Crystal structures and properties of four coordination polymers constructed from flexible pamoic acid

Article abstract of DOI:10.1016/j.poly.2010.04.004

Four novel coordination polymers constructed from flexible pamoic acid, namely [Co(pam)(4,4′-bipy)]_n·nH₂O (1), [Ni(pam)(4,4′-bipy)(H₂O)₂]_n· 2nCH₃CN (2), [Cd(pam)(py)₂]_n·npy (3) and [Mn₂(pam)₂ (py)6(H₂O)₂] _n·2npy (4), (H₂pam = pamoic acid, 4,4′-bipy = 4,4′-bipyridine, py pyridine), have been synthesized and characterized by elemental analysis, infrared spectra and X-ray crystallography. Complex 1 is a 2-D coordination polymer constructed from chelating bis-bidentate pam and 4,4′-bipyridine bridging ligands. Complex 2 is a 2-D coordination polymer assembled by bis-monodentate pam and 4,4′-bipyridine, where acetonitrile is filled in the rectangle channels. Both 2-D coordination polymers display undulated (4,4) grid layers as sql topology. Complex 3 displays a 1-D polymeric chain using chelating bisbidentate pam as bridging ligand. Complex 4 exhibits an interesting bis-monodentate pam-Mn(II) 1-D polymeric chain, in which exist two-type six-coordinated manganese centers. Mn(1) is bound to four pyridine ligands, whereas Mn(2) is combined to two pyridine and two H₂O molecules. Their thermal stabilities have been investigated. Cadmium complex 3 displays strong green luminescence with emission maximum at 543 nm.

Full text of DOI:10.1016/j.poly.2010.04.004

Polyhedron 29 (2010) 2075–2080
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Crystal structures and properties of four coordination polymers constructed
from flexible pamoic acid
a
a
b
Xue-Min Shi a, Ming-Xing Li a,c, , Xiang He , Hong-Jiang Liu , Min Shao
*
a Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, China
b Instrumental Analysis and Research Center, Shanghai University, Shanghai 200444, China
c State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China
a r t i c l e i n f o
a b s t r a c t
Four novel coordination polymers constructed from flexible pamoic acid, namely [Co(pam)(4,40-
bipy)]nꢀnH2O (1), [Ni(pam)(4,40-bipy)(H2O)2]nꢀ2nCH3CN (2), [Cd(pam)(py)2]nꢀnpy (3) and [Mn2(pam)2
(py)6(H2O)2]nꢀ2npy (4), (H2pam = pamoic acid, 4,40-bipy = 4,40-bipyridine, py = pyridine), have been syn-
thesized and characterized by elemental analysis, infrared spectra and X-ray crystallography. Complex 1
is a 2-D coordination polymer constructed from chelating bis-bidentate pam and 4,40-bipyridine bridging
ligands. Complex 2 is a 2-D coordination polymer assembled by bis-monodentate pam and 4,40-bipyri-
dine, where acetonitrile is filled in the rectangle channels. Both 2-D coordination polymers display undu-
lated (4,4) grid layers as sql topology. Complex 3 displays a 1-D polymeric chain using chelating bis-
bidentate pam as bridging ligand. Complex 4 exhibits an interesting bis-monodentate pam-Mn(II) 1-D
polymeric chain, in which exist two-type six-coordinated manganese centers. Mn(1) is bound to four pyr-
idine ligands, whereas Mn(2) is combined to two pyridine and two H2O molecules. Their thermal stabil-
ities have been investigated. Cadmium complex 3 displays strong green luminescence with emission
maximum at 543 nm.
Article history:
Received 19 November 2009
Accepted 5 April 2010
Available online 13 April 2010
Keywords:
Coordination polymer
Pamoic acid
4,40-Bipyridine
Crystal structure
Thermal analysis
Luminescence
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
groups, which has one half-molecule in the asymmetric unit and
the two naphthyl rings are linked with a methylene bridge.
The construction of coordination polymers has evoked consid-
erable attention and become a quite active research field due to
their diverse and intriguing polymeric structures with potential
applications as functional materials [1–4]. The final structures of
coordination polymers are dependent mainly upon the geometrical
and electronic properties of ligands and metal ions, and also
strongly influenced by other factors such as counter-ion, solvent,
pH value, temperature, and metal-to-ligand ratio [5,6]. In particu-
lar, aromatic polycarboxylate and N-heterocyclic ligands have been
shown to be good building blocks in the design of coordination
polymers with desired topologies owing to their rich coordination
modes and H-bonding interactions.
H2pam as a bridging ligand possesses both flexibility and rigidity,
since two napthyl rings can freely rotate at different degrees across
the methylene (–CH2–) group, which can potentially exhibit vari-
ous coordinate modes and diverse frameworks. Several H2pam
complexes have been synthesized and structurally characterized
[9–12]. Most of them contain chelating phen and 2,20-bipy as co-
ligands. With the aim of further understanding the coordination
behavior of pamoic acid, we have prepared four new H2pam coor-
dination polymers. Herein, we report their synthesis, crystal struc-
tures, thermal stabilities and luminescence.
4,40-Methylenebis(3-hydroxy-2-naphthoic acid) (pamoic acid,
Scheme 1) is used in the pharmaceutical industry as a counter
ion to obtain long-acting formulations of certain basic drugs
[7,8]. In spite of pamoic acid is a common industrial precursor,
its coordination behavior is not very clear to date. Pamoic acid is
a multifunctional ligand containing both carboxylic and phenoxy
2. Experimental
2.1. Materials and methods
All chemicals were analytical grade and obtained from commer-
cial sources without further purification. Elemental analyses for C,
H and N were carried out with a Vario EL III elemental analyzer.
Infrared spectra were recorded with a Nicolet A370 FT-IR spec-
trometer using KBr pellets in the 4000–400 cmꢁ1 region. The pow-
der X-ray diffraction data were recorded on a Rigaku DLMAX-2550
diffractometer. Thermal analyses were completed on a Mettler
* Corresponding author at: Department of Chemistry, College of Science,
Shanghai University, Shang-Da Road, 99#, Shanghai 200444, China. Tel.: +86 21
66132803; fax: +86 212797.
E-mail address: mx_li@mail.shu.edu.cn (M.-X. Li).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.04.004

2076
X.-M. Shi et al. / Polyhedron 29 (2010) 2075–2080
61.26; H, 4.14; N, 7.36%. IR (KBr, cmꢁ1): 3469s, 2258m, 1638m,
1613s, 1576s, 1508m, 1461s, 1401s, 1343s, 1231m, 826s, 751s.
2.2.3. [Cd(pam)(py)2]nꢀnpy (3)
An aqueous solution (2 mL) containing Cd(NO3)2ꢀ4H2O (0.062 g,
0.2 mmol) was dropped slowly into a stirred pyridine solution
(5 mL) containing pamoic acid (0.039 g, 0.1 mmol) and 1,10-phe-
nanthroline (0.018 g, 0.1 mmol). The resulting mixture was al-
lowed to stand at room temperature. Slow evaporation for 1
week afforded light yellow prismatic crystals of 3 in 57% yield
(0.042 g, based on H2pam). Anal. Calc. for C38H29CdN3O6: C,
62.01; H, 3.97; N, 5.71. Found: C, 61.68; H, 3.99; N, 5.77%. IR
(KBr, cmꢁ1): 3440m, 2930w, 1638s, 1547s, 1452s, 1396s, 1349s,
812s, 749s, 700m.
Scheme 1. Coordination modes of pam in 1–4: (a) chelating bis-bidentate, (b) bis-
monodentate.
2.2.4. [Mn2(pam)2(py)6(H2O)2]nꢀ2npy (4)
An aqueous solution (2 mL) containing MnSO4ꢀH2O (0.051 g,
0.3 mmol) was dropped slowly into a stirred pyridine solution
(5 mL) containing pamoic acid (0.039 g, 0.1 mmol) and 4,40-bipyr-
idine (0.016 g, 0.1 mmol). The resulting mixture was allowed to
stand at room temperature. Slow evaporation for 2 weeks afforded
yellow block crystals of 4 in 50% yield (0.039 g, based on H2pam).
Anal. Calc. for C86H72Mn2N8O14: C, 66.58; H, 4.68; N, 7.22. Found:
C, 65.83; H, 4.62; N, 6.76%. IR (KBr, cmꢁ1): 3068m, 1639s,
1597m, 1554s, 1456s, 1394s, 1351s, 810m, 744s, 699s.
Toledo TGA/SDTA85e thermal analyzer at a heating rate of 10 °C
minꢁ1 in nitrogen. Luminescent spectrum was recorded on a Shi-
madzu RF-5301 spectrophotometer.
2.2. Synthesis of complexes
2.2.1. [Co(pam)(4,40-bipy)]nꢀnH2O (1)
A mixture of Co(NO3)2ꢀ6H2O (0.117 g, 0.4 mmol), pamoic acid
(0.077 g, 0.2 mmol), 4,40-bipyridine (0.031 g, 0.2 mmol) and NaOH
(0.016 g, 0.4 mmol) in 10 mL ethanol/H2O (v/v = 4:1) was placed in
a 15 mL Teflon-lined stainless steel reactor, which was sealed and
heated in an oven at 140 °C for 72 h. Red block crystals of 1 were
obtained in 28% yield (0.035 g, based on H2pam). Anal. Calc. for
C33H24CoN2O7: C, 63.98; H, 3.91; N, 4.52. Found: C, 63.56; H,
4.19; N, 4.32%. IR (KBr, cmꢁ1): 3406m, 2937w, 1637m, 1608s,
1539s, 1458s, 1402s, 1324s, 808s, 757m.
2.3. X-ray crystallography
The single crystal X-ray diffraction measurements of 1–4 were
carried out on a Bruker Smart Apex-II CCD diffractometer with
graphite monochromatic Mo K
a radiation (k = 0.71073 Å) using
both / and -scan modes at 296(2) K. Determinations of the crys-
x
tal system, orientation matrix, and cell dimensions were per-
formed according to the established procedures. Lorentz
polarization and absorption correction were applied. The struc-
tures were solved by the direct methods and refined on F2 by
full-matrix least-squares techniques with SHELXTL-2000 program
[13]. All non-hydrogen atoms were refined anisotropically, and
hydrogen atoms were placed geometrically and refined using the
riding model. The crystal data and structural refinements are sum-
marized in Table 1. Selected bond distances and angles are given in
Table 2. The measured and simulated powder X-ray diffraction pat-
2.2.2. [Ni(pam)(4,40-bipy)(H2O)2]nꢀ2nCH3CN (2)
A mixture of Ni(NO3)2ꢀ6H2O (0.043 g, 0.15 mmol), pamoic acid
(0.039 g, 0.1 mmol), 4,40-bipyridine (0.016 g, 0.1 mmol) and NaOH
(0.008 g, 0.2 mmol) in 10 mL acetonitrile/H2O (v/v = 1:4) was
placed in a 15 mL Teflon-lined stainless steel reactor, which was
sealed and heated in an oven at 140 °C for 72 h. Light green block
crystals of 2 were obtained in 42% yield (0.030 g, based on H2pam).
Anal. Calc. for C37H32NiN4O8: C, 61.78; H, 4.48; N, 7.78. Found: C,
Table 1
Crystal data and structural refinements for complexes 1–4.
Compound
1
2
3
4
Formula
C33H24CoN2O7
619.47
triclinic
C37H32NiN4O8
719.38
monoclinic
P2/c
13.932(2)
8.007(1)
16.168(3)
90
108.855(2)
90
1706.9(5)
2
C38H29CdN3O6
736.04
triclinic
C86H72Mn2N8O14
1551.40
triclinic
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
ꢀ
ꢀ
ꢀ
P1
P1
P1
10.483(2)
11.449(2)
13.690(2)
79.570(2)
82.829(2)
65.931(2)
1473.2(4)
2
11.755(3)
12.180(3)
12.835(4)
64.648(4)
74.074(4)
82.573(4)
1596.8(8)
2
10.036(3)
13.534(4)
14.417(4)
92.329(5)
95.839(4)
106.177(4)
1866.1(9)
1
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ1
)
1.397
0.634
1.400
0.627
1.531
0.738
1.380
0.412
l
(mmꢁ1
)
F (000)
638
748
748
806
Reflections collected
Unique reflections
Goodness-of-fit
7759
5127
1.080
8639
3009
1.044
8293
5548
0.971
9724
6471
0.980
R1 [I > 2
wR2 (all data)
r
(I)]
0.0689
0.2232
0.0473
0.0952
0.0730
0.2011
0.0697
0.1517

X.-M. Shi et al. / Polyhedron 29 (2010) 2075–2080
2077
Table 2
3. Results and discussion
3.1. Synthesis and infrared spectra
Selected bond distances (Å) and angles (°) for complexes 1–4.
1a
Co(1)–N(2)
Co(1)–O(1)
Co(1)–O(2)
N(2)–Co(1)–N(1)
N(2)–Co(1)–O(2)
2.074(4)
2.081(4)
2.223(4)
101.1(2)
154.9(2)
Co(1)–N(1)
2.086(4)
2.424(5)
2.026(4)
87.3(2)
Co(1)–O(4)#1
Co(1)–O(5)#1
N(1)–Co(1)–O(2)
O(5)–Co(1)–O(1)
Pamoic acid has poor solubility in many common solvents at
room temperature. Complexes 1 and 2 were prepared by solvo-
thermal reactions of H2pam and metal nitrates in the presence of
4,40-bipyridine and NaOH in mixed solvent systems. The 4,40-
bipyridine and pam dianion play bridging ligands in the resulting
coordination polymers. Complexes 3 and 4 were prepared by sol-
vent evaporating method involved H2pam and metal salts in a pyr-
idine-water mixed solvent system. The pyridine can act as an
organic base and monodentate ligand in the reactions. Although
1,10-phenanthroline and 4,40-bipyridine were respectively added
to the reaction mixtures of 3 and 4, however, both complexes con-
tain none of them. Only pam dianion and pyridine coordinate to
metal ions to form polymers.
155.9(2)
2b
Ni(1)–O(1W)
Ni(1)–O(1)
O(1W)–Ni(1)–N(1)#1
3c
Cd(1)–N(2)
Cd(1)–N(1)
Cd(1)–O(2)
N(2)–Cd(1)–O(2)
N(1)–Cd(1)–O(5)#1
2.064(2)
2.083 (2)
176.3(1)
Ni(1)–N(1)
O(1W)#1–Ni(1)–N(1)
O(1)–Ni(1)–O(1)#1
2.073(2)
176.3(1)
178.3(1)
2.285(7)
2.300(7)
2.321(5)
146.1(2)
147.9(2)
Cd(1)–O(6)#1
Cd(1)–O(1)
Cd(1)–O(5)#1
O(6)#1–Cd(1)–O(1)
N(1)–Cd(1)–N(2)
2.349(6)
2.387(6)
2.344(5)
150.8(2)
88.7(2)
4d
Mn(1)–O(1)
Mn(1)–N(1)
Mn(1)–N(2)
2.155(3)
2.279(4)
2.316(4)
Mn(2)–N(3)
Mn(2)–O(4)
Mn(2)–O(1W)
2.318(5)
2.150(3)
2.161(4)
The absence of characteristic absorption of
1700 cmꢁ1 indicates that pamoic acid is completely deprotoned
in 1–4. The
as(COOꢁ) vibrations of carboxylate groups occur at
1637, 1638, 1638, and 1639 cmꢁ1 for 1–4, respectively. While
those of
s(COOꢁ) occur at 1402, 1343, 1395, and 1351 cmꢁ1
respectively. The
s) different values of 235 cmꢁ1 for 1
mas(COOH) near
m
a
b
c
#1 x + 1, y ꢁ 1, z.
#1 ꢁx + 1, y, ꢁz + 1/2.
#1 x ꢁ 1, y, z.
m
,
D
(mas
ꢁ
m
d
#1 ꢁx + 1, ꢁy + 1, ꢁz + 1.
and 243 cmꢁ1 for 3 are much smaller than those of 295 cmꢁ1 for
2 and 288 cmꢁ1 for 4, which are consistent with the chelating
bis-bidentate carboxyl coordinate mode in 1, 3, and the bis-mono-
dentate mode in 2, 4 (Scheme 1) [14,15]. Their formulas have been
confirmed by elemental analysis and X-ray structural analysis.
terns of coordination polymers 1–4 are shown in Fig. S2 (supple-
mentary data).
Fig. 1. Views of (a) asymmetric unit, (b) 2-D double-layered polymeric network, (c) 2-D (4,4) grid layer as sql topology, (d) packing diagram of 1.

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X.-M. Shi et al. / Polyhedron 29 (2010) 2075–2080
3.2. Description of crystal structures
Fig. 1d, which is porous and incorporated lattice water in the
channels.
3.2.1. [Co(pam)(4,40-bipy)]nꢀnH2O (1)
3.2.2. [Ni(pam)(4,40-bipy)(H2O)2]nꢀ2nCH3CN (2)
X-ray structural analysis revealed that complex 1 is a two-
dimensional coordination polymer formed by 4,40-bipyridine and
pam bridging ligands. As shown in Fig. 1a, the cobalt center adopts
a distorted octahedral geometry, coordinated by two nitrogen
atoms from different 4,40-bipyridine and four oxygen atoms from
two pam ligands. Both 4,40-bipyridine ligands are arranged in cis
conformation with a N(1)–Co(1)–N(2) angle of 101.1(2)°. Average
Co–N bond distance is 2.080 Å. It is obviously less than the Cd–N
distance of 2.335(3) Å in a 3-D coordination polymer [Cd5(OAc)4
(OH)2(pam)2(4,40-bipy)2]n [14]. Both carboxyl groups of pam adopt
the chelating bis-bidentate coordination mode (Scheme 1a). The
Co–O bond distances vary from 2.026(4) to 2.424(5) Å. Previously,
Du et al. have structurally characterized two 2-D coordination
polymer [Cu(pam)(4,40-bipy)(dmf)2]n and [Cd(pam)(4,40-bipy)2]nꢀn-
H2O, in which 4,40-bipyridine ligands coordinate to metal ions in
trans conformation [10].
Complex 2 is a two-dimensional coordination polymer formed
by 4,40-bipyridine and pam bridging ligands. As shown in Fig. 2a,
the nickel center is six-coordinated by two nitrogen and four oxy-
gen atoms, forming a distorted octahedral geometry. On the equa-
torial plane, two 4,40-bipyridine ligands are arranged in cis
conformation with a N(1)–Ni(1)–N(1A) angle of 91.5(1)°. The Ni–
N bond distance is 2.073(2) Å. Two aqua molecules coordinate to
nickel ion with Ni–O bond distance 2.064(2) Å. The pam dianion
exhibits the bis-monodentate coordination mode (Scheme 1b).
Two monodentate carboxyl groups occupy the axial positions with
Ni–O bond distance 2.083(2) Å. This is obviously different with the
coordination structure of 1.
Each pam bidentate ligand links two Ni(II) centers to form an
infinite polymeric chain along a axis (Fig. 2b). The dihedral angle
between both naphthyl rings is 77.8°. Such 1-D chains are further
linked by 4,40-bipyridine to form a 2-D polymeric network. It also
displays an undulated 2-D (4,4) grid layer as sql topology
(Fig. 2c). The 2-D layered networks are arranged in a parallel
fashion to afford 1-D rectangle channels, in which the guest
CH3CN molecules filled (Fig. 2d). Both hydroxide groups of pam
are uncoordinated, and bound to carboxyl O(1) with strong intra-
molecular hydrogen bond of O(3)–H(3)ꢀ ꢀ ꢀO(1) 2.514(3) Å. The car-
boxyl O(2) combines O(1W) through H-bond of O(1W)–
H(1WA)ꢀ ꢀ ꢀO(2) 2.635(3) Å.
The V-shaped pam dianion acts as a tetradentate ligand to link
up two cobalt ions to form a 1-D zigzag chain. The dihedral angle
between both naphthyl rings is 84.1°. The adjacent 1-D chains
are further connected by 4,40-bipyridine linkers to form a 2-D dou-
ble-layered polymeric network (Fig. 1b). It displays an undulated
2-D (4,4) grid layer as sql topology (Fig. 1c). Both hydroxide groups
of pam are uncoordinated and bound to carboxyl O(2) and O(4)
with strong hydrogen bonds of O(3)–H(3)ꢀ ꢀ ꢀO(2) 2.547(5) Å and
O(6)–H(6)ꢀ ꢀ ꢀO(4) 2.594(5) Å. The packing diagram is shown in
Fig. 2. Views of (a) asymmetric unit, (b) 2-D polymeric network, (c) 2-D (4,4) grid layer as sql topology, (d) packing diagram of 2, CH3CN fills in the rectangle tunnel.

X.-M. Shi et al. / Polyhedron 29 (2010) 2075–2080
2079
3.2.3. [Cd(pam)(py)2]nꢀnpy (3)
monodentate carboxyl groups [Mn(2)–O 2.150(3) Å] in trans
configuration.
Complex 3 is a one-dimensional coordination polymer. As
shown in Fig. 3a, the cadmium center is in a distorted octahedral
geometry, coordinated by two pyridyl nitrogen and four oxygen
atoms from two chelating carboxyl groups. Average Cd–N bond
distance is 2.29 Å. Cd–O bond distances vary from 2.321(6) to
2.348(7) Å. The pam dianion adopts the chelating bis-bidentate
coordination mode. Each pam tetradentate ligand links two Cd(II)
ions to form a 1-D infinite chain along a axis (Fig. 3b). The Cdꢀ ꢀ ꢀCd
separation is 11.755(3) Å. Every Cd(II) center is bound by two pyr-
idine ligands in cis fashion. The N(1)–Cd(1)–N(2) bond angle is
88.7(2)°. The 1-D polymeric chains are parallel stacked as shown
in Fig. 3c. There exist uncoordinated pyridine molecules in the
crystal lattice. Both hydroxide groups of pam are uncoordinated
and bound to carboxyl O(2) and O(5) with strong hydrogen bonds
of O(3)–H(3)ꢀ ꢀ ꢀO(2) 2.560(7) Å and O(4)–H(4)ꢀ ꢀ ꢀO(5) 2.557(7) Å.
The flexible skeleton of pam is twisted and the hydroxy and car-
boxyl groups adopt a trans conformation to minimize the steric
hindrance. The dihedral angle between both naphthyl rings is
82.6°. The uncommon cis conformation of pam was observed in
[Zn(pam)(phen)]n [12]. Comparing the structures of 1 and 3, both
metal centers are cis six-coordinated by two pyridyl groups and
two chelating carboxyl groups. Two 3-hydroxy-2-naphthoate
pieces of pam are arranged in similar trans conformation. Different
with the 1-D polymeric chain of 3, the complex 1 displays a 2-D
polymeric layer by introducing bridging 4,40-bipyridine ligand.
Each pam dianion adopts the bis-monodentate coordination
mode to bridge Mn(1) and Mn(2) ions. This leads to the formation
of
a
1-D polymeric chain. The Mn(1)ꢀ ꢀ ꢀMn(2) separation is
15.419(4) Å, which is obviously longer than the Cdꢀ ꢀ ꢀCd separation
in 3. The dihedral angle between both naphthyl rings is 86.1°. The
1-D polymeric chains are arranged in a parallel fashion as shown in
packing diagram. Uncoordinated pyridine is incorporated in the
crystal lattice. Both hydroxide groups of pam are uncoordinated
and bound to carboxyl O(2) and O(5) with strong hydrogen bonds
of O(3)–H(3)ꢀ ꢀ ꢀO(2) 2.537(5) Å and O(6)–H(6)ꢀ ꢀ ꢀO(5) 2.532(5) Å.
Unlike the well-known 2,20-dihydroxy-1,10-binaphthyl (binol) li-
gand which contains coordinated hydroxide groups, the hydroxide
groups of pam are free in all reported pam compounds. Pam prefers
to form 1-D polymeric chains with the metal ions, which can be ex-
tended to 2-D coordination polymers by introducing bridging li-
gands such as 4,40-bipyridine.
3.3. Thermal stabilities and luminescence
Thermal analyses for coordination polymers 1–4 were per-
formed in the temperature range of 20–800 °C. Their TGA curves
are shown in Fig. S3. Complex 1 lost 2.86% lattice water near
50 °C (calc. 2.90%). [Co(4,40-bipy)(pam)]n is stable up to 350 °C,
and then released 4,40-bipy and pam ligands. The resulting residue
is Co2O3 (found 13.59%, calc. 13.40%). Complex 2 lost two lattice
acetonitrile molecules in 150–200 °C (found 11.32%, calc.
11.41%). The 4,40-bipy and pam ligands released after 350 °C. The
final residue is NiO (found 12.61%, calc. 10.10%). Complex 3 re-
leased lattice pyridine before 150 °C (found 11.63%, calc. 10.75%).
Two coordinated pyridine molecules released in 170–270 °C
(found 22.49%, calc. 21.50%). Pam ligand decomposed in the tem-
perature range of 300–600 °C (found 49.75%, calc. 50.32%). The fi-
nal, thermal stable residue is CdO (found 16.13%, calc. 17.45%).
Complex 4 lost coordinated water near 110 °C (found 2.24%, calc.
2.32%). In the range of 120–320 °C, the complex 4 lost two lattice
pyridine and six coordinated pyridine molecules with a total
weight-loss of 42.48% (calc. 40.78%). Pam ligand decomposed in
320–800 °C (found 49.75%, calc. 50.32%). The final residue is
3.2.4. [Mn2(pam)2(py)6(H2O)2]nꢀ2npy (4)
Complex 4 displays an interesting 1-D polymeric chain, in
which exist two-type manganese coordination centers. As shown
in Fig. 4, each asymmetric unit contains two independent Mn(II)
ions, two pam ligands, two coordinated aqua molecules, and six
coordinated pyridine as well as two lattice pyridine molecules.
The Mn(1) center adopts a centro-symmetric octahedral coordina-
tion geometry, being surrounded by four pyridine and two mono-
dentate carboxylic groups in trans configuration. Mn(1)–N bond
distances vary from 2.279(4) to 2.316(4) Å. Mn(1)–O distance is
2.156(3) Å. The Mn(2) center is also in a centro-symmetric octahe-
dral geometry, but coordinated by two pyridine [Mn(2)–N
2.318(5) Å], two H2O molecules [Mn(2)–O 2.160(5) Å], and two
Fig. 3. Views of (a) asymmetric unit (lattice pyridine is omitted), (b) 1-D polymeric chain, and (c) packing diagram of 3.

2080
X.-M. Shi et al. / Polyhedron 29 (2010) 2075–2080
Fig. 4. The asymmetric unit and packing diagram of 4.
MnO2 (found 13.71%, calc. 11.21%). Comparing the structures and
thermal stabilities of above four pam coordination polymers,
pam adopts chelating and bridging coordinate mode, which leads
to higher thermal stability. Usually, pam ligand starts to decom-
pose after 320 °C [17].
Acknowledgments
Financially supported by the Leading Academic Discipline Pro-
ject of Shanghai Municipal Education Commission (J50102), and
the Natural Science Foundation of Shanghai (10ZR1411100).
Generally, d10 transition metal complexes display varied lumi-
nescence in the solid state. Organic ligands and their coordination
modes obviously affect their emission wavelengths and lumines-
cent mechanisms. We have determined the luminescence of cad-
mium complex 3. Upon excitation at 378 nm, this compound
exhibits strong green luminescence with maximum emission peak
at 543 nm (Fig. S4). The free pamoic acid shows a weak emission
peak at 473 nm. Generally, ligand-to-metal charge transfer (LMCT)
is the most common assignment for the luminescence of cadmium
complexes [16]. Most of naphthyl carboxylate–cadmium(II) com-
plexes exhibit green luminescence [9,17]. So we assign the lumi-
nescent mechanism of 3 to a LMCT mechanism, where the
electron is transferred from pam ligand to Cd(II).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2010.04.004.
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Four novel coordination polymers containing flexible pamoic
acid ligand were synthesized. They possess 1-D and 2-D polymeric
structures. Both carboxyl groups of pamoic acid adopt bis-mono-
dentate and bis-bidentate coordination modes. This study demon-
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through bifunctional carboxyl groups. Hydroxide groups of pam
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