First stable nitrate-encapsulated sandwich type polyoxometalate: Synthesis, structural characterization, and catalytic performance

Article abstract of DOI:10.1016/j.inoche.2014.02.008

A stable sandwich type Keggin polyoxometalate, Na₄K ₅[K₃Cu₃(NO₃)(A-α-PW ₉O₃₄)₂], has been synthesized and crystallized by a simple reaction method. Elemental analysis, FTIR, UV-vis, X-ray single crystal, thermal gravimetry, and cyclic voltammetry were used for the characterization of synthesized POM. The TBA salt of [K₃Cu ₃(PW₉O₃₄)₂]^{9 -} revealed high catalytic activity and 74-99% selectivity in the liquid phase epoxidation of alkenes with aqueous H₂O₂. The X-ray structure of this complex reveals that three Cu(II) ions are sandwiched between two A-α-PW₉O₃₄ moieties and that a nitrate monoanion is encapsulated in the same plane as the three Cu(II) atoms. The nitrate is coplanar with the three copper atoms, which are each in a distorted square-pyramidal environment. After recrystallization, the NO₃ ^- group in the central belt didn't exit, in which this phenomenon is attributed to the type of counterion in the complex (as a result of mixing Na⁺ and K⁺ as counterions). This compound showed excellent stability in different pH and also didn't dissociate with hydrogen peroxide.

Full text of DOI:10.1016/j.inoche.2014.02.008

First Stable Nitrate-Encapsulated Sandwich Type Polyoxometalate: Synthesis,
Structural Characterization, and Catalytic Performance
Mostafa Riahi Farsani, Bahram Yadollahi, Hadi Amiri Rudbari, Akbar
Amini, Tom Caradoc-Davis, Jason R. Price
PII:
DOI:
Reference:
S1387-7003(14)00048-3
doi: 10.1016/j.inoche.2014.02.008
INOCHE 5450
To appear in:
Inorganic Chemistry Communications
Received date:
Accepted date:
4 January 2014
6 February 2014
Please cite this article as: Mostafa Riahi Farsani, Bahram Yadollahi, Hadi Amiri
Rudbari, Akbar Amini, Tom Caradoc-Davis, Jason R. Price, First Stable Nitrate-
Encapsulated Sandwich Type Polyoxometalate: Synthesis, Structural Characteriza-
tion, and Catalytic Performance, Inorganic Chemistry Communications (2014), doi:
1
0.1016/j.inoche.2014.02.008
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ACCEPTED MANUSCRIPT
First Stable Nitrate-Encapsulated Sandwich Type Polyoxometalate: Synthesis,
Structural Characterization, and Catalytic Performance
a
*a
a
a
Mostafa Riahi Farsani , Bahram Yadollahi , Hadi Amiri Rudbari , Akbar Amini , Tom
b
b
Caradoc-Davis , Jason R. Price
a
Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
b
Australian Synchrotron, 800 Blackburn Road, Clayton, Melbourne, Victoria 3168, Australia
Keywords: Sandwich type polyoxometalates, Nitrate-encapsulated, Catalysis, Epoxidation,
Hydrogen peroxide
*
Corresponding Author. Tel: +98-311-7932742; fax: +98-311-6689732; e-mail: yadollahi@chem.ui.ac.ir,
yadollahi.b@gmail.com
1

ACCEPTED MANUSCRIPT
Abstract
A stable sandwich type Keggin polyoxometalate, Na K [K Cu (NO )(A-α-PW O ) ], has been
4
5
3
3
3
9
34 2
synthesized and crystallized by a simple reaction method. Elemental analysis, FTIR, UV-vis, X-
ray single crystal, thermal gravimetry and cyclic voltammetry were used for characterization of
9
-
synthesized POM. The TBA salt of [K Cu (PW O ) ] revealed high catalytic activity and 74-
3
3
9
34 2
9
9% selectivity in the liquid phase epoxidation of alkenes with aqueous H O . The X-ray
2 2
structure of this complex reveals that three Cu(II) ions are sandwiched between two A-α-PW O
9
34
moieties and that a nitrate monoanion is encapsulated in the same plane as the three Cu(II)
atoms. The nitrate is coplanar with the three copper atoms, which are each in a distorted square-
-
pyramidal environment. After recrystallization NO group in the central belt didn’t exit, this
3
+
phenomenon attributed to the type of counter ion in the complex (as a result of mixing Na and
+
K as counter ions). This compound showed excellent stability in different pH and also didn’t
dissociate with hydrogen peroxide.
2

ACCEPTED MANUSCRIPT
The oxidation or oxygenation of organic compounds catalyzed by transition metal centers has
been extensively studied and is still subject of high interest [1-5]. One major goal in this field of
research is synthesis of effective, custom-made, and nontoxic catalysts to achieve lowering of
costs and environmentally friendly conditions in industrial processes. Generally, important
requirements for these technologies are stable catalysts with high product selectivity’s without
waste of the applied oxidant [6].
Polyoxometalates (POMs) have been widely used in diverse as catalysis, medicine and material
science [7-10]. Particular interest has been focused on transition metal-substituted
polyoxometalates because of their unique in its topological and significant catalytic activities
[
11-14]. Sandwich type polyoxometalates based on trivacant Keggin moieties represent the
1
0-
largest subfamily. The first sandwich type polyoxoanion, [Co (H O) (B-α-PW O ) ] , was
4
2
2
9
34 2
discovered by Weakley et al in 1973 [15]. Over the last 40 years of research activity, many
sandwich type species including Weakley, Hervé [16], Krebs [17], and Knoth [18,19] types have
been identified [20,21].
In 1985 for the first time, Knoth reported the sandwich POMs are based on two A-α-Keggin
9
-
fragments, e.g. [A-α-PW O ] [19]. Knoth et al reported an unstable encapsulation of a
9
34
monoanion in the A-type sandwich polyoxometalates with potassium countercations. After
eighteen years, Hill et al reported carbonate encapsulated in the A-type sandwich POM of Y(III)
ions [22]. Unfortunately all of the A-type sandwich complexes are unstable in solution and
eventually isomerize into the B-type sandwich structures based on UV-visible spectroscopic data
[
18]. Herve et al, by UV-visible studies on K [(Co(OH ) ) (PW O ) ], showed that in aqueous
12 2 2 3 9 34 2
solution these compounds were decomposed and two different intermediate species formed [23].
3

ACCEPTED MANUSCRIPT
Perhaps one reason for decomposing of these compounds is type of counter ions or encapsulated
anion in central belts. For example Hill et al had shown that a high concentration of sodium ions
stabilizes lacunary sandwich type species [24-26]. In some of unstable polyoxometalates with A-
+
+
type structure, which reported in previous years, only K or Na are counter ions and just in
+
+
structures with both of Na and K as counter ions stability could be seen [18,19,24,28-30].
To the best of our knowledge, Na K [K Cu (NO )(A-α-PW O ) ] is a stable sandwich POM
4
5
3
3
3
9
34 2
with three transition metals in the belt which reported here. Nevertheless, up to now, catalytic
epoxidation using sandwich type phosphotungstates with A-type structure are limited to alkenes
due to complications in the synthesis of the material and instability of these compounds in
solvents [27-30].
Nevertheless, the potentially attractive catalytic properties of A-type sandwich polyoxometalates
cause a strong motivation for this kind of polyoxometalates. In the past decades, much attention
has been devoted to the synthesis of transition-metal substituted POMs without idea for the
simple method for synthesis of this compounds and improved stabilization of A-type sandwich
polyoxometalates.
Herein, for the first time, we report the synthesis of a stable A-type sandwich polyoxometalate
-
+
+
with encapsulated NO in central belt [31] and a mixture of two counter ions, K and Na , for
3
stability purpose.
Reaction of Na WO with Cu nitrate salt in an aqueous solution produced Na K [K Cu (NO )(A-
2
4
4
5
3
3
3
-
α-PW O ) ] (1) in very good yield (79%). The synthesis of 1 requires the presence of NO .
9
34 2
3
Knoth and co-workers was shown by excess KCl the unstable K M (PW ) (M = Mn, Fe, Cu,
1
2
3
9 2
Zn, Pd, Ce) complexes were formed [19]. But in our synthetic method, Na K [K Cu (NO )(A-α-
4
5
3
3
3
PW O ) ] was stable at different conditions.
9
34 2
4

ACCEPTED MANUSCRIPT
The X-ray structure of 1 showed that dimeric polyoxoanion Na K [K Cu (NO )(A-α-PW O ) ]
4
5
3
3
3
9
34 2
9
-
2+
+
(
1) consists of two [A-α-PW O ] moieties linked by three Cu and three K ions, resulting in a
9 34
2
+
+
sandwich type structure (Figure 1). The central belt is composed of three Cu and three K ions
in alternating positions leading to a polyanion with idealized D symmetry. The three copper
3
h
ions are equivalent and exhibit square-pyramidal coordination and the vacancies between copper
ions are occupied by potassium ions. This arrangement was expected because some of the
dimeric, sandwich-type polyoxometalates contain two or three transition metal ions in the central
belt and the vacancies between them are usually occupied by sodium or potassium ions [32-36].
The crystal structure also shows that a nitrate anion is encapsulated inside the central cavity of
the Cu (A-α-PW ) structure (Figure 2). The nitrate is coplanar with the three copper atoms,
3
9 2
which are each in a distorted square-pyramidal environment. The pyramidal apices face inward
and are occupied by the nitrate oxygen atoms. The A-α-PW groups are directly over each other;
9
and there is no “side-slip” such as that observed in Cu (A-α-AsW ) [32].
3
9 2
As Knoth report, this structure with potassium counter ions was unstable [19] He showed that
coordination of nitrate is readily reversible; and the nitrate anion was lost upon recrystallization
of K Cu (PW ) .NO from neutral water and regained at lower pH in the presence of nitrate.
1
2
3
9 2
3
This complexation of an anion by another anion can be rationalized by postulating that there is
little negative charge density in the region of the belt. The negative charge probably remains
largely localized on the polyoxometalate groups whereas the belt, consisting of three positive Cu
metals, probably has localized positive charge. In our reported structure, we changed the
potassium counter ions with a mixture of potassium and sodium ions, which resulted higher
stability for the nitrate-encapsulated sandwich type complex.
5

ACCEPTED MANUSCRIPT
As mentioned above, complex 1 is the first example of a stable structure containing monoanion
2
-
encapsulated in a sandwich type POM. Carbonate (CO ), a dianion, encapsulated in the A-type
3
sandwich complex, K (YOH ) (CO )(A-α-PW O ) .22H O (2), as a POM that is structurally
1
1
2 3
3
9
34 2
2
similar to 1 was reported by Hill [22]. In contrast to complex 1, the complex 2 is stabilized by
potassium as counter ion.
Pope and Müller define these anion-encapsulated sandwich type structures as cryptates since
they have well-defined bonding interactions [9]. In contrast, there are also large classes of
reduced polyoxovanadates that have been referred to as clathrates in which the host guest
-
-
interactions are significantly weaker. In these compounds, a variety of anions (including Cl , Br ,
-
2-
I , and CO ) can act as templates for the induced self-assembly of the cluster shell [37-39].
3
The decomposition characteristics and thermal stability of this complex in the solid state were
assessed by thermogravimetric analysis (Figure 3). Two distinct mass loss regions are observed
below 450 °C. First, there is a weight loss of approximately 7.7% between 30 and 200 °C that is
associated with the loss of 25 water molecules (both crystalline lattice solvent molecules and
coordinated aqua ligands) per molecule of Na K [K Cu (NO )(A-α-PW O ) ]. In addition, there
4
5
3
3
3
9
34 2
is a weight loss of approximately 0.8% from 400 to 450 °C, corresponding to the loss of 1 equiv
NO per molecule of Na K [K Cu (NO )(A-α-PW O ) ] [40].
3
4
5
3
3
3
9
34 2
-
The infrared spectrum of this complex shows band assignable to NO at 1391. The characteristic
3
-1
vibrational modes of the PO unit (1100 and 1066 cm ) also show splitting, implying that there
4
is a loss of local symmetry as expected for the A-type trivacant Keggin unit. In addition, the
terminal W=O and bridging W-O-W stretches characteristic of all heteropolytungstates are
present. This compound indicated similar infrared spectra after recrystallization (see Figure 4)
-1
and characteristic band at 1391cm showed nitrate retention [41]. Loosed of the ν stretching
6

ACCEPTED MANUSCRIPT
frequencies characteristic by FTIR, confirmed NO decomposition by heating a solid sample to
3
4
50°C (Figure 5).
The cyclic voltammetry (CV) of Na K [K Cu (NO )(A-α-PW O ) ] was recorded in sodium
4
5
3
3
3
9
34 2
acetate buffer solutions (0.02 M NaOAc/HOAc with 0.38 M NaNO ). The pattern is showed to
3
irreversible waves observed in the electro active range of the supporting electrolyte. The cyclic
voltammogram of this complex (Figure 6) shows one peak in the negative potential range
VI
features the redox processes of W centers and is located in the domain where analogous W-
based processes were also obtained for sandwich type POMs [42]. Anodic peak at 0.85 V
2
+
attributed to the redox processes of Cu centers. The results indicated that with an increase in the
scan rate, the peak separation potential (E ) increased. As such, the increasing sizes of the
p
anodic and cathodic peak currents are almost the same, and the peak currents (I–I′) are
proportional to the square root of the scan rates (Figure 7), which indicates that the redox
processes are diffusion-confined over a specific range of scan rate. The same solution could be
kept and used after 2 days without any change in the cyclic voltammogram of the complex [43].
UV-vis spectrum of this polyoxometalate displays no sharp maxima for the Cu-centered d-d
transition bands in the visible region because the electronic spectrum is dominated by the charge-
transfer (oxygen-to-tungsten) bands of the polyoxoanion framework (Figure 8a).
The stability of Na K [K Cu (NO )(A-α-PW O ) ] in solution was assessed by monitoring its
4
5
3
3
3
9
34 2
UV-vis spectrum between pH 1 and 10. All of the spectra were reproducible with respect to
absorbencies and wavelengths (Fig. 8b). For above reason, the absorbance bond was selected in
UV region because these peaks were better defined when the pH decreased. Monitoring of the
UV-vis spectrum for this complex confirmed the stability which obtained by cyclic voltammetry.
7

ACCEPTED MANUSCRIPT
All of these observations suggested that Na K [K Cu (NO )(A-α-PW O ) ] is stable in solution
4
5
3
3
3
9
34 2
but K salts of this complex haven’t stability in different range of pH in solvent (Fig 8c) [44].
9
-
Catalytic studies of tetra-n-butylammonium (TBA) salt of [Cu K (A-PW O ) ] in the
3
3
9
34 2
epoxidation of representative organic substrates with H O as oxidant and MeCN as solvent was
2
2
also performed [45]. The catalytic oxidation results are presented in Table 1. By 2 equivalent of
9
-
H O and 0.5 mol% TBA salt of [Cu K (A-PW O ) ] , styrene, cyclohexene and cyclooctene
2
2
3
3
9
34 2
resulted mainly corresponded epoxides with high selectivity at 47-65% substrate conversion
46].
[
In the case of styrene, 65% conversion with 74% selectivity for styrene epoxide and 26% for
benzaldehyde was obtained. Especially for cyclooctene, only cyclooctene oxide was obtained
selectively. TBA H [Cu K (PW ) ] showed 47% conversion for cyclohexene with 83%
7
2
3
3
9 2
selectivity towards cyclohexene oxide and 17% for 1-cyclohexene-3-on. Also, these oxidation
9
-
reaction with H O and TBA salt of [Cu K (A-PW O ) ] as catalyst were carried out in
2
2
3
3
9
34 2
different solvents. It was found that CH CN at the same condition present the best activity and
3
selectivity. At the reaction condition, the presence of catalyst was crucial for progress of
oxidation and in the absence of catalyst the progress of reaction was very low. In comparison
with previous similar catalysts in epoxidation of alkenes, our catalytic system shows very good
results in both of conversion and selectivity [27-30,47]. The infrared spectra of the [Cu K (A-
3
3
9
-
PW O ) ] which obtained at the end of reactions, indicated that stability of the catalysts had
9
34 2
occurred.
Here, the first example of a stable central belt nitrate encapsulated A-type sandwich
polyoxometalate was reported. This synthetic procedure opens up a new route to synthesis of the
stable sandwich type polyoxometalate structures directly from their Keggin analogues. All of
8

ACCEPTED MANUSCRIPT
observations showed that Na K [K Cu (NO )(A-α-PW O ) ] was stable in aqueous and in
4
5
3
3
3
9
34 2
9
-
MeCN solution. The TBA salt of [Cu K (A-PW O ) ] revealed good catalytic activity and 74-
3
3
9
34 2
9
9% selectivity in the liquid phase oxidation of model organic compounds with aqueous H O .
2 2
The superiority of the catalyst lies in its good conversion with high selectivity.
Appendix A. Supplementary material
The single crystal X-ray diffraction measurement was carried out at MX1 beam lines at the
Australian Synchrotron, Melbourne. Diffraction data were collected using Si <111>
monochromated synchrotron X-ray radiation [λ=0.71080 (MX1)] at 100 (2) K with BlueIce
software [48] and were corrected for Lorentz and polarization effects using the XDS software
[
49]. The structures were solved by direct methods and the full-matrix least-squares refinements
were carried out using SHELXL [50] Details concerning collections and analyses are reported in
Table 2. CCDC 955495 contains the supplementary crystallographic data for this structure. This
data can be obtained free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article could be
found, in the online version, at http://dx.doi.org/10.1016/j.ica.2012.10.030.
Acknowledgments
Support for this research by the University of Isfahan is acknowledged.
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9
34 2
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[
4
5
3
3
3
9
34 2
2
4
2
Na HPO (0.24, 1.7 mmol) were dissolved in 100 mL H O followed by an addition of
2
4
2
Cu(NO ) ·6H O (0.31 g, 1.01 mmol), resulting in a cloudy suspension. The pH was adjusted to
3
2
2
7
.5 by drop wise addition of 6 M HCl, and a green solution formed. The produced green solution
heated at 90 ºC for 1 h and then allowed to cool to room temperature. Powder KCl (0.6 g,
.0mmol) was added, and the solution was kept at room temperature. After several weeks, dark
8
green needle crystals were formed (yield 79% based on W). Synthesis of
K [Cu (PW O ) (NO )][19]: Na HPW O .xH2O (30 g, 11 mmol) and copper nitrate three
1
2
3
9
34 2
3
8
9
34
hydrate (5.06 g, 21 mmol) were added simultaneously to 240 mL of water. The mixture was
stirred for 2 min to obtain a clear green solution. This was filtered; potassium chloride (34 g) was
added to the filtrate, and the mixture was then stirred for another 2 min and filtered to obtain of
-1
K [Cu (PW O ) (NO )]. FTIR (KBr pellets) (cm ): 1100(s), 1065(s), 1043(sh), 945(sh),
1
2
3
9
34 2
3
8
71(m), 810(m), 741(s), 640(s). Elemental analysis calcd (%) for K [Cu (PW O ) (NO )]: Cu,
12 3 9 34 2 3
1
3

ACCEPTED MANUSCRIPT
3
6
.68; K, 9.06; N, 0.27; P, 1.20; W, 63.87. Found (%):Cu, 3.65; K, 9.0; N, 0.27; P, 1.23; W,
3.62.
9
-
The tetra-n-butylammonium (TBA) salt of [Cu K (NO )(PW O ) ] was prepared by a
3
3
3
9
34 2
metathesis reaction. To 0.555 g (0.1 mmol) of Na K [Cu K (PW ) ](K1) in 30 mL of H O was
4
5
3
3
9 2
2
added with stirring 0.322 g (10 mmol) of TBABr. CH Cl (250 mL) was added to this cloudy
2
2
solution, and the mixture was shaken in a separatory funnel. After standing for 30 min, the
mixture separated into a cloudy colorless upper layer and a clear yellow lower layer. The bottom
organic layer was collected and concentrated to thick oil with a rotary evaporator. A yellow solid
was then precipitated from the concentrated organic layer by addition of diethyl ether (100 mL).
The resulting solid was collected on a medium frit and dried under vacuum for 24 h (yield 80%).
IR and elemental analysis established that Na K [Cu K (NO )(PW O ) ] had not changed
4
5
3
3
3
9
34 2
during the conversion of Na K [Cu K (PW O ) (NO )] to TBA H [Cu K (PW O ) ]. FTIR
4
5
3
3
9
34 2
3
7
2
3
3
9
34 2
-1
(
2% KBr pellet, 1300-400 cm ): 1100(s), 1065(s), 1041(sh), 943(sh), 870(m), 808(m), 744(s),
6
1
42(s). Elemental analysis calcd for TBA H [Cu K (PW O ) ]: C, 20.92; H, 3.98; Cu, 2.96; K,
7 2 3 3 9 34 2
.82; N, 0.22; P, 0.96; W, 51.46 [MW = 6430.18]; Found: C, 20.88; H, 3.93; Cu, 2.91; K, 1.86;
N, 0.20; P, 0.94; W, 50.40.12.
32] A.C. Stowe, S. Nellutla, N.S. Dalal, U. Kortz, Magnetic properties of lone pair containing,
sandwich-type polyoxoanions: a detailed study of the hetero atom effect, Eur. J. Inorg. Chem.
004, 3792-3797.
33] H. Liu, C. Qin, Y.G. Wei, L. Xu, G.G. Gao, F.Y. Li, X.S. Qu, Copper-complex-linked
[
2
[
polytungsto-bismuthate (-antimonite) chain containing sandwich Cu(II) ions partially modified
with imidazole ligand, Inorg. Chem. 47 (2008) 4166-4172.
1
4

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[
34] U. Kortz, S. Nellutla, A.C. Stowe, N.S. Dalal, J. van Tol, B.S. Bassil, Structure and
8
-
magnetism of the tetra-copper(II)-substituted heteropolyanion [Cu K (H O) (α-AsW O ) ] ,
4
2
2
8
9
33 2
Inorg. Chem. 43 (2004) 144-154.
35] U. Kortz, N.K. Al-Kassem, M.G. Savelieff, N.A. Al Kadi, M. Sadakane, Synthesis and
characterization of copper-, zinc-, manganese-, and cobalt-substituted dimeric heteropolyanions,
[
n-
III
III
2+
2+
IV
IV
[
(α-XW O ) M (H O) ] (n = 12, X = As , Sb , M = Cu , Zn ; n = 10, X = Se , Te , M =
9 33 2 3 2 3
2
+
10-
2+
2+
2+
Cu ) and [(α-AsW O ) WO(H O)M (H O) ] (M = Zn , Mn , Co ), Inorg. Chem. 40
9
33 2
2
2
2
2
(
2001) 4742-4749.
36] G. Zhu, Y.V. Geletii, J. Song, C. Zhao, E.N. Glass, J. Bacsa, C.L. Hill, Di- and tri-cobalt
[
silicotungstates: synthesis, characterization, and stability studies, Inorg. Chem. 52 (2013) 1018-
024.
37] A. Müller, M. Penk, R. Rohlfing, E. Krickemeyer, J. Döring, Topologically interesting
1
[
cages for negative ions with extremely high “coordination number”: an unusual property of V-O
clusters, Angew. Chem. Int. Ed. 29 (1990) 926-927.
[
38] G.K. Johnson, E.O. Schlemper, Existence and structure of the molecular ion 18-
vanadate(IV), J. Am. Chem. Soc. 100 (1978) 3645-3646.
[
39] A. Müller, E. Krickemeyer, M. Penk, H.J. Walberg, H. Bögge, Spherical mixed-valence
5
-
[
V O ] , an example from an unusual cluster family, Angew. Chem. Int. Ed. 26 (1987) 1045-
15 36
1
046.
[
40] Thermogravimetric analysis (TGA) was performed on a thermogravimetric analyzer TG50
−
1
in air from 25 to 800 °C at a heating rate of 5 °Cmin .
[
41] Infrared spectra (KBr pellets) were recorded on a JASCO, FT/IR-6300 instrument.
1
5

ACCEPTED MANUSCRIPT
[
42] D. Jabbour, B. Keita, I.-M. Mbomekalle, L. Nadjo , U. Kortz, Investigation of multi-nickel-
substituted tungstophosphates and their stability and electrocatalytic properties in aqueous
media, Eur. J. Inorg. Chem. 2004, 2036-2044.
[
43] The CV studies are performed at 25±2°C using a three-electrode assembly in 10 mL glass
cell including a Ag/AgCl (3 M KCl) electrode as the reference, a Pt plate as the counter
electrode, and the glassy carbon electrode (GCE) as the working electrode. All the potentials
were measured and reported vs. Ag/AgCl (3 M KCl). The CV measurements were carried out on
Autolab/Potentiostat/Galvanostat-302N, and controlled by Nova 1.8 software (Eco Chemie,
Utrecht, Netherlands).
[
[
44] UV-vis spectra were recorded on JASCO V-670 UV-vis spectrophotometer (190-2700 nm).
45] Typical procedure for catalytic epoxidation of alkenes: The oxidation reaction was carried
out as follows: TBA H [Cu K (PW O ) ] (0.005mmol), CH CN (3 mL), substrate (1 mmol),
7
2
3
3
9
34 2
3
and H O 30% (2mmol) were charged in the reaction flask. The reaction was carried out at 363 K
2
2
and detected with GC by the internal standard method.
46] The oxidation products were quantitatively analyzed by gas chromatography (GC) on a
Shimadzu GC-16A instrument using a 2m column packed with silicon DC-200 and FID detector.
47] X. Zhang, Q. Chen, D.C. Duncan, R.J. Lachicotte, C.L. Hill, Multiiron polyoxoanions:
Synthesis, characterization, X-ray crystal structure, and catalytic H O -based alkene oxidation by
[
[
2
2
III
[
[
(n-C H ) N] [Fe (H O) (PW O ) ], Inorg. Chem. 36 (1997) 4381-4386.
4 9 4 6 4 2 2 9 34 2
48] T.M. McPhillips, S.E. McPhillips, H.J. Chiu, A.E. Cohen, A.M. Deacon, P.J. Ellis, E.
Garman, A. Gonzalez, N.K. Sauter, R.P. Phizackerley, S.M. Soltis, P. Kuhn, Blu-ice and the
distributed control system: software for data acquisition and instrument control at
macromolecular crystallography beamlines, J. Synchrotron Radiat. 9 (2002) 401-406.
1
6

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[
49] W. Kabschi, Automatic processing of rotation diffraction data from crystals of initially
unknown symmetry and cell constants, J. Appl. Crystallogr. 26 (1993) 795-800.
50] G.M. Sheldrick, A short history of SHELX, Acta Crystallogr. A 64 (2008) 112-122.
[
1
7

ACCEPTED MANUSCRIPT
9
-
Figure 1. Combined polyhedral/ball-and-stick representation of the anions [Cu K (PW O ) ]
3
3
9
34 2
(
1): The WO octahedral are shown in purple, and the balls represent copper (green), potassium
6
(pale blue), nitrogen (blue), phosphor (yellow) and oxygen (red)
1
8

ACCEPTED MANUSCRIPT
Figure 2. Ball-and-stick representation of the central belt in 1
1
9

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Figure 3. Thermogravimetric curve showing the loss of crystalline water molecules (from 30 to
2
00 °C) and NO (from 350 to 400 °C) in complex
3
2
0

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Figure 4. Infrared spectra of Na K [K Cu (NO )(A-α-PW O ) ] (red = fresh complex, blue =
4
5
3
3
3
9
34 2
recrystallized complex)
2
1

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Figure 5. Infrared spectra of Na K [K Cu (NO )(A-α-PW O ) ] (red = fresh complex, blue = NO
4
5
3
3
3
9
34 2
3
decomposed after heating to 450 °C)
2
2

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Figure 6. Cyclic voltammogram of 1 mM Na K [K Cu (NO )(A-α-PW O ) ] obtained in the
4
5
3
3
3
9
34 2
−
1
solution of 0.02 M (pH 4.8) NaOAc/HOAc buffer with 0.38 M NaNO , scan rate 25mVs
3
2
3

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Figure 7. Cyclic voltammogram of 1 mM Na K [K Cu (NO )(A-α-PW O ) ] obtained in the
4
5
3
3
3
9
34 2
solution of 0.02 M (pH 4.8) NaOAc/HOAc buffer with 0.38 M NaNO , at different scan rates
3
2
4

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Figure 8a. Electronic absorption spectrum of 3 mM Na K [K Cu (NO )(A-α-PW O ) ]
4
5
3
3
3
9
34 2
(dilution-corrected).
2
5

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Figure 8b. Electronic absorption spectra obtained during acid/base titration of 3 mM
Na K [K Cu (NO )(A-α-PW O ) ] (dilution-corrected).
4
5
3
3
3
9
34 2
2
6

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Figure 8c. Electronic absorption spectra obtained during acid/base titration of 3 mM
K [Cu (NO )(A-α-PW O ) ] (dilution-corrected).
1
2
3
3
9
34 2
2
7

ACCEPTED MANUSCRIPT
a
Table 1. Epoxidation of alkenes in the presence of TBA H [Cu K (PW ) ]
7
2
3
3
9 2
b
b
Entry Alkenes
1
products
Conversion (%)
47
Selectivity (%)
83
2
3
54
65
99
74
a
Reaction condition: alkene (1 mmol), catalyst (0.005 mmol), acetonitrile (3
mL), reaction time 7 h and H O 30% (2 mmol) at 60ºC.
2
2
b
Conversions and yields were determined by GC analysis using an internal
standard.
2
8

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Table 2. Crystal structure data for Na K [K Cu (NO )(A-α-PW O ) ].22H O
4
5
3
3
3
9
34 2
2
Empirical formula
Cu K NNa O P W H
3 9 4 93 2 18 44
Formula weight
5551.73
Colour
Light green
100(2) K
Temperature
Wavelength
0.71073 Å
Crystal system, space group
Hexagonal, P6(3)/m
12.2440(17)
12.2440(17)
32.560(7)
90
a[Å]
b[Å]
c[Å]
α[°]
β[°]
γ[°]
90
120
3
Volume [A ]
4227.3(17)
3
Z
2, 4.327 Mg/m
-1
Absorption coefficient
F(000)
25.743 mm
4830
Theta range for data collection
Limiting indices
0.63 to 26.99 deg.
-15 ≤ h ≤15, -15 ≤ k ≤ 15, -41 ≤ l ≤ 41
Reflections collected / unique
Completeness to theta = 26.99
65703 / 3076 [R = 0.0606]
int
97.7
2
9