Spontaneous stepwise self-assembly of a polyoxometalate-organic hybrid into catalytically active one-dimensional anisotropic structures

Article abstract of DOI:10.1002/chem.201402974

An inorganic-organic hybrid surfactant with a hexavanadate cluster as the polar head group was designed and observed to assemble into micelle structures, which further spontaneously coagulate into a 1D anisotropic structure in aqueous solutions. Such a hierarchical self-assembly process is driven by the cooperation of varied noncovalent interactions, including hydrophobic, electrostatic, and hydrogen-bonding interactions. The hydrophobic interaction drives the quick formation of the micelle structure; electrostatic interactions involving counterions leads to the further coagulation of the micelles into larger assemblies. This process is similar to the crystallization process, but the specific counterions and the directional hydrogen bonding lead to the 1D growth of the final assemblies. Since most of the hexavanadates are exposed to the surface, the 1D assembly with nanoscale thickness is a highly efficient heterogeneous catalyst for the oxidation of organic sulfides with appreciable recyclability. Surfing hybrids: Inorganic-organic hybrid surfactant with hexavanadate as the polar head group was programmed to assemble into a 1D structure with the cooperation of hydrophobic, electrostatic, and hydrogen-bonding interactions (see figure); these last interactions are directional and lead to the anisotropic assemblies. The nanobelts were highly efficient heterogeneous catalysts for oxidation of organic sulfides because most of the hexavanadates are exposed onto the surface.

Full text of DOI:10.1002/chem.201402974

DOI: 10.1002/chem.201402974
Full Paper
&
Organic–Inorganic Hybrids
Spontaneous Stepwise Self-Assembly of a Polyoxometalate–
Organic Hybrid into Catalytically Active One-Dimensional
Anisotropic Structures
[a, b]
[c]
[b]
[a, b]
[a]
[b]
Panchao Yin,
Aruuhan Bayaguud, Peng Cheng, Fadi Haso,
Lang Hu, Joy Wang,
[b]
[d]
[c]
[d]
[c]
Dmitri Vezenov, Randall E. Winans, Jian Hao, Tao Li,* Yongge Wei,* and
[a, b]
Tianbo Liu*
Abstract: An inorganic–organic hybrid surfactant with
a hexavanadate cluster as the polar head group was de-
signed and observed to assemble into micelle structures,
which further spontaneously coagulate into a 1D anisotropic
structure in aqueous solutions. Such a hierarchical self-as-
sembly process is driven by the cooperation of varied non-
covalent interactions, including hydrophobic, electrostatic,
and hydrogen-bonding interactions. The hydrophobic inter-
action drives the quick formation of the micelle structure;
electrostatic interactions involving counterions leads to the
further coagulation of the micelles into larger assemblies.
This process is similar to the crystallization process, but the
specific counterions and the directional hydrogen bonding
lead to the 1D growth of the final assemblies. Since most of
the hexavanadates are exposed to the surface, the 1D as-
sembly with nanoscale thickness is a highly efficient hetero-
geneous catalyst for the oxidation of organic sulfides with
appreciable recyclability.
Introduction
drogen bonding, hydrophobic interactions, and aromatic stack-
ing interactions, in one self-assembly process is challenging,
but critical for the design of the building units and program-
The self-assembly of molecules, nanoparticles, and colloids into
well-defined micro- and macrostructures represents one of the
key bottom-up protocols in building up artificial devices and
[3]
ming the self-assembly process. The emergence of multifunc-
tional building units and the need of assemblies with compli-
cated structures has prompted researchers to focus on the ra-
tional design of the noncovalent interactions to work coopera-
[
1]
basic functional units of virus and cell. The self-assembly
strategies give us the ability to meet the requirements of both
morphology and functionality in materials design across multi-
ple-length scales, while starting from relatively simple building
[3b,c]
tively in the self-assembly process.
A detailed study of the
self-assembly mechanism (e.g., kinetics and intermediate state)
resulting from the cooperative work of various noncovalent in-
teractions is instructive for establishing the design rules for
[
1c,2]
units.
Despite the great achievements scientists have been
making in supramolecular chemistry and materials science,
a thorough understanding of the comprehensive roles of non-
covalent interactions, including electrostatic interactions, hy-
[4]
synthesizing starting units of functional assemblies.
Polyoxometalates (POMs) are a large group of nanoscopic
metal oxide clusters with well-defined molecular structures
and wide applications in catalytic, photoelectronic, and mag-
[
a] Dr. P. Yin, F. Haso, L. Hu, Prof. Dr. T. Liu
Department of Polymer Science, The University of Akron
Akron, Ohio 44325-3909 (USA)
[5]
netic materials; medicine; and nanoscale building scaffolds.
Many POMs are highly negatively charged and their surfaces
are abundant in oxo, hydroxo, or bound water ligands, provid-
ing opportunities for intermolecular electrostatic and hydro-
Phone: (+1)3309723496
E-mail: tliu@uakron.edu
[6]
[b] Dr. P. Yin, P. Cheng, F. Haso, J. Wang, Prof. Dr. D. Vezenov, Prof. Dr. T. Liu
gen-bonding interactions. Meanwhile, covalently grafting or-
ganic functional groups onto POM surfaces has been devel-
oped rapidly in recent years as the obtained novel amphiphilic
inorganic–organic hybrid materials can expand the compatibili-
Department of Chemistry, Lehigh University
Bethlehem, Pennsylvania 18015 (USA)
[
c] A. Bayaguud, Dr. J. Hao, Prof. Dr. Y. Wei
Department of Chemistry, Tsinghua University
Beijing 100084 (P. R. China)
[7]
ty of hydrophilic POMs in organic media. On the other hand,
the processing of the POMs into nanoscaled materials could
enhance their heterogeneous catalytic activity and build multi-
E-mail: yonggewei@mail.tsinghua.edu.cn
[d] Dr. R. E. Winans, Dr. T. Li
X-ray Science Division, Advanced Photon Source
Argonne National Laboratory, Argonne, Illinois 60439 (USA)
E-mail: taoli@aps.anl.gov
[8]
responsive and/or bio/photoelectronic-active devices. Herein,
we report the unique spontaneous self-assembly process of
long-alkyl-chain-functionalized POM hybrid molecules into
a 1D nanobelt structure, cooperatively driven by hydrophobic,
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201402974.
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hydrogen-bonding, and electrostatic interactions, with the di-
rectional hydrogen bonding playing a key role for the aniso-
tropic features of the assemblies. Suggested by time-resolved
small-angle X-ray scattering (SAXS) and TEM studies on their
aqueous solutions, the hybrid molecules quickly assemble into
micelle structures, followed by a slowly coagulation process of
the micelles into nanobelt structures. Moreover, due to its
nanoscale thickness (ca. 20 nm), the resulting 1D assembly
structure has an extremely high surface area, demonstrating its
potential application as highly efficient heterogeneous catalyst
in oxidation desulfurization reactions.
Results and Discussion
Molecular structure of the hybrid surfactant
The molecular structure of the hybrid anion [V O -
6
13
2À
2À
(
OCH ) CNH (OCH ) CNHCH C H COOC H ] (1 ) is a typical
2 3 2 2 3 2 6 4 16 33
single-tailed surfactant with the hexavanadate cluster as the
[9]
polar head group (Figure 1a and Supporting Information).
The surfactant was synthesized through the so-called post-
functionalization protocol by a reaction of a hexavanadate unit
containing amino groups with a chloro-functionalized alkyl tail
in stoichiometric ratio (see Experimental Section and Support-
[
7c]
ing Information). The large super-octahedron-shaped hexa-
vanadate polar head group is about 0.8 nm in size with
[
9]
a charge of À2. Its surface is composed of terminal oxo (V=
O ) and m -bridge oxo ligands (V-O -V), providing multiple hy-
t
2
b
drogen-bond-acceptor positions. Two amine groups are incor-
porated into the organic fragments of 1, providing potential
hydrogen-bond donors. Single-crystal X-ray diffraction analysis
of TBA ·1 (TBA, tetrabutyl ammonium) indicates that the
2
hybrid molecule links to each of two neighboring clusters with
double NÀH···O hydrogen bonds to form 1D chain structures
+
(
Figure 1a). Mediated by the bulky TBA ions, the chains of
hexavanadate clusters are aligned and packed into the (001)
lattice plane (Figure 1b). The zig-zag-shaped long alkyl chains
of the hybrids pack together to fill the space between the lat-
tice planes (Figure 1c).
Figure 1. a) Hydrogen bonding between hexavanadate head groups of the
hybrid molecules; atom code: light grey sphere, C; small dark sphere, H;
dark sphere, O; large octant sphere, V; small octant sphere, N. b) Packing of
+
hybrid molecules and their counterions, TBA in lattice plane (001). c) Pack-
Formation and characterization of the 1D anisotropic assem-
blies
ing of (001) plane through alkyl chain interaction. Color code: grey sphereT-
+
BA ; grey octahedron, VO
6
.
As a typical preparation procedure for the nanostructures, H ·1
2
2
À
À1
(
1
with protons as counterions, 2.5 mgmL ) was dissolved
(Figure S1 in Supporting Information). One-dimensional aggre-
gates with 100–300 mm in length dispersed in the solution
were easily observed under optical microscope (Figure 2a).
SEM and TEM results suggest that these aggregates are uni-
form 1D nanobelts with thickness and width at nanometer
scale, while their lengths are at micrometer scale (Figure 2b
and c). Atomic force microscopy (AFM) results confirm the belt
shape of the aggregates in solution and are able to accurately
determine the thickness of the nanobelts as about 20 nm (Fig-
ure 2d, e, and f). High-resolution TEM studies reveal the lay-
ered structures and the pattern packed by the polar head
groups of surfactants on the nanobelt surface, suggesting
a typical multilayer model (Figure 3 and 4b). There is no evi-
in aqueous KOH solution (pH ~13.3) without any external stim-
ulus. Complex H ·1 was obtained by replacing the TBA ions
of TBA ·1 with protons through a biphasic ion exchange tech-
nology (see Experimental Section and Supporting Information).
+
2
2
Complex H ·1 can be temporarily dissolved in aqueous KOH
solution, driven by the acid–base reaction that increases the
effective charge on the hexavanadates. The freshly obtained
2
KOH solution of H ·1 is clear and does not contain large assem-
blies right after the preparation, suggested by its low scattered
2
intensity at 908 from static light scattering (SLS) studies (ca.
00 kcps; scattered intensity for benzene, 113 kcps). However,
1
the solution became cloudy several hours after the preparation
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ty of hybrid surfactant during the above preparation
process of nanobelt structures, ruling out the possi-
bility that the decomposition of the hybrid surfactant
leads to the formation of nanobelts (see Supporting
Information). The above crystal structural analysis
+
suggests that the bulky TBA ions strongly mediate
the interlayer attraction, which is responsible for the
obtaining of millimeter-scale needle-like single crys-
+
tals of TBA ·1. However, K does not favor the
2
growth of the assemblies along the z-direction,
which therefore contributes to the nanoscaled thick-
ness of the nanobelt structures of H ·1 in aqueous
2
KOH solutions.
SAXS and TEM studies on the sequence of self-as-
sembly of H ·1 in KOH solution
2
Time-resolved SAXS and TEM studies indicate that,
after the dissolution in KOH aqueous solution, the
hybrid molecules firstly self-assemble into micelles,
which further coagulate into nanobelt structures.
SAXS measurements of the freshly prepared H ·1 so-
2
lution with KOH (pH ~13.3) show a typical curve of
core–shell structures with a total radius, core radius,
and shell thickness of 4.2, 2.5, and 1.7 nm, respective-
[10]
ly (Figure 4a). The core–shell structure is consistent
with the model of flower-like micelles formed by the
hybrids, which is confirmed by the TEM studies of
freshly prepared H ·1 solution (Figure 5a). The SAXS
2
curve of the solution containing the assembled struc-
À1
tures shows a sharp peak at q=0.202 ꢁ (d=2p/q=
3.11 nm), possibly corresponding to the interlayer dis-
tance of the lamellar packing of the hybrids (the
[
11]
Figure 2. a) Optical microscopy images of the aggregates in mother liquor. b) SEM image
of 1D anisotropic atructures (scale bar, 5 mm). c) TEM image of assembly structures. d)
and e) AFM images of 1D anisotropic structures obtained under liquid. f) Height profile
across the nanobelt taken along the selected line in d).
length of single hybrid is 3.30 nm) (Figure 4b).
Time-resolved SAXS studies on the freshly prepared
solution indicate that this sharp peak appeared and
grew with time, while at the same time the charac-
teristic oscillation curve for the micelles became
dent morphological change of the nanobelts in their mother
liquors for at least two weeks according to the SEM studies,
confirming their thermodynamic stability as the final assem-
blies (Figure S2 in Supporting Information). Additionally, FT-IR
weaker and completely disappeared after 680 min (Figure 4c).
Detailed SAXS kinetic study data is summarized in Figure 4d
À1
by plotting the intensity of the sharp peak (q=0.202 ꢁ ) due
to the nanobelt and the intensity of micelle curve versus time.
Both plots show typical sigmoidal shape, suggesting a slow ini-
tial coagulation of micelle structures at the beginning of the
1
and H NMR measurements were applied to confirm the stabili-
[12]
self-assembly process. During the self-assembly process, the
micelles coagulate first and form primary layer structures at
a 60 min lag phase, as suggested by the TEM studies (Fig-
ure 5b and 5c). This is typical for some step-wise association
processes as the growth of the aggregates gradually acceler-
[13]
ates the further aggregation.
Effect of pH and counterions on the coagulation of micelles
to give assembly structures
The formation of the assembly structures in the hybrid solu-
tions with different pHs or different types of counterions has
been explored by means of SEM and SAXS measurements. The
Figure 3. a) TEM image of the multilayer structure (inset, zoom in image of
the layers; the three grey lines highlight the boundaries between the
layers). b) TEM image of the pattern on the surface of the 1D anisotropic
structures.
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pH of the aqueous solution H ·1 was tuned from 13.3 to 7.0
2
through the addition of extra KOH solution or HCl solution.
SEM studies indicate that the belt-like structures can be ob-
served in the solutions with pH range from 13.3 to 9.0, while ir-
regular aggregates without any ordered structures were ob-
served in solutions under conditions of lower pH (Figure 6, and
Figures S3 and S4 in Supporting Information). The protonation
Figure 6. SEM images of the aggregates in solutions of H
2
·1 with a) pH 11.9
(
scale bar, 2 mm), b) pH 10.8 (scale bar, 2.5 mm), c) pH 10.5 (scale bar, 1 mm),
d) pH 9.8 (scale bar, 1 mm), e) pH 9.0 (scale bar, 20 mm), and f) pH 7.8 (scale
bar, 10 mm).
of the two amino groups of the hybrid at low pH could reduce
the net charges of the polar head groups as well as the
formed micelles. Therefore, the electrostatic interaction be-
tween the micelles becomes weaker, while the van der Waals
attraction will be dominant. Such a nonspecific interaction
(
van der Waals attraction) finally leads to the fast coagulation
of the micelles to irregular aggregates at low pH. On the other
hand, SAXS measurements on the hybrid solutions at the iden-
tical pH (~12.6) containing LiOH, NaOH, KOH, or NH ·H O, re-
3
2
spectively, show that micelles form in all solutions at the be-
ginning, while nanobelt structures are only eventually ob-
served in KOH and NH ·H O solutions (see supporting informa-
3
2
+
+
tion). K and NH4 have smaller hydrated radii among these
cations and therefore have stronger affinity with the micelles,
leading to easier coagulation of micelles and formation of the
nanobelts at higher pH. Suggested by SAXS measurements,
+
spherical micelle structures are stable in solution with Na or
Figure 4. a) Left: SAXS curve of initial solution just after preparation and
fitted with core-shell model; right: graphical representation of the micelle
structure. b) Left: SAXS curve of solution containing assemblies; right:
graphical representation of multilayer structure. c) Time-resolved SAXS re-
sults of the solution of the hybrid from 0 to 680 min time. d) Plot of normal-
ized intensities of micelle peak and assemblies peak versus time.
+
Li as the counterions without forming either nanobelt or ir-
regular aggregates in these solutions (see Supporting Informa-
tion).
The role of directional hydrogen bonding in the formation
of 1D nanobelt
It has been confirmed above that the nanobelt structure is due
to the binding of cations to the anionic micellar surface, which
decreases the stability of the micelles leading to the further co-
agulation and the growth of large structures. The directional
noncovalent interactions are responsible for anisotropic prop-
[8a,14]
erties of supramolecular assemblies.
Cronin et al. investi-
gated the self-assembly of pyrene-containing hybrids into 1D
nanofibres on hydrophilic surfaces, revealing that directional
Figure 5. TEM images of a) micelles, b) primary layer phase, and c) growing
layer phase structures.
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[
8a]
p–p stacking drove the 1D growth of the nanofibres. Herein,
the hydrogen-bond interaction between the polar head
groups is believed to be critical for the growth of the nanobelt
structures by providing a directional interaction that leads to
the 1D anisotropic assemblies. FT-IR studies of the single crys-
tals of TBA ·1, nanobelt structures (prepared in solution at pH
2
~
13.3 and separated as a solid sample through centrifugation),
an H ·1 sample prepared through ion exchange (see experi-
2
mental section), and irregular aggregates of the hybrid (pre-
pared and separated in solution at pH ~7.0) indicate that the
characteristic peaks of V=O vibration are at 943, 945, 952, and
t
À1
9
56 cm , respectively (see Figure S5 and S6 in Supporting In-
formation). The lower V=O vibration frequencies confirm the
t
existence of hydrogen-bond interaction, since the involvement
of terminal oxo ligand of the polar head groups in hydrogen
Figure 7. a) SEM image of the assemblies dispersed in acetonitrile after
1
day. b) Reaction scheme for the oxidation of sulfide catalyzed by the as-
bonding slightly elongates the bond length of V=O , and con-
t
semblies. c) Kinetic curves of the concentrations of reactant and products in
the reaction catalyzed by 6 mg nanobelts (S, p-tolylsulfide; SO, sulfide mon-
sequently lowers the V=O vibration frequencies. The first and
t
second samples have orderly packed hybrid structures and
show lower vibrational frequencies, implying the critical role of
hydrogen bonding in forming 1D-ordered structures. More-
over, proved by the time-resolved SAXS measurements, the
formation of nanobelt structures becomes significantly slower
when adding 1m urea or replacing H O with D O in the KOH
2
oxide; SO , sulfone). d) Reaction time of oxidation of sulfide with different
loading amount of nanobelts.
erogeneous catalysis provides both reasonably fast rate (1.5 h)
and good recyclability for the catalysts. Due to their high sur-
face area, our heterogeneous catalysts (90 min) show higher
reaction rate than the previous Keggin-type POM-based het-
2
2
solution of the hybrid (lag phase periods >2 days). The plausi-
ble explanation is that the added urea or D O prefer to interact
2
[15]
with the hybrids’ polar head groups through hydrogen bond-
ing, which hinders the interhybrid hydrogen bonding. Hydro-
gen bonds can only form with the specific donor and acceptor
positions, which force the growth of the hybrid assemblies to
proceed in one specific direction to form 1D nanostructure.
erogeneous catalyst (150 min).
Conclusion
In summary, a new inorganic-organic hybrid surfactant with
a hexavanadate cluster as the polar head group was designed,
synthesized, and programmed to self-assemble into 1D nano-
belt structures. The assembly mechanism was proved to be
the coagulation of hybrid micelles into layered structures with
the cooperation of hydrophobic, electrostatic, and hydrogen-
bonding interactions, while the last one is particularly impor-
tant as it is directional and leads to the anisotropic assemblies.
The assemblies were highly efficient heterogeneous catalysts
for oxidation of organic sulfides, because of their nanoscale
thickness and the exposure of most of the hexavanadates onto
the surface.
Assemblies works as heterogeneous catalyst
The surface of the nanobelts with nanoscaled thickness is fully
covered by catalytically active hexavanadates, making them
potential high efficient heterogeneous catalysts. Herein, the
catalytic efficiency of nanobelts is evaluated based on the reac-
tion time of catalyzed oxidative desulfurization with hydrogen
peroxide. The 1D assemblies are stable in acetonitrile and were
used to catalyze the oxidation of methyl p-tolylsulfide with
two equivalents of H O (wt, 30%) (Figure 7a,b, and Supporting
2
2
Information). The sulfide was fully oxidized into sulfide monox-
ide and sulfone (molar ratio, 1:1) after running the reaction for
1.5 h at 408C with the loading of nanobelts (6.0 mg, Figure 7c).
Experimental Section
After another three hours, all the sulfide monoxide was finally
turned into sulfone (Figure 7c). SEM studies indicate that the
belt structures remain after the reaction (Figure S7 in Support-
ing Information). The catalysts were easily re-collected through
centrifugation and further reactions proved that the catalysts
did not lose catalytic efficiency for at least two more cycles.
Moreover, catalytic reactions with different loading amounts of
the heterogeneous catalysts (0–6 mg of nanobelts) and one
Synthesis of TBA ·1
2
A solution of cetyl 4-(chloromethyl)benzoate (0.39 g, 1 mmol) and
[(n-C H ) N] [V O {(OCH ) CNH } ] (1.23 g, 1 mmol) in N,N-dimethyl
4
9 4
2
6
13
2 3
2 2
formamide (15 mL) was stirred for 48 h at 808C, then cooled to
room temperature. A solution of tetrabutyl ammonium hydroxide
(1.04 g, 0.8M) in methanol (1.25 mL) was added to the reaction so-
lution and stirred for 30 min at room temperature; the resulting so-
lution was added to deionized water (100 mL) for precipitating.
After standing for a few days, the solution was filtered and the pre-
cipitate was washed by deionized water three times and then
dried in air. The solid was dissolved in acetonitrile and filtered to
remove insoluble substance; the filtrate was precipitated by
adding diethyl ether and then separated by centrifugation. The
homogeneous catalyst (TBA ·1, soluble in acetonitrile, 6 mg)
2
were carried out. The time needed for the sulfide to be fully
consumed is inversely proportional to the amount of the het-
erogeneous catalysts (Figure 7d). The reaction goes faster with
the homogeneous catalyst (reaction time 40 min), but the het-
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acetonitrile–dissolution–diethyl ether–precipitation procedure was
repeated two more times and yield the final product (0.32 g,
work supported as part of the Institute for Atom-efficient
Chemical Transformations (IACT), an Energy Frontier Research
Center funded by the U.S. Department of Energy, Office of Sci-
ence, and Office of Basic Energy Sciences. P.Y. acknowledges
the department fellowship from chemistry department of
Lehigh University and Bob Jagendorf for providing us with the
picture of factory. T.L. and R.E.W. are thankful for the use of the
Advanced Photon Source, an Office of Science User Facility op-
erated for the U.S. Department of Energy (DOE) and Office of
Science by Argonne National Laboratory, supported by the U.S.
DOE under Contract No. ED-AC02-06CH11357. Y.W. acknowl-
edges the support of Tsinghua University Initiative Foundation
Research Program No. 20101081771 and NSFC (Nos. 21225103
and 21221062) and THSJZ. We thank Dr. Xiaobing Zuo and Dr.
Byeongdu Lee for helpful discussions.
2
0.4%). Single crystals of TBA ·1 were afforded by slow diffusion of
2
1
solution of (TBA ·1) in acetonitrile into deionized water. HNMR
2
(
400 MHz, [D ]DMSO): d=0.85 (t, J=6.7 Hz, 3H; CH , tail), 0.93 (t,
6 3
+
J=7.3 Hz, 24H; CH , [Bu N] ), 1.23 (m, 24H; (CH ) , tail), 1.30/
3
4
+
2 12
+
1
2
3
.32(m, 16H, CH ; [Bu N] ), 1.57 (m, 16H; CH , [Bu N] ), 1.69 (m,
H; COOCH -CH , tail), 3.17 (t, J=7.3 Hz, 16H; NCH , [Bu N] ),
2
4
2
4
+
2
2
2
4
.85/3.87 (d, J=6.4 Hz, 2H; NHCH , tail), 4.23 (t, J=6.5 Hz, 2H;
2
COOCH , tail), 4.67 (s, 6H, (OCH ) , side without tail), 4.87 (s, 6H;
2
2 3
(
OCH ) , side with tail), 7.47/7.49(d, J=8.2 Hz, 2H; CH, phenyl), 7.84/
2 3
7
3
1
.86 ppm (d, J=8.2 Hz, 2H; CH, phenyl); IR (KBr pellet): n˜ =3350,
314, 2960, 2926, 2873, 2854, 1720, 1611, 1483, 1469, 1274, 1101,
À1
087, 1065, 945, 816, 796, 720, 583 cm ; ESI (MeCN): m/z: 554.38
2À
À
À
[1 ], 1109.14 [(1+H) ], 1350.61 [(1+TBA) ]; elemental analysis
calcd (%) for C H N O V : C 48.24, H 7.97, N 3.52; found: C
6
4
126
4
21 6
4
8.48, H 7.92 N 3.44.
Crystal data for TBA ·1
Keywords: catalysis · noncovalent interactions · organic–
inorganic hybrid · polyoxometalates · self-assembly
2
Formula: C H N O V ; M =1593.33, triclinic, P 1¯ , a=10.690(2),
6
4
126
4
21
6
r
b=11.537(5), c=31.412(14) ꢁ, a=84.74(4), b=82.61(3), g=
3
À3
À1
8
9.47(3)8, V=3826(3) ꢁ , Z=2, 1 =1.383 gcm , m=0.772 mm
,
calcd
3
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0
2
.0635). R =0.0954 for 9474 independent reflections with [I>
1
2
s(I)], wR =0.1737 for all data. The data were collected at 101(2) K
2
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