Organic-inorganic hybrid polyoxometalate and its graphene oxide-Fe3O4 nanocomposite, synthesis, characterization and their applications as nanocatalysts for the Knoevenagel condensation and the synthesis of 2,3-dihydroquinazolin-4(1: H)-ones

Article abstract of DOI:10.1039/c6ra15339a

The simple and high yield synthesis of H₆Cu₂[PPD]₆[SiW₉Cu₃O₃₇]·12H₂O (PPD = p-phenylenediamine) as a new organic-inorganic hybrid polyoxometalate is reported. The new compound consists of trimetal-substitution polyoxometalate of A-β-SiW₉Cu₃O₃₇^10-, water molecules and coordinated and noncoordinated PPD molecules. H₆Cu₂[PPD]₆[SiW₉Cu₃O₃₇]·12H₂O was firmly grafted on graphene oxide decorated with Fe₃O₄ nanoparticles. These nanocomposites were characterized by elemental analyses, thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR), X-ray photoelectron spectrum (XPS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and alternating gradient force magnetometer (AGFM). The results indicate that the size range of the nanoparticles are between 20 and 60 nm. The catalytic activity of H₆Cu₂[PPD]₆[SiW₉Cu₃O₃₇]·12H₂O and the magnetically reusable nanocomposite of GO@Fe₃O₄@H₆Cu₂[PPD]₆[SiW₉Cu₃O₃₇]·12H₂O were investigated in the Knoevenagel condensation and synthesis of 2,3-dihydroquinazolin-4(1H)-ones.

Full text of DOI:10.1039/c6ra15339a

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Page 1 of 33
RSC Advances
Organic–inorganic hybrid polyoxometalate and its graphene oxide-Fe3O4
nanocomposite, synthesis, characterization and their applications as nanocatalysts
for the Knoevenagel condensation and the synthesis of 2,3-dihydroquinazolin-
4(1H)-ones
Roushan Khoshnavazi*, Leila Bahrami, Forugh Havasi
View Article Online
DOI: 10.1039/C6RA15339A
The simple and high yield synthesis of H6Cu2[PPD]6[SiW9Cu3O37].12H2O (PPD= p-
phenylenediamine) as a new organic-inorganic hybrid polyoxometalate is reported. The new
compound consists of trimetal-substitution polyoxometalate of A-β-SiW9Cu3O3710-, water
molecules
and
coordinated
and
noncoordinated
PPD
molecules.
H6Cu2[PPD]6[SiW9Cu3O37].12H2O was firmly grafted on graphene oxide decorated with
Fe3O4 nanoparticles. These nanocomposites were characterized by elemental analyses,
thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR), X-ray photoelectron
spectrum (XPS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM),
energy dispersive X-ray analysis (EDX), and alternating gradient force magnetometer
(AGFM). The results indicate that the size range of the nanoparticles are between 20-60 nm.
The catalytic activity of H6Cu2[PPD]6[SiW9Cu3O37].12H2O and the magnetically reusable
nanocomposite of GO@Fe3O4@H6Cu2[PPD]6[SiW9Cu3O37].12H2O were investigated in the
Knoevenagel condensation and synthesis of 2,3-dihydroquinazolin-4(1H)-ones.

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Page 2 of 33
Introduction
The design of active, selective and recyclable heterogeneous catalysts based on
polyoxometalates (POMs) have attracted great interest because of their controllable
shape and size, highly negative charges and their numerous advantageous properties.1
Keggin-type POMs such as H3PMo12O40, H3PW12O40, and H4SiW12O40 (also known
as heteropolyacids, HPAs) are strong Brønsted acid that make them useful as solid-
2-6
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acid catalysts for many acid catalyzed organic transformations. DespitDeOIt:h10e.10a3b9/oC6vReA15339A
advantages, application of POMs is restricted because of low surface area (< 10 m2/g)
and high solubility in water and polar organic solvents.7 Dispersion of POMs on a
support such as silica,8 zeolite,9 or design of catalysts based on polyoxometalate
nanoparticles10 can dissolve these problems and improve their catalytic activity.
Functionalization of classical POMs by organic compounds with suitable functional
groups not only provides a powerful way to gain multifarious new compounds but
also affords a new method to modify catalytic performance of POMs.11The design and
synthesis of inorganic–organic hybrid materials based on POMs has received
considerable attention due to their application in catalysis, sorption, and electrical
conductivity.12,13 A wide variety of organic molecules have to be combined with
POMs to explore the novel functional property and morphology of the type of
inorganic–organic hybrid materials.14,15 Magnetic separation renders the recovery of
catalysts from liquid-phase reactions much easier than by cross-flow filtration and
centrifugation. It is simple, economical and promising for industrial applications.16
Among the various magnetic nanoparticles under investigation, Fe3O4 nanoparticles
are arguably the most extensively studied as a core magnetic support because of their
simple synthesis, low cost, and relatively large magnetic susceptibility of Fe3O4 SPNs-
.17 Thanks to its exceptionally high surface area (2630 m2/g) and abundant oxygenate
groups such as epoxy, hydroxyl, and carboxyl groups18,19 on their surface, Graphene

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oxide (GO) is as an ideal support for improving POMs catalytic activity.20 If the
graphene oxide is loaded with Fe3O4 nanoparticles, the combined supporting material
has key properties such as magnetic separation, the large surface area and ease of
functionalizing with various chemical groups to increase their dependence toward
target compounds.21 Heterogeneous catalysts such as graphene oxide-Fe3O4 have
attracted a great deal of attention in recent years due to their high catalytic activity and
interesting structures.22 The Fe3O4
-GO magnetic nanoparticles have beenDmOIo: 1s0t.10u3s9e/Cf6uRlA15339A
View Article Online
as heterogeneous catalysts because of their numerous applications in biotechnology,
nanocatalysis, and medicine.23 In this paper, we report the synthesis and
characterization of the new nanosized polyoxometalate-based inorganic–organic
hybrid material, H6Cu2[PPD]6[SiW9Cu3O37]
reusable nanocomposites of GO@Fe3O4@HybPOM as novel and efficient catalysts
for synthesis of benzylidenemalononitrile and 2,3-dihydroquinazolin-4(1 )-one
·12H2O (HybPOM) and the magnetically
H
derivatives. The magnetic properties make the complete recovery of the catalyst
possible by means of an external magnetic field.
Experimental
General
All reagents and solvents were commercially obtained from Merck chemical company
and used without further purification. The Na9H[β-SiW9O34]·18H2O was prepared and
characterized according to the method mentioned in the literature.24 Graphene oxide
(GO) was prepared by modified Hummers’ method.25 The C, H, and N microanalyses
were carried out with CHNS-O Elemental Analyzer Vario EL III, ELEMENTAR,
Hanau-Germany while the amount of Fe, W and Cu were measured by inductively
coupled plasma mass spectrometry (ICP-MS). Powder XRD was obtained by an
X'PertPro Panalytical, Holland diffractometer in 40kV and 30mA with a CuKα
radiation (λ=1.5418Å). The XPS spectra of the supported catalyst was recorded on a

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VG Microtech Twin anode XR3E2 X-ray source and aconcentric hemispherical
analyzer operated at a base pressure of 5 ×10-10 mbar using AlKa (h
=1486.6 eV).
υ
Peak fitting of all spectra were undertaken using the Shirley background correction
and Gaussian–Lorentzian peak shapes. Binding energies (BEs) were referenced to C
1s peak at 284.5 eV. Low-resolution survey spectra, as well as higher-resolution
spectra for C, Fe, O, W, and Cu were collected. Infrared spectra were recorded on a
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Bruker Vector 22 FT-IR using KBr plate. The morphology of nanocomDpOoI:s1i0t.1e0s39w/C6aRsA15339A
revealed by a scanning electron microscope (FESEM-TESCAN MIRA3). The
elements in the nanocomposite samples were probed with energy-dispersive X-ray
(EDX) spectroscopy accessory to the FESEM-TESCAN MIRA3 scanning electron
microscopy. The magnetic properties were investigated by a home-made alternative
gradient force magnetometer (AGFM) in the magnetic field range of −5000 to 5000
Oe at room temperature. Thermo gravimetric analysis and differential thermal
analysis (TGA) were carried out using a STA PT-1000 LINSEIS. PEG with molecular
weight of 400 was used in reactions (PEG-400).
Preparation of nano materials
Preparation of H6Cu2[PPD]6[SiW9Cu3O37]·12H2O nanohybrid (HybPOM)
A 2.00 g of Na9H[β
-
SiW9O34]
·18H2O was dissolved in water (100 mL) at room
temperature. Cu(C2H3O2)2
·
H2O (3.00 g) was added to the solution while stirring,
resulting in a blue solution. Then, 0.7 g of PPD was slowly added to this blue solution
while stirring, producing a blue-brown precipitate. After stirring for 4 h, the precipitate
color changed from blue-brown to black. Obtained black precipitate was centrifuged
and washed several times with water and acetonitrile, then was air-dried at room
temperature. Yield 1.6 g, 80%. Anal. Calcd.ForC36H78N12O49SiW9Cu5: C, 12.48; H,

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2.25; N, 4.85; W, 47.90; Cu, 9.17. Found: C, 12.11; H, 2.03; N, 4.71; W, 48.95; Cu,
9.95.
Preparation of GO─Fe3O4
GO–Fe3O4 composites were synthesized by co-precipitation reaction of Fe2+ and Fe3+
ions in the presence of GO. To a 200 mL aqueous solution containing FeCl2·4H2O
(1.7 g) and FeCl3·6H2O (2.51 g) (molar ratio 1:2), GO (0.5 g) was added and the
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DOI: 10.1039/C6RA15339A
mixture sonicated for 30 min. The resulting mixture was deoxygenated by bubbling
with nitrogen gas for10 min, followed by heating to 80 °C for 10 min. NH4OH (10
mL, 8 M) was added rapidly to the heating solution and was left to stir for 1 h. After
cooling to ambient temperature, the formed GO–Fe3O4 composites were magnetically
collected, washed two times with deionized water (100 mL), and dried at 50 °C.
Preparation of GO@Fe3O4@HybPOM
To disperse 0.50 g GO-Fe3O4 in 30 mL in absolute ethanol, amount of 0.50 g of
HybPOM was added and the mixture was sonicated for 10 min to form a homogeneous
dispersion. Then, the mixture was stirred under reflux condition for 24 h. The obtained
solid was then magnetically collected from the solution and washed three times with
water and ethanol and dried at 50 °C. The elemental analysis of
GO@Fe3O4@HybPOM show that the nanocomposite contains Fe, 25.00; W, 23.00
and Cu, 4.78 %.
General procedure for the Knoevenagel condensation by HybPOM
HybPOM (0.007 g) was added to a mixture of aromatic aldehyde (1 mmol),
malononitrile or ethylcyanoacetate (1.2 mmol) in PEG/water = 1:1 (1 mL), and then
the mixture was stirred at room temperature for the appropriate time. The progress
was monitored by TLC (eluent: n-hexane/EtOAc, 2:1). After completion of the
reaction, 5 mL of EtOAc was added and the catalyst was separated by centrifuge, and

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Page 6 of 33
then the reaction mixture was extracted with H2O and EtOAc. The organic layer was
dried over MgSO4 and then evaporated under reduced pressure. After evaporation of
EtOAc, the obtained products were recrystallized from hot EtOH and the pure
products were obtained in 85-98% yields (Table 2).
General procedure for the Knoevenagel condensation by GO@Fe3O4@HybPOM
View Article Online
GO@Fe3O4@HybPOM (0.01g) was added to a mixture of aromatic aldehyde (1
DOI: 10.1039/C6RA15339A
mmol) and malononitrile or ethylcyanoacetate (1.2 mmol) in PEG/water = 1:1 (1 mL),
and then the mixture was stirred at room temperature for the appropriate time.
The progress was monitored by TLC (eluent: n-hexane/EtOAc, 2:1). After completion
of the reaction, 5 mL of EtOAc was added and catalyst was separated by an external
magnet, and then the mixture was extracted with H2O and EtOAc. The organic layer
was dried over MgSO4 and then evaporated under reduced pressure. After evaporation
of EtOAc, the obtained products were recrystallized from hot EtOH and pure products
were obtained in 85-98% yields (Table 2).
General procedure for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones by
HybPOM
A mixture of aldehydes (1 mmol), 2-aminobenzamide (1 mmol) and HybPOM (0.005
g) was stirred in ethanol (5 mL) under reflux conditions for the appropriate time, as
shown in Table 4. Reaction progress was monitored by TLC. After completion of the
reaction (disappearance of starting materials), the reaction mixture was cooled to room
temperature, and then the catalyst was separated by centrifuge and reused as such for
the next experiment. The decanted was evaporated to remove the solvent; the crude
solid product was washed with diethyl ether to obtain pure 2,3-dihydroquinazolin-
4(1H)-ones in 90-98% yields (Table 4).

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General procedure for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones by
GO@Fe3O4@HybPOM
A mixture of aldehydes (1 mmol), 2-aminobenzamide (1 mmol) and nanocatalyst
(0.007g) was stirred in ethanol (5 mL) under reflux conditions for the appropriate time
as shown in Table 4. Reaction progress was monitored by TLC. After completion of
the reaction, the reaction mixture was cooled to room temperature, and then the
View Article Online
catalyst was separated by an external magnet and reused as such for the next
DOI: 10.1039/C6RA15339A
experiment. The filtrate was evaporated to remove the solvent; the crude solid product
was washed with diethyl ether to obtain pure 2,3-dihydroquinazolin-4(1
90–98% yields (Table 4).
H)-ones in
The NMR spectra data of organic products
For all NMR measurements the chemical shifts are given with respect to
tetramethylsilane (TMS) as an internal standard.
2-Benzylidene-malononitrile (table 2, entry 1):Mp: 82-83 ˚C;55 1H NMR (400 MHz,
CDCl3) δ (ppm): 7.1 (t, J = 8.0 Hz, 2H), 7.6 (t, J = 8.0 Hz, 1H), 7.8 (d, J = 8.20 Hz, 2H), 8
(s, 1H); 13C NMR (100 MHz, CDCl3); δ = 159.3, 134.2, 133.1, 130.7, 117.2, 117.2, 86.9.
2-(4-methoxybenzylidene)malononitrile (table 2, entry 2):Mp:112-114 ˚C;55 1H-NMR
(400MHz, CDCl3): δ (ppm):7.91 (d, J = 10.5 Hz, 2H), 7.65 (s, 1H), 7.01 (d, J = 9.0 Hz, 2H),
3.91 (s, 3H); 13C-NMR (100 MHz, CDCl3) δ (ppm): 158.9, 154.4, 136.4, 128.9, 121.2, 120.2,
114.3, 112.9, 111.5, 81.5, 55.9.
2-(4-nitrobenzylidene)malononitrile (table 2, entry 4):Mp:158-159 ˚C;55 1H-NMR
13
(400MHz, CDCl3): δ (ppm): 8.41 (d, J=8.84, 2H), 8.10 (d,J=8.84, 2H), 7.90 (s, 1H); C-
NMR (100 MHz, CDCl3) δ (ppm): 156.8, 150.4, 135.8, 131.3, 124.6, 112.6,111.5, 87.5.

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2-(2-chlorobenzylidene)malononitrile (table 2, entry 5):Mp:79-82 ˚C;57 1H-NMR
13
(400MHz, CDCl3): δ (ppm): 7.80 (d, J=7.84, 2H), 7.74 (s, 1H), 7.71 (d, J=7.84, 2H); C-
NMR (100 MHz, CDCl3) δ (ppm):158.4, 133.1, 131.8, 129.9, 129.6, 113.4, 112.3, 83.5.
2-(4-chlorobenzylidene)malononitrile (table 2, entry 6):Mp:162-164 ˚C ;58 1H-NMR
(400MHz, CDCl3): δ (ppm):7.78(m, 3H), 7.69(d, J=6.8 Hz, 2H). 13C-NMR (100 MHz,
CDCl3) δ (ppm):159.6, 134.2, 132.9, 131.1, 130.8, 114.6, 113.5, 84.6.
1
Ethyl 2-cyano-3-(3-nitrophenyl)acrylate(table 2, entry 8):Mp:130-132 ˚CD;O59I: 10H.10-3N9/MC6RRA15339A
(400MHz, CDCl3): δ (ppm):1.44 (t, J = 8.00 Hz, 3H), 4.44 (q, J = 8.10 Hz, 2H), 7.28 (d,J=
8.20 Hz, 1H), 7.76 (t,J = 8.25 Hz, 1H), 8.33 (s, 1H), 8.43(d,J = 8.78 Hz, 1H), 8.72 (s, 1H);
13C-NMR (100 MHz, CDCl3) δ (ppm):160.9, 151.2, 148.2, 134.8, 132.4, 130.0, 126.4, 126.2,
113.9, 106.3, 62.6, 13.5.
View Article Online
Ethyl 2-cyano-3-phenylacrylate (table 2, entry 9):Mp:50-52 ˚C;55 1H-NMR (400MHz,
CDCl3): δ (ppm):1.49( t, J= 6.8 Hz, 3H) 4.16( q, J= 6.8 Hz, 2H) 6.99-7.01 ( m, 3H) 7.65 (d,
J=8.4Hz, 1H) 7.66-7.90 ( m, 2H);13C-NMR (100 MHz, CDCl3) δ (ppm): 162.5, 155.1, 155.0,
133.3, 131.4, 131.1, 129.3, 115.5, 103.0, 62.7, 14.2.
Ethyl 3-(4-chlorophenyl)-2-cyanoacrylate (table 2, entry 12):Mp:87-89 ˚C;60 1H-NMR
(400MHz, CDCl3): δ (ppm):8.20 (s, 1H), 7.93 (d, J = 8.0 Hz, 2H), 7.48 (d, J = 8.4 Hz, 2H),
13
4.39 (q, J = 7.2 Hz,2H), 1.40 (t, J = 7.2 Hz, 3H); C-NMR (100 MHz, CDCl3) δ (ppm):
162.2, 153.3, 139.5,132.1, 129.9, 129.6, 115.2, 103.6, 62.8, 14.1.
2-Phenyl-2,3-dihydroquinazolin-4(1H)-one(table 4, entry 1):Mp:223-224 ˚C;62 1H-NMR
(400 MHz, DMSO-d6): δ (ppm):8.29 (s, 1H), 7.63 (d, J = 7.8 Hz, 1H), 7.51 (d, J = 7.1 Hz,
2H), 7.41-7.35 (m, 3H), 7.26 (t, J = 7.8 Hz, 1H), 7.11 (s, 1H), 6.76 (d, J = 7.8 Hz, 1H), 6.69
13
(t, J = 7.8 Hz, 1H), 5.76 (s, 1H); C-NMR (100 MHz, DMSO-d6) δ (ppm):163.6, 147.8,
141.6, 133.3, 128.4, 128.3, 127.3, 126.8, 117.1, 114.9, 114.4, 66.5.
2-(4-Bromophenyl)-2,3-dihydoquinazolin-4(1H)-one (table 4, entry 2):Mp:197-200 ˚C;52
1H-NMR (400 MHz, DMSO-d6): δ (ppm):8.17-8.13 (m, 1H), 7.80-7.78 (m, 1H), 7.63-7.60

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(m, 3H), 7.47-7.45 (m, 2H), 7.28-7.24 (m, 1H), 6.74 (d, J= 8.4, 1H), 6.71-6.68 (m, 1H), 5.76
(s, 1H); 13C-NMR (100 MHz, DMSO-d6) δ (ppm):164.3, 154.4, 148.1, 133.9, 132.3, 130.2,
130.0, 127.8, 126.5, 118.1, 117.8, 114.9, 110.3, 61.3.
2-(4-Chlorophenyl)-2,3-dihydroquinazolin-4(1H)-one(table 4, entry 4):Mp:202-203
˚C;62 1H-NMR (400 MHz, DMSO-d6): δ (ppm):8.33 (s, 1H), 7.62 (dd, J = 8.0 Hz, J = 1.1
Hz, 1H), 7.52 (d, J = 8.6 Hz, 2H), 7.47 (d, J = 8.6 Hz, 2H), 7.27-7.23 (m, 1H), 7.14 (s, 1H),
13
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DOI: 10.1039/C6RA15339A
6.76 (dd, J = 8.0 Hz, J = 1.1 Hz,1H), 6.70-6.66 (m, 1H), 5.77 (s, 1H); C-NMR (100 MHz,
DMSO-d6) δ (ppm):163.4, 147.6, 140.6, 133.3, 132.9, 128.7, 128.2, 127.3, 117.2, 114.9,
114.4, 65.7.
2-(2-Chlorophenyl)-2,3-dihydroquinazolin-4(1H)-one (table 4, entry 5): Mp: 228-230 ˚C
;
63 1H-NMR (400 MHz, DMSO-d6): δ (ppm):8.40 (s, 1H), 7.62 (d, J = 7.6 Hz, 1H), 7.53 (s,
1H), 7.44-7.41 (m, 3H), 7.27 (t, J = 7.6 Hz, 1H), 7.21 (s, 1H), 6.77 (d, J = 7.6 Hz, 1H), 6.70
13
(t, J = 7.6 Hz, 1H), 5.78 (s, 1H); C-NMR (100 MHz, DMSO-d6) δ (ppm):164.1, 148.3,
141.9, 137.9, 133.6, 129.5, 128.7, 127.8, 127.6, 124.3, 117.6, 115.2, 114.8, 66.9.
2-(2-Hydroxy-4-methoxyphenyl)-2,3-dihydroquinazolin-4(1H)-one(table 4, entry 6):
Mp:262-263 ˚C;64 1H-NMR (400 MHz, DMSO-d6): δ (ppm):9.35 (s, 1H), 7.68 (d, J = 6.8
Hz, 1H), 7.57 (s, 1H), 7.22 (d, J = 8.4 Hz, 1H), 7.15-7.13 (m, 1H), 6.98 (s, 1H), 6.68-6.66
13
(m, 2H), 6.38 (s, 1H), 6.29-6.27 (m, 1H), 5.96 (s, 1H), 3.65 (s, 3H); C-NMR (100 MHz,
DMSO-d6) δ (ppm):163.5, 159.2, 147.7, 143.3, 133.3, 129.4, 127.3, 118.9, 117.0, 114.9,
114.3, 113.6, 112.5, 66.2, 55.0.
2-(3-Nitrophenyl)-2,3-dihydoquinazolin-4(1H)-one(table 4, entry 7): Mp:180-182 ˚C;63
1H-NMR (400 MHz, DMSO-d6): δ (ppm):8.25 (s, 1H), 8.09 (d, J= 7.2, 1H), 7.89 (d, J= 6.4,
1H), 7.83-7.80 (m, 1H), 7.70-7.63 (m, 2H), 7.30 (t, J= 7.2, 1H), 7.04 (s, 1H), 6.80-6.72 (m,
2H), 6.36 (s, 1H); 13C-NMR (100 MHz, DMSO-d6) δ (ppm):163.2, 149.3, 147.4, 147.2,
133.5, 128.0, 127.3, 123.5, 117.4, 114.8, 114.5, 65.2.

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2-(4-Methoxyphenyl)-2,3-dihydoquinazolin-4(1H)-one(table 4, entry 9): Mp:182-183
˚C;64 1H-NMR (400 MHz, DMSO-d6): δ (ppm):8.20 (s, 1H), 7.64-7.62 (d, J= 6, 1H), 7.28-
7.24 (t, J= 6, 1H), 7.15 (d, J= 1.6, 1H), 7.04-6.97 (m, 2H), 6.95 (s, 1H), 6.78-6.76 (d, J= 8,
2H), 5.71 (s, 1H), 3.77 (s, 3H); 13C-NMR (100 MHz, DMSO-d6) δ (ppm):163.6, 159.4,
147.9, 133.4, 133.2, 128.1, 127.3, 117.0, 114.9, 114.3, 113.6, 66.2, 55.1.
2-(4-Methylphenyl)-2,3-dihydroquinazolin-4(1H)-one (table 4, entry 10): Mp: 225-226
˚C ;49 1H-NMR (400 MHz, DMSO-d6): δ (ppm):8.22 (s, 1H), 7.62 (dd, J = 8.0 Hz, JVi=ew1Ar.ti3cle Online
DOI: 10.1039/C6RA15339A
Hz, 1H) 7.38 (d, J = 7.8 Hz, 2H), 7.25-7.21 (m, 1H), 7.20 (d, J = 7.8 Hz, 2H), 7.04 (s, 1H),
6.74 (d, J = 8.0 Hz, 1H), 6.68-6.64 (m, 1H), 5.71 (s, 1H), 2.29 (s, 3H); 13C-NMR (100 MHz,
DMSO-d6) δ (ppm):164.1, 148.4, 139.1, 138.2, 133.7, 129.3, 127.8, 127.2, 117.5, 115.4,
114.9, 66.8, 21.2.
Results and discussions
In this paper, we report a simple and mild synthesis route through self-assembly
polyoxometalate and p-phenylenediamine (PPD) as organic ligand π-electron donor
to produce a polyoxometalate-based inorganic-organic hybrid. First, by addition of
10-
Cu2+ ion to the lacunary 9-tungstosilicate, β-SiW9O34
solution, trimetallo
derivatives of [SiW9Cu3O37]10- are formed. The solution color is turned from colorless
to blue. With addition of PPD molecule to the blue aqueous solution, a blue-brown
precipitate formed. PPD molecule via one of its NH2 groups replaced terminal water
molecules from substituted Cu2+ ions. The precipitate color finally changed from blue-
brown to black because of charge transfer interaction between POM cluster anion and
PPD organic molecule.26 The proposed structure for anionic section of nanohybid
material is shown in Fig. 1.

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DOI: 10.1039/C6RA15339A
Fig. 1 The proposed structure to anionic section of nanohybrid materials of HybPOM.
For easier recovery and separation instead of centrifuge, functionalized nanosized
polyoxometalate of HybPOM was placed on the GO-Fe3O4 magnetic nanoparticles.
GO-Fe3O4 nanoparticles were prepared by Hummers’ method procedure.25
A quantitative analysis of O 1s XPS spectra of GO sample by Gaussian curves fitting
show that the relative atomic concentrations (atom %) of carboxyl or carbonyl groups,
epoxy, hydroxyl, or carboxyl groups, and oxygen atoms in water and/or chemisorbed
oxygen species are 24.08, 47.56 and 28.35%, respectively.
Due to abundant functional groups (such as epoxy, hydroxyl, and carboxyl groups) on
the surface, graphene oxide (GO) is ready to the attack the nucleophiles.
Organic compounds with functional amine groups may be loaded onto GO surface through
the nucleophilic substitution followed by formation of C-N bond. It may also be loaded onto
the surface of graphene oxide by the chemical reaction between amino groups and carboxylic
acid groups on the edge of GO sheets (scheme 1). Such methods are strong enough to firmly
deposit organic substrates with amine groups on the graphene oxide sheets.27
Common methods such as titration with Hammett indicators and temperature programmed
desorption of adsorbed molecules such as ammonia or pyridine, adsorption microcalorimetry

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and NMR spectroscopy have been employed to describe the acidity of POMs in the solid
state both qualitatively and quantitatively. Potentiometric titration with n-butylamine allows
us to estimate the number of acid sites and their distribution.28 The titration curves show that
HybPOM and Go/Fe3O4/HybPOM with the initial electrode potential -165.9 and -73.8 mV
are classified as very weak and weak acids, respectively. Difference in the acid strength of
HybPOM and Go/Fe3O4/HybPOM is attributed to the total number of free NH2 groups on
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them. For Go/Fe3O4/ HybPOM, some of the NH2 groups are involved in the bonding with
DOI: 10.1039/C6RA15339A
Go/Fe3O4 nanoparticle. The titration curves of HybPOM and Go/Fe3O4/HybPOM is
presented in the supporting information (Fig. S3).
Scheme 1 Preparation of the nanohybrid of HybPOM, and magnetically-recoverable nanocomposit
of GO@Fe3O4@HybPOM.

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DOI: 10.1039/C6RA15339A
Fig. 2 FT-IR spectra of (a) PPD, (b) [SiW9O37Cu3(H2O)3]10- and (c) HybPOM.
FT-IR spectra of HybPOM hybrid material show the characteristic band of PPD and
the trimetallo derivatives of [SiW9O37Cu3(H2O)3]10- heteropolyanions moieties with
some variations in the band vibrational frequencies or intensities (Fig. 2). The alkaline
salts of complex anions which often crystallize with many water molecules and
involve hydrogen bonds lead to a decrease in the frequencies of the metal-oxygen
stretching. With large organic PPD molecules,29 as is expected, the effects arising
from cation size, cation polarizing power and crystallization solvent molecules are
diminished so that the POM characteristic bands are observed clearly in the range
1000–700 cm-1.
The N–H stretch band (3300–3400cm-1) from PPD molecule overlap with OH
stretching vibration band (~3500 cm-1) from water molecule but other bands can be
observed in the IR spectra of HybPOM hybrid materials.
In Fig. 3 FT-IR spectra of GO, GO/Fe3O4, HybPOM were given for comparison with
that of GO@Fe3O4@HybPOM.

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DOI: 10.1039/C6RA15339A
Fig. 3 FT-IR spectra of (a) GO, (b) GO/Fe3O4, (c) HybPOM and (d) GO@Fe3O4@HybPOM.
Peaks at 573-630 cm-1 in the IR spectra of GO/Fe3O4 and GO@Fe3O4@HybPOM are
attributed to Fe–O stretching vibration. The complete IR pattern of corresponding
trimetallo POM of [SiW9Cu3O37]10- with some variations in band frequencies and
intensities were observed in those of GO@Fe3O4@HybPOMin range of 1000-700 cm-
1. A small blue shift is observed in the frequencies of the band stretching due to
disappearance of anion-anion interactions. The vibration modes of the quinoidal
benzene rings appear at 1510 and 1620 cm-1 for GO@Fe3O4@HybPOM which
overlapped with the bending vibrations of amide bond of N–H.30 The C-N stretching
vibrations appear at 1200-1400 cm-1. The O-H and N-H stretching vibrations appear
as broad and strong bands at range of 3200-3650 cm-1.
The GO-Fe3O4 powder exhibit a total mass loss of 12.35 % at 100-800 ºC, which are
attributed to the removal of adsorbed water and the decomposition and vaporization
of various oxygen-containing functional groups at different positions on the surface
of the GO-Fe3O4 (Fig. 4a).

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DOI: 10.1039/C6RA15339A
Fig. 4 TG analysis of (a) GO@Fe3O4, (b) HybPOM and (c) GO@Fe3O4@HybPOM.
The thermogravimetric analysis (TGA) curve of the hybrid materials HybPOM show
two mass loss regions below 600°C (Fig. 4b). First, 30–200°C with 6.12 weight loss
which are assigned to lattice water loss equal to 12 (6.24 %) molecules for HybPOM.
Second, 200–550°C with approximately 18.19 weight loss for HybPOM is attributed
to loss of 6 (18.73 %) PPD molecules.
Results of TGA are confirmed well by CHN analysis of HybPOM. TGA of
GO@Fe3O4@HybPOM (Fig. 4c) nanocomposite exhibit two steps of mass loss at 25-
225 ºC and 225-800 ºC with 8.60 and 17.50% weight loss, respectively, which are
attributed to the release of water and PPD molecules along oxygen-containing
functional groups on GO-Fe3O4 surface..
This large weight loss indicates the loading of the polyoxometalate-based inorganic–
organic hybrid material on the GO-Fe3O4. From the TGA curves, it can be concluded
that GO@Fe3O4@HybPOM nanocomposites exhibit a higher thermal stability than

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HybPOM nanohybrides. This enhancement in the thermal stability is due to some
ionic interaction between graphene-Fe3O4 and the amine group of the aniline ring.
These may form a coordinate bond between Fe and N, as Fe can facilitate back
bonding between the d-orbital and NH2 group of the aniline ring.30
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DOI: 10.1039/C6RA15339A
Fig. 5 XRD spectra of (a) Na9H[β-XW9O34]·nH2O, (b) HybPOM, (c) GO@Fe3O4 (d)
GO@Fe3O4@HybPOM and (inset) GO.
The compounds of β-SiW9O3410- (Fig. 5a) and PDA are crystalline in the solid state,
while X-ray powder diffractions show that HybPOM is typical amorphous state,
implying that the hybrid materials have less-ordered structures (Fig. 5b). However, it
10-
can be observed that the XRD of HybPOM contain XRD pattern of both β-SiW9O34
and PPD. X-ray diffraction (XRD) measurements were also performed to obtain
crystalline structural information for the GO, GO-Fe3O4, GO@Fe3O4@HybPOM. The
broad diffraction peak around 18.72° corresponds to C (002) reflection of GO (Fig. 5
inset).30
At the GO-Fe3O4, the intense diffraction peaks indexed to (220), (311), (400), (422),
(511), (440), and (533) planes appearing at 2θ = 30.52°, 35.85°, 43.58°, 53.96°,

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57.43°, 63.16° and 74.65°,respectively, and the peak positions and relative intensities
match well with the standard XRD data for the cubic phase Fe3O4 with a face-centered
cubic (fcc) structure (JCPDS No. 19−629) (Fig. 5c).31 Disappearance of the reflection
plane at (002) and merging of the planes of Fe3O4 show the good interfacial interaction
between the planes. The XRD of GO@Fe3O4@HybPOM show corresponding peaks
of the GO-Fe3O4 and the amorphous XRD pattern of HybPOM as background (Fig.
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5d).
Fig. 6 SEM images of (a) HybPOM, (b) GO, (c) GO@Fe3O4 (d) GO@Fe3O4@HybPOM
The SEM images of HybPOM reveal the relatively uniform spherical nanometer
particles with a diameter of less than 80 nm (Fig. 6a). The SEM images of GO sheets,
GO-Fe3O4, and GO@Fe3O4@HybPOM composites are presented in Fig. 6b-c. The
images illustrate that the GO sheets shows a stacked and crumpled morphology (Fig.
6b).32 From the SEM image, it could be observed that the surface of GO sheets were
decorated tightly with Fe3O4 nanoparticles (Fig. 6c).

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Interestingly, Fe3O4 nanoparticles were only observed on the basal surface and the
edges of GO at very high coverage and without significant aggregation. This indicates
that Fe3O4 nanoparticles were mainly nucleated and grown on GO substrate and that
their free nucleation was effectively suppressed. The stacking of GO-Fe3O4 observed
in SEM images is probably due to strong magnetic interaction among Fe3O4
nanoparticles in neighboring layers. The SEM images of GO@Fe3O4@HybPOM
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show that these magnetic nanocomposites are uniform with a mean size of ~50 nm
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particles, but with some self-aggregation (Fig. 6d).
In order to shed more light on the elemental composition and preparation progress,
the chemical compositions of HybPOM and GO@Fe3O4@HybPOM were analyzed
by EDX. The EDX analysis of HybPOM hybrid material shows peaks of W, O, Si,
C, N, Cu (Fig. 7a).
Fig. 7 EDX spectra of (a) HybPOM, (b) GO@Fe3O4@HybPOM.
The magnetization of GO–Fe3O4 and GO@Fe3O4@HybPOM was measured at room
temperature, as shown in Fig. 8. The magnetic hysteresis loops are S-like curves. For
GO–Fe3O4 hybrid, the magnetic remanence was nearly zero (Fig. 8a). This indicated
that there was almost no remaining magnetization when the external magnetic field
was removed, suggesting that GO–Fe3O4 exhibit a superpara magnetic behavior.

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Fig. 8 Magnetization curves of (a) GO@Fe3O4, (b) GO@Fe3O4@HybPOM.
The specific saturation magnetization of GO–Fe3O4, is 49.31emu/g, which is smaller
than the reported value of bulk Fe3O4 of 92 emu/g.33 The specific saturation
magnetization of GO@Fe3O4@HybPOM is 17.94 emu/g (Fig. 8b). Decrease in
saturation magnetization observed for GO@Fe3O4@HybPOM could be attributed to
the increased mass and the loading polyoxometalate-based inorganic–organic hybrids.
Even with this reduction in the saturation magnetization, complete magnetic
separation of GO@Fe3O4@HybPOM was achieved in ˂10 s by placing a magnet near
the vessels containing the aqueous dispersion of the nanoparticles.
XPS analysis was used to gain further insights into chemical compositions of samples.
Fig. 9a depicts the XPS survey spectrum of GO@Fe3O4@HybPOM. As expected, W
4f, C 1s, N 1s, O 1s, Fe 2p and Cu 2p peaks were observed in the XPS survey spectrum.
The W 4f spectrum can be deconvoluted into doublets, as indicated in Fig. 9b. This
doublet consists of W 4f7/2 line at 35.2 eV and W 4f5/2 line at 37.2 eV, which are
assigned to the W in the W–O bond configuration and typically observed for the
W6+.34

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DOI: 10.1039/C6RA15339A
Fig. 9 XPS survey spectra of (a) GO@Fe3O4@HybPOM and high-resolution XPS spectra
of N 1s (inset), and Cu 2p (inset) (b)W 4f, (c) C 1s, (d) O 1s, (e) Fe 2p.
The peaks observed at 284.5 and 530.4 eV (Fig. 9c and d) can be assigned to the
binding energy of C 1s and O 1s, respectively. From the C1s XPS spectrum, different
peaks corresponding to C-C, C-N, C-O and C=O are observed at 284.5, 285.3, 286.0
and 286.8, respectively. The peak of the COOH at 287.8 eV almost disappeared upon
the amide formation with the amine groups of HybPOM. The binding energy appears
at 399-402 eV which could be attributed to the N1s protonated and nonprotonated N
atoms (Fig. 9a inset). The binding energy peaks at 711.8 and 725.1 eV (Fig. 9e) are
corresponding to Fe 2p3/2 and Fe 2p1/2, respectively, which are very close to the
literature values.35 The disappearance of charge transfer satellite of Fe 2p3/2 around
720 eV reveals the formation of mixed oxides of Fe2+ and Fe3+ such as Fe3O4. The
XPS spectra from 953 to 935 eV demonstrate the photoelectron spectrum of the Cu
2p. As shown in Fig. 9a (inset), there are two main Cu 2p XPS peaks at 933.2 and
953.1 eV, which could be due to the Cu2+ double peaks for Cu 2p3/2 and Cu 2p1/2,
respectively.36-38 The satellite peak at 941.6 eV located at higher binding energy than

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that of the main Cu 2p3/2 peak, is typically associated with copper in the bivalent
binding energy state.36-39
Catalytic studies
Catalytic application of nanohybrids of HybPOM and nanocomposites of
GO@Fe3O4@HybPOM for the Knoevenagel condensation
The Knoevenagel reaction is one of the most important reactions to form C-C bonds
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to the important olefin syntheses. The Knoevenagel adducts are available
DOI: 10.1039/C6RA15339A
intermediates for further transformations such as Diels–Alder and Michael
additions.40 Knoevenagel condensations of aldehydes and active methylene
compounds have been carried out in the presence of a base41 or Lewis acid.42 In this
study, the catalytic activity of HybPOM organic–inorganic polyoxometalates hybrids
were investigated in the Knoevenagel condensation reaction as novel, efficient and
heterogeneous catalysts under mild conditions. First, in order to optimize the
Knoevenagel condensation reaction conditions, the reaction was achieved with
benzaldehyde and malononitrile as model reaction (Table 1).

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As shown in Table 1, the amount of 0.007 g of HybPOM was found to be ideal for the
Knoevenagel condensations and the best results were obtained using PEG/water = 1:1
(PEG, polyethylene glycol) as solvent. A series of aromatic aldehydes carrying either
electron-donating or electron-withdrawing substitutions were subjected to the
optimized reaction conditions and the expected products were obtained in short time
periods and at high yields (Table 2).
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DOI: 10.1039/C6RA15339A
There are several advantages for supporting HybPOM on the GO-Fe3O4, such as,
easier recovery, improvement of efficiency and magnetic separation. Knoevenagel
condensation was carried out to investigative the catalytic activity of
GO@Fe3O4@HybPOM nanocomposites. As shown in Table 1, amount of 0.010 g of
GO@Fe3O4@HybPOM was found to be ideal for the Knoevenagel condensations and
the best results were obtained using PEG/water = 1:1 (PEG, polyethylene glycol) as
solvent.

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Like the above conditions, Knoevenagel condensation was probed by
GO@Fe3O4@HybPOM catalysts under the optimized reaction conditions (Table 2).
As shown in Table 1, the expected products were obtained in short time periods and
at high yields.
Catalytic application of nanohybrid of HybPOM and nanocomposite of
GO@Fe3O4@HybPOM for the synthesis of 2,3-dihydroquinazolin-4(1H)-one
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DOI: 10.1039/C6RA15339A
derivatives
2,3-Dihydroquinazolin-4(1H)-ones is an important class of heterocyclic compounds
influencing numerous cellular processes.43 These exhibit a wide range of biological
activities such as antitumor, antibiotic, antidefibrillatory, antipyretic, analgesic,
antihypertonic, diuretic,antihistamine, antidepressant, and vasodilating behavior.44
Several strategies for their synthesis were already developed: condensation of
anthranilamide with an aldehyde or ketone using p-toluenesulfonic acid as a catalyst,45
desulfurization of 2-thioxo-4(3
H
)-quinazolinones,46 reaction of isatoic anhydride with
Schiff-bases,47 one-step conversion of 2-nitrobenzamides to 2,3-dihydro-4(1
H)-
quinazolinones,48 and a one-pot three-component condensation of isatoic anhydride,
aldehydes and amines.49
The catalysts reported for the above stated one-pot procedure include inorganic
catalysts like aluminiumtris (dihydrogen phosphate),50 silica sulfuric acid,51 magnetic
Fe3O4 particles,52 reaction media like ionic liquid53 and Asymmetric Brønsted
acid.54Some of these methodologies involve strongly acidic conditions, toxic
catalysts, hazardous organic solvents and long reaction times. Thus, there is a need for
a non-acidic and novel catalyst that could overcome the above drawbacks.
After successfully synthesizing a series of benzylidenemalononitrile derivatives in
excellent yields, we also explored the use of this catalyst system for the synthesis of
2,3-dihydroquinazolin-4(1H)-ones from aldehyde derivatives and 2-aminobenzamide.

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The preliminary investigation was to screen the solvent and different amounts of
catalyst on the reaction of benzaldehyde with 2-aminobenzamide (Table 3). The
model reaction was carried out in the presence of different solvents, temperatures and
amounts of catalyst. The best results were obtained with 2-aminobenzamide (1 mmol)
and benzaldehyde (1 mmol) in the presence of catalyst HybPOM (0.005 g) and EtOH
(5 mL) as solvent under reflux condition (Table 3, entry 3).
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DOI: 10.1039/C6RA15339A
After optimizing the reaction conditions, the reaction of various aldehydes with 2-
aminobenzamide were tested. Results are summarized in Table 4. Synthesis of 2,3-
dihydroquinazolin-4(1 )-one derivatives was carried out to investigative catalytic
H
activity of GO@Fe3O4@HybPOMnanocomposite.
The model reaction was carried out in the presence of different solvents, various
temperatures and different amounts of catalyst. The best results were obtained with 2-
aminobenzamide (1mmol) and benzaldehyde (1 mmol) in the presence of catalyst
GO@Fe3O4@HybPOM(0.007 g) and EtOH (5 mL) as solvent under reflux conditions
(Table 3, entry 3). After optimizing the reaction conditions, the reaction of various
aldehydes with 2-aminobenzamide were tested. Results are summarized in Table 4.

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DOI: 10.1039/C6RA15339A

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DOI: 10.1039/C6RA15339A
Fig. 10 Reusability of HybPOM (A) and GO@Fe3O4@HybPOM (B) in the reaction
of benzaldehyde with malononitrile (columns a) and the reaction of 2-
aminobenzamide with benzaldehyde (columns b).
Catalysts recovery and reuse
Finally, the reusability of the nanohybrid and nanocomposite were investigated. Fig.
10 shows the yield of five consecutive cycles for the preparation of 2-
benzylidenemalononitrile (a) and 2-Phenyl-2,3-dihydroquinazolin-4(1
nanohybrid of HybPOM andGO@Fe3O4@HybPOM, respectiviely.
H)-one (b) by
After the reaction reached completion, the catalyst was recovered, washed with EtOAc
and then reused in the next run. The heterogeneous catalyst showed good recyclability
and can be reused for at least five times without significant loss of its catalytic activity.
The FT-IR spectrum showed no significant structural changes for catalysts after five
consecutive runs (Fig. 11). In order to determine whether the metal leaches out from the
solid catalyst during reaction, the hot filtration test was undertaken for the synthesis of 2-(3-
bromophenyl)-2,3-dihydoquinazolin-4(1H)-one from the reaction of 2-aminobenzamide
with 3-bromobenzaldehyde. The catalyst was separated by applying an external magnet when
the reaction had proceeded to nearly 50% completion, and the filtrate was allowed to react
further.

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DOI: 10.1039/C6RA15339A
Fig. 11 FT-IR spectra of (A) (a) recycled HybPOM for 5 times (b) HybPOM and (B) (a)
recycled GO@Fe3O4@HybPOM for 5 times (b) GO@Fe3O4@HybPOM.
The reaction monitoring showed that no further progress of the reaction is observed,
confirming that the metal does not leach from the nanocatalyst under hot conditions. The
metal Fe, W and Cu leaching from GO@Fe3O4@HybPOM were tested by ICP-MS. The
results showed that Fe, W and Cu contents of the GO@Fe3O4@HybPOM after
consecutive runs compared with those of the initial GO@Fe3O4@HybPOM were only
decreased by less than 1 %.
Conclusion
In summary, in this paper we have described 1) a simple and high yield synthesis of
new
functionalized
organic–inorganic
polyoxometalates
hybrids
of
H6Cu2[PPD]6[SiW9Cu3O37].12H2O (HybPOM
)
and 2) preparation of new
GO@Fe3O4@HybPOM nanocomposite by successfully supporting of HybPOM onto
graphene oxide decorated with Fe3O4 nanoparticles. HybPOM -functionalized

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graphene hybrid materials were synthesized by covalently bonding HybPOM onto
grapheme oxide via the amide formation and the chemical reaction between amine-
functionalized POM and oxygen-containing groups (e.g., epoxy and carboxyl groups)
in graphene oxide. The new organic–inorganic polyoxometalates hybrid and
nanocomposite were characterized by the elemental analyses, TGA, FT-IR, XPS,
XRD, SEM, EDX and AGFM. The results indicate that the size ranges of the
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nanocomposites are between 20-60 nm. The catalytic activity of new NPs was
DOI: 10.1039/C6RA15339A
investigated in the Knoevenagel condensation and synthesis of 2,3-
dihydroquinazolin-4(1 )-ones. The nano organic–inorganic hybrids and their
H
magnetically reusable nanocomposites were found as effective and easily recoverable
heterogeneous catalyst for a wide range of arylaldehydes. Therefore, the newly
developed hybrid materials are promising for a wide range of multifunctional
applications.
Acknowledgements
The authors would like to thank the University of Kurdistan Research Council for their
support of this work.
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