Effects of the size of aromatic chelate ligands and d10 metal ions on the structures of dicarboxylate complexes: From dinuclear molecule to helical chains and 2D network

Article abstract of DOI:10.1016/j.molstruc.2008.04.010

Four new mixed-ligand complexes, namely [Zn₂(pam)₂(2,2′-bpy)₂] (1), [Cd(pam)(2,2′-bpy)₂]_n (2), [Zn(pam)(phen)]_n (3) and [Cd (pam)(phen)]_n · 0.5n CH₃CH₂OH · 0.5nH₂O (4) (H₂pam = pamoic acid, 2,2′-bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) have been synthesized under hydro(solvo)thermal conditions. Complex 1 possesses a discrete dinuclear metallamacrocyclic structure. Complex 2 is a 1D homochiral helical coordination polymer that is built from achiral components, whereas 3 displays a 1D helical chain structure. 4 is an unusual 2D double-layered structure generated by π ? π interactions of two 2D networks. The structural differences of these complexes are mainly due to the differences of the size of the rigid aromatic chelate ligands and d¹⁰ metal ions. It appears that the chelate ligands and metal ions of the larger size favor the formation of high-dimensional structures, whereas those of the smaller size favor the formation of low-dimensional structures in the present system. The photoluminescence and thermal stability of these complexes were investigated.

Full text of DOI:10.1016/j.molstruc.2008.04.010

Journal of Molecular Structure 891 (2008) 364–369
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Effects of the size of aromatic chelate ligands and d10 metal ions on the structures
of dicarboxylate complexes: From dinuclear molecule to helical chains and 2D
network
Zhong-Xi Han a, Ji-Jiang Wang a,b, Huai-Ming Hu a, , Xiao-Li Chen a,b, Qing-Ran Wu a, Dong-Sheng Li b,
*
Qi-Zhen Shi a
a Department of Chemistry, Shaanxi Key Laboratory of Physico-inorganic Chemistry, Northwest University, Xi’an 710069, China
b Department of Chemistry and Chemical Engineering, Shaanxi Key Laboratory of Chemical Reaction Engineering, Yanan University, Yan’an 716000, China
a r t i c l e i n f o
a b s t r a c t
Four new mixed-ligand complexes, namely [Zn2(pam)2(2,20-bpy)2] (1), [Cd(pam)(2,20-bpy)2]n (2),
[Zn(pam)(phen)]n (3) and [Cd (pam)(phen)]n ꢀ 0.5n CH3CH2OH ꢀ 0.5nH2O (4) (H2pam = pamoic acid, 2,20-
bpy = 2,20-bipyridine, phen = 1,10-phenanthroline) have been synthesized under hydro(solvo)thermal
conditions. Complex 1 possesses a discrete dinuclear metallamacrocyclic structure. Complex 2 is a 1D
homochiral helical coordination polymer that is built from achiral components, whereas 3 displays a
1D helical chain structure. 4 is an unusual 2D double-layered structure generated by p ꢀ ꢀ ꢀ p interactions
of two 2D networks. The structural differences of these complexes are mainly due to the differences of the
size of the rigid aromatic chelate ligands and d10 metal ions. It appears that the chelate ligands and metal
ions of the larger size favor the formation of high-dimensional structures, whereas those of the smaller
size favor the formation of low-dimensional structures in the present system. The photoluminescence
and thermal stability of these complexes were investigated.
Article history:
Received 9 February 2008
Received in revised form 4 April 2008
Accepted 7 April 2008
Available online 12 April 2008
Keywords:
Coordination polymer
Crystal structures
Pamoic acid
d10 metal ions
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
various coordination modes and diverse metal–organic frame-
work (MOF) architectures. Meanwhile, it also possesses both
The construction of coordination polymers has attracted consid-
erable attention in recent years due to their interesting properties
and promising applications in the areas of catalysis, gas storage,
magnetism and optics [1]. Polynuclear d10 metal (CuI, AgI, AuI, ZnII
or CdII) complexes have been found to exhibit intriguing structures
and photoluminescent properties [2]. A series of d10 metal organic
frameworks have been described recently [3]. However, to the best
of our knowledge, the studies on the effects of the size of the rigid
aromatic chelate ligands and d10 metal ions on framework forma-
tion of their complexes have rarely been reported [4].
It is well known that the final framework of coordination com-
pounds depends both on the coordination geometry of the metal
ions and on the properties of the organic ligands. When long/flex-
ible/V-shaped bridging dicarboxylate ligands are used to connect
metal ions, their versatile coordination modes may lead to new
architectures with fantastic structures and desirable properties
[4,5].
rigidity and flexibility, since the naphthyl rings can freely rotate
around the methylene (–CH2–) groups according to the small
change in the coordination environment in order to minimize ste-
ric hindrance. In addition, pamoic acid (H2pam) is a very cheap
industrial precursor and used as a counter ion to obtain long-act-
ing pharmaceutical formulations of certain basic drugs [6]. As far
as we know, H2pam metal complexes have scarcely been studied
previously.
The judicious selection of auxiliary ligands has a significant
effect on the formation and structure of final metal complexes.
Aromatic chelate ligands, such as 1,10-phenanthroline (phen)
and 2,20-bipyridine (2,20-bpy) are important in maintaining the
dimensionality of the coordination polymers and may provide po-
tential supramolecular recognition sites for p–p aromatic stacking
interactions to form interesting supramolecular structures such
as double-stranded helices and molecular zippers [5b,7].
With the aim of understanding the coordination chemistry of
H2pam and studying the influence of the size of aromatic chelate
ligands and d10 metal ions on the framework structures of their
complexes, we are currently interested in the structures of metal
pamoate complexes with the mixed ligand. Herein, we report four
interesting d10 metal complexes, namely [Zn2(pam)2(2,20-bpy)2]
Pamoic acid (H2pam) is a multifunctional ligand containing
both carboxylic and phenoxy groups, which can potentially afford
* Corresponding author. Tel./fax: +86 29 88303331.
E-mail address: Chemhu1@nwu.edu.cn (H.-M. Hu).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.04.010

Z.-X. Han et al. / Journal of Molecular Structure 891 (2008) 364–369
365
(1), [Cd(pam)(2,20-bpy)2]n (2), [Zn(pam)(phen)]n (3) and
2.3. X-ray crystallography
[Cd(pam)(phen)]n ꢀ 0.5nCH3CH2OH ꢀ 0.5nH2O (4). All four pamoate
complexes contain pam2ꢁ spacers and auxiliary ligands (2,20-bpy/
phen), and display very different structures, ranging from dinucle-
ar molecule to helical chains and 2D Network.
Intensity data were collected on a Bruker Smart APEX II CCD dif-
fractometer with graphite-monochromated Mo–Ka radiation
(k = 0.71073 Å) at room temperature. Empirical absorption correc-
tions were applied by using the SADABS program. The structures
were solved by direct methods and refined by the full-matrix
least-squares based on F2 using SHELXTL-97 program [8]. All
non-hydrogen atoms were refined anisotropically and the hydro-
gen atoms of organic ligands were generated geometrically. Crystal
data and structural refinement parameters for 1–4 are summarized
in Table 1 and selected bond distances and bond angles are listed in
Table S1, Supplementary Material.
2. Experimental section
2.1. Materials and methods
The reagents and solvents employed were commercially avail-
able and used as received without further purification. Elemental
analyses (C, H, N) were determined with a Vario EL III elemental
analyzer. The FT-IR spectra were recorded from KBr pellets in the
range 4000–400 cmꢁ1 on a Bruker EQUINOX-55 spectrometer.
Thermogravimetric analyses (TGA) were performed under nitrogen
with a heating rate of 10 °C ꢀ minꢁ1 using a METTLER TGA851 ther-
mogravimetric analyzer. Fluorescence spectra were performed on a
Hitachi F-4500 fluorescence spectrophotometer at room
temperature.
3. Results and discussion
3.1. Crystal structures
3.1.1. Crystal structure of [Zn2 (pam)2 (2,20-bpy)2] (1)
Complex 1 is a dinuclear metallamacrocyclic complex contain-
ing cavity without guest molecule. As shown in Fig. 1a, there are
one ZnII ion, one pam2ꢁ anion and one 2,20-bpy ligand in the asym-
metric unit. Each ZnII ion is coordinated to three oxygen atoms of
two pam2ꢁ ligands and two nitrogen atoms of a 2,20-bpy ligand,
and is located in a slightly distorted square–pyramidal geometry.
However, the distance of 2.510(3) Å between Zn1 and O2 of car-
boxylate group of pam2ꢁ ligand suggests a nonnegligible interac-
tion between them. Thus, the ZnII ion can be regarded as a
distorted octahedron. The average Zn–N bond length is
2.066(3) Å and Zn–O bond lengths are in the range 1.983(3)–
2.276(2) Å. Zn1 and Zn1A are bridged by two pam2ꢁ ligands with
a distance 10.513(2) Å. Each pam2ꢁ ligand in 1 adopts a trans con-
formation and serves as a monodentate–bidentate bridging ligand,
linking two ZnII ions (see Scheme 1a). It is interesting that the adja-
cent metallamacrocycle are stacked through significant C–H ꢀ ꢀ ꢀ p
interactions between the naphthyl rings and pyridyl rings from
adjacent metallamacrocycle with the edge-to-face separation of
3.4–3.7 Å, resulting in 1D supramolecular double-chain structures
containing micropores (Fig. 1b). Although the area is ca.
10.513 Å ꢂ 10.687 Å [based on Zn1–Zn1A and C12–C12A dis-
tances] in each micropore structure, the real volume of the cavity
is further reduced due to the significant offset stacking of adjacent
metallamacrocycles.
2.2. Synthesis
2.2.1. Synthesis of [Zn2(pam)2 (2,20-bpy)2](1)
A
mixture of
Zn(OAc)2 ꢀ 2H2O
(0.10 mmol),
H2pam
(0.10 mmol), NaOH (0.20 mmol) and 2,20-bpy (0.10 mmol) in
6 mL water–ethanol (1:5) was stirred for 30 min in air, then
sealed in a 15 mL Telfon-lined stainless steel container, which
was heated to 160 °C for 72 h. After cooling to room temperature
at a rate of 2 °C per hour, yellow crystals were obtained in ca. 52%
yield. Anal. found (calcd) for C66H44Zn2N4O12: C, 65.15 (65.14); H,
3.60 (3.62), N, 4.61 (4.63); FT-IR (KBr, cmꢁ1): 3410(m), 1639(m),
1604(w), 1574(w), 1507(m), 1447(m), 1393(m), 1335(w),
1244(w), 811(m), 763(m), 735(m), 653(w), 630(m), 551(w),
516(m), 486(w), 433(w), 411(w).
2.2.2. Synthesis of [Cd(pam)(2,20-bpy)2]n(2)
The preparation of 2 was similar to that of 1 except that
Cd(NO3)2 ꢀ 4H2O (0.10 mmol) was used instead of Zn(OAc)2 ꢀ 2H2O.
Pale-yellow crystals were obtained in ca. 60% yield. Anal. found
(calcd) for C43H30CdN4O6: C, 63.64(63.62);
H 3.73(3.70); N,
6.88(6.90); FT-IR (KBr, cmꢁ1): 3410(m), 1635(m), 1597(w),
1508(w), 1443(m), 1387(m), 1244(w), 856(m), 736(m), 647(w),
597(w), 550(w), 483(w).
3.1.2. Crystal structure of [Cd (pam)(2,20-bpy)2]n(2)
2.2.3. Synthesis of [Zn(pam)(phen)]n(3)
Unexpectedly, when ZnII ion is replaced by CdII ion, a d10 metal
ion with larger radius, structurally different 1D helical coordina-
tion polymer is formed in 2 under similar reaction conditions for
the preparation of 1. X-ray crystallography shows 2 is a 1D homo-
chiral helical coordination polymer that is built from achiral com-
ponents. As illustrated in Fig. 2a, there are one CdII ion, one pam2ꢁ
anion, two 2,20-bpy ligands in the asymmetric unit. The coordina-
tion polyhedron around each CdII ion is a square antiprism with
four oxygen atoms of two chelating pam2ꢁ ligands and four nitro-
gen atoms of two chelating 2,20-bpy ligands. The average Cd–N
bond distance (2.428(7) Å) is similar to those of other CdII coordi-
nation polymers with mixed ligands, such as 1D polymer
A mixture of Zn(OAc)2 ꢀ 2H2O (0.1 mmol), H2pam (0.10 mmol),
NaOH (0.20 mmol) and phen ꢀ H2O (0.10 mmol) in 6 mL water–eth-
anol (1:5) was stirred for 30 min in air, then sealed in a 15 mL Tel-
fon-lined stainless steel container, which was heated to 160 °C for
72 h. After cooling to room temperature at a rate of 2 °C per hour,
pale-yellow large block crystals were obtained in ca. 60% yield.
Anal. found (calcd) for C35H22N2O6 Zn: C, 64.48 (66.46); H, 3.46
(3.48); N, 4.45 (4.43); FT-IR (KBr, cmꢁ1): 3425(m), 1638(s),
1581(s), 1550(s), 1509(s), 1452(s), 1407(s), 1344(s), 1322(s),
854(m), 767(m), 645(w), 594(w), 551(w), 479(w).
2.2.4. Synthesis of [Cd(pam)(phen)]n ꢀ 0.5nCH3 CH2 OH ꢀ 0.5nH2O(4)
The preparation of 4 was similar to that of 3 except that
Cd(OAc)2 ꢀ 2H2O (0.10 mmol) was used instead of Zn(OAc)2 ꢀ 2H2O.
Colorless crystals were obtained in ca. 65% yield. Anal. found
(calcd) for C36H26CdN2O7: C, 60.74(60.76); H, 3.68(3.66); N,
3.96(3.94); FT-IR (KBr, cmꢁ1): 3422(m), 1637(m), 1548(m),
1512(m), 1456(m), 1369(w), 1236(w), 808(m), 766(m), 746(w),
723(m), 549(m), 520(w), 486(w), 435(w).
[Cd(bpea)(phen)2]
(bpea = biphenylethene-4,40-dicarboxylate)
(2.477(3) Å) [9]. The Cd–O bond distances range from 2.308(7) to
2.760(6) Å, which are also comparable to those in the literatures
[10]. The two carboxylate groups of pam2ꢁ ligand in 2 adopt a trans
conformation and exhibit another kind of chelating bis(bidentate)
bridging with CdII atoms, as shown in Scheme 1b. [Cd(2,20-
bpy)2]2+ molecular corners are bridged by pam2ꢁ ligands to form
infinite helical chain running along a axis (Fig. 2b). The helix is gen-

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Z.-X. Han et al. / Journal of Molecular Structure 891 (2008) 364–369
Table 1
Crystal data and structural refinement parameters for complexes 1–4
Complex
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
C66H44N4O12 Zn2
1215.79
Monoclinic
P21/n
12.4791(7)
12.3400(7)
17.9739(10)
90
105.932(1)
90
2661.5(3)
2
C43H30CdN4O6
811.11
C35H22N2O6Zn
631.92
Monoclinic
P21/c
13.6026(17)
11.8085(15)
18.570(2)
90
107.245(2)
90
2848.8(6)
4
1.473
0.914
1296
C36H26CdN2O7
710.99
Monoclinic
P2/n
11.6092(7)
15.6578(10)
18.8917(14)
90
107.8080(10)
90
3269.5(4)
4
1.444
0.719
1440
Orthorhombic
P212121
9.3119(6)
14.1906(9)
26.0335(17)
90
90
90
3440.1(4)
4
1.566
a/Å
b/Å
c/Å
a/°
b/°
c/°
V/Å3
Z
q
(g cmꢁ3
)
1.517
0.975
1248
calc
l (mmꢁ1
F(000)
)
0.694
1648
k (Mo–Ka)/Å
0.71073
13204
4718
382
1.028
0.71073
17532
6080
490
0.957
0.71073
13791
5059
399
1.015
0.71073
16297
5824
419
1.046
Reflections collected
Unique reflections
Parameters
S on F2
R1, wR2 [I > 2r(I)]
R1, wR2 (all data)
0.0397, 0.0872
0.0707, 0.0988
0.227 and ꢁ0.290
0.0532, 0.1076
0.1148, 0.1329
0.368 and ꢁ0.395
0.0390, 0.1165
0.0555, 0.1278
0.457 and ꢁ0.327
0.0463, 0.1280
0.0766, 0.1410
0.898 and ꢁ0.417
D qmin
(e Åꢁ3
)
and max
M
O
M
O
O
O
HO
HO
OH
OH
O
O
M
O M
O
(a)
(b)
M
M
O
O
M
O
O
OH
OH
HO
OH
O
O
M
O M
O
M
(c)
(d)
Scheme 1. The coordination modes of pam2ꢁ ligand in 1–4.
Fig. 1. (a) A perspective view of dinuclear metallamacrocycle in 1. (b) The 1D do-
uble-chain structures viewed along the b axis in 1. All hydrogen atoms have been
omitted for clarity.
ther reduced due to the significant offset stacking of adjacent heli-
cal chains.
erated around the 21 screw axis with an exceptionally long pitch of
26.034(2) Å, equal to the length of the c axis. Notably, each pair of
nearly perpendicular 2,20-bpy ligands bonded to the CdII atom
point away from the helical axis; this steric orientation may lead
to the generation of 2.
In complex 2, the neighboring chains are linked to each other
via p ꢀ ꢀ ꢀ p interactions between pyridyl and adjacent naphthyl
rings (the nearest carbon to carbon separation of 3.3 Å) to lead to
a 3D supramolecular framework containing 1D chiral channels
(Fig. 2c). Although the area is 7.991 Å ꢂ 14.493 Å (based on Cd–
Cd) in each channel structure, the real volume of the cavity is fur-
3.1.3. Crystal structure of [Zn(pam)(phen)]n (3)
To further examine the influence of the auxiliary ligands on the
structure of 1, a larger size aromatic chelate ligand phen is used in-
stead of 2,20-bpy. Consequently, 3, which feature a 1D helical chain
polymer, was obtained. As shown in Fig. 3a, there are one ZnII ion,
one pam2ꢁ anion and one phen molecule in the asymmetric unit.
The ZnII ion is in a distorted square pyramidal geometry coordi-
nated by two nitrogen atoms from a chelate phen, two oxygen
atoms from the chelating carboxylate group of a pam2ꢁ ligand.
An oxygen atom from the monodentate carboxylate group of an-
other pam2ꢁ ligand occupies the remaining site. Similar to 1, the

Z.-X. Han et al. / Journal of Molecular Structure 891 (2008) 364–369
367
Fig. 2. (a) Coordination environment of the CdII ion in 2. (b) The 1D helical structure
in 2. (c) The 3D chiral network viewed along a axis in 2. All hydrogen atoms have
been omitted for clarity.
distance of 2.602(3) Å between Zn1 and O2 of a carboxylate group
of pam2ꢁ ligand suggests a nonnegligible interaction between
them. Thus, the ZnII ion can be regarded as a distorted octahedron.
The bond lengths of Zn–O and Zn–N are similar to those in other
zinc carboxylate coordination polymers [4]. Unlike those in com-
plexes 1 and 2, each pam2ꢁ ligand in 3 adopts cis conformation
and bridges two ZnII atoms in monodentate and chelating biden-
tate mode (Scheme 1c) to form a 1D infinite helical chain as shown
in Fig. 3b. Interestingly, the adjacent chains are linked to each other
via C–H ꢀ ꢀ ꢀ p interactions between phen molecules and adjacent
naphthyl rings (the carbon to carbon separation of 3.4–3.6 Å) to
lead to a 1D supramolecular double-chain structures viewed along
the b axis (Fig. 3c).
Fig. 3. (a) Coordination environments of the ZnII ion in 3. (b) The 1D helical chain
structures in 3. (c) The 1D double-chain structures viewed along the b axis in 3. All
hydrogen atoms have been omitted for clarity.
bidentate) (Scheme 1b) and bis(chelating/bridging bidentate)
(Scheme 1d). The dinuclear species [Cd2(pam)2(phen)2], which
has a Cd–Cd distance of 3.867(2) Å, can be regarded as a secondary
building unit (SBU). These SBUs are linked by pam2ꢁ ligands into
2D networks with phen ligands attached to one side of the net-
works (Fig. 4b), and the adjacent two 2D networks in face-to-face
manner are further packed into a double-layered structure by
weak p ꢀ ꢀ ꢀ p interactions between phen molecules (the nearest dis-
tance 3.718 Å) (Fig. 4c). Although the area of the 2D networks is
11.609 Å ꢂ 15.031 Å (based on Cd–Cd) in each channel structure,
the real volume of the cavity is further reduced due to the signifi-
cant offset stacking of adjacent two 2D networks. Calculations
using PLATON [11] revealed that the free volume of channels con-
stitute about 22% of the crystal volume and are filled with
CH3CH2OH and H2O solvent molecules.
In a comparison of the structures of 1–4, it is found that coordi-
nation geometry of the central metal ions and the sizes of the aux-
iliary ligands have significant effects on the formation and
structures of the resulting complexes. As demonstrated by a com-
parison of complexes 1/3 and 2/4, the high coordination number of
the metal ion is an important factor for the formation of a high-
dimensional structure. In addition, different aromatic chelates also
have a significant effect on the structures, as evidenced by the fact
that the structures of 1/2 are significantly different from that of 3/4.
3.1.4. Crystal structure of [Cd(pam)(phen)]n ꢀ 0.5nCH3CH2
OH ꢀ 0.5nH2O (4)
Similar to 3, using phen in place of 2,20-bpy of 2 under the same
reaction conditions, 4 is achieved. Complex 4 features an unusual
2D double-layered structure generated by p ꢀ ꢀ ꢀ p interactions. As
shown in Fig. 4a, there are one CdII ion, two half pam2ꢁ anions,
one half water and one half ethanol molecules in the asymmetric
unit. Each CdII ion is coordinated to five oxygen atoms of three
pam2ꢁ ligands and two nitrogen atoms of one phen molecule to
furnish a distorted capped-octahedral geometry. The Cd–N bond
distances (2.320(1) and 2.352(1) Å) are similar to those of other
CdII coordination polymers with mixed ligands, such as 1D polymer
[Cd(mpa)(phen)]n and [Cd2(mpa)2(2,20-bpy)2]n (mpa = m-phthal-
ate) [4]. The Cd–O bond lengths fall in the range 2.250(1)–
2.763(2) Å, which are also comparable to those in the literatures
[10]. There are two types of coordination modes for the bridging
pam2ꢁ ligands in a trans conformation in 4, namely bis (chelating

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Z.-X. Han et al. / Journal of Molecular Structure 891 (2008) 364–369
Fig. 4. (a) Coordination environments of the CdII ion in 4. (b) The 2D network viewed along the b axis in 4. (c) Double-layered structure generated by p ꢀ ꢀ ꢀ p interactions in 4.
Carbon atoms of phen in (b) are omitted for clarity.
Furthermore, the comparison of 1–4 with 1D polymer [M(mpa)
(phen)]n, [M2(mpa)2(2,20-bpy)2]n (M = Zn or Cd and mpa =
m-phthalate) [4], [Cu2(mpa)2(phen)2(H2O)]n and [Cu(mpa)(2,20-
bpy)(H2O)]n ꢀ 2nH2O [5b] shows that the higher flexibility and
greater lengths of dicarboxylate ligands may play a key role in
determining the structures of the complexes.
(Calcd.: 92.51%; Found: 86.90%). Polymer 4 lost CH3CH2OH and
H2O solvent molecules below 140 °C. The TG curve of the dehy-
drated product shows no weight loss up to 267 °C, followed by a
continuously two-step weight loss of 82.02% from 267 to 634 °C
(Cald: 82.22%). The TGA result of 4 indicates that the 2D net does
not decompose and is stable below 267 °C. The TGA results of 1–
4 show that they are stable below 250 °C, which indicate their good
thermal stability.
3.2. Thermal analyses studies
To study the thermal stabilities of these complexes, thermo-
gravimetric analyses (TGA) of complexes 1–4 were performed
(Fig. S2, Supplementary Material, shows the TG curves for 1–4).
In TG analysis of 1, there is no weight loss until 294 °C. A continu-
ous weight loss can be detected from 294 to 498 °C attributed to
the complete decomposition of pam2ꢁ and 2,20-bpy (Calcd.:
89.25%; Found: 87.85%). Polymer 2 is very stable. There is no
weight loss until 318 °C. The weight reduces to 85.96% (Calcd.:
86.15%) at 645 °C, which is presumed to be the complete decompo-
sition of pam2ꢁ and 2,20-bpy. TG analyses of polymer 3 shows that
there is a continuously two-step weight loss in the range of 252–
650 °C, corresponding to the decomposition of pam2ꢁ and phen
3.3. Luminescent properties
The solid-state photoluminescent spectra of complexes 1–4 are
depicted in Fig. 5. Complex 1 exhibits two intense emission peaks
at ca. 461 and 528 nm upon excitation at 340 nm. The emission
peak is located at 528 nm, which means a red shift of ca. 51 nm rel-
ative to that of free H2pam ligand (kmax = 477 nm) (Fig. S1, Supple-
mentary Material, shows solid state emission spectrum of free
*
H2pam). We tentatively assign it to the intraligand (p–p ) fluores-
cence since a weak similar emission with kmaxat 477 nm is also ob-
served for free ligand. The peak at 461 nm would be distributed to
the intraligand emission from 2,20-bpy ligand [4,12]. Complex 2

Z.-X. Han et al. / Journal of Molecular Structure 891 (2008) 364–369
369
vor the formation of low-dimensional structures in the present
system.
2
Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (Grant No. 20573083) and the Natural Science
Foundation of Shaanxi Province (Grant No. 2004B09).
1
3
Appendix A. Supplementary data
4
CCDC Nos. 620299, 620300, 620301 and 620302 for 1, 2, 3 and 4
contain the supplementary crystallographic data. These data can
be obtained free of charge at www.ccdc.cam.ac.uk/conts/retriev-
ing.html [or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK. Fax: (internat) +44 1223
336 033; 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.molstruc.2008.04.010.
400
450
500
550
600
650
Wavelength (nm)
Fig. 5. The emission spectra of 1–4 in the solid state at room temperature upon
excitation at 340 nm.
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The emission peak is located at 523 nm for 2, and compared with
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complex 3 exhibits an intense blue radiation emission upon excita-
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In summary, four new d10 metal complexes with different struc-
tures have been synthesized under hydro(solvo)thermal condi-
tions. Complex 1, [Zn2(pam)2(2,20-bpy)2], possesses a discrete
dinuclear
metallamacrocyclic
structure.
Complex
2,
[Cd(pam)(2,20-bpy)2]n, is a 1D homochiral helical coordination
polymer that is built from achiral components. Complex 3,
[Zn(pam)(phen)]n, displays a 1D helical chain structure. Complex
4, [Cd(pam)(phen)]n ꢀ 0.5nCH3CH2OH ꢀ 0.5nH2O, exhibits an unu-
sual 2D double-layered structure generated by p ꢀ ꢀ ꢀ p interactions
of two 2D networks. The structural differences of these complexes
are mainly due to the differences of the size of the rigid aromatic
chelate ligands and d10 metal ions. It appears that the chelate li-
gands and metal ions of the larger size favor the formation of
high-dimensional structures, whereas those of the smaller size fa-
[12] X.M. Zhang, M.L. Tong, M.L. Gong, X.M. Chen, Eur. J. Inorg. Chem. (2003) 138.
[13] J. Zhang, Z.J. Li, Y. Kang, J.K. Cheng, Y.G. Yao, Inorg. Chem. 43 (2004) 8085.
[14] B.L. Wu, D.Q. Yuan, F.L. Jiang, R.H. Wang, L. Han, Y.F. Zhou, M.C. Hong, Eur. J.
Inorg. Chem. (2004) 695.
[15] X.J. Zhang, X.P. Zhou, D. Li, Crys. Growth Des. 6 (2006) 1440.