Hydrothermal synthesis, structure and property of a zinc coordination polymer based on aromatic polycarboxylate and phenanthroline ligands

Article abstract of DOI:10.1002/zaac.200600260

A zinc coordination polymer [Zn(μ₂-H₂bta) _1/2(μ₄-H₂bta)_1/2(phen)(H ₂O)]_n (1) (H₄bta = benzene- 1,2,4,5-tetra-carboxylic acid, phen = 1, 10-phenanthroline) has been hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric and single-crystal X-ray diffraction analyses. Compound 1 displays pucker layer structure formed from Zn²⁺ ions and μ₂-H₂bta^2- and μ₄-H ₂bta^2- bridging ligands, and it is linked into three dimensional (3D) supramolecular frameworks through the hydrogen bonds and π-π interactions. It exhibits strong blue fluorescence at room temperature in the solid state.

Full text of DOI:10.1002/zaac.200600260

DOI: 10.1002/zaac.200600260
Hydrothermal Synthesis, Structure and Property of a Zinc Coordination
Polymer Based on Aromatic Polycarboxylate and Phenanthroline Ligands
Xiao-Yang Yu, Jing Lu, Jie-Hui Yu, Xiao Zhang, Ji-Qing Xu*, and Tie-Gang Wang
Changchun, Jilin / China College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin
University
Received September 14th, 2006.
Abstract.
A
zinc coordination polymer [Zn(µ2-H2bta)1/2(µ4-
benzene-1,2,4,5-tetra-
is linked into three dimensional (3D) supramolecular frameworks
through the hydrogen bonds and π-π interactions. It exhibits strong
blue fluorescence at room temperature in the solid state.
H2bta)1/2(phen)(H2O)]n (1) (H4bta
ϭ
carboxylic acid, phen ϭ 1, 10-phenanthroline) has been hydrother-
mally synthesized and characterized by elemental analysis, IR spec-
troscopy, thermogravimetric and single-crystal X-ray diffraction
analyses. Compound 1 displays pucker layer structure formed from
Zn2ϩ ions and µ2-H2bta2Ϫ and µ4-H2bta2Ϫ bridging ligands, and it
Keywords: Zinc; Coordination polymer; Benzene-1,2,4,5-tetra-
carboxylic acid; Hydrothermal synthesis; fluorescence
Introduction
π-π aromatic stacking interactions to form interesting struc-
tures [2(h), 5].
The design and synthesis of new coordination polymers
have received much attention recently owing to their inter-
esting crystal structures and potential application in mag-
netism, electrical conductivity, luminescence, biology and
catalysis etc. [1]. To date, a variety of coordination polymers
with different structures based on different bridging ligands
especially aromatic polycarboxylate ligands have been syn-
thesized [2]. Among these ligands, benzene-1,2,4,5-tetracar-
boxylic acid (H4bta) possesses several interesting character-
istics. Firstly, it has four carboxyl groups inducing multiple
coordination modes with transition metal centers and pro-
viding abundant structural motifs; Secondly, it can act not
only as hydrogen bond donors but also as acceptors be-
cause of the existence of deprotonated and/or protonated
carboxyl groups [2(h)-2(m), 3]. So it is regarded as an excel-
lent candidate of bridging ligands to build different kinds
of coordination polymers, including one dimensional (1D)
chain [2(i), 2(k), 2(o), 3(a), 4(b)], two dimensional (2D)
layer [2(h), 2(l), 4(a), 4(d)] and three dimensional (3D) net-
work compounds [2(j), 3(d), 4(c)]. Furthermore, the intro-
duction of a second aromatic organonitrogen ligands such
as 1, 10-phenanthroline (phen) and 2, 2Ј-bipyridine are aslo
important in the syntheses of coordination polymers and
may provide potential supramolecular recognition sites for
On the other hand, d10 metal coordination polymers are
noted extensively because they exhibit not only intriguing
structures but also photoluminescent properties [6]. One of
our research interests is focused on a systematic study of
the preparation of coordination polymers by using multi-
carboxylate bridging ligands and azacyclo terminal ligands
and d10 metal. In this paper, we report a d10 metal co-
ordination polymers [Zn(µ2-H2bta)1/2(µ4-H2bta)1/2(phen)-
(H2O)]n (1) which shows strong blue fluorescent emission
at room temperature in the solid state.
Experimental Section
Materials and general methods
All chemicals were obtained commercially and used without
further purification. Infrared spectrum was recorded as KBr pellets
by using a Perkin-Elmer Spectrum One FT-IR spectrometer in the
4000-400 cmϪ1 region. Elemental analyses for C, H and N were
performed on a Perkin-Elmer 2400 element analyzer. Fluorescent
data were obtained from an Edingburgh FS900 instrument at room
temperature. Thermogravimetric analysis was performed on a Per-
kin-Elmer TGA-7 instrument with a heating rate of 20 °C·minϪ1
in air.
Synthesis
* Prof. Ji-Qing Xu
[Zn(µ2-H2bta)1/2(µ4-H2bta)1/2(phen)(H2O)]n(1): A mixture of ZnCl2
(0.14 g, 1.0 mmol), H4bta (0.38 g, 1.5 mmol), 1,10-phen (0.12 g,
0.6 mmol) and H2O (20 ml) was continuously stirred for 2 h in air
at room temperature and the pH was adjusted to 3.0 with sodium
hydroxide aqueous solution. The resulting solution was sealed in a
30 ml Teflon-lined stainless steel vessel and heated at 170 °C for 4
College of Chemistry and State Key Laboratory of Inorganic Syn-
thesis and Preparative Chemistry
Jilin University
Changchun, Jilin, 130023 / China
Fax: ϩ86-431-5168624;
E-mail: xjq@mail.jlu.edu.cn
490
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Z. Anorg. Allg. Chem. 2007, 633, 490Ϫ494

A Zinc Coordination Polymer
days under autogenous pressure. After slowly cooling to ambient
temperature, light yellow columnar crystals were obtained and
washed with distilled water. The yield based on Zinc is approxi-
mately 48 %. Anal. Calc. (Found) for C22H14N2O9Zn (%), C: 51.24
(51.07), H: 2.74 (2.63); N: 5.43 (5.45).
IR (KBr, pellet): δ(OH) 3258 s; δ(COOH) 1706 s; νasym(COOϪ)
1564 vs; ν(C-C)skeletal 1518 m, 1494 m, 1426 m; νsym(COOϪ) 1358 s;
δ(CHaromatic in-plane
)
1289 w, 1226 s, 1130 w, 1112 m; δ(CHaromatic)out-of-plane
923 m, 850 s, 801 m, 776 w, 724 s cmϪ1
.
X-ray single-crystal structure determinations
Suitable single crystal of as-synthesized compound with the dimen-
sions of 0.25 ϫ 0.15 ϫ 0.05 mm for 1 was carefully selected and
glued to thin glass fibers with epoxy resin. Data for compound
1 were collected on a Siemens SMART CCD diffractometer with
Fig. 1 Perspective view of crystal structure of 1, showing the coor-
dination environments of ZnII atoms and two kinds of coordination
˚
graphite-monochromated MoKα radiation (λ ϭ 0.71073 A) at
modes of µ2-H2bta2Ϫ
.
room temperature. The structure was solved by using the direct
methods with SHELXL program and refined by full-matrix least-
squares technique. All of the non-hydrogen atoms were refined an-
isotropic parameters. All the hydrogen atoms were located from
difference Fourier map and refined with isotropic temperature fac-
tors. The structure was then refined on F2 with SHELXL-97. De-
tails of the final refinements, the selected parameters of bond
lengths, angles and hydrogen bonds of compound 1 are given in
Table 1 and 2, respectively.
˚
Table 1 Selected bond lengths /A and bond angles /° for com-
pound 1.
Zn(1)-OW1
Zn(1)-O(3)
Zn(1)-N(1)
Zn(1)-N(2)
Zn(1)-O(2)
Zn(1)-O(1)
O(1)-C(15)
O(5)-C(15)
O(2)-C(18)
O(4)-C(18)
O(3B)-C(22)
O(8)-C(22)
O(6)-C(17)
O(7)-C(17)
2.0686(18)
2.0957(15)
2.1107(19)
2.1188(18)
2.1303(15)
2.2110(16)
1.292(3)
1.222(3)
1.251(3)
1.252(3)
1.233(3)
OW1-Zn(1)-O(3)
OW1-Zn(1)-N(1)
O(3)-Zn(1)-N(1)
OW1-Zn(1)-N(2)
O(3)-Zn(1)-N(2)
OW1-Zn(1)-O(2)
O(3)-Zn(1)-O(2)
N(1)-Zn(1)-O(2)
N(2)-Zn(1)-O(2)
OW1-Zn(1)-O(1)
O(3)-Zn(1)-O(1)
N(1)-Zn(1)-O(1)
N(2)-Zn(1)-O(1)
O(2)-Zn(1)-O(1)
95.98(7)
173.45(7)
90.56(7)
94.33(8)
169.65(7)
88.23(7)
94.67(6)
90.90(7)
86.49(7)
84.90(8)
84.65(6)
96.08(7)
95.43(6)
172.99(6)
Crystal refinement data of 1
[Zn(µ2-H2bta)1/2(µ4-H2bta)1/2(phen)(H2O)]n
ϵ
C22H14N2O9Zn,
¯
M ϭ 515.72, triclinic, space group P1. a ϭ 9.6922(9), b ϭ
˚
1.289(3)
1.315(3)
1.207(3)
10.2132(9), c ϭ 11.3887(10) A, α ϭ 87.345(1)°, β ϭ 72.154(1)°, γ ϭ
3
65.327(1)°. V ϭ 970.79(15) A . Z ϭ 2. ρcalc ϭ 1.764 g/cm3.
˚
F(000) ϭ 524. R(wR) ϭ 0.0382(0.0896) for 3865 reflections with
I>2σ(I).
Symmetry code: (B) 1ϩx, y, z;
Results and Discussion
while when pH value being larger than 7, only powder
product was obtained. It can be explained that the com-
pounds obtained under different pH value contain mul-
ticarboxylate ligands with different extent of deprotonation.
In fact, when different metals react with the same multicar-
boxylic acid, different pH values of reaction system are re-
quired for getting the compound with multicarboxylate li-
gands possessing the same extent of deprotonation. For ex-
ample, when pH value of reaction system being 7.0, the
compound {[Fe(OH)(H2bta)](H2O)}n with partly depro-
tonated benzene-1,2,4,5-tetracarboxylate ligands rather
than the compound with fully deprotonated one was ob-
tained [8].
Synthesis
Compound 1 was synthesized under mid-temperature
hydrothermal conditions and pH value of reaction system
being 3.0. The pH value of reaction system and the reaction
temperature are important factors effecting formation of
compound 1. When pH value of reaction system being 6.0
and other reaction conditions being unchanged, compound
[Zn(µ4-bta)1/2(phen)(H2O)]n (2) was got, in which benzene-
1,2,4,5-tetracarboxylate ligands are fully deprotonated1),
Additionally, reaction temperature and time are also im-
portant factors for the synthesis of compound 1. When the
reaction temperature was lower than 150 °C or the crystalli-
zation time was longer than 6 days, no perfect crystal
product was obtained.
1) [Zn(µ4-bta)1/2(phen)(H2O)]n (2) Compound 2 was obtained using
procedure similar to that of 1, except that the pH was adjust to 6.0
with sodium hydroxide solution. Yellow crystals of 2 were obtained.
The yield of crystal material was based on ZnII is approximately
57 %, Anal. Calcd. (Found) for C17H11N2O5Zn (%), C:
52.53(52.63), H: 2.85(3.04); N: 7.21(7.05); Crystal data for 2:
Monoclinic, P21/n, a ϭ 7.9585(4), b ϭ 11.7976(5), c ϭ 15.3951(7),
β ϭ 99.6080, V ϭ 100.416(2), Z ϭ 4, λ(Mo Kα) ϭ 0.71073, R1 ϭ
0.0331, wR2 ϭ 0.0945 [I>2σ(I)]; R indices (all data): R1 ϭ 0.0346,
wR2 ϭ 0.0955; Reflections collected: 7843; Independent reflection
(Rint): 2796 [Rint ϭ 0.0424]. The result of single crystal structure
determination indicates that compound 2 and the compound re-
ported in ref. [7] are the same one. CCDC NO. 60797 for 2
Structure description of 1
In the crystal structure of 1, which is isostructural with
[Co(C10H4O8)(C12H8N2)(H2O)] [10], as shown in Figure 1,
the ZnII atom displaying distorted octahedral coordination
Z. Anorg. Allg. Chem. 2007, 490Ϫ494
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491

X.-Y. Yu, J. Lu, J.-H. Yu, X. Zhang, J.-Q. Xu, T.-G. Wang
Table 2 Hydrogen bonds of complex 1
˚
˚
˚
D-H···A···
d(D-H)/ A
d(H..A)/ A
d(D..A)/ A
ЄDHA/°
O6-H10···O4A
O8-H12···O1B
OW1-H13···O4
OW1-H14···O5 C
C20-H11···O8
C13-H9···O6
0.907
1.056
0.915
0.845
0.899
0.881
0.909
1.710
1.457
1.802
1.976
2.464
2.362
2.766
2.593
2.484
2.667
2.721
2.756
2.693
3.112
163.58
162.30
156.71
146.37
99.31
102.45
103.87
C5-H5···O5 D
Symmetry code: (A) xϪ1, yϩ1, z; (B) xϩ1, y, z; (C) 1Ϫx, 1Ϫy, 1Ϫz; (D)
Ϫxϩ1, Ϫyϩ1, Ϫzϩ1.
Table 3 Sum of bond-valences of oxygen atoms in compound 1 a)
(b)
(b)
Oi
Vi
O1
O2
O3
O4
O5
O6
1.24
O7
O8
1.32
1.77
1.77
2.00
1.64
1.63
1.64
Fig. 2 View of the 2D layer structure of 1.
a) The valences of hydrogen bonds have been included in sum of bond-valen-
ces of oxygen atoms in the table; b) The valences of O-H bond do not have
been included.
is coordinated by two nitrogen atoms N1, N2 from phen
ligand, one water molecule Ow1, two oxygen atoms O2, O3
from two µ4-H2bta2Ϫ groups and one oxygen atom O1 from
µ2-H2bta2Ϫ group. H2bta2Ϫ ligands exhibit two kinds of co-
ordination modes in compound 1, µ4-H2bta2Ϫ and µ2-
H2bta2Ϫ. In µ4-H2bta2Ϫ bridging ligand the two carboxyl
groups in para positions, O3B-C22-O8-H12 and O3A-
C22A-O8A-H12A, are undeprotonated and this has been
proved by sum of bond-valence being 1.32 for O8 [13]
(Table 3). The other two carboxyl groups in µ4-H2bta2Ϫ are
deprotonated and it has been justified by bond-valence sum
being 1.77 and 1.64 for O2 and O4, respectively. It has been
similarly justified that in µ2-H2bta2Ϫ ligand there are also
two carboxyl groups, O7-C17-O6-H10 and O7A-C17A-
O6A-H10A, being undeprotonated and the other two car-
boxyl groups being deprotonated. The located positions of
hydrogen for undeprotonated carboxyl groups through sum
of bond-valence of relevant oxygen atoms are in agreement
with those found from difference Fourier map.
Fig. 3 View of the hydrogen bonded network structure along the
a-axis (phen ligands are omitted for clarity).
H2bta2Ϫ as hydrogen acceptor bonds to O8 of undepro-
tonated carboxyl group from µ4-H2bta2Ϫ. The 2D layer
structure becomes more stable because of the effect of the
intralayer hydrogen bonding (Fig. 2). There are also inter-
layer hydrogen bonds which link 2D layers into 3D supra-
molecular structure in which channels with different size
exist (Fig. 3). O5C of coordinated carboxyl group of µ2-
H2bta2Ϫ as hydrogen acceptor bonds to water molecule
Ow1; O6 of uncoordinated carboxyl group of µ2-H2bta2Ϫ
as hydrogen donor bonds to O4A from µ4-H2bta2Ϫ. In
addition, there exist also C-H···O hydrogen bonds in the
supramolecular net work of compound 1.
As shown in Figure 2, ZnII atoms are connected into 1D
ribbons along a axis by µ4-H2bta2Ϫ ligands through four
monodentate-coordinated carboxyl groups, and two depro-
tonated carboxyl groups in para position of µ2-H2bta2Ϫ
adopt monodentate-coordinated mode to bridge the 1D
ribbons into 2D layer in [111] plane. In the layer there exist
˚
˚
14-membered A ring ca. (5.872(3) A ϫ 4.779(3) A) and 34-
˚
˚
membered B ring ca. (13.813(7) A ϫ 7.156(4) A), in which
coordinated phen are filled. There are π-π interactions be-
tween phen and µ2-H2bta2Ϫ which made the architecture
more stable.
The adjacent 2D layers are connected through hydrogen
bonding (Table 2) to form a 3D supramolecular network.
Within the layer, the coordinated water molecule Ow1 as
hydrogen donor bonds to O4 of µ4-H2bta2Ϫ as hydrogen
acceptor, and O1B of coordinated carboxyl group of µ2-
Fluorescence properties
Solid-state fluorescence spectra of 1 and 2 at room tempera-
ture are depicted in Figure 4. The main peaks of 1 and 2
locate at the nearly same positions: 388(shoulder), 422(423),
492
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Z. Anorg. Allg. Chem. 2007, 490Ϫ494

A Zinc Coordination Polymer
1,2,4,5-tetracarboxylate as bridging ligands were hydrother-
mally synthesized in which compound 1 has a covalent layer
structure and compound 2 has a covalent chain structure
although the structure of compound 2 has been reported
already [7]. Both compounds exhibit good thermal stability
and intense blue photoluminescence in the solid state.
CCDC 607896 (1) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
at www.ccdc.cam.ac.uk/conta/retrieving.html or form the Cam-
bridge Crystallographic Data Center, 12, Union Rood Cambridge.
CB2 1EZ, UK; fax: (internat.) ϩ44-1223/336033; E-mail:
deposit@ccdc.cam.ac.uk
Acknowledgement. This work was financially supported by the
National Natural Science Foundation of China (No. 20571032 and
No. 20333070).
Fig. 4 Solid-state fluorescence emission spectrum of 1 (a) and
2 (b) at room temperature.
460 and 486 nm upon excitation at 270 nm. According to
the previously reported observation, intense fluorescence
emission band with an emission maximum at 422 (423) nm
may be assigned to the emission of ligand-to-metal charge
transfer (LMCT) [6b]. The emission at 388 nm may be as-
cribed to intraligands charge transfer of coordinated phen
because of its similarity to the emission of free phen·H2O
[11]. The emission bands at 460 and 486 nm are neither
LMCT nor metal-to-ligand charge transfer (MLCT) in nat-
ure, but rather are assigned to intraligand emission, as re-
ported for other zinc(II) complexes with N-donor ligands
[12]. These research results reveal that compounds 1 and 2
may be potential intense blue light emitting materials due
to their good thermal stability and non-solubility in water
and common organic solvents.
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