Experimental and theoretical studies on vanadium bromoperoxidase activity of alkyne arm dioxidovanadium(V) complex: Crystal structure, spectral studies, and DFT calculations

Article abstract of DOI:10.1016/j.poly.2018.02.009

The alkyne arm bearing dioxidovanadium(V) complex was synthesized by the reaction of vanadium sulphate, 1-[2-hydroxy-4-(prop-2-yn-1-yloxy)phenyl]ethanone and propane-1,2-diamine. The synthesized complex was characterized by various spectral techniques and its structure was determined using single-crystal X-ray diffraction analysis. Vanadium centre has square-pyramidal based geometry with an axial oxido ligand and the equatorial positions are occupied by another oxido ligand and phenolato oxygen, imine nitrogen and free amine nitrogen atoms. DFT and TD-DFT calculations were examined to identify the electronic structure, and electronic transitions of the complex observed in the absorption spectra. The percentage of intermolecular interactions in the crystal structure has been evaluated by 3D Hirshfeld surfaces and 2D fingerprint plots. The C–H?π and intermolecular interactions of the complex were examined using Bader's theory of QTAIM by ADF 2017. The dioxidovanadium(V) complex mimics as an efficient vanadium-dependent bromoperoxidase towards the bromination of phenol red in acetonitrile medium at room temperature.

Full text of DOI:10.1016/j.poly.2018.02.009

Accepted Manuscript
Experimental and theoretical studies on vanadium bromoperoxidase activity of
alkyne arm dioxidovanadium(V) complex: crystal structure, spectral studies,
and DFT calculations
M.A. Neelakantan, Chithiraivel Balakrishnan, P. Kowsalya, V. Selvarani
PII:
S0277-5387(18)30076-7
https://doi.org/10.1016/j.poly.2018.02.009
POLY 13044
DOI:
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
16 December 2017
9 February 2018
Please cite this article as: M.A. Neelakantan, C. Balakrishnan, P. Kowsalya, V. Selvarani, Experimental and
theoretical studies on vanadium bromoperoxidase activity of alkyne arm dioxidovanadium(V) complex: crystal
structure, spectral studies, and DFT calculations, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.
2
018.02.009
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Experimental and theoretical studies on vanadium bromoperoxidase
activity of alkyne arm dioxidovanadium(V) complex: crystal structure,
spectral studies, and DFT calculations
*
M.A. Neelakantan , Chithiraivel Balakrishnan, P. Kowsalya, V. Selvarani
Chemistry Research Centre, National Engineering College, K.R. Nagar, Kovilpatti - 628 503, Thoothukudi
District, Tamil Nadu, India
*
Corresponding Author
E-mail Address: drmaneelakantan@gmail.com

Abstract
The alkyne arm bearing dioxidovanadium(V) complex was synthesized by the reaction of
vanadium sulphate, 1-[2-hydroxy-4-(prop-2-yn-1-yloxy)phenyl]ethanone and propane-1,2-
diamine. The synthesized complex was characterized by various spectral techniques and its
structure was determined using single-crystal X-ray diffraction analysis. Vanadium centre has
square-pyramidal based geometry with an axial oxido ligand and the equatorial positions are
occupied by another oxido ligand and phenolato oxygen, imine nitrogen and free amine
nitrogen atoms. DFT and TD-DFT calculations were examined to identify the electronic
structure, and electronic transitions of the complex observed in the absorption spectra. The
percentage of intermolecular interactions in the crystal structure has been evaluated by 3D
Hirshfeld surfaces and 2D fingerprint plots. The C-H···π and intermolecular interactions of
the complex were examined using Bader’s theory of QTAIM by ADF 2017. The
dioxidovanadium(V) complex mimics as an efficient vanadium-dependent bromoperoxidase
towards the bromination of phenol red in acetonitrile medium at room temperature.
Keywords: Dioxidovanadium(V) complex; Crystal structure; Non-covalent interactions;
Bromoperoxidase activity

1
.
Introduction
Vanadium coordination chemistry has attracted increasing interest due to its presence
in abiotic and biotic systems [1]. It is an ultra-trace element essential for healthy growth,
development, and survival of higher organisms. The biological role of vanadium is evidenced
from bacteria (vanadium replaces molybdenum in some azotobacter species) [2] and plants
(
in algae, lichens, and fungi as vanadium-dependent haloperoxidase) [3]. Vanadium exists in
different oxidation states from -3 to +5 [4], and its coordination chemistry plays a vital role in
the process of interaction with various biomolecules [5]. In vivo, under physiological
conditions, vanadium complexes prevail in oxidation states +4 and +5. Vanadium is highly
oxophilic in higher oxidation states [6]. In high-valant vanadium complexes, the element
functions as an electron transfer catalyst in the processes of homolytic and heterolytic
oxidation of organic substances [7] and have effects over biological systems [8]. The catalytic
activity induces many researchers to develop innovative vanadium complexes mimicking
vanadium-dependent haloperoxidase [9]. Recently, we reported the vanadium-dependent
bromoperoxidase activity of some vanadium(IV) Schiff base complexes [10].
A wide range of weak intermolecular forces is involved in bio-molecular recognition
processes, which helpfully demonstrate the binding attraction and specificity. Among the
various intermolecular interactions [11], CH···π, H···H, and π··· π interactions attracted
significant attention in recent years because of their importance in several areas of chemistry
and biochemistry [12]. There are extensive explorations on non-covalent interactions in small
organic molecules [13]. It is incredibly much essential to know the information of non-
covalent interactions present in metal complexes, but the studies on these compounds are
exceptionally scattered [14].
With all these in mind and continuation of our interest towards vanadium complexes,
the present studies involve the synthesis of an alkyne arm bearing dioxidovanadium(V)
complex and its structural analysis by spectral and single crystal X-ray techniques. The nature
and percentage of intermolecular interactions in the crystal structure have been evaluated by
3
D Hirshfeld surfaces and 2D fingerprint plots. The vanadium-dependent bromoperoxidase
activity of the dioxidovanadium(V) complex was evaluated by the oxidative bromination of
phenol red as a model substrate to bromophenol blue.
2
.
Experimental section

2
.1. Materials and physical methods
,4-dihydroxyacetophenone, propargyl bromide, potassium carbonate, and vanadyl
2
sulphate was purchased from Sigma Aldrich and triethylamine from Merck. All the solvents
were reagent grade and used as received. Elemental analyses were performed on a Thermo
Finnigan Flash EA 1112 series carbon, hydrogen, and nitrogen analyzer. IR spectra were
recorded on a Shimadzu 8400S spectrophotometer. Electronic absorption spectral
measurement was carried out in acetonitrile using Shimadzu UV-2450 spectrophotometer.
2
.2. Synthesis of dioxidovanadium(V) complex
A methanol solution (10 mL) of 1,2-diaminopropane (10 mM) was added to a
methanolic solution of 1-[2-hydroxy-4-(prop-2-yn-1-yloxy)phenyl]ethanone (20 mM) and the
resulting mixture was stirred and reflux for 2h. Then five mL aqueous solution of VOSO (10
4
mM) was added followed by the addition of triethylamine (10 mM). The reaction mixture
was refluxed for 3h. Filtration collected the yellow coloured precipitate and washed several
times with hot ethanol and isopropyl alcohol (Scheme 1). The yellow crystals of suitable
quality for X-ray analysis were obtained by slow evaporation of DMSO and methanol
solution.
Yield: 89 %. Yellow color solid. M.P.: 245°C. Anal. Calcd. for C14
H
17
N
2
4
O V. Found
(
Calculated) (%) C: 51.22 (51.23), H: 5.20 (5.22), N: 8.52 (8.53). UV-Vis (CH CN): λmax =
3
–
1
2
81, 332, 405 nm. FT-IR (KBr): ν, cm 3271 (–C≡C–H), 2912 (asymmetric –C–H), 2845
5
1
(
symmetric –C–H), 2116 (–C≡C–), 1601 (–C=N), 889, 915 (V=O). V NMR (DMSO-d
6
,
ppm): –531.4.
2
.3. X-ray crystallography
Single crystal X-ray data of dioxidovanadium(V) complex was collected using a
Bruker Kappa Apex II X-ray diffractometer [15]. The X-ray radiation employed was
generated from a Mo sealed X-ray tube (Kα = 0.70173 Å at 296(2) K with a potential of 40
kV, 40 mA) connected with a graphite monochromator in the analogous mode. The relevant
cell was finding out and refined by nonlinear least squares and Bravais lattice methods. The
unit cell was established by checking the h k l overlays on different frames of data by
comparing with both the orientation matrices. PARST and SHELXL-97 acquired the
geometrical parameters. Hydrogen and non-hydrogen atoms were refined with anisotropic

2
thermal parameters. Full matrix least square method on F was refined to convergence the
structure. Olex2 was utilized for the final data collection and structure plots [16].
2
.4. Theoretical methods
The QTAIM analysis was performed by using the Amsterdam density functional
(
ADF) modeling suite (2017) [17] package at GGA:PW91 level and TZ2P basis set. QTAIM
2
analysis provides topology properties such as electron density (ρ), Laplacian ( ρ), local
potential energy (V
b
) and kinetic potential energy (G ) at bond critical points for all the non-
b
covalent contacts. The interaction energy for different intermolecular interactions was also
calculated by using Espinosa-Molins-Lecomte (EML) relationship [18]. The molecular
electrostatic potential analysis (MESP) has been performed using crystal explorer 3.1
software. Hirshfeld surface analysis and 2D fingerprint plots were also calculated using
crystal explorer 3.1 [19a]. The molecular orbitals analysis [19b] and Mayer [19c] and orbital
occupancy perturbed bond order [19d] calculations were done using the Multiwfn program
[
19e].
2
.5. Vanadium bromoperoxidase activity
Bromination of phenol red to bromophenol blue utilizing dioxidovanadium(V)
complex as a catalyst was studied by absorption spectroscopy. Bromination activity tests
were done at a constant temperature of 30±0.5°C in the presence of H and KBr in the mild
acidic medium. An aliquot of an acetonitrile solution of 0.1 mmol of catalyst was added to
0% H so that the final concentration of H in the reaction mixture was one mM,
followed by the addition of HClO (final concentration 2.0 mM) and 4.0 mol/L of KBr.
2
O
2
3
2
O
2
2
O
2
4
Reactions were started by the addition of 0.25 mmol of phenol red, and the solution was
stirred at a constant temperature of 25°C. The spectral measurements were kept at pH = 5.8
by the addition of NaH
2
PO
4
-Na
2
HPO [20]. The bromination reaction was observed by the
4
slow vanishing of the ~400 nm band, and an increase in the absorbance of the peak at ~590
nm due to the development of the bromophenol blue product and spectral changes were
recorded at the 5 min intervals. The reaction was complete under the ambient conditions after
∼
4 h. The kinetic aspects of dioxidovanadium(V) complex were carried out by monitoring
the increasing the formation of the product absorbance at ~590 nm by the initial rate method.
The acetonitrile solution of 0.1 mmol of catalyst was added under stirring 0.1 mM 30% H
.2 mM HClO and 0.4 mmol of KBr and the reaction mixture was thermostated at 25°C.
2
2
O ,
0
4

With an increase of the substrate (phenol red) concentration from 10 to 50 equiv. with respect
to the catalyst (0.1 mmol), the dependence of the rates on the substrate concentration was
determined.
3
.
Results and discussion
3
.1. Crystal structure description
The ORTEP diagram and atom numbering scheme of the dioxidovanadium(V) are
shown in Fig. 1. The crystallographic data and structure refinement parameters, selected bond
length and bond angles are presented in Tables 1 & 2. The asymmetric unit of the complex
consists of monomeric dioxidovanadium(V) complex. The crystal structure of the compound
crystallized into a centrosymmetric triclinic crystal system with P-1 space group. The
vanadium atom of the complex is pentacoordinate in a square pyramidal environment
coordinated to the tridentate Schiff base, via phenolic oxygen, N(amino-nitrogen) and
N(azomethine) atoms and the remaining two coordinations are occupied by oxo groups. The
geometry of penta-coordinated metal center is typically ascertained by the Addison parameter
(
τ) [τ = (α-β)/60, where α and β are the two major Ligand-Metal-Ligand angles of the
coordination sphere (τ = ~0.00 for a square pyramid and τ = ~1.00 for a trigonal bipyramid)]
21a]. The calculated τ value of vanadium(V) complex is 0.042 indicates that the
[
dioxidovanadium (V) complex have square pyramidal based geometry.
The crystal packing of dioxidovanadium(V) complex viewed down the ‘a’ axis (Fig.
S1) shows phenyl ring in planar conformation. The bond lengths of N(1)-V(1) and N(2)-V(1)
are 2.1923(16) and 2.1113(16) Å, respectively. The bond length of O(1)-V(1), O(3)-V(1) and
O(4)-V(1) are 1.899(13), 1.6160(15) and 1.6541(14) Å, respectively. The bond angles,
O(3)-V(1)-O(4), O(3)-V(1)-O(1) and O(4)-V(1)-O(1) are 107.72(8)°, 103.90(7)° and
9
9
7.46(6)°, respectively. The bond angles of O(3)-V(1)-N(2) and O(4)-V(1)-N(2) are
6.63(7)° and 92.03(7)°, respectively. These bond length and bond angle values indicate that
the present complex structure is square pyramid [21b]. The hydrogen bond parameters of the
dioxidovanadium(V) complex are presented in Table 3. In dioxidovanadium(V) complex, the
crystal packing is stabilized by N-H···O, C-H···O, and C-H···π intermolecular interactions.
In the crystal structure, the molecules at (x, y, z) and (1-x, 1-y, 1-z;) are linked by C4-H4
2
·
··O2 hydrogen bonds, generating a centrosymmetric dimeric ring motif R
2
(8) (Fig. 2). A
weak intermolecular C10-H10···π interaction is also observed in the complex. The molecules
at position (x,y,z) and (1+x,y,z) are linked by C-H···π interaction (Fig. 3), and so the H10

(
bonded to C10) is at a distance of 2.81Å away from the centroid of the phenyl ring C2-
2
C7(Cg ) with C10 centroid distance of 3.615(3)Å. The propargyl group attached to the
aromatic ring in the complex assumes an extended conformation, which can be seen from the
O2-C8-C9-C10 torsion angles of -37(1)°. The C13 atom is found to be disordered over two
sets of sites [site occupancies = 0.529(7) and 0.471(7)].
3
.2. Spectroscopic studies
The IR spectrum of dioxidovanadium(V) complex shows several bands in the 400-
–
1
4
000 cm
region (Fig. S2). The compound 1-[2-hydroxy-4-(prop-2-yn-1-
yloxy)phenyl]ethanone (A) exhibits a strong absorption band of carbonyl group frequency at
–
1
1
631 cm . This band disappears during the reaction of A with vanadium sulphate and
–
1
propane-1,2-diamine, and a strong band at 1601 cm corresponds to the presence of the
–
1
azomethine -N coordinated to the vanadium ion [22]. The absorption at 3305 cm
corresponds to the N–H stretching frequency of complexed primary amino group. The C-O
–
1
(
phenolic) stretching appears at 1540 cm in the complex indicates the coordination of
–
1
deprotonated phenolic oxygen with the vanadium ion. The absorption band at 2912 cm is
–
1
due to the aromatic ν(C-H) stretching of the complex. A medium absorption band at 2845 cm
indicates the presence of alkyl ν(C-H) stretching. The complex exhibits medium absorption
–
1
–1
bands at 2116 cm and at 1266 cm corresponds to the presence of terminal alkyl group (-
−
1
C≡C) and C-O-C (alkyl ether) stretching vibrations. The two vibrations at 889 and 915 cm
corresponds to the antisymmetric and symmetric stretching vibrations of the
dioxidovanadium (V) moiety [21,23].
The electronic absorption spectrum of dioxidovanadium(V) complex was recorded in
acetonitrile solution (Fig. S3a). The complex exhibits an intense band at 332 nm is assigned
to π(L) → d (V) LMCT transition and another strong band at 405 nm is due to π → π*
π
transition of the ligand. The TD-DFT computed absorption spectrum of dioxidovanadium(V)
complex is shown in Fig. S3b and the transitions are given in Table 5. The lowest energy
absorption band at 417 nm is due to π → π* transition of the ligand, whereas the strong
absorption band appeared at 338 nm is due to the π(L) → dxz(V)-p
x
(Oax) LMCT transition of
the metal complex. V NMR spectrum of dioxidovanadium(V) complex was recorded in
DMSO-d solution (Fig. S4). The complex exhibits a single band at –531.4 ppm shows that
the dioxidovanadium(V) complex occurs in the monomeric form [24].
5
1
6

The FMOs (Frontier Molecular Orbitals) of the dioxidovanadium(V) complex are
given in Table 4 and Fig. S5. The orbital occupancy perturbed Mayer bond order calculations
show that the LUMO is a weak antibonding orbital. The LUMO is mainly located in three
metal-based orbitals such as dxy(V)-p
x
(Oeq) as LUMO+1, dxz(V)-p (Oax) as LUMO+3 and a
x
2
z
d
orbital as LUMO+2. These orbitals have an anti-bonding character for the V−Oax, and
V−Oeq interactions and the orbital percentage of vanadium metal ion is 68.7 % (LUMO+3),
0.3 % (LUMO+2) and 73.3 % (LUMO+1). These molecular orbitals reveal that covalent
7
bonding is between the metal and ligand in dioxidovanadium(V) complex. Electron
localization function (ELF) has been widely used for studying the nature of bond in organic
and inorganic molecules, and the value is within the range of 0 to 1. The value of Mayer bond
order is in agreement with the empirical bond order, for single, double and triple bond and the
value is close to 1.0, 2.0 and 3.0 respectively. A large ELF value means that electrons are
greatly localized, indicating that there is a covalent bond [19e]. The calculated electron
localization function (ELF) values (η) for the dioxidovanadium(V) complex demonstrate that
the V−Oax and V−Oeq (η = 0.94 for V−Oax and η = 0.97 for V−Oeq) bonds are strong in
covalent bond character. The V−O1, V−N1 and V−N2 (η = 0.72 for V−O1, η = 0.69 for
V−N1 and η = 0.74 for V−N2) bonds are weak in covalent bond character. The calculated
Mayer bond orders (1.92 for V−Oax, and 1.95 for V−Oeq, 0.63 for V−O1, 0.32 for V−N1 and
0
.29 for V−N2, respectively) corroborate this [21b].
3
.3. Hirshfeld surface analysis and 2D-Fingerprint plot
Hirshfeld surface and 2D fingerprint plot analysis were carried out to understand the
various intermolecular interactions present in the dioxidovanadium(V) complex. Hirshfeld
surface analysis shows that the structure of the complex is mainly characterized by H···H,
O···H, and C–H···π contacts. The dnorm surfaces are mapped over a fixed color scale of -
0
.584 (red) to 1.193 Å (blue), shape-index mapped in the color range of -1.0 (concave) to 1.0
(
convex) Å, and curvedness in the range of -4.0 (flat) to 4.0 (singular) Å (Fig. 4). In dnorm
form, the color scale of red indicates shorter than van der Waals radii separation, white for
equal van der Waals radii and blue indicates longer than van der Waals radii. These colors
are used to visualize the intermolecular contacts. In dnorm form, the O···H interaction
observed as the red areas (Fig. 4), and another spot in dnorm form corresponds to C···H and
H···H interactions. The shape index indicates the shape of the electron density surface around
the molecular interactions and the curvedness form shows the electron density around the

molecule. The O···H intermolecular interactions appear as two distinct spikes of almost equal
lengths in the 2D fingerprint plots. Among the two spike bottom left area (donor) corresponds
to O···H interactions and bottom right (acceptor) corresponds to H···O interactions.
Similarly, the C···H interactions also represented by a spike in the bottom left (donor) and
H···C interactions posed by a spike in the bottom right (acceptor). The percentage of the
intermolecular interactions are represented in Fig. 5. From the figure 4, the H···H contacts
have the most significant contribution (38.2 %) to the total Hirshfeld surface, and is due to
the presence of much higher propensity for H···H contacts. The contribution of O···H/H···O
contacts in the complex is 30.4 %, and C···H/H···C is 26.1 % but this was overshadowed by
the H···H contribution which is attributed due to the presence of –CH
.4. Molecular electrostatic potential(MSEP) maps
The MESP map is used to identify the electron rich and electron deficient sites of the
3
substituent.
3
complex and is useful in predicting the intermolecular interactions in the molecules (Fig. S6).
In MESP maps, the positive electrostatic region/electron deficient /π-hole (blue region)
indicates hydrogen donor potential whereas hydrogen bond acceptors are represented by
negative electrostatic potential/electron rich/σ-hole (red region). The non-covalent
interactions occur between the electropositive and electronegative regions. In dimer of the
complex, the positive electrostatic region at hydrogen interacts with the negative electrostatic
region at oxygen. Each benzene ring participates in two short C-H···π contacts interacting
with the aliphatic hydrogen atoms. The chelate ring also interacts with aliphatic hydrogen and
form C-H···π contacts.
3
.5. QTAIM analysis
The strength of O···H/H···O, C···H/H···C interactions present in the
dioxidovanadium(V) complex was studied by Bader’s theory of atoms in molecules (AIM).
The AIM analysis for the dimer of the complex has been investigated by ADF using
GGA:PW91 functional at TZ2P basis set [25]. It provides topological parameters including
electron density and Laplacian operators at the bond critical points (Fig. 6 & Table S1). The
Laplacian electron density values are positive indicates that closed-shell interactions are
present in the dimer. The ratio of –V(r)/G((r) is less than unity suggests that all the
interactions are non-covalent [26]. The local stabilization energy for the different non-
covalent interactions was also estimated through an Espinosa-Molins-Lecomte (EML)

relationship (I.E = 0.5 V
b
, where V is local potential energy density at the BCP) [18].
b
Various intermolecular interactions stabilize the crystal packing. Among the interactions, C–
H···π interactions having the higher interaction energy compared to that of O···H and
chelating ring π-interactions. From these observations, it is clear that C–H···π interaction
more stabilize the crystal packing. Similarly QTAIM analysis was studied for supramolecules
of dioxidovanadium(V) complex. It also gave the same result which indicates that all the
interactions are non-covalent in nature and C–H···π interaction stabilizes crystal packing
(
Fig. S7 & Table S1).
3
.6. Vanadium haloperoxidases activity
Vanadium haloperoxidase (VHPO) catalyzes the bromination of organic compounds
in the presence of hydrogen peroxide (H
2
2
O ) and potassium bromide (KBr). Metal
complexes, which are capable of catalyzing bromide oxidation are considered as functional
bromoperoxidase mimics [27]. The bromoperoxidase activity of the metal complexes has
been measured by the kinetic study of catalytic bromination of phenol red to bromophenol
blue [28]. The catalytic activity of synthesized dioxidovanadium(V) complex was examined
using phenol red as a model organic substrate, which is converted to bromophenol blue
during the reaction (Scheme S1) and the course of the reaction was monitored using
electronic absorption spectroscopy. The addition of dioxidovanadium(V) complex to the
substrate gradually decreases the absorption intensity of phenol red at 443 nm, and a new
band appears at 592 nm due to bromophenol blue. This demonstrates that the
dioxidovanadium(V) complex acts as a catalyst for the conversion of phenol red to
bromophenol. The formation of the isosbestic point at 490 nm support the catalytic
conversion phenol red to bromophenol blue (Fig. 7a). The Michaelis-Menten model
developed for enzyme kinetics was used to study the kinetics of oxidation of bromophenol in
the presence of dioxidovanadium(V) complex as a catalyst, exhibit saturation kinetics (Fig.
7
b). Hanes-Woolf plot of [S]/rate vs. [S] was used to calculate the Michaelis-Menten binding
constant (K ), maximum velocity (Vmax) and rate constant for dissociation of substrates (kcat
Fig. 7c & Table 5). An experiment conducted in the absence of dioxidovanadium(V)
M
)
(
complex shows no change in the absorbance at 495 nm demonstrate the effect of
dioxidovanadium(V) complex as catalyst (Fig. 7d). The probable mechanism of the catalytic
process under the mild acidic condition is the dioxidovanadium(V) (A) which acts as a
catalyst is first converted into hydroxyl intermediate (B). In the presence of H
2
2
O , the

hydroxyl species leads to transient formation peroxido intermediates (C-E) and finally
dioxiran-1-ium ion intermediate (F). The dioxiran-1-ium ion intermediate (F) oxidizes the
-
bromide ion (Br ) into bromonium ion intermediate (G). The intermediate G accept a proton
from a surrounding water molecule leads to the formation of hypobromite adduct (H) with the
release of hypobromous acid (HOBr) followed by renovation of the native state (A) [29]. The
TD-DFT computational study was employed to support the experimental investigations of
catalytic conversion of phenol red to bromophenol blue in the presence of
dioxidovanadium(V) complex as catalyst (Fig. S8). The UV-vis spectra were computed for
transiently formed intermediate species (B-F). The observed results show that peroxo species
formation is accompanied by the disappearance of the intense band at 331 nm is in good
agreement with the experimental data.
4
.
Conclusions
Dioxidovanadium(V) complex has been synthesized and characterized by different
spectral techniques. Single crystal X-ray diffractcion analysis has structurally characterized
the structure of the complisex reveal square pyramidal based geometry around the vanadium
ion. The intermolecular interactions present in the complex studied by Hirshfeld surface
analysis shows that the structure of the complex is mainly characterized by H···H, O···H, and
C–H···π contacts, with the H···H contacts, have 38.2% contribution to the total Hirshfeld
surface. The QTAIM studies suggest that C–H···π interaction more stabilize the crystal
packing. The synthesized compound exhibit bromoperoxidase activity by converting the
model substrate, phenol red to bromophenol blue, efficiently mimicking the functional
models of vanadium-dependent bromoperoxidase enzyme.
Acknowledgement
Dr. M.A.N. gratefully acknowledged the financial support from Science and Engineering
Research Board (SERB), Department of Science and Technology (DST), Government of
India, New Delhi (EMR-II/2014/000081). C. B is thankful to CSIR, India for his fellowship.
STIC, Cochin is acknowledged for performing the SCXRD analysis.
Supplementary data
CCDC 882668 contains the supplementary crystallographic data for dioxidovanadium(V).
The data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html

or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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Scheme 1 Synthesis of dioxidovanadium(V) complex

Fig. 1. ORTEP view (50% probability level) of the molecular structure of
dioxidovanadium(V) complex.

Fig. 2. Crystal packing diagram of dioxidovanadium(V) complex, showing the formation of
2
centrosymmetric R
2
(8) dimer.

Fig. 3. C-H···π interaction for the dioxidovanadium(V) complex.

d
norm
Shape-index
Curvedness
and d form of
Fig. 4. Hirshfeld surfaces mapped over dnorm, shape index, d
i
e
dioxidovanadium(V) complex.

H···H (38.2%)
O···H / H···O (30.4%)
C···H / H···C (26.1%)
H···H
O···H / H···O
C···H / H···C
Others
Fig. 5. 2D Fingerprint plots of dioxidovanadium(V) complex, H···H (left), O···H/H···O
middle) and C···H/H···C (right) contacts showing the percentage of contact contributed to
the total Hirshfeld surface area of the molecule.
(

Fig. 6. Molecular plots for dimers dioxidovanadium(V) complex
showing the different intermolecular contacts in the presence of
bond critical points (red spheres).

(
a)
(b)
(
c)
(d)
–
3
Fig. 7. (a) Oxidative bromination of phenol red (1.0×10
M) catalyzed by
−
4
dioxidovanadium(V) complex (10 M) in acetonitrile; (b) Plot of rate vs. substrate
concentration for dioxidovanadium(V) complex; (c) Hanes-Woolf plot for
dioxidovanadium(V) complex and (d) Absorbance vs. Time plot of a mixture of KBr, H
HClO and Phenol red in absence of dioxidovanadium(V) complex.
2
2
O ,
4

Table 1
Crystallographic data and collection parameters for dioxidovanadium(V) complex.
Parameters
dioxidovanadium(V) complex
Empirical formula
Formula weight
C
14
H
17
N
2
O V
4
328.24
293(2) K
0.71073 A
Temperature
Wavelength
Crystal system, space group
Unit cell dimensions
a = 7.6670(9) (Å)
b = 8.7413(11) (Å)
c = 11.3835(14) (Å)
Volume
Triclinic, P-1
α = 69.383(7) (
β = 88.086(5) (
ꢁ = 83.115(5) (
ꢀ
)
)
)
ꢀ
ꢀ
3
708.88(15) (Å )
3
Z, Calculated density
Absorption coefficient
F(000)
2, 1.538 Mg/m
–
1
0.717 mm
340
0.24 × 0.21 × 0.2
1.91 to 28.35 (
Crystal size(mm)
Theta range for data collection
Limiting indices
ꢀ
)
-10<=h<=10, -11<=k<=11, -14<=l<=15
12703 / 3510 [R(int) = 0.0240]
Reflections collected / unique
Refinement method
Data / restraints / parameters
2
Full-matrix least-squares on F
2510 / 3 / 210
2
Goodness-of-fit on F
1.048
Final R indices [I>2σ(I)]
R indices (all data)
R1 = 0.0357, wR2 = 0.0966
R1 = 0.0425, wR2 = 0.1016
–
3
Largest diff. peak and hole
0.559 and -0.417 (e. Å )

Table 2
Selected bond lengths (Å) and bond angles (°) for dioxidovanadium(V) complex.
Bond length (Å)
C(1)-N(1)
Bond angle (°)
1.290(2)
2.1923(16)
2.1113(16)
1.8993(13)
1.6160(15)
1.6541(14)
1.319(2)
1.160(4)
0.9300
O(3)-V(1)-O(4)
O(3)-V(1)-O(1)
O(4)-V(1)-O(1)
O(3)-V(1)-N(2)
O(4)-V(1)-N(2)
O(1)-V(1)-N(2)
O(3)-V(1)-N(1)
O(4)-V(1)-N(1)
O(1)-V(1)-N(1)
N(2)-V(1)-N(1)
N(2)-C(13)-H(13)
C(14)-C(13)-H(13)
C(12)-C(13')-N(2)
O(3)-V(1)-O(4) #1
O(4)-V(1)-O(4) #1
O(1)-V(1)-O(4) #1
N(2)-V(1)-O(4) #1
N(1)-V(1)-O(4) #1
107.72(8)
99.95(7)
97.46(6)
96.63(7)
92.03(7)
153.46(6)
96.87(8)
154.31(7)
83.39(6)
77.55(6)
109.5
N(1)-V(1)
N(2)-V(1)
O(1)-V(1)
O(3)-V(1)
O(4)-V(1)
C(7)-O(1)
C(9)-C(10)
C(10)-H(10)
C(1)-C(11)
C(11)-H11(A)
C(11)-H11(B)
C(11)-H11(C)
C(13)-N(2)
C(12)-N(1)
C(13)-C(14)
C(12)-C(13)
O(4)-V(1)#1
1.511(3)
0.9600
0.9600
109.5
0.9600
108.9(2)
172.23(7)
77.86(6)
80.32(5)
77.53(5)
79.98(5)
1.493(3)
1.469(3)
1.561(3)
1.482(4)
2.4603(15)

Table 3
Hydrogen bonding parameters for dioxidovanadium(V) complex, D = donor, A = acceptor
(
Å, °).
D–H···A
D–H
0.90
0.90
0.93
0.96
-
H···A
2.18
0.90
2.54
2.52
2.81
D···A
D–H···A
141
(i)
N2-H2A···O1
2.940(2)
3.033(2)
3.446(3)
3.472(3)
3.614(3)
(ii)
N(2)-H(2B)···O(3)
158
(iii)
C4-H4···O2
166
(
iv)
C11-H11B···O4
170
(
v)
C10-H10···Cg2
145
2
Symmetry codes: (i) 1-x,-y,-z; (ii) -x,-y,-z (iii) 1-x,1-y,1-z; (iv) x,1+y,z ; (v) 1+x,y,z and Cg
is the centroid of the C2-C7 ring.

Table 4
Energies and Mulliken population analysis derived FMO compositions of
dioxidovanadium(V) complex
Molecular orbital
Description
Contribution (%)
L
V
O
ax
O
eq
 (eV)
-2.01
-1.89
-2.36
-7.82
2
LUMO+2
LUMO+3
LUMO+1
HOMO
d
z
(V)
13.5
15.6
9.4
70.3
68.7
73.3
2.7
10.7
9.1
2.8
3.2
5.5
6.6
d
xz(V)-p
x
(Oax
)
d
xy(V)-p
x
(Oeq
)
14.5
1.9
π(L)
92.2

Table 5
Calculated absorption bands for dioxidovanadium(V) complex.
Wavelength
λ) (nm)
Oscillator
strength (f)
0.049
Orbital distribution
Assignment
(
4
3
3
2
17
76
38
89
HOMO → LUMO (95%)
HOMO → LUMO+1 (92%)
HOMO → LUMO+3 (68%)
HOMO → LUMO+2 (52%)
π(L) → π*(L)
0.005
0.072
0.099
π(L) → dxy(V)-p
x
(Oeq
)
π(L) → dxz(V)-p
x
(Oax
)
2
z
π(L) → d
(V)

Table 6
M
Kinetic parameters (Vmax, K , kcat) for the bromination of phenol red by dioxidovanadium(V)
complex.
−
1
−1
Catalyst
V
max (M min )
K
M
(M)
k
cat (h )
−
3
−3
dioxidovanadium(V)
complex
5.17 × 10
3.29 × 10
310.20

Graphical Abstract
Graphical Abstract
Dioxidovanadium(V) complex was synthesized and structurally characterized. Non covalent
interactions in the complex and vanadium dependent bromoperoxidase activity was studied.
[
30]