Chains, ladders and sheets of d10 metal-organic polymers generated from the flexible bipyridyl ligands

Article abstract of DOI:10.1016/j.poly.2007.07.048

By use of the three-layer diffusion method, reactions of flexible bipyridyl ligands (4,4′-bpp or 3,3′-bpp) with M(II) salts (M = Zn, Cd) and multi-carboxylate ligands resulted in the formation of four interesting d¹⁰ metal-organic coordination polymers: [Zn(μ-4,4′-bpp)Br₂]_n (1), [Zn(μ-4,4′-bpp)(1,2-bdc)]_n · nH₂O (2), [Zn(μ-3,3′-bpp)(1,3-bdc)]_n · nCH₃OH · 2nH₂O (3) and [Cd(μ-3,3′-bpp)(C₄H₂O₄)]_n · 3nH₂O (4) (4,4′-bpp = 2,2′-bis(4-pyridylmethyleneoxy)-1,1′-biphenylene; 3,3′-bpp = 2,2 ′-bis(3-pyridylmethyleneoxy)-1,1′-biphenylene; bdc=benzenedicarboxylate, C₄H₄O₄ = fumaric acid). Complex 1 has a 2D sheet structure consisting of two unusual zigzag Zn(II) chains which are nearly perpendicular to each other. Complex 2 is comprised of two-leg ladders, in which [Zn(4,4′-bpp)] chains serve as the side rails and 1,2-bdc ligands serve as the cross rungs. In complex 3, every two 1,3-bdc ligands connect the neighbouring Zn(II)-3,3′-bpp dimetallic rings in η¹ coordination modes into an interesting chain structure. Complex 4 consists of an anionic macrocycle-containing cadmium dicarboxylate sheets that are separated by 3,3′-bpp. These d¹⁰ metal complexes exhibit high thermal stabilities and strong luminescence efficiencies.

Full text of DOI:10.1016/j.poly.2007.07.048

Available online at www.sciencedirect.com
Polyhedron 26 (2007) 5309–5316
www.elsevier.com/locate/poly
Chains, ladders and sheets of d10 metal–organic polymers
generated from the flexible bipyridyl ligands
Yaqiong Gong, Ruihu Wang, Daqiang Yuan, Weiping Su, Yougui Huang,
*
Chengyang Yue, Feilong Jiang , Maochun Hong
State Key Laboratory of Structural Chemistry, Fujian Institute of the Research on the Structure of Matter,
Chinese Academy of Sciences, Fuzhou 350002, China
Received 26 April 2007; accepted 27 July 2007
Available online 14 September 2007
Abstract
By use of the three-layer diffusion method, reactions of flexible bipyridyl ligands (4,40-bpp or 3,30-bpp) with M(II) salts (M = Zn, Cd)
and multi-carboxylate ligands resulted in the formation of four interesting d10 metal–organic coordination polymers: [Zn(l-4,40-
bpp)Br2]n (1), [Zn(l-4,40-bpp)(1,2-bdc)]n Æ nH2O (2), [Zn(l-3,30-bpp)(1,3-bdc)]n Æ nCH3OH Æ 2nH2O (3) and [Cd(l-3,30-bpp)(C4H2O4)]n Æ
0
3nH2O (4) (4,40-bpp = 2,20-bis(4-pyridylmethyleneoxy)-1,10-biphenylene; 3,30-bpp = 2,2 -bis(3-pyridylmethyleneoxy)-1,10-biphenylene;
bdc=benzenedicarboxylate, C4H4O4 = fumaric acid). Complex 1 has a 2D sheet structure consisting of two unusual zigzag Zn(II) chains
which are nearly perpendicular to each other. Complex 2 is comprised of two-leg ladders, in which [Zn(4,40-bpp)] chains serve as the side
rails and 1,2-bdc ligands serve as the cross rungs. In complex 3, every two 1,3-bdc ligands connect the neighbouring Zn(II)-3,30-bpp dime-
tallic rings in g1 coordination modes into an interesting chain structure. Complex 4 consists of an anionic macrocycle-containing cad-
mium dicarboxylate sheets that are separated by 3,30-bpp. These d10 metal complexes exhibit high thermal stabilities and strong
luminescence efficiencies.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Flexible bipyridyl; d10 Metal; Multi-carboxylate; Crystal structure; Coordination polymer; Optical properties
1. Introduction
drical complexes [5–7]. With the aim of introducing
valuable functional chiral spacers into pyridine-donor
ligands, the two flexible bipyridyl ligands 2,20-bis(4-pyr-
idylmethyleneoxy)-1,10-biphenylene (4,40-bpp) and 2,20-
The design of metal–organic coordination frameworks
has undergone explosive growth over the past decade
because of their intriguing structures and, more impor-
tantly, their potential applications as functional materials
[1–4]. Recently, optically active 1,1-bi-2-naphthol (BINOL)
has been widely used as a starting material and an auxiliary
in asymmetric synthesis or chiral recognition owing to its
axial chirality and configurational stability. Based on
BINOL-derived ligands, Lin and co-workers have recently
prepared a series of well-documented single-, double-, tri-
ple- and quadruple-stranded as well as circular and cylin-
bis(3-pyridylmethyleneoxy)-1,10-biphenylene
(3,30-bpp)
have been designed and synthesized by bringing monopyri-
dine functional groups and a dipyridyl connector into the
reaction system (Scheme 1).
In constructing coordination polymers, 4,40-bpp or 3,30-
bpp can be recognized as a useful starting material, since
their configurations can be greatly altered along the 1,10
bond to meet the considerable requirements for the con-
struction of metal–organic frameworks. Moreover, due to
the flexibility and conformational freedom of 4,40-bpp or
3,30-bpp, they promise great possibilities for generating
an infinite variety of aesthetic frameworks with useful
properties [8–10]. Recently, we have studied the above
*
Corresponding author. Tel.: +86 591 83714605; fax: +86 591
83714946.
E-mail address: fjiang@fjirsm.ac.cn (F. Jiang).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.07.048

5310
Y. Gong et al. / Polyhedron 26 (2007) 5309–5316
determined on an Elemental Vario ELIII elemental ana-
N
lyzer. Fluorescent spectra were measured on an Edinburgh
Instruments analyzer model FL920. Thermal analyses were
performed using a Thermal Analyst 2100 TA Instrument
and a SDT 2960 Simultaneous TGA-DTA Instrument.
N
O
O
N
O
O
N
4,4'-bpp
3,3'-bpp
2.2. Synthesis of complexes
Scheme 1. Structure of 4,40-bpp and 3,30-bpp ligands.
2.2.1. Synthesis of [Zn(l-4,40-bpp)Br2]n (1)
{M–bpp} systems with the introduction of multi-carboxyl-
ate ligands. With various flexible coordination modes for
carboxylate group ligands, dicarboxylate ligands can
bridge two or more different metal centers and produce
neutral architectures. These additional ligands could exhi-
bit a variety of bridging abilities and have a strong ten-
dency to form multidimensional structures, which would
be markedly different from those of M–(4,40-bpp) and
M–(3,30-bpp) complexes [11–17]. The combination of
bipyridyl and dicarboxylate with d10-metal ions could pro-
duce some unique frameworks with beautiful aesthetics and
useful properties.
A solution of ZnBr2 Æ 4H2O (0.029 g, 0.10 mmol) in H2O
(5 mL) was carefully covered by a buffer layer, prepared by
mixing MeOH and water (in a 1:1 ratio). Then a solution of
4,40-bpp (0.036 g, 0.10 mmol) in MeOH (5 mL) was slowly
added above the buffer layer. Over a period of four weeks,
light yellow block crystals formed on the buffer layer.
Yield: 0.040 g (68%). Elementary Anal. Calc. for
C24H20Br2N2O2Zn (593.61): C, 48.56; H, 3.40; N, 4.72.
Found: C, 48.51; H, 3.43; N, 4.68%. IR (KBr, cmꢀ1):
3430 (vw), 2923 (w), 1623 (s), 1596 (w), 1505 (s), 1483 (s),
1444 (s), 1328 (m), 1269 (s), 1234 (s), 1147 (s), 1054 (m),
1029 (s), 862 (w), 751 (s), 707 (s), 492 (vw).
Herein, we report the syntheses, crystal structures, ther-
mal stability and the fluorescence properties of four new
complexes: [Zn(l-4,40-bpp)Br2]n (1), [Zn(l-4,40-bpp)(1,2-
bdc)]n Æ nH2O (2), [Zn(l-3,30-bpp)(1,3-bdc)]n Æ nCH3O-
H Æ 2nH2O (3) and [Cd(l-3,30-bpp)(C4H2O4)]n Æ 3nH2O (4)
(bdc = benzenedicarboxylate, C4H4O4 = fumaric acid).
The research results reported here are of interest with
respect to the following aspects: (1) the introduction of
multi-carboxylate ligands to {M–bpp} systems via the
three-layer diffusion method plays an important role in
the formation of fascinating metal–organic frameworks,
which is significant for further exploring coordination
polymer chemistry; (2) complexes 1–4 with flexible bipyr-
idyl ligands present novel and unprecedented topologies
such as perpendicularly linked chains, two-leg ladders
and macroanionic sheets structures; (3) combination of
d10 center metals with the conjugated aromatic or pyridine
rings from both ligands provides fluorescent materials; (4)
complexes such as 1 and 3, owing to absence of inversion
centers, could function for a second harmonic generation
(SHG) response.
2.2.2. Synthesis of [Zn(l-4,40-bpp)(1,2-bdc)]n Æ nH2O (2)
A solution of ZnBr2 Æ 4H2O (0.029 g, 0.10 mmol),
NaOH (0.008 g, 0.20 mmol) and 1, 2-H2bdc (0.017 g,
0.10 mmol) in H2O (5 mL) was carefully covered by a buf-
fer layer (MeOH:H2O = 1:1). Then a solution of 4,40-bpp
(0.036 g, 0.10 mmol) in MeOH (5 mL) was slowly added
above the buffer layer. Over a period of four weeks, light
yellow block crystals of 2 formed at the buffer layer Yield:
0.051 g (83%). Elementary Anal. Calc. for C32H26N2O7Zn
(615.93): C, 62.40; H, 4.25; N, 4.55. Found: C, 62.15; H,
4.61; N, 4.50%. IR (KBr, cmꢀ1): 3435 (w), 3038 (w), 2853
(w), 1621 (w), 1595 (m), 1479 (m), 1432 (s), 1290 (w),
1231 (s), 1162 (m), 1118 (w), 1029 (m), 812 (w), 751 (s),
726 (s), 643 (w), 494 (w).
2.2.3. Synthesis of [Zn(l-3,30-bpp)(1,3-
bdc)]n Æ nCH3OH Æ 2nH2O (3)
A solution of ZnBr2 Æ 4H2O (0.029 g, 0.10 mmol), NaOH
(0.008 g, 0.20 mmol) and 1,3-H2bdc (0.017 g, 0.10 mmol) in
H2O (5 mL) was carefully covered by buffer layer
(MeOH:H2O = 1:1). Then a solution of 3,30-bpp (0.036 g,
0.10 mmol) in MeOH (5 mL) was slowly added above the
buffer layer. Light yellow block crystals were produced at
the buffer layer after a few weeks. Yield: 0.048 g (72%). Ele-
mentary Anal. Calc. for C33H32N2O9Zn (666.01): C, 59.51;
H, 4.84; N, 4.21. Found: C, 59.43; H, 4.88; N, 4.16%. IR
(KBr, cmꢀ1): 3065 (vw), 2927 (w), 1594 (m), 1500 (s),
1481 (s), 1444 (s), 1432 (s), 1284 (m), 1252 (s), 1227 (s),
1194 (m), 1161 (w), 1107 (s), 1050 (m), 1019 (s), 966 (vw),
871 (w), 751 (s), 701 (s), 669 (w), 616 (vw).
2. Experimental
2.1. General
2,20-Biphenol and 4-picolyl chloride hydrochloride were
purchased from Acros Ltd. Company and were used with-
out further purification, the other reagents were commer-
cially available and were used as purchased. The 4,40-bpp
and 3,30-bpp ligands were prepared according to the litera-
ture methods [9]. The NMR spectra were recorded on a
Varian Inova-500 spectrophotometer at room temperature.
The mass spectra were measured on a Fisons VG platform.
The IR spectra as KBr discs were recorded on a Magna 750
FT-IR spectrophotometer. C, H and N analyses were
2.2.4. Synthesis of [Cd(l-3,30-bpp)(C4H2O4)]n Æ 3nH2O
(4)
A solution of CdBr2 Æ 4H2O (0.034 g, 0.10 mmol) and
fumaric acid (0.012 g, 0.10 mmol) in H2O (5 mL) was care-

Y. Gong et al. / Polyhedron 26 (2007) 5309–5316
5311
fully covered by a buffer layer (MeOH:H2O = 1:1). Then a
solution of 3,30-bpp (0.036 g, 0.10 mmol) in MeOH (5 mL)
was slowly added above the buffer layer. Light yellow block
crystals of 4 were obtained at the buffer layer after a few
weeks. Yield: 0.048 g (75%). Elementary Anal. Calc. for
C28H28CdN2O9 (648.95): C, 51.82; H, 4.35; N, 4.32.
Found: C, 52.21; H, 3.99; N, 4.30%. IR (KBr, cmꢀ1):
3109 (vw), 2922 (w), 2165 (w), 1618 (w), 1595 (m), 1583
(m), 1500 (w), 1489 (m), 1453 (s), 1438 (s), 1286 (w), 1271
(s), 1241 (s), 1191 (m), 1161 (w), 1128 (s), 1049 (m), 1031
(m), 937 (vw), 911 (vw), 866 (w), 783 (m), 685 (s), 648
(w) 615 (vw), 544 (vw), 486 (vw), 454 (vw).
in Table 1. Selected bond lengths and angles are listed in
Table 2.
3. Results and discussion
3.1. Description of crystal structures
3.1.1. [Zn(l-4,40-bpp)Br2]n (1)
Single crystal X-ray diffraction analysis reveals that
complex 1 is a chain structure and crystallizes in the ortho-
rhombic space group C222. As depicted in Fig. 1a, complex
1 contains two independent Zn(II) centers. Each Zn(II)
center has a slightly distorted tetrahedral geometry and is
coordinated by two terminal bromide anions (Zn(1)–
2.3. X-ray crystallography
˚
Br(1) 2.360(5) A, Br(1)–Zn(1)–Br(1A) 117.84(3)ꢁ; and
˚
Single crystals of these complexes with appropriate
dimensions were mounted on a glass fiber and used for
data collection. Data were collected at 293(2) K on a Sie-
mens Smart CCD diffractometer with graphite-monochro-
Zn(2)–Br(2) 2.348(8) A, Br(2)–Zn(2)–Br(2A) 115.14(5)ꢁ).
The remaining two coordinative sites of the Zn(II) center
in each line are occupied by two nitrogen atoms from dif-
ferent 4,40-bpp ligands. The bond distances between the
Zn(II) center and the nitrogen donor are Zn(1)–N(1)
˚
mated Mo Ka radiation (k = 0.71073 A). Empirical
˚
absence of the centers of symmetries meets the essential
requirement of a SHG response. Absorption corrections
were applied by using the SADABS program for the Siemens
area detector. The structures were solved with direct meth-
ods and all calculations were performed using the SHELXTL
package [18]. The structures displacement parameters were
calculated for all non-hydrogen atoms. The positions of H
atoms were generated geometrically and treated as riding
on their parent atoms. Details of the crystal data are listed
2.044(3), Zn(2)–N(2) 2.061(4) A.
Because of steric exclusion, the pyridyl rings of two
independent 4,40-bpp ligands are highly twisted, the dihe-
dral angles between the two pyridyl rings are 68.5ꢁ and
21.0ꢁ. The dihedral angles between the two phenyl rings
in two 4,40-bpp ligands are 127.6ꢁ and 71.5ꢁ. The Zn(II)
centers are linked by the twisted 4,40-bpp ligands into a zig-
zag chain structure. It is noteworthy that the two chains in
1 are nearly perpendicular to each other, as shown in
Table 1
Crystallographic data for complexes 1–4
Complexes
1
2
3
4
Formula
C
593.61
0.45 · 0.28 · 0.22
orthorhombic
C222
12.631
14.540
25.6933(10)
90
90
24H20Br2N2O2Zn
C32H26N2O7Zn
615.93
0.38 · 0.26 · 0.20
triclinic
C33H32N2O9Zn
666.01
0.52 · 0.48 · 0.40
triclinic
C28H28CdN2O9
648.95
0.32 · 0.24 · 0.41
monoclinic
C2
12.9512(10)
31.835(2)
8.6952(7)
90
100.022(2)
90
3530.3(5)
4
1.210
0.663
1296
Formula weight
Crystal size (mm)
Crystal system
Space group
ꢀ
ꢀ
P1
P1
˚
a (A)
10.234(3)
11.079(3)
12.982(4)
90.652(2)
107.426(2)
102.549(4)
1366.1(7)
2
1.502
0.953
640
173(2)
10.132(3)
11.409(3)
14.038(4)
86.80(1)
73.84(1)
73.69(1)
1495.4(7)
2
1.479
0.882
692
173(2)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
3
˚
V (A )
4718.76(18)
8
1.671
2.460
2352
Z
Dcalc (Mg mꢀ3
)
l (mmꢀ1
F(000)
T (K)
)
173(2)
173(2)
˚
k (Mo Ka) (A)
0.71073
16959
5341
141
1.042
0.0373, 0.0794
0.0443, 0.0824
0.0818 and ꢀ0.855
0.71073
11240
6661
379
1.046
0.0353, 0.1008
0.0399, 0.1029
0.687 and ꢀ0.704
0.71073
11674
6767
414
1.062
0.0422, 0.1019
0.0471, 0.1052
0.968 and ꢀ0.641
0.71073
3805
1695
199
1.165
0.0608, 0.1686
0.0731, 0.1819
0.843 and ꢀ0.686
Reflections collected
Unique reflections
Parameters
Goodness-of-fit (S) of F2
R1, wR2 [I > 2r(I)]a
R1, wR2 (all data)b
ꢀ3
˚
Maximum and minimum Dq (e A
)
P
P
a
R1 = iFoj ꢀ jFci/ jFoj.
P
P
wR2=[ w(Fo ꢀ Fc2)2/ w(Fo4)]1/2, w = [r2(Fo2) + (aP)2 + bP]ꢀ1, P = (2Fc2 + Fo2)/3.
b
2

5312
Y. Gong et al. / Polyhedron 26 (2007) 5309–5316
Table 2
˚
Selected bond lengths (A) and angles (ꢁ) for 1–4
Compound 1
Zn1–Br1
2.360(5)
96.10(2)
107.76(1)
112.65(1)
Zn1–N1
2.044(3)
112.65(1)
107.76(1)
117.84(3)
Zn2–N2
Zn2–Br2A
N2–Zn1–N2A
N2A–Zn2–Br2A
2.061(4)
2.348(8)
99.7(3)
N2–Zn2–Br2A
N2–Zn1–Br2
Br2A–Zn2–Br
2 N2A–Zn2–Br2
107.17(1)
113.28(1)
115.14(5)
107.17(1)
N1–Zn1–N1A
N1A–Zn1–Br1
N1A–Zn1–Br1A
N1–Zn1–Br1
N1–Zn1–Br1A
Br1–Zn1–Br1A
113.28(1)
Compound 2
Zn1–O1
O1–Zn1–O3B
O1–Zn1–N2A
1.9246(1)
111.45(6)
132.34(6)
Zn1–O3B
O3B–Zn1–N2
O1–Zn1–N1
1.953(1)
104.18(6)
101.20(6)
Zn1–N2A
O3B–Zn1–N1
2.049(2)
96.90(6)
Zn1–N1
N2A–Zn(1)-N1
2.0751(2)
104.91(6)
Compound 3
Zn1–O1
O1–Zn1–O3B
O1–Zn1–N2A
1.974(2)
98.00(7)
110.60(7)
Zn1–N2A
O1–Zn1–N1
O3B–Zn1–N1
2.019(2)
111.19(8)
111.36(7)
Zn1–O3B
O3B1–Zn1–N2A
1.983(2)
116.61(7)
Zn1–N1
N2A–Zn1–N1
2.053(2)
109.62(8)
Compound 4
Cd–N1A
2.302(8)
178.8(4)
89.9(2)
89.85(2)
90.43(2)
90.43(2)
Cd–O1
Cd–O3
2.416(9)
2.418(1)
90.57(2)
92.6(3)
54.6(4)
165.1(3)
89.6(2)
Cd–O1B
Cd–O4
2.324(9)
2.362(9)
89.42(2)
89.42(2)
72.4(3)
Cd–O2
2.486(8)
89.6(2)
125.5(3)
87.2(4)
53.1(3)
141.9(4)
147.3(3)
N1A–Cd–N1
N1A–Cd–O1B
N1–Cd–O1B
N1A–Cd–O4
N1–Cd–O4
N1–Cd–O2
O1B–Cd–O2
O4–Cd–O2
O1–Cd–O2
O3–Cd–O2
O1B–Cd–O4
N1–Cd–O3
O1B–Cd–O3
O4–Cd–O3
O1–Cd–O3
N1A–Cd–O2
N1A–Cd–O1
N1–Cd–O1
O1B–Cd–O1
O4–Cd–O1
N1A–Cd–O3
140.3(3)
90.57(2)
Symmetry codes: For 1 A: ꢀx + 1/2, ꢀy + 1/2, B: ꢀx, ꢀy + 1,z, C: ꢀx + 1, ꢀy + 1, z. For 2 A: x ꢀ 1, y, z, B: ꢀx + 1, ꢀy + 2, ꢀz + 1. For 3 A: ꢀx,
ꢀy + 2, ꢀz + 1, B: xꢀ1, y, z. For 4 A: x, ꢀy, z, B: ꢀx, ꢀy, ꢀz + 1, C: x, ꢀy, ꢀz + 2.
Fig. 1a. View of the coordination environment of the Zn(II) center in 1
(A: ꢀx + 1/2, ꢀy + 1/2, z; B: ꢀx, ꢀy + 1, z; C: ꢀx + 1, ꢀy + 1; D: x ꢀ 1/
2, y ꢀ 1/2, z).
Fig. 1b. View of the vertical polymer chains in 1.
˚
O(1) 1.9246(13), Zn(1)–O(3B) 1.9534(13) A, O(1)–Zn(1)–
O(3B) 111.45(6)ꢁ).
Fig. 1b. The Znꢁ ꢁ ꢁZn separation in both chains is of the
˚
same distance, 9.630 A, while the two nearest Zn(II) centers
The legs of such a ladder are made up of [Zn(4,40-bpp)]n
chains, in which Zn(II) ions are bridged by 4,40-bpp ligands
and each ligand acts as an exo-bidentate ligand. In the legs,
two phenyl rings and two pyridyl rings of each 4,40-bpp
ligand are twisted more evidently than those in 1. The dihe-
dral angles between them are 111.5ꢁ and 51.3ꢁ, respectively.
The cross rungs of the ladder are made up of 1,2-bdc
ligands, where each of the carboxyl groups in a monoden-
tate coordination mode bridges two Zn(II) ions on either
side of the ladder. Interestingly, the dihedral angles
between the phenyl rings and their corresponding carboxyl-
ates are 94.2ꢁ and 99.0ꢁ, respectively, indicating that the
˚
are at a distance of 11.728 A. No guest molecules are
observed within the distorted rings owing to the high dis-
tortion and flexibility of 4,40-bpp.
3.1.2. [Zn(l-4,40-bpp)(1,2-bdc)]n Æ nH2O (2)
The structure of 2 comprises a two-leg ladder running
along the [001] direction. An ORTEP view of complex 2
is shown in Fig. 2a. The Zn(II) ion adopts a distorted tet-
rahedral coordination geometry and is coordinated by two
nitrogen atoms from different 4,40-bpp ligands (Zn(1)–
˚
N(2A) 2.0438(15), Zn(1)–N(1) 2.0751(15) A) and two car-
boxyl groups from two different 1,2-bdc ligands (Zn(1)–

Y. Gong et al. / Polyhedron 26 (2007) 5309–5316
5313
Fig. 3a. View of the coordination environment of the Zn(II) center in 3
(A: ꢀx, ꢀy + 2, ꢀz + 1; B: x ꢀ 1, y, z).
Fig. 2a. View of the coordination environment of the Zn(II) center in 2
(A: x ꢀ 1, y, z; B: ꢀx + 1, ꢀy + 2, ꢀz + 1).
structed from 1,3-bdc and Zn(II) ions, and the Zn–N bond
distances are typical, with values of 2.019(0) and
2.052(7) A. The angles O(1)–Zn(1)–O(3B) of 98.00(7)ꢁ
˚
carboxylates are approximately perpendicular, respec-
and O(3B)–Zn(1)–N(2A) of 116.61(7)ꢁ indicate a slight dis-
tortion compared with the ideal value of 109ꢁ280. The dihe-
dral angle of the two pyridyl rings attaching to the Zn(II)
ion is 83.2ꢁ, i.e. they are approximately perpendicular to
each other. The 3,30-bpp ligand acts as exo-bidentate,
and its pyridyl rings are twisted out of the plane of the link-
ing phenyl rings by 69.0ꢁ and 73.7ꢁ, while the two phenyl
rings of 3,30-bpp themselves have a drastic twisting with
the dihedral angle between them being 25.6ꢁ. The combina-
tion of these twistings allows 3,30-bpp to link two Zn(II)
ions into a dimetallic ring with the Znꢁ ꢁ ꢁZn separation
tively, to phenyl rings. In addition, the Znꢁ ꢁ ꢁZn separation
˚
among the legs of the ladder is 10.233 A and the Znꢁ ꢁ ꢁZn
˚
separation in the cross rungs is 5.153 A, as shown in
Fig. 2b.
3.1.3. [Zn(l-3,30-bpp)(1,3-bdc)]n Æ nCH3OH Æ 2nH2O (3)
The structure of 3 consists of neutral 1D chains through
the connection of [Zn(3,30-bpp)] units and 1,3-bdc bridging
ligands (Fig. 3a). The central Zn(II) ion is coordinated tet-
rahedrally by two monodentate carboxylate oxygen atoms
from two different 1,3-bdc ligands and two nitrogen atoms
from two 3,30-bpp ligands. The Zn–O bond lengths are
˚
being 8.139 A.
In addition, both carboxyl groups of the 1,3-bdc ligand
link the metal Zn(II) ion in a monodentate fashion and
they are deprotonated which is consistent with the IR data
(no absorption peaks in the 1715–1680 cmꢀ1 region). The
˚
1.9721(17) and 1.9836(16) A, in good agreement with those
bond lengths found in other extended structures con-
˚
Znꢁ ꢁ ꢁZn distance separated by 1,3-bdc is 10.132 A. The
dihedral angles between the phenyl rings and their corre-
sponding carboxylates are 33.7ꢁ and 49.7ꢁ, indicating a
slight twist between them. Thus, every two 1,3-bdc ligands,
acting in the monodentate mode, connect the neighbouring
Fig. 2b. View of two-leg ladder structure in 2.
Fig. 3b. View of 1D polymeric chain with dimetallic rings of 3.

5314
Y. Gong et al. / Polyhedron 26 (2007) 5309–5316
dimetallic rings formed by the 3,30-bpp ligand and Zn(II)
centers into an interesting 1D chain structure as shown in
Fig. 3b.
3.1.4. [Cd(l-3,30-bpp)(C4H2O4)]n Æ 3nH2O (4)
Complex 4 consists of anionic macrocyclic cadmium
dicarboxylate sheets which are separated by 3,30-bpp. The
local coordination environment around the Cd(II) center
in 4 can be described as a greatly distorted pentagonal bipyr-
amid, as shown in Fig. 4a. Two nitrogen donors from two
3,30-bpp ligands take up two vertexes of the coordination
polyhedron to stop the layer from developing into a 3D
˚
framework (Cd–N(1) 2.302(8), Cd–N(1A) 2.302(8) A,
N(1)–Cd–N(1A) 178.8(4)ꢁ). The equatorial plane of the
coordination polyhedron is composed of five oxygen atoms
belonging to three fumarate ligands. Two of the three fuma-
rate units bind the Cd(II) ions through a chelating interac-
tion, while the remaining one exhibits a chelating/bridging
bis-bidentate mode. All of five the Cd–O bond lengths are
in the range of the documented Cd–O(carboxy) distances
Fig. 4b. View of 2D structure of the macroanionic cadmium maleic sheets
in 4.
˚
(2.324(9)–2.486(8) A). The oxygen atom O(1), which partic-
ipates in the chelate-bridged interaction, bridges two Cd(II)
˚
atoms to form Cd2O2 dimers (Cdꢁ ꢁ ꢁCd, 3.825 A) through the
monodentate interaction, and exhibits the shortest coordina-
˚
tion distance (Cd–O(1), 2.324(9) A). The above binuclear
Cd2O2 subunit is connected to four neighbouring subunits
forming a network which is topologically equivalent to a
(4,4) network. Thus, the binuclear subunits are inter-con-
nected through fumarate ligands, which bridge the Cd2O2
to generate a parallegram-like sheet with dimensions of
Fig. 4c. View of the hybrid layer of 4.
˚
16.809 · 14.288 A, as measured from the centers of the binu-
clear subunits (Fig. 4b).
dimetallic ring, where the dihedral angles between the
two phenyl rings and the two pyridyl rings of the 3,30-
bpp ligand are 75.3ꢁ and 3.1ꢁ, respectively. Thus, the
metal–metal layers are planar with two N atoms from
the 3,30-bpp ligand pointing above and below the plane.
The layers are linked by strong p–p interactions, and the
adjacent layers stacking mode can be described as the
ABAB type in a staggered arrangement, as shown in
Fig. 4d.
Moreover, every two 3,30-bpp ligands, both in exo-
bidentate modes, are attached to the hybrid through the
Cd–N bonds to form a hybrid layer as shown in Fig. 4c.
It is noteworthy that 3,30-bpp, twisted due to the steric
exclusion requirement, links two Cd(II) centers into a big
3.2. TGA results
To study the stability of the polymers, the thermogravi-
metric analyses (TGA) for these complexes were performed
on polycrystalline samples under a nitrogen atmosphere.
The TG curves showed neither weight loss nor structural
change up to about 260 ꢁC, demonstrating that the frame-
works of 1–4 were retained up to these high temperatures.
Immediately above this point, the samples began to lose
ligands, the whole frameworks collapsed in a continuous
fashion and finally decomposed into unidentified products.
3.3. Luminescence properties
Luminescent polynuclear d10 metal complexes (such as
Zn(II) and Cd(II)) are of great interest because of their
Fig. 4a. View of 4 showing the coordination environment around the
Cd(II) center (A: x, ꢀy, z, B: ꢀx, ꢀy, ꢀz + 1, C: x, ꢀy, ꢀz + 2).

Y. Gong et al. / Polyhedron 26 (2007) 5309–5316
5315
intramolecular p–p* and n–p* transitions of the ligands,
but are also attributable to ligand-to-metal charge transfers
(LMCT) [19].
In comparison with complex 1, a blue-shift of 61 nm has
been observed in complex 2, partially due to the replace-
ment of the Brꢀ anion by the ligand 1,3-bdc. Although
complexes 2 and 3 have different structural motifs, both
complexes demonstrate some similar photoluminescence
behaviours. The blue-shifted emissions of 2 and 3 may orig-
inate from their larger conjugated systems for the two types
of ligands as well as their similar distorted tetrahedral coor-
dination geometries of d10 metal centers, where each of the
Zn(II) ions is coordinated by two pyridyl N atoms and two
carboxylate O atoms.
Complexes such as 1 and 3 do not have a center of sym-
metry, which meets the essential requirement of a SHG
response. Thus, Kurtz powder SHG measurements on the
acentric 1 and 3 were performed, and very weak SHG emis-
sions were observed for both complexes. The weak SHG
efficiency may be due to the following fact: the acentricities
of 1 and 3 are caused by their twist of the bpp ligands and
the arrangements of the individual chains result in a partial
cancellation of the effective dipolar moments [20,21].
Fig. 4d. View of the layers constructed of the ꢁ ꢁ ꢁABABꢁ ꢁ ꢁ type for 4.
potential application in chemical optical sensors, photosen-
sitization and electroluminescent devices. Here, the photo-
luminescence of these complexes was examined and the
solid-state emission spectra are shown in Fig. 5. Complex
1 exhibits a broad emission band with the maximum inten-
sity at 502 nm upon excitation at 370 nm, while complexes
2 and 3 produce an intense pure blue sharp emission with
the maximum at ca. 441 nm and a broad emission band
with the maximum intensity at 457 nm, respectively, with
excitation at 370 nm. For complex 4, two broad emissions
at 490 and 526 nm can be observed. For contrast, the free
4,40-bpp and 3,30-bpp molecules display the luminescence
at around 480 nm in the solid state. Generally, the intra-
ligand fluorescence emission wavelength is determined by
the energy gap between the p and p* molecular orbitals
of the free ligand, which is simply related to the extent of
p conjugation in the system. As for the metal complexes,
the red or blue shifted emissions of complexes 1–4 com-
pared to their free ligands are not only assigned to the
4. Conclusions
In summary, a series of novel coordination polymers
with interesting structural motifs have been synthesized
from the flexible bipyridyl ligands (4,40-bpp or 3,30-bpp)
and d10 metal ions (Zn2+ or Cd2+) as well as carboxylate
ligands by the three-layer diffusion method. Complex 1 is
a chain structure containing two unusual nearly vertical
zigzag Zn(II) chains, and 2 comprises a two-leg ladder,
where the legs and cross rungs are made of [Zn(4,40-bpp)]n
chains and bdc ligands, respectively. In 3, every two 1,3-
bdc ligands connect the neighbouring dimetallic rings into
an interesting 1D structure, while the 2D structure in 4 con-
sists of macroanionic cadmium fumarate sheets separated
by 3,30-bpp ligands. Moreover, TGA measurements exhibit
that complexes 1–4 have very similar thermal stability, and
studies on the luminescent emissions of these obtained
compounds reveal that the d10 metal ions cause red or blue
shifts of the emissions, assigned to intramolecular p–p* and
n–p* transitions of the ligands.
Complex 1
Complex 2
20000
Complex 3
Complex 4
15000
Acknowledgements
10000
5000
0
The authors are grateful to 973 Program
(2006CB932900), the National Nature Science Foundation
of China (20571074 and 20631050) and the Nature Science
Foundation of Fujian province for financial support of this
work.
Appendix A. Supplementary material
350
400
450
500
550
600
650
700
750
Wavelength (nm)
CCDC 268340, 268341, 292808 and 292809 contain the
Fig. 5. The emission spectra of 1–4 in the solid state at room temperature.
supplementary crystallographic data for 1, 2, 3 and 4.

5316
Y. Gong et al. / Polyhedron 26 (2007) 5309–5316
A.S.C. Chan, Angew. Chem., Int. Ed. 39 (2000) 2468;
(c) M.C. Hong, W.P. Su, R. Cao, M. Fujita, J.X. Lu, Chem. Eur. J. 6
(2000) 427.
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. Supplementary data
associated with this article can be found, in the online
version, at doi:10.1016/j.poly.2007.07.048.
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