Mononuclear oxidodiperoxido vanadium(V) complex: synthesis, structure, VHPO mimicking oxidative bromination, and potential detection of hydrogen peroxide

Article abstract of DOI:10.1080/00958972.2018.1439936

An oxidodiperoxidovanadium(V) complex, (NH₄)[VO(O₂)₂(phen)](H₂O)₂, has been synthesized and structurally characterized. The complex crystallizes in the P2₁/c space group. The vanadium center is seven-coordinate with pentagonal bipyramidal geometry. The compound was designed in order to develop a VHPO mimic, so it was tested for VHPO activity through the single pot bromination of phenol red to bromophenol blue whereby, it afforded positive response to establish that the complex is indeed a VHPO mimic. In addition, the compound is capable of detection of H₂O₂.

Full text of DOI:10.1080/00958972.2018.1439936

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Mononuclear oxidodiperoxido vanadium(V)
complex: synthesis, structure, VHPO mimicking
oxidative bromination, and potential detection of
hydrogen peroxide
Haimanti Adhikari & Kalyan K. Mukherjea
To cite this article: Haimanti Adhikari & Kalyan K. Mukherjea (2018): Mononuclear oxidodiperoxido
vanadium(V) complex: synthesis, structure, VHPO mimicking oxidative bromination,
and potential detection of hydrogen peroxide, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2018.1439936
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Journal of Coordination Chemistry, 2018
https://doi.org/10.1080/00958972.2018.1439936
Mononuclear oxidodiperoxido vanadium(V) complex:
synthesis, structure, VHPO mimicking oxidative bromination,
and potential detection of hydrogen peroxide
Haimanti Adhikari and Kalyan K. Mukherjea
department of Chemistry, Jadavpur university, Kolkata, india
ABSTRACT
ARTICLE HISTORY
received 7 august 2017
accepted 26 January 2018
An oxidodiperoxidovanadium(V) complex, (NH4)[VO(O2)2(phen)]
(H2O)2, has been synthesized and structurally characterized. The
complex crystallizes in the P21/c space group. The vanadium center
is seven-coordinate with pentagonal bipyramidal geometry. The
compound was designed in order to develop a VHPO mimic, so it was
tested for VHPO activity through the single pot bromination of phenol
red to bromophenol blue whereby, it afforded positive response to
establish that the complex is indeed a VHPO mimic. In addition, the
compound is capable of detection of H2O2.
KEYWORDS
oxidodiperoxido vanadium
complex; structure;
bromoperoxidation catalysis;
h2o2 detection
1. Introduction
Vanadium haloperoxidase (VHPO) is the first isolated vanadium-dependent enzyme from
the marine algae Ascophyllum nodosum. In 1984 and later, it was found in some lichens and
other marine algae as well [1, 2]. Vanadium-containing complexes have obtained attention
due to their wide biological and catalytic properties such as haloperoxidation, nitrogen
fixation, metalloprotein function, insulin-mimicking activities [3, 4]. The incorporation of
halogen atoms in many organic compounds by nature leads to the formation of halogenated
antibiotics, drugs, or signaling molecules in biological systems [5]. Halogenated compounds,
CONTACT Kalyan K. mukherjea
k_mukherjea@yahoo.com, kkmukherjee@chemistry.jdvu.ac.in
the supplementary material for this article is available online at https://doi.org/10.1080/00958972.2018.1439936.
© 2018 informa uK limited, trading as taylor & francis Group

2
H. ADHIKARI AND K. K. MUKHERJEA
usually found in marine organisms, especially marine macroalgae, seem to be important
factors of halogen transfers in the coastal marine environment [6–8]. Among halogenating
enzymes, haloperoxidases utilize hydrogen peroxide for electrophilic halogenation via the
oxidation of halides [5, 9–12].
Vanadium-dependent haloperoxidase (VHPO) enzymes show antioxidant activity and
are believed to take part in chemical defense in some biological systems [13,14]. VHPOs are
classified according to the most electronegative halide that they can oxidize, i.e. chloroper-
oxidases (VCPO) can catalyze the oxidation of chloride as well as of bromide and iodide, and
bromoperoxidases (VBPO) react with bromide and iodide, whereas iodoperoxidases (VIPO)
are specific for iodide. Until recently, only chloro- and bromoperoxidases from eukaryotic
species have been studied, showing a fragmental view of this large enzyme family. Novel
types of VHPO discovered in marine bacteria now give some clues to explore new biosyn-
thetic pathways of natural halogenated compounds through in vitro heterologous expres-
sion. Further studies on the structure–function relationships in the catalytic and specificity
mechanism are warranted to shed light on the evolution of the VHPO family.
These VHPOs can halogenate particular substrates in phenyl rings [15]. It has been
reported earlier that VHPOs oxidize the halide ion through coordinating hydrogen peroxide;
the nature of the oxidized halide species seems to depend on the nature of the organic
substrate. Then halogenation of appropriate organic substrate occurs by these oxidized
halogen species. They can also oxidize a second equivalent of hydrogen peroxide, producing
dioxygen [16]. The main active center of VHPO has been reported to contain a VO4N moiety
[17]. Although the mechanism of VHPO is not yet fully established, in order to explore the
relationship between the structure and the catalytic activity of the enzyme mimics, a large
number of vanadium complexes have been synthesized [18–20]. Extracted VHPO enzyme
also was tested in vitro for the bromination reaction of phenol red to understand its mech-
anism [21]. As a peroxido group is present in the active site, peroxidovanadium compounds
are considered to be more effective to mimic the VHPO system. So the present work has
been undertaken to develop compounds containing peroxidovanadium moiety. Accordingly,
a compound, [VO(O2)2(phen)](NH4)(H2O)2], has been synthesized, whose characterization
was undertaken using UV–vis spectroscopy, IR, NMR, mass spectroscopy, and X-ray
crystallography.
Because of some unique properties, hydrogen peroxide has been used for years in various
fields [22]. So, determination of H2O2 has a great practical importance. Although there are
several methods of detection of it, the colorimetric method of assay appears to be more cost
effective and simple [23–25]. Envisaging the simplicity of metal complex-based methods,
we concentrated our attention to develop a simple H2O2 sensing model system with the
peroxido vanadium complex. Eventually, the complex was found to act both as a VHPO
mimic as well as a H2O2 sensing agent.
2. Experimental
2.1. Materials
Ammonium metavanadate (NH4VO3) was obtained from S.D. Fine Chem. Ltd. (India). Extra
pure varieties of 1,10-phenanthroline, hydrogen peroxide (30% w/v), phenol red, and meth-
anol (G.R.) were the products of E. Merck (India) and were used directly. All other reagents

JOURNAL OF COORDINATION CHEMISTRY
3
used were of analytical grade. The analytical grade solvents used for physicochemical studies
were further purified before use wherever necessary, by literature methods [26].
2.2. Synthesis of the metal complex (NH4)[VO(O2)2(phen)](H2O)2
Ammonium metavanadate (0.117 g, 1 mmol) was dissolved in 1.0 mL of hydrogen peroxide
taken in a beaker and placed in an ice bath at 0–5 °C, and the pH of the resulting solution
was made 3 by adding dilute HNO3. In a separate beaker, the ligand (1,10-phenanthroline)
(0.198 g, 1 mmol) was dissolved in methanol and the solution was added dropwise to the
ammonium metavanadate solution in hydrogen peroxide with constant stirring. After the
addition was complete, the mixture was stirred for about 2 h resulting in a yellow solution
which was filtered and the filtrate was kept at 4 °C for slow evaporation. Yellow needle-shaped
crystals of ammoniumdiaqua oxidodiperoxidophenanthrolinevanadate(V) separated out
([VO(O2)2(phen)](NH4)(H2O)2) after a few days. Yield: 0.2217 g, 61%. IR (KBr, pellet, cm−1):
1517 m (νC–C), 1426s, 724s (νC–N), 926s (νO–O), 622s, 584s (νV–O). UV–vis (H2O)=224, 271
(λmax), 293 nm. ES mass (m/z): 365.09 (Figure S2).
2.3. X-ray structure
The crystal structure of the vanadium complex was determined by single-crystal X-ray dif-
fraction. All geometric and intensity data were collected at room temperature using an
automated Bruker SMART APEX-II diffractometer equipped with a CCD detector and fine
focus 1.75 kW sealed tube Mo Kα X-ray source (λ = 0.71073 Å) [27]. All data were corrected
for Lorentz and polarization effects [27]. The data were processed using SAINT and absorption
corrections were made using SADABS [27]. Structures were solved by the combination of
Patterson and Fourier techniques and refined by full-matrix least-square method using the
SHELX suite of programs [28a]. All hydrogens belonging to 1 were placed in their calculated
positions and refined using a riding model. Anisotropic refinement was carried out for all
non-hydrogen atoms. Perspective views of the molecules were obtained by Mercury [28b]
and ORTEP3 [28c].
The X-ray crystallographic data (CIF file) for the structure reported in this paper have been
deposited in the Cambridge Crystallographic Data Center (CCDC) and the deposition number
is CCDC 1533513.
2.4. Physical measurements for the characterization of the complexes
UV–vis spectra were recorded on a Shimadzu U-1800 spectrophotometer; IR spectra (KBr
disk) were recorded on a Perkin Elmer IR spectrophotometer. Electrical conductivity of a
10−3 M dm−3 aqueous solution of the complex was measured with a Systronics 304 digital
conductivity meter. Magnetic susceptibility measurements were made with a vibrating sam-
ple magnetometer PAR 155 model. All pH measurements were made with an Elico (India)
digital pH meter. The mass spectral analyses were done using a mass spectrometer (model:
XEVO-G2QTOF#YCA351).

4
H. ADHIKARI AND K. K. MUKHERJEA
2.5. Assessment of bromination activity
The bromination reaction was carried out in an aqueous medium at 30 0.5 °C. The reactions
involving bromide were performed under constant temperature. Solutions used for kinetic
measurements were maintained at a constant concentration of H+ (pH = 5.0) by the addition
of NaH2PO4–Na2HPO4 [29].The rate of this reaction is described by the rate lawdc∕dt = kcxcycz
1
3
2
, and the equation of log (dc/dt)=logk + xlogc1 + ylogc2 + zlogc3 is obtained. It corresponds
to −log (dA/dt)=−xlogc1−b (b = logk + ylogc2 + zlogc3), where A is the measurable absorb-
ance of the resultant solution; k is the reaction rate constant; c1, c2, c3 are the concentrations
of the vanadium complex, KBr and phenol red, respectively; while x, y, z are the corresponding
reaction orders. A plot of absorbance data at 592 nm versus time gave a straight line and
from the slope of this line the reaction rate of the oxidovanadium complex (dA/dt) was
obtained. By changing the concentration of the complex, a series of dA/dt data were obtained
and from a plot of −log (dA/dt) versus −logc1 the reaction rate constant (k) was calculated.
3. Results and discussion
The aim of the present work is to develop a bromoperoxidase mimic, one of the demanding
fields of biochemical research. The strategy adopted to attain the goal is to synthesize the
oxidodiperoxidovanadium(V) complex followed by examining the catalytic bromination of
phenol red to bromophenol blue and subsequent exploitation of the compound in H2O2
sensing.
3.1. Synthetic aspects of the complex
Although the synthesis of an oxidodiperoxido vanadium complex with 1,10-phenanthroline
was reported earlier, no mention of the structurally characterized mononuclear oxidodiper-
oxido vanadium compound with 1,10-phenanthroline could be found in literature [30]. We
have been successful in characterizing the oxidodiperoxido vanadium compound (NH4)
[VO(O2)2(phen)](H2O)2 structurally and the crystal data are reported in the present work. The
complexes were synthesized following Scheme 1.
3.2. Crystal structure of the complex
Single-crystal X-ray diffraction analysis (Table 1) reveals that the complex crystallizes in the
monoclinic P21/c space group. An ORTEP view of the asymmetric unit of the complex is
shown in Figure 1. The crystal structure of the oxidodiperoxido vanadium complex consists
of a discrete monomeric anionic unit, [VO(O2)2(phen)], with an ammonium moiety as counter
cation. Two H2O molecules are also found in the crystal lattice. In this complex, the vanadium
atom is surrounded with a N2O5 coordination sphere which is defined by one neutral biden-
tate ligand 1,10-phenanthroline (phen) (N, N donors), two peroxido, and an oxido moiety.
One of the two ring-nitrogen atoms of the neutral bidentate phen ligand, N2, occupies
the equatorial plane together with the two peroxido groups of oxygen atoms O1, O2, O3,
O4. The coordination environment around the vanadium can be described as a distorted
seven-coordinate pentagonal-bipyramid. The axial positions of the coordination sphere are
occupied by the oxido group O5 and one ring-nitrogen atom N1 of the bidentate ligand

JOURNAL OF COORDINATION CHEMISTRY
5
Scheme 1. schematic representation for the preparation of the complex.
Table 1. X-ray diffraction analysis data of complexes.
Parameter
Complex
empirical formula
M
C
12h16n3o7 V
365.22
T/K
λ/Å
373
0.71073
monoclinic
P 1 21/c 1
Crystal system
space group
unit cell dimensions
a/Å
b/Å
c/Å
α/°
β/°
7.0581(4)
13.5897(7)
16.5083(9)
90
96.242(4)
90
γ/°
V/ Å3
1574.05(15)
4, 1.541
Z, D/g cm−3
f(000)
752
Crystal size/mm
2θ range for data collection (°)
reflection
0.2 × 0.1 × 0.08
3.9 to 55.34
25,888
independent reflections (rint)
Completeness to θ = θmax (%)
3671, 0.0838
100
0.669
linear absorption coefficient μ (mm−1
refinement method
)
full-matrix least-squares on F2
3671 / 4 / 230
0.989
data / restraints / parameters
Goodness-of-fit on F2
final r indices [I > 2σ(I)]
r1 = 0.0562,
wr2 = 0.1408
r1 = 0.1065,
wr2 = 0.1645
0.50, −0.43
r indices (all data)
largest diff. peak, hole/Å3
1,10-phen. Butler has already established that generally vanadium with an oxidodiperoxido
arrangement and with one bidentate or two monodentate ligands crystallizes in a distorted
pentagonal bipyramidal geometry [16]. A similar kind of structure with a different ligand
system has been reported earlier [31]. The structural parameters are consistent with other
vanadium(V) oxido-peroxido complexes which generally feature the vanadium atom coor-
dinated to an oxido atom in an axial position and the peroxide group bound in the equatorial
positions [32]. The length of the oxido V–O5 double bond is 1.609(3) Å, which is consistent
with values found in other typical oxidovanadium(V) complexes [33]. The trans effect can
be observed in the elongation of the apical coordinated N1 of the bidentate phen ligand
(V1–N1) bond [2.336(3) Å], compared with the equatorial V1–N2 distance [2.152(3) Å]. Again,

6
H. ADHIKARI AND K. K. MUKHERJEA
Figure 1. orteP view of the structure of the complex with ellipsoids at 30% probability.
the V1–N2 bond distance [2.152(3) Å] is longer than the V1–O1, V1–O2, V1–O3, and V1–O4
bond distances (1.869(3), 1.902(3), 1.870(3), and 1.923(3) Å, respectively) due to the trans
effect of the oxygen atoms of two η2-peroxido ligands. The equatorial V–O (peroxido) bonds
have comparable lengths as above mentioned values, with O–O bond distances of 1.461(3)
Å (O1–O2) and 1.449(4) Å (O3–O4) while the O1–V1–O2 and O3–V1–O4 angles are 45.60(10)°
and 44.90(11)°, respectively. The O5–V1–O3–O4 and O5–V1–O1–O2 torsion angles are
90.92(17) and −90.29(16), respectively. The bidentate neutral 1,10-phen ligand binds the
metal forming one five-membered chelate ring at the vanadium center with the correspond-
ing bite angle of 73.05(10)° (N1–V1–N2). The relevant bond lengths and angles are presented
in Table 2. Hydrogen bonds are present in between two asymmetric units and are shown in
Figure 2. Extended interactions are avoided for clarity.
3.3. IR and UV–vis spectroscopic characterization of the complex
The characteristic IR spectra of oxidodiperoxidovanadium complexes usually show sharp
bands in the 942–970 cm−1 region due to the ν(V=O) [34] mode and the four bands can be
expected corresponding to normal vibrations involving the (O2)V(O2) group because of vana-
dium – peroxo oxygen-stretching vibrations (νl, ν2, ν3 and ν4 (V–Op)) (Op = peroxo oxygen)
[35]. For these kinds of systems, the νl and ν2 (V–Op) vibrations occur at approximately ν ~
630 cm−1 and the ν3 and ν4 (V–Op) vibrations occur at about ν ~ 520 cm−1 for symmetric and
antisymmetric stretching, respectively [35]. But, in the case of pentagonal bipyramidal struc
-
tures, νl and ν2 (V–Op) vibrations and ν3 and ν4 (V–Op) vibrations occur at ν = 620 and
ν = 590 cm−1, respectively [35]. Hence, the present findings of the appearance of the νl and
ν2 vibrations at ν = 622 cm−1 and ν3 and ν4 vibrations appear at ν = 584 cm−1 support the
presence of the (O2)V(O2) group and pentagonal bipyramidal geometry.
A strong band is at ν = 926 cm−1 for the O–O intra-stretching mode of the V (O2) group.
A low-intensity stretch ν(V=O) is positioned at 955 cm−1. The strong vibration bands at
1517 cm-1 and 1426 cm−1, 724 cm−1 are due to the C–C and C–N vibration of the ligand in
the complex, respectively.

JOURNAL OF COORDINATION CHEMISTRY
7
Table 2. selected bond lengths (Å) and angles (°) of the complex.
Bond lengths (Å)
V1–o1
V1–n2
V1–o4
n1–C10
n2–C12
C8–C7
1.868(3)
2.153(3)
1.923(3)
1.312(4)
1.356(4)
1.380(6)
1.421(5)
1.347(6)
V1–o2
V1–o5
o1–o2
n1–C11
C10–C9
C7–C11
C12–C4
C3–C4
1.902(2)
1.610(2)
1.464(3)
1.361(4)
1.414(6)
1.408(5)
1.412(4)
1.397(6)
V1–n1
V1–o3
o3–o4
2.334(3)
1.868(2)
1.450(4)
1.322(4)
1.362(7)
1.446(6)
1.384(5)
1.420(5)
1.317(6)
n2–Cl
C9–C8
C7–C6
C1–C2
C4–C5
C5–C6
C11–C12
C2–C3
Bond angles (°)
o1–V1–o2
o1–V1–o4
o2–V1–o4
o5–V1–o2
o5–V1–o3
o3–V1–o2
o3–V1–o4
o2–o1–V1
o3–o4–V1
45.68(10)
132.16(11)
158.45(11)
100.05(13)
104.41(12)
133.02(12)
44.97(11)
68.40(13)
65.51(14)
o1–V1–n1
o2–V1–n1
n2–V1–n1
o5–V1–n1
o5–V1–o4
o3–V1–n1
o4–V1–n1
o1–o2–V1
C10–n1–V1
85.90(11)
79.10(10)
73.10(10)
164.97(12)
100.78(12)
86.42(11)
79.35(10)
65.92(13)
129.7(3)
o1–V1–n2
o2–V1–n2
o5–V1–o1
o5–V1–n2
o3–V1–o1
o3–V1–n2
o4–V1–n2
o4–o3–V1
C11–n1–V1
128.94(11)
84.27(10)
104.36(13)
91.87(12)
89.22(12)
133.44(12)
89.60(11)
69.52(14)
112.7(2)
Figure 2. PoV-ray image of h-bonding between different asymmetric units in wireframe presentation.
The electronic spectrum of the vanadium compound exhibits λmax at 224 nm
(ε = 14,460 M−1 cm−1). This is due to the LMCT transition of O22− → vanadium(V); the shoulder
at 293 nm (ε = 3990 M−1 cm−1) and a strong band at 271 nm (ε = 11,120 M−1 cm−1) maybe
assigned as the intra ligand π → π* transitions of the aromatic ring of the coordinated ligand.
The mass spectral results also support the formulation of the complexes (see synthesis
of the complexes).

8
H. ADHIKARI AND K. K. MUKHERJEA
3.4. Bromination activity for mimicking V-HPOs
The [VO(O2)]+ core of the peroxovanadium(V) complex (NH4)[VO(O2)2(phen)](H2O)2 is to some
extent equivalent to the respective mono-peroxovanadium(V) intermediate species of the
VHPO enzymes which plays a key role in the enzymatic processes [36–40] in the presence
of H2O2. Herein, the catalytic bromination activity of the complex has been tested using
phenol red as substrate, which is characterized by the conversion of phenol red to bromo-
phenol blue. The reaction is rapid and stoichiometric. The reaction process is presented in
Scheme 2.
Addition of the solution of the vanadium complex to the standard reaction of bromide,
in a phosphate buffer with phenol red as a trap for oxidized bromine, resulted in change in
color of the solution from yellow to blue. The electronic absorption showed a decrease in
absorbance of the peak at 443 nm for the loss of phenol red and an increase of the peak at
592 nm with production of bromophenol blue (shown in Figure 3).
3.4.1. Kinetic studies of bromination
To understand the kinetics of this reaction, the reaction was followed in aqueous medium
at 30 0.5 °C and was monitored by a gradual change in the concentration of the complex.
The rate of this reaction is expressed by the rate law dc∕dt = kcxcycz. According to the
1
3
2
Beer–Lambert law, A = εdc, which on differentiation we get dA/dt = εd(dc/dt). Then, the
equation −log (dA/dt)=−xlogc1−b (b = logk + ylogc2 + zlogc3) is obtained (ε, the molar
absorption coefficient, for bromophenol blue = 14 500 M−1 cm−1 at 592 nm; ‘d’ is the light
path length of the sample cell (d = 1)), where A is the measurable absorbance of bromophe-
nol blue at 592 nm, k is the reaction rate constant, and c1, c2, c3 are the concentrations of the
vanadium complex, KBr and phenol red, respectively; x, y, z are the corresponding orders of
the reaction. Plots of absorbance data at 592 nm versus time for various concentration of
the complex gave straight lines and from the slopes of these lines a series of reaction rates
of the complex (dA/dt) were obtained (Figure 4). From Figure 4, it has been observed that
after ~75 min, the rate of reaction increases slowly which can be supported by the visible
difference in the respective absorbance values. The plot of −log (dc/dt) versus −logc
Scheme 2. the reactive process of bromination reaction for the complex.

JOURNAL OF COORDINATION CHEMISTRY
9
Figure 3. oxidative bromination of phenol red catalyzed by the oxidovanadium complex (0.02 mmol).
spectral changes at 10 min intervals. spectral data taken of aliquots in ph = 5.0 aqueous phosphate buffer,
c(phosphate buffer) = 50 mmol l−1, c(KBr) = 0.4 mol l−1, c(phenol red) = 0.1 mmol l−1.
Figure 4. a series of linear calibration plots of the absorbance at 592 nm dependence of time for different
concentrations of complex. Conditions used: ph 5.0, c(KBr) = 0.4 m l−1, c(h2o2) = 0.02 m l−1, c(phenol red)
= 10−4 m l−1. c(complex 2/m l−1) = a: 1 × 10−6; b: 2.15 × 10−6; c: 3.23 × 10−6; d: 4.31 × 10−6; e: 5.38 × 10−6.
(Figure 5) gives a straight line with a slope of 1.0276 and an intercept of 2.0224. The orders
of the reaction with respect to KBr and phenol red (y and z) are considered to be 1 according
to the literature [41]; c2 and c3 are known to be 0.4 and 10−4 M L−1, respectively, so the reaction
rate constant (k) for this complex can be calculated as 0.238 × 103 (M L−1)−2 s−1. The result
shows that the order of the reaction with respect to the oxidodiperoxidovanadium complex

10
H. ADHIKARI AND K. K. MUKHERJEA
Figure 5. −log(dc/dt) vs. −log c (c is the concentration of the complex); conditions used: c (phosphate
buffer) = 50 mm l−1, ph = 5.0, c(KBr) = 0.4 mol l−1, c(phenol red) = 10−4 m l−1.
in bromination reaction is close to 1, confirming the first-order dependence on vanadium
species.
The mechanism of action matches the earlier proposition [20, 40, 42]. The bromide ion
(Br−) is oxidized rapidly by the [VO(O2)2N2]- moiety and converted to the bromonium ion
+
(Br+) which exists in reaction medium as Br3 , Br2, or HOBr [43]. Attack of a bromide ion at
one of the protonated peroxido atoms and the uptake of a proton from the medium leads
to the generation of hypobromous acid (HOBr) followed by restoration of the ion to its native
state by the attack of H2O2 on the intermediate [40]. The in situ generated bromonium ion
in the form of hypobromous acid attacks the organic substrate (phenol red) to form the
corresponding brominated derivative (here bromophenol blue). We compared the catalytic
activity and kinetic data of some complexes reported previously (Table 3). It is found that
peroxidovanadium complexes show higher catalytic activity than those of oxidovanadium
complexes such as 2 and 3 [24], probably because of its built-in peroxido moiety [44].
Therefore, it maybe considered that the catalytic activity of the complexes may have a con-
nection with their structural motifs.
3.4.2. Effect of the concentration of H2O2 on bromination
The dependence of the concentration of H2O2 on the catalytic bromination reaction has
been calculated to develop a new H2O2 detection method. The results show that the absorb-
ance at 592 nm depends linearly on the concentration of H2O2 along with the formation of
bromophenol blue (Figure 6). The present work reveals that the detection limit of H2O2
concentration is 0.1594 mol L−1, approximately 0.16 mol L−1 (Figure 7). It indicates that above
this concentration limit the catalyst can detect H2O2. This value is much lower than previously
reported literature values [25, 26]. We have compared our work with previously reported
values that are presented in Table 4. Although, the earlier report by Liu and coworkers [25]

JOURNAL OF COORDINATION CHEMISTRY
11
Table 3. Comparisons of the kinetic data for the complexes.
k(M L−1)−2s−1
Ref.
Complexes
1
2
3
4
1.5754 × 103
0.238 × 103
0.187 × 103
0.184 × 103
[30(b)]
this work
[24]
[25]
1 na[Vo(o2)2(C10h8n2)]·8h2o; 3 (Vo)2(2,2′-bipy)2(bta)(h2o)2; 4 (Vo)2(1,10-phen)2(bta)(h2o)2.
Figure 6. the measurable absorbance dependence on the concentration of h2o2 at 10 min intervals of
the complex. Condition used: ph 5.0, c(KBr) = 0.4 m l−1, c(complex 1) = 0.02 m l-1, c(phenol red) = 10−4 m
l−1. c(h2o2/m l−1) = 0.2, 0.4, 0.6, 0.8, 1.0. (a: 35 min; b: 45 min; c: 55 min; d: 65 min; e: 75 min).
presented a lower detection limit of H2O2, they used metal clusters instead of metal
complexes.
Hence, the above observations suggest that the present complex maybe used as a simple
system for the detection or sensing of H2O2 through the bromoperoxidation catalysis of
phenol red, and possesses potential diagnostic property for sensing and estimation of H2O2.
3.5. Kinetic stability of the complex
Since the bromoperoxidation was monitored spectrometrically until complete conversion
of the substrate over 8 h, the kinetic study of the decomposition of the complex for ~15 h
in aqueous buffer solution was carried out to prove the stability of the complex (Figure S1)
during conversion of phenol red. Electronic absorption spectra of the complex solution were
recorded after 3 min intervals to see the change in absorbance with respect to time. The
absorbance values at 271 nm were plotted against respective time and fitted in a first-order
rate equation, from which the dissociation constant (Kdiss) was obtained. The dissociation
constant (Kdiss) was (1.889 0.02)×10−5 s−1. This clearly establishes the stability of the com-
plex during the course of the reaction.

12
H. ADHIKARI AND K. K. MUKHERJEA
Figure 7. the linear calibration plot of the absorbance at 592 nm on the concentration of h2o2 after
35 min for 1 as catalyzer.
Table 4. Comparative study of h2o2 detection.
Detection limit value (mol/ L−1)
Ref.
Name of compound
[Vo(tp)(pz)(sCn)]·1/2Ch2Cl2
[Vo(tp)(pztp)]·2h2o
(Vo)2(1,10-phen)2(bta)(h2o)2
[Vo(o2)2(phen)](nh4)(h2o)2
0.48
1.1
1.0
[25]
[25]
[24]
0.16
this work
4. Conclusion
The vanadium(V) oxidodiperoxido complex with 1,10-phenanthroline ligand has been syn-
thesized and structurally characterized. The complex exhibits good vanadium-based bro-
moperoxidase activity (VBrPO) in the model system and also presents a sensitive optical
response in the presence of a low concentration of H2O2. So the compound can be used as
a H2O2 sensor as well. A comparison of literature values indicates that the present complex
is a better candidate for H2O2 detection via bromination of phenol red. Based on the results,
we expect that a simple and sensitive H2O2 detection device will be exploited in the future.
Further research on the potential application of the H2O2 detection is ongoing.
Acknowledgements
HA is thankful to UGC for providing Junior Research Fellowship. Thanks are due to Jadavpur University
for facilities. The authors are thankful to Dr. Kuntal Pal, University of Calcutta, for assistance.
Disclosure statement
No potential conflict of interest was reported by the authors.

JOURNAL OF COORDINATION CHEMISTRY
13
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