An inorganic-organic hybrid supramolecular complex (H3O)4[(CoC14H12N2O10)1.5(SiW12O40)]·2H2O: Synthesis, structure, properties, and application to catalytic elimination methanol

Article abstract of DOI:10.1080/00958972.2015.1064527

An organic-inorganic hybrid supramolecular complex, (H₃O)₄[(CoC₁₄H₁₂N₂O₁₀)_1.5(SiW₁₂O₄₀)]·2H₂O, is constructed by tungstosilicate anion and 2,3-pyridinedicarboxylic acid cobalt coordination complex via intermolecular forces. Crystal data of the title complex: trigonal system, P-3c1 space group, a = 20.363(3) ?, b = 20.363(3) ?, c = 27.685(5) ?, α = 90 °, β = 90 °, γ = 90 °, V = 9942(3) ?³, Z = 4, Rint = 0.0383, R2 = 0.1645, GOOF = 1.083. The complex has been hydrothermally synthesized and characterized by Infrared spectra, TG-DTA, fluorescence, cyclic voltammetry, and single-crystal X-ray diffraction. The complex exhibits good catalytic activity for elimination of methanol in the gas phase, when the initial concentration of methanol is 2.76 g m^-3, and flow rate is 10 mL min^-1 at 140 °C, the elimination rate of methanol is 82.6% over 0.2 g of complex.

Full text of DOI:10.1080/00958972.2015.1064527

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An inorganic-organic hybrid
supramolecular complex
(H3O)4[(CoC14H12N2O10)1.5(SiW12O40)]·2H2O:
synthesis, structure, properties, and
application to catalytic elimination
methanol
Hanxi Xiaoa, Yuzhe Hana, Qian Fanga, Qing Caib & Qian Denga
a Department of Chemistry and Chemical Engineering, Hunan
University of Science Technology, Xiangtan, China
b Chemistry Department, City College of New York, City University
of New York, New York, USA
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To cite this article: Hanxi Xiao, Yuzhe Han, Qian Fang, Qing Cai & Qian Deng (2015): An inorganic-
organic hybrid supramolecular complex (H3O)4[(CoC14H12N2O10)1.5(SiW12O40)]·2H2O: synthesis,
structure, properties, and application to catalytic elimination methanol, Journal of Coordination
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Journal of Coordination Chemistry, 2015
http://dx.doi.org/10.1080/00958972.2015.1064527
An inorganic-organic hybrid supramolecular complex
(H3O)4[(CoC14H12N2O10)1.5(SiW12O40)]·2H2O: synthesis,
structure, properties, and application to catalytic elimination
methanol
HANXI XIAO†, YUZHE HAN†, QIAN FANG†, QING CAI‡ and QIAN DENG*†
†Department of Chemistry and Chemical Engineering, Hunan University of Science Technology,
Xiangtan, China
‡Chemistry Department, City College of New York, City University of New York, New York, USA
(Received 17 February 2015; accepted 4 June 2015)
Catalytic performance
An organic–inorganic hybrid supramolecular complex, (H3O)4[(CoC14H12N2O10)1.5(SiW12O40)]·
2H2O, is constructed by tungstosilicate anion and 2,3-pyridinedicarboxylic acid cobalt coordination
complex via intermolecular forces. Crystal data of the title complex: trigonal system, P-3c1 space
group, a = 20.363(3) Å, b = 20.363(3) Å, c = 27.685(5) Å, α = 90 °, β = 90 °, γ = 90 °, V = 9942(3)
Å3, Z = 4, Rint = 0.0383, R2 = 0.1645, GOOF = 1.083. The complex has been hydrothermally
synthesized and characterized by Infrared spectra, TG-DTA, fluorescence, cyclic voltammetry, and
single-crystal X-ray diffraction. The complex exhibits good catalytic activity for elimination of
methanol in the gas phase, when the initial concentration of methanol is 2.76 g m−3, and flow rate is
10 mL min−1 at 140 °C, the elimination rate of methanol is 82.6% over 0.2 g of complex.
Keywords: Tungstosilicate acid; Cobalt; Pyridinedicarboxylic acid; Catalytic elimination; Methanol;
Organic–inorganic hybrid
*Corresponding author. Email: dengqian10@126.com
© 2015 Taylor & Francis

2
H. Xiao et al.
1. Introduction
Polyoxometalates (POMs) are important building blocks in the construction of functional
materials which have properties like multiply charged, multi-morphology, and multi-
dimensional adjustable [1]. As “molecular devices”, POMs are a good multi-electron accep-
tor, which can be used as polydentate ligands. According to the molecular design principles,
the metal ions coordinate with ligands to generate organic–inorganic complexes, then
combine with polyoxometalates for interesting structures, giving complex structures and
properties [2].
Since heteropolyacid chemistry developed, it is cross-promoted and osmosis with solid
materials, analysis, organic, physical, biochemical, and energy science; the development of
solid inorganic materials have entered a new area.
A variety of layered, chain, porous, and other new nanocluster acid compounds have
been synthesized to provide data for heteropolyacid chemistry.
Liu et al. [3] have synthesized three complexes with Co, Cu, and Ag, 2,6-pyridine dicar-
boxylic acid and tungstosilicate. The 2,6-pyridine dicarboxylic acid decomposes in the pres-
ence of metal ions for three complexes. Yang et al. [4] reported a dilacunary γ-Keggin
silicotungstate [γ-SiW10O36]8− by controlling the pH of the reaction system. The two lacu-
nary sites of polyoxoanions are occupied with two [Cu(en)2(H2O)]2+ groups via Cu–O–W
bonds. A new polyoxometalate complex was hydrothermally synthesized with Cu and
5,6-diamino-1,10-phenanthroline by Yang et al. [5]. The complex was used to fabricate a
bulk-modified carbon paste electrode (1-CPE). The result indicated that 1-CPE is stable
over hundreds of cycles and possessed electrocatalytic activity toward reduction reactions
of nitrite.
Felices et al. [6] isolated four organic–inorganic hybrid compounds built up of mono
lacunary precursor [SiW11O39]8−, copper ion, and 4′4-bipyridine. Harriman et al. [7]
reported three Wells-Dawson-type heteropolyanion-supported porphyrin complexes which
show excellent photocatalytic activity. By their multiple coordination requirements, elec-
tron-rich and unique molecular structures [8], transition metals are suitable to link polyox-
ometalate building blocks to form new structures with potentially controllable oxophilicity
from the molecular level. An unusual antibacterial complex based on polyoxometalate and
cobalt-gatifloxacin has been synthesized by Liu et al. [9]. The complex has good antibacte-
rial activity and is a low-cost antibacterial compound.
Shen et al. [10] synthesized and characterized microtubes of SiMoW11 Keggin polyox-
ometalates containing either a Mo(V) or Mo(VI) atom. They found that Mo-substituted
Keggin tungstosilicate microtubes in their reduced state are more stable than the all-tung-
sten Keggin tungstosilicate microtubes. Han et al. [11] synthesized a series of all-inorganic,
high-nuclearity cobalt-phosphate molecular catalysts. The new compounds are the first
POM-based Co–Pi (cobalt–phosphate) cluster molecular catalysts for visible light-driven
water oxidation as a functional model of the oxygen-evolving complex in photosystem II
(PSII).
Pyridine dicarboxylic acid is a rigid polydentate ligand which has N and O donors.
Depending on the location of N and O, heteropolyacid and metal ions could coordinate with
pyridine dicarboxylic acid by coordination, H-bonding or π–π stacking to form different
structures. Therefore, they are valuable building blocks for inorganic–organic complex
engineering [12–14].
Due to the interest in these materials, we synthesize an inorganic–organic hybrid complex
using 2,3-pyridine dicarboxylic acid, cobalt nitrate, and Keggin-type silicotungstic acid as

Structure, catalytic properties of hybrid complex
3
reactants by the hydrothermal method. The crystal structure, thermal stability, fluorescence
(FL), and oxidation–reduction characteristics of the complex were examined. The catalytic
performance for elimination of methanol was explored.
2. Experimental
2.1. Materials and methods
All chemicals were purchased from commercial sources and used without purification. The
crystal structure was determined using a Bruker Smart Apex II CCD area detector single-
crystal diffractometer. Infrared spectra (IR) were recorded as KBr pellets on a Perkin-Elmer
FTIR-2000 spectrometer. Thermogravimetric differential (TG-DTA) analyses were carried
out on a WCT-1-D simultaneous thermal analyzer in air between room temperature and
700 °C at a heating rate of 10 °C min−1. UV–vis spectra were measured on a TU-1810
spectrophotometer. Emission/Excitation spectra of FL were obtained on a Hitachi F4500
fluorescence spectrophotometer. Cyclic voltammetry (CV) spectra were tested on an
Electrochemical workstation CH1760C of Shanghai Chen-Hua Instrument with the scan rate
of 20 mV s−1. The products of the catalytic reaction were analyzed online by a GC-9800
gas chromatograph (GC) equipped with a column packed with Porapak-Q and using a flame
ionization detector.
2.2. Hydrothermal synthesis
Na2SiO3·9H2O (0.0284 g, 0.1 mmol) and Na2WO4·2H2O (0.3597 g, 1.2 mmol) were suc-
cessively dissolved in 5 mL water, then the pH of the solution was adjusted to 1.75 with
1 : 1 (v : v) H2SO4. After stirring for 1 h at 60 °C, bright solution of Keggin-type dode-
catungstosilicate acid solution was obtained. A mixture of Co(NO3)2·H2O (0.0294 g,
0.1 mmol) and pyridine-2,3-dicarboxylic acid (0.0167 g, 0.1 mmol) was added into the
tungstosilicate acid solution. This solution was sealed in a 20 mL Teflon-lined autoclave at
170 °C for 80 h, then the autoclave was cooled to room temperature at 10 °C h−1. Rosaline
block crystals were filtered and washed with distilled water. Yield: 32.00% (based on W).
2.3. X-ray crystallography
A
0.34 × 0.32 × 0.30 mm crystal of the complex was selected for single-crystal
X-ray diffraction. The reflection intensities of the crystal were collected at 293 K using a
Bruker SMART Apex II CCD area detector single-crystal diffractometer with graphite-
monochromated Mo-Kα (λ = 0.71073 Å) radiation in the range θ = 1.87–24.99°. All
non-hydrogen atoms were refined with anisotropic displacement parameters. The structure
was solved by direct methods and refined by full-matrix least-squares on F2 using the
Shelxtl-97 program package [15]. All hydrogens of the crystal water were added by differ-
ent Fourier methods while other hydrogens were finally refined as a riding mode using the
default Shelxtl parameters.
The detailed crystallographic data and structure refinement parameters are summarized in
table 1. Selected bond angles and lengths of the complex are listed in table 2.
Crystallographic data for the structures reported in this paper have been deposited in the
Cambridge Crystallographic Data Center. CCDC ID of the complex is 999915.

4
H. Xiao et al.
Table 1. Crystal data and structure refinement for the complex.
Parameters
Complex
Formula
(H3O)4[(CoC14H12N2O10 1.5
)
(SiW12O40)]·2H2O
Mr
3625.95
0.34 × 0.32 × 0.30
Crystal size (mm3)
Crystal system
Space group
a (Å)
Trigonal
P-3c1
20.363(3)
b (Å)
20.363(3)
c (Å)
27.685(5)
α (°)
90
β (°)
90
γ (°)
120.00
9942(3)
V (Å3)
Z
4
Dc/(g cm−3
)
2.348
Range (°)
1.87–24.99
F (0 0 0), e
hkl range
5080
−24 ≤ h ≤ 24, −24 ≤ k ≤ 24, 19 ≤ l ≤ 32
Refl. measured
Refl. unique
R1 [I > 2σ (I)]
R2 [I > 2σ (I)]
Rint
70,628
7346
0.0579
0.1645
0.0383
284
Parameters
GOOF(S)
1.083
Table 2. Selected bond lengths (Å) and angles (°) for the complex with estimated standard devia-
tions in parentheses.
Si(1)–O(10)
Si(1)–O(19)a
W(2)–O(2)
W(2)–O(5)
W(3)–O(3)
W(3)–O(7)
Co(1)–O(14)
Co(1)–N(1)
1.661(15)
1.618(11)
1.9065
1.9094
1.9170
1.7225
2.22(2)
1.930(17)
1.32(3)
1.45(3)
0.96
109.4(3)
100.39
89.35
99.81
73.34
Si(1)–O(19)
Si(1)–O(19)b
W(2)–O(4)
W(2)–O(6)
W(3)–O(6)
W(3)–O(8)
Co(1)–O(15)
Co(1)–O(14)c
C(1)–C(2)
1.618(9)
1.618(11)
1.7063
1.9591
1.9055
1.8860
1.831(17)
2.22(2)
1.27(3)
1.36(3)
0.93
109.4(4)
158.21
101.39
171.17
157.45
89.28
101.54
93.7(8)
169.3(6)
90.9(8)
127.9(13)
124(2)
128(2)
119(2)
109
N(1)–C(3)
C(4)–C(5)
C(4)–C(11)
C(1)–H(1)
O(14)–H(14A)
O(10)–Si(1)–O(19)
O(2)–W(2)–O(4)
O(2)–W(2)–O(8)a
O(4)–W(2)–O(6)
O(6)–W(2)–O(19)
O(19)–(2)–O(8)a
O(7)–W(3)–O(8)
O(14)–Co(1)–O(15)
O(15)–Co(1)–N(1)
O(14)–Co(1)–O(14)c
Co(1)–O(15)–C(5)
C(2)–C(1)–C(11)
N(1)–C(4)–C(11)
O(15)–C(5)–C(4)
Co(1)–O(14)–H(14A)
C(11)–C(1)–H(1)
O(10)–Si(1)–O(19)a
O(2)–W(2)–O(5)
O(4)–W(2)–O(5)
O(4)–W(2)–O(19)
O(6)–W(2)–O(8)a
O(3)–W(3)–O(6)
O(7)–W(3)–O(9)
O(14)–Co(1)–N(1)
N(1)–Co(1)–N(1)c
O(15)–Co(1)–O(15)c
Co(1)–N(1)–C(3)
C(1)–C(2)–C(3)
C(5)–C(4)–C(11)
C(1)–C(11)–C(4)
H(14A)–O(14)–H(14B)
N(1)–C(3)–H(3)
84.38
101.75
98.8(8)
83.0(7)
71.7(8)
118.8(17)
115(2)
118(2)
113(2)
109
122
118

Structure, catalytic properties of hybrid complex
5
2.4. Catalytic reaction
Catalytic reactions were carried out in a continuous-flow fixed-bed microreactor. The cat-
alytic properties of the complex were tested by eliminating methanol. 0.2ethanol. 0.2c
properties of the complex were reaction tube (φ/8 mm; L/200 mm) as catalyst. A simu-
lacrum of polluted air containing reaction substrate was prepared by bubbling clean air into
a bottle filled with methanol solution and diluting the methanol gas with clean and dry air.
The initial concentration of reaction substrate was adjusted by adjusting the flow velocity of
the bubbling gas and dilution air. The feed gas flowed through the reactor, and the catalytic
elimination reaction was carried out at different temperatures, controlled by a thermostat.
The concentration of feed gas was detected online by gas chromatographic (GC102-N, FID
detector) about every 10 min until the concentration was constant, which means the reaction
reaches balance. The inorganic products of the effluent gasses were monitored by a PdCl2
[0.2 (wt.%)] solution and saturated lime-water solution. The concentration of organic com-
pounds of the effluent gasses was analyzed online by a gas GC. Blank experiments were
carried out without the complex.
In this research, the elimination rate of methanol was adopted to evaluate the catalytic
activity of the catalysts.
3. Results and discussion
3.1. Crystal structure of the complex
Single-crystal X-ray diffraction analysis reveals that the complex consists of one
[SiW12O40]4−, 1.5 [(H2O)2Co(2,3-pyridine dicarboxylic acid)2], four H3O+, and two water
molecules (figure 1). The heteropolyanion [SiW12O40]4− possesses the classical
α-Keggin-type structure with Td symmetry. The Si is surrounded by four oxygens with
Si–O bonds ranging from 1.618 to 1.661 Å. The O–Si–O bond angles are 109.4–109.6°,
which suggests a distorted tetrahedron formation. All W ions have WO6 octahedral environ-
ments. The W–O bond distances are divided into three groups: W–Oa (center oxygen atom),
1.9180–2.3532 Å; W–Ob/c (bridging oxygen), 1.9065–1.9170 Å; W–Od (terminal oxygen),
1.7063–1.7225 Å. O–W–O bond angles are between 73.34 and 171.49° which suggests that
the WO6 octahedra are distorted.
The [(H2O)2Co(2,3-pyridine dicarboxylic acid)2] unit has one Co2+ with two 2,3-pyridine
dicarboxylic acids and two water molecules.
The Co(II) has octahedral coordination, bound to two waters, two pairs of N in pyridine
and carboxylate oxygen individually from b- and a-PDCA. Each N and carboxylate oxygen
of 2,3-pyridine dicarboxylic acid forms a five-membered ring with Co. Two N, one
carboxylate oxygen, and one water constituted the equatorial plane. The other carboxylate
oxygen and water occupy the two axial positions [16]. The Co–O distances range from
1.831(17) to 2.22(2) Å and Co–N are 1.930(17) Å, which is similar to the distances of other
2,3-pdc and Co complexes [17, 18]. The unit cell consists of four crystallographically inde-
pendent molecules (figure 2).
Intramolecular π–π stacking exists in the complex (figure 3). The centroid distance of the
two aromatic rings (that containing N1 and N1′) is 3.5603 Å. The dihedral angle between
two aromatic ring planes (N1 and N1′) is 11.8 ° in offset face-to-face π–π stacking. The
complex exhibits an extended two-dimensional supramolecular network via π–π stacking
interactions (figure 4).

6
H. Xiao et al.
Figure 1. Crystal structure of the complex.
3.2. IR spectrum
The IR spectra of H4SiW12O40 and our complex are shown in figures 5 and 6. The IR of
the complex exhibit four characteristic peaks of the Keggin anions from 700 to 1200 cm−1.
Bands at 1130, 983, 922, and 794 cm−1 correspond to ν(Si–Oa), ν(W–Od), ν(W–Oc), and
ν(W–Ob), respectively [19–21].
A pattern of bands at 3446 and 3099 cm−1 are ascribed (figure 6) to the ν(O–H) in crys-
tallographic water and ν(N–H) of the 2,3-pyridine dicarboxylic acid. 3000, 1602, 1578, and
1441 cm−1 are characteristic peaks of 2,3-pyridine dicarboxylic acid. The absorption at
879 cm−1 is ascribed to H-pyridine ring plane bending vibration; 1725, 1228, and 882 cm−1
are from C=O, C–O and O–H stretches of the COO– groups.
Comparing with H4SiWO12O40, the four characteristic peaks have a small red-shift or
blue-shift, suggesting that 2,3-pyridine dicarboxylic acid interacts with heteropolyacid anion
changing the force constants of Si–Oa, W–Od, and W–Ob/c. The results validate the Keggin
framework still remains in the complex.
3.3. TG analysis
TG-DTA analysis of the compound was performed from room temperature to 800 °C with
10 °C min−1 heating rate in air (figure 7). There are four weight loss steps in the TG-DTA
curve. The first occurs from room temperature to 180 °C. The second step shows a 17.46%

Structure, catalytic properties of hybrid complex
7
Figure 2. The cell structure of the complex.
weight loss between 280 and 350 °C. From 350 to 530 °C is the third step and the fourth is
from 530 to 640 °C with a sharp exothermic peak. The weight losses correspond to removal
of crystal water, coordinated water, 2,3-pyridine dicarboxylic acid, and decomposition of
silicotungstic heteropolyacid framework, sequentially. The final golden yellow residue may
be mixture of SiO3, MoO3, and CoO. The whole process shows an overall 21.53% weight
loss which agrees with the calculated value of 23.13%. The complex has a high decomposi-
tion temperature to indicate that it has high thermal stability. The results provide basis to set
the catalytic reaction temperature.
3.4. UV spectrum
The UV spectra of H4SiW12O40, 2,3-pyridine dicarboxylic acid, and the complex were mea-
sured in aqueous solution at room temperature from 200 to 450 nm (figure 8). The spectrum
of H4SiW12O40 shows two absorptions at 213 and 260 nm, which are the character peaks of
heteropolyacid. The peak at 213 nm corresponds with Od → W charge transfer transition of
W=Od bonds. The Od → W charge transfer transitions avoid the influence from the skeletal
structure of heteropolyanions. The peak at 260 nm corresponds with Ob/c → W charge
transfer transition of W–O–W bonds. The 2,3-pyridine dicarboxylic acid absorptions are at
205 and 280 nm, corresponding with the π–π* transitions.
The complex has three absorptions at 209, 257, and 339 nm. The peaks at 209 and
257 nm correspond with Od → W and Ob/c → W charge transfer transitions, respectively,

8
H. Xiao et al.
Figure 3. The π–π stacking of the complex.
consistent with the skeletal structure of heteropolyanions. According to crystal field
theory and semiconductors bond theory, the peak at 339 nm belongs to the absorption of
Co(II) → O MLCT between 2,3-pyridine dicarboxylic acid and cobalt [22, 23].
3.5. Fluorescence properties
H4SiW12O40 and the complex exhibit blue fluorescence [24, 25] (figure 9) at ambient tem-
perature. The maximum emission peaks of H4SiW12O40 and the complex are located at 471
and 476 nm upon excitation at 236 nm. The fluorescence intensity of H4SiW12O40 is stron-
ger than of the complex. Fluorescence emission wavelength of the complex is red shifted
5 nm from H4SiW12O40 [26].
The crystal size of the complex is bigger than H4SiW12O40. The electrons have been tied
with the polyanion surface, increasing the non-radiative transitions, so that the fluorescence
intensity of the complex is lower than H4SiW12O40. The silicotungstate anion structure is
stabilized when [SiW12O40]4− coordinates with 2,3-pyridine dicarboxylic acid and Co2+,
reducing the electronic transition energy, causing the red shift.
3.6. Cyclic voltammetry
Platinum electrodes were used as the working electrode and the indicator electrode and a
calomel electrode as the reference electrode. Scanning voltage is from −0.6 to 0.6 V and

Structure, catalytic properties of hybrid complex
9
Figure 4. The two-dimensional structure by π–π interactions.
Figure 5. IR spectra of H4SiW12O40
.

10
H. Xiao et al.
Figure 6. IR spectra of the complex.
Figure 7. DTA and TG diagrams of the complex.
Figure 8. UV spectroscopy of the complex.

Structure, catalytic properties of hybrid complex
11
Figure 9. Fluorescence spectra of the complex.
scanning speed is 10 mV s−1 with 0.50 mol L−1 NaCl solution as electrolyte. The CV of
1 × 10−3 mol L−1 complex or H4SiW12O40 solutions was measured at room temperature
using N2 to expel dissolved oxygen.
The CV curve (figure 10) shows typical CV behavior. In the potential range from
−0.6 to +0.1 V, there is one pair of redox peaks at −0.297/−0.489 V for complex
(−0.332/−0.280 V for H4SiW12O40). The redox peaks correspond to two-electron quasi-
reversible processes [27–29] of silicontungstate anion, as follows:
SiW12O440ꢀ þ 2eꢀ ¼ SiW12O640ꢀ
SiW12O46ꢀ0 þ 2eꢀ þ 2Hþ ¼ H2SiW12O46ꢀ0
The mean peak potentials E1/2 = ((Epa + Epc)/2) are −0.384 V for complex and −0.411 V for
H4SiW12O40. According to the literature [30], after the oxidation reaction, if E1/2 < −0.35 V,
Figure 10. CV curves of H4SiW12O40 and the complex.

12
H. Xiao et al.
the reductive product heteropoly blues (HPBs) has strong reducing ability. The HPBs can
be easily oxidized by O2 in air to achieve regeneration of the catalyst. Compared with
silicotungstate, the onset oxidation potential of the complex is more positive, which means
the oxidative capacity has increased. This is propitious to carry on the catalytic oxidation
reaction.
3.7. Catalytic performance
Blank experiments showed that methanol was hardly eliminated without the complex as the
catalyst. There is no new peak except that of methanol in gas GC spectra when the catalytic
reaction was undergoing. At the same time, the saturated limewater grew turbid and the
color of 0.2% PdCl2 solution did not change, indicating that CO2 but not CO is the product
of catalytic elimination of methanol. The controlled trial was done with silicotungstic acid
as the catalyst.
When the reaction temperatures were from 30 to 210 °C, catalytic elimination of metha-
nol was tested at an initial methanol concentration of 2.76 g m−3 and a flow velocity of
10 mL min−1 over 0.2 g complex or silicotungstate, respectively. Effect of the reaction tem-
perature on the elimination rate of methanol is shown in figure 11. With increase of tem-
perature, the elimination rate increases initially and then falls. When the temperature is
30 °C, the elimination rate of methanol is 36.0% over the silicotungstic acid and 38.7%
over compound.
Below 110 °C, the effect of complex and silicotungstic acid are nearly the same. But the
elimination effect of the complex is much better than of silicotungstic acid when the tem-
perature is higher than 110 °C. The maximum elimination rate of methanol over complex is
82.6% at 140 °C with the amount eliminated per unit time of 22.79 × 10−6 g min−1. The
elimination rate of methanol only slightly declines when the temperature continues to rise
above 180 °C. Elimination rate of methanol over H4SiW12O40 declined when the tempera-
ture was more than 140 °C and a new peak has been detected by gas chromatographic,
indicating that the methanol was not thoroughly mineralized and a by-product formed.
Principally, either for silicotungstate or complex, the heteroatom Si and polyatom W are
the highest valence. Heteropolyacids have higher oxidizability than the familiar inorganic
Figure 11. Catalytic performance.

Structure, catalytic properties of hybrid complex
13
acid and have a cage structure. The special structure creates gaps that allow the small
organic molecule into the heteropolyacids’ framework. It is called “false liquid,” which has
the characteristics of homogeneous catalysis. Therefore, both the silicotungstate and com-
plex have the same catalytic abilities to eliminate methanol at low temperature. When the
temperature rises to 120 °C, the methanol absorption over silicotungstic acid is reduced,
leading to catalytic ability rapidly declining. After 2,3-pyridine dicarboxylic acid coordi-
nates with H4SiW12O40, the absorption ability of complex for methanol is improved,
enhancing the catalytic reaction. Thus, the elimination rate of the complex still is good at
high temperature. The complex has a supramolecular network framework that stabilizes its
structure, retaining high catalytic activity at 180 °C, coinciding with its thermostability.
4. Conclusion
This paper describes a Keggin-type organic–inorganic hybrid, (H3O)4[(CoC14H12N2O10)1.5
(SiW12O40)]·2H2O, based on POM, 2,3-pyridine dicarboxylic acid and cobalt nitrate.
Single-crystal X-ray diffraction analysis reveals that the complex consists of one
[SiW12O40]4−, 1.5 six-coordinate Co with 2,3-pyridine dicarboxylic acid as [(H2O)2Co(2,3-
pyridine dicarboxylic acid)2], four protonated H3O+, and two water molecules. The complex
exhibits blue fluorescence and has strong oxidation capacity. Compared with H4SiW12O40
the catalytic ability and stability of the complex are obviously improved. The complex has
good catalytic activity from 120 to 180 °C. The elimination of methanol reaches maximum
value (82.6%) with the concentration of methanol of 2.76 g m−3 and the flow velocity
10 mL min−1 at 140 °C. It can completely convert methanol to CO2 and H2O. This suggests
that the complex has strong oxidation ability and good catalytic activity.
Three complexes with Co, Cu, Ag metal, 2,6-pyridine dicarboxylic acid, and tungstosili-
cate have been described [3]. Their synthesis conditions and reaction products are different,
using 2,6-pdc instead of 2,3-pdc. The pyridine-2,6-dicarboxylate decomposes in the
synthesis of these compounds, with carboxyl removed from the 6-position of pyridine. The
O on the 2-position of pyridine and the N of pyridine coordinated with Co, forming a
six-coordinate structure. One Co can coordinate three pyridine molecules. The three
pyridine rings perpendicular to each other formed a large volume ligand structure, which
cannot form π–π stacking. The molecules combine each other only with hydrogen bonds.
My complex can form hydrogen bonds and π–π stacking, forming a more stable three-
dimensional network structure. In addition, my complex has an excellent catalytic activity
of eliminating volatile organic compounds, such as methanol.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by Special and Key Laboratory of Functional Materials and Resource Chemistry of Guizhou
Provincial Education Department [grant number GAFMRC201302]; Key Laboratory of Theoretical Organic Chemistry
and Functional Molecules of Ministry of Education.

14
H. Xiao et al.
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