Self-assembled hybrid molybdenum phosphonate porous nanomaterials and their catalytic activity for the synthesis of benzimidazoles

Article abstract of DOI:10.1002/cctc.201402291

A new porous organic-inorganic hybrid molybdenum phosphonate nanomaterial (HMoP-1) was synthesized through the reaction of benzene-1,3,5-triphosphonic acid and molybdenum(V) chloride under hydrothermal conditions in the absence of any structure-directing

Full text of DOI:10.1002/cctc.201402291

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DOI: 10.1002/cctc.201402291
Self-Assembled Hybrid Molybdenum Phosphonate Porous
Nanomaterials and Their Catalytic Activity for the
Synthesis of Benzimidazoles
Malay Pramanik and Asim Bhaumik*[a]
A new porous organic–inorganic hybrid molybdenum phos-
phonate nanomaterial (HMoP-1) was synthesized through the
reaction of benzene-1,3,5-triphosphonic acid and molybde-
num(V) chloride under hydrothermal conditions in the absence
of any structure-directing agent. The morphology of the
hybrid material was found to be different at different synthesis
temperatures. The material synthesized at 423 K (HMoP-1-LT)
has spherical particle morphology, and the material synthe-
sized at 453 K (HMoP-1-HT) has self-assembled flakelike mor-
phology. Powder XRD, field-emission SEM, high-resolution TEM,
N2 sorption, solid-state 13C cross-polarization magic-angle spin-
ning NMR and 31P magic-angle spinning NMR analyses, X-ray
photoelectron spectroscopy, thermogravimetric differential
thermal analysis, NH3 temperature-programmed adsorption,
and FTIR spectroscopic techniques were employed to charac-
terize the samples and understand the morphological diversity.
The orthorhombic crystal phase of the material was estab-
lished through REFLEX and CELSIZ unit cell refinement pro-
grams. The calculated unit cell parameters of HMoP-1-HT are
a=8.001(0.046) ꢀ b=7.029 (0.039) ꢀ, c=6.010 (0.036) ꢀ;
whereas HMoP-1-LT is amorphous in nature. HMoP-1-HT shows
outstanding catalytic activity and high recycling efficiency for
the green and efficient one-pot condensation reaction for the
synthesis of bioactive 2-aryl benzimidazoles in excellent yields
at room temperature.
Introduction
Owing to the enhanced surface properties and structural diver-
sity, the porous organic–inorganic hybrid materials have found
huge potential applications in catalysis,[1] nanotechnology,[2]
light harvesting,[3] chemical sensing,[4] gas storage,[5] separa-
tion,[6] and biomedical research.[7] Their design and synthesis
have become an art to develop the next-generation functional-
ized solid-state materials. Thus, hybrid materials can provide
an unmatched variety of structural motifs as potential building
blocks for the development of extended porous solids.[8]
Among the various types of open-framework porous nanoma-
terials invented to date, hybrid metal phosphonates are partic-
ularly interesting because of their versatility in potential appli-
cations.[9] Although research of this class of materials is under
rapid development, the poor structural compatibility, and rela-
tively lower ability of further processing of these organo-
phosphonate-based porous hybrid materials, has restricted
their engineering applications. The tetrahedral nature of the
phosphonate group bearing oxygen atoms and very strong co-
ordinative interaction with metal ion (Mn+) makes the metal
phosphonate chemistry more challenging when designing the
open-framework hybrid architectures.[10] However, most of the
porous metal phosphonates developed so far are predomi-
nantly based on either linear mono- or diphosphonic acids as
the organic spacer group. The thermal and mechanical stability
of these materials are restricted because of limited cross-link-
ing.[11] Thus, to enhance the cross-linking in the porous frame-
work, by multidentate phosphonic acid sites of the ligand as
the organic scaffold, we have introduced a triphosphonic acid
(benzene-1,3,5-triphosphonic acid), inside the inorganic metal
ions, to produce the porous organic–inorganic hybrid metal
phosphonate materials.[12] In this context it is pertinent to men-
tion that the synthesis and potential application of hybrid mo-
lybdenum phosphonates with an open framework structure
remain of interest owing to their multidimensional structural
features.[13] To date, most of the attention has been paid to-
wards the synthesis of inorganic molybdenum phosphate and
polyoxometalate materials having open-framework structures,
and hybrid molybdenum phosphonate materials having
unique structural diversity.[14] However, there are very few re-
ports on the synthesis of organic–inorganic hybrid molybde-
num phosphonate materials with an open framework struc-
ture[15] and their application based on surface properties.
The synthesis of substituted benzimidazoles has attracted
huge research interest owing to its presence in a large number
of natural products and pharmacologically active com-
pounds.[16] Substituted benzimidazoles show a wide spectrum
of pharmacological and biological properties, such as antiviral,
antifungal, antimicrobial, anthelmintic, and anticancer activi-
ties.[17] More than five clinically important drug molecules, such
as carbendazime, mebendazole, thiabendazole, pimozide, and
omeprazole containing benzimidazole as the parent nucleus
[a] M. Pramanik, Prof. Dr. A. Bhaumik
Department of Materials Science
Indian Association for the Cultivation of Science
Jadavpur, Kolkata, 700 032 (India)
E-mail: msab@iacs.res.in
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201402291.
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have been synthesized and extensively used worldwide.[18]
Thus, a wide range of research activities have been focused on
the design these compounds, specially through catalytic path-
ways involving microwave-assisted synthesis, solar thermal en-
ergies, Lewis acid catalysis, and solid-supported homogeneous
catalysis to increase the product yield and minimize the reac-
tion time and temperature.[19] However, many of these meth-
ods have several drawbacks, such as long reaction time, high
reaction temperature, leaching of the metal ions, and expen-
sive reagents. In some cases, 2-substituted and 1,2-disubstitut-
ed benzimidazole were generated simultaneously with poor
selectivity.[19] Thus, a green and eco-friendly methodology for
the production of 2-aryl benzimidazole is highly desirable.
Herein, we report a new supermicroporous molybdenum
phosphonate material with high BET surface area and crystal-
line novel open-framework structure. The conversion from
noncrystalline nanoparticles into crystalline flakelike morpholo-
gy was achieved very efficiently by changing the reaction tem-
perature. Furthermore, porous organic–inorganic hybrid mate-
rials with positively charged metal ion (Mo5+) at higher oxida-
tion state can play a crucial role as a nanoreactor to conduct
the condensation reaction involving two or more reactant mol-
ecules with desired selectivity.[20] This hybrid molybdenum
phosphonate material showed excellent catalytic properties for
the one-pot synthesis of 2-aryl benzimidazoles through the
condensation reaction of o-phenylenediamine and substituted
aromatic aldehydes at room temperature within 30 min reac-
tion time. To the best of our knowledge, this is the first report
of organic–inorganic hybrid molybdenum phosphonate with
open-framework structure and its potential as a nanoreactor
for the synthesis of 2-arylbenzimidazoles, which could elimi-
nate the drastic and hazardous reaction conditions, such as
the use of hazardous organic solvents, reactants, high reaction
temperature, and long reaction time. The hybrid molybdenum
phosphonate catalyst can be easily separated through simple
filtration and can be reused five times without significant loss
of its catalytic activity.
Figure 1. Small-angle powder XRD pattern of HMoP-1-HT.
Figure 2. Wide-angle powder XRD pattern of HMoP-1-HT. Difference be-
tween experimental and theoretical PXRD pattern is shown in the inset.
the coordination between all the three phosphonic acid of the
organophosphonate precursor molecule and molybdenum is
less and the crystallization does not take place properly; as
a consequence the 3D network cannot crystallize. As a result,
the material HMoP-1-LT is amorphous in nature (inset of Fig-
ure S1). However, at higher hydrothermal temperature (453 K),
proper coordination and crystallization takes place and a crys-
talline 3D porous network was formed with open framework
structure.[22] The wide-angle powder XRD (PXRD) pattern of the
material (HMoP-1-HT) did not match with any crystalline phase
previously reported in the JCPDS database. Thus, the crystal
structure of HMoP-1-HT was evaluated from the experimental
PXRD pattern with REFLEX software. The extent of matching
between the theoretical wide-angle XRD and experimental
PXRD was verified by CELSIZ unit cell refinement program
(inset of Figure 2). The diffraction peaks could be assigned as
a new orthorhombic crystal phase and the corresponding crys-
tal parameters are a=8.001(0.046) ꢀ, b=7.029 (0.039) ꢀ, c=
6.010 (0.036) ꢀ. The unit-cell volume (V=338.332 ꢀ3) together
with the very low standard deviation (ESD=3.411) is in good
agreement with the predicted crystal parameters and the
actual crystal structure. The unit-cell parameters with standard
deviations are given in Table 1 and the corresponding Miller in-
dices for the different planes of the material (HMoP-1-HT) are
Results and Discussion
Mesophase and nanostructure
The small-angle XRD pattern for HMoP-1-HT is shown in
Figure 1. As seen from the figure, this hybrid molybdenum
phosphonate material has one broad peak corresponding to
the mesophase at 2q=2.568. This could be attributed to the
presence of disordered mesophase as a result of the self-as-
sembly of nanoparticles.[12,21] The interparticle distance corre-
sponding to the small-angle peak is 3.4 nm, suggesting that
the nanostructure of HMoP-1-HT is generated by the self-as-
sembly of very tiny nanoparticles. However, for HMoP-1-LT
sample no such peak was observed in the small-angle XRD
pattern (see the Supporting Information, Figure S1). This result
suggests that at lower hydrothermal temperature, the self-as-
sembled nanostructure/mesophase is not formed. The wide-
angle X-ray diffraction pattern of the HMoP-1-HT sample is
shown in Figure 2. At lower hydrothermal temperature (423 K),
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Table 1. Crystal parameters of HMoP-1-HT.
Chemical formula
Formula weight
C6H3P3O9Mo1.8
488.13
[gmolꢁ1
]
Symmetry
orthorhombic
Lattice parameters
a=8.001 (0.046) ꢀ b=7.029 (0.039) ꢀ c=6.010
(0.036) ꢀ
Volume (ESD)
Wavelength [ꢀ]
Range of data
collection
V=338.332 (3.411) ꢀ3
1.5406
10ꢂ2qꢂ70
Angular step [8]
Time per step [s]
0.02 (w)
25
Scheme 1. Probable mechanistic pathway for the formation of hybrid nano-
particles and nanoflakes at different temperatures.
Electron microscopic analysis
Table 2. Indexing of orthorhombic crystal phase of HMoP-1-HT.
The characteristic high-resolution TEM (HRTEM) images of the
molybdenum phosphonate sample HMoP-1-LT are shown in
Figure S2a and S2b. As seen from the images, this low-tem-
perature-synthesized material possesses uniform spherical par-
ticle morphology (particle size ꢀ45–50 nm). The representative
HRTEM images of the HMoP-1-HT sample are shown in Fig-
ure S2c. The closer view of the image reveals the self-assem-
bled unsymmetrical flakelike morphology of the material with
dimension of approximately 150–155 nm. The flakes have a hi-
erarchical structure that is generated by the self-assembling of
nanoparticles of dimension of approximately 16–18 nm. Fur-
thermore, the closer view of an individual particle reveals
a nanoflake-like morphology (Figure S2d). These nanoparticles
are generated by the self-assembling of very tiny nanospheres
(dimension ꢀ3–4 nm). This self-assembled nanostructure is the
origin of one broad small-angle X-ray diffraction peak of
HMoP-1-HT as shown in Figure 1. The uniform white spots of
dimension of approximately 1.6 nm throughout the individual
nanoflake (Figure S2d) are the signature of the presence of the
supermicropores in the material. The supermicropores could
be attributed to the cross-linking between metal and benzene-
1,3,5-triphosphonic acid bearing three phosphonic acid
groups. The clear crystal fringes are also observable from the
HRTEM image (Figure S3) of HMoP-1-HT. The representative
SEM images of the material HMoP-1-LT are shown in Figure 3a
and 3b. The finely monodispersed nanoparticles with dimen-
sions of approximately 45 nm are spread throughout the speci-
men. The flakelike morphology with a dimension of approxi-
mately 150–160 nm is clearly observable for the sample HMoP-
1-HT; as shown in Figure 3c. A closer view of the SEM image
(Figure 3d) of HMoP-1-HT reveals that every flake was generat-
ed by the assembly of very tiny nanospheres.
h
k
l
2q
d
1
0
0
1
0
1
2
1
1
0
1
3
3
0
3
2
1
1
0
1
2
5
5
1
3
1
0
1
0
1
1
0
0
1
2
2
2
0
1
3
2
3
0
1
3
4
2
0
1
4
4
2
0
0
1
0
1
1
0
1
0
1
1
0
0
1
0
0
3
3
2
1
3
1
1
2
1
4
11.635
12.590
13.058
16.615
19.611
20.298
22.874
23.949
28.347
29.311
31.666
33.072
35.584
41.704
42.204
44.225
46.820
48.217
49.186
55.762
58.136
60.199
61.375
62.332
65.202
69.174
7.605
7.030
6.779
5.335
4.526
4.374
3.887
3.715
3.148
3.046
2.825
2.708
2.522
2.165
2.141
2.047
1.940
1.887
1.852
1.648
1.586
1.537
1.510
1.489
1.430
1.358
listed in Table 2. Observed and calculated d spacing corre-
sponding to a given plane are in very close agreement.
As the hydrothermal synthesis temperature decreases, the
particle size of the hybrid molybdenum phosphonate (HMoP-
1-LT) increases (observable from electron-microscopy analysis,
see below), different from the behavior of the material synthe-
sized at higher temperature (HMoP-1-HT). From the thermody-
namics point of view this can be explained by the fact that as
the particle size of the nanoparticle increases, the tendency of
self-assembly decreases gradually.[23] Thus the HMoP-1-HT
nanoparticles are susceptible for self-assembly to form the re-
spective mesophase. On the other hand, in the case of HMoP-
1-LT, owing to its comparatively bigger particle sizes and their
amorphous nature, the self-assembly process is prohibited
(Scheme 1).
BET surface area and porosity
The permanent architectural porosity of hybrid molybdenum
phosphonate nanomaterials has been determined through N2
adsorption–desorption analysis at liquid N2 temperature and
the results are shown in Figure 4. The pore size of the materi-
als was calculated by means of nonlocal density functional
theory (NLDFT) and the results are shown in Figure 5. The BET
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surface area of HMoP-1-HT is 183 m2 gꢁ1 with a corresponding
pore volume of 0.148 cm3 gꢁ1. The isotherm for HMoP-1-HT can
be classified as a mixture of type I and IV isotherms according
to standard IUPAC nomenclature.[24] Furthermore, in the inter-
mediate relative pressure region (P/P0 =0.1–0.6), the N2 adsorp-
tion amount increases gradually, a characteristic of multilayer
adsorption and the presence of a considerable amount of mes-
opores in the material.[25] Moreover, at higher relative pressure
(P/P0 >0.75) the amounts of N2 adsorption increase greatly,
suggesting the presence of interparticle porosity in HMoP-1-
HT. The desorption isotherm of the material does not show
any hysteresis loop. Further, the t-method micropore analysis
revealed that the material consists of an internal micropore
area of 122 m2 gꢁ1 together with an external mesopore area of
61 m2 gꢁ1. The corresponding micropore and mesopore
volume is 8ꢂ10ꢁ2 cm3 gꢁ1 and 6ꢂ10ꢁ2 cm3 gꢁ1, respectively.
The NLDFT pore-size distribution of the material further sug-
gests that the HMoP-1-HT material is composed of two types
of pores having the dimension of approximately 1.6 and
2.7 nm, respectively. The supermicroporosity of the material
was generated by 3D cross-linking within the open-framework
structure between organophosphonic acid ligand and molyb-
denum, and the mesoporosity (2.7 nm) of the material could
be originated by the self-assembly of hybrid nanoparticles (ob-
servable from both the SEM and TEM analysis). On the other
hand, the isotherm for material HMoP-1-LT points to a nonpo-
rous nature with a BET surface area of only 32 m2 gꢁ1 and
a pore volume of 2ꢂ10ꢁ2 cm3 gꢁ1. This nonporous nature is
probably the result of insufficient cross-linking between the
metal and organophosphonic acid ligand at lower hydrother-
mal temperature (423 K). Hence, owing to the ineffective 3D
cross-linking and lack of crystallization at low temperature in
HMoP-1-LT, the internal surface area of the material is lower
than that of the material synthesized at higher temperature
(453 K).
Figure 3. Field-emission SEM image of a, b) HMoP-1-LT and c, d) HMoP-1-HT.
Figure 4. N2 adsorption and desorption isotherms for HMoP-1-HT and HMoP-
1-LT at 77 K. Adsorption points are marked by filled circles and triangles, de-
sorption points by empty circles and triangles.
Thermal analysis
The thermal stability of the hybrid molybdenum phosphonate
HMoP-1-HT was examined by using thermogravimetric analysis
under N2 atmosphere with a heating rate of 108Cminꢁ1 (Fig-
ure S4). The material exhibits two-step mass losses of total
37.8 wt% through the temperature interval 298–800 K. The
first 11.85 wt% endothermic weight loss is assigned to the loss
of adsorbed water molecule present at the surface of the
porous framework. The second 25.95 wt% exothermic mass
loss is probably caused by the breaking of CꢁC and CꢁP
bonds during burning of the organic framework. High exother-
mic peak maxima at 773 K suggested very high stability of the
hybrid molybdenum phosphonate framework. Thus, from the
thermal analysis data it can be suggested that the porous mo-
lybdenum(V) phosphonate material HMoP-1-HT has considera-
bly good thermal stability.
Figure 5. NLDFT pore-size distribution for HMoP-1-HT (filled circles) and
HMoP-1-LT (filled triangles).
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Bonding and framework structure
The FTIR spectrum of HMoP-1-HT was shown in Figure S5. The
peak at 547 cmꢁ1 could be assigned for the characteristic
stretching vibration of the MoꢁO bond. The broad peak cen-
tered at 1025 cmꢁ1 could be assigned to the stretching vibra-
tion of the tetrahedral CPO3 group. The presence of benzene
ring in the porous framework is confirmed by the characteristic
stretching vibration at 1405 cmꢁ1. The peak at 1630 cmꢁ1 is re-
sponsible for bending vibration of adsorbed water molecules
in the porous framework. The broad peak centered at 3427
and 3203 cmꢁ1 is probably caused by the free adsorbed water
molecule and free PꢁOH groups in the porous framework.
Thus the FTIR spectroscopic result suggest the presence of
benzene-1,3,5-triphosphonic acid in the porous architecture.
The absence of peaks at 961 cmꢁ1 and 1385 cmꢁ1 signifies that
the material does not contain any M=Ot (Ot =terminal oxo
group) and P=O in the framework.[26]
Figure 7. 31P MAS–NMR spectrum of HMoP-1-HT.
UV/Vis diffuse reflectance spectroscopy
The solid state UV/Vis reflectance spectroscopy is a very impor-
tant characterization tool to confirm the oxidation state of the
central metal ion in the organic–inorganic hybrid materials.
The UV/Vis reflectance spectra for the HMoP-1-HT, HMoP-1-LT,
and HMoP-1-HT (after catalysis) are shown in Figure 8. For
Solid-state magic-angle spinning NMR studies
Solid state 13C cross-polarization magic-angle spinning NMR
(13C CP–MAS–NMR) and 31P magic-angle spinning NMR
(31P MAS–NMR) experiments generally provide information
about the chemical environment around C and P nuclei in the
hybrid metal phosphonate framework. In Figure 6, the 13C CP–
Figure 8. UV/Vis reflectance spectra of HMoP-1-HT, HMoP-1-LT, and HMoP-1-
HT (after catalysis).
HMoP-1-HT, the absorption band at 744–834 nm is related to
Mo5+ ions to the hybrid phosphonate framework.[28] The char-
acteristic peak of Mo5+ is also observable at 401 nm and attrib-
Figure 6. 13C CP–MAS–NMR spectrum of HMoP-1-HT.
2
2
uted to the B2! B1 transition.[29] The peak centered at 260 nm
could be attributed to the presence of chromophoric phenyl
group in the porous hybrid framework. The high-energy ab-
sorption peak at 214 nm could be attributed to the charge
transfer from oxygen atom to molybdenum(V) atoms.[30] After
the catalytic reaction, the UV/Vis diffuse reflectance spectrum
of HMoP-1-HT does not alter, which indicates that the structur-
al environment and oxidation state of molybdenum remain un-
altered after catalysis. For HMoP-1-LT, the absence of peaks in
the lower energy region (600–900 nm) indicates the presence
of Mo6+ ions in the framework.[30] The large intensity of the
high-energy absorption peak at approximately 218 nm also
MAS–NMR spectrum of HMoP-1-HT is shown. It exhibits two
peaks at 131.6 and 135.4 ppm with almost similar intensity, in-
dicating the presence of two types of carbon with equal
number of atoms (shown in the inset of Figure 6). On the
other hand, the 31P MAS–NMR spectrum of HMoP-1-HT sample
(Figure 7) displays one strong signal at 11.9 and a very weak
one at 18.5 ppm. These signals could be attributed to the
[(OMo)3P]3ꢁC6H3 and [(OH)(OMo)2P]3ꢁC6H3 species, respectively.
These spectroscopic results further suggest the presence of or-
ganic fragment (C6PO3H3) in the porous molybdenum(V) phos-
phonate framework of HMoP-1-HT.[27]
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suggests the strong charge transfer interaction between
oxygen atom to molybdenum(VI) atoms. The red-shifting of
the charge-transfer spectrum of HMoP-1-LT relative to that of
HMoP-1-HT is also a good indication of the higher oxidation
state of Mo in HMoP-1-LT.
Molecular formula of HMoP-1-HT
Thermogravimetric differential thermal analysis (TG–DTA) of
the sample HMoP-1-HT indicates the presence of 25.9 wt% or-
ganics in the material. On the other hand, the CHN analysis
data suggest the presence of 14.8 wt% carbon and 1.8 wt%
hydrogen in this porous framework. Furthermore, inductively
coupled plasma atomic emission spectroscopy (ICP–AES) stud-
ies reveal the presence of 41.6 wt% molybdenum in HMoP-1-
HT. Furthermore, the energy-dispersive spectrometry (EDS)
analysis of the sample reveals the presence of 18.86 wt%
phosphorus. Thus, the molar ratio of C/Mo/P=2.05:0.72:1 is in
good agreement with the calculated C/P molar ratio of 2:1 in
the synthesized organophosphorous ligand (benzene-1,3,5-tri-
phosphonic acid). From the FTIR and solid-state 13C CP–MAS–
NMR and 31P MAS–NMR study, also the presence of benzene-
1,3,5-triphosphonic acid in the porous framework is confirmed.
Thus, probable molecular formula of the porous architecture of
HMoP-1-HT can be written as C6P3O9Mo1.8, Mo0.46Ox, yH2O.
X-ray photoelectron spectroscopy analysis
Figure 10. High resolution XPS for a) Mo3d and b) Mo3p orbitals of HMoP-
1-HT, HmoP-1-LT, and HMoP-1-HT (after catalysis).
X-ray photoelectron spectroscopy (XPS) has proven to be not
only a powerful scientific tool for investigating the electronic
structure in solids but also utilized in the analysis of composi-
tion, bonding, and local structure of the material. The XPS
survey spectrum of the HMoP-1-HT and HMoP-1-LT material re-
veals the presence of elements, such as oxygen, molybdenum,
carbon, and phosphorus (Figure 9). The HMoP-1-HT material
shows the major peaks at 135.03, 192.47, 235.01, 287.34,
399.62, 416.89, 532.61, and 744.91 eV, which corresponds to
P2p, P2s, Mo3d, C1s, Mo3p3/2, Mo3p1/2, O1s, and OKLL peaks,
respectively [OKLL: the energy of the electrons ejected from
the atoms due to the filling of the O1s state (K shell) by an
electron of the L shell coupled with the ejection of an electron
from L shell]. After high-resolution XPS, the Mo spectrum of
HMOP-1-HT for 3d orbitals (Figure 10a) contains two peaks at
233.70 and 236.80 eV for Mo3d5/2 and Mo3d3/2, respectively,
whereas for HMoP-1-LT the peaks are observed at 234.68 and
237.82 eV, respectively. The results signify the presence of
Mo5+ in HMoP-1-HT and Mo6+ in HMoP-1-LT.[31] The high-reso-
lution spectra for 3p orbitals of Mo in both materials contain
two well-resolved peaks at 399.62 and 416.89 eV for HMoP-1-
HT, and at 400.67 and 418.03 eV for HMoP-1-LT, respectively.
These peaks are responsible for Mo3p3/2 and Mop1/2 of Mo5+
and Mo6+ moiety in the porous hybrid material of HMoP-1-HT
and HMoP-1-LT, respectively. (Figure 10b) For HMoP-1-HT, the
peak at 286.32 eV is caused by the presence of sp2 hybridized
carbon in the porous material. (Figure S6a) The peaks at
135.03 and 192.47 eV is caused by the presence of P2p and
P2s in the hybrid material (Figure S6b and S6c). The broad
peak centered at 532.61 eV is assigned to the O1s of the mate-
rial (Figure S6d). The broadening of the peak is caused by the
presence of two types of oxygen atoms in the material, bridg-
ing and nonbridging oxygen atoms towards the metal ion.[32]
Quantification of the elements present in the material through
XPS analysis suggests the presence of elements in the ratio C/
P/Mo/O=2.08:1:0.76:8.64. Hence, the molecular formula of the
material (HMoP-1-HT) is C6P3O9Mo1.8, Mo0.48Ox, yH2O (x+y=
16.92), which almost completely matches with the chemical
Figure 9. XPS survey curve of HMoP-1-HT and HMoP-1-LT.
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formula extracted from the other (TG–DTA, ICP–AES, and EDS)
experimental results. The XPS survey spectrum of the HMoP-1-
LT material reveals the presence of elements, such as carbon,
phosphorus, molybdenum, and oxygen (Figure 9) in the ratio
of C/P/Mo/O=1.98:1:0.72:9.23. Hence, the molecular formula
of HMoP-1-LT is C6P3O9Mo1.5, Mo0.66Ox, yH2O (x+y=18.69).
From the high-resolution XPS spectrum (Figure 10a and b) it is
clear that after catalysis the oxidation state of Mo does not
change, which also supports our previous results of UV/Vis dif-
fuse reflectance spectra.
Scheme 2. Reaction pathway for the formation of 2-arylbenzimidazole.
Table 3. Synthesis of 2-arylbenzimidazole over HMoP-1-HT catalyst.[a]
Entry
1
R
Product
Yield [%][b]
Ph
93
Temperature-programmed desorption analysis
Temperature-programmed desorption (TPD) of ammonia was
measured to evaluate the total acidity and strength of the acid
sites in the porous molybdenum phosphonate material. The
desorption of ammonia started at very low temperature
(Figure 11). Two broad peaks with low intensity at approxi-
2
3
4
p-NO2C6H4
p-BrC6H4
p-ClC6H4
95
90
91
5
6
7
8
p-FC6H4
93
86
87
92
2-thiophenyl
m-BrC6H4
p-OCH3C6H4
9[c]
Ph
Ph
Ph
Ph
62
53
40
–
Figure 11. NH3 TPD profile of HMoP-1-HT.
10[d]
11[e]
12[f]
mately 326 and 417 K, respectively, are probably caused by the
weakly adsorbed NH3 to the Lewis and Bronsted acid sites of
the porous matrix (HMoP-1-HT). As the temperature increases,
one intense peak is observed at 595 K, which is probably re-
sponsible for the highly acidic Bronsted sites of the material.[33]
The Lewis acidity of the material arises as a result of the pres-
ence of Mo in the hybrid material and the Bronsted acidity of
the material is generated by the presence of free ꢁP(OH)
groups in the porous material. The total acidity evaluated from
the NH3–TDP analysis of the material (HMoP-1-HT) is
1.45 mmolgꢁ1.
[a] Reaction conditions: aldehyde (1 mmol); 1,2-phenylenediamine
(1 mmol); 5 wt% catalyst HMoP-1-HT with respect to corresponding alde-
hyde; reaction temperature=298 K; reaction time=30 min. [b] All prod-
ucts were characterized by 1H and 13C NMR spectra and yield refers to iso-
lated products. [c] Reaction was performed with 5 wt% HMoP-1-LT as the
catalyst. [d] Reaction was performed with H3PO4 as the catalyst. [e] Reac-
tion was performed with MoCl5 as the catalyst. [f] Reaction was per-
formed in the absence of any catalyst.
Such a material with high surface acidity can be used as
a
catalyst for the condensation reaction at ambient
temperature.
densation of o-phenylenediamine and substituted aromatic al-
dehydes (Table 3). The yield of the 2-aryl benzimidazole prod-
ucts were measured by weighing the final products and these
Catalysis over HMoP-1
The porous hybrid molybdenum phosphonate material was
used as a catalyst for the selective one-pot synthesis of 2-aryl-
benzimidazoles at room temperature (Scheme 2) by the con-
1
compounds were identified by H and 13C NMR spectroscopy
(see the Supporting Information). The electron-donating or
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-withdrawing groups in the substituted aldehydes do not
hamper the product yield; keeping this in mind we proposed
a reaction mechanism for the formation of 2-arylbenzimidazole
over HMoP-1 as shown in Scheme 3 (only Lewis acidic sites are
Table 4. Recycling efficiency of the catalyst HMoP-1-HT for the synthesis
of 2- arylbenzimidazole.[a]
Cycle number
Yield [%]
1
2
3
4
5
93.0
92.4
91.8
90.7
89.8
[a] Reaction conditions: aldehyde (1 mmol), 1,2-phenylenediamine
(1 mmol), 5 wt% catalyst HMoP-1-HT with respect to the corresponding
aldehyde, reaction temperature=298 K, reaction time=30 min.
1-HT catalyst. To demonstrate the highly acid catalytic activity
of the material (HMoP-1-HT), we also performed one another
catalytic reaction, Hantzsh ester synthesis (Scheme 4) in etha-
nol at 333 K.[36] The corresponding results are listed in Table 5,
suggesting a high yield of the product 1,4-dihydropyridine.
This result suggested that HMoP-1-HT can be employed as an
efficient acid catalyst for a wide range of organic reactions.
Scheme 3. Probable reaction mechanism and catalytic role of HMoP-1-HT in
the selective synthesis of 2-arylbenzimidazoles.
Recycling efficiency of the catalyst
represented for clear imaging). In this reaction mechanism, the
molybdenum(V) with vacant d orbitals in the porous hybrid
framework and free ꢁP(OH) groups in the material play the
crucial role for activating the carbonyl carbon of the substitut-
ed aldehydes. The molybdenum(V) or free ꢁP(OH) generate
a high electrophilicity in the carbonyl carbon of the aldehyde.
We synthesized two types of hybrid molybdenum phospho-
nate materials HMoP-1-HT and HMoP-1-LT to check the effect
of surface area and morphology on the catalytic performance
for the synthesis of 2-arylbenzimidazole with benzaldehyde as
a reference carbonyl compound. The yield of 2-phenylbenzimi-
dazole was only 62% if HMoP-1-LT (BET surface area 32 m2 gꢁ1)
was used as a catalyst but the yield largely increased to 93% if
HMoP-1-HT (BET surface area=183 m2 gꢁ1) was the catalyst. As
the surface area of the catalysts decreased, the mass transport
through the porous channel was largely prohibited, which is
reflected in the isolated yield of the product. Moreover, as the
particle size decreased, the number and uniformity of the
active catalytic sites (here MoV) increased gradually; this effect
is also responsible for the higher catalytic efficiency of HMoP-
1-HT (particle size ꢀ3–4 nm) over HMoP-1-LT (particle size 45–
50 nm).[34] If the reaction was performed in the absence of any
catalyst, no benzimidazole product was isolated even after pro-
longed reaction time. In this context we performed a reaction
by using MoCl5 and H3PO4 as the catalysts and isolated benzi-
midazole in 40% and 53% yield. There are few iron(III)-contain-
ing homogeneous and heterogeneous catalysts that are also
used as catalysts for the production of benzimidazole but the
yield is very low and the reaction time and temperature are
high[35] compared with the conditions for our reported HMoP-
The catalyst was recovered from the reaction mixture by filtra-
tion and was washed with methanol and acetone repeatedly
to remove the polar and nonpolar substrates from the surface
of the catalyst (HMoP-1-HT). Before the recycling test, the cata-
lyst was dried overnight at 333 K and the procedure was re-
peated for five times (Figure S7). The reusability of the catalyst
was tested by using benzaldehyde as the reference carbonyl
compound (Table 4). As seen from Figure S7 the product yields
were very consistent suggesting high catalytic efficiency of
HMoP-1-HT in the synthesis of 2-arylbenzimidazoles. Further-
more, to test whether any metal (Mo) or organics (benzene-
1,3,5-triphosphonic acid) are leached out from HMoP-1-HT
during the reaction, in one reaction cycle the catalyst was sep-
arated from the reaction mixture after 25 min through filtra-
tion. At this stage, the yield of the product was 71%. Then the
reaction was continued without the catalyst at room tempera-
ture for another 5 h. After 5 h the product was analyzed and
the conversion was found to increase by a very insignificant
amount (yield 71.5%). This result confirms that during the cat-
alytic reaction no leaching of the catalyst takes place and the
catalytic pathway is completely heterogeneous in nature.
Conclusions
We report a highly crystalline new organic–inorganic hybrid
porous molybdenum(V) phosphonate material by using ben-
zene-1,3,5-triphosphonic acid as an organic scaffold under hy-
drothermal condition. Nanoparticles and agglomerated flake-
like morphology of the materials were obtained simply by
tuning the hydrothermal synthesis temperature. The hybrid
phosphonate material HMoP-1-HT showed high surface area
and uniform supermicropores and mesopores. This porous
hybrid material was utilized as an efficient catalyst for the syn-
thesis of biologically important value-added 2-arylbenzimida-
zoles through one-pot condensation reaction under green and
mild reaction conditions. A wide variety of commercially avail-
able important drug molecules contain 2-arylbenzimidazoles or
Scheme 4. Reaction pathway for the formation Hantzsh ester.
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washing by water and ethanol.
The materials, namely HMoP-1-HT
(hydrothermal temperature 453 K)
and HMoP-1-LT (hydrothermal
temperature 423 K) were dried
under vacuum desiccators.
Table 5. Hantzsh ester synthesis over HMoP-1-HT catalyst.[a]
Entry
R1
R2
Product
Yield [%][b]
1
OC2H5
Ph
82
Instrumentation
2
3
OC2H5
OC2H5
p-BrC6H4
78
83
PXRD patterns were recorded on
a Bruker d-8 Advance diffractome-
ter operated at 40 kV and 40 mA
and calibrated with a standard sili-
con sample, using Ni-filtered CuKa
(l=0.15406 nm). JEOL JEM6700F
field-emission scanning electron
microscope was used for the de-
termination of the morphology of
powder samples. The pore struc-
ture was explained by a JEOL
JEM2010 transmission electron
p-NO2C6H4
[a] Reaction conditions: aldehyde (1 mmol), 1,3-dicarbonyl compound (2 mmol), ammonium acetate
(1.5 mmol), 5 wt% catalyst, HMoP-1-HT with respect to corresponding aldehyde, reaction temperature=333 K,
reaction time=30 min, solvent EtOH (3 mL). [b] Product yield was calculated by weight.
1,4-dihydropyridines as a parent nucleus. Thus, our novel
microscope operated at an accelerating voltage of 200 kV. N2 ad-
sorption/desorption isotherms of the samples were recorded on
a Quantachrome Autosorb 1-C/TPD, at 77 K. Prior to the measure-
ments, the samples were degassed at 423 K for 12 h under high
vacuum. UV/Vis diffuse reflectance spectra were obtained by using
a Shimadzu UV 2401PC spectrophotometer with an integrating
sphere attachment. BaSO4 pellet was used as a background stan-
dard. FTIR spectra were recorded by using a Nicolet MAGNA-FT
IR750 Spectrometer Series II. 1H NMR and 13C experiments were
performed on a Bruker DPX-300 NMR spectrometer. TGA and DTA
of the samples were performed in a TGA instrument thermal ana-
lyzer TA-SDT Q-600 under N2 flow. XPS was performed on an Omi-
cron nanotech operated at 15 kV and 20 mA with a monochromatic
AlKa X-ray source. TPD–NH3 was performed in a Micromeritics In-
strument Corporation ChemiSorb 2720 pulse chemisorption
system.
hybrid HMoP-1-HT catalyst has huge potential to be explored
for selective synthesis of bioactive molecules, such as substitut-
ed 2-arylbenzimidazoles and 1,4-dihydropyridines. The novel
porous nanocatalyst developed herein may open up new ave-
nues in the synthesis of organic fine chemicals under eco-
friendly conditions.
Experimental Section
Materials
Commercially available 1,3,5-tribromobenzene (98%), triethyl phos-
phite (98%), molybdenum(V) chloride (95%), and 1,3-diisopropyl-
benzene were purchased from Sigma–Aldrich. Anhydrous Nickel(II)
bromide (99%) were purchased from Avra Chemicals.
Synthesis of benzene-1,3,5-triphosphonic acid
Catalytic reactions
Benzene-1,3,5-triphosphonic acid was prepared by the previously
reported procedure.[37] The compound was characterized by 1H,
13C, 31P NMR, and IR spectroscopy. 1H NMR (500 MHz, D2O): d=
8.07 ppm (t, 3JPH) 15 Hz); 13C NMR (500 MHz, D2O): d= 135.23;
136.07 ppm; 31P NMR (500 MHz, D2O): d=12.87 ppm. IR (KBr): n˜ =
In the typical catalytic reaction, a 10 mL round bottom flask was
charged with o-phenylenediamine (1 mmol), various substituted al-
dehydes (1 mmol), and 5 wt% HMoP-1-HT in ethanol (5 mL) at RT.
The whole mixture was stirred well with a magnetic stirrer for
30 min. After the confirmation of the final product through thin
layer chromatography, the reaction mixture was filtered and the
catalyst was washed with ethanol. The crude product was isolated
by vacuum evaporation of the ethanolic solution. The crude prod-
uct was diluted with CH2Cl2 and washed with brine solution re-
peatedly and dried over anhydrous Na2SO4. The pure products
were collected by vacuum evaporation of the organic part. The
yield of the products was confirmed by weighing and the purity
3387, 3088, 2925, 2319, 1142, 1001, 943, 691, 536, 470 cmꢁ1
.
Synthesis of the porous molybdenum(V) phosphonate
In the typical synthesis of hybrid molybdenum phosphonate, ben-
zene-1,3,5-triphosphonic acid (1.90 g, 6 mmol) was dissolved into
a water–ethanol (1:1) mixture (40 mL). In another beaker, molybde-
num(V) chloride (2.94 gm, 10.8 mmol) was dissolved into dry etha-
nol (30 mL) separately. The synthetic gel was prepared by the
dropwise addition of the phosphonic acid solution to the ethanolic
metal salt solution within 1 h under vigorous stirring condition.
After 2–3 h, the pH of the synthetic gel was increased by 4 by ad-
dition of 12.5% aqueous ammonia solution. The deep greenish
color gel was further stirred overnight and transferred to two
Teflon lined pressure vessel and kept at 453 K and 423 K for 24 h.
The Teflon leaned autoclaves were cooled to RT very slowly
(108Chꢁ1). The materials were isolated by filtration with repeated
1
was confirmed by H and 13C NMR spectroscopy data.
Acknowledgements
MP wishes to thank CSIR, New Delhi for Senior Research Fellow-
ships. AB wishes to thank DST, New Delhi for instrumental sup-
port through DST Unit on Nanoscience and DST-SERB project
grants.
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[16] a) M. J. Tebbe, W. A. Spitzer, F. Victor, S. C. Miller, C. C. Lee, T. R. Sattel-
berg, Sr., E. McKinney, J. C. Tang, J. Med. Chem. 1997, 40, 3937–3946;
b) M. T. Migawa, J. L. Giradet, J. A. Walker, G. W. Koszalka, S. D. Chamber-
lain, J. C. Drach, L. B. Townsend, J. Med. Chem. 1998, 41, 1242–1251;
c) M. J. Climent, A. Corma, S. Iborra, S. Martinez-Silvestre, ChemCatChem
2013, 5, 3866–3874.
[17] M. Roth, M. L. Morningstar, P. L. Boyer, S. H. Hughes, R. W. Buckheit, Jr.,
C. J. Michejda, J. Med. Chem. 1997, 40, 4199–4207.
[18] a) P. Lindberg, P. Nordberg, T. Alminger, J. Med. Chem. 1986, 29, 1327–
1329; b) K. J. Spivak, Z. Amit, Physiol. Behav. 1986, 36, 457–463; c) G.
Navarrete-Vꢃzquez, L. Yꢄpez, A. H. Campos, Bioorg. Med. Chem. 2003,
11, 4615–4622.
[19] a) R. N. Nadaf, S. A. Siddiqui, T. Daniel, R. J. Lahoti, K. V. Srinivasan, J. Mol.
Catal. A 2004, 214, 155–160; b) V. A. Sontakke, S. Ghosh, P. P. Lawande,
B. A. Chopade, V. S. Shinde, ISRN Org. Chem. 2013, 2013, 1–7; c) N. D.
Kokare, J. N. Sangshetti, D. B. Shinde, Synthesis 2007, 18, 2829–2834.
[20] a) A. P. Wight, M. E. Davis, Chem. Rev. 2002, 102, 3589–3614; b) J. Weit-
kamp, M. Hunger, U. Rymsa, Microporous Mesoporous Mater. 2001, 48,
255–270; c) M. Pramanik, A. Bhaumik, J. Mater. Chem. A 2013, 1,
11210–11220.
[21] Y. Zhou, M. Antonietti, J. Am. Chem. Soc. 2003, 125, 14960–14961.
[22] J. Ovenstone, K. Yanagisawa, Chem. Mater. 1999, 11, 2770–2774.
[23] R. Thiruvengadathan, V. Korampally, A. Ghosh, N. Chanda, K. Gangopad-
hyay, S. Gangopadhyay, Rep. Prog. Phys. 2013, 76, 066501.
Keywords: heterocycles
organic–inorganic hybrid composites · self-assembly
· mesophases · molybdenum ·
[1] a) C. Zou, Z. Zhang, X. Xu, Q. Gong, J. Li, C.-D. Wu, J. Am. Chem. Soc.
2012, 134, 87–90; b) A. Corma, U. Diaz, T. Garcia, G. Sastre, A. Velty, J.
Am. Chem. Soc. 2010, 132, 15011–15021.
[2] a) C. D. S. Brites, P. P. Lima, N. J. O. Silva, A. Millan, V. S. Amaral, F. Palacio,
L. D. Carlos, J. Lumin. 2013, 133, 230–232; b) T. Govindaraju, Nanoscale
2012, 4, 6102–6117; c) H. S. Huang, K. H. Chang, N. Suzuki, Y. Yamauchi,
C. C. Hu, K. C. W. Wu, Small 2013, 9, 2520–2526.
[3] M. Waki, N. Mizoshita, Y. Maegawa, T. Hasegawa, T. Tani, T. Shimada, S.
Inagaki, Chem. Eur. J. 2012, 18, 1992–1998.
[4] a) A. A. Khan, L. Paquiza, A. Khan, J. Mater. Sci. 2010, 45, 3610–3625;
b) T. H. T. Thi, R. Dagnelie, S. Crunaireza, L. Nicole, Chem. Soc. Rev. 2011,
40, 621–639.
[5] a) Z. Guo, H. Wu, G. Srinivas, Y. Zhou, S. Xiang, Z. Chen, Y. Yang, W.
Zhou, M. O’Keeffe, B. Chen, Angew. Chem. Int. Ed. 2011, 50, 3178–3181;
Angew. Chem. 2011, 123, 3236–3239; b) S. B. Kalidindi, H. Oh, M. Hirsch-
er, D. Esken, C. Wiktor, S. Turner, G. V. Tendeloo, R. A. Fischer, Chem. Eur.
J. 2012, 18, 10848–10856.
[6] a) J. C. Hicks, J. H. Drese, D. J. Fauth, M. L. Gray, G. Qi, C. W. Jones, J. Am.
Chem. Soc. 2008, 130, 2902–2903; b) J. H. Chang, S. Y. Lee, J. Lee, Curr.
Org. Chem. DOI: 10.2174/1385272811317100003.
ˇ
´
[24] J. Zecevic, C. J. Gommes, H. Friedrich, P. E. de Jongh, K. P. de Jong,
Angew. Chem. Int. Ed. 2012, 51, 4213–4217; Angew. Chem. 2012, 124,
4289–4293.
[7] a) E. Ruiz-Hitzky, M. Darder, P. Aranda, K. Ariga, Adv. Mater. 2010, 22,
323–336; b) X. Bi, H. Zhang, T. Fan, CN102580640A, 2012.
[8] a) Y. Yamauchi, N. Suzuki, P. Gupta, K. Sato, N. Fukata, M. Murakami, T.
Shimizu, S. Inoue, T. Kimura, Sci. Technol. Adv. Mater. 2009, 10, 025005;
b) C. H. Chen, V. M. B. Crisostomo, W. N. Li, L. Xu, S. L. Suib, J. Am. Chem.
Soc. 2008, 130, 14390–14391; c) R. D. K. Misra, D. Depan, J. Shah, Phys.
Chem. Chem. Phys. 2013, 15, 12988–12997; d) L. Raehm, A. Mehdi, C.
Wickleder, C. Reye, R. J. P. Corriu, J. Am. Chem. Soc. 2007, 129, 12636–
12637; e) Y. Yamauchi, J. Ceram. Soc. Jpn. 2013, 121, 831–840.
[9] a) X. Z. Lin, Z. Y. Yuan, Eur. J. Inorg. Chem. 2012, 2661–2664; b) T.
Kimura, K. Kato, Y. Yamauchi, Chem. Commun. 2009, 4938–4940;
c) R. M. P. Colodrero, G. K. Angeli, M. B. Garcia, P. O. Pastor, D. Villemin,
E. R. Losilla, E. Q. Martos, G. B. Hix, M. A. G. Aranda, K. D. Demadis, A.
Cabeza, Inorg. Chem. 2013, 52, 8770–8783; d) P. Xiao, RSC Adv. 2013, 3,
5127–5130.
[25] a) M. Kruk, M. Jaroniec, Chem. Mater. 2001, 13, 3169–3183; b) A. Modak,
J. Mondal, A. Bhaumik, ChemCatChem 2013, 5, 1749–1753.
[26] a) G. Cao, R. C. Haushalter, K. G. Strohmaiert, Inorg. Chem. 1993, 32,
127–128; b) J. Li, G. Wang, Z. Shi, M. Yang, R. L. Luck, Solid State Sci.
2009, 11, 1955–1960.
[27] Y. Yan, U. T. Bornscheuer, R. D. Schmid, Biotechnol. Bioeng. 2002, 78, 31–
34.
[28] F. H. Elbatal, A. M. Abdelghany, R. L. Elwan, J. Mol. Struct. 2011, 1000,
103–108.
[29] S. M. Horner, S. Y. Tyree, Jr., Inorg. Chem. 1963, 2, 568–571.
[30] K. Sarkar, T. Yokoi, T. Tatsumi, A. Bhaumik, Microporous Mesoporous
Mater. 2008, 110, 405–412.
[31] K. Antoniak, P. Kowalik, W. Prochniak, M. Konkol, A. Wach, P. Kustrowski,
J. Ryczkowski, Appl. Catal. A 2012, 423, 114–120.
[10] a) J. Morizzi, M. Hobday, C. Rix, J. Mater. Chem. 2001, 11, 794–798;
b) S. S. Iremonger, J. Liang, R. Vaidhyanathan, I. Martens, G. K. H. Shimi-
zu, T. D. Daff, M. Z. Aghaji, S. Yeganegi, T. K. Woo, J. Am. Chem. Soc.
2011, 133, 20048–20051.
[32] G. D. Khattak, M. A. Salim, A. S. Al-Harthi, D. J. Thompson, L. E. Wenger,
J. Non-cryst. Solids 1997, 212, 180–191.
[33] a) S. K. Das, M. K. Bhunia, A. K. Sinha, A. Bhaumik, ACS Catal. 2011, 1,
493–501; b) A. Sinhamahapatra, N. Sutradhar, B. Roy, P. Pal, H. C. Bajaj,
A. B. Panda, Appl. Catal. B 2011, 103, 378–387; c) G. V. A. Martins, G. Ber-
lier, C. Bisio, S. Coluccia, H. O. Pastore, L. Marchese, J. Phys. Chem. C
2008, 112, 7193–7200.
[34] a) Y. Riadi, R. Mamouni, R. Azzalou, M. E. Haddad, S. Routier, G. Guillau-
met, S. Lazar, Tetrahedron Lett. 2011, 52, 3492–3495; b) P. Salehi, M.
Dabiri, M. A. Zolfigol, S. Otokesh, M. Baghbanzadeh, Tetrahedron Lett.
2006, 47, 2557–2560.
[35] A. Dutta, J. Mandal, A. K. Patra, A. Bhaumik, Chem. Eur. J. 2012, 18,
13372–13378.
[36] M. Khoshneviszadeh, N. Edraki, K. Javidnia, A. Alborzi, B. Pourabbas, J.
Mardaneh, R. Miri, Bioorg. Med. Chem. 2009, 17, 1579–1586.
[37] D. Kong, J. Zon, J. McBee, A. Clearfield, Inorg. Chem. 2006, 45, 977–986.
[11] a) G. Guerrero, P. H. Mutin, A. Vioux, Chem. Mater. 2000, 12, 1268–1272;
b) M. Vasylyev, R. Neumann, Chem. Mater. 2006, 18, 2781–2783.
[12] a) M. Pramanik, A. Bhaumik, Chem. Eur. J. 2013, 19, 8507–8514; b) M.
Pramanik, A. K. Patra, A. Bhaumik, Dalton Trans. 2013, 42, 5140–5149.
[13] a) Y. Sui, X. Fang, R. Hu, Y. Xu, X. Zhou, X. Fu, Mater. Lett. 2007, 61,
1354–1357; b) N. G. Armatas, W. Ouellette, K. Whitenack, J. Pelcher, H.
Liu, E. Romaine, C. J. O’Connor, J. Zubieta, Inorg. Chem. 2009, 48, 8897–
8910; c) Y. Sui, X. Fu, J. Chen, L. Yin, Catal. Commun. 2008, 9, 2616–
2619; d) H. Tan, W. Chen, D. Liu, X. Feng, Y. Li, A. Yan, E. Wang, Dalton
Trans. 2011, 40, 8414–8418; e) J. D. Compain, P. Mialane, J. Marrot, F. Se-
cheresse, W. Zhu, E. Oldfield, A. Dolbecq, Chem. Eur. J. 2010, 16, 13741–
13748.
[14] a) C. Lv, R. N. N. Khan, J. Zhang, J. Hu, J. Hao, Y. Wei, Chem. Eur. J. 2013,
19, 1174–1178; b) H. El Moll, A. Dolbecq, I. M. Mbomekalle, J. Marrot, P.
Deniard, R. Dessapt, P. Mialane, Inorg. Chem. 2012, 51, 2291–2302; c) S.
Tanaka, M. Annakaab, K. Sakai, Chem. Commun. 2012, 48, 1653–1655.
[15] a) Y. H. Chuang, H. Liu, C. J. O’Connor, J. Zubieta, Inorg. Chem. Commun.
2008, 11, 1205–1208; b) K. P. Rao, V. Balraj, M. P. Minimol, K. Vidyasagar,
Inorg. Chem. 2004, 43, 4610–4614.
Received: May 2, 2014
Revised: May 27, 2014
Published online on August 14, 2014
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