the carboxyphenyl groups from two
Cd(3)–O(4B)
Cd(3)–O(11)
2.335(18)
Symmetry transformations used to generate equivalent atoms: #1 x,
ꢁy + 1, z ꢁ 1/2; #2 ꢁx + 1/2, y + 1/2, ꢁz + 3/2; #3 x, ꢁy, z + 1/2; #4
ꢁx + 1/2, y ꢁ 1/2, ꢁz + 1/2; #5 x ꢁ 1/2, ꢁy + 1/2, z ꢁ 1/2; #6 x + 1/2,
ꢁy + 1/2, z + 1; #7 ꢁx, y, ꢁz + 1.
˚
adjacent layers, with an Oꢀ ꢀ ꢀO distance of 2.607(6) A
(Fig. 1d). The hydrogen bonding data are summarized in
Table S1. There are other O–Hꢀ ꢀ ꢀO and C–Hꢀ ꢀ ꢀO hydro-
gen bonds within the 2D network, which further consoli-
date the structure [14].
3.1.2. [Cd(HL)(H2O)4] (3)
When the reaction of ligand H3L with Cd(NO3)2 ꢀ 4H2O
was carried out by the layering method instead of a hydro-
thermal reaction as used for the preparation of 1 and 2, the
new complex 3 was obtained. The crystallographic data
showed that complex 3 crystallizes the in monoclinic P21/
n space group and the Cd(II) atom has a pentagonal bipyr-
amid coordination geometry with an O7 donor set, as illus-
trated in Fig. 2a. Two oxygen atoms (O1 and O2) from the
carboxyphenyl group of the ligand and three other oxygen
atoms (O8, O9 and O10) from coordinated water molecules
occupy planar positions with Cd–O bond lengths ranging
˚
from 2.301(2) to 2.435(2) A (Table 2). The axial positions
are occupied by one oxygen atom (O3A) from the iminodi-
acetate group of another ligand and O7 from another coor-
dinated water molecule, with Cd–O bond lengths of
˚
2.282(2) and 2.237(2) A (Table 2), respectively. As illus-
trated in Scheme 2b, each HL2ꢁ ligand links two Cd(II)
atoms in 3, in which the carboxyphenyl group is in a
l1–g1:g1 chelating mode, and one carboxylate of the imi-
nodiacetate group takes a l1–g1:g0 monodentate fashion
and the other one does not take part in the coordination.
It is noteworthy that the coordination mode of the ligand
in 3 is quite different from that in 1 and 2, as discussed
above. Firstly, one carboxylate unit from the iminodiace-
tate group of the ligand remains protonated and is free
of coordination in 3, which was confirmed by the observa-
tion of a vibration band at 1720 cmꢁ1 in the IR spectrum,
however, the one in 1 and 2 non-deprotonated and free of
Scheme 2. Coordination modes of the ligand in complexes 1–4.
observed. Such coordination mode makes a 2D network
structure of 1, as illustrated in Fig. 1b in which the
carboxyphenyl groups and coordinated water molecules
are omitted for clarity.

Q. Chu et al. / Polyhedron 27 (2008) 812–820
817
water molecules (O7 and O10) and carboxyphenyl group
from adjacent chains, with Oꢀ ꢀ ꢀO distances ranging from
˚
2.707(3) to 3.192(4) A (Table S1). Then the 2D layers are
further connected through O–Hꢀ ꢀ ꢀO hydrogen bonds
between the oxygen atoms of the coordinated water mole-
cules (O8 and O9) and the free arm of iminodiacetate
group from an adjacent layer with Oꢀ ꢀ ꢀO distances of
˚
2.814(3) and 2.946(3) A (Table S1).
3.1.3. [Cd3(L)2(H2O)9] ꢀ 7H2O (4)
In order to further investigate the pH influence on the
formation and structure of the complex, the pH value of
the ligand solution was carefully adjusted to 7.0, while
the other experiment conditions remained the same as
those used for the preparation of 3. As a result, complex
4, with an entirely different structure, was obtained and
the result of crystallographic analysis confirmed that all
the carboxylate groups of the ligand are deprotonated
and coordinated with the metal atoms in 4. The complete
deprotonation of all three carboxylate groups in 4 was also
confirmed by IR spectroscopy since no vibration band
around 1700 cmꢁ1 for a protonated carboxylate group
was observed in the IR spectrum of 4. The complex crystal-
lizes in the monoclinic C2/m space group, and in the repeat
unit there are two Cd(II) atoms (Cd2 and Cd3) sitting on a
˚
symmetry plane with a separation of 2.44 A and one disor-
dered carboxylate group of the iminodiacetate of the
L3ꢁ ligand was found near these two Cd(II) atoms. Thus
Cd2 and Cd3 are disordered Cd(II) with an occupancy of
0.5. As shown in Fig. 3a, Cd1 is six coordinated by four
oxygen atoms (O2, O3, O2A and O6A) from three different
L3ꢁ ligands, and two oxygen atoms (O7, O8) from two
coordinated water molecules, with Cd–O bond lengths
˚
ranging from 2.261(7) to 2.446(6) A (Table 2). While Cd2
and Cd3 are also six coordinated, it is with four oxygen
atoms (O3, O4, O3A and O4A) from two L3ꢁ ligands
and two oxygen atoms (O9, O10) from two coordinated
water molecules for Cd2, and two oxygen atoms (O4B
and O4BA) from two L3ꢁ ligands, and four oxygen atoms
(O10B, O11, O13 and O13A) from four coordinated water
molecules for Cd3. In addition, two Cd1 atoms (e.g. Cd1
and Cd1A in Fig. 3a) are bridged by two carboxylate oxy-
gen atoms (O2 and O2A) to form a Cd2O2 rhombic ring.
Therefore, each L3ꢁ ligand connects four Cd(II) atoms in
two different forms (Scheme 2c and d) in 4 using its three
carboxylate groups, and the central nitrogen atom (N1)
does not take part in the coordination since the Cd1–N1
Fig. 2. (a) Coordination environment of the Cd(II) atom in 3 with the
ellipsoids drawn at the 30% probability level, hydrogen atoms are omitted
for clarity. (b) 1D zigzag chain structure of 3 with hydrogen atoms omitted
for clarity. (c) 3D packing structure of 3 with hydrogen bonds indicated by
dashed lines.
coordination is the carboxyphenyl group. Moreover, the
nitrogen atom of the ligand also does not take part in coor-
dination, and four water molecules participate in coordina-
tion to satisfy the coordination need of the Cd(II) atom in
3. As a result of such differences, a 1D chain-like structure
for complex 3 is generated, in which the ligand, utilizing its
carboxyphenyl group and one of the iminodiacetate
groups, acts as bridge to link the Cd(II) atoms into a zigzag
chain structure (Fig. 2b).
˚
distance is 2.70 A.
The most striking feature of complex 4 is that the
Cd(II) centers are connected by the L3ꢁ ligand to furnish
a 2D network with two different types of cavities filled
with water molecules. Firstly, as illustrated in Fig. 3b,
six Cd(II) atoms are linked by four L3ꢁ ligands to gener-
ate a near rectangular ring, and four Cd1 atoms are
located at the four corners. Then further connection of
the rectangular rings through the Cd2O2 rhombic rings
results in the formation of an infinite 2D network as
In the packing structure of 3, as shown in Fig. 3c, the 1D
chains are firstly linked into a 2D layer by O–Hꢀ ꢀ ꢀO hydro-
gen bonds between the oxygen atoms of the coordinated

818
Q. Chu et al. / Polyhedron 27 (2008) 812–820
a
b
c
Fig. 3. (a) Coordination environments of the Cd(II) atoms in 4 with the ellipsoids drawn at the 30% probability level, hydrogen atoms and uncoordinated
water molecules are omitted for clarity. Top: disordered part with Cd2; bottom: disordered part with Cd3. (b) A near rectangular ring with six Cd(II)
atoms linked by four L3ꢁ ligands. (c) 2D network structure of 4. The hydrogen atoms and uncoordinated water molecules are omitted for clarity.
depicted in Fig. 3c. In the crystal packing mode, the 2D
sheets are further linked into 3D structure by
3.2. Effect of synthetic conditions on the structure of the
complexes
a
C–Hꢀ ꢀ ꢀO hydrogen bonds between the C11 atom of an
iminodiacetate group and the O1 atom from an adjacent
˚
It has been reported that synthetic conditions, such as
pH value, reaction temperature, solvent, etc., are the key
factors in assembling MOFs [15,16]. As to the synthesis
of 3 and 4, all the reaction conditions are the same except
for the difference of the reaction pH. As a result, complex
layer, with
a
Cꢀ ꢀ ꢀO distance of 3.552(13) A, and
C–Hꢀ ꢀ ꢀO hydrogen bonds also exist in the crystal packing
diagram, which further consolidate the structure (Fig. S2,
Table S1).

Q. Chu et al. / Polyhedron 27 (2008) 812–820
819
3, obtained at a relatively low pH value, is a 1D zigzag
3
2
1
0
120
100
80
60
40
20
0
chain structure with each Cd(II) center bonded by four
water molecules. However in 4, obtained at a high pH, a
more complicated 2D network was generated. Therefore,
a rough conclusion could be made that an increase of the
pH value in the synthetic process would generate higher
dimensionality of the final structure, which is in agreement
with the previous reports [17].
In addition, complex 1 was synthesized at a lower pH
value and a 2D sheet was obtained rather than a 1D zigzag
chain, as in 3. It might be ascribed to the fact that complex
1 was formed at a high reaction temperature, namely
140 °C under a hydrothermal process, which is considered
to be in favor of generating high dimensional structures
[18].
Τ
χ
Μ
0
50
100
150
200
250
300
T /K
Fig. 5. Temperature dependence of vMT and 1/vM for 2. The solid line
shows the Curie–Weiss fitting.
From the points discussed above, it is suggested that the
increase of reaction pH and temperature may result in a
higher connectivity of the carboxylate ligand and further
feature a more complicated high dimensional structure.
they could be assigned to the p–p* intraligand fluorescence
due to their resemblance to the emission of the H3L ligand.
The enhancement and slight shift of the emissions for 1, 3
and 4 compared to that of the free ligand probably result
from the fact that the coordination of Cd(II) ions increases
the ligand conformational rigidity and thus reduces the loss
of energy by thermal vibrational decay [20].
3.3. Photoluminescence properties of complexes 1, 3 and 4
Inorganic–organic hybrid coordination compounds,
especially with d10 metal centers, have been investigated
for fluorescence properties owing to their potential applica-
tions as luminescent materials, such as light-emitting
diodes (LEDs) [19]. Therefore, in the present study, the
photoluminescence properties of 1, 3 and 4 as well as the
free H3L ligand were investigated in the solid state at room
temperature. As shown in Fig. 4, intense emission bands
were observed at 407 nm (kex = 360 nm) for the H3L
ligand, 422 nm (kex = 350 nm) for 1, 414 nm (kex = 360 nm)
for 3 and 392 nm (kex = 342 nm) for 4, respectively. These
emissions cannot be attributed to either a metal-to-ligand
charge transfer (MLCT) or a ligand-to-metal charge trans-
fer (LMCT) because the Cd(II) ions are in a d10 configura-
tion and are difficult to oxidize or to reduce. Therefore,
3.4. Magnetic properties of complex 2
The magnetic susceptibility of 2 versus temperature at a
field of 2 kOe is shown in Fig. 5, where vM is the susceptibility
per Co(II) ion. The vMT value is 2.50 cm3 molꢁ1 K at 300 K,
which is significantly larger than the spin-only value of
1.875 cm3 molꢁ1 K and decreases upon cooling to
0.54 cm3 molꢁ1 K at 2 K. The magnetic susceptibility above
30 K obeys the Curie–Weiss law with a Weiss constant,
h = ꢁ24.11 K, and a Curie constant, C = 2.88 cm3 molꢁ1 K.
The high value of C (1.875 cm3 molꢁ1 K for spin-only Co2+
)
and negative h value may be due to the spin–orbit coupling,
which is remarkable for the 4T1g state of Co2+ in an octahe-
dral ligand field [21].
392
342
4
350
4
422
4. Conclusion
360
414
1
1
In conclusion, we have successfully synthesized a new
carboxylate containing ligand and four new coordination
polymers were isolated accordingly under different pH con-
ditions. The results revealed that the reaction pH plays an
important role in modulating the architecture of coordina-
tion compounds. In addition, complexes 1, 3 and 4 showed
p–p* intraligand fluorescence in the solid state at room
temperature, and the magnetic property of complex 2 was
also investigated.
3
3
407
360
L
L
300
350
400
450
500
550
Acknowledgements
Wavelength (nm)
This work was supported by the National Basic Re-
search Program of China (Grant No. 2007CB925103)
Fig. 4. Excitation and emission spectra of the H3L ligand and 1, 3 and 4 in
the solid state at room temperature.

820
Q. Chu et al. / Polyhedron 27 (2008) 812–820
[5] P.M. Forster, N. Stock, A.K. Cheetham, Angew. Chem., Int. Ed. 44
(2005) 7608.
[6] (a) T. Steiner, Angew. Chem., Int. Ed. 41 (2002) 48;
(b) C. Janiak, J. Chem. Soc., Dalton Trans. (2000) 3885;
(c) M. Nishio, CrystEngComm 6 (2004) 130.
and the National Science Fund for Distinguished Young
Scholars (Grant No. 20425101), which are gratefully
acknowledged.
Appendix A. Supplementary material
[7] SAINT, Version 6.02a; Bruker AXS Inc.: Madison, W1, 2002.
[8] G.M. Sheldrick, SADABS, Program for Bruker Area Detector
Absorption Correction, University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
[9] G.M. Sheldrick, SHELXS-97, Program for Crystal Structure Solution,
University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[10] G.M. Sheldrick, SHELXL-97, Program for Crystal Structure Refine-
ment, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[11] ABSCOR: T. Higashi, Program for Absorption Correction, Rigaku
Corporation, Tokyo, Japan, 1995.
[12] DIRDIF-94: P.T. Beurskens, G. Admiraal, G. Beurskens, W.P.
Bosman, R. De Gelder, R. Israel, J.M.M. Smits, The DIRDIF-94
program system, Technical Report of the Crystallography Labora-
tory, University of Nijmegen, The Netherlands, 1994.
[13] TEXSAN: Crystal Structure Analysis Package, Molecular Structure
Corporation (1985 and 2004).
CCDC 645328, 645329, 645330 and 645331 contain the
supplementary crystallographic data for complexes 1, 2, 3
and 4, respectively. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/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. Supplemen-
tary data associated with this article can be found, in the
online version, at doi:10.1016/j.poly.2007.11.029.
References
[14] (a) G.R. Desiraju, T. Steiner, The Weak Hydrogen Bond, IUCr
Monograph on Crystallography, vol. 9, Oxford Science, Oxford,
1999;
[1] (a) L. Carlucci, G. Ciani, D.M. Proserpio, Coord. Chem. Rev. 246
(2003) 247;
(b) H.J. Choi, M.P. Suh, J. Am. Chem. Soc. 126 (2004) 15844;
(c) S.K. Dey, B. Bag, K.M.A. Malik, M.S. El Fallah, J. Ribas, S.
Mitra, Inorg. Chem. 42 (2003) 4029;
(b) C. Janiak, T.G. Scharmann, Polyhedron 22 (2003) 1123, and
references therein;
(c) B.R. Bhogala, A. Nangia, Cryst. Growth Des. 3 (2003) 547.
[15] (a) R.Q. Fang, X.M. Zhang, Inorg. Chem. 45 (2006) 4801;
(b) R.S. Rarig, J. Zubieta, J. Chem. Soc., Dalton Trans. (2001) 3446;
(c) M.M. Gomez-Alcantara, A. Cabeza, M.A.G. Aranda, A. Guag-
liardi, J.G. Mao, A. Clearfield, Solid State Sci. 6 (2004) 479;
(d) Z.G. Guo, R. Cao, X.J. Li, D.Q. Yuan, W.H. Bi, X.D. Zhu, Y.F.
Li, Eur. J. Inorg. Chem. (2007) 742.
(d) O. Ohmori, M. Fujita, Chem. Commun. (2004) 1586;
(e) R. Lescouezec, J. Vaissermann, L.M. Toma, R. Carrasco, F.
Lloret, M. Julve, Inorg. Chem. 43 (2004) 2234;
(f) T. Kusukawa, M. Fujita, J. Am. Chem. Soc. 124 (2002) 13576.
[2] (a) C. Janiak, J. Chem Soc., Dalton Trans. (2003) 2781;
(b) S.L. James, Chem. Soc. Rev. 32 (2003) 276;
(c) D. Maspoch, D. Ruiz-Molina, J. Veciana, J. Mater. Chem. 14
(2004) 2713;
[16] (a) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M.
O’Keefe, O.M. Yaghi, Science 295 (2002) 469;
(d) J.S. Seo, D. Whang, H. Lee, S.I. Jun, J. Oh, Y.J. Jeon, K. Kim,
Nature 404 (2000) 982;
(b) N. Stock, T. Bein, Angew. Chem., Int. Ed. 43 (2004) 749.
[17] L. Pan, T. Frydel, M.B. Sander, X. Huang, J. Li, Inorg. Chem. 40
(2001) 1271.
[18] J. Chen, M. Ohba, D. Zhao, W. Kaneko, S. Kitagawa, Cryst. Growth
Des. 6 (2006) 664.
[19] (a) U.H.F. Bunz, Chem. Rev. 100 (2000) 1605;
(b) W. Wang, H. Schmider, Q. Wu, Y.S. Zhang, S. Wang, Inorg.
Chem. 39 (2000) 2397;
(c) Y.B. Chen, J. Zhang, J.K. Cheng, Y. Kang, Z.J. Li, Y.G. Yao,
Inorg. Chem. Commun. 7 (2004) 1139.
[20] (a) S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798;
(b) A. Vogler, H. Kunkely, Coord. Chem. Rev. 250 (2006) 1622;
(c) R.Q. Fan, D.S. Zhu, Y. Mu, G.H. Li, Y.L. Yang, Q. Su, S.H.
Feng, Eur. J. Inorg. Chem. (2004) 4891;
(e) B. Chen, N.W. Ockwig, A.R. Millward, D.S. Contreras, O.M.
Yaghi, Angew. Chem., Int. Ed. 44 (2005) 4745;
(f) S.-L. Zheng, X.-M. Chen, Aust. J. Chem. 57 (2004) 703.
[3] (a) S.S.Y. Chui, S.M.F. Lo, J.P.H. Charmant, A.G. Orpen, I.D.
Williams, Science 283 (1999) 1148;
(b) Z.H. Zhang, Y. Song, T.-a. Okamura, Y. Hasegawa, W.Y. Sun,
N. Ueyama, Inorg. Chem. 45 (2006) 2896;
(c) R.Q. Zou, H. Sakurai, Q. Xu, Angew. Chem., Int. Ed. 45 (2006)
2542.
[4] (a) R.B. Walsh, C.W. Padgett, P. Metrangolo, G. Resnati, T.W.
Hanks, W.T. Pennington, Cryst. Growth Des. 1 (2001) 165;
(b) J.Y. Zhang, P.W. Miller, M. Nieuwenhuyzen, S.L. James, Chem.
Eur. J. 12 (2006) 2448;
(d) Q. Chu, L.Y. Kong, T.-a. Okamura, H. Kawaguchi, W.L. Meng,
W.Y. Sun, N. Ueyama, Z. Anorg. Allg. Chem. 633 (2007) 326;
(e) L. Wen, Y. Li, Z. Lu, J. Lin, C. Duan, Q. Meng, Cryst. Growth
Des. 6 (2006) 530.
(c) H.F. Zhu, W. Zhao, T.-a. Okamura, J. Fan, W.Y. Sun, N.
Ueyama, New. J. Chem. 28 (2004) 1010;
(d) R.M. Silva, M.D. Smith, J.R. Gardinier, Inorg. Chem. 45 (2006)
2132;
[21] O. Kahn, Molecular Magnetism, VCH Publishers, Inc., New York,
1993.
(e) P.A. Gale, Coord. Chem. Rev. 199 (2000) 181.