Metalation and DFT studies of metal organic frameworks UiO-66(Zr) with vanadium chloride as allyl alcohol epoxidation catalyst

Article abstract of DOI:10.1016/j.molstruc.2019.126940

UiO-66(Zr)-V as metal organic framework was prepared by metalation of the UiO-66(Zr) nodes with VCl₃. The characterization of the prepared catalyst was carried out using XRD, EDX, FT IR, BET, ICP, Raman, DRS, SEM and XPS techniques. The density functional theory (DFT) was used in order to find the most stable position of the vanadium of metallated UiO-66(Zr). It was found that UiO-66(Zr)-V has been generated via metalation of V(V) ions with two OH groups of Zr-based nodes. The XPS results confirmed DFT studies. The catalytic activity of UiO-66(Zr)-V for epoxidation of some allyl alcohols such as trans-2-hexene-1-ol, geraniol, 1-octene-3-ol and 3-methyl-2-buten-1-ol with 46–97% conversions and 100% selectivity is considerable.

Full text of DOI:10.1016/j.molstruc.2019.126940

Journal Pre-proof
Metalation and DFT studies of metal organic frameworks UiO-66(Zr) with vanadium
chloride as allyl alcohol epoxidation catalyst
Elham Geravand, Faezeh Farzaneh, Mina Ghiasi
PII:
S0022-2860(19)31031-2
DOI:
https://doi.org/10.1016/j.molstruc.2019.126940
MOLSTR 126940
Reference:
To appear in: Journal of Molecular Structure
Received Date: 3 June 2019
Revised Date: 22 July 2019
Accepted Date: 17 August 2019
Please cite this article as: E. Geravand, F. Farzaneh, M. Ghiasi, Metalation and DFT studies of metal
organic frameworks UiO-66(Zr) with vanadium chloride as allyl alcohol epoxidation catalyst, Journal of
Molecular Structure (2019), doi: https://doi.org/10.1016/j.molstruc.2019.126940.
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Graphical abstact:
Metalation and DFT studies of metal organic frameworks UiO-66(Zr) with
vanadium chloride as allyl alcohol epoxidation catalyst
Elham Geravand, Faezeh Farzaneh*, Mina Ghiasi
The metal organic framework UiO-66(Zr)-V was prepared by metalation of the UiO-66(Zr)
nodes with VCl3. Utilization the density functional theory (DFT) was used in order to find the
most stable position of the vanadium of metallated UiO-66(Zr). It was found that UiO-66(Zr)-V
has been generated via metalation of V(V) ions with two OH groups of Zr-based nodes. The
catalytic activity of UiO-66(Zr)-V on the epoxidation of allyl alcohol is considerable.

Title page
Metalation and DFT studies of metal organic frameworks UiO-66(Zr)
with vanadium chloride as allyl alcohol epoxidation catalyst
Elham Geravand, Faezeh Farzaneh*, Mina Ghiasi
Department of Chemistry, Faculty of Physics & Chemistry, Alzahra University, P.O.Box
1993891176, Vanak, Tehran, Iran
*Corresponding author to: Faezeh Farzaneh,
Tel.: +98-21-88258977; fax: +98-21-+98-21-88041344;
E-mail address: faezeh_farzaneh@yahoo.com, Farzaneh@alzahra.ac.ir
1

Metalation and DFT studies of metal organic frameworks UiO-66(Zr)
with vanadium chloride as allyl alcohol epoxidation catalyst
Elham Geravand, Faezeh Farzaneh*, Mina Ghiasi
Department of Chemistry, Faculty of Physics & Chemistry, Alzahra University, P.O.Box 1993891176, Vanak,
Tehran, Iran
Abstract
UiO-66(Zr)-V as metal organic framework was prepared by metalation of the UiO-66(Zr)
nodes with VCl3. The characterization of the prepared catalyst was carried out using XRD, EDX,
FT IR, BET, ICP, Raman, DRS, SEM and XPS techniques. The density functional theory (DFT)
was used in order to find the most stable position of the vanadium of metallated UiO-66(Zr). It
was found that UiO-66(Zr)-V has been generated via metalation of V(V) ions with two OH
groups of Zr-based nodes. The XPS results confirmed DFT studies. The catalytic activity of
UiO-66(Zr)-V for epoxidation of some allyl alcohols such as trans-2-hexene-1-ol, geraniol, 1-
octene-3-ol and 3-methyl-2-buten-1-ol with 46–97% conversions and 100% selectivity is
considerable.
Keywords: Metal organic frameworks, UiO-66(Zr), Vanadium chloride , allyl alcohols, epoxidation,
DFT calculation
____________________________________________________________
*Corresponding author to: Faezeh Farzaneh,
Tel.: +98-21-88258977; fax: +98-21-+98-21-88041344;
E-mail address: faezeh_farzaneh@yahoo.com, Farzaneh@alzahra.ac.ir
2

1. Introduction
Inorganic organic hybrid materials include coordination polymers or porous coordination
polymers which is designated as metal organic frameworks (MOFs). They are obtained by a
combination of metal ions and organic linkers as bridging ligands. Since the synthesis MOF
reported by Yaghi and coworkers, more than 70000 MOF have ben synthesized [1-4] . Due to
their tailorable porosity and higher specific surface. MOFs have been used in various
applications such as separation, gas adsorption [5], sensor [6], drug delivery [7], optical
luminescence [6] ion exchange [8] and catalysis [6, 9]. They have also been used as acidic
and basic catalysts in a variety of organic transformation reactions. Compared to zeolites and
other porous materials with a rather high catalytic sites density, MOFs with more available
catalytic sites in contact with reacting substances are considerable [10, 11]. Amongst which,
zirconium-based MOFs of the UiO-66 family are reported to have exceptional high thermal,
chemical and mechanical stability [11, 12]. UiO-66 with Zr6O4(OH)4 octahedral cluster are
linked to 12 carboxylates of terephthalate ligands each in three dimensions to form highly
porous network [12-14].
Post synthetic modification methods [13] such as modification of surface, linker exchange,
metalation and metal exchange have been carried out on many MOFs since their nodes [15]
and organic linker sites [16] can be used as support sites.
It is known that missing linkers or ligand defects create accessible Zr-sites in the UiO-66(Zr)
framework. In this regard, several experimental techniques have been developed in order to
control the amount of open Zr-sites within the UiO-66 material [15]. The stability of the
modified UiO-66(Zr) in contact with oxidants such as hydrogen peroxide or TBHP makes it
3

attractive to be used as oxidation catalyst [15-18]. Recall that epoxidation of allyl alcohols has
been the subject of growing interest in the production of chemicals for both industry and
academic area because epoxides are widely used as intermediate chemicals in the production
of valuable organic and polymer products [19, 20]. Moreover, epoxides have also been
applied as precursors for making fine chemicals [21, 22]. Traditionally, transition metal
complexes have been used as oxidation catalysts for epoxidation reactions [20]. Example
includes vanadium complexes which have been used as catalyst for the epoxidation of alkenes
in general and allylic alcohols in particular [19, 23-24]. V-containing MOFs have also been
used successfully for some oxidation type reactions [15, 25-26].
In this study, UiO-66(Zr)-V was initially prepared by immobilization of VCl3 on UiO-
66(Zr) and used as heterogeneous catalyst for epoxidation of allyl alcohols. Theoretical study
using DFT method was also carried out in order to find the most stable position of V(V) ions
within MOF.
2. Experimental section
Materials and characterization techniques are reported in supplementary section.
2.1. synthesis
2.1.1. Synthesis of UiO-66(Zr)
UiO-66(Zr) was prepared according to the reported procedure [27] with some modification.
See supplementary.
2.1.2. Synthesis of UiO-66(Zr)-V
4

0.125g (0.8 mmol) VCl3 was added to a solution of UiO-66(Zr) (0.086g in 10 mL DMF) and
the mixture was then kept at 80 °C for 5 days. The green precipitate was centrifuged, washed
with fresh DMF and kept in methanol for 24 h. This procedure was repeated three times. The
yellowish green solid was subsequently centrifuged, washed with methanol and dried in a
vacuum oven at 1000 C for 24 h.
2.2. Catalytic procedure
In a typical procedure, substrate (10 mmol) and TBHP (12 mmol) were added to the desired
amount of catalyst in acetonitrile (5 mL) and the mixture heated at reflux for the appropriate
time. Upon completion, the catalyst was collected by filtration on a fine frit, washed with
acetonitrile and then dried in an oven. The catalyst was reused at least three times without a
significant decrease in catalytic activity or selectivity. The products were identified with GC
and GC-Mass techniques.
2.3. Computational Scheme
The energy and structural details of all studied compounds including [Zr6O4(OH)4] clusters
and the complexes between vanadium and [Zr6O4(OH)4] molecule from different directions
have been evaluated using the density functional theory (DFT) [28] without imposing any
symmetry constrains. The B3LYP method [29] has been used for the close shell systems.
The calculations were performed with standard 6-31+G* basis set. In the following, some
single point calculations using B3LYP/6311+G** to confirm the B3LYP/631+G* predicted
5

results have been performed. It is noticeable that DFT methods, are suitable methods for
calculations of compounds involving metals. The most impressive advantage of density
functional methods is to increase the precision of computational without increasing of
computing time.
The frequency calculations have been performed to confirm that an optimized structure refers
to local minimum without any imaginary frequencies. Additionally, thermochemistry
information including enthalpies and Gibbs energies were evaluated from the frequency
calculations at STP conditions. All calculated enthalpies have been corrected with consideration
of zero-point energy (ZPE). The solvent effects were investigated using polarized continuum
(overlapping spheres) model (PCM) of Tomasi and coworkers [30] at the same level of
calculations. All calculations were performed using the Gaussian 2003 [31] software.
3. Results and discussion
Initially, UiO-66(Zr) was prepared as reported before [27]. Subsequently, vanadium chloride
immobilized on UiO-66(Zr). The obtained vanadium-MOF with high stability, could be a good
candidate as support for many organic transformation reactions.
3.1. Characterization
3.1.1. XRD Patterns
6

The XRD patterns of the prepared UiO-66(Zr) and UiO-66 (Zr)-V are shown in Fig. 1a-b,
respectively. Particularly significant is the consistency due to the same crystalline structure
since the crystalinity of UiO-66(Zr) did not change after immobilization of vanadium
chloride, [12, 15, 32-36]. Observation of a slight reduction in the XRD pattern of peak
intensities of the immobilized vanadium on MOF may be due to the slight change in the
regular structure of MOF. Therefore, it seems that not only the framework of UiO-66 (Zr)
has not been collapsed during the formation of UiO-66 (Zr)-V, but also the crystalline
structure of the generated MOF remained intact in the metalation process.
3.1.2. SEM and EDX
The morphology of UiO-66(Zr) and UiO-66(Zr)-V determine by SEM revealed the
spherical agglomerations [37] of particles in the size of 60-90 nm (Figure S1a,b). On the
other hand , comparison of the EDX confirmed the presence of V and Cl atoms on the
immobilized UiO-66(Zr) (Fig. 2a, b).
3.1.3. FT IR Spectra
The FTIR spectra of UiO-66(Zr) and UiO-66(Zr)-V are shown in Fig. 3a, b, respectively.
It was found that all of UiO-66(Zr) framework bands are consistent with those reported in
the literature [32, 33] and remained unchanged after deposition of VCl3 (Fig. 3b).
3.1.4. TGA analysis
7

The UiO-66(Zr) and UiO-66(Zr)-V were examined by thermal gravimetric analysis (TGA)
to confirm their thermal and structural identities. The TGA of UiO-66(Zr) exhibited three
major weight loss regions (Fig. 4a). The first and the second were attributed to the departure
0
of methanol, and DMF at 28 and 393 C (18% weight loss), respectively. Whereas removal
0
of methanol was occurred between 25 to 100 0C, the DMF was lost between 100 to 200 C.
0
The third weight loss region occurred around 400 to 592 C (38% weight loss) due to the
BDC linkers degradation [38].
UiO-66(Zr)-V catalyst showed thermal stabilities slightly less than that of UiO-66 with
0
significant decomposition temperature of approximately 160 to 500 C framework due to
BDC linkers (33% weight loss). Finally, a small weight loss (4% ) at 501 0C was attributed to
the oxidation of the vanadium (Fig. 4b) [39].
By comparison of the TGA of UiO-66 and V-UiO66 as well as the reported articles [15], the
difference in the thermal stability should be due to the metalation of OH linkers of UiO-66 with
vanadium compounds and changing the composition of MOF linkers. Recall that any changes in
guest molecule or solvent or coordination of linkers affect the TGA diagrams [15].
3.1. 5. Raman spectra
The Raman spectra of UiO-66(Zr) and UiO-66(Zr)-V are shown in Fig. 5 a, b, respectively.
It has been shown that the −OH groups on the node of the Zr-based MOFs is metallated with
vanadium (V) ions [17].
8

The Raman spectra of UiO-66(Zr)-V differs with that of UiO-66(Zr) in two bands which
appear at 1015 and 1242 cm-1 attributed to V-O-Zr vibrations [15]. The low intensities of
these bands are either due to the low percent of vanadium or low density of metalation.
3.1.6. N2 adsorption desorption
N2 adsorption-desorption isotherms of UiO-66(Zr) and UiO-66(Zr)-V and the obtained related
parameters are presented in Fig. 6 and Table 1, respectively. In this study, the adsorption isotherm
of UiO-66 is the same as reported previously [40- 43]. As seen in this Table, the surface area was
decreased from 1063.19 to the 1019.5 (m2g-1). This decrease should be due to the immobilization
of vanadium chloride on the surface of UiO-66.The mean pore diameter and total pore volume of
UiO-66 (Zr) [33] are observed with rather no change after incorporation of V(V) ions into the SBU
clusters. Therefore, the average crystal structure is nearly maintained upon incorporation of V(V)
ions (Table 1). Obviously, low decreases in specific surface area of UiO-66(Zr)-V are observed
after incorporate of V(V) ions on the UiO-66(Zr) [12] (Table 1). This observation may be due to
the fact that the −OH groups on the Zr node of UiO-66(Zr) have also been metallated with V(V)
ions. This trend was also observed in the Raman results, accordingly.
3.1. 6. XPS
For further analyses of the UiO-66(Zr)-V, chemical status and surface chemical
composition. XPS spectra were used as shown in Fig. 7a. The survey scan of UiO-66(Zr)-V
indicated the presence of V, Cl, Zr, O and C elements. Fig.7b shows that the binding energies
9

of Zr 3d5/2 and Zr 3d3/2 are 182.87 eV and 185.22 eV, respectively. Based on the observed
binding energies, the existence of Zr IV species in the zirconium-oxo cluster is concluded [37,
44]. On the other hand, the binding energies of V2p3/2 and V2p1/2 were found to be 517.68 and
525.01 eV [45], respectively (Fig. 7c). A binding energy of 517.68 eV indicates the presence
of V(V) species in the UiO-66(Zr)-V [15].
The XPS spectra of O, Zr and V were also measured in order to confirm the existence of a
linkage between UiO-66(Zr)-V and VCl3 molecules. Moreover, deconvolution of binding
energy signal of O1s into two peaks observed at 531.96 eV and 530.46 eV by Gaussian fitting
clearly indicates the presence of O–Zr and O–V bonds in the UiO-66(Zr)-V (Fig. 7d). The
presence of chloride was also confirmed by the binding energy peak of Cl2p at 199.48 eV
(Fig. 7e) [46].
Based on the ICP analysis of UiO-66(Zr), the amount of Zr ions was found to be 28.45%.
Moreovere, the amount of Zr and V(V) ions in UiO-66(Zr)-V were determined as 27.94% and
5.76%, respectively. It can be concluded that the Zr amount in UiO-66(Zr)-V after metalation
has not nearly changed (Table 1).
3.1.8. UV spectra
The UV-visible diffuse-reflectance spectrum (DRS) of the UiO-66(Zr), attributed to the
adsorption of Zr–O oxoclusters [37] is shown in Figure S2a. The DRS spectrum of UiO-
66(Zr)-V also shows two main absorption peaks at 250 to 400 nm and another extra shoulder
around 300 to 400 nm due to the VV species (Figure S2 b) [15]. As seen in Figure S2 b, the
UV-vis absorption edges of the UiO-66(Zr)-V shifted to longer wavelengths in comparison to
10

that of UiO-66(Zr) upon the incorporation of vanadium chloride into the UiO-66. The
absorption peaks observed in the near-visible and the visible regions in the UV-visible
spectrum of UiO-66(Zr)-V are mainly attributed to the ligand-to-metal charge transfer [47-
48].
The indirect band gap (Eg) values of UiO-66(Zr) and UiO-66(Zr)-V were calculated by
means of the UV-vis absorption data using the Tauc equation [αhv =A (hv-Eg)2] [49- 50].
Based on the obtained results, it was found that the grafting of vanadium specious decreased
the band gap of UiO66 (Zr) from 3.9 to 3.is due to the ligand to metal charge transfer (Figure
S3).
3.2. Computational studies
3.21. Geometry optimization of [Zr6O4(OH)4] cluster
The model system has been used for [Zr6O4(OH)4] cluster from Uio-66 is constructed using the
crystallographic data available in literature [51]. The Comparison between X-ray crystallography
data and the optimized geometry of [Zr6O4(OH)4] cluster are presented in Fig. 8a,b respectively.
The optimized structure of cluster of [Zr6O4(OH)4], at B3LYP/6-31G* level without any
symmetry constrains is shown in Fig. 8b. The average bond distance between Zr and O atom is
2.28Å that is in good agreement with X-ray crystallography data, 2.26 Å. A comparison between
X-ray [52] data and theoretical results shows that the standard deviation of bond distances, for
the B3LYP/6-31G* is about 0.13 (Table 2).
3.2.2. Interaction between vanadium (V) and [Zr6O4(OH)4] clusters
11

In order to investigate the position of vanadium on UiO-66 followed to find the most stable
position of them, the proposed structures were optimized at B3LYP/6-311++G** level. In the
previous reports [15, 17, 51], it was shown that the UiO-66 has missing linkers due to
coordination to water and solvent molecules. Huong Giang and co-workers demonstrated that VV
IV
and Ti
can be directly incorporated onto the hexa zirconium oxo hydroxo [Zr6O4(OH)4]
clusters of UiO-66 by reacting with the OH groups especially those that arise from the missing
linkers. In the other hand, they indicated five complexes could be formed from connection of
[Zr6O4(OH)4] clusters with vanadium (V) [15, 17]. Besides, they believed that this method of
connection between OH groups of UiO-66 and ions could be used for other metal ions. Based on
the above mentioned results, in the present research, the five different complexes derived from
three clusters linkages of UiO-66(Fig. 9) designated as Com I, Com II, Com III, Com IV and
Com V were studied with (DFT) theory in order to calculate the formation of complexes from
different positions and investigate on the stability of five proposed complexes by determination
of geometrical details and energetic state of the most thermodynamically stable complex.
As seen in Fig. 9, The [Zr6O4(OH)4] cluster as A, B, C have bridging OH groups on the node
of UiO-66. When the solvent molecules coordinate to sites of the nodes of [Zr6O4(OH)4] cluster
(A), the [Zr6O4(OH)4] cluster (A) convert to the [Zr6O4(OH)4] cluster (B and C) with missing
linkers. In the [Zr6O4(OH)4] cluster (B and C), OH groups present at the missing-linker sites of
the nodes and could be connected to vanadium ions and formed Com I, Com II, Com III, Com
IV and Com V (Figure 9).
The interaction between [Zr6O4(OH)4] cluster and vanadium in the optimized structures was
analyzed. The complexation energy (∆Ecom) of five possible complexes were calculated using the
equation 1, then the obtained results are given in Table 3.
12

∆Ecom = E opt [Zr6O4(OH)4]-V – (E opt [Zr6O4(OH)4] + Eopt V
)
(1)
The complexation energy was estimated as the difference in energies of isolated [Zr6O4(OH)4]
cluster and vanadium (V) ion at their optimized structure, and optimized complex, [Zr6O4(OH)4]-
V.
All calculated thermodynamic functions for the predicted complexes, such as enthalpies
(∆Hcom), Gibbs free energies (∆Gcom) and entropies (∆Scom) are evaluated in the solvents for the
most stable complex, Table 3. As the theoretical results indicate the negative ∆Ecom value for all
possible complexes exception of complexes (V) shows the tendency of vanadium ion to interact
with the [Zr6O4(OH)4] cluster. As seen in Table 3 and Fig. 10, the stability order of complex of
[Zr6O4(OH)4]-V is Com(I)˃ Com(II)˃ Com(III)˃ Com (IV)˃ Com(V). To confirm the
calculated results and in order to obtain more trusty relative energies the single point calculations
at B3LYP/6-311++G** level on different complexes have been done and the same trend have
been seen.
Generally, the Gibbs free energy gives the preferential tendency to chemical processes. From the
analysis of presented results in Table 3 the following conclusions can be concluded: 1) the
complexation of the vanadium from complex (I) in solvent media is more favorable
thermodynamically than the other complexes. Details of selected bond distances and bond angles
for complex (I) as the most stable complex are given in Table 4, respectively.; 2) The predicted
complexation enthalpy values for all possible complexes exception of complexes (V) indicated
the exothermic interaction between vanadium and [Zr6O4(OH)4] cluster. The energy level of
proposed structures with V are shown in Fig. 10. It should be mentioned the Comp I has been
chosen as the most stable one. The good agreement between theoretical and experimental results
confirm the predicted results.
13

3. 3. Catalytic study
In order to investigate the catalytic activity of UiO-66(Zr)-V and UiO-66(Zr) for the
epoxidation of allyl alcohols with TBHP, trans-2-hexen-1-ol was used as the model substrate.
The prepared UiO-66 did not show significant catalytic activity perhaps due to the presence
of ZrIV in MOF lattice. This result is consistent with those reported before for the low activity
of UiO-66 for oxidation type reactions [16]. It was interesting that incorporation of V(V) ions
into the UiO-66(Zr) designated as UiO-66(Zr)-V increased the catalytic activity of UiO-
66(Zr)-V. Various reaction parameters such as the amount of catalyst, reaction time and
solvent were evaluated in order to optimize reaction condition.
Initially, the effect of the catalyst amount on the epoxidation of trans-2-hexene-1-ol was
carried out using 10, 30 and 50 mg catalyst within different times in CH3CN under reflux
condition (Table 5). Therefore, the best catalytic activity was obtained using 30 mg of catalyst
within 9 h (Table 5).
To study the effect of solvent on the reaction, epoxidation, of trans-2-hexene-1-ol was
carried out within 9 h in either protic or aprotic solvents using 30 mg of catalyst. The
obtained results as shown in Fig. 11, indicate that the substrate conversions are higher in
aprotic solvents including acetonitrile, dichloromethane, n-hexane and chloroform in
comparison to those protic solvents such as methanol and ethanol [52] [Fig. 11]. Therefore,
the order of solvent effect of CHCl3 < n-hexane ~ CH2Cl2 < CH3CN is concluded.
In the next step, epoxidation of geraniol, 1-octene-3-ol and 3-methyl-2-buten-1-ol were
carried out using CH3CN as solvent with 30 mg of catalyst within 1 to 11 h (Table 6, Fig. 12).
We have included the epoxidation result of trans-2-hexene-1-ol in Table 6 in order to make
14

the comparison with other allyl alcohols more convenient. As indicated in Table 6, the four
allyl alcohols used in this research afford the corresponding epoxides with 100% selectivities.
Finally, the reusability of UiO-66(Zr)-V as catalyst was investigated in the epoxidation of
trans-2-hexen-1ol. For this, the catalyst of the first run was separated from reaction after
completion by centrifuge, washed with acetonitrile and dried before using in the next run. It was
found that the catalyst could be reused for three consecutive cycles although a slight decrease in
the activity was observed in the third cycle (Fig. 13). Study of the XRD patterns of UiO-66(Zr)-
V before and UiO-66(Zr)-V after reaction showed that no change in the structure of UiO-
66(Zr)-V catalyst was observed. The XRD patterns of the second and third runs were similar
accordingly.
In order to have insight into the reaction mechanism, diphenylamine as a radical
scavenger [53] was used in the epoxidation of trans-2-hexen-1-ol. Observation of no
inhibition in the epoxidation conversion supports the operation of a concerted oxygen
transfer from the oxidant to allyl alcohol substrate. As such, the initial coordination of both
allylic alcohol and TBHP to the metal center is followed by oxygen transfer from peroxide
to double bond of alcohol via a simultaneous process [19, 24, 25, 54, 55]. Recall that
epoxidation reaction is slower in protic solvent since it retards the nucleophilic attack of
TBHP to the metal center due to hydrogen bonding. On the other hand, the polarity of
aprotic solvent should not be a determining factor in the epoxidation since
concerted reaction rates tend not to depend on solvent polarity [56]. As such, a combination
of boiling point as well as dielectric constant consistent with the solvent trend exhibited in
Figure 11 might be operating.
4. Conclusion
15

In summary, UiO-66(Zr)-V was prepared by metalation of the UiO-66(Zr) using VCl3. The
presence of V(V) ions as active site in MOF was proved by means of XPS and ICP. Theoretical
calculations were also performed using DFT to study the molecular structure of metalated UiO-
66(Zr) with the most stable position of vanadium. In fact, the PXRD patterns of UiO-66(Zr) and
UiO-66(Zr)-V have consistency due to the same crystalline structure. Actually, after
immobilization of vanadium chloride, the crystalinity did not changed. Compared to the
reported articles, the synthesized UiO-66 (Zr) using HCl as modulator contains significant
amount of missing-linker defects. In this work, the presence of vanadium metalation via the OH
group to UiO-66(Zr) was evidenced. Support for such binding comes from Raman spectrum
which shows the presence of V-O-Zr vibration. The ICP as well as XPS results confirm the
presence of V(V) in the UiO-66(Zr)-V (V). Therefore, the coordination of V(V) to two oxygens
of OH groups was concluded.
Finally, successful epoxidation of four allyl alcohols in moderate to high conversion yields
approved the catalytic activity of the prepared MOF. The heterogeneous catalytic activity of the
UiO-66(Zr)-V together with stability and reusability for three epoxidation runs with 100%
selectivities is promising and its application in the academic area as well as industry is
recommended.
Acknowledgement
The financial support from the Alzahra University is gratefully acknowledged.
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16

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Figure Captions:
Fig. 1. The XRD spectra of (a) UiO-66(Zr) and (b) UiO-66(Zr)-V c) UiO-66(Zr)-V after
reaction.
Fig. 2. EDS image of a) UiO-66(Zr) b) UiO-66(Zr)-V.
Fig. 3. The FTIR spectra of a) UiO-66(Zr) and b) UiO-66(Zr)-V.
Fig. 4. TGA curves of the a) UiO-66(Zr) and b) UiO-66(Zr)-V.
20

Fig. 5. The Raman spectra of a) UiO-66(Zr) and b) UiO-66(Zr)-V.
Fig. 6. Nitrogen adsorption–desorption isotherms at 77 K for a) UiO-66(Zr) and b) UiO-66(Zr)-
V.
Fig. 7. The XPS spectra of UiO-66(Zr)-V sample: (a) survey scan, (b) Zr 3d, (c) V 2p. (d) O 1s
and (e) Cl 2p.
Fig. 8. Comparison between X-ray and optimized structure (a) six-center octahedral zirconium
oxide cluster, b) optimized [Zr6O4(OH)4] cluster at B3LYP/6-31G** level.
Fig. 9. Proposed reaction path between of vanadium (V) and [Zr6O4(OH)4] cluster (A, B, C) to
form different complexes including (I) to (V).
Fig. 10. The relative energy diagram of different proposed compounds (I, II, III, IV and V).
Fig. 11. The solvent effect on the conversion and selectivity of trans-2-hexen-1-ol using UiO-
66(Zr)-V as catalyst.
Fig. 12. Conversion and selectivity of of trans-2-hexen-1-ol with different amounts of the UiO-
66(Zr)-V as catalyst in different times of reaction.
Fig. 13. The effect of recycling of UiO-66(Zr)-V catalyst on epoxidation of trans-2-hexen-1-ol,
under optimum condition.
21

Table 2: Comparison between some selected experimental (Exp.)
and calculated (The.) geometrical parameters of [Zr6O4(OH)4] cluster.
Connected atom
Bond distance (Å)
Zr4-O5
Exp.
The.
2.261
2.261
2.261
2.261
2.261
2.261
2.261
2.261
2.261
2.267
2.340
2.268
2.300
2.310
2.307
2.303
2.268
2.286
Zr4-O2
Zr6-O7
Zr6-O11
Zr6-O13
Zr8-O7
Zr9-O11
Zr9-O2
Zr9-O13
Zr10-O7
2.261
2.261
2.217
2.252
0.13
Zr10-O12
Standard deviation
Bond angle (˚)
O2-Zr1-O14
O14-Zr4-O5
76.60
76.60
72
72
O5-Zr4-O14
76.60
102.27
102.28
71.98
99.38
108.16
10.32
Zr1-O14 –Zr9
Zr10-O11 –Zr6
Standard deviation

Table1. Textural properties and ICP of UiO-66(Zr) and UiO-66(Zr)-V materials.
Material
SBET(m2g-1) Mean pore
diameter (nm)
Total pore volume ICP (Zr) (wt%) ICP (V) (wt%)
(cm3g-1)
UiO-66(Zr)
1068.3
1019.5
2.2346
2.3388
0.5968
0.5961
28.45
27.94
------
5.76
UiO-66(Zr)-V

Table 3. Thermodynamic data for the different complexes, including enthalpies (∆Hcom),
Gibbs free energies (∆Gcom) and entropies (∆Scom).
aꢀESin
bꢀECom
cꢀHCom
dꢀGCom
ꢀ
SCom
Com
Complex I
Complex II
Complex III
Complex IV
Complex V
-94.901
-95.491
-109.23
-102.71
-63.12
-60.0
-88.5354
-0.024
-93.017
-46.777
-45.070
5.758
-93.607
-47.367
-45.660
5.168
-88.39585 -0.021
-43.14845 -0.017
-41.6896
10.87545
-0.016
-0.023
-12.24
a∆ESincom at B3LYP/6-311++G** level,
b∆Ecom = E opt [Zr6O4(OH)4]-V – (E opt [Zr6O4(OH)4] + Eopt V) at hf/3-21g level
cꢀHcom=ꢀE+ꢀnRT, d ꢀGcom=ꢀH-TꢀS

Table 4. Selected some bond lengths (Å) and
bond angles (˚) of [Zr6O4(OH)4]-V complex.
Bond distance (Å)
2.350
2.141
1.793
1.789
2.140
2.133
Zr1- O14
Zr8- O14
Zr8-O15
Zr1-O16
V22-O15
V22-O16
Bond angle (˚)
O3-Zr1-O16
O14-Zr8-O15
Zr1- O3-Zr8
Zr1- O16-V22
Zr8- O15- V22
O16- V22-O16
61.71
89.19
86.65
124.47
104.49
113.52

Table 5. Conversion and selectivity of of trans-2-hexen-1-ol with different amounts of the UiO-
66-V as catalyst in different times of reaction a.
Reaction time
1 h
3 h
5 h
7 h
9h
11h
Amounts of
Conv. (%) (Sel. (%))b
catalyst (mg)
12 (100)
18 (100)
15 (100)
21 (100)
39 (100)
27 (100)
26 (100)
56 (100)
29 (100)
32(100)
68 (100)
58 (100)
44(100)
52(100)
10
30
50
88 (100) 91(100)
58 (100) 56(100)
a Reaction conditions: 10,30 and 50 mg cat, 10 mmol trans-2-Hexen-1-ol, 12 mmol 70 wt% TBHP, 5 mL CH3CN.
b Conversion (%) and selectivity (%) were determined by GC and GC-Mass with an internal standard method.

Table 6. Results obtained for epoxidation of different allyl alcohols in the
Presence of UiO-66(Zr)-V as catalyst.
Entry Substrate conversion(%)
(Time)
1
Epoxide selectivity (%)
(TON)b
CH3
CH3
O
OH
OH
H3C
CH3
H3C
CH3
87 (7h)
100 (256)
CH3
CH3
2
H3C
OH
H3C
OH
O
97 (11h)
88 (9h)
100 (286)
O
H3C
OH
3
4
H3C
OH
100 (259)
OH
OH
H3C
O
H3C
46 (7h)
100 (135)
a Reaction conditions: 30 mg,catalyst, substrate (allyl alcohols, 10 mmol),
TBHP (12 mmol), solvent (acetonitril, 5 ml, reflux at 80 °C).
bTON is the mmol of product to mmol of vanadium present in catalyst.