Temperature-induced racemic compounds and chiral conglomerates based on polyoxometalates and lanthanides: Syntheses, structures and catalytic properties

Article abstract of DOI:10.1039/c4ce01802h

By controlling the reaction temperatures, four new architectures based on Evans-Showell type polyoxometalate, [Ln(H₂O)₅][Ln(H₂O)₇][Co₂Mo₁₀H₄O₃₈] 6H₂O (Ln =

Full text of DOI:10.1039/c4ce01802h

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Temperature-induced racemic compounds and
chiral conglomerates based on polyoxometalates
and lanthanides: syntheses, structures and
catalytic properties†
Cite this: DOI: 10.1039/c4ce01802h
Haiyan An,* Lin Wang, Ying Hu and Fei Fei
By controlling the reaction temperatures, four new architectures based on Evans–Showell type
polyoxometalate, ijLnIJH
2 5 2 7 2 4 2 4 3 2 6
O) ]ijLnIJH O) ]ijCo Mo10H O38] 6H O (Ln = Sm 1; Eu 2), and (NH ) [Ln(H O) ]
[
Co 38] 6H O (Ln = Sm 3; Eu 4) have been synthesized and characterized by elemental analysis,
2
Mo10
H
4
O
2
IR spectroscopy, TG analysis, solid diffuse reflective spectrum, powder X-ray diffraction and single crystal
X-ray diffraction. Compounds 1 and 2 are racemic compounds, obtained at the higher temperature
(85 °C). They show a 1D ladderlike structure constructed from left-handed chain and right-handed chain
linked by lanthanide cations, which represent the first 1D self assembly based on Evans–Showell type poly-
oxometalate. When the reaction temperature was decreased to room temperature (25 °C), two chiral spe-
6
−
2 4 38
cies 3 and 4 were obtained, showing a mono-supporting structure composed of one [Co Mo10H O ]
3
+
polyoxoanion and one [Ln(H
2
O)
6
]
1
unit. They crystallize in the chiral space group P2 , as conglomerates of
Received 2nd September 2014,
Accepted 10th October 2014
two enantiomerically pure crystals. Their absolute configuration were determined by the Flack parameters
and solid state circular dichroism spectroscopy. The structural differences between 1(2) and 3(4) reveal that
the reaction temperature is the key factor controlling the products from racemic compounds to conglom-
erates. Four compounds 1–4 acted as Lewis acid–base catalysts through a heterogeneous manner to catal-
yse cyanosilylation with excellent efficiency.
DOI: 10.1039/c4ce01802h
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all racemates can form conglomerate crystals (in which mole-
cules form condensates comprising only one enantiomer, but
Introduction
The construction of chiral polyoxometalates (POMs) is a topi-
cal area owing to their intriguing variety of architectures and
topologies, as well as potential applications in catalysis,
the sample as a whole is racemic), indicating the difficulty to
1
1
realize spontaneous resolution. Hill's group documented
the first spontaneous resolution of chiral POMs. Two enantio-
merically pure chiral hafnium-substituted polyoxometalates
1
nonlinear optics, medicine. In recent years, thanks to the
1
0−
prominent work of Pope, Hill, Yamase, Kortz, Cronin, Wang,
Su, Wei and Hasenknopf, a few chiral compounds based
ijHfIJPW O ) ] were synthesized in the absence of any chi-
11 39 2
1
2
ral source upon crystallization. Wei and co-workers success-
fully discovered two interesting examples of chiral POMs
2
–6
on POMs have been prepared.
Usually, these chiral
1
3
POM-based compounds can be synthesized using chiral
inducement, including chiral organic ligands and chiral
formed by spontaneous resolution: one is by assembling
achiral Lindqvist and Anderson anions into a triad via organic
ligands with rotatable covalent bonds; the other is a novel
POM-based chiral macrocycle from the achiral Lindqvist
hexamolybdate and bisarylamines. Wang et al. used the clas-
7
–9
metal–organic compounds.
Spontaneous resolution from
achiral materials is the other interesting, but challenging
1
0
method to prepare chiral POMs. Statistically, only 5–10% of
6
−
sical Waugh-type polyoxoanion [MnMo O ] as a model, and
9
32
6
−
changed the racemic [MnMo O32] from a racemic com-
College of Chemistry, Dalian University of Technology, Dalian 116023, PR China.
E-mail: anhy@dlut.edu.cn; Tel: +86 411 84657675
9
pound via a racemic solid solution to a conglomerate by
+
†
Electronic supplementary information (ESI) available: The coordination modes
adjusting the linkers from imidazole molecules to Na and
3
+
of Sm cations in 1 and 3, 3D supramolecular topology structure for 3, IR, TG
curves and PXRD patterns for 1–4, PXRD and IR figures after catalysis and
before catalysis for 1 and 3 are available. Study on recycling of catalysts 1 and 3
are listed in Table S2. CCDC 428383–428386. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c4ce01802h
14
finally transition-metal cations. Although some groups have
made great contributions to construct chiral POMs by sponta-
neous resolution, the information on the factors which medi-
ate the formation of conglomerates vs. racemic compounds
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has been little known up to now. Therefore, it is still a formi-
dable challenge to build POM-based conglomerates and race-
mic compounds and look for the factors that control their
formation.
solvent-free conditions using only a low loading of the cata-
lyst, which can be recovered and reused without displaying
any significant loss of activity.
To meet such a challenge, we choose the reaction system
Experimental section
Materials and measurements
6
−
of Evans–Showell type ijCo
2
Mo10
H
4
O
38
]
anion as subunit
6
−
and lanthanides as linker, because: (i) the [Co Mo H O ]
2
10
4
38
anion possesses a point group symmetry D2 which will
All chemicals were commercially purchased and used
induce the formation of chiral species, similar to
without further purification. The metal chlorides LnCl
3
(Ln =
6
−
15
[
MnMo O32] polyoxoanion with a D3 symmetry; (ii) no
9
Sm, Eu) were prepared by dissolving Ln O (99.9%) in
2
3
information on structure and property has been reported in
hydrochloric acid, followed by drying and crystallization.
(NH [Co 38]·7H O was synthesized according to
the literature, and characterized by means of IR spectros-
6
−
using [Co
2
Mo10
H
4
O
38
]
as building block for the fabrication
4
)
6
2
Mo10
H
4
O
2
1
5,22
of extended frameworks since its structure was solved at
1
969; (iii) there are two terminal oxygen atoms on each
copy. Elemental analyses (H and N) were performed on a
Perkin-Elmer 2400 CHN elemental analyzer; Co, Mo, Sm and
Eu were analyzed on a PLASMA-SPEC (I) ICP atomic emission
6
−
molybdenum center of [Co
it have strong coordination ability to lanthanides to form
new inorganic architectures. We herein expect that the
2
Mo10
H
4
O
38
]
anion which make
−1
spectrometer. IR spectra were recorded in the range 400–4000 cm
6
−
[
Co
2
Mo10
H
4
O
38
]
anion should be a suitable building unit
on an Alpha Centaur FT/IR Spectrophotometer using KBr
pellets. TG analyses were performed on a Perkin-Elmer TGA7
utilized in constructing chiral POMs through controlling the
reaction conditions.
−
1
instrument in flowing N with a heating rate of 10 °C·min .
2
It is well-known that many external factors, such as pH
values, solvent systems, and metal-to-POM ratios impose cru-
cial influences on the structures of compounds, although it
remains a considerable difficulty to control the structures of
POM-based materials. Most research results suggest that a
subtle alteration by means of these factors can lead to totally
PXRD patterns of the samples were recorded on a Rigaku
Dmax 2000 X-ray diffractometer with graphite mono-
chromatized Cu-Kα radiation (λ = 0.154 nm) and 2θ varying
from 5 to 50°. Diffuse reflectivity spectra were collected on a
finely ground sample with a Cary 500 spectrophotometer
equipped with a 110 mm diameter integrating sphere, which
were measured from 200 to 800 nm. CD spectra were mea-
sured on JASCO J-810.
1
6–18
different products.
However, one factor, reaction temper-
ature is often ignored to achieve this kind of goal. So far,
there are very limited examples of temperature-controlled self
assembly of non-chiral POMs. For instance, Niu and
coworkers reported three new inorganic–organic hybrid
arsenomolybdates originated from different temperature
ranges corresponding to different proportions of oxidized
Synthesis of ijSmIJH O) ]ijSmIJH O) ]ijCo Mo H O ]·6H O
2
5
2
7
2
10
4
38
2
(1). In a typical synthesis procedure for 1, SmCl
3
(0.015 g,
0.06 mmol) and (NH ) [Co Mo H O ]·7H O (0.058 g,
4
6
2
10
4
38
2
0.03 mmol) were dissolved in 10 mL water. Then 10 mL
acetonitrile was added to the above solution. The pH value of
the mixture was about 3.00. The mixture was heated at 85 °C
for 20 h and dark green plate-shaped crystals of 1 were col-
lected in about 30% yield (based on Mo). Elemental analyses:
calc. for 1: H, 1.73; Co, 5.09; Mo, 41.46; Sm, 12.99%. Found
1
9
AsIJIII) atoms; Cronin's group successfully isolated two 3D
open framework materials using a preassembled anion
2
+
8
{P W48}, and electrophilic manganese Mn linkers by the
2
0
temperature control; Dessapt et al. studied the reactivity of
2
−
−1
MoO
4
toward six organoammonium cations at different
H, 1.81 Co, 5.34; Mo, 41.20; Sm, 13.26%. FTIR data (cm ):
synthesis temperatures, and obtained 16 organic–inorganic
3432(s), 1631(m), 943(vs), 921(vs), 854(m), 633(vs), 596(vs),
559(s), 453(m).
2
1
hybrid materials. It is thus of considerable interest to inves-
tigate whether reaction temperature can play a vital factor on
the formation of chiral POMs.
Synthesis of ijEuIJH O) ]ijEuIJH O) ]ijCo Mo H O ]·6H O
2
5
2
7
2
10
4
38
2
(2). The preparation of 2 was similar to that of 1 except that
In this work, we study the interactions between the Evans–
EuCl (0.015 g, 0.06 mmol) was used instead of SmCl . The
3
3
6
−
Showell type cluster ijCo
2
Mo10
H
4
O
38
]
and lanthanide cations
pH value of the mixture was about 3.05. Dark green plate-
shaped crystals of compound 2 were obtained in about 20%
yield (based on Mo). Elemental analyses: calc. for 2: H, 1.73;
Co, 5.09; Mo, 41.40; Eu, 13.11. Found H, 1.89; Co, 5.33; Mo,
at different temperatures. Four new compounds were
obtained, namely [Ln(H O) ][Ln(H O) ][Co Mo H O ]·6H O
2
5
2
7
2
10
4
38
2
(
(
Ln = Sm 1; Eu 2), and (NH
4
)
3
[Ln(H
2
O)
6
][Co
2
Mo10
H
4
O
38]·6H
2
O
−
1
Ln = Sm 3; Eu 4). Compounds 1 and 2 obtained at 85 °C are
41.27; Eu, 13.35%. FTIR data (cm ): 3396(s), 1626(m),
952(vs), 914(vs), 631(vs), 600(vs), 572(s), 445(m).
constructed from left-handed chain and right-handed chain
to form a 1D racemic ladder, representing the first examples
of 1D extended structures based on the Evans–Showell type
polyoxoanion. Compounds 3 and 4 obtained at 25 °C are
chiral conglomerates, which crystallize in the chiral space
group P2 . All four compounds as Lewis acid–base catalysts
1
are very efficient in the cyanosilylation of carbonyl com-
pounds and allow the reaction to be carried out under
Synthesis of IJNH ) ijSmIJH O) ]ijCo Mo H O ]·6H O (3).
4
3
2
6
2
10
4
38
2
In a typical synthesis procedure for 3, SmCl
3
(0.015 g,
0.06 mmol) and (NH ) [Co Mo H O ]·7H O (0.058 g, 0.03 mmol)
4
6
2
10
4
38
2
were dissolved in 10 mL water. Then 10 mL acetonitrile was
added to the above solution. The pH value of the mixture was
about 3.00. The mixture was kept at room temperature for
several days, and then dark green block crystals of 3 were
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collected in about 40% yield (based on Mo). Elemental
analyses: calc. for 3: H, 1.90; N, 1.99; Co, 5.59; Mo, 45.47; Sm,
Other restraints such as ‘isor’ were used in the refinements
for obtaining reasonable atom sites and thermal parameters.
A summary of the crystallographic data and structural deter-
mination for 1–4 is provided in Table 1.
CSD reference number: 428383, 428384, 428385, 428386
for 1–4.
7
6
9
.13%. Found: H, 2.11; N, 2.24; Co, 5.34; Mo, 45.62; Sm,
.97%. FTIR data (cm ): 3436(s) 1632(m), 1404(m), 952(vs),
17(vs), 854(m), 631(vs), 596(vs), 547(s), 445(w).
−
1
4 3 2 6 2 4 2
Synthesis of IJNH ) ijEuIJH O) ]ijCo Mo10H O38]·6H O (4).
The preparation of 4 was similar to that of 3 except that
EuCl (0.015 g, 0.06 mmol) was used instead of SmCl . The
General procedure for cyanosilylation reactions
3
3
pH value of the mixture was about 3.05. Dark green block
crystals of compound 4 were obtained in about 35% yield
A typical procedure for the cyanosilylation reaction of alde-
hydes is as follows: 2 mol% catalyst (1–4) was added to a mix-
(
1
based on Mo). Elemental analyses: calc. for 4: H, 1.89; N,
.99; Co, 5.58; Mo, 45.44; Eu, 7.20%. Found: H, 2.13; N, 1.87;
ture of aldehyde (0.5 mmol) and IJCH
the absence of solvent. The reaction mixture was stirred at
room temperature under a N atmosphere. The progress of
3 3
) SiCN (1.5 mmol), in
−
1
Co, 5.73; Mo, 45.29; Eu, 7.41%. FTIR data (cm ): 3433(m),
2
1
5
633(m), 1403(s), 948(vs), 915(vs), 854(m), 632(vs), 600(vs),
47(s), 449(w).
the reaction was monitored by GC analysis. After the reaction
was completed, the catalyst was removed by filtration and
centrifugation of the reaction mixture. All products (cyanohy-
drin trimethylsilyl ethers) were confirmed by a comparison of
X-ray crystallography
1
their GC retention times, GC-MS spectra, and/or H spectra
The crystallographic data of four compounds were collected
on the Bruker Smart CCD diffractometer with Mo Kα radia-
tion (λ = 0.71073 Å ) by ω and θ scan modes at 293 K for 1
and at 296 K for 2–4. Empirical absorption correction was
applied. The structures of 1–4 were solved by the direct
with those of authentic data. GC analysis was performed
using HP6890/5973MS with a cross-linked (95%)-dimethyl-
(
5%)-diphenylpolysiloxane column of 30 m length.
Results and discussion
Synthesis
2
method and refined by the full-matrix least squares on F
2
3
using the SHELXTL-97 software. All of the non-hydrogen
atoms were refined anisotropically in 1–4. The hydrogen
atoms attached to oxygen atoms of polyoxoanions and water
molecules were not located in 1–4. Site occupancies of the
partial crystal water molecules and/or partial free ammonium
molecules in 1–4 were set to be less than 1 through the
refinement of their thermal parameters due to disorder.
The reaction of IJNH ) ijCo Mo H O ]·7H O and LnCl (Ln =
4
6
2
10
4
38
2
3
Sm, Eu) has been investigated. Four compounds with two
kinds of structures were obtained. Compounds 1(2) and 3(4)
were synthesized under the same reaction conditions, except
for the alteration of the reaction temperature. It is clear that the
reaction temperature of the reaction system is the key factor
Table 1 Crystal data and structure refinement for 1–4
Complex
1
2
3
4
Formula
Formula weight
T (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
H
40Co
2
Mo10
O
56Sm
2
H
40Co
2
Mo10
O56Eu
2
H
40Co
2
3
Mo10N O50Sm
H
2 3
40Co Mo10N O50Eu
2314.28
293(2)
Triclinic
P¯1
12.458(3)
13.915(3)
14.341(3)
74.555(3)
85.531(3)
89.871(2)
2388.5(9)
2
2317.50
296(2)
Triclinic
P¯1
12.360(4)
13.803(4)
14.183(4)
74.436(5)
85.442(5)
89.734(5)
2323.2(12)
2
2109.96
296(2)
Monoclinic
P2IJ1)
10.5118(5)
18.6632(8)
12.2190(6)
90
114.115(2)
90
2111.57
296(2)
Monoclinic
P2IJ1)
10.5122(5)
18.6663(9)
12.2157(6)
90
114.060(2)
90
2188.76IJ18)
2
γ (°)
U (Å )
3
2187.96IJ18)
2
4.948
Z
−1
μ (mm
)
5.750
6.084
5.037
Flack parameters
Reflections collected
Independent reflections
RIJint)
0.025(8)
9942
9942
0.0000
1.046
0.0280
0.0743
0.0283
0.0745
0.042(8)
8771
8771
0.0000
1.054
0.0301
0.0812
0.0302
0.0813
13309
8270
0.0319
1.024
0.0384
0.0981
0.0478
0.1039
11088
7967
0.0581
1.071
0.0976
0.2265
0.1362
0.2493
2
GOF on F
a
R
1
[I > 2σIJI)]
[I > 2σIJI)]
b
wR
2
1
R (all data)
wR
2
(all data)
P||F
| − |F
||/P
|F
|. wR
=
P[w(F 2
− F
c
) ]/ [w(F
P
) ]
.
a
b
2 2
2 2 1/2
R
1
=
o
c
o
2
o
o
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influencing the structures and topologies of these com-
pounds. At higher temperature (85 °C), racemic compounds
two CoO octahedra share an edge. As suggested by Evans
and Showell, the polyoxoanion [Co Mo H O ] has a point
2 10 4 38
6
6
−
1
and 2 [Ln(H
2
O)
5
][Ln(H
2
O)
7
][Co
2
Mo10
H
4
O
38] are isolated,
2
group symmetry D , and possesses two enantiomers (shown
exhibiting a 1D ladderlike frame; with a decrease of the tem-
in Scheme 1).
perature to room temperature (25 °C), 0D mono-supporting
chiral architectures 3 and 4 (NH ) [Ln(H O) ][Co Mo10H O ]
4 3 2 6 2 4 38
Isostructural compounds 1 and 2 crystallize in the centro-
symmetric space group P ¯1 , thus two enantiomers of the poly-
are formed by chiral resolution of Evans–Showell type POM
with lanthanides. The increasing temperature makes the
solution reaction more effective, so more lanthanide cations
oxoanion can coexist in the crystal lattice. Herein compound
1 is described as an example in detail. The structure of 1
exhibits a unique 1D ladderlike chain assembled by
+
6−
3+
substitute NH4 to coordinate to the terminal oxygen atoms
ijCo Mo H O38]
polyoxoanions and Sm
cations. In
2
10
4
of polyoxoanions to produce extended structures. Then, we
can assume that compounds 3 and 4 are the kinetic phase
because they are formed at milder conditions. On the other
hand, compounds 1 and 2 seem to be the thermodynamic
phase. To our best knowledge, compounds 1(2) and 3(4) rep-
resent the first example of temperature-controlled structural
changes from racemic compounds to chiral conglomerates in
the field of POMs.
the asymmetric unit, one crystallization-independent
6
−
3+
[Co
2
Mo10
H
4
O
38
]
anion is linked by two unique Sm cations
(Fig. 1a). In the polyoxoanion, four of the 10 crystallographi-
3
+
cally unique oxygen atoms surrounding the two Co ions,
are bound to hydrogen atoms, which are identified by the cal-
culation of bond valence sums. Six kinds of oxygen atoms
exist in the cluster according to the manner of oxygen coordi-
nation, that is terminal oxygen Ot, terminal oxygen Ot′ linked
3
+
3+
3+
When Gd or Tb ion with smaller ionic radii was used
to Sm , double-bridging oxygen Ob, central oxygen Oc (μ -OH
3
3
+
3+
instead of Sm or Eu ion, at room temperature (25 °C) two
chiral compounds that are isostructural to compounds 3 and
atom of a Co and two Mo atoms), central oxygen Od (μ
atom of a Co and three Mo atoms), central oxygen Oq (μ
4
4
-O
-O
4
were also obtained, while at higher temperature (85 °C),
atom of two Co and two Mo atoms). Thus the Mo–O bond
lengths fall into six classes: Mo–Ot 1.681(6)–1.725(6) Å, Mo–Ot′
1.713(6)–1.728(6) Å, Mo–Ob 1.874(6)–1.972(6) Å, Mo–Oc
2.229(5)–2.288(6) Å, Mo–Od 1.989(5)–2.363(5) Å and Mo–Oq
2.222(5)–2.333(5) Å in 1. The central Co–O distances are
1.871(5)–1.958(5) Å, and the O–Co–O angles are in the range of
83.5(2)–175.8(2)°. All bond lengths and bond angles are within
two racemic high-dimensional structures in which partial
3
+
3+
Gd and Tb ions are eight-coordinate geometry were sepa-
rated. The experimental results further indicate that the reac-
tion temperature is the key factor mediating the formation of
chiral conglomerates vs. racemic compounds in the reaction
system of Evans–Showell type POM, as well as the solid-state
structures adopted by these compounds are imposed by the
nature of the lanthanide cations used.
Many parallel experiments indicate that stoichiometry
and pH value also can affect the quality of crystals. The
products are obviously affected by the stoichiometry of
Ln /ijCo Mo H O38]
isolated by the 2 : 1 Ln /[Co
Ln /[Co
the crystal quality of compounds 1–4 was poor, and the yields
were reduced. The optimal pH range of the reaction is
from 2.0 to 4.0. For a low pH (pH < 2.0) no reaction occurs;
for a high pH (pH > 4.0) the hydrolysis of the lanthanide
cations makes a mass of precipitates. This is consistent
with the stable pH range of Evans–Showell type cluster
1
5,22
the normal ranges.
The two crystallization-independent SmIJIII) cations display
a similar coordination sphere (Fig. S1†). Sm(1) cation, joined
6
−
neighboring [Co
2
Mo10
H
4
O
38
]
polyoxoanions together as
linker, has a tricapped trigonal prism coordination environ-
ment, defined by four terminal oxygen atoms from two
3
+
6−
.
Compounds 1–4 can be well
2
10
4
3
+
6−
6−
2
Mo10
H
4
O
38
]
ratio. When the
[Co
2
Mo10
H
4
O
38
]
units [Sm–O 2.448(5)–2.628(6) Å] and five
2.399(6)–2.557(8) Å]. The nine-
coordinate Sm(2) links to two terminal oxygen atoms from
3
+
6−
2
Mo10
H
4
O
38
]
ratio increased from 2 : 1 to 3 : 1 or 4 : 1,
water molecules [Sm–OH
2
6
−
two [Co
2
Mo10
H
4
O
38
]
molecules [Sm–O 2.483(6)–2.526(6) Å]
2.430(7)–2.539(8) Å] to
and seven water molecules [Sm–OH
2
complete a tricapped trigonal prism coordination geometry.
The average Sm–O bond length is 2.480 Å.
6
−
Interestingly, in 1 homochiral ijCo
2
Mo10
H
4
O
38
]
anions
6
− 24
[Co Mo H O ] .
are linked by Sm(1) cations to generate a 1D chiral chain
2 10 4 38
Crystal structures of 1 and 2
Single-crystal X-ray crystallographic analyses reveal that the
6
−
heteropolymolybdate ijCo
2
Mo10
H
4
O
38
]
in compounds 1–4 is
a typical Evans–Showell type polyoxoanion. The polyoxoanion
6
−
[
Co Mo H O ] was first prepared by Friedheim and Keller
2 10 4 38
2
5
in 1906, and was structurally determined as its ammonium
1
5
salt by Evans and Showell in 1969. The structure of
6
−
[
Co Mo H O ] can be deduced from the planar Anderson
2
10
4
38
6−
6−
38
Scheme 1 L-ijCo
2
Mo10
H
4
O
38
]
and D-[Co
2
Mo10
H
4
O
]
with D
2
3
−
ion [CoMo
6
H
6
O
24
]
5
by removing one {MoO } group from
symmetry viewed as two “parent clusters” {CoMo
5
O
19} turning one
3
−
each of two [CoMo H O24] ions, turning one ~45° around
6
6
~45° around the anionic equatorial plane and joining together by
the anionic equatorial plane and joining them so that the
sharing an edge.
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(
Fig. 2a). Adjacent opposite-handed chiral chains are inter-
connected by Sm(2) cations to produce a 1D non-chiral lad-
derlike structure along the c axis (shown in Fig. 2b). To our
best knowledge, compounds 1 and 2 represent the first exam-
6
−
ples of 1D architectures based on [Co Mo H O38] unit.
2
10
4
Then adjacent non-chiral ladderlike chains are linked
together by hydrogen-bonding interactions (O14⋯O1W
2.861, O9⋯O1W 2.866, O22⋯O2W 2.910 Å) between terminal
oxygen atoms of polyoxoanions and coordinated water mole-
cules to form an interesting 2D supramolecular network (see
Fig. 3a). Furthermore, 2D supramolecular layers are joined
up to yield a 3D supramolecular framework via other
hydrogen-bonding interactions (O21⋯O4W 2.713, O25⋯O4W
2
.904, O36⋯O6W 2.882, O12⋯O8W 2.858 Å) (see Fig. 3b).
Free water molecules are filled in the cavities and participate
in the extensive hydrogen-bonding interactions with the poly-
oxoanion framework.
Crystal structures of 3 and 4
The preparation of compounds 3 and 4 was similar to that of
compounds 1 and 2 except that the reaction temperature was
adjusted from 85 °C to room temperature (25 °C). Single crys-
tal structural analysis revealed that compounds 3 and 4 are
isostructural, and crystallize in the chiral space group P21
with Flack parameters of 0.025(8) (3) and 0.042(8) (4). Thus,
compound 3 will be described. Compound 3 exhibits a
mono-supporting
structure
assembled
by
chiral
Fig. 1 (a) ORTEP drawing of 1 with thermal ellipsoids at 50%
probability. Free water molecules are omitted for clarity. (b) ORTEP
drawing of 3 with thermal ellipsoids at 50% probability. Free water
molecules and ammonia ions are omitted for clarity.
6
−
3+
ijCo Mo H O38] polyoxoanion and one Sm cation with
2
10
4
Fig. 3 (a) 2D supramolecular layer in 1, showing the strong hydrogen
Fig.
ijCo
2
(a) In compound 1, the homochiral polyoxoanions
bonds between polyoxoanions and coordinated water molecules with
blue colour. (b) A view along the b axis illustrating the 3D
6
−
3+
2
Mo10
H
4
O
38
]
are respectively connected by Sm
to a left-
handed chain and a right-handed chain. (b) Polyhedral representation
supramolecular framework displaying the interbedded hydrogen bonds
with yellow colour in 1 (color code: Co, yellow; Mo, pink/blue; Sm,
green; O, red). Free water molecules are omitted for clarity.
of 1D non-chiral ladder in 1, showing the left-handed and right-
3+
handed chiral chains linked by Sm cations.
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+
three NH4 balancing the charges. The structure of
(see Fig. 4b). Furthermore, 2D supramolecular layers are
connected to yield a 3D supramolecular chiral framework via
6
−
[
Co Mo H O ] anion is also an Evans–Showell type, simi-
2
10
4 38
lar to compound 1. Six kinds of oxygen atoms exist in the
cluster according to the manner of oxygen coordination.
Then, the Mo–O bond lengths fall into six classes: Mo–Ot
the strong hydrogen-bonding interactions (O20⋯O6W 2.730 Å)
+
(Fig. 5). Free water molecules and NH ions are filled in the
4
cavities of 3D supramolecular structures and participate in the
extensive hydrogen-bonding interactions with the poly-
oxoanion framework. A better insight into the nature of such
3D supramolecular framework can be achieved by reducing the
structure to simple node and linker net. According to the sim-
plification principle, each Sm(1) cation is linked with four
1
1
1
.682(5)–1.730(5) Å, Mo–Ot′ 1.727(5)–1.740(5) Å, Mo–Ob
.847(5)–1.987(5) Å, Mo–Oc 2.233(5)–2.287(5) Å, Mo–Od
.980(5)–2.369(5) Å and Mo–Oq 2.210(5)–2.363(5) Å in 3. The
central Co–O distances are 1.857(4)–1.936(5) Å, and the
O–Co–O angles are in the range of 83.8(2)–175.9(2)°. The
asymmetric unit in the structure of 3 consists of one
crystallographically independent chiral Evans–Showell type
6
−
6−
[Co Mo H O38] units, and the [Co Mo H O38] unit is
2
10
4
2
10
4
bonded to four adjacent Sm(1) cations through hydrogen
bonds. Therefore, the resulting 3D supramolecular chiral
frame is a uninodal 4-connected diamond-related net with
3
+
polyoxoanion linked by one Sm unit (Fig. 1b). The crystallo-
3
+
graphically unique Sm ion bonded to the polyoxoanion as
supporter, is coordinated by three oxygen atoms from the
POM [Sm–O 2.446(5)–2.491(5) Å] and six water molecules
6
Schläfli symbol of 6 , as shown in Fig. S3.†
2
6
Bond valence sum calculations show that all Mo atoms
are in the +6 oxidation state, Co atoms are in the +3 oxida-
tion state, and lanthanide sites are in the +3 oxidation state.
These results are consistent with the charge balance
considerations.
[
Sm–OH 2.437(6)–2.523(6) Å] to form a monocapped square
2
antiprismatic coordination geometry (Fig. S2†). The average
Sm–O bond length is 2.477 Å.
Remarkably, in 3 theses mono-supporting chiral subunits
are firstly joined up together by the strong hydrogen-bonding
interactions (O33⋯O2W 2.766 Å) between terminal oxygen
atoms of polyoxoanions and coordinated water molecules to
form a 1D supramolecular chiral chain (shown in Fig. 4a).
Then adjacent homochiral chains are linked together by
other hydrogen-bonding interactions (O30⋯O3W 2.892 Å) to
generate an interesting 2D supramolecular wavelike network
FT-IR spectroscopy
IR spectra of compounds 1–4 display similar characteristic
patterns
of
the
Evans-Showell
type
structure
6
−
ijCo Mo H O38] (see Fig. S4a–S4d†), in agreement with
2
10
4
2
2
those reported in literature. The spectra can be divided into
the following typical regions: (1) 3600–2800 cm correspond-
ing to the O–H and N–H stretchings; (2) 1700–1400 cm cor-
responding to the region of the O–H and N–H bendings; (3)
−
1
−
1
−
1
1
000–850 cm assignable to the Mo–O terminal stretchings;
−
1
(
4) 750–500 cm
assignable to the Mo–O–Mo bridge
stretchings (the vibrations of the Mo–O–Co bonds and the
water librations are also located in this last region). Below
−
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. Notice that the IR spectra of
Fig. 4 (a) Polyhedron and ball-stick view of the 1D supramolecular
chiral chain in 3 through the hydrogen-bonding interactions between
the terminal oxygen atoms of polyoxoanions and coordinating water
molecules. (b) View of 2D supramolecular chiral sheet in 3 showing the
hydrogen-bonding interactions between polyoxoanions and coordinat-
ing water molecules, (color code: Co, yellow; Mo, blue; Sm, green; O,
red; hydrogen bond, green).
Fig. 5 View of the 3D supramolecular chiral framework of 3 along the
c axis, (color code: Co, yellow; Mo, blue; Sm, green; O, red; hydrogen
bond, green or yellow).
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3
1
and 4 respectively show an additional vibration band at
−
1
404 and 1403 cm which is attributable to the N–H bending
+
in the NH
4
cations, compared with those of 1 and 2. These
results are consistent with the single-crystal X-ray analyses.
TG analysis
Thermal gravimetric (TG) curve of 1 is shown in Fig. S5a.†
The TG curve exhibits a multi-step continuous weight loss
process and gives a total weight loss of 16.1% in the range of
4
0–600 °C, which agrees with the calculated value of 16.3%.
The weight loss of 13.4% from 40 to 270 °C corresponds to
the loss of all lattice and coordinated water molecules (calc.
1
4.0%). The weight loss of 2.7% from 275 to 470 °C is due to
the loss of composition water molecules and oxygen mole-
cules from the residual metal oxides (calc. 2.3%). The TG
curves of 2 exhibits similar weight loss stages to those of 1
(
see Fig. S5b†), and gives a total weight loss of 16.3% in the
range of 40–600 °C, which agrees with the calculated value of
6.2%.
Thermal gravimetric (TG) curve of 3 is shown in Fig. S5c.†
1
The TG curve exhibits a multi-step continuous weight loss
process and gives a total weight loss of 15.5% in the range of
4
0–600 °C, which agrees with the calculated value of 15.1%.
The weight loss of 10.5% from 40 to 265 °C corresponds to
the loss of all lattice and coordinated water molecules (calc.
1
0.2%). The weight loss of 5.0% from 267 to 480 °C is due to
the loss of composition water molecules, ammonia mole-
cules, and oxygen molecules from the residual metal oxides.
The TG curve of 4 exhibits similar weight loss stages to
those of 3 (see Fig. S5d†), and gives a total weight loss of
Fig. 6 (a) UV–vis diffuse reflectance spectra of bulk compounds 1 and
2
. (b) UV–vis diffuse reflectance spectra of bulk compounds 3 and 4.
1
5.2% in the range of 40–600 °C, which agrees with the calcu-
lated value of 15.1%.
3
+
of a regular octahedral configuration low-spin Co in the
PXRD characterization
6
−
27
[Co
2
Mo10
H
4
O
38
]
anion.
The PXRD patterns for 1–4 are presented in Fig. S6.† The dif-
fraction peaks of both calculated and experimental patterns
match well, indicating the phase purities of these com-
pounds. The differences of PXRD patterns of 1(2) and 3(4)
also indicate that both kinds of compounds have different
structures. These conclusions are in agreement with the
results of the single crystal X-ray analysis.
CD spectroscopy
One pair of enantiomers L-3 and D-3 were separated manu-
ally. The solid state CD spectra of the bulk samples of L-3
and D-3 are mirror images of each other, which indicated that
both compounds are enantiomers (Fig. 7). In the λ = 200–400 nm
wavelength range, L-3 and D-3 showed clearly cotton effects
at about 252 nm and 316 nm. The two absorption bands
can be assigned to the O → Mo LMCT transition for
UV–vis diffuse reflective spectroscopy
The diffuse reflectivity for solid samples of 1–4 were
performed. The absorption (A) data were calculated from the
reflectivity using the function: A = logIJ1/R%) where R is the
reflectivity at a given wavelength (λ). The A versus λ plots are
displayed in Fig. 6. On the UV region (200–400 nm), the plots
display two intense absorption bands at 223, 304 nm for 1,
6
−
ijCo
2
Mo10
H
4
O
38
]
anion.
Catalysis study
Cyanosilylation reaction provides a convenient route to cya-
nohydrins, which are key derivatives in the synthesis of fine
chemicals and pharmaceuticals. In order to obtain cyanohy-
drin molecules, the use of a catalyst with Lewis acid or base
character through which both the substrate and the cyanide
precursor are activated is necessary. In this sense, the
starting substrates commonly used are aldehydes or ketones
with trimethylsilyl cyanide (TMSCN) as the nucleophilic
2
27, 305 nm for 2, 225, 303 nm for 3, and 225, 303 nm for 4,
which are characteristic of O → Mo charge transfer for POMs.
On the visible region (400–800 nm), there are also two
absorption bands at 440, 605 nm for 1, 442, 607 nm for 2,
2
8
4
41, 605 nm for 3 and 441, 605 nm for 4, which are respec-
1
1
1
1
tively attributed to the A → T and A → T transition
1
g
2g
1g
1g
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Firstly, the cyanosilylation of benzaldehyde acts as a
model reaction to investigate the catalytic nature of com-
pounds 1–4. The reaction was carried out with 2 mol% of cat-
alysts under the conditions described in Table 2. All our
compounds effectively catalyzed the cyanosilylation to afford
the corresponding cyanohydrin trimethylsilyl ether with yield
of up to about 98%. In a comparison of the reactivity
of our catalysts with that of some previously reported
POM-based compounds IJ[Cu
2
IJbpy)IJH
2 2 2 11
O)5.5] ijH W O38] and
2
9
TBA H [(SiYW10O ) ]), it was found to be higher than
8
2
36 2
the first one (benzaldehyde, 24 h, and yield = 98.1%), which
uses solvent conditions, and less than the second one,
which is a homogeneous catalyst and uses solvent conditions
(
benzaldehyde, 15 min, and yield = 94%).
Fig. 7 The solid state CD spectra of the crystalline powders L-3 and
D-3, respectively showing the opposite Cotton effects.
Subsequently, the cyanosilylation reaction of various
kinds of aromatic aldehyde substrates in the presence of
catalysts 1 and 3 was further studied. With a substrate like
2
-hydroxybenzaldehyde, 4-methylbenzaldehyde, or 4-fluoro-
agent. In this work, we test the activity of four compounds
benzaldehyde, the yield is high (Table 2). It seems that the
nature of the substituent on the aromatic ring had no dra-
matic effect on the reaction yield. When sterically more hin-
dered 1-napthaldehyde is used as the substrate, the yield is
1
–4 as heterogeneous catalysts in the aldehyde cyano-
silylation reaction under solvent-free condition at room
temperature.
a
Table 2 Cyanosilylation of aldehydes catalyzed by compounds 1–4
b
Compound
Aldehyde
Time (h)
Yield (%)
1
2
3
4
5
5
5
5
98.2
98.1
98.4
98.0
1
3
2
2
98.4
98.0
1
3
3
3
96.5
97.9
1
3
4
4
97.3
90.1
1
3
5
5
61.5
80.1
Blank
5
5
13.7
4
IJNH )
6
2
ijCo Mo10
H
4
O
38
]
59.9
a
b
Reaction conditions: catalyst 2 mol%, aldehyde 0.5 mmol, TMSCN 1.5 mmol, without solvent, room temperature (25 °C) under N
2
.
Yields
were determined by GC analysis using naphthalene as an internal standard.
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very poor suggesting that the aldehyde here is not accommo-
dated as per the transition-state geometry requirement for
driving the reaction to the product according to the Lewis
References
1 (a) V. Soghomonian, Q. Chen, R. C. Haushalter, J. Zubieta
and C. J. O'Connor, Science, 1993, 259, 1596; (b) D. Y. Du,
L. K. Yan, Z. M. Su, S. L. Li, Y. Q. Lan and E. B. Wang,
Coord. Chem. Rev., 2013, 257, 702; (c) X. X. Zheng, L. Zhang,
J. Y. Li, S. Z. Luo and J. P. Cheng, Chem. Commun., 2011, 47,
12325.
2 (a) F. B. Xin and M. T. Pope, J. Am. Chem. Soc., 1996, 118,
7731; (b) M. Sadakane, M. H. Dickman and M. T. Pope,
Inorg. Chem., 2001, 40, 2715; (c) M. Inoue and T. Yamase,
Bull. Chem. Soc. Jpn., 1995, 68, 3055; (d) X. K. Fang,
T. M. Anderson and C. L. Hill, Angew. Chem., Int. Ed., 2005,
44, 3540.
3 (a) U. Kortz, M. G. Savelieff, F. Y. A. Ghali, L. M. Khalil,
S. A. Maalouf and D. I. Sinno, Angew. Chem., Int. Ed., 2002,
41, 4070; (b) C. Streb, D. L. Long and L. Cronin, Chem.
Commun., 2007, 471.
4 (a) H. Y. An, E. B. Wang, D. R. Xiao, Y. G. Li, Z. M. Su and
L. Xu, Angew. Chem., Int. Ed., 2006, 45, 904; (b) H. Q. Tan,
Y. G. Li, Z. M. Zhang, C. Qin, X. L. Wang, E. B. Wang and
Z. M. Su, J. Am. Chem. Soc., 2007, 129, 10066.
3
0
acid effect of lanthanides.
To probe the heterogeneity of the catalysts, after the cata-
lytic reactions, the catalysts were recovered from their reac-
tion media. Solids of 1 and 3 could be easily isolated from
the reaction suspension by a simple filtration and reused at
least three times without an appreciable loss of its high cata-
lytic performance (from 98.2% to 96.9% yield; from 98.4% to
9
6.4% yield see Table S2†). The PXRD patterns of the
retrieved catalysts were identical to those of the fresh cata-
lysts (Fig. S7†). The IR spectra of the recovered compounds 1
and 3 were also identical to those of the freshly prepared
samples (Fig. S8†). These observations suggested that 1 and 3
are true heterogeneous catalysts. In addition, infrared spec-
troscopy of the catalysts 1 and 3 impregnated with benzaldehyde
−
1
exhibited one broad C–O stretch at 1689.6 and 1691.0 cm ,
respectively. The vIJC–O) stretch had a red shift of ~12.2 and
−
1
−1
1
0.8 cm
from 1701.8 cm
of the free benzaldehyde
(
see Fig. S9†). This experiment demonstrated the possible
3
+
activation of the substrate by the Sm cations as Lewis acid
site in 1 and 3. Furthermore, the control experiment for
cyanosilylation of benzaldehyde with (NH ) [Co Mo10H O38]·7H O
4 6 2 4 2
5 (a) Y. Q. Lan, S. L. Li, Z. M. Su, K. Z. Shao, J. F. Ma,
X. L. Wang and E. B. Wang, Chem. Commun., 2008, 58; (b)
L. Xu, C. Qin, X. L. Wang, Y. G. Wei and E. B. Wang, Inorg.
Chem., 2003, 42, 7342.
6 B. Hasenknopf, K. Micoine, E. Lacôte, S. Thorimbert,
M. Malacria and R. Thouvenot, Eur. J. Inorg. Chem., 2008, 5001.
7 (a) X. K. Fang, T. M. Anderson, Y. Hou and C. L. Hill, Chem.
Commun., 2005, 5044; (b) J. D. Compain, P. Mialane,
A. Dolbecq, J. Marrot, A. Proust, K. Nakatani, P. Yu and
F. Sécheresse, Inorg. Chem., 2009, 48, 6222.
precursor in a homogeneous manner gave 59.9% yield, which
is far lower than that of 1 and 3 in the heterogeneous man-
ner. The higher yield with 1 and 3 is possibly attributed to
3
+
the synergistic effect of the Lewis acid (Sm cations) and the
6
−
2 4 38
Lewis base (surface oxygen atoms of the [Co Mo10H O ]
POM) that activate respectively aldehydes and TMSCN at the
same time.
8
(a) W. W. Ju, H. T. Zhang, X. Xu, Y. Zhang and Y. Xu, Inorg.
Chem., 2014, 53, 3269; (b) H. Naruke, J. Iijima and T. Sanji,
Inorg. Chem., 2011, 50, 7535; (c) Q. X. Han, C. He, M. Zhao,
B. Qi, J. Y. Niu and C. Y. Duan, J. Am. Chem. Soc., 2013, 135,
10186; (d) Z. M. Zhang, Y. G. Li, S. Yao, E. B. Wang,
Y. H. Wang and R. Clérac, Angew. Chem., Int. Ed., 2009, 48,
1581; (e) Z. M. Zhang, S. Yao, Y. G. Li, R. Clérac, Y. Lu,
Z. M. Su and E. B. Wang, J. Am. Chem. Soc., 2009, 131,
14600.
Conclusions
In summary, we have reported two racemic compounds (1, 2)
and two chiral conglomerates (3, 4) in the reaction system of
Evans–Showell type polyoxoanion ijCo Mo H O ] and lan-
6
−
2
10
4
38
thanide cations by changing the temperatures. The reaction
temperature playing a crucial role to mediate the formation
of racemic species vs. conglomerates in the field of POMs, is
for the first time demonstrated. Furthermore, these new
POM materials containing lanthanides are efficient heteroge-
neous Lewis acid–base catalysts for cyanosilylation of various
aldehyde compounds under solvent-free conditions. The suc-
cessful isolation of these species not only certainly stimulates
researchers' interest to develop new catalytic materials
containing POMs and lanthanides, but also provides incen-
tives for more studies to spontaneous resolution of chiral
POMs by controlling the reaction temperatures.
9 (a) Y. Z. Wang, H. L. Li, C. Wu, Y. Yang, L. Shi and L. X. Wu,
Angew. Chem., Int. Ed., 2013, 52, 4577; (b) T. Noguchiab and
N. Kimizuka, Chem. Commun., 2014, 50, 599.
10 (a) Q. Tang, S. X. Liu, Y. W. Liu, S. J. Li, F. J. Ma, J. X. Li,
S. T. Wang and C. Z. Liu, Dalton Trans., 2013, 42, 8512; (b)
Y. Wang, S. L. Pan, H. W. Yu, X. Su, M. Zhang, F. F. Zhang
and J. Han, Chem. Commun., 2013, 49, 306; (c) M. Sarma,
T. Chatterjee, H. Vindhya and S. K. Das, Dalton Trans., 2012,
4
1, 1862; (d) J. Iijima, E. Ishikawa, Y. Nakamuraa and
H. Naruke, Inorg. Chim. Acta, 2010, 363, 1500; (e) Y. Wang,
L. M. Wang, Z. F. Li, Y. Y. Hu, G. H. Li, L. N. Xiao,
T. G. Wang, D. F. Zheng, X. B. Cui and J. Q. Xu,
CrystEngComm, 2013, 15, 285.
Acknowledgements
The authors thank the National Natural Science Foundation
of China (21371027, 20901013) and Fundamental Research
Funds for the Central Universities (DUT12LK01) for financial
supports.
11 (a) I. Katsuki, Y. Motoda, Y. Sunatsuki, N. Matsumoto,
T. Nakashima and M. Kojima, J. Am. Chem. Soc., 2002, 124,
This journal is © The Royal Society of Chemistry 2014
CrystEngComm

View Article Online
Paper
CrystEngComm
6
29; (b) C. P. Brock, W. B. Schweizer and J. D. Dunitz, J. Am.
20 S. G. Mitchell, T. Boyd, H. N. Miras, D. L. Long and
L. Cronin, Inorg. Chem., 2011, 50, 136.
Chem. Soc., 1991, 113, 9811; (c) Y. Ma, Z. B. Han, Y. K. He
and L. G. Yang, Chem. Commun., 2007(40), 4107.
2 Y. Hou, X. K. Fang and C. L. Hill, Chem. – Eur. J., 2007, 13,
21 R. Dessapt, D. Kervern, M. Bujoli-Doeuff, P. Deniard,
M. Evain and S. Jobic, Inorg. Chem., 2010, 49, 11309.
22 (a) G. A. Tsigdinos, Ph.D. Thesis, Boston University, 1961; (b)
A. L. Nolan, R. C. Burns and G. A. Lawrance, J. Chem. Soc.,
Dalton Trans., 1996, 2629; (c) U. Lee and H. C. Joo, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2010, 66, i10.
23 (a) G. M. Sheldrick, SHELXL 97, Program for Crystal Structure
Refinement, University of Göttingen, Germany, 1997; (b)
G. M. Sheldrick, SHELXL 97, Program for Crystal Structure
Solution, University of Göttingen, Germany, 1997.
24 J. Moreau, O. Delpoux, E. Devers, M. Digne and S. Loridant,
J. Phys. Chem. A, 2012, 116, 263.
1
1
9
442.
3 (a) J. Zhang, J. Hao, Y. G. Wei, F. P. Xiao, P. C. Yin and
L. S. Wang, J. Am. Chem. Soc., 2010, 132, 14; (b) F. P. Xiao,
J. Hao, J. Zhang, C. L. Lv, P. C. Yin, L. S. Wang and
Y. G. Wei, J. Am. Chem. Soc., 2010, 132, 5956.
4 (a) H. Q. Tan, Y. G. Li, W. L. Chen, D. Liu, Z. M. Su, Y. Lu
and E. B. Wang, Chem. – Eur. J., 2009, 15, 10940; (b)
H. Q. Tan, Y. G. Li, W. L. Chen, A. X. Yan, D. Liu and
E. B. Wang, Cryst. Growth Des., 2012, 12, 1111.
1
1
5 H. T. Evans and J. S. Showell, J. Am. Chem. Soc., 1969, 91,
6
881.
25 C. Friedheim and F. Keller, Ber. Dtsch. Chem. Ges., 1906, 39,
4301.
26 I. D. Brown and D. Altermatt, Acta Crystallogr., Sect. B:
Struct. Sci., 1985, 41, 244.
1
6 (a) X. L. Wang, D. Zhao, A. X. Tian and J. Ying,
CrystEngComm, 2013, 15, 4516; (b) H. Y. Liu, H. Wu, J. Yang,
Y. Y. Liu, B. Liu, Y. Y. Liu and J. F. Ma, Cryst. Growth Des.,
2
011, 11, 2920.
27 C. I. Cabello, F. M. Cabrerizo, A. Alvarez and H. J. Thomas,
J. Mol. Catal. A: Chem., 2002, 186, 89.
28 (a) K. Suzuki, M. Sugawa, Y. Kikukawa, K. Kamata,
K. Yamaguchi and N. Mizuno, Inorg. Chem., 2012, 51, 6953;
(b) R. F. D'Vries, M. Iglesias, N. Snejko, E. Gutiérrez-Puebla
and M. A. Monge, Inorg. Chem., 2012, 51, 11349.
29 (a) Q. X. Han, X. P. Sun, J. Li, P. T. Ma and J. Y. Niu, Inorg.
Chem., 2014, 53, 6107; (b) Y. J. Kikukawa, K. Suzuki,
M. Sugawa, T. Hirano, K. Kamata, K. Yamaguchi and
N. Mizuno, Angew. Chem., Int. Ed., 2012, 51, 3686.
30 R. F. D'Vries, V. A. Peña-O'Shea, N. Snejko, M. Iglesias,
E. Gutiérrez-Puebla and M. A. Monge, Cryst. Growth Des.,
2012, 12, 5535.
1
1
1
7 (a) J. Q. Sha, J. Peng, Y. Q. Lan, Z. M. Su, H. J. Pang,
A. X. Tian, P. P. Zhang and M. Zhu, Inorg. Chem., 2008, 47,
5
145; (b) G. G. Gao, C. Y. Song, X. M. Zong, D. F. Chai,
H. Liu, Y. L. Zou, J. X. Liu and Y. F. Qiu, CrystEngComm,
014, 16, 5150.
8 (a) K. Suzuki, M. Shinoe and N. Mizuno, Inorg. Chem., 2012,
1, 11574; (b) F. Yu, X. J. Kong, Y. Y. Zheng, Y. P. Ren,
L. S. Long, R. B. Huang and L. S. Zheng, Dalton Trans., 2009,
503; (c) H. Y. Zhao, J. W. Zhao, B. F. Yang, H. He and
2
5
9
G. Y. Yang, CrystEngComm, 2013, 15, 8186.
9 J. Y. Niu, J. A. Hua, X. Ma and J. P. Wang, CrystEngComm,
2
012, 14, 4060.
CrystEngComm
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