A μ-AsO4-Bridging Hexadecanuclear Ni-Substituted Polyoxotungstate

Article abstract of DOI:10.1021/acs.inorgchem.1c00056

A novel tetrahedral μ-AsO4-bridging hexadecanuclear Ni-substituted silicotungstate (ST) Na21H10[(AsO4){Ni8(OH)6(H2O)2(CO3)2(A-α-SiW9O34)2}2]·60H2O (1) was made by the reactions of trivacant [A-α-SiW9O34]10- ({SiW9}) units with Ni2+ cations and Na3AsO4·12H2O and characterized by IR spectrometry, elemental analysis, thermogravimetric analysis (TGA), and powder X-ray diffraction (PXRD). 1 contains a novel polyoxoanion [(AsO4){Ni8(OH)6(H2O)2(CO3)2(A-α-SiW9O34)2}2]31- built by four trivacant Keggin [A-α-SiW9O34]10- fragments linked through an unprecedented [(AsO4){Ni8(OH)6(H2O)2(CO3)2}2]9+ cluster, where the tetrahedral AsO4 acts as an exclusively μ2-bridging unit to link multiple Ni centers; such a connection mode appears for the first time in polyoxometalate chemistry. Furthermore, the electrochemical and catalytic oxidation properties of compound 1 have been investigated.

Full text of DOI:10.1021/acs.inorgchem.1c00056

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A μ‑AsO4‑Bridging Hexadecanuclear Ni-Substituted
Polyoxotungstate
Chen Lian, Hai-Lou Li, and Guo-Yu Yang*
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ABSTRACT: A novel tetrahedral μ-AsO4-bridging hexadecanu-
clear Ni-substituted silicotungstate (ST) Na21H10[(AsO4)-
{Ni8(OH)6(H2O)2(CO3)2(A-α-SiW9O34)2}2]·60H2O (1) was
made by the reactions of trivacant [A-α-SiW9O34]10− ({SiW9})
units with Ni2+ cations and Na3AsO4·12H2O and characterized by
IR spectrometry, elemental analysis, thermogravimetric analysis
(TGA), and powder X-ray diffraction (PXRD). 1 contains a novel
polyoxoanion [(AsO4){Ni8(OH)6(H2O)2(CO3)2(A-α-
SiW9O34)2}2]31− built by four trivacant Keggin [A-α-SiW9O34]10−
fragments linked through an unprecedented [(AsO4)-
{Ni8(OH)6(H2O)2(CO3)2}2]9+ cluster, where the tetrahedral
AsO4 acts as an exclusively μ2-bridging unit to link multiple Ni
centers; such a connection mode appears for the first time in
polyoxometalate chemistry. Furthermore, the electrochemical and catalytic oxidation properties of compound 1 have been
investigated.
22
[{Ni6(H2O)4(μ2−H2O)4(μ3−OH)2}(χ-SiW9O34)2]10−
,
INTRODUCTION
■
2 3
[ N i 9 ( O H ) 3 ( H 2 O ) 6 ( H P O 4 ) 2 ( P W 9 O 3 4 ) 3 ] 1 6 −
,
Polyoxometalates (POMs), a unique and attractive class of
nanoscale metal-oxo clusters, are constituted by the con-
densation of the edge-, corner-, and face-sharing MO6
polyhedral building units of early transition metals (e.g., W,
Mo, V, and Nb).1−7 The characteristic negative charges endow
them the merits of acting as multidentate O-donor inorganic
ligands. Especially for lacunary POM fragments, the high
reactivity of the exposed surface oxygen atoms facilitates the
integration with versatile metal cations, thereby generating the
functionalized metal-substituted POMs with huge potential
applications.8−11
2 4
25
[Ni9 (OH)6 (H2 O)6 (CO3 )3 (A-α-SiW9 O3 4 )2 ]1 4 −
,
[{Ni4(OH)3(A-α-SiW9O34)}4(OOC(CH2)3COO)6]32−
,
2 6
27
[Ni1 2 (OH)9 WO4 (W7 O2 6 (OH))(PW9 O3 4 )3 ]2 5 −
,
[Ni14(AleH)5(Ale)2(H2O)11(OH)7(A-α-SiW9O34)]12−
,
2 8
[Ni1 4 (OH)6 (H2 O)1 0 (HPO4 )4 (P2 W1 5 O5 6 )4 ]3 4 −
,
2 9
2 8 −
[ { N i 4 ( O H ) 3 ( P O 4 ) } 4 ( P W 9 O 3 4
)
]
,
4
[ N i 1 2 ( O H ) 9 ( C O 3 ) 3 ( P O 4 ) ( S i W 9 O 3 4 ) 3 ] 2 4 −
,
[Ni1 3 (H2 O)3 (OH)9 (PO4 )4 (SiW9 O3 4 )3 ]2 5 −
,
and
Our
30
[Ni25(H2O)2OH)18(CO3)2(PO4)6(SiW9O34)6]50−
.
group has also been active in making POTs with novel
architectures and excellent performance for decades using the
hydrothermal technique and has obtained numerous in-
organic−organic hybrid Ni-substituted POTs, representing
the breakthroughs from isolation to expansion and from
o l i g o m e r s t o p o l y m e r s , s u c h a s [ N i 6 ( μ 3 -
OH)3 (H2O)6(enMe)3(B-a-SiW9O3 4)]−,31 [Ni6 (μ3-
Transition metal (TM)-substituted polyoxotungstates
(POTs) as an important subclass have been a rather hot
subject and have attracted extensive attention. Extraordinary
efforts have brought the flourishing development of TM-
substituted POTs that not only depend on their flexible and
diversified configurations realized by the elaborate regulation
of synthesis strategies but also driven by their prominent
performance in the fields of magnetism, medicine, catalysis,
and materials.12−20 The number of novel architectures
constructed by various TM cations incorporated into lacunary
POTs reported in the literature is constantly increasing with
time. Among them, Ni-substituted POTs have been intensively
explored, and representative cases of structurally, catalytically,
and electrochemically intriguing Ni-substituted POTs include
OH)3(H2O)3(dien)3H3(α-P2W15−O56)],32 [{Ni7(μ3-
3 3
O H ) 3 O 2 ( d a p ) 3 ( H 2 O ) 6 } ( B - α - P W 9 O 3 4 ) ] 2 −
,
[H6Ni20P4W34(OH)4O136(enMe)8(H2O)6]6−,34 {[Ni6(Tris)-
Received: January 7, 2021
Published: February 25, 2021
[H2{Ni5(H2O)5(OH)3(χ-SiW9O34)(β-SiW8O31)}2]24−
,
21
[Ni7(H2O)4(OH)6(SiW8O31)2]12−
,
[Ni7(OH)4(H2O)-
(CO3 )2 (HCO3 )(A-α-SiW9 O3 4 )(β-SiW1 0 O3 7 )]1 0 −
,
https://dx.doi.org/10.1021/acs.inorgchem.1c00056
© 2021 American Chemical Society
Inorg. Chem. 2021, 60, 3996−4003
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Article
3 5
1 2 −
( e n ) 3 ( B T C ) 1 . 5 ( B - α - P W 9 O 3 4 ) ] 8
}
,
condition of alkalinity. Parallel experiments reveal that the pH
of the reaction solution has great influence on the isolation of
the target product. The pH region between 9.2 and 9.8 favors
the formation of 1, and the highest yield was obtained at pH
9.5. Additionally, since the indispensable AsO4 tetrahedral
bridging group in the polyoxoanion was derived from the
introduction of Na3AsO4·12H2O, the effect of the amount of
Na3AsO4·12H2O on the assembly of the target product was
also taken into account. When the dosage varied within the
range of 0.300−0.550 g, 1 could be made, affording the highest
yield when 0.400 g of Na3AsO4·12H2O was added. We also
attempted to obtain the subunit by completely removing
Na3AsO4·12-H2O, but no crystalline products were isolated in
such a system. Additionally, we tried to replace AsO4 with the
tetrahedral PO4 under the same conditions, which did not yield
a similar structure.
[H2Ni24P4W36(OH)12O136(enMe)12(OAc)4(H2O)12]2−, and
[Ni(en)(H2 O)2 ]2 [H4 Ni4 0 P8 W7 2 (OH)1 8 O2 7 2 (en)1 8
-
(OAc)2(WO4)2(H2O)18]8−.36 Since the properties of com-
pounds are intricately linked to their structural features, the
design and preparation of novel Ni-substituted POTs with
anticipative architectures is still attractive in POM chemistry.
Additionally, it is unambiguous that there are extremely few
reports where pure inorganic tetrahedral groups, such as AsO4
and PO4, act as bridges or connectors in the construction of
ST-based aggregates, although a large number of Ni-containing
STs have already been obtained to date. These findings
provide us with an excellent opportunity and motivate our
efforts in this field. Herein, we use [A-α-SiW9O34]10− ({SiW9}),
Na3AsO4·12H2O, and Ni salts with the participation of
Na2CO3 to explore the possibility of making novel high-
nuclear Ni-substituted poly(STs) bridged by the tetrahedral
group. The introduction of sodium arsenate affords a
fundamental source to obtain the tetrahedral connector during
the course of the structural construction. Adding a large
Structure Description. Single-crystal X-ray diffraction
manifests that 1 crystallizes in the monoclinic space group
C2/c (Table 1) and consists of a unique μ-AsO4-bridging
2−
amount of CO3 not only provides a reaction system with a
Table 1. Crystallographic Data and Structure Refinement
high pH value that is conducive to the formation of POTs with
a high-nuclear Ni-oxo cluster substitution but can also
cooperate with the tetrahedral AsO4 group to produce novel
configurations. Fortunately, we successfully prepared a novel μ-
AsO4-bridging hexadecanuclear Ni-substituted ST
Na2 1 H1 0 [(AsO4 ){Ni8 (OH)6 (H2 O)2 (CO3 )2 (A-α-
SiW9O34)2}2]·60H2O (1) in which the polyoxoanion can be
considered to be fabricated by an unseen [(AsO4)-
{Ni8(OH)6(H2O)2(CO3)2}2]9+ cluster and four {SiW9} frag-
ments through 24 μ-O linkers and 12 μ4-O linkers.
Intriguingly, the [(AsO4){Ni8(OH)6(H2O)2(CO3)2}2]9+ clus-
t e r i s c o m p o s e d o f t w o e q u i v a l e n t
[Ni8(OH)6(H2O)2(CO3)2]6+ fragments that are connected
by a tetrahedral μ-AsO4 group. Furthermore, the electro-
chemical and catalytic oxidation properties of 1 have been
investigated.
for 1
1
empirical formula
formula weight
crystal system
space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å−3
Z
μ (mm−1
F(000)
T (K)
C4H150AsNa21Ni16O228Si4W36
12075.27
monoclinic
C2/c
44.3458(19)
14.7101(6)
39.7346(17)
90
115.1840(10)
90
23456.3(17)
4
)
)
19.136
21720
296(2)
EXPERIMENTAL SECTION
■
limiting indices
−52 ≤ h ≤ 52
−17 ≤ k ≤ 17
−47 ≤ l ≤ 47
100809
Synthesis of 1. 1 was synthesized by the reactions of Na10[A-α-
SiW9O34]·18H2O (2.995 g, 1.078 mmol), NiCl2·6H2O (0.702 g, 2.954
mmol), Na2CO3 (1.002 g, 9.453 mmol), and [H2N(CH3)2]·Cl (0.704
g, 8.634 mmol) with Na3AsO4·12H2O (0.402 g, 0.948 mmol). The
mixture was dissolved in 40 mL of distilled water, vigorously stirred
for 15 min (pH 9.5), sealed in a 200 mL Teflon reactor at 100 °C for
2 h, and then cooled to ambient temperature. The pH value after the
reaction was 9.3. Filtering and evaporating the solution for several
days resulted in green block crystals of 1. Yield: ca. 21.35% (based on
NiCl2·6H2O). Elemental analysis calcd for 1 (%): C, 0.40; H, 1.25; N,
0.00. Found: C, 0.48; H, 1.23; N, 0.26.
no. of reflections collected
no. of independent reflections
Rint
data/restrains/parameters
GOF on F2
20350
0.0584
20350/66/1449
1.007
final R indices [I > 2σ(I)]
R1 = 0.0446
wR2 = 0.1159
R1 = 0.0525
wR2 = 0.1202
3.682, −2.736
R indices (all data)
RESULTS AND DISCUSSION
■
largest difference peak and hole (e Å−3
)
Synthetic Discussion. Up to now, there have been few
studies on the μ-AsO4-bridging POTs,37 let alone μ-AsO4-
bridging high-nuclear Ni-containing POTs, which is mainly
because the tetrahedral group usually acts as a μ3- or μ4-
bridging unit to stabilize the cores of the Ni-oxo clusters rather
than as a μ2-bridging unit to connect the Ni-substituted POTs
to form larger poly(POTs).28−30 To overcome this obstacle, a
hexadecanuclear Ni-substituted ST polyoxoanion [(AsO4)-
{Ni8(OH)6(H2O)2(CO3)2(A-α-SiW9O34)2}2]31− (1a, Figure
1a and b), 60 lattice water molecules, and 21 Na+ ions.
Bond valence sum (BVS) calculations38 demonstrate that the
oxidation states of all W, As, Si, and Ni atoms are +6, +5, +4,
and +2, respectively (Table S1). Furthermore, the BVS values
of O15, O16, O19, O21, O25, and O28 are 1.054, 1.059,
1.097, 1.039, 1.034, and 1.094, respectively, confirming that all
the μ3-O atoms are OH groups; the values of the terminal O35
and O41 are 0.309 and 0.299, indicating coordinate water
2−
large amount of inorganic CO3 was purposely introduced in
the synthesis process, which was expected to play the role of a
stabilizer to combine with the Ni-oxo clusters; therefore, the
tetrahedral AsO4 possesses more opportunities as a μ-bridging
unit to link Ni-substituted POTs. 1 was prepared under the
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ions in the [(AsO4){Ni8(OH)6(H2O)2(CO3)2}2]9+ cluster
exhibit a six-coordinate octahedral geometry with Ni−O
bond lengths of 2.012(7)−2.237(7) Å. Additionally, the
hexadecanuclear Ni-oxo cluster can be structurally interpreted
as being formed by four defective-cubane {Ni4} clusters with
the assistance of one μ-AsO4 and four μ3-CO3.
It should be noted that Hill’s group has also reported a
hexadecanuclear Ni-oxo cluster-substituted tetramer
[{Ni4(OH)3(AsO4)}4(B-a-PW9O34)4]28− (2, Figure S2a).39
However, several structural differences can be easily observed
between them. 1a is a silicotungstate comprised of [A-α-
SiW9O34]10− units, while 2 is a tungstophosphate tetramer with
[B-a-PW9O34]9− units (Figure S2c and d). Hexadecanuclear
Ni-oxo clusters are discrepant; 1a contains four defective-
cubane {Ni4} clusters, while there are four cubane {Ni4}
clusters in 2 (Figure S2e and f). 1a includes two types of
inorganic groups (four CO3 groupsand one AsO4 groups) that
work together to connect and stabilize the {Ni16} cluster, but
the four AsO4 groups in 2 support the central {Ni16} cluster. 1a
possesses four coordinate water molecules, but 2 is without
coordinate water molecules. The distribution motifs of the four
POT units in 1a and 2 are distinguishing, exhibiting the
sloping triangular pyramid configuration and the tetrahedral
configuration, respectively (Figure S2g/h).
Alternatively, 1a can be viewed as two dimeric subunits,
[Ni8(OH)6(H2O)2(CO3)2(A-α-SiW9O34)2]14− {Ni8(SiW9)2},
that are connected via a AsO4 tetrahedron (Figure 2a and b)
in which the AsO4 plays the role of a purely inorganic μ2-
bridging unit to realize the structure that is scarcely observed
in POM chemistry. Each {Ni8(SiW9)2} subunit is comprised of
two [Ni4(OH)3(H2O)(A-α-SiW9O34)]5− {Ni4(SiW9)} seg-
ments connected by two μ3-CO3 ligands (Figure 2c). In each
{Ni4(SiW9)}, the trivacant {SiW9} block incorporates a
defective-cubane {Ni4O3} cluster in which three corner-sharing
Ni atoms (Ni1, Ni2, and Ni3) at the bottom that form a triad
occupy the lacunary sites of {SiW9} and are capped by the
apical Ni4 atom via three μ3-OH and two μ3-CO3. The Ni−Ni
distances in the {Ni4O3} cluster are in the range of 2.926−
3.680 Å (Figure S3). Two μ3-CO3 not only guarantee the
junction of the Ni triad to the apical Ni but also to the
corresponding Ni centers of the neighboring {Ni4(SiW9)}
segment. The dimeric {Ni8(SiW9)2} subunit can be also
Figure 1. (a) The polyoxoanion 1a, (b) the simplified structure of 1a,
(c) the hexadecanuclear Ni-oxo cluster [(AsO4 )-
{Ni8(OH)6(H2O)2(CO3)2}2]9+, and (d) the simplified structure
[(AsO4){Ni8(OH)6(H2O)2(CO3)2}2]9+.
molecules. The [(AsO4){Ni8(OH)6(H2O)2(CO3)2(A-α-
SiW9O34)2}2]31− polyoxoanion is a tetrameric assembly
where an unprecedented μ-AsO4-bridging hexadecanuclear
Ni-oxo cluster [(AsO4){Ni8(OH)6(H2O)2(CO3)2}2]9+ (Figure
1c and d) is encapsulated by four {SiW9} fragments through 24
μ-O from 24 W atoms and 12 μ4-O from four central SiO4
groups. Noticeably, the hexadecanuclear Ni-oxo cluster
contains two types of inorganic groups, namely tetrahedral
AsO4 and triangle CO32−, and they play the roles of connector
and stabilizer, respectively, giving rise to a novel [(AsO4)-
{Ni8(OH)6(H2O)2(CO3)2}2]9+ cluster. To the best of our
knowledge, such a linking mode is rarely present in POM
c h e m i s t r y . T h e N i - o x o c l u s t e r [ ( A s O 4 ) -
{Ni8(OH)6(H2O)2(CO3)2}2]9+ can be described as a fusion
of two equivalent octanuclear Ni-oxo clusters
[Ni8(OH)6(H2O)2(CO3)2]6+ bridged by a μ-AsO4 linker.
Each [Ni8(OH)6(H2O)2(CO3)2]6+ cluster is formed by the
condensation of two edge-sharing defective-cubane {Ni4}
clusters and additionally stabilized by two μ3-CO3. All Ni
Figure 2. (a) The polyoxoanion 1a, (b) the dimeric [Ni8(OH)6(H2O)2(CO3)2(A-α-SiW9O34)2]14− subunit; (c) the [Ni4(OH)3(H2O)(A-α-
SiW9O34)]5− segment, (d) the [Ni8(OH)6(H2O)2(CO3)2]6+ cluster, and (e) the trivacant [A-α-SiW9O34]10− block. Color codes are as follows:
WO6, red; SiO4, yellow; Ni atom, bright green; O atom, red; and C atom, black.
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perceived as a special sandwich configuration in which a
[Ni8(OH)6(H2O)2(CO3)2]6+ cluster (Figure 2d and e) is
encapsulated by two {SiW9} blocks by means of 12 μ-O and 6
μ4-O atoms from two {SiW9} moieties. This {Ni8(SiW9)2}
subunit is somewhat similar to the structure of
[Co8(OH)6(H2O)2(CO3)3(A-α-SiW9O34)2]16− (3) previously
reported by Mialane et al.40 Apart from the different elements
of the functional metal atoms, the most significant discrepancy
that needs to be emphasized is the bridged CO32− anion. 3 has
an additional μ-CO3 connecting to two apical Co atoms from
the {Co4} clusters to further stabilize the structure, and the
remaining terminal oxygen points to the outside. However, a
AsO4 group is grafted to the {Ni8(SiW9)2} subunit in the same
position of 1, which not only exerts a stabilizing effect similar
to the μ2-CO3 anion but additionally joins the other subunit to
form a tetramer (Figure S4). In addition, the polyoxoanions
are arranged in the fashion of −A−B−A− along the a and c
axes and show an organized −A−A−A− array along the b axis
(Figure S5).
Furthermore, the electrocatalytic properties of 1 toward the
reduction of hydrogen peroxide (H2O2) and bromate (BrO3 )
−
were also recorded out under the same supporting electrolyte
at a scan rate of 50 mV s−1. As shown in Figure S9, compound
1 has moderate electrocatalytic activities toward the reduction
−
of H2O2 and BrO3 . According to the method introduced by
Keita,45,46 the catalytic efficiency is defined as CAT =
[Ip(POM, substrate) − Ip(POM)]/Ip(POM) × 100%. Based
on the current of peak II (−0.769 V), the CAT values for
H2O2 at concentrations of 0, 5 × 10−4, 1 × 10−3, 3 × 10−3, 5 ×
10−3, 7 × 10−3, and 9 × 10−3 mol L−1 were calculated to 0,
41.0%, 81.6%, 109.9%, 119.9%, 138.3%, and 158.2%,
−
respectively, whereas the CAT values for BrO3 were 0,
19.3%, 23.1%, 27.5%, 33.7%, 39.9%, and 46.7% (Figure 3b).
These results clearly indicate that 1 has better electrocatalytic
−
activities in regard to H2O2 than BrO3 .
Catalytic Oxidation. The catalytic oxidation of sulfides has
attracted widespread and lasting attention, as the oxidation
products sulfones or sulfoxides have multiple applications in
many organic reactions.47,48 POMs have presented good
catalytic activities for the oxidation of sulfides due to their
unique characteristics such as multiple active sites, redox
properties, high stability, etc.49−51 Additionally, the rational
selection of oxidants is also crucial in the catalytic oxidation
process; H2O2 is considered to be a “green oxidant” and is
widely favored.52,53 Additionally, it is generally believed that
the combination of H2O2 and POMs can form a peroxygen
active intermediate, thereby accelerating the oxidation
reaction.54,55 Herein, we explored the performance of 1 as a
heterogeneous catalyst in the acetonitrile solvent using H2O2
as an oxidant to catalyze the oxidation of various sulfides. The
conversion rate of the sulfides and the selectivity of the
catalytic products, sulfoxides and sulfones, were examined by
GC (Figure S10).
Electrochemical Properties. The electrochemical per-
formance of 1 was executed in a pH 5.0 supporting electrolyte
(0.5 mol L−1 Na2SO4 + H2SO4) by the modified CPE. As
shown in Figure 3a, the CV at a scan rate of 50 mV s−1 exhibits
In this catalytic experiment, we first selected methyl phenyl
sulfide (MPS) as the substrate and conducted a blank
comparison experiment. It is clear that 1 has the potential as
a catalyst (Table S2, entries 1 and 2). Besides, a group of
parallel dynamic experiments for the catalytic oxidation of
MPS were carried out to examine the heterogeneity of the
catalytic process under the conditions of 60 °C, 3 mL of
CH3CN as the solvent, and 0.5 mmol substrate. As a control,
the catalyst of one reaction was removed by filtration after 20
min of reaction at the reaction temperature, and then the
reaction systems were sampled at intervals of 20 min. As shown
in Figure 4, the conversion of MPS hardly continued to
increase over time after removing the catalyst, providing strong
evidence for the heterogeneous catalytic process.
Due to the unsatisfactory catalytic effect of compound 1
under the conditions of 1 h, 60 °C, and 3 O/S (91%
conversion and 55% selectivity), we tried to improve the
conversion and selectivity by raising the temperature,
prolonging the reaction time, and increasing the amount of
oxidant; finally, the optimal reaction conditions were 2 h, 70
°C, and 5 O/S (100% conversion and 100% selectivity) (Table
S2). Subsequently, we conducted a series of catalytic oxidation
experiments on various thioethers under the optimal
conditions to verity the universality of 1 as a sulfide oxidation
catalyst. In the selection of sulfide substrates, we considered
the introduced electron-withdrawing or electron-donating
groups (Table 2, entries 7, 10, and 11), the positions of the
aryl sulfide substituents (Table 2, entries 7−9 and 11−13), the
steric hindrance effect (Table 2, entries 1−3 and 4−6), etc., all
Figure 3. (a) Cyclic voltammograms of 1 at a scan rate of 50 mV s−1.
(b) Graph of CAT vs the concentrations of H2O2 and NaBrO3 for 1.
two pairs of redox waves (I/I′ and II/II′) in the potential
region of −1.0 to 0 V, which are assigned to the redox process
of the W centers in the polyoxoanion.41−43 The corresponding
mean peak potentials are −0.379 (I/I′) and −0.714 V (II/II′)
based on the formula E1/2 = (Epa + Epc)/2 (versus the Ag/
AgCl electrode). In addition, the peak potentials become more
negative under the cathodic currents of II after elevating the
scan rate from 100 to 500 mV s−1; the current intensities are
inversely proportional to the scan rates, which manifests such
that the redox process of 1 is surface-controlled (Figure S8).44
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100% conversion and selectivity, while the selectivity of aryl
sulfides with ortho substituent groups is very low (2-
bromothio-anisole and 2-ethoxythioanisole), which is presum-
ably due to the steric hindrance effect (Table 2, entries 7−9
and 11−13). As far as we know, the activity of 1 for the
catalytic oxidation of sulfides is superior to that of the
previously reported Zr-substituted silicotungstate tetramer.56
We speculate it may be related to the presence of more
protonated oxygen atoms in the structure of 1, which is
consistent with the literature.57
Furthermore, under optimal conditions MPS was used as the
substrate to investigate the cyclicity of catalyst 1. After each
reaction, the catalyst was recovered by filtration and reused in
the next round. After five cycles, the catalyst still showed
desirable catalytic activity. The MPS was completely oxidized,
and the selectivity for MPSO2 was as high as 97% (Figure 5).
Figure 4. Dynamic conversion profiles of MPS catalyzed by 1. Red
shows the removal of the catalyst during the reaction. Reaction
conditions are as follows: 0.5 mmol substrate, 3 O/S, 500 S/C, and 3
mL of CH3CN at 60 °C.
Table 2. Selective Oxidation of Various Sulfides
Figure 5. Recycling of the catalytic oxidation of MPS at 70 °C and 5
O/S.
Moreover, the stability of 1 in the catalytic oxidation reaction
was confirmed by the good consistency of the IR spectra of the
catalyst before and after the reaction (Figure S11).
CONCLUSIONS
■
In summary, a novel tetrahedral μ-AsO4-bridging hexadecanu-
clear Ni-substituted silicotungstate Na21H10[(AsO4)-
{Ni8(OH)6(H2O)2(CO3)2(A-α-SiW9O34)2}2]·60H2O (1) was
made. The polyoxoanion is constituted by four [A-α-
SiW9O34]10− fragments linked through an unprecedented
[(AsO4){Ni8(OH)6(H2O)2(CO3)2}2]9+ cluster. It is worth
pointing out that the tetrahedral AsO4 acts as an exclusively μ-
bridging unit linking multiple Ni centers to realize the whole
structure, showing that such a linking mode appears for the
first time in POM chemistry. In addition, 1 has a moderate
electrocatalytic performance for H2O2 and NaBrO3 and shows
a good catalytic activity for the catalytic oxidation of various
sulfides as a heterogeneous catalyst. Additionally, recycling
experiments demonstrate its good conversion and selectivity
over five cycles. This work not only provides us with a feasible
synthetic strategy for constructing Ni-substituted POMs with
novel configurations using tetrahedral AsO4 as μ-bridging unit
but also develops the application potential of Ni-substituted
POMs in the field of sulfide catalytic oxidation.
of which may have a large impact on the conversion and
selectivity. The results of the catalytic oxidation for 15 sulfides
under the same conditions are summarized in Table 2. It can
be clearly observed that 1 shows the good catalytic activity for
most of the selected sulfides and can almost completely
convert these sulfides into corresponding sulfones or
sulfoxides, except for thiophene sulfides (benzothiophene
and dibenzothiophene). It is worth mentioning that the aryl
sulfides containing electron-withdrawing or electron-donating
groups, whether at the meta or para position, have an almost
4000
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Article
efficient visible-light-driven hydrogen evolution. CCS Chem. 2020, 2,
2095−2103.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c00056.
■
sı
(8) Liu, Z.-J.; Wang, X.-L.; Qin, C.; Zhang, Z.-M.; Li, Y.-G.; Chen,
W.-L.; Wang, E.-B. Polyoxometalate-assisted synthesis of transition-
metal cubane clusters as artificial mimics of the oxygen-evolving
center of photosystem II. Coord. Chem. Rev. 2016, 313, 94−110.
(9) Dolbecq, A.; Dumas, E.; Mayer, C. R.; Mialane, P. Hybrid
organic-inorganic polyoxometalate compounds: from structural
diversity to applications. Chem. Rev. 2010, 110, 6009−6048.
(10) Li, H.-L.; Lian, C.; Yin, D.-P.; Yang, G.-Y. Nonanuclear
heterometal five-layer sandwich-type polyoxometalate. Inorg. Chem.
2020, 59, 6131−6136.
Bond valences of some atoms; relevant figures; and IR,
PXRD, and TG curves (PDF)
Accession Codes
CCDC 2015606 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(11) Artetxe, B.; Reinoso, S.; San Felices, L.; Lezama, L.; Gutiérrez-
Zorrilla, J. M.; García, J. A.; Galán-Mascarós, J. R.; Haider, A.; Kortz,
U.; Vicent, C. Cation-directed dimeric versus tetrameric assemblies of
lanthanide-stabilized dilacunary Keggin tungstogermanates. Chem. -
Eur. J. 2014, 20, 12144−12156.
(12) Huang, L.; Wang, S.-S.; Zhao, J.-W.; Cheng, L.; Yang, G.-Y.
Synergistic combination of multi-ZrIV cations and lacunary Keggin
germanotungstates leading to a gigantic Zr24-cluster-substituted
polyoxometalate. J. Am. Chem. Soc. 2014, 136, 7637−7642.
(13) Ibrahim, M.; Lan, Y.; Bassil, B. S.; Xiang, Y.; Suchopar, A.;
Powell, A. K.; Kortz, U. Hexadecacobalt(II)-containing polyoxome-
talate-based single-molecule magnet. Angew. Chem., Int. Ed. 2011, 50,
4708−4711.
AUTHOR INFORMATION
Corresponding Author
Guo-Yu Yang − MOE Key Laboratory of Cluster Science,
School of Chemistry and Chemical Engineering, Beijing
Institute of Technology, Beijing 102488, China; orcid.org/
0000-0002-0911-2805; Email: ygy@bit.edu.cn
■
Authors
Chen Lian − MOE Key Laboratory of Cluster Science, School
of Chemistry and Chemical Engineering, Beijing Institute of
Technology, Beijing 102488, China
Hai-Lou Li − MOE Key Laboratory of Cluster Science, School
of Chemistry and Chemical Engineering, Beijing Institute of
Technology, Beijing 102488, China
(14) Zhao, J.-W.; Zhang, J.; Zheng, S.-T.; Yang, G.-Y. Combination
between lacunary polyoxometalates and high-nuclear transition metal
clusters under hydrothermal conditions: first (3, 6)-connected
framework constructed from sandwich-type polyoxometalate building
blocks containing a novel {Cu8} cluster. Chem. Commun. 2008, 570−
572.
(15) Wu, Q.; Li, Y.-G.; Wang, Y.-H.; Wang, E.-B.; Zhang, Z.-M.;
Clérac, R. Mixed-valent {Mn14} aggregate encapsulated by the
Complete contact information is available at:
i n o r g a n i c
p o l y o x o m e t a l a t e
s h e l l :
https://pubs.acs.org/10.1021/acs.inorgchem.1c00056
[MnIII13MnIIO12(PO4)4(PW9O34)4]31‑. Inorg. Chem. 2009, 48,
1606−1612.
Notes
(16) Li, H.-L.; Lian, C.; Yin, D.-P.; Jia, Z.-Y.; Yang, G.-Y. A new
hepta-nuclear Ti-oxo-cluster-substituted tungstoantimonate and its
catalytic oxidation of thioethers. Cryst. Growth Des. 2019, 19, 376−
380.
(17) Han, X.-B.; Zhang, Z.-M.; Zhang, T.; Li, Y.-G.; Lin, W. B.; You,
W.; Su, Z.-M.; Wang, E.-B. Polyoxometalate-based cobalt-phosphate
molecular catalysts for visible light-driven water oxidation. J. Am.
Chem. Soc. 2014, 136, 5359−5366.
(18) Godin, B.; Chen, Y.-G.; Vaissermann, J.; Ruhlmann, L.;
Verdaguer, M.; Gouzerh, P. Coordination chemistry of the hexavacant
tungstophos-phate [H2P2W12O48]12‑ with FeIII ions: towards original
structures of increa-sing size and complexity. Angew. Chem., Int. Ed.
2005, 44, 3072−3075.
(19) Li, H.-L.; Lian, C.; Yin, D.-P.; Yang, G.-Y. A new octa-Mn-
substituted poly (polyoxotungstate). Dalton Trans. 2019, 48, 14306−
14311.
(20) Zhao, J.-W.; Zhang, J.; Zheng, S.-T.; Yang, G.-Y. Combination
of lacunary polyoxometalates and high-nuclear transition-metal
clusters under hydrothermal conditions. 5. a novel tetrameric cluster
of [{FeIIFeIII12(μ3-OH)12(μ4-PO4)4}(B-α-PW9O34)4]22‑. Inorg. Chem.
2007, 46, 10944−10946.
(21) Zhang, Z. M.; Wang, E. B.; Qi, Y. F.; Li, Y. G.; Mao, B. D.; Su,
Z. M. Synthesis, characterization, and crystal structures of double-
cubane-substituted and asymmetric penta-Ni-substituted dimeric
polyoxometalates. Cryst. Growth Des. 2007, 7, 1305−1311.
(22) Zhang, Z. M.; Li, Y. G.; Wang, E. B.; Wang, X. L.; Qin, C.; An,
H. Y. Synthesis, characterization, and crystal structures of two novel
high-nuclear nickel-substituted dimeric polyoxometalates. Inorg.
Chem. 2006, 45, 4313−4315.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the NSFC (nos. 21831001,
21571016, and 91122028) and the NSFC for Distinguished
Young scholars (no. 20725101).
REFERENCES
■
(1) Long, D. L.; Burkholder, E.; Cronin, L. Polyoxometalate clusters,
nanostructures and materials: from self assembly to designer materials
and devices. Chem. Soc. Rev. 2007, 36, 105−121.
(2) Wang, S.-S.; Yang, G.-Y. Recent advances in polyoxometalate-
catalyzed reactions. Chem. Rev. 2015, 115, 4893−4962.
(3) Zheng, S.-T.; Yang, G.-Y. Recent advances in paramagnetic-TM-
substituted polyoxometalates (TM= Mn, Fe, Co, Ni, Cu). Chem. Soc.
Rev. 2012, 41, 7623−7646.
(4) Bassil, B. S.; Ibrahim, M.; Al-Oweini, R.; Asano, M.; Wang, Z.;
van Tol, J.; Dalal, N. S.; Choi, K.-Y.; Biboum, R. N.; Keita, B.; Nadjo,
L.; Kortz, U. A Planar {Mn19(OH)12}26+ Unit Incorporated in a 60-
Tungsto-6-Silicate Polyanion. Angew. Chem., Int. Ed. 2011, 50, 5961−
5964.
(5) Jin, L.; Zhu, Z.-K.; Wu, Y.-L.; Qi, Y.-J.; Li, X.-X.; Zheng, S.-T.
Record high-nuclearity polyoxoniobates: discrete nanoclusters
{Nb114}, {Nb81}, and {Nb52}, and extended frameworks based on
{Cu3Nb78} and {Cu4Nb78}. Angew. Chem., Int. Ed. 2017, 56, 16288−
16292.
(6) Li, H.-L.; Lian, C.; Chen, L.-J.; Zhao, J.-W.; Yang, G.-Y. Two
Ce3+-substituted selenotungstates regulated by N, N-dimethylethanol-
amine and dimethylamine hydrochloride. Inorg. Chem. 2019, 58,
8442−8450.
(7) Li, H.-L.; Zhang, M.; Lian, C.; Lang, Z.-L.; Lv, H. J.; Yang, G.-Y.
Ring-shaped polyoxometalate built by {Mn4PW9} and PO4 units for
(23) Clemente-Juan, J. M.; Coronado, E.; Galán-Mascarós, J. R.;
Gómez-García, C. J. Increasing the nuclearity of magnetic
polyoxometalates. syntheses, structures, and magnetic properties of
salts of the heteropoly complexes [Ni3(H2O)3(PW10O39)H2O]7‑,
4001
https://dx.doi.org/10.1021/acs.inorgchem.1c00056
Inorg. Chem. 2021, 60, 3996−4003

Inorganic Chemistry
pubs.acs.org/IC
Article
1 0 ‑
[ N i ( H O ) ( P W
O
) ]
2
,
a n d
(40) Lisnard, L.; Mialane, P.; Dolbecq, A.; Marrot, J.; Clemente-
Juan, J. M.; Coronado, E.; Keita, B.; de Oliveira, P.; Nadjo, L.;
Sécheresse, F. Effect of cyanato, azido, carboxylato, and carbonato
ligands on the formation of cobalt (II) polyoxometalates: character-
ization, magnetic, and electrochemi-cal studies of multinuclear cobalt
clusters. Chem. - Eur. J. 2007, 13, 3525−3536.
4
2
2
9
3 4
[Ni9(OH)3(H2O)6(HPO4)2(PW9O34)3]16‑. Inorg. Chem. 1999, 38,
55−63.
̀
(24) Pichon, C.; Mialane, P.; Dolbecq, A.; Marrot, J.; Riviere, E.;
Bassil, B. S.; Kortz, U.; Keita, B.; Nadjo, L.; Sécheresse, F. Octa-and
nonanuclear nickel (II) polyoxometalate clusters: synthesis and
electrochemical and magnetic characterizations. Inorg. Chem. 2008,
47, 11120−11128.
(25) Rousseau, G.; Oms, O.; Dolbecq, A.; Marrot, J.; Mialane, P.
Route for the elaboration of functionalized hybrid 3d-substituted
trivacant Keggin anions. Inorg. Chem. 2011, 50, 7376−7378.
(26) Zhang, H.-M.; Li, Y.-G.; Lu, Y.; Clérac, R.; Zhang, Q.; Wu, Z.-
M.; Feng, X.-J.; Wang, E.-B. A new Ni12 cluster based on
polyoxometalate ligands. Inorg. Chem. 2009, 48, 10889−10891.
(27) Paille, G.; Boulmier, A.; Bensaid, A.; Ha-Thi, M.-H.; Tran, T.-
(41) Li, H.-L.; Wang, Y.-L.; Zhang, Z.; Yang, B.-F.; Yang, G.-Y. A
new tetra-Zr(IV)-substituted polyoxotungstate aggregate. Dalton
Trans. 2018, 47, 14017−14024.
(42) Keita, B.; de Oliveira, P.; Nadjo, L.; Kortz, U. The ball-Shaped
heteropolytungstates [{Sn(CH3)2(H2O)}24{Sn(CH3)2}12(A-
XW9O34)12]36‑ (X = P, As): stability, redox and electrocatalytic
properties in aqueous media. Chem. - Eur. J. 2007, 13, 5480−5491.
(43) Chen, W.-C.; Wang, X.-L.; Jiao, Y.-Q.; Huang, P.; Zhou, E.-L.;
Su, Z.-M.; Shao, K.-Z. pH-controlled and sulfite anion-directed
assembly of a family of cerium (III)-containing polyoxotungstates
clusters. Inorg. Chem. 2014, 53, 9486−9497.
(44) Zhao, J. W.; Shi, D. Y.; Chen, L. J.; Ma, P. T.; Wang, J. P.;
Zhang, J.; Niu, J. Y. Tetrahedral polyoxometalate nanoclusters with
tetrameric rare-earth cores and germanotungstate vertexes. Cryst.
Growth Des. 2013, 13, 4368−4377.
(45) Keita, B.; Belhouari, A.; Nadjo, L.; Contant, R. Electrocatalysis
by polyoxometalate/vbpolymer systems: reduction of nitrite and nitric
oxide. J. Electroanal. Chem. 1995, 381, 243−250.
(46) Chen, L. J.; Cao, J.; Li, X. H.; Ma, X.; Luo, J.; Zhao, J. W. The
first purely inorganic polyoxotungstates constructed from dimeric
tungstoanti-monate-based iron-rare-earth heterometallic fragments.
CrystEngComm 2015, 17, 5002−5013.
(47) Li, H. L.; Lian, C.; Chen, L. J.; Zhao, J. W.; Yang, G.-Y. Two
unusual nanosized Nd3+-substituted selenotungstate aggregates
simultaneously comprising lacunary Keggin and Dawson polyox-
otungstate segments. Nanoscale 2020, 12, 16091−16101.
(48) Fernández, I.; Khiar, N. Recent Developments in the Synthesis
and Utilization of Chiral Sulfoxides. Chem. Rev. 2003, 103, 3651−
3706.
̀
T.; Pino, T.; Marrot, J.; Riviere, E.; Hendon, C. H.; Oms, O.; Gomez-
Mingot, M.; Fontecave, M.; Mellot-Draznieks, C.; Dolbecq, A.;
Mialane, P. An unprecedented {Ni14SiW9} hybrid polyoxometalate
with high photo-catalytic hydrogen evolution activity. Chem. Commun.
2019, 55, 4166−4169.
(28) Ibrahim, M.; Xiang, Y. X.; Bassil, B. S.; Lan, Y. H.; Powell, A.
K.; de Oliveira, P.; Keita, B.; Kortz, U. Synthesis, magnetism, and
electro-chemistry of the Ni14-and Ni5-containing heteropolytungstates
[ N i 1 4 ( O H ) 6 ( H 2 O ) 1 0 ( H P O 4 ) 4 ( P 2 W 1 5 O 5 6 ) 4 ] 3 4 − a n d
[Ni5(OH)4(H2O)4(β-GeW9O34)(β-GeW8O30(OH))]13−. Inorg.
Chem. 2013, 52, 8399−8408.
(29) Han, X.-B.; Qin, C.; Wang, X.-L.; Tan, Y.-Z.; Zhao, X.-J.; Wang,
E.-B. Bio-inspired assembly of cubane-adjustable polyoxometalate-
based high-nuclear nickel clusters for visible light-driven hydrogen
evolution. Appl. Catal., B 2017, 211, 349−356.
(30) Han, X.-B.; Li, Y.-G.; Zhang, Z.-M.; Tan, H.-Q.; Lu, Y.; Wang,
E.-B. Polyoxometalate-based nickel clusters as visible light-driven
water oxidation catalysts. J. Am. Chem. Soc. 2015, 137, 5486−5493.
(31) Zheng, S.-T.; Yuan, D.-Q.; Jia, H.-P.; Zhang, J.; Yang, G.-Y.
Combination between lacunary polyoxometalates and high-nuclear
transition metal clusters under hydrothermal conditions: I. from
isolated cluster to 1-D chain. Chem. Commun. 2007, 1858−1860.
(32) Liu, Y.-C.; Fu, C.-H.; Zheng, S.-T.; Zhao, J.-W.; Yang, G.-Y.
Hexa-substituted polyoxometalates made of trivacant Dawson
{P2W15} fragments and {Ni6} clusters under hydrothermal conditions.
Dalton Trans. 2013, 42, 16676−16679.
(33) Zhao, J.-W.; Jia, H.-P.; Zhang, J.; Zheng, S.-T.; Yang, G.-Y. A
combination of lacunary polyoxometalates and high-nuclear tran-
sition-metal clusters under hydrothermal conditions. part II: from
double cluster, dimer, and tetramer to three-dimensional frameworks.
Chem. - Eur. J. 2007, 13, 10030−10045.
(34) Zheng, S.-T.; Zhang, J.; Clemente-Juan, J. M.; Yuan, D.-Q.;
Yang, G.-Y. Poly (polyoxotungstate)s with 20 nickel centers: from
nanoclusters to one-dimensional chains. Angew. Chem., Int. Ed. 2009,
48, 7176−7179.
(35) Zheng, S.-T.; Zhang, J.; Li, X.-X.; Fang, W.-H.; Yang, G.-Y.
Cubic polyoxometalate-organic molecular cage. J. Am. Chem. Soc.
2010, 132, 15102−15103.
(49) Duarte, T. A. G.; Pires, S. M. G.; Santos, I. C. M. S.; Simoes, M.
̃
M. Q.; Neves, M. G. P. M. S.; Cavaleirob, A. M. V.; Cavaleiro, J. A. S.
A MnIII) polyoxotungstate in the oxidation of organosulfur
compounds by H2O2 at room temperature: an environmentally safe
catalytic approach. Catal. Sci. Technol. 2016, 6, 3271−3278.
(50) Wang, J. W.; Niu, Y. J.; Zhang, M.; Ma, P. T.; Zhang, C.; Niu, J.
Y.; Wang, J. P. Organophosphonate-functionalized lanthanopolyox-
omolybdate: synthesis, characterization, magnetism, luminescence,
and catalysis of H2O2-based thioether oxidation. Inorg. Chem. 2018,
57, 1796−1805.
(51) Yahya, R.; Craven, M.; Kozhevnikova, E. F.; Steiner, A.;
Samunual, P.; Kozhevnikov, I. V.; Bergbreiter, D. E. Polyisobutylene
oligomer-bound polyoxometalates as efficient and recyclable catalysts
for biphasic oxidations with hydrogen peroxide. Catal. Sci. Technol.
2015, 5, 818−821.
(52) Doherty, S.; Knight, J. G.; Carroll, M. A.; Ellison, J. R.; Hobson,
S. J.; Stevens, S.; Hardacre, C.; Goodrich, P. Efficient and selective
hydrogen peroxidemediated oxidation of sulfides in batch and
segmented and continuous flow using a peroxometalate-based
polymer immobilised ionic liquid phase catalyst. Green Chem. 2015,
17, 1559−1571.
(53) Lin, Z.-J.; Zheng, H.-Q.; Chen, J.; Zhuang, W.-E.; Lin, Y.-X.; Su,
J.-W.; Huang, Y.-B.; Cao, R. Encapsulation of phosphotungstic acid
into metal-organic frameworks with tunable window sizes: screening
of PTA@MOF catalysts for ffficient oxidative desulfurization. Inorg.
Chem. 2018, 57, 13009−13019.
(36) Huang, L.; Zhang, J.; Cheng, L.; Yang, G.-Y. Poly(polyoxometa-
late)s assembled by {Ni6PW9} units: from ring-shaped Ni24-tetramers
to rod-shaped Ni40-octamers. Chem. Commun. 2012, 48, 9658−9660.
(37) Li, H. L.; Liu, Y. J.; Zheng, R.; Chen, L. J.; Zhao, J.-W.; Yang,
G.-Y. Trigonal pyramidal {AsO2(OH)} bridging tetranuclear rare-
earth encap-sulated polyoxotungstate aggregates. Inorg. Chem. 2016,
55, 3881−3893.
(38) Brown, I. D.; Altermatt, D. Bond-valence parameters obtained
from a systematic analysis of the inorganic crystal structure database.
Acta Crystallogr., Sect. B: Struct. Sci. 1985, B41, 244−247.
(39) Lv, H. J.; Chi, Y. N.; van Leusen, J.; Kögerler, P.; Chen, Z. Y.;
Bacsa, J.; Geletii, Y. V.; Guo, W. W.; Lian, T. Q.; Hill, C. L.
[{Ni4(OH)3AsO4}4(B-α-PW9O34)4]28‑: a new polyoxometalate struc-
tural family with catalytic hydrogen evolution activity. Chem. - Eur. J.
2015, 21, 17363−17370.
(54) Takahashi, E.; Kamata, K.; Kikukawa, Y.; Sato, S.; Suzuki, K.;
Yamaguchi, K.; Mizuno, N. Synthesis and oxidation catalysis of a
tisubstituted phosphotungstate, and identification of the active oxygen
species. Catal. Sci. Technol. 2015, 5, 4778−4789.
(55) Ribeiro, S.; Granadeiro, C. M.; Silva, P.; Paz, F. A. A.; de Biani,
F. F.; Cunha-Silva, L.; Balula, S. S. An efficient oxidative
desulfurization process using terbium-polyoxometalate@MIL-
101(Cr). Catal. Sci. Technol. 2013, 3, 2404−2414.
4002
https://dx.doi.org/10.1021/acs.inorgchem.1c00056
Inorg. Chem. 2021, 60, 3996−4003

Inorganic Chemistry
pubs.acs.org/IC
Article
(56) Zhang, Z.; Wang, Y.-L.; Liu, Y.; Huang, S.-L.; Yang, G.-Y. Three
ring-shaped Zr(IV)-substituted silicotungstates: syntheses, structures
and their properties. Nanoscale 2020, 12, 18333−18341.
(57) Kholdeeva, O. A.; Maksimov, G. M.; Maksimovskaya, R. I.;
Kovaleva, L. A.; Fedotov, A.; Grigoriev, V. A.; Hill, C. L. A dimeric
titanium-containing polyoxometalate. synthesis, characterization, and
catalysis of H2O2-based thioether oxidation. Inorg. Chem. 2000, 39,
3828−3837.
4003
https://dx.doi.org/10.1021/acs.inorgchem.1c00056
Inorg. Chem. 2021, 60, 3996−4003