Crystal structure and catalytic properties of three inorganic-organic hybrid constructed from heteropolymolybdate and aminopyridine

Article abstract of DOI:10.1016/j.jssc.2013.01.003

Three new organic-inorganic hybrid compounds (2-C₅H ₇N₂)₃·(SiMo₁₂O ₄₀)·(C₄H₈N₄) _0.5·(C₅H₆N₂) ₂·(H₂O)₂ (1), (3-C₅H ₇N₂)₈·(SiMo₁₂O ₄₀)₂·(C₅H₇N₃) ₂·(H₈O₄)·(H₂O) ₈ (2) and (4-C₅H₇N₂) ₆·(SiMo₁₂O₄₀) (3) composed the heteropolymolybdate α-H₄SiMo₁₂O₄₀ and the organic substrate 2/3/4-aminopyridine have been hydrothermally synthesized and characterized by routine methods. Compounds 1 and 2 exhibit a three-dimensional supramolecular network via hydrogen bond and π-π stacking interactions. Compound 2 contains a tetramolecular water cluster which consists of four water molecules connected by hydrogen bonds. These compounds exhibit good thermal stability and photoluminescent phenomena. Compounds 1 and 3 are active for catalytic oxidation of methanol in a continuous-flow fixed-bed micro-reactor, when the initial concentration of methanol is 2.75 g m^-3 in air and flow rate is 10 mL min^-1 at 150 °C, corresponding to the elimination rate of methanol i.e. 87.7% and 76.8%, respectively.

Full text of DOI:10.1016/j.jssc.2013.01.003

Journal of Solid State Chemistry 200 (2013) 60–69
Contents lists available at SciVerse ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Crystal structure and catalytic properties of three inorganic–organic hybrid
constructed from heteropolymolybdate and aminopyridine
Qian Deng, Yilan Huang, Zhenshan Peng, Zengjin Dai, Minru Lin, Tiejun Cai n
College of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new organic–inorganic hybrid compounds (2-C5H7N2)3 ꢀ (SiMo12O40)ꢀ (C4H8N4)0.5 ꢀ (C5H6N2)2 ꢀ (H2O)2
(1), (3-C5H7N2)8 ꢀ (SiMo12O40)2 ꢀ (C5H7N3)2 ꢀ (H8O4) ꢀ (H2O)8 (2) and (4-C5H7N2)6 ꢀ (SiMo12O40) (3) composed
Received 22 October 2012
Received in revised form
4 January 2013
the heteropolymolybdate
a-H4SiMo12O40 and the organic substrate 2/3/4-aminopyridine have been
hydrothermally synthesized and characterized by routine methods. Compounds 1 and 2 exhibit a three-
dimensional supramolecular network via hydrogen bond and stacking interactions. Compound
Accepted 6 January 2013
Available online 24 January 2013
p–p
2 contains a tetramolecular water cluster which consists of four water molecules connected by hydrogen
bonds. These compounds exhibit good thermal stability and photoluminescent phenomena. Compounds
1 and 3 are active for catalytic oxidation of methanol in a continuous-flow fixed-bed micro-reactor, when
the initial concentration of methanol is 2.75 g mꢁ3 in air and flow rate is 10 mL minꢁ1 at 150 1C,
corresponding to the elimination rate of methanol i.e. 87.7% and 76.8%, respectively.
& 2013 Elsevier Inc. All rights reserved.
Keywords:
Silicomolybdic acid
Aminopyridine
p–p stacking
Catalytic elimination
Methanol
1. Introduction
oxidant and aldehyde as the sacrificial agent under mild conditions.
Zhang et al. [14] reported the synthesis of a novel sandwich-
The design and synthesis of organic–inorganic hybrid have
become a significant area of research for chemists in recent years
due to the possibility of combining different characteristics of the
components to get unusual structures or properties. Polyoxome-
talates (POMs) are excellent molecular acceptors which can form
different nature, size and shape of the organic and inorganic
compounds with N, S, O etc., organic electronic donor through the
molecular self-assembly [1–3]. Polyoxometalate (POM) clusters
with unrivaled structural diversity offer interesting and exciting
perspectives in many important areas such as catalysis, photochro-
matic materials, non-linear optical materials, electrochemistry,
magnetism and medicine [4–11].
type based on earth-abundant elements without organic ligands
11H[Sn4(SiW9O34)2]ꢀ 25H2O which is the first POM photocata-
K
lyst reported with visible-light activity for H2 evolution reaction.
The examples of inorganic–organic hybrids [CuI8(BTA)4(HBTA)8
(SiMo12O40)] ꢀ 2H2O and [CuII6(OH)4(BTA)4(SiW12O40)(H2O)6]ꢀ 6H2O
(HBTA:1-H-1,2,3-benzotriazole) based on metal-HBTA multinuclear
subunits and polyoxometalates were reported by Wang et al. [15]
which show excellent photocatalytic activity for the degradation of
methylene blue in UV irradiation. There are few papers about
organic–inorganic hybrid POMs used for catalytic eliminating volatile
organic compounds (VOC). Our group used Anderson type [Cr(OH)6
3ꢁ
3ꢁ
Mo6O18
]
and Keggin type [PMo12O40
]
anions as the structure
The research and application of POM in catalytic fields have
received the attention of chemists due to its important and wide
application prospect. Mizuno et al. [12] synthesized a novel organic-
building units to synthetize a series new types of POM complexes
with aminopyridine through the supramolecular force, which have
very good catalytic acetone effect in the low temperature [16,17]. We
also reported the synthesis and catalytic properties of two supramo-
lecular compounds [(C7N2H7)3(C7N2H6)(PMo12O40)] ꢀ 2H2O (I) and
[(C7N2H7)3(C7N2H6)2(AsMo12O40)] ꢀ 3H2O (C7N2H6¼benzimidazole)
(II) which are active for catalytic oxidation of methanol. When the
initial concentration of the methanol is 5.37 g mꢁ3 in air and the flow
velocity is 4.51 mL minꢁ1, methanol is completely eliminated at
150 1C for I and 160 1C for II [18].
solvent-soluble tetra-n-butylammonium (TBA) salt of
negatively charged germanodecatungstate [g-H2GeW10O36]
a
6ꢁ
highly
which
could act as an efficient homogeneous catalyst for Knoevenagel
condensation of active methylene compounds with carbonyl com-
pounds. Li et al. [13] reported the oxidation of dibenzothiophene to
the corresponding sulfoxide and sulfone in an emulsion system
composed of polyoxometalate anion [C18H37N(CH3)3]5[PV2Mo10O40
]
as both the surfactant and catalyst, using molecular oxygen as the
In this article, three new types of organic and inorganic
hybrid compounds using 2/3/4-aminopyridine as organic ligands
were synthesized by the hydrothermal method and the property
of catalytic elimination methanol and acetone was analyzed.
The synthesis of compounds based on aminopyridine and
n Corresponding author. Fax: þ86 731 58291379.
E-mail address: tjcai53@163.com (T. Cai).
0022-4596/$ - see front matter & 2013 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jssc.2013.01.003

Q. Deng et al. / Journal of Solid State Chemistry 200 (2013) 60–69
61
Table 1
Crystal data and structure refinement for Compounds 1–3.
Compound 1
Compound 2
Compound 3
Formula
C27H41N12SiMo12O42
2385.09
C50H94N22Si2Mo24O92
4834.20
C30H42N12SiMo12O40
2390.13
Mr
Crystal. size (mm3)
Crystal system
Space group
0.20 ꢂ 0.40 ꢂ 0.50
monoclinic
0.25 ꢂ 0.27 ꢂ 0.32
tetragonal
0.092 ꢂ 0.32 ꢂ 0.32
trigonal
P21/c
P4(2)/n
R-3
13.3326(3)
14.3504(2)
21.584(4)
˚
a (A)
22.4570(5)
21.9599(5)
14.3504(2)
29.0183(6)
21.584(4)
10.475(4)
˚
b (A)
˚
c (A)
a
b
g
(deg.)
90.00
90.00
90.00
115.9050(10)
90.00
90.00
90.00
(deg.)
(deg.)
90.00
120.00
4226(2)
3
5914.4(2)
5975.85(17)
˚
V (A )
Z
4
2
3
Dcalcd (g cm–3
)
2.679
2.685
2.817
2.713
3432
m
(MoK
a
) (cm–1
)
2.587
2.566
F (000) e
4564
4636
hkl range
ꢁ15rhr14, ꢁ25rkr26, ꢁ26rlr26
ꢁ18rhr18, ꢁ12rkr18, ꢁ38rlr34
ꢁ25rhr25, ꢁ25rkr25, ꢁ12rlr12
Refl. measured
Refl. unique
Rint
41,010
34,675
10,274
10,334
7124
1656
0.0268
0.0358
0.2491
Param. refined
835
430
186
R (F)/wR (F2)a (all refl.)
GoF (F2)a
0.0518/0.1195
1.129
0.0784/0.1462
1.082
0.0704/0.1756
1.008
–3
1.560/ꢁ1.137
1.348/ꢁ0.728
1.152/ꢁ1.318
˚
Drfin (max/min) (e A )
Table 2
Table 3
˚
˚
Selected bond lengths (A) and angles (deg.) for Compound 1 with estimated
standard deviations in parentheses.
Selected bond lengths (A) and angles (deg.) for Compound 2 with estimated
standard deviations in parentheses.
Mo1–O35
1.660(5)
1.894(5)
1.940(5)
1.620(5)
1.629(5)
99.7(3)
Mo1–O32
1.885(5)
1.937(5)
2.346(4)
1.625(5)
1.631(5)
102.2(3)
73.39(18)
74.56(18)
86.4(2)
Mo1–O15
1.657(4)
1.873(4)
1.916(4)
1.616(4)
1.616(4)
102.9(2)
97.8(2)
Mo1–O1
1.918(4)
1.943(5)
2.348(4)
1.624(4)
1.624(4)
87.46(19)
87.26(19)
168.1(2)
86.20(17)
74.04(16)
84.97(17)
73.17(16)
109.32(19)
109.6(2)
Mo1–O14
Mo1–O36
Mo1–O2
Mo1–O8
Mo1–O11
Mo1–O38
Mo1–O4
Mo1–O6
Si1–O38
Si1–O15
Si1–O6
Si1–O7#1
Si1–O37
Si1–O39
Si1–O6#1
Si1–O7
O35–Mo1–O32
O11–Mo1–O38
O14–Mo1–O38
O35–Mo1–O38
O14–Mo1–O11
O35–Mo1–O11
O32–Mo1–O36
O32–Mo1–O14
O38–Si1–O15
O15–Si1–O37
O15–Si1–O39
Si1–O38–Mo6
Mo6–O38–Mo2
Mo6–O38–Mo1
Mo1–O32–Mo2
Mo1–O36–Mo6
O35–Mo1–O14
O36–Mo1–O38
O32–Mo1–O38
O36–Mo1–O11
O32–Mo1–O11
O14–Mo1–O36
O35–Mo1–O36
O15–Mo1–O2
O15–Mo1–O4
O2–Mo1–O4
O15–Mo1–O1
O2–Mo1–O1
O4–Mo1–O1
O15–Mo1–O8
O2–Mo1–O8
O6–Si1–O6#1
O6–Si1–O7#1
O6#1–Si1–O7#1
Si1–O6–Mo5
Si1–O6–Mo3
Mo5–O6–Mo3
Mo3–O3–Mo5
Mo1–O4–Mo3
O4–Mo1–O8
O1–Mo1–O8
O15–Mo1–O6
O2–Mo1–O6
O4–Mo1–O6
O1-Mo1-O6
O8–Mo1–O6
O6–Si1–O7
O6#1–Si1–O7
O7#1–Si1–O7
84.39(19)
86.44(19)
169.8(2)
86.0(2)
91.19(19)
103.1(2)
86.51(18)
158.99(19)
98.2(2)
158.9(2)
159.0(2)
98.4(3)
101.4(2)
89.0(2)
91.1(2)
158.89(19)
109.6(3)
109.60(19)
109.3(2)
124.0(2)
123.8(2)
92.49(14)
120.5(2)
120.5(2)
109.7(2)
109.3(2)
109.6(2)
123.9(2)
91.05(15)
92.37(16)
120.7(2)
120.6(3)
O38–Si1–O37
O38–Si1–O39
O37–Si1–O39
Si1–O38–Mo2
Si1–O38–Mo1
Mo2–O38–Mo1
Mo2–O33–Mo6
109.4(2)
109.7(2)
109.1(2)
124.3(2)
124.2(2)
91.20(15)
120.2(2)
109.4(3)
Si1–O6–Mo1
124.1(2)
91.51(14)
91.56(14)
121.1(2)
110.7
Mo5–O6–Mo1
Mo3–O6–Mo1
Mo5–O8–Mo1
H5W–O3W–H6
Symmetry operations: #1¼ ꢁxþ3/2, ꢁyþ1/2, z.
polyoxomolybdate and their application in oxidation elimination
of organic pollutants in the gas phase have rarely been reported.
Methanol and acetone are the typical small molecule organic
pollutants. The Chinese Industrial Standard GB16297-1996 states
that the maximum allowable concentration of methanol and
acetone are 0.22 and 0.4 g mꢁ3, respectively in a workshop
atmosphere. Thus the elimination of methanol and acetone is
significant in environment protection.
performed using a Perkin–Elmer 2400 CHN elemental analyzer.
Mo and Si were determined by a SHIMADZU ICP emission
Spectrometer. Infrared spectra were recorded as KBr pellets on a
Perkin–Elmer FTIR-2000 spectrometer. UV spectra were mea-
sured on a Perkin–Elmer Lambda-35 UV spectrophotometer. TG
analyses were carried out on a WCT-1D simultaneous thermal
analyzer in air atmosphere between room temperature and
700 1C at a heating rate of 10 1C minꢁ1. Emission/excitation
spectra were obtained on a Hitachi F4500 fluorescence spectro-
photometer. The products of the catalytic reaction were analyzed
on-line by a GC-9800 gas chromatograph (GC) equipped with a
column packed with Porapak-Q and using a flame ionization
detector.
2. Experimental
2.1. Materials and methods
All chemicals were purchased from commercial sources
and used without further purification. Elemental analysis was

62
Q. Deng et al. / Journal of Solid State Chemistry 200 (2013) 60–69
2.2. Synthesis
with the rate of 10 1C hꢁ1. Brown block crystals were filtered and
washed with distilled water. Yeild: 54.46% (based on Mo). Anal.
for C27H41N12SiMo12O42 (%): calcd. C—13.60, H—1.73, N—7.05,
Mo—48.27, Si—1.18; found C—13.62, H—1.69, N—6.97,
Mo—48.18, Si—1.25.
2.2.1. Synthesis of H4SiMo12O40
A mixture of Na2SiO3 ꢀ 9H2O (0.284 g, 1 mmol), Na2MoO4 ꢀ
2H2O (2.419 g, 10 mmol) and NaVO3 ꢀ 2H2O (0.316 g, 2 mmol)
was dissolved in 60 mL distilled water at 80 1C, the pH of the
mixture was adjusted to about 2.0 with 1:1 (v:v) H2SO4, the
bright red solution was obtained after stirring for 1 h [9].
2.2.3. Synthesis of Compound 2
The synthesis method is similar to Compound 1 except using
CuBr2 (0.045 g, 0.2 mmol, used as initiator), 3-aminopyridine
(0.028 g, 0.3 mmol ) instead of CoSO4 and 2-aminopyridine respec-
tively at 180 1C. Red block crystals were filtered and washed with
distilled water. Yeild: 57.64% (based on Mo). Anal. for C50H94N22Si2-
Mo24O92 (%): calcd. C—12.43, H—1.96, N—6.37, Mo—47.63,
Si—1.16; found C—12.35, H—1.90, N—6.18, Mo—47.54, Si—1.12.
2.2.2. Synthesis of Compound 1
A mixture of CoSO4 (0.052 g, 0.2 mmol, used as initiator), 2-
aminopyridine (0.024 g, 0.25 mmol) and H4SiMo12O40 (12 mL,
0.2 mmol) was put into the 18 mL Teflon-lined autoclave at
170 1C for 5 days, then slow cooling to the room temperature
2.2.4. Synthesis of Compound 3
Table 4
˚
Selected bond lengths (A) and angles (deg.) for Compound 3 with estimated
The synthesis method is similar to Compound 1 except using
Ni(Ac)2 (0.046 g, 0.2 mmol, used as initiator) and 4-aminopyridine
(0.019 g, 0.2 mmol) instead of CoSO4 and 2-aminopyridine respec-
tively at 180 1C. The black block crystals were filtered and washed
with distilled water. Yeild: 45.16% (based on Mo). Anal. for
standard deviations in parentheses.
Mo1–O14
1.648(7)
1.813(18)
1.964(14)
2.043(13)
1.612(12)
111.3(6)
79.1(8)
Mo1–O40
1.717(16)
1.858(14)
1.950(18)
2.372(11)
1.63(2)
Mo1–O10
Mo1–O9
Mo1–O100
Mo1–O4
Mo1–O90
Mo1–O1
C30H42N12SiMo12O40 (%): calcd. C—15.08, H—1.77, N—7.03,
Si1–O1
Si1–O2
Mo—48.17, Si—1.18; found C—15.21, H—1.73, N—7.12,
Mo—48.30, Si—1.22.
O14–Mo1–O40
O40–Mo1–O10
O40–Mo1–O9
O14–Mo1–O4
O10–Mo1–O4
O14–Mo1–O100
O10–Mo1–O100
O4–Mo1–O100
O40–Mo1–O90
O9–Mo1–O90
O100–Mo1–O90
O40–Mo1–O1
O9–Mo1–O1
O100–Mo1–O1
O1–Si1–O2
O14–Mo1–O10
O14–Mo1–O9
O10–Mo1–O9
O40–Mo1–O4
O9–Mo1–O4
O40–Mo1–O100
O9–Mo1–O100
O14–Mo1–O90
O10–Mo1–O90
O4–Mo1–O90
O14–Mo1–O1
O10–Mo1–O1
O4–Mo1–O1
O90–Mo1–O1
O1–Si1–O1#2
O1–Si1–O1#4
109.9(6)
109.3(6)
90.3(8)
139.2(8)
92.6(5)
19.9(5)
91.5(7)
155.9(7)
93.3(8)
2.3. X-ray crystallography
91.2(6)
20.4(5)
89.0(7)
The reflection intensities of the crystal of the title compounds
were collected at 293 K using a Bruker SMART Apex II CCD area
100.8(7)
157.7(7)
19.8(5)
90.7(5)
90.7(7)
175.2(6)
155.5(4)
57.0(6)
detector single-crystal diffractometer with graphite-mono-
˚
82.7(6)
chromatized Mo Ka (l¼0.71073 A) radiation by the j–o scan
87.6(6)
method. The absorption corrections were based on multiple and
symmetry equivalent reflections in the data set using the SADABS
[19] program. The structure was solved by direct methods and
refined by full-matrix least-squares on F2 using the Shelxtl-97
[20] program package. All non-hydrogen atoms were finally
refined with anisotropic displacement parameters. All hydrogen
atoms of the crystal water were added by different Fourier
54.7(6)
107.4(5)
70.4(5)
71.7(6)
69.9(4)
108.9(4)
180.0(17)
O1#3–Si1–O1#2
O1#3–Si1–O2
71.1(4)
110.1(4)
Symmetry operations: #1¼xꢁy, x, ꢁz , #2¼ ꢁxþy, ꢁx, z , #3¼y, ꢁxþy, ꢁz,
#4¼ ꢁx, ꢁy, ꢁz.
Fig. 1. Continuous flow reaction fixed-bed micro-reactor system.

Q. Deng et al. / Journal of Solid State Chemistry 200 (2013) 60–69
63
Fig. 2. (a) Crystal structure of Compound 1; (b) intramolecular and intermolecular hydrogen bonds in Compound 1; (c)
p
–p
stacking in Compound 1; (d). the three-
dimensional structure by hydrogen bonds connect and p–p stacking interaction along the a-axis in Compound 1.
methods while other hydrogen atoms were finally refined as a
riding mode using the default Shelxtl parameters.
Table 5
Hydrogen-bonding geometry (A deg.) for Compound 1.
˚
The disordered polyoxoanions in Compound 3 were refined
using O (Oa, Ob) atoms split over two equivalent sites. The
detailed crystallographic data and structure refinement para-
meters for Compounds 1–3 are summarized in Table 1. Selected
bond angles and lengths of Compounds 1–3 are listed in Tables 2–4.
Crystallographic data for the structures reported in this paper have
been deposited in the Cambridge Crystallographic Data Center.
CCDC ID of Compounds 1, 2 and 3 are 859,389, 856,292, and
871,733 respectively.
Donor-H ꢀ ꢀ ꢀ Acceptor
D–H
H ꢀ ꢀ ꢀ A
D ꢀ ꢀ ꢀ A
D–H ꢀ ꢀ ꢀ A
O1W–H1WA ꢀ ꢀ ꢀ O8
N1–H1A ꢀ ꢀ ꢀ O36
N1–H1B ꢀ ꢀ ꢀ O23
O1W–H1WB ꢀ ꢀ ꢀ N6
N3–H3A ꢀ ꢀ ꢀ O9
0.85
2.29
1.97
2.12
2.54
2.21
2.10
2.16
2.22
2.28
2.38
2.41
2.10
2.51
2.33
2.49
2.36
1.94
2.51
2.41
2.50
2.11
2.50
2.48
2.10
2.21
2.57
2.50
2.26
2.30
2.46
3.103(10)
2.820(14)
2.926(14)
3.009(14)
3.063(11)
2.922(13)
2.922(11)
3.081(10)
3.056(10)
3.073(10)
3.009(14)
2.944(10)
3.208(10)
3.116(10)
3.086(12)
3.070(19)
2.75(3)
161
169
155
115
176
161
148
176
150
138
1270
167
139
1530
12700
140
157
128
1370
135
150
144
1380
161
167
146
139
141
140
151
1#
0.86
0.86
0.85
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.93
0 0.93
0.93
0.93
0.93
0.93
0.93
0.93
0.93
2#
3#
N3–H3B ꢀ ꢀ ꢀ O22
N4–H4A ꢀ ꢀ ꢀ O4
3#
N5–H5A ꢀ ꢀ ꢀ O28
N5–H5B ꢀ ꢀ ꢀ O6
3#
3#
4#
N6–H6 ꢀ ꢀ ꢀ O5
N6–H6 ꢀ ꢀ ꢀ O1W
N7–H7A ꢀ ꢀ ꢀ O14
N7–H7B ꢀ ꢀ ꢀ O26
N7–H7B ꢀ ꢀ ꢀ O27
N7–H7B ꢀ ꢀ ꢀ O29
N9–H9A ꢀ ꢀ ꢀ O29
N9–H9B ꢀ ꢀ ꢀ O2W
N10–H10A ꢀ ꢀ ꢀ O35
N10–H10A ꢀ ꢀ ꢀ O28
*N11–H11A ꢀ ꢀ ꢀ O13
*N11–H11B ꢀ ꢀ ꢀ O25
C5–H5 ꢀ ꢀ ꢀ O1
2.4. Catalytic reaction
2#
2#
2#
5#
The Compounds 1–3 were used as the catalysts applied in the
elimination of methanol and acetone. Catalytic reactions were
carried out in a continuous-flow fixed-bed micro-reactor (Fig. 1).
The simulacrum of polluted air containing reaction substrate
was prepared by bubbling clean air into a container filled with
reaction substrate and diluting the gas with clean dry air. The
initial concentration of reaction substrate was controlled by
adjusting the flow of the bubbling gas and dilution air.
0.084 mmol Compound 1 (also for Compounds 2 and 3) was
1#
5#
4#
3.119(14)
3.097(14)
3.17(2)
2.88(2)
1#
6#
3.304(14)
3.236(12)
2.996(12)
3.120(14)
3.381(18)
3.262(15)
3.04(3)
C5–H5 ꢀ ꢀ ꢀ O34
C7–H7 ꢀ ꢀ ꢂ O20
C12–H12A ꢀ ꢀ ꢀ O26
C14–H14 ꢀ ꢀ ꢀ O36
C17–H17 ꢀ ꢀ ꢀ O27
C22–H22A ꢀ ꢀ ꢀ O2W
C23–H23 ꢀ ꢀ ꢀ O1W
C28–H28 ꢀ ꢀ ꢀ O17
loaded in the reaction tube (j/8 mm; L/200 mm) as a catalyst for
1#
2#
catalytic oxidation methanol (0.042 mmol for catalytic oxidation
acetone). The concentration of feed gas was detected on-line by
gas chromatographic (GC102-N, FID detector) about every 10 min
for a sample analysis until the concentration unchanged, which
means the reaction was in balance. The retention time of
methanol and acetone are 0.83 and 1.87 min, respectively. Then
catalytic reaction for eliminating reaction substrate proceed, the
eliminating rate of reaction substrate was determined at the
different reaction temperatures. The concentration of organic
compounds of the effluent gases were analyzed on-line by a gas
chromatograph. The inorganic products of the effluent gases were
3.071(17)
3.306(15)
4#
Symmetry operations: 1#¼ ꢁ1þx, y, z, 2#¼x, 1/2-y, ꢁ1/2þz, 3#¼1ꢁx, 1/2þy, 3/
2ꢁz, 4#¼x, 1/2ꢁy, 1/2þz, 5#¼ ꢁ1þx, 1/2ꢁy, -1/2þz, 6#¼1ꢁx, ꢁ1/2þy, 3/2ꢁz.
monitored by a 0.2 (wt%) PdCl2 solution and a saturated lime-
water solution. Blank experiments were carried out without the
Compounds 1–3.

64
Q. Deng et al. / Journal of Solid State Chemistry 200 (2013) 60–69
Fig. 3. (a) The crystal structure of Compound 2; (b) p–p stacking in Compound 2; (c) the tetramolecular water clusters in Compound 2; (d) the three-dimensional structure
by hydrogen bonds connect and p–p stacking interaction along the b-axis in Compound 2.
3. Results and discussion
Table 6
Hydrogen-bonding geometry(A deg.) for Compound 2.
˚
3.1. Description of crystal structures
Donor-H ꢀ ꢀ ꢀ Acceptor
D–H
H ꢀ ꢀ ꢀ A
D ꢀ ꢀ ꢀ A
D–H ꢀ ꢀ ꢀ A
Compound 1 consists of one typical Keggin polyoxoanion
N1–H1A ꢀ ꢀ ꢀ O2W
N1–H1B ꢀ ꢀ ꢀ O16
O1W–H1W ꢀ ꢀ ꢀ O1W
N2–H2 ꢀ ꢀ ꢀ N3
0.86
0.86
0.85
0.86
0.85
0.86
0.86
0.85
0.86
0.85
0.85
0.85
0.86
0.86
0.85
0.93
0.93
0.93
2.14
2.30
2.03
2.37
2.06
2.37
2.26
1.97
1.91
2.34
2.48
2.42
2.20
2.25
1.33
2.38
2.32
2.36
2.29
2.980(13)
3.057(12)
2.875(7)
3.16(2)
166
147
175
153
149
129
165
162
165
136
1300
14300
176
165
125
143
161
156
170
[SiMo12O40]
4ꢁ, three protonated cations [C5H7N2]þ, two [C5H6
1#
2#
3#
4#
N2] molecules, half [C4H8N4]2þ and two water molecules (Fig. 2a).
4ꢁ
[SiMo12O40
]
anion contains a center SiO4 tetrahedron and four
O1W–H2W ꢀ ꢀ ꢀ O9
N3–H3A ꢀ ꢀ ꢀ O2W
N3–H3B ꢀ ꢀ ꢀ O17
O2W–H3W ꢀ ꢀ ꢀ O20
N4–H4A ꢀ ꢀ ꢀ O1W
O2W–H4W ꢀ ꢀ ꢀ O3
O2W–H4W ꢀ ꢀ ꢀ O5
O2W–H4W ꢀ ꢀ ꢀ O14
*N5–H5A ꢀ ꢀ ꢀ N1
*N5–H5B ꢀ ꢀ ꢀ O2
O3W–H5W ꢀ ꢀ ꢀ O3W
C1–H1 ꢀ ꢀ ꢀ O17
2.822(6)
2.988(10)
3.094(8)
2.791(8)
2.747(7)
3.011(7)
3.096(7)
3.145(7)
3.06(2)
Mo3O13 three metal cluster. Three MoO6 octagonal are linked by
the edge to form a Mo3O13 group, while four Mo3O13 groups and
one SiO4 center tetrahedron are linked by angle, Si–O distance
3#
4#
˚
ranging from 1.620 (5) to 1.631 (5) A, the O–Si–O bond angles are
in the range 109.1 (2)–109.7 (2)1, which show that the SiO4 is
slightly deviated from tetrahedron. The bond distances of Mo–Ot,
5#
5#
6#
3#
7#
˚
Mo–Oa and Mo–Ob are from 1.660 (5) to 1.690 (5) A, 2.314 (5) to
˚
3.09(3)
2.349 (5) and 1.823 (5) to 2.000 (5) A respectively. O–Mo–O bond
1.95(3)
angles are between 157.7 (2) and 171.6 (2)1, which imply that the
MoO6 octagonals are the distorted octagonals.
Between the compound molecules, there exist many intramo-
lecular hydrogen bonds and intermolecular hydrogen bonds
3.171(11)
3.220(11)
3.226(15)
3.213(10)
C3–H3 ꢀ ꢀ ꢀ O8
1#
8#
3#
C5–H5 ꢀ ꢀ ꢀ O18
C8–H8 ꢀ ꢀ ꢀ O4
(Fig. 2b). 2-aminopyridine molecules as donor provide hydrogen
Symmetry operations: 1#¼3/2ꢁx, 3/2-y, z, 2#¼1/2ꢁy, x, 3/2ꢁz, 3#¼1ꢁx, 1-y,
2ꢁz, 4#¼y, 3/2ꢁx, 3/2ꢁz, 5#¼3/2ꢁx, 1/2ꢁy, z, 6#¼1/2ꢁx, 3/2ꢁy, z, 7#¼
3/2ꢁy, x, 3/2ꢁz, 8#¼ ꢁ1/2þx, 1/2þy, 2ꢁz.
4ꢁ
atoms to the oxygen atoms from [SiMo12O40
]
anion in the same
structure unit forming the intramolecular hydrogen bonds (such
as: N7-H7A ꢀ ꢀ ꢀ O14, d (N ꢀ ꢀ ꢀ O)¼2.944(10),+N–H ꢀ ꢀ ꢀ O¼1671;
*N11-H11B ꢀ ꢀ ꢀ O25, d (N ꢀ ꢀ ꢀ O)¼2.88 (5),+N–H ꢀ ꢀ ꢀ O¼1501). At
the same time, 2-aminopyridine as the donor provide hydrogen
Distances between different ring centroids of two 2-amino-
˚
pyridine molecules from the same structure unit is less than 4.0 A,
which indicate intramolecular stacking interactions [21,22]
atoms to oxygen atoms from the adjacent structure unit
p–p
4ꢁ
[SiMo12O40
]
anion and water molecules forming the intermo-
(Fig. 2c). The dihedral angle between two 2-aminopyridine
lecular hydrogen bonds. (such as: *N11-H11A ꢀ ꢀ ꢀ O13 [x, 1/2ꢁy,
molecules plane (that containing N5 and N3) is 3.7391. The
1/2þz],
d
(N ꢀ ꢀ ꢀ O)¼3.17 (2),+N–H ꢀ ꢀ ꢀ O¼1351; N6–H6 ꢀ ꢀ
centroid distance of two rings of the 2-aminopyridine molecules
˚
(N5 and N3) is 3.911 A, which exists the intramolecular p–p
ꢀ O1W [x, 1/2ꢁy, 1/2þz],
H ꢀ ꢀ ꢀ O¼1271) (Table 5).
d
(N ꢀ ꢀ ꢀ O)¼3.009 (14),+N–
stacking in the same structure unit. At the same time, there exist

Q. Deng et al. / Journal of Solid State Chemistry 200 (2013) 60–69
65
Fig. 4. (a) The crystal structure of Compound 3; (b) intramolecular and intermolecular hydrogen bonds in Compound 3; (c) the three-dimensional structure by hydrogen
bonds connect along the c-axis in Compound 3.
intermolecular
p
–
p
stacking in the adjacent structure unit,
Table 7
Hydrogen-bonding geometry (A deg.) for Compound 3.
˚
because the distance of centroid of two rings of 2-
aminopyridine molecules and [C4H6N3]2þ (that containing N7
and N11) is 3.767 A and the dihedral angle is 7.5131.
Donor-H ꢀ ꢀ ꢀ Acceptor
D–H
H ꢀ ꢀ ꢀ A
D ꢀ ꢀ ꢀ A
D–H ꢀ ꢀ ꢀ A
˚
Compound 1 exhibits an extended three-dimensional supramo-
N(1)–H(1A) ꢀ ꢀ ꢀ O(14)
N(1)–H(1B) ꢀ ꢀ ꢀ O(4)
N(1)–H(1B) ꢀ ꢀ ꢀ O(90)
N(4)–H(4) ꢀ ꢀ ꢀ O(7)
N(4)–H(4) ꢀ ꢀ ꢀ O(70)
N(4)–H(4) ꢀ ꢀ ꢀ O(4)
N(4)–H(4) ꢀ ꢀ ꢀ O(40)
C(2)–H(2) ꢀ ꢀ ꢀ O(100)
C(4)–H(4A) ꢀ ꢀ ꢀ O(4)
C(4)–H(4A) ꢀ ꢀ ꢀ O(14)
C(5)–H(5) ꢀ ꢀ ꢀ O(90)
1#
2#
3#
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.93
0.93
0.93
0.93
2.17
2.38
2.40
2.01
2.11
2.55
2.58
2.15
2.55
2.58
2.47
3.013(18)
3.08(2)
169
138
1540
161
1670
12100
13000
177
118
1310
146
lecular network via hydrogen bonding and
(Fig. 2d).
p
–
p
stacking interactions
3.19(2)
4ꢁ
2.840(18)
2.956(19)
3.088(19)
3.202(19)
3.08(3)
Compound 2 consists of a typical [SiMo12O40
]
anion, four
[C5H7N2]þ cations, one [C5H7N3] molecule and six water mole-
cules (Fig. 3a). The intramolecular hydrogen bonds and intermo-
lecular hydrogen bonds exist between the complexes molecules
(e.g.N1-H1A ꢀ ꢀ ꢀ O2W, d (N ꢀ ꢀ ꢀ O)¼2.980(13),+N–H ꢀ ꢀ ꢀ O¼1661;
4#
4#
1#
4#
5#
3#
3.10(2)
3.27(2)
N1-H1B ꢀ ꢀ ꢀ O16 [3/2ꢁx,1/2ꢁy,z],
d
(N ꢀ ꢀ ꢀ O)¼3.057(12),+N–
stack-
3.28(2)
H ꢀ ꢀ ꢀ O¼1471). The intermolecular and intramolecular
p–p
ing also exist in the Compound 2 (Fig. 3b). The distance of
centroids of two rings of 3-aminopyridine molecules and
[C5H5N2] (that containing N3 and N5) from the same structure
Symmetry operations: 1#¼ ꢁ1/3þy, 1/3ꢁxþy, 1/3ꢁz, 2#¼1/3ꢁy, 2/3þxꢁy,
2/3þz, 3#¼1/3ꢁx, 2/3ꢁy, 2/3ꢁz, 4#¼xꢁy, x, ꢁz, 5#¼1/3ꢁxþy, 1/3ꢁx, 1/3þz.
˚
unit is 3.876 A, the dihedral angle is 21.0241.The distance of
are þ6 oxidation states. Mo (V) is dark blue so the color of Compound
3 is black which is obviously deeper than Compounds 1 and 2. The Si
is coordinated by 8 oxygen atoms each of them has 50% occupancy
over the two positions. MoO6 octahedron consists of a centra Mo
atom, one terminal oxygen atom (Ot), two triply bridging oxygen
atoms (Oa) and eight doubly bridging oxygen atoms (Ob), Ot and Ob
are refined disordered with six occupancy factor (sof) at 0.5.
The intramolecular and intermolecular hydrogen bonding
interaction is also existed between the complexes molecules
forming the supramolecular structure (Fig. 4b). (such as: N4–
H4 ꢀ ꢀ ꢀ O7, d(N ꢀ ꢀ ꢀ O)¼2.840(18), +N–H ꢀ ꢀ ꢀ O¼1611; N4–H4 ꢀ ꢀ ꢀ
O70, d(N ꢀ ꢀ ꢀ O)¼2.956(19), +N–H ꢀ ꢀ ꢀ O¼1671. *N1–H1A ꢀ ꢀ ꢀ O14
[ꢁ1/3þy,1/3ꢁxþy,1/3ꢁz], d(N ꢀ ꢀ ꢀ O)¼3.013(18), +N–H ꢀ ꢀ ꢀ
O¼1691; C5–H5 ꢀ ꢀ ꢀ O90 [1/3ꢁx,2/3ꢁy,2/3ꢁz], d(N ꢀ ꢀ ꢀ O)¼
3.28(2), +N–H ꢀ ꢀ ꢀ O¼1461). Compound 3 exhibits an extended
three-dimensional supramolecular network via hydrogen bond-
ing interactions (Fig. 4c) (Table 7).
centroids of two rings of 3-aminopyridine molecules (that con-
taining N1 and N1* [1.5ꢁx, 1.5ꢁy, z]) from two adjacent
˚
structure units is 3.616 A and the dihedral angle is 8.8831.
Compound 2 exhibits an extended three-dimensional supramo-
lecular network via hydrogen bonding and
tions (Fig. 3d).
p–p stacking interac-
The most significant structure of Compound 2 is a tetramole-
cular water cluster which consists of four water molecules
connected by hydrogen bond, belongs to I4 symmetry (Fig. 3c).
(O3W–H5W ꢀ ꢀ ꢀ O3W [3/2ꢁy, x, 3/2ꢁz], d (O ꢀ ꢀ ꢀ O)¼1.95(3),
+N–H ꢀ ꢀ ꢀ O¼1251) (Table 6).
Compound 3 consists of a [SiMo MoV2O40
]
6ꢁ
anion and six
anion contains a
VI
10
6ꢁ
[C5H7N2]þ cations (Fig. 4a). [SiMo MoV2O40
]
VI
10
center SiO4 tetrahedron and 12 MoO6 octahedrons. Based on bond
valence sum calculations [23] and charge balance consideration,
two Mo atoms from the [SiMo12O40
6ꢁ
]
are þ5 and the other 10

66
Q. Deng et al. / Journal of Solid State Chemistry 200 (2013) 60–69
3.2. Characterization of compounds
896, 773 cmꢁ1 in Compound 2 and 3419, 2975, 943, 896,
778 cmꢁ1 in Compound 3, which ascribe to v(O–H), v(N–H),
v(Mo–Ot), v(Mo–Oa) and v(Mo–Ob) respectively. Bands at 1660,
1642, 1542, 1473 cmꢁ1 in Compound 1, 1632, 1550, 1483,
1385 cmꢁ1 and 1661, 1622, 1542, 1474 cmꢁ1 are attributed to
the characteristic peaks of 2-aminopyridine, 3-aminopyridine,
4-aminopyridine in the Compounds 1–3 respectively.
3.2.1. Infrared spectra
The IR spectrums (Fig. 5) exhibit a complex pattern of bands at
3409, 2975, 943, 859, 776 cmꢁ1 in Compound 1, 3419, 2975, 946,
3.2.2. UV spectra
The UV spectra (Fig. 6a–c) of 1–3 were measured in the
aqueous solution at room temperature in the region of 350–
200 nm. The spectra of 2-aminopyridine appear absorption peaks
in 229 and 293 nm, which corresponds to annular conjugate
system transition and
p–p* transition absorption. The spectra of
Compound 1 appear absorption peaks in 226 and 288 nm which
corresponds to O-Mo LMCT (Ligand-to-metalcharge-transfer)
charge transfer transition and 2-aminopyridine molecular-Mo
charge transfer transition absorption. The wide absorption peak of
Compound 1 in 288 nm overlap with the
tion peak (293 nm) in 2-aminopyridine.
p–p* transition absorp-
The result of Compound 2 is similar with Compound 1 (the
absorption peaks of Compound 2 appeared in 228 and 287 nm
range).
The 226 nm absorption peak of Compound 3 corresponding to
O-Mo LMCT (Ligand-to-metalcharge-transfer) charge transfer
Fig. 5. The IR spectroscopy of Compound 1–3.
Fig. 6. (a) The UV spectroscopy of Compound 1; (b) the UV spectroscopy of Compound 2; (c) the UV spectroscopy of Compound 3.

Q. Deng et al. / Journal of Solid State Chemistry 200 (2013) 60–69
67
Fig. 7. (a) The TG-DTA of the Compound 1; (b) the TG-DTA of the Compound 2; (c) the TG-DTA of the Compound 3.
transition absorption and 297 nm absorption peak attribute to 4-
aminopyridine molecular-Mo charge transfer transition absorp-
tion which is red-shifted in comparison with 4-aminopyridine,
that may attributed to the forming of the charge transfer com-
plexes forming new conjugate system which narrow the transi-
2 are located at 563 and 560 nm upon excitation at 223 and
210 nm respectively (Fig. 8a–c). The maximum emission band of
Compounds 1 and 2 are red-shifted in comparison with that of
2-aminopyridine (excitation peak 226 nm, emission peak
478 nm) and 3-aminopyridine (excitation peak 210 nm emission
peak 475 nm). The significant red-shift of the compound’s lumi-
tion energy levels. The
aminopyridine molecules in 262 nm corresponds to the weak
p–p* transition absorption peak of 4-
nescence may be caused by the inter-planar pyridine–pyridine
stacking interactions, which result in a decrease of the HOMO–
LUMO energy gap [24].
p–
shoulder peak of Compound 3 in 240–250 nm range.
p
The maximum emission peak of Compound 3 is located at
522 nm upon excitation at 210 nm which is reasonable to
3.2.3. Thermogravimetric analysis
The TG-DTA analysis of Compounds 1–3 were performed in the
temperature range of room temperatureꢁ700 1C (Fig. 7a–c).
There are three obvious exothermic peaks for Compound 1 (283,
333 and 417 1C), four exothermic peaks for Compound 2 (323,
387, 435 and 464 1C), two exothermic peaks for Compound 3 (372
and 443 1C). TG analysis of Compound 1 shows a 23.33% weight
loss before 390 1C (23.42% for Compound 2 before 405 1C, 23.84%
for Compound 3 before 386 1C) which correspond to the release of
crystal water and organic ligand molecules in accordance with the
calculated value (23.54% for Compound 1, 22.30% for Compound
2 and 23.71% for Compound 3). The peak at 417 1C for Compound 1,
435 and 464 1C for Compound 2 and 443 1C for Compound 3 may be
due to the thermal decomposition of the polyoxoanions framework.
The final residue is assumed to be MoO3, MoSi2 and MoO2.
attribute this emission to the intraligand
p–p* transition. The
maximum emission peak is aslo red-shifted in comparison
with 4-aminopyridine (excitation peak 222 nm, emission
peak 495 nm) which may be attributed to the forming of the
4-aminopyridine molecular-Mo LMCT (Ligand-to-metal charge-
transfer) in Compound 3 that affect the energy level transition.
3.2.5. Catalytic properties
Blank experiments showed that the reaction substrate in a
simulacrum of polluted air was hardly eliminated without
compounds as the catalyst. From the results of the effluent gases
after catalytic reaction, there is no new peak in the GC diagram,
indicating no new organic compounds formed; lime saturated
water formed precipitate and the color of the 0.2% PdCl2 solution
did not change, indicating that there was CO2 but no CO.
Products of the elimination of reaction substrate were CO2 and
H2O.
3.2.4. Fluorescence properties
Compounds 1–3 exhibit fluorescence properties at ambient
temperature. The maximum emission peaks of Compounds 1 and

68
Q. Deng et al. / Journal of Solid State Chemistry 200 (2013) 60–69
Fig. 8. (a) Emission spectrum for Compound 1 and 2-aminopyridine in the solid state; (b) Emission spectrum for Compound 2 and 3-aminopyridine in the solid state;
(c) Emission spectrum for Compound 3 and 4-aminopyridine in the solid state.
Fig. 9. Effect of the reaction temperature on the elimination rate of methanol.
ꢁ1
The results of methanol elimination prove that Compounds 1 and
3 have good oxidation catalytic activity in the test temperature
while Compound 2 does not show the catalytic activity (Fig. 9). With
the rise of temperature from 25 to 150 1C the catalytic activity of
Compounds 1 and 3 improve successively.
The elimination rate of the methanol is 87.7% (For Compound 1)
and 76.8% (For Compound 3) when the reaction temperature is
150 1C, flow velocity of 10 mL minꢁ1, and the concentration of
methanol of 2.75 g mꢁ3. Compound 2 has no catalytic activity that
may attribute to the polarity of the water in Compound 2 that
weakens the adsorbing organic reactant ability and the tetramole-
cular water cluster ring structure which favors formation of more
intramolecular and intermolecular hydrogen bonding to make it
6.1 g mꢁ3 in air and the flow velocity is 4.5 mL min
while
the Compounds 10–30 [15] ((2-C5H7N2)4(PMo12O40)2 ꢀ (2-C5H6N2)6 ꢀ
(C4H8N4)ꢀ H2O (Compound 10), (3-C5H7N2)6 ꢀ (PMo12O40)2 ꢀ (3-
C5H6N2)4 ꢀ H8O4 ꢀ (H2O)8 (Compound 20), (4-C5H7N2)6(PMo12O40)2 ꢀ
(4-C5H6N2)4 ꢀ (C4H6N3) (Compound 30)) show catalytic activity for
the oxidation of acetone in the same reaction conditions that may
attributed to the oxidizing of the main building blocks structure
3ꢁ
4ꢁ
[PMo12O40
]
in Compounds 10–30 is stronger than [SiMo12O40
]
in
Compounds 1–3. Furthermore, acetone is a symmetrical structure
which is more stable than methanol that makes it more difficult to
be oxidized.
structurally more stable [15]. Compound 3 has two Mo atom from
4. Conclusion
6ꢁ
the [SiMo12O40
]
are þ5 oxidation states which reduces oxidiz-
ability of the Compound 3, so Compound 3 has lower catalytic
activity than Compound 1.
In this work, three 3D organic–inorganic hybrids based on POM
and 2/3/4-aminopyridine ligand were synthesized successfully
under hydrothermal conditions. There are a number of hydrogen
The results of acetone elimination prove that Compounds 1–3 do
not show the catalytic activity when the reaction temperature is
from 25 to 160 1C, the initial concentration of the acetone is
bonds and
p–p stacking interactions that existed between the
Compounds 1 and 2 molecules which form the 3D supramolecular

Q. Deng et al. / Journal of Solid State Chemistry 200 (2013) 60–69
69
structure. Compound 3 exhibits an extended three-dimensional
supramolecular network via hydrogen bonding interactions. The
Compounds 1 and 3 have good oxidation catalytic activity while it
does not show catalytic activity in oxidation catalytic acetone. The
elimination rate of the methanol are 87.7% and 76.8%.
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Acknowledgments
The Project was supported by the Hunan Provincial Science
and Technology Plan projects, the Organic Chemistry Key Subject
of Hunan Province and Key Laboratory of Theoretical Chemistry
and Molecular Simulation of Ministry of Education, and the
Hunan University of Science and Technology.
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Appendix A. Supporting information
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