A Ni-containing decaniobate incorporating organic ligands: Synthesis, structure, and catalysis for allylic alcohol epoxidation

Article abstract of DOI:10.1039/c7ra03254d

An organic-inorganic hybrid polyoxoniobate, Na₈{Ni[Ni(en)]₂Nb₁₀O₃₂}·28H₂O (1) (en = ethanediamine), has been synthesized and characterized. It represents the first example of a trinuclear nickel-containing polyoxoniobate. The catalysis of 1 for allylic alcohol epoxidation was investigated at room temperature in aqueous solution, and was found to catalyze the epoxidation of 3-methyl-2-buten-1-ol with high conversion (98%) and selectivity (94%). Furthermore, magnetic measurements showed that the compound exhibits ferromagnetic interactions.

Full text of DOI:10.1039/c7ra03254d

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A Ni-containing decaniobate incorporating organic
ligands: synthesis, structure, and catalysis for allylic
alcohol epoxidation†
Cite this: RSC Adv., 2017, 7, 28696
*
Li Li, Yanjun Niu, Kaili Dong, Pengtao Ma, Chao Zhang, Jingyang Niu
*
and Jingping Wang
An organic–inorganic hybrid polyoxoniobate, Na8{Ni[Ni(en)]2Nb10O32}$28H2O (1) (en ¼ ethanediamine),
has been synthesized and characterized. It represents the first example of a trinuclear nickel-containing
polyoxoniobate. The catalysis of 1 for allylic alcohol epoxidation was investigated at room temperature in
aqueous solution, and was found to catalyze the epoxidation of 3-methyl-2-buten-1-ol with high
conversion (98%) and selectivity (94%). Furthermore, magnetic measurements showed that the
compound exhibits ferromagnetic interactions.
Received 20th March 2017
Accepted 17th May 2017
DOI: 10.1039/c7ra03254d
rsc.li/rsc-advances
On the other hand, POMs have been widely used as catalysts
for epoxidation reactions with hydrogen peroxide in the past
few years.11a,b Epoxide alcohols, as an important intermediate
Introduction
Polyoxoniobates (PONbs), an important subclass of poly-
oxometalates (POMs), have been investigated since the last
century due to their unique characteristics of high basicity and
high surface charge endowing them with spectroscopic,
magnetic, and catalytic properties.1,2 Nevertheless, in comparison
with other POMs, the development of PONbs is still in its infancy
owing to difficulties in controlling their synthesis, especially the
narrow working pH range of PONbs.3 Generally, most of the re-
ported PONbs focus on heteropolyoxoniobates with the typical
examples [XNb12O40]16ꢀ (X ¼ Si, Ge),4a [Ti2O2][XNb12O40]12ꢀ (X ¼
and nal product of the organic chemical industry, have already
been applied in the eld of ne chemicals, such as components
of cosmetic formulations for moister and cleaning of skin.
Traditionally, one of the useful approaches for the synthesis of
required epoxide alcohols is the epoxidation reactions of allylic
alcohols in the presence of H2O2 as the oxidation agent.11c–e
Therefore, we focus on the synthesis of TM-containing PONbs
and expect to discover good efficiency in the catalytic epoxida-
tion of allylic alcohols.
Herein, the sodium salt of nickel-decaniobate derivative
Na8{Ni[Ni(en)]2Nb10O32}$28H2O (1) was obtained by the hydro-
thermal and diffusional method, which was composed of a {Ni
[Ni(en)]2} cluster coordinated by two monolacunary [Nb5O18]11ꢀ
units. Furthermore, the Ni2+ ions at both ends of the {Ni
[Ni(en)]2} cluster are functionalized by one en molecule
respectively, resulting in a pseudosandwich-type PONb-based
organic–inorganic hybrid compound. Most notably, it repre-
sents the rst example of trinuclear Ni-containing PONb and
extends into a one-dimensional (1D) chain by high-nuclear
sodium-clusters. Furthermore, the catalytic epoxidation of
allylic alcohols has also been preliminary studied. To the best of
our knowledge, this is the rst example of the epoxidation of
allylic alcohols using PONb as an efficient catalyst at room
temperature in aqueous solution.
Si, Ge),4b,c [Nb2O2][SiNb12O40]10ꢀ
,
and [SiNb18O54]14ꢀ
.
Up to
4d
4e
now, isopolyoxoniobates including [Nb10O28]6ꢀ
,
[Nb20O54]8ꢀ
,
5a
5b
[Nb24O72H9]15ꢀ
,
[HNb27O76]16ꢀ, [H10Nb31O93(CO3)]23ꢀ
,
and
5c
5d
[Nb32O96H28]4ꢀ (ref. 2b) have been isolated. In addition,
a number of transition-metal (TM)-containing PONbs have also
been obtained. The few examples of the PONbs are {Ti2Nb8},6a
{TiNb9},6b {Ti12Nb6},6c {V3Nb12},7a {V4Nb6},7b {V4Nb10},7c
{PV2Nb12},7d {XV8Nb8} (X ¼ P, V),7e {PV6Nb12},7f {VNb14},7g
{V8Nb48},7h {Cu24Nb56}, {Cu25.5Nb56},8a {CuNb11},8b {Co14Nb36},9a
{Co8Nb24},9b {NiNb12},10a {NiNb9},10b {Ni10Nb32}.10c Introducing
TMs with d electrons into the reaction can enrich the diversity of
structures and properties in polyoxoniobates.
Henan Key Laboratory of Polyoxometalate Chemistry, Institute of Molecular and
Crystal Engineering, College of Chemistry and Chemical Engineering, Henan
University, Kaifeng 475004, Henan, China. E-mail: jyniu@henu.edu.cn; jpwang@
henu.edu.cn; Fax: +86-371-23886876
Results and discussion
† Electronic supplementary information (ESI) available: Bond valence sum
calculations of
O and Ni (Tables S1 and S2), additional structural gures Synthesis
(Fig. S1 and S2), additional measurements (Fig. S3–S8, Tables S3 and S4),
catalytic properties (Fig. S9, S10, Tables S5 and S6). CCDC 1526285 for 1. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c7ra03254d
An interesting TM-substituted PONb Na8{Ni[Ni(en)]2Nb10O32}$
28H2O (1) was synthesized using the hydrothermal synthesis
method by reaction of the SeO2, Ni(NO3)2$6H2O, and
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described as {W10O32} reported by Fuchs et al.13 It consists of
two equivalent lacunary [Nb5O18]
11ꢀ subunits fused together by
four bridging oxygen atoms and the [Nb5O18]11ꢀ unit is ob-
tained by removal of one {NbO6} octahedron from well-known
Lindqvist anion [Nb6O19]18ꢀ (Fig. S1†). There are four types of
oxygen atoms in the {Ni[Ni(en)]2Nb10O32} unit: ten terminal
oxygen atoms (Ot), twelve bridging m2-oxygen atoms, four
bridging m3-oxygen atoms, four bridging m4-oxygen atoms, and
two central m6-oxygen atom. The bond lengths of Nb–Ot, Nb–m2-
O, Nb–m3-O, Nb–m4-O and Nb–Oc in {Ni[Ni(en)]2Nb10O32} are in
Scheme 1 The preparation process of 1.
˚
˚
the range of 1.766(5)–1.773(5) A, 2.029(4)–2.032(4) A, 2.052(4)–
˚
˚
˚
2.098(4) A, 1.929(4)–2.012(4) A and 2.350(4)–2.410(4) A. In the
{Ni[Ni(en)]2} cluster, three nickel ions constitute a linear {Ni3}
cluster via four bridging oxygen atoms (Fig. 1b). The Ni ions in
{Ni[Ni(en)]2} cluster are all in the octahedral coordination
environment, Ni1 ion is coordinated by four m2-O and two
central oxygen atoms from two [Nb5O18]11ꢀ units (Fig. 1c) and
Ni2 ions are completed by two N atoms from an en ligand and
four O oxygen atoms from two [Nb5O18]11ꢀ skeletons (Fig. 1d).
As shown in Fig. 2, the adjacent cluster anions in 1 are linked
alternately via {Na8} clusters into one-dimensional (1D) chain. It
represents the rst example of a high-nuclear sodium-cluster-
containing in PONb. The Na+ ions in the {Na8} cluster could
be divided into four groups according to the difference between
their coordinated environments. The Na1, Na2 and Na3 ions are
all embedded in octahedral geometries with different coordi-
nation environments whereas Na4 ions exhibit a square
pyramid geometry. On the one hand, Na1 and Na2 ions links
each other by sharing two m2-O atoms forming a type of [Na2]2+
dimeric clusters in the edge-sharing mode, meanwhile the
adjacent [Na2]2+ clusters are connected by two m2-O atoms
generating a [Na4]4+ tetrameric cluster. On the other hand, Na3
and Na4 ions also join together by sharing two m2-O atoms
forming another type of [Na2]2+ dimeric clusters. Moreover, one
K7HNb6O19$13H2O with the presence of en at the pH value of
12.3–12.8 (Scheme 1). Parallel experiments show that the nal
product depend on three key factors: (a) the introduction of en
ligand. Its presence during the course of the reaction is crucial
because the polyoxoanion could not be obtained if 1,2-dia-
minopropane or 1,3-diaminopropane was used to replace it or
in the absence of it; (b) using NaOH solution to adjust pH value.
Its presence is necessary to obtain pure bulk samples and the
crystals could not be gained when NaOH solution was replaced
by LiOH, KOH, or CsOH solution. The results conrm that
counter cations can have signicant effects on the synthesis; (c)
the presence of SeO2. Notably, although SeO2 was used as
a staring material in the system, no selenium atom was
observed in the compound. When SeO2 was removed from the
reaction, no crystals were afforded. The specic role of SeO2 was
not well understood, and SeO2 may play a synergistic action
with other materials in the reaction and the similar phenomena
have been previously reported.12
Crystal structure
Single-crystal X-ray diffraction analysis indicates that the
structure of compound 1 possesses a cluster of {Ni[Ni(en)]2-
Nb10O32} along with eight Na+ cations and twenty-eight water
molecules. Compound 1 crystallizes in the triclinic molecular
ꢀ
symmetry, P1 space group. The {Ni[Ni(en)]2Nb10O32} cluster is
constructed by a {Ni[Ni(en)]2} cluster sandwiched into the novel
{Nb10O32} fragment (Fig. 1a). And the {Nb10O32} unit can be
Fig. 2 (a) Combined polyhedral/ball-and-stick representation of the
Fig. 1 (a) Ball-and-stick representation of the {Ni[Ni(en)]2Nb10O32
}
{Ni[Ni(en)]2Nb10O32} unit; (b) ball-and-stick representation of the {Na8}
unit; (b) view of the {Ni[Ni(en)]2} cluster in 1; (c) the coordinated cluster; (c) combined polyhedral/ball-and-stick representation of one-
environment of Ni1 in 1; (d) the coordinated environment of Ni2 in 1. All dimensional (1D) of 1. All hydrogens, and lattice water molecules are
hydrogens, sodium ions, and lattice water molecules are omitted for omitted for clarity. Colour code: Nb (green), Ni (pink), N (blue), C (gray),
clarity. Colour code: Nb (green), Ni (pink), N (blue), C (gray) and O (red). Na (yellow) and O (red) respectively.
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[Na4]4+ and two [Na2]2+ dimeric clusters are connected by
sharing four m2-O atoms forming the {Na8} cluster and dis-
playing a unique cruciform structure.
The phase purity of 1 was characterized by the powder X-ray
diffraction (PXRD) pattern of the bulk products (Fig. S3†). The
PXRD pattern is in good agreement with the simulated XRPD
patterns resulted from single-crystal X-ray diffraction, which
conrms that the phase is pure. And the difference in intensity
may be due to the preferred orientation of the powder samples.
The band valence sum (BVS) calculations of compound 1
conrm that the oxidation states of the Ni and Nb atoms are +2,
+5, respectively.14 The BVS values for all oxygen atoms and
nickel atoms in 1 are also listed in Tables S1 and S2.†
Fig. 3 The ESI mass spectrum of {Ni(Nien)2Nb10O32} in the range of m/
z ¼ 0ꢀ1500.
IR and UV spectra
The infrared spectrum of compound 1 was recorded between
4000 and 400 cmꢀ1 with KBr pellet. The IR spectra shows seven
characteristic vibration bands in the low-wavenumber region (v
< 1000 cmꢀ1) belonging to the Lindqvist hexaniobate structure,
the peak at 867 cmꢀ1 can be assigned to terminal Nb–Ot char-
acteristic vibration, as well as peaks at 667–419 cmꢀ1 can be
attributed to bridging Nb–Ob vibration. In comparison with the
precursor K7HNb6O19$13H2O, the bridging Nb–Ob vibration
band splits into more components and shows slightly red shis,
which may originate from the coordination of Ni2+ with the
bridging oxygen atoms of the PONb anion.15 Moreover, the
peaks at 1025 cmꢀ1 can be assigned to C–N bond characteristic
vibration of organic-ligand en (Fig. S4†).
Magnetic properties
The magnetic susceptibility for 1 was measured at 2–300ꢀK1
under a 1000 Oe magnetic eld. Their plots of cMT and cM
versus T are illustrated in Fig. 4. Along with the temperature
decreased, the cMT product of 1 increased from 5.355 emu K
molꢀ1 at 300 K to a maximum of 8.622 emu K molꢀ1 at 5 K.
This characteristic thermal behavior is indicative of an overall
ferromagnetic coupling between nickel ions.17 Upon the
temperature lower than 5 K, the rapid drop of the cMT
products may also be assigned to zero-eld splitting. The
experimental data have been well tted by the Curie Weiss law
(cM ¼ C/(T ꢀ q)) above 1.8 K with the following Curie and
Weiss constants: 5.234 emu molꢀ1 K and 5.317 K, respectively
(Fig. 4 and S9†). The positive Weiss constant conrms the
presence of the ferromagnetic couplings between Ni2+
centers.18 When the experimental cMT value of 5.355 emu K
molꢀ1 at room temperature (300 K) is compared with that of
the spin-only value of 3 emu K molꢀ1 for 3 non-interacting
Ni2+ ions (S ¼ 1) with g ¼ 2.0, we can see that the experi-
mental cMT value is higher than the calculate cMT value. So
there exist spin–orbit coupling and ferromagnetic couplings
among Ni2+ ions.9b,10c
UV-vis absorption spectrum of compound 1 (3 ꢁ 10ꢀ6 mol
Lꢀ1) in the aqueous solution displays one strong absorption
band at 192 nm and one wide absorption band at 225 nm
(Fig. S5 and S6†), which can be tentatively assigned to the pp–
dp charge-transfer transitions of oxygen-to-niobium bonds.12b
In comparison with UV spectra of the precursor K7HNb6O19-
$13H2O, the absorption band at 225 nm shows slightly blue
shis, which results from the coordination of Ni2+ with the
oxygen atoms of the PONb anion.15
ESI-MS studies
During the course of this study, negative electrospray ioniza-
tion mass spectrometry (ESI-MS) allowed us to identify intact
polyanions {Ni[Ni(en)]2Nb10O32}.16 The compound
1 was
dissolved in a minimum amount of water, and a few drops
of this aqueous solution were mixed with acetonitrile
(V(H2O) : V(CH3CN) ¼ 1 : 1). ESI-MS data shows two dominant
series of multiply charged peaks which can be attributed to
series of peaks for ꢀ3 and ꢀ2 charged ions (Fig. 3). The series
of ꢀ3 and ꢀ2 ion peaks can be attributed to {NaxHyNi
3ꢀ
[Ni(en)]2Nb10O32
}
(x + y + 3 ¼ 8), {NaxHyNi[Ni(en)]2Nb10
-
2ꢀ
O32
}
(x + y + 2 ¼ 8) polyanions on the basis of their m/z
values, showing the presence of intact cluster in the mixture
solution. Primary peaks centered at m/z 587.95 and 904.45 are
clearly observed in the m/z 0–1500 range (Fig. 3, S7 and S8†).
The extended peaks at around m/z 587.95 and 904.45 are
provided in the ESI (Tables S3 and S4†).
Fig. 4 The plots of cMT and cMꢀ1 versus T for 1 between 2 and 300 K.
(outside: cMT; inside: 1/cMꢀ1).
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atoms play the main role in the process of the epoxidation
Catalytic properties
reactions. Under optimal conditions (12 mmol catalyst, 5 mmol
Compound 1 was investigated as a heterogeneous catalyst in
allylic alcohols epoxidation with H2O2 and allylic alcohols can
be transform to epoxy alcohols as major products and the cor-
responding aldehydes and polyols were formed together as by-
products (Table S5†). Initial experiments were carried out by
using 3-methyl-2-buten-1-ol as a model substrate with the
assistance of H2O2. Furthermore, the results of a series of
parallel experiments showed that the conversion increased as
the catalyst or H2O2 dosage increased (Table 1, entries 1–3 and
6), and didn't change obviously with the increase of reaction
temperature and reaction time. As shown in Table 1, 3-methyl-2-
buten-1-ol was oxidized to epoxy alcohol with 98% conversion
substrate and
8 mmol H2O2), 3-methyl-2-buten-1-ol was
oxidized to epoxide with 98% conversion and 94% selectivity at
25 ꢂC for 5 min (Table 1, entry 3). Aer the epoxidation reaction,
the product was separated from the aqueous phase by extrac-
tion with ethyl acetate. And the catalyst still existed in the
aqueous solution aer extraction, so the aqueous phase could
be used for the next run.19 The catalytic activity of compound 1
was not obviously changed upon completion of the sixth run
(Fig. S10†), but the catalytic activity of K7HNb6O19$13H2O was
decreased upon the process of duplicate operation (Fig. S11†).
Aer epoxidation was completed, the catalyst was retrieved
from the solvent/oxidant/substrate system by centrifugation.
According to the comparisons of IR spectra of the fresh catalyst
and the used catalyst aer the sixth-run reaction (Fig. S12†), the
noticeable differences of the IR spectrum are at the peaks of
1388 and 668 cmꢀ1. The results suggested that the framework
structure of the catalyst was partially decomposed. The reason
for the differences in IR spectra may be that the recovered
catalyst has been partly peroxidated by H2O2.20
The catalytic activities of other allylic alcohols like 2-methyl-
2-propen-1-ol, trans-2-hexen-1-ol and crotyl alcohol were also
tested under the same reaction conditions (Tables 1 and S8†).
The results showed that 1 was active for these allylic alcohols as
well (Table 1, entries 8–10). 3-Methyl-2-buten-1-ol affords the
highest epoxide yields and selectivity, while 2-methyl-2-propen-
1-ol and trans-2-hexen-1-ol are less reactive corresponding to
36% conversion and 94% selectivity (Table 1, entry 8) and 41%
ꢂ
and 94% selectivity at a temperature of 25 or 35 C for 5 min
(entries 3 and 7). This fact indicated that the conversion and
selectivity of transformation to epoxide cannot achieve an
obviously higher level as expected when the temperature is
ꢂ
signicantly higher than 25 C. Moreover, the performance of
epoxidation under low temperature ensures better security and
allows the reduction of operating costs, so the temperature of
25 ꢂC is the optimal reaction temperature. On the basis of these
results, the catalyst and H2O2 dosage were the crucial factors for
the conversion of epoxy alcohols. In contrast to catalyst 1,
a blank experiment without 1 (Table 1, entry 5) indicated that
the epoxidation scarcely happened and the epoxidation reaction
with the precursor K7HNb6O19$13H2O indicated that the
conversion was 95% (Table S6,† entry 3). As a result, the
conversion of allylic alcohols epoxidation reactions of 1 was
better than that of K7HNb6O19$13H2O, which suggests that Nb
Table 1 Epoxidation of various allylic alcohols with H2O2 in water catalyzed by compound 1
Entry
Substrate
Product
30%H2O2 (mmol)
Time (min)
Con.a (%)
Sel. (%)
1b
2
3
3
5
8
8
8
8
8
5
5
5
15
5
36
80
98
97
5
94
94
94
94
60
93
94
4
5c
6d
7e
5
5
84
98
8
9
8
8
60
60
36
41
94
93
10f
8
60
71
81
a
b
Conversion determined by GC with dodecane as an internal standard. The products were identied by GC-MS. Reaction conditions for the
entries 1 to 5: catalyst (12 mmol), substrate (5 mmol) and H2O (3 mL) at 25 ꢂC. c Blank experiment, the reaction was carried out without catalyst.
d
e
Reaction conditions: catalyst (6 mmol), substrate (5 mmol) and H2O (3 mL) at 25 ꢂC. Reaction conditions for the entries 7 to 10: catalyst (12
mmol), substrate (5 mmol) and H2O (3 mL) at 35 ꢂC. f cis- and trans-mixture.
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Table 2 Crystal structure data for compound 1
conversion and 93% selectivity (Table 1, entry 9), respectively. In
addition, crotyl alcohol gave 71% conversion and 81% selec-
tivity (Table 1, entry 10). This result suggests that 1 can effi-
ciently catalyze allylic alcohols epoxidation. Comparing with the
reactivity for other allylic alcohols of catalyst 1 and K7HNb6-
O19$13H2O, the reactivity of K7HNb6O19$13H2O is slightly
higher than that of catalyst 1 (Table S8†). Aer epoxidation was
completed, hydrogen peroxide consumption was determined
iodometrically,21 and the results indicated that the conversion
of transformation to epoxy alcohols is related to the consump-
tion of hydrogen peroxide (Table S9†).
Formula
Mr (g molꢀ1
T (K)
C4N4Nb10Ni3O60H72Na8
2425.80
293(2)
ꢀ
P1
)
Space group
Crystal system
Triclinic
˚
a (A)
12.5635(8)
12.9279(9)
13.1370(9)
61.8590(10)
63.6420(10)
61.2230(10)
1582.83(19)
1
˚
b (A)
˚
c (A)
a (deg)
b (deg)
g (deg)
3
˚
V (A )
Z
Dc (g cmꢀ3
)
2.545
2.783
1186.0
Experimental section
Materials and methods
m (mmꢀ1
F (000)
)
2q range (deg)
Data/restraints/
parameters
3.664 to 50.196
5578/0/238
The raw material K7HNb6O19$13H2O were prepared as
described in the literature and characterized by IR spectrum.22
All chemicals were purchased from commercial sources and
used as received. Elemental analyses (C, H, N) were performed
on an Elementar Vario EL cube CHNS analyzer. The IR spectrum
was recorded on a Bruker-Vertex 70 FT-IR spectrometer using
KBr pellets in a range of 4000–400 cmꢀ1. The UV spectra were
recorded with a U1900 spectrometer (distilled water as solvent)
in the range of 800–190 nm. Powder X-ray diffraction (PXRD)
data were recorded on a Bruker AXS D8 Advance instrument
Reections collected
Index ranges
8189
ꢀ14 # h # 14, ꢀ15 # k # 15, ꢀ13 # l # 15
GOF on F2
1.021
R1, wR2 [I > 2s(I)]
R1, wR2 [all data]
R1 ¼ 0.0411, wR2 ¼ 0.0992
R1 ¼ 0.0545, wR2 ¼ 0.1077
ray diffraction intensity data collection were mounted on a Bruker
Apex-II CCD diffractometer using graphite-monochromatized Mo
Ka radiation (l ¼ 0.71073 A) at 293(2) K (Table 2). Routine Lorentz
˚
with Cu Ka radiation (l ¼ 1.5418 A) in the angular range 2q ¼ 5–
50ꢂ at 293 K. Variable-temperature magnetic susceptibility data
were obtained on Quantum Design MPMS3 magnetometer in
the temperature range of 1.8–300 K with an applied eld of 1000
Oe. The mass spectrometer used for the measurements was AB
SCIEX Triple TOF 4600. The epoxidation products were identi-
ed by Agilent Technologies 7890B/5977B GC-MS instrument,
and the conversion determined by BRUKER 450-GC instrument.
Synthesis of compound 1. Ni(NO3)2$6H2O (0.175 g) was added
in distilled water (0.833 mL) under stirring. When the solid is
dissolved, en (0.23 mL) was added to obtain the amaranthine
solution. Then the resulting solution was added dropwise to the
solution of K7HNb6O19$13H2O (0.137 g, 0.1 mmol) and SeO2
(0.045 g, 0.4 mmol) in water (10 mL) under stirring. Subsequently,
the pH value of the mixture was adjusted to 12.3–12.8 using NaOH
(2 mol Lꢀ1) solution and then stirred for about 30 min. The
mixture was put into a Teon-lined autoclave (23 mL) and kept at
140 ꢂC for 96 h, then cooled to room temperature and ltered.
Aer that, the ltrate was transferred to a straight glass tube,
ethanol/water (1 : 3) was carefully layered onto the resulting
amaranthine solution, and then the pure alcohol was layered onto
the ethanol/water phase. Aer about one month the light-blue
crystals are found in the test tube. Yield: 54% (based on K7HNb6-
O19$13H2O). Elemental analysis (%) calculated for compound 1: C
1.98, H 2.99, N 2.31; found for C 1.83, H 2.94, N 2.28. Selected IR
(KBr, cmꢀ1): 3248 (vs.), 2174 (m), 1663 (s), 1585 (w), 1458 (w), 1023
(s), 867 (s), 775 (w), 667 (s), 621 (w), 546 (m), 483 (m), 419 (m).
˚
and polarization corrections were applied, and a multi-scan
absorption correction was performed using the SADABS program.
The structure was solved by direct methods and rened by the full-
matrix least-squares method on F2 using the SHELXS-97 and
SHELXL-2014 program suite.23 In the nal renement, the Nb and
Na atoms were rened anisotropically; the O, C and N atoms were
rened isotropically. The hydrogen atoms of the organic groups
were placed in calculated positions and then rened using a riding
model with a uniform value of Uiso ¼ 1.2 or 1.5Ueq. All H atoms on
water molecules were directly included in the molecular formula.
Conclusions
In summary, we have synthesized and characterized a novel
organic–inorganic hybrid PONb which contains trinuclear
nickel cluster. Furthermore, compound 1 shows catalytic
activity for the epoxidation of various allylic alcohols with
hydrogen peroxide. The successful synthesis of compound 1
enriches the structural diversity of PONbs and further proves
that the use of metal–ligand cations could provide new way to
synthesize diverse PONb anion architecture. In the following
work, we will concentrate on improving the activity and selec-
tivity for allylic alcohols epoxidation and the synthesis of novel
PONb derivatives.
Acknowledgements
X-ray crystallography
A suitable single crystal was selected from its mother liquor and We gratefully acknowledge the National Natural Science Foun-
sealed in a thin glass tube since the crystal is easily efflorescent. X- dation of China (21371048), Key Lab of Polyoxometalate Science
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Henan Province for nancial support.
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