Synergistic combination of multi-ZrIV cations and lacunary keggin germanotungstates leading to a gigantic Zr24-cluster- Substituted Polyoxometalate

Article abstract of DOI:10.1021/ja413134w

Synergistic directing roles of six lacunary fragments resulted in an unprecedented Zr₂₄-cluster substituted poly(polyoxotungstate) Na ₁₀K₂₂[Zr₂₄O₂₂(OH) ₁₀(H₂O)₂(W₂O₁₀H) ₂(GeW₉O₃₄)₄(GeW₈O ₃₁)₂]·85H₂O (Na₁₀K ₂₂·1·85H₂O), which contains the largest [Zr₂₄O₂₂(OH)₁₀(H₂O)₂] (Zr₂₄) cluster in all the Zr-based poly(polyoxometalate)s to date. The most remarkable feature is that the centrosymmetric Zr₂₄-cluster- based hexamer contains two symmetry-related [Zr₁₂O ₁₁(OH)₅(H₂O)(W₂O₁₀H) (GeW₉O₃₄)₂(GeW₈O₃₁)] ^16- trimers via six μ₃-oxo bridges and was simultaneously trapped by three types of different segments of B-α-GeW₉O₃₄, B-α-GeW₈O ₃₁, and W₂O₁₀. The other interesting characteristic is that there are two pairs of intriguing triangular atom alignments: one is composed of the Zr(2,4,6,8,11) and W21 atoms and the other contains the Ge(1-3), Zr(3,5,7,9,10,12) and W26 atoms, and the Zr5 atom is inside the triangle; a linking mode is unobserved. The oxygenation reactions of thioethers by H₂O₂ were evaluated when Na ₁₀K₂₂·1·85H₂O served as a catalyst. Results show that it is an effective catalyst for oxygenation of thioethers by H₂O₂. The unique redox property of oxygen-enriched polyoxotungstate fragments and Lewis acidity of the Zr cluster imbedded in Na₁₀K₂₂·1·85H₂O provide a sufficient driving force for the catalytic conversion from thioethers to sulfoxides/sulfones.

Full text of DOI:10.1021/ja413134w

Article
pubs.acs.org/JACS
Synergistic Combination of Multi-ZrIV Cations and Lacunary Keggin
Germanotungstates Leading to a Gigantic Zr24-Cluster-Substituted
Polyoxometalate
Ling Huang,† Sa-Sa Wang,† Jun-Wei Zhao,*,‡ Lin Cheng,† and Guo-Yu Yang*,†
†State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou, Fujian 350002, China
‡Henan Key Laboratory of Polyoxometalate Chemistry, College of Chemistry and Chemical Engineering, Henan University, Kaifeng,
Henan 475004, China
S
* Supporting Information
ABSTRACT: Synergistic directing roles of six lacunary fragments resulted in an
unprecedented Zr24-cluster substituted poly(polyoxotungstate) Na10K22[Zr24O22(OH)10-
(H2O)2(W2O10H)2(GeW9O34)4(GeW8O31)2]·85H2O (Na10K22·1·85H2O), which contains
the largest [Zr24O22(OH)10(H2O)2] (Zr24) cluster in all the Zr-based poly-
(polyoxometalate)s to date. The most remarkable feature is that the centrosymmetric
Zr24-cluster-based hexamer contains two symmetry-related [Zr12O11(OH)5(H2O)(W2-
O10H)(GeW9O34)2(GeW8O31)]16− trimers via six μ3-oxo bridges and was simultaneously
trapped by three types of different segments of B-α-GeW9O34, B-α-GeW8O31, and W2O10.
The other interesting characteristic is that there are two pairs of intriguing triangular atom
alignments: one is composed of the Zr(2,4,6,8,11) and W21 atoms and the other contains
the Ge(1−3), Zr(3,5,7,9,10,12) and W26 atoms, and the Zr5 atom is inside the triangle; a
linking mode is unobserved. The oxygenation reactions of thioethers by H2O2 were evaluated when Na10K22·1·85H2O served as a
catalyst. Results show that it is an effective catalyst for oxygenation of thioethers by H2O2. The unique redox property of oxygen-
enriched polyoxotungstate fragments and Lewis acidity of the Zr cluster imbedded in Na10K22·1·85H2O provide a sufficient
driving force for the catalytic conversion from thioethers to sulfoxides/sulfones.
cluster incorporated POTs and evaluating catalytic properties
remain a great challenge. Whether the giant Zr-cluster can be
incorporated to lacunary POT skeletons is very interesting and
challenging topic.
INTRODUCTION
■
Polyoxometalates (POMs) coupled with their rich electronic
properties and molecular characteristics have realized applica-
tions in diverse fields such as catalysis, medicine, and
magnetism.1 Currently, the design and synthesis of unique
POMs with a higher number of transition metal (TM) centers
are predominantly driven by their catalytic and magnetic
properties as well as structural aesthetic appreciation. To date,
TM cluster incorporated polyoxotungstates (POTs) are now
All the above poly(POT)s are generally prepared by reaction
of multilacunary POT precursors with TM ions under
conventional solutions. Recently, the hydrothermal method
has been used by our lab to make TM-substituted POTs in the
reaction systems of lacunary POT fragments and divalent Ni2+/
Cu2+/Fe2+ ions, resulting in a series of novel TM-cluster-
substituted POTs.4 The introduction of tri/tetravalence TM
ions, like Cr3+, Ti4+, and Zr4+ ions, into the above reaction
systems has also greatly attracted our interest. On the other
hand, the P-/Si-centered fragments are usually used as the
precursors in the most of the known Zr-substituted POTs, but
only few Ge-centered fragments are used as the precursors. If
Ge-centered precursor reacts with Zr-salt, can the high-nuclear
Zr-cluster substituted POTs be made? Considering the above-
mentioned reasons and inspirations from our previous work,
the trilacunary [A-α-GeW9O34]10− fragment was chosen as the
precursor to make Zr-substituted POTs (Supporting Informa-
tion, Scheme S1). Fortunately, a Zr24-cluster substituted
well-established and numerous giant-cluster-based poly(POT)s
2a
have been made such as [Mn19(OH)12(SiW10O37)6]34−
,
2b
2c
28−
[H56Fe28P8W48O248
]
,
[{Co4(OH)3PO4}4(PW9O34)4]28−
,
2d
[Cu20Cl(OH)24(H2O)12(P8W48O184)]25−
,
[Nb4O6(α-Nb3-
2e
2f
SiW9O40)4]20−
,
[(P2W15Ti3O62)4{Ti(OH)3}4Cl]45−
,
2g
[(P8W48O184){(P2W14MnIII4O60)(P2W15MnIII3O58)2}4]152−
,
[(NH4)20[{(W)W5O21(SO4)}12{(FeIII(H2O))30}(SO4)13-
2h
(H2O)34]]12−
,
and [{NiII (Tris)(en)3(BTC)1.5(B-α-PW9-
6
2i
O34)}8]36−
;
however, the analogous chemistry of zirconium
is less developed, though the Zr-based POTs possess useful
catalytic properties.3a−c Since the first Zr-based POT [Zr3(μ2-
OH)3(A-β-SiW9O34)2]11− was made in 1989,3d so far the
maximum number of Zr atoms in substituted POTs is only six
3e
as observed in [Zr6O2(OH)4(H2O)3(β-SiW10O37)3]14−
,
[Zr6-
3f
(O2)6(OH)6(γ-SiW10O36)3]18−
,
and [Zr6O4(OH)4(H2O)2-
Thus, exploring giant Zr-
Received: December 25, 2013
Published: May 12, 2014
3g
(CH3COO)5(AsW9O33)2]11−
.
© 2014 American Chemical Society
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poly(POT), Na10K22[Zr24O22(OH)10(H2O)2(W2O10H)2-
(GeW9O34)4(GeW8O31)2]·85H2O (Na10K22·1·85H2O), has
been synthesized. 1 has the largest [Zr24O22(OH)10(H2O)2]
(Zr24) cluster in all the Zr-based POTs up to date, in which the
Zr24 cluster was trapped by different fragments of B-α-
GeW9O34 (B-GeW9), B-α-GeW8O31 (B-GeW8), and W2O10
(W2). Moreover, the oxygenation reaction of thioethers by
H2O2 is chosen as an object due to the importance in organic
chemistry. Results indicate that 1 is an effective catalyst during
the course of oxygenation of thioethers. We believe that the
unique redox property of oxygen-enriched POT fragments and
the Lewis acidity of the Zr cluster imbedded in 1 provide a
sufficient driving force for the catalytic conversion from
thioethers to sulfoxides/sulfones, which can be consolidated
by our experiments (vide infra) and the fact that neither
thioethers nor sulfoxides are rapidly oxidized by the oxidants at
room temperature in the absence of catalysts, although the
oxidation of thioethers to the corresponding sulfoxides as well
as oxidation of the sulfoxides to the corresponding sulfones by
H2O2 is thermodynamically favorable.5
the isomerized B-GeW9 frag-ments were partially degraded to
the B-GeW8 segments. As to A- and B-GeW9, the latter is more
stable than the former, which has been confirmed by the above
isomerization of A-GeW9 → B-GeW9. The rational reason is
that the A-GeW9 has six exposed surface O atoms at its
trivacant site, while the B-GeW9 owns seven such O atoms,
which results in that the B-GeW9 as a heptadentate ligand can
better enhance the stability of the products than the A-GeW9 as
a hexadentate ligand when they chelated to the in situ formed
Zr cluster. The B-GeW8 segment is a tetra-lacunary Keggin unit
and derived from the degradation of B-GeW9 by removing a
WO6 group. As to the W2O10 dimer formed by two edge-
sharing WO6 octahedra, it can be understood as the
congregation of two degradative WO6 groups. In our previous
study, the degradative WO6 groups from the [A-α-PW9O34]9−
precursor can reconstruct the tetratungstate W4O16 core made
up of four edge-sharing WO6 octahedra.4e The W4O16 core can
be viewed as the fusion of two W2O10 moieties by sharing two
edges.
The experimental powder X-ray diffraction (PXRD) pattern
of 1 is consistent with the simulated pattern derived from the
single crystal X-ray diffraction data, indicating the good purity
of the sample phase (Figure S2, Supporting Information). X-ray
structure analysis reveals that 1 is a centrosymmetric Zr24-
cluster hexamer [Zr24O22(OH)10(H2O)2(W2O10H)2-
(GeW9O34)4(GeW8O31)2]32− (Figures 1a and 2a), which
consists of two symmetry-related 1a trimers [Zr12O11(OH)5-
(H2O)(W2O10H)(GeW9O34)2(GeW8O31)]16− (Figure 2b) via
six μ3-oxo bridges. Twelve OH bridges and two coordination
water molecules O(126,126A) in 1 are localized by bond
valence sum (BVS) calculations (Table S1, Supporting
Information).6a,b 1 displays two remarkable features: the
coexistence of three POT fragments, namely, GeW8, GeW9,
and W2 and the occurrence of an unprecedented S-shaped giant
Zr24 cluster (Figure 2c and Supporting Information Figure S3)
that is incorporated to the skeleton of 1 and stabilized by six
mixed lacunary fragments and two W2O10 segments. In the Zr24
cluster, interestingly, Zr(2,4−12) ions form an edge-sharing
dioctahedral distribution fashion and Zr(1,3) ions are situated
on both sides of the edge-sharing dioctahedron (Figure 3).
Notably, the W(1,2) and Zr(1,2) atoms illustrate the
distribution motif of a truncated cubane with an appended
Zr2 atom (Figure 2d), which is somewhat similar to the
appended Mn4O4 core with an appended Mn ion in
[MnIII2MnII (μ3-O)2(H2O)4(B-β-SiW8O31)(B-β-SiW9O34)(γ-
SiW10O36)]148− reported by Cronin et al.6c 1a is constructed
from three Zr-substituted Keggin-type POT units 1aa, 1ab, and
1ac via the bridging O/OH, Zr(1,2), and W(1,2) atoms. 1aa,
1ac, and 1ab can be viewed as two tri-Zr substituted GeW9
units and one penta-Zr substituted GeW8 unit. 1aa is a
trilacunary GeW9 unit capped by a Zr3 core made of Zr(7−9)
atoms via a corner-sharing μ4-O atom (Figure 2e). The Zr7 ion
is eight-coordinated, while Zr(8,9) ions are seven-coordinated
(Figure S4a,b, Supporting Information). 1ac is also a trilacunary
GeW9 unit capped by a Zr3 core built by Zr(10−12) ions
(Figure 2g). But the obvious difference from 1aa is that 1ac
contains a seven-coordinated Zr10 ion and two eight-
coordinated Zr(11, 12) ions (Figure S4e,f, Supporting
Information). 1ab is a tetralacunary GeW8 unit capped by a
Zr5 cluster built by Zr(3−7) ions (Figure 2f). The Zr(5−7)
ions are located at the trilacunary sites, the Zr3 ion is
encapsulated to the fourth lacunary site of GeW8 unit while the
Zr4 ion caps on the window surrounded by Zr(3,5,6) ions
RESULTS AND DISCUSSION
■
Structural Description. Colorless crystals of Na10K22·1·85
H2O were made by the hydrothermal reaction of [A-α-
GeW9O34]10− (A-GeW9), ZrOCl2·8H2O and Na2CO3 (Their
molar ratio is 0.32:0.62:0.40) in sodium acetate buffer at 200
°C for 3 days. Though the A-GeW9 fragment was used as the
starting material, 1 (Figure 1a) contains B-GeW9 and B-GeW8
units (Figure 1b), indicating that the isomerization of A-GeW9
→ B-GeW9 and the degradation of B-GeW9 → B-GeW8 must
have taken place during the course of the reaction; that is, the
isomerization is prior, and the degradation is hind (Figure S1,
Supporting Information). As shown in Figure 1a, 1 includes
four B-GeW9, two B-GeW8, and two W2O10 units, showing that
Figure 1. (a) Structures of the hexamer 1. ;(b) isomerization of the A-
GeW9 ion, and the degradation of the B-GeW9 fragment, as well as the
formation of the W2O10 group. Color codes: O, red; Zr, green.
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Figure 2. Ball-and-stick representations of the (a) polyanion 1, (b) trimer 1a, (c) the Zr24 cluster in 1, (d) the distribution motif of W1, W2, Zr1, and
Zr2 atoms, (e, f, and g) three Zr-substituted Keggin-type POT units in 1a. Color codes: O, red; OH, blue; W, purple; Ge, yellow, Zr, green.
Figure 3. Alignment of 24 the Zr ions of the Zr24-cluster in 1. Color
code: blue, hydroxyl atoms.
through two μ3-O and two μ4-O atoms. The Zr3 ion is eight-
coordinated and the remaining Zr(4−6) ions are seven-
coordinated (Figure S4c,d, Supporting Information). It should
be pointed out that the Zr7 ion simultaneously occupies the
defect sites of 1aa and 1ab. Notably, 12 crystallographically
independent Zr ions show three different coordination geo-
metries: Zr(1,2,4,5,9,10) ions display the distorted mono-
capped octahedra, Zr(3,7,11,12) ions adopt the distorted
bicapped trigonal prisms, and Zr(6,8) ions reside in the
distorted monocapped trigonal prisms (Figure S5, Supporting
Information).
Another interesting feature of 1 is that there are two pairs of
intriguing triangular atom alignments (Figure 4): one is
composed of the Zr(2,4,6,8,11) and W21 atoms, and this
linking mode resembles the Ni6 clusters observed in [Ni-
(enMe)2]3[H6Ni20P4W34(OH)4O136(enMe)8(H2O)6]·12H2O4e
and [Ni(en)2(H2O)2]6{Ni6(Tris)(en)3(BTC)1.5(B-α-
PW9O34)}8·12en·54 H2O;4f the other contains the Ge(1−3),
Zr(3,5,7,9,10,12), and W26 atoms, and the Zr5 atom is inside
the triangle, so that the linking mode is unobserved. Two
triangles are connected each other via a μ-O, six μ3-O, and
seven μ4-O atoms. It is notable that the Zr1 ion cannot be
located in the POM skeleton pocket, and it plays a crucial role
in linking two symmetry-related Zr12 cores to form the
unprecedented S-shaped Zr24 cluster. In the solid state, 1 is
stabilized by Na+ and K+ countercations, which are closely
associated with the cluster polyanions. In the packing
Figure 4. Two pairs of triangular alignments.
arrangement in the bc plane, cluster polyanions are arranged
in the −AAA− fashion (Figure S6, Supporting Information).
In addition, similar to 1, other TM-substituted germanotung-
states containing GeW9 and GeW8 fragments have been
observed in [Cu3(H2O)(B-β-GeW9O33(OH))(B-β-GeW8O30-
(OH))]12− (2a), [Co(H2O)2{Co3(B-β-GeW9O33(OH))(B-β-
GeW8O30(OH))}2]22− (2b), [Mn(H2O)2{Mn3(H2O)(B-β-
GeW9O33(OH))(B-β-GeW8O30 (OH))}2]22− (2c) (Figure
S7a, Supporting Information)7 and [Cu10(H2O)2(N3)4-
(GeW9O34)2(GeW8O31)2]24− (3) (Figure S7b, Supporting
Information).8 However, the most remarkable differences
between 1, 2, and 3 lie in three aspects: (a) GeW9 and
GeW8 fragments in 1 are B-α-configuration while those in 2
and 3 are B-β-configuration; (b) 1 was made under
hydrothermal conditions by means of the A-α-GeW9 precursor
and the transformation pathway from A-α-GeW9 to B-α-GeW9
and B-α-GeW8 occurred, whereas 2 and 3 were made by the [γ-
GeW10O36]8− precursor and the evolution of [γ-GeW10O36]8−
to B-β-GeW9 and B-β-GeW8 happened; (c) the number of TM
centers in 1 is much larger than those in 2 and 3. A comparison
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of 1 with 2 and 3 shows that the number of the TM cations
incorporated by POM skeletons increases when the number of
the lacunary POM units increases. For example, three Cu/Co/
Mn ions are contained in 2 when the number of lacunary POM
units is two and 10 Cu ions in 3 when the number of lacunary
POM units is four. With regard to 1, the number of lacunary
POM units is elevated to six, and 24 Zr cations are trapped.
Additionally, in comparison with previously reported POT
Table 1. Results for Oxygenation of Various Thioethers with
30% H2O2 Catalyzed by Na10K22·1·85H2O in MeCN
aggregates with over 24 TM ions such as [H56Fe28P8W48-
(Fe28),2b [(P8W48O184){(P2W14MnIII4O60)(P2W15-
28−
O248
]
MnIII3O58)2}4]152− (Mn40),2g [(NH4)20[{(W)W5O21(SO4)}12-
{(FeIII(H2O))30}(SO4)13(H2O)34]]12− (Fe30),2h and [{NiII -
6
(Tris)(en)3(BTC)1.5(B-α-PW9O34)}8]36− (Ni48),2i several
obvious discrepancies can be found: (i) the tetravalence Zr4+
ions are introduced to 1 while the chemical valences of TM
ions in Fe28, Mn40, Fe30, and Ni48 are lower than 4; (b) 1, Fe28,
Mn40, Fe30, and Ni48 consist of three (trivacant B-GeW9,
tetravacant B-GeW8, W2), one (hexavacant P2W12), three
(trivacant P2W15, tetravacant P2W14, multivacant P8W48), one
({(W)W5}), and one (trivacant B-PW9) POT units, respec-
tively; (c) to reduce the steric hindrance, the POT units in
them are not coplanar and exhibit different spatial alignments;
(d) 1 and Ni48 are hydro-thermally made, whereas the
remaining are synthesized in conventional aqueous conditions.
From the above we can see that the introduction of multivacant
POT fragments (i.e., P2W12, P8W48) and anionic components
(i.e., SO42−, Tris, BTC) can effectively increase the number of
TM ions in the products, which offer us great enlightenment in
the preparations of much higher TM-substituted POMs.
Catalytic Oxidation. The catalytic oxidations of organic
compounds under mild conditions are of both considerable
intellectual interest and potential utility.9 Catalytic oxidation of
organic sulfide remains a topical interest owing to the versatile
utility of both sulfoxide and sulfone in organic synthesis.10
While a plethora of oxygen donors are available, utilization of
“green” oxygen donors such as H2O2 has become increasingly
prominent.11 According to the previous reports,12 thioethers
can be efficiently oxidized by H2O2 in the presence of
titanopolytungstates to produce the corresponding oxygenated
products (sulfoxides, RR′SO and sulfones, RR′SO2) in
practically quantitative yield based on both H2O2 and substrate
consumed (Scheme 1). Because Zr and Ti belong to the same
a
b
The conversion based on substrate consumed. Reaction conditions
for the entries 1 and 2: substrate, 0.5 mmol; H2O2, 1 mmol; Na10K22·1·
c
85H2O, 0.5 × 10−2 mmol; MeCN10, mL. Reaction conditions for
entries 3 to 16: substrate, 0.5 mmol; H2O2, 1.5 mmol; Na10K22·1·
85H2O, 0.5 × 10−2 mmol; MeCN, 10 mL.
are very low. Among all the reactions, entry 6 has the highest
conversion, which is just about 23%. However, in the presence
of Na10K22·1·85 H2O as a catalyst to activate H2O2, the
conversion and selectivity are greatly improved, indicating that
Na10K22·1·85 H2O is an effective catalyst for oxygenation of
thioethers by H2O2 (Table 1). Particularly, entries 4 and 5
manifest the formation of 100% sulfone. The introduction of
electron-donating groups on the aromatic ring of aryl−alkyl
thioethers (entries 5−8) gave a higher ratio of sulfone than the
introduction of electron-withdrawing groups (entries 9−13). It
was also found that the position property of the substituents of
aryl−alkyl thioethers (entries 3−13) should affect the ratio of
sulfone and sulfoxide and the ortho-substituent groups
increased the conversion of sulfoxide. Additionally, the steric
hindrance effect of aryl−aryl thioethers has an obvious
influence on the conversion of oxygenated products (entries
14−15) and the large steric hindrance produces a lower-
conversion.
Scheme 1. Catalytic Oxidation of Thioethers
group in the periodic table of elements, using Na10K22·1·85H2O
as a catalyst, catalytic oxidations of various thioethers with
H2O2 have been successfully achieved and give rise to the
corresponding oxygenated products. Products were identified
by GC−MS spectra. The selectivity of sulfoxide and sulfone
products and the conversion of initial sulfides were quantified
by GC spectra. Table 1 and Table S2 (Supporting Information)
summarize the reactivity data for oxidation of 11 representative
thioethers in MeCN at room temperature/60 °C in the
presence of Na10K22·1·85H2O and in the absence of Na10K22·1·
85H2O, respectively.
To check the recyclability of the heterogeneous catalyst
Na10K22·1·85H2O, entry 5 worked as an example for
investigation. Additional substrate and H2O2 were added into
the reaction mixture when the previous run was completed.
The results exhibit that the catalytic activity was not obviously
changed after six-run duplicate operations (Table S3,
As we can see in Table S2, most of the oxidation reaction can
happen in the absence of Na10K22·1·85H2O, but the conversion
and selectivity of the majority of catalytic oxidation reactions
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Supporting Information). The catalyst can be easily recovered
from the solvent/oxidant/substrate system by filtration upon
completion of the sixth run. The recovery percent reached up
to 98%, and the filtrate showed negligible reactivity when extra
substrate and H2O2 were added into it. According to the
comparisons of IR spectra (Figure S8, Supporting Information)
and PXRD patterns (Figure S10, Supporting Information) of
the fresh catalyst and the recovered catalyst after the sixth-run
reaction, the structural integrity of the recovered catalyst was
still retained. The reason for some trivial differences in IR and
PXRD spectra may be that the recovered catalyst has been
partly peroxidated by H2O2. The comparisons of IR spectra of
the fresh catalyst and that of the catalysts after first-run reaction
for entries 3, 8, 11, and 14 are shown in Figure S9 (Supporting
Information). In comparison with previous reported re-
sults,10c,13 Na10K22·1·85H2O displays comparatively better
catalytic activities toward oxidations of thioethers under similar
conditions. For example, for the oxidation of thioanisole (entry
3) with Na10K22·1·85H2O as a catalyst, the conversion was 99%
and the turnover frequency (TOF) was 99 h−1 at 60 °C, which
are slightly higher than those (conversion: 92%, TOF: 38 h−1)
using [γ-1,2-H2SiV2W10O40]/SiO2 as a catalyst at 20 °C.13a As
to entry 3, when MnSO4·H2O catalyst and 3 equiv H2O2 were
utilized and the reaction time was prolonged to 24 h, although
the conversion was up to 100%, the selectivities to sulfone and
sulfoxide were 57% and 43%, respectively.13b Similarly, with
regard to entry 3, employing 2,6-bis(acetylamino)pyridine and
2,6-bis(3-{4-[3,5-bis(phenylmethoxy)phenylmethoxy]phenyl}-
propanoylamino)pyridine as catalysts with 2.5 equiv H2O2 at 30
°C gave a time of flight (TOF) of 6.8 h−1 and 16 h−1,
respectively.13c In the case of entry 14, when (Bu4N)4[γ-
SiW10O34(H2O)2] worked as a catalyst with 1 equiv of H2O2
without an additional additive, the conversion of phenyl sulfide
to the sulfoxide is tardy at 23 °C, generating only 38% after 3
h.10c Overall, the catalytic oxidation of thioethers in this work
may be potentially useful for the removal of organic sulfur
content.
(POT)s. Cooperative actions between Zr4+ ions and POT
components might potentially improve catalytic activities
exemplified by oxygenation of thioethers by H2O2. The key
points of the synthetic procedures have been well established.
Further work with the aim of making novel poly(POT)s with
special functionalities is in progress by making use of the
reactions of those TM/lanthanide cations with the larger ionic
radii and high-coordination numbers with multilacunary POTs
or mixed multivacant POTs under hydrothermal conditions.
Furthermore, some functional organic ligands will be
introduced to this system to prepare novel organic−inorganic
hybrid high-nuclear Zr/lanthanide substituted POT aggregates.
It can be believed that this finding is very important in
exploring the syntheses of large or supralarge TM-cluster
substituted poly(POT)s.
EXPERIMENTAL SECTION
■
Physical Measurements. K8Na2[A-α-GeW9O34]·25H2O was
prepared by a literature method.14 All other chemicals employed in
this study were analytical reagent. H elemental analysis was carried out
with a Vario EL III elemental analyzer. IR spectra (KBr pellets) were
recorded on an ABB Bomen MB 102 spec-trometer. PXRD patterns
were collected on a Bruker D8 Advance XRD diffractometer using Cu
Kα radiation. Thermogravimetric analysis was performed in a dynamic
air atmosphere with a heating rate of 10 °C/min using a Mettler TGA/
SDTA 851e thermal analyzer. GC spectra were carried out with a
Varian 430-GC gas chromatograph. GC−MS spectra were obtained
from a Varian 450-GC/240-MS gas chromatograph−mass spectrom-
eter.
X-ray Crystallography. A suitable single crystal was selected
under an optical microscope and mounted onto the end of a thin glass
fiber using cyanoacrylate adhesive. The intensity data were collected
on a Mercury CCD diffractometer with graphite-monochromated Mo
Kα radiation (λ = 0.71073 Å) at room temperature. All absorption
corrections were performed by using the SADABS program. The
structure was solved by direct methods and refined by full-matrix least-
squares on F2 using the SHELXTL-97 program package.15 ICSD-
425690 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from the ICSD
database via http://www.fiz-karlsruhe.de/request. Crystal data:
CONCLUSIONS
H186Ge6K22Na10O337W56Zr24, Mr = 19590.01, triclinic, P1, a =
̅
■
17.1764(4), b = 20.7259(6), c = 23.1192(5) Å, α = 67.465(2)°, β =
76.759(2)°, γ = 73.217(2)°, V = 7212.6(3) Å3, Z = 1, ρcalcd = 4.510 g
cm−3, μ = 24.131 mm−1, F(000) = 8706, GOF = 1.059. A total of
An unprecedented Zr24-cluster substituted poly(POT) Na10K22·
1·85H2O has been successfully made under hydrothermal
conditions and contains the largest [Zr24O22-(OH)10(H2O)2]
cluster in POM chemistry. More interestingly, the Zr24 cluster
was simultaneously trapped by inequivalent fragments of B-
GeW9, B-GeW8, and W2. The formation of an Na10K22·1·
85H2O not only exemplifies the possibility that more giant Zr-
clusters can be incorporated to lacunary POT skeletons, but
also suggests the potential of combination of Zr4+ cations with
other vacant POT fragments to create novel Zr-cluster-based
POM materials in the rapid expansion and development era of
POM chemistry. Moreover, catalytic oxidations of various
thioethers by H2O2 using Na10K22·1·85H2O as a catalyst have
been evaluated. In comparison with previous reported
results,10c,13 Na10K22·1·85H2O can be viewed as an effective
catalyst for oxygenation of thioethers by H2O2 and may have
the potential for the removal of organic sulfur content. In the
following work, more catalytic reactions and relevant catalytic
mechanism will be explored and developed. The isolation of
this large-Zr-cluster substituted poly(POT) confirms that the
combination of the hydrothermal technique, lacunary POTs,
and TM cations with larger ionic radius, high positive charges,
and high-coordination number can provide an effective strategy
for making large or supralarge TM-cluster substituted poly-
70793 reflections were collected, 25299 of which were unique (Rint
=
0.0634). R1/wR2 = 0.0498/0.1222 for 1849 parameters and 20748
reflections (I > 2σ(I)).
Synthesis for Na10K22·1·85H2O. K8Na2[A-α-GeW9O34]·25H2O
(1.0 g, 0.32 mmol) and ZrOCl2·8H2O (0.2 g, 0.62 mmol) were
stirred in 8 mL of 0.5 mol·L−1 sodium acetate buffer (pH = 4.8), and
then Na2CO3 (1 mol·L−1, 0.4 mL) was dropwise added under
continuous stirring for 20 min. The resulting solution was sealed in a
35 mL stainless steel reactor with a Teflon liner and heated at 200 °C
for 3 days and then cooled to room temperature. Colorless prismatic
crystals of 1 were obtained. Yield: 0.23 g (45%) for 1 based on
ZrOCl2·8H2O. Elemental analysis (%) calcd for 1: H, 0.96; Na, 1.17;
K, 4.39; Ge, 2.22; Zr, 11.18; W, 52.55. Found: H, 0.88; Na, 1.00; K,
4.59; Ge, 2.56; Zr, 10.97; W, 52.24. IR (KBr, cm−1): 3406 m, 1621 s,
965 s, 903 m, 766 w, 713 w, 459 m.
Experimental Procedure of Catalytic Oxidation of Various
Thioethers with H2O2 Catalyzed by Na10K22·1·85H2O. The
catalytic oxidation of various thioethers was carried out in 25 mL
glass vessel under vigorous agitation with a magnetic stirring bar at
ambient temperature (25 °C) or heated (60 °C) at reflux. A desired
amount of solid catalyst was placed into the glass vessel, then a
solution containing thioether, acetonitrile, and dodecane (an internal
standard for GC-analysis) was added. The reaction vessel was sealed
and stirred at 25 °C or placed into a thermostated oil-bath (60 °C).
7641
dx.doi.org/10.1021/ja413134w | J. Am. Chem. Soc. 2014, 136, 7637−7642

Journal of the American Chemical Society
Article
After the reaction, the vessel was cooled to room temperature and
diluted with ether for GC analysis. The thioether oxidation products
(sulfoxide and sulfone) were identified with GC−MS and quantified
using gas chromatography with internal standard techniques.
Recyclability of the catalyst: the oxidation of methyl 4-
methoxyphenyl sulfide (entry 5 in Table 1) was selected as a probe
reaction. At first, 0.5 mmol of methyl 4-methoxyphenyl sulfide, 1.5
mmol of H2O2, and 0.5 × 10−2 mmol of Na10K22·1·85H2O were added
into 10 mL of MeCN. The mixture was stirred 1 h at 60 °C. Upon the
completion of the reaction, another 0.5 mmol of methyl 4-
methoxyphenyl sulfide and 1.5 mmol of H2O2 were added. After
that, the mixture was stirred 1 h at 60 °C again. The process was
repeatedly carried out.
Determination of Lattice Water Molecules. Lattice water
molecules are located in the interspaces of cluster polyanions. Na10K22·
1·85H2O is highly hydrated, and when it is exposed to the X-ray beam
for the collection of intensity data, the water molecules of
crystallization are easily lost from the structure. Therefore, some
water molecules of crystallization cannot be directly determined by X-
ray diffraction. A combination of elemental analysis and thermogravi-
metric analysis (Figure S11, Supporting Information) confirms the
number of water molecules of crystallization in Na10K22·1·85H2O,
which is not uncommon in giant poly(POM) species.16
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ASSOCIATED CONTENT
* Supporting Information
Synthesis, BVS, catalysis, detailed structure description, TG,
and IR. This material is available free of charge via the Internet
at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
ygy@fjirsm.ac.cn; zhaojunwei@henu.edu.cn
■
(9) (a) Jørgensen, K. A. Chem. Rev. 1989, 89, 431. (b) Meunier, B.
Chem. Rev. 1992, 92, 1411.
(10) (a) Fernandez, I.; Khair, N. Chem. Rev. 2003, 103, 3651.
(b) Mikola-jaczyk, M.; Drabowicz, J.; Kielbasinski, P. Chiral Sulfur
Reagents: Applications in Symmetric and Stereoselective Synthesis; CRC:
Boca Raton, 1997. (c) Phan, T. D.; Kinch, M. A.; Barker, J. E.; Ren, T.
Tetrahedron Lett. 2005, 46, 397.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(11) (a) Gresley, N. M.; Griffith, W. P.; Laemmel, A. C.; Nogueira,
H. I. S.; Parkin, B. C. J. Mol. Catal. A Chem. 1997, 117, 185.
This work was supported by the NSFC (Grant Nos. 91122028,
21221001, 50872133, and 21101055), the NSFC for
Distinguished Young Scholars (Grant No. 20725101), and
973 Program (Grant Nos. 2014CB932101 and
2011CB932504).
(b) Carraro, M.; Nsouli, N.; Oelrich, H.; Sartorel, A.; Soraru, A.; Mal,
̀
S. S.; Scorrano, G.; Walder, L.; Kortz, U.; Bonchio, M. Chem.Eur. J.
2011, 17, 8371. (c) Kamata, K.; Hirano, T.; Kuzuya, S.; Mizuno, N. J.
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Am. Chem. Soc. 2009, 131, 6997. (d) Bregeault, J.-M.; Vennat, M.;
Salles, L.; Piquemal, J.-Y.; Mahha, Y.; Briot, E.; Bakala, P. C.;
Atlamsani, A.; Thouvenot, R. J. Mol. Catal. A 2006, 250, 177.
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Chem. 2000, 39, 3828. (b) Gall, R. D.; Hill, C. L.; Walker, J. E. Chem.
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