Hydrothermal synthesis of 3D Copper(II)-Organic Frameworks: In situ Formation of 3-Hydroxopyrazine-2-carboxylate from 3-Aminopyrazine-2-carboxylic acid

Article abstract of DOI:10.1002/zaac.201300253

Themetal organic framework, [Cu₅(C₅H ₂N₂O₃)4(H₂O)4(NO₃) ₂· 10H₂O]n (1), was synthesized by a hydrothermal reaction via copper nitrate and in situ generated 3-hydroxopyrazine-2- carboxylate from 3- aminopyrazine-2-carboxylic acid. Compound 1 was characterized by elemental analysis, infrared spectroscopy, TG analysis, and singlecrystal X-ray diffraction. It has a 3D structure constructed from Cu2+ cations, bridging NO₃ anions, and 3-hydroxopyrazine-2-carboxylate units. The NO₃ - anions act as μ2-bridging ligand and the 3-hydroxopyrazine- 2-carboxylate units coordinate pentadentately through the two oxygen atoms of their carboxylate group, the oxygen atom of the hydroxyl group and two nitrogen atoms. The ligands link the CuII ions to form trinuclear units. These are further connected to form a novel 3D MOF, with a novel 4-nodal 3,3,3,4-connected net topology of an unprecedented point (Schla?fli) symbol (6.7.9)(64.8.9)(7.102)(72.10).

Full text of DOI:10.1002/zaac.201300253

Job/Unit: Z13253
/KAP1
Date: 14-08-13 15:56:53
Pages: 6
ARTICLE
DOI: 10.1002/zaac.201300253
Hydrothermal Synthesis of 3D Copper(II)-Organic Frameworks: In situ
Formation of 3-Hydroxopyrazine-2-carboxylate from 3-Aminopyrazine-2-
carboxylic Acid
Saeed Dehghanpour,*[a] Khadijeh Jahani,[a] Ali Mahmoudi,[b]
Mogtaba Babakhodaverdi,[a] Robabehsadat Tabatabaei,[a] and Behrouz Notash[c]
Keywords: 3-Hydroxypyrazine-2-carboxylate; Hydrothermal synthesis; Copper; Metal organic framework
Abstract. The metal organic framework, [Cu5(C5H2N2O3)4(H2O)4(NO3)2· units. The NO3– anions act as μ2-bridging ligand and the 3-hydroxopy-
10H2O]n (1), was synthesized by a hydrothermal reaction via copper razine-2-carboxylate units coordinate pentadentately through the two
nitrate and in situ generated 3-hydroxopyrazine-2-carboxylate from 3-
aminopyrazine-2-carboxylic acid. Compound 1 was characterized by
oxygen atoms of their carboxylate group, the oxygen atom of the hy-
droxyl group and two nitrogen atoms. The ligands link the CuII ions
elemental analysis, infrared spectroscopy, TG analysis, and single- to form trinuclear units. These are further connected to form a novel
crystal X-ray diffraction. It has a 3D structure constructed from Cu2+
cations, bridging NO3 anions, and 3-hydroxopyrazine-2-carboxylate
3D MOF, with a novel 4-nodal 3,3,3,4-connected net topology of an
unprecedented point (Schläfli) symbol (6.7.9)(64.8.9)(7.102)(72.10).
–
droxylation of pyrazinecarboxylic acid derivatives as ligands
have been reported under hydrothermal condition.[18–23]
Herein, we describe the in situ formation of 3-aminopyr-
azine-2-carboxylic acid into 3-hydroxopyrazine-2-carboxylate
(L) and its 3D metal organic framework with CuII,
[Cu5(C5H2N2O3)4(H2O)4(NO3)2·10H2O]n (1), under hydro-
thermal condition. Weng et al. also reported the in situ forma-
tion of 3-hydroxopyrazine-2-carboxylate from decarboxylation
and hydroxylation of 2,3-pyrazinedicarboxylic acid in hydro-
thermal condition.[22]
Introduction
The design and synthesis of metal organic frameworks has
attracted extensive interest owing to their intriguing architec-
tures and topologies and their versatile promising applications
in fields such as catalysis, luminescence, magnetism, sorption,
ion exchange, non-linear optics, and electricity.[1–5] Over the
past decades, a large number of metal organic frameworks
based on the linkage of metal ions (or clusters) with the or-
ganic bridging N/O/S-donor ligands have been reported. How-
ever, the exploration of new ligands has remained a challenge
for researchers in coordination chemistry.[6–8]
In situ ligand transformations/synthesis under hydro-/solvo-
thermal conditions, such as cycloaddition of organic nitriles to
azides or ammonia,[9–11] decarboxylation of arene carboxyl-
ates,[12] hydroxylation of aromatic rings,[13] carbon–carbon
bond formations by reductive or oxidative coupling,[14] and
cleavage and formation of C–N, C–O, and S–S bonds[15,16]
represent a potential new direction for the construction of
novel metal organic frameworks.[17] Among the varieties of
ligands used in the in situ reaction mentioned above, pyrazine-
carboxylic acid and its derivatives have been found as chal-
lenging candidates for the in situ ligand transformations. Oxi-
dation hydrolysis, decarboxylation, oxalate formation, and hy-
Results and Discussion
Compound 1 was obtained from the hydrothermal reaction
of Cu(NO3)2 and 3-aminopyrazine-2-carboxylic acid (molar
ratio = 2:1) in an aqueous solution at 120 °C for three days.
This compound is stable in air at ambient temperature and is
almost insoluble in the most common solvents such as water,
acetonitrile, chloroform, acetone, and toluene.
A series of parallel experiments [molar ratio of Cu(NO3)2:L
= 2:1, 1:1, and 1:2; T = 120 to 210 °C in steps of 10 °C,
t = 3 d] demonstrated that factors such as molar ratio and reac-
tion temperature were important in isolation of the final crys-
talline product. Compound 1 can only be prepared using the
molar ratio of reagents and temperature mentioned in the Ex-
perimental Section. Hydroxylation of aromatic rings and N-
heterocycle ligands,[24–26] and decarboxylation and hydroxyla-
tion of 2,3-pyrazine dicarboxylic acid and pyrazine-2,3,5-tri-
carboxylic acid in the presence of NaOH has also been
found in hydrothermal preparation of metal organic frame-
works.[21–23] Herein, deamination and hydroxylation of 3-ami-
nopyrazine-2-carboxylic acid occurred and then 3-hydroxopyr-
* Dr. S. Dehghanpour
E-Mail: Dehganpour_farasha@yahoo.com
[a] Department of Chemistry
Alzahra University
P.O.Box 1993891176, Tehran, Iran
[b] Department of Chemistry
Islamic Azad University
Karaj Branch, Karaj, Iran
[c] Chemistry Department
Shahid Beheshti University
G. C., Evin, Tehran 1983963113, Iran
Z. Anorg. Allg. Chem. 0000, ᭿,(᭿), 0–0
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azine-2-carboxylate, (L) formed a new 3D metal organic Table 1. Crystal data and single-crystal X-ray diffraction refinement
details for compound 1.
framework, 1, in the presence of Cu(NO3)2. Kim also prepared
3-hydroxypyrazine-2-carboxylic acid from 3-aminopyrazine-2-
carboxylic acid using diazotization at refluxed condition.[27]
Demetallation of 1 demonstrates in situ formation of the 3-
hydroxypyrazine-2-carboxylic acid. Complex 1 was dissolved
in HCl solution (3 m) and heated to 40 °C. The solution was
allowed to stand at 50 °C overnight. The green color of the
solution faded gradually and became colorless. The mixture
was cooled and neutralized with NH4OH. The precipitate was
filtered, washed with ice water, and dried to ligand as a color-
Formula
C20H36Cu5N10O32
Formula weight
Temperature /K
Wavelength /Å
Crystal system
Space group
a /Å
1246.29
120
0.71073
monoclinic
P21/c
14.745(3)
11.024(2)
13.287(3)
97.27(3)
2142.4(8)
2
1.932
2.56
b /Å
c /Å
β /°
V /Å3
1
less solid. The H NMR spectrum and also mass spectrum of
Z
the extracted ligand [(500 MHz, [D6]DMSO, 25 °C): δ = 7.71
(d, J = 4 Hz, 1 H), 7.86 (d, J = 3 Hz, 1 H), 11.51 (b) ppm; m/z
= 140] clearly show in situ formation of 3-hydroxypyrazine-2-
carboxylic acid.
Density /g·cm–3
μ /mm–1
F(000)
1254
Crystal size /mm
Theta range for data collection
Index ranges
0.20ϫ0.14ϫ0.13
2.4 to 29.2
–19 Յ h Յ 20
–13 Յ k Յ 15
–18 Յ l Յ 18
13708
The IR spectrum of 1 has a strong band at 1610 cm–1 due
to the antisymmetric stretching of the carboxylate [νasym(COO–)]
and symmetric stretching of the carboxylate [νsym(COO–)]
appears at 1363 cm–1. The stretching vibrations of C–O bands
appear at 1196 and 1233 cm–1. The IR spectrum of 1 exhibits
Reflections collected
Independent reflections
Absorption correction
Max. and min. transmission
Refinement method
5622
numerical
–
the characteristic band corresponding to NO3 , which appears
0.732 and 0.629
full-matrix least-squares on F2
4713 / 3 / 362
1.234
R1 = 0.0583, wR2 = 0.1001
R1 = 0.0757, wR2 = 0.1055
1.61 and –0.81
at 1384 cm–1. The broad band at 3435 cm–1 can be attributed
to the O–H stretching of the coordinated and guest H2O mole-
cules.[28,29] The absorption bands were observed at 360 and
376 nm due to π–π* and/or charge transfer transition. The vis-
ible region of the spectrum for 1 displays a single broad band
at 681 nm due to d–d transitions.[30]
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I Ͼ 2σ(I)]
R indices (all data)
Largest diff. peak and hole /e·Å–3
The perspective view of 1 indicating atom-numbering
scheme is illustrated in Figure 1. The crystallographic data for
compound 1 is summarized in Table 1. Selected bond lengths,
and bond angles are listed in Table 2. Single crystal X-ray dif-
fraction analysis reveals that 1 has 3D framework. Cu1 is six
coordinated, displaying a distorted octahedral coordination en-
vironment (Figure 1). The equatorial positions are occupied by
two oxygen atoms of L, nitrogen and oxygen atoms of another
L, and the axial positions are both coordinated to the oxygen
of nitrate ions. The bonding parameters (Table 2) clearly indi-
Table 2. Selected bond lengths /Å and angles /° of compound 1.
Bond lengths
Cu1–O3
Cu1–O1
Cu1–O2
Cu1–N2
Cu1–O4
Cu2–O8
Cu2–N1
Cu2–N5
1.904(3)
1.951(3)
1.975(3)
1.988(3)
2.428(3)
1.958(3)
1.988(3)
1.998(3)
Cu2–N4
Cu2–O7
Cu3–O10
Cu3–O10
Cu3–O9
Cu3–O9
Cu3–O15
Cu3–O15
2.026(3)
2.282(3)
1.920(3)
1.920(3)
1.963(3)
1.963(3)
2.440(4)
2.440(4)
cate the differences caused by Jahn-Teller effect in the central Bond angles
O3–Cu1–O1
94.24(12)
90.14(11)
175.19(11) O10–Cu3–O10
170.99(12) O10–Cu3–O9
93.47(13)
82.33(12)
103.96(13) O10–Cu3–O9
88.74(13)
88.27(13)
80.86(13)
N5–Cu2–O7
N4–Cu2–O7
113.64(13)
84.22(12)
180.000
Cu1 atom, elongation along the axial direction and compres-
O3–Cu1–O2
sion around the equatorial positions. Such effect is widely ob-
O1–Cu1–O2
served in CuII complexes.[31,32]
O3–Cu1–N2
87.46(12)
92.54(12)
92.54(12)
87.46(12)
180.00(18)
92.24(12)
87.76(12)
87.50(12)
92.50(12)
87.76(12)
92.24(12)
92.50(12)
87.50(12)
180.00(15)
O1–Cu1–N2
O2–Cu1–N2
O3–Cu1–O4
O1–Cu1–O4
O2–Cu1–O4
N2–Cu1–O4
O8–Cu2–N1
O8–Cu2–N5
N1–Cu2–N5
O8–Cu2–N4
N1–Cu2–N4
N5–Cu2–N4
O8–Cu2–O7
N1–Cu2–O7
O10–Cu3–O9
O10–Cu3–O9
O9–Cu3–O9
O10–Cu3–O15
O10–Cu3–O15
173.81(13) O9–Cu3–O15
88.00(12)
90.40(13)
82.25(13)
97.41(13)
159.86(14) O9–Cu3–O15
90.93(13)
95.19(12)
O9–Cu3–O15
O10–Cu3–O15
O10–Cu3–O15
O9–Cu3–O15
O15–Cu3–O15
Cu3 (Cu3 is on a symmetry center) is also six coordinated
with four oxygen atoms from two L ligands and two oxygen
Figure 1. View of the coordination environment of CuII in 1.
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Hydrothermal Synthesis of 3D Copper(II)-Organic Frameworks
atoms from coordinated H2O. The equatorial positions are oc-
cupied by four oxygen atoms from two L ligands. The axial
positions are both coordinated to water molecules and show
significantly longer bond lengths. The elongation of the axial
Cu–O bond [Cu3–O15 2.440(4) Å] may be ascribed to the
Jahn-Teller effect.
Unlike Cu3 and Cu1, Cu2 is five coordinated to oxygen and
nitrogen atoms from one L ligand and one oxygen atom from
a water molecule, two nitrogen atoms from two different L
ligands, resulting in a distorted square pyramidal arrangement.
The structural index τ,[33] which is a measure of square pyram-
idal distortion, is 0.23 for Cu2, indicating a distorted square
pyramidal environment. However, the Cu2 atom has an ad-
ditional weak interaction with the oxygen atom of the hydroxo
(3-hydroxopyrazine-2-carboxylate). The Cu–O distance [Cu2–
O3, 2.734(3) Å] is considerably longer than that of the other
Cu–O bond lengths in 1.
Figure 3. One ring constructed by L (type B), Cu2, and Cu3.
In the asymmetric unit, L ligands can be divided into two
distinct types. Type A ligand acts as a μ3-bridge pentadentate
mode to link two Cu1 atoms and one Cu2 atom, whereas type
B acts as a μ3-bridge to link two Cu2 atoms and one Cu3 atom.
–
On the other hand, NO3 ligands link Cu1 atoms as a μ2-
bridge. The various coordination environments of the copper
–
atoms and the interesting arrangements of L and NO3 ligands
Figure 4. View of a section of the 3D network of 1.
result in the formation of the 3D framework with channels,
which are occupied by the H2O molecules. L (type B) is che-
lated to central Cu2 atoms through N4 and O8 atoms and is as a (3,4)-connected four nodal net. This net topology is unpre-
also linked to another Cu2 atom by N4 atom to from a chain cedent with (6.7.9)LA(64.8.9)cu1(7.102)LB(72.10)cu2 Schläfli
along the c axis. This ligand is also chelated to central Cu3 symbol.[34]
atoms through O9 and O10 atoms, which leads to the forma-
The crystal water molecules fill the channels and coordi-
tion of a 2D layered structure (Figure 2). This layer contains a nated water molecules bind to each other and to the oxygen
26 membered ring (Cu2–L–Cu2–L–Cu3– Cu2–L–Cu2–L– atoms of hydroxyl, carboxyl, and nitrate groups through hydro-
Cu3) extended along the bc plane (Figure 3). On the other gen bonding (Table 3). The total solvent accessible volume of
hand, each Cu1 is linked to another Cu1 atom by two oxygen the channels in the unit cell is 654.1 Å3 (after removing of the
atoms of NO3– to form [Cu(NO3)]n chain along the c axis, lattice water molecules), which accounts for 30.1% of the total
where each [Cu(NO3)]n chain doubly links to neighboring cell volume as calculated by PLATON.[35] However, the
chains by L ligands (type A) and these L ligands further link PXRD pattern of the sample after dehydration shows structural
to Cu2 atoms by N1 resulting in the formation of the 3D collapse of 1. It must be noted that all reported spectroscopic
framework (Figure 4).
data here was performed on the sample before dehydration.
The thermogravimetric (TG) behavior of 1 was investigated
in the temperature range of 25–800 °C with a heating rate of
10 K·min–1 in air (Figure 5). It exhibits two weight loss steps.
The first weight loss of 12.96% (calculated: 14.44%) in the
range of 30–126 °C corresponds to the release of guest water
molecules. The decomposition of compound 1 starts beyond
230 °C with a total weight loss of 65.3% (calculated: 67.90%)
at the second stage. The remaining weight of compound corre-
sponds to the calculated value for CuO.
Conclusions
The in situ generation of 3-hydroxopyrazine-2-carboxylate
(L) from 3-aminopyrazine-2-carboxylic acid in the presence
of copper(II) nitrate during hydrothermal syntheses leads to
Figure 2. The 2D network constructed by L (type B), Cu2 and Cu3.
To classify the net, we define the copper atom (Cu2), L formation of a 3D metal organic framework, 1. Compound 1
(type A and B) as 3 connected nodes and another copper atom presents a new (3,3,3,4)-connected 4-nodal net with (6.7.9)
(Cu1) as 4 connected node. Then, complex 1 can be simplified (64.8.9)(7.102)(72.10) topology symbol. The result may facili-
Z. Anorg. Allg. Chem. 0000, 0–0
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Table 3. Hydrogen bonds /Å,° of compound 1.
D–H···A
Symmetry transformations for A
D–H
H···A
D···A
D–H···A
O7–H7A···O9
–x+1, y–1/2, –z+1/2
–x+1, y–1/2, –z+1/2
x+1, –y+1/2, z+1/2
x+1, y, z
x, y, z
–x, –y, –z+1
–x+1, –y+1, –z+1
–x+1, y–1/2, –z+1/2
–x, –y, –z
0.74 (6)
0.80 (2)
0.81 (8)
0.90 (9)
0.83 (7)
0.81 (2)
0.82 (8)
0.95
2.08 (6)
2.04 (3)
2.35 (8)
1.91 (9)
1.99 (7)
2.15 (3)
1.94 (8)
2.47
2.811 (4)
2.754 (7)
3.137 (5)
2.789 (5)
2.796 (6)
2.910 (4)
2.712 (5)
3.355 (5)
3.334 (5)
173 (6)
149 (6)
165 (7)
164 (8)
164 (6)
156 (6)
158 (8)
155
O7–H7B···O14A
O11–H11A···O1
O11–H11B···O4
O12–H12A···O5
O12–H12B···O2
O15–H15A···O16
C9–H9···O11
C10–H10···O2
0.95
2.46
153
(m), 1319 (w), 1233 (m), 1196 (s), 1089 (w), 946 (w), 820 (m), 621
(w), 506 (w) cm–1.
Structural Analysis and Refinement: Crystals of 1 suitable for X-
ray crystallography were obtained as described above. Diffraction data
for 1 were collected with a STOE-IPDSII diffractometer using graph-
ite-monochromated Mo-Kα radiation (λ = 0.71073 Å). Data were col-
lected and integrated using the STOE X-AREA software package.[36]
A numerical absorption correction was applied using X-RED and X-
SHAPE software.[37] The structure was solved by direct methods
(SHELXS-97).[38] The structure refinement was performed by a full-
matrix least-squares method against F2 (SHELXL-97). All non-hydro-
gen atoms were refined anisotropically, all hydrogen atoms were in-
serted in the calculated positions.
Crystallographic data (excluding structure factors) for the structure in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting the de-
pository number CCDC-924779 (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
Figure 5. TGA curve of compound 1.
tate the exploration of new ligand synthesis and construction
of MOFs with novel topology. The thermal behavior of 1 exhi-
bit two steps of weight losses and the final residue is calculated
to be CuO.
Acknowledgements
Financial support of the project by the Alzahra University is gratefully
acknowledged.
Experimental Section
General: All reagents were analytical grade commercial products and
were used without further purification. Elemental analyses were per-
formed with a Heraeus CHN-ORAPID elemental analyzer. Infrared
spectra were recorded with a Bruker Tensor 27 spectrophotometer.
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4
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Received: May 18, 2013
Published Online: ᭿
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5

Job/Unit: Z13253
/KAP1
Date: 14-08-13 15:56:53
Pages: 6
S. Dehghanpour et al.
ARTICLE
S. Dehghanpour,* K. Jahani, A. Mahmoudi,
M. Babakhodaverdi, R. Tabatabaei, B. Notash ................ 1–6
Hydrothermal Synthesis of 3D Copper(II)-Organic Frame-
works: In situ Formation of 3-Hydroxopyrazine-2-carboxylate
from 3-Aminopyrazine-2-carboxylic Acid
6
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© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 0000, 0–0