Synthesis, characterization and immobilization of a novel mononuclear vanadium (V) complex on modified magnetic nanoparticles as catalyst for epoxidation of allyl alcohols

Article abstract of DOI:10.1002/aoc.4168

The 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) undergoes hydrolysis in the presence of VO(SO₄) in an alkaline solution, affording mainly the bis(2-pyridyl carbonyl)amid) VO₂ complex, designated as [VO₂(bpca)]. Single-crystal X-ray crystallography revealed that the coordination of V in complex is a distorted square-pyramid coordinated with three nitrogen of bis(2-pyridyl carbonyl)amid) ligand and two binding oxygen atoms. The prepared complex which successfully supported on modified Fe₃O₄ nanoparticles using tetraethylorthosilicate (TEOS) and (3-aminopropyl)trimethoxysilane(APTMS)was designated as Fe₃O₄@SiO₂@APTMS@[VO₂(bpca)] complex (nanocatalyst). The complex and nanocatalyst were characterized by means of FT-IR, XRD, VSM, SEM and TEM. The catalytic activity of [VO₂(bpca)] complex and Fe₃O₄@SiO₂@APTMS@complex as catalysts 1 and 2 were evaluated by the epoxidation of geraniol, 3-methyl-2-buten-1-ol, trans-2-hexen-1-ol and 1-octen-3-ol with 70–98% conversions and 95–100% selectivities. Based on the obtained results, the heterogeneity and reusability of the catalyst seems promising. In addition, the in vitro antibacterial activity of [VO₂ (bpca)] complex have also been evaluated and compared to the activities of other vanadium complexes, tptz ligand and two standard antibacterial drugs, Nalidixic acid and Vancomycin.

Full text of DOI:10.1002/aoc.4168

Received: 2 August 2017
DOI: 10.1002/aoc.4168
Revised: 6 October 2017
Accepted: 8 October 2017
F U L L P A P E R
Synthesis, characterization and immobilization of a novel
mononuclear vanadium (V) complex on modified magnetic
nanoparticles as catalyst for epoxidation of allyl alcohols
Zahra Azarkamanzad1 | Faezeh Farzaneh1
Mohammad Azarkish3
| Mahboobeh Maghami1 | Jim Simpson2 |
1 Department of Chemistry, Faculty of
The 2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine (tptz) undergoes hydrolysis in the pres-
ence of VO(SO4) in an alkaline solution, affording mainly the bis(2‐pyridyl
carbonyl)amid) VO2 complex, designated as [VO2(bpca)]. Single‐crystal X‐ray
crystallography revealed that the coordination of V in complex is a distorted
square‐pyramid coordinated with three nitrogen of bis(2‐pyridyl carbonyl)
amid) ligand and two binding oxygen atoms. The prepared complex
which successfully supported on modified Fe3O4 nanoparticles using
tetraethylorthosilicate (TEOS) and (3‐aminopropyl)trimethoxysilane(APTMS)
was designated as Fe3O4@SiO2@APTMS@[VO2(bpca)] complex (nanocatalyst).
The complex and nanocatalyst were characterized by means of FT‐IR, XRD,
VSM, SEM and TEM. The catalytic activity of [VO2(bpca)] complex and
Fe3O4@SiO2@APTMS@complex as catalysts 1 and 2 were evaluated by the
epoxidation of geraniol, 3‐methyl‐2‐buten‐1‐ol, trans‐2‐hexen‐1‐ol and
1‐octen‐3‐ol with 70–98% conversions and 95–100% selectivities. Based on the
obtained results, the heterogeneity and reusability of the catalyst seems prom-
ising. In addition, the in vitro antibacterial activity of [VO2 (bpca)] complex
have also been evaluated and compared to the activities of other vanadium
complexes, tptz ligand and two standard antibacterial drugs, Nalidixic acid
and Vancomycin.
Physics & Chemistry, Alzahra University,
P.O. Box 1993891176, Vanak, Tehran, Iran
2 Department of Chemistry, University of
Otago, PO Box 56, Dunedin 9054, New
Zealand
3 Department of Chemistry, Payame Noor
University (PNU), 19395‐4697 Tehran,
Iran
Correspondence
Faezeh Farzaneh, Department of
Chemistry, Faculty of Physics &
Chemistry, Alzahra University, P.O. Box
1993891176, Vanak, Tehran, Iran.
Email: faezeh_farzaneh@yahoo.com;
farzaneh@alzahra.ac.ir
KEYWORDS
allylalcohols, bis (2‐pyridyl carbonyl)amide, epoxidation, nanomagnet, vanadium (V) complex
1 | INTRODUCTION
and anticancer activity,[2] it has driven a considerable
amount of research. Synthesis of vanadium complexes
Although there has been little concern on vanadium
complexes research up to 1980, focus were then directed
toward the synthesis of different types of vanadium
coordination compounds within the last two decades.
Due to the presence of vanadium in biological systems,
in the active centre of some enzymes (haloperoxidases
and nitrogenases) and its insulin enhancing action[1]
containing polypyridyl ligands have been carried out
[3,4]
and used as anti‐protozoa,
anti‐tumor,[4,5] antipara-
sitic,[5] DNA cleavage, insulin mimetic activity, oral
insulin substitutes for the treatment of diabetes and for
the treatment of obesity and hypertension.[6] Moreover,
due to the relevance to biochemical field and its medicinal
applications[7] and as a probe in protein studies,[8]
Appl Organometal Chem. 2017;e4168.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4168

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AZARKAMANZAD ET AL.
vanadium compounds are used in several industrial
fields such as homogeneous[9] and heterogeneous[10]
catalysts and battery fabrication.[11] Vanadium
complexes including simple vanadium (III, IV, and V)
oxide nanoparticles as heterogeneous catalyst for
epoxidation of allyl alcohols.
2 | EXPERIMENTAL
compounds such as VCl3,[12] VO(acac)2,[13] NaVO3
[14]
as well as vanadium complexes with polydentate ligands
such as salophene,[15] 3‐hydroxy‐4‐pyrone and
3‐hydroxy‐ 4‐pyridinone,[16] hydrazones,[17] Schiff
bases,[18] tris(pyrazolyl) ethanol,[19] pyrazine‐2‐carboxyl-
2.1 | Materials and methods
All materials were of commercial reagent grade and used
without further purification. FT‐IR spectra were recorded
on a Bruker Tensor 27 FT‐IR spectrometer using KBr
pellets over the range of 4,000–400 cm‐1. Elemental
analyses were performed on a Heraeus CHN‐O‐Rapid
elemental analyzer. The amount of vanadium and iron
in the Fe3O4@SiO2@APTMS@[VO2(bpca)] nanocatalyst
was determined by atomic absorption spectroscopy
(AAS) with a GBC flame spectrophotometer (1.48% V,
76.45% Fe). Magnetic susceptibility measurements were
carried out using a vibrating sample magnetometer
(VSM) (BHV‐55, Riken, Japan) in the magnetic field
range of ‐8000 to 8000 Oe at room temperature. Thermal
analysis measurements, TGA, were recorded on a
Shimadzu model 50 instrument using 20 mg of
[VO2(bpca)]. The X‐ray powder diffraction (XRD) data
were recorded on a Siefert XRD 3003 PTS diffractometer,
using Cu Kα1 radiation (k = 1.5406 Å). Scanning electron
microscopy (SEM) images were taken by KYKY‐EM3200‐
26 KV. Transmission electron microscopy (TEM) images
were taken by Zeiss‐EM10C‐100 KV. Epoxidation
products were analyzed by GC and GC‐Mass using
Agilent 6890 series with a FID detector, HP‐5, 5%
phenylmethylsiloxane capillary and Agilent 5973
network, mass selective detector, HP‐5 MS 6989 network
GC system, respectively.
[20]
[21]
ate,
bishydroxamic acid (BHA)
and bis (aryl)‐2‐
pyridylmethanol[22] have been used for the homogeneous
catalytic oxidation with H2O2, t‐BuOOH, cumene
hydroperoxide (CHP) and O2. An application of
oxovanadium (IV) compounds as oxidation catalysts
was first discovered by Sharpless in the regioselective
epoxidation of allylic alcohols.[23] Vanadium complexes
are promising homogeneous catalysts for the epoxidation
of allylic alcohols,[16] homoallylic alcohols[21] and
alkenes,[18a] oxidative decarboxylation,[15] oxidation of
sulfides[24] and oxidation of alkenes, alkanes and aro-
matic hydrocarbons,[17] Synthesis of epoxide is important
because it is widely used in the preparation of natural
products and biologically active substances.[25] Moreover,
epoxides are also used in synthetic organic chemistry and
industrial technology for production of various chemicals
including pharmaceuticals and agrochemicals. Several
vanadium (IV and V) complexes have been reported as
highly active, stereo‐ and/or regioselective catalysts in
the epoxidation of allylic alcohols, with moderate to high
activity.[26,27] In recent years, many reports appeared in
the literature regarding immobilization of transition
metal complexes onto solid supports including silica
gel, mesoporous silicas and clays due to advantages such
as easy separation and recycling of catalysts and products
purification.[27,28] Other type of heterogeneous catalytic
systems are nanomagnetic catalysts since catalyst can
easily be separated from the reaction medium using an
external magnetic field. Such simple processes also avoid
loss of catalyst activity and increases its reusability and
improve its recovery rate during separation process in
comparison to conventional filtration or centrifugation.
Additionally, since nanocatalyst provides large specific
surface area and high catalytic activity, better catalytic
properties is also expected.[29] It can be emphasized that
magnetic or nanomagnetic particles have been widely
applied as catalyst in many reactions such as
hydrogenation, Suzuki–Miyaura reaction, oxidation and
epoxidation reactions.[27,30]
2.2 | Synthesis bis(2‐pyridyl carbonyl)
amid) VO2 complex: [VO2(bpca)] complex 1
An aqueous solution (2 mL) of vanadyl sulfate hydrate
(1 mmol, 225.4 mg) was added dropwise to a solution
containing L‐Leucine (1 mmol, 131.2 mg), potassium
hydroxide (1 mmol, 56.1 mg) and salicylaldehyde (1 mmol,
0.11 mL) in 15 ml methanol in order to adjust the pH of
solution exactly at 7.5‐8. Then, a solution of 2,4,6‐
tris(2‐pyridyl)‐1,3,5‐triazine (tptz) (1 mmol, 312.3 mg) in
methanol (5 ml) was added dropwise and stirred for 2 h.
The resultant mixture was then filtered and the filtrate
was held at room temperature for several days until a pale
brown crystal was precipitated. It was then collected by
suction filtration on a fine frit, washed with ethanol and
diethyl ether, and air dried. For further purification, the
pale brown microcrystalline precipitate was recrystallized
by a 1:1:2:2 MeOH/CH2Cl2/CH3CN/toluene solution.
After 5 days, the shiny pale brown crystal of the complex
In this study, 2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine (tptz)
underwent hydrolysis in the presence of VO(SO4) in an
alkaline solution, affording mainly the bis(2‐pyridyl
carbonyl)amid)VO2 complex, designated as [VO2(bpca)]
complex followed by immobilization on modified iron

AZARKAMANZAD ET AL.
3 of 14
[VO2(bpca)] formed in room temperature was filtered and
designated as catalyst 1. The solid complex yield was 90%
(556 mg). Decomp. Point, 314 °C. Anal. Calc. for C12H8
N3O4V (MW = 309.15 g mol‐1): C, 34.99; H, 2.30; N,
12.89. Found: C, 34.75; H, 2.62; N, 12.94%. IR (KBr pellet,
cm‐1): 3078, 766 and 700 (C‐H aromatic and pyridyl
cyclic), 1723 (C = O), 1322 (C‐N), 1603 (C = N), 1652
(C = C), 953 (V = O). UV–Vis: λmax (nm) (ε, M‐1 L cm‐
1) (dichloromethane): 238 (20800), 274 (4800), 280 (4600).
2.5 | Preparation of magnetic
nanoparticles Fe3O4 (MNPs), silica coated
magnetite nanoparticles SCMNPs and
modified SCMNPs (Fe3O4@SiO2@APTMS)
These compounds were prepared according to the previ-
[39,40]
ously reported procedures
.
2.6 | Immobilization of [VO2 (bpca)]
complex onto (Fe3O4@SiO2@APTMS)
To a stirring solution of complex 1 (1 mmol, 309.15 mg)
in 20 ml ethanol, Fe3O4@SiO2@APTMS (1 g) was
added and the mixture heated at 90 °C for 12 h. The
solid was then magnetically separated, washed with
ethanol and dried at room temperature to afford
Fe3O4@SiO2@APTMS@complex as a brown solid and
designated as catalyst 2.
2.3 | X‐ray crystallography
2.3.1 | X‐ray crystal structure
determination
Brown plate‐like crystals of [VO2 (bpca)] (1) were grown
from a solution of the compound (1) in 1:1:2:2 MeOH/
CH2Cl2/CH3CN/Toluene. X‐ray measurements were
carried out on an Agilent Duo diffractometer using MoKα
radiation (λ = 0.71073 Å) with data collection, reduction
2.7 | Catalytic procedure
and
absorption
corrections
controlled
using
Catalytic experiments were carried out in a 10 mL glass
reaction flask fitted with a water condenser. In a typical
procedure, catalyst 2 (50 mg) was dissolved in 5 ml aceto-
nitrile. Then, allyl alcohol (10 mmol) and TBHP solution
70% in H2O (12 mmol, 1.6 ml) were added and the mix-
ture heated at reflux for 1 h. The reaction was monitored
at periodic time intervals using gas chromatography. The
epoxidation products were identified by comparison of
their retention times with those of the authentic samples.
At the end of the reaction, the catalyst was separated by
means of an external magnet, washed with acetonitrile,
diethyl ether and then air dried. The catalyst was reused
at least three times without a significant decrease in
catalytic selectivity.
CrysAlisPro[31] with data collected at 100(2) K. Data were
reduced and multi‐scan absorption corrections were
applied using CrysAlisPro.[31] The structure was solved
[32]
by direct methods using SHELXT
and refined by
full‐matrix least‐squares on F2 using SHELXL‐2014/7
and TITAN2000.[34] All non‐hydrogen atoms were refined
anisotropically and all hydrogen atoms bound to carbon
were placed in the calculated positions, and their thermal
parameters were refined isotropically with Ueq = 1.2
Ueq(C). The data were deposited in Cambridge
Crystallographic Data Center with deposition number
CCDC 966868. Details of the X‐ray measurements, The
molecular plot and packing diagram were drawn using
Mercury.[35] Additional metrical data were calculated
using PLATON[36] and tabular material was produced
using WINGX.[37] Details of the X‐ray measurements
and crystal data for complex is given in Table S1, selected
bond distances and angles in Table S2 and hydrogen
bonds are detailed in Table S3.
[33]
3 | RESULTS AND DISCUSSIONS
The 2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine (tptz) undrgoes
hydrolysis in the presence of VO(SO4) in an alkaline solu-
tion, affording mainly the bis(2‐pyridyl carbonyl)amid)
VO2 complex, designated as [VO2(bpca)] (Scheme 1)
2.4 | In vitro antibacterial assay
The in vitro antibacterial activity was investigated against
two Gram‐positive (Bacillus subtilis ATCC 6633 and
Staphylococcus aureus ATCC 6538) and two Gram‐
negative (Escherichia coli ATCC 35218 and Pseudomonas
aeruginosa ATCC 27853) bacteria. In orderto compare the
results, nalidixic acid (30 mg/disk) and vancomycin
(30 mg/disk) were used as standard antibacterial drugs.
The determination was carried out by the paper‐disk
3.1 | Description of [VO2 (bpca)] complex
structure
3.1.1 | Molecular and crystal structure
The molecular structure of dioxo(bis(2‐pyridyl carbonyl)
amid))vanadium(V), [VO2(bpca)], 1, is shown in
Figure 1. The molecule is almost planar with an rms
deviation of 0.0866 Å from a meanplane through the 17
non‐hydrogen atoms that comprise the bpca ligand. The
diffusion method [38]
.

4 of 14
AZARKAMANZAD ET AL.
However, a more precise description of the geometry
can be obtained by calculating the τ5 index.[41]
τ5 ¼ ðβ –αÞ=60
α and β are the two largest L—M—L angles for the
5‐coordinate complex. In this instance β is the angle N1
—V1—N2 = 151.28(8) see Table S2 and α is O2—V1—
N3 = 132.56(9). Hence τ = 0.31, closer to the value 0
required for a perfect square pyramidal structure, which
further supports the description of the coordination
geometry as a distorted square pyramid, Figure 2.
SCHEME 1 Preparation of [VO2(bpca)] complex 1 (catalyst 1)
from hydrolysis of 2,4,6‐tri(2‐pyridyl)‐1,3,5‐triazine and VO(SO4)
The Cambridge Structural Database (Version 5.38
November 2017)[42] reveals 26 individual complexes with
the bis(2‐pyridyl carbonyl)amido ligand in compounds
that contain only one amido ligand a single transition
metal atom. Interestingly these were exclusively Cu(II)
complexes. The simplest examples were nitrate salts
of diaqua‐(bis(2‐pyridyl carbonyl)amido)copper(II).[43]
Removing these restrictions showed 163 complexes with
the one or more such ligands and also widened the
spectrum of metals involved to include Mn, Re, Fe, Ru,
Co, Rh, Pd and Pt. However, a particularly notable result
of this search was that vanadium complexes were
conspicuous by their absence, in any oxidation state of
the metal. A further search shows that complexes
of the dioxovanadium(V) cation with an O2VN3
coordination sphere are not common, with only seven
examples found. The compound most similar to 1 is
(hydroxyisoamethyrinato)‐dioxo‐vanadium(V).[44] Other
close relatives are derivatives based on 2,2':6',2”‐
terpyridyl[45] with anionic counter ions.
The V1—N1 and V1—N2 distances, 2.079(2) and
2.0837(19) Å to the pyridyl N atoms in 1 are somewhat
shorter than the mean V—N distances of 2.105(8) to
the pyridyl rings of these unique 2,2':6',2”‐terpyridyl
complexes containing the dioxovanadium(V) cation.
The distance V1—N3 2.0655(19) Å to the deprotonated
central amide N atom is even shorter, which may impact
of the V—N distances to the outer pyridyl rings. The rel-
atively short V—N distances in this complex impose
additional strain on the remainder of the bis(2‐pyridyl
carbonyl)amido ligand. Hence the O—C—C, O—C—N
and C—C—N angles about the C7 and C8 atoms of the
carbonyl groups vary wildly from the ideal value of
120°, ranging from O(7)‐C(7)‐N(3) = 128.4(2) to N(3)‐
C(6)‐C(5) = 110.64(18), Table S2. Such strain was
originally implicated in the hydrolysis of 2‐4‐6‐tris(2‐
pyridyl)‐1,3,5‐triazine (tptz) and its pyrimidyl analogue
promoted by copper(II) by Lerner and Lippard in the
1970s.[46] Hydrolysis produced copper(II) complexes of
the bis(2‐pyridyl carbonyl)amido ligand and the
corresponding pyrimidyl derivative, in a reaction similar
FIGURE 1 The molecular structure of complex1 showing the
atom numbering, with ellipsoids drawn at the 50% probability level
V atom lies only 0.3106(9) Å from that plane. This planar-
ity is further exemplified by the fact that the outer pyridyl
rings of the ligand are inclined at 9.28(9)° to one another
and subtend angles of 2.28(8)° and 1.50(8)° respectively to
the adjacent five membered V1,N1,C5,C5,N3 and V1,N2,
C8,C7,N3 chelate rings. The central vanadium(V) atom
is 5‐coordinate binding the two oxo‐atoms and the three
nitrogen atoms of the deprotonated bpcaH ligand. The
coordination geometry is best described as highly
distorted square pyramidal with the V atom 0.531(1)Å
out of the best fit plane through N1,N2,N3,O2 in the
direction of O1, Figure 2.
FIGURE 2 The distorted square pyramidal coordination sphere
of complex 1

AZARKAMANZAD ET AL.
5 of 14
to the one described here for the preparation of 1.
Subsesquently
a number of other Cu(II) induced
hydrolysis reactions of tptz have been reported[47] and
it has been proposed that the hydrolysis occurs due to
nucleophilic attack on the triazine ring by water or
OH¯ ion following coordination of the tptz to the metal.
Steric strain in the resulting complex would facilitate
the hydrolysis process.[48]
In the crystal structure two discrete π…π stacking
interactions are found between the N1, C1…C5 (centroid
Cg3) and N2,C8…C12 (centroid Cg4) rings with Cg3…
Cg4 distances 3.5142(12) Å (symmetry operation 3/2‐x,‐
1/2 + y,1/2‐z) and 3.8026(12) Å (symmetry operation
1/2‐x,‐1/2 + y,1/2‐z) respectively. These contacts are
supported by C4—H4…O1 and C10—H10…O1 hydrogen
bonds, Table S3, with atom O1 acting as a bifurcated
acceptor, Figure 3, and stack the molecules in an offset
fashion along the a axis direction. These offset layers
extend along c as a result of four additional C— H…O
contacts, Table S3, generating a three dimensional
network, Figure 4.
FIGURE 5 FT‐IR spectra of (a) 2,4,6‐ tris(2‐pyridyl)‐1,3,5‐triazine
(tptz) and (b) [VO2 (bpca)] complex 1
bands at 1524, 1468 and 1402 cm‐1and an intense band
at 1367 cm‐1. Since the reported separation between
υ(C = N) and υ(C = C) is close to 20 cm‐1 for polypyridyl
compounds, therefore observation of these bands may be
due to either C = N and C = C vibrations of triazine
and polypyridyl rings. The observed vibrations are
consistent with those reported before [46b, 49]. The FT‐IR
spectrum of [VO2(bpca)] complex 1 shows two sharp
bands at 1723 and 1322 cm‐1 due to the C = O and C–N
stretching vibrations, respectively. The observation of
these two strong bands in complex but not in tptz
indicates that hydrolysis of tptz has occurred. The position
of the C = O and C‐N vibrations indicates that there is no
resonance between lone pair of nitrogen and C = O
groups [50]. The υ(C = N) and υ(C = C) bands of the pyr-
idyl rings of the coordinated bpca ligand in complex 1
appear at 1652 and 1603 cm‐1. Three bands displayed at
3078, 766 and 700 cm‐1 due to the υ(C–H) stretching and
bending mode of the aromatic rings and the υ(C–H)
modes of the pyridyl rings, respectively.[46b] The FT‐IR
spectrum of complex 1 in KBr matrix confirms the
presence of the V = O vibration band at 953 cm–1. The
broad, strong feature displayed at 936 cm–1 for ν (V = O)
could be assigned to the symmetric or asymmetric
stretching vibrations.[51] The obtained results suggests
the coordination of bis(2‐pyridylcarbony1) amido ligand
which is formed from hydrolysis of tptz ligand.
3.1.2 | FT‐IR spectra
The FT‐IR spectra of free 2,4,6‐ tris(2‐pyridyl)‐1,3,5‐
triazine (tptz) and [VO2(bpca)] complex 1 are shown in
Figure 5a and b, respectively. Free tptz displays three
FIGURE 3 π…π stacking in the crystal structure of complex 1
3.1.3 | UV spectra
The electronic absorption spectrum of complex 1 is
shown in Figure 6. The UV–Vis data of the [VO2 (bpca)]
complex 1 in dichloromethane is presented in the
experimental section. The vanadium(V) complex 1 in
CH2Cl2 exhibits three bands at 238, 274 and 280 nm.
The first band observed at 238 nm can be assigned to
FIGURE 4 Overall packing of complex 1, viewed along the a axis
direction

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AZARKAMANZAD ET AL.
3.2 | Characterization
Fe3O4@SiO2@APTMS@[VO2 (bpca)]
complex
MNPs were prepared by precipitation of iron (II) and iron
(III) ions in basic solution under nitrogen atmosphere.[40]
Subsequent coating with silica to forming Fe3O4@SiO2
core‐shell particles followed by modification with
aminopropyl trimethoxysilane (APTMS) afforded MNPs
designated as Fe3O4@SiO2@APTMS. Finally, immobiliza-
tion of complex 1 within Fe3O4@SiO2@APTMS resulted in
the formation of the desired product designated as
Fe3O4@SiO2@APTMS@complex (Scheme 2). The chemi-
cal analysis determination showed 1.48% V and 76.45% Fe.
The FT‐IR spectra of Fe3O4, Fe3O4@SiO2,
Fe3O4@SiO2@APTMS, complex 1, Fe3O4@SiO2@-
APTMS@Complex 1 before and after using as catalyst are
shown in Figure 8a‐f, respectively. Observation of a broad
band in the spectrum of Fe3O4 with relatively low intensity
centered at 3400 cm‐1 to 1600 cm‐1 should be attributed
either to Fe‐OH group surface, or stretching and bending
vibrations of the adsorbed water (Figure 8a). The
stretching vibration of Fe‐O also appears at 580 cm‐1. The
band appears at 1050 cm‐1 due to Si‐O stretching demon-
strates the presence of SiO2 components (Figure 8b).[40,52]
After functionalizing of silica coated magnetic
nanoparticles with APTMS, a new bands appeared at
2858‐2922 cm‐1 due to the N‐H and C‐H stretching
vibrations.[53] The FT‐IR spectrum of complex 1 and
FIGURE 6 Electronic spectra of complex 1 (5 × 10 ‐5 M in CH2Cl2
at 25 °C)
the aromatic ring π → π* transition. The other bands
displaying at 274 and 280 nm are due to n → π* type
electronic transitions.
3.1.4 | TGA/DTG curves
The TGA/DTG curves of [VO2(bpca)] complex 1 is shown
in Figure 7. The TGA curve shows two step weight loss at
300 °C and 400 °C together with exothermic peaks in the
DTG curve. The total weight loss of the sample is about
60%. The first weight loss of the sample from 280 to
300 °C is about 20% which is accompanied by a second
40% weight loss due to the decomposition of bpca ligand.
At 450 °C, the major phase is vanadium pentaoxide. The
crystalinity of the sample was also revealed from XRD
results as shown in Figure S1. This pattern shows the
formation of V2O5 (JCPS card no. 41‐1426) as the major
product.
Fe3O4@SiO2@APTMS@Complex
1
are shown in
Figure 8d and e, respectively. Upon immobilization of
vanadium complex on the modified nanoparticles, the
appearance of a peak at 960 cm‐1 due to the ν(V = O)
confirms the occurrence of complex immobilization. On
the other hand, the FT‐IR spectrum of [VO2(bpca)]
complex 1 shows a sharp band at 1723 cm‐1 due to the
C = O stretching vibration, The disappearance of C = O
vibration band after immobilization of the VO2 (bpca)
indicates the coordination of complex and formation of
SCHEME 2 Preparation steps of Fe3O4@SiO2@APTMS@complex 1
(catalyst 2). (tetraethyl orthosilicate (TEOS) and aminopropyl
trimethoxysilane (APTMS)
FIGURE 7 TGA/DTG curves of the complex 1 (catalyst 1)

AZARKAMANZAD ET AL.
7 of 14
FIGURE 9 Magnetization curves of (a) Fe3O4, (b) Fe3O4@SiO2,
(c) Fe3O4@SiO2@APTMS, (d)Fe3O4@SiO2@APTMS@complex 1
(catalyst 2) before and (e) after using as catalyst
saturation magnetization of about 62 emu/g. The silica
coated Fe3O4 magnetite nanoparticles also showed
superparamagnetic behavior with decreased saturation
magnetization to about 60.74 emu/g. After coating of
Fe3O4@SiO2 nanoparticles with aminosilane agents, the
superparamagnetic behavior of Fe3O4@SiO2@APTMS
was found to be about 59.17 emu/g. Immobilization of
complex 1 within the Fe3O4@SiO2@APTMS surface
exhibited a decrease in superparamagnetic property
of saturation magnetization to about 57.30 emu/g.
Recall that the superparamagnetic property of
Fe3O4@SiO2@APTMS@complex 1 prevents aggregation
and enables it to disperse rapidly when the magnetic field
is removed.[40,54]
The X‐ray diffraction pattern of (a) Fe3O4, (b)
Fe3O4@SiO2, (c) Fe3O4@SiO2@APTMS, (d) Fe3O4@-
SiO2@APTMS@complex 1 before and (e) after using as
catalyst are shown in Figure 10a‐e, respectively. As shown
in Figure 10a, the obtained Fe3O4 has highly crystalline
cubic spinel structure in agree with the standard Fe3O4
(cubic phase) XRD spectrum (JCPDSNo.19‐0629).[54,55]
The similar set of characteristic peaks observed for
Fe3O4@SiO2, Fe3O4@SiO2@APTMS, Fe3O4@SiO2@-
APTMS@complex 1 (Figure 10b‐e) indicate the stability
of the crystalline phase of silica coating and surface
functionalization.
FIGURE 8 The FT‐IR spectra of (a) Fe3O4, (b) Fe3O4@SiO2, (c)
Fe3O4@SiO2@APTMS, (d) complex 1 (catalyst 1), (e,f)
Fe3O4@SiO2@APTMS@Complex1 (catalyst 2) before and after
using as catalyst
new C = N band between bpca ligand C = O imide groups
and amine groups of the modified nanoparticles
(Scheme 2). The bands appear at 1684 and 1648 cm‐1 are
assigned to the stretching vibrations of imine and C = N
pyridyl rings of the coordinated bpca ligand, respectively
(Figure 8e).
To study the magnetic properties of magnetite nano-
particles, the hysteresis loops of magnetite and functional-
ized magnetite nanoparticles were investigated at room
temperature using vibrating sample magnetometry
(VSM). Magnetization curves of Fe3O4, Fe3O4@SiO2,
Fe3O4@SiO2@APTMS, Fe3O4@SiO2@APTMS@complex
1 before and after using as catalyst are shown in
Figure 9a‐e, respectively. The magnetization curve of
Fe3O4 exhibited superparamagnetic property with
The SEM, TEM image and EDX pattern of
Fe3O4@SiO2@APTMS@complex 1 presented in Figure 11
a‐c, show the core and shell of the prepared nanoparticles
with the average particle size of 30 nm. The EDX pattern
of Fe3O4@SiO2@APTMS@complex
1
confirms the
presence of vanadium complex on modified iron
nanomagnet (Figure 11b).

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AZARKAMANZAD ET AL.
FIGURE 10 XRD pattern for(a) Fe3O4, (b) Fe3O4@SiO2, (c)
Fe3O4@SiO2@APTMS (d) Fe3O4@SiO2@APTMS@complex 1
(catalyst 2) before using and (e) after using as catalyst
3.3 | Catalytic studies
To find the optimum reaction conditions, we initially
investigated the influence of factors such as oxidant, the
amount of catalyst and reaction time on the conversion
and selectivity of geraniol epoxidation. The epoxidation
of geraniol was carried out as the model reaction in the
presence of H2O2 and TBHP at room temperature in
acetonitrile as solvent. It was found that TBHP is a better
oxidizing agent due to higher geraniol conversion (H2O2
30% (12 mmol, 1.2 mL) used as oxidizing agent and only
26% of 2, 3‐epoxygeraniol was detected in the reaction
mixture). To optimize the amount of catalyst and the best
reaction time, epoxidation of geraniol was carried out
using 10, 30, 50 and 70 mg of catalyst within different times
(Table 1 and Figure 12). As indicated in Table 1, utilization
of 10 mg of catalyst showed the highest geraniol conversion
within 4 h (entry 1, Table 1). Interestingly, increasing the
amount of catalyst to 30 and 50 mg exhibited increase in
geraniol conversion during 4 h while keeping the
selectivity in 100% (entries 2 and 3, Table 1). On the other
hand, whereas an increase in the amount of catalyst to
70 mg increased the geraniol conversion, a concomitant
decrease in selectivity was observed (entry 4, Table 1). In
order to show the effect of V species in the epoxidation
reaction, the epoxidation of geraniol with TBHP was
investigated in the presence of Fe3O4@SiO2@APTMS,
and only 7% of 2, 3‐epoxygeraniol was detected in the
reaction mixture. As can be seen, the catalytic activity of
Fe3O4@SiO2@APTMS@complex 1 (catalyst 2) is more
than complex 1 (catalyst 1).
FIGURE 11 (a) Scanning electron microscopy (SEM), (b) EDX
and (c) transmission electron microscopy (TEM) images of
nanoparticles Fe3O4@SiO2@APTMS@complex 1 (catalyst 2)
catalyst 2 (Figure 13). As seen in Figure 13, epoxidation
reaction of geraniol in CH3CN, CCl4, CHCl3, n‐hexane,
CH2Cl2 and EtOH proceeded with 92%, 91%, 91%, 89%,
85% and 67% conversions, respectively. Compared to halo-
genated and n‐hexane solvents, CH3CN seemed to be
more suitable due to its modest toxicity. Among other
solvents CH3CN and CCl4 have the highest yield of epox-
idation product, this could be attributed to higher boiling
point of them in comparison to other.
A variety of solvents were also tested for geraniol
epoxidation using Fe3O4@SiO2@APTMS@complex 1 as
The reusability of Fe3O4@SiO2@APTMS@complex 1
as catalyst 2 was investigated in the epoxidation of

AZARKAMANZAD ET AL.
9 of 14
TABLE 1 Conversion and selectivity of geraniol with different amounts of the Fe3O4@SiO2@APTMS@complex 1 as catalyst 2 in different
reaction timesa
Conversion (selectivity)%
Amounts of catalyst (mg)
1 h
2 h
3 h
4 h
10
31 (100)
37 (100)
42 (100)
47 (100)
30
50
70
62 (100)
91 (100)
92 (100)
69 (100)
92 (100)
95 (99)
74 (100)
94 (100)
97 (95)
79 (100)
95 (100)
98 (95)b
aReaction conditions: 10, 30, 50 and 70 mg catalyst, 10 mmol geraniol, 12 mmol TBHP, 5 ml CH3CN.
bThe by product is 6,7‐epoxygeraniol.
cycles with slight decrease in activity from 92 % to the
88 % (Figure 14).
The powder XRD and the FT‐IR spectra of the catalyst
after 4 cycles showed that the overall structure of the
material remained intact after the catalytic experiments
(Figure 10e and Figure 8f), for fresh and recovered catalyst
materials also showed that the structure was maintained
after the reaction. So the Fe3O4@SiO2@APTMS@complex
1 (catalyst 2) is stable in these reaction conditions.
In the next step, 3‐methyl‐2‐buten‐1‐ol, trans‐2‐Hexen‐
1‐ol and 1‐Octen‐3‐ol were then examined for epoxidation
reactions using acetonitrile as solvent and TBHP as oxi-
dant in the presence of 20 mg [VO2 (bpca)] complex as
catalyst 1 and 50 mg of Fe3O4@SiO2@APTMS@complex
1 as catalyst 2 (Table 4) in different times of reaction
(Table 2, 3). The products were characterized by compari-
son of the GC and GC–Mass spectra. Hence, it could be
concluded that Fe3O4@SiO2@APTMS@complex 1 exhib-
ited high selectivity for catalyzing the epoxidation of allyl
alcohols. In comparison the catalytic activity of catalyst 1
as homogeneous and catalyst 2 as heterogeneous one, even
though the first one shows good activity toward the
corresponding products, but the stability and having
higher TON of second one should be considerable.
FIGURE 12 Conversion and selectivity of geraniol at different
times in the presence 50 mg of the Fe3O4@SiO2@APTMS@complex
1 (catalyst 2)
FIGURE 13 The effect of solvent on the conversion and
selectivity of geraniol using Fe3O4@SiO2@APTMS@complex 1
(catalyst 2)
geraniol with TBHP under the optimized reaction condi-
tions. At the end of reaction, the catalyst was separated
by external magnet from reaction mixture after comple-
tion of the first run, washed with acetonitrile and dried
before using in the next run. After using the recovered
catalyst with fresh starting materials, it was concluded
that the catalyst could be reused for four consecutive
FIGURE 14 The effect of recycling of Fe3O4@SiO2@APTMS‐
@complex 1 (catalyst 2) on epoxidation of geraniol, under
optimum condition

10 of 14
AZARKAMANZAD ET AL.
TABLE 2 Conversion and selectivity of trans‐2‐hexen‐1‐ol with
Fe3O4@SiO2@APTMS@complex 1 as catalyst 2 in different reaction
timesa
TABLE 4 Results obtained for epoxidation of different allyl alco-
hols in the presence of complex 1 (catalyst 1) and
Fe3O4@SiO2@APTMS@complex 1 (catalyst 2)
Entry Reaction time (h) Conversion (%) Selectivity (%)
Catalyst 1
Catalyst 2
Catalyst 1
Catalyst 2
1
2
3
4
5
6
7
1
2
20
27
31
75
89
94
92
100
100
100
100
100
100
100
1
3
4
100 (657)
92 (1 h)
100 (1 h)
100 (155)
6
2
8
10
aReaction conditions: catalyst 2: 50 mg, substrate: trans‐2‐hexen‐1‐ol
(10 mmol),TBHP (12 mmol), solvent (acetonitril, 5 mL, reflux at 80 °C).
98 (1 h)
98 (4 h)
94 (1 h)
94 (8 h)
100 (151)
100 (38)
100 (671)
100 (84)
3
4
TABLE 3 Conversion and selectivity of 1‐octen‐3‐ol with 50 mg
amount of the Fe3O4@SiO2@APTMS@complex 1 as catalyst 2 in
different times of reactiona
Entry Reaction time (h) Conversion (%) Selectivity (%)
70 (12 h)
54 (8 h)
100 (42)
100 (10)
1
2
3
4
5
6
7
8
9
1
2
0
0
0
0
aReaction conditions: catalyst 1, 20 mg, catalyst 2, 50 mg, substrate (allyl alco-
hols, 10 mmol),
4
45
50
54
59
70
75
100
100
100
100
100
100
100
100
TBHP (12 mmol), solvent (acetonitril, 5 ml, reflux at 80 °C).
bTOF is the mmol of product to mmol of vanadium present in catalyst
per hour.
6
8
10
12
14
24
aReaction conditions: catalyst 2: 50 mg, substrate1‐octen‐3‐ol, (10 mmol),
TBHP (12 mmol), solvent (acetonitril, 5 ml, reflux at 80 °C).
Homogeneous catalysts usually exhibit high activity but
have difficulty in separation, recovery and reuse. On the
contrary, heterogeneous catalysts benefit facile separation
and recycling but always suffer from inferior activity than
homogeneous counterparts in most catalytic processes.[56]
To have a better insight into the reaction mechanism,
epoxidation reaction of geraniol was carried out in the
presence of diphenylamine as a radical scavenger.[57]
The fact that no decreasing in the epoxide yield was
observed revealed that no radical intermediate is associ-
ated in the oxidation process. Therefore, the formation
of the epoxide seems to have occurred via the initial
coordination of both allylic alcohol and hydroperoxide
to the metal center followed by oxygen transfer from
peroxide to alcohol via a concerted process.[58]
SCHEME 3 Suggested mechanism of allyl alcohol epoxidation
with TBHP catalyzed by the V(V) complex 1
in coordination sphere of the vanadium complex
(Scheme 3, III). The Lewis acidity of the V center increases
the oxidizing power of the peroxo group and the allyl
alcohol is subsequently oxygenated by nucleophilic attack
to the electrophilic oxygen atom of the coordinated TBHP
peroxide with generation of IV.[59] Spectroscopic and com-
putational methods applied to vanadium dioxo and
oxodiperoxo complexes support a reaction mechanism
involving an activation state formed between the complex,
oxidant and allyl alcohol (Scheme 2, III).[27,59]
Subsequently, the epoxide is resulted with elimination of
tert‐butanol and regeneration of catalyst.
Based on the suggested mechanism (Scheme 3),[27,58,59]
after coordination of TBHP and allyl alcohol to vanadium
and formation of III, the next process involves the inter-
action between allyl alcohol and TBHP molecules present

AZARKAMANZAD ET AL.
11 of 14
TABLE 5 Comparison of our results with those of previously reported heterogeneous catalytic epoxidation of geraniol of some vanadium
complexes with TBHP
Entry
Catalyst
Conversion (%)
Selectivity (%)
TOF(h‐1)
Ref.
[27a]
1
Fe3O4@SiO2@APTMS@V‐MIL‐101
100
100
49
[27b]
[27c]
2
VOsalpr/SCMNPs
N,N'‐bis(3‐salicylidenaminopropyl)amine (salpr)
100
100
186
3
VO(Sal‐his)/al‐MCM‐41
99
99
505
N‐salicylidene‐L‐histidine (Sal‐his)
[27c]
[60]
[60]
[28]
4
5
6
7
VO/AlMCM41
27
77
97
98
81
422
92
68
‐
CMK‐3@ [VO(acac)2]
100
98
CMK‐3@APTES@ [VO(acac)2]with amine
[VO(acac)2]APTES@PCH
42
porous clay heterostructure (PCH)
[28]
8
9
[VO(acac)2]APTES@SBA‐15
34
92
88
‐
Current work
100
657
Comparison of our results with those of the previously
reported heterogeneous catalytic epoxidation of geraniol
of some vanadium complexes with TBHP is provided in
Table 5.
Vancomycin and the other vanadium complexes.
B. subtilis and S. aureus (as Gram‐positive bacteria) and
E. coli and P. aeruginosa (as Gram‐negative bacteria) are
microorganisms used in this work. As presented in (entry 8,
Table 6) and Figure 15, tptz exhibits moderate activity
against S. aureus, B. subtilis and P. aeruginosa with no
activity against E. coli. Compared to the ligand antibacte-
rial activities with those of corresponding complexes as
reported previously,[62] it is seen that complex exhibit more
inhibitory effects than the parent ligand. Such increased
3.4 | Antibacterial activities
The in vitro antibacterial activity of [VO2(bpca)] complex
was studied and compared with the activities of two
standard antibacterial drugs, viz, Nalidixic acid and
TABLE 6 Antibacterial activity data of tptz ligand and several of its complexes
Inhibition zone (mm)
Entry
Compound [ref.]
E. coli
P. aeruginosa
S. aureus
B. Subtilis
1
[VO2(bpca)] (1)
18
21
20
20
2
L2VOa (2) [61a]
VO2Lb (3) [61b]
18
20
_
_
20
20
7
15
19
6
3
_
c
4
[VOL1L2]SO4 (4) [61c]
5
d
5
[VO(PMFP‐EA)(Bipy)(H2O)]ClO4 (5) [61d]
[61e]
7
n.a
n.a
n.a
11
n.a.
n.a.
10
n.a
13
10
17
12
_
6
[VLCl] (6)
n.a
n.a
n.a.
13
24
8
7
[NH(CH2CH3)3][VO2(L2)]f (7) [61f]
_
8
Tptz (8)
10
23
22
9
Nalidixic acid (9)
10
Vancomycin (10)
n.a = no activity
a1‐((2, 4‐dimethylphenylimino)methyl)naphthalen‐2‐ol abbreviated as (HL).
b4, 4′‐Bis‐({2‐[(2‐hydroxy‐phenylimino)‐methyl]‐benzylidene}‐amino)‐biphenyl‐3,3′‐diol.
c1‐(1‐(pyridine‐2‐yl)ethylidene)thiosemicarbazide (L1) and.
1‐(1‐(2,4‐dihydroxyphenyl)ethylidene)thiosemicarbazide (L2)
d1‐phenyl‐3‐methyl‐4‐formyl‐2‐pyrazolin‐5one (PMFP).
e1,6‐bis(aminophenoxy)hexane and Salicylaldehyde.
f2‐amino‐3‐((E)‐(2‐hydroxy‐3‐methoxybenzylidene)amino)maleonitrile (H2L2).

12 of 14
AZARKAMANZAD ET AL.
pH 7.5‐8 designated as [VO2 (bpca)] Complex 1. The
molecular structure of complex 1 has been determined
by single‐crystal X‐ray crystallography.
This complex crystallizes in the Monoclinic space
group P 21/n, and the vanadium coordination is a
distorted square‐pyramid. Complex 1 immobilized on
the modified iron oxide nanomagnet and designated as
Fe3O4@SiO2@APTMS@Complex 1. Activity of complex
1 as catalyst 1 and Fe3O4@SiO2@APTMS@Complex 1 as
catalyst 2 as homogenous and heterogeneous catalyst
were investigated for epoxidation of allyl alcohols in
presence of TBHP. It was found that the TON number of
heterogeneous system is higher than homogenous one.
Easy preparation, mild reaction conditions, high yield,
easy of catalyst separation and recyclability of the solid
catalyst candidates catalyst 2 as a useful catalysis system
for epoxidation of allyl alcohols.
FIGURE 15 Difference between the antibacterial activities metal
complexes (1–7): (1) [VO2(bpca)] (2) L2VO, (3) VO2L, (4) [VOL1L2]
SO4, (5) [VO(PMFP‐EA)(Bipy)(H2O)]ClO4, (6) [VLCl], (7)
[NH(CH2CH3)3][VO2(L2)] and tptz ligand (8) in comparison with
standard antibacterial drugs (9, 10)
activity of the metal chelates may interpreted on the basis
of chelation theory[63] in which complexes act as more
powerful and potent bacteriostatic agents than the free
ligands, thus inhibiting the growth of bacteria.[64]
ACKNOWLEDGEMENTS
The financial support from Alzahra University is
gratefully acknowledged.
Generally, the permeability of the bacterial cell wall is
the necessity for the efficacy of the biocide compounds
against diverse microorganisms. As such, the lipid
membrane surrounding the cell favors the passage of only
lipid soluble materials. Therefore, liposolubility is the
dominant factor that controls the antimicrobial activity.
On chelation, the delocalization of electrons provided by
overlap of the ligand orbital and partial sharing of the
metal ion positive charge with donor groups increases
the complex lipophilicity.[65] This in turn enhances the
penetration of the complexes into lipid membranes
followed by deactivation of various cellular enzymes
which have vital roles on the various microorganism
metabolic pathways.[66] Results obtained in this work for
the antibacterial activity of [VO2(bpca)] (entry 1, Table 6)
has been compared with those of the previously reported
vanadium metal complex (entries 2‐7, Table 6) together
with Nalidixic acid and Vancomycin effects (entries 9‐10,
Table 6). It can be concluded that [VO2(bpca)] inhibits
all tested bacteria. Particularly significant is that whereas
the antibacterial activities of (VO2(bpca)) complex against
P. aeruginosa is significant (entry 1, Table 6), other
reported vanadium complexes(entries 2‐7, Table 6) and
standard drugs (entries 9‐10, Table 6) were found to be
no efficient in this case.
ORCID
Faezeh Farzaneh http://orcid.org/0000-0001-5651-8018
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How to cite this article: Azarkamanzad Z,
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