Evans-Showell-type polyoxometalate constructing novel 3D inorganic architectures with alkaline earth metal linkers: Syntheses, structures and catalytic properties

Article abstract of DOI:10.1039/c7dt01302g

Four new architectures containing [Co₂Mo₁₀H₄O₃₈]^6- polyoxoanions, (C₂N₂H₁₀)₂[Sr(H₂O)₅][Co₂Mo₁₀H₄O

Full text of DOI:10.1039/c7dt01302g

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EvansꢀShowellꢀtype polyoxometalate constructing novel 3D
inorganic architectures with alkaline earth metal linkers:
syntheses, structures and catalytic properties
Received 00th January 20xx,
Accepted 00th January 20xx
Yujiao Hou, Haiyan An*, Baojun Ding, Yanqin Li
DOI: 10.1039/x0xx00000x
6
ꢀ
www.rsc.org/
Four
new
architectures
containing
1, (C
O 3 and (C
[Co Mo H O ]
polyoxoanions,
2
10
4
38
(
(
(
C
2
C
3
C
2
N
2
N
2
N
2
H
H
H
10
)
)
2
[Sr(H
[Sr(H
2
O)
O)
5
][Co
][Co
2
Mo10
Mo10
H
H
4
O
O
38]ꢁ2H
38]ꢁ3H
2
O
2
N
2
H
10
)
2
[Ba(H
12)[Ba(H O)
2
O)
3
][Co
2
Mo10
][Co
H
4
O
38
]
ꢁ3H
2
O
2,
12
2
2
5
2
4
2
3
N
2
H
2
4
][Ba(H
2
O)
4
2
Mo10
H
4
O38]ꢁ2H
2
O 4
3 2
10 = ethylenediamine; C N H12 = 1,3ꢀpropanediamine) have been synthesized and characterized by
elemental analysis, IR spectroscopy, solid diffuse reflective spectroscopy, TG analysis, powder Xꢀray
diffraction and single crystal Xꢀray diffraction. Compounds 1 and 2 achieved in the presence of
6ꢀ
2+
2+
ethylenediamine, are built up of EvansꢀShowellꢀtype anions [Co
2 4
Mo10H O38] , linked by Sr or Ba cations
form 3D frameworks. To our knowledge, compound 1(2) represents the first example of 3D architectures in
6
ꢀ
which the EvansꢀShowell anions [Co
2
Mo10
H
4
O
38
]
were linked by pure alkaline earth cations. When
propanediamine was used instead of ethylenediamine, compounds 3 and 4 with 2D network were obtained.
phenomenon indicates that the organic cations which adjust the reaction pH values, can induce different
dimensional inorganic frameworks. As heterogeneous catalysts, compounds 1‒4 show excellent catalytic
performance in the cyanosilylation of carbonyl compounds. Furthermore, these catalytic reactions were
performed under solventꢀfree conditions using only a low amount of the catalysts, and these catalysts can be
recovered and reused without displaying any significant loss of activity. As far as we know, compounds 1‒4
represent the first examples of cyanosilylation catalyzed by POMꢀbased species containing alkaline earth
cations.
Introduction
allꢀinorganic elements, which are able to endow solid materials with
new structures and composite properties. Therefore, choosing
appropriate POMs and metal linkage units to achieve functional
assemblies is a promising way to get new types of 3D inorganic
Polyoxometalates (POMs), as inorganic high nuclear metal oxides
mainly Mo, W, V, Nb and Ta), have been an increasingly important
(
topic, owing to their intriguing architectures and numerous potential
applications in catalysis, medicine, electronics, magnetism and
framework materials possessing both stability and versatility.
6ꢀ
EvansꢀShowellꢀtype POM [Co
2
Mo10
H
4
O
38
]
with two terminal
1
ꢀ8
optics.
Over the past decade, many chemists from various
oxygen atoms, seized our attention, not merely holding strong
coordination ability forming new inorganic architectures, but also
disciplines have redirected their efforts to the field of
threeꢀdimensional (3D) extended frameworks based on POMs
through suitable linkers, not only from a structural point of view but
also from the significant applications of 3D materials which range
from catalysis, chemical separation and gas storage. However, 3D
solid materials built up of POM building blocks are inclined to be
20
possessing highly catalytic properties as Lewis acidꢀbase catalysts.
To the best of our knowledge, only one example of 3D architectures
6ꢀ
based on [Co
2
Mo10
H
][Co
4
O
38
]
has been reported by our group:
9ꢀ18
21
[
Ln(H O) ][Ln(H
2
7
2
O)
5
2
Mo10
H
4
O38]ꢁ5H
2
O
(Ln
=
Gd, Tb).
Meanwhile, the cheap alkaline earth metal cations not only hold the
similar radius and coordination nodes with rare earth metal cations,
but have potential applications as catalysts, scintillators, laser and
1
9
linked by metalꢀorganic coordination fragments. So far, very few of
D frameworks constructed from POMs are achieved through the
3
2
2ꢀ26
fluorescent lamp.
Thus, constructing 3D inorganic framework
compounds with excellent catalytic properties based on
EvansꢀShowellꢀtype POM [Co Mo10H O38] linked by alkaline earth
2 4
College of Chemistry, Dalian University of Technology, Dalian 116023, P. R. China
6
ꢀ
metal cations, is still an appealing and challenging work.
Cyanosilylation of carbonyl compounds yields cyanohydrin ether,
which is an important intermediate for fine chemicals and
27,28
pharmaceuticals.
Hence, to design and synthesize efficient
catalysts for cyanosilylation of carbonyl compounds is a meaningful
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Journal Name
ARTICLE
issue in current research. So far, the cyanosilylation is mostly Experimental section
catalyzed by electrophilic and nucleophilic catalysts, such as,
29,30
Materials and methods
phosphines, phosphazanes, and alkaline earth metal oxides.
Examples of cyanosilylation reaction catalyzing by POMs are very
rare up to the present date. In 2012, Mizuno and coworkers firstly
All chemicals were commercially purchased and used without
further purification. (NH [Co 38]·7H O was synthesized
according to the literatures, and characterized by means of IR
1
0ꢀ
4
)
6
2
8,39
Mo10
H
4
O
2
used polyoxoanion [{Y(H
2
O)
2
}
2
(αꢀSiW10
O
36
)
2
]
as a Lewis
3
acidꢀbase catalyst, which showed excellent catalytic effect for
cyanosilylation of ketones and aldehydes with trimethylsilyl cyanide
spectroscopy. Elemental analyses (C, H and N) were performed on a
PerkinꢀElmer 2400 CHN elemental analyzer; Co, Mo, Ba and Sr
were analyzed on a PLASMAꢀSPEC (I) ICP atomic emission
(
TMSCN). In the same year, their group introduced a series of rare
earth cations with larger ionic radii into the bilacunary
ꢀ
1
1
0ꢀ
3+
3+
3+
spectrometer. IR spectra were recorded in the range 400–4000 cm
[
{Ln(H
2
O)
2
(acetone)}
2
(αꢀSiW10
O
36
)
2
]
(Ln = Y , Nd , Eu ,
3
+
3+
on an Alpha Centaur FT/IR Spectrophotometer using KBr pellets.
TG analyses were performed on a PerkinꢀElmer TGA7 instrument in
Tb , or Dy ), to improve the catalytic performance of
cyanosilylation of carbonyl compounds with TMSCN as
homogeneous catalysts. In 2014, Niu’s group took advantage of
ꢀ
1
3
3
flowing N
samples were recorded on
diffractometer with graphite monochromatized Cu−Kα radiation (λ =
.154 nm) and 2θ varying from 5 to 50°. UVꢀvis spectra were
2
with a heating rate of 10 ºC·min . PXRD patterns of the
8
ꢀ
a
Rigaku Dmax 2000 Xꢀray
[
H
2
W
11
O
38
]
as building block to obtain a Lewis acidꢀbase
catalyst
heterogeneous
2 2 2 11 38 3 2 3
[Cu (bpy)(H O)5.5] [H W O ] H O·0.5CH CN}, which can drive
0
{
2
35
acquired on an Analytik Jena SPECORD S600 spectrophotometer
equipped with a diodeꢀarray detector and an immersible fiberꢀoptic
probe. Electrochemical data were obtained at room temperature
using a BAS CVꢀ50 W electrochemical analyzer equipped with a
glassyꢀcarbon working electrode, a Ptꢀwire auxiliary electrode, and a
Ag/AgCl (3M NaCl) BAS reference electrode.
cyanosilylation with good performance. In 2015, Sun and
coworkers successfully isolated one inorganicꢀorganic hybrid
compound
2 2 4 2 2 5 30 2
{[Cu12(pbtz) (Hpbtz) (OH) (H O)16][Na(H O)P W O110]}·16H O,
which can also catalyze cyanosilylation reactions through
a
3
6
heterogeneous manner. Recently, our group reported compounds
6
ꢀ
containing [Co
2
Mo10
H
4
O
38
]
as heterogeneous
38]·6H O (Ln = Sm, Eu) and
Mo10 38]·5H O exhibit excellent
catalysts:
Experimental Measurements
[
[
Ln(H
Zn (H
2
O)
O)
5
][Ln(H
2
O)][Co
]H
2
Mo10
H
4
O
2
2
2
5
(4,4’ꢀbipy)
3
2
[Co
2
H
4
O
2
Synthesis of(C
In a typical synthesis procedure for 1, a mixture of Sr(NO
0.0423 g, 0.2 mmol) and (NH [Co 38]·7H O (0.2 g, 0.1
2 2 10 2 2 5 2 4 2
N H ) [Sr(H O) ][Co Mo10H O38]ꢁ2H O (1)
catalytic effect under solventꢀfree conditions in the cyanosilylation
3 2
)
2
0
reactions. From the above researches, the development of efficient
and cheap heterogeneous catalysts for cyanosilylation of carbonyl
compounds with TMSCN still is a significant work in current
researches. Meanwhile, POMꢀbased catalysts for cyanosilylation
reactions mainly utilized rare earth cations or transition metal cations
as Lewis acid catalytic sites to date. In view of the similar radius of
alkaline earth metals with rare earth metal cations, it is thus of
considerable interest to investigate whether POMꢀbased compounds
containing alkaline earth metal cations can effectively catalyze the
cyanosilylation reaction as heterogeneous catalysts.
(
4
)
6
2
Mo10
H
4
O
2
mmol) was dissolved in 15 mL water. Then, one drop of
ethylenediamine were introduced dropwise into the system, the pH
ꢀ1
value of the mixture was adjusted to 3.0 using 4 mol L HCl under
stirring, and the solution was refluxed at 80 °C for 12 h. The filtrate
was kept for two days under ambient conditions, and then dark green
triangular shaped crystals of 1 were isolated in about 62% yield
(
based on Mo). Elemental analyses: Calcd for 1 Mo, 47.33; Co, 5.91;
Sr, 4.33; C, 2.37; N, 2.76; H, 1.89 (%). Found: Mo, 47.63; Co, 5.72;
ꢀ1
Sr, 4.02; C, 2.65; N, 2.90; H, 1.63 (%). FTIR data (cm ): 3500(s),
6
ꢀ
2 4 38
Taking account of these, we took advantage of [Co Mo10H O ]
3
8
192(m), 1680(s), 1500(vs), 1315(w), 1085(w), 939(vs), 906(vs),
25(m), 640(vs), 605(vs) and 522(s).
as building blocks and alkaline earth metal cations as linkers, and
expected to construct 3D inorganic frameworks with excellent
catalytic effect of cyanosilylation reaction. Fortunately, we
Synthesis of (C
The preparation of 2 was similar to that of 1 except that Ba(NO
0.0423 g, 0.2 mmol) was used instead of Sr(NO (0.0523g, 0.2
2 2 10 2 2 3 2 4 2
N H ) [Ba(H O) ][Co Mo10H O38]ꢁ3H O (2)
3 2
)
successfully
obtained
O) ][Co
O) ][Co
O) ][Co
O) ][Ba(H
four
38]ꢁ2H
38]ꢁ3H
38]ꢁ3H
][Co Mo10
compounds,
O
namely
1,
(
3 2
)
(
(
(
(
C
2
C
2
C
3
C
3
N
N
2
2
H
H
H
H
10
10
12
)
)
)
2
2
2
[Sr(H
[Ba(H
[Sr(H
2
5
2
Mo10
Mo10
Mo10
H
H
H
4
4
O
2
mmol). The pH value of the mixture was about 3.0. Dark green
triangular shaped crystals of compound 2 were obtained in about
2
3
2
4
O
2
O
2,
and
4.
N
2
2
5
2
O
2
O
3
6
4
4
0% yield (based on Mo). Elemental analyses: Calcd for 2 Mo,
6.56; Co, 5.72; Ba, 6.66; C, 2.33; N, 2.72; H, 1.86 (%). Found: Mo,
N
2
12)[Ba(H
2
4
2
O)
4
2
H
4
O38]ꢁ2H
2
O
Compounds 1 and 2 are obtained in the presence of ethylenediamine,
which represent the first examples of 3D covalent structures based
on EvansꢀShowellꢀtype polyoxoanion and alkaline earth metal
6.91; Co, 5.55; Ba, 6.87; C, 2.01; N, 2.99; H, 1.56 (%). FTIR data
ꢀ1
(
cm ): 3510(s), 3183(m), 1674(s), 1509(vs), 1313(w), 1082(w),
9
36(vs), 904(vs), 827(m), 642(vs), 607(vs) and 524(s).
cations. Compounds
3 and 4 are got in the presence of
Synthesis of (C [Sr(H O) ][Co 38]ꢁ3H O (3)
3
N
2
H
12
)
2
2
5
2
Mo10H
4
O
2
propanediamine, exhibiting interesting 2D covalent networks. As the
first Lewis acidꢀbase catalysts based on POMs and alkaline metal
cations, all four compounds show excellent performance in the
cyanosilylation of carbonyl compounds and allow the reaction to be
performed under solventꢀfree conditions using only a low amount of
the catalysts, which can be recovered and reused without displaying
any significant loss of activity.
The preparation of 3 was similar to that of 1 except that one drop
of propanediamine were introduced dropwise into the system instead
of ethylenediamine. The pH value of the mixture was about 2.8.
Dark green rhomboid shaped crystals of compound 3 were obtained
in about 61% yield (based on Mo). Elemental analyses: Calcd for 3
Mo, 46.19; Co, 5.67; Sr, 4.22; C, 3.47; N, 2.70; H, 2.33 (%). Found:
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Mo, 46.01; Co, 5.79; Sr, 4.56; C, 3.22; N,2.89; H, 2.50 (%). FTIR compounds. In the presence of ethylenediamine, compounds 1 and 2
ꢀ
1
data (cm ): 3490(s), 3153(m), 1654(vs), 1529(s), 1509(s), 1353(w), were separated, exhibiting a 3D microporous frame constructed from
6
ꢀ
9
26(vs), 894(vs), 827(w), 632(vs), 602(vs) and 514(w).
Synthesis of
12)[Ba(H
The preparation of 4 was similar to that of 3 except that Ba(NO
0.0423 g, 0.2 mmol) was used instead of Sr(NO (0.0523g, 0.2 earth metal cations and protonated propanediamine. To further study
isolated [Co
2
Mo10
H
4
O
38
]
polyoxoanions, alkaline earth metal
cations and protonated ethylenediamine. In the presence of
(
C
3
N
2
H
2
O)
4
][Ba(H
2
O)
4
][Co
2
Mo10H
4
O
38]ꢁ2H
2
O (4)
propanediamine, two 2D structures 3 and 4 were isolated, which are
6ꢀ
3
)
2
2 4 38
constructed from isolated [Co Mo10H O ] polyoxoanions, alkaline
(
3 2
)
mmol). The pH value of the mixture was about 2.7. Dark green the influence of the organic cations, we also attempted to use other
prismatic shaped crystals of compound 4 were obtained in about organic cations such as butanediamine and 1,2ꢀpropanediamine
5
4
4
9% yield (based on Mo). Elemental analyses: Calcd for 4 Mo, instead of ethylenediamine or 1,3ꢀpropanediamine under the similar
6.19; Co, 5.67; Ba, 4.22; C, 3.47; N, 2.70; H, 2.33 (%). Found: Mo, reaction conditions, but we only got the raw materials
4 6 2 4 2
6.01; Co, 5.79; Ba, 4.56; C, 3.22; N,2.89; H, 2.50 (%). FTIR data (NH ) [Co Mo10H O38]·7H O. Meanwhile, no crystals were
ꢀ
1
(
8
cm ): 3453(m), 3063(m),1584(vs), 1500(w), 1383(vs), 926(vs), obtained without the addition of organic cations under the similar
94(w), 637(vs), 606(w) and 514(w). conditions .
When other alkaline earth metal cations such as Mg and Ca
were introduced to the reaction system, we only got compound 5,
2
+
2+
XꢀRay crystallography
6
ꢀ
which is constructed from isolated [Co
2 4 38
Mo10H O ] and protonated
The crystallographic data of all compounds were collected on the
Bruker Smart CCD diffractometer with Mo Kα radiation(λ=0.71073
Å) by ω and θ scan modes. Empirical absorption correction was
applied. The structures of 1‒4 were solved by the direct method and
refined by the Fullꢀmatrix least squares on
SHELXTLꢀ97 software. All of the nonꢀhydrogen atoms were
refined anisotropically in 1‒4. The hydrogen atoms attached to water
molecules were not located in 1‒4. The restraints such as 'isor' or
organic cations (Fig. S5). This result may be because the ionic radii
2+
2+
of Mg and Ca are smaller and their coordination ability is weaker
2+
2+
than Sr and Ba with large ionic radii. The similar phenomenon
that the differences of ionic radii of metal cations lead to different
structures have been reported in the reaction system of POMs and
2
F
using the
3
7
20,21,40
rare earth metal cations.
Further, if organic cation was not
2+
2+
added to the solution of Mg /Ca and POMs, only precipitation can
+
+
+
+
be obtained. Alkaline metal cations (such as Na , K , Rb and Cs )
were also attempted to be introduced into the reaction system under
the similar reaction conditions, but only raw materials
'
dfix' were used in the refinements for obtaining reasonable atom
sites and thermal parameters. A summary of the crystallographic
data and structural determination for 1‒4 is provided in Table S1.
CCDC reference numbers: 1542000ꢀ1542003 for compounds 1‒4,
(
4 6 2 4 2
NH ) [Co Mo10H O38]·7H O were got. To probe the effect of the
reaction condition, many parallel experiments were proceeded,
which indicate that stoichiometry, pH value and reaction temperature
can affect the quality of crystals. The products are apparently
1542889 for compound 5.
Cyanosilylation
2+
2+
6ꢀ
influenced by the stoichiometry of Sr (Ba )/[Co
2
Mo10
H
4
O
38] .
Compounds 1(2) and 3(4) can be well isolated by the 2:1
The detailed reaction conditions are shown in the captions of
Table 1. A typical procedure for the cyanosilylation reaction of
aldehyde is as follows: 2 mol% catalyst (1–4) was added to a
2
+
2+
6ꢀ
2 4 38
Sr (Ba )/[Co Mo10H O ] ratio. When the ratio was adjusted from
2
:1 to 3:1 or 1:1, the crystal quality of the compounds was poor, and
the yields were reduced. The optimal pH value is from 2.5 to 4.0.
For a low pH (pH = 2), compound 5 was obtained; for a high pH (pH
mixture of aldehyde (0.5 mmol) and (CH
absence of solvent. The reaction mixture was stirred at room
temperature under a N atmosphere. The progress of the reaction was
3 3
) SiCN (1.5 mmol), in the
=
4 6 2 4 2
4.3) the raw materials (NH ) [Co Mo10H O38]·7H O were isolated.
2
In addition, the best reaction temperature is 80 °C. At lower
temperature (25 °C), no reaction occurred; at higher temperature
monitored by GC analysis. After the reaction was completed, the
catalyst was removed by filtration and centrifugation of the reaction
mixture. All products (cyanohydrin trimethylsilyl ethers) were
confirmed by a comparison of their GC retention times, GCꢀMS
spectra. GC analysis was performed using HP6890/5973MS with a
crossꢀlinked (95%)ꢀdimethylꢀ(5%)ꢀdiphenylpolysiloxane column of
(
100 °C), crystals with poor quality can be obtained.
Crystal structures of 1 and 2
Single crystal Xꢀray diffraction analyses exhibit that compounds 1
and 2 crystallize in Cc space group and display a unique 3D
framework assembled by EvansꢀShowellꢀtype polyoxoanions
30 m length.
Results and discussion
6
ꢀ
2+
2+
[
[
[
[
Co
Co
CoMo
2
Mo10
Mo10
H
H
4
O
O
38
]
]
and Sr or Ba cations. The structure of
can be deduced from the planar Anderson ion
6
ꢀ
2
4
38
3
Synthesis
−
6
H
6
O
24
]
by removing one {MoO
5
} group from each of two
ions, turning one ~45° around the anionic
octahedra
share an edge. In the polyoxoanion, four of the 10
3
−
2
+
2+
CoMo
6
H
6
O
24
]
4 6 2 4 2
The reaction of (NH ) [Co Mo10H O38]·7H O and Sr or Ba
equatorial plane and joining them so that the two CoO
6
cations in the presence of ethylenediamine or propanediamine has
been investigated. Four compounds with four kinds of structures
were obtained. Compounds 1(2) and 3(4) were synthesized under the
similar reaction conditions, except for the alternation of the organic
cations. It is clear that the organic cations of the reaction system are
the key factor influencing the structures and topologies of these
3
+
crystallographically unique oxygen atoms surrounding the two Co
ions, are bound to hydrogen atoms, which are identified by the
calculation of bond valence sums. Six kinds of oxygen atoms exist in
the cluster according to the manner of oxygen coordination, that is
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2+
2+
terminal oxygen Ot, terminal oxygen Ot′ linked to Sr or Ba , the (10,3)ꢀd topology according to the literatures (Fig. 3).
doubleꢀbridging oxygen Ob, central oxygen Oc (ꢂ3ꢀOH atom of a Interestingly, along the axis, the topology of compound 1 consists
c
Co and two Mo atoms), central oxygen Od (ꢂ4ꢀO atom of a Co and of two different 1D helical chiral chains: right hand and left hand
three Mo atoms), central oxygen Oq (ꢂ4ꢀO atom of two Co and two (Fig. 3d). Such intriguing architectures and topologies is very rare.
Mo atoms). Thus the Mo–O bond lengths fall into six classes: Mo–
Ot 1.692(4)–1.723(4) Å, Mo–Ot′ 1.713(5)–1.723(6) Å, Mo–Ob
1
1
1
1
1
.878(4)–1.975(4) Å, Mo–Oc 2.226(4)–2.316(4) Å, Mo–Od
.893(4)–2.347(3) Å and Mo–Oq 2.272(4)–2.308(4) Å in 1; Mo–Ot
.683(6)–1.724(6) Å, Mo–Ot′ 1.709(5)–1.712(4) Å, Mo–Ob
.881(6)–1.979(5) Å, Mo–Oc 2.250(5)–2.311(5) Å, Mo–Od
.987(5)–2.329(5) Å and Mo–Oq 2.272(5)–2.328(5) Å in 2. The
central Co–O distances are 1.869(3)–1.949(4) Å in 1 and 1.863(3)–
1
8
.960(5) Å in 2, and the O–Co–O angles are in the range of
3.78(15)–175.80(16)° in 1 and 83.6(2)–176.2(2)° in 2. All bond
32,33
lengths and bond angles are within the normal ranges.
Just as Fig. 1a, the asymmetric unit of compound 1 is composed
6
ꢀ
2+
of one crystallizationꢀindependent [Co Mo H O ] anion, one Sr
2
10
4
38
2+
cation and two protonated ethylenediamine. The Sr cation is
eightꢀcoordinated, forming doubleꢀcapped trigonal prism
coordination geometry, which was defined by five water molecules
Sr−OH2 2.592(4)−2.643(4) Å] and three terminal oxygen atoms
a
[
6ꢀ
from three [Co Mo H O ] units [Sr−O 2.574(4)−2.615(4) Å]
2
10
4
38
(
Fig. S1a). The average bond length of Sr−O bond is 2.599 Å.
Similarly, the asymmetric unit of compound 2 is composed of one
6
−
2+
crystallizationꢀindependent [Co Mo H O ] anion, one Ba cation
2
10
4
38
2
+
and two protonated ethylenediamine. The Ba
sevenꢀcoordinated, forming singleꢀcapped trigonal prism
coordination geometry, which was defined by three water molecules
Ba−OH2 2.804(8)−2.861(8) Å] and four terminal oxygen atoms
cation is
a
[
6
−
Fig. 1 (a) ORTEP drawing of 1 with thermal ellipsoids at 50% probability.
b) ORTEP drawing of 2 with thermal ellipsoids at 50% probability.(color
code: Co, yellow; Mo, green; Sr, purple; Ba, pink; O, red).
from three [Co Mo H O ] units [Ba−O 2.732(5)−2.984(6) Å]
2
10
4
38
(
(
Fig. S2a). The average bond length of Ba−O bond is 2.829 Å. It is
noteworthy that compounds 1 and 2 both display 3D frameworks
6
ꢀ
2+
2+
assembled by [Co Mo H O ] polyoxoanions and Sr /Ba
2
10
4
38
cations. To our best knowledge, compounds 1 and 2 represent the
6ꢀ
first examples of 3D architectures based on [Co Mo H O ] units
2
10
4
38
and alkaline earth metals, and the second examples of 3D
6
−
architectures based on [Co Mo H O ] . In compound 1, the chiral
[
2
10
4
38
6ꢀ
2+
Co Mo H O ] clusters are linked by some Sr ions to form 1D
2 10 4 38
chiral chain (Fig. S1b), then adjacent oppositeꢀhanded chiral chains
2
+
are interconnected by Sr cations to produce a 2D nonchiral layer
along the axis (Fig. 2b). Furthermore, these 2D sheets are joined
together via the Sr−O−Sr bonds to form a 3D framework (Fig. 2c).
The resulting 3D framework contains 1D channels along the axis.
a
b
Each 1D channel splits into three smaller channels. Their dimensions
are respectively ca. 3.0 × 6.7, 3.7 × 5.2, and 4.4 × 5.0 Å in 1 along
the
b axis. Free water molecules and ethylenediamine molecules are
filled in the channels and coordinated water molecules are included
into them. The solvent accessible volume of 1 and 2 after removal of
the water molecules and ethylenediamine molecules are respectively
about 20.5% and 20.9%, as determined by using PLATON. From the
6−
view of topology, the [Co
2
Mo10
H
4
O
38
]
unit is covalently bonded to
three adjacent Sr cations, and each Sr cation is linked with three
6
−
[
Co
2 4 38
Mo10H O ] units. Therefore, the overall 3D framework can be
6
−
rationalized as a 3ꢀconnected net by assigning the [Co
2
4 38
Mo10H O ]
units and Sr ions as three connected node which are topologically
equivalent nodes (Fig. 3). Careful examination indicated that the
3
Schläfli symbol for this binodal network is 10 , which is assigned to
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6
−
Fig. 2 (a) Polyhedral representation of two enantiomers of [Co
2
Mo10
H O
4 38
]
square antiprismatic geometry. However, the asymmetric unit of
2
+
2+
2+
polyoxoanion in 1. (b) 2D nonchiral layer in 1, showing the alternately compounds 1(2) both hold one metal cation Sr (Ba ), and Sr and
2
+
arranged leftꢀhanded and rightꢀhanded chiral chains along the a axis (c) View Ba cations show doubleꢀcapped trigonal prism and singleꢀcapped
along the a axis illustrating the 3D framework. Free water molecules are trigonal prism coordination geometry, respectively. Owing to the
omitted for clarity. (color code: Co, yellow; Mo, green/blue; Sr, purple; O, different charges and different coordination modes of alkaline earth
red).
metal cations and rare earth metal caitons, compounds 1(2) and
reported species exhibit different 3D topological structures. From the
view
of
O)
topology,
38]ꢁ5H
compounds
O can be rationalized as
[
Ln(H
2
O)
7
][Ln(H
2
5
2
][Co Mo10
H
4
O
2
a
binodal 4ꢀconnected SrAl
2
(sra) net by assigning the
6
−
[
2 4 38
Co Mo10H O ]
units and Ln(1) ions as four connected node with
2
3
Schläfli symbol of 4 ·6 ·8. And topological analysis reveals that the
simplified framework of compounds 1(2) feature a 3,3ꢀconnected 3D
network with the Schläfli symbol (10,3)ꢀd, which consists of two
different 1D helical chiral chains: right hand and left hand that is rare
for POMs. Thus it can be seen that metal cations can affect
structures of the compounds.
6
−
2+
6−
2 4 38
Fig. 3 (a) 3ꢀConnected [Co Mo10H O ] unit coordinated with three Sr
2+
2 4 38
cations. (b) 3ꢀConnected Sr node linked with three [Co Mo10H O ]
clusters. (c) A schematic view of the 3D 3,3ꢀconnected network with the
topology along the b axis. (d) Scheme of the 1D leftꢀhanded and rightꢀhanded
chiral chain along the c axis.
6
ꢀ
2 4
Similarly, in compound 2, the chiral [Co Mo10H O38] clusters are
2
+
linked by some Ba ions to form nonchiral 1D double chains (Fig.
S2b). Next, the adjacent chains are joined together to form a 2D
layer along the
b axis (Fig. 4a). Then the 2D sheets are
interconnected via the Ba−O−Ba bonds to form a 3D framework
6
−
(
Fig. 4b). From the view of topology, the [Co
2
Mo10
H
4
O
38
]
unit is
covalently bonded to three adjacent Ba cations, and each Ba cation is
6
−
linked with three [Co
2
Mo10
H
4
O
38
]
units. Therefore, the overall 3D
framework can be also rationalized as a 3,3ꢀconnected net by
6−
Fig. 4 (a) Polyhedron view of the 2D sheet along b axis in 2. (b) View along
the c axis illustrating the 3D framework in 2. Free water molecules are
omitted for clarity.(color code: Co, yellow; Mo, green/blue; Ba, pink; O, red).
assigning the [Co
2
Mo10
H
4
O
38
]
units and Ba cations as three
3
connected node with Schläfli symbol of 10 , as shown in Fig. 5. It is
noteworthy that the topology of compound 2 is also made up of two
different helical chiral chains: right hand and left hand (Fig. 5d).
So far, except for compounds 1 and 2, only one example of 3D
6ꢀ
architectures based on [Co
2
Mo10
H
4
O
38
]
has been reported by our
38]ꢁ5H (Ln Gd,
group: [Ln(H O) ][Ln(H O)
2
7
2
5
][Co
2
Mo10
H
4
O
2
2+
O
=
2
1
2+
Tb). Owing to the similar ionic radii between Sr (Ba ) cations
and rare earth metal cations, all these compounds have 3D
frameworks. Compared 3D structures of compounds 1 and 2 with
those of reported compounds, we found that different metal cations
can produce different 3D structures. Compounds 1 and 2 crystallize
in
Ln(H
space group. In [Ln(H
C
c
space
group,
while
[
2
O)
7
][Ln(H
2
O)
5
][Co
O)
2
Mo10H
4
O
38]ꢁ5H O crystallize in P2(1)/c
O) ][Co Mo10H O38]ꢁ5H O, two
2 4 2
2
2
7
][Ln(H
2
5
unique Ln cations display two different coordination sphere. Ln(1)
cation is nineꢀcoordinated, forming a tricapped trigonal prism
coordination environment, and Ln(2) cation, joined neighboring
6−
[
Co
2
Mo10
H
4
O
38
]
polyoxoanions together as linker, displays a
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6ꢀ
terminal oxygen atoms from three [Co
2
Mo10
H
4
O
38
]
[Sr−O
2
2
.641(4)−2.811(4) Å]. The average bonds length of Sr−O bond is
.425 Å (Fig. S3a). Similarly, the asymmetric unit of 4 consists of
2
+
one crystallographically independent polyoxoanion, two Ba and
2
+
one protonated propanediamine. The two Ba cations exhibit
different coordination environment. Ba1 exists in the six
coordination environment, forming
coordination geometry, and coordinates to four water molecules
Ba−OH 2.707(5)−2.729(5) Å] and two terminal oxygen atoms from
two [Co
a
distorted octahedron
[
2
6
ꢀ
2 4 38
Mo10H O ]
units [Ba−O 2.841(5)−2.850(5)Å]. Ba2 exists
in the eight coordination environment, forming a doubleꢀcapped
trigonal prism coordination geometry, and coordinates to four water
molecules [Ba−OH 2.793(5)−2.876(5)Å] and four terminal oxygen
2
6ꢀ
atoms from four [Co Mo H O ] units [Ba−O 2.738(5)−2.974(5)
2
10
4
38
Å]. The average bond length of BaꢀO bond is 2.845(5)Å (Fig. S4a,
b).
Interestingly, both compounds of 3 and 4 show 2D network
6
ꢀ
6
−
2+
6−
structures. In compound 3, the chiral [Co Mo H O ] clusters are
2 10 4 38
Fig. 5 (a) 3ꢀConnected [Co
2
Mo10
4 38
H O ]
unit coordinated with three Ba
2+
2
+
linked by some Sr ions to form a 1D chiral chain (Fig. S3b), then
adjacent oppositeꢀhanded chiral chains are interconnected by Sr
cations to produce a 2D nonchiral layer along the axis (Fig. 7a). It's
worth noting that 2D sheets are interconnected by hydrogen bonds
among polyoxoanions and nitrogen atoms of propanediamine (O···N
2.729ꢀ2.825Å in 3) to develop a 3D supramolecular framework (Fig.
2 4 38
cations. (b) 3ꢀConnected Ba node linked with three [Co Mo10H O ]
2+
clusters. (c) A schematic view of the 3D 3,3ꢀconnected network with the
topology along the b axis. (d) Scheme of the 1D leftꢀhanded and rightꢀhanded
chiral chain along the c axis.
b
Crystal structures of 3 and 4
6ꢀ
7
b). Similarly, in compound 4, the chiral [Co Mo H O ] clusters
2 10 4 38
When propanediamine was used instead of ethylenediamine under are linked by some Ba ions to form nonchiral 1D double chains
2
+
the similar conditions with compounds 1 and 2, two different (Fig. S4c). Next, the adjacent chains are joined together to form a 2D
compounds 3 and 4 were isolated from the solution. Single crystal layer along
structural analysis reveals that compound 3 crystallizes in the space bonds among polyoxoanions and nitrogen atoms of propanediamine
group 21/n. The asymmetric unit in the structure of 3 is composed (O···N 2.759ꢀ2.924Å in 4) to develop a 3D supramolecular
of [Co
protonated propanediamine balancing the charges. Compound 4
crystallizes in the space group ꢀ1, which is composed of +6 oxidation state, Co atoms are in the +3 oxidation state, and the
c axis. Then 2D sheets are joined together by hydrogen
P
6ꢀ
2+
2
Mo10
H
4
O
38
]
polyoxoanion and one Sr cation with two framework (Fig. 8).
Bond valence sum calculations show that all Mo atoms are in the
P
6ꢀ
2+
[
Co
2
Mo10
H
4
O
38
]
polyoxoanion and two Ba cations with one alkaline earth metal cations are in the +2 oxidation state. These
protonated propanediamine balancing the charges, and it also plays a results are consistent with the charge balance considerations.
D network structure. The structure of [Co Mo10H O ] anion is as
2 4 38
42
6
ꢀ
2
well an EvansꢀShowell type. According to the environment of the
oxygen coordination, the oxygen atoms can divide into six kinds.
Therefore, the bond lengths of MoꢀO fall into six categories: Mo–Ot
1
1
1
1
1
1
.688(5)–1.720(4) Å, Mo–Ot′ 1.696(5)–1.713(5) Å, Mo–Ob
.872(4)–1.985(4) Å, Mo–Oc 2.254(4)–2.295(4) Å, Mo–Od
.969(4)–2.412(4) Å and Mo–Oq 2.270(4)–2.344(4) Å in 3. Mo–Ot
.699(10)–1.754(9) Å, Mo–Ot′ 1.702(6)–1.725(9) Å, Mo–Ob
.898(8)–1.975(9) Å, Mo–Oc 2.233(9)–2.281(8) Å, Mo–Od
.991(8)–2.326(8) Å and Mo–Oq 2.297(8)–2.311(7) Å in 4. The
central Co–O distances are 1.859(4)–1.955(4) Å, and the O–Co–O
angles are in the range of 84.11(18)–176.11(15)° in compound 3.
The central Co–O distances are 1.875(8)–1.958(8) Å, and the O–Co–
O angles are in the range of 84.3(4)–174.3(3)° in compound 4. And
the bond lengths and bond angles are in agreement with the normal
ranges, similar to compounds 1 and 2.
The asymmetric unit in 3 is composed of one crystallographically
2
+
independent EvansꢀShowellꢀtype polyoxoanion linked by one Sr
2+
anion with two protonated propanediamine. The Sr cation exists in
the nine coordination environment, forming a singleꢀcapped square
antiprism coordination geometry (Fig. 6a), which are coordinated by
five water molecules [Sr−OH
2.524(5)−2.853(5) Å] and four
2
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Fig. 6 (a) ORTEP drawing of 3 with thermal ellipsoids at 50% probability.
Fig. 8 (a) Polyhedron view of the 2D sheet along b axis. (b) View of the 3D
supramolecular framework of 4 along the c axis. Free water molecules are
omitted for clarity. (color code: Co, yellow; Mo, green; Ba, pink; O, red).
(b) ORTEP drawing of 4 with thermal ellipsoids at 50% probability.(color
code: Co, yellow; Mo, green; Sr, purple; Ba, pink; O, red).
FTꢀIR spectroscopy and PXRD
In correspondence with the reported literatures, the IR spectra of
compounds 1ꢀ4 show similar characteristic vibrational bands of the
6
ꢀ
EvansꢀShowellꢀtype structure [Co
2
Mo10
H
4
O
38
]
(Fig. S6). The
terminal Mo‒O units and the bridging Mo‒O‒Mo groups (M=Mo,
ꢀ
1
ꢀ1
Co) are located at 850‒950 cm and 580‒690cm , respectively. In
−
1
addition, the bands at 3600−2800 cm can be attributed to the
stretching vibrations of O−H and N−H and 1700−1400 cm can be
correspond to the bending vibrations of the O−H and N−H. Below
−1
−
1
5
00 cm , the spectrum is rather difficult to analyze, the bending of
the Mo−Ot and Mo−Ob bonds can be mixed with the Mo−Oc
stretching vibrations. These results are in agreement with their single
crystal structural analyses.
The PXRD patterns for 1–4 are presented in Fig. S7. The
diffraction peaks of both calculated and experimental patterns match
well, indicating the phase purities of these compounds. These
conclusions are in agreement with the results of the single crystal
Xꢀray analysis.
Thermal gravimetric (TG) Analysis
The TG curve of 1 is shown in Fig. S8a, which was carried out in
the N atmosphere within the scope of 30 to 800°C. According to the
2
TG curve, we can know that 1 exhibits three weight loss steps, and
the total weight loss is 16.0%, which meets the calculated weight
loss of 15.7%. The first weight loss from 30 to 200°C is 5.0%,
corresponding to all the lattice water and partial ethylenediamine.
The second weight loss of 8.0% from 200 to 560°C, mainly
attributes to the partial ethylenediamine and coordinated water (calc.
Fig. 7 (a) 2D nonchiral layer in 3, showing the alternately arranged
leftꢀhanded and rightꢀhanded chiral chains along the b axis. (b) View of the
3
D supramolecular framework of 3 along the c axis. Free water molecules are
omitted for clarity. (color code: Co, yellow; Mo, green/blue; Sr, purple; O,
red)
1
2.5%). The last weight loss of 2.7% from 570 to 800°C arises from
the loss of oxygen molecules.
The TG curve of 2 is shown in Fig. S8b, which was carried out in
the N atmosphere within the scope of 30 to 700°C. According to the
2
TG curve, we can know that 2 exhibits three weight loss steps, and
the total weight loss is 16.4%, which meets the calculated weight
loss of 16.0%. The first weight loss from 30 to 200°C is 4.7%,
corresponding to all the lattice water and partial ethylenediamine.
The second weight loss of 8.4% from 200 to 500°C, mainly
attributes to the partial ethylenediamine and coordinated water (calc.
1
2.8%). The last weight loss of 3.6% from 500 to 700°C arises from
the loss of oxygen molecules.
The TG curve of 3 is shown in Fig. S8c, which was carried out in
the N atmosphere within the scope of 30 to 800°C. According to the
2
TG curve, we can know that 3 exhibits three weight loss steps, and
the total weight loss is 17.3%, which meets the calculated weight
loss of 17.6%. The first weight loss from 30 to 120°C is 3.0%,
corresponding to all the lattice water and partial propanediamine.
The second weight loss of 9.7% from 120 to 600°C, mainly
attributes to the partial propanediamine and coordinated water(calc.
1
3.0%). The last weight loss of 4.6% from 600 to 800°C arises from
the loss of oxygen molecules.
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The TG curve of 4 is shown in Fig. S8d, which was carried out in the Ag/AgCl electrode), respectively. The first peak at ꢀ0.8V
the N atmosphere within the scope of 30 to 800°C. According to the corresponds to the reduction of the molybdenum unit in the
2
TG curve, we can know that 4 exhibits three weight loss steps, and polyoxoanion framework, and the second peak at ꢀ0.48V is ascribed
the total weight loss is 13.4%, which meets the calculated weight to the oxidation of molybdenum unit, which indicates that the
loss of 13.1%. The first weight loss from 30 to 200°C is 3.9%, reduction is irreversible. This is because EvansꢀShowellꢀtype
corresponding to all the lattice water (calc. 4.1%). The second polyoxoanion contains two terminal cisꢀoxygen atoms which make
weight loss of 5.6% from 200 to 500°C, mainly attributes to the the reduction process is irreversible. Similar phenomenon has been
partial propanediamine and coordinated water. The last weight loss observed in other polyoxomolybdates with two terminal cisꢀoxygen
4
3,44
of 4.6% from 500 to 800°C arises from the loss of remainder atoms.
The third peak at ꢀ0.32V corresponds to the reduction of
coordinated water and oxygen molecules.
cobalt unit, and the last two anodic peaks at ꢀ0.27V and +0.6V
belong to the oxidation of cobalt unit. The above domain where the
4
5,46
UVꢀVis spectroscopy
waves are located is alike to other Coꢀbased complexes.
The
cyclic voltammograms reveal the presence of irreversible redox
processes of molybdenum and cobalt units. This phenomenon is due
to subsequent decomposition of the cluster, which was confirmed by
the UVꢀVis spectrum of the buffer solution (Fig S9). Furthermore,
the CV curve from +0.6 to ꢀ0.6 V was detected (Fig S10), and the
redox potentials Ⅲ Ⅵ Ⅴ can be seen, which thus can be ascribed
to redox peaks of cobalt unit. If the measurement is cycled from +1.5
to ꢀ1.3 V, no other new peak appeared (Fig S11). For 1, the cathodic
peak potentials shift towards the negative direction and the anodic
peak potentials to the positive direction with increasing scan rates
In order to get the absorption bands located in both the ultraviolet
and visible regions, the diffuse reflectivity for solid samples of four
compounds are shown in Fig. 9. The absorption (
calculated from the reflectivity using the function:
A
) date were
A
= log(1/R%)
where R is the reflectivity at a given wavelength (λ). On the UV
region (200ꢀ400 nm), there are two absorption bands at 224 nm, 305
nm for 1, 223 nm, 304 nm for 2, 225 nm, 303 nm for 3, and 225 nm
3
[
03 nm for 4, which are assigned to O→Mo charge transfer for
Co Mo H O ] polyoxoanions. On the vision region (400ꢀ800
2 10 4 38
6ꢀ
nm), the plots display two absorption bands at 441 nm, 607 nm for 1,
40 nm, 605 nm for 2, 442 nm, 607 nm for 3 and 441 nm, 604 nm
–1
from 25 to 400 mV s . The peak currents are almost proportional to
4
the scan rate, which indicate that the redox process are
1
1
1
for 4, which were respectively assigned to the A → T and A
→
in the [Co Mo H O ] anion.
47ꢀ49
1
g
2g
1g
3+
surfaceꢀcontrolled.
Compounds 2‒4 exhibit similar CV curves
1
T1g transition of a regular octahedral configuration lowꢀspin Co
–1
with compound 1 at the scan rate from 25 to 400 mVs
(Fig S12).
6ꢀ
41
2
10
4
38
Fig. 10 The cyclic voltammograms of the 1 in pH 4 (0.2 M CH
CH COOH) aqueous solution at different scan rates (from inner to outer:
5, 50, 100, 200, 300 and 400, mV s ). The inset shows the peak current
3
COONa
+
3
−1
2
versus the scan rate plot.
Fig. 9 (a) UV−vis diffuse reflectance spectra of bulk 1. (b) UV−vis diffuse
reflectance spectra of bulk 2. (c) UV−vis diffuse reflectance spectra of bulk
Catalysis study
3
. (d) UV−vis diffuse reflectance spectra of bulk 4.
Because of the importance of cyanohydrins as key intermediates
in the synthesis of organic compounds, such as αꢀhydroxy acids,
αꢀhydroxy aldehydes and βꢀaminoalcohols, the development of
efficient catalysts for cyanosilylation is a very important subject in
current research. Among the catalysts employed for the
cyanosilylation reaction, both acid catalysts and base catalysts can
act as catalysts to promote cyanosilylation. In addition, various
cyanating reagents have been adopted in the synthesis of
cyanohydrins, but trimethylsilyl cyanide (TMSCN) is the most
widely used and safest cyanating regents for nucleophilic addition to
Electrochemistry studies
The electrochemical properties of 1‒4 were investigated by cyclic
voltammetry (CV) in a pH=4 (0.2 M CH COONa+CH COOH)
3
3
buffer solution at different scan rates. Compound 1 was taken as a
representative (as shown in Fig. 10). The cyclic voltammetric
response was initially scanned in the positive direction from a
starting potential of −1.2 V. For 1, it can be clearly seen that in the
potential range of +0.800 to ꢀ1.200 V, five redox peaks appear and
the mean peak potentials are ꢀ0.80, ꢀ0.48, ꢀ0.32,ꢀ0.27 and +0.6 V (vs.
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33
carbonyl compounds to give cyanohydrin trimethylsilyl ether. In the fresh prepared samples (Fig. S13). These observation indicated
particular, it is expected that POMs with large negative charges can that 1 and 3 are true heterogeneous catalysts. Additionally, infrared
nucleophilically activate TMSCN, thus resulting in promotion of spectroscopy of the compounds
1 and 3 impregnated with
cyanosilylations, as observed for Lewis base catalyzed benzaldehyde showed one broad CꢀO stretch at 1688.7 and 1689.4
ꢀ
1
cyanosilylations. In this sense the starting substrates commonly used cm , respectively. The v(CꢀO) stretch occurred a red shift of ~ 13.1
ꢀ
1
ꢀ1
are aldehydes or ketones with TMSCN as the nucleophilic regent. and 12.4 cm from 1701.8 cm of the free benzaldehyde (Fig. S14).
Therefore, we detected the activity of compounds 1‒4 as The red shift illustrated the possible activation of the substrate by
heterogeneous catalysnosilylation in the aldehyde cyanosilylation catalysts
reaction under solventꢀfree condition at room temperature. cyanosilylation of benzaldehyde with [Co
1 and 3. Furthermore, the control experiment for
6ꢀ
2
4 38
Mo10H O ] precursor in
Firstly, we selected the cyanosilylation of benzaldehyde as a a homogeneous manner gave 65.4% yield, which is far lower than
model reaction to evaluate the catalytic activities for compounds 1‒ that of 1 and 3 in the heterogeneous manner. The higher yields of 1
4
. The reaction was carried out with 2 mol% of catalysts under the and 3 is possibly attributed to the synergistic effect of the Lewis acid
2+
conditions describe in Table 1. All compounds effectively catalyzed (Sr cations) and the Lewis base (surface oxygen atoms of the
the cyanosilylation to afford the corresponding cyanohydrin [Co Mo H O ] POM) that activated respectively aldehydes and
6
ꢀ
2
10
4
38
trimethysilyl ether with yield of up to about 99%. The catalytic TMSCN at the same time.
effects of four compounds were compared with those of POMs
reported in the literatures, displayed in detail in Table S4. In a
comparison of the activity of our catalysts with that of some
previous
reported
POMꢀbased
compounds,
such
Sm; Eu),
[Cu (bpy)(H O) ] [H W O ] · 3H O · 0.5CH CN} and
2 2 5.5 2 2 11 38 2
as
[
Ln(H O) ][Ln(H O) ][Co Mo H O ] 6H O (Ln
=
2
5
2
7
2
10
4
38
2
{
{
3
[Cu (pbtz) (Hpbtz) (OH) (H O) ][Na(H O)P W O ]}·16H O,
12
2
2
4
2
16
2
5
30 110
2
it was found to be less than the former two (benzaldehyde, 5h, yield
98.4%), because the yield was 87% in the same time under similar
=
reaction condition with compound 1 as catalyst. Although the yield
of compound 1 was very close to the third compound, the third one
need more time and uses solvent conditions (benzaldehyde, 24 h,
yield = 98.1%). The last one need more time while the yield was far
less than that of compound 1 (benzaldehyde, 24 h, and yield =
6
1.7%). Besides, in an equivalent ratio of compound 1 and 3,
compound 1 showed higher catalytic results than 3. Given the fact
that the similar composition between both compounds, the different
catalytic activity may be ascribed to the different structures. As
heterogeneous catalyst, compound 1 showing a 3D microporous
framework may result in more exposure of the active sites than the
2
D network structures in 3.
Subsequently, various organic substrates containing aldehydes
with different electronic effects are converted into the corresponding
cyanosilylation products through the catalyzed reaction. With a
substrate like 2ꢀhydroxybenzaldehyde, 4ꢀmethylbenzaldehyde, or
4ꢀnitrobenzaldehyde, the yield is high, too (Table 1). It indicates that
the nature of the substituent on the aromatic ring didn’t dramatically
affect the reaction yield. In contrast, a drastic decrease of catalytic
activity occurred when substrate with the large steric hindrance was
introduced, such as: 1ꢀnapthaldehyde. It reveals that the large steric
hindrance of substrate makes the substrate hardly approach to the
alkaline earth metal cations of the catalyst at the process of
cyanosilylation reaction, leading to poor yield.
To further study the catalyst recyclability and stability in the
catalytic process. The used catalysts were readily recovered from the
catalytic reaction describe above by filtration. The filtrate of the
reaction media showed no catalytic effect for the catalytic reaction of
aldehyde. The isolated catalysts were reused at least three times
without an appreciate loss of its high catalytic performance (from
Fig. 11 (a) Powder Xꢀray diffraction (PXRD) patterns of 1 (b) Powder Xꢀray
diffraction (PXRD) patterns of 3: calculated pattern from crystal data (blue
line); experimental pattern before catalysis (red line); recovered catalyst 1 or
3
after 3 catalytic runs of the cyanosilylation of benzaldehyde (black line).
9
9%‒93.7%) (Table. S3). The PXRD patterns of retrieved catalysts
were identical to those of the fresh catalysts(Fig. 11). The IR spectra
of the recovered compounds 1 and 3 were also identical to those of
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DOI: 10.1039/C7DT01302G
a
6ꢀ
Table 1 Cyanosilylation of aldehydes catalyzed by compounds 1–4 . polyoxoanions [Co
2
Mo10
H
4
O
38
]
and alkaline earth metal cations.
O
Compounds 1 and 2 represent the first examples of 3D covalent
structures based on EvansꢀShowellꢀtype polyoxoanion and alkaline
earth metal cations. Additionally, these compounds are efficient
heterogeneous Lewis acidꢀbase catalysts for cyanosilylation of
carbonyl compounds under solventꢀfree conditions. To the best of
our knowledge, this is the first time that inorganic 3D structures
based on POMs and alkaline earth metal cations are used as catalysts
in the cyanosilylation. Thus, the successful isolation of these
compounds inspire us to develop new catalytic materials containing
POMs and alkaline earth metal cations.
O
Si
C
2
% Cat., neat
98K, N
H
Si CN
R
CH
+
2
2
R
CN
Time Yield
Compound
Aldehyde
b
(
h)
(%)
99.0
95.6
95.3
93.2
1
2
3
4
6
6
O
Acknowledgment
7
The authors thank the National Natural Science Foundation of China
21371027, 21274015, 21102013, 20901013), Natural Science
Foundation of Liaoning Province (2015020232) and Fundamental
Research Funds for the Central Universities (DUT15LK02,
DUT15LN18, DUT16ZD205) for financial supports.
(
7
1
3
O
O
O
6
7
97
H C
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DOI: 10.1039/C7DT01302G
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Table of Contents
Evans-Showell-type polyoxometalate constructing novel 3D
inorganic architectures with alkaline earth metal linkers:
syntheses, structures and catalytic properties
Yujiao Hou, Haiyan An*, Baojun Ding, Yanqin Li
College of Chemistry, Dalian University of Technology, Dalian 116023, P. R. China
Two 3D frameworks and two 2D networks with excellent catalytic effect of
cyanosilylation were successfully obtained, originated from Evans-Showell-type
6
-
2+
2+
2 4
polyoxoanions [Co Mo10H O38] and alkaline earth metal cations (Sr , Ba ).