A series of Cd(II) complexes with ππ stacking and hydrogen bonding interactions: Structural diversities by varying the ligands

Article abstract of DOI:10.1016/j.jssc.2010.11.016

Seven new Cd(II) complexes consisting of different phenanthroline derivatives and organic acid ligands, formulated as [Cd(PIP)₂(dnba) ₂] (1), [Cd(PIP)(ox)]·H₂O (2), [Cd(PIP)(1,4-bdc) (H₂O)]·4H₂O (3), [Cd(3-PIP)₂(H ₂O)₂]·4H₂O (4), [Cd₂(3-PIP) ₄(4,4′-bpdc)(H₂O)₂]·5H ₂O (5), [Cd(3-PIP)(nip)(H₂O)]·H₂O (6), [Cd₂(TIP)₄(4,4′-bpdc)(H₂O) ₂]·3H₂O (7) (PIP=2-phenylimidazo[4,5-f]1,10- phenanthroline, 3-PIP=2-(3-pyridyl)imidazo[4,5-f]1,10-phenanthroline, TIP=2-(2-thienyl)imidazo[4,5-f]1,10-phenanthroline, Hdnba=3,5-dinitrobenzoic acid, H₂ox=oxalic acid, 1,4-H₂bdc=benzene-1,4-dicarboxylic acid, 4,4′-H₂bpdc=biphenyl-4,4′-dicarboxylic acid, H₂nip=5-nitroisophthalic acid) have been synthesized under hydrothermal conditions. Complexes 1 and 4 possess mononuclear structures; complexes 5 and 7 are isostructural and have dinuclear structures; complexes 2 and 3 feature 1D chain structures; complex 6 contains 1D double chain, which are further extended to a 3D supramolecular structure by ππ stacking and hydrogen bonding interactions. The N-donor ligands with extended π-system and organic acid ligands play a crucial role in the formation of the final supramolecular frameworks. Moreover, thermal properties and fluorescence of 17 are also investigated.

Full text of DOI:10.1016/j.jssc.2010.11.016

Journal of Solid State Chemistry 184 (2011) 280–288
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
A series of Cd(II) complexes with
interactions: Structural diversities by varying the ligands
p
– stacking and hydrogen bonding
p
Xiuli Wang n, Jinxia Zhang, Guocheng Liu, Hongyan Lin
Faculty of Chemistry and Chemical Engineering, Bohai University, Jinzhou 121000, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Seven new Cd(II) complexes consisting of different phenanthroline derivatives and organic acid ligands,
formulated as [Cd(PIP)2(dnba)2] (1), [Cd(PIP)(ox)] ꢀ H2O (2), [Cd(PIP)(1,4-bdc)(H2O)] ꢀ 4H2O (3), [Cd(3-
PIP)2(H2O)2] ꢀ 4H2O (4), [Cd2(3-PIP)4(4,40-bpdc)(H2O)2]ꢀ 5H2O (5), [Cd(3-PIP)(nip)(H2O)] ꢀ H2O (6), [Cd2
(TIP)4(4,40-bpdc)(H2O)2]ꢀ 3H2O (7) (PIP¼2-phenylimidazo[4,5-f]1,10-phenanthroline, 3-PIP¼2-(3-pyridyl)
imidazo[4,5-f]1,10-phenanthroline, TIP¼2-(2-thienyl)imidazo[4,5-f]1,10-phenanthroline, Hdnba¼3,5-dini-
trobenzoic acid, H2ox¼oxalic acid, 1,4-H2bdc¼benzene-1,4-dicarboxylic acid, 4,40-H2bpdc¼biphenyl-4,
40-dicarboxylic acid, H2nip¼5-nitroisophthalic acid) have been synthesized under hydrothermal conditions.
Complexes 1 and 4 possess mononuclear structures; complexes 5 and 7 are isostructural and have dinuclear
structures; complexes 2 and 3 feature 1D chain structures; complex 6 contains 1D double chain, which are
Received 24 July 2010
Received in revised form
3 November 2010
Accepted 8 November 2010
Available online 19 November 2010
Keywords:
Hydrothermal synthesis
Crystal structures
N ligands
further extended to a 3D supramolecular structure by
p–p stacking and hydrogen bonding interactions.
Cadmium complexes
Organic carboxylate
The N-donor ligands with extended -system and organic acid ligands play a crucial role in the formation of
p
the final supramolecular frameworks. Moreover, thermal properties and fluorescence of 1–7 are also
investigated.
& 2010 Elsevier Inc. All rights reserved.
1. Introduction
contain both an extended
acting as hydrogen bond acceptors/donors or of forming coordination
interactions to some metal ions, as well as extending the -system
themselves [25]. Therefore, these ligands as good candidates have
attracted our interest for construction of metal–organic supramole-
cular architectures. On the other hand, polycarboxylate ligands, such as
benzenecarboxylates have been extensively employed to construct
coordination polymers exhibiting a wide range of structural diversities
and potential applications as functional materials [26–28].
In this paper, we report the syntheses, structures and properties of
seven new Cd(II) complexes, namely, [Cd(PIP)2(dnba)2] (1), [Cd(PIP)
(ox)] ꢀ H2O (2), [Cd(PIP)(1,4-bdc)(H2O)] ꢀ 4H2O (3), [Cd(3-PIP)2
(H2O)2]ꢀ 4H2O (4), [Cd2(3-PIP)4(4,40-bpdc)(H2O)2]ꢀ 5H2O (5), [Cd(3-
PIP)(nip)(H2O)] ꢀ H2O (6), [Cd2(TIP)4(4,40-bpdc)(H2O)2]ꢀ 3H2O (7). All
structures are extended into three dimensional (3D) supramolecular
p-system and an imidazole ring, capable of
The design and construction of discrete and polymeric metal–
organic complexes with coordination bonds and noncovalent
intermolecular forces have attracted great attention in recent years
[1–7]. To date, much researches have focused on controlling motifs
of metal–organic complexes through coordination bonds, whereas
relatively less attention has been given to noncovalent interactions
[6–9]. In general, it has been recognized that noncovalent inter-
molecular forces such as hydrogen bonding interactions, being
reasonably strong and highly directional, can be used as structure-
directing tools in generating many molecular solids with novel
p
properties [10–14]. The p–p stacking interaction is also an impor-
tant and powerful noncovalent intermolecular interaction for
directing the supramolecular architectures [15,16]. A successful
strategy in constructing such solid materials is to employ appro-
priate versatile functional ligands which have strong coordination
ability as well as providing the hydrogen bond acceptors/donors
frameworks by strong p–p stacking and hydrogen bonding interac-
tions. On the basis of synthesis and structural characterization, the
role of intermolecular forces in the creation of molecular architectures
is discussed. The thermal stabilities and luminescent properties of
complexes 1–7 have been reported (Scheme 1).
and p-conjugated system for extending their networks [16–18].
As is known, the 1,10-phenanthroline (phen) ligand has been
widely used to construct supramolecular architectures [19,20]. As
important phen derivatives, to our knowledge, 2-phenylimidazo[4,5-f]
1,10-phenanthroline (PIP), 2-(3-pyridyl)imidazo[4,5-f]1,10-phenan-
throline (3-PIP), 2-(2-thienyl)imidazo[4,5-f]1,10-phenanthroline (TIP)
are less investigated [7,21–24]. Compared with phen, these ligands
2. Experimental section
2.1. General materials and methods
n Corresponding author. Fax: +86 416 3400158.
Solvents and starting materials for synthesis were commercially
available and used as received. The N-donor ligands PIP, 3-PIP and
E-mail address: wangxiuli@bhu.edu.cn (X. Wang).
0022-4596/$ - see front matter & 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2010.11.016

X. Wang et al. / Journal of Solid State Chemistry 184 (2011) 280–288
281
2.2.4. [Cd(3-PIP)2(H2O)2] ꢀ 4H2O (4)
The synthetic procedure for 4 is the same as that for 1 except
that 3-PIP (0.015 g, 0.05 mmol) was used instead of PIP, and Hdnba
(0.021 g, 0.1 mmol) was not used. Yellow block crystals suitable
for X-ray diffraction of complex 4 were isolated by mechanical
separation from amorphous solid in 28% yield (based on Cd(II) salt).
Anal. Calcd for C36H34CdN10O6: C 53.00, H 4.17, N 17.18%. Found:
C 53.06, H 4.21, N 17.14%. IR (KBr, cmꢁ1): 3326(w), 3060(w),
2360(m), 1608(w), 1581(s), 1477(m), 1386(s), 1338(m), 1213(s),
1128(m), 1080(s), 823(m), 732(m).
2.2.5. [Cd2(3-PIP)4(4,40-bpdc)(H2O)2] ꢀ 5H2O (5)
The synthetic procedure for 5 is the same as that for 1 except
that 3-PIP (0.015 g, 0.05 mmol) and 4,40-H2bpdc (0.0246 g,
0.1 mmol) were used instead of PIP and Hdnba. Yellow block
crystals suitable for X-ray diffraction of complex 5 were isolated by
mechanical separation from amorphous solid in 25% yield (based
on Cd(II) salt). Anal. Calcd for C86H62Cd2N20O11: C 58.10, H 3.49,
N 15.76%. Found: C 58.03, H 3.52, N 15.74%. IR (KBr, cmꢁ1):
3425(w), 3062(w), 2362(m), 1570(s), 1460(m), 1386(s), 1070(m),
947(m), 821(w), 731(m).
Scheme 1. Structures of the PIP, 3-PIP, TIP ligands and organic acid ligands appeared
in complexes 1–7.
TIP were synthesized by the methods of the literature [29] and
characterized by FT-IR spectra and 1HNMR. FT-IR spectra (KBr
pellets) were taken on a Magna FT-IR 560 spectrometer. Thermo-
gravimetric data for complexes 1–7 were performed using a Pyris
Diamond thermal analyzer. Elemental analyses (C, H, and N) were
performed on a Perkin-Elmer 240C analyzer. Fluorescence spectra
were recorded at room temperature on a Hitachi F-4500 fluores-
cence/phosphorescence spectrophotometer.
2.2.6. [Cd(3-PIP)(nip)(H2O)] ꢀ H2O (6)
The synthetic procedure for 6 is the same as that for 1 except that
3-PIP (0.015 g, 0.05 mmol) and H2nip (0.0211 g, 0.1 mmol) were used
instead of PIP and Hdnba. Yellow block crystals suitable for X-ray
diffraction of complex 6 were isolated by mechanical separation
from amorphous solid in 45% yield (based on Cd(II) salt). Anal. Calcd
for C26H18CdN6O8: C 47.64, H 2.75, N 12.83%. Found: C 47.58, H 2.78,
N 12.85%. IR (KBr, cmꢁ1): 3334(m), 3080(w), 2367(w), 1600(s),
1562(m), 1523(m), 1446(m), 1353(s), 1194(m), 1079(m), 962(m),
825(m), 718(s), 633(m).
2.2. Synthesis
2.2.1. [Cd(PIP)2(dnba)2] (1)
A mixture of Cd(NO3)2 ꢀ 4H2O (0.031 g, 0.1 mmol), PIP (0.015 g,
0.05 mmol), Hdnba (0.0212 g, 0.1 mmol), NaOH (0.2 mmol), and
H2O (8 mL) was stirred for 20 min and sealed in a 25 mL Teflon-
lined stainless-steel container. The container was heated to 170 1C
and held at this temperature for 4 days. It was then cooled to room
temperature at a rate of 5 1C hꢁ1. Yellow block crystals suitable
for X-ray diffraction of complex 1 were isolated by mechanical
separation from amorphous solid in 25% yield (based on Cd(II) salt).
Anal. Calcd for C52H30CdN12O12: C 55.35, H 2.66, N 14.90%. Found:
C 55.31, H 2.69, N 14.87%. IR (KBr, cmꢁ1): 3095 (w), 2970(w),
2855(w), 2360(w), 1615(s), 1538(s), 1346(s), 1079(m), 818(s), 733(s).
2.2.7. [Cd2(TIP)4(4,40-bpdc)(H2O)2] ꢀ 3H2O (7)
The synthetic procedure for 7 is the same as that for 1 except that
TIP (0.015 g, 0.05 mmol) and 4,40-H2bpdc (0.0246 g, 0.1 mmol) were
used instead of PIP and Hdnba. Yellow block crystals suitable for X-ray
diffraction of complex 7 were isolated by mechanical separation from
amorphous solid in 30% yield (based on Cd(II) salt). Anal. Calcd for
C
82H58Cd2N16O9S4: C 55.77, H 3.29, N 12.69%. Found: C 55.73, H 3.32,
N 12.63%. IR (KBr, cmꢁ1): 3356(w), 3040(w), 2365(w), 1605(m),
1578(s), 1523(m), 1378(s), 1059(m), 1000(m), 833(s), 773(s), 730(s),
698(s), 676(s).
2.2.2. [Cd(PIP)(ox)] ꢀ H2O (2)
The synthetic procedure for 2 is the same as that for 1 except
that H2ox (0.0126 g, 0.1 mmol) was used instead of Hdnba. Yellow
block crystals suitable for X-ray diffraction of complex 2 were
isolated by mechanical separation from amorphous solid in 40%
yield (based on Cd(II) salt). Anal. Calcd for C21H13CdN4O5: C 49.05,
H 2.53, N 10.90%. Found: C 49.02, H 2.54, N 10.87%. IR (KBr, cmꢁ1):
3486(m), 3065(w), 2843(w), 2360(w), 1652(s), 1592(s), 1463(s),
1308(s), 1079(m), 795(s), 733(s).
2.3. X-ray crystallographic study
A Bruker Apex CCD diffractometer (MoK
a radiation, graphite
˚
monochromator,
l
¼0.71073 A) was used to collect data. The
structures were solved by direct methods with SHELXS-97 and
Fourier techniques and refined by the full-matrix least-squares
method on F2 with SHELXL-97 [30,31]. All non-hydrogen atoms
were refined anisotropically, the H-atoms from nitrogen atom of
imidazole ring in PIP, 3-PIP, or TIP were located in different Fourier
synthesis maps, and other hydrogen atoms of the ligands were
generated theoretically onto the specific atoms and refined iso-
tropically with fixed thermal factors. The H-atoms of water
molecules have not been localized. All the crystal data and
structure refinement details for the seven complexes are given
in Table 1. The data of relevant bond distances and angles are listed
in Table S1. Crystallographic data for the structures reported in this
paper have been deposited in the Cambridge Crystallographic Data
Center with CCDC reference numbers 784,899, 784,900, 784,901,
784,902, 784,903, 784,904, and 784,905 for complexes 1, 2, 3, 4, 5, 6,
and 7, respectively.
2.2.3. [Cd(PIP)(1,4-bdc)(H2O)] ꢀ 4H2O (3)
The synthetic procedure for 3 is the same as that for 1 except
that 1,4-H2bdc (0.0166 g, 0.1 mmol) was used instead of Hdnba.
Yellow block crystals suitable for X-ray diffraction of complex 3
were isolated by mechanical separation from amorphous solid in
23% yield (based on Cd(II) salt). Anal. Calcd for C27H26CdN4O9:
C 48.87, H 3.92, N 8.45%. Found: C 48.81, H 3.95, N 8.41%. IR (KBr,
cmꢁ1): 3456(w), 3062(w), 2361(w), 1581(s), 1477(m), 1446(m),
1392(m), 1342(s), 1288(m), 1234(m), 1172(w), 1072(w), 948(m),
844(m), 802(m), 753(s), 698(m).

282
X. Wang et al. / Journal of Solid State Chemistry 184 (2011) 280–288
Table 1
Crystal data and structure refinement parameters for complexes 1ꢁ7.
Complex
1
2
3
4
5
6
7
Formula
C52H30CdN12O12
1127.28
C21H13CdN4O5
513.75
C27H26CdN4O9
662.93
C36H34CdN10O6
815.13
C86H62Cd2N20O11
1776.38
C26H18CdN6O8
654.86
C82H58Cd2N16O9S4
1764.48
Fw
Crystal system
Space group
Monoclinic
P21/c
Monoclinic
P21/c
Triclinic
Orthorhombic
Pbcn
Tetragonal
I41/a
Triclinic
Pꢁ1
Tetragonal
I41/a
Pꢁ1
14.0642(10)
8.9750(9)
9.4948(15)
13.805(5)
20.627(2)
9.002(5)
20.587(5)
˚
a (A)
22.4799(15)
15.6391(10)
17.6523(17)
12.6855(12)
10.7833(17)
13.591(2)
9.278(5)
20.627(2)
35.584(5)
11.139(5)
12.831(5)
20.587(5)
34.824(5)
˚
b (A)
25.858(5)
˚
c (A)
a
b
g
(deg)
90
90
93.820(2)
102.414(2)
104.722(2)
1303.5(3)
90.000(5)
90.000(5)
90.000(5)
3312(2)
90
69.824(5)
83.066(5)
85.805(5)
1198.1(10)
90.000(5)
90.000(5)
90.000(5)
14759(5)
102.1330(10)
90
99.6480(10)
90
90
(deg)
(deg)
90
3
4834.0(6)
1981.3(3)
15140(3)
˚
V (A )
Z
Dc (g cm-3
4
4
2
4
8
2
8
)
1.549
1.722
1.145
1020
1.689
0.902
672
1.635
1.559
1.815
0.979
656
1.588
m
(mm-1
)
0.531
0.725
0.641
0.763
F(000)
2280
1664
7214
7152
Tot. data
26,348
9462
9887
11,306
5140
31,413
4123
38,506
6686
6169
52,395
6537
Uniq. data
3477
4202
Rint
0.0381
0.0403/0.0982
0.980
0.0348
0.0318/0.0652
1.025
0.0693
0.0480/0.0942
0.881
0.0289
0.0311/0.0879
1.059
0.1253
0.0539/0.1199
1.000
0.0308
0.0433/0.0790
1.010
0.0742
0.0340/0.0737
1.079
b
R1a/wR2
GOF on F2
P
P
a
R1¼ :Fo9ꢁ9Fc:/ 9Fo9.
P
P
b
wR2¼{ [w(F2o ꢁF2c)2]/ [w(F2o)2]}1/2
.
3. Results and discussion
unique zigzag chain structure (Fig. 2b), where the Cd–Cd–Cd angle,
defined by the orientation of the ox ligands in the chain, is
100.016(6)1. The PIP ligands in 2 are arranged in a parallel fashion
at both sides of the chain, leading to a structure suitable to form
3.1. Description of crystal structures for 1–7
p
–
p
stacking interactions. The 1D zigzag chains are further extended
3.1.1. [Cd(PIP)2(dnba)2] (1)
into a 3D supramolecular architecture by intermolecular stacking
p–p
The crystal structure of 1 consists of a discrete mononuclear
[Cd(PIP)2(dnba)2]. As shown in Fig. 1a, each Cd(II) atom is six-
coordinated and adopts a distorted octahedral arrangement, being
ligated by four nitrogen atoms from two chelating PIP ligands with
˚
(3.800 A) and hydrogen bonding interactions between the N atom of
imidazole group and carboxylate oxygen atom [N(4)–H(4A)?O(3)
2.767 A, 1681](Fig. 2c, Fig. S2a, S2b). The results indicate that the weak
˚
˚
noncovalent interactions are important in the formation of the final
bond distances of 2.325(3)–2.429(3) A, and two oxygen atoms of
˚
supramolecular structure of 2.
two dnba ligands (Cd1–O1¼2.298(3), Cd1–O3¼2.298(3) A). The
N1, N5, N6, and O3 atoms comprise the equatorial plane, whereas
the N2 and O1 atoms are located in the axial positions. The adjacent
discrete mononuclears are arranged into a 1D supramolecular
p–p stacking interactions (3.679,
3.771 and 3.878 A) and one kind of hydrogen bonding interactions
between the N atom of imidazole group and carboxylate oxygen
atom [N(3)–H(1)?O(4) 2.8081 A, 1681 and N(7)–H(7A)?O(2)
2.7323 A, 1641] (Fig. 1b, Fig. S1a, S1b). The adjacent 1D supramo-
lecular chains are further connected by another kind of hydrogen
3.1.3. [Cd(PIP)(1,4-bdc)(H2O)] ꢀ 4H2O (3)
The structure of 3 is also a 1D zigzag chain. The asymmetric unit
of 3 is composed of one Cd atom, one PIP ligand, one 1,4-bdc ligand,
one coordinated water molecule and four uncoordinated water
molecules (Fig. 3a). Each Cd(II) atom is coordinated by four
carboxylic oxygen atoms from two different 1,4-bdc ligands and
one oxygen atom from one coordinated water molecule, and two
nitrogen atoms from one chelating PIP ligands, thereby forming a
seven-coordinated structure with a N2O5 donor set. The Cd–O bond
architecture by intermolecular
˚
˚
˚
bonding interactions between the C atom of pyridine group and
carboxylate oxygen atom [C(14)–H(14A)?O(7) 3.2743 A, 1311,
and C(43)–H(43A)?O(8) 3.4429 A, 1661] to form a 2D supramo-
˚
˚
lengths are in the range 2.238(4)–2.527(4) A, and the Cd–N bond
lengths are in the range 2.335(4)–2.405(4) A. Each Cd atom is
˚
˚
linked to adjacent Cd atoms through the bridging bis-chelating
1,4-bdc ligands, forming a unique zigzag chain structure (Fig. 3b),
where the Cd–Cd–Cd angle, defined by the orientation of the
1,4-bdc ligands in the chain, is 95.588(4)1. The PIP ligands in 3 are
arranged in a parallel fashion at both sides of the chain, leading to a
lecular network (Fig. 1c, Fig. S1c). The adjacent 2D supramolecular
layers are further connected by intermolecular
˚
p–p stacking
interactions (3.954 A) to form a 3D supramolecular network
(Fig. 1d, Fig. S1d).
structure suitable to form p–p stacking interactions. The adjacent
1D zigzag chains are further extended into a 2D supramolecular
˚
architecture by intermolecular p–p stacking interactions (3.705 A)
and two kinds of hydrogen bonding interactions between the N atom of
imidazole group and carboxylate oxygen atom [N(4)–H(4A)?O(4)
3.1.2. [Cd(PIP)(ox)] ꢀ H2O (2)
The structure of 2 is a 1D zigzag chain. The asymmetric unit of 2
is composed of one Cd atom, one PIP ligand, one ox ligand and one
uncoordinated water molecule (Fig. 2a). Each Cd(II) atom displays a
distorted octahedral coordination geometry, which is coordinated
by four oxygen atoms from two ox ligands and two nitrogen atoms
from one chelating PIP ligand. The Cd–O bond lengths are in the
˚
2.8644 A, 1491], and between the oxygen atom of coordinated
˚
water and carboxylate oxygen atom [O(5)–H(5A)?O(2) 2.7251 A,
1571] (Fig. 3c, Fig. S3a). The adjacent 2D supramolecular architec-
˚
˚
range of 2.238(2)–2.317(2) A, and the Cd–N bond lengths are in the
tures are further connected by intermolecular p–p stacking
interactions (3.921 A) to form a 3D supramolecular network
(Fig. 3d, Fig. S3b).
˚
range of 2.296(3)–2.312(3) A. Each Cd atom is linked to adjacent Cd
atoms through the bridging bis-chelating ox ligands, forming a

X. Wang et al. / Journal of Solid State Chemistry 184 (2011) 280–288
283
Fig. 1. View of (a) the coordination environment for Cd(II) atom in 1 (thermal ellipsoids are at the 30% probability level); (b) the 1D chain of 1 formed through intermolecular
stacking and hydrogen bonding interactions; (c) the 2D layer of 1 formed between 1D chains by hydrogen bonding interactions; and (d) the 3D structure of 1 formed
through stacking interactions between different supramolecular layers.
p–p
p–p
˚
3.1.4. [Cd(3-PIP)2(H2O)2] ꢀ 4H2O (4)
3.666, 3.743, and 3.941 A) and hydrogen bonding interactions
The crystal structure of 4 consists of a discrete mononuclear
[Cd(3-PIP)2(H2O)2] ꢀ 4H2O. As shown in Fig. 4a, each Cd(II) atom is
six-coordinated and adopts a distorted octahedral arrangement,
being ligated by four nitrogen atoms from two chelating 3-PIP
between the N atom of imidazole group and oxygen atom of
coordinated water molecules [N(3)–H(3 A)?O(5) 2.6978 A, 1561]
˚
(Fig. 5b, Fig. S5a, S5b).
˚
ligands with bond distances of 2.3653–2.3712 A, and two oxygen
atoms from two coordinated water molecules with bond distances
3.1.6. [Cd(3-PIP)(nip)(H2O)] ꢀ H2O (6)
˚
of 2.2188(15) A. Moreover, there are four uncoordinated water
The structure of 6 is a 1D double chain structure. The asymmetric
unit of 6 is composed of one Cd atom, one 3-PIP ligand, one nip
ligand, one coordinated water molecule and one uncoordinated
water molecule (Fig. 6a). Each Cd(II) atom displays a distorted
octahedral coordination geometry, which is coordinated by two
carboxylic oxygen atoms from two different nip ligands and one
oxygen atom from one coordinated water molecule, two chelating
nitrogen atoms of the 3-PIP ligand and one nitrogen atom from
3-pyridyl group of another 3-PIP ligand. The O2 atom from the nip
ligand has a weak bonding interaction with the Cd(II) atom (Cd(1)–
molecules in 4. The adjacent discrete mononuclears are arranged
into a 2D supramolecular architecture by intermolecular
p–p
˚
stacking interactions (3.536, 3.574, 3.591, and 3.682 A) and hydro-
gen bonding interactions between the N atom of imidazole group
and oxygen atom of coordinated water molecules [N(3)–H(3B)?
˚
O(1) 2.6477 A, 1601] (Fig. 4b, Fig. S4a). The adjacent 2D supramo-
lecular architectures are further connected by intermolecular p–p
˚
stacking interactions (3.644 A) to form a 3D supramolecular net-
work (Fig. 4c, Fig. S4b).
˚
O(2)¼2.613(5) A), which is longer than ones found in other
complexes [32], indicative of weak interactions between the oxygen
atom and the Cd(II) center. The Cd–O bond lengths are in the range
3.1.5. [Cd2(3-PIP)4(4,40-bpdc)(H2O)2] ꢀ 5H2O (5)
˚
The crystal structure of 5 consists of a discrete dinuclear [Cd2(3-
PIP)4(4,40-bpdc)(H2O)2] ꢀ 5H2O. As shown in Fig. 5a, each Cd(II)
atom is six-coordinated and adopts a distorted octahedral arrange-
ment, being ligated by four nitrogen atoms from two chelating
2.286(6)–2.541(5) A, and the Cd–N bond lengths are in the range
˚
2.357(5)–2.419(5) A. It was noted that the coordination environ-
ment of the Cd(II) atom in 6 is clearly different from complexes
4 and 5, the N atom from individual 3-pyridyl group of 3-PIP act as
the bridging site. Each Cd atom is linked to adjacent Cd atoms
through the bridging 3-PIP ligands, forming a unique linear chain
structure. The adjacent two linear chains are further connected into
a double chain structure through the bridging bis-monodentate nip
ligands (Fig. 6b). The adjacent 1D double chains are further arranged
˚
3-PIP ligands with bond distances of 2.337(5)–2.376(5) A, and two
oxygen atoms from 4,40-bpdc and one water molecule, respectively,
˚
[Cd1–O1¼2.226(4), Cd1–O5¼2.320(4) A]. Moreover, there are five
uncoordinated water molecules in 5. The adjacent discrete dinuc-
lears (Fig. 5a) are arranged into a 3D supramolecular architecture
by intermolecular
p–p
stacking interactions (3.609, 3.617, 3.656,
into a 2D supramolecular architecture by intermolecular p–p

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X. Wang et al. / Journal of Solid State Chemistry 184 (2011) 280–288
Fig. 2. View of (a) the coordination environment for Cd(II) atom in 2 (thermal ellipsoids are at the 30% probability level); (b) the 1D zigzag chain in 2; and (c) the 3D
supramolecular structure of 2 formed through stacking and hydrogen bonding interactions.
p–p
˚
˚
stacking interactions (3.817 A) and one kind of hydrogen bonding
interactions between the oxygen atom of coordinated water
molecule and carboxylate oxygen atom [O(3)–H(3C)?O(5)
face distances between the paired TIP rings are 3.868 and 3.902 A
(Fig. S7b). In fact, stacking interactions play an important role in
p–p
the formation and stabilization of the supramolecular structure [16].
˚
2.7716 A, 1721] (Fig. 6c, Fig. S6a). The adjacent 2D supramolecular
architectures are further connected by intermolecular
˚
p–p stacking
3.2. Effect of the N-donor ligands and organic carboxylate
anions on the structures of the complexes
interactions (3.674 A) and another kind of hydrogen bonding
interactions between the N atom of imidazole group and carbox-
˚
ylate oxygen atom [N(5)–H(5A)?O(4) 2.7340 A, 1611] to form a 3D
supramolecular network (Fig. 6d, Fig. S6b).
In this paper, the structural differences of 1–7 indicate that both
phen derivatives and organic carboxylate anions play an important
role in the formation of such coordination architectures. Comparing
complexes 1–3 obtained from the same PIP and Cd(NO3)2 under the
same conditions, in 1, pair of crossed PIP ligands coordinate to one
Cd(II) atom, and dnba carboxylate anions exhibit monodentate
coordination mode. The existence of the substituted –NO2 groups
increases the steric hindrance of the dnba ligand, resulting in the
mononuclear structure of 1. In2 and 3, only one PIP ligand coordinates
3.1.7. [Cd2(TIP)4(4,40-bpdc)(H2O)2] ꢀ 3H2O (7)
Complexes 7 and 5 are isostructural, which has similar neutral
coordination environment to that of 5, also shows distorted
octahedral geometry (Fig. 7). Compared with 5, the arranged fashion
of the thienyl group of TIP ligands in 7 is different, leading to
a structure suitable to form
p–p interactions. Thus, the face-to-

X. Wang et al. / Journal of Solid State Chemistry 184 (2011) 280–288
285
Fig. 3. View of (a) the coordination environment for Cd(II) atom in 3 (thermal ellipsoids are at the 30% probability level); (b) the 1D zigzag chain in 3; (c) the 2D supramolecular
structure of 3 formed between 1D chains by p–p stacking and hydrogen bonding interactions; and (d) the 3D structure of 3 formed through p–p stacking interactions between
different supramolecular layers.
Fig. 4. View of (a) the coordination environment for Cd(II) atom in 4 (thermal ellipsoids are at the 30% probability level); (b) the 2D supramolecular structure of 4 formed
through stacking and hydrogen bonding interactions; and (c) the 3D structure of 4 formed through stacking interactions between different supramolecular layers.
p–
p
p–p
to one Cd(II) atom, the ox and 1,4-bdc carboxylate anions adopt
bridging bis-chelating coordination mode and serve as a m2 bridge,
resulting in 1D zigzag chains in 2 and 3. The structural differences in
1–3 show the influence of the number of the carboxylate groups.
Complexes 4–6 based on the same 3-PIP and Cd(NO3)2 also demon-
strate the influence of the carboxylate anions on their structures.
In 4, the two water molecules and pair of crossed 3-PIP ligands all
coordinate to one Cd(II) atom, resulting in the mononuclear structure
of 4. In 5, pair of crossed 3-PIP ligands coordinate to one Cd(II) atom,
one 4,40-bpdc carboxylate anion bridges two Cd(II) centers to form a
very stable dinuclear structure. Clearly, the longer linear 4,40-bpdc
ligand helps the formation of the discrete dinuclear complex 5.
Compared with PIP ligand in complexes 1–3, 3-PIP ligand in com-
plexes 4–6 has one extra coordination site, i.e. the nitrogen atom of

286
X. Wang et al. / Journal of Solid State Chemistry 184 (2011) 280–288
Fig. 5. View of (a) the dinuclear compound 5 (thermal ellipsoids are at the 30% probability level); (b) the 3D supramolecular framework of 5 formed through p–p stacking and
hydrogen bonding interactions.
Fig. 6. View of (a) the coordination environment for Cd(II) atom in 6 (thermal ellipsoids are at the 30% probability level); (b) the double chain structure in 6 based on the
dinuclear unit; (c) the 2D supramolecular structure of 6 formed between 1D chains by stacking and hydrogen bonding interactions; and (d) the 3D structure of 6 formed
through stacking and hydrogen bonding interactions between different supramolecular layers.
p–p
p–p
pyridyl group of 3-PIP ligand, which could coordinate to the Cd atom
as the bridging site. Fortunately, we obtained complex 6 with 1D
double chain structure. In 6, it is noted that the coordination
environment of the Cd(II) atom is clearly different from that of
complexes 4 and 5, the N atom from individual 3-pyridyl group of
3-PIP act as the bridging site. Each Cd atom is linked to adjacent Cd
atoms through the bridging 3-PIP ligands, forming a unique linear
chain structure. The adjacent two linear chains are further extended
into a double chain structure through the bridging bis-monodentate
nip ligands.
neutral N-donor chelating ligands. Although complexes 1 and 4
show similar mononuclear structures, the interactions of the
neutral ligands in them are slightly different. In 1, the mononuclear
p–p
structures connect with adjacent mononuclear structures through
four types of
bonds to form a 3D supramolecular structure. However, in 4, the
mononuclear structures interact through five types of inter-
action and N–H?O hydrogen bond to form a 3D supramolecular
structure. Complexes and are isostructural. In 5, the
dinuclear structures interact through six types of interaction
p–p interactions and C–H?O and N–H?O hydrogen
p–p
7
5
p–p
The supramolecular structures constructed by
p–p
stacking and
and N–H?O hydrogen bonding interaction to form a 3D supra-
hydrogen bonding interactions can be modified by varying the
molecular structure. However, in 7, the dinuclear structures

X. Wang et al. / Journal of Solid State Chemistry 184 (2011) 280–288
287
Fig. 7. View of the dinuclear compound 7 (thermal ellipsoids are at the 30% probability level).
interact by eight types of
bond to form a 3D supramolecular structure. Compared with 5,
there exist interactions between TIP ligands in 7 with face-to-
face distances of 3.868 and 3.902 A. In contrast 2, 3, and 6, in 2, the
zigzag chains are further stacked via one type of interaction and
p
–
p
interaction and N–H?O hydrogen
a rapid weight loss from 360 to 530 1C corresponds to the organic
ligands and the remaining residue is CdO (obsd 7.49%, calcd 7.28%).
p–p
˚
3.4. Luminescent properties of 1–7
p–p
N–H?O hydrogen bond to form a 3D supramolecular structure.
The solid-state luminescence properties of complexes 1–7 are
measured at room temperature (Fig. 8). The emission of ligand PIP
occurs at 444 nm upon excitation at 280 nm. Complexes 2 and 3
exhibit intense fluorescent emission bands with maximum at 474
and 510 nm, respectively, upon excitation at 300 nm, displaying
some shifts relative to that of free PIP ligand. Therefore, the
emission of complexes 2 and 3 may be attributed to ligand-to-
metal charge transfer (LMCT) based on PIP ligand. The emission
profile of 1 is very weak compared with that of 2 and 3, which may
be attributed to the significant difference of their structures. The
emission for complexes 4–6 exhibit intense fluorescent emission
bands with maximum at 494, 533, and 510 nm, respectively, upon
excitation at 300 nm, while the free ligand 3-PIP shows lumines-
cence in the solid state at lmax¼424 nm upon excitation at
lex¼260 nm under the same experimental conditions. Complex
7 exhibits intense luminescent emission at lmax¼551 nm upon
excitation at lex¼310 nm, while the free ligand TIP shows lumi-
nescence in the solid state at lmax¼443 nm upon excitation at
lex¼293 nm under the same experimental conditions. Compared
with that of the free ligand 3-PIP, the emission profiles of 4–6 are
red-shifted, which may be due to the increase of conjugation upon
metal coordination and originate from the ligand-to-metal charge-
transfer (LMCT) [33].
However, in 3 and 6, the chain structures are linked by two types of
p–p
interaction and two types of hydrogen bonds to form a 3D
supramolecular structure. It is noteworthy that the structure of
is entirely different from that of the related structure
3
[Cd(BDC)(phen)2(C2H5OH)(H2O)], where the two Cd(II) atoms are
only bridged by BDC ligands to form a 1D zigzag chain [32]. The
N-donor ligands with extended
formation and stabilization of the final supramolecular frameworks.
p-system play crucial role in the
3.3. Thermogravimetric analyses
Thermogravimetric analyses (TGA) are performed to gauge the
thermal stabilities of these complexes as shown in Fig. S8. For 1,
there is only one-step weight loss. TGA shows complex 1 is stable
below 350 1C. The successive mass loss from 350 to 713 1C may be
attributed to the gradual elimination of the organic ligands. The
remaining weight of 10.3% corresponds to the final product CdO
(calcd, 11.4%). For 2–7, there are two separate weight loss steps,
respectively. For 2, the first weight loss of 3.2% occurs at about
87 1C, which is attributed to the evacuation of crystallized water
molecules (calcd, 3.5%). The second gradual elimination of the
organic ligands between 344 and 820 1C corresponds to the loss of
69.56%. The remaining weight of 26.24% corresponds to the
percentage (calcd, 25.00%) of the Cd and O components, indicating
that the final product is CdO. The TG curve of complex 6 was similar
to that of complex 2, but the first weight loss of 5.3% is attributed to
the evacuation of crystallized water molecules and coordinated
water molecules (calcd, 5.5%). The remaining weight of 20.69%
corresponds to the final product CdO (calcd, 19.16%). The TG curves
of complexes 3–5 and 7 indicate that the framework of these
compounds all began to collapse from 360 1C. In complex 3, the
mass loss region from 100 to 155 1C is due to dehydration of the
crystallized water molecules and coordinated water molecules
(obsd 14.00%, calcd 13.58% for 3). The successive mass loss from
360 to 436 1C may be attributed to the rapid weight loss of the
organic ligands. A residue of CdO remained (obsd 20.17%, calcd
19.37%). The resulting residue of compounds 4 and 5 remain as CdO
(obsd 15.50%, calcd 15.75% for 4; obsd 7.49%, calcd 7.23% for 5) after
the complete decomposition of the organic ligands. In compound 7,
4. Conclusions
Seven new supramolecular architectures have been successfully
isolated under hydrothermal conditions by reactions of different
phen derivatives and Cd(II) salts together with organic carboxylate
anions auxiliary ligands. The influence of the N-donor ligands and
organic carboxylate anions on the structures of the complexes has
been studied. Complexes 1 and 4 have mononuclear structures,
while complexes 5 and 7 have dinuclear structures; complexes
2 and 3 feature chain structures; complex 6 contains double chain
structure. The structural difference of 1–7 indicates that phen
derivatives and organic carboxylate anions play an important role
in the formation of final architectures. Complexes 1–7 are further
extended to a 3D structure by
interactions. As important phen derivatives, the key role of PIP,
p–p stacking and hydrogen bonding

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X. Wang et al. / Journal of Solid State Chemistry 184 (2011) 280–288
Talent-supporting Program Foundation of Liaoning Province (nos.
2009R03 and 2009A028) are greatly acknowledged.
Appendix A. Supporting information
Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.jssc.2010.11.016.
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Acknowledgments
Financial supports of this research by the NCET-09-0853, the
National Natural Science Foundation of China (no. 20871022) and