1D- and 2D-architectures via self-assembly of the novel sandwich-type polyoxometalate [Zn2Sb2(B-α-ZnW9O 34)2]14-

Article abstract of DOI:10.1039/c2ce25319d

Two novel 1D and 2D polyoxometalate (POM) frameworks based on the new [Zn₂Sb₂(B-α-ZnW₉O₃₄) ₂]^14- building block were selectively obtained from one-pot transformations of the trilacunary Keg

Full text of DOI:10.1039/c2ce25319d

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PAPER
1
D- and 2D-architectures via self-assembly of the novel sandwich-type
142
polyoxometalate [Zn Sb (B-a-ZnW O ) ] {
2
2
9 34 2
Lubin Ni and Greta R. Patzke*
Received 5th March 2012, Accepted 29th June 2012
DOI: 10.1039/c2ce25319d
142
2 2 9 34 2
Two novel 1D and 2D polyoxometalate (POM) frameworks based on the new [Zn Sb (B-a-ZnW O ) ]
building block were selectively obtained from one-pot transformations of the trilacunary
92
Keggin-type [B-a-SbW
9
O
33
]
precursor via Sb/Zn exchange, followed by self-assembly of the
sandwich-type polyanions. The compounds were characterized in detail with a wide range of
analytical methods, including single crystal and powder X-ray diffraction, thermogravimetric
analysis and various spectroscopic techniques, and their photoluminescence properties were
investigated at room temperature. Electrochemical behavior of the 1D and 2D {Zn Sb }-based
2
2
POMs was characterized by means of cyclic voltammetry (CV) in sodium acetate buffer solution.
Both compounds are effective catalysts for the oxidation of cyclohexanol with hydrogen peroxide.
9 10
alcohol oxidation, oxidative aromatization or cyclization of
Introduction
1
1
acetylacetone.
Polyoxometalates (POMs) are oxoclusters of early transition
metal oxides (preferably Mo, W, V and Nb) covering an
inexhaustible range of structural motifs with manifold catalytic,
New structural motifs of Zn-POMs are in the focus of ongoing
research activities, as illustrated by the development of the Keggin-type
82
POM [{Zn(OH )(m
2
3
-OH)} {Zn(OH
2
2
)
2
}
2
{c-HSiW10
O
36
}
2
]
as a
1
bioactive, magnetic and other important properties. As POMs
12
powerful catalyst for alcohol oxidation, as well as by new hexa-
cross the border between molecular architectures and the
13
sandwiched Zn-POMs or compounds with [{Zn W(O)O } ]
4+
2
3 2
nanoscale, they are essential building blocks for composites
2
and other functional materials. However, exerting full control
14
hexaprismane
cores.
Furthermore,
[WZn{Co(H O)}
2 2
122
(
ZnW
9 34 2
O ) ]
with 1D polymeric chains has been found to
15
over all stages of POM synthesis, from 0D molecular structures
3
to 3D hierarchical arrangements, remains a key challenge. We
catalyze the selective oxidation of styrene to benzaldehyde.
142
The [M
2
(H
2
O)
2
Bi
2
(b-B-MW
9
O
34
)
2
]
(M = Co, Zn) POMs
thus present a multiscale approach towards new zinc-containing
polytungstoantimonates, proceeding from 0D POM building
blocks over 1D polymeric chains to higher dimensional net-
works.
are further new examples, but their catalytic and isomerization
16
properties remain to be investigated. To the best of our
knowledge, Zn/Sb-combinations have rarely been reported for
n2
the [MW9-11
The novel
Zn Sb (B-a-ZnW
emerged from our research as the first combination of the key
O
33-39
]
lacunary POM family.
polyoxotungstoantimonate
Sb }, has most recently
Sandwich-type transition-metal-substituted POMs (TMSPs)
are a large compound class of current research interest, e.g. as
zinc-containing
142
[
2
2
9
O
34
)
2
]
,
{Zn
2
2
4
,5
versatile catalysts for water oxidation or organic processes.
n2
Generally, their lacunary [MW9-11O33-39
]
(M = main group
4
element) building blocks are a rich source for new materials.
3+
17
{
ZnW O }-building block with Sb cations. Focusing on the
9 34
,6,8
molecular properties, we investigated the synthetic conditions for
the formation of a- and b-{Zn Sb } isomers, respectively,
However, considerably less of them contain central transition
2
2
7
metal heteroatoms (M = Fe, Co, Ni, Cu, Mn, Zn). Zn-substituted
n2
17
together with catalytic and theoretical studies. In the following,
we proceed from this 0D tuning level, i.e. the creation of new
POM motifs, to an investigation into the 1D and 2D self-
assembly properties of the lacunary {Zn Sb } moiety.
representatives, e.g. sandwich-type [WZnM (ZnW
2
9
O
34
)
2
]
(M =
8
Zn, Mn, Ru, Pd, Pt, Rh) compounds, display outstanding
catalytic activity in key organic transformations, such as ‘‘green’’
2
2
The tremendous influence of countercations on POM assem-
blies remains challenging to control, because the wide range of
cation-related effects renders the selective use of countercations
for POM design difficult to apply. Countercations direct the
primary POM cluster type, they steer their packing motifs and
the linkage of POM nodes, and they finally assist the formation
Institute of Inorganic Chemistry, University of Zurich, Winterthurerstrasse
1
90, CH-8057 Zurich, Switzerland. E-mail: greta.patzke@aci.uzh.ch;
Fax: +41 44 635 68 02; Tel: +41 44 635 46 91
Electronic supplementary information (ESI) available: Crystallographic,
{
bond valence data, crystal structure representations, UV-vis/FT-IR/
Raman and PL spectra, PXRD patterns, thermogravimetric curves and
cyclic voltammograms of (1) and (2). For ESI see DOI: 10.1039/
c2ce25319d
1
8
of large ‘‘blackberry’’ POM aggregates. From the application-
oriented point of view, all-inorganic POM catalysts are favorable
6
778 | CrystEngComm, 2012, 14, 6778–6782
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4
with respect to stability and recyclability so that exploring the
(GCE, modified or unmodified), a saturated Ag/AgCl reference
electrode and a Pt wire as the counter electrode.
structure-directing potential of inorganic additives is crucial for
19
informed POM production. Therefore, we pursued an ‘‘all-in-
2+
one’’ approach using Zn
as an attractive, low-cost and
Synthesis of (NH ) [Zn(H O) ](H O) {[Zn (H O) ][Zn Sb
2
4
5
2
6
3
3
2
2
8
2
environmentally friendly control agent for the 0D to 2D modifica-
(B-a-ZnW O ) ]}?20H O (1)
9
34 2
2
92
20
tion of the flexible lacunary [B-a-SbW
Two novel polymeric Zn/Sb-polytungstoantimonates (NH
2
Zn(H O) ](H O) {[Zn (H O) ][Zn Sb (B-a-ZnW ]}?20H O
9 33
O ]
precursor.
0
.377 g (0.150 mmol) of Na
in 25 mL of water and heated to 85 uC under stirring. After 20
min, 0.098 g (0.450 mmol) of Zn(OAc) ?6H O was added in
9 9 2
[SbW O33]?19.5H O was dissolved
4 5
)
[
2
6
3
3
2
2
8
2
2
9
O
34
)
2
2
1
2
2
(
1) and (NH ) [Zn(H O) ] {[Na Zn (H O) ][Zn Sb (B-a-ZnW O ) ]}?
9 34 2
4
2
2
2
6 2
2
3
2
19
2
2
2
individual portions. The solution underwent a color change from
colorless to light yellow. The mixture was left stirring for 90 min
at 85 uC, followed by cooling to room temperature and filtration.
In a second step, an additional amount of 0.033 g (0.150 mmol)
1
4H
2
O (2) were selectively obtained from the trilacunary
[B-a-SbW 33]?19.5H O {SbW } in the presence
precursor Na
9
9
O
2
9
2
+
of zinc acetate by switching the initial Zn concentration (Fig. 1).
Yellow crystals of (2) were formed in the presence of excess
Zn(OAc)
addition of 1.0 M NH
4
2
?6H
2
O was added under stirring for 0.5 h, followed by
2
Zn(OAc) , whereas light yellow crystals of (1) were isolated with
2
+
Cl solution (0.25 mL) to the yellow
9
lower Zn concentrations. Interestingly, the {SbW } precursor is
1
22
filtrate. Slow evaporation of the solution afforded yellow cry-
stals after approx. 10 d. Yield: 0.168 g, 38% based on W. TGA
showed a weight loss of 11.6% in the 30–210 uC temperature
range, corresponding to the loss of coordinating and solvent
transformed into trivacant Keggin [B-a-ZnW O ]
9 34
{ZnW } in
9
aqueous solution through heating at 85 uC and the addition of zinc
cations (Fig. 1).
2
1
water molecules (expected 11.4%). FT-IR (cm ): 1620(m),
411(s), 932(vs), 854(vs), 837(s), 707(s), 675(m), 432(m).
Experimental
1
2
1
Raman (cm ): 1035 (vs), 993(vs), 872(s). Elemental analysis
calcd. (found): W 56.49 (54.90); Zn 7.81 (8.55); Sb 4.16 (4.05); N
Materials and methods
9 9 2
Na [B-a-SbW O33]?19.5H O as precursor material was prepared
1
.20 (1.13); H 1.67 (1.55).
2
3
according to the literature and its purity was confirmed with
FT-IR spectra. Other chemicals were commercially purchased
and used without further purification. Elemental analyses were
performed by Mikroanalytisches Labor Pascher, Remagen,
Germany. Fourier transform infrared (FT-IR) spectra were
recorded on a Perkin-Elmer BXII spectrometer with KBr pellets.
Raman spectroscopy was performed on a Renishaw Ramascope
Synthesis of (NH
4
)
2
[Zn(H
2 6 2 2 3 2 2 2
O) ] {[Na Zn (H O)19][Zn Sb
(
B-a-ZnW ]}?14H
9
O
34
)
2
2
O (2)
The above synthetic procedure was modified for the synthesis of
(2) as follows: an increased amount of Zn(OAc) ?6H O, i.e. 0.053
2
2
g (0.242 mmol) instead of 0.033 g (0.150 mmol) was added in
the second step. Yield: 0.195 g, 42% based on W. TGA displayed
a weight loss of 13.1% in the 30–160 uC temperature range,
corresponding to the loss of coordinating and solvent water
1
5
000 with a green SpectraPhysics Argon laser (wavelength of
24.5 nm and 50 mW capacity). TG measurements were
performed on a Netzsch STA 449 C between 25 and 800 uC
2
1
21
with a heating rate of 5 K min in nitrogen atmosphere. UV/vis
spectra were recorded on a Perkin-Elmer Lambda 650S spectro-
meter and photoluminescence measurements on a Perkin-Elmer
LS 50B Spectrometer, respectively. Cyclic voltammetry experi-
molecules (expected 13.2%). FT-IR (cm ): 1623(m), 1419(s),
2
1
910(vs), 833(vs), 703(s), 671(m), 415(m). Raman (cm ): 1035
(vs), 991(vs), 869(s). Elemental analysis calcd. (found): W 54.05
(52.90); Zn 9.61 (9.81); Sb 3.97 (4.09); Na 0.75 (1.29); N 0.45
(0.40); H 1.61 (1.50).
ments were performed using
a
Metrohm Computrace
Voltammetric Analyzer model 757 VA operated with 757 VA
Computrace software (Metrohm). The three-electrode cell
system consisted of a 2 mm glassy carbon working electrode
X-ray crystallography
Data collections of compounds (1) and (2) were performed on an
Oxford Xcalibur Ruby CCD single-crystal diffractometer (MoK
˚
radiation, l = 0.71073 A) at 183(2) K. Routine Lorentz and
a
polarization corrections were applied, and an absorption correc-
2
4
tion was performed using the program CrysAlis (multi-scan).
Structural analysis was performed using Win-GX for Windows
2
software. Direct methods were used to locate heavy metal atoms
5
(
SHELXS-97) and the remaining atoms were located from
2
6
successive Fourier maps (SHELXL-97). Further details on the
crystal structure data can be obtained from ICSD/FIZ Karlsruhe
via www.fiz-karlsruhe.de/icsd.html (fax (+49) 7247-808-666;
e-mail: crysdata@fiz-karlsruhe.de), on quoting the depository
numbers CSD 424140 and 424141 for compounds (1) and (2),
respectively. Hydrogen atoms were not included in the
refinements and heavy metal atoms (Sb, Zn, and W, Na) were
refined anisotropically. Oxygen atoms were refined isotropically,
because anisotropic refinement of light atoms in POMs is
1
42
Fig. 1 Formation of the [Zn
9
2
Sb
2
(B-a-ZnW
9
O
34
)
2
]
building block
2
2+
precursor and subsequent Zn -assisted trans-
9 33
from [B-a-SbW O ]
2
7
formation into nodes for 1D and 2D architectures.
often difficult in the presence of manifold heavy metal atoms.
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A summary of crystallographic data and structure refinements for
1) and (2) is given in Table S1, and selected bond lengths are
(
summarized in Table S2.{
Catalytic experiments
Oxidation reactions were carried out in a 10 mL round-bottom
2 2
flask. Catalyst, solvent, substrate, and 30% aqueous H O were
successively placed into a round-bottom flask. A Teflon-coated
magnetic stirring bar was added and the reaction mixture was stirred
at 85 uC. Reaction conditions: 0.25 mmol substrate, 1.25 mmol
Fig. 2 Polyhedral/ball-and-stick
102
{[Zn (H O) ][Zn Sb (ZnW O ) ]}
representations
of
(a)
2
2
8
2
2
9
34 2
polyanion in (1); (b) structure of
(
30%) H O , 1.0 mmol catalyst, 0.50 mL H O, 85 uC, 7 h. All yields
the 1D polymeric connection in (1); (c) schematic arrangement of 1D
2
2
2
142
reported in this manuscript are based on alcohol conversion.
Reaction products were characterized and quantified with a gas
chromatograph (Finnigan Trace GC Ultra) equipped with a flame
ionization detector and fitted with a ZB-5MS Phenomenex column
ladder-like chain along the c axis ([Zn
2
Sb
Zn linkers = blue pillars, symmetry codes: a, 1 2 x, 2y, 2z; b, 2x, 2y,
z; b, 2x, 2y, 2z; c, 1 + x, y, z).
2
(ZnW
9
O
34
)
2
]
= red spheres,
2+
2
The {Zn
sodium cations through ten terminal oxygen atoms of ten
different {WO } octahedra (Fig. 3a). The octahedrally coordi-
2 2
Sb } unit in (2) coordinates six zinc cations and four
(
30 m length, 0.25 mm internal diameter, 0.25 mm film thickness)
using dodecane as internal reference. Products were furthermore
identified by GC-MS (Finnigan Trace DSQ GC-MS systems).
6
2
+
+
nated Zn and Na cations can be further differentiated into
two subsets. Zn8 and Na2 are capping the {Zn Sb } moieties and
2
2
Results and discussion
their coordination environments are completed by five water
molecules. Zn5 and Zn6 are two connecting nodes which
Crystal structures of (1) and (2)
2 2
coordinate two terminal oxygen atoms of two {Zn Sb } units
The compositions of (1) and (2) were determined from the
combination of X-ray crystallography data with various addi-
tional analytical techniques (Table S1 and ESI{). Single-crystal
X-ray diffraction of compounds (1) and (2) shows that they dis-
play different triclinic arrangements of the novel sandwich-type
via Zn–O–W bonds (Zn5–O38–W13, Zn6–O55–W10, Zn5–
O59a–W4a, Zn6–O54a–W2a, symmetry code: a, 2x, 2y, 2 2
˚
z; Zn–O distances: 2.051(9)–2.143(9) A) together with four aqua
ligands, whereas the Na1 cation is attached to three {Zn Sb
2
2
}
clusters through W12, W3 and W6b (2x, 1 2 y, 1 2 z) via m-oxo
bridges as a 3-connecting node.
1
42
[
Zn Sb (B-a-ZnW O ) ]
34 2
{Zn Sb } polyanion which is linked
2 2
2
2
+
9
2
by Zn cations either into 1D polymeric chains in (1) or into 2D
This leads to a 2D sheet-like polymeric network of {Zn Sb }
2
2
polymeric layers in (2), respectively. The {Zn Sb } moiety contains
2
2
clusters in (2) which is maintained by zinc and sodium cations
Fig. 3b). The topology of this network can be described
as follows: the {Zn Sb } clusters represent 4, 6-connecting
2
+
a belt of two Zn and two Sb cations which link the trivacant
3+
(
Keggin-type {ZnW } fragments in a sandwich-type fashion. The
9
2
2
Zn1 and Zn1a atoms of this metal belt display distorted octahedral
coordination by oxygen atoms, while the two central Sb atoms
exhibit distorted square-pyramidal coordinations. Furthermore,
the Zn2 and Zn2a heteroatoms are located on tetrahedral sites in
nodes, Na1 atoms are 3-connecting nodes and Zn5 as well as
Zn6 are bridging connector ligands between two clusters
(
Fig. 3c). Therefore, the Schl a¨ fli symbol for this 3,4,6-
2
2
2
2
2
4
2
connected trinodal network is (3.4.5) (3 .4 .5 .6 .7 .8 .9)
the center of the {ZnW } shells (cf. Figs. S5 and S6{).
2
2
2
3 .6 .7 ). The polymeric layer material (2) furthermore
9
(
The bond valence sum (BVS) values of zinc (1.98–2.17 for (1),
displays a solid state 3D supramolecular network via extensive
hydrogen bonding interactions between the terminal oxygen
atoms of the polyanion and the aqua ligand around Zn8
1
.92–2.14 for (2)), antimony (3.10 for (1), 2.98 for (2)) and
tungsten atoms (5.90–6.03 for (1) and 5.73–6.08 for (2)) are in
line with the oxidation states of +2, +3 and +6 as expected from
2
8
all analytical methods (Tables S3 and S4{).
The {Zn Sb } moiety of (1) furthermore coordinates four
Zn cations (Zn3) via terminal oxygen atoms of four different
WO } octahedra (Fig. 2a). These zinc cations are connecting
nodes between two neighboring {Zn Sb } units via Zn–O–W
bonds (Zn3–O23–W4, Zn3–O13b–W5b, symmetry code: b, 2x,
y, 2z ), and their coordination spheres are completed by four
2
2
2
+
{
6
2
2
2
˚
aqua ligands (Zn–O distances: 2.074(9)–2.134(11) A). As a
consequence, (1) displays a ladder-like 1D network of {Zn Sb
2
2
}
2
+
and Zn linkers (Fig. 2b and 2c). The polymeric chains are
further connected into a 3D supramolecular network via
extensive hydrogen bonding interactions between the terminal
oxygen atom of the polyanion and the aqua ligand around Zn3
Fig. 3 Polyhedral/ball-and-stick
Na Zn (H O)19Zn Sb (ZnW
work; (c) construction principle of 2D layers ([Zn
representations
of
(2):
(a)
…
˚
and Zn4 (O O = 2.667–2.750 A), between the m
-oxygen atom
62
2
…
[
2
3
2
2
2
9
O
34
)
2
]
polyanion; (b) 2D polymeric net-
of the cluster and the aqua ligand of Zn4 (O O = 2.760–
142
2
2 9 34 2
Sb (ZnW O ) ]
˚
.037 A), and between two aqua ligands of Zn3 and Zn4 (O
…
2+
+
3
O
polyanions = red spheres, Zn linkers = blue pillars, Na linkers =
˚
=
2.834–3.049 A; Fig. S7{).
yellow pillars, symmetry codes: a, 2x, 2y, 2 2 z).
6
780 | CrystEngComm, 2012, 14, 6778–6782
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…
˚
2
and Zn5 (O O = 2.686–2.818 A), between the m -oxygen atom
…
of the cluster and the aqua ligand of Zn5, Zn6 (O O = 2.659–
˚
.004 A), and between two aqua ligands of Zn6 and Zn5
3
…
˚
(
O
O = 2.743–2.899 A; Fig. S8{).
Scheme 1 Cyclohexanol oxidation catalyzed by (1) and (2).
compounds with four characteristic emission peaks around 423,
10
Characterization of (1) and (2)
Phase purity of compounds (1) and (2) was confirmed by
comparison of experimental X-ray powder diffraction (PXRD)
patterns with simulated patterns from single-crystal X-ray
diffraction data (Figs. S12 and S13{). FT-IR spectra of
compounds (1) and (2) display the characteristic vibration bands
4
43, 484 and 530 nm. The closed d electronic shell configura-
2+
tion of Zn cations leads to the absence of d–d transitions in the
photoemission spectra. LMCT (ligand-to-metal charge transfer)
processes, however, are based on transitions from ligand p
orbitals to different metal orbitals, i.e. d orbitals, low-lying s
1
0,11
of the {ZnW
9
O
34} unit (Fig. S10).
Absorption bands at
for (1), and at 910(s), 833(vs),
03(vs) for (2) are attributed to the characteristic u(W–O ), u(W–
31
orbitals or empty p orbitals. Therefore, the emission peaks
2
1
9
32(s), 837(vs), 707(vs) cm
around 423 and 443 nm are probably connected to {Zn
13
2
Sb
2
}
7
t
cluster formation and LMCT phenomena.
In line with
O
b
) and u(W–O
tered at 1620 and 1410 cm can be assigned to d(H–O–H) and
d(NH vibrations which confirm the presence of water
c
) frequencies, respectively. Resonances cen-
photoluminescence spectra of other Zn-containing POMs with
30
2
1
related lacunary building blocks, the emission peaks around
3
4
)
1
4
84 nm of (1) and (2) arise from T1uA A1g transitions derived
molecules and ammonium cations as determined from single
from OAW LMCT transitions within the {SbW } fragments.
9
crystal X-ray diffraction. u(W–O ) and u(W–O ) vibrations of (1)
t
b
and (2) are furthermore evident from characteristic Raman
Catalytic oxidation of cyclohexanol
2
1
21
bands at 951 and 881 cm or 938 and 876 cm , respectively
Fig. S11). Both FT-IR and Raman spectra agree with the results
of X-ray structure determination.
1) and (2) undergo similar thermal decomposition pathways
(
Moreover, catalytic studies were explored for homogeneous
oxidation of cyclohexanol into cyclohexanone by (1) and (2) in
the presence of H
The catalytic efficiency of (2) is lower than of (1) (yields: 98% for
1) and 87% for (2), respectively). This may be due to a higher
extent of Na- and Zn-assisted linking among the catalytically
2 2
O at 85 uC for 7 h (Scheme 1, cf. Experimental).
(
as shown by the related shapes of their thermogravimetric (TG)
(
curves (Fig. S14). Concerning (1), a rapid weight loss of 11.6%
(calcd. 11.4%) in the 30–210 uC range corresponds to loss of
lattice water molecules, followed by a slower weight loss between
active {ZnW } units which might shield their active sites. Further
9
investigations on the influence of preparative history and crystal
structure on the catalytic properties of zinc-containing polytung-
stoantimonates are currently under way.
1
30–580 uC, mainly caused by evaporation of ammonia.
Cyclic voltammograms (CVs) of aqueous solutions of (1) and
(
2) are strongly pH-dependent (Figs. S15 and S16{). Upon
higher pH values, the redox signals become weaker and finally
vanish completely due to protonation effects. The quasi-
reversible peak (I-I9) between 20.5 and 21.0 V at pH 4.0
corresponds to redox processes at the W(VI) centers, whilst the
irreversible oxidation peak (II9) around 0.08 V can be assigned to
Conclusions
In summary, two novel Zn/Sb-containing sandwiched polyox-
1
4n2
ometalates [Zn Sb (B-a-ZnW O ) ]
with polymeric struc-
tural motifs were obtained from the one-step reaction of the
2
2
9
34 2 n
3
+ 29
the oxidation of metallic Sb(0) to oxygenic Sb
.
92
2+
lacunary [B-a-SbW
9
O
33
]
precursor with Zn
cations in
UV/vis diffuse reflectance spectra in the range between 190
aqueous solution. The new solution-based transformation of
1
and 700 nm (Fig. S9{) display two absorption bands centered at
22
the {SbW
9
} fragment into a Keggin-type [B-a-ZnW
9
O
34
]
unit
2
65 and 312 nm for (1), and 267 and 370 nm for (2), respectively.
was induced by heating and addition of a zinc source.
Arrangement of the Zn-containing building block into different
polymeric networks, respectively, is steered through adjusting the
Absorption bands at higher energies arise from p –d charge-
p
p
3
0
transfer transitions of the Ob(c)AW bonds, whereas the low
energy bands are likely due to OAZn charge transfer or W–O–
2
+
2+
7b
Zn concentration. Zn cations are used for structure control
on different levels: (a) as internal 0D tools for the transformation
of {SbW } precursor into the new {Zn Sb } polyanion, (b) for
Sb intervalence band transfer in the visible region. The
colorless {SbW } precursor is transformed into the visible light
absorbing compounds (1) and (2) with band gaps of 2.98 and
9
9
2
2
3
+
2+
2 2
linking {Zn Sb } into 1D ladders in (1), and (c) to alternatively
2
{
2
.76 eV, respectively. Assembly of Sb and Zn via sandwiched
Zn Sb } polyanions in combination with a hybridization of O
p orbitals with d or s metal orbitals shifts the valence band
connect {Zn
2
Sb
concentration in solution. Electrochemical and
luminescence properties of (1) and (2) are mainly determined
by the features of the {Zn Sb } building block. Our work opens
2
} nodes into 2D frameworks in (2) by increasing
2
2
2
+
the Zn
position up, thus opening up perspectives for the development of
visible-light-driven POM photocatalysts.
2
2
up new ways to explore and to control assemblies and structural
transformations of TM-POM-based coordination polymers as
tuneable functional materials.
Photoluminescence properties of (1) and (2)
1
Given that the d cations can influence the photoluminescent
0
properties of the different {Zn Sb } cluster arrangements in (1)
2
2
Acknowledgements
and (2), room temperature photoluminescent spectra of both
compounds were recorded (Fig. S17{). Excitation at 325 nm (1)
and 385 nm (2) led to related blue photoluminescence of both
This work was supported by the Swiss National Science
foundation (SNSF Professorship PP00P2_133483/1 and Sinergia
This journal is ß The Royal Society of Chemistry 2012
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3 J.-Y. Niu, X. Ma, J.-W. Zhao, P.-T. Ma, C. Zhang and J.-P. Wang,
CrystEngComm, 2011, 13, 1834.
4 Y. Kikukawa, K. Yamaguchi and N. Mizuno, Inorg. Chem., 2010, 49,
Grant No. CRSII2_136205/1) and by the University of Zurich. L.
N. thanks the Chinese Scholarship Council for a PhD fellowship.
8
194.
5 J. Tang, X.-L. Yang, X.-W. Zhang, M. Wang and C.-D. Wu, Dalton
Trans., 2010, 39, 3396.
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782 | CrystEngComm, 2012, 14, 6778–6782
This journal is ß The Royal Society of Chemistry 2012