In situ hydrothermal syntheses, crystal structures and luminescent properties of two novel zinc(II) coordination polymers based on tetrapyridyl ligand

Article abstract of DOI:10.1016/j.ica.2010.10.020

Two novel Zn(II) coordination polymers, [Zn(2-pytpy)(fum)] _n·nH₂O (1) and [Zn₆(4-pytpy) ₃(mal)₄]_n·5n(H₂O) (2), (2-pytpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine, 4-pytpy = 4′-(4-pyridyl)-4,2′:6′,4″-terpyridine, H ₂fum = fumaric acid and H₂mal = malic acid) have been hydrothermally synthesized and structurally characterized. Notably, in situ ligand reactions occur in the formation of complexes 1 and 2, in which maleic acid is converted into fumaric acid and malic acid, respectively. Complex 1 is a 1D infinite chain structure, which is extended into a supramolecular layer by intermolecular π...π stacking interactions. Complex 2 is a 3D network structure, in which the bidentate-bridging 4-pytpy ligands link the layers based on the tetranuclear Zn(II) subunits to form the (4,10)-connected network. The luminescent properties of 1 and 2 have been investigated with emission spectra and UV-Vis diffuse reflectance spectra in the solid state. Additionally, these two complexes possess great thermal stabilities.

Full text of DOI:10.1016/j.ica.2010.10.020

Inorganica Chimica Acta 366 (2011) 134–140
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
In situ hydrothermal syntheses, crystal structures and luminescent properties
of two novel zinc(II) coordination polymers based on tetrapyridyl ligand
⇑
Juan Song, Bao-Cheng Wang, Huai-Ming Hu , Lei Gou, Qing-Ran Wu, Xiao-Le Yang, Yi-Qing Shangguan,
Fa-Xin Dong, Gang-Lin Xue
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University,
Xi’an 710069, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 May 2010
Received in revised form 15 October 2010
Accepted 19 October 2010
Available online 26 October 2010
Two novel Zn(II) coordination polymers, [Zn(2-pytpy)(fum)]nꢀnH2O (1) and [Zn6(4-pytpy)3(mal)4]nꢀ5n(H2O)
(2), (2-pytpy = 40-(4-pyridyl)-2,20:60,200-terpyridine, 4-pytpy = 40-(4-pyridyl)-4,20:60,400-terpyridine,
H2fum = fumaric acid and H2mal = malic acid) have been hydrothermally synthesized and structurally
characterized. Notably, in situ ligand reactions occur in the formation of complexes 1 and 2, in which
maleic acid is converted into fumaric acid and malic acid, respectively. Complex 1 is a 1D infinite chain
structure, which is extended into a supramolecular layer by intermolecular
p. . .p stacking interactions.
Keywords:
Zinc
40-(4-Pyridyl)-terpyridine
In situ hydrothermal synthesis
Crystal structure
Luminescent property
Complex 2 is a 3D network structure, in which the bidentate-bridging 4-pytpy ligands link the layers
based on the tetranuclear Zn(II) subunits to form the (4,10)-connected network. The luminescent prop-
erties of 1 and 2 have been investigated with emission spectra and UV–Vis diffuse reflectance spectra in
the solid state. Additionally, these two complexes possess great thermal stabilities.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
removaland exchange[16]. The 40-(4-pyridyl)-2,20:60,200-terpyridine
(2-pytpy, see Scheme 1), as a potentially tetradentate ligand,
The design of coordination polymer architectures is an impor-
tant goal for synthetic chemistry as it provides an opportunity to
control the properties of materials at the molecular level [1–3].
The most successful strategies for the design of coordination poly-
mers are based on a building block approach because final struc-
tural frameworks can dramatically change when the organic
building blocks vary [4,5]. Recently, the in situ ligand synthesis as
a new approach to prepare coordination polymers has been noted
extensively, in which ligand precursor is used to react with metal
salts directly to produce single crystals containing new organic li-
gand [6,7]. In situ hydrothermal reactions usually provide not only
very stable materials for potential applications, such as lumines-
cence, magnetism, absorption, catalysis and ion-exchange [8–12],
but also products that are inaccessible or not easily obtainable by
conventional methods [13].
has been intensively explored because of its versatility as building
blocks for coordination polymers [17–23]. However, its isomeric com-
pound, 40-(4-pyridyl)-4,20:60,400-terpyridine (4-pytpy, see Scheme 1),
as a rigid trigonal ligand, has been rarely reported in the realm of
coordination chemistry [24,25]. Its rigidity and trigonal geometry
may lead to the formation of nanosized cages, porous frameworks
enclosing cavities, and channels [26,27].
Our crucial aim of this work is to explore the in situ hydrother-
mal reactions for tuning the structural assembly, which may
provide further insights in designing novel hybrid crystalline mate-
rials. In this paper, we present the in situ hydrothermal syntheses
and crystal structures of two novel Zn(II) coordination polymers,
[Zn(2-pytpy)(fum)]nꢀnH2O (1) and [Zn6(4-pytpy)3(mal)4]nꢀ5n(H2O)
(2), as well as their luminescent properties and thermal stabilities.
Maleic acid, as O-donor ligand, has received much more atten-
tion. It is frequently employed in the construction of polynuclear
metal carboxylate clusters due to the isomerization and the hydrox-
ylation of the ethylene group by the in situ hydrothermal reactions
[14,15]. An interesting Co(II) complex was synthesized by the reac-
tion of the hydroxylation of the ethylene group in maleic acid, which
exhibits complicated magnetic properties tunable by guest water
2. Experimental
2.1. General methods
2-Pytpy and 4-pytpy ligands were prepared according to the lit-
erature method with some modifications [28,29], other chemicals
were of reagent grade and used without further purification. Ele-
mental analyses (C, H, N) were performed on an elementar Vario
EL I elemental analyzer. Infrared spectra were recorded on a
Bruker EQUINOX 55 spectrometer as KBr pellets in the range of
⇑
Corresponding author. Tel./fax: +86 29 88303331.
E-mail addresses: ChemHu1@nwu.edu.cn, Xraydiff@163.com (H.-M. Hu).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.10.020

J. Song et al. / Inorganica Chimica Acta 366 (2011) 134–140
135
N
N
tem was heated at 180 °C. The yellow rhombus crystals were
obtained, washed with distilled water (5 mL), and dried in air to give
0.0204 g, yield: 63.1% based on Zn. Anal. Calc. (for C76H64N12O25Zn6:
C, 47.10; H, 3.32; N, 8.67. Found: C, 47.19; H, 3.21; N, 8.61. IR (KBr,
cmꢁ1): 3423 m, 1631 s, 1597 m, 1419 w, 1399 s, 1350 m, 1288 w,
1121 m, 1070 w, 1028 w, 836 m, 818 m, 669 w, 640 m, 629 w, 591
w, 502 m.
O
OH
OH
N
N
N
N
N
N
O
2-pytpy
4-pytpy
maleic acid
2.6. The solid-state UV–Vis diffuse reflectance spectra
Scheme 1. Molecular structures of the ligands used in the paper.
The solid-state UV–Vis diffuse reflectance spectra were per-
formed at room temperature using a Shimadzu UV-2550 double
monochromator spectrophotometer. The instrument is equipped
with an integrating sphere and controlled by a personal computer.
BaSO4 was used as a 100% reflectance standard for all materials.
The UV–Vis diffuse reflectance measurements were taken in the
range of 200–700 nm. Data were collected in reflectance (%R)
mode. Samples were prepared by grinding them to a fine powder
and spreading them on a compacted surface of the powdered stan-
dard material, preloaded into a sample holder.
400–4000 cmꢁ1
. Luminescence spectra were measured on a
HitachiF-4500 spectrophotometer at room temperature. Thermal
gravimetry analyses (TGA) were carried out with a Universal
V2.6 DTA system at a rate of 10 °C/min in a nitrogen atmosphere.
2.2. Preparation of 2-pytpy
A mixture of 2-acetylpyridine (3.21 g, 26.7 mmol), pyridine-4-
carboxaldehyde (3.26 g, 26.7 mmol) and NaOH (1.60 g, 40.0 mmol)
was dissolved in ethanol (50 mL) with stirred at 0 °C for 2 h,
resulted in the formation of a light yellow solution. Then, added
2-acetylpyridine (3.21 g, 26.7 mmol) and excessive ammonium
acetate (10.00 g, 129.7 mmol), stirred at 80 °C under nitrogen
atmosphere for 5 h. After the mixture was cooling to room temper-
ature, the resulting white precipitate was filtered off, recrystallized
with methanol, and dried in vacuo to give colourless needle
crystals in 31.7% yield based on pyridine-4-carboxaldehyde
(3.06 g). Anal.Calc. for C20H14N4: C, 77.40; H, 4.55; N, 18.05. Found:
C, 77.57; H, 4.34; N, 18.09. IR (KBr, cmꢁ1): 3418 w, 3049 m, 1703 m,
1585 s, 1530 s 1468 s, 1407 w, 1391 s, 1264 m, 1069 m, 985 m, 901
m, 893 w, 809 s, 735 w, 616 m, 521 m.
2.7. X-ray crystallography
Intensity data of 1 and 2 were collected on a Bruker Smart Apex
II CCD diffractometer with graphite-monochromated Mo Ka radia-
tion (k = 0.71073 Å) at room temperature. Empirical absorption
corrections were applied using the SADABS program. The structures
were solved by the direct method and refined by the full-matrix
least-squares on F2 with SHELX-97 program package [30,31]. All
non-hydrogen atoms were refined anisotropically and hydrogen
atoms of organic ligands were generated geometrically. The crystal
data and structural refinement results are summarized in Table 1.
The selected bond distances and angles are listed in Table S1 (Sup-
plementary information).
2.3. Preparation of 4-pytpy
The preparation of 4-pytpy was similar to that of 2-pytpy ex-
cept that 4-acetylpyridine was used instead of 2-acetylpyridine.
The colourless block crystals were obtained in 35.3% yield based
on pyridine-4-carboxaldehyde (3.42 g). Anal. Calc. for C20H14N4:
C, 77.40; H, 4.55; N, 18.05. Found: C, 77.34; H, 4.69; N, 17.98. IR
(KBr, cmꢁ1): 3422 w, 3026 m, 1706 m, 1590 s, 1534 s, 1424 w,
1396 s, 1319 m, 1218 m, 1062 w, 989 m, 891 m, 817 s, 743 w,
672 w, 622 m, 580 m, 493 m.
Table 1
Crystallographic data and structural refinement parameters for 1and 2.a.
Complexes
1
2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system, space group
C
24H18N4O5Zn
C76H64N12O25Zn6
1937.61
507.79
296(2)
296(2)
0.71073
monoclinic,
P21/n
0.71073
monoclinic, C2/c
a (Å)
b (Å)
c (Å)
8.6622(5)
24.636(1)
10.9851(5)
90
115.560(3)
90
2114.8(2)
4
1.595
34.471(5)
10.926(1)
22.395(3)
90
120.743(2)
90
7249(2)
4
1.775
2.4. Preparation of [Zn(2-pytpy)(fum)]nꢀnH2O (1)
A
mixture of ZnCl2ꢀ2H2O (0.0136 g, 0.1 mmol), 2-pytpy
a
(°)
b (°)
(0.0312 g, 0.1 mmol), maleic acid (0.0232 g, 0.2 mmol) in distilled
water (10 mL) was placed in a Teflon-lined stainless steel vessel
and adjusted the pH value of the mixture to 6.0 with 0.5 mol Lꢁ1
NaOH aqueous solution. The reaction system was heated at
160 °C for 72 h, followed by slowly cooling down to room temper-
ature at a rate of 5 °C hꢁ1. The colourless block crystals were ob-
tained and dried in air to give 0.0327 g, yield: 64.3% based on Zn.
Anal. Calc. for C24H18N4O5Zn: C, 56.76; H, 3.57; N, 11.03. Found:
C, 56.53; H, 3.42; N, 11.16. IR (KBr, cmꢁ1): 3359 m, 3250 m, 3071
m, 1691 w, 1572 s, 1471 m, 1394 s, 1249 m, 1209 m, 1158 m,
1095 w, 996 w, 962 m, 897 m, 811 m, 794 s, 744 m, 694 m, 621
w, 578 w , 509 w.
c
(°)
V (Å3)
Z
Calculated density (g cmꢁ3
)
Absorption coefficient (mmꢁ1
F(0 0 0)
)
1.208
1040
2.048
3936
h range for data collection (°)
Index range
2.22–25.05
ꢁ5 ꢂ h ꢂ 10
ꢁ29 ꢂ k ꢂ 29
ꢁ13 ꢂ l ꢂ 12
10 512
3738
99.7%
1.048
1.99–25.05
ꢁ31 ꢂ h ꢂ 40
ꢁ12 ꢂ k ꢂ 13
ꢁ26 ꢂ l ꢂ 25
17 546
6385
99.5%
1.017
Reflections collected
Reflections unique
Completeness to h = 25.05
Goodness-of-fit (GOF) on F2
Independent reflections (Rint
R1, wR2 [I > 2 (I)]
R1, wR2 (all data)
Largest difference in peak, hole (e Åꢁ3
)
0.0190
0.0577
r
0.0248, 0.0662
0.0306, 0.0685
0.247, ꢁ0.230
0.0565, 0.1362
0.0917, 0.1542
0.957, ꢁ0.739
2.5. Preparation of [Zn6(4-pytpy)3(mal)4]nꢀ5n(H2O) (2)
)
Complex 2 was prepared in a similar procedure as 1, by using 4-
pytpy (0.0312 g, 0.1 mmol) in place of 2-pytpy, and the reaction sys-
2
[wðF20 ꢁ F2CÞ ]/
R .
[(F20)2]]1/2
a
R =
R
||F0| ꢁ |FC||/
R
|F0|, wR2 = [
R

136
J. Song et al. / Inorganica Chimica Acta 366 (2011) 134–140
2-pytpy ligand and one lattice water molecule. As shown in Fig. 1a,
3. Results and discussion
the Zn1 center is five-coordinated to three nitrogen atoms (N1, N2,
N3) from the same 2-pytpy ligand, and two oxygen atoms (O1 and
O3) from different fum2ꢁ ligands, respectively. The coordination
geometry of Zn1 center can be described as a distorted square-pyr-
amid, the N1, N2, N3, O3 atoms comprise the equatorial plane and
the O1 atom occupies the axial position. The distances of Zn–N fall
in the range of 2.086(2)–2.177(2) Å, and the Zn–O bond lengths
3.1. Syntheses
2-Pytpy and 4-pytpy were synthesized in high purity and
acceptable yield according to the method reported by Kröhnke
with some modifications. The reaction time was shortened from
24 h to 7 h. Therefore, our modified procedure is a more conve-
nient method to prepare 2-pytpy and 4-pytpy ligands, as well as
its isomeric compounds.
Complexes 1 and 2 have been successfully prepared under
hydrothermal conditions. It is noteworthy that the in situ reactions
occur in the formation of 1 and 2, in which maleic acid was con-
verted into fumaric acid and malic acid, respectively (see Scheme
2). We used maleic acid as the ligand precursor to react with
ZnCl2ꢀ2H2O in the presence of 2-pytpy ligand to obtain [Zn(2-pyt-
py)(fum)]nꢀnH2O (1), in which maleic acid was converted into fu-
maric acid by the isomerization reaction. To our knowledge, the
key influencing factor for the in situ reactions is temperature. The
in situ cis–trans isomeric transformation of substituted ethylene
was occurred under 140 °C, because fumaric acid is much stable
than maleic acid at high temperature [32–36]. At the same time,
the in situ cis–trans isomerization can occur with several metal
salts, such as Cu(I), Cd(II) and Zn(II) ions [37–39], which indicates
metal ion is not one of the key factors for the in situ cis–trans isom-
erization of maleic acid. While in the formation of 2, the hydroxyl-
ation of the ethylene group of maleic acid has been observed. It has
long been known that HCl could catalyze the conversion of maleic
acid into malic acid with addition of water. The mechanism of the
in situ ligand synthesis of malic acid is probably similar to that of
ethylene hydration reactions to form alcohols in acidic conditions
[40,41]. It must be mentioned that if the Zn(II) salts directly react
with the malate and 4-pytpy ligands, we only obtained Zn(II) coor-
dination polymers with 4-pytpy ligands and without malate anions
[15], which suggests that the in situ ligand synthesis is favorable to
form coordination polymers with mixed ligands.
3.2. IR spectra
The IR spectra of 2-pytpy, 4-pytpy, 1 and 2 exhibit characteristic
bands of the 40-(4-pyridyl)-terpyridine (2-pytpy and 4-pytpy) at
about 1590 cmꢁ1 (C@C), 1390 cmꢁ1 (ring deformation mode C–
m
C) and 810 cmꢁ1 (out-of-ring bend C–H). In the IR spectra of 1
and 2, the absence of any strong bands around 1700 cmꢁ1 indicates
that the carboxylate groups of organic-acid are completely
deprotonated [42,43]. The differences between
mas(COO) and
m
s(COO) (
D
= 208 cmꢁ1 for 1, 232 cmꢁ1 for 2) suggest that the
carboxylate groups coordinate to the Zn(II) ions in monodentate
coordination modes [44,45]. These IR spectra are in good agree-
ment with the results of X-ray structural analyses.
3.3. Description of crystal structures
Fig. 1. (a) The coordination environment of the Zn(II) in 1 with partial atom
numbering schemes (symmetric code A: ꢁx + 2, ꢁy + 2, ꢁz + 2). Hydrogen atoms
and uncoordinated water molecules are omitted for clarity. (b) The view of the 1D
chain in 1. (c) Packing diagram of the 2D layer supported by two types of
3.3.1. [Zn(2-pytpy)(fum)]nꢀnH2O (1)
Complex 1 crystallizes in the monoclinic P21/n space group. The
asymmetric unit of 1 contains one crystallographically indepen-
dent Zn(II) atom, two half l
2-fum2ꢁ anion, one tridentate-chelating
intermolecular p. . .p stacking interactions in 1.
HO
isomerization
O
HO
HO
O
O
O
hydroxylation
HO
OH
O
OH
O
OH
Scheme 2. The in situ hydrothermal reactions occur in the formation of 1 and 2.

J. Song et al. / Inorganica Chimica Acta 366 (2011) 134–140
137
Fig. 2. (a) The coordination environment of the Zn(II) in 2 with partial atom numbering schemes (symmetric code A: x + 1/2, ꢁy + 5/2). Hydrogen atoms and uncoordinated
water molecules are omitted for clarity. (b) The view of the tetranuclear Zn(II) subunit in 2. (c) The view of the 2D layer constructed from Zn(II) centers and mal2ꢁ anions in 2.
(d) The topological network of 2D layer in 2. The 6-connected tetranuclear Zn(II) subunits are marked as green balls , and 3-connected mononuclear Zn(II) tetrahedron are
marked as pink balls, respectively. (e) The view of the 3D structure of 2. (f) The view of the 3D topological network of 2. The 10-connected tetranuclear Zn(II) subunits are
marked as green balls , and 4-connected mononuclear Zn(II) tetrahedron are marked as pink balls, respectively.
vary from 1.982(1) Å to 1.986(1) Å, which are consistent with the
corresponding values reported for Zn-fumaric and Zn-pyridyl com-
plexes [46–48].
Notably, H2fum is completely deprotonated and acts as a bis-
monodentate bridging ligand bonding with Zn(II) ions to form a
1D infinite chain structure (Fig. 1b), and the minimum intrachain
Zn. . .Zn distance is 8.080(2) Å. In the solid state, two types of
In complex 1, four pyridyl rings of the 2-pytpy ligand are non-
planar, N4 pyridyl ring is twisted relative to the central one (N2
pyridyl ring) with a large angle of 32.27°, while the other two pyr-
idyl rings are nearly co-planar with the central one, the corre-
sponding dihedral angles are 3.03° (N1 pyridyl ring) and 4.63°
(N3 pyridyl ring), respectively. In 1, the rotation of the N4 pyridyl
ring with the central one is larger than others. The reasons for this
phenomenon are the repulsion force arising from the central pyri-
dine-b-hydrogen atoms and the formation of intermolecular
hydrogen bonds to stabilize the compound [49,50]. The other rea-
son may be N1, N2 and N3 pyridyl rings coordinated to Zn(II) cen-
ter in the same equatorial plane of square-pyramidal coordination
geometry.
p. . .p stacking interactions are observed, as illustrated in Fig. 1c.
The central and one terminal pyridyl rings of 2-pytpy interact with
the terminal and central pyridyl rings from the adjacent chains
[3.929(2) Å and 3.845(2) Å for centroid–centroid distances]. There-
fore, these 1D chains are linked to each other to form a 2D layer by
these two types of intermolecular p. . .p stacking interactions.
It should be pointed out that although different pyridyl ligands
(py = pyridine, phen = 1,10-phenanthroline) were used in the
formation of [Zn(fum)(py)3]nꢀn(py)ꢀn(H2O) [51,52], [Zn(phen)
(fum)]nꢀn(H2fum) [46] and 1, they all show 1D zigzag chain struc-
tures. However, some differences exist between these complexes.
The average Zn–N and Zn–O bond distances in [Zn(fum)(py)3]n

138
J. Song et al. / Inorganica Chimica Acta 366 (2011) 134–140
ꢀn(py)ꢀn(H2O) [2.175(3) Å and 1.998(3) Å] are longer than the
corresponding values in [Zn(phen)(fum)]nꢀn(H2fum) [(2.049(2) Å
and 1.961(2) Å] and 1 [2.147(1) Å and 1.988 (1) Å)], which indicate
that chelating ligands are coordinated to metal centers much more
stably than that of the monodentate ligands. Additionally,
p. . .p
stacking interactions were not observed in [Zn(fum)(py)3]n
ꢀn(py)ꢀn(H2O). However, in [Zn(phen)(fum)]nꢀn(H2fum) and 1, they
all extended into supramolecular layers by intermolecular
p. . .p
stacking interactions. In all, ligands containing big conjugated
systems are apt to form more stable complexes than the corre-
sponding complexes with monodentate ligands.
3.3.2. [Zn6(4-pytpy)3(mal)4]nꢀ5n(H2O) (2)
X-ray structural analysis revealed that 2 is a 3D polymeric net-
work. In 2, the asymmetric unit contains three crystallographically
independent Zn(II) atoms, two
l
3-mal2ꢁ anions, one and a half
bidentate-bridging 4-pytpy ligand and five lattice water molecules.
As shown in Fig. 2a, the Zn1 center is coordinated to five oxygen
atoms (O1, O6, O8, O9, and O3A) from mal2ꢁ anions and one nitro-
gen atom (N1) from 4-pytpy ligand. The coordination geometry of
Zn1 center can be described as a distorted octahedron, the O1, O6,
O9, O3A atoms comprise the equatorial plane and the N1, O8 atoms
occupy the axial positions [N1–Zn1–O8 = 173.4(2)°]. Zn2 is also
six-coordinated with a distorted octahedral geometry. The basal
positions are occupied by O3, O4, O8 and O1A, O1 and N6A atoms
occupy the axial positions [O1–Zn2–N6A = 176.8(2)°]. While Zn3
center is four-coordinated to O7, O5A, O10A, N4 with a distorted
tetrahedral geometry, the corresponding angles are 101.7(2)°
(O5A–Zn3–O7), 112.1(2)° (O5A–Zn3–O10A), 114.7(2)° (O7–Zn3–
O10A), 119.3(2)° (O5A–Zn3–N4), 114.2(2)° (O7–Zn3–N4) and
95.5(2)° (O10A–Zn3–N4).
The most interesting feature of 2 is its tetranuclear Zn(II) sub-
unit, which is composed of four edge-sharing ZnNO5 octahedra
(Fig. 2b). In 2, the tetranuclear Zn(II) subunits are linked through
six ZnNO3 tetrahedra to construct a 2D layer (Fig. 2c). If the tetra-
nuclear Zn(II) subunit is as a six-linked node and the mononuclear
Zn(II) tetrahedron as a three-linked node, the 2D layer can be sim-
plified to a 2D topological network with Schläfli symbol of
(46.66.83)(43)2 (Fig. 2d). The 2D layers are further connected with
the bidentate-bridging 4-pytpy ligands to generate a 3D network
(Fig. 2e). To simplify this 3D structure, we can consider the tetra-
nuclear subunit as a 10-linked node and the mononuclear Zn(II)
tetrahedron as a four-linked node, thus, the 3D structure can be
formulated as a (4,10)-connected network with Schläfli symbol of
(34.412.511.614.73.81)(3.45)2 (Fig. 2f). Notably, this is the first struc-
tural paradigm for a coordination polymer with such a (4,10)-con-
nected topological net.
Fig. 3. The solid-state diffuse reflectance spectra of 2-pytpy and 1 (a), 4-pytpy and
2 (b) at room temperature.
sion spectra of 2-pytpy and 1, 4-pytpy and 2 in the solid state are
depicted in Fig. 4. 2-Pytpy and 4-pytpy are isomeric conjugated or-
ganic compounds, they both exhibit strong emission band at
375 nm upon excitation at 310 nm. In contrast with terpyridyl
derivatives, the emission energy is expectable [57]. At room tem-
perature, the similar emission at 383 nm and 385 nm were ob-
served for
1 and 2 at the same excitation condition. It is
suggested that the emission of 1 and 2 originated from ligand-
based intramolecular charge transfer (ICT) [58]. Notably, a lower
energy emission was also detected at 522 nm for 1, which indicates
3.4. The solid-state UV–Vis properties
that the intermolecular
p. . .p stacking interactions exist. The
enhancement of luminescence may be attributed to ligand chela-
tion to the Zn(II) centers, which effectively increases the rigidity
of the coordination polymers and reduces the loss of energy by
radiationless decay [59].
The UV–Vis diffuse reflectance spectra of the complexes 1 and 2
were carried out in the solid state at room temperature. As shown
in Fig. 3, the spectra of 2-pytpy and 4-pytpy shows intense peaks at
*
324 nm and 338 nm, respectively, which can be ascribed to
p ? p
transitions of pytpy ligand [53,54]. The solid-state UV–Vis diffuse
reflectance spectra of 1 and 2 are also depicted in Fig. 3. The bands
are located at 265 nm (broad band) and 322 nm for 1, 260 nm
(broad band) and 320 nm for 2, respectively. They all possess sim-
3.6. Thermogravimetric analysis and PXRD patterns
Thermal gravimetry analyses (TGA) were performed to gauge the
thermal stabilities of complexes 1 and 2. As shown in Fig. S1, the
TGA curve of 1 and 2 are divided into three stages. The first weight
loss of 3.11% occurs under 175 °C for 1 and 4.43% under 190 °C for 2,
which can be attributed to the loss of lattice water molecule (calcd
3.55% for 1 and 4.66% for 2). The second step weight loss of 61.05%
between 385 °C and 452 °C for 1 and 48.53% between 301 °C and
412 °C for 2 indicated the decomposition of pytpy ligands (2-pytpy
ilar absorption spectra and tentatively assigned to ligand-based
*
p
? p transitions.
3.5. Luminescent properties
The Zn(II) terpyridyl complexes are well known for their versa-
tile luminescent properties at room temperature [55,56]. The emis-

J. Song et al. / Inorganica Chimica Acta 366 (2011) 134–140
139
Graduate Innovation and Creativity Funds (Grant No. 09YZZ48)
and the Open Foundation of Key Laboratory of Synthetic and Natural
Functional Molecule Chemistry of Ministry of Education.
Appendix A. Supplementary material
CCDC 747632(1) and 747633(2) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.ica.2010.10.020.
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