Mimicing bromoperoxidase for copper complexes: Synthesis, structures and properties of Cu(II)-triazine pyrazolyl complex

Article abstract of DOI:10.1016/j.poly.2015.01.038

Copper complexes [Cu₂(μ₂-C₂O₄)(HC₂O₄)(L₁)]·(H₂C₂O₄) (1), [Cu₂(Bpz^?T-OEt)₂Cl₂CuCl₄] (Bpz^?T-EtOH = L₂) (2) and [Cu₂(Bpz^?T-O)₄]·4pz^?·4H₂O (3) (Bpz^?T-O = L₃) (L₁ = 2,4-bis(3,5-dimethyl-1H-pyrazol-1-yl)-6-diethylamino-1,3,5-triazine, Bpz^?T = 2,4,6-tri(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine) have been synthesized in the reaction of Cu(Ac)₂·2H₂O, oxalic acid, L₁ (for 1) or Bpz^?T (for 2 and 3) and CuCl₂·2H₂O with solution methods. They were characterized by elemental analysis, IR, UV-Vis and thermogravimetric analyses (TG), and the single-crystal X-ray diffraction analysis. Structural analysis reveals that center metal Cu atoms in the complexes 1 and 3 are six-coordination modes, forming distorted octahedron geometries with N2, O2 and N6 donors, respectively. While Cu atom in the complex 2 is four-coordination and five-coordination modes, forming tetragonal pyramid and tetrahedron geometry with N3 Cl2 and N6, respectively. The complexes exhibit catalytic bromination activity in a single-pot reaction of the conversion of phenol red to bromophenol blue in a mixed system of H₂O-DMF-KBr at the constant temperature of 30 ± 0.5 °C with a buffer solution of NaH₂PO₄-Na₂HPO₄ (pH 5.8), indicating that they can be considered as a potential functional model of bromoperoxidase.

Full text of DOI:10.1016/j.poly.2015.01.038

Accepted Manuscript
Mimicing bromoperoxidase for copper complexes: Synthesis, structures and
properties of Cu(II)—triazine pyrazolyl complex
Xiao Dong Feng, Rui Zhang, Xin Yu Wang, Xiao Xi Zhang, Ji Xiao Wang,
Yong Heng Xing, Li Xian Sun
PII:
S0277-5387(15)00065-0
DOI:
http://dx.doi.org/10.1016/j.poly.2015.01.038
POLY 11176
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
8 December 2014
31 January 2015
Please cite this article as: X.D. Feng, R. Zhang, X.Y. Wang, X.X. Zhang, J.X. Wang, Y.H. Xing, L.X. Sun, Mimicing
bromoperoxidase for copper complexes: Synthesis, structures and properties of Cu(II)—triazine pyrazolyl complex,
Polyhedron (2015), doi: http://dx.doi.org/10.1016/j.poly.2015.01.038
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Mimicing bromoperoxidase for copper complexes:
Synthesis, structures and properties of Cu(II)—
triazine pyrazolyl complex
Xiao Dong Feng1, Rui Zhang1,2, Xin Yu Wang1, Xiao Xi Zhang1, Ji Xiao Wang1, Yong Heng Xing1*,
Li Xian Sun3
5
College of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian City, 11602
2 Dandong The second senior middle school, Dandong City, 118000
3
Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology,
Guilin 541004, P.R. China
10
15
*Cooresponding author Prof. Y. –H Xing; e-mail: xingyongheng2000@163.com; tel: 0411-82156987

Abstract:
Copper complexes [Cu2(µ2-C2O4)(HC2O4)(L1)]·(H2C2O4) (1), [Cu2(Bpz*T-OEt)2Cl2CuCl4] (Bpz*T-
EtOH = L2) (2) and [Cu2(Bpz*T-O)4]·4pz*·4H2O (3) (Bpz*T-O = L3) (L1 = 2,4-bis(3,5-dimethyl-1H-
pyrazol-1-yl)-6-diethylamino-1,3,5-triazine, Bpz*T
=
2,4,6-tri(3,5-dimethylpyrazol-1-yl)-1,3,5-
5
triazine) have been synthesized in the reaction of Cu(Ac)2·2H2O, oxalic acid, L1 (for 1) or Bpz*T(for 2
and 3) and CuCl2·2H2O with solution methods. They were characterized by elemental analysis, IR,
UV-vis and thermogravimetric analyses (TG), and the single-crystal X-ray diffraction analysis.
Structural analysis reveals that centre metal Cu atoms in the complexes 1 and 3 are six-coordination
modes, forming distorted octahedron geometries with N2, O2 and N6 donors, respectively. While Cu
10 atom in the complex 2 is four-coordination and five-coordination modes, forming tetragonal pyramid
and tetrahedron geometry with N3 Cl2 and N6, respectively. The complexes exhibit catalytic
bromination activity in a single-pot reaction of the conversion of phenol red to bromophenol blue in a
mixed system of H2O-DMF-KBr at the constant temperature of 30 0.5 C with a buffer solution of
NaH2PO4–Na2HPO4 (pH=5.8), indicating that they can be considered as a potential functional model
15 of bromoperoxidase.
Keywords: Copper complex; Triazine pyrazolyl compound; Crystal structure; Mimicing
bromoperoxidase.
20

1. Introduction
The vanadium haloperoxidases (V-HPOs) from two kinds of the red algal species [1-2], Corallina
officinalis and Corallina piluliferahaveave have been studied for a long time owning to the biological
and catalytic properties [3]. Structural analysis reveals that they all show a high degree of amino acid
homology in their active centres and have nearly identical structural features, with vanadium atom in a
proved trigonal-bipyramidal NO4 coordination geometry which is covalently bonded to three oxygen
atoms in the equatorial plane, Nε of the histidine and an OH on axial positions [4-7].
5
Vanadium haloperoxidases are able to accelerate the oxidative halogenation of organic
compounds in the presence of hydrogen peroxide, organic hydroperoxides or molecular oxygen.
10 Among these systems, V-HPOs have received an increasing attention mainly due to their catalytic
ability for the oxidation of halides to the corresponding hypohalous acids in the presence of hydrogen
peroxide, resulting in the halogenation of certain organic substrates [8, 9] [Reaction(1)]:
R―H + H2O2 + X– + H+ → R―X + 2H2O (1)
Though, vanadium haloperoxidases are of great importance in nature, they are not widely used in
15 catalytic bromination reaction of actual industry. Nature vanadium haloperoxidases are difficult to be
extracted, moreover, the application of V-HPOs has been restricted by the disadvantages of lower
stability and active, and the catalysis reaction mechanism was not clear yet [10-13]. Based on the
points above, we attempted to synthesize efficient metal complexes with organic ligands to mimic the
biological activity. To our best knowledge, a number of vanadium complexes have been synthesized
20 with various ligands, including aminoacid-derivatized oxidovanadium complexes [14] (VVO(sal-
phe)(OMe)(MeOH), VIVO(sal-ala)(2,2’-bipy)·H2O, VIVO(sal-ala)(1,10-phen)·0.5H2O), oxovanadium
Schiff base complexes [15] ([VO2(C9H7NO3)](C10H10N2)0.5, [VO(C10H8N2)(C9H7NO3)]3,
[VO(C12H8N2)(C9H7NO3)]·2.33H2O ), poly(pyrazolyl)borate and organic carboxylic acid oxo-
3

vanadium (IV) complexes [16] (Tp*VO(pz*)(CH3COO), Tp*VO(pz*)(CCl3COO)， Tp*VO(pz*)(m-
NO2-C6H4COO)·CH3CN) and so on, have been so far well developed in the coordination chemistry of
vanadium [17-20].
In addition, copper complex is also a kind of bioenzyme [21-24], it has been proven to be an
active metal centre in the best studied superoxide dismutase (SOD), which is an important anti-
oxidizing enzyme, might protect cells as a scavenger of superoxide anion free radical that is related to
aging, tumours and inflammation[25-29]. Copper SOD model complexes can overcome the
disadvantages of natural superoxide dismutase, and get a profound understanding of the enzyme as
well as coordination and biological medicinal chemistry [30-32]. However, the catalytic bromination
5
10 activity of copper complexes has not been reported so far.
In order to study on the function properties of copper complexes, here, we synthesized three
copper triazine pyrazolyl complexes, [Cu2(µ2-C2O4)(HC2O4)(L1)]·(H2C2O4) (1), [Cu2(Bpz*T-OEt)2Cl2
CuCl4] (2) and [Cu2(Bpz*T-O)4]·4pz*·4H2O (3) (pz*= pyrazolyl, L1 = 2,4-bis(3,5-dimethyl-1H-
pyrazol-1-yl)-6-diethylamino-1,3,5-triazine, Bpz*T
15 triazine), and studied the bromination reaction activity.
=
2,4,6-tri(3,5-dimethylpyrazol-1-yl)-1,3,5-
2. Experimental Section
2.1. Reagents and instruments
All the chemicals used were analytical grade and without further purification. L1 and Bpz*T (L1 =
2, 4-bis(3, 5-dimethyl-1H-pyrazol-1-yl)-6-diethylamino-1,3,5-triazine, Bpz*T = 2, 4, 6-tri (3, 5-
20 dimethylpyrazol-1-yl)-1,3,5-triazine) were synthesized according to the literature method [33, 34].
Elemental analyses for C, H, and N were 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
4

range 200-4000 cm-1. UV-vis spectra were recorded on JASCO V-570 spectrometer (200-2000 nm, in
form of solid sample). The X−ray powder diffraction data was collected on a Bruker AXS D8
Advance diffractometer using Cu–Kα radiation (λ = 1.5418 Å) in the 2θ range of 5–60° with a step
size of 0.02° and a scanning rate of 3°/min. Thermogravimetric analyses (TG) were performed under
atmosphere with a heating rate of 10 oC min-1 on a Perkin Elmer Diamond TG/DTA.
5
2.2. Synthesis of complexes
Complex [Cu2(µ2-C2O4)(HC2O4)2(L1)]·(H2C2O4) (1): Cu(Ac)2·2H2O(0.040 g, 0.2 mmol) and
H2C2O4 (0.045 g, 0.5 mmol) were dissolved in anhydrous ethanol (10mL), and stirred for 1 h at room
temperature, then added L1 (0.034 g, 0.1 mmol) dissolved in 5 mL anhydrous ethanol into the reaction
10 system dropwise, stirred at room temperature for 3 h, The precipitate was separated by filtration.
Then, the solution was placed at room temperature for a few days and green crystals of complex 1
were obtained. Yield: 0.11 g, 71% (Based on Cu(II)). Elemental anal (%) calcd for C42H56N16O16Cu2:
C, 43.18; H, 4.83; N, 19.18. Found: C, 43.33; H, 4.60; N, 19.25. IR (KBr, cm–1 ν): 3239 (ν
H),
＝ －
C
,
2980, 2925 (ν -CH3), 1631 (ν C=O), 1597, 1432, 1323 (ν C/ν C N), 1141 (ν N=N), 492 (ν Cu=N). UV-vis
＝
C
＝
15 (λmax, nm): 258, 288 (π-π*), 368 (LMCT), 774 (d-d*).
Complex [Cu2(Bpz*T-OEt)2Cl2CuCl4] (2): CuCl2·2H2O(0.034 g, 0.2 mmol), Bpz*T(0.054 g,
0.15mmol), were dissolved in anhydrous ethanol (15 mL), stirred at room temperature for 3 h, mixed
solution was separated by filtration, the green filtrate was stored at room temperature for several days
and green precipitate was obtained. Then, the precipitate was dissolved in CH2Cl2. After two days,
20 green crystals suitable for X-ray diffraction were obtained. Yield: 0.052 g, 76% (Based on Cu(II)).
Elemental anal (%) calcd for C30H42N14O2Cl6Cu3: C, 34.85, H, 4.09, N, 18.96. Found: C, 34.69; H,
5

4.12; N, 18.87. IR (KBr, cm–1, ν ): 3275 (ν － － ), 2980, 2933 (ν －CH3), 1570, 1410, 1322 (ν C C/ν C
＝
＝
C
H
N), 1130, 995(ν N=N), 477 (ν Cu=N). UV-vis (λmax, nm): 262, 290 (π-π*), 420 (LMCT), 792 (d-d*).
Complex [Cu2(Bpz*T-O)4]·4pz*·4H2O (3): The synthesized method of complex 3 was similar to
that of complex 2, CuCl2·2H2O (0.017 g, 0.1 mmol), Bpz*T (0.072 g, 0.2mmol) were dissolved in
ethanol-water (2:1) mixed solution, stirred at room temperature for 3 h, The precipitate was separated
by filtration, the blue filtrate was placed at room temperature for several days and the blue crystals
were obtained. Yield: 0.068 g, 78% (Based on Cu(II)). Elemental anal (%) Calcd. for
C72H92N36O8Cu2: C, 50.37; H, 5.84; N, 29.37. Found: C, 50.39; H, 5.86; N, 29.33. IR (KBr, ν, cm–1 ):
5
3261 (ν － － ), 2972, 2922 (ν －CH3), 1623 (ν C=O), 1563, 1416, 1272 (ν C C/ν C N), 1137, 1031 (ν N=N),
＝
＝
C
H
10 485 (ν Cu=N). UV-vis (λmax, nm): 266, 286 (π-π*), 348 (LMCT), 712 (d-d*).
2.3 X-ray Crystallographic Determination
The crystals of 1-3 were mounted on glass fibers for X-ray measurement, respectively. Reflection
data were collected at room temperature on a Bruker AXS SMART APEX II CCD diffratometer with
graphite-monochromatized Mo-Kα radiation (λ = 0.71073 Å) and ω scan mode. All the measured
15 independent reflections (I > 2σ (I)) were used in the structural analyses, and semi-empirical absorption
corrections were applied using the SADABS program. The structures were solved by the direct
method using the SHELXL-97[35]. All hydrogen atoms of the organic ligands were fixed at
calculated positions geometrically and refined by using a riding model. The hydrogen atoms of the
lattice water were found in difference Fourier map. The non-hydrogen atoms were refined with
20 anisotropic thermal parameters. Crystallographic data and the structure refinement are given in Table
1. The selected bond lengths and bond angles are listed in Table S1. Hydrogen bonds of the
complexes 1-3 are given in Table S2.
6

Table 1 Crystallographic data and structure refinement for complexes 1-3
Complexes
Formula
M (g mol-1)
Crystal system
Space group
a (Å)
1
2
3
C42H56N16O12Cu2 C30H42N14O2Cl6Cu3 C72H92N36O8Cu2
1168.13
Triclinic
P-1
1034.10
Triclinic
P-1
1716.92
Orthorhombic
pca2(1)
31.222(6)
15.922(3)
16.877(3)
90
9.799(3)
11.493(3)
12.815(3)
72.555(3)
89.928(4)
69.314(3)
1279.2(6)
2
11.451(2)
11.736(2)
16.611(3)
90.351(3)
107.008(3)
101.146(3)
2089.9(7)
2
b (Å)
c (Å)
α (º)
90
β (º)
90
γ (º)
V (Å3)
8390(3)
4
Z
Dcalc (Mg m−3)
1.516
1.643
1.359
Crystal size (mm) 0.697×0.207×0.101 0.725×0.144×0.091 0.28×0.06×0.05
F(000)
µ(Mo-Kα) / mm-1
θ (°)
606
0.916
1050
1.944
3591
0.582
2.00 to 25.43
1.95 to 27.46
3.03 to 27.48
Reflections
collected
6605
12562
72636
Independent
reflections
4611
9084
17706
(I > 2σ(I))
Parameters
Flack
364
496
1043
——
——
0.011(13)
∆(ρ) (e Å-3)
0.826 and -0.595
1.062
0.619 and -0.610
0.997
0.947 and -0.499
0.998
Goodness-of-fit
a
R1
0.0599(0.0884)b
0.1502(0.1678)b
0.0599(0.1189)b
0.1281(0.1566)b
0.0544(0.1005)b
0.1324(0.1534)b
a
wR2
2
2 2
2 2
*a R = Σ Fo − Fc / Σ  Fo , wR2 = {Σ[w(Fo −Fc ) ] / Σ[w(Fo ) ]}1/2; [Fo> 4σ(Fo)].
b Based on all data
8

2.4 Measurement of bromination activity in solution
Copper complex was dissolved in a mixed solution of 25 mL H2O-DMF (DMF: 2 mL; H2O: 23
mL). The bromination reaction activity tests were carried out at the constant temperature of 30 0.5 oC
with a buffer solution of NaH2PO4–Na2HPO4 (pH=5.8). Reactions were initiated with the presence of
phenol red solution, H2O2 and KBr. The copper complex with six different concentrations were placed
in six cuvettes, and then put into the constant temperature water bath. The spectral changes were
recorded using a 1000 UV-vis spectrophotometer at 5 min intervals, and the resulting data were
collected during the reaction. The bromine reaction rate constant of copper complexes can be obtained
5
10 according to the method of literatures [36, 37].
3. Results and Discussion
3.1 Synthesis
We have successfully synthesized complexes 1-3 with solution reactions (Scheme 1a). To meet
the coordination conditions of the corresponding ligands and copper atom together in the reaction
15 system, we have endeavored to search for the most optimal reaction parameters. All the synthetic
manipulations were carried out at room temperature. We used anhydrous ethanol to synthesize
complexes 1 and 2, while ethanol-water mixed solution for complex 3. We initially used solution
method to synthesize complex 2, however, we only got the powder of 2, which was further
recrystallized in CH2Cl2 to get nice single crystals for X-ray diffraction. This shows that solvent
20 changes affect the crystal growth of the complexes.
In addition, through these experiment results, we surprisingly found that the ligand structures of
complex 2 and 3 are different from the ligand used in the starting material. For 2, the 3, 5-
dimethylpyrazolyl group in the 2-position of triazine ring from Bpz*T ligand is substituted by an
9

ethoxy group. For 3, the reaction result is similar to complex 2, and the 3, 5-dimethylpyrazolyl is
substituted by an oxygen atom forming an unsaturated ketone conjugate species. Through a large
number of experiments and analysis, we thought there may be an in situ reaction in the process of
synthesizing complexes 2 and 3. The detail reaction mechanism is shown in Scheme 1b.
HO
O
O
N
N
N
N
N
N
N
O
Cu(ac)22H2O/H2C2O4
EtOH
N
N
O
N
N
O
N
N
(1)
N
N
Cu
N
N
Cu
N
N
N
N
O
O
N
O
O
N
N
O
OH
N
N
N
N
N
N
N
N
N
N
Cl
Cl
Cu
Cl
N
Cl
N
CuCl2 2H2O
EtOH
O
Cu
Cu
Cl
O
(2)
(3)
N
N
Cl
N
N
N
N
O
N
N N N
N
N
N
NH
CuCl2 2H2O
N
N
N
N
EtOH-H2O (2:1)
Cu
N
N
N
N
N
N
HN
O
5
a
+
N
N
O
N
N
N
N
N
N
N
N
N
N
N
N
CuCl2
EtOH
N
N
Cl
Cu
Cl
Cl
Cl
metal ion(Cu2+
)
N
N
N
N
N
N
N
N
N
(2)
O
N
N
Cu
O
Cu
N
N
N
N
N
N
N
N
N
N
Cl
Cl
O
N
NH
OH
+
O
N
N
N
N
N
N
N
N
metal ion(Cu2+
)
H2O
N
N
N
N
N
N
CuCl2
(3)
Cu
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
HN
O
b
Scheme 1.: The reaction process of the complexes 1-3 (a); The in situ reaction mechanism routes of
complex 2 and 3 (b).
10 3.2 IR spectra.
10

The IR spectra of the complexes 1−3 are examined (Fig. S1-S3). For the complexes 1-3, the
spectra have bands at 3239-3275 cm-1 for the complexes assigned to =C-H stretching vibrations, and
bands at 2980-2922 cm-1 assigned to -C-H stretching vibrations. The strong peaks in the range of
1597–1272 cm-1 account for the appearance of νC C/νC of the pyrazole and triazine rings, and N-N
＝
＝
N
5
stretching vibration are in the range of 1141-995 cm-1, Cu-N stretching vibration in the range of 428-
480 cm-1. In addition, the bands at 1631 cm-1 and 1623 cm-1 for 1 and 3 are assigned to C=O
vibrations. The IR spectra data of the complexes 1-3 was listed in Table S3.
3.3 UV–vis spectra.
The UV–vis absorption spectra of complexes 1-3 (Fig. S4-S6) are recorded in the form of solid
10 sample and their characteristic of the UV-vis bands are listed in Table S4. They have similar
absorption patterns. Bands at 258 and 288 nm for 1, 262, 290 nm for 2 and 266, 286 nm for 3 are
attributed to the π-π* transition of the ligand. The band at 368 nm for 1, 420nm for 2 and 348 nm for 3
are assigned to the charge transitions from the ligands to Cu(II) atom (LMCT) of N→Cu. The broad
peak at 774 nm for 1, 792 nm for 2 and 712 nm for 3 can be caused by the d→d* transition of Cu2+
15 cation, respectively.
3.4 Structural Description
Structural analysis shows that complex 1 is crystallized in the triclinic system with P-1 space
group. The molecular structure of 1 consists of two cooper atoms, two L1 ligands, three coordinated
oxalic acid ligands and a free oxalic acid molecule (Fig.1 a). Two copper atoms are crystallographic
20 equivalent, and they are linked by a dianionic oxalate ligand. Cu1 atom displays a distorted octahedra
geometry, and it is coordinated by three nitrogen atoms (N4, N6 and N8) from L1 ligand, one oxygen
atom (O2) from coordinated oxalic acid and two oxygen atoms (O5, O6) from bridging oxalic acid.
11

For L1 ligand, it adopts terminal tridentate chelating coordination mode, the bond length of Cu–N is in
the range of 1.944(3)-2.176(4) Å. And for the coordinated oxalic acid group, it adopts terminal
monodentate coordination mode, the lengths of Cu–O is in the range of 1.949(3)-2.312(3) Å. The
angles of the N-Cu-O and N-Cu-N are in the range of 89.11(14)-168.76(12) ° and 75.95(13)-
151.95(13) °, respectively. The angle of the O-Cu-O is 87.37(12) °.
5
In addition, there are two kinds of inter-hydrogen bonds in the structure of the complex 1, (i) the
hydrogrn bonds of C–H···O(C4–H4C⋅⋅⋅O3#1: 3.352(6) Å, 141.3°; C6–H6A···O7#2: 3.398(8) Å, 159.7°,
#1: 2-x, -y, z-2, #2: 1+x, y, z ) are between the carbon atom from L1 ligand and the oxygen atom from
the coordinated oxalic acid ligand (O7) and free oxalic acid (O3); (ii) hydrogen bonds of O–
10 H···O(O3–H3···O1#1: 2.666(8) Å, 136.4°; O8–H8···O5: 2.777(6) Å, 172.2°) are between two oxygen
atoms from the coordinated oxalic acid and free oxalic acid. The molecules are connected to 1D
chains structure by the hydrogen interactions of C4–H4C⋅⋅⋅O3 and O3–H3···O1 (Fig.1 b). Then, the
neighbour chains are connected to 2D sheets structure by hydrogen interactions of O8–H8···O5 (Fig.1
c). Finally, the hydrogen bond C6–H6A···O7#2 linked these layers to construct a 3D packing
15 framework (Fig.S9).
20
25
30
12

a
c
5
Fig 1. a: The molecular structure of 1; b: an infinite helical chain structure of 1; c: a view of a 2D
supermolecular network structure formed by the hydrogen bonds;
Single crystal X-ray diffraction analysis reveals that complex 2 is crystallized in the triclinic
system with P-1 space group. The molecular structure of 2 consists of three copper atoms, two L2
ligand (Bpz*T-EtOH = L2), six chlorine ions (Fig.2 a). Cu1 may be best described as tetragonal
10 pyramid geometry, and it is coordinated by three nitrogen atoms (N3, N5 and N7) from L2 ligand, two
chlorine ions (Cl1, Cl2). The coordination environment of Cu2 is the same as Cu1. The central atom
Cu3 can be described as tetrahedra geometry, it is coordinated by four chlorine ions (Cl2, Cl4, Cl5 and
Cl6). Adjacent [Cu2(Bpz*T-EtO)2Cl2] unit are connected by CuCl4 unit. For L2 ligand, it adopts a
terminal tridentate chelating coordination mode, the bond lengths of Cu–N is in the range of 1.931(4)–
13

2.118(4) Å. By comparison, it is found that the Cu–Npz* bond length is longer than that of Cu–Ntriazine
.
Therefore, the coordination ability of nitrogen from triazine ring is stronger than that from pyrazolyl
ring. For chlorine ions, it adopts the terminal monodentate coordination mode, the lengths of Cu–Cl is
in the range of 2.1893(16)–2.5665(16) Å. Similarly, the bond distance of bridging chlorine with
copper atom (Cu–Clb) is slightly longer than that of terminal chlorine (Cu–Clt), the coordination ability
of terminal chlorine is stronger than that of bridging chlorine. The angles of the N-Cu-N and N-Cu-Cl
are in the range of 76.53(17)-152.65(17)° and 87.84(13)-160.26(14)°, respectively. Furthermore, the
angle of Cl(1)-Cu(1)-Cl(2) is 101.85(6)°, and Cl-Cu(3)-Cl is in the range of 97.68(6)-133.73(7)°.
5
In addition, in the molecular packing of the complex 2, there is a kind of hydrogen bonds of C–
10 H⋅⋅⋅O, which comes from between carbon atoms (C6) and oxygen atom (O2) of L2 ligand, (C6–
H6A⋅⋅⋅O2#3, 3.292(8) Å, 137.5°, #3: 1+x, y, z ). Adjacent molecules are linked forming a 1D chain
structure via the hydrogen bond (Fig.2 b).
14

a
5
b
Fig 2. a: The molecular structure of 2. b: A view of a 1D chain by hydrogen bonding interaction in 2.
The complex 3 crystallizes in the Orthorhombic system with space group Pca2(1). The
asymmetric unit of complex 3 contains two Cu atoms, four coordinated L3 ligands, four free 3,5
10 dimethylpyrazole ligands (Bpz*T-O = L3) and four lattice water molecules. Cu1 may be described as
distorted octahedron, and it is coordinated by six nitrogen atoms (N1, N5, N7, N8, N12 and N14) from
two L3 ligands. For L3, it adopts a terminal tridentate chelating coordination mode, the bond lengths
of Cu–N is in the range of 1.931(4)–2.258(4) Å. The angles of the N-Cu-N are in the range of
74.54(15)–176.46(15) °.
15
In the molecular packing of the complex 3, the hydrogen bonds can be divided into three kinds:
(i) the inter-hydrogen bonds of O–H···O (O4W–H4WA···O2W: 2.694(8) Å, 125.7°. O1W–
H10A···O3W#5: 2.698(7) Å, 143.9°. #5: x, y, 1+z.) between two free water (O2W, O4W, O1W,
O3W) and (O2W–H2WA···O1#4: 2.768Å, 143.99°. #4: 1+x, y, -1+z.) between a free water (O2W)
and an oxygen atom (O1#4) from complex molecule form two chain-bonds, which are specified as
2
C
2
1
20
(6) [38]. (ii) the bond of O–H···N (O3W–H10C···N17: 3.405(6) Å, 138.3°) between
(6) and C1
oxygen atom from free water and a nitrogen atom from L3 ligand also forms a chain-hydrogen bond.
15

(iii) intra-hydrogen bonds C–H···N (C48–H48A···N23: 2.957(6) Å, 133.1°; C17–H17A···N10:
2.957(6) Å, 132.9°) between the carbon atom and nitrogen atom from L3 ligand, would be specified as
S(6) [38], six atoms forming two closed hexatomic rings. In addition, two inter-hydrogen bonds of C–
H···N (C34-H34C···N31#6: 3.370(7) Å, 155.8°; C34–H34C···N32#7: 3.361(7) Å, 140.8°. #6: 1.5-x, -
1+y, -0.5+z, #7: 1.5-x, -1+y, -0.5+z.) form a bifurcated hydrogen bond.
5
a
10
15
20
25
b
Fig 3. a: The molecular structure of 3. b: a view of the intramolecular hydrogen bonds in 3
16

3.5 Thermal properties
To examine the thermal stability of complexes 1–3, thermogravimetric analysis (TG) was carried
out at a heating rate of 10 ºC/min under nitrogen in the temperature range of 30–1000 ºC (Fig. S7). In
1, the results show that the initial weight loss of 31.93% before 220 ºC is due to the release of a lattice
oxalic acid and coordinated oxalic acid, two 3,5-dimethyl pyrazolyl moieties (calc. 31.94%). The
second weight loss occurs in the temperature range of 220–1000 ºC, which is ascribed to the release of
the framework of the triazine ring of the L3 ligand, and the final residue corresponds to copper oxide.
In 2, the first weight loss of 13.56% before 221 ºC is attributed to the reduction of a 3, 5-dimethyl
pyrazolyl and a C2H5O moiety (calc.13.81%). The second weight loss of 37.12% was attributed to the
5
10 release of two 3,5-dimethyl pyrazolyl moieties, two coordinated chlorine ions, a triazine ring and a
C2H5O moiety (calc. 37.12%) in the temperature range of 221–479 ºC. The final residue corresponds
to a copper dichloride and two copper oxides (obsd. 28.5%; calc. 25.69%). In 3, the first weight loss
of 9.78% before 235 ºC is attributed to the reduction of four free water and a free 3, 5-dimethyl
pyrazolyl moiety (calc.9.62%). The second weight loss of 16.93% was attributed to the release of
15 three free 3, 5-dimethyl pyrazolyl moieties (calc. 16.38%) in the temperature range of 235–302 ºC. In
the temperature range of 302–324 ºC, the weight loss equaled to 16.56%, ascribed to the release of
organic ligands (calc. 16.93%). The final residue corresponded to two copper oxide molecules and the
residual carbon.
3.6 Mimicking bromination reaction.
20
We found copper complexes are able to mimic a reaction in which copper complex could catalyze
the phenol red in the presence of H2O2 and bromide potassium to bromophenol blue through
experiments. Herein, the bromination reaction activity of complexes 1, 2 and 3 using phenol red as an
organic substrate, which is shown by the conversion of phenol red to bromophenol blue have been
17

investigated. The reaction is rapid and stoichiometric, producing the halogenated product by the
reaction of oxidized halogen species with the organic substrate, and the reactive process is shown in
Scheme 2.
O
O
O
O
Br
S
S
O
O
KBr Cu Complex
H2O2
OH
OH
Br
Br
Br
OH
OH
5
Scheme 2 The reactive process of bromination reaction for the complexes.
The addition of solution of complex 2 to the standard reaction system of bromide potassium in a
phosphate buffer with phenol red as a trap for oxidized bromine resulted in the visible colour change
of the solution from yellow to blue. The electronic absorption recorded a decrease in absorbance of
10 the peak at 443 nm with the loss of phenol red and an increase of the peak at 592 nm with production
of the bromophenol blue (shown in Fig. 4), investigating that complex 2 possesses better catalytic
activity [39, 40].
18

Fig 4. Oxidative bromination of phenol red catalyzed by 2. Spectral changes at 10 min intervals. The
reaction mixture contained phosphate buffer (pH 5.8), KBr (0.4 mol·L-1), phenol red (10-4 mol·L-1) and
complex 2 (0.1 µmol·L-1).
Take complex 2 as an example to carry out kinetic studies of mimicking bromination reaction. A
series of dA/dt data were obtained by changing the concentration of the copper complex, then the plot
of -log (dc/dt) vs -logc for complex 2 was depicted according to the data of Fig. 5, obtaining a straight
line (Fig. 6) with a slope of 1.0965 and an intercept of 0.646. The former confirms the first-order
reaction is close dependent on concentration of copper. Based on the equation of “b=log k + ylog c2 +
zlog c3”, the reaction rate constant, k, is determined by the concentrations of KBr and phenol red (c2
5
10 and c3), the reaction orders of KBr and phenol red (y and z), as well as b. While in the experiment,
considering that the reaction orders of KBr and phenol red (y and z) are 1 according to the literature; c2
and c3 are known to be 0.4 mol/L and 10-4 mol/L, respectively, so the reaction rate constant (k) for
complex 2 can be calculated as 5.648×103 (mol/L)-2 s-1.
Similar plots for 1, 3 and Cu(NO3)2 were generated in the same way (Fig. S8 ). The values of the
15 slope and the intercept are 1.0820, 1.2033 and 1.0823, 1.3181 for 1 and 3, respectively, 1.1409, 0.6327
for starting material of Cu(NO3)2.
19

Fig 5. A series of linear calibration plots of the absorbance at 592 nm dependence of time for
different concentration of the complex 2. Condition used: pH=5.8, c(KBr)=0.4 mol·L-1, c(H2O2)=1
mol·L-1, c(phenol red)=10-4 mol·L-1. c(complex 0.5/mmol·L-1)= a: 1.5×10-3; b: 3.6×10-3; c: 4×10-3;
d: 7.3×10-3 ; e: 8.4×10-3 , f: 1.15×10-2.
5
Fig 6. –log (dc/dt) dependence of –logc for 2 in DMF-H2O at 30 0.5oC (c is the concentration of the
complex 2)
The cyclic catalytic brominated reaction mechanism is shown in Scheme 3, (1): the copper
10 complex (CuLL′) is easily to form an transitional intermediate species of [CuLL′O2H] with H2O2 as an
oxidation regent; (2): the transitional intermediate species is transformed to copper radicals species
[CuLO2] and H2L′ rapidly; (3): Br- is oxidized by the [CuLO2], at the same time, Br+ and CuLL′ are
formed. It is found that the catalytic reaction rate would be mainly based on the stability of the formed
copper radical species [CuLO2].
20

H
O
H2O2/H+
(1)
O
L-Cu
+ H+
Cu
L
L'
L'
-H2L'
(2)
L-Cu+-O-O
(3)
+ Br- + H+ +H2L'
Cu
+ Br+ + OH-
L'
L
-
(Br+ = HOBr, Br2, Br3
)
(4)
+ organic substrate (RH)
RX +H+
L: L1/L2/L3
Scheme 3. The cyclic catalytic brominated reaction mechanism
The experiment results showed that: (i) the reaction orders of the copper complexes in the
5
bromination reaction are all close to 1, confirming appreciatively the first-order dependence on copper;
(ii) the reaction rate constants of the three complexes is 2>1>3( Table 2). Although the reaction rate
constant of starting material of Cu(NO3)2 is slightly larger than those of the complexes, concentration
of Cu in the complexes(7-18%) is much lower than that of starting material of Cu(NO3)2(34%), this is
much more decreasing environment pollution in the catalytic reaction system, to be in favor of the
10 implementation of the green catalytic reaction.
Table 2 Kinetic data for the complexes in DMF–H2O at 30 0.5 oC*
Complexes
m
b
k(mol L-1)-2s-1
1.56(5)×103
5.64(8)×103
1.20(1)×103
1.08(2)
1.09(6)
1.08(2)
1.20(3)
0.64(6)
1.31(3)
1
2
3
* Conditions used: c(phosphate buffer) = 50 mmol·L-1, pH = 5.8, c(KBr) = 0.4 mol·L-1, c(phenol red) = 10-4mol·L-1L-1.‘‘x’’ is the
reaction order of the copper complex; ‘‘b’’ is the intercept of the line; ‘‘k’’ is the reaction rate constant for the copper complex.
15
Analysis results found that Cu(II) complexes show high catalytic activity. The order of the
reaction rate constant for complexes is 2>1>3. As we can see, there are similar ligands in the structure
21

of complexes, they just have different coordination patterns leading to the different intermediate
species, which can also influenced the catalytic activity. Three Cu atoms adopt four-coordination and
five-coordination respectively, while 1 and 3 adopt six-coordination, therefore, it is easier to form a
transitional intermediate species of [CuLL′O2H] owing to steric hindrance, thus its catalytic activity is
the highest. For 1 and 3, both of them have two Cu atoms, but complex 3 adopts six-coordination
sandwich structure, and the center Cu atom is surrounded by two L3 ligands tightly, so it is difficult to
form an transitional intermediate to play a catalytic role. All these phenomena above showed that the
catalytic activity of the complexes may have great connection with their structural characterization.
5
With the reaction process, it was surprising to find that the color of brominated reaction by
10 catalysis of copper complex changed slowly with reaction time. The color of bromophenol blue turned
gradually into a kind of light yellow species whose absorbance is stronger than that of bromophenol
blue. As shown in Fig. 7, the absorbance of the peak at 592 nm which was characteristic of the
bromophenol blue product was decrease and an increase in the absorbance of the peak at 420 nm was
observed. Through a large number of experimental studies, we thought that the change of color might
15 rise from photodegradation: under the action of Cu complex, the bromophenol blue was catalysised
and degraded tardily into new species which structure was similar to the phenol red. In general, Cu
complex not only can be used as the catalyst of brominated reaction, but also have an effect on the
photocatalysis.
22

Fig 7. Bromophenol blue was changed by the degraded of complexes 1 - 3
4. Conclusion
5
Three new copper complexes, supported by pincer-N-heterocyclic ligands, have been
successfully synthesized for the first time. The single-crystal X-ray diffraction analysis reveals that
centre metal atoms Cu in complexes 1, 3 are six-coordination modes, forming distorted octahedron
geometries. Cu atoms in complexes 2 are four-coordination and five-coordination modes, forming
tetragonal pyramid and tetrahedron geometry. We tested the catalytic bromination reaction activities
10 with phenol red as an organic substrate in the presence of H2O2, KBr and a phosphate buffer solution
and finally found high catalytic activity, which indicated that copper complexes can be considered as
potential functional models of bromoperoxidase.
Supporting Information Available
The selected bond lengths and angles of complexes 1-3 are listed in Table S1; their hydrogen
15 bonds are shown in Table S2. IR data and UV-vis absorption bands of the complexes 1-3 are shown in
Table S3 and Table S4. Figure S1-S3 and Figure S4-S6 presented the infrared spectra, UV–vis spectra
of the complexes 1-3, respectively. Tables of atomic coordinates, isotropic thermal parameters, and
complete bond distances and angles have been deposited with the Cambridge Crystallographic Data
Center. Copies of this information may be obtained free of charge, by quoting the publication citation
23

and deposition numbers CCDC 1013924 (1), 1013980 (2) and 1013925 (3), from the Director, CCDC,
12 Union Road. Cambridge, CB2 1EZ, UK (Fax+44-1223-336033; e-mail deposit@ccdc.cam.ac.uk;
http://www.ccdc.cam.ac.uk
5
Acknowledgments
This work was supported by the grants of the National Natural Science Foundation of China
(No.21371086) and Guangxi Key Laboratory of Information Materials, Guilin University of Electronic
10 Technology, P. R. China (Project No. 1210908-06-K)
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29