From 1D to 3D single-crystal-to-single-crystal structural transformations based on linear polyanion [Mn4(H2O)18WZnMn 2(H2O)2(ZnW9O34) 2]4-

Article abstract of DOI:10.1021/ic2020572

A 1D anionic polyoxometalate, [Mn₄(H₂O) ₁₈WZnMn₂(H₂O)₂(ZnW₉O ₃₄)₂]^4-, undergoes 1D to 3D single-crystal-to-single-crystal structural transformati

Full text of DOI:10.1021/ic2020572

Communication
pubs.acs.org/IC
From 1D to 3D Single-Crystal-to-Single-Crystal Structural
Transformations Based on Linear Polyanion
[Mn4(H2O)18WZnMn2(H2O)2(ZnW9O34)2]4−
Lian-Xu Shi, Wen-Feng Zhao, Xuan Xu, Jing Tang, and Chuan-De Wu*
Department of Chemistry, Zhejiang University, Hangzhou 310027, People's Republic of China
S
* Supporting Information
1D polyanionic chains based on {Zn3Mn2W19} anions that are
linked by MnII cations.11 Considering that there is no sodium
cation in the crystal lattice of 1 based on elemental analysis and
structural study, we have used hydronium cations to keep the
charge balance. The {Zn3Mn2W19} unit acts as a hexadentate
ligand to coordinate six MnII cations through six terminal
oxygen atoms of six {WO6} octahedra (Figure 1a). According
ABSTRACT: A 1D anionic polyoxometalate,
[Mn4(H2O)18WZnMn2(H2O)2(ZnW9O34)2]4−, undergoes
1D to 3D single-crystal-to-single-crystal structural trans-
formations that are induced by transition-metal cations
(Co2+ and Cu2+) and solvent molecules. These solid
materials present interesting catalytic activity for the
oxidative aromatization of Hantzsch 1,4-dihydropyridines
that is dependent on the inserted heterogeneous metal
cations.
olid materials based on polyoxometalates (POMs) have
S
received considerable contemporary attention because of
their interesting topological architectures and properties and
have potential applications in diverse fields of catalysis,
medicine, and magnetics.1−4 A general method for the
construction of solid POMs is “one-pot” reaction. However,
their compositions and framework structures cannot be
precisely controlled.5 Recently, “step-by-step aggregation”
technology was proven to be a more efficient method for the
synthesis of functional solid POMs.6,7 Particularly, single-
crystal-to-single-crystal (SCSC) structural transformation often
results in interesting materials that cannot be obtained by a
traditional synthesis method.8
Figure 1. (a) Ball-and-stick and polyhedral representations of the
polyoxoanion [Mn4(H2O)18WZnMn2(H2O)2(ZnW9O34)2]4− in 1. (b)
S i d e v i e w o f t h e 1 D p o l y a n i o n i c c h a i n o f
[Mn4(H2O)18WZnMn2(H2O)2(ZnW9O34)2]4− (the terminal MnII
sites are highlighted as superimposed balls). (c) View of the 3D
supramolecular framework of 1 (hydrogen bonds are shown as dotted
lines).
The sandwich-type POMs [WM{M′(H2O)}2(MW9O34)2]12−
(M = Zn2+ and Co2+; M′ = Co2+, Mn2+, and Cu2+, etc.) have a
functional WM′MM′ ring belt between two {B-α-MW9O34}
units.9 We have used them as functional building blocks to
construct a series of solids that present interesting catalytic
properties.10 However, the framework structures of these
compounds are confined as 1D linear networks or discrete
clusters. To further understand the coordination ability of
[WM{M′(H2O)}2(MW9O34)2]12−, we have synthesized a 1D
anionic chain network of [H3O]4[Mn4(H2O)18]-
[WZnMn2(H2O)2(ZnW9O34)2]·18H2O (1) by using [WZn-
{MnII(H2O)}2(ZnW9O34)2]12− ({Zn3Mn2W19}) as building
blocks and MnII ions as connecting nodes. Induced by
heterogeneous transition-metal cations (Co2+ and Cu2+) and
solvent molecules, solid 1 was transformed into two interesting
3D solid frameworks {[M2(H2O)6][Mn4(H2O)16][WZn(Mn-
(H2O))2(ZnW9O34)2]}·10H2O [M = CoII (2) and CuII (3)] in
an SCSC structural transformation fashion.
to the coordination environments, there are two kinds of
octahedrally coordinated MnII cations. The first kind serves as a
connecting node, which coordinates to two terminal oxygen
atoms of two {Zn3Mn2W19} units and four aqua ligands. The
second kind terminates on the {Zn3Mn2W19} unit, and the
octahedral coordination environment is furnished by five water
molecules. The {Zn3Mn2W19} units are linked by MnII cations
to form a 1D linear network (Figure 1b). The polymeric chains
are further held together by extensive hydrogen bonding to
form a 3D supramolecular network (Figure 1c). Thermogravi-
metric analysis (TGA) showed that a weight loss of 12.0%
occurred between 30 and 340 °C, corresponding to the loss of
water molecules (expected 12.8%).
The reaction of {Zn3Mn2W19} and MnCl2·4H2O at 80 °C for
1 day afforded light-brown crystals of 1. Single-crystal X-ray
diffraction (XRD) analysis revealed that compound 1
Received: June 21, 2011
crystallizes in the triclinic P1 space group, which consists of
Published: November 10, 2011
̅
© 2011 American Chemical Society
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Inorganic Chemistry
Communication
The motile anionic chains and substitutable hydronium
cations make it possible to insert heterogeneous transition-
metal cations in the crystal lattice of 1. Because water molecules
can prompt movement of the polymeric chains, a crucial step is
how to extract out the lattice water molecules without
destroying the single crystallinity of 1. When the crystals
were submersed in methanol, compound 1 lost its crystallinity
very quickly. However, compound 1 can retain its crystallinity
for 1 week in a mixed solvent of water and methanol
unit cell volume decreases 14.6% [from 2536.3(1) Å3 for 1 to
2165.5(1) Å3 for 2], and the distance between the terminal
MnII cation and the tungsten atoms of two neighboring chains
decreases from 5.06(1) Å in 1 to 3.77(2) Å in 2. Single-crystal
structural analysis and TGA revealed that eight water molecules
in the formular unit were lost after SCSC structural
transformation. The SCSC framework transformation was
further confirmed by comparing the powder XRD patterns of
compounds 1 and 2.
Catalysts that contain heterogeneous metal cations often
present excellent catalytic activity because of the synergistic
effect.12 Because Hantzsch 1,4-dihydropyridines (DHPs) and
their derivatives are an important class of bioactive
molecules,13,14 we have chosen the oxidative aromatization of
Hantzsch DHPs to evaluate the catalytic activity of compounds
1−3.
When a mixture of diethyl 2,6-dimethyl-1,4-dihydropyridine-
3,5-dicarboxylate (DHP-a) and 30% H2O2 in THF was heated
at 60 °C for 6 h under stirring, the product yield is 40.9%
(Table 1, entry 1). When 1, 2 or 3 was added into the reaction
(VH O:VMeOH = 1:1). On the basis of this finding, we submersed
2
the freshly prepared crystals of 1 in a mixture of cobalt nitrate,
water, and methanol at 50 °C for 3 days. The color of the
resulting crystalline solid of compound 2 changed to red while
monitored by optical microscopy. Under identical reaction
conditions, when cobalt nitrate was replaced by copper(II)
nitrate, a crystalline sample of compound 3 was isolated as
green crystals.
Single-crystal XRD analysis revealed that compounds 2 and 3
are isomorphous and crystallize in the triclinic P1 space
̅
group.11 Herein we only discuss the crystal structure of 2 in
detail. Compared with the crystal structure of 1, the linear
skeleton is retained in 2. The MnII sites were assigned
according to their original positions in compound 1, while the
additional metal sites between the polymeric chains were
assigned to CoII cations in compound 2 (Figure 2). It is
Table 1. Catalytic Oxidation of Dihydropyridines to Pyridine
a
Derivatives
b
entry
substrate
R
catalyst
yield (%)
1
2
3
4
5
6
7
8
DHP-a
DHP-a
DHP-a
DHP-a
DHP-b
DHP-c
DHP-d
DHP-d
H
H
H
H
40.9
65.0
>99.9
43.8
60.7
82.5
86.4
1
2
3
2
2
2
2
CH3
Ph
2-Fury
H
c
97.6
F i g u r e 2 . ( a ) 1 D p o l y a n i o n i c c h a i n o f
[Mn4(H2O)18WZnMn2(H2O)2(ZnW9O34)2]4− in 2. (b) View of the
3D framework structure of 2, showing the linkage between the
polymeric chains (CoII sites are highlighted as superimposed balls, and
water ligands are omitted for clarity). (c) Top view of the lamellar
network in 2.
a
DHP (0.05 mmol), catalyst (10 mol %), and 30% H2O2 (0.2 mmol)
b
c
in THF were stirred at 60 °C for 6 h. Determined by GC. The sixth
cycle.
mixture, the product yield increased (Table 1, entries 2−4). It
is worth noting that DHP-a almost quantitatively transformed
into the aromatized product in the presence of 2 (Table 1,
entry 3). Catalyst 2 also prompted the oxidation of a range of
DHPs for the formation of corresponding pyridine derivatives
with satisfied yields (Table 1, entries 5−7).
After 2 was suspended in THF at 60 °C for 6 h under
stirring, DHP-a and 30% H2O2 were added into the hot filtrate.
After the mixture was heated at 60 °C for another 6 h under
stirring, gas chromatography (GC) analysis showed that the
product yield is identical with that of the background reaction,
which thus demonstrates the heterogeneous catalytic nature of
2. Catalyst 2 can be simply recovered by filtration, which was
reused for the successive run without deterring the catalytic
activity (Table 1, entry 8). The catalytic results of compound 2
are slightly inferior to that of the homogeneous cobalt acetate
in the literature.14 However, a stoichiometric rather than a
catalytic amount of the homogeneous catalyst was used for the
oxidization of Hantzsch DHPs. These results indicate that the
catalytic activity can be fine-tuned by synergizing the
functionalities of multiple metal sites in a POM-based solid.
interesting that one aqua ligand of the second manganese
cation was substituted by a terminal oxygen atom of the
neighboring chain. As a result, the chains are joined together by
the MnII cations to form a lamellar network. The inserted CoII
cation coordinates to three oxygen atoms of three chains and
three aqua ligands in a distorted octahedral geometry, which
further links up the lamellar networks to form the 3D solid
framework of 2.
Elemental analysis has revealed that there is only a trace of
MnII cations (0.37%) in the plasma after SCSC transformation
from 1 to 2, which should be from the surface MnII cations that
are replaced by abundant ambient CoII cations.9,10b We
speculate that the transformation from 1 to 2 should be a
synergistic movement of the polymeric chains and MnII cations,
while the transportation of CoII cations is controlled by
diffusive equilibrium. The movement of the polymeric chain is
evident from the reduction of the distance between the
neighboring chains [from 12.614(1) to 11.889(1) Å along the a
axis and from 13.939(1) to 12.271(1) Å along the b axis]. The
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Inorganic Chemistry
Communication
(7) (a) Yang, H.; Gao, S.; Lu, J.; Xu, B.; Lin, J.; Cao, R. Inorg. Chem.
̈
In summary, we have constructed a POM-based solid by
using {Mn2Zn3W19} as a building block and MnII cation as a
connecting node. Compound 1 undergoes interesting 1D to 3D
SCSC structural transformations that are induced by
heterogeneous metal cations and solvent molecules. The
gradual loss of water molecules in the crystal lattice plays a
very important role for SCSC structural transformations. This
work should provide a new pathway for the synthesis of high-
dimensional solid POMs with modulated functionality for
potential applications.
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ASSOCIATED CONTENT
* Supporting Information
■
S
́ ́
(9) (a) Tourne, C. M.; Tourne, G. F.; Zonnevijlle, F. Dalton Trans.
Experimental procedures, additional figures, a table, and
crystallographic data in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org.
1991, 143. (b) Hill, C. L.; Weinstock, I. A. Nature 1997, 388, 332.
(c) Neumann, R.; Dahan, M. Nature 1997, 388, 353. (d) Ben-Daniel,
R.; Weiner, L.; Neumann, R. J. Am. Chem. Soc. 2002, 124, 8788.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: cdwu@zju.edu.cn.
■
(11) Crystal data for 1: H88Mn6O110W19Zn3, M = 5867.60, triclinic, a
= 12.6138(4) Å, b = 13.9393(4) Å, c = 16.8356(5) Å, α = 82.597(2)°,
β = 73.703(3)°, γ = 63.213(3)°, V = 2536.32(13) Å3, space group P1,
̅
ACKNOWLEDGMENTS
Z = 1, μ = 22.975 mm−1, R1 = 0.0896, wR2(F2) = 0.2254, and S =
1.338. Crystal data for 2: H68Co2Mn6O102W19Zn3, M = 5837.30,
triclinic, a = 11.8890(11) Å, b = 12.2712(8) Å, c = 16.2733(14) Å, α =
77.537(7)°, β = 87.576(7)°, γ = 69.196(7)°, V = 2165.5(3) Å3, space
■
This work was financially supported by the NNSF of China
(Grant 21073158), the Zhejiang Provincial Natural Science
Foundation of China (Grant Z4100038), and the Fundamental
Research Funds for the Central Universities (Grant
2010QNA3013).
group P1, Z = 1, μ = 57.031 mm−1, R1 = 0.0673, wR2(F2) = 0.1643,
̅
and S = 1.025. Crystal data for 3: H68Cu2Mn6O102W19Zn3, M =
5846.52, triclinic, a = 11.9163(14) Å, b = 12.2608(12) Å, c =
16.2768(15) Å, α = 77.604(8)°, β = 87.472(8)°, γ = 69.13(1)°, V =
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