Synthesis, structures and properties of the catalytic bromination reaction of a series of novel scorperate oxidovanadium complexes with the potential detection of hydrogen peroxide in water

Article abstract of DOI:10.1016/j.saa.2013.06.081

A series of scorpionate oxovanadium (IV) complexes: [VO(Tp ^4I)(pz)(SCN)]·1/2CH2Cl2 (1), [VO(Tp)(pzTp)] ·2H ₂O (2), [VO(Bp)(Tp^4I)] (3) and [VO(C₅H ₇O₂)(Tp^4I)]·CH₃OH (4) (Bp: [H₂B(pz)²], Tp: [HB(pz)³], Tp^4I: [HB(4I-pz)³], pzTp: [B(pz)⁴]) have been synthesized and characterized by elemental analysis, IR spectra, UV-Vis spectroscopy, powder X-ray diffraction, single-crystal X-ray diffraction and thermal gravimetric analysis (TG). Structural analysis shows that the coordination environment of vanadium atom is N₅O, to form a distorted octahedron geometry. In addition, the catalytic activities of the bromination reactions for complexes 1 and 2 in phosphate buffer with phenol red as a trap were evaluated primary by UV/Vis spectroscopy, and a practical application of H₂O₂ detection was firstly observed in the catalytic reaction system.

Full text of DOI:10.1016/j.saa.2013.06.081

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 115 (2013) 476–482
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, structures and properties of the catalytic bromination
reaction of a series of novel scorperate oxidovanadium complexes
with the potential detection of hydrogen peroxide in water
a
b
a
a,
⇑
a
a
a
Rui Zhang , Jing Liu , Chen Chen , Yong-Heng Xing , Qing-Lin Guan , Ya-Nan Hou , Xuan Wang ,
a
c,
⇑
Xiao-Xi Zhang , Feng-Ying Bai
a
College of Chemistry and Chemical Engineering, Liaoning Normal University, Huanghe Road 850#, Dalian 116029, PR China
Regenerative Medicine Centre, First Affiliated Hospital of Dalian Medical University, Dalian 116011, PR China
College of Life Science, Liaoning Normal University, Dalian 116029, PR China
b
c
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
4
I
Four scorpionate oxovanadium (IV) complexes: [VO(Tp )(pz)(SCN)]Á1/2CH
2
Cl
2
(1), [VO(Tp)(pzTp)]Á2H
2
O
ꢀ
ꢀ
Four novel oxidovanadium
complexes.
Poly(pyrazolyl)borate ligand modified
by iodine.
4
I
4I
3À
(
[
2), [VO(Bp)(Tp )] (3) and [VO(C
5
H
7 2
O
)(Tp )]ÁCH
3
OH (4) (Bp: [H
2
B(pz)[2-]];Tp: [HB(pz) ];Tp[4I]:
3
À
4À
HB(4I-pz) ];pzTp: [B(pz) ]) have been synthesized and characterized by elemental analysis, IR, UV–
Vis spectroscopy, powder X-ray diffraction, single-crystal X-ray diffraction and thermal gravimetric anal-
yses (TG).
ꢀ
ꢀ
ꢀ
Crystal structure.
Bromination reaction activity.
Potential detection of hydrogen
peroxide.
a r t i c l e i n f o
a b s t r a c t
4
I
Article history:
A series of scorpionate oxovanadium (IV) complexes: [VO(Tp )(pz)(SCN)]Á1/2CH Cl (1), [VO(Tp)(pzTp)]
2
2
Received 28 March 2013
Received in revised form 13 June 2013
Accepted 19 June 2013
4I
4I
2À
3À
4I
Á2H
2
O (2), [VO(Bp)(Tp )] (3) and [VO(C
5
7
H O
2
)(Tp )]ÁCH
3
OH (4) (Bp: [H
2
B(pz) ], Tp: [HB(pz) ], Tp :
3À
4À
[
HB(4I-pz) ], pzTp: [B(pz) ]) have been synthesized and characterized by elemental analysis, IR spec-
tra, UV–Vis spectroscopy, powder X-ray diffraction, single-crystal X-ray diffraction and thermal gravi-
metric analysis (TG). Structural analysis shows that the coordination environment of vanadium atom
Available online 1 July 2013
is N
5
O, to form a distorted octahedron geometry. In addition, the catalytic activities of the bromination
Keywords:
reactions for complexes 1 and 2 in phosphate buffer with phenol red as a trap were evaluated primary
by UV/Vis spectroscopy, and a practical application of H
reaction system.
Oxidovanadium complex
Poly(4-I-pyrazolyl)borate
Bromination reaction activity
Synthesis
O
2 2
detection was firstly observed in the catalytic
Ó 2013 Elsevier B.V. All rights reserved.
Crystal structure
⇑
Corresponding authors. Tel.: +86 411 82156987.
E-mail addresses: yhxing2000@yahoo.com (Y.-H. Xing), baifengying2000@163.com (F.-Y. Bai).
1
386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.06.081

R. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 115 (2013) 476–482
477
Introduction
carried out on a Perkin Elmer 240C automatic analyzer. The infrared
spectra were recorded on a JASCO FT/IR-480 spectrometer with
pressed KBr pellets in the range 200–4000 cm . UV–Vis spectra
were recorded on JASCO V-570 spectrometer (200–1100 nm, in
form of solid sample).
À1
Vanadium complexes have been studied for a long time owning
to the biological and catalytic properties of relevant systems, such
as haloperoxidation, nitrogen fixation, metalloprotein, and insulin
mimicking [1,2]. Among these systems, vanadium haloperoxidases
(
V-HPOs) have received continuing attention since their unique
Synthesis of the complexes
characteristics and potential catalyzing activities in oxidation reac-
tions, which are able to oxidize the two-electron oxidation/oxy-
4
I
[VO(Tp )(pz)(SCN)]Á1/2CH
2 2
Cl (1)
+
+
À
(0.0163 g, 0.1 mmol), Tp4I (0.063 g, 0.1 mmol), pz
genation of halide to an {X }, where {X } is X
2
, X and/or XOH,
VOSO
4
3
i.e. hypohalous acid in the presence of peroxides [3–6].
(0.0068 g, 0.1 mmol) and KSCN (0.0097 g, 0.1 mmol) were
dissolved in methanol (10 mL), stirred at room temperature for
4 h, and then produced a large amount of violet precipitate. The
product was separated by filtration, and the purple crystals were
The structure of V-HPOs active centers reveals that the central
vanadium is in a trigonal–bipyramidal environment by four oxygen
e
atoms and the axially binding N of a histidine residue, which is
embedded in the protein through an extensive hydrogen-bonding
network. The active site is considered to consist of oxidovanadium
with V@O moiety containing O, N donor ligands [7–11]. In particu-
recrystallized from CH
63.4%. Anal. Calc. For C13.5
15.26. Found: C, 19.64; H, 1.48; N, 15.28.
2
Cl
2
solution. Yield (based on V): 0.052 g,
H
12ON
9
BClSVI : C, 19.62; H, 1.47; N,
3
lar, the interaction of simple vanadium species (VO2 and VO ) with
various ON or NN donor atoms having bioactive ligands is of grow-
ing interest recently. Based on the points above, we are trying to find
some stable artificial enzyme mimics, such as VO-Tp (Tp: poly(pyr-
azolyl)borate ligands) complexes [12–15]. To our best knowledge, a
number of vanadium complexes have been synthesized for studying
and understanding the relationship between their structures and
catalytic activities [16–20]. However, It is worth to mention that
chelate scorpionate ligands used in the complexes are almost the
common and simple poly(pyrazolyl)borate ligands, such as:
+
3+
[VO(Tp)(pzTp)]Á2H
2
O (2)
A methanol solution of Tp (0.025 g, 0.1 mmol) and pzTp
(0.0318 g, 0.1 mmol) was added dropwise to an aqueous solution
4
(10 mL) of VOSO (0.0163 g, 0.1 mmol) with continuous stirring
for 3 h to get a blue mixture. The precipitate was filtered out,
and the light blue filtrate was placed at room temperature for sev-
eral days. Blue crystals suitable for X-ray diffraction were obtained.
Yield (based on V): 0.029 g, 48.57%. Anal. Calc. For C21H O N B
28 3 14 2-
V: C, 42.24; H, 4.73; N 32.84. Found: C, 42.25; H, 4.72; N, 32.86.
2
À
4I
3À
4À
3À
Ã
2 2
[H B(pz) ] (Bp), [HB(pz) ] (Tp), [HB(3,5-Me pz) ] (Tp ), [HB(4I-
3À
4I
pz) ] (Tp ), and [B(pz) ] (pzTp), and the poly(pyrazolyl)borate
ligands were divided into three kinds, such as: (i) the scorpionate
[VO(Bp)(Tp )] (3)
The synthesized method of complex 3 was similar to that of
complex 2, however, ligands Tp and pzTp were replaced by Tp4I
(0.063 g, 0.1 mmol) and Bp (0.0147 g, 0.1 mmol). The bluish violet
crystals were obtained. Yield (based on V): 0.032 g, 39.77%. Anal.
2 2
peroxidevanadium complexes: VO(O )(pzH)(Tp) and VO(O )(pz)
(
pzTp), etc. [21]; (ii) the scorpionate oxovanadium complexes:
Ã
TpVO(acac) [22] and Tp VO(Me-acac), etc. [23]; (iii) the scorpionate
oxovanadium complexes with carboxylic acids: Tp VO(pzH )(HOO-
CCH CH COO) [24] and Tp VO(pz )(C H COO), etc. [25]. Although a
2 2 6 5
Ã
Ã
2 3
Calc. For C15H15O N10B VI : C, 22.39; H, 1.88; N, 17.41. Found: C,
Ã
Ã
22.41; H, 1.87; N, 17.44.
number of oxovanadium complexes containing scorpionate ligands
have been reported, vanadium complexes with substituted scorpio-
nate ligands, namely, pyrazole ring of which is modified by other
4
I
[VO(C
5
H
7
O
2
)(Tp )]ÁCH
3
OH (4)
4
I
VO(acac)
2
(0.027 g, 0.1 mmol) and Tp (0.063 g, 0.1 mmol)
functional groups (ph, NO
2
, I, etc.) are relatively rare. Therefore,
were dissolved in methanol (15 mL), and stirred for 4 h at room
temperature and gave a violet solution. The mixed solution was
placed at room temperature for a few days, and then the purple
crystals were obtained. Yield (based on V): 0.11 g, 71.15%. Anal.
H O N B V I : C, 22.54; H, 2.09; N, 10.87. Found:
32 7 12 2 2 6
C, 22.55; H, 2.12; N, 10.86.
we are interested in studying on modified Tp ligands by iodine
and their oxidovanadium complexes. As we all know that iodine is
a functional group with special property (e.g. donor electron ability,
large ion radius, inducing action and so on). In this work, it is found
that the H atom of the pz ring from Tp is replaced by iodine, leading
Calc. For C29
4
I
to the change of some chemical characterization of ligand Tp (e.g.
the coordination ability and solubility, etc.) comparable to Tp, thus,
in order to study the influence of the structure and the function of
the oxovanadium complexes on this diversification, we designed
X-ray single crystal structural determination
The crystals of 1–4 were mounted on glass fibers for X-ray mea-
surement, respectively. Reflection data were collected at room
temperature on a Bruker AXS SMART APEX II CCD diffratometer
with graphite-monochromatized Mo K
and a scan mode. All the measured independent reflections
(I > 2 (I)) were used in the structural analyses, and semi-empirical
absorption corrections were applied using SADABS program [27].
The structures were solved by the direct method using SHELXL-
97 [28]. All hydrogen atoms of the organic ligands were fixed at
calculated positions geometrically and refined by using a riding
4I
and synthesized four new complexes, [VO(Tp )(pz)(SCN)]Á1/2CH2-
4I
Cl
2
(1), [VO(Tp)(pzTp)]Á2H
2
O (2), [VO(Bp)(Tp )] (3) and [VO(C
OH (4) by the reaction of oxovanadium starting
material (VOSO or VO(acac)
), Tp ligand (Bp, Tp, Tp4I or pzTp) with
5 7-
H
4
I
O
2
)(Tp )]ÁCH
3
a radiation (k = 0.71073 Å)
x
4
2
two common auxiliary ligands (pyrazolyl and KSCN) in the mixture
solution of methanol and water at room temperature. These
complexes were characterized by elemental analysis, IR spectra,
UV–Vis spectroscopy, single-crystal X-ray diffraction and thermo
gravimetric analyses (TG).
r
3
model. The hydrogen atoms of the lattice water or free CH O group
were found in difference Fourier map. The non-hydrogen atoms
were refined with anisotropic thermal parameters.
Experimental section
Materials and methods
Measurement of bromination activity in solution
All the chemicals used were analytical grade and without further
purification. The scorpionate ligands were synthesized according to
the literature method [26]. Elemental analyses for C, H, and N were
The bromination reaction activity tests were carried out at the
constant temperature of 30 °C ± 0.5 °C. Oxidovanadium complexes
were dissolved in a mixed solution of 25 mL H O–DMF (DMF:
2

4
78
R. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 115 (2013) 476–482
2
mL; H
were maintained at a constant concentration of H (pH 5.8) by the
addition of NaH PO ANa HPO buffer solution [29]. Reactions were
2
O: 23 mL). The solutions used for kinetic measurements
indicate the absence of the ACH
3
/ACH
2
. The characteristic bands
+
À1
around 2500 cm are assigned to BAH stretching vibration from
4
I
À1
À1
2
4
2
4
the Bp, Tp, Tp or pzTp moiety: 2524 cm for 1, 2493 cm for
À1
À1
initiated with the presence of phenol red solution. The oxidovanadi-
um complexes with five different concentrations were confected in
five cuvettes which were put into the constant temperature of
warming water and spectral changes were recorded using a 721
UV–Vis spectrophotometer every interval 5 min. Finally, we col-
lected the resulting data during the reaction. It is assumed that
the rate of this reaction is described by the rate equation: dc/
2, 2507 cm for 3 and 2489 cm for 4, respectively. The strong
À1
À1
À1
bands at 1507 cm for 1, 1507 cm for 2, 1504 cm for 3 and
1519 cm for 4 are attributed to the stretching vibration of C@N
À1
from the pz or 4I-pz of the scorpionate ligands. Two wide and
À1
À1
strong bands at 1580 cm and 1370 cm for the complex 4 are
attributed to the absorption of the asymmetric and symmetric
stretching vibration of the C@O group. Band of SCN group is at
x
1
y
2
3
z
À1
dt = kc c c , then the equation of ‘‘log(dc/dt) = logk + xlogc
1
+ -
’’ was obtained, it is corresponding to ‘‘Àlog(dc/
À b (b = logk + ylogc + zlogc )’’ where k is the reac-
tion rate constant; c , c and c are the concentrations of the com-
2087 cm for 1. The strong and sharp stretching vibration bands
À1
ylogc
2
+ zlogc
3
of the V@O are observed in the region of 970–977 cm , which is
dt) = Àxlogc
1
2
3
similar to those in related complexes [31]. The strong absorption
À1
À1
4
À1
1
2
3
bands at 610 cm for 1, 611 cm for 3 and 610 cm for 4 are as-
I
À1
plex, KBr and phenol red, respectively; while x, y, z are the
corresponding reaction orders. According to Lambert–Beer’s law,
signed to the CAI vibration of Tp ligands. Band of 463 cm is due
À1
to the VAO stretching vibration, while bands at 356–481 cm are
A =
e
Á d Á c, which is differential, dA/dt =
e
Á d Á (dc/dt), where A is
assigned to stretching vibration of VAN bonds [31–33]. The infra-
red spectra of the complexes (1–4) are consistent with the struc-
tural characterization of the complexes 1–4.
the measurable absorbance of the resultant;
coefficient, which of bromophenol blue is measured as 14,500 M
e
is molar absorption
À1
-
À1
cm at 592 nm; d is light path length of sample cell (d = 1). When
the measurable absorbance data were plotted versus reaction time,
a line was obtained and the reaction rate of the complexes (dA/dt)
was given by the slope of the line. By changing the concentration
of oxovanadium complexes in the reaction system, a series of dA/
dt data could be obtained. The reaction rate constant (k) could be ob-
UV–Vis absorption spectra
The UV–Vis absorption spectra of the complexes 1, 2 and 4 are
recorded in form of the solid sample (Fig. 1). They have similar
absorption patterns. In the high-frequency region, the absorption
Ã
peaks at 266 nm for the complex 2 is assigned to
p–p
transition
tained according to a plot of Àlog(dc/dt) versus Àlogc
1
and were fit-
of the pyrazoly ring from the Tp ligands and pzTp ligands, and
ted using the curve-fitting software in the program Microsoft Excel
by generating a least squares fit to a general equation of the form
absorption peaks at 340 nm for 1 and 330 nm for 4 are assigned
Ã
to n–p
transitions of the scorpionate ligands. In the visible range,
‘
‘y = mx À b’’, in which ‘‘m’’ is the reaction order of the oxovanadium
the complexes 1, 2 and 4 exhibit two set of absorption peaks at
504–544 nm and 658–762 nm, peaks at 714 nm for 1, 658 nm for
2 and 762 nm for 4 are traditionally assigned to d–d transitions
of the central metal vanadium, peaks at 538 nm for 1, 504 nm for
2 and 544 nm for 4 are attributed to d–d transitions produced from
ligands to metal [34,35].
complexes in this reaction and ‘‘b’’ is the intercept of the line. In the
experiment, considering that the reaction orders of KBr and phenol
red (y and z) are 1 according to the literature [7,30]; c
known as 0.4 mol/L and 10 mol/L, respectively. Based on the
2
and c
3
are
À4
2 3
equation of ‘‘b = logk + ylogc + zlogc ’’, and then the reaction rate
constant (k) can be obtained. The bromination of phenol red was
monitored by the measurement of the absorbance at 592 nm for
the reaction solution which were taken at specific time points and
diluted into the phosphate buffer solution (pH = 5.8).
Structural description of complexes 1–4
The molecular structures of complexes 1–4 are depicted in
Fig. 2. Some selected bond distances, bond angles and hydrogen
bonds are summarized in Tables S1 and S2.
Results and discussion
Structural analysis shows that the complex 1 is crystallized in
the monoclinic system with P2(1)/n space group. The asymmetric
unit of 1 is completed by one vanadium atom, one terminal oxygen
Synthesis
4
I
By analyzing the preparation process of the complexes 1–4, it is
atom, one coordinated Tp ligand, one pz and one -SCN group, and
0.5 free dichloromethane molecule. This vanadium atom is coordi-
nated by one terminal oxygen atom (O), three nitrogen atoms (N2,
found that starting materials are different. VOSO
–3, while VO(acac) was used for 4. The complexes 1 and 4 were
synthesized in the methanol solutions, while the complexes 2 and
were in the mixed solution of methanol–water. All the synthesis
4
was used for
1
2
4
I
N4 and N6) from Tp ligand, one nitrogen atom (N7) from pz and
one nitrogen atom (N9) from -SCN atom, to form a distorted octa-
hedron geometry (Fig. 2a). The bond lengths of VAN are in the
range of 2.025 (9)–2.301(8) Å. The distance of VAO is 1.586(7) Å.
The angles of the OAVAN and NAVAN are in the range of
95.8(4)–175.2(4)° and 79.4(3)–164.5(4)°, respectively. In addition,
there are two kinds of hydrogen bonds in the complex 1: (i) hydro-
3
were accomplished at room temperature. It is worth to mention
that, we only obtained the powder of complex 1 in the reaction
solution, then we dissolved it in CH Cl , and successfully got the
2 2
single crystals. As we all known that it is difficult to get directly
the single crystals of VO-Tp complexes from the reaction solution,
so the complexes must be recrystallized in the other solvents, e.g.
4
I
gen bond between the terminal oxygen atoms and CAH of Tp
4
I
2
CH Cl
2
. In addition, the complexes 1–4 are all stable at room tem-
ligand; (ii) hydrogen bond of nitrogen from Tp and sulfur from
SCN group. The molecules are connected to a 2D superamolecular
perature, and can be easily soluble in DMF. Detail IR and UV–Vis
spectra data are provided in supplement material.
#
1
sheet by the hydrogen interactions of C4AH3Á Á ÁO (3.4261(0) Å,
#2
1
68.07(0)°, #1: À0.5 + x, 1.5 À y, À0.5 + z) and N8AH7Á Á ÁS
Spectra properties
(3.3612(0) Å, 164.03(0)°, #2: 0.5 À x, À0.5 + y, 1.5 À z) (Fig. S5).
X-ray single crystal analysis indicates that the complex 2 is
crystallized in the monoclinic system with P2(1)/n space group.
The crystal structure comprises a monomeric TpVO(pzTp) neutral
complex molecule and two lattice water molecules. In the
asymmetric unit, vanadium atom is coordinated by one terminal
oxygen (O) atom, three nitrogen atoms (N1, N3 and N5) from three
pyrazolyl moieties of Tp and two nitrogen atoms (N7 and N9) from
IR spectra
The IR spectra of the complexes 1–4 are shown in Figs. S1–S4
and the selected data are listed in Table 1. The weak peaks ob-
served at 3100–3200 cm are attributed to the @CAH stretching
vibration. Bands at 2900–3000 cm are attributed to the vibration
of ACAH, while it is not observed for the complexes 2 and 3, which
À1
À1

R. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 115 (2013) 476–482
479
Table 1
IR data (cm ) for complexes 1–4.
four pyrazolyl moieties of pzTp (Fig. 2b), to form a distorted
octahedron geometry. The VAO bond distance is 1.616(6) Å. The
bond lengths of VAN are in the range of 2.110(12)–2.290(12) Å.
The angles of the OAVAN and NAVAN are in the range of
95.6(5)–177.0(5)° and 80.3(5)–164.0(7)°, respectively. In addition,
there are two kinds of hydrogen bonds in the complex 2: (i) hydro-
gen bond between the lattice water molecule and the CAH of Tp
ligand; (ii) hydrogen bond between lattice water molecule and
the NAH of the pzTp ligand. And the molecules of the complex 2
are linked to form a 1D chain superamolecular structure by the
À1
Complex @CAH ACH
ACH
3
/
BAH SCN
C@N V@O CAI VAN
2
1
3186,
115
2994,
2923
2524 2087 1507 970
610 481, 457,
438, 400,
3
2
3
3141
3122
–
–
2493
2507
–
–
1507 977
1504 976
–
401
611 456, 393,
69
610 413, 356
3
4
3119
2967,
2489
–
1519 972
2920
#
3
hydrogen interactions of N14AH14BÁ Á ÁO2W (2.9511 Å, 125.23°,
#
4
#
0
3: 0.5 + x, y, z) and C4AH4AÁ Á ÁO2W
.5 + x, 0.5 À y, À0.5 + z) (Fig. S6).
Structural crystal analysis shows that the complex 3 is crystal-
(3.3424 Å, 148.4°, #4:
lized in the orthorhombic system with Pnma space group. The
molecular structure contains one vanadium atom, one terminal
4
I
oxygen atom, one Bp ligand and one Tp ligand. The vanadium
atom is coordinated by one terminal oxygen (O) atom, three nitro-
4
I
gen atoms (N1, N3 and N1A) from Tp ligand and two nitrogen
atoms (N5 and N5A) from Bp ligand to form a distorted octahedron
geometry (Fig. 2c). The VAO bond distance is 1.575(7) Å. The bond
lengths of VAN are in the range of 2.071(7)–2.239(9) Å. The angles
of the OAVAN and NAVAN are in the range of 94.7(3)–172.0(4)°
and 79.5(2)–166.8(3)°, respectively.
4I
The crystal structure of 4 comprises two monomeric [Tp ]-
VO(acac) neutral molecules and one free methanol molecule
(Fig. 2d). The framework structure of the complex is the same as
Fig. 1. The UV–Vis spectra for the complexes 1, 2 and 4.
Fig. 2. (a) The molecular structure of the complex 1; (b) the molecular structure of the complex 2; (c) the molecular structure of the complex 3; (d) the molecular structure of
the complex 4 (the hydrogen atoms and the free dichloromethane molecule are omitted for clarity).

4
80
R. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 115 (2013) 476–482
that of the complex reported previously by our group [36]. How-
ever, due to the presence of the lattice methanol molecule, it is
found that the connection fashion of the hydrogen bonds is differ-
ent. As is shown in Fig. S7, hydrogen bonds come from the terminal
oxygen atom and CAH of the Tp4I ligand, furthermore, the mole-
cule of the complex 4 is linked to form a 1D chain superamolecular
1
2
3
4
1
00
8
0
#
5
60
40
structure by the hydrogen bonding interactions of O7AH7AÁ Á ÁO1
(
2.8797 Å, 154.15°, #5: 0.5 + x, 0.5 À y, 0.5 + z), C28AH28AÁ Á ÁO7
#6
(
3.3506 Å, 159.49°) and C20AH20AÁ Á ÁO4
6: 1 À x, 1 À y, 1 À z).
By comparison, it is found that there is an obvious difference
among the coordination abilities of three nitrogen atoms of Tp or
(3.4163 Å, 156.10°,
#
2
0
0
4
I
Tp , the VAN bond distances trans to the V@O bonds for the four
complexes are considerably longer than the other VAN bonds and
this is mainly because of the consequence of the strong trans
influence of the terminal oxo group. Furthermore, the angles of
0
200
400
600
800
1000
o
T/ C
O(terminal) AVAN(trans) of the four complexes are all closed to 180°,
Fig. 3. The TG curves for the complexes 1–4.
which are 175.2(4)°, 177.0(5)°, 172.0(4)° and 173.29(14)°, respec-
tively. It is similar to those reported in the literature [25]. While
the order of the angles of O
t
AVAN(trans) is 2 > 1 > 4 > 3, it should
single-crystal diffraction data (Figs. S8–S10). The phase of the cor-
responding complex is considered as purities owning to the agree-
ment of the peak positions. The different intensity may be due to
the preferred orientation of the powder samples.
be attributed to the different substituted scorpionate ligands.
4
I
While for the complexes with Tp , the differences of the
corresponding angles were influenced by the steric hindrance of
the second ligands.
Functional mimics of the vanadium haloperoxidases
Thermal properties
Mimicking bromination reaction of the complexes
It is well known that oxidovanadium complexes are able to mi-
mic a reaction in which vanadium haloperoxidases could catalyze
To examine the thermal stability of the complexes 1–4, thermal
gravimetric analysis (TG) was carried out at a heating rate of
0 °C/min under the condition of N atomosphere with the
2
1
the bromination of organic substrates in the presence of H
2 2
O
temperature range of 30–1000 °C (Fig. 3). In 1, the result shows
the initial weight loss of 60.14% before 545 °C is due to the release
of the half free dichloromethane molecule, one -SCN, one -pz and
and bromide. For example, the bromination of trimethoxybenzene
+
[
6], benzene, salicylaldehyde and phenol by the VO
2
ion [37], and
O] and related species
38]. Herein, we have investigated the bromination reaction
+
2 2
the bromination of phenol red by [VO(O )H
[
4
I
parts of Tp ligand (they could be including BH, one pz and two I
atoms) (calc 60.14%). The second weight loss occurs in the range
of 545–1000 °C, which is ascribed to the release of the remaining
activity of the complexes 1 and 2 using phenol red as an organic
substrate, which is shown by the conversion of phenol red to bro-
mophenol blue. The reaction is rapid and stoichiometric, producing
the halogenated product by the reaction of oxidized halogen spe-
cies with the organic substrate, and the reactive process is shown
in Scheme S1.
4
I
part of TP ligand, and the final residue is corresponded to vana-
dium oxide and nitride. The TG behaviours of these four complexes
are slightly different due to the differences of their structures. The
TG curve of 2 is divided into three steps. The first weight loss of
2
8.84% in the range of 30–352 °C was attributed to two lattice
The electronic abosorption recorded a decrease in absorbance of
the peak at 443 nm with the loss of phenol red and an increase of
water molecules and two uncoordinated pyrazolyl moiety of the
pzTp ligand. The second weight loss occurs in the range of 352–
4
34 °C, with a percentage weight loss of 24.27%, which is ascribed
to the release of BH moiety and two coordinated pyrazolyl moiety
of the pzTp ligand. The last step of decomposition occurred within
the range of 434–1000 °C, which is considered the loss of
framework of Tp ligand, and the final residue is corresponding to
vanadium oxide and nitride. The TG curve of 3 shows three stages:
The initial weight loss of 3.06% in the range of 30–271 °C is attrib-
uted to the release of two BAH moieties. The second weight loss of
1
6.76% in the range of 271A337 °C is due to the release of two
pyrazolyl moieties of the Bp ligand. The last step is observed in
37–1000 °C, which is considered the loss of framework of the
3
Tp ligand. The TG curve of 4 can be divided into two stages. The
initial weight loss of 11.8% in the range of 21–184 °C is due to
the release of one free methyl alcohol molecule, two BAH moieties
and one I group. The second weight loss of 73.14% in the range of
1
84–1000 °C is according to the release of five I groups, six pyraz-
olyl groups and one acac group. The final residue is corresponded
to two V@O moieties and one acac group.
Fig. 4. Oxidative bromination of phenol red catalyzed by 1. Spectral changes at
XRD analysis
1
0 min intervals. The reaction mixture contained phosphate buffer (pH 5.8), KBr
À1
À4
À1
À1
(
0.4 mol L ), phenol red (10 mol L ) and complex 1 (0.1 lmol L ). (For
The powder X-ray diffraction data of the complexes 1, 2 and 4
interpretation of the references to colour in this figure legend, the reader is
were obtained and compared with the corresponding simulated
referred to the web version of this article.)

R. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 115 (2013) 476–482
481
Fig. 5. (I) The cycle catalytic brominated reaction mechanism. (II) A series of linear calibration plots of the absorbance at 592 nm dependence of time for different
À4
À2
concentration of the complex 1. Condition used: pH = 5.8, c(KBr) = 0.4 mol/L, c(H
3
2
O
2
) = 1 mol/L, c(phenol red) = 10 mol/L. c(complex 1/mmol/L) = (a) 1.94 Â 10 ; (b):
À2
À2
À2
À2
.87 Â 10 ; (c): 5.81 Â 10 ; (d): 7.75 Â 10 ; (e): 9.68 Â 10 . (III) –log(dc/dt) dependence of Àlogc for 1 in DMF–H
2
O at 30 ± 0.5 °C (c is the concentration of the complex
1).
the peak at 592 nm with production of the bromophenol blue
shown in Fig. 4), investigating that the complex 1 possess better
catalytic activity. The results of the mimic catalytic activities for
and 4 are similar to that of 1.
dependence on vanadium; (ii) the order of the reaction rate con-
stants for them is 1 > 2, which is probably due to the influence of
the iodine ion.
(
2
In the meantime, we carried out some reactions with other
transition metal complexes as catalysts (e.g. Cu, Co, Ni compounds,
etc.) for comparison, the results indicated that the compounds
almost exhibit the catalytic bromination activity in our experiment
system except the copper compounds, catalytic activity of which is
close to that of the vanadium complexes. Based on the upwards
views, the halide oxidation catalytic cycle mechanism for
vanadium peroxidase in this work is proposed in Fig. 5-I. The
Kinetic studies of mimicking bromination reaction
Take the complex 1 for an example to carry out kinetic studies
of mimicking bromination reaction. A series of dA/dt data (Fig. 5-II)
were obtained by changing the concentration of the oxovanadium
complex, then the plot of –log(dc/dt) versus Àlogc for the complex
1
was depicted according to the data of Fig. 5-II, obtaining a
straight line (Fig. 5-III) with a slope of 1.0314 and an intercept of
2
peroxidovanadium inermediate species of [VO(O )Tp] was formed
À2.0537. Similar plots for 2 were generated in the same way
by the action of oxidovanadium complexes with H
2
O
2
(step a).
À
(
Figs. S11 and S12), and values of the slope and the intercept are
Then Br is oxidized rapidly by [VO(O
2
)Tp], with the creation of
+
1
.0458 and À2.1349, respectively. The experiment results showed
2
Br and [VO Tp] at the same time (step b). The oxidize bromides
that: (i) the reaction orders of the oxidovanadium complexes in
can be used to perform a halogenation reaction when an organic
substrate is present (step c). While, the hydrogen peroxide was
bromination reactions are all close to 1, confirming the first-order
Fig. 6. (I) The linear calibration plot of the absorbance at 592 nm on the concentration of H
2
O
2
from 0.48 mol/L used the complex 1 as catalyzer in DMF–H
2
O at 30 ± 0.5 °C. (II)
The linear calibration plot of the absorbance at 592 nm on the concentration of H
2
O
2
from 1.1 mol/L used the complex 2 as catalyzer in DMF–H O at 30 ± 0.5 °C.
2

4
82
R. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 115 (2013) 476–482
decomposed into water and dioxygen in the absence of a substrate
step d) [39].
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Acknowledgement
This work was supported by the grants of the National Natural
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