The structure and fluorescence properties of two novel mixed-ligand supramolecular frameworks with different structural motifs

Article abstract of DOI:10.1002/1099-0682(200210)2002:10<2730::AID-EJIC2730>3.0.CO;2-G

Two novel coordination polymers formed by cobalt nitrate and 1,2-bis(4-pyridyl)ethane with the homologous ligands 2-aminoterephthalic acid and terephthalic acid, respectively, have been prepared. One displays a fivefold diamond-type feature while the other exhibits a twofold interpenetrating structural motif. The thermal and photoluminescence properties associated with their structures have been characterized and studied. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.

Full text of DOI:10.1002/1099-0682(200210)2002:10<2730::AID-EJIC2730>3.0.CO;2-G

FULL PAPER
The Structure and Fluorescence Properties of Two Novel Mixed-Ligand
Supramolecular Frameworks with Different Structural Motifs
Zhi-Yong Fu,[a,b] Xin-Tao Wu,*[a] Jing-Cao Dai,[a] Sheng-Min Hu,[a] Wen-Xin Du,[a]
Han-Hui Zhang,[c] and Rui-Qing Sun[c]
Keywords: Crystal engineering / Cobalt / Fluorescence / Supramolecular chemistry
Two novel coordination polymers formed by cobalt nitrate
and 1,2-bis(4-pyridyl)ethane with the homologous ligands 2-
structural motif. The thermal and photoluminescence proper-
ties associated with their structures have been characterized
aminoterephthalic acid and terephthalic acid, respectively, and studied.
have been prepared. One displays a fivefold diamond-type
feature while the other exhibits a twofold interpenetrating
( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
2002)
Introduction
O,OЈ-donor ligands adopt different coordination modes
forming different kinds of building blocks, which finally ag-
gregate to generate different supramolecular architectures,
due to the influence of the substituent groups. These differ-
ent structures show similar fluorescence spectra: they both
display strong fluorescence emission at 400 nm.
The construction of functional metal-organic frame-
works is of great interest due to their intriguing network
topologies and their potential applications as micropor-
ous,[1] magnetic,[2] nonlinear optical[3] and fluorescent mat-
erials.[4] Molecular self-assembly has been proven as an ef-
fective way of constructing various fascinating supramolec-
ular frameworks. The basic building blocks recognize each
other in a reaction system and aggregate to form the bulk
structure.[5] Lots of supramolecular frameworks have al-
ready been produced in the past decade based upon the
principle of crystal engineering.[6] However, the mechanism
of molecular self-assembly is unclear and the result of self-
assembly is unpredictable, therefore an understanding of
the factors that govern the assembly process is necessary for
technological development. Recently, considerable attention
has been focused on the influence of the factors involved in
molecular self-assembly processes, such as the solvent sys-
tem,[7] template,[8] counterion,[9] and the conformational
freedom of the ligands.[10] We are particularly interested in
self-assembly and the functionalities associated with differ-
ent coordination conformations. Here, we report two novel
mixed organic ligand supramolecular compounds [Co{1,2-
Results and Discussion
2-Aminoterephthalic acid and terephthalic acid were
chosen as starting materials as one has a substituted amino
group while the other has none. These two organic acids
react with 1,2-bis(4-pyridyl)ethane and cobalt nitrate in a
1:1:1 ratio under the same conditions. The O-donors accept
different coordination modes (Scheme 1), which finally re-
sults in different coordination frameworks.
bis(4-pyridyl}ethane)(2-aminoterephthalate)]
[Co{1,2-bis(4-pyridyl)ethane}(terephthalate)]
(1)
(2).
and
The
[a]
State Key Laboratory of Structural Chemistry, Fujian Institute
of Research on the Structure of Matter, Chinese Academy of
Sciences,
Fuzhou, Fujian350002, China
Fax: (internat.) ϩ86-591/371-4946
E-mail: wxt@ms.fjirsm.ac.cn
[b]
[c]
Graduate School of the Chinese Academy of Sciences
Fuzhou, Fujian350002, China
Scheme 1. The coordination modes of the carboxylate group: a)
unidentate and chelating bis-bidentate; b) bidentate; c) chelating bi-
dentate
Department of Chemistry, Fuzhou University
Fuzhou, Fujian 350002, China
2730
 WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1434Ϫ1948/02/1010Ϫ2730 $ 20.00ϩ.50/0 Eur. J. Inorg. Chem. 2002, 2730Ϫ2735

Mixed-Ligand Supramolecular Frameworks with Different Structural Motifs
FULL PAPER
Crystal Structures
molecules were found in the cage of the adamantane unit
and distortions of the unit can arise from the application
of different ligands. Four 2-aminoterephthalate ligands and
two 1,2-bis(4-pyridyl)ethane ligands bridge six Co atoms to
form a hexagonal circuit. The distance between the Co cen-
ters is determined by the length of 2-aminoterephthalate
An ORTEP view of a Co center of compound 1 is shown
in Figure 1. The Co atom has a distorted tetrahedral coor-
dination geometry, being coordinated by two N atoms of
two 1,2-bis(4-pyridyl)ethane molecules [Co1ϪN2b
ϭ
˚
˚
2.101(11) A, Co1ϪN3 ϭ 2.063(11) A], two O atoms from
one chelating bis-bidentate carboxylate group [Co1ϪO1a ϭ
˚
˚
(10.729 A) or 1,2-bis(4-pyridyl)ethane (13.349 A). Figure 3
shows that five independent equivalent networks are inter-
penetrated within the structure (fivefold diamondoid
mode). The nodes of four other nets are arranged between
the top-most and bottom-most extremities of an adam-
antane unit of the first net. Although many diamond-re-
lated nets displaying various interpenetration modes ran-
ging from two- to ninefold have been reported,[13] the five-
fold interpenetration of 1 is novel in the presence of the
mixed organic ligands with different lengths. To the best of
our knowledge, with coordination polymers only two other
examples of a fivefold diamond-type net have been previ-
ously observed. They are [Cu(L2)](BF4) (L ϭ 1,4-dicyano-
benzene) and [Cu(bpe)2](BF4) generated by the reaction of
CuBF4 with 1,4-dicyanobenzene and bpe, respectively.[14]
˚
˚
2.050(10) A, Co(1)ϪO2a ϭ 2.224(10) A], and one O atom
of one unidentate carboxylate group [Co1ϪO3 ϭ 2.024(9)
˚
A], which provide the four connecting nodes resulting in an
unsymmetrical adamantane-type unit (Figure 2). No guest
Figure 1. ORTEP drawing of 1 around the Co center (ellipsoids at
30% probability); the hydrogen atoms are omitted for clarity; the
N1 and N11 atoms of compound 1 were located from the E-map
directly, and the displacement parameters of them were of 0.5 to
0.5 statistically; symmetry codes: a ϭ Ϫx, 1 ϩ y, z Ϫ 1/4; b ϭ x, 2
Ϫ y, z ϩ 1/4
Figure 3. The interpenetration model for complex 1
For the preparation of compound 2, the terephthalate li-
gand was used instead of 2-aminoterephthalate ligand. The
Co center has a distorted octahedral coordination geo-
metry, with two oxygen donors of one chelating bis-bident-
˚
ate carboxylate group [Co1ϪO1 ϭ 2.200(3) A, Co1ϪO2 ϭ
˚
2.192(3) A] and two oxygen donors of two bridging bident-
ate carboxylate groups in the horizontal direction
˚
˚
(Co1ϪO3 ϭ 2.017 A, Co1ϪO4a ϭ 2.028 A). The coordina-
tion sphere is completed by two nitrogen donors of 1,2-
bis(4-pyridyl)ethane [Co1ϪN1 ϭ 2.163(3) A, Co1ϪN2b ϭ
Figure 2. View of the adamantane units of 2; the large black balls
represent the Co atoms
˚
Eur. J. Inorg. Chem. 2002, 2730Ϫ2735
2731

Z.-Y. Fu, X.-T. Wu, J.-C. Dai, S.-M. Hu, W.-X. Du, H.-H. Zhang, R.-Q. Sun
FULL PAPER
box. The aggregation of the building blocks results in a 3-
D framework, and the 3-D networks interlock with each
other displaying a twofold-interpenetrating mode. As
shown in Figure 6, in the axial direction every two rods (rod
a and b) in the cuboidal block are associated with one par-
ticular quadrate ring (ring 1) of the other framework
through which they pass, while in the horizontal direction
one rod (rod c) is associated with two particular quadrate
rings (ring 2 and 3) of the other framework through which
it penetrates.
Figure 4. View of the dimetal unit of 2; hydrogen atoms have been
omitted, and the ellipsoids at 30% probability represent C, N O,
and Co; symmetry codes: a ϭ Ϫx, Ϫy, Ϫz; b ϭ x, y ϩ 1, z Ϫ 1;
c ϭ 1 Ϫ x, Ϫ1 Ϫ y, Ϫ1 Ϫ z; d ϭ 1 Ϫ x, Ϫy, Ϫz; e ϭ Ϫ1 ϩ x, y,
z; f ϭ Ϫ1 ϩ x, 1 ϩ y, 1 ϩ z; g ϭ Ϫx, Ϫ1 Ϫ y, 1 Ϫ z
Figure 6. The interpenetration model for complex 2
˚
2.152(3) A] in the axial direction (Figure 4). The coordina-
Under the same reaction conditions, compounds 1 and 2
exhibit different structural motifs. The coordination mode
of the carboxylate group is an essential factor in affecting
the bulk structures of 1 and 2. One of the characteristics of
these reactions is that the substituent groups in the homo-
logous O,OЈ-donor ligands are slightly different, which af-
fects the pH values in the reaction systems (obsd. 6.22 in 1
and 5.13 in 2). These different basicities, which most prob-
ably make the carboxylate groups in 1 and 2 accept different
coordination modes, lead to different supramolecular archi-
tectures.
tion mode in compound 2 generates a novel cuboidal build-
ing block (Figure 5). Each corner of the cuboidal block is
occupied by a binuclear subunit and the Co···Co separation
˚
in the binuclear subunit is 4.27 A. Eight terephthalate li-
gands form the length and width of the cuboidal block
while eight 1,2-bis(4-pyridyl)ethane ligands make up the
height of it. No guest molecule is included in the cuboidal
IR Spectroscopy
The IR spectrum of compound 1 shows the characteristic
bands of the dicarboxylate groups of the 2-aminotereph-
thalate ligands at 1618Ϫ1549 cmϪ1 for the asymmetric vi-
bration and at 1421Ϫ1396 cmϪ1 for the symmetric vibra-
tion. While the IR spectrum of compound 2 shows the
characteristic bands of the dicarboxylate groups of the
terephthalate ligands at 1610Ϫ1552 cmϪ1 for the asymmet-
ric vibration and at 1410Ϫ1394 cmϪ1 for the symmetric vi-
bration. The splitting of νasym(CO2) in compound 1 and
compound 2 confirms that the carboxylate groups have two
different coordination modes,[15] in agreement with their
crystal structures. The absence of the expected character-
istic bands at 1730Ϫ1690 cmϪ1 for the protonated carb-
oxylate groups indicates the complete deprotonation of 2-
aminoterephthalic acid and terephthalic acid in the reaction
with Co ions.[16]
Figure 5. Structure of the cuboidal block of 2, showing eight Co2
units linked by eight terephthalate anions and eight 1,2-bis(4-pyrid-
yl)ethane units
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Eur. J. Inorg. Chem. 2002, 2730Ϫ2735

Mixed-Ligand Supramolecular Frameworks with Different Structural Motifs
FULL PAPER
Thermal and Fluorescent Properties
Compounds 1 and 2 were heated to 600 °C under N2.
Their thermal decomposition behavior (Figure 7) is very
similar. No obvious decomposition was observed in until ca
430 °C. The TGA data show that 1 has an obvious weight
loss starting at about 435 °C ( 437 °C for 2).
Figure 8. Solid-state emission spectra of the coordination polymers
at room temperature: a) compound 1; b) compound 2
atom has a distorted octahedral coordination geometry.
However, despite this distinct disparity, the ligands coordin-
ated around the metal ions in 1 and 2 are similar (Figure 1
and Figure 4). The Co center in 1 has one chelating bis-
bidentate carboxylate group, one unidentate carboxylate
group, and two 1,2-bis(4-pyridyl)ethane ligands while in 2
there are one chelating bis-bidentate carboxylate group, two
bridging bidentate carboxylate groups, and two 1,2-bis(4-
pyridyl)ethane ligands. These similar environments may be
the reason, for the similar thermal and photoluminescence
behaviors (Figure 7 and 8).
Figure 7. The TGA-DTA diagram for the coordination polymers:
a) compound 1; b) compound 2
The emission spectra of compounds 1 and 2 in the solid
state at room temperature are shown in Figure 8. It can be
seen that 1 exhibits an intense photoluminescence emission
at 400 nm (Figure 8a, λex ϭ 300 nm) while 2 also exhibits
an intense photoluminescence emission at 400 nm (Fig-
ure 8b, λex ϭ 310 nm). These emissions may be assigned as
ligand-to-metal charge transfer (LMCT).[17] Due to their
high thermal stability, 1 and 2 may be good candidates for
emitting diode devices.
It is very interesting to note that 1 and 2 exhibit similar
thermal behaviors and photoluminescence spectra despite Conclusion
having different structural motifs. What is the reason for
these phenomena? Due to the fact that thermal behaviors
Two novel coordination polymers formed by cobalt ni-
and photoluminescence behavior are closely associated with trate and 1,2-bis(4-pyridyl)ethane with the homologous li-
the metal ions and the ligands coordinated around them, gands 2-aminoterephthalic acid and terephthalic acid have
we decided to look again at the coordination environments been prepared and characterized. Compound 1 displays a
of the metal ions in 1 and 2. In 1 the Co atom has a dis- fivefold diamond-type net while compound 2 exhibits a
torted tetrahedral coordination geometry while in 2 the Co twofold-interpenetrating structural motif. The two com-
Eur. J. Inorg. Chem. 2002, 2730Ϫ2735
2733

Z.-Y. Fu, X.-T. Wu, J.-C. Dai, S.-M. Hu, W.-X. Du, H.-H. Zhang, R.-Q. Sun
FULL PAPER
Synthesis of [Co{1,2-bis(4-pyridyl)ethane}(terephthalate)] (2): An
aqueous mixture (10 cm3) containing Co(NO3)2·6H2O (0.292 g,
1 mmol), 1,2-bis(4-pyridyl)ethane (0.184 g, 1 mmol), terephthalic
acid (0.166 g, 1 mmol) and NaOMe (0.108 g, 2 mmol) was placed
in a Parr Teflon-lined stainless steel bomb (25 cm3). The bomb was
heated at 5 °C·minϪ1 to 160 °C; after 24 h at 160 °C it was cooled
to 90 °C at the rate of 0.1 °C·minϪ1, then maintained at that tem-
perature for 12 h. Finally, it was cooled at 0.1 °C·minϪ1 to 20 °C.
The bomb was opened to give red block crystals in 75% yield.
C20H16CoN2O4 (407.3): calcd. C 58.98, H 3.96, N 6.88; found C
58.87, H 3.92, N 6.89. IR (KBr): ν˜ ϭ 3057w, 2933w, 1610s, 1568s,
1552s, 1510m, 1500m, 1427m, 1410s, 1394s, 1306w, 1221w, 1018m,
841s, 818m, 748s, 550s, 523m cm1.
pounds have similar thermal behaviors and photolumines-
cence spectra. In this paper, we have shown that the amino
group in 2-aminoterephthalic acid plays an important role
in affecting the coordination mode of the carboxylate
group, causing 1 to have a structural motif that is clearly
different from that of 2. Their thermal and photolumines-
cence properties are closely associated with the coordina-
tion environments around the metal centers.
Experimental Section
General Remarks: All reactions were carried out in hydrothermal
conditions. All chemicals are commercially available and used as
received without further purification. The C, H and N microana-
lyses were carried out with a Vario EL III elemental analyzer.
Infrared spectra (KBr pellets) were recorded in the range from
4000Ϫ400 cmϪ1 on a Nicolet Magna 750 FT-IR spectrometer.
Thermogravimetric analyses (TGA) were performed under nitrogen
with a heating rate of 10 °C·minϪ1 using a TA5200/MDSC2910
system. Fluorescent spectra were measured with an Edinburgh FL-
FS90 TCSPC system at the Spectroscopy Lab of Fuzhou Univer-
sity.
X-ray Crystallographic Study: Crystallographic data for compound
1 and compound 2 are listed in Table 1. For compound 1, a red
block crystal with dimensions of 0.40 ϫ 0.14 ϫ 0.14 mm was used.
For compound 2, a red block crystal with dimensions of 0.30 ϫ
0.22 ϫ 0.12 mm was used. Data for 1 and 2 were collected at room
temperature on a Siemens SMART-CCD area-detector diffracto-
˚
meter with Mo-Kα radiation (λ ϭ 0.71073 A) and a graphite mon-
ochromator using the ω-scan mode. Data reductions and absorp-
tion corrections were performed with SMART and SADABS soft-
ware, respectively. For all structural analyses, all calculations were
performed on an indy workstation from Silicon Graphics with the
program SHELXTL.[11] The structures were solved by direct
methods. The refinement of structures was performed by full-mat-
rix least-squares techniques on F2 using SHELXL-97.[12] All non-
hydrogen atoms were treated anisotropically. The nitrogen atoms
of 2-aminoterephthalate exhibit disorder. They were located from
Synthesis of [Co{1,2-bis(4-pyridyl)ethane}(2-aminoterephthalate)]
(1): An aqueous mixture (10 cm3) containing Co(NO3)2·6H2O
(0.292 g, 1 mmol), 1,2-bis(4-pyridyl)ethane (0.184 g, 1 mmol), 2-
aminoterephthalic acid (0.181 g, 1 mmol) and NaOMe (0.108 g,
2 mmol) was placed in a Parr Teflon-lined stainless steel bomb (25
cm3). The bomb was heated at 5 °C·minϪ1 to 160 °C; after 24 h at
160 °C it was cooled to 90 °C at the rate of 0.1 °C·minϪ1, then
maintained at that temperature for 12 h. Finally, it was cooled at
0.1 °C·minϪ1 to 20 °C. The bomb was opened to give red block
crystals in 62% yield. C20H17CoN3O4 (422.3): calcd. C 56.86, H
4.06, N 9.95; found C 56.96, H 4.01, N 9.97. IR (KBr): ν˜ ϭ 3442m,
3338m, 3055w, 2945w, 1618s, 1564s, 1549s, 1498m, 1446m, 1421s,
1396s, 1375m, 1333w, 1261s, 1072w, 1028s, 847s, 816m, 768s, 702w,
536w, 517w cm1.
˚
Table 2. Selected bond lengths (A) and bond angles (deg) for 1
and 2
[Co{1,2-bis(4-pyridyl)ethane}(2-aminoterephthalate)] (1)[a]
Co(1)ϪO(3)
Co(1)ϪO(1a)
Co(1)ϪN(3)
Co(1)ϪN(2b)
Co(1)ϪO(2a)
2.024(9) N(2)ϪCo(1c)
2.050(10) O(2)ϪCo(1d)
2.063(11) O(1)ϪCo(1d)
2.101(11) Co(1)ϪO(4)
2.224(10)
2.101(11)
2.224(10)
2.050(10)
2.347(9)
O(3)ϪCo(1)ϪO(1a) 147.2(4) N(3)ϪCo(1)ϪO(2a) 157.9(4)
O(3)ϪCo(1)ϪN(3) 106.5(4) N(2b)ϪCo(1)ϪO(2a) 88.6(4)
Table 1. Crystal data and refinement details for the structures of 1
and 2
O(1a)ϪCo(1)ϪN(3) 97.7(4)
O(3)ϪCo(1)ϪN(2b) 96.9(4)
O(1a)ϪCo(1)ϪN(2b) 101.2(4) N(3)ϪCo(1)ϪO(4)
O(3)ϪCo(1)ϪO(4)
O(1a)ϪCo(1)ϪO(4) 99.2(4)
89.6(4)
60.0(4)
Complex
1
2
N(3)ϪCo(1)ϪN(2b) 98.5(5)
O(3)ϪCo(1)ϪO(2a) 93.4(4)
O(1a)ϪCo(1)ϪO(2a) 60.3(4)
N(2b)ϪCo(1)ϪO(4) 156.9(4)
O(2a)ϪCo(1)ϪO(4) 92.1(4)
Empirical formula
Space group
C20H17CoN3O4 C20H16CoN2O4
¯
P41
P1
˚
a, A
9.1737(4)
9.1737(4)
24.6489(16)
90°
90°
90°
2074.37(19)
4
10.0719(3)
10.23420(10)
10.8551(3)
80.34°
66.6430(10)°
75.474(2)°
991.45(4)
2
[Co{1,2-bis(4-pyridyl)ethane}(terephthalate)] (2)[b]
˚
b, A
˚
c, A
α
β
γ
Co(1)ϪO(3)
Co(1)ϪO(4a)
Co(1)ϪN(2b)
Co(1)ϪN(1)
O(3)ϪCo(1)ϪO(4a) 110.08(11) N(1)ϪCo(1)ϪO(2)
O(3)ϪCo(1)ϪN(2b) 88.43(12) O(3)ϪCo(1)ϪO(1)
2.017(3) Co(1)ϪO(2)
2.028(3) Co(1)ϪO(1)
2.152(3) O(4)ϪCo(1a)
2.192(3)
2.200(3)
2.028(3)
3
˚
V, A
2.163(3) N(2b)ϪCo(1)ϪO(2) 90.90(11)
Z
85.36(11)
155.72(11)
µ(Mo-Kα), mmϪ1
0.856
1.352
5098
0.891
1.364
5139
3450
dcalcd, g/cm3
O(4a)ϪCo(1)ϪN(2b) 89.31(11) O(4a)ϪCo(1)ϪO(1) 93.97(11)
O(3)ϪCo(1)ϪN(1) 92.04(12) N(2b)ϪCo(1)ϪO(1) 88.58(12)
Measured reflections
Independent reflections
Observed reflections
[I Ͼ 2σ(I)]
2051
O(4a)ϪCo(1)ϪN(1) 94.00(11) N(1)ϪCo(1)ϪO(1)
N(2b)ϪCo(1)ϪN(1) 176.26(12) O(2)ϪCo(1)ϪO(1)
89.47(12)
60.01(10)
1247
2612
O(3)ϪCo(1)ϪO(2)
95.95(10) O(4a)ϪCo(1)ϪO(2) 153.96(11)
R
wR
0.0790
0.1465
0.0502
0.1145
0.000/0.000
[a]
Symmetry codes: (a) Ϫx, y ϩ 1, z Ϫ 1/4, (b) x, 2 Ϫ y, z ϩ 1/4;
[b]
Max/mean shift in final cycle 0.000/0.000
(c) Ϫx ϩ 2, y, z Ϫ 1/4; (d) x Ϫ 1, Ϫy, z ϩ 1/4. Symmetry codes:
(a) Ϫx, Ϫy, Ϫz; (b) x, y ϩ 1, z Ϫ 1
2734
Eur. J. Inorg. Chem. 2002, 2730Ϫ2735

Mixed-Ligand Supramolecular Frameworks with Different Structural Motifs
FULL PAPER
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CCDC-181331 (1) and -181332 (2) contain the supplementary crys-
tallographic data for this paper. These data can be obtained free
of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
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Acknowledgments
This work is supported by grants from the State Key Laboratory
of Structural Chemistry, Fujian Institute of Research on the Struc-
ture of Matter, Chinese Academy of Sciences (CAS), the Ministry
of Science and Technology of China (001CB1089), the National
Science Foundation (29733090, 29890210, 29873053) of China and
the Science Foundation of the Chinese Academy of Sciences
G. M. Sheldrick, SHELXL-97, Program for X-ray Crystal
Structure Refinement; University of Göttingen: Göttingen,
Germany, 1997.
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