A new Mo/V-oxide-based cationic species templated by Keggin polyoxotungstates (4-) and its catalytic activity in benzene hydroxylation

Article abstract of DOI:10.1016/j.molstruc.2012.06.054

Three new polyoxotungstate-templated Mo/V-oxide-based organic-inorganic hybrid compounds, [Mo₂V₂O₉(bpy) ₆][XW_12-xV_xO₄₀] (X = Si(1) and Ge(2), x = 0; X = P(3), x = 1) have been hy

Full text of DOI:10.1016/j.molstruc.2012.06.054

Journal of Molecular Structure 1030 (2012) 83–88
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
A new Mo/V-oxide-based cationic species templated by Keggin
polyoxotungstates (4-) and its catalytic activity in benzene hydroxylation
b,
Qing Wu a, Hua Yang b,c, Hong-Wei Cheng a, Zhi-Guang Liu a, Wan-Sheng You a, , Shuang Gao
⇑
⇑
a Institute of Chemistry for Functionalized Materials, Liaoning Normal University, 850 Huanghe Road, Dalian 116029, PR China
b Dalian Institute of Chemical Physics, The Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, PR China
c Graduate School of the Chinese Academy of Sciences, Beijing 100049, PR China
h i g h l i g h t s
"
"
"
A new Mo/V-oxide-based cationic species.
A Mo/V-oxide-based cation templated by Keggin polyoxotungstates.
Catalysis of benzene hydroxylation.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 May 2012
Received in revised form 25 June 2012
Accepted 26 June 2012
Available online 9 July 2012
Three new polyoxotungstate-templated Mo/V-oxide-based organic–inorganic hybrid compounds,
[Mo2V2O9(bpy)6][XW12ꢀxVxO40] (X = Si(1) and Ge(2), x = 0; X = P(3), x = 1) have been hydrothermally
synthesized and structurally characterized by single-crystal X-ray diffraction. They are isomorphic and
consist of Keggin polyoxotungstate anions and a novel Mo/V-oxide-based cationic species, [Mo2V2O9
(bpy)6]4+. The cationic species exhibits a finite Z-shaped chain, which is composed of corner-sharing
{MoO4N2}. Octahedra and {VO2N4} octahedra via V–O–Mo–O–Mo–O–V mode. Electrochemical measure-
ments of 1 and 3 show that three pairs of semi-reversible redox peaks are corresponding to redox pro-
cesses of W and Mo centers. 1 and 3 are active catalysts for the hydroxylation of benzene with oxygen
as the oxidant. Most interestingly, their active sites are on the cation [Mo2V2O9(bpy)6]4+ instead of the
Keggin polyoxotungstate anions.
Keywords:
Polyoxometalate
Organic–inorganic hybrid
Mo/V-oxide-based cation
Hydroxylation
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
[PMo12O40] [17] and the 1D Keggin-templated pure Mo-oxide-
based organic–inorganic hybrid cationic chain, Ca[Mo5O14
Organic–inorganic hybrid materials based on polyoxometalates
have attracted considerable interest in recent years due to the
spectacular crystal structures and properties [1–8]. Employing
2,20-bipy, 4,40-bipy, 1,2,3-trz, 1,2,4-trz, Hbpa, pyz, etc., as ligands,
neutral MoVI-oxide-based organic–inorganic hybrid materials had
been synthesized [9–15]. Generally, the metal oxides exhibit anio-
nic (or neutral) phase and are charge-mismatching with other
anions so that it is an immense challenge to synthesize organic–
inorganic materials based MoVI-oxide-based cationic framework.
In 2007, Wang et al. reported the first 1D double-Keggin-templated
Mo/Mn-oxide-based organic–inorganic cationic chain [{Mn(bpy)
(py)(H2O)2}{Mo12O34(bpy)12}][PMo12O40]2ꢁ2H2O [16], then our
group reported the 2D Keggin-templated Mo/V-oxide-based
organic–inorganic hybrid cationic framework [Mo9VO28(bpy)9]
(bpy)5][PMo11VO40][0.5bpy]ꢁ4.5H2O [18]. In self-assembling the
Mo-oxide-based organic–inorganic cationic framework, it is found
that polyoxometalate anions may adopt an important role in tem-
plates inducing the self-assembly of the cationic framework and
the charge compensating anions. It is also found that they are only
3ꢀ
Keggin PMo
O
or PMo11VO4ꢀ until now. It would be interesting
12
40
40
nꢀ
to explore the role of Keggin XW
O
anions in inducing
12
40
self-assembly of Mo-oxide-based organic–inorganic cationic
frameworks and their crystallization. In addition, Keggin vana-
dium-substituted polyoxomolybdates have been reported as effi-
cient catalysts for benzene hydroxylation in recent years [19–22].
However, among these vanadium modified heteropolyacid cata-
lysts, the catalytic active sites are all in their anion parts. Herein
we employed Keggin polyoxotungstates (XW12ꢀxVxO440ꢀ, X = Si and
Ge, x = 0; X = P, x = 1) as templates to synthesize three isostructural
organic–inorganic hybrid compounds based on
V-oxide-based cationic framework, [Mo2V2O9(bpy)6][SiW12O40] 1;
[Mo2V2O9(bpy)6][GeW12O40 2; [Mo2V2O9(bpy)6][PW11VO40 3.
a new Mo/
⇑
Corresponding authors. Tel.: +86 411 82159378; fax: +86 411 82156858.
E-mail addresses: wsyou@lnnu.edu.cn (W.-S. You), sgao@dicp.ac.cn (S. Gao).
]
]
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.06.054

84
Q. Wu et al. / Journal of Molecular Structure 1030 (2012) 83–88
The catalytic behavior of 1 and 3 showed that the Mo/V-oxide-
based cation is the truly active site for the benzene hydroxylation.
The structures were solved by direct methods and refined by
Full-Matrix Least-squares methods on F2 using the SHELXS-97
software. All of the non-hydrogen atoms were refined anisotrop-
ically. The hydrogen atoms attached to carbon atoms were added
theoretically. A summary of the crystallographic data and struc-
tural determination for them is provided in Table 1. Selected
bond lengths, bond angles and hydrogen bonds of 1, 2 and 3
are listed in Tables S1–S4. CCDC-840480, 840481 and 840482
contain the supplementary crystallographic data for 1, 2 and 3
in this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Center via www.ccdc.cam.a-
c.uk/data_request/cif.
2. Experimental section
2.1. Materials and general methods
H4SiW12O40ꢁ19H2O, H4GeW12O40ꢁ28H2O and K4PW11VO40ꢁ2H2O
were synthesized according to the literature methods and identified
by IR spectroscopy [23–25]. [(CH3)4N]4[SiW12O40] and [(CH3)4N]4
[PW11VO40] were synthesized according to simple precipitation
methods, using (CH3)4NOH, H4SiW12O40ꢁ19H2O and K4PW11
VO40ꢁ2H2O as the raw materials, identified by IR spectroscopy. All
other chemicals were purchased from commercial sources and used
without further purification. C, H and N content were determined
by a Perkin–Elmer 2400 CHN elemental analyzer after the samples
were dried at 50 °C for 6 h to remove adsorbed water molecules. IR
spectra were recorded in the range 400–4000 cmꢀ1 on a TENSOR27
Bruker AXS spectrometer with a pressed KBr pellet. TG–DTA analy-
sis was carried out on a Pyris Diamond TG/DTA instrument in
immobile airflow with a heating rate of 10 °C minꢀ1. X-ray powder
diffraction (XRPD) patterns were recorded on a D8 Advance instru-
2.3. Catalytic benzene hydroxylation of 1 and 3
1 or 3 (0.05 mmol), ascorbic acid (5 mmol), 2,2,6,6-tetramethyl-
1-piperidine-N-oxyl free radical (1 mmol), 6.8 mL of acetonitrile
and benzene (10 mmol) were added into a 50 mL stainless steel
autoclave with magnetic stirrer. The reaction was carried out un-
der 2 MPa of O2 for 80 min at 80 °C. After cooling, 0.2 g toluene
was added as internal standard. The products were detected by
GC 7890A equipped with FID and a capillary column SE-30. Oven
temperature was programmed from 50 °C to 180 °C.
ment in the angular range of 2h = 5–60° at 293 K with CuKa radia-
tion. All electrochemical measurements were carried out on a CHI
600B electrochemical workstation at room temperature. The work-
ing electrodes were the modified carbon paste electrodes (1-CPE
and 3-CPE). A platinum wire was used as the counter electrode
and an Ag/AgCl (3 M KCl) was the reference electrode. The modified
carbon paste electrodes of 1 and 3 were fabricated as follows: 0.5 g
of graphite powder and 30 mg of 1 or 3 were mixed and ground to-
gether with an agate mortar and pestle to achieve a uniform and dry
mixture. To the mixture, 0.3 mL of paraffine was added and stirred
with a glass rod, then the homogenized mixture was used to pack
3 mm inter diameter quartz tubes. The surface was wiped with
weighing paper. The electrical contact was established with a cop-
per rod through the back of the electrode.
Yield of phenol=% ¼ phenol=initial benzene ꢂ 100%:
Selectivity to phenol=% ¼ phenol=ðphenol þ benzoquinone
þ diphenols þ biphenyl
þ other byproductÞ ꢂ 100%:
3. Results and discussion
3.1. Synthesis
The successful isolation of 1, 2 and 3 depends on the use of
hydrothermal techniques. However, hydrothermal synthesis is a
relatively complex process because many factors can influence
the outcome of reaction, such as the ratio of initial reactants,
2.1.1. Synthesis of [Mo2V2O9(bpy)6][SiW12O40] 1
A mixture of H4SiW12O40ꢁ19H2O (0.1 mmol), MoO3 (0.5 mmol),
V2O5 (0.1 mmol), 2,20-bpy (0.5 mmol), and water (10 mL) was
sealed in a 23 mL Teflon reactor under autogenous pressure at
160 °C for 4 days, and then cooled to room temperature at a rate
of 10 °C hꢀ1. Yellow crystals were obtained in 43% yield (based
on W). Calcd for C60H48N12O49SiMo2V2W12 (4249.15): C 16.95, H
1.13, N 3.95%. Found: C 16.94, H 1.17, N 3.93%.
Table 1
Crystallographic data and structural refinement summary for complexes 1, 2 and 3.
Complexes
Formula
1
2
3
C
60H48N12O49
C60H48N12O49
GeMo2V2W12
4293.65
C60H48N12O49
PMo2V3W11
4119.12
SiMo2V2W12
4249.15
2.1.2. Synthesis of [Mo2V2O9(bpy)6][GeW12O40] 2
F.W.
The preparation of 2 was similar to that of 1 except that H4Ge-
Crystal
system
Space group
a (Å)
b (Å)
c (Å)
Triclinic
Triclinic
Triclinic
W
12O40ꢁ28H2O was used instead of H4SiW12O40ꢁ19H2O. Yellow
crystals were obtained in 17% yield (based on W). Calcd for
60H48N12O49GeMo2V2W12 (4293.65): C 16.77, H 1.12, N 3.91%.
P-1
P-1
P-1
11.1453(12)
12.2880(13)
16.2631(17)
106.852(10)
94.839(2)
90.4140(10)
2122.9(4)
1
11.1267(13)
12.3320(14)
16.2852(19)
106.847(2)
94.900(2)
90.486(2)
2129.6(4)
1
3.348
1934
2.16–25.02
10743
11.1597(12)
12.2580(13)
16.2745(17)
106.963(2)
94.685(2)
90.365(2)
2121.2(4)
1
3.225
1866
1.83–25.02
10693
C
Found: C 16.71, H 1.14, N 3.90%.
a
(°)
2.1.3. Synthesis of [Mo2V2O9(bpy)6][PW11VO40] 3
b (°)
The preparation of 3 was similar to that of 1 except that
K4PW11VO40ꢁ2H2O was used instead of H4SiW12O40ꢁ19H2O, and
the hydrothermal reaction took place at 170 °C for 3 days. Red
crystals were obtained in 40% yield (based on W). Calcd for
c
(°)
V (Å3)
Z
Dc (mg/m3)
F(000)
h range (°)
3.324
1916
1.83–23.90
C60H48N12O49PMo2V3W11 (4119.12): C 17.48, H 1.16, N 4.08%;
Found: C 17.15, H 1.21, N 4.00%.
Refl. collected 9710
Indep. refl.
6518
7411
7384
[Rint = 0.0358]
1.054
0.0631
[Rint = 0.0380]
1.000
0.0604
[Rint = 0.0343]
1.079
0.0632
2.2. X-ray crystallographic study
GOF on F2
Final Ra
Final Rw
a
Crystal data of 1, 2 and 3 were collected with a SMART APEX II-
CCD X-ray single crystal diffractometer at 293 K with graphite-
monochromatic MoKa radiation (k = 0.71073 Å).
0.1318
0.1583
0.1640
a
R1
=
R
||F0| ꢀ |Fc||/R|F0|.

Q. Wu et al. / Journal of Molecular Structure 1030 (2012) 83–88
85
Fig. 1. ORTEP drawing of structural unit of 1, 2 and 3 with thermal ellipsoids at 30% probability. All hydrogen atoms are omitted for clarity.
Fig. 3. Polyhedral and ball-stick representation of the two-dimensional supramo-
lecular layer in 1, and 3. All atoms are omitted for clarity. Keggin
2
H
heteropolyoxometalate anions = blue polyhedra, MoO2N4 octahedra = purple,
VO2N4 octahedra = yellow, C = gray, N = blue. (For interpretation of the references
to color in this figure legend, the reader is referred to the web version of this
article.)
Fig. 2. Packing diagram of 1, 2 and 3 viewed along the crystallographic b axis.
Keggin heteropolyoxometalate anions = blue polyhedra. (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of
this article.)
3.2. Crystal structure
X-ray crystallography shows that 1, 2 and 3 are isomorphic and
consist of a Mo/V-oxide-based cation [Mo2V2O9(bpy)6]4+ and a
4ꢀ
heteropolyanion [XM12O40
]
(X = Si and Ge, M = W; X = P,
reaction time, pH value, temperature, etc. [26–28]. Synthetic
experiments of 1, 2 and 3 showed that the pH value of the reaction
system is crucial for the crystallization. 1, 2 and 3 could only be
obtained in the pH range of 4.5–5.5. In addition, we attempted to
use H3PW12O40ꢁ29H2O or K5BW12O40ꢁ14H2O instead of H4Si-
M = 11/12 W + 1/12 V), as shown in Fig. 1. The heteropolyanion
exhibits the well-known -Keggin structure [29,30], which is
a
formed from twelve MO6 octahedra and one XO4 tetrahedron.
The central X atom is located at the inversion center, which indi-
cates that the central X atom is surrounded by a cube of eight oxy-
gen atoms with each oxygen site half-occupied. For 3, each W atom
is disordered with one crystallographically independent metal po-
sition constrained as 11/12 W and 1/12 V. All X–O and M–O bond
lengths are in the normal ranges (Tables S1–S3).
W
12O40ꢁ19H2O, H4GeW12O40ꢁ28H2O and K4PW11VO40ꢁ2H2O to syn-
thesize corresponding compounds, but failed. The experimental
result demonstrates the formation or the crystallization of
[Mo2V2O9(bpy)6]4+ ions may depend on ꢀ4 valence Keggin anions.

86
Q. Wu et al. / Journal of Molecular Structure 1030 (2012) 83–88
Fig. 4. The X-ray powder diffraction (XRPD) of simulated (a) and experimental patterns (b) of 1 and 3.
Fig. 5. Cyclic voltammograms of the 1-CPE and 3-CPE in the CH3COOH–CH3COONa solution (pH = 4) at different scan rates (from inner to outer: 50, 100, 150, 200, 250, 300,
350, 400 mV sꢀ1).
The [Mo2V2O9(bpy)6]4+ cation is an organic–inorganic hybrid
molybdenum–vanadium oxide framework, which exhibits a finite
Z-shaped chain. All Mo centers possess the octahedral {MoO4N2}
coordination geometries (Mo–N = 2.236(17)–2.270(15) Å, Mo–
O = 1.671(14)–2.213(13) Å) and all V centers possess the octahe-
dral {VO2N4} coordination geometries (V–N = 2.107(16)–2.291
(16) Å, V–O = 1.586(14)–1.657(13) Å). The bpy ligands are coordi-
nated directly to the Mo and V centers. It is noted that the finite
Z-shaped chain is composed of corner-sharing {MoO4N2} octahedra
and {VO2N4} octahedra via V–O–Mo–O–Mo–O–V mode. The angles
of Mo–O–V and O–Mo–O are 161.7–162.5 and 85.6–86.5°, respec-
tively. Viewed along the crystallographic b axis, the molybdenum–
vanadium oxide cations and the Keggin polyxometalate anions are
arrayed along the c axis (Fig. 2). In addition to the electrostatic
interactions in 1, 2 and 3, there are weak hydrogen-bonding inter-
actions between the cationic chains and the polyoxometalate an-
ions, as shown in Fig. 3 and Table S4.
3.3. IR spectra
The IR spectra of 1, 2 and 3 are shown in Fig. S1. The character-
istic peaks at 921, 963, 864 and 795 cmꢀ1 for 1 are attributed to
m
as(Si–O),
878, 964, 824 and 778 cmꢀ1 for 2 are attributed to
as(W–Ot), as(W–Ob–W) and as(W–Oc–W) vibrations, respec-
tively. In the IR spectrum of 3, the characteristic peaks at 960,
864, 811 cmꢀ1 are attributed to
as(W–Ot), as(W–Ob–W) and
as(W–Oc–W) vibrations while peaks at 1086, 1063 cmꢀ1 are
m
as(W–Ot),
m
as(W–Ob–W) and
m
as(W–Oc–W) vibrations;
m
as(Ge–O),
m
m
m
m
m
m
attributed to m(P–O) vibrations [23]. A series of characteristic peaks
at 1161–1605 cmꢀ1 are attributed to the bpy ligand for 1, 2 and 3.
3.4. TG analysis
The TG curves of 1, 2 and 3 are shown in Fig. S2. Their weight
loss below 400 °C corresponds to the loss of adsorbed water and
air. The weight loss in the range of 400–580 °C is ascribed to the
loss of organic molecules bpy, 22.55% (calcd 22.03%) for 1,
21.95% (calcd 21.80%) for 2, 23.55% (calcd 22.72%) for 3.
In 1, 2 and 3, all Mo atoms are in +6 oxidation state, and all V
atoms are in +5 oxidation state, based on the charge balance con-
sideration and bond valence sum calculations [31,32].

Q. Wu et al. / Journal of Molecular Structure 1030 (2012) 83–88
87
Table 3
3.5. XRD analysis
Catalytic activities of 1 and 3 and their recycle ones in the hydroxylation of benzene.
Runb
Yield of phenola (%)
The experimental and simulated XRPD patterns of 1 and 3 are
shown in Fig. 4. The diffraction peaks match well in position, indi-
cating the crystal phase purity. The difference in reflection intensi-
ties between the simulated and the experimental patterns is due to
the different orientation of the crystals in the powder samples [33].
[Mo2V2O9(bpy)6][SiW12O40
]
[Mo2V2O9(bpy)6][PW11VO40]
1
2
3
4
5
6
6.13
6.20
6.57
6.27
6.26
6.15
6.33
6.61
6.36
6.50
6.23
6.45
3.6. Cyclic voltammetry
a
Reaction conditions: catalyst 0.05 mmol, benezene 10 mmol, acetonitrile
Fig. 5 shows that the cyclic voltammetric behavior of 1-CPE and
3-CPE in the CH3COOH–CH3COONa solution (pH = 4) at different
scan rates. Three pairs of semi-reversible redox peaks, which are
labeled as I–I0, II–II0 and III–III0, were observed in the potential do-
main of ꢀ800 to 600 mV. The mean peak potentials at the scan rate
of 200 mV sꢀ1 (E1/2 = (Epa + Epc)/2) were +305 (I–I0), +6 (II–II0),
ꢀ333 (III–III0), for 1-CPE, +325 (I–I0), ꢀ160 (II–II0), ꢀ343 (III–III0)
mV for 3-CPE, respectively. Redox peaks II–II0 and III–III0 corre-
spond to processes of W centers and peak I–I0 corresponds to pro-
cess of Mo center. With the scan rate increasing, the peak
potentials change gradually: the cathodic peak potentials shifted
to the negative direction and the corresponding anodic peak poten-
tials to the positive direction, namely, the peak-to-peak separation
between the corresponding cathodic and anodic peaks increased,
but the mean peak potentials did not change on the whole. This
might be because the hybrid materials are solid and the electron
exchanging rate between the graphite and the hybrid materials is
decreased to some extent [34].
6.8 mL, TEMPO 1 mmol, ascorbic acid 5 mmol, O2 2.0 MPa, 80 °C, 80 min for each
run.
b
After each run, reaction mixture was centrifuged and the solution was removed,
reactant (except the catalyst) was recharged to perform the next reaction.
are shown in Figs. S3 and S4. Compared them with Fig. S1 and
Fig. 4 respectively, it is found that corresponding main peaks in
IR spectra and diffraction peaks in XRD patterns are consistent.
This shows that 1 and 3 are stable in the catalytic reactions.
4. Conclusions
Three new polyoxotungstate-templated Mo/V-oxide-based or-
ganic–inorganic hybrid compounds, [Mo2V2O9(bpy)6][XW12ꢀxVx
O40] (X = Si and Ge, x = 0; X = P, x = 1), have been reported. They
are isomorphic and consist of classical Keggin polyoxotungstate
anions and a novel Mo/V-oxide-based cationic species, [Mo2-
V2O9(bpy)6]4+. The cationic species exhibits a finite Z-shaped chain.
The experimental result demonstrates the formation or the crystal-
lization of [Mo2V2O9(bpy)6]4+ ions depends on ꢀ4 valence Keggin
anions. Electrochemical measurement of 1 and 3 shows three pairs
of semi-reversible centers. 1 and 3 were found to be active in the
benzene hydroxylation using oxygen as the oxidant. redox
3.7. Catalytic hydroxylation of benzene
Recently, we found that benzene could be oxidized quickly to
phenol on the V-based catalysts by O2 in the existence of TEMPO
(2,2,6,6-tetramethyl-1-piperidine-N-oxyl free radical) [35,36]. So
the catalytic performances of 1 and 3 and their control ones were
screened in the same reaction conditions. As shown in Table 2, sim-
ilar to [(CH3)4N]4[PMo11VO40][22] (entry 5), a classic catalyst in the
benzene hydroxylation, both 1 and 3 exhibit good catalytic activi-
ties with above 99% selectivity for phenol. The yields of phenol can
reach up to 6.13% and 6.33% (entries 1 and 2), respectively. As it is
known, the catalytic activity of [(CH3)4N]4[PMo11VO40] catalyst de-
pends on its anion part. For the control experiments, [(CH3)4N]4[Si-
peaks corresponding to redox processes of
W and Mo The
Mo/V-oxide-based cationic species, [Mo2V2O9(bpy)6]4+, should be
truly reactive parts. So We supposed a compound both with the ac-
4ꢀ
tive anion [PMo11VO40
]
and the active cation [Mo2V2O9(bpy)6]4+
would be an efficient catalyst in the benzene hydroxylation. With
this purpose, the synthesis and catalysis of [Mo2V2O9(bpy)6]
[PMo11VO40] is ongoing.
W
12O40] and [(CH3)4N]4[PW11VO40] were studied in the same
Acknowledgment
reactions, but both of the phenol yields were trace (entry 3 and
4). These results indicated that the active sites of 1 and 3 for ben-
Financial support from the Major State Basic Research Develop-
ment Program of China (No. 2009CB623505) is gratefully
acknowledged.
zene hydroxylation is the cation [Mo2V2O9(bpy)6]4+ rather than the
4ꢀ
anions [SiW12O40
]
or [PW11VO40]
4ꢀ. It is the first example that
the catalytic activity is truly from the cationic part of polyoxomet-
alate compounds for benzene hydroxylation.
Appendix A. Supplementary material
As shown in Table 3, the catalytic activity of 1 and 3 remains al-
most unchanged in recycles of 6 runs for benzene hydroxylation
reactions. This shows that it is a heterogeneous catalysis. After
the 6 recycles, IR spectra and XRD patterns of filtrated catalysts
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molstruc.2012.
06.054.
Table 2
References
Catalytic activities of 1 and 3 and their control ones in the hydroxylation of benzene.
Entry Catalysts
Yield of
Selectivity to
phenol (%)
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phenola (%)
1
2
3
4
5
[Mo2V2O9(bpy)6][SiW12O40
[Mo2V2O9(bpy)6][PW11VO40
[(CH3)4N]4[SiW12O40
[(CH3)4N]4[PW11VO40
[(CH3)4N]4[PMo11VO40
]
6.13
6.33
Trace
Trace
6.96
>99
>99
–
–
>99
]
]
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]
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