The construction of coordination networks based on imidazole-based dicarboxylate ligand containing hydroxymethyl group

Article abstract of DOI:10.1039/c0ce00369g

Reaction of Cd(ii), Fe(ii), and Cu(ii) with a new ligand 2-(hydroxymethyl)-1H-imidazole-4,5-dicarboxylic acid (H₄hmIDC) and 4,4′-bipyridine (bpy) affords three coordination polymers of {[Cd(H ₂hmIDC)(bpy)]·0.5bpy·H₂O}_n (1), [Fe₂(HhmIDC)₂]_n (2), and {[Cu ₂(ITC)(bpy)(H₂O)₃]·2.5H ₂O}_n (3) (ITC = imidazole-2,4,5-tricarboxylic acid), respectively. Complex 1 and complex 3 are (4,4) nets in topological view and display in different packing mode, while hydroxymethyl group in complex 3 is oxidized to carboxylic group in situ. Complex 2 is a rare example of a cdl-e network containing both tetrahedral and square nodes. The hydroxymethyl groups act as a precursor and undergo different reactions directed by metal ions.

Full text of DOI:10.1039/c0ce00369g

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PAPER
www.rsc.org/crystengcomm | CrystEngComm
The construction of coordination networks based on imidazole-based
dicarboxylate ligand containing hydroxymethyl group†
a
a
b
a
a
Sheng-Run Zheng, Song-Liang Cai, Mei Pan, Jun Fan, Tian-Tian Xiao and Wei-Guang Zhang
a
*
Received 4th July 2010, Accepted 20th August 2010
DOI: 10.1039/c0ce00369g
Reaction of Cd(II), Fe(II), and Cu(II) with a new ligand 2-(hydroxymethyl)-1H-imidazole-4,5-
dicarboxylic acid (H4hmIDC) and 4,40-bipyridine (bpy) affords three coordination polymers of
{[Cd(H2hmIDC)(bpy)]$0.5bpy$H2O}n (1), [Fe2(HhmIDC)2]n (2), and
{[Cu2(ITC)(bpy)(H2O)3]$2.5H2O}n (3) (ITC ¼ imidazole-2,4,5-tricarboxylic acid), respectively.
Complex 1 and complex 3 are (4,4) nets in topological view and display in different packing mode, while
hydroxymethyl group in complex 3 is oxidized to carboxylic group in situ. Complex 2 is a rare example
of a cdl-e network containing both tetrahedral and square nodes. The hydroxymethyl groups act as
a precursor and undergo different reactions directed by metal ions.
choice of organic ligands and metal ions, we can achieve a metal–
organic system directed by the synergistic metal and ligand
effects at both two levels. However, studies on this type of ligand
are still less explored.
Introduction
The design and synthesis of coordination polymers has devel-
oped rapidly due to their intriguing architectures and topologies,
as well as their potential applications in molecular selection, ion
exchange, adsorption, fluorescence, catalysis, phosphorescence,
magnetic properties etc.1–3 A lot of factors, such as coordination
environment of the metal centres, the choice of ligands, anions
etc. can affect the self-assemble process. Especially, the structures
of the ligands, the coordination fashions of the metal ions and,
even more importantly, the synergistic metal and ligand effects
play a key role in the manipulation of the final structures of their
complexes.4,5 In general, the choice of metal ions affects the
organic ligand in two ways: (i) to regulate the coordination mode
of the ligands according to their different coordinate geometry
and coordinate ability to different donor groups; for example,
2-substitued benzimidazol group is easy to coordinate to Ag(I)
ion but usually remains uncoordinated when using metals with
octahedral geometry such as Cd(II), Mn(II) ions etc.5l During
these reactions, all the covalent bonds in the ligand are not
changed, the difference by introducing different metal ions is just
to affect the supramolecular interactions (coordination bonds,
hydrogen bonds and so on) around the ligand. Thus, we can say
that the metal ions affect the organic ligand at supramolecular
level. (ii) to induce in situ synthesis of new ligands from the
original ligand.6,7 At this time, covalent bonds in the original
ligands are broken off or reformed during the reactions, leading
to a new ligand, thus we can say that the metal ions induce the
ligand change at a molecular level. Therefore, by the careful
Imidazole-4,5-dicarboxylic acid (H3IDC), a planar rigid ligand
containing two nitrogen and four oxygen atoms, has attracted
much interest in coordination chemistry and has proven to be an
excellent building block for forming a series of MOFs with
different structures and useful properties.8,9 Accordingly, similar
ligands, which differ only in groups on the 2-position of the
imidazole ring such as 2-ethyl-1H-imidazole-4,5-dicarboxylic
acid, 2-propyl-1H-imidazole-4,5-dicarboxylic acid10 and 2-pyr-
idinyl-1H-imidazole-4,5-dicarboxylic acid11 have been designed
and studied extensively. However, the introduction of a hydro-
philic group on this site has not been explored.
Inspired by the above consideration, herein we introduce
a hydrophilic hydroxymethyl group on the 2-positon of imida-
zole-4,5-dicarboxylic acid and a new ligand 2-(hydroxymethyl)-
1H-imidazole-4,5-dicarboxylic acid (H4hmIDC) was obtained.
This group is flexible where it can either change its coordination
mode or undergo in situ ligand formation by using different
metal ions.
Results and discussion
Reaction behaviour of H4hmIDC directed by metal ions
Hydrothermal reaction of Cd(CH3COO)2$2H2O, FeSO4$7H2O
and CuSO4$5H2O with H4hmIDC gives complexes 1–3. As
shown in Scheme 1, the ligand undergoes different reaction
depending on the metal ions. When using Cd(II) ion, the
hydroxymethyl group remains uncoordinated and the ligand just
acts as imidazole-4,5-dicarboxylic acid. While using Fe(II) ion,
which is usually easy to be converted to high oxygen affinitive
Fe(III) ion, the hydroxymethyl group become coordinative and
the coordination mode is greatly changed compared to complex
1. The reason may comes from the fact that deprotonation of
hydroxymethyl group will lead to the enhancement of coordi-
nation ability of the oxygen atom, while the Fe(III) ions can
facilitate the deprotonation process, thus leading to the
aSchool of Chemistry and Environment, South China Normal University,
Guangzhou, 510006, P. R. China. E-mail: wgzhang@scnu.edu.cn; Fax:
+86-20-39310187
bMOE Laboratory of Bioinorganic and Synthetic Chemistry, State Key
Laboratory of Optoelectronic Materials and Technologies, School of
Chemistry and Chemical Engineering, Sun Yat-Sen University,
Guangzhou, 510275, China
† Electronic supplementary information (ESI) available: Additional
structure figures, table of selected bond lengths and angles, XRPD and
crystallographic
782465–782467. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c0ce00369g
information.
CCDC
reference
numbers
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Crystal structure of 1
Single-crystal X-ray analysis has revealed that complex 1 crys-
tallizes in the orthorhombic space group Fdd2, as shown in Table
1. The Cd(II) ion has a distorted octahedral geometry, being
chelated by N and O atoms in the equatorial plane to form two
stable five-membered rings, as shown in Fig. 1a. The two axial
sites are occupied by bpy molecules. All the Cd(II)–O bonds
ꢀ
(from 2.355(3) A to 2.446(2) A) and Cd(II)–N bonds (from
ꢀ
ꢀ
ꢀ
2.266(3) A to 2.366(3) A) falls in normal range. The connections
of the Cd(II) atoms by H2hmIDC2ꢀ form the one dimensional
chain-like structure of 1 and the 1D chain is linked by bpy spacer
leading to 2D network (Fig. 2b), which can be considered as (4,4)
ꢀ
net, as shown in Fig. 2c. The grid in the (4,4) net is 11.7834(14) A
ꢀ
ꢁ 6.7908(8) A. The coordination mode of the ligand is similar to
H3IDC that have been reported.12 The hydroxymethyl group
Scheme 1 The reation of ligand H4hmIDC with different metal ions
retains uncoordinated and just form O–H/O hydrogen bonds
ꢀ
ꢀ
(O(5)–H(5A)/O(4), H/O 1.84 A, O/O 2.652(7) A, :OHO
172ꢂ, symmetry code: 1/4 ꢀ x, ꢀ1/4 + y, ꢀ1/4 + z) to carboxyl
group on the adjacent 2D layer. Thus the (4,4) nets are packing
formation of Fe(III)–O bonds. Moreover, in complex 3, the using
of Cu(II) ion induces the oxidation of hydroxymethyl group to
carboxyl group and a new ligand imidazole-2,4,5-tricarboxylic
acid (H4ITC) is formed in situ. Since carboxyl group is easier to
be deprotonated than hydroxymethyl group, thus the formation
of Cu(II)–O bond are facilitated. To the best of our
knowledge, the oxidation of 2-(hydroxymethyl)-1H-imidazole-
4,5-dicarboxylic acid (H4hmIDC) to imidazole-2,4,5-tricarboxy-
lic acid (H4ITC) under hydrothermal conditions has not been
documented so far. Therefore, this ligand can be considered as
a precursor which may display different reaction behaviours
and serve as multi-functional building blocks under different
conditions.
Table 1 Crystallographic data for complexes 1–3
Complex
1
2
3
Empirical
formula
C21H18CdN5O6 C12H6Fe2N4O10 C16H19Cu2N4O11.50
Mw/g molꢀ1
Crystal system Orthorhombic Monoclinic
548.80
477.91
578.43
Monoclinic
P21/n
Space group
ꢀ
Fdd2
C2/c
a/A
ꢀ
23.374(4)
27.595(4)
13.619(2)
90
8.444(5)
9.314(5)
18.782(11)
90
9.7125(16)
18.472(3)
11.850(2)
90
b/A
ꢀ
c/A
a/ꢂ
b/ꢂ
g/ꢂ
90
90
95.106(7)
90
94.310(2)
90
3
ꢀ
V/A
8784(2)
16
1.660
1.043
1.88–28.00
4400
308
298(2)
13 138
1471.2(15)
4
2.158
2120.0(6)
4
1.812
Z
Dc/g cmꢀ3
m/mmꢀ1
q Range/ꢂ
F(100)
2.046
2.077
2.18–26.00
952
129
298(2)
3894
2.05–27.00
1172
322
298(2)
12 324
Parameters
T/K
Reflections
collected
Rint
0.0310
4822
0.0349
1451
0.0278
4592
Unique
reflections
R1 [I > 2s(I)]
wR2 (all data)
0.0282
0.0697
0.0525
0.1730
0.0394
0.1262
Fig. 1 (a) The coordination environment of Cd(II) and H2hmimda2ꢀ in
1. (b) The 1D chain in 1. (c) The 2D (4,4) net in 1. (d) The packing mode
of 2D nets in 1.
Flack parameter 0.18(2)
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HhmIDC3ꢀ ligands to give the distorted octahedral geometry,
and Fe2 is six-coordinated by two nitrogen atom and two oxygen
atoms from two different chelated HhmIDC3ꢀ ligands in the
equatorial plane and two oxygen atoms of hydroxymethyl group
from two ligands to show a octahedral geometry. Every Fe(III)
ions link four ligand to form a 4-connected node, and the ligand
which coordinates to four Fe(III) centers (two Fe1 centers and
two Fe2 center) are further linked to constructed a three-
dimensional framework. In fact, all the Fe(III) ions in 2 are linked
by carboxyl group to form a 3D 412$63-pcu net14 if the imidazole
rings are neglected (ESI, Fig. S2).†
To better understand the structure of complex 2, the Fe(III)
sites and the connecting ligands can be regarded as topologically
4-connected nodes. As shown in Fig. 2b–d, the Fe1 has a dis-
torted tetrahedral geometry, while the Fe2 and HhmIDC3ꢀan-
ions have a distorted square planar geometry. Therefore, the
overall 3D network can be simplified to a trinodal 4-connected
(42$84)(43628)2(44$62) cdl-e topology (Fig. 2e). As we know, 4-
connected network have been intensively investigated. Normally,
the planar nodes prefer to assemble into a 2D (4,4) net rather
than the less common 3D NbO (6482-a), CdSO4 (658), and lvt
(4284) nets, while the tetrahedral node usually forms a 3D dia-
mond network, etc.15 The combination of planar and tetrahedral
nodes would give rise to complicated 3D 4-connected network,
such as pts (4284) net, (64$82)(63$83)2(65$8) net etc.16,17 However,
to the best of our knowledge, complex 2 is a rare example of
synthesized MOF with a cdl-e net, which containing equivalent
tetrahedral and square node.
From complex 1 to complex 2, the oxygen atom on hydroxy-
methyl group transfers from uncoordinated to coordinated,
corresponding to the transfer of its function from hydrogen
bonding to coordinating, which can be seen as an alteration at
supramolecular level. The magic of crystal engineering is largely
dependent on the diversity of supramolecular interactions, thus
this change leads to great difference in the final framework, as we
expected.
Fig. 2 (a) The coordination environment of Fe(III) in 2. Symmetry
codes: (i) ꢀx + 5/2, y + 1/2, ꢀz + 1/2; (ii) x ꢀ 1/2, y + 1/2, z; (iii) ꢀx + 2, y,
ꢀz + 1/2; (iv) ꢀx + 3/2, ꢀy + 1/2, ꢀz; (v) ꢀx + 2, ꢀy, ꢀz. (b) 4-Connected
Fe1 node in 2. (c) 4-Connected Fe2 node in 2. (d) 4-Connected Hhmimda-
in 2. (e) A schematic representation of trinodal 4-connected network of 2.
Crystal structure of 3
along b direction in abcdabcd mode (distance between two
ꢀ
adjacent layers is about 6.8987 A), as shown in fig. 2d. It is
It is interesting to note that in complex 3, oxidation occurred and
H4hmIDC was transformed into imidazole-2,4,5-tricarboxylic
acid (H4ITC) under hydrothermal conditions in the presence of
Cu(II) ions. The changes of hydroxymethyl groups related to the
formation of new C–O covalent bonds, therefore, it can be seen
as at molecular level. The oxidation from hydroxymethyl group
to carboxyl group is common in organic synthesis,18 but less used
to in situ formation of new ligand in construction of coordination
polymer. Due to the lack of enough Cu(I) species in the final
product, we suggest the oxidant is oxygen in air rather than
Cu(II) and the oxidation process may be catalyzed by Cu(II) ions.
However, the oxidation mechanism is still under investigation.
In the asymmetrical unit of complex 3, there are two inde-
pendent Cu(II) ions, one ITC4ꢀ ligand and one bpy ligand,
respectively (Fig. 3a). The two Cu(II) ions are five-coordinate and
described as a distorted tetragonal pyramid. The five coordinate
sites of Cu1 are occupied by one oxygen atom and one nitrogen
atom from one ligand, one nitrogen atom from one bpy ligand
and two water oxygen atoms. While the coordination environ-
ment of Cu2 is similar to Cu1, except that the water molecule in
interesting to note that the 2D networks are packing interlaced in
complex 1, which is less common compared to parallel packing.
Small channels are formed along a axis, which are occupied by
uncoordinated bpy molecules (ESI, Fig. S1).†
Crystal structure of 2
In order to utilize the oxygen atom on the hydroxymethyl group,
we choose Fe(II) ion instead of Cd(II) ion. The result shows that
the hydroxymethyl group binds to Fe(III) ion (from the oxidation
ꢀ
of Fe(II)) with bond distance of 2.240(5) A, which is slightly
longer than Fe(III)–O bonds formed between Fe(III) ion and
ꢀ
ꢀ
carboxyl group (from 2.072(4) A to 2.151(4) A), but still falls in
typical Fe–O bond.13 The multi-dentate coordination mode of
HhmIDC3ꢀ undoubtedly combines the Fe(III) ions into a 3D
network as revealed by single-crystal X-ray analysis. As shown in
Fig. 2a, there are two independent Fe(III) atoms: Fe1 is coordi-
nated by four oxygen atoms from two different chelated
HhmIDC3ꢀ ligands and two oxygen atoms from two different
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the crystal samples are pure. The difference in reflection intensity
between the simulated and experimental patterns is due to
a certain degree of preferred orientation of the powder samples
during data collection.
Compared with the emissions of the ligand, complex 1 show
much weaker emission intensity, indicative of a heavy-atom
quenching effect.
Conclusions
In conclusion, we have designed an imidazole-based dicarboxy-
late ligand containing a hydroxymethyl group-2-(hydroxy-
methyl)-1H-imidazole-4,5-dicarboxylic acid, which can display
quite flexible reaction behaviours under different hydrothermal
conditions. The hydroxymethyl group is neither be coordinated
nor oxidated when using Cd(II) ion, and becomes coordinated
when using more oxygen-affinitive Fe(III) ion, and further
changes into carboxyl group by reaction with Cu(II) ion. It is
interesting that the behaviour of the hydroxymethyl group is
largely dependent on the metal ions we used, which show a strong
synergistic effect between the metal ions and ligand, not only at
supramolecular level but also at molecular level. The results show
that the introduction of a suitable functional group on the ligand
may be an effective way to obtain diversified coordination
frameworks from the same simple ligand as a precursor.
Experimental
Materials and method
Fig. 3 (a) The coordination environment of Cu(II) and imtc3ꢀ in 3. (b)
The 2D (4,4) network in 3. (c) The packing mode of 2D net in 3.
The ligand 2-(hydroxymethyl)-1H-imidazole-4,5-dicarboxylic
acid (H4hmIDC) was prepared according to the literature.20 All
the other reagents were of analytical grade and used without any
further purification. Elemental analyses of C, H and N were
determined with a Thermo FlashEA112 elemental analyzer. IR
spectra were recorded by using Shimadzu IR Prestige-21 spec-
trometer with KBr pellets in the range from 4000 to 400 cmꢀ1. 1H-
NMR and 13C-NMR spectra were recorded at 293 K on Varian
400 (400 MHz) using TMS as an internal standard, Visible and
fluorescence spectra was measured on Agilent 8453 spectropho-
tometer. LC-MS was measured at an Agilent LC-MS equipment.
X-ray powder diffraction measurements were carried out on
a Bruker D8 Advance diffractometer at 40 kV, 40 mA with
a Cu-target tube and a graphite monochromator. Solid-state
fluorescent spectra were measured with an Hitachi F-2500
spectrophotometer with a xenon arc lamp as the light source at
room temperature.
the equatorial plane is replaced by carboxyl group. The existence
of carboxyl group on 2-position dramatically affect the confor-
mation of the two carboxyl group on the 4- and 5- position. In
complex 1 and complex 2, the two carboxyl groups of the ligand
are approximately co-planar to the imidazole ring (for complex
1, the angle is about 1ꢂ and 3ꢂ, for complex 2, the angle is about
9ꢂ and 21ꢂ), while one of the carboxyl groups is almost perpen-
dicular to the ring (5ꢂ and 75ꢂ) in complex 3. This may be due to
the steric hindrance which is enhanced when the five-number ring
is formed from O6 and N2.
Two imta4ꢀ ligands link four Cu(II) ions to form ring-shaped
SBUs, which are further extended by bpy into a 2D network (fig.
3b). The 2D network is a (4,4) net if the ring-shaped SBUs are
regarded as 4-connected node. The 2D nets are packing in abcabc
mode as show in Fig. 3c. There are small channels along
a direction and occupied by water molecule (ESI, Fig. S3).† If
3
ꢀ
only the water molecules are removed, complex 3 has 260 A
Preparation of 2-(hydroxymethyl)-1H-imidazole-4,5-dicarboxy-
lic acid (H4hmIDC)
potential solvent volume (12%) estimated by PLATON.19
The ligand H4hmIDC was prepared in two steps as depicted in
the ESI, Scheme S1.† In the first step, 2-(hydroxy-
methyl)benzimidazole was synthesized according to the litera-
ture:20 A mixture of o-phenylendiamine (10.8 g, 0.1 mol) and
glycolic acid (7.6 g, 0.1 mol) was refluxed for 1 h in hydrochloric
acid (4 M, 100 mL). The green solution was neutralized by
ammonia. The white precipitation that formed was filtered and
recrystallisation from water. Yield, 72%. In the second step, A
solution of 30% Hydrogen peroxide (26 mL) was added dropwise
XRPD patterns and photoluminescence
X-Ray powder diffraction profiles for complexes 1 to complex 3
are illustrated in the ESI, Fig. S4–S6.† The powder XRD pattern
of compounds 1 to complex 3 are in good agreement with those
simulated on the basis of the single-crystal structures, respec-
tively. The diffraction peaks on experimental patterns and
simulated patterns correspond well in position, suggesting that
886 | CrystEngComm, 2011, 13, 883–888
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to a solution of 2-(hydroxymethyl)benzimidazole (3.70 g,
ꢂ
X-Ray crystallography
0.025 mol) in concentrated sulfuric acid (26 mL) at 110 C over
ꢂ
A single crystal of the complex with suitable dimensions was
mounted onto the end of a thin glass fiber. X-Ray diffraction
intensity data were collected at 298(2) K on an Bruker Apex II
2 h. The reaction mixture was heated at 110 C for another 2 h
and then poured into ice water (ca. 130 mL). The precipitation
that formed was filtered and washed with water. Yield, 65%. 1H-
NMR (DMSO-d6) d ¼ 9.08 (1 H, s, H2), 4.56 (2 H, s, H1); 13C-
NMR (DMSO-d6) d ¼ 159.7 (2 C, d, J ¼ 16 Hz, C4), d ¼ 148.5 (1
C, s, C2), d ¼ 128.7 (2 C, d, J ¼ 8 Hz, C3), d ¼ 54.0 (1 C, s, C1)
(ESI, Fig. S7);† MS(LCMS) found: m/z 186.5 (ESI, Fig. S8).†
Anal. calcd for C6H6N2O5: C 38.72, H 3.25, N 15.05. Found: C
38.79, H 3.32, N 15.18%. IR (KBr, n/cmꢀ1: 3483 s, 3381 m,
3103 w, 2924 w, 2849 w, 2637 w, 1717 w, 1578 s, 1506 s, 1427 m,
1306 m, 1078 s, 995 w, 775 m, 652 w, 536 w.
ꢀ
Smart CCD diffractometer (Mo-Ka radiation, l ¼ 0.71073 A).
All empirical absorption corrections were applied by using the
SADABS program.21 Structure was solved by direct methods
followed by difference Fourier syntheses, and then refined by
full-matrix least squares technique on F2 using SHELXL.22 All
the non-hydrogen atoms were refined with anisotropic para-
meters, while H atoms were placed in calculated positions and
refined using a riding model, except for the H atoms of
uncoordinated water molecules in complex 3. Two H atoms of
uncoordinated water molecule for O(4w) in complex 3 were
located in the difference Fourier map and refined isotropically;
the O–H distance involving the water molecules were refined with
Synthesis of {[Cd(H2hmIDC)(bpy)]$0.5bpy$H2O}n (1)
A mixture of Cd(CH3COO)2$2H2O (26.7 mg, 0.10 mmol),
H4hmIDC (18.6 mg, 0.10 mmol), 4,40-bipyridine (15.6 mg,
0.10 mmol), Et3N (0.1 mL) and EtOH–H2O (1 : 1, 8 mL) was
sealed in a 10 mL Teflon-lined stainless-steel reactor and then
heated to 120 ꢂC for 72 h under autogenous pressure. After
the sample was slowly cooled to room temperature at a rate of
ꢀ
a DFIX restraint of 0.88–0.92 A. O(5) atom in complex 1 is
crystallographically disordered over two close sites, and treated
with half occupancy for each. Crystallographic data and refine-
ment parameters are listed in Table 1.
Acknowledgements
5
ꢂC hꢀ1, colourless block crystals of 1 were collected after
washing with water and ethanol (yield: 68%). Anal. calcd for
C21H18CdN5O6: C 45.96, H 3.31, N 12.76. Found: C 46.05, H
3.28, N 12.69%. IR (KBr, n/cmꢀ1: 3571 w, 3406 s, 3260 s, 3104 w,
2963 w, 2856 w, 2361 s, 2340 s, 1658 w, 1605 w, 1580 w, 1535 s,
1479 s 1408 s, 1269 s, 1219 m, 1123 s, 1065 m, 1045 w, 1024 w,
870 w, 806 s, 785 w, 628 m, 612 w, 482 w.
This work was supported by the National Science Foundation of
China (grant no. 20771040).
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ꢁ
ꢂ
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12.51. Found: C 32.24, H 1.38, N 12.47%. IR (KBr, n/cmꢀ1
:
3437 s, 2968 w, 2853 w, 2361 s, 2340 s, 1724 w, 1692 w, 1658 w,
1640 w, 1612 s, 1562 w, 1462 w, 1258 m, 1059 s, 1022 w, 876 w,
669 s, 648 w, 542 m, 426 w.
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Synthesis of {[Cu2(ITC)(bpy)(H2O)3]$2.5H2O}n (3)
A mixture of CuSO4$5H2O (25.0 mg, 0.10 mmol), H4hmIDC
(18.6 mg, 0.10 mmol), 4,40-bipyridine (15.6 mg, 0.10 mmol), Et3N
(0.1 mL) and EtOH–H2O (1 : 1, 8 mL) was sealed in a 10 mL
Teflon-lined stainless-steel reactor and then heated to 120 ꢂC for
72 h under autogenous pressure. After the sample was slowly
cooled to room temperature at a rate of 5 ꢂC hꢀ1, beautiful dark-
blue needle-like crystals of 3. yield: 35%. Anal. calcd for
C16H19Cu2N4O11.50: C 33.22, H 3.31, N 9.69. Found: C 33.18, H
3.37, N 9.65%. IR (KBr, n/cmꢀ1: 3435 s, 2924 s, 2853 m, 2359 s,
2342 s, 1726 w, 1692 w, 1658 m, 1597 s, 1442 m, 1344 m, 1221 w,
1119 s, 1072 w, 877 w, 808 m, 669 s, 648 w.
This journal is ª The Royal Society of Chemistry 2011
CrystEngComm, 2011, 13, 883–888 | 887

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888 | CrystEngComm, 2011, 13, 883–888
This journal is ª The Royal Society of Chemistry 2011