Inorganic Chemistry
Article
Elemental analysis (%) calcd for 1: K 6.72, Sc 1.29, P 0.89, W 57.96,
C 1.37; found: K 6.90, Sc 1.48, P 0.96, W 57.45, C 1.66.
concentration buffer, especially at higher pH (such as 5.5),
would provide more acetate ions, facilitating its coordination
with Sc.
2
.3. Synthesis of Na [Sc (CH COO) PW O ]·10H O·
3
7 2 3 2 10 38 2
CH COONa (2). 2 was prepared by a procedure similar to that of
2
Single-crystal X-ray diffraction analysis reveals that com-
pound 1 crystallizes in the tetragonal space group I4/mmm. As
shown in Scheme 1, 1 contains a mono-Sc-substituted Keggin-
1
, and the only difference is that 0.5 M NaAc/HAc buffer solution
(pH = 5.5) was used instead of the 0.3 M buffer (pH = 4.5). The pH
value after the reaction is about 5.7, and NaCl (0.100 g, 1.71 mmol)
was added into the filtrate to promote crystallization. After several
weeks of evaporation, colorless block single crystals of 2 were
collected by filtration and air-dried (yield: 23% based on P).
Compound 2 can only be prepared under pH 5.5. The experiments
under other pH condition below or above 5.5 led to the formation of
precipitate. In addition, compounds 1 and 2 were never seen together
in the same batch. In addition, the preparation of 2 using [α-
4
−
type polyanion cluster, [Sc(H
O)PW11O39] , with C3v
2
4
−
symmetry. The [Sc(H O)PW O ] cluster can be viewed
2
11 39
as incorporating a Sc ion into the classical monovacant Keggin-
7−
type [α-PW O ] . In this cluster, Sc ion coordinates with
1
1
39
7−
five O atoms from [α-PW O ] and one water molecule to
1
1
39
exhibit a distorted octahedral geometry. Notably, both
positional disorder and atomic occupancy disorder can be
observed in the structure. The central P is surrounded by eight
half-occupied oxygen atoms, and four metal centers are
occupied by disordered Sc and W with an occupancy of 25%
and 75%, respectively. Monosubstituted Keggin-type clusters
are important members in the POM family, and many
−
1
PW O ] is unsuccessful. Selected IR (2% KBr pellet, ν/cm ):
11
39
3
8
390(s), 1625(s), 1535(s), 1469(m), 1401(s), 1048(s), 950(s),
79(m), 802(w), 643(m) cm . Elemental analysis (%) calcd for 2:
−1
Na 6.49, Sc 2.82, P 0.97, W 57.62, C 3.01; found: Na 6.50, Sc 2.94, P
.95, W 57.20, C 2.68.
.4. X-ray Crystallography. The intensity data of 1 and 2 were
0
2
collected on a Bruker APEX 2 DUO CCD single-crystal
diffractometer equipped with a sealed Mo tube and a graphite
monochromator (λ = 0.71073 Å) at 120 K. The crystals were
mounted in a Hampton cryoloop with oil to prevent the loss of crystal
transition metals have been introduced into the lacunary site
36−42
of {XW O }.
Compared with other 3d metal-substituted
1
1
39
POMs, Sc-substituted Keggin-type POM has rarely been
reported. In 2006, the mono-Sc-substituted Keggin was been
waters. Then, both structures were solved by direct methods and
3
1
2
detected by P NMR in the solution of Sc ion and
refined by the full-matrix least-squares method fitting on (Σw(|F | − |
0
32−34
7
−
2
2
F | ) )) using the SHELXTL program package (Bruker).
The H
[PW11
O
39
39] . In addition, monosubstituted [Sc(H
2
O)-
c
4
−
atoms of the crystal waters were not located, and all heavy atoms were
refined with anisotropic thermal parameters. The crystal data and
structure refinement details for the three compounds are summarized
in Table S1, and the selected bond length and bond angles are given
in Table S2. The crystallographic data have been deposited to the
SiW O ] subunits were isolated in a 2D hybrid {[Cu-
1
1
2
8
(en) (H O)] [Cu(en) ] [(α-SiW O )Sc(H O)] (C O )}.
2
2
2
2 2
11 39
2
2
2
4
To our knowledge, compound 1 represents the first discrete
mono-Sc-substituted Keggin cluster.
Compound 2 crystallizes in the triclinic space group P1
possesses novel di-Sc-substituted cluster,
Sc (CH COO) PW O ] , with C symmetry. After decom-
̅
and
a
2
were defined by single-crystal X-ray diffraction data combined with
7−
[
2
3
2
10 38
3
9
−
position and recombination, the added [A-α-PW O ]
elemental analysis.
.5. Hydrolysis of DMNP. First, the 0.5 M HAc/NaAc solution
9
34
2
precursor was transformed to a rare disubstituted Keggin
1
1−
was prepared and the pH was adjusted to 7.0 by NaOH before the
addition of POMs or other catalysts. According to the calculation, at
pH 7.0 the ratio of HAc to NaAc is about 1:175 and acetate ions are
the predominant species. In some experiments, deionized water was
used instead of 0.5 M HAc/NaAc solution. For all hydrolysis
experiments, the aqueous solution of POM catalyst (0.006 mmol, 0.4
mL) and DMNP methanol solution (0.02 mmol, 0.1 mL) were
separately prepared, and their combination starts the reaction. The
catalytic reaction was carried out at room temperature with stirring
[α(1,8)-PW O ] and the two vacant sites are occupied by
10 38
two Sc ions (Scheme 1). In this polyanion, each Sc center is
coordinated with five O atoms from lacunary polyanion
11−
2
[
α(1,8)-PW O ]
1
0
38
exhibiting a monocapped trigonal prism geometry (Figure S2).
The Sc−O bond lengths are in the range of 2.02(5)−2.44(1)
Å. The polyanion can also be described as assembling two
{
W O } triads and two {W O Sc(OAc)} subunits around a
3 13 2 12
3
1
and was monitored by P NMR spectroscopy at various intervals of
time. The conversion of DMNP was calculated according to the peak
area ratio of the products to DMNP and the products.
central PO4 tetrahedron, where the two Sc centers are
separated without sharing any oxygen atom and where the
Sc···Sc distance is 5.02 Å. As in 2, the coordinated water
molecule of Sc is replaced by acetate, and the Sc ions in the
two clusters exhibit different coordination environment, which
might lead to different Lewis acid catalytic activity. Compared
with monosubstituted and trisubstituted POMs, the examples
of disubstituted POMs are limited. Several ditransition-metal-
3
. RESULTS AND DISCUSSION
.1. Synthesis and Structure. As shown in Scheme 1,
3
compounds 1 and 2 were synthesized by the conventional
aqueous solution method using a trilacunary Keggin-type
precursor, Na [A-α-PW O ], and scandium nitrate as starting
substituted POMs based on {α(1,8)-XW10
O38} (X = Ge, As)
9
9
34
materials in a NaAc/HAc buffer solution. The structural
transformation from {A-α-PW O } to monolacunary {α-
have been reported as subunits to construct dimeric, trimeric,
43,44
or tetrameric POM clusters.
To our knowledge, the
9
34
PW O } or dilacunary {α-PW O } happens during the
discrete disubstituted POM based on Keggin {α(1,8)-
1
1
39
10 38
synthesis of the two Sc-substituted POMs, which has also been
XW O } remains largely unexplored.
1
0
38
35
observed in literature reports. The control experiments
indicate that the pH value and the concentration of NaAc/
HAc buffer play important roles in the synthesis of 1 and 2.
Compound 1 was synthesized in 0.3 M NaAc/HAc buffer (pH
3.2. Catalytic Hydrolysis of Nerve Agent Simulant.
Compared with the reported insoluble Sc-containing POMs,
the synthesized two Sc-substituted Keggin clusters show
relatively good water solubility with the maximum solubility
of about 0.02 mmol/L. Compound 1 is only soluble in water.
In addition to water, compound 2 can also be dissolved in
some polar organic solvents, such as MeOH, DMF, and
no change was observed in their IR spectra (Figure S7),
4
.5), while compound 2 was isolated in 0.5 M NaAc/HAc
buffer (pH 5.5). When the pH value or concentration of buffer
were changed, only amorphous precipitates were obtained. We
speculate that on one side the formation of lacunary POM
subunit is sensitive to pH; on the other side, a high
C
Inorg. Chem. XXXX, XXX, XXX−XXX
Chi, Yingnan
